应用前脑特异性Rac1敲除小鼠探讨可卡因成瘾神经元结构可塑性变化机制

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. We previously demonstrated that repeated cocaine treatment induce structural remodeling of dendrites and spines in different brain area, including the nucleus accumbens (NAc) and caudoputamen (CPu). The Rho family of small GTPases, including Rac, RhoA and Cdc42, are important regulators of the actin rearrangement which play key roles in dendritic morphogenesis. Althrough many investigations illustrate the importance of Rho family GTPase in dendritic morphogenesis, it remains unclear whether they also function to regulate the dendritic reorganization induced by repeated cocaine treatment. Our recent data showed that Rac1 activation was reduced in the NAc but increased in the CPu following repeated cocaine treatment. Inhibition of Rac1 activity by a Rac1-specific chemical inhibitor NSC23766 or the dominant negative mutant of Rac1 (Rac1N17) attenuated the cocaine-induced increase in dendrites and spine density in the CPu. Moreover, NSC23766 reversed the increased number of asymmetric spine synapses in the CPu following chronic cocaine exposure. And Rac1N17 in the CPu attenuated the cocaine-induced conditioned place preference. Thus, Rac1 signaling is differentially regulated in the NAc and Cpu after repeated cocaine treatment, and induction of Rac1 activation in the Cpu is important for cocaine exposure-induced remodeling of dendritic spines and behavioral plasticity. These preliminary results lead us to hypothesize that Rac1 plays a far more complicated role in cocaine-induced dendritic remodeling. By using a complex methods, including the construction of forebrain specific Rac1 knockout mice, we aimed at answer the following questions: whether Rac1 GTPase signaling is involved in the structural plasticity after chronic cocaine treatment in different brain ares? And by what downstream effectors, the Rac1 GTPase 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 Rac1 GTPase 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变化。课题组前期发现可卡因诱导相关脑区神经元发生树突重塑。小GTP酶Rac1是Rho家族最受关注的分子之一。我们近期研究提示Rac1在可卡因成瘾中呈现出高度复杂性与多样性，但具体分子机制尚不清楚。为进一步探讨Rac1在可卡因成瘾中作用与分子机制，本研究应用Cre／loxP系统构建前脑特异性Rac1基因敲除小鼠，集中探讨可卡因作用下， Rac1是否参与前脑不同神经核区结构可塑性改变，并且在不同神经核发挥何种生物学效应；进一步，Rac1通过何种信号分子发挥其生物学效应。我们提出假说：可卡因通过激活或者抑制相关神经核区Rac1，进一步激活或者抑制相关下游信号分子诱导神经元结构可塑性改变，而可卡因成瘾中Rac1在不同神经核区发挥不同生物学效应。上述问题的解答为进一步阐明Rac1信号通路在可卡因成瘾中的机制，寻找新的治疗药物成瘾的靶点和药物打下基础。

针对可卡因成瘾，运用前脑特异性基因敲除小鼠、慢病毒转染、免疫组化等综合性手段，系统地研究了神经元结构可塑性变化的信号分子机制，集中探讨了可卡因作用下，Rac1信号通路对可卡因诱导的神经元树突重塑的调控，发现Rac1信号通路在可卡因诱导的神经元树突重塑、行为学变化中发挥重要的调控作用；进一步的细胞学研究发现D1多巴胺受体通过Rac1与RhoA调节PFC神经元树突重构；与此同时，电镜超微结构发现D1和D3受体在可卡因诱导的纹状体超微突触连接结构的重塑中起到相反的调控作用。进一步我们针对帕金森病神经元结构重塑异常，探讨了相关治疗策略，发现新型水凝胶联合活化素B对帕金森病具有很好的治疗作用。上述研究发表在Neurobiology of Disease，Molecular Neurobiology，Addiction Biology，Biomaterials等杂志。