Stretch-induced endothelin B receptor-mediated apoptosis in vascular smooth muscle cells

Growing evidence suggests that a pressure-induced increase in the synthesis of endothelin (ET-1) is involved in arterial remodeling and, as a consequence, in the manifestation of chronic hypertension. To study potential stretch-induced changes in gene expression and their functional consequences, we have cultured rat aortic smooth muscle cells (raSMC) and porcine aortic endothelial cells (PAEC) on flexible elastomer membranes. The cells were periodically stretched (up to 20% elongation, 0.5 Hz, 6 h) and the expression of prepro-ET-1 and that of the endothelin A and B receptors (ET(A)-R and ET(B)-R) were analyzed by semi-quantitative RT-PCR analysis and ELISA (ET-1). In contrast to PAEC where ET-1 synthesis was up-regulated up to eightfold on exposure to cyclic stretch, ET-1 synthesis in raSMC was decreased by more than 80% under these conditions. ET(A) R -mRNA expression in stretched raSMC declined to 50% whereas ET(B) R -mRNA levels were increased up to 10-fold. One functional consequence of this apparent shift in receptor abundance was an apoptosis-promoting action of exogenous ET-1 (10 nM), as judged by the appearance of subdiploid peaks during FACS analysis, caspase-3 activation and chromatin condensation. This ET-1-induced apoptosis appeared to be ET(B)-R mediated, as it was completely suppressed by the ET(B)-R antagonist BQ 788 but not by the ET(A)-R antagonist BQ 123. Moreover, raSMC derived from homozygous spotting lethal rats, which lack a functional ET(B)-R, showed no signs of apoptosis after exposure to cyclic strain and exogenous ET-1. These findings suggest a central role for the endothelin system in the onset of hypertension-induced remodeling in conduit arteries, which may proceed via an initial stretch-induced apoptosis of the smooth muscle cells.