Bone Cell Biology Group, Discipline of Orthopaedics and Trauma, University of Adelaide, North Terrace, Adelaide, South Australia, Australia 5000.
Endocrinology. 2010 Oct;151(10):4613-25. doi: 10.1210/en.2010-0334. Epub 2010 Aug 25.
The extrarenal synthesis of 1α,25 dihydroxyvitamin D3 (1,25D) has been demonstrated in a number of cell types including osteoblasts and cells of the monocyte/macrophage lineage. The skeleton appears responsive to serum levels of the 1,25D precursor, 25 hydroxyvitamin D3 (25D), in terms of bone mineralization parameters. The effect of metabolism of 25D into active 1,25D by osteoclast lineage cells is unknown. We found that CYP27B1 mRNA expression increased with exposure of human peripheral blood mononuclear cells (PBMCs) to macrophage colony-stimulating factor in the presence or absence of receptor activator of nuclear factor-κB ligand. Consistent with this, human osteoclast cultures incubated with 25D produced measurable quantities of 1,25D. Osteoclast formation from either mouse RAW264.7 cells or human PBMCs in the presence of physiological concentrations of 25D resulted in significant up-regulation of the key osteoclast transcription factor, nuclear factor of activated T cells-c1 in PBMCs and a number of key osteoclast marker genes in both models. The expression of the osteoblast coupling factor, ephrin-b2, was also increased in the presence of 25D. Levels of CYP27B1 and nuclear factor of activated T cells-1 mRNA correlated during osteoclastogenesis and also in a cohort of human bone samples. CYP27B1 short-hairpin RNA knockdown in RAW264.7 cells decreased their osteoclastogenic potential. 25D dose dependently reduced the resorptive capacity of PBMC-derived osteoclasts without compromising cell viability. 25D also reduced resorption by RAW264.7- and giant cell tumor-derived osteoclasts. Conversely, osteoclasts formed from vitamin D receptor-null mouse splenocytes had increased resorptive activity compared with wild-type cells. We conclude that 25D metabolism is an important intrinsic mechanism for optimizing osteoclast differentiation, ameliorating osteoclast activity, and potentially promoting the coupling of bone resorption to formation.
1α,25 二羟维生素 D3（1,25D）的肾外合成已在包括成骨细胞和单核/巨噬细胞谱系细胞在内的许多细胞类型中得到证实。骨骼似乎对血清中 1,25D 前体 25 羟维生素 D3（25D）的水平敏感，表现在骨矿化参数上。破骨细胞谱系细胞将 25D 代谢为活性 1,25D 的作用尚不清楚。我们发现，在存在或不存在核因子-κB 受体激活剂配体的情况下，人外周血单核细胞（PBMC）暴露于巨噬细胞集落刺激因子后，CYP27B1 mRNA 表达增加。与此一致，用 25D 孵育人破骨细胞培养物可产生可测量量的 1,25D。在生理浓度 25D 的存在下，从鼠 RAW264.7 细胞或人 PBMC 形成破骨细胞导致 PBMC 中关键破骨细胞转录因子核因子活化 T 细胞-c1 和两种模型中许多关键破骨细胞标记基因的显著上调。骨细胞偶联因子 Ephrin-b2 的表达也在 25D 存在下增加。在破骨细胞发生过程中以及在人类骨样本的队列中，CYP27B1 和核因子活化 T 细胞-1 mRNA 的表达相关。RAW264.7 细胞中 CYP27B1 短发夹 RNA 敲低降低了其破骨细胞生成潜能。25D 剂量依赖性地降低了 PBMC 来源的破骨细胞的吸收能力，而不损害细胞活力。25D 还降低了 RAW264.7 和巨细胞瘤来源的破骨细胞的吸收作用。相反，与野生型细胞相比，来自维生素 D 受体缺失的鼠脾细胞形成的破骨细胞具有增强的吸收活性。我们得出结论，25D 代谢是优化破骨细胞分化、改善破骨细胞活性并可能促进骨吸收与形成偶联的重要内在机制。
