Abstract 176: Rapid Stretching and Cyclic Transverse Strain Induce Robust Activation of Focal Adhesion Kinase Signaling in Cardiac Myocytes
This study assesses the mechanical detection mechanism directing cellular adaptation to changes in load in vitro. Distinct types of myocardial hypertrophy in response to different disease states suggest a discriminatory mechanism of the heart perhaps at the cellular level. Our hypothesis is that the direction and rate of cyclic mechanical strain regulate protein phosphorylation in cultured neonatal rat cardiomyocytes. The Flexcell stretch device administers cyclic strain of desired amplitude and frequency upon our cell culture model determining the rate at which strain is applied. Focal adhesion kinase (FAK) is a membrane associating protein which has been shown to have a strain dependent increase in phosphorylation. Using western blot detection, this work shows strain rate dependence as well with a 50% increase in FAK phosphorylation over 0.5 to 2.0 Hz at 10% strain (n=4, p<0.05). Initial results suggest this activation is amplified downstream with corresponding ERK 1/2 phosphorylation. Correlate work distinguishes cell-density dependence of the magnitude of these phosphorylation events. Also, we previously mimicked in vivo alignment of cardiac myocytes with micron scaled architecture of parallel grooves and here orient cultured neonatal rat myocytes to a uniaxial force vector either transverse or longitudinal to the cell polar axis. Results show anisotropic effects with a 25% higher FAK phosphorylation due to cyclic strain across the transverse axis compared with the long axis with 10% strain (n=2). Uniaxial cyclic stretch induces at least a 3 fold increase in ERK 1/2 phosphorylation over basal levels of unstretched cells (n=4, p<0.05) with a higher increase with transverse stretch activation compared to the longitudinal stretch. We conclude that cardiomyocytes exhibit mechanical sensitivity to the direction of force as well as a temporal sensitivity to perturbing forces.