Breaking barrier integrity in alveolar epithelial cells leads to modification in the expression profile of tight junction and ion transporter genes

Abstract

Acute lung injury is associated with epithelial disruption and abnormal transepithelial Na+ transport affecting lung oedema clearance and injury recovery. In the past, we reported that ENaC expression is downregulated in alveolar epithelial cells in presence of pro‐inflammatory conditions. However, the impact of loss of barrier integrity on ion channels and genes important for barrier integrity in these cells is not known. In the present work, we determined if loss of barrier integrity, in absence of inflammation, would have an impact on the gene expression profile of rat alveolar epithelial cells in primary culture, focussing on ion transporter and tight junction genes. We found that mechanical wounding (MW), induces a ~60% decrease of α,β and γENaC mRNA expression at 6h and 24h and ~40% decrease of αNa/K‐ATPase mRNA expression. ENaC short‐circuit current (Isc) recorded in Ussing chamber was decreased by 80% at 6h following MW and was correlated to αENaC mRNA expression (R=0,8379). Beside ENaC and Na/K‐ATPase, the expression profile of genes important for restauration of barrier integrity or epithelial differentiation was investigated at 6h following MW. There was an upregulation of tight junction genes (Cldn3 (171%), Cldn4 (288%), but not of Cldn5 and Cldn18. Integrin (Itgb3 (160%)) and epithelial markers (Ker8 (153%), Ker18 (209%)) were upregulated at 6h along with Ker14 (279%). While Cldn 3 and Cldn4 expressions were back to normal after 24h, αENaC gene expression was normalized only after 48h. This expression profile was also observed if we disrupt tight junction with a short EDTA treatment. Altogether the present data suggest that breaking epithelial barrier integrity leads to a change in epithelial cells phenotype where the cells prepare themselves to repair and restore tight junctions and cell polarity. Our results show that disruption of barrier integrity also affects ENaC expression and activity. These data will help to better understand the consequences of alveolar epithelial injury in the resolution of edema following lung injury.