Integrin subunit beta3 plays a crucial role in the movement of osteoclasts from the periosteum to the bone surface.
We have shown that, when mouse parietal bones were incubated in culture medium containing indomethacin, the number of tartrate-resistant acid phosphatase-positive osteoclasts (TRAP + OCs) on the bone surface was drastically reduced (down-regulation), and the number on the periosteal membrane adjacent to the resorbing surface was increased. Subsequent incubation of bones with prostaglandin E2 (PGE2) rapidly reversed these changes (up-regulation). In the work reported here, the osteoclast-associated integrin subunit beta3 was stained by immunohistochemistry. The beta3-positive osteoclast (beta3 + OC) population on freshly isolated bone was comprised of about 67% TRAP + OCs and 33% TRAP OCs. Like TRAP + OCs, beta3 + OCs were reduced in number on the surface of bones incubated with indomethacin, but, in contrast to the TRAP + OCs, beta3 + OCs were not seen on the periosteal membrane. Following up-regulation of TRAP + OCs with PGE2, large numbers of beta3 + OCs appeared on the bone surface and, again, were not seen on the periosteal membrane. Echistatin, a peptide that binds to the alphavbeta3 integrin on osteoclasts, was found to inhibit the up-regulation of TRAP + OCs in a dose-dependent manner but had no effect on the down-regulation of TRAP + OCs. Similarly, echistatin inhibited the upregulation of beta3 + OCs on the bone surface, and, under these conditions, beta3 + OCs were observed on the periosteal membrane. The addition of anti-beta3 antibody also inhibited the up-regulation of TRAP + OCs in response to PGE2. The association of beta3 protein expression with the up-regulated osteoclast and the inhibition of up-regulation by echistatin and by anti-beta3 antibody provide strong evidence that beta3 plays an essential role in the movement of osteoclasts from the membrane to the bone.
Holt
I
I
Charles Salt Research Centre, The Robert Jones and Agnes Hunt Orthopaedic and District Hospital NHS Trust, Oswestry, Shropshire, United Kingdom.
Marshall
M J
MJ
D000135:Acid Phosphatase / Q000032:analysis; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000276:immunology / Q000378:metabolism*; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D015232:Dinoprostone / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D039661:Integrin beta3; D016023:Integrins / Q000276:immunology / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D008808:Mice, Inbred CBA; D010010:Osteoclasts / Q000737:chemistry / Q000166:cytology* / Q000201:enzymology; D010120:Oxytocics / Q000494:pharmacology; D010294:Parietal Bone / Q000166:cytology*; D010455:Peptides / Q000494:pharmacology; D010521:Periosteum / Q000166:cytology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D010980:Platelet Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism*
D000894:Anti-Inflammatory Agents, Non-Steroidal; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D039661:Integrin beta3; D016023:Integrins; D036341:Intercellular Signaling Peptides and Proteins; D010120:Oxytocics; D010455:Peptides; D010975:Platelet Aggregation Inhibitors; D010980:Platelet Membrane Glycoproteins; C057986:echistatin; D000135:Acid Phosphatase; D015232:Dinoprostone; D007213:Indomethacin