Genome-wide profiling identifies epithelial cell genes associated with asthma and with treatment response to corticosteroids

Abstract

Airway inflammation and epithelial remodeling are two key features of asthma. IL-13 and other cytokines produced during T helper type 2 cell-driven allergic inflammation contribute to airway epithelial goblet cell metaplasia and may alter epithelial-mesenchymal signaling, leading to increased subepithelial fibrosis or hyperplasia of smooth muscle. The beneficial effects of corticosteroids in asthma could relate to their ability to directly or indirectly decrease epithelial cell activation by inflammatory cells and cytokines. To identify markers of epithelial cell dysfunction and the effects of corticosteroids on epithelial cells in asthma, we studied airway epithelial cells collected from asthmatic subjects enrolled in a randomized controlled trial of inhaled corticosteroids, from healthy subjects and from smokers (disease control). By using gene expression microarrays, we found that chloride channel, calcium-activated, family member 1 (CLCA1), periostin, and serine peptidase inhibitor, clade B (ovalbumin), member 2 (serpinB2) were up-regulated in asthma but not in smokers. Corticosteroid treatment down-regulated expression of these three genes and markedly up-regulated expression of FK506-binding protein 51 (FKBP51). Whereas high baseline expression of CLCA1, periostin, and serpinB2 was associated with a good clinical response to corticosteroids, high expression of FKBP51 was associated with a poor response. By using airway epithelial cells in culture, we found that IL-13 increased expression of CLCA1, periostin, and serpinB2, an effect that was suppressed by corticosteroids. Corticosteroids also induced expression of FKBP51. Taken together, our findings show that airway epithelial cells in asthma have a distinct activation profile and identify direct and cell-autonomous effects of corticosteroid treatment on airway epithelial cells that relate to treatment responses and can now be the focus of specific mechanistic studies.

Fig. 1.

PCR validation of microarray findings. PCR validation of selected genes differentially expressed in epithelial brushings from asthmatic subjects compared with healthy control subjects (A) and genes responsive to corticosteroids in the clinical trial of inhaled fluticasone in asthmatics (B). Fold induction by microarray was statistically significant (P < 0.05, Bonferroni corrected) for all genes shown. Fold induction by PCR (for validation) was statistically significant (P < 0.05) for all genes except the periostin response to fluticasone (POSTN, P = 0.064).

Fig. 2.

Baseline FKBP51 expression correlates inversely with lung function response to fluticasone. Baseline (pretreatment) FKBP51 mRNA expression levels (as measured by PCR) in subjects subsequently randomized to inhaled fluticasone correlated with treatment-related improvements in lung function at 4 weeks (r = −0.62, P = 0.007) (A) and at 8 weeks (r = −0.63, P = 0.009) (B).

Fig. 3.

In vitro effects of IL-13 and corticosteroids on lung epithelial cells. Dexamethasone inhibits induction of periostin (A) and serpinB2 (B) by IL-13 in BEAS-2B cells grown in monolayer (*, P < 0.05 compared with IL-13-exposed cells without dexamethasone). FKBP51 is not induced by IL-13 but is induced by dexamethasone in a dose-dependent manner (C) (*, P < 0.05 compared with cells not exposed to dexamethasone). Dexamethasone (Dex) and budesonide (Bud) inhibit induction of periostin (D) and serpinB2 (E) and CLCA1 (F) by IL-13 and induce expression of FKBP51 (G) in primary airway epithelial cells grown at an ALI (*, P < 0.05 compared with all other groups; †, P < 0.05 compared with all groups except Bud; ‡, P < 0.05 compared with all groups except Dex).