Probiotic Bacteria and the Gastrointestinal Barrier: miRNAs, Signaling Pathways and Molecular Repair Mechanisms
Final Report Abstract
Infections by Gram-negative enteropathogenic Escherichia coli (EPEC) are a main cause of diarrheal diseases in infants. The adhesion of pathogens to intestinal epithelial cells as well as the concerted injection of virulence factors by the type III secretion system (T3SS) result in the disruption of intestinal barrier functions leading to increased permeability. In contrast, probiotic Lactobacilli are known to exhibit health-promoting features. However, it has not been determined whether this effect is due to Lactobacilli acting directly on the pathogens to reduce the adhesion or whether it is mediated by competitive binding to the intestinal cells. Here, we investigated the efficacy of Lactobacillus strains to interfere with the adhesion of the prototype EPEC strain E2348/69 to human intestinal cell (T84) monolayers used as epithelial barrier model. Only distinct Lactobacillus strains and/or their culture supernatants inhibited EPEC adherence to T84 cells. We found the inhibitory activity to be due to specific secreted Lactobacillus’ glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Human GAPDH did not inhibit EPEC adherence. We showed that purified extracellular GAPDH derived from L. gasseri PZ1160 and L. rhamnosus W65 are sufficient to reduce EPEC adhesion to T84 cells in a dose-dependent manner. Further, Lactobacillus’ cellular supernatants inhibited the expression of bundle-forming pili (Bfp) a major EPEC virulence factor. This activity was found to be distinct from the secreted GAPDH. The identity of this factor needs to be addressed in future studies. In summary, in this study we identified a twofold inhibitory activity of specific Lactobacillus strains mediated by secreted GAPDH and by a thus far unknown soluble factor and by this contributed to our understanding of the probiotic effects of Lactobacilli. Our findings are further supported by the fact that GAPDH has recently been described to be a ´moonlighting protein`. Moonlighting proteins are multifunctional proteins, which in addition to their main - mostly name-giving - function exhibit additional biologically unrelated activities and are often localized at different cellular compartments. In bacteria, most of the characterized moonlighting proteins have been found in pathogens and are associated to virulence.
Publications
- MicroRNAs regulate tight junction proteins and modulate epithelial/endothelial barrier functions. Tissue Barriers. 2014 Aug 8;2(4):e944446
Cichon C, Sabharwal H, Rüter C, Schmidt MA
(See online at https://doi.org/10.4161/21688362.2014.944446) - Apical and basolateral IL-8, CXCL1 and miR-146a responses in human intestinal epithelial T84 and in monocytic THP-1 cells to probiotic E. coli Nissle 1917 and enteropathogenic E. coli. Infection and Immunity
Sabharwal H, Cichon C, Ölschläger TA, Sonnenborn U, Schmidt MA
(See online at https://doi.org/10.1128/IAI.00402-16)
