Department of Cellular Physiological Chemistry, Graduate School, Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.
Genes Cells. 2012 Jul;17(7):568-75. doi: 10.1111/j.1365-2443.2012.01608.x. Epub 2012 May 31.
Osteoclasts, multinucleated bone-resorbing cells, are specialized cells derived from the monocyte/macrophage lineage. Therefore, it is essential for mononuclear precursors to find a fusion partner during its differentiation. Our previous study showed an important role of cell communication via Mac-1 (CD11b/CD18) during osteoclastogenesis. However, the counter receptor of Mac-1 was still unknown. Flow cytometric analysis showed that bone marrow-derived mononuclear cells, used as osteoclast precursors, expressed intercellular adhesion molecule-1 and -2. Quantitative RT-PCR analysis revealed that expression level of ICAM-2 was higher than that of ICAM-1 in bone marrow cells. The osteoclastogenesis induced by receptor activator of NF-kappaB ligand (RANKL) was inhibited by anti-ICAM-2 neutralizing antibody but not by anti-ICAM-1 neutralizing antibody. The inhibitory effect of anti-ICAM-2 antibody on osteoclastogenesis was enhanced by simultaneous treatment of anti-CD11b neutralizing antibody. Furthermore, osteoclastogenesis induced by tumor necrosis factor α (TNFα) was also inhibited by anti-ICAM-2 neutralizing antibody. The involvement of lymphocytes in osteoclastogenesis was excluded, because anti-ICAM-2 antibody inhibited osteoclastogenesis using bone marrow-derived cells from immunodeficiency mice. Immunocytochemical staining demonstrated colocalization of ICAM-2 and Mac-1 during osteoclastogenesis; however, Mac-1 immunoreactivity was lost in differentiated multinucleated osteoclast. These results suggest the important role of ICAM-2/Mac-1 binding in osteoclastogenesis induced by either RANKL or TNFα.
破骨细胞是一种多核的骨吸收细胞，是由单核细胞/巨噬细胞系分化而来的特化细胞。因此，单核细胞前体在分化过程中找到融合伙伴至关重要。我们之前的研究表明，在破骨细胞发生过程中，细胞间通过 Mac-1（CD11b/CD18）进行通讯起着重要作用。然而，Mac-1 的对应受体仍不清楚。流式细胞术分析显示，作为破骨细胞前体的骨髓单核细胞表达细胞间黏附分子-1 和 -2。定量 RT-PCR 分析显示，骨髓细胞中 ICAM-2 的表达水平高于 ICAM-1。核因子-κB 受体激活剂配体（RANKL）诱导的破骨细胞发生被抗 ICAM-2 中和抗体抑制，但抗 ICAM-1 中和抗体没有抑制作用。同时用抗 CD11b 中和抗体处理可增强抗 ICAM-2 抗体对破骨细胞发生的抑制作用。此外，肿瘤坏死因子 α（TNFα）诱导的破骨细胞发生也被抗 ICAM-2 中和抗体抑制。由于抗 ICAM-2 抗体抑制了免疫缺陷小鼠来源的骨髓细胞的破骨细胞发生，因此排除了淋巴细胞参与破骨细胞发生的可能性。免疫细胞化学染色显示在破骨细胞发生过程中 ICAM-2 和 Mac-1 共定位；然而，在分化的多核破骨细胞中 Mac-1 免疫反应性丧失。这些结果表明 ICAM-2/Mac-1 结合在 RANKL 或 TNFα 诱导的破骨细胞发生中起着重要作用。
