Role of CD137L in peripheral nerve injury induced neuropathic pain

摘要 神经胶质细胞的激活和促炎介质的产生参与了神经病的发病机制 疼痛。临床前研究表明，中枢神经系统(CNS)的巨噬细胞--小胶质细胞是至关重要的 早期调节因子在周围神经损伤诱导的神经病理性疼痛中的发展。然而，其他 研究表明，小胶质细胞的激活和各种促炎因子的产生在 对神经损伤后神经再生和功能恢复的有益作用。而且，我们初步的 研究表明，与外周巨噬细胞相似，脊髓小胶质细胞表现出促炎作用。 脊神经损伤早期的表型和后期的抗炎表型 L5横断术(L5Tx，一种公认的神经病理性疼痛小鼠模型)。我们建议这两个人 小胶质细胞的激活状态对应于一组独特的小胶质细胞功能。通过最优调节 与其说完全抑制小胶质细胞的激活，不如说我们有可能 限制小胶质细胞在神经病理性疼痛发展中的作用 保留小胶质细胞在神经再生中的有益特性。我们认为CD137配体 (CD137L)表达于小胶质细胞表面，以促炎症和负性调节的方式起作用 CD137L可以潜在地将激活的小胶质细胞中的促炎和抗炎平衡转向抗炎 炎症状态。然而，CD137L的大部分已知功能都是通过对 外周免疫细胞。CD137L在中枢神经系统小胶质细胞中的作用尚未得到广泛研究 小胶质细胞CD137L在神经病理性疼痛发生中的作用尚不清楚。在这项研究中，我们将 小胶质细胞CD137L在周围神经损伤性神经病病理生理中的作用 通过检查两种神经病理性疼痛的小鼠模型。我们假设小胶质细胞 CD137L参与周围神经损伤后痛样行为的发生 负性调节CD137L可促进小胶质细胞活化向抗 炎症状态，从而减少周围神经损伤引起的痛样行为。这个中心 假说将通过三个特定的目的来检验：1)表征CD137L在外周的参与 神经损伤引起的痛样行为。将在使用和不使用CD137L的小鼠身上测试类似疼痛的行为 表情。2)评价大鼠周围神经损伤后脊髓小胶质细胞的活化状态。 与小胶质细胞CD137L表达的关系将通过评估监测小胶质细胞的激活 流式细胞仪检测小胶质细胞表型。以及3)确定CD137依赖与CD137- 周围神经损伤、CD137L介导的痛样行为和小胶质细胞的独立通路 回应。总之，我们相信对CD137L的研究可能导致新的治疗方法 显著减少神经病理性疼痛，同时对神经恢复的不良影响最小。

Summary Glial activation and production of proinflammatory mediators contribute to the pathogenesis of neuropathic pain. Pre-clinical studies implicate microglia, the macrophages of the central nervous system (CNS), as critical early regulators in the development of peripheral nerve injury-induced neuropathic pain. However, other studies indicate that microglial activation and the production of various proinflammatory factors play a beneficial role in nerve regeneration and functional recovery following nerve injury. Moreover, our preliminary studies show that similar to peripheral macrophages, spinal cord microglia exhibit a proinflammatory phenotype at early time points and an anti-inflammatory phenotype at later time points following spinal nerve L5 transection (L5Tx, a well-established murine model of neuropathic pain). We propose that these two microglial activation states correspond to unique sets of microglial functions. By optimally regulating microglial activation rather than completely inhibiting the activation of microglia, we can potentially limit the contribution of microglia to the development of neuropathic pain while simultaneously preserving the beneficial properties of microglia in nerve regeneration. We believe that CD137 ligand (CD137L) expressed on microglial surface acts in a proinflammatory manner and that negatively modulating CD137L can potentially shift the pro- vs. anti-inflammatory balance in activated microglia towards an anti- inflammatory state. However, most of the known functions of CD137L have been obtained from studies on peripheral immune cells. The role of CD137L in CNS microglia has not been studied extensively and the role of microglial CD137L in the development of neuropathic pain is unknown. In this study, we will determine the role of microglial CD137L in the pathophysiology of peripheral nerve injury-induced neuropathic pain through the examination of two murine models of neuropathic pain. We hypothesize that microglial CD137L is involved in the development of peripheral nerve injury -induced pain-like behaviors and that negatively modulating CD137L can promote a shift in microglial activation towards an anti- inflammatory state and thus reduce peripheral nerve injury-induced pain-like behaviors. This central hypothesis will be tested via three specific aims: 1) Characterize the involvement of CD137L in peripheral nerve injury-induced pain-like behaviors. Pain-like behaviors will be tested in mice with and without CD137L expression. 2) Evaluate the activation status of spinal cord microglia following peripheral nerve injury in relation to the expression of microglial CD137L. Microglial activation will be monitored through assessing microglial phenotype via flow cytometry. And 3) determine the involvement of CD137-dependent vs. CD137- independent pathways in peripheral nerve injury-induced, CD137L-mediated pain-like behaviors and microglial responses. In sum, we believe that the investigation of CD137L could lead to novel treatment that could significantly reduce neuropathic pain while has minimal adverse impact on nerve recovery.