M2受体在东莨菪碱抗抑郁效应中的作用及机制研究

Currently, antidepressants are the mainstay in the treatment for major depressive disorder (MDD), but they require several weeks of dosing for full treatment efficacy to emerge efficacy. Clinical studies demonstrate that scopolamine, a non-selective muscarinic acetylcholine receptor (M receptor) antagonist, produces rapid therapeutic effects in depressed patients. However, which one of the five M receptor subtypes mediates its antidepressant efficacy has not been well understood. Previous studies suggest M2 receptor may be a potential target, and the actions of scopolamine involve rapid activation of mTORC1 (mechanistic target of rapamycin complex 1) signaling. Our preliminary work found that a selective M2 receptor antagonist could improve depressive-like behavior in depressed rats and increase mTORC1 signaling. Accordingly, we hypothesize that scopolamine exerts antidepressant efficacy through blockade of M2 receptor and subsequent activation of mTORC1 signaling. Here, we will provide clinical evidence by examining the expression of human peripheral blood lymphocyte M2 receptor and analyzing its correlation with MDD and scopolamine's efficacy. With selective M2 receptor agonists/antagonist administration, as well as M2 receptor knockdown and over-expression in a rat model of depression, the modulatory role of M2 receptor and its regulated mTORC1 signal transduction in scopolamine's antidepressant efficacy will be discussed. This research could contribute to the development of rapid-acting antidepressants for MDD.

当前抑郁症（MDD）的治疗药物多起效缓慢，近来证实毒蕈碱型乙酰胆碱受体（M受体）非选择性拮抗剂东莨菪碱具有快速抗抑郁效应，但其作用靶点和机理并不清楚。已有研究提示M2受体亚型及mTORC1信号通路可能参与了东莨菪碱的抗抑郁过程。我们前期也发现，拮抗M2受体可有效缓解抑郁模型大鼠的行为学症状，并激活内侧前额叶皮层的mTORC1信号通路。因此我们认为东莨菪碱通过阻断内侧前额叶皮层的M2受体来增强谷氨酸能传导，激活mTORC1信号并促进突触发生，而发挥抗抑郁作用。本项目拟借助已开展的东莨菪碱治疗MDD的临床试验，对人外周血的M2受体含量进行检测，分析其与MDD发病以及东莨菪碱抗抑郁疗效的相关性；利用正常和抑郁模型大鼠，通过对M2受体功能（激动剂/拮抗剂）和基因表达上（慢病毒敲减）的干预，探讨M2受体在东莨菪碱抗抑郁中的作用及其对mTORC1信号的调控机制，从而为快速抗抑郁药的研发提供特异靶点。

当前抑郁症（MDD）的治疗药物多起效缓慢，近来证实毒蕈碱型乙酰胆碱受体（M受体）非选择性拮抗剂东莨菪碱具有快速抗抑郁效应，但其作用靶点和机理并不清楚。已有研究提示M2受体亚型及mTORC1信号通路可能参与了东莨菪碱的抗抑郁过程。我们前期也发现，拮抗M2受体可有效缓解抑郁模型大鼠的行为学症状，并激活内侧前额叶皮层的mTORC1信号通路。因此我们认为东莨菪碱通过阻断内侧前额叶皮层的M2受体来增强谷氨酸能传导，激活mTORC1信号并促进突触发生，而发挥抗抑郁作用。本项目一方面开展了为期4周的随机、双盲、安慰剂对照的东莨菪碱治疗抑郁症的临床研究，拟在确定东莨菪碱抗抑郁疗效的同时，借助血液样本探讨外周血M2受体和抑郁症发病和东莨菪碱抗抑郁疗效的相关性。共纳入了66名抑郁症患者，在口服抗抑郁药艾司西酞普兰的同时，连续三天分别肌注生理盐水以及高、低两种剂量东莨菪碱。研究结果显示，与安慰剂（生理盐水）相比，高剂量及低剂量的东莨菪碱附加草酸艾司西酞普兰均未显示出更快的抗抑郁起效作用，其原因可能在于肌注的方式东莨菪碱无法达到有效血药浓度。另一方面，基于动物实验，我们发现：（1）采用GABA-A受体激动剂muscimol沉默大鼠mPFC神经元后，可以阻断东莨菪碱的抗抑郁作用，提示mPFC是东莨菪碱发挥抗抑郁效应的主要脑区；（2）向大鼠侧脑室注射M2受体选择性阻断剂MCT也具有明显的抗抑郁作用。通过AAV-CHRM2敲减双侧mPFC的M2受体表达，相对空载体组，M2敲减组的抑郁样行为明显减少，再给予东莨菪碱也不再有明显的抗抑郁作用，提示M2受体是介导东莨菪碱抗抑郁作用的重要靶点；（3）MCT注射后，mPFC的BDNF表达明显增加，mTORC1活性显著增强。提前向侧脑室注射mTORC1抑制剂rapamycin 可以阻断MCT的抗抑郁效应，证明BDNF-mTORC1信号通路可能是MCT抗抑郁的下游机制。本研究的发现可为将来新型快速有效抗抑郁药的研发提供理论基础。