Michikawa M, Fan Q W, Isobe I, Yanagisawa K
Department of Dementia Research, National Institute for Longevity Sciences, Obu, Aichi, Japan.
J Neurochem. 2000 Mar;74(3):1008-16. doi: 10.1046/j.1471-4159.2000.0741008.x.
Many studies have shown that apolipoprotein E (apoE) plays important roles in maintaining intracellular lipid homeostasis in nonneuronal cells. However, little is known about the extracellular transport of lipids in the CNS. In this study, we determined whether and to what degree lipid efflux from astrocytes and neurons depended on apoE. Our results showed that exogenously added apoE promoted the efflux of cholesterol and phosphatidylcholine from both astrocytes and neurons in culture, resulting in the generation of high-density lipoprotein-like particles. The order of potency of the apoE isoforms as lipid acceptors was apoE2 > apoE3 = apoE4 in astrocytes and apoE2 > apoE3 > apoE4 in neurons. Treatment with brefeldin A, monensin, and a protein kinase C inhibitor, H7, abolished the ability of apoE to promote cholesterol efflux from cultured astrocytes, without altering apoE-mediated phosphatidylcholine efflux. In contrast, the efflux of both cholesterol and phosphatidylcholine promoted by apoE was abolished following treatment with heparinase or lactoferrin, which block the interaction of apoE with heparan sulfate proteoglycans (HSPGs) or low-density lipoprotein receptor-related protein (LRP), respectively. This study suggests that apoE promotes lipid efflux from astrocytes and neurons in an isoform-specific manner and that cell surface HSPGs and/or HSPG-LRP pathway may mediate this apoE-promoted lipid efflux.
许多研究表明，载脂蛋白E（apoE）在维持非神经细胞内的脂质稳态中发挥着重要作用。然而，关于中枢神经系统（CNS）中脂质的细胞外转运却知之甚少。在本研究中，我们确定了星形胶质细胞和神经元的脂质流出是否以及在何种程度上依赖于apoE。我们的结果表明，外源性添加的apoE促进了培养的星形胶质细胞和神经元中胆固醇和磷脂酰胆碱的流出，导致生成高密度脂蛋白样颗粒。在星形胶质细胞中，apoE异构体作为脂质受体的效力顺序为apoE2 > apoE3 = apoE4，在神经元中为apoE2 > apoE3 > apoE4。用布雷菲德菌素A、莫能菌素和蛋白激酶C抑制剂H7处理可消除apoE促进培养的星形胶质细胞中胆固醇流出的能力，而不改变apoE介导磷脂酰胆碱流出的能力。相反，用肝素酶或乳铁蛋白处理后，apoE促进的胆固醇和磷脂酰胆碱流出均被消除，肝素酶和乳铁蛋白分别阻断了apoE与硫酸乙酰肝素蛋白聚糖（HSPGs）或低密度脂蛋白受体相关蛋白（LRP）的相互作用。本研究表明，apoE以异构体特异性方式促进星形胶质细胞和神经元的脂质流出，并且细胞表面HSPGs和/或HSPG-LRP途径可能介导这种apoE促进的脂质流出。
