Hypoxia-inducible factor 1-dependent induction of intestinal trefoil factor protects barrier function during hypoxia

Mucosal organs such as the intestine are supported by a rich and complex un derlying vasculature. For this reason, the intestine, and particularly barr ier-protective epithelial cells. are susceptible to damage related to dimin ished blood flow and concomitant tissue hypoxia. We sought to identify comp ensatory mechanisms that protect epithelial barrier during episodes of inte stinal hypoxia. Initial studies examining T84 colonic epithelial cells reve aled that barrier function is uniquely resistant to changes elicited by hyp oxia. A search for intestinal-specific. barrier-protective factors revealed that the human intestinal trefoil factor (ITF) gene promoter bears a previ ously unappreciated binding site for hypoxia-inducible factor (HIF)-1. Hypo xia resulted in parallel induction of ITF mRNA and protein. Electrophoretic mobility shift assay analysis using ITF-specific, HIF-1 consensus motifs r esulted in a hypoxia-inducible DNA binding activity, and loading cells with antisense oligonucleotides directed against the alpha chain of HIF-1 resul ted in a loss of ITF hypoxia inducibility. Moreover, addition of anti-ITF a ntibody resulted in a loss of barrier function in epithelial cells exposed to hypoxia, and the addition of recombinant. human ITF to vascular endothel ial cells partially protected endothelial cells from hypoxia-elicited barri er disruption. Extensions of these studies in vivo revealed prominent hypox ia-elicited increases in intestinal permeability in ITF null mice. HIF-1-de pendent induction of ITF may provide an adaptive link for maintenance of ba rrier function during hypoxia.