The most common genetic cause of amyotrophic lateral sclerosis (ALS) is a GGGGCC (G4C2) hexanucleotide repeat expansions in first intron of the C9orf72 gene. The accumulation of repetitive RNA sequences can mediate toxicity potentially through the formation of intranuclear RNA foci that sequester key RNA-binding proteins (RBPs), and non-ATG mediated translation into toxic dipeptide protein repeats. However, the contribution of RBP sequestration to the mechanisms underlying RNA-mediated toxicity remain unknown. Here we show that the ALS-associated RNA-binding protein, Matrin-3 (MATR3), colocalizes with G4C2 RNA foci in patient tissues as well as iPSC-derived motor neurons harboring the C9orf72 mutation. Hyperexpansion of C9 repeats perturbed subcellular distribution and levels of endogenous MATR3 in C9-ALS patient-derived motor neurons. Interestingly, we observed that ectopic expression of human MATR3 strongly mitigates G4C2-mediated neurodegeneration in vivo. MATR3-mediated suppression of C9 toxicity was dependent on the RNA-binding domain of MATR3. Importantly, we found that expression of MATR3 reduced the levels of RAN-translation products in mammalian cells in an RNA-dependent manner. Finally, we have shown that knocking down endogenous MATR3 in C9-ALS patient-derived iPSC neurons decreased the presence of G4C2 RNA foci in the nucleus. Overall, these studies suggest that MATR3 genetically modifies the neuropathological and the pathobiology of C9orf72 ALS through modulating the RNA foci and RAN translation.

中文翻译：

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Matrin-3 对 C9orf72 ALS/FTD 相关神经变性的 RNA 依赖性抑制


肌萎缩侧索硬化症 (ALS) 最常见的遗传原因是 C9orf72 基因第一个内含子中的 GGGGCC (G4C2) 六核苷酸重复扩增。重复RNA序列的积累可以通过形成核内RNA焦点来介导潜在的毒性，该核内RNA焦点隔离关键的RNA结合蛋白(RBP)，以及非ATG介导的翻译成有毒二肽蛋白重复序列​​。然而，RBP 隔离对 RNA 介导的毒性机制的贡献仍然未知。在这里，我们发现 ALS 相关 RNA 结合蛋白 Matrin-3 (MATR3) 与患者组织中的 G4C2 RNA 灶以及携带 C9orf72 突变的 iPSC 衍生运动神经元共定位。 C9 重复的过度扩张扰乱了 C9-ALS 患者来源的运动神经元中内源性 MATR3 的亚细胞分布和水平。有趣的是，我们观察到人 MATR3 的异位表达可以强烈减轻 G4C2 介导的体内神经变性。 MATR3 介导的 C9 毒性抑制依赖于 MATR3 的 RNA 结合域。重要的是，我们发现 MATR3 的表达以 RNA 依赖性方式降低了哺乳动物细胞中 RAN 翻译产物的水平。最后，我们发现敲除 C9-ALS 患者来源的 iPSC 神经元中的内源性 MATR3 会减少细胞核中 G4C2 RNA 灶的存在。总体而言，这些研究表明 MATR3 通过调节 RNA 焦点和 RAN 翻译，从基因上改变了 C9orf72 ALS 的神经病理学和病理学。