The FMR1 CGG repeat as functional element and therapeutic target in Fragile X associated disorders

FMR1重复序列作为脆性X疾病的功能元件和治疗靶点。 短串联重复序列(STR)扩增可导致约50种遗传性神经系统疾病。然而， 疾病相关基因座只代表了约300万个STR中的一小部分 人类基因组。尽管它们在人类疾病中很重要，但更广泛的问题是 这些重复元件在正常神经生物学中发挥的内在作用在很大程度上是未知的。我们 最近发现了FMR1基因5‘非编码区CGG重复序列的一种保守的天然功能。 这种重复在脆性X综合征(FXS)中扩大，FXS是自闭症和智力障碍的常见原因 残疾)和脆性X相关震颤/共济失调综合征(FXTAS，与年龄相关 神经退行性疾病)。在正常和扩展大小时，FMR1 CGG重复触发 在没有Aug起始密码子(CGG Ran)的情况下翻译多个隐含蛋白 译文)。我们最近描述了CGG重复和RAN翻译如何充当上游 开放阅读框架(UORF)，以阻止脆性X蛋白FMRP的翻译。使用 报告分析与RAN翻译结合阻断反义寡核苷酸 (RAN ASOS)在人类神经元中，我们发现CGG重复和RAN翻译 从根本上抑制FMRP合成。代谢型谷氨酸受体可减轻这种抑制作用 (MGluR)激活，这是突触可塑性的一种形式，对学习和 记忆，并与脆性X相关疾病有关。基于这些发现，我们的中央 假设RAN翻译和串联微卫星重复序列在 对它们所在基因的调节，以及这些天然功能的异常 会导致人类疾病。我们在这个项目中的目标有三个方面：1)确定机构 通过CGG重复和RAN翻译调节FMRP的合成，2)调查 在小鼠模型和人类中扰乱这种调控环路的后果 神经元，以及3)评估ASO是否可用于同时抑制RAN 翻译和激活FXS和FXTAS人神经元FMRP合成作为迈向 新的治疗进展。

The FMR1 repeat as functional element and therapeutic target in Fragile X disorders. Short Tandem repeat (STR) expansions cause ~50 inherited neurological diseases. However, disease associated loci represent only a small fraction of the ~3 million STRs present in the human genome. Despite their importance in human disease, the broader question of what intrinsic roles these repetitive elements play in normal neurobiology is largely unexplored. We recently discovered a conserved and native function for CGG repeats in the 5’ UTR of FMR1. This repeat expands in Fragile X Syndrome (FXS, a common cause of autism and intellectual disability) and Fragile X-associated Tremor/Ataxia Syndrome (FXTAS, an age related neurodegenerative disorder). At normal and expanded sizes, FMR1 CGG repeats trigger translation of multiple cryptic proteins in the absence of an AUG start codon (CGG RAN translation). We recently described how CGG repeats and RAN translation act as an upstream open reading frame (uORF) to impede translation of the fragile X protein, FMRP. Using a combination of reporter assays as well as RAN translation blocking antisense oligonucleotides (RAN ASOs) in human neurons, we found that both the CGG repeats and RAN translation inhibit FMRP synthesis basally. This inhibition is alleviated by metabotropic glutamate receptor (mGluR) activation, which underlies a form of synaptic plasticity important for learning and memory and implicated in Fragile X-associated disorders. Based on these findings, our central hypothesis is that RAN translation and tandem microsatellite repeats have native functions in the regulation of the genes in which they reside, and that aberrancies in these native functions contribute to human disease. Our goals in this project are 3 fold: 1) Determine the mechanisms by which CGG repeats and RAN translation regulate FMRP synthesis, 2) investigate what consequences result from disrupting this regulatory loop in both mouse models and human neurons, and 3) evaluate whether ASOs can be used to simultaneously suppress RAN translation and activate FMRP synthesis in FXS and FXTAS human neurons as a step towards novel therapeutic development.