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Cellular and molecular events in osseointegration at the dental implant surface remain largely unknown. We hypothesized that bone marrow stromal cells (BMSCs) participate in this process, and that osterix (Osx) promotes implant osseointegration. To prove this hypothesis, we tracked double-labeled BMSCs in implantation sites created in nude mice transplanted with these cells. We also inserted implants into the femurs of our established transgenic mice after local administration of viruses encoding Osx, to determine the osteogenic effects of Osx. Immunohistochemical results demonstrated that BMSCs can recruit from peripheral circulation and participate in wound healing and osseointegration after implantation. Microcomputed tomography (microCT) analysis revealed an increased bone density at the bone-to-implant interface in the Osx group, and histomorphometric analysis indicated an elevated level of bone-to-implant contact in the Osx group. We concluded that exogenous BMSCs participate in the osseointegration after implantation, and that Osx overexpression accelerates osseointegration.

Dlx5 plays an important role in the embryonic development of mineralized tissues. We hypothesized that Dlx5 also functions in regulating post-natal bone formation in mice. To prove this hypothesis, we infected 5-day-old bone sialoprotein (BSP)/avian retroviral receptor gene (TVA) transgenic mice with replication-competent retroviral vectors expressing wild-type Dlx5 (RCAS- Dlx5WT) and mutated Dlx5 at arginine (R) 31 of its homeodomain (RCAS- Dlx5RH). Immunohistochemistry indicated that RCAS- Dlx5WT increased BSP and osteopontin (OPN) expression, whereas it decreased that of osteocalcin (OC). RCAS- Dlx5RH mediated opposite effects. Semi-quantitative RT-PCR confirmed these results. Ex vivo overexpression of RCAS- Dlx5WT in BSP/TVA calvarial cells promoted, whereas that of RCAS- Dlx5RH inhibited, mineralized nodule formation as compared with that in control cells. Our results suggest that Dlx5 promotes expression of early markers of osteogenic differentiation and increases mineralization post-natally.