Bone formation stimulation by semiconductor laser via Cbfa1/Pebp2αA

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Bone formation acceleration following low-intensity laser treatment has been demonstrated in both animal and cell culture models, however, the action mechanisms of irradiation on bone are unclear. We previously reported that low-intensity laser irradiation stimulated bone nodule formation through enhanced cellular proliferation and differentiation, thus, in the present study, we attempted to determine whether insulin-like growth factor (IGF)-I is responsible for the action observed. Osteoblast-like cells were isolated from fetal rat calvariae and cultured with rat recombinant (r) IGF-I, IGF-I-antibody (Ab), and/or the cells were irradiated once (3.75 J/cm^2) with a low- intensity Ga-Al-As laser (830 nm) at the subconfluent stage. The cells were cultured for 24 days and stained using the von-Kossa technique. Treatment with recombinant IGF-I for 6 days significantly stimulated the number and area of bone nodules as compared to the control (1.4-1.6-fold), and these effects were quite similar to those by laser irradiation. Moreover, the stimulatory effect by laser irradiation was abrogated dose-dependently by treatment with IGF-I-Ab for 6 days. To confirm the mechanisms responsible for the action of laser irradiation IGF-I protein levels and gene expression in rat calvarial cells were also examined. IGF-I production in the medium was significantly increased at 3 and 6 days after laser irradiation as compared to the control, and the cell mass center expressed IGF-I. Gene expression, examined by semi-quantitative RT-PCR, was also found to be significantly stimulated at 1 and 3 days after irradiation, and returned to the control level thereafter. These results indicate that the stimulatory effect of bone nodule formation by low-intensity laser irradiation may be at least partly mediated by IGF-I expression. Gene expression of Cbfa1/Pebp2αA by laser irradiation is in progress.