圧縮力は培養後期における破骨細胞の分化・融合を抑制する

osteoclast

北海道歯学会

北海道歯学雑誌

Orthodontic force consists of tensile and compressive force. On the pressure side, osteoclasts are subjected to compressive force. In contrast, on the tension side, osteoclasts are subjected to tensile force. Here we present our reports about the direct effects of compressive force on osteoclast. We found no other reports that demonstrated the change of the osteoclasts when they are cultured long term after compression. Therefore, we investigated the effects of compressive force on osteoclastogenesis when we cultured osteoclasts long term after application of a compressive force in this study. We cultured RAW264.7 (RAW) cells with a culture medium added receptor activator of nuclear factor-κB ligand (RANKL) for 7 days and observed the change in the number of osteoclasts. Osteoclasts increased up to the 6th day, but decreased after that. To investigate the effects of compressive force, we added weight to osteoclasts at day 3, and cultured them for 24, 48 and 72 h. The control group was cultured without weight. The compressed off (CF→ off) group was cultured for 24 h with weight, and then cultured without it. The compressed (CF) group was cultured with weight. The number of osteoclasts were counted and compared. The number of osteoclasts increased when we applied compressive force for 24 h from the 3rd day. At day 5 , CF→ off group and CF group increased more than the control group. No significant difference was recognized among the former two groups. This suggested the possibility that over 24 h compression did not promote osteoclast differentiation and fusion. On the 6th day, the control group increased more than the other groups. In addition, the control group increased during the culture of the 5th day to the 6th day, but the other groups decreased. These results suggested the possibility that the compressive force suppressed differentiation and fusion of osteoclasts in late stages. Comparing the control group with the CF group about mRNA expression of osteoclastassociated genes, including nuclear factor of activated T cells c1 (NFATc1), TRAP, receptor activator of NF-κB (RANK), dendritic cell specific trans membrane protein (DC-STAMP), and osteoclast stimulatory trans membrane protein (OCSTAMP) on the 4th day, no significant differences were observed. But on the 5th day, the CF group was significantly suppressed. This showed the compressive force suppressed expression of osteoclast-associated genes in the late stages. These results suggested that compressive force suppressed osteoclast differentiation and fusion by suppressing expression of osteoclast-associated genes in late stages of the experiment.