Detection of poly(ADP-ribose) synthetase activity in alveolar macrophages of rats exposed to nitrogen dioxide and ozone

Transcriptional profiling of lung macrophages following ozone exposure in mice identifies signaling pathways regulating immunometabolic activation

Macrophages play a key role in ozone-induced lung injury by regulating both the initiation and resolution of inflammation. These distinct activities are mediated by pro-inflammatory and anti-inflammatory/proresolution macrophages which sequentially accumulate in injured tissues. Macrophage activation is dependent, in part, on intracellular metabolism. Herein, we used RNA-sequencing (seq) to identify signaling pathways regulating macrophage immunometabolic activity following exposure of mice to ozone (0.8 ppm, 3 h) or air control. Analysis of lung macrophages using an Agilent Seahorse showed that inhalation of ozone increased macrophage glycolytic activity and oxidative phosphorylation at 24 and 72 h post-exposure. An increase in the percentage of macrophages in S phase of the cell cycle was observed 24 h post ozone. RNA-seq revealed significant enrichment of pathways involved in innate immune signaling and cytokine production among differentially expressed genes at both 24 and 72 h after ozone, whereas pathways involved in cell cycle regulation were upregulated at 24 h and intracellular metabolism at 72 h. An interaction network analysis identified tumor suppressor 53 (TP53), E2F family of transcription factors (E2Fs), cyclin-dependent kinase inhibitor 1A (CDKN1a/p21), and cyclin D1 (CCND1) as upstream regulators of cell cycle pathways at 24 h and TP53, nuclear receptor subfamily 4 group a member 1 (NR4A1/Nur77), and estrogen receptor alpha (ESR1/ERα) as central upstream regulators of mitochondrial respiration pathways at 72 h. To assess whether ERα regulates metabolic activity, we used ERα-/- mice. In both air and ozone-exposed mice, loss of ERα resulted in increases in glycolytic capacity and glycolytic reserve in lung macrophages with no effect on mitochondrial oxidative phosphorylation. Taken together, these results highlight the complex interaction between cell cycle, intracellular metabolism, and macrophage activation which may be important in the initiation and resolution of inflammation following ozone exposure.

Ozone-Induced DNA Damage: A Pandora's Box of Oxidatively Modified DNA Bases

Ozone is a major component of air pollution and carries potentially mutagenic and harmful affects to health. The oxidation of isolated calf thymus DNA (CT-DNA) led to the nearly quantitative loss of normal DNA 2'-deoxyribonucleosides in the following order: T > G > C ≫ A. The major modification of pyrimidines (T, C, and 5-methylcytosine (5mC)) was the corresponding 5-hydroxyhydantoin derivative after complete digestion of DNA to its component 2'-deoxyribonucleosides. The oxidation of 5mC was 2.5-fold more susceptible than C considering the relative mole fraction of 5mC to C in CT-DNA. Other common oxidation products of pyrimidines (e.g., 5,6-dihydroxy-5,6-dihydropyrimidines, the so-called pyrimidine 5,6-glycols) were formed with a lower yield than 5-hydroxyhydantoin derivatives. In addition, several common oxidation products of G were observed (e.g., 8-oxo-7,8-dihydroguanine (8oxoG)) albeit with relatively minor yields. The sum of individual products was notably less than the loss of 2'-deoxyribonucleosides from which they were derived. In a search for additional products, we discovered the formation of pyrimidine ring fragments, predominantly N-formamide and N-urea, which were measured as a dinucleotide next to a nonmodified nucleotide upon partial digestion of oxidized DNA. Interestingly, the latter fragments were also observed in dinucleotides containing 8oxoG, indicating the formation of tandem lesions during ozonolysis of DNA. The oxidation of DNA upon exposure to ozone can be explained by reactions of an intermediate ozonide. These studies underline the complexity of ozone-induced DNA damage and provide valuable information to assess the formation of this damage in cellular DNA.