纹状体mTORC2信号通路对可卡因成瘾神经元结构重塑的调控

Drug addiction is a long-lasting brain disease. Repeated exposure to cocaine can induce persistent alterations in the brain. The structural remodeling of dendrites and spines is thought to play a critical role in cocaine addiction. Such neuroadaptations may contribute to the changes in synaptic plasticity underlying cocaine addiction. We previously demonstrated that repeated cocaine treatment induce structural remodeling of dendrites and spines in the nucleus accumbens (NAc) and caudoputamen (CPu) and several signaling pathways, such as Rac1, are critically involved in cocaine-induced dendritic remodeling. The Mechanistic target of rapamycin (mTOR) is a protein serine/threonine kinase that crucially control a variety of biological processes. mTOR is found in two functionally distinct complexes, mTORC1 and mTORC2. Dysregulation of mTOR signaling is associated with neurodevelopmental and neuropsychiatric disorders. Althrough many investigations illustrate the importance of mTOR signaling in drug addiction, it remains unclear whether they also function to regulate the dendritic reorganization induced by repeated cocaine treatment.. Our recent data showed that mTORC2 is activated after cocaine treatment, including the increase of the expression of Rictor, a key molecular of mTORC2,and Akt phosphorylation. Meanwhile, we found that A-443654, a small molecule which increases mTORC2-mediated phosphorylation of Akt at Ser473 (independently of mTORC1), promoted cocaine-induced dendritic remodeling. Moreover, imunocolocalization analysis showed that Rictor and Rac1 are colocalized in the MSNs in striatum, and immunoprecipitation analysis showed that Tiam1 associated with Rictor in striatum. These preliminary results lead us to hypothesize that mTORC2 signaling might play important role in cocaine-induced dendritic remodeling. By using a complex methods, including the construction of forebrain and striatum specific Rictor knockout mice, we aimed at answer the following questions: whether mTORC2 signaling is involved in the structural plasticity after chronic cocaine treatment in striatum? And by what downstream effectors, the mTORC2 signaling regulate dendritic remodeling and actin reorganization after chronic cocaine treatment? The answers to these questions will provide further insight into the molecular and cellular mechanism of drug addiction and may provide new leads to the development of novel therapeutics targeting mTOR signaling.

可卡因成瘾的核心问题是中枢神经系统产生结构可塑性改变。mTOR是丝氨酸/苏氨酸激酶，在体内以mTORC1及mTORC2 复合体形式存在。课题组前期发现小GTP酶Rac1在可卡因成瘾神经元结构重塑中起重要作用。我们近期研究提示mTORC2核心分子Rictor可能通过Rac1在可卡因成瘾神经元结构重塑中发挥作用，但具体机制尚不清楚。本研究针对mTORC2通路，应用Cre／loxP系统构建前脑与纹状体特异性Rictor基因敲除小鼠，探讨可卡因作用下，mTORC2通路是否调控神经元结构重塑及成瘾相关行为学，并且mTORC2通路通过何种下游信号分子，特别是否通过Rac1，发挥生物学效应。我们假设：可卡因通过激活纹状体mTORC2通路，进一步激活相关下游信号分子，如Rac1，诱导神经元结构重塑。上述问题的解答为进一步阐明mTORC2通路在可卡因成瘾中的作用，为该领域基础研究和治疗提供新的理论与方法。

药物成瘾的核心问题是中枢神经系统产生神经元结构可塑性改变。可卡因成瘾导致NAc区神经元结构可塑性及相关行为改变。mTOR是丝氨酸/苏氨酸激酶，在体内以mTORC1及mTORC2 复合体形式存在。近年来，mTORC1信号通路在毒品成瘾中的作用引人关注，然而mTORC2在药物成瘾中的作用远不明了。我们发现在7天可卡因成瘾模型中，mTORC2关键组分Rictor表达下降，其下游关键效应分子AKt的Ser473位点磷酸化水平下降，提示在可卡因慢性成瘾模型中，NAc区mTORC2信号通路被抑制。我们构建了Rictor过表达病毒及AKt S473持续激活病毒，特异性激活小鼠NAc脑区的mTORC2信号通路，发现可卡因所导致的神经元树突棘改变及小鼠行为学改变得到恢复。课题组前期发现小GTP酶Rac1在可卡因成瘾神经元结构重塑中起重要作用。我们通过激活mTORC2信号通路，发现可卡因成瘾所导致的Rac1信号下调得到恢复，因此推测mTORC2核心分子Rictor可能通过Rac1在可卡因成瘾神经元结构重塑中发挥作用。此外我们发现在NAc特异性敲除D1受体的小鼠中，可卡因所导致的mTORC2信号通路下调得到恢复，而在D2受体敲除的小鼠则没有改变。综上所述，我们的研究提示可卡因可能通过D1受体调控mTORC2通路，作用于下游Rac1信号通路，从而诱导神经元结构重塑及成瘾相关行为学改变。本研究进一步阐明mTORC2通路在可卡因成瘾中的作用，为该领域基础研究和治疗提供新的理论与方法。