YTHDC1 functions as a molecular chaperone to suppress ALS-linked hnRNPA1 mutants from aggregation

Proteostasis failure drives multiple neurodegenerative disorders (NDs), and ATP-independent chaperone pathways that support neuronal proteostasis remain poorly defined. Here, we identify the N6-methyladenosine (m⁶A)-binding protein YTHDC1 as an ATP-independent molecular chaperone, whose activity is mediated by a highly acidic polyaspartate/glutamate (polyD/E) segment. YTHDC1 prevents protein misfolding and aggregation, unfolds kinetically trapped substrates, and resolubilizes pre-formed aggregates. Deletion of the polyD/E segment abolishes these activities, whereas aromatic-cage mutants retain chaperone activity, demonstrating independence from m⁶A recognition. We identify the amyotrophic lateral sclerosis (ALS)-associated RNA-binding protein hnRNPA1 as a YTHDC1 client. YTHDC1 maintains liquid-like hnRNPA1 condensates, delays fibrillization of disease-associated mutants, and limits stress-granule sequestration, while mitigating mutant hnRNPA1-induced neurite growth defects in primary neurons. These findings define a proteostatic function of YTHDC1 and highlight its chaperone activity as a potential target for mitigating protein aggregation in ALS-related NDs.