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Delayed tooth movement in Runx2^+/- mice associated with mTORC2 in stretch-induced bone formation.

ABSTRACT: 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 RUNX2, 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 in vivo. Continuous stretch was conducted to bone marrow stromal cells (BMSCs) as an in vitro 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 in vivo and in vitro. 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 via mTORC2 activation.

SUBMITTER: Aonuma T

PROVIDER: S-EPMC7264061 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Delayed tooth movement in Runx2<sup>+/-</sup> mice associated with mTORC2 in stretch-induced bone formation.

Aonuma Tomo T Tamamura Nagato N Fukunaga Tomohiro T Sakai Yuichi Y Takeshita Nobuo N Shigemi Shohei S Yamashiro Takashi T Thesleff Irma I Takano-Yamamoto Teruko T

Bone reports 20200527

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 <i>RUNX2</i>, 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 Ru ...[more]

PMID: 32509933

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Project description:BackgroundStatins are the most widely used drugs in elderly patients; the most common clinical application of statins is in aged hyperlipemia patients. There are few studies on the effects and mechanisms of statins on bone in elderly mice with hyperlipemia. The study is to examine the effects of atorvastatin on bone phenotypes and metabolism in aged apolipoprotein E-deficient (apoE-/-) mice, and the possible mechanisms involved in these changes.MethodsTwenty-four 60-week-old apoE-/- mice were randomly allocated to two groups. Twelve mice were orally gavaged with atorvastatin (10 mg/kg body weight/day) for 12 weeks; the others served as the control group. Bone mass and skeletal microarchitecture were determined using micro-CT. Bone metabolism was assessed by serum analyses, qRT-PCR, and Western blot. Bone marrow-derived mesenchymal stem cells (BMSCs) from apoE-/- mice were differentiated into osteoblasts and treated with atorvastatin and silent information regulator 1 (Sirt1) inhibitor EX-527.ResultsThe results showed that long-term administration of atorvastatin increases bone mass and improves bone microarchitecture in trabecular bone but not in cortical bone. Furthermore, the serum bone formation marker osteocalcin (OCN) was ameliorated by atorvastatin, whereas the bone resorption marker tartrate-resistant acid phosphatase 5b (Trap5b) did not appear obviously changes after the treatment of atorvastatin. The mRNA expression of Sirt1, runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), and OCN in bone tissue were increased after atorvastatin administration. Western blot showed same trend in Sirt1 and Runx2. The in vitro study showed that when BMSCs from apoE-/- mice were pretreated with EX527, the higher expression of Runx2, ALP, and OCN activated by atorvastatin decreased significantly or showed no difference compared with the control. The protein expression of Runx2 showed same trend.ConclusionsAccordingly, the current study validates the hypothesis that atorvastatin can increase bone mass and promote osteogenesis in aged apoE-/- mice by regulating the Sirt1-Runx2 axis.

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Delayed tooth movement in Runx2^+/- mice associated with mTORC2 in stretch-induced bone formation.

Publications

Delayed tooth movement in Runx2<sup>+/-</sup> mice associated with mTORC2 in stretch-induced bone formation.

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Delayed tooth movement in Runx2+/- mice associated with mTORC2 in stretch-induced bone formation.

Publications

Delayed tooth movement in Runx2<sup>+/-</sup> mice associated with mTORC2 in stretch-induced bone formation.

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OmicsDI is part of the ELIXIR infrastructure

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Delayed tooth movement in Runx2^+/- mice associated with mTORC2 in stretch-induced bone formation.