Phenylalanine-tRNA aminoacylation is compromised by ALS/FTD-associated C9orf72 C4G2 repeat RNA

The expanded hexanucleotide GGGGCC repeat mutation in the C9orf72 gene is the main genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. Under one disease mechanism, sense and antisense transcripts of the repeat are predicted to bind various RNA-binding proteins, compromise their function and cause cytotoxicity. Here we identify phenylalanine-tRNA synthetase (FARS) subunit alpha (FARSA) as the main interactor of the CCCCGG antisense repeat RNA in cytosol. The aminoacylation of tRNAPhe by FARS is inhibited by antisense RNA, leading to decreased levels of charged tRNAPhe. Remarkably, this is associated with global reduction of phenylalanine incorporation in the proteome and decrease in expression of phenylalanine-rich proteins in cellular models and patient tissues. In conclusion, this study reveals functional inhibition of FARSA in the presence of antisense RNA repeats. Compromised aminoacylation of tRNA could lead to impairments in protein synthesis and further contribute to C9orf72 mutation-associated pathology. GGGGCC repeat expansion in the C9orf72 gene causes amyotrophic lateral sclerosis and frontotemporal dementia. Here the authors show that CCCCGG antisense repeat RNA binds and inhibits phenylalanine-tRNA synthetase resulting in decreased levels of tRNAphe and phenylalanine rich proteins.

Automated summary

In this study, the authors found that the expansion of GGGGCC repeat in the C9orf72 gene leads to amyotrophic lateral sclerosis and frontotemporal dementia. They identified CCCCGG antisense repeat RNA as the main binder and inhibitor of phenylalanine-tRNA synthetase, resulting in decreased levels of tRNAphe and phenylalanine-rich proteins.