Mucus and mucins during gastrointestinal infections

Abstract

The gastrointestinal tract is protected by a continuously secreted mucus layer formed by mucin glycoproteins. The mucus layer and mucins change dynamically during infection. The main focus of this thesis was to investigate the changes in mucin and the mucus layer in the gastrointestinal tract during infection with the gastrointestinal pathogens C. rodentium (a mouse model for intestinal A/E pathogens), ETEC and H.pylori. To be able to compare the results from murine studies to the effect of infection in humans, we needed an in vitro mucosal surface to most resemble the in vivo environment. Therefore, we developed a method of culture to create an in vitro model suitable for studies of host-pathogen interactions at the mucosal surface that caused the cells to polarize, form functional tight junctions, a three-dimensional architecture resembling colonic crypts, and produce an adherent mucus layer.

We investigated the effect of infection with H. pylori on mucin synthesis in vivo. The results of our non-radioactive “pulse” experiments showed H. pylori colonization in the mucus niche of the murine stomach leads to decreased mucin production and secretion rate. H. pylori infection also decreased levels of MUC1 in the mucosa. The effect of C. rodentium infection on the distinct aspects of the mucus layer and mucins was also investigated during this work. Our results in the WT mice demonstrated mucus transcription and secretion are dynamically altered in response to the infection. Furthermore, the clearance of the infection coincides with the reformation of the organized inner mucus layer and an increased mucus thickness, which corresponded with altered ion channel activities.

To examine the effect of the cytokine environment on the changes of mucin and mucus layer, we infected WT and IFN-γ-/- mice with C. rodentium that resulted in a vast enhancement of mucus thickness in the IFN-γ-/- mice compared to the WT animals. The effect of individual cytokines was further studied using our in vitro model with and without infection with C. rodentium/ETEC. The outcome demonstrated that changes in the goblet cells, mucin and mucus layer during infection is dependent on the combined impact of the pathogen and cytokines, and that the presence of the Th2 cytokines accelerated the process of mucin synthesis.