Host defense cathelicidins are essential for maintaining the mucin barrier in the colon

DROUIN D; HOLANI R; MARIN M; CHADEE K; COBO E

Calgary

Jornada; Snyder Institute Summer Student Research Day Abstract Submission; 2017

Snyder Institute, University of Calgary

Mucin, MUC2, is a glycoprotein secreted by colonic epithelial cells that provides a protective layer of mucus to the colon. Disruptions in the intestinal mucus barrier correlate to enteric infectious diseases. Escherichia coli and Salmonella typhimurium, causative of diarrheic colitis in livestock and humans, disturb the mucus layer. Cathelicidins are peptides secreted by colonic epithelial cells and leukocytes with key roles in gut innate defenses. I aimed to determine if the only human cathelicidin (LL-37) contributes to the epithelial barrier and production of intestinal mucin. My results show the colonic mucin layer is severely defective in mice deficient in cathelicidins (Cramp-/-) compared with wild type. Studies of histology and confocal microscopy using Ulex Europaeus Agglutinin I (UEA I) lectin to detect mucin glycoproteins containing fucose residues demonstrated that Cramp-/- mice display a reduced amount of mucin produced and secreted by goblet cells, with respect to the wild type. Mechanistically, pre-treatment of cultured human colonic epithelial cells (LS174T) with synthetic LL-37 (20 μg/mL; 1 h) did not induce mRNA gene expression of MUC2, cathelicidins and tight junction proteins (occludin and claudins 1 and 4) in response to either bacterial virulence factor lipopolysaccharide (LPS; 1 μg/mL) or cyclic AMP agonist forskolin (10 μM; 16 h). Exogenous cathelicidins did mitigate endogenous cathelicidin expression in response to LPS. This project is novel in demonstrating that cathelicidins are necessary to establish/maintain a healthy mucin barrier in the colon. While cathelicidins do not increase mucin gene expression, this peptide seems to be involved in promoting the secretion of mucin.