Sphingolipid Biology And Disease

鞘磷脂是细胞信号通路的重要介体和调节者。我们的研究主要集中在以鞘糖脂(GSLS)和鞘氨醇-1-磷酸为代表的两类鞘磷脂的作用上。我们的工作旨在定义这些鞘脂的正常功能，并了解它们在疾病过程中的作用。GSLs存在于细胞膜的外叶，集中在特殊的信号结构中。它们尤其以神经节苷脂(含唾液酸的GSLS)的形式存在于神经细胞中。通过对编码GSLS合成酶的基因的遗传破坏，我们创造了一系列表达有限糖鞘糖脂结构的小鼠。我们正在使用这些小鼠来发现GSLS的功能。当负责GSL降解的细胞机制出现缺陷时，GSL储存病就会导致严重的神经变性。例如泰-萨克斯病和高谢病。我们正试图通过建立疾病的动物模型来了解GSLS的积累是如何导致神经退化的。 我们今年的主要成就包括建立了缺乏GM3合成酶的突变小鼠(CMP-NeuAc：乳糖基神经酰胺α2，3-唾液酸基转移酶；EC 2.4.99-)。这些突变小鼠无法合成GM3神经节苷脂，这是一种简单且分布广泛的神经鞘糖脂。突变的小鼠是存活的，看起来没有重大异常，但表现出对胰岛素的高度敏感性。突变小鼠胰岛素敏感性增强的基础被发现是骨骼肌中胰岛素受体磷酸化增强。重要的是，突变小鼠免受高脂饮食诱导的胰岛素抵抗。 我们还继续了对鞘氨醇-1-磷酸G蛋白偶联受体S1P1的研究。我们之前已经在小鼠中证明了S1P1的全局敲除导致血管平滑肌细胞(VSMCs)对血管的覆盖缺陷。由于S1P1受体的表达不限于特定的细胞类型，目前尚不清楚S1P1受体是通过直接作用于VSMC还是间接通过其在内皮细胞(ECs)的活动来以细胞自主的方式控制VSMC对血管的覆盖。通过使用Cre/loxP系统，我们仅在内皮细胞中干扰了S1P1基因。条件突变胚胎的表型与在S1P1全球缺失的胚胎中获得的表型相似。因此，血管平滑肌细胞的血管覆盖由内皮细胞中S1P1受体的活性决定。

Sphingolipids are important mediators and regulators of cell signaling pathways. Our studies have focused on the actions of two classes of sphingolipids represented by glycosphingolipids (GSLs) and sphingosine-1-phosphate. Our work is aimed at defining the normal functions of these sphingolipids and understanding their roles in disease processes. GSLs are found in the outer leaflet of the plasma membrane and are concentrated in specialized signaling structures. They are particularly abundant in neuronal cells in the form of gangliosides (sialic acid containing GSLs). Through genetic disruption of genes that encode synthetic enzymes for GSLs, we have created a series of mice that express limited glycosphingolipid structures. We are using these mice to discover the functions of GSLs. When the cellular machinery responsible for GSL degradation is defective, GSL storage diseases result in which profound neurodegeneration occurs. Examples are Tay-Sachs and Gaucher diseases. We are attempting to understand how the accumulation of GSLs cause neurodegeneration through the construction of animal models of the diseases. Our major accomplishments this year include the establishment of mutant mice that lack GM3 synthase (CMP-NeuAc:lactosylceramide alpha2,3-sialyltransferase; EC 2.4.99.-). These mutant mice were unable to synthesize GM3 ganglioside, a simple and widely distributed glycosphingolipid. The mutant mice were viable and appeared without major abnormalities but showed a heightened sensitivity to insulin. A basis for the increased insulin sensitivity in the mutant mice was found to be enhanced insulin receptor phosphorylation in skeletal muscle. Importantly, the mutant mice were protected from high-fat diet-induced insulin resistance. We also continued our studies on the G-protein coupled receptor for sphingosine-1-phosphate, S1P1. We had previously shown the the global knockout of S1P1 in mice caused defective coverage of blood vessels by vascular smooth muscle cells (VSMCs). Since S1P1 receptor expression is not restricted to a particular cell type, it was not known whether the S1P1 receptor controlled VSMC coverage of vessels in a cell-autonomous fashion by functioning directly in VSMCs or indirectly through its activity in endothelial cells (ECs). By using the Cre/loxP system, we disrupted the S1P1 gene solely in ECs. The phenotype of the conditional mutant embryos mimicked the one obtained in the embryos globally deficient in S1P1. Thus, vessel coverage by VSMCs is directed by the activity of the S1P1 receptor in ECs.