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The Polycomb Protein Bmi1 Plays a Crucial Role in the Prevention of 1,25(OH)2 D Deficiency-Induced Bone Loss.

Authors
  • Sun, Haijian1
  • Qiao, Wanxin1
  • Cui, Min1
  • Yang, Cuicui1
  • Wang, Rong1
  • Goltzman, David2
  • Jin, Jianliang1
  • Miao, Dengshun1
  • 1 State Key Laboratory of Reproductive Medicine, Research Center for Bone and Stem Cells, Department of Anatomy, Histology and Embryology, Key Laboratory for Aging & Disease, Nanjing Medical University, Nanjing, China. , (China)
  • 2 Calcium Research Laboratory, McGill University Health Centre and Department of Medicine, McGill University, Montreal, Quebec, Canada. , (Canada)
Type
Published Article
Journal
Journal of Bone and Mineral Research
Publisher
Wiley (John Wiley & Sons)
Publication Date
Mar 01, 2020
Volume
35
Issue
3
Pages
583–595
Identifiers
DOI: 10.1002/jbmr.3921
PMID: 31725940
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

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 D3 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 (Bmi1Tg ) mice. We then compared the bone phenotypes of Bmi1Tg 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 γH2 A.X, p16, IL-1β, and TNF-α-positive cells and decreasing γH2A.X, p16, p19, p53, p21, IL-1β, 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. © 2019 American Society for Bone and Mineral Research. © 2019 American Society for Bone and Mineral Research.

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