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

Multi-Omics analysis reveals molecular insights into the effects of acute ozone exposure on lung tissues of normal and obese male mice

Certain sub-groups, including men and obese individuals, are more susceptible to ozone (O3) exposure, but the underlying molecular mechanisms remain unclear. In this study, the male mice were divided into two dietary groups: one fed a high-fat diet (HFD), mimicking obesity conditions, and the other fed a normal diet (ND), then exposed to 0.5 ppm and 2 ppm O3 for 4 h per day over two days. The HFD mice exhibited significantly higher body weight and serum lipid biochemical indicators compared to the ND mice. Obese mice also exhibited more severe pulmonary inflammation and oxidative stress. Using a multi-omics approach including proteomics, metabolomics, and lipidomics, we observed that O3 exposure induced significant pulmonary molecular changes in both obese and normal mice, primarily arachidonic acid metabolism and lipid metabolism. Different molecular biomarker responses to acute O3 exposure were also observed between two dietary groups, with immune-related proteins impacted in obese mice and PPAR pathway-related proteins affected in normal mice. Furthermore, although not statistically significant, O3 exposure tended to aggravate HFD-induced disturbances in lung glycerophospholipid metabolism. Overall, this study provides valuable molecular insights into the responses of lung to O3 exposure and highlights the potential impact of O3 on obesity-induced metabolic changes.

Effects of Ozone on Sickness and Depressive-like Behavioral and Biochemical Phenotypes and Their Regulation by Serum Amyloid A in Mice

Ozone (O₃) is an air pollutant that primarily damages the lungs, but growing evidence supports the idea that O₃ also harms the brain; acute exposure to O₃ has been linked to central nervous system (CNS) symptoms such as depressed mood and sickness behaviors. However, the mechanisms by which O₃ inhalation causes neurobehavioral changes are limited. One hypothesis is that factors in the circulation bridge communication between the lungs and brain following O₃ exposure. In this study, our goals were to characterize neurobehavioral endpoints of O₃ exposure as they relate to markers of systemic and pulmonary inflammation, with a particular focus on serum amyloid A (SAA) and kynurenine as candidate mediators of O₃ behavioral effects. We evaluated O₃-induced dose-, time- and sex-dependent changes in pulmonary inflammation, circulating SAA and kynurenine and its metabolic enzymes, and sickness and depressive-like behaviors in Balb/c and CD-1 mice. We found that 3 parts per million (ppm) O₃, but not 2 or 1 ppm O₃, increased circulating SAA and lung inflammation, which were resolved by 48 h and was worse in females. We also found that indoleamine 2,3-dioxygenase (Ido1) mRNA expression was increased in the brain and spleen 24 h after 3 ppm O₃ and that kynurenine was increased in blood. Sickness and depressive-like behaviors were observed at all O₃ doses (1-3 ppm), suggesting that behavioral responses to O₃ can occur independently of increased SAA or neutrophils in the lungs. Using SAA knockout mice, we found that SAA did not contribute to O₃-induced pulmonary damage or inflammation, systemic increases in kynurenine post-O₃, or depressive-like behavior but did contribute to weight loss. Together, these findings indicate that acute O₃ exposure induces transient symptoms of sickness and depressive-like behaviors that may occur in the presence or absence of overt pulmonary neutrophilia and systemic increases of SAA. SAA does not appear to contribute to pulmonary inflammation induced by O₃, although it may contribute to other aspects of sickness behavior, as reflected by a modest effect on weight loss.

Characterization of low-dose ozone-induced murine acute lung injury

Ozone is a toxic and highly reactive gaseous oxidizing chemical with well‐documented adverse health effects in humans. On the basis of animal and human data, environmental guidelines and air quality standards recommend a threshold for exposure of no more than 0.063 ppm of ozone (daily concentrations). This research describes a standardized sensitive model of sterile murine lung inflammation induced by exposing mice to acute (0, 4 or 24 hr), yet low, levels of ozone (0.005, 0.05 or 0.5 ppm), one that are below the current recommendations for what is considered a safe or “ambient” ozone concentration for humans. Ozone led to concentration and time‐dependent phlogistic cell death in the bronchoalveolar lavage, lung epithelial damage and hemorrhage. Interestingly, we observed distinct large bright CD11b positive cells in the bronchoalveolar lavage, upregulation of lung vascular and alveolar ATP synthase as well as plasminogen and bronchiolar angiostatin expression in ozone‐exposed mice, platelet and neutrophil accumulation in the lung vasculature and an eotaxin‐2, IL‐16, CXCL5, CXCL12, and CXCL13 dominant inflammatory response leading to lung injury. Using a fluorescent intravital microscopy set up, we quantified ozone‐induced extensive alveolar cellular damage. We observed ozone‐induced actin filament disorganization, perturbed respiratory mechanics, acute suppression of the alveolar reactive oxygen species (ROS) production and mitochondrial potential in ventilated lungs. We present evidence of systemic, as well as pulmonary toxicity, at 40‐fold lower ozone concentrations than previously reported in mice. The findings are important in establishing a sensitive means of quantifying structural and functional lung disorganization following exposure to an aerosolized pollutant, even at levels of ozone exposure previously thought to be safe in humans.

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.

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

BACKGROUND

Interleukin-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.

METHODS

Wildtype 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.

RESULTS

In 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.

CONCLUSIONS

The 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.

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.

The N-terminal region of serum amyloid A3 protein activates NF-κB and up-regulates MUC2 mucin mRNA expression in mouse colonic epithelial cells

Serum amyloid A (SAA) is the major acute-phase protein and a precursor of amyloid A (AA) in AA amyloidosis in humans and animals. SAA isoforms have been identified in a wide variety of animals, such as SAA1, SAA2, SAA3, and SAA4 in mouse. Although the biological functions of SAA isoforms are not completely understood, recent studies have suggested that SAA3 plays a role in host defense. Expression of SAA3 is increased on the mouse colon surface in the presence of microbiota in vivo, and it increases mRNA expression of mucin 2 (MUC2) in murine colonic epithelial cells in vitro, which constitutes a protective mucus barrier in the intestinal tract. In this study, to identify responsible regions in SAA3 for MUC2 expression, recombinant murine SAA1 (rSAA1), rSAA3, and rSAA1/3, a chimera protein constructed with mature SAA1 (amino acids 1–36) and SAA3 (amino acids 37–103), and vice versa for rSAA3/1, were added to murine colonic epithelial CMT-93 cells, and the mRNA expressions of MUC2 and cytokines were measured. Inhibition assays with NF-κB inhibitor or TLR4/MD2 inhibitor were also performed. Up-regulation of MUC2 mRNA expression was strongly stimulated by rSAA3 and rSAA3/1, but not by rSAA1 or rSAA1/3. Moreover, NF-κB and TLR4/MD2 inhibitors suppressed the increase of MUC2 mRNA expression. These results suggest that the major responsible region for MUC2 expression exists in amino acids 1–36 of SAA3, and that up-regulations of MUC2 expression by SAA3 and SAA3/1 are involved with activation of NF-κB via the TLR4/MD2 complex.

Mechanisms of Asthma in Obesity. Pleiotropic Aspects of Obesity Produce Distinct Asthma Phenotypes

The majority of patients with severe or difficult-to-control asthma in the United States are obese. Epidemiological studies have clearly established that obese patients tend to have worse asthma control and increased hospitalizations and do not respond to standard controller therapy as well as lean patients with asthma. Less clear are the mechanistic underpinnings for the striking clinical differences between lean and obese patients with asthma. Because obesity is principally a disorder of metabolism and energy regulation, processes fundamental to the function of every cell and system within the body, it is not surprising that it affects the respiratory system; it is perhaps surprising that it has taken so long to appreciate how dysfunctional metabolism and energy regulation lead to severe airway disease. Although early investigations focused on identifying a common factor in obesity that could promote airway disease, an appreciation has emerged that the asthma of obesity is a manifestation of multiple anomalies related to obesity affecting all the different pathways that cause asthma, and likely also to de novo airway dysfunction. Consequently, all the phenotypes of asthma currently recognized in lean patients (which are profoundly modified by obesity), as well as those unique to one's obesity endotype, likely contribute to obese asthma in a particular individual. This perspective reviews what we have learned from clinical studies and animal models about the phenotypes of asthma in obesity, which show how specific aspects of obesity and altered metabolism might lead to de novo airway disease and profoundly modify existing airway disease.

Serum amyloid A: an ozone-induced circulating factor with potentially important functions in the lung-brain axis

Accumulating evidence suggests that O₃ exposure may contribute to CNS dysfunction. Here, we posit that inflammatory and acute-phase proteins in the circulation increase after O₃ exposure and systemically convey signals of O₃ exposure to the CNS. To model acute O₃ exposure, female Balb/c mice were exposed to 3 ppm O₃ or forced air for 2 h and were studied after 6 or 24 h. Of 23 cytokines and chemokines, only KC/CXCL1 was increased in blood 6 h after O₃ exposure. The acute-phase protein serum amyloid A (A-SAA) was significantly increased by 24 h, whereas C-reactive protein was unchanged. A-SAA in blood correlated with total leukocytes, macrophages, and neutrophils in bronchoalveolar lavage from O₃-exposed mice. A-SAA mRNA and protein were increased in the liver. We found that both isoforms of A-SAA completely crossed the intact blood-brain barrier, although the rate of SAA2.1 influx was approximately 5 times faster than that of SAA1.1. Finally, A-SAA protein, but not mRNA, was increased in the CNS 24 h post-O₃ exposure. Our findings suggest that A-SAA is functionally linked to pulmonary inflammation in our O₃ exposure model and that A-SAA could be an important systemic signal of O₃ exposure to the CNS.-Erickson, M. A., Jude, J., Zhao, H., Rhea, E. M., Salameh, T. S., Jester, W., Pu, S., Harrowitz, J., Nguyen, N., Banks, W. A., Panettieri, R. A., Jr., Jordan-Sciutto, K. L. Serum amyloid A: an ozone-induced circulating factor with potentially important functions in the lung-brain axis.

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.

RESULTS AND 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.

Repeated Mouse Lung Exposures to Stachybotrys chartarum Shift Immune Response from Type 1 to Type 2

After a single or multiple intratracheal instillations of Stachybotrys chartarum (S. chartarum or black mold) spores in BALB/c mice, we characterized cytokine production, metabolites, and inflammatory patterns by analyzing mouse bronchoalveolar lavage (BAL), lung tissue, and plasma. We found marked differences in BAL cell counts, especially large increases in lymphocytes and eosinophils in multiple-dosed mice. Formation of eosinophil-rich granulomas and airway goblet cell metaplasia were prevalent in the lungs of multiple-dosed mice but not in single- or saline-dosed groups. We detected changes in the cytokine expression profiles in both the BAL and plasma. Multiple pulmonary exposures to S. chartarum induced significant metabolic changes in the lungs but not in the plasma. These changes suggest a shift from type 1 inflammation after an acute exposure to type 2 inflammation after multiple exposures to S. chartarum. Eotaxin, vascular endothelial growth factor (VEGF), MIP-1α, MIP-1β, TNF-α, and the IL-8 analogs macrophage inflammatory protein-2 (MIP-2) and keratinocyte chemoattractant (KC), had more dramatic changes in multiple- than in single-dosed mice, and parallel the cytokines that characterize humans with histories of mold exposures versus unexposed control subjects. This repeated exposure model allows us to more realistically characterize responses to mold, such as cytokine, metabolic, and cellular changes.

Effects of mannose-binding lectin on pulmonary gene expression and innate immune inflammatory response to ozone

Ozone is a common, potent oxidant pollutant in industrialized nations. Ozone exposure causes airway hyperreactivity, lung hyperpermeability, inflammation, and cell damage in humans and laboratory animals, and exposure to ozone has been associated with exacerbation of asthma, altered lung function, and mortality. The mechanisms of ozone-induced lung injury and differential susceptibility are not fully understood. Ozone-induced lung inflammation is mediated, in part, by the innate immune system. We hypothesized that mannose-binding lectin (MBL), an innate immunity serum protein, contributes to the proinflammatory events caused by ozone-mediated activation of the innate immune system. Wild-type (Mbl(+/+)) and MBL-deficient (Mbl(-/-)) mice were exposed to ozone (0.3 ppm) for up to 72 h, and bronchoalveolar lavage fluid was examined for inflammatory markers. Mean numbers of eosinophils and neutrophils and levels of the neutrophil attractants C-X-C motif chemokines 2 [Cxcl2 (major intrinsic protein 2)] and 5 [Cxcl5 (limb expression, LIX)] in the bronchoalveolar lavage fluid were significantly lower in Mbl(-/-) than Mbl(+/+) mice exposed to ozone. Using genome-wide mRNA microarray analyses, we identified significant differences in transcript response profiles and networks at baseline [e.g., nuclear factor erythroid-related factor 2 (NRF2)-mediated oxidative stress response] and after exposure (e.g., humoral immune response) between Mbl(+/+) and Mbl(-/-) mice. The microarray data were further analyzed to discover several informative differential response patterns and subsequent gene sets, including the antimicrobial response and the inflammatory response. We also used the lists of gene transcripts to search the LINCS L1000CDS(2) data sets to identify agents that are predicted to perturb ozone-induced changes in gene transcripts and inflammation. These novel findings demonstrate that targeted deletion of Mbl caused differential levels of inflammation-related gene sets at baseline and after exposure to ozone and significantly reduced pulmonary inflammation, thus indicating an important innate immunomodulatory role of the gene in this model.

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.

Inflammasome, IL-1 and inflammation in ozone-induced lung injury

Exposure to ambient ozone causes airway hyperreactivity and lung inflammation, which represent an important health concern in humans. Recent clinical and experimental studies contributed to the understanding of the mechanisms of epithelial injury, inflammation and airway hyperreactivity, which is reviewed here. The present data suggest that ozone induced oxidative stress causes inflammasome activation with the release of IL-1, other cytokines and proteases driving lung inflammation leading to the destruction of alveolar epithelia with emphysema and respiratory failure. Insights in the pathogenic pathway may allow to identify novel biomarkers of ozone-induced lung disease and therapeutic targets.

γδ T Cells Are Required for M2 Macrophage Polarization and Resolution of Ozone-Induced Pulmonary Inflammation in Mice

We examined the role of γδ T cells in the induction of alternatively activated M2 macrophages and the resolution of inflammation after ozone exposure. Wildtype (WT) mice and mice deficient in γδ T cells (TCRδ^-/- mice) were exposed to air or to ozone (0.3 ppm for up to 72h) and euthanized immediately or 1, 3, or 5 days after cessation of exposure. In WT mice, M2 macrophages accumulated in the lungs over the course of ozone exposure. Pulmonary mRNA abundance of the M2 genes, Arg1, Retnla, and Clec10a, also increased after ozone. In contrast, no evidence of M2 polarization was observed in TCRδ^-/- mice. WT but not TCRδ^-/- mice expressed the M2c polarizing cytokine, IL-17A, after ozone exposure and WT mice treated with an IL-17A neutralizing antibody exhibited attenuated ozone-induced M2 gene expression. In WT mice, ozone-induced increases in bronchoalveolar lavage neutrophils and macrophages resolved quickly after cessation of ozone exposure returning to air exposed levels within 3 days. However, lack of M2 macrophages in TCRδ^-/- mice was associated with delayed clearance of inflammatory cells after cessation of ozone and increased accumulation of apoptotic macrophages in the lungs. Delayed restoration of normal lung architecture was also observed in TCRδ^-/- mice. In summary, our data indicate that γδ T cells are required for the resolution of ozone-induced inflammation, likely because γδ T cells, through their secretion of IL-17A, contribute to changes in macrophage polarization that promote clearance of apoptotic cells.

Increased airway reactivity and hyperinsulinemia in obese mice are linked by ERK signaling in brain stem cholinergic neurons

Obesity is a major risk factor for asthma, which is characterized by airway hyperreactivity (AHR). In obesity-associated asthma, AHR may be regulated by non-TH2 mechanisms. We hypothesized that airway reactivity is regulated by insulin in the CNS, and that the high levels of insulin associated with obesity contribute to AHR. We found that intracerebroventricular (ICV)-injected insulin increases airway reactivity in wild-type, but not in vesicle acetylcholine transporter knockdown (VAChT KD(HOM-/-)), mice. Either neutralization of central insulin or inhibition of extracellular signal-regulated kinases (ERK) normalized airway reactivity in hyperinsulinemic obese mice. These effects were mediated by insulin in cholinergic nerves located at the dorsal motor nucleus of the vagus (DMV) and nucleus ambiguus (NA), which convey parasympathetic outflow to the lungs. We propose that increased insulin-induced activation of ERK in parasympathetic pre-ganglionic nerves contributes to AHR in obese mice, suggesting a drug-treatable link between obesity and asthma.

Immunological characteristics and management considerations in obese patients with asthma

Obesity is associated with severe, poorly controlled asthma that does not respond as well to therapy as asthma in leaner asthmatics. Important insights gained from animal models of obesity and asthma suggests that different forms of obesity may lead to different manifestations of airway disease: obesity is associated with both innate increased airway reactivity and altered responses to aeroallergen and pollutant challenges. In humans, at least two broad groups of obese asthmatics have been recognized: one that is likely unique to obesity and another that is likely lean allergic asthma much complicated by obesity. This article will discuss what we have learned about the immunological and pathophysiological basis of asthma in obesity from animal and human studies, and how this might guide therapy.

Obesity and asthma: beyond T(H)2 inflammation

Obesity is a major risk factor for asthma. Likewise, obesity is known to increase disease severity in asthmatic subjects and also to impair the efficacy of first-line treatment medications for asthma, worsening asthma control in obese patients. This concept is in agreement with the current understanding that some asthma phenotypes are not accompanied by detectable inflammation, and may not be ameliorated by classical anti-inflammatory therapy. There are growing evidences suggesting that the obesity-related asthma phenotype does not necessarily involve the classical T(H)2-dependent inflammatory process. Hormones involved in glucose homeostasis and in the pathogeneses of obesity likely directly or indirectly link obesity and asthma through inflammatory and non-inflammatory pathways. Furthermore, the endocrine regulation of the airway-related pre-ganglionic nerves likely contributes to airway hyperreactivity (AHR) in obese states. In this review, we focused our efforts on understanding the mechanism underlying obesity-related asthma by exploring the T(H)2-independent mechanisms leading to this disease.