Epigenetics, the missing link in hypertension

Redox imbalance driven epigenetic reprogramming and cardiovascular dysfunctions: phytocompounds for prospective epidrugs

BACKGROUND

Cardiovascular diseases (CVDs) are the major contributor to global mortality and are gaining incremental attention following the COVID-19 outbreak. Epigenetic events such as DNA methylation, histone modifications, and non-coding RNAs have a significant impact on the incidence and onset of CVDs. Altered redox status is one of the major causative factors that regulate epigenetic pathways linked to CVDs. Various bioactive phytocompounds used in alternative therapies including Traditional Chinese Medicines (TCM) regulate redox balance and epigenetic phenomena linked to CVDs. Phytocompound-based medications are in the limelight for the development of cost-effective drugs with the least side effects, which will have immense therapeutic applications.

PURPOSE

This review comprehends certain risk factors associated with CVDs and triggered by oxidative stress-driven epigenetic remodelling. Further, it critically evaluates the pharmacological efficacy of phytocompounds as inhibitors of HAT/HDAC and DNMTs as well as miRNAs regulator that lowers the incidence of CVDs, aiming for new candidates as prospective epidrugs.

METHODS

PRISMA flow approach has been adopted for systematic literature review. Different Journals, computational databases, search engines such as Google Scholar, PubMed, Science Direct, Scopus, and ResearchGate were used to collect online information for literature survey. Statistical information collected from the World Health Organization (WHO) site (https://www.who.int/news-room/fact-sheets/detail/cardiovascular-diseases-(cvds)) and the American Heart Association of Heart Disease and Stroke reported the international and national status of CVDs.

RESULTS

The meta-analysis of various studies is elucidated in the literature, shedding light on major risk factors such as socioeconomic parameters, which contribute highly to redox imbalance, epigenetic modulations, and CVDs. Going forward, redox imbalance driven epigenetic regulations include changes in DNA methylation status, histone modifications and non-coding RNAs expression pattern which further regulates global as well as promoter modification of various transcription factors leading to the onset of CVDs. Further, the role of various bioactive compounds used in herbal medicine, including TCM for redox regulation and epigenetic modifications are discussed. Pharmacological safety doses and different phases of clinical trials of these phytocompounds are elaborated on, which shed light on the acceptance of these phytocompounds as prospective drugs.

CONCLUSION

This review suggests a strong linkage between therapeutic and preventive measures against CVDs by targeting redox imbalance-driven epigenetic reprogramming using phytocompounds as prospective epidrugs. Future in-depth research is required to evaluate the possible molecular mechanisms behind the phytocompound-mediated epigenetic reprogramming and oxidative stress management during CVD progression.

The pharmaco-epigenetics of hypertension: a focus on microRNA

Hypertension is a major harbinger of cardiovascular morbidity and mortality. It predisposes to higher rates of myocardial infarction, chronic kidney failure, stroke, and heart failure than most other risk factors. By 2025, the prevalence of hypertension is projected to reach 1.5 billion people. The pathophysiology of this disease is multifaceted, as it involves nitric oxide and endothelin dysregulation, reactive oxygen species, vascular smooth muscle proliferation, and vessel wall calcification, among others. With the advent of new biomolecular techniques, various studies have elucidated a gaping hole in the etiology and mechanisms of hypertension. Indeed, epigenetics, DNA methylation, histone modification, and microRNA-mediated translational silencing appear to play crucial roles in altering the molecular phenotype into a hypertensive profile. Here, we critically review the experimentally determined associations between microRNA (miRNA) molecules and hypertension pharmacotherapy. Particular attention is given to the epigenetic mechanisms underlying the physiological responses to antihypertensive drugs like candesartan, and other relevant drugs like clopidogrel, aspirin, and statins among others. Furthermore, how miRNA affects the pharmaco-epigenetics of hypertension is especially highlighted.

Epigenetic DNA Methylation and Protein Homocysteinylation: Key Players in Hypertensive Renovascular Damage

Hypertension has been a threat to the health of people, the mechanism of which, however, remains poorly understood. It is clinically related to loss of nephron function, glomerular sclerosis, or necrosis, resulting in renal functional declines. The mechanisms underlying hypertension's development and progression to organ damage, including hypertensive renal damage, remain to be fully elucidated. As a developing approach, epigenetics has been postulated to elucidate the phenomena that otherwise cannot be explained by genetic studies. The main epigenetic hallmarks, such as DNA methylation, histone acetylation, deacetylation, noncoding RNAs, and protein N-homocysteinylation have been linked with hypertension. In addition to contributing to endothelial dysfunction and oxidative stress, biologically active gases, including NO, CO, and H2S, are crucial regulators contributing to vascular remodeling since their complex interplay conducts homeostatic functions in the renovascular system. Importantly, epigenetic modifications also directly contribute to the pathogenesis of kidney damage via protein N-homocysteinylation. Hence, epigenetic modulation to intervene in renovascular damage is a potential therapeutic approach to treat renal disease and dysfunction. This review illustrates some of the epigenetic hallmarks and their mediators, which have the ability to diminish the injury triggered by hypertension and renal disease. In the end, we provide potential therapeutic possibilities to treat renovascular diseases in hypertension.

Epigenetics of hypertension as a risk factor for the development of coronary artery disease in type 2 diabetes mellitus

Hypertension, a multifaceted cardiovascular disorder influenced by genetic, epigenetic, and environmental factors, poses a significant risk for the development of coronary artery disease (CAD) in individuals with type 2 diabetes mellitus (T2DM). Epigenetic alterations, particularly in histone modifications, DNA methylation, and microRNAs, play a pivotal role in unraveling the complex molecular underpinnings of blood pressure regulation. This review emphasizes the crucial interplay between epigenetic attributes and hypertension, shedding light on the prominence of DNA methylation, both globally and at the gene-specific level, in essential hypertension. Additionally, histone modifications, including acetylation and methylation, emerge as essential epigenetic markers linked to hypertension. Furthermore, microRNAs exert regulatory influence on blood pressure homeostasis, targeting key genes within the aldosterone and renin-angiotensin pathways. Understanding the intricate crosstalk between genetics and epigenetics in hypertension is particularly pertinent in the context of its interaction with T2DM, where hypertension serves as a notable risk factor for the development of CAD. These findings not only contribute to the comprehensive elucidation of essential hypertension but also offer promising avenues for innovative strategies in the prevention and treatment of cardiovascular complications, especially in the context of T2DM.

Causality between heart failure and epigenetic age: a bidirectional Mendelian randomization study

AIMS

Heart failure (HF) is a prevalent age-related cardiovascular disease with poor prognosis in the elderly population. This study aimed to establish the causal relationship between ageing and HF by conducting a bidirectional Mendelian randomization (MR) analysis on epigenetic age (a marker of ageing) and HF.

METHODS AND RESULTS

Genome-wide association study data for epigenetic age (GrimAge, HorvathAge, HannumAge, and PhenoAge) and HF were collected and assessed for significant genetic variables. A bidirectional MR analysis was carried out using the random-effects inverse-variance weighted (IVW) method as the primary approach, while other methods (MR-Egger, weighted median, simple mode, and weighted mode) and multiple sensitivity analyses (heterogeneity analysis, leave-one-out sensitivity analysis, and horizontal pleiotropy analysis) were employed to evaluate the impact of epigenetic age on HF and vice versa. Bidirectional MR analysis of two samples revealed that the epigenetic PhenoAge clock increased the risk of HF [IVW odds ratio (OR) 1.015, 95% confidence interval (CI) 1.002-1.028, P = 0.028 and weighted median OR 1.020, 95% CI 1.001-1.038, P = 0.039]. Other results were not statistically significant.

CONCLUSIONS

The bidirectional MR analysis demonstrated a causal link between genetically predicted epigenetic age and HF in individuals of European descent. Further research into epigenetic age in other populations and additional genetic information related to HF is warranted.

Epigenome-wide association study in Chinese monozygotic twins identifies DNA methylation loci associated with blood pressure

BACKGROUND

Hypertension is a crucial risk factor for developing cardiovascular disease and reducing life expectancy. We aimed to detect DNA methylation (DNAm) variants potentially related to systolic blood pressure (SBP) and diastolic blood pressure (DBP) by conducting epigenome-wide association studies in 60 and 59 Chinese monozygotic twin pairs, respectively.

METHODS

Genome-wide DNA methylation profiling in whole blood of twins was performed using Reduced Representation Bisulfite Sequencing, yielding 551,447 raw CpGs. Association between DNAm of single CpG and blood pressure was tested by applying generalized estimation equation. Differentially methylated regions (DMRs) were identified by comb-P approach. Inference about Causation through Examination of Familial Confounding was utilized to perform the causal inference. Ontology enrichment analysis was performed using Genomic Regions Enrichment of Annotations Tool. Candidate CpGs were quantified using Sequenom MassARRAY platform in a community population. Weighted gene co-expression network analysis (WGCNA) was conducted using gene expression data.

RESULTS

The median age of twins was 52 years (95% range 40, 66). For SBP, 31 top CpGs (p < 1 × 10-4) and 8 DMRs were identified, with several DMRs within NFATC1, CADM2, IRX1, COL5A1, and LRAT. For DBP, 43 top CpGs (p < 1 × 10-4) and 12 DMRs were identified, with several DMRs within WNT3A, CNOT10, and DAB2IP. Important pathways, such as Notch signaling pathway, p53 pathway by glucose deprivation, and Wnt signaling pathway, were significantly enriched for SBP and DBP. Causal inference analysis suggested that DNAm at top CpGs within NDE1, MYH11, SRRM1P2, and SMPD4 influenced SBP, while SBP influenced DNAm at CpGs within TNK2. DNAm at top CpGs within WNT3A influenced DBP, while DBP influenced DNAm at CpGs within GNA14. Three CpGs mapped to WNT3A and one CpG mapped to COL5A1 were validated in a community population, with a hypermethylated and hypomethylated direction in hypertension cases, respectively. Gene expression analysis by WGCNA further identified some common genes and enrichment terms.

CONCLUSION

We detect many DNAm variants that may be associated with blood pressure in whole blood, particularly the loci within WNT3A and COL5A1. Our findings provide new clues to the epigenetic modification underlying hypertension pathogenesis.

Maternal exercise upregulates the DNA methylation of Agtr1a to enhance vascular function in offspring of hypertensive rats

The angiotensin II signaling system regulates vascular dysfunction and is involved in the programming of hypertension. Maternal exercise has been linked to both short-term and long-term benefits for the mother and fetus. However, the impacts of maternal exercise on the intravascular renin-angiotensin system (RAS) in hypertensive offspring remain unexamined. This study examined whether maternal exercise has an epigenetic effect in repressing angiotensin II type 1 receptor (AT₁R) expression, which leads to favorable alterations in the mesenteric artery (MA) function of spontaneously hypertensive offspring. Spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) pregnant rats were randomly divided into an exercise group and a control group. Blood pressure, vascular tone, AT₁R protein and mRNA expression, and AT₁R gene (Agtr1a) promoter methylation status were examined in the MAs of 3-month-old male offspring. Maternal exercise significantly reduced the resting blood pressure and cardiovascular reactivity of offspring from SHRs. Furthermore, Ang II-AT₁R activity in regulating vascular tone and AT₁R expression was decreased in the MAs of the SHR offspring from the exercise groups. Importantly, exercise during gestation suppressed AT₁R expression via hypermethylation of the Agtr1a promoter region and upregulated DNA methyltransferase (DNMT) expression in MAs of SHR offspring. These results suggest that maternal exercise upregulates DNMT expression, resulting in hypermethylation and repression of the Agtr1a gene, which may prevent MA dysfunction in the offspring of SHRs. A mechanistic model on the epigenetics of exercise during pregnancy. Maternal exercise during pregnancy triggers hypermethylation and transcriptional suppression of the Agtr1a gene via increased DNMT1 and DNMT3B expression in MAs of SHR offspring. Downregulation of AT1R expression reduces the contribution of Ang II to vascular tone, ultimately improving vascular structure and function. VSMC vascular smooth muscle cell; Ang II angiotensin II; AT1aR angiotensin type 1 receptor (AT1R) alpha subtypes; Agtr1a AT1R alpha isoform gene; MAs mesenteric arteries; BP blood pressure.

In Silico Identification of Human miR-26a-1 from Hypertension Genome Sequence

Background:

Hypertension is a global public health issue that is becoming more prevalent. It is a non-communicable disease and a great public health problem affecting almost half of the world’s adult population. Being multifactorial, hypertension is a key risk factor for stroke, coronary artery disease, heart failure, and chronic renal failure. However, the cellular and molecular mechanisms that regulate it remain mostly unknown. According to numerous studies, microRNAs (miRNAs) have been implicated in a range of cellular processes in the development of illnesses. The current study aims to identify miRNAs in hypertension from genome sequences found in public genomic databases.

Materials and Methods:

In this study, we have used bioinformatic approaches to identify miR-26a- 1 for hypertension using the NCBI database, miRBase and target scan. Finally, the RNA fold was used to create the secondary structure of miR-26a-1.

Results and Discussion:

Careful evaluation of secondary structure result showed that hsa-miR- 26a-1 has a minimum free energy of - 37.30 kcal. The correlation between miR-26a-1 and hypertension genome sequence was identified.

Conclusion:

These computational approaches have concluded that miR-26a-1 can be used as a diagnosis, prognosis and effective therapeutic target for treating hypertension. Thus, further research could enlighten the role of miR-26a-1 in hypertension.

Summary of Known Genetic and Epigenetic Modification Contributed to Hypertension

Hypertension is a multifactorial disease due to a complex interaction among genetic, epigenetic, and environmental factors. Characterized by raised blood pressure (BP), it is responsible for more than 7 million deaths per annum by acting as a leading preventable risk factor for cardiovascular disease. Reports suggest that genetic factors are estimated to be involved in approximately 30 to 50% of BP variation, and epigenetic marks are known to contribute to the initiation of the disease by influencing gene expression. Consequently, elucidating the genetic and epigenetic mediators associated with hypertension is essential for better discernment of its pathophysiology. By deciphering the unprecedented molecular hypertension basis, it could help to unravel an individual's inclination towards hypertension which eventually could result in an arrangement of potential strategies for prevention and therapy. In the present review, we discuss known genetic and epigenetic drivers that contributed to the hypertension development and summarize the novel variants that have currently been identified. The effect of these molecular alterations on endothelial function was also presented.

Apparent mineralocorticoid excess: comprehensive overview of molecular genetics

Apparent mineralocorticoid excess is an autosomal recessive form of monogenic disease characterized by juvenile resistant low-renin hypertension, marked hypokalemic alkalosis, low aldosterone levels, and high ratios of cortisol to cortisone metabolites. It is caused by defects in the HSD11B2 gene, encoding the enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), which is primarily involved in the peripheral conversion of cortisol to cortisone. To date, over 50 deleterious HSD11B2 mutations have been identified worldwide. Multiple molecular mechanisms function in the lowering of 11β-HSD2 activity, including damaging protein stability, lowered affinity for the substrate and cofactor, and disrupting the dimer interface. Genetic polymorphism, environmental factors as well as epigenetic modifications may also offer an implicit explanation for the molecular pathogenesis of AME. A precise diagnosis depends on genetic testing, which allows for early and specific management to avoid the morbidity and mortality from target organ damage. In this review, we provide insights into the molecular genetics of classic and non-classic apparent mineralocorticoid excess and aim to offer a comprehensive overview of this monogenic disease.

DNA methylation: a potential mediator between air pollution and metabolic syndrome

Given the global increase in air pollution and its crucial role in human health, as well as the steep rise in prevalence of metabolic syndrome (MetS), a better understanding of the underlying mechanisms by which environmental pollution may influence MetS is imperative. Exposure to air pollution is known to impact DNA methylation, which in turn may affect human health. This paper comprehensively reviews the evidence for the hypothesis that the effect of air pollution on the MetS is mediated by DNA methylation in blood. First, we present a summary of the impact of air pollution on metabolic dysregulation, including the components of MetS, i.e., disorders in blood glucose, lipid profile, blood pressure, and obesity. Then, we provide evidence on the relation between air pollution and endothelial dysfunction as one possible mechanism underlying the relation between air pollution and MetS. Subsequently, we review the evidence that air pollution (PM, ozone, NO2 and PAHs) influences DNA methylation. Finally, we summarize association studies between DNA methylation and MetS. Integration of current evidence supports our hypothesis that methylation may partly mediate the effect of air pollution on MetS.

Novel methylation mark and essential hypertension

Background

Essential hypertension (EH) is an important risk factor for various cardiovascular, cerebral and renal disorders. It is a multi-factorial trait which occurs through complex interplay between genetic, epigenetic, and environmental factors. Even after advancement of technology and deciphering the involvement of multiple signalling pathways in blood pressure regulation, it still remains as a huge global concern.

Main body of the abstract

Genome-wide association studies (GWAS) have revealed EH-associated genetic variants but these solely cannot explain the variability in blood pressure indicating the involvement of additional factors. The etiopathogenesis of hypertension has now advanced to the level of epigenomics where aberrant DNA methylation is the most defined epigenetic mechanism to be involved in gene regulation. Though role of DNA methylation in cancer and other mechanisms is deeply studied but this mechanism is in infancy in relation to hypertension. Generally, 5-methylcytosine (5mC) levels are being targeted at both individual gene and global level to find association with the disease. But recently, with advanced sequencing techniques another methylation mark, N6-methyladenine (6mA) was found and studied in humans which was earlier considered to be absent in case of eukaryotes. Relation of aberrant 6mA levels with cancer and stem cell fate has drawn attention to target 6mA levels with hypertension too.

Conclusion

Recent studies targeting hypertension has suggested 6mA levels as novel marker and its demethylase, ALKBH1 as probable therapeutic target to prevent hypertension through epigenetic programming. This review compiles different methylation studies and suggests targeting of both 5mC and 6mA levels to cover role of methylation in hypertension in broader scenario.

Revealing new therapeutic opportunities in hypertension through network-driven integrative genetic analysis and drug target prediction approach

Epidemiological studies have established that untreated hypertension (HTN) is a major independent risk factor for developing cardiovascular diseases (CVD), stroke, renal failure, and other conditions. Several important studies have been published to prevent and manage HTN; however, antihypertensive agents' optimal choice remains controversial. Therefore, the present study is undertaken to update our knowledge in the primary treatment of HTN, specifically in the setting of other three important diseases. MicroRNAs (miRNAs) are remarkably stable short endogenous conserved non-coding RNAs that bind to the mRNA at its (3' UTR) to regulate its gene expression by causing translational repression or mRNA degradation. Through their coordinated activities on different pathways and networks, individual miRNAs control normal and pathological cellular processes. Therefore, to identify the critical miRNA-mRNA-TF interactions, we performed systematic bioinformatics analysis. We have also employed the molecular modelling and docking approach to identify the therapeutic target that delivers novel empathies into Food and Drug Administration approved and herbal drug response physiology. Gene Expression Omnibus (GEO) was employed to identify the differentially expressed genes (DEGs) and hub genes- KNG1, HLA-DPB1, CXCL8, IL1B, and BCL2. The HTN associated feed-forward loop (FFL) network included miR-9-5p, KNG1 and AR. We employed high throughput screening to get the best interacting compounds, telmisartan and limonin, that provided a significant docking score (-13.3 and -12.0 kcal/mol) and a potential protective effect that may help to combat the impact of HTN. The present study provides novel insight into HTN etiology through the identification of mRNAs and miRNAs and associated pathways.

Targeting the Renin-Angiotensin-Aldosterone System to Prevent Hypertension and Kidney Disease of Developmental Origins

The renin-angiotensin-aldosterone system (RAAS) is implicated in hypertension and kidney disease. The developing kidney can be programmed by various early-life insults by so-called renal programming, resulting in hypertension and kidney disease in adulthood. This theory is known as developmental origins of health and disease (DOHaD). Conversely, early RAAS-based interventions could reverse program processes to prevent a disease from occurring by so-called reprogramming. In the current review, we mainly summarize (1) the current knowledge on the RAAS implicated in renal programming; (2) current evidence supporting the connections between the aberrant RAAS and other mechanisms behind renal programming, such as oxidative stress, nitric oxide deficiency, epigenetic regulation, and gut microbiota dysbiosis; and (3) an overview of how RAAS-based reprogramming interventions may prevent hypertension and kidney disease of developmental origins. To accelerate the transition of RAAS-based interventions for prevention of hypertension and kidney disease, an extended comprehension of the RAAS implicated in renal programming is needed, as well as a greater focus on further clinical translation.

Epigenetic modification: a regulatory mechanism in essential hypertension

Essential hypertension (EH) is a multifactorial disease of the cardiovascular system that is influenced by the interplay of genetic, epigenetic, and environmental factors. The molecular dynamics underlying EH etiopathogenesis is unknown; however, earlier studies have revealed EH-associated genetic variants. Nevertheless, this finding alone is not sufficient to explain the variability in blood pressure, suggesting that other risk factors are involved, such as epigenetic modifications. Therefore, this review highlights the potential contribution of well-defined epigenetic mechanisms in EH, specifically, DNA methylation, post-translational histone modifications, and microRNAs. We further emphasize global and gene-specific DNA methylation as one of the most well-studied hallmarks among all epigenetic modifications in EH. In addition, post-translational histone modifications, such as methylation, acetylation, and phosphorylation, are described as important epigenetic markers associated with EH. Finally, we discuss microRNAs that affect blood pressure by regulating master genes such as those implicated in the renin-angiotensin-aldosterone system. These epigenetic modifications, which appear to contribute to various cardiovascular diseases, including EH, may be a promising research area for the development of novel future strategies for EH prevention and therapeutics.

DNA methylation of the Tacr2 gene in a CUMS model of depression

Tacr2, the gene encoding the NK2 receptor, belongs to G protein-coupled receptors. Accumulating evidence has indicated that the tachykinin receptors may contribute to the pathophysiology of depression. During the last decade, some studies have shown that Tacr2 activation is involved in the modulation of emotional processes. However, the extent, to which stress impacts Tacr2 expression remains unclear. The molecular mechanisms underlying depression also remain poorly understood. In this study, we subjected adult male Sprague Dawley (SD) rats to chronic unpredictable mild stress (CUMS) to induce a depression-like phenotype. We then measured the body weight and performed the sucrose preference test, forced swimming test (FST) and open field test to detect the effects of stress on anhedonia and activity. Western blotting and real-time PCR were used to study the protein and mRNA expression levels of Tacr2, respectively, in the hypothalamus. To explore DNA methylation of the Tacr2 gene, we used methylated DNA immunoprecipitation sequencing (MeDIP-seq). Additionally, we used the bisulfite sequencing PCR (BSP) to further verify the DNA methylation levels of the Tacr2 receptor gene in rats. We found that the CUMS-sensitive rats exhibited a decrease in body weight and sucrose preference, a decrease in the distance traveled, rearing frequency and velocity in the open field test, and an increase in immobility time in the FST. Compared with the expression in the control rats, Tacr2 protein and mRNA expression in the hypothalamus significantly increased in the CUMS-sensitive rats; however, the DNA methylation levels of the Tacr2 gene were significantly lower than in the control rats. In summary, according to our findings, the stress-induced increase in Tacr2 expression in the hypothalamus correlated with a specific decrease in DNA methylation of the Tacr2 gene. These results may enrich the understanding of the pathological processes of depression and provide insights into therapeutic approaches for its treatment.

Integrative Bioinformatics Approaches for Identification of Drug Targets in Hypertension

High blood pressure or hypertension is an established risk factor for a myriad of cardiovascular diseases. Genome-wide association studies have successfully found over nine hundred loci that contribute to blood pressure. However, the mechanisms through which these loci contribute to disease are still relatively undetermined as less than 10% of hypertension-associated variants are located in coding regions. Phenotypic cell-type specificity analyses and expression quantitative trait loci show predominant vascular and cardiac tissue involvement for blood pressure-associated variants. Maps of chromosomal conformation and expression quantitative trait loci (eQTL) in critical tissues identified 2,424 genes interacting with blood pressure-associated loci, of which 517 are druggable. Integrating genome, regulome and transcriptome information in relevant cell-types could help to functionally annotate blood pressure associated loci and identify drug targets.

DNA Methylation and Histone Modification in Hypertension

Systemic hypertension, which eventually results in heart failure, renal failure or stroke, is a common chronic human disorder that particularly affects elders. Although many signaling pathways involved in the development of hypertension have been reported over the past decades, which has led to the implementation of a wide variety of anti-hypertensive therapies, one half of all hypertensive patients still do not have their blood pressure controlled. The frontier in understanding the molecular mechanisms underlying hypertension has now advanced to the level of epigenomics. Particularly, increasing evidence is emerging that DNA methylation and histone modifications play an important role in gene regulation and are involved in alteration of the phenotype and function of vascular cells in response to environmental stresses. This review seeks to highlight the recent advances in our knowledge of the epigenetic regulations and mechanisms of hypertension, focusing on the role of DNA methylation and histone modification in the vascular wall. A better understanding of the epigenomic regulation in the hypertensive vessel may lead to the identification of novel target molecules that, in turn, may lead to novel drug discoveries for the treatment of hypertension.

The Epigenetic Machinery in Vascular Dysfunction and Hypertension

Hypertension (HT) is among the major components of the metabolic syndrome, i.e., obesity, dyslipidemia, and hyperglycemia/insulin resistance. It represents a significant health problem with foremost risks for chronic cardiovascular disease and a significant cause of morbidity and mortality worldwide. Therefore, it is not surprising that this disorder constitutes a serious public health concern. Although multiple studies have stressed the multifactorial nature of HT, the pathogenesis remains largely unknown. However, if we want to reduce the global prevalence of HT, restrain the number of deaths (currently 9.4 million/year in the world), and alleviate the socio-economic burden, a deeper insight into the mechanisms is urgently needed in order to define new meaningful therapeutic targets. Recently, the role of epigenetics in the development of various complex diseases has attracted much attention. In the present review, we provide a critical update on the available literature and ongoing research regarding the epigenetic modifications of genes involved in several pathways of elevated blood pressure, especially those linked to the vascular epithelium. This review also focuses on the role of microRNA (miRNA) in the regulation of gene expression associated with HT and of fetal programming mediating susceptibility to HT in adulthood.

Epigenetics for the pediatric cardiologist

A genetic basis of congenital heart disease (CHD) has been known for decades. In addition to the sequence of the genome, the contribution of epigenetics to pediatric cardiology is increasingly recognized. Multiple epigenetic mechanisms, including DNA methylation, histone modification, and RNA-based regulation, are known mediators of cardiovascular disease, including both development and progression of CHD and its sequelae. Basic understanding of the concepts of epigenetics will be essential to all pediatric cardiologists in order to understand mechanisms of pathophysiology, pharmacotherapeutic concepts, and to understand the role of epigenetics in precision medicine.

The epigenetic promise to improve prognosis of heart failure and heart transplantation

Heart transplantation is still the only possible life-saving treatment for end-stage heart failure, the critical epilogue of several cardiac diseases. Epigenetic mechanisms are being intensively investigated because they could contribute to establishing innovative diagnostic and predictive biomarkers, as well as ground-breaking therapies both for heart failure and heart transplantation rejection. DNA methylation and histone modifications can modulate the innate and adaptive immune response by acting on the expression of immune-related genes that, in turn, are crucial determinants of transplantation outcome. Epigenetic drugs acting on methylation and histone-modification pathways may modulate Treg activity by acting as immunosuppressive agents. Moreover, the identification of non-invasive and reliable epigenetic biomarkers for the prediction of allograft rejection and for monitoring immunosuppressive therapies represents an attractive perspective in the management of transplanted patients. MiRNAs seem to fit particularly well to this purpose because they are differently expressed in patients at high and low risk of rejection and are detectable in biological fluids besides biopsies. Although increasing evidence supports the involvement of epigenetic tags in heart failure and transplantation, further short and long-term clinical studies are needed to translate the possible available findings into clinical setting.

Is There a Role for Genomics in the Management of Hypertension?

Hypertension (HTN) affects about 1 billion people worldwide and the lack of a single identifiable cause complicates its treatment. Blood pressure (BP) levels are influenced by environmental factors, but there is a strong genetic component. Linkage analysis has identified several genes involved in Mendelian forms of HTN and the associated pathophysiological mechanisms have been unravelled, leading to targeted therapies. The majority of these syndromes are due to gain-of-function or loss-of-functions mutations, resulting in an alteration of mineralocorticoid, glucocorticoid, or sympathetic pathways. The diagnosis of monogenic forms of HTN has limited practical implications on the population and a systematic genetic screening is not justifiable. Genome-wide linkage and association studies (GWAS) have identified single nucleotide polymorphisms (SNPs), which influence BP. Forty-three variants have been described with each SNP affecting systolic and diastolic BP by 1.0 and 0.5 mmHg, respectively. Taken together Mendelian inheritance and all GWAS-identified HTN-associated variants explain 2–3% of BP variance. Epigenetic modifications, such as DNA methylation, histone modification and non-coding RNAs, have become increasingly recognized as important players in BP regulation and may justify a further part of missing heritability. In this review, we will discuss how genetics and genomics may assist clinicians in managing patients with HTN.

Blood pressure and expression of microRNAs in whole blood

Background

Blood pressure (BP) is a complex, multifactorial clinical outcome driven by genetic susceptibility, behavioral choices, and environmental factors. Many molecular mechanisms have been proposed for the pathophysiology of high BP even as its prevalence continues to grow worldwide, increasing morbidity and marking it as a major public health concern. To address this, we evaluated miRNA profiling in blood leukocytes as potential biomarkers of BP and BP-related risk factors.

Methods

The Beijing Truck Driver Air Pollution Study included 60 truck drivers and 60 office workers examined in 2008. On two days separated by 1–2 weeks, we examined three BP measures: systolic, diastolic, and mean arterial pressure measured at both pre- and post-work exams for blood NanoString nCounter miRNA profiles. We used covariate-adjusted linear mixed-effect models to examine associations between BP and increased miRNA expression in both pooled and risk factor-stratified analyses.

Results

Overall 43 miRNAs were associated with pre-work BP (FDR<0.05). In stratified analyses different but overlapping groups of miRNAs were associated with pre-work BP in truck drivers, high-BMI participants, and usual alcohol drinkers (FDR<0.05). Only four miRNAs were associated with post-work BP (FDR<0.05), in ever smokers.

Conclusion

Our results suggest that many miRNAs were significantly associated with BP in subgroups exposed to known hypertension risk factors. These findings shed light on the underlying molecular mechanisms of BP, and may assist with the development of a miRNA panel for early detection of hypertension.

Hydrogen sulfide alleviates hypertensive kidney dysfunction through an epigenetic mechanism

Hypertension is a major risk factor for chronic kidney disease (CKD), and renal inflammation is an integral part in this pathology. Hydrogen sulfide (H₂S) has been shown to mitigate renal damage through reduction in blood pressure and ROS; however, the exact mechanisms are not clear. While several studies have underlined the role of epigenetics in renal inflammation and dysfunction, the mechanisms through which epigenetic regulators play a role in hypertension are not well defined. In this study, we sought to identify whether microRNAs are dysregulated in response to angiotensin II (ANG II)-induced hypertension in the kidney and whether a H₂S donor, GYY4137, could reverse the microRNA alteration and kidney function. Wild-type (C57BL/6J) mice were treated without or with ANG II and GYY4137 for 4 wk. Blood pressure, renal blood flow, and resistive index (RI) were measured. MicroRNA microarrays were conducted and subsequent target prediction revealed genes associated with a proinflammatory response. ANG II treatment significantly increased blood pressure, decreased blood flow in the renal cortex, increased RI, and reduced renal function. These effects were ameliorated in mice treated with GYY4137. Microarray analysis revealed downregulation of miR-129 in ANG II-treated mice and upregulation after GYY4137 treatment. Quantitation of proteins involved in the inflammatory response and DNA methylation revealed upregulation of IL-17A and DNA methyltransferase 3a, whereas H₂S production enzymes and anti-inflammatory IL-10 were reduced. Taken together, our data suggest that downregulation of miR-129 plays a significant role in ANG II-induced renal inflammation and functional outcomes and that GYY4137 improves renal function by reversing miR-129 expression.NEW & NOTEWORTHY We investigated epigenetic changes that occur in the hypertensive kidney and how H₂S supplementation reverses adverse effects. Inflammation, aberrant methylation, and dysfunction were observed in the hypertensive kidney, and these effects were alleviated with H₂S supplementation. We identify miR-129 as a potential regulator of blood pressure and H₂S regulation.

Genetic Programming of Hypertension

The heritability of hypertension (HTN) is widely recognized and as a result, extensive studies ranging from genetic linkage analyses to genome-wide association studies are actively ongoing to elucidate the etiology of both monogenic and polygenic forms of HTN. Due to the complex nature of essential HTN, however, single genes affecting blood pressure (BP) variability remain difficult to isolate and identify and have rendered the development of single-gene targeted therapies challenging. The roles of other causative factors in modulating BP, such as gene-environment interactions and epigenetic factors, are increasingly being brought to the forefront. In this review, we discuss the various monogenic HTN syndromes and corresponding pathophysiologic mechanisms, the different methodologies employed in genetic studies of essential HTN, the mechanisms for epigenetic modulation of essential HTN, pharmacogenomics and HTN, and finally, recent advances in genetic studies of essential HTN in the pediatric population.

Personal exposure to fine particulate matter and blood pressure: A role of angiotensin converting enzyme and its DNA methylation

BACKGROUND

The underlying intermediate mechanisms about the association between fine particulate matter (PM2.5) air pollution and blood pressure (BP) were unclear. Few epidemiological studies have explored the potential mediation effects of angiotensin-converting enzyme (ACE) and its DNA methylation.

METHODS

We designed a longitudinal panel study with 4 follow-ups among 36 healthy college students in Shanghai, China from December 17, 2014 to July 11, 2015. We measured personal real-time exposure to PM2.5, serum ACE level, and blood methylation of ACE gene and the repetitive elements. We applied linear mixed-effects models to examine the effects of PM2.5 on ACE protein, DNA methylation and BP markers. Furthermore, we conducted mediation analyses to evaluate the potential pathways.

RESULTS

An interquartile range increase (26.78μg/m(3)) in 24-h average exposure to PM2.5 was significantly associated with 1.12 decreases in ACE average methylation (%5mC), 13.27% increase in ACE protein, and increments of 1.13mmHg in systolic BP, 0.66mmHg in diastolic BP and 0.82mmHg in mean arterial pressure. ACE hypomethylation mediated 11.78% (P=0.03) of the elevated ACE protein by PM2.5. Increased ACE protein accounted for 3.90~13.44% (P=0.35~0.68) of the elevated BP by PM2.5. Repetitive-element methylation was also decreased but did not significantly mediate the association between PM2.5 and BP.

CONCLUSIONS

This investigation provided strong evidence that short-term exposure to PM2.5 was significantly associated with BP, ACE protein and ACE methylation. Our findings highlighted a possible involvement of ACE and ACE methylation in the effects of PM2.5 on elevating BP.

Epigenetic Modifications in Essential Hypertension

Essential hypertension (EH) is a complex, polygenic condition with no single causative agent. Despite advances in our understanding of the pathophysiology of EH, hypertension remains one of the world’s leading public health problems. Furthermore, there is increasing evidence that epigenetic modifications are as important as genetic predisposition in the development of EH. Indeed, a complex and interactive genetic and environmental system exists to determine an individual’s risk of EH. Epigenetics refers to all heritable changes to the regulation of gene expression as well as chromatin remodelling, without involvement of nucleotide sequence changes. Epigenetic modification is recognized as an essential process in biology, but is now being investigated for its role in the development of specific pathologic conditions, including EH. Epigenetic research will provide insights into the pathogenesis of blood pressure regulation that cannot be explained by classic Mendelian inheritance. This review concentrates on epigenetic modifications to DNA structure, including the influence of non-coding RNAs on hypertension development.

Matrix Metalloproteinase 2 as a Potential Mediator of Vascular Smooth Muscle Cell Migration and Chronic Vascular Remodeling in Hypertension

For vascular remodeling in hypertension, it is essential that vascular smooth muscle cells (VSMCs) reshape in order to proliferate and migrate. The extracellular matrix (ECM) needs to be degraded to favor VSMC migration. Many proteases, including matrix metalloproteinases (MMPs), contribute to ECM proteolysis and VSMC migration. Bioactive peptides, hemodynamic forces and reactive oxygen-nitrogen species regulate MMP-2 expression and activity. Increased MMP-2 activity contributes to hypertension-induced maladaptive arterial changes and sustained hypertension. New ECM is synthesized to supply VSMCs with bioactive mediators, which stimulate hypertrophy. MMP-2 stimulates the interaction of VSMCs with newly formed ECM, which triggers intracellular signaling via integrins to induce a phenotypic switch and persistent migration. VSMCs switch from a contractile to a synthetic phenotype in order to migrate and contribute to vascular remodeling in hypertension. MMPs also disrupt growth factors bound to ECM, thus contributing to their capacity to regulate VSMC migration. This review sheds light on the proteolytic effects of MMP-2 on ECM and non-ECM substrates in the vasculature and how these effects contribute to VSMC migration in hypertension. The inhibition of MMP activity as a therapeutic target may make it possible to reduce arterial maladaptation caused by hypertension and prevent the resulting fatal cardiovascular events.

Prenatal dexamethasone-induced programmed hypertension and renal programming

AIMS

Antenatal glucocorticoids can induce long-term effects on offspring health, including hypertension. Programmed hypertension has been observed in a prenatal dexamethasone (DEX) exposure model. However, how renal programming responds to prenatal DEX at different stages of development and the impact of DEX on programmed hypertension remain unclear. Therefore, we utilized RNA next-generation sequencing (NGS) to analyze the renal transcriptome in the offspring to examine whether key genes and pathways are responsible for DEX-induced renal programming and hypertension.

MAIN METHODS

Pregnant rats received intraperitoneal dexamethasone from gestational day 16 to 22. Prenatal DEX-induced programmed hypertension was examined in male offspring at 16 weeks of age.

KEY FINDINGS

Prenatal DEX modified 431 renal transcripts from the nephrogenesis stage to adulthood in a constant manner. At the pre-hypertensive and established hypertension stages, we identified 11 and 13 differentially expressed genes related to blood pressure regulation, respectively. Among these genes, Npr3, Ptgs2, Agt, Edn3, Ephx2, Agtr1b, and Gucy1a3 are associated with endothelium-derived hyperpolarizing and contractile factors (EDHF and EDCF). Genes in the arachidonic acid metabolism pathway may potentially be key genes contributing to programmed hypertension. In addition, DEX induced soluble epoxide hydrolase expression (Ephx2 gene encoding protein).

SIGNIFICANCE

Prenatal DEX elicits an imbalance between EDHFs and EDCFs that might lead to renal programming and hypertension. The arachidonic acid metabolism pathway is a common pathway contributing to programmed hypertension. Our results highlight candidate genes and pathways involved in renal programming as targets for therapeutic approaches to prevent programmed hypertension in children exposed to antenatal corticosteroids.