Deficiency of the BKCa potassium channel displayed significant implications for the physiology of the human bronchial epithelium

Plasma membrane large-conductance calcium-activated potassium (BKCa) channels are important players in various physiological processes, including those mediated by epithelia. Like other cell types, human bronchial epithelial (HBE) cells also express BKCa in the inner mitochondrial membrane (mitoBKCa). The genetic relationships between these mitochondrial and plasma membrane channels and the precise role of mitoBKCa in epithelium physiology are still unclear. Here, we tested the hypothesis that the mitoBKCa channel is encoded by the same gene as the plasma membrane BKCa channel in HBE cells. We also examined the impact of channel loss on the basic function of HBE cells, which is to create a tight barrier. For this purpose, we used CRISPR/Cas9 technology in 16HBE14o- cells to disrupt the KCNMA1 gene, which encodes the α-subunit responsible for forming the pore of the plasma membrane BKCa channel. Electrophysiological experiments demonstrated that the disruption of the KCNMA1 gene resulted in the loss of BKCa-type channels in the plasma membrane and mitochondria. We have also shown that HBE ΔαBKCa cells exhibited a significant decrease in transepithelial electrical resistance which indicates a loss of tightness of the barrier created by these cells. We have also observed a decrease in mitochondrial respiration, which indicates a significant impairment of these organelles. In conclusion, our findings indicate that a single gene encodes both populations of the channel in HBE cells. Furthermore, this channel is critical for maintaining the proper function of epithelial cells as a cellular barrier.

Responsiveness of human bronchial fibroblasts and epithelial cells from asthmatic and non-asthmatic donors to the transforming growth factor-β1 in epithelial-mesenchymal trophic unit model

BACKGROUND

The asthma-related airway wall remodeling is associated i.a. with a damage of bronchial epithelium and subepithelial fibrosis. Functional interactions between human bronchial epithelial cells and human bronchial fibroblasts are known as the epithelial-mesenchymal trophic unit (EMTU) and are necessary for a proper functioning of lung tissue. However, a high concentration of the transforming growth factor-β₁ (TGF-β₁) in the asthmatic bronchi drives the structural disintegrity of epithelium with the epithelial-to-mesenchymal transition (EMT) of the bronchial epithelial cells, and of subepithelial fibrosis with the fibroblast-to-myofibroblast transition (FMT) of the bronchial fibroblasts. Since previous reports indicate different intrinsic properties of the human bronchial epithelial cells and human bronchial fibroblasts which affect their EMT/FMT potential beetween cells derived from asthmatic and non-asthmatic patients, cultured separatelly in vitro, we were interested to see whether corresponding effects could be obtained in a co-culture of the bronchial epithelial cells and bronchial fibroblasts. In this study, we investigate the effects of the TGF-β₁ on the EMT markers of the bronchial epithelial cells cultured in the air-liquid-interface and effectiveness of FMT in the bronchial fibroblast populations in the EMTU models.

RESULTS

Our results show that the asthmatic co-cultures are more sensitive to the TGF-β₁ than the non-asthmatic ones, which is associated with a higher potential of the asthmatic bronchial cells for a profibrotic response, analogously to be observed in '2D' cultures. They also indicate a noticeable impact of human bronchial epithelial cells on the TGF-β₁-induced FMT, stronger in the asthmatic bronchial fibroblast populations in comparison to the non-asthmatic ones. Moreover, our results suggest the protective effects of fibroblasts on the structure of the TGF-β₁-exposed mucociliary differentiated bronchial epithelial cells and their EMT potential.

CONCLUSIONS

Our data are the first to demonstrate a protective effect of the human bronchial fibroblasts on the properties of the human bronchial epithelial cells, which suggests that intrinsic properties of not only epithelium but also subepithelial fibroblasts affect a proper condition and function of the EMTU in both normal and asthmatic individuals.

Chemical constituents of tobacco smoke induce the production of interleukin-8 in human bronchial epithelium, 16HBE cells

Background

Interleukin-8 (IL-8) functions as a major chemoattractant and plays pivotal roles in the initiation and development of chronic obstructive pulmonary disease (COPD), and tobacco smoke is a most risk factor contributing to the development of COPD. Hence, we have screened some of the tobacco smoke-derived chemical compounds that potentially induce the production of IL-8 in human bronchial epithelium, 16HBE cells.

Methods

Twenty-eight hazardous smoke components belonging to 9 classes including nicotine, ammonia, aromatic amines, polycyclic aromatic hydrocarbons, phenols, carbonyls, hydrocyanic acid, nitrosamines and other volatile organics were used in the experiments. Proliferation of 16HBE cells was determined by cell counting kit-8 kit, luciferase activity was measured in IL-8 reporter gene-expressing 16HBE cells, and IL-8 levels in culture supernatants were quantified by enzyme-linked immunosorbent assay.

Results

At the non-toxic dosages, chemical compounds belonging to nicotine, aromatic amines, benzopyrene, phenols, aldehydes, and some other volatile organics dose-dependently increased IL-8 reporter gene expression. Consistently, the representative compounds belonging to nicotine, aromatic amines, benzopyrene, phenols, aldehydes, and some other volatile organics significantly and dose-dependently increased IL-8 levels in the culture supernatants of 16HBE cells, among these compounds, benzopyrene is a most potent stimulator for inducing IL-8 production.

Conclusions

The present study has identified particular tobacco smoke constituents responsible for inducing the IL-8 production in human bronchial epithelium, which might help shed light on the pathogenesis of tobacco smoke-induced COPD.