Stephen Schaffer - US grants

The hearts noninsulin-dependent diabetes mellitus are highly susceptible to ischemic and hypertensive damage, respond poorly to stress and are more prone to developing congestive heart failure than the nondiabetic. Since the majority of the 10 million Americans with this type of diabetes die of cardiovascular disease, it is important to begin addressing the causes underlying these cardiovascular complications. The aim of this proposal is to continue studying the consequences of one of the cardiovascular problems of noninsulin-dependent diabetes mellitus, the development of a cardiomyopathy. An animal model appropriate for the study of noninsulin-dependent diabetes mellitus-induced cardiomyopathy has been developed and partially characterized. Hearts from these animals exhibit abnormal carbohydrate metabolism, reduced mechanical function and impaired calcium movement. In this proposal, the effect of NIDDM on calcium transport and one of the factors which regulate calcium transport, membrane phosphorylation, will be examined. Isolated sarcolemmal and sarcoplasmic reticular studies will focus on differences in membrane phosphorylation resulting from diabetes-mediated alterations in intrinsic protein phosphatase and kinase activities, as well as changes in the properties of certain phosphorylatable protein substrates. In vivo phosphorylation of isolated NIDDM and nondiabetic hearts will be carried out. In some experiments the heart will be stimulated by the introduction of certain protein kinase activators. Sarcolemma and sarcoplasmic reticulum from unstimulated and stimulated hearts will be isolated and their calcium transport properties and phosphorylation patterns examined. Also examined will be the effect of the protein kinase activators on mechanical function of the diabetic and nondiabetic heart. These studies will provide information on the physiological significance of some of the diabetes-linked defects. The relevance of these changes will also be explored by examining the effect of diabetes on kinase-mediated changes in calcium transients of isolated myocytes using fura 2 as the calcium probe.

DESCRIPTION: (Adapted from the Investigator's Abstract): Diabetic patients have a two-fold higher mortality rate following myocardial infarction than their non-diabetic counterparts. Despite this, the effect of diabetes on ischemic injury is controversial. In some studies, ischemia reperfusion injury is actually reduced in diabetic models. One likely source of this variability is in the levels of cardioprotective and cardiotoxic factors in the diabetic animal. A major goal of the proposed research is to identify some of the regulatory factors found in the diabetic heart. Preliminary data suggest that one of the important factors is hyperglycemia. The proposal introduces the hypothesis that glucose enhances the production of diacylglycerol, leading to activation of protein kinase C, followed by up regulation of the cardioprotective factor, Bcl-2. PKC and Bcl-2 levels will be monitored by Western blot analysis. In addition, the role of catecholamines and angiotensin-2 as factors augmenting ischemic damage and reversing glucose-induced up regulation of Bcl-2 will be examined. The extent of apoptosis, necrosis, mitochondrial membrane potential changes and caspase activation will be examined in the presence of elevated glucose and following treatment with neurohumoral factors prior to a hypoxic stimulus. Cell culture studies will be complimented by studies using an isolated heart model to test the hypothesis that hypertensive diabetic hearts will be more susceptible to an ischemic insole because of elevated levels of angiotensin.