title: Glucose-regulated anaplerosis and cataplerosis in pancreatic beta-cells: possible implication of a pyruvate/citrate shuttle in insulin secretion.
abstract: The hypothesis proposing that anaplerosis and cataplerosis play an important role in fuel signaling by providing mitochondrially derived coupling factors for stimulation of insulin secretion was tested. A rise in citrate coincided with the initiation of insulin secretion in response to glucose in INS-1 beta-cells. The dose dependence of glucose-stimulated insulin release correlated closely with those of the cellular contents of citrate, malate, and citrate-derived malonyl-CoA. The glucose-induced elevations in citrate, alpha-ketoglutarate, malonyl-CoA, and the 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium reduction state, an index of beta-cell metabolic activity, were unaffected by the Ca2+ chelator EGTA. Glucose induced a rise in both mitochondrial and cytosolic citrate and promoted efflux of citrate from the cells. The latter amounted to approximately 20% of glucose carbons entering the glycolytic pathway. Phenylacetic acid, a pyruvate carboxylase inhibitor, reduced the glucose-induced rise in citrate in INS-1 cells and insulin secretion in both INS-1 cells and rat islets. The results indicate the feasibility of a pyruvate/citrate shuttle in INS-1 beta-cells, allowing the regeneration of NAD+ in the cytosol and the formation of cytosolic acetyl-CoA, malonyl-CoA, and NADPH. The data suggest that anaplerosis and cataplerosis are early signaling events in beta-cell activation that do not require a rise in Ca2+. It is proposed that citrate is a signal of fuel abundance that contributes to beta-cell activation in both the mitochondrial and cytosolic compartments and that a major fate of anaplerotic glucose carbons is external citrate.
authors.affiliation: Department of Nutrition, University of Montreal, the Centre de Recherches du CHUM and Institut du Cancer, Quebec, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Farfari
authors.forename: V
authors.initials: V
authors.lastname: Schulz
authors.forename: B
authors.initials: B
authors.lastname: Corkey
authors.forename: M
authors.initials: M
authors.lastname: Prentki
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002951:Citrates / Q000378:metabolism; D002952:Citric Acid Cycle / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000502:physiology*; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D007329:Insulin Antagonists / Q000494:pharmacology; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D010648:Phenylacetates / Q000494:pharmacology; D011766:Pyruvate Carboxylase / Q000037:antagonists & inhibitors; D011773:Pyruvates / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000502:physiology
chemical_list: D002951:Citrates; D004791:Enzyme Inhibitors; D007328:Insulin; D007329:Insulin Antagonists; D010648:Phenylacetates; D011773:Pyruvates; D011766:Pyruvate Carboxylase; C025136:phenylacetic acid; D005947:Glucose; D002118:Calcium