title: Endogenous β-glucocerebrosidase activity in Abca12⁻/⁻epidermis elevates ceramide levels after topical lipid application but does not restore barrier function.
abstract: 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 [(14)C]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.
authors.affiliation: Lipid Metabolism Unit and Center for Computational and Integrative Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114.
authors.forename: Jorge F
authors.initials: JF
authors.lastname: Haller
authors.forename: Paul
authors.initials: P
authors.lastname: Cavallaro
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Hernandez
authors.forename: Lee
authors.initials: L
authors.lastname: Dolat
authors.forename: Stephanie J
authors.initials: SJ
authors.lastname: Soscia
authors.forename: Ruth
authors.initials: R
authors.lastname: Welti
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Grabowski
authors.forename: Michael L
authors.initials: ML
authors.lastname: Fitzgerald
authors.forename: Mason W
authors.initials: MW
authors.lastname: Freeman
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002518:Ceramides / Q000032:analysis / Q000378:metabolism; D002855:Chromatography, Thin Layer; D004817:Epidermis / Q000187:drug effects / Q000196:embryology / Q000378:metabolism*; D005962:Glucosylceramidase / Q000378:metabolism*; D005963:Glucosylceramides / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D008055:Lipids / Q000032:analysis / Q000737:chemistry; D051379:Mice; D018345:Mice, Knockout; D009924:Organ Culture Techniques; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012867:Skin / Q000187:drug effects / Q000196:embryology / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; C532573:Abca12 protein, mouse; D002518:Ceramides; D005963:Glucosylceramides; D008055:Lipids; D005962:Glucosylceramidase
keywords: ABCA12 antibody; glucosylceramide; harlequin ichthyosis; skin permeability barrier