Repeat‐associated non‐AUG translation in C9orf72‐ALS/FTD is driven by neuronal excitation and stress

Nucleotide repeat expansions (NREs) are prevalent mutations in a multitude of neurodegenerative diseases. Repeat‐associated non‐AUG (RAN) translation of these repeat regions produces mono or dipeptides that contribute to the pathogenesis of these diseases. However, the mechanisms and drivers of RAN translation are not well understood. Here we analyzed whether different cellular stressors promote RAN translation of dipeptide repeats (DPRs) associated with the G4C2 hexanucleotide expansions in C9orf72, the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). We found that activating glutamate receptors or optogenetically increasing neuronal activity by repetitive trains of depolarization induced DPR formation in primary cortical neurons and patient derived spinal motor neurons. Increases in the integrated stress response (ISR) were concomitant with increased RAN translation of DPRs, both in neurons and different cell lines. Targeting phosphorylated‐PERK and the phosphorylated‐eif2α complex reduces DPR levels revealing a potential therapeutic strategy to attenuate DPR‐dependent disease pathogenesis in NRE‐linked diseases. Synopsis Through an ALS/FTD‐linked C9orf72 nucleotide repeat expansion (NRE) mutation model, the authors provide a new mechanistic understanding for the role of NRE‐linked non‐AUG translation in driving disease pathogenesis in neurons and novel therapeutic approaches to reduce NRE‐linked neurodegeneration. Different cell‐types differential express repeat associated non‐AUG‐dependent (RAN) translation products. RAN translation leads to the accumulation of toxic dipeptide repeats (DPRs) in cells, of which we have measured long half‐lives for these DPRs. The production and accumulation of DPRs increases in response to a spectrum of stressful cellular stimuli. In neurons, excitotoxic stressors or increased neuronal activity DPR levels through increased usage of RAN translation mechanisms. FDA approved compounds that were previously administered in clinical trials to treat other neurological and neuromuscular disorders, can modify RAN translation in cells. Graphical Abstract Through an ALS/FTD‐linked C9orf72 nucleotide repeat expansion (NRE) mutation model, the authors provide a new mechanistic understanding for the role of NRE‐linked non‐AUG translation in driving disease pathogenesis in neurons and novel therapeutic approaches to reduce NRE‐linked neurodegeneration.