Department of Medical Sciences, Uppsala University, Uppsala, Sweden.
PLoS One. 2010 Oct 11;5(10):e13305. doi: 10.1371/journal.pone.0013305.
It has been shown that high vitamin A intake is associated with bone fragility and fractures in both animals and humans. However, the mechanism by which vitamin A affects bones is unclear. In the present study, the direct effects of retinoic acid (RA) on human and murine osteoclastogenesis were evaluated using cultured peripheral blood CD14(+) monocytes and RAW264.7 cells. Both the activity of the osteoclast marker tartrate resistant acid phosphatase (TRAP) in culture supernatant and the expression of the genes involved in osteoclast differentiation together with bone resorption were measured. To our knowledge, this is the first time that the effects of RA on human osteoclast progenitors and mature osteoclasts have been studied in vitro. RA stimulated proliferation of osteoclast progenitors both from humans and mice. In contrast, RA inhibited differentiation of the receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclastogenesis of human and murine osteoclast progenitors via retinoic acid receptors (RARs). We also show that the mRNA levels of receptor activator of nuclear factor κB (RANK), the key initiating factor and osteoclast associated receptor for RANKL, were potently suppressed by RA in osteoclast progenitors. More importantly, RA abolished the RANK protein in osteoclast progenitors. This inhibition could be partially reversed by a RAR pan-antagonist. Furthermore, RA treatment suppressed the expression of the transcription factor nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) and increased the expression of interferon regulatory factor-8 (IRF-8) in osteoclast progenitors via RARs. Also, RA demonstrated differential effects depending on the material supporting the cell culture. RA did not affect TRAP activity in the culture supernatant in the bone slice culture system, but inhibited the release of TRAP activity if cells were cultured on plastic. In conclusion, our results suggest that retinoic acid increases proliferation of human osteoclast progenitors and that it inhibits RANK-stimulated osteoclast differentiation by suppressing RANK.
已证实，高维生素 A 摄入与动物和人类的骨脆弱和骨折有关。然而，维生素 A 影响骨骼的机制尚不清楚。在本研究中，使用培养的外周血 CD14(+)单核细胞和 RAW264.7 细胞评估了视黄酸（RA）对人源和鼠源破骨细胞形成的直接影响。同时测量了培养上清液中破骨细胞标志物抗酒石酸酸性磷酸酶（TRAP）的活性以及参与破骨细胞分化和骨吸收的基因的表达。据我们所知，这是首次在体外研究 RA 对人破骨细胞前体和成熟破骨细胞的影响。RA 刺激了来自人和小鼠的破骨细胞前体的增殖。相比之下，RA 通过视黄酸受体（RAR）抑制了核因子κB 受体激活剂配体（RANKL）诱导的人源和鼠源破骨细胞前体的分化。我们还表明，核因子κB 受体激活剂（RANK）的 mRNA 水平，即 RANKL 的关键起始因子和破骨细胞相关受体，在破骨细胞前体中被 RA 强烈抑制。更重要的是，RA 使破骨细胞前体中的 RANK 蛋白失活。这种抑制作用可以部分被 RAR 泛拮抗剂逆转。此外，RA 处理通过 RAR 抑制破骨细胞前体中核因子活化 T 细胞胞浆 1（NFATc1）的转录因子的表达，并增加干扰素调节因子-8（IRF-8）的表达。此外，RA 表现出取决于支持细胞培养的物质的差异效应。RA 不会影响骨切片培养系统中培养上清液中的 TRAP 活性，但如果细胞在塑料上培养，则抑制 TRAP 活性的释放。总之，我们的结果表明，视黄酸增加了人破骨细胞前体的增殖，并且通过抑制 RANK 来抑制 RANK 刺激的破骨细胞分化。
