Intestinal Glycocalyx and Enterocyte Microvilli Integrate into a Stratified Transcellular Structure Optimized for Size-exclusion Barrier Function and Epithelial Homeostasis

Cell surface glycoprotein complexes, commonly known as glycocalyx, are structures that have been suggested to be involved in a multitude of tissue specific functions including hydration, structural support, filtration and protection against pathogens [1]. In the gastrointestinal tract, membrane-anchored fibrous glycoproteins composed primarily of mucins, a family of high molecular weight-heavily glycosylated proteins, come together to form the intestinal glycocalyx. Previous studies have implied that this enteric cell surface organization help establish a physical barrier that segregates the lumen of the intestine from the host in addition to acting as a molecular filter [2]. How glycocalyx molecular architecture relates to its proposed functions remains elusive due to the challenge in preserving the large-size mucin molecules and in visualizing the complex. Traditional scanning and transmission electron microscopy techniques do not preserve the delicate, hydrated structure of the intestinal glycocalyx. Further, conventional heavy metal stains do not effectively bind to mucins. Here, we performed freeze-etch electron microscopy on murine small intestine enterocytes along with electron tomography to examine the structural details of intestinal glycocalyx.