Selection and Inhibitory Effect Analysis of siRNAs Specific to ORF2–4 of Porcine Reproductive and Respiratory Syndrome Virus

Inhibition of porcine reproductive and respiratory syndrome virus replication by adenovirus-mediated RNA interference both in porcine alveolar macrophages and swine

Porcine reproductive and respiratory syndrome virus (PRRSV) has been mainly responsible for the heavy economic losses in many swine-producing regions. Current vaccination strategies and antiviral drugs provide only limited protection. Consequently, there is a need to develop a new antiviral strategy. In this study, two recombinant adenoviruses expressing short-hairpin RNAs (shRNAs) directed against ORF1b of PRRSV S1 strain were constructed and the inhibition of PRRSV replication was determined. The results showed that pretreatment with these shRNAs delivered by recombinant adenovirus could induce a significant inhibition of viral RNA and protein level in Marc-145 cells infected with PRRSV S1 strains. One recombinant adenovirus (rAd-P2) was found to be also effective in inhibiting the replication of highly virulent PRRSV SY0608 strain in Marc-145 cells and porcine alveolar macrophages at both the protein and ORF1b mRNA level. The antiviral effect was dose-dependent and sustained for at least 96h. Twenty 6-week old piglets were assigned to four groups each with five piglets. Groups 1 and 2 were inoculated intramuscularly with rAd-P2 and mock construct rAd-mP2 individually. After 24h, groups 1, 2 and 3 were challenged intramuscularly with the SY0608 strain. Group 4 remained unchallenged but with PBS as mock. The results showed that the viral load of PRRSV in serum and lung tissue of swine was suppressed effectively by rAd-P2. The clinical signs and pathological lesions in the pigs inoculated with rAd-P2 were milder than those in rAd-mP2 negative and PRRSV control. These results indicated that shRNAs mediated by the adenovirus could inhibit PRRSV infection sufficiently in vitro as well as in vivo. RNAi mediated by recombinant adenovirus might be a potential new tool for controlling PRRSV infection. Of course, the protective efficiency of rAd-P2 should be made by using a large number of pigs in future.

Effective suppression of replication of porcine reproductive and respiratory syndrome virus by adenovirus-mediated small interfering RNAs targeting ORF1b, 5 and 7 genes

Porcine reproductive and respiratory syndrome virus has caused hundreds of thousands of deaths in pig farms in many swine-producing areas in the world in recent years. However, at present there is no effective method to prevent and control the disease, and there is a need to develop new antiviral strategies. In this study, four recombinant adenoviruses expressing shRNAs targeting ORF1b, ORF5 and ORF7 were constructed, and it was found that they could down-regulate effectively specific gene expression and inhibit viral replication in MARC-145 cells when compared to the controls. They could also inhibit effectively PRRSV replication in porcine alveolar macrophages. The inhibition effect was dose-dependent and could be sustained for at least 96h in macrophages. In addition, PRRSV replication could be suppressed significantly by shRNA in cells infected previously or simultaneously with PRRSV. The results indicated that the shRNA-expressing rAd5 targeting to various gene regions of PRRSV might be a potential anti-PRRSV strategy.