Additive effect of LRP8/APOER2 R952Q variant to APOE epsilon2/epsilon3/epsilon4 genotype in modulating apolipoprotein E concentration and the risk of myocardial infarction: a case-control study

Interplay of Low-Density Lipoprotein Receptors, LRPs, and Lipoproteins in Pulmonary Hypertension

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LDLR regulates oxidized LDL level, which is increased in lung and blood from PAH patients.

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LRP1 preserving vascular homeostasis is decreased in PAH patients.

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LRP5/6 regulating Wnt signaling is upregulated in PH.

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The LRP8 (aka ApoER2) ligand ApoE protects from PAH.

The low-density lipoprotein receptor (LDLR) gene family includes LDLR, very LDLR, and LDL receptor–related proteins (LRPs) such as LRP1, LRP1b (aka LRP-DIT), LRP2 (aka megalin), LRP4, and LRP5/6, and LRP8 (aka ApoER2). LDLR family members constitute a class of closely related multifunctional, transmembrane receptors, with diverse functions, from embryonic development to cancer, lipid metabolism, and cardiovascular homeostasis. While LDLR family members have been studied extensively in the systemic circulation in the context of atherosclerosis, their roles in pulmonary arterial hypertension (PAH) are understudied and largely unknown. Endothelial dysfunction, tissue infiltration of monocytes, and proliferation of pulmonary artery smooth muscle cells are hallmarks of PAH, leading to vascular remodeling, obliteration, increased pulmonary vascular resistance, heart failure, and death. LDLR family members are entangled with the aforementioned detrimental processes by controlling many pathways that are dysregulated in PAH; these include lipid metabolism and oxidation, but also platelet-derived growth factor, transforming growth factor β1, Wnt, apolipoprotein E, bone morpohogenetic proteins, and peroxisome proliferator-activated receptor gamma. In this paper, we discuss the current knowledge on LDLR family members in PAH. We also review mechanisms and drugs discovered in biological contexts and diseases other than PAH that are likely very relevant in the hypertensive pulmonary vasculature and the future care of patients with PAH or other chronic, progressive, debilitating cardiovascular diseases.

PCSK9 (Proprotein Convertase Subtilisin/Kexin Type 9) Triggers Vascular Smooth Muscle Cell Senescence and Apoptosis: Implication of Its Direct Role in Degenerative Vascular Disease

OBJECTIVE

PCSK9 (proprotein convertase subtilisin/kexin type 9) plays a critical role in cholesterol metabolism via the PCSK9-LDLR (low-density lipoprotein receptor) axis in the liver; however, evidence indicates that PCSK9 directly contributes to the pathogenesis of various diseases through mechanisms independent of its LDL-cholesterol regulation. The objective of this study was to determine how PCSK9 directly acts on vascular smooth muscle cells (SMCs), contributing to degenerative vascular disease. Approach and Results: We first examined the effects of PCSK9 on cultured human aortic SMCs. Overexpression of PCSK9 downregulated the expression of ApoER2 (apolipoprotein E receptor 2), a known target of PCSK9. Treatment with soluble recombinant human ApoER2 or the DNA synthesis inhibitor, hydroxyurea, inhibited PCSK9-induced polyploidization and other cellular responses of human SMCs. Treatment with antibodies against ApoER2 resulted in similar effects to those observed with PCSK9 overexpression. Inducible, SMC-specific knockout of Pcsk9 accelerated neointima formation in mouse carotid arteries and reduced age-related arterial stiffness. PCSK9 was expressed in SMCs of human atherosclerotic lesions and abundant in the "shoulder" regions of vulnerable atherosclerotic plaques. PCSK9 was also expressed in SMCs of abdominal aortic aneurysm, which was inversely related to the expression of smooth muscle α-actin.

CONCLUSIONS

Our findings demonstrate that PCSK9 inhibits proliferation and induces polyploidization, senescence, and apoptosis, which may be relevant to various degenerative vascular diseases.

Lipoprotein receptor signalling in atherosclerosis

The founding member of the lipoprotein receptor family, low-density lipoprotein receptor (LDLR) plays a major role in the atherogenesis through the receptor-mediated endocytosis of LDL particles and regulation of cholesterol homeostasis. Since the discovery of the LDLR, many other structurally and functionally related receptors have been identified, which include low-density lipoprotein receptor-related protein (LRP)1, LRP5, LRP6, very low-density lipoprotein receptor, and apolipoprotein E receptor 2. The scavenger receptor family members, on the other hand, constitute a family of pattern recognition proteins that are structurally diverse and recognize a wide array of ligands, including oxidized LDL. Among these are cluster of differentiation 36, scavenger receptor class B type I and lectin-like oxidized low-density lipoprotein receptor-1. In addition to the initially assigned role as a mediator of the uptake of macromolecules into the cell, a large number of studies in cultured cells and in in vivo animal models have revealed that these lipoprotein receptors participate in signal transduction to modulate cellular functions. This review highlights the signalling pathways by which these receptors influence the process of atherosclerosis development, focusing on their roles in the vascular cells, such as macrophages, endothelial cells, smooth muscle cells, and platelets. Human genetics of the receptors is also discussed to further provide the relevance to cardiovascular disease risks in humans. Further knowledge of the vascular biology of the lipoprotein receptors and their ligands will potentially enhance our ability to harness the mechanism to develop novel prophylactic and therapeutic strategies against cardiovascular diseases.

Apolipoprotein E2 modulates cell cycle function to promote proliferation in pancreatic cancer cells via regulation of the c-Myc–p21Waf1signalling pathway

Apolipoprotein E2 (ApoE2) is reportedly critical for cell proliferation and survival, and has been identified as a potential tumour-associated marker in many kinds of cancer. However, studies of the function and mechanisms of ApoE2 in pancreatic cancer proliferation and development are rare. In this study, we performed an analysis to determine the modulatory effects of ApoE2–LRP8 (lipoprotein receptor-related protein 8) pathway on cell cycle and cell proliferation, and explored its mechanisms in pancreatic cancer. High expression levels of ApoE2–LRP8/c-Myc were detected in tumour tissues and cell lines by immunohistochemistry and Western blotting. It was also shown that ApoE2–LRP8 induced phosphorylation of ERK1/2 to activate c-Myc and contribute to cell-cycle-related protein expression. ApoE2 conditions induced c-Myc binding to target gene sequences in the p21Waf1promoter, resulting in decreased transcription. ERK/c-Myc contributes to the promotion of the expression levels of cyclin D1, cdc2, and cyclin B1, and reduces p21Waf1activity, thereby promoting cell cycle distribution. We demonstrated the function of ApoE2–LRP8 in the activation of the ERK–c-Myc–p21Waf1signalling cascade and the modulation of G1/S and G2/M transition, indicating ApoE2–LRP8’s important role in the cancer cell proliferation. ApoE2 could serve as a diagnostic marker and chemotherapeutic target in pancreatic cancer.

ApoER2 (Apolipoprotein E Receptor-2) Deficiency Accelerates Smooth Muscle Cell Senescence via Cytokinesis Impairment and Promotes Fibrotic Neointima After Vascular Injury

OBJECTIVE

Genome-wide studies showed that mutation in apoER2 (apolipoprotein E receptor-2) is additive with ε4 polymorphism in the APOE gene on cardiovascular disease risk in humans. ApoE or apoER2 deficiency also accelerates atherosclerosis lesion necrosis in hypercholesterolemic mice and promotes neointima formation after vascular injury. This study tests the hypothesis that apoE and apoER2 modulate vascular occlusive diseases through distinct mechanisms. Approach and Results: Carotid endothelial denudation induced robust neointima formation in both apoE-/- and apoER2-deficient Lrp8-/- mice. The intima in apoE-/- mice was rich in smooth muscle cells, but the intima in Lrp8-/- mice was cell-poor and rich in extracellular matrix. Vascular smooth muscle cells isolated from apoE-/- mice were hyperplastic whereas Lrp8-/- smooth muscle cells showed reduced proliferation but responded robustly to TGF (transforming growth factor)-β-induced fibronectin synthesis indicative of a senescence-associated secretory phenotype, which was confirmed by increased β-galactosidase activity, p16INK4a immunofluorescence, and number of multinucleated cells. Western blot analysis of cell cycle-associated proteins showed that apoER2 deficiency promotes cell cycle arrest at the metaphase/anaphase. Coimmunoprecipitation experiments revealed that apoER2 interacts with the catalytic subunit of protein phosphatase 2A. In the absence of apoER2, PP2A-C (protein phosphatase 2A catalytic subunit) failed to interact with CDC20 (cell-division cycle protein 20) thus resulting in inactive anaphase-promoting complex and impaired cell cycle exit.

CONCLUSIONS

This study showed that apoER2 participates in APC (anaphase-promoting complex)/CDC20 complex formation during mitosis, and its absence impedes cytokinesis abscission thereby accelerating premature cell senescence and vascular disease. This mechanism is distinct from apoE deficiency, which causes smooth muscle cell hyperplasia to accelerate vascular disease.

ApoE4: an emerging therapeutic target for Alzheimer's disease

BACKGROUND

The growing body of evidence indicating the heterogeneity of Alzheimer's disease (AD), coupled with disappointing clinical studies directed at a fit-for-all therapy, suggest that the development of a single magic cure suitable for all cases may not be possible. This calls for a shift in paradigm where targeted treatment is developed for specific AD subpopulations that share distinct genetic or pathological properties. Apolipoprotein E4 (apoE4), the most prevalent genetic risk factor of AD, is expressed in more than half of AD patients and is thus an important possible AD therapeutic target.

REVIEW

This review focuses initially on the pathological effects of apoE4 in AD, as well as on the corresponding cellular and animal models and the suggested cellular and molecular mechanisms which mediate them. The second part of the review focuses on recent apoE4-targeted (from the APOE gene to the apoE protein and its interactors) therapeutic approaches that have been developed in animal models and are ready to be translated to human. Further, the issue of whether the pathological effects of apoE4 are due to loss of protective function or due to gain of toxic function is discussed herein. It is possible that both mechanisms coexist, with certain constituents of the apoE4 molecule and/or its downstream signaling mediating a toxic effect, while others are associated with a loss of protective function.

CONCLUSION

ApoE4 is a promising AD therapeutic target that remains understudied. Recent studies are now paving the way for effective apoE4-directed AD treatment approaches.

TG haplotype in the LRP8 is associated with myocardial infarction in south Indian population

Myocardial infarction (MI) is a complex multifactorial cardiovascular disease. India experiences a much greater burden of MI, also suggesting an experimental increase of this burden in the future. The absolute reasons for MI are context dependent and differ with different geographical settings. Several reports indicate that SNPs that are associated with certain diseases in other populations may not be associated with Indian population. It is, therefore, important to validate the association of SNPs. Low density lipoprotein receptor related protein 8 (LRP8) gene plays central role in human lipoprotein metabolism as it facilitates the clearance of bad cholesterol LDL, VLDL from plasma and is reported to be associated with MI in the western population. However, this gene has not been studied in the South Indian population. We aim to test the role of the LRP8 gene variants correlating with the lipid profile in MI patients in South Indian population. We sequenced regions of SNPs rs10788952, rs7546246, rs2297660 and rs5174 of LRP8 in 100 MI patients and 100 age-matched controls. Our result revealed a total of 4 variations. None of the SNPs were significantly associated with MI (p>0.973). Interestingly, haplotype based association analysis showed TG and CG of rs10788952 and rs7546246 significantly associated with MI (p<0.01 and p<0.00005) and in particular, haplotype TG was positively correlated with the risk of MI, as this increased the LDL and total cholesterol level in MI patients in south Indians. Our results suggest that haplotype TG is a risk factor for MI in South Indian population.

New Insights in the Pathophysiology of Antiphospholipid Syndrome

The antiphospholipid syndrome (APS) is an autoimmune disorder characterized by an elevated risk for arterial and venous thrombosis and pregnancy-related morbidity. Since the discovery of the disease in 1980s, numerous studies in cell culture systems, in animal models, and in patient populations have been reported, leading to a deeper understanding of the pathogenesis of APS. These studies have determined that circulating autoantibodies, collectively called antiphospholipid antibodies (aPL), the majority of which recognize cell surface proteins attached to the plasma membrane phospholipids, play a causal role in the development of the disease. The binding of aPL to the cell surface antigens triggers interaction of the complex with transmembrane receptors to initiate intracellular signaling in critical cell types, including platelets, monocytes, endothelial cells, and trophoblasts. Subsequent alteration of various cell functions results in inflammation, thrombus formation, and pregnancy complications. Apolipoprotein E receptor 2 (apoER2), a lipoprotein receptor family member, has been implicated as a mediator for aPL actions in platelets and endothelial cells. Nitric oxide (NO) is a signaling molecule known to exert potent antithrombotic, anti-inflammatory, and anti-atherogenic effects. NO insufficiency and oxidative stress have been linked to APS pathogenesis. This review will focus on the recent findings on how apoER2 and dysregulation of NO production contribute to aPL-mediated pathologies in APS.

Apolipoprotein E levels and apolipoprotein E genotypes in incident cardiovascular disease risk in subjects of the Prevention of Renal and Vascular End-stage disease study

BACKGROUND

Apolipoprotein E (apoE) is a component of all major lipoprotein classes with multiple functions including clearance of circulating triglyceride-rich lipoprotein particles and hepatic production of triglyceride-rich lipoprotein, thus affording several avenues for apoE involvement in atherosclerosis development. ApoE has 3 isoforms (E2, E3, and E4) based on a common genetic polymorphism. Numerous studies have been performed assessing cardiovascular disease (CVD) risk relative to the 6 resulting genotypes; however, surprisingly, few studies have been performed assessing risk attributable to apoE plasma levels either alone or in addition also taking into account apoE genotypes.

OBJECTIVE

To examine the role of apoE levels together with apoE genotypes on incident CVD risk in a large population-based cohort and also to afford preliminary characterization of atherogenic apoE-containing lipoprotein particles.

METHODS

Cox multivariable proportional hazards modeling was performed on a cohort of the Prevention of Renal and Vascular End-Stage Disease (PREVEND) study as a function of apoE levels and apoE genotypes adjusted for age, gender, and past history of CVD. Further modeling was performed with single addition of clinical and biomarker parameters to elucidate the nature of apoE-associated risk.

RESULTS

High apoE levels were demonstrated to be associated with CVD risk (hazard ratio per apoE standard deviation, 1.20; 95% confidence interval, 1.11-1.31; P < .0001) both overall and within the high-frequency apoE genotype groups (ε2ε3, ε3ε3, and ε3ε4). Only on addition of apoB-containing lipoprotein parameters to models, did apoE levels lose association with risk.

CONCLUSIONS

ApoE levels positively associate with incident CVD risk with apoE-associated risk likely residing in apoB-containing lipoproteins.

APOE and LDLR Gene Polymorphisms and Dyslipidemia Tracking. Rio de Janeiro Study

BACKGROUND

Studies show an association between changes in apolipoprotein E (ApoE) and LDLR receptor with the occurrence of dyslipidemia.

OBJECTIVES

To investigate the association between polymorphisms of the APOE (ε2, ε3, ε4) and LDLR (A370T) genes with the persistence of abnormal serum lipid levels in young individuals followed up for 17 years in the Rio de Janeiro Study.

METHODS

The study included 56 individuals (35 males) who underwent three assessments at different ages: A1 (mean age 13.30 ± 1.53 years), A2 (22.09 ± 1.91 years) and A3 (31.23 ± 1.99 years). Clinical evaluation with measurement of blood pressure (BP) and body mass index (BMI) was conducted at all three assessments. Measurement of waist circumference (WC) and serum lipids, and analysis of genetic polymorphisms by PCR-RFLP were performed at A2 and A3. Based on dyslipidemia tracking, three groups were established: 0 (no abnormal lipid value at A2 and A3), 1 (up to one abnormal lipid value at A2 or A3) and 2 (one or more abnormal lipid values at A2 and A3).

RESULTS

Compared with groups 0 and 1, group 2 presented higher mean values of BP, BMI, WC, LDL-c and TG (p < 0.01) and lower mean values of HDL-c (p = 0.001). Across the assessments, all individuals with APOE genotypes ε2/ε4 and ε4/ε4 maintained at least one abnormal lipid variable, whereas those with genotype ε2/ε3 did not show abnormal values (χ2 = 16.848, p = 0.032). For the LDLR genotypes, there was no significant difference among the groups.

CONCLUSIONS

APOE gene polymorphisms were associated with dyslipidemia in young individuals followed up longitudinally from childhood.

Genetic variants of ApoE and ApoER2 differentially modulate endothelial function

It is poorly understood why there is greater cardiovascular disease risk associated with the apolipoprotein E4 (apoE) allele vs. apoE3, and also greater risk with the LRP8/apolipoprotein E receptor 2 (ApoER2) variant ApoER2-R952Q. Little is known about the function of the apoE-ApoER2 tandem outside of the central nervous system. We now report that in endothelial cells apoE3 binding to ApoER2 stimulates endothelial NO synthase (eNOS) and endothelial cell migration, and it also attenuates monocyte-endothelial cell adhesion. However, apoE4 does not stimulate eNOS or endothelial cell migration or dampen cell adhesion, and alternatively it selectively antagonizes apoE3/ApoER2 actions. The contrasting endothelial actions of apoE4 vs. apoE3 require the N-terminal to C-terminal interaction in apoE4 that distinguishes it structurally from apoE3. Reconstitution experiments further reveal that ApoER2-R952Q is a loss-of-function variant of the receptor in endothelium. Carotid artery reendothelialization is decreased in ApoER2(-/-) mice, and whereas adenoviral-driven apoE3 expression in wild-type mice has no effect, apoE4 impairs reendothelialization. Moreover, in a model of neointima formation invoked by carotid artery endothelial denudation, ApoER2(-/-) mice display exaggerated neointima development. Thus, the apoE3/ApoER2 tandem promotes endothelial NO production, endothelial repair, and endothelial anti-inflammatory properties, and it prevents neointima formation. In contrast, apoE4 and ApoER2-R952Q display dominant-negative action and loss of function, respectively. Thus, genetic variants of apoE and ApoER2 impact cardiovascular health by differentially modulating endothelial function.

Meta-analysis of apolipoprotein E gene polymorphism and susceptibility of myocardial infarction

A number of case-control studies have been conducted to clarify the association between ApoE polymorphisms and myocardial infarction (MI); however, the results are inconsistent. This meta-analysis was performed to clarify this issue using all the available evidence. Searching in PubMed retrieved all eligible articles. A total of 33 studies were included in this meta-analysis, including 18752 MI cases and 18963 controls. The pooled analysis based on all included studies showed that the MI patients had a decreased frequency of the ε2 allele (OR = 0.78, 95% CI = 0.70–0.87) and an increased frequency of the ε4 allele (OR = 1.15, 95% CI = 1.10–1.20); The results also showed a decreased susceptibility of MI in the ε2ε3 vs. ε3ε3 analysis (OR = 0.79, 95% CI = 0.68–0.90) and in the ε2 vs. ε3 analysis (OR = 0.78, 95% CI = 0.69–0.89), an increased susceptibility of MI in the ε3ε4 vs. ε3ε3 analysis (OR = 1.26, 95% CI = 1.12–1.41), in the ε4 vs. ε3 analysis (OR = 1.22, 95% CI = 1.12–1.32) and in the ε4ε4 vs. ε3ε3 analysis (OR = 1.59, 95% CI = 1.15–2.19). However, there were no significant associations among polymorphisms and MI for the following genetic models: frequency of the ε3 allele (OR = 0.99, 95% CI = 0.96–1.02); ε2ε2 vs. ε3ε3 analysis (OR = 0.73, 95% CI = 0.40–1.32); or ε2ε4 vs. ε3ε3 analysis (OR = 1.10, 95% CI = 0.99–1.21). Our results suggested that the ε4 allele of ApoE is a risk factor for the development of MI and the ε2 allele of ApoE is a protective factor in the development of MI.

A novel molecular diagnostic marker for familial and early-onset coronary artery disease and myocardial infarction in the LRP8 gene

BACKGROUND

Many single-nucleotide polymorphisms have been associated with coronary artery disease (CAD)/myocardial infarction (MI) by genome-wide association studies, but the diagnostic value of these variants is limited. Functional single-nucleotide polymorphism R952Q in LRP8 is associated with familial and early-onset CAD/MI. The objective of this study is to test whether fine mapping and haplotype analysis for single-nucleotide polymorphisms flanking R952Q may identify a haplotype that may serve as a molecular diagnostic marker for familial and early-onset CAD/MI.

METHODS AND RESULTS

Five single-nucleotide polymorphisms (rs7546246, rs2297660, rs3737983, R952Q, and rs5177) were genotyped and analyzed in GeneQuest (381 patients with familial, early-onset CAD and 183 patients with MI versus 560 controls) and the Italian population (248 patients with familial MI versus 308 controls). One novel risk haplotype, TACGC, was found only in patients with CAD and MI but not in controls. It was significantly associated with CAD (P=7.4×10(-7)) and MI (P=2.2×10(-9)) in GeneQuest. The finding was replicated in the Italian cohort (P=0.041). Sib-transmission disequilibrium test analysis showed a significant association between haplotype TACGC and CAD in GeneQuest II (P=0.039). Haplotype TACGC was not present in a South Korean population of 611 patients with CAD and 294 normal controls. TACGC/TACGC homozygotes tended to develop CAD/MI earlier and showed higher low-density lipoprotein cholesterol levels than heterozygotes (P<0.05).

CONCLUSIONS

The rare haplotype TACGC in LRP8 confers a significant risk of familial, early-onset CAD/MI. Because the risk haplotype exists only in patients with familial and early-onset CAD/MI, we propose that it may be a molecular diagnostic marker for diagnosis of familial, early-onset CAD/MI in some white populations.

Apolipoprotein E receptor-2 deficiency enhances macrophage susceptibility to lipid accumulation and cell death to augment atherosclerotic plaque progression and necrosis

Genome-wide association studies have linked LRP8 polymorphisms to premature coronary artery disease and myocardial infarction in humans. However, the mechanisms by which dysfunctions of apolipoprotein E receptor-2 (apoER2), the protein encoded by LRP8 gene, influence atherosclerosis have not been elucidated completely. The current study focused on the role of apoER2 in macrophages, a cell type that plays an important role in atherosclerosis. Results showed that apoER2-deficient mouse macrophages accumulated more lipids and were more susceptible to oxidized LDL (oxLDL)-induced death compared to control cells. Consistent with these findings, apoER2 deficient macrophages also displayed defective serum-induced Akt activation and higher levels of the pro-apoptotic protein phosphorylated p53. Furthermore, the expression and activation of peroxisome proliferator-activated receptor γ (PPARγ) were increased in apoER2-deficient macrophages. Deficiency of apoER2 in hypercholesterolemic LDL receptor-null mice (Lrp8(-/-)Ldlr(-/-) mice) also resulted in accelerated atherosclerosis with more complex lesions and extensive lesion necrosis compared to Lrp8(+/+)Ldlr(-/-) mice. The atherosclerotic plaques of Lrp8(-/-)Ldlr(-/-) mice displayed significantly higher levels of p53-positive macrophages, indicating that the apoER2-deficient macrophages contribute to the accelerated atherosclerotic lesion necrosis observed in these animals. Taken together, this study indicates that apoER2 in macrophages limits PPARγ expression and protects against oxLDL-induced cell death. Thus, abnormal apoER2 functions in macrophages may at least in part contribute to the premature coronary artery disease and myocardial infarction in humans with LRP8 polymorphisms. Moreover, the elevated PPARγ expression in apoER2-deficient macrophages suggests that LRP8 polymorphism may be a genetic modifier of cardiovascular risk with PPARγ therapy.

Multi-allelic haplotype association identifies novel information different from single-SNP analysis: a new protective haplotype in the LRP8 gene is against familial and early-onset CAD and MI

Our previous studies identified a functional SNP, R952Q in the LRP8 gene, that was associated with increased platelet activation and familial and early-onset coronary artery disease (CAD) and myocardial infarction (MI) in American and Italian Caucasian populations. In this study, we analyzed four additional SNPs near R952Q (rs7546246, rs2297660, rs3737983, rs5177) to identify a specific LRP8 SNP haplotype that is associated with familial and early-onset CAD and MI. We employed a case-control association design involving 381 premature CAD and MI probands and 560 controls in GeneQuest, 441 individuals from 22 large pedigrees in GeneQuest II, and 248 MI patients with family history and 308 controls in an Italian cohort. Like R952Q, LRP8 SNPs rs7546246, rs2297660, rs3737983, and rs5177 were significantly associated with early-onset CAD/MI in both population-based and family-based association studies in GeneQuest. The results were replicated in the GeneQuest II family-based population and the Italian population. We then carried out a haplotype analysis for all five SNPs including R952Q. One common haplotype (TCCGC) was significantly associated with CAD (P=4.0×10(-11)) and MI (P=6.5×10(-12)) in GeneQuest with odds ratios of 0.53 and 0.42, respectively. The results were replicated in the Italian cohort (P=0.004, OR=0.71). The sib-TDT analysis also showed significant association between the TCCGC haplotype and CAD in GeneQuest II (P=0.001). These results suggest that a common LRP8 haplotype TCCGC confers a significant protective effect on the development of familial, early-onset CAD and/or MI.

Identification of a functional apolipoprotein E promoter polymorphism regulating plasma apolipoprotein E concentration

OBJECTIVE

There is compelling evidence that the plasma apolipoprotein E (APOE) concentration, in addition to the APOE ε2/ε3/ε4 genotype, influences plasma lipoprotein levels, but the functional genetic variants influencing the plasma APOE concentration have not been identified.

APPROACH AND RESULTS

Genome-wide association studies in 2 cohorts of healthy, middle-aged subjects identified the APOE locus as the only genetic locus showing robust associations with the plasma APOE concentration. Fine-mapping of the APOE locus confirmed that the rs7412 ε2-allele is the primary genetic variant responsible for the relationship with plasma APOE concentration. Further mapping of the APOE locus uncovered that rs769446 (-427T/C) in the APOE promoter is independently associated with the plasma APOE concentration. Expression studies in 199 human liver samples demonstrated that the rs769446 C-allele is associated with increased APOE mRNA levels (P=0.015). Transient transfection studies and electrophoretic mobility shift assays in human hepatoma HepG2 cells corroborated the role of rs769446 in transcriptional regulation of APOE. However, no relationships were found between rs769446 genotype and plasma lipoprotein levels in 2 cohorts (n=1648 and n=1039) of healthy middle-aged carriers of the APOE ε3/ε3 genotype.

CONCLUSIONS

rs769446 is a functional polymorphism involved in the regulation of the plasma APOE concentration.

The cloning, characterization, and expression profiling of the LRP8 gene in duck (Anas platyrhynchos)

Low-density lipoprotein receptor-related protein 8 (LRP8) is a member of the low-density lipoprotein receptor gene family that functions in body lipoprotein homeostasis. In this study, reverse transcription-polymerase chain reaction, rapid amplification of cDNA ends, and real-time PCR were performed to characterize the duck LRP8 gene. The cDNA of duck LRP8 contained a 14-bp 5' UTR, a 2754-bp open reading frame, and a 189-bp 3' UTR. The duck LRP8 encoded a protein of 917 amino acid residues composed of five functional domains and resembling other members of the LDLR family, and it displayed high nucleotide and amino acid homology to the LRP8 sequences in other avian species. The mRNA expression level of LRP8 was greater in duck extra-hepatic adipose tissue than in the liver. The peak expression values of LRP8 in both liver and adipose tissues occurred at week 1 and were significantly higher than the values observed during any other week (p < 0.05). Differences in the expression patterns of LRP8 mRNA from weeks 2 to 8 of growth were observed in different organs. A consistent low expression was observed in the liver, and fluctuating expression was observed in the subcutaneous adipose tissue (up- and then down-regulated) and abdominal adipose tissue (down-, then up-, then down-regulated). These findings suggest that LRP8 might play more important roles in regulating lipid metabolism in extra-hepatic adipose tissues than in the liver during early growth after hatching in the duck.

Identification of ADAMTS7 as a novel locus for coronary atherosclerosis and association of ABO with myocardial infarction in the presence of coronary atherosclerosis: two genome-wide association studies

BACKGROUND

We tested whether genetic factors distinctly contribute to either development of coronary atherosclerosis or, specifically, to myocardial infarction in existing coronary atherosclerosis.

METHODS

We did two genome-wide association studies (GWAS) with coronary angiographic phenotyping in participants of European ancestry. To identify loci that predispose to angiographic coronary artery disease (CAD), we compared individuals who had this disorder (n=12,393) with those who did not (controls, n=7383). To identify loci that predispose to myocardial infarction, we compared patients who had angiographic CAD and myocardial infarction (n=5783) with those who had angiographic CAD but no myocardial infarction (n=3644).

FINDINGS

In the comparison of patients with angiographic CAD versus controls, we identified a novel locus, ADAMTS7 (p=4·98×10(-13)). In the comparison of patients with angiographic CAD who had myocardial infarction versus those with angiographic CAD but no myocardial infarction, we identified a novel association at the ABO locus (p=7·62×10(-9)). The ABO association was attributable to the glycotransferase-deficient enzyme that encodes the ABO blood group O phenotype previously proposed to protect against myocardial infarction.

INTERPRETATION

Our findings indicate that specific genetic predispositions promote the development of coronary atherosclerosis whereas others lead to myocardial infarction in the presence of coronary atherosclerosis. The relation to specific CAD phenotypes might modify how novel loci are applied in personalised risk assessment and used in the development of novel therapies for CAD.

FUNDING

The PennCath and MedStar studies were supported by the Cardiovascular Institute of the University of Pennsylvania, by the MedStar Health Research Institute at Washington Hospital Center and by a research grant from GlaxoSmithKline. The funding and support for the other cohorts contributing to the paper are described in the webappendix.