ABSTRACT
Skin barrier function is primarily assigned to the outer epidermal layer, the stratum corneum (SC), mainly composed of corneocytes and lipid-enriched extracellular matrix. Epidermal ceramides (Cers) are essential barrier lipids, containing ultra-long-chain (ULC) fatty acids (FAs) with a unique ω-hydroxy group, which is necessary for binding to corneocyte proteins. In the SC, Cers are believed to derive from glucosylated intermediates, namely glucosylceramides (GlcCers), as surmised from human Gaucher's disease and related mouse models. Tamoxifen (TAM)-induced deletion of the endogenous GlcCer-synthesizing enzyme UDP-glucose:ceramide glucosyltransferase (UGCG) in keratin K14-positive cells resulted in epidermal GlcCer depletion. Although free extractable Cers were elevated in total epidermis and as well in SC, protein-bound Cers decreased significantly in Ugcg(f/fK14CreERT2) mice, indicating glucosylation to be required for regular Cer processing as well as arrangement and extrusion of lipid lamellae. The almost complete loss of protein-bound Cers led to a disruption of the water permeability barrier (WPB). UGCG-deficient mice developed an ichthyosis-like skin phenotype marked by impaired keratinocyte differentiation associated with delayed wound healing. Gene expression profiling of Ugcg-mutant skin revealed a subset of differentially expressed genes involved in lipid signaling and epidermal differentiation/proliferation, correlating to human skin diseases such as psoriasis and atopic dermatitis. Peroxisome proliferator-activated receptor beta/delta (PPARß/δ), a Cer-sensitive transcription factor was identified as potential mediator of the altered gene sets.
Subject(s)
Cell Differentiation , Ceramides/metabolism , Epidermal Cells , Glucosylceramides/metabolism , Glucosyltransferases/metabolism , Keratinocytes/cytology , Animals , Epidermis/metabolism , Gene Expression Profiling , Glucosyltransferases/genetics , Humans , Keratinocytes/metabolism , Lipids/biosynthesis , Mice , Peroxisome Proliferator-Activated Receptors/genetics , Peroxisome Proliferator-Activated Receptors/metabolism , Phenotype , Signal Transduction/genetics , Skin Physiological PhenomenaABSTRACT
Glycosphingolipids (GSLs) constitute major components of enterocytes and were hypothesized to be potentially important for intestinal epithelial polarization. The enzyme UDP-glucose ceramide glucosyltransferase (Ugcg) catalyzes the initial step of GSL biosynthesis. Newborn and adult mice with enterocyte-specific genetic deletion of the gene Ugcg were generated. In newborn mutants lacking GSLs at day P0, intestinal epithelia were indistinguishable from those in control littermates displaying an intact polarization with regular brush border. However, those mice were not consistently able to absorb nutritional lipids from milk. Between postnatal days 5 and 7, severe defects in intestinal epithelial differentiation occurred accompanied by impaired intestinal uptake of nutrients. Villi of mutant mice became stunted, and enterocytes lacked brush border. The defects observed in mutant mice caused diarrhea, malabsorption, and early death. In this study, we show that GSLs are essential for enterocyte resorptive function but are primarily not for polarization; GSLs are required for intracellular vesicular transport in resorption-active intestine.
