Obesity is a risk factor for asthma. Obese subjects also respond to the air pollutant, ozone (O3), an asthma trigger, with greater decrements in lung function than lean individuals. Understanding the mechanistic basis for the relationship between obesity and asthma is the focus of this application. We have established that obese mice obese mice can serve as a useful model for such studies. Obese mice have innate airway hyper- responsiveness (AHR), a characteristic feature of asthma. Compared to lean mice, obese mice also have greater responses to acute O3 exposure. Our preliminary data indicate that endothelin likely contributes to the innate AHR of obesity: endothelin expression is increased in the lungs of obese mice and endothelin receptor antagonists attenuate obesity-related AHR. Our data also indicate that increased NF-?B activation likely contributes to obesity-related increases in the response to O3: of the many genes whose expression is induced by acute O3 exposure, only a fraction are induced to a greater extent in obese versus lean mice. These are, for the most part, genes involved in inflammation and immunity, and most are NF-?B dependent. It is increasingly understood that obesity is a condition of adipose tissue and systemic oxidative stress. Our preliminary data indicate that obesity also increases oxidative stress in the lung, resulting in increased lipid peroxidation. Notably, oxidative stress and/or lipid peroxidation products have been demonstrated to induce to both endothelin expression and NF-?B activation. Hence, our hypothesis is that pulmonary oxidative stress contributes to the effects of obesity in the lung, by driving endothelin expression and by exacerbating O3- induced NF-?B activation. To address this hypothesis, we will measure lipid peroxidation and protein carbonylation products as well as antioxidants in the lungs and blood after room air exposure or at various times after acute O3 exposure. To determine whether endothelin contributes to obesity-related AHR by inducing endothelin expression, we will treat obese and lean mice with a variety of endothelin receptor specific antagonists, and measure their impact on AHR. We will examine the effects of obesity on endothelin and endothelin receptor expression. We will determine whether treatment of obese mice with antioxidants attenuates obesity-related elevations in lung endothelin expression and reduces obesity-related AHR. We will also determine if we can reverse pulmonary oxidative stress and its sequelae with dietary restriction. We will use EMSA and Western blotting for I?B, p50, and p65 to determine O3-induced NF-?B activation is increased in obese mice. To determine the importance of NF-?B, we will measure responses to O3 in NF-?B p50-/- and wildtype mice with diet induced obesity. Experiments will be repeated in transgenic mice expressing an I?B1 mutant that is resistant to degradation driven by a CC10 promoter. These mice are resistant to NF-?B activation in airway epithelial cells. If borne out, this hypothesis would provide the rationale for therapeutic strategies (endothelin receptor antagonists, antioxidants) already in human use for other purposes, and could thus lead to rapid translation to the obese asthmatic.
Obesity is an important risk factor for asthma and also exacerbates the pulmonary effects of the air pollutant, ozone. The goal of this research project is to try and understand how obesity induces these effects. The focus of our research is the inflammation and oxidative stress associated with obesity. Understanding the mechanistic basis for the augmented pulmonary responses to air pollution may lead to new therapeutic strategies for this increasingly at risk population.
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|Zhu, Ming; Hug, Christopher; Kasahara, David I et al. (2010) Impact of adiponectin deficiency on pulmonary responses to acute ozone exposure in mice. Am J Respir Cell Mol Biol 43:487-97|
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