The purpose of this proposal is to elucidate the mechanism whereby S-nitrosation (SNO) confers cardioprotection from ischemia-reperfusion injury. S-nitrosation is a recently described protein modification in which a nitric oxide moiety is covalently attached to a thiol group of a cysteine residue, leading to the formation of S-nitrosothiols. SNO is a reversible modification that has been shown to modify the activity of target proteins. Additionally, SNO has been reported to protect thiol groups from oxidative damage. Potential sources for the endogenous production of nitric oxide in cardiac myocytes include nitric oxide synthase and non-enzymatic means. Brief occlusion of a coronary artery generally results in cardiac ischemia-reperfusion injury. This type of injury can lead to cardiac dysfunction, which is initially reversible (myocardial stunning) and later irreversible (infarction), and ventricular arrhythmias. However, cardioprotective effects result from ischemic preconditioning, a protective mechanism of the heart that develops from several brief episodes of ischemia. This cardioprotective measure has been reported to increase S-nitrosation formation in the cardiac myocyte. Furthermore, hearts from females exhibit endogenous cardioprotection, which has been shown to be NOS-dependent. However, studies have yet to fully characterize the signaling pathways necessary for SNO formation or the mechanism(s) through which SNO formation exerts cardioprotection. Therefore, further studies are needed in order to examine the role of S-nitrosation in cardioprotection. The role of S-nitrosation will be addressed in the specific aims of this proposal and are as follows: 1) determine the specific signaling pathways that are necessary for S-nitrosation formation in cardioprotection, 2) identify the specific cysteine residues that are SNO during cardioprotection, and 3) determine if S-nitrosation exerts cardioprotective effects by shielding critical thiol groups from oxidative damage. The overall hypotheses of this proposal are as follows: 1.) SNO formation and cardioprotection is initiated upon activation of specific signaling pathways, 2.) SNO occurs at specific cysteine residues on key target proteins, and 3.) SNO provides cardioprotection by blocking against oxidative damage.
The specific aims of the proposed study will determine the role of S-nitrosation in cardioprotection and resolve the mechanism through which S- nitrosation serves to protect against ischemia-reperfusion injury. These results will also help to clarify inconsisties in the literature that relate to the role of nitric oxide synthase in cardioprotection. Additionally, these results may allow for improvements in the treatment of human cardiac patients by identifying novel targets for therapeutic intervention.
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