Slc26a3 deletion alters pH-microclimate, mucin biosynthesis, microbiome composition and increases Tnfα expression in murine colon.

AIM: SLC26A3 (DRA) mediates the absorption of luminal Cl- in exchange for HCO3- in the distal intestine. Its expression is lost in congenital chloride diarrhoea (CLD) and strongly decreased in the presence of intestinal inflammation. To characterize the consequences of a loss of Slc26a3 beyond disturbed electrolyte transport, colonic mucus synthesis, surface accumulation and composition, pH microclimate, microbiome composition and development of inflammation was studied in slc26a3-/- mice. METHODS: The epithelial surface pH microclimate and the surface mucus accumulation in vivo was assessed by two photon microscopy in exteriorized mid colon of anesthetized slc26a3-/- and wt littermates. Mucus synthesis, composition and inflammatory markers were studied by qPCR and immunohistochemistry and microbiome composition by 16S rRNA sequencing. RESULTS: Colonic pH microclimate was significantly more acidic in slc26a3-/- and to a lesser extent in cftr-/- than wt mice. Goblet cell thecae per crypt were decreased in slc26a3-/- and increased in cftr-/- mid-distal colon. Mucus accumulation in vivo was reduced, but much less so than in cftr-/- colon, which is possibly related to the different colonic fluid balance. Slc26a3-/- colonic luminal microbiome displayed strong decrease in diversity. These alterations preceded and maybe causally related to increased mucosal Tnfα mRNA expression levels and leucocyte infiltration in the mid-distal colon of slc26a3-/- but not in cftr-/- mice. CONCLUSIONS: These findings may explain the strong increase in the susceptibility of slc26a3-/- mice to DSS damage, and offer insight into the mechanisms leading to an increased incidence of intestinal inflammation in CLD patients.