Sphingolipid Biology And Disease

鞘脂是细胞信号传导途径的重要介质和调节剂。我们的研究集中在两类鞘脂的作用，代表鞘糖脂（GSL）和鞘氨醇-1-磷酸。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。GSL存在于质膜的外小叶中，并集中在专门的信号结构中。它们以神经节苷脂（含唾液酸的GSL）的形式在神经元细胞中特别丰富。通过对编码GSL合成酶的基因进行遗传破坏，我们创造了一系列表达有限鞘糖脂结构的小鼠。我们正在使用这些小鼠来发现GSL的功能。当负责GSL降解的细胞机制有缺陷时，GSL储存疾病导致发生严重的神经变性。例如Tay-Sachs病、Sandhoff病和Gaucher病。我们正试图通过建立疾病的动物模型来了解GSL的积累如何导致神经退行性变。 我们今年的主要成就包括证明Sandhoff病小鼠大脑中扩大的巨噬细胞/小胶质细胞群体是由周围细胞浸润复合的。与细胞浸润相一致的是星形胶质细胞中巨噬细胞炎性蛋白1 α（MIP-1 α）（一种白细胞趋化因子）的表达增加。MIP-1 α表达的缺失导致Sandhoff病小鼠的浸润和巨噬细胞/小胶质细胞相关病理以及神经元凋亡显著减少。这些没有MIP-1 α的小鼠表现出改善的神经系统状态和更长的寿命。结果表明，Sandhoff病的发病机制涉及MIP-1 α的增加，MIP-1 α诱导单核细胞浸润大脑，扩大活化的巨噬细胞/小胶质细胞群，并触发神经元凋亡，导致快速的神经退行性过程 我们还继续对鞘氨醇-1-磷酸的G蛋白偶联受体S1 P1进行了研究。为了确定S1 P1受体在T细胞上的确切作用，我们建立了T细胞特异性S1 P1敲除小鼠。突变小鼠显示出成熟T细胞进入外周的出口受阻。S1 P1受体的表达在成熟胸腺细胞中上调，其缺失改变了胸腺细胞对1-磷酸鞘氨醇的趋化反应。结果表明，T细胞上S1 P1受体的表达控制着它们从胸腺中出来并进入血液，因此，在调节外周T细胞数量方面具有核心作用。

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, Sandhoff 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 a demonstration the expanded macrophage/microglial population in the brain of Sandhoff disease mice is compounded by the infiltration of cells from the periphery. Coincident with the cellular infiltration was an increased expression of macrophage-inflammatory protein 1alpha (MIP-1alpha), a leukocyte chemokine, in astrocytes. Deletion of MIP-1alpha expression resulted in a substantial decrease in infiltration and macrophage/microglial-associated pathology together with neuronal apoptosis in Sandhoff disease mice. These mice without MIP-1alpha showed improved neurologic status and a longer lifespan. The results indicate that the pathogenesis of Sandhoff disease involves an increase in MIP-1alpha that induces monocytes to infiltrate the brain, expand the activated macrophage/microglial population, and trigger apoptosis of neurons, resulting in a rapid neurodegenerative course We also continued our studies on the G-protein coupled receptor for sphingosine-1-phosphate, S1P1. To determine the precise role of the S1P1 receptor on T-cells, we established a T-cell-specific S1P1 knock-out mouse. The mutant mice showed a block in the egress of mature T-cells into the periphery. The expression of the S1P1 receptor was up-regulated in mature thymocytes, and its deletion altered the chemotactic responses of thymocytes to sphingosine 1-phosphate. The results indicated that the expression of the S1P1 receptor on T-cells controls their exit from the thymus and entry into the blood and, thus, has a central role in regulating the numbers of peripheral T-cells..