The Airway: More Than Just Oxygen Exchange

When air is inhaled, it travels through the airway to the lungs, where the oxygen is exchanged for carbon dioxide. A single layer of epithelial cells lines the airway, providing a layer of protection against airborne pathogens and toxins. The airway epithelium also produces mucus, which is an added layer of protection against foreign bodies and chemicals, capturing them before they reach the lungs. Airway mucus dysfunction can lead to conditions like asthma or cystic fibrosis. Pathogenic substances that enter the airway include airborne allergens or viruses, but also include toxic substances, such as cigarette smoke, which is voluntarily inhaled. This epithelium is also the site of infection by viruses, including adenoviruses, which cause the common cold, pneumonia, and a multitude of other conditions.

Lifeline® is excited to announce the addition of NEW diseased bronchial/tracheal epithelial cells – cystic fibrosis and NEW diseased small airway cells – asthma + chronic obstructive pulmonary disorder (COPD). These are new additions to our lung/airway catalog and are great models for studying airway diseases like asthma, cystic fibrosis, and COPD. They are both optimized for growth in BronchiaLife™ medium and maintain a normal cellular appearance for up to 15 population doublings. Try them out today!

These new cells join our other lung and airway cells, which include:

Small airway epithelial cells
Bronchial/tracheal epithelial cells
• Laryngeal epithelial cells
Lobar bronchial epithelial cells
Lung smooth muscle cells
Bronchial/tracheal smooth muscle cells
Lung fibroblasts
Lung microvascular endothelial cells

Lifeline® Lung and Airway Epithelial Cells in Epigenetics Research

Cigarette smoking is a significant risk factor for chronic obstructive pulmonary disease, or COPD, which occurs in patients who are chronic smokers. Exposure to cigarette smoke actively changes the phenotype of airway epithelial cells, driven by changes in gene expression and epigenetics. Direct DNA mutations are not the only way to alter protein expression or activity; epigenetic marks, such as methylation or acetylation, can also dictate whether a gene is turned on or off. Aberrant epigenetic changes, in turn, can result in protein expression changes that alter cellular behavior.

In a 2018 study in Scientific Reports, Glass and colleagues set out to define the epigenetic landscape of human airway epithelial cells exposed to cigarette smoke and determine how epigenetic changes affect the transcriptome. Using Lifeline® primary human bronchial epithelial cells (HBECs), they first performed global ChIP-seq analysis in differentiated cells grown in an air-liquid interface (an in vitro culture method that mimics the airway environment). Following treatment with cigarette smoke vapor for up to four days, they looked at H3K27 acetylation (H3K27Ac), which marks active promoters, to examine how gene expression was altered.

Compared to cells exposed to normal air, cells exposed to cigarette smoke vapor showed a number of changes in H3K27Ac marks, indicating accessible regions for transcription. These epigenetic flags were present at some transcription factor promoters, including B-MYB and E2F1. Other genes associated with smoke-induced H3K27Ac were genes involved in cellular stress and cell death. To determine whether the altered epigenetic marks affected gene expression, the authors performed gene expression analysis using microarray in their HBEC model, and compared it with that from previously published data obtained from small airway epithelial cells from human non-smokers and smokers.

They identified 30 genes whose expression was associated with the duration of smoke exposure over the four days of treatment. Fourteen of these genes were differentially expressed in smokers and non-smokers. Finally, the researchers investigated whether the genes marked by H3K27Ac had an associated change in transcript expression. This analysis illustrated that the expression of a group of genes marked by H3K27Ac did increase over time, suggesting that smoke-induced chromatin alterations changes gene expression, which in turn, could affect cellular phenotypes. The results of this study could provide clues to the pathways affected by cigarette smoke that lead to COPD and related airway diseases.

Viral infection of human host cells causes a cascade of gene expression changes that facilitate the manufacturing of new viruses. When a virus infects a host cell, the viral genome begins to be transcribed by the cellular machinery. The E1A region of the adenoviral genome is the first to be transcribed and the translated E1A protein interacts with certain host cell proteins to alter host cell gene expression. For example, E1A interaction with p300 (a histone acetyltransferase) inhibits its acetyltransferase activity, resulting in epigenetically controlled changes in gene expression. In a 2018 study in the Journal of Virology, Hsu and colleagues investigated the intricacies of E1A interaction with p300 and how this interaction affects viral gene expression.

Using live cell imaging of cells expressing fluorescently tagged p300 and E1A, the authors first demonstrated that the two proteins were colocalized. To map the regions required for p300 interaction, they observed colocalized of deletion mutants and identified two acidic peptides comprised of amino acids (aa) 133–138 and aa189–200. Importantly, using luciferase reporter assays to visually report transcriptional activity, they found that mutation of these regions also disrupted transcriptional activation of early adenoviral promoter regions. Using confluent Lifeline® primary human bronchial/tracheal epithelial cells (HBTECs), the authors illustrated that mutation of the two p300-binding regions in E1A had different effects on early viral promoters. While expression of E2, E4, and E3 viral genes were decreased 18 hours after infection, L3 expression was not as significantly affected. Additionally, the authors showed that the effects of E1A on transcriptional activation was also dependent on E1A interaction with multisubunit mediator complexes, which are activators of RNA polymerase II-dependent transcription.

The authors next determined the effects of E1A on histone acetylation using Lifeline® HBTECs by evaluating the changes in histone acetylation of viral promoters, as well as changes in the association of transcriptional activators (TATA box-binding protein [TBP] and RNA polymerase II) with the same viral promoters using ChIP-seq. In HBTECs expressing E1A with mutant p300-binding regions, levels of H3K18 and H3K27 acetylation at E2early, E3, and E4 promoters was reduced, although TBP and RNA polymerase II association were only disrupted at the E2early promoter. Loss of p300 binding to E1A did not affect association of TBP and RNA polymerase II at the E4 promoter, although it did significantly decrease E4 mRNA, suggesting that the loss of p300 binding affects E4 transcription after TBP and RNA polymerase II binding.

Together, the results of this study demonstrate that interaction of p300 with the E1A viral protein regulates transcription of viral genes through acetylation of viral gene promoters and subsequent regulation of gene expression.

Let us know how you are using Lifeline® cells in your research! Our blog is posted every other week and could feature your research study!