Inflammation causes expression of NGF in epithelial cells of the rat colon.

Nerve growth factor (NGF) is a neurotrophin implicated in intestinal pathophysiology, such as impaired barrier function, altered motility and a lowered threshold to noxious stimuli in colitis. We evaluated the cellular source of NGF and determined the effect of inflammation on its expression in TNBS-induced colitis in the rat. Receptors for NGF were studied by immunocytochemistry, showing that submucosal neurons expressed both trkA and p75(NTR). NGF presence and activity was assessed by bioassay, ELISA, western blotting and immunocytochemistry. Bioassay of colonic mucosa using the PC12 cell line showed low levels in control tissue but a marked increase in NGF activity with inflammation. Western blotting showed the appearance of 13 kDa NGF in inflamed mucosa by 6 h, declining over time to become similar to control by 35 days. Semi-quantitative PCR showed minimal mRNA for NGF in control mucosa that increased sharply by 6 h post-TNBS. Laser-capture microdissection was used to collect colonic epithelial cells, where mRNA for NGF was markedly increased by 6 h post-TNBS. While the epithelium of the inflamed colon was positive for NGF by immunocytochemistry, other cell types remained negative. A potential precursor form of NGF, but not 13 kDa NGF itself, was detected in several epithelial cell lines and a mucosal mast cell line. We conclude that NGF is principally synthesized by epithelial cells in the inflamed colon, where the presence of specific receptors suggests the potential for wide-spread action.