Hyperinsulinemia causes and maintains insulin resistance just as insulin resistance causes and maintains insulin hypersecretion. Because of this interdependency, determining which came first is problematic. There are no compelling data that support hyperinsulinemia (elevated insulin secretion in the absence of elevated glucose) or insulin resistance as the initiating event: both coexist. Type 2 diabetes occurs when the ss-cell fails to compensate for insulin resistance. The sustained elevation in insulin secretion develops through a mechanism independent from the well-established pathway described for fuel-stimulated secretion. The focus of this application is to identify the mechanism of basal hypersecretion and to determine ways to reverse it. We hypothesize that environmental factors or nutrient excess increase the redox state leading to increases in reactive oxygen (or nitrogen) species (ROS). Thus, nutrient excess results in ROS generation. Glucose-independent stimulation of insulin secretion leads to initial insulin resistance and obesity and might ultimately lead to development of diabetes in susceptible individuals. The following aims will test this concept: 1. What are the mechanisms of increased basal insulin secretion by GL (11 mM glucose plus 0.3 mM oleate), mono-oleoylglyceride (MG) and ROS? We hypothesize that secretion of insulin results from increases in the mitochondrial redox state that hyperpolarize the mitochondrial membrane potential (??) leading to generation of ROS and counter regulation by autophagy. 2. What are the protective mechanisms that counteract basal hypersecretion? Mitochondrial autophagy has been linked to ROS production. While ROS generators stimulate autophagy, the inhibition of autophagy results in even greater increased mitochondrial ROS and RIRR. We hypothesize that mitochondrial autophagy is a ROS triggered compensatory mechanism that counteracts elevated ROS production in conditions such as GL, thereby preventing basal hypersecretion. 3. Can hypersecretion of insulin in vivo be reversed by manipulating redox, ROS or autophagy in vivo or ex vivo? Aims 1 and 2 will identify the pathways involved in basal hypersecretion and Aim 3 will attempt to use the information gained to reverse hypersecretion. We hypothesize that islets from mice fed a high fat diet (HFD) will exhibit increased ROS and autophagy, and normalization of ROS will reverse hypersecretion and irreversibility will be characterized by RIRR. Completion of the proposed experiments will identify ss-cell alterations that cause hyperinsulinemia, determine and provide new insights into the consequences of preventing basal hypersecretion on the development of insulin resistance. Support for the ss-cell-mediated insulin resistance hypothesis would lead to radically different strategies for the treatment of insulin resistance and Type 2 diabetes
Hyperinsulinemia causes and maintains insulin resistance just as insulin resistance causes and maintains insulin hypersecretion. Type 2 diabetes (T2D) occurs when the ss- cell fails to secrete enough insulin to compensate for insulin resistance. Completion of the proposed experiments will identify ss-cell alterations that cause hyperinsulinemia, determine and provide new insights into the consequences of preventing basal hypersecretion on the development of insulin resistance. Support for the ss-cell- mediated insulin resistance hypothesis would lead to radically different strategies for the treatment of insulin resistance and Type 2 diabetes.
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