P2X7R: a novel therapeutic target in implant loosening

总结 临床骨科最常见的问题之一仍然是“无菌性松动”， 炎性骨质溶解植入物的磨损颗粒刺激巨噬细胞产生炎症 细胞因子，其诱导局部骨质溶解并抑制骨质溶解的成骨修复。我们的长期目标是 发现新的潜在机制，从而确定新的治疗目标， “无菌性松动”。该R21 A1应用程序将测试细胞外ATP（eATP） 增加骨科磨损颗粒的生物活性。 与总体假设一致，我们的初步结果表明，磨损颗粒刺激 巨噬细胞释放ATP eATP是P2 X7 R的唯一已知配体，P2 X7 R是主要的巨噬细胞 eATP水平升高的受体。eATP刺激P2 X7 R会增加某些类型的炎症， 以前没有在“无菌性松动”中进行过研究。因此，目标1（原理验证目标）将决定 eATP和P2 X7 R如何影响磨损颗粒的生物活性。 通过eATP刺激P2 X7 R可以激活NLRP 3炎性体，并且NLRP 3炎性体是 主要负责将pro-IL 18和pro-IL 18加工成响应磨损颗粒的活性细胞因子。 然而，NLRP 3炎性体必须在活化之前被引发。我们的初步结果表明， 磨损颗粒可以引发和激活NLRP 3炎性小体。我们以前表明， 细菌病原体相关分子模式（PAMPs）的粘附大大增加了生物 粒子的活动。因此，目标2（机械目标）将确定磨损颗粒（具有和 没有粘附的PAMP）影响ATP释放、P2 X7 R和NLRP 3炎性体。 P2 X7 R的高度特异性药物样拮抗剂可以减轻动物模型中的炎症，并在临床上应用。 其他炎症性疾病的试验。因此，目标3（翻译目标）将决定 P2 X7 R拮抗剂对磨损颗粒生物活性的影响。 该项目是理想的R21机制：它是高风险的，因为没有以前的研究， eATP或P2 X7 R在“无菌性松动”中的作用。P2 X7 R具有潜在的高影响力， 拮抗剂在用于其它炎性病症的临床试验中耐受良好。我们的团队拥有 因此，我们拥有必要的专业知识，因此能够有效地完成该项目。

SUMMARY One of the most common problems in clinical orthopaedics continues to be “aseptic loosening” due to inflammatory osteolysis. Wear particles from the implants stimulate macrophages to produce inflammatory cytokines, which induce local osteolysis and inhibit osteogenic repair of the osteolysis. Our long-term goal is to discover novel underlying mechanisms and thereby identify novel therapeutic targets for patients with “aseptic loosening”. This R21 A1 application will test the overall hypothesis that extracellular ATP (eATP) increases the biologic activity of orthopaedic wear particles. Consistent with the overall hypothesis, our preliminary results indicate that wear particles stimulate macrophages to release ATP. eATP is the only known ligand for P2X7R, which is the primary macrophage receptor for elevated levels of eATP. Stimulation of P2X7R by eATP increases some types of inflammation but has not previously been studied in “aseptic loosening”. Aim 1 (proof-of-principle aim) will therefore determine how eATP and P2X7R affect the biologic activity of wear particles. Stimulation of the P2X7R by eATP can activate the NLRP3 inflammasome and the NLRP3 inflammasome is primarily responsible for processing pro-IL1ß and pro-IL18 to the active cytokines in response to wear particles. However, the NLRP3 inflammasome must be primed prior to activation. Our preliminary results suggest that wear particles can both prime and activate the NLRP3 inflammasome. We previously showed that the adherence of bacterial pathogen-associate molecular patterns (PAMPs) substantially increases the biologic activity of the particles. Aim 2 (mechanistic aim) will therefore determine how wear particles (with and without adherent PAMPs) affect ATP release, the P2X7R, and the NLRP3 inflammasome. Highly-specific, drug-like antagonists of P2X7R can reduce inflammation in animal models and are in clinical trials for other inflammatory conditions. Aim 3 (translational aim) will therefore determine the effects of antagonists of P2X7R on biologic activity of the wear particles. This project is ideal for the R21 mechanism: It is high risk because there are no previous studies on the effects of eATP or P2X7R in “aseptic loosening”. It has the potential for high impact because the P2X7R antagonists were well tolerated in clinical trials for other inflammatory conditions. Our team possesses the necessary expertise and thus is uniquely positioned to efficiently complete this project.