Biochemical Mechanism of Beta-Cell Destruction

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Autoimmune diabetes is characterized by an inflammatory reaction in and around pancreatic islets that is followed by the selective destruction of insulin producing β-cells. The conventional wisdom is that cytokines, released during islet inflammation, contribute to the development of autoimmune diabetes by directly impairing β-cell function and reducing β-cell mass. In support of this hypothesis, treatment of islets with IL-1 alone, or in combination with IFN-γ and/or TNF, results in an inhibition of insulin secretion and oxidative metabolism, induction of DNA damage and a loss of β-cell viability that is mediated by iNOS expression and the production of nitric oxide by β-cells. For over 30 years there has been an intense focus on determining the mechanisms by which IL-1 damages β-cells, yet there is little direct evidence supporting a role for IL-1 in the development of autoimmune diabetes. Pancreatic β-cells are terminally differentiated with a limited capacity for self-renewal, yet produce a hormone (insulin) that is essential for organismal survival. IL-1 is a pyrogenic cytokine that is well known to induce fever and inflammation during infection and injury. If the β-cell response to IL-1 were solely damaging, then most individuals would be highly susceptible to diabetes, as 90 % of the volume of blood that enters the pancreas travels through islets (which represents 1% of the wet weight of the pancreas) such that β-cells would be bathed in IL-1 during infection and injury. This application will examine the hypothesis that there is a physiological role for IL-1 signaling in β-cells that is designed to protect these cells from impending danger or insult. In support of this hypothesis, we provide preliminary evidence showing that nitric oxide attenuates DNA damage induced β-cell apoptosis. By understanding the delicate balance between the damaging and protective actions of cytokines on β-cell function and survival, we hope to elucidate the physiological and pathophysiological roles of IL-1 signaling in β-cells. There are two specific aims. 1. To test the hypothesis that β-cells maintain a robust oxidant defense system that provides protection against damaging reactive nitrogen and oxygen species. 2. To test the hypothesis that nitric oxide, produced following cytokine treatment, attenuates DNA damage associated apoptosis by regulating the activation of transducing kinases of the DNA damage response (DDR). A number of biochemical, molecular, immunological, cell biological, and transgenic techniques will be utilized to investigate the cellular pathways through which nitric oxide and its reactive intermediates participate in the protection of β-cells from damage. It is hoped that insights into the mechanisms controlling the protective responses activated in β-cells following cytokine stimulate that are gained from these studies will influence the design of therapeutic strategies aimed that are based on activating protective pathways in β-cell as a mechanism to maintain functional β-cell mass and attenuate the development of diabetes or recurrence of diabetes in the transplantation setting.