title: Presence of a functional receptor for GLP-1 in osteoblastic cells, independent of the cAMP-linked GLP-1 receptor.
abstract: Glucagon-like peptide 1 (GLP-1) controls glucose metabolism in extrapancreatic tissues through receptors other than the pancreatic cAMP-linked GLP-1 receptor; also, GLP-1 induces an insulin- and PTH-independent bone anabolic action in insulin-resistant and type-2 diabetic rats. Here we searched for the presence and characteristics of GLP-1 receptors in osteoblastic MC3T3-E1 cells. [(125)I]-GLP-1 specific binding to MC3T3-E1 cells was time- and temperature-dependent, reaching maximal value at 30 min at 25 degrees C; in these conditions, [(125)I]-GLP-1 binding was dissociable, and displaced by GLP-1, partially by GLP-2, but not by exendin-4 (Ex-4), exendin-9 (Ex-9), glucagon or insulin; Scatchard analysis of the unlabeled GLP-1 data showed high and low affinity binding sites; cross-linking of GLP-1 binding revealed an estimated 70 kDa band, almost undetectable in the presence of 10(-6) M GLP-1. GLP-1, Ex-9, insulin or glucagon failed to modify cellular cAMP content, while GLP-2 and Ex-4 increased it. However, GLP-1 induced an immediate hydrolysis of glycosylphosphatidylinositols (GPIs) generating short-lived inositolphosphoglycans (IPGs), and an increase in phosphatidylinositol-3 kinase (PI3K) and mitogen activated protein kinase (MAPK) activities; Ex-4 also affected GPIs, but its action was delayed with respect to that of GLP-1. This incretin was found to decrease Runx2 but increased osteocalcin gene expression, without affecting that of osteoprotegerin or the canonical Wnt pathway activity in MC3T3-E1 cells which do not express the pancreatic GLP-1 receptor. Our data demonstrate for the first time that GLP-1 can directly and functionally interact with osteoblastic cells, possibly through a GPI/IPG-coupled receptor.
authors.affiliation: Department of Metabolism, Nutrition & Hormones, Fundación Jiménez Díaz, Madrid, Spain.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Nuche-Berenguer
authors.forename: Sergio
authors.initials: S
authors.lastname: Portal-Núñez
authors.forename: Paola
authors.initials: P
authors.lastname: Moreno
authors.forename: Nieves
authors.initials: N
authors.lastname: González
authors.forename: Alicia
authors.initials: A
authors.lastname: Acitores
authors.forename: Ana
authors.initials: A
authors.lastname: López-Herradón
authors.forename: Pedro
authors.initials: P
authors.lastname: Esbrit
authors.forename: Isabel
authors.initials: I
authors.lastname: Valverde
authors.forename: María L
authors.initials: ML
authors.lastname: Villanueva-Peñacarrillo
mesh_terms: D016475:3T3 Cells; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D000077270:Exenatide; D005786:Gene Expression Regulation; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism* / Q000494:pharmacology; D053767:Glucagon-Like Peptide 2 / Q000494:pharmacology; D000067757:Glucagon-Like Peptide-1 Receptor; D006801:Humans; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D018027:Receptors, Glucagon / Q000235:genetics / Q000378:metabolism*; D014688:Venoms / Q000494:pharmacology
chemical_list: C000593833:GLP1R protein, human; C000593834:Glp1r protein, mouse; C000593835:Glp1r protein, rat; D053767:Glucagon-Like Peptide 2; D000067757:Glucagon-Like Peptide-1 Receptor; D010281:Parathyroid Hormone; D010455:Peptides; D018027:Receptors, Glucagon; D014688:Venoms; D005576:Colforsin; D052216:Glucagon-Like Peptide 1; D000077270:Exenatide; D000242:Cyclic AMP; D000262:Adenylyl Cyclases