Functions of alpha-Synuclein in Neurotransmitter Release

描述（由申请人提供）：帕金森病（PD）是第二常见的神经退行性疾病，影响1.8%的65岁以上人群。帕金森病的一个临床标志是脑神经元内蛋白质包涵体的形成，称为路易体。路易体的主要成分是α-突触核蛋白，发现其在家族性PD和散发性PD的神经元中积累。PD患者的治疗策略并不十分成功，因为临床症状发生在神经元功能受损到难以挽救的程度的阶段。治疗策略的改进取决于更好地理解PD的病理生理发展，包括由α-突触核蛋白积聚诱导的症状前神经元功能障碍。先前已发现α-突触核蛋白水平升高会损害症状性PD前的神经递质释放。然而，造成这种损害的机制知之甚少。由于α-突触核蛋白主要表达于神经末梢，这些神经末梢通常太小而无法使用高灵敏度的电生理方法，因此先前的研究无法直接评估许多必要的突触前因子的贡献，例如动作电位、电压依赖性钙离子内流和通过内吞作用的囊泡再循环。为了确定在神经末梢中升高的α-突触核蛋白的主要细胞和分子靶点，我们的研究将利用Held的萼，一种大型哺乳动物突触，其可用于膜片钳技术。在初步实验中，我们发现，升高的α-突触核蛋白抑制囊泡胞吐在萼突触。这一观察结果为进一步研究升高的α-突触核蛋白抑制胞吐作用的机制提供了基础。在目标1中，我们将确定升高的α-突触核蛋白和钙信号之间的相互作用。在目标2中，我们将确定是否升高的α-突触核蛋白通过影响囊泡池，内吞作用和动员减少胞吐。在目标3中，我们将确定在花萼确定的机制是否适用于中脑多巴胺能神经元，这与神经变性的发展有关。实现这些目标可以提供关于在有症状的神经退行性疾病之前α-突触核蛋白的积累如何导致突触传递受损的关键信息。本项目可以揭示PD的病理生理变化过程，并有助于开发针对这些变化的新治疗方法。

DESCRIPTION (provided by applicant): Parkinson's disease (PD) is the second most common neurodegenerative disease, which affects 1.8% of people over the age of 65 years. One clinic hallmark of PD is formation of intracellular proteinaceous inclusions, termed Lewy Bodies, in the brain neurons. The main constituent of the Lewy Bodies is alpha-synuclein, which is found to accumulate in neurons in both familial forms of PD and sporadic PD. Therapeutic strategies for PD patients have not been very successful, because clinical symptoms occur at a stage when the neuronal functions have been damaged to an extent hard to rescue. Improvement of the therapeutic strategies depends on better understanding of the pathophysiological development of PD, including presymptomatic neuronal dysfunctions induced by alpha-synuclein accumulation. Increased level of alpha-synuclein has previously been found to impair neurotransmitter release prior to the symptomatic PD. However, mechanisms causing such impairment are poorly understood. Because alpha-synuclein is mainly expressed in nerve terminals, which are usually too small for using the highly sensitive electrophysiology methods, previous studies could not directly evaluate contributions of many essential presynaptic factors, such as action potential, voltage dependent calcium entry, and vesicle recycling through endocytosis. In order to identify the primary cellular and molecular targets of elevated alpha-synuclein in nerve terminals, our studies will take advantage of the calyx of Held, a large mammalian synapse which is accessible to patch-clamp techniques. In preliminary experiments, we found that elevated alpha-synuclein inhibited vesicle exocytosis at the calyx synapse. This observation provides the foundation to further investigate the mechanisms underlying the inhibited exocytosis by elevated alpha-synuclein. In Aim 1, we will determine the interaction between elevated alpha-synuclein and calcium signaling. In Aim 2, we will determine whether elevated alpha-synuclein reduces exocytosis by affecting vesicle pool, endocytosis and mobilization. In Aim 3 we will determine whether the mechanisms identified at the calyx apply to midbrain dopaminergic neurons, which are related to the development of neurodegeneration. Achieving these aims can provide crucial information on how accumulation of alpha-synuclein causes the impairment of synaptic transmission prior to the symptomatic neurodegenerative disorders. This project can shed light on the process of pathophysiological changes in PD, and help the development of new therapeutic approaches targeting to these changes.