Inhibition of porcine reproductive and respiratory syndrome virus replication with exosome-transferred artificial microRNA targeting the 3′ untranslated region

Porcine reproductive and respiratory syndrome (PRRS) is an economically important swine disease. As part of the development of RNA interference (RNAi) strategy against the disease, in this study a recombinant adenovirus (rAd) expressing the artificial microRNA (amiRNA) targeting the 3′ untranslated region (UTR) was used to investigate the exosome-mediated amiRNA transfer from different pig cell types to porcine alveolar macrophages (PAMs). Quantitative RT-PCR showed that the sequence-specific amiRNA was expressed in and secreted via exosomes from the rAd-transduced pig kidney cell line PK-15, PAM cell line 3D4/163, kidney fibroblast cells (PFCs) and endometrial endothelial cells (PEECs) with different secretion efficiencies. Fluorescent microscopy revealed that the dye-labeled amiRNA-containing exosomes of different cell origins were efficiently taken up by all of the five types of pig cells tested, including primary PAMs. Quantitative RT-PCR showed that the amiRNA-containing exosomes of different cell origins were taken up by primary PAMs in both time- and dose-dependent manners. Both quantitative RT-PCR and viral titration assays showed that the exosome-delivered amiRNA had potent anti-viral effects against three different PRRSV strains. These data suggest that the exosomes derived from pig cells could serve as an efficient miRNA transfer vehicle, and that the exosome-delivered amiRNA had potent anti-viral effects against different PRRSV strains.