Role of interleukin-6 in murine airway responses to ozone

Inconsequential role for chemerin-like receptor 1 in the manifestation of ozone-induced lung pathophysiology in male mice

We executed this study to determine if chemerin-like receptor 1 (CMKLR1), a Gi/o protein-coupled receptor expressed by leukocytes and non-leukocytes, contributes to the development of phenotypic features of non-atopic asthma, including airway hyperresponsiveness (AHR) to acetyl-β-methylcholine chloride, lung hyperpermeability, airway epithelial cell desquamation, and lung inflammation. Accordingly, we quantified sequelae of non-atopic asthma in wild-type mice and mice incapable of expressing CMKLR1 (CMKLR1-deficient mice) following cessation of acute inhalation exposure to either filtered room air (air) or ozone (O3), a criteria pollutant and non-atopic asthma stimulus. Following exposure to air, lung elastic recoil and airway responsiveness were greater while the quantity of adiponectin, a multi-functional adipocytokine, in bronchoalveolar lavage (BAL) fluid was lower in CMKLR1-deficient as compared to wild-type mice. Regardless of genotype, exposure to O3 caused AHR, lung hyperpermeability, airway epithelial cell desquamation, and lung inflammation. Nevertheless, except for minimal genotype-related effects on lung hyperpermeability and BAL adiponectin, we observed no other genotype-related differences following O3 exposure. In summary, we demonstrate that CMKLR1 limits the severity of innate airway responsiveness and lung elastic recoil but has a nominal effect on lung pathophysiology induced by acute exposure to O3.

"Air That Once Was Breath" Part 1: Wildfire-Smoke-Induced Mechanisms of Airway Inflammation - "Climate Change, Allergy and Immunology" Special IAAI Article Collection: Collegium Internationale Allergologicum Update 2023

BACKGROUND

Wildfires are a global concern due to their wide-ranging environmental, economic, and public health impacts. Climate change contributes to an increase in the frequency and intensity of wildfires making smoke exposure a more significant and recurring health concern for individuals with airway diseases. Some of the most prominent effects of wildfire smoke exposure are asthma exacerbations and allergic airway sensitization. Likely due to the delayed recognition of its health impacts in comparison with cigarette smoke and industrial or traffic-related air pollution, research on the composition, the mechanisms of toxicity, and the cellular/molecular pathways involved is poor or non-existent.

SUMMARY

This review discusses potential underlying pathological mechanisms of wildfire-smoke-related allergic airway disease and asthma. We focused on major gaps in understanding the role of wildfire smoke composition in the development of airway disease and the known and potential mechanisms involving cellular and molecular players of oxidative injury at the epithelial barrier in airway inflammation. We examine how PM2.5, VOCs, O3, endotoxin, microbes, and toxic gases may affect oxidative stress and inflammation in the respiratory mucosal barrier. We discuss the role of AhR in mediating smoke's effects in alarmin release and IL-17A production and how glucocorticoid responsiveness may be impaired by IL-17A-induced signaling and epigenetic changes leading to steroid-resistant severe airway inflammation.

KEY MESSAGE

Effective mitigation of wildfire-smoke-related respiratory health effects would require comprehensive research efforts aimed at a better understanding of the immune regulatory effects of wildfire smoke in respiratory health and disease.

Interleukin-11 receptor subunit α-1 is required for maximal airway responsiveness to methacholine after acute exposure to ozone

Interleukin (IL)-11, a multifunctional cytokine, contributes to numerous biological processes, including adipogenesis, hematopoiesis, and inflammation. Asthma, a respiratory disease, is notably characterized by reversible airway obstruction, persistent lung inflammation, and airway hyperresponsiveness (AHR). Nasal insufflation of IL-11 causes AHR in wild-type mice while lung inflammation induced by antigen sensitization and challenge, which mimics features of atopic asthma in humans, is attenuated in mice genetically deficient in IL-11 receptor subunit α-1 (IL-11Rα1-deficient mice), a transmembrane receptor that is required conjointly with glycoprotein 130 to transduce IL-11 signaling. Nevertheless, the contribution of IL-11Rα1 to characteristics of nonatopic asthma is unknown. Thus, based on the aforementioned observations, we hypothesized that genetic deficiency of IL-11Rα1 attenuates lung inflammation and increases airway responsiveness after acute inhalation exposure to ozone (O3), a criteria pollutant and nonatopic asthma stimulus. Accordingly, 4 and/or 24 h after cessation of exposure to filtered room air or O3, we assessed lung inflammation and airway responsiveness in wild-type and IL-11Rα1-deficient mice. With the exception of bronchoalveolar lavage macrophages and adiponectin, which were significantly increased and decreased, respectively, in O3-exposed IL-11Rα1-deficient as compared with O3-exposed wild-type mice, no other genotype-related differences in lung inflammation indices that we quantified were observed in O3-exposed mice. However, airway responsiveness to acetyl-β-methylcholine chloride (methacholine) was significantly diminished in IL-11Rα1-deficient as compared with wild-type mice after O3 exposure. In conclusion, these results demonstrate that IL-11Rα1 minimally contributes to lung inflammation but is required for maximal airway responsiveness to methacholine in a mouse model of nonatopic asthma.

Effects of Anesthesia on Ozone-Induced Lung and Systemic Inflammation

PURPOSE

Anesthetics are required for procedures that deliver drugs/biologics, infectious/inflammatory agents, and toxicants directly to the lungs. However, the possible confounding effects of anesthesia on lung inflammation and injury are underreported. Here, we evaluated the effects of two commonly used anesthetic regimens on lung inflammatory responses to ozone in mice.

METHODS

We tested the effects of brief isoflurane (Iso) or ketamine/xylazine/atipamezole (K/X/A) anesthesia prior to ozone exposure (4 h, 3 ppm) on lung inflammatory responses in mice. Anesthesia regimens modeled those used for non-surgical intratracheal instillations and were administered 1-2 h or 24 h prior to initiating ozone exposure.

RESULTS

We found that Iso given 1-2 h prior to ozone inhibited inflammatory responses in the lung, and this effect was absent when Iso was given 23-24 h prior to ozone. In contrast, K/X/A given 1-2 h prior to ozone increased lung and systemic inflammation.

CONCLUSION

Our results highlight the need to comprehensively evaluate anesthesia as an experimental variable in the assessment of lung inflammation in response to ozone and other inflammatory stimuli.

Ozone-Induced Oxidative Stress, Neutrophilic Airway Inflammation, and Glucocorticoid Resistance in Asthma

Despite recent advances in using biologicals that target Th2 pathways, glucocorticoids form the mainstay of asthma treatment. Asthma morbidity and mortality remain high due to the wide variability of treatment responsiveness and complex clinical phenotypes driven by distinct underlying mechanisms. Emerging evidence suggests that inhalation of the toxic air pollutant, ozone, worsens asthma by impairing glucocorticoid responsiveness. This review discusses the role of oxidative stress in glucocorticoid resistance in asthma. The underlying mechanisms point to a central role of oxidative stress pathways. The primary data source for this review consisted of peer-reviewed publications on the impact of ozone on airway inflammation and glucocorticoid responsiveness indexed in PubMed. Our main search strategy focused on cross-referencing "asthma and glucocorticoid resistance" against "ozone, oxidative stress, alarmins, innate lymphoid, NK and γδ T cells, dendritic cells and alveolar type II epithelial cells, glucocorticoid receptor and transcription factors". Recent work was placed in the context from articles in the last 10 years and older seminal research papers and comprehensive reviews. We excluded papers that did not focus on respiratory injury in the setting of oxidative stress. The pathways discussed here have however wide clinical implications to pathologies associated with inflammation and oxidative stress and in which glucocorticoid treatment is essential.

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.

Androgens augment pulmonary responses to ozone in mice

Ozone causes airway hyperresponsiveness, a defining feature of asthma, and is an asthma trigger. In mice, ozone-induced airway hyperresponsiveness is greater in males than in females, suggesting a role for sex hormones in the response to ozone. To examine the role of androgens in these sex differences, we castrated 4-week-old mice. Controls underwent sham surgery. At 8 weeks of age, mice were exposed to ozone (2ppm, 3 h) or room air. Twenty-four hours later, mice were anesthetized and measurements of airway responsiveness to inhaled aerosolized methacholine were made. Mice were then euthanized and bronchoalveolar lavage was performed. Castration attenuated ozone-induced airway hyperresponsiveness and reduced bronchoalveolar lavage cells. In intact males, flutamide, an androgen receptor inhibitor, had similar effects to castration. Bronchoalveolar lavage concentrations of several cytokines were reduced by either castration or flutamide treatment, but only IL-1α was reduced by both castration and flutamide. Furthermore, an anti-IL-1α antibody reduced bronchoalveolar lavage neutrophils in intact males, although it did not alter ozone-induced airway hyperresponsiveness. Our data indicate that androgens augment pulmonary responses to ozone and that IL-1α may contribute to the effects of androgens on ozone-induced cellular inflammation but not airway hyperresponsiveness.

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.

Chemokine (C-C Motif) Receptor-Like 2 is not essential for lung injury, lung inflammation, or airway hyperresponsiveness induced by acute exposure to ozone

Inhalation of ozone (O₃), a gaseous air pollutant, causes lung injury, lung inflammation, and airway hyperresponsiveness. Macrophages, mast cells, and neutrophils contribute to one or more of these sequelae induced by O₃. Furthermore, each of these aforementioned cells express chemokine (C‐C motif) receptor‐like 2 (Ccrl2), an atypical chemokine receptor that facilitates leukocyte chemotaxis. Given that Ccrl2 is expressed by cells essential to the development of O₃‐induced lung pathology and that chemerin, a Ccrl2 ligand, is increased in bronchoalveolar lavage fluid (BALF) by O₃, we hypothesized that Ccrl2 contributes to the development of lung injury, lung inflammation, and airway hyperresponsiveness induced by O₃. To that end, we measured indices of lung injury (BALF protein, BALF epithelial cells, and bronchiolar epithelial injury), lung inflammation (BALF cytokines and BALF leukocytes), and airway responsiveness to acetyl‐β‐methylcholine chloride (respiratory system resistance) in wild‐type and mice genetically deficient in Ccrl2 (Ccrl2‐deficient mice) 4 and/or 24 hours following cessation of acute exposure to either filtered room air (air) or O₃. In air‐exposed mice, BALF chemerin was greater in Ccrl2‐deficient as compared to wild‐type mice. O₃ increased BALF chemerin in mice of both genotypes, yet following O₃ exposure, BALF chemerin was greater in Ccrl2‐deficient as compared to wild‐type mice. O₃ increased indices of lung injury, lung inflammation, and airway responsiveness. Nevertheless, no indices were different between genotypes following O₃ exposure. In conclusion, we demonstrate that Ccrl2 modulates chemerin levels in the epithelial lining fluid of the lungs but does not contribute to the development of O₃‐induced lung pathology.

Impact of ozone on claudins and tight junctions in the lungs

Claudins (CLDNs) are a major transmembrane protein component of tight junctions (TJs) in endothelia and epithelia. CLDNs are not only essential for sustaining the role of TJs in cell permeability but are also vital for cell signaling through protein-protein interactions. Ozone induces oxidative stress and lung inflammation in humans and experimental models, but the impact of ozone on claudins remains poorly understood. This study was to determine the expression of TJ proteins, such as claudin 3, 4, 5, and 14 following ozone exposure. Mice were exposed to 0.1, 1, or 2 ppm of ozone or ambient air for 6 h for 3 days. The impact of ozone on CLDNs, Nrf2, Keap1, and reactive oxygen species (ROS) were estimated using immunoblotting, immunohistochemical staining, confocal imaging, and ELISA analysis in mice and bronchial epithelial cells. Mice exposed to ozone experienced increased airway inflammatory cell infiltration and bronchial hyper-responsiveness compared to control mice. Additionally, CLDN3, CLDN4, ROS, Nrf2, and Keap1 protein expression increased, and lung CLDN14 protein expression decreased, in mice exposed to ozone compared with control mice. These results indicate that CLDNs are involved in airway inflammation following ozone exposure, suggesting that ozone affects TJ proteins through oxidative mechanisms.

Chronic exposure to electronic cigarettes results in impaired cardiovascular function in mice

Proponents for electronic cigarettes (E-cigs) claim that they are a safe alternative to tobacco-based cigarettes; however, little is known about the long-term effects of exposure to E-cig vapor on vascular function. The purpose of this study was to determine the cardiovascular consequences of chronic E-cig exposure. Female mice (C57BL/6 background strain) were randomly assigned to chronic daily exposure to E-cig vapor, standard (3R4F reference) cigarette smoke, or filtered air ( n = 15/group). Respective whole body exposures consisted of four 1-h-exposure time blocks, separated by 30-min intervals of fresh air breaks, resulting in intermittent daily exposure for a total of 4 h/day, 5 days/wk for 8 mo. Noninvasive ultrasonography was used to assess cardiac function and aortic arterial stiffness (AS), measured as pulse wave velocity, at three times points (before, during, and after chronic exposure). Upon completion of the 8-mo exposure, ex vivo wire tension myography and force transduction were used to measure changes in thoracic aortic tension in response to vasoactive-inducing compounds. AS increased 2.5- and 2.8-fold in E-cig- and 3R4F-exposed mice, respectively, compared with air-exposed control mice ( P < 0.05). The maximal aortic relaxation to methacholine was 24% and 33% lower in E-cig- and 3R4F-exposed mice, respectively, than in controls ( P < 0.05). No differences were noted in sodium nitroprusside dilation between the groups. 3R4F exposure altered cardiac function by reducing fractional shortening and ejection fraction after 8 mo ( P < 0.05). A similar, although not statistically significant, tendency was also observed with E-cig exposure ( P < 0.10). Histological and respiratory function data support emphysema-associated changes in 3R4F-exposed, but not E-cig-exposed, mice. Chronic exposure to E-cig vapor accelerates AS, significantly impairs aortic endothelial function, and may lead to impaired cardiac function. The clinical implication from this study is that chronic use of E-cigs, even at relatively low exposure levels, induces cardiovascular dysfunction. NEW & NOTEWORTHY Electronic cigarettes (E-cigs) are marketed as safe, but there has been insufficient long-term exposure to humans to justify these claims. This is the first study to report the long-term in vivo vascular consequences of 8 mo of exposure to E-cig vapor in mice (equivalent to ~25 yr of exposure in humans). We report that E-cig exposure increases arterial stiffness and impairs normal vascular reactivity responses, similar to other risk factors, including cigarette smoking, which contribute to the development of cardiovascular disease.

Effects of Exposure to Ozone on the Ocular Surface in an Experimental Model of Allergic Conjunctivitis

Based on previous findings that ozone can induce an inflammatory response in the ocular surface of an animal model and in cultured human conjunctival epithelial cells, we investigated whether exposure to ozone exacerbates symptoms of allergic conjunctivitis. We evaluated the effects of exposure to ozone on conjunctival chemosis, conjunctival injection, corneal and conjunctival fluorescein staining scores, production of inflammatory cytokines in tears, and aqueous tear production in a mouse model of allergic conjunctivitis. To validate our in vivo results, we used interleukin (IL)-1α-pretreated conjunctival epithelial cells as an in vitro substitute for the mouse model. We evaluated whether exposure to ozone increased the inflammatory response and altered oxidative status and mitochondrial function in IL-1α-pretreated conjunctival epithelial cells. In the in vivo study, ozone induced increases in conjunctival chemosis, conjunctival injection, corneal and conjunctival fluorescein staining scores, and production of inflammatory cytokines, accompanied by a decrease in tear volume. In the in vitro study, exposure to ozone led to additional increases in IL-6 and tumor necrosis factor-α mRNA levels, which were already induced by treatment with IL-1α. Ozone did not induce any changes in cell viability. Pretreatment with IL-1α increased the expression of manganese superoxide dismutase, and exposure to ozone led to additional increments in the expression of this antioxidant enzyme. Ozone did not induce any changes in mitochondrial activity or expression of mitochondrial enzymes and proteins related to mitochondrial function, with the exception of phosphor-mammalian target of rapamycin. Treatment with butylated hydroxyanisole, a free radical scavenger, attenuated the ozone-induced increases in IL-6 expression in IL-1α-pretreated conjunctival epithelial cells. Therefore, we conclude that exposure to ozone exacerbates the detrimental effects on the integrity of the ocular surface caused by conjunctival allergic reactions, and further increases the inflammatory response in IL-1α-pretreated conjunctival epithelial cells.

Plasminogen activator inhibitor-1 does not contribute to the pulmonary pathology induced by acute exposure to ozone

Expression of plasminogen activator inhibitor (PAI)-1, the major physiological inhibitor of fibrinolysis, is increased in the lung following inhalation of ozone (O₃), a gaseous air pollutant. PAI-1 regulates expression of interleukin (IL)-6, keratinocyte chemoattractant (KC), and macrophage inflammatory protein (MIP)-2, which are cytokines that promote lung injury, pulmonary inflammation, and/or airway hyperresponsiveness following acute exposure to O₃ Given these observations, we hypothesized that PAI-1 contributes to the severity of the aforementioned sequelae by regulating expression of IL-6, KC, and MIP-2 following acute exposure to O₃ To test our hypothesis, wild-type mice and mice genetically deficient in PAI-1 (PAI-1-deficient mice) were acutely exposed to either filtered room air or O₃ (2 ppm) for 3 h. Four and/or twenty-four hours following cessation of exposure, indices of lung injury [bronchoalveolar lavage fluid (BALF) protein and epithelial cells], pulmonary inflammation (BALF IL-6, KC, MIP-2, macrophages, and neutrophils), and airway responsiveness to aerosolized acetyl-β-methylcholine chloride (respiratory system resistance) were measured in wild-type and PAI-1-deficient mice. O₃ significantly increased indices of lung injury, pulmonary inflammation, and airway responsiveness in wild-type and PAI-1-deficient mice. With the exception of MIP-2, which was significantly lower in PAI-1-deficient as compared to wild-type mice 24 h following cessation of exposure to O₃, no other genotype-related differences occurred subsequent to O₃ exposure. Thus, following acute exposure to O₃, PAI-1 neither regulates pulmonary expression of IL-6 and KC nor functionally contributes to any of the pulmonary pathological sequelae that arise from the noxious effects of inhaled O₃.

Effect of Obesity on Acute Ozone-Induced Changes in Airway Function, Reactivity, and Inflammation in Adult Females

We previously observed greater ozone-induced lung function decrements in obese than non-obese women. Animal models suggest that obesity enhances ozone-induced airway reactivity and inflammation. In a controlled exposure study, we compared the acute effect of randomized 0.4ppm ozone and air exposures (2 h with intermittent light exercise) in obese (N = 20) (30<BMI<40Kg/m2) vs. non-obese (N = 20) (BMI<25Kg/m2) non-smoking 18–35 year old women. We measured spirometry and bronchial reactivity to inhaled methacholine (3h post-exposure). Inflammation and obesity markers were assessed in the blood (pre, 4h post, and 20h post exposures) and induced-sputum (4h post-exposures and on 24h pre-exposure training day, no exercise): measures of C reactive protein (CRP) (blood only), leptin (blood only), adiponectin, interleukins IL-6, IL-1b, and IL-8, and tumor necrosis factor alpha, and sputum cell differential cell counts. The pre- to post-exposure decrease in forced vital capacity after ozone (adjusted for the change after air exposure) was significantly greater in the obese group (12.5+/-7.5 vs. 8.0+/-5.8%, p<0.05). Post ozone exposure, 6 obese and 6 non-obese subjects responded to methacholine at ≤ 10mg/ml (the maximum dose); the degree of hyperresponsiveness was similar for the two groups. Both BMI groups showed similar and significant ozone-induced increases in sputum neutrophils. Plasma IL-6 was increased by exercise (4 hr post air exposure vs. pre) only in the obese but returned to pre-air exposure levels at 20hr post-exposure. Plasma IL-6 was significantly increased at 4hr post ozone exposure in both groups and returned to pre-exposure levels by 20h post-exposure. These results confirm our previous findings of greater post-ozone spirometric decrements in obese young women. However, acute ozone-induced airway reactivity to methacholine and airway inflammation did not differ by obesity at the exposure and exercise levels used.

Regulation of IL-17A expression in mice following subacute ozone exposure

Exposure to subacute ozone (O3) causes pulmonary neutrophil recruitment. In mice, this recruitment requires IL-17A. Ozone also causes expression of IL-23 and IL-1, which can induce IL-17A. The purpose of this study was to examine the hypothesis that IL-23 and IL-1 contribute to IL-17A expression and subsequent neutrophil recruitment after subacute O3 exposure. Wild-type, IL-23(-/-), and Flt3l(-/-) mice were exposed to air or 0.3 ppm O3 for 72 h. Flt3l(-/-) mice lack conventional dendritic cells (cDC) that can express IL-23 and IL-1. Other wild-type mice were pre-treated with saline or the IL-1R1 antagonist anakinra prior to O3 exposure. After exposure, bronchoalveolar lavage (BAL) was performed and lung tissue harvested. The results indicated that pulmonary Il17a mRNA abundance and IL-17A(+) F4/80(+) cells were significantly reduced in O3-exposed IL-23(-/-) vs in wild-type mice. In contrast, anakinra had no effect on Il23a or Il17a pulmonary mRNA abundance or on BAL concentrations of the neutrophil survival factor G-CSF, but anakinra did reduce BAL neutrophil numbers, likely because anakinra also reduced BAL IL-6. Compared to air, O3 caused a significant increase in DC numbers in wild-type, but not in Flt3(-/-) mice. However, there was no significant difference in Il23a or Il17a mRNA abundance or in BAL neutrophil count in O3-exposed Flt3(-/-) vs in wild-type mice. From these results, it was concluded that IL-23 but not IL-1 contributes to the IL-17A expression induced by subacute O3 exposure. Induction of IL-23 by O3 does not appear to require cDC.

Sex-specific IL-6-associated signaling activation in ozone-induced lung inflammation

Background

Acute ozone (O₃) exposure has known deleterious effects on the respiratory system and has been linked with respiratory disease and infection. Inflammatory lung disease induced by air pollution has demonstrated greater severity and poorer prognosis in women vs. men. Both severe damage to the bronchial-alveolar epithelium and malfunctioning of bronchial-blood barrier have been largely attributed to the pathobiology of O₃-induced inflammatory response, but the associated mechanisms in the male and female lung remain unknown.

Methods

Here, we investigated sex-based differential regulation of lung interleukin-6 (IL-6) and its downstream signaling pathways JAK2/STAT3 and AKT1/NF-κB in response to O₃ exposure in a mouse model. We exposed male and female mice (in different stages of the estrous cycle) to 2 ppm of O₃ or filtered air (FA) for 3 h, and we harvested lung tissue for protein expression analysis by Western blot.

Results

We found significant up-regulation of IL-6 and IL-6R in females and IL-6 in males in response to O₃ vs. FA. Ozone exposure induced a significant increase in STAT3-Y705 phosphorylation in both females and males. Males exposed to O₃ had decreased levels of JAK2, but increased JAK2 (Y1007+Y1008) phosphorylation, while females exposed to O₃ showed significant up-regulation of both proteins. Both NF-κB (p105/p50) and AKT1 protein levels were significantly increased only in females exposed to O₃. In addition, females exposed to O₃ during proestrus displayed increased expression of selected genes when compared to females exposed to O₃ in other estrous cycle stages.

Conclusions

Together, our observations indicate a sex-based and estrous cycle-dependent differential lung inflammatory response to O₃ and involvement of two converging JAK2/STAT3 and AKT1/NF-κB pathways. To our knowledge, this is the first study specifically addressing the impact of the estrous cycle in O₃-associated lung inflammatory pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-016-0069-7) contains supplementary material, which is available to authorized users.

Resistin deficiency in mice has no effect on pulmonary responses induced by acute ozone exposure

Acute exposure to ozone (O3), an air pollutant, causes pulmonary inflammation, airway epithelial desquamation, and airway hyperresponsiveness (AHR). Pro-inflammatory cytokines-including IL-6 and ligands of chemokine (C-X-C motif) receptor 2 [keratinocyte chemoattractant (KC) and macrophage inflammatory protein (MIP)-2], TNF receptor 1 and 2 (TNF), and type I IL-1 receptor (IL-1α and IL-1β)-promote these sequelae. Human resistin, a pleiotropic hormone and cytokine, induces expression of IL-1α, IL-1β, IL-6, IL-8 (the human ortholog of murine KC and MIP-2), and TNF. Functional differences exist between human and murine resistin; yet given the aforementioned observations, we hypothesized that murine resistin promotes O3-induced lung pathology by inducing expression of the same inflammatory cytokines as human resistin. Consequently, we examined indexes of O3-induced lung pathology in wild-type and resistin-deficient mice following acute exposure to either filtered room air or O3. In wild-type mice, O3 increased bronchoalveolar lavage fluid (BALF) resistin. Furthermore, O3 increased lung tissue or BALF IL-1α, IL-6, KC, TNF, macrophages, neutrophils, and epithelial cells in wild-type and resistin-deficient mice. With the exception of KC, which was significantly greater in resistin-deficient compared with wild-type mice, no genotype-related differences in the other indexes existed following O3 exposure. O3 caused AHR to acetyl-β-methylcholine chloride (methacholine) in wild-type and resistin-deficient mice. However, genotype-related differences in airway responsiveness to methacholine were nonexistent subsequent to O3 exposure. Taken together, these data demonstrate that murine resistin is increased in the lungs of wild-type mice following acute O3 exposure but does not promote O3-induced lung pathology.

Evaluating potential response-modifying factors for associations between ozone and health outcomes: a weight-of-evidence approach

BACKGROUND

Epidemiologic and experimental studies have reported a variety of health effects in response to ozone (O3) exposure, and some have indicated that certain populations may be at increased or decreased risk of O3-related health effects.

OBJECTIVES

We sought to identify potential response-modifying factors to determine whether specific groups of the population or life stages are at increased or decreased risk of O3-related health effects using a weight-of-evidence approach.

METHODS

Epidemiologic, experimental, and exposure science studies of potential factors that may modify the relationship between O3 and health effects were identified in U.S. Environmental Protection Agency's 2013 Integrated Science Assessment for Ozone and Related Photochemical Oxidants. Scientific evidence from studies that examined factors that may influence risk were integrated across disciplines to evaluate consistency, coherence, and biological plausibility of effects. The factors identified were then classified using a weight-of-evidence approach to conclude whether a specific factor modified the response of a population or life stage, resulting in an increased or decreased risk of O3-related health effects.

DISCUSSION

We found "adequate" evidence that populations with certain genotypes, preexisting asthma, or reduced intake of certain nutrients, as well as different life stages or outdoor workers, are at increased risk of O3-related health effects. In addition, we identified other factors (i.e., sex, socioeconomic status, and obesity) for which there was "suggestive" evidence that they may increase the risk of O3-related health effects.

CONCLUSIONS

Using a weight-of-evidence approach, we identified a diverse group of factors that should be considered when characterizing the overall risk of health effects associated with exposures to ambient O3.

γδ T cells are required for pulmonary IL-17A expression after ozone exposure in mice: role of TNFα

Ozone is an air pollutant that causes pulmonary symptoms. In mice, ozone exposure causes pulmonary injury and increases bronchoalveolar lavage macrophages and neutrophils. We have shown that IL-17A is important in the recruitment of neutrophils after subacute ozone exposure (0.3 ppm for 24–72 h). We hypothesized that γδ T cells are the main producers of IL-17A after subacute ozone. To explore this hypothesis we exposed wildtype mice and mice deficient in γδ T cells (TCRδ^−/−) to ozone or room air. Ozone-induced increases in BAL macrophages and neutrophils were attenuated in TCRδ^−/− mice. Ozone increased the number of γδ T cells in the lungs and increased pulmonary Il17a mRNA expression and the number of IL-17A⁺ CD45⁺ cells in the lungs and these effects were abolished in TCRδ^−/− mice. Ozone-induced increases in factors downstream of IL-17A signaling, including G-CSF, IL-6, IP-10 and KC were also decreased in TCRδ^−/− versus wildtype mice. Neutralization of IL-17A during ozone exposure in wildtype mice mimicked the effects of γδ T cell deficiency. TNFR2 deficiency and etanercept, a TNFα antagonist, also reduced ozone-induced increases in Il17a mRNA, IL-17A⁺ CD45⁺ cells and BAL G-CSF as well as BAL neutrophils. TNFR2 deficient mice also had decreased ozone-induced increases in Ccl20, a chemoattractant for IL-17A⁺ γδ T cells. Il17a mRNA and IL-17A⁺ γδ T cells were also lower in obese Cpe^fat versus lean WT mice exposed to subacute ozone, consistent with the reduced neutrophil recruitment observed in the obese mice. Taken together, our data indicate that pulmonary inflammation induced by subacute ozone requires γδ T cells and TNFα-dependent recruitment of IL-17A⁺ γδ T cells to the lung.

Pivotal role of IL-6 in the hyperinflammatory responses to subacute ozone in adiponectin-deficient mice

Adiponectin is an adipose-derived hormone with anti-inflammatory activity. Following subacute ozone exposure (0.3 ppm for 24-72 h), neutrophilic inflammation and IL-6 are augmented in adiponectin-deficient (Adipo(-/-)) mice. The IL-17/granulocyte colony-stimulating factor (G-CSF) axis is required for this increased neutrophilia. We hypothesized that elevated IL-6 in Adipo(-/-) mice contributes to their augmented responses to ozone via effects on IL-17A expression. Therefore, we generated mice deficient in both adiponectin and IL-6 (Adipo(-/-)/IL-6(-/-)) and exposed them to ozone or air. In ozone-exposed mice, bronchoalveolar lavage (BAL) neutrophils, IL-6, and G-CSF, and pulmonary Il17a mRNA expression were greater in Adipo(-/-) vs. wild-type mice, but reduced in Adipo(-/-)/IL-6(-/-) vs. Adipo(-/-) mice. IL-17A(+) F4/80(+) cells and IL-17A(+) γδ T cells were also reduced in Adipo(-/-)/IL-6(-/-) vs. Adipo(-/-) mice exposed to ozone. Only BAL neutrophils were reduced in IL-6(-/-) vs. wild-type mice. In wild-type mice, IL-6 was expressed in Gr-1(+)F4/80(-)CD11c(-) cells, whereas in Adipo(-/-) mice F4/80(+)CD11c(+) cells also expressed IL-6, suggesting that IL-6 is regulated by adiponectin in these alveolar macrophages. Transcriptomic analysis identified serum amyloid A3 (Saa3), which promotes IL-17A expression, as the gene most differentially augmented by ozone in Adipo(-/-) vs. wild-type mice. After ozone, Saa3 mRNA expression was markedly greater in Adipo(-/-) vs. wild-type mice but reduced in Adipo(-/-)/IL-6(-/-) vs. Adipo(-/-) mice. In conclusion, our data support a pivotal role of IL-6 in the hyperinflammatory condition observed in Adipo(-/-) mice after ozone exposure and suggest that this role of IL-6 involves its ability to induce Saa3, IL-17A, and G-CSF.

Effects of ozone exposure on the ocular surface

Changes in the ocular surface induced by ozone have received limited research attention. Here, we investigate the effects of ozone exposure on the integrity of the ocular surface, the production of inflammatory cytokines in tears, and changes in mucin-secreting cells in a mouse model. In addition, ozone-induced nuclear factor-κB (NF-κB)-mediated inflammatory processes were evaluated in cultured human conjunctival epithelial cells. In vivo, ozone induced the breakdown of corneal epithelial integrity, decreased the number of mucin-secreting cells, and induced the production of inflammatory cytokines, without altering tear volume. In vitro, ozone exposure led to increases in NF-κB nuclear translocation, κB-dependent transcriptional activity, NF-κB inhibitor α (IκBα) proteolysis, and expression of phosphorylated IκBα (p-IκBα), but did not cause cytotoxicity or cellular apoptosis. In addition, ozone induced the expression of inflammatory cytokines, Toll-like receptors, and C-C chemokine receptors, but decreased the expression of mucins. Furthermore, inhibition of NF-κB with pyrrolidine dithiocarbamate before exposure of cultured human conjunctival epithelial cells to ozone prevented changes in IκBα and p-IκBα levels in association with a decrease in the levels of inflammatory cytokines. Therefore, we conclude that ozone exposure interferes with ocular surface integrity and induces inflammation involving NF-κB-mediated processes at the level (and/or upstream) of IκBα. Understanding the role of ozone in the initiation of inflammatory processes on the animal ocular surface and in cultured human conjunctival epithelial cells can help elucidate the pathogenesis of ocular surface damage and suggest protective strategies for preserving a healthy ocular surface against ozone exposure.

CD36 mediates endothelial dysfunction downstream of circulating factors induced by O3 exposure

Inhaled pollutants induce the release of vasoactive factors into the systemic circulation, but little information is available regarding the nature of these factors or their receptors. The pattern recognition receptor CD36 interacts with many damage-related circulating molecules, leading to activation of endothelial cells and promoting vascular inflammation; therefore, we hypothesized that CD36 plays a pivotal role in mediating cross talk between inhaled ozone (O3)-induced circulating factors and systemic vascular dysfunction. O3 exposure (1 ppm × 4h) induced lung inflammation in wild-type (WT) mice, which was absent in the CD36 deficient (CD36(-/-)) mice. Acetylcholine (ACh)-evoked vasorelaxation was impaired in isolated aortas from O3-exposed WT mice but not in vessels from CD36(-/-) mice. To delineate whether vascular impairments were caused by lung inflammation or CD36-mediated generation of circulating factors, naïve aortas were treated with diluted serum from control or O3-exposed WT mice, which recapitulated the impairments of vasorelaxation observed after inhalation exposures. Aortas from CD36(-/-) mice were insensitive to the effects of O3-induced circulating factors, with robust vasorelaxation responses in the presence of serum from O3-exposed WT mice. Lung inflammation was not a requirement for production of circulating vasoactive factors, as serum from O3-exposed CD36(-/-) mice could inhibit vasorelaxation in naïve WT aortas. These results suggest that O3 inhalation induces the release of circulating bioactive factors capable of impairing vasorelaxation to ACh via a CD36-dependent signaling mechanism. Although lung inflammatory and systemic vascular effects were both dependent on CD36, the presence of circulating factors appears to be independent of CD36 and inflammatory responses.

Role of the adiponectin binding protein, T-cadherin (cdh13), in pulmonary responses to subacute ozone

Adiponectin, an adipose derived hormone with pleiotropic functions, binds to several proteins, including T-cadherin. We have previously reported that adiponectin deficient (Adipo(-/-)) mice have increased IL-17A-dependent neutrophil accumulation in their lungs after subacute exposure to ozone (0.3 ppm for 72 hrs). The purpose of this study was to determine whether this anti-inflammatory effect of adiponectin required adiponectin binding to T-cadherin. Wildtype, Adipo(-/-) , T-cadherin deficient (T-cad(-/-) ), and bideficient (Adipo(-/-)/T-cad(-/-) ) mice were exposed to subacute ozone or air. Compared to wildtype mice, ozone-induced increases in pulmonary IL-17A mRNA expression were augmented in T-cad(-/-) and Adipo(-/-) mice. Compared to T-cad(-/-) mice, there was no further increase in IL-17A in Adipo(-/-)/T-cad(-/-) mice, indicating that adiponectin binding to T-cadherin is required for suppression of ozone-induced IL-17A expression. Similar results were obtained for pulmonary mRNA expression of saa3, an acute phase protein capable of inducing IL-17A expression. Comparison of lung histological sections across genotypes also indicated that adiponectin attenuation of ozone-induced inflammatory lesions at bronchiolar branch points required T-cadherin. BAL neutrophils and G-CSF were augmented in T-cad(-/-) mice and further augmented in Adipo(-/-)/T-cad(-/-) mice. Taken together with previous observations indicating that augmentation of these moieties in ozone exposed Adipo(-/-) mice is partially IL-17A dependent, the results indicate that effects of T-cadherin deficiency on BAL neutrophils and G-CSF are likely secondary to changes in IL-17A, but that adiponectin also acts via T-cadherin independent pathways. Our results indicate that T-cadherin is required for the ability of adiponectin to suppress some but not all aspects of ozone-induced pulmonary inflammation.

Blood specimen biomarkers of inflammation, matrix degradation, angiogenesis, and cardiac involvement: a future useful tool in assessing clinical outcomes of COPD patients in clinical practice?

Chronic obstructive pulmonary disease (COPD) is characterized by airflow limitation that is not fully reversible; this airflow limitation is both progressive and associated with an abnormal inflammatory response of the lung to noxious particles or gasses. COPD is undoubtedly an umbrella term, and it seems unlikely that all patients with COPD have the same underlying disease processes; thus, there is a need for differential treatment of different subgroups. A potential solution is to find modifiable biomarkers that can assist in drug development and distinguish subgroups of COPD. With the exception of lung function tests, there are currently no well-validated biomarkers or surrogate endpoints that can be used to establish the efficacy of a drug for COPD. This article discusses biomarkers of inflammation (fibrinogen, C-reactive protein, pulmonary and activation-regulated chemokine/CC-chemokine ligand-18, serum surfactant protein D, interleukin (IL)-6, IL-8 and tumor necrosis factor α, complement factor C5a), angiogenesis factors as a part of the pathogenetic aspect in this disease (vascular endothelial growth factor, angiogenin, and IL-8), and matrix degradation biomarkers. Troponin and natriuretic peptides are presented as biomarkers of cardiac involvement in the light of COPD comorbidities. Trials based on research on known clinical variables such as FEV1, BODE, and 6MWT in combination with biomarkers from lung and blood specimens will probably clarify part of the prognosis and natural history of the disease. This will also represent an additional step in COPD phenotyping and new treatment possibilities.

Systemic inflammation, depression and obstructive pulmonary function: a population-based study

Background

Levels of Interleukin-6 (IL-6) and C-creative protein (CRP) indicating systemic inflammation are known to be elevated in chronic diseases including chronic obstructive pulmonary disease (COPD) and depression. Comorbid depression is common in patients with COPD, but no studies have investigated whether proinflammatory cytokines mediate the association between pulmonary function and depressive symptoms in healthy individuals with no known history of obstructive pulmonary diseases.

Methods

In a population-based sample (n = 2077) of individuals aged 55 and above with no known history of obstructive pulmonary disease in the Singapore Longitudinal Ageing Study (SLAS), we analyzed the relationships between IL-6 and CRP, depressive symptoms (GDS-15 ≥5) and obstructive pulmonary function (FEV1% predicted and FEV1/FVC% predicted).

Results

High serum levels of IL-6 and CRP were associated with greater prevalence of depressive symptoms (p < 0.05). High IL-6, high CRP and depressive symptoms were independently associated with decreased FEV1% predicted and FEV1/FVC% predicted after adjusting for smoking status, BMI and number of chronic inflammatory diseases. Increasing grades of combination of inflammatory markers and/or depressive symptoms was associated with progressive increases in pulmonary obstruction. In hierarchical models, the significant association of depressive symptoms with pulmonary obstruction was reduced by the presence of IL-6 and CRP.

Conclusions

This study found for the first time an association of depressive symptoms and pulmonary function in older adults which appeared to be partly mediated by proinflammatory cytokines. Further studies should be conducted to investigate proinflammatory immune markers and depressive symptoms as potential phenotypic indicators for chronic obstructive airway disorders in older adults.

Endogenous osteopontin promotes ozone-induced neutrophil recruitment to the lungs and airway hyperresponsiveness to methacholine

Inhalation of ozone (O₃), a common environmental pollutant, causes pulmonary injury, pulmonary inflammation, and airway hyperresponsiveness (AHR) in healthy individuals and exacerbates many of these same sequelae in individuals with preexisting lung disease. However, the mechanisms underlying these phenomena are poorly understood. Consequently, we sought to determine the contribution of osteopontin (OPN), a hormone and a pleiotropic cytokine, to the development of O₃-induced pulmonary injury, pulmonary inflammation, and AHR. To that end, we examined indices of these aforementioned sequelae in mice genetically deficient in OPN and in wild-type, C57BL/6 mice 24 h following the cessation of an acute (3 h) exposure to filtered room air (air) or O₃ (2 parts/million). In wild-type mice, O₃ exposure increased bronchoalveolar lavage fluid (BALF) OPN, whereas immunohistochemical analysis demonstrated that there were no differences in the number of OPN-positive alveolar macrophages between air- and O₃-exposed wild-type mice. O₃ exposure also increased BALF epithelial cells, protein, and neutrophils in wild-type and OPN-deficient mice compared with genotype-matched, air-exposed controls. However, following O₃ exposure, BALF neutrophils were significantly reduced in OPN-deficient compared with wild-type mice. When airway responsiveness to inhaled acetyl-β-methylcholine chloride (methacholine) was assessed using the forced oscillation technique, O₃ exposure caused hyperresponsiveness to methacholine in the airways and lung parenchyma of wild-type mice, but not OPN-deficient mice. These results demonstrate that OPN is increased in the air spaces following acute exposure to O₃ and functionally contributes to the development of O₃-induced pulmonary inflammation and airway and lung parenchymal hyperresponsiveness to methacholine.

Augmented pulmonary responses to acute ozone exposure in obese mice: roles of TNFR2 and IL-13

BACKGROUND

Acute ozone (O(3)) exposure results in greater inflammation and airway hyperresponsiveness (AHR) in obese versus lean mice.

OBJECTIVES

We examined the hypothesis that these augmented responses to O(3) are the result of greater signaling through tumor necrosis factor receptor 2 (TNFR2) and/or interleukin (IL)-13.

METHODS

We exposed lean wild-type (WT) and TNFR2-deficient (TNFR2(-/-)) mice, and obese Cpe(fat) and TNFR2-deficient Cpe(fat) mice (Cpe(fat)/TNFR2(-/-)), to O(3) (2 ppm for 3 hr) either with or without treatment with anti-IL-13 or left them unexposed.

RESULTS

O(3)-induced increases in baseline pulmonary mechanics, airway responsiveness, and cellular inflammation were greater in Cpe(fat) than in WT mice. In lean mice, TNFR2 deficiency ablated O(3)-induced AHR without affecting pulmonary inflammation; whereas in obese mice, TNFR2 deficiency augmented O(3)-induced AHR but reduced inflammatory cell recruitment. O(3) increased pulmonary expression of IL-13 in Cpe(fat) but not WT mice. Flow cytometry analysis of lung cells indicated greater IL-13-expressing CD(4+) cells in Cpe(fat) versus WT mice after O(3) exposure. In Cpe(fat) mice, anti-IL-13 treatment attenuated O(3)-induced increases in pulmonary mechanics and inflammatory cell recruitment, but did not affect AHR. These effects of anti-IL-13 treatment were not observed in Cpe(fat)/TNFR2(-/-) mice. There was no effect of anti-IL-13 treatment in WT mice.

CONCLUSIONS

Pulmonary responses to O(3) are not just greater, but qualitatively different, in obese versus lean mice. In particular, in obese mice, O(3) induces IL-13 and IL-13 synergizes with TNF via TNFR2 to exacerbate O(3)-induced changes in pulmonary mechanics and inflammatory cell recruitment but not AHR.

Pulmonary inflammation induced by subacute ozone is augmented in adiponectin-deficient mice: role of IL-17A

Pulmonary responses to ozone, a common air pollutant, are augmented in obese individuals. Adiponectin, an adipose-derived hormone that declines in obesity, has regulatory effects on the immune system. To determine the role of adiponectin in the pulmonary inflammation induced by extended (48-72 h) low-dose (0.3 parts per million) exposure to ozone, adiponectin-deficient (Adipo(-/-)) and wild-type mice were exposed to ozone or to room air. In wild-type mice, ozone exposure increased total bronchoalveolar lavage (BAL) adiponectin. Ozone-induced lung inflammation, including increases in BAL neutrophils, protein (an index of lung injury), IL-6, keratinocyte-derived chemokine, LPS-induced CXC chemokine, and G-CSF were augmented in Adipo(-/-) versus wild-type mice. Ozone also increased IL-17A mRNA expression to a greater extent in Adipo(-/-) versus wild-type mice. Moreover, compared with control Ab, anti-IL-17A Ab attenuated ozone-induced increases in BAL neutrophils and G-CSF in Adipo(-/-) but not in wild-type mice, suggesting that IL-17A, by promoting G-CSF release, contributed to augmented neutrophilia in Adipo(-/-) mice. Flow cytometric analysis of lung cells revealed that the number of CD45(+)/F4/80(+)/IL-17A(+) macrophages and γδ T cells expressing IL-17A increased after ozone exposure in wild-type mice and further increased in Adipo(-/-) mice. The IL-17(+) macrophages were CD11c(-) (interstitial macrophages), whereas CD11c(+) macrophages (alveolar macrophages) did not express IL-17A. Taken together, the data are consistent with the hypothesis that adiponectin protects against neutrophil recruitment induced by extended low-dose ozone exposure by inhibiting the induction and/or recruitment of IL-17A in interstitial macrophages and/or γδ T cells.

Impact of aging on pulmonary responses to acute ozone exposure in mice: role of TNFR1

CONTEXT

Chamber studies in adult humans indicate reduced responses to acute ozone with increasing age. Age-related changes in TNFα have been observed. TNFα induced inflammation is predominantly mediated through TNFR1.

OBJECTIVE

To examine the impact of aging on inflammatory responses to acute ozone exposure in mice and determine the role of TNFR1 in age-related differences.

MATERIALS AND METHODS

Wildtype and TNFR1 deficient (TNFR1(-/-)) mice aged 7 or 39 weeks were exposed to ozone (2 ppm for 3 h). Four hours after exposure, bronchoalveolar lavage (BAL) was performed and BAL cells, cytokines, chemokines, and protein were examined.

RESULTS

Ozone-induced increases in BAL neutrophils and in neutrophil chemotactic factors were lower in 39- versus 7-week-old wildtype, but not (TNFR1(-/-)) mice. There was no effect of TNFR1 genotype in 7-week-old mice, but in 39-week-old mice, BAL neutrophils and BAL concentrations of MCP-1, KC, MIP-2, IL-6 and IP-10 were significantly greater following ozone exposure in TNFR1(-/-) versus wildtype mice. BAL concentrations of the soluble form of the TNFR1 receptor (sTNFR1) were substantially increased in 39-week-old versus 7-week-old mice, regardless of exposure.

DISCUSSION AND CONCLUSION

The data suggest that increased levels of sTNFR1 in the lungs of the 39-week-old mice may neutralize TNFα and protect these older mice against ozone-induced inflammation.

The role of the extracellular matrix protein mindin in airway response to environmental airways injury

BACKGROUND

Our previous work demonstrated that the extracellular matrix protein mindin contributes to allergic airways disease. However, the role of mindin in nonallergic airways disease has not previously been explored.

OBJECTIVES

We hypothesized that mindin would contribute to airways disease after inhalation of either lipopolysaccharide (LPS) or ozone.

METHODS

We exposed C57BL/6J and mindin-deficient (-/-) mice to aerosolized LPS (0.9 μg/m3 for 2.5 hr), saline, ozone (1 ppm for 3 hr), or filtered air (FA). All mice were evaluated 4 hr after LPS/saline exposure or 24 hr after ozone/FA exposure. We characterized the physiological and biological responses by analysis of airway hyperresponsiveness (AHR) with a computer-controlled small-animal ventilator (FlexiVent), inflammatory cellular recruitment, total protein in bronchoalveolar lavage fluid (BALF), proinflammatory cytokine profiling, and ex vivo bronchial ring studies.

RESULTS

After inhalation of LPS, mindin-/- mice demonstrated significantly reduced total cell and neutrophil recruitment into the airspace compared with their wild-type counterparts. Mindin-/- mice also exhibited reduced proinflammatory cytokine production and lower AHR to methacholine challenge by FlexiVent. After inhalation of ozone, mice had no detectible differences in cellular inflammation or total BALF protein dependent on mindin. However, mindin-/- mice were protected from increased proinflammatory cytokine production and AHR compared with their C57BL/6J counterparts. After ozone exposure, bronchial rings derived from mindin-/- mice demonstrated reduced constriction in response to carbachol.

CONCLUSIONS

These data demonstrate that the extracellular matrix protein mindin modifies the airway response to both LPS and ozone. Our data support a conserved role of mindin in production of proinflammatory cytokines and the development of AHR in two divergent models of reactive airways disease, as well as a role of mindin in airway smooth muscle contractility after exposure to ozone.

Protective role of interleukin-10 in ozone-induced pulmonary inflammation

BACKGROUND

The mechanisms underlying ozone (O₃)-induced pulmonary inflammation remain unclear. Interleukin-10 (IL-10) is an anti-inflammatory cytokine that is known to inhibit inflammatory mediators.

OBJECTIVES

We investigated the molecular mechanisms underlying interleuken-10 (IL-10)-mediated attenuation of O₃-induced pulmonary inflammation in mice.

METHODS

Il10-deficient (Il10(-/-)) and wild-type (Il10(+/+)) mice were exposed to 0.3 ppm O₃ or filtered air for 24, 48, or 72 hr. Immediately after exposure, differential cell counts and total protein (a marker of lung permeability) were assessed from bronchoalveolar lavage fluid (BALF). mRNA and protein levels of cellular mediators were determined from lung homogenates. We also used global mRNA expression analyses of lung tissue with Ingenuity Pathway Analysis to identify patterns of gene expression through which IL-10 modifies O₃-induced inflammation.

RESULTS

Mean numbers of BALF polymorphonuclear leukocytes (PMNs) were significantly greater in Il10(-/-) mice than in Il10(+/+) mice after exposure to O₃ at all time points tested. O₃-enhanced nuclear NF-κB translocation was elevated in the lungs of Il10(-/-) compared with Il10(+/+) mice. Gene expression analyses revealed several IL-10-dependent and O₃-dependent mediators, including macrophage inflammatory protein 2, cathepsin E, and serum amyloid A3.

CONCLUSIONS

Results indicate that IL-10 protects against O₃-induced pulmonary neutrophilic inflammation and cell proliferation. Moreover, gene expression analyses identified three response pathways and several genetic targets through which IL-10 may modulate the innate and adaptive immune response. These novel mechanisms of protection against the pathogenesis of O₃-induced pulmonary inflammation may also provide potential therapeutic targets to protect susceptible individuals.

Role of nerve growth factor in ozone-induced neural responses in early postnatal airway development

Airway neural plasticity contributes to the process of airway remodeling in response to airway irritants. However, the mechanisms of neural remodeling in the airways during the early postnatal period, when responses to airway irritation may be most sensitive, have not been characterized. This study used a rat model to examine a possible mechanism of ozone (O(3))-induced neural hyperresponsiveness during a critical period of developmental, postnatal day (PD) 6, that may be mediated by the neurotrophin nerve growth factor (NGF), resulting in an enhanced release of inflammatory neuropeptide substance P (SP) from airway nerves. Rat pups between PD6-PD28 were killed 24 hours after exposure to O(3) (2 ppm, 3 hours) or filtered air (FA), to establish a timeline of NGF synthesis, or else they were exposed to O(3) or NGF on PD6 or PD21 and re-exposed to O(3) on PD28, and killed on PD29. Measurement endpoints included NGF mRNA in tracheal epithelial cells, NGF protein in bronchoalveolar lavage fluid, airway SP-nerve fiber density (NFD), and SP-positive airway neurons in vagal ganglia. Acute exposure to O(3) increased NGF in bronchoalveolar lavage fluid on PD10 and PD15, and mRNA expression in epithelial cells on PD6, compared with FA controls. NGF protein and mRNA expression in the O(3)-PD6/O(3)-PD28 groups were significantly higher than in the O(3)-PD21/O(3)-PD28 and O(3)-PD6/FA-PD28 groups. NGF-PD6/O(3)-PD28 increased the SP innervation of airway smooth muscle and SP-positive sensory neurons, compared with the NGF-PD21/O(3)-PD28 or NGF-PD6/FA-PD28 groups. NGF enhanced sensory innervation, which may mediate acute responses or prolong sensitivity to O(3) during early life. The model may be relevant in O(3) responses during early childhood.

Role of interleukin-6 in elastase-induced lung inflammatory changes in mice

Interleukin-6 (IL-6) is known to be involved in the pathogenesis of various inflammatory diseases, but its role in the development of pulmonary emphysema remains unclear. Wild-type (WT) and IL-6-deficient mice received either phosphate-buffered saline (PBS) or porcine pancreatic elastase (PPE) intratracheally. The development of emphysema was determined by measuring the mean linear intercept (Lm). The lung specimens were also subjected to immunohistochemistry for single-stranded DNA to detect apoptotic cells. Lung mechanics and airway responsiveness to inhaled methacholine were analyzed. Bronchoalveolar lavage (BAL) fluid was subjected to evaluation of inflammatory cell accumulation and cytokine measurement. PPE treatment caused significant increases in Lm and lung compliance, which was attenuated by IL-6 deficiency. The increases in apoptotic cells in the lung were attenuated in IL-6 null mice. Airway responsiveness was not affected by PPE challenge or IL-6 deficiency. Intratracheal PPE increased the cell counts in BAL fluid throughout the observation, which was suppressed in IL-6 null mice. In BAL fluid, PPE-induced increases in the levels of macrophage inflammatory protein (MIP)-1alpha and eotaxin were mitigated by IL-6 deficiency. PPE-induced up-regulation of matrix metalloproteinase (MMP)-12 in the lung was attenuated by IL-6 deficiency. These results indicate that IL-6 may play an important role in the development of elastase-induced lung inflammatory changes.

Onset of obesity in carboxypeptidase E-deficient mice and effect on airway responsiveness and pulmonary responses to ozone

When compared with lean, wild-type mice, obese Cpefat mice, 14 wk of age and older, manifest innate airway hyperresponsiveness (AHR) to intravenous methacholine and enhanced pulmonary inflammation following acute exposure to ozone (O3). The purpose of this study was to examine the onset of these augmented pulmonary responses during the onset of obesity. Thus airway responsiveness and O3-induced pulmonary inflammation and injury were examined in 7- and 10-wk-old Cpefat and age-matched, wild-type, C57BL/6 mice. Compared with age-matched controls, 7- and 10-wk-old Cpefat mice were approximately 25 and 61% heavier, respectively. Airway responsiveness to intravenous methacholine was assessed via forced oscillation in unexposed Cpefat and wild-type mice. The 10- but not 7-wk-old Cpefat mice exhibited innate AHR. O3 exposure (2 ppm for 3 h) increased markers of pulmonary inflammation and injury in the bronchoalveolar lavage fluid of all mice. However, most markers were greater in Cpefat vs. wild-type mice, regardless of age. Serum levels of leptin, a satiety hormone and proinflammatory cytokine, were increased in Cpefat vs. wild-type mice of both age groups, but the serum levels of other systemic inflammatory markers were greater only in 10-wk-old Cpefat vs. wild-type mice. These results demonstrate that a 25% increase in body weight is sufficient to augment pulmonary responses to O3, but innate AHR is not manifest until the mice become much heavier. These results suggest that the mechanistic bases for these responses are different and may develop according to the nature and degree of the chronic systemic inflammation that is present.

Obesity enhances eosinophilic inflammation in a murine model of allergic asthma

BACKGROUND AND PURPOSE

Obesity is associated with deterioration in asthma outcomes. Although airways eosinophil accumulation is characteristic of lung allergic diseases, little is known about the influence of obesity on the allergic eosinophil trafficking from bone marrow to lung tissues, and recruitment to airways lumen. Here, we have assessed the effects of diet-induced obesity on allergic eosinophilic inflammation in mice, examining eosinophil trafficking from bone marrow to airways, and production of T(H)1/T(H)2 cytokines.

EXPERIMENTAL APPROACH

C57BL/6 mice fed for 10 weeks with standard chow or high-fat diet were sensitized and challenged with ovalbumin. At 24-96 h post-ovalbumin challenge, bronchoalveolar lavage (BAL) fluid, lung tissue and bone marrow were examined.

KEY RESULTS

The high-fat-fed mice exhibited increased body weight and epididymal fat, glucose intolerance and alterations in lipid profile compared with the lean mice. Obesity markedly elevated serum leptin and lowered adiponectin levels. Ovalbumin challenge in obese mice promoted a markedly higher eosinophil accumulation in bone marrow and connective tissue surrounding the bronchial and bronchiolar segments. Eosinophil number in BAL fluid of obese mice was lower at 24 and 48 h. Levels of interleukin (IL)-5, eotaxin, tumour necrosis factor-alpha and IL-10 in BAL fluid of obese mice were significantly higher than in lean mice.

CONCLUSIONS AND IMPLICATIONS

Diet-induced obesity enhanced eosinophil trafficking from bone marrow to lung tissues, and delayed their transit through the airway epithelium into the airway lumen. Consequently, eosinophils remain longer in lung peribronchiolar segments due to overproduction of T(H)1/T(H)2 cytokines and chemokines.

TLR4 is necessary for hyaluronan-mediated airway hyperresponsiveness after ozone inhalation

RATIONALE

Ozone is a common environmental air pollutant that contributes to hospitalizations for respiratory illness. The mechanisms, which regulate ozone-induced airway hyperresponsiveness, remain poorly understood. We have previously reported that toll-like receptor 4 (TLR4)-deficient animals are protected against ozone-induced airway hyperresponsiveness (AHR) and that hyaluronan (HA) mediates ozone-induced AHR. However, the relation between TLR4 and hyaluronan in the airway response to ozone remains unexplored.

OBJECTIVES

We hypothesized that HA acts as an endogenous TLR4 ligand for the development of AHR after ozone-induced environmental airway injury.

METHODS

TLR4-deficient and wild-type C57BL/6 mice were exposed to either inhaled ozone or intratracheal HA and the inflammatory and AHR response was measured.

MEASUREMENTS AND MAIN RESULTS

TLR4-deficient mice have similar levels of cellular inflammation, lung injury, and soluble HA levels as those of C57BL/6 mice after inhaled ozone exposure. However, TLR4-deficient mice are partially protected from AHR after ozone exposure as well as after direct intratracheal instillation of endotoxin-free low molecular weight HA. Similar patterns of TLR4-dependent cytokines were observed in the bronchial alveolar lavage fluid after exposure to either ozone or HA. Exposure to ozone increased immunohistological staining of TLR4 on lung macrophages. Furthermore, in vitro HA exposure of bone marrow-derived macrophages induced NF-kappaB and production of a similar pattern of proinflammatory cytokines in a manner dependent on TLR4.

CONCLUSIONS

Our observations support the observation that extracellular matrix HA contributes to ozone-induced airways disease. Furthermore, our results support that TLR4 contributes to the biological response to HA by mediating both the production of proinflammatory cytokines and the development of ozone-induced AHR.

Impact of adiponectin deficiency on pulmonary responses to acute ozone exposure in mice

Obese mice have increased responses to acute ozone (O(3)) exposure. T-cadherin is a binding protein for the high-molecular weight isoforms of adiponectin, an anti-inflammatory hormone that declines in obesity. The objective of the present study was to determine whether adiponectin affects pulmonary responses to O(3), and whether these effects are mediated through T-cadherin. We performed bronchoalveolar lavage (BAL) and measured pulmonary responsiveness to methacholine after acute air or O(3) exposure (2 ppm for 3 h) in adiponectin-deficient (Adipo(-/-)) or T-cadherin-deficient (T-Cad(-/-)) mice. O(3) increased pulmonary responses to methacholine and increased BAL neutrophils and protein to a greater extent in wild-type than in Adipo(-/-) mice, whereas T-cadherin deficiency had no effect. O(3)-induced increases in BAL IL-6 and keratinocyte-derived chemokine (KC), which contribute to O(3)-induced pulmonary neutrophilia, were also greater in wild-type than in Adipo(-/-) mice. In contrast, responses to O(3) were not altered by transgenic overexpression of adiponectin. To determine which adiponectin isoforms are present in the lung, Western blotting was performed. The hexameric isoform of adiponectin dominated in serum, whereas BAL was dominated by the high-molecular weight isoform of adiponectin. Interestingly, serum adiponectin was greater in T-Cad(-/-) versus wild-type mice, whereas BAL adiponectin was lower in T-Cad(-/-) versus wild-type mice, suggesting that T-cadherin may be important for transit of high-molecular weight adiponectin from the blood to the lung. Our results indicate that adiponectin deficiency inhibits pulmonary inflammation induced by acute O(3) exposure, and that T-cadherin does not mediate the effects of adiponectin responsible for these events.

Obesity, airway hyperresponsiveness, and inflammation

Epidemiological data indicate that obesity is a risk factor for asthma, but the mechanistic basis for this relationship is not established. Here we review data from human subjects and animal models investigating the relationship between obesity and airway hyperresponsiveness, a characteristic feature of asthma. We discuss obesity as a state of chronic systemic inflammation resulting from interactions between adipocytes and adipose tissue macrophages that are recruited to obese adipose tissue. Finally, we focus on the possibility that aspects of this inflammation, particularly obesity-related changes in TNF-alpha, leptin, and adiponectin, may contribute to airway hyperresponsiveness in obesity. Determining how obesity promotes asthma may uncover novel therapeutic strategies that are effective in the obese asthmatic subject.

Pulmonary responses to subacute ozone exposure in obese vs. lean mice

The purpose of this study was to determine whether obesity affects pulmonary responses following a 3-day ozone exposure. Obese db/db and lean wild-type mice were exposed to ozone (0.3 ppm) for 72 h. In wild-type mice, ozone exposure caused pulmonary injury and inflammation, and these events were associated with reduced pulmonary compliance. In db/db mice, ozone-induced neutrophil recruitment to the lung was reduced and no reduction in compliance was observed. Similar results were obtained in obese Cpe(fat) mice, indicating that loss of leptin signaling in db/db mice does not account for these obesity-related changes. To examine the role of interleukin (IL)-6 in this obesity-related difference in ozone responsiveness, wild-type and IL-6-deficient mice were raised on 10% or 60% fat diets. Compared with 10% fat-fed mice, wild-type 60% fat-fed mice were obese and had reduced neutrophil recruitment following ozone. IL-6 deficiency reduced ozone-induced neutrophil recruitment in 10% fat-fed mice. In contrast, in obese mice, no effect of IL-6 deficiency on neutrophil recruitment was observed. Obesity-related differences in the effect of ozone on compliance were observed in both wild-type and IL-6-deficient mice. Obesity-related differences in serum IL-6 were observed and may account for obesity-related differences in the effect of IL-6 deficiency on neutrophil recruitment. In summary, the neutrophilic inflammation induced by prolonged low level ozone exposure was attenuated in obese mice and appeared to result from an absence of IL-6-dependent neutrophil recruitment in the obese mice.

Markers of early disease and prognosis in COPD

COPD is a complex disease with multiple pathological components, which we unfortunately tend to ignore when spirometry is used as the only method to evaluate the disorder. Additional measures are needed to allow a more complete and clinically relevant assessment of COPD. The earliest potential risk factors of disease in COPD are variations in the genetic background. Genetic variations are present from conception and can determine lifelong changes in enzyme activities and protein concentrations. In contrast, measurements in blood, sputum, exhaled breath, broncho-alveolar lavage, and lung biopsies may vary substantially over time. This review explores potential markers of early disease and prognosis in COPD by examining genetic markers in the α₁-antitrypsin, cystic fibrosis transmembrane conductance regulator (CFTR), and MBL-2 genes, and by examining the biochemical markers fibrinogen and C-reactive protein (CRP), which correlate with degree of pulmonary inflammation during stable conditions of COPD. Chronic lung inflammation appears to contribute to the pathogenesis of COPD, and markers of this process have promising predictive value in COPD. To implement markers for COPD in clinical practice, besides those already established for the α₁-antitrypsin gene, further research and validation studies are needed.

Ozone modulates IL-6 secretion in human airway epithelial and smooth muscle cells

Although ozone enhances leukocyte function and recruitment in airways, the direct effect of ozone in modulating structural cell-derived inflammatory mediators remains unknown. Using a coculture model comprised of differentiated human airway epithelial cells (NHBE) and smooth muscle cells (ASM), we postulate that ozone regulates IL-6 secretion in basal and cytokine-primed structural cells. Air-liquid interface (ALI) cultures of NHBE cells underwent differentiation as determined by mucin secretion, transepithelial electrical resistance (TEER), and ultrastructure parameters. Whereas TNF enhanced basal secretion of IL-6 (57 +/- 3%), ozone exposure at 0.6 ppm for 6 h augmented IL-6 levels in basal (41 +/- 3%) and TNF- (50 +/- 5%) primed cocultures compared with that derived from NHBE or ASM monolayers alone. Levels of PGE(2), 6-keto-PGF(1alpha), PGF(2alpha), and thromboxane B(2) (TxB(2)) levels in basal and TNF-primed cocultures revealed that ozone selectively enhanced PGE(2) production in TNF- (6 +/- 3-fold) primed cocultures, with little effect (P > 0.05) on diluent-treated cultures. In accordance with ozone-induced increases in PGE(2) levels, cyclooxygenase inhibition with indomethacin partially abolished IL-6 secretion. Surprisingly, indomethacin had little effect on constitutive secretion of IL-6 in cocultures, whereas indomethacin completely restored ozone-mediated TEER reduction in TNF-primed cocultures. Collectively, our data for the first time suggest a dual role of ozone in modulating IL-6 secretion and TEER outcomes in a PGE(2)-dependent (in presence of TNF stimulus) and -independent manner (in absence of cytokine stimulus).

Role of metallothionein in lung inflammation induced by ozone exposure in mice

Metallothionein (MT) is a free radical scavenger induced by inflammatory stimuli; however, its roles in inflammation have not been fully investigated. In the present study, we genetically determined the role of MT in ozone (O(3))-induced lung inflammation using MT-I/II null (-/-) mice. Subacute (65 h) exposure to O(3) (0.3 ppm) induced lung inflammation and enhanced vascular permeability, which was significantly greater in MT(-/-) than in corresponding wild-type mice. Electron microscopically, O(3) exposure induced vacuolar degeneration of pulmonary endothelial and epithelial cells, and interstitial edema with focal loss of the basement membrane, which was more prominent in MT(-/-) than in wild-type mice. O(3) -induced lung expression of interleukin-6 was significantly greater in MT(-/-) than in wild-type mice; however, lung expression of the chemokines examined was comparable in both genotypes of mice in the presence of O(3). Following O(3) exposure, the formation of oxidative stress-related molecules/adducts, such as heme oxidase-1, inducible nitric oxide synthase, 8-hydroxy-2'-deoxyguanosine, and nitrotyrosine, in the lung was significantly greater in MT(-/-) than in wild-type mice. Collectively, MT protects against O(3)-induced lung inflammation, at least partly, via the regulation of pulmonary endothelial and epithelial integrity and its antioxidative property.

Role of cathepsin S in ozone-induced airway hyperresponsiveness and inflammation

Ambient ozone has been linked to the worsening of symptoms of patients with obstructive diseases such as chronic obstructive pulmonary disease (COPD) and asthma. We investigated the role of cathepsin S on ozone-induced airway hyperresponsiveness (AHR) and inflammation, using the selective cathepsin S inhibitor, Compound A. Balb/c mice were exposed to ozone at a concentration of 3 ppm or air for 3 h, following administration by gavage of Compound A or vehicle. Bronchoalveolar lavage (BAL) was performed 3 h and 20-24 h following exposure, AHR was measured at 20-24 h only. Ozone exposure, compared to air exposure increased BAL cathepsin S levels, AHR and BAL inflammatory cells. Compound A (30 mg kg(-1) p.o.) dosing compared to vehicle dosing inhibited ozone-induced AHR (-logPC100 vehicle: -0.70+/-0.12, n=8 vs. cathepsin S inhibitor: -1.30+/-0.06, P<0.001, n=8) at 20-24 h and BAL neutrophilia at 3 h and 20-24 h (P<0.05, n=6). Ozone exposure increased levels of BAL cytokines IL-6, TNF-alpha and IFN-gamma. Compound A reduced IL-6 at 3 h and 20-24 h (P<0.05, n=5) and TNF-alpha, at 20-24 h (P<0.05, n=6). These data indicate an important role for cathepsin S in the regulation of ozone-induced AHR and neutrophil cell recruitment and suggest that cathepsin S may be a target in the treatment of oxidative stress-induced AHR and inflammation.

Role of p38 mitogen-activated protein kinase in ozone-induced airway hyperresponsiveness and inflammation

Ozone is a potent oxidant and causes airway hyperresponsiveness and neutrophilia. To determine the role of p38 mitogen-activated protein kinase (MAPK) activation, we studied the effect of a p38alpha inhibitor SD-282 (Scios Inc, Fremont, CA USA) on ozone-induced airway hyperresponsiveness and neutrophilia. Balb/c mice received SD-282 (30 or 90 mg/kg i.p) or vehicle 1 h before exposure to either ozone (3 ppm, 3 h) or air. Three hours after exposure, lungs were analysed for cytokine levels and bronchoalveolar lavage was performed. Another set of mice were dosed 6 h after exposure and 1 h before assessing airway hyperresponsiveness. SD-282 (90 mg/kg) significantly inhibited ozone-induced airway hyperresponsiveness (-LogPC(150): SD-282: -1.73+/-0.14 vs. vehicle: -0.99+/-0.15, P<0.05). Bronchoalveolar lavage neutrophil numbers were time-dependently increased in vehicle-dosed, ozone-exposed mice, greatest at 20-24 h after exposure. SD-282 (30 and 90 mg/kg) significantly inhibited ozone induced neutrophil numbers at 3 h and 20-24 h after ozone SD-282 significantly inhibited ozone-induced increases in phosphorylated p38 MAPK expression, and in cyclooxygenase-2 (COX-2), interleukin-6 (IL-6) and IL-1beta but not MIP-1alpha gene expression. We conclude that p38 MAPK is involved in ozone-induced airway hyperresponsiveness and lung neutrophilia. Inhibition of p38 MAPK with small molecule kinase inhibitors may be a means of reducing ozone-induced inflammation and airway hyperresponsiveness.

No effect of metformin on the innate airway hyperresponsiveness and increased responses to ozone observed in obese mice

We have previously reported that obese db/db mice exhibit innate airway hyperresponsiveness. These mice also have enhanced inflammatory responses to ozone, a common air pollutant that exacerbates asthma. Since db/db mice are diabetic as well as obese, the purpose of the present study was to determine whether metformin, an antihyperglycemic agent, alters the pulmonary phenotype of db/db mice. Lean wild-type (C57BL/6J) and obese db/db mice were treated by gavage with water or metformin (300 microg/g) once a day for 2 wk. Twenty-four hours after the last treatment, in mice of both genotypes, we either measured airway responsiveness to methacholine by forced oscillation, or we exposed the mice to ozone (2 parts per million for 3 h) and examined the ensuing inflammatory response. Compared with water, treatment with metformin caused a significant decrease in fasting blood glucose in obese mice. Airway responsiveness was increased in db/db versus wild-type mice, but metformin did not affect responsiveness in either group. Four hours after exposure to ozone, there was a significant increase in bronchoalveolar lavage fluid neutrophils and chemokines in mice of both genotypes, but the magnitude of these changes was greater in db/db than wild-type mice. Metformin did not affect ozone-induced inflammation in mice of either genotype. The results indicate that hyperglycemia is unlikely to account for the pulmonary phenotype of obese mice.

Interleukin-6 mediates lung injury following ischemic acute kidney injury or bilateral nephrectomy

Patients with acute kidney injury frequently have pulmonary complications. Similarly ischemic acute kidney injury or bilateral nephrectomy in rodents causes lung injury characterized by pulmonary edema, increased pulmonary capillary leak and interstitial leukocyte infiltration. Interleukin-6 is a pro-inflammatory cytokine that is increased in the serum of patients with acute kidney injury and predicts mortality. Here we found that lung neutrophil infiltration, myeloperoxidase activity, the neutrophil chemokines KC and MIP-2 and capillary leak all increased within 4 h following acute kidney injury in wild-type mice. These pathologic factors were reduced in interleukin-6-deficient mice following acute kidney injury or bilateral nephrectomy. The lungs of mutant mice had reduced KC but MIP-2 was similar to that of wild type mice. Wild-type mice, treated with an interleukin-6 inactivating antibody, had decreased lung myeloperoxidase activity and KC levels following acute kidney injury. Our study shows that interleukin-6 contributes to lung injury following acute kidney injury.

Effect of obesity on pulmonary inflammation induced by acute ozone exposure: role of interleukin-6

To determine the role of interleukin (IL)-6 in the increased ozone (O3)-induced inflammation and injury observed in obese vs. lean mice, lean wild-type and leptin-deficient obese (ob/ob) mice were injected with anti-IL-6 antibody (Ab) or isotype control Ab 24 h before exposure to either O3 (2 ppm for 3 h) or room air. Four or 24 h after O3 exposure, bronchoalveolar lavage (BAL) was performed, and the lungs were harvested for Western blotting. Anti-IL-6 Ab caused substantial reductions in O3-induced increases in BAL IL-6 in mice of both genotypes. Four hours following O3, ob/ob mice had increased BAL neutrophils compared with controls, and anti-IL-6-Ab virtually abolished this difference. At 24 h, O3-induced increases in BAL protein and BAL serum albumin were augmented in ob/ob vs. wild-type mice, and anti-IL-6 Ab ablated these obesity-related differences in epithelial barrier injury. O3 increased tyrosine phosphorylation of STAT-3 and STAT-1. There was no effect of obesity on STAT-3 phosphorylation, whereas obesity decreased STAT-1 expression, resulting in reduced STAT-1 phosphorylation. IL-6 neutralization did not alter STAT-3 or STAT-1 phosphorylation in ob/ob or wild-type mice. O3 increased BAL leukemia inhibitory factor (LIF) to a greater extent in obese than in lean mice, and LIF may account for effects on STAT phosphorylation. Our results suggest that IL-6 plays a complex role in pulmonary responses to O3, a role that differs between wild-type and ob/ob mice. Moreover, obesity-related differences in activation of STAT proteins may contribute to some of the differences in the response of obese vs. lean mice.

Diet-induced obesity causes innate airway hyperresponsiveness to methacholine and enhances ozone-induced pulmonary inflammation

We previously reported that genetically obese mice exhibit innate airway hyperresponsiveness (AHR) and enhanced ozone (O(3))-induced pulmonary inflammation. Such genetic deficiencies in mice are rare in humans, and they may not be representative of human obesity. Thus the purpose of this study was to determine the pulmonary phenotype of mice with diet-induced obesity (DIO), which more closely mimics the cause of human obesity. Therefore, wild-type C57BL/6 mice were reared from the time of weaning until at least 30 wk of age on diets in which either 10 or 60% of the calories are derived from fat in the form of lard. Body mass was approximately 40% greater in mice fed 60 vs. 10% fat diets. Baseline airway responsiveness to intravenous methacholine, measured by forced oscillation, was greater in mice fed 60 vs. 10% fat diets. We also examined lung permeability and inflammation after exposure to room air or O(3) (2 parts/million for 3 h), an asthma trigger. Four hours after the exposure ended, O(3)-induced increases in bronchoalveolar lavage fluid protein, interleukin-6, KC, macrophage inflammatory protein-2, interferon-gamma-inducible protein-10, and eotaxin were greater in mice fed 60 vs. 10% fat diets. Innate AHR and augmented responses to O(3) were not observed in mice raised from weaning until 20-22 wk of age on a 60% fat diet. These results indicate that mice with DIO exhibit innate AHR and enhanced O(3)-induced pulmonary inflammation, similar to genetically obese mice. However, mice with DIO must remain obese for an extended period of time before this pulmonary phenotype is observed.

Ozone exposure in a mouse model induces airway hyperreactivity that requires the presence of natural killer T cells and IL-17

Exposure to ozone, which is a major component of air pollution, induces a form of asthma that occurs in the absence of adaptive immunity. Although ozone-induced asthma is characterized by airway neutrophilia, and not eosinophilia, it is nevertheless associated with airway hyperreactivity (AHR), which is a cardinal feature of asthma. Because AHR induced by allergens requires the presence of natural killer T (NKT) cells, we asked whether ozone-induced AHR had similar requirements. We found that repeated exposure of wild-type (WT) mice to ozone induced severe AHR associated with an increase in airway NKT cells, neutrophils, and macrophages. Surprisingly, NKT cell-deficient (CD1d(-/-) and Jalpha18(-/-)) mice failed to develop ozone-induced AHR. Further, treatment of WT mice with an anti-CD1d mAb blocked NKT cell activation and prevented ozone-induced AHR. Moreover, ozone-induced, but not allergen-induced, AHR was associated with NKT cells producing interleukin (IL)-17, and failed to occur in IL-17(-/-) mice nor in WT mice treated with anti-IL-17 mAb. Thus, ozone exposure induces AHR that requires the presence of NKT cells and IL-17 production. Because NKT cells are required for the development of two very disparate forms of AHR (ozone- and allergen-induced), our results strongly suggest that NKT cells mediate a unifying pathogenic mechanism for several distinct forms of asthma, and represent a unique target for effective asthma therapy.