Mimicking the Intestinal Host–Pathogen Interactions in a 3D In Vitro Model: The Role of the Mucus Layer

Abstract

The intestinal mucus lines the luminal surface of the intestinal epithelium. This mucus is a dynamic semipermeable barrier and one of the first-line defense mechanisms against the outside environment, protecting the body against chemical, mechanical, or biological external insults. At the same time, the intestinal mucus accommodates the resident microbiota, providing nutrients and attachment sites, and therefore playing an essential role in the host–pathogen interactions and gut homeostasis. Underneath this mucus layer, the intestinal epithelium is organized into finger-like protrusions called villi and invaginations called crypts. This characteristic 3D architecture is known to influence the epithelial cell differentiation and function. However, when modelling in vitro the intestinal host–pathogen interactions, these two essential features, the intestinal mucus and the 3D topography are often not represented, thus limiting the relevance of the models. Here we present an in vitro model that mimics the small intestinal mucosa and its interactions with intestinal pathogens in a relevant manner, containing the secreted mucus layer and the epithelial barrier in a 3D villus-like hydrogel scaffold. This 3D architecture significantly enhanced the secretion of mucus. In infection with the pathogenic adherent invasive E. coli strain LF82, characteristic of Crohn’s disease, we observed that this secreted mucus promoted the adhesion of the pathogen and at the same time had a protective effect upon its invasion. This pathogenic strain was able to survive inside the epithelial cells and trigger an inflammatory response that was milder when a thick mucus layer was present. Thus, we demonstrated that our model faithfully mimics the key features of the intestinal mucosa necessary to study the interactions with intestinal pathogens.

Animal and In Vitro Models as Powerful Tools to Decipher the Effects of Enteric Pathogens on the Human Gut Microbiota

“…This approach more accurately represents the complex non-flat architecture of the intestinal mucosal environment [ 24 , 25 ]. Caco-2 and HT-29 cells were cultured on hydrogel scaffolds to demonstrate that mucus was a protective factor against bacterial colonization by adherent-invasive E. coli (AIEC) [ 26 ]. Raw and mucin-coated 3D gelatin electrospun membranes were successfully used as scaffolds to culture the human gut microbiota in vitro and reproduce the three-dimensional architecture of the intestinal mucosa and the arrangement of bacteria on it [ 27 , 28 , 29 ].…”

Mucosa‐Mimetic Materials for the Study of Intestinal Homeostasis and Disease

“…[ 55 ] Further, the role of the mucus layer was elucidated by mimicking host‐pathogen interactions in an in vitro model. [ 56 ] Generally, there is a trade‐off between efficiently synthesizing mucus with more accurate material properties and generating the correct mucin composition for the tissue being targeted. This balance has not been fully addressed by existing methods of mucus collection.…”

In Vitro Models for Investigating Intestinal Host–Pathogen Interactions

“…[322,323] By applying this cocultured cell line, García-Díaz et al successfully built a 3D in vitro model to mimic the in vivo situation, such as physiological dimensions and mechanical properties. [119] By doing so, they found that mucus present in 3D topography can significantly modulate the inter-action between pathogenic E. coli LF82 (AIEC) and the epithelium. Other researchers proposed an approach of using native mucins to form hydrogels from either a mixture of the components from native mucus, or rehydration of purified commercial mucins, i.e., porcine gastric mucin (PGM) and bovine submaxillary mucin (BSM).…”