Diabetes mellitus is associated with a cardiomyopathy that occurs in the absence of hypertension or coronary artery disease and that is characterized by ventricular hypertrophy, decreased ventricular diastolic relaxation, and a reduced peak filling rate. Diabetic cardiomyopathy may develop because of the dysfunctional accumulation of lipids in cardiac myocytes. Insulin action is dependent on the activation of an intracellular signaling pathway that stimulates the serine/threonine kinase Akt2, leading to increased glucose uptake, glucose oxidation and glycogen synthesis. Insulin- stimulated Akt2 activation also may result in altered lipid metabolism. The primary hypothesis of this project is that diabetic cardiomyopathy develops as a result of reduced stimulation of the Akt2 signaling pathway that leads to alterations in intracellular phospholipase activity and abnormal lipid metabolism. Several intracellular PLA2s are expressed in heart, including cPLA2 and iPLA2 . Diabetic myocardium is characterized by an increase in the expression and activity of cPLA2 and iPLA , which liberate free fatty acids, including arachidonic acid, and lysophospholipids from membrane phospholipids. Preliminary data suggests that Akt2 regulates cardiac glucose metabolism and intracellular phospholipase A2 (PLA2) activity. In this project, the specific role of Akt2 in the pathogenesis of diabetic cardiomyopathy will be investigated in mice lacking this kinase. In addition, the biochemical and biological relationship between Akt2 and the intracellular phospholipases cPLA2 and iPLA2 in the pathogenesis of diabetic cardiomyopathy will be investigated by use of cPLA2 -/- akt2-/- and iPLA2 -/- akt2-/- double knockout mice. Experimental results from this project will help to define specific signaling mechanisms involved in the regulation of cardiac myocyte function, metabolism and response to ischemic injury.
Diabetes mellitus, a common disease that is associated with high blood sugar, leads to a tremendous amount of suffering and death in the United States. Patients with diabetes are known to develop a heart problem called diabetic cardiomyopathy that can lead to heart failure. Blood sugar levels are regulated by the action of the hormone insulin that is released from the pancreas and that acts in many tissues throughout the body, causing glucose to go into cells and out of the bloodstream. When insulin travels to different tissues and binds to cells, it activates a cascade of enzymes inside of cells, called signaling proteins, leading to the increased ability of cells to take up glucose from the bloodstream. A critical protein inside of cells that relays the insulin signal is called Akt2. In both juvenile and adult onset forms of diabetes, Akt2 is not activated properly in heart cells. In this proposal, we investigate whether defective Akt2 action is responsible for the heart abnormalities that develop in diabetes. The analysis of the role of Akt2 in diabetic cardiomyopathy may lead to new therapies that may help to reduce the high mortality rate associated with diabetes.
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