伏隔核中趋化因子CCL2调节神经病理性疼痛和抑郁的机制

The patients with neuropathic pain suffer from severe pain and negative affect including depression and anxiety. Recent studies have demonstrated that neuroinflammation in the central nervous system plays an important role in the development and maintenance of neuropathic pain and depression. Nucleus Accumbens (NAc) is impportant in mediating chronic pain and affect. By using Bio-Plex pro assay,we examined the expression of 8 different cytokines and chemokines in the NAc after spinal nerve ligation (SNL)-induced neuropathic pain, and found that CCL2 was the most upregulated mediator among them. However, whether and how CCL2 is involved in neuropathic pain and depression remain unclear. In this project, we will investigate the role and mechanism of CCL2 in neuropathic pain and depression-like behaviors by using behavioral, morphological, and electrophysiological approaches, including: (1) The expression and distribution of CCL2 and its major receptor CCR2 in the NAc in neuropathic pain. (2)The role of CCL2/CCR2 on SNL-induced neuropathic pain and depression. (3) The regulation and mechanism of CCR2 on NMDA current and AMPA current of medium spiny neurons (MSNs). (4) The role of CCR2 on the modulation of SNL-induced glutamategic synaptic long-term depression.This project will reveal a novel mechanism of CCL2 in neuropathic pain and depression and provide new strategy for the development of novel durgs targeting both pain and depression.

神经病理性疼痛患者不但遭受疼痛的折磨，还伴有抑郁焦虑等不良情绪。近年的研究提示CNS内的神经炎症反应在疼痛和抑郁的产生中有重要作用。伏隔核（NAc）是参与慢性疼痛和情绪调节的重要脑区。我们用悬液芯片检测了神经病理性疼痛小鼠NAc内8种炎症因子的表达变化，发现趋化因子CCL2的表达上调最明显。本项目将采用行为学、形态学、电生理等多种方法，研究NAc中CCL2在神经病理性疼痛以及伴随的抑郁样情绪中的作用，内容包括：（1）神经病理性疼痛小鼠NAc中CCL2和受体CCR2的表达变化和细胞分布；（2）CCL2/CCR2在SNL引起的痛觉过敏和抑郁样情绪中的作用；（3）CCR2对中型棘突神经元NMDA和AMPA受体通道电流的调节和机制；（4）CCR2对SNL引起的谷氨酸能突触长时程抑制变化的作用。本研究将揭示CCL2在NAc中介导神经病理性疼痛和抑郁情绪的机制，为开发新的镇痛且抗抑郁的药物提供思路。

神经病理性疼痛患者通常伴有抑郁情绪。以往的研究显示，趋化因子介导的炎症反应参与多种疾病，包括神经退行性疾病、抑郁和慢性疼痛。伏隔核（NAc）是介导疼痛感觉和抑郁的关键脑区。本项目通过悬液芯片检测了脊神经结扎诱导的神经病理性疼痛小鼠NAc中细胞因子和趋化因子的表达，筛选出差异表达的趋化因子CCL2。CCL2和受体CCR2在NAc中多巴胺D1受体（D1R）和D2受体（D2R）均有表达并在SNL后表达升高。NAc内注射慢病毒包装的CCR2 shRNA缓解了SNL诱导的痛觉过敏和抑郁样行为。与此相应，正常小鼠NAc内注射CCL2过表达慢病毒诱导了小鼠疼痛行为和抑郁样行为。通过电刺激前额叶皮层（mPFC）向NAc的传入纤维结合电生理全细胞膜片钳记录D1R阳性和D2R阳性的中棘突神经元（D1R-MSNs和D2R-MSNs），显示SNL增加了D1R-MSNs和D2R-MSNs中NMDA受体介导的电流，并被CCR2拮抗剂所抑制。CCR2 shRNA也降低了NMDAR介导的电流，该作用由NR2B亚单位介导。免疫双标显示NAc区NR2B与D1R和D2R均共标，SNL增加了NAc壳区NR2B磷酸化，且依赖于CCR2受体。SNL或CCL2孵育NAc脑片增加ERK磷酸化。MEK抑制剂抑制SNL或CCL2诱导的ERK激活。NAc内微量注射NR2B拮抗剂或MEK抑制剂减轻了SNL诱导的神经病理性疼痛和抑郁样行为。研究也显示，SNL造成NAc区MSNs中低频刺激诱导的LTD受损，该作用由CCR2介导（未发表结果）。本项目证明NAc壳区的CCL2/CCR2通过激活D1R-MSNs和D2R-MSNs中的ERK磷酸化NMDA受体亚单位NR2B，增加突触传递功能，从而促进SNL诱导的神经病理性疼痛和抑郁样行为，抑制NAc区CCL2/CCR2/ERK/NR2B信号通路可缓解神经病理性疼痛和抑郁。