Proteolysis of Myelin as a Source of Neuropathic Pain

描述(申请人提供)：神经病理性疼痛(NP)是具有神经免疫功能障碍的某些特征的“由于影响躯体感觉神经系统的损伤或疾病而直接引起的疼痛”。作为对周围神经损伤的反应，在损伤的神经和节段性脊髓中，辅助性T细胞(Th)淋巴细胞的运输和主要组织相容性复合体(MHC)II(对于识别Th细胞的捕获和抗原递送是必不可少的)的诱导是NP发生的必要条件和充分条件。MHCII与NP的不同诱导有关，但与炎性疼痛无关，但其抗原及其形成过程仍不清楚。我们开创性的项目集中在这样一个组织命题上，即免疫优势抗原在受损的有髓神经中形成，是低阈值机械性过敏症的来源。触摸是由非伤害性大的有髓(Ab)传入发出的信号，在受伤后，这些传入开始将轻微的触摸解释为毁灭性的疼痛(机械性疼痛)。我们的尖端初步数据确定了一种解释这种现象的全新机制：基质金属蛋白酶(MMPs)选择性地分解髓鞘碱性蛋白(MBP)，释放隐藏的免疫优势表位MBP84-104和MBP69-86，通常不受免疫监视。我们清楚地证明，免疫优势的MBP多肽在注射到完整的神经中时会产生强烈的痛觉异常。一个有趣的发现是，内源性免疫优势的MBP69-86表位与MHCII共同定位于损伤神经的抗原提呈雪旺细胞中，靠近Ranvier的动作电位产生节点。使用最先进的生化和分子工具(例如Illumina珠芯片基因阵列、MALDI-TOF质谱仪、Invenity、NextBio、GeneGo和专有的基质金属蛋白酶底物数据库)和基础(神经病理、行为、系统)方法，我们将表征MBP残基在伤害性感受中的T细胞依赖和独立作用(目标1)。有髓纤维的分子结构域负责MBP在T细胞归巢和运动中的作用，以及神经中MBP残留物的受体(目标2)。重要的是，我们确定电压门控钠通道的表达和谷氨酸受体亚单位的脊髓释放依赖于基质金属蛋白酶的活性。该提案的结论重点是新的催化和非催化的基质金属蛋白酶靶点，在调节T细胞的运输和整合到脊髓神经胶质信号网络，促进适应不良的中枢可塑性和异常的神经免疫突触发生(目标3)。这一多学科计划将金属蛋白分解生物化学(Alex Strongin，Ph.D.，Sanford-Burnham Medical Research Inst.)、外周髓鞘形成和神经炎症中MMPs的神经生物学(Veronica Shubayev，M.D.，UCSD)和疼痛通路(Tony Yaksh，Ph.D.，UCSD)方面的领先专业知识和最大资源与创新的研究设计相结合，我们相信，这必将改变我们对诊断和治疗实践的机械理解，预测和防止向NP状态的转变。

DESCRIPTION (provided by applicant): Neuropathic pain (NP) is 'pain arising as a direct consequence of a lesion or disease affecting the somatosensory nervous system' that has certain features of a neuroimmune disorder. In response to peripheral nerve damage, T helper (Th) lymphocyte trafficking and induction of major histocompatibility complex (MHC) II (essential to the capture and antigen presentation for Th cell recognition) in the injured nerve and the segmental spinal cord are 'necessary and sufficient' for the development of NP. MHCII has been implicated in differential induction of NP but not inflammatory pain, but the antigens and the processes of their formation remain elusive. Our groundbreaking program centers on the organizing thesis that immunodominant antigens, formed in damaged myelinated nerves, are at the source of low-threshold mechanical hyperpathia. Touch is signaled by non-nociceptive large myelinated (Ab) afferents, which after injury begin interpreting light touch as devastating pain (mechanical allodynia). Our cutting-edge preliminary data have determined a fundamentally novel mechanism explaining this phenomenon: selective proteolysis of myelin basic protein (MBP) by matrix metalloproteinases (MMPs) releases the cryptic immunodominant epitopes, MBP84-104 and MBP69-86, normally sheltered from immunosurveillance. We clearly demonstrate that immunodominant MBP peptides produce robust allodynia upon injection into intact nerve. An intriguing finding is that endogenous immunodominant MBP69-86 epitope co-localizes with MHCII in antigen-presenting Schwann cells of the injured nerve, in close proximity to the action potential-generating nodes of Ranvier. Using state-of-the-art biochemical and molecular tools (e.g. Illumina BeadChip gene arrays, MALDI-TOF mass spectrometry, Ingenuity, NextBio, GeneGo and proprietary MMP substrate database) and fundamental (neuropathological, behavioral, systems) approaches, we will characterize the T cell-dependent and -independent actions of MBP residues in nociception (Aim 1). The molecular domains of myelinated fibers responsible for MBP action in T cell homing and locomotion, and also, the receptors for MBP residues in nerve will be determined (Aim 2). Importantly, we determined that voltage gated sodium channel expression and the spinal release of a glutamate receptor subunit depend on MMP activity. The concluding focus of the proposal are the novel catalytic and non- catalytic MMP targets in regulating T cell trafficking and integration into the spinal neuro-glial signaling network, facilitating maladaptive central plasticity and aberrant neuroimmune synaptogenesis (Aim 3). This multi- disciplinary program merges the leading expertise and utmost resources in biochemistry of metalloproteolysis (Alex Strongin, Ph.D., Sanford-Burnham Medical Research Inst.), neurobiology of MMPs in peripheral myelination and neuroinflammation (Veronica Shubayev, M.D., UCSD), and pain pathways (Tony Yaksh, Ph.D., UCSD) with innovative study designs, which we believe are bound to transform our mechanistic understanding diagnostic and therapeutic practices predicting and preventing the transition to the NP state.