Sanz-Garcia Carlos, McMullen Megan R, Chattopadhyay Saurabh, Roychowdhury Sanjoy, Sen Ganes, Nagy Laura E
Department of Inflammation and Immunity Lerner Research Institute Cleveland Clinic Cleveland OH.
Department of Medical Microbiology and Immunology University of Toledo College of Medicine and Life Sciences Toledo OH.
Hepatol Commun. 2019 Oct 10;3(12):1626-1641. doi: 10.1002/hep4.1441. eCollection 2019 Dec.
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 ( ), we tested the hypothesis that nontranscriptional activity of IRF3 protects mice from HFD-induced liver injury. C57BL/6, , and 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 or mice, both lacking IRF3 transcriptional activity. Liver injury, apoptosis, and fibrosis were exacerbated in compared to C57BL/6 mice following the HFD; this increase was ameliorated in mice. Similarly, expression of inflammatory cytokines as well as numbers of neutrophils and infiltrating monocytes was increased in mice compared to C57BL/6 and mice. While the HFD increased the ubiquitination of IRF3, a response associated with IRF3-mediated apoptosis, in 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 mice was primarily associated with retardation of nuclear translocation of p65 and decreased expression of nuclear factor kappa B (NFκB)-dependent inflammatory cytokines. 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.
干扰素调节因子3（IRF3）具有转录和非转录功能。转录活性依赖于IRF3的丝氨酸磷酸化，而不依赖转录的IRF3介导的细胞凋亡则需要泛素化。IRF3还在细胞质中与核因子κB激酶（IKKβ）抑制剂结合，限制p65的核转位。IRF3缺陷小鼠对高脂饮食（HFD）诱导的肝损伤高度敏感；然而，尚不清楚IRF3的转录和/或非转录活性是否具有保护作用。我们使用仅表达IRF3非转录功能的小鼠模型，检验了IRF3的非转录活性可保护小鼠免受HFD诱导的肝损伤这一假说。将C57BL/6、IRF3转录活性缺失的小鼠和IRF3完全缺失的小鼠喂食HFD 12周。在C57BL/6小鼠中，尽管肝脏中IRF3蛋白减少，但HFD增加了干扰素（IFN）依赖性基因的表达。HFD对IRF3转录活性缺失的小鼠或IRF3完全缺失的小鼠的IFN依赖性基因表达没有影响。与C57BL/6小鼠相比，喂食HFD后，IRF3完全缺失的小鼠的肝损伤、细胞凋亡和纤维化加剧；而在IRF3转录活性缺失的小鼠中这种增加有所改善。同样，与C57BL/6小鼠和IRF3转录活性缺失的小鼠相比，IRF3完全缺失的小鼠中炎性细胞因子的表达以及中性粒细胞和浸润单核细胞的数量增加。虽然HFD增加了IRF3的泛素化，这是与IRF3介导的细胞凋亡相关的反应，但在IRF3转录活性缺失的小鼠中，对肝损伤的保护并非由于肝细胞或免疫细胞凋亡的差异。相反，IRF3转录活性缺失的小鼠对HFD诱导的肝损伤的保护主要与p65核转位的延迟和核因子κB（NFκB）依赖性炎性细胞因子表达的降低有关。综上所述，这些数据表明IRF3的非转录功能可能通过减少NFκB信号传导，在减轻HFD引起的肝脏炎症环境方面发挥重要作用。
