In patients with type II diabetes, cardiovascular disease (CVD) is highly prevalent and a major cause of premature mortality and plasma homocysteine (Hcy) levels are increased by 3-4 folds. Hyperhomocysteinemia (hHcy), elevated plasma concentrations of Hcy, has been established as an independent and significant risk factor for CVD, and has been suggested to be responsible for CVD in diabetes that is not explained by traditional risk factors. However, the role of HHcy in diabetic atherosclerosis has not been studied in experimental model. We have previously proposed that Hcy promotes atherosclerosis by stimulating vascular aortic smooth muscle cell (VSMC) proliferation and by inhibiting endothelial cell (EC) growth, and reported that HHcy accelerated spontaneous atherosclerosis in mice. Recently, we found that Hcy potentiated the diabetic inhibitions on EC growth and eNOS activities in human aortic endothelial cells (HAEC). A PKC inhibitor, GFX, reversed these inhibitions. We hypothesize that Hcy potentiates diabetic endothelium damage and eNOS inactivation via PKC activation, which contributes to high prevalence of atherosclerosis in diabetes. This project will study this hypothesis utilizing three linked specific aims. First, in Aim 1, experiments will evaluate the role and mechanisms of Hcy on endothelial cell growth inhibition in diabetes using in vitro and in vivo models. Second, in Aim 2, studies are proposed to determine the role and mechanism of Hcy in eNOS inactivation and PKC activation. Third, in Aim 3, studies will determine the effect of HHcy on endothelial function and atherosclerosis in animal model of diabetes and atherosclerosis. We believe this project will lead to fundamental new insights into the identification of mechanistic links between Hcy and diabetic atherosclerosis. If we can identify the key events in Hcy-induced atherosclerosis in diabetes, genetic or biochemical approaches to block these steps could lead to new therapeutic approaches