G protein coupling of lipid metabolism in diabetic heart

Washington University, Saint Louis MO

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Abstract

Both Type I and Type II diabetes are accompanied by a profound switch in myocardial substrate utilization form one which utilizes nearly equal amounts of glucose and fatty acid to a state which predominantly employs FA for substrate. G-proteins in he heart have important effects in mediated the electrical and contractile proteins for myocardium which depend, in part, on an appropriate membrane microenvironment to carry out their specific functions. In the diabetic state profound changes in lipid synthesis occur including alterations in phosphatidylinositol (to which Gq is coupled through phospholipase C leading to IP3 generation) and in the content of plasmalogen which have dramatic effects on membrane fluidity and dynamics. During the last fie years substantial evidence has been accrued demonstrating the altered activity and function of the G-protein axis in diabetic myocardium. These include decreases in beta adrenergic receptor number, increases in Gq-protein mass, altered G-protein receptor-effector coupling, increases in PKCepsilon activity and changes in intracellular calcium ion homeostasis. Thus, it seems likely that altered G signaling contributes to, or underlies the propagation of the pathophysiology manifest in the diabetic heart. The primary hypothesis of Project 4 is that diabetic cardiomyopathy develops as a result of abnormal stimulation of Gq and Gi protein- mediated signaling pathways that leads to alterations in intracellular phospholipases, peroxisomal lipid metabolism and lipid second messenger generation. In order to test this model of diabetic cardiomyopathy we will evaluate the functional and biochemical sequelae of increased or decreased G protein-mediated signal transduction in diabetic murine myocardium. In particular, we will determine whether reduced Gq and Gi signaling in the heart inhibits the development of cardiomyopathy in diabetic mice. G protein signaling will be attenuated by use of RGS4, a GTPase activating protein for Gq and Gi family members. The identify of the specific G protein involved will be determined by targeted disruption of individual Galpha subunit genes. In addition, we will evaluate whether increased Gq signaling potentiates the development of diabetic cardiomyopathy. Furthermore, we will determine whether Gq or Gi signal transduction in heart promotes PLA2 activation and changes in lipid metabolism. Finally, we will examine the transduction in heart promotes PLA2 activation and changes in lipid metabolism. Finally, we will examine the physiological role of the sarcolemmal phospholipase cPLA2gamma, in the pathogenesis of diabetic cardiomyopathy and we will determine whether G protein-mediated signaling regulates activation of this phospholipase.