title: Retinal pigment epithelial cells express a functional receptor for glucagon-like peptide-1 (GLP-1).
abstract: Glucagon-like peptide-1 (GLP-1) is a gut-derived incretin hormone that has been shown to improve glucose homeostasis in type 2 diabetes. The biological effects of GLP-1 are mediated by its specific receptor GLP-1R that is expressed in a wide range of tissues, where it is responsible of the extra-pancreatic effects of GLP-1. Since the retinal pigment epithelium (RPE), that forms the outer retinal barrier, has a key role in protecting from diabetic retinopathy (DR), we investigated the potential expression and function of GLP-1R in a RPE cell line. ARPE-19 cells were cultured in DMEM/F12 supplemented with 10% FBS. The expression of GLP-1R was evaluated at both mRNA and protein levels. Then, the activation postreceptor intracellular signal transduction pathways (extracellular signal-regulated kinases 1 and 2 [ERK1/2] and protein kinase B [PKB]) were assessed by western blot in normal cells or silenced for GLP-1R in the presence or absence of 10 nmol/L GLP-1. The potential connections between intracellular signalling pathways triggered by GLP-1 stimulation were performed before incubating cells with kinase pharmacological inhibitors of mitogen-activated protein kinase (MEK)1/2, phosphatydilinositol-3kinase (PI3K), or epidermal growth factor receptor (EGFR). The results showed that GLP1R is expressed at both mRNA and protein level in ARPE-19 cells. Stimulation with GLP-1 strongly activated PKB and ERK1/2 phosphorylation till 40 min of exposure. GLP-1-mediated activation of both kinases was dependent on the upstream activation of PI3K and EGFR. Finally, treatment with GLP-1 did not affect the spontaneous release of VEGF-A from ARPE-19 cells. In conclusion, this paper showed that the presence of functional GLP-1R is expressed in RPE cells. These data might represent the rationale to further investigate the potential direct beneficial effects of GLP-1 treatment against DR.
authors.affiliation: Department of Internal Medicine, University of Genoa, IRCCS Azienda Ospedaliera Universitaria San Martino-IST Istituto Nazionale per la Ricerca sul Cancro, 6 Viale Benedetto XV, 16132 Genoa, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Puddu
authors.forename: Roberta
authors.initials: R
authors.lastname: Sanguineti
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Montecucco
authors.forename: Giorgio L
authors.initials: GL
authors.lastname: Viviani
mesh_terms: D002460:Cell Line; D002470:Cell Survival; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism; D020868:Gene Silencing; D052216:Glucagon-Like Peptide 1 / Q000494:pharmacology*; D000067757:Glucagon-Like Peptide-1 Receptor; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D018027:Receptors, Glucagon / Q000378:metabolism*; D055213:Retinal Pigment Epithelium / Q000166:cytology* / Q000473:pathology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013997:Time Factors; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; C000593833:GLP1R protein, human; D000067757:Glucagon-Like Peptide-1 Receptor; D018027:Receptors, Glucagon; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D052216:Glucagon-Like Peptide 1; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt