Colonic Microbiome and Barrier Dysfunction Contribute to Susceptibility to Colitis in NHE3xRag2 Double Knockout Mice

Intestinal Na⁺/H⁺ exchanger NHE3 is functionally and/or transcriptionally repressed in IBD. NHE3^-/- mice develop chronic colitis, IBD-like microbial dysbiosis, and are highly susceptible to mucosal injury. Here, we show a dramatic susceptibility of Rag2/NHE3 knockout (DKO) to colitis in the naïve T cell transfer model. Compared to Rag2^-/-, DKO mice develop early onset severe colitis, T-cell and neutrophil infiltration, elevated mucosal inflammatory cytokines, and increased epithelial permeability. This response was suppressed by broad-spectrum antibiotics. In fecal 16S rRNA amplicon profiling, genotype and antibiotic use were the predominant determinants of microbial diversity. The composition of the Firmicutes phylum was most significantly altered in DKO mice (Rag2 vs. DKO), with changes in among Lactobacillales (Lactobacillus, 24.1 vs. 15.6%; Enterococcus, 0.3 vs. 2.5%), Turicibacterales (1.7 vs. 4.8%), Erisipelotrichales (1.7 vs. 30.8%), and a dramatic decrease in Clostridiales (23.1 vs. 5.6%).   Fecal transplant from T-cell-transferred DKO mice into Abx-pretreated Rag2^-/- mice was not sufficient to fully recapitulate the donors’ severity of colitis, with the exception of significant difference in weight gain and a significantly elevated colonic neutrophil infiltration. Our data suggest that impaired epithelial Na⁺/H⁺ exchange contributes to the susceptibility to T-cell mediated colitis via both altered colonic microbiota and an epithelial barrier defect.