Neuronal events and molecular pathways in active dendrite degeneration

描述(申请人提供)：树突和轴突延伸到神经元细胞体很远的距离，因此可以独立于它而受到损害。众所周知，轴突具有自己的主动退变程序，该程序是独立控制的，与细胞体的退变程序在分子上是不同的。目前还不知道树突是否有类似的程序。树突对神经元的正常功能和轴突一样重要，在癫痫发作和中风时会表现出形态上的变化。因此，我们将在一个简单的模型系统中研究树枝晶的退化过程。果蝇树突状突起神经元是幼虫角质层下的感觉神经元，其树突状结构与中枢神经元的复杂程度相似。我们可以在每种动物中识别出相同的单个细胞，并可以用紫外线激光从这个细胞上切下一个树突。我们有初步证据表明，这种损伤引起了类似于横断后轴突变性(沃勒变性)的主动变性程序：远端树突在24小时内完全解体，这种分解被WLD(S)或沃勒变性慢速蛋白的表达所阻断。在这项提案中，我们概述了一系列实验，以确定树突退变过程中发生的主要事件和执行退变程序的分子途径。我们将利用我们在实时成像和神经元基本细胞生物学方面的专业知识来确定首先分解哪些亚细胞系统：肌动蛋白、微管或膜运输。我们将使用现有的遗传工具来阻断已知的自毁机制，包括caspase和泛素蛋白酶体系统，以确定树突是使用凋亡程序还是轴突退化程序。我们还将研究候选细胞器，线粒体和溶酶体是否对分解树突起重要作用。从我们的实验中过表达WLD(S)蛋白，我们知道它有可能阻止树突退化的程序。因此，我们将筛选转基因果蝇的候选基因和过表达文库，以确定改变树突退化过程的其他方法。使用一个简单的模型系统来识别树突变性过程中的主要细胞和分子事件，以及改变它们的方法，将迅速促进我们对神经元如何应对包括癫痫发作和中风在内的环境应激的理解。与公共卫生相关：树突在应激包括癫痫发作和中风的情况下表现出损伤和退化的形态迹象。我们将使用一个简单的模型系统来研究树突退化过程中发生的细胞和分子事件，并将识别可以减缓退化程序的蛋白质。

DESCRIPTION (provided by applicant): Dendrites and axons extend long distances from the neuronal cell body and so can be damaged independently from it. It is known that axons possess their own active degeneration program that is controlled separately and is molecularly distinct from that of the cell body. It is not known whether dendrites possess a similar program. Dendrites are as important for normal neuronal function as axons, and exhibit morphological changes during seizures and stroke. We will therefore investigate the process of dendrite degeneration in a simple model system. Drosophila dendritic arborization neurons are sensory neurons under the larval cuticle that elaborate large dendritic trees similar in complexity to central neurons. We can identify the same individual cell in every animal, and can sever a single dendrite from this cell with a UV laser. We have preliminary evidence that this injury elicits an active degeneration program similar to axon degeneration after transection (Wallerian degeneration): distal dendrites are completely disassembled within 24 hours, and this disassembly is blocked by expression of the Wld(s), or Wallerian degeneration slow, protein. In this proposal, we outline a series of experiments to identify the major events that occur during dendrite degeneration and the molecular pathways that execute the degeneration program. We will use our expertise in live imaging and the basic cell biology of neurons to determine which subcellular systems are dismantled first: actin, microtubules or membrane trafficking. We will use available genetic tools to block known self-destruct machinery including caspases and the ubiquitin proteasome system to determine whether dendrites use the apoptotic or axonal degeneration program. We will also investigate whether candidate organelles, mitochondria and lysosomes, are important for dismantling dendrites. From our experiments overexpressing the Wld(s) protein, we know that it is possible to block the program of dendrite degeneration. We will therefore screen candidate genes and an overexpression library of transgenic Drosophila to identify additional ways to alter the course of dendrite degeneration. Using a simple model system to identify major cellular and molecular events during dendrite degeneration, and ways to change them, will rapidly advance our understanding of how neurons respond to environmental stresses including seizures and stroke. PUBLIC HEALTH RELEVANCE: Dendrites exhibit morphological signs of damage and degeneration under stresses including seizures and stroke. We will use a simple model system to investigate the cellular and molecular events that take place during dendrite degeneration, and will also identify proteins that can slow the degeneration program.