Effects of inhaled ozone on gene expression profiles in mouse lung macrophages

Acute exposure to inhaled ozone causes oxidative stress, lung injury, and inflammation. Activated macrophages play a key role in both the initiation and resolution of the inflammatory response to inhaled ozone; this activity is mediated by distinct subsets, broadly classified as proinflammatory (M1) and anti-inflammatory/pro-resolution (M2) macrophages. Successful resolution of inflammation and tissue repair require balanced activity of M1 and M2 macrophages. In this context, overactivation of M1 macrophages or inadequate activation of M2 macrophages results in a failure to resolve inflammation and prolonged injury. Thus, identifying signaling mechanisms contributing to aberrant activation of lung macrophages is critical to mitigating lung injury and decrements in pulmonary function caused by this ubiquitous air pollutant. The purpose of the present study was to identify mechanisms regulating macrophage activation in response to acute exposure to ozone by characterizing global transcriptional profiles using RNA-seq. We hypothesized that gene expression patterns would be distinctly regulated at 24 and 72 hr post exposure to ozone as these time points reflect different phases of the inflammatory response, namely initiation and resolution, when macrophage subpopulations derived from different origins would predominate. We identified significant enrichment of pathways involved in innate immune signaling and cytokine production among differentially expressed genes at 24 and 72 hr post exposure. In addition, we observed a preponderance of pathways involved in cell cycle regulation at 24 hr and intracellular metabolism at 72 hr post exposure. These studies are significant as they permit the identification of signaling pathways representing prospective therapeutic targets to fine tune macrophage responses and limit ozone-induced lung injury.