Abstract
Cystic fibrosis is characterized by recurring pulmonary exacerbations that lead to the deterioration of lung function and eventual lung failure. Excessive inflammatory responses by airway epithelia have been linked to the overproduction of the inflammatory cytokine IL-6 and IL-8. The mechanism by which this occurs is not fully understood, but normal IL-1β mediated activation of the production of these cytokines occurs via H2O2 dependent signaling. Therefore, we speculated that CFTR dysfunction causes alterations in the regulation of steady state H2O2. We found significantly elevated levels of H2O2 in three cultured epithelial cell models of CF, one primary and two immortalized. Increases in H2O2 heavily contributed to the excessive IL-6 and IL-8 production in CF epithelia. Proteomic analysis of three in vitro and two in vivo models revealed a decrease in antioxidant proteins that regulate H2O2 processing, by ≥2 fold in CF vs. matched normal controls. When cells are stimulated, differential expression in CF versus normal is enhanced; corresponding to an increase in H2O2 mediated production of IL-6 and IL-8. The cause of this redox imbalance is a decrease by ∼70% in CF cells versus normal in the expression and activity of the transcription factor Nrf-2. Inhibition of CFTR function in normal cells produced this phenotype, while N-acetyl cysteine, selenium, an activator of Nrf-2, and the overexpression of Nrf-2 all normalized H2O2 processing and decreased IL-6 and IL-8 to normal levels, in CF cells. We conclude that a paradoxical decrease in Nrf-2 driven antioxidant responses in CF epithelia results in an increase in steady state H2O2, which in turn contributes to the overproduction of the pro-inflammatory cytokines IL-6 and IL-8. Treatment with antioxidants can ameliorate exaggerated cytokine production without affecting normal responses.
Highlights
Cystic Fibrosis (CF) is an autosomal recessive genetic disorder caused by a genetic defect in the cystic fibrosis transmembrane conductance regulator (CFTR), a protein that functions primarily as a chloride channel [1]
Since significant increases were observed in the 9HTEo2 pCEP-R which express CFTR but lack its function, we tested the effect of the inhibition of CFTR on steady state H2O2 levels in well differentiated human primary tracheal epithelia from three different donors
Signaling mechanisms that increase inflammatory cytokine production are of great interest
Summary
Cystic Fibrosis (CF) is an autosomal recessive genetic disorder caused by a genetic defect in the cystic fibrosis transmembrane conductance regulator (CFTR), a protein that functions primarily as a chloride channel [1]. The most common mutation in humans (DF508) results in the misprocessing, subsequent degradation, and loss of function of CFTR [1]. This results in the dysregulation of ion and fluid transport across the epithelium and a number of secondary defects that exacerbate inflammation, which in the airways culminate in respiratory failure [2]. A hall mark of CF lung disease is exaggerated production of inflammatory cytokines, such as IL-6 [3] and IL-8 [4], which result in excessive inflammation. Early onset of lung infection and the accompanying inflammatory response become self sustaining [5], and destroy the airways, impair gas exchange, and lead to respiratory failure and death.
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