Intestinal Mucin Is a Chaperone of Multivalent Copper

Mucus protects the body by many mechanisms, but a role in managing toxic transition metals was not previously known. Here we report that secreted mucins, the major mucus glycoproteins coating the respiratory and intestinal epithelia, are specific copper-binding proteins. Most remarkably, the intestinal mucin, MUC2, has two juxtaposed copper binding sites, one that accommodates Cu2+ and the other Cu1+, which can be formed in situ by reduction with vitamin C. Copper is an essential trace metal because it is a cofactor for a variety of enzymes catalyzing electron transfer reactions, but copper damages macromolecules when unregulated. We observed that MUC2 protects against copper toxicity while permitting nutritional uptake into cells. These findings introduce mucins, produced in massive quantities to guard extensive mucosal surfaces, as extracellular copper chaperones and potentially important players in physiological copper homeostasis.

Discovery of a MUC3B gene reconstructs the membrane mucin gene cluster on human chromosome 7

Human tissue surfaces are coated with mucins, a family of macromolecular sugar-laden proteins serving diverse functions from lubrication to formation of selective biochemical barriers against harmful microorganisms and molecules. Membrane mucins are a distinct group of mucins that are attached to epithelial cell surfaces where they create a dense glycocalyx facing the extracellular environment. All mucin proteins carry long stretches of tandemly repeated sequences that undergo extensive O-linked glycosylation to form linear mucin domains. However, the repetitive nature of mucin domains makes them prone to recombination and render their genetic sequences particularly difficult to read with standard sequencing technologies. As a result, human mucin genes suffer from significant sequence gaps that have hampered investigation of gene function in health and disease. Here we leveraged a recent human genome assembly to identify a previously unmapped MUC3B gene located within a cluster of four structurally related membrane mucin genes that we entitle the MUC3 cluster at q22 locus in chromosome 7. We found that MUC3B shares high sequence identity with the known MUC3A gene, and that the two genes are governed by evolutionarily conserved regulatory elements. Furthermore, we show that MUC3A, MUC3B, MUC12 and MUC17 in the human MUC3 cluster are exclusively expressed in intestinal epithelial cells. Our results complete existing genetic gaps in the MUC3 cluster that is a conserved genetic unit during primate evolution. We anticipate our results to be the starting point for detection of new polymorphisms in the MUC3 cluster associated with human diseases. Moreover, our study provides the basis for exploration of intestinal mucin gene function in widely used experimental models such as human intestinal organoids and genetic mouse models.

Effects of Dietary Mannan Oligosaccharides on Non-Specific Immunity, Intestinal Health, and Antibiotic Resistance Genes in Pacific White Shrimp Litopenaeus vannamei

This study was conducted to comprehensively investigate the beneficial effects of a mannan oligosaccharide product (hereinafter called MOS) on Litopenaeus vannamei and optimum level of MOS. Five isonitrogenous and isolipid diets were formulated by adding 0%, 0.02%, 0.04%, 0.08%, and 0.16% MOS in the basal diet. Each diet was randomly fed to one group with four replicates of shrimp in an 8-week feeding trial. The results showed that dietary MOS improved the growth performance and the ability of digestion of shrimp. Dietary MOS significantly increased the activity of total superoxide dismutase, catalase, and glutathione peroxidase and decreased the content of malondialdehyde in plasma of shrimp. Dietary MOS significantly increased the activity of alkaline phosphatase and lysozyme in plasma and the hemocyte counts. Dietary MOS significantly upregulated the expression of Toll, lysozyme, anti-lipopolysaccharide factor, Crustin, and heat shock protein 70 in the hepatopancreas. And dietary MOS significantly upregulated the expression of intestinal mucin-2, mucin-5B, and mucin-19, while it decreased the expression of intestinal mucin-1 and macrophage migration inhibitory factor. Dietary MOS improved the bacterial diversity; increased the abundance of Lactobacillus, Bifidobacterium, Blautia, and Pseudoalteromonas; and decreased the abundance of Vibrio in the intestine. Shrimp fed MOS diets showed lower mortality after being challenged by Vibrio parahaemolyticus. Notably, this study found a decrease in antibiotic resistance genes and mobile genetic elements after MOS supplementation for the first time. The present results showed that diet with MOS supplementation enhanced the organismal antioxidant capacity and immunity, improved intestinal immunity, optimized intestinal microecology, mitigated the degree of antibiotic resistance, and increased the resistance to V. parahaemolyticus in L. vannamei, especially when supplemented at 0.08% and 0.16%.

Effects of supplemental β-carotene on growth performance, immune function and intestinal mucin in weaned piglets

Background Weaning stress causes intestinal immune system disorders. β-carotene displays anti-inflammatory,which can prevent the development of inflammatory diseases. The aim of this study was to determine the effect of supplemental β-carotene on growth performance, immune function and intestinal mucin in weaned piglets.Results A total of 45 piglets with the average body weight of 4.62 ± 0.06 kg (14 d of age) were randomly assigned to 3 treatments with 5 replicate pens per treatment and 3 pigs per pen and weaned at 21 d. The control group (CG) fed the basal diets from 14 d to 24 d of age. The low-dose group (LG) and the high-dose group (HG) fed the basal diets supplemented with 40 or 80 mg/kg β-carotene from 14 d to 24 d of age, respectively. Compared with the CG, t he average daily gain (ADG) and average daily feed intake (ADFI) of piglets in the HG were increased (p<0.05). And the IgA and IL-10 levels in serum in the HG were also higher than those in the CG (p<0.05). The IgM, TNF-α and IL-6 levels in serum in the β-carotene groups were lower than those in the CG (p<0.05). Periodic Acid-Schiff stain results showed that the content of mucopolysaccharide and the number of goblet cells in the intestine in the β-carotene groups were more than those in the CG (p<0.05). The results of immunofluorescence showed that the expression of MUC1 in the intestine in the β-carotene groups was lower than that in the CG (p<0.05). And the expression of mucin1 mRNA in the intestine in the β-carotene groups was also lower than that in the CG (p<0.05). However, compared with the CG, the expression of mucin2 mRNA in the intestine in the HG was increased (p<0.05).Conclusion Supplemental β-carotene could improve growth performance, immune function and intestinal mucin in weaned piglets. It is suspected that our pre-protection of β-carotene in weaned piglets may help weaned piglets safely through the weaning period.

Assembly Mechanism of Mucin and von Willebrand Factor Polymers

SUMMARYThe respiratory and intestinal tracts are exposed to physical and biological hazards accompanying the intake of air and food. Likewise, the vasculature is threatened by inflammation and trauma. Mucin glycoproteins and the related von Willebrand factor (VWF) guard the vulnerable cell layers in these diverse systems. Colon mucins additionally house and feed the gut microbiome. Here we present an integrated structural analysis of multimerized intestinal mucin MUC2. Our findings reveal the shared mechanism by which complex macromolecules responsible for blood clotting, mucociliary clearance, and the intestinal mucosal barrier form protective polymers and hydrogels. Specifically, cryo-electron microscopy and crystal structures show how disulfide-rich bridges and pH-tunable interfaces control successive assembly steps in the endoplasmic reticulum and Golgi. Remarkably, a densely O-glycosylated mucin domain performs a specific organizational role in MUC2. The mucin assembly mechanism and its adaptation for hemostasis provide the foundation for rational manipulation of barrier function and coagulation.