ABSTRACT
High mobility group box 1 (HMGB1) is a NF released extracellularly as a late mediator of lethality in sepsis and as an early mediator of inflammation following injury. Here we demonstrate that in contrast to the proinflammatory role of HMGB1, preconditioning with HMGB1 results in protection following hepatic ischemia/reperfusion (I/R). Pretreatment of mice with HMGB1 significantly decreased liver damage after I/R. The protection observed in mice pretreated with HMGB1 was associated with a higher expression of IL-1R-associated kinase-M, a negative regulator of TLR4 signaling, compared with controls. We thus explored the possibility that HMGB1 preconditioning was mediated through TLR4 activation. HMGB1 preconditioning failed to provide protection in TLR4 mutant (C3H/HeJ) mice, but successfully reduced damage in TLR4 wild-type (C3H/HeOuj) mice. Our studies demonstrate that in contrast to the role of HMGB1 as an early mediator of inflammation and organ damage in hepatic I/R, HMGB1 preconditioning can be protective.
Subject(s)
HMGB1 Protein/administration & dosage , Liver/blood supply , Reperfusion Injury/metabolism , Reperfusion Injury/prevention & control , Transplantation Conditioning/methods , Amino Acid Sequence , Animals , HMGB1 Protein/genetics , HeLa Cells , Humans , Injections, Intravenous , Interleukin-1 Receptor-Associated Kinases , Intracellular Signaling Peptides and Proteins , Lipopolysaccharides/administration & dosage , Liver/pathology , Male , Mice , Mice, Inbred C3H , Mice, Inbred C57BL , Mice, Mutant Strains , Molecular Sequence Data , Protein Serine-Threonine Kinases/biosynthesis , Reperfusion Injury/enzymology , Toll-Like Receptor 4/deficiency , Toll-Like Receptor 4/physiology , Up-Regulation/physiologyABSTRACT
Hepatic ischemia occurs in the settings of trauma, transplantation, and elective liver resections. The initiating events that account for local organ damage are only partially understood. Interferon (IFN) regulatory factor-1 (IRF-1) is a transcription factor that regulates the expression of a number of genes involved in both innate and acquired immunity; however, its function in liver injury is unknown. Therefore, the purpose of this study was to investigate the role of IRF-1 in hepatic ischemia-reperfusion (I/R) injury. In C57BL/6 mice undergoing 60 min of hepatic ischemia, IRF-1 protein expression increased as early as 1 h after reperfusion. IRF-1 knockout mice were significantly protected from hepatic I/R-induced damage compared with their wild-type controls. Hepatic I/R injury resulted in marked activation of the MAP kinase c-Jun NH(2)-terminal kinase (JNK) in wild-type mice but not IRF-1 knockout mice. IRF-1 knockout mice also exhibited significantly lower hepatic expression of TNF-alpha, IL-6, ICAM-1, and inducible nitric oxide synthase (iNOS) mRNA. Adenoviral delivery of IRF-1 into C57BL/6 mice resulted in increased liver damage even without an ischemic insult. This injury was associated with increased JNK activation and hepatic iNOS expression. Because IRF-1 contributed to liver injury, we also examined for inflammatory signals that regulated IRF-1 gene expression in cultured hepatocytes. Whereas IFN-gamma and IFN-beta were strong inducers of IRF-1 mRNA (>10-fold) in a time- and dose-dependent manner, TNF-alpha and IL-1beta also induced IRF-1 mRNA to a lesser extent (2- to 3-fold). IL-6 and lipopolysaccharide had no effect on IRF-1 expression. This study demonstrates that IRF-1 exerts a harmful role in hepatic I/R injury by modulating the expression of multiple inflammatory mediators. We further show that IRF-1-mediated injury involves the activation of JNK and that hepatocellular IRF-1 expression itself is regulated by specific cytokines.
Subject(s)
Liver/blood supply , Liver/immunology , Reperfusion Injury/immunology , Transcription Factors/immunology , Animals , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Rats , Rats, Sprague-Dawley , Reperfusion Injury/pathologyABSTRACT
Endogenous ligands from damaged cells, so-called damage-associated molecular pattern molecules, can activate innate immunity via TLR4 signaling. Hepatic warm ischemia and reperfusion (I/R) injury and inflammation is largely TLR4 dependent. We produced TLR4 chimeric mice to assess whether the TLR4-dependent injury required TLR4 expression on liver parenchymal or nonparenchymal cells. Chimeric mice were produced by adoptive transfer of donor bone marrow cells into irradiated recipient animals using reciprocal combinations of TLR4 wild-type (WT; C3H/HeOuj) and TLR4 mutant (C3H/HeJ) mouse bone marrow. Wild-type chimeric mice bearing TLR4 mutant hemopoietic cells and TLR4 mutant mice transplanted with their own bone marrow-derived cells were protected from hepatic I/R and exhibited decreased JNK and NF-kappaB activation compared with WT chimeric mice transplanted with their own bone marrow. In contrast, TLR4 mutant mice transplanted with TLR4 WT bone marrow were not protected from liver I/R and demonstrated pronounced increases in JNK and NF-kappaB activation when compared with autochthonous transplanted mutant mice. In addition, depletion of phagocytes taking up gadolinium chloride failed to provide any additional protection to TLR4 mutant mice, but substantially reduced damage in WT mice after hepatic I/R. Together, these results demonstrate that TLR4 engagement on actively phagocytic nonparenchymal cells such as Kupffer cells is required for warm I/R-induced injury and inflammation in the liver.
