title: Uncoupling protein-2 contributes significantly to high mitochondrial proton leak in INS-1E insulinoma cells and attenuates glucose-stimulated insulin secretion.
abstract: Proton leak exerts stronger control over ATP/ADP in mitochondria from clonal pancreatic beta-cells (INS-1E) than in those from rat skeletal muscle, due to the higher proton conductance of INS-1E mitochondria [Affourtit and Brand (2006) Biochem. J. 393, 151-159]. In the present study, we demonstrate that high proton leak manifests itself at the cellular level too: the leak rate (measured as myxothiazol-sensitive, oligomycin-resistant respiration) was nearly four times higher in INS-1E cells than in myoblasts. This relatively high leak activity was decreased more than 30% upon knock-down of UCP2 (uncoupling protein-2) by RNAi (RNA interference). The high contribution of UCP2 to leak suggests that proton conductance through UCP2 accounts for approx. 20% of INS-1E respiration. UCP2 knock-down enhanced GSIS (glucose-stimulated insulin secretion), consistent with a role for UCP2 in beta-cell physiology. We propose that the high mitochondrial proton leak in beta-cells is a mechanism which amplifies the effect of physiological UCP2 regulators on cytoplasmic ATP/ADP and hence on insulin secretion.
authors.affiliation: MRC Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 0XY, UK. ca@mrc-dunn.cam.ac.uk
authors.forename: Charles
authors.initials: C
authors.lastname: Affourtit
authors.forename: Martin D
authors.initials: MD
authors.lastname: Brand
mesh_terms: D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism / Q000502:physiology*; D008564:Membrane Potentials; D008689:Methacrylates / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism / Q000502:physiology*; D009840:Oligomycins / Q000494:pharmacology; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption; D010766:Phosphorylation; D034622:RNA Interference; D051381:Rats; D013844:Thiazoles / Q000494:pharmacology; D000071246:Uncoupling Protein 2