Luo Xiaoqin, Xiao Lei, Yang Haixia, Zhang Ruijuan, Jiang Manli, Ni Jiahua, Lei Ting, Wang Nanping
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.
Cardiovascular Research Center, School of Medicine, Xi'an Jiaotong University, Xi'an, 710061 China.
Nutr Metab (Lond). 2014 Dec 8;11(1):55. doi: 10.1186/1743-7075-11-55. eCollection 2014.
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.
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).
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.
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.
高同型半胱氨酸血症（HHcy）是肝脏疾病（如脂肪肝和肝纤维化）的独立危险因素。然而，同型半胱氨酸（Hcy）在肝细胞中这种促氧化作用的潜在机制仍 largely 未知。因此，我们研究了 Hcy 对血红素加氧酶-1（HO-1）基因表达的影响，HO-1 是血红素分解代谢中的主要限速酶，也是维持细胞氧化还原稳态的关键抗氧化解毒酶。
在体内，将 20 只 8 周龄的雄性 C57BL/6 小鼠随机分为两组。一组喂食普通饲料（普通饲料组；n = 10），另一组小鼠喂食补充蛋氨酸的饲料（蛋氨酸组，饮用水中含 1 mg kg(-1) 天(-1) L-蛋氨酸；n = 10），持续 4 周。在体外，用不同剂量的同型半胱氨酸（Hcy）刺激 HepG2 细胞。
与喂食普通饲料的小鼠相比，补充蛋氨酸 4 周导致 C57BL/6 小鼠血浆 Hcy 浓度显著升高，肝脏中 HO-1 表达降低。此外，与对照小鼠相比，补充蛋氨酸的小鼠肝脏中超氧化物歧化酶（SOD）活性受损，氧化应激标志物（如丙二醛（MDA））水平升高。在培养的肝细胞中，Hcy 处理剂量依赖性地降低了 HO-1 的 mRNA 和蛋白质水平。然而，Hcy 对 HO-1 的主要转录调节因子 Nrf2 的基因表达没有影响。相反，Hcy 诱导了 HO-1 的转录抑制因子 Bach1 的表达。此外，Hcy 刺激 Bach1 的核定位，但阻止 Nrf2 的核定位。此外，我们发现敲低 Bach1 减弱了 Hcy 对 HO-1 表达的抑制作用。
总体而言，我们的结果表明，Bach1 通过抑制 HO-1 表达在 Hcy 触发的活性氧生成中起重要作用，这可能是由于 Bach1 和 Nrf2 之间相互作用紊乱所致。
