Cigarette smoking reprograms apical junctional complex molecular architecture in the human airway epithelium in vivo

Extracellular Vesicles from Airway Secretions: New Insights in Lung Diseases

Lung diseases (LD) are one of the most common causes of death worldwide. Although it is known that chronic airway inflammation and excessive tissue repair are processes associated with LD such as asthma, chronic obstructive pulmonary disease (COPD) or idiopathic pulmonary fibrosis (IPF), their specific pathways remain unclear. Extracellular vesicles (EVs) are heterogeneous nanoscale membrane vesicles with an important role in cell-to-cell communication. EVs are present in general biofluids as plasma or urine but also in secretions of the airway as bronchoalveolar lavage fluid (BALF), induced sputum (IS), nasal lavage (NL) or pharyngeal lavage. Alterations of airway EV cargo could be crucial for understanding LD. Airway EVs have shown a role in the pathogenesis of some LD such as eosinophil increase in asthma, the promotion of lung cancer in vitro models in COPD and as biomarkers to distinguishing IPF in patients with diffuse lung diseases. In addition, they also have a promising future as therapeutics for LD. In this review, we focus on the importance of airway secretions in LD, the pivotal role of EVs from those secretions on their pathophysiology and their potential for biomarker discovery.

Cellular and functional heterogeneity of the airway epithelium

The airway epithelium protects us from environmental insults, which we encounter with every breath. Not only does it passively filter large particles, it also senses potential danger and alerts other cells, including immune and nervous cells. Together, these tissues orchestrate the most appropriate response, balancing the need to eliminate the danger with the risk of damage to the host. Each cell subset within the airway epithelium plays its part, and when impaired, may contribute to the development of respiratory disease. Here we highlight recent advances regarding the cellular and functional heterogeneity along the airway epithelium and discuss how we can use this knowledge to design more effective, targeted therapeutics.

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.

Invited review: human air-liquid-interface organotypic airway tissue models derived from primary tracheobronchial epithelial cells-overview and perspectives

The lung is an organ that is directly exposed to the external environment. Given the large surface area and extensive ventilation of the lung, it is prone to exposure to airborne substances, such as pathogens, allergens, chemicals, and particulate matter. Highly elaborate and effective mechanisms have evolved to protect and maintain homeostasis in the lung. Despite these sophisticated defense mechanisms, the respiratory system remains highly susceptible to environmental challenges. Because of the impact of respiratory exposure on human health and disease, there has been considerable interest in developing reliable and predictive in vitro model systems for respiratory toxicology and basic research. Human air-liquid-interface (ALI) organotypic airway tissue models derived from primary tracheobronchial epithelial cells have in vivo–like structure and functions when they are fully differentiated. The presence of the air-facing surface allows conducting in vitro exposures that mimic human respiratory exposures. Exposures can be conducted using particulates, aerosols, gases, vapors generated from volatile and semi-volatile substances, and respiratory pathogens. Toxicity data have been generated using nanomaterials, cigarette smoke, e-cigarette vapors, environmental airborne chemicals, drugs given by inhalation, and respiratory viruses and bacteria. Although toxicity evaluations using human airway ALI models require further standardization and validation, this approach shows promise in supplementing or replacing in vivo animal models for conducting research on respiratory toxicants and pathogens.

m6A RNA methylation regulators could contribute to the occurrence of chronic obstructive pulmonary disease

N6‐methyladenosine (m6A) RNA methylation, the most prevalent internal chemical modification of mRNA, has been reported to participate in the progression of various tumours via the dynamic regulation of m6A RNA methylation regulators. However, the role of m6A RNA methylation regulators in chronic obstructive pulmonary disease (COPD) has never been reported. This study aimed to determine the expression and potential functions of m6A RNA methylation regulators in COPD. Four gene expression data sets were acquired from Gene Expression Omnibus. Gene ontology function, Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses, weighted correlation network analysis and protein‐protein interaction network analysis were performed. The correlation analyses of m6A RNA methylation regulators and key COPD genes were also performed. We found that the mRNA expressions of IGF2BP3, FTO, METTL3 and YTHDC2, which have the significant associations with some key genes enriched in the signalling pathway and biological processes that promote the development progression of COPD, are highly correlated with the occurrence of COPD. In conclusion, six central m6A RNA methylation regulators could contribute to the occurrence of COPD. This study provides important evidence for further examination of the role of m6A RNA methylation in COPD.

Effect of sub-chronic exposure to cigarette smoke, electronic cigarette and waterpipe on human lung epithelial barrier function

BACKGROUND

Taking into consideration a recent surge of a lung injury condition associated with electronic cigarette use, we devised an in vitro model of sub-chronic exposure of human bronchial epithelial cells (HBECs) in air-liquid interface, to determine deterioration of epithelial cell barrier from sub-chronic exposure to cigarette smoke (CS), e-cigarette aerosol (EC), and tobacco waterpipe exposures (TW).

METHODS

Products analyzed include commercially available e-liquid, with 0% or 1.2% concentration of nicotine, tobacco blend (shisha), and reference-grade cigarette (3R4F). In one set of experiments, HBECs were exposed to EC (0 and 1.2%), CS or control air for 10 days using 1 cigarette/day. In the second set of experiments, exposure of pseudostratified primary epithelial tissue to TW or control air exposure was performed 1-h/day, every other day, until 3 exposures were performed. After 16-18 h of last exposure, we investigated barrier function/structural integrity of the epithelial monolayer with fluorescein isothiocyanate-dextran flux assay (FITC-Dextran), measurements of trans-electrical epithelial resistance (TEER), assessment of the percentage of moving cilia, cilia beat frequency (CBF), cell motion, and quantification of E-cadherin gene expression by reverse-transcription quantitative polymerase chain reaction (RT-qPCR).

RESULTS

When compared to air control, CS increased fluorescence (FITC-Dextran assay) by 5.6 times, whereby CS and EC (1.2%) reduced TEER to 49 and 60% respectively. CS and EC (1.2%) exposure reduced CBF to 62 and 59%, and cilia moving to 47 and 52%, respectively, when compared to control air. CS and EC (1.2%) increased cell velocity compared to air control by 2.5 and 2.6 times, respectively. The expression of E-cadherin reduced to 39% of control air levels by CS exposure shows an insight into a plausible molecular mechanism. Altogether, EC (0%) and TW exposures resulted in more moderate decreases in epithelial integrity, while EC (1.2%) substantially decreased airway epithelial barrier function comparable with CS exposure.

CONCLUSIONS

The results support a toxic effect of sub-chronic exposure to EC (1.2%) as evident by disruption of the bronchial epithelial cell barrier integrity, whereas further research is needed to address the molecular mechanism of this observation as well as TW and EC (0%) toxicity in chronic exposures.

Post-transcriptional air pollution oxidation to the cholesterol biosynthesis pathway promotes pulmonary stress phenotypes

The impact of environmentally-induced chemical changes in RNA has been fairly unexplored. Air pollution induces oxidative modifications such as 8-oxo-7,8-dihydroguanine (8-oxoG) in RNAs of lung cells, which could be associated with premature lung dysfunction. We develop a method for 8-oxoG profiling using immunocapturing and RNA sequencing. We find 42 oxidized transcripts in bronchial epithelial BEAS-2B cells exposed to two air pollution mixtures that recreate urban atmospheres. We show that the FDFT1 transcript in the cholesterol biosynthesis pathway is susceptible to air pollution-induced oxidation. This process leads to decreased transcript and protein expression of FDFT1, and reduced cholesterol synthesis in cells exposed to air pollution. Knockdown of FDFT1 replicates alterations seen in air pollution exposure such as transformed cell size and suppressed cytoskeleton organization. Our results argue of a possible novel biomarker and of an unseen mechanism by which air pollution selectively modifies key metabolic-related transcripts facilitating cell phenotypes in bronchial dysfunction.

Gonzales-Rivera et al. develop a method for 8-oxoG profiling using immunocapturing and RNA sequencing. They show that the FDFT1 transcript is susceptible to air pollution-induced oxidation, after identifying 42 transcripts that are differentially oxidized in bronchial epithelial BEAS-2B cells under air pollution conditions relative to clean air. FDFT1 oxidation affects cholesterol synthesis pathway, leading to phenotypes associated with several lung diseases.

Respiratory microbiome and epithelial interactions shape immunity in the lungs

The airway epithelium represents a physical barrier to the external environment acting as the first line of defence against potentially harmful environmental stimuli including microbes and allergens. However, lung epithelial cells are increasingly recognized as active effectors of microbial defence, contributing to both innate and adaptive immune function in the lower respiratory tract. These cells express an ample repertoire of pattern recognition receptors with specificity for conserved microbial and host motifs. Modern molecular techniques have uncovered the complexity of the lower respiratory tract microbiome. The interaction between the microbiota and the airway epithelium is key to understanding how stable immune homeostasis is maintained. Loss of epithelial integrity following exposure to infection can result in the onset of inflammation in susceptible individuals and may culminate in lung disease. Here we discuss the current knowledge regarding the molecular and cellular mechanisms by which the pulmonary epithelium interacts with the lung microbiome in shaping immunity in the lung. Specifically, we focus on the interactions between the lung microbiome and the cells of the conducting airways in modulating immune cell regulation, and how defects in barrier structure and function may culminate in lung disease. Understanding these interactions is fundamental in the search for more effective therapies for respiratory diseases.

Intermittent exposure to whole cigarette smoke alters the differentiation of primary small airway epithelial cells in the air-liquid interface culture

Cigarette smoke (CS) is the leading risk factor to develop COPD. Therefore, the pathologic effects of whole CS on the differentiation of primary small airway epithelial cells (SAEC) were investigated, using cells from three healthy donors and three COPD patients, cultured under ALI (air-liquid interface) conditions. The analysis of the epithelial physiology demonstrated that CS impaired barrier formation and reduced cilia beat activity. Although, COPD-derived ALI cultures preserved some features known from COPD patients, CS-induced effects were similarly pronounced in ALI cultures from patients compared to healthy controls. RNA sequencing analyses revealed the deregulation of marker genes for basal and secretory cells upon CS exposure. The comparison between gene signatures obtained from the in vitro model (CS vs. air) with a published data set from human epithelial brushes (smoker vs. non-smoker) revealed a high degree of similarity between deregulated genes and pathways induced by CS. Taken together, whole cigarette smoke alters the differentiation of small airway basal cells in vitro. The established model showed a good translatability to the situation in vivo. Thus, the model can help to identify and test novel therapeutic approaches to restore the impaired epithelial repair mechanisms in COPD, which is still a high medical need.

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.

Novel biomarker genes which distinguish between smokers and chronic obstructive pulmonary disease patients with machine learning approach

Background

Chronic obstructive pulmonary disease (COPD) is combination of progressive lung diseases. The diagnosis of COPD is generally based on the pulmonary function testing, however, difficulties underlie in prognosis of smokers or early stage of COPD patients due to the complexity and heterogeneity of the pathogenesis. Computational analyses of omics technologies are expected as one of the solutions to resolve such complexities.

Methods

We obtained transcriptomic data by in vitro testing with exposures of human bronchial epithelial cells to the inducers for early events of COPD to identify the potential descriptive marker genes. With the identified genes, the machine learning technique was employed with the publicly available transcriptome data obtained from the lung specimens of COPD and non-COPD patients to develop the model that can reflect the risk continuum across smoking and COPD.

Results

The expression levels of 15 genes were commonly altered among in vitro tissues exposed to known inducible factors for earlier events of COPD (exposure to cigarette smoke, DNA damage, oxidative stress, and inflammation), and 10 of these genes and their corresponding proteins have not previously reported as COPD biomarkers. Although these genes were able to predict each group with 65% accuracy, the accuracy with which they were able to discriminate COPD subjects from smokers was only 29%.

Furthermore, logistic regression enabled the conversion of gene expression levels to a numerical index, which we named the “potential risk factor (PRF)” index. The highest significant index value was recorded in COPD subjects (0.56 at the median), followed by smokers (0.30) and non-smokers (0.02). In vitro tissues exposed to cigarette smoke displayed dose-dependent increases of PRF, suggesting its utility for prospective risk estimation of tobacco products.

Conclusions

Our experimental-based transcriptomic analysis identified novel genes associated with COPD, and the 15 genes could distinguish smokers and COPD subjects from non-smokers via machine-learning classification with remarkable accuracy. We also suggested a PRF index that can quantitatively reflect the risk continuum across smoking and COPD pathogenesis, and we believe it will provide an improved understanding of smoking effects and new insights into COPD.

Sensing of apoptotic cells through Axl causes lung basal cell proliferation in inflammatory diseases

Epithelial cell proliferation, division, and differentiation are critical for barrier repair following inflammation, but the initial trigger for this process is unknown. Here we define that sensing of apoptotic cells by the TAM receptor tyrosine kinase Axl is a critical indicator for tracheal basal cell expansion, cell cycle reentry, and symmetrical cell division. Furthermore, once the pool of tracheal basal cells has expanded, silencing of Axl is required for their differentiation. Genetic depletion of Axl triggers asymmetrical cell division, leading to epithelial differentiation and ciliated cell regeneration. This discovery has implications for conditions associated with epithelial barrier dysfunction, basal cell hyperplasia, and continued turnover of dying cells in patients with chronic inflammatory pulmonary diseases.

Exosomal miRNAs in Lung Diseases: From Biologic Function to Therapeutic Targets

Increasing evidence suggests the potential role of extracellular vesicles (EVs) in many lung diseases. According to their subcellular origin, secretion mechanism, and size, EVs are currently classified into three subpopulations: exosomes, microvesicles, and apoptotic bodies. Exosomes are released in most biofluids, including airway fluids, and play a key role in intercellular communication via the delivery of their cargo (e.g., microRNAs (miRNAs)) to target cell. In a physiological context, lung exosomes present protective effects against stress signals which allow them to participate in the maintenance of lung homeostasis. The presence of air pollution alters the composition of lung exosomes (dysregulation of exosomal miRNAs) and their homeostatic property. Indeed, besides their potential as diagnostic biomarkers for lung diseases, lung exosomes are functional units capable of dysregulating numerous pathophysiological processes (including inflammation or fibrosis), resulting in the promotion of lung disease progression. Here, we review recent studies on the known and potential role of lung exosomes/exosomal miRNAs, in the maintaining of lung homeostasis on one hand, and in promoting lung disease progression on the other. We will also discuss using exosomes as prognostic/diagnostic biomarkers as well as therapeutic tools for lung diseases.

PTEN in Lung Cancer: Dealing with the Problem, Building on New Knowledge and Turning the Game Around

Lung cancer is the most common malignancy and cause of cancer deaths worldwide, owing to the dismal prognosis for most affected patients. Phosphatase and tensin homolog deleted in chromosome 10 (PTEN) acts as a powerful tumor suppressor gene and even partial reduction of its levels increases cancer susceptibility. While the most validated anti-oncogenic duty of PTEN is the negative regulation of the PI3K/mTOR/Akt oncogenic signaling pathway, further tumor suppressor functions, such as chromosomal integrity and DNA repair have been reported. PTEN protein loss is a frequent event in lung cancer, but genetic alterations are not equally detected. It has been demonstrated that its expression is regulated at multiple genetic and epigenetic levels and deeper delineation of these mechanisms might provide fertile ground for upgrading lung cancer therapeutics. Today, PTEN expression is usually determined by immunohistochemistry and low protein levels have been associated with decreased survival in lung cancer. Moreover, available data involve PTEN mutations and loss of activity with resistance to targeted treatments and immunotherapy. This review discusses the current knowledge about PTEN status in lung cancer, highlighting the prevalence of its alterations in the disease, the regulatory mechanisms and the implications of PTEN on available treatment options.

Epithelial-mesenchymal transition is driven by transcriptional and post transcriptional modulations in COPD: implications for disease progression and new therapeutics

COPD is a common and highly destructive disease with huge impacts on people and health services throughout the world. It is mainly caused by cigarette smoking though environmental pollution is also significant. There are no current treatments that affect the overall course of COPD; current drugs focus on symptomatic relief and to some extent reducing exacerbation rates. There is an urgent need for in-depth studies of the fundamental pathogenic mechanisms that underpin COPD. This is vital, given the fact that nearly 40%-60% of the small airway and alveolar damage occurs in COPD well before the first measurable changes in lung function are detected. These individuals are also at a high risk of lung cancer. Current COPD research is mostly centered around late disease and/or innate immune activation within the airway lumen, but the actual damage to the airway wall has early onset. COPD is the end result of complex mechanisms, possibly triggered through initial epithelial activation. To change the disease trajectory, it is crucial to understand the mechanisms in the epithelium that are switched on early in smokers. One such mechanism we believe is the process of epithelial to mesenchymal transition. This article highlights the importance of this profound epithelial cell plasticity in COPD and also its regulation. We consider that understanding early changes in COPD will open new windows for therapy.

Cigarette Smoke Induced Lung Barrier Dysfunction, EMT, and Tissue Remodeling: A Possible Link between COPD and Lung Cancer

Chronic obstructive pulmonary disease (COPD) and lung cancer, closely related to smoking, are major lung diseases affecting millions of individuals worldwide. The generated gas mixture of smoking is proved to contain about 4,500 components such as carbon monoxide, nicotine, oxidants, fine particulate matter, and aldehydes. These components were considered to be the principle factor driving the pathogenesis and progression of pulmonary disease. A large proportion of lung cancer patients showed a history of COPD, which demonstrated that there might be a close relationship between COPD and lung cancer. In the early stages of smoking, lung barrier provoked protective response and DNA repair are likely to suppress these changes to a certain extent. In the presence of long-term smoking exposure, these mechanisms seem to be malfunctioned and lead to disease progression. The infiltration of inflammatory cells to mucosa, submucosa, and glandular tissue caused by inhaled cigarette smoke is responsible for the destruction of matrix, blood supply shortage, and epithelial cell death. Conversely, cancer cells have the capacity to modulate the proliferation of epithelial cells and produce of new vascular networks. Comprehension understanding of mechanisms responsible for both pathologies is necessary for the prevention and treatment of COPD and lung cancer. In this review, we will summarize related articles and give a glance of possible mechanism between cigarette smoking induced COPD and lung cancer.

Exaggerated BMP4 signalling alters human airway basal progenitor cell differentiation to cigarette smoking-related phenotypes

Airway remodelling in chronic obstructive pulmonary disease (COPD) originates, in part, from smoking-induced changes in airway basal stem/progenitor cells (BCs). Based on the knowledge that bone morphogenetic protein 4 (BMP4) influences epithelial progenitor function in the developing and adult mouse lung, we hypothesised that BMP4 signalling may regulate the biology of adult human airway BCs relevant to COPD.BMP4 signalling components in human airway epithelium were analysed at the mRNA and protein levels, and the differentiation of BCs was assessed using the BC expansion and air-liquid interface models in the absence/presence of BMP4, BMP receptor inhibitor and/or small interfering RNAs against BMP receptors and downstream signalling.The data demonstrate that in cigarette smokers, BMP4 is upregulated in ciliated and intermediate undifferentiated cells, and expression of the BMP4 receptor BMPR1A is enriched in BCs. BMP4 induced BCs to acquire a smoking-related abnormal phenotype in vitro mediated by BMPR1A/Smad signalling, characterised by decreased capacity to differentiate into normal mucociliary epithelium, while generating squamous metaplasia.Exaggerated BMP4 signalling promotes cigarette smoking-relevant airway epithelial remodelling by inducing abnormal phenotypes in human airway BCs. Targeting of BMP4 signalling in airway BCs may represent a novel target to prevent/treat COPD-associated airway disease.

Deducting MicroRNA-Mediated Changes Common in Bronchial Epithelial Cells of Asthma and Chronic Obstructive Pulmonary Disease-A Next-Generation Sequencing-Guided Bioinformatic Approach

Asthma and chronic obstructive pulmonary disease (COPD) are chronic airway inflammatory diseases that share some common features, although these diseases are somewhat different in etiologies, clinical features, and treatment policies. The aim of this study is to investigate the common microRNA-mediated changes in bronchial epithelial cells of asthma and COPD. The microRNA profiles in primary bronchial epithelial cells from asthma (AHBE) and COPD (CHBE) patients and healthy subjects (NHBE) were analyzed with next-generation sequencing (NGS) and the significant microRNA changes common in AHBE and CHBE were extracted. The upregulation of hsa-miR-10a-5p and hsa-miR-146a-5p in both AHBE and CHBE was confirmed with quantitative polymerase chain reaction (qPCR). Using bioinformatic methods, we further identified putative targets of these microRNAs, which were downregulated in both AHBE and CHBE: miR-10a-5p might suppress BCL2, FGFR3, FOXO3, PDE4A, PDE4C, and PDE7A; miR-146a-5p might suppress BCL2, INSR, PDE4D, PDE7A, PDE7B, and PDE11A. We further validated significantly decreased expression levels of FOXO3 and PDE7A in AHBE and CHBE than in NHBE with qPCR. Increased serum miR-146a-5p level was also noted in patients with asthma and COPD as compared with normal control subjects. In summary, our study revealed possible mechanisms mediated by miR-10a-5p and miR-146a-5p in the pathogenesis of both asthma and COPD. The findings might provide a scientific basis for developing novel diagnostic and therapeutic strategies.

Identification of Novel Genes in Human Airway Epithelial Cells associated with Chronic Obstructive Pulmonary Disease (COPD) using Machine-Based Learning Algorithms

The aim of this project was to identify candidate novel therapeutic targets to facilitate the treatment of COPD using machine-based learning (ML) algorithms and penalized regression models. In this study, 59 healthy smokers, 53 healthy non-smokers and 21 COPD smokers (9 GOLD stage I and 12 GOLD stage II) were included (n = 133). 20,097 probes were generated from a small airway epithelium (SAE) microarray dataset obtained from these subjects previously. Subsequently, the association between gene expression levels and smoking and COPD, respectively, was assessed using: AdaBoost Classification Trees, Decision Tree, Gradient Boosting Machines, Naive Bayes, Neural Network, Random Forest, Support Vector Machine and adaptive LASSO, Elastic-Net, and Ridge logistic regression analyses. Using this methodology, we identified 44 candidate genes, 27 of these genes had been previously been reported as important factors in the pathogenesis of COPD or regulation of lung function. Here, we also identified 17 genes, which have not been previously identified to be associated with the pathogenesis of COPD or the regulation of lung function. The most significantly regulated of these genes included: PRKAR2B, GAD1, LINC00930 and SLITRK6. These novel genes may provide the basis for the future development of novel therapeutics in COPD and its associated morbidities.

Epithelial mesenchymal transition (EMT): a universal process in lung diseases with implications for cystic fibrosis pathophysiology

Cystic Fibrosis (CF) is a genetic disorder that arises due to mutations in the Cystic Fibrosis Transmembrane Conductance Regulator gene, which encodes for a protein responsible for ion transport out of epithelial cells. This leads to a disruption in transepithelial Cl-, Na + and HCO₃− ion transport and the subsequent dehydration of the airway epithelium, resulting in infection, inflammation and development of fibrotic tissue. Unlike in CF, fibrosis in other lung diseases including asthma, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis has been well characterised. One of the driving forces behind fibrosis is Epithelial Mesenchymal Transition (EMT), a process where epithelial cells lose epithelial proteins including E-Cadherin, which is responsible for tight junctions. The cell moves to a more mesenchymal phenotype as it gains mesenchymal markers such as N-Cadherin (providing the cells with migration potential), Vimentin and Fibronectin (proteins excreted to help form the extracellular matrix), and the fibroblast proliferation transcription factors Snail, Slug and Twist. This review paper explores the EMT process in a range of lung diseases, details the common links that these have to cystic fibrosis, and explores how understanding EMT in cystic fibrosis may open up novel methods of treating patients with cystic fibrosis.

Inhaled Therapy in Respiratory Disease: The Complex Interplay of Pulmonary Kinetic Processes

The inhalation route is frequently used to administer drugs for the management of respiratory diseases such as asthma or chronic obstructive pulmonary disease. Compared with other routes of administration, inhalation offers a number of advantages in the treatment of these diseases. For example, via inhalation, a drug is directly delivered to the target organ, conferring high pulmonary drug concentrations and low systemic drug concentrations. Therefore, drug inhalation is typically associated with high pulmonary efficacy and minimal systemic side effects. The lung, as a target, represents an organ with a complex structure and multiple pulmonary-specific pharmacokinetic processes, including (1) drug particle/droplet deposition; (2) pulmonary drug dissolution; (3) mucociliary and macrophage clearance; (4) absorption to lung tissue; (5) pulmonary tissue retention and tissue metabolism; and (6) absorptive drug clearance to the systemic perfusion. In this review, we describe these pharmacokinetic processes and explain how they may be influenced by drug-, formulation- and device-, and patient-related factors. Furthermore, we highlight the complex interplay between these processes and describe, using the examples of inhaled albuterol, fluticasone propionate, budesonide, and olodaterol, how various sequential or parallel pulmonary processes should be considered in order to comprehend the pulmonary fate of inhaled drugs.

Transgenic up-regulation of Claudin-6 decreases fine diesel particulate matter (DPM)-induced pulmonary inflammation

Claudin-6 (Cldn6) is a tetraspanin transmembrane protein that contributes to tight junctional complexes and has been implicated in the maintenance of lung epithelial barriers. In the present study, we tested the hypothesis that genetic up-regulation of Cldn-6 influences inflammation in mice exposed to short-term environmental diesel particulate matter (DPM). Mice were subjected to ten exposures of nebulized DPM (PM2.5) over a period of 20 days via a nose-only inhalation system (Scireq, Montreal, Canada). Using real-time RT-PCR, we discovered that the Cldn6 gene was up-regulated in control mice exposed to DPM and in lung-specific transgenic mice that up-regulate Cldn-6 (Cldn-6 TG). Interestingly, DPM did not further enhance Cldn-6 expression in Cldn-6 TG mice. DPM caused increased cell diapedesis into bronchoalveolar lavage fluid (BALF) from control mice; however, Cldn-6 TG mice had less total cells and PMNs in BALF following DPM exposure. Because Cldn-6 TG mice had diminished cell diapedesis, other inflammatory intermediates were screened to characterize the impact of increased Cldn-6 on inflammatory signaling. Cytokines that mediate inflammatory responses including TNF-α and IL-1β were differentially regulated in Cldn6 TG mice and controls following DPM exposure. These results demonstrate that epithelial barriers organized by Cldn-6 mediate, at least in part, diesel-induced inflammation. Further work may show that Cldn-6 is a key target in understanding pulmonary epithelial gateways exacerbated by environmental pollution.

PTEN Physically Interacts with and Regulates E2F1-mediated Transcription in Lung Cancer

PTEN phosphorylation at its C-terminal (C-tail) serine/threonine cluster negatively regulates its tumor suppressor function. However, the consequence of such inhibition and its downstream effects in driving lung cancer remain unexplored. Herein, we ascertain the molecular mechanisms by which phosphorylation compromises PTEN function, contributing to lung cancer. Replacement of the serine/threonine residues with alanine generated PTEN-4A, a phosphorylation-deficient PTEN mutant, which suppressed lung cancer cell proliferation and migration. PTEN-4A preferentially localized to the nucleus where it suppressed E2F1-mediated transcription of cell cycle genes. PTEN-4A physically interacted with the transcription factor E2F1 and associated with chromatin at gene promoters with E2F1 DNA-binding sites, a likely mechanism for its transcriptional suppression function. Deletion analysis revealed that the C2 domain of PTEN was indispensable for suppression of E2F1-mediated transcription. Further, we uncovered cancer-associated C2 domain mutant proteins that had lost their ability to suppress E2F1-mediated transcription, supporting the concept that these mutations are oncogenic in patients. Consistent with these findings, we observed increased PTEN phosphorylation and reduced nuclear PTEN levels in lung cancer patient samples establishing phosphorylation as a bona fide inactivation mechanism for PTEN in lung cancer. Thus, use of small molecule inhibitors that hinder PTEN phosphorylation is a plausible approach to activate PTEN function in the treatment of lung cancer. Abbreviations AKT V-Akt Murine Thymoma Viral Oncogene CA Cancer adjacent CDK1 Cyclin dependent kinase 1 CENPC-C Centromere Protein C ChIP Chromatin Immunoprecipitation co-IP Co-immunoprecipitation COSMIC Catalog of Somatic Mutations In Cancer CREB cAMP Responsive Element Binding Protein C-tail Carboxy terminal tail E2F1 E2F Transcription Factor 1 ECIS Electric Cell-substrate Impedance Sensing EGFR Epidermal Growth Factor Receptor GSI Gamma Secretase Inhibitor HDAC1 Histone Deacetylase 1 HP1 Heterochromatin protein 1 KAP1/TRIM28 KRAB-Associated Protein 1/Tripartite Motif Containing 28 MAF1 Repressor of RNA polymerase III transcription MAF1 homolog MCM2 Minichromosome Maintenance Complex Component 2 miRNA micro RNA MTF1 Metal-Regulatory Transcription Factor 1 PARP Poly(ADP-Ribose) Polymerase PD-1 Programmed Cell Death 1 PD-L1 Programmed Cell Death 1 Ligand 1 PI3K Phosphatidylinositol-4,5-Bisphosphate 3-Kinase PLK Polo-like Kinase pPTEN Phosphorylated PTEN PTEN Phosphatase and Tensin Homolog deleted on chromosome ten PTM Post Translational Modification Rad51 RAD51 Recombinase Rad52 RAD52 Recombinase RPA1 Replication protein A SILAC Stable Isotope Labeling with Amino Acids in Cell Culture SRF Serum Response Factor TKI Tyrosine Kinase inhbitors TMA Tissue Microarray TOP2A DNA Topoisomerase 2A.

Vitamin D supplementation of initially vitamin D-deficient mice diminishes lung inflammation with limited effects on pulmonary epithelial integrity

In disease settings, vitamin D may be important for maintaining optimal lung epithelial integrity and suppressing inflammation, but less is known of its effects prior to disease onset. Female BALB/c dams were fed a vitamin D₃‐supplemented (2280 IU/kg, VitD⁺) or nonsupplemented (0 IU/kg, VitD⁻) diet from 3 weeks of age, and mated at 8 weeks of age. Male offspring were fed the same diet as their mother. Some offspring initially fed the VitD⁻ diet were switched to a VitD⁺ diet from 8 weeks of age (VitD^−/+). At 12 weeks of age, signs of low‐level inflammation were observed in the bronchoalveolar lavage fluid (BALF) of VitD⁻ mice (more macrophages and neutrophils), which were suppressed by subsequent supplementation with vitamin D₃. There was no difference in the level of expression of the tight junction proteins occludin or claudin‐1 in lung epithelial cells of VitD⁺ mice compared to VitD⁻ mice; however, claudin‐1 levels were reduced when initially vitamin D‐deficient mice were fed the vitamin D₃‐containing diet (VitD^−/+). Reduced total IgM levels were detected in BALF and serum of VitD^−/+ mice compared to VitD⁺ mice. Lung mRNA levels of the vitamin D receptor (VDR) were greatest in VitD^−/+ mice. Total IgG levels in BALF were greater in mice fed the vitamin D₃‐containing diet, which may be explained by increased activation of B cells in airway‐draining lymph nodes. These findings suggest that supplementation of initially vitamin D‐deficient mice with vitamin D₃ suppresses signs of lung inflammation but has limited effects on the epithelial integrity of the lungs.

Tobacco Smoke Induces and Alters Immune Responses in the Lung Triggering Inflammation, Allergy, Asthma and Other Lung Diseases: A Mechanistic Review

Many studies have been undertaken to reveal how tobacco smoke skews immune responses contributing to the development of chronic obstructive pulmonary disease (COPD) and other lung diseases. Recently, environmental tobacco smoke (ETS) has been linked with asthma and allergic diseases in children. This review presents the most actual knowledge on exact molecular mechanisms responsible for the skewed inflammatory profile that aggravates inflammation, promotes infections, induces tissue damage, and may promote the development of allergy in individuals exposed to ETS. We demonstrate how the imbalance between oxidants and antioxidants resulting from exposure to tobacco smoke leads to oxidative stress, increased mucosal inflammation, and increased expression of inflammatory cytokines (such as interleukin (IL)-8, IL-6 and tumor necrosis factor α ([TNF]-α). Direct cellular effects of ETS on epithelial cells results in increased permeability, mucus overproduction, impaired mucociliary clearance, increased release of proinflammatory cytokines and chemokines, enhanced recruitment of macrophages and neutrophils and disturbed lymphocyte balance towards Th2. The plethora of presented phenomena fully justifies a restrictive policy aiming at limiting the domestic and public exposure to ETS.

Airway Epithelium Dysfunction in Cystic Fibrosis and COPD

Cystic fibrosis is a genetic disease caused by mutations in the CFTR gene, whereas chronic obstructive pulmonary disease (COPD) is mainly caused by environmental factors (mostly cigarette smoking) on a genetically susceptible background. Although the etiology and pathogenesis of these diseases are different, both are associated with progressive airflow obstruction, airway neutrophilic inflammation, and recurrent exacerbations, suggesting common mechanisms. The airway epithelium plays a crucial role in maintaining normal airway functions. Major molecular and morphologic changes occur in the airway epithelium in both CF and COPD, and growing evidence suggests that airway epithelial dysfunction is involved in disease initiation and progression in both diseases. Structural and functional abnormalities in both airway and alveolar epithelium have a relevant impact on alteration of host defences, immune/inflammatory response, and the repair process leading to progressive lung damage and impaired lung function. In this review, we address the evidence for a critical role of dysfunctional airway epithelial cells in chronic airway inflammation and remodelling in CF and COPD, highlighting the common mechanisms involved in the epithelial dysfunction as well as the similarities and differences of the two diseases.

Bronchial extracellular matrix from COPD patients induces altered gene expression in repopulated primary human bronchial epithelial cells

Chronic obstructive pulmonary disease (COPD) is a serious global health problem characterized by chronic airway inflammation, progressive airflow limitation and destruction of lung parenchyma. Remodeling of the bronchial airways in COPD includes changes in both the bronchial epithelium and the subepithelial extracellular matrix (ECM). To explore the impact of an aberrant ECM on epithelial cell phenotype in COPD we developed a new ex vivo model, in which normal human bronchial epithelial (NHBE) cells repopulate and differentiate on decellularized human bronchial scaffolds derived from COPD patients and healthy individuals. By using transcriptomics, we show that bronchial ECM from COPD patients induces differential gene expression in primary NHBE cells when compared to normal bronchial ECM. The gene expression profile indicated altered activity of upstream mediators associated with COPD pathophysiology, including hepatocyte growth factor, transforming growth factor beta 1 and platelet-derived growth factor B, which suggests that COPD-related changes in the bronchial ECM contribute to the defective regenerative ability in the airways of COPD patients.

Mandatory role of HMGA1 in human airway epithelial normal differentiation and post-injury regeneration

Due to high levels of expression in aggressive tumors, high mobility group AT-hook 1 (HMGA1) has recently attracted attention as a potential anti-tumor target. However, HMGA1 is also expressed in normal somatic progenitor cells, raising the question: how might systemic anti-HMGA1 therapies affect the structure and function of normal tissue differentiation? In the present study, RNA sequencing data demonstrated HMGA1 is highly expressed in human airway basal stem/progenitor cells (BC), but decreases with BC differentiation in air-liquid interface cultures (ALI). BC collected from nonsmokers, healthy smokers, and smokers with chronic obstructive pulmonary disease (COPD) displayed a range of HMGA1 expression levels. Low initial expression levels of HMGA1 in BC were associated with decreased ability to maintain a differentiated ALI epithelium. HMGA1 down-regulation in BC diminished BC proliferation, suppressed gene expression related to normal proliferation and differentiation, decreased airway epithelial resistance, suppressed junctional and cell polarity gene expression, and delayed wound closure of airway epithelium following injury. Furthermore, silencing of HMGA1 in airway BC in ALI increased the expression of genes associated with airway remodeling in COPD including squamous, epithelial-mesenchymal transition (EMT), and inflammatory genes. Together, the data suggests HMGA1 plays a central role in normal airway differentiation, and thus caution should be used to monitor airway epithelial structure and function in the context of systemic HMGA1-targeted therapies.

Chronic inhalation of e-cigarette vapor containing nicotine disrupts airway barrier function and induces systemic inflammation and multiorgan fibrosis in mice

Electronic (e)-cigarettes theoretically may be safer than conventional tobacco. However, our prior studies demonstrated direct adverse effects of e-cigarette vapor (EV) on airway cells, including decreased viability and function. We hypothesize that repetitive, chronic inhalation of EV will diminish airway barrier function, leading to inflammatory protein release into circulation, creating a systemic inflammatory state, ultimately leading to distant organ injury and dysfunction. C57BL/6 and CD-1 mice underwent nose only EV exposure daily for 3-6 mo, followed by cardiorenal physiological testing. Primary human bronchial epithelial cells were grown at an air-liquid interface and exposed to EV for 15 min daily for 3-5 days before functional testing. Daily inhalation of EV increased circulating proinflammatory and profibrotic proteins in both C57BL/6 and CD-1 mice: the greatest increases observed were in angiopoietin-1 (31-fold) and EGF (25-fold). Proinflammatory responses were recapitulated by daily EV exposures in vitro of human airway epithelium, with EV epithelium secreting higher IL-8 in response to infection (227 vs. 37 pg/ml, respectively; P < 0.05). Chronic EV inhalation in vivo reduced renal filtration by 20% ( P = 0.017). Fibrosis, assessed by Masson's trichrome and Picrosirius red staining, was increased in EV kidneys (1.86-fold, C57BL/6; 3.2-fold, CD-1; P < 0.05), heart (2.75-fold, C57BL/6 mice; P < 0.05), and liver (1.77-fold in CD-1; P < 0.0001). Gene expression changes demonstrated profibrotic pathway activation. EV inhalation altered cardiovascular function, with decreased heart rate ( P < 0.01), and elevated blood pressure ( P = 0.016). These data demonstrate that chronic inhalation of EV may lead to increased inflammation, organ damage, and cardiorenal and hepatic disease.

Zinc deficiency as a codeterminant for airway epithelial barrier dysfunction in an ex vivo model of COPD

There is now convincing evidence that the airway epithelium drives the pathogenesis of COPD. A major aspect of this is the disease-related reduction in barrier function that is potentiated by dysregulation of tight junction (TJ) protein complexes. However, a significant number of studies using in vitro smoke exposure models have not observed alterations in barrier permeability. We have previously shown that zinc (Zn) is an influential cytoprotective factor for the airway epithelium, and its depletion by cigarette smoke produces disease-related modifications consistent with inflammatory changes in COPD. We hypothesized that Zn deficiency is a significant co-stimulus with cigarette smoke extract (CSE) for potentiating the leaky barrier phenotype exhibited in COPD. We employed an ex vivo model of differentiated human airway epithelium exposed to Zn depletion and CSE to determine the contribution of Zn in maintaining normal epithelial permeability. Western blot analysis demonstrated a significant downregulation of the TJ proteins such as ZO-1 (−1.93-fold, P<0.05) and Claudin-1 (−3.37-fold, P<0.01) with the combination exposure. Assessment of barrier function via paracellular ionic conductance and tracer permeability also showed that Zn depletion was an important factor, which potentiated an increase in epithelial permeability (P<0.001 for both) compared to Zn depletion or CSE exposures in isolation. Visual inspection of the epithelium using transmission electron microscopy revealed a marked reduction in junction complexes between the adjacent airway epithelial cells treated with a combination of Zn depletion and CSE. These observations identify Zn deficiency as a significant codeterminant with CSE as a factor leading to an increase in airway epithelial permeability. Hence, as Zn dyshomeostasis has been reported in the airway epithelium exposed to chronic cigarette smoke and inflammation, targeting these phenomena may represent a promising strategy to ameliorate the leaky barrier phenotype that is synonymous with COPD.

Fgf10-Hippo Epithelial-Mesenchymal Crosstalk Maintains and Recruits Lung Basal Stem Cells

The lung harbors its basal stem/progenitor cells (BSCs) in the protected environment of the cartilaginous airways. After major lung injuries, BSCs are activated and recruited to sites of injury. Here, we show that during homeostasis, BSCs in cartilaginous airways maintain their stem cell state by downregulating the Hippo pathway (resulting in increased nuclear Yap), which generates a localized Fgf10-expressing stromal niche; in contrast, differentiated epithelial cells in non-cartilaginous airways maintain quiescence by activating the Hippo pathway and inhibiting Fgf10 expression in airway smooth muscle cells (ASMCs). However, upon injury, surviving differentiated epithelial cells spread to maintain barrier function and recruit integrin-linked kinase to adhesion sites, which leads to Merlin degradation, downregulation of the Hippo pathway, nuclear Yap translocation, and expression and secretion of Wnt7b. Epithelial-derived Wnt7b, then in turn, induces Fgf10 expression in ASMCs, which extends the BSC niche to promote regeneration.

Lung development, regeneration and plasticity: From disease physiopathology to drug design using induced pluripotent stem cells

Lungs have a complex structure composed of different cell types that form approximately 17 million airway branches of gas-delivering bronchioles connected to 500 million gas-exchanging alveoli. Airways and alveoli are lined by epithelial cells that display a low rate of turnover at steady-state, but can regenerate the epithelium in response to injuries. Here, we review the key points of lung development, homeostasis and epithelial cell plasticity in response to injury and disease, because this knowledge is required to develop new lung disease treatments. Of note, canonical signaling pathways that are essential for proper lung development during embryogenesis are also involved in the pathophysiology of most chronic airway diseases. Moreover, the perfect control of these interconnected pathways is needed for the successful differentiation of induced pluripotent stem cells (iPSC) into lung cells. Indeed, differentiation of iPSC into airway epithelium and alveoli is based on the use of biomimetics of normal embryonic and fetal lung development. In vitro iPSC-based models of lung diseases can help us to better understand the impaired lung repair capacity and to identify new therapeutic targets and new approaches, such as lung cell therapy.

Airway epithelial barrier dysfunction in the pathogenesis and prognosis of respiratory tract diseases in childhood and adulthood

The lungs are in direct contact with the environment through the tubular structure that constitutes the airway. Starting from the nasal orifice, the airway is exposed to foreign particles including infectious agents, allergens, and other substances that can damage the airways. Therefore, the airway must have a functional epithelial barrier both in the upper and lower airways to protect against these threats. As with the skin, it is likely that the pathogenesis of respiratory diseases is a consequence of epithelial barrier defects in these airways. The characteristics of this system, starting from the beginning of life and extending into maturing and aging, determine the prognosis of respiratory diseases. In this article, we discuss the pathogenesis, clinical phenotype, and prognosis of respiratory diseases from newborns to adulthood in the context of epithelial barrier function and dysfunction.

Smoking-Dependent Distal-to-Proximal Repatterning of the Adult Human Small Airway Epithelium

RATIONALE

Small airways are the primary site of pathologic changes in chronic obstructive pulmonary disease (COPD), the major smoking-induced lung disorder.

OBJECTIVES

On the basis of the concept of proximal-distal patterning that determines regional specialization of the airway epithelium during lung development, we hypothesized that a similar program operates in the adult human lung being altered by smoking, leading to decreased regional identity of the small airway epithelium (SAE).

METHODS

The proximal and distal airway signatures were identified by comparing the transcriptomes of large and small airway epithelium samples obtained by bronchoscopy from healthy nonsmokers. The expression of these signatures was evaluated in the SAE of healthy smokers and smokers with COPD compared with that of healthy nonsmokers. The capacity of airway basal stem cells (BCs) to maintain region-associated phenotypes was evaluated using the air-liquid interface model.

MEASUREMENTS AND MAIN RESULTS

The distal and proximal airway signatures, containing 134 and 233 genes, respectively, were identified. These signatures included known developmental regulators of airway patterning, as well as novel regulators such as epidermal growth factor receptor, which was associated with the proximal airway phenotype. In the SAE of smokers with COPD, there was a dramatic smoking-dependent loss of the regional transcriptome identity with concomitant proximalization. This repatterning phenotype was reproduced by stimulating SAE BCs with epidermal growth factor, which was up-regulated in the SAE of smokers, during differentiation of SAE BCs in vitro.

CONCLUSIONS

Smoking-induced global distal-to-proximal reprogramming of the SAE represents a novel pathologic feature of COPD and is mediated by exaggerated epidermal growth factor/epidermal growth factor receptor signaling in SAE BCs.

Airway inflammation in chronic obstructive pulmonary disease (COPD): a true paradox

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is primarily an airway condition, which mainly affects cigarette smokers and presents with shortness of breath that is progressive and poorly reversible. In COPD research, there has been a long held belief that airway disease progression is due to inflammation. Although this may be true in the airway lumen with innate immunity activated by the effect of smoke or secondary to infection, the accurate picture of inflammatory cells in the airway wall, where the pathophysiological COPD remodeling occurs, is uncertain and debatable. Areas covered: The current review provides a comprehensive literature survey of the changes in the main inflammatory cells in human COPD patients and focuses on contrarian views that affect the prevailing dogma on inflammation. The review also delves into the role of oxidative stress and inflammasomes in modulating the immune response in COPD. Further, the effects of inflammation in affecting the epithelium, fibroblasts, and airway remodeling are discussed. Expert commentary: Inflammation as a driving force for airway wall damage and remodelling in early COPD is at the very least 'oversimplified' and is likely to be misleading. This has serious implications for rational thinking about the illness, including pathogenesis and designing therapy.

Temporal dynamics of ovine airway epithelial cell differentiation at an air-liquid interface

The respiratory tract and lungs are subject to diverse pathologies with wide-ranging implications for both human and animal welfare. The development and detailed characterization of cell culture models for studying such forms of disease is of critical importance. In recent years the use of air-liquid interface (ALI)-cultured airway epithelial cells has increased markedly, as this method of culture results in the formation of a highly representative, organotypic in vitro model system. In this study we have expanded on previous knowledge of differentiated ovine tracheal epithelial cells by analysing the progression of differentiation over an extensive time course at an ALI. We observed a pseudo-stratified epithelium with ciliation and a concurrent increase in cell layer thickness from 9 days post-ALI with ciliation approaching a maximum level at day 24. A similar pattern was observed with respect to mucus production with intensely stained PAS-positive cells appearing at day 12. Ultrastructural analysis by SEM confirmed the presence of both ciliated cells and mucus globules on the epithelial surface within this time-frame. Trans-epithelial electrical resistance (TEER) peaked at 1049 Ω × cm² as the cell layer became confluent, followed by a subsequent reduction as differentiation proceeded and stabilization at ~200 Ω × cm². Importantly, little deterioration or de-differentiation was observed over the 45 day time-course indicating that the model is suitable for long-term experiments.

Cigarette smoke disrupts monolayer integrity by altering epithelial cell-cell adhesion and cortical tension

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality. Cigarette smoke (CS) drives disease development and progression. The epithelial barrier is damaged by CS with increased monolayer permeability. However, the molecular changes that cause this barrier disruption and the interaction between adhesion proteins and the cytoskeleton are not well defined. We hypothesized that CS alters monolayer integrity by increasing cell contractility and decreasing cell adhesion in epithelia. Normal human airway epithelial cells and primary COPD epithelial cells were exposed to air or CS, and changes measured in protein levels. We measured the cortical tension of individual cells and the stiffness of cells in a monolayer. We confirmed that the changes in acute and subacute in vitro smoke exposure reflect protein changes seen in cell monolayers and tissue sections from COPD patients. Epithelial cells exposed to repetitive CS and those derived from COPD patients have increased monolayer permeability. E-cadherin and β-catenin were reduced in smoke exposed cells as well as in lung tissue sections from patients with COPD. Moreover, repetitive CS caused increased tension in individual cells and cells in a monolayer, which corresponded with increased polymerized actin without changes in myosin IIA and IIB total abundance. Repetitive CS exposure impacts the adhesive intercellular junctions and the tension of epithelial cells by increased actin polymer levels, to further destabilize cell adhesion. Similar changes are seen in epithelial cells from COPD patients indicating that these findings likely contribute to COPD pathology.

Mechanistic Evaluation of the Impact of Smoking and Chronic Obstructive Pulmonary Disease on the Nasal Epithelium

Chronic obstructive pulmonary disease (COPD) is one of the major causes of chronic morbidity and mortality worldwide. The development of markers of COPD onset is hampered by the lack of accessibility to the primary target tissue, and there is a need to consider other sample sources as surrogates for biomarker research. Airborne toxicants pass through the nasal epithelium before reaching the lower airways, and the similarity with bronchial histology makes it an attractive surrogate for lower airways. In this work, we describe the transcriptomics findings from the nasal epithelia of subjects enrolled in a clinical study focusing on the identification of COPD biomarkers. Transcriptomic data were analyzed using the biological network approach that enabled us to pinpoint the biological processes affected in the upper respiratory tract in response to smoking and mild-to-moderate COPD. Our results indicated that nasal and lower airway immune responses were considerably different in COPD subjects and caution should be exercised when using upper airway samples as a surrogate for the lower airway. Nevertheless, the network approach described here could present a sensitive means of identifying smokers at risk of developing COPD.

Decreased phosphatase PTEN amplifies PI3K signaling and enhances proinflammatory cytokine release in COPD

The phosphatidylinositol 3-kinase (PI3K) pathway is activated in chronic obstructive pulmonary disease (COPD), but the regulatory mechanisms for this pathway are yet to be elucidated. The aim of this study was to determine the expression and role of phosphatase and tensin homolog deleted from chromosome 10 (PTEN), a negative regulator of the PI3K pathway, in COPD. PTEN protein expression was measured in the peripheral lung of COPD patients compared with smoking and nonsmoking controls. The direct influence of cigarette smoke extract (CSE) on PTEN expression was assessed using primary lung epithelial cells and a cell line (BEAS-2B) in the presence or absence of l-buthionine-sulfoximine (BSO) to deplete intracellular glutathione. The impact of PTEN knockdown by RNA interference on cytokine production was also examined. In peripheral lung, PTEN protein was significantly decreased in patients with COPD compared with the subjects without COPD (P < 0.001) and positively correlated with the severity of airflow obstruction (forced expiratory volume in 1-s percent predicted; r = 0.50; P = 0.0012). Conversely, phosphorylated Akt, as a marker of PI3K activation, showed a negative correlation with PTEN protein levels (r = -0.41; P = 0.0042). In both primary bronchial epithelial cells and BEAS-2B cells, CSE decreased PTEN protein, which was reversed by N-acetyl cysteine treatment. PTEN knockdown potentiated Akt phosphorylation and enhanced production of proinflammatory cytokines, such as IL-6, CXCL8, CCL2, and CCL5. In conclusion, oxidative stress reduces PTEN protein levels, which may result in increased PI3K signaling and amplification of inflammation in COPD.

Use of airway epithelial cell culture to unravel the pathogenesis and study treatment in obstructive airway diseases

Asthma and chronic obstructive pulmonary disease (COPD) are considered as two distinct obstructive diseases. Both chronic diseases share a component of airway epithelial dysfunction. The airway epithelium is localized to deal with inhaled substances, and functions as a barrier preventing penetration of such substances into the body. In addition, the epithelium is involved in the regulation of both innate and adaptive immune responses following inhalation of particles, allergens and pathogens. Through triggering and inducing immune responses, airway epithelial cells contribute to the pathogenesis of both asthma and COPD. Various in vitro research models have been described to study airway epithelial cell dysfunction in asthma and COPD. However, various considerations and cautions have to be taken into account when designing such in vitro experiments. Epithelial features of asthma and COPD can be modelled by using a variety of disease-related invoking substances either alone or in combination, and by the use of primary cells isolated from patients. Differentiation is a hallmark of airway epithelial cells, and therefore models should include the ability of cells to differentiate, as can be achieved in air-liquid interface models. More recently developed in vitro models, including precision cut lung slices, lung-on-a-chip, organoids and human induced pluripotent stem cells derived cultures, provide novel state-of-the-art alternatives to the conventional in vitro models. Furthermore, advanced models in which cells are exposed to respiratory pathogens, aerosolized medications and inhaled toxic substances such as cigarette smoke and air pollution are increasingly used to model e.g. acute exacerbations. These exposure models are relevant to study how epithelial features of asthma and COPD are affected and provide a useful tool to study the effect of drugs used in treatment of asthma and COPD. These new developments are expected to contribute to a better understanding of the complex gene-environment interactions that contribute to development and progression of asthma and COPD.

Aberrant DNA methylation and expression of SPDEF and FOXA2 in airway epithelium of patients with COPD

Background

Goblet cell metaplasia, a common feature of chronic obstructive pulmonary disease (COPD), is associated with mucus hypersecretion which contributes to the morbidity and mortality among patients. Transcription factors SAM-pointed domain-containing Ets-like factor (SPDEF) and forkhead box protein A2 (FOXA2) regulate goblet cell differentiation. This study aimed to (1) investigate DNA methylation and expression of SPDEF and FOXA2 during goblet cell differentiation and (2) compare this in airway epithelial cells from patients with COPD and controls during mucociliary differentiation.

Methods

To assess DNA methylation and expression of SPDEF and FOXA2 during goblet cell differentiation, primary airway epithelial cells, isolated from trachea (non-COPD controls) and bronchial tissue (patients with COPD), were differentiated by culture at the air-liquid interface (ALI) in the presence of cytokine interleukin (IL)-13 to promote goblet cell differentiation.

Results

We found that SPDEF expression was induced during goblet cell differentiation, while FOXA2 expression was decreased. Importantly, CpG number 8 in the SPDEF promoter was hypermethylated upon differentiation, whereas DNA methylation of FOXA2 promoter was not changed. In the absence of IL-13, COPD-derived ALI-cultured cells displayed higher SPDEF expression than control-derived ALI cultures, whereas no difference was found for FOXA2 expression. This was accompanied with hypomethylation of CpG number 6 in the SPDEF promoter and also hypomethylation of CpG numbers 10 and 11 in the FOXA2 promoter.

Conclusions

These findings suggest that aberrant DNA methylation of SPDEF and FOXA2 is one of the factors underlying mucus hypersecretion in COPD, opening new avenues for epigenetic-based inhibition of mucus hypersecretion.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-017-0341-7) contains supplementary material, which is available to authorized users.

Immune-mediated inflammation in the pathogenesis of emphysema: insights from mouse models

The cellular mechanisms that result in the initiation and progression of emphysema are clearly complex. A growing body of human data combined with discoveries from mouse models utilizing cigarette smoke exposure or protease administration have improved our understanding of emphysema development by implicating specific cell types that may be important for the pathophysiology of chronic obstructive pulmonary disease. The most important aspects of emphysematous damage appear to be oxidative or protease stress and sustained macrophage activation and infiltration of other immune cells leading to epithelial damage and cell death. Despite the identification of these associated processes and cell types in many experimental studies, the reasons why cigarette smoke and other pollutants result in unremitting damage instead of injury resolution are still uncertain. We propose an important role for macrophages in the sequence of events that lead and maintain this chronic tissue pathologic process in emphysema. This model involves chronic activation of macrophage subtypes that precludes proper healing of the lung. Further elucidation of the cross-talk between epithelial cells that release damage-associated signals and the cellular immune effectors that respond to these cues is a critical step in the development of novel therapeutics that can restore proper lung structure and function to those afflicted with emphysema.

EGF-Amphiregulin Interplay in Airway Stem/Progenitor Cells Links the Pathogenesis of Smoking-Induced Lesions in the Human Airway Epithelium

The airway epithelium of cigarette smokers undergoes dramatic remodeling with hyperplasia of basal cells (BC) and mucus-producing cells, squamous metaplasia, altered ciliated cell differentiation and decreased junctional barrier integrity, relevant to chronic obstructive pulmonary disease and lung cancer. In this study, we show that epidermal growth factor receptor (EGFR) ligand amphiregulin (AREG) is induced by smoking in human airway epithelium as a result of epidermal growth factor (EGF)-driven squamous differentiation of airway BC stem/progenitor cells. In turn, AREG induced a unique EGFR activation pattern in human airway BC, distinct from that evoked by EGF, leading to BC- and mucous hyperplasia, altered ciliated cell differentiation and impaired barrier integrity. Further, AREG promoted its own expression and suppressed expression of EGF, establishing an autonomous self-amplifying signaling loop in airway BC relevant for promotion of EGF-independent hyperplastic phenotypes. Thus, EGF-AREG interplay in airway BC stem/progenitor cells is one of the mechanisms that mediates the interconnected pathogenesis of all major smoking-induced lesions in the human airway epithelium. Stem Cells 2017;35:824-837.

Tumour-associated neutrophils and loss of epithelial PTEN can promote corticosteroid-insensitive MMP-9 expression in the chronically inflamed lung microenvironment

Matrix metalloproteinase-9 (MMP-9) is increased in a number of pathological lung conditions, where the proteinase contributes to deleterious remodelling of the airways. While both lung cancer and COPD are associated with increased MMP-9 expression, the cellular and molecular drivers of MMP-9 remain unresolved. In this study, MMP-9 transcript measured within the tumour region from patients with non-small-cell lung cancer (NSCLC) and coexisting COPD was found to be uniformly increased relative to adjacent tumour-free tissue. MMP-9 gene expression and immunohistochemistry identified tumour-associated neutrophils, but not macrophages, as a predominant source of this proteinase. In addition, PTEN gene expression was significantly reduced in tumour and there was evidence of epithelial MMP-9 expression. To explore whether PTEN can regulate epithelial MMP-9 expression, a small interfering (si)RNA knockdown strategy was used in Beas-2B bronchial epithelial cells. PTEN knockdown by siRNA selectively increased MMP-9 expression in response to lipopolysaccharide in a corticosteroid-insensitive manner. In summary, tumour-associated neutrophils represent an important source of MMP-9 in NSCLC, and loss of epithelial PTEN may further augment steroid-insensitive expression.