Loss of soluble guanylyl cyclase in platelets contributes to atherosclerotic plaque formation and vascular inflammation

Variants in genes encoding the soluble guanylyl cyclase (sGC) in platelets are associated with coronary artery disease (CAD) risk. Here, by using histology, flow cytometry and intravital microscopy, we show that functional loss of sGC in platelets of atherosclerosis-prone Ldlr^-/- mice contributes to atherosclerotic plaque formation, particularly via increasing in vivo leukocyte adhesion to atherosclerotic lesions. In vitro experiments revealed that supernatant from activated platelets lacking sGC promotes leukocyte adhesion to endothelial cells (ECs) by activating ECs. Profiling of platelet-released cytokines indicated that reduced platelet angiopoietin-1 release by sGC-depleted platelets, which was validated in isolated human platelets from carriers of GUCY1A1 risk alleles, enhances leukocyte adhesion to ECs. I mp or ta ntly, p ha rm ac ol ogical sGC stimulation increased platelet angiopoietin-1 release in vitro and reduced leukocyte recruitment and atherosclerotic plaque formation in atherosclerosis-prone Ldlr^-/- mice. Therefore, pharmacological sGC stimulation might represent a potential therapeutic strategy to prevent and treat CAD.

Acute mental stress drives vascular inflammation and promotes plaque destabilization in mouse atherosclerosis

AIMS

Mental stress substantially contributes to the initiation and progression of human disease, including cardiovascular conditions. We aim to investigate the underlying mechanisms of these contributions since they remain largely unclear.

METHODS AND RESULTS

Here, we show in humans and mice that leucocytes deplete rapidly from the blood after a single episode of acute mental stress. Using cell-tracking experiments in animal models of acute mental stress, we found that stress exposure leads to prompt uptake of inflammatory leucocytes from the blood to distinct tissues including heart, lung, skin, and, if present, atherosclerotic plaques. Mechanistically, we found that acute stress enhances leucocyte influx into mouse atherosclerotic plaques by modulating endothelial cells. Specifically, acute stress increases adhesion molecule expression and chemokine release through locally derived norepinephrine. Either chemical or surgical disruption of norepinephrine signalling diminished stress-induced leucocyte migration into mouse atherosclerotic plaques.

CONCLUSION

Our data show that acute mental stress rapidly amplifies inflammatory leucocyte expansion inside mouse atherosclerotic lesions and promotes plaque vulnerability.

Abstract MP10: The Long Non-coding RNA LINC02502 Modulates Vascular Smooth Muscle Cell Phenotypes

Background: Genome-wide association studies led to the identification of several genomic loci associated with coronary artery disease risk. One such locus is chromosome 4q27 which harbors the long non-coding RNA (lncRNA) LINC02502 and the PDE5A gene. PDE5A encodes phosphodiesterase 5a, the enzyme that degrades the second messenger cyclic guanosine monophosphate. We previously showed that differential PDE5A expression is mediated via LINC02502 -mediated scaffolding of the transcription factor REST.

Methods and Results: In a screening of vascular cell types, we identified vascular smooth muscle cells (VSMC) to express both PDE5A and LINC02502 . Using RNA interference, we studied the ability of VSMC to migrate in the presence or absence of LINC02502 in in vitro scratch wound healing assays. Knockdown of LINC02502 led to a significant reduction of VSMC migration. VSMC proliferation was determined using BrdU incorporation assays. After knockdown of LINC02502 , VSMC proliferation was decreased. To investigate whether LINC02502 influences inflammatory phenotypes, we ectopically overexpressed the lncRNA in VSMC and analyzed a panel of inflammatory transcripts using quantitative PCR. In general, overexpression of LINC02502 rendered VSMC more inflammatory. Particularly, LINC02502 increased the expression of interleukin-1β, chemokine (C-X-C motif) ligand 1, and fractalkine. Importantly, we did not make these observations secondary to overexpression of PDE5A, suggesting that LINC02502 regulates these transcripts in an independent manner. In silico analysis, however, revealed that LINC02502 -regulated targets were enriched for predicted targets of REST.

Conclusion: The lncRNA LINC02502 is a candidate for mediating the risk of coronary artery disease at the chromosome 4q27 locus via regulating PDE5A . Independent of PDE5A regulation, LINC02502 promotes pro-atherosclerotic phenotypes in VSMC, i.e., migration, proliferation, and expression of inflammatory transcripts. Modulating LINC02502 might be a novel approach to prevent and treat coronary atherosclerosis via multiple pathways.

A proteomic atlas of the neointima identifies novel druggable targets for preventive therapy

Aims 

In-stent restenosis is a complication after coronary stenting associated with morbidity and mortality. Here, we sought to investigate the molecular processes underlying neointima formation and to identify new treatment and prevention targets.

Methods and results 

Neointima formation was induced by wire injury in mouse femoral arteries. High-accuracy proteomic measurement of single femoral arteries to a depth of about 5000 proteins revealed massive proteome remodelling, with more than half of all proteins exhibiting expression differences between injured and non-injured vessels. We observed major changes in the composition of the extracellular matrix and cell migration processes. Among the latter, we identified the classical transient receptor potential channel 6 (TRPC6) to drive neointima formation. While Trpc6  ^−/− mice presented reduced neointima formation compared to wild-type mice (1.44 ± 0.39 vs. 2.16 ± 0.48, P = 0.01), activating or repressing TRPC6 in human vascular smooth muscle cells resulted in increased [vehicle 156.9 ± 15.8 vs. 1-oleoyl-2-acetyl-sn-glycerol 179.1 ± 8.07 (10³ pixels), P = 0.01] or decreased migratory capacity [vehicle 130.0 ± 26.1 vs. SAR7334 111.4 ± 38.0 (10³ pixels), P = 0.04], respectively. In a cohort of individuals with angiographic follow-up (n = 3068, males: 69.9%, age: 59 ± 11 years, follow-up 217.1 ± 156.4 days), homozygous carriers of a common genetic variant associated with elevated TRPC6 expression were at increased risk of restenosis after coronary stenting (adjusted odds ratio 1.49, 95% confidence interval 1.08–2.05; P = 0.01).

Conclusions 

Our study provides a proteomic atlas of the healthy and injured arterial wall that can be used to define novel factors for therapeutic targeting. We present TRPC6 as an actionable target to prevent neointima formation secondary to vascular injury and stent implantation.

Functional investigation of the coronary artery disease gene SVEP1

A missense variant of the sushi, von Willebrand factor type A, EGF and pentraxin domain containing protein 1 (SVEP1) is genome-wide significantly associated with coronary artery disease. The mechanisms how SVEP1 impacts atherosclerosis are not known. We found endothelial cells (EC) and vascular smooth muscle cells to represent the major cellular source of SVEP1 in plaques. Plaques were larger in atherosclerosis-prone Svep1 haploinsufficient (ApoE-/-Svep1+/-) compared to Svep1 wild-type mice (ApoE-/-Svep1+/+) and ApoE-/-Svep1+/- mice displayed elevated plaque neutrophil, Ly6Chigh monocyte, and macrophage numbers. We assessed how leukocytes accumulated more inside plaques in ApoE-/-Svep1+/- mice and found enhanced leukocyte recruitment from blood into plaques. In vitro, we examined how SVEP1 deficiency promotes leukocyte recruitment and found elevated expression of the leukocyte attractant chemokine (C-X-C motif) ligand 1 (CXCL1) in EC after incubation with missense compared to wild-type SVEP1. Increasing wild-type SVEP1 levels silenced endothelial CXCL1 release. In line, plasma Cxcl1 levels were elevated in ApoE-/-Svep1+/- mice. Our studies reveal an atheroprotective role of SVEP1. Deficiency of wild-type Svep1 increased endothelial CXCL1 expression leading to enhanced recruitment of proinflammatory leukocytes from blood to plaque. Consequently, elevated vascular inflammation resulted in enhanced plaque progression in Svep1 deficiency.

Association of the coronary artery disease risk gene GUCY1A3 with ischaemic events after coronary intervention

Aim

A common genetic variant at the GUCY1A3 coronary artery disease locus has been shown to influence platelet aggregation. The risk of ischaemic events including stent thrombosis varies with the efficacy of aspirin to inhibit platelet reactivity. This study sought to investigate whether homozygous GUCY1A3 (rs7692387) risk allele carriers display higher on-aspirin platelet reactivity and risk of ischaemic events early after coronary intervention.

Methods and results

The association of GUCY1A3 genotype and on-aspirin platelet reactivity was analysed in the genetics substudy of the ISAR-ASPI registry (n = 1678) using impedance aggregometry. The clinical outcome cardiovascular death or stent thrombosis within 30 days after stenting was investigated in a meta-analysis of substudies of the ISAR-ASPI registry, the PLATO trial (n = 3236), and the Utrecht Coronary Biobank (n = 1003) comprising a total 5917 patients. Homozygous GUCY1A3 risk allele carriers (GG) displayed increased on-aspirin platelet reactivity compared with non-risk allele (AA/AG) carriers [150 (interquartile range 91–209) vs. 134 (85–194) AU⋅min, P < 0.01]. More homozygous risk allele carriers, compared with non-risk allele carriers, were assigned to the high-risk group for ischaemic events (>203 AU⋅min; 29.5 vs. 24.2%, P = 0.02). Homozygous risk allele carriers were also at higher risk for cardiovascular death or stent thrombosis (hazard ratio 1.70, 95% confidence interval 1.08–2.68; P = 0.02). Bleeding risk was not altered.

Conclusion

We conclude that homozygous GUCY1A3 risk allele carriers are at increased risk of cardiovascular death or stent thrombosis within 30 days after coronary stenting, likely due to higher on-aspirin platelet reactivity. Whether GUCY1A3 genotype helps to tailor antiplatelet treatment remains to be investigated.

Abstract 471: Influence of Platelet-specific Soluble Guanylyl Cyclase Deficiency on Atherosclerotic Plaque Formation

Introduction: The genomic locus harboring the GUCY1A3 gene has been associated with coronary artery disease (CAD) with the risk variant reducing GUCY1A3 expression via allele-specific transcription factor binding. The gene encodes the alpha 1 -subunit of the soluble guanylyl cyclase (sGC) which produces the second messenger cyclic guanosine monophosphate (cGMP) upon activation by nitric oxide, thereby influencing the function of vascular smooth muscle cells and platelets.

Aim: To investigate whether a reduction in sGC expression specifically in platelets influences atherosclerotic plaque formation.

Methods: By crossbreeding Pf4-Cre and sGC β 1 fl/fl mice, platelet-specific sGC knockout (PS-sGC -/- ) mice were generated. These were crossbred with Ldlr -/- mice to generate PS-sGC -/- Ldlr -/- mice. PS-sGC -/- Ldlr -/- and Ldlr -/- mice were fed a high-cholesterol diet (HCD) for 10 weeks. Serial sections of the aortic root were analyzed by Masson-Trichrome staining. Inflammatory cells in aortae were assessed using flow cytometry. In vitro adhesion assays using wildtype endothelial cells (EC) and monocytes were performed in presence of plasma of activated platelets.

Results: PS-sGC -/- Ldlr -/- (n=13) mice displayed enhanced total plaque size compared to Ldlr -/- (n=15) mice (247·10 3 vs. 190·10 3 μm 2 , p<0.05). After HCD, more neutrophils (747 vs. 448, p<0.05) and Ly6C high monocytes (366 vs. 207, p<0.05) were detected in PS-sGC -/- Ldlr -/- compared to Ldlr -/- mice indicating enhanced recruitment of these cells in PS-sGC -/- Ldlr -/- mice. In in vitro adhesion assays, incubation of mouse aortic EC and monocytes with plasma from PS-sGC -/- platelets resulted in enhanced adhesion of monocytes to EC compared to plasma from wildtype platelets (13%, p<0.01).

Conclusion and Outlook: Platelet-specific knockout of sGC led to increased atherosclerotic plaque formation and inflammation. In vitro adhesion assay results point to an enhanced stimulation of leukocyte adhesion to endothelial cells in PS-sGC -/- mice. Hence, factors released by platelets secondary to reduced sGC expression could mediate increased risk of CAD. Inhibiting platelet activation in carriers of the human risk variant might therefore be a promising therapeutic strategy to reduce risk of CAD.

Genetic alterations in the NO-cGMP pathway and cardiovascular risk

In the past ten years, several chromosomal loci have been identified by genome-wide association studies to influence the risk of coronary artery disease (CAD) and its risk factors. The GUCY1A3 gene encoding the α₁ subunit of the soluble guanylyl cyclase (sGC) resides at one of these loci and has been strongly associated with blood pressure and CAD risk. More recently, further genes in the pathway encoding the endothelial nitric oxide synthase, the phosphodiesterases 3A and 5A, and the inositol 1,4,5-trisphosphate receptor I-associated protein (IRAG), i.e., NOS3, PDE3A, PDE5A, and MRVI1, respectively, were likewise identified as CAD risk genes. In this review, we highlight the genetic findings linking variants in NO-cGMP signaling and cardiovascular disease, discuss the potential underlying mechanisms which might propagate the development of atherosclerosis, and speculate about therapeutic implications.

Functional Characterization of the GUCY1A3 Coronary Artery Disease Risk Locus

BACKGROUND

A chromosomal locus at 4q32.1 has been genome-wide significantly associated with coronary artery disease risk. The locus encompasses GUCY1A3, which encodes the α₁ subunit of the soluble guanylyl cyclase (sGC), a key enzyme in the nitric oxide/cGMP signaling pathway. The mechanism linking common variants in this region with coronary risk is not known.

METHODS

Gene expression and protein expression were analyzed with quantitative polymerase chain reaction and immunoblotting, respectively. Putative allele-specific transcription factors were identified with in silico analyses and validated via allele-specific quantification of antibody-precipitated chromatin fractions. Regulatory properties of the lead risk variant region were analyzed with reporter gene assays. To assess the effect of zinc finger E box-binding homeobox 1 transcription factor (ZEB1), siRNA-mediated knockdown and overexpression experiments were performed. Association of GUCY1A3 genotype and cellular phenotypes was analyzed with vascular smooth muscle cell migration assays and platelet aggregation analyses.

RESULTS

Whole-blood GUCY1A3 mRNA levels were significantly lower in individuals homozygous for the lead (rs7692387) risk variant. Likewise, reporter gene assays demonstrated significantly lower GUCY1A3 promoter activity for constructs carrying this allele. In silico analyses located a DNase I hypersensitivity site to rs7692387 and predicted binding of the transcription factor ZEB1 rather to the nonrisk allele, which was confirmed experimentally. Knockdown of ZEB1 resulted in more profound reduction of nonrisk allele promoter activity and a significant reduction of endogenous GUCY1A3 expression. Ex vivo-studied platelets from homozygous nonrisk allele carriers displayed enhanced inhibition of ADP-induced platelet aggregation by the nitric oxide donor sodium nitroprusside and the phosphodiesterase 5 inhibitor sildenafil compared with homozygous risk allele carriers. Moreover, pharmacological stimulation of sGC led to reduced migration only in vascular smooth muscle cells homozygous for the nonrisk allele. In the Hybrid Mouse Diversity Panel, higher levels of GUCY1A3 expression correlated with less atherosclerosis in the aorta.

CONCLUSIONS

Rs7692387 is located in an intronic site that modulates GUCY1A3 promoter activity. The transcription factor ZEB1 binds preferentially to the nonrisk allele, leading to an increase in GUCY1A3 expression, higher sGC levels, and higher sGC activity after stimulation. Finally, human and mouse data link augmented sGC expression to lower risk of atherosclerosis.

Role of sGC-dependent NO signalling and myocardial infarction risk

The NO/cGMP pathway plays an important role in many physiological functions and pathophysiological conditions. In the last few years, several genetic and functional studies pointed to an underestimated role of this pathway in the development of atherosclerosis. Indeed, several genetic variants of key enzymes modulating the generation of NO and cGMP have been strongly associated with coronary artery disease and myocardial infarction risk. In this review, we aim to place the genomic findings on components of the NO/cGMP pathway, namely endothelial nitric oxide synthase, soluble guanylyl cyclase and phosphodiesterase 5A, in context of preventive and therapeutic strategies for treating atherosclerosis and its sequelae.

Molecular variants of soluble guanylyl cyclase affecting cardiovascular risk

Soluble guanylyl cyclase (sGC) is the physiological receptor for nitric oxide (NO) and NO-releasing drugs, and is a key enzyme in several cardiovascular signaling pathways. Its activation induces the synthesis of the second messenger cGMP. cGMP regulates the activity of various downstream proteins, including cGMP-dependent protein kinase G, cGMP-dependent phosphodiesterases and cyclic nucleotide gated ion channels leading to vascular relaxation, inhibition of platelet aggregation, and modified neurotransmission. Diminished sGC function contributes to a number of disorders, including cardiovascular diseases. Knowledge of its regulation is a prerequisite for understanding the pathophysiology of deficient sGC signaling. In this review we consolidate the available information on sGC signaling, including the molecular biology and genetics of sGC transcription, translation and function, including the effect of rare variants, and present possible new targets for the development of personalized medicine in vascular diseases.

A global analysis of Y-chromosomal haplotype diversity for 23 STR loci

In a worldwide collaborative effort, 19,630 Y-chromosomes were sampled from 129 different populations in 51 countries. These chromosomes were typed for 23 short-tandem repeat (STR) loci (DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS385ab, DYS437, DYS438, DYS439, DYS448, DYS456, DYS458, DYS635, GATAH4, DYS481, DYS533, DYS549, DYS570, DYS576, and DYS643) and using the PowerPlex Y23 System (PPY23, Promega Corporation, Madison, WI). Locus-specific allelic spectra of these markers were determined and a consistently high level of allelic diversity was observed. A considerable number of null, duplicate and off-ladder alleles were revealed. Standard single-locus and haplotype-based parameters were calculated and compared between subsets of Y-STR markers established for forensic casework. The PPY23 marker set provides substantially stronger discriminatory power than other available kits but at the same time reveals the same general patterns of population structure as other marker sets. A strong correlation was observed between the number of Y-STRs included in a marker set and some of the forensic parameters under study. Interestingly a weak but consistent trend toward smaller genetic distances resulting from larger numbers of markers became apparent.