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

Abstract

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 IFN-γ, and distal colitis, suggesting its role in epithelial barrier homeostasis. Aim To investigate the role of NHE3 in maintaining mucosal integrity. Methods Control or DSS-treated, 6–8 wk 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 NK cells in the IEL and LPL compartments, representing the source of IFN-γ. NHE3−/− mice display alterations in epithelial gene and protein expression patterns which 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. Conclusion 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.

Reduced colonic microbial diversity is associated with colitis in NHE3-deficient mice

“…7A and data not shown). Consistent with our earlier observations (12), all conventional NHE3 Ϫ/Ϫ mice died within 5 days with intestinal bleeding, dramatically lower erythrocyte count, hemoglobin, and hematocrit ( Fig. 7A and data not shown).…”

“…Ϫ/Ϫ mice maintained on the original mixed genetic background develop bacterially mediated, spontaneous distal colitis, which could be ameliorated by the oral administration of broad-spectrum antibiotics (16), and display remarkably high susceptibility to DSS-induced mucosal injury (12). We described increased bacterial adhesion by in situ hybridization and bacterial translocation by tissue gram staining in the distal colon of NHE3 Ϫ/Ϫ mice, and our collaborators recently described changes in the mucous structure and bacterial penetrance (11,16).…”

“…Ϫ/Ϫ mice bred into pure FVB/N genetic background at the University of Cincinnati display diarrhea-predominant phenotype (Shull and Worrell; personal communications), whereas mice on the original mixed 129/Black Swiss background housed at the University of Arizona develop very mild or no diarrhea but clear symptoms of distal colitis (12,15,16). This discrepancy in symptoms may be strain related; crossing NHE3…”

“…In agreement with those clinical observations, our group described the role of NHE3 in the modulation of inflammatory processes and the maintenance of mucosal integrity. NHE3-deficient mice spontaneously develop colitis (16) and are highly susceptible to DSS-induced intestinal injury (12). More recently, we demonstrated the importance of NHE3 in the maintenance of intestinal barrier integrity and in modulating the inflammatory process in IL-10-deficient mice (15).…”

“…Ϫ/Ϫ mice housed in conventional facility are highly susceptible to the cytotoxic effects of DSS (12). To determine whether changes in the microbial environment modulate the DSS-induced morbidity and mortality, we compared the effects of 4% DSS in drinking water in conventional, barrier, and reconventionalized WT and NHE3 Ϫ/Ϫ mice.…”