Modulation of ENaC, CFTR, and iNOS expression in bronchial epithelial cells after stimulation with Staphylococcus epidermidis (94B080) and Staphylococcus aureus (90B083)

Abstract

Bacteria affect the respiratory epithelium, which is covered by airway surface liquid (ASL) and mucus. Ion concentrations in the ASL are determined by the cystic fibrosis transmembrane conductance regulator (CFTR) and the epithelial Na(+) channel (ENaC). Neonatal sepsis is a major risk factor for subsequent pulmonary disease in preterm newborns. Predominating are coagulase-negative staphylococci (e.g., Staphylococccus epidermidis and Staphylococccus aureus). The aim of this study was to investigate modulation of CFTR, ENaC, mucins, proinflammatory cytokines, and inducible nitric oxide synthase (iNOS) in respiratory epithelial cells after S. epidermidis 94B080 and S. aureus 90B083 exposure. Bronchial epithelial cells were incubated with S. epidermidis 94B080 and S. aureus 90B083 (neonatal blood isolates) for 1-36 h. Expression of CFTR, ENaC, iNOS, and mucins was analyzed by real-time PCR and Western blotting. Release of cytokines was analyzed by ELISA, and production of NO by the Griess assay. Expression of CFTR significantly decreased after 36 h incubation with S. epidermidis and more prominently with S. aureus, whereas S. epidermidis caused a significant increase in the expression of β- and γ-ENaC. Expression of iNOS increased, but NO was not detected. Both staphylococci caused a decrease in the intracellular Ca(2+) concentration. S. aureus induced increased secretion of IL-6, IL-8, and transforming nuclear factor (TNF)-α in a time-dependent manner as compared with S. epidermidis. In conclusion, expression of ENaC, CFTR, and iNOS is modulated by exposure to S. aureus 90B083 and S. epidermidis 94B080. S. aureus is more potent in causing release of IL-6, IL-8, and TNF-α by bronchial epithelial cells as compared with S. epidermidis. The mRNA expression for the mucus proteins MUC2, MUC5AC, and MUC5B could not be measured, neither in the presence nor in the absence of bacteria.

Keywords: Airway epithelium; CFTR; ENaC; Staphylococcus aureus 90B083; Staphylococcus epidermidis 94B080; cytokines; iNOS.