A region with a major effect on blood pressure is located on rat chromosome 1. We have previously isolated this region in reciprocal congenic strains (WKY.SHR-Sa and SHR.WKY-Sa) derived from a cross of the spontaneously hypertensive rat (SHR) with the Wistar-Kyoto rat (WKY) and shown that there are two distinct BP quantitative trait loci (QTLs), BP1 and BP2, in this region. Sisa1, a congenic sub-strain from the SHR.WKY-Sa animals carrying an introgressed segment of 4.3Mb, contains BP1. Here, we report further dissection of BP1 by the creation of two new mutually exclusive congenic sub-strains (Sisa1a and Sisa1b) and interrogation of candidate genes by expression profiling and targeted transcript sequencing. Only one of the sub-strains (Sisa1a) continued to demonstrate a BP difference but with a reduced introgressed segment of 3Mb. Exonic sequencing of the twenty genes located in the Sisa1a region did not identify any major differences between SHR and WKY. However, microarray expression profiling of whole kidney samples and subsequent quantitative RT-PCR identified a single gene, Spon1 that exhibited significant differential expression between the WKY and SHR genotypes at both 6 and 24 weeks of age. Western blot analysis confirmed an increased level of the Spon1 gene product in SHR kidneys. Spon1 belongs to a family of genes with anti-angiogenic properties. These findings justify further investigation of this novel positional candidate gene in BP control in hypertensive rat models and humans.

Variants in the gene encoding the γ-subunit of the epithelial sodium channel (SCNN1G) are associated with both Mendelian and quantitative effects on blood pressure. Here, in four cohorts of 1611 white European families comprising a total of 8199 individuals, we undertook staged testing of candidate SNPs for SCNN1G (supplemented with imputation based on data from the 1000 Genomes Project) followed by a meta-analysis in all families of the strongest candidate. We also examined relationships between the genotypes and relevant intermediate renal phenotypes as well as expression of SCNN1G in human kidneys. We found that an intronic SNP of SCNN1G (rs13331086) was significantly associated with age-, sex- and BMI-adjusted blood pressure in each of the four populations (P < 0.05). In an inverse variance-weighted meta-analysis of this SNP in all four populations each additional minor allele copy was associated with a 1 mmHg increase in systolic blood pressure and 0.52 mmHg increase in diastolic blood pressure (SE = 0.33, P = 0.002 for SBP; SE = 0.21, P = 0.011 for DBP). The same allele was also associated with higher 12-h overnight urinary potassium excretion (P = 0.04), consistent with increased epithelial sodium channel activity. Renal samples from hypertensive subjects showed a non-significant (P = 0.07) 1.7-fold higher expression of SCNN1G compared with normotensive controls. These data provide genetic and phenotypic evidence in support of a role for a common genetic variant of SCNN1G in blood pressure determination.

Ms1/STARS is a novel muscle-specific actin-binding protein that specifically modulates the myocardin-related transcription factor (MRTF)-serum response factor (SRF) regulatory axis within striated muscle. This ms1/STARS-dependent regulatory axis is of central importance within the cardiac gene regulatory network and has been implicated in cardiac development and postnatal cardiac function/homeostasis. The dysregulation of ms1/STARS is associated with and causative of pathological cardiac phenotypes, including cardiac hypertrophy and cardiomyopathy. In order to gain an understanding of the mechanisms governing ms1/STARS expression in the heart, we have coupled a comparative genomic in silico analysis with reporter, gain-of-function, and loss-of-function approaches. Through this integrated analysis, we have identified three evolutionarily conserved regions (ECRs), α, SINA, and DINA, that act as cis-regulatory modules and confer differential cardiac cell-specific activity. Two of these ECRs, α and DINA, displayed distinct regulatory sensitivity to the core cardiac transcription factor GATA4. Overall, our results demonstrate that within embryonic, neonatal, and adult hearts, GATA4 represses ms1/STARS expression with the pathologically associated depletion of GATA4 (type 1/type 2 diabetic models), resulting in ms1/STARS upregulation. This GATA4-dependent repression of ms1/STARS expression has major implications for MRTF-SRF signaling in the context of cardiac development and disease.

Summary

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.

Background

Better sudden cardiac death risk markers are needed in ischemic cardiomyopathy (ICM). Increased heterogeneity of electrical restitution is an important mechanism underlying the risk of ventricular arrhythmia (VA). Our aim was to develop and test a novel quantitative surface electrocardiogram–based measure of VA risk in patients with ICM: the Regional Restitution Instability Index (R2I2).

Methods and Results

R2I2, the mean of the standard deviation of residuals from the mean gradient for each ECG lead at a range of diastolic intervals, was measured retrospectively from high-resolution 12-lead ECGs recorded during an electrophysiology study. Patient groups were as follows: Study group, 26 patients with ICM being assessed for implantable defibrillator; Control group, 29 patients with supraventricular tachycardia undergoing electrophysiology study; and Replication group, 40 further patients with ICM. R2I2 was significantly higher in the Study patients than in Controls (mean ± standard error of the mean: 1.09±0.06 versus 0.63±0.04, P<0.001). Over a median follow-up period of 23 months, 6 of 26 Study group patients had VA or death. R2I2 predicted VA or death independently of demographic factors, electrophysiology study result, left ventricular ejection fraction, or QRS duration (Cox model, P=0.029). R2I2 correlated with peri-infarct zone as assessed by cardiac magnetic resonance imaging (r=0.51, P=0.024). The findings were replicated in the Replication group: R2I2 was significantly higher in 11 of 40 Replication patients experiencing VA (1.18±0.10 versus 0.92±0.05, P=0.019). In combined analysis of ICM cohorts, R2I2 ≥1.03 identified subjects with significantly higher risk of VA or death (43%) compared with R2I2 <1.03 (11%) (P=0.004).

Conclusions

In this pilot study, we have developed a novel VA risk marker, R2I2, and have shown that it correlated with a structural measure of arrhythmic risk and predicted risk of VA or death in patients with ICM. R2I2 may improve risk stratification and merits further evaluation. (J Am Heart Assoc. 2012;1:e001552 doi: 10.1161/JAHA.112.001552.)

Background

STARS (STriated muscle Activator of Rho Signaling) is a sarcomeric protein expressed early in cardiac development that acts as an acute stress sensor for pathological remodeling. However the role of STARS in cardiac development and function is incompletely understood. Here, we investigated the role of STARS in heart development and function in the zebrafish model and in vitro.

Methodology and Principal Findings

Expression of zebrafish STARS (zSTARS) first occurs in the somites by the 16 somite stage [17 hours post fertilization (hpf)]. zSTARS is expressed in both chambers of the heart by 48 hpf, and also in the developing brain, jaw structures and pectoral fins. Morpholino-induced knockdown of zSTARS alters atrial and ventricular dimensions and decreases ventricular fractional shortening (measured by high-speed video microscopy), with pericardial edema and decreased or absent circulation [abnormal cardiac phenotypes in 126/164 (77%) of morpholino-injected embryos vs. 0/152 (0%) of control morpholino embryos]. Co-injection of zsrf (serum response factor) mRNA rescues the cardiac phenotype of zSTARS knockdown, resulting in improved fractional shortening and ventricular end-diastolic dimensions. Ectopic over-expression of STARS in vitro activates the STARS proximal promoter, which contains a conserved SRF site. Chromatin immunoprecipitation demonstrates that SRF binds to this site in vivo and the SRF inhibitor CCG-1423 completely blocks STARS proximal reporter activity in H9c2 cells.

Conclusions/Significance

This study demonstrates for the first time that STARS deficiency severely disrupts cardiac development and function in vivo and revealed a novel STARS-SRF feed-forward autoregulatory loop that could play an essential role in STARS regulation and cardiac function.

Background: being unmarried is associated with worse health and increased mortality risk. Telomere length has emerged as a marker for biological ageing but it is unclear how telomere length relates to marital status.

Objective: to examine the relationship between telomere length and marital status in a sample of middle-aged adults.

Design and subjects: cross-sectional analysis among 321 adults aged 40–64 years.

Methods: telomere length was measured by PCR (T/S ratio). Participants provided information on healthy lifestyle activities including smoking, alcohol use, diet, exercise, obesity as well as social support.

Results: participants married or living with a partner had a mean T/S ratio of 1.70 and those widowed, divorced, separated or never married had a mean T/S ratio of 1.58 in a model adjusted for age, gender and race/ethnicity (P < 0.001). When the analysis was further adjusted for diet, alcohol consumption, exercise, smoking, social support, poverty and obesity, persons married or living with a partner had a higher mean T/S ratio of 1.69 than their unmarried counterparts (1.59) (P = 0.004).

Conclusions: these results indicate that unmarried individuals have shorter telomeres. This relationship between marital status and telomere length is independent of presumed benefits of marriage such as social support and a healthier lifestyle.

Fibroblast growth factor 21 (FGF21) is a novel master regulator of metabolic profile. The biological actions of FGF21 are elicited upon its klotho beta (KLB)-facilitated binding to FGF receptor 1 (FGFR1), FGFR2 and FGFR3. We hypothesised that common polymorphisms in the FGF21 signalling pathway may be associated with metabolic risk. At the screening stage, we examined associations between 63 common single-nucleotide polymorphisms (SNPs) in five genes of this pathway (FGF21, KLB, FGFR1, FGFR2, FGFR3) and four metabolic phenotypes (LDL cholesterol – LDL-C, HDL-cholesterol – HDL-C, triglycerides and body mass index) in 629 individuals from Silesian Hypertension Study (SHS). Replication analyses were performed in 5478 unrelated individuals of the Swiss CoLaus cohort (imputed genotypes) and in 3030 directly genotyped individuals of the German Myocardial Infarction Family Study (GerMIFS). Of 54 SNPs that met quality control criteria after genotyping in SHS, 4 (rs4733946 and rs7012413 in FGFR1; rs2071616 in FGFR2 and rs7670903 in KLB) showed suggestive association with LDL-C (P=0.0006, P=0.0013, P=0.0055, P=0.011, respectively) and 1 (rs2608819 in KLB) was associated with body mass index (P=0.011); all with false discovery rate q<0.5. Of these, only one FGFR2 polymorphism (rs2071616) showed replicated association with LDL-C in both CoLaus (P=0.009) and men from GerMIFS (P=0.017). The direction of allelic effect of rs2071616 upon LDL-C was consistent in all examined populations. These data show that common genetic variations in FGFR2 may be associated with LDL-C in subjects of white European ancestry.

Fibroblast growth factor 21 (FGF21) is a novel master regulator of metabolic profile. The biological actions of FGF21 are elicited upon its klotho beta (KLB)-facilitated binding to FGF receptor 1 (FGFR1), FGF receptor 2 (FGFR2) and FGF receptor 3 (FGFR3). We hypothesised that common polymorphisms in the FGF21 signalling pathway may be associated with metabolic risk. At the screening stage we examined associations between 63 common single nucleotide polymorphisms (SNPs) in 5 genes of this pathway (FGF21, KLB, FGFR1, FGFR2, FGFR3) and 4 metabolic phenotypes (LDL cholesterol - LDL-C, HDL-cholesterol, triglycerides and body mass index - BMI) in 629 individuals from Silesian Hypertension Study. Replication analyses were performed in 5,478 unrelated individuals of the Swiss CoLaus cohort (imputed genotypes) and in 3,030 directly genotyped individuals of the German Myocardial Infarction Family Study. Of 54 SNPs that met quality control criteria after genotyping in Silesian Hypertension Study, four (rs4733946 and rs7012413 in FGFR1; rs2071616 in FGFR2 and rs7670903 in KLB) showed suggestive association with LDL-C (p=0.0006, p=0.0013, p=0.0055, p=0.011, respectively) and one (rs2608819 in KLB) was associated with BMI (p=0.011); all with false discovery rate q<0.5. Of these, only one FGFR2 polymorphism (rs2071616) showed replicated association with LDL-C in both the CoLaus cohort (p=0.009) and men from the German Myocardial Infarction Family Study (p=0.017). The direction of allelic effect of rs2071616 upon LDL-C was consistent in all examined populations. These data show that common genetic variation in FGFR2 may be associated with LDL-C in subjects of white European ancestry.

Objective

A rare mutation in low density lipoprotein receptor-related protein 6 gene (LRP6) was identified as the primary molecular defect underlying monogenic form of coronary artery disease. We hypothesised that common variants in LRP6 could predispose subjects to elevated LDL-cholesterol (LDL-C).

Methods and Results

12 common (minor allele frequency ≥0.1) single nucleotide polymorphisms in LRP6 were genotyped in 703 individuals from 213 Polish pedigrees (Silesian Cardiovascular Study families). The family-based analysis revealed that the minor allele of rs10845493 clustered with elevated LDL-C in offspring more frequently than expected by chance (p=0.0053). The quantitative analysis restricted to subjects free of lipid-lowering treatment confirmed the association between rs10845493 and age-, sex- and BMI-adjusted circulating levels of LDL-C in families as well as 2 additional populations - 218 unrelated subjects from Silesian Cardiovascular Study replication panel and 1138 individuals from Young Men Cardiovascular Association cohort (p=0.0268, p=0.0476 and p=0.0472, respectively). In the inverse variance weighted meta-analysis of the 3 populations each extra minor allele copy of rs10845493 was associated with 0.14 mmol/L increase in age-, sex- and BMI-adjusted LDL-C (SE=0.05, p=0.0038).

Conclusions

Common polymorphism in the gene underlying monogenic form of coronary artery disease impacts on risk of LDL-C elevation.

Objectives

Men show higher rates of cardiovascular morbidity and mortality than pre-menopausal women and this sexual dimorphism may be related to sex-specific effects of sex steroids on cardiovascular risk factors. Unlike androgens, estrogens were not extensively investigated in relation to cardiovascular phenotypes in men.

Methods

We examined associations of estradiol and estrone and their precursors (total testosterone and androstenedione) with traditional cardiovascular risk factors (lipids, blood pressure, body mass) in 933 young (median age – 19 years), apparently healthy Polish men.

Results

Total estradiol was associated with total cholesterol (p=0.006) and HDL-cholesterol (p<0.001) and estrone showed the strongest associations with both total cholesterol (p<0.001) and LDL-cholesterol (p<0.001) in the unadjusted ANOVA analysis. In the multivariable adjusted models in which other independent variables were held as constant one standard deviation increase in estradiol level was associated with 6%-standard deviation increase in total cholesterol (standardized B=0.06, p=0.038) and 6%-standard deviation decrease in HDL-cholesterol (standardized B=-0.06, p=0.036). An increase in estrone levels by one standard deviation was associated with respective 12%- and 13%-standard deviation increases in total cholesterol (standardized B=0.12, p<0.001) and LDL-cholesterol levels (standardized B=0.12, p<0.001) after controlling for other predictors of lipids. Estrone correlated linearly with androstenedione (r=0.28, p<0.001) but there was no correlation between estradiol and testosterone. Estrogens retained their independent associations with lipids after adjustment for their biochemical precursors in the multivariable analysis.

Conclusions

Increased levels of estrogens are associated with unfavourable lipid profile in men and that this association is apparent early in life, before cardiovascular disease manifestations.

BACKGROUND

Men exhibit higher risk of nondiabetic renal diseases than women. This male susceptibility to renal disease may be mediated by gender-specific factors such as sex hormones.

METHODS

We have undertaken a cross-sectional examination of associations between renal function (creatinine clearance estimated based on Cockcroft–Gault equation) and circulating levels of sex steroids (total testosterone, total estradiol, estrone, androstenedione, dehydroepiandrosterone sulfate (DHEA-S), and dihydrotestosterone) in 928 young (mean age: 18.5 ± 1.2 years) men.

RESULTS

Both androstenedione and DHEA-S showed inverse linear associations with renal function in the crude analysis of lean men (those with body mass index (BMI) less than median). However, only DHEA-S retained its association with renal function in lean subjects after adjustment—assuming no changes in other independent variables 1 s.d. increase in DHEA-S was associated with 13%-s.d. decrease in creatinine clearance (P = 0.004). Testosterone decreased across tertiles of creatinine clearance only in the crude analysis of nonlean (BMI greater than median) subjects (P < 0.001). The adjusted regression analysis that assumed no changes in other independent variables showed that 1 s.d. increase in total testosterone was associated with 11%-s.d. decrease in creatinine clearance of nonlean men (P = 0.006). Factor analysis confirmed an inverse association of renal function with both sex steroids and a different pattern of their loadings on glomerular filtration–related factors in lean (DHEA-S) and nonlean (testosterone) subjects.

CONCLUSIONS

Our data may suggest that androgens are inversely associated with estimated renal function in apparently healthy men without history of cardiovascular disease.

Recently, genome wide association studies (GWAS) have identified a number of single nucleotide polymorphisms (SNPs) as being associated with coronary heart disease (CHD). We estimated the effect of these SNPs on incident CHD, stroke and total mortality in the prospective cohorts of the MORGAM Project. We studied cohorts from Finland, Sweden, France and Northern Ireland (total N = 33,282, including 1,436 incident CHD events and 571 incident stroke events). The lead SNPs at seven loci identified thus far and additional SNPs (in total 42) were genotyped using a case-cohort design. We estimated the effect of the SNPs on disease history at baseline, disease events during follow-up and classic risk factors. Multiple testing was taken into account using false discovery rate (FDR) analysis. SNP rs1333049 on chromosome 9p21.3 was associated with both CHD and stroke (HR = 1.20, 95% CI 1.08–1.34 for incident CHD events and 1.15, 0.99–1.34 for incident stroke). SNP rs11670734 (19q12) was associated with total mortality and stroke. SNP rs2146807 (10q11.21) showed some association with the fatality of acute coronary event. SNP rs2943634 (2q36.3) was associated with high density lipoprotein (HDL) cholesterol and SNPs rs599839, rs4970834 (1p13.3) and rs17228212 (15q22.23) were associated with non-HDL cholesterol. SNPs rs2943634 (2q36.3) and rs12525353 (6q25.1) were associated with blood pressure. These findings underline the need for replication studies in prospective settings and confirm the candidacy of several SNPs that may play a role in the etiology of cardiovascular disease.

Background

Renal dysfunction is a frequent comorbidity associated with high mortality in patients with chronic heart failure (CHF). The intrinsic biological age might affect the ability of the kidney to cope with the challenging environment caused by CHF. We explored the association between leukocyte telomere length, a marker for biological age, and renal function in patients with CHF.

Methods and results

Telomere length was determined by a real-time quantitative polymerase chain reaction in 866 CHF patients. Renal function was estimated with the simplified Modification of Diet in Renal Disease equation. The median age was 74 (interquartile range 64–79) years, 61% male, left ventricular ejection fraction of 30 (23–44)%, and the estimated glomerular filtration rate was 53 (40–68) ml/min/1.73 m2. Telomere length was associated with renal function (correlation coefficient 0.123, P < 0.001). This relationship remained significant after adjustment for age, gender, age of CHF onset (standardized-beta 0.091, P = 0.007). Also additionally adjusting for the severity of CHF and baseline differences did not change our findings.

Conclusion

The association between shorter leukocyte telomere length and reduced renal function in heart failure suggests that intrinsic biological aging affects the ability of the kidney to cope with the systemic changes evoked by heart failure.

BACKGROUND

Modern genotyping platforms permit a systematic search for inherited components of complex diseases. We performed a joint analysis of two genomewide association studies of coronary artery disease.

METHODS

We first identified chromosomal loci that were strongly associated with coronary artery disease in the Wellcome Trust Case Control Consortium (WTCCC) study (which involved 1926 case subjects with coronary artery disease and 2938 controls) and looked for replication in the German MI [Myocardial Infarction] Family Study (which involved 875 case subjects with myocardial infarction and 1644 controls). Data on other single-nucleotide polymorphisms (SNPs) that were significantly associated with coronary artery disease in either study (P<0.001) were then combined to identify additional loci with a high probability of true association. Genotyping in both studies was performed with the use of the GeneChip Human Mapping 500K Array Set (Affymetrix).

RESULTS

Of thousands of chromosomal loci studied, the same locus had the strongest association with coronary artery disease in both the WTCCC and the German studies: chromosome 9p21.3 (SNP, rs1333049) (P=1.80×10−14 and P=3.40×10−6, respectively). Overall, the WTCCC study revealed nine loci that were strongly associated with coronary artery disease (P<1.2×10−5 and less than a 50% chance of being falsely positive). In addition to chromosome 9p21.3, two of these loci were successfully replicated (adjusted P<0.05) in the German study: chromosome 6q25.1 (rs6922269) and chromosome 2q36.3 (rs2943634). The combined analysis of the two studies identified four additional loci significantly associated with coronary artery disease (P<1.3×10−6) and a high probability (>80%) of a true association: chromosomes 1p13.3 (rs599839), 1q41 (rs17465637), 10q11.21 (rs501120), and 15q22.33 (rs17228212).

CONCLUSIONS

We identified several genetic loci that, individually and in aggregate, substantially affect the risk of development of coronary artery disease.

Mean platelet volume (MPV) and platelet count (PLT) are highly heritable and tightly regulated traits. We performed a genome-wide association study for MPV and identified one SNP, rs342293, as having highly significant and reproducible association with MPV (per-G allele effect 0.016 ± 0.001 log fL; P < 1.08 × 10−24) and PLT (per-G effect −4.55 ± 0.80 109/L; P < 7.19 × 10−8) in 8586 healthy subjects. Whole-genome expression analysis in the 1-MB region showed a significant association with platelet transcript levels for PIK3CG (n = 35; P = .047). The G allele at rs342293 was also associated with decreased binding of annexin V to platelets activated with collagen-related peptide (n = 84; P = .003). The region 7q22.3 identifies the first QTL influencing platelet volume, counts, and function in healthy subjects. Notably, the association signal maps to a chromosome region implicated in myeloid malignancies, indicating this site as an important regulatory site for hematopoiesis. The identification of loci regulating MPV by this and other studies will increase our insight in the processes of megakaryopoiesis and proplatelet formation, and it may aid the identification of genes that are somatically mutated in essential thrombocytosis.

Adult height is a model polygenic trait, but there has been limited success in identifying the genes underlying its normal variation. To identify genetic variants influencing adult human height, we used genome-wide association data from 13,665 individuals and genotyped 39 variants in an additional 16,482 samples. We identified 20 variants associated with adult height (P < 5 × 10−7, with 10 reaching P < 1 × 10−10). Combined, the 20 SNPs explain ~3% of height variation, with a ~5 cm difference between the 6.2% of people with 17 or fewer ‘tall’ alleles compared to the 5.5% with 27 or more ‘tall’ alleles. The loci we identified implicate genes in Hedgehog signaling (IHH, HHIP, PTCH1), extracellular matrix (EFEMP1, ADAMTSL3, ACAN) and cancer (CDK6, HMGA2, DLEU7) pathways, and provide new insights into human growth and developmental processes. Finally, our results provide insights into the genetic architecture of a classic quantitative trait.

Background

Myocyte stress 1 (MS1) is a striated muscle actin binding protein required for the muscle specific activity of the evolutionary ancient myocardin related transcription factor (MRTF)/serum response factor (SRF) transcriptional pathway. To date, little is known about the molecular mechanisms that govern skeletal muscle specific expression of MS1. Such mechanisms are likely to play a major role in modulating SRF activity and therefore muscle determination, differentiation and regeneration. In this study we employed a comparative in silico analysis coupled with an experimental promoter characterisation to delineate these mechanisms.

Results

Analysis of MS1 expression in differentiating C2C12 muscle cells demonstrated a temporal differentiation dependent up-regulation in ms1 mRNA. An in silico comparative sequence analysis identified two conserved putative myogenic regulatory domains within the proximal 1.5 kbp of 5' upstream sequence. Co-transfecting C2C12 myoblasts with ms1 promoter/luciferase reporters and myogenic regulatory factor (MRF) over-expression plasmids revealed specific sensitivity of the ms1 promoter to MyoD. Subsequent mutagenesis and EMSA analysis demonstrated specific targeting of MyoD at two distinct E-Boxes (E1 and E2) within identified evolutionary conserved regions (ECRs, α and β). Chromatin immunoprecipitation (ChIP) analysis indicates that co-ordinated binding of MyoD at E-Boxes located within ECRs α and β correlates with the temporal induction in ms1 mRNA.

Conclusion

These findings suggest that the tissue specific and differentiation dependent up-regulation in ms1 mRNA is mediated by temporal binding of MyoD at distinct evolutionary conserved E-Boxes within the ms1 5' upstream sequence. We believe, through its activation of ms1, this is the first study to demonstrate a direct link between MyoD activity and SRF transcriptional signalling, with clear implications for the understanding of muscle determination, differentiation and regeneration.

Aims

To describe temporal profiles of plasma matrix metalloproteinases (MMP-2 and MMP-9), and their relationship with echocardiographic (ECG) parameters of left ventricular (LV) function and remodelling, after acute myocardial infarction (AMI) in man.

Methods and results

Plasma MMP-2 and MMP-9 were assayed at intervals (0-12, 12-24, 24-48, 48-72, 72-96, and >96 h) in 91 patients with AMI (ST-elevation/non-ST-elevation 77/24; 73% male; 40% anterior site) and on a single occasion in 172 age- and sex-matched control subjects with stable coronary artery disease. ECG assessment of LV volumes, LV ejection fraction (LVEF), and wall motion index score were assessed before discharge and at follow-up (median 176, range 138-262 days) for patients and on a single occassion in controls. Plasma MMP-2 was similar at all times after AMI, elevated when compared with control (P = 0.005-0.001) and unrelated to LV function or volume during index admission or at follow-up. Maximal MMP-9 was seen at 0-12 h and was elevated when compared with control (P = 0.002) followed by fall to a plateau. Both maximal and plateau MMP-9 concentration correlated with white blood cell (WBC, P = 0.023 to <0.001) and neutrophil count (P = 0.014 to <0.001). Maximal MMP-9 had independent predictive value for lower LVEF (P = 0.004) during admission and for greater change in LV end-diastolic volume between admission and follow-up (R = 0.3, P = 0.016). In contrast, higher plateau levels of MMP-9 were associated with relative preservation of LV function (increasing LVEF, P = 0.002; decreasing WMIS, P = 0.009) and less change in end-systolic volume and end-diastolic volumes after discharge (P = 0.001 and 0.024, respectively).

Conclusion

Both MMP-9 and MMP-2 are elevated following AMI. The biphasic profile of plasma MMP-9 is related to LV remodelling and function following AMI in man. Higher early levels of MMP-9 associate with the extent of LV remodelling and circulating WBC levels. In contrast, higher plateau levels later after AMI are associated with relative preservation of LV function. Temporal profile, rather than absolute magnitude, of MMP-9 activity appears to be important for LV remodelling after AMI.

We describe here the results of the first genome-wide survey of candidate exon repetition events in expressed sequences from human, mouse, rat, chicken, zebrafish and fly. Exon repetition is a rare event, reported in <10 genes, in which one or more exons is tandemly duplicated in mRNA but not in the gene. To identify candidates, we analysed database sequences for mRNA transcripts in which the order of the spliced exons does not follow the linear genomic order of the individual gene [events we term rearrangements or repetition in exon order (RREO)]. Using a computational approach, we have identified 245 genes in mammals that produce RREO events. RREO in mRNA occurs predominantly in the coding regions of genes. However, exon 1 is never involved. Analysis of the open reading frames suggests that this process may increase protein diversity and regulate protein expression via nonsense-mediated RNA decay. The sizes of the exons and introns involved around these events suggest a gene model structure that may facilitate non-linear splicing. These findings imply that RREO affects a significant subset of genes within a genome and suggests that non-linear information encoded within the genomes of complex organisms could contribute to phenotypic variation.

Exon repetition describes the presence of tandemly repeated exons in mRNA in the absence of duplications in the genome. Its existence challenges our understanding of gene expression, because the linear organization of sequences in apparently normal genes must be subverted during RNA synthesis or processing. It is restricted to a small number of genes in some of which over half of the mRNA contains specific patterns of repetition. Although it is sometimes assumed to arise by trans-splicing, there is no evidence of this and the efficiency is very much higher than for examples of bona fide trans-splicing in mammals. Furthermore, a potentially ubiquitous reaction such as trans-splicing is not consistent with a phenomenon that involves such a high proportion of the products of so few genes. Instead, it seems more probable that exon repetition is caused by a specific trans-acting factor. We have tested this and demonstrate for the two best characterized examples that the property is restricted to specific alleles of the affected genes and is determined in cis. It is not determined by exonic splicing signals, as had been suggested previously. In heterozygotes, RNA transcribed from the two alleles of an affected gene can have fundamentally different fates.

In order to assess whether gene expression variability could be influenced by several SNPs acting in cis, either through additive or more complex haplotype effects, a systematic genome-wide search for cis haplotype expression quantitative trait loci (eQTL) was conducted in a sample of 758 individuals, part of the Cardiogenics Transcriptomic Study, for which genome-wide monocyte expression and GWAS data were available. 19,805 RNA probes were assessed for cis haplotypic regulation through investigation of ∼2,1×109 haplotypic combinations. 2,650 probes demonstrated haplotypic p-values >104-fold smaller than the best single SNP p-value. Replication of significant haplotype effects were tested for 412 probes for which SNPs (or proxies) that defined the detected haplotypes were available in the Gutenberg Health Study composed of 1,374 individuals. At the Bonferroni correction level of 1.2×10−4 (∼0.05/412), 193 haplotypic signals replicated. 1000G imputation was then conducted, and 105 haplotypic signals still remained more informative than imputed SNPs. In-depth analysis of these 105 cis eQTL revealed that at 76 loci genetic associations were compatible with additive effects of several SNPs, while for the 29 remaining regions data could be compatible with a more complex haplotypic pattern. As 24 of the 105 cis eQTL have previously been reported to be disease-associated loci, this work highlights the need for conducting haplotype-based and 1000G imputed cis eQTL analysis before commencing functional studies at disease-associated loci.

Author Summary

In order to assess whether gene expression variability could be influenced by the presence of more than one cis-acting SNP, we have conducted a systematic genome-wide search for haplotypic cis eQTL effects in a sample of 758 individuals and replicated the findings in an independent sample of 1,374 subjects. In both studies, genome-wide monocytes expression and genotype data were available. We identified 105 genes whose monocyte expression was under the influence of multiple cis-acting SNPs. About 75% of the detected genetic effects were related to independent additive SNP effects and the last quarter due to more complex haplotype effects. Of note, 24 of the genes identified to be affected by multiple cis eSNPs have been previously reported to reside at disease-associated loci. This could suggest that such multiple locus-specific genetic effects could contribute to the susceptibility to human diseases.

A large number of genome-wide association studies have been performed during the past five years to identify associations between SNPs and human complex diseases and traits. The assignment of a functional role for the identified disease-associated SNP is not straight-forward. Genome-wide expression quantitative trait locus (eQTL) analysis is frequently used as the initial step to define a function while allele-specific gene expression (ASE) analysis has not yet gained a wide-spread use in disease mapping studies. We compared the power to identify cis-acting regulatory SNPs (cis-rSNPs) by genome-wide allele-specific gene expression (ASE) analysis with that of traditional expression quantitative trait locus (eQTL) mapping. Our study included 395 healthy blood donors for whom global gene expression profiles in circulating monocytes were determined by Illumina BeadArrays. ASE was assessed in a subset of these monocytes from 188 donors by quantitative genotyping of mRNA using a genome-wide panel of SNP markers. The performance of the two methods for detecting cis-rSNPs was evaluated by comparing associations between SNP genotypes and gene expression levels in sample sets of varying size. We found that up to 8-fold more samples are required for eQTL mapping to reach the same statistical power as that obtained by ASE analysis for the same rSNPs. The performance of ASE is insensitive to SNPs with low minor allele frequencies and detects a larger number of significantly associated rSNPs using the same sample size as eQTL mapping. An unequivocal conclusion from our comparison is that ASE analysis is more sensitive for detecting cis-rSNPs than standard eQTL mapping. Our study shows the potential of ASE mapping in tissue samples and primary cells which are difficult to obtain in large numbers.