Mechanical Force Effects on Cellular
Functions
Yeh-Chuin Poh
Department of Mechanical Science and Engineering
5th May 2011
May 2011
Introduction
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
May 2011
2
Introduction: Forces are Important in
Living Cells
Forces play a major role in biological functions like:
Cell spreading
Cell migration (wound healing)
Cell contraction
Cell division
Regulates cell functions
Gene expression
Protein synthesis
Cell proliferation
Ingber, Nat. Rev. Mol. Cell. Biol., 2005
May 2011
3
Cells Respond to External Mechanical
Stimuli
Wu, CC et al., PNAS, 2007
Kurpinski, K et al., PNAS, 2006
May 2011
Katsumi, A et al., JCB, 2002
4
Cells Respond to External Mechanical
Stimuli
Discher et al, Science Rev 2009
Hahn and Schwartz, Nat Rev Mol Cell Bio 2009
Discher et al, Science 2005
May 2011
5
Force Unfolding of Proteins and Opening
of Ion Channels Within Cells
-spectrin undergoes force induced
structure change exposing binding
sites for ligands.
Mechanosensitive ion channels
Vogel & Sheetz, Nat Rev Mol Cell Biol, 2006
C Johnson et al., Science, 2009
May 2011
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Stress Induced Src Activation is Rapid
Normalized
emission ratio
1.4
+EGF
1.2
20 s
12 s
EGF
1.0
0
3
100 200
Time (s)
Normalized
emission ratio
1.2
300
+Stress
+
1.1
+EGF
1.0
0
1
2
Time (s)
3
S Na et al., PNAS, 2008
May 2011
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Rac Signaling Pathway
PDGF
PDGF R
Extracellular
Plasma membrane
Cytoplasm
Src
Rac
M Ouyang et al., PNAS, 2008
May 2011
8
Stressed Induced Rac Signaling Pathway
is Different from Soluble Factor
+PP1 (10 mM, 1 hr)
-Stress
+Stress
3.0
Overlay
0.3 s
1.0 s
5.0 s
0.5
Brightfield
Poh et al., PLoS ONE, 2009
May 2011
9
E-cadherin are mechanosensors
Vinculin potentiates Ecadherin
mechanosensing and is
recruited to actinanchored sites within
adherens junctions in a
myosin II–dependent
manner
Le Duc et al., JCB, 2010
May 2011
10
Mechanical Effects on Stem Cells
• Maintain Pluripotency in ESCs
mouse
LIF
2i
human
bFGF
mTOR
• Induce differentiation
a.
b.
c.
d.
e.
RA
SaB-vitamin C
Proprietary chemicals
Endogenous factors
Natural products
• iPS cell reprogamming with defined factors
a.
b.
May 2011
Yamanaka coktail
Other defined factors
Lutolf MP et al., Nat Biotechnol, 2005
11
Pluripotency
Mechanical Effects on Stem Cells
Force
Force
Discher, DE et al., Science, 2009
May 2011
12
Substrate Rigidity Dictates Mesenchymal
Stem Cells Differentiation Lineage
Neurogenic
Myogenic
Osteogenic
Engler et al, Cell 2006
May 2011
13
Soft Substrate Promotes Self-Renewal of
Embryonic Stem Cells
F Chowdhury et al, PLoS ONE 2010
May 2011
14
Cell Shape Affects Human Mesenchymal
Stem Cell Differentiation Lineage
Chen, CS et al., Dev. Cell, 2004
May 2011
15
Topography Controls Adult Stem Cell
Fate
Chen, CS et al., Dev. Cell, 2004
May 2011
16
Direct Mechanical Stress Induces
Embryonic Stem Cell Differentiation
Chowdhury et al, Nat Mat 2009
May 2011
17
Stress Induced Spreading of Embryonic
Stem Cell
Chowdhury et al, Nat Mat 2009
May 2011
18
Biomaterials in Stem Cell Differentiation
OrthomimeticsTM received CE
Mark of approval for the repair
or articular cartilage and bone.
Currently undergoing clinical trial.
May 2011
19
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)
May 2011
20
Thank you for your
attention!
May 2011
21
Membrane-targeted Src reporter
GC
CFP SH2
Plasma membrane
substrate YFP
Y. Wang et al. Nature 2005
433 nm
433 nm
476 nm
527 nm
Src + ATP
SH2
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