ArgGlyAsp (RGD) peptides and the anti-vitronectin receptor antibody 23C6 inhibit dentine resorption and cell spreading by osteoclasts

Abstract

Studies with a range of monoclonal and polyclonal antisera to components of the human, rat, and chick vitronectin receptor, αVβ3, and the VLA β1 chain show that chick and rat osteoclasts express similar integrin receptors to those described in man. Biochemical analysis with monoclonal antibody 23C6 confirmed the presence on chick osteoclasts of a vitronectin receptor heterodimer of similar size ($\text{110}\text{95}$ kDa reduced) to that immunoprecipitated from human osteoclastoma giant cells. The synthetic peptide GRGDSP, corresponding to the cell adhesion sequence in fibronectin, but not GRGESP peptide, induced significant (P < 0.005) osteoclast retraction in chick and rat osteoclasts at IC₅₀s (±SEM) of 210.0 ± 14.4 and 191.4 ± 13.7 μM, respectively; monoclonal anti-vitronectin receptor αVβ3 complex antibody, 23C6, produced similar changes in chick osteoclasts (IC₅₀ = 1.45 ± 0.22 μM). Antibody 23C6 inhibited the number of pits resorbed in dentine by chick osteoclasts over a concentration range of 4.4 to 88 μg/ ml; a significant 76% reduction (P = 0.03) was observed at a final concentration of 88 μg/ml (6 μM). The effect of peptides upon dentine resorption was less dramatic. No consistent inhibition was seen using chick osteoclasts. Inhibitory effects on resorption by rat osteoclasts were, however, observed; significant reduction in resorption occurred with both GRGDSP (78%; P < 0.01) and GRGESP (67%; P = 0.02) peptides at 400 μM peptide concentration. These data demonstrate that osteoclast function can be disrupted by low concentrations of the anti-vitronectin receptor antibody, 23C6. The inhibitory effects of the peptides used in this study produced effects on dentine resorption which were generally weaker and variable, although osteoclast cell adhesion was consistently inhibited in an ArgGlyAsp (RGD)-dependent manner. We conclude that the vitronectin receptor may play an important role in effecting resorption of mineralized tissues by osteoclasts.