Department of Pathophysiology, Ehime University Graduate School of Medicine, Toon, Ehime, 791-0295, Japan.
Division of Integrative Pathophysiology, Proteo-Science Center (PROS), Ehime University, Toon, Ehime, 791-0295, Japan.
J Bone Miner Res. 2024 Apr 19;39(3):341-356. doi: 10.1093/jbmr/zjae015.
Rheumatoid arthritis (RA) is an inflammatory autoimmune disease characterized by synovitis, bone and cartilage destruction, and increased fracture risk with bone loss. Although disease-modifying antirheumatic drugs have dramatically improved clinical outcomes, these therapies are not universally effective in all patients because of the heterogeneity of RA pathogenesis. Therefore, it is necessary to elucidate the molecular mechanisms underlying RA pathogenesis, including associated bone loss, in order to identify novel therapeutic targets. In this study, we found that Budding uninhibited by benzimidazoles 1 (BUB1) was highly expressed in RA patients' synovium and murine ankle tissue with arthritis. As CD45+CD11b+ myeloid cells are a Bub1 highly expressing population among synovial cells in mice, myeloid cell-specific Bub1 conditional knockout (Bub1ΔLysM) mice were generated. Bub1ΔLysM mice exhibited reduced femoral bone mineral density when compared with control (Ctrl) mice under K/BxN serum-transfer arthritis, with no significant differences in joint inflammation or bone erosion based on a semi-quantitative erosion score and histological analysis. Bone histomorphometry revealed that femoral bone mass of Bub1ΔLysM under arthritis was reduced by increased osteoclastic bone resorption. RNA-seq and subsequent Gene Set Enrichment Analysis demonstrated a significantly enriched nuclear factor-kappa B pathway among upregulated genes in receptor activator of nuclear factor kappa B ligand (RANKL)-stimulated bone marrow-derived macrophages (BMMs) obtained from Bub1ΔLysM mice. Indeed, osteoclastogenesis using BMMs derived from Bub1ΔLysM was enhanced by RANKL and tumor necrosis factor-α or RANKL and IL-1β treatment compared with Ctrl. Finally, osteoclastogenesis was increased by Bub1 inhibitor BAY1816032 treatment in BMMs derived from wildtype mice. These data suggest that Bub1 expressed in macrophages plays a protective role against inflammatory arthritis-associated bone loss through inhibition of inflammation-mediated osteoclastogenesis.
类风湿关节炎（RA）是一种炎症性自身免疫性疾病，其特征为滑膜炎、骨和软骨破坏以及骨丢失导致骨折风险增加。尽管疾病修饰抗风湿药物显著改善了临床结局，但由于 RA 发病机制的异质性，这些疗法并非对所有患者都普遍有效。因此，有必要阐明 RA 发病机制的分子机制，包括相关的骨丢失，以确定新的治疗靶点。在这项研究中，我们发现，Budding uninhibited by benzimidazoles 1（BUB1）在 RA 患者的滑膜和患有关节炎的鼠踝关节组织中高度表达。由于 CD45+CD11b+髓样细胞是鼠滑膜细胞中高度表达 BUB1 的群体之一，因此生成了髓样细胞特异性 Bub1 条件性敲除（Bub1ΔLysM）小鼠。与对照（Ctrl）小鼠相比，Bub1ΔLysM 小鼠在 K/BxN 血清转移关节炎下表现出股骨骨矿物质密度降低，基于半定量侵蚀评分和组织学分析，关节炎症或骨侵蚀没有显著差异。骨组织形态计量学显示，关节炎下 Bub1ΔLysM 小鼠的股骨骨量减少是由于破骨细胞骨吸收增加所致。RNA-seq 及其后续基因集富集分析表明，在 RANKL 刺激的骨髓来源巨噬细胞（BMM）中上调基因中，核因子-κB 途径显著富集。实际上，与 Ctrl 相比，用 Bub1ΔLysM 衍生的 BMM 进行的破骨细胞生成在 RANKL 和肿瘤坏死因子-α或 RANKL 和 IL-1β处理下得到增强。最后，BUB1 抑制剂 BAY1816032 在源自野生型小鼠的 BMM 中增加了破骨细胞生成。这些数据表明，巨噬细胞中表达的 Bub1 通过抑制炎症介导的破骨细胞生成，在炎性关节炎相关骨丢失中发挥保护作用。
