紀要論文 矯正力によって加えられたメカニカルストレスに対するラット歯槽骨骨細胞のsclerostin産生能の変化

藤原, 敦  ,  青木, 啓太  ,  渡邉, 竜太  ,  佐藤, 和彦  ,  矢野, 航  ,  江尻, 貞一  ,  北井, 則行

内容記述
メカニカルストレスに対する骨細胞の応答機構を明らかにする目的で、ラット臼歯に矯正力を加えメカニカルストレスの方向を反転させることで、新たに生じる骨改造現象における骨細胞のsclerostin産生能の変化を経時的に検索した。ラット上顎第一臼歯、第二臼歯間にゴムを挿入し、挿入直後、3時間、6時間、12時間、18時間、24時間後および1日、3日、5日、7日後に固定した。固定後、上顎骨を摘出しμCT装置にて撮影した。脱灰パラフィン切片を作製しTRAP染色、SOSTmRNA in situ Hybridizationおよびsclerostin免疫染色を行った。上顎第一臼歯近心口蓋根(MP)と遠心口蓋根(DP)間の根間中隔歯槽骨を近心部、中央部、遠心部、頬側部、口蓋側部に分けて観察した。ゴム挿入後、1日で根間中隔遠心面とDP間の間隙が消失した。3日目に根間中隔遠心面にTRAP陽性破骨細胞が発現し、5日目以降に根間中隔遠心面とDP間に再び間隙が形成された。また、挿入後6時間で根間中隔中央部と遠心部の骨細胞におけるSOSTmRNA発現が消失したが、抗sclerostin抗体陽性反応は認められた。同部位の抗体陽性反応が消失したのは12時間後であった。根間中隔頬側部と口蓋側部の骨細胞では、12時間後でSOSTmRNA発現が消失し、抗体陽性反応は18時間後に消失した。5日目には抗体陽性反応が頬側部で再び認められた。したがって、矯正力が加わると、骨細胞が6時間から12時間でsclerostin産生を停止し、その6時間後にsclerostinが骨基質中から消失することが示された。また、DPによって直接圧迫される根間中隔中央部・遠心部に比べ、頬側部では矯正力によるメカニカルストレスが弱くなる可能性が考えられ、骨細胞がsclerostin産生を停止・再開するまでの時間が、メカニカルストレスの強度に影響を受ける可能性も示唆された。This study clarified the mechanism involved in alveolar bone osteocyte response to mechanical stress. We applied orthodontic force to rat molars and investigated the bone remodeling induced in response to the resulting stress, particularly with respect to changes over time in the rats’alveolar osteocytes’ sclerostin production. Orthodontic elastics were inserted between the first and second molars of the rat maxillae, with the rats then sacrificed and their maxillae excised either immediately afterwards; at 3h, 6h, 12h, 18h, and 24h afterwards; or at 3, 5 or 7 days afterwards. After fixation, the maxillae were scanned with microCT; decalcified paraffin sections were made from them; and TRAP staining, SOSTmRNA in situ Hybridization, and sclerostin immunostaining performed. The alveolar bone interradicular septum (IRS), between the first-molar medial palatal root (MP) and distal palatal root (DP), was separated into medial, central, distal, buccal and palatal regions for analysis. Results showed that 24 hours after insertion of the elastics, the previously-existing gap between the IRS distal surface and the DP had disappeared. At 3 days, TRAP revealed osteoclast expression on the IRS distal surface, and at 5 days and thereafter, a gap once again began to form between the IRS distal surface and the DP. Furthermore, only 6 hours after elastic insertion, in the central and distal regions, osteocyte SOSTmRNA expression had disappeared; conversely, these regions showed positive for anti-sclerostin antibodies, with these positive results having disappeared at 12 hours. In the buccal and palatal regions, on the other hand, it took 12 hours for the osteocyte SOSTmRNA expression to disappear, and positive results for anti-sclerostin antibodies had disappeared only after 18 hours. Finally, after 5 days, positive reactions for anti-sclerostin antibodies were again seen in the buccal region. In light of the above findings, it would seem that when orthodontic force is applied, directly-stressed osteocytes stop producing sclerostin from 6 hours to 12 hours. After cession of sclerostin production by osteocytes,it takes 6 hours to disappear whole sclerostin in the bone. Also, compared with the central and distal regions of the IRS (regions which received direct pressure from the DP), the buccal region received less mechanical stress from the orthodontic force, and differences in sclerostin production between them seemed to indicate that the arresting of sclerostin production, as well as the delay required before it starts to be produced again, are both directly related to the strength of the mechanical stress the osteocytes receive.
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