Integrin β1 silencing in osteoblasts alters substrate-dependent responses to 1,25-dihydroxy vitamin D3

Surface microroughness increases osteoblast differentiation and enhances responses of osteoblasts to 1,25-dihydroxyvitamin D-3 [1 alpha,25(OH)(2)D-3]. The observations that beta(1) integrin expression is increased in osteoblasts grown on Ti substrates with rough microarchitecture, and that it is regulated by 1 alpha,25(OH)(2)D-3 in a surface-dependent manner, suggest that beta(1) may play a role in mediating osteoblast response. To test this hypothesis, we silenced beta(1) expression in MG63 human osteoblast-like cells using small interfering RNA (siRNA) and examined the responses of the beta(1)-silenced osteoblasts to surface microtopography and 1 alpha,25(OH)(2)D-3. To better understand the role of beta(1), MG63 cells were also treated with two different monoclonal antibodies to human beta(1) to block ligand binding. beta(1)-silenced MG63 cells grown on a tissue culture plastic had reduced alkaline phosphatase activity and levels of osteocalcin, transforming growth factor beta(1), prostaglandin E-2, and osteoprotegerin in comparison with control cells. Moreover, beta(1)-silencing inhibited the effects of surface roughness on these parameters and partially inhibited effects of 1 alpha,25(OH)(2)D-3. Anti beta(1) antibody AIIB2 had no significant effect on cell number and osteocalcin, but decreased alkaline phosphatase; MAB2253Z caused dose-dependent decreases in cell number and alkaline phosphatase and an increase in osteocalcin. Effects of 1 alpha,25(OH)(2)D-3 on cell number and alkaline phosphatase were reduced and effects on osteocalcin were increased. These findings indicate that beta(1) plays a major and complex role in osteoblastic differentiation modulated by either surface microarchitecture or 1 alpha,25(OH)(2)D-3. The results also show that beta(1) mediates, in part, the synergistic effects of surface roughness and 1 alpha,25(OH)(2)D-3. (c) 2006 Elsevier Ltd. All rights reserved.