Tau acetylation at K331 has limited impact on tau pathology in vivo.

Post-translational modifications regulate tau aggregation and propagation, yet how amyloid pathology shapes the tau modification landscape remains unclear. Using liquid chromatography-tandem mass spectrometry, we compared tau modifications in MAPT knock-in (MAPT KI) mice and MAPT/App double knock-in mice with AppNL-G-F amyloid pathology. Only subtle differences were detected, with a tendency toward increased acetylation within the repeat domain. Because K321 and K331 lie in the fibril-forming core, their roles were further examined. Acetylation at these sites was absent in cynomolgus monkey brains. To test functional relevance, we generated acetylation-mimicking MAPTK331Q knock-in mice on the MAPT KI background. Despite tau expression, these mice showed reduced tau phosphorylation at 24 months, with unchanged insoluble tau and seeding activity. Thus, K331 acetylation does not promote tau pathology.