Colonic bile acids regulate epithelial wound healing

Background Epithelial restitution is an essential process for maintenance of intestinal barrier function. While previously published data have shown bile acids to be involved in regulation of epithelial barrier function in in vivo models of colonic inflammation, their roles in regulating restitution are not yet known. Here, we investigated the effects of bile acids on epithelial restitution and the molecular pathways involved in colonic epithelial healing. Methods Wounds were created by pinch biopsy in C5BL/6 mice during colonic endoscopy. Animals received daily topical application of deoxycholic acid (DCA; 150 μM) or the “therapeutic” bile acid, ursodeoxycholic acid (UDCA; 150 μM). Images of the wounds were taken at day 2 and day 6 post wounding and the area of the wounds was measured by Image J ®software. T 84 colonic epithelial cells, grown as monolayers on transparent permeable supports, were wounded at T=0. Cells were treated with DCA (50 – 150 μM), UDCA (50 – 150 μM, a farnesoid X receptor (FXR) agonist, GW4064 (10 μM), or the cystic fibrosis transmembrane conductance regulator (CFTR) channel blockers, CFTR(inh)‐172 (10 μM) or GlyH‐101 (25 μM). Restitution was measured as wound area after 48 h and expressed as % T=0 wound area. HEK‐293 cells were transfected with vectors expressing FXR and the luciferase gene under control of the CFTR promoter. Protein expression was assessed by western blotting, mRNA levels were assessed by q‐PCR and cell migration by Boyden chamber assay. Results Wound healing was significantly delayed in animals treated with DCA compared to control (Day 6 Wound Area −0.41 ± 0.15 mm 2 , p= 0.0287, N=5). DCA also inhibited wound closure in cultured epithelial monolayers and attenuated cell migration in Boyden chamber assays, without significantly altering cell proliferation. Nuclear accumulation of FXR was detected upon DCA stimulation, while activation of FXR by GW4064 inhibited epithelial wound closure to 35.1 ± 1.1%, compared to 51.6 ± 5 % in vehicle‐treated controls (n = 5; p < 0.05) and decreased T 84 cell migration in Boyden chambers to 57 ± 9.6 % (n = 3; p <0.05) of that in controls. To address the mechanism by which DCA exerts its action on wound healing, levels of CFTR expression was measured. Both, DCA and GW4064, attenuated CFTR mRNA levels, along with total and surface CFTR protein expression, whereas promoter/reporter assays revealed that transcriptional downregulation of CFTR by DCA is mediated in an FXR specific manner. Furthermore, inhibition of CFTR activity with either CFTR(inh)‐172 or GlyH‐101 mimicked the effects of FXR on wound healing. In contrast, UDCA (50 – 150 μM) enhanced wound healing in both in vitro and in vivo models and prevented the effects of DCA in cell migration and restitution assays. Conclusions In conclusion, these studies suggest that bile acids are important regulators of epithelial wound healing and are therefore good targets for the development of new drugs to modulate intestinal barrier function in disease treatment. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .