CTNNAL1 promotes the structural integrity of bronchial epithelial cells through the RhoA/ROCK1 pathway

Abstract

Adhesion molecules play critical roles in maintaining the structural integrity of the airway epithelium in airways under stress. Previously, we reported that catenin alpha-like 1 (CTNNAL1) is downregulated in an asthma animal model and upregulated at the edge of human bronchial epithelial cells (HBECs) after ozone stress. In this work, we explore the potential role of CTNNAL1 in the structural adhesion of HBECs and its possible mechanism. We construct a CTNNAL1‒/‒ mouse model with CTNNAL1-RNAi recombinant adeno-associated virus (AAV) in the lung and a CTNNAL1-silencing cell line stably transfected with CTNNAL1-siRNA recombinant plasmids. Hematoxylin and eosin (HE) staining reveals that CTNNAL1‒/‒ mice have denuded epithelial cells and structural damage to the airway. Silencing of CTNNAL1 in HBECs inhibits cell proliferation and weakens extracellular matrix adhesion and intercellular adhesion, possibly through the action of the cytoskeleton. We also find that the expressions of the structural adhesion-related molecules E-cadherin, integrin β1, and integrin β4 are significantly decreased in ozone-treated cells than in vector control cells. In addition, our results show that the expression levels of RhoA/ROCK1 are decreased after CTNNAL1 silencing. Treatment with Y27632, a ROCK inhibitor, abolished the expressions of adhesion molecules induced by ozone in CTNNAL1-overexpressing HBECs. Overall, the findings of the present study suggest that CTNNAL1 plays a critical role in maintaining the structural integrity of the airway epithelium under ozone challenge, and is associated with epithelial cytoskeleton dynamics and the expressions of adhesion-related molecules via the RhoA/ROCK1 pathway.

1. Introduction

Adhesion molecules on the airway epithelium are a large family of transmembrane receptors that have been identified to be important for maintaining epithelial integrity, maintaining homeostasis, and promoting the inflammatory response [1–3]. Destruction of bronchial epithelial integrity induced by abnormal adhesion is critical for asthma pathogenesis [4,5]. In our previous study, we found that the expression of catenin alpha-like 1 (CTNNAL1) is downregulated in asthma patients and in an ovalbumin-stressed asthmatic mouse model, but markedly increased in human bronchial epithelial cells (HBECs) in the lungs and at the edge of HBECs exposed to ozone stress [6–8]. Moreover, CTNNAL1 has been shown to promote wound repair in bronchial epithelial cells (BECs), inhibit ozone-induced airway epithelial-mesenchymal transition, and regulate mucus hypersecretion induced by house dust mite (HDM) [9,10]. These data indicate that CTNNAL1 may have a protective effect on airway epithelial homeostasis.

The maintenance of respiratory microenvironment homeostasis depends on the airway epithelium. In the presence of environmental pollutants and allergens, the airway epithelium not only acts as an initial barrier but also participates in inflammatory activation. An increasing number of studies have shown that airway epithelial cells play a central role in the pathogenesis of airway diseases, such as asthma and chronic obstructive pulmonary disease (COPD) [11,12]. The denudation of ciliated cells in asthma patients suggests that the airway epithelial barrier is often compromised [12,13]. Therefore, we hypothesized that CTNNAL1 may be involved in the structural integrity of airway epithelial cells.