Enhanced insulin signalling ameliorates C9orf72 hexanucleotide repeat expansion toxicity in Drosophila

G4C2 repeat expansions within the C9orf72 gene are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The repeats undergo repeat-associated non-ATG translation to generate toxic dipeptide repeat proteins. Here, we show that insulin/Igf signalling is reduced in fly models of C9orf72 repeat expansion using RNA-sequencing of adult brain. We further demonstrate that activation of insulin/Igf signalling can mitigate multiple neurodegenerative phenotypes in flies expressing either expanded G4C2 repeats or the toxic dipeptide repeat protein poly-GR. Levels of poly-GR are reduced when components of the insulin/Igf signalling pathway are genetically activated in the diseased flies, suggesting a mechanism of rescue. Modulating insulin signalling in mammalian cells also lowers poly-GR levels. Remarkably, systemic injection of insulin improves the survival of flies expressing G4C2 repeats. Overall, our data suggest that modulation of insulin/Igf signalling could be an effective therapeutic approach against C9orf72 ALS/FTD. Overall design: mRNA profiles from heads of old female control (elavGS/+) and polyGR100 flies

C9orf72基因内的G4C2重复扩增是肌萎缩侧索硬化症（amyotrophic lateral sclerosis, ALS）与额颞叶痴呆（frontotemporal dementia, FTD）最常见的遗传致病诱因。该重复序列可发生重复相关非ATG翻译（repeat-associated non-ATG translation），进而产生毒性二肽重复蛋白（toxic dipeptide repeat proteins）。本研究在C9orf72重复扩增果蝇模型中，通过对成年果蝇大脑开展RNA测序（RNA-sequencing）分析，发现其胰岛素/胰岛素样生长因子（insulin/Igf）信号通路活性显著降低。我们进一步证实，激活胰岛素/Igf信号通路，能够缓解两类转基因果蝇的多种神经退行性表型：一类为携带扩增型G4C2重复序列的果蝇，另一类为表达毒性二肽重复蛋白poly-GR的果蝇。当在患病果蝇中通过遗传学手段激活胰岛素/Igf信号通路的相关组分时，poly-GR的蛋白水平会显著下调，这提示了一种潜在的疾病挽救机制。在哺乳动物细胞中调控胰岛素信号通路，同样可降低poly-GR的蛋白水平。尤为值得一提的是，全身性注射胰岛素能够延长表达G4C2重复序列的果蝇的存活时长。综上，本研究数据表明，调控胰岛素/Igf信号通路或可成为对抗C9orf72相关ALS/FTD的有效治疗策略。实验整体设计：采集老年雌性对照果蝇（elavGS/+）与polyGR100果蝇的头部组织，进行mRNA表达谱分析。