Identification of Repeat-Associated, Non-ATG (RAN) translation modulators in neurodegenerative disease

脆性X相关性震颤/共济失调综合征（FXTAS）是由脆性X智力低下1（FMR 1）基因5'非翻译区（UTR）CGG-三核苷酸重复扩增引起的神经退行性疾病。蛋白质翻译起始的非典型模式，称为重复相关的非ATG（RAN）翻译，通过触发异常均聚蛋白质的合成在FXTAS和其他核苷酸扩增病症的发病机制中起关键作用，所述异常均聚蛋白质在神经元包涵体中积累并在疾病模型中引起毒性。为了了解RAN翻译是如何工作的以及它是如何被抑制的，我在FXTAS的黑腹果蝇模型中对RAN翻译的调节剂进行了基于候选人的筛选。该筛选鉴定出RNA解旋酶贝儿（DDX 3，在人类中）在基于果蝇和人类细胞的测定中对RAN翻译至关重要。该提案将确定DDX 3如何促进RAN翻译以及贝儿/DDX 3的遗传抑制是否会导致果蝇和哺乳动物神经元中的RAN翻译依赖性毒性。这项工作应该提供机制的见解，如何RAN翻译发生，同时提供了一个路线图，合理的治疗开发FXTAS和其他重复扩增疾病。

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder caused by the expansion of CGG-trinucleotide repeats in the 5’ untranslated region (UTR) of the gene fragile-X mental retardation 1 (FMR1). An atypical mode of protein translational initiation, known as repeat-associated, non- ATG (RAN) translation, plays a key role in the pathogenesis of FXTAS and other nucleotide-expansion disorders by triggering synthesis of aberrant homopolymeric proteins that accumulate in neuronal inclusions and elicit toxicity in disease models. To understand how RAN translation works and how it might be suppressed, I performed a candidate-based screen for modulators of RAN translation in a Drosophila melanogaster model of FXTAS. This screen identified the RNA helicase belle (DDX3, in humans) as critical for RAN translation in both flies and human cell-based assays. This proposal will determine how DDX3 facilitates RAN translation and whether genetic inhibition of belle/DDX3 alleviates RAN translation-dependent toxicity in Drosophila and mammalian neurons. This work should provide mechanistic insights into how RAN translation occurs while providing a roadmap for rational therapeutic development in FXTAS and other repeat expansion disorders.