Ischemic reperfusion (I/R) is known to trigger an increase of reactive oxygen species in the myocardium. Although high levels of oxidants can cause damages, low doses of oxidant elicit a protective effect, such as during preconditioning induced by cycles of brief I/R. Our recent data suggest that induction of antioxidant and detoxification genes dominates the gene expression network of oxidants in cardiomyocytes. A master switch controlling the expression of these genes is the transcription factor Nrf2. We found that 2 to 4 cycles of 5 min ischemia and 5 min reperfusion cause elevation of Nrf2 protein in the myocardium. With isolated cardiomyocytes, oxidants cause rapid onset of Nrf2 protein translation. Stress generally causes global reduction of protein translation. Recent studies suggest that several genes containing an Internal Ribosomal Entry Site (IRES) in the 5'Untranslated Region (5'UTR) of mRNA can escape the general translational control and undergo stress induced protein translation. A group of IRES Trans-Acting Factors (ITAFs) appears to be critical in recruiting the ribosomes to initiate the translation of these genes. Little is known about which proteins and how they are translated when the myocardium or cardiomyocytes encounter oxidative stress. We plan to take advantage of genomic and proteomic technologies to test the hypothesis that """"""""cycles of brief I/R cause selective increase of Nrf-2 protein in the myocardium through IRES mediated translation"""""""".
The Specific Aims i nclude 1) Test that Nrf2 protein translation occurs in the myocardium by cycles of brief I/R and mediates preconditioning induced cardiac protection;2) Test that lack of well defined Kozak sequence and formation of stable """"""""stems and loops"""""""" secondary structure in 5'UTR enable a battery of genes to undergo I/R induced protein translation;3) Test that Nrf2 mRNA contains an IRES that allows rapid protein translation in cardiomyocytes following cycles of brief I/R or low dose of oxidants;4) Test that cardiomyocytes express a unique set of ITAFs to regulate Nrf2 protein translation in response to I/R. The field of stress induced protein translation is in its stage of infancy. Although Nrf2 plays a critical role in cytoprotection among various cell types, the function and regulation of Nrf2 have not been well studied in cardiomyocytes. Studying the mechanism of protein translation under oxidative stress becomes a necessary task in understanding the transition to heart failure from adaptive response.
This grant proposes to study the mechanism of Nrf2 protein translation in cardiomyocytes and in the myocardium following oxidative stress.
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