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.

Differential Regulation of Degradation and Immune Pathways Underlies Adaptation of the Ectosymbiotic Nematode Laxus Oneistus to Oxic-Anoxic Interfaces

Eukaryotes may experience oxygen deprivation under both physiological and pathological conditions. Because oxygen shortage leads to a reduction in cellular energy production, all eukaryotes studied so far conserve energy by suppressing their metabolism. However, the molecular physiology of animals that naturally and repeatedly experience anoxia is underexplored. One such animal is the marine nematode Laxus oneistus. It thrives, invariably coated by its sulfur-oxidizing symbiont Candidatus Thiosymbion oneisti, in anoxic sulfidic or hypoxic sand. Here, transcriptomics and proteomics showed that, whether in anoxia or not, L. oneistus mostly expressed genes involved in ubiquitination, energy generation, oxidative stress response, immune response, development, and translation. Importantly, ubiquitination genes were also highly expressed when the nematode was subjected to anoxic sulfidic conditions, together with genes involved in autophagy, detoxification and ribosome biogenesis. We hypothesize that these degradation pathways were induced to recycle damaged cellular components (mitochondria) and misfolded proteins into nutrients. Remarkably, when L. oneistus was subjected to anoxic sulfidic conditions, lectin and mucin genes were also upregulated, potentially to promote the attachment of its thiotrophic symbiont. Furthermore, the nematode appeared to survive oxygen deprivation by using an alternative electron carrier (rhodoquinone) and acceptor (fumarate), to rewire the electron transfer chain. On the other hand, under hypoxia, genes involved in costly processes (e.g., amino acid biosynthesis, development, feeding, mating) were upregulated, together with the worm’s Toll-like innate immunity pathway and several immune effectors (e.g., Bacterial Permeability Increasing proteins, fungicides). In conclusion, we hypothesize that, in anoxic sulfidic sand, L. oneistus upregulates degradation processes, rewires oxidative phosphorylation and by reinforces its coat of bacterial sulfur-oxidizers. In upper sand layers, instead, it appears to produce broad-range antimicrobials and to exploit oxygen for biosynthesis and development.

Ingested Engineered Nanomaterials Affect the Expression of Mucin Genes—An In Vitro-In Vivo Comparison

The increasing use of engineered nanomaterials (ENM) in food has fueled the development of intestinal in vitro models for toxicity testing. However, ENM effects on intestinal mucus have barely been addressed, although its crucial role for intestinal health is evident. We investigated the effects of ENM on mucin expression and aimed to evaluate the suitability of four in vitro models of increasing complexity compared to a mouse model exposed through feed pellets. We assessed the gene expression of the mucins MUC1, MUC2, MUC5AC, MUC13 and MUC20 and the chemokine interleukin-8 in pre-confluent and confluent HT29-MTX-E12 cells, in stable and inflamed triple cultures of Caco-2, HT29-MTX-E12 and THP-1 cells, and in the ileum of mice following exposure to TiO2, Ag, CeO2 or SiO2. All ENM had shared and specific effects. CeO2 downregulated MUC1 in confluent E12 cells and in mice. Ag induced downregulation of Muc2 in mice. Overall, the in vivo data were consistent with the findings in the stable triple cultures and the confluent HT29-MTX-E12 cells but not in pre-confluent cells, indicating the higher relevance of advanced models for hazard assessment. The effects on MUC1 and MUC2 suggest that specific ENM may lead to an elevated susceptibility towards intestinal infections and inflammations.

Nutrient Digestibility, Growth, Mucosal Barrier Status, and Activity of Leucocytes From Head Kidney of Atlantic Salmon Fed Marine- or Plant-Derived Protein and Lipid Sources

Nutrient digestibility, growth, and mucosal barrier status of fish skin, gills, and distal intestine were studied in Atlantic salmon fed feeds based on marine or plant-derived ingredients. The barrier status was assessed by considering the expression of four mucin genes, five genes that encode antimicrobial proteins, distal intestine micromorphology, and design-based stereology of the midgut epithelium. In addition, the head kidney leukocytes were examined using flow cytometry; to understand the differences in their counts and function. Five experimental feeds containing the main components i) fishmeal and fish oil (BG1), ii) soybean meal (BG2; to induce enteritis), iii) fishmeal as the main protein source and rapeseed oil as the main lipid source (BG3), iv) a mix of plant protein concentrates as the protein sources and fish oil as the lipid source (BG4), and v) plant and marine ingredients in the ratio 70:30 (BG5) were produced for the study. Atlantic salmon with initial weight 72.7 ± 1.2 g was offered the experimental feeds for 65 days. The results revealed that the weights of all fish groups doubled, except for fish fed BG2. Fish fed the BG2 diet had lower blood cholesterol concentration, developed enteritis, had lower expression of muc2 in the distal intestine, and had a compromised barrier status in the intestine. Expression of both the mucin genes and genes that encode antimicrobial peptides were tissue-specific and some were significantly affected by diet. The fish fed BG1 and BG3 had more head kidney lymphocyte-like cells compared to BG5-fed fish, and the phagocytic activity of macrophage-like cells from the head kidney was the highest in fish fed BG1. The intestinal micromorphology and the mucosal mapping suggest two different ways by which plant-based diets can alter the gut barrier status; by either reducing the mucous cell sizes, volumetric densities and barrier status (as noted for BG2) or increasing volumetric density of mucous cells (as observed for BG4 and BG5). The results of the compromised intestinal barrier in fish fed plant ingredients should be further confirmed through transcriptomic and immunohistochemical studies to refine ingredient composition for sustainable and acceptable healthy diets.

Genome-wide meta-analysis of pneumonia suggests a role for mucin biology and provides novel drug repurposing opportunities

ABSTRACTPneumonia remains one of the leading causes of death worldwide, particularly amongst the elderly and young children. We performed a genome-wide meta-analysis of lifetime pneumonia diagnosis (N=266,277), that encompassed the largest collection of cases published to date. Genome-wide significant associations with pneumonia were uncovered for the first time beyond the major histocompatibility complex region, with three novel loci, including a signal fine-mapped to a cluster of mucin genes. Moreover, we demonstrated evidence of a polygenic effect of common and low frequency pneumonia associated variation impacting several other mucin genes and O-glycosylation, further suggesting a role for these processes in pneumonia pathophysiology. The pneumonia GWAS was then leveraged to identify drug repurposing opportunities, including evidence that supports the use of lipid modifying agents in the prevention and treatment of the disorder. We also propose how polygenic risk could be utilised for precision drug repurposing through pneumonia risk scores constructed using variants mapped to pathways with known drug targets. In summary, we provide novel insights into the genetic architecture of pneumonia susceptibility, with future study warranted to functionally interrogate novel association signals and evaluate the suitability of the compounds prioritised by this study as repositioning candidates.

Bmi-1 regulates mucin levels and mucin O-glycosylation in the submandibular gland of mice

Mucins, the major components of salivary mucus, are large glycoproteins abundantly modified with O-glycans. Mucins present on the surface of oral tissues contribute greatly to the maintenance of oral hygiene by selectively adhering to the surfaces of microbes via mucin O-glycans. However, due to the complex physicochemical properties of mucins, there have been relatively few detailed analyses of the mechanisms controlling the expression of mucin genes and the glycosyltransferase genes involved in glycosylation. Analysis performed using supported molecular matrix electrophoresis, a methodology developed for mucin analysis, and knockout mice without the polycomb group protein Bmi-1 revealed that Bmi-1 regulates mucin levels in the submandibular gland by suppressing the expression of the mucin Smgc gene, and that Bmi-1 also regulates mucin O-glycosylation via suppression of the glycosyltransferase Gcnt3 gene in the submandibular gland.

Periostin: contributor to abnormal airway epithelial function in asthma?

Periostin may serve as a biomarker for type-2-mediated eosinophilic airway inflammation in asthma. We hypothesised that type-2 cytokine IL-13 induces airway epithelial expression of periostin, which in turn contributes to epithelial changes observed in asthma.We studied the effect of IL-13 on periostin expression in BEAS-2B and air-liquid interface (ALI)-differentiated primary bronchial epithelial cells (PBECs). Additionally, effects of recombinant human periostin on epithelial-to-mesenchymal transition (EMT) markers and mucin genes were assessed. In bronchial biopsies and induced sputum from asthma patients and healthy controls, we analysed periostin single cell gene expression and protein levels.IL-13 increased POSTN expression in both cell types, which was accompanied by EMT-related features in BEAS-2B. In ALI-differentiated PBECs, IL-13 increased periostin basolateral and apical release. Apical administration of periostin increased the expression of MMP9, MUC5B and MUC5AC. In bronchial biopsies, POSTN expression was mainly confined to basal epithelial cells, ionocytes, endothelial cells and fibroblasts, showing higher expression in basal epithelial cells from asthma patients versus controls. Higher protein levels of periostin, expressed in epithelial and subepithelial layers, was confirmed in bronchial biopsies from asthma patients compared to healthy controls. Although sputum periostin levels were not higher in asthma, levels correlated with eosinophil numbers and coughing up mucus.Periostin expression is increased by IL-13 in bronchial epithelial cells and higher in bronchial biopsies from asthma patients. This may have important consequences, as administration of periostin increased epithelial expression of mucin genes, supporting the relationship of periostin with type-2 mediated asthma and mucus secretion.