PHF6 peptide drives tau pathology seeding in Alzheimer's disease extracellular vesicles

Tauopathies, including Alzheimer's disease (AD), are neurodegenerative disorders marked by abnormal tau protein aggregation and lesion propagation. While a spatio-temporal staging of tau lesions is observed in AD, the specific tau species responsible for this prion-like cell-to-cell transfer and subsequent aggregation remain elusive. Human brain-derived extracellular vesicles (BD-EVs) from AD patients are known to contain seeds that contribute to tau pathology spreading, yet the precise nature of these nucleation-active tau species and their heterogeneity across different tauopathies is not fully understood.

Researchers isolated extracellular vesicles (EVs) from human frozen brain tissue samples, including those from Alzheimer's disease, Progressive Supranuclear Palsy, Pick's disease patients, and non-demented controls. They performed tau immunoprecipitation followed by high-resolution mass spectrometry to comprehensively define the proteomic profile of tau within these EVs. Subsequently, the seeding capacity of these isolated EVs was rigorously tested using in vitro assays to assess their ability to induce new tau aggregate formation.

Tau profiles within BD-EVs demonstrated distinct differences across various tauopathies. Notably, multiple tau peptides located within the microtubule binding region were specifically enriched in Alzheimer's disease extracellular vesicles compared to other tauopathies and controls. These specific tau peptides are implicated in mediating tau seeding activity.

Of these identified peptides, the PHF6 (VQIVYK)-containing proteins were found to primarily mediate the observed tau seeding activity, highlighting its critical role in the propagation of tau pathology. This suggests that the specific composition of tau fragments within EVs dictates their pathological potential, with PHF6 emerging as a key driver for the enhanced EVs-mediated tau propagation seen in AD patients.