Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan.
J Neurosci Res. 2012 Apr;90(4):870-7. doi: 10.1002/jnr.22796. Epub 2011 Dec 20.
Alzheimer's disease (AD) is characterized by senile plaques caused by amyloid-β peptide (Aβ) accumulation. It has been reported that Aβ generation and accumulation occur in membrane microdomains, called lipid rafts, which are enriched in cholesterol and glycosphingolipids. Moreover, the ablation of cholesterol metabolism has been implicated in AD. Neprilysin (NEP), a neutral endopeptidase, is one of the major Aβ-degrading enzymes in the brain. Activation of NEP is a possible therapeutic target. However, it remains unknown whether the activity of NEP is regulated by its association with lipid rafts. Here we show that only the mature form of NEP, which has been glycosylated in the Golgi, exists in lipid rafts, where it is directly associated with phosphatidylserine. Moreover, the localization of NEP in lipid rafts is enhanced by its dimerization, as shown using the NEP E403C homodimerization mutant. However, the protease activities of the mature form of NEP, as assessed by in vitro peptide hydrolysis, did not differ between lipid rafts and nonlipid rafts. We conclude that cholesterol and other lipids regulate the localization of mature NEP to lipid rafts, where the substrate Aβ accumulates but does not modulate the protease activity of NEP.
阿尔茨海默病（AD）的特征是由淀粉样β肽（Aβ）积累引起的老年斑。据报道，Aβ的产生和积累发生在膜微区，称为脂筏，其富含胆固醇和糖脂。此外，胆固醇代谢的缺失与 AD 有关。神经肽酶（NEP）是大脑中主要的 Aβ降解酶之一。NEP 的激活是一种可能的治疗靶点。然而，目前尚不清楚 NEP 的活性是否受其与脂筏的关联调节。在这里，我们表明只有在高尔基体内糖基化的成熟形式的 NEP 存在于脂筏中，在那里它直接与磷脂酰丝氨酸相关联。此外，如使用 NEP E403C 同源二聚化突变体所示，NEP 的二聚化增强了 NEP 在脂筏中的定位。然而，通过体外肽水解评估的成熟形式的 NEP 的蛋白酶活性在脂筏和非脂筏之间没有差异。我们的结论是，胆固醇和其他脂质调节成熟 NEP 到富含 Aβ的脂筏的定位，但不调节 NEP 的蛋白酶活性。
