Selective Actions of Mitochondrial Fission/Fusion Genes on Metabolism-Secretion Coupling in Insulin-releasing Cells

doi:10.1074/jbc.M806251200

Selective Actions of Mitochondrial Fission/Fusion Genes on Metabolism-Secretion Coupling in Insulin-releasing Cells^*^♦

Departments of ^‡Cell Physiology and Metabolism and ^§Cell Biology, University of Geneva, CH-1211, Geneva 4, Switzerland, and ^¶Department of Endocrinology and Metabolism, University of Pisa, 56126 Pisa, Italy

3 To whom correspondence should be addressed: 1 rue Michel-Servet, CH-1211, Geneva 4, Switzerland. Fax: 41-22-379-5543; E-mail: Claes.Wollheim{at}medecine.unige.ch.

Abstract

Mitochondria form filamentous networks that undergo continuous fission/fusion. In the pancreatic β-cells, mitochondria are essential for the transduction of signals linking nutrient metabolism to insulin granule exocytosis. Here we have studied mitochondrial networks in the insulinoma cell line INS-1E, primary rat and human β-cells. We have further investigated the impact of mitochondrial fission/fusion on metabolism-secretion coupling in INS-1E cells. Overexpression of hFis1 caused dramatic mitochondrial fragmentation, whereas Mfn1 evoked hyperfusion and the aggregation of mitochondria. Cells overexpressing hFis1 or Mfn1 showed reduced mitochondrial volume, lowered cellular ATP levels, and as a consequence, impaired glucose-stimulated insulin secretion. Decreased mitochondrial ATP generation was partially compensated for by enhanced glycolysis as indicated by increased lactate production in these cells. Dominant-negative Mfn1 elicited mitochondrial shortening and fragmentation of INS-1E cell mitochondria, similar to hFis1. However, the mitochondrial volume, cytosolic ATP levels, and glucose-stimulated insulin secretion were little affected. We conclude that mitochondrial fragmentation per se does not impair metabolism-secretion coupling. Through their impact on mitochondrial bioenergetics and distribution, hFis1 and Mfn1 activities influence mitochondrial signal generation thereby insulin exocytosis.

Footnotes

↵4 The abbreviations used are: DN, dominant-negative; WT, wild type; ECFP, mitochondrial targeted enhanced cyan fluorescent protein; mitoECFP, mitochondrial targeted ECFP; RFP, red fluorescent protein; mitoRFP, mitochondrial RFP; FCCP, carbonyl cyanide p-trifluoromethoxyphenylhydrazone; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; TUNEL, terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling.
↵* This work was supported by the Swiss National Foundation and EuroDia (Grant LSHM-CT-2006-518153), a European Community-funded project under framework program 6 (to C. B. W.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵ The on-line version of this article (available at http://www.jbc.org) contains six supplemental figures.
↵♦ This article was selected as a Paper of the Week.
↵1 Both authors contributed equally to this work.
↵2 A recipient of a fellowship from the Korea Research Foundation Grant (KRF-2006-013-E00082).
- Received August 13, 2008.
- Revision received September 30, 2008.
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