Diabetic myocardial disease (cardiomyopathy) is receiving increased attention as a major cause of cardiac failure and death. We have described lesions in the myocardium and intramural coronary arteries of the genetically diabetic mouse C57BL/KsJ db/db that constitute a diabetic cardiomyopathy. More recently we observed similar morphologic changes in myocardial biopsies from diabetic subjects. In our studies concerning the pathogenesis of this cardiomyopathy we have found defective fatty acid Beta-oxidation and pyruvate oxidation, suggesting impairment in the pyruvate dehydrogenase and Beta-hydroxyacyl-CoA dehydrogenase systems in cardiac mitochondria of the db/db 1 mouse. We now hypothesize that this cardiomyopathy has its basis in an abnormality of the plasma membrane that leads to an impaired response following the binding of insulin to the cell surface, resulting in inhibition of fatty acid and pyruvate oxidation. The impaired response may arise from defective production of the insulin second messenger(s). In order to test this hypothesis we propose; 1) to extend our study on the defective oxidative metabolism of the db/db mouse heart by assessing the activity of pyruvate dehydrogenase, Beta-hydroxylacyl-CoA dehydrogenase and Beta-ketoacyl-CoA thiolase in isolated mitochondria during progression of the cardiomyopathy; 2) to determine the content of CoA, carnitine and their derivatives in the heart of the db/db mouse.; 3) to analyse the lipid content of the plasma membranes in the db/db mouse heart.; 4) to test for impaired generation of insulin's second messenger by the abnormal plasma membrane by assaying pyruvate dehydrogenase activity in a subcellular system; 5) to study the effect of insulin on the activation of Beta-hydroxyacyl-CoA dehydrogenase and Beta-ketoacyl-CoA thiolase in a similar subcellular system; 6) to test the mechanism of insulin modulation (phosphorylation-dephosphorylation) of Beta-hydroxyacyl-CoA dehydrogenase and Beta-ketoacyl-CoA thiolase activities; and 7) to assess the myocardial protective and metabolic effects afforded by dietary restriction, and insulin and Clofibrate treatment in the db/db mouse. Thus this project is designed to fill gaps in knowledge regarding insulin regulation of fatty acid metabolism and to establish whether the diabetic cardiomyopathy in the mouse arises from impaired generation of insulin's second messenger and defective cardiac Beta-oxidation.
