The GGGGCC hexanucleotide expansion in C9orf72 (C9) is the most frequent known cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), yet a clear understanding of how C9 fits into the broader context of ALS/FTD pathology has remained lacking. The repetitive RNA derived from the C9 repeat is known to sequester hnRNPH, a splicing regulator, into insoluble aggregates, resulting in aberrant alternative splicing. Furthermore, hnRNPH insolubility and altered splicing of a robust set of targets have been observed to correlate in C9 and sporadic ALS/FTD patients alike, suggesting that changes along this axis are a core feature of disease pathogenesis. Here, we characterize previously uncategorized RNA splicing defects involving widespread intron retention affecting almost 2000 transcripts in C9ALS/FTD brains exhibiting a high amount of sequestered, insoluble hnRNPH. These intron retention events appear not to alter overall expression levels of the affected transcripts but rather the protein-coding regions. These retained introns affect transcripts in multiple cellular pathways predicted to be involved in C9 as well as sporadic ALS/FTD etiology, including the proteasomal and autophagy systems. The retained intron pre-mRNAs display a number of characteristics, including enrichment of hnRNPH-bound splicing enhancer motifs and a propensity for G-quadruplex (G-Q) formation, linking the defective splicing directly to high amounts of sequestered hnRNPH. Together, our results reveal previously undetected splicing defects in high insoluble hnRNPH-associated C9ALS brains, suggesting a feedback between effective RNA-binding protein dosage and protein quality control in C9, and perhaps all, ALS/FTD.

中文翻译：

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广泛的内含子保留损害 C9orf72 ALS 大脑中的蛋白质稳态

的六核苷酸GGGGCC扩张C9orf72(C9) 是肌萎缩侧索硬化 (ALS) 和额颞叶痴呆 (FTD) 的最常见的已知原因，但仍然缺乏对 C9 如何适应更广泛的 ALS/FTD 病理学背景的清楚了解。已知源自 C9 重复的重复 RNA 将剪接调节因子 hnRNPH 隔离成不溶性聚集体，从而导致异常的选择性剪接。此外，已观察到 hnRNPH 不溶性和一组强大目标的改变剪接与 C9 和散发性 ALS/FTD 患者相关，这表明沿该轴的变化是疾病发病机制的核心特征。在这里，我们表征了以前未分类的 RNA 剪接缺陷，这些缺陷涉及广泛的内含子保留，影响 C9ALS/FTD 大脑中的近 2000 个转录本，表现出大量的隔离、不溶性 hnRNPH。这些内含子保留事件似乎不会改变受影响转录物的整体表达水平，而是改变蛋白质编码区域。这些保留的内含子影响预测涉及 C9 以及散发性 ALS/FTD 病因（包括蛋白酶体和自噬系统）的多种细胞途径中的转录物。保留的内含子前 mRNA 显示出许多特征，包括富集 hnRNPH 结合的剪接增强子基序和形成 G-四链体 (GQ) 的倾向，将有缺陷的剪接直接与大量隔离的 hnRNPH 联系起来。总之，我们的结果揭示了以前未检测到的高不溶性 hnRNPH 相关 C9ALS 大脑中的剪接缺陷，表明有效的 RNA 结合蛋白剂量和 C9 中的蛋白质质量控​​制之间存在反馈，也许所有，ALS/FTD。