Membrane mucins of the intestine at a glance

Alterations in mucosa branched N-glycans lead to dysbiosis and downregulation of ILC3: a key driver of intestinal inflammation

The perturbation of the symbiotic relationship between microbes and intestinal immune system contributes to gut inflammation and Inflammatory Bowel Disease (IBD) development. The host mucosa glycans (glycocalyx) creates a major biological interface between gut microorganisms and host immunity that remains ill-defined. Glycans are essential players in IBD immunopathogenesis, even years before disease onset. However, how changes in mucosa glycosylation shape microbiome and how this impact gut immune response and inflammation remains to be clarified. Here, we revealed that alterations in the expression of complex branched N-glycans at gut mucosa surface, modeled in glycoengineered mice, resulted in dysbiosis, with a deficiency in Firmicutes bacteria. Concomitantly, this mucosa N-glycan switch was associated with a downregulation of type 3 innate lymphoid cells (ILC3)-mediated immune response, leading to the transition of ILC3 toward an ILC1 proinflammatory phenotype and increased TNFα production. In addition, we demonstrated that the mucosa glycosylation remodeling through prophylactic supplementation with glycans at steady state was able to restore microbial-derived short-chain fatty acids and microbial sensing (by NOD2 expression) alongside the rescue of the expression of ILC3 module, suppressing intestinal inflammation and controlling disease onset. In a complementary approach, we further showed that IBD patients, often displaying dysbiosis, exhibited a tendency of decreased MGAT5 expression at epithelial cells that was accompanied by reduced ILC3 expression in gut mucosa. Altogether, these results unlock the effects of alterations in mucosa glycome composition in the regulation of the bidirectional crosstalk between microbiota and gut immune response, revealing host branched N-glycans/microbiota/ILC3 axis as an essential pathway in gut homeostasis and in preventing health to intestinal inflammation transition.

Clca1 deficiency exacerbates colitis susceptibility via impairment of mucus barrier integrity and gut microbiota homeostasis

The intestinal mucus barrier has emerged as a promising therapeutic target for inflammatory bowel disease. Understanding its regulatory mechanisms is critical for elucidating ulcerative colitis (UC) pathogenesis, improving diagnostics, guiding treatments, and preventing relapse. Chloride Channel Accessory 1 (Clca1), a constituent of the mucus layer, remains understudied in colitis. Here, we investigated Clca1's role in mucosal immunity and intestinal homeostasis using experimental colitis models. Clca1-deficient (Clca1-/-) mice displayed compromised mucus layer integrity, reduced neutrophil infiltration, and gut microbiota dysbiosis. Notably, Clca1-/- mice exhibited exacerbated colitis severity following dextran sulfate sodium (DSS) challenge, accompanied by a diminished goblet cell populations. Fecal microbiota transplantation (FMT) studies revealed that gut microbiota critically modulates divergent phenotypic outcomes between genotypes. Our findings establish Clca1 as a multifunctional regulator of mucus barrier integrity through mechanisms involving goblet cell maintenance, neutrophil-mediated immunity, and host-microbiota crosstalk. These results advance the understanding of UC pathogenesis and identify Clca1-associated pathways as potential targets for barrier restoration therapies.

Immune Regulation of Goblet Cell and Mucus Functions in Health and Disease

The mucosal surfaces of the body are the most vulnerable points for infection because they are lined by single or multiple layers of very active epithelial cells. The main protector of these cells is the mucus system generated by the specialized goblet cell secreting its main components, the gel-forming mucins. The organization of the mucus varies from an attached mucus that is impenetrable to bacteria in the large intestine to a nonattached, more penetrable mucus in the small intestine. The respiratory tract mucus system clears particles and microorganisms from healthy lungs but causes disease if reorganized to an attached mucus that cannot be efficiently transported. Similarly, transformation of large intestine mucus from impenetrable to penetrable causes chronic inflammation directed toward the intestinal microbiota. Mucus-producing goblet cells are regulated by and responsive to signals from immune cells, and at the same time signal back to the immune system. In this review we focus on the relationship of immune cells with intestinal goblet cells and mucus, making parallels to the respiratory tract.

MUC1 and MUC4 expression are inversely correlated and trigger immunological response and transport pathways in adult-type diffuse gliomas

Adult-type diffuse gliomas arise from glial or progenitor cells. These tumors are currently classified as astrocytoma isocitrate dehydrogenase (IDH)-mutant or IDH-mutant oligodendroglioma with co-deletion of chromosomal arms 1p and 19q, both of which could be either slow-growing tumors, or glioblastoma (GBM), which is a more aggressive tumor. Despite advances in diagnosis and treatment, the median survival time after GBM diagnosis remains low at approximately 15 months, with a 5-year overall survival (OS) rate of 6.8 %. Therefore, new biomarker and therapeutic target discoveries are required to improve prognosis. Mucin 1 (MUC1) and MUC4 are membrane-bound mucins and potential biomarkers of several tumors. However, the role of these mucins in adult gliomas has not been well explored. In this retrospective study, in silico analysis of data from patients with adult-type diffuse glioma revealed differential methylation and expression patterns of MUC1 and MUC4 between GBM and non-GBM groups. In the GBM group, decreased methylation and elevated expression of MUC1 were observed (r = -0.25, p < 0.0001), whereas increased methylation and decreased expression of MUC4 were observed (r = -0.13, p = 0.1344). Conversely, in the non-GBM group, MUC1 exhibited higher methylation and lower expression (r = -0.27, p < 0.0001), whereas MUC4 showed lower methylation and higher expression (r = -0.32, p < 0.0001). The expression of these genes influenced OS in adult patients with glioma (p = 0.0344), with high MUC1 and low MUC4 expression associated with worse OS. MUC1 and MUC4 expression correlated with that of MUC20 in both GBM (r = 0.54) and non-GBM (r = 0.53) groups (p < 0.0001). Functional enrichment analysis identified the biological roles of MUC1-co-expressed genes as involvement in innate immunity, antigen processing, and proinflammatory responses in both the non-GBM and GBM groups, and integrin-based signaling pathways in the GBM group. MUC4-co-expressed genes are involved in ion transport in GBM patients. Using molecular docking, we observed that MUC1 domains physically interact with immune response-related proteins, such as receptors for advanced glycation end products (RAGE), major histocompatibility complex II (MHC-II), and extracellular matrix receptor integrin alpha 2 (ITGA2). To our knowledge, this is the first retrospective study and in silico analysis demonstrating the relevance and correlation of MUC1 and MUC4 in adult gliomas. These findings elucidate the molecular mechanisms underlying adult-type diffuse glioma progression and highlight MUC1 and MUC4 as potential prognostic markers and therapeutic targets for glioma management.

The structure-function relationships and interaction between polysaccharides and intestinal microbiota: A review

The gut microbiota, as a complex ecosystem, can affect many physiological aspects of the host's diet, disease development, drug metabolism, and immune system regulation. Polysaccharides have various biological activities including antioxidant, anti-tumor, and regulating gut microbiota, etc. Polysaccharides cannot be degraded by human digestive enzymes. However, the interaction between gut microbiota and polysaccharides can lead to the degradation and utilization of polysaccharides. Disordered intestinal flora leads to diseases such as diabetes, hyperlipidemia, tumors, and diarrhea. Notably, polysaccharides can regulate the gut microbiota, promote the proliferation of probiotics and the SCFAs production, and thus improve the related-diseases and maintain body health. The relationship between polysaccharides and gut microbiota is gradually becoming clear. Nevertheless, the structure-function relationships between polysaccharides and gut microbiota still need further exploration. Hence, this paper systematically reviews the structure-function relationships between polysaccharides and gut microbiota from four aspects including molecular weight, glycosidic bonds, monosaccharide composition, and advanced structure. Moreover, this review outlines the effect of polysaccharides on gut microbiota metabolism and improves diseases by regulating gut microbiota. Furthermore, this article introduces the impact of gut microbiota on polysaccharide metabolism. The findings can provide the scientific basis for in-depth research on body health and reasonable diet.

Gut Microbiota and Osteoarthritis: From Pathogenesis to Novel Therapeutic Opportunities

Osteoarthritis (OA) is the most common chronic degenerative joint disease, characterized by cartilage damage, synovial inflammation, subchondral bone sclerosis, marginal bone loss, and osteophyte development. Clinical manifestations include inflammatory joint pain, swelling, osteophytes, and limitation of motion. The pathogenesis of osteoarthritis has not yet been fully uncovered. With ongoing research, however, it has been gradually determined that OA is not caused solely by mechanical injury or aging, but rather involves chronic low-grade inflammation, metabolic imbalances, dysfunctional adaptive immunity, and alterations in central pain processing centers. The main risk factors for OA include obesity, age, gender, genetics, and sports injuries. In recent years, extensive research on gut microbiota has revealed that gut dysbiosis is associated with some common risk factors for OA, and that it may intervene in its pathogenesis through both direct and indirect mechanisms. Therefore, gut flora imbalance as a pathogenic factor in OA has become a hotspot topic of research, with potential therapeutic connotations. In this paper, we review the role of the gut microbiota in the pathogenesis of OA, describe its relationship with common OA risk factors, and address candidate gut microbiota markers for OA diagnosis. In addition, with focus on OA therapies, we discuss the effects of direct and indirect interventions targeting the gut microbiota, as well as the impact of gut bacteria on the efficacy of OA drugs.

Exploring the Link Between Mucin 2 and Weaning Stress-Related Diarrhoea in Piglets

To explore the relationship between intestinal mucin 2 (MUC2) and weaning-induced diarrhoea in piglets, we analysed Min and Landrace piglets. The piglets were divided into a healthy weaned group, a weaned diarrhoea group, and a healthy unweaned control group. Intestinal tissues were collected, and goblet cell numbers, sizes, and degrees of intestinal injury were observed and recorded. Intestinal tissue MUC2 mRNA and protein expression were analysed via quantitative real-time PCR (qRT-PCR) and Western blotting. Min pigs presented significantly lower diarrhoea rates and intestinal injury scores than Landrace pigs (p < 0.01). The intestinal injury scores in the weaned diarrhoea group were significantly greater than those in the unweaned groups (p < 0.05), with Min pigs consistently exhibiting lower injury scores than Landrace pigs. Specifically, unweaned Min pigs presented significantly greater duodenal MUC2 mRNA (p < 0.05), and weaned healthy Min pigs presented notably greater expression in both the duodenum and jejunum (p < 0.01). These findings reveal enhanced intestinal protection against weaning stress and diarrhoea in Min pigs, with elevated MUC2 levels likely contributing to lower injury scores and milder symptoms, thus highlighting the influence of genetic differences.

Intestinal permeability, food antigens and the microbiome: a multifaceted perspective

The gut barrier encompasses several interactive, physical, and functional components, such as the gut microbiota, the mucus layer, the epithelial layer and the gut mucosal immunity. All these contribute to homeostasis in a well-regulated manner. Nevertheless, this frail balance might be disrupted for instance by westernized dietary habits, infections, pollution or exposure to antibiotics, thus diminishing protective immunity and leading to the onset of chronic diseases. Several gaps of knowledge still exist as regards this multi-level interaction. In this review we aim to summarize current evidence linking food antigens, microbiota and gut permeability interference in diverse disease conditions such as celiac disease (CeD), non-celiac wheat sensitivity (NCWS), food allergies (FA), eosinophilic gastrointestinal disorder (EOGID) and irritable bowel syndrome (IBS). Specific food elimination diets are recommended for CeD, NCWS, FA and in some cases for EOGID. Undoubtfully, each of these conditions is very different and quite unique, albeit food antigens/compounds, intestinal permeability and specific microbiota signatures orchestrate immune response and decide clinical outcomes for all of them.

The MYO1B and MYO5B motor proteins and the sorting nexin SNX27 regulate apical targeting of membrane mucin MUC17 in enterocytes

A dense glycocalyx, composed of the megaDalton-sized membrane mucin MUC17, coats the microvilli in the apical brush border of transporting intestinal epithelial cells, called enterocytes. The formation of the MUC17-based glycocalyx in the mouse small intestine occurs at the critical suckling-weaning transition. The glycocalyx extends 1 µm into the intestinal lumen and prevents the gut bacteria from directly attaching to the enterocytes. To date, the mechanism behind the positioning of MUC17 to the brush border is not known. Here, we show that the actin-based motor proteins MYO1B and MYO5B, and the sorting nexin SNX27, regulate apical targeting of MUC17 in enterocytes. We demonstrate that MUC17 turnover at the brush border is slow and controlled by MYO1B and SNX27. Furthermore, we report that MYO1B regulates MUC17 protein levels in enterocytes, whereas MYO5B specifically governs MUC17 levels at the brush border. Together, our results extend our understanding of the apical targeting of membrane mucins and provide mechanistic insights into how defective positioning of MUC17 renders enterocytes sensitive to bacterial challenges.

Effect of bioactive compounds in processed Camellia sinensis tea on the intestinal barrier

The human intestinal tract plays a pivotal role in safeguarding the body against noxious substances and microbial pathogens by functioning as a barrier. This barrier function is achieved through the combined action of physical, chemical, microbial, and immune components. Tea (Camellia sinensis) is the most widely consumed beverage in the world, and it is consumed and appreciated in a multitude of regions across the globe. Tea can be classified into various categories, including green, white, yellow, oolong, black, and dark teas, based on the specific processing methods employed. In recent times, there has been a notable surge in scientific investigation into the various types of tea. The recent surge in research on tea can be attributed to the plethora of bioactive compounds it contains, including polyphenols, polysaccharides, pigments, and theanine. The processing of different teas affects the active ingredients to varying degrees, resulting in a range of chemical reactions and the formation of different types and quantities of ingredients. The bioactive compounds present in tea are of great importance for the maintenance of the integrity of the intestinal barrier, operating through a variety of mechanisms. This literature review synthesizes scientific studies on the impact of the primary bioactive compounds and different processing methods of tea on the intestinal barrier function. This review places particular emphasis on the exploration of the barrier repair and regulatory effects of these compounds, including the mitigation of damage to different barriers following intestinal diseases. Specifically, the active ingredients in tea can alleviate damage to physical barriers and chemical barriers by regulating barrier protein expression. At the same time, they can also maintain the stability of immune and biological barriers by regulating the expression of inflammatory factors and the metabolism of intestinal flora. This investigation can establish a strong theoretical foundation for the future development of innovative tea products.

Intestinal epithelial glycocalyx and intestinal disease

With the continuous research on glycobiology, more and more diseases are found to be associated with the glycocalyx. Glycocalyx can be categorized as endothelial glycocalyx and epithelial glycocalyx. Past studies mostly target endothelial glycocalyx, and this review focuses on the structure and function of intestinal epithelial glycocalyx, its degradation mechanism and biological relevance to different diseases of the intestinal tract, as well as the targeted delivery of drugs to organs by nanoparticle libraries mimicking the glycocalyx, in order to provide a theoretical basis for the study of potential diagnostic markers and therapeutic targets of intestinal epithelial glycocalyx in intestinal diseases.

Galacto-oligosaccharides regulate intestinal mucosal sialylation to counteract antibiotic-induced mucin dysbiosis

Intestinal mucin offers a physical barrier to maintain host-commensal homeostasis. Glycosylation is essential for the appropriate functioning of mucin. Galacto-oligosaccharides (GOS) have been used as a prebiotic with proven intestinal benefits, while their regulatory mechanism on mucin remains unclear. This study employed an antibiotic-treated rat model to mimic gut dysbiosis and attempted to restore gut dysbiosis using GOS. The gut microbiome and intestinal mucus O-glycosylations (O-glycans) in the small intestine were profiled by high-throughput sequencing and glycomics. The sialic acid phenotype at the end of O-glycans was further validated with lectin staining. Expressions of key enzymes in sialic acid metabolism and epithelial morphology were determined as well. Antibiotics significantly increased the relative abundance of Escherichia/Shigella and decreased the relative abundance of Lactobacillus. This was accompanied by decreased microbial sialidase activity and increased sialic acid in the digesta, as well as an increase in epithelial sialidase activity. Analysis of key sialylation enzymes showed the upregulation of α 2,6 sialylation (e.g. ST6GALNACs) and downregulation of α 2,3 sialylation (e.g. ST3GALs) after antibiotic treatment. The glycomics results revealed that antibiotics increased core 4 and α 2,6 sialylated O-glycans and decreased core 1, core 3 and α 2,3 sialylated O-glycans in the intestinal mucus of rats, which was further confirmed by lectin staining. Intestinal histology results demonstrated that antibiotic treatment led to the dysbiosis of intestinal mucus homeostasis. To further test the role of microbiota in regulating intestinal mucus sialylation, we supplemented GOS with antibiotics. The results showed that GOS reversed the effects of antibiotics on the gut microbiota and intestinal mucus O-glycans (especially sialylated O-glycans), characterized by an increase of Lactobacillus and α 2,3 sialylated O-glycans and a decrease of Escherichia/Shigella and α 2,6 sialylated O-glycans. What's more, GOS reduced the stimulation of the intestinal mucosa by lipopolysaccharide (LPS) by increasing α 2,3 sialylated intestinal alkaline phosphatase (IAP) to enhance IAP activity, thereby restoring intestinal mucus homeostasis. Overall, GOS counteracts antibiotic-induced mucin deficiency by remedying the gut ecology and changing the mucin sialylation pattern, as reflected by the increase of α 2,3 sialylated O-glycans and the decrease of α 2,6 sialylated O-glycans.

Intestinal nanoparticle delivery and cellular response: a review of the bidirectional nanoparticle-cell interplay in mucosa based on physiochemical properties

Orally administered nanocarriers play an important role in improving druggability, promoting intestinal absorption, and enhancing therapeutic applications for the treatment of local and systemic diseases. However, the delivering efficiency and cell response in mucosa to orally administered nanocarriers is affected by the physiological environment and barriers in the gastrointestinal tract, the physicochemical properties of the nanocarriers, and their bidirectional interactions. Goblet cells secrete and form extracellular mucus, which hinders the movement of nanoparticles. Meanwhile, intestinal epithelial cells may absorb the NPs, allowing for their transcytosis or degradation. Conversely, nanoparticle-induced toxicity may occur as a biological response to the nanoparticle exposure. Additionally, immune response and cell functions in secretions such as mucin, peptide, and cytokines may also be altered. In this review, we discuss the bidirectional interactions between nanoparticles and cells focusing on enterocytes and goblet cells, M cells, and immune cells in the mucosa according to the essential role of intestinal epithelial cells and their crosstalk with immune cells. Furthermore, we discuss the recent advances of how the physiochemical properties of nanoparticles influence their interplay, delivery, and fate in intestinal mucosa. Understanding the fate of nanoparticles with different physiochemical properties from the perspective of their interaction with cells in mucosa provides essential support for the development, rational design, potency maximation, and application of advanced oral nanocarrier delivery systems.

Targeting Human Pancreatic Cancer with a Fluorophore-Conjugated Mucin 4 (MUC4) Antibody: Initial Characterization in Orthotopic Cell Line Mouse Models

Background/Objectives: Pancreatic cancer is the third leading cause of death related to cancer. The only possible cure presently is complete surgical resection; however, this is limited by difficulty in clearly defining tumor margins. Enhancement of the visualization of pancreatic ductal adenocarcinoma (PDAC) tumor margins using near-infrared dye-conjugated tumor-specific antibodies was pioneered by using anti-CEA, anti-CA19.9, and anti-MUC5AC in orthotopic mouse models of pancreatic cancer. Recently, an antibody to Mucin 4 (MUC4) conjugated to a fluorescent probe has shown promise in targeting colon tumors in orthotopic mouse models. Methods: In the present study, we targeted pancreatic cancer using an anti-MUC4 antibody conjugated to IRDye800 (anti-MUC4-IR800) in orthotopic mouse models. Two pancreatic cancer human cell lines were used, SW1990 and CD18/HPAF. Results: Anti-MUC4-IR800 targeted the two pancreatic cancer cell line tumors in orthotopic mouse models with high tumor-to-pancreas ratios and high tumor-to-liver ratios, with greater targeting seen in SW1990. Conclusions: The present results suggest anti-MUC4-IR800's potential to be used in fluorescence-guided surgical resection of pancreatic cancer.

A New Strategy for Dietary Nutrition to Improve Intestinal Homeostasis in Diarrheal Irritable Bowel Syndrome: A Perspective on Intestinal Flora and Intestinal Epithelial Interaction

BACKGROUND AND OBJECTIVES

Although a reasonable diet is essential for promoting human health, precise nutritional regulation presents a challenge for different physiological conditions. Irritable Bowel Syndrome (IBS) is characterized by recurrent abdominal pain and abnormal bowel habits, and diarrheal IBS (IBS-D) is the most common, seriously affecting patients' quality of life. Therefore, the implementation of precise nutritional interventions for IBS-D has become an urgent challenge in the fields of nutrition and food science. IBS-D intestinal homeostatic imbalance involves intestinal flora disorganization and impaired intestinal epithelial barrier function. A familiar interaction is evident between intestinal flora and intestinal epithelial cells (IECs), which together maintain intestinal homeostasis and health. Dietary patterns, such as the Mediterranean diet, have been shown to regulate gut flora, which in turn improves the body's health by influencing the immune system, the hormonal system, and other metabolic pathways.

METHODS

This review summarized the relationship between intestinal flora, IECs, and IBS-D. It analyzed the mechanism behind IBS-D intestinal homeostatic imbalance by examining the interactions between intestinal flora and IECs, and proposed a precise dietary nutrient intervention strategy.

RESULTS AND CONCLUSION

This increases the understanding of the IBS-D-targeted regulation pathways and provides guidance for designing related nutritional intervention strategies.

Developments in the field of intestinal toxicity and signaling pathways associated with rodent exposure to micro(nano)plastics

The broad spread of micro(nano)plastics (MNPs) has garnered significant attention in recent years. MNPs have been detected in numerous human organs, indicating that they may also be hazardous to humans. The toxic effects of MNPs have been demonstrated in marine species and experimental animals. The primary pathway and target organ for MNPs entering the human body is the intestinal system, and increasing research has been done on the harmful effects and subsequent mechanisms of exposure to MNPs. Studies on how MNPs affect gut health in humans are scarce, nevertheless. Since rodents are frequently employed as animal models for human ailments, research on rodents exposed to MNPs can provide a more accurate representation of human circumstances. This study examined the effects of MNPs on intestinal microecology, inflammation, barrier function, and ion transport channels in rodents. It also reviewed the signal pathways involved, such as oxidative stress, nuclear factor (NF)-κB, Toll-like receptor (TLR) 4, inflammatory corpuscles, muscarinic acetylcholine receptors (mAChRs), mitogen-activated protein kinase (MAPK), and cell death. This review will offer a conceptual framework for the management and avoidance of associated illnesses.

Potential mechanisms of traditional Chinese medicine in the treatment of liver cirrhosis: a focus on gut microbiota

Cirrhosis, a pathological stage that develops from various chronic liver diseases, is characterized by liver fibrosis, pseudolobular formation, and chronic inflammation. When it progresses to the decompensated phase, the mortality rate of cirrhosis can reach 80%. The role of gut microbiota in the progression of liver diseases has received significant attention. Numerous studies have shown that regulating gut microbiota has significant therapeutic effects on preventing and reversing liver cirrhosis. This article reviewed the mechanisms by which gut microbiota influence liver cirrhosis, explaining the effective therapeutic effects of traditional Chinese medicine. Through multi-directional regulation involving signaling pathways, gut microbiota diversity, and restoration of intestinal barrier function, traditional Chinese medicine has been promising in ameliorating liver cirrhosis, providing treatment options and pharmacological guidance for the occurrence and development of liver cirrhosis.

The Caenorhabditis elegans cuticle and precuticle: a model for studying dynamic apical extracellular matrices in vivo

Apical extracellular matrices (aECMs) coat the exposed surfaces of animal bodies to shape tissues, influence social interactions, and protect against pathogens and other environmental challenges. In the nematode Caenorhabditis elegans, collagenous cuticle and zona pellucida protein-rich precuticle aECMs alternately coat external epithelia across the molt cycle and play many important roles in the worm's development, behavior, and physiology. Both these types of aECMs contain many matrix proteins related to those in vertebrates, as well as some that are nematode-specific. Extensive differences observed among tissues and life stages demonstrate that aECMs are a major feature of epithelial cell identity. In addition to forming discrete layers, some cuticle components assemble into complex substructures such as ridges, furrows, and nanoscale pillars. The epidermis and cuticle are mechanically linked, allowing the epidermis to sense cuticle damage and induce protective innate immune and stress responses. The C. elegans model, with its optical transparency, facilitates the study of aECM cell biology and structure/function relationships and all the myriad ways by which aECM can influence an organism.

Ileal mucus viscoelastic properties differ in Crohn's disease

Crohn's disease (CD) is an inflammatory bowel disease that can affect any part of the gastrointestinal tract, frequently involving the terminal ileum. While colonic mucus alterations in CD patients have been described, terminal ileal mucus and its mechanobiological properties have been neglected. Our study is the first of its kind to decipher the viscoelastic and network properties of ileal mucus. With that aim, oscillatory rheological shear measurements based on an airway mucus protocol that was thoroughly validated for ileal mucus were performed. Our pilot study analyzed terminal ileum mucus from controls (n = 14) and CD patients (n = 14). Mucus network structure was visualized by scanning electron microscopy. Interestingly, a statistically significant increase in viscoelasticity as well as a decrease in mesh size was observed in ileal mucus from CD patients compared to controls. Furthermore, rheological data were analyzed in relation to study participants' clinical characteristics, revealing a noteworthy trend between non-smokers and smokers. In conclusion, this study provides the first data on the viscoelastic properties and structure of human ileal mucus in the healthy state and Crohn's disease, demonstrating significant alterations between groups and highlighting the need for further research on mucus and its effect on the underlying epithelial barrier.

Revealing Glycosylation Patterns in In Vitro-Produced Mucus Exposed to Pasteurized Mucus-Associated Intestinal Microbes by MALDI-TOF-MS and PGC-LC-MS/MS

The human intestinal mucus layer protects against pathogenic microorganisms and harmful substances, whereas it also provides an important colonization niche for mutualistic microbes. The main functional components of mucus are heavily glycosylated proteins, called mucins. Mucins can be cleaved and utilized by intestinal microbes. The mechanisms between intestinal microbes and the regulation of mucin glycosylation are still poorly understood. In this study, in vitro mucus was produced by HT29-MTX-E12 cells under Semi-Wet interface with Mechanical Stimulation. Cells were exposed to pasteurized nonpathogenic bacteria Akkermansia muciniphila, Ruminococcus gnavus, and Bacteroides fragilis to evaluate influence on glycosylation patterns. Following an optimized protocol, O- and N-glycans were efficiently and reproducibly released, identified, and semiquantified using MALDI-TOF-MS and PGC-LC-MS/MS. Exposure of cells to bacteria demonstrated increased diversity of sialylated O-glycans and increased abundance of high mannose N-glycans in in vitro produced mucus. Furthermore, changes in glycan ratios were observed. It is speculated that bacterial components interact with the enzymatic processes in glycan production and that pasteurized bacteria influence glycosyltransferases or genes involved. These results highlight the influence of pasteurized bacteria on glycosylation patterns, stress the intrinsic relationship between glycosylation and microbiota, and show the potential of using in vitro produced mucus to study glycosylation behavior.

Stress-induced mucin 13 reductions drive intestinal microbiome shifts and despair behaviors

Depression is a prevalent psychological condition with limited treatment options. While its etiology is multifactorial, both chronic stress and changes in microbiome composition are associated with disease pathology. Stress is known to induce microbiome dysbiosis, defined here as a change in microbial composition associated with a pathological condition. This state of dysbiosis is known to feedback on depressive symptoms. While studies have demonstrated that targeted restoration of the microbiome can alleviate depressive-like symptoms in mice, translating these findings to human patients has proven challenging due to the complexity of the human microbiome. As such, there is an urgent need to identify factors upstream of microbial dysbiosis. Here we investigate the role of mucin 13 as an upstream mediator of microbiome composition changes in the context of stress. Using a model of chronic stress, we show that the glycocalyx protein, mucin 13, is selectively reduced after psychological stress exposure. We further demonstrate that the reduction of Muc13 is mediated by the Hnf4 transcription factor family. Finally, we determine that deleting Muc13 is sufficient to drive microbiome shifts and despair behaviors. These findings shed light on the mechanisms behind stress-induced microbial changes and reveal a novel regulator of mucin 13 expression.

Physiology of lower gastrointestinal tract

BACKGROUND

The lower gastrointestinal (GI) tract, formed from the midgut and hindgut, encompasses the colon, rectum and anal canal.

AIM

The aim of this review is to provide an overview of the anatomy and physiology of the lower GI tract.

METHODS

Literature review on anatomy and physiology of the lower GI tract, including normal motility and phases of defecation. It derives its blood supply from the superior and inferior mesenteric arteries while it is innervated by the extrinsic autonomic (the thoracolumbar and sacral nerves) and the intrinsic enteric nervous system. The colon has four layers: mucosa, submucosa, muscularis externa and serosa. The anal canal ends in the internal and external anal sphincters (EASs) involved in continence and defecation. The lower GI tract is predominantly involved in digestion, absorption, defecation and protection. Defecation is a complex process that requires inter-neural (enteric and autonomic nervous systems), neurohormonal and neuromuscular coordination. It has four phases which include basal, pre-expulsive, expulsive and end phase. High-propagating contractions in the colon propel stool to the rectum leading to rectal distention and the recruitment of the recto-anal inhibitory reflex. Once able, the EAS, under full conscious control, is then relaxed allowing stool to be evacuated. Other defecation reflexes include the gastrocolic, gastroileal and coloanal reflexes.

CONCLUSIONS

Recent advances provide novel techniques to investigate motility patterns including high-resolution manometry protocols with automated assessments, magnetic resonance imaging techniques for defecography, wireless motility capsules and fecobionics.

Network and structural analysis of quail mucins with expression pattern of mucin 1 and mucin 4 in the intestines of the Iraqi common quail (Coturnix coturnix)

Background and Aim

In avian and other species, mucins (MUCs) play a crucial role in the gastrointestinal tract (GIT), and constitute a large group of O-glycosylated glycoproteins, are glycoconjugate proteins. MUCs present in two forms: (1) membrane-attached on cell surfaces to repel external threats and (2) detachable, gel-forming proteins in the soluble form. In quail GIT, the specific types of MUCs that are expressed remain largely unknown. We investigated the expression of MUC1 and MUC4 MUCs in the GIT of Iraqi common quails and conducted network and structural analyses of all known MUC types across quail breeds.

Materials and Methods

Histological and gene expression analyses of MUC1 and MUC4 were conducted using fresh small intestine and large intestine samples from 10 quails. Using the STRING Database, Chimera software, and PrankWeb-ligand binding site prediction tool, network and structural analyses of all reported types of quail MUCs were conducted.

Results

Most intestinal MUCs in quails were acidic, with few neutral MUCs detectable through Alcian blue and periodic acid-schiff stains. Acidic MUCs were more expressed in the duodenum, ileum, cecum, and colon, whereas neutral MUCs were more expressed in the jejunum. MUC1 and MUC4 messenger RNA expression was significantly higher in the jejunum and colon than in the duodenum and ileum. The analysis of the network revealed that MUC 1, 15, 16, and 24 formed homologous networks, while MUC 2, 4, 5, and 6 formed heterologous networks. Specific MUC combinations, including MUC5A-MUC6, MUC5A-MUC5B, and MUC5B-MUC6, show higher intermolecular hydrogen bond formation affinity. MUC15, MUC16, and MUC24 showed minimal interaction with other MUC types. Among the analyzed MUCs, MUC5B, and MUC6 had the highest probability for binding, while MUC2, MUC4, and MUC5A showed lower probabilities despite greater numbers of binding sites.

Conclusion

This study's results offer significant insights into quails' MUCs' composition, expression, network interactions, and binding sites, advancing knowledge of MUC-related processes in gastrointestinal physiology and their potential connection to gastrointestinal diseases.

The role of glycans in health and disease: Regulators of the interaction between gut microbiota and host immune system

The human gut microbiota is home to a diverse collection of microorganisms that has co-evolved with the host immune system in which host-microbiota interactions are essential to preserve health and homeostasis. Evidence suggests that the perturbation of this symbiotic host-microbiome relationship contributes to the onset of major diseases such as chronic inflammatory diseases including Inflammatory Bowel Disease. The host glycocalyx (repertoire of glycans/sugar-chains at the surface of gut mucosa) constitutes a major biological and physical interface between the intestinal mucosa and microorganisms, as well as with the host immune system. Glycans are an essential niche for microbiota colonization and thus an important modulator of host-microorganism interactions both in homeostasis and in disease. In this review, we discuss the role of gut mucosa glycome as an instrumental pathway that regulates host-microbiome interactions in homeostasis but also in health to inflammation transition. We also discuss the power of mucosa glycosylation remodelling as an attractive preventive and therapeutic strategy to preserve gut homeostasis.

Glucose stockpile in the intestinal apical brush border in C. elegans

Revealing the mechanisms of glucose transport is crucial for studying pathological diseases caused by glucose toxicities. Numerous studies have revealed molecular functions involved in glucose transport in the nematode Caenorhabditis elegans, a commonly used model organism. However, the behavior of glucose in the intestinal lumen-to-cell remains elusive. To address that, we evaluated the diffusion coefficient of glucose in the intestinal apical brush border of C. elegans by using fluorescent glucose and fluorescence recovery after photobleaching. Fluorescent glucose taken in the intestine of worms accumulates in the apical brush border, and its diffusion coefficient of ∼10-8 cm2/s is two orders of magnitude slower than that in bulk. This result indicates that the intestinal brush border is a viscous layer. ERM-1 point mutations at the phosphorylation site, which shorten the microvilli length, did not significantly affect the diffusion coefficient of fluorescent glucose in the brush border. Our findings imply that glucose enrichment is dominantly maintained by the viscous layer composed of the glycocalyx and molecular complexes on the apical surface.

N-glycoproteomic analyses of human intestinal enteroids, varying in histo-blood group geno- and phenotypes, reveal a wide repertoire of fucosylated glycoproteins

Human noroviruses, globally the main cause of viral gastroenteritis, show strain specific affinity for histo-blood group antigens (HBGA) and can successfully be propagated ex vivo in human intestinal enteroids (HIEs). HIEs established from jejunal stem cells of individuals with different ABO, Lewis and secretor geno- and phenotypes, show varying susceptibility to such infections. Using bottom-up glycoproteomic approaches we have defined and compared the N-linked glycans of glycoproteins of seven jejunal HIEs. Membrane proteins were extracted, trypsin digested, and glycopeptides enriched by hydrophilic interaction liquid chromatography and analyzed by nanoLC-MS/MS. The Byonic software was used for glycopeptide identification followed by hands-on verifications and interpretations. Glycan structures and attachment sites were identified from MS2 spectra obtained by higher-energy collision dissociation through analysis of diagnostic saccharide oxonium ions (B-ions), stepwise glycosidic fragmentation of the glycans (Y-ions), and peptide sequence ions (b- and y-ions). Altogether 694 unique glycopeptides from 93 glycoproteins were identified. The N-glycans encompassed pauci- and oligomannose, hybrid- and complex-type structures. Notably, polyfucosylated HBGA-containing glycopeptides of the four glycoproteins tetraspanin-8, carcinoembryonic antigen-related cell adhesion molecule 5, sucrose-isomaltase and aminopeptidase N were especially prominent and were characterized in detail and related to donor ABO, Lewis and secretor types of each HIE. Virtually no sialylated N-glycans were identified for these glycoproteins suggesting that terminal sialylation was infrequent compared to fucosylation and HBGA biosynthesis. This approach gives unique site-specific information on the structural complexity of N-linked glycans of glycoproteins of human HIEs and provides a platform for future studies on the role of host glycoproteins in gastrointestinal infectious diseases.

The role of goblet cells in Crohn' s disease

The prevalence of Crohn's disease (CD), a subtype of inflammatory bowel disease (IBD), is increasing worldwide. The pathogenesis of CD is hypothesized to be related to environmental, genetic, immunological, and bacterial factors. Current studies have indicated that intestinal epithelial cells, including columnar, Paneth, M, tuft, and goblet cells dysfunctions, are strongly associated with these pathogenic factors. In particular, goblet cells dysfunctions have been shown to be related to CD pathogenesis by direct or indirect ways, according to the emerging studies. The mucus barrier was established with the help of mucins secreted by goblet cells. Not only do the mucins mediate the mucus barrier permeability and bacterium selection, but also, they are closely linked with the endothelial reticulum stress during the synthesis process. Goblet cells also play a vital role in immune response. It was indicated that goblet cells take part in the antigen presentation and cytokines secretion process. Disrupted goblet cells related immune process were widely discovered in CD patients. Meanwhile, dysbiosis of commensal and pathogenic microbiota can induce myriad immune responses through mucus and goblet cell-associated antigen passage. Microbiome dysbiosis lead to inflammatory reaction against pathogenic bacteria and abnormal tolerogenic response. All these three pathways, including the loss of mucus barrier function, abnormal immune reaction, and microbiome dysbiosis, may have independent or cooperative effect on the CD pathogenesis. However, many of the specific mechanisms underlying these pathways remain unclear. Based on the current understandings of goblet cell's role in CD pathogenesis, substances including butyrate, PPARγagonist, Farnesoid X receptor agonist, nuclear factor-Kappa B, nitrate, cytokines mediators, dietary and nutrient therapies were all found to have potential therapeutic effects on CD by regulating the goblet cells mediated pathways. Several monoclonal antibodies already in use for the treatment of CD in the clinical settings were also found to have some goblet cells related therapeutic targets. In this review, we introduce the disease-related functions of goblet cells, their relationship with CD, their possible mechanisms, and current CD treatments targeting goblet cells.

Equine enteroid-derived monolayers recapitulate key features of parasitic intestinal nematode infection

Stem cell-derived organoid cultures have emerged as attractive experimental models for infection biology research regarding various types of gastro-intestinal pathogens and host species. However, the large size of infectious nematode larvae and the closed structure of 3-dimensional organoids often hinder studies of the natural route of infection. To enable easy administration to the apical surface of the epithelium, organoids from the equine small intestine, i.e. enteroids, were used in the present study to establish epithelial monolayer cultures. These monolayers were functionally tested by stimulation with IL-4 and IL-13, and/or exposure to infectious stage larvae of the equine nematodes Parascaris univalens, cyathostominae and/or Strongylus vulgaris. Effects were recorded using transcriptional analysis combined with histochemistry, immunofluorescence-, live-cell- and scanning electron microscopy. These analyses revealed heterogeneous monolayers containing both immature and differentiated cells including tuft cells and mucus-producing goblet cells. Stimulation with IL-4/IL-13 increased tuft- and goblet cell differentiation as demonstrated by the expression of DCLK1 and MUC2. In these cytokine-primed monolayers, the expression of MUC2 was further promoted by co-culture with P. univalens. Moreover, live-cell imaging revealed morphological alterations of the epithelial cells following exposure to larvae even in the absence of cytokine stimulation. Thus, the present work describes the design, characterization and usability of an experimental model representing the equine nematode-infected small intestinal epithelium. The presence of tuft cells and goblet cells whose mucus production is affected by Th2 cytokines and/or the presence of larvae opens up for mechanistic studies of the physical interactions between nematodes and the equine intestinal mucosa.

Advancements in hydrogel-based drug delivery systems for the treatment of inflammatory bowel disease: a review

Inflammatory bowel disease (IBD) is a chronic disorder that affects millions of individuals worldwide. However, current drug therapies for IBD are plagued by significant side effects, low efficacy, and poor patient compliance. Consequently, there is an urgent need for novel therapeutic approaches to alleviate IBD. Hydrogels, three-dimensional networks of hydrophilic polymers with the ability to swell and retain water, have emerged as promising materials for drug delivery in the treatment of IBD due to their biocompatibility, tunability, and responsiveness to various stimuli. In this review, we summarize recent advancements in hydrogel-based drug delivery systems for the treatment of IBD. We first identify three pathophysiological alterations that need to be addressed in the current treatment of IBD: damage to the intestinal mucosal barrier, dysbiosis of intestinal flora, and activation of inflammatory signaling pathways leading to disequilibrium within the intestines. Subsequently, we discuss in depth the processes required to prepare hydrogel drug delivery systems, from the selection of hydrogel materials, types of drugs to be loaded, methods of drug loading and drug release mechanisms to key points in the preparation of hydrogel drug delivery systems. Additionally, we highlight the progress and impact of the hydrogel-based drug delivery system in IBD treatment through regulation of physical barrier immune responses, promotion of mucosal repair, and improvement of gut microbiota. In conclusion, we analyze the challenges of hydrogel-based drug delivery systems in clinical applications for IBD treatment, and propose potential solutions from our perspective.

Advances in Brain-Gut-Microbiome Interactions: A Comprehensive Update on Signaling Mechanisms, Disorders, and Therapeutic Implications

The complex, bidirectional interactions between the brain, the gut, and the gut microbes are best referred to as the brain gut microbiome system. Animal and clinical studies have identified specific signaling mechanisms within this system, with gut microbes communicating to the brain through neuronal, endocrine, and immune pathways. The brain, in turn, modulates the composition and function of the gut microbiota through the autonomic nervous system, regulating gut motility, secretion, permeability, and the release of hormones impacting microbial gene expression. Perturbations at any level of these interactions can disrupt the intricate balance, potentially contributing to the pathogenesis of intestinal, metabolic, neurologic, and psychiatric disorders. Understanding these interactions and their underlying mechanisms holds promise for identifying biomarkers, as well as novel therapeutic targets, and for developing more effective treatment strategies for these complex disorders. Continued research will advance our knowledge of this system, with the potential for improved understanding and management of a wide range of disorders. This review provides an update on the current state of knowledge regarding this system, with a focus on recent advancements and emerging research areas.

A novel cysteine-rich adaptor protein is required for mucin packaging and secretory granule stability in vivo

Mucins are large, highly glycosylated extracellular matrix proteins that line and protect epithelia of the respiratory, digestive, and urogenital tracts. Previous work has shown that mucins form large, interconnected polymeric networks that mediate their biological functions once secreted. However, how these large matrix molecules are compacted and packaged into much smaller secretory granules within cells prior to secretion is largely unknown. Here, we demonstrate that a small cysteine-rich adaptor protein is essential for proper packaging of a secretory mucin in vivo. This adaptor acts via cysteine bonding between itself and the cysteine-rich domain of the mucin. Loss of this adaptor protein disrupts mucin packaging in secretory granules, alters the mobile fraction within granules, and results in granules that are larger, more circular, and more fragile. Understanding the factors and mechanisms by which mucins and other highly glycosylated matrix proteins are properly packaged and secreted may provide insight into diseases characterized by aberrant mucin secretion.

The importance of the gut microbiome and its signals for a healthy nervous system and the multifaceted mechanisms of neuropsychiatric disorders

Increasing evidence links the gut microbiome and the nervous system in health and disease. This narrative review discusses current views on the interaction between the gut microbiota, the intestinal epithelium, and the brain, and provides an overview of the communication routes and signals of the bidirectional interactions between gut microbiota and the brain, including circulatory, immunological, neuroanatomical, and neuroendocrine pathways. Similarities and differences in healthy gut microbiota in humans and mice exist that are relevant for the translational gap between non-human model systems and patients. There is an increasing spectrum of metabolites and neurotransmitters that are released and/or modulated by the gut microbiota in both homeostatic and pathological conditions. Dysbiotic disruptions occur as consequences of critical illnesses such as cancer, cardiovascular and chronic kidney disease but also neurological, mental, and pain disorders, as well as ischemic and traumatic brain injury. Changes in the gut microbiota (dysbiosis) and a concomitant imbalance in the release of mediators may be cause or consequence of diseases of the central nervous system and are increasingly emerging as critical links to the disruption of healthy physiological function, alterations in nutrition intake, exposure to hypoxic conditions and others, observed in brain disorders. Despite the generally accepted importance of the gut microbiome, the bidirectional communication routes between brain and gut are not fully understood. Elucidating these routes and signaling pathways in more detail offers novel mechanistic insight into the pathophysiology and multifaceted aspects of brain disorders.

Targeting the Microbiome to Improve Gut Health and Breathing Function After Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition characterized by impaired motor and sensory function, as well as internal organ pathology and dysfunction. This internal organ dysfunction, particularly gastrointestinal (GI) complications, and neurogenic bowel, can reduce the quality of life of individuals with an SCI and potentially hinder their recovery. The gut microbiome impacts various central nervous system functions and has been linked to a number of health and disease states. An imbalance of the gut microbiome, i.e., gut dysbiosis, contributes to neurological disease and may influence recovery and repair processes after SCI. Here we examine the impact of high cervical SCI on the gut microbiome and find that transient gut dysbiosis with persistent gut pathology develops after SCI. Importantly, probiotic treatment improves gut health and respiratory motor function measured through whole-body plethysmography. Concurrent with these improvements was a systemic decrease in the cytokine tumor necrosis factor-alpha and an increase in neurite sprouting and regenerative potential of neurons. Collectively, these data reveal the gut microbiome as an important therapeutic target to improve visceral organ health and respiratory motor recovery after SCI.

Research Highlights

Cervical spinal cord injury (SCI) causes transient gut dysbiosis and persistent gastrointestinal (GI) pathology.Treatment with probiotics after SCI leads to a healthier GI tract and improved respiratory motor recovery.Probiotic treatment decreases systemic tumor necrosis factor-alpha and increases the potential for sprouting and regeneration of neurons after SCI.The gut microbiome is a valid target to improve motor function and secondary visceral health after SCI.

Rhubarb extract rebuilding the mucus homeostasis and regulating mucin-associated flora to relieve constipation

In clinical trials, rhubarb extract (Rb) was demonstrated to efficiently alleviate constipation. We would like to find out the underlying mechanism of rhubarb relieving constipation. However, there are few studies on the effects of rhubarb on colonic mucus secretion and constipation. The aim of this study was to investigate the effects of rhubarb on colonic mucus secretion and its underlying mechanism. The mice were randomly divided into four groups. Group I was the control group and Group II was the rhubarb control group, with Rb (24 g/kg body weight [b.w.]) administered through intragastric administration for three days. Group III mice were given diphenoxylate (20 mg/kg b.w.) for five days via gavage to induce constipation. Group IV received diphenoxylate lasting five days before undergoing Rb administration for three days. The condition of the colon was evaluated using an endoscope. Particularly, the diameter of blood vessels in the colonic mucosa expanded considerably in constipation mice along with diminishing mucus output, which was in line with the observation via scanning electron microscope (SEM) and transmission electron microscope (TEM). We also performed metagenomic analysis to reveal the microbiome related to mucin gene expression level referring to mucin secretion. In conclusion, Rb relieves constipation by rebuilding mucus homeostasis and regulating the microbiome.

Mechanism Underlying the Regulation of Mucin Secretion in the Uterus during Pregnancy

The function of endometrial epithelial cells is to secrete various substances that are rich in growth factors and nutrients. These substances support both embryo implantation and its subsequent development into a fetus. A vast number of mucins are expressed in endometrial epithelial cells, and they play an important role in regulating the processes of embryo implantation, pregnancy, and parturition. Previous studies have shown that mucin forms a mucus layer covering endometrial epithelial cells, which helps resist damage from foreign bacteria and their toxins. Therefore, this article aims to investigate the location of mucins in the endometrium, the mechanism of mucin secretion by the endometrium, and the regulation of mucins in the uterine epithelium by reproductive hormones, as well as the role of mucins in the protection of the epithelium's structure. This research aims to provide a foundational understanding for future studies on the role and mechanism of endometrial mucins throughout the pregnancy cycle.

Host-pathogen interaction: Enterobacter cloacae exerts different adhesion and invasion capacities against different host cell types

New antibiotics are urgently needed due to the huge increase of multidrug-resistant bacteria. The underexplored gram-negative bacterium Enterobacter cloacae is known to cause severe urinary tract and lung infections (UTIs). The pathogenicity of E. cloacae in UTI has only been studied at the bioinformatic level, but until now not within systematic in vitro investigations. The present study assesses different human cell lines for monitoring the early steps of host-pathogen interaction regarding bacterial adhesion to and invasion into different host cells by flow cytometric adhesion assay, classical cell counting assay, gentamicin invasion assay, and confocal laser scanning microscopy. To our knowledge, this is the first report in which E. cloacae has been investigated for its interaction with human bladder, kidney, skin, and lung cell lines under in vitro conditions. Data indicate that E. cloacae exerts strong adhesion to urinary tract (bladder and kidney) and lung cells, a finding which correlates with the clinical relevance of the bacterium for induction of urinary tract and lung infections. Furthermore, E. cloacae ATCC 13047 barely adheres to skin cells (A-431) and shows no relevant interaction with intestinal cells (Caco-2, HT-29), even in the presence of mucin (HT29 MTX). In contrast, invasion assays and confocal laser scanning microscopy demonstrate that E. cloacae internalizes in all tested host cells, but to a different extent. Especially, bladder and kidney cells are being invaded to the highest extent. Defective mutants of fimH and fimA abolished the adhesion of E. cloacae to T24 cells, while csgA deletion had no influence on adhesion. These results indicate that E. cloacae has different pattern for adhesion and invasion depending on the target tissue, which again correlates with the clinical relevance of the pathogen. For detailed investigation of the early host-pathogen interaction T24 bladder cells comprise a suitable assay system for evaluation the bacterial adhesion and invasion.

Allergen Stability in Food Allergy: A Clinician's Perspective

PURPOSE OF REVIEW

The globally rising food allergy prevalence is associated with the urgent need for new disease prevention methods, efficient treatment, and reliable risk assessment methods for characterization of food allergens. Due to inter-individual variations in the digestive system, food allergens are degraded to a different extent in each person. Food processing also influences allergen digestion.

RECENT FINDINGS

In this review, we provide an overview of the digestive system with focus on relevance for food allergy. Main food proteins causing allergic reactions are evaluated, and the combined role of food processing and digestion for allergen stability is highlighted. Finally, clinical implications of this knowledge are discussed. Recent literature shows that allergen digestibility is dependent on food processing, digestive conditions, and food matrix. Digestion affects proteins allergenicity. It is currently not possible to predict the immunogenicity of allergens solely based on protein stability.

Polysaccharide from Smilax glabra Roxb Mitigates Intestinal Mucosal Damage by Therapeutically Restoring the Interactions between Gut Microbiota and Innate Immune Functions

Smilax glabra Roxb (S. glabra) is a conventional Chinese medicine that is mainly used for the reliability of inflammation. However, bioactive polysaccharides from S. glabra (SGPs) have not been thoroughly investigated. Here, we demonstrate for the first time that SGPs preserve the integrity of the gut epithelial layer and protect against intestinal mucosal injury induced by dextran sulfate sodium. Mechanistically, SGPs mitigated colonic mucosal injury by restoring the association between the gut flora and innate immune functions. In particular, SGPs increased the number of goblet cells, reduced the proportion of apoptotic cells, improved the differentiation of gut tight junction proteins, and enhanced mucin production in the gut epithelial layer. Moreover, SGPs endorsed the propagation of probiotic bacteria, including Lachnospiraceae bacterium, which strongly correlated with decreased pro-inflammatory cytokines via the blocking of the TLR-4 NF-κB and MyD88 pathways. Overall, our study establishes a novel use of SGPs for the treatment of inflammatory bowel disease (IBD)-associated mucosal injury and provides a basis for understanding the therapeutic effects of natural polysaccharides from the perspective of symbiotic associations between host innate immune mechanisms and the gut microbiome.

MUC17 mutations and methylation are associated with poor prognosis in adult-type diffuse glioma patients

Diffuse gliomas are tumors that arise from glial or glial progenitor cells. They are currently classified as astrocytoma isocitrate dehydrogenase (IDH)-mutant or oligodendroglioma IDH-mutant, and 1p/19q-codeleted, both slower-growing tumors, or glioblastoma (GBM), a more aggressive tumor. Despite advances in the diagnosis and treatment of gliomas, the median survival time after diagnosis of GBM remains low, approximately 15 months, with a 5-year overall survival rate of only 6.8%. Therefore, new biomarkers that could support the earlier diagnosis and prognosis of these tumors would be of great value. MUC17, a membrane-bound mucin, has been identified as a potential biomarker for several tumors. However, the role of this mucin in adult gliomas has not yet been explored. Here, we show for the first time, in a retrospective study and by in silico analysis that MUC17 is one of the relevant mutant genes in adult gliomas. Moreover, that an increase in MUC17 methylation correlates with an increase in glioma malignancy grade. Patients with MUC17 mutations had a poorer prognosis than their wild-type counterparts in both GBM and non-GBM glioma cohorts. We also analyzed mutational profiles that correlated strongly with poor survival. Therefore, in this study, we present a new potential biomarker for further investigation, especially for the prognosis of adult diffuse gliomas.

Mechanism of Acupuncture and Moxibustion on Promoting Mucosal Healing in Ulcerative Colitis

The latest guideline about ulcerative colitis (UC) clinical practice stresses that mucosal healing, rather than anti-inflammation, is the main target in UC clinical management. Current mucosal dysfunction mainly closely relates to the endoscopic intestinal wall (mechanical barrier) injury with the imbalance between intestinal epithelial cells (IECs) regeneration and death, as well as tight junction (TJ) dysfunction. It is suggested that biological barrier (gut microbiota), chemical barrier (mucus protein layer, MUC) and immune barrier (immune cells) all take part in the imbalance, leading to mechanical barrier injury. Lots of experimental studies reported that acupuncture and moxibustion on UC recovery by adjusting the gut microbiota, MUC and immune cells on multiple targets and pathways, which contributes to the balance of IEC regeneration and death, as well as TJ structure recovery in animals. Moreover, the validity and superiority of acupuncture and moxibustion were also demonstrated in clinic. This study aims to review the achievements of acupuncture and moxibustion on mucosal healing and analyse the underlying mechanisms.

Low-grade intestinal inflammation two decades after pelvic radiotherapy

BACKGROUND

Radiotherapy is effective in the treatment of cancer but also causes damage to non-cancerous tissue. Pelvic radiotherapy may produce chronic and debilitating bowel symptoms, yet the underlying pathophysiology is still undefined. Most notably, although pelvic radiotherapy causes an acute intestinal inflammation there is no consensus on whether the late-phase pathophysiology contains an inflammatory component or not. To address this knowledge gap, we examined the potential presence of a chronic inflammation in mucosal biopsies from irradiated pelvic cancer survivors.

METHODS

We biopsied 24 cancer survivors two to 20 years after pelvic radiotherapy, and four non-irradiated controls. Using tandem mass tag (TMT) mass spectrometry and mRNA sequencing (mRNA-seq), we charted proteomic and transcriptomic profiles of the mucosal tissue previously exposed to a high or a low/no dose of radiation. Changes in the immune cell populations were determined with flow cytometry. The integrity of the protective mucus layers were determined by permeability analysis and 16S rRNA bacterial detection.

FINDINGS

942 proteins were differentially expressed in mucosa previously exposed to a high radiation dose compared to a low radiation dose. The data suggested a chronic low-grade inflammation with neutrophil activity, which was confirmed by mRNA-seq and flow cytometry and further supported by findings of a weakened mucus barrier with bacterial infiltration.

INTERPRETATION

Our results challenge the idea that pelvic radiotherapy causes an acute intestinal inflammation that either heals or turns fibrotic without progression to chronic inflammation. This provides a rationale for exploring novel strategies to mitigate chronic bowel symptoms in pelvic cancer survivors.

FUNDING

This study was supported by the King Gustav V Jubilee Clinic Cancer Foundation (CB), The Adlerbertska Research Foundation (CB), The Swedish Cancer Society (GS), The Swedish State under the ALF agreement (GS and CB), Mary von Sydow's foundation (MA and VP).

Mucin glycans and their degradation by gut microbiota

The human intestinal tract is inhabited by a tremendous number of microorganisms, which are collectively termed "the gut microbiota". The intestinal epithelium is covered with a dense layer of mucus that prevents penetration of the gut microbiota into underlying tissues of the host. Recent studies have shown that the maturation and function of the mucus layer are strongly influenced by the gut microbiota, and alteration in the structure and function of the gut microbiota is implicated in several diseases. Because the intestinal mucus layer is at a crucial interface between microbes and their host, its breakdown leads to gut bacterial invasion that can eventually cause inflammation and infection. The mucus is composed of mucin, which is rich in glycans, and the various structures of the complex carbohydrates of mucins can select for distinct mucosa-associated bacteria that are able to bind mucin glycans, and sometimes degrade them as a nutrient source. Mucin glycans are diverse molecules, and thus mucin glycan degradation is a complex process that requires a broad range of glycan-degrading enzymes. Because of the increased recognition of the role of mucus-associated microbes in human health, how commensal bacteria degrade and use host mucin glycans has become of increased interest. This review provides an overview of the relationships between the mucin glycan of the host and gut commensal bacteria, with a focus on mucin degradation.

Interaction between mucus layer and gut microbiota in non-alcoholic fatty liver disease: Soil and seeds

ABSTRACT

The intestinal mucus layer is a barrier that separates intestinal contents and epithelial cells, as well as acts as the "mucus layer-soil" for intestinal flora adhesion and colonization. Its structural and functional integrity is crucial to human health. Intestinal mucus is regulated by factors such as diet, living habits, hormones, neurotransmitters, cytokines, and intestinal flora. The mucus layer's thickness, viscosity, porosity, growth rate, and glycosylation status affect the structure of the gut flora colonized on it. The interaction between "mucus layer-soil" and "gut bacteria-seed" is an important factor leading to the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Probiotics, prebiotics, fecal microbiota transplantation (FMT), and wash microbial transplantation are efficient methods for managing NAFLD, but their long-term efficacy is poor. FMT is focused on achieving the goal of treating diseases by enhancing the "gut bacteria-seed". However, a lack of effective repair and management of the "mucus layer-soil" may be a reason why "seeds" cannot be well colonized and grow in the host gut, as the thinning and destruction of the "mucus layer-soil" is an early symptom of NAFLD. This review summarizes the existing correlation between intestinal mucus and gut microbiota, as well as the pathogenesis of NAFLD, and proposes a new perspective that "mucus layer-soil" restoration combined with "gut bacteria-seed" FMT may be one of the most effective future strategies for enhancing the long-term efficacy of NAFLD treatment.

The MYO1B and MYO5B motor proteins and the SNX27 sorting nexin regulate membrane mucin MUC17 trafficking in enterocytes

A dense glycocalyx, composed of the megaDalton-sized membrane mucin MUC17, coats the microvilli in the apical brush border of transporting intestinal epithelial cells, called enterocytes. The establishment of the MUC17-based glycocalyx in the mouse small intestine occurs at the critical suckling-weaning transition. The enterocytic glycocalyx extends 1 µm into the intestinal lumen and prevents the gut bacteria from directly attaching to the enterocytes. To date, the mechanism behind apical targeting of MUC17 to the brush border remains unknown. Here, we show that the actin-based motor proteins MYO1B and MYO5B, and the sorting nexin SNX27 regulate the intracellular trafficking of MUC17 in enterocytes. We demonstrate that MUC17 turnover at the brush border is slow and controlled by MYO1B and SNX27. Furthermore, we report that MYO1B regulates MUC17 protein levels in enterocytes, whereas MYO5B specifically governs MUC17 levels at the brush border. Together, our results extend our understanding of the intracellular trafficking of membrane mucins and provide mechanistic insights into how defective trafficking pathways render enterocytes sensitive to bacterial invasion.

View from the Biological Property: Insight into the Functional Diversity and Complexity of the Gut Mucus

Due to mucin's important protective effect on epithelial tissue, it has garnered extensive attention. The role played by mucus in the digestive tract is undeniable. On the one hand, mucus forms "biofilm" structures that insulate harmful substances from direct contact with epithelial cells. On the other hand, a variety of immune molecules in mucus play a crucial role in the immune regulation of the digestive tract. Due to the enormous number of microorganisms in the gut, the biological properties of mucus and its protective actions are more complicated. Numerous pieces of research have hinted that the aberrant expression of intestinal mucus is closely related to impaired intestinal function. Therefore, this purposeful review aims to provide the highlights of the biological characteristics and functional categorization of mucus synthesis and secretion. In addition, we highlight a variety of the regulatory factors for mucus. Most importantly, we also summarize some of the changes and possible molecular mechanisms of mucus during certain disease processes. All these are beneficial to clinical practice, diagnosis, and treatment and can provide some potential theoretical bases. Admittedly, there are still some deficiencies or contradictory results in the current research on mucus, but none of this diminishes the importance of mucus in protective impacts.

Protective Effect of Irsogladine against Aspirin-Induced Mucosal Injury in Human Induced Pluripotent Stem Cell-Derived Small Intestine

Background and Objectives: Acetylsalicylic acid (ASA) is widely used for preventing cerebrovascular and cardiovascular diseases. Gastrointestinal (GI) tract injury is one of the major complications of aspirin use, potentially leading to severe GI bleeding. However, no drugs for preventing aspirin-induced small intestinal injury have been developed. The aim of this study was to establish a human experimental model for investigating aspirin-induced small intestinal mucosal injury. In addition, we evaluated the protective effect of Irsogladine against aspirin-induced small intestinal mucosal injury using human induced pluripotent stem cell-derived 2D monolayer crypt-villus structural small intestine (2D-hiPSC-SI). Materials and Methods: Human iPS cell-derived intestinal organoids were seeded and cultured in Air-liquid interface. The permeability of 2D-hiPSC-SI was evaluated using Lucifer yellow. Changes in structure and mucosal permeability of 2D-hiPSC-SI after addition of aspirin were confirmed over time, and changes in intestinal epithelium-related markers were evaluated by real-time qPCR and Immunofluorescence staining. The effect of Irsogladine on prevention of aspirin mucosal injury was examined by adding Irsogladine to the culture medium. Results: Cultured 2D-hiPSC-SI showed multi-lineage differentiation into small intestinal epithelium comprised of absorptive cells, goblet cells, enteroendocrine cells, and Paneth cells, which express CD10, MUC2, chromogranin A, and lysozyme, respectively. RNA in situ hybridization revealed intestinal stem cells that express Lgr5. ASA administration induced an increase in the mucosal permeability of 2D-hiPSC-SI. ASA-injured 2D-hiPSC-SI showed decreased mRNA expression of multi-lineage small intestinal cell markers as well as intestinal stem cell marker Lgr5. Administration of Irsogladine on the basal side of the 2D-hiPSC-SI resulted in significant increases in Mki67 and Muc2 mRNA expression by 2D-hiPSCs at 48 h compared with the control group. Administration of 400 µg/mL Irsogladine to the ASA-induced small intestinal injury model resulting in significantly decreased mucosal permeability of 2D-hiPSC-SI. In immunofluorescence staining, Irsogladine significantly increased the fluorescence intensity of MUC2 under normal conditions and administration of 400 µg/mL ASA. Conclusions: we established a novel ASA-induced small intestinal injury model using human iPSC-derived small intestine. Irsogladine maintains mucosal permeability and goblet cell differentiation against ASA-induced small intestinal injury.

A Review of Xyloglucan: Self-Aggregation, Hydrogel Formation, Mucoadhesion and Uses in Medical Devices

The present paper reviews the self-aggregation, gel-forming and adsorption properties of xyloglucan (XG), and its main applications as a medical device for wound dressings, mucosal protection and ocular lubrication, as well as its uses as an excipient. XG is a branched polysaccharide composed of a central backbone of D-glucose units linked by β(1→4)-glycosidic bonds, decorated with D-xylose units through α(1→6) glycosidic bonds, and with some D-galactose units anchored to these D-xylose units via β(1→2) bonds. XG forms self-aggregates with a hierarchically ordered morphology in aqueous solutions, leading to the formation of nanofibers. Consequently, XG is a hydrogel-forming polymer able to retain large amounts of water. Inside the human digestive tract, XG is enzymatically degalactosylated, but the backbone with xylose side chains remains stable until excretion. Degalactosylated XG undergoes a fully reversible sol–gel transition, forming hydrogels between upper and lower critical temperatures. XG adsorbs on intestinal mucosa and creates a diffusion barrier that reduces permeability and also prevents bacterial infections by reducing their infiltration. Therefore, orally administered XG is considered a mucosa protectant.

Nociceptor neurons direct goblet cells via a CGRP-RAMP1 axis to drive mucus production and gut barrier protection

Neuroepithelial crosstalk is critical for gut physiology. However, the mechanisms by which sensory neurons communicate with epithelial cells to mediate gut barrier protection at homeostasis and during inflammation are not well understood. Here, we find that Nav1.8+CGRP+ nociceptor neurons are juxtaposed with and signal to intestinal goblet cells to drive mucus secretion and gut protection. Nociceptor ablation led to decreased mucus thickness and dysbiosis, while chemogenetic nociceptor activation or capsaicin treatment induced mucus growth. Mouse and human goblet cells expressed Ramp1, receptor for the neuropeptide CGRP. Nociceptors signal via the CGRP-Ramp1 pathway to induce rapid goblet cell emptying and mucus secretion. Notably, commensal microbes activated nociceptors to control homeostatic CGRP release. In the absence of nociceptors or epithelial Ramp1, mice showed increased epithelial stress and susceptibility to colitis. Conversely, CGRP administration protected nociceptor-ablated mice against colitis. Our findings demonstrate a neuron-goblet cell axis that orchestrates gut mucosal barrier protection.

Regulated Restructuring of Mucins During Secretory Granule Maturation In Vivo

Mucins are large, highly glycosylated transmembrane and secreted proteins that line and protect epithelial surfaces. However, the details of mucin biosynthesis and packaging in vivo are largely unknown. Here, we demonstrate that multiple distinct mucins undergo intragranular restructuring during secretory granule maturation in vivo, forming unique structures that are spatially segregated within the same granule. We further identify temporally-regulated genes that influence mucin restructuring, including those controlling pH (Vha16-1), Ca²⁺ ions (fwe) and Cl^- ions (Clic and ClC-c). Finally, we show that altered mucin glycosylation influences the dimensions of these structures, thereby affecting secretory granule morphology. This study elucidates key steps and factors involved in intragranular, rather than intergranular segregation of mucins through regulated restructuring events during secretory granule maturation. Understanding how multiple distinct mucins are efficiently packaged into and secreted from secretory granules may provide insight into diseases resulting from defects in mucin secretion.

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 the 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 renders 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 the investigation of gene function in health and disease. Here we leveraged a recent human genome assembly to characterize a previously unmapped MUC3B gene located at the q22 locus on chromosome 7, within a cluster of four structurally related membrane mucin genes that we name the MUC3 cluster. 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 expressed in intestinal epithelial cells (IECs). Our results complete existing genetic gaps in the MUC3 cluster which is a conserved genetic unit in vertebrates. We anticipate our results to be the starting point for the detection of disease-associated polymorphisms in the human MUC3 cluster. Moreover, our study provides the basis for the exploration of intestinal mucin gene function in widely used experimental models such as human intestinal organoids and genetic mouse models.