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 D3 [1α,25(OH)2D3]. The observations that β1 integrin expression is increased in osteoblasts grown on Ti substrates with rough microarchitecture, and that it is regulated by 1α,25(OH)2D3 in a surface-dependent manner, suggest that β1 may play a role in mediating osteoblast response. To test this hypothesis, we silenced β1 expression in MG63 human osteoblast-like cells using small interfering RNA (siRNA) and examined the responses of the β1-silenced osteoblasts to surface microtopography and 1α,25(OH)2D3. To better understand the role of β1, MG63 cells were also treated with two different monoclonal antibodies to human β1 to block ligand binding. β1-silenced MG63 cells grown on a tissue culture plastic had reduced alkaline phosphatase activity and levels of osteocalcin, transforming growth factor β1, prostaglandin E2, and osteoprotegerin in comparison with control cells. Moreover, β1-silencing inhibited the effects of surface roughness on these parameters and partially inhibited effects of 1α,25(OH)2D3. Anti β1 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 1α,25(OH)2D3 on cell number and alkaline phosphatase were reduced and effects on osteocalcin were increased. These findings indicate that β1 plays a major and complex role in osteoblastic differentiation modulated by either surface microarchitecture or 1α,25(OH)2D3. The results also show that β1 mediates, in part, the synergistic effects of surface roughness and 1α,25(OH)2D3.