Human Fecal Mucin Glycosylation as a New Biomarker in Inflammatory Bowel Diseases

Sialylation in the gut: From mucosal protection to disease pathogenesis

Sialylation, a crucial post-translational modification of glycoconjugates, entails the attachment of sialic acid (SA) to the terminal glycans of glycoproteins and glycolipids through a tightly regulated enzymatic process involving various enzymes. This review offers a comprehensive exploration of sialylation within the gut, encompassing its involvement in mucosal protection and its impact on disease progression. The sialylation of mucins and epithelial glycoproteins contributes to the integrity of the intestinal mucosal barrier. Furthermore, sialylation regulates immune responses in the gut, shaping interactions among immune cells, as well as their activation and tolerance. Additionally, the gut microbiota and gut-brain axis communication are involved in the role of sialylation in intestinal health. Altered sialylation patterns have been implicated in various intestinal diseases, including inflammatory bowel disease (IBD), colorectal cancer (CRC), and other intestinal disorders. Emerging research underscores sialylation as a promising avenue for diagnostic, prognostic, and therapeutic interventions in intestinal diseases. Potential strategies such as sialic acid supplementation, inhibition of sialidases, immunotherapy targeting sialylated antigens, and modulation of sialyltransferases have been utilized in the treatment of intestinal diseases. Future research directions will focus on elucidating the molecular mechanisms underlying sialylation alterations, identifying sialylation-based biomarkers, and developing targeted interventions for precision medicine approaches.

Fecal-adherent mucus is a non-invasive source of primary human MUC2 for structural and functional characterization in health and disease

The O-glycoprotein Mucin-2 (MUC2) forms the protective colon mucus layer. While animal models have demonstrated the importance of Muc2, few studies have explored human MUC2 in similar depth. Recent studies have revealed that secreted MUC2 is bound to human feces. We hypothesized human fecal MUC2 (HF-MUC2) was accessible for purification and downstream structural and functional characterization. We tested this via histologic and quantitative imaging on human fecal sections; extraction from feces for proteomic and O-glycomic characterization; and functional studies via growth and metabolic assays in vitro. Quantitative imaging of solid fecal sections showed a continuous mucus layer of varying thickness along human fecal sections with barrier functions intact. Lectin profiling showed HF-MUC2 bound several lectins but was weak to absent for Ulex europaeus 1 (α1,2 fucose-binding) and Sambucus nigra agglutinin (α2,6 sialic acid-binding), and did not have obvious b1/b2 barrier layers. HF-MUC2 separated by electrophoresis showed high molecular weight glycoprotein bands (∼1-2 MDa). Proteomics and Western analysis confirmed the enrichment of MUC2 and potential MUC2-associated proteins in HF-MUC2 extracts. MUC2 O-glycomics revealed diverse fucosylation, moderate sialylation, and little sulfation versus porcine colonic MUC2 and murine fecal Muc2. O-glycans were functional and supported the growth of Bacteroides thetaiotaomicron (B. theta) and short-chain fatty acid (SCFA) production in vitro. MUC2 could be similarly analyzed from inflammatory bowel disease stools, which displayed an altered glycomic profile and differential growth and SCFA production by B. theta versus healthy samples. These studies describe a new non-invasive platform for human MUC2 characterization in health and disease.

From ASCA breakthrough in Crohn's disease and Candida albicans research to thirty years of investigations about their meaning in human health

Anti-Saccharomyces cerevisiae antibodies (ASCA) are human antibodies that can be detected using an enzyme-linked immunosorbent assay involving a mannose polymer (mannan) extracted from the cell wall of the yeast S. cerevisiae. The ASCA test was developed in 1993 with the aim of differentiating the serological response in two forms of inflammatory bowel disease (IBD), Crohn's disease and ulcerative colitis. The test, which is based on the detection of anti-oligomannosidic antibodies, has been extensively performed worldwide and there have been hundreds of publications on ASCA. The earlier studies concerned the initial diagnostic indications of ASCA and investigations then extended to many human diseases, generally in association with studies on intestinal microorganisms and the interaction of the micro-mycobiome with the immune system. The more information accumulates, the more the mystery of the meaning of ASCA deepens. Many fundamental questions remain unanswered. These questions concern the heterogeneity of ASCA, the mechanisms of their generation and persistence, the existence of self-antigens, and the relationship between ASCA and inflammation and autoimmunity. This review aims to discuss the gray areas concerning the origin of ASCA from an analysis of the literature. Structured around glycobiology and the mannosylated antigens of S. cerevisiae and Candida albicans, this review will address these questions and will try to clarify some lines of thought. The importance of the questions relating to the pathophysiological significance of ASCA goes far beyond IBD, even though these diseases remain the preferred models for their understanding.