Extracellular vesicles as carriers of neurotrophic signals during sympathetic neuronal circuit development

项目概要/摘要。神经生长因子（NGF）是交感神经系统正常布线所必需的。 神经系统发育过程中。由靶器官分泌的NGF与其受体TrkA结合， 支配节后神经元的轴突。在结合后，TrkA受体被内化成信号传导通路。 内体（SE），其中它可以在远端轴突中局部地发出信号，或者逆行地运输到细胞体 节后神经元。TrkA-SE从最终靶向细胞体的运输对于许多人来说是至关重要的。 包括生存和突触形成的发育过程。有趣的是，突触前神经元 存在于脊髓中的节前神经元在数量上与交感节后神经元相匹配。 神经元，并通过扩展，最终的目标，即使TrkA不表达在节前神经元。的 支配这种突触前匹配的营养线索还有待确定。 我们现在有初步的数据，TrkA可以从体树突结构域分泌后， 通过包含在细胞外囊泡（EV）中的逆行运输。在这个提议中，我们问这个细胞内 长距离信号（TrkA+ SE）通过细胞外囊泡（TrkA+ SE）调节细胞间信号的分泌 EV）生产。我们还询问这些TrkA+ EV是否能够进行神经营养信号传导。我们推测 TrkA+ EVs可能构成一种新的神经营养信号，调节节前神经元的分化， 生存EV生物学是一个新兴的领域，但EV的一系列功能主要在非神经元细胞中被描述。 系统. EV在组织修复、免疫监视、miRNAs的运输和免疫应答中具有已证实的作用。 信号级联的激活。虽然最近有一些EV研究关注神经元， EV以前没有被证明参与营养神经发育过程。 我们将检验这样的假设，即逆行转运的TrkA可以从交感神经分泌到EV中。 神经元并转移到新生突触处的节前神经元以支持营养信号传导。目标1： 将在分子上定义来自交感节后神经元的TrkA+ EV，并确定信号传导是否 TrkA的下游影响它们的生产。在目标2中，我们将确定上级颈椎中的细胞类型 神经节内化TrkA+ EV，以及TrkA+ EV是否对节前神经元具有神经营养作用。这些实验 将决定形式，功能，以及这种潜在的新型营养信号模式的作用位点。我们长久以来- 本学期的目标是探索一种新型的神经元-神经元通信，这种通信可能对系统匹配至关重要 在功能回路的发展过程中：神经营养性EV的分泌和长距离作用。

Project Summary/Abstract. Nerve growth factor (NGF) is required for the proper wiring of the sympathetic nervous system during development. NGF secreted by target organs binds to its receptor, TrkA, on the distal axons of innervating postganglionic neurons. Upon binding, the TrkA receptor is internalized into a signaling endosome (SE) where it can either signal locally in the distal axon or it is retrogradely trafficked to the cell body of the postganglionic neuron. Trafficking of the TrkA-SE from the final target to the cell body is critical for many developmental processes including survival and synapse formation. Interestingly, the survival of presynaptic preganglionic neurons residing in the spinal cord quantitatively matches that of sympathetic postganglionic neurons and, by extension, the final target, even though TrkA is not expressed on preganglionic neurons. The trophic cue governing this presynaptic matching has yet to be identified. We now have preliminary data that TrkA can be secreted from the somatodendritic domain after retrograde transport by inclusion in extracellular vesicles (EVs). In this proposal, we ask how this intracellular long-distance signal (TrkA+ SE) regulates the secretion of an intercellular signal via extracellular vesicle (TrkA+ EV) production. We also ask whether these TrkA+ EVs are capable of neurotrophic signaling. We speculate that TrkA+ EVs may constitute a novel trophic signal for preganglionic neurons and regulate their differentiation and survival. EV biology is a nascent field, but a range of EV functions have been described mainly in non-neuronal systems. EVs have a demonstrated role in tissue repair, immune surveillance, transportation of miRNAs, and activation of signaling cascades. Although there have been a handful of recent EV studies focusing on neurons, EVs have not previously been shown to participate in trophic neurodevelopmental processes. We will test the hypothesis that retrogradely transported TrkA can be secreted in EVs from sympathetic neurons and transferred to preganglionic neurons at nascent synapses to support trophic signaling. In Aim 1, we will molecularly define TrkA+ EVs from sympathetic postganglionic neurons and determine if signaling downstream of TrkA affects their production. In Aim 2, we will determine what cell types in the superior cervical ganglia internalize TrkA+ EVs and if TrkA+ EVs are neurotrophic for preganglionic neurons. These experiments will determine the form, function, and locus of action of this potentially novel mode of trophic signaling. Our long- term goal is to explore a new type of neuron-neuron communication that may be critical for systems matching during the development of a functional circuit: secretion and long-distance action of neurotrophic EVs.