Antisense, but not sense, repeat expanded RNAs activate PKR/eIF2a-dependent ISR in C9ORF72 FTD/ALS

• Type of Material: Article
• Authors: Janani Parameswaran, Emory University; Nancy Zhang, Emory University; Elke Braems, Katholieke University Leuven; Kedamawit Tilahun, Emory University; Devesh C Pant, Emory University; Keena Yin, Emory University; Seneshaw Asress, Emory University; Kara Heeren, Katholieke University Leuven; Anwesha Banerjee, Emory University; Emma Davis, Emory University; Samantha L Schwartz, Emory University; Graeme Conn, Emory University; Gary Bassell, Emory University; Ludo van den Bosch, Katholieke Univ Leuven; Jie Jiang, Emory University
• Language: English
• Date: 2023-04-19
• Publisher: eLIFE SCIENCES PUBL LTD
• Publication Version: Final Published Version
• Copyright Statement: Parameswaran et al.
• Final Published Version (URL): http://dx.doi.org/10.7554/eLife.85902
• Title of Journal or Parent Work: ELIFE
• Volume: 12
• Grant/Funding Information: NIH R01NS114253 to Gary J Bassell.; ALS Association 22-PDF-605 to Devesh C Pant.; FWO-Vlaanderen G0C1620N to Ludo Van Den Bosch.; Fonds Wetenschappelijk Onderzoek G0C1620N to Ludo Van Den Bosch.; NIH 5R21NS114908-02 to Gary J Bassell, Jie Jiang.; ALS Association 21-PDF-585 to Janani Parameswaran.; FWO-Vlaanderen 1145621N to Elke Braems.; National Institute of Neurological Disorders and Stroke R01NS114253 to Anwesha Banerjee, Gary J Bassell.; This paper was supported by the following grants:; National Institutes of Health R01AG068247 to Jie Jiang.
• Keywords: Zebrafish; PROTEIN-KINASE; PKR; C9ORF72; Science & Technology; AMYOTROPHIC-LATERAL-SCLEROSIS; RAN TRANSLATION; Life Sciences & Biomedicine - Other Topics; HEXANUCLEOTIDE REPEAT; FRONTOTEMPORAL LOBAR DEGENERATION; integrated stress response; EXPANSION; TOXICITY; antisense RNA; FOCI; ALS; Life Sciences & Biomedicine; FTD; Biology; UNCONVENTIONAL TRANSLATION

Abstract

GGGGCC (G4C2) hexanucleotide repeat expansion in the C9ORF72 gene is the most common genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). The repeat is bidirectionally transcribed and confers gain of toxicity. However, the underlying toxic species is debated, and it is not clear whether antisense CCCCGG (C4G2) repeat expanded RNAs contribute to disease pathogenesis. Our study shows that C9ORF72 antisense C4G2 repeat expanded RNAs trigger the activation of the PKR/eIF2α-dependent integrated stress response independent of dipeptide repeat proteins that are produced through repeat-associated non-AUG initiated translation, leading to global translation inhibition and stress granule formation. Reducing PKR levels with either siRNA or morpholinos mitigates integrated stress response and toxicity caused by the antisense C4G2 RNAs in cell lines, primary neurons, and zebrafish. Increased phosphorylation of PKR/eIF2α is also observed in the frontal cortex of C9ORF72 FTD/ALS patients. Finally, only antisense C4G2, but not sense G4C2, repeat expanded RNAs robustly activate the PKR/eIF2α pathway and induce aberrant stress granule formation. These results provide a mechanism by which antisense C4G2 repeat expanded RNAs elicit neuronal toxicity in FTD/ALS caused by C9ORF72 repeat expansions.