Regulatory Mechanisms of Implant-Induced Osteolysis

 描述（由申请人提供）：骨科植入物是修复退行性和失效关节以及节段性骨缺损的最常见方法。然而，炎症和随之而来的骨质溶解是骨科植入物的常见并发症，这些并发症是对植入物衍生碎片的反应。后续翻修手术更具挑战性，并且具有更大的失败、发病率和死亡率风险，尤其是在老龄化人群中。我们的长期研究目标是破译植入物碎片介导的骨溶解的生物学和病理学机制。在以前的工作中，我们已经展示了骨科颗粒（PMMA，PE等）。靶向破骨细胞（OC）祖细胞并激活NF-κ B B通路，这被认为是炎症反应中心和OC分化所必需的。我们进一步表明PMMA颗粒通过靶向TAK 1、NEMO、TRAF 6和IKK 2增强NF-κ B B活化。该过程加剧破骨细胞生成并导致骨质溶解。最近，我们发现了一种新的机制，即在调节性T细胞（Tcells）中，叉头蛋白Foxp 3调节TRAF 6/NEMO/IKK 2信号传导复合物，导致NF-κ B B活化，大量产生生长因子、细胞因子和趋化因子。这种高细胞因子血症导致造血干细胞（HSC）的过度增殖和具有高OC潜能的骨髓祖细胞的早期/原始群体的扩增。我们现在有证据表明PMMA颗粒在体内诱导这种炎症途径。我们还发现PMMA颗粒直接调节髓系祖细胞中的Notch/RNBPJ信号传导，导致OC相关转录因子（NF-κ B B和NFATc 1）的活化。因此，我们认为PMMA颗粒和其他可能的植入材料在骨髓微环境中的多种细胞类型（包括淋巴细胞和髓系祖细胞）中触发炎性旁分泌和自分泌信号通路。这些回路的信号传导开关包括Foxp 3、Notch/RBPJ和NF-κ B B转录因子，以旁分泌和自分泌模式响应骨髓应激驱动骨髓细胞扩增。基于该信息，我们假设PMMA颗粒通过未鉴定的“应激”机制，通过下调Foxp 3功能来调节T细胞活化，导致T细胞表型转换为具有增强的NF-κ B B活性的致病性T辅助细胞。这一步导致产生骨和促炎因子，扩大骨髓祖细胞群，增强OC形成。我们进一步假设，PMMA颗粒有助于直接激活髓系祖细胞中的Notch信号传导，从而激活RBPJ和NFATc 1。因此，我们建议：1）研究PMMA颗粒靶向淋巴细胞以增强骨髓增殖和增加OC负荷的旁分泌机制，2）研究PMMA通过RBPJ调节OCP中骨髓增殖的自分泌机制及其对破骨细胞生成的贡献，以及3）确定Foxp 3和RBPJ在PMMA诱导的胫骨和颅骨骨质溶解中的作用。将使用适当的细胞、分子和遗传小鼠模型和工具来测试这些目标。

 DESCRIPTION (provided by applicant): Orthopedic implants are the most common approach to repair degenerative and failing joints as well as segmental bone defects. However, inflammation and ensuing osteolysis are frequent complications of orthopedic implants arising in response to implant-derived debris. Subsequent revision surgeries are more challenging and carry greater risk of failure, morbidity and mortality, especially in the aging population. Our lon-term research goal is to decipher the biologic and pathologic mechanisms underlying implant debris- mediated osteolysis. In previous work, we have shown orthopedic particles (PMMA, PE, etc.) target osteoclast (OC) progenitors and activate NF-B pathway, which is considered central for inflammatory responses and essential for OC differentiation. We further showed that PMMA particles enhance NF-B activation by targeting TAK1, NEMO, TRAF6, and IKK2. This process exacerbates osteoclastogenesis and leads to osteolysis. Recently, we identified a novel mechanism underlying regulation of TRAF6/NEMO/IKK2 signaling complex by the forkhead protein Foxp3 in regulatory T cells (Tregs), leading to NF-B activation, abundant production of growth factors, cytokines and chemokine. This hyper-cytokinemia led to hyperproliferation of hematopoietic stem cells (HSCs) and to expansion of early/primitive population of myeloid progenitors that possessed high OC potential. We now have evidence that PMMA particles induce this inflammatory pathway, in vivo. We also found that PMMA particles directly regulate Notch/RNBPJ signaling in myeloid progenitors leading to activation of OC-related transcription factors (NF-B and NFATc1). Hence, we posit that PMMA particles, and likely other implant materials, trigger inflammatory paracrinic and autocrinic signaling circuits in multiple cell typesin the bone marrow microenvironment including lymphocytes and myeloid progenitors. The signaling switches of these circuits include Foxp3, Notch/RBPJ, and NF-B transcription factors, driving myeloid cell expansion in response to bone marrow stress in paracrinic and autocrinic modes. Based on this information, we hypothesize that PMMA particles, by unidentified "stress" mechanism, modulate T cell activation by down-regulating Foxp3 function, resulting with T cell phenotypic switch into pathogenic T helper cells with enhanced NF-B activity. This step leads to production of osteotropic and pro-inflammatory factors that expand the myelo-progenitor population and enhance OC formation. We further hypothesize that PMMA particles contribute to activation of Notch signaling directly in myeloid progenitors leading to activation of RBPJ and NFATc1. Hence we propose to: 1) Investigate the paracrine mechanism(s) by which PMMA particles target lymphocytes to enhance myelo- proliferation and increase OC burden, 2) Investigate the autocrine mechanism underlying PMMA regulation of myelo-proliferation in OCPs by RBPJ and its contribution to osteoclastogenesis, and 3) Determine the role of Foxp3 and RBPJ in PMMA-induced tibial and calvarial osteolysis. Appropriate cellular, molecular, and genetic mouse models and tools will be used to test these Aims.