title: Adenosine A(2A) receptor ligation inhibits osteoclast formation.
abstract: Adenosine is generated in increased concentrations at sites of injury/hypoxia and mediates a variety of physiological and pharmacological effects via G protein-coupled receptors (A(1), A(2A), A(2B), and A(3)). Because all adenosine receptors are expressed on osteoclasts, we determined the role of A(2A) receptor in the regulation of osteoclast differentiation. Differentiation and bone resorption were studied as the macrophage colony-stimulating factor-1-receptor activator of NF-κB ligand formation of multinucleated tartrate-resistant acid phosphatase (TRAP)-positive cells from primary murine bone marrow-derived precursors. A(2A) receptor and osteoclast marker expression levels were studied by RT-PCR. Cytokine secretion was assayed by enzyme-linked immunosorbent assay. In vivo examination of A(2A) knockout (KO)/control bones was determined by TRAP staining, micro-computed tomography, and electron microscopy. The A(2A) receptor agonist, CGS21680, inhibited osteoclast differentiation and function (half maximal inhibitory concentration, 50 nmol/L), increased the percentage of immature osteoclast precursors, and decreased IL-1β and tumor necrosis factor-α secretion, an effect that was reversed by the A(2A) antagonist, ZM241385. Cathepsin K and osteopontin mRNA expression increased in control and ZM241385-pretreated osteoclasts, and this was blocked by CGS21680. Micro-computed tomography of A(2A)KO mouse femurs showed a significantly decreased bone volume/trabecular bone volume ratio, decreased trabecular number, and increased trabecular space. A(2A)KO femurs showed an increased TRAP-positive osteoclast. Electron microscopy in A(2A)KO femurs showed marked osteoclast membrane folding and increased bone resorption. Thus, adenosine, acting via the A(2A) receptor, inhibits macrophage colony-stimulating factor-1-receptor activator of NF-κB ligand-stimulated osteoclast differentiation and may regulate bone turnover under conditions in which adenosine levels are elevated.
authors.affiliation: Division of Translational Medicine, Department of Medicine, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Aránzazu
authors.initials: A
authors.lastname: Mediero
authors.forename: Firas M
authors.initials: FM
authors.lastname: Kara
authors.forename: Tuere
authors.initials: T
authors.lastname: Wilder
authors.forename: Bruce N
authors.initials: BN
authors.lastname: Cronstein
mesh_terms: D015502:Absorptiometry, Photon; D000135:Acid Phosphatase / Q000378:metabolism; D058908:Adenosine A2 Receptor Agonists / Q000494:pharmacology; D058917:Adenosine A2 Receptor Antagonists / Q000494:pharmacology; D000818:Animals; D015519:Bone Density / Q000502:physiology; D001862:Bone Resorption / Q000473:pathology; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D005260:Female; D005269:Femur / Q000502:physiology; D007527:Isoenzymes / Q000378:metabolism; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D010010:Osteoclasts / Q000166:cytology* / Q000378:metabolism; D053245:RANK Ligand / Q000494:pharmacology; D043705:Receptor, Adenosine A2A / Q000502:physiology*; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000037:antagonists & inhibitors; D011994:Recombinant Proteins; D000071681:Tartrate-Resistant Acid Phosphatase
chemical_list: D058908:Adenosine A2 Receptor Agonists; D058917:Adenosine A2 Receptor Antagonists; D016207:Cytokines; D007527:Isoenzymes; D053245:RANK Ligand; D043705:Receptor, Adenosine A2A; D011994:Recombinant Proteins; D016173:Macrophage Colony-Stimulating Factor; D016186:Receptor, Macrophage Colony-Stimulating Factor; D000135:Acid Phosphatase; C000605511:Acp5 protein, mouse; D000071681:Tartrate-Resistant Acid Phosphatase