Disparate oxidant gene expression of airway epithelium compared to alveolar macrophages in smokers

Expression of endocannabinoid system components in human airway epithelial cells: impact of sex and chronic respiratory disease status

Cannabis smoking is the dominant route of delivery, with the airway epithelium functioning as the site of first contact. The endocannabinoid system is responsible for mediating the physiological effects of inhaled phytocannabinoids. The expression of the endocannabinoid system in the airway epithelium and contribution to normal physiological responses remains to be defined. To begin to address this knowledge gap, a curated dataset of 1090 unique human bronchial brushing gene expression profiles was created. The dataset included 616 healthy subjects, 136 subjects with asthma, and 338 subjects with COPD. A 32-gene endocannabinoid signature was analysed across all samples with sex and disease-specific analyses performed. Immunohistochemistry and immunoblots were performed to probe in situ and in vitro protein expression. CB₁, CB₂, and TRPV1 protein signal is detectable in human airway epithelial cells in situ and in vitro, justifying examining the downstream endocannabinoid pathway. Sex status was associated with differential expression of 7 of 32 genes. In contrast, disease status was associated with differential expression of 21 of 32 genes in people with asthma and 26 of 32 genes in people with COPD. We confirm at the protein level that TRPV1, the most differentially expressed candidate in our analyses, was upregulated in airway epithelial cells from people with asthma relative to healthy subjects. Our data demonstrate that the endocannabinoid system is expressed in human airway epithelial cells with expression impacted by disease status and minimally by sex. The data suggest that cannabis consumers may have differential physiological responses in the respiratory mucosa.

Analysis of the Status of the Cutaneous Endogenous and Exogenous Antioxidative System of Smokers and the Short-Term Effect of Defined Smoking Thereon

The daily consumption of tobacco products leads to a boost in free radical production in tissues, promoting the risk for malignancies, metabolic alterations and chronic-inflammatory diseases. This study aimed to broaden the knowledge of the status of the antioxidative (AO) system in the skin, compared to the blood, of healthy appearing smokers. Both, the basic status compared to non-smokers and the short-term impact of controlled cigarette consumption in smokers were analyzed. Our study showed that the basic level of the AO system of smokers significantly differed from that of non-smokers. As determined by resonant Raman spectroscopy (RRS), the levels of exogenous AOs were decreased in both, the skin, in vivo (β-carotene and lycopene), and blood plasma (β-carotene only). In contrast, the levels of glutathione (GSH), the prototypical endogenous AO, which were analyzed by fluorimetric assays in cutaneous tape strips and blood plasma, were increased in the skin, although unchanged in the blood of smokers. Elevated cutaneous GSH levels were reflected by an elevated overall radical scavenging activity in the skin, as quantified by non-invasive electron paramagnetic resonance (EPR) spectroscopy. Analysis of the expression of selected stress-associated genes in blood immune cells by quantitative RT-PCR in subgroups of non-smokers and smokers additionally demonstrated the downregulation of AKR1C2 in smokers, and its negative correlation with blood plasma levels of the protective immune mediator interleukin-22, assessed by the ELISA technique. Controlled cigarette consumption did not alter exogenous or endogenous AOs in the skin of smokers, but decreased lycopene levels in blood plasma. Moreover, there was a decline in blood IL-22 levels, while no relevant response of blood cell gene expressions was found after the considered short time. Our data therefore demonstrate a strengthened endogenous AO status in the skin of smokers, which may indicate a long-term adaptation to chronic oxidative stress in this specific organ. While this effect was not clearly visible in the blood, this compartment seems to be useful as an immediate indicator of the body's AO consumption. Moreover, decreased levels of AKR1C2, which we show for the first time to be expressed in immune cells, may be a candidate marker for long-term smoking. In addition, this study demonstrates that the rate constant of a spin probe decline determined by EPR spectroscopy mainly represents the endogenous AO status of a tissue.

Cigarette smoke and glutathione: Focus on in vitro cell models

Cigarette smoke (CS) is one of the most important preventable risk factors for the development of respiratory diseases, cardiovascular diseases, stroke, and various types of cancer. Due to its high intracellular concentration and central role in maintaining the cellular redox state, glutathione (GSH) is one of the key players in several enzymatic and non-enzymatic reactions necessary for protecting cells against CS-induced oxidative stress. A plethora of in vitro cell models have been used over the years to assess the effects of CS on intracellular GSH and its disulphide forms, i.e. glutathione disulphide (GSSG) and S-glutathionylated proteins. In this review, we described the effects of cell exposure to CS on cellular GSH and formation of its oxidized forms and adducts (GSH-conjugates). We also discussed the limitations and relevance of in vitro cell models of exposure to CS and critically assessed the congruence between smokers and in vitro cell models. What emerges clearly is that results obtained in vitro should be interpreted with extreme caution, bearing in mind the limitations of the specific cell model used. Despite this, in vitro cell models remain important tools in the assessment of CS-induced oxidative damage.

Systems biology analysis of publicly available transcriptomic data reveals a critical link between AKR1B10 gene expression, smoking and occurrence of lung cancer

Background

Cigarette smoking is associated with an increased risk of developing respiratory diseases and various types of cancer. Early identification of such unfavorable outcomes in patients who smoke is critical for optimizing personalized medical care.

Methods

Here, we perform a comprehensive analysis using Systems Biology tools of publicly available data from a total of 6 transcriptomic studies, which examined different specimens of lung tissue and/or cells of smokers and nonsmokers to identify potential markers associated with lung cancer.

Results

Expression level of 22 genes was capable of classifying smokers from non-smokers. A machine learning algorithm revealed that AKR1B10 was the most informative gene among the 22 differentially expressed genes (DEGs) accounting for the classification of the clinical groups. AKR1B10 expression was higher in smokers compared to non-smokers in datasets examining small and large airway epithelia, but not in the data from a study of sorted alveolar macrophages. Moreover, AKR1B10 expression was relatively higher in lung cancer specimens compared to matched healthy tissue obtained from nonsmoking individuals. Although the overall accuracy of AKR1B10 expression level in distinction between cancer and healthy lung tissue was 76%, with a specificity of 98%, our results indicated that such marker exhibited low sensitivity, hampering its use for cancer screening such specific setting.

Conclusion

The systematic analysis of transcriptomic studies performed here revealed a potential critical link between AKR1B10 expression, smoking and occurrence of lung cancer.

Compartmentalization of anti-oxidant and anti-inflammatory gene expression in current and former smokers with COPD

BACKGROUND

Patients with chronic obstructive pulmonary disease (COPD) have high oxidative stress associated with the severity of the disease. Nuclear factor erythroid-2 related factor 2 (Nrf2)-directed stress response plays a critical role in the protection of lung cells to oxidative stress by upregulating antioxidant genes in response to tobacco smoke. There is a critical gap in our knowledge about Nrf-2 regulated genes in active smokers and former-smokers with COPD in different cell types from of lungs and surrogate peripheral tissues.

METHODS

We compared the expression of Nrf2 and six of its target genes in alveolar macrophages, nasal, and bronchial epithelium and peripheral blood mononuclear cells (PBMCs) in current and former smokers with COPD. We compared cell-type specific of Nrf2 and its target genes as well as markers of oxidative and inflammatory stress.

RESULTS

We enrolled 89 patients; expression all Nrf2 target gene measured were significantly higher in the bronchial epithelium from smokers compared to non-smokers. None were elevated in alveolar macrophages and only one was elevated in each of the other compartments.

CONCLUSION

Bronchial epithelium is the most responsive tissue for transcriptional activation of Nrf2 target genes in active smokers compared to former-smokers with COPD that correlated with oxidative stress and inflammatory markers. There were no consistent trends in gene expression in other cell types tested.

TRIAL REGISTRATION

Clinicaltrials.gov : NCT01335971.

Pathway-analysis of published genome-wide association studies of lung cancer: A potential role for the CYP4F3 locus

The fatty acids (FAs) metabolism is suggested to play a pivotal role in the development of lung cancer, and we explored that by conducting a pathway-based analysis. We performed a meta-analysis of published datasets of six genome wide association studies (GWASs) from the Transdisciplinary Research in Cancer of the Lung (TRICL) consortium, which included 12 160 cases with lung cancer and 16 838 cancer-free controls. A total of 30 722 single-nucleotide polymorphisms (SNPs) from 317 genes relevant to FA metabolic pathways were identified. An additional dataset from the Harvard Lung Cancer Study with 984 cases and 970 healthy controls was also added to the final meta-analysis. In the initial meta-analysis, 26 of 28 SNPs that passed false discovery rate multiple tests were mapped to the CYP4F3 gene. Among the 26 top ranked hits was a proxy SNP, CYP4F3 rs4646904 (P = 8.65 × 10-6 , FDR = 0.018), which is suggested to change splicing pattern/efficiency and to be associated with gene expression levels. However, after adding data of rs4646904 from the Harvard GWAS, the significance in the combined analysis was reduced to P = 3.52 × 10-3 [odds ratio (OR) = 1.07, 95% confidence interval (95%CI) = 1.03-1.12]. Interestingly, the small Harvard dataset also pointed to the same direction of the association in subgroups of smokers (OR = 1.07) and contributed to a combined OR of 1.13 (95% CI = 1.06-1.20, P = 6.70 × 10-5 ). The results suggest that a potentially functional SNP in CYP4F3 (rs4646904) may contribute to the etiology of lung cancer, especially in smokers. Additional mechanistic studies are warranted to unravel the potential biological significance of the finding.

Are healthy smokers really healthy?

Cigarette smoke contains more than 4500 chemicals which have toxic, mutagenic and carcinogenic effects. Strong evidences have shown that current smokers take a significantly higher risk of cardiovascular diseases, chronic obstructive pulmonary disease (COPD) and lung cancer than nonsmokers. However, less attention has been paid to the smoking induced abnormalities in the individuals defined as healthy smokers who are normal with spirometry, radiographic images, routine physical exam and categorized as healthy control group in many researches. Actually, ‘healthy smokers’ are not healthy. This narrative review focuses on the smoking related pathophysiologic changes mainly in the respiratory system of healthy smokers, including inflammation and immune changes, genetic alterations, structural changes and pulmonary dysfunction.

Whole exome sequencing identifies novel candidate genes that modify chronic obstructive pulmonary disease susceptibility

Background

Chronic obstructive pulmonary disease (COPD) is characterized by an irreversible airflow limitation in response to inhalation of noxious stimuli, such as cigarette smoke. However, only 15–20 % smokers manifest COPD, suggesting a role for genetic predisposition. Although genome-wide association studies have identified common genetic variants that are associated with susceptibility to COPD, effect sizes of the identified variants are modest, as is the total heritability accounted for by these variants. In this study, an extreme phenotype exome sequencing study was combined with in vitro modeling to identify COPD candidate genes.

Results

We performed whole exome sequencing of 62 highly susceptible smokers and 30 exceptionally resistant smokers to identify rare variants that may contribute to disease risk or resistance to COPD. This was a cross-sectional case-control study without therapeutic intervention or longitudinal follow-up information. We identified candidate genes based on rare variant analyses and evaluated exonic variants to pinpoint individual genes whose function was computationally established to be significantly different between susceptible and resistant smokers. Top scoring candidate genes from these analyses were further filtered by requiring that each gene be expressed in human bronchial epithelial cells (HBECs). A total of 81 candidate genes were thus selected for in vitro functional testing in cigarette smoke extract (CSE)-exposed HBECs. Using small interfering RNA (siRNA)-mediated gene silencing experiments, we showed that silencing of several candidate genes augmented CSE-induced cytotoxicity in vitro.

Conclusions

Our integrative analysis through both genetic and functional approaches identified two candidate genes (TACC2 and MYO1E) that augment cigarette smoke (CS)-induced cytotoxicity and, potentially, COPD susceptibility.

Electronic supplementary material

The online version of this article (doi:10.1186/s40246-015-0058-7) contains supplementary material, which is available to authorized users.

Role of nicotinamide adenine dinucleotide phosphate oxidase in mediating vesicant-induced interleukin-6 secretion in human airway epithelial cells

Aerosolized exposure to the chemical warfare vesicant sulfur mustard and its analog nitrogen mustard (HN2) is known to induce airway lesions associated with secretion of proinflammatory cytokines such as IL-6. We have shown recently that HN2 challenge induced IL-6 secretion in human airway epithelial cells, a process mediated via epidermal growth factor receptor (EGFR) signaling. In this study, we evaluated the role of redox signaling in regulating HN2-induced, EGFR-mediated IL-6 secretions in primary cultured normal human bronchial epithelial cells (NHBECs) in the air-liquid interface. HN2-induced EGFR phosphorylation and IL-6 secretion in NHBECs were inhibited by the antioxidant N-acetyl-L-cysteine (NAC) and by the flavoprotein inhibitor diphenyleneiodonium chloride (DPI). These observations suggested that the inflammatory response in NHBECs after HN2 challenge was mediated via oxidative stress. HN2 exposure induced increased reactive oxygen species (ROS) formation and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity in NHBECs, findings that were inhibited by NAC and DPI treatment. Among NADPH oxidase isoforms, mRNA expression of dual oxidase (DUOX)1 and DUOX2 were up-regulated by HN2. Furthermore, knockdown of DUOX1 or DUOX2 by short hairpin RNA resulted in inhibition of ROS generation, EGFR pathway activation, and IL-6 secretion in NHBECs. These results provide evidence that redox signaling plays a pivotal role in the HN2-induced airway inflammation and underscore the importance of DUOX1 and DUOX2 in vesicant-induced IL-6 secretion in human airway epithelial cells.

Coordinated DNA methylation and gene expression changes in smoker alveolar macrophages: specific effects on VEGF receptor 1 expression

Cigarette smoking is implicated in numerous diseases, including emphysema and lung cancer. The clinical expression of lung disease in smokers is not well explained by currently defined variations in gene expression or simple differences in smoking exposure. Alveolar macrophages play a critical role in the inflammation and remodeling of the lung parenchyma in smoking-related lung disease. Significant gene expression changes in alveolar macrophages from smokers have been identified. However, the mechanism for these changes remains unknown. One potential mechanism for smoking-altered gene expression is via changes in cytosine methylation in DNA regions proximal to gene-coding sequences. In this study, alveolar macrophage DNA from heavy smokers and never smokers was isolated and methylation status at 25,000 loci determined. We found differential methylation in genes from immune-system and inflammatory pathways. Analysis of matching gene expression data demonstrated a parallel enrichment for changes in immune-system and inflammatory pathways. A significant number of genes with smoking-altered mRNA expression had inverse changes in methylation status. One gene highlighted by this data was the FLT1, and further studies found particular up-regulation of a splice variant encoding a soluble inhibitory form of the receptor. In conclusion, chronic cigarette smoke exposure altered DNA methylation in specific gene promoter regions in human alveolar macrophages.

RNA-Seq quantification of the human small airway epithelium transcriptome

Background

The small airway epithelium (SAE), the cell population that covers the human airway surface from the 6^th generation of airway branching to the alveoli, is the major site of lung disease caused by smoking. The focus of this study is to provide quantitative assessment of the SAE transcriptome in the resting state and in response to chronic cigarette smoking using massive parallel mRNA sequencing (RNA-Seq).

Results

The data demonstrate that 48% of SAE expressed genes are ubiquitous, shared with many tissues, with 52% enriched in this cell population. The most highly expressed gene, SCGB1A1, is characteristic of Clara cells, the cell type unique to the human SAE. Among other genes expressed by the SAE are those related to Clara cell differentiation, secretory mucosal defense, and mucociliary differentiation. The high sensitivity of RNA-Seq permitted quantification of gene expression related to infrequent cell populations such as neuroendocrine cells and epithelial stem/progenitor cells. Quantification of the absolute smoking-induced changes in SAE gene expression revealed that, compared to ubiquitous genes, more SAE-enriched genes responded to smoking with up-regulation, and those with the highest basal expression levels showed most dramatic changes. Smoking had no effect on SAE gene splicing, but was associated with a shift in molecular pattern from Clara cell-associated towards the mucus-secreting cell differentiation pathway with multiple features of cancer-associated molecular phenotype.

Conclusions

These observations provide insights into the unique biology of human SAE by providing quantit-ative assessment of the global transcriptome under physiological conditions and in response to the stress of chronic cigarette smoking.

Biologic phenotyping of the human small airway epithelial response to cigarette smoking

Background

The first changes associated with smoking are in the small airway epithelium (SAE). Given that smoking alters SAE gene expression, but only a fraction of smokers develop chronic obstructive pulmonary disease (COPD), we hypothesized that assessment of SAE genome-wide gene expression would permit biologic phenotyping of the smoking response, and that a subset of healthy smokers would have a “COPD-like” SAE transcriptome.

Methodology/Principal Findings

SAE (10th–12th generation) was obtained via bronchoscopy of healthy nonsmokers, healthy smokers and COPD smokers and microarray analysis was used to identify differentially expressed genes. Individual responsiveness to smoking was quantified with an index representing the % of smoking-responsive genes abnormally expressed (I_SAE), with healthy smokers grouped into “high” and “low” responders based on the proportion of smoking-responsive genes up- or down-regulated in each smoker. Smokers demonstrated significant variability in SAE transcriptome with I_SAE ranging from 2.9 to 51.5%. While the SAE transcriptome of “low” responder healthy smokers differed from both “high” responders and smokers with COPD, the transcriptome of the “high” responder healthy smokers was indistinguishable from COPD smokers.

Conclusion/Significance

The SAE transcriptome can be used to classify clinically healthy smokers into subgroups with lesser and greater responses to cigarette smoking, even though these subgroups are indistinguishable by clinical criteria. This identifies a group of smokers with a “COPD-like” SAE transcriptome.

Transcriptomic studies of the airway field of injury associated with smoking-related lung disease

The "field of injury" hypothesis proposes that exposure to an inhaled insult such as cigarette smoke elicits a common molecular response throughout the respiratory tract. This response can therefore be quantified in any airway tissue, including readily accessible epithelial cells in the bronchus, nose, and mouth. High-throughput technologies, such as whole-genome gene expression microarrays, can be employed to catalog the physiological consequences of such exposures in the airway epithelium. Pulmonary diseases such as chronic obstructive pulmonary disease, lung cancer, and asthma are also thought to be associated with a field of injury, and in patients with these diseases, airway epithelial cells can be a useful surrogate for diseased tissue that is often difficult to obtain. Global measurement of mRNA and microRNA expression in these cells can provide useful information about the molecular pathogenesis of such diseases and may be useful for diagnosis and for predicting prognosis and response to therapy. In this review, our aim is to summarize the history and state of the art of such "transcriptomic" studies in the human airway epithelium, especially in smoking and smoking-related lung diseases, and to highlight future directions for this field.

Alveolar macrophage gene expression is altered in the setting of alcohol use disorders

BACKGROUND

Alcohol use disorders (AUDs) are associated with an increased susceptibility to a variety of common and devastating pulmonary diseases including community- and hospital-acquired pneumonias, as well as the acute respiratory distress syndrome (ARDS). Alveolar macrophages play an important role in preventing the development of these disorders through maintaining lung sterility and resolving lung inflammation. Although alcohol exposure has been associated with aberrant alveolar macrophage function in animal models, the clinical relevance of these observations in humans is not established. Therefore, we sought to determine the effects of AUDs on human alveolar macrophage gene expression.

METHODS

Whole genome microarray analysis was performed on alveolar macrophages obtained by bronchoalveolar lavage from a test cohort of subjects with AUDs (n = 7), and controls (n = 7) who were pair-matched on age, gender, and smoking. Probe set expression differences in this cohort were validated by real-time reverse transcription-polymerase chain reaction (RT RT-PCR). Functional analysis with web-based bioinformatics tools was utilized with microarray data to assess differentially expressed candidate genes (p < 0.01) based on alcohol consumption. Alveolar macrophage mRNA samples from a second cohort of subjects with AUDs (n = 7) and controls (n = 7) were used to confirm gene expression differences related to AUDs.

RESULTS

In both the test and the confirmatory cohorts, AUDs were associated with upregulation of alveolar macrophage gene expression related to apoptosis, including perforin-1, granzyme A, and CXCR4 (fusin). Pathways governing the regulation of progression through cell cycle and immune response were also affected, as was upregulation of gene expression for mitochondrial superoxide dismutase. Overall, 12 genes' expression was affected by AUDs independent of smoking.

CONCLUSIONS

Alcohol use disorders are associated with unique changes in human alveolar macrophage gene expression. Novel therapies targeting alveolar macrophage gene expression in the setting of AUDs may prove to be clinically useful in limiting susceptibility for pulmonary disorders in these individuals.

The air-liquid interface and use of primary cell cultures are important to recapitulate the transcriptional profile of in vivo airway epithelia

Organotypic cultures of primary human airway epithelial cells have been used to investigate the morphology, ion and fluid transport, innate immunity, transcytosis, infection, inflammation, signaling, cilia, and repair functions of this complex tissue. However, we do not know how closely these cultures resemble the airway surface epithelium in vivo. In this study, we examined the genome-wide expression profile of tracheal and bronchial human airway epithelia in vivo and compared it with the expression profile of primary cultures of human airway epithelia grown at the air-liquid interface. For comparison, we also investigated the expression profile of Calu-3 cells grown at the air-liquid interface and primary cultures of human airway epithelia submerged in nutrient media. We found that the transcriptional profile of differentiated primary cultures grown at the air-liquid interface most closely resembles that of in vivo airway epithelia, suggesting that the use of primary cultures and the presence of an air-liquid interface are important to recapitulate airway epithelia biology. We describe a high level of similarity between cells of tracheal and bronchial origin within and between different human donors, which suggests a very robust expression profile that is specific to airway cells.

Similar gene expression profiles in smokers and patients with moderate COPD

Chronic obstructive pulmonary disease (COPD) is characterized by multiple cellular and structural changes affecting the airways, lung parenchyma and vasculature, some of which are also identified in smokers without COPD. The molecular mechanisms underlying these changes remain poorly understood. With the aim of identifying mediators potentially implicated in the pathogenic processes that occur in COPD and their potential relationship with cigarette smoking, we evaluated the mRNA expression of genes involved in inflammation, tissue remodeling and vessel maintenance. Lung tissue samples were obtained from 60 patients who underwent lung resection (nonsmokers, n=12; smokers, n=12; and moderate COPD, n=21) or lung transplant (severe-to-very severe COPD, n=15). PCR arrays containing 42 genes coding for growth factors/receptors, cytokines, metalloproteinases, adhesion molecules, and vessel maintenance mediators were used. Smoking-induced changes include the up-regulation of inflammatory genes (IL-1β, IL-6, IL-8, CCL2, and CCL8) and the decreased expression of growth factor/receptor genes (BMPR2, CTGF, FGF1, KDR and TEK) and genes coding for vessel maintenance factors (EDNRB). All these genes exhibited a similar profile in moderate COPD patients. The up-regulation of MMP1 and MMP9 was the main change associated with COPD. Inflammatory genes as well as the endothelial selectin gene (SELE) were down-regulated in patients with more severe COPD. Clustering analysis revealed a closer relationship between moderate COPD and smokers than between both subsets of COPD patients for this selected set of genes. The study reveals striking similarities between smokers and COPD patients with moderate disease emphasizing the crucial role of cigarette smoking in the genesis of these changes, and provides additional evidence of the involvement of the matrix metalloproteinase's in the remodeling process of the lung in COPD.