Ursodeoxycholic acid inhibits pneumonia caused by PRCV through the activation of TLR4-IRF3 mediated type Ⅰ interferon pathway

Porcine Respiratory Coronavirus (PRCV) is a genetic variant of Transmissible Gastroenteritis Virus (TGEV). It is only pathogenic to the respiratory tract, mainly manifesting as atypical interstitial pneumonia and mild subclinical symptoms. In addition, PRCV can also serve as a potential animal respiratory coronavirus model for the study of human respiratory coronaviruses. Developing effective PRCV antagonists is of great significance for the prevention and control of this disease. In this study, we found that Ursodeoxycholic acid (UDCA) can significantly inhibit the infection of PRCV in Porcine respiratory epithelial cells (NPTR). Further studies have shown that UDCA inhibits PRCV mainly through two mechanisms: First, UDCA can directly disrupt the components of the viral envelope and induce the disintegration of viral structure; Second, UDCA can significantly promote the secretion of IFN-β in NPTR cells, enhance the phosphorylation and nuclear translocation of STAT1, and up-regulate the expression of the interferon-stimulated genes ISG15 and MX1. Molecular dynamics simulations showed that UDCA can be embedded into the hydrophobic pocket of the TLR4 dimerization domain, thereby activating the TLR4-IRF3 signaling pathway, inducing the production of IFN-β, and inhibiting PRCV infection. Schaftoside, an inhibitor of the TLR4 signaling pathway, can effectively reverse the anti-PRCV activity of UDCA. Finally, an ex vivo lung tissue slice model of piglets was established to verify that UDCA can effectively reduce the PRCV viral load and inflammatory response in lung tissues. The results of this study provide a scientific basis for the development of antiviral drugs against PRCV and offer new insights into the research on human respiratory coronaviruses.