LAUSR

Abstract Porcinereproductiveandrespiratorysyndromevirus (PRRSV) causes significant economic losses to the pork industry worldwide. Previously, we demonstrated that heme oxygenase‐1 (HO‐1) interferes with PRRSV replication. To elucidate the mechanisms involved, here we assess whether the HO‐1 downstream metabolites biliverdin (BV) and/or iron mediate the HO‐1 antiviral effect. We demonstrate a BV concentration‐dependent suppression of PRRSV replication and show that virions are not directly inactivated by BV. Additionally, BV or N‐acetyl cysteine (NAC) significantly reduced reactive oxygen species (ROS) in PRRSV‐infected MARC‐145 cells; however, because NAC did not reduce viral load, the BV antiviral effect is independent of decreased ROS levels. Moreover, a secondary metabolite of BV, bilirubin (BR), specifically mediates this anti‐PRRSV activity via a nitric oxide (NO)‐dependent cGMP/PKG signaling pathway. While increased iron via addition of FeCl3 did not interfere with PRRSV replication, iron depletion by deferoxamine (DFO) after cobalt‐protoporphyrin IX induction of HO‐1 did not restore PRRSV replication. Collectively, our findings identify a HO‐1‐BV/BR‐NO‐cGMP/PKG cascade as a novel pathway underlying the host cell antiviral effect. These results provide a unique insight into the molecular mechanisms underlying the antiviral effects of the stress‐responsive protein HO‐1 during PRRSV infection. Graphical abstract Figure. No Caption available. HighlightsHO‐1 metabolite BV inhibits PRRSV replication in vitro.BV suppression of PRRSV infection is independent on ROS reduction.BV secondary metabolite BR mediates the antiviral effect of BV.BR inhibits PRRSV infection via a NO‐dependent cGMP/PKG signaling pathway.