Ambient Particulate Matter-Induced CCL20 Production in Airway Epithelial Cells is NADPH Oxidase-Dependent

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RATIONALE: The exacerbation and/or induction of asthma can be linked to exposure to airborne particulate matter (PM), although the mechanism(s) are unknown. We have previously shown that mice exposed to ambient PM collected in urban Baltimore (AUB) developed airway hyperresponsiveness, concomitant with recruitment and activation of dendritic cells and Th2 cells. To begin to understand the mechanisms by which AUB induces dendritic cell recruitment, we conducted a gene expression profiling experiment of mouse epithelial cells exposed to AUB. We found that AUB-induced increases in the expression of the immature dendritic cell chemokine, CCL20, and pro-oxidant genes in the NADPH oxidase pathway (Ncf4, Noxo1). The goal of the current study was to define the role of oxidative stress in CCL20 production.

METHODS: Tracheal epithelial cells were harvested from A/J or Cybb^tm1Din/J mice and wildtype C57BL/6 mice and exposed to AUB (50 μg/ml) with or without apocynin (100 μM or 1 mM) for 24 hours in vitro. Cytokine levels were determined by ELISA.

RESULTS: As expected AUB increased CCL20 production from A/J cells. Treatment with the NADPH oxidase inhibitor apocynin resulted in a significant decrease in CCL20 release. To further explore the role of NADPH oxidase, we examined CCL20 production in epithelial cells from Cybb^tm1Din/J mice, which lack gp91^phox the major subunit of the NADPH oxidase complex. Interestingly, we found that CCL20 production is significantly decreased in the knockout in comparison to C57BL/6 controls.

CONCLUSIONS: Our results suggest that PM may initiate DC recruitment through epithelial cell production of CCL20 in a NADPH oxidase-dependent manner.