The Role of the Complement System in Spinal Mechanisms of Chronic Pain

项目总结/摘要 持续性疼痛影响着1亿美国人和1500万乌克兰人。免疫系统关键在于 有助于炎症性和神经性疼痛的发病机制， 特定的免疫介质通过其促进伤害感受性神经元通路的致敏， 这对于开发更有效的治疗策略至关重要。补体系统是一个主要的 先天免疫的一个组成部分，通过多种机制促进宿主防御。尽管增长 有证据表明补体系统参与各种慢性疼痛状态，其潜在机制是 没有被很好地理解。我们的主要目标是美国和乌克兰集团之间的这一合作建议， 是为了阐明补体依赖性脊髓机制，有助于发展的神经病理性 在更广泛的层面上，促进建立和加强乌克兰的可持续研究能力。 机械性超敏反应和自发性疼痛是神经病理性疼痛的共同特征。主要 从脊髓到大脑的伤害性输出通路是这种异常疼痛处理的基础 背角（DH）的I投射神经元（PNs）。我们的膜片钳记录从这些神经元使用 创新性完整脊髓制备证实了以下脊髓输出的异常调节 备用神经损伤（SNI），一种常见的神经病理性疼痛模型，可以很好地再现许多临床特征， 神经性疼痛最近的研究表明，神经病理性疼痛与一个强大的上调， 脊髓中的补体效应物，其最终导致产生高度活性的补体 产物C5 a。鞘内施用C5 a产生异常性疼痛，而C5敲除（KO）和C5 a 受体（C5 aR 1）拮抗剂在神经性疼痛的动物模型中产生镇痛作用。我们的初步 数据显示C5 aR 1 KO预防SNI后的机械超敏反应。在DH中发现了C5 aR 1 主要作用于已知在SNI后DH中被激活的小胶质细胞。此外，C5 aR 1表达是 在SNI之后增加。我们将使用多学科的方法，包括膜片钳记录，光遗传学， 刺激和多光子Ca 2+成像在创新性完整脊髓制备中结合行为 C5 a/C5 aR 1信号传导在神经病理性疾病中起重要作用， 通过小胶质细胞依赖性信号传导影响中枢致敏作用来处理疼痛， 第一层脊神经与棘上结构的连接。这一建议将提供机械的见解， 补体系统在中枢神经系统疼痛处理中的功能，并可能导致新的 针对补体系统的止痛药。在其更广泛的影响，该项目将促进建立 乌克兰大脑疾病研究卓越中心，并帮助吸引年轻的乌克兰科学家， 这一领域，提供他们的培训和推进慢性疼痛研究在这个国家。

PROJECT SUMMARY / ABSTRACT Persistent pain affects 100 million Americans and 15 million Ukrainians. The immune system critically contributes to pathogenesis of inflammatory and neuropathic pain, and precise understanding of mechanisms through which particular immune mediators contribute to sensitization of nociceptive neuronal pathways will be essential for developing more efficacious treatment strategies. The complement system is a principal component of innate immunity that contributes to host defenses via diverse mechanisms. In spite of growing evidence implicating the complement system in various chronic pain states, the underlying mechanisms are not well understood. Our main objectives for this collaborative proposal between the US and Ukrainian groups are to elucidate complement-dependent spinal mechanisms that contribute to the development of neuropathic pain, and at a broader level, to promote building and strengthening sustainable research capacity in Ukraine. Mechanical hypersensitivity and spontaneous pain are common features of neuropathic pain. The main nociceptive output pathway from the spinal cord to the brain underlying this abnormal pain processing is lamina I projection neurons (PNs) of dorsal horn (DH). Our patch-clamp recordings from these neurons using an innovative intact spinal cord preparation demonstrate abnormal regulation of spinal cord output following spared nerve injury (SNI), a common model of neuropathic pain that well reproduces many features of clinical neuropathic pain. Recent studies suggest that neuropathic pain is associated with a robust upregulation of complement effectors in the spinal cord, which ultimately leads to production of a highly active complement product, C5a. Intrathecal administration of C5a produces allodynia, whereas C5 knockout (KO) and C5a receptor (C5aR1) antagonists produce analgesic effects in animal models of neuropathic pain. Our preliminary data show that C5aR1 KO prevents mechanical hypersensitivity following SNI. C5aR1 in the DH is found primarily on microglia that is known to be activated in the DH after SNI. Moreover C5aR1 expression is increased after SNI. We will use a multidisciplinary approach including patch-clamp recordings, optogenetic stimulation and multi-photon Ca2+ imaging in innovative intact spinal cord preparation combined with behavioral pharmacology to test our central hypothesis that C5a/C5aR1 signaling plays important roles in neuropathic pain processing by impacting central sensitization via microglia-dependent signaling that enhances the output of lamina I PNs of the DH to the supraspinal structures. This proposal will provide mechanistic insight into the function of the complement system in the CNS pain processing, and may lead to the development of new analgesic drugs that target complement system. In its broader impact, this project will promote establishment of Center for Excellence in brain disorder research in Ukraine, and help attracting young Ukrainian scientists to this field, providing their training and advancing chronic pain research in this country.