Glucocorticoid‐Driven Transcriptomes in Airway Epithelial Cell Models: Commonalities, Differences and Functional Insights
Authors: Mostafa Mahmoud M , Rider Christopher F , Newton Robert 
Published: November 2023

RATIONALE

Glucocorticoids, typically in an inhaled form, represent the main pharmacotherapeutic option for the treatment of asthma. Acting on the glucocorticoid receptor (GR, NR3C1), glucocorticoids exert anti‐inflammatory effects on target tissues by reducing the expression of numerous inflammatory genes. It is well established that transcriptional activation of multiple “anti‐inflammatory” genes by GR plays a role reducing inflammatory gene expression and/or function at transcriptional, post‐transcriptional, translational and also post‐translational levels. Despite this, a major fraction of those genes induced by glucocorticoids have unknown or unclear functional consequences. Furthermore, consideration of the cell type‐ or line‐specific nature of glucocorticoid is needed to promote understanding of glucocorticoid‐driven transcriptional networks.

AIMS

To provide a descriptive summary of glucocorticoid‐driven gene expression profiles in pulmonary type II A549 and bronchial epithelial BEAS‐2B cells, two commonly‐used epithelial cell lines, and primary human bronchial epithelial (HBE) cells. Both, induction and repression of gene expression are essential components in mediating glucocorticoid function, however, for the purpose of this study, only induced genes are described.

METHODS

Gene expression profiling of RNA extracted from HBE, A549 and BEAS‐2B cells following 6 h of budesonide (300 nM) was performed using Affymetrix Prime View microarrays. Genes that show induction (fold ≥ 2, ANOVA P ≤ 0.05), when compared to untreated, in any of the cell types were used for further comparisons (391 genes). The genes in this pool were also grouped based on a less stringent cutoff (fold ≥ 1.25). Representative genes from each group were validated by qPCR. Gene ontology and Ingenuity Pathway Analysis (IPA) were performed using genes induced in each cell type independently, as well as for groups of commonly regulated genes.

RESULTS

Using the stringent cutoff criteria (fold ≥ 2, ANOVA P ≤ 0.05) for genes induced by glucocorticoid, only 19 genes (~ 5%) were common to all three epithelial cell models and a major fraction of the induced genes was apparently unique to each cell type. However, applying a less stringent cut‐off (fold ≥ 1.25) to this same pool of 391 genes revealed 91 genes (23%) that were commonly induced in all three cell models. Likewise, increased numbers of mutually upregulated genes were observed between any two models. A correspondingly lower percentage of genes were uniquely upregulated in a single cell model (34% of the genes in the pool). Representative genes from each group were validated by qPCR. Gene ontology analysis of commonly upregulated genes showed a significant enrichment of transcriptional control genes and genes involved in signaling.

CONCLUSTIONS

Induction of gene expression is an essential component of glucocorticoid function. While the profile of gene induction differs between cell types, genes with conserved inducibility may represent the key players in shaping glucocorticoid responses. Many such genes are consistent with the anti‐inflammatory effects of glucocorticoids.

Support or Funding Information

Supported by: The Lung Association ‐ Alberta & NWT, AstraZeneca, Canadian Institutes of Health Research.