Pathogenic Mechanisms in Fragile X Tremor Ataxia Syndrome

描述（由申请人提供）：脆性X轴震颤共济失调综合征（FXTAS）是步态障碍和震颤的常见病因，影响比例超过1：800的男性。FXTAS是由脆性X智力低下基因FMR 1的5'非翻译区中的扩增的“CGG”核苷酸重复引起的。在患者和动物模型中，这种扩增的CGG重复序列与FMR 1 mRNA表达升高、神经变性和含有扩增的CGG重复序列mRNA和几种蛋白质的泛素阳性核内神经元包涵体相关.迄今为止的工作集中在CGG重复序列在通过RNA功能获得机制引起神经变性中的潜在作用。然而，疾病病理学的关键方面不容易通过纯mRNA介导的隔离过程来解释。 我们的中心假设是CGG重复扩增通过多种重叠的分子机制促成FXTAS中的神经元变性。这些机制包括顺式FMR 1基因的转录失调和RNA介导的功能获得毒性，导致异常RNA剪接事件和蛋白质质量控制途径的改变。我们检验这一假设的建议分为三个目标。目的1将研究FMR 1 mRNA转录增加的机制，重点是FMR 1基因座的组蛋白乙酰化状态。目的2将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。目标3将采用来自FXTAS患者成纤维细胞的可诱导多能干细胞，其分化成神经元。我们将确定这些人FXTAS神经元的替代转录组谱，以解决FXTAS中RNA结合蛋白的螯合导致异常mRNA剪接的假设。总之，这些研究应该显着扩展我们对这种神经退行性疾病的理解，并有助于确定适当的候选治疗靶点。 公共卫生相关性：脆性X震颤共济失调综合征（FXTAS）是一种常见的遗传性退行性疾病，可导致老年男性行走困难、四肢颤抖和痴呆。我们的工作提出了测试FXTAS的遗传原因通过两种重叠机制导致神经元死亡的想法：它增加了突变基因转录成RNA，并使RNA对神经元有毒，这样这些细胞处理和降解其他RNA和蛋白质的方式就会出现问题。为了验证我们的假设，我们将利用果蝇模型的疾病，我们还将从患者中获得诱导性多能干细胞，这样我们就可以研究具有致病突变的人源性神经元。总而言之，我们认为这些研究将告诉我们很多关于FXTAS的病因以及我们需要采取哪些措施来开发治疗方法的信息。

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.