Hydrogel properties on intestinal surfaces in health and disease

The human intestine forms a highly dynamic barrier consisting of a constantly renewing epithelial cell monolayer covered by a mucus layer. This hydrogel barrier dynamically contributes to tissue homeostasis and prevents pathogen invasion physically, as well as through antimicrobial peptides. Changes in mucus composition and viscoelastic properties are neglected parameters in the understanding of human intestinal disease. Distinct changes of the mucus have previously been described for patients suffering from inflammatory bowel disease. However, data for the terminal ileum, a critical intestinal area due to the increase in bacterial load, are scarce. Furthermore, the impact of biophysical and biochemical triggers contained in the mucus layer has not been studied yet, mostly due to a lack of model systems. The introduction of infinitively self-replicating human intestinal organoids generated from stem cells that comprise all major intestinal cell types allow for performing these analyses. Thus, we hypothesize that biophysical and biochemical properties of the mucus layer, as well as their modulation by microbiota are key regulators of intestinal barrier function. Self-renewing, mucus-producing in vitro models comprising human 2D- and 3D-epithelial monolayers, will be applied to identify mucus-related features of the intestinal epithelial barrier of healthy and diseased tissue samples (Figure 20). The models focus on the small intestine and comprise a (patho)physiological structure with an easily accessible apical side. Subsequently, the impact of biophysical and biochemical stimuli on the
properties of the secreted mucus in comparison with native intestinal mucus isolated from healthy individuals and patients with Crohn’s disease and its contribution to epithelial barrier function will be studied. The composition of the generated mucus will be accessed via immunostaining and proteomic analysis, while the (micro)rheological properties will be determined on the live cell model as well as after isolation and purification in comparison with human native and fully synthetic mucus samples. The mucus-secreting epithelial barrier will be further characterized directly by transepithelial electrical resistance measurements and indirectly via particle diffusion, as well as viral and bacterial penetration through the mucus. Based on the findings, we expect to prospectively develop strategies how to modulate the system towards a rather protective direction.