Astrocyte and mitochondrial footprints in brain-derived extracellular vesicles predict tau pathology

Tauopathies are neurodegenerative disorders characterized by abnormal tau aggregation, with primary 3R (e.g., Picks disease, PiD) and 4R (e.g., progressive supranuclear palsy, PSP) variants posing a significant diagnostic challenge. Here, we examined brain-derived extracellular vesicles (BD-EVs) isolated from the prefrontal cortex of PiD (3R), PSP (4R), and non-demented controls (CTRL) to determine if these vesicles reflect disease-specific proteomic signatures. We found that while tau pathology does not substantially alter BD-EV concentration or the enrichment of core vesicular markers, it does influence their size distribution and protein cargo. BD-EV samples from PiD patients exhibited a greater abundance of small vesicles and distinct protein profiles when compared to PSP and CTRL. Weighted Gene Co-expression Network Analysis (WGCNA) identified four key protein modules to account for variance between patient groups Endoplasmic Reticulum, Mitochondria, Microtubules, and Trivalent Inorganic Cation Transport. In PiD, astrocyte-derived mitochondrial proteins were significantly elevated, whereas neuronal microtubule-related proteins were diminished relative to both PSP and CTRL. Notably, changes in the mitochondrion and microtubule modules enhanced the detection of PiD pathology. Cellular origin annotation revealed a marked shift in BD-EV composition: PiD samples exhibited an increased astrocytic signature, while both PiD and PSP showed a reduction in neuronal proteins compared to CTRL. Crucially, the enrichment of astrocytic mitochondrial and endoplasmic reticulum proteins, alongside reduced neuronal proteins, correlated strongly with the severity of tau pathology (AT8-stained aggregates) in patient brains. These findings demonstrate that BD-EVs capture tau isoform-specific cellular and molecular alterations, offering a window into disease mechanisms at the neuron-glia interface. By linking distinct protein signatures and their cellular origins to tau pathology severity, our results highlight the potential of BD-EV profiling as a biomarker strategy for distinguishing between and monitoring the progression of 3R and 4R tauopathies.