Multiscale modelling of angiogenesis during bone regeneration...Best Doctoral Thesis Award European Society of Biomechanics The world is full of accidents… 7/07/2015 Aurélie Carlier

To heal or not to heal? Multiscale modelling of angiogenesis

during bone regeneration

Aurélie Carlier

Best Doctoral Thesis Award European Society of Biomechanics

http://www.ulg.ac.be/

The world is full of accidents…

7/07/2015 Aurélie Carlier – ESB Best Doctoral Thesis Award 2

Fracture healing

7/07/2015 3 Aurélie Carlier – ESB Best Doctoral Thesis Award

Fracture healing


Fracture healing


Fracture healing


Fracture healing


Treatment strategies

• USA: 6 million fractures/year

o 5-10 % delayed healing or non-union

• mechanical problem

o external/internal fixation

• biological problem

o bone grafting • autologous

• allogeneic

• synthetic

o tissue engineering


[TE, Van

Blitterswijk

et al.]

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Objectives

• computational modelling is a useful tool

o study the complex interplay between factors

o observe emergent behavior (multiscale models)

o propose and test possible biological mechanisms

o design and test experimental strategies

7/07/2015 9

Objective 1: development of a novel multiscale bioregulatory

model including a detailed description of angiogenesis

Objective 2: development of a novel multiscale bioregulatory

model including a detailed description of oxygen

Objective 3: application of the novel multiscale model to

cases of impaired bone regeneration

Aurélie Carlier – ESB Best Doctoral Thesis Award

Bone regeneration model






Hypothesis

7/07/2015 13

• bone is a highly vascularised tissue

• due to vessel rupture oxygen tension will decrease

o from 14 to 1.6% (after 10 days, sheep tibia) [Epari et al., Bone, 2008]

→ need for revascularisation

(angiogenesis) to heal the fracture

→ influence of oxygen on fracture healing

[Duvall et al.,

JBMR, 2007]

[Macdonald et al.,

Med. Biol. Eng. Comput., 2013]




The influence of oxygen


• Each process has its specific oxygen ‘working range’

• These ‘working ranges’ must be based on experimental

evidence!

0.1 0.8 2 7 4 5 6.5 8 12 1.5

oxygen tension (%)



Sprouting angiogenesis


quiescent vessel

VEGF

sprouting



VE

GF

blood vessel integrity ?


Aurélie Carlier – ESB Best Doctoral Thesis Award 7/07/2015

VEGFR-2 Notch1 VEGF Dll4

TIP STALK STALK

VE

GF

D

V’ N’

D

V’ N’

D

V’ N’

Dll4-Notch signaling !

19



Blood flow


[Carmeliet et al., Nature, 2010]



Numerical methods


• compute new position of each tip cell

o speed

o direction

• anastomosis?

• update the intracellular level of every EC

• sprouting?

• calculate continuous variables

• continue loop until endtime

Computational model results

VEGF O2 tension

7/07/2015 24

days post fracture

low high


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Computational model results

bone active blood vessels

7/07/2015 25

days post fracture

low high











Tissue fractions

26 7/07/2015 Aurélie Carlier – ESB Best Doctoral Thesis Award

Average oxygen concentration


Dll4 over- and underexpression

28

Dll4 standard

Dll4 over-

expression

Dll4 under-

expression

VEGFR-2 levels

7/07/2015 Aurélie Carlier – ESB Best Doctoral Thesis Award

Preliminary conclusions

• first multiscale model of fracture healing

• rigorous summary of the state-of-the-art literature on the

influence of oxygen on fracture healing

• first step towards a full implementation of blood flow

• captures many aspects of

o tip cell selection

• salt and pepper pattern

• increased tip cell density due to loss of Dll4 and in high VEGF

o bone regeneration

• emergent behavior

• interaction: angiogenesis ↔ osteogenesis


Towards clinical applications

30

computational

model

large segmental

defects

NF-1

patients

bone graft

healing


Normal versus critical size

7/07/2015 31

bone formation

5 mm 0.5 mm

90 days 35 days

low high











Normal versus critical size

7/07/2015 32

active blood vessels

5 mm 0.5 mm

90 days 35 days











Muscle damage is important!

damaged muscle

7/07/2015 33

healthy muscle



bone

bone

low

high



















Optimal timing of treatment


Towards clinical applications

35

computational

model

large segmental

defects

NF-1

patients

bone graft

healing


NF1 patients


[Pannier et al., OTSR, 2011]

[Schindeler et al., Bone, 2008]

NF1 model results

bone normal patients bone NF1 patients

7/07/2015 37

days post fracture

low high











NF1 model results

blood vessels normal patients blood vessels NF1 patients

7/07/2015 38

days post fracture











NF1 model results

fibrous tissue normal patients fibrous tissue NF1 patients

7/07/2015 39

days post fracture

low high











Preliminary conclusions

• powerful framework to investigate the non-linear oxygen

dependent dynamics

• oxygen model captures the fundamental mechanisms of

bone regeneration

o large bone defects

o bone graft healing

o NF1 patients

• important role of the host environment


Conclusions

• Establishment of a novel computational framework of

bone regeneration including:

o a multiscale description of sprouting angiogenesis,

including the Dll4-Notch signalling pathway

o a first implementation of blood flow

o an accurate description of the influence of oxygen on

the behaviour of skeletal cells

41 Aurélie Carlier – ESB Best Doctoral Thesis Award

[LEGENDO, KU Leuven]

7/07/2015

Conclusions

• Application to three cases of impaired healing:

• large segmental defects: • mechanism of action

• design of a treatment strategy

• bone graft healing: • accurate prediction of the experimentally observed bone formation

patterns

• bone healing in NF1 patients: • first model to capture the effect of a NF1 mutation on bone healing

• captures the different degrees of severity of impaired bone healing

42 Aurélie Carlier – ESB Best Doctoral Thesis Award 7/07/2015

Conclusions


Outlook

• extensive quantitative characterization of the bone

regeneration process

o influence of the host environment


Outlook

45

[Carlier et al., WIREs Syst Biol, 2015]


References • Carlier, A., Brems, H., Ashbourn, J.M.A., Nica, I., Legius, E., Geris, L. (2015)

Capturing the wide variety of impaired fracture healing phenotypes in NF1 patients with eight key factors: a computational study. under review

• Carlier, A., Geris, L., Lammens, J., Van Oosterwyck, H. (2015). Bringing computational models of bone regeneration to the clinic. WIREs Syst Biol Med, doi:10.1002/wsbm.1299

• Carlier, A., van Gastel, N., Geris, L., Carmeliet, G., Van Oosterwyck, H. (2014). Size does matter: an integrative in vivo-in silico approach for the treatment of critical size bone defects. PLoS Comput Biol, 10(11), e1003888

• Carlier, A., Geris, L., van Gastel, N., Carmeliet, G., Van Oosterwyck, H. (2014). Oxygen as a critical determinant of bone fracture healing – a multiscale model. J Theor Biol, 365, 247-264

• Carlier, A., Geris, L., Bentley, K., Carmeliet, G., Carmeliet, P., Van Oosterwyck, H. (2012). MOSAIC: A Multiscale Model of Osteogenesis and Sprouting Angiogenesis with Lateral Inhibition of Endothelial Cells. PLoS Comput Biol, 8(10), e1002724,

• Chai, Y.C., Carlier, A., Bolander, J., Roberts, S.J., Geris, L., Schrooten, J., Van Oosterwyck, H., Luyten, F.P. (2012). Current views on calcium phosphate osteogenicity and the translation into effective bone regeneration strategies. Acta Biomaterialia, 8(12), 3876-3887

• Carlier, A., Chai, Y., Moesen, M., Theys, T., Schrooten, J., Van Oosterwyck, H., Geris, L. (2011). Designing optimal calcium phosphate scaffold-cell combinations using an integrative model based approach. Acta Biomaterialia, 7, 3573-3585


Acknowledgements • Prof. dr. ir. Liesbet Geris (ULG) (supervisor)

• Prof. dr. ir. Hans Van Oosterwyck (KUL) (supervisor)

• Prof. dr. Katie Bentley (collaborator)

• Prof. dr. Geert Carmeliet (collaborator)

• dr. Nick van Gastel (collaborator)

• dr. Hilde Brems (collaborator)

• Research Foundation Flanders (FWO-Vlaanderen)

• Prometheus, division of Skeletal Tissue Engineering

at the KU Leuven

http://erc.europa.eu/index.cfm

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Multiscale modelling of angiogenesis during bone regeneration...Best Doctoral Thesis Award European Society of Biomechanics The world is full of accidents… 7/07/2015 Aurélie Carlier