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 2

Sdr9c7 deletion reduces permeability barrier function and CLE formation.

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Sdr9c7 deletion reduces permeability barrier function and CLE formation...
(A) Gross appearance of Sdr9c7+/+ and Sdr9c7–/– newborns at 1 hour after birth. Although the newborns (Sdr9c7+/+, Sdr9c7+/–, Sdr9c7–/–) were indistinguishable at birth, Sdr9c7–/– mice show erythema and wrinkled skin consistent with increased TEWL soon after birth. (B) Skin permeability as assessed by TEWL on the dorsal skin surface of Sdr9c7+/+ (n = 6), Sdr9c7+/– (n = 7), and Sdr9c7–/– (n = 10) mice (mean ± SEM, *P < 0.001). (C) Toluidine blue exclusion assay using neonatal Sdr9c7+/+ and Sdr9c7–/– mice. (D) Histology of dorsal skin sections from newborn Sdr9c7+/+ and Sdr9c7–/– mice stained with hematoxylin and eosin. Scale bars: 20 µm. (E and F) Transmission electron microscopy of the stratum corneum in Sdr9c7+/+ and Sdr9c7–/– newborn mice. Scale bars = 200 μm. (E) There is a normal external lipid membrane monolayer, the corneocyte-bound lipid envelope (CLE), in Sdr9c7+/+ mice. (F) In contrast, the CLE is either absent, partially formed irregularly, or loosely attached to the CCE in Sdr9c7–/– mice. (G) The levels of covalently bound CerOS are significantly reduced in the epidermis of Sdr9c7–/– (KO) mice compared with that of Sdr9c7+/+ (WT) mice (mean ± SEM, n = 3 or 4, Student’s t test, P < 0.001).