Emerging roles for histone deacetylases in pulmonary hypertension and right ventricular remodeling (2013 Grover Conference series)

Dysregulation of the Long Noncoding RNA X-Inactive-Specific Transcript Expression in Male Patients with Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a sex-biased disease with female sex as a significant risk factor. Increased expression of the long noncoding RNA X-inactive-specific transcript (Xist), as induced by an intersectin-1s protein fragment with proliferative potential (EHITSN), may explain the sexual dimorphism of female pulmonary artery endothelial cells (ECs) and at least in part, the imbalance sex/ratio of PAH. Xist is essential for X-chromosome inactivation and dosage compensation of X-linked genes. Herein, increased Xist expression was detected in a subset of ECs and lung tissue samples of male patients with PAH. The role of different Xist expression levels in ECs of male patients with PAH (ECPAH) was studied in several lines of male ECPAH in conjunction with molecular, biochemical, morphologic, and functional approaches. Male ECPAH showed on average 10.3-fold increase in high Xist versus low Xist, a significant association between Xist levels and their proliferative potential, and a heterogeneous methylation of the Xist/XIST antisense RNA (Tsix) locus. Interestingly, Xist up-regulation in male ECPAH decreased the expression of Krueppel-like factor 2 (Klf2), via EHITSN interaction with enhancer of zeste polycomb repressive complex 2 subunit (EZH2), the catalytic subunit of the polycomb repressive complex 2. Moreover, the studies demonstrate that EHITSN-triggered p38/ETS domain-containing protein Elk1/AP-1 transcription factor subunit (c-Fos) signaling is a pathologic mechanism central to ECPAH proliferation and the dynamic crosstalk with cell cycle regulatory proteins cyclin A1/cyclin D2 and Xist-EZH2-Klf2 interaction participate directly and differentially in establishing the proliferative profile of male ECPAH.

Role of histone deacetylase inhibitors in non-neoplastic diseases

Background

Epigenetic dysregulation has been implicated in the development and progression of a variety of human diseases, but epigenetic changes are reversible, and epigenetic enzymes and regulatory proteins can be targeted using small molecules. Histone deacetylase inhibitors (HDACis), as a class of epigenetic drugs, are widely used to treat various cancers and other diseases involving abnormal gene expression.

Results

Specially, HDACis have emerged as a promising strategy to enhance the therapeutic effect of non-neoplastic conditions, including neurological disorders, cardiovascular diseases, renal diseases, autoimmune diseases, inflammatory diseases, infectious diseases and rare diseases, along with their related mechanisms. However, their clinical efficacy has been limited by drug resistance and toxicity.

Conclusions

To date, most clinical trials of HDAC inhibitors have been related to the treatment of cancer rather than the treatment of non-cancer diseases, for which experimental studies are gradually underway. Discussions regarding non-neoplastic diseases often concentrate on specific disease types. Therefore, this review highlights the development of HDACis and their potential therapeutic applications in non-neoplastic diseases, either as monotherapy or in combination with other drugs or therapies.

Association between plasma proteome and pulmonary heart disease: A two-stage Mendelian randomization analysis

Pulmonary heart disease (PHD) involves altered structure and function of the right ventricle caused by an abnormal respiratory system that causes pulmonary hypertension. However, the association between changes in plasma proteomics and PHD remains unclear. Hence, we aimed to identify causal associations between genetically predicted plasma protein levels and PHD. Mendelian randomization was performed to test the target proteins associated with PHD. Summary statistics for the human plasma proteome and pulmonary heart disease were acquired from the UK Biobank (6038 cases and 426 977 controls) and the FinnGen study (6753 cases and 302 401 controls). Publicly available pQTLs datasets for human plasma proteins were obtained from a largescale genome-wide association study in the INTERVAL study. The results were validated using a case-control cohort. We first enrolled 3622 plasma proteins with conditionally independent genetic variants; three proteins (histo-blood group ABO system transferase, activating signal cointegration 1 complex subunit 1, and calcium/calmodulin-dependent protein kinase I [CAMK1]) were significantly associated with the risk of pulmonary heart disease in the UK Biobank cohort. Only CAMK1 was successfully replicated (odds ratio: 1.1056, 95% confidence interval: 1.019-1.095, p = 0.0029) in the FinnGen population. In addition, the level of CAMK1 in 40 patients with PHD was significantly higher (p = 0.023) than that in the control group. This work proposes that CAMK1 is associated with PHD, underscoring the importance of the calcium signaling pathway in the pathophysiology to improve therapies for PHD.

Advances in epigenetic modifications of autophagic process in pulmonary hypertension

Pulmonary hypertension is characterized by pulmonary arterial remodeling that results in increased pulmonary vascular resistance, right ventricular failure, and premature death. It is a threat to public health globally. Autophagy, as a highly conserved self-digestion process, plays crucial roles with autophagy-related (ATG) proteins in various diseases. The components of autophagy in the cytoplasm have been studied for decades and multiple studies have provided evidence of the importance of autophagic dysfunction in pulmonary hypertension. The status of autophagy plays a dynamic suppressive or promotive role in different contexts and stages of pulmonary hypertension development. Although the components of autophagy have been well studied, the molecular basis for the epigenetic regulation of autophagy is less understood and has drawn increasing attention in recent years. Epigenetic mechanisms include histone modifications, chromatin modifications, DNA methylation, RNA alternative splicing, and non-coding RNAs, which control gene activity and the development of an organism. In this review, we summarize the current research progress on epigenetic modifications in the autophagic process, which have the potential to be crucial and powerful therapeutic targets against the autophagic process in pulmonary hypertension development.

Tensions in Taxonomies: Current Understanding and Future Directions in the Pathobiologic Basis and Treatment of Group 1 and Group 3 Pulmonary Hypertension

In the over 100 years since the recognition of pulmonary hypertension (PH), immense progress and significant achievements have been made with regard to understanding the pathophysiology of the disease and its treatment. These advances have been mostly in idiopathic pulmonary arterial hypertension (IPAH), which was classified as Group 1 Pulmonary Hypertension (PH) at the Second World Symposia on PH in 1998. However, the pathobiology of PH due to chronic lung disease, classified as Group 3 PH, remains poorly understood and its treatments thus remain limited. We review the history of the classification of the five groups of PH and aim to provide a state-of-the-art review of the understanding of the pathogenesis of Group 1 PH and Group 3 PH including insights gained from novel high-throughput omics technologies that have revealed heterogeneities within these categories as well as similarities between them. Leveraging the substantial gains made in understanding the genomics, epigenomics, proteomics, and metabolomics of PAH to understand the full spectrum of the complex, heterogeneous disease of PH is needed. Multimodal omics data as well as supervised and unbiased machine learning approaches after careful consideration of the powerful advantages as well as of the limitations and pitfalls of these technologies could lead to earlier diagnosis, more precise risk stratification, better predictions of disease response, new sub-phenotype groupings within types of PH, and identification of shared pathways between PAH and other types of PH that could lead to new treatment targets. © 2023 American Physiological Society. Compr Physiol 13:4295-4319, 2023.

Future Perspectives of Pulmonary Hypertension Treatment

Since the discovery of three major pathophysiological mechanisms of pulmonary arterial hypertension (PAH), including prostacyclin, endothelin and nitric oxide pathways, the therapeutic options for PAH have increased. Nevertheless, despite these advances, the prognosis remains unsatisfactory for many patients with PAH. With the progress of both pre-clinical and clinical research on PAH, several novel therapeutic targets have been identified for the treatment of PAH. In this study, we review updated information of novel pathophysiological pathways of pulmonary hypertension, mainly focusing on WHO Group I PAH. Drugs based on these pathways are currently under clinical or pre-clinical investigation, however they have been approved for clinical use. Large clinical trials are required to validate the clinical safety and effects of these novel therapies.

The Impact of Sex Chromosomes in the Sexual Dimorphism of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a sex-biased disease with a poorly understood female prevalence. Emerging research suggests that nonhormonal factors, such as the XX or XY sex chromosome complement and sex bias in gene expression, may also lead to sex-based differences in PAH incidence, penetrance, and progression. Typically, one of females' two X chromosomes is epigenetically silenced to offer a gender-balanced gene expression. Recent data demonstrate that the long noncoding RNA X-inactive specific transcript, essential for X chromosome inactivation and dosage compensation of X-linked gene expression, shows elevated levels in female PAH lung specimens compared with controls. This molecular event leads to incomplete inactivation of the females' second X chromosome, abnormal expression of X-linked gene(s) involved in PAH pathophysiology, and a pulmonary artery endothelial cell (PAEC) proliferative phenotype. Moreover, the pathogenic proliferative p38 mitogen-activated protein kinase/ETS transcription factor ELK1 (Elk1)/cFos signaling is mechanistically linked to the sexually dimorphic proliferative response of PAECs in PAH. Apprehending the complicated relationship between long noncoding RNA X-inactive specific transcript and X-linked genes and how this relationship integrates into a sexually dimorphic proliferation of PAECs and PAH sex paradox remain challenging. We highlight herein new findings related to how the sex chromosome complement and sex-differentiated epigenetic mechanisms to control gene expression are decisive players in the sexual dimorphism of PAH. Pharmacologic interventions in the light of the newly elucidated mechanisms are discussed.

Identification of potential histone deacetylase inhibitory biflavonoids from Garcinia kola (Guttiferae) using in silico protein-ligand interaction

Overactivity of histone deacetylases (HDACs) is the underlying cause of some cancers, thus, inhibiting their overactivities is a rational treatment option. However, endeavors to employ current anti-HDACs agents in cancer treatment have yielded limited success. Consequently, there is need to explore anti-HDACs natural products, especially from plants sources, because of the intimate relationship plant products and drug discovery have enjoyed over the centuries. To identify possible HDACs inhibitors, Garcinia kola (Guttiferae) seed-derived compounds were screened in silico for HDAC-inhibitory tendencies because of their reported anticancer potentials. Fifteen G. kola-derived compounds and givinostat were docked with five selected HDACs using AutodockVina, while the binding interactions of the compounds with high binding affinities for the five HDACs were viewed with Discovery Studio Visualizer BIOVIA, 2016. Results indicated that four of the compounds studied, including amentoflavone, Garcinia biflavonoid 1, Garcinia biflavonoid 2 and kolaflavanone have higher binding propensity for all the five HDACs relative to givinostat, the standard HDAC inhibitor. This study indicated that inhibition of HDAC might be another key mechanism accountable for the bioactivities of G. kola and its intrinsic compounds. The results from this study implied that the compounds could be further investigated as drugable HDAC inhibitors with potential pharmacological applications in the treatment of cancers.

Mechanisms Contributing to the Dysregulation of miRNA-124 in Pulmonary Hypertension

Chronic pulmonary hypertension (PH) is a fatal disease characterized by the persistent activation of pulmonary vascular cells that exhibit aberrant expression of genes including miRNAs. We and others reported that decreased levels of mature microRNA-124 (miR-124) plays an important role in modulating the activated phenotype of pulmonary vascular cells and HDAC inhibitors (HDACi) can restore the levels of mature miR-124 and reverse the persistently activated phenotype of PH vascular cells. In this study, we sought to determine the mechanisms contributing to reduced levels of miRNAs, as well as how HDACi restores the levels of reduced miRNA in PH vascular cells. We found that pulmonary artery fibroblasts isolated from IPAH patients (PH-Fibs) exhibit reduced levels of mature miR-124 and several other miRNAs including let-7i, miR-224, and miR-210, and that these reduced levels can be restored by HDACi. Using miR-124 expression in human PH-Fibs as a model, we determined that reduced miR-124 gene transcription, not decreased expression of miRNA processing genes, is responsible for reduced levels of mature miR-124 in human PH-Fibs. Using both DNase I Sensitivity and chromatin immunoprecipitation assays, we found that the miR-124-1 gene exhibits a more condensed chromatin structure in human PH-Fibs, compared to corresponding controls. HDACi relaxed miR-124-1 chromatin structure, evidenced by increased levels of the open chromatin mark H3K27Ac, but decreased levels of closed chromatin mark H3K27Me³. Most importantly, the delivery of histone acetyltransferase (HAT) via CRISPR-dCas9-HAT and guiding RNAs to the promoter of the miR-124-1 gene increased miR-124-1 gene transcription. Thus, our data indicate epigenetic events play important role in controlling miR-124 and likely other miRNA levels and epigenetic regulators such as HDACs appear to be promising therapeutic targets for chronic PH.

Endothelial Dysfunction in Pulmonary Hypertension: Cause or Consequence?

Pulmonary arterial hypertension (PAH) is a rare, complex, and progressive disease that is characterized by the abnormal remodeling of the pulmonary arteries that leads to right ventricular failure and death. Although our understanding of the causes for abnormal vascular remodeling in PAH is limited, accumulating evidence indicates that endothelial cell (EC) dysfunction is one of the first triggers initiating this process. EC dysfunction leads to the activation of several cellular signalling pathways in the endothelium, resulting in the uncontrolled proliferation of ECs, pulmonary artery smooth muscle cells, and fibroblasts, and eventually leads to vascular remodelling and the occlusion of the pulmonary blood vessels. Other factors that are related to EC dysfunction in PAH are an increase in endothelial to mesenchymal transition, inflammation, apoptosis, and thrombus formation. In this review, we outline the latest advances on the role of EC dysfunction in PAH and other forms of pulmonary hypertension. We also elaborate on the molecular signals that orchestrate EC dysfunction in PAH. Understanding the role and mechanisms of EC dysfunction will unravel the therapeutic potential of targeting this process in PAH.

Fluid-electrolyte homeostasis requires histone deacetylase function

Histone deacetylase (HDAC) enzymes regulate transcription through epigenetic modification of chromatin structure, but their specific functions in the kidney remain elusive. We discovered that the human kidney expresses class I HDACs. Kidney medulla-specific inhibition of class I HDACs in the rat during high-salt feeding results in hypertension, polyuria, hypokalemia, and nitric oxide deficiency. Three new inducible murine models were used to determine that HDAC1 and HDAC2 in the kidney epithelium are necessary for maintaining epithelial integrity and maintaining fluid-electrolyte balance during increased dietary sodium intake. Moreover, single-nucleus RNA-sequencing determined that epithelial HDAC1 and HDAC2 are necessary for expression of many sodium or water transporters and channels. In performing a systematic review and meta-analysis of serious adverse events associated with clinical HDAC inhibitor use, we found that HDAC inhibitors increased the odds ratio of experiencing fluid-electrolyte disorders, such as hypokalemia. This study provides insight on the mechanisms of potential serious adverse events with HDAC inhibitors, which may be fatal to critically ill patients. In conclusion, kidney tubular HDACs provide a link between the environment, such as consumption of high-salt diets, and regulation of homeostatic mechanisms to remain in fluid-electrolyte balance.

Isoform-specific characterization of class I histone deacetylases and their therapeutic modulation in pulmonary hypertension

Pharmacological modulation of class I histone deacetylases (HDAC) has been evaluated as a therapeutic strategy for pulmonary hypertension (PH) in experimental models of PH. However, information of their expression, regulation and transcriptional targets in human PH and the therapeutic potential of isoform-selective enzyme modulation are lacking. Comprehensive analysis of expression and regulation of class I HDACs (HDAC1, HDAC2, HDAC3 and HDAC8) was performed in cardiopulmonary tissues and adventitial fibroblasts isolated from pulmonary arteries (PAAF) of idiopathic pulmonary arterial hypertension (IPAH) patients and healthy donors. Cellular functions and transcriptional targets of HDAC enzymes were investigated. Therapeutic effects of pan-HDAC (Vorinostat), class-selective (VPA) and isoform-selective (CAY10398, Romidepsin, PCI34051) HDAC inhibitors were evaluated ex vivo (IPAH-PAAF, IPAH-PASMC) and in vivo (rat chronic hypoxia-induced PH and zebrafish angiogenesis). Our screening identifies dysregulation of class I HDAC isoforms in IPAH. Particularly, HDAC1 and HDAC8 were consistently increased in IPAH-PAs and IPAH-PAAFs, whereas HDAC2 and HDAC8 showed predominant localization with ACTA2-expressing cells in extensively remodeled IPAH-PAs. Hypoxia not only significantly modulated protein levels of deacetylase (HDAC8), but also significantly caused dynamic changes in the global histone lysine acetylation levels (H3K4ac, H3K9/K14ac and H3K27ac). Importantly, isoform-specific RNA-interference revealed that HDAC isoforms regulate distinct subset of transcriptome in IPAH-PAAFs. Reduced transcript levels of KLF2 in IPAH-PAAFs was augmented by HDAC8 siRNA and HDAC inhibitors, which also attenuated IPAH-associated hyperproliferation and apoptosis-resistance ex vivo, and mitigated chronic hypoxia-induced established PH in vivo, at variable degree. Class I HDAC isoforms are significantly dysregulated in human PAH. Isoform-selective HDAC inhibition is a viable approach to circumvent off-target effects.

Pharmacology of Pulmonary Arterial Hypertension: An Overview of Current and Emerging Therapies

Pulmonary arterial hypertension is a rare and devastating disease characterized by an abnormal chronic increase in pulmonary arterial pressure above 20 mmHg at rest, with a poor prognosis if not treated. Currently, there is not a single fully effective therapy, even though a dozen of drugs have been developed in the last decades. Pulmonary arterial hypertension is a multifactorial disease, meaning that several molecular mechanisms are implicated in its pathology. The main molecular pathways regulating the pulmonary vasomotor tone-endothelin, nitric oxide, and prostacyclin-are the most biologically and therapeutically explored to date. However, drugs targeting these pathways have already found their limitations. In the last years, translational research and clinical trials have made a strong effort in suggesting and testing novel therapeutic strategies for this disease. These approaches involve targeting the main molecular pathways with novel drugs, drug repurposing for novel targets, and also using combinatorial therapies. In this review, we summarize current strategies and drugs targeting the endothelin, nitric oxide, and prostacyclin pathways, as well as, the emerging new drugs proposed to cope with vascular remodelling, metabolic switch, perivascular inflammation, epigenetic modifications, estrogen deregulation, serotonin, and other neurohumoral mechanisms characteristic of this disease. Nowadays, pulmonary arterial hypertension remains an incurable disease; however, the incoming new knowledge makes us believe that new promising therapies are coming to the clinical arena soon.

The DNA Damage Response and HIV-Associated Pulmonary Arterial Hypertension

The HIV-infected population is at a dramatically increased risk of developing pulmonary arterial hypertension (PAH), a devastating and fatal cardiopulmonary disease that is rare amongst the general population. It is increasingly apparent that PAH is a disease with complex and heterogeneous cellular and molecular pathologies, and options for therapeutic intervention are limited, resulting in poor clinical outcomes for affected patients. A number of soluble HIV factors have been implicated in driving the cellular pathologies associated with PAH through perturbations of various signaling and regulatory networks of uninfected bystander cells in the pulmonary vasculature. While these mechanisms are likely numerous and multifaceted, the overlapping features of PAH cellular pathologies and the effects of viral factors on related cell types provide clues as to the potential mechanisms driving HIV-PAH etiology and progression. In this review, we discuss the link between the DNA damage response (DDR) signaling network, chronic HIV infection, and potential contributions to the development of pulmonary arterial hypertension in chronically HIV-infected individuals.

Targeting histone acetylation in pulmonary hypertension and right ventricular hypertrophy

Epigenetic mechanisms, including DNA methylation and histone post-translational modifications (PTMs), have been known to regulate chromatin structure and lineage-specific gene expression during cardiovascular development and disease. However, alterations in the landscape of histone PTMs and their contribution to the pathogenesis of incurable cardiovascular diseases such as pulmonary hypertension (PH) and associated right heart failure (RHF) remain largely unexplored. This review focusses on the studies in PH and RHF that investigated the gene families that write (histone acetyltransferases), read (bromodomain-containing proteins) or erase (histone deacetylases [HDACs] and sirtuins [SIRT]) acetyl moieties from the ε-amino group of lysine residues of histones and non-histone proteins. Analysis of cells and tissues isolated from the in vivo preclinical models of PH and human pulmonary arterial hypertension not only confirmed significant alterations in the expression levels of multiple HDACs, SIRT1, SIRT3 and BRD4 proteins but also demonstrated their strong association to proliferative, inflammatory and fibrotic phenotypes linked to the pathological vascular remodelling process. Due to the reversible nature of post-translational protein acetylation, the therapeutic efficacy of numerous small-molecule inhibitors (vorinostat, valproic acid, sodium butyrate, mocetinostat, entinostat, tubastatin A, apabetalone, JQ1 and resveratrol) have been evaluated in different preclinical models of cardiovascular disease, which revealed the promising therapeutic benefits of targeting histone acetylation pathways in the attenuation of cardiac hypertrophy, fibrosis, left heart dysfunction, PH and RHF. This review also emphasizes the need for deeper molecular insights into the contribution of epigenetic changes to PH pathogenesis and therapeutic evaluation of isoform-specific modulation in ex vivo and in vivo models of PH and RHF. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.1/issuetoc.

HDAC inhibition improves cardiopulmonary function in a feline model of diastolic dysfunction

Heart failure with preserved ejection fraction (HFpEF) is a major health problem without effective therapies. This study assessed the effects of histone deacetylase (HDAC) inhibition on cardiopulmonary structure, function, and metabolism in a large mammalian model of pressure overload recapitulating features of diastolic dysfunction common to human HFpEF. Male domestic short-hair felines (n = 31, aged 2 months) underwent a sham procedure (n = 10) or loose aortic banding (n = 21), resulting in slow-progressive pressure overload. Two months after banding, animals were treated daily with suberoylanilide hydroxamic acid (b + SAHA, 10 mg/kg, n = 8), a Food and Drug Administration-approved pan-HDAC inhibitor, or vehicle (b + veh, n = 8) for 2 months. Echocardiography at 4 months after banding revealed that b + SAHA animals had significantly reduced left ventricular hypertrophy (LVH) (P < 0.0001) and left atrium size (P < 0.0001) versus b + veh animals. Left ventricular (LV) end-diastolic pressure and mean pulmonary arterial pressure were significantly reduced in b + SAHA (P < 0.01) versus b + veh. SAHA increased myofibril relaxation ex vivo, which correlated with in vivo improvements of LV relaxation. Furthermore, SAHA treatment preserved lung structure, compliance, blood oxygenation, and reduced perivascular fluid cuffs around extra-alveolar vessels, suggesting attenuated alveolar capillary stress failure. Acetylation proteomics revealed that SAHA altered lysine acetylation of mitochondrial metabolic enzymes. These results suggest that acetylation defects in hypertrophic stress can be reversed by HDAC inhibitors, with implications for improving cardiac structure and function in patients.

MEF2 and the Right Ventricle: From Development to Disease

Pulmonary arterial hypertension is a progressive and ultimately life-limiting disease in which survival is closely linked to right ventricular function. The right ventricle remains relatively understudied, as it is known to have key developmental and structural differences from the left ventricle. Here, we will highlight what is known about the right ventricle in normal physiology and in the disease state of pulmonary arterial hypertension. Specifically, we will explore the role of the family of MEF2 (myocyte enhancer factor 2) transcription factors in right ventricular development, its response to increased afterload, and in the endothelial dysfunction that characterizes pulmonary arterial hypertension. Finally, we will turn to review potentially novel therapeutic strategies targeting these pathways.

Correlation of cardiomyocyte apoptosis with duration of hypertension, severity of hypertension and caspase-3 expression in hypertensive rats

Correlation of cardiomyocyte apoptosis with duration of hypertension, severity of hypertension and caspase-3 expression in hypertensive rats was analyzed. Sixty male Sprague-Dawley (SD) rats were selected and randomly divided into the observation group (n=30) and control group (n=30), and the rat models of hypertension were established by virtue of transverse aortic constriction (TAC). The rats in the two groups were further divided into the 7-day subgroup (n=10), 14-day subgroup (n=10) and 28-day subgroup (n=10), respectively according to their survival time after TAC. The blood pressure values of the rats in each group were measured through intubation of carotid artery to calculate the mean arterial pressure (MAP). The conditions of cardiomyocyte apoptosis were detected using terminal dexynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. Enzyme-linked immunosorbent assay (ELISA) was applied to measure the expression of caspase-3 in the myocardial tissues, and correlation analysis was performed. The MAPs in 7-, 14- and 28-day subgroups of the observation group were significantly higher than those in the corresponding subgroups of the control group (P<0.05). The 7-, 14- and 28-day subgroups of the observation group had remarkably elevated myocardial caspase-3 expression levels compared with the subgroups of the control group (P<0.05). The apoptosis rates of myocardial cells in the three subgroups of the observation group were obviously higher than those in the corresponding subgroups of the control group (P<0.05). Pearson's correlation analysis indicated that the cardiomyocyte apoptosis rate of hypertensive rats was positively correlated with the duration of hypertension, severity of hypertension and caspase-3 expression (P<0.05). Hypertension can induce apoptosis of myocardial cells, and the apoptosis becomes more serious with the constantly elevated level and prolonged duration of hypertension. In addition, the activity of caspase-3 has a close correlation with cardiomyocyte apoptosis.

Insights on the epigenetic mechanisms underlying pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH), characterized by localized increased arterial blood pressure in the lungs, is a slow developing long-term disease that can be fatal. PAH is characterized by inflammation, vascular tone imbalance, pathological pulmonary vascular remodeling, and right-sided heart failure. Current treatments for PAH are palliative and development of new therapies is necessary. Recent and relevant studies have demonstrated that epigenetic processes may exert key influences on the pathogenesis of PAH and may be promising therapeutic targets in the prevention and/or cure of this condition. The aim of the present mini-review is to summarize the occurrence of epigenetic-based mechanisms in the context of PAH physiopathology, focusing on the roles of DNA methylation, histone post-translational modifications and non-coding RNAs. We also discuss the potential of epigenetic-based therapies for PAH.

Epigenetic Regulation and Its Therapeutic Potential in Pulmonary Hypertension

Recent advances in epigenetics have made a tremendous impact on our knowledge of biological phenomena and the environmental stressors on complex diseases. Understanding the mechanism of epigenetic reprogramming during the occurrence of pulmonary hypertension (PH) is important for advanced studies and clinical therapy. In this article, we review the discovery of novel epigenetic mechanisms associated with PH including DNA methylation, histone modification, and noncoding RNA interference. In addition, we highlight the role of epigenetic mechanisms in adult PAH resulting from undesirable perinatal environments-Extrauterine growth restriction (EUGR) and Intrauterine growth retardation (IUGR). Lastly, we give a comprehensive summary for the remaining challenges and discuss future methods of epigenetic targeted therapy for pulmonary hypertension.

Pulmonary arterial hypertension: pathogenesis and clinical management

Pulmonary hypertension is defined as a resting mean pulmonary artery pressure of 25 mm Hg or above. This review deals with pulmonary arterial hypertension (PAH), a type of pulmonary hypertension that primarily affects the pulmonary vasculature. In PAH, the pulmonary vasculature is dynamically obstructed by vasoconstriction, structurally obstructed by adverse vascular remodeling, and pathologically non-compliant as a result of vascular fibrosis and stiffening. Many cell types are abnormal in PAH, including vascular cells (endothelial cells, smooth muscle cells, and fibroblasts) and inflammatory cells. Progress has been made in identifying the causes of PAH and approving new drug therapies. A cancer-like increase in cell proliferation and resistance to apoptosis reflects acquired abnormalities of mitochondrial metabolism and dynamics. Mutations in the type II bone morphogenetic protein receptor (BMPR2) gene dramatically increase the risk of developing heritable PAH. Epigenetic dysregulation of DNA methylation, histone acetylation, and microRNAs also contributes to disease pathogenesis. Aberrant bone morphogenetic protein signaling and epigenetic dysregulation in PAH promote cell proliferation in part through induction of a Warburg mitochondrial-metabolic state of uncoupled glycolysis. Complex changes in cytokines (interleukins and tumor necrosis factor), cellular immunity (T lymphocytes, natural killer cells, macrophages), and autoantibodies suggest that PAH is, in part, an autoimmune, inflammatory disease. Obstructive pulmonary vascular remodeling in PAH increases right ventricular afterload causing right ventricular hypertrophy. In some patients, maladaptive changes in the right ventricle, including ischemia and fibrosis, reduce right ventricular function and cause right ventricular failure. Patients with PAH have dyspnea, reduced exercise capacity, exertional syncope, and premature death from right ventricular failure. PAH targeted therapies (prostaglandins, phosphodiesterase-5 inhibitors, endothelin receptor antagonists, and soluble guanylate cyclase stimulators), used alone or in combination, improve functional capacity and hemodynamics and reduce hospital admissions. However, these vasodilators do not target key features of PAH pathogenesis and have not been shown to reduce mortality, which remains about 50% at five years. This review summarizes the epidemiology, pathogenesis, diagnosis, and treatment of PAH.

Hallmarks of Pulmonary Hypertension: Mesenchymal and Inflammatory Cell Metabolic Reprogramming

SIGNIFICANCE

The molecular events that promote the development of pulmonary hypertension (PH) are complex and incompletely understood. The complex interplay between the pulmonary vasculature and its immediate microenvironment involving cells of immune system (i.e., macrophages) promotes a persistent inflammatory state, pathological angiogenesis, and fibrosis that are driven by metabolic reprogramming of mesenchymal and immune cells. Recent Advancements: Consistent with previous findings in the field of cancer metabolism, increased glycolytic rates, incomplete glucose and glutamine oxidation to support anabolism and anaplerosis, altered lipid synthesis/oxidation ratios, increased one-carbon metabolism, and activation of the pentose phosphate pathway to support nucleoside synthesis are but some of the key metabolic signatures of vascular cells in PH. In addition, metabolic reprogramming of macrophages is observed in PH and is characterized by distinct features, such as the induction of specific activation or polarization states that enable their participation in the vascular remodeling process.

CRITICAL ISSUES

Accumulation of reducing equivalents, such as NAD(P)H in PH cells, also contributes to their altered phenotype both directly and indirectly by regulating the activity of the transcriptional co-repressor C-terminal-binding protein 1 to control the proliferative/inflammatory gene expression in resident and immune cells. Further, similar to the role of anomalous metabolism in mitochondria in cancer, in PH short-term hypoxia-dependent and long-term hypoxia-independent alterations of mitochondrial activity, in the absence of genetic mutation of key mitochondrial enzymes, have been observed and explored as potential therapeutic targets.

FUTURE DIRECTIONS

For the foreseeable future, short- and long-term metabolic reprogramming will become a candidate druggable target in the treatment of PH. Antioxid. Redox Signal. 28, 230-250.

Histone deacetylase adaptation in single ventricle heart disease and a young animal model of right ventricular hypertrophy

BackgroundHistone deacetylase (HDAC) inhibitors are promising therapeutics for various forms of cardiac diseases. The purpose of this study was to assess cardiac HDAC catalytic activity and expression in children with single ventricle (SV) heart disease of right ventricular morphology, as well as in a rodent model of right ventricular hypertrophy (RVH).MethodsHomogenates of right ventricle (RV) explants from non-failing controls and children born with a SV were assayed for HDAC catalytic activity and HDAC isoform expression. Postnatal 1-day-old rat pups were placed in hypoxic conditions, and echocardiographic analysis, gene expression, HDAC catalytic activity, and isoform expression studies of the RV were performed.ResultsClass I, IIa, and IIb HDAC catalytic activity and protein expression were elevated in the hearts of children born with a SV. Hypoxic neonatal rats demonstrated RVH, abnormal gene expression, elevated class I and class IIb HDAC catalytic activity, and protein expression in the RV compared with those in the control.ConclusionsThese data suggest that myocardial HDAC adaptations occur in the SV heart and could represent a novel therapeutic target. Although further characterization of the hypoxic neonatal rat is needed, this animal model may be suitable for preclinical investigations of pediatric RV disease and could serve as a useful model for future mechanistic studies.

Epigenetic mechanisms in pulmonary arterial hypertension: the need for global perspectives

Pulmonary arterial hypertension (PAH) is a severe and progressive disease, characterised by high pulmonary artery pressure that usually culminates in right heart failure. Recent findings of alterations in the DNA methylation state of superoxide dismutase 2 and granulysin gene loci; histone H1 levels; aberrant expression levels of histone deacetylases and bromodomain-containing protein 4; and dysregulated microRNA networks together suggest the involvement of epigenetics in PAH pathogenesis. Thus, PAH pathogenesis evidently involves the interplay of a predisposed genetic background, epigenetic state and injurious events. Profiling the genome-wide alterations in the epigenetic mechanisms, such as DNA methylation or histone modification pattern in PAH vascular cells, may explain the great variability in susceptibility and disease severity that is frequently associated with pronounced remodelling and worse clinical outcome. Moreover, the influence of genetic predisposition and the acquisition of epigenetic alterations in response to environmental cues in PAH progression and establishment has largely been unexplored on a genome-wide scale. In order to gain insights into the molecular mechanisms leading to the development of PAH and to design novel therapeutic strategies, high-throughput approaches have to be adopted to facilitate systematic identification of the disease-specific networks using next-generation sequencing technologies, the application of these technologies in PAH has been relatively trivial to date.

An epigenetic component is hypothesised in PAH: an overview of the current literature and future perspectiveshttp://ow.ly/7miS3002BYw

The emerging role of epigenetics in pulmonary arterial hypertension: an important avenue for clinical trials (2015 Grover Conference Series)

Epigenetics is an emerging field of research and clinical trials in cancer therapy that also has applications for pulmonary arterial hypertension (PAH), as there is evidence that epigenetic control of gene expression plays a significant role in PAH. The three types of epigenetic modification include DNA methylation, histone modification, and RNA interference. All three have been shown to be involved in the development of PAH. Currently, the enzymes that perform these modifications are the primary targets of neoplastic therapy. These targets are starting to be explored for therapies in PAH, mostly in animal models. In this review we summarize the basics of each type of epigenetic modification and the known sites and molecules involved in PAH, as well as current targets and prospects for clinical trials.

Suberoylanilide hydroxamic acid attenuates paraquat-induced pulmonary fibrosis by preventing Smad7 from deacetylation in rats

BACKGROUND

Recent evidence suggests that a histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), has anti-fibrotic effect. However, the exact mechanism of its anti-fibrotic potential remains is unclear. In this study, we investigated the molecular mechanism of SAHA in attenuating pulmonary fibrosis by regulating stability of Smad7 in paraquat (PQ)-induced lung fibrosis animal model and cultured pulmonary fibroblasts.

METHODS

Rats with paraquat-induced lung fibrosis were fed with a SAHA solution (15 mg/kg) by gastric gavage. Human pulmonary fibroblasts (HFL1) pre-treated with TGF-β1 (5 ng/mL) were treated with SAHA (5 µM).

RESULTS

SAHA (histone deacetylase inhibitor, HDACi) suppressed PQ-induced lung fibrosis in rats by stabilizing Smad7 level, thus attenuating Smad3 activity, resulting in the inhibition of fibroblast differentiation and collagen expression. In vitro study showed that SAHA suppressed TGF-β1-induced fibroblast differentiation into myofibroblasts. SAHA exerted its antifibrotic effect through preventing Smad7 from deacetylation most maybe by inhibiting TGF-β1-induced HDAC1 activity.

CONCLUSIONS

SAHA repressed PQ-induced lung fibrosis via preventing Smad7 from deacetylation.

The Expanding Complexity of Estrogen Receptor Signaling in the Cardiovascular System

Estrogen has important effects on cardiovascular function including regulation of vascular function, blood pressure, endothelial relaxation, and the development of hypertrophy and cardioprotection. However, the mechanisms by which estrogen mediates these effects are still poorly understood. As detailed in this review, estrogen can regulate transcription by binding to 2 nuclear receptors, ERα and ERβ, which differentially regulate gene transcription. ERα and ERβ regulation of gene transcription is further modulated by tissue-specific coactivators and corepressors. Estrogen can bind to ERα and ERβ localized at the plasma membrane as well as G-protein-coupled estrogen receptor to initiate membrane delimited signaling, which enhances kinase signaling pathways that can have acute and long-term effects. The kinase signaling pathways can also mediate transcriptional changes and can synergize with the ER to regulate cell function. This review will summarize the beneficial effects of estrogen in protecting the cardiovascular system through ER-dependent mechanisms with an emphasis on the role of the recently described ER membrane signaling mechanisms.