Keywords: a. neural degeneration; h. other (stress granules)
Arginine-rich dipeptide repeat proteins (R-DPRs), abnormal translational products of a GGGGCC hexanucleotide repeat expansion in C9ORF72, play a critical role in C9ORF72-relatedamyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), the most common familial form of ALS and FTD (c9ALS/FTD). R-DPRs undergo phase separation to form condensates in vitro and, as a c9ALS/FTD pathological hallmark, aggregate and sometimes co-aggregate with TDP-43 in patients. However, how these processes are regulated is unclear. Here, we show that poly(ADP-ribose) (PAR) interacts with R-DPRs, promotes R-DPR phase separation and toxicity in vitro, and correlates with insoluble R-DPR and TDP-43 in patient postmortem tissue. Loss of PAR suppresses R-DPR aggregation and neurodegeneration in fly or cellular models of c9ALS/FTD. Our findings identified PAR as a pathogenic contributor promoting R-DPR condensation both in vitro and in vivo, suggesting the potential of R-DPR condensation as a target for c9ALS/FTD therapeutic intervention.