Regulatory Mechanisms of Implant-Induced Osteolysis

 描述(申请人提供)：骨科植入物是修复退行性和失败的关节以及节段性骨缺损的最常见的方法。然而，炎症和随之而来的骨溶解是骨科植入物对植入物碎片的反应产生的常见并发症。随后的翻修手术更具挑战性，失败、发病率和死亡率更大的风险，特别是在老龄化人口中。我们的长期研究目标是破译种植体碎屑介导的骨溶解的生物学和病理学机制。在以前的工作中，我们展示了骨科颗粒(PMMA、PE等)。靶向破骨细胞(OC)前体细胞并激活NF-B通路，该通路被认为是炎症反应的中心和OC分化的关键。我们进一步表明，PMMA颗粒通过靶向TAK1、NEMO、TRAF6和IKK2来增强NF-B的激活。这一过程加剧了破骨细胞的形成，并导致骨溶解。最近，我们发现了一种新的机制，即在调节性T细胞(Treg)中通过叉头蛋白Foxp3调节TRAF6/NEMO/IKK2信号复合体，导致核因子-B激活，大量产生生长因子、细胞因子和趋化因子。这种高细胞分裂素血症导致造血干细胞(HSCs)的过度增殖，并导致具有高OC潜能的早期/原始髓系祖细胞群体的扩张。我们现在有证据表明，PMMA颗粒在体内诱导了这种炎症途径。我们还发现，PMMA颗粒直接调节髓系祖细胞中的Notch/RNBPJ信号，导致OC相关转录因子(NF-B和NFATc1)的激活。因此，我们假设PMMA颗粒，以及可能的其他植入材料，在包括淋巴细胞和髓系祖细胞在内的骨髓微环境中的多种细胞类型中触发炎性旁分泌和自分泌信号通路。这些通路的信号开关包括FOXP3、Notch/RBPJ和NF-B转录因子，在旁分泌和自分泌模式下驱动髓系细胞在骨髓应激反应中的扩张。基于这一信息，我们假设PMMA颗粒通过下调Foxp3功能来调节T细胞的激活，从而导致T细胞表型转换为具有增强的NF-B活性的致病T辅助细胞。这一步导致了促骨和促炎因子的产生，从而扩大了骨髓祖细胞群体，促进了OC的形成。我们进一步假设，PMMA颗粒直接参与了髓系祖细胞Notch信号的激活，导致了RBPJ和NFATc1的激活。因此，我们建议：1)研究PMMA颗粒靶向淋巴细胞促进骨髓增殖和增加OC负荷的旁分泌机制(S)；2)研究PMMA调节RBPJ促进OCPs骨髓增殖的自分泌机制及其在破骨细胞形成中的作用；3)确定Foxp3和RBPJ在PMMA诱导的胫骨和颅骨溶解中的作用。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.