C9orf72 poly-PR forms anisotropic condensates causative of nuclear TDP-43 pathology

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Dipeptide-repeat (DPR) proteins from C9orf72 mutations form inclusions in familial ALS/FTD.
• Previous cell models struggled to replicate DPR aggregation for most types.
• Understanding DPR aggregation is crucial for C9-ALS/FTD pathogenesis.

Purpose of the Study:

• To develop a controllable, chemical-free method for studying DPR protein aggregation.
• To investigate the impact of poly-PR condensates on cellular mechanisms, particularly TDP-43.
• To explore the potential role of DPR condensates as an early pathological event in C9-ALS/FTD.

Main Methods:

• Utilized optogenetics for spatial and temporal control of poly-PR condensation in cultured cells.
• Included human motor neurons in the experimental models.
• Observed and characterized nuclear and cytoplasmic poly-PR aggregates and their interaction with TDP-43.

Main Results:

• Achieved efficient, chemical-free poly-PR condensation and aggregation using optogenetics.
• Nuclear poly-PR condensates exhibited anisotropic, hollow-center morphology, resembling TDP-43 anisosomes.
• Condensates induced nuclear TDP-43 granulation without activating stress responses and sequestered TDP-43 in a demixed state.

Conclusions:

• Poly-PR condensation and subsequent nuclear TDP-43 dysfunction may be an early pathological mechanism in C9-ALS/FTD.
• Anisosome-type condensates formed by disease-linked proteins could be a common feature in neurodegenerative diseases.
• Optogenetics provides a powerful tool for studying protein aggregation in neurodegenerative disease models.