Cortactin is Required to Maintain Intestinal Epithelial Barrier Homeostasis

Abstract

A stable intestinal epithelium is the basis for healthy intestines. Epithelial dysfunction causes increased intestinal permeability and bacterial translocation that may eventually cause an aberrant immune response as seen in chronic inflammatory diseases of the intestines such as ulcerative colitis (UC) and Crohn disease (CD). The actin cytoskeleton regulates epithelial barrier integrity through tight junction and adherens junction molecules, but the role of actin regulators such as cortactin (CTTN) is not well understood. Analyzing CTTN‐KO mice, we found that these animals have increased basal intestinal permeability similar to what has been demonstrated in the vasculature. Furthermore, CTTN‐KO mice were more susceptible to DSS‐induced experimental colitis with animals dying already after 5 days of DSS treatment. Histopathological analysis of CTTN‐KO colons revealed differences in the intestinal epithelial structure such as hypoplasia, edema, hemorrhage and infiltration already under basal conditions which it worsened after experimental colitis. Immunofluorescence staining of colon tissues of mice demonstrated a reduced expression and localization at junctions of ZO‐1 and E‐cadherin and intestinal epithelial crypt disassembly. Using a stable CTTN‐depleted Caco‐2 cell line, we confirmed epithelial dysfunction including reduced transepithelial electrical resistance, increased paracellular flux of 4 kDa FITC‐dextran and weaker cortical actin rings. This was accompanied by a decreased expression and internalization of ZO‐1, occludin, claudin‐1 and E‐cadherin; while claudin‐4 and b‐catenin remained unchanged. Interestingly, expression of the pore‐forming claudin‐2 was increased and neutrophils transmigrated more rapidly. While CTTN depletion did not cause increased apoptosis, we observed increased proliferation and stress fiber formation that may be responsible for the observed barrier dysfunction. Importantly, CTTN localized at cell contacts in colon biopsies of healthy individuals, whereas in IBD patients we observed strong translocation of CTTN into the cytosol and loss of colocalization with actin and ZO‐1. Our data imply that CTTN controls intestinal barrier integrity by controlling actin cytoskeleton and intercellular junction functionality causing epithelial dysfunction as seen in IBD.Support or Funding InformationThis work was supported by grants and a Ph.D stipend from the Mexican Council for Science and Technology (333396 to AFCM & 179895 to MS and a special fund PNPC.2013‐2014)