Zhao Peng, Waxman Stephen G, Hains Bryan C
Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
J Neurosci. 2007 Feb 28;27(9):2357-68. doi: 10.1523/JNEUROSCI.0138-07.2007.
Many patients with traumatic spinal cord injury (SCI) report pain that persists indefinitely and is resistant to available therapeutic approaches. We recently showed that microglia become activated after experimental SCI and dynamically maintain hyperresponsiveness of spinal cord nociceptive neurons and pain-related behaviors. Mechanisms of signaling between microglia and neurons that help to maintain abnormal pain processing are unknown. In this study, adult male Sprague Dawley rats underwent T9 spinal cord contusion injury. Four weeks after injury when lumbar dorsal horn multireceptive neurons became hyperresponsive and when behavioral nociceptive thresholds to mechanical and thermal stimuli were decreased, we tested the hypothesis that prostaglandin E2 (PGE2) contributes to signaling between microglia and neurons. Immunohistochemical data showed specific localization of phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2), an upstream regulator of PGE2 release, to microglial cells and a neuronal localization of the PGE2 receptor E-prostanoid 2 (EP2). Enzyme immunoassay analysis showed that PGE2 release was dependent on microglial activation and ERK1/2 phosphorylation. Pharmacological antagonism of PGE2 release was achieved with the mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one] and the microglial inhibitor minocycline. Cyclooxygenase-2 expression in microglia was similarly reduced by MEK1/2 inhibition. PD98059 and EP2 receptor blockade with AH6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) resulted in a decrease in hyperresponsiveness of dorsal horn neurons and partial restoration of behavioral nociceptive thresholds. Selective targeting of dorsal horn microglia with the Mac-1-SAP immunotoxin, a chemical conjugate of mouse monoclonal antibody to CD11b and the ribosome-inactivating protein saporin, resulted in reduced microglia staining, reduction in PGE2 levels, and reversed pain-related behaviors [corrected]. On the basis of these observations, we propose a PGE2-dependent, ERK1/2-regulated microglia-neuron signaling pathway that mediates the microglial component of pain maintenance after injury to the spinal cord.
许多创伤性脊髓损伤（SCI）患者报告称疼痛持续存在且对现有治疗方法无效。我们最近发现，实验性脊髓损伤后小胶质细胞被激活，并动态维持脊髓伤害性神经元的高反应性和疼痛相关行为。小胶质细胞与神经元之间有助于维持异常疼痛处理的信号传导机制尚不清楚。在本研究中，成年雄性Sprague Dawley大鼠接受T9脊髓挫伤损伤。损伤后四周，当腰段背角多感受神经元变得高反应性，且对机械和热刺激的行为伤害性阈值降低时，我们测试了前列腺素E2（PGE2）参与小胶质细胞与神经元之间信号传导的假说。免疫组织化学数据显示，PGE2释放的上游调节因子磷酸化细胞外信号调节激酶1/2（pERK1/2）特异性定位于小胶质细胞，而PGE2受体E-前列腺素2（EP2）定位于神经元。酶免疫分析表明，PGE2释放依赖于小胶质细胞激活和ERK1/2磷酸化。使用丝裂原活化蛋白激酶激酶1/2（MEK1/2）抑制剂PD98059 [2-(2-氨基-3-甲氧基苯基)-4H-1-苯并吡喃-4-酮]和小胶质细胞抑制剂米诺环素可实现对PGE2释放的药理学拮抗作用。MEK1/2抑制同样降低了小胶质细胞中环氧合酶-2的表达。PD98059和用AH6809（6-异丙氧基-9-氧代氧杂蒽-2-羧酸）阻断EP2受体导致背角神经元高反应性降低和行为伤害性阈值部分恢复。用Mac-1-SAP免疫毒素选择性靶向背角小胶质细胞，Mac-1-SAP是小鼠抗CD11b单克隆抗体与核糖体失活蛋白皂草素的化学偶联物，可导致小胶质细胞染色减少、PGE2水平降低并逆转疼痛相关行为[校正后]。基于这些观察结果，我们提出了一条依赖PGE2、由ERK1/2调节的小胶质细胞-神经元信号通路，该通路介导脊髓损伤后疼痛维持的小胶质细胞成分。
