title: Biosynthesis of acylceramide in murine epidermis: characterization by inhibition of glucosylation and deglucosylation, and by substrate specificity.
abstract: We have investigated the physiological significance of the glucosylation of ceramides and the subsequent deglucosylation of glucosylceramide in the synthetic pathway of acylceramide. In this metabolic pathway using [14C]-serine in organ culture, newborn murine (BALB/c) epidermis synthesizes several types of ceramides, including acylceramide, as analyzed by thin-layer chromatography. When conduritol-B-epoxide, a specific inhibitor of beta-glucocerebrosidase, was added to the culture medium, the synthesis of acylceramide was significantly suppressed in concert with a significant increase in acylglucosylceramide. Furthermore, addition of d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, an inhibitor of glucosyltransferase, also specifically abolished the synthesis of acylceramide whereas non-acylated ceramides were relatively less affected. We further determined whether the physiological substrate of glucosyltransferase is omega-hydroxyceramide (C30) or non-omega-hydroxylated ceramides. Of those, only non-omega-hydroxylated ceramides proved to be good substrates for glucosyltransferase in vitro. Our parallel in vitro study also demonstrated that murine epidermis contains enzymatic activity by which omega-hydroxyglucosylceramide or omega-hydroxyceramide can be converted to acylglucosylceramide or acylceramide. Collectively, these findings indicate that the majority of acylceramides found in the stratum corneum may be synthesized through a distinct sequence of enzymatic reactions consisting of the glucosylation of ceramides by glucosyltransferase, omega-hydroxylation of glucosylceramide, the acylation of omega-hydroxyglucosylceramide (possibly by an omega-acyltransferase), and the deglucosylation of acylglucosylceramide by beta-glucocerebrosidase.
authors.affiliation: Department of Dermatology, Jichi Medical University, Tochigi, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Takagi
authors.forename: Hidemi
authors.initials: H
authors.lastname: Nakagawa
authors.forename: Noboru
authors.initials: N
authors.lastname: Matsuo
authors.forename: Tomoko
authors.initials: T
authors.lastname: Nomura
authors.forename: Minoru
authors.initials: M
authors.lastname: Takizawa
authors.forename: Genji
authors.initials: G
authors.lastname: Imokawa
mesh_terms: D000215:Acylation; D000217:Acyltransferases / Q000502:physiology; D000818:Animals; D002518:Ceramides / Q000378:metabolism*; D004817:Epidermis / Q000378:metabolism*; D005962:Glucosylceramidase / Q000037:antagonists & inhibitors*; D005963:Glucosylceramides / Q000378:metabolism; D005964:Glucosyltransferases / Q000037:antagonists & inhibitors*; D006031:Glycosylation; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D013379:Substrate Specificity
chemical_list: D002518:Ceramides; D005963:Glucosylceramides; D000217:Acyltransferases; D005964:Glucosyltransferases; D005962:Glucosylceramidase