Uchida Y, Hara M, Nishio H, Sidransky E, Inoue S, Otsuka F, Suzuki A, Elias P M, Holleran W M, Hamanaka S
Departments of Dermatology, University of California, San Francisco, CA 94143, USA.
J Lipid Res. 2000 Dec;41(12):2071-82.
Epidermal ceramides (Cer) comprise a heterogeneous family of seven species, including two unique omega-hydroxylated Cer, that are key components of the stratum corneum (SC) intercellular lamellar membranes responsible for the epidermal permeability barrier. Although both glucosylceramide (GlcCer) and the phospho-sphingolipid sphingomyelin (SM) are potential precursors of SC Cer, based on reported chemical structures of epidermal GlcCer and SC Cer, it is assumed that all major subfractions of SC Cer are generated from lamellar body-derived GlcCer. Yet, we and others have shown that SM-derived Cer are required for normal barrier homeostasis. Moreover, two pools of SM, one from plasma membrane, the other from lamellar body-derived contents, are potentially available for Cer production. To clarify the role of SM as a potential precursor of bulk or specific SC Cer, we compared Cer moieties in epidermal SM, Cer generated from epidermal SM by sphingomyelinase treatment, Cer within SC, and Cer that persist in Gaucher SC, where GlcCer cannot generate Cer due to an absence of beta-glucocerebrosidase. Using gas chromatography-mass spectrometry, fast atom bombardment-mass spectrometry, and nuclear magnetic resonance for Cer characterization, epidermal SM comprise three major subfractions with distinctive amide-linked (N-acyl) fatty acid (FA) compositions: that is, either long-chain FA (SM-1; C(22;-26)), short-chain FA (SM-2; primarily C(16)), and short-chain alpha-hydroxy FA (SM-3; C(16;-18)). In contrast, only trace quantities of omega-hydroxy FA were present. For each SM subfraction, the sphingoid base was either sphingosine or sphinganine, but phytosphingosine was not detected. Comparison of these SM with corresponding sphingomyelinase-generated epidermal Cer and SC Cer revealed that the Cer moieties of SM-1 and SM-3 are equivalent to Cer 2 (NS) and Cer 5 (AS), respectively. Moreover, both Cer 2 and Cer 5 occurred in Gaucher SC, whereas other Cer subfractions did not occur. These results indicate that two epidermal SM, that is, SM-1 and SM-3, are important precursors of two corresponding Cer in mammalian SC, that is, Cer 2 and Cer 5, but other Cer species, including the omega-hydroxy Cer species, do not derive from SM.
表皮神经酰胺（Cer）由七种不同的物质组成，包括两种独特的ω-羟基化神经酰胺，它们是角质层（SC）细胞间层状膜的关键成分，负责表皮通透屏障。尽管葡萄糖神经酰胺（GlcCer）和磷酸鞘脂鞘磷脂（SM）都是SC神经酰胺的潜在前体，但根据已报道的表皮GlcCer和SC神经酰胺的化学结构，推测SC神经酰胺的所有主要亚组分均由板层小体衍生的GlcCer产生。然而，我们和其他人已经表明，SM衍生的神经酰胺是正常屏障稳态所必需的。此外，有两池SM，一池来自质膜，另一池来自板层小体衍生的成分，都有可能用于神经酰胺的产生。为了阐明SM作为大量或特定SC神经酰胺潜在前体的作用，我们比较了表皮SM中的神经酰胺部分、经鞘磷脂酶处理从表皮SM产生的神经酰胺、SC中的神经酰胺以及在高雪氏病角质层中持续存在的神经酰胺，在高雪氏病角质层中，由于缺乏β-葡萄糖脑苷脂，GlcCer无法产生神经酰胺。使用气相色谱-质谱联用、快原子轰击-质谱联用和核磁共振来表征神经酰胺，表皮SM包含三个主要亚组分，它们具有独特的酰胺连接（N-酰基）脂肪酸（FA）组成：即长链FA（SM-1；C（22 - 26））、短链FA（SM-2；主要是C（16））和短链α-羟基FA（SM-3；C（16 - 18））。相比之下，仅存在痕量的ω-羟基FA。对于每个SM亚组分，鞘氨醇碱基要么是鞘氨醇，要么是二氢鞘氨醇，但未检测到植物鞘氨醇。将这些SM与相应的鞘磷脂酶产生的表皮神经酰胺和SC神经酰胺进行比较，发现SM-1和SM-3的神经酰胺部分分别等同于神经酰胺2（NS）和神经酰胺5（AS）。此外，神经酰胺2和神经酰胺5都存在于高雪氏病角质层中，而其他神经酰胺亚组分则不存在。这些结果表明，两种表皮SM，即SM-1和SM-3，是哺乳动物SC中两种相应神经酰胺，即神经酰胺2和神经酰胺5的重要前体，但其他神经酰胺种类，包括ω-羟基神经酰胺种类，并非源自SM。
