The role of the Wnt/β-catenin pathway in the effect of implant topography on MG63 differentiation

Wnt/β-catenin signaling plays a key role in bone formation. To assess the role of this signaling cascade in the response of osteoblasts to the implant topography, human MG63 osteoblasts are cultured on micropitted/nanotubular surface topographies (MNTs) and the transcriptional expressions of Wnt/β-catenin pathway receptors, activators, and inhibitors are measured. β-catenin signaling and cell differentiation are studied in the absence and presence of exogenous Dickkopf 1 (Dkk1) on the MNTs and exogenous Wnt3a on a smooth surface. The expressions of the Wnt/β-catenin pathway receptor low-density lipoprotein receptor-related protein 6 and pathway ligand Wnt3a are up-regulated by the MNTs whereas those of the pathway inhibitors including Dkk1/2 and secreted frizzled-related protein 1/2 are down-regulated by the MNTs, indicating regulation of the Wnt/β-catenin pathway modulators to activate the pathway. Consequently, the β-catenin signaling activity is enhanced by the MNTs as well as cell differentiation in terms of osteogenesis-related gene expressions and alkaline phosphatase and collagen products. On the smooth surface, exogenous Wnt3a stimulates β-catenin signaling and cell differentiation while exogenous Dkk1 attenuates the enhancement by the MNTs. The results explicitly demonstrate that the implant topography regulates the product of the Wnt/β-catenin pathway modulators from the cells and in turn activates the cell Wnt/β-catenin pathway promoting osteoblast differentiation.