MicroRNA-23 inhibits PRRSV replication by directly targeting PRRSV RNA and possibly by upregulating type I interferons

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression post-transcriptionally and play critical roles in intricate networks of host-pathogen interactions and innate immunity. Porcine reproductive and respiratory syndrome (PRRS) is one of the most important diseases affecting swine industry worldwide. Here, we demonstrated that miR-23, miR-378, and miR-505 were antiviral host factors against PRRS virus (PRRSV). Over-expression of the three miRNAs inhibited PRRSV infection in a dose-dependent manner, respectively. Blockage of the three endogenously expressed miRNAs significantly enhanced PRRSV replication. Different type 2 PRRSV strains harbored conserved miR-23, miR-378, and miR-505 target sites (TSs) that were sufficient to confer miRNA-mediated repression of PRRSV replication. Interestingly, miR-23 was capable of inducing type I interferon expression during PRRSV infection through IRF3/IRF7 activation, which might further lead to the inhibition of virus infection. These results suggest that miR-23, miR-378, and miR-505, especially miR-23, may have the potential to be used as antiviral therapy against PRRSV infection.