C9orf72 poly-PR condensation induces nuclear TDP-43 pathology and is inhibited by RNA in an optogenetic cell model

Proteinaceous inclusions formed by C9orf72 derived dipeptide-repeat (DPR) proteins are a histopathological hallmark in ∼50% of familial amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD) cases. However DPR aggregation/inclusion formation could not be efficiently recapitulated in cell models for four out of five DPRs. We utilised the Cry2olig optogenetic module to achieve chemical-free and controllable poly-PR condensation/aggregation in cultured cells. This approach revealed that poly-PR forms anisotropic condensates in the nucleus and that RNA limits their fusion-dependent growth. Poly-PR self-assembly induced nuclear TDP-43 condensation without activation of cellular stress response. Poly-PR cytoplasmic redistribution and aggregation could be also achieved with prolonged light stimulation. Cytoplasmic poly-PR assemblies were more persistent than its nuclear condensates, selectively sequestered TDP-43 and surrounded spontaneous stress granules. Our data suggest that poly-PR condensation in the nucleus and cytoplasm, causative of TDP-43 dysfunction, may constitute an early pathological event in C9-ALS/FTD. The opto-DPR platform described here is a useful tool for modelling cytopathologies elicited by DPR aggregation for mechanistic research and drug discovery.

Highlights

- Optogenetics can be used to model C9orf72 DPR condensation in cultured cells.

- Opto-PR forms hollow nuclear condensates, and RNA limits their growth by fusion.

- Opto-PR self-assembly leads to stress-independent nuclear TDP-43 condensation.

- Prolonged opto-stimulation induces persistent cytoplasmic opto-PR/TDP-43 assemblies.