In mammalian skin, permeability barrier function and desquamation are mediated by intercellular stratum corneum lipids. The metabolic pathways whereby epidermis generates lipid for these stratum corneum functions is not well-understood, however, several inherited skin diseases characterized by abnormal desquamation and associated with discrete lipid metabolic defects provide models for the study of these pathways. Some diseases are characterized by accumulation of very long chain (v.l.c.) n-alkanes, also found in normal skin. These studies are based upon the hypothesis that epidermis synthesizes alkanes from fatty acids or alcohols; that changes in the number or function of peroxisomes, a cellular organelle involved in fatty alcohol and v.l.c. fatty acid metabolism, are involved in n-alkane accumulation in outer epidermis; and that delineation of the underlying defect in neutral lipid storage disease (NLSDI), where triglycerides accumulate in viable cells, but alkanes accumulate in stratum corneum, will further illuminate the origin of epidermal alkanes. The defect in NLSDI is postulated to be an intercellular triacylglycerol lipase that generates diacylglycerols for phospholipid biosynthesis. Evidence for alkane biosynthesis will be sought using radiolabelled v.l.c. fatty acids in cultured human keratinocytes (CHK), rodent epidermis in vivo, and in mutant fibroblasts and products analyzed by radiochemical GLC. The relationship of alkane synthesis to differentiation will be assessed in isolated epidermal layers and in CHK cultured by a variety of methods designed to alter differentiation. Peroxisomes will be quantitated in relation to differentiation by ultrastructural cytochemistry for catalase and by three functional assays for peroxisome specific pathways in both CHK and rodent epidermis. The cause of NLSDI will be probed in three NLSDI fibroblast cell lines using radiolabelled precursors and by measurement of pool size using recombinant diacylglycerol kinase. Delineation of the metabolic defect in NLSDI will contribute to our understanding of glycerolipid metabolism and to the origin of epidermal alkanes. Studies with mutant cells which exhibit defects in v.l.c. fatty acid oxidation will aid in our understanding of the role of peroxisomes in normal epidermal lipid metabolism.
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