Rawlings A V, Harding C R
AVR Consulting, Ltd., Cheshire, UK.
Dermatol Ther. 2004;17 Suppl 1:43-8. doi: 10.1111/j.1396-0296.2004.04s1005.x.
Over the past decade, great progress has been made toward elucidating the structure and function of the stratum corneum (SC), the outermost layer of the epidermis. SC cells (corneocytes) protect against desiccation and environmental challenge by regulating water flux and retention. Maintenance of an optimal level of hydration by the SC is largely dependent on several factors. First, intercellular lamellar lipids, organized predominantly in an orthorhombic gel phase, provide an effective barrier to the passage of water through the tissue. Secondly, the diffusion path length also retards water loss, since water must traverse the tortuous path created by the SC layers and corneocyte envelopes. Thirdly, and equally important, is natural moisturizing factor (NMF), a complex mixture of low-molecular-weight, water-soluble compounds first formed within the corneocytes by degradation of the histidine-rich protein known as filaggrin. Each maturation step leading to the formation of an effective moisture barrier--including corneocyte strengthening, lipid processing, and NMF generation--is influenced by the level of SC hydration. These processes, as well as the final step of corneodesmolysis that mediates exfoliation, are often disturbed upon environmental challenge, resulting in dry, flaky skin conditions. The present paper reviews our current understanding of the biology of the SC, particularly its homeostatic mechanisms of hydration.
在过去十年中，在阐明表皮最外层角质层（SC）的结构和功能方面取得了巨大进展。SC细胞（角质形成细胞）通过调节水通量和潴留来防止干燥和环境挑战。SC维持最佳水合水平在很大程度上取决于几个因素。首先，主要以正交晶凝胶相组织的细胞间层状脂质为水通过组织提供了有效的屏障。其次，扩散路径长度也会阻碍水分流失，因为水必须穿过由SC层和角质形成细胞包膜形成的曲折路径。第三，同样重要的是天然保湿因子（NMF），它是一种低分子量水溶性化合物的复杂混合物，最初是在角质形成细胞内通过降解富含组氨酸的蛋白质丝聚合蛋白而形成的。导致有效保湿屏障形成的每个成熟步骤——包括角质形成细胞强化、脂质加工和NMF生成——都受SC水合水平的影响。这些过程以及介导角质层分离的角质层崩解的最后步骤，在受到环境挑战时常常受到干扰，导致皮肤干燥、起皮。本文综述了我们目前对角质层生物学的理解，特别是其水合稳态机制。
