Nontranscriptional Activity of Interferon Regulatory Factor 3 Protects Mice From High-Fat Diet-Induced Liver Injury

Interferon regulatory factor 3 (IRF3) has both transcriptional and nontranscriptional functions. Transcriptional activity is dependent on serine phosphorylation of IRF3, while transcription-independent IRF3-mediated apoptosis requires ubiquitination. IRF3 also binds to inhibitor of nuclear factor kappa B kinase (IKKβ) in the cytosol, restricting nuclear translocation of p65. IRF3-deficient mice are highly sensitive to high-fat diet (HFD)-induced liver injury; however, it is not known if transcriptional and/or nontranscriptional activity of IRF3 confers protection. Using a mouse model only expressing nontranscriptional functions of IRF3 (Irf3 ^S1/S1), we tested the hypothesis that nontranscriptional activity of IRF3 protects mice from HFD-induced liver injury. C57BL/6, Irf3 ^-/-, and Irf3 ^S1/S1 mice were fed an HFD for 12 weeks. In C57BL/6 mice, the HFD increased expression of interferon (IFN)-dependent genes, despite a decrease in IRF3 protein in the liver. The HFD had no impact on IFN-dependent gene expression Irf3 ^-/- or Irf3 ^S1/S1 mice, both lacking IRF3 transcriptional activity. Liver injury, apoptosis, and fibrosis were exacerbated in Irf3 ^-/- compared to C57BL/6 mice following the HFD; this increase was ameliorated in Irf3 ^S1/S1 mice. Similarly, expression of inflammatory cytokines as well as numbers of neutrophils and infiltrating monocytes was increased in Irf3 ^-/- mice compared to C57BL/6 and Irf3 ^S1/S1 mice. While the HFD increased the ubiquitination of IRF3, a response associated with IRF3-mediated apoptosis, in Irf3 ^S1/S1 mice, protection from liver injury was not due to differences in apoptosis of hepatocytes or immune cells. Instead, protection from HFD-induced liver injury in Irf3 ^S1/S1 mice was primarily associated with retardation of nuclear translocation of p65 and decreased expression of nuclear factor kappa B (NFκB)-dependent inflammatory cytokines. Conclusion: Taken together, these data identify important contributions of the nontranscriptional function of IRF3, likely by reducing NFκB signaling, in dampening the hepatic inflammatory environment in response to an HFD.