Early growth response-1 (EGR-1) expression in the liver in hemorrhagic shock (HS) is localized to hepatocytes and upregulated by hypoxia or reactive oxygen species (ROS) exposure in vitro

Abstract

Abstract Introduction: HS is a major cause of morbidity/mortality in trauma patients. EGR-1, a transcription factor, is induced by a variety of cellular stresses including hypoxia, which generates reactive oxygen species. EGR-1 triggers the expression of numerous key inflammatory mediators. We identified an increase in EGR-1 expression in HS using gene arrays. We hypothesize that the early induction of EGR-1 expression in the shock phase of HS occurs in hepatocytes as a result of hypoxia and/or redox stress. Methods: In vivo EGR-1 expression was assessed by subjecting mice to HS (25mmHG). Liver isolated at varying times was assessed for EGR-1 expression by Northern and Western blotting. EGR-1 localization was determined by immunoflourescence. Rat hepatocytes were obtained by collagenase perfusion and subjected to hypoxia (1%) or hydrogen peroxide treatment (0.2mM) for varying times with Egr-1 expression evaluated by Western blotting. Results: Mice (n = 3) subjected to HS expressed EGR-1 mRNA by 1hr of HS, while protein and DNA-binding activity was evident by 2.5hrs. No EGR-1 expression was seen in sham-treated animals. Immunoflourescence identified EGR-1 nuclear localization in mouse hepatocytes. EGR-1 induction in vitro in cultured rat hepatocytes rendered hypoxic (1%) was seen within 1hr, with peak levels at 6hrs (n = 2). Exposing normoxic hepatocytes to hydrogen peroxide (0.2mM) also induced a rapid increase in EGR-1 protein (1hr). Conclusions: These data show that the transcription factor, EGR-1 is rapidly upregulated in hepatocytes during HS without resuscitation. The observation that either hypoxia or hydrogen peroxide alone are strong inducers of EGR-1 in hepatocytes in vitro suggests that redox stress is involved in the HS-induced upregulation of EGR-1.