Cryo-EM structure of pro-aggregant P301L/S320F double-mutant tau filaments formed in mouse brains following peripheral AAV delivery

Tauopathies are characterized by the accumulation of abnormally phosphorylated tau filaments, with disease-specific folds revealed by cryo-electron microscopy (cryo-EM). Here, we delivered a recombinant human tau carrying the P301L/S320F double mutation into AppNL-G-F/MAPT double knock-in mice using a blood-brain-barrier-permeable AAV (AAV-PHP.eB), enabling rapid induction of tau aggregation in vivo. The mutant tau was systemically administered via retro-orbital injection, providing a minimally invasive approach for widespread neuronal transduction. Phosphorylated tau aggregation, as well as seeding activity, were observed without the need for exogenous seeds. Our cryo-EM analysis resolved a novel filament fold incorporating residues 279-329, in which the P301L and S320F mutations introduced stabilizing interactions that reinforced filament assembly. This conformation was distinct from previously reported folds, including Alzheimer and Pick tau filaments. Moreover, the filaments adopted a more compact architecture than those observed in patient-derived samples or other model mice. This finding demonstrates that P301L/S320F double-mutant tau adopts a structurally unique, highly aggregation-prone fold, and that this system provides a rapid platform for modeling tau filament formation.