Lipoxygenases Mediate the Effect of Essential Fatty Acid in Skin Barrier Formation

Abstract

A barrier to water loss is vital to maintaining life on dry land. Formation of the mammalian skin barrier requires both the essential fatty acid linoleate and the two lipoxygenases 12R-lipoxygenase (12R-LOX) and epidermal lipoxygenase-3 (eLOX3), although their roles are poorly understood. Linoleate occurs in O-linoleoyl--hydroxyceramide, which, after hydrolysis of the linoleate moiety, is covalently attached to protein via the free -hydroxyl of the ceramide, forming the corneocyte lipid envelope, a scaffold between lipid and protein that helps seal the barrier. Here we show using HPLC-UV, LC-MS, GC-MS, and 1 H NMR that O-linoleoyl--hydroxyceramide is oxygenated in a regio-and stereospecific fashion by the consecutive actions of 12R-LOX and eLOX3 and that these products occur naturally in pig and mouse epidermis. 12R-LOX forms 9R-hydroperoxy-linoleoyl--hydroxyceramide, further converted by eLOX3 to specific epoxyalcohol (9R,10R-trans-epoxy-11E-13R-hydroxy) and 9-keto-10E,12Z esters of the ceramide; an epoxy-ketone derivative (9R,10R-trans-epoxy-11E-13-keto) is the most prominent oxidized ceramide in mouse skin. These products are absent in 12R-LOX-deficient mice, which crucially display a near total absence of protein-bound -hydroxyceramides and of the corneocyte lipid envelope and die shortly after birth from transepidermal water loss. We conclude that oxygenation of O-linoleoyl--hydroxyceramide is required to facilitate the ester hydrolysis and allow bonding of the -hydroxyceramide to protein, providing a coherent explanation for the roles of multiple components in epidermal barrier function. Our study uncovers a hitherto unknown biochemical pathway in which the enzymic oxygenation of ceramides is involved in building a crucial structure of the epidermal barrier.

Ultrastructure of skin from Refsum disease with emphasis on epidermal lamellar bodies and stratum corneum barrier lipid organization

“…There, phytanic acid could replace linoleic acid in acylglucosylceramides, leading to barrier defects similar to those seen in essential fatty acid deficiency (EFAD) [7] and certain other ichthyosis that lack a CLE (i.e., ALOX mutations [LOX 12 and eLOX [30]]), and neutral lipid storage disease [26]. PA, if substituted for linoleic acid (LA) in the acyl group of acylglycosylceramides likely would serve as a substrate for the lipase that generates the ω-acyl Cer component for the CLE.…”

UVA irradiation of fatty acids and their oxidized products substantially increases their ability to generate singlet oxygen

“…Fatty acids are ubiquitously present in human cells but also exhibit the so-called ''acid-mantle of the stratum corneum'' that is important for both permeability barrier formation and cutaneous antimicrobial defense. 44,45 Consequently, the generation of singlet oxygen may affect cellular and skin integrity leading to the frequently reported disturbance of the skin barrier, skin ageing and even skin malignancies. The photosensitized generation of singlet oxygen by endogenous photosensitizers such as flavins and its role for those adverse reactions are well documented.…”

Epidermal Lamellar Granules

“…The action of a flipase at about the time of LG fusion and extrusion could lead to ω-hydroxyceramide with the appropriate orientation. It is speculated that acylglucosylceramide does arrive in the plasma membrane with the glucosyl moiety on the cytoplasmic side, and that the ester-linked fatty acid can be removed through the action of an acid lipase following 2 specific lipoxygenase attacks [44] at the acidic interface between the granular and cornified layers. Flipase action at this time could both expose the glucosyl moiety to β-glucocerebrosidase at the interface and bring the hydroxyl group into apposition with the nascent cornified envelope proteins to which it becomes attached.…”