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Updated: Nov 1, 2025
Measuring RAN Peptide Toxicity in C. elegans
Published on: April 30, 2020
Multiple pathways of toxicity induced by C9orf72 dipeptide repeat aggregates and G4C2 RNA in a cellular model
Frédéric Frottin1,2, Manuela Pérez-Berlanga1,3, F Ulrich Hartl1
1Max Planck Institute of Biochemistry, Martinsried, Germany.
Abstract:
The most frequent genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia is a G4C2 repeat expansion in the C9orf72 gene. This expansion gives rise to translation of aggregating dipeptide repeat (DPR) proteins, including poly-GA as the most abundant species. However, gain of toxic function effects have been attributed to either the DPRs or the pathological G4C2 RNA. Here, we analyzed in a cellular model the relative toxicity of DPRs and RNA. Cytoplasmic poly-GA aggregates, generated in the absence of G4C2 RNA, interfered with nucleocytoplasmic protein transport, but had little effect on cell viability. In contrast, nuclear poly-GA was more toxic, impairing nucleolar protein quality control and protein biosynthesis. Production of the G4C2 RNA strongly reduced viability independent of DPR translation and caused pronounced inhibition of nuclear mRNA export and protein biogenesis. Thus, while the toxic effects of G4C2 RNA predominate in the cellular model used, DPRs exert additive effects that may contribute to pathology.
Insights
The C9orf72 G4C2 repeat expansion causes ALS and FTD. Toxic RNA effects predominated over toxic protein effects in cellular models, though both contribute to disease.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Background:
- The C9orf72 G4C2 repeat expansion is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD).
- This genetic defect leads to the production of toxic dipeptide repeat (DPR) proteins and pathological G4C2 RNA.
- The relative contribution of DPRs versus G4C2 RNA to cellular toxicity remains unclear.
Purpose of the Study:
- To investigate the distinct toxic effects of DPRs and G4C2 RNA in a cellular model.
- To determine the impact of cytoplasmic versus nuclear poly-GA aggregates on cellular functions.
- To compare the toxicity of DPRs and G4C2 RNA in the context of C9orf72-associated neurodegenerative diseases.
Main Methods:
- Utilized a cellular model to express and analyze the effects of poly-GA aggregates (a key DPR) and G4C2 RNA.
- Assessed nucleocytoplasmic protein transport, nucleolar protein quality control, and protein biosynthesis.
- Evaluated cell viability and nuclear mRNA export.
Main Results:
- Cytoplasmic poly-GA aggregates impaired nucleocytoplasmic transport but had minimal impact on cell viability.
- Nuclear poly-GA aggregates were more toxic, disrupting nucleolar function and protein synthesis.
- G4C2 RNA production significantly reduced cell viability, inhibited nuclear mRNA export, and impaired protein biogenesis, independent of DPR translation.
Conclusions:
- G4C2 RNA toxicity is predominant in this cellular model of C9orf72 repeat expansion disorders.
- DPRs, particularly nuclear poly-GA, exert additive toxic effects that likely contribute to the pathology of ALS and FTD.
- Understanding the distinct roles of RNA and DPRs is crucial for developing targeted therapies.
