Effect of MTHFR Gene Polymorphism Impact on Atherosclerosis via Genome-Wide Methylation

DNA methylation and cardiovascular disease in humans: a systematic review and database of known CpG methylation sites

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of death worldwide and considered one of the most environmentally driven diseases. The role of DNA methylation in response to the individual exposure for the development and progression of CVD is still poorly understood and a synthesis of the evidence is lacking.

RESULTS

A systematic review of articles examining measurements of DNA cytosine methylation in CVD was conducted in accordance with PRISMA (preferred reporting items for systematic reviews and meta-analyses) guidelines. The search yielded 5,563 articles from PubMed and CENTRAL databases. From 99 studies with a total of 87,827 individuals eligible for analysis, a database was created combining all CpG-, gene- and study-related information. It contains 74,580 unique CpG sites, of which 1452 CpG sites were mentioned in ≥ 2, and 441 CpG sites in ≥ 3 publications. Two sites were referenced in ≥ 6 publications: cg01656216 (near ZNF438) related to vascular disease and epigenetic age, and cg03636183 (near F2RL3) related to coronary heart disease, myocardial infarction, smoking and air pollution. Of 19,127 mapped genes, 5,807 were reported in ≥ 2 studies. Most frequently reported were TEAD1 (TEA Domain Transcription Factor 1) and PTPRN2 (Protein Tyrosine Phosphatase Receptor Type N2) in association with outcomes ranging from vascular to cardiac disease. Gene set enrichment analysis of 4,532 overlapping genes revealed enrichment for Gene Ontology molecular function "DNA-binding transcription activator activity" (q = 1.65 × 10^-11) and biological processes "skeletal system development" (q = 1.89 × 10^-23). Gene enrichment demonstrated that general CVD-related terms are shared, while "heart" and "vasculature" specific genes have more disease-specific terms as PR interval for "heart" or platelet distribution width for "vasculature." STRING analysis revealed significant protein-protein interactions between the products of the differentially methylated genes (p = 0.003) suggesting that dysregulation of the protein interaction network could contribute to CVD. Overlaps with curated gene sets from the Molecular Signatures Database showed enrichment of genes in hemostasis (p = 2.9 × 10^-6) and atherosclerosis (p = 4.9 × 10^-4).

CONCLUSION

This review highlights the current state of knowledge on significant relationship between DNA methylation and CVD in humans. An open-access database has been compiled of reported CpG methylation sites, genes and pathways that may play an important role in this relationship.

Epigenetic factors in atherosclerosis: DNA methylation, folic acid metabolism, and intestinal microbiota

Atherosclerosis is a complex disease, influenced by both genetic and non-genetic factors. The most important epigenetic mechanism in the pathogenesis of atherosclerosis is DNA methylation, which involves modification of the gene without changes in the gene sequence. Nutrients involved in one-carbon metabolism interact to regulate DNA methylation, especially folic acid and B vitamins. Deficiencies in folic acid and other nutrients, such as vitamins B6 and B12, can increase homocysteine levels, induce endothelial dysfunction, and accelerate atherosclerotic pathological processes. Supplemented nutrients can improve DNA methylation status, reduce levels of inflammatory factors, and delay the process of atherosclerosis. In this review, the influence of intestinal flora on folate metabolism and epigenetics is also considered.

Genetic Risk Factors of Intracranial Atherosclerosis

PURPOSE OF REVIEW

Intracranial atherosclerosis (ICAS) is the most common cause of stroke throughout the world. It also increases the risk of recurrent stroke and dementia. As a complex and multifactorial disease, ICAS is influenced by multiple genetic, biological, and environmental factors. This review summarizes the candidate gene and genome-wide studies aimed at discovering genetic risk factors of ICAS.

RECENT FINDINGS

Numerous studies have focused on the association between single-nucleotide polymorphisms (SNPs) of atherosclerosis-related genes and the risk of ICAS. Variants in adiponectin Q (ADIPOQ), ring finger protein 213 (RNF213), apolipoprotein E (APOE), phosphodiesterase 4D (PDE4D), methylenetetrahydrofolate reductase (MTHFR), lipoprotein lipase (LPL), α-adducin (ADD1) genes, angiotensin-converting enzyme (ACE), and other genes related to renin-angiotensin-aldosterone system have been associated with ICAS. We review the available evidences on the candidate genes and SNPs associated with genetic susceptibility to ICAS, and point out future developments of this field. Genetic discoveries could have clinical implications for intracranial atherosclerotic disease.

Epigenetics and MicroRNAs in Pharmacogenetics

Germline pharmacogenetics has so far mainly studied common variants in "pharmacogenes," i.e., genes encoding drug metabolizing enzymes and transporters (DMET genes), certain auxiliary and regulatory genes, and drug target genes. Despite remarkable progress in understanding genetically determined differences in pharmacokinetics and pharmacodynamics of drugs, currently known common variants even in important pharmacogenes explain genetic variability only partially. This suggests "missing heritability" that may in part be due to rare variants in the classical pharmacogenes, but current evidence suggests that largely unexplored resources with potential for pharmacogenetics exist, both within already known pharmacogenes and in entirely new areas. In particular, recent studies suggest that epigenetic processes and noncoding RNAs, including mostly microRNAs (miRNAs), represent important and largely unexplored layers of DMET gene regulation that may fill some of the gaps in understanding interindividual variability and lead to new biomarkers. In this chapter we summarize recent advances in the understanding of genetic variability in epigenetic and miRNA-mediated processes with focus on their significance for DMET regulation and pharmacokinetic or pharmacological endpoints.

DNA Methylation and the Potential Role of Methyl-Containing Nutrients in Cardiovascular Diseases

Patients suffering from cardiovascular diseases (CVDs) experience a low quality of life and increase pressure on healthcare systems both nationally and globally. DNA methylation, which refers to the pathway by which DNA methyltransferase facilitates the addition of a methyl group to DNA, is of critical importance in this respect primarily because the epigenetic modification is implicated in a range of serious conditions including atherosclerosis, CVDs, and cancer. Research findings indicate that the number of epigenetic alterations can be elicited (both in utero and in adults) through the administration of certain nutritional supplements, including folic acid and methionine; this is partly attributable to the effect employed by methyl-containing nutrients in DNA methylation. Thus, for the purpose of illuminating viable therapeutic measures and preventive strategies for CVDs, research should continue to explore the intricate associations that exist between epigenetic regulation and CVD pathogenesis. This review centers on an exposition of the mechanism by which DNA methylation takes place, the impact it has on a range of conditions, and the potential clinical value of nutrition, driven mainly by the observation that nutritional supplements such as folic acid can affect DNA methylation.

Genetic and Epigenetic Regulation of Aortic Aneurysms

Aneurysms are characterized by structural deterioration of the vascular wall leading to progressive dilatation and, potentially, rupture of the aorta. While aortic aneurysms often remain clinically silent, the morbidity and mortality associated with aneurysm expansion and rupture are considerable. Over 13,000 deaths annually in the United States are attributable to aortic aneurysm rupture with less than 1 in 3 persons with aortic aneurysm rupture surviving to surgical intervention. Environmental and epidemiologic risk factors including smoking, male gender, hypertension, older age, dyslipidemia, atherosclerosis, and family history are highly associated with abdominal aortic aneurysms, while heritable genetic mutations are commonly associated with aneurysms of the thoracic aorta. Similar to other forms of cardiovascular disease, family history, genetic variation, and heritable mutations modify the risk of aortic aneurysm formation and provide mechanistic insight into the pathogenesis of human aortic aneurysms. This review will examine the relationship between heritable genetic and epigenetic influences on thoracic and abdominal aortic aneurysm formation and rupture.

Novel Approaches to Investigate One-Carbon Metabolism and Related B-Vitamins in Blood Pressure

Hypertension, a major risk factor for heart disease and stroke, is the world's leading cause of preventable, premature death. A common polymorphism (677C→T) in the gene encoding the folate metabolizing enzyme methylenetetrahydrofolate reductase (MTHFR) is associated with increased blood pressure, and there is accumulating evidence demonstrating that this phenotype can be modulated, specifically in individuals with the MTHFR 677TT genotype, by the B-vitamin riboflavin, an essential co-factor for MTHFR. The underlying mechanism that links this polymorphism, and the related gene-nutrient interaction, with hypertension is currently unknown. Previous research has shown that 5-methyltetrahydrofolate, the product of the reaction catalysed by MTHFR, appears to be a positive allosteric modulator of endothelial nitric oxide synthase (eNOS) and may thus increase the production of nitric oxide, a potent vasodilator. Blood pressure follows a circadian pattern, peaking shortly after wakening and falling during the night, a phenomenon known as 'dipping'. Any deviation from this pattern, which can only be identified using ambulatory blood pressure monitoring (ABPM), has been associated with increased cardiovascular disease (CVD) risk. This review will consider the evidence linking this polymorphism and novel gene-nutrient interaction with hypertension and the potential mechanisms that might be involved. The role of ABPM in B-vitamin research and in nutrition research generally will also be reviewed.