The effects of vitamin D on osteoblast mineralization are well documented. Reports of the effects of vitamin D on osteoclasts, however, are conflicting, showing both inhibition and stimulation. Finding that resorbing osteoclasts in human bone express vitamin D receptor (VDR), we examined their response to different concentrations of 25-hydroxy vitamin D3 [25(OH)D3] (100 or 500 nmol·L-1) and 1,25-dihydroxy vitamin D3 [1,25(OH)2D3] (0.1 or 0.5 nmol·L-1) metabolites in cell cultures. Specifically, CD14+ monocytes were cultured in charcoal-stripped serum in the presence of receptor activator of nuclear factor kappa-B ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). Tartrate-resistant acid phosphatase (TRAP) histochemical staining assays and dentine resorption analysis were used to identify the size and number of osteoclast cells, number of nuclei per cell and resorption activity. The expression of VDR was detected in human bone tissue (ex vivo) by immunohistochemistry and in vitro cell cultures by western blotting. Quantitative reverse transcription-PCR (qRT-PCR) was used to determine the level of expression of vitamin D-related genes in response to vitamin D metabolites. VDR-related genes during osteoclastogenesis, shown by qRT-PCR, was stimulated in response to 500 nmol·L-1 of 25(OH)D3 and 0.1-0.5 nmol·L-1 of 1,25(OH)2D3, upregulating cytochrome P450 family 27 subfamily B member 1 (CYP27B1) and cytochrome P450 family 24 subfamily A member 1 (CYP24A1). Osteoclast fusion transcripts transmembrane 7 subfamily member 4 (tm7sf4) and nuclear factor of activated T-cell cytoplasmic 1 (nfatc1) where downregulated in response to vitamin D metabolites. Osteoclast number and resorption activity were also increased. Both 25(OH)D3 and 1,25(OH)2D3 reduced osteoclast size and number when co-treated with RANKL and M-CSF. The evidence for VDR expression in resorbing osteoclasts in vivo and low-dose effects of 1,25(OH)2D3 on osteoclasts in vitro may therefore provide insight into the effects of clinical vitamin D treatments, further providing a counterpoint to the high-dose effects reported from in vitro experiments.

中文翻译：

---

人体骨组织中维生素 D 受体的表达以及破骨细胞再吸收的剂量依赖性激活。

维生素 D 对成骨细胞矿化的影响已有详细记录。然而，关于维生素 D 对破骨细胞影响的报道是相互矛盾的，既显示出抑制作用，也显示出刺激作用。发现人骨中的重吸收破骨细胞表达维生素 D 受体 (VDR)，我们检查了它们对不同浓度的 25-羟基维生素 D3 [25(OH)D3]（100 或 500 nmol·L-1）和 1,25- 的反应。细胞培养物中的二羟基维生素 D3 [1,25(OH)2D3]（0.1 或 0.5 nmol·L-1）代谢物。具体而言，在核因子κ-B配体受体激活剂(RANKL)和巨噬细胞集落刺激因子(M-CSF)存在下，在炭剥离的血清中培养CD14+单核细胞。使用抗酒石酸酸性磷酸酶（TRAP）组织化学染色测定和牙本质吸收分析来确定破骨细胞的大小和数量、每个细胞的细胞核数量和吸收活性。通过免疫组织化学检测人骨组织（离体）中 VDR 的表达，并通过蛋白质印迹法检测体外细胞培养物中 VDR 的表达。定量逆转录 PCR (qRT-PCR) 用于测定维生素 D 相关基因响应维生素 D 代谢物的表达水平。qRT-PCR 显示，破骨细胞生成过程中的 VDR 相关基因受到 500 nmol·L-1 25(OH)D3 和 0.1-0.5 nmol·L-1 1,25(OH)2D3 的刺激，上调细胞色素P450 家族 27 亚家族 B 成员 1 (CYP27B1) 和细胞色素 P450 家族 24 亚家族 A 成员 1 (CYP24A1)。破骨细胞融合转录跨膜 7 亚家族成员 4 (tm7sf4) 和活化 T 细胞胞质核因子 1 (nfatc1)，这些因子因维生素 D 代谢物而下调。破骨细胞数量和吸收活性也增加。当与 RANKL 和 M-CSF 共同治疗时，25(OH)D3 和 1,25(OH)2D3 均可减少破骨细胞的大小和数量。因此，VDR 在体内重吸收破骨细胞中表达的证据以及 1,25(OH)2D3 在体外对破骨细胞的低剂量作用可能有助于深入了解临床维生素 D 治疗的作用，进一步提供与高剂量作用的对照体外实验报告。