title: Proteasome dysfunction mediates high glucose-induced apoptosis in rodent beta cells and human islets.
abstract: The ubiquitin/proteasome system (UPS), a major cellular protein degradation machinery, plays key roles in the regulation of many cell functions. Glucotoxicity mediated by chronic hyperglycaemia is detrimental to the function and survival of pancreatic beta cells. The aim of our study was to determine whether proteasome dysfunction could be involved in beta cell apoptosis in glucotoxic conditions, and to evaluate whether such a dysfunction might be pharmacologically corrected. Therefore, UPS activity was measured in GK rats islets, INS-1E beta cells or human islets after high glucose and/or UPS inhibitor exposure. Immunoblotting was used to quantify polyubiquitinated proteins, endoplasmic reticulum (ER) stress through CHOP expression, and apoptosis through the cleavage of PARP and caspase-3, whereas total cell death was detected through histone-associated DNA fragments measurement. In vitro, we found that chronic exposure of INS-1E cells to high glucose concentrations significantly decreases the three proteasome activities by 20% and leads to caspase-3-dependent apoptosis. We showed that pharmacological blockade of UPS activity by 20% leads to apoptosis in a same way. Indeed, ER stress was involved in both conditions. These results were confirmed in human islets, and proteasome activities were also decreased in hyperglycemic GK rats islets. Moreover, we observed that a high glucose treatment hypersensitized beta cells to the apoptotic effect of proteasome inhibitors. Noteworthily, the decreased proteasome activity can be corrected with Exendin-4, which also protected against glucotoxicity-induced apoptosis. Taken together, our findings reveal an important role of proteasome activity in high glucose-induced beta cell apoptosis, potentially linking ER stress and glucotoxicity. These proteasome dysfunctions can be reversed by a GLP-1 analog. Thus, UPS may be a potent target to treat deleterious metabolic conditions leading to type 2 diabetes.
authors.affiliation: CNRS UMR 5203, INSERM U661, and Montpellier 1 & 2 University, Institute of Functional Genomics, Montpellier, France; Laboratory for Diabetes Cell Therapy, Institute for Research in Biotherapy, University Hospital St-Eloi, Montpellier, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Broca
authors.affiliation: CNRS UMR 5203, INSERM U661, and Montpellier 1 & 2 University, Institute of Functional Genomics, Montpellier, France; Laboratory for Diabetes Cell Therapy, Institute for Research in Biotherapy, University Hospital St-Eloi, Montpellier, France.
authors.forename: Elodie
authors.initials: E
authors.lastname: Varin
authors.affiliation: Laboratory for Diabetes Cell Therapy, Institute for Research in Biotherapy, University Hospital St-Eloi, Montpellier, France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Armanet
authors.affiliation: B2PE Laboratory (Biology & Pathology of Endocrine Pancreas), BFA Unit, Univ. Paris-Diderot, CNRS EAC4413, Paris, France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Tourrel-Cuzin
authors.affiliation: Cell Isolation and Transplantation Center, Department of Surgery, Geneva University Hospitals and University of Geneva, Geneva, Switzerland.
authors.forename: Domenico
authors.initials: D
authors.lastname: Bosco
authors.affiliation: CNRS UMR 5203, INSERM U661, and Montpellier 1 & 2 University, Institute of Functional Genomics, Montpellier, France; Laboratory for Diabetes Cell Therapy, Institute for Research in Biotherapy, University Hospital St-Eloi, Montpellier, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Dalle
authors.affiliation: CNRS UMR 5203, INSERM U661, and Montpellier 1 & 2 University, Institute of Functional Genomics, Montpellier, France; Laboratory for Diabetes Cell Therapy, Institute for Research in Biotherapy, University Hospital St-Eloi, Montpellier, France; Department of Endocrinology-Diabetes-Nutrition, University Hospital Lapeyronie, Montpellier, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Wojtusciszyn
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects / Q000235:genetics; D000077270:Exenatide; D015870:Gene Expression; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D006943:Hyperglycemia / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008297:Male; D010455:Peptides / Q000494:pharmacology; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism*; D061988:Proteasome Inhibitors / Q000494:pharmacology; D059748:Proteolysis / Q000187:drug effects; D051381:Rats; D015398:Signal Transduction; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D014688:Venoms / Q000494:pharmacology
chemical_list: C497249:DDIT3 protein, human; C497251:Ddit3 protein, rat; D007004:Hypoglycemic Agents; D010455:Peptides; D061988:Proteasome Inhibitors; D025801:Ubiquitin; D014688:Venoms; D051742:Transcription Factor CHOP; D000077270:Exenatide; D011065:Poly(ADP-ribose) Polymerases; D053148:Caspase 3; D046988:Proteasome Endopeptidase Complex; D005947:Glucose