Uncoupling protein-2 contributes significantly to high mitochondrial proton leak in INS-1E insulinoma cells and attenuates glucose-stimulated insulin secretion

Charles Affourtit (1) , Martin D Brand

1 Dunn Human Nutrition Unit

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, C. and Brand, M. D. (2006), Biochem. J. 393, 151-159]. Here 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 4x higher in INS-1E cells than in myoblasts. This relatively high leak activity was decreased more than 30% upon knock-down of uncoupling protein-2 (UCP2) by RNAi. The high contribution of UCP2 to leak suggests that proton conductance through UCP2 accounts for approximately 20% of INS-1E respiration. UCP2 knock-down enhanced 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 to amplify the effect of physiological UCP2 regulators on cytoplasmic ATP/ADP and hence on insulin secretion.

Mots clés: Life Sciences

Charles Affourtit, Martin D Brand. Uncoupling protein-2 contributes significantly to high mitochondrial proton leak in INS-1E insulinoma cells and attenuates glucose-stimulated insulin secretion. Biochemical Journal, 2007, 409 (1), pp.199-204. ⟨10.1042/BJ20070954⟩. ⟨hal-00478847⟩