Ozone-induced Airway Hyperresponsiveness Research Articles

The Gut Microbiome and Ozone-induced Airway Hyperresponsiveness. Mechanisms and Therapeutic Prospects.

In recent years, several new asthma therapeutics have been developed. Although many of these agents show promise in treating allergic asthma, they are less effective against nonallergic forms of asthma. The gut microbiome has important roles in human health and disease, and a growing body of evidence indicates a link between the gut microbiome and asthma. Here, we review those data focusing on the role of the microbiome in mouse models of nonallergic asthma including obese asthma and asthma triggered by exposure to air pollutants. We describe the impact of antibiotics, diet, and early life events on airway responses to the air pollutant ozone, including in the setting of obesity. We also review potential mechanisms responsible for gut-lung interactions focusing on bacterial-derived metabolites, the immune system, and hormones. Finally, we discuss future prospects for gut microbiome-targeted therapies such as fecal microbiome transplantation, prebiotics, probiotics, and prudent use of antibiotics. Better understanding of the role of the microbiome in airway responses may lead to exploration of new microbiome-targeted therapies to control asthma, especially nonallergic forms of asthma.

Gut microbiota from androgen-altered donors alter pulmonary responses to ozone in female mice.

In mice, both androgens and the gut microbiota modify pulmonary responses to ozone. We hypothesized that androgens affect gut microbiota and thereby impact pulmonary responses to ozone. To address this hypothesis, we transferred cecal microbiota from male castrated or sham castrated C57BL/6J mice into female germ‐free recipient C57BL/6J mice. Four weeks later mice were exposed to ozone (2 ppm) or room air for 3 hr. The gut microbiomes of castrated versus sham castrated donors differed, as did those of recipients of microbiota from castrated versus sham castrated donors. In recipients, ozone‐induced airway hyperresponsiveness was not affected by donor castration status. However, compared to mice receiving microbiota from sham castrated donors, mice receiving microbiota from castrated donors had elevated numbers of bronchoalveolar lavage (BAL) neutrophils despite evidence of reduced lung injury as measured by BAL protein. Serum concentrations of IL‐17A and G‐CSF were significantly greater in recipients of castrated versus sham castrated microbiota. Furthermore, BAL neutrophils correlated with both serum IL‐17A and serum G‐CSF. Our data indicate that androgen‐mediated effects on the gut microbiota modulate pulmonary inflammatory responses to ozone and suggest a role for circulating IL‐17A and G‐CSF in these events.

IL-33, diet-induced obesity, and pulmonary responses to ozone

BackgroundObesity augments pulmonary responses to ozone. We have reported that IL-33 contributes to these effects of obesity in db/db mice. The purpose of this study was to determine whether IL-33 also contributes to obesity-related changes in the response to ozone in mice with diet-induced obesity.MethodsMale wildtype C57BL/6 mice and mice deficient in ST2, the IL-33 receptor, were placed on chow or high fat diets for 12 weeks from weaning. Because the microbiome has been implicated in obesity-related changes in the pulmonary response to ozone, mice were either housed with other mice of the same genotype (same housed) or with mice of the opposite genotype (cohoused). Cohousing transfers the gut microbiome from one mouse to its cagemates.ResultsDiet-induced increases in body mass were not affected by ST2 deficiency or cohousing. In same housed mice, ST2 deficiency reduced ozone-induced airway hyperresponsiveness and neutrophil recruitment in chow-fed but not HFD-fed mice even though ST2 deficiency reduced bronchoalveolar lavage IL-5 in both diet groups. In chow-fed mice, cohousing abolished ST2-related reductions in ozone-induced airway hyperresponsiveness and neutrophil recruitment, but in HFD-fed mice, no effect of cohousing on these responses to ozone was observed. In chow-fed mice, ST2 deficiency and cohousing caused changes in the gut microbiome. High fat diet-feeding caused marked changes in the gut microbiome and overrode both ST2-related and cohousing-related differences in the gut microbiome observed in chow-fed mice.ConclusionOur data indicate a role for IL-33 in pulmonary responses to ozone in chow-fed but not high fat diet-fed mice and are consistent with the hypothesis that these diet-related differences in the role of IL-33 are the result of changes in the gut microbiome.

Sex Differences in the Impact of Dietary Fiber on Pulmonary Responses to Ozone.

Ozone causes airway hyperresponsiveness, a defining feature of asthma. We have reported that the gut microbiome contributes to sex differences in ozone-induced airway hyperresponsiveness. Altering dietary fiber affects the gut microbiome. The purpose of this study was to determine the effects of dietary fiber on pulmonary responses to ozone and whether these effects differ by sex. We fed male and female mice fiber-free diets or diets enriched in one of two types of dietary fiber, cellulose and pectin, for 3 days before ozone exposure. Compared with control diets or pectin-enriched diets, cellulose-enriched diets attenuated ozone-induced airway hyperresponsiveness in male but not female mice. In contrast, fiber-free diets augmented responses to ozone in female but not male mice. Analysis of 16S rRNA sequencing of fecal DNA also indicated sex differences in the impact of dietary fiber on the gut microbiome and identified bacterial taxa that were associated with ozone-induced airway hyperresponsiveness. Our data suggest that microbiome-based therapies such as prebiotics may provide an alternative therapeutic strategy for air pollution-triggered asthma, but they indicate that such therapeutics may need to be tailored differently for males and females.

Early life microbiome perturbation alters pulmonary responses to ozone in male mice.

Early life changes in the microbiome contribute to the development of allergic asthma, but little is known about the importance of the microbiome for other forms of asthma. Ozone is a nonatopic asthma trigger that causes airway hyperresponsiveness and neutrophil recruitment to the lungs. The purpose of this study was to test the hypothesis that early life perturbations in the gut microbiome influence subsequent responses to ozone. To that end, we placed weanling mouse pups from The Jackson Laboratories or from Taconic Farms in sex‐specific cages either with other mice from the same vendor (same‐housed) or with mice from the opposite vendor (cohoused). Mice were maintained with these cagemates until use. The gut microbial community differs in mice from Jackson Labs and Taconic Farms, and cohousing mice transfers fecal microbiota from one mouse to another. Indeed, 16S rRNA sequencing of fecal DNA indicated that differences in the gut microbiomes of Jackson and Taconic same‐housed mice were largely abolished when the mice were cohoused. At 10–12 weeks of age, mice were exposed to room air or ozone (2 ppm for 3 hr). Compared to same‐housed mice, cohoused male but not female mice had reduced ozone‐induced airway hyperresponsiveness and reduced ozone‐induced increases in bronchoalveolar lavage neutrophils. Ozone‐induced airway hyperresponsiveness was greater in male than in female mice and the sex difference was largely abolished in cohoused mice. The data indicate a role for early life microbial perturbations in pulmonary responses to a nonallergic asthma trigger.

Microbiota Contribute to Obesity-related Increases in the Pulmonary Response to Ozone.

Obesity is a risk factor for asthma, especially nonatopic asthma, and attenuates the efficacy of standard asthma therapeutics. Obesity also augments pulmonary responses to ozone, a nonatopic asthma trigger. The purpose of this study was to determine whether obesity-related alterations in gut microbiota contribute to these augmented responses to ozone. Ozone-induced increases in airway responsiveness, a canonical feature of asthma, were greater in obese db/db mice than in lean wild-type control mice. Depletion of gut microbiota with a cocktail of antibiotics attenuated obesity-related increases in the response to ozone, indicating a role for microbiota. Moreover, ozone-induced airway hyperresponsiveness was greater in germ-free mice that had been reconstituted with colonic contents of db/db than in wild-type mice. In addition, compared with dietary supplementation with the nonfermentable fiber cellulose, dietary supplementation with the fermentable fiber pectin attenuated obesity-related increases in the pulmonary response to ozone, likely by reducing ozone-induced release of IL-17A. Our data indicate a role for microbiota in obesity-related increases in the response to an asthma trigger and suggest that microbiome-based therapies such as prebiotics may provide an alternative therapeutic strategy for obese patients with asthma.

17β-Estradiol affects lung function and inflammation following ozone exposure in a sex-specific manner.

Inflammatory lung diseases affect men and women disproportionately, suggesting that fluctuations of circulating hormone levels mediate inflammatory responses. Studies have shown that ozone exposure contributes to lung injury and impairment of innate immunity with differential effects in men and women. Here, we hypothesized that 17β-estradiol enhances inflammation and airway hyperresponsiveness (AHR), triggered by ozone exposure, in the female lung. We performed gonadectomy and hormone treatment (17β-estradiol, 2 wk) in C57BL/6J female and male mice and exposed animals to 1 ppm of ozone or filtered air for 3 h. Twenty-four hours later, we tested lung function, inflammatory gene expression, and changes in bronchoalveolar lavage fluid (BALF). We found increased AHR and expression of inflammatory genes after ozone exposure. These changes were higher in females and were affected by gonadectomy and 17β-estradiol treatment in a sex-specific manner. Gonadectomized male mice displayed higher AHR and inflammatory gene expression than controls exposed to ozone; 17β-estradiol treatment did not affect this response. In females, ovariectomy reduced ozone-induced AHR, which was restored by 17β-estradiol treatment. Ozone exposure also increased BALF lipocalin-2, which was reduced in both male and female gonadectomized mice. Treatment with 17β-estradiol increased lipocalin-2 levels in females but lowered them in males. Gonadectomy also reduced ozone-induced expression of lung IL-6 and macrophage inflammatory protein-3 in females, which was restored by treatment with 17β-estradiol. Together, these results indicate that 17β-estradiol increases ozone-induced inflammation and AHR in females but not in males. Future studies examining diseases associated with air pollution exposure should consider the patient's sex and hormonal status.

The interleukin-33 receptor contributes to pulmonary responses to ozone in male mice: role of the microbiome

BackgroundInterleukin-33 is released in the airways following acute ozone exposure and has the ability to cause airway hyperresponsiveness, a defining feature of asthma. Ozone causes greater airway hyperresponsiveness in male than female mice. Moreover, sex differences in the gut microbiome account for sex differences in this response to ozone. The purpose of this study was to determine whether there were sex differences in the role of interleukin-33 in ozone-induced airway hyperresponsiveness and to examine the role of the microbiome in these events.MethodsWildtype mice and mice genetically deficient in ST2, the interleukin-33 receptor, were housed from weaning with either other mice of the same genotype and sex, or with mice of the same sex but opposite genotype. At 15 weeks of age, fecal pellets were harvested for 16S rRNA sequencing and the mice were then exposed to air or ozone. Airway responsiveness was measured and a bronchoalveolar lavage was performed 24 h after exposure.ResultsIn same-housed mice, ozone-induced airway hyperresponsiveness was greater in male than female wildtype mice. ST2 deficiency reduced ozone-induced airway hyperresponsiveness in male but not female mice and abolished sex differences in the response to ozone. However, sex differences in the role of interleukin-33 were unrelated to type 2 cytokine release: ozone-induced increases in bronchoalveolar lavage interleukin-5 were greater in females than males and ST2 deficiency virtually abolished interleukin-5 in both sexes. Since gut microbiota contribute to sex differences in ozone-induced airway hyperresponsiveness, we examined the role of the microbiome in these ST2-dependent sex differences. To do so, we cohoused wildtype and ST2 deficient mice, a situation that allows for transfer of microbiota among cage-mates. Cohousing altered the gut microbial community structure, as indicated by 16S rRNA gene sequencing of fecal DNA and reversed the effect of ST2 deficiency on pulmonary responses to ozone in male mice.ConclusionsThe data indicate that the interleukin-33 /ST2 pathway contributes to ozone-induced airway hyperresponsiveness in male mice and suggest that the role of interleukin-33 is mediated at the level of the gut microbiome.

Ozone-induced changes in the serum metabolome: Role of the microbiome.

Ozone is an asthma trigger. In mice, the gut microbiome contributes to ozone-induced airway hyperresponsiveness, a defining feature of asthma, but the mechanistic basis for the role of the gut microbiome has not been established. Gut bacteria can affect the function of distal organs by generating metabolites that enter the blood and circulate systemically. We hypothesized that global metabolomic profiling of serum collected from ozone exposed mice could be used to identify metabolites contributing to the role of the microbiome in ozone-induced airway hyperresponsiveness. Mice were treated for two weeks with a cocktail of antibiotics (ampicillin, neomycin, metronidazole, and vancomycin) in the drinking water or with control water and then exposed to air or ozone (2 ppm for 3 hours). Twenty four hours later, blood was harvested and serum analyzed via liquid-chromatography or gas-chromatography coupled to mass spectrometry. Antibiotic treatment significantly affected 228 of the 562 biochemicals identified, including reductions in the known bacterially-derived metabolites, equol, indole propionate, 3-indoxyl sulfate, and 3-(4-hydroxyphenyl)propionate, confirming the efficacy of the antibiotic treatment. Ozone exposure caused significant changes in 334 metabolites. Importantly, ozone-induced changes in many of these metabolites were different in control and antibiotic-treated mice. For example, most medium and long chain fatty acids declined by 20–50% with ozone exposure in antibiotic-treated but not control mice. Most taurine-conjugated bile acids increased with ozone exposure in antibiotic-treated but not control mice. Ozone also caused marked (9-fold and 5-fold) increases in the polyamines, spermine and spermidine, respectively, in control but not antibiotic-treated mice. Each of these metabolites has the capacity to alter airway responsiveness and may account for the role of the microbiome in pulmonary responses to ozone.

Sex Differences in Pulmonary Responses to Ozone in Mice. Role of the Microbiome.

We have previously reported that the mouse gut microbiome contributes to pulmonary responses to ozone, a common asthma trigger, and that short-chain fatty acids, end products of bacterial fermentation, likely contribute to this role of the microbiome. A growing body of evidence indicates that there are sex-related differences in gut microbiota and these differences can have important functional consequences. The purpose of this study was to determine whether there are sex-related differences in the impact of the gut microbiota on pulmonary responses to ozone. After acute exposure to ozone, male mice developed greater airway hyperresponsiveness than female mice. This difference was abolished after antibiotic ablation of the gut microbiome. Moreover, weanling female pups housed in cages conditioned by adult male mice developed greater ozone-induced airway hyperresponsiveness than weanling female pups raised in cages conditioned by adult females. Finally, ad libitum oral administration via drinking water of the short-chain fatty acid propionate resulted in augmented ozone-induced airway hyperresponsiveness in male, but not female, mice. Overall, these data are consistent with the hypothesis that the microbiome contributes to sex differences in ozone-induced airway hyperresponsiveness, likely as a result of sex differences in the response to short-chain fatty acids.

The Microbiome Regulates Pulmonary Responses to Ozone in Mice.

Previous reports demonstrate that the microbiome impacts allergic airway responses, including airway hyperresponsiveness, a characteristic feature of asthma. Here we examined the role of the microbiome in pulmonary responses to a nonallergic asthma trigger, ozone. We depleted the microbiota of conventional mice with either a single antibiotic (ampicillin, metronidazole, neomycin, or vancomycin) or a cocktail of all four antibiotics given via the drinking water. Mice were then exposed to room air or ozone. In air-exposed mice, airway responsiveness did not differ between antibiotic- and control water-treated mice. Ozone caused airway hyperresponsiveness, the magnitude of which was decreased in antibiotic cocktail-treated mice versus water-treated mice. Except for neomycin, single antibiotics had effects similar to those observed with the cocktail. Compared with conventional mice, germ-free mice also had attenuated airway responsiveness after ozone. 16S ribosomal RNA gene sequencing of fecal DNA to characterize the gut microbiome indicated that bacterial genera that were decreased in mice with reduced ozone-induced airway hyperresponsiveness after antibiotic treatment were short-chain fatty acid producers. Serum analysis indicated reduced concentrations of the short-chain fatty acid propionate in cocktail-treated mice but not in neomycin-treated mice. Dietary enrichment with pectin, which increased serum short-chain fatty acids, also augmented ozone-induced airway hyperresponsiveness. Furthermore, propionate supplementation of the drinking water augmented ozone-induced airway hyperresponsiveness in conventional mice. Our data indicate that the microbiome contributes to ozone-induced airway hyperresponsiveness, likely via its ability to produce short-chain fatty acids.

TNF-stimulated gene 6 promotes formation of hyaluronan–inter-α-inhibitor heavy chain complexes necessary for ozone-induced airway hyperresponsiveness

Exposure to pollutants, such as ozone, exacerbates airway inflammation and hyperresponsiveness (AHR). TNF-stimulated gene 6 (TSG-6) is required to transfer inter-α-inhibitor heavy chains (HC) to hyaluronan (HA), facilitating HA receptor binding. TSG-6 is necessary for AHR in allergic asthma, because it facilitates the development of a pathological HA-HC matrix. However, the role of TSG-6 in acute airway inflammation is not well understood. Here, we hypothesized that TSG-6 is essential for the development of HA- and ozone-induced AHR. TSG-6-/- and TSG-6+/+ mice were exposed to ozone or short-fragment HA (sHA), and AHR was assayed via flexiVent. The AHR response to sHA was evaluated in the isolated tracheal ring assay in tracheal rings from TSG-6-/- or TSG-6+/+, with or without the addition of exogenous TSG-6, and with or without inhibitors of Rho-associated, coiled-coil-containing protein kinase (ROCK), ERK, or PI3K. Smooth-muscle cells from mouse tracheas were assayed in vitro for signaling pathways. We found that TSG-6 deficiency protects against AHR after ozone (in vivo) or sHA (in vitro and in vivo) exposure. Moreover, TSG-6-/- tracheal ring non-responsiveness to sHA was reversed by exogenous TSG-6 addition. sHA rapidly activated RhoA, ERK, and Akt in airway smooth-muscle cells, but only in the presence of TSG-6. Inhibition of ROCK, ERK, or PI3K/Akt blocked sHA/TSG-6-mediated AHR. In conclusion, TSG-6 is necessary for AHR in response to ozone or sHA, in part because it facilitates rapid formation of HA-HC complexes. The sHA/TSG-6 effect is mediated by RhoA, ERK, and PI3K/Akt signaling.

Mechanistic Basis for Obesity-related Increases in Ozone-induced Airway Hyperresponsiveness in Mice.

Obesity is a risk factor for asthma, especially nonallergic asthma. Ozone, a common air pollutant, is a nonallergic asthma trigger. Importantly, ozone-induced decrements in lung function are greater in obese and overweight human subjects than in lean individuals. Obese mice also exhibit exaggerated pulmonary responses to ozone. Ozone causes greater increases in pulmonary resistance, in bronchoalveolar lavage neutrophils, and in airway hyperresponsiveness in obese than in lean mice. Our data indicate that IL-33 plays a role in mediating these events. Ozone causes greater release of IL-33 into bronchoalveolar lavage fluid in obese than in lean mice. Furthermore, an antibody blocking the IL-33 receptor, ST2, attenuates ozone-induced airway hyperresponsiveness in obese but not in lean mice. Our data also indicate a complex role for tumor necrosis factor (TNF)-α in obesity-related effects on the response to ozone. In obese mice, genetic deficiency in either TNF-α or TNF-α receptor 2 augments ozone-induced airway hyperresponsiveness, whereas TNF-α receptor 2 deficiency virtually abolishes ozone-induced airway hyperresponsiveness in lean mice. Finally, obesity is known to alter the gut microbiome. In female mice, antibiotics attenuate obesity-related increases in the effect of ozone on airway hyperresponsiveness, possibly by altering microbial production of short-chain fatty acids. Asthma control is often difficult to achieve in obese patients with asthma. Our data suggest that therapeutics directed against IL-33 may ultimately prove effective in these patients. The data also suggest that dietary manipulations and other strategies (prebiotics, probiotics) that alter the microbiome and/or its metabolic products may represent a new frontier for treating asthma in obese individuals.

Augmented Responses to Ozone in Obese Mice Require IL-17A and Gastrin-Releasing Peptide.

Ozone and obesity both increase IL-17A in the lungs. In mice, obesity augments the airway hyperresponsiveness and neutrophil recruitment induced by acute ozone exposure. Therefore, we examined the role of IL-17A in obesity-related increases in the response to ozone observed in obese mice. Lean wild-type and obese db/db mice were pretreated with IL-17A-blocking or isotype antibodies, exposed to air or ozone (2 ppm for 3 h), and evaluated 24 hours later. Microarray analysis of lung tissue gene expression was used to examine the mechanistic basis for effects of anti-IL-17A. Compared with lean mice, ozone-exposed obese mice had greater concentrations of BAL IL-17A and greater numbers of pulmonary IL-17A+ cells. Ozone-induced increases in BAL IL-23 and CCL20, cytokines important for IL-17A+ cell recruitment and activation, were also greater in obese mice. Anti-IL-17A treatment reduced ozone-induced airway hyperresponsiveness toward levels observed in lean mice. Anti-IL-17A treatment also reduced BAL neutrophils in both lean and obese mice, possibly because of reductions in CXCL1. Microarray analysis identified gastrin-releasing peptide (GRP) receptor (Grpr) among those genes that were both elevated in the lungs of obese mice after ozone exposure and reduced after anti-IL-17A treatment. Furthermore, ozone exposure increased BAL GRP to a greater extent in obese than in lean mice, and GRP-neutralizing antibody treatment reduced obesity-related increases in ozone-induced airway hyperresponsiveness and neutrophil recruitment. Our data indicate that IL-17A contributes to augmented responses to ozone in db/db mice. Furthermore, IL-17A appears to act at least in part by inducing expression of Grpr.

Mesenchymal stem cells alleviate oxidative stress–induced mitochondrial dysfunction in the airways

Oxidative stress-induced mitochondrial dysfunction can contribute to inflammation and remodeling in patients with chronic obstructive pulmonary disease (COPD). Mesenchymal stem cells protect against lung damage in animal models of COPD. It is unknown whether these effects occur through attenuating mitochondrial dysfunction in airway cells. We sought to examine the effect of induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) on oxidative stress-induce mitochondrial dysfunction in human airway smooth muscle cells (ASMCs) invitro and in mouse lungs invivo. ASMCs were cocultured with iPSC-MSCs in the presence of cigarette smoke medium (CSM), and mitochondrial reactive oxygen species (ROS) levels, mitochondrial membrane potential (ΔΨm), and apoptosis were measured. Conditioned medium from iPSC-MSCs and transwell cocultures were used to detect any paracrine effects. The effect of systemic injection of iPSC-MSCs on airway inflammation and hyperresponsiveness in ozone-exposed mice was also investigated. Coculture of iPSC-MSCs with ASMCs attenuated CSM-induced mitochondrial ROS, apoptosis, and ΔΨm loss in ASMCs. iPSC-MSC-conditioned medium or transwell cocultures with iPSC-MSCs reduced CSM-induced mitochondrial ROS but not ΔΨm or apoptosis in ASMCs. Mitochondrial transfer from iPSC-MSCs to ASMCs was observed after direct coculture and was enhanced by CSM. iPSC-MSCs attenuated ozone-induced mitochondrial dysfunction, airway hyperresponsiveness, and inflammation in mouse lungs. iPSC-MSCs offered protection against oxidative stress-induced mitochondrial dysfunction in human ASMCs and in mouse lungs while reducing airway inflammation and hyperresponsiveness. These effects are, at least in part, dependent on cell-cell contact, which allows for mitochondrial transfer, and paracrine regulation. Therefore iPSC-MSCs show promise as a therapy for oxidative stress-dependent lung diseases, such as COPD.

Hyaluronan mediates ozone-induced airway hyperresponsiveness in mice.

Hyaluronan mediates ozone-induced airway hyperresponsiveness in mice.

IL-33 Drives Augmented Responses to Ozone in Obese Mice.

Background:Ozone increases IL-33 in the lungs, and obesity augments the pulmonary effects of acute ozone exposure.Objectives:We assessed the role of IL-33 in the augmented effects of ozone observed in obese mice.Methods:Lean wildtype and obese db/db mice were pretreated with antibodies blocking the IL-33 receptor, ST2, and then exposed to ozone (2 ppm for 3 hr). Airway responsiveness was assessed, bronchoalveolar lavage (BAL) was performed, and lung cells harvested for flow cytometry 24 hr later. Effects of ozone were also assessed in obese and lean mice deficient in γδ T cells and their wildtype controls.Resultsand Discussion: Ozone caused greater increases in BAL IL-33, neutrophils, and airway responsiveness in obese than lean mice. Anti-ST2 reduced ozone-induced airway hyperresponsiveness and inflammation in obese mice but had no effect in lean mice. Obesity also augmented ozone-induced increases in BAL CXCL1 and IL-6, and in BAL type 2 cytokines, whereas anti-ST2 treatment reduced these cytokines. In obese mice, ozone increased lung IL-13+ innate lymphoid cells type 2 (ILC2) and IL-13+ γδ T cells. Ozone increased ST2+ γδ T cells, indicating that these cells can be targets of IL-33, and γδ T cell deficiency reduced obesity-related increases in the response to ozone, including increases in type 2 cytokines.Conclusions:Our data indicate that IL-33 contributes to augmented responses to ozone in obese mice. Obesity and ozone also interacted to promote type 2 cytokine production in γδ T cells and ILC2 in the lungs, which may contribute to the observed effects of IL-33.Citation:Mathews JA, Krishnamoorthy N, Kasahara DI, Cho Y, Wurmbrand AP, Ribeiro L, Smith D, Umetsu D, Levy BD, Shore SA. 2017. IL-33 drives augmented responses to ozone in obese mice. Environ Health Perspect 125:246–253; http://dx.doi.org/10.1289/EHP272

Ozone-induced airway hyperresponsiveness: roles of ROCK isoforms.

Acute ozone (O3) inhalation has been shown to cause airway and pulmonary epithelial injury with accompanying inflammation responses. Robust evidence exists that O3 induces airway hyperresponsiveness (AHR) in humans and in animal models. Several pathways exist that culminate in airway smooth muscle contraction, but the mechanism(s) by which O3 elicits AHR are unclear. Here, we review the recent report by Kasahara et al. (Kasahara DI, Mathews JA, Park CY, Cho Y, Hunt G, Wurmbrand AP, Liao JK, Shore SA. Am J Physiol Lung Cell Mol Physiol 309: L736-L746, 2015.) describing the role of two Rho kinase (ROCK) isoforms in O3-induced AHR utilizing a murine haploinsufficiency model. Compared with wild-type (WT) mice, the authors report that ROCK1(+/-) and ROCK2(+/-) mice exhibited significantly reduced AHR following acute exposure to O3. Additionally, WT mice treated with fasudil, an FDA-approved ROCK1/2 inhibitor, recapitulated reduction in AHR as seen in ROCK haplotypes. It was suggested that, although the two ROCK isoforms are both induced by Rho, they have different mechanisms by which they mediate O3-induced AHR: ROCK1 via hyaluronan signaling vs. ROCK2 acting downstream of inflammation at the level of airway smooth muscle contraction. These observations provide an important framework to develop novel ROCK-targeting therapies for acute O3-induced AHR.

Group 2 innate lymphoid cells mediate ozone-induced airway inflammation and hyperresponsiveness in mice

Asthmatic patients are highly susceptible to air pollution and in particular to the effects of ozone (O3) inhalation, but the underlying mechanisms remain unclear. Using mouse models of O3-induced airway inflammation and airway hyperresponsiveness (AHR), we sought to investigate the role of the recently discovered group 2 innate lymphoid cells (ILC2s). C57BL/6 and BALB/c mice were exposed to Aspergillus fumigatus, O3, or both (3 ppm for 2 hours). ILC2s were isolated by means of fluorescence-activated cell sorting and studied for Il5 and Il13 mRNA expression. ILC2s were depleted with anti-Thy1.2 mAb and replaced by means of intratracheal transfer of exvivo expanded Thy1.1 ILC2s. Cytokine levels (ELISA and quantitative PCR), inflammatory cell profile, and AHR (flexiVent) were assessed in the mice. In addition to neutrophil influx, O3 inhalation elicited the appearance of eosinophils and IL-5 in the airways of BALB/c but not C57BL/6 mice. Although O3-induced expression of IL-33, a known activator of ILC2s, in the lung was similar between these strains, isolated pulmonary ILC2s from O3-exposed BALB/c mice had significantly greater Il5 and Il13 mRNA expression than C57BL/6 mice. This suggested that an altered ILC2 function in BALB/c mice might mediate the increased O3 responsiveness. Indeed, anti-Thy1.2 treatment abolished but ILC2s added back dramatically enhanced O3-induced AHR. O3-induced activation of pulmonary ILC2s was necessary and sufficient to mediate asthma-like changes in BALB/c mice. This previously unrecognized role of ILC2s might help explain the heightened susceptibility of human asthmatic airways to O3 exposure.

ROCK insufficiency attenuates ozone-induced airway hyperresponsiveness in mice.

Ozone causes airway hyperresponsiveness (AHR) and pulmonary inflammation. Rho kinase (ROCK) is a key regulator of smooth muscle cell contraction and inflammatory cell migration. To determine the contribution of the two ROCK isoforms ROCK1 and ROCK2 to ozone-induced AHR, we exposed wild-type, ROCK1(+/-), and ROCK2(+/-) mice to air or ozone (2 ppm for 3 h) and evaluated mice 24 h later. ROCK1 or ROCK2 haploinsufficiency did not affect airway responsiveness in air-exposed mice but significantly reduced ozone-induced AHR, with a greater reduction in ROCK2(+/-) mice despite increased bronchoalveolar lavage (BAL) inflammatory cells in ROCK2(+/-) mice. Compared with wild-type mice, ozone-induced increases in BAL hyaluronan, a matrix protein implicated in ozone-induced AHR, were lower in ROCK1(+/-) but not ROCK2(+/-) mice. Ozone-induced increases in other inflammatory moieties reported to contribute to ozone-induced AHR (IL-17A, osteopontin, TNFα) were not different in wild-type vs. ROCK1(+/-) or ROCK2(+/-) mice. We also observed a dose-dependent reduction in ozone-induced AHR after treatment with the ROCK1/ROCK2 inhibitor fasudil, even though fasudil was administered after induction of inflammation. Ozone increased pulmonary expression of ROCK2 but not ROCK1 or RhoA. A ROCK2 inhibitor, SR3677, reduced contractile forces in primary human airway smooth muscle cells, confirming a role for ROCK2 in airway smooth muscle contraction. Our results demonstrate that ozone-induced AHR requires ROCK. Whereas ROCK1-dependent changes in hyaluronan may contribute to ROCK1's role in O3-induced AHR, the role of ROCK2 is downstream of inflammation, likely at the level of airway smooth muscle contraction.