The toxicity of the RNA CGG repeats in FXTAS

FXTAS 中 RNA CGG 重复序列的毒性

• 批准号: 8897690
• 负责人: LUBOV T TIMCHENKO
• 金额: $ 13.55万
• 依托单位: CINCINNATI CHILDRENS HOSP MED CTR
• 依托单位国家: 美国
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8897690
• 关键词: toxicity; RNA; CGG; repeats; FXTAS

DESCRIPTION (provided by applicant): Fragile X-associated Tremor/Ataxia Syndrome (FXTAS) is a progressive neurodegenerative disease characterized by tremor with ataxia, brain atrophy and cognitive defects. FXTAS is caused by CGG expansions, varying in the length from ~55 to 200 repeats (CGG55-200), in the 5' UTR of the FMR1 gene. The CGG expansions more than 200 repeats in the same gene cause the Fragile X Syndrome (FXS), an intellectual disability, distinct from FXTAS. Long CGG expansions silence the transcription of the FMR1 gene; while short expansions elevate the transcription of the FMR1. Numerous models show that the FMR1 mRNA with CGG55-200 repeats or RNA CGG55-200 repeats outside of the FMR1 mRNA cause neurodegeneration. The main pathologic feature of FXTAS is the formation of the ubiquitin (Ub)-positive inclusions that contain the proteasome and several RNA-binding proteins. However, the role of the Ub- proteasome system and RNA-binding proteins in the FXTAS pathology is not understood. The primary targets of the RNA CGG repeats also remain unknown. Previous work in my lab was focused on the mechanisms for Myotonic Dystrophies type 1 and type 2 which are caused by RNA CUG and CCUG repeats. In the course of these studies, we have found that CUG and CCUG repeats alter RNA metabolism by interaction with different RNA-binding proteins and by formation of soluble and precipitated RNA-protein complexes (RPCs). CUG and CCUG RNAs form soluble complexes with RNA-binding protein, CUGBP1, increasing CUGBP1 stability. CCUG repeats also affect protein degradation via formation of large RPCs, containing the proteasome and stress-related proteins. We propose that, similar to DM, short (55-200) RNA CGG repeats form soluble and precipitated RPCs. We suggest that soluble rCGG-RPCs might contain RNA-binding proteins such as CUGBP1, Pur� and hnRNP A2/B1, affecting their function. In support of this hypothesis, we have found that CUGBP1 is increased in brains of FMR1-CGG98 knock in mice. It is known that the precipitated rCGG repeats (foci) bind Sam68, MBNL1 and hnRNP G. We suggest that the excessive binding of these proteins to the precipitated RPCs may attract the proteasome leading to the Ub-positive inclusions. The main hypothesis of this application is that the brain atrophy and neurodegeneration in FXTAS is due to: (1) misregulation of RNA processing by RNA-binding proteins bound in soluble and precipitated RPCs; and (2) due to altered protein degradation. To determine the role of these toxic events in the FXTAS pathology, we propose to identify the primary targets of the rCGG100 and the FMR1-CGG90 RNAs using a tet-regulated cell model (Aim 1). The role of elevation of CUGBP1 in the neurodegeneration in vivo will be determined in rCGG90 transgenic and FMR1-CGG98 knock in mice of different age (Aim 2). These studies will help to identify the molecular mechanism of FXTAS and will provide a background for the development of therapy for FXTAS.

描述（由申请人提供）：脆性 X 相关震颤/共济失调综合征 (FXTAS) 是一种进行性神经退行性疾病，其特征是震颤伴共济失调、脑萎缩和认知缺陷，FXTAS 是由 CGG 扩张引起的，长度从约 55 到 55 不等。 FMR1 基因的 5' UTR 中有 200 个重复 (CGG55-200)，CGG 扩展超过。与 FXTAS 不同，同一基因中的 200 个重复会导致脆性 X 综合征 (FXS)，这是一种智力障碍。具有 CGG55-200 重复序列的 mRNA 或 FMR1 mRNA 之外的 RNA CGG55-200 重复序列会导致神经变性。FXTAS 的主要病理特征是。含有蛋白酶体和几种 RNA 结合蛋白的泛素 (Ub) 阳性包涵体的形成 然而，Ub 蛋白酶体系统和 RNA 结合蛋白在 FXTAS 病理学中的作用尚不清楚。 RNA CGG 重复序列也仍然未知。在这些研究过程中，我实验室的工作重点是由 RNA CUG 和 CCUG 重复序列引起的 1 型和 2 型强直性肌营养不良的机制。我们发现 CUG 和 CCUG 重复通过与不同的 RNA 结合蛋白相互作用以及通过形成可溶性和沉淀的 RNA-蛋白复合物 (RPC) 来改变 RNA 代谢，CUG 和 CCUG RNA 与 RNA 结合蛋白 CUGBP1 形成可溶性复合物，从而增加。 CUGBP1 的稳定性也通过形成含有蛋白酶体和应激相关蛋白的大 RPC 来影响蛋白质降解。 (55-200) RNA CGG 重复序列形成可溶性和沉淀的 RPC。我们认为可溶性 rCGG-RPC 可能含有 RNA 结合蛋白，例如 CUGBP1、Pur� 和 hnRNP A2/B1，从而影响其功能。发现 FMR1-CGG98 敲除的小鼠大脑中 CUGBP1 增加，已知沉淀的 rCGG 重复序列（灶点）结合。 Sam68、MBNL1 和 hnRNP G。我们认为这些蛋白质与沉淀的 RPC 的过度结合可能会吸引蛋白酶体，导致 Ub 阳性包涵体。该应用的主要假设是 FXTAS 中的脑萎缩和神经变性是由于。 ：(1) 可溶性和沉淀的 RPC 中结合的 RNA 结合蛋白对 RNA 加工的错误调节；以及 (2) 由于蛋白质降解的改变而导致这些毒性的作用。 FXTAS 病理学事件中，我们建议使用 tet 调节的细胞模型来确定 rCGG100 和 FMR1-CGG90 RNA 的主要靶标（目标 1），将在 rCGG90 中确定 CUGBP1 在体内神经变性中的作用。对不同年龄的小鼠进行转基因和 FMR1-CGG98 敲除（目标 2）将有助于确定 FXTAS 的分子机制并提供背景。用于开发 FXTAS 疗法。