Uncoupling protein-2 attenuates glucose-stimulated insulin secretion in INS-1E insulinoma cells by lowering mitochondrial reactive oxygen species

Charles Affourtit,Martin Jastroch,Martin D Brand

doi:10.1016/j.freeradbiomed.2010.12.020

Abstract

Glucose-stimulated insulin secretion (GSIS) by pancreatic β cells is regulated by mitochondrial uncoupling protein-2 (UCP2), but opposing phenotypes, GSIS improvement and impairment, have been reported for different Ucp2-ablated mouse models. By measuring mitochondrial bioenergetics in attached INS-1E insulinoma cells with and without UCP2, we show that UCP2 contributes to proton leak and attenuates glucose-induced rises in both respiratory activity and the coupling efficiency of oxidative phosphorylation. Strikingly, the GSIS improvement seen upon UCP2 knockdown in INS-1E cells is annulled completely by the cell-permeative antioxidant MnTMPyP. Consistent with this observation, UCP2 lowers mitochondrial reactive oxygen species at high glucose levels. We conclude that UCP2 plays both regulatory and protective roles in β cells by acutely lowering GSIS and chronically preventing oxidative stress. Our findings thus provide a mechanistic explanation for the apparently discrepant findings in the field.

Highlights

Uncoupling protein-2 attenuates glucose-stimulated insulin secretion in INS-1E insulinoma cells by lowering mitochondrial reactive oxygen species
By measuring mitochondrial bioenergetics in attached INS-1E insulinoma cells with and without uncoupling protein-2 (UCP2), we show that UCP2 contributes to proton leak and attenuates glucose-induced rises in both respiratory activity and the coupling efficiency of oxidative phosphorylation
We have reported previously that knockdown of UCP2 by RNAi leads to improved Glucose-stimulated insulin secretion (GSIS) in INS-1E insulinoma cells [13]

Summary

Introduction

Uncoupling protein-2 attenuates glucose-stimulated insulin secretion in INS-1E insulinoma cells by lowering mitochondrial reactive oxygen species. Glucose-stimulated insulin secretion (GSIS) by pancreatic β cells is regulated by mitochondrial uncoupling protein-2 (UCP2), but opposing phenotypes, GSIS improvement and impairment, have been reported for different Ucp2-ablated mouse models. The GSIS improvement seen upon UCP2 knockdown in INS-1E cells is annulled completely by the cell-permeative antioxidant MnTMPyP Consistent with this observation, UCP2 lowers mitochondrial reactive oxygen species at high glucose levels. Genetic knockout of Ucp in mice was established originally on a mixed 129/SVJ × C57BL/6 background and resulted in greatly improved GSIS [3,8] When this Ucp2-ablated strain was backcrossed onto three different genetic backgrounds, the GSIS phenotype was lost completely [8]. The improved glucose tolerance reported by Zhang et al [3] was not

Results

Discussion

Conclusion