In amyotrophic lateral sclerosis (ALS) motor neurons (MNs) undergo dying-back, where the distal axon degenerates before the soma. The hexanucleotide repeat expansion (HRE) in C9ORF72 is the most common genetic cause of ALS, but the mechanism of pathogenesis is largely unknown with both gain- and loss-of-function mechanisms being proposed. To better understand C9ORF72-ALS pathogenesis, we generated isogenic induced pluripotent stem cells. MNs with HRE in C9ORF72 showed decreased axonal trafficking compared with gene corrected MNs. However, knocking out C9ORF72 did not recapitulate these changes in MNs from healthy controls, suggesting a gain-of-function mechanism. In contrast, knocking out C9ORF72 in MNs with HRE exacerbated axonal trafficking defects and increased apoptosis as well as decreased levels of HSP70 and HSP40, and inhibition of HSPs exacerbated ALS phenotypes in MNs with HRE. Therefore, we propose that the HRE in C9ORF72 induces ALS pathogenesis via a combination of gain- and loss-of-function mechanisms.

在肌萎缩性侧索硬化症（ALS）中，运动神经元（MNs）消亡，远端轴突在躯体之前退化。C9ORF72中的六核苷酸重复扩增（HRE）是ALS的最常见遗传原因，但发病机理在很大程度上尚不清楚，同时提出了功能获得和丧失的机制。为了更好地了解C9ORF72 -ALS的发病机制，我们产生了等基因诱导的多能干细胞。在C9ORF72中具有HRE的MN与基因校正的MNs相比，显示出减少的轴突运输。但是，敲除C9ORF72并不能概括健康对照组中MN的这些变化，提示功能增强机制。相反，在具有HRE的MN中敲除C9ORF72会加剧轴突运输缺陷，凋亡增加以及HSP70和HSP40的水平降低，并且对HSP的抑制会加剧具有HRE的MN中的ALS表型。因此，我们建议C9ORF72中的HRE通过获得和丧失功能机制的组合诱导ALS发病。