The Axl Genes in Osteoblast Response to Titanium in vitro

Titanium (Ti) and Ti alloys have been widely used as dental implants because of their mechanical strength, durability and excellent biocompatibility. Variations in the Ti surface characteristics have been shown to induce phenotypic and functional changes both in vivo and in vitro. We have shown that surface roughness has a number of effects on bone cells including altered morphology, attachment, proliferation, and furthermore, these surfaces fundamentally alter gene expression. The most notable of the genes with an apparent response to surface roughness was the Axl receptor tyrosine kinase. OBJECTIVES: To examine the changes in expression levels of the Axl/Gas6 gene system and their relationship to markers of osteogenic importance in bone cells in response to two Ti surfaces of differing topographies. METHODS: Bone cells were incubated for 3, 12, 24 and 72 h after attachment to two Ti surfaces, smooth polished (SMO) and sandblasted/acid etched (SLA). Levels of gene expression were measured, using RT-PCR, for the Axl, Gas6 and several bone associated genes such as, osteopontin (OP) and GAPDH genes. The levels of expression were calculated densitometrically relative to GAPDH. RESULTS: The levels of Axl changed with both time and surface. These changes were correlated with the expression of Gas6 and some bone associated genes. CONCLUSION: Ti surface topographies have effects on cell behaviour, both in vivo and in vitro, which may be controlled by the activities of both Axl and/or Gas6. Supported by grants from the ITI Foundation, Switzerland and the CRDC, UK.