DNAX-associated protein 12 kD size (DAP12) is a dominant immunoreceptor tyrosine-based activation motif (ITAM)-signaling adaptor that activates costimulatory signals essential for osteoclastogenesis. Although several DAP12-associated receptors (DARs) have been identified in osteoclasts, including triggering receptor expressed on myeloid cells 2 (TREM-2), C-type lectin member 5 A (CLEC5A), and sialic acid-binding Ig-like lectin (Siglec)-15, their precise role in the development of osteoclasts and bone remodeling remain poorly understood. In this study, mice deficient in Trem-2, Clec5a, Siglec-15 were generated. In addition, mice double deficient in these DAR genes and FcεRI gamma chain (FcR)γ, an alternative ITAM adaptor to DAP12, were generated. Bone mass analysis was conducted on all mice. Notably, Siglec-15 deficient mice and Siglec-15/FcRγ double deficient mice exhibited mild and severe osteopetrosis respectively. In contrast, other DAR deficient mice showed normal bone phenotype. Likewise, osteoclasts from Siglec-15 deficient mice failed to form an actin ring, suggesting that Siglec-15 promotes bone resorption principally by modulating the cytoskeletal organization of osteoclasts. Furthermore, biochemical analysis revealed that Sigelc-15 activates macrophage colony-stimulating factor (M-CSF)-induced Ras-associated protein-1 (RAP1)/Ras-related C3 botulinum toxin substrate 1 (Rac1) pathway through formation of a complex with p130CAS and CrkII, leading to cytoskeletal remodeling of osteoclasts. Our data provide genetic and biochemical evidence that Siglec-15 facilitates M-CSF-induced cytoskeletal remodeling of the osteoclasts.

DNAX 相关蛋白 12 kD 大小 (DAP12) 是一种显性免疫受体酪氨酸激活基序 (ITAM) 信号转导接头，可激活破骨细胞生成必需的共刺激信号。尽管在破骨细胞中已鉴定出几种 DAP12 相关受体 (DAR)，包括骨髓细胞表达的触发受体 2 (TREM-2)、C 型凝集素成员 5 A (CLEC5A) 和唾液酸结合 Ig 样凝集素。 Siglec)-15，它们在破骨细胞发育和骨重塑中的确切作用仍然知之甚少。在这项研究中，产生了Trem-2 、 Clec5a 、 Siglec-15缺陷的小鼠。此外，还产生了这些 DAR 基因和 FcεRI 伽马链 (FcR)γ（DAP12 的替代 ITAM 接头）双缺陷的小鼠。对所有小鼠进行骨量分析。值得注意的是， Siglec-15缺陷小鼠和Siglec-15/FcRγ双缺陷小鼠分别表现出轻度和重度骨石症。相比之下，其他 DAR 缺陷小鼠表现出正常的骨表型。同样， Siglec- 15 缺陷小鼠的破骨细胞未能形成肌动蛋白环，这表明 Siglec-15 主要通过调节破骨细胞的细胞骨架组织来促进骨吸收。此外，生化分析表明，Sigelc-15 通过与巨噬细胞集落刺激因子 (M-CSF) 形成复合物，激活巨噬细胞集落刺激因子 (M-CSF) 诱导的 Ras 相关蛋白 1 (RAP1)/Ras 相关 C3 肉毒杆菌毒素底物 1 (Rac1) 通路。 p130CAS 和 CrkII，导致破骨细胞的细胞骨架重塑。我们的数据提供了遗传和生化证据，表明 Siglec-15 促进 M-CSF 诱导的破骨细胞细胞骨架重塑。