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）是一种神经退行性疾病，由脆性x智力迟钝1 （FMR1）基因5 '非翻译区（UTR）的cgg -三核苷酸重复扩增引起。一种非典型的蛋白质翻译启动模式，即重复相关的非ATG （RAN）翻译，在FXTAS和其他核苷酸扩张疾病的发病机制中发挥关键作用，通过触发异常的均聚蛋白的合成，这些均聚蛋白在神经元包涵体中积累，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是如何被抑制的，我在果蝇FXTAS模型中进行了基于候选的RAN翻译调节剂筛选。在基于果蝇和人类细胞的分析中，该筛选确定了RNA解旋酶belle （DDX3，在人类中）对RAN翻译至关重要。本研究将确定DDX3如何促进RAN翻译，以及belle/DDX3基因抑制是否减轻果蝇和哺乳动物神经元中RAN翻译依赖性毒性。这项工作将提供RAN翻译如何发生的机制见解，同时为FXTAS和其他重复扩张疾病的合理治疗发展提供路线图。

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.