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

脆性X相关震颤/共济失调综合征(FXTAS)是由脆性X智力低下1(FMR1)基因5‘非翻译区CGG-三核苷酸重复序列扩增引起的一种神经退行性疾病。一种非典型的蛋白质翻译起始模式，称为重复相关的非ATG(RAN)翻译，在FXTAS和其他核苷酸扩张障碍的发病机制中发挥关键作用，它通过触发异常同源多聚体蛋白的合成积累在神经元包涵体中，并在疾病模型中引发毒性。为了了解RAN翻译是如何工作的，以及它可能是如何被抑制的，我在FXTAS的果蝇黑腹果蝇模型中对RAN翻译的调节子进行了基于候选人的筛选。这一筛选确定了RNA解旋酶Belle(DDX3，在人类中)对于苍蝇和人类细胞检测中的RAN翻译都至关重要。这一建议将确定DDX3如何促进RAN翻译，以及Belle/DDX3的基因抑制是否减轻了果蝇和哺乳动物神经元中RAN翻译依赖的毒性。这项工作应该为RAN翻译是如何发生的提供机械性的见解，同时为FXTAS和其他重复扩张性疾病的合理治疗开发提供路线图。

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.