S1899 Genetic Ablation of Bach1 Followed By Upregulation of Heme Oxygenase-1 Improved Nonalcoholic Steatohepatitis in Rodent Model

Abstract

Backgrounds/Aims: Bach1 is a transcriptional repressor of heme oxygenase-1 (HO-1). HO1 has cytoprotective activities through its antioxidant and anti-inflammatory properties. In this study, we investigated the effect of bach1 knockout on an animal model of NASH. Methods: Ten-week old male C57BL/6J mice (WT) and bach1 deficient mice (KO) were pair-fed either a chow or methionine/choline deficient (MCD) diet for 8 weeks (n=15 each). At fixed periods, mice were sacrificed, and livers and blood were collected. Histological findings were assessed by HE and Azan-Mallory staining. Serum transaminases were analyzed enzymatically. Hepatic mRNA expression of HO-1, TGF-β1, αSMA, peroxisome proliferator activated receptor α (PPARα) and microsomal triglyceride transfer protein (MTP) were analyzed by real-time PCR. Hepatic content of triglycerides (TG) was analyzed enzymatically. As the determination of hepatic oxidative stress generation, hepatic malondialdehyde (MDA) content was analyzed enzymatically. Results: Whereas MCD diet promoted significantly greater weight loss (chow -15%; MCD -40%, P < 0.05), significant change was not observed between WT and KO mice on each diet. At 8 weeks on MCD diet, liver inflammation and steatosis were pathohistologically significantly attenuated in KO mice when compared with WT mice, but changes found in the serum level of ALT were not significant. The expression of hepatic HO-1 mRNA was increased in KO mice when compared with WT mice (6.1fold). Upregulation of hepatic MDA content by MCD diet (4.2-fold) was inhibited in KO mice thoroughly. MCD diet feeding increased hepatic content of TG in WT mice (6.1-fold). But, in KO mice, such change was repressed significantly. In WT mice, MCD diet reduced hepatic PPARα and MTP mRNA expression significantly, whereas such a change was not observed in KO mice. Hepatic expression of TGF-β1 and αSMA mRNA was expressed at higher levels in WT mice after 1 and 4 weeks on the MCD diet when compared to KO mice. Such changes were not observed in WT and KO mice on chow diet. Conclusions: Up-regulation of HO-1 induced by Gene ablation of bach1 improved steatosis, at least in part, through themechanism of hepatic secretion of TG associated with PPARα-MTP pathway. HO-1 also inhibited ROS generation in the liver and suppressed the activation of hepatic stellate cells, suggesting its causal relation to liver fibrosis. We speculate that HO-1 plays a protective role in the development of NASH through its cytoprotective and anti-oxidant activities.