30 September 2004
Background: Mechanical forces associated with blood flow are critical in the regulation of vascular smooth muscle cell (VSMC) growth, migration, differentiation and apoptosis as fundamental features in the pathogenesis of vascular disease. We investigated the effect of pulse pressure on VSMC apoptosis. Methods: Using a perfused transcapillary co-culture system, bovine thoracic aortic SMC (BASMC) were exposed to increases in pulsatile flow (0.3–17 ml/min) and hence pulse pressure (amplitude of pulse 6–50 mm Hg) in the absence or presence of bovine aortic endothelial cells (BAEC). The extent of apoptosis was determined by measuring caspase-3 activity, the levels of pro- and anti-apoptotic Bcl-2 family proteins, FasL and cellular apoptosis susceptibility (CAS) protein expression and the extent of DNA fragmentation. Results: Changes in pulse pressure resulted in a significant force- and time-dependent increase in caspase-3 activity in BASMC. This effect was maximal after 6 h, independent of BAEC presence, and attenuated following inhibition of mitogen-activated protein kinase (MAPK) activity with PD98059. In parallel cultures, there was a significant increase in Bad and Bax expression, concomitant with an increase in DNA fragmentation, and a significant decrease in Bcl-2 and Bcl-X<sub>L</sub> expression. The pro-apoptotic effects of pulse pressure were specific for differentiated cells but independent of p53, inasmuch as FasL and CAS expression were enhanced in differentiated adult cells but decreased in de-differentiated embryonic cells in response to flow. Conclusions: These results suggest that pulse pressure promotes phenotypically distinct VSMC apoptosis in vitro in an endothelial-independent, MAPK-dependent, manner.