title: A role for cytosolic isocitrate dehydrogenase as a negative regulator of glucose signaling for insulin secretion in pancreatic ß-cells.
abstract: Cytosolic NADPH may act as one of the signals that couple glucose metabolism to insulin secretion in the pancreatic ß-cell. NADPH levels in the cytoplasm are largely controlled by the cytosolic isoforms of malic enzyme and isocitrate dehydrogenase (IDHc). Some studies have provided evidence for a role of malic enzyme in glucose-induced insulin secretion (GIIS) via pyruvate cycling, but the role of IDHc in ß-cell signaling is unsettled. IDHc is an established component of the isocitrate/α-ketoglutarate shuttle that transfers reducing equivalents (NADPH) from the mitochondrion to the cytosol. This shuttle is energy consuming since it is coupled to nicotinamide nucleotide transhydrogenase that uses the mitochondrial proton gradient to produce mitochondrial NADPH and NAD(+) from NADP(+) and NADH. To determine whether flux through IDHc is positively or negatively linked to GIIS, we performed RNAi knockdown experiments in ß-cells. Reduced IDHc expression in INS 832/13 cells and isolated rat islet ß-cells resulted in enhanced GIIS. This effect was mediated at least in part via the KATP-independent amplification arm of GIIS. IDHc knockdown in INS 832/13 cells did not alter glucose oxidation but it reduced fatty acid oxidation and increased lipogenesis from glucose. Metabolome profiling in INS 832/13 cells showed that IDHc knockdown increased isocitrate and NADP(+) levels. It also increased the cellular contents of several metabolites linked to GIIS, in particular some Krebs cycle intermediates, acetyl-CoA, glutamate, cAMP and ATP. The results identify IDHc as a component of the emerging pathways that negatively regulate GIIS.
authors.affiliation: Molecular Nutrition Unit and the Montreal Diabetes Research Center at the Centre de Recherche du Centre Hospitalier de l'Université de Montréal, CR-CHUM, Montreal, Quebec, Canada.
authors.forename: Claudiane
authors.initials: C
authors.lastname: Guay
authors.forename: Erik
authors.initials: E
authors.lastname: Joly
authors.forename: Emilie
authors.initials: E
authors.lastname: Pepin
authors.forename: Annie
authors.initials: A
authors.lastname: Barbeau
authors.forename: Lisa
authors.initials: L
authors.lastname: Hentsch
authors.forename: Marco
authors.initials: M
authors.lastname: Pineda
authors.forename: S R Murthy
authors.initials: SR
authors.lastname: Madiraju
authors.forename: Henri
authors.initials: H
authors.lastname: Brunengraber
authors.forename: Marc
authors.initials: M
authors.lastname: Prentki
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D003600:Cytosol / Q000201:enzymology*; D004734:Energy Metabolism; D005227:Fatty Acids / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D055785:Gene Knockdown Techniques; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism*; D007521:Isocitrate Dehydrogenase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D015398:Signal Transduction
chemical_list: D005227:Fatty Acids; D007328:Insulin; D034741:RNA, Small Interfering; D007521:Isocitrate Dehydrogenase; D005947:Glucose