Non-insulin-dependent diabetes mellitus (NIDDM) is characterized by a defect in glucose-stimulated insulin secretion from pancreatic beta-cells that can lead to frank diabetes. Intensive searches for the mechanisms underlying this progressive failure of beta-cells suggest a role for free fatty acids (FFAs). In 1997, in collaboration with Daniel Ricquier, we reported the discovery of uncoupling protein 2 (UCP2), a homologue of the brown fat UCP with genetic linkage to hyperinsulinemia. We propose that there is an important link between areas of investigation, which may provide insight into the regulation of metabolic fuel usage and regulation of insulin secretion. First, many studies have linked the regulation of Ucp2 expression in adipose and muscle tissues to changes in energy metabolism, particularly the level of free fatty acids (FFAs). Second, FFAs are known to modulate glucose-stimulated insulin secretion. Third, several lines of evidence, including preliminary studies presented in this application, support the conclusion that changes in UCP2 expression in pancreatic beta-cells can affect the sensitivity to glucose for stimulation of insulin secretion. Our two main objectives for this new project period are as follow: First to characterize the metabolic disturbances of pancreatic beta-cells from our Ucp2-/-mice, and define the role of Ucp2 in insulin secretion. Using the Ucp2-/- mouse model, we will test the hypothesis that the loss in glucose-stimulated insulin secretion following chronic exposure to FFAs is due to increased expression of UCP2 in beta-cells. Second, we propose to investigate the mechanisms of transcriptional regulation of the Ucp2 gene in pancreatic beta-cells. During the previous 3-yr project period we characterized the mouse Ucp2 promoter and identified an enhancer region (86/-44) composed of Sp 1, SRE and double E-box motifs. This region is required for basal and PPAR-induced expression of the Ucp2 gene in adipose cells. The PPAR-response is mediated by the double E-boxes. In this new project period we will use the INS-1 beta-cell subclone, 1NS(832/13), as well as transgenic mice expressing UCP2 promoter reporter constructs to test the hypothesis that FFAs and/or glucose regulate UCP2 expression through the proximal tripartite enhancer region, and we will identify the trans-activating factors implicated in its regulation through classical transfection and gel shift approaches. These studies will characterize the interplay between FFAs and glucose on control of UCP2 expression at the molecular level as well as the consequence of UCP2 modulation on insulin secretion.
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