Objectives The hexanucleotide repeat expansion in the C9orf72 gene is the most common mutation associated with amyotrophic lateral sclerosis (C9-ALS) and frontotemporal dementia (C9-FTD). Until now, it is unknown which factors define whether C9orf72 mutation carriers develop ALS or FTD. Our aim was to identify protein biomarker candidates in the cerebrospinal fluid (CSF) which differentiate between C9-ALS and C9-FTD and might be indicative for the outcome of the mutation. Methods We compared the CSF proteome of 16 C9-ALS and 8 C9-FTD patients and 11 asymptomatic C9orf72 mutation carriers (CAR) by isobaric tags for relative and absolute quantitation. Eleven biomarker candidates were selected from the pool of differentially regulated proteins for further validation by multiple reaction monitoring and single-molecule array in a larger cohort (n=156). Results In total, 2095 CSF proteins were identified and 236 proteins were significantly different in C9-ALS versus C9-FTD including neurofilament medium polypeptide (NEFM) and chitotriosidase-1 (CHIT1). Eight candidates were successfully validated including significantly increased ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCHL1) levels in C9-ALS compared with C9-FTD and controls and decreased neuronal pentraxin receptor (NPTXR) levels in C9-FTD versus CAR. Conclusions This study presents a deep proteomic CSF analysis of C9-ALS versus C9-FTD patients. As a proof of concept, we observed higher NEFM and CHIT1 CSF levels in C9-ALS. In addition, we also show clear upregulation of UCHL1 in C9-ALS and downregulation of NPTXR in C9-FTD. Significant differences in UCHL1 CSF levels may explain diverging ubiquitination and autophagy processes and NPTXR levels might reflect different synapses organisation processes.

中文翻译：

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C9orf72六核苷酸重复扩增在肌萎缩性侧索硬化和额颞叶痴呆中的不同CSF蛋白谱

目的C9orf72基因中的六核苷酸重复扩增是与肌萎缩性侧索硬化症（C9-ALS）和额颞痴呆（C9-FTD）相关的最常见突变。到目前为止，尚不清楚哪些因素定义C9orf72突变携带者会发展为ALS还是FTD。我们的目的是在脑脊液（CSF）中鉴定出可区分C9-ALS和C9-FTD的蛋白生物标志物候选物，并可能指示突变的结果。方法我们通过同量异位标签比较了16例C9-ALS和8例C9-FTD患者和11例无症状C9orf72突变携带者（CAR）的CSF蛋白质组的相对和绝对定量。从差异调节蛋白库中选择11种生物标志物候选物，以通过更大规模的队列研究（n = 156）中的多反应监测和单分子阵列进一步验证。结果总共鉴定出2095个CSF蛋白，其中C9-ALS与C9-FTD包括神经丝培养基多肽（NEFM）和壳三糖苷酶-1（CHIT1）相比有236种蛋白有显着差异。已成功验证了八种候选药物，包括与C9-FTD和对照相比，C9-ALS中的泛素羧基末端水解酶同工酶L1（UCHL1）水平显着提高，而C9-FTD与CAR相比，神经元五味素受体（NPTXR）水平降低。结论本研究对C9-ALS与C9-FTD患者进行了深入的蛋白质组CSF分析。作为概念证明，我们在C9-ALS中观察到更高的NEFM和CHIT1 CSF水平。此外，我们还显示了C9-ALS中UCHL1的明显上调和C9-FTD中的NPTXR的下调。