MECHANISMS OF ACCELERATED VASCULAR DISEASE IN DIABETES

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Patients with diabetes suffer greater cardiovascular morbidity and mortality than non-diabetic subjects. The lethal cardiovascular sequelae of diabetes are related to intrinsic myocardial dysfunction ("diabetic cardiomyopathy"), increased vulnerability to myocardial ischemia and accelerated atherogenesis which cannot be fully accounted for on the basis of traditional risk factors. This Program Project will investigate a novel, unifying hypothesis that links the diverse cause of increased cardiovascular mortality in diabetic patients to a single mechanism involving abnormal regulation of calcium-independent phospholipase A2 (PLA2) in the heart and blood vessels. Activation of this enzyme mediated by increased glycolytic flux in diabetes leads to enhanced release of arachidonic acid and downstream effects of this lipid second messenger to produce both cardiac and vascular derangements. Project 2 of the Program Project will test this unifying hypothesis as it pertains specifically to the pathogenesis of macrovascular disease in diabetes. Combining the well characterized and widely used rat models of streptozotocin-induced diabetes and vascular response to balloon injury, we will test the hypothesis that by inappropriately regulating calcium- independent PLA2 activity through enhanced glycolytic flux, diabetes promotes neointimal proliferation, endothelial cell dysfunction, and enhanced vascular thrombogenicity. We will also induce diabetes with streptozotocin in LDL receptor -/- mice to determine whether diabetes accelerates the atherogenic process and to characterize the role of calcium-independent PLA2 in this effect. Subcellular sites of increased arachidonic acid turnover induced by diabetes in vascular endothelial cells, smooth muscle cells and macrophages will be identified and the role of calcium-independent PLA2 in accelerated arachidonoyl phospholipid turnover during the inflammatory and proliferative responses of diabetic arteries to injury will be characterized. We will also test key tenets of the unifying hypothesis in human vascular disease by characterizing calcium-independent PLA2 activity and phospholipid metabolism in atherosclerotic lesions from diabetic patients. The results of this project will contribute importantly to the overall objective of the Program Project to elucidate fundamental mechanisms that underlie both the myocardial and vascular complications of diabetes and, ultimately, facilitate development of new therapy to diminish the lethal consequences of diabetic cardiovascular disease.