TSC2 AND ERK SIGNALING IN MTOR-DEPENDENT REGENERATION AND NEUROPATHIC PAIN

描述（由申请人提供）：外周损伤后的急性疼痛是一种重要的适应性生理反应。疼痛有助于减少再次受伤，从而加快恢复。急性疼痛通常会在伤口愈合后消失。然而，在许多涉及周围神经损伤的情况下，急性疼痛转化为慢性疼痛，在伤口完全愈合后持续很长时间，并且可能严重衰弱。周围神经损伤引起再生反应，也可能导致长期致敏，导致慢性疼痛的发展。感觉神经元中的蛋白质合成是轴突再生以及损伤后致敏和疼痛的发展和维持所必需的。我们的目标是获得对控制蛋白质合成的信号通路的新见解，以响应神经损伤，从而制定刺激神经恢复而不同时促进慢性疼痛发展的策略。 进化上保守的哺乳动物雷帕霉素靶蛋白（mTOR），蛋白质合成机制的主要调节因子，以及细胞外信号调节激酶（ERK）通路与轴突再生和神经性疼痛的发展有关。通过在感觉神经元中有条件地删除负调节因子tuberin（TSC 2）来激活mTOR足以维持再生生长，但它是否影响神经损伤诱导的疼痛的发展尚不清楚。ERK 1/2信号传导是mTOR活性的主要上游调节因子。虽然致敏和再生轴突生长是已知需要蛋白质合成的两个过程，但尚未探索ERK 1/2信号在调节感觉神经元中蛋白质合成中的作用。此外，在迄今为止进行的研究中，没有区分ERK亚型，ERK 1或ERK 2，参与致敏和再生轴突生长。我们的初步数据显示ERK 2作为伤害感受器致敏的关键同种型和作为轴突再生的负调节剂。这一挑衅性的结果挑战了目前ERK 1/2信号在轴突再生中的作用模型。 我们建议在这里确定重叠的分子事件，调节轴突再生和神经损伤后从急性疼痛到慢性疼痛的转换。具体来说，我们将确定是否ERK信号调节蛋白质合成幼稚或受伤的初级感觉神经元。我们将确定哪种ERK亚型影响感觉神经元的再生能力，以及这种作用是否依赖于ERK介导的蛋白质合成调节。最后，我们将评估TSC 2，ERK 1和ERK 2缺失对神经损伤引起的疼痛的发展和维持的影响。总之，这些实验将测试TSC 2和ERK信号传导是否收敛到mTOR依赖性蛋白质翻译，以调节神经再生和损伤诱导的慢性疼痛的发展。 公共卫生相关性：周围神经损伤的恢复可能相对较好，但损伤也可能导致永久性神经功能缺损，包括神经再支配失败和慢性疼痛的发展。在这里，我们建议了解如何的分子机制，有助于促进轴突再生的相互作用的分子途径，导致从急性到慢性神经病理性疼痛周围神经损伤后的转换。最终的目标是确定方法，从而可以选择性地促进损伤后的轴突修复，而不同时促进慢性神经性疼痛的发展。

DESCRIPTION (provided by applicant): Acute pain in the wake of peripheral injury is an important, adaptive physiological response. Pain helps to reduce re-injury, thus hastening recovery. Acute pain normally resolves when the injury heals. However, in many cases involving damage to peripheral nerves, acute pain transforms into chronic pain, which persists long after wounds have fully healed, and can be severely debilitating. Injury to peripheral nerves elicits a regenerative response and may also lead to long-term sensitization that contributes to the development of chronic pain. Protein synthesis in sensory neurons is required for both axon regeneration and for the development and maintenance of sensitization and pain following injury. Our goal is to gain new insights into the signaling pathways controlling protein synthesis in response to nerve injury to develop strategies that stimulate neurological recovery without coincidently promoting the development of chronic pain. The evolutionarily conserved mammalian Target Of Rapamycin (mTOR), a master regulator of the protein synthesis machinery, and the extracellular signal-regulated kinase (ERK) pathway are linked to both axon regeneration and to the development of neuropathic pain. Activation of mTOR by conditional deletion of the negative regulator tuberin (TSC2) in sensory neurons is sufficient to sustain regenerative growth, but whether it affects the development of nerve injury-induced pain is not known. ERK1/2 signaling is a major upstream regulator or mTOR activity. Although sensitization and regenerative axon growth are two processes known to require protein synthesis, the role or ERK1/2 signaling in regulating protein synthesis in sensory neurons has not been explored. Furthermore, in the studies performed to date, no discrimination was made regarding which ERK isoform, ERK1 or ERK2, is involved in sensitization and regenerative axon growth. Our preliminary data reveal ERK2 as the critical isoform for nociceptor sensitization and as a negative regulator of axon regeneration. This provocative result challenges the current model of the role of ERK1/2 signaling in axon regeneration. We propose here to identify the overlapping molecular events that regulate axon regeneration and the conversion from acute to chronic pain after nerve injury. Specifically, we will determine if ERK signaling regulates protein synthesis in naive or injured primary sensory neurons. We will determine which ERK isoform affects the regenerative ability of sensory neurons and if this effect is dependent on ERK-mediated regulation of protein synthesis. Finally, we will evaluate the effect of TSC2, ERK1 and ERK2 deletion on the development and maintenance of nerve injury-induced pain. Together, these experiments will test whether TSC2 and ERK signaling converge to mTOR-dependent protein translation to regulate nerve regeneration and the development of injury-induced chronic pain. PUBLIC HEALTH RELEVANCE: Recovery from peripheral nerve injury can be relatively good, but the damage can also lead to permanent neurological deficits including failure of reinnervation and the development of chronic pain. Here we propose to understand how the molecular mechanisms that help to promote axonal regeneration interact with the molecular pathways that result in the conversion from acute to chronic neuropathic pain after peripheral nerve injury. The ultimate goal is to identify approaches whereby one can selectively promote axon repair after injury without simultaneously promoting the development of chronic neuropathic pain.