Mechanisms of magnesium-stimulated adhesion of osteoblastic cells to commonly used orthopaedic implants

Poor cell adhesion to orthopaedic and dental implants may result in implant failure. Cellular adhesion to biomaterial surfaces primarily is mediated by integrins, which act as signal transduction and adhesion proteins. Because integrin function depends on divalent cations, we investigated the effect of magnesium ions modified bioceramic substrata (Al₂O₃-Mg²⁺) on human bone-derived cell (HBDC) adhesion, integrin expression, and activation of intracellular signalling molecules. Immunohistochemistry, flow cytometry, cell adhesion, cell adhesion blocking, and Western blotting assays were used. Our findings demonstrated that adhesion of HBDC to Al₂O₃-Mg²⁺ was increased compared to on the Mg²⁺-free Al₂O₃. Furthermore, HBDC adhesion decreased significantly when the fibronectin receptor α5β1-and β1-integrins were blocked by functional blocking antibodies. HBDC grown on the Mg²⁺-modified bioceramic expressed significantly enhanced levels of β1-, α5β1-, and α3β1-integrins receptors compared to those grown on the native unmodified Al₂O₃. Tyrosine phosphorylation of intracellular integrin-dependent signalling proteins as well as the expression of key signalling protein Shc isoforms (p46, p52, p66), focal adhesion kinase, and extracellular matrix protein collagen type I were significantly enhanced when HBDC were grown on Al₂O₃-Mg²⁺ compared to the native Al₂O₃. We conclude that cell adhesion to biomaterial surfaces is probably mediated by α5β1- and β1-integrin. Cation-promoted cell adhesion depends on 5β1- and β1-integrins associated signal transduction pathways involving the key signalling protein Shc and results also in enhanced gene expression of extracellular matrix proteins. Therefore, Mg²⁺ supplementation of bioceramic substrata may be a promising way to improve integration of implants in orthopaedic and dental surgery.