Localization and Composition of Lipids in Neonatal Mouse Stratum Granulosum and Stratum Corneum

Abstract

Recent cytochemical and freeze-fracture experiments indicate that intercellular lipids, derived from the secreted contents of epidermal lamellar bodies, may be important for the permeability barrier in skin. During keratinization extensive changes occur in the morphology and histochemistry of intercellular lamellae that coincide with profound alterations in the lipid composition of the stratum granulosum and stratum corneum. In the present study we have separated stratum granulosum from stratum corneum and measured their lipid compositions. In the stratum granulosum polar and neutral lipids are almost equally abundant, and are found cytochemically both between and within cells. Lamellar bodies examined by cytochemical techniques contain free sterols and neutral sugars, suggesting the presence of glycosphingolipids, but little phospholipid. On the other hand, the stratum corneum contains predominantly neutral lipids and sphingolipids which are found primarily in cell membrane regions. Based upon these data, we suggest that lamellar bodies secrete glycolipids and free sterols, which are then extensively metabolized to free fatty acids, ceramides, and sterol esters. Together with some remaining free sterols these coalesce to form the broad bilayers of the stratum corneum interstices. These hydrophobic lipids are thus ideally situated and suited to function as the principal epidermal permeability barrier.