Ozone Induces Nerve Growth Factor Expression in Tracheal Epithelial Cells in Early Postnatal Life

Abstract

Nerve growth factor (NGF) is produced in the airway epithelium. The purpose of this study was to determine if ozone, a chemical irritant associated with air pollution, alters NGF message levels specifically in tracheal airway epithelial cells at early postnatal ages. Fisher‐344 rat pups were exposed to 2ppm ozone or filtered air for 3 hours on postnatal days (PD) 6, 15 or 21. Twelve hours after exposure, tracheal epithelial cells were isolated and treated in culture with IgG, resulting in an enriched population containing 96.04%±0.60% (n=3) epithelial cells and 3.97%±0.60% (n=3) immune cells. Total RNA was extracted and transcribed into cDNA. NGF mRNA expression was amplified using the real‐time PCR system and analyzed via the comparative threshold method and expressed relative to endogenous β‐actin. At PD 6, the relative NGF mRNA expression in ozone treated rats showed a significant 2‐fold increase in comparison to the air treated animals (p≤0.05, n=3 per group). At PD 15 (n=7 per group) and 21 (n=3 per group), there were no significant changes in NGF mRNA expression between ozone and air treated animals. Thus, the increase in NGF mRNA levels in response to ozone exposure seen at PD 6 was specifically from the tracheal epithelial cells and not immune cells in this cell population. The increase in NGF expression at PD 6 suggests increased sensitivity to ozone exposure compared to PD15 and 21.