Role of Microglia in Chronic Visceral Pain

描述(由申请人提供)：内脏器官过敏是包括肠易激综合征(IBS)在内的许多功能性消化疾病的主要特征，IBS是一种影响多达15%的美国人口的衰弱疾病，仍是一个令人头疼的临床挑战。尽管有大量的科学研究对其机制进行了研究，但内脏高敏感性(VH)在许多情况下会演变为一种抗拒常规治疗的慢性疾病。为了更好地了解慢性VH的机制，我们开发了一种动物模型，在该模型中，大鼠在没有明显的结肠炎的情况下表现出慢性VH的症状和神经元的过度兴奋。该模型是由新生大鼠的结肠刺激(CI)诱导的，并导致随后的症状学，一直持续到成年。利用脑梗塞大鼠，我们最近注意到一种新的宿主免疫反应，其特征是脊髓中的巨噬细胞样细胞被称为小胶质细胞。全身应用米诺环素或鞘内应用TNP-ATP阻断P2X4受体(由ATP激活的配体门控阳离子通道，并仅由过度活跃的小胶质细胞在脊髓表达)可抑制新生CI处理的成年大鼠的VH。我们的观察在两个层面上耐人寻味：1)它显示了新生儿结肠损伤后几个月(出生后第120天)小胶质细胞的激活，2)它首次揭示了小胶质细胞在内脏疼痛中发挥作用的证据。因此，在这项建议中，我们假设过度活跃的小胶质细胞有助于慢性VH和脊髓中神经元的过度兴奋。首先，我们建议通过识别选择高活性小胶质细胞的分子靶点来建立脑梗塞大鼠VH与高活性小胶质细胞表型之间的相关性，其次，我们建议通过使用米诺环素抑制小胶质细胞的激活或选择性地阻断磷酸化的p38和P2X4受体来逆转神经元的高兴奋性和慢性VH，这两个靶点在高活性小胶质细胞上表达。这些研究将有助于将药物干预的靶点扩大到脊髓内的非神经元部位，并提高生物疗法的止痛效力，同时将不良副作用降至最低。与公共卫生相关内脏疼痛是许多胃肠疾病的特征，如肠易激综合征。它可能是由内脏的急性炎症引起的，或者是先前损伤的残余；其后果可能会使患者及其家人虚弱，并使治疗临床医生感到沮丧。为了改善治疗方案并重新燃起许多顽固性内脏痛患者的希望，我们在这项应用中展示了通过阻断脊髓中新的细胞和分子靶点成功逆转慢性内脏痛大鼠疼痛行为的初步证据。我们建议的独特之处包括这些目标远离最初受伤地点的位置、跨学科的方法以及我们的调查团队的多样化专业知识。

DESCRIPTION (provided by applicant): Hypersensitivity of visceral organs is a main characteristic of numerous functional digestive disorders including irritable bowel syndrome (IBS): a debilitating disorder that affects up to 15% of the US population and one that continues to present a vexing clinical challenge. Despite the large body of scientific studies that have examined its mechanisms, visceral hypersensitivity (VH) evolves in many cases into a chronic condition recalcitrant to conventional treatment. To better understand the mechanisms of chronic VH, we developed an animal model in which rats exhibit symptoms of chronic VH and neuronal hyperexcitability in the absence of obvious colon inflammation. The model is induced by colon irritation (CI) in neonatal rats and results in a consequent symptomatology that carries into adulthood. Using rats with CI, we recently noted a novel host immune response, characterized by activation of macrophage-like cells in the spinal cord called microglia. Inhibiting microglial activation by systemic administration of minocycline or by intrathecal application of TNP- ATP to block P2X4 receptors (ligand-gated cation channels activated by ATP and expressed in the spinal cord exclusively by hyperactive microglia) reversed VH in adult rats treated with neonatal CI. Our observation is intriguing on two levels: 1) it demonstrates microglial activation several months following neonatal colonic insult (at postnatal day PND 120), and 2) it reveals, for the first time, evidence for a microglial role in visceral pain. Therefore, in this proposal we hypothesize that hyperactive microglia contribute to chronic VH and neuronal hyperexcitability in the spinal cord. First, we propose to establish a correlation between VH and a hyperactive phenotype of microglia in rats with CI by identifying molecular targets selective for hyperactive microglia, and second, we propose to reverse neuronal hyperexcitability and chronic VH by suppressing microglial activation using minocycline or by selectively blocking phosphorylated-p38 and P2X4 receptors, two targets specifically expressed on hyperactive microglia. These studies will help expand the targets of pharmacological intervention to non-neuronal sites within the spinal cord, and improve the analgesic potency of biologic therapies, while minimizing undesirable side effects. PUBLIC HEALTH RELEVANCE Visceral pain is a hallmark of many gastroenterological ailments such as irritable bowel syndrome. It may be caused by acute inflammation of an internal organ or be residual to previous injury; its consequences can be debilitating to the patients and to their families and frustrating to the treating clinician. To ameliorate treatment options and renew the hope of many patients with intractable visceral pain, we show in this application preliminary evidence for successful reversal of pain behavior in rats with chronic visceral pain by blocking novel cellular and molecular targets in the spinal cord. Unique features of our proposal include the remote location of these targets from the site of the initial injury, the interdisciplinary approach, and the diversified expertise of our team of investigators.