The anion exchanger slc26a3 regulates colonic mucus expansion during steady state and in response to prostaglandin E2, while Cftr regulates de novo mucus release in response to carbamylcholine.

The intestinal epithelium is covered by mucus that protects the tissue from the luminal content. Studies have shown that anion secretion via the cystic fibrosis conductance regulator (Cftr) regulates mucus formation in the small intestine. However, mechanisms regulating mucus formation in the colon are less understood. The aim of this study was to explore the role of anion transport in the regulation of mucus formation during steady state and in response to carbamylcholine (CCh) and prostaglandin E2 (PGE2). The broad-spectrum anion transport inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS), CftrdF508 (CF) mice, and the slc26a3 inhibitor SLC26A3-IN-2 were used to inhibit anion transport. In the distal colon, steady-state mucus expansion was reduced by SLC26A3-IN-2 and normal in CF mice. PGE2 stimulated mucus expansion without de novo mucus release in wild type (WT) and CF colon via slc26a3 sensitive mechanisms, while CCh induced de novo mucus secretion in WT but not in CF colon. However, when added simultaneously, CCh and PGE2 stimulated de novo mucus secretion in the CF colon via DIDS-sensitive pathways. A similar response was observed in CF ileum that responded to CCh and PGE2 with DIDS-sensitive de novo mucus secretion. In conclusion, this study suggests that slc26a3 regulates colonic mucus expansion, while Cftr regulates CCh-induced de novo mucus secretion from ileal and distal colon crypts. Furthermore, these findings demonstrate that in the absence of a functional Cftr channel, parallel stimulation with CCh and PGE2 activates additional anion transport processes that help release mucus from intestinal goblet cells.

Low-grade intestinal inflammation two decades after pelvic radiotherapy.

BACKGROUND: Radiotherapy is effective in the treatment of cancer but also causes damage to non-cancerous tissue. Pelvic radiotherapy may produce chronic and debilitating bowel symptoms, yet the underlying pathophysiology is still undefined. Most notably, although pelvic radiotherapy causes an acute intestinal inflammation there is no consensus on whether the late-phase pathophysiology contains an inflammatory component or not. To address this knowledge gap, we examined the potential presence of a chronic inflammation in mucosal biopsies from irradiated pelvic cancer survivors. METHODS: We biopsied 24 cancer survivors two to 20 years after pelvic radiotherapy, and four non-irradiated controls. Using tandem mass tag (TMT) mass spectrometry and mRNA sequencing (mRNA-seq), we charted proteomic and transcriptomic profiles of the mucosal tissue previously exposed to a high or a low/no dose of radiation. Changes in the immune cell populations were determined with flow cytometry. The integrity of the protective mucus layers were determined by permeability analysis and 16S rRNA bacterial detection. FINDINGS: 942 proteins were differentially expressed in mucosa previously exposed to a high radiation dose compared to a low radiation dose. The data suggested a chronic low-grade inflammation with neutrophil activity, which was confirmed by mRNA-seq and flow cytometry and further supported by findings of a weakened mucus barrier with bacterial infiltration. INTERPRETATION: Our results challenge the idea that pelvic radiotherapy causes an acute intestinal inflammation that either heals or turns fibrotic without progression to chronic inflammation. This provides a rationale for exploring novel strategies to mitigate chronic bowel symptoms in pelvic cancer survivors. FUNDING: This study was supported by the King Gustav V Jubilee Clinic Cancer Foundation (CB), The Adlerbertska Research Foundation (CB), The Swedish Cancer Society (GS), The Swedish State under the ALF agreement (GS and CB), Mary von Sydow's foundation (MA and VP).