The Role of Cell-specific TLR-4 Signaling in Developing Chronic Pain

 描述(由申请人提供)：受疼痛影响的美国人比心脏病、中风和癌症加起来还要多。特别是，神经病理性疼痛是这些疼痛发生率的很大一部分原因。神经病理性疼痛发生的机制备受追捧，因为目前的治疗方法不能缓解一半的患者。神经元损伤或刺激导致的适应不良的超兴奋性在神经病理性疼痛的发展中起着巨大的作用，识别能够调节神经元活动的治疗靶点将是可行的治疗方案。有趣的是，TLR4在外周感觉神经元上表达，这表明神经元直接被TLR4激动剂(内毒素、HMGB1、游离脂肪酸等)激活。在导致神经病理性疼痛的周围神经系统可塑性中发挥积极作用。这项研究将集中在周围神经系统，利用基因工具来阐明DRG伤害性神经元与巨噬细胞/小胶质细胞TLR4在神经病理性疼痛发生中的功能作用。重要的是，与神经元中TLR4激活有关的下游信号事件在很大程度上是未知的，并提供了额外的一层治疗焦点。普赖斯实验室的证据表明，通过真核细胞翻译起始因子-4E(EIF4E)的翻译控制信号机制在神经病理性疼痛的发生和维持中是必需的；其他研究小组最近表明，TLR4可能激活调节eIF4E的MAPK途径。这一建议的一个关键特征是，我们将首次研究TLR4在体内特定细胞群中的生理相关性，以确定伤害性受体或巨噬细胞/小胶质细胞TLR4是否对神经病理性疼痛的发生是必要的和/或充分的。我们将利用cre-lox转基因系统，利用新开发的小鼠对TLR4进行细胞特异性消融或重新激活，并继续开发零再激活小鼠(Joel Elmquist)。我们将这些动物与Nav1.8-cre(感觉神经元)和LysM-cre(巨噬细胞/小胶质细胞)动物杂交，以评估这些特定群体在发展神经病理性疼痛方面的作用。我们的研究旨在了解驱动慢性疼痛的机制，并将这些分子洞察力推向缓解疼痛的新治疗策略。为了实现这些目标，我们提出了以下具体目标：1)确定在指导阶段细胞特异性TLR4-eIF4E信号在神经病理性疼痛发生中的作用；2)在第二阶段确定伤害性感受器和小胶质细胞中TLR4的表达在神经病理性疼痛中的作用。这些研究有望通过靶向伤害性感受器和小胶质细胞TLR4信号、翻译控制和表型转换来为治疗和预防慢性疼痛提供新的治疗途径。西奥多·普莱斯博士和乔尔·埃尔姆奎斯特博士分别在慢性疼痛发展和小鼠遗传学方面具有互补的专业知识，是这个项目的理想导师。

 DESCRIPTION (provided by applicant): More Americans are affected by pain than heart disease, stroke, and cancer combined. In particular, neuropathic pain is responsible for a large percentage of these incidences of pain. The mechanisms that underlay the development of neuropathic pain are highly sought after, because current therapeutics fails to offer relief in ove half of patients. Neuronal injury or stimulation leading to maladaptive hyperexcitability appears to play a huge role in the development of neuropathic pain and the identification of therapeutic targets that can modulate neuronal action will be important as viable treatment options. Interestingly, TLR4 has been shown to be expressed on peripheral sensory neurons, which suggests neurons are activated directly by TLR4 agonists (LPS, HMGB1, free fatty acids etc.) to play an active role in peripheral nervous system plasticity leading to neuropathic pain. This study will focus on the peripheral nervous system bringing genetic tools to clarify the functional role of DRG nociceptive neurons versus macrophage/microglia TLR4 in developing neuropathic pain. Importantly, downstream signaling events connected to TLR4 activation in neurons are largely unknown and provide an additional layer of therapeutic focus. The Price lab has generated evidence that translation control signaling mechanisms via the eukaryotic translation initiation factor-4E (eIF4E) are required for the development and maintenance of neuropathic pain; and other groups have recently shown that TLR4 may activate the MAPK pathway that modulates eIF4E. A key feature of this proposal is that we will, for the first time, study the physiological relevance of TLR4 in specific cell populations in vivo to determine whether nociceptor or macrophage/microglia TLR4 is necessary and/or sufficient for the development of neuropathic pain. We will take advantage of the cre-lox transgenic system offering cell-specific ablation or reactivation of TLR4 using newly developed floxed mice and continued development of null-reactivatable mice (Joel Elmquist). We will cross these animals with Nav1.8-cre (sensory neuron) and LysM-cre (macrophage/microglia) animals to assess these particular populations in developing neuropathic pain. Our research is aimed at understanding mechanisms driving chronic pain and moving these molecular insights toward new therapeutic strategies for pain alleviation. To accomplish these goals we propose the following specific aims: 1) Determine the role of cell-specific TLR4-eIF4E signaling to develop neuropathic pain during the mentored phase, and 2) Determine the contribution of TLR4 expression in nociceptors vs. microglia to neuropathic pain in phase II. These studies will hopefully suggest novel therapeutic avenues for the treatment and prevention of chronic pain by targeting nociceptor and microglial TLR4 signaling, translational control, and phenotype switching. Drs. Theodore Price and Joel Elmquist are ideally suited as mentors for this project with their complementary expertise in chronic pain development and mouse genetics, respectively.