Upstream open reading frame with NOTCH2NLC GGC expansion generates polyglycine aggregates and disrupts nucleocytoplasmic transport: implications for polyglycine diseases

• DOI: 10.1007/s00401-021-02375-3
• Publication Date: 2021-10-25T13:20:27Z
• Authors: Shaoping Zhong; Yangye Lian; Wenyi Luo; Rongkui Luo; Xiaoling Wu; Jun Ji; Yuan Ji; Jing Ding; Xin Wang
• Keywords: 0303 health sciences; Intranuclear Inclusion Bodies; Active Transport, Cell Nucleus; Nerve Tissue Proteins; Neurodegenerative Diseases; Mice; Open Reading Frames; 03 medical and health sciences; Protein Biosynthesis; Animals; Humans; Intercellular Signaling Peptides and Proteins; Peptides; Trinucleotide Repeat Expansion

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.