Hepatocyte nuclear factor 4α regulates the expression of pancreatic β-cell genes implicated in glucose metabolism and nutrient-induced insulin secretion

Mutations in the HNF4 alpha gene are associated with the subtype 1 of maturity-onset diabetes of the young (MODY1), which is characterized by impaired insulin secretory response to glucose in pancreatic beta -cells. Hepatocyte nuclear factor 4 alpha (HNF4 alpha) is a transcription factor critical for liver development and hepatocyte-specific gene expression. However, the role of HNF4 alpha in the regulation of pancreatic beta -cell gene expression and its correlation with metabolism secretion coupling have not been previously investigated. The tetracycline-inducible system was employed to achieve tightly controlled expression of both wild type (WT) and dominant-negative mutant (DN) of HNF4 alpha in INS-1 cells. The induction of WT-HNF4 alpha resulted in a left shift in glucose-stimulated insulin secretion, whereas DN-HNPF4 alpha selectively impaired nutrient-stimulated insulin release, Induction of DN-HNF4 alpha also caused defective mitochondrial function substantiated by reduced [C-14]pyruvate oxidation, attenuated substrate-evoked mitochondrial membrane hyperpolarization, and blunted nutrient-generated cellular ATP production. Quantitative evaluation of HNF4 alpha -regulated pancreatic p-cell gene expression revealed altered mRNA levels of insulin, glucose transporter-2, L-pyruvate kinase, aldolase B, 2-oxoglutarate dehydrogenase El subunit, and mitochondrial uncoupling protein-2, The patterns of HNF4a-regulated gene expression are strikingly similar to that of its downstream transcription factor HNF1 alpha, Indeed, HNF4a changed the HNF1 alpha mRNA levels and HNF1 alpha promoter luciferase activity through altered HNF4 alpha binding. These results demonstrate the importance of HNF4 alpha in beta -cell metabolism-secretion coupling.