title: Activation of PPARβ/δ protects pancreatic β cells from palmitate-induced apoptosis by upregulating the expression of GLP-1 receptor.
abstract: We previously showed that activated peroxisome proliferator-activated receptor (PPAR)β/δ can protect pancreatic β cells against lipotoxic apoptosis. However, the molecular mechanism remained unclear. Glucagon-like peptide-1 receptor (GLP-1R) has been reported to exhibit a protective effect against lipotoxic apoptosis in pancreatic β cells. In the present study, we aimed to investigate the underlying molecular mechanisms that PPARβ/δ activation suppressed apoptosis and improved β cell function impaired by fatty acids, focusing on contribution of GLP-1R. Isolated rat islets and rat insulin-secreting INS-1 cells were treated with the PPARβ/δ agonist GW501516 (GW) in the presence or absence of palmitate (PA) and transfected with siRNA for PPARβ/δ or treated with the PPARβ/δ antagonist GSK0660. Apoptosis was assessed by DNA fragmentation, Hoechst 33342 staining and flow cytometry. GLP-1R expression in INS-1 cells and islets was assayed by immunoblotting, quantitative PCR (qPCR) and immunofluorescence staining. SREBP-1c, Caveolin-1, Akt, Bcl-2, Bcl-xl and caspase-3 expression was measured using immunoblotting and qPCR. Our results showed that PPARβ/δ activation decreased apoptosis in β cells and robustly stimulated GLP-1R expression under lipotoxic conditions. GW enhanced glucose-stimulated insulin secretion (GSIS) impaired by PA through stimulation of GLP-1R expression in β cells. Moreover, SREBP-1c/Caveolin-1 signaling was involved in PPARβ/δ-regulated GLP-1R expression. Finally, GW exerted anti-apoptotic effects via interfering with GLP-1R-dependent Akt/Bcl-2 and Bcl-xl/caspase-3 signaling pathways. Our study suggested that the anti-apoptotic action of GW may involve its transcriptional regulation of GLP-1R, and PPARβ/δ activation may represent a new therapeutic method for protecting pancreatic β cells from lipotoxicity.
authors.affiliation: Division of Endocrinology, West China Hospital of Sichuan University, Chengdu, Sichuan, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Yang
authors.affiliation: West China School of Medicine, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Yuzhen
authors.initials: Y
authors.lastname: Tong
authors.affiliation: Laboratory of Endocrinology and Metabolism, West China Hospital of Sichuan University, Chengdu, Sichuan, China.
authors.forename: Meng
authors.initials: M
authors.lastname: Gong
authors.affiliation: Laboratory of Transplantation Engineering, West China Hospital of Sichuan University, Chengdu, China.
authors.forename: Yanrong
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Laboratory of Transplantation Engineering, West China Hospital of Sichuan University, Chengdu, China.
authors.forename: Chengshi
authors.initials: C
authors.lastname: Wang
authors.affiliation: Laboratory of Endocrinology and Metabolism, West China Hospital of Sichuan University, Chengdu, Sichuan, China.
authors.forename: Mingliang
authors.initials: M
authors.lastname: Zhou
authors.affiliation: Division of Endocrinology, West China Hospital of Sichuan University, Chengdu, Sichuan, China.
authors.forename: Qiu
authors.initials: Q
authors.lastname: Yang
authors.affiliation: Division of Endocrinology, West China Hospital of Sichuan University, Chengdu, Sichuan, China.
authors.forename: Tingrui
authors.initials: T
authors.lastname: Mao
authors.affiliation: Division of Endocrinology, West China Hospital of Sichuan University, Chengdu, Sichuan, China. Electronic address: buddyjun@hotmail.com.
authors.forename: Nanwei
authors.initials: N
authors.lastname: Tong
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002478:Cells, Cultured; D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D047494:PPAR delta / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D048068:PPAR-beta / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010168:Palmitates / Q000494:pharmacology*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018027:Receptors, Glucagon / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013450:Sulfones / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D013876:Thiophenes / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects
chemical_list: C529769:GSK0660; C425931:GW 501516; C000593835:Glp1r protein, rat; D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin; D047494:PPAR delta; D048068:PPAR-beta; D010168:Palmitates; D034741:RNA, Small Interfering; D018027:Receptors, Glucagon; D013450:Sulfones; D013844:Thiazoles; D013876:Thiophenes
keywords: Apoptosis; ELISA; Ex; FBS; FDA; FFA; FITC; G protein coupled receptor; GLP-1R; GPCR; GSIS; GW; GW501516; HBSS; Hanks' balanced salt solution; KRBH; PA; PI; PPARβ/δ; Palmitate; Pancreatic β cells; SREBP-1c; T2D; enzyme-linked immunosorbent assay; exendin-4; fetal bovine serum; fluorescein diacetate; fluorescein isothiocyanate; free fatty acid; glucagon-like peptide-1 receptor; glucose-free Krebs–Ringer bicarbonate HEPES buffer; glucose-stimulated insulin secretion; palmitate; peroxisome proliferator-activated receptor β/δ; propidium iodide; qPCR; quantitative polymerase chain reaction; sterol regulatory element binding protein-1c; type 2 diabetes