Role of Smooth Muscle Cells in Graft Intimal Hyperplasia

Cleveland Clinic Lerner Com-Cwru, Cleveland OH

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Abstract

DESCRIPTION (provided by applicant): Prosthetic grafts are used widely in vascular reconstructive surgery, but their long-term patency is limited, in part due to the development of anastomotic intimal hyperplasia characterized by accumulation of smooth muscle cells (SMC) and deposition of extracellular matrix, particularly collagen type I. We have shown that: 1) prosthetic graft material induces monocytic cells to oxidize LDL 2) hypercholesterolemia in rabbits increases cholesterol accumulation in graft compared to native aorta, 3) lipid oxidation products accumulate in grafts compared to adjacent aorta, and 4) oxidized LDL (oxLDL) stimulates platelet-derived growth factor (PDGF) and collagen production by graft SMC but has less effect on aortic SMC. In preliminary studies we have shown that reactive oxygen species (ROS) stimulate a very rapid increase in SMC collagen synthesis without an increase in mRNA. Also ROS increase intracellular concentration of free calcium ([Ca2+]i) and activate protein kinase C-delta (PKCdelta). PKC8 can phosphorylate proteins in the translation initiation complex. Based on our preliminary studies, we propose as an overall hypothesis that lipid oxidation products formed within synthetic vascular grafts create an oxidative stress that stimulates collagen production by SMC though several mechanisms including, a rise in [Ca2+]i and increased translation due to PKCdelta-mediated phosphorylation of initiation factors. Elevated collagen contributes to the development of intimal hyperplasia. We will test our hypothesis by investigating the mechanisms of ROS-induced collagen production and the elevated sensitivity of graft SMC. We will assess levels of endogenous antioxidants in aortic and graft SMC. We will explore the role of elevated [Ca2+]i in increased collagen production, and the mechanism of ROS mediated increase in [Ca2+]i, particularly the role of TRPC6 calcium channels. We will investigate the role of ROS-activated PKCdelta in the increased collagen synthesis. Finally, we will assess the mechanism of translational regulation of collagen production, specifically the role of phosphorylation of initiation factors, and the existence of cellular factors that influence transcript-specific regulation of procollagen mRNA translation. The proposed studies will determine the role of oxLDL and ROS in the increased collagen production by SMC from synthetic vascular grafts compared to SMC from native aorta. Studies will also address the efficacy of antioxidants to control the collagen production. This will lead to a better understanding of the role of lipids in graft healing, and ultimately, to methods limiting collagen synthesis and the development of intimal hyperplasia of prosthetic grafts, thereby prolonging patency of small-diameter vascular grafts.