Autocrine regulation of epithelial permeability by hypoxia: Role for polarized release of tumor necrosis factor α

Background & Aims: The intestinal mucosa is lined by a monolayer of protective epithelial cells. This barrier is regulated by immune-derived factors such as interferon gamma (IFN-γ). Because of the high volume of blood flow, the intestine is a primary target for hypoxic damage. We hypothesize that epithelial cytokine responses are regulated by hypoxia. Methods: T84 intestinal epithelial cells were used to assess alterations in permeability, major histocompatibility complex class II induction, cytokine receptor expression, and cytokine release in response to combinations of IFN-γ and cellular hypoxia. Results: Hypoxia potentiated the influence of IFN-γ on epithelial barrier function. Such responses were conferrable in a ≥10-kilodalton conditioned media fraction from hypoxic epithelia. Subsequent experiments identified this factor as epithelium-derived tumor necrosis factor α (TNF-α). Add-back of recombinant TNF-α in combination with IFN-γ to normoxic epithelia recapitulated hypoxia and identified basolaterally polarized TNF-α receptor types I and II on intestinal epithelia. A similar pattern of TNF-α–receptor expression was observed on native intestinal epithelia. Specific inhibition of TNF-α using neutralizing antibody or α- N-phthalimidoglutarimide (thalidomide) resulted in reversal of the hypoxia-evoked responses. Conclusions: These studies indicate that during hypoxia, epithelium-derived mediators such as TNF-α have the potential to regulate permeability through autocrine pathways. GASTROENTEROLOGY 1998;114:657-668