Urano Yasuomi, Hayashi Ikuo, Isoo Noriko, Reid Patrick C, Shibasaki Yoshikazu, Noguchi Noriko, Tomita Taisuke, Iwatsubo Takeshi, Hamakubo Takao, Kodama Tatsuhiko
Department of Molecular Biology and Medicine, Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo 153-8904, Japan.
J Lipid Res. 2005 May;46(5):904-12. doi: 10.1194/jlr.M400333-JLR200. Epub 2005 Feb 16.
Cholesterol has been implicated in the pathogenesis of Alzheimer's disease (AD). Although the underlying mechanisms are not yet clear, several studies have provided evidence for the involvement of cholesterol-rich lipid rafts in the production of amyloid beta peptide (Abeta), the major component of amyloid deposits in AD. In this regard, the gamma-secretase complex is responsible for the final cleavage event in the processing of beta-amyloid precursor protein (betaAPP), resulting in Abeta generation. The gamma-secretase complex is a multiprotein complex composed of presenilin, nicastrin (NCT), APH-1, and PEN-2. Recent reports have suggested that gamma-secretase activity is predominantly localized in lipid rafts, and presenilin and NCT have been reported to be localized in lipid rafts. In this study, various biochemical methods, including coimmunoprecipitation, in vitro gamma-secretase assay, and methyl-beta-cyclodextrin (MbetaCD) treatment, are employed to demonstrate that all four components of the active endogenous gamma-secretase complex, including APH-1 and PEN-2, are associated with lipid rafts in human neuroblastoma cells (SH-SY5Y). Treatment with statins, 3-hydroxy-3-methylglutaryl-CoA-reductase inhibitors, significantly decreased the association of the gamma-secretase complex with lipid rafts without affecting the distribution of flotillin-1. This effect was partially abrogated by the addition of geranylgeraniol. These results suggest that both cholesterol and protein isoprenylation influence the active gamma-secretase complex association with lipid rafts.
胆固醇与阿尔茨海默病（AD）的发病机制有关。尽管其潜在机制尚不清楚，但多项研究已为富含胆固醇的脂筏参与淀粉样β肽（Aβ）的产生提供了证据，Aβ是AD淀粉样沉积物的主要成分。在这方面，γ-分泌酶复合物负责β-淀粉样前体蛋白（βAPP）加工过程中的最终切割事件，从而导致Aβ的产生。γ-分泌酶复合物是一种由早老素、尼卡斯特林（NCT）、APH-1和PEN-2组成的多蛋白复合物。最近的报道表明，γ-分泌酶活性主要定位于脂筏中，并且早老素和NCT已被报道定位于脂筏中。在本研究中，采用了多种生化方法，包括免疫共沉淀、体外γ-分泌酶测定和甲基-β-环糊精（MβCD）处理，以证明活性内源性γ-分泌酶复合物的所有四个组分，包括APH-1和PEN-2，都与人神经母细胞瘤细胞（SH-SY5Y）中的脂筏相关。用他汀类药物（3-羟基-3-甲基戊二酰辅酶A还原酶抑制剂）处理可显著降低γ-分泌酶复合物与脂筏的结合，而不影响小窝蛋白-1的分布。添加香叶基香叶醇可部分消除这种作用。这些结果表明，胆固醇和蛋白质异戊二烯化均影响活性γ-分泌酶复合物与脂筏的结合。
