Dysfunctional nitric oxide signalling increases risk of myocardial infarction.

Myocardial infarction, a leading cause of death in the Western world, usually occurs when the fibrous cap overlying an atherosclerotic plaque in a coronary artery ruptures. The resulting exposure of blood to the atherosclerotic material then triggers thrombus formation, which occludes the artery. The importance of genetic predisposition to coronary artery disease and myocardial infarction is best documented by the predictive value of a positive family history. Next-generation sequencing in families with several affected individuals has revolutionized mutation identification. Here we report the segregation of two private, heterozygous mutations in two functionally related genes, GUCY1A3 (p.Leu163Phefs*24) and CCT7 (p.Ser525Leu), in an extended myocardial infarction family. GUCY1A3 encodes the α1 subunit of soluble guanylyl cyclase (α1-sGC), and CCT7 encodes CCTη, a member of the tailless complex polypeptide 1 ring complex, which, among other functions, stabilizes soluble guanylyl cyclase. After stimulation with nitric oxide, soluble guanylyl cyclase generates cGMP, which induces vasodilation and inhibits platelet activation. We demonstrate in vitro that mutations in both GUCY1A3 and CCT7 severely reduce α1-sGC as well as ß1-sGC protein content, and impair soluble guanylyl cyclase activity. Moreover, platelets from digenic mutation carriers contained less soluble guanylyl cyclase protein and consequently displayed reduced nitric-oxide-induced cGMP formation. Mice deficient in α1-sGC protein displayed accelerated thrombus formation in the microcirculation after local trauma. Starting with a severely affected family, we have identified a link between impaired soluble-guanylyl-cyclase-dependent nitric oxide signalling and myocardial infarction risk, possibly through accelerated thrombus formation. Reversing this defect may provide a new therapeutic target for reducing the risk of myocardial infarction.

Expression pattern in human macrophages dependent on 9p21.3 coronary artery disease risk locus.

OBJECTIVE: Genome-wide association studies identified a risk haplotype on chromosome 9p21.3 to be associated with coronary artery disease (CAD) and myocardial infarction (MI). Since this region does not contain a clear candidate gene with known pathophysiology, we performed a haplotype-specific expression study in human macrophages during pro-inflammatory stimulation to investigate the locus-dependent expression patterns in a model of atherosclerosis, the underlying cause for CAD and MI. METHODS: Blood samples were taken from 40 male stable MI patients either homozygous for 9p21.3 risk (n = 20) or non-risk haplotype (n = 20) as well as from 28 healthy male individuals (n = 14 for each haplotype). Monocytes were isolated by density gradient centrifugation followed by differentiation into macrophages via M-CSF. Macrophages were either incubated with a pro-inflammatory IFNγ-LPS cocktail or kept untreated as controls. After 24 h, RNA was isolated and applied to Affymetrix Human Exon 1.0 ST Arrays. RESULTS: Macrophages from MI patients and controls stratified for 9p21.3 haplotypes, exhibited marked differences in gene expression. Most pronounced differences were found in inflammatory mediators, like the chemokines CCL8 and CCL2 and the lectines CLEC4E and CLEC5A. Differences in expression changes could be seen most obviously during inflammatory stimulation for both, the interleukins IL12B and IL1B, and members of metallothionein gene family. CONCLUSION: These findings show that gene expression is different in 9p21.3 haplotype-stratified macrophages. While these effects are relatively small in our in vitro model of atherosclerosis, these biological effects may contribute to a long term effect in risk haplotype carriers increasing susceptibility to CAD and MI.

Genetic association study identifies HSPB7 as a risk gene for idiopathic dilated cardiomyopathy.

Dilated cardiomyopathy (DCM) is a structural heart disease with strong genetic background. Monogenic forms of DCM are observed in families with mutations located mostly in genes encoding structural and sarcomeric proteins. However, strong evidence suggests that genetic factors also affect the susceptibility to idiopathic DCM. To identify risk alleles for non-familial forms of DCM, we carried out a case-control association study, genotyping 664 DCM cases and 1,874 population-based healthy controls from Germany using a 50K human cardiovascular disease bead chip covering more than 2,000 genes pre-selected for cardiovascular relevance. After quality control, 30,920 single nucleotide polymorphisms (SNP) were tested for association with the disease by logistic regression adjusted for gender, and results were genomic-control corrected. The analysis revealed a significant association between a SNP in HSPB7 gene (rs1739843, minor allele frequency 39%) and idiopathic DCM (p = 1.06 × 10⁻6, OR  = 0.67 [95% CI 0.57-0.79] for the minor allele T). Three more SNPs showed p < 2.21 × 10⁻5. De novo genotyping of these four SNPs was done in three independent case-control studies of idiopathic DCM. Association between SNP rs1739843 and DCM was significant in all replication samples: Germany (n =564, n = 981 controls, p = 2.07 × 10⁻³, OR = 0.79 [95% CI 0.67-0.92]), France 1 (n = 433 cases, n = 395 controls, p =3.73 × 10⁻³, OR  = 0.74 [95% CI 0.60-0.91]), and France 2 (n = 249 cases, n = 380 controls, p = 2.26 × 10⁻4, OR  = 0.63 [95% CI 0.50-0.81]). The combined analysis of all four studies including a total of n = 1,910 cases and n = 3,630 controls showed highly significant evidence for association between rs1739843 and idiopathic DCM (p = 5.28 × 10⁻¹³, OR= 0.72 [95% CI 0.65-0.78]). None of the other three SNPs showed significant results in the replication stage.This finding of the HSPB7 gene from a genetic search for idiopathic DCM using a large SNP panel underscores the influence of common polymorphisms on DCM susceptibility.