Bach1与Nrf2调控γ-谷氨酰半胱氨酸合成酶对大鼠慢性阻塞性肺疾病的作用

为了探讨Bach1 (BTB and CNC homology 1)与红系衍生的核因子相关因子2（Nrf2）和γ-谷氨酰半胱氨酸合成酶（γ-GCS）的表达变化在慢性阻塞性肺疾病（COPD）中的作用和意义,用气管内注入脂多糖及熏香烟的复合刺激法建立大鼠COPD 模型．观察两组大鼠的肺组织病理学改变,测两组大鼠的肺功能指标;应用免疫组化、Western印迹、原位杂交和逆转录 聚合酶链反应（RT-PCR）等方法检测Bach1与Nrf2及γ GCS 在两组大鼠的肺组织中的表达．结果显示,COPD组的肺功能指标（FEV_0.3、FEV_0.3/FVC%、PEF）明显恶化;光镜下肺组织病理改变符合COPD的特征性改变;γ GCS与Nrf2 的mRNA及蛋白质表达在COPD组大鼠肺组织中明显增强;而Bach1 mRNA及蛋白质在COPD组和对照组的表达无明显差别．且核/胞浆分离技术表明,Nrf2蛋白在对照组主要表达于胞浆,胞核中表达水平较弱,在COPD组胞浆、胞核均有表达,但是在胞核中的水平明显升高;Bach1蛋白在对照组主要表达于胞核中,胞浆中无明显表达,在COPD组主要表达于胞浆,胞核中无明显表达．相关性分析表明,γ-GCS mRNA与FEV_0.3、FEV_0.3/FVC%、PEF均呈负相关;Nrf2蛋白表达与γ GCS mRNA呈正相关;Bach1蛋白与γ GCS mRNA呈负相关．上述结果提示,Bach1与Nrf2和γ-GCS可能均在大鼠COPD的发病中发挥作用,且Bach1和Nrf2可能通过竞争性机制调控γ-GCS的表达,影响COPD的发生和发展．     

Molecular basis of the Keap1–Nrf2 system

Nrf2 (NF-E2-related factor 2) is a master regulator of cellular responses against environmental stresses. Nrf2 induces the expression of detoxification and antioxidant enzymes, and Keap1 (Kelch-like ECH-associated protein 1), an adaptor subunit of Cullin 3-based E3 ubiquitin ligase, regulates Nrf2 activity. Keap1 also acts as a sensor for oxidative and electrophilic stresses. Keap1 retains multiple sensor cysteine residues that detect various stress stimuli. Increasing attention has been paid to the roles that Nrf2 plays in the protection of our bodies against drug toxicity and stress-induced diseases. On the other hand, Nrf2 is found to promote both oncogenesis and cancer cell resistance against chemotherapeutic drugs. Thus, although Nrf2 acts to protect our body from deleterious stresses, cancer cells hijack the Nrf2 activity to support their malignant growth. Nrf2 has emerged as a new therapeutic target, and both inducers and inhibitors of Nrf2 are awaited. Studies challenging the molecular basis of the Keap1–Nrf2 system functions are now critically important to improve translational studies of the system. Indeed, recent studies identified cross talk between Nrf2 and other signaling pathways, which provides new insights into the mechanisms by which the Keap1–Nrf2 system serves as a potent regulator of our health and disease.     

Regulation of Nrf2—an update

Nrf2:INrf2 (Keap1) are cellular sensors of oxidative and electrophilic stress. Nrf2 is a nuclear factor that controls the expression and coordinated induction of a battery of genes that encode detoxifying enzymes, drug transporters, antiapoptotic proteins, and proteasomes. In the basal state, Nrf2 is constantly degraded in the cytoplasm by its inhibitor, INrf2. INrf2 functions as an adapter for Cul3/Rbx1 E3 ubiquitin ligase-mediated degradation of Nrf2. Chemicals, including antioxidants, tocopherols including α-tocopherol (vitamin E), and phytochemicals, and radiation antagonize the Nrf2:INrf2 interaction and lead to the stabilization and activation of Nrf2. The signaling events involve preinduction, induction, and postinduction responses that tightly control Nrf2 activation and repression back to the basal state. Oxidative/electrophilic signals activate unknown tyrosine kinases in a preinduction response that phosphorylates specific residues on Nrf2 negative regulators, INrf2, Fyn, and Bach1, leading to their nuclear export, ubiquitination, and degradation. This prepares nuclei for unhindered import of Nrf2. Oxidative/electrophilic modification of INrf2 cysteine 151 followed by PKC phosphorylation of Nrf2 serine 40 in the induction response results in the escape or release of Nrf2 from INrf2. Nrf2 is thus stabilized and translocates to the nucleus, resulting in a coordinated activation of gene expression. This is followed by a postinduction response that controls the “switching off” of Nrf2-activated gene expression. GSK3β, under the control of AKT and PI3K, phosphorylates Fyn, leading to Fyn nuclear localization. Fyn phosphorylates Nrf2 Y568, resulting in nuclear export and degradation of Nrf2. The activation and repression of Nrf2 provide protection against oxidative/electrophilic stress and associated diseases, including cancer. However, deregulation of INrf2 and Nrf2 due to mutations may lead to nuclear accumulation of Nrf2 that reduces apoptosis and promotes oncogenesis and drug resistance.     

Nutritional strategies to modulate inflammation and oxidative stress pathways via activation of the master antioxidant switch Nrf2

The nuclear factor E2-related factor 2 (Nrf2) plays an important role in cellular protection against cancer, renal, pulmonary, cardiovascular and neurodegenerative diseases where oxidative stress and inflammation are common conditions. The Nrf2 regulates the expression of detoxifying enzymes by recognizing the human Antioxidant Response Element (ARE) binding site and it can regulate antioxidant and anti-inflammatory cellular responses, playing an important protective role on the development of the diseases. Studies designed to investigate how effective Nrf2 activators or modulators are need to be initiated. Several recent studies have shown that nutritional compounds can modulate the activation of Nrf2–Keap1 system. This review aims to discuss some of the key nutritional compounds that promote the activation of Nrf2, which may have impact on the human health.     

Differential responses of the Nrf2-Keap1 system to laminar and oscillatory shear stresses in endothelial cells

The Nrf2-Keap1 system coordinately regulates cytoprotective gene expression via the antioxidant responsive element (ARE). The expression of several ARE-regulated genes was found to be up-regulated in endothelial cells by laminar shear stress, suggesting that Nrf2 contributes to the anti-atherosclerosis response via the ARE. To gain further insight into the roles that Nrf2 plays in the development of atherosclerosis, we examined how Nrf2 regulates gene expression in response to anti-atherogenic laminar flow (L-flow) or pro-atherogenic oscillatory flow (O-flow). Exposure of human aortic endothelial cells (HAECs) to L-flow, but not to O-flow, induced the expression of cytoprotective genes, such as NAD(P)H quinone oxidoreductase 1 (NQO1) by 5-fold and heme oxygenase-1 by 8-fold. The critical contribution of Nrf2 to the expression induced by L-flow was ascertained in siRNA-mediated knock-down experiments. Two cyclooxygenase-2 (COX-2) specific inhibitors attenuated Nrf2 nuclear accumulation in the acute phase of L-flow exposure. A downstream product of COX-2, 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2), activated the Nrf2 regulatory pathway in HAECs through binding to the cysteines of Keap1. These results demonstrate that 15d-PGJ2 is essential for L-flow to activate Nrf2 and induce anti-atherosclerotic gene expression. Whereas both L-flow and O-flow induced the nuclear accumulation of Nrf2 to comparable levels, chromatin immunoprecipitation analysis revealed that Nrf2 binding to the NQO1 ARE was significantly diminished in the case of O-flow compared with that of L-flow. These results suggest that O-flow inhibits Nrf2 activity at the DNA binding step, thereby suppressing athero-protective gene expression and hence predisposing the blood vessels to the formation of atherosclerosis.