Blocking RAN translation without altering repeat RNAs rescues C9ORF72-related ALS and FTD phenotypes.

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• C9orf72 repeat expansions are the leading genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD).
• Disease pathogenesis is linked to toxic repeat RNAs and/or dipeptide repeat proteins (DPRs) produced via repeat-associated non-AUG (RAN) translation.
• Disentangling the specific toxic contributions of RNA versus DPRs is crucial for therapeutic development.

Purpose of the Study:

• To investigate whether targeting DPR production can mitigate C9orf72-mediated neurotoxicity.
• To differentiate the toxic effects of repeat RNAs from DPRs in a C9orf72 mouse model and patient-derived cells.

Main Methods:

• Engineered a mutation in the CUG codon to specifically disrupt DPR synthesis while maintaining repeat RNA expression.
• Assessed behavioral, pathological, and molecular phenotypes in a C9orf72 mouse model with the DPR-disrupting mutation.
• Utilized base editing to target the CUG codon in patient-induced pluripotent stem cell-derived neurons.

Main Results:

• Disruption of DPR synthesis alleviated behavioral deficits, motor neuron loss, neuroinflammation, and p-TDP-43 inclusions in C9orf72 mice.
• RNA foci persisted despite the reduction in DPRs, indicating RNA toxicity is not the sole driver.
• Base editing improved molecular phenotypes and survival in patient-derived neurons, confirming the therapeutic potential of targeting DPRs.

Conclusions:

• Dipeptide repeat proteins (DPRs), not repeat RNAs, are the primary drivers of neurotoxicity in C9orf72-associated ALS and FTD.
• Targeting DPR production represents a promising therapeutic strategy for these devastating neurodegenerative diseases.
• This study provides a foundation for developing therapies that specifically inhibit DPR synthesis.