Maturation of intestinal barrier function by Glial cell line‐derived neurotrophic factor (GDNF) is mediated by inactivation of p38 MAPK

Abstract

Recent data demonstrate that the glial cell line‐derived neurotrophic factor (GDNF) is involved in intestinal epithelial barrier differentiation. In the present study we analysed the mechanism underlying GDNF‐induced intestinal epithelial barrier maturation.As demonstrated previously application of recombinant GDNF on immature intestinal epithelial monolayers (Caco2 and HT29B6 cells) for 24h resulted in increased transepithelial electric resistance (TER) and a reduced permeability of 4 kDa FITC‐Dextran in a transwell filter system. This confirmed that GDNF contributes to intestinal epithelial barrier maturation. Barrier differentiation by GDNF was associated with a significant reduction of phosphorylated p38MAP kinase. Inactivation of p38 MAP kinase by incubation of immature Caco2 and HT29B6 monolayers with SB‐202190 mimicked GDNF‐induced barrier maturation. Vice versa, activation of p38 MAPK by Anisomycin led to augmented epithelial permeability. Furthermore, p38 MAPK activation by Anisomycin blocked GDNF‐induced barrier maturation. As revealed by immunostaining GDNF‐induced barrier maturation was paralleled by augmented staining patterns of tight junction proteins claudin‐1, claudin‐5, occludin and ZO‐1. In preliminary experiments the desmosomal protein Desmoglein2, which is regulated by p38 MAPK was upregulated in Western Blot analysis. Accordingly, in immunostaining Dsg2 was distributed to the cell borders following GDNF application indicating a maturation of desmosomal adhesion.In summary our present data show that GDNF contributes to epithelial barrier maturation by inactivation of p38 MAPK signaling which appears to affect Dsg2 integrity and thereby may stabilize tight junction stability.