Early posttransplant reductions in club cell secretory protein associate with future risk for chronic allograft dysfunction in lung recipients: results from a multicenter study

BACKGROUND

Chronic lung allograft dysfunction (CLAD) increases morbidity and mortality for lung transplant recipients. Club cell secretory protein (CCSP), produced by airway club cells, is reduced in the bronchoalveolar lavage fluid (BALF) of lung recipients with CLAD. We sought to understand the relationship between BALF CCSP and early posttransplant allograft injury and determine if early posttransplant BALF CCSP reductions indicate later CLAD risk.

METHODS

We quantified CCSP and total protein in 1606 BALF samples collected over the first posttransplant year from 392 adult lung recipients at 5 centers. Generalized estimating equation models were used to examine the correlation of allograft histology or infection events with protein-normalized BALF CCSP. We performed multivariable Cox regression to determine the association between a time-dependent binary indicator of normalized BALF CCSP level below the median in the first posttransplant year and development of probable CLAD.

RESULTS

Normalized BALF CCSP concentrations were 19% to 48% lower among samples corresponding to histological allograft injury as compared with healthy samples. Patients who experienced any occurrence of a normalized BALF CCSP level below the median over the first posttransplant year had a significant increase in probable CLAD risk independent of other factors previously linked to CLAD (adjusted hazard ratio 1.95; p = 0.035).

CONCLUSIONS

We discovered a threshold for reduced BALF CCSP to discriminate future CLAD risk; supporting the utility of BALF CCSP as a tool for early posttransplant risk stratification. Additionally, our finding that low CCSP associates with future CLAD underscores a role for club cell injury in CLAD pathobiology.

E-cigarette and food flavoring diacetyl alters airway cell morphology, inflammatory and antiviral response, and susceptibility to SARS-CoV-2

Diacetyl (DA) is an α-diketone that is used to flavor microwave popcorn, coffee, and e-cigarettes. Occupational exposure to high levels of DA causes impaired lung function and obstructive airway disease. Additionally, lower levels of DA exposure dampen host defenses in vitro. Understanding DA’s impact on lung epithelium is important for delineating exposure risk on lung health. In this study, we assessed the impact of DA on normal human bronchial epithelial cell (NHBEC) morphology, transcriptional profiles, and susceptibility to SARS-CoV-2 infection. Transcriptomic analysis demonstrated cilia dysregulation, an increase in hypoxia and sterile inflammation associated pathways, and decreased expression of interferon-stimulated genes after DA exposure. Additionally, DA exposure resulted in cilia loss and increased hyaluronan production. After SARS-CoV-2 infection, both genomic and subgenomic SARS-CoV-2 RNA were increased in DA vapor- compared to vehicle-exposed NHBECs. This work suggests that transcriptomic and physiologic changes induced by DA vapor exposure damage cilia and increase host susceptibility to SARS-CoV-2.

Occupational asthma and rhinitis due to wheat flour: sublingual specific immunotherapy treatment

BACKGROUND

There are several potential sensitizers in the bakery environment and wheat flour appears to be the dominant sensitizer in most bakeries. Apart from traditional drug therapy or a change in profession, there are no effective therapies for workers who develop serious respiratory symptoms in the workplace.

OBJECTIVES

To describe clinical and laboratory findings in workers with asthma and/or rhinitis induced by wheat flour who underwent sublingual specific immunotherapy (SLIT).

METHODS

Since drug therapy and prevention strategies were not effective, five bakers were elected to undergo SLIT. A three-year study was led by administering a sublingual wheat flour extract. Questionnaires, allergy and respiratory tests were performed before and after SLIT.

RESULTS

After SLIT an improvement in symptoms is observed in every patient: Asthma Control Test and a quality-of-life questionnaire show higher scores and as a result, workers have reduced the use of drug therapy. We observed significantly reduced exhaled nitric oxide (FeNO) and eosinophil cationic protein (ECP) levels after SLIT, hypothesizing that these parameters may be used to monitor the effectiveness of immunotherapy. The improvement of FEV1 (forced expiratory volume in 1second) and responsiveness to bronchoprovocative tests with methacholine denotes a possible role of SLIT in treating patients with low-respiratory tract involvement, even though more data are needed.

DISCUSSIONS

This is the first report in the literature on the use of SLIT for baker's asthma and rhinitis. SLIT for occupational wheat flour allergy should be possible and efficient, saving vocational training, professionalism, and avoiding job loss.

EGFR-Dependent IL8 Production by Airway Epithelial Cells After Exposure to the Food Flavoring Chemical 2,3-Butanedione

2,3-Butanedione (DA), a component of artificial butter flavoring, is associated with the development of occupational bronchiolitis obliterans (BO), a disease of progressive airway fibrosis resulting in lung function decline. Neutrophilic airway inflammation is a consistent feature of BO across a range of clinical contexts and may contribute to disease pathogenesis. Therefore, we sought to determine the importance of the neutrophil chemotactic cytokine interleukin-8 (IL-8) in DA-induced lung disease using in vivo and in vitro model systems. First, we demonstrated that levels of Cinc-1, the rat homolog of IL-8, are increased in the lung fluid and tissue compartment in a rat model of DA-induced BO. Next, we demonstrated that DA increased IL-8 production by the pulmonary epithelial cell line NCI-H292 and by primary human airway epithelial cells grown under physiologically relevant conditions at an air-liquid interface. We then tested the hypothesis that DA-induced epithelial IL-8 protein occurs in an epidermal growth factor receptor (EGFR)-dependent manner. In these in vitro experiments we demonstrated that epithelial IL-8 protein is blocked by the EGFR tyrosine kinase inhibitor AG1478 and by inhibition of tumor necrosis factor-alpha converting enzyme using the small molecule inhibitor, TAPI-1. Finally, we demonstrated that DA-induced IL-8 is dependent upon ERK1/2 and Mitogen activated protein kinase kinase activation downstream of EGFR signaling using the small molecule inhibitors AG1478 and PD98059. Together these novel in vivo and in vitro observations support that EGFR-dependent IL-8 production occurs in DA-induced BO. Further studies are warranted to determine the importance of IL-8 in BO pathogenesis.

Models of toxicity of diacetyl and alternative diones

Diacetyl (DA; 2,3-butanedione), with the chemical formula (CH3CO)2 is a volatile organic compound with a deep yellow color and a strong buttery flavor and aroma. These properties have made DA a particularly useful and common food flavoring ingredient. However, because of this increased occupational use, workers can be exposed to high vapor concentrations in the workplace. Despite being listed by the USFDA to be 'generally regarded as safe' (GRAS), multiple lines of evidence suggest that exposure to high concentrations of DA vapor causes long-term impairments in lung function with lung function testing indicating evidence of either restrictive or obstructive airway narrowing in affected individuals. A growing number of pre-clinical studies have now addressed the short and long-term toxicity associated with DA exposure providing further insight into the toxicity of DA and related diones. This review summarizes these observations.

The Diacetyl-Exposed Human Airway Epithelial Secretome: New Insights into Flavoring-Induced Airways Disease

Bronchiolitis obliterans (BO) is an increasingly important lung disease characterized by fibroproliferative airway lesions and decrements in lung function. Occupational exposure to the artificial food flavoring ingredient diacetyl, commonly used to impart a buttery flavor to microwave popcorn, has been associated with BO development. In the occupational setting, diacetyl vapor is first encountered by the airway epithelium. To better understand the effects of diacetyl vapor on the airway epithelium, we used an unbiased proteomic approach to characterize both the apical and basolateral secretomes of air-liquid interface cultures of primary human airway epithelial cells from four unique donors after exposure to an occupationally relevant concentration (∼1,100 ppm) of diacetyl vapor or phosphate-buffered saline as a control on alternating days. Basolateral and apical supernatants collected 48 h after the third exposure were analyzed using one-dimensional liquid chromatography tandem mass spectrometry. Paired t tests adjusted for multiple comparisons were used to assess differential expression between diacetyl and phosphate-buffered saline exposure. Of the significantly differentially expressed proteins identified, 61 were unique to the apical secretome, 81 were unique to the basolateral secretome, and 11 were present in both. Pathway enrichment analysis using publicly available databases revealed that proteins associated with matrix remodeling, including degradation, assembly, and new matrix organization, were overrepresented in the data sets. Similarly, protein modifiers of epidermal growth factor receptor signaling were significantly altered. The ordered changes in protein expression suggest that the airway epithelial response to diacetyl may contribute to BO pathogenesis.

Proteomic Analysis of Primary Human Airway Epithelial Cells Exposed to the Respiratory Toxicant Diacetyl

Occupational exposures to the diketone flavoring agent, diacetyl, have been associated with bronchiolitis obliterans, a rare condition of airway fibrosis. Model studies in rodents have suggested that the airway epithelium is a major site of diacetyl toxicity, but the effects of diacetyl exposure upon the human airway epithelium are poorly characterized. Here we performed quantitative LC-MS/MS-based proteomics to study the effects of repeated diacetyl vapor exposures on 3D organotypic cultures of human primary tracheobronchial epithelial cells. Using a label-free approach, we quantified approximately 3400 proteins and 5700 phosphopeptides in cell lysates across four independent donors. Altered expression of proteins and phosphopeptides were suggestive of loss of cilia and increased squamous differentiation in diacetyl-exposed cells. These phenomena were confirmed by immunofluorescence staining of culture cross sections. Hyperphosphorylation and cross-linking of basal cell keratins were also observed in diacetyl-treated cells, and we used parallel reaction monitoring to confidently localize and quantify previously uncharacterized sites of phosphorylation in keratin 6. Collectively, these data identify numerous molecular changes in the epithelium that may be important to the pathogenesis of flavoring-induced bronchiolitis obliterans. More generally, this study highlights the utility of quantitative proteomics for the study of in vitro models of airway injury and disease.

Integrating murine gene expression studies to understand obstructive lung disease due to chronic inhaled endotoxin

RATIONALE

Endotoxin is a near ubiquitous environmental exposure that that has been associated with both asthma and chronic obstructive pulmonary disease (COPD). These obstructive lung diseases have a complex pathophysiology, making them difficult to study comprehensively in the context of endotoxin. Genome-wide gene expression studies have been used to identify a molecular snapshot of the response to environmental exposures. Identification of differentially expressed genes shared across all published murine models of chronic inhaled endotoxin will provide insight into the biology underlying endotoxin-associated lung disease.

METHODS

We identified three published murine models with gene expression profiling after repeated low-dose inhaled endotoxin. All array data from these experiments were re-analyzed, annotated consistently, and tested for shared genes found to be differentially expressed. Additional functional comparison was conducted by testing for significant enrichment of differentially expressed genes in known pathways. The importance of this gene signature in smoking-related lung disease was assessed using hierarchical clustering in an independent experiment where mice were exposed to endotoxin, smoke, and endotoxin plus smoke.

RESULTS

A 101-gene signature was detected in three murine models, more than expected by chance. The three model systems exhibit additional similarity beyond shared genes when compared at the pathway level, with increasing enrichment of inflammatory pathways associated with longer duration of endotoxin exposure. Genes and pathways important in both asthma and COPD were shared across all endotoxin models. Mice exposed to endotoxin, smoke, and smoke plus endotoxin were accurately classified with the endotoxin gene signature.

CONCLUSIONS

Despite the differences in laboratory, duration of exposure, and strain of mouse used in three experimental models of chronic inhaled endotoxin, surprising similarities in gene expression were observed. The endotoxin component of tobacco smoke may play an important role in disease development.

Innate immune activation by inhaled lipopolysaccharide, independent of oxidative stress, exacerbates silica-induced pulmonary fibrosis in mice

Acute exacerbations of pulmonary fibrosis are characterized by rapid decrements in lung function. Environmental factors that may contribute to acute exacerbations remain poorly understood. We have previously demonstrated that exposure to inhaled lipopolysaccharide (LPS) induces expression of genes associated with fibrosis. To address whether exposure to LPS could exacerbate fibrosis, we exposed male C57BL/6 mice to crystalline silica, or vehicle, followed 28 days later by LPS or saline inhalation. We observed that mice receiving both silica and LPS had significantly more total inflammatory cells, more whole lung lavage MCP-1, MIP-2, KC and IL-1β, more evidence of oxidative stress and more total lung hydroxyproline than mice receiving either LPS alone, or silica alone. Blocking oxidative stress with N-acetylcysteine attenuated whole lung inflammation but had no effect on total lung hydroxyproline. These observations suggest that exposure to innate immune stimuli, such as LPS in the environment, may exacerbate stable pulmonary fibrosis via mechanisms that are independent of inflammation and oxidative stress.

c-Kit is essential for alveolar maintenance and protection from emphysema-like disease in mice

RATIONALE

Previously, we demonstrated a candidate region for susceptibility to airspace enlargement on mouse chromosome 5. However, the specific candidate genes within this region accounting for emphysema-like changes remain unrecognized. c-Kit is a receptor tyrosine kinase within this candidate gene region that has previously been recognized to contribute to the survival, proliferation, and differentiation of hematopoietic stem cells. Increases in the percentage of cells expressing c-Kit have previously been associated with protection against injury-induced emphysema.

OBJECTIVES

Determine whether genetic variants of c-Kit are associated with spontaneous airspace enlargement.

METHODS

Perform single-nucleotide polymorphism association studies in the mouse strains at the extremes of airspace enlargement phenotype for variants in c-Kit tyrosine kinase. Characterize mice bearing functional variants of c-Kit compared with wild-type controls for the development of spontaneous airspace enlargement. Epithelial cell proliferation was measured in culture.

MEASUREMENTS AND MAIN RESULTS

Upstream regulatory single-nucleotide polymorphisms in the divergent mouse strains were associated with the lung compliance difference observed between the extreme strains. c-Kit mutant mice (Kit(W-sh)/(W-sh)), when compared with genetic controls, developed altered lung histology, increased total lung capacity, increased residual volume, and increased lung compliance that persist into adulthood. c-Kit inhibition with imatinib attenuated in vitro proliferation of cells expressing epithelial cell adhesion molecule.

CONCLUSIONS

Our findings indicate that c-Kit sustains and/or maintains normal alveolar architecture in the lungs of mice. In vitro data suggest that c-Kit can regulate epithelial cell clonal expansion. The precise mechanisms that c-Kit contributes to the development of airspace enlargement and increased lung compliance remain unclear and warrants further investigation.

Strain-dependent genomic factors affect allergen-induced airway hyperresponsiveness in mice

Asthma is etiologically and clinically heterogeneous, making the genomic basis of asthma difficult to identify. We exploited the strain-dependence of a murine model of allergic airway disease to identify different genomic responses in the lung. BALB/cJ and C57BL/6J mice were sensitized with the immunodominant allergen from the Dermatophagoides pteronyssinus species of house dust mite (Der p 1), without exogenous adjuvant, and the mice then underwent a single challenge with Der p 1. Allergic inflammation, serum antibody titers, mucous metaplasia, and airway hyperresponsiveness were evaluated 72 hours after airway challenge. Whole-lung gene expression analyses were conducted to identify genomic responses to allergen challenge. Der p 1-challenged BALB/cJ mice produced all the key features of allergic airway disease. In comparison, C57BL/6J mice produced exaggerated Th2-biased responses and inflammation, but exhibited an unexpected decrease in airway hyperresponsiveness compared with control mice. Lung gene expression analysis revealed genes that were shared by both strains and a set of down-regulated genes unique to C57BL/6J mice, including several G-protein-coupled receptors involved in airway smooth muscle contraction, most notably the M2 muscarinic receptor, which we show is expressed in airway smooth muscle and was decreased at the protein level after challenge with Der p 1. Murine strain-dependent genomic responses in the lung offer insights into the different biological pathways that develop after allergen challenge. This study of two different murine strains demonstrates that inflammation and airway hyperresponsiveness can be decoupled, and suggests that the down-modulation of expression of G-protein-coupled receptors involved in regulating airway smooth muscle contraction may contribute to this dissociation.

Gender influences the response to experimental silica-induced lung fibrosis in mice

Accumulating evidence suggests that gender can have a profound effect on incidence and severity of a variety of pulmonary diseases. To address the influence of gender on the development of silica-induced pulmonary fibrosis, we instilled 0.2 g/kg silica into male and female C57BL/6 mice and examined the fibrotic and inflammatory response at 14 days postexposure. Both silica-exposed male and female mice had significant increases in total lung hydroxyproline compared with saline controls. However, silica-exposed female mice had significantly less total lung hydroxyproline than silica-exposed male mice. This observation was confirmed by color thresholding image analysis. Interestingly, silica-exposed female mice had significantly more inflammatory cells, the majority of which were macrophages, as well as higher levels of the macrophage-specific chemokines MCP-1 and CCL9 in whole lung lavage compared with silica-exposed male mice. We also show that at baseline, estrogen receptor α (ERα) mRNA expression is lower in female mice than in males and that ERα mRNA expression is decreased by silica exposure. Finally, we show that the response of ovariectomized female mice to silica instillation is similar to that of male mice. These observations together show that gender influences the lung response to silica.

The role of Scgb1a1+ Clara cells in the long-term maintenance and repair of lung airway, but not alveolar, epithelium

To directly test the contribution of Scgb1a1(+) Clara cells to postnatal growth, homeostasis, and repair of lung epithelium, we generated a Scgb1a1-CreER "knockin" mouse for lineage-tracing these cells. Under all conditions tested, the majority of Clara cells in the bronchioles both self-renews and generates ciliated cells. In the trachea, Clara cells give rise to ciliated cells but do not self-renew extensively. Nevertheless, they can contribute to tracheal repair. In the postnatal mouse lung, it has been proposed that bronchioalveolar stem cells (BASCs) which coexpress Scgb1a1 (Secretoglobin1a1) and SftpC (Surfactant Protein C), contribute descendants to both bronchioles and alveoli. The putative BASCs were lineage labeled in our studies. However, we find no evidence for the function of a special BASC population during postnatal growth, adult homeostasis, or repair. Rather, our results support a model in which the trachea, bronchioles, and alveoli are maintained by distinct populations of epithelial progenitor cells.

Host-environment interactions in exposure-related diffuse lung diseases

Diffuse lung disease (DLD), also known as interstitial lung disease (ILD), comprises a group of relatively rare but devastating lung diseases that involve varying degrees of acute and chronic inflammation, and which may present with end-stage fibroproliferation. There are currently no proven therapeutic strategies to halt progression of DLDs. Thinking about DLDs has evolved over time from hypotheses invoking inflammation as the prime mover in the etiology of disease, to the current hypothesis that interactions between a damaged and frustrated epithelium, and the response of underlying mesenchymal cells that takes place, contribute to the fibroproliferative milieu. The greatest challenge to understanding the role of environmental exposures in pathogenesis of DLDs is that there is no clear consensus on the etiology and pathogenesis of these diseases. Emerging data on the relationship between loss of epithelial integrity and mesenchymal fibroproliferation support the hypothesis that the damage to the epithelium is a critical component in the development of DLDs that progress to a fibroproliferative presentation. Thus it follows that environmental stress which impacts the well-being of the epithelium may play a critical role in shifting the balance of lung homeostasis through ongoing insult as a result of exposure to environmental agents. Animal models that recapitulate the vulnerable epithelium observed in patients who develop fibrotic lung disease associated with DLDs will provide the best opportunity to understand mechanisms associated with the etiology of these diseases.

Evaluating genome-wide DNA methylation changes in mice by Methylation Specific Digital Karyotyping

Background

The study of genome-wide DNA methylation changes has become more accessible with the development of various array-based technologies though when studying species other than human the choice of applications are limited and not always within reach. In this study, we adapted and tested the applicability of Methylation Specific Digital Karyotyping (MSDK), a non-array based method, for the prospective analysis of epigenetic changes after perinatal nutritional modifications in a mouse model of allergic airway disease. MSDK is a sequenced based method that allows a comprehensive and unbiased methylation profiling. The method generates 21 base pairs long sequence tags derived from specific locations in the genome. The resulting tag frequencies determine in a quantitative manner the methylation level of the corresponding loci.

Results

Genomic DNA from whole lung was isolated and subjected to MSDK analysis using the methylation-sensitive enzyme Not I as the mapping enzyme and Nla III as the fragmenting enzyme. In a pair wise comparison of the generated mouse MSDK libraries we identified 158 loci that are significantly differentially methylated (P-value = 0.05) after perinatal dietary changes in our mouse model. Quantitative methylation specific PCR and sequence analysis of bisulfate modified genomic DNA confirmed changes in methylation at specific loci. Differences in genomic MSDK tag counts for a selected set of genes, correlated well with changes in transcription levels as measured by real-time PCR. Furthermore serial analysis of gene expression profiling demonstrated a dramatic difference in expressed transcripts in mice exposed to perinatal nutritional changes.

Conclusion

The genome-wide methylation survey applied in this study allowed for an unbiased methylation profiling revealing subtle changes in DNA methylation in mice maternally exposed to dietary changes in methyl-donor content. The MSDK method is applicable for mouse models of complex human diseases in a mixed cell population and might be a valuable technology to determine whether environmental exposures can lead to epigenetic changes.

In utero supplementation with methyl donors enhances allergic airway disease in mice

Asthma is a complex heritable disease that is increasing in prevalence and severity, particularly in developed countries such as the United States, where 11% of the population is affected. The contribution of environmental and genetic factors to this growing epidemic is currently not well understood. We developed the hypothesis, based on previous literature, that changes in DNA methylation resulting in aberrant gene transcription may enhance the risk of developing allergic airway disease. Our findings indicate that in mice, a maternal diet supplemented with methyl donors enhanced the severity of allergic airway disease that was inherited transgenerationally. Using a genomic approach, we discovered 82 gene-associated loci that were differentially methylated after in utero supplementation with a methyl-rich diet. These methylation changes were associated with decreased transcriptional activity and increased disease severity. Runt-related transcription factor 3 (Runx3), a gene known to negatively regulate allergic airway disease, was found to be excessively methylated, and Runx3 mRNA and protein levels were suppressed in progeny exposed in utero to a high-methylation diet. Moreover, treatment with a demethylating agent increased Runx3 gene transcription, further supporting our claim that a methyl-rich diet can affect methylation status and consequent transcriptional regulation. Our findings indicate that dietary factors can modify the heritable risk of allergic airway disease through epigenetic mechanisms during a vulnerable period of fetal development in mice.

Chronic LPS inhalation causes emphysema-like changes in mouse lung that are associated with apoptosis

Lipopolysaccharide (LPS) is ubiquitous in the environment. Recent epidemiologic data suggest that occupational exposure to inhaled LPS can contribute to the progression of chronic obstructive pulmonary disease. To address the hypothesis that inhaled LPS can cause emphysema-like changes in mouse pulmonary parenchyma, we exposed C57BL/6 mice to aerosolized LPS daily for 4 weeks. By 3 days after the end of the 4-week exposure, LPS-exposed mice developed enlarged airspaces that persisted in the 4-week recovered mice. These architectural alterations in the lung are associated with enhanced type I, III, and IV procollagen mRNA as well as elevated levels of matrix metalloproteinase (MMP)-9 mRNA, all of which have been previously associated with human emphysema. Interestingly, MMP-9-deficient mice were not protected from the development of LPS-induced emphysema. However, we demonstrate that LPS-induced airspace enlargement was associated with apoptosis within the lung parenchyma, as shown by prominent TUNEL staining and elevated cleaved caspase 3 immunoreactivity. Antineutrophil antiserum-treated mice were partially protected from the lung destruction caused by chronic inhalation of LPS. Taken together, these findings demonstrate that inhaled LPS can cause neutrophil-dependent emphysematous changes in lung architecture that are associated with apoptosis and that these changes may be occurring through mechanisms different than those induced by cigarette smoke.

Bakery flour dust exposure causes non-allergic inflammation and enhances allergic airway inflammation in mice

BACKGROUND

Baker's asthma is one of the most commonly reported occupational lung diseases in countries where fresh bread is baked daily in large quantities, and is characterized by rhinitis, bronchial hyperresponsiveness, and reversible airflow obstruction. Epidemiological studies have identified pre-existing atopy as an important risk factor for developing baker's asthma, yet the aetiology and pathogenesis of baker's asthma remain poorly understood.

OBJECTIVE

We sought to develop a mouse model of baker's asthma that could be used to characterize the development and progression of baker's asthma.

METHODS

We were unable to sensitize mice to bakery flour dust or flour dust extract. We assessed total inflammatory cells, cellular differential, total serum IgE and the pro-inflammatory cytokine response to oropharyngeally instilled bakery flour dust or flour dust extract by itself or in the context of ovalbumin (OVA) sensitization and challenge.

RESULTS

Both bakery flour dust and flour dust extract consistently elicited a neutrophilic inflammation in a Toll-like receptor 4-independent manner; suggesting that endotoxin is not playing a role in the inflammatory response to flour dust. Moreover, bakery flour dust and dust extract significantly enhance the inflammatory response in OVA-sensitized and challenged mice.

CONCLUSIONS

Bakery flour dust and flour dust extract are strongly pro-inflammatory and can cause non-allergic airway inflammation and can enhance allergen-mediated airway inflammation.

Ambient ozone primes pulmonary innate immunity in mice

Exposure to ozone in air pollution in urban environments is associated with increases in pulmonary-related hospitalizations and mortality. Because ozone also alters clearance of pulmonary bacterial pathogens, we hypothesized that inhalation of ozone modifies innate immunity in the lung. To address our hypothesis, we exposed C57BL/6J mice to either free air or ozone, and then subsequently challenged with an aerosol of Escherichia coli LPS. Pre-exposure to ozone resulted in [corrected] higher concentrations of both total protein and proinflammatory cytokines in lung lavage fluid, enhanced LPS-mediated signaling in lung tissue, and higher concentrations of serum IL-6 following inhalation of LPS. However, pre-exposure to ozone dramatically reduced inflammatory cell accumulation to the lower airways in response to inhaled LPS. The reduced concentration of cells in the lower airways was associated with enhanced apoptosis of both lung macrophages and systemic circulating monocytes. Moreover, both flow cytometry and confocal microscopy indicate that inhaled ozone causes altered distribution of TLR4 on alveolar macrophages and enhanced functional response to endotoxin by macrophages. These observations indicate that ozone exposure increases both the pulmonary and the systemic biologic response to inhaled LPS by priming the innate immune system.

The IL-1 type 1 receptor is required for the development of LPS-induced airways disease

BACKGROUND

The contribution of IL-1beta signaling through the IL-1 type 1 receptor (IL-1R1) to the development of persistent LPS-induced airway disease has not been investigated.

OBJECTIVE

To determine the importance of signaling through the IL-1 type 1 receptor in the development of LPS-induced airway disease.

METHODS

We exposed IL-1R1-deficient (C57BL/6(IL-1RI-/-)) mice to an aerosol of LPS or filtered air for 1 day, 1 week, or 4 weeks.

RESULTS

After 4 weeks of LPS inhalation, C57BL/6(IL-1RI-/-) mice failed to develop significant submucosal thickening, whereas C57BL/6 mice had significantly thickened submucosa in small, medium, and large airways compared with those of unexposed control mice. Cell proliferation in the airways of both the 1-week and 4-week LPS-exposed C57BL/6(IL-1RI-/-) mice was significantly reduced compared with LPS-exposed C57BL/6 mice. mRNA for type III alpha-3 procollagen was significantly elevated over baseline in C57BL/6 yet remained unchanged compared with baseline in C57BL/6(IL-1RI-/-) mice after 1 week or 4 weeks of LPS inhalation. mRNA for tissue inhibitor of metalloprotease 1 in C57BL/6 mice in the 1-week and 4-week groups was significantly elevated over both control mice and C57BL/6(IL-1RI-/-) mice.

CONCLUSION

These data support the hypothesis that signaling through the IL-1 receptor modulates extracellular matrix homeostasis in response to inhaled LPS.

CLINICAL IMPLICATIONS

Attenuating IL-1R1-mediated signaling might be an effective therapy against the development of airway remodeling in chronic inflammatory diseases.

CD44 regulates macrophage recruitment to the lung in lipopolysaccharide-induced airway disease

LPS from bacteria is ubiquitous in the environment and can cause airway disease and modify allergic asthma. Identification of gene products that modulate the biologic response to inhaled LPS will improve our understanding of inflammatory airways disease. Previous work has identified quantitative trait loci for the response to inhaled LPS on chromosomes 2 and 11. In these regions, 28 genes had altered RNA expression after inhalation of LPS, including CD44, which was associated with differences in both TNF-alpha levels and neutrophil recruitment into the lung. It has previously been shown that CD44 can modulate macrophage recruitment in response to Mycobacterium tuberculosis, as well as clearance of neutrophils after lung injury with both bleomycin and live Escherichia coli bacteria. In this study, we demonstrate that the biologic response to inhaled LPS is modified by CD44. Macrophages failed to be recruited to the lungs of CD44-deficient animals at all time points after LPS exposure. CD44-deficient macrophages showed reduced motility in a Transwell migration assay, reduced ability to secrete the proinflammatory cytokine TNF-alpha, reduced in vivo migration in response to monocyte chemotactic protein-1, and diminished adhesion to vascular endothelia in the presence of TNF-alpha. In addition, CD44-deficient animals had 150% fewer neutrophils at 24 h and 50% greater neutrophils 48 h after LPS exposure. These results support the role of CD44 in modulating the biologic response to inhaled LPS.

CD14 is an essential mediator of LPS-induced airway disease

Chronic lipopolysaccharide (LPS) inhalation in rodents recapitulates many classic features of chronic obstructive pulmonary disease seen in humans, including airways hyperresponsiveness, neutrophilic inflammation, cytokine production in the lung, and small airways remodeling. CD14-deficient mice (C57BL/6(CD14-/-)) have an altered response to systemic LPS, and yet the role of CD14 in the response to inhaled LPS has not been defined. We observed that C57BL/6(CD14-/-) mice demonstrate no discernable physiological or inflammatory response to a single LPS inhalation challenge. However, the physiological (airways hyperresponsiveness) and inflammatory (presence of neutrophils and TNF-alpha in whole lung lavage fluid) responsiveness to inhaled LPS in C57BL/6(CD14-/-) mice was restored by instilling soluble CD14 intratracheally. Intratracheal instillation of wild-type macrophages into C57BL/6(CD14-/-) mice restored neutrophilic inflammation only and failed to restore airways hyperresponsiveness or TNF-alpha protein in whole lung lavage. These findings demonstrate that CD14 is critical to LPS-induced airway disease and that macrophage CD14 is sufficient to initiate neutrophil recruitment into the airways but that CD14 may need to interact with other cell types as well for the development of airways hyperresponsiveness and for cytokine production.

Using mouse genomics to understand idiopathic interstitial fibrosis

Idiopathic interstitial pneumonia represents a broad category of lung disorders characterized by scarring or fibrosis of the lung accompanied by varying degrees of inflammation. A number of important hypotheses based on clinical observations have substantially contributed to our understanding of the pathogenesis of the most insidious and devastating of the idiopathic interstitial pneumonias, idiopathic interstitial fibrosis (IIF). Patients with IIF usually present late in the course of their illness; thus, animal models of the early, preclinical stage of these diseases are needed. Although no model faithfully recapitulates the clinical course of disease or the histopathology observed in humans, all result in scarring of the lung and may therefore be used to understand the biological processes that contribute to this scarring. The purpose of this article is to summarize the application of mouse genetic and genomic tools to these models to advance our understanding of IIF and to describe emerging agnostic approaches to identifying genes important to the fibroproliferative component of IIF.

Leukocyte-derived IL-10 reduces subepithelial fibrosis associated with chronically inhaled endotoxin

Endotoxin (LPS), a Gram-negative cell wall component, has potent proinflammatory properties. Acute LPS exposure causes airway inflammation; chronic exposure causes airway hyperreactivity and remodeling. IL-10 is an important antiinflammatory cytokine, which is decreased in patients with airway disease, such as asthma and cystic fibrosis. To examine the physiologic and therapeutic role of IL-10 in acute and chronic LPS-induced airway disease. Mice were exposed to aerosolized LPS once or daily for 4 wk. Endpoints were airway inflammation, airway reactivity to methacholine, extracellular matrix protein expression, and histologic analysis. IL-10-deficient mice developed significantly enhanced airway cellularity and remodeling when compared with C57BL/6 mice after chronic LPS inhalation. However they demonstrated less airway hyperreactivity associated with higher inducible nitric oxide synthase (iNOS), endothelial NOS (eNOS), and lung lavage fluid nitrite levels. In a bone marrow transplantation model, the IL-10 antiinflammatory effect was dependent on the hematopoietic but not on the parenchymal IL-10 expression. Induced epithelial human IL-10 expression protected from the LPS effects and led to decreased collagen production. IL-10 attenuates chronic LPS-induced airway inflammation and remodeling. Physiologically, the antiinflammatory effect of IL-10 is mediated by hematopoietic cells. Therapeutically, adenovirus-driven expression of human IL-10 in airway epithelia is sufficient for its protective effect on inflammation and remodeling. The role of IL-10 on airway hyperreactivity is complex: IL-10 deficiency protects against LPS-induced hyperreactivity, and is associated with higher eNOS, iNOS, and airway nitrate levels.

Toll-like receptor 4 antagonist (E5564) prevents the chronic airway response to inhaled lipopolysaccharide

Although chronic inhalation of endotoxin or lipopolysaccharide (LPS) causes all of the classic features of asthma, including airway hyperreactivity, airway inflammation, and airway remodeling, the mechanisms involved in this process are not clearly understood. The objective of this study was to determine whether intratracheal treatment with LPS antagonist (E5564, a lipid A analog) prevented the development of chronic endotoxin-induced airway disease in a mouse model of environmental airway disease. Pretreatment with 10 and 100 microg of E5564 was found to inhibit the airway response (hyperreactivity and inflammation) for up to 48 h after the administration of the compound. Repeated dosing with 50 microg of E5564 intratracheally did not cause any measurable toxicity. Therefore, in a chronic experiment, mice were treated with either E5564 (50 microg) or vehicle three times weekly for 5 wk and simultaneously daily exposed to either LPS (4.65 +/- 0.30 microg/m3) or saline aerosol. E5564 was effective in decreasing the airway hyperreactivity to methacholine, the air space neutrophilia, the interleukin-6 in the lung lavage fluid, and the neutrophil infiltration of the airways 36 h after 5 wk of LPS inhalation. Less collagen deposition was observed in the airways of E5564-treated mice compared with vehicle-treated mice after a 4-wk recovery period. Our results indicate that E5564, a Toll-like receptor 4 antagonist, minimizes the physiological and biological effects of chronic LPS inhalation, suggesting a therapeutic role for competitive LPS antagonists in preventing or reducing endotoxin-induced environmental airway disease.

The critical role of hematopoietic cells in lipopolysaccharide-induced airway inflammation

Rapid and selective recruitment of neutrophils into the airspace in response to LPS facilitates the clearance of bacterial pathogens. However, neutrophil infiltration can also participate in the development and progression of environmental airway disease. Previous data have revealed that Toll-like receptor 4 (tlr4) is required for neutrophil recruitment to the lung after either inhaled or systemically administrated LPS from Escherichia coli. Although many cell types express tlr4, endothelial cell expression of tlr4 is specifically required to sequester neutrophils in the lung in response to systemic endotoxin. To identify the cell types requiring trl4 expression for neutrophil recruitment after inhaled LPS, we generated chimeric mice separately expressing tlr4 on either hematopoietic cells or on structural lung cells. Neutrophil recruitment into the airspace was completely restored in tlr4-deficient mice receiving wild-type bone marrow. By contrast, wild-type animals receiving tlr4-deficient marrow had dramatically reduced neutrophil recruitment. Moreover, adoptive transfer of wild-type alveolar macrophages also restored the ability of tlr4-deficient recipient mice to recruit neutrophils to the lung. These data demonstrate the critical role of hematopoietic cells and alveolar macrophages in initiating LPS-induced neutrophil recruitment from the vascular space to the airspace.

LPS binding protein is important in the airway response to inhaled endotoxin

BACKGROUND

Inhaled endotoxin is a risk factor for asthma exacerbation, and endotoxin inhalation by itself recapitulates many of the classical features of asthma in mice, including reversible airflow obstruction and inflammation, airways hyperresponsiveness, and airway remodeling.

OBJECTIVE

Our objective was to determine the importance of LPS binding protein (LBP) in the response to inhaled LPS.

METHODS

We challenged LBP-deficient mice (C57BL/6(LBP-/-)) and C57BL/6 mice with inhaled endotoxin for 4 hours, 5 days, or 4 weeks, followed by 3 days of recovery.

RESULTS

LBP in the lung was significantly increased in LPS-exposed C57BL/6 mice from all 3 groups. Only LPS-exposed C57BL/6 mice had significantly enhanced airway responsiveness to inhaled methacholine. Total lavage cells in LPS-exposed C57BL/6(LBP-/-) mice were significantly reduced compared with those seen in LPS-exposed C57BL/6 mice; however, the percentage of PMNs was similarly increased in both the C57BL/6 and C57BL/6(LBP-/-) mice. TNF-alpha, IL-1 beta, and IL-6 protein concentrations in whole-lung lavage fluid from C57BL/6(LBP-/-) mice were also significantly reduced when compared with those seen in C57BL/6 mice. In C57BL/6(LBP-/-) mice submucosal cell proliferation was significantly reduced in the 1-week group when compared with that seen in similarly exposed C57BL/6 mice. The 4-week exposed C57BL/6 mice had significantly thickened airway submucosa and significantly increased lavaged TGF-beta(1) protein compared with that seen in C57BL/6(LBP-/-) mice.

CONCLUSIONS

These findings indicate that LBP is one of the critical molecules regulating the acute and chronic airway response to inhaled LPS.

The role of Toll-like receptor 4 in environmental airway injury in mice

Inhalation of toxins commonly found in air pollution contributes to the development and progression of asthma and environmental airway injury. In this study, we investigated the requirement of toll-like receptor 4 (TLR4) in mice for pulmonary responses to three environmental toxins: aerosolized lipopolysaccharide, particulate matter (residual oil fly ash), and ozone. The physiologic and biologic responses to these toxins were evaluated by the extent of airway responsiveness, neutrophil recruitment to the lower respiratory tract, changes in inflammatory cytokines, and the concentration of protein in the lavage fluid. Genetically engineered, TLR4-deficient mice (C57BL/6(TLR4-/-)) were unresponsive to inhaled lipopolysaccharide, except for minimal increases in some inflammatory cytokines. In contrast, C57BL/6(TLR4-/-) mice did not differ from wild-type mice in their airway response to instilled residual oil fly ash or acute ozone exposure; however, we found that, despite a robust inflammatory response, C57BL/6(TLR4-/-) mice are protected against the development of airway hyperresponsiveness after subchronic ozone exposure. These data demonstrate in the mouse that the requirement of TLR4 for pulmonary inflammation depends on the nature of the toxin and appears specific to toxin and exposure conditions.

Fibrinolysis in LPS-induced chronic airway disease

To examine the role of the fibrinolytic system in LPS-induced airway disease, we compared the effect of a chronic LPS challenge in plasminogen activator inhibitor-deficient (C57BL/6JPAI-1-/-) mice and wild-type (WT) C57BL/6J mice. Physiological and biological assessments were performed, immediately after, and 4 wk after an 8-wk exposure to LPS or saline. Immediately after the LPS exposure, WT mice had increased estimates of airway reactivity to methacholine compared with C57BL/6JPAI-1-/- mice; however, airway inflammation was similar in both LPS-exposed groups. Significant increases in both active transforming growth factor (TGF)-beta1 and active matrix metalloproteinase (MMP)-9 was detected after LPS exposure in WT but not C57BL/6JPAI-1-/- mice. C57BL/6JPAI-1-/- mice showed significantly less TGF-beta1 in the lavage and higher MMP-9 in the lung tissue than WT mice at the end of exposure and 4 wk later. After LPS exposure, both WT and C57BL/6JPAI-1-/- mice had substantial expansion of the subepithelial area of the medium [diameter (d) = 90-129 microm]- and large (d > 129 microm)-size airways when compared with saline-exposed mice. Subepithelial fibrin deposition was prevalent in WT mice but diminished in C57BL/6JPAI-1-/-. PAI-1 expression by nonciliated bronchial epithelial cells was enhanced in LPS-exposed WT mice compared with the saline-exposed group. Four weeks after LPS inhalation, airway hyperreactivity and the expansion of the subepithelial area in the medium and large airways persisted in WT but not C57BL/6JPAI-1-/- mice. We conclude that an active fibrinolytic system can substantially alter the development and resolution of the postinflammatory airway remodeling observed after chronic LPS inhalation.

Subchronic endotoxin inhalation causes persistent airway disease

The endotoxin component of organic dusts causes acute reversible airflow obstruction and airway inflammation. To test the hypothesis that endotoxin alone causes airway remodeling, we have compared the response of two inbred mouse strains to subchronic endotoxin exposure. Physiological and biological parameters were evaluated after 1 day, 5 days, or 8 wk of exposure to endotoxin [lipopolysaccharide (LPS)] in endotoxin-sensitive (C3HeB/FeJ) and endotoxin-resistant (C3H/HeJ) mice. After 5 days or 8 wk of LPS exposure, only C3HeB/FeJ had elevated airway hyperreactivity to inhaled methacholine. Only the C3HeB/FeJ mice had significant inflammation of the lower respiratory tract after 1 day, 5 days, or 8 wk of LPS exposure. Stereological measurements of small, medium, and large airways indicated that an 8-wk exposure to LPS resulted in expansion of the submucosal area only in the C3HeB/FeJ mice. Cell proliferation as measured by bromodeoxyuridine incorporation contributed to the expansion of the submucosa and was only significantly elevated in C3HeB/FeJ mice actively exposed to LPS. C3HeB/FeJ mice had significantly elevated levels of interleukin-1beta protein in whole lung lavage after 1 day and 5 days of LPS exposure and significantly elevated protein levels of total and active transforming growth factor-beta1 in whole lung lavage fluid after 5 days of LPS exposure. Our findings demonstrate that subchronic inhalation of LPS results in the development of persistent airway disease in endotoxin-responsive mice.

Neutrophils play a critical role in development of LPS-induced airway disease

We investigated the role of neutrophils in the development of endotoxin-induced airway disease via systemic neutrophil depletion of C3H/HeBFeJ mice and coincident inhalation challenge with lipopolysaccharide (LPS) over a 4-wk period. Mice were made neutropenic with intraperitoneal injections of neutrophil antiserum before and throughout the exposure period. Experimental conditions included LPS-exposed, antiserum-treated; LPS-exposed, control serum-treated; air-exposed, antiserum-treated; and air-exposed, control serum-treated groups. Physiological, biological, and morphological assessments were performed after a 4-wk exposure and again after a 4-wk recovery period. After the 4-wk exposure, LPS-induced inflammation of the lower airways was significantly attenuated in the neutropenic mice, although airway responsiveness (AR) to methacholine (MCh) remained unchanged. After the recovery period, LPS-exposed neutrophil-replete mice had increased AR to MCh when compared with the LPS-exposed neutropenic animals. Morphometric data indicate that the 4-wk exposure to LPS leads to a substantial expansion of the subepithelial area of the medium-sized airways (90-129 microm diameter) in nonneutropenic mice but not neutropenic mice, and this difference persisted even after the recovery period. Expression of bronchial epithelial and subepithelial transforming growth factor-beta1 (TGF-beta1) was diminished in the challenged neutropenic mice compared with the neutrophil-sufficient mice. These studies demonstrate that neutrophils play a critical role in the development of chronic LPS-induced airway disease.

Primary lung fibroblasts from the 129 mouse strain exhibit reduced growth factor responsiveness in vitro

Lung fibroblasts are activated to proliferate and produce connective tissue during the development of lung fibrosis. The 129 mouse strain does not develop asbestos-induced fibrogenesis, whereas several other inbred strains rapidly respond to inhaled fibers. Thus, in the experiments presented here, we have compared the responses of primary lung fibroblasts isolated from 129 and C57BL/6 mice. The 129 and C57BL/6 mouse lung fibroblasts (MLFs) proliferated similarly in 10% fetal bovine serum (FBS), but after quiescence, the 129 MLFs grew more slowly in serum and responded less to the BB isoform of platelet-derived growth factor. This is consistent with our finding that the mRNA for the PDGF-a receptor exhibits reduced expression by the 129 MLFs compared to those from C57BL/6 mice. Fibroblasts from the SJL mouse strain, from a C57BL/6-129 hybrid, and from the 3T3 cell line all proliferated more vigorously than MLFs from the 129 mice. In addition, the 129 MLFs exhibited reduced expression of alpha1 procollagen mRNA consequent to treatment with tumor necrosisfactor alpha. Based on these new findings, we suggest that the reduced fibrogenesis in asbestos-exposed 129 mice is due to an intrinsic difference in the ability of the lung fibroblasts to respond to peptide growth factors.

Reduced tumor necrosis factor-alpha and transforming growth factor-beta1 expression in the lungs of inbred mice that fail to develop fibroproliferative lesions consequent to asbestos exposure

Tumor necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta mRNA and protein expression and the degree of fibroproliferative response to inhaled asbestos fibers are clearly reduced in the 129 inbred mouse strain as compared with typical fibrogenesis observed in the C57BL/6 inbred strain. The C57BL/6 mice showed prominent lesions at bronchiolar-alveolar duct (BAD) junctions where asbestos fibers deposit and responding macrophages accumulate. The 129 mice, however, were generally indistinguishable from controls even though the numbers of asbestos fibers deposited in the lungs of all exposed animals were the same. Quantitative morphometry of H&E-stained lung sections comparing the C57BL/6 and 129 mice showed significantly less mean cross-sectional area of the BAD junctions in the 129 animals, apparent at both 48 hours and 4 weeks after exposure. In addition, fewer macrophages had accumulated at these sites in the 129 mice. Nuclear bromodeoxyuridine immunostaining demonstrated that the number of proliferating cells at first alveolar duct bifurcations and in adjacent terminal bronchioles was significantly reduced in the 129 strain compared with C57BL/6 mice at 48 hours after exposure (P < 0.01). TNF-alpha and TGF-beta1 gene expression, as measured by in situ hybridization, was reduced in the 129 mice at 48 hours after exposure, and expression of TNF-alpha and TGF-beta1 protein, as measured by immunohistochemistry, was similarly reduced or absent in the 129 animals. We postulate that the protection afforded the 129 mice is related to reduction of growth factor expression by the bronchiolar-alveolar epithelium and lung macrophages.

TNF-alpha receptor knockout mice are protected from the fibroproliferative effects of inhaled asbestos fibers

We have demonstrated that C57BL/6-129 hybrid mice with genes for both the 55kd and 75kd receptors for TNF-alpha knocked out (TNF-alphaRKO) fail to develop fibroproliferative lesions after asbestos exposure. There is good evidence that TNF-alpha plays a major role in mediating interstitial pulmonary fibrosis. Our findings support this view and we present here new data obtained by in situ hybridization showing that expression of the genes coding for transforming growth factor alpha (TGF-alpha) and platelet-derived growth factor A-chain (PDGF-A) is reduced in the TNF-alphaRKO mice compared with control animals. In accordance with this observation, data on bromodeoxyuridine (BrdU) incorporation in the lungs of the TNF-alphaRKO mice show no increases over unexposed control animals. In contrast, wild-type control mice exposed to asbestos exhibit 15- to 20-fold increases in BrdU uptake and consequently develop fibrogenic lesions. Even though the levels of TNF-alpha gene expression and protein production were increased in the asbestos-exposed TNF-alphaRKO mice, the lack of receptor signaling protected the mice from developing fibroproliferative lesions. We agree with the view that TNF-alpha is essential for the development of interstitial pulmonary fibrosis and postulate that TNF-alpha mediates its effects through activation of other growth factors such as PDGF and TGF-alpha that control cell growth and matrix production.