Effect of hypercholesteremia on lipid raft-mediated T cell activation

脂筏高度富集胆固醇和鞘脂（鞘糖脂（GSL）和鞘磷脂（SM））。在这些脂质成分中，胆固醇对维持筏结构具有关键作用。使用药物（如甲基-13-环糊精（MβCD））从细胞膜中去除胆固醇通常会导致筏介导的细胞功能破坏。因此，尽管有些人担心药物对信号传导事件的副作用，但这种实验方法已被广泛用于验证胆固醇在筏组织和功能中的重要性。与许多操纵脂筏中胆固醇水平的研究相反，解决鞘脂在筏功能中的作用的报告很少。先前的研究表明，中国仓鼠卵巢（CHO）突变细胞中SM水平的降低诱导胆固醇在脂筏中的分布减少。此外，据报道，在Madin-Darby犬培养物中添加外源性神经节苷脂 关于我们 肾（MDCK）细胞或CHO-K1细胞从脂质微结构域置换糖基磷脂酰肌醇（GPI）锚定蛋白。所有这些研究表明，鞘脂含量的变化改变筏脂质和蛋白质成分。然而，这些研究都没有有助于我们理解任何功能的变化膜筏的鞘脂水平的操纵。虽然GSL缺乏对功能性筏形成的影响已被提出，鞘脂是否是筏介导的信号转导所必需的仍有待解决。在本研究中，我们研究了鞘脂在淋巴细胞筏组织和功能中的作用，特别是通过使用特异性GSL合成抑制剂D-PdR来研究GSL的作用。我们证明了GPI锚定蛋白的表达状态受到GSL水平降低的影响。此外，我们的研究结果表明，膜筏中GSL水平的降低通过GPI锚定蛋白调节信号传导，但不通过TCR。通过比较D-磷脂酰肌醇和MMCD的作用，我们还发现GSL和胆固醇去除对脂筏中GPI锚定蛋白的影响有明显不同。少

Lipid rafts are highly enriched in cholesterol and sphingolipids (glycosphingolipids (GSLs) and sphingomyelin (SM)). Among these lipid components, cholesterol has a critical function for maintaining raft structure. Cholesterol depletion from cell membranes using drugs, such as methyl-13-cyclodextrin (MβCD), generally results in disruption of raft-mediated cellular functions. Thus, despite some concerns about side effects of the drug on signaling events, this experimental approach has been widely used to verify the importance of cholesterol in raft organization and function.In contrast to many studies manipulating the cholesterol level in lipid rafts, reports that address a role for sphingolipids in raft function are scarce. A previous study demonstrated that reduction of SM levels in Chinese hamster ovary (CHO) mutant cells induced decreased distribution of cholesterol in lipid rafts. Moreover, it was reported that addition of exogenous gangliosides to the culture of Madin-Darby canine … More kidney (MDCK) cells or CHO-K1 cells displaced glycosylphosphatidylinositol (GPI)-anchored proteins from lipid microdomains. All these studies suggested that changes in sphingolipid contents alter raft lipid and protein constituents. However, none of these studies contributed to our understanding of any functional change in membrane rafts by the manipulation of sphingolipid levels. Although an effect of GSL deficiency on functional raft formation has been suggested, whether sphingolipids are essential for raft-mediated signal transduction remains to be addressed. In the present study, we investig ated a role for sphingolipids in raft organization and function in lymphocytes, focusing particularly on a role for GSLs by the usage of a specific GSL synthesis inhibitor, D-PDMP. We demonstrated that the expression state of GPI-anchored proteins is affected by reduction of GSL levels. Further, our results showed that a reduced level of GSLs in membrane rafts modulates signaling through GPI-anchored proteins, but not through the TCR. By comparing the effect of D-PDMP with that of MMCD, we also identified that GSL and cholesterol depletion have distinctly different influences on GPI-anchored proteins in lipid rafts. Less