M. Mallicote1, C. Gayer1 1Children’s Hospital Los Angeles,Los Angeles, CA, USA
Introduction: Activation of the farnesoid X receptor (FXR) has been reported to decrease gut permeability in colonic murine injury models like DSS colitis, protecting against intestinal bacterial translocation. However, we have shown that FXR knock out (FXR-KO) mice have attenuated barrier dysfunction when challenged with LPS, which affects the small bowel much more than the colon. These observations suggest that FXR may function differently in the small versus large bowel. We hypothesize that FXR-KO animals will have increased intestinal barrier permeability in the colon while less barrier permeability in the small intestine.
Methods: Four cm segments of terminal ileum and proximal colon were collected from WT and FXR-KO mice. Luminal contents were gently flushed out and replaced with a fluorescein isothiocyanate-dextran (FITC) solution with or without 2 mg/ml LPS. Both ends of the intestinal segments were then sealed with 2-0 silk ties. Each sealed intestinal segment was then placed in 2 ml of phosphate-buffered saline and barrier leakage was assessed by measuring FITC levels in PBS at 0, 1, 2, 4, 8, 16, and 24-hour time intervals. Two-way repeated measures ANOVA was performed as appropriate.
Results: Ileal barrier permeability in FXR-KO mice was significantly increased at 24 hours compared to WT mice at baseline. However, when challenged with LPS, the ileal barrier permeability was attenuated in FXR-KO mice but was worsened in WT mice at 24 hours. No difference was seen in colonic barrier permeability in FXR-KO mice when compared to WT controls. When treated with LPS, WT animals showed significantly increased barrier permeability at 8 hours, while FXR-KO animals did not show a change in barrier function
Conclusions: These data suggest that FXR affects the intestinal barrier differently in the small intestine versus the colon, both at baseline and in response to inflammatory stimuli. Understanding these differential effects is crucial if we are to target FXR in diseases such as Crohn’s disease that affects both the small bowel and colon.