Visualization and intracellular dynamic tracking of exosomes and exosomal miRNAs using single molecule localization microscopy.

Exosomes are small membrane vesicles secreted by a wide variety of cells. Studies have demonstrated that exosomal miRNAs can influence the biological processes of recipient cells. Therefore, direct imaging and tracking of exosomal miRNAs in living recipient cells are essential for exosome functional analysis. However, the moderate spatial resolution of conventional fluorescence microscopy limits the precise imaging and tracking of exosomes considering their relatively small size (<100 nm). Here, we took advantage of single molecule localization microscopy (SMLM) to realize the visualization and dynamic tracking of exosomes and exosomal miRNAs in living cells. First, we demonstrated simultaneous SMLM imaging of HeLa-derived exosomes and two kinds of exosomal miRNAs (mir-21 and mir-31) and tracked their movement after cellular uptake. The motion of exosomes within the intercellular filamentous structures was observed successfully. Moreover, dual-color SMLM based dynamic tracking revealed that as one kind of natural carrier of cellular cargoes, exosomes can encapsulate mir-21 inside to prevent enzyme degradation during transfer and then release them into recipient cells. These findings can provide new insights into the pathway of intercellular communication and affirm that SMLM is a powerful technique to track the motion of exosomes and exosomal contents in recipient cells.