氧化和化学应激的防御性转导通路——Nrf2/ARE

Nrf2/ARE是近年新发现的机体抵抗内外界氧化和化学等刺激的防御性转导通路．生理条件下,NF-E2相关因子2(Nrf2,NF-E2-related factor 2)在细胞质中与Keap1结合处于非活性、易降解的状态.在内外界自由基和化学物质刺激时,Keap1的构象改变或者Nrf2直接被磷酸化,导致Nrf2与Keap1解离而活化．活化的Nrf2进入细胞核,与抗氧化反应元件(ARE)结合,启动ARE下游的Ⅱ相解毒酶、抗氧化蛋白、蛋白酶体/分子伴侣等基因转录和表达以抵抗内外界的有害刺激．MAPK、PI3K/AKT、PKC等信号通路分子广泛参与了Nrf2的活化和核转位过程,但是具体何种通路被激动、何种通路发挥主导作用,取决于刺激物种类、刺激方式和细胞类型．本文就Nrf2分子结构、Nrf2活化机制、Nrf2/ARE调控的下游基因、与Nrf2相关的信号通路分子以及其在肿瘤、炎症、衰老等应用领域的最新进展进行综述．     

内皮细胞和平滑肌细胞氧化应激时Nrf2/ARE信号通路对抗氧化基因表达的调控:与动脉粥样硬化和先兆子痫的关系

动脉粥样硬化、糖尿病、慢性肾功能衰竭和先兆子痫等血管疾病时活性氧(reactive oxygen species,ROS)生成增加,容易导致内皮依赖性血管舒张功能的损害和血管损伤,而细胞可以诱导多种编码Ⅱ相解毒酶和抗氧化蛋白的基因表达,从而减轻ROS和亲电子物质介导的细胞损伤。一个被称为抗氧化反应元件(antioxidant response element,ARE)或亲电子反应元件(electrophile response element,EpRE)的顺式转录调控元件,可以介导诸如亚铁血红素加氧酶1、γ-谷氨酰半胱氨酸合成酶、硫氧还蛋白还原酶、谷胱甘肽-S转移酶和NAD(P)H:苯醌氧化还原酶等基因的转录。其他抗氧化酶,如超氧化物歧化酶、过氧化氢酶和非酶清除剂(如谷胱甘肽)等也参与ROS的清除。转录因子NF-E2相关因子2(nuclear factor-erythroid 2-related factor 2, Nrf2)是属于Cap‘n’Collar家族的转录因子,具有碱性亮氨酸拉链(basic region-leucine zipper,bZIP),它在ARE介导的抗氧化基因表达中起重要的作用。在正常情况下,Kelch样环氧氯丙烷相关蛋白-1(Kelch-like ECH-associated protein-1,Keapl)与Nrf2耦联,并与肌动蛋白细胞骨架结合被锚定于胞浆,但是在半胱氨酸残基发生氧化的情况下,Nrf2和Keapl解耦联,进入细胞核并与ARE结合,从而激活多种抗氧化基因和Ⅱ相解毒酶基因的转录。蛋白激酶C、丝裂原活化蛋白激酶和磷脂酰肌醇-3激酶参与Nrf2／ARE信号转导的调控。本文综述了有关Nrf2／ARE信号转导通路在血管稳态和动脉硬化、先兆子痫等疾病情况下内皮及平滑肌细胞对抗持续性氧化应激中起的作用。     

Nrf2及天然产物导向的Nrf2激活剂研究进展

氧化应激能够破坏细胞内氧化还原平衡,造成系统和组织损伤,最终引起一系列疾病的产生。转录因子E2相关因子2(Nrf2),受Kelch样环氧氯丙烷相关蛋白1(Keap1)蛋白的调控,是细胞氧化应激反应中的关键因子,在氧化应激条件下,Nrf2从Keap1中分离,然后进入细胞核与抗氧化反应元件(ARE)结合,增加了Ⅱ相解毒酶的表达,保护细胞免受氧化损伤。天然产物对于药物发现具有重要意义,研究显示,Nrf2激活剂绝大多数也是天然产物或天然产物的衍生物。本文介绍Nrf2-Keap1信号通路的作用机制以及常见的天然产物导向的Nrf2激活剂。     

Involvement of Nrf2 and Keap1 in the activation of antioxidant responsive element (ARE) by chemopreventive agent peptides from soft-shelled turtle

The antioxidant response element (ARE) is a cis-acting enhancer sequence located in the region containing genes related to antioxidant and detoxification. Under oxidative stress, the induction of nuclear factor-E2-related factor 2 (Nrf2)/ARE is considered as a fundamental process involved in defending reactive oxygen species (ROS) and providing protection against toxic xenobiotics. In this study, we obtained seven antioxidant peptides from soft-shelled turtle and concluded that Glu-Asp-Tyr-Gly-Ala (EDYGA) is the most potent ARE-luciferase inducer. To gain fundamental insights into the role of EDYGA in oxidative stress, we evaluated the effects of EDYGA on the Nrf2/Keap1 system in HepG₂ cells. The results revealed that EDYGA modulated the Nrf2/ARE pathway by enhancing Nrf2 level through the stabilization of Nrf2, which was accomplished by a decrease in the level of Keap1. These actions eventually led to an increase in nuclear Nrf2 accumulation and ARE-binding activity. Moreover, silencing Nrf2 markedly reduced ARE-driven activity induced by EDYGA. Docking results proved that glutamate residues of peptide EDYGA directly bind to Arg 415 of Kelch domain receptor pocke. The results were helpful in understanding the antioxidant activity of peptides from soft-shelled turtle which have potential to be used in foods and drugs as functional ingredients.