The role of cell signaling defects on the proliferation of osteoblasts on the calcium phosphate apatite thin film

The intracellular signal transduction controlling the proliferation of osteoblastic cells on a thin film of poorly crystalline calcium phosphate apatite crystals (PCA) was studied in vitro. The PCA thin film was prepared on polystyrene culture dishes or cover glasses using phosphate-buffered calcium ion solution, which was made oversaturated by heating an undersaturated solution prepared at low temperature. The PCA thin film was used for cell culture without additional surface treatment. Several differences were found between the cells plated on a cell culture dish and the cells cultured on the PCA surface. Entry into S-phase of the cell cycle was markedly delayed and there was a low proliferation rate of osteblast. On the PCA thin film, the cells spread in a more slender shape. Also, the formation of focal adhesions and stress fibers, examined using immunocytochemical staining, was strikingly weaker in the cells on PCA. The activation of focal adhesion kinase (FAK) was low as well. Expression of cyclins D1 and E was also lower. The Ras–Extracellular signal-regulated kinase (ERK)–MAP kinase signaling pathway was weakly activated by stimulation with serum. These results demonstrate that the low cell proliferation on the PCA surface appears to be due to insufficient activation of signaling that forces the cell cycle to progress and this may be due to weak adhesion signaling in cells on that surface.