Maria G. Stathopoulou

Six Novel Loci Associated with Circulating VEGF Levels Identified by a Meta-analysis of Genome-Wide Association Studies

Vascular endothelial growth factor (VEGF) is an angiogenic and neurotrophic factor, secreted by endothelial cells, known to impact various physiological and disease processes from cancer to cardiovascular disease and to be pharmacologically modifiable. We sought to identify novel loci associated with circulating VEGF levels through a genome-wide association meta-analysis combining data from European-ancestry individuals and using a dense variant map from 1000 genomes imputation panel. Six discovery cohorts including 13,312 samples were analyzed, followed by in-silico and de-novo replication studies including an additional 2,800 individuals. A total of 10 genome-wide significant variants were identified at 7 loci. Four were novel loci (5q14.3, 10q21.3, 16q24.2 and 18q22.3) and the leading variants at these loci were rs114694170 (MEF2C, P = 6.79x10-13), rs74506613 (JMJD1C, P = 1.17x10-19), rs4782371 (ZFPM1, P = 1.59x10-9) and rs2639990 (ZADH2, P = 1.72x10-8), respectively. We also identified two new independent variants (rs34528081, VEGFA, P = 1.52x10-18; rs7043199, VLDLR-AS1, P = 5.12x10-14) at the 3 previously identified loci and strengthened the evidence for the four previously identified SNPs (rs6921438, LOC100132354, P = 7.39x10-1467; rs1740073, C6orf223, P = 2.34x10-17; rs6993770, ZFPM2, P = 2.44x10-60; rs2375981, KCNV2, P = 1.48x10-100). These variants collectively explained up to 52% of the VEGF phenotypic variance. We explored biological links between genes in the associated loci using Ingenuity Pathway Analysis that emphasized their roles in embryonic development and function. Gene set enrichment analysis identified the ERK5 pathway as enriched in genes containing VEGF associated variants. eQTL analysis showed, in three of the identified regions, variants acting as both cis and trans eQTLs for multiple genes. Most of these genes, as well as some of those in the associated loci, were involved in platelet biogenesis and functionality, suggesting the importance of this process in regulation of VEGF levels. This work also provided new insights into the involvement of genes implicated in various angiogenesis related pathologies in determining circulating VEGF levels. The understanding of the molecular mechanisms by which the identified genes affect circulating VEGF levels could be important in the development of novel VEGF-related therapies for such diseases.

What is the contribution of two genetic variants regulating VEGF levels to type 2 diabetes risk and to microvascular complications

Vascular endothelial growth factor (VEGF) is a key chemokine involved in tissue growth and organ repair processes, particularly angiogenesis. Elevated circulating VEGF levels are believed to play a role in type 2 diabetes (T2D) microvascular complications, especially diabetic retinopathy. Recently, a genome-wide association study identified two common single nucleotide polymorphisms (SNPs; rs6921438 and rs10738760) explaining nearly half of the variance in circulating VEGF levels. Considering the putative contribution of VEGF to T2D and its complications, we aimed to assess the effect of these VEGF-related SNPs on the risk of T2D, nephropathy and retinopathy, as well as on variation in related traits. SNPs were genotyped in several case-control studies: French and Danish T2D studies (Ncases = 6,920-Ncontrols = 3,875 and Ncases = 3,561-Ncontrols = 2,623; respectively), two French studies one for diabetic nephropathy (Ncases = 1,242-Ncontrols = 860) and the other for diabetic retinopathy (Ncases = 1,336-Ncontrols = 1,231). The effects of each SNP on quantitative traits were analyzed in a French general population-based cohort (N = 4,760) and two French T2D studies (N = 3,480). SNP associations were assessed using logistic or linear regressions. In the French population, we found an association between the G-allele of rs6921438, shown to increase circulating VEGF levels, and increased T2D risk (OR = 1.15; P = 3.7×10−5). Furthermore, the same allele was associated with higher glycated hemoglobin levels (β = 0.02%; P = 9.2×10−3). However, these findings were not confirmed in the Danes. Conversely, the SNP rs10738760 was not associated with T2D in the French or Danish populations. Despite having adequate statistical power, we did not find any significant effects of rs6921438 or rs10738760 on diabetic microvascular complications or the variation in related traits in T2D patients. In spite of their impact on the variance in circulating VEGF, we did not find any association between SNPs rs6921438 and rs10738760, and the risk of T2D, diabetic nephropathy or retinopathy. The link between VEGF and T2D and its complications might be indirect and more complex than expected.

A Genome-Wide Association Study Identifies rs2000999 as a Strong Genetic Determinant of Circulating Haptoglobin Levels

Haptoglobin is an acute phase inflammatory marker. Its main function is to bind hemoglobin released from erythrocytes to aid its elimination, and thereby haptoglobin prevents the generation of reactive oxygen species in the blood. Haptoglobin levels have been repeatedly associated with a variety of inflammation-linked infectious and non-infectious diseases, including malaria, tuberculosis, human immunodeficiency virus, hepatitis C, diabetes, carotid atherosclerosis, and acute myocardial infarction. However, a comprehensive genetic assessment of the inter-individual variability of circulating haptoglobin levels has not been conducted so far. We used a genome-wide association study initially conducted in 631 French children followed by a replication in three additional European sample sets and we identified a common single nucleotide polymorphism (SNP), rs2000999 located in the Haptoglobin gene (HP) as a strong genetic predictor of circulating Haptoglobin levels (Poverall = 8.1×10−59), explaining 45.4% of its genetic variability (11.8% of Hp global variance). The functional relevance of rs2000999 was further demonstrated by its specific association with HP mRNA levels (β = 0.23±0.08, P = 0.007). Finally, SNP rs2000999 was associated with decreased total and low-density lipoprotein cholesterol in 8,789 European children (Ptotal cholesterol = 0.002 and PLDL = 0.0008). Given the central position of haptoglobin in many inflammation-related metabolic pathways, the relevance of rs2000999 genotyping when evaluating haptoglobin concentration should be further investigated in order to improve its diagnostic/therapeutic and/or prevention impact.

Cardiovascular diseases and genome-wide association studies.

Genome-Wide Association Studies (GWAS) on cardiovascular diseases and related quantitative traits revealed numerous genetic variants, which however have been partially replicated, probably due to the heterogeneity of the clinical phenotypes and the populations studied. Even if novel biological pathways have been identified through these studies, there is still a long way until the validation of causal variants and their use in clinical practice as factors for prevention, risk assessment and as targets for the development of new medications. GWAS methodologies should, in the following years, integrate gene-gene and gene-environment interaction analyses in a global research strategy and also involve subsequent transcriptomic and proteomic investigations. The GWAS era is very promising but it is just at the beginning.

Associations of vascular endothelial growth factor (VEGF) with adhesion and inflammation molecules in a healthy population

Vascular endothelial growth factor (VEGF) is implicated in numerous pathologies through complex relationships with cellular adhesion molecules (CAMs) and inflammation markers. These have not been assessed in non-pathological conditions. Our aim was the evaluation of associations between VEGF and CAM/inflammation molecules in a healthy population, and of possible genomic interplays in order to better apprehend the underlying mechanisms leading to the pathology. We examined the associations between VEGF and ICAM-1, VCAM-1, E-, L-, P-selectins, TNF-α, CRP and IL-6 plasma levels in 403 healthy individuals. Gene expression of CAM/inflammation molecules and VEGF isoforms (121, 145, 165, and 189) were quantified in peripheral blood mononuclear cells (PBMCs). The effect of four genetic variants (explaining ≈ 50% of the heritability of circulating VEGF levels) and of their interactions on plasma and mRNA levels of CAM/inflammation molecules was examined. VEGF was associated with ICAM-1 and E-selectin in plasma. In PBMCs, VEGF(145) mRNA was associated with ICAM-1, L-selectin and TNF-α expression. Interactions of the genetic variants were shown to affect ICAM-1, E-selectin, IL-6 and TNF-α plasma levels, while rs4416670 was associated with L-selectin expression. These findings propose a biological connection between VEGF and CAM/inflammation markers. Common genetic and transcriptional mechanisms may link these molecules and control their effect in healthy conditions.

A common variant highly associated with plasma VEGFA levels also contributes to the variation of both LDL-C and HDL-C

Vascular endothelial growth factor A (VEGFA) is among the most-significant stimulators of angiogenesis. Its effect on cardiovascular diseases and on the variation of related risk factors such as lipid parameters is considered important, although as yet unclear. Recently, we identified four common variants (rs6921438, rs4416670, rs6993770, and rs10738760) that explain up to 50% of the heritability of plasma VEGFA levels. In the present study, we aimed at assessing the contribution of these variants to the variation of blood lipid levels (including apoE, triglycerides, total cholesterol, low- and high-density lipoprotein cholesterol levels (LDL-C and HDL-C)] in healthy subjects. The effect of these single-nucleotide polymorphisms (SNPs) on lipid levels was assessed using linear regression in discovery and replication samples (n = 1,006 and n = 1,145; respectively), followed by a meta-analysis. Their gene×gene and gene×environment interactions were also assessed. SNP rs6921438 was associated with HDL-C (β = −0.08 mmol/l, Poverall = 1.2 × 10−7) and LDL-C (β = 0.13 mmol/l, Poverall = 1.5 × 10−4). We also identified a significant association between the interaction rs4416670×hypertension and apoE variation (Poverall = 1.7 × 10−5). Therefore, our present study shows a common genetic regulation between VEGFA and cholesterol homeostasis molecules. The SNP rs6921438 is in linkage disequilibrium with variants located in an enhancer- and promoter-associated histone mark region and could have a regulatory effect in the expression of surrounding genes, including VEGFA.

The role of vitamin D receptor gene polymorphisms in the bone mineral density of Greek postmenopausal women with low calcium intake.

The aim of this study was to investigate the effect of common vitamin D receptor (VDR) gene polymorphisms on the bone mineral density (BMD) of Greek postmenopausal women. Healthy postmenopausal women (n=578) were recruited for the study. The BMD of the lumbar spine and hip was measured using dual-energy X-ray absorptiometry with the Lunar DPX-MD device. Assessment of dietary calcium intake was performed with multiple 24-h recalls. Genotyping was performed for the BsmI, TaqI and Cdx-2 polymorphisms of the VDR gene. The selected polymorphisms were not associated with BMD, osteoporosis or osteoporotic fractures. Stratification by calcium intake revealed that in the low calcium intake group (<680 mg/day), all polymorphisms were associated with the BMD of the lumbar spine (P<.05). After adjustment for potential covariates, BsmI and TaqI polymorphisms were associated with the presence of osteoporosis (P<.05), while the presence of the minor A allele of Cdx-2 polymorphism was associated with a lower spine BMD (P=.025). In the higher calcium intake group (>680 mg/day), no significant differences were observed within the genotypes for all polymorphisms. The VDR gene is shown to affect BMD in women with low calcium intake, while its effect is masked in women with higher calcium intake. This result underlines the significance of adequate calcium intake in postmenopausal women, given that it exerts a positive effect on BMD even in the presence of negative genetic predisposition.

Low-Density Lipoprotein Receptor-Related Protein 5 Polymorphisms Are Associated with Bone Mineral Density in Greek Postmenopausal Women: An Interaction with Calcium Intake

The low-density lipoprotein receptor-related protein 5 (LRP5) has been shown to play a significant role in bone biology. This study aimed to assess the association of four common polymorphisms of the LRP5 gene with bone mineral density (BMD) and possible genexcalcium intake interactions in Greek postmenopausal women. For this observational cross-sectional association study, healthy postmenopausal women (N=578) were recruited (between December 2006 and January 2008) and genotyped for four polymorphisms (rs1784235, rs491347, rs4988321, and rs4988330) in the LRP5 gene. Measurements of BMD were performed and detailed medical, dietary, and anthropometric data were recorded. Student t tests and multiple linear regression models were applied after controlling for potential covariates (ie, age, weight, height, and calcium intake). None of the polymorphisms was associated with the presence of osteoporosis, fractures, and hip BMD. All polymorphisms were associated with unadjusted spine BMD, with the exception of rs4988330. Only rs4988321 was associated with adjusted spine BMD, where the presence of the A allele was associated with significantly lower spine BMD compared with the GG genotype (P=0.002). An interaction of the rs4988321 polymorphism with calcium intake (P=0.016) was found. The carriers of the A allele demonstrated significantly lower spine BMD compared to GG homozygotes (P=0.001) only in the lowest calcium intake group (<680 mg/day), whereas in the highest calcium intake group no differences were found in BMD between genotypes. These findings demonstrate that both rs4988321 polymorphism and its interaction with calcium intake are associated with BMD, whereas higher calcium intake was shown to decrease the negative effect of this polymorphism on BMD.

Alcohol Consumption, Beverage Preference, and Diet in Middle-Aged Men from the STANISLAS Study

The question about differences in dietary patterns associated with beer, wine, and spirits is still unresolved. We used diet data from 423 middle-aged males of the STANISLAS Study. Using adjusted values for covariates, we observed a negative significant association between increasing alcohol intakes and the consumption of milk, yogurt, and fresh/uncured cheese, sugar and confectionery, vegetables and fruits, and a significant positive relationship with cheese, meat and organs, pork-butchers meat, and potatoes. In addition, the first dietary pattern identified by factor analysis (characterized a more prudent diet) was inversely related to alcohol intakes. Conversely, when analyzing daily consumption of specific food groups and diet patterns according to beverage preference (wine, beer, and spirits), no significant difference was observed. In conclusion, in this sample of middle-aged French males, there was a linear trend between increasing alcohol intakes and worsening of quality of diet, while no difference was observed according to beverage preference.

Evaluation of the Antioxidant Effect of a New Functional Food Enriched with Sideritis euboea in Healthy Subjects

Sideritis euboea is a Greek plant that is traditionally consumed as a beverage (mountain tea). From in vitro studies, its extract has shown antioxidant and estrogenic activities. In our study we used S. euboea as an enriching food factor in order to produce a new functional food, a jelly dessert, in order to explore its antioxidant effects if consumed on a daily basis by healthy subjects. In this placebo-controlled clinical trial, 63 subjects were recruited for a 1-month nutritional intervention. Twelve subjects were excluded. The remaining 51 subjects were randomly classified in the intervention group (daily consumption of the jelly containing 0.3 g of S. euboea extract) or the placebo group (daily consumption of the same jelly without the enrichment). Vitamins C, A, and E, glutathione, coenzyme Q10, total nitrites, nitrates, total nitrogen oxide, nitrites/nitrates ratio, and total antioxidant status were measured in blood samples before and after the intervention. After the intervention, free glutathione and coenzyme Q10 increased, and nitrites decreased significantly in both groups. The other antioxidant markers were not altered. No statistical significant differences were observed between the two groups. The daily consumption of the functional food, for 30 days, had no effects on the antioxidant status of healthy volunteers.