IRG1 induced by heme oxygenase-1/carbon monoxide inhibits LPS-mediated sepsis and pro-inflammatory cytokine production

Cell Mol Immunol. 2016 Mar;13(2):170-9. doi: 10.1038/cmi.2015.02. Epub 2015 Feb 2.


The immunoresponsive gene 1 (IRG1) protein has crucial functions in embryonic implantation and neurodegeneration. IRG1 promotes endotoxin tolerance by increasing A20 expression in macrophages through reactive oxygen species (ROS). The cytoprotective protein heme oxygenase-1 (HO-1), which generates endogenous carbon monoxide (CO), is expressed in the lung during Lipopolysaccharide (LPS) tolerance and cross tolerance. However, the detailed molecular mechanisms and functional links between IRG1 and HO-1 in the innate immune system remain unknown. In the present study, we found that the CO releasing molecule-2 (CORM-2) and chemical inducers of HO-1 increased IRG1 expression in a time- and dose-dependent fashion in RAW264.7 cells. Furthermore, inhibition of HO-1 activity by zinc protoporphyrin IX (ZnPP) and HO-1 siRNA significantly reduced expression of IRG1 under these conditions. In addition, treatment with CO and HO-1 induction significantly increased A20 expression, which was reversed by ZnPP and HO-1 siRNA. LPS-stimulated TNF-α was significantly decreased, whereas IRG1 and A20 were increased by CORM-2 application and HO-1 induction, which in turn were abrogated by ZnPP. Interestingly, siRNA against IRG1 and A20 reversed the effects of CO and HO-1 on LPS-stimulated TNF-α production. Additionally, CO and HO-1 inducers significantly increased IRG1 and A20 expression and downregulated TNF-α production in a LPS-stimulated sepsis mice model. Furthermore, the effects of CO and HO-1 on TNF-α production were significantly reversed when ZnPP was administered. In conclusion, CO and HO-1 induction regulates IRG1 and A20 expression, leading to inhibition of inflammation in vitro and in an in vivo mice model.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carbon Monoxide / pharmacology*
  • Cell Line
  • Gene Expression Regulation / drug effects*
  • Heme Oxygenase-1 / antagonists & inhibitors
  • Heme Oxygenase-1 / immunology*
  • Hydro-Lyases / immunology*
  • Lipopolysaccharides / toxicity*
  • Male
  • Membrane Proteins / antagonists & inhibitors
  • Membrane Proteins / immunology*
  • Mice
  • Sepsis / chemically induced
  • Sepsis / immunology*
  • Sepsis / pathology
  • Tumor Necrosis Factor alpha-Induced Protein 3 / immunology*
  • Tumor Necrosis Factor-alpha / immunology*


  • Lipopolysaccharides
  • Membrane Proteins
  • Tumor Necrosis Factor-alpha
  • Carbon Monoxide
  • Heme Oxygenase-1
  • Hmox1 protein, mouse
  • Tumor Necrosis Factor alpha-Induced Protein 3
  • Tnfaip3 protein, mouse
  • Hydro-Lyases
  • Irg1 protein, mouse