Mechanisms of Natural Phosphatidylserine Exposure in the Nervous System

项目摘要/摘要 一个有功能的神经系统需要通过支持细胞来积极地维持神经元结构。一些人 支持细胞是吞噬细胞，通过检测“Eat-me”吞噬不必要的或受损的神经元部分。 暴露在神经细胞膜上的信号。磷脂酰丝氨酸(PS)已被证明是一种强大的神经元 Eat-Me信号在许多神经变性事件中介导神经元的吞噬作用。通常隐藏在 质膜的内叶，这种磷脂专门暴露在退变的部分。 神经元诱导吞噬作用。然而，健康神经元是否暴露在其表面的PS尚不清楚。 与体内的吞噬作用无关。使用活体系统可视化外周PS暴露 对于感觉神经元，人们发现果蝇的某些神经元自然地暴露在树突上的PS。 在不引起吞噬的情况下形成空间定义的图案。这一发现提出了两个具体而重要的问题 问题：(1)PS是如何在这些树突上保持空间暴露的？(2)是什么阻止了这些PS- 使树突不被吞噬细胞吞噬？这项建议的总体目标是 研究这种意外的PS暴露对健康神经元的机制原因，并阐明 这些暴露在PS中的神经元受到保护，免受吞噬诱导的变性。回答这些问题 问题是我们朝着阐明神经元-吞噬细胞相互作用的长期目标迈出的重要一步。 神经系统的发育、维持和退化。为达致这些目标， 提出了以下两个目标：(1)阐明天然PS暴露在树突上的机制。 具体地说，内源性PS Flippase ATP8A将在特定神经元中进行荧光标记以进行研究 顺着树突分布的翻转酶是否决定了自然PS暴露的模式。此外， 树突激发和膜电位在自然PS暴露中的作用将被研究。(2)界定 调节树突对PS诱导的退化易感性的途径。飞行员RNAi屏幕显示 间隔连接元件和DEG/ENaC钠通道参与调节电阻 PS-暴露树突状细胞的吞噬作用。因此，将测试间隔连接蛋白是否保护PS- 暴露树突不被吞噬，以及神经元活动是否促进PS相关的退化。 总之，这些目标将定义天然神经元性PS暴露的分子基础，并揭示新的 神经保护的机制。在这个项目中获得的知识对于理解如何 不同类型的神经元利用相同的吞噬信号以不同的方式与吞噬细胞相互作用。

PROJECT SUMMARY/ABSTRACT A functional nervous system requires active maintenance of neuronal structures by supporting cells. Some supporting cells are phagocytes that engulf unnecessary or damaged neuronal parts by detecting “eat-me” signals exposed on neuronal membranes. Phosphatidylserine (PS) has been shown to be a potent neuronal eat-me signal that mediates phagocytosis of neurons in many neurodegenerative events. Normally hidden in the inner leaflet of the plasma membrane, this phospholipid is exposed specifically on the degenerative parts of neurons to induce phagocytosis. However, it is unknown whether heathy neurons expose PS on their surface in ways unrelated to phagocytosis in vivo. Using an in vivo system to visualize PS exposure on peripheral sensory neurons, it was discovered that certain neurons in Drosophila naturally expose PS on their dendrites in spatially defined patterns without inducing phagocytosis. This finding raises two specific and important questions: (1) How is PS exposure spatially maintained on these dendrites? (2) What prevents these PS- exposing dendrites from being engulfed by phagocytes? The overall objectives of this proposal are to investigate the mechanistic causes of this unexpected PS exposure on healthy neurons and to elucidate how these PS-exposing neurons are protected against phagocytosis-induced degeneration. Answering these questions is an important step toward our long-term goal of elucidating neuron-phagocyte interactions in the development, maintenance, and degeneration of the nervous system. To achieve these objectives, the following two aims are proposed: (1) Elucidate the mechanisms underlying natural PS exposure on dendrites. Specifically, the endogenous PS flippase ATP8A will be fluorescently tagged in specific neurons to investigate whether the flippase distribution along dendrites defines the patterns of natural PS exposure. In addition, the roles of dendrite excitation and membrane potential in natural PS exposure will be examined. (2) Define the pathways that regulate susceptibility of dendrites to PS-induced degeneration. A pilot RNAi screen revealed the involvement of a septate junction component and a Deg/ENaC sodium channel in regulating the resistance of PS-exposing dendrites to phagocytosis. Thus, it will be tested whether septate junction proteins protect PS- exposing dendrites from being engulfed and whether neuronal activity promotes PS-related degeneration. Together, these aims will define the molecular basis of natural neuronal PS exposure and reveal new mechanisms of neuroprotection. The knowledge gained in this project will be important for understanding how different neuronal types utilize the same phagocytic signal to interact with phagocytes in diverse ways.