Smoking induces shifts in cellular composition and transcriptome within the bronchial mucus barrier

Comprehensive analysis of resilience of human airway epithelial barrier against short-term PM2.5 inorganic dust exposure using in vitro microfluidic chip and ex vivo human airway models

BACKGROUND AND OBJECTIVE

The updated World Health Organization (WHO) air quality guideline recommends an annual mean concentration of fine particulate matter (PM2.5) not exceeding 5 or 15 μg/m3 in the short-term (24 h) for no more than 3-4 days annually. However, more than 90% of the global population is currently exposed to daily concentrations surpassing these limits, especially during extreme weather conditions and due to transboundary dust transport influenced by climate change. Herein, the effect of respirable

METHODS

Silica particles at an average size of 1 μm, referred to as

RESULTS

In the AEB-on-a-chip platform, short-term exposure to 800 μg/mL PM2.5 disrupted AEB integrity via increasing barrier permeability, decreasing cell adhesion-barrier markers such as ZO-1, Vinculin, ACE2, and CD31, impaired cell viability and increased the expression levels of proinflammatory markers; IFNs, IL-6, IL-1s, TNF-α, CD68, CD80, and Inos, mostly under dynamic conditions. Besides, decreased tissue viability, impaired tissue integrity via decreasing of Vinculin, ACE2, β-catenin, and E-cadherin, and also proinflammatory response with elevated CD68, IL-1α, IL-6, IFN-Ɣ, Inos, and CD80 markers, were observed after PM2.5 exposure in ex vivo tissue.

CONCLUSION

The duration and concentration of PM2.5 that can be exposed during extreme weather conditions and natural events aligns with our exposure model (0-800 μg/mL 72 h). At this level of exposure, the resilience of the epithelial barrier is demonstrated by both AEB-on-a-chip platform emulating dynamic forces in the body and ex vivo bronchial biopsy slices. Lung-on-a-chip models will serve as reliable exposure models in this context.

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Key Words

• PM2.5
• airway epithelial barrier
• microfluidic systems
• particulate matter
• silica particles

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Grants

• 2019K12-149080 Presidency of the Republic of Turkey Strategy and Budget Department
• 1139B412102522 Scientific and Technological Research Council of Turkey (TUBITAK)

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Affiliation(s)

Ozlem Goksel Department of Pulmonary Medicine, Division of Immunology and Allergy, Laboratory of Occupational & Environmental Respiratory Diseases and Asthma, Faculty of Medicine, Ege University, Izmir, Turkey Translational Pulmonary Research Center (EgeSAM), Ege University, Izmir, Turkey
Meryem Irem Sipahi Department of Biotechnology and Biomedicine, Technical University of Denmark, Kongens Lyngby, Denmark
Sena Yanasik Department of Bioengineering, Faculty of Engineering, Ege University, Izmir, Turkey
Pelin Saglam-Metiner Translational Pulmonary Research Center (EgeSAM), Ege University, Izmir, Turkey Department of Bioengineering, Faculty of Engineering, Ege University, Izmir, Turkey
Sema Benzer Department of Bioengineering, Faculty of Engineering, Ege University, Izmir, Turkey
Leila Sabour-Takanlou Department of Medical Biology, Faculty of Medicine, Ege University, Izmir, Turkey
Maryam Sabour-Takanlou Department of Medical Biology, Faculty of Medicine, Ege University, Izmir, Turkey
Cigir Biray-Avci Department of Medical Biology, Faculty of Medicine, Ege University, Izmir, Turkey
Ozlem Yesil-Celiktas Translational Pulmonary Research Center (EgeSAM), Ege University, Izmir, Turkey Department of Bioengineering, Faculty of Engineering, Ege University, Izmir, Turkey METU MEMS Center, Ankara, Turkey

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Mucins 3A and 3B Are Expressed in the Epithelium of Human Large Airway

Aberrant mucus secretion is a hallmark of chronic obstructive pulmonary disease (COPD). Expression of the membrane-tethered mucins 3A and 3B (MUC3A, MUC3B) in human lung is largely unknown. In this observational cross-sectional study, we recruited subjects 45-65 years old from the general population of Stockholm, Sweden, during the years 2007-2011. Bronchial mucosal biopsies, bronchial brushings, and bronchoalveolar lavage fluid (BALF) were retrieved from COPD patients (n = 38), healthy never-smokers (n = 40), and smokers with normal lung function (n = 40). Protein expression of MUC3A and MUC3B in bronchial mucosal biopsies was assessed by immunohistochemical staining. In a subgroup of subjects (n = 28), MUC3A and MUC3B mRNAs were quantified in bronchial brushings using microarray. Non-parametric tests were used to perform correlation and group comparison analyses. A value of p < 0.05 was considered statistically significant. MUC3A and MUC3B immunohistochemical expression was localized to ciliated cells. MUC3B was also expressed in basal cells. MUC3A and MUC3B immunohistochemical expression was equal in all study groups but subjects with emphysema had higher MUC3A expression, compared to those without emphysema. Smokers had higher mRNA levels of MUC3A and MUC3B than non-smokers. MUC3A and MUC3B mRNA were higher in male subjects and correlated negatively with expiratory air flows. MUC3B mRNA correlated positively with total cell concentration and macrophage percentage, and negatively with CD4/CD8 T cell ratio in BALF. We concluded that MUC3A and MUC3B in large airways may be a marker of disease or may play a role in the pathophysiology of airway obstruction.

Genetic regulators of sputum mucin concentration and their associations with COPD phenotypes

Hyper-secretion and/or hyper-concentration of mucus is a defining feature of multiple obstructive lung diseases, including chronic obstructive pulmonary disease (COPD). Mucus itself is composed of a mixture of water, ions, salt and proteins, of which the gel-forming mucins, MUC5AC and MUC5B, are the most abundant. Recent studies have linked the concentrations of these proteins in sputum to COPD phenotypes, including chronic bronchitis (CB) and acute exacerbations (AE). We sought to determine whether common genetic variants influence sputum mucin concentrations and whether these variants are also associated with COPD phenotypes, specifically CB and AE. We performed a GWAS to identify quantitative trait loci for sputum mucin protein concentration (pQTL) in the Sub-Populations and InteRmediate Outcome Measures in COPD Study (SPIROMICS, n = 708 for total mucin, n = 215 for MUC5AC, MUC5B). Subsequently, we tested for associations of mucin pQTL with CB and AE using regression modeling (n = 822-1300). Replication analysis was conducted using data from COPDGene (n = 5740) and by examining results from the UK Biobank. We identified one genome-wide significant pQTL for MUC5AC (rs75401036) and two for MUC5B (rs140324259, rs10001928). The strongest association for MUC5B, with rs140324259 on chromosome 11, explained 14% of variation in sputum MUC5B. Despite being associated with lower MUC5B, the C allele of rs140324259 conferred increased risk of CB (odds ratio (OR) = 1.42; 95% confidence interval (CI): 1.10-1.80) as well as AE ascertained over three years of follow up (OR = 1.41; 95% CI: 1.02-1.94). Associations between rs140324259 and CB or AE did not replicate in COPDGene. However, in the UK Biobank, rs140324259 was associated with phenotypes that define CB, namely chronic mucus production and cough, again with the C allele conferring increased risk. We conclude that sputum MUC5AC and MUC5B concentrations are associated with common genetic variants, and the top locus for MUC5B may influence COPD phenotypes, in particular CB.