Nanoarchitecture and dynamics of the mouse enteric glycocalyx examined by freeze-etching electron tomography and intravital microscopy

Abstract

The glycocalyx is a highly hydrated, glycoprotein-rich coat shrouding many eukaryotic and prokaryotic cells. The intestinal epithelial glycocalyx, comprising glycosylated transmembrane mucins, is part of the primary host-microbe interface and is essential for nutrient absorption. Its disruption has been implicated in numerous gastrointestinal diseases. Yet, due to challenges in preserving and visualizing its native organization, glycocalyx structure-function relationships remain unclear. Here, we characterize the nanoarchitecture of the murine enteric glycocalyx using freeze-etching and electron tomography. Micrometer-long mucin filaments emerge from microvillar-tips and, through zigzagged lateral interactions form a three-dimensional columnar network with a 30 nm mesh. Filament-termini converge into globular structures~30 nm apart that are liquid-crystalline packed within a single plane. Finally, we assess glycocalyx deformability and porosity using intravital microscopy. We argue that the columnar network architecture and the liquid-crystalline packing of the filament termini allow the glycocalyx to function as a deformable size-exclusion filter of luminal contents.

A proximal-to-distal survey of healthy adult human small intestine and colon epithelium by single-cell transcriptomics

“…5B), finding secreted MUC2 and transmembrane MUC13 expressed across all regions and colon-enriched MUC1, MUC4, and MUC5B. While GCs are the major mucus-secreting intestinal lineage, AE and ACC express transmembrane mucins that form a glycocalyx to protect against pathogenic bacteria 128,129 . Regional mucin expression across these lineages showed high MUC13, MUC17, and MUC3A in AEs and several enriched in ACCs (Fig.…”

Colon Innervating TRPA1 Positive Nociceptors Influence Mucosal Health In Mice

“…Different goblet cell markers (Cdx2, Dll1, Foxa2, Tff3, Dll4, Vamp8, Prkd1, and Foxa3) and Fcgbp were significantly decreased in desensitized animals. Decrease in Muc 3 (a major transmembrane mucin present on the N-terminal of extracellular mucin domain tip of the enterocyte microvilli) points to compromised cell protection (due to its role in densely glycosylated glycocalyx) and altered signal transduction pathways associated to microbe: host interactions 23 . In contrast, another cell surface associated with Muc15 was significantly higher in desensitized animals and has role in carcinogenesis and protein metabolism 24 .…”

Integrity of the Intestinal Barrier: The Involvement of Epithelial Cells and Microbiota—A Mutual Relationship

“…Mucus is formed primarily of mucins, highly glycosylated large proteins characterized by the presence of 3 domains: the N’ terminal domain, central domain–composed of protein core (called PTS sequences), containing the amino acids residues: proline, threonine and serine, and C’ terminal domain. The protein core of mucin is protected from endogenous protease degradation, due to glycan formation dependent on O-glycosylation within the Golgi apparatus [ 20 , 24 , 25 ]. There are more than 20 subtypes of mucins identified in humans.…”

“…Enterocytes are structurally polarized with the apical surface directed to the lumen and the basolateral surface facing the lamina propria . From the apical site, enterocytes form microvilli, actin-based protrusions that increase tremendously the absorptive surface of nutrients, and are described as a brush border [ 20 , 25 ]. Absorptive enterocytes present the pIgR that mediate transportation of dimeric IgA and polymeric IgM from the lamina propria across the epithelial barrier to mucosal surfaces [ 48 ].…”