In vitro and in vivo delivery of RNAs of interest holds promise for gene therapy. Recently, exosomes are considered as a kind of rational vehicle for RNA delivery, especially miRNA and/or siRNA, while the loading efficiency is limited. In this study, we engineered the exosomes for RNA loading by constructing a fusion protein in which the exosomal membrane protein CD9 was fused with RNA binding protein, while the RNA of interest either natively harbors or is engineered to have the elements for the binding. By proof-of-principle experiments, we here fused CD9 with HuR, an RNA binding protein interacting with miR-155 with a relatively high affinity. In the exosome packaging cells, the fused CD9-HuR successfully enriched miR-155 into exosomes when miR-155 was excessively expressed. Moreover, miR-155 encapsulated in the exosomes in turn could be efficiently delivered into the recipient cells and recognized the endogenous targets. In addition, we also revealed that the CD9-HuR exosomes could enrich the functional miRNA inhibitor or CRISPR/dCas9 when the RNAs were engineered to have the AU rich elements. Taken together, we here have established a novel strategy for enhanced RNA cargo encapsulation into engineered exosomes, which in turn functions in the recipient cells.

Recently, exosomes have been emerged as promising drug delivery carriers, while certain tissues are intrinsically resistant to exosomes. Therapeutically improving the drug delivery efficiency in these tissues/organs would certainly broaden the potential application of exosomes in future. Ultrasound-targeted microbubble destruction (UTMD) is a promising technique for non-invasive, targeted drug delivery. In this study, we explore the possibility that UTMD assists exosome delivery in these intrinsically resistant tissues. Mice were subjected to tail vein injection of DiR-labeled exosomes together with/without UTMD of SonoVueTM, followed by in vivo and ex vivo tracking of the exosomes. As expected, heart, adipose tissue, and skeletal muscle were found reluctant to exosomes from different origins. Targeted destruction of the ultrasound microbubbles (SonoVueTM) in the heart and adipose tissue region significantly increased the exosome infiltration and endocytosis there, as revealed by fluorescence imaging and confocal laser scanning microscope (CLSM). UTMD treatment 1 h prior to exosome injection failed to facilitate the exosome endocytosis in the targeted region, indicating that the transient promoting effects of UTMD. Moreover, increases of UTMD (numerous pulses) did not linearly enhance the exosome delivery. Together, our study here has established a novel strategy for targeted delivery of exosomes in the reluctant tissues, by combining the advantages of ultrasound microbubbles and exosomes in drug delivery.

Therapeutically intervening the function of RNA in vivo remains a big challenge. We here developed an exosome-based strategy to deliver engineered RNA-binding protein for the purpose of recruiting specific RNA to the lysosomes for degradation. As a proof-of-principle study, RNA-binding protein HuR was fused to the C-terminus of Lamp2b, a membrane protein localized in both exosome and lysosome. The fusion protein was able to be incorporated into the exosomes. Moreover, exosomes engineered with Lamp2b-HuR successfully decreased the abundance of RNA targets possibly via lysosome-mediated degradation, especially when the exosomes were acidified. The system was specifically effective in macrophages, which are lysosome enriched and resistant to routine transfection mediated RNAi strategy. In the CCl4-induced liver injury mouse model, we found that delivery of acidified exosomes engineered with Lamp2b-HuR significantly reduced liver fibrosis, together with decreased miR-155 and other inflammatory genes. In summary, the established exosome-based RNA-binding protein delivery strategy, namely “exosome-mediated lysosomal clearance”, takes the advantage of exosome in targeted delivery and holds great promise in regulating a set of genes in vivo.

No abstract

Exosome-mediated nucleic acids delivery has been emerging as a promising strategy for gene therapy. However, the intrinsic offtarget effects due to non-specific uptake of exosomes by other tissues remain the big hurdle for clinical application. In this study, we aimed to enhance the efficacy and minimize the off-target effects by simultaneously encapsulating engineered mRNA translationally activated by tissue-specific microRNA (miRNA) and increasing targeted delivery efficiency via ultrasound-targeted microbubble destruction (UTMD). Briefly, the upstream of interest transcript was engineered to harbor an internal ribosome entry site (IRES) modified with two miRNA recognition sites. In vitro reporter experiments revealed that the engineered mRNA could be encapsulated into exosomes and can be translationally activated by corresponding miRNAs in the recipient cells. By a proof-of-principle in vivo experiment, we encapsulated miR-148a (an adipose relatively specific miRNA)-responsive PGC1a mRNA into exosomes and delivered the exosomes into the adipose tissue with the aid of UTMD. Efficient PGC1a translation was activated in the adipose tissue, together with obvious browning induction. Moreover, there was much lower off-target translation of PGC1 a in lungs and other tissues. Taken together, our study establishes a novel adipose-specific exosome delivery strategy to enhance efficacy and minimize off-target effects simultaneously.