Changes in Mucosal Homeostasis Predispose NHE3 Knockout Mice to Increased Susceptibility to DSS-Induced Epithelial Injury

Background & Aims: NHE3 is a target of inhibition by proinflammatory cytokines and pathogenic bacteria, an event contributing to diarrhea in infectious and idiopathic colitis. In mice, NHE3 deficiency leads to mild diarrhea, increased intestinal expression of interferon (IFN)-γ, and distal colitis, suggesting its role in epithelial barrier homeostasis. Our aim was to investigate the role of NHE3 in maintaining mucosal integrity. Methods: Control or dextran sulfate sodium (DSS)-treated, 6- to 8-week-old wild-type (WT) and NHE3^-/- mice were used for the experiments. Small intestines were dissected for further analysis. Results: NHE3^-/- mice have elevated numbers of CD8α⁺ T and natural killer cells in the intraepithelial lymphocytes and lamina propria lymphocytes compartments, representing the source of IFN-γ. NHE3^-/- mice display alterations in epithelial gene and protein expression patterns that predispose them to a high susceptibility to DSS, with accelerated mortality resulting from intestinal bleeding, hypovolemic shock, and sepsis, even at a very low DSS concentration. Microarray analysis and intestinal hemorrhage indicate that NHE3 deficiency predisposes mice to DSS-induced small intestinal injury, a segment never reported as affected by DSS, and demonstrate major differences in the colonic response to DSS challenge in WT and NHE3^-/- mice. In NHE3^-/- mice, broad-spectrum oral antibiotics or anti-asialo GM1 antibodies reduce the expression of IFN-γ and iNOS to basal levels and delay but do not prevent severe mortality in response to DSS treatment. Conclusions: These results suggest that NHE3 participates in mucosal responses to epithelial damage, acting as a modifier gene determining the extent of the gut inflammatory responses in the face of intestinal injury.