Downregulation of ENaC expression and activity by Pseudomonas LPS in alveolar epithelial cells

Abstract

Pseudomonas aeruginosa is a gram negative bacteria that causes chronic infection in cystic fibrosis patients and is known to modulate the epithelial Na channel (ENaC) expression in experimental chronic pneumonia models. For this reason, we tested if LPS from P. aeruginosa could modulate the expression and activity of ENaC in alveolar epithelial cells. Alveolar epithelial cells purified from rat lung were cultured on permeable filters for 4 days before the cells were treated on the apical side with 15 μg/ml of Pseudomonas LPS. The treatment decreased gradually the total transepithelial current with the lowest point reached at 4h with a 35% decline compared to untreated cells. The ENaC (amiloride‐sensitive) portion of this current was declined by 53% at 4h. The α and βENaC mRNA were decreased respectively to 55% and 54% of control by a 4h LPS treatment. Estimation of ENaC activity at the apical membrane following amphotericin B permeabilisation of the basolateral membrane in presence of a Na gradient shows a 52% decrease in 4h LPS treated cells. The decline in ENaC current elicited by LPS is therefore the consequence of a decreased activity of the channel. Ro‐31 8820 a PKC inhibitor abolished the downregulation of ENaC activity in the cells and also restored the α and γENaC mRNA level back to normal. These results show that LPS downregulates ENaC mRNA expression and activity in alveolar epithelial cells by a PKC‐sensitive pathway.Supported by CCFF and CIHR