Lara Bellini1, Mélanie Campana1, Claude Rouch1, Marta Chacinska2,3, Marco Bugliani4, Kelly Meneyrol1, Isabelle Hainault5, Véronique Lenoir6,7,8, Jessica Denom1, Julien Véret1, Nadim Kassis1, Bernard Thorens9, Mark Ibberson10, Piero Marchetti4, Agnieszka Blachnio-Zabielska2,3, Céline Cruciani-Guglielmacci1, Carina Prip-Buus6,7,8, Christophe Magnan1, Hervé Le Stunff11,12. 1. Unité Biologie Fonctionnelle et Adaptative, CNRS UMR 8251, Équipe Régulation de la glycémie par le système nerveux central, Université Paris Diderot, 4 rue Marie-Andrée-Lagroua-Weill-Hallé, 75205, Paris CEDEX 13, France. 2. Department of Physiology, Medical University of Bialystok, Bialystok, Poland. 3. Department of Hygiene, Epidemiology and Metabolic Disorders, Medical University of Bialystok, Bialystok, Poland. 4. Department of Clinical and Experimental Medicine, Islet Laboratory, University of Pisa, Pisa, Italy. 5. Inserm, UMR 1138, Centre de Recherche des Cordeliers, Paris, France. 6. Inserm U1016, Institut Cochin, Paris, France. 7. CNRS UMR 8104, Paris, France. 8. Université Paris Descartes, Sorbonne Paris Cité, Paris, France. 9. Centre for Integrative Genomics, University of Lausanne, Lausanne, Switzerland. 10. Vital-IT Group, SIB Swiss Institute of Bioinformatics, Lausanne, Switzerland. 11. Unité Biologie Fonctionnelle et Adaptative, CNRS UMR 8251, Équipe Régulation de la glycémie par le système nerveux central, Université Paris Diderot, 4 rue Marie-Andrée-Lagroua-Weill-Hallé, 75205, Paris CEDEX 13, France. hlestunff62@gmail.com. 12. Université Paris-Sud, Paris-Saclay Institute of Neuroscience, CNRS UMR 9197, Orsay, France. hlestunff62@gmail.com.
Abstract
AIMS/HYPOTHESIS: Dietary n-3 polyunsaturated fatty acids, especially docosahexaenoic acid (DHA), are known to influence glucose homeostasis. We recently showed that Elovl2 expression in beta cells, which regulates synthesis of endogenous DHA, was associated with glucose tolerance and played a key role in insulin secretion. The present study aimed to examine the role of the very long chain fatty acid elongase 2 (ELOVL2)/DHA axis on the adverse effects of palmitate with high glucose, a condition defined as glucolipotoxicity, on beta cells. METHODS: We detected ELOVL2 in INS-1 beta cells and mouse and human islets using quantitative PCR and western blotting. Downregulation and adenoviral overexpression of Elovl2 was carried out in beta cells. Ceramide and diacylglycerol levels were determined by radio-enzymatic assay and lipidomics. Apoptosis was quantified using caspase-3 assays and poly (ADP-ribose) polymerase cleavage. Palmitate oxidation and esterification were determined by [U-14C]palmitate labelling. RESULTS: We found that glucolipotoxicity decreased ELOVL2 content in rodent and human beta cells. Downregulation of ELOVL2 drastically potentiated beta cell apoptosis induced by glucolipotoxicity, whereas adenoviral Elovl2 overexpression and supplementation with DHA partially inhibited glucolipotoxicity-induced cell death in rodent and human beta cells. Inhibition of beta cell apoptosis by the ELOVL2/DHA axis was associated with a decrease in ceramide accumulation. However, the ELOVL2/DHA axis was unable to directly alter ceramide synthesis or metabolism. By contrast, DHA increased palmitate oxidation but did not affect its esterification. Pharmacological inhibition of AMP-activated protein kinase and etomoxir, an inhibitor of carnitine palmitoyltransferase 1 (CPT1), the rate-limiting enzyme in fatty acid β-oxidation, attenuated the protective effect of the ELOVL2/DHA axis during glucolipotoxicity. Downregulation of CPT1 also counteracted the anti-apoptotic action of the ELOVL2/DHA axis. By contrast, a mutated active form of Cpt1 inhibited glucolipotoxicity-induced beta cell apoptosis when ELOVL2 was downregulated. CONCLUSIONS/ INTERPRETATION: Our results identify ELOVL2 as a critical pro-survival enzyme for preventing beta cell death and dysfunction induced by glucolipotoxicity, notably by favouring palmitate oxidation in mitochondria through a CPT1-dependent mechanism.
AIMS/HYPOTHESIS: Dietary n-3 polyunsaturated fatty acids, especially docosahexaenoic acid (DHA), are known to influence glucose homeostasis. We recently showed that Elovl2 expression in beta cells, which regulates synthesis of endogenous DHA, was associated with glucose tolerance and played a key role in insulin secretion. The present study aimed to examine the role of the very long chain fatty acid elongase 2 (ELOVL2)/DHA axis on the adverse effects of palmitate with high glucose, a condition defined as glucolipotoxicity, on beta cells. METHODS: We detected ELOVL2 in INS-1 beta cells and mouse and human islets using quantitative PCR and western blotting. Downregulation and adenoviral overexpression of Elovl2 was carried out in beta cells. Ceramide and diacylglycerol levels were determined by radio-enzymatic assay and lipidomics. Apoptosis was quantified using caspase-3 assays and poly (ADP-ribose) polymerase cleavage. Palmitate oxidation and esterification were determined by [U-14C]palmitate labelling. RESULTS: We found that glucolipotoxicity decreased ELOVL2 content in rodent and human beta cells. Downregulation of ELOVL2 drastically potentiated beta cell apoptosis induced by glucolipotoxicity, whereas adenoviral Elovl2 overexpression and supplementation with DHA partially inhibited glucolipotoxicity-induced cell death in rodent and human beta cells. Inhibition of beta cell apoptosis by the ELOVL2/DHA axis was associated with a decrease in ceramide accumulation. However, the ELOVL2/DHA axis was unable to directly alter ceramide synthesis or metabolism. By contrast, DHA increased palmitate oxidation but did not affect its esterification. Pharmacological inhibition of AMP-activated protein kinase and etomoxir, an inhibitor of carnitine palmitoyltransferase 1 (CPT1), the rate-limiting enzyme in fatty acid β-oxidation, attenuated the protective effect of the ELOVL2/DHA axis during glucolipotoxicity. Downregulation of CPT1 also counteracted the anti-apoptotic action of the ELOVL2/DHA axis. By contrast, a mutated active form of Cpt1 inhibited glucolipotoxicity-induced beta cell apoptosis when ELOVL2 was downregulated. CONCLUSIONS/ INTERPRETATION: Our results identify ELOVL2 as a critical pro-survival enzyme for preventing beta cell death and dysfunction induced by glucolipotoxicity, notably by favouring palmitate oxidation in mitochondria through a CPT1-dependent mechanism.
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