title: CGRP inhibits osteoprotegerin production in human osteoblast-like cells via cAMP/PKA-dependent pathway.
abstract: The osteoprotegerin (OPG)/receptor activator of nuclear factor-kappaB ligand (RANKL)/receptor activator of nuclear factor-kappaB (RANK) system was evaluated as a potential target of CGRP anabolic activity on bone. Primary cultures of human osteoblast-like cells (hOB) express calcitonin receptor-like receptor (CLR) and receptor activity modifying protein 1, and, because CGRP stimulates cAMP (one of the modulators of OPG production in osteoblasts), it was investigated whether it affects OPG secretion and expression in hOB. CGRP treatment of hOB (10(-11) M-10(-7) M) dose-dependently inhibited OPG secretion with an EC(50) of 1.08 x 10(-10) M, and also decreased its expression. This action was blocked by the antagonist CGRP(8-37). Forskolin, a stimulator of cAMP production, and dibutyryl cAMP also reduced the production of OPG. CGRP (10(-8) M) enhanced protein kinase A (PKA) activity in hOB, and hOB exposure to the PKA inhibitor, H89 (2 x 10(-6) M), abolished the inhibitory effect of CGRP on OPG secretion. Conditioned media from CGRP-treated hOB increased the number of multinucleated tartrate-resistant acid phosphatase-positive cells and the secretion of cathepsin K in human peripheral blood mononuclear cells compared with the conditioned media of untreated hOB. These results show that the cAMP/PKA pathway is involved in the CGRP inhibition of OPG mRNA and protein secretion in hOB and that this effect favors osteoclastogenesis. CGRP could thus modulate the balance between osteoblast and osteoclast activity, participating in the fine tuning of all of the bone remodeling phases necessary for the subsequent anabolic effect.
authors.affiliation: Department of Pharmacology, Chemotherapy and Medical Toxicology, University of Milan, Via Vanvitelli 32, 20129 Milan, Italy.
authors.forename: I
authors.initials: I
authors.lastname: Villa
authors.forename: E
authors.initials: E
authors.lastname: Mrak
authors.forename: A
authors.initials: A
authors.lastname: Rubinacci
authors.forename: F
authors.initials: F
authors.lastname: Ravasi
authors.forename: F
authors.initials: F
authors.lastname: Guidobono
mesh_terms: D000135:Acid Phosphatase / Q000032:analysis; D000368:Aged; D016723:Bone Remodeling / Q000502:physiology; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology / Q000502:physiology*; D000077221:Calcitonin Gene-Related Peptide Receptor Antagonists; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D056657:Cathepsin K; D002403:Cathepsins / Q000494:pharmacology; D002469:Cell Separation; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005264:Femoral Fractures / Q000473:pathology; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000032:analysis; D007963:Leukocytes, Mononuclear / Q000187:drug effects; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D008875:Middle Aged; D010006:Osteoblasts / Q000187:drug effects / Q000502:physiology*; D010010:Osteoclasts / Q000187:drug effects / Q000502:physiology; D053244:Osteoprotegerin; D010446:Peptide Fragments / Q000494:pharmacology; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018015:Receptors, Calcitonin Gene-Related Peptide / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism*; D015398:Signal Transduction; D000071681:Tartrate-Resistant Acid Phosphatase
chemical_list: D000077221:Calcitonin Gene-Related Peptide Receptor Antagonists; D002352:Carrier Proteins; D006023:Glycoproteins; D007527:Isoenzymes; D008562:Membrane Glycoproteins; D053244:Osteoprotegerin; D010446:Peptide Fragments; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018015:Receptors, Calcitonin Gene-Related Peptide; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor; C505686:TNFRSF11A protein, human; C506030:TNFRSF11B protein, human; C505688:TNFSF11 protein, human; C058636:calcitonin gene-related peptide (8-37); D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D002403:Cathepsins; C534130:CTSK protein, human; D056657:Cathepsin K; D015740:Calcitonin Gene-Related Peptide