Submitted on November 25, 2008
Revised on January 21, 2009
Accepted on February 2, 2009
Ozone modulates IL-6 secretion in human airway epithelial and smooth muscle cells
Gautam Damera1, Hengjiang Zhao1, Miao Wang1, Michael A Smith2, Christopher Kirby1, William F Jester1, John A Lawson1, and Reynold A Panettieri, Jr.1*
1 University of Pennsylvania
2 Villanova University
* To whom correspondence should be addressed. E-mail: rap{at}mail.med.upenn.edu.
Although ozone enhances leukocyte function and recruitment in airways, the direct effect of ozone in modulating structural cell-derived inflammatory mediators remains unknown. Using a co-culture model comprised of differentiated human airway epithelial cells (NHBE) and smooth muscle cells (ASM), we postulate that ozone regulates IL-6 secretion in basal and cytokine-primed structural cells. Air-liquid interface (ALI) cultures of NHBE cells underwent differentiation as determined by mucin secretion, trans-epithelial electrical resistance (TEER) and ultrastructure parameters. While TNF enhanced basal secretion of IL-6 (57% ± 3%), ozone exposure at 0.6 ppm for 6h augmented IL-6 levels in basal (41% ± 3%) and TNF- (50% ± 5%) primed co-cultures as compared with that derived from NHBE or ASM monolayers alone. Levels of PGE2, 6keto-PGF1
, PGF2 and TXB2 levels in basal and TNF-primed co-cultures revealed that ozone selectively enhanced PGE2 production in TNF- (6-fold ± 3-fold) primed co-cultures, with little effect (P > 0.05) on diluent-treated cultures. In accordance with ozone-induced increases in PGE2 levels, cyclooxygenase inhibition with indomethacin partially abolished IL-6 secretion. Surprisingly, indomethacin had little effect on constitutive secretion of IL-6 in co-cultures while indomethacin completely restored ozone-mediated TEER reduction in TNF-primed co-cultures. Collectively, our data for the first time suggest a dual role of ozone in modulating IL-6 secretion and TEER outcomes in a PGE2-dependent (in presence of TNF-stimulus) and -independent manner (in absence of cytokine stimulus).
