title: Long-Term Exposure of Pancreatic β-Cells to Palmitate Results in SREBP-1C-Dependent Decreases in GLP-1 Receptor Signaling via CREB and AKT and Insulin Secretory Response.
abstract: The effects of prolonged exposure of pancreatic β-cells to high saturated fatty acids on glucagon-like peptide-1 (GLP-1) action were investigated. Murine islets, human pancreatic 1.1B4 cells, and rat INS-1E cells were exposed to palmitate for 24 hours. mRNA and protein expression/phosphorylation were measured by real-time RT-PCR and immunoblotting, respectively. Specific short interfering RNAs were used to knockdown expression of the GLP-1 receptor (Glp1r) and Srebf1. Insulin release was assessed with a specific ELISA. Exposure of murine islets, as well as of human and INS-1E β-cells, to palmitate reduced the ability of exendin-4 to augment insulin mRNA levels, protein content, and release. In addition, palmitate blocked exendin-4-stimulated cAMP-response element-binding protein and v-akt murine thymoma viral oncogene homolog phosphorylation, whereas phosphorylation of MAPK-ERK kinase-1/2 and ERK-1/2 was not altered. Similarly, RNA interference-mediated suppression of Glp1r expression prevented exendin-4-induced cAMP-response element-binding protein and v-akt murine thymoma viral oncogene homolog phosphorylation, but did not impair exendin-4 stimulation of MAPK-ERK kinase-1/2 and ERK-1/2. Both islets from mice fed a high fat diet and human and INS-1E β-cells exposed to palmitate showed reduced GLP-1 receptor and pancreatic duodenal homeobox-1 (PDX-1) and increased sterol regulatory element-binding protein (SREBP-1C) mRNA and protein levels. Furthermore, suppression of SREBP-1C protein expression prevented the reduction of PDX-1 and GLP-1 receptor levels and restored exendin-4 signaling and action. Finally, treatment of INS-1E cells with metformin for 24 h resulted in inhibition of SREBP-1C expression, increased PDX-1 and GLP-1 receptor levels, consequently, enhancement of exendin-4-induced insulin release. Palmitate impairs exendin-4 effects on β-cells by reducing PDX-1 and GLP-1 receptor expression and signaling in a SREBP-1C-dependent manner. Metformin counteracts the impairment of GLP-1 receptor signaling induced by palmitate.
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Annalisa
authors.initials: A
authors.lastname: Natalicchio
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Biondi
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Marrano
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Rossella
authors.initials: R
authors.lastname: Labarbuta
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Tortosa
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Rosaria
authors.initials: R
authors.lastname: Spagnuolo
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Rossella
authors.initials: R
authors.lastname: D'Oria
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Carchia
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Leonardini
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Angelo
authors.initials: A
authors.lastname: Cignarelli
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Sebastio
authors.initials: S
authors.lastname: Perrini
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Laviola
authors.affiliation: Department of Emergency and Organ Transplantation (A.N., G.B., N.M., R.L., F.T., R.S., R.D., A.L., A.C., S.P., L.L., F.G.), Section of Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari Aldo Moro, I-70124 Bari, Italy; and IRGS Biogem (E.C.), I-83031 Ariano Irpino, Avellino, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Giorgino
mesh_terms: D000818:Animals; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D000077270:Exenatide; D000067757:Glucagon-Like Peptide-1 Receptor / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010168:Palmitates / Q000494:pharmacology*; D010455:Peptides / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D051780:Sterol Regulatory Element Binding Protein 1 / Q000378:metabolism*; D014688:Venoms / Q000494:pharmacology
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin; D010168:Palmitates; D010455:Peptides; D051780:Sterol Regulatory Element Binding Protein 1; D014688:Venoms; D000077270:Exenatide; D051057:Proto-Oncogene Proteins c-akt