MECHANICS OF AORTIC SMOOTH MUSCLE CELLS DURING CYCLIC STRETCH

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MECHANICS OF AORTIC SMOOTH MUSCLE CELLS DURING
CYCLIC STRETCH

• Jeremiah J. Wille1, Wei Du2,
• Elliot L. Elson1,3, Ruth J. Okamoto1,2
• 1Dept of Biomedical Engineering
• 2Dept of Mechanical Engineering
• 3Dept of Biochemistry Molecular Biophysics
• Washington University in St. Louis, MO
• June 24, 2006

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BACKGROUND

• Vascular smooth muscle cells provide an active
  tone to blood vessels
• Cells respond to load and facilitate vessel
  remodeling
• Need to determine passive and active properties
  of vascular smooth muscle cells for
  microstructural and computational models

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MEASURING CELL MECHANICS

• Active properties have been measured in in
  individual isolated cells and native vessels
  under isometric loads
• Bioartificial tissues
• provide a 3D environment for the cells
• proportion of cell force to the overall tissue
  force is greater

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MEASURING CELL MECHANICS
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RING FABRICATION
a
c
b
Collagen Solution

Bovine Aortic Smooth Muscle Cells
e
f
d
Incubation in a humidified environment at 5 CO2
and 37oC
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MECHANICAL TESTING
Computer for data acquisition and motor control
Isometric force transducer
Heated tissue bath
Micrometer
Stepper motor
4 X
Enlarged view
Side view
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PHARMACOLOGIC AGENTS

• CYTOCHALASIN D
• Cytochalasin D disrupts actin filaments and
  inhibits polymerization
• Removal of the actin cytoskeleton eliminates the
  cell contributed force
• NOREPINEPHRINE
• Norepinephrine binds to alpha adrenergic
  receptors, releasing intracellular calcium and
  inducing SMC contraction
• PAPAVERINE
• Papaverine inhibits cyclic nucleotide
  phosphodiesterases (hydrolysis of cAMP and cGMP)
  which in turn increases cAMP/cGMP levels. cAMP
  leads to closure of Ca channels and opening of
  K channels and ultimately the relaxation of the
  SMC

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PEAK FORCE
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CELL FORCE ESTIMATION
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MATRIX SCALING
CytoD
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PEAK FORCES WITH NE/PAP
Papaverine Added
CytoD Added
NE Added
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AMPLITUDE
13
AMPLITUDE
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FREQUENCY
0.001 Hz
0.010 Hz
0.100 Hz
0.250 Hz
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Tissue
Matrix
Cell
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CONCLUSIONS

• Bioartificial tissues provide a new approach to
  the study of active and passive cell mechanics
• Cell stiffness decreases with increasing
  amplitude of cyclic stretch
• Cells adapt to slowly varying length during
  cyclic stretch
• Amplitude of cyclic stretch appears more
  important than strain (relative to baseline
  length)

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ACKNOWLEDGEMENTS

• Judy Fee
• Robert Mecham
• Whitaker Foundation
• Graduate Fellowship (JJW)

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QUESTIONS?
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RING FABRICATION
INCUBATION
GELS

• 2 mg/ml Type I collagen
• 106 cells/ml
• 1 ml total volume

• After 6 hours removed
• from molds and placed
• on spacers
• Media changed every
• other day

MEDIA

• DMEM
• 5 CCS
• 100 mM NEAA
• 2 mM L-Glutamine
• Pen/Strep