Effects of urocortins on intestinal epithelial permeability in the mouse colon
Authors: Liu Sumei , Karo Aaron , Bhargava Aditi 
Published: May 2023

Background and Aims: Urocortins (UCN1, UCN2, and UCN3) belong to the corticotropin-releasing factor (CRF)-like peptide family and bind to two subtypes of CRF receptors (CRF1 and CRF2) to exert their biological effects. UCN1 binds to both CRF1 and CRF2 with equal high affinity, whereas UCN2 and UCN3 bind exclusively to CRF2 and are endogenous agonists of CRF2. CRF and UCNs are expressed in the gastrointestinal tract. CRF has been implicated in stress-stimulated intestinal ion secretion and intestinal epithelial permeability. However, the effects of UCNs on intestinal epithelial permeability remain largely uninvestigated. The aim of the present study was to investigate the role of UCNs in the regulation of intestinal epithelial permeability. Methods: Mucosa/submucosa preparations from proximal colon of wild type (WT) and Crhr2 −/− male mice were mounted in Ussing flux chambers for measurement of transepithelial tissue resistance (TER), which serves as an approximate indicator of tight junction (or paracellular) permeability. Horseradish peroxidase (HRP) flux rate from the luminal side to the basolateral side of the colonic epithelium was used as a measurement of transcellular permeability. Results: In WT mice, application of UCN1, UCN2, and UCN3 to the basolateral side of the mucosa/submucosa preparation decreased baseline TER in a concentration-dependent manner with an IC50 (in nM) of 275, 201, and 288, respectively. Application of tetrodotoxin (TTX, 1μM), a voltage-gated Na+ channel blocker, or cromolyn sodium (10 μM), a mast cell stabilizer, to the basolateral side of the preparations significantly suppressed UCNs-evoked decrease of TER. The selective CRF1 receptor antagonist NBI 27914 (10 μM) failed to reverse UCNs-evoked decrease of TER. However, the selective CRF2 receptor antagonist antisauvagine-30 (1μM) significantly reduced this effect. In addition, UCN2 and UCN3 had no effect on baseline TER in Crhr2 −/− mice. All three UCNs increased HRP flux rate across the colonic epithelium in WT mice with an EC50 of 139 nM for UCN1, 136 nM for UCN2, and 148 nM for UCN3. UCNs-induced increase of HRP flux was prevented by cromolyn but was unaffected by TTX. NBI 27914 failed to reduce UCNs-induced enhancement of HRP flux, but antisauvagine-30 significantly reduced this action. Moreover, UCN2 and UCN3 had no effect on HRP flux in Crhr2 −/− mice. Conclusions: The results suggest that UCNs increase both paracellular and transcellular permeability in the proximal colon. Both enteric neurons and mast cells are involved in UCNs-induced increase of paracellular permeability, while only mast cells are involved in UCNs-induced increase of transcellular permeability. The effects of UNCs on intestinal permeability are mediated by the CRF2 receptors. Thus, modulation of CRF2 receptors in the colon may be relevant to the management of stress-related increase of intestinal permeability. NIH R15 DK097460-01A1 (SL) and University of Wisconsin-La Crosse Research, Service, and Educational Leadership grant (AK). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.