Endogenous β-glucocerebrosidase activity in Abca12−/−epidermis elevates ceramide levels after topical lipid application but does not restore barrier function

• Published in: Journal of lipid research Vol. 55; no. 3; pp. 493 - 503
• Main Authors: Haller, Jorge F., Cavallaro, Paul, Hernandez, Nicholas J., Dolat, Lee, Soscia, Stephanie J., Welti, Ruth, Grabowski, Gregory A., Fitzgerald, Michael L., Freeman, Mason W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-03-2014; The American Society for Biochemistry and Molecular Biology; Elsevier
• Subjects: ABCA12 antibody; Animals; ATP-Binding Cassette Transporters - deficiency; ATP-Binding Cassette Transporters - genetics; ATP-Binding Cassette Transporters - metabolism; Ceramides - analysis; Ceramides - metabolism; Chromatography, Thin Layer; Epidermis - drug effects; Epidermis - embryology; Epidermis - metabolism; Glucosylceramidase - metabolism; glucosylceramide; Glucosylceramides - administration & dosage; Glucosylceramides - metabolism; Glucosylceramides - pharmacology; harlequin ichthyosis; HEK293 Cells; Humans; Immunoblotting; Immunohistochemistry; Lipids - analysis; Lipids - chemistry; Mice; Mice, Knockout; Organ Culture Techniques; Reverse Transcriptase Polymerase Chain Reaction; Skin - drug effects; Skin - embryology; Skin - metabolism; skin permeability barrier; harlequin ichthyosis; ABCA12 antibody; skin permeability barrier; glucosylceramide
• ISSN: 0022-2275; 1539-7262
• DOI: 10.1194/jlr.M044941

ABCA12 mutations disrupt the skin barrier and cause harlequin ichthyosis. We previously showed Abca12−/− skin has increased glucosylceramide (GlcCer) and correspondingly lower amounts of ceramide (Cer). To examine why loss of ABCA12 leads to accumulation of GlcCer, de novo sphingolipid synthesis was assayed using [14C]serine labeling in ex vivo skin cultures. A defect was found in β-glucocerebrosidase (GCase) processing of newly synthesized GlcCer species. This was not due to a decline in GCase function. Abca12−/− epidermis had 5-fold more GCase protein (n = 4, P < 0.01), and a 5-fold increase in GCase activity (n = 3, P < 0.05). As with Abca12+/+ epidermis, immunostaining in null skin showed a typical interstitial distribution of the GCase protein in the Abca12−/− stratum corneum. Hence, we tested whether the block in GlcCer conversion could be circumvented by topically providing GlcCer. This approach restored up to 15% of the lost Cer products of GCase activity in the Abca12−/− epidermis. However, this level of barrier ceramide replacement did not significantly reduce trans-epidermal water loss function. Our results indicate loss of ABCA12 function results in a failure of precursor GlcCer substrate to productively interact with an intact GCase enzyme, and they support a model of ABCA12 function that is critical for transporting GlcCer into lamellar bodies.