CGG repeat associated translation in Fragile X-associated Tremor/Ataxia Syndrome

脆性X相关性震颤/共济失调综合征（FXTAS）是人类神经系统疾病的一大类 这是由核苷酸重复序列的不稳定性和扩展引起的。在FXTAS中，CGG核苷酸重复序列在 脆性X基因FMR 1的5'非翻译区，并触发聚集的蛋白质内含物的形成 在病人的大脑中。我们的团队发现FXTAS CGG重复序列被翻译成有毒的均聚物， 尽管它的位置在一个典型的开放阅读框架之外，但它通过一个称为重复的过程， 相关的非AUG启动（RAN）翻译。RAN翻译的蛋白质在患者组织中积累， 在多个模型系统中导致CGG重复相关毒性。在本建议书中，我们将探讨如何 这种可选择的翻译起始是机械发生的。我们的初步数据表明， CGG重复序列处的翻译通过细胞应激选择性地增强，这通常阻断蛋白质合成。 平行地，CGG重复直接引起细胞应激并触发应激颗粒形成。我们的中央 假设是CGG RAN翻译和细胞应激参与了一个前馈循环， 神经变性我们的合作团队将通过使用生物化学技术直接测试这一假设 以及果蝇、小鼠和人的FXTAS诱导多能干细胞模型。在目标1中， 确定细胞应激如何选择性激活RAN翻译，特别关注起始因子 这一过程的基础。在目标2中，我们将阐明CGG重复序列如何引起细胞应激和影响 应激颗粒动力学以及该过程中的干预是否影响重复毒性。在目标3中，我们将测试 选择性阻断细胞应激通路是否可以破坏这种前馈回路并减轻CGG 在疾病模型中重复相关毒性。这些研究将共同阐明世界上的关键事件 FXTAS和其他核苷酸重复扩增疾病的发病机制，同时严格测试两种 选择性RAN翻译封锁的补充和创新方法。

Fragile X-associated tremor/Ataxia syndrome (FXTAS) is one of a large class of human neurological disorders that result from instability and expansion of nucleotide repeats. In FXTAS, a CGG nucleotide repeat expands in the 5’ untranslated region of the fragile X gene, FMR1, and triggers formation of aggregated protein inclusions in the patient brains. Our group found that the FXTAS CGG repeat gets translated into toxic homopolymeric proteins despite its location outside of a canonical open reading frame through a process known as repeat associated Non-AUG initiated (RAN) translation. RAN translated proteins accumulate in patient tissues and contribute to CGG repeat associated toxicity in multiple model systems. In this proposal, we will explore how this alternative translational initiation occurs mechanistically. Our preliminary data suggests that RAN translation at CGG repeats is selectively enhanced by cellular stress, which typically blocks protein synthesis. In parallel, CGG repeats directly elicit cellular stress and trigger stress granule formation. Our central hypothesis is that CGG RAN translation and cellular stress participate in a feed-forward loop that drives neurodegeneration. Our collaborative team will directly test this hypothesis by using biochemical techniques as well as drosophila, mouse and human induced pluripotent stem cell models of FXTAS. In Aim 1 we will determine how cellular stress selectively activates RAN translation, focusing specifically on initiation factors that underlie this process. In Aim 2, we will elucidate how CGG repeats elicit cellular stress and influence stress granule dynamics and whether interventions in this process impact repeat toxicity. In Aim 3, we will test whether selective blockade of cellular stress pathways can disrupt this feed forward loop and alleviate CGG repeat associated toxicity across disease models. Together, these studies will illuminate critical events in the pathogenesis of FXTAS and other nucleotide repeat expansion disorders while rigorously testing two complementary & innovative approaches to selective RAN translation blockade.