脑基底核环路对灵长类情感认知功能的影响

Cognition and emotion are controlled and regulated by the complex interactions of neuronal cells in different brain regions. The basal ganglia are situated at the base of the forebrain and are strongly connected with the cerebral cortex, thalamus and other brain areas. The basal ganglia are associated with a variety of functions, including voluntary motor control, procedural learning relating to routine behaviors, cognitive, and emotional functions. The main components of the basal ganglia are the striatum (caudate nucleus and putamen), the globus pallidus, the substantia nigra, the nucleus accumbens, and the subthalamic nucleus. The largest component, the striatum, receives input from the cortex and substantia nigra and many other brain areas but sends output only to other components of the basal ganglia. Parkinson disease affects dopaminergic neurons in the substnatia nigra to influence the function of striatum. Huntington disease affects medium spiny neurons in the striatum as well as cortical neurons. Although both diseases are characterized as movement disorders, the early symptoms of these diseases are cognitive and emotional abnormalities. Both diseases also share the common pathological feature, which is the accumulation of misfolded proteins in axons of neurons. Also, both diseases are age-dependent and occur in the middle ages (40-60 years). All these suggest that the basal ganglia function involving the cortex-striatum and substantia-striatum connections may be impaired by aging-related toxicity of misfolded proteins in axonal terminals in the striatum, and this impairment may lead to cognition and emotion dysfunction during the early disease stage. We have established a non-human primate model of such an early disease model by expressing Parkinson disease protein, alpha-synuclein A53T, in the substantia nigra. We found that aging increases the accumulation of the disease proteins in axonal terminals, which causes axonal degeneration. Using this monkey model, we will investigate how aging and misfolded proteins for Parkinson and Huntington diseases, when expressed in the substantia nigra or the cortex, affect the striatal dopamine level, axonal structure, synaptic protein levels, and learning or emotion of monkeys. These studies aim to provide insight into how aging and misfolded proteins affect the cortex-striatum and substantia nigra-striatum pathways to impair cognitive and emotional function in primates.

基底核（Basal ganglia，或称为基底神经节）是大脑深部一系列神经核团组成的功能整体。近来的研究发现它还参与记忆和情感等高级认知功能。基底核的病变可导致多种运动和认知障碍，包括帕金森氏症和亨廷顿氏症等。这两种病的早期症状表现为认知功能减退，情感改变，并与脑老化有关。然而老龄化和神经退行性疾病如何改变人脑基底核环路对情感认知功能的调节仍然不清楚，并且多数研究基底核环路的结果主要从低等动物脑部中获得。本项目利用灵长类（猕猴）研究脑老化和神经退行性疾病蛋白对基底核中黑质－纹状体和大脑皮层－纹状体通路的影响。利用病毒载体将带有导致帕金森病与亨廷顿病的变异基因选择性地表达在猕猴黑质和大脑皮层，然后检查纹状体中神经元突触的蛋白表达，多巴胺递质水平、神经细胞突触结构变化以及猴情绪与认知功能。本项目旨在揭示神经退行性疾病如何影响基底核环路功能并为治疗与防治这一类重大疾病提供重要的理论依据。

本项目利用非人类灵长类（猕猴）研究脑老化和神经退行性疾病蛋白对基底核的影响。基底核在神经退行型疾病（帕金森病， 亨延顿病中）中容易受损， 并表现随衰老出现的变异蛋白沉淀与累积。我们将不同年龄的猕猴脑纹状体中的突触小体分离出来，进行蛋白质组学分析。我们发现随衰老过程的发生，泛素蛋白酶体的活性逐渐降低，而泛素连接酶UBE2N的蛋白表达水平在突触小体中有所升高。同时，猕猴组织的突触小体随衰老的发生其泛素化水平也逐渐升高，并且这一现象能够被UBE2N的去除而阻断。为了研究帕金森病突变α-synuclein蛋白在猕猴脑中的累积与老龄化的关系，我们构建了可以表达突变α-synuclein (A53T)的病毒载体。 将该病毒载体注射入猕猴脑黑质部位后， 突变的α-synuclein (A53T)蛋白能够在神经元中形成类似于帕金森病人脑中出现的路易氏小体聚集。 我们将帕金森病致病基因alpha-synuclein注射到不同年龄的猕猴中脑黑质，发现致病蛋白在老年猴中累积明显, 造成的轴突损伤更严重。我们还用病毒载体表达更具毒性的ALS致病蛋白TDP-43在猴脑黑质区，我们发现致病蛋白能严重损伤神经细胞,并造成肢体活动障碍. 由于中脑黑质中的多巴胺神经细胞投射纹状体, 我们将进一步研究基底核神经环路中纹状体神经细胞是如何在此动物模型中受到损伤。以上结果表明，突变蛋白能够造成猴脑组织神经元的病变，且老龄化能够促进突变蛋白在神经元中的毒性作用， 从而影响纹状体中神经环路的功能及认知与情感功能。鉴于灵长类动物与其它种属在生理与病理上有着巨大的差别，本项目的结果对了解脑基底核环路功能与相关的神经退行性疾病的机制以及它们的防治和治疗有着重大的指导意义。