In this study, we aimed to investigate the impact of NTRs on the formation of poly-GA aggregates and explore their broader chaperone role in DPR pathology. We also sought to identify the minimal regions of NTRs necessary and sufficient for reducing poly-GA aggregates in the cytoplasm.

The expansion of the intronic G4C2 repeat within the C9orf72 gene represents the most prevalent genetic cause of ALS and FTD. The pathogenic cascade involves a combination of loss of function of the C9orf72 protein and the toxic gain of function resulting from the formation of repeat RNA foci and distinct dipeptide repeat proteins (DPRs) generated through repeat-associated non-AUG translation (RAN). Among the DPRs, poly-GA stands out as a prominently expressed species, forming detergent-insoluble cytoplasmic aggregates in post-mortem human brain samples. However, the precise triggers initiating the pathological cascade and the potential for therapeutic intervention to reverse or alleviate these aberrant processes remain poorly understood.

We conducted a comprehensive screen of NTRs and assessed their effects on the aggregation of poly-GA. Additionally, we generated NTR fragment constructs with N-terminal or C-terminal truncations to systematically dissect the HEAT repeats and identify the specific regions essential for reducing poly-GA aggregates.

Our study identified several NTRs as potential modifiers of poly-GA pathology. Moreover, we found that NTRs exhibited the ability to reduce the aggregation of other arginine-rich DPRs, including poly-GR and poly-PR, indicating a broader chaperone role in DPR pathology. Through the generation of NTR fragment constructs, we identified minimal regions that are necessary and sufficient for reducing poly-GA aggregates in the cytoplasm.

The findings from this study provide valuable mechanistic insights into the role of NTRs as modifiers of DPR aggregation, highlighting their potential as therapeutic targets. Further investigations utilizing in vivo C9 mouse models will be crucial for exploring the underlying molecular mechanisms of ALS/FTD.