Fragile X Phenotypes Modulated by Altered Signaling to the Synaptic Cytoskeleton

描述（由申请人提供）：树突棘的小尺寸掩盖了它们在兴奋性突触传递和最终复杂行为中所起的复杂作用。棘的细胞骨架结构主要由肌动蛋白丝组成。这些细丝乍一看可能很简单，但实际上却非常复杂。它们动态地组装成不同的结构，并作为一个平台，在脊椎发生和经验依赖性可塑性过程中协调脊柱的精细反应。在人类和小鼠中调节突触肌动蛋白的通路中的突变与神经系统疾病（人类）和相关的内表型（小鼠）相关。我的实验室研究了一种信号通路，该通路通过激活Rac下游的WAVE 1来驱动脊髓中的肌动蛋白重新聚合。本申请的目的是分析脆性X综合征的致病基因Fmr 1和WAVE 1之间的上位性。我们的中心假设是WAVE 1升高和肌动蛋白调节异常显着导致脆性X综合征的突触和行为表型。这一假设是由基于以下的强有力的初步数据指导的：1）在Fmr 1缺失小鼠中，Rac活性升高，Rac的抑制使LTD正常化。2）我们以前的工作表明WAVE 1的丢失导致与Fmr 1丢失相反的突触表型。3)WAVE 1 mRNA是FMRP的直接靶点，我们的初步数据显示在Fmr 1敲除小鼠中WAVE 1蛋白增加。4)我们的数据表明突触肌动蛋白动力学在FXS小鼠模型中显著改变，过度活跃的Rac信号传导模拟了这种异常。5)我们的初步数据显示，在Wave 1杂合子小鼠中，Fmr 1无效记忆障碍得到了挽救。这项资助的具体目的是：1）定量分析脊柱肌动蛋白动力学和FMRP丢失之间的联系; 2）测试WAVE 1的遗传减少是否使Fmr 1无效缺陷正常化; 3）通过WAVE 1过表达体内测试Fmr 1无效表型的模拟。由于该提案利用多学科方法来分析Fmr 1的丢失如何导致WAVE 1水平异常、脊柱肌动蛋白动力学改变和行为缺陷，因此可以预期在理解脆性X综合征模型中肌动蛋白信号传导与神经元功能障碍的机制方面取得了根本性进展。因此，拟议的研究与NIH的使命的一部分有关，即研究基因突变与神经系统疾病机制之间的联系。

DESCRIPTION (provided by applicant): The small size of dendritic spines belies the elaborate role they play in excitatory synaptic transmission and ultimately complex behaviors. The cytoskeletal architecture of the spine is predominately composed of actin filaments. These filaments, which at first glance might appear simple, are also surprisingly complex. They dynamically assemble into different structures and serve as a platform for orchestrating the elaborate responses of the spine during spinogenesis and experience-dependent plasticity. Mutations in pathways that regulate synaptic actin in humans and mice are associated with neurological disorders (humans) and related endophenotypes (mice). My laboratory studies a signaling pathway that drives de novo actin polymerization in spines by the activation of WAVE1 downstream of Rac. The objective of this application is to analyze epistasis between Fmr1, the causative gene in Fragile X Syndrome, and WAVE1. Our central hypothesis is that elevated WAVE1 and dysregulation of actin significantly contributes to the synaptic and behavioral phenotypes of Fragile X Syndrome. This hypothesis is guided by strong preliminary data based on: 1) In Fmr1 null mice, Rac activity is elevated and inhibition of Rac normalizes LTD. 2) Our previous work showing that loss of WAVE1 results in synaptic phenotypes opposite those of Fmr1 loss. 3) WAVE1 mRNA is a direct target of FMRP and our preliminary data shows an increase in WAVE1 protein in Fmr1 null mice. 4) Our data that demonstrates synaptic actin dynamics are significantly altered in a mouse model of FXS and overactive Rac signaling mimics this abnormality. 5) Our preliminary data showing Fmr1 null memory impairments are rescued in mice also heterozygous for Wave1. The specific aims of this grant are: 1) quantitatively analyze the link between spine actin dynamics and loss of FMRP; 2) test if genetic reduction of WAVE1 normalizes Fmr1 null deficits; and 3) test for mimicry of Fmr1 null phenotypes by WAVE1 overexpression in vivo. Because this proposal utilizes a multidisciplinary approach to analyze how loss of Fmr1 results in abnormal WAVE1 levels, altered spine actin dynamics, and behavioral deficits, a fundamental advance in understanding the mechanisms linking actin signaling to neuronal dysfunction in a model of Fragile X Syndrome can be anticipated. Thus the proposed research is relevant to that part of NIH's mission that pertains to the investigation of the mechanisms linking genetic mutations to mechanisms of neurological disease.