Kajikawa Shuhei, Taguchi Yuu, Hayata Tadayoshi, Ezura Yoichi, Ueta Ryo, Arimura Sumimasa, Inoue Jun-Ichiro, Noda Masaki, Yamanashi Yuji
Division of Genetics, The Institute of Medical Science, The University of Tokyo, Shirokanedai, Minato-ku, Tokyo, 108-8639, Japan.
Division of Cellular and Molecular Biology, The Institute of Medical Science, The University of Tokyo, Shirokanedai, Minato-ku, Tokyo, 108-8639, Japan.
Biochem Biophys Res Commun. 2018 Apr 15;498(4):967-974. doi: 10.1016/j.bbrc.2018.03.090. Epub 2018 Mar 17.
Bone mass is determined by coordinated acts of osteoblasts and osteoclasts, which control bone formation and resorption, respectively. Osteoclasts are multinucleated, macrophage/monocyte lineage cells from bone marrow. The Dok-family adaptors Dok-1, Dok-2 and Dok-3 are expressed in the macrophage/monocyte lineage and negatively regulate many signaling pathways, implying roles in osteoclastogenesis. Indeed, mice lacking Dok-1 and Dok-2, the closest homologues with redundant functions, develop osteopenia with increased osteoclast counts compared to the wild-type controls. Here, we demonstrate that Dok-3 knockout (KO) mice also develop osteopenia. However, Dok-3 KO, but not Dok-1/-2 double-KO (DKO), mice develop larger osteoclasts within the normal cell-count range, suggesting a distinctive role for Dok-3. Indeed, Dok-3 KO, but not Dok-1/-2 DKO, bone marrow-derived cells (BMDCs) generated larger osteoclasts with more nuclei due to augmented cell-to-cell fusion in vitro. In addition, while Dok-1/-2 DKO BMDCs generated more osteoclasts, Dok-1/-2/-3 triple-KO (TKO) BMDCs generated osteoclasts increased in both number and size. Furthermore, Dok-1/-2/-3 TKO mice showed the combined effects of Dok-3 and Dok-1/-2 deficiency: severe osteopenia with more and larger osteoclasts. Together, our findings demonstrate that Dok-3 and Dok-1/-2 play distinctive but cooperative roles in osteoclastogenesis and protect mice from osteopenia, providing physiological and pathophysiological insight into bone homeostasis.
骨量由成骨细胞和破骨细胞的协同作用决定，它们分别控制骨形成和骨吸收。破骨细胞是来自骨髓的多核巨噬细胞/单核细胞系细胞。Dok家族衔接蛋白Dok-1、Dok-2和Dok-3在巨噬细胞/单核细胞系中表达，并对许多信号通路起负调控作用，提示其在破骨细胞生成中发挥作用。实际上，与野生型对照相比，缺乏功能冗余的最接近同源物Dok-1和Dok-2的小鼠出现骨质减少，破骨细胞数量增加。在此，我们证明Dok-3基因敲除（KO）小鼠也会出现骨质减少。然而，Dok-3 KO小鼠而非Dok-1/-2双基因敲除（DKO）小鼠在正常细胞计数范围内形成了更大的破骨细胞，提示Dok-3具有独特作用。实际上，由于体外细胞间融合增强，Dok-3 KO而非Dok-1/-2 DKO骨髓来源细胞（BMDCs）形成了具有更多细胞核的更大破骨细胞。此外，虽然Dok-1/-2 DKO BMDCs产生了更多破骨细胞，但Dok-1/-2/-3三基因敲除（TKO）BMDCs产生的破骨细胞在数量和大小上均增加。此外，Dok-1/-2/-3 TKO小鼠表现出Dok-3和Dok-1/-2缺乏的联合效应：严重骨质减少，伴有更多更大的破骨细胞。总之，我们的研究结果表明，Dok-3和Dok-1/-2在破骨细胞生成中发挥独特但协同的作用，并保护小鼠免于骨质减少，为骨稳态提供了生理和病理生理学见解。
