A Pyruvate Cycling Pathway Involving Cytosolic NADP-dependent Isocitrate Dehydrogenase Regulates Glucose-stimulated Insulin Secretion

Olga Ilkayeva,A. Dean Sherry,Sarah M. Ronnebaum,Shawn C. Burgess,Thomas C. Becker,Robert D. Stevens,Mette V. Jensen,Danhong Lu,Christopher B. Newgard,Jamie W. Joseph

doi:10.1074/jbc.m511908200

Abstract

Glucose-stimulated insulin secretion (GSIS) from pancreatic islet beta-cells is central to control of mammalian fuel homeostasis. Glucose metabolism mediates GSIS in part via ATP-regulated K+ (KATP) channels, but multiple lines of evidence suggest participation of other signals. Here we investigated the role of cytosolic NADP-dependent isocitrate dehydrogenase (ICDc) in control of GSIS in beta-cells. Delivery of small interfering RNAs specific for ICDc caused impairment of GSIS in two independent robustly glucose-responsive rat insulinoma (INS-1-derived) cell lines and in primary rat islets. Suppression of ICDc also attenuated the glucose-induced increments in pyruvate cycling activity and in NADPH levels, a predicted by-product of pyruvate cycling pathways, as well as the total cellular NADP(H) content. Metabolic profiling of eight organic acids in cell extracts revealed that suppression of ICDc caused increases in lactate production in both INS-1-derived cell lines and primary islets, consistent with the attenuation of pyruvate cycling, with no significant changes in other intermediates. Based on these studies, we propose that a pyruvate cycling pathway involving ICDc plays an important role in control of GSIS.

Highlights

Membrane depolarization, activation of voltage-dependent Ca2ϩ channels, and subsequent influx of Ca2ϩ to stimulate insulin release [1, 2]
Cells were incubated with a range of 3–20 mM glucose, and insulin secretion, NADPH, and NADP was measured for each condition
Recent work has begun to provide evidence that this export of mitochondrial substrates is involved in the regulation of insulin secretion [3, 15, 20, 21, 32, 36, 37]

Summary

Introduction

Membrane depolarization, activation of voltage-dependent Ca2ϩ channels, and subsequent influx of Ca2ϩ to stimulate insulin release [1, 2]. Suppression of ICDc impairs the glucose-induced increment in pyruvate cycling flux and NADPH levels and results in increases in lactate production in both INS-1-derived cell lines and primary islets, consistent with suppressed pyruvate cycling.

Results

Conclusion