Diet, microbiome, and the intestinal epithelium: an essential triumvirate?

Abstract

The intestinal epithelium represents a critical barrier protecting the host against diverse luminal noxious agents, as well as preventing the uncontrolled uptake of bacteria that could activate an immune response in a susceptible host. The epithelial monolayer that constitutes this barrier is regulated by a meshwork of proteins that orchestrate complex biological function such as permeability, transepithelial electrical resistance, and movement of various macromolecules. Because of its key role in maintaining host homeostasis, factors regulating barrier function have attracted sustained attention from the research community. This paper will address the role of bacteria, bacterial-derived metabolism, and the interplay of dietary factors in controlling intestinal barrier function.

Figure 1

Intestinal epithelial responses to diet and microbes. Diets containing fermentable fibers, resistant starches and the like result in increased gut fermentation and SCFA production. A constant diet containing these elements would shift the host gut microbiome to increase the proportion of SCFA-producing bacteria. In turn, increase in SCFA production would also increase protection of the epithelium through strengthening the barrier as mediated by increased TJ protein production and TEER, as well as decreased permeability and bacterial translocation. Similarly, a diet containing probiotic bacteria would in time increase barrier function and integrity. Conversely, diet that promotes the increase in populations of pathogenic or opportunistic bacteria (as with intake of milk fat) within the landscape would have the opposite effects, decreasing TJ protein production and altering their distribution, as well as decreasing TEER and thereby compromising barrier integrity. This would then result in increased barrier permeability resulting in increased bacterial translocation and thereby increasing pathology such as increased intestinal inflammation.