Aonuma Tomo, Tamamura Nagato, Fukunaga Tomohiro, Sakai Yuichi, Takeshita Nobuo, Shigemi Shohei, Yamashiro Takashi, Thesleff Irma, Takano-Yamamoto Teruko
Division of Orthodontics and Dentofacial Orthopedics, Tohoku University Graduate School of Dentistry, 4-1, Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan.
Department of Orthodontics and Dentofacial Orthopedics, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Okayama City, Okayama 700-8558, Japan.
Bone Rep. 2020 May 27;12:100285. doi: 10.1016/j.bonr.2020.100285. eCollection 2020 Jun.
Runt-related transcription factor 2 (Runx2) is an essential transcription factor for osteoblast differentiation, and is activated by mechanical stress to promote osteoblast function. Cleidocranial dysplasia (CCD) is caused by mutations of , and CCD patients exhibit malocclusion and often need orthodontic treatment. However, treatment is difficult because of impaired tooth movement, the reason of which has not been clarified. We examined the amount of experimental tooth movement in Runx2 mice, the animal model of CCD, and investigated bone formation on the tension side of experimental tooth movement . Continuous stretch was conducted to bone marrow stromal cells (BMSCs) as an model of the tension side of tooth movement. Compared to wild-type littermates the Runx2 mice exhibited delayed experimental tooth movement, and osteoid formation and osteocalcin (OSC) mRNA expression were impaired in osteoblasts on the tension side of tooth movement. Runx2 heterozygous deficiency delayed stretch-induced increase of DNA content in BMSCs, and also delayed and reduced stretch-induced alkaline phosphatase (ALP) activity, OSC mRNA expression, and calcium content of BMSCs in osteogenic medium. Furthermore Runx2 mice exhibited delayed and suppressed expression of mammalian target of rapamycin (mTOR) and rapamycin-insensitive companion of mTOR (Rictor), essential factors of mTORC2, which is regulated by Runx2 to phosphorylate Akt to regulate cell proliferation and differentiation, in osteoblasts on the tension side of tooth movement and . Loss of half Runx2 gene dosage inhibited stretch-induced PI3K dependent mTORC2/Akt activity to promote BMSCs proliferation. Furthermore, Runx2 BMSCs in osteogenic medium exhibited delayed and suppressed stretch-induced expression of mTOR and Rictor. mTORC2 regulated stretch-elevated Runx2 and ALP mRNA expression in BMSCs in osteogenic medium. We conclude that Runx2 mice present a useful model of CCD patients for elucidation of the molecular mechanisms in bone remodeling during tooth movement, and that Runx2 plays a role in stretch-induced proliferation and osteogenesis in BMSCs mTORC2 activation.
runt相关转录因子2（Runx2）是成骨细胞分化所必需的转录因子，可被机械应力激活以促进成骨细胞功能。锁骨颅骨发育不全（CCD）由Runx2突变引起，CCD患者表现出错牙合畸形，通常需要正畸治疗。然而，由于牙齿移动受损，治疗困难，其原因尚未阐明。我们检测了CCD动物模型Runx2小鼠的实验性牙齿移动量，并研究了实验性牙齿移动张力侧的骨形成。对骨髓基质细胞（BMSCs）进行连续拉伸，作为牙齿移动张力侧的模型。与野生型同窝小鼠相比，Runx2小鼠的实验性牙齿移动延迟，牙齿移动张力侧的成骨细胞中类骨质形成和骨钙素（OSC）mRNA表达受损。Runx2杂合缺陷延迟了拉伸诱导的BMSCs中DNA含量的增加，也延迟并降低了拉伸诱导的碱性磷酸酶（ALP）活性、OSC mRNA表达以及成骨培养基中BMSCs的钙含量。此外，Runx2小鼠在牙齿移动张力侧的成骨细胞中，哺乳动物雷帕霉素靶蛋白（mTOR）和雷帕霉素不敏感的mTOR伴侣（Rictor）的表达延迟且受到抑制，mTORC2的这些关键因子受Runx2调节以使Akt磷酸化，从而调节细胞增殖和分化。Runx2基因剂量减半会抑制拉伸诱导的PI3K依赖性mTORC2/Akt活性，以促进BMSCs增殖。此外，成骨培养基中的Runx2 BMSCs在拉伸诱导下mTOR和Rictor的表达延迟且受到抑制。mTORC2调节成骨培养基中BMSCs拉伸升高的Runx2和ALP mRNA表达。我们得出结论，Runx2小鼠是阐明牙齿移动过程中骨重塑分子机制的CCD患者有用模型，并且Runx2在拉伸诱导的BMSCs增殖和成骨过程中通过mTORC2激活发挥作用。
