Mucus barrier, mucins and gut microbiota: the expected slimy partners?

Abstract

The gastrointestinal tract is often considered as a key organ involved in the digestion of food and providing nutrients to the body for proper maintenance. However, this system is composed of organs that are extremely complex. Among the different parts, the intestine is viewed as an incredible surface of contact with the environment and is colonised by hundreds of trillions of gut microbes. The role of the gut barrier has been studied for decades, but the exact mechanisms involved in the protection of the gut barrier are various and complementary. Among them, the integrity of the mucus barrier is one of the first lines of protection of the gastrointestinal tract. In the past, this ‘slimy’ partner was mostly considered a simple lubricant for facilitating the progression of the food bolus and the stools in the gut. Since then, different researchers have made important progress, and currently, the regulation of this mucus barrier is gaining increasing attention from the scientific community. Among the factors influencing the mucus barrier, the microbiome plays a major role in driving mucus changes. Additionally, our dietary habits (ie, high-fat diet, low-fibre/high-fibre diet, food additives, pre- probiotics) influence the mucus at different levels. Given that the mucus layer has been linked with the appearance of diseases, proper knowledge is highly warranted. Here, we debate different aspects of the mucus layer by focusing on its chemical composition, regulation of synthesis and degradation by the microbiota as well as some characteristics of the mucus layer in both physiological and pathological situations.

Clostridium tyrobutyricum Protects against LPS-Induced Colonic Inflammation via IL-22 Signaling in Mice

“…The intestinal barrier is the first line to protect the gastrointestinal tract, and the mucus layer has a vital role in preventing chemical and biological disruptions and maintaining intestinal homeostasis [ 22 , 23 ]. The mucin not only protects epithelial cells from dehydration and mechanical stress, but it also has the ability to remove debris and bacteria via the intestinal flow [ 22 , 24 , 25 ]. MUC2 is the main component of the intestinal mucus in both the small and large intestine.…”

Human Intestinal Barrier: Effects of Stressors, Diet, Prebiotics, and Probiotics

“…These and other structures present diverse defensive factors in the barrier. These defensive barriers include the mucus layers ( 4 ). Mucin 2 is the most abundant mucus protein secreted by goblet cells.…”

“…In the thicker and loosely adherent outer layer of mucus, bacteria and their products are abundant, but these bacteria do not access the epithelium. This outer layer of mucus is thicker in the colon than that in the small intestine where it may reach 800 μM ( 4 ), which is considerable given that the height of the entire villus ranges from 500–1,600 μM.…”

Commercial porcine gastric mucin contributes to variation in production of small molecule virulence factors byPseudomonas aeruginosawhen cultured in different formulations of artificial sputum medium

“…As PGM was the most complex additive to our SCFM2 formulation, we hypothesized that commercial PGM was a source of contaminating iron in ASM. Mucins are a critical component of in vitro culture media for modeling the microbial interactions of CF lung infections (13, 83, 84), as well as other mucosal body sites (85, 86). The mucin concentration of CF sputum ranges from 16-30 mg/mL (1).…”