Xiong Huaqi, Callaghan Debbie, Jones Aimee, Walker Douglas G, Lue Lih-Fen, Beach Thomas G, Sue Lucia I, Woulfe John, Xu Huaxi, Stanimirovic Danica B, Zhang Wandong
Neurobiology Program, Institute for Biological Sciences, National Research Council of Canada, Ottawa, Canada.
Neurobiol Dis. 2008 Mar;29(3):422-37. doi: 10.1016/j.nbd.2007.10.005. Epub 2007 Nov 4.
Alzheimer's disease (AD) is characterized by overproduction of A beta derived from APP cleavage via beta- and gamma-secretase pathway. Recent evidence has linked altered cholesterol metabolism to AD pathogenesis. In this study, we show that AD brain had significant cholesterol retention and high beta- and gamma-secretase activities as compared to age-matched non-demented controls (ND). Over one-half of AD patients had an apoE4 allele but none of the ND. beta- and gamma-secretase activities were significantly stimulated in vitro by 40 and 80 microM cholesterol in AD and ND brains, respectively. Both secretase activities in AD brain were more sensitive to cholesterol (40 microM) than those of ND (80 microM). Filipin-stained cholesterol overlapped with BACE and A beta in AD brain sections. Cholesterol (10-80 microM) added to N2a cultures significantly increased cellular cholesterol, beta- and gamma-secretase activities and A beta secretion. Similarly, addition of cholesterol (20-80 microM) to cell lysates stimulated both in vitro secretase activities. Ergosterol slightly decreased beta-secretase activity at 20-80 microM, but strongly inhibited gamma-secretase activity at 40 microM. Cholesterol depletion reduced cellular cholesterol, beta-secretase activity and A beta secretion. Transcription factor profiling shows that several key nuclear receptors involving cholesterol metabolism were significantly altered in AD brain, including decreased LXR-beta, PPAR and TR, and increased RXR. Treatment of N2a cells with LXR, RXR or PPAR agonists strongly stimulated cellular cholesterol efflux to HDL and reduced cellular cholesterol and beta-/gamma-secretase activities. This study provides direct evidence that cholesterol homeostasis is impaired in AD brain and suggests that altered levels or activities of nuclear receptors may contribute to cholesterol retention which likely enhances beta- and gamma-secretase activities and A beta production in human brain.
阿尔茨海默病（AD）的特征是通过β-和γ-分泌酶途径切割淀粉样前体蛋白（APP）产生过量的β-淀粉样蛋白（Aβ）。最近的证据表明胆固醇代谢改变与AD发病机制有关。在本研究中，我们发现与年龄匹配的非痴呆对照（ND）相比，AD脑有显著的胆固醇潴留以及较高的β-和γ-分泌酶活性。超过一半的AD患者携带载脂蛋白E4（apoE4）等位基因，而ND中无人携带。在体外，AD和ND脑内分别用40和80微摩尔胆固醇可显著刺激β-和γ-分泌酶活性。AD脑中两种分泌酶活性对胆固醇（40微摩尔）比ND脑（80微摩尔）更敏感。在AD脑切片中，用菲律宾菌素染色的胆固醇与β-位点淀粉样前体蛋白裂解酶（BACE）和Aβ重叠。向N2a培养物中添加胆固醇（10 - 80微摩尔）可显著增加细胞胆固醇、β-和γ-分泌酶活性以及Aβ分泌。同样，向细胞裂解物中添加胆固醇（20 - 80微摩尔）可刺激两种体外分泌酶活性。麦角固醇在20 - 80微摩尔时轻微降低β-分泌酶活性，但在40微摩尔时强烈抑制γ-分泌酶活性。胆固醇耗竭降低了细胞胆固醇、β-分泌酶活性和Aβ分泌。转录因子分析表明，AD脑中涉及胆固醇代谢的几个关键核受体发生了显著改变,包括肝X受体β（LXR-β）、过氧化物酶体增殖物激活受体（PPAR）和甲状腺激素受体（TR）减少，而维甲酸X受体（RXR）增加。用LXR、RXR或PPAR激动剂处理N2a细胞可强烈刺激细胞胆固醇向高密度脂蛋白（HDL）外流，并降低细胞胆固醇以及β-/γ-分泌酶活性。本研究提供了直接证据表明AD脑中胆固醇稳态受损，并提示核受体水平或活性的改变可能导致胆固醇潴留，这可能会增强人脑内β-和γ-分泌酶活性以及Aβ生成。
