Role and molecular mechanism of HO-1-mediated NF-κB modulation in fibrosis progression of nonalcoholic steatohepatitis

ObjectiveTo investigate the potential effects and molecular mechanisms of heme oxygenase-1 (HO-1)-mediated modulation of nuclear factor-kappa B (NF-κB), and its downstream activation of intercellular adhesion molecule 1 (ICAM-1) and platelet derived growth factor (PDGF), in fibrosis progression of non-alcoholic steatohepatitis (NASH) using the methionine and choline deficient (MCD) mouse model of NASH. Methods Forty C57BL/6J male mice (18-20 g) were randomly divided into four groups (n=10 each): NASH model group, administered the MCD diet; HO-1 agonist group, administered the MCD diet with intraperitoneal (ip) injections of hemin (30 μmol/kg every other day); HO-1 inhibitor group, administered the MCD diet with ip injections of zinc protoporphyrin (ZnPP-IX; 20 μmol/kg every other day); and control group, administered a methionine and choline sufficient (MCS) diet, without agonist nor inhibitor injections. After eight weeks, the mice were sacrificed and resected liver tissues used to assess successful model establishment by histological analysis (hematoxylin-eosin and Masson staining) and the differential mRNA expression of HO-1, NF-κB, ICAM-1, and PDGF by real-time quantitative PCR (GAPDH normalized) and protein expression of HO-1 and PDGF by western blotting ( β-actin normalized). Significance of an intergroup difference was assessed by single-factor analysis of variance test, and the Student-Newman-Keuls test was used for pairwise comparisons. ResultsThe NASH model group showed the appropriate histologic features of hepatic steatosis, necroinflammation and fibrogenesis, while the control group showed normal lobular architecture. In addition, the NASH model group showed significantly higher expression of HO-1, NF-κB, ICAM-1 and PDGF mRNA (all P＜0.05), and concomitant increases in HO-1 and PDGF protein. The group treated with HO-1 agonist showed significant down-regulation of the NASH-induced NF-κB, ICAM-1 and PDGF expressions, while the opposite effect (accompanied by severe liver injury) was observed in the group treated with HO-1 inhibitor. Conclusion Inhibiting HO-1 activation in NASH could attenuate NF-κB signaling and expression of its downstream effectors ICAM-1 and PDGF to protect against fibrosis- and inflammation-related liver injury.