SDR9C7 catalyzes critical dehydrogenation of acylceramides for skin barrier formation
Takuya Takeichi, … , Alan R. Brash, Masashi Akiyama
Takuya Takeichi, … , Alan R. Brash, Masashi Akiyama
Published October 31, 2019
Citation Information: J Clin Invest. 2020;130(2):890-903. https://doi.org/10.1172/JCI130675.
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Research Article Dermatology

SDR9C7 catalyzes critical dehydrogenation of acylceramides for skin barrier formation

Abstract

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.

Authors

Takuya Takeichi, Tetsuya Hirabayashi, Yuki Miyasaka, Akane Kawamoto, Yusuke Okuno, Shijima Taguchi, Kana Tanahashi, Chiaki Murase, Hiroyuki Takama, Kosei Tanaka, William E. Boeglin, M. Wade Calcutt, Daisuke Watanabe, Michihiro Kono, Yoshinao Muro, Junko Ishikawa, Tamio Ohno, Alan R. Brash, Masashi Akiyama

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Figure 3

Epidermal accumulation of EOS-triol in Sdr9c7 null mice.

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Epidermal accumulation of EOS-triol in Sdr9c7 null mice. (A) Representat...
(A) Representative TLC analysis of lipids extracted from Sdr9c7+/+, Sdr9c7+/–, and Sdr9c7–/– epidermis. Sdr9c7–/– mice show the appearance of a major new polar lipid running between CerOS and Glc-CerEOS. In all 3 Sdr9c7 genotypes, note the normal appearance of CerEOS, which is absent in the Pnpla1 knockout (right lane). The experiment was repeated 4 times with consistent results. (B) Normal-phase LC-MS analysis of WT and knockout Sdr9c7 epidermal lipids. The chromatograms show the total ion current profile (m/z 950–1350) of LC-MS analysis of MeOH/CHCl3 epidermal extracts of WT (top panel, blue profile), and Sdr9c7–/– (bottom panel, red profile) using an Advantage 5-μm silica column (250 × 4.6 mm) run with gradient elution of hexane/isopropanol/glacial acetic acid (95:5:0.1) to hexane/isopropanol/glacial acetic acid (75:25:0.1) over 30 minutes using a Waters Alliance 2690 HPLC system coupled to a TSQ Vantage mass spectrometer. Note the prominent peak at approximately 20.5 minutes in the knockout, which is undetectable using this methodology in the WT. (C) Partial mass spectrum (m/z 1000–1150) of the 20.5-minute peak, with ion fragments identifying the product as CerEOS containing esterified trihydroxy-C18:1 fatty acid (EOS-triol).