Tau phosphorylation from neuronal adaptation to Alzheimer's disease

Tau phosphorylation is classically associated with neurodegeneration, yet similar phosphorylation patterns emerge during physiological states and acute stress responses. How these overlapping patterns of phosphorylated Tau (pTau) relate to neuronal adaptation and Alzheimer's disease pathology remains unresolved. We synthesize findings from human to rodent and fly brains and from neuronal cell models, across neurodevelopment, sleep, hibernation, cellular stress, and disease. Across these contexts, pTau changes are associated with altered Tau localization and functions involving synaptic transmission, mitochondrial activity, RNA metabolism, and genomic integrity. Physiological and acute stress responses are generally transient and reversible, whereas aging, repeated stress, and amyloid-β-associated stress can promote persistent pTau accumulation, impaired clearance, aggregation, and neurodegeneration. We propose that pathological Tau phosphorylation reflects dysregulation of a shared adaptive response rather than activation of an entirely distinct pathway. The critical determinants may be phosphorylation persistence, subcellular localization, proteoform composition, and the capacity to restore Tau homeostasis.