During the formation of the stratum corneum (SC) barrier, the extracellular spaces of viable epidermis, rich in glycans, are filled with a highly organized lipid matrix and the plasma membranes of keratinocytes are replaced by cornified lipid envelopes. These structures comprise cross‐linked proteins, including transmembrane glycoproteins and proteoglycans, covalently bound to a monolayer of cell surface ceramides. Little is known about the presence and distribution of glycans on the SC corneocytes despite their possible involvement in SC hydration, cohesion and desquamation. In this work, we visualized ultrastructurally and quantified the distribution of glycans on the surface of native and delipidated corneocytes. The cells were harvested at different depths of the SC, allowing us to define the relationship between the distribution of various glycans, proteoglycans and glycoproteins, and other changes occurring in SC. At the cell periphery, we found a correlation between the depth‐related alterations of corneodesmosome glycoproteins and α‐d‐mannosyl and N‐acetyl‐d‐glucosamine‐labelling patterns. Elimination of the terminal sugars, α‐linked fucose and α‐(2,3) linked sialic acid, was less abrupt, but also the initial extent of their peripheral distribution was overall lower than that of concanavalin A and wheat germ agglutinin lectin‐detected glycans. Diffuse labelling of heparan sulphate glycosaminoglycans disappeared completely from the outermost corneocytes, whereas that of several simple carbohydrates could be detected at all SC levels. Our results suggest that specific glycan distribution may participate in the progressive changes of SC, as it evolves from the SC compactum to the SC disjunctum, towards desquamation.
The ultrastructural study of the intercellular spaces of the human stratum corneum was based on transmission electron microscopy of thin vertical sections and freeze-fracture replicas, field emission scanning electron microscopy and immunofluorescence confocal laser scanning microscopy. The maturation of the corneosomes and their enzymatic degradation could be depicted at strategic interfaces. These sharp and rapid metamorphoses are now relatively well understood from a morphological point of view. But morphology raises a lot of unsolved physiological problems.
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