Mechanisms of the recognition of degenerating dendrites

项目总结/摘要 神经元突起的局部变性是神经回路重塑的重要机制， 神经元损伤由变性引起的神经元碎片必须被吞噬细胞迅速清除， 防止炎症并促进随后的神经元再生。虽然异常识别和 神经元碎片的清除与神经炎症、自身免疫和神经退行性疾病有关。 尽管有许多疾病，但吞噬细胞如何区分周围健康的神经突和退化的神经突仍是未知数。在 特别是，三个重要的问题仍然没有答案：什么是退化神经突的信号， 能被吞噬细胞识别退化神经突识别信号的受体是什么？ 识别信号是如何在退化的神经突上特异性地暴露的？我们新的体内数据提供了 能帮助我们解开这些谜题的重要线索使用我们新的体内探针，我们发现 “吃我”信号磷脂酰丝氨酸（PS）在健康树突的表面上不存在，但在树突表面暴露。 在发育重塑和物理损伤中退化的树突。在这些观察的基础上， 本项目旨在阐明树突中PS暴露和识别的体内机制 退化使用果蝇感觉神经元作为模型系统。我们的长期目标是 树突退化和修复的自主和非自主机制。对于这个项目，我们 我提出以下三个目标：1）确定PS暴露在识别和吞噬中的作用 退化的树突PS暴露在损伤后吞噬树突中的必要性将是 通过（i）用PS结合蛋白掩蔽树突表面上的PS，和（ii）阻断树突表面上的PS， PS在特定神经元中的生物合成。PS在触发枝晶吞噬和 将通过异位诱导PS暴露于神经元中来测试变性。2)调查CED-1 家族成员德雷珀识别退化的树突。我们的研究结果表明，德雷珀认识到， 退化的树突将进行两项互补的体内竞争试验，以确定 德雷珀直接与PS互动。3)确定PS暴露如何在神经元中调节， 退化的树突通过对候选基因进行功能丧失研究， 将确定在树突退化期间调节PS暴露的翻转酶和乱序酶。的 将通过检测树突损伤后的半胱天冬酶活性和通过检测半胱天冬酶在PS暴露中的作用来研究半胱天冬酶在PS暴露中的作用。 破坏了神经元中的半胱天冬酶通路。总之，这些目标将揭示神经元的体内机制。 碎片探测由于哺乳动物和昆虫中神经元碎片的清除需要相同的CED-1 吞噬受体家族，这项研究将揭示可能与 神经退行性疾病

Project Summary/Abstract Local degeneration of neuronal processes is an important mechanism in neural circuit remodeling and neuronal injury. The neuronal debris resulting from degeneration must be promptly cleared by phagocytes to prevent inflammation and to facilitate the subsequent neuronal regrowth. Although aberrant recognition and clearance of neuronal debris are implicated in neuroinflammation, autoimmunity, and neurodegenerative diseases, it is unknown how phagocytes distinguish degenerative neurites from surrounding healthy ones. In particular, three important questions remain unanswered: what is the signal on degenerating neurites that allows the recognition by phagocytes? What is the receptor for the recognition signal of degenerating neurites? How is the recognition signal specifically exposed on degenerating neurites? Our new in vivo data provided important clues that will help us to solve these puzzles. Using our new in vivo probes, we discovered that the ‘eat-me’ signal phosphatidylserine (PS) is absent on the surface of healthy dendrites but is exposed on degenerating dendrites in both developmental remodeling and physical injury. Building on these observations, this project aims to elucidate the in vivo mechanisms of PS exposure and recognition in dendrite degeneration using Drosophila sensory neurons as a model system. Our long term objective is to uncover autonomous and non-autonomous mechanisms of dendrite degeneration and repair. For this project, we propose the following three aims: 1) Determine the role of PS exposure in the recognition and engulfment of degenerating dendrites. The necessity of PS exposure in engulfment of dendrites after injury will be determined by (i) masking PS on the dendrite surface with PS-binding proteins, and (ii) blocking the biosynthesis of PS in specific neurons. The sufficiency of PS in triggering dendrite engulfment and degeneration will be tested by ectopically inducing PS exposure in neurons. 2) Investigate how the CED-1 family member Draper recognizes degenerating dendrites. Our results suggest that Draper recognizes degenerating dendrites. Two complementary in vivo competition assays will be performed to determine if Draper directly interacts with PS. 3) Determine how PS exposure is regulated in neurons and degenerating dendrites. By conducting loss-of-function studies of candidate genes, the identities of PS flippases and scramblases that regulate PS exposure during dendrite degeneration will be determined. The role of caspases in PS exposure will be investigated by examining caspase activity after dendrite injury and by disrupting the caspase pathway in neurons. Together, these aims will reveal in vivo mechanisms of neuronal debris sensing. As the clearance of neuronal debris in both mammals and insects requires the same CED-1 family of engulfment receptor, this study will reveal conserved mechanisms that may be relevant to neurodegenerative disorders.