Handelmann G E, Boyles J K, Weisgraber K H, Mahley R W, Pitas R E
Gladstone Institute of Cardiovascular Disease, Department of Pathology, University of California 94141-9100.
J Lipid Res. 1992 Nov;33(11):1677-88.
Previous studies suggest that during nerve regeneration apoE acts as a lipid transport protein that assists in the rapid initial extension of axons and then in their myelination. To determine whether apoE and/or apoE-containing lipoproteins can modulate axon growth, we assessed their effect on the out-growth of neurites from neurons in mixed cultures of fetal rabbit dorsal root ganglion cells in vitro. Incubation with beta-very low density lipoprotein (beta-VLDL) particles, which are rich in apoE and cholesterol, increased neurite outgrowth and branching. Unesterified cholesterol added to the cultures had a similar, but less pronounced, effect. These data suggest that cholesterol might be the component responsible for the enhanced neurite growth. In contrast, purified, lipid-free apoE added to the cultures reduced neurite branching. Neurite branching was also reduced when purified apoE was added along with beta-VLDL or cholesterol; however, the striking finding was that under these conditions the neurites extended farther from the neuronal cell body. Dorsal root ganglion cells were examined for the presence of receptors for native and apoE-enriched beta-VLDL. Immunocytochemistry, ligand blots, 45Ca2+ blots, and studies of the interaction of the cells with fluorescent lipoproteins provided evidence of two types of receptors for apoE-containing lipoproteins on neurons: the low density lipoprotein (LDL) receptor, which binds native beta-VLDL, and the LDL receptor-related protein, which binds apoE-enriched beta-VLDL. These findings indicate that apoE may play two complementary roles in neurite outgrowth. When complexed with lipoproteins, apoE stimulates neurite growth by the receptor-mediated delivery of cholesterol and perhaps other components necessary for neurite outgrowth. When apoE as a free protein is added together with apoE-containing lipoproteins, apoE decreases neurite branching and promotes neurite extension away from the cell body. These actions, which would be complementary in promoting target-directed nerve growth in vivo, provide the first direct evidence that apoE and apoE-containing lipoproteins can modulate the outgrowth of neuronal processes.
先前的研究表明，在神经再生过程中，载脂蛋白E作为一种脂质转运蛋白，有助于轴突的快速初始延伸，然后参与其髓鞘形成。为了确定载脂蛋白E和/或含载脂蛋白E的脂蛋白是否能调节轴突生长，我们在体外评估了它们对胎兔背根神经节细胞混合培养物中神经元神经突生长的影响。与富含载脂蛋白E和胆固醇的β-极低密度脂蛋白（β-VLDL）颗粒孵育，可增加神经突的生长和分支。添加到培养物中的游离胆固醇有类似但不太明显的作用。这些数据表明胆固醇可能是导致神经突生长增强的成分。相反，添加到培养物中的纯化无脂载脂蛋白E减少了神经突分支。当纯化的载脂蛋白E与β-VLDL或胆固醇一起添加时，神经突分支也减少了；然而，引人注目的发现是，在这些条件下，神经突从神经元细胞体延伸得更远。检测背根神经节细胞是否存在天然和富含载脂蛋白E的β-VLDL的受体。免疫细胞化学、配体印迹、45Ca2+印迹以及细胞与荧光脂蛋白相互作用的研究提供了证据，证明神经元上存在两种含载脂蛋白E的脂蛋白受体：结合天然β-VLDL的低密度脂蛋白（LDL）受体，以及结合富含载脂蛋白E的β-VLDL的LDL受体相关蛋白。这些发现表明，载脂蛋白E可能在神经突生长中发挥两种互补作用。当与脂蛋白复合时，载脂蛋白E通过受体介导的胆固醇以及可能的神经突生长所需的其他成分的递送刺激神经突生长。当游离蛋白形式的载脂蛋白E与含载脂蛋白E的脂蛋白一起添加时，载脂蛋白E减少神经突分支并促进神经突从细胞体延伸。这些作用在促进体内靶向神经生长方面是互补的，首次直接证明了载脂蛋白E和含载脂蛋白E的脂蛋白可以调节神经元突起的生长。
