C9orf72 related poly-Glycine-Alanine promotes tau phosphorylation and cell death via ERK1/2 interaction in cellular models

Frontotemporal lobar degeneration (FTLD), particularly cases linked to the C9ORF72 GGGGCC repeat expansion (r(G4C2)exp), is closely associated with TAR DNA-binding protein 43 (TDP-43) pathology but also exhibits concurrent tau pathology characterized by hyperphosphorylation and neurofibrillary tangles (NFTs). Despite evidence suggesting heightened tau pathology severity in C9ORF72 mutation carriers compared to other FTLD subtypes, the mechanistic interplay between r(G4C2)exp and tau dysregulation remains poorly understood. Using a cellular model, we demonstrated that (GA)₅₀ causes significant neuronal cell death. We found that (GA)₅₀ was shown to specifically bind to extracellular-regulated kinase 1/2 (ERK1/2) protein, leading to its hyperphosphorylation. This activation of ERK1/2 was associated with increased tau phosphorylation and aggregation. Importantly, inhibiting ERK1/2 activity with U0126 significantly reduced tau phosphorylation, aggregation, and cell death in cells overexpressing (GA)₅₀. These in vitro findings suggest that (GA)₅₀-driven ERK1/2 hyperphosphorylation may represent potential driver of tau pathology in C9ORF72-related FTLD, highlighting the ERK1/2 signaling or its interaction with poly-glycine-alanine (GA) as a potential therapeutic target.