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Interferon Type I Regulates Inflammasome Activation and High Mobility Group Box 1 Translocation in Hepatocytes During Ehrlichia?Induced Acute Liver Injury

ABSTRACT: IFN?I signaling exacerbate liver pathology and contribute to sepsis following fatal Ehrlichia infection by promoting Ehrlichia replication and mediating detrimental inflammasome activation. Inflammasomes are an important innate immune host defense against intracellular microbial infection. Activation of inflammasomes by microbial or host ligands results in cleavage of caspase?1 (canonical pathway) or caspase?11 (noncanonical pathway), release of interleukin (IL)?1?, IL?18, high mobility group box 1 (HMGB1), and inflammatory cell death known as pyroptosis. Ehrlichia are obligate, intracellular, gram?negative bacteria that lack lipopolysaccharide but cause potentially life?threatening monocytic ehrlichiosis in humans and mice that is characterized by liver injury followed by sepsis and multiorgan failure. Employing murine models of mild and fatal ehrlichiosis caused by infection with mildly and highly virulent Ehrlichia muris (EM) and Ixodes ovatus Ehrlichia (IOE), respectively, we have previously shown that IOE infection triggers type I interferon (IFN?I) response and deleterious caspase?11 activation in liver tissues, which promotes liver injury and sepsis. In this study, we examined the contribution of IFN?I signaling in hepatocytes (HCs) to Ehrlichia?induced liver injury. Compared to EM infection, we found that IOE enter and replicate in vitro cultured primary murine HCs and induce secretion of IFN? and several chemokines, including regulated upon activation, normal T?cell expressed, and secreted (RANTES), monocyte chemoattractant protein 1 (MCP1), monokine induced by gamma (MIG)/chemokine (C?X?C motif) ligand 9 (CXCL9), macrophage inflammatory protein 1 alpha (MIP1?), keratinocyte?derived chemokine (KC), and granulocyte?macrophage colony?stimulating factor (GM?CSF). Notably, in vitro stimulation of uninfected and Ehrlichia?infected HCs with recombinant IFN? triggered activation of caspase?1/11, cytosolic translocation of HMGB1, and enhanced autophagy and intracellular bacterial replication. Secretion of HMGB1 by IOE?infected HCs was dependent on caspase?11. Primary HCs from IOE? but not EM?infected mice also expressed active caspase?1/11. Conclusion: HC?specific IFN?I signaling may exacerbate liver pathology during infection with obligate intracellular Ehrlichia by promoting bacterial replication and detrimental caspase?11?mediated inflammasome activation.

SUBMITTER: Kader M

PROVIDER: S-EPMC7789844 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:High mobility group box-1 (HMGB1), recognized as a representative of damage-associated molecular patterns, is released during cell injury/death, triggering the inflammatory response and ultimately resulting in tissue damage. Dozens of studies have shown that HMGB1 is involved in certain diseases, but the details on how injured hepatocytes release HMGB1 need to be elicited. AIM:To reveal HMGB1 release mechanism in hepatocytes undergoing oxidative stress. METHODS:C57BL6/J male mice were fed a high-fat diet for 12 wk plus a single binge of ethanol to induce severe steatohepatitis. Hepatocytes treated with H2O2 were used to establish an in vitro model. Serum alanine aminotransferase, liver H2O2 content and catalase activity, lactate dehydrogenase and 8-hydroxy-2-deoxyguanosine content, nicotinamide adenine dinucleotide (NAD+) levels, and Sirtuin 1 (Sirt1) activity were detected by spectrophotometry. HMGB1 release was measured by enzyme linked immunosorbent assay. HMGB1 translocation was observed by immunohistochemistry/immunofluorescence or Western blot. Relative mRNA levels were assayed by qPCR and protein expression was detected by Western blot. Acetylated HMGB1 and poly(ADP-ribose)polymerase 1 (Parp1) were analyzed by Immunoprecipitation. RESULTS:When hepatocytes were damaged, HMGB1 translocated from the nucleus to the cytoplasm because of its hyperacetylation and was passively released outside both in vivo and in vitro. After treatment with Sirt1-siRNA or Sirt1 inhibitor (EX527), the hyperacetylated HMGB1 in hepatocytes increased, and Sirt1 activity inhibited by H2O2 could be reversed by Parp1 inhibitor (DIQ). Parp1 and Sirt1 are two NAD+-dependent enzymes which play major roles in the decision of a cell to live or die in the context of stress . We showed that NAD+ depletion attributed to Parp1 activation after DNA damage was caused by oxidative stress in hepatocytes and resulted in Sirt1 activity inhibition. On the contrary, Sirt1 suppressed Parp1 by negatively regulating its gene expression and deacetylation. CONCLUSION:The functional inhibition between Parp1 and Sirt1 leads to HMGB1 hyperacetylation, which leads to its translocation from the nucleus to the cytoplasm and finally outside the cell.

Project description:Acetaminophen (APAP) overdoses are of major clinical concern. Growing evidence underlines a pathogenic contribution of sterile postinjury inflammation in APAP-induced acute liver injury (APAP-ALI) and justifies development of anti-inflammatory therapies with therapeutic efficacy beyond the therapeutic window of the only current treatment option, N-acetylcysteine (NAC). The inflammatory mediator, high mobility group box 1 (HMGB1), is a key regulator of a range of liver injury conditions and is elevated in clinical and preclinical APAP-ALI. The anti-HMGB1 antibody (m2G7) is therapeutically beneficial in multiple inflammatory conditions, and anti-HMGB1 polyclonal antibody treatment improves survival in a model of APAP-ALI. Herein, we developed and investigated the therapeutic efficacy of a partly humanized anti-HMGB1 monoclonal antibody (mAb; h2G7) and identified its mechanism of action in preclinical APAP-ALI. The mouse anti-HMGB1 mAb (m2G7) was partly humanized (h2G7) by merging variable domains of m2G7 with human antibody-Fc backbones. Effector function-deficient variants of h2G7 were assessed in comparison with h2G7 in vitro and in preclinical APAP-ALI. h2G7 retained identical antigen specificity and comparable affinity as m2G7. 2G7 treatments significantly attenuated APAP-induced serum elevations of alanine aminotransferase and microRNA-122 and completely abrogated markers of APAP-induced inflammation (tumor necrosis factor, monocyte chemoattractant protein 1, and chemokine [C-X-C motif] ligand 1) with prolonged therapeutic efficacy as compared to NAC. Removal of complement and/or Fc receptor binding did not affect h2G7 efficacy.ConclusionThis is the first report describing the generation of a partly humanized HMGB1-neutralizing antibody with validated therapeutic efficacy and with a prolonged therapeutic window, as compared to NAC, in APAP-ALI. The therapeutic effect was mediated by HMGB1 neutralization and attenuation of postinjury inflammation. These results represent important progress toward clinical implementation of HMGB1-specific therapy as a means to treat APAP-ALI and other inflammatory conditions. (Hepatology 2016;64:1699-1710).

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Interferon Type I Regulates Inflammasome Activation and High Mobility Group Box 1 Translocation in Hepatocytes During Ehrlichia?Induced Acute Liver Injury

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