Chronic stress impairs collateral blood flow recovery in aged mice.

Chronic stress is associated with increased risk of cardiovascular diseases. Aging is also associated with vascular dysfunction. We hypothesize that chronic stress accelerates collateral dysfunction in old mice. Mice were subjected to either chronic social defeat (CSD) or chronic cold stress (CCS). The CSD mice were housed in a box inside an aggressor's cage and exposed to the aggressor. The CCS group was placed in iced water. After chronic stress, mice underwent femoral artery ligation (FAL) and flow recovery was measured. For the CSD group, appearance and use scores of the foot and a behavioral test were performed. CSD impaired collateral flow recovery after FAL. Further, stressed mice had greater ischemic damage, impaired foot function, and altered behavior. The CCS mice also showed impaired collateral flow recovery. Chronic stress causes hind limb collateral dysfunction in old mice, a conclusion reinforced by the fact that two types of stress produced similar changes.

miR-125a-5p impairs endothelial cell angiogenesis in aging mice via RTEF-1 downregulation.

Increasing evidence suggests that microRNAs (miRNAs) play important roles in impaired endothelial cell (EC) angiogenesis during aging. However, their exact roles in the aging process remain unclear. We aimed to determine whether miRNAs cause angiogenesis defects in ECs during aging and to uncover the underlying mechanisms. To study the miRNA-induced changes in ECs during aging, we performed microarray analyses on arterial ECs collected from young and aging mice. Using qRT-PCR, we showed that microRNA-125a-5p (mir-125a-5p) expression was approximately 2.9 times higher in old endothelial cells (OECs) compared with samples collected from young animals. Western blot assays showed a lower expression level of an mir-125a-5p target known as related transcriptional enhancer factor-1 (RTEF-1) in OECs compared with its expression levels in young cells. Overexpression of mir-125a-5p in young endothelial cells (YECs) using pre-mir-125a-5p caused the downregulation of RTEF-1, endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF) and resulted in impaired angiogenesis, as evidenced by spheroid sprouting and tube formation assays in vitro. Conversely, repression of mir-125a-5p in OECs using anti-mir-125a-5p increased RTEF-1, eNOS and VEGF expression and improved EC angiogenesis. Importantly, impaired angiogenesis caused by knock-down of RTEF-1 was not efficiently rescued by anti-mir-125a-5p. Dual-luciferase reporter gene analysis showed that RTEF-1 is a direct target of mir-125a-5p, which regulates angiogenesis by repressing RTEF-1 expression and modulating eNOS and VEGF expression. These findings indicate that mir-125a-5p and RTEF-1 are potential therapeutic targets for improving EC-mediated angiogenesis in elderly individuals.

Platelet neuropeptide Y is critical for ischemic revascularization in mice.

We previously reported that the sympathetic neurotransmitter neuropeptide Y (NPY) is potently angiogenic, primarily through its Y2 receptor, and that endogenous NPY is crucial for capillary angiogenesis in rodent hindlimb ischemia. Here we sought to identify the source of NPY responsible for revascularization and its mechanisms of action. At d 3, NPY(-/-) mice demonstrated delayed recovery of blood flow and limb function, consistent with impaired collateral conductance, while ischemic capillary angiogenesis was reduced (~70%) at d 14. This biphasic temporal response was confirmed by 2 peaks of NPY activation in rats: a transient early increase in neuronally derived plasma NPY and increase in platelet NPY during late-phase recovery. Compared to NPY-null platelets, collagen-activated NPY-rich platelets were more mitogenic (~2-fold vs. ~1.6-fold increase) for human microvascular endothelial cells, and Y2/Y5 receptor antagonists ablated this difference in proliferation. In NPY(+/+) mice, ischemic angiogenesis was prevented by platelet depletion and then restored by transfusion of platelets from NPY(+/+) mice, but not NPY(-/-) mice. In thrombocytopenic NPY(-/-) mice, transfusion of wild-type platelets fully restored ischemia-induced angiogenesis. These findings suggest that neuronally derived NPY accelerates the early response to femoral artery ligation by promoting collateral conductance, while platelet-derived NPY is critical for sustained capillary angiogenesis.

Donor site healing dynamics: molecular, histological, and noninvasive imaging assessment in a porcine model.

Understanding the physiology of donor site healing will lead to advances in how these wounds are treated and may ultimately allow faster healing, more frequent autografting, and more effective care of the burn-injured patient. Unfortunately, a paucity of data exists regarding perfusion metrics over the course of donor site healing. Furthermore, there are no studies that interrelate indices of perfusion with the molecular and cellular processes of donor site healing. Male Duroc pigs were anesthetized and donor site wounds were created using a Zimmer dermatome at a depth of 0.060 inch (1.52 mm). Digital photographs, laser Doppler images, and punch biopsies were obtained before and after excision and on days 2, 4, 7, 9, 11, 14, and 16 until wounds were healed. RNA isolation was performed and quantitative polymerase chain reaction was used to examine differential gene expression over the time course. Formalin-fixed biopsies were embedded in paraffin, sectioned, stained, and examined. Wound surfaces were 83% re-epithelialized by day 16. Perfusion peaked on day 2 then declined, but it remained significantly elevated compared to before excision (P < .05). From day 9 onward, mean perfusion units were not significantly different from baseline (P < .05). Twenty-two representative genes were selected for examination. RNA expression of collagen, tenascin-cytoactin, inflammatory cytokines, remodeling enzymes, growth factors, and Wnt was increased. Inflammatory cells and cytokines were demonstrated histologically. Nuclei per high powered field peaked at day 7 and neodermal thickness increased daily to day 14. A novel porcine model for donor site wound healing that interrelates re-epithelilaizationand perfusion with molecular and cellular indices has been demonstrated.

A new murine model of stress-induced complex atherosclerotic lesions.

The primary purpose of this investigation was to determine whether ApoE(-/-) mice, when subjected to chronic stress, exhibit lesions characteristic of human vulnerable plaque and, if so, to determine the time course of such changes. We found that the lesions were remarkably similar to human vulnerable plaque, and that the time course of lesion progression raised interesting insights into the process of plaque development. Lard-fed mixed-background ApoE(-/-) mice exposed to chronic stress develop lesions with large necrotic core, thin fibrous cap and a high degree of inflammation. Neovascularization and intraplaque hemorrhage are observed in over 80% of stressed animals at 20 weeks of age. Previously described models report a prevalence of only 13% for neovascularization observed at a much later time point, between 36 and 60 weeks of age. Thus, our new stress-induced model of advanced atherosclerotic plaque provides an improvement over what is currently available. This model offers a tool to further investigate progression of plaque phenotype to a more vulnerable phenotype in humans. Our findings also suggest a possible use of this stress-induced model to determine whether therapeutic interventions have effects not only on plaque burden, but also, and importantly, on plaque vulnerability.

Polymorphisms in dipeptidyl peptidase IV gene are associated with the risk of myocardial infarction in patients with atherosclerosis.

BACKGROUND: Dipeptidyl peptidase IV (DPP-IV) is not only important in pancreatic ß-cell regulation but also has proinflammatory actions that can contribute to atherosclerosis progression. Previously, we showed that DPP-IV is co-localized with CD31 (an endothelial cell marker) in the neovessels within the human atherosclerotic plaques. These characteristics of DPP-IV may predispose patients with coronary artery disease (CAD) to plaque rupture and thus to myocardial infarction. The goal of this investigation was to determine whether genetic alterations in DPP-IV predispose to plaque vulnerability and myocardial infarction (MI). METHODS: Between Aug 2004, and March 2007, blood samples of patients (age <60) with angiographically documented CAD were collected. Demographic, clinical, risk factor, and angiographic data were recorded. Eight hundred and seventy five patients of European ancestry with angiographic CAD were divided into those with MI (n=421) and those without (n=454). A genome-wide association study was performed using the Affymetrix 6.0 chip to identify loci that predispose to MI. In the current study we only focused on DPP4 gene to assess the association of single nucleotide polymorphisms (SNPs) in the DPP-IV gene and risk of MI in patients with CAD. For genotyped SNPs, association was tested by logistic regression with significance level of 0.05. Plasma DPP-IV level was measured using a commercial ELISA kit. RESULTS: Average patients' age at diagnosis of CAD was 46.8years for MI group and 50.8 in the non MI group. There was no difference in distribution of traditional risk factors between the two groups. We identified one SNP (rs3788979) that was significantly related to angiographic CAD with MI, vs. without MI (OR: 1.36, p=0.03). The association of the identified SNP to MI risk was not attenuated after adjustment for traditional risk factors. The SNP was associated with lower levels of plasma DPP-IV (p=0.005). Moreover, CAD patients with the major alleles (GG) and no MI had highest plasma DPP-IV levels. (481.6, p=0.002). CONCLUSIONS: A polymorphism in the DPP-IV gene in patients with known CAD may increase the risk of MI. This SNP is associated with decreased plasma DPP4 level in patients with MI.

Plasma HDL cholesterol and risk of myocardial infarction: a mendelian randomisation study.

BACKGROUND: High plasma HDL cholesterol is associated with reduced risk of myocardial infarction, but whether this association is causal is unclear. Exploiting the fact that genotypes are randomly assigned at meiosis, are independent of non-genetic confounding, and are unmodified by disease processes, mendelian randomisation can be used to test the hypothesis that the association of a plasma biomarker with disease is causal. METHODS: We performed two mendelian randomisation analyses. First, we used as an instrument a single nucleotide polymorphism (SNP) in the endothelial lipase gene (LIPG Asn396Ser) and tested this SNP in 20 studies (20,913 myocardial infarction cases, 95,407 controls). Second, we used as an instrument a genetic score consisting of 14 common SNPs that exclusively associate with HDL cholesterol and tested this score in up to 12,482 cases of myocardial infarction and 41,331 controls. As a positive control, we also tested a genetic score of 13 common SNPs exclusively associated with LDL cholesterol. FINDINGS: Carriers of the LIPG 396Ser allele (2·6% frequency) had higher HDL cholesterol (0·14 mmol/L higher, p=8×10(-13)) but similar levels of other lipid and non-lipid risk factors for myocardial infarction compared with non-carriers. This difference in HDL cholesterol is expected to decrease risk of myocardial infarction by 13% (odds ratio [OR] 0·87, 95% CI 0·84-0·91). However, we noted that the 396Ser allele was not associated with risk of myocardial infarction (OR 0·99, 95% CI 0·88-1·11, p=0·85). From observational epidemiology, an increase of 1 SD in HDL cholesterol was associated with reduced risk of myocardial infarction (OR 0·62, 95% CI 0·58-0·66). However, a 1 SD increase in HDL cholesterol due to genetic score was not associated with risk of myocardial infarction (OR 0·93, 95% CI 0·68-1·26, p=0·63). For LDL cholesterol, the estimate from observational epidemiology (a 1 SD increase in LDL cholesterol associated with OR 1·54, 95% CI 1·45-1·63) was concordant with that from genetic score (OR 2·13, 95% CI 1·69-2·69, p=2×10(-10)). INTERPRETATION: Some genetic mechanisms that raise plasma HDL cholesterol do not seem to lower risk of myocardial infarction. These data challenge the concept that raising of plasma HDL cholesterol will uniformly translate into reductions in risk of myocardial infarction. FUNDING: US National Institutes of Health, The Wellcome Trust, European Union, British Heart Foundation, and the German Federal Ministry of Education and Research.

A genome-wide association study identifies LIPA as a susceptibility gene for coronary artery disease.

BACKGROUND: eQTL analyses are important to improve the understanding of genetic association results. We performed a genome-wide association and global gene expression study to identify functionally relevant variants affecting the risk of coronary artery disease (CAD). METHODS AND RESULTS: In a genome-wide association analysis of 2078 CAD cases and 2953 control subjects, we identified 950 single-nucleotide polymorphisms (SNPs) that were associated with CAD at P<10(-3). Subsequent in silico and wet-laboratory replication stages and a final meta-analysis of 21 428 CAD cases and 38 361 control subjects revealed a novel association signal at chromosome 10q23.31 within the LIPA (lysosomal acid lipase A) gene (P=3.7×10(-8); odds ratio, 1.1; 95% confidence interval, 1.07 to 1.14). The association of this locus with global gene expression was assessed by genome-wide expression analyses in the monocyte transcriptome of 1494 individuals. The results showed a strong association of this locus with expression of the LIPA transcript (P=1.3×10(-96)). An assessment of LIPA SNPs and transcript with cardiovascular phenotypes revealed an association of LIPA transcript levels with impaired endothelial function (P=4.4×10(-3)). CONCLUSIONS: The use of data on genetic variants and the addition of data on global monocytic gene expression led to the identification of the novel functional CAD susceptibility locus LIPA, located on chromosome 10q23.31. The respective eSNPs associated with CAD strongly affect LIPA gene expression level, which was related to endothelial dysfunction, a precursor of CAD.

Aging causes collateral rarefaction and increased severity of ischemic injury in multiple tissues.

OBJECTIVE: Aging is a major risk factor for increased ischemic tissue injury. Whether collateral rarefaction and impaired remodeling contribute to this is unknown. We quantified the number and diameter of native collaterals and their remodeling in 3-, 16-, 24-, and 31-month-old mice. METHODS AND RESULTS: Aging caused an "age-dose-dependent" greater drop in perfusion immediately after femoral artery ligation, followed by a diminished recovery of flow and increase in tissue injury. These effects were associated with a decline in collateral number, diameter, and remodeling. Angiogenesis was also impaired. Mechanistically, these changes were not accompanied by reduced recruitment of T cells or macrophages to remodeling collaterals. However, endothelial nitric oxide synthase signaling was dysfunctional, as indicated by increased protein nitrosylation and less phosphorylated endothelial nitric oxide synthase and vasodilator-stimulated phosphoprotein in collateral wall cells. The cerebral circulation exhibited a similar age-dose-dependent loss of collateral number and diameter and increased tortuosity, resulting in an increase in collateral resistance and infarct volume (eg, 6- and 3-fold, respectively, in 24-month-old mice) after artery occlusion. This was not associated with rarefaction of similarly sized arterioles. Collateral remodeling was also reduced. CONCLUSIONS: Our findings demonstrate that aging causes rarefaction and insufficiency of the collateral circulation in multiple tissues, resulting in more severe ischemic tissue injury.

Effects of aging on time course of neovascularization-related gene expression following acute hindlimb ischemia in mice.

BACKGROUND: Molecular analysis of neovascularization related genes by time course in response to ischemia has not been described in the context of aging. We aimed to provide a progressively deeper understanding of how aging compromises neovascularization. METHODS: Young (3-month) and old (18-month) C57Bl mice were subjected to left hindlimb ischemia. Necrosis score was evaluated in calf muscles. Calf muscles, peripheral blood, bone marrow were harvested at different time points. The expressions of matrix metalloproteiniase-9 (MMP9), endothelial nitric oxide synthase (eNOS), vascular endothelial growth factor (VEGF), stromal derived growth factor-1 (SDF1), hypoxia inducible factor-1α (HIF1α), VEGF receptor-1 (Flt1), VEGF receptor-2 (Flk1), angiopoietin-1 (Ang1), CD133, CD26 were detected by RT-PCR or Western blotting. White blood cells were counted in the peripheral blood. Gene expression data were compared by two-way analysis of variance. RESULTS: MMP9, HIF-1α and SDF-1 were more upregulated during acute ischemia in old vs. young mice, reflecting increased ischemia in aging mice. However VEGF and eNOS exhibited lower expression in old vs. young mice, despite greater ischemia intensity. Ang1 and Flk1 showed similar expression in old vs. young mice. MMP9 peaked earlier in peripheral blood in young vs. old mice. Concurrent decreasing CD26 and increasing CD133 expression in aging bone marrow suggest aging impairs progenitor cell mobilization, CONCLUSIONS: Our results indicate that a complex array of defects occur with aging that interfere with optimal neovascularization. These include potential impaired mobilization of progenitor cells to ischemic tissue, decreased levels of eNOS and VEGF and delayed responses to ischemia.

Aging-induced collateral dysfunction: impaired responsiveness of collaterals and susceptibility to apoptosis via dysfunctional eNOS signaling.

Despite positive animal studies, clinical angiogenesis trials have been disappointing, possibly due to risk factors present in humans but usually unexplored in animals. We recently demonstrated aging causes impaired collateral remodeling and collateral dropout; here, we investigate potential mechanisms responsible for these findings. Four-, 10-, and 18-month-C57BL/6J mice were subjected to femoral artery ligation; flow was measured using laser Doppler perfusion imaging. Endothelial nitric oxide synthase (eNOS) and phosphorylated eNOS were measured in calf muscle. Apoptosis was assessed in endothelial (EC) and smooth muscle (SMC) cells isolated from young and old mice. Angiogenesis was measured using a Matrigel plug assay. Lethally irradiated young and old mice received bone marrow cells (BMC) from either young or old donors and were subjected to femoral artery ligation (FAL). BMC mobilization and homing were assessed. Flow recovery was impaired and less eNOS and phosphorylated eNOS was present in older vs. young mice (p < 0.001 and p = 0.015, respectively). ECs and SMCs from older mice were more sensitive to an apoptotic stimulus, but were rescued by NO-enhancing drugs. In older mice, angiogenesis (Matrigel plug assay) was impaired, as was mobilization and homing of BM progenitor cells following FAL. Although both mobilization and homing improved when older mice received BMC transplantation from young donors, flow recovery failed to improve. Aging impairs BMC mobilization and homing, collateral responsiveness to angiogenic stimuli, and increases EC and SMC susceptibility to apoptosis via dysfunctional eNOS signaling. The latter could contribute to impaired remodeling and collateral dropout. These finding identify potential obstacles to therapeutic interventions in elderly patients.

Of mice and men: neuropeptide Y and its receptors are associated with atherosclerotic lesion burden and vulnerability.

Neuropeptide Y (NPY), a sympathetic and platelet-derived vascular mitogen and angiogenic factor, has been implicated in atherosclerosis in animal and human genetic studies. Here we evaluate its association with human and murine atherosclerosis, and assess the role of platelet-derived NPY in lesion vulnerability. NPY immunoreactivity (NPY-ir) was measured in the platelet-poor and platelet-rich (PRP) plasmas, and NPY receptors (mitogenic Y1R and angiogenic Y2 and Y5Rs), CD26/DPPIV (a protease forming Y2/Y5-selective agonist), CD31-positive vascularity, and lesion morphology assessed by histo- and immunocyto-chemistry-in patients with peripheral artery disease (PAD) and healthy volunteers, and in lard-fed ApoE-/- mice. NPY and NPY-R immunostaining was greater in lesions from PAD patients compared to normal vessels of healthy volunteers (p < 0.001), and localized to smooth muscle cells, macrophages, and adventitial/neovascular endothelial cells. CD26/DPPIV staining co-localized with CD31-positive endothelial cells only in atherosclerotic lesions. NPY-ir in PRP (but not plasma) and vascular immunostaining was higher (p < 0.05 and 0.001, respectively) in men (not women) with PAD compared to healthy subjects. A similar gender specificity was observed in mice. PRP NPY-ir levels correlated with lesion area (p = 0.03), necrotic core area, and the necrotic core-to-lesion area ratio (p < 0.01) in male, but not female, mice. Also males with neovascularized lesions had higher PRP NPY-ir levels than those lacking lesion microvessels (p < 0.05). NPY and its Rs are up-regulated in human and murine atherosclerotic lesions suggesting pathogenic role. DPPIV expression by microvascular endothelium in atherosclerotic tissue may shift NPY's affinity toward angiogenic Y2/Y5Rs, and thus enhance angiogenesis and lesion vulnerability. Remarkably, plaque neovascularization was associated with increased NPY-ir in PRP in males but not females, suggesting that platelet NPY may be a novel mediator/marker of lesion vulnerability particularly in males, for reasons that remain to be determined. Both animal and human data suggest that NPY is an important contributor to, and platelet NPY-ir a marker of, atherosclerotic lesion burden and vulnerability but only in males, perhaps due to androgen-dependent up-regulation of NPY, previously shown in rats.

Gender differences affect blood flow recovery in a mouse model of hindlimb ischemia.

Blood flow restoration to ischemic tissue is affected by various risk factors. The aim of this study was to examine gender effects on arteriogenesis and angiogenesis in a mouse ischemic hindlimb model. C57BL/6J mice were subjected to unilateral hindlimb ischemia. Flow recovery was less and hindlimb use impairment was greater in females. No gender difference in vessel number was found at baseline, although 7 days postsurgery females had fewer α-smooth muscle actin-positive vessels in the midpoint of the adductor region. Females had higher hindlimb vascular resistance, were less responsive to vasodilators, and were more sensitive to vasoconstrictors postligation. Western blotting showed that females had higher baseline levels of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS) in the calf, while 7 days postligation males had higher levels of VEGF, eNOS, and phosphorylated vasodilator stimulated phosphoprotein. Females had less angiogenesis in a Matrigel plug assay and less endothelial cell proliferation in vitro. Females have impaired recovery of flow, a finding presumably caused by multiple factors including decreased collateral remodeling, less angiogenesis, impaired vasodilator response, and increased vasoconstrictor activity; our results also suggest the possibility that new collateral formation, from capillaries, is impaired in females.

Large-scale association analysis identifies 13 new susceptibility loci for coronary artery disease.

We performed a meta-analysis of 14 genome-wide association studies of coronary artery disease (CAD) comprising 22,233 individuals with CAD (cases) and 64,762 controls of European descent followed by genotyping of top association signals in 56,682 additional individuals. This analysis identified 13 loci newly associated with CAD at P < 5 × 10⁻8 and confirmed the association of 10 of 12 previously reported CAD loci. The 13 new loci showed risk allele frequencies ranging from 0.13 to 0.91 and were associated with a 6% to 17% increase in the risk of CAD per allele. Notably, only three of the new loci showed significant association with traditional CAD risk factors and the majority lie in gene regions not previously implicated in the pathogenesis of CAD. Finally, five of the new CAD risk loci appear to have pleiotropic effects, showing strong association with various other human diseases or traits.

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.

Pathway-Wide Association Study Implicates Multiple Sterol Transport and Metabolism Genes in HDL Cholesterol Regulation.

Pathway-based association methods have been proposed to be an effective approach in identifying disease genes, when single-marker association tests do not have sufficient power. The analysis of quantitative traits may be benefited from these approaches, by sampling from two extreme tails of the distribution. Here we tested a pathway association approach on a small genome-wide association study (GWAS) on 653 subjects with extremely high high-density lipoprotein cholesterol (HDL-C) levels and 784 subjects with low HDL-C levels. We identified 102 genes in the sterol transport and metabolism pathways that collectively associate with HDL-C levels, and replicated these association signals in an independent GWAS. Interestingly, the pathways include 18 genes implicated in previous GWAS on lipid traits, suggesting that genuine HDL-C genes are highly enriched in these pathways. Additionally, multiple biologically relevant loci in the pathways were not detected by previous GWAS, including genes implicated in previous candidate gene association studies (such as LEPR, APOA2, HDLBP, SOAT2), genes that cause Mendelian forms of lipid disorders (such as DHCR24), and genes expressing dyslipidemia phenotypes in knockout mice (such as SOAT1, PON1). Our study suggests that sampling from two extreme tails of a quantitative trait and examining genetic pathways may yield biological insights from smaller samples than are generally required using single-marker analysis in large-scale GWAS. Our results also implicate that functionally related genes work together to regulate complex quantitative traits, and that future large-scale studies may benefit from pathway-association approaches to identify novel pathways regulating HDL-C levels.

Lack of association between the Trp719Arg polymorphism in kinesin-like protein-6 and coronary artery disease in 19 case-control studies.

OBJECTIVES: We sought to replicate the association between the kinesin-like protein 6 (KIF6) Trp719Arg polymorphism (rs20455), and clinical coronary artery disease (CAD). BACKGROUND: Recent prospective studies suggest that carriers of the 719Arg allele in KIF6 are at increased risk of clinical CAD compared with noncarriers. METHODS: The KIF6 Trp719Arg polymorphism (rs20455) was genotyped in 19 case-control studies of nonfatal CAD either as part of a genome-wide association study or in a formal attempt to replicate the initial positive reports. RESULTS: A total of 17,000 cases and 39,369 controls of European descent as well as a modest number of South Asians, African Americans, Hispanics, East Asians, and admixed cases and controls were successfully genotyped. None of the 19 studies demonstrated an increased risk of CAD in carriers of the 719Arg allele compared with noncarriers. Regression analyses and fixed-effects meta-analyses ruled out with high degree of confidence an increase of ≥2% in the risk of CAD among European 719Arg carriers. We also observed no increase in the risk of CAD among 719Arg carriers in the subset of Europeans with early-onset disease (younger than 50 years of age for men and younger than 60 years of age for women) compared with similarly aged controls as well as all non-European subgroups. CONCLUSIONS: The KIF6 Trp719Arg polymorphism was not associated with the risk of clinical CAD in this large replication study.

Design of the Coronary ARtery DIsease Genome-Wide Replication And Meta-Analysis (CARDIoGRAM) Study: A Genome-wide association meta-analysis involving more than 22 000 cases and 60 000 controls.

BACKGROUND: Recent genome-wide association studies (GWAS) of myocardial infarction (MI) and other forms of coronary artery disease (CAD) have led to the discovery of at least 13 genetic loci. In addition to the effect size, power to detect associations is largely driven by sample size. Therefore, to maximize the chance of finding novel susceptibility loci for CAD and MI, the Coronary ARtery DIsease Genome-wide Replication And Meta-analysis (CARDIoGRAM) consortium was formed. METHODS AND RESULTS: CARDIoGRAM combines data from all published and several unpublished GWAS in individuals with European ancestry; includes >22 000 cases with CAD, MI, or both and >60 000 controls; and unifies samples from the Atherosclerotic Disease VAscular functioN and genetiC Epidemiology study, CADomics, Cohorts for Heart and Aging Research in Genomic Epidemiology, deCODE, the German Myocardial Infarction Family Studies I, II, and III, Ludwigshafen Risk and Cardiovascular Heath Study/AtheroRemo, MedStar, Myocardial Infarction Genetics Consortium, Ottawa Heart Genomics Study, PennCath, and the Wellcome Trust Case Control Consortium. Genotyping was carried out on Affymetrix or Illumina platforms followed by imputation of genotypes in most studies. On average, 2.2 million single nucleotide polymorphisms were generated per study. The results from each study are combined using meta-analysis. As proof of principle, we meta-analyzed risk variants at 9p21 and found that rs1333049 confers a 29% increase in risk for MI per copy (P=2×10⁻²°). CONCLUSION: CARDIoGRAM is poised to contribute to our understanding of the role of common genetic variation on risk for CAD and MI.

Meta-analysis and imputation refines the association of 15q25 with smoking quantity.

Smoking is a leading global cause of disease and mortality. We established the Oxford-GlaxoSmithKline study (Ox-GSK) to perform a genome-wide meta-analysis of SNP association with smoking-related behavioral traits. Our final data set included 41,150 individuals drawn from 20 disease, population and control cohorts. Our analysis confirmed an effect on smoking quantity at a locus on 15q25 (P = 9.45 x 10(-19)) that includes CHRNA5, CHRNA3 and CHRNB4, three genes encoding neuronal nicotinic acetylcholine receptor subunits. We used data from the 1000 Genomes project to investigate the region using imputation, which allowed for analysis of virtually all common SNPs in the region and offered a fivefold increase in marker density over HapMap2 (ref. 2) as an imputation reference panel. Our fine-mapping approach identified a SNP showing the highest significance, rs55853698, located within the promoter region of CHRNA5. Conditional analysis also identified a secondary locus (rs6495308) in CHRNA3.