Negative Regulation of Osteoclastogenesis by Inflammatory Signals

描述（由申请人提供）：炎症信号对破骨细胞生成的负调节风湿性关节炎（RA）是一种慢性炎症性疾病，其中免疫细胞和滑膜成纤维细胞产生促炎细胞因子，特别是TNF和IL-1，并驱动导致受影响关节破坏的炎症状态。炎症的一个重要后果是破骨细胞的产生，破骨细胞是有效吸收骨的髓系细胞，因此直接导致RA的骨侵蚀和发病率。本申请将集中于抑制破骨细胞生成的机制。TLR（Toll样受体）是炎症的有效激活剂，并参与驱动炎性骨吸收。然而，在它们激活炎症的同时，TLR还诱导有效的稳态机制以限制炎症的强度，从而限制相关的组织损伤。疾病进展是相对无效的反馈抑制的证据，其不能抑制炎症和骨吸收。因此，我们已经启动了研究，以了解在炎症的生理消退和疾病的静止期发生的有效的稳态调节。我们的总体假设是，生理稳态机制的增强代表了限制与炎症相关的骨吸收的有效方法，因此可以形成新的治疗方法的基础。 我们已经发现TLR刺激通过抑制RANK（破骨细胞生成所需的关键受体）来强烈抑制破骨细胞生成。TLR介导的抑制机制涉及通过活化的TNF-α转化酶（TACE，也称为ADAM-17）诱导M-CSF受体（c-Fms）脱落和蛋白水解加工，可能导致细胞对M-CSF无应答。切割的c-Fms随后经历一系列蛋白水解反应，导致产生50-kDa细胞内结构域切割片段（称为MICD）。有趣的是，我们的研究结果表明，MICD能够易位到细胞核中，并且MICD的表达增强破骨细胞生成。炎症信号也会减少MICD的产生。我们将使用与RA发病机制直接相关的人类系统以及小鼠系统来测试MICD和TACE在炎症性疾病中的体内作用。该项目的长期目标是：1）了解c-Fms脱落和加工成MICD调节破骨细胞生成的分子机制以及TACE与该过程的关联，以及2）确定MICD在M-CSF信号传导和破骨细胞和巨噬细胞分化中的作用。我们预计，我们的研究将产生对稳态调节的见解，不仅可以用于治疗干预，以抑制与关节破坏相关的骨吸收，而且还将扩大对M-CSF在骨免疫学领域的作用的理解。 公共卫生相关性：骨的侵蚀是慢性炎性疾病如类风湿性关节炎的发展和恶化的关键因素。破骨细胞是引起骨质侵蚀的特定细胞，并且该应用探索了可以抑制破骨细胞的新机制。通过阻止炎症环境中破骨细胞的发育和激活，我们可以阻止骨侵蚀，从而预防疾病的发展。

DESCRIPTION (provided by applicant): Negative Regulation of Osteoclastogenesis by Inflammatory signals Rheumatoid arthritis (RA) is a chronic inflammatory disease in which immune cells and synovial fibroblasts produce pro-inflammatory cytokines, in particular TNF and IL-1, and drive an inflammatory state leading to destruction of affected joints. One important consequence of inflammation is the generation of osteoclasts, myeloid lineage cells that effectively resorb bone and thus are directly responsible for bone erosion and morbidity in RA. This application will focus on mechanisms of inhibition of the generation of osteoclasts. TLRs (Toll-like Receptors) are potent activators of inflammation and have been implicated in driving inflammatory bone resorption. However, at the same time that they activate inflammation, TLRs also induce potent homeostatic mechanisms to limit the intensity of inflammation and thus limit associated tissue damage. Disease progression is evidence of relatively ineffective feedback inhibition that is unable to restrain inflammation and bone resorption. Thus, we have initiated studies to understand the effective homeostatic regulation that occurs during physiological resolution of inflammation and quiescent phases of disease. Our overall hypothesis is that augmentation of physiological homeostatic mechanisms represents an effective approach to limiting bone resorption associated with inflammation and thus can form the basis for novel therapeutic approaches. We have found that TLR stimulation strongly suppresses osteoclastogenesis by inhibiting RANK, a key receptor required for osteoclastogenesis. The mechanism of TLR-mediated inhibition involves induction of a M-CSF receptor (c-Fms) shedding and proteolytic processing by activated TNF-alpha converting enzyme (TACE, also known as ADAM-17), potentially leading to cellular unresponsiveness to M-CSF. Cleaved c-Fms subsequently undergoes a series of proteolytic reactions that results in generation of the 50-kDa intracellular domain cleavage fragments (referred to as MICD). Interestingly, our results reveal that MICD is able to translocate into the nucleus, and expression of MICD enhances osteoclastogenesis. MICD generation is also diminished by inflammatory signals. We will use human systems that are directly relevant for RA pathogenesis as well as mouse system to test the in vivo role of MICD and TACE in inflammatory diseases. The long-term goals of this project are to: 1) understand molecular mechanisms by which c-Fms shedding and processing into MICD regulate osteoclastogenesis and the association of TACE with this process, and 2) identify the role of MICD in M-CSF signaling and differentiation of osteoclasts and macrophages. We anticipate that our studies will yield insights into homeostatic regulation that can not only be exploited for therapeutic interventions to suppress bone resorption associated with joint destruction but will also broaden understanding of the actions of M-CSF in the field of osteoimmunology. PUBLIC HEALTH RELEVANCE: The erosion of bone is a key factor in the development and exacerbation of chronic inflammatory diseases, such as rheumatoid arthritis. Osteoclasts are the specific cells that cause bone erosion, and this application explores new mechanisms whereby osteoclasts can be inhibited. By deterring the development and activation of osteoclasts in inflammatory settings, we can hinder bone erosion and therefore prevent disease development.