Dempster David W, Hughes-Begos Christine E, Plavetic-Chee Katarina, Brandao-Burch Andrea, Cosman Felicia, Nieves Jeri, Neubort Simon, Lu Shi Shou, Iida-Klein Akiko, Arnett Tim, Lindsay Robert
Regional Bone Center, Helen Hayes Hospital, New York State Department of Health, West Haverstraw, New York 10993, USA.
J Cell Biochem. 2005 May 1;95(1):139-48. doi: 10.1002/jcb.20388.
The prevailing view for many years has been that osteoclasts do not express parathyroid hormone (PTH) receptors and that PTH's effects on osteoclasts are mediated indirectly via osteoblasts. However, several recent reports suggest that osteoclasts express PTH receptors. In this study, we tested the hypothesis that human osteoclasts formed in vitro express functional PTH type 1 receptors (PTH1R). Peripheral blood monocytes (PBMC) were cultured on bone slices or plastic culture dishes with human recombinant RANK ligand (RANKL) and recombinant human macrophage colony-stimulating factor (M-CSF) for 16-21 days. This resulted in a mixed population of mono- and multi-nucleated cells, all of which stained positively for the human calcitonin receptor. The cells actively resorbed bone, as assessed by release of C-terminal telopeptide of type I collagen and the formation of abundant resorption pits. We obtained evidence for the presence of PTH1R in these cells by four independent techniques. First, using immunocytochemistry, positive staining for PTH1R was observed in both mono- and multi-nucleated cells intimately associated with resorption cavities. Second, PTH1R protein expression was demonstrated by Western blot analysis. Third, the cells expressed PTH1R mRNA at 21 days and treatment with 10(-7) M hPTH (1-34) reduced PTH1R mRNA expression by 35%. Finally, bone resorption was reproducibly increased by two to threefold when PTH (1-34) was added to the cultures. These findings provide strong support for a direct stimulatory action of PTH on human osteoclasts mediated by PTH1R. This suggests a dual regulatory mechanism, whereby PTH acts both directly on osteoclasts and also, indirectly, via osteoblasts.
多年来的主流观点一直认为破骨细胞不表达甲状旁腺激素(PTH)受体,且PTH对破骨细胞的作用是通过成骨细胞间接介导的。然而,最近的几份报告表明破骨细胞表达PTH受体。在本研究中,我们检验了以下假设:体外形成的人破骨细胞表达功能性1型PTH受体(PTH1R)。将外周血单核细胞(PBMC)在骨切片或塑料培养皿上与人重组核因子κB受体活化因子配体(RANKL)和重组人巨噬细胞集落刺激因子(M-CSF)一起培养16 - 21天。这产生了单核和多核细胞的混合群体,所有细胞对人降钙素受体染色均呈阳性。通过I型胶原C末端肽的释放和大量吸收陷窝的形成评估,这些细胞能积极地吸收骨。我们通过四种独立技术获得了这些细胞中存在PTH1R的证据。首先,使用免疫细胞化学方法,在与吸收腔密切相关的单核和多核细胞中均观察到PTH1R的阳性染色。其次,通过蛋白质印迹分析证实了PTH1R蛋白的表达。第三,细胞在21天时表达PTH1R mRNA,用10(-7) M 人PTH(1 - 34)处理可使PTH1R mRNA表达降低35%。最后,当向培养物中添加PTH(1 - 34)时,骨吸收可重复性地增加两到三倍。这些发现为PTH通过PTH1R对人破骨细胞的直接刺激作用提供了有力支持。这表明存在一种双重调节机制,即PTH既直接作用于破骨细胞,也通过成骨细胞间接作用。