A functional Sp1/Egr1-tandem repeat polymorphism in the 5-lipoxygenase gene is not associated with myocardial infarction

Identification of Important Genes Associated with the Development of Atherosclerosis

Atherosclerosis is one of the most important medical problems due to its prevalence and significant contribution to the structure of temporary and permanent disability and mortality. Atherosclerosis is a complex chain of events occurring in the vascular wall over many years. Disorders of lipid metabolism, inflammation, and impaired hemodynamics are important mechanisms of atherogenesis. A growing body of evidence strengthens the understanding of the role of genetic and epigenetic factors in individual predisposition and development of atherosclerosis and its clinical outcomes. In addition, hemodynamic changes, lipid metabolism abnormalities, and inflammation are closely related and have many overlapping links in regulation. A better study of these mechanisms may improve the quality of diagnosis and management of such patients.

Role of Sp1 in atherosclerosis

Specificity protein (Sp) is a famous family of transcription factors including Sp1, Sp2 and Sp3. Sp1 is the first one of Sp family proteins to be characterized and cloned in mammalian. It has been proposed that Sp1 acts as a modulator of the expression of target gene through interacting with a series of proteins, especially with transcriptional factors, and thereby contributes to the regulation of diverse biological processes. Notably, growing evidence indicates that Sp1 is involved in the main events in the development of atherosclerosis (AS), such as inflammation, lipid metabolism, plaque stability, vascular smooth muscle cells (VSMCs) proliferation and endothelial dysfunction. This review is designed to provide useful clues to further understanding roles of Sp1 in the pathogenesis of AS, and may be helpful for the design of novel efficacious therapeutics agents targeting Sp1.

Genetic and Epigenetic Regulation of Lipoxygenase Pathways and Reverse Cholesterol Transport in Atherogenesis

Atherosclerosis is one of the most important medical and social problems of modern society. Atherosclerosis causes a large number of hospitalizations, disability, and mortality. A considerable amount of evidence suggests that inflammation is one of the key links in the pathogenesis of atherosclerosis. Inflammation in the vascular wall has extensive cross-linkages with lipid metabolism, and lipid mediators act as a central link in the regulation of inflammation in the vascular wall. Data on the role of genetics and epigenetic factors in the development of atherosclerosis are of great interest. A growing body of evidence is strengthening the understanding of the significance of gene polymorphism, as well as gene expression dysregulation involved in cross-links between lipid metabolism and the innate immune system. A better understanding of the genetic basis and molecular mechanisms of disease pathogenesis is an important step towards solving the problems of its early diagnosis and treatment.

Sp1 promotes dental pulp stem cell osteoblastic differentiation through regulating noggin

Based on the high self-renewal ability and osteoblastic differentiation capacity, dental pulp stem cells (DPSCs) are suggested to be promising cell source for osteogenesis. Therefore, illustrating the mechanism of osteoblastic differentiation of DPSCs is required. This current study aims to illustrate the role and mechanism of Sp1 in regulating osteoblastic differentiation of DPSCs. In this study, we downregulated Sp1 in DPSCs and evaluated the osteoblastic differentiation by measuring Runx2 and OCN expression with Western blot analysis and by Alizarin red staining. Furthermore, we investigated the mechanism of Sp1 regulating noggin with Firefly luciferase reporter gene assay and ChIP assay, and correspondingly evaluated the function of noggin in Sp1-regulated osteoblastic differentiation of DPSCs. We found that knockdown of Sp1 inhibits the expression of ALP, Runx2, COL1A1 and OCN, and decreases ALP staining, Alizarin red staining. Sp1 binds to noggin promoter and inhibits noggin expression, thus correspondingly regulates DPSCs osteoblastic differentiation. In conclusion, our study revealed that Sp1 regulates DPSCs osteoblastic differentiation through noggin and that Sp1/noggin can provide new perspective for enhancing DPSCs osteogenesis.

Common Polymorphisms in the 5-Lipoxygenase Pathway and Risk of Incident Myocardial Infarction: A Danish Case-Cohort Study

BACKGROUND

The 5-lipoxygenase pathway (5-LOX) has been implicated in the development of cardiovascular disease and studies have suggested that genetic polymorphisms related to key enzymes in this pathway may confer risk of myocardial infarction (MI). This study investigated the association of pre-selected genetic polymorphisms in four candidate genes of 5-LOX (arachidonate 5-lipoxygenase and its activating protein (ALOX-5 and FLAP), leukotriene A4 hydroxylase (LTA4-H) and leukotriene C4 synthase (LTC4-S)) with incident MI.

METHODS

In a Danish cohort including 57,053 participants, aged 50-64 at enrolment and recruited from 1993-97, we conducted a case-cohort study including cases with incident MI and a randomly selected sub cohort of 3,000 participants. Cases were identified from national registries through July 2013. A total of 22 SNPs were selected and genotyped using the commercially available KASP™ assay. A tandem-repeat polymorphism, located in the ALOX-5 gene, was genotyped by multi-titre plate sequencing. Haplotypes were inferred using PHASE 2.1.

RESULTS

During a median follow-up of 17.0 years we identified 3,089 cases of incident MI. In FLAP, two SNPs were negatively associated with incident MI (rs9551963 & rs17222842) while one SNP (rs2247570) located in LTA4-H, was associated with higher risk of MI when comparing subjects with two copies of the variant allele to homozygotes for the wild type. However, only rs17222842 remained significantly associated with MI after correcting for multiple testing. Furthermore, the promoter polymorphism rs59439148 was associated with risk of MI in men. For male carriers of two variant alleles we found a hazard ratio of 1.63 (95% CI: 1.06;2.52) compared to homozygotes for the wild type. Previously described haplotypes (Hap-A -B, -E and -K) were not associated with MI in our population.

CONCLUSION

In conclusion, some common polymorphisms in the 5-lipoxygenase pathway were modestly associated with incident MI, suggesting a potential role for this pathway in the development of cardiovascular disease.

5-Lipoxygenase Gene Variants Are Not Associated With Atherosclerosis or Incident Coronary Heart Disease in the Multi-Ethnic Study of Atherosclerosis Cohort

Background

The arachidonate 5‐lipoxygenase enzyme plays a crucial role in mediating inflammation to maintain homeostasis, yet certain allelic variants of the 5‐lipoxygenase gene, ALOX5, may increase risk of atherosclerosis and coronary heart disease (CHD). Further, relations between ALOX5 and disease outcomes may be enhanced or attenuated depending on the bioavailability of 5‐lipoxygenase enzyme substrates. By using a candidate gene approach in 6153 Multi‐Ethnic Study of Atherosclerosis (MESA) participants, associations were determined among 1348 ALOX5 single nucleotide polymorphisms (SNPs) and carotid intima‐media thickness (cIMT) as well as incident CHD, and interactions with plasma concentrations of arachidonic acid, eicosapentaenoic acid, or docosahexaenoic acid were tested.

Methods and Results

Multivariable linear regression was used to test for associations between cIMT and ALOX5 SNPs, and Cox regression was used for incident CHD. Bonferroni correction was used for multiple hypothesis testing. No significant associations between ALOX5 SNPs and cIMT or CHD events were observed. Levels of arachidonic acid, eicosapentaenoic acid, or docosahexaenoic acid concentrations did not modify the relations of ALOX5 with either outcome.

Conclusions

ALOX5 gene variants do not appear to be related to clinical CHD events or subclinical atherosclerosis regardless of bioavailable enzyme substrate levels in this multiethnic cohort. Further studies that directly examine protein expression or enzyme activity may better define the arachidonate 5‐lipoxygenase pathway in disease development and progression.

Role of promoter DNA sequence variations on the binding of EGR1 transcription factor

In response to a wide variety of stimuli such as growth factors and hormones, EGR1 transcription factor is rapidly induced and immediately exerts downstream effects central to the maintenance of cellular homeostasis. Herein, our biophysical analysis reveals that DNA sequence variations within the target gene promoters tightly modulate the energetics of binding of EGR1 and that nucleotide substitutions at certain positions are much more detrimental to EGR1-DNA interaction than others. Importantly, the reduction in binding affinity poorly correlates with the loss of enthalpy and gain of entropy-a trend indicative of a complex interplay between underlying thermodynamic factors due to the differential role of water solvent upon nucleotide substitution. We also provide a rationale for the physical basis of the effect of nucleotide substitutions on the EGR1-DNA interaction at atomic level. Taken together, our study bears important implications on understanding the molecular determinants of a key protein-DNA interaction at the cross-roads of human health and disease.

Quantifying diet for nutrigenomic studies

The field of nutrigenomics shows tremendous promise for improved understanding of the effects of dietary intake on health. The knowledge that metabolic pathways may be altered in individuals with genetic variants in the presence of certain dietary exposures offers great potential for personalized nutrition advice. However, although considerable resources have gone into improving technology for measurement of the genome and biological systems, dietary intake assessment remains inadequate. Each of the methods currently used has limitations that may be exaggerated in the context of gene × nutrient interaction in large multiethnic studies. Because of the specificity of most gene × nutrient interactions, valid data are needed for nutrient intakes at the individual level. Most statistical adjustment efforts are designed to improve estimates of nutrient intake distributions in populations and are unlikely to solve this problem. An improved method of direct measurement of individual usual dietary intake that is unbiased across populations is urgently needed.

No effect of high-dose atorvastatin on leukotriene B₄ formation from neutrophils in patients treated with coronary bypass surgery: a randomized placebo-controlled double-blinded trial with a crossover design

Inflammation plays a pivotal role in the pathophysiology of cardiovascular disease, (CVD) and leukotrienes may play a role in atherogenesis. Statins reduce mortality from CVD by reducing LDL cholesterol and potentially by other (pleiotropic) mechanisms. The aim of this study was to investigate if atorvastatin exerts an anti-inflammatory effect by reducing leukotriene B₄ (LTB₄) formation from stimulated neutrophils in patients treated with coronary artery bypass grafting. The study was a randomized, placebo-controlled, double-blinded crossover study. Patients (n=80) were allocated to 80 mg atorvastatin or placebo for 6 weeks before crossing over to the opposite treatment for another 6 weeks. There was no significant correlation between baseline LDL cholesterol levels on formation of LTB₄, and atorvastatin had no effect on LTB₄ formation. Hence, this study does not support any effect of atorvastatin on LTB₄ formation as part of the explanation for its beneficial effect on CVD.

Genetic determinants of 5-lipoxygenase pathway in a Spanish population and their relationship with cardiovascular risk

OBJECTIVE

Leukotrienes (LT) play a role in inflammation, cardiovascular diseases, and cancer. Although some studies suggest that there are genes that determine variability of some LT-related phenotypes, the genetic influence on these phenotypes has not been evaluated.

METHODS

The relative contributions of genetic and environmental influences to the 5-lipoxygenase pathway-related phenotypes (5-Lipoxygenase, five lipoxygenase activating protein (FLAP), LTA(4)-hydrolase and LTC(4)-synthase expression, and LTB(4)-plasma concentration and LTB(4) production by stimulated whole blood) were assessed in a sample of 934 individuals in 35 extended families. Our design is based on extended families recruited through a probands with idiopathic thrombophilia. This strategy allows us the analysis of the effects of measured covariates (such as sex, age and smoking), genes, and environmental variables shared by members of a household.

RESULTS

All of these phenotypes showed significant genetic contributions, with heritabilities ranging from 0.33 to 0.51 for enzyme expression and from 0.25 to 0.50 for LTB(4) production of the residual phenotypic variance. Significant phenotypic and genetic correlation among the LT-related traits was found. More importantly, FLAP and LTA(4)-hydrolase expression exhibit significant genetic correlations with arterial thrombosis, indicating that some of the genes that influence quantitative variation in these phenotypes also influence the risk of thrombosis.

CONCLUSION

This is the first study that quantifies the genetic component of 5-Lipoxygenase pathway phenotypes. The high heritability of these traits and the significant genetic correlations between arterial thrombosis and some of these phenotypes suggest that the exploitation of correlated quantitative phenotypes will aid the search for susceptibility genes.

Genetic contribution of the leukotriene pathway to coronary artery disease

We evaluated the genetic contribution of the leukotriene (LT) pathway to risk of coronary artery disease (CAD) in 4,512 Caucasian and African American subjects ascertained through elective cardiac evaluation. Of the three previously associated variants, the shorter "3" and "4" alleles of a promoter repeat polymorphism in ALOX5 increased risk of CAD in African Americans (OR = 1.4, 95% CI 1.0-1.9; p = 0.04), whereas a haplotype of LTA4H (HapK) was associated with CAD in Caucasians (OR = 1.2, 95% CI 1.01-1.4; p = 0.03). In Caucasians, first-stage analysis of 254 haplotype-tagging SNPs in 15 LT pathway genes with follow-up of 19 variants in stage 2 revealed an LTA4H SNP (rs2540477) that increased risk of CAD (OR = 1.2, 95% CI 1.1-1.5; p = 0.003) and a PLA2G4A SNP (rs12746200) that decreased risk of CAD (OR = 0.7, 95% CI 0.6-0.9; p = 0.0007). The PLA2G4A rs12746200 variant also decreased risk of experiencing a major adverse cardiac event (MACE = myocardial infarction, stroke, or death) over 3 years of follow-up (HR = 0.7, 95% CI 0.5-0.9; p = 0.01), consistent with its cardioprotective effect. Functional experiments demonstrated that stimulated monocytes from carriers of LTA4H variants HapK or rs2540477 had 50% (p = 0.002) and 33% (p = 0.03) higher LTB(4) production, respectively, compared to non-carriers. These ex vivo results are consistent with LTB(4) being the direct product of the reaction catalyzed by LTA4H and its role in promoting monocyte chemotaxis to sites of inflammation, including the artery wall of atherosclerotic lesions. Taken together, this study provides additional evidence that functional genetic variation of the LT pathway can mediate atherogenic processes and the risk of CAD in humans.

Fatty acid interactions with genetic polymorphisms for cardiovascular disease

PURPOSE OF REVIEW

The number of studies investigating interactions between genes and nutrients for cardiovascular disease continues to grow, and holds tremendous potential for reducing disease risk at the level of the individual genotype. However, understanding the limitations and challenges of interaction studies, whether of observational or interventional design, is essential for critical evaluation of these studies.

RECENT FINDINGS

Nutrient-gene interactions for cardiovascular disease both parallel and extend nutrition studies, encompassing both traditional and novel cardiovascular risk factors. Fatty acid quality, lipid metabolism, inflammation, postprandial metabolism, fatty liver and macronutrient-gene interactions for obesity and metabolic syndrome represent a subset of the major areas of recent focus. With few exceptions, however, studies of gene-nutrient interactions are limited to a single population.

SUMMARY

Gene-nutrient research will continue to expand as genome-wide association studies uncover new sources of genetic variability associated with cardiovascular risk. However, in addition to investigation of newly discovered variants, continuing efforts must focus on the confirmation of previously reported genetic associations and interactions in additional populations.

Polyunsaturated fatty acids and cardiovascular disease: implications for nutrigenetics

Cardiovascular disease (CVD) arises as a result of genetic predisposition in the context of a disease-promoting environment. While several risk factors have been identified for CVD, such as elevated serum lipid levels and hypertension, most of the genes identified thus far do not appear to involve such 'conventional' risk factors. Moreover, the interactions between genes and environment, such as a diet high in certain fats, adds another level of complexity to CVD and renders identification of the underlying genetic factors even more difficult. Polyunsaturated fatty acids (PUFAs), such as the omega-6 and omega-3 fatty acids, which have multiple roles in membrane structure, lipid metabolism, blood clotting, blood pressure, and, in particular, inflammation, have been linked to the reduction in CVD. Linoleic (omega-6) and alpha-linolenic acid (omega-3) are essential fatty acids that can be converted into long-chain PUFAs, such as arachidonic acid (AA) and eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA), respectively. These long-chain PUFAs are metabolized by enzymatically catalyzed systems via cyclooxygenases and lipoxygenases. The 5-lipoxygenase (5-LO)/leukotriene (LT) biosynthesis pathway has been biochemically and genetically associated with CVD traits in mice and humans, particularly in the context of dietary AA and EPA/DHA. In this review, we summarize the biochemical metabolism of omega-3 and omega-6 PUFAs, evaluate the evidence for genetic and nutrigenetic contributions of 5-LO pathway genes to CVD, and discuss the potential of future studies that could identify other gene-dietary interactions between PUFAs and CVD traits.

Functional analysis of 5-lipoxygenase promoter repeat variants

Variants of a hexanucleotide repeat polymorphism in the promoter of the 5-lipoxygenase (5-LO) gene have been associated with cardiovascular disease traits in humans, which may be due, at least in part, to differential expression of the at-risk alleles. To more fully characterize these variants, we carried out gene expression and DNA methylation studies in primary leukocytes from healthy individuals carrying various 5-LO promoter alleles. Regardless of genotype, 5-LO and 5-LO-activating protein (FLAP) gene expression was higher in granulocytes compared with monocytes and lymphocytes, whereas leukotriene A4 hydrolase (LTA4H) expression was higher in monocytes. In all three leukocyte populations, 5-LO mRNA levels were positively correlated with those of FLAP and LTA4H, with the highest correlation observed in granulocytes. In lymphocytes, individuals homozygous for the shorter 3 and 4 repeat alleles had between 20-35% higher 5-LO, FLAP and LTA4H expression compared with homozygous carriers of the wild-type 5 repeat allele (P = 0.03-0.0001). DNA methylation analysis of four CpG islands in a 1500 bp region encompassing the 5-LO promoter and the first approximately 100 bp of intron 1 revealed relatively low overall DNA methylation across all genotypes and leukocyte populations. However, analysis of the promoter repeats themselves demonstrated that, regardless of cell population, the 4 allele was methylated approximately twice as much as the 3 allele (P < 0.0001). Our results demonstrate that, in lymphocytes, the shorter repeat alleles of the 5-LO promoter lead to higher gene expression, which may be regulated through differential DNA methylation of the CpGs located within these repeats.

Functional variants of the human 5-lipoxygenase gene and their genetic diagnosis

Variants in the 5-lipoxygenase (ALOX5) gene are first-line candidate causes for interindividual differences in diseases where leukotrienes play a key role, e.g., inflammatory and immune diseases, atherosclerosis, asthma or the acute respiratory distress syndrome (ARDS). We developed and validated Pyrosequencing screening assays for single nucleotide polymorphism (dbSNP-IDs rs4986832, rs4987105, rs2115819, rs3740107, rs1565096, rs2291427, rs10571382, rs2242334, rs2229136, rs3802548), and a capillary electrophoresis assay for the ALOX5 Sp1/Egr1 promoter tandem repeat polymorphism. This selection spans the whole ALOX5 gene range and includes all variants with reported functional associations. A gene structure analysis in DNAs from 187 healthy unrelated Caucasians revealed two haploblocks, one in the promoter and one spanning six SNPs from rs3740107G>A in intron 6 to rs2229136A>G in exon 13. The five-repeat genotype was the most frequent Sp1/Egr1 promoter tandem repeat variant (allelic frequency 84%). These assays and analyses provide a solid basis for future assessments of the genetic modulation of leukotriene production.

Nutrigenetic association of the 5-lipoxygenase gene with myocardial infarction

BACKGROUND

5-Lipoxygenase (5-LO) catalyzes the rate-limiting step of the biosynthesis of proinflammatory leukotrienes from arachidonic acid (AA) and has been associated with atherosclerosis in animal models and humans. We previously reported that variants of a 5-LO promoter repeat polymorphism were associated with carotid atherosclerosis in humans, an effect that was exacerbated by high dietary AA but mitigated by high dietary n-3 fatty acids.

OBJECTIVE

We sought to confirm these initial observations with a more clinically relevant phenotype such as myocardial infarction (MI).

DESIGN

The 5-LO polymorphism was genotyped in 1885 Costa Rican case-control pairs and tested for association with MI. Functional experiments were carried out to determine whether the associated alleles had differences in mRNA expression.

RESULTS

The frequency of variant genotype groups did not differ significantly between cases and controls. However, a significant gene x diet interaction was observed, in which, relative to the common 5 repeat allele, the 3 and 4 alleles were associated with a higher MI risk in the high (> or = 0.25 g/d) dietary AA group (odds ratio: 1.31; 95% CI: 1.07, 1.61) and with a lower risk in the low (<0. 25 g/d) AA group (0.77; 0.63, 0.94) (P for interaction = 0.015). Using allele-specific quantitation, the short alleles had expression approximately twice that of the 5 allele (P < 0.0001).

CONCLUSIONS

The 3 and 4 variants lead to higher 5-LO expression and provide additional evidence that these alleles are associated with greater risks of atherosclerosis and MI in the context of a high-AA diet.

Common polymorphisms of ALOX5 and ALOX5AP and risk of coronary artery disease

Recent human genetic studies suggest that allelic variants of leukotriene pathway genes influence the risk of clinical and subclinical atherosclerosis. We sequenced the promoter, exonic, and splice site regions of ALOX5 and ALOX5AP and then genotyped 7 SNPs in ALOX5 and 6 SNPs in ALOX5AP in 1,552 cases with clinically significant coronary artery disease (CAD) and 1,583 controls from Kaiser Permanente including a subset of participants of the coronary artery risk development in young adults study. A nominally significant association was detected between a promoter SNP in ALOX5 (rs12762303) and CAD in our subset of white/European subjects (adjusted odds ratio per minor allele, log-additive model, 1.32; P = 0.002). In this race/ethnic group, rs12762303 has a minor allele frequency of 15% and is tightly linked to variation at the SP1 variable tandem repeat promoter polymorphism. However, the association between CAD and rs12762303 could not be reproduced in the atherosclerosis risk in communities study (hazard rate ratio per minor allele; 1.08, P = 0.1). Assuming a recessive mode of inheritance, the association was not significant in either population study but our power to detect modest effects was limited. No significant associations were observed between all other SNPs and the risk of CAD. Overall, our findings do not support a link between common allelic variation in or near ALOX5 or ALOX5AP and the risk of CAD. However, additional studies are needed to exclude modest effects of promoter variation in ALOX5 on the risk of CAD assuming a recessive mode of inheritance.

The potential link between atherosclerosis and the 5-lipoxygenase pathway: investigational agents with new implications for the cardiovascular field

The 5-lipoxygenase pathway is responsible for the production of leukotrienes--inflammatory lipid mediators that have a role in innate immunity, but that can also have pathological effects in inflammatory diseases. Recently, a potential link between leukotriene production and atherosclerosis has been proposed. The expression of leukotriene biosynthetic enzymes and leukotriene receptors has been identified in coronary and carotid atherosclerotic plaques, and the levels of biosynthetic enzymes have been correlated with the clinical symptoms of unstable plaques. Genetic variants in 5-lipoxygenase pathway genes have also been associated with a relative risk of developing myocardial infarction and stroke. On the basis of these discoveries, antileukotriene compounds are now being evaluated for the treatment of cardiovascular disease. Several tool compounds have been shown to limit the progression of lesion development in preclinical models of atherosclerosis, and three compounds, including two drugs previously developed for asthma, are undergoing clinical trials in patients with acute coronary syndromes.