Ozone is known to cause lung injury and resident cells of the respiratory tract, i.e., epithelial cells and macrophages, respond to inhaled ozone in a variety of ways that affect their survival, morphology, and functioning. However, a complete understanding of the sex-associated and the cell type-specific gene expression changes in response to ozone exposure is still limited. Through transcriptomics, we aimed to analyze gene expression alterations and associated enrichment of biological pathways enrichment in three distinct cell type-enriched compartments of ozone-exposed murine lungs. We sub-chronically exposed adult males and females to 0.8ppm ozone or filtered air. RNA-Seq was performed on airway epithelium-enriched airways, parenchyma, and purified airspace macrophages. Differential gene expression and biological pathway analyses were performed and supported by cellular and immunohistochemical analyses. While a majority of differentially expressed genes (DEGs) in ozone-exposed versus air-exposed groups were common between both sexes, sex-specific DEGs were also identified in all the three tissue compartments. As compared to ozone-exposed males, ozone-exposed females had significant alterations in gene expression in three compartments. Pathways relevant to cell division and DNA repair were enriched in the ozone-exposed airways indicating ozone-induced airway injury and repair which was further supported by immunohistochemical analyses. In addition to cell division and DNA repair pathways, inflammatory pathways were also enriched within the parenchyma supporting contribution by both epithelial and immune cells. Finally, immune response and cytokine-cytokine receptor interactions were enriched in macrophages, indicating ozone-induced macrophage activation. Lastly, our analyses also revealed ozone-induced upregulation of mucoinflammation- and mucous cell metaplasia-associated pathways.

Cystic fibrosis is characterized by dehydration of the airway surface liquid layer with persistent mucus obstruction. Th2 immune responses are often manifested as increased mucous cell density (mucous cell metaplasia) associated with mucus obstruction. IL-33 is a known inducer of Th2 immune responses, but its roles in mucus obstruction and related phenotypes in a cystic fibrosis-like lung disease model (i.e., Scnn1b-Tg-positive [Tg+]) mouse, remain unclear. Accordingly, IL-33 knockout (IL-33 KO) Tg+ mice were examined and compared with IL-33 heterozygous (IL-33 HET) Tg+ mice. As compared with IL-33 HET /Tg+ mice, IL-33 KO /Tg+ mice had complete absence of bronchoalveolar lavage fluid eosinophilia, accompanied with significant reduction in bronchoalveolar lavage fluid concentration of IL-5, a cytokine associated with eosinophil differentiation and recruitment, and IL-4, a major Th2 cytokine. As compared with IL-33 HET /Tg+ mice, IL-33 KO /Tg+ mice had significantly reduced levels of Th2-associated gene signatures (Slc26a4, Clca1, Retnla, and Chi3l4), along with complete loss of intracellular mucopolysaccharide staining in the airway epithelium. As compared with IL-33 HET /Tg+ mice, although the IL-33 KO /Tg+ mice had significantly reduced levels of MUC5AC protein expression, they showed no reduction in the degree of mucus obstruction, MUC5B protein expression, bacterial burden, and neonatal mortality. Interestingly, the histological features, including subepithelial airway inflammation and alveolar space enlargement, were somewhat exaggerated in IL-33 KO /Tg+ mice compared with IL-33 HET /Tg+ mice. Taken together, our data indicate that although IL-33 modulates Th2 inflammatory responses and MUC5AC protein production, mucus obstruction is not dependent on IL-33.

Centrosome amplification (CA) has been implicated in the progression of various cancer types.Although studies have shown that overexpression of PLK4 promotes CA, the effect of tumor microenvironment on PLK4 regulation is understudied. The aim of this study was to examine the role of hypoxia in promoting CA via PLK4. We found that hypoxia induced CA via HIF-1α. We quantified the prevalence of CA in tumor cell lines and tissue sections from breast cancer (BC), pancreatic adenocarcinoma (PDAC), colorectal cancer (CRC), and prostate cancer (PC) and found that CA was prevalent in cells with increased HIF-1α levels under normoxic conditions. HIF-1α levels were correlated with the extent of CA and PLK4 expression in clinical samples.We analyzed the correlation between PLK4 and HIF1A mRNA levels in The Cancer Genome Atlas (TCGA) datasets to evaluate the role of PLK4 and HIF-1α in BC and PDAC prognosis.High HIF1A and PLK4 levels in BC and PDAC patients were associated with poor overall survival. We confirmed PLK4 as a transcriptional target of HIF-1α and demonstrated that in PLK4 knockdown cells, hypoxia-mimicking agents did not affect CA and expression of CAassociated proteins, underscoring the necessity of PLK4 in HIF-1α-related CA. To further dissect the HIF-1α-PLK4 interplay, we used HIF-1α-deficient cells overexpressing PLK4 and showed a significant increase in CA compared with HIF-1α-deficient cells harboring wild-type PLK4. These findings suggest that HIF-1α induces CA by directly upregulating PLK4 and could help us risk-stratify patients and design new therapies for CA-rich cancers.Implications: Hypoxia drives CA in cancer cells by regulating expression of PLK4, uncovering a novel HIF-1α/ PLK4 axis.

Increased levels of ambient ozone, one of the six criteria air pollutants, result in respiratory tract injury and worsening of ongoing lung diseases. However, the effect of ozone exposure on the respiratory tract undergoing active lung development and simultaneously experiencing mucoinflammatory lung diseases, such as cystic fibrosis, remains unclear. To address these questions, we exposed Scnn1b transgenic (Scnn1b-Tg+) mice, a mouse model of cystic fibrosis–like lung disease, and littermate wild-type (WT) mice to ozone from postnatal days (PND) 3–20 and examined the lung phenotypes at PND21. As compared with filtered air (FA)–exposed WT mice, the ozone-exposed WT mice exhibited marked alveolar space enlargement, in addition to significant eosinophilic infiltration, type 2 inflammation, and mucous cell metaplasia. Ozone-exposed Scnn1b-Tg+ mice also exhibited significantly increased alveolar space enlargement, which was also accompanied by exaggerated granulocytic infiltration, type 2 inflammation, and a greater degree of mucus obstruction. The alveolar space enlargement in ozone-exposed WT, FA-exposed Scnn1b-Tg+, and ozone-exposed Scnn1b-Tg+ mice was accompanied by elevated levels of MMP12 protein in macrophages and Mmp12 mRNA in the lung homogenates. Finally, although bacterial burden was largely resolved by PND21 in FA-exposed Scnn1b-Tg+ mice, ozone-exposed Scnn1b-Tg+ mice exhibited compromised bacterial clearance, which was also associated with increased levels of IL-10, an immunosuppressive cytokine, and marked mucus obstruction. Taken together, our data show that ozone exposure results in alveolar space remodeling during active phases of lung development and markedly exaggerates the mucoinflammatory outcomes of pediatric-onset lung disease, including bacterial infections, granulocytic inflammation, mucus obstruction, and alveolar space enlargement.

Lung epithelial lining fluid (ELF) harbors a variety of proteins that influence homeostatic and stress responses in the airspaces. Exosomes, nano-sized extracellular vesicles, contain many proteins that vary in abundance and composition based on the prevailing conditions. Ozone causes inflammatory responses in the airspaces of experimental animals and humans. However, the exosomal protein signatures contained within the ELF from ozone-exposed lung airspaces remain poorly characterized. To explore this, we hypothesized that ozone triggers the release of exosome-bound inflammatory proteins from various cells that reflect mucoobstructive lung disease. Accordingly, we repetitively exposed adult male and female C57BL/6 mice to HEPA-filtered air (air) or 0.8 ppm ozone (4 h per day) for 14 days (five consecutive days of exposure, 2 days of rest, five consecutive days of exposure, 2 days of rest, four consecutive days of exposure). Exosome-bound proteomic signatures, as well as the levels of soluble inflammatory mediators in the bronchoalveolar lavage fluid (BALF), were determined 12–16 h after the last exposure. Principal component analyses of the exosome-bound proteome revealed a clear distinction between air-exposed and ozone-exposed mice, as well as between ozone-exposed males and ozone-exposed females. In addition to 575 proteins that were enriched in both sexes upon ozone exposure, 243 and 326 proteins were enriched uniquely in ozone-exposed males and females, respectively. Ingenuity pathway analyses on enriched proteins between ozone- and air-exposed mice revealed enrichment of pro-inflammatory pathways. More specifically, macrophage activation-related proteins were enriched in exosomes from ozone-exposed mice. Cytokine analyses on the BALF revealed elevated levels of G-CSF, KC, IP-10, IL-6, and IL-5 in ozone-exposed mice. Finally, the histopathological assessment revealed significantly enhanced intracellular localization of mucoinflammatory proteins including MUC5B and FIZZ1 in ozone-exposed mice in a cell-specific manner indicating the cellular sources of the proteins that are ferried in the exosomes upon ozone-induced lung injury. Collectively, this study identified exosomal, secretory, and cell-specific proteins and biological pathways following repetitive exposure of mice to ozone.