Sex differences in heart mitochondria regulate diastolic dysfunction.

Heart failure with preserved ejection fraction (HFpEF) exhibits a sex bias, being more common in women than men, and we hypothesize that mitochondrial sex differences might underlie this bias. As part of genetic studies of heart failure in mice, we observe that heart mitochondrial DNA levels and function tend to be reduced in females as compared to males. We also observe that expression of genes encoding mitochondrial proteins are higher in males than females in human cohorts. We test our hypothesis in a panel of genetically diverse inbred strains of mice, termed the Hybrid Mouse Diversity Panel (HMDP). Indeed, we find that mitochondrial gene expression is highly correlated with diastolic function, a key trait in HFpEF. Consistent with this, studies of a "two-hit" mouse model of HFpEF confirm that mitochondrial function differs between sexes and is strongly associated with a number of HFpEF traits. By integrating data from human heart failure and the mouse HMDP cohort, we identify the mitochondrial gene Acsl6 as a genetic determinant of diastolic function. We validate its role in HFpEF using adenoviral over-expression in the heart. We conclude that sex differences in mitochondrial function underlie, in part, the sex bias in diastolic function.

Polymorphic Variants in the GRK5 Gene Promoter Are Associated With Diastolic Dysfunction in Coronary Artery Bypass Graft Surgery Patients.

BACKGROUND: The G-protein-coupled receptor kinase 5 (GRK5) is a mediator of cardiovascular homeostasis and participates in inflammation and cardiac fibrosis, both being involved in the development of diastolic dysfunction (DD). While mechanisms of transcriptional regulation of the GRK5 promoter are unclear, we tested the hypotheses, that (1) GRK5 expression varies depending on functional single nucleotide polymorphisms (SNPs) in the GRK5 promoter and (2) this is associated with DD in patients undergoing coronary artery bypass graft (CABG) surgery. METHODS: We amplified and sequenced the GRK5 promoter followed by cloning, reporter assays, and electrophoretic mobility shift assays (EMSA). GRK5 messenger ribonucleic acid (mRNA) expression was determined in right atrial tissue sampled from 50 patients undergoing CABG surgery. In another prospective study, GRK5 genotypes were associated with determinants of diastolic function using transesophageal echocardiography in 255 patients with CABG with normal systolic left ventricular (LV) function. Specifically, we measured ejection fraction (EF), transmitral Doppler early filling velocity (E), tissue Doppler early diastolic lateral mitral annular velocity (E' lateral), and calculated E/E', E' norm and the difference of E' lateral and E' norm to account for age-related changes in diastolic function. RESULTS: We identified 6 SNPs creating 3 novel haplotypes with the greatest promoter activation in haplotype tagging (ht) SNP T(-678)C T-allele constructs (P < .001). EMSAs showed allele-specific transcription factor binding proving functional activity. GRK5 mRNA expression was greatest in TT genotypes (TT: 131 fg/µg [95% CI, 108-154]; CT: 109 [95% confidence interval {CI}, 93-124]; CC: 83 [95% CI, 54-112]; P = .012). Moreover, GRK5 genotypes were significantly associated with determinants of diastolic function. Grading of DD revealed more grade 3 patients in TT compared to CT and CC genotypes (58% vs 38% vs 4%; P = .023). E´ lateral was lowest in TT genotypes (P = .007) and corresponding E/E' measurements showed 1.27-fold increased values in TT versus CC genotypes (P = .01), respectively. While E' norm values were not different between genotypes (P = .182), the difference between E' lateral and E' norm was significantly higher in TT genotypes compared to CC and CT genotypes (-1.2 [interquartile range {IQR}, 2.7], -0.5 [IQR, 3.4], and -0.4 [IQR, 4.2; P = .035], respectively). CONCLUSIONS: A functional GRK5 SNP results in allele-dependent differences in GRK5 promoter activity and mRNA expression. This is associated with altered echocardiographic determinants of diastolic function. Thus, SNPs in the GRK5 promoter are associated with altered perioperative diastolic cardiac function. In the future, preoperative testing for these and other SNPs might allow to initiate more specific diagnostic and perioperative pathways to benefit patients at risk.

TNNT2 mutations in the tropomyosin binding region of TNT1 disrupt its role in contractile inhibition and stimulate cardiac dysfunction.

Muscle contraction is regulated by the movement of end-to-end-linked troponin-tropomyosin complexes over the thin filament surface, which uncovers or blocks myosin binding sites along F-actin. The N-terminal half of troponin T (TnT), TNT1, independently promotes tropomyosin-based, steric inhibition of acto-myosin associations, in vitro. Recent structural models additionally suggest TNT1 may restrain the uniform, regulatory translocation of tropomyosin. Therefore, TnT potentially contributes to striated muscle relaxation; however, the in vivo functional relevance and molecular basis of this noncanonical role remain unclear. Impaired relaxation is a hallmark of hypertrophic and restrictive cardiomyopathies (HCM and RCM). Investigating the effects of cardiomyopathy-causing mutations could help clarify TNT1's enigmatic inhibitory property. We tested the hypothesis that coupling of TNT1 with tropomyosin's end-to-end overlap region helps anchor tropomyosin to an inhibitory position on F-actin, where it deters myosin binding at rest, and that, correspondingly, cross-bridge cycling is defectively suppressed under diastolic/low Ca2+ conditions in the presence of HCM/RCM lesions. The impact of TNT1 mutations on Drosophila cardiac performance, rat myofibrillar and cardiomyocyte properties, and human TNT1's propensity to inhibit myosin-driven, F-actin-tropomyosin motility were evaluated. Our data collectively demonstrate that removing conserved, charged residues in TNT1's tropomyosin-binding domain impairs TnT's contribution to inhibitory tropomyosin positioning and relaxation. Thus, TNT1 may modulate acto-myosin activity by optimizing F-actin-tropomyosin interfacial contacts and by binding to actin, which restrict tropomyosin's movement to activating configurations. HCM/RCM mutations, therefore, highlight TNT1's essential role in contractile regulation by diminishing its tropomyosin-anchoring effects, potentially serving as the initial trigger of pathology in our animal models and humans.

Adenosine kinase inhibition enhances microvascular dilator function and improves left ventricle diastolic dysfunction.

OBJECTIVE: Inhibition of adenosine kinase (ADK), via augmenting endogenous adenosine levels exerts cardiovascular protection. We tested the hypothesis that ADK inhibition improves microvascular dilator and left ventricle (LV) contractile function under metabolic or hemodynamic stress. METHODS AND RESULTS: In Obese diabetic Zucker fatty/spontaneously hypertensive heart failure F1 hybrid rats, treatment with the selective ADK inhibitor, ABT-702 (1.5 mg/kg, intraperitoneal injections for 8-week) restored acetylcholine-, sodium nitroprusside-, and adenosine-induced dilations in isolated coronary arterioles, an effect that was accompanied by normalized end-diastolic pressure (in mm Hg, Lean: 3.4 ± 0.6, Obese: 17.6 ± 4.2, Obese + ABT: 6.6 ± 1.4) and LV relaxation constant, Tau (in ms, Lean: 6.9 ± 1.5, Obese: 13.9 ± 1.7, Obese + ABT: 6.0 ± 1.1). Mice with vascular endothelium selective ADK deletion (ADKVEC KO) exhibited an enhanced dilation to acetylcholine in isolated gracilis muscle (lgEC50 WT: -8.2 ± 0.1, ADKVEC KO: -8.8 ± 0.1, P < .05) and mesenteric arterioles (lgEC50 WT: -7.4 ± 0.2, ADKVEC KO: -8.1 ± 1.2, P < .05) when compared to wild-type (WT) mice, whereas relaxation of the femoral artery and aorta (lgEC50 WT: -7.03 ± 0.6, ADKVEC KO: -7.05 ± 0.8) was similar in the two groups. Wild-type mice progressively developed LV systolic and diastolic dysfunction when they underwent transverse aortic constriction surgery, whereas ADKVEC -KO mice displayed a lesser degree in decline of LV function. CONCLUSIONS: Our results indicate that ADK inhibition selectively enhances microvascular vasodilator function, whereby it improves LV perfusion and LV contractile function under metabolic and hemodynamic stress.

Genome-wide interaction study of single-nucleotide polymorphisms and alcohol consumption on blood pressure: The Ansan and Ansung study of the Korean Genome and Epidemiology Study (KoGES).

Hypertension is a common disease worldwide. Alcohol consumption is one of the risk factors for hypertension, however, it is unclear how alcohol consumption elevates blood pressure. Blood pressure could be affected by interactions between genetic variations and alcohol consumption. Thus, we performed a genome-wide interaction study (GWIS) to assess the effect of gene-alcohol consumption interaction on blood pressure among adults aged ≥40 years from the Ansan and Ansung cohort study (n = 6,176), a part of the Korean Genome Epidemiology Study (KoGES). As a result, rs1297184, single-nucleotide polymorphism (SNP) in locus LGR5 was significant (PGWIS = 8.78 × 10-9 ) in GWIS analysis on diastolic blood pressure, but not on systolic blood pressure. However, there was a heteroscedasticity of alcohol consumption. In the GWIS analysis, applying the inverse-variance weighting to correct the systematic inflation slightly attenuated the strength of interaction (PGWIS_IVW = 7.14 × 10-8 ). This interaction was replicated in the Health Examinees cohort (p = .026), a large-scale community-based cohort (n = 18,708). In conclusion, we identified a possible novel interaction between an SNP (rs1297184) and alcohol consumption on blood pressure.

MicroRNA profiles in plasma samples from young metabolically healthy obese patients and miRNA-21 are associated with diastolic dysfunction via TGF-ß1/Smad pathway.

BACKGROUND: Metabolically healthy obese patients accounts for a large part of obese population, but its clinical significance and cardiac dysfunction are often underestimated. The microRNA profiles of metabolically healthy obese patients were investigated in the study, and the selected microRNA (miRNA) based on our microarray assay will be further verified in a relatively large metabolically healthy obese population. METHODS: microRNA microarray was performed from six metabolically healthy obese and 6 health control blood samples. Based on the bioinformatics analysis, we further measured RT-PCR, fibrosis markers, echocardiograms, and TGF-ß1/Smad signaling pathway in 600 metabolically healthy obese population. RESULTS: We found that miRNAs expression characteristics in metabolically healthy obese groups were markedly different from healthy control group. MiRNA-21 was significantly increased in the samples of metabolically healthy obese patients. Besides, miRNA-21 levels were associated with cardiac fibrosis marker. Meanwhile, higher miRNA-21 levels were related to elevated E/E'. Besides, patients with the highest miRNA-21 quartile showed the lowest ratio of E/A. These associations between miRNA-21 and diastolic function parameters were independent of obesity and other confounding variables. Of note, TGF-ß1and Smad 3 were significantly upregulated while Smad 7 was downregulated according to the miRNA-21 quartiles in metabolically healthy obese group. CONCLUSIONS: We demonstrated the profiles of circulating microRNAs in metabolically healthy obese patients. Increased plasma miRNA-21 levels were related to impaired diastolic function independent of other relevant confounding variables. MiRNA-21 could be one of the mechanistic links between obesity and diastolic dysfunction through regulating cardiac fibrosis via TGF-ß1/Smad signaling pathway in obese hearts, which may serve as a novel target of disease intervention.

Indoleamine 2,3-dioxygenase and ischemic heart disease: a Mendelian Randomization study.

Tryptophan is an essential amino acid. Indoleamine 2,3-dioxygenase (IDO), the rate-limiting enzyme in the tryptophan-kynurenine pathway, is positively associated with cardiac events, and may be relevant to cancer. We used Mendelian Randomization to obtain unconfounded estimates of the association of IDO1 with ischemic heart disease (IHD), ischemic stroke and their risk factors, all-cancer, cancer of the prostate, lung and bronchus, and breast. We obtained genetic instruments independently and strongly (p-value < 5 × 10-8) predicting plasma IDO1 from a proteome genome-wide association study (GWAS), and applied them to consortia GWAS of the outcomes, including the UK Biobank SOFT CAD GWAS (cases < = 76 014, non-cases < = 264 785) for IHD. Estimates were obtained using inverse variance weighting; with MR-Egger, weighted median and MR-PRESSO as sensitivity analyses. IDO1 was inversely associated with IHD (odds ratio (OR) 0.96 per standard deviation, 95% confidence interval (CI) 0.93 to 1.00, p-value = 0.04), diabetes (OR 0.91, 95% CI 0.85 to 0.97) and prostate cancer (OR 0.96, 95% CI 0.93 to 0.99) with a directionally consistent estimate for stroke (OR 0.98, 95% CI 0.95 to 1.02) but not with blood pressure, or the other cancers considered. IDO1 might be a potential therapeutic target for IHD, diabetes and prostate cancer.

Genetically determined pattern of left ventricular function in normal and hypertensive hearts.

We sought to assess the inheritance of left ventricular (LV) function using speckle-tracking echocardiography and the impact of hypertension on modifying the genetically determined pattern of contraction in a population of twins. We recruited 92 Caucasian twin pairs, including 74 hypertensive (HTN) siblings. Beyond standard echocardiographic protocol, a speckle-tracking analysis was performed, including global longitudinal strain (GLS). Systolic function, as assessed by ejection fraction, showed moderate heritability (61%); however, GLS showed higher and dominant heritability (75%). Heterogeneity models revealed that there were no differences between the HTN and non-HTN subjects regarding the heritability of GLS. However, the heritability estimates of diastolic function parameters, including early diastolic strain rate, were low. LV systolic biomechanics is highly heritable. GLS shows dominant heritability, despite the presence of early-stage hypertensive heart disease. Early diastolic parameters are rather determined by environmental factors. These findings suggest the presence of a genetic framework that conserves systolic function despite the expression of diastolic dysfunction and may underlie the phenotypic progression towards heart failure with preserved ejection fraction.

Point mutations in the tri-helix bundle of the M-domain of cardiac myosin binding protein-C influence systolic duration and delay cardiac relaxation.

Cardiac myosin binding protein-C (cMyBP-C) is an essential regulatory protein required for proper systolic contraction and diastolic relaxation. We previously showed that N'-terminal domains of cMyBP-C stimulate contraction by binding to actin and activating the thin filament in vitro. In principle, thin filament activating effects of cMyBP-C could influence contraction and relaxation rates, or augment force amplitude in vivo. cMyBP-C binding to actin could also contribute to an internal load that slows muscle shortening velocity as previously hypothesized. However, the functional significance of cMyBP-C binding to actin has not yet been established in vivo. We previously identified an actin binding site in the regulatory M-domain of cMyBP-C and described two missense mutations that either increased (L348P) or decreased (E330K) binding affinity of recombinant cMyBP-C N'-terminal domains for actin in vitro. Here we created transgenic mice with either the L348P or E330K mutations to determine the functional significance of cMyBP-C binding to actin in vivo. Results showed that enhanced binding of cMyBP-C to actin in L348P-Tg mice prolonged the time to end-systole and slowed relaxation rates. Reduced interactions between cMyBP-C and actin in E330K-Tg mice had the opposite effect and significantly shortened the duration of ejection. Neither mouse model displayed overt systolic dysfunction, but L348P-Tg mice showed diastolic dysfunction presumably resulting from delayed relaxation. We conclude that cMyBP-C binding to actin contributes to sustained thin filament activation at the end of systole and during isovolumetric relaxation. These results provide the first functional evidence that cMyBP-C interactions with actin influence cardiac function in vivo.

Associations of methylenetetrahydrofolate reductase C677T genotype with blood pressure levels in Chinese population with essential hypertension.

OBJECTIVE: To confirm the association between baseline blood pressure (BP) levels and the methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism in patients with essential hypertension. METHODS: A total of 347 patients were enrolled from the Dongzhi community in Anhui Province, China. The C677T polymorphism of the MTHFR gene was detected using high-throughput TaqMan allelic discrimination assay. Baseline BP was measured using a standardized mercury-gravity monometer. RESULTS: In the whole sample, the frequency of the MTHFR C677T genotypes CC, CT, and TT were 38.6%, 48.1%, and 13.3%, respectively. In a recessive model (CC+CT versus TT genotypes), baseline diastolic blood pressure (DBP) was significantly higher in patients with the TT genotype compared to those with the CT or CC genotypes (P= 0.013). We also divided all patients into three groups based on the tertiles of the baseline BP distribution. Compared to subjects in the lowest tertile of DBP, the adjusted odds of having the TT genotype among subjects in the highest tertile was 2.6 (95% CI: 1.1 to 6.2). However, no significant associations were observed between baseline systolic blood pressure (SBP) and the MTHFR C677T polymorphism. CONCLUSIONS: The MTHFR gene polymorphism could be an important genetic determinant of baseline DBP levels in Chinese essential hypertensive patients.

A Large-Scale Multi-ancestry Genome-wide Study Accounting for Smoking Behavior Identifies Multiple Significant Loci for Blood Pressure.

Genome-wide association analysis advanced understanding of blood pressure (BP), a major risk factor for vascular conditions such as coronary heart disease and stroke. Accounting for smoking behavior may help identify BP loci and extend our knowledge of its genetic architecture. We performed genome-wide association meta-analyses of systolic and diastolic BP incorporating gene-smoking interactions in 610,091 individuals. Stage 1 analysis examined ∼18.8 million SNPs and small insertion/deletion variants in 129,913 individuals from four ancestries (European, African, Asian, and Hispanic) with follow-up analysis of promising variants in 480,178 additional individuals from five ancestries. We identified 15 loci that were genome-wide significant (p < 5 × 10-8) in stage 1 and formally replicated in stage 2. A combined stage 1 and 2 meta-analysis identified 66 additional genome-wide significant loci (13, 35, and 18 loci in European, African, and trans-ancestry, respectively). A total of 56 known BP loci were also identified by our results (p < 5 × 10-8). Of the newly identified loci, ten showed significant interaction with smoking status, but none of them were replicated in stage 2. Several loci were identified in African ancestry, highlighting the importance of genetic studies in diverse populations. The identified loci show strong evidence for regulatory features and support shared pathophysiology with cardiometabolic and addiction traits. They also highlight a role in BP regulation for biological candidates such as modulators of vascular structure and function (CDKN1B, BCAR1-CFDP1, PXDN, EEA1), ciliopathies (SDCCAG8, RPGRIP1L), telomere maintenance (TNKS, PINX1, AKTIP), and central dopaminergic signaling (MSRA, EBF2).

Investigation of OPG/RANK/RANKL Genes as a Genetic Marker for Cardiac abnormalities in Thalassemia Major Patients.

OBJECTIVE: The aim of the study was to investigate the role of osteoprotegerin (OPG)/RANK/RANKL variants in left ventricular hypertrophy (LVH) and diastolic dysfunction in thalassemia major patients MATERIALS AND METHOD: One hundred and five beta-thalassemia patients who were older than 10 years of age were enrolled for the study. Two-dimensional and M-mode echocardiography analysis was done in all patients. Genotyping for OPG [rs2073617 (950 T>C), rs2073618 (1181G>C)], RANK [(rs1805034(+34694 C>T), rs12458117 (+34901 G>A) and rs75404003 (+35966insdelC)], and RANKL (rs2277438, rs9594782) variants was done using the PCR-RFLP method. Serum OPG levels were estimated by ELISA. RESULTS: Mean age of patients was 16.36 ± 5.08 years. LVH and diastolic dysfunction was present in 33 (31.4%) and 24 (22.8%) patients, respectively. Thalassemia patients having minor allele of OPG rs2073618, RANK rs75404003 and RANKL rs9594782 SNPs were at high risk for LVH as suggested by high odds ratio of 2.470, 3.783, and 2.148, respectively; however, none of the SNPs tested were statistically significantly associated after applying Bonferroni corrections for multiple testing adjustment. No significant association of any SNP with diastolic dysfunction was observed. Serum OPG levels were found significantly higher in thalassemia patients with diastolic dysfunction (P = 0.006). CONCLUSION: OPG rs2073618, RANK rs75404003, and RANKL rs9594782 SNPs may predispose LVH in thalassemia patients. Patients with diastolic dysfunction showed increased levels of serum OPG.

Xanthine oxidase gene variants and their association with blood pressure and incident hypertension: a population study.

OBJECTIVE: The enzyme xanthine oxidoreductase (XOR) generates uric acid in the terminal steps of the purine metabolism; meanwhile reactive oxygen species are formed. We hypothesized that uric acid production, as assessed indirectly from XOR variants, is associated with hypertension. METHODS: Among 2769 participants (48.3% men; mean age 40.7 years) randomly recruited from European populations, we genotyped 25 tagging XOR SNPs and measured blood pressure (BP) at baseline and follow-up (median 8.8 years). The relation between variants of the XOR gene with changes in pulse pressure and mean arterial pressure over time; and incidence of hypertension, were analyzed. RESULTS: Compared with nonminor allele carriers, pulse pressure increased approximately 2 mmHg more in minor allele carriers of rs11904439 (P = 0.01), whereas mean arterial pressure and DBP increased approximately 1 mmHg less in minor allele carriers of rs2043013 (P = 0.01). In 2050, participants normotensive at baseline, hazard ratios contrasting risk of hypertension in minor allele carriers vs. nonminor allele carriers were 1.31 (95% confidence interval 1.03-1.68; P = 0.02) and 1.69 (95% confidence interval 1.11-2.57; P = 0.01) for rs11904439 and rs148756340, respectively. With the false discovery rate set at 0.25, the aforementioned associations retained significance. The changes in SBP from baseline to follow-up and the serum levels of uric acid at baseline (n = 1949) were not associated with XOR. CONCLUSION: Pending confirmation, our findings suggest that variation in uric acid production, as captured by genetic variation in XOR, might be a predictor of changes in BP and in the risk of hypertension.

Experimentally Increasing the Compliance of Titin Through RNA Binding Motif-20 (RBM20) Inhibition Improves Diastolic Function In a Mouse Model of Heart Failure With Preserved Ejection Fraction.

BACKGROUND: Left ventricular (LV) stiffening contributes to heart failure with preserved ejection fraction (HFpEF), a syndrome with no effective treatment options. Increasing the compliance of titin in the heart has become possible recently through inhibition of the splicing factor RNA binding motif-20. Here, we investigated the effects of increasing the compliance of titin in mice with diastolic dysfunction. METHODS: Mice in which the RNA recognition motif (RRM) of one of the RNA binding motif-20 alleles was floxed and that expressed the MerCreMer transgene under control of the αMHC promoter (referred to as cRbm20ΔRRM mice) were used. Mice underwent transverse aortic constriction (TAC) surgery and deoxycorticosterone acetate (DOCA) pellet implantation. RRM deletion in adult mice was triggered by injecting raloxifene (cRbm20ΔRRM-raloxifene), with dimethyl sulfoxide (DMSO)-injected mice (cRbm20ΔRRM-DMSO) as the control. Diastolic function was investigated with echocardiography and pressure-volume analysis; passive stiffness was studied in LV muscle strips and isolated cardiac myocytes before and after elimination of titin-based stiffness. Treadmill exercise performance was also studied. Titin isoform expression was evaluated with agarose gels. RESULTS: cRbm20ΔRRM-raloxifene mice expressed large titins in the hearts, called supercompliant titin (N2BAsc), which, within 3 weeks after raloxifene injection, made up ≈45% of total titin. TAC/DOCA cRbm20ΔRRM-DMSO mice developed LV hypertrophy and a marked increase in LV chamber stiffness as shown by both pressure-volume analysis and echocardiography. LV chamber stiffness was normalized in TAC/DOCA cRbm20ΔRRM-raloxifene mice that expressed N2BAsc. Passive stiffness measurements on muscle strips isolated from the LV free wall revealed that extracellular matrix stiffness was equally increased in both groups of TAC/DOCA mice (cRbm20ΔRRM-DMSO and cRbm20ΔRRM-raloxifene). However, titin-based muscle stiffness was reduced in the mice that expressed N2BAsc (TAC/DOCAcRbm20ΔRRM-raloxifene). Exercise testing demonstrated significant improvement in exercise tolerance in TAC/DOCA mice that expressed N2BAsc. CONCLUSIONS: Inhibition of the RNA binding motif-20-based titin splicing system upregulates compliant titins, which improves diastolic function and exercise tolerance in the TAC/DOCA model. Titin holds promise as a therapeutic target for heart failure with preserved ejection fraction.

Direct Estimates of the Genomic Contributions to Blood Pressure Heritability within a Population-Based Cohort (ARIC).

Blood pressure (BP) is a heritable trait with multiple environmental and genetic contributions, with current heritability estimates from twin and family studies being ~ 40%. Here, we use genome-wide polymorphism data from the Atherosclerosis Risk in Communities (ARIC) study to estimate BP heritability from genomic relatedness among cohort members. We utilized data on 6,365,596 and 9,578,528 genotyped and imputed common single nucleotide polymorphisms (SNPs), in 8,901 European ancestry (EA) and 2,860 African Ancestry (AA) ARIC participants, respectively, and a mixed linear model for analyses, to make four observations. First, for BP measurements, the heritability is ~20%/~50% and ~27%/~39% for systolic (SBP)/diastolic (DBP) blood pressure in European and African ancestry individuals, respectively, consistent with prior studies. Second, common variants with allele frequency >10% recapitulate most of the BP heritability in these data. Third, the vast majority of BP heritability varies by chromosome, depending on its length, and is largely concentrated in noncoding genomic regions annotated as DNaseI hypersensitive sites (DHSs). Fourth, the majority of this heritability arises from loci not harboring currently known cardiovascular and renal genes. Recent meta-analyses of large-scale genome-wide association studies (GWASs) and admixture mapping have identified ~50 loci associated with BP and hypertension (HTN), and yet they account for only a small fraction (~2%) of the heritability.

Novel Genes Affecting Blood Pressure Detected Via Gene-Based Association Analysis.

Hypertension is a common disorder and one of the most important risk factors for cardiovascular diseases. The aim of this study was to identify more novel genes for blood pressure. Based on the publically available SNP-based P values of a meta-analysis of genome-wide association studies, we performed an initial gene-based association study in a total of 69,395 individuals. To find supplementary evidence to support the importance of the identified genes, we performed GRAIL (gene relationships among implicated loci) analysis, protein-protein interaction analysis, functional annotation clustering analysis, coronary artery disease association analysis, and other bioinformatics analyses. Approximately 22,129 genes on the human genome were analyzed for blood pressure in gene-based association analysis. A total of 43 genes were statistically significant after Bonferroni correction (P < 2.3×10(-6)). The evidence obtained from the analyses of this study suggested the importance of ID1 (P = 2.0×10(-6)), CYP17A1 (P = 4.58×10(-9)), ATXN2 (P = 1.07×10(-13)), CLCN6 (P = 4.79×10(-9)), FURIN (P = 1.38×10(-6)), HECTD4 (P = 3.95×10(-11)), NPPA (P = 1.60×10(-6)), and PTPN11 (P = 8.89×10(-10)) in the genetic basis of blood pressure. The present study found some important genes associated with blood pressure, which might provide insights into the genetic architecture of hypertension.

Cardiac hypertrophy reduction in SHR by specific silencing of myocardial Na(+)/H(+) exchanger.

We examined the effect of specific and local silencing of sodium/hydrogen exchanger isoform 1 (NHE1) with a small hairpin RNA delivered by lentivirus (L-shNHE1) in the cardiac left ventricle (LV) wall of spontaneously hypertensive rats, to reduce cardiac hypertrophy. Thirty days after the lentivirus was injected, NHE1 protein expression was reduced 53.3 ± 3% in the LV of the L-shNHE1 compared with the control group injected with L-shSCR (NHE1 scrambled sequence), without affecting its expression in other organs, such as liver and lung. Hypertrophic parameters as LV weight-to-body weight and LV weight-to-tibia length ratio were significantly reduced in animals injected with L-shNHE1 (2.32 ± 0.5 and 19.30 ± 0.42 mg/mm, respectively) compared with L-shSCR-injected rats (2.68 ± 0.06 and 21.53 ± 0.64 mg/mm, respectively). Histochemical analysis demonstrated a reduction of cardiomyocytes cross-sectional area in animals treated with L-shNHE1 compared with L-shSCR (309,81 ± 20,86 vs. 424,52 ± 21 µm(2), P < 0.05). Echocardiography at the beginning and at the end of the treatment showed that shNHE1 expression for 30 days induced 9% reduction of LV mass. Also, animals treated with L-shNHE1 exhibited a reduced LV wall thickness without changing LV diastolic dimension and arterial pressure, indicating an increased parietal stress. In addition, midwall shortening was not modified, despite the increased wall tension, suggesting an improvement of cardiac function. Chronic shNHE1 expression in the heart emerges as a possible methodology to reduce pathological cardiac hypertrophy, avoiding potentially undesired effects caused from a body-wide inhibition of NHE1.

Cardiac specific expression of threonine 5 to alanine mutant sarcolipin results in structural remodeling and diastolic dysfunction.

The functional importance of threonine 5 (T5) in modulating the activity of sarcolipin (SLN), a key regulator of sarco/endoplasmic reticulum (SR) Ca2+ ATPase (SERCA) pump was studied using a transgenic mouse model with cardiac specific expression of threonine 5 to alanine mutant SLN (SLNT5A). In these transgenic mice, the SLNT5A protein replaces the endogenous SLN in atria, while maintaining the total SLN content. The cardiac specific expression of SLNT5A results in severe cardiac structural remodeling accompanied by bi-atrial enlargement. Biochemical analyses reveal a selective downregulation of SR Ca2+ handling proteins and a reduced SR Ca2+ uptake both in atria and in the ventricles. Optical mapping analysis shows slower action potential propagation in the transgenic mice atria. Doppler echocardiography and hemodynamic measurements demonstrate a reduced atrial contractility and an impaired diastolic function. Together, these findings suggest that threonine 5 plays an important role in modulating SLN function in the heart. Furthermore, our studies suggest that alteration in SLN function can cause abnormal Ca2+ handling and subsequent cardiac remodeling and dysfunction.

MTHFR C677T polymorphism affects normotensive diastolic blood pressure independently of blood lipids.

BACKGROUND: Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism was found to be associated with hypertension. High blood pressure (BP) is a major risk factor for cardiovascular disease, gestational hypertension, and high-risk pregnancy. BP is a complex trait strongly associated with blood lipid parameters. However, studies of the effect of MTHFR C677T polymorphism on BP levels independently of blood lipids are scarce. Our objective was to analyze and quantify the effect of MTHFR C677T polymorphism on normotensive BP independently of blood lipids. METHODS: MTHFR C677T genotyping was done for 151 Israeli women attending the genetics clinic at Soroka Medical Center. Biochemical (blood lipids) and BP data were extracted from Soroka Medical Center records. BP was regarded as a continuous parameter using analysis of covariance and post hoc Tukey's HSD (honestly significant difference) analysis. RESULTS: The frequencies of genotypes CC, TT, and CT were 41%, 12%, and 47%, respectively. A significant (P < 0.0001) association was found between genotype and diastolic BP (DBP) when adjusted to body mass index and age. Mean DBP was significantly lower for CC than for TT genotypes (71.2 vs. 78.7 mm Hg); however the difference between the heterozygotes (73.9 mm Hg) and the other 2 genotypes was not significant. Cholesterol, LDLcalc (LDLcalculaed), and homocysteine blood levels significantly contributed to the effect of MTHFR C677T polymorphism on the DBP trait. There was also significant association between genotype and folic acid levels. CONCLUSIONS: MTHFR C677T polymorphism significantly affects DBP in Israeli women, independently of blood lipids. Each C to T substitution is associated with a mean 3.4-mm Hg increase in DBP.

Multivariate modeling of body mass index, pulse pressure, systolic and diastolic blood pressure in Chinese twins.

Systolic and diastolic blood pressure, pulse pressure (PP), and body mass index (BMI) are heritable traits in human metabolic health but their common genetic and environmental backgrounds are not well investigated. The aim of this article was to explore the phenotypic and genetic associations among PP, systolic blood pressure (SBP), diastolic blood pressure (DBP), and BMI. The studied sample contained 615 twin pairs (17-84 years) collected in the Qingdao municipality. Univariate and multivariate structural equation models were fitted for assessing the genetic and environmental contributions. The AE model combining additive genetic (A) and unique environmental (E) factors produced the best fit for each four phenotypes. Heritability estimated in univariate analysis ranged from 0.42 to 0.74 with the highest for BMI (95% CI 0.70-0.78), and the lowest for PP (95% CI 0.34-0.49). The multivariate model estimated (1) high genetic correlations for DBP with SBP (0.87), PP with SBP (0.75); (2) low-moderate genetic correlations between PP and DBP (0.32), each BP component and BMI (0.24-0.37); (3) moderate unique environmental correlation for PP with SBP (0.68) and SBP with DBP (0.63); (4) there was no significant unique environmental correlation between PP and BMI. Overall, our multivariate analyses revealed common genetic and environmental backgrounds for PP, BP, and BMI in Chinese twins.