Verification of extracellular vesicle-mediated functional mRNA delivery via RNA editing

The secretion and delivery of mRNA by extracellular vesicles (EVs) may contribute to intercellular communications. Several reporter assays have been developed to quantify EV-mediated functional delivery of mRNA into recipient cells. However, mRNA delivery efficiency can often be overestimated by experimental artifacts, resulting in “pseudo-delivery” of reporter proteins rather than mRNA. In this study, we revealed that substantial amounts of reporter proteins expressed in donor cells are secreted into the medium and interfere with the reporter assay. To eliminate this pseudo-delivery, we established a functional RNA delivery assay that employs an RNA editing tool, enabling the verification of bona fide delivery of mRNA into recipient cells. The donor cells expressed a reporter gene containing a stop codon in a non-functional open reading frame. After EV-mediated delivery of reporter mRNAs to the recipient cells, guide RNAs and RNA editing enzymes (dCas13b-hADAR2 fusion proteins) correct the RNA sequence and induce the expression of functional reporter proteins in the recipient cells. Using this system, we showed that EVs containing alphavirus-derived replicon successfully delivered functional RNA and expressed the reporter proteins. The RNA delivery assay using RNA editing enables the precise analysis of EV-mediated mRNA delivery.