Requirement for Protein Kinase C in Reactive Oxygen Species–Induced Apoptosis of Vascular Smooth Muscle Cells

Abstract

Background —Vascular smooth muscle cell (VSMC) apoptosis is a component of a variety of cardiovascular diseases and may be related to reactive oxygen species (ROS). This study was designed to determine the role of protein kinase C (PKC) in ROS-induced VSMC apoptosis. Methods and Results —Rat aortic VSMCs were exposed to H 2 O 2 , and the nature of cell death was characterized in the absence or presence of different PKC inhibitors. The results demonstrate that exposure of VSMCs to H 2 O 2 led to a dose-dependent (25 to 100 μmol/L) and time-dependent (peak at 2 minutes) activation of PKC. Among the PKC isoforms α, β, δ, ε, and ζ, only PKC-α and PKC-ε were found to change their intracellular distribution on H 2 O 2 treatment. Apoptosis was the predominant form of cell death when PKC had been activated by H 2 O 2 alone or by H 2 O 2 in the presence of 50 nmol/L phorbol 12-myristate 13-acetate. In contrast, necrosis became the predominant form of cell death when PKC had been downregulated by prolonged exposure to 200 nmol/L phorbol 12,13-dibutyrate or inhibited by 50 nmol/L staurosporine, 100 nmol/L calphostin C, or 30 μmol/L H-7. In addition, caspase-3 was activated in H 2 O 2 -induced VSMC apoptosis but not when PKC was downregulated or inhibited. Inhibition of caspase-3 by 50 μmol/L Ac-DEVD-CHO could significantly attenuate H 2 O 2 -induced apoptosis and was not associated with the induction of necrosis. Conclusions —We conclude that in VSMCs, PKC converts the ROS-induced signals from necrotic cell death to the activation of an apoptotic cell death program. These data imply a novel and important role of PKC for the pathogenesis of such vascular diseases as atherosclerosis, restenosis, and hypertension.