Enrichment of Phosphorylated Tau (Thr181) and Functionally Interacting Molecules in Chronic Traumatic Encephalopathy Brain-derived Extracellular Vesicles.

Chronic Traumatic Encephalopathy (CTE) is a tauopathy that affects individuals with a history of mild repetitive brain injury. The initial neuropathologic changes of CTE include perivascular deposition of phosphorylated microtubule-associated protein tau (p-tau). Extracellular vesicles (EVs) are known to carry pathogenic molecules, such as tau in Alzheimer's disease and CTE suggesting their contribution in pathogenesis. We therefore examined the protein composition of EVs separated from CTE and an age-matched control brain tissues by tandem mass tag -mass spectrometry. The reporter ion intensity was used to quantify the identified molecules. A total of 516 common proteins were identified among three sets of experiments. Weighted protein co-expression network analysis identified 18 unique modules of co-expressed proteins. Two modules were significantly correlated with total tau (t-tau) and p-tau protein in the isolated EVs and enriched in cellular components and biological processes for synaptic vesicle secretion and multivesicular body-plasma membrane fusion. The p-tau (Thr181) level is significantly higher in CTE EVs compared to control EVs and can distinguish the two groups with 73.6% accuracy. A combination of t-tau or p-tau (Thr181) with SNAP-25, PLXNA4 or UBA1, enhanced the accuracy to 96.3, 93.8 and 93.8%, respectively. Bioinformatic protein-protein interaction analysis revealed the functional interaction of SNAP-25 and PLXNA4 with tau, suggesting their interaction in CTE EVs. These data indicate the future application of identified EV proteins for monitoring the CTE risk assessments and understanding the EV-mediated disease progression mechanism.