Vasoactive substances regulate vascular smooth muscle cell apoptosis - Countervailing influences of nitric oxide and angiotensin II

This study tests the hypothesis that the control of vascular smooth muscle cell (VSMC) apoptosis is regulated by the antagonistic balance between vasoactive substances such as NO and angiotensin II (Aug II). Moreover, it is postulated that the cellular signaling pathways involved in regulating vessel tone are also coupled to the regulation of programmed cell death. Using an in vitro model system, we documented that the addition of NO donor molecules S-nitroso-N-acetylpenicillamine or sodium nitroprusside to VSMC dose-dependently induced apoptosis as documented by DNA laddering and quantified by analysis of cellular chromatin morphology. The mediator role of the guanylate cyclase signaling pathway in NO-induced apoptosis was evidenced by (1) induction of apoptosis by the 8-bromo-cGMP analogue, (2) potentiation of NO-induced apoptosis by cGMP-specific phosphodiesterase inhibition. and (3) the prevention of NO-induced apoptosis by the inhibition of the cGMP-dependent protein kinase I alpha. In contrast, Ang II directly antagonized NO donor- and cGMP analogue-induced apoptosis via activation of the type I Ang II receptor. These findings suggest that the countervailing balance between NO and Ang II may determine the overall cell population within the vessel wall by regulating genetic programs determining cell death as well as cell growth.