Antioxidant Defense Mechanisms: Nrf2/Keap1 Signaling in Aging Heart

描述(由申请人提供)：美国老龄管理局预计，到2050年，美国将有20.2%的人口达到65岁，而2000年这一比例为12.4%。老龄化人口的这种增加是主要令人担忧的，因为他们容易出现多种健康并发症。随着年龄的增长，抗氧化能力的下降和ROS/RNS的积累是多种健康问题的主要原因，包括老年人的心脏肥大、心肌病、心肌梗死和心力衰竭等心血管疾病。我们最近的发现表明，运动通过核红系-2P45相关因子-2(Nrf2)增强抗氧化功能。Nrf2是一种氧化还原敏感蛋白。 掌握氧化还原动态平衡基因的转录调控因子，有助于防御氧化应激。Nrf2受胞质抑制因子Kelch样ECH相关蛋白(Keap1)的调控。我们实验室的研究表明，急性运动(15-20米/分钟，每天50分钟，连续2天)可诱导Nrf2核移位，并促进心脏的细胞保护机制/途径。然而，AE后一周的恢复使Nrf2及其目标抗氧化剂效果恢复到对照组(久坐)小鼠的水平。因此，可能需要更长的时间，但适度的运动来激活Nrf2/ARE-抗氧化信号。重要的是，与年龄匹配的野生型(WT)小鼠相比，废除Nrf2导致Nrf2-/-小鼠的抗氧化剂和氧化应激显著放松。令人惊讶的是，与年轻(2个月)WT小鼠相比，老年(24个月)WT小鼠和年轻Nrf2-/-WT小鼠对AE的易感性程度相似。此外，与年轻的WT小鼠相比，老年WT小鼠的心脏中ROS水平也有所增加。值得注意的是，衰老的Nrf2-/-小鼠表现出氧化应激，而WT小鼠在2周的运动后表现出改善的心肌抗氧化功能。有趣的是，与年龄匹配的久坐不动的WT小鼠相比，运动WT增加了Nrf2核转位。这些观察结果强调了加强内源性细胞保护机制以对抗年龄诱导的ROS/RNS和氧化应激的重要性。因此，我们认为Nrf2的激活对于维持细胞内氧化还原动态平衡和保护心肌免受年龄相关的氧化应激是必不可少的。到目前为止，改善心脏Nrf2功能的非药理学(体育锻炼)机制还没有被研究过。基于Nrf2的关键作用和我们实验室的初步证据，我们提出了以下假设。假设：运动诱导的增强的Nrf2/ARE信号促进抗氧化防御机制，从而防止心脏中与年龄相关的氧化应激。为了验证这一假设，我们提出了以下目标。具体目的1：确定Keap1基因敲除是否激活Nrf2/ARE-抗氧化信号并保护心脏免受年龄诱导的氧化应激。具体目标2：确定慢性适度运动是否激活Nrf2/ARE信号，保护老化的心脏免受肥厚的影响。

DESCRIPTION (provided by applicant): The Administration on Aging projects that by the year 2050, 20.2% of the population in the United States will be age sixty-five and older compared to 12.4% in the year 2000. This increase in the aging population is of major concern as they are prone to develop multiple health complications. Age dependent decline in antioxidant potential and accumulation of ROS/RNS are primary causes for multiple health problems, including cardiovascular diseases such as cardiac hypertrophy, cardiomyopathy, myocardial infarction and heart failure in the elderly. Our recent findings indicate that exercise escalates antioxidant function through nuclear erythroid-2 p45 related factor-2 (Nrf2). Nrf2 is a redox-sensitive protein and master transcriptional regulator of redox homeostatic genes, which facilitate the defense against oxidative stress. The Nrf2 is regulated by Kelch like ECH associated protein (Keap1), a cytosolic repressor. Studies from our laboratory reveal that acute exercise (AE; 15-20 meter/min for 50 min/day, for 2 days) induces Nrf2 nuclear translocation and promotes cytoprotective mechanisms/pathways in the heart. However, one-week recovery following the AE returns Nrf2 and its target antioxidant effects back to levels seen in control (sedentary) mice. Thus, it may necessitate more prolonged, but moderate exercise to activate Nrf2/ARE-antioxidant signaling. Importantly, abrogation of Nrf2 results in dramatic deregulation of antioxidants and oxidative stress in Nrf2-/- when compared to age matched wild-type (WT) mice upon AE. Surprisingly, the degree of susceptibility to AE was similar in aged (>24 months) WT and young Nrf2-/- when compared to young (2 months) WT mice. In addition, increased ROS levels were also observed in the hearts of aging WT, when compared to young WT mice. Of note, the aging Nrf2-/- mice exhibited oxidative stress, while the WT mice showed improved myocardial antioxidant function after 2-weeks of exercise. Interestingly, the exercised WT had increased Nrf2 nuclear translocation, when compared to age- matched sedentary WT mice. These observations emphasize the importance of enhancing the endogenous cytoprotective mechanisms to combat age-induced ROS/RNS and oxidative stress. Thus, we propose that activation of Nrf2 is essential for maintaining intracellular redox homeostasis and protecting myocardium from age-associated oxidative stress. Hither to, non-pharmacological (physical exercise) mechanisms that improve Nrf2 function in the heart have not been investigated. Based on the critical role for Nrf2 and preliminary evidence from our laboratory, we propose the following hypothesis. Hypothesis: Enhanced Nrf2/ARE signaling induced by exercise promotes antioxidant defense mechanisms and thereby prevents age-associated oxidative stress in the heart. To test this hypothesis, we propose the following aims. Specific Aim 1: To determine whether genetic knockdown of Keap1 activates Nrf2/ARE-antioxidant signaling and protects the heart from age-induced oxidative stress. Specific Aim 2: To determine whether chronic moderate exercise activates Nrf2/ARE-signaling and protects the aging heart from hypertrophy.