Kameda Yusuke, Takahata Masahiko, Mikuni Shintaro, Shimizu Tomohiro, Hamano Hiroki, Angata Takashi, Hatakeyama Shigetsugu, Kinjo Masataka, Iwasaki Norimasa
Hokkaido University, Department of Orthopedic Surgery, School of Medicine, Sapporo, Japan.
Hokkaido University, Department of Orthopedic Surgery, School of Medicine, Sapporo, Japan.
Bone. 2015 Feb;71:217-26. doi: 10.1016/j.bone.2014.10.027. Epub 2014 Nov 8.
Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) is an immunoreceptor that regulates osteoclast development and bone resorption in association with an immunoreceptor tyrosine-based activation motif (ITAM) adaptor protein, DNAX-activating protein 12kDa (DAP12). Although Siglec-15 has an important role in physiologic bone remodeling by modulating RANKL signaling, it is unclear whether it is involved in pathologic bone loss in which multiple osteoclastogenic factors participate in excessive osteoclastogenesis. Here we demonstrated that Siglec-15 is involved in estrogen deficiency-induced bone loss. WT and Siglec-15(-/-) mice were ovariectomized (Ovx) or sham-operated at 14wk of age and their skeletal phenotype was evaluated at 18 and 22wk of age. Siglec-15(-/-) mice showed resistance to estrogen deficiency-induced bone loss compared to WT mice. Although the number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts increased after ovariectomy in both WT and Siglec-15(-/-) mice, the increase was lower in Siglec-15(-/-) mice than in WT mice. Importantly, osteoclasts in Siglec-15(-/-) mice were small and failed to spread on the bone surface, indicating impaired osteoclast differentiation. Because upregulated production of TNF-α as well as RANKL is mainly responsible for estrogen deficiency-induced development of osteoclasts, we examined whether Siglec-15 deficiency affects TNF-α-induced osteoclastogenesis in vitro. The TNF-α mediated induction of TRAP-positive multinucleated cells was impaired in Siglec-15(-/-) cells, suggesting that Siglec-15 is involved in TNF-α induced osteoclastogenesis. We also confirmed that signaling through osteoclast-associated receptor/Fc receptor common γ chain, which is an alternative ITAM adaptor to DAP12, rescues multinucleation but not cytoskeletal organization of TNF-α and RANKL-induced Siglec-15(-/-) osteoclasts, indicating that the Siglec-15/DAP12 pathway is especially important for cytoskeletal organization of osteoclasts in both RANKL and TNF-α induced osteoclastogenesis. The present findings indicate that Siglec-15 is involved in estrogen deficiency-induced differentiation of osteoclasts and is thus a potential therapeutic target for postmenopausal osteoporosis.
唾液酸结合免疫球蛋白样凝集素15（Siglec-15）是一种免疫受体，它与基于免疫受体酪氨酸的激活基序（ITAM）衔接蛋白DNAX激活蛋白12千道尔顿（DAP12）共同调节破骨细胞的发育和骨吸收。尽管Siglec-15通过调节RANKL信号通路在生理性骨重塑中发挥重要作用，但尚不清楚它是否参与多种破骨细胞生成因子参与过度破骨细胞生成的病理性骨质流失。在此，我们证明Siglec-15参与雌激素缺乏诱导的骨质流失。将野生型（WT）和Siglec-15基因敲除（-/-）小鼠在14周龄时进行卵巢切除（Ovx）或假手术，并在18周龄和22周龄时评估它们的骨骼表型。与WT小鼠相比，Siglec-15（-/-）小鼠对雌激素缺乏诱导的骨质流失具有抗性。尽管在WT和Siglec-15（-/-）小鼠卵巢切除后，抗酒石酸酸性磷酸酶（TRAP）阳性破骨细胞数量均增加，但Siglec-15（-/-）小鼠的增加幅度低于WT小鼠。重要的是，Siglec-15（-/-）小鼠中的破骨细胞较小，且无法在骨表面铺展，表明破骨细胞分化受损。由于TNF-α以及RANKL的上调产生是雌激素缺乏诱导破骨细胞发育主要原因，我们研究了Siglec-15缺乏是否会影响体外TNF-α诱导的破骨细胞生成。在Siglec-15（-/-）细胞中，TNF-α介导的TRAP阳性多核细胞诱导受损，这表明Siglec-15参与TNF-α诱导的破骨细胞生成。我们还证实，通过破骨细胞相关受体/Fc受体共同γ链（它是DAP12的一种替代ITAM衔接蛋白）的信号传导可挽救TNF-α和RANKL诱导的Siglec-15（-/-）破骨细胞的多核化，但不能挽救其细胞骨架组织，这表明Siglec-15/DAP12途径对于RANKL和TNF-α诱导的破骨细胞生成中破骨细胞的细胞骨架组织尤为重要。目前的研究结果表明，Siglec-15参与雌激素缺乏诱导的破骨细胞分化，因此是绝经后骨质疏松症的潜在治疗靶点。
