Isolation of urinary extracellular vesicles from Tamm-Horsfall protein-depleted urine and their application in the development of a lectin-exosome-binding assay

Urine is a readily available source of relatively large quantities of extracellular vesicles (EVs). However, the isolation of urinary EVs (uEVs) is complicated by the presence of Tamm-Horsfall protein (THP), which polymerizes and co-precipitates as a contaminant. This may make glycan analysis of uEVs difficult since THP is heavily glycosylated. To facilitate glycosylation analysis and address the need for elimination of non-uEV glycans, we present a modification of the uEV isolation procedure and use the isolated uEVs in the development of a lectin-exosome binding assay. Salt precipitation was employed to remove THP under conditions originally described for its separation from urine, followed by differential centrifugation. The quality of the isolated uEVs was examined by electron microscopy, SDS-PAGE, and immunoblotting. The uEVs were subsequently immobilized on solid phase and probed with labeled plant lectins using the lectin-exosome binding assay. Our results indicate that the isolated uEVs had preserved structural integrity and reacted with labeled plant lectins in a selective, carbohydrate-dependent manner. The basic lectin binding pattern of uEVs obtained by our method can be used as a reference for assessing the composition of their surface glycans in different physiological and pathological conditions.