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方法的疗效有限，缺乏疼痛特异性药物靶点。mass相关的g蛋白偶联受体（Mrgprs）是一种新的g蛋白偶联受体（gpcr）家族，在小直径感觉神经元中特异性表达。我们的初步工作表明，一些Mrgprs，特别是MrgprC，可能构成一种新的抑制持续疼痛的系统。鞘内注射一种多肽（BAM 8-22）和一种小分子非多肽MrgprC激动剂（化合物58）均可减轻大鼠和野生型小鼠的神经性疼痛。然而，在Mrpgr突变小鼠中，BAM 8-22失去了对神经性疼痛的镇痛作用。利用行为学、电生理学和分子生物学的互补方法，我们旨在评估MrgprC作为神经性疼痛治疗的新靶点的治疗价值，更重要的是，研究MrgprC介导的疼痛抑制的细胞和分子机制。具体来说，Aim 1将详细描述鞘内给药两种MrgprC激动剂对L5脊髓神经损伤后大鼠触觉异常性痛、机械性痛觉过敏、热痛觉过敏和自发性疼痛的影响。然后我们将检验MrgprC siRNA处理是否会降低BAM 8-22的镇痛效果。我们还将研究早期干预BAM 8-22是否延长神经性疼痛的衰减，增强神经性疼痛的吗啡镇痛，并预防大鼠术后疼痛。在Aim 2中，我们将采用体外电生理学和分子生物学方法研究mrgprc介导的背根神经节（DRG）神经元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激活是否会减弱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Aim 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研究，以确定MrgprC激动剂是否减弱背角神经元对重复有害输入的敏感性，并使神经损伤引起的神经过度兴奋性正常化。我们将研究神经损伤是否会改变脊髓和DRGs中内源性Mrgpr配体BAM 22的表达。我们假设MrgprC激动剂可能在神经性疼痛状态下起抗痛觉过敏作用。由于MrgprC是人类MrgprX1的同源物，我们的研究结果可能对开发新的药物先导和基于机制的治疗策略具有重要意义，可以治疗神经性疼痛，副作用少。

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.