Oxidative stress enhances the expression of IL-33 in human airway epithelial cells

Interleukin-33 (IL-33) is a cytokine belonging to the IL-1 family, and its possible involvement in the pathophysiology of COPD and viral-induced exacerbations has been demonstrated. IL-33 has been shown to be increased in the airway epithelial cells from COPD patients, but the regulating mechanism of IL-33 expression in airway epithelial cells remains largely unknown. In the current study, we examined whether oxidative stress, which participates in the pathogenesis of COPD, affects the expression of IL-33 in airway epithelial cells and also evaluated the effect during viral infection.

The involvement of oxidative stress in the expression of IL-33, and its signal pathway was examined after stimulation with hydrogen peroxide (H₂O₂), with or without stimulation by polyinosinic-polycytidylic acid [poly (I:C)], a synthetic analogue of dsRNA that mimics viral infection, or rhinovirus infection in NCI-H292 cells and primary human bronchial epithelial cells (HBECs). In addition, the effect of antioxidant, N-acetylcysteine (NAC) in the expression of IL-33 was compared between HBECs from healthy subjects and those from COPD patients.

Treatment with H₂O₂ significantly potentiated IL-33 expression in NCI-H292 cells, and the potentiation was reversed by NAC treatment. Mitogen-activated protein kinase (MAPK) inhibitors, but not nuclear factor-kappa B inhibitors, also significantly decreased the H₂O₂-potentiated IL-33 expression. In addition, H₂O₂ significantly potentiated the poly (I:C)- or rhinovirus-stimulated IL-33 expression. In HBECs from healthy subjects, H₂O₂-potentiated IL-33 expression and its reversal by NAC was also confirmed. Under the condition without H₂O₂-stimulation, treatment with NAC significantly decreased the expression of IL-33 in HBECs from COPD patients, but not in those from healthy subjects.

These results demonstrate that oxidative stress involves in the expression of IL-33 in airway epithelial cells via MAPK signal pathway and it augments IL-33 expression during viral infection. This mechanism may participate in the regulation of IL-33 expression in airway epithelial cells in COPD and the viral-induced exacerbations. Modulation of this pathway could become a therapeutic target for viral-induced exacerbations of COPD.