title: ATP and UTP at low concentrations strongly inhibit bone formation by osteoblasts: a novel role for the P2Y2 receptor in bone remodeling.
abstract: There is increasing evidence that extracellular nucleotides act on bone cells via multiple P2 receptors. The naturally-occurring ligand ATP is a potent agonist at all receptor subtypes, whereas ADP and UTP only act at specific receptor subtypes. We have reported that the formation and resorptive activity of rodent osteoclasts are stimulated powerfully by both extracellular ATP and its first degradation product, ADP, the latter acting at nanomolar concentrations, probably via the P2Y1 receptor subtype. In the present study, we investigated the actions of ATP, ADP, adenosine, and UTP on osteoblastic function. In 16-21 day cultures of primary rat calvarial osteoblasts, ADP and the selective P2Y1 agonist 2-methylthioADP were without effect on bone nodule formation at concentrations between 1 and 125 microM, as was adenosine. However, UTP, a P2Y2 and P2Y4 receptor agonist, known to be without effect on osteoclast function, strongly inhibited bone nodule formation at concentrations >or= 1 microM. ATP was inhibitory at >or= 10 microM. Rat osteoblasts express P2Y2, but not P2Y4 receptor mRNA, as determined by in situ hybridization. Thus, the low-dose effects of extracellular nucleotides on bone formation and bone resorption appear to be mediated via different P2Y receptor subtypes: ADP, signalling through the P2Y1 receptor on both osteoclasts and osteoblasts, is a powerful stimulator of osteoclast formation and activity, whereas UTP, signalling via the P2Y2 receptor on osteoblasts, blocks bone formation by osteoblasts. ATP, the 'universal' agonist, can simultaneously stimulate resorption and inhibit bone formation. These findings suggest that extracellular nucleotides could function locally as important negative modulators of bone metabolism, perhaps contributing to bone loss in a number of pathological states.
authors.affiliation: Department of Anatomy & Developmental Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Astrid
authors.initials: A
authors.lastname: Hoebertz
authors.forename: Siva
authors.initials: S
authors.lastname: Mahendran
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Burnstock
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Arnett
mesh_terms: D000241:Adenosine / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects / Q000201:enzymology; D004305:Dose-Response Relationship, Drug; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism*; D010012:Osteogenesis / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D013268:Stimulation, Chemical; D014544:Uridine Triphosphate / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D018048:Receptors, Purinergic P2; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000241:Adenosine; D014544:Uridine Triphosphate