Seed-competent tau oligomers’ activity correlates with the rate of progression in sporadic Alzheimer's disease patients

BackgroundWhile it is clear that abnormal tau structures contribute to the clinical symptoms of Alzheimer's disease (AD), which of the many structural entities found in the AD brain underlie templated misfolding and progression of disease remains uncertain. However, their identification is crucial to target for more effective diagnostics and therapeutics.ObjectiveTo identify the most pathogenic tau species driving Alzheimer's disease progression.MethodsWe compared the biochemical and templated seeding properties of tau isolated from post-mortem brain tissue of patients with varying rates of clinical progression, categorized as rapid, slow, or typical, based on longitudinal decline in cognitive performance assessed by Clinical Dementia Rating Sum of Boxes scores. Sarkosyl-insoluble filamentous preparations were compared to aqueous-soluble preparations. Focusing on the aqueous-soluble proteins, we further characterized the most efficient seeding species using size-exclusion chromatography and quantifying oligomers using dot blot under both native and denaturing conditions.ResultsA rapidly progressive course corresponded to enhanced tau seeding behavior, with the strongest correlations observed in the aqueous-soluble fraction. Using size-exclusion chromatography, we demonstrated that the seeding activity of fractions containing oligomers, correlated most strongly with disease aggressiveness. Moreover, quantifying oligomers using dot blot under both native and denaturing conditions, we found that rapid progressors had higher levels of oligomeric tau, which was also more stable.ConclusionsAqueous-soluble oligomeric tau species may be an important driver of AD progression. Substantial heterogeneity was observed even in purified samples, suggesting that variations in tau conformers among patients may contribute to differences in clinical disease progression.