title: A novel ATP-synthase-independent mechanism coupling mitochondrial activation to exocytosis in insulin-secreting cells.
abstract: Pancreatic β-cells sense glucose, promoting insulin secretion. Glucose sensing requires the sequential stimulation of glycolysis, mitochondrial metabolism and Ca2+entry. To elucidate how mitochondrial activation in β-cells contributes to insulin secretion, we compared the effects of glucose and the mitochondrial substrate methylsuccinate in the INS-1E insulin-secreting cell line at the respective concentrations at which they maximally activate mitochondrial respiration. Both substrates induced insulin secretion with distinct respiratory profiles, mitochondrial hyperpolarization, NADH production and ATP-to-ADP ratios. In contrast to glucose, methylsuccinate failed to induce large [Ca2+] rises and exocytosis proceeded largely independently of mitochondrial ATP synthesis. Both glucose- and methylsuccinate-induced secretion was blocked by diazoxide, indicating that Ca2+is required for exocytosis. Dynamic assessment of the redox state of mitochondrial thiols revealed a less marked reduction in response to methylsuccinate than with glucose. Our results demonstrate that insulin exocytosis can be promoted by two distinct mechanisms one of which is dependent on mitochondrial ATP synthesis and large Ca2+transients, and one of which is independent of mitochondrial ATP synthesis and relies on small Ca2+signals. We propose that the combined effects of Ca2+and redox reactions can trigger insulin secretion by these two mechanisms.
authors.affiliation: Mitochondrial Function, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building G, Lausanne CH-1015, Switzerland Umberto.DeMarchi@rd.nestle.com.
authors.forename: Umberto
authors.identifier: http://orcid.org/0000-0002-6011-5446
authors.initials: U
authors.lastname: De Marchi
authors.affiliation: Mitochondrial Function, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building G, Lausanne CH-1015, Switzerland.
authors.forename: Aurelie
authors.initials: A
authors.lastname: Hermant
authors.affiliation: Mitochondrial Function, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building G, Lausanne CH-1015, Switzerland.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Thevenet
authors.affiliation: Natural Bioactives and screening, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building H, Lausanne CH-1015, Switzerland.
authors.forename: Yann
authors.initials: Y
authors.lastname: Ratinaud
authors.affiliation: Mitochondrial Function, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building G, Lausanne CH-1015, Switzerland.
authors.forename: Jaime
authors.initials: J
authors.lastname: Santo-Domingo
authors.affiliation: Natural Bioactives and screening, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building H, Lausanne CH-1015, Switzerland.
authors.forename: Denis
authors.initials: D
authors.lastname: Barron
authors.affiliation: Mitochondrial Function, Nestlé Institute of Health Sciences, EPFL Innovation Park, Building G, Lausanne CH-1015, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Wiederkehr
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D045744:Cell Line, Tumor; D003981:Diazoxide / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D006019:Glycolysis / Q000187:drug effects / Q000502:physiology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D057054:Molecular Imaging; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats; D059010:Single-Cell Analysis; D013386:Succinates / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D007328:Insulin; D013386:Succinates; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; C039138:methylsuccinic acid; D005947:Glucose; D003981:Diazoxide; D002118:Calcium
keywords: Ca2+ signaling; Mitochondria; Redox signaling; Signal transduction; β-cells