Neuroprotective Secreted Amyloid Precursor Protein Acts by Disrupting Amyloid Precursor Protein Dimers
Neuroprotective Secreted Amyloid Precursor Protein Acts by Disrupting Amyloid Precursor Protein Dimers
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DOI：
10.1074/jbc.m808755200
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发表时间：
2009-05-29
影响因子：
4.8
通讯作者：
Wouters, Fred S.
中科院分区：
文献类型：
--
作者：
Gralle, Matthias;Botelho, Michelle Gralle;Wouters, Fred S.
淀粉样前体蛋白（APP）在细胞生长和分化以及阿尔茨海默病的神经退行性过程中均有涉及。APP的受调控的蛋白水解作用产生具有生物活性的片段，例如具有神经保护作用的分泌型胞外域sAPPα和具有神经毒性的β - 淀粉样肽。此外，有人提出完整的跨膜APP发挥一种信号传导作用，这对于正常的突触可塑性以及痴呆中的神经元功能障碍可能都很重要。为了理解APP信号传导，我们使用量子点追踪APP的单分子，并使用荧光寿命成像显微镜对APP同二聚化进行定量，以检测神经母细胞瘤活细胞中的福斯特共振能量转移。通过使用合成荧光团进行选择性标记，我们表明APP在质膜上的二聚化程度明显高于细胞内膜。硫酸乙酰肝素对APP在质膜上几乎完全的二聚化有显著作用。重要的是，这项技术首次从结构上确定了通过相关生理细胞外配体的结合引发APP信号传导；我们的结果表明APP是神经保护因子sAPPα的受体，因为sAPPα的结合会破坏APP二聚体，并且sAPPα对APP二聚体的这种破坏对于保护神经母细胞瘤细胞免受饥饿诱导的细胞死亡是必要的。只有表达可逆二聚化的野生型APP的细胞，而非共价二聚化的突变型APP的细胞，可受到sAPPα的保护。这些发现表明，增加sAPPα的产生或破坏APP二聚体可能对神经元存活具有潜在的有益影响。
The amyloid precursor protein (APP) is implied both in cell growth and differentiation and in neurodegenerative processes in Alzheimer disease. Regulated proteolysis of APP generates biologically active fragments such as the neuroprotective secreted ectodomain sAPP alpha and the neurotoxic beta-amyloid peptide. Furthermore, it has been suggested that the intact transmembrane APP plays a signaling role, which might be important for both normal synaptic plasticity and neuronal dysfunction in dementia. To understand APP signaling, we tracked single molecules of APP using quantum dots and quantitated APP homodimerization using fluorescence lifetime imaging microscopy for the detection of Forster resonance energy transfer in living neuroblastoma cells. Using selective labeling with synthetic fluorophores, we show that the dimerization of APP is considerably higher at the plasma membrane than in intracellular membranes. Heparan sulfate significantly contributes to the almost complete dimerization of APP at the plasma membrane. Importantly, this technique for the first time structurally defines the initiation of APP signaling by binding of a relevant physiological extracellular ligand; our results indicate APP as receptor for neuroprotective sAPP alpha, as sAPP alpha binding disrupts APP dimers, and this disruption of APP dimers by sAPP alpha is necessary for the protection of neuroblastoma cells against starvation-induced cell death. Only cells expressing reversibly dimerized wild-type, but not covalently dimerized mutant APP are protected by sAPP alpha. These findings suggest a potentially beneficial effect of increasing sAPP alpha production or disrupting APP dimers for neuronal survival.