Poly-GR impairs translation elongation and increases ribotoxic stress response in C9ORF72-ALS/FTD
Hexanucleotide repeat expansion in the C9ORF72 gene is the most frequent inherited cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Poly-GR is one of the most toxic dipeptide repeat (DPR) proteins translated from the RNA repeats.  It has been shown to affect protein synthesis, but how this contributes to neurodegeneration is not clear. Here, we found that poly-GR inhibits global translation by perturbing translation elongation. We identified that the transcripts with relatively slow elongation rate tend to be further stalled by poly-GR in iPSC-differentiated neurons. This increases ribosome collision and ZAKa-mediated ribotoxic stress response (RSR), which elevates the phosphorylation of p38  and promotes cell death. Knockdown of ZAKa or pharmacological inhibition of p38 can ameliorate the GR toxicity, and improve the survival of C9ORF72-ALS/FTD patient-derived iPSC-neurons. Our study reveals molecular mechanism of poly-GR mediated toxicity on global translatome, and identifies RSR as a potential therapeutic target for C9ORF72-ALS/FTD. Overall design: Comparative gene expression profiling analysis of RNA-seq data for i3Neuron cells expressing GFP or GR50 from total input lysates or polysome associated mRNA before and after adding Harringtonine