Mechanisms of extracellular vesicle uptake in stressed retinal pigment epithelial cell monolayers.

PURPOSE: Extracellular vesicles (EVs) can mediate long-distance communication in polarized RPE monolayers. Specifically, EVs from oxidatively stressed donor cells (stress EVs) rapidly reduced barrier function (transepithelial resistance, TER) in naïve recipient monolayers, when compared to control EVs. This effect on TER was dependent on dynamin-mediated EV uptake, which occurred rapidly with EVs from oxidatively stressed donor cells. Here, we further determined molecular mechanisms involved in uptake of EVs by naïve RPE cells.
METHODS: RPE cells were grown as monolayers in media supplemented with 1% FBS followed by transfer to FBS-free media. Cultures were used to collect control or stress EVs upon treatment with H2O2, others served as naïve recipient cells. In recipient monolayers, TER was used to monitor EV-uptake-based activity, live-cell imaging confirmed uptake. EV surface proteins were quantified by protein chemistry.
RESULTS: Clathrin-independent, lipid raft-mediated internalization was excluded as an uptake mechanism. Known ligand-receptor interactions involved in clathrin-dependent endocytosis include integrins and proteoglycans. Desialylated glycans and integrin-receptors on recipient cells were necessary for EV uptake and subsequent reduction of TER in recipient cells. Protein quantifications confirmed elevated levels of ligands and neuraminidase on stress EVs. However, control EVs could confer activity in the TER assay if exogenous neuraminidase or additional ligand was provided.
CONCLUSIONS: In summary, while EVs from both stressed cells and control contain cargo to communicate stress messages to naive RPE cells, stress EVs contain surface ligands that confer rapid uptake by recipient cells. We propose that EVs potentially contribute to RPE dysfunction in aging and disease.