Trans-synaptic control of presynaptic neurotransmitter release

调节突触连接的发育、维持和可塑性的机制功能障碍 与许多神经精神和神经发育障碍有关，因此对这些过程的深入分子理解对于减轻这些疾病造成的严重健康负担至关重要。 对于大脑中的信息处理至关重要的突触通信的一个方面是维持 突触前神经递质释放和突触后功能之间精确的功能对准，但控制这方面的“突触稳态”的局部信号知之甚少。 这个项目将集中在最近发现的海马神经元的稳态通路，其功能是 当突触后受体激活不足时，调节突触前神经递质的释放。我的实验室 最近描述了一种独特的稳态信号传导途径，其将突触失活与突触后树突中的mTOR复合物1（mTORC 1）信号传导偶联。mTORC 1激活反过来驱动局部树突状细胞， 翻译和释放脑源性神经营养因子（BDNF），这elevened代偿性增加， 神经递质释放从并列突触前终端，但只有当这些终端已最近 活跃这种通过局部突触前活动的突触稳态的状态依赖性门控确保了突触内稳态的耦合。 mTORC 1跨突触信号传导到尖峰驱动的神经递质释放。在前期的研究中，我们发现BDNF通过蛋白酶体依赖性的降解， 突触调节因子tomosyn 1（Tomo 1），由E3泛素连接酶HRD 1催化。在这些 研究中，我们发现了一个意想不到的和关键的作用，活性依赖性招聘的蛋白酶体轴突终扣。我们现在提出测试的核心假设，活动依赖性隔离蛋白酶体在突触前末梢赋予状态依赖性门控突触稳态驱动 突触后mTORC 1信号传导。我们的研究将探讨如何调节磷酸化的19 S 蛋白酶体亚基Rpt 6动态调节蛋白酶体在轴突中的分布（目的1），定义轴突终末中连接神经活动的核心信号通路（特别是P/Q/N电压门控Ca 2+通道 活性）与对突触靶向重要的蛋白酶体的翻译后修饰（Aim 2），以及 定义控制轴突末端蛋白酶体隔离的分子机制（目标3）。的每一个中 这些目标，揭示了mTORC 1跨突触稳态信号转导机制的关系 将受到严格的测试。所提出的实验采用最先进的突触囊泡光学成像技术 循环和释放，靶向mTORC 1信号传导和蛋白酶体磷酸化的遗传模型，严格 电生理测量，并集中在突触生物学的一个全新领域。的 这些发现有望大大促进我们对局部稳态机制的理解， 协调突触后活动与突触前神经递质释放的空间和时间调节。

Dysfunction in mechanisms that regulate the development, maintenance, and plasticity of synaptic connections have been linked to many neuropsychiatric and neurodevelopmental disorders, and thus a deep molecular understanding of these processes will be crucial in relieving the severe health burden these disorders impose. One aspect of synaptic communication that is critical for information processing in the brain is the maintenance of precise functional alignment between presynaptic neurotransmitter release and postsynaptic function at individual synapses, but the local signals that control this aspect of “synaptic homeostasis” are poorly understood. This project will focus on a recently discovered homeostatic pathway in hippocampal neurons that functions to tune presynaptic neurotransmitter release when postsynaptic receptor activation is deficient. My laboratory has recently described a unique homeostatic signaling pathway that couples synaptic inactivity to mTOR complex 1 (mTORC1) signaling in postsynaptic dendrites. mTORC1 activation, in turn, drives the local dendritic translation and release of brain-derived neurotrophic factor (BDNF), which elicits compensatory increases in neurotransmitter release from apposed presynaptic terminals but only if those terminals have been recently active. This state-dependent gating of synaptic homeostasis by local presynaptic activity ensures coupling of mTORC1 trans-synaptic signaling to spike-driven neurotransmitter release. During the previous period of support, we discovered that BDNF elicits presynaptic compensation via the proteasome-dependent degradation of the synaptic regulator tomosyn1 (Tomo1), which is catalyzed by the E3 ubiquitin ligase HRD1. During these investigations, we uncovered an unexpected and critical role for activity-dependent recruitment of the proteasome to axonal boutons. We now propose to test the central hypothesis that activity-dependent sequestration of proteasomes in presynaptic terminals confers state-dependent gating of synaptic homeostasis driven by postsynaptic mTORC1 signaling. Our investigations will examine how regulated phosphorylation of the 19S proteasome subunit Rpt6 dynamically regulates proteasome distribution in axons (Aim 1), define the core signaling pathway in axon terminals that links neural activity (and specifically, P/Q/N voltage-gated Ca2+ channel activity) with posttranslational modifications of the proteasome important for synaptic targeting (Aim 2), and define the molecular mechanisms that control proteasome sequestration in axon terminals (Aim 3). In each of these aims, the relationship of the mechanisms uncovered with mTORC1 trans-synaptic homeostatic signaling will be rigorously tested. The proposed experiments employ state of the art optical imaging of synaptic vesicle cycling and release, genetic models targeting mTORC1 signaling and proteasome phosphorylation, rigorous electrophysiological measurements, and are focused on a fundamentally new area of synaptic biology. The findings are expected to significantly advance our understanding of local homeostatic mechanisms that act to coordinate postsynaptic activity with spatial and temporal adjustments in presynaptic neurotransmitter release.