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的功能障碍 已经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。 突触交流的一个方面对大脑中的信息处理至关重要，那就是维持 关于单个突触的突触前神经递质释放和突触后功能之间的精确功能匹配，但控制这一方面的局部信号尚不清楚。 该项目将专注于最近在海马神经元中发现的一条内稳态通路，该通路的功能是 当突触后受体激活不足时，调整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通路，该通路将突触失活与mTOR复合体1(MTORC1)信号偶联在突触后树突中。MTORC1激活反过来又驱动局部树突状 翻译和释放脑源性神经营养因子(BDNF)，引起代偿性增加 来自相对的突触前终末的神经递质释放，但仅当这些终末最近 激活。这种由局部突触前活动对突触内稳态的状态依赖的门控确保了 MTORC1跨突触信号传递到尖峰驱动的神经递质释放。在之前的支持阶段，我们发现BDNF通过蛋白酶体依赖的降解引起突触前补偿。 突触调节因子Tomform1(Tomo1)，由E3泛素连接酶Hrd1催化。在此期间 在这项研究中，我们发现了蛋白酶体在轴突末端的活性依赖的招募中一个意想不到的关键作用。我们现在建议验证一个中心假设，即突触前终末蛋白酶体的活性依赖隔离赋予状态依赖的突触内稳态门控，由 突触后mTORC1信号。我们的调查将研究19S的磷酸化是如何调控的 蛋白酶体亚基Rpt6动态调节蛋白酶体在轴突中的分布(目标1)，定义轴突终末连接神经活动(特别是P/Q/N电压门控钙通道)的核心信号通路 活性)与对突触靶向重要的蛋白酶体的翻译后修饰(目标2)，以及 确定控制轴突终末蛋白酶体隔离的分子机制(目标3)。在每一个中 这些目的、mTORC1跨突触内稳态信号机制之间的关系 将接受严格的测试。拟议的实验采用了最先进的突触小泡光学成像技术 循环和释放，针对mTORC1信号和蛋白酶体磷酸化的遗传模型，严格 电生理测量，并专注于突触生物学的一个全新领域。这个 这些发现有望极大地促进我们对局部动态平衡机制的理解，这些机制作用于 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.