Regulatory Pathways in Osteoclasts and Immune Cells during Inflammatory Arthritis

描述(申请人提供)：在类风湿性关节炎(RA)期间，免疫细胞激活增加导致局部骨侵蚀和全身性骨丢失，两者都由破骨细胞(OCS)介导。树突状细胞(DC)是类风湿关节炎(RA)相关炎症反应的关键成分，因为它们负责T淋巴细胞的激活，这是由于自身抗原的异常呈递。中性粒细胞可以通过招募更多的DC来进一步增强炎症状态，并通过主动分泌炎性和促破骨细胞因子来促进局部骨侵蚀。不幸的是，阻断炎症细胞因子活性的传统药物疗法在控制症状和疾病进展方面可能不够充分。我们的总体目标是确定对调节类风湿性关节炎的炎症和溶骨成分至关重要的信号分子，并为新的和更有效的治疗方法奠定基础。我们之前已经发现，PLC？2是类风湿关节炎相关的骨稳态和炎症反应的关键调节剂。然而，PLC？2与更普遍表达的PLC？1有很高的同源性，从而使其难以特异性靶向。甘油二酯(DAG)是PLC？2催化活性的下游产物，本课题组和其他研究小组的数据表明，它介导了PLC？2在OCS和免疫细胞中的功能。为了研究DAG的作用，我们现在将注意力转向DGK？，一种通过将DAG转化为磷脂酸(PA)来降低细胞DAG水平的酶。因此，DGK？-缺乏会导致DAG的积累。我们的初步数据显示DGK？在OCS、中性粒细胞和DC中高表达。我们还发现，缺乏DGK？的小鼠。有明显的骨质疏松表型，其特征是骨小梁数量和厚度减少，OC的形成和功能增强。因此，我们的数据表明DGK？是破骨细胞激活的负性调节因子。基于这一信息，我们的中心假设是DGK？通过对DAG的调节，是PLC？2下游骨和免疫细胞的共同调节因子。在体外和体内调节破骨细胞的形成和骨吸收。具体目标2：检查DGK的作用？血清诱导性关节炎的发生、消退及其对中性粒细胞活化的影响。具体目标3：确定DGK的作用？在抗原诱导的关节炎中的作用及其对DC介导的T细胞激活的影响。这个应用程序的目标是展示DGK的重要性？在OCS、中性粒细胞和DC的激活和功能方面，作为一种靶向RA的骨溶解和炎症成分的途径。这一新方法可能为新的类风湿关节炎治疗措施奠定基础。 公共卫生相关性：考虑到炎症性关节炎和相关的骨丢失在西方人群中的影响，我们研究的意义在于确定DGK6是一种新的骨稳态调节因子。本应用程序的目的是证明DGK6在OCS、中性粒细胞和DC的激活和功能中的重要性，作为一种靶向类风湿关节炎的溶骨和炎症成分的方法。这一新的方法可能为治疗类风湿性关节炎和炎症性骨丢失的新的治疗措施奠定基础。

DESCRIPTION (provided by applicant): During Rheumatoid Arthritis (RA), increased immune cell activation leads to focal bone erosion as well as systemic bone loss, both mediated by osteoclasts (OCs). Dendritic cells (DCs) are critical components of the inflammatory response associated with RA as they are responsible for the activation of T lymphocytes, due to abnormal presentation of self-antigens. Neutrophils can further enhance the inflammatory condition by recruiting more DCs and contribute to local bone erosion by actively secreting inflammatory and pro-osteoclastogenic cytokines. Unfortunately, traditional pharmacotherapy to block the activity of inflammatory cytokines can be inadequate in controlling symptoms and disease progression. Our overall goal is to identify signaling molecules that are critical to modulate the inflammatory and osteolytic components of RA and that may lay the groundwork for novel and more effective therapeutic approaches. We have previously found that PLC?2 is a critical modulator of bone homeostasis and inflammatory responses associated with RA. However, PLC?2 shares high homology with the more ubiquitously expressed PLC?1, thus rendering its specific targeting difficult. Diacylglycerol (DAG) is a downstream product of PLC?2 catalytic activity and data from our group and others indicate that it mediates PLC?2 function in OCs and immune cells. In order to study the role of DAG, we now turned our attention to DGK?, an enzyme that decreases cellular levels of DAG by converting it to phosphatidic acid (PA). Thus, DGK?-deficiency causes accumulation of DAG. Our preliminary data indicate that DGK? is highly expressed in OCs, neutrophils and DCs. We also found that mice lacking DGK? have a substantial osteoporotic phenotype, characterized by reduced trabecular number and thickness and enhanced OC formation and function. Thus, our data indicate that DGK? is a negative modulator of osteoclast activation. Based on this information, our central hypothesis is that DGK?, via modulation of DAG, is a common regulator of bone and immune cells downstream of PLC?2. Thus, we propose to: Specific Aim 1: Investigate the mechanism by which DGK? modulates osteoclast formation and bone resorption in vitro and in vivo. Specific Aim 2: Examine the role of DGK? in development and resolution of serum induced arthritis and its effect on neutrophil activation. Specific Aim 3: Determine the role of DGK? in antigen-induced arthritis and its effect in DC- mediated T cell activation. The goal of this application is to demonstrate the importance of DGK? in the activation and functionality of OCs, neutrophils and DCs as a way to target both the osteolytic and inflammatory components of RA. This novel approach might lay the basis for new therapeutic interventions for RA. PUBLIC HEALTH RELEVANCE: Considering the impact of inflammatory arthritis and associated bone loss in the western population, the significance of our study consists in having identified DGK6 as a novel regulator of bone homeostasis. The goal of this application is to demonstrate the importance of DGK6 in the activation and functionality of OCs, neutrophils and DCs as a way to target both the osteolytic and inflammatory components of Rheumatoid Arthritis. This novel approach might lay the basis for new therapeutic interventions for Rheumatoid Arthritis and inflammatory bone loss.