Mechanisms of Endosome Trafficking in Neurons

描述（由申请人提供）：突触前末梢的一个定义特征是存在突触囊泡（SV），即储存和分泌神经递质的分泌细胞器。SV功能由细胞器膜蛋白组成来指定。因此，控制SV形成和组成的机制是突触功能的关键。在这个建议中，我们专注于囊泡的生物合成途径控制的适配器复合物AP-3，外套复合物，分类膜蛋白从早期内体SV。SV蛋白的组成是由两种亚型的适配器复合物AP-3，神经元和无处不在，后者被认为是专门参与溶酶体生物合成。神经元AP-3亚型的遗传缺陷阻碍SV膜蛋白的靶向。令人惊讶的是，空小鼠突变体的溶酶体分选途径，普遍存在的AP-3路线，触发积累的SV特异性蛋白的SV。这些意想不到的结果使我们提出了新的概念，即存在于同一内体上的SV和溶酶体分选机制竞争膜蛋白以递送到两种替代途径（SV或溶酶体）中。这一概念与溶酶体的传统观点不同，溶酶体被视为参与处理正常和病理细胞成分的末端细胞器。此外，我们的模型提供了一种新的方法来了解溶酶体靶向机制对影响儿童和成人个体的家族性和散发性神经变性的贡献。我们的中心假设是：AP-3亚型特异性机制的目标SV膜蛋白从一个共同的内体室两个竞争的途径：无论是SV的生物合成路线或后期内体-溶酶体path. In本提案中，我们将集中在四个预测来自我们的假设。将使用影响SV和内-溶酶体靶向的小鼠缺陷模型、高分辨率免疫电子和体内成像显微镜以及分离的SV和内体的分子分析的组合来系统地探索这些预测。在这个建议中获得的信息将照亮我们的理解，如何在生理和病理条件下，后期内体-溶酶体分选过程影响突触。公共卫生相关性：我们提出了一个模型，这将有助于了解溶酶体和突触如何接口，并有助于神经退行性疾病和精神疾病的知识。

DESCRIPTION (provided by applicant): A defining feature of presynaptic terminals is the presence of synaptic vesicles (SVs), secretory organelles that store and secrete neurotransmitters. SVs functions are specified by the organelle membrane protein composition. Thus, mechanisms controlling SV formation and composition are pivotal for synapse function. In this proposal we focus on the vesicle biogenesis pathway controlled by the adaptor complex AP-3, a coat complex that sorts membrane proteins from early endosomes to SVs. SV protein composition is regulated by two isoforms of the adaptor complex AP-3, neuronal and ubiquitous, the later thought to participate exclusively in lysosome biogenesis. Genetic defects in the neuronal AP-3 isoform hinder targeting of SV membrane proteins. Surprisingly, null mouse mutants in a lysosomal sorting pathway, the ubiquitous AP-3 route, trigger accruement of SV-specific proteins in SVs. These unexpected results lead us to propose the novel concept that SV and lysosomal sorting mechanisms present on the same endosome compete for membrane proteins to be delivered into two alternative routes, SVs or lysosomes. This concept departs from the traditional view of lysosomes, which are viewed as terminal organelles involved in the disposal of normal and pathological cellular components. Furthermore, our model provides a novel way to understand the contribution of lysosome targeting mechanisms to familial and sporadic forms of neurodegeneration that affect children and adult individuals. Our central hypothesis is that: AP-3-isoform-specific mechanisms target SV membrane proteins from a common endosomal compartment to two competing pathways: either to a SV biogenesis route or to a late endosome-lysosomal path. In this proposal, we will focus on four predictions derived from our hypothesis. These predictions will be systematically explored using a combination of mouse deficient models that affect SV and endo- lysosomal targeting, high-resolution immuno-electron and in vivo imaging microscopy, as well as the molecular analysis of isolated SVs and endosomes. Information gained in this proposal will illuminate our understanding of how late endosomes-lysosome sorting processes affect synapses under physiological and pathological conditions. PUBLIC HEALTH RELEVANCE: We propose a model that will contribute knowledge to understand how lysosomes and synapses interface and contribute to neurodegenerative and psychiatric disorders.