PI(3,5)P2在神经特异性囊泡运输通路中的作用

In recent years, defects in vesicular trafficking have been found underlying a variety of neurological conditions. It is important for both basic and translational research to discover the mechanism of vesicular trafficking in neurons, especially neuronal specific trafficking pathways. PI(3,5)P2 is an important signaling phospholipid required for endomembrane homeostasis. Dysregulation in PI(3,5)P2 levels results in neurodegenerative phenotypes in mice and several types of neurological diseases in human. The extreme sensitivity of the nervous system to loss of PI(3,5)P2 suggests that some neuronal specific vesicular pathway(s) are regulated by PI(3,5)P2. Neep21 is an endosomal protein whose expression is mostly restricted to the brain. Neep21 positive endosomes mediate the endocytosis of many physiologically critical cargos including AMPA-type glutamate receptors, L1/NgCAM, and APP. Based on our preliminary results, we propose that PI(3,5)P2 regulates a general transport pathway through Neep21 positive endosomes. In this study, we will analyze the effect of PI(3,5)P2 on the dynamics and functions of Neep21 endosomes using a series of imaging and trafficking tools. Our study will uncover novel molecular mechanisms for neurological diseases caused by PI(3,5)P2 deficiency and provide promising new drug targets for vesicular trafficking related neuropathies.

近年来的研究表明，囊泡转运通路异常是导致神经系统疾病的重要因素。研究神经细胞中的囊泡运输通路，尤其是神经特异性囊泡运输，具有重要的临床和学术意义。磷脂酰肌醇3,5二磷酸(PI(3,5)P2)是一种维持囊泡系统稳态的磷脂分子。PI(3,5)P2的缺陷导致小鼠神经系统退行性病变和多种人类神经系统疾病，提示PI(3,5)P2可能调控神经特异性囊泡转运，但机制尚不清楚。Neep21是一种在神经系统特异表达的胞内体蛋白。Neep21胞内体运输包括AMPA型谷氨酸受体、L1/NgCAM, APP等一系列具有重要生理功能的货物蛋白。综合前期结果，我们提出如下假说：PI(3,5)P2通过调控Neep21胞内体的动态结构和生物学功能来影响神经系统囊泡转运。本课题以Neep21胞内体为切入点，研究PI(3,5)P2在神经细胞囊泡运输中的调控及作用机制。预期研究结果将为囊泡转运相关神经系统疾病提供新的治疗靶点。

PI(3,5)P2是一种重要的磷脂类信号分子，在真核细胞的囊泡运输通路中发挥极其关键的作用。申请人前期工作发现神经系统¬对PI(3,5)P2具有特殊的敏感性。近年来，越来越多的人类神经系统疾病, 如CMT-4J综合症、纹状体黑质变性、Yunis-Varon综合症等，被发现是由PI(3,5)P2通路的遗传缺陷引起的。然而这种神经系统敏感性的机制目前研究较少。NEEP21（Neuron-enriched endosomal protein of 21 kD）是一种在神经系统中特异性表达的单次跨膜蛋白，调控包括AMPA型谷氨酸受体、L1/NgCAM、APP等在内的一系列具有重要生理功能的货物蛋白的内吞与转运。本课题的假说是：NEEP21位于PI(3,5)P2信号通路的下游，介导了神经系统对于PI(3,5)P2的特殊敏感性。在本课题中，我们探索了PI(3,5)P2与神经特异性囊泡蛋白NEEP21的空间定位和功能调控。我们发现：1）NEEP21胞内体与PI(3,5)P2合成蛋白Vac14、PI(3,5)P2结合蛋白TRPML1共定位；2）PI(3,5)P2缺失导致NEEP21囊泡定位变化；3）PI(3,5)P2动态变化的缺陷导致NEEP21受困于高尔基体；4）PI(3,5)P2缺陷能够导致神经突起变细，而NEEP21可以回补这一现象。我们的发现为揭示PI(3,5)P2缺陷的致病机制填上了重要的一环，并为PI(3,5)P2缺陷相关疾病提供了分子靶点。