Yeh-Chuin Poh Department of Mechanical Science and Engineering5th May 2011

Mechanical Force Effects on Cellular Functions

May 2011

Introduction

2May 2011

What is “mechanotransduction”?

The process and mechanisms by which living cells sense mechanical forces and convert them into biochemical signals.

-S. Na et al, Science Signaling 2008

Introduction: Forces are Important in Living Cells

3May 2011

Forces play a major role in biological functions like:Cell spreadingCell migration (wound healing)Cell contractionCell division

Regulates cell functionsGene expressionProtein synthesisCell proliferation

Ingber, Nat. Rev. Mol. Cell. Biol., 2005

Cells Respond to External Mechanical Stimuli

4May 2011

Wu, CC et al., PNAS, 2007

Katsumi, A et al., JCB, 2002Kurpinski, K et al., PNAS, 2006

Cells Respond to External Mechanical Stimuli

5May 2011

Hahn and Schwartz, Nat Rev Mol Cell Bio 2009

Discher et al, Science Rev 2009

Discher et al, Science 2005

Force Unfolding of Proteins and Opening of Ion Channels Within Cells

6May 2011

C Johnson et al., Science, 2009

-spectrin undergoes force induced structure change exposing binding sites for ligands.

Mechanosensitive ion channels

Vogel & Sheetz, Nat Rev Mol Cell Biol, 2006

Stress Induced Src Activation is Rapid

7May 2011

0 1 2 3

1.0

1.1

1.2

+EGF

No

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ized

em

issi

on

rat

io

Time (s)

+

0 3 100 200 3001.0

1.2

1.4

EGF

No

rmal

ized

emis

sio

n r

atio

Time (s)

12 s 20 s

+Stress

+EGF

0 1 2 3

1.0

1.1

1.2

+EGF

No

rmal

ized

em

issi

on

rat

io

Time (s)

+

0 3 100 200 3001.0

1.2

1.4

EGF

No

rmal

ized

emis

sio

n r

atio

Time (s)

12 s 20 s

+Stress

+EGF

S Na et al., PNAS, 2008

Rac Signaling Pathway

8May 2011

M Ouyang et al., PNAS, 2008

Plasma membrane

PDGF

PD

GF

R

Src

Rac

Extracellular

Cytoplasm

Stressed Induced Rac Signaling Pathway is Different from Soluble Factor

9May 2011

Poh et al., PLoS ONE, 2009

Overlay

0.5

3.0

0.3 s 1.0 s 5.0 s

-Stress +Stress

Brightfield

+PP1 (10 M, 1 hr)

E-cadherin are mechanosensors

10May 2011

Vinculin potentiates E-cadherin mechanosensing and is recruited to actin-anchored sites within adherens junctions in a myosin II–dependent manner

Le Duc et al., JCB, 2010

Mechanical Effects on Stem Cells

11May 2011

• Maintain Pluripotency in ESCs mouse human LIF bFGF 2i mTOR

• Induce differentiationa. RAb. SaB-vitamin Cc. Proprietary chemicalsd. Endogenous factorse. Natural products

• iPS cell reprogamming with defined factorsa. Yamanaka coktailb. Other defined factors Lutolf MP et al., Nat Biotechnol, 2005

Mechanical Effects on Stem Cells

12May 2011

Force

Discher, DE et al., Science, 2009

ForcePlu

ripot

ency

Substrate Rigidity Dictates Mesenchymal Stem Cells Differentiation Lineage

13May 2011

Engler et al, Cell 2006

Neurogenic Myogenic Osteogenic

Soft Substrate Promotes Self-Renewal of Embryonic Stem Cells

14May 2011

F Chowdhury et al, PLoS ONE 2010

Cell Shape Affects Human Mesenchymal Stem Cell Differentiation Lineage

15May 2011

Chen, CS et al., Dev. Cell, 2004

Topography Controls Adult Stem Cell Fate

16May 2011

Chen, CS et al., Dev. Cell, 2004

Direct Mechanical Stress Induces Embryonic Stem Cell Differentiation

17May 2011

Chowdhury et al, Nat Mat 2009

Stress Induced Spreading of Embryonic Stem Cell

18May 2011

Chowdhury et al, Nat Mat 2009

Biomaterials in Stem Cell Differentiation

19May 2011

OrthomimeticsTM received CE Mark of approval for the repair or articular cartilage and bone. Currently undergoing clinical trial.

20May 2011

Conclusion• Cells respond to mechanical stimuli by altering cell shape, migration, contraction

and division

• Cell signaling pathways induced by mechanical stress and soluble factors are different

• Mechanical environment (shape, substrate rigidity, forces, topography) affects stem cells differentiation lineage

• Directed differentiation of stem cells requires both chemical and mechanical cues

• Substrate rigidity may also promote embryonic stem cell self-renewal

• Stem cells have promising therapeutic advantages. We need better mechanistic understanding of developmental and homeostatic conditions (physiological, pathological)

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Thank you for your attention!

May 2011

22May 2011

Y. Wang et al. Nature 2005

GC CFP SH2 substrate YFP

Plasma membrane

Membrane-targeted Src reporter

433 nm

SH2

Src + ATP

476 nm433 nm

527 nm

23May 2011