Glucocorticoids enhance airway epithelial barrier integrity
Highlights
► Glucocorticoids potentiate permeability barrier function in airway epithelial cells. ► Budesonide (BUD) and fluticasone propionate (FP) potentiate permeability barrier function in airway epithelial cells. ► Glucocorticoids potentiate tight junction formation in airway epithelial cells. ► Glucocorticoids enhance EGFR signaling in airway epithelial cells.
Introduction
Asthma is characterized by allergic inflammation and remodeling of the airways [1]. Asthma is a highly complex disease and its pathogenesis remains largely unknown [2]. To date, the first-line therapy for the treatment of asthma is an inhaled corticosteroid (ICS) used for long-term control [3], [4].
The therapeutic role of glucocorticoids (GCs) in allergic diseases, including asthma, is mainly attributed to their powerful anti-inflammatory properties [5]. It is well documented that the central mechanism of the anti-inflammatory properties of GCs is their ability to diminish the infiltration of inflammatory cells into affected tissues [6], [7]. Emerging evidence indicates that airway epithelial cells play a central role in asthma pathogenesis by secreting numerous cytokines and chemokines [8], [9]. Early in vitro studies demonstrated that primary airway epithelial cells expressed functional GC receptors to which radiolabeled ligands bound with high affinity [10]. In airway epithelial cells, treatment with GCs activated a Gal4 response element-mediated reporter that inhibited activating protein-1 and nuclear translocation of transcription factor κB activation, which led to the hypothesis that epithelial cells were a target for the anti-inflammatory effects of ICSs [11].
Although the therapeutic effects of GCs in asthma are largely mediated by the inhibition of inflammatory genes [6], other mechanisms of action could be involved in their therapeutic effects in asthma. Damage to the airways epithelium is a prominent feature in chronic asthma. Apical junctional complexes in the airway epithelium consist mostly of apical tight junctions (TJs) and underlying adherence junctions (AJs) [12]. TJs are responsible for the control of paracellular transport between epithelial cells [13], [14]. A recent study showed that the bronchial epithelial barrier in asthma was compromised, and TJ formation in bronchial epithelial cell cultures obtained from asthmatic patients were significantly lower than from non-asthmatic subjects [15].
The inflamed and damaged airways of asthmatics have been implicated in their increased susceptibility to allergens and viral infections. Therefore, improving this vulnerability of the airways by restoring epithelial integrity could be a potential therapeutic approach for asthma [16]. A previous study that evaluated bronchial biopsies before and after GC treatments of different lengths and courses of administration clearly showed that GCs promoted the restoration of epithelial integrity in asthma [17]. However, the precise roles of GCs on the permeability barrier function of airway epithelial cells are mostly unknown. In the present study, we investigated the effects of GCs on the permeability barrier function and development of TJs in cultured human airway epithelial cells.
Section snippets
Cells and reagents
Transformed human bronchial epithelial cells (16HBE140 −; abbreviated as 16HBE cells) [18] were kindly provided by Associate Professor Dieter C. Gruenert (Gene Therapy Center, Cardiovascular Research Institute, Department of Laboratory Medicine, University of California). Calu-3 cells were obtained from the American Type Culture Collection (Rockville, MD). Dexamethasone (Dex), fluticasone propionate (FP) [19], budesonide (BD) [20], and fluorescein isothiocyanate-labeled dextran (FITC-dextran; 4
Dex potentiates permeability barrier formation
First, to clarify the role of GCs in permeability barrier integrity, we examined the effects of Dex on the development of TER in Calu-3 cells. Calu-3 cells were cultured with or without 10− 6 M Dex applied to the apical and basolateral surfaces of cell monolayers for 5 days. TER of the cells cultured without Dex reached a plateau on day 4 (Fig. 1A). In contrast, TER of the cells cultured with Dex continued to increase up to day 5 (Fig. 1A). Adding varying concentrations of Dex (10− 8, 10− 7, 10− 6 M)
Discussion
Airway epithelial cells are the first site of contact with inhaled allergens, particulates, and viruses. The damaged airway epithelial barrier in asthmatics has been implicated as a cause for their increased susceptibility to allergens and viral infections. Therefore, improving this vulnerability of the airways by restoring epithelial integrity could be a potential therapeutic approach in asthma [9], [16]. In the present study, we found that GCs could improve epithelial barrier integrity and
Acknowledgments
This work was supported in part by the Grants-in-Aid for Scientific Research (C) program of the Ministry of Education, Culture, Sports, Science and Technology of the Japanese Government, the Nihon University Joint Research Grant, and the Matching Fund Subsidy for Private Universities from the Ministry of Education, Culture, Sports, Science and Technology of the Japanese Government.
References (31)
- et al.
The inhaled Steroid Treatment as Regular Therapy in early asthma (START) study: rationale and design
Control Clin Trials
(2001) - et al.
Glucocorticosteroid inhibition of cytokine production: relevance to antiallergic actions
J Allergy Clin Immunol
(1996) Epithelium dysfunction in asthma
J Allergy Clin Immunol
(2007)- et al.
Breakdown in epithelial barrier function in patients with asthma: identification of novel therapeutic approaches
J Allergy Clin Immunol
(2009) - et al.
A comparative study of the effects of an inhaled corticosteroid, budesonide, and a beta 2-agonist, terbutaline, on airway inflammation in newly diagnosed asthma: a randomized, double-blind, parallel-group controlled trial
J Allergy Clin Immunol
(1992) Relative safety and efficacy of inhaled corticosteroids
J Allergy Clin Immunol
(1998)- et al.
MAGUK proteins: structure and role in the tight junction
Semin Cell Dev Biol
(2000) - et al.
Asthma. From bronchoconstriction to airways inflammation and remodeling
Am J Respir Crit Care Med
(2000) - et al.
The many paths to asthma: phenotype shaped by innate and adaptive immunity
Nat Immunol
(2010) - et al.
Efficacy and safety of inhaled corticosteroids. New developments
Am J Respir Crit Care Med
(1998)