Bone Homeostasis and Pathology - Rochester, NY · § Factors regulang bone homeostasis § Disorders of bone homeostasis: -Bone loss -Abnormal bone acquisi

BoneHomeostasisandPathology

Instructor:RomanEliseev

Outline:§ Boneanatomyandcomposi<on§ Boneremodeling§  Factorsregula<ngbonehomeostasis§ Disordersofbonehomeostasis:

-Boneloss-Abnormalboneacquisi<on

§ MethodsandMouseModels

AdultSkeletonAxialSkeleton

AppendicularSkeleton

Imagefromwww.pngall.com

206bones

AdultBoneArchitecture

Diaphysis

Epiphysis

Cor<calboneMarrowcavity

Trabecularbone

Metaphysis

BoneHistology

Trabecularbone

Cor<calbone

Marrowfat

Bonemarrow

Subchondralbone

BoneComposi<onBoneisamineralizedorganicmatrixcomposedof:

•  TypeIcollagenandnon-collagenousproteins(osteoid)•  Hydroxyapa<tecrystals(Ca5(PO4)3(OH))

Bone-formingcellsareosteoblasts(OB)thatproducecollagenIanddepositHA

Osteoblasts

Bone

BoneisFormedbyOsteoblasts

Wagneretal.,PPARRes.,2010

OBsoriginatefromBoneMarrowStromal(a.k.a.MesenchymalStem)Cells(BMSC)andterminallydifferen<ateintoosteocytes(OT).

BoneisResorbedbyOsteoclasts

ImagefromSciencePhotoLibrary

Osteoclasts(OC)areboneresorbingmul<nucleatedcellsthatoriginatefromhematopoie<ccells(monocyte/macrophage)

BoneForma<onvsResorp<on=DynamicEquilibrium(~10%ofadulthumanskeletonis

replacedannually)

Homeostasis=equilibrium(Greek:ὁμοίως+στάσις)

Boneforma<on

Bonerosorp<on

LiningcellsOB

BONE

BloodvesselBMSC

BMSC–bonemarrowstromal(a.k.a.mesenchymalstem)cell

OB–osteoblastOT–osteocyte

TGFb,IGF1,OCN CollagenI

OT

IntactBone

Apoptosis(~70%)

LiningcellsOB

BONE

BloodvesselBMSC


OB–osteoblastOT–osteocyteHSC–hematopoie<cstemcell

OCP–osteoclastprecursor

OT

Remodeling:Ini<alPhase

HSC

OCPRANKL,m-CSF?

OB

BONE

BloodvesselBMSC


OB–osteoblastOT–osteocyteOC–osteoclast

OT

Remodeling:Resorp<onPit

pH≤4

OC

pH≤4

OC

OBOB

BONE

BloodvesselBMSC

TGFb,IGF1

Remodeling:Recruitment/Ac<va<onofBMSCsintoOsteogenicLineage

OB

BONE

BloodvesselBMSC

OT

Remodeling:NewBoneForma<on

Newbone

Osteoblast

Osteocyte

Osteoclast

TRAP Staining

HistologyofBoneRemodeling

Image–courtesyofDr.J.Jonason

PhasesofRemodeling

FactorsRegula<ngBoneHomeostasis

Harada S and Rodan GA., (2003) Nature 423: 349-355.

DisordersofBoneHomeostasis

Boneforma<onbyosteoblastsBone

rosorp<onbyosteoclasts

BONELOSS

Bonerosorp<onbyosteoclasts Bone

forma<onbyosteoblasts

BONEGAIN

•  Osteogenesis Imperfecta (aka, Brittle Bone Disease) •  Most commonly inherited bone disorder •  Autosomal dominant mutations (over 800 identified) in the genes encoding the α1

and α2 chains of type I collagen •  Clinical features include; skeletal fragility with increased fracture risk, blue sclera,

hearing loss, dental imperfections, joint laxity

•  Osteopetrosis (aka, Marble Bone Disease)

•  Osteoporosis

•  Paget Disease

•  Hyperparathyroidism


CourtesyofDr.J.Jonason

•  Osteogenesis Imperfecta (aka, Brittle Bone Disease)

•  Osteopetrosis (aka, Marble Bone Disease) •  Rare genetic disease characterized by reduced bone resorption •  Autosomal dominant or recessive mutations affecting osteoclast numbers or function •  Clinical features include; frequent fractures, scoliosis, cranial nerve deficits, anemia •  First genetic disease treated with a bone marrow transplant

•  Osteoporosis







•  Osteoporosis •  Common disease associated with decreased bone mass and increased fracture risk •  Caused by both genetic and environmental factors •  High societal burden with ~2 million fractures in the US annually due to osteoporosis,

at a cost of around 22 billion dollars to treat







•  Osteoporosis

•  Paget’s Disease •  Uncontrolled bone remodeling leading, ultimately, to areas of high bone mass that

are architecturally unsound •  Onset in late adulthood with causes unknown (likely to be a combination of genetic

and environmental factors) •  Most prominent clinical feature is bone pain, but can also lead to fracture, bone

deformities, and nerve compression






•  Osteoporosis

•  Paget’s Disease

•  Hyperparathyroidism •  Excess parathyroid hormone (PTH) in the bloodstream due to over-activity of the

parathyroid glands •  Can be primary (due to hyperplasia or tumor of the glands) or secondary (due to

hypocalcemia and compensatory increases in PTH secretion) •  Results in increased bone resorption leading to increased fracture risk



ImagesfromBionewsTexas

-Fracture-Delayed

repair

Osteoporosis

§  Osteoporosisisfoundin70%oftheelderlypopula6on

§  Post-menopausalwomenaremostaffected(25millionAmericanwomenwithOsteoporosis)

§  1.9millionfracturesannuallyduetolowbonemass.

§  1of3womenwilldevelopavertebralfracturebyage65,and1of3womenwilldevelopahipfracturebyage85.

§  $22billiondollarsperyearisspentontrea6ngOsteoporosis.

EpidemiologyofOsteoporosis

Journal of Bone and Mineral Research Volume 29, Issue 9, pages 1917-1925, 20 AUG 2014 DOI: 10.1002/jbmr.2286 http://onlinelibrary.wiley.com/doi/10.1002/jbmr.2286/full#jbmr2286-fig-0001

EpidemiologyofOsteoporosis

C57Bl/6Jmice:

DEXA Dual Energy X-ray Absorptiometry

T-score = comparison to healthy young bone Z-score = comparison to a reference group of

the same age, race, and gender as the patient

DiagnosisofOsteoporosis


An<-resorp<vedrugs:Bisphosphonates

TreatmentofOsteoporosis

Watts NB and Diab DL., (2010) Journal of Clinical Endocrinology and Metabolism. (95)4: 1555-1565.

SERMS


SERMS:Selec<veEstrogenReceptorModulators

Ac6on:Drugsthatactasestrogenagonists,ac<va<ngtheestrogenreceptorinordertoreduceosteoclastac<vityandboneresorp<on.

Drug:Raloxifene(Evista)

Dose:60mg/dayformanyyears

Notes:Notaseffec<veasbisphosphonates.Onlyappearstoprotectspineandnothipsfromfracture.


Boneanabolicagents

PTH: rPTH(1-34); Forteo. Under clinical investigation for the use in fracture non-union repair, treatment of osteoporosis.

BMPs: rBMP2 and rBMP7. Under clinical investigation and use for the repair of fracture non-union (InFuse). Recent complications in spinal fusion.

Neutralizing antibodies for Wnt inhibitors: anti-Dkk1 and anti-SOST. Under research and pre-clinical investigation for treatment of OA and fracture repair.

LabMethodstoAssessBoneHomeostasis

DEXA


micro-CT

Shumetal.,PLoSOne,2016


Histology/Histomorphometry


PrimaryMeasurements:-BoneArea(B.Ar.)vsTotalArea(T.Ar.)-Surface,i.e.BoneSurface(BS)-CellNumberperSurface/Area

=OB.N.=OT.N.

OsteoMeasureorVisiopharm


Histology/Histomorphometry


PrimaryMeasurements:-Surface:OsteoclastSurfaceperBoneSurface(OC.S./BS)-CellNumber:OsteoclastNumberperBoneSurface(N.OC/BS)


DynamicBoneLabeling(BoneForma<on)

MiceareinjectedwithAlizarinRed10dbeforesacrifice&withCalcein5dbeforesacrifice.Bonearefrozenandsec<oned.Labeledboneisvisualizedusingfluorescencemicroscopy.


DerivedIndices:-MineralizingSurface(MS/BS)-MineralApposi<onRate(MAR)-BoneForma<onRate(BFR)


BoneTurnoverSerumMarkers

Forma<on: Resorp<on:

P1NP CTXPerrecommendaKonoftheInternaKonalOsteoporosisFoundaKon(IOF)andtheInternaKonalFederaKonforClinicalChemistry(IFCC)

UsefulMouseModels

Osteolineage-specificCreModels:•  BMSC:Prx1,Nes<n,LepR,aSMA,Osx•  OB:Osx(early),Col13.2kb(early),Col1

2.3kb(late),OCN(late)•  OT:DMP1

UsefulMouseModels

Osteoclast-specificCreModels:•  CD11b•  Lyzm•  Trap

Take-HomeMessage

Bonehomeostasisisadynamicequilibriumdueto

opposingac<onsandcouplingofbone-formingOBsandbone-resorbingOCs.

Documents

Bone Homeostasis and Pathology - Rochester, NY · § Factors regulang bone homeostasis § Disorders of bone homeostasis: -Bone loss -Abnormal bone acquisi