title: Homocysteine downregulates gene expression of heme oxygenase-1 in hepatocytes.
abstract: BACKGROUND
  Hyperhomocysteinemia (HHcy) is an independent risk factor for liver diseases, such as fatty liver and hepatic fibrosis. However, the mechanisms underlying this pro-oxidative effect of homocysteine (Hcy) in hepatocytes remain largely unknown. Thus, we investigated the effect of Hcy on the gene expression of heme oxygenase-1 (HO-1), the primary rate-limiting enzyme in heme catabolism and a key anti-oxidant detoxification enzyme in maintaining cellular redox homeostasis.
  
  
  METHODS
  In vivo, twenty male C57BL/6 mice at 8 weeks of age were randomly divided into two groups. One group was fed a chow diet (chow group; n = 10), the other group of mice was fed a methionine-supplemented diet (Met group, 1 mg kg(-1) day(-1) L-methionine in drinking water; n = 10) for 4 weeks. In vitro, HepG2 cells were stimulated with different doses of homocysteine (Hcy).
  
  
  RESULTS
  Four weeks' methionine supplementation caused a significant increase of plasma Hcy concentration and a decrease of HO-1 expression in the liver of C57BL/6 mice than mice received chow diet. Besides, SOD enzyme activities were impaired and the level of oxidative stress markers, such as malondialdehyde (MDA) were elevated in the liver from mice supplemented with methionine compared with control mice. In cultured hepatocytes, Hcy treatment reduced both the mRNA and protein levels of HO-1 dose-dependently. However, Hcy had no effect on the gene expression of Nrf2, the major transcriptional regulator of HO-1. Instead, Hcy induced the expression of Bach1, a transcriptional repressor of HO-1. In addition, Hcy stimulated the nuclear localization of Bach1 but prevented that of Nrf2. Furthermore, we found that knockdown of Bach1 attenuated the suppression of the HO-1 expression by Hcy.
  
  
  CONCLUSIONS
  Collectively, our results demonstrated that Bach1 plays an important role in Hcy-triggered ROS generations through inhibiting HO-1 expression, likely, resulting from the disturbed interplay between Bach1 and Nrf2.
authors.affiliation: Cardiovascular Research Center, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China ; Department of Public Health, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China ; Nutrition and Food Safety Engineering Research Center of Shaanxi Province, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China.
authors.forename: Xiaoqin
authors.initials: X
authors.lastname: Luo
authors.affiliation: Cardiovascular Research Center, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China.
authors.forename: Lei
authors.initials: L
authors.lastname: Xiao
authors.affiliation: Cardiovascular Research Center, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China ; Department of Public Health, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China ; Nutrition and Food Safety Engineering Research Center of Shaanxi Province, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China.
authors.forename: Haixia
authors.initials: H
authors.lastname: Yang
authors.affiliation: Department of Public Health, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China ; Nutrition and Food Safety Engineering Research Center of Shaanxi Province, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China.
authors.forename: Ruijuan
authors.initials: R
authors.lastname: Zhang
authors.affiliation: Cardiovascular Research Center, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China.
authors.forename: Manli
authors.initials: M
authors.lastname: Jiang
authors.affiliation: Cardiovascular Research Center, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China.
authors.forename: Jiahua
authors.initials: J
authors.lastname: Ni
authors.affiliation: Cardiovascular Research Center, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China.
authors.forename: Ting
authors.initials: T
authors.lastname: Lei
authors.affiliation: Cardiovascular Research Center, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China ; Institute of Cardiovascular Science, Peking University, Beijing, 100191 China.
authors.forename: Nanping
authors.initials: N
authors.lastname: Wang
keywords: Bach1; Heme Oxygenase-1; Homocysteine; Nrf2; Reactive oxygen species