Received for publication April 24, 2008.
Revised July 14, 2008.
Accepted for publication July 14, 2008.

The Alpha_1D-Adrenergic Receptor Induces Vascular Smooth Muscle Apoptosis via a p53-Dependent Mechanism

Abstract

Activation of the endogenous alpha1-adrenergic receptor (AR) associated human aortic smooth muscle cells resulted in a dose and time-dependent increase in the levels of mitochondrial reactive oxygen species (ROS). ROS increases were apparent within 10 min and maximal after 45 min. Prolonged activation (>4 hr) of the alpha₁-AR resulted in smooth muscle cell apoptosis. Both the increase in ROS and apoptotic cell death were blocked by the non selective alpha₁-AR antagonist prazosin as well as the selective alpha_1D-AR antagonist BMY 7378. Increases in ROS and apoptosis produced by alpha₁-AR activation were also blocked by the p38 MAP kinase inhibitor SB 202190 and the NAPDH oxidase inhibitor apocynin. The ERK1/2 inhibitor PD 98059 or the JNK inhibitor SP 600125 were without effect on increases in ROS levels or apoptosis. Pifithrin alpha, an inhibitor of the tumor suppressor protein p53, had no effect on ROS generation but did block alpha_1D-AR-induced apoptosis. Activation of the alpha_1D-AR resulted in translocation of p53 to the mitochondria. The mitochondrial translocation of p53 was blocked by prazosin, BMY 7378, apocynin, SB 202190 and pifithrin alpha. Apoptosis was also blocked by siRNA directed against p53.These data show that the alpha_1D-AR is coupled to the generation of mitochondrial ROS by a pathway involving p38 and NADPH oxidase. Sustained activation of the alpha_1D-AR results in smooth muscle cell apoptosis in a pathway that involves the tumor suppressor protein p53 and the mitochondrial translocation of p53. The data also provide evidence of a linkage between the alpha_1D-AR and p53.

Key words: Adrenergic, Gq/11 family, Immunocytochemistry, Apoptosis, Reactive intermediates