Mechanisms of RANKL Mediated Osteoclast Activation

描述(申请人提供)：炎性骨溶解，如类风湿性关节炎和骨科植入物松动，反映加速的破骨细胞(OC)的招募和激活。因此，发现局部炎症招募和激活OCS的方法对于预防这种严重的并发症至关重要。我们的首要目标是详细说明细胞因子，如肿瘤坏死因子、RANKL和M-CSF介导骨丢失的机制。我们通过表征不同的肿瘤坏死因子靶细胞在破骨细胞生成过程中的作用，并详细描述了肿瘤坏死因子促进破骨细胞生成的许多细胞内事件，达到了先前应用的目的。在目前的提案中，我们转向所有病理性骨吸收所必需的细胞因子，即RANKL，其晶体结构与其受体RANK的复合体，我们在当前的资助期解析。虽然RANKL对OC的分化是必不可少的，但它也增强了成熟OC的骨吸收活性，我们发现这一过程依赖于细胞因子对细胞骨架适配器蛋白Paxlin和小GTP酶Rac的调节。此外，我们对RANKL/RANK晶体结构以及RANKL与诱骗受体OPG富含半胱氨酸结构域的分辨，使我们能够开发基于结构的RANKL拮抗剂来阻断OC中的RANKL信号。鉴于抑制RANK信号通路已被证明具有治疗益处，这些新型RANKL抑制剂可能会影响病理性骨溶解的治疗。因此，我们假设：1)RANKL激活OC是通过帕西林介导的；2)RANKL激活OC是通过RAC介导的；3)基于结构的RANKL拮抗剂将阻止OC的发展和功能。因此，我们的具体目标是：1)确定帕西林介导OCRANKL激活的机制；2)确定RANKL在OC中激活RAC的机制；3)在OC中设计RANKL和OPG的变异体，破坏OC中的RANKL信号。与公共卫生相关。破骨细胞是破坏骨骼的细胞，因此，它们的活性增加导致了大多数形式的病理性骨丢失，如骨质疏松症或类风湿性关节炎。激活破骨细胞的关键分子称为RANKL(RANKL)。这项建议的目的是深入了解RANKL激活破骨细胞的机制，并设计候选药物来抑制这一事件，从而防止病理性骨丢失。

DESCRIPTION (provided by applicant): Inflammatory osteolysis, as occurs in rheumatoid arthritis and orthopedic implant loosening, reflects accelerated osteoclast (OC) recruitment and activation. Hence, discovering the means by which local inflammation recruits and activates OCs is central to preventing this crippling complication. Our overriding goal has been to detail the mechanisms by which cytokines, such as TNF, RANKL and M-CSF mediate bone loss. We have achieved the aims of our previous application by characterizing the contributions of various TNF target cells to the osteoclastogenic process and detailing many of the intracellular events by which TNF promotes osteoclastogenesis. In the present proposal we turn to the cytokine essential for all pathological bone resorption, namely RANKL, whose crystal structure, in complex with its receptor, RANK, we resolved in the current funding period. While RANKL is essential for OC differentiation, it also enhances the bone resorptive activity of the mature OC, a process we find depends upon the cytokine's regulation of the cytoskeletal adaptor protein, paxillin and the small GTPase, Rac. Furthermore, our resolution of the RANKL/RANK crystal structure and that of RANKL with the cysteine-rich domains of OPG, the decoy receptor, positions us to develop structure-based RANKL antagonists to arrest RANK signaling in the OC. Given that inhibition of the RANK signaling pathway has proven therapeutic benefit, these novel RANKL inhibitors may impact the treatment of pathological osteolysis. Thus, we hypothesize that: 1) RANKL activation of the OC is mediated via paxillin 2) RANKL activation of the OC is mediated via Rac and 3) Structure-based RANKL antagonists will arrest OC development and function. Our Specific Aims are therefore to 1) Determine the mechanisms by which paxillin mediates RANKL activation of the OC 2) Determine the mechanisms by which RANKL activates Rac in the OC and 3) Engineer variants of RANKL and OPG that disrupt RANK signaling in the OC. PUBLIC HEALTH RELEVANCE. Osteoclasts are the cells which destroy bone, and thus, their increased activity is responsible for most forms of pathological bone loss such as osteoporosis or that attending rheumatoid arthritis. The key molecule which activates ostoclasts is known as RANK ligand (RANKL). The purpose of this proposal is to gain insight into the mechanism by which RANKL activates osteoclasts and to design candidate drugs which will inhibit this event and consequently, prevent pathological bone loss.