Mechanotransduction of rat aortic vascular smooth muscle cells requires RhoA and intact actin filaments

The growth-promoting effect of mechanical stress on vascular smooth muscle cells (VSMCs) has been implicated in the progress of vascular disease in hy pertension. Extracellular signal-regulated kinases (ERKs) have been implica ted in cellular responses, such as vascular remodeling, induced by mechanic al stretch. However, it remains to be determined how mechanical stretch act ivates ERKs. The cytoskeleton seems the most likely candidate for force tra nsmission into the interior of the cell. Therefore, we examined (1) whether the cytoskeleton involves mechanical stretch-induced signaling, (2) whethe r Rho is activated by stretch, and (3) whether Rho mediates the stretch-ind uced signaling in rat cultured VSMCs. Mechanical stretch activated ERKs, wi th a peak response observed at 20 minutes, followed by a significant increa se in DNA synthesis. Treatment with the ERK kinase-l inhibitor, PD98059, in hibited the stretch-induced increase in DNA synthesis. Cytochalasin D, whic h selectively disrupts the network of actin filaments, markedly inhibited s tretch-induced ERK activation. In the control state, RhoA was observed pred ominantly in the cytosolic fraction, but it was translocated in part to the particulate fraction in response to mechanical stretch. Botulinum C3 exoen zyme, which inactivates Rho p21 (known to participate in the reorganization of the actin cytoskeleton), attenuated stretch-induced ERK activation. Inh ibition of Rho kinase (p160ROCK) also suppressed stretch-induced ERK activa tion dose dependently. Our results suggest that mechanotransduction in VSMC s is dependent on intact actin filaments, that Rho is activated by stretch, and that Rho/p160ROCK mediates stretch-induced ERK activation and vascular hyperplasia.