MrgprC, A New Target for the Treatment of Neuropathic Pain

描述（由申请人提供）：神经性疼痛的治疗继续挑战临床医生，部分原因是现有治疗的疗效有限，缺乏疼痛特异性药物靶点。MAS相关的G蛋白偶联受体（Mrs）代表了一个新的G蛋白偶联受体（GPCR）家族，其特异性表达于小直径感觉神经元。我们的初步工作表明，一些MrgprC，特别是MrgprC，可能构成一个新的持续性疼痛的抑制系统。鞘内施用肽（BAM 8-22）和小分子非肽MrgprC激动剂（化合物58）均减弱大鼠和野生型小鼠中的神经性疼痛。然而，BAM 8-22在Mrpgr突变小鼠中失去了对神经性疼痛的镇痛作用。利用互补的行为，电生理和分子生物学方法，我们的目标是评估MrgprC作为一种新的靶点在治疗神经性疼痛的治疗价值，重要的是，检查MrgprC介导的疼痛抑制的细胞和分子机制。具体地，目的1将详细表征鞘内施用两种MrgprC激动剂对L5脊神经损伤后大鼠的触觉异常性疼痛、机械性痛觉过敏、热痛觉过敏和自发性疼痛的影响。然后，我们将检查MrgprC siRNA处理是否降低BAM 8-22的镇痛功效。我们还将研究早期干预BAM 8-22是否能减轻神经性疼痛，增强神经性疼痛中的吗啡镇痛，并预防大鼠术后疼痛。在目标2中，我们将采用体外电生理和分子生物学方法研究背根神经节（DRG）神经元中MrgprC介导的疼痛抑制的细胞和分子机制。我们将使用功能丧失和功能获得策略来确定MrgprC激活是否减弱DRG细胞中的高压门控（HVA）钙电流。我们将进一步确定神经损伤是否上调未损伤DRG神经元中MrgprC的表达和功能。在目标3中，我们将研究MrgprC介导的中枢神经系统疼痛抑制的神经生理学基础。我们将进行体内电生理学研究，以确定MrgprC激动剂是否减弱背角神经元对重复性有害输入的敏感性，并使神经损伤诱导的已建立的神经元过度兴奋正常化。我们将研究神经损伤是否会改变BAM 22（一种内源性Mrgpr配体）在脊髓和DRG中的表达。我们推测MrgprC激动剂在神经病理性疼痛状态期间可能起抗痛觉过敏剂的作用。由于MrgprC是人类MrgprX 1的直系同源物，我们的研究结果可能对开发新的药物先导物和基于机制的治疗策略具有重要意义，用于管理神经性疼痛，副作用很少。 公共卫生相关性：我们的初步研究表明，激活的一个重要成员的马斯相关的G蛋白偶联受体，MrgprC，可能会抑制神经病理性疼痛。在这个提议中，我们将使用互补的动物行为，电生理和分子生物学方法，以更好地评估MrgprC激动剂治疗神经性疼痛的治疗效用，并了解药物作用的细胞和分子机制。目前的研究可能会发现一个新的疼痛特异性治疗靶点，并导致一个新的机制为基础的方法来治疗神经性疼痛。

DESCRIPTION (provided by applicant): The treatment of neuropathic pain continues to challenge clinicians, in part because of limited efficacy of available treatments and a lack of pain-specific drug targets. Mas-related G-protein-coupled receptors (Mrgprs) represent a novel family of G-protein-coupled receptors (GPCRs) that are specifically expressed in small-diameter sensory neurons. Our preliminary work suggests that some Mrgprs, in particular MrgprC, may constitute a novel inhibitory system for persistent pain. Intrathecal administration of a peptide (BAM 8-22) and a small molecule non-peptide MrgprC agonist (compound 58) both attenuated neuropathic pain in rats and in wild type mice. However, BAM 8-22 lost this analgesic action on neuropathic pain in Mrpgr mutant mice. Using complementary behavioral, electrophysiological, and molecular biological approaches, we aim to assess the therapeutic value of MrgprC as a novel target in the treatment of neuropathic pain, and importantly, to examine the cellular and molecular mechanisms underlying MrgprC-mediated pain inhibition. Specifically, Aim 1 will characterize in detail the effects of intrathecal administration of the two MrgprC agonists on tactile allodynia, mechanical hyperalgesia, heat hyperalgesia and spontaneous pain in rats after an L5 spinal nerve injury. We will then examine whether MrgprC siRNA treatment reduces the analgesic efficacy of BAM 8-22. We will also investigate whether an early intervention with BAM 8-22 prolongs attenuation of neuropathic pain, enhances morphine analgesia in neuropathic pain, and prevents postsurgical pain in rats. In Aim 2, we will employ in vitro electrophysiological and molecular biological approaches to study the cellular and molecular mechanisms underlying MrgprC-mediated pain inhibition in the dorsal root ganglion (DRG) neurons. We will use both loss-of-function and gain-of-function strategies to determine if MrgprC activation attenuates high-voltage-gated (HVA) calcium current in DRG cells. We will further determine whether nerve injury up regulates the expression and function of MrgprC in uninjured DRG neurons. In Aim 3 we will study the neurophysiologic basis for MrgprC-mediated pain inhibition in the central nervous system. We will conduct in vivo electrophysiological studies to determine if MrgprC agonist attenuates dorsal horn neuronal sensitization to repetitive noxious inputs and normalizes the established neuronal hyperexcitability induced by the nerve injury. We will investigate whether nerve injury alters the expression of BAM 22, an endogenous Mrgpr ligand, in spinal cord and in DRGs. We postulate that MrgprC agonists may function as anti-hyperalgesic agents during the neuropathic pain state. Because MrgprC is an ortholog to the human MrgprX1, our findings may have important implications for developing new drug leads and mechanism-based treatment strategies for managing neuropathic pain with few side effects. PUBLIC HEALTH RELEVANCE: Our preliminary studies suggest that activation of an important member of Mas-related G protein-coupled receptors, MrgprC, may inhibit neuropathic pain. In this proposal, we will use complementary animal behavioral, electrophysiological, and molecular biological approaches to better assess the therapeutic utility of MrgprC agonist for the treatment of neuropathic pain and to understand the cellular and molecular mechanisms underlying the drug action. Current study may identify a new pain-specific treatment target and lead to a novel mechanism-based approach to the treatment of neuropathic pain.