Pathogenic Mechanisms in Fragile X Tremor Ataxia Syndrome

描述(由申请人提供)：脆性X震颤共济失调综合征(FXTAS)是一种常见的步态障碍和颤抖的原因，影响1：800以上的男性。FXTAS是由脆性X智力低下基因FMR1的5‘非翻译区中一个扩大的“CGG”核苷酸重复引起的。在患者和动物模型中，这种扩大的CGG重复与FMR1 mRNA的表达升高、神经变性和包含扩大的CGG重复mRNA和几种蛋白质的核内泛素阳性神经元包涵体有关。到目前为止，工作主要集中在CGG重复在通过RNA功能增益机制引发神经退化方面的潜在作用。然而，疾病病理的关键方面并不容易用一个纯粹的mRNA介导的隔离过程来解释。我们的中心假设是CGG重复序列的扩张通过多个重叠的分子机制促进了FXTAS神经元的退变。这些机制包括顺式和RNA介导的FMR1基因转录失调、导致异常RNA剪接事件的功能毒性获得和蛋白质质量控制途径的改变。我们提出的检验这一假设的建议分为三个目标。目的1将研究FMR1mRNA转录增加的机制，重点是FMR1基因座的组蛋白乙酰化状态。目的2研究泛素蛋白酶体系统在FXTAS发病机制中的作用。目标一和目标二都将利用FXTAS的果蝇模型以及患者来源的淋巴母细胞。目的3将使用来自FXTAS患者成纤维细胞的可诱导多能干细胞，并将其分化为神经元。我们将确定这些人FXTAS神经元的替代转录组谱，以解决这样的假设，即RNA结合蛋白在FXTAS中的隔离导致异常的mRNA剪接。综上所述，这些研究将大大扩展我们对这种神经退行性疾病的理解，并有助于确定合适的候选治疗靶点。 公共卫生相关性：脆性X颤动共济失调综合征(FXTAS)是一种常见的遗传性退行性疾病，会导致老年人行走困难、四肢颤抖和痴呆症。我们的工作建议通过两种重叠的机制来检验FXTAS的遗传原因导致神经元死亡的想法：它增加突变基因转录成RNA，并使RNA对神经元有毒，这样问题就会随着这些细胞处理和降解其他RNA和蛋白质的方式而发展。为了验证我们的假设，我们将利用这种疾病的果蝇模型，我们还将从这种疾病患者中提取可诱导的多能干细胞，以便我们可以研究具有致病突变的人类来源神经元。综上所述，我们认为这些研究将告诉我们很多关于FXTAS的原因以及我们需要做些什么来开发治疗方法。

DESCRIPTION (provided by applicant): Fragile X Tremor Ataxia Syndrome (FXTAS) is a common erited cause of gait disorder and tremor affecting upwards of 1:800 males. FXTAS is caused by an expanded "CGG" nucleotide repeat in the 5' untranslated region of the Fragile X Mental Retardation gene, FMR1. In patients and animal models, this expanded CGG repeat is associated with elevated FMR1 mRNA expression, neurodegeneration, and ubiquitin- positive intranuclear neuronal inclusions that contain the expanded CGG repeat mRNA and several proteins. Work to date has focused on the potential role of the CGG repeat in eliciting neurodegeneration via an RNA gain-of-function mechanism. However, critical aspects of disease pathology are not easily explained by a pure mRNA mediated sequestration process. Our central hypothesis is that the CGG repeat expansion contributes to neuronal degeneration in FXTAS via multiple, overlapping molecular mechanisms. These mechanisms include transcriptional dysregulation of the FMR1 gene in cis and RNA mediated gain of function toxicity leading to anomalous RNA splicing events and alterations in protein quality control pathways. Our proposal to test this hypothesis is divided into three aims. Aim 1 will examine the mechanisms by which FMR1 mRNA transcription is increased, focusing on the histone acetylation status at the FMR1 locus. Aim 2 will examine the role of the ubiquitin proteasome system in FXTAS pathogenesis. Both aims one and two will utilize a drosophila model of FXTAS as well as patient derived lymphoblasts. Aim 3 will employ inducible pluripotent stem cells from FXTAS patient fibroblasts that are differentiated into neurons. We will determine the alternative transcriptome profile of these human FXTAS neurons to address the hypothesis that sequestration of RNA binding proteins in FXTAS leads to aberrant mRNA splicing. Taken together, these studies should significantly extend our understanding of this neurodegenerative disorder and assist in identification appropriate candidate therapeutic targets. PUBLIC HEALTH RELEVANCE: Fragile X Tremor Ataxia syndrome (FXTAS) is a common inherited rodegenerative disorder that causes difficulties with walking, shaking of the limbs and dementia in older men. Our work proposes to test the idea that the genetic cause of FXTAS leads to neuronal death by two overlapping mechanisms: it increases the transcription of the mutant gene into RNA and it makes that RNA toxic to neurons, such that problems develop with the way these cells process and degrade other RNAs and proteins. To test our hypothesis we will utilize a fruit fly model of the disorder and we will also derive inducible pluripotent stem cells from patients with the disease so that we can study human derived neurons with the causative mutation. Taken together, we feel these studies will tell us a lot about what causes FXTAS and what we need to do to develop treatments for it.