Apolipoprotein E as vascular risk factor in neurodegenerative dementia

Apolipoprotein E (ApoE) is the major lipid-carrier protein in the brain, and several studies provided evidence that ApoE epsilon4 allele can be considered a genetic risk factor for vascular diseases. Findings indicate that Alzheimer disease (AD) and vascular dementia (VaD) may have common risk factors and/or pathogenesis, but their interrelationships still need to be clearly defined. Since ApoE4 imparts risk for both hyperlipidemia and AD, it seemed worthwhile to investigate the possible role of ApoE in the pathogenesis of AD and VaD. To this task, we examined in healthy volunteers, and AD and VaD patients: i) the frequency of ApoE isoforms; and ii) the influence of ApoE genotype on serum lipid levels. Our findings suggest that epsilon4 allele is an important risk factor for the development not only of the Alzheimer type, but also of the vascular type of dementia. In contrast, epsilon2 allele could have a protective role in AD dementia. These results confirm the hypothesis that serum ApoE concentration is dependent on ApoE genotype, but do not support the view that it has to be considered a relevant biochemical marker for AD and VaD.     

Apolipoprotein E: Implications for AD neurobiology, epidemiology and risk assessment

Alzheimer disease (AD) is a common and devastating dementing illness for which there is no effective neuroprotective therapy or cure. The presence of the apolipoprotein E (apoE) ε4 allele is a well-established genetic modifier (risk factor) of sporadic AD. In this review, we provide an update on the implications of apoE for the neurobiology and epidemiology of AD. Moreover, recent evidence is adduced indicating that (i) many AD risk factors are potentially modifiable by adaptive lifestyle changes and pharmacotherapy and (ii) the potency of these modifiable AD determinants and responsiveness to intervention are often significantly impacted by the presence or absence of the ε4 allele. Delineation of the influences of the APOE genotype on modifiable AD risk factors and prevention may spur consideration of APOE testing for presymptomatic individuals seeking to define their personal risk.     

载脂蛋白E基因多态性与散发性老年性痴呆病的关系

目的:探讨载脂蛋白E(apoE)外显子4和增强子元件基因多态性与散发性Alzheimer病(AD)的关系。方法:应用聚合酶链反应-限制性片段长度多态性(PCR-RFLP)技术分别检测apoE外显子4和内含子1内增强子元件(IE1)基因型。结果:(1)ApoE外显子4基因多态性:AD组ε3/4基因型频率(0.381)和ε4等位基因频率(0.226)显著高于对照组(P＜0.05)。(2)ApoEIE1基因多态性AD组G/G基因型频率(0.595)显著高于对照组(P＜0.05)。(3)有apoEε4个体患AD风险为无ε4个体的3倍,比值比为2.932,95%可信区间1.379~6.226;G/G基因型个体患AD风险为G/C、C/C个体的2倍,比值比为2.223,95%可信区间1.075~4.599;经统计分析发现apoEε4与IE1G/G呈非常显著性正相关(P＜0.01);排除apoEε4后发现IE1G/G与AD发病风险无关。结论:ApoEε4等位基因是个体发生AD的危险因素,IE1G/G增加AD发病风险是因其与ε4相关所致。     

Apolipoprotein E isoform-specific regulation of dendritic spine morphology in apolipoprotein E transgenic mice and Alzheimer's disease patients

Dendritic spines are postsynaptic sites of excitatory input in the mammalian nervous system. Apolipoprotein (apo) E participates in the transport of plasma lipids and in the redistribution of lipids among cells. A role for apoE is implicated in regeneration of synaptic circuitry after neural injury. The apoE4 allele is a major risk factor for late-onset familial and sporadic Alzheimer's disease (AD) and is associated with a poor outcome after brain injury. ApoE isoforms are suggested to have differential effects on neuronal repair mechanisms. In vitro studies have demonstrated the neurotrophic properties of apoE3 on neurite outgrowth. We have investigated the influence of apoE genotype on neuronal cell dendritic spine density in mice and in human postmortem tissue. In order to compare the morphology of neurons developing under different apoE conditions, gene gun labeling studies of dendritic spines of dentate gyrus (DG) granule cells of the hippocampus were carried out in wild-type (WT), human apoE3, human apoE4 expressing transgenic mice and apoE knockout (KO) mice; the same dendritic spine parameters were also assessed in human postmortem DG from individuals with and without the apoE4 gene. Quantitative analysis of dendritic spine length, morphology, and number was carried out on these mice at 3 weeks, 1 and 2 years of age. Human apoE3 and WT mice had a higher density of dendritic spines than human E4 and apoE KO mice in the 1 and 2 year age groups (P<0.0001), while at 3 weeks there were no differences between the groups. These age dependent differences in the effects of apoE isoforms on neuronal integrity may relate to the increased risk of dementia in aged individuals with the apoE4 allele. Significantly in human brain, apoE4 dose correlated inversely with dendritic spine density of DG neurons cell in the hippocampus of both AD (P=0.0008) and aged normal controls (P=0.0015). Our findings provide one potential explanation for the increased cognitive decline seen in aged and AD patients expressing apoE4.     

Human apoE isoforms differentially regulate brain amyloid-β peptide clearance

The apolipoprotein E (APOE) ε4 allele is the strongest genetic risk factor for late-onset, sporadic Alzheimer's disease (AD). The APOE ε4 allele markedly increases AD risk and decreases age of onset, likely through its strong effect on the accumulation of amyloid-β (Aβ) peptide. In contrast, the APOE ε2 allele appears to decrease AD risk. Most rare, early-onset forms of familial AD are caused by autosomal dominant mutations that often lead to overproduction of Aβ(42) peptide. However, the mechanism by which APOE alleles differentially modulate Aβ accumulation in sporadic, late-onset AD is less clear. In a cohort of cognitively normal individuals, we report that reliable molecular and neuroimaging biomarkers of cerebral Aβ deposition vary in an apoE isoform-dependent manner. We hypothesized that human apoE isoforms differentially affect Aβ clearance or synthesis in vivo, resulting in an apoE isoform-dependent pattern of Aβ accumulation later in life. Performing in vivo microdialysis in a mouse model of Aβ-amyloidosis expressing human apoE isoforms (PDAPP/TRE), we find that the concentration and clearance of soluble Aβ in the brain interstitial fluid depends on the isoform of apoE expressed. This pattern parallels the extent of Aβ deposition observed in aged PDAPP/TRE mice. ApoE isoform-dependent differences in soluble Aβ metabolism are observed not only in aged but also in young PDAPP/TRE mice well before the onset of Aβ deposition in amyloid plaques in the brain. Additionally, amyloidogenic processing of amyloid precursor protein and Aβ synthesis, as assessed by in vivo stable isotopic labeling kinetics, do not vary according to apoE isoform in young PDAPP/TRE mice. Our results suggest that APOE alleles contribute to AD risk by differentially regulating clearance of Aβ from the brain, suggesting that Aβ clearance pathways may be useful therapeutic targets for AD prevention.     

ApoE 4 reduces the expression of Aβ degrading enzyme IDE by activating the NMDA receptor in hippocampal neurons

Apolipoprotein E (ApoE) 4 is a potent risk factor for Alzheimer's disease (AD). However, the mechanism underlying ApoE4 function in the pathology of AD is not well understood. We report here that, in comparison with ApoE2 and ApoE3, ApoE4 significantly reduces levels of insulin-degrading enzyme (IDE), which is responsible for the cellular clearance of Aβ in neurons. This differential regulation of IDE by various ApoE isoforms was blocked by coincubation with N-methyl-d-aspartic acid (NMDA) receptor inhibitors and receptor-associated protein (RAP), which blocked the interaction between ApoE and members of the low-density lipoprotein (LDL) receptor family. Moreover, inhibition of the NMDA receptor increased IDE levels in neurons, while activation of the NMDA receptor-reduced IDE expression. Further studies demonstrate that, as a pathway downstream of the NMDA receptor, cAMP-dependent protein kinase (PKA) contributes to the NMDA receptor-reduced IDE expression. These results suggest that ApoE4 down-regulates IDE expression in neurons by binding to its receptor and stimulating the NMDA receptor pathway, which may account for its role in AD pathogenesis.     

apoE isoforms and measures of anxiety in probable AD patients and Apoe-/- mice

Increased anxiety may occur in up to 70% of AD patients during the course of their illness. Here we show that human apoE isoforms, which differ in AD risk, have differential effects on measures of anxiety in adult Apoe-/- male mice expressing human apoE3 or apoE4 in their brains and male probable AD (PRAD) patients. Compared with wild-type mice, Apoe-/- mice without human apoE or with apoE4, but not apoE3, showed increased measures of anxiety. These behavioral alterations were associated with reduced microtubule-associated protein 2-positive neuronal dendrites in the central nucleus of the amygdala. Consistent with the mouse data, male and female PRAD patients with epsilon4/epsilon4 showed higher anxiety scores than those with epsilon3/epsilon3. We conclude that human apoE isoforms have differential effects on measures of anxiety.     

载脂蛋白E在阿尔茨海默病中的表达及其意义

目的探讨载脂蛋白E（apoE）基因多态性和ε4等位基因与阿尔茨海默病（Alzheimer disease,AD）的关系,以及apoE在AD老年斑形成过程中的作用。方法从北京医院病理科1982—2003年尸检材料中选出27例AD,均按照美国多中心合作建立的阿尔茨海默病的病理诊断标准诊断,其中23例为肯定AD,4例为可疑AD。另选年龄相仿的对照组67例,为北京医院病理科同期非神经系统疾病死亡的尸检标本。分别应用免疫组织化学SP法检测β-淀粉蛋白（β-amyloid,AB）、Tau蛋白,以及SP法和ABC法免疫组织化学双标技术检测Aβ／apoE在AD脑组织中的表达;对23例肯定AD脑组织进行老年斑和神经原纤维缠结计数及形态学观察。应用聚合酶链反应-限制性片段长度多态性（PCR—RFLP）技术,对所有的AD及对照组标本进行apoE基因多态性分析。结果AB免疫组织化学染色显示AD脑组织内有4种不同类型的老年斑,即弥漫性非神经突斑、弥漫性神经突斑、有核心的神经突斑、有核心的非神经突斑。Aβ／apoE免疫组织化学双标染色显示有的老年斑A6和apoE均阳性,其在上述4种类型的老年斑中阳性表达率分别为4．28％、84．71％、8．50％、2．51％,弥漫性神经突斑Aβ／apoE免疫组织化学双标染色均阳性的表达率明显高于其他类型老年斑,P〈0．01。AD组apoEε4等位基因的频率明显高于对照组,P〈0．01。23例肯定的AD中,具有apoEε4等位基因的AD脑组织内的老年斑和神经原纤维缠结的数量均明显多于无apoEε4等位基因的AD脑组织,P〈0．01。结论apoE基因多态性与AD发生有关;apoEaε4等位基因是AD发病的重要危险因素,与AD脑组织病变的形成和进展有密切关系;apoE蛋白可能在AD弥漫性非神经突斑向弥漫性神经突斑进展过程中发挥了重要作用。     

The importance of plasma apolipoprotein E concentration in addition to its common polymorphism on inter-individual variation in lipid levels: results from Apo Europe

Interindividual variation in the concentration of plasma lipids which are associated with coronary artery disease (CAD) risk is determined by a combination of genetic and environmental factors. This study investigates the effects of apoE genotype and plasma concentration on cholesterol and triglycerides (TG) levels in subjects from five countries: Finland, France, Northern Ireland, Portugal, and Spain. Age and sex significantly influenced serum cholesterol, TG and apoE concentrations. The age effect differs in males and females. The allele frequencies of the apoE gene, one of the most widely studied CAD susceptibility genes, were determined: the epsilon2 allele frequency and the apoE concentration showed a north-south increasing gradient while the epsilon4 allele frequency showed the reverse. ApoE plays an important role in lipid metabolism. Total cholesterol and TG concentrations were significantly dependent on apoE genotype in both sexes. These differences in lipids between genotypes were more pronounced when plasma apoE concentrations were taken into account.     

Intronic CYP46 polymorphism along with ApoE genotype in sporadic Alzheimer Disease: from risk factors to disease modulators

Increasing biological and clinical findings argue for a link between brain cholesterol turnover and Alzheimer Disease (AD), high cerebral levels of the former increasing Abeta load. Cerebral cholesterol elimination involves two mechanisms dependent on Apolipoprotein E (ApoE) and cholesterol 24-hydroxylase (CYP46). The aim of this study was to evaluate an intronic variation in CYP46 (intron 2, T --> C ) along with ApoE genotype as risk factors for AD and to establish the correlation between CYP46/ApoE polymorphism and disease progression. One-hundred and fifty-seven AD patients, who had been followed periodically through 1-year follow-up after enrollment, and 134 age- and gender-matched controls entered the study. The distribution of CYP46 genotypes was significantly different in AD compared to controls (P<0.004), being CYP*C allele higher in AD patients ( P<0.002). ApoE 4 genotype was more frequent in AD (41.4%) than in controls (15.9%, P<0.0001). The odds ratio (OR) for AD risk in CYP46*C carriers was 2.8, and in ApoE epsilon4 carriers was 4.05; the OR for having both CYP46*C and ApoE epsilon4 was 17.75, demonstrating the their synergic effect on AD risk. In AD patients, CYP46*C along with ApoE epsilon4 genotype were associated with a higher cognitive decline at 1-year follow-up (P<0.02). These findings provide direct evidence that CYP46 and ApoE polymorphisms synergically increase the risk for AD development, and influence on the rate of cognitive decline.     

−1154G/A and −2578C/A polymorphisms of the vascular endothelial growth factor gene in Tunisian Alzheimer patients in relation to β-amyloid (1–42) and total tau protein

Recent evidences indicate that polymorphisms within the promoter region of the vascular endothelial growth factor (VEGF) gene may elevate the risk for Alzheimer's disease (AD). To further investigate, we have analyzed association between promoter polymorphisms of the VEGF gene in 93 AD patients and age and sex matched 113 controls from Tunisian population. The distribution of genotype and allele frequencies of the VEGF (−2578C/A) and (−1154G/A) polymorphisms did not differ significantly between AD and control groups (p > 0.05). In the subgroup of ApoE ?4 carriers, the −2578A was observed to be significantly higher in the AD patients than in the control individuals. After adjusting the data by gender, age and the ApoE ?4 status using logistic regression, the −2578A allele was found to increase the risk for sporadic AD by 1.7-fold. The present study provides the evidence that the −2578A allele may be associated with the development of AD in the individuals with ApoE ?4 allele. In addition, AD patients carrying the −2578A allele had lower Aβ42 (p = 0.029) levels than those without this allele, particularly in subjects with ApoE ?4 allele.     

Alzheimer病中载脂蛋白E基因与α1—抗糜蛋白酶基因的相互 …

目的 探讨中国汉族Ａｌｚｈｅｉｍｅｒ病患者中载脂蛋白Ｅ基因多态性与α１抗糜蛋白酶基因多态性之间的关系。方法 应用聚合酶链式反应（ＰＣＲ）－限制性片段长度多态性（ＲＦＬＰ）方法,在１２５例ＡＤ患者和１４０便正常人中观察发ＡＡＣＴ信号肽基因和ＡｐｏＥ基因多态性的分布,并对ＡＡＣＰ信号肽基因多态性与ＡｐｏＥ基因ε４等位基因进行关联分析。结果 （１）ＡＡＣＴ信号肽基因多态性与ＡＤ之间不存在任何关联;（２）     

Genotype-related differences of hippocampal apolipoprotein E levels only in early stages of neuropathological changes in Alzheimer's disease

Inheritance of the epsilon4 allele of apolipoprotein E (APOE, gene; apoE, protein) represents the most common genetic risk factor for developing Alzheimer's disease (AD), but the role of apoE in AD pathogenesis is yet to be clarified. A number of studies investigating apoE expression and protein levels in AD brain in correlation to its genetic polymorphism has yielded controversial results. We designed our approach based on neuropathological characteristics of AD to investigate apoE levels in relation to the APOE genotype and AD-related neurofibrillary changes, and amyloid deposits. We determined hippocampal apoE levels by reducing sodium dodecylsulfate-polyacrylamide gel electrophoresis and immunoblotting in 70 Braak-staged and APOE-genotyped autopsy brains. In our stage-, age- and gender-matched case sample, we found a significant increase of hippocampal apoE in the APOE epsilon3 homozygotes with beginning AD-related pathology (Braak stages I and II) compared with brain samples free of neurofibrillary changes and amyloid deposits. In the APOE epsilon4 allele carriers no such increase was found. In both genotype groups, severely affected brain samples with widespread neurofibrillary changes (Braak stages V and VI) and amyloid deposits (Braak stage C) showed low apoE levels comparable to those found in unaffected brain samples (Braak stage 0).Our data suggests that the isoform-specific impact of apoE on the development of AD may be of crucial importance only in the early stages of the disease. These stages are believed to represent phases of the disease in which the beginning neurodegeneration can be compensated by plastic reorganization.     

Insulin, insulin-degrading enzyme and amyloid-beta peptide in Alzheimer's disease: review and hypothesis

Clinical and epidemiological studies have found that type 2 diabetes, and hyperinsulinaemia, increased the risk of developing Alzheimer's disease (AD) in the elderly. The link between hyperinsulinaemia and AD may be insulin-degrading enzyme (IDE). This enzyme degrades both insulin and amylin, peptides related to the pathology of type 2 diabetes, along with amyloid-beta peptide (Abeta), a short peptide found in excess in the AD brain. We review the current evidence, which suggests that hyperinsulinaemia may elevate Abeta through insulin's competition with Abeta for IDE. Genetic studies have also shown that IDE gene variations are associated with the clinical symptoms of AD as well as the risk of type 2 diabetes. The deficiency of IDE can be caused by genetic variation or by the diversion of IDE from the metabolism of Abeta to the metabolism of insulin. It is intriguing to notice that both hyperinsulinaemia and IDE gene variations are related to the risk of AD when the Apolipoprotein E4 (ApoE4) allele, the major risk factor of late-onset AD, is not present. Further studies of the role of IDE in the pathogenesis of AD, which may uncover potential treatment target, are much needed.     

ApoE genotype does not affect plasma tPA and PAI-1 antigen levels

The presence of one or two apoliprotein E4 (apoE4) alleles constitutes a major risk factor for Alzheimer's disease (AD) and coronary heart disease (CHD). Numerous observations have suggested that misregulation of proteases may be instrumental in both diseases. Tissue-type plasminogen activator (tPA) has been recently demonstrated to play a key role in neuronal plasticity and in experimental neurodegeneration. One receptor for the ApoE protein is the LRP/α2 macroglobulin receptor, which also binds to and endocytoses tPA and plasminogen activator inhibitor I (PAI-1). Here we tested whether the apoE genotype has an influence on the plasma levels of these proteins. We demonstrate that there is no difference in plasma levels of tPA- and PAI-1-antigens between middled-aged individuals with one apoE4 allele and those having none. This suggests that the impact of apoE4 on Alzheimer's disease is not the result of altered clearance of tPA or PAI-1 by the LRP receptor. Am. J. Med. Genet. 74:172–175, 1997. © 1997 Wiley-Liss, Inc.     

ApoE genotype is a risk factor in nonpresenilin early-onset alzheimer's disease families

The apolipoprotein E (ApoE) genotype is a significant risk factor and modulator of age of onset of Alzheimer's disease (AD). We analyzed the effect of the ApoE genotype in two distinct early-onset familial AD groups: families with a mutation in the presenilin-1 gene (PS-1) on chromosome 14, and families without a mutation detectable in the PS-1, presenilin-2 (PS-2), and the amyloid precursor protein (APP) gene (non-PS early-onset familial AD). The ApoE genotype is clearly shown not to modulate age of onset in families with a mutation in the PS-1 gene and families with no lesion detectable in either the presenilin or APP gene. The effects of a double dose of ApoE4 on age of onset were not assessed in the PS-1 AD families due to the lack of any affected ApoE4 homozygotes in the sample set; this insufficiency will need to be assessed in further studies. There was no association between the ApoE4 allele and AD in the PS-1 families. Non-PS early-onset AD families were shown to have a significantly higher frequency of ApoE4 compared to controls and the PS-1 AD group. These observations are important and suggest that 1) other genetic and environmental factors modify the AD phenotype in PS-1 and non-PS early-onset families; and 2) the ApoE4 allele is a significant risk factor in the etiology of non-PS early-onset AD and will be a useful adjunct in the diagnosis of unaffected family members. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 81:117–121, 1998. © 1998 Wiley-Liss, Inc.     

载脂蛋白E基因多态性与中国人阿尔茨海默病和颈动脉粥样硬化相关性研究

为了探讨中国散发性阿尔茨海默病（SAD)颈动脉粥样硬化（CAS）与ApoE基因多态性的关系,应用聚合酶链式反应－限制性片段长度多态性（PCR－RFLP）技术检测46名SAD患者、31名CAS患者及50名正常老年人的ApoE基因多态性分布特征。结果显示SAD组及CAS组ApoE ε4等位基因频率均高于对照组（P＜0．05）;SAD组为15．2％,CAS组为14．5％,对照组为3．0％,但CAS组ApoEε2等位基因频率明显高于SAD组（P＜0．05）;CAS组为41．9％,SAD组为21．7％本研究提示,ApoE4等位基因是SAD和CAS的共同危险因素,但ApoE2等位基因对CAS病人患AD具有保护作用。