Effects on gene expression of bone and cell-adhesive proteins by biomaterials

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The purpose of this study was to investigate the mechanism of adhesion of osteoblast to biomaterials. Firstly, the effect of the difference of the biomaterials on the adhesion of osteoblasts to them was investingated. Cell adhesion rate of a human osteosarcoma derived cell line (Saos2) to hydroxyapatite was same to that to titanium incubated without serum, whereas cell adhesion rate of Saos2 to hydroxyapatite was higher than that to titanium with serum. From these results, we speculated that the proteins within serum effected cell adhesion to biomaterials. We carried out the tranfection of osteopontin (OP) into Saos2. OP is a noncollagenous protein in bone matrix. It is reported that OP enhanced adhesive activity of osteoblast-like cells in vitro. We investigated the effect on adhesive activity of osteoblast-like cell to titanium by transfection of OP. Human OP cDNA given FLAG tag to C-terminus was subcloned to retrovirus vector (pBabe-puro). Selection was carried out with DMEM contained ouromyciiL Saos2 cell line that expressed OP-FLAG was cloned (Saos2-OP). Expression of OP was observed in only Saos2-OP by the RT-PCR and production of OP included FLAG tag was confirmed in only Saos2-OP. There was a significant difference between the numbers of Saos2-OP and parental cells attached to the titanium disc and polystyrene dish after 12 and 24 hours of incubation in serum-free DMEM, although there was no significance among the numbers of attached cells after 6 hours. Observation of SEM revealed the difference between the shapes of Saos2-OP and Saos2. The shape of Saos2-OP was smaller and thicker, compared with Saos2, and there were small global structure on the surface of Saos2-OP, but not on the surface of Saos2. These results suggested that human osteopontin is a potent enhancer of osteoblast-like cell adhesion to titanium, and that transfection of osteopontin influenced the shape of Saos2.