The Polycomb Protein Bmi1 Plays a Crucial Role in the Prevention of 1,25(OH)2D Deficiency-Induced Bone Loss
The Polycomb Protein Bmi1 Plays a Crucial Role in the Prevention of 1,25(OH)2D Deficiency-Induced Bone Loss
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Polycomb 蛋白 Bmi1 在预防 1,25(OH)2 D 缺乏引起的骨质流失中发挥着至关重要的作用。
DOI：
10.1002/jbmr.3921
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发表时间：
2019-12-17
影响因子：
6.2
通讯作者：
Miao, Dengshun
中科院分区：
文献类型：
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作者：
Sun, Haijian;Qiao, Wanxin;Miao, Dengshun
我们分析了杂合性 Cyp27b1 无效 (Cyp27b1(+/-)) 小鼠及其野生型 (WT) 同窝小鼠的骨骼表型，以确定 Cyp27b1 的单倍体不足是否会加速骨丢失，并检查这种丢失的潜在机制。我们发现衰老的 Cyp27b1(+/-) 小鼠血清 1,25-二羟基维生素 D [1,25(OH)(2)D] 水平显着降低，表现出骨质疏松表型。与此同时，B 淋巴瘤莫洛尼鼠白血病病毒 (Mo-MLV) 插入区 1 (Bmi1) 在基因和蛋白质水平上的表达均减少。使用染色质免疫沉淀 (ChIP)-PCR、电泳迁移率变动测定 (EMSA) 和荧光素酶报告基因测定，我们发现 1,25(OH)(2)D-3 通过维生素 D 受体 (VDR) 在转录水平上调 Bmi1 表达。为了确定间充质干细胞（MSC）中Bmi1的过度表达是否可以纠正1,25（OH）（2）D缺乏引起的骨质流失，我们使用Prx1驱动的Bmi1转基因小鼠（Bmi1（Tg））小鼠在MSC中过度表达Bmi1。然后，我们将 Cyp27b1(+/-) 背景下的 Bmi1(Tg) 小鼠的骨表型与 Cyp27b1(+/-) 小鼠和 WT 小鼠的骨表型进行了比较，所有小鼠均在 8 个月大。我们发现MSCs中Bmi1的过度表达通过增加成骨细胞骨形成、减少破骨细胞骨吸收、增加骨体积和增加骨矿物质密度来纠正Cyp27b1(+/-)小鼠的骨表型。 MSC 中的 Bmi1 过表达还可以通过降低活性氧 (ROS) 水平、提高血清总超氧化物歧化酶水平、降低 γ H(2)A.X、p16、IL-1 β 和 TNF-α 阳性细胞并降低 γ H2A.X、p16、p19、p53、p21、IL-1β 和 IL-6 表达水平。此外，1,25(OH)(2)D 刺激 WT 小鼠而非 Bmi1(-/-) 小鼠的 MSC 离体和体外成骨分化，体内给予 1,25(OH)(2)D 增加 WT 小鼠的成骨细胞骨形成，但不增加 Bmi1(-/-) 小鼠的成骨细胞骨形成。我们的结果表明，Bmi1 是 1,25(OH)(2)D 的关键下游靶标，在预防 1,25(OH)(2)D 缺乏引起的骨质流失中发挥着至关重要的作用。 (c) 2019 年美国骨与矿物质研究学会。
We analyzed the skeletal phenotypes of heterozygous null Cyp27b1 (Cyp27b1(+/-)) mice and their wild-type (WT) littermates to determine whether haploinsufficiency of Cyp27b1 accelerated bone loss, and to examine potential mechanisms of such loss. We found that serum 1,25-dihydroxyvitamin D [1,25(OH)(2)D] levels were significantly decreased in aging Cyp27b1(+/-) mice, which displayed an osteoporotic phenotype. This was accompanied by a reduction of expression of the B lymphoma Moloney murine leukemia virus (Mo-MLV) insertion region 1 (Bmi1) at both gene and protein levels. Using chromatin immunoprecipitation (ChIP)-PCR, electrophoretic mobility shift assay (EMSA) and a luciferase reporter assay, we then showed that 1,25(OH)(2)D-3 upregulated Bmi1 expression at a transcriptional level via the vitamin D receptor (VDR). To determine whether Bmi1 overexpression in mesenchymal stem cells (MSCs) could correct bone loss induced by 1,25(OH)(2)D deficiency, we overexpressed Bmi1 in MSCs using Prx1-driven Bmi1 transgenic mice (Bmi1(Tg)) mice. We then compared the bone phenotypes of Bmi1(Tg) mice on a Cyp27b1(+/-) background, with those of Cyp27b1(+/-) mice and with those of WT mice, all at 8 months of age. We found that overexpression of Bmi1 in MSCs corrected the bone phenotype of Cyp27b1(+/-) mice by increasing osteoblastic bone formation, reducing osteoclastic bone resorption, increasing bone volume, and increasing bone mineral density. Bmi1 overexpression in MSCs also corrected 1,25(OH)(2)D deficiency-induced oxidative stress and DNA damage, and cellular senescence of Cyp27b1(+/-) mice by reducing levels of reactive oxygen species (ROS), elevating serum total superoxide dismutase levels, reducing the percentage of gamma H(2)A.X, p16, IL-1 beta, and TNF-alpha-positive cells and decreasing gamma H2A.X, p16, p19, p53, p21, IL-1 beta, and IL-6 expression levels. Furthermore, 1,25(OH)(2)D stimulated the osteogenic differentiation of MSCs, both ex vivo and in vitro, from WT mice but not from Bmi1(-/-) mice and 1,25(OH)(2)D administration in vivo increased osteoblastic bone formation in WT, but not in Bmi1(-/-) mice. Our results indicate that Bmi1, a key downstream target of 1,25(OH)(2)D, plays a crucial role in preventing bone loss induced by 1,25(OH)(2)D deficiency. (c) 2019 American Society for Bone and Mineral Research.