HNRNPK alleviates RNA toxicity by counteracting DNA damage in C9orf72 ALS

Elke Braems, Valérie Bercier (Lead / Corresponding author), Evelien Van Schoor, Kara Heeren, Jimmy Beckers, Laura Fumagalli, Lieselot Dedeene, Matthieu Moisse, Ilse Geudens, Nicole Hersmus, Arpan R Mehta, Bhuvaneish T Selvaraj, Siddharthan Chandran, Ritchie Ho, Dietmar R Thal, Philip Van Damme, Bart Swinnen, Ludo Van Den Bosch

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)
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Abstract

A 'GGGGCC' repeat expansion in the first intron of the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The exact mechanism resulting in these neurodegenerative diseases remains elusive, but C9 repeat RNA toxicity has been implicated as a gain-of-function mechanism. Our aim was to use a zebrafish model for C9orf72 RNA toxicity to identify modifiers of the ALS-linked phenotype. We discovered that the RNA-binding protein heterogeneous nuclear ribonucleoprotein K (HNRNPK) reverses the toxicity of both sense and antisense repeat RNA, which is dependent on its subcellular localization and RNA recognition, and not on C9orf72 repeat RNA binding. We observed HNRNPK cytoplasmic mislocalization in C9orf72 ALS patient fibroblasts, induced pluripotent stem cell (iPSC)-derived motor neurons and post-mortem motor cortex and spinal cord, in line with a disrupted HNRNPK function in C9orf72 ALS. In C9orf72 ALS/FTD patient tissue, we discovered an increased nuclear translocation, but reduced expression of ribonucleotide reductase regulatory subunit M2 (RRM2), a downstream target of HNRNPK involved in the DNA damage response. Last but not least, we showed that increasing the expression of HNRNPK or RRM2 was sufficient to mitigate DNA damage in our C9orf72 RNA toxicity zebrafish model. Overall, our study strengthens the relevance of RNA toxicity as a pathogenic mechanism in C9orf72 ALS and demonstrates its link with an aberrant DNA damage response, opening novel therapeutic avenues for C9orf72 ALS/FTD.

Original languageEnglish
Pages (from-to)465-488
Number of pages24
JournalActa Neuropathologica
Volume144
Issue number3
Early online date27 Jul 2022
DOIs
Publication statusPublished - Sept 2022

Keywords

  • C9orf72
  • ALS
  • RNA toxicity
  • HNRNPK
  • RRM2
  • DNA damage

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