Antenatal Ureaplasma Infection Causes Colonic Mucus Barrier Defects: Implications for Intestinal Pathologies

Chorioamnionitis is a risk factor for necrotizing enterocolitis (NEC). Ureaplasma parvum (UP) is clinically the most isolated microorganism in chorioamnionitis, but its pathogenicity remains debated. Chorioamnionitis is associated with ileal barrier changes, but colonic barrier alterations, including those of the mucus barrier, remain under-investigated, despite their importance in NEC pathophysiology. Therefore, in this study, the hypothesis that antenatal UP exposure disturbs colonic mucus barrier integrity, thereby potentially contributing to NEC pathogenesis, was investigated. In an established ovine chorioamnionitis model, lambs were intra-amniotically exposed to UP or saline for 7 d from 122 to 129 d gestational age. Thereafter, colonic mucus layer thickness and functional integrity, underlying mechanisms, including endoplasmic reticulum (ER) stress and redox status, and cellular morphology by transmission electron microscopy were studied. The clinical significance of the experimental findings was verified by examining colon samples from NEC patients and controls. UP-exposed lambs have a thicker but dysfunctional colonic mucus layer in which bacteria-sized beads reach the intestinal epithelium, indicating undesired bacterial contact with the epithelium. This is paralleled by disturbed goblet cell MUC2 folding, pro-apoptotic ER stress and signs of mitochondrial dysfunction in the colonic epithelium. Importantly, the colonic epithelium from human NEC patients showed comparable mitochondrial aberrations, indicating that NEC-associated intestinal barrier injury already occurs during chorioamnionitis. This study underlines the pathogenic potential of UP during pregnancy; it demonstrates that antenatal UP infection leads to severe colonic mucus barrier deficits, providing a mechanistic link between antenatal infections and postnatal NEC development.

Microbiota-accessible fiber activates short-chain fatty acid and bile acid metabolism to improve intestinal mucus barrier in broiler chickens

IMPORTANCE

The intestinal mucus barrier, located at the interface of the intestinal epithelium and the microbiota, is the first line of defense against pathogenic microorganisms and environmental antigens. Dietary polysaccharides, which act as microbiota-accessible fiber, play a key role in the regulation of intestinal microbial communities. However, the mechanism via which dietary fiber affects the intestinal mucus barrier through targeted regulation of the gut microbiota is not clear. This study provides fundamental evidence for the benefits of dietary fiber supplementation in broiler chickens through improvement in the intestinal mucus barrier by targeted regulation of the gut ecosystem. Our findings suggest that the microbiota-accessible fiber-gut microbiota-short-chain fatty acid/bile acid axis plays a key role in regulating intestinal function.

Impact of Western Diet and Ultra-Processed Food on the Intestinal Mucus Barrier

The intestinal epithelial barrier plays a key role in the absorption of nutrients and water, in the regulation of the interactions between luminal contents and the underlying immune cells, and in the defense against enteric pathogens. Additionally, the intestinal mucus layer provides further protection due to mucin secretion and maturation by goblet cells, thus representing a crucial player in maintaining intestinal homeostasis. However, environmental factors, such as dietary products, can disrupt this equilibrium, leading to the development of inflammatory intestinal disorders. In particular, ultra-processed food, which is broadly present in the Western diet and includes dietary components containing food additives and/or undergoing multiple industrial processes (such as dry heating cooking), was shown to negatively impact intestinal health. In this review, we summarize and discuss current knowledge on the impact of a Western diet and, in particular, ultra-processed food on the mucus barrier and goblet cell function, as well as potential therapeutic approaches to maintain and restore the mucus layer under pathological conditions.

Mucolytic bacteria license pathobionts to acquire host-derived nutrients during dietary nutrient restriction

Pathobionts employ unique metabolic adaptation mechanisms to maximize their growth in disease conditions. Adherent-invasive Escherichia coli (AIEC), a pathobiont enriched in the gut mucosa of patients with inflammatory bowel disease (IBD), utilizes diet-derived L-serine to adapt to the inflamed gut. Therefore, the restriction of dietary L-serine starves AIEC and limits its fitness advantage. Here, we find that AIEC can overcome this nutrient limitation by switching the nutrient source from the diet to the host cells in the presence of mucolytic bacteria. During diet-derived L-serine restriction, the mucolytic symbiont Akkermansia muciniphila promotes the encroachment of AIEC to the epithelial niche by degrading the mucus layer. In the epithelial niche, AIEC acquires L-serine from the colonic epithelium and thus proliferates. Our work suggests that the indirect metabolic network between pathobionts and commensal symbionts enables pathobionts to overcome nutritional restriction and thrive in the gut.

Undigestible Gliadin Peptide Nanoparticles Penetrate Mucus and Reduce Mucus Production Driven by Intestinal Epithelial Cell Damage

Wheat protein is the most consumed plant protein in our diet, and there is an increased prevalence of wheat/gluten intolerance and adherence to a gluten-free diet in many countries. Despite the known immunodominant effect of undigested gliadin peptides responsible for gluten-related intolerance, it remains unclear if and how gliadin peptides self-assemble into ordered nanostructures during gastrointestinal digestion, as well as their biological impact on the mucus barrier function. In this study, we purified undigestible gliadin peptide nanoparticles (UGPNs) by ultracentrifugation and characterized their structural and physiochemical properties. The results demonstrate that the UGPNs are self-assembled nanostructures generated by cationic amino acids (Lys and Arg)-capped surfactant-like peptides (SLPs), mainly derived from γ-gliadin and α-gliadin. SLPs trigger the concentration-dependent self-assembly driven by β-sheet conformational transitions above their critical aggregation concentration (cac, ∼0.1 mg/mL). UGPNs can easily penetrate the mucus layer in Caco-2/HT29-MTX cocultures with a high P_app value (∼5.7 × 10^-6 cm/s) and reduce the production and thickness of the mucus layer driven by intestinal epithelial cell damage. Isothermal titration calorimetry and Langmuir monolayer studies indicate that the self-assembled state of UGPNs significantly affects their binding to DPPC/DOPE lipid membrane models. These results highlight the relevance of the self-assembly of gliadin peptides as a trigger of mucosal inflammation-related wheat/gluten intolerance.

Lactic Acid Bacteria May Impact Intestinal Barrier Function by Modulating Goblet Cells

SCOPE

Lactic acid bacteria (LAB) are recognized to promote gastrointestinal health by mechanisms that are not fully understood. LABs might modulate the mucus and thereby enhance intestinal barrier function. Herein, we investigate effects of different LAB strains and species on goblet cell genes involved in mucus synthesis.

METHODS AND RESULTS

Gene expression profiles of goblet-cell-associated products (mucin MUC2, trefoil factor 3, resistin-like molecule β, carbohydrate sulfotransferase 5, and galactose-3-O-sulfotransferase 2) induced by LAB or their derived conditioned medium in human goblet cell line LS174T are studied. Effects of LAB on gene transcription are assessed with or without exposure to TNF-α, IL-13, or the mucus damaging agent tunicamycin. LAB do impact the related genes in a species- and strain-specific fashion and their effects are different in the presence of the cytokines and tunicamycin. Bioactive factors secreted by some strains are also found to regulate goblet cell-related genes.

CONCLUSION

Our findings provide novel insights in differences in modulatory efficacy on mucus genes between LAB species and strains. This study further unravels direct interactions between LAB and intestinal goblet cells, and highlights the importance of rationally selecting appropriate LAB candidates to achieve specific benefits in the gut.

Mucus Detachment by Host Metalloprotease Meprin β Requires Shedding of Its Inactive Pro-form, which Is Abrogated by the Pathogenic Protease RgpB

The host metalloprotease meprin β is required for mucin 2 (MUC2) cleavage, which drives intestinal mucus detachment and prevents bacterial overgrowth. To gain access to the cleavage site in MUC2, meprin β must be proteolytically shed from epithelial cells. Hence, regulation of meprin β shedding and activation is important for physiological and pathophysiological conditions. Here, we demonstrate that meprin β activation and shedding are mutually exclusive events. Employing ex vivo small intestinal organoid and cell culture experiments, we found that ADAM-mediated shedding is restricted to the inactive pro-form of meprin β and is completely inhibited upon its conversion to the active form at the cell surface. This strict regulation of meprin β activity can be overridden by pathogens, as demonstrated for the bacterial protease Arg-gingipain (RgpB). This secreted cysteine protease potently converts membrane-bound meprin β into its active form, impairing meprin β shedding and its function as a mucus-detaching protease.