Exposure to traffic-related air pollution such as diesel exhaust (DE) is associated with an increase in thelevel of reactive oxygen species (ROS) in multiple cell types. These ROS include the superoxide anionradical, hydrogen peroxide, lipid peroxides and hydroxyl radical. ROS can have deleterious effects on cells,but they are also known to be involved in normal transmembrane signaling and metabolic control in thecardiovascular system. For instance, two potent vasoconstrictors, angiotensin II and endothelin-1, canincrease production of ROS by smooth muscle cell NADPH oxidase, thus causing an increase in theintracellular concentrations of superoxide and hydrogen peroxide. Superoxide can bind to nitric oxide (NO)to form peroxynitrite, which can cause cellular injury, but also limit the amount of NO available for vasorelaxation.ROS generated in this way can also oxidize tetrahydrobiopterin, a necessary cofactor for NOsynthase (NOS), resulting in uncoupling of NOS and production of more superoxide and peroxynitrite.Consumption of NO by superoxide in this way can result in vasoconstriction. ROS are thus able to influencecardiovascular performance and vascular reactivity. Glutathione (GSH) is an abundant non-protein thiolwhich is a potent scavenger of ROS, including hydrogen peroxide, lipid peroxides, and importantly,peroxitrite (ONOO-). GSH is a tripeptide thiol present in millimolar concentrations in most cells. The first andrate-limiting step in GSH synthesis is carried out by the enzyme glutamate cysteine ligase (GCL), which iscomposed of two subunits, a catalytic subunit (GCLC) and a modifier or regulatory subunit (GCLM).Importantly, single nucleotide polymorphisms (SNPs) in both GCLC and GCLM have been shown to beimportant in myocardial infarction, as well as controlling vascular reactivity in humans. In this project, we willinvestigate the reasons for this effect of GCL by using a comparative approach. We will 1) use mousemodels of differential GCL expression and activity to investigate its role in DE-induced changes in vascularreactivity 2), use cultured endothelial cells from these mice and from humans to investigate the underlyingbiochemical events responsible for GSH and DE-induced modulation of endothelial NO production; and 3)characterize genetically defined inbred strains of mice that have variability in their vascular responses to DE,and identify single nucleotide polymorphisms (SNPs) and quantitative trait loci that are associated with thesechanges in mice. Using these tools we will define the role of GSH synthesis in DE-induced changes invascular reactivity, investigate the underlying pathophysiological mechanisms, and map and identify geneticdeterminants of DE-induced changes in vascular reactivity. These candidate genes will then be referred toProjects 1 and 2 where they will be further evaluated as potential genetic factors in DE-induced vascularabnormalities in humans.
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