Common Apo Research Articles

Nature throws curveballs

The article by Martins et al.1 in this issue of Neurology proposes a novel approach to study the rate of progression in Alzheimer disease (AD). Predicting the course of AD is important for counseling patients and caregivers and for planning studies of intervention. Accurate modeling of the course of AD may also provide insights into its pathophysiology. The common APOE e4 allele confers an increased risk in late-onset AD.2 APOE e4 may be associated with beta-amyloid and tangle pathology.3 The less common APOE e2 allele may reduce risk. The rate of progression after the onset of AD is not as clearly related to the APOE allele, but if the APOE allele is associated with progression of pathology, earlier disease onset should be associated with more rapid progression. The current inconsistent relationship between APOE allele and prognosis has been difficult to reconcile with its relationship to onset of disease. Modeling the clinical course of AD relies on appropriate study designs: following a well-defined sample of patients; enrolling patients at the same stage of disease; and …

Apolipoprotein E gene polymorphisms are associated with psoriasis but do not determine disease response to acitretin

Psoriasis is associated with abnormal plasma lipid metabolism and a high frequency of cardiovascular events. Increased lipid levels are also seen in patients with psoriasis treated with acitretin. Apolipoprotein E (ApoE) variants have been linked to hypertriglyceridaemia and hypercholesterolaemia in normal individuals. Two coding single nucleotide polymorphisms at +3937 and +4075 define the three common ApoE alleles e2, e3 and e4. To test the hypothesis that particular ApoE polymorphism(s) are associated with psoriasis and that specific ApoE allelic variant(s) may be a marker for predicting disease response to acitretin. DNA was genotyped for ApoE polymorphisms using a radioactive hybridization technique in cohorts of patients with psoriasis, including patients with chronic plaque psoriasis (CPP, n = 212), guttate psoriasis (GP, n = 94), palmoplantar pustulosis (PPP, n = 101), controls (n = 137), acitretin responders (n =106) and acitretin nonresponders (n = 84). The frequency of the e4 allele (+3937C/+4075C) was significantly higher in patients with CPP and GP than in controls (P = 0.008 and P = 0.02, respectively). There was no significant difference in allele frequencies between patients with PPP and controls. Allelic distribution was similar in acitretin responders and nonresponders. These data demonstrate an association between the Apo e4 allele and CPP and GP, suggesting a possible pathogenic role for ApoE in psoriasis. Our results do not support a link between disease response to acitretin and the e2, e3 or e4 allelic variants of ApoE.

Give me A5 for lipoprotein hydrolysis!

APOA5 is a newly identified apolipoprotein that plays a crucial role in the regulation of plasma triglyceride levels. In several human studies, common APOA5 single nucleotide polymorphisms have been strongly associated with elevated plasma triglyceride levels. In this issue of the JCI, Marçais et al. report that the rare Q139X mutation in APOA5 leads to severe hypertriglyceridemia by exerting a dominant-negative effect on the plasma lipolytic system for triglyceride-rich lipoproteins. The presented data support the idea that the molecular mechanism of APOA5 function may include the enhancement of binding between lipoproteins and proteoglycans at the vascular wall and activation of proteoglycan-bound lipoprotein lipase.

Determination of the Functionality of Common APOA5 Polymorphisms

Common variants of APOA5 have consistently shown association with differences in plasma triglyceride (TG) levels. These single nucleotide polymorphisms (SNPs) fall into three common haplotypes: APOA5*1, with common alleles at all sites; APOA5*2, with rare alleles of -1131T--> C, -3A--> G, 751G--> T, and 1891T--> C; and APOA5*3, distinguished by the c56C--> G (S19W). Molecular modeling of the apoAV signal peptide (SP) showed an increased angle of insertion (65 degrees ) at the lipid/water interface of Trp-19 SP compared with Ser-19 SP (40 degrees ), predicting reduced translocation. This was confirmed by 50% reduction of Trp-19-encoded SP.secretory alkaline phosphatase (SEAP) fusion protein secreted into the medium from HepG2 cells compared with the Ser-19.SEAP fusion protein (p < 0.002). Considering APOA5*2 SNPs, there was no significant difference in the relative luciferase expression in Huh7 cells transiently transfected with a -1131T construct compared with the -1131C (fragments -1177 to -516 or -1177 to -3). Similarly, for the -3A--> G in the Kozak sequence, in vitro transcription/translation assays and primer extension inhibition assays showed no alternate AUG initiation codon usage, demonstrating that -3A--> G did not influence translation efficiency. Although 1891T--> C in the 3'-untranslated region disrupts a putative Oct-1 transcription factor binding site, when inserted 3' of the luciferase gene the T--> C change demonstrated no significant difference in luciferase expression. Thus, association of APOA5*2 SNPs with TG levels is not due to the individual effects of any of these SNPs, although cooperativity between the SNPs cannot be excluded. Alternatively, the effect on TG levels may reflect the strong linkage disequilibrium with the functional APOC3 SNPs.

Hypertriglyceridemia: Interaction between APOE and APOAV Variants

Schaefer et al. (1) recently reported an association between a distinct combination of variants in the apolipoprotein E ( APOE ) and APOAV genes and hypertriglyceridemia. Among 170 hypertriglyceridemic (HTG) patients, all carriers of APOE22 (n = 7) had at least 1 APOAV Trp19 allele, but this combination was not found in controls with triglyceride (TG) concentrations within the reference interval. APOE is a structural component of TG-rich lipoproteins; it serves as a ligand for lipoprotein receptors and plays an important role in the catabolism of remnant particles (2)(3). Of the 3 common apoE isoforms, apoE4 (Cys112>Arg) and apoE2 (Arg158>Cys) differ from the commonest isoform, apoE3, by a single amino acid substitution. The APOE4 allele has been shown to be associated with increased plasma cholesterol and with an increased risk of coronary heart disease. In contrast, the APOE2 allele is associated with low plasma concentrations of cholesterol and is believed to be protective against coronary heart disease [reviewed in Refs. (2)(3)]. APOAV …

W12-P-062 The relationship between BMI and common carotid plaques or apo B and bifurcation plaques are independent of HS-CRP concentration

W12-P-062 The relationship between BMI and common carotid plaques or apo B and bifurcation plaques are independent of HS-CRP concentration

Three Novel Mutations in the Apolipoprotein E Gene in a Sample of Individuals with Type 2 Diabetes Mellitus

Apolipoprotein E (apoE) is found in association with triglyceride-rich lipoproteins and is the ligand for the removal of these particles from the plasma. Genetic variations in exon 4 lead to three common gene variants: E2, E3, and E4. We performed apoE genotyping in 765 individuals with type 2 diabetes. We identified three new variant heteroduplex patterns. Sequencing of these variants revealed three novel mutations that were related to biochemical and clinical characteristics. One mutation produced a frameshift at amino acid position 166, which predicted termination of protein synthesis. This individual had a heteroduplex pattern and sequence of E3E3, which was associated with a change in the plasma isoelectric focusing pattern and a 70% lower plasma concentration of apoE compared with healthy individuals. The other mutations were both single base changes. A CGC>CAC change at amino acid position 150 predicted a substitution of Arg>His. This individual had a heteroduplex pattern and sequence of E2E2, which was not associated with major changes in plasma lipids or apoE concentration. The third individual had a CGC>CCC base change at amino acid position 114, which predicted an Arg>Pro change. This person had a heteroduplex pattern and sequence of E3E3, higher plasma total cholesterol, and moderately decreased plasma apoE. The frequency of new mutations in this sample (1 in 255) is higher than that of a healthy population (1 in 7900). Further screening for common apoE gene variants in individuals at risk for dyslipidemia may reveal abnormal heteroduplex patterns and uncover further mutations in this important lipid-regulating gene.

The association of the apolipoprotein E gene promoter polymorphisms and haplotypes with serum lipid and lipoprotein concentrations

Background: Apolipoprotein E (ApoE) is known to modulate lipoprotein transport and metabolism. The common APOE ɛ2/ɛ3/ɛ4 polymorphism explains part of the variation in plasma cholesterol levels. Polymorphisms of the APOE gene regulatory region are suggested to be involved in explaining variation of lipoprotein levels within the APOE ɛ2/ɛ3/ɛ4 genotypes. Objectives: To study the associations of the APOE gene promoter polymorphisms −219G/T and +113G/C and their haplotypes with serum lipid and lipoprotein concentrations, especially within the most common APOE ɛ3/ɛ3 genotype group. Subjects and methods: From 219 middle-aged Finnish men, APOE genotypes were determined and haplotypes estimated. Plasma lipoproteins were isolated by ultracentrifugation and their lipids were measured. Results: The studied APOE promoter polymorphisms and haplotypes associated with certain lipid variables independently of the APOE ɛ2/ɛ3/ɛ4 genotype. Within the APOE ɛ3/ɛ3 group, both −219G/G and +113G/G genotypes associated statistically significantly with higher levels of very low-density lipoprotein (VLDL) cholesterol, apoB and triglycerides, and tended to associate with lower HDL-cholesterol concentrations than the other genotypes. Compared with the −219T/+113C/ɛ3 haplotype, the more common −219G/+113G/ɛ3 haplotype was found more frequently among the group having high (over median) VLDL-cholesterol and triglyceride concentrations (OR 2.6, p < 0.001 and OR=2.1, p = 0.009, respectively). Conclusions: In addition to the APOE ɛ2/ɛ3/ɛ4 polymorphism, the promoter polymorphisms −219G/T and +113G/C as well as their haplotype modulate lipid and lipoprotein concentrations in middle-aged Finnish men.

ApoE: Crossroads between Alzheimer's Disease and Atherosclerosis

Apolipoprotein E (apoE) is a major constituent of lipoproteins in the plasma and in the brain. There are three common apoE isoforms, termed E2, E3, and E4. By virtue of its ability to bind to lipoprotein receptors, apoE plays a key role in the metabolism of triglyceride-rich lipoproteins in the plasma. Homozygous carriers of apoE2 have an increased risk to develop type III hyperlipoproteinemia, whereas apoE4 is associated with elevated levels of low-density lipoprotein cholesterol. In the brain, apoE is associated with cholesterol-rich lipoproteins and is involved in the transport of cholesterol to neurons. The genetic polymorphism of apoE is among the strongest determinants of the risk and mean age of onset of Alzheimer's disease. The mechanism by which apoE isoforms differentially contribute to disease expression is not known.

The influence of serum apolipoprotein E concentration and polymorphism on serum lipid parameters in hemodialysis patients

Background: Apolipoprotein E (ApoE) polymorphism has been shown to influence serum lipid parameters and ApoE levels in both healthy subjects and hemodialysis (HD) patients. Conversely, ApoE concentration significantly affects serum lipid levels in the general population, independently of ApoE polymorphism, by modulating lipoprotein production, lipolytic conversion, and receptor-mediated clearance. Therefore, studying the effect of ApoE polymorphism on serum lipid levels without taking into account ApoE levels could lead to confounding results. However, such a combined study has not been performed in HD patients to date. Methods: Three hundred one patients without diabetes on long-term maintenance HD therapy and 200 matched healthy subjects were studied. Determination of levels of fasting serum ApoE and other lipid parameters, as well as common ApoE genotypes, was performed in all subjects. Results: HD patients had a significantly lower prevalence of the ɛ4 allele and greater levels of ApoE compared with the control population. ApoE2 allele carriers had significantly lower levels of ApoB and serum total, low-density lipoprotein, and non-high-density lipoprotein cholesterol, as well as increased ApoE levels. When ApoE levels were included in analysis, ApoE levels themselves were proven to be important determinants of serum lipid levels, whereas the effect of ApoE polymorphism became more pronounced. The combination of these 2 factors explains a much greater percentage of the variation in the studied parameters than each factor alone. Conclusion: For the first time, our study provides data to support that ApoE concentration in combination with the ApoE polymorphism significantly influences serum lipid parameters in HD patients.

Maternal apo E genotype is a modifier of the Smith-Lemli-Opitz syndrome

Background: Smith-Lemli-Opitz syndrome (MIM 270400) is an autosomal recessive malformation and mental retardation syndrome that ranges in clinical severity from minimal dysmorphism and mild mental retardation to severe congenital anomalies...

Exploration of multilocus effects in a highly polymorphic gene, the apolipoprotein (APOB) gene, in relation to plasma apoB levels.

A detailed exploration of all the polymorphisms in candidate genes is required to better characterize the relationship between gene variability and complex traits. We propose a novel strategy for investigating the association between a highly polymorphic gene and a phenotype, by combining a multilocus genotype analysis and an haplotype analysis. For the multilocus genotype analysis, a data mining tool--termed DICE (Detection of Informative Combined Effects)--was developed to identify the best subset of polymorphisms that are associated--individually or in combination--with the phenotype. For the haplotype analysis, we used our recently developed method of haplotype-phenotype association to determine the most informative and parsimonious haplotype model fitting the data. We illustrate this strategy by investigating the association between twelve polymorphisms of the APOB gene and plasma apoB levels in 1442 European subjects. After exploring all main effects and interactions between polymorphisms, DICE identified the N4311S polymorphism as the most informative polymorphism in relation to apoB levels. Haplotype analysis led to the same conclusion. Additionally, DICE identified the E4154K (EcoRI) and the T2488T (XbaI) polymorphisms as potentially interesting. This selection was not modified by inclusion of the common APOE polymorphism in the analysis.

Haplotype analysis of the apolipoprotein gene cluster on human chromosome 11

Members of the apolipoprotein gene cluster ( APOA1/C3/A4/A5) on human chromosome 11q23 play an important role in lipid metabolism. Polymorphisms in both APOA5 and APOC3 are strongly associated with plasma triglyceride concentrations. The close genomic locations of these two genes as well as their functional similarity have hindered efforts to define whether each gene independently influences human triglyceride concentrations. In this study, we examined the linkage disequilibrium and haplotype structure of 49 SNPs in a 150-kb region spanning the gene cluster. We identified a total of five common APOA5 haplotypes with a frequency of greater than 8% in samples of northern European origin. The APOA5 haplotype block did not extend past the 7 SNPs in the gene and was separated from the other apolipoprotein gene in the cluster by a region of significantly increased recombination. Furthermore, one previously identified triglyceride risk haplotype of APOA5 ( APOA5*3) showed no association with three APOC3 SNPs previously associated with triglyceride concentrations, in contrast to the other risk haplotype ( APOA5* 2), which was associated with all three minor APOC3 SNP alleles. These results highlight the complex genetic relationship between APOA5 and APOC3 and support the notion that APOA5 represents an independent risk gene affecting plasma triglyceride concentrations in humans.

Apolipoprotein E genotyping in the Malay, Chinese and Indian ethnic groups in Malaysia—a study on the distribution of the different apoE alleles and genotypes

Background: Apolipoprotein E (apoE) is encoded by a polymorphic gene located on chromosome 19. The three common apoE alleles are ε2, ε3 and ε4. We studied the frequencies of the apoE alleles and genotypes in the three ethnic groups—Malay, Chinese and Indian—in Malaysia using DNA amplification followed by agarose gel electrophoresis. Methods: EDTA blood was collected and DNA was extracted using proteinase K–SDS digestion and purified by phenol–chloroform extraction. The apoE gene sequence was amplified using the PCR and apoE genotyping was performed by restriction enzyme digestion with HhaI. Results: Genotyping of the apoE gene produces six genotypes—E2/E2, E2/E3, E3/E3, E2/E4, E3/E4 and E4/E4. The most common apoE genotype in the Malays, Chinese and Indians studied was E3/E3, thus the most common apoE allele was ε3. The three common apoE genotypes were E3/E3 followed by E3/E4 and E2/E3, except in the Indians where E2/E3 was not detected. The three apoE alleles were confirmed in the Malays, Chinese and Indians except for the ε2 allele which was absent in the Indians. Conclusion: The combined frequency of the apoE alleles in the Malays, Chinese and Indians was 0.058, 0.829 and 0.114 for ε2, ε3 and ε4, respectively.

Population genetics of apolipoproteins A-IV, E, and H, and the angiotensin converting enzyme (ACE): associations with lipids, and apolipoprotein levels in American Samoans.

Distributions of alleles at three apolipoprotein loci (APO E, APO H, and APO A-IV) and an insertion/deletion (I/D) polymorphism at the angiotensin converting enzyme (ACE) locus among 274 American Samoans are described here. Genotypes at each locus are examined for associations with quantitative lipid (total cholesterol (total-c), LDL-cholesterol (LDL-c), HDL-cholesterol (HDL-c), and triglycerides) and apolipoprotein (APO AI, APO AII, APO E, and APO B) levels. Genotype frequencies at all four loci are in Hardy-Weinberg equilibrium. The most common APO A-IV genotype (1-1) was observed in 252 American Samoans (97%). The three most common APO E genotypes were 3-3 (47%), 3-4 (30%), and 2-3 (12%). The most frequent APO H genotype was 2-2 (86%). The most common ACE genotype (I/I) was observed in 75% of sampled individuals, and 23% were I/D heterozygotes. APO E genotypic variation was associated with total-c, HDL-c, LDL-c, and all four quantitative apolipoproteins (AI, AII, E, and B). APO A-IV genotypes were associated significantly with total cholesterol, LDL-c, and APO-B levels. APO H showed little association with any quantitative lipid or apolipoprotein. ACE D/D homozygotes had higher AII levels. ACE showed a consistent association with APO AII levels, with either APO A-IV or APO E as a covariate. The interaction term between ACE and APO E was also significantly associated with total-c and APO E levels, and the ACE genotype showed a significant main effect on APO AI levels in multivariate analyses.

The common polymorphism of apolipoprotein E: geographical aspects and new pathophysiological relations.

Apolipoprotein E (apoE) has important functions in systemic and local lipid transport, but also has other functions. The gene (APOE) shows a common polymorphism with three alleles--APOE*2, APOE*3, and APOE*4. Their frequencies vary substantially around the world, but APOE*3 is the most common almost everywhere and is often considered to be the ancestral or "wild-type" allele for that reason. However, there are several arguments for APOE*4 being the ancestral allele. But then, why has APOE*3 become so frequent? And why has APOE*4 not become extinct? The proportion of APOE*4 carriers increases from only 10-15% in southern Europe to 40-50% in the north. The gradient may be a trace of the demic expansion of agriculture that began about 10,000 years ago, but it may also reflect the possibility that APOE*4 carriers are less likely to develop vitamin D deficiency. The common APOE polymorphism is associated with varying risk of cardiovascular disease and Alzheimer's disease, but other interesting aspects may emerge in the future.

Capillary electrophoresis with laser-induced fluorescence detection for fast and reliable apolipoprotein E genotyping

The use of capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection for the rapid determination of apolipoprotein E (apoE) genotypes was studied. High resolution and sensitive detection of the concerned DNA restriction fragments was achieved using CE buffers with hydroxypropylmethylcellulose (HPMC) as sieving polymer and ethidium bromide (EB) as fluorescent intercalating agent. In order to achieve adequate resolutions in short analysis times, parameters such as concentration of HPMC and EB, separation voltage, and length and coating of the capillary were evaluated. Using a separation buffer with 0.8% (w/w) HPMC and 7 μ M EB, characteristic DNA-fragment profiles could be obtained for all common apoE genotypes at an overall rate of ten samples per hour. The method allows direct injection of untreated PCR samples and the use of standard fused-silica capillaries which are effectively coated following a short, one-step rinse procedure. With a simple computerized algorithm based on migration-time ratios for pattern assignment, highly reliable apoE genotyping was achieved. Overall, in terms of speed, ease of use and objectivity the presented method provides a significant improvement over previously reported CE-based procedures for apoE genotyping.

Apolipoprotein E in Apolipoprotein B (apo B)- and Non-apo B-containing Lipoproteins in 3523 Participants in the Stanislas Cohort: Biological Variation and Genotype-specific Reference Limits

Apolipoprotein (apo) E is a component of two major classes of plasma lipoproteins, apo B- (apo E-LpB) and non-apo B-containing (apo E-Lp-non-B) lipoproteins. The factors that affect total apo E in particles [lipoprotein E (LpE), apo E-Lp-non-B, and apo E-LpB], are incompletely characterized. We studied the determinants of these lipoparticles in a sample population of presumably healthy individuals: 1784 children (age range, 8-18 years) and 1739 adults (age range, 19-50 years). Serum concentrations of LpE and apo E-Lp-non-B were measured by electroimmunoassays, and the concentration of apo E-LpB was calculated by a difference method. Serum LpE and apo E-Lp-non-B were higher in females than in males. Their concentrations decreased with age until 20-25 years and then increased in men but not in women. apo E-LpB concentrations increased up to 20-25 years and were similar in both sexes. Thereafter, adult men had higher values than women. Individuals carrying the epsilon2 allele had higher mean apo E-Lp-non-B concentrations and lower apo E-LpB concentrations than did individuals carrying the epsilon3 allele. Individuals with the epsilon4 allele showed an inverse profile compared with those with the epsilon2 allele. Age, gender, the common apo E polymorphism, puberty, serum lipid concentrations, and alcohol consumption were significantly associated with total LpE, apo E-Lp-non-B, and apo E-LpB concentrations. Reference limits were established according to age, gender, and the common apo E polymorphism. Because measurements of LpE, apo E-Lp-non-B, and apo E-LpB concentrations may improve cardiovascular risk assessment, the proposed reference limits will aid interpretation of the results in clinical or therapeutic trials.

ApoE epsilon3-haplotype modulates Alzheimer beta-amyloid deposition in the brain.

ApoE epsilon4 allele increases the risk of late-onset Alzheimer disease (AD) as well as the amount of beta-amyloid deposition in the brain. Because half of AD patients do not have ApoE epsilon4, it is important to search for other determinants of ApoE that modify AD risk. We tested whether the haplotype background of the most common ApoE allele, epsilon3, influences brain amyloid deposition or the risk of neuropathologically verified AD in a population-based sample of elderly Finns. To exclude the effects of ApoE protein polymorphism we focused these analyses on subjects homozygous for epsilon3. Haplotypes were defined using polymorphisms at positions - 491 and -219 of the ApoE promoter and at position +113 of intron-1. We found that epsilon3-haplotypes containing the promoter allele -219T were associated with reduced amyloid deposition and reduced risk of neuropathologically verified AD as compared to epsilon3-haplotypes containing -219G. The functional polymorphism(s) responsible for the haplotypic difference remains to be identified. These results indicate that there is significant allelic variation in the ApoE gene region, which modulates brain amyloid deposition and AD risk, independent of the ApoE protein polymorphism.

IS A POLYMORPHISM OF THE APOLIPOPROTEIN E GENE ASSOCIATED WITH PREECLAMPSIA?

Objective: Apolipoprotein E (apo E) is pivotal in lipid metabolism. In women with preeclampsia, an atherogenic state is observed. We hypothesized that a particular genotype of apo E may be associated with preeclampsia. Methods: Genomic DNA was extracted from 55 normotensive and 49 preeclamptic women (defined according to the American College of Obstetricians and Gynecologists criteria). DNA was amplified by PCR and digested simultaneously by AflIII and HaeII giving profiles identifying all the possible genotypes of apo E. Results: The most common isoform apo E3 was found both for normotensive and preeclamptic women (76% and 85%, respectively). The frequency of apo E2 and E4, which are more atherogenic, was not higher in the preeclamptic population. Conclusion: We were unable to demonstrate that the “atherogenic state” of preeclampsia is associated with a particular genotype of apo E. Familial studies show that shared genetic and environmental factors are involved in lipid variability. However, owing to the diversity of factors contributing to the development of preeclampsia (fetal and paternal genotypes), these data do not allow to rule-out a possible contribution of maternal apo E to preeclampsia.