Elias P M, Menon G K, Grayson S, Brown B E
Dermatology Service, Veterans Administration Medical Center, San Francisco, California 94121.
J Invest Dermatol. 1988 Jul;91(1):3-10. doi: 10.1111/1523-1747.ep12463279.
During the formation of the mammalian epidermal permeability barrier, lipids are sequestered in the stratum corneum intercellular spaces, transforming from a relatively polar lipid mixture to predominantly nonpolar species. Certain lipid catabolic enzymes, which co-localize with these lipids, may regulate this process. In order to localize the sites within the outer epidermis where polar lipids are catabolized, and their relationship to the alterations in membrane structure that occur in these layers, we compared the biochemical localization of polar lipids, the ultrastructure, and freeze-fracture morphology, as well as the localization of phospholipases within the outer epidermis. Both histochemical staining of frozen sections and biochemical studies of protease- and tape-stripped whole stratum corneum demonstrated small amounts of polar lipids in the stratum compactum, while in contrast, the stratum disjunctum was devoid of both phospholipids and glycosphingolipids. Phospholipase activity was present within lamellar bodies, among secreted lamellar body disks at the granular-cornified layer interface, and within the intercellular spaces of the stratum compactum. Both the depletion of polar lipids from the stratum compactum and deletion of these substances from the stratum disjunctum correlated with sequential changes in membrane structure observed by transmission electron microscopy and freeze-fracture. Thus, a phospholipase-mediated attack on phospholipids (with a parallel assault by other lipid catabolic enzymes on other polar species), may induce both the initial fusion and elongation of lamellar body disks and the subsequent formation of the hydrophobic membrane bilayers found in the mid-to-outer stratum corneum. These studies also may require modification of traditional views of the stratum corneum as a metabolically inert tissue, revealing its intercellular lipid domains to be partially in an active state of flux.
在哺乳动物表皮渗透屏障形成过程中，脂质被隔离在角质层细胞间间隙，从相对极性的脂质混合物转变为主要是非极性物质。某些与这些脂质共定位的脂质分解酶可能调节这一过程。为了确定极性脂质在表皮外层被分解代谢的部位，以及它们与这些层中发生的膜结构改变的关系，我们比较了极性脂质的生化定位、超微结构、冷冻断裂形态，以及磷脂酶在表皮外层的定位。冷冻切片的组织化学染色和蛋白酶处理及胶带剥离的全角质层的生化研究均表明，致密层中存在少量极性脂质，而相比之下，分离层中既没有磷脂也没有糖鞘脂。磷脂酶活性存在于板层小体中、颗粒层-角质层界面处分泌的板层小体圆盘之间，以及致密层的细胞间间隙中。致密层中极性脂质的消耗和分离层中这些物质的缺失均与透射电子显微镜和冷冻断裂观察到的膜结构的连续变化相关。因此，磷脂酶介导的对磷脂的攻击（其他脂质分解酶对其他极性物质的平行攻击）可能诱导板层小体圆盘的初始融合和伸长，以及随后在角质层中到外层发现的疏水膜双层的形成。这些研究也可能需要修正角质层是代谢惰性组织的传统观点，揭示其细胞间脂质区域部分处于活跃的通量状态。
