Reactive oxygen species (ROS) play both physiological and pathological roles in the heart and critically regulate survival and death of cardiomyocytes (CMs). NADPH oxidases purposefully produce ROS, including superoxide and hydrogen peroxide, by transferring electrons from NADPH or NADH to molecular oxygen. We have been focusing on NADPH oxidase 4 (Nox4), one of the major NADPH oxidase isoforms expressed in intracellular membranes in the heart, and we have discovered its key features. Excessive activation of Nox4 in response to hypertrophic stimuli, aging, and ischemia/reperfusion (I/R) leads to increases in oxidative stress, mitochondrial dysfunction, CM cell death, and cardiac dysfunction. On the other hand, basal production of ROS by either Nox2 or Nox4 during ischemia and reperfusion acts as a physiological second messenger to induce hypoxic adaptation. These studies suggest that the activity of Nox4 is supposed to be kept at appropriate levels in order to avoid accumulation of ROS either above or below physiological levels. How the activity of Nox4 is controlled in CMs under various pathophysiological conditions is poorly understood. Nox4 is believed to be regulated primarily at the level of transcription/translation. However, using yeast two-hybrid screening, we have identified that Nox4 physically associates with Fyn, a non-receptor type tyrosine kinase and that Fyn- mediated phosphorylation of Nox4 negatively regulates Nox4 and serves as an important negative feedback mechanism to limit excessive oxidative stress in the heart. We here test our hypotheses 1) that Fyn-mediated phosphorylation of Nox4 at Y566 inhibits interaction between Nox4 and p22phox and negatively regulates ROS production by Nox4, and 2) that activation of endogenous Fyn in response to PO and ischemic preconditioning (IPC) induces phosphorylation/suppression of Nox4 at Y566, thereby attenuating the NADPH oxidase activity of Nox4 and protecting the heart from PO and I/R injury. Using both molecular signaling and in vivo physiology approaches, we will show the molecular mechanism of the Fyn-mediated suppression of Nox4 and the functional significance of Fyn-mediated regulation of Nox4 during PO and IPC in vivo. Our study will elucidate a novel and direct PTM mechanism by which Nox4, the major ROS-producing enzyme in the heart, is regulated by stress and its functional significance during cardiac conditions frequently associated with aging. Our study will provide an important clue to better control the activity of Nox4 in the heart during cardiac stress in cardiovascular patients.

Public Health Relevance

Excessive production of free radicals and peroxide, termed reactive oxygen species (ROS), in response to stresses, including high blood pressure and heart attack, causes malfunction and death of heart cells and leads to heart failure in elderly patients. We will investigate how the function of an enzyme termed Nox4, an important source of ROS in the heart, is modulated and how this mechanism affects cardiac damage during cardiac stress. Knowledge obtained from this project should lead to a novel strategy to modify the activity of Nox4, thereby preventing cardiac damage caused by excessive ROS in patients.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Research Project (R01)
Project #
5R01AG023039-15
Application #
9226002
Study Section
Cardiac Contractility, Hypertrophy, and Failure Study Section (CCHF)
Program Officer
Kohanski, Ronald A
Project Start
2004-02-15
Project End
2019-01-31
Budget Start
2017-02-01
Budget End
2018-01-31
Support Year
15
Fiscal Year
2017
Total Cost
$350,639
Indirect Cost
$130,111
Name
Rutgers University
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
078795851
City
Newark
State
NJ
Country
United States
Zip Code
07103
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Sadoshima, Junichi (2017) Department of Cell Biology and Molecular Medicine, Rutgers New Jersey Medical School. Circ Res 121:1127-1129
Oka, Shin-Ichi; Hirata, Tsuyoshi; Suzuki, Wataru et al. (2017) Thioredoxin-1 maintains mTOR function during oxidative stress in cardiomyocytes. J Biol Chem :
Saito, Toshiro; Sadoshima, Junichi (2017) Unexpected Functional Consequences of the Loss of the Autophagy-Related Conjugation System. Circ Res 120:610-612
Mizushima, Wataru; Sadoshima, Junichi (2017) BAG3 plays a central role in proteostasis in the heart. J Clin Invest 127:2900-2903
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