Local mechanism of new bone formatior in bone grafting-interaotion between cells in the graft and cells in host-

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Although autogenous bone grafting is currently available treatment. local mechanism of new bone formation has riot been analyzed clearly. The aim of this study was to examine the relationship between cells in the graft and host for new bone formation. We used GFP transgenic rats and wild-type rats, and ectopic isograft model that harvested femur was transplanted into back muscles between these kinds of rats was established. Gratis were divided into two groups, without treatment(experimental group) and treated by liquid nitrogen(control croup). Specimens were examined by immunohistochemistry for origin of osteoblast and osteoclast, real time RT-PCR, and in situ hybridization for temporal and spatial expression of BMP signaling. Eclopic new bone formation was found in the medullary canal at day 7 after grafting, and remodeling was followed in experimental group. No bone formation was found in control group. At day 7, osteoblasts were mainly originated from graft. Osteoblasts originated from host increased at day 14.and almost all of the osteoblasts were replaced by host at day 42.Transient increase of BMP-4.BMPRIA, 2, and noggin mRNA was found in experimental group, but only BMPRIA and 2 mRNA in control group. BMP-4 mRNA was expressed in graft cells at day 7 and in both graft and host cells at day 14.Collectively our results indicated the possibility for the First time that cells in graft induced host cells to bone formation by expressing BMP-4 mRNA.