Aeroallergens Derived from Alternaria alternata Stimulate COX2‐dependent Expression of Antioxidant Defense Enzymes in Human Bronchial Epithelial Cells

Abstract

Alternaria aeroallergens stimulate allergic inflammation and exacerbation of respiratory distress in patients with asthma. Our previous studies have demonstrated that release of ATP and subsequent increases in intracellular [Ca2+] was the result of Alternaria induced oxidative stress. Stimulation of Human Bronchial Epithelial Cells (HBECs) with Alternaria extract for 12 hours induced the expression of several phase II antioxidant enzymes, including cyclooxygenase 2 (COX2) which exhibited a 19 fold increase in mRNA expression. HBE cells loaded with CellRox™ Orange, a fluorogenic probe used for detecting oxidative stress, revealed that blocking COX2 inhibited resveratrol mediated inhibition of Alternaria induced oxidative stress. Furthermore induction of COX2 following Alternaria exposure was associated with an increase in expression of prostaglandin D2 synthase and PGD2 secretion into the extracellular media. Moreover, 15‐deoxy Δ12,14‐protaglandin J2 (15d‐PGJ2) a metabolic product of PGD2 was also shown to decrease Alternaria induced oxidative stress. These results suggest that upregulation of COX2 following sustained exposure to Alternaria induces PGD2 synthesis and subsequent formation of 15d‐PGJ2, a known activator of Nrf2 signaling and ultimately, increased expression of phase II antioxidant enzymes.