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.
Supplementation of antioxidant drugs against various oxidative stress mediated diseases have been failed and resulted in deleterious side effects. Our recent discovery indicated that acute exercise (AE) can activate cell defense system through a protein factor called Nrf2 (nuclear-erythroid-2-like factor-2). In this study, we will fid potential methods (physical exercise and small molecules) to promote antioxidant defense mechanisms, which can protect the heart from age-associated diseases in humans.
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