These studies are designed to determine how fatty acids (FFA) stimulate beta-cell compensation early in obesity and yet cause dysfunction and death of compensated beta-cells and NIDDM late in obesity. We have found that PPARalpha serves as the FFA """"""""receptor"""""""" in islets. Compensatory hyperinsulinemia induced by elevations of FFA can be duplicated in vitro by the PPARalpha ligands, clofibrate (CF) plus 9-cis retinoic acid (RA). ZDF rats are unable to compensate for high levels of fatty acids, PPARalpha is markedly reduced in their islets and CF/RA has no effect. Fat accumulates in their islets and ultimately causes apoptosis of beta cells and diabetes. To prove this, we will over-express PPARalpha in beta cells of ZDF rats and determine if this rescues beta-cells from the cytotoxic effects of fatty acids. To determine if the low PPARalpha is secondary to the OB-R receptor mutation, PPARalpha mRNA will be quantified in islets made to over-express wild type OBR. Finally, we will assess the effects of normalizing PPARalpha expression on apoptogenic effects of FFA and on reducing the flux of FFA into ceramide and DAG, key signals in the apoptotic pathway. The studies should indicate the mechanisms by which FFA cause compensatory changes in beta-cells in the early years of obesity but cause dysfunction apoptosis of beta-cells, and diabetes, in the late years.
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