It has been reported that 1,25 dihydroxyvitamin D [1,25(OH)₂D] deficiency leads to the loss of mandibular bone, however the mechanism is unclear. We investigated whether the Sirt1/FOXO3a signaling pathway is involved in this process. Using a 1,25(OH)₂D deficiency model induced by genetic deletion in mice of 25-hydroxyvitamin D-1α hydroxylase [1α(OH)ase^-/- mice]. We first documented a sharp reduction of expression levels of Sirt1 in the 1α(OH)ase^-/- mice in vivo. Next, we demonstrated dose-dependent upregulation of Sirt1 by treatment with exogenous 1,25(OH)₂D₃ in vitro. We then identified a functional VDR binding site in the Sirt1 promoter. By crossing Prx1-Sirt1 transgenic mice with 1α(OH)ase^-/- mice we demonstrated that the overexpression of Sirt1 in mesenchymal stem cells (MSCs) greatly improved the 1α(OH)ase^-/- mandibular bone loss phenotype by increasing osteoblastic bone formation and reducing osteoclastic bone resorption. In mechanistic studies, we showed, in 1α(OH)ase^-/- mice, decreases of Sirt1 and FoxO3a, an increase in oxidative stress as reflected by a reduction of the antioxidant enzymes peroxiredoxin1 (Prdx1), SOD1 and SOD2 expression, and an increase of markers for osteocyte senescence and senescence associated secretory phenotypes (SASP), including β-galactosidase (β-gal), p16, p53 and p21. The targeted overexpression of Sirt1 in the 1α(OH)ase^-/- mice restored the expression levels of these molecules. Finally, we demonstrated that a Sirt1 agonist can upregulate FOXO3a activity by increasing deacetylation and nuclear translocation. Overall, results from this study support the concept that targeted increases in Sirt1/FOXO3a signaling levels can greatly improve the bone loss caused by 1,25(OH)₂D deficiency.

中文翻译：

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SIRT1/FOXO3a轴在预防1,25(OH)2D缺乏引起的下颌骨丢失中发挥重要作用

据报道，1,25二羟基维生素D[1,25(OH) _2D ]缺乏会导致下颌骨丢失，但其机制尚不清楚。我们研究了 Sirt1/FOXO3a 信号通路是否参与该过程。使用25-羟基维生素 D-1α 羟化酶 [1α(OH)ase ^{-/-小鼠] 小鼠中基因缺失诱导的 1,25(OH)} ₂ D 缺乏模型。^{我们首先记录了 1α(OH)ase -/-}小鼠体内Sirt1 表达水平的急剧下降。接下来，我们在体外用外源 1,25(OH) ₂ D ₃处理证明了 Sirt1 的剂量依赖性上调。然后我们在 Sirt1 启动子中鉴定了一个功能性 VDR 结合位点。通过将 Prx1-Sirt1 转基因小鼠与 1α(OH)ase ^-/-小鼠杂交，我们证明间充质干细胞 (MSC) 中 Sirt1 的过度表达通过增加成骨细胞骨来极大地改善 1α(OH)ase ^-/-下颌骨丢失表型形成并减少破骨细胞骨吸收。在机制研究中，我们发现，在 1α(OH)ase ^-/-小鼠中，Sirt1 和 FoxO3a 减少，氧化应激增加（表现为抗氧化酶过氧化还原蛋白 1 (Prdx1)、SOD1 和 SOD2 表达减少，以及氧化应激增加）。骨细胞衰老和衰老相关分泌表型 (SASP) 标志物增加，包括 β-半乳糖苷酶 (β-gal)、p16、p53 和 p21。Sirt1 在 1α(OH)ase ^-/-小鼠中的靶向过度表达恢复了这些分子的表达水平。最后，我们证明 Sirt1 激动剂可以通过增加脱乙酰化和核转位来上调 FOXO3a 活性。总的来说，这项研究的结果支持这样的观点：有针对性地增加 Sirt1/FOXO3a 信号水平可以极大地改善由 1,25(OH) ₂ D 缺乏引起的骨质流失。