Molecular profiling of neuronal extracellular vesicles reveals brain tissue specific signals.

Extracellular vesicles (EVs) released by neurons (nEVs) provide an opportunity to measure biomarkers from the brain circulating in the periphery. No study yet has directly compared molecular cargo in brain tissue to nEVs found in circulation in humans. In 5 matched sets of brain tissue, serum, total EVs, and nEVs, obtained from the Bartoli Brain Tumor Laboratory at Columbia University, we compared the levels microRNAs and environmental chemicals because microRNAs are one of the most studied nEV cargoes and offer great potential as biomarkers and environmental chemical load in nEVs is understudied and could reveal chemical burden in the brain. We also compared metabolomic profiles in a different set of matched serum, total EVs, and nEVs since metabolites in nEVs are also understudied but could offer potential biomarkers. Highly expressed brain tissue miRNAs showed stronger correlations with nEVs than serum or total EVs. We detected several environmental chemical pollutant classes in nEVs. The chemical pollutant concentrations in nEVs were more strongly correlated with brain tissue levels (r = 0.72, P = 7.2e-16) than those observed between brain tissue and serum (r = 0.7, P = 5.8e-15) or total EVs (r = 0.58, P = 1.5e-09). Compared to serum and total EVs, we observed an enrichment of metabolites with known signaling roles, such as bile acids, oleic acid, phosphatidylserine, and isoprenoids in nEVs. We provide evidence that nEV cargo is closely correlated with brain tissue content, further supporting their utility as a brain liquid biopsy in humans.