Neuroprotective mechanism of apolipoprotein E

在大脑中，载脂蛋白E（ApoE）由星形胶质细胞和小胶质细胞分泌，在脂质运输中起重要作用。此外，ApoE可能保护神经元免受多种损伤。我们的目的是阐明ApoE保护神经元的分子机制。结果：原代神经元在无血清条件下培养时细胞死亡。在无血清培养基中加入ApoE3时，它们的死亡明显受到抑制，而在无血清培养基中加入ApoE4时，它们的死亡明显促进。神经元中的Tau蛋白被显著磷酸化。为了证实这一概念，我们将缺乏Reelin的小鼠与缺乏ApoE的小鼠进行了配对，发现在缺乏Reelin的情况下，大脑神经元中的tau磷酸化随着ApoE的减少而增加。与tau磷酸化水平的变化相一致，我们发现GSK-3β活性在缺乏Reelin的小鼠中增加，在缺乏Reelin和ApoE的小鼠中进一步增加。CDK-5活性在缺乏Reelin、ApoE或两者都缺乏的小鼠中相似。在dab1缺失小鼠中，GSK-3β和CDK-5活性升高，与ApoE水平无关。两种磷酸酶的活性在所有测试条件下都相似，进一步支持了tau磷酸化增加主要是由于激酶活性增加的观点。结论：这些数据支持一种新的、配体介导的信号转导级联——由RAD复合物的组装启动，该复合物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.