Individual responses to ozone vary widely with some individuals having a much lower threshold of ozone sensitivity for pulmonary toxicity. Therefore, a complex of individual genetic factors likely controls the transmission and propagation of oxidant signaling following ozone exposure. Epidemiologic studies support the role of the wild-type NADPH quinone oxidoreductase1 (NQO1) genotype as an asthma susceptibility factor in the presence of ozone. NQO1 catalyzes the obligate 2-electron reduction of quinones and is considered an intracellular antioxidant. Our preliminary data demonstrate that NQO1 is required for ozone-induced IL-8/ KC expression, increased neutrophilic airway inflammation, and airway hyperresponsiveness in mice. This poses a conundrum to explain how an oxidoreductase that recycles antioxidants propagates ROS signaling linking oxidant stress to an inflammatory response. We will use primary human airway epithelial cells and mouse (wild-type and NQO1-null) model systems to test the following unprecedented hypothetical mechanism to explain how NQO1 links oxidant stress to epithelial inflammation: NQO1 and ozone-generated ROS are central regulators of airway inflammation following ozone exposure. We propose that NQO1 regulates the intracellular redox environment resulting in a shift in the balance of isoprostanes (isoP). In the presence of NQO1, ROS and F2-isoP activate NF-(B, resulting in increased IL-8/ KC expression and increased neutrophilic inflammation. In the absence of NQO1, the cell favors A2-isoP production, which inhibits NF-(B activation, causing the paradoxical effect of blocking IL-8/ KC expression and neutrophilic inflammation.
The specific aims are:
Aim 1 a: To determine whether following ozone exposure, NQO1 mediates neutrophilic inflammation and airway hyperresponsiveness via upregulation of the neutrophil chemokines KC/ IL-8.
Aim 1 b: To determine whether NQO1 expression in structural airway epithelial cells and/or in hematopoetic cells is required for pulmonary responses to ozone.
Aim 2 a: To determine whether NQO1 alters the cellular redox state, inducing a relative reducing environment as determined by levels of reduced: oxidized (-tocopherol, reduced: oxidized ubiquinone and reduced: oxidized glutathione.
Aim 2 b: To determine whether following ozone exposure, NQO1 causes a shift in isoprostane production with a relative increase in F2- isoP formation and conversely, a loss of NQO1 in vivo, causes increased formation of A2-isoP.
Aim 3 a: To determine whether following ozone exposure, F2-isoP and/or ozone-generated ROS upregulate IL-8/KC expression by NF-(B activation.
Aim 3 b: To determine whether this regulation is abrogated in the absence of NQO1 by A2-isoP inhibition of NF-(B release from I(B.
Ozone is an environmental health threat to vulnerable populations including patients with chronic cardiopulmonary disease. We propose that a candidate for a genetic susceptibility factor related to ozone-induced pulmonary toxicity is NADPH quinone oxidoreductase 1 (NQO1). We hypothesize that NQO1 functions as a gate-keeper in airway epithelial cells to transmit ozone-generated oxidant stress to an inflammatory response which causes ozone-triggered airway disease.
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