INTEGRIN SUBUNIT BETA-3 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 cultur e medium containing indomethacin, the number of tartrate-resistant aci d phosphatase-positive osteoclasts (TRAP + OCs) on the bone surface wa s drastically reduced (down-regulation), and the number on the periost eal membrane adjacent to the resorbing surface was increased. Subseque nt incubation of bones with prostaglandin E2 (PGE2) rapidly reversed t hese changes (up-regulation). In the work reported here, the osteoclas t-associated integrin subunit beta 3 was stained by immunohistochemist ry. The beta 3-positive osteoclast (beta 3 + OC) population on freshly isolated bone was comprised of about 67% TRAP + OCs and 33% TRAP - OC s. Like TRAP + OCs, beta 3 + OCs were reduced in number on the surface of bones incubated with indomethacin, but, in contrast to the TRAP OCs, beta 3 + OCs were not seen on the periosteal membrane. Following up-regulation of TRAP + OCs with PGE2, large numbers of beta 3 + OCs a ppeared on the bone surface and, again, were not seen on the periostea l membrane. Echistatin, a peptide that binds to the alpha nu beta 3 in tegrin on osteoclasts, was found to inhibit the up-regulation of TRAP + OCs in a dose-dependent manner but had no effect on the down-regulat ion of TRAP + OCs. Similarly, echistatin inhibited the upregulation of beta 3 + OCs on the bone surface, and, under these conditions, beta 3 + OCs were observed on the periosteal membrane. The addition of anti- beta 3 antibody also inhibited the up-regulation of TRAP + OCs in resp onse to PGE2. The association of beta 3 protein expression with the up -regulated osteoclast and the inhibition of up-regulation by echistati n and by anti-beta 3 antibody provide strong evidence that beta 3 play s an essential role in the movement of osteoclasts from the membrane t o the bone. (C) 1998 Wiley-Liss, Inc.