Blood Pressure Genome-wide Association Study Research Articles

Unveiling blood pressure-associated genes in aortic cells through integrative analysis of GWAS and RNA modification-associated variants.

Genome-wide association studies (GWAS) have identified more than a thousand loci for blood pressure (BP). Functional genes in these loci are cell-type specific. The aim of this study was to elucidate potentially functional genes associated with BP in the aorta through the utilization of RNA modification-associated single-nucleotide polymorphisms(RNAm-SNPs). Utilizing large-scale genetic data of 757,601 individuals from the UK Biobank and International Consortium of Blood Pressureconsortium, we identified associations between RNAm-SNPs and BP. The association between RNAm-SNPs, gene expression, and BP were examined. A total of 355 RNAm-SNPs related to m6A, m1A, m5C, m7G, and A-to-I modification were associated with BP. The related genes were enriched in the pancreatic secretion pathway and renin secretion pathway. The BP GWAS signals were significantly enriched with m6A-SNPs, highlighting the potential functional relevance of m6A in physiological processes influencing BP. Notably, m6A-SNPs in CYP11B1, PDE3B, HDAC7, ACE, SLC4A7, PDE1A, FRK, MTHFR, NPPA, CACNA1D, and HDAC9 were identified. Differential methylation and differential expression of the BP genes in FTO-overexpression and METTL14-knockdown vascular smooth muscle cells were detected. RNAm-SNPs were associated with ascending and descending aorta diameter and the genes showed differential methylation between aortic dissection (AD) cases and controls. In scRNA-seq study, we identified ARID5A, HLA-DPB1, HLA-DRA, IRF1, LINC01091, MCL1, MLF1, MLXIPL, NAA16, NADK, RERG, SRM, and USP53 as differential expression genes for AD in aortic cells. The present study identified RNAm-SNPs in BP loci and elucidated the associations between the RNAm-SNPs, gene expression, and BP. The identified BP-associated genes in aortic cells were associated with AD.

Multi-ancestry genetic analysis of gene regulation in coronary arteries prioritizes disease risk loci

Genome-wide association studies (GWASs) have identified hundreds of risk loci for coronary artery disease (CAD). However, non-European populations are underrepresented in GWASs, and the causal gene-regulatory mechanisms of these risk loci during atherosclerosis remain unclear. We incorporated local ancestry and haplotypes to identify quantitative trait loci for expression (eQTLs) and splicing (sQTLs) in coronary arteries from 138 ancestrally diverse Americans. Of 2,132 eQTL-associated genes (eGenes), 47% were previously unreported in coronary artery; 19% exhibited cell-type-specific expression. Colocalization revealed subgroups of eGenes unique to CAD and blood pressure GWAS. Fine-mapping highlighted additional eGenes, including TBX20 and IL5. We also identified sQTLs for 1,690 genes, among which TOR1AIP1 and ULK3 sQTLs demonstrated the importance of evaluating splicing to accurately identify disease-relevant isoform expression. Our work provides a patient-derived coronary artery eQTL resource and exemplifies the need for diverse study populations and multifaceted approaches to characterize gene regulation in disease processes.

Genetically Predicted Blood Pressure and Cognition in Midlife: A UK Biobank Study.

This UK Biobank study uses a mendelian randomization approach to mitigate the variability and confounding that has affected previous analyses of the relationship between measured blood pressure (BP) and cognition and thus delineate the true association between the two. Systolic BP (SBP) and diastolic BP polygenic risk scores (PRSs) were calculated using summary statistics from the International Consortium of Blood Pressure-Genome Wide Association Study (n=299 024). Adjusted nonlinear mixed-effects regression models were used, including a natural splines term for BP-PRS with outcomes of fluid intelligence, reaction time (RT), and composite attention score. Moderating effects of age, sex, and antihypertensive use were assessed in separate models. There were 448 575 participants (mean age, 56.3 years; age range, 37-72 years) included in the analysis after genetic and neurological disease exclusions. Genetic propensity for high SBP had an approximately linear association with worsened fluid intelligence (P=0.0018). This relationship was significantly moderated by age (P<0.0001). By contrast, genetic propensity for high and low SBP and diastolic BP predicted worse attention function (P=0.0099 and P=0.0019), with high PRSs predicting worse function than low PRSs. Genetic propensity for low SBP and diastolic BP was associated with considerably worse RTs, while for high SBP-PRSs, the RT plateaued (P<0.0001). The relationships between RT and the PRSs were significantly moderated by sex (P<0.0001) and antihypertensive use (P<0.0001). Genetic propensity for high and low BP impacts on midlife cognition in subtle ways and differentially affects cognitive domains. While a genetic propensity to low BP may preserve nontimed tests in midlife, it may come at a trade-off with worsened attention scores and RT.

Trimethylamine N-oxide and its precursors in relation to blood pressure: A mendelian randomization study.

ObjectivePrevious studies have demonstrated that trimethylamine N-oxide (TMAO) and its precursors, including choline, betaine, and carnitine, are closely associated with blood pressure (BP) changes. Nevertheless, with the limitation of reverse causality and confounder in observational studies, such a relationship remains unclear. We aimed to assess the causal relationship of TMAO and its precursors with BP by the Mendelian Randomization (MR) approach.MethodIn this study, two-sample MR was used to reveal the causal effect of TMAO and its precursors on BP. Pooled data of TMAO and its precursors was from genome-wide association studies (GWAS) which includes summary data of human metabolome in 2,076 European participants from Framingham Heart Study. Summary-level data for BP was extracted from the International Consortium of Blood Pressure-Genome Wide Association Studies. Inverse variance weighted (IVW), MR Egger regression, Maximum likelihood, Weighted median, and MR pleiotropy residual sum and outlier test (MR-PRESSO) were used in this MR analysis.ResultsA total of 160 independent SNP loci were associated with TMAO and three precursors, including 58 associated with TMAO, 29 associated with choline, 44 associated with betaine, and 29 associated with carnitine, were selected. MR results suggested that a 1 unit increase in TMAO should be associated with a 1SD increase in systolic BP mmHg (beta: 0.039, SE, 0.072, p = 0.020). Additionally, our findings also indicated that a 1 unit increase in carnitine should be associated with a 1SD increase in systolic BP mmHg (beta: 0.055, SE: 0.075, p = 0.039). This result was also confirmed by sensitivity analysis methods such as Maximum likelihood, MR-PRESSO, and Weighted median. No effects of betaine or choline on systolic or diastolic BP were observed in the present study.ConclusionOur study provides evidence of a causal relationship of TMAO and its precursors with BP, suggesting that mediating the generation of TMAO would be beneficial for lowering BP.

Examining Individual and Synergistic Contributions of PTSD and Genetics to Blood Pressure: A Trans-Ethnic Meta-Analysis.

Growing research suggests that posttraumatic stress disorder (PTSD) may be a risk factor for poor cardiovascular health, and yet our understanding of who might be at greatest risk of adverse cardiovascular outcomes after trauma is limited. In this study, we conducted the first examination of the individual and synergistic contributions of PTSD symptoms and blood pressure genetics to continuous blood pressure levels. We harnessed the power of the Psychiatric Genomics Consortium-PTSD Physical Health Working Group and investigated these associations across 11 studies of 72,224 trauma-exposed individuals of European (n = 70,870) and African (n = 1,354) ancestry. Genetic contributions to blood pressure were modeled via polygenic scores (PGS) for systolic blood pressure (SBP) and diastolic blood pressure (DBP) that were derived from a prior trans-ethnic blood pressure genome-wide association study (GWAS). Results of trans-ethnic meta-analyses revealed significant main effects of the PGS on blood pressure levels [SBP: β = 2.83, standard error (SE) = 0.06, p < 1E-20; DBP: β = 1.32, SE = 0.04, p < 1E-20]. Significant main effects of PTSD symptoms were also detected for SBP and DBP in trans-ethnic meta-analyses, though there was significant heterogeneity in these results. When including data from the largest contributing study – United Kingdom Biobank – PTSD symptoms were negatively associated with SBP levels (β = −1.46, SE = 0.44, p = 9.8E-4) and positively associated with DBP levels (β = 0.70, SE = 0.26, p = 8.1E-3). However, when excluding the United Kingdom Biobank cohort in trans-ethnic meta-analyses, there was a nominally significant positive association between PTSD symptoms and SBP levels (β = 2.81, SE = 1.13, p = 0.01); no significant association was observed for DBP (β = 0.43, SE = 0.78, p = 0.58). Blood pressure PGS did not significantly moderate the associations between PTSD symptoms and blood pressure levels in meta-analyses. Additional research is needed to better understand the extent to which PTSD is associated with high blood pressure and how genetic as well as contextual factors may play a role in influencing cardiovascular risk.

KIDNEY DNA METHYLATION AS A DRIVER OF HERITABLE PREDISPOSITION TO BLOOD PRESSURE AND HYPERTENSION

Objective: We aim to bridge the knowledge gap between “sequence” (discoveries from genome-wide association study (GWAS)) and “consequence” (human hypertension) by illuminating the effects of blood pressure (BP)-associated genetic variants on molecular targets operating at epigenome in the renal tissue. Design and method: We conducted cis-methylation quantitative trait loci (mQTL) analysis on methylation data from 374,826 CpGs in 195 human kidney samples. Based on the intersection between blood pressure variants from all previous GWAS and mQTLs, we performed a colocalisation analysis to explore whether the overlapping BP GWAS and kidney cis-mQTL signals track the same genetic variant. We then used Mendelian randomisation (MR) to investigate the causal effects of renal methylation signals on BP-defining traits. Results: Through examination of the effects of 821 common BP GWAS variants on kidney CpG site methylation in a unique collection of 195 human kidneys, we identified 578 kidney genes as kidney CpG site partners for the BP GWAS variants. For 54% of BP GWAS kidney mGenes, the CpG signal was proximal to the transcription start site (distance &lt; 1500 bp). For example, cg04510874 (the CpG partner of rs4932373 BP GWAS kidney mSNP) mapped onto a CpG island and the promoter sequence of FES (a target for naproxen – a non-steroidal anti-inflammatory medication with high BP known as one of its side effects). The extent of methylation at this CpG site and the renal expression of FES showed opposite directions of association with the rs4932373 genotype. Colocalisation and Mendelian randomisation analyses revealed a total of 99 unique genes with a causal link to BP through kidney DNA methylation. Conclusions: Through integration of DNA methylation data from a large collection of human kidney samples we colocalised GWAS association and cis-mQTL signals in known BP GWAS loci and uncovered 99 kidney genes with a causal effect on BP, that acts through DNA methylation.

The relationship between blood pressure and risk of atrial fibrillation: a Mendelian randomization study.

Observational studies suggest elevated blood pressure (BP) as the leading risk factor for incident atrial fibrillation (AF), but whether this relationship is causal remains unknown. In this study, we used Mendelian randomization (MR) to investigate the potential causal association of BP levels with the risk of developing AF. Genetic variants associated with the BP traits were retrieved from the International Consortium of Blood Pressure-Genome Wide Association Studies (N = 299024). From 901 reported variants, 894 were assessed in a dedicated Genome-Wide Association Study of AF genetics, including >1000000 subjects of European ancestry. We used two-sample MR analyses to examine the potential causal association of systolic BP (SBP) and diastolic BP (DBP) as well as of pulse pressure (PP) with AF. MR analysis identified a potentially causal association between AF and SBP [odds ratio (OR): 1.018 per 1 mmHg increase, 95% confidence interval (CI): 1.012-1.024, P < 0.001], DBP (OR: 1.026, 95% CI: 1.016-1.035, P < 0.001), and PP (OR: 1.014, 95% CI: 1.001-1.028, P = 0.033). These findings were robust in sensitivity analyses, including the MR-Egger method and the MR pleiotropy residual sum and outlier test (MR-PRESSO). The causal relationship of BP and AF did not change when single-nucleotide polymorphisms associated with possible confounders (i.e. coronary artery disease and obesity) of the causal relationship were excluded. The association between increased BP levels and the risk of AF is likely causal and applies for different BP indices. Independently from other risk factors, optimal BP control might represent an important therapeutic target for AF prevention in the general population.

Blood Pressure Genetic Risk Score Predicts Blood Pressure Responses to Dietary Sodium and Potassium: The GenSalt Study (Genetic Epidemiology Network of Salt Sensitivity).

We examined the association between genetic risk score (GRS) for blood pressure (BP), based on single nucleotide polymorphisms identified in previous BP genome-wide association study meta-analyses, and salt and potassium sensitivity of BP among participants of the GenSalt study (Genetic Epidemiology Network of Salt Sensitivity). The GenSalt study was conducted among 1906 participants who underwent a 7-day low-sodium (51.3 mmol sodium/d), 7-day high-sodium (307.8 mmol sodium/d), and 7-day high-sodium plus potassium (60 mmol potassium/d) intervention. BP was measured 9× at baseline and at the end of each intervention period using a random zero sphygmomanometer. Associations between systolic BP (SBP), diastolic BP, and mean arterial pressure GRS and respective SBP, diastolic BP, and mean arterial pressure responses to the dietary interventions were assessed using mixed linear regression models that accounted for familial dependencies and adjusted for age, sex, field center, body mass index, and baseline BP. As expected, baseline SBP, diastolic BP, and mean arterial pressure significantly increased per quartile increase in GRS (P=2.7×10-8, 9.8×10-8, and 6.4×10-6, respectively). In contrast, increasing GRS quartile conferred smaller SBP, diastolic BP, and mean arterial pressure responses to the low-sodium intervention (P=1.4×10-3, 0.02, and 0.06, respectively) and smaller SBP responses to the high-sodium and potassium interventions (P=0.10 and 0.05). In addition, overall findings were similar when examining GRS as a continuous measure. Contrary to our initial hypothesis, we identified an inverse relationship between BP GRS and salt and potassium sensitivity of BP. These data may provide novel implications on the relationship between BP responses to dietary sodium and potassium and hypertension.

Abstract MP037: Blood Pressure Genetic Risk Score Predicts Blood Pressure Responses to Dietary Sodium and Potassium Interventions: The GenSalt Study

Salt-sensitivity of blood pressure (BP) is a risk factor for hypertension, cardiovascular disease and all-cause mortality. Although documented as an important BP endophenotype, the relationship between genetic loci implicated in BP and BP salt-sensitivity remains unexamined. We assessed the hypothesis that weighted genetic risk scores (GRS), based on SNPs identified in previous BP genome-wide association study meta-analyses, would predict BP salt-sensitivity among participants of the Genetic Epidemiology Network of Salt-Sensitivity (GenSalt) study. The GenSalt study was conducted among 1,906 participants from 633 Han Chinese families. Participants underwent a 7-day low sodium (51.3 mmol sodium/day), 7-day high sodium (307.8 mmol sodium/day), and 7-day high sodium plus potassium (60 mmol potassium/day) feeding study. BP was measured nine times at baseline and at the end of each intervention period using a random-zero sphygmomanometer. The relationships between systolic BP (SBP), diastolic BP (DBP) and mean arterial pressure (MAP) GRS and respective SBP, DBP and MAP responses to the dietary interventions were assessed using mixed linear regression models that accounted for familial dependencies and adjusted for age, gender, field center, and baseline body mass index and BP. As expected, baseline SBP, DBP, and MAP significantly increased per quartile increase in GRS(p=5.6 х 10 -11 , p=1.3 х 10 -7 , and p=9.9 х 10 -5 ). In contrast, increasing GRS quartile conferred smaller SBP, DBP, and MAP responses to the low sodium intervention (p=4.2 х 10 -3 , p=0.02, and p=7.3 х 10 -3 , respectively) and smaller SBP responses to the high sodium and potassium interventions (p=0.05 and p=0.03, respectively) ( Figure ). Similar results were obtained when the data were analyzed per standard deviation increase in GRS. In summary, we identified an inverse relationship between BP GRS and BP salt-sensitivity. Further studies will be needed to elucidate the biological mechanisms contributing to this novel finding.

Integrative network analysis reveals molecular mechanisms of blood pressure regulation.

Genome‐wide association studies (GWAS) have identified numerous loci associated with blood pressure (BP). The molecular mechanisms underlying BP regulation, however, remain unclear. We investigated BP‐associated molecular mechanisms by integrating BP GWAS with whole blood mRNA expression profiles in 3,679 individuals, using network approaches. BP transcriptomic signatures at the single‐gene and the coexpression network module levels were identified. Four coexpression modules were identified as potentially causal based on genetic inference because expression‐related SNPs for their corresponding genes demonstrated enrichment for BP GWAS signals. Genes from the four modules were further projected onto predefined molecular interaction networks, revealing key drivers. Gene subnetworks entailing molecular interactions between key drivers and BP‐related genes were uncovered. As proof‐of‐concept, we validated SH2B3, one of the top key drivers, using Sh2b3 −/− mice. We found that a significant number of genes predicted to be regulated by SH2B3 in gene networks are perturbed in Sh2b3 −/− mice, which demonstrate an exaggerated pressor response to angiotensin II infusion. Our findings may help to identify novel targets for the prevention or treatment of hypertension.

Discovering pure gene-environment interactions in blood pressure genome-wide association studies data: a two-step approach incorporating new statistics.

Environment has long been known to play an important part in disease etiology. However, not many genome-wide association studies take environmental factors into consideration. There is also a need for new methods to identify the gene-environment interactions. In this study, we propose a 2-step approach incorporating an influence measure that capturespure gene-environment effect. We found that pure gene-age interaction has a stronger association than considering the genetic effect alone for systolic blood pressure, measured by counting the number of single-nucleotide polymorphisms (SNPs)reaching a certain significance level. We analyzed the subjects by dividing them into two age groups and found no overlap in the top identified SNPs between them. This suggested that age might have a nonlinear effect on genetic association. Furthermore, the scores of the top SNPs for the two age subgroups were about 3times those obtained when using all subjects for systolic blood pressure. In addition, the scores of the older age subgroup were much higher than those for the younger group. The results suggest that genetic effects are stronger in older age and that genetic association studies should take environmental effects into consideration, especially age.

Multiphase analysis by linkage, quantitative transmission disequilibrium, and measured genotype: systolic blood pressure in complex Mexican American pedigrees.

We apply a multiphase strategy for pedigree-based genetic analysis of systolic blood pressure data collected in a longitudinal study of large Mexican American pedigrees. In the first phase, we conduct variance-components linkage analysis to identify regions that may harbor quantitative trait loci. In the second phase, we carry out pedigree-based association analysis in a selected region with common and low-frequency variants from genome-wide association studies and whole genome sequencing data. Using sequencing data, we compare approaches to pedigree analysis in a 10 megabase candidate region on chromosome 3 harboring a gene previously identified by a consortium for blood pressure genome-wide association studies. We observe that, as expected, the measured genotype analysis tends to provide larger signals than the quantitative transmission disequilibrium test. We also observe that while linkage signals are contributed by common variants, strong associations are found mainly at rare variants. Multiphase analysis can improve computational efficiency and reduce the multiple testing burden.

Genetic Implication of a Novel Thiamine Transporter in Human Hypertension

This study coupled 2 strategies-trait extremes and genome-wide pooling-to discover a novel blood pressure (BP) locus that encodes a previously uncharacterized thiamine transporter. Hypertension is a heritable trait that remains the most potent and widespread cardiovascular risk factor, although details of its genetic determination are poorly understood. Representative genomic deoxyribonucleic acid (DNA) pools were created from male and female subjects in the highest- and lowest-fifth percentiles of BP in a primary care population of >50,000 patients. The peak associated single-nucleotide polymorphisms were typed in individual DNA samples, as well as in twins/siblings phenotyped for cardiovascular and autonomic traits. Biochemical properties of the associated transporter were evaluated in cellular assays. After chip hybridization and calculation of relative allele scores, the peak associations were typed in individual samples, revealing an association between hypertension, systolic BP, and diastolic BP and the previously uncharacterized solute carrier SLC35F3. The BP genetic association at SLC35F3 was validated by meta-analysis in an independent sample from the original source population, as well as the International Consortium for Blood Pressure Genome-Wide Association Studies (across North America and western Europe). Sequence homology to a putative yeast thiamine (vitamin B1) transporter prompted us to express human SLC35F3 in Escherichia coli, which catalyzed [(3)H]-thiamine uptake. SLC35F3 risk-allele homozygotes (T/T) displayed decreased erythrocyte thiamine content on microbiological assay. In twin pairs, the SLC35F3 risk allele predicted heritable cardiovascular traits previously associated with thiamine deficiency, including elevated cardiac stroke volume with decreased vascular resistance, and elevated pressor responses to environmental (cold) stress. Allelic expression imbalance confirmed that cis variation at the human SLC35F3 locus influenced expression of that gene, and the allelic expression imbalance peak coincided with the hypertension peak. Novel strategies were coupled to position a new hypertension-susceptibility locus, uncovering a previously unsuspected thiamine transporter whose genetic variants predicted several disturbances in cardiac and autonomic function. The results have implications for the pathogenesis and treatment of systemic hypertension.

Replication of the top 10 most significant polymorphisms from a large blood pressure genome-wide association study of northeastern Han Chinese East Asians

The replication of genome-wide significant association signals in independent populations is a practical approach for characterizing gene-disease relationships. Therefore, we sought to explore the top 10 polymorphisms from a large blood pressure genome-wide association study of northeastern Han Chinese East Asians. This was a hospital-based study involving 1009 patients with essential hypertension and 756 normotensive controls from Qiqihar city, China. Genotyping was conducted with a polymerase chain reaction-ligase detection reaction method. All polymorphisms except for rs6825911 satisfied Hardy-Weinberg equilibrium. Overall, the genotype differences between the patients and controls were significant for rs35444 (P<0.001), rs11191548 (P=0.017) and rs17249754 (P=0.017). The per-minor-allele odds ratios of rs35444, rs11191548 and rs17249754 were 0.54 (95% confidence interval (95% CI): 0.46-0.62; P<0.01), 1.23 (95% CI: 1.07-1.43; P=0.005) and 1.23 (95% CI: 1.07-1.41; P=0.004), respectively. Similarly, the carriers of minor homozygotes had a significant reduction in adjusted systolic and diastolic blood pressure for rs35444 (P<0.01) but an increase for both rs11191548 (P<0.01) and rs17249754 (P<0.04). Further application of the genetic risk score method indicated that subjects with risk scores of 8, 10 and 12-16 had 1.66-fold (95% CI: 1.01-2.72), 1.72-fold (95% CI: 1.03-2.86) and 1.97-fold (95% CI: 1.12-3.46) increases, respectively, in the odds of developing hypertension, and similar increases were also observed for blood pressure. Taken together, our findings demonstrate that although only three of the top 10 polymorphisms were successfully validated in the northeastern Han Chinese population, the genetic risk score analyses led us to more profound insights into the possible joint effects of multiple polymorphisms on hypertension risk and blood pressure variation.

Genome-wide Association Analysis of Blood-Pressure Traits in African-Ancestry Individuals Reveals Common Associated Genes in African and Non-African Populations

High blood pressure (BP) is more prevalent and contributes to more severe manifestations of cardiovascular disease (CVD) in African Americans than in any other United States ethnic group. Several small African-ancestry (AA) BP genome-wide association studies (GWASs) have been published, but their findings have failed to replicate to date. We report on a large AA BP GWAS meta-analysis that includes 29,378 individuals from 19 discovery cohorts and subsequent replication in additional samples of AA (n = 10,386), European ancestry (EA) (n = 69,395), and East Asian ancestry (n = 19,601). Five loci (EVX1-HOXA, ULK4, RSPO3, PLEKHG1, and SOX6) reached genome-wide significance (p < 1.0× 10(-8)) for either systolic or diastolic BP in a transethnic meta-analysis after correction for multiple testing. Three of these BP loci (EVX1-HOXA, RSPO3, and PLEKHG1) lack previous associations with BP. We also identified one independent signal in a known BP locus (SOX6) and provide evidence for fine mapping in four additional validated BP loci. We also demonstrate that validated EA BP GWAS loci, considered jointly, show significant effects in AA samples. Consequently, these findings suggest that BP loci might have universal effects across studied populations, demonstrating that multiethnic samples are an essential component in identifying, fine mapping, and understanding their trait variability.

The non-synonymous polymorphism at position 114 of the WRN protein affects cholesterol efflux in vitro and correlates with cholesterol levels in vivo

Werner syndrome (WS) is a recessive disorder characterized by the premature onset of a number of age-related diseases. The objective of the present study was to examine the degree of associations between non-synonymous coding Single Nucleotide Polymorphisms (SNPs) in the WRN gene and markers of obesity, diabetes, and hypertension using meta-analyses publically available and to test their effect in WS fibroblasts. The P-value, after genomic control correction, for each non-synonymous coding SNP present in the WRN gene was retrieved from the International Consortium for Blood Pressure Genome-Wide Association Study, the Genome Wide Associations Scans for Total Cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides, and the Meta-Analyses of Glucose and Insulin-related traits Consortium. For SNPs significantly associated with cholesterol traits, we generated expression vectors containing the amino acid changes and measured cholesterol uptake and efflux in transfected WS fibroblasts. One SNP (rs2230009) changing a valine for an isoleucine at position 114 of the WRN protein was nominally associated with cholesterol and LDL-cholesterol measurements (P-values<0.05). Interestingly, a WRN cDNA expression vector bearing a valine at position 114 instead of isoleucine significantly affected cholesterol efflux in WS fibroblasts. These results implicate a functional effect of this WRN polymorphism on cholesterol metabolism.

Alanine-Glyoxylate Aminotransferase-2 Metabolizes Endogenous Methylarginines, Regulates NO, and Controls Blood Pressure

Asymmetric dimethylarginine is an endogenous inhibitor of NO synthesis that may mediate cardiovascular disease. Alanine-glyoxylate aminotransferase-2 (AGXT2) has been proposed to degrade asymmetric dimethylarginine. We investigated the significance of AGXT2 in methylarginine metabolism in vivo and examined the effect of this enzyme on blood pressure. In isolated mouse kidney mitochondria, we show asymmetric dimethylarginine deamination under physiological conditions. We demonstrate increased asymmetric dimethylarginine, reduced NO, and hypertension in an AGXT2 knockout mouse. We provide evidence for a role of AGXT2 in methylarginine metabolism in humans by demonstrating an inverse relationship between renal (allograft) gene expression and circulating substrate levels and an association between expression and urinary concentrations of the product. Finally, we examined data from a meta-analysis of blood pressure genome-wide association studies. No genome-wide significance was observed, but taking a hypothesis-driven approach, there was a suggestive association between the T allele at rs37369 (which causes a valine-isoleucine substitution and altered levels of AGXT2 substrate) and a modest increase in diastolic blood pressure (P=0.0052). Although the effect of variation at rs37369 needs further study, these findings suggest that AGXT2 is an important regulator of methylarginines and represents a novel mechanism through which the kidney regulates blood pressure.

Abstract 88: Systems Biology Approaches to Exploring Molecular Mechanisms Underlying Blood Pressure Regulation

Blood pressure (BP) is a complex trait that is influenced by both genetic and environment factors. Recent genome-wide association studies (GWAS) have identified about 30 genetic loci that are associated with systolic and diastolic blood pressure (SBP, DBP) and hypertension. However, the molecular mechanisms underlying the GWAS associations remain unclear. We hypothesize that BP-associated genetic variants with both strong and subtle effects drive shifts in gene subnetworks that in turn affect BP. We surveyed BP-associated molecular interactions in Framingham offspring cohort participants (n=2461; 55% women; age range 40-92 yrs.) by integrating gene expression profiles, expression-associated SNPs (eSNPs), and BP GWAS with network approaches. Peripheral whole blood samples were collected and large-scale transcriptomic microarray analysis was performed on all available participants who attended a clinic visit in 2005-2008. Based on pedigrees the samples were split into a discovery set (n=1421) and a replication set (n=820). The expression levels of 661 genes (FDR &lt; 20%) and the eigengenes of 3 coexpression modules (CoEMs), which were found to be significantly correlated with SBP or DBP in the discovery set, were tested in the replication set. Seventy-two genes were replicated at FDR &lt; 20%. The 72-gene BP-correlated signature and 2 of the three CoEMs were found to be significantly enriched for eSNPs with low p value associations with BP in the International Consortium of Blood Pressure (ICBP) GWAS at p&lt;0.001, suggesting that these gene sets play causal roles in BP regulation. The putative causal BP gene sets were in turn integrated with tissue-specific Bayesian networks and a protein-protein interaction network to identify central network nodes (key drivers or KDs) that drive these BP-related gene sets. One hundred and ten KDs including TSPAN2, ECT2 and KCNK3 were identified. The BP causal gene sets and their KDs are enriched for BP-related biological processes including ion transport, nervous system development, and blood coagulation. Our systems biology analysis not only predicts novel BP risk genes, but also uncovers a network structure that entails the molecular interactions among BP and cardiovascular risk genes in a tissue-specific fashion.

Recapitulation of genome-wide association studies on pulse pressure and mean arterial pressure in the Korean population

Increased pulse pressure (PP) and decreased mean arterial pressure (MAP) are strong prognostic predictors of adverse cardiovascular events. Recently, the International Consortium for Blood Pressure Genome-Wide Association Studies (ICBP-GWAS) reported eight loci that influenced PP and MAP. The ICBP-GWAS examined 51 cohorts--comprising 122 671 individuals of European ancestry--and identified eight SNPs: five that governed PP and three that controlled MAP. Six of these loci were novel. To replicate these newly identified loci and examine genetic architecture of PP and MAP between European and Asian populations, we conducted a meta-analysis of the eight SNPs combining data from ICBP and general population-based Korean cohorts. Two SNPs (rs13002573 (FIGN) and rs871606 (CHIC2)) for PP and two SNPs (rs1446468 (FIGN) and rs319690 (MAP4)) for MAP were replicated in Koreans. Although our GWAS only found moderate association, we believe that the findings promote us to propose that a similar genetic architecture governs PP and MAP in Asians and Europeans. However, further studies will be needed to confirm the possibility using other Asian population.

Common Genetic Variation of Blood Pressure Traits and Their Relation to End-Organ Damage

### Study Hypothesis Initial genome-wide association studies (GWAS) for hypertension, a common cardiovascular risk factor, have delivered unexpectedly few and modest associations. The authors of the International Consortium for Blood Pressure Genome-Wide Association Studies set out to identify novel genetic variants in relation to blood pressure, intermediate phenotypes, and cardiovascular disease risk. A joint effort combining data on 200 000 individuals of European descent increased the power to detect DNA variants with small effect sizes. ### How Was the Hypothesis Tested? The authors used a staged approach for discovery, replication, and biological translation of their findings. At the identification stage, they performed a meta-analysis on genome-wide single nucleotide polymorphism (SNP) associations and off-treatment systolic and diastolic blood pressure measurements, as well as the dichotomous variable of hypertension, based on 29 studies (n≈70 000 individuals). In 3 resource-efficient sequential follow-up steps of de novo genotyping and SNP look-up in existing GWAS datasets, top hits were validated in >133 000 independent individuals of European descent. Sex and body mass index interaction analyses were performed for the top GWAS findings to understand potential effect modification. To identify possible causal mechanisms, top GWAS loci were looked up in diverse existing expression SNP data sets for cis -acting gene expression. In addition, neighboring nonsynonymous coding SNPs (linkage disequilibrium r 2 >0.8) were searched because amino acid sequence alterations harbor high potential to provide mechanistic insights. Furthermore, genetic loci were investigated in relation to ≈300 serum metabolites in >10 000 individuals of metabolomic and lipidomic studies. More than 6000 copy number variation-tagging SNPs were available for the correlation of structural genomic variation and blood pressure …