Pronounced impact of Th1/E47cs mutation compared with -491 AT mutation on neural APOE gene expression and risk of developing Alzheimer's disease

Possession of the apolipoprotein E (APOE) epsilon4 allele is the most frequently associated genetic susceptibility factor for Alzheimer's disease (AD). Recently, new polymorphisms in the regulatory region of the APOE gene have been described. We analysed the effects of three of these mutations (-491 AT, -427 CT and Th1/E47cs) on disease risk in a large case-control study, and tested their impacts on APOE allelic expression in brain tissues. The Th1/E47cs T allele was associated with an increased risk of occurrence of AD, while the -491 T allele was associated with a decreased risk, independently of the APOE epsilon2/epsilon3/epsilon4 polymorphism effect. However, the impact of the Th1/E47cs mutation was the strongest. The -427 CT polymorphism was not associated with the disease. In AD subjects heterozygous for the epsilon4 allele, analysis of allelic expression showed that the relative expression levels of the epsilon4 allele were higher than those of the corresponding controls. Consistent with epidemiological data, the relative level of expression of the epsilon4 allele was modified accordingly to the presence or absence of the two main promoter polymorphisms, indicating, in vivo, the deleterious effect of the Th1/E47cs T allele and the protective effect of the -491 T allele in population. These data indicate that in addition to the qualitative effect of the APOE epsilon2/epsilon3/epsilon4 polymorphisms on the AD occurrence, the quantitative variation of expression of these alleles due to functional APOE promoter mutations, is a key determinant of AD development.      

Heparan sulfate proteoglycan 2 polymorphism in Alzheimer's disease and correlation with neuropathology

A genetic association of an intronic single nucleotide polymorphism site of heparan sulfate proteoglycan 2 (HSPG2) with Alzheimer's disease (AD) was investigated among Finnish AD patients (n=213) and controls (n=269). No association of the HSPG2 polymorphism alone was observed with AD. However, an association of HSPG2 A allele with AD was detected in apolipoprotein (APOE) epsilon4 allele carriers. The odds ratio for AD was doubled in subjects carrying both epsilon4 and HSPG2 A alleles (OR=6.6) when compared to subjects with epsilon4 allele alone (OR=3.1). The impact of HSPG2 polymorphism on beta amyloid and tau pathology was studied using immunohistochemistry. Paired helical filament labeling was significantly more pronounced in AD patients carrying both epsilon4 and HSPG A alleles when compared to epsilon4 carriers lacking the HSPG2 A allele. In conclusion, HSPG2 A allele may possess an additive risk effect among the APOE epsilon4 carriers in AD.     

No association between low density lipoprotein receptor genetic variants and Alzheimer's disease risk.

A number of studies suggest that brain cholesterol metabolism may play a role in Alzheimer's disease (AD) development, probably through modulation of amyloid beta production. The discovery that apolipoprotein E (APOE) epsilon4 allele is a risk factor for sporadic AD raises the possibility that the receptors to which APOE binds on the surface of neurons are also involved in the neurodegenerative process. To evaluate the relationship between low density lipoprotein receptor (LDLR) genetic variant and AD, independently or in concert with the APOE epsilon4 allele, we examined three LDLR polymorphisms located in exons 8 (rs 11669576), 10 (rs 5930), and 13 (rs 5925), in a large group of 322 Spanish AD patients and 314 controls. The current study does not demonstrate an association between LDLR genotypes or haplotypes and AD, neither in the total sample nor when the populations were stratified for the presence or absence of the APOE epsilon4 allele.     

Independent association of an APOE gene promoter polymorphism with increased risk of myocardial infarction and decreased APOE plasma concentrations-the ECTIM study

Apolipoprotein E (APOE) is a major protein in lipid metabolism existing in three common isoforms: APOE2, -3 and -4. The varepsilon4 allele of the APOE gene ( APOE ) coding for the APOE4 isoform is associated with an increased risk of myocardial infarction (MI) and of Alzheimer's disease (AD). Recently, several polymorphisms in the APOE regulatory region have been reported. Some of these have been associated with AD and modified APOE allelic mRNA expression in AD brains. Here, we have investigated whether three of these promoter polymorphisms (-491AT, -427CT and -219GT) can also modify cardiovascular risk. The hypothesis was tested in a large multicentre case-control study of MI, the ECTIM Study, on 567 cases and 678 controls. Among the three APOE promoter polymorphisms tested, only the-219T allele was associated with a significantly increased risk of MI (OR = 1.29, 95% CI: 1.09-1.52, P < 0.003) and the effect was shown to be independent of the presence of the other mutations, including the APOE epsilon2/epsilon3/epsilon4 polymorphism. Moreover, the-219T allele greatly decreased the APOE plasma concentrations in a dose-dependent manner ( P < 0.008). These data indicate that the-219GT polymorphism of the APOE regulatory region emerges as a new genetic susceptibility risk factor for MI and constitutes another common risk factor for both neurodegenerative and cardiovascular diseases.     

Reduced hippocampal insulin-degrading enzyme in late-onset Alzheimer's disease is associated with the apolipoprotein E-epsilon4 allele

Abeta is the major component of amyloid plaques characterizing Alzheimer's disease (AD). Abeta accumulation can be affected by numerous factors including increased rates of production and/or impaired clearance. Insulin-degrading enzyme (IDE) has been implicated as a candidate enzyme responsible for the degradation and clearance of Abeta in the brain. We have previously shown that AD patients exhibit abnormalities in insulin metabolism that are associated with apoliprotein E (APOE) status. The possible association of IDE with AD, as well as the link between APOE status and insulin metabolism, led us to examine the expression of IDE in AD. We report that hippocampal IDE protein is reduced by approximately 50% in epsilon4+ AD patients compared to epsilon4- patients and controls. The allele-specific decrease of IDE in epsilon4+ AD patients is not associated with neuronal loss since neuron-specific enolase levels were comparable between the AD groups, regardless of APOE status. Hippocampal IDE mRNA levels were also reduced in AD patients with the epsilon4 allele compared to AD and normal subjects without the epsilon4 allele. These findings show that reduced IDE expression is associated with a significant risk factor for AD and suggest that IDE may interact with APOE status to affect Abeta metabolism.     

No cross-sectional influence of APOE epsilon4 dose on clinical tests in Alzheimer's disease

This study sought to determine if there are detectible influences on the symptoms of Alzheimer's disease (AD) from the genetic risk factor for AD, the epsilon4 allele of apolipoprotein-E (APOE). Using data from two cohorts of AD patients, a cross-sectional latent variable model of AD was tested with three symptom factors explaining variability in the observed variables after taking a general neurological factor into account. No significant influence of epsilon4 was detected. APOE's effect in AD may occur prior to clinical symptoms, or may simply be more subtle than these instruments can detect.     

The CDC2 I-G-T haplotype associated with the APOE epsilon4 allele increases the risk of sporadic Alzheimer's disease in Sicily

The cell division cycle 2 (CDC2) gene is a candidate susceptibility gene for Alzheimer's disease (AD). We investigated the CDC2 genotype, and allele and haplotype frequencies in AD patients and matched controls, distinguishing between apolipoprotein E (APOE) epsilon4 allele carriers and non-carriers. APOE epsilon4 is an established predictor of AD risk. APOE and CDC2 genotypes were examined in 109 sporadic AD patients and in 110 healthy age- and sex-matched controls from Sicily. The epsilon4 allele of APOE was predictive of AD risk in our study group (odds ratio: 5.37, 95% CI 2.77-10.41; P<0.0001). Genotype and allele frequencies of the three tested CDC2 polymorphisms (Ex6+7I/D, Ex7-15 G>A, Ex7-14 T>A) were not significantly different between AD patients and controls. However, a significant different distribution of a specific CDC2 haplotype (I-G-T) was found between AD patients and controls when analyzing APOE epsilon4-positive subjects (P=0.0288). Moreover, the combined presence of the I-G-T haplotype and the epsilon4 allele almost doubled the risk of AD (odds ratio: 10.09, 95% CI 3.88-26.25; P<0.0001) compared to carriers of epsilon4 alone. This study suggests that the I-G-T haplotype of the CDC2 gene increases the risk of AD in APOE epsilon4 carriers.     

Association of genetic variants of ABCA1 with Alzheimer's disease risk.

ABCA1 plays key roles in cholesterol transport and apolipoprotein E (APOE) metabolism in the brain. To evaluate the relationship between ABCA1 genetic variants and Alzheimer's disease (AD), independently or in concert with the APOE epsilon4 allele, we examined three ABCA1 polymorphisms located in the coding region (R219K, I883M, and R1587K) and two ABCA1 polymorphisms in the promoter region (C-14T and C-477T) in a group of 372 Spanish AD patients and 440 controls. The ABCA1 219K, 883I, 1587R haplotype was significantly associated with AD, conferring a risk of 1.78 (P = 0.007). The ABCA1 C-14T polymorphism modified the risk of AD in an APOE epsilon4 allele-dependent fashion: in APOE epsilon4 carriers, homozygous for the ABCA1 -14T allele had 3.7 times higher risk of developing AD (OR = 13.99) than carriers of the ABCA1 -14CC and CT genotypes (OR = 3.79). These data suggest that the development of AD might be influenced by either a qualitative change of the ABCA1 protein caused by coding region variants (219K, 883I, and 1587R), or by a quantitative change in ABCA1 expression caused by promoter region variant (-14T) in concert with the APOE epsilon4 allele.     

The --491 TT apolipoprotein E promoter polymorphism is associated with reduced risk for sporadic Alzheimer's disease

Homozygosity for the A allele of the -491 A/T apolipoprotein E (APOE) promoter polymorphism has recently been reported to be associated with sporadic Alzheimer's disease (AD). Two hundred and fifty one patients with AD and an equal number of controls derived from the same region in a Spanish population, were genotyped for -491 A/T and epsilon2/epsilon3/epsilon4 APOE polymorphisms. We did not detect an elevated -491 AA genotype frequency when comparing AD cases to controls. In contrast, persons homozygous for the T allele were at a significantly reduced risk of AD (odds ratio of 0.10, P=0.006). Multiple logistic regression analysis indicated that the -491 TT polymorphism added information on the risk of AD which was independent of that of the APOE epsilon4 allele.     

No association between the genes for butyrylcholinesterase K variant and apolipoprotein E4 in late-onset Alzheimer's disease

Butyrylcholinesterase (BChE) as well as acetylcholinesterase has been suggested to be associated with Alzheimer's disease (AD). Lehmann et al. [1997: Hum Mol Genet 6:1933-1936] recently reported the synergism between the gene for the K variant of BChE (BCHE-K) and the epsilon4 allele of apolipoprotein E (APOE epsilon4) in late-onset confirmed AD with Caucasian subjects. The authors found that the allelic frequency of BCHE-K was 0.17 in 74 subjects with late-onset histopathologically diagnosed AD, which was higher than the frequencies in elderly control subjects (0.09) and in other dementias (0.07-0.10). The association of BCHE-K with late-onset AD was limited to carriers of APOE epsilon4, giving odds ratios of confirmed late-onset AD of 6.9-12.8. In the present study, we report the BCHE-K allelic frequencies in late-onset AD cases and in age-matched controls of the Korean population, which were 0.22 and 0.17, respectively. We could not find any association between BCHE-K and AD regardless of APOE epsilon4 carrier status. However, APOE epsilon4 clearly showed higher frequency in AD (0.33) than in elderly controls (0.09), giving an odds ratio of 5.2 (95% confidence interval, 2.7-10.0). Our results do not support the conclusion that BCHE-K, or a nearby gene on chromosome 3, acts in synergy with APOE epsilon4 as a susceptibility gene for late-onset AD, at least in the Korean population.     

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.     

Apolipoprotein C-I is an APOE genotype-dependent suppressor of glial activation

ABSTRACT: BACKGROUND: Inheritance of the human epsilon4 allele of the apolipoprotein (apo) E gene (APOE) significantly increases the risk of developing Alzheimer's disease (AD), in addition to adversely influencing clinical outcomes of other neurologic diseases. While apoE isoforms differentially interact with amyloid beta (Abeta), a pleiotropic neurotoxin key to AD etiology, more recent work has focused on immune regulation in AD pathogenesis and on the mechanisms of innate immunomodulatory effects associated with inheritance of different APOE alleles. APOE genotype modulates expression of proximal genes including APOC1, which encodes a small apolipoprotein that is associated with Abeta plaques. Here we tested the hypothesis that APOE-genotype dependent innate immunomodulation may be mediated in part by apoC-I. METHODS: ApoC-I concentration in cerebrospinal fluid from control subjects of differing APOE genotypes was quantified by ELISA. Real-time PCR and ELISA were used to analyze apoC-I mRNA and protein expression, respectively, in liver, serum, cerebral cortex, and cultured primary astrocytes derived from mice with targeted replacement of murine APOE for human APOE epsilon3 or epsilon4. ApoC-I direct modulation of innate immune activity was investigated in cultured murine primary microglia and astrocytes, as well as human differentiated macrophages, using specific toll-like receptor agonists LPS and PIC as well as Abeta. RESULTS: ApoC-I levels varied with APOE genotype in humans and in APOE targeted replacement mice, with epsilon4 carriers showing significantly less apoC-I in both species. ApoC-I potently reduced pro-inflammatory cytokine secretion from primary murine microglia and astrocytes, and human macrophages, stimulated with LPS, PIC, or Abeta. CONCLUSIONS: ApoC-I is immunosuppressive. Our results illuminate a novel potential mechanism for APOE genotype risk for AD; one in which patients with an epsilon4 allele have decreased expression of apoC-I resulting in increased innate immune activity.     

Vascular genetic factors and human longevity

Complex inter-relationships between age-associated illnesses, such as vascular disease and Alzheimer's disease (AD), suggest that biological and genetic pathways may be worthy of examination in centenarian populations to provide insights into human longevity. This is also borne out by the involvement of lipoprotein metabolism and a number of vascular genetic risk factors. Repeated findings of a higher frequency of the apolipoprotein E (APOE) epsilon4 allele in middle-aged subjects compared with centenarians were reported. Furthermore, we have also shown how in different populations there is a significant trend in reduction of serum APOE levels from APOE epsilon2- to epsilon4-carrier as well as significant differences in serum APOE levels respect to age in epsilon4-carriers but only after adjustment for HDL cholesterol. In contrast, findings of increased prevalence of the angiotensin I converting enzyme 1 (ACE1) D allele in French centenarians have not been replicated, suggesting the possibility that regional differences may occur in ACE1(*)D frequency within Europe in centenarians, as has been recently reported for APOE epsilon2 and epsilon4 alleles. A number of studies have examined the potential role in longevity of other genes involved in vascular risk, haemostasis, and blood pressure regulation [methyltetrahydrofolatereductase (MTHFR), apolipoprotein A1 (APOA-I), apolipoprotein C3 (APOC-III), apolipoprotein A4 (APOA-IV), paraoxonase 1 (PON1), plasminogen activator inhibitor type I (PAI-1)], with contrasting results. While further studies are needed to confirm the possible role of APOE concentration as putative longevity factor, this paper provides an overview of genetic vascular factors potentially involved in human longevity.     

Alpha-2 macroglobulin gene in early- and late-onset Alzheimer disease.

Alpha-2-macroglobulin (A2M) is a proteinase inhibitor that is present in senile plaques and may play a role in metabolism of amyloid beta (A beta) peptide. Recently it was reported that inheritance of the deletion allele (A2M-2) confers increased risk for late-onset Alzheimer disease (AD) with significance of this effect similar to the epsilon4 allele of apolipoprotein E (APOE). We examined the distribution of A2M genotypes and alleles in a cohort of 146 AD patients and 160 age-matched non-demented individuals. There was no evidence for association in the total sample or in subsets stratified by age or APOE epsilon4 status. These results suggest that this polymorphism is not a strong genetic risk factor for either early- or late-onset forms of the disorder. However, they do not exclude the possibility that an AD susceptibility allele is located elsewhere in A2M or a nearby gene.     

Apolipoprotein E epsilon4 influences on episodic recall and brain structures in aging pilots

The apolipoprotein (APOE) epsilon4 allele is associated with cognitive deficits and hippocampal atrophy in nondemented middle-aged and older adults. It is not known to what extent this genetic risk factor for Alzheimer's disease (AD) impacts performance in late middle-aged and older workers in cognitively demanding occupations. This cross-sectional analysis examines brain-cognitive-genetic relationships in actively flying general aviation pilots, half of whom are APOE epsilon4 carriers. Fifty pilots were studied with structural MRI and memory tasks. Average visual paired associate memory recall performance was lower in APOE epsilon4 carriers than non-carriers. Memory performance correlated positively with hippocampal volume, but no structural differences were found in hippocampal or frontal volumes with respect to APOE epsilon4 allele. These results were evident in healthy professionals without any presenting memory problems and without selection for a family history of AD. These findings point to basic memory testing as a sensitive tool for detecting APOE epsilon4-related influences on memory in aging workers.     

Apolipoprotein E-epsilon4 alleles in cerebral amyloid angiopathy and cerebrovascular pathology associated with Alzheimer's disease.

The presence of apolipoprotein E-epsilon4 (APOE-epsilon4) allele has been implicated as a risk factor for Alzheimer's disease (AD). We examined the frequencies of APOE-epsilon4 alleles in age-matched controls and subgroups of 190 AD subjects exhibited cerebral amyloid angiopathy (CAA) and other frequently associated lesions. CAA was evident in 96% of the AD subjects, which were divided into two groups, one bearing mild or no apparent CAA and the other with moderate to severe CAA. APOE-epsilon4 allele frequency (48%) in the latter advanced CAA group was six times higher than in those who exhibited mild CAA. In the advanced CAA subjects, the occurrence of an epsilon4 allele was increased by a factor of 17 (95% confidence interval, 7.56 to 38.9). This was despite the fact that neocortical amyloid-beta plaque densities in the two groups were similar and that all of the AD subjects had met the accepted neuropathological criteria. We also observed that the degree of CAA severity was greatest in the group of subjects with the epsilon4/epsilon4 genotype. The association between CAA and APOE-epsilon4 was further implicated in two non-AD subjects among neurological controls with severe CAA. These two subjects, both homozygous for the APOE-epsilon4 allele, were primarily diagnosed as having Creutzfeldt-Jakob disease and Pick's disease in the absence of significant neocortical amyloid deposition. Allele frequency comparisons between neurological control subjects with CAA and those without likewise accorded a strong relationship between the APOE-epsilon4 allele and the presence of CAA. More remarkably, the epsilon4 allele frequency was highly associated with AD subjects exhibiting lobar or intracerebral hemorrhage, all of whom had advanced CAA. We observed that 36% of the AD subjects had concomitant cerebrovascular pathology resulting from single infarcts, multiple microinfarcts, ischemic white matter lesions, or petechial hemorrhages. Although the difference in APOE genotype distribution between subjects with and without cerebrovascular lesions did not reach statistical significance, we did note that the frequency of the epsilon4 allele was significantly higher in subjects with such pathology as compared with those without. However, we found no evidence to suggest that the acquisition of an APOE-epsilon4 allele or one of the alleles, epsilon2 or epsilon3, was a factor in the occurrence of atherosclerosis localized in the basal surface arteries. Analyses of our sample also confirm that there was a lower frequency of the APOE-epsilon2 allele in AD subjects and that the frequency of the epsilon4 allele in AD subjects with concomitant diffuse Lewy body disease was intermediate between controls and AD subjects. Our results suggest that the APOE-epsilon4 allele is a significant factor in the development of CAA in AD and reveal the possibility that APOE is an independent factor in CAA and other vascular abnormalities associated with AD.     

HFE variants, APOE and Alzheimer's disease: findings from the population-based Rotterdam study

Iron is a reactive oxygen species and has been implicated in the pathogenesis of Alzheimer's disease (AD). In a population-based cohort study, including 268 incident AD patients and 2079 control individuals, we investigated the influence of the HFE C282Y and H63D variants and the apolipoprotein E4 (APOE epsilon 4) allele on the incidence, and age at onset of AD. There was no significant difference in the frequency of HFE variants in AD patients compared to controls. There was no significant effect modification by the APOE epsilon 4 allele. The mean age at onset was earlier in H63D homozygotes compared to non-carriers of this variant, in men (76.9+/-3.2 compared to 82.2+/-1.7) and women (82.1+/-3.9 compared to 84.5+/-1.7). In addition, in APOE epsilon 4 carriers, the mean age at onset of AD was earlier in men homozygous for the H63D variant (73.2+/-2.1 versus 78.7+/-1.6, p=0.05). Our results suggest that HFE variants are not strong determinants of AD in the general population but may modify the age of onset.     

Alpha-1 antichymotrypsin and alpha-2 macroglobulin gene polymorphisms are not associated with Korean late-onset Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial disorder with possible involvement of several genetic and environmental factors. For late-onset AD (LOAD), the epsilon4 allele of apolipoprotein E (APOE) has been identified as a major susceptible gene. However, the observation that APOE epsilon4 accounted for approximately one half of the genetic variance of LOAD prompted many researchers to undertake genome surveys to identify other susceptible genes. Recently, several candidate genes such as alpha-1 antichymotrypsin (ACT) and alpha-2 macroglobulin (A2M) were reported to be associated with LOAD. To evaluate the possible association between these genes and LOAD in Korean population, we genotyped ACT A/T and A2M 5-bp deletion (exon 18) polymorphisms in 89 LOAD cases and 50 age-matched healthy controls. The frequencies of ACT A and A2M 5-bp deletion alleles in LOAD and controls were 0.39 vs. 0.37, and 0.05 vs. 0.05, respectively. Although APOE epsilon4 clearly showed higher frequency in LOAD (0.34) than that in controls (0.09), giving an odds ratio of 5.14 (95% confidence interval, 2.31-11.76), neither ACT nor A2M showed statistically significant difference between LOAD and controls regardless of APOE carrier status. Our results do not support previously reported association of ACT and A2M with LOAD, at least in Korean population.     

A polymorphism of the interleukin-1 beta gene at position +3953 influences progression and neuro-pathological hallmarks of Alzheimer's disease

Interleukin-1 (IL-1) gene polymorphisms are associated with an increased risk of Alzheimer's disease (AD) and it has been suggested that altered immune responses of the brain may play a role in the pathogenesis of the disease. Here we investigated whether IL-1beta polymorphisms affected neuro-pathological features and clinical status of AD patients with autopsy confirmed diagnosis of the disease. AD patients (n=133) were genotyped for the polymorphic regions in the apolipoprotein E epsilon (APOE epsilon) and interleukin-1beta (IL-1beta) genes. APOE epsilon4 carriers showed increased neuritic amyloid plaques (NP) and neurofibrillary tangles (NFT). The IL-1beta +3953 polymorphism influenced survival in AD patients and those with the TT genotype and without the APOE epsilon4 allele showed the shortest cumulative survival. Patients with the +3953 IL-1beta T and without the APOE epsilon4 alleles had reduced NP and NFT, a delayed ages at onset and death, but a decreased duration of the disease. On the other hand a different polymorphism of the IL-1beta gene at position -511 did not influence any AD features. Our findings suggest that IL-1beta gene by affecting brain immune responses may influence the age at onset of the disease, survival and AD progression.