Permalink : http://hdl.handle.net/2115/68793

KEYWORDS : 破骨細胞;圧縮力;メカニカルストレス;osteoclast;compressive force;mechanical stress

歯科矯正力により歯牙には牽引側では伸展力が，圧迫側では圧縮力が作用する．我々は破骨細胞に直接圧縮力を加えた際の影響について報告しているが，破骨細胞に圧縮力を加えた後，長期的に培養した場合の動態については未だ報告がない．本研究では，破骨細胞に圧縮力を加え，長期的に培養して分化誘導系に与える影響を検討した．RANKL添加培養液を用いてRAW264.7細胞を７日間培養し，破骨細胞数の推移を観察した．培養６日目までは破骨細胞数は増加したが，それ以降は減少傾向を示した．次に培養３日目に圧縮力を破骨細胞に加え24, 48および72時間培養した．圧縮力を加えず培養したものを対照群，圧縮力を24時間加えた後それを解放して培養したものを解放群，圧縮力を加えたまま培養したものを圧縮群とした．培養３日目から24時間圧縮力を加えると，破骨細胞数は増加した．培養５日目の時点では解放群，圧縮群では対照群と比較して増加した．しかし，解放群，圧縮群の間に有意差が認められなかったことから，24時間以上圧縮力を加えても破骨細胞の分化・融合を促進しない可能性が示唆された．培養６日目の時点では，解放群，圧縮群では対照群と比較して破骨細胞数が減少した．また培養５日目から６日目の間において対照群では破骨細胞数が増加したが，他の群では減少した．これらの結果より，圧縮力は培養後期における破骨細胞の分化・融合を抑制する可能性が示唆された．対照群と圧縮群の破骨細胞関連遺伝子であるNFATc1, RANK, TRAP, DC-STAMPおよびOC-STAMPのmRNA発現量を比較すると，培養４日目の時点では有意差が認められなかったが，培養５日目の時点では圧縮群ではそれらすべての発現が有意に抑制されていた．以上より，圧縮力は培養後期において破骨細胞関連遺伝子の発現を抑制することで破骨細胞の分化・融合を抑制することが示唆された．
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.