The long-term objective of this proposal is to understand what happens to pancreatic islets in diabetes, with a particular emphasis upon beta cells. All forms of human and experimental diabetes are characterized by a severe impairment of glucose-induced insulin secretion and limitations of beta cell mass. Past work has provided new information about the pathogenesis of the secretory defects and the mechanisms that regulate beta cell mass. The present proposal seeks to extend this work with the following specific aims: 1) To determine the molecular mechanisms responsible for the beta cell dysfunction found in experimental diabetes. The hypothesis that will be tested is that alterations in transcription factors, especially pdx-1, play a key role in the altered gene expression that leads to altered beta cell function. Changes in gene expression of transcription factors and other putative b-cell signalling molecules will be correlated with changes in insulin secretion and beta cell mass. Attempts will be made to generate a double transgenic mouse in collaboration with Dr. Joel Haebner that will allow tetracycline-induced regulation of pdx-1 levels in islets in the hopes of further testing this hypothesis. 2) To evaluate the effect of GLUT-2 overexpression in islet b-cells in transgenic mice. Transgenic mice will be used to test the hypothesis that GLUT-2 enhances the action of glucokinase through a mechanism independent of glucose transport; 3) To test the hypothesis that translocation of glucokinase occurs in islet cells and has functional consequences for glucose-induced insulin secretion. A combined morphologic, physiologic, and biochemical approach will be employed; 4) To test the hypothesis that the deposition of extracellular amyloid in islets is enhanced by hyperglycemia and is toxic to beta cells, thus contributing to the pathogenesis of diabetes. These experiments will employ transgenic mouse islets expressing human amylin and human islets that are transplanted into diabetic and non-diabetic mice.
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