SDR9C7 catalyzes critical dehydrogenation of acylceramides for skin barrier formation

• Published in: The Journal of clinical investigation 2020-02, Vol.130 (2), p.890-903
• Main Authors: Takeichi, Takuya, Hirabayashi, Tetsuya, Miyasaka, Yuki, Kawamoto, Akane, Okuno, Yusuke, Taguchi, Shijima, Tanahashi, Kana, Murase, Chiaki, Takama, Hiroyuki, Tanaka, Kosei, Boeglin, William E, Calcutt, M Wade, Watanabe, Daisuke, Kono, Michihiro, Muro, Yoshinao, Ishikawa, Junko, Ohno, Tamio, Brash, Alan R, Akiyama, Masashi
• Format: Article
• Language: English
• Subjects: Analysis; Anopheles; Biomedical research; Ceramide; Ceramides; Chromatography; Defects; Dehydrogenases; Dehydrogenation; Dermatitis; Diseases; Epidermis; Epoxy resins; Fatty acids; Genes; Ichthyosis; Ketones; Linoleic acid; Lipids; Lipoxygenase; Liquid chromatography; Mutants; Mutation; NAD; Pathogenesis; Patients; Permeability; Plant lipids; Protein binding; Proteins; Reductase; Skin; Skin diseases; Stratum corneum; Unsaturated fatty acids
• ISSN: 0021-9738; 1558-8238
• DOI: 10.1172/JCI130675

The corneocyte lipid envelope, composed of covalently bound ceramides and fatty acids, is important to the integrity of the permeability barrier in the stratum corneum, and its absence is a prime structural defect in various skin diseases associated with defective skin barrier function. SDR9C7 encodes a short-chain dehydrogenase/reductase family 9C member 7 (SDR9C7) recently found mutated in ichthyosis. In a patient with SDR9C7 mutation and a mouse Sdr9c7-KO model, we show loss of covalent binding of epidermal ceramides to protein, a structural fault in the barrier. For reasons unresolved, protein binding requires lipoxygenase-catalyzed transformations of linoleic acid (18:2) esterified in ω-O-acylceramides. In Sdr9c7-/- epidermis, quantitative liquid chromatography-mass spectometry (LC-MS) assays revealed almost complete loss of a species of ω-O-acylceramide esterified with linoleate-9,10-trans-epoxy-11E-13-ketone; other acylceramides related to the lipoxygenase pathway were in higher abundance. Recombinant SDR9C7 catalyzed NAD+-dependent dehydrogenation of linoleate 9,10-trans-epoxy-11E-13-alcohol to the corresponding 13-ketone, while ichthyosis mutants were inactive. We propose, therefore, that the critical requirement for lipoxygenases and SDR9C7 is in producing acylceramide containing the 9,10-epoxy-11E-13-ketone, a reactive moiety known for its nonenzymatic coupling to protein. This suggests a mechanism for coupling of ceramide to protein and provides important insights into skin barrier formation and pathogenesis.