Role of TNFa in Osteoclast-Mediated Bone Loss

描述(申请人提供)：炎症性侵袭性关节炎，如类风湿性关节炎(RA)，骨破坏与促炎细胞因子的产生增加有关，促炎细胞因子通过增加炎症关节中破骨细胞前体(OCP)向成熟破骨细胞的分化而促进局部骨吸收。骨免疫学的最新进展表明，破骨细胞不仅是骨吸收细胞，还通过自分泌和旁分泌机制产生促进炎症和自身免疫的因子。然而，破骨细胞产生的因素可能直接影响类风湿性关节炎的发生和发展，目前还没有得到很好的研究。利用基因芯片分析，我们发现在肿瘤坏死因子-甘油三酯关节炎小鼠的OCP中，血管内皮生长因子-C的表达显著增加。血管内皮生长因子是淋巴血管生成所必需的淋巴源性生长因子。但其在破骨细胞功能中的作用尚未被研究，淋巴系统在类风湿关节炎关节破坏发病机制中的作用也知之甚少。为了探讨血管内皮生长因子-C在这一环境中的作用，我们开展了一系列的初步研究，结果表明：1)RANKL和肿瘤坏死因子诱导OCP和OCS表达血管内皮生长因子-C；2)血管内皮生长因子-C刺激破骨细胞性骨吸收；3)类风湿关节炎关节显著增加淋巴管形成；4)抑制血管内皮生长因子-C信号转导降低肿瘤坏死因子-甘油三酯小鼠关节炎症的严重程度。根据这些发现，我们推测在炎症关节中，OCPs和OCs被RANKL和TNF激活而产生VEGF-C，通过自分泌和旁分泌机制刺激血管生成和破骨细胞生成，同时介导关节炎症和骨侵蚀。这些假设将在三个具体目标中得到检验。在目标1中，我们将研究RANKL和肿瘤坏死因子刺激OCPs和破骨细胞产生VEGF-C的机制。在目标2中，我们将研究血管内皮生长因子-C对破骨细胞功能的影响及其下游信号通路。在目标3中，我们将使用VEGFR3阻断方法来确定血管内皮生长因子-C信号在类风湿关节炎发病机制中的功能重要性。这些研究将提供有关有机氯农药如何通过淋巴管生成刺激血管疙瘩形成的新信息。最终，它们将导致开发新的特定治疗剂来预防和治疗炎症性侵蚀性关节炎患者。与公共卫生相关。本研究旨在通过影响破骨细胞功能和淋巴管生成，探讨骨吸收破骨细胞在类风湿关节炎发生发展中的作用。这一结果将加深我们对破骨细胞和淋巴生物学的了解，并为开发治疗关节炎的新疗法提供新的方向。

DESCRIPTION (provided by applicant): Bone destruction in inflammatory erosive arthritis, such as rheumatoid arthritis (RA), is associated with increased production of pro-inflammatory cytokines, which promote focal bone resorption by increasing the differentiation of osteoclast precursors (OCP) to mature osteoclasts in inflamed joints. Recent progress in Osteoimmunology indicates that osteoclasts are not only bone resorbing cells; they also produce factors that contribute to inflammation and autoimmunity by autocrine and paracrine mechanisms. However, osteoclast-produced factors that could affect the development and progression of RA directly have not been well studied. Using microarray analysis, we identified that VEGF-C expression is significantly increased in OCPs from TNF- Tg arthritic mice. VEGF-C is a lymphogenic growth factor essential for lymphoangiogenesis. But its role in osteoclast function has not been investigated and little is known about the role of the lymphatic system in the pathogenesis of joint destruction in RA. To explore the involvement of VEGF-C in this setting, we carried out a series preliminary studies and demonstrated that 1) RANKL and TNF induce VEGF-C expression in OCPs and OCs; 2) VEGF-C stimulates osteoclastic bone resorption; 3) RA joints have remarkably increased lymphatic vessel formation; and 4) inhibition of VEGF-C signaling reduces the severity of joint inflammation in TNF-Tg mice. Based on these findings, we hypothesize that in inflammatory joints OCPs and OCs are activated by RANKL and TNF to produce VEGF-C, which mediates joint inflammation and bone erosion simultaneously by stimulating vasculogenesis and osteoclastogenesis via autocrine and paracrine mechanisms. These hypotheses will be tested in 3 specific aims. In Aim 1, we will investigate the mechanisms by which RANKL and TNF stimulate OCPs and osteoclasts to produce VEGF-C. In Aim 2, we will examine the effects of VEGF-C on osteoclast function and the downstream signaling pathways involved. In Aim 3, we will determine the functional importance of VEGF-C signaling in the pathogenesis of RA using a VEGFR3 blockade approach. These studies will provide new information on how OCPs stimulate pannus formation via lymphangiogenesis. Ultimately they should lead to the development of novel specific therapeutic agents to prevent and treat patients with inflammatory erosive arthritis. PUBLIC HEALTH RELEVANCE. The proposed study is aimed to investigate the role of bone resorbing osteoclasts in the development and progression of rheumatoid arthritis by affecting osteoclast function and lymphangiogenesis in mouse models of arthritis. The results will enhance our understanding of osteoclast and lymphatic biology and provide new direction for developing a novel therapy to treat arthritis.