Diabetes mellitus is a lifelong incapacitating disease with worldwide prevalence estimated at 150 million patients in 2000. Loss of sufficient insulin production by the pancreatic beta-cell is a hallmark of both type 1 and type 2 diabetes. A hierarchy of transcription factors including Foxa1, Foxa2 (formerly hepatocyte nuclear factor 3alpha and beta) and HNF4alpha (hepatocyte nuclear factor 4alpha) controls development of the endocrine pancreas. These regulatory proteins also play a major role in the etiology of diabetes as evidenced by the fact that all MODY genes with the exception of MODY2 encode transcription factors. While Foxa1, Foxa2 and HNF4alpha are expressed in the liver in addition to the pancreas, we hypothesize that their critical role in mediating glucose homeostasis is exerted at least in part in the pancreatic beta-cell. Given the embryonic or perinatal lethality of mice homozygous for null mutations in these genes, we have begun to assess their function in pancreatic development and metabolism through conditional gene targeting using the IoxP/Cre recombinase system. In preliminary work required for this application we have generated and tested all IoxP and Cre mice necessary for the proposed experiments.
The specific aims of this proposal are: First, we will determine the role of Foxa2 in endocrine cell lineage allocation and of Foxa2 AND Foxa1 in the establishment of the pancreatic primordia by employing a novel pan-endoderm expressed Cre-line derived in our lab. Second, we will characterize the metabolic defects in Foxa2 deficient beta-cells in adult mice using an inducible Cre-recombinase system and investigate the regulation and function of a novel Foxa2 target, Schad (short-chain 3-hydroxyacyI-CoA dehydrogenase) identified using endocrine pancreas-enriched cDNA arrays developed in my lab. Third, we will investigate the contribution of HNF4alpha to beta-cell survival and stimulus-secretion coupling. Together these studies will further our understanding of the transcriptional regulation of beta-cell metabolism and the pathogenesis of diabetes. Insights gained about the role of Foxa1, Foxa2 and HNF4alpha in beta-cell function will be incorporated into future therapeutic strategies, including the derivation of insulin-producing cells from stem or precursor cells for use in cell replacement therapy, which holds great promise as a cure for diabetes.
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