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 anaesthetized 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 in wt mice. Goblet cell thecae per crypt were decreased in slc26a3-/- and increased in cftr-/- 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 of 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.
Keywords: CFTR; anion exchange; inflammatory bowel disease; intestinal electrolyte transport; mucus barrier; pH regulation.
© 2020 The Authors. Acta Physiologica published by John Wiley & Sons Ltd on behalf of Scandinavian Physiological Society.