Department of Biochemistry, Temple University School of Medicine, Philadelphia, PA 19140.
Department of Microbiology, Immunology & Cell Biology, West Virginia University School of Medicine, Morgantown, WV 26506.
J Cell Physiol. 2011 Apr;226(4):1082-1089. doi: 10.1002/jcp.22423.
Osteoclasts are specialized macrophage derivatives that secrete acid and proteinases to mobilize bone for mineral homeostasis, growth, and replacement or repair. Osteoclast differentiation generally requires the monocyte growth factor m-CSF and the TNF-family cytokine RANKL, although differentiation is regulated by many other cytokines and by intracellular signals, including Ca(2+). Studies of osteoclast differentiation in vitro were performed using human monocytic precursors stimulated with m-CSF and RANKL, revealing significant loss in both the expression and function of the required components of store-operated Ca(2+) entry over the course of osteoclast differentiation. However, inhibition of CRAC using either the pharmacological agent 3,4-dichloropropioanilide (DCPA) or by knockdown of Orai1 severely inhibited formation of multinucleated osteoclasts. In contrast, no effect of CRAC channel inhibition was observed on expression of the osteoclast protein tartrate resistant acid phosphatase (TRAP). Our findings suggest that despite the fact that they are down-regulated during osteoclast differentiation, CRAC channels are required for cell fusion, a late event in osteoclast differentiation. Since osteoclasts cannot function properly without multinucleation, selective CRAC inhibitors may have utility in management of hyperresorptive states.
破骨细胞是一种专门的巨噬细胞衍生物，它分泌酸和蛋白酶来动员骨骼以维持矿物质内稳态、生长、替代或修复。破骨细胞分化通常需要单核细胞生长因子 m-CSF 和 TNF 家族细胞因子 RANKL，尽管分化受到许多其他细胞因子和细胞内信号的调节，包括 Ca(2+)。体外破骨细胞分化的研究使用 m-CSF 和 RANKL 刺激人单核细胞前体进行，结果表明，在破骨细胞分化过程中，储存操作 Ca(2+)内流所需成分的表达和功能显著丧失。然而，使用药理学试剂 3,4-二氯丙酰苯胺 (DCPA) 或敲低 Orai1 抑制 CRAC，严重抑制多核破骨细胞的形成。相比之下，CRAC 通道抑制对破骨细胞蛋白抗酒石酸酸性磷酸酶 (TRAP) 的表达没有影响。我们的发现表明，尽管 CRAC 通道在破骨细胞分化过程中下调，但它们对于细胞融合是必需的，细胞融合是破骨细胞分化的晚期事件。由于破骨细胞如果没有多核化就不能正常发挥功能，因此选择性 CRAC 抑制剂可能在治疗高吸收状态方面具有应用价值。
