Laboratory of Genetics, Department of Biotechnology, Agricultural University of Athens, Athens, Greece.
Division of Immunology, Biomedical Sciences Research Center "Alexander Fleming", Athens, Greece.
Front Immunol. 2019 Feb 5;10:97. doi: 10.3389/fimmu.2019.00097. eCollection 2019.
Receptor activator of nuclear factor-κB ligand (RANKL), a member of the Tumor Necrosis Factor (TNF) superfamily, constitutes the master regulator of osteoclast formation and bone resorption, whereas its involvement in inflammatory diseases remains unclear. Here, we used the human TNF transgenic mouse model of erosive inflammatory arthritis to determine if the progression of inflammation is affected by either genetic inactivation or overexpression of RANKL in transgenic mouse models. TNF-mediated inflammatory arthritis was significantly attenuated in the absence of functional RANKL. Notably, TNF overexpression could not compensate for RANKL-mediated osteopetrosis, but promoted osteoclastogenesis between the pannus and bone interface, suggesting RANKL-independent mechanisms of osteoclastogenesis in inflamed joints. On the other hand, simultaneous overexpression of RANKL and TNF in double transgenic mice accelerated disease onset and led to severe arthritis characterized by significantly elevated clinical and histological scores as shown by aggressive pannus formation, extended bone resorption, and massive accumulation of inflammatory cells, mainly of myeloid origin. RANKL and TNF cooperated not only in local bone loss identified in the inflamed calcaneous bone, but also systemically in distal femurs as shown by microCT analysis. Proteomic analysis in inflamed ankles from double transgenic mice overexpressing human TNF and RANKL showed an abundance of proteins involved in osteoclastogenesis, pro-inflammatory processes, gene expression regulation, and cell proliferation, while proteins participating in basic metabolic processes were downregulated compared to TNF and RANKL single transgenic mice. Collectively, these results suggest that RANKL modulates modeled inflammatory arthritis not only as a mediator of osteoclastogenesis and bone resorption but also as a disease modifier affecting inflammation and immune activation.
核因子-κB 受体激活剂配体（RANKL）是肿瘤坏死因子（TNF）超家族的成员，构成破骨细胞形成和骨吸收的主要调节剂，而其在炎症性疾病中的作用尚不清楚。在这里，我们使用人类 TNF 转基因小鼠模型的侵蚀性炎症性关节炎来确定炎症的进展是否受到转基因小鼠模型中 RANKL 的遗传失活或过表达的影响。在缺乏功能性 RANKL 的情况下，TNF 介导的炎症性关节炎明显减轻。值得注意的是，TNF 的过表达不能补偿 RANKL 介导的骨质硬化症，但促进了肉芽组织和骨界面之间的破骨细胞形成，这表明在炎症关节中存在 RANKL 独立的破骨细胞形成机制。另一方面，在双转基因小鼠中同时过表达 RANKL 和 TNF 加速了疾病的发作，并导致严重的关节炎，其特征是明显升高的临床和组织学评分，表现为侵袭性肉芽组织形成、骨吸收延长和大量炎症细胞的积累，主要来源于骨髓来源。RANKL 和 TNF 不仅在炎症性跟骨中发现的局部骨丢失中合作，而且在双转基因小鼠的远端股骨中也在系统中合作，这通过 microCT 分析显示。在过度表达人 TNF 和 RANKL 的双转基因小鼠的炎症踝关节中进行的蛋白质组学分析显示，大量参与破骨细胞形成、促炎过程、基因表达调控和细胞增殖的蛋白质丰富，而参与基本代谢过程的蛋白质与 TNF 和 RANKL 单转基因小鼠相比下调。总之，这些结果表明 RANKL 不仅作为破骨细胞形成和骨吸收的介质，而且作为影响炎症和免疫激活的疾病修饰因子，调节模拟炎症性关节炎。
