Psychiatry, Graduate School of Medicine, Osaka University, Osaka, Japan.
EMBO J. 2020 Oct 1;39(19):e102700. doi: 10.15252/embj.2019102700. Epub 2020 Aug 24.
Nucleotide repeat expansions in the C9orf72 gene cause frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). Transcribed repeat RNA accumulates within RNA foci and is also translated into toxic dipeptide repeat proteins (DPR). The mechanism of repeat RNA accumulation, however, remains unclear. The RNA exosome complex is a multimeric ribonuclease involved in degradation of defective RNA. Here, we uncover the RNA exosome as a major degradation complex for pathogenic C9orf72-derived repeat RNA. Knockdown of EXOSC10, the catalytic subunit of the complex, enhanced repeat RNA and DPR protein expression levels. RNA degradation assays confirmed that EXOSC10 can degrade both sense and antisense repeats. Furthermore, EXOSC10 reduction increased RNA foci and repeat transcripts in patient-derived cells. Cells expressing toxic poly-GR or poly-PR proteins accumulate a subset of small nucleolar RNA precursors, which are physiological substrates of EXOSC10, as well as excessive repeat RNA, indicating that arginine-rich DPR proteins impair the intrinsic activity of EXOSC10. Collectively, arginine-rich DPR-mediated impairment of EXOSC10 and the RNA exosome complex compromises repeat RNA metabolism and may thus exacerbate C9orf72-FTLD/ALS pathologies in a vicious cycle.
C9orf72 基因中的核苷酸重复扩展会导致额颞叶变性（FTLD）和肌萎缩侧索硬化症（ALS）。转录的重复 RNA 在 RNA 焦点内积累，并且也被翻译为有毒的二肽重复蛋白（DPR）。然而，重复 RNA 积累的机制仍不清楚。RNA 外切酶复合物是一种多聚核糖核酸酶，参与缺陷 RNA 的降解。在这里，我们发现 RNA 外切酶复合物是致病 C9orf72 衍生的重复 RNA 的主要降解复合物。复合物的催化亚基 EXOSC10 的敲低增加了重复 RNA 和 DPR 蛋白的表达水平。RNA 降解分析证实 EXOSC10 可以降解有义和反义重复序列。此外，EXOSC10 的减少增加了患者来源细胞中的 RNA 焦点和重复转录本。表达有毒的 poly-GR 或 poly-PR 蛋白的细胞积累了一小部分小核仁 RNA 前体，这些前体是 EXOSC10 的生理底物，以及过量的重复 RNA，这表明精氨酸丰富的 DPR 蛋白会损害 EXOSC10 的内在活性。总之，精氨酸丰富的 DPR 介导的 EXOSC10 和 RNA 外切酶复合物的损伤会破坏重复 RNA 代谢，从而可能在恶性循环中加剧 C9orf72-FTLD/ALS 病理学。
