神经酰胺(Ceramide)是以神经酰胺为骨架的一类磷脂,主要有神经酰胺磷酸胆碱和神经酰胺磷酸乙醇胺。磷脂是细胞膜的主要成分之一,角质层中约40%~50%的皮脂由神经酰胺构成。神经酰胺在保持角质层水分平衡方面起着重要作用,它通过在角质层中形成网状结构来维持皮肤的水分。因此,神经酰胺具有良好的保湿作用。
外用效果神经酰胺是近年来开发出的最新一代保湿剂,是一种水溶性脂质物质,能快速渗透进皮肤,并与角质层中的水结合,形成网状结构锁住水分。它广泛用于护肤品中,能够强化皮肤屏障功能。
神经酰胺对皮肤的作用神经酰胺的合成可通过三种途径进行:
加强皮肤的抗衰老功能。
The Lass (longevity-assurance homologue) family members, which are highly conserved among eukaryotes, function in ceramide synthesis. In the mouse, there are at least five Lass family members, Lass1, Lass2, Lass4, Lass5 and the hitherto uncharacterized Lass6. To investigate specific roles for each Lass member in ceramide synthesis, we cloned these five mouse proteins. Overproduction of any Lass protein in cultured cells resulted in an increase in cellular ceramide, but the ceramide species produced varied. Overproduction of Lass1 increased C18:0-ceramide levels preferentially, and overproduction of Lass2 and Lass4 increased levels of longer ceramides such as C22:0- and C24:0-ceramides. Lass5 and Lass6 produced shorter ceramide species (C14:0- and C16:0-ceramides); however, their substrate preferences towards saturated/unsaturated fatty acyl-CoA differed. In addition to differences in substrate preferences, we also demonstrated by Northern blotting that Lass family members are differentially expressed among tissues. Additionally, we found that Lass proteins differ with regard to glycosylation. Of the five members, only Lass2, Lass5 and Lass6 were N-glycosylated, each at their N-terminal Asn residue. The occurrence of N-glycosylation of some Lass proteins provides topological insight, indicating that the N-termini of Lass family members probably face the luminal side of the endoplasmic reticulum membrane. Furthermore, based on a proteinase K digestion assay, we demonstrated that the C-terminus of Lass6 faces the cytosolic side of the membrane. From these data we propose topology for the conserved Lag1 motif in Lass family members, namely that the N-terminal region faces the luminal side and the C-terminal region the cytosolic side of the endoplasmic reticulum membrane.