活化型免疫复合物通过诱导破骨细胞分化促进类风湿性关节炎骨损伤的分子机制研究

Molecular mechanisms for the arthritogenic effect of immunocomplexes (IC) found in circulation of patients with rheumatoid arthritis (RA) have been the focus of research in the field of arthritis and rheumatism in the past decade. However, so far most studies mainly concentrate on the ability of anti-citrullinated protein antibodies (ACPA)-containing ICs (ACPA-IC) to induce inflammatory cytokine production by innate immune cells. Our previous work has found that, in addition to the reported APCA-ICs, calreticulin (CRT)-containing and lactoferrin (LTF)-containing ICs (CRT-IC and LTF-IC, respectively) in circulation strongly correlate with RA in humans, and more importantly, such RA-related ICs are not only able to stimulate inflammatory cytokine production by monocytes/macrophages but also independently induce rapid differentiation of human monocytes into osteoclasts. Based upon the generally accepted concept that imbalanced bone homeostasis due to accelerated osteoclast differentiation is a key factor in RA-related bone erosion, we hypothesize that RA-related superactive ICs such as CRT-IC and LTF-IC could play a key role in accelerating osteoclast differentiation in vivo thereby contributing to the imbalanced bone homeostasis and subsequent bone erosion in RA. The proposed project is designed to dissect, through series of in vivo and in vitro experiments, the underlying molecular mechanisms for rapid osteoclasts differentiation driven by super-active RA-ICs (as represented by CRT-IC and LTF-IC), with the aim to find additional clues for pathogenic bone damage in RA and novel treatment strategy for the disease.

类风湿性关节炎（RA）患者体内特有免疫复合物（IC）的致病机制是国际风湿免疫学界近十年来的研究热点，但相关研究多停留在抗瓜氨酸修饰蛋白抗体（ACPA）与瓜氨酸化抗原复合物（APCA-IC）对固有免疫细胞的促炎作用上。我们的前期工作发现，除了已经报道的几种ACPA-IC之外，血液中的钙网蛋白（CRT）免疫复合物（CRT-IC）及乳铁蛋白（LTF）免疫复合物（LTF-IC）与RA病程密切相关，且此类IC对人单核巨噬细胞不仅具有强刺激性，还能在体外诱导单核细胞迅速分化为破骨细胞。基于骨平衡失调在RA骨损伤中扮演重要角色这一国际风湿免疫学届的共识，我们提出以活化型IC通过诱导破骨细胞分化以干扰骨平衡并参与RA骨损伤的假说。本项目将通过一系列体内、外实验对CRT-IC等活化型IC诱导破骨细胞分化这一现象进行深入研究，以发现RA骨损伤的新机制，探索RA治疗的新靶点。

本项目围绕免疫复合物（IC）对破骨细胞（OC）分化以及骨平衡的影响及其在RA骨损伤中的作用一关键科学问题，从体外细胞水平，RA患者以及小鼠模型三方面进行了探讨。在为期四年的执行期中，我们顺利完成了各项研究任务，取得了一系列有价值的创新性研究成果，并在此基础上对研究内容做了适当拓展和延伸。我们的主要研究结论是：1）IC 可经FcγRIIa-SFK-STAT5通路诱导一种区别于经典OC（COC）的非经典OC（NOC）分化; 2) 在RANKL诱导OC分化的早期加入IC可抑制COC的分化; 3) 在松质骨面FcγRIIa促进COC分化，导致骨质疏松；在关节滑膜处，由于关机炎沉积的IC诱导NOC分化，参与骨侵蚀的发生; 4) IC可以通过FcγRIIa对巨噬细胞的极化产生影响，促进TAM向M1极化抑制肿瘤生长。四年来共有4名硕士和3名博士研究生参与了本项目的研究并顺利毕业。关于IC对破骨细胞分化与RA相关性的研究，我们得出在关节局部沉积的IC通过诱导NOC分化促进骨侵蚀，可溶性的IC通过促进COC分化诱导骨质疏松的假说，部分内容已经在J Immunol. 、Front. Immunol等SCI收录期刊上发表标注本项目资助的学术论著4篇，另有2篇论文已经修回。这一工作有助于我们对RA骨侵蚀以及骨质疏松致病机理的更深理解，也为RA的治疗提供了新线索和思路。