Biochemical Mechanism of Beta-Cell Destruction

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Project Summary/Abstract 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 suggests that cytokines, released during islet inflammation, contribute to the development of autoimmune diabetes by directly impairing b-cell function and reducing β-cell mass. In support of this hypothesis, treatment of islets with IL-1 alone, or in combination with IFN-g 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 test 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. 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 thee aims that will test the hypotheses that: 1) the thioredoxin/peroxiredoxin antioxidant system protects b-cells from reactive oxygen and nitrogen species; 2) nitric oxide, in a b-cell selective manner, attenuates DNA damage response (DDR) signaling by inhibiting mitochondrial oxidative metabolism and decreasing the levels ATP and NAD levels; and 3) IL-1 signaling promotes an adaptive protective response in endocrine cells. 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 stimulation that are gained from these studies will influence the design of therapeutic strategies aimed to activate protective pathways in b-cell as a mechanism to limit the loss of function β-cell mass during the development of diabetes or recurrence of diabetes in the transplantation setting.