Postsynaptic Protein Trafficking and Synapse Remodeling

描述（申请人提供）：突触可塑性对大脑、学习和记忆的发展至关重要。hebbian型可塑性如长时程增强和长时程抑制是一种快速的突触特异性修饰。相比之下，内稳态可塑性涉及突触的全局修改，在更长的时间尺度上运作，并且被认为是维持和协调神经元网络功能的关键。hebbian型可塑性主要由AMPA受体的转运介导，但对稳态可塑性的机制知之甚少。近年来，泛素-蛋白酶体系统在突触上的活性依赖蛋白转换已成为与包括稳态可塑性在内的各种突触可塑性相关的重要机制。然而，目前尚不清楚活性如何协调突触中伴随的泛素化/降解和特定蛋白质群的募集。在活性调节蛋白中，GKAP是突触后密度的主要支架蛋白之一，为PSD-95/NMDA受体复合物和Shank/Homer提供分子连接。我们的初步研究表明，活性通过Ca2????控制GKAP从突触的募集和移除依赖性蛋白激酶II （CaMKII）。此外，我们发现GKAP的活动依赖性周转是海马神经元突触缩放所必需的。在本研究中，我们将研究CaMKII控制GKAP泛素化/降解或向突触募集的分子机制，以及GKAP在突触上的转换在各种类型的突触可塑性中的功能意义。Aim 1将使用诱变和生化分析相结合的方法，绘制诱导GKAP泛素化的CaMKII磷酸化位点和泛素化的赖氨酸位点。目的2侧重于通过分子遗传学方法了解DLC、MyoV和CaMKII在GKAP募集到突触中的作用。我们还将进行实时成像，以更高的时空分辨率了解动态GKAP贩运。目的3将通过使用缺乏活性依赖性转换的GKAP突变体，评估突触中GKAP移除/募集对突触组成的活性依赖性修饰和各种形式的突触可塑性的功能意义。由于异常突触可塑性与多种神经和神经精神疾病有关，因此所提出的研究不仅将使我们对突触组成长期变化的分子机制获得新的和基本的见解，而且还与这些脑部疾病有关。

DESCRIPTION (provided by applicant): Synaptic plasticity is essential for the development of brain, learning and memory. Hebbian-type plasticity such as long-term potentiation and long-term depression is rapid and synapse-specific modification. In contrast, homeostatic plasticity involves global modification of synapses, operates over longer timescales, and is believed to be crucial for the maintaining and orchestrating neuronal network function. Hebbian-type plasticity is mediated mainly by the trafficking of AMPA receptors but not much is known for the mechanisms of homeostatic plasticity. Recently, activity-dependent protein turnover at the synapses by ubiquitin-proteasome system has emerged as crucial mechanisms associated with various types of synaptic plasticity including homeostatic plasticity. However, it is unknown how activity orchestrates concomitant ubiquitination/degradation and recruitment of specific group of proteins at synapses. Among the activity-regulated proteins, GKAP is one of the major scaffolding proteins in the postsynaptic densities and provides a molecular link for PSD-95/NMDA receptor complex and Shank/Homer. Our preliminary studies suggest that activity controls the recruitment and removal of GKAP from synapses, both through Ca2????dependent protein kinase II (CaMKII). Further, we found that the activity-dependent turnover of GKAP is required for synaptic scaling in hippocampal neurons. In this proposal, we will investigate the molecular mechanisms by which CaMKII controls ubiquitination/degradation or recruitment of GKAP to synapses, and the functional significance of the GKAP turnover at the synapses in various types of synaptic plasticity. Aim 1 will map the CaMKII phosphorylation site(s) and ubiquitinated lys site(s) that induce ubiquitination of GKAP, using a combination of mutagenesis and biochemical assays. Aim 2 focuses on understanding the role of DLC, MyoV, and CaMKII for GKAP recruitment to synapses by molecular genetic approaches. We will also perform real-time imaging to understand dynamic GKAP trafficking with greater spatio-temporal resolution. Aim 3 will assess the functional significance of GKAP removal/recruitment at synapses for the activity-dependent modification of synapse compositions and various forms of synaptic plasticity, by using GKAP mutants lacking the activity- dependent turnover. Since aberrant synaptic plasticity is implicated for a variety of neurological and neuropsychiatric diseases, the proposed studies will not only allow us to gain novel and fundamental insight into the molecular mechanisms for long-lasting changes in synapse compositions but also are relevant to these brain diseases.