Contribution of M-Tyrosine to the Adverse Effects of Oxidative Stress

Oxidative stress increases with age and likely contributes to a variety of age-related diseases, but the processes by which oxidative stress causes cellular damage and contributes to aging and its associated pathologies are not completely understood. This proposal seeks to study the role of atypical tyrosine isomers, which differ from endogenous tyrosine in the positioning of their hydroxyl group on the benzyl ring, in the harmful effects of oxidative stress. Under conditions of oxidative stress, hydroxyl radicals can attack the benzyl ring of phenylalanine and form these abnormal tyrosine isomers including meta-tyrosine. For decades elevations in m-tyrosine concentrations have been measured simply as a surrogate marker of oxidative stress burden. However, emerging evidence suggests m-tyrosine is directly harmful to cells and may actually contribute to oxidative stress-induced cell damage and disease pathogenesis. A proposed mechanism for the harmful effects of m-tyrosine is the aberrant charging of this amino acid to phenylalanine-tRNA which then results in the subsequent incorporation of m-tyrosine into newly synthesized proteins. Potentially this could have a range of effects on these proteins given the chemical differences between the hydrophobic phenylalanine and the polar m-tyrosine residue, but the ultimate downstream consequences triggered by these substitutions remain unexplored. The proposed project seeks to utilize the model organism C. elegans to elucidate the downstream pathways by which m-tyrosine is toxic to cells, perhaps via the induction of apoptotic pathways, and to also explore a novel role for the enzyme tyrosine aminotransferase within the cellular antioxidant response by metabolizing m-tyrosine and hence preventing incorporation into proteins. Three aims have been designed to assess this hypothesis. Because the C. elegans germline is significantly altered following exposure to m-tyrosine, Aim 1 will determine whether m-tyrosine adversely affects the C. elegans germline by inducing apoptosis. Aim 2 will determine whether tyrosine aminotransferase can catalyze the metabolism of m-tyrosine and thus reduce its toxic effects both in vitro and in vivo. Aim 3 will use novel resistance mutants that were recently identified ina forward genetic screen to study cellular pathways essential for m-tyrosine toxicity. The successful completion of this project will extend the current understanding of how m-tyrosine generated by oxidative stress contributes to cell toxicity and disease pathology. Furthermore, these studies would define a novel role for tyrosine aminotransferase within the cellular antioxidant response through the elimination of toxic tyrosine isomers. The results from this project may in turn lead to the development of new therapies for age-associated diseases in which m-tyrosine plays a direct pathologic role. In addition to the research project, the proposal also includes a training component involving coursework, conferences, and career development activities to promote the trainee's development into a physician-scientist who will be able to have a leadership role in research and patient care. PUBLIC HEALTH RELEVANCE: There is evidence for increased oxidative stress in aging and age-related diseases. How oxidative stress contributes to cellular damage and disease is not fully known. These studies seek to further explain how oxidative stress-generated amino acids are harmful to cells and to define a protective function of amino acid metabolism in the antioxidant response pathway.