The role of fas signaling in rheumatoid arthritis

描述（由申请人提供）：RA是一种慢性自身免疫性疾病，表现为持续性滑膜炎症、细胞浸润和促炎细胞因子产生，并导致进行性软骨和骨破坏。虽然RA相关自身免疫表型的机制尚未完全阐明，但细胞凋亡不足是疾病发病机制的基本因素。外源性凋亡途径的介体包括参与凋亡信号起始的死亡受体Fas，以及参与凋亡信号传递的FADD和半胱天冬酶-8。Fas、FADD或caspase-8的淋巴细胞特异性缺失揭示了这些信号传导介质在增殖中的非凋亡作用。特别令人感兴趣的是FADD和半胱天冬酶-8的B细胞特异性缺失损害toll样受体（TLR）诱导的增殖，对NF κ B和MAPK信号传导途径的下游活化具有潜在后果。虽然淋巴细胞对于RA的起始是必需的，但巨噬细胞对于这种使人衰弱的疾病的持续是至关重要的。这些细胞是高度活化的，表达增加水平的TLR 3和4，并通过产生降解酶、细胞因子和趋化因子而导致滑膜炎症和软骨及骨破坏，并且不像B细胞，不增殖。然而，缺乏Fas和它的信号介质，特别是在骨髓细胞尚未被检查。对髓系细胞区室中特异性缺乏Fas的老年CreLysMFasflox/flox小鼠的初步评价显示，选择性缺失该信号传导介质通过增加外周血驻留单核细胞的水平以及增加总脾巨噬细胞和炎性脾巨噬细胞的数量和活化水平来破坏外周中的髓系细胞稳态。基于这些数据，我们提出Fas及其下游信号伙伴FADD和caspase-8是炎症的抑制因子。在这项研究中，我们将确定骨髓细胞特异性缺失Fas及其信号传导伙伴对骨髓细胞发育以及炎症性关节炎的发展和严重程度的影响。此外，我们建议确定在巨噬细胞中需要Fas，FADD和caspase-8信号转导的非凋亡途径。类风湿性关节炎的治疗旨在靶向纠正缺陷的Fas信号传导，尽管这可能具有有害的结果，如果Fas对于非凋亡细胞功能是必需的，如在Fas信号传导介质的B细胞特异性缺失中所见。因此，本项目旨在阐明与Fas启动的外源性凋亡途径相关的信号传导介质的新型髓样细胞特异性非凋亡作用。总之，该提议采用细胞特异性方法来鉴定Fas、FADD和半胱天冬酶-8在巨噬细胞功能、对炎性关节炎发展的易感性以及最重要的TLR信号传导中的非凋亡参与，迄今为止从未对其进行过研究。 公共卫生相关性：细胞凋亡缺陷与类风湿关节炎的发病机制以及滑膜中炎性巨噬细胞的持续存在有关。类风湿性关节炎的治疗旨在靶向纠正缺陷的Fas信号传导，尽管这可能具有有害的结果，如果Fas对于非凋亡细胞功能是必需的，如在Fas信号传导介质的B细胞特异性缺失中所见。因此，该项目旨在阐明与Fas启动的外源性凋亡途径经典相关的信号传导介质的新的髓样细胞特异性非凋亡作用。

DESCRIPTION (provided by applicant): RA, a chronic autoimmune disease, manifests in persistent synovial inflammation, cellular infiltration, and pro-inflammatory cytokine production, and results in progressive cartilage and bone destruction. While the mechanisms underlying RA-associated autoimmune phenotypes are not fully elucidated, insufficient apoptosis is a fundamental player in disease pathogenesis. Mediators of the extrinsic apoptotic pathway include the death receptor Fas, involved in initiation of the apoptotic signal, and FADD and caspase-8, involved in transmission of the apoptotic signal. Lymphocyte-specific deletion of Fas, FADD, or caspase-8 reveals non-apoptotic roles for these signaling mediators in proliferation. Of particular interest is that B cell-specific deletion of FADD and caspase-8 impairs toll-like receptor (TLR)-induced proliferation with potential consequences on downstream activation of NFKB and MAPK signaling pathways. While lymphocytes are necessary for the initiation of RA, macrophages are crucial for the persistence of this debilitating disease. These cells are highly activated, express increased levels of TLR3 and 4, and contribute to synovial inflammation and cartilage and bone destruction through the production of degradative enzymes, cytokines, and chemokines, and unlike B cells, do not proliferate. However, deficiency of Fas and its signaling mediators specifically in myeloid cells has yet to be examined. Preliminary evaluation of aged CreLysMFasflox/flox mice, which lack Fas specifically in the myeloid cell compartment, shows that selective deletion of this signaling mediator disrupts myeloid cell homeostasis in the periphery by increasing levels of peripheral blood resident monocytes, as well as increasing both the number and activation level of total and inflammatory splenic macrophages. Based on these data, we propose that Fas and its downstream signaling partners, FADD and caspase-8, are suppressors of inflammation. In this study we will determine the impact of myeloid cell-specific deletion of Fas and its signaling partners on myeloid cell development as well as development and severity of inflammatory arthritis. Also, we propose to determine the non-apoptotic pathways that require Fas, FADD and caspase-8 signaling in macrophages. Therapies for rheumatoid arthritis have been aimed at targeting correction of defective Fas-signaling, though this may have detrimental outcomes should Fas be necessary for non-apoptotic cellular functions, as seen in B cell-specific deletion of Fas-signaling mediators. Therefore, this project aims to elucidate novel myeloid cell-specific non-apoptotic roles for signaling mediators classically associated with the Fas-initiated extrinsic apoptotic pathway. In summary, this proposal takes a cell-specific approach to identify the non-apoptotic involvement of Fas, FADD and caspase-8 in macrophage function, susceptibility to the development of inflammatory arthritis, and most importantly in TLR signaling, which to date has never been examined. PUBLIC HEALTH RELEVANCE: Defective apoptosis is associated with rheumatoid arthritis pathogenesis as well as the persistence of inflammatory macrophages in the synovium. Therapies for rheumatoid arthritis have been aimed at targeting correction of defective Fas-signaling, though this may have detrimental outcomes should Fas be necessary for non-apoptotic cellular functions, as seen in B cell-specific deletion of Fas- signaling mediators. Therefore, this project aims to elucidate novel myeloid cell-specific non- apoptotic roles for signaling mediators classically associated with the Fas-initiated extrinsic apoptotic pathway.