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CHARACTERIZATION OF NERVE GROWTH FACTOR (NGF) IN ESOPHAGEAL EPITHELIUM
W Wan, N Mak, DJ Mulder, CJ Justinich
GI Diseases Research Unit, Departments of Pediatrics, Physiology and Medicine, Queen’s University, Kingston Ontario
INTRODUCTION: Nerve growth factor (NGF) is an essential neurotrophic factor for neuronal survival at mucosal surfaces. Acid is known to modulate NGF production. NGF has not been characterized in esophageal epithelium. Whether acid-reflux alters NGF expression is unknown.
AIM: To characterize neurotrophins in esopagheal epithelium and to demonstrate acid-induced upregulation of NGF.
METHODS: Studies were performed using a transformed human esophageal epithelial cell line (HET-1A). RT-PCR was performed for neurotrophins, Western blot for NGF of HET-1A cell lysates and concentrated supernatants and bioactive NGF concentration was measured using a standardized pheochromocytoma cell-line (PC12) bioassay. HET-1A cells were exposed to acidified media (pH 5.5) or capsaicin (500nM) for 5 minute pulses, 6 and 24 hours. We then examined the effect of acid on secretion of NGF from esophageal biopsy explants.
RESULTS: Acid and capsaicin increased NGF mRNA in HET-1A cells. Western blot was not sensitive enough to detect changes in the pro-NGF or biologically active 2.5 S-NGF. Functionally active NGF protein as determined by the PC12 assay revealed a 5-6 fold increase in NGF from cells or biopsies in the presence of acid or capsaicin.
CONCLUSIONS: Biologically active NGF is secreted by esophageal epithelial cells and NGF secretion increases in conditions mimicking acid reflux disease. Neurotrophins from esophageal epithelium may play a role in reflux esophagitis.