Aryl Hydrocarbon Receptor Nuclear Translocator/Hypoxia-inducible Factor-1β Plays a Critical Role in Maintaining Glucose-stimulated Anaplerosis and Insulin Release from Pancreatic β-Cells

Renjitha Pillai,Peter Huypens,Mei Huang,Stephanie Schaefer,Tanya Sheinin,Shawn D Wettig,Jamie W Joseph

doi:10.1074/jbc.m110.149062

Abstract

The metabolic pathways that are involved in regulating insulin secretion from pancreatic β-cells are still incompletely understood. One potential regulator of the metabolic phenotype of β-cells is the transcription factor aryl hydrocarbon receptor nuclear translocator (ARNT)/hypoxia-inducible factor (HIF)-1β. ARNT/HIF-1β levels are profoundly reduced in islets obtained from type 2 diabetic patients. However, no study to date has investigated key pathways involved in regulating insulin release in β-cells that lack ARNT/HIF-1β. In this study, we confirm that siRNA-mediated knockdown of ARNT/HIF-1β inhibits glucose-stimulated insulin secretion. We next investigated the metabolic consequence of the loss of ARNT/HIF-1β knockdown. We demonstrate that β-cells with reduced ARNT/HIF-1β expression levels exhibit a 31% reduction in glycolytic flux without significant changes in glucose oxidation or the ATP:ADP ratio. Metabolic profiling of β-cells treated with siRNAs against the ARNT/HIF-1β gene revealed that glycolysis, anaplerosis, and glucose-induced fatty acid production were down-regulated, and all are key events involved in glucose-stimulated insulin secretion. In addition, both first and second phase insulin secretion in islets were significantly reduced after ARNT/HIF-1β knockdown. Together, our data suggest an important role for ARNT/HIF-1β in anaplerosis, and it may play a critical role in maintaining normal secretion competence of β-cells.

Highlights

Expression profiling of type 2 diabetic human islets showed that aryl hydrocarbon receptor nuclear translocator (ARNT)/hypoxia-inducible factor (HIF)-1␤ was reduced by 90% [35]
It was demonstrated that ARNT/HIF-1␤ may control the expression levels of other candidate genes for type 2 diabetes, such as HNF4␣, the insulin receptor, IRS-2, and Akt2, all of which play an important role in glucose homeostasis (44 – 47)
Based on the available literature, we hypothesized that ARNT/HIF-1␤ would be required for maintaining glycolytic flux and normal glucose-stimulated insulin release (GSIS)

Summary

Introduction

2 To whom correspondence should be addressed: School of Pharmacy, Important support for the KATP channel-independent pathway of glucose-stimulated insulin release (GSIS) comes from studies showing that glucose can still elicit a significant increase in insulin secretion in conditions where KATP channels are held open by application of diazoxide and high Kϩ [12, 13] or in islets obtained from rodents that lack functional KATP channels (7, 8, 11, 14 –18) These studies suggest that mitochondrial glucose metabolism generates other signals besides changes in the ATP:ADP ratio that are important for stimulus-secretion coupling in pancreatic ␤-cells (11, 19 –23). Our novel findings that ARNT/HIF-1␤ plays a role in regulating biphasic insulin secretion and anaplerosis as well as other key metabolic pathways suggest that the mechanism of ARNT/HIF-1␤-regulated insulin release appears to be independent of ATP production and likely involves the altered KATP-independent pathway of insulin release

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Results

Conclusion