Proinflammatory cytokines induce neurotrophic factor expression in enteric glia: a key to the regulation of epithelial apoptosis in Crohn's disease

Abstract

Objectives: Imbalanced apoptosis of enterocytes is likely to be 1 of the mechanisms underlying Crohn's disease (CD). Apoptosis of enterocytes is regulated by glial-derived neurotrophic factor (GDNF), which is increased in CD. The cellular source of GDNF during gut inflammation is unclear. The aim of the study was to identify the source of GDNF in CD during gut inflammation.

Materials and methods: Glial fibrillary acidic protein (GFAP), GDNF, and smooth muscle actin (SMA) was detected in the gut from patients with CD by immunohistochemistry. Cultured enteric glia cells (EGC) were labeled with anti-GFAP, anti-GDNF, and antibodies and a Golgi marker (anti-58K antibodies) after blocking Golgi export with monensin. Cultured EGCs were treated with interleukin-1beta (IL-1beta), tumor necrosis factor-alpha, and lipopolysaccharides. Secretion of neurotrophic factors was detected by enzyme-linked immunosorbent assay.

Results: Mucosal GFAP-positive EGCs are increased in the colon of patients with CD. This type of glia but not subepithelial myofibroblasts expresses significant amounts of GDNF. In vitro GDNF is continuously secreted from cultured EGCs. The neurotrophic factor secretion could be stimulated by IL-1beta, tumor necrosis factor-alpha, and lipopolysaccharides in a time- and dose-dependent manner. The increased GDNF secretion by EGCs sustained for>12 hours after withdrawal of the proinflammatory cytokines.

Conclusions: A mucosal GFAP expressing EGC population is dramatically increased in CD. This population is a major cellular source of the upregulated GDNF in the inflamed gut. Therefore, mucosal EGC may play a key role in protecting the gut epithelium and may contribute to reestablish the integrity of the injured epithelium.