Oxidation of cholesterol by amyloid precursor protein and β-amyloid peptide
Oxidation of cholesterol by amyloid precursor protein and β-amyloid peptide
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DOI：
10.1074/jbc.m409071200
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发表时间：
2005-02-25
影响因子：
4.8
通讯作者：
Alkon, DL
中科院分区：
文献类型：
--
作者：
Nelson, TJ;Alkon, DL
阿尔茨海默病（AD）的特征在于神经毒性肽β-淀粉样蛋白的积累，其由淀粉样前体蛋白（APP）的蛋白水解产生。APP是一种大的膜结合铜结合蛋白，其在维持突触功能中是必不可少的，并且可能在突触发生中起作用。β-淀粉样蛋白已被证明有助于伴随AD的氧化应激。AD的后期阶段以神经元凋亡为特征。然而，AIPP的生化功能和β-淀粉样蛋白的毒性机制仍不清楚。在这项研究中，我们发现β-淀粉样蛋白和APP都可以氧化胆固醇形成7 β-羟基胆固醇，这是一种在纳摩尔浓度下具有神经毒性的促凋亡氧化固醇。7 β-羟基胆固醇抑制培养的大鼠海马H19-7/IGF-IR神经元细胞分泌可溶性APP，抑制肿瘤坏死因子-α-转化酶α-分泌酶活性，但对β位点APP-裂解酶1活性无影响。7 β-羟基胆固醇也是α-蛋白激酶C的有效抑制剂，Ki值约为0.2 nm。胆固醇和β-淀粉样蛋白之间的反应速率与胆固醇代谢酶的反应速率相当（k（cat）= 0.211 min（-1））。AIPP产生7 β-羟基胆固醇的速率比β-淀粉样蛋白低200倍。胆固醇的氧化伴随着化学计量的过氧化氢的产生，并需要二价铜。结果表明，APP的功能可能是产生低水平的7-羟基胆固醇。β-淀粉样蛋白产生的更高水平可能有助于在阿尔茨海默病中观察到的氧化应激和细胞损失。
Alzheimer's disease (AD) is characterized by accumulation of the neurotoxic peptide beta-amyloid, which is produced by proteolysis of amyloid precursor protein (APP). APP is a large membrane-bound copper-binding protein that is essential in maintaining synaptic function and may play a role in synaptogenesis. beta-Amyloid has been shown to contribute to the oxidative stress that accompanies AD. Later stages of AD are characterized by neuronal apoptosis. However, the biochemical function of AIPP and the mechanism of the toxicity of beta-amyloid are still unclear. In this study, we show that both beta-amyloid and APP can oxidize cholesterol to form 7beta-hydroxycholesterol, a proapoptotic oxysterol that was neurotoxic at nanomolar concentrations. 7beta-Hydroxycholesterol inhibited secretion of soluble APP from cultured rat hippocampal H19-7/IGF-IR neuronal cells and inhibited tumor necrosis factor-alpha-converting enzyme alpha-secretase activity but had no effect on beta-site APP-cleaving enzyme 1 activity. 7beta-Hydroxycholesterol was also a potent inhibitor of alpha-protein kinase C, with a K-i of similar to0.2 nm. The rate of reaction between cholesterol and beta-amyloid was comparable to the rates of cholesterol-metabolizing enzymes (k(cat) = 0.211 min(-1)). The rate of production of 7beta-hydroxycholesterol by AIPP was similar to200 times lower than by beta-amyloid. Oxidation of cholesterol was accompanied by stoichiometric production of hydrogen peroxide and required divalent copper. The results suggest that a function of APP may be to produce low levels of 7-hydroxycholesterol. Higher levels produced by beta-amyloid could contribute to the oxidative stress and cell loss observed in Alzheimer's disease.