Neuronal intranuclear inclusion disease (NIID) is neurodegenerative disease characterized by widespread inclusions. Despite the identification of GGC repeat expansion in 5’UTR of NOTCH2NLC gene in adult-onset NIIDs, its pathogenic mechanism remains unclear. Gain-of-function poly-amino-acid proteins generated by unconventional translation have been revealed in nucleotide repeat expansion disorders, inspiring us to explore the possibility of unconventional translation in NIID. Here we demonstrated that NOTCH2NLC 5’UTR triggers the translation of a polyglycine (polyG)-containing protein, N2NLCpolyG. N2NLCpolyG accumulates in p62-positive inclusions in cultured cells, mouse models, and NIID patient tissues with NOTCH2NLC GGC expansion. Translation of N2NLCpolyG is initiated by an upstream open reading frame (uORF) embedding the GGC repeats. N2NLCpolyG tends to aggregate with the increase of GGC repeat units, and displays phase separation properties. N2NLCpolyG aggregation impairs nuclear lamina and nucleocytoplasmic transport but does not necessarily cause acute death on neuronal cells. Our study suggests a similarity of pathogenic mechanisms between NIID and another GGC-repeat disease, fragile X-associated tremor ataxia syndrome. These findings expand our knowledge of protein gain-of-function in NIID, and further highlight evidence for a novel spectrum of diseases caused by aberrant polyG protein aggregation, namely the polyG diseases.

神经元核内包涵体病 (NIID) 是一种以广泛包涵体为特征的神经退行性疾病。尽管在成人发病的 NIID 中发现了NOTCH2NLC基因5'UTR 中的 GGC 重复扩增，但其致病机制仍不清楚。非常规翻译产生的功能获得性多氨基酸蛋白已在核苷酸重复扩增障碍中得到揭示，启发我们探索在 NIID 中进行非常规翻译的可能性。在这里，我们证明了NOTCH2NLC 5'UTR 触发了含有多聚甘氨酸 (polyG) 的蛋白质 N2NLCpolyG 的翻译。N2NLCpolyG 在培养细胞、小鼠模型和具有NOTCH2NLC的 NIID 患者组织中的 p62 阳性包涵体中积累GGC 扩展。N2NLCpolyG 的翻译由嵌入 GGC 重复的上游开放阅读框 (uORF) 启动。N2NLCpolyG随着GGC重复单元的增加而趋于聚集，并表现出相分离特性。N2NLCpolyG 聚集会损害核层和核质转运，但不一定会导致神经元细胞急性死亡。我们的研究表明 NIID 与另一种 GGC 重复疾病，脆性 X 相关震颤共济失调综合征之间的致病机制相似。这些发现扩展了我们对 NIID 中蛋白质功能获得的认识，并进一步突出了由异常 polyG 蛋白聚集引起的新型疾病谱的证据，即 polyG 疾病。