MITOCHONDRIAL DEACETYLATION IS AN ACTIVATING SIGNAL MEDIATED BY SIRTUIN 3 FOR METABOLISM-SECRETION COUPLING IN PANCREATIC BETA CELLS

Metabolism-secretion coupling describes the molecular mechanism linking nutrient sensing to insulin secretion in pancreatic beta-cells. This process requires the activation of mitochondria, leading to ATP production and coupling factors, which amplify secretion. Several mitochondrial derived coupling factors were proposed but the mechanisms linking mitochondria to the amplification of insulin exocytosis remain elusive. Little attention has been devoted to the regulation by mitochondrial acetylation, despite the crucial role of mitochondria and the expression of matrix NAD-dependent deacethylases (mitochondrial sirtuins) in beta-cell. To determine the impact of mitochondrial acetylation on metabolism-secretion coupling in insulin-secreting cells, we have combined functional investigations with quantitative proteomics in pancreatic INS1E beta-cells, devoid of the mitochondrial deacetylase Sirtuin-3 (Sirt3). Glucose-stimulated Sirt3-KO cells showed reduced Ca2+ rises compared to control cells. Basal oxygen consumption was increased, ATP-synthase dependent respiration decreased and the second phase of ATP production absent. Impaired mitochondrial function due to unbalanced acetylation was reflected in the aberrant insulin secretion. Quantitative proteomics showed significant difference in 39 mitochondrial lysine acetylation sites. Six glucose-stimulated proteins were identified with differential acetylation levels. Dynamic mitochondrial acetylation mediated by Sirt3 regulates metabolism in glucose-stimulated beta cells by controlling mitochondrial ATP production and Ca2+ homeostasis.