1

Muscles are remarkably adaptive Any doubts

2

Musculoskeletal Issues

Disease genetics Muscular dystrophy Cancer AIDS cachexia Obesity diabetes

Casting

Bedrest

Spinal cord or nerve injury

Surgery rehab disuse

Aging

Microgravity

3

4

5

6

7

Sarcomere (Basic Contractile Apparatus)

8

9

Cellular Energy Production

10

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

2

Musculoskeletal Issues

Disease genetics Muscular dystrophy Cancer AIDS cachexia Obesity diabetes

Casting

Bedrest

Spinal cord or nerve injury

Surgery rehab disuse

Aging

Microgravity

3

4

5

6

7

Sarcomere (Basic Contractile Apparatus)

8

9

Cellular Energy Production

10

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

3

4

5

6

7

Sarcomere (Basic Contractile Apparatus)

8

9

Cellular Energy Production

10

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

4

5

6

7

Sarcomere (Basic Contractile Apparatus)

8

9

Cellular Energy Production

10

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

5

6

7

Sarcomere (Basic Contractile Apparatus)

8

9

Cellular Energy Production

10

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

6

7

Sarcomere (Basic Contractile Apparatus)

8

9

Cellular Energy Production

10

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

7

Sarcomere (Basic Contractile Apparatus)

8

9

Cellular Energy Production

10

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

8

9

Cellular Energy Production

10

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

9

Cellular Energy Production

10

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

10

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

11

TYPE of FIBER

CharacteristicSlow Oxidative

(I)Fast Oxidative

(IIa)Fast Glycolytic

(IIb)

Myosin ATPase activity LOW HIGH HIGH

Speed of Contraction SLOW FAST FAST

Fatigue Resistance HIGH Intermediate LOW

Oxidative Capacity HIGH HIGH LOW

Anaerobic Enzyme Content LOW Intermediate HIGH

Mitochondria MANY MANY FEW

Capillaries MANY MANY FEW

Myoglobin Content HIGH HIGH LOW

Color of Fiber RED RED WHITE

Glycogen Content LOW Intermediate HIGH

Myoglobin Content HIGH HIGH LOW

Fiber Diameter SMALL Intermediate LARGE

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

12

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

13

Tetanic Contraction

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

14

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

15

PCSA (cm2) = Muscle Mass (g) cosine Θ

ρ (gcm3) Fiber Length (cm)

Θ is the pennation angle of the muscle fibers

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

16

Effects of Muscle Length and Contraction Velocity

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

17

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

18

Muscles Respond to Loads

Transduction of mechanical load

Forces transmitted through extracellular matrix

Generate chemical signals Activate voltage gated

channels Activate IGF secretion

(autocrine signaling)

Transduction of neural activation

Ca2+ increase ndash activate Ca2+ - calmodulin calcineurin pathway

Alter gene expression in favor of protein synthesis

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

19

Protein Synthesis

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

20

Protein Degradation

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

21

Muscle Development and Maintenance

Proliferate after heavy use or muscle injury

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

22

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

23

Tidball J Appl Phsyiol 2005

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

24

Haszele and Price Endocrinology 2004

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

25

Myostatin is a member of the TGF-b superfamily that regulates development and tissue homeostasis

Myostatin is expressed almost exclusively in skeletal muscle and acts as a negative regulator of muscle growth

Rodent models of experimental disease states show upregulated myostatin mRNA

Studies in humans show that a lack of functional myostatin results in increased muscle mass due to hyperplasia andor hypertrophy

Interest in Myostatin

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

26

Se-Jin Lee Annual Review Cell Dev Bio 2004

TGFβ Superfamily

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

27

Activation of Myostatin Pathway

Activation of Myostatin Pathway

Myostatin Pathway Blockade

Skeletal Muscle Growth Leanness

Muscle Wasting Cachexia Syndrome

Myostatin Effects

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

28

Naturally deficient Naturally deficient myostatin genemyostatin gene

Myostatinrsquos Obvious Effects

Genetically created deficient myostatin gene

(Knockout)

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

29

Myostatin and Humans

But not just cattle and But not just cattle and mice helliphellipmice helliphellip

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

30

Se-Jin Lee Annual Review Cell Dev Bio 2004

Inhibition of the Myostatin Inhibitor

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

31

Myostatin Signaling

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

32

Myostatin vs Other Established Muscle Metabolism Pathways

Mature Myocyte Myoblast

IGF1

PI3KAkt

FOXO

Ubiquitin-ProteasomePathway

(Atrogin-1 MuRF-1)

PROTEIN (eg MHC)DEGRADATION

mTOR

GSK3

eIF2B 4EBP1S6K

PROTEINSYNTHESIS

MyoDMEF2

CdK2 CdK inhibitors(p21)

PhosphoSMAD23

DifferentiationMyogenesis

+

-

PhosphoActRIIb

MYOSTATIN

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

33

Skeletal muscle wasting is prevalent in a variety of diseases

Weightlessness during space flight

Cancer cachexia

Muscular dystrophy

Geriatric sarcopenia

Obesitydiabetes

Skeletal muscle wasting results in reduced muscle strength disability and impaired quality of life

No current therapy to prevent or reverse muscle atrophy

Potential for Blocking Myostatin

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

34

Suspended at 30ordm for 14 days

Access to 100 of cage

Food and water ad libitum

12-h photoperiod

Disuse Models

Human bedrest (6ordm Head Down Tilt)

Durations - days to months Cardiovascular muscle and bone

effects Controlled diet

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

35

791090

2

4

6

8

10

12

14

16

US P TS P

So

leu

s W

et M

ass

(mg

)

Muscle Mass

Whole Animal Leg Strength

Hindlimb Suspension Effects

Isolated Muscle Strength

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

36

2200

2250

2300

2350

2400

2450

2500

2550

2600

2650

2700

0 2 4 6 8 10 12 14

Day of Study

Bo

dy

Mas

s (g

ram

s)

US D

US P

TS D

TS P

Body Mass

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

37

15

16

17

18

19

20

21

22

US P US D TS P TS D

Lea

n B

od

y M

ass

(g

)

0

asymp

Lean Body Mass

US gt TSPlt0001

D gt PPlt0001

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

38

Study Design

Subjects ndash 10 male volunteers 18-45 years old 10 day strict horizontal bed rest with restricted 5 day

lead in and 4 day follow up periods Controlled diet ndash 55 carb 30 fat 15 protein Caloric intake set to maintain body weight

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

39

RawImage

Partially ProcessedImage

Double Threshold Analysis

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

40

Quadriceps Size Change

50

60

70

80

90

Pre-Bed Rest End-Bed Rest

Mea

n C

SA

S

lice

(cm

2 )

-50

-10

-8

-6

-4

-2

0

Δ C

hang

e M

ean

CS

A (

)

p lt 0001

MRI images obtained with Tr = 550ms Te = 10ms Slice thickness = 1cm with 0 overlap Pre-BR and end-BR slices aligned on anatomical features Analysis from distal end of rectus femoris to highest portion of thigh excluding the

gluteus maximus

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

41

GDF8 vs Δ Muscle Size

Correlation found between absolute level of GDF8 expression pre-bed rest with change in muscle size

Correlations between Δ muscle size and Δ myostatin expression were not observed

-10

-8

-6

-4

-2

000 10 20 30 40

Pre-BR GDF8GAPDH

Δ Q

uads

Mea

n C

SA

(

)

r = - 066p lt 005

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-

42

Summary of Muscle Feedback

Muscle Strength (PCSA)

IGF-1

ProteinDegradation

ExternalLoads Demands

Insulin

Protein Synthesis

Circulating IGF-1

Satellite CellActivation

+

Myostatin

MuscleHypertrophy

MuscleHyperplasia

+

Transduction Mechanical Electrical

--

-

-