Growing evidence suggests that intestinal mucosa homeostasis impacts immunity, metabolism, the Central Nervous System (CNS), and behavior. Here, we investigated the effect of the monosaccharide fucose on inflammation, metabolism, intestinal microbiota, and social behavior in the Dextran Sulfate Sodium (DSS)-induced chronic colitis mouse model. Our data show that chronic colitis is accompanied by the decrease of the serum tryptophan level and the depletion of the intestinal microbiota, specifically tryptophan-producing E. coli and Bifidobacterium. These changes are associated with defects in the male mouse social behavior such as a lack of preference towards female bedding in an odor preference test. The addition of fucose to the test animals’ diet altered the bacterial community, increased the abundance of tryptophan-producing E. coli, normalized blood tryptophan levels, and ameliorated social behavior deficits. At the same time, we observed no ameliorating effect of fucose on colon morphology and colitis. Our results suggest a possible mechanism by which intestinal inflammation affects social behavior in male mice. We propose fucose as a promising prebiotic, since it creates a favorable environment for the beneficial bacteria that promote normalization of serum tryptophan level and amelioration of the behavioral abnormalities in the odor preference test.

Intestinal mucus protects epithelial and immune cells from the gut resident microorganisms, and provides growth-promoting factors as mucus-derived O-glycans for beneficial bacteria. A lack of intestinal protective mucus results in changes in the commensal microflora composition, mucosal immune system reprogramming, and inflammation. Previous work has shown that fucose, the terminal glycan chain component of the intestinal glycoprotein Mucin2, and fucoidan polysaccharides have an anti-inflammatory effect in some mouse models of colitis. This study evaluates the effect of fucose on reproductive performance in heterozygous mutant Muc2 female mice. We found that even though Muc2^+/− females are physiologically indistinguishable from C57Bl/6 mice, they have a significantly reduced reproductive performance upon dietary fucose supplementation. Metagenomic analysis reveals that the otherwise healthy wild-type siblings of Muc2^−/− animals have reduced numbers of some of the intestinal commensal bacterial species, compared to C57BL/6 mice. We propose that the changes in beneficial microflora affect the immune status in Muc2^+/− mice, which causes implantation impairment. In accordance with this hypothesis, we find that macrophage polarization during pregnancy is impaired in Muc2^+/− females upon addition of fucose. Metabolic profiling of peritoneal macrophages from Muc2^+/− females reveals their predisposition towards anaerobic glycolysis in favor of oxidative phosphorylation, compared to C57BL/6-derived cells. In vitro experiments on phagocytosis activity and mitochondrial respiration suggest that fucose affects oxidative phosphorylation in a genotype-specific manner, which might interfere with implantation depending on the initial status of macrophages. This hypothesis is further confirmed in BALB/c female mice, where fucose caused pregnancy loss and opposed implantation-associated M2 macrophage polarization. Taken together, these data suggest that intestinal microflora affects host immunity and pregnancy outcome. At the same time, dietary fucose might act as a differential regulator of macrophage polarization during implantation, depending on the immune status of the host.

The mucus layer in the intestine plays a critical role in regulation of host–microbe interactions and maintaining homeostasis. Disruptions of the mucus layer due to genetic, environmental, or immune factors may lead to inflammatory bowel diseases (IBD). IBD frequently are accompanied with infections, and therefore are treated with antibiotics. Hence, it is important to evaluate risks of antibiotic treatment in individuals with vulnerable gut barrier and chronic inflammation. Mice with a knockout of the Muc2 gene, encoding the main glycoprotein component of the mucus, demonstrate a close contact of the microbes with the gut epithelium which leads to chronic inflammation resembling IBD. Here we demonstrate that the Muc2^−/− mice harboring a gut protozoan infection Tritrichomonas sp. are susceptible to an antibiotic-induced depletion of the bacterial microbiota. Suppression of the protozoan infection with efficient metronidazole dosage or L-fucose administration resulted in amelioration of an illness observed in antibiotic-treated Muc2^−/− mice. Fucose is a monosaccharide presented abundantly in gut glycoproteins, including Mucin2, and is known to be involved in host–microbe interactions, in particular in microbe adhesion. We suppose that further investigation of the role of fucose in protozoan adhesion to host cells may be of great value.

In vitro models are of great importance in advancing our understanding of human diseases, especially complex disorders with unknown etiologies like inflammatory bowel diseases (IBD). One of the key IBD features is the increased intestinal permeability. The disruption of the intestinal barrier can occur due to a destructive inflammatory response involving intestinal cell death. Alternatively, proteins that form tight junctions (TJ) fail to form function complexes and promote epithelial barrier disruption. The mechanisms behind this process are not fully understood. Thus, in vitro models that facilitate studying the intestinal barrier and its molecular components are of particular importance in the context of IBD. There are in vitro and ex vivo models that can be used to recapitulate some aspects of IBD. Among these are intestinal explants, crypts, and epithelial 3D-organoids. Here we describe some practical limitations of isolated crypts, gut tissue explants, and intestinal organoids as models in epithelial barrier biology, and TJ in particular. Our findings demonstrate that only 3D intestinal organoids formed from single cells are suitable to study barrier permeability in vitro, as primary crypt-derived organoids do not retain epithelial integrity due to cell death. Importantly, 3D organoids raised in culture conditions may fail to recapitulate inflammatory and barrier phenotypes of the source mouse model. To study the features of the inflamed epithelium, ex vivo intestinal explants and crypts were employed. We show here that isolated crypts do not preserve native TJ structure in a long-term experimental setting and tend to disintegrate in the unsupported culture environment. However, intestinal explants were stable in culture conditions for about 24 hours and demonstrated their applicability for short-term living tissue imaging and fluorescence recovery after photobleaching (FRAP). Thus, a combination of 3D organoids and intestinal explants provides a more accurate experimental platform to understand the intestinal epithelial barrier.

Scent signals play an important role in the life of rodents. The scent of the opposite sex can modulate immunity. In mice populations with natural specific pathogens, in males, the scent of a female leads to a redistribution of leukocytes between the lung and the blood, resistance to the influenza virus, and a decrease in antibody production, but not in the development of inflammation induced by bacterial endotoxins. This study demonstrates the effect of the scent of soiled bedding of specific pathogen-free (SPF) status female mice on the percentage of different types of leukocytes in the blood, the expression of Nos2, Arg1, and Foxp3 genes, and the presence of M1/M2 macrophages in the lungs of male BALB/c mice. The scent of the female SPF mice caused a redistribution between T- and B-cells in the blood, the increase in the expression of Nos2, Arg1 genes, and the percentage of M1 type macrophages in the lung, but did not affect the different types of T-cells in the periphery or the lungs. Activation of macrophages in the lung is part of mucosal immunity, which is necessary for males as an adaptive mechanism to prevent potential infection during the search for a sexual partner.