Regional Variations in Seeding Activity, Phosphorylation, and Protein Levels of Tau in Alzheimer’s Disease Brain

In Alzheimer’s disease (AD), hyperphosphorylated tau propagates across brain regions through its seeding activity, much like prions. We assessed regional tau seeding activity and phosphorylation by RT-QuIC, western blotting (WB), and mass spectrometry in entorhinal cortex (ENT), inferior/middle/superior temporal gyri (ITG/MTG/STG), and cerebellum (CER). Tau-seeding was highest in ENT among the brain regions examined and correlated positively with Braak staging. AD-derived RT-QuIC products formed tau fibrils, propagating intracellularly in cell models. WB showed significantly higher pTau217/pTau396 in ITG vs. STG/CER. Seeding-activity correlated with WB levels of pTau217/pTau262/pTau396 (p = 0.004, p = 0.0028, p = 0.003) and Braak/Thal staging in temporal regions. Anti-tau antibodies varied in immunodepleting seeding (pTau217 > TAU5 > pTau181 > pTau396). Mass spectrometry identified 11 phospho-sites in ITG tau, while pTau231/pTau262/pTau263/pTau396 were AD-specific. Regional tau-seeding correlates with local phospho-tau levels and pathology, supporting plasma pTau217 for diagnosis and seeding activity as a potential biomarker.