Roles of Epidermal Lipids in Barrier Formation

Abstract

The epidermis is continuously exposed to deleterious external stimuli, such as ultraviolet irradiation, dryness, mechanical stress, xenotoxic chemicals and microbial pathogens, and it deploys multiple barriers to protect internal tissues as well as the skin from these insults to maintain normal cellular functions. The epidermis consists of four layers - stratum basale, stratum spinosum, stratum granulosum and enucleated stratum corneum. The stratum corneum deploys most barriers, and it is the lipids in the stratum corneum that play a critical role in forming the epidermal permeability barrier. In particular, in the stratum corneum, ceramide is the lipid, made up of heterogeneous molecules not reported in other tissues, that is essential for barrier formation. Ceramide metabolites also contribute to formation of a competent permeability barrier formation. Additionally, these ceramide metabolites in the nucleated layers of the epidermis serve as modulator lipids in the formation of the antimicrobial barrier through increasing antimicrobial peptide production.