Regulation of Osteoclastogenesis and Arthritic Bone Resorption by RBP-J

破骨细胞不仅在生理性骨发育和骨吸收中负责骨吸收 重塑，但也在以炎性骨溶解为特征的疾病中，如类风湿性关节炎(RA)。 炎症性骨吸收是复杂的，对标准的抗吸收治疗具有抵抗力。此外，目前 骨溶解的治疗通常会引起长期副作用，包括骨重建/修复缺陷和/或 免疫抑制。因此，有一个重要的医学需求尚未得到满足，那就是发现新的机制 主要或选择性地调节炎症性破骨细胞的形成，将对骨骼的不良影响降至最低 疾病环境中的重塑或免疫反应。人们对这些机制的了解要少得多。 我们特别关注肿瘤坏死因子介导的破骨细胞生成和骨破坏。 肿瘤坏死因子是导致炎症性骨吸收的关键致病因子。在之前的项目期间，我们确定了 转录抑制因子RBP-J作为显著抑制肿瘤坏死因子诱导的关键负性调节因子 破骨细胞生成和炎症性骨吸收，而不是RANKL诱导的破骨细胞生成和骨 改建。然而，RBP-J的下游靶点具体涉及肿瘤坏死因子介导的 破骨细胞的形成还不是很清楚。在本应用程序中，我们将Hs2st1确定为RBP-J的直接靶标 肿瘤坏死因子诱导的破骨细胞生成。Hs2st1是一种硫酸乙酰肝素(HS)生物合成酶，它将硫酸盐添加到 细胞表面HS链的2-O-位置。Hs2st1介导的HS硫酸盐化影响Hs2st1与Hs2st1相互作用 HS及其结合蛋白，从而调节各种细胞活动。RBP-J缺乏使肿瘤坏死因子 在破骨细胞分化过程中开启Hs2st1的表达。然而，它的作用和机制介导了 Hs2st1在破骨细胞形成中的作用，尤其是在炎症环境中的作用，目前还不清楚。我们发现RBP-J和 Hs2st1主要调节肿瘤坏死因子的诱导，但对RANKL诱导的破骨细胞生成和基础骨形成的影响很小。 骨量。根据我们的初步结果，在这项提案中，我们将1)研究Hs2st1和RBP- 用遗传学方法研究J-Hs2st1轴在炎症性骨吸收中的作用，2)研究 Hs2st1促进肿瘤坏死因子诱导破骨细胞生成的机制。我们发现Hs2st1抑制了 肿瘤坏死因子诱导的内源性干扰素β途径，破骨细胞生成的关键自分泌反馈抑制环。因此， 为此，我们将主要关注Hs2st1对干扰素β途径的调控。 拟议研究的成功完成将建立一种新的范式，其中以前的 RBP-J、RBP-J新靶向Hs2st1、HS和HS特异性结合蛋白介导的未识别网络 专门管理炎症性破骨细胞的形成。由于该网络似乎不会影响生理 破骨细胞发生和骨重建，在这个范例中确定的参与者和机制将提供一种 开发有吸引力的抑制炎性骨的治疗方法的合理框架 吸收，最大限度地减少对骨骼重塑/修复的副作用。

Osteoclasts are responsible for bone resorption not only in physiological bone development and remodeling, but also in diseases characterized by inflammatory osteolysis, such as rheumatoid arthritis (RA). Inflammatory bone resorption is complex and resistant to standard anti-resorptive therapies. Moreover, current treatments of osteolysis often cause long-term side effects, including bone remodeling/repair defects and/or immunosuppression. Therefore, there is an important medical unmet need to discover new mechanisms that predominantly or selectively regulate inflammatory osteoclastogenesis, minimizing undesirable effects on bone remodeling or immune response in disease settings. These mechanisms are much less understood. We have focused particular attention on TNF-mediated osteoclastogenesis and bone destruction since TNF is a key pathogenic factor driving inflammatory bone resorption. In the previous project period, we identified the transcription repressor RBP-J as a crucial negative regulator that prominently restrains TNF-induced osteoclastogenesis and inflammatory bone resorption, but not RANKL-induced osteoclastogenesis and bone remodeling. However, the downstream targets of RBP-J specifically involved in TNF-mediated osteoclastogenesis are not well understood. In this application, we identified Hs2st1 as a direct RBP-J target in TNF-induced osteoclastogenesis. Hs2st1 is a heparan sulfate (HS) biosynthetic enzyme that adds sulfate to the 2-O-position of the HS chain on cellular surface. HS sulfation mediated by Hs2st1 affects the interaction between HS and their binding proteins, thereby modulating various cellular activities. RBP-J deficiency enables TNF to turn on the expression of Hs2st1 in osteoclast differentiation. However, the function of and mechanisms mediated by Hs2st1 in osteoclastogenesis, especially in inflammatory settings, are unclear. We found that both RBP-J and Hs2st1 predominantly regulate TNF-induced, but minimally affect RANKL-induced osteoclastogenesis and basal bone mass. Based on our preliminary results, in this proposal, we will 1) investigate the role of Hs2st1 and RBP- J-Hs2st1 axis in vivo in inflammatory bone resorption using genetic approaches, and 2) investigate the mechanisms by which Hs2st1 promotes TNF-induced osteoclastogenesis. We found that Hs2st1 suppresses TNF-induced endogenous IFNβ pathway, a key autocrine feedback inhibitory loop for osteoclastogenesis. Thus, we will primarily focus on the regulation of IFNβ pathway by Hs2st1 in this aim. Successful completion of the proposed studies will establish a novel paradigm wherein a previously unrecognized network mediated by RBP-J, RBP-J new target Hs2st1, HS and HS specific binding proteins specifically governs inflammatory osteoclastogenesis. Since this network appears not to impact physiological osteoclastogenesis and bone remodeling, the players and mechanisms identified in this paradigm will provide a rational framework for developing attractive therapeutic approaches for suppressing inflammatory bone resorption, minimizing side effect on bone remodeling/repair.