Differential impact of exportin-1-mediated nuclear export of RNAs on the RNA content of extracellular vesicle subpopulations

Extracellular vesicles (EVs) are membrane-enclosed subcellular structures released by all cell types. EVs have important roles in both cellular homeostasis and intercellular communication. Recent progress in the field revealed substantial heterogeneity of EVs even within the size-based EV categories. Here we addressed the question whether the exportin-1 (XPO1)-mediated nuclear export of RNAs contributed to the EV heterogeneity. Size-based populations were separated from the conditioned media of three cell lines (U937, THP-1 and 5/4E8) in steady-state condition. The effects of activation and leptomycin B treatment (to inhibit the XPO1-mediated nuclear export of RNAs) were also tested in the case of the two monocytic cell lines. Agilent Pico and Small chips were used to characterize RNAs, fragment analysis was performed, and EV-associated miRNAs were tested by Taqman assays. As expected, we found the highest small RNA/total RNA ratio and the lowest rRNA/total RNA proportion in small EVs (similar to 50-150 nm). Profiles of the small RNAs within different size-based EV categories significantly differed based on the activation status of the EV releasing cells. Leptomycin B had a differential inhibition on the tested small RNAs in EVs, even within the same EV size category. A similar heterogeneity of the EV miRNA content was observed upon cellular activation and nuclear export inhibition. Here we complement the already existing knowledge on EV heterogeneity by providing evidence that the RNA cargo varies depending on the EV size-based category, the releasing cell type, the functional status of the releasing cells and the exportin-1-mediated nuclear export of RNAs.