Neuronal Dysfunction in Fragile X Tremor Ataxia Syndrome

描述(由申请人提供)： 目的：脆性X相关颤动共济失调综合征(FXTAS)是一种常见的遗传性神经退行性疾病，以痴呆、步态障碍和震颤为特征。它是由脆性X智力低下基因FMR1中扩大的CGG核苷酸重复引起的。这种重复序列的扩大干扰了脆性X蛋白FMRP的翻译，使其在患者和动物模型中的基础和活性依赖表达较低。有新的证据表明，FMRP功能障碍也可能导致其他神经退行性疾病，如阿尔茨海默病。我们的应用解决了FMRP不足在FXTAS发病机制中是否起有意义作用的关键问题。为了开始解决这个问题，我们评估了FXTAS小鼠模型中是否存在神经元功能障碍。我们推测CGG重复会阻止突触FMRP的产生，导致突触可塑性缺陷，这可能与患者的临床表型有关。我们的初步结果表明，FXTAS模型小鼠的突触可塑性发生了变化，这反映了完全缺乏FMRP的脆性X综合征(FXS)小鼠模型中的变化。突触电生理学的这些变化在机制上是不同的，并与基础和活性依赖的FMRP表达的减少有关。这些初步发现导致了我们的中心假设，即扩展的CGG重复FMR1 mRNA的翻译效率低下导致FXTAS的神经元功能障碍和临床疾病。拟议实验的中心目标是确定这种神经元功能障碍在FXTAS模型小鼠中发生的机制，长期目标是为患有FXTAS和其他神经退行性疾病的退伍军人开发新的治疗靶点。研究计划/方法：为了解决我们的中心假设，我们将利用分子、细胞和电生理技术的组合，我们的实验室已经在这些技术中建立了专业知识。我们将首先确定在CGG-KI和FMR1KO小鼠的培养神经元和海马片中mGluR依赖的长期抑郁改变的机制特征。为了有可能将这些发现转化为治疗开发，我们将利用FXS模型中已建立的工作，其中FMRP表达完全丢失。在这些系统中，I型mGluRs的拮抗剂可以缓解动物模型中所见的表型的许多方面。FXS正在进行这些药物的第二阶段和第三阶段试验。因此，我们将在FXTAS模型中使用已知在FXTAS小鼠或患者中异常的已建立的行为分析来测试mGluR拮抗剂的潜在疗效。临床意义：这项工作的长期目标是为FXTAS和其他退行性疾病(如阿尔茨海默病)的患者开发合理的治疗方法，FMRP可能在疾病发病机制中发挥作用。拟议的实验应该确定FMRP功能障碍在FXTAS中的重要作用，并可能在其他神经退行性疾病中发挥作用。这些研究还提供了一种已经在临床试验中的有前景的治疗剂的临床前测试，从而提供了快速临床转化的希望。总之，建议的实验是新颖的、可行的，对FXTAS和更常见的神经退行性疾病，如阿尔茨海默病，都具有很高的意义

DESCRIPTION (provided by applicant): Objectives: Fragile X associated Tremor Ataxia Syndrome (FXTAS) is a common inherited neurodegenerative disorder characterized by dementia, gait disorder and tremor. It results from an expanded CGG nucleotide repeat in the Fragile X Mental Retardation gene, FMR1. This repeat expansion interferes with translation of the Fragile X protein, FMRP, such that it's basal and activity-dependent expression is lower in patients and in animal models. There is emerging evidence that FMRP dysfunction may also contribute to other neurodegenerative disorders such as Alzheimer's disease. Our application addresses the critical question of whether FMRP insufficiency plays a meaningful role in FXTAS pathogenesis. To begin addressing this question, we evaluated whether neuronal dysfunction was present in a mouse model of FXTAS. We reasoned that the CGG repeat would block production of FMRP at synapses, leading to defects in synaptic plasticity that could contribute to the clinical phenotype in patients. Our preliminary results demonstrate alterations in synaptic plasticity in FXTAS model mice that mirror changes seen in mouse models of Fragile X Syndrome (FXS) that completely lack FMRP. These changes in synaptic electrophysiology are mechanistically distinct and correlate with a decrease in both basal and activity dependent expression of FMRP. These preliminary findings lead to our central hypothesis that translational inefficiency of expanded CGG repeat FMR1 mRNA contributes to neuronal dysfunction and clinical disease in FXTAS. The central objective of the proposed experiments is to define the mechanisms by which this neuronal dysfunction occurs in FXTAS model mice, with a long-term objective of developing novel therapeutic targets for Veterans with FXTAS and other neurodegenerative conditions. Research Plan/Methods: To address our central hypothesis, we will utilize a combination of molecular, cellular and electrophysiological techniques in which our labs already have established expertise. We will first determine the mechanistic features by which mGluR dependent long term depression is altered in cultured neurons and hippocampal slices from CGG-KI and FMR1 KO mice. To potentially translate these findings toward therapeutic development, we will take advantage of established work in models of FXS, where FMRP expression is completely lost. In these systems, antagonists to type I mGluRs alleviate many aspects of the phenotype seen in animal models. Phase II and III trials are ongoing in FXS with these drugs. Thus, we will test the potential efficacy of mGluR antagonists in a model of FXTAS using established behavioral assays known to be abnormal in FXTAS mice or patients. Clinical Relevance: The long term objective of this work is rational therapeutic development for patients with FXTAS and other degenerative disorders such as Alzheimer's disease where FMRP may play a role in disease pathogenesis. The proposed experiments should define an important role for FMRP dysfunction in FXTAS and potentially in other neurodegenerative disorders. These studies also provide pre-clinical testing of a promising therapeutic agent already in clinical trials, thus offering the promise of rapid clinical translation. In sum, the proposed experiments are novel, feasible and of high significance to both FXTAS and more common neurodegenerative disorders such as Alzheimer's disease