Low-grade Inflammation, Cytokines, and Beta-Cell Dysfunction in Type 2 Diabetes

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DESCRIPTION (provided by applicant): The long-term goal of this research is to identify the early mechanisms of pancreatic beta-cell dysfunction in development of diabetes. Evidence suggests that inflammation, mediated by at least in part by cytokines, is a key component in both type 1 diabetes (T1D) and type 2 diabetes (T2D). In T1D, the current consensus is that cytokines produced locally within the islets at very high doses by immune cells play a critical role in the destruction of pancreatic beta cells. In T2D, circulating cytokine levels are elevated early in the development of the disease due to low-grade systemic inflammation. However, circulating cytokine levels associated with low- grade systemic inflammation are ~100-1000x lower than seen within the islet during direct immune cell infiltration associated with T1D. To date, the effects of these low-level cytokines on beta-cells have not been systematically examined, particularly in models of obesity and T2D. Our preliminary data show for the first time that specific cytokine combinations, present at concentrations found in the blood of obese and diabetic individuals, are sufficient to induce excess basal intracellular free calcium, reduce endoplasmic reticulum (ER) calcium storage, and impair insulin secretion in pancreatic islets. Furthermore, these cytokine effects are more severe in islets from pre-diabetic db/db mice, a mouse model of T2D. The hypothesis for this proposal is that circulating cytokines at concentrations typical of low-grade systemic inflammation directly cause beta-cell dysfunction by disrupting intracellular calcium handling in diabetes-prone individuals. Using molecular, electrophysiological, and imaging-based approaches, we will test this hypothesis by addressing three specific aims: (I) Compare the effects of low-grade inflammation on islet calcium handling and markers of cell stress in islets from normal and diabetes-prone mice, (II) Determine the cellular sites of cytokine-induced dysfunction in beta-cells, (III) Determine the in vivo effects of low-grade inflammation in normal vs. diabetes-prone or obese mice. Collectively, these studies will elucidate novel aspects of cytokine action at concentrations present in the systemic circulation in obese and diabetic individuals. Identifying early stages in cytokine-mediated beta-cell dysfunction will open new avenues of therapeutic intervention to prevent beta-cell dysfunction in early T2D.