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.

Members of the solute carrier 26 (SLC26) family have emerged as important players in mediating anions fluxes across the plasma membrane of epithelial cells, in cooperation with the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. Among them, SLC26A3 acts as a chloride/bicarbonate exchanger, highly expressed in the gastrointestinal, pancreatic and renal tissues. In humans, mutations in the SLC26A3 gene were shown to induce congenital chloride-losing diarrhea (CLD), a rare autosomal recessive disorder characterized by life-long secretory diarrhea. In view of some reports indicating subfertility in some male CLD patients together with SLC26-A3 and -A6 expression in the male genital tract and sperm cells, we analyzed the male reproductive parameters and functions of SLC26A3 deficient mice, which were previously reported to display CLD gastro-intestinal features. We show that in contrast to Slc26a6, deletion of Slc26a3 is associated with severe lesions and abnormal cytoarchitecture of the epididymis, together with sperm quantitative, morphological and functional defects, which altogether compromised male fertility. Overall, our work provides new insight into the pathophysiological mechanisms that may alter the reproductive functions and lead to male subfertility in CLD patients, with a phenotype reminiscent of that induced by CFTR deficiency in the male genital tract.

Our results thus provide new insights into the development of inflammation and relapse in UC and suggest that the stem cell niche in the colon may influence pathogenesis of the disease.

These results suggest that the variation of glutathione levels along the villus-crypt axis in the intestine is due to gradients in expression of mediators such as glutamate cysteine ligase modifier subunit and Nrf2. The protective effects of glutamine supplementation seem to be most pronounced in the crypt, where it upregulates proliferation, glutathione levels and alters actin dynamics.

Carbonic anhydrase XIV (Car14) is highly expressed in the hepatocyte, with predominance in the canalicular membrane and its active site in the extracellular milieu. The aim of this study is to determine the physiological relevance of Car14 for biliary fluid and acid/base output, as well as its role in the maintenance of hepatocellular and cholangiocyte integrity. The common bile duct of anesthetized car14−/− and car14+/+ mice was cannulated and hepatic HCO3− output was measured by microtitration and bile flow gravimetrically before and during stimulation with intravenously applied tauroursodeoxycholic acid (TUDCA). Morphological alterations and hepatic damage were assessed histologically and immunohistochemically in liver tissue from 3- to 52-week-old car14−/− and car14+/+ mice, and gene and/or protein expression was measured for pro-inflammatory cytokines, fibrosis, and cholangiocyte markers. Biliary basal and more so TUDCA-stimulated HCO3− output were significantly reduced in car14−/− mice of all age groups, whereas bile flow and hepatic and ductular morphology were normal at young age. Car14−/− mice developed fibrotic and proliferative changes in the small bile ducts at advanced age, which was accompanied by a reduction in bile flow, and an upregulation of hepatic cytokeratin 19 mRNA and protein expression. Membrane-bound Car14 is essential for biliary HCO3− output, and its loss results in gradual development of small bile duct disease and hepatic fibrosis. Bile flow is not compromised in young adulthood, suggesting that Car14-deficient mice may be a model to study the protective role of biliary canalicular HCO3− against luminal noxi to the cholangiocyte.

Genetic defects in SLC26A3 (DRA), an intestinal Cl − /HCO 3 − exchanger, result in congenital chloride diarrhea (CLD), marked by lifelong acidic diarrhea and a high risk of inflammatory bowel disease. Slc26a3 −/− mice serve as a model to understand the pathophysiology of CLD and search for treatment options. This study investigates the microbiota changes in slc26a3 −/− colon, the genotype-related causes for the observed microbiota alterations, its inflammatory potential, as well as the corresponding host responses. The luminal and the mucosa-adherent cecal and colonic microbiota of cohoused slc26a3 −/− and wt littermates were analyzed by 16S rRNA gene sequencing. Fecal microbiota transfer from cohoused slc26a3 −/− and wt littermates to germ-free wt mice was performed to analyze the stability and the inflammatory potential of the communities. The cecal and colonic luminal and mucosa-adherent microbiota of slc26a3 −/− mice was abnormal from an early age, with a loss of diversity, of short-chain fatty acid producers, and an increase of pathobionts. The transfer of slc26a3 −/− microbiota did not result in intestinal inflammation and the microbial diversity in the recipient mice normalized over time. A strong increase in the expression of Il22, Reg3β/γ, Relmβ , and other proteins with antimicrobial functions was observed in slc26a3 −/− colon from juvenile age, while the mucosal and systemic inflammatory signature was surprisingly mild. The dysbiotic microbiota, low mucosal pH, and mucus barrier defect in slc26a3 −/− colon are accompanied by a stark upregulation of the expression of a panel of antimicrobial proteins. This may explain the low inflammatory burden in the gut of these mice.

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Mutations in the CFTR chloride channel result in intestinal obstructive episodes in cystic fibrosis (CF) patients and in CF animal models. In this study, we explored the possibility of reducing the frequency of obstructive episodes in cftr−/− mice through the oral application of a gut-selective NHE3 inhibitor tenapanor and searched for the underlying mechanisms involved. Sex- and age-matched cftr+/+ and cftr−/− mice were orally gavaged twice daily with 30 mg kg− 1 tenapanor or vehicle for a period of 21 days. Body weight and stool water content was assessed daily and gastrointestinal transit time (GTT) once weekly. The mice were sacrificed when an intestinal obstruction was suspected or after 21 days, and stool and tissues were collected for further analysis. Twenty-one day tenapanor application resulted in a significant increase in stool water content and stool alkalinity and a significant decrease in GTT in cftr+/+ and cftr−/− mice. Tenapanor significantly reduced obstructive episodes to 8% compared to 46% in vehicle-treated cftr−/− mice and prevented mucosal inflammation. A decrease in cryptal hyperproliferation, mucus accumulation, and mucosal mast cell number was also observed in tenapanor- compared to vehicle-treated, unobstructed cftr−/− mice. Overall, oral tenapanor application prevented obstructive episodes in CFTR-deficient mice and was safe in cftr+/+ and cftr−/− mice. These results suggest that tenapanor may be a safe and affordable adjunctive therapy in cystic fibrosis patients to alleviate constipation and prevent recurrent DIOS.