Effect of ANG II on endothelial cell apoptosis and survival and its impact on skeletal muscle angiogenesis after electrical stimulation

Biotechnology and Bioengineering Center, Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin Submitted 30 January 2008 ; accepted in final form 17 April 2008 We have previously shown that skeletal muscle angiogenesis induced by electrical stimulation is significantly attenuated when SS-13 BN /Mcwi rats are fed a high-salt diet. This effect was associated with a large increase in endothelial cell (EC) apoptosis. We hypothesized that the low levels of ANG II during high-salt diet would increase EC apoptosis and consequently diminish the angiogenic response. To test this hypothesis, a series of in vitro and in vivo studies was performed. EC apoptosis and viability were evaluated after incubation with ANG II under serum-free conditions. After 24 h of incubation, ANG II increased EC viability and Bcl-2-to-Bax ratio along with a dose-dependent decrease in EC apoptosis. This effect was blocked by the ANG II type 1 receptor antagonist losartan. To confirm our in vitro results, ANG II (3 ng·kg –1 ·min –1 ) was chronically infused in rats fed a high-salt diet (4% NaCl). ANG II decreased EC apoptosis and produced a significant increase (40%) in skeletal muscle angiogenesis after electrical stimulation. These in vivo results were in agreement with our in vitro results and demonstrate that the attenuation of ANG II levels during a high-salt diet may induce EC apoptosis and consequently block the angiogenic response induced by electrical stimulation. Furthermore, under normal conditions, ANG II increases EC viability and protects EC from apoptosis possibly by inactivation of the mitochondrial apoptotic pathway. renin angiotensin system; endothelial cell apoptosis; angiogenesis Address for reprint requests and other correspondence: A. S. Greene, Dept. of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226 (e-mail: agreene{at}mcw.edu )