Neuroprotective mechanism of apolipoprotein E

目的：在脑内，载脂蛋白E(ApoE)由星形胶质细胞和小胶质细胞分泌，在脂质转运中发挥重要作用。此外，载脂蛋白E还可以保护神经元免受多种伤害。我们的目的是阐明ApoE保护神经元的分子机制。结果：当原代神经元在无血清条件下培养时，它们发生了细胞死亡。在无血清培养液中加入ApoE3可显著抑制其死亡，而在无血清培养液中加入ApoE4则可显著促进其死亡。然后，神经元中的tau蛋白被显著磷酸化。为了证实这一概念，我们将Reelin缺陷小鼠与ApoE缺陷小鼠配对，发现在没有Reelin的情况下，脑神经元中tau的磷酸化程度随着ApoE数量的减少而增加。与tau-磷酸化水平的变化相平行，我们发现在Reelin缺乏的小鼠中，葛兰素史克-3的β活性增加，在同时缺乏Reelin和ApoE的小鼠中进一步增加。在缺乏Reelin和/或ApoE的小鼠中，CDK-5活性相似。Dab1基因缺陷小鼠的GSK-3β和CDK-5活性增加，与载脂蛋白E水平无关。这些数据进一步支持了两种磷酸酶的活性在所有测试条件下都是相似的。结论：这些数据支持一种新的、配体介导的信号转导级联反应，该信号转导通路是由RAD复合体组装而来的，该RAD复合体抑制激酶活性并控制tau磷酸化。

Specific Aim : In the brain, apolipoprotein E(ApoE) is secreted from astrocytes and microglias, and plays important roles in lipid transportation. Furthermore, ApoE may protect neurons from many kinds of insults. Our aim is to elucidate the molecular mechanisms where ApoE protect neurons.Results : When primary neurons were cultured under serum-free conditions, they underwent cell deaths. When ApoE3 was added to the serum-free medium, their deaths were significantly inhibited, On the other hand, when ApoE4 was added to the serum-free medium, their deaths were significantly promoted. Tau protein in the neurons were significantly phosphorylated, then. To substantiate this concept, we mated Reelin-deficient mice to ApoE-deficient mice and found that in the absence of Reelin, tau-phosphorylation in neurons of the brain increased as the amount of ApoE decreased. Paralleling the change in tau-phosphorylation levels, we found that GSK-3β activity increased in Reelin-deficient mice and further increased in mice lacking both Reelin and ApoE. CDK-5 activity was similar in mice lacking Reelin, ApoE, or both. GSK-3β and CDK-5 activity increased in Dab1-deficient mice, independent of ApoE levels. Further supporting the idea that increased tau-phosphorylation results primarily from increased kinase activity, the activity of 2 phosphatases were similar in all conditions tested.Conclusions : These data support a novel, ligand-mediated signal transduction cascade-initiated by the assembly of a RAD complex that suppresses kinase activity and controls tau-phosphorylation.