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

项目摘要/摘要。神经生长因子(NGF)是交感神经正确连接所必需的 神经系统在发育过程中。靶器官分泌的NGF与其远端受体TrkA结合 支配节后神经元的轴突。结合后，TrkA受体被内化为一种信号 内体(SE)，它可以在远端轴突中局部发出信号，或者被逆行输送到细胞体 神经节后神经元。TrkA-SE从最终靶向细胞体的运输对许多人来说是至关重要的 发育过程，包括存活和突触形成。有趣的是，突触前神经元的存活 脊髓内节前神经元与交感神经节后神经元的数量相匹配 神经元和最终靶点，尽管TrkA在节前神经元上不表达。这个 支配这种突触前匹配的营养线索尚未确定。 我们现在有初步数据表明TrkA可以从躯体树突域分泌出来 细胞外小泡(EVS)内含物逆行转运。在这项提案中，我们问的是细胞内的 远距离信号(TrkA+SE)通过胞外小泡(TrkA+SE)调节细胞间信号的分泌 EV)生产。我们还询问这些TrkA+EV是否能够发出神经营养信号。我们推测 TrkA+EVS可能构成节前神经元的一种新的营养信号，调节其分化和分化 生死存亡。EV生物学是一个新的领域，但EV的一系列功能主要是在非神经元中描述的 系统。EV在组织修复、免疫监视、miRNAs的运输以及 信号的激活级联。尽管最近有一些电动汽车研究集中在神经元上， EV以前没有被证明参与营养神经发育过程。 我们将验证这样的假设，即逆行运输的TrkA可以在EV中从交感神经分泌 并转移到新生突触的节前神经元，以支持营养信号。在目标1中，我们 是否会从分子上定义来自交感神经节后神经元的TrkA+EV，并确定信号 TrkA的下游影响它们的生产。在目标2中，我们将确定上颈椎的细胞类型。 神经节内化TrkA+EVS，如果TrkA+EVS对节前神经元具有神经营养作用。这些实验 将决定这种潜在的新的营养信号模式的形式、功能和作用地点。我们的长- 学期目标是探索一种可能对系统匹配至关重要的新型神经元-神经元通信 在一个功能回路的发展过程中：神经营养性EVS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.