The non-transcriptional activity of IRF3 modulates hepatic immune cell populations in acute-on-chronic ethanol administration in mice

Background & Aims: Interferon regulatory factor 3 (IRF3) is a transcription factor mediating antiviral responses, yet recent evidence indicates that IRF3 also has critical non-transcriptional functions, including activating RIG-I-like receptors-induced IRF-3-mediated pathway of apoptosis (RIPA) and restricting activity of NF-kappa B. Using a novel murine model expressing only non-transcriptional IRF3 activity (Irf3(S1/S1)), we tested the hypothesis that non-transcriptional functions of IRF3 modulate innate immune responses in the Gao-binge (acute-on-chronic) model of alcohol-related liver disease. Methods: IRF3 and IRF3-mediated signals were analysed in liver samples from 5 patients transplanted for alcoholic hepatitis and 5 healthy controls. C57BL/6, Irf3(-/-) and Irf3(S1/S1) mice were exposed to Gao-binge ethanol-induced liver injury. IRF3-mediated RIPA was investigated in cultured macrophages. Results: Phospho-IRF3 and IRF3-mediated signals were elevated in livers of patients with alcoholic hepatitis. In C57BL/6 mice, Gao-binge ethanol exposure activated IRF3 signaling and resulted in hepatocellular injury. Indicators of liver injury were differentially impacted by Irf3 genotype. Irf3(-/-), but not Irf3(S1/S1), mice were protected from steatosis, elevated alanine/aspartate aminotransferase levels and inflammatory cytokine expression. In contrast, neutrophil accumulation and endoplasmic reticulum stress were independent of genotype. Protection from Gao-binge injury in Irf3(-/-) mice was associated with an increased ratio of Ly6C(low) (restorative) to Ly6C(high) (inflammatory) cells compared to C57BL/6 and Irf3(S1/S1) mice. Reduced ratios of Ly6C(low)/Ly6C(high) in C57BL/6 and Irf3(S1/S1) mice were associated with increased apoptosis in the Ly6C(low) population in response to Gao-binge. Activation of primary macrophage cultures with Poly (I:C) induced translocation of IRF3 to the mitochondria, where it associated with Bax and activated caspases 3 and 9, processes indicative of activation of the RIPA pathway. Conclusions: Taken together, these data identify that the non-transcriptional function of IRF3 plays an important role in modulating the innate immune environment in response to Gao-binge ethanol exposure, via regulation of immune cell apoptosis. Lay summary: Activation of the innate immune system contributes to inflammation in the progression of alcohol-related liver disease, as well as to the resolution of injury. Here we show that the protein IRF3 modulates the innate immune environment of the liver in a mouse model of alcoholic hepatitis. It does this by increasing the apoptotic cell death of immune cells that promote the resolution of injury. (C) 2019 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.