The role of fatty acid elongation in epidermal structure and function.

Heterogeneous molecular species of epidermal ceramide (Cer) play critical roles in forming a competent permeability barrier of lamellar membrane structures in the stratum corneum, which is a prerequisite to preventing excess water loss for terrestrial mammals. Lipids containing very long chain lengths of fatty acids (VLCFA) (hydrocarbon chain lengths over 28) have been found in selected tissues, including epidermis. In particular, ω-hydroxy (ω-OH) VLCFA as well as Cer containing ω-OH VLCFA and ω-O-acylCer (acylCer) are unique to epidermis. The fatty acid elongation system that generates VLCFA, which requires four enzymatic steps, has been characterized, while recent studies using transgenic animals have further revealed the importance of ω-OH Cer species for barrier formation and have also elucidated the synthetic pathway of these essential Cer species in conjunction with VLCFA metabolism. This review article discusses the generation of VLCFA and unique epidermal Cer species containing VLFCA in the relation to their roles in epidermis.