An emerging body of evidence suggests that vascular cell programmed cell death or apoptosis may be an important determinant of vascular remodeling and lesion formation during the pathogenesis of diseases such as hypertension and atherosclerosis. Although the phenomenon is well described, the factors that regulate vascular smooth muscle cell (VSMC) death in vascular disease are poorly characterized. The applicant is intrigued by his observation that angiotensin II (Ang 11) inhibits VSMC apoptosis via the AT-1 receptor, yet induces VSMC apoptosis via the AT-2 receptor. However, little is known about the mechanisms by which G-protein-coupled receptors modulate programmed cell death. The goal of the proposed project is to systematically dissect the signal transduction pathways that couple extracellular factors such as Ang II with intracellular mediators of the genetic program governing VSMC suicide. The observation that a single ligand (Ang II) can induce diametric effects on the regulation of VSMC apoptosis provides the applicant with a unique opportunity to define the molecular mechanisms by which cell membrane receptor activation specifies whether VSMC survive or die. The proposed project will test the hypothesis that the opposing effects of AT-1 vs AT-2 receptor stimulation on VSMC fate involves a differential activation of G-proteins that transduce countervailing influences on the activation of protein kinase-mediated signals coupled to the regulation of VSMC apoptosis. Specifically, the studies will focus on defining the role of a sequential signaling cascade involving PI-3-kinase, ERK and Akt as essential mediators of the anti-apoptotic effect of Ang II. The proposed project will utilize both pharmacologic and genetic approaches to systematically define the components of the signal transduction that are necessary and sufficient for preventing VSMC death in response to Ang II. Genetic engineering technologies will be employed to create novel in vitro and in vivo model systems for characterizing the molecular determinants of VSMC fate. It is anticipated that the comparative analysis of AT-1 vs AT-2 receptors will elucidate how differences in structural motifs encoded in Ang 11 receptors selectively specify whether VSMC live or die by differential activation of G-proteins, PI-3-kinase, ERK and Akt. These studies will provide important new insights into the molecular mechanisms governing the cell suicide program in VSMC and the potential role of apoptosis in the pathogenesis of vascular diseases.
