1α,25(OH)₂D₃ Regulation of integrin expression is substrate dependent

Osteoblasts are attachment-dependent cells that interact with their surface through integrin-mediated mechanisms. Their differentiation is regulated by 1,25-dihydroxyvitamin D3 [1α,25(OH)₂D₃] and is affected by substrate chemistry and microtopography, suggesting that 1α,25(OH)₂D₃ may regulate integrin expression in a surface-specific manner. To test this hypothesis, osteoblast-like human MG63 cells were grown on tissue culture plastic and on grit-blasted and acid-etched titanium disks with a complex microtopography to induce osteoblast differentiation. Expression of α₂, α₅, α_v, β₁, and β₃ integrals were quantified by real-time polymerase chain reaction (PCR) as a function of time in culture and treatment with 1α,25(OH)₂D₃. Results were correlated with expression of osteocalcin, a marker of a differentiated osteoblast. Osteocalcin mRNA increased with time and 1α,25(OH) ₂D₃ treatment and these changes were greater in cultures on the titanium disks. Integrin expression varied with time in culture and this was also surface dependent. At each time point, β₁ and α₂ mRNAs were greater on titanium than on plastic, whereas α₅ expression was reduced and α_v, β₃ expression was unaffected. 1α,25(OH)₂D ₃ increased β₁ mRNA on both surfaces at all time points, but it increased α₂ expression only in 8-d cultures. 1α,25(OH)₂D₃ caused reduced α₅ expression only in cultures grown on plastic for 8 d, and had no effect on either α_v or β₃ expression regardless of surface. These results show that integrin expression in human osteoblast-like cells is differentially modulated by 1α,25(OH)₂D₃ in a time-dependent manner that is sensitive to the surface on which the cells are grown.