Cystic Fibrosis Pathogens Activate Ca²⁺-dependent Mitogen-activated Protein Kinase Signaling Pathways in Airway Epithelial Cells

Much of the pulmonary disease in cystic fibrosis is associated with polymorphonuclear leukocyte-dominated airway inflammation caused by bacterial infection. Respiratory epithelial cells express the polymorphonuclear chemokine interleukin-8 (IL-8) in response to ligation of asialylated glycolipid receptors, which are increased on damaged or regenerating cells and those with cystic fibrosis transmembrane conductance regulator mutations. Because both Pseudomonas aeruginosa and Staphylococcus aureus, the most common pathogens in cystic fibrosis, bind asialylated glycolipid receptors such as asialoGM1, we postulated that diverse bacteria can activate a common epithelial signaling pathway to elicit IL-8 expression. P. aeruginosa PAO1 but not pil mutants and S. aureus RN6390 but not the agr mutant RN6911 stimulated increases in [Ca ²⁺]_i in 1HAEo- airway epithelial cells. This response stimulated p38 and ERK1/2 mitogen-activated protein kinase (MAPK) signaling cascades resulting in NF-κB activation and IL-8 expression. Ligation of the asialoGM1 receptor or thapsigargin-elicited Ca²⁺ release activated this pathway, whereas P. aeruginosa lipopolysaccharide did not. The rapid kinetics of epithelial activation precluded bacterial invasion of the epithelium. Recognition of asialylated glycolipid receptors on airway epithelial cells provides a common pathway for Gram-positive and Gram-negative organisms to initiate an epithelial inflammatory response.