Regulation of airway epithelial cell migration by the cystic fibrosis transmembrane conductance regulator.

Abstract

The airway epithelium is a critical barrier between the noxious particles in inspired air and the lung tissue. Mucociliary clearance is an essential function of the airway epithelium to protect against infection and airway damage. By this process, inhaled particles are trapped in the mucus lining the airway and propelled out of the airways by ciliary movement. Transport of Cl- and Na+ ions controls fluid secretion in the airways and the depth and viscosity of the periciliary liquid layer essential for cilia movement. The ion channel cystic fibrosis transmembrane conductance regulator (CFTR), transports Cl- and HCO3 - in the airways and other tissues, and controls the depth of the periciliary liquid layer. Cystic fibrosis is a fatal genetic disease in which CFTR is dysfunctional. As a result, mucociliary clearance is impaired and airways become chronically infected with microorganisms. Microorganism colonization results in recurrent inflammation and cycles of damage to the epithelial barrier followed by wound repair, eventually resulting in airway remodeling and ultimately respiratory failure. It has recently been demonstrated that the loss of CFTR function impairs epithelial restitution in the absence of infection. This suggests the CFTR plays a direct role in airway wound repair. To test this hypothesis, the role of CFTR in the initial step of epithelial wound repair-cell migration- was assessed. An impedance based assay was used to objectively measure cell migration rates of human bronchial epithelial cells. Inhibition of CFTR transport and silencing of CFTR protein expression were used to assess the effect of the loss of functional CFTR on cell migration rate. The migration rate of an airway epithelial cell line isolated from a cystic fibrosis patient was also compared to that of an airway epithelial cell line isolated from a healthy lung. A functional effect of CFTR on the process of lamellipodia protrusion during cell migration was also assessed morphometrically. Time lapse video images were also captured during wound closure of airway epithelial cells to assess how cell migration occurs. Additionally, the dependence of airway epithelial cell migration on Cl- and HCO3 - transport was assessed using ion substitution and selective inhibitors of CFTR and other transporters of these ions. Further, the effect of changes in extracellular pH on migration rate was assessed. The results of these studies revealed a role for CFTR transport of Cl- and HCO3 - to regulate airway epithelial cell migration. These studies contribute to the basic understanding of the repair process of the airways following damage and may potentially be important for the design of new treatments to limit airway damage in cystic fibrosis.