==== Front Int J Mol Sci Int J Mol Sci ijms International Journal of Molecular Sciences 1422-0067 MDPI 33255338 10.3390/ijms21238901 ijms-21-08901 Review Epigenetic Regulation of Pulmonary Arterial Hypertension-Induced Vascular and Right Ventricular Remodeling: New Opportunities? https://orcid.org/0000-0001-7202-4771Kocken Jordy M. M. 12 da Costa Martins Paula A. 123* 1 Department of Molecular Genetics, Faculty of Sciences and Engineering, Maastricht University, 6229 ER Maastricht, The Netherlands; j.kocken@maastrichtuniversity.nl 2 CARIM School for Cardiovascular Diseases, Faculty of Health, Medicine and Life Sciences, Maastricht University, 6229 ER Maastricht, The Netherlands 3 Unidade de Investigação Cardiovascular, Departamento de Cirurgia e Fisiologia, Faculdade de Medicina, Universidade do Porto, 4200-319 Porto, Portugal * Correspondence: p.dacostamartins@maastrichtuniversity.nl 24 11 2020 12 2020 21 23 890129 10 2020 20 11 2020 © 2020 by the authors.2020Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Pulmonary artery hypertension (PAH) is a rare chronic disease with high impact on patients’ quality of life and currently no available cure. PAH is characterized by constant remodeling of the pulmonary artery by increased proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs), fibroblasts (FBs) and endothelial cells (ECs). This remodeling eventually leads to increased pressure in the right ventricle (RV) and subsequent right ventricle hypertrophy (RVH) which, when left untreated, progresses into right ventricle failure (RVF). PAH can not only originate from heritable mutations, but also develop as a consequence of congenital heart disease, exposure to drugs or toxins, HIV, connective tissue disease or be idiopathic. While much attention was drawn into investigating and developing therapies related to the most well understood signaling pathways in PAH, in the last decade, a shift towards understanding the epigenetic mechanisms driving the disease occurred. In this review, we reflect on the different epigenetic regulatory factors that are associated with the pathology of RV remodeling, and on their relevance towards a better understanding of the disease and subsequently, the development of new and more efficient therapeutic strategies. right ventricle remodelinghypertrophypulmonary arterial hypertensionnon-coding RNAsepigenetics ==== Body 1. Pulmonary Hypertension 1.1. Clinical Presentation Pulmonary hypertension (PH) is a human pathophysiological condition defined by a mean pulmonary arterial pressure (mPAP) ≥25 mmHg at rest. PH can further be classified in five distinct groups, based on clinical presentation, overlapping hemodynamics and/or treatment strategies: pulmonary arterial hypertension (PAH), PH due to left heart disease, PH due to hypoxia or lung disease, PH due to chronic thromboembolism and PH due to unclear mechanisms [1]. This progressive disease is characterized by the remodeling of the pulmonary artery leading to vascular obstruction which, in turn, leads to increased blood pressure in order to preserve the blood flow [2,3]. PAH is further defined by a pulmonary capillary wedge pressure (PCWP) ≤15 mmHg and pulmonary vascular resistance (PVR) ≥3 Wood Units combined with mPAP ≥25 mmHg [1,4]. The disease can originate from idiopathic or heritable etiologies but can also be induced by certain drugs and/or toxins, or be associated with other diseases such as HIV, connective tissue, or congenital heart disease [1]. Currently, the prevalence of PAH in the western world is 2.7 per 100,000 individuals and is, therefore, considered as a rare disease, even though prevalence has been increasing in the last fifteen years [5,6]. Despite being rare, the disease highly impacts on the quality of life of the patients and subsequently on the healthcare system [7,8]. Patients with PAH display a plethora of symptoms varying from dyspnea, fatigue, swollen ankles and cyanosis [9], nevertheless diagnosis is challenging and involves multiple disciplines due to the many differences in etiologies. Patients with a history of hereditary PAH (hPAH) are tested for known genetic mutations in genes such as probable cation-transporting ATPase 13A3 (ATP13A3), bone morphogenetic protein receptor type II (BMPR2), Serine/threonine-protein kinase receptor R3 (ACVRL1), endoglin (ENG), mothers against decapentaplegic homolog 1, 4 and 9 (SMAD1 SMAD4 and SMAD9), caveolin (CAV1), T-box transcription factor 4 (TBX4), Eukaryotic translation initiation factor 2-alpha kinase 4 (EIF2AK4), Growth differentiation factor 2 (GDF2), aquaporin 1 (AQP1), SRY-box 17 (SOX17) and potassium two pore domain channel subfamily K member 3 (KCNK3), while simultaneously undergoing physical examination, exercise testing, biomarker analysis and right heart catherization [1,10,11,12]. During PAH, the pulmonary artery undergoes chronic remodeling induced by constant proliferation of pulmonary endothelial cells (EC) and increased resistance to apoptosis which leads to an occlusion of the artery and subsequent pulmonary hypertension as depicted in Figure 1 [13,14,15]. The BMPR2 protein is known to be downregulated not only in the pulmonary vasculature of hPAH patients that harbor a mutation in the same gene, but also in patients that are suffering from a different etiology of the disease [16]. Although BMPR2 mutations are not always prevalent in patients, the upstream targets may still be affected by certain cellular or molecular processes such as microRNA (miRNA) regulation [17] or viral HIV infection [18,19], all leading to lower BMPR2 protein levels and subsequent development of a pathophysiological response [20,21]. Whereas survival rates of patients are much dependent on the etiology of PAH and symptom severity, on average, a five-year survival rate between 40–60% is observed [22,23]. Roughly 33% of PAH patients succumb from right heart failure (RHF), a chronic end-stage cardiac disease originating from the inability of the right ventricle (RV) to compensate for the PAH [22,24]. 1.2. Vascular Remodeling Whereas PAH is characterized by progressive pulmonary vasculature remodeling, disease severity very much depends on its etiology, with patients harboring a genetic mutation being the most affected [25]. During the development of PAH, a plethora of pathways can be dysregulated. While here we focus on the three major signaling axis that are disrupted, namely the endothelial nitric oxide (NO), endothelin-1 (ET-1), and prostacyclin (PGI2) pathways [26,27,28], the contribution of other important pathways involving BMPR2/transforming growth factor beta (TGFβ) or RhoA/Rho-kinase (RhoA/ROCK) signaling have been extensively described in other reviews [29,30]. NO is produced in ECs by cleavage of the terminal amino group of the L-arginine amino acid by endothelial nitric oxide synthase (eNOS) and helps regulate the vasculature homeostasis [31]. Once generated, NO is transported outside the ECs where it will enter the bloodstream and influence neighboring smooth muscle cell function (SMCs) by regulating the formation of cyclic 3′,5′ guanosine monophosphate (cGMP) [32]. cGMP binds to either cGMP-dependent protein kinases, cGMP-binding phosphodiesterase or cGMP-regulated ion channels, leading to relaxation of the SMCs and lowering of blood pressure [33]. During PAH, NO has been suspected to be reduced in patients compared to healthy controls but while this holds true in some studies [26], other however, described increased eNOS levels in the pulmonary artery of hypertensive patients [34]. This discrepancy is also reflected in patients after treatment with NO inhalation, as younger patients of PAH benefit from NO administration while others do not respond to the treatment at all [35]. More recently developed therapies focus on the cGMP signaling pathway, either by inhibiting phosphodiesterase type 5 (PDE5), an enzyme that breaks down cGMP, or increasing the bioavailability of soluble guanylate cyclase (sGC), a source of cGMP [36]. However, and once again, not all patients benefit from the cGMP stimulators and while the reason why has not yet been elucidated, it may be attributed to different protocols and dosages used during the different clinical studies [37,38]. Another signaling pathway disrupted in PAH is the PGI2 signaling pathway. PGI2 originates mostly from ECs and has a vasodilating effect by activating specific cell surface receptors, mainly prostaglandin (IP) receptors, which are part of the G-coupled Protein Cell Receptors (GPCRs) family [39]. These receptors are coupled to activate adenylate cyclase which, in turn, converts adenosine triphosphate (ATP) into cyclic adenosine monophosphate (cAMP), a potent signaling molecule involved in multiple cellular processes including proliferation of pulmonary SMCs [40]. cAMP works through the activation of two downstream molecules, the exchange protein activated by cAMP (Epac) and Protein Kinase A (PKA) which work in synergy to inhibit extracellular signal-regulated kinases 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK) phosphorylation leading to inhibition of pulmonary SMC proliferation [41]. Epac was shown to be decreased in pulmonary artery smooth muscle cells (PASMCs) of PAH patients when compared to healthy controls and also in monocrotaline (MCT) rat models [42]. Targeted therapies for PGI2 have been available since 2009 and PAH patients administered with a continuous intravenous drip (24 h/day) of PGI2 have a higher improvement of clinical symptoms and survival rate, compared to patients receiving inhalation or oral administration of the drugs [43]. ET-1 is a 21 amino acid-long peptide, mainly released by the endothelium, with a potent vasoconstricting effect, opposed to NO and PGI2 which are vasodilating [44]. After being released by ECs, ET-1 is found to be circulating in the bloodstream in relatively low levels and while its levels can be measured to give insight in the general release of the peptide they do not account for the amount of peptide that is actually bound to cellular receptors [45]. ET-1 binds to two specific receptors, ETA and ETB, on vascular SMCs and myocytes, with ETB also being found on ECs [46]. Binding of ET-1 to its receptors in SMCs leads to activation of phospholipase C (PLC) and an increase in diacylglycerol and inositol triphosphate, followed by augmented intracellular calcium and subsequent incremented cellular contraction [47]. Increases of diacylglycerol and calcium in VSCMs also activates protein kinase C (PKC), suspected of activating a cascade of protein kinases and enhancing the cellular proliferative capacity [48]. Furthermore, activation of endothelial ETB results in NO release and increased vasorelaxation in the pulmonary artery, but the direct influence of ET-1 in the process is considered to be minimal [49]. Current pharmacological treatment options available are ETA and ETB receptor antagonists, such as bosentan, macitentan or ambrisentan, while sitaxsentan has been withdrawn due to increased hepatic toxicity in patients [50]. Bosentan and macitentan act on both ETA and ETB, despite a preference for blocking ETA, improving patient outcome parameters such as 6-min walking distance, dyspnea, and reducing clinical worsening [51,52,53]. Ambrisentan is a specific ETA antagonist and is able to improve patient clinical outcome and quality of life while showing fewer side effects compared to bosentan or macitentan [54]. Unfortunately, ET-1 also affects pulmonary fibroblasts by inducing proliferation and increasing matrix deposition and stiffening in the pulmonary artery, further increasing the arterial pressure [55]. During PAH, not only the pulmonary circulation is affected by the hypertension, but recent studies suggest that vasculature dysfunction of the systemic circulation also develops. A recent study demonstrated that patients suffering from PAH, and more specifically idiopathic PAH (iPAH) or PAH patients with systemic sclerosis, display an increased risk of developing coronary artery disease (CAD), leading to lower survival expectations [56]. 1.3. Right Ventricular Remodeling During PAH, the RV undergoes prolonged pressure overload. Initially, and as an adaptive response to maintain the pulmonary circulation, the RV endures hypertrophic remodeling, characterized by an increase in cardiomyocyte (CM) size, increased intrinsic contractility and capillary angiogenesis as a way to provide sufficient oxygen and nutrients to the enlarged myocardium [57]. If pressure overload remains, as in PAH, the adaptive response gradually shifts to maladaptive remodeling towards RV failure [58] as depicted in Figure 1. The molecular and cellular responses that drive RV hypertrophy are distinct of what has been described for left ventricular (LV) hypertrophy [59]. As an example, during PAH, whereas chronic hypoxia induces activation of Hypoxia-inducible factor 1-alpha (HIF-1α) and leads to increased angiogenesis in the RV, pressure overload of the LV induces capillary rarefaction with decreased capillary networks surrounding the CMs [57,60]. Furthermore, while the LV stiffens and displays contractile dysfunction, the RV undergoes hypercontractile remodeling in order to preserve the pulmonary flow [61,62]. Hypercontractility of the RV leads to a shift in mitochondrial metabolism, from free fatty acid (FFA) oxidation to anaerobic glycolysis, to overcome the decreased supply of oxygen and to keep up with the increased energy demand of the CMs [63]. However, as glycolysis is normally used by a cell to overcome peak energy demands, switching to continuous glycolysis leads to chronic energy starvation in the myocardium [64]. During glycolysis, glucose enters the CM through the glucose transporter 1 (GLUT1) and glucose transporter 4 (GLUT4) glucose channels, to be processed further into pyruvate. Further processing leads to the production of ATP, through the Krebs cycle, or to lactate formation [65]. Previous studies using MCT or pulmonary artery banding (PAB), two models of PH in rats, showed that upon RV hypertrophy, activation of pyruvate dehydrogenase kinases (PDK) followed by phosphorylate pyruvate dehydrogenase (PDH) inhibits the ability of CMs to catalyze pyruvate, therefore leading to a dependence on glycolysis for energy production [66]. Another adverse effect of the metabolic switch is the accumulation of reactive oxygen species (ROS) in CMs. HIF-1α activation leads to increased PDK activity, followed by mitochondrial complex II ROS generation [67,68,69]. Whereas previous studies revealed negative effects of ROS in the progression of HF [70,71], in animal models, reducing ROS during RV hypertrophy showed contradicting results [72,73]. While the response to ROS is similar between both ventricles during hypertrophy, the RV appears to be much more susceptible to changes in ROS homeostasis compared to the LV [74,75]. Increased intracellular ROS not only causes damage of proteins and DNA but also induces inflammation through the induction of pro-inflammatory chemokines, cytokines and transcription factors [76]. In PAH, the inflammatory response in the RV is marked by an increase in infiltrating CD45+/CD68+ cells [77] and pro-inflammatory cytokine signaling involving molecules such as tumor necrotic factor α (TNF-α) and interleuking-1 (IL-1) family members [78,79]. Whereas increased and sustained inflammation during RV hypertrophy appears to be beneficial at short term by leading to increased angiogenesis, it does affect CM functionality at long term, by decreasing contractility and increasing ROS production [80,81]. Despite many stimuli and regulatory mechanisms being identified and characterized, there is no cure yet available for PAH and RVH. Presently available therapies focus on symptomatic treatment and slowing down disease progression. The ultimate treatment option available is either lung transplantation, combined with RV support, or palliative support if long-term treatment options are no longer available or possible [82,83]. Looking at these outcomes, new areas in the biomedical field are being investigated in order to identify new potential therapeutic targets to reduce RV remodeling during PAH. 2. Epigenetic Regulation 2.1. Chromatin Modifications The concept of epigenetic regulation was introduced in 1942 by Conrad Waddington, and initially described the process of the influence of genotypes on the phenotype during development [84]. However, later in 1996, Russo and colleagues, defined epigenetics more in line with our current definition: heritable changes in the genome that affect the phenotype without changing the DNA sequence [85]. Epigenetic inheritance functions in several distinct ways, including DNA methylation and histone modifications, but also through non-coding RNAs (ncRNAs), among others. DNA methylation, which includes the process of new methylation, maintenance and removal of methyl groups, occurs at specific sites of the DNA, namely CpG or CG sites, where a cytosine is followed by a guanine base in the 5′ to 3′ direction. Conjugation with the methyl functional group is mainly catalyzed by two enzymes, DNA methyltransferases 3A and 3B (DNMT3A and DNMT3B, respectively), both consisting of two chromatin reading domains, PWWP and ATRX-DNMT3-DNMT3L (ADD), and the methyltransferase (MTase) domain [86]. Whilst cytosine enriched areas display higher methylation percentages, promoter areas of active genes are protected from methylation due to their enrichment in Histone 3 Lys4 trimethylation (H3K4me3) [87] as binding of the enzymatic ADD domain to the K4me3 tail prevents methylation of the promoter [88]. Binding of ADD to trimethylated H3K4 induces activation of the MTase domain, initiating the process of DNA methylation. While active promoters are free of methylated sites, the transcriptional region of active transcribed genes are enriched with methylated CpG sites [89]. During transcription by RNA polymerase II, another methyltransferase, SET domain containing 2 (SETD2), trimethylates H3K36, which is then able to bind PWWP and initiate methylation by DNMT3B [90]. In order to maintain methylation sites during DNA replication, two enzymes, DNA methyltransferase 1 (DNMT1) and ubiquitin-like, containing PHD and RING finger domains, 1 (UHRF1) need to work together [91]. UHRF1 binds to the methylated sites and then recruits DNMT1, which, unless bound to UHRF1 and similar to DNMT3, is autoinhibiting [92]. Demethylation occurs upon oxidation of the methylated cytosine to 5-carboxylcytosine (5caC), 5-hydroxymethylcytosine (5hmC) or 5-formylcytosine (5fC) by ten-eleven translocation (TET) methylcytosine dioxygenases [93]. These intermediate functional groups are then either removed by thymine DNA glycosylase (TDG) or passively diluted by DNA replication, leading to new unmethylated DNA strands [93,94,95]. While DNA methylation occurs at high rates, it has been observed that methylation is not present at transcription binding sites during binding [96] which, together with the ability of methylation to induce heterochromatin formation through DNMTs and lymphocyte-specific-helicase (LSH), gives rise to the function of DNA methylation as a transcriptional repressing process [97,98]. Histones are a group of proteins in the nuclei that organize and pack DNA. In 1964, the first experimental paper was released showing acetylation of histones and suggesting their role in RNA synthesis [99]. Acetylation of the lysine on the N-terminus leads to a removal of the lysine’s charge which, by weakening the bond between histones and DNA leads to easier accessibility of the DNA to proteins [100,101]. Eventually, additional studies showed lysine in histones to be targeted by two opposing enzymes: histone acetyltransferases (HATs) and histone deacetylase (HDACs) [102]. HATs can be divided into two main groups, type-A HATs and type-B HATs and within these two subgroups, the type-A HATs can be classified in three major families based on their conformation and amino-acid sequence: MOZ, Ybf2/Sas3, Sas2 and Tip60 (MYST), Gcn5-related N-acetyltransferases (GNAT) and p300/CREB-binding protein (p300/CBP) [103]. The type-A HATs are predominantly found in the nuclei but while the three families work through similar mechanisms starting with a deprotonation of the lysine’s amine followed by nucleophilic substitution facilitated by Acetyl CoA [104], they have different acetylation targets within the histones [105]. HDACs, in turn, deacetylate histones by a different mechanism that is not based on a cofactor but rather on zinc or NAD+ [106]. HDACs are either part of the histone deacetylation family or the Sirtuin protein family, and four classes can be distinguished based on the sequence similarity of the different enzymes [107]. Class I, II and IV are part of the same family and use zinc for their deacetylation mechanism, while class III HDACs’ use NAD+ [107]. During the reaction between acetylated histones and HDACs, zinc functions as a proton shuttle to stabilize the chemical binding and eventually the stable release acetate [108]. HDAC Class III enzymes act through a reduction/oxidation chemical reaction with the co-enzyme NAD+, and inducing transfer of acetyl groups from the lysine amino acid towards the ADP-ribose that is part the NAD+ co-enzyme [109]. The general consensus is that acetylation of histones, by allowing genes to be more accessible for transcription factor, increase gene expression [102]. Another histone modification is the phosphorylation of serines, threonines and tyrosines of in the N-terminus [110]. Momentarily, two functions were described for histone phosphorylation; those being DNA repair and transcription regulation [111]. Several histone phosphorylation sites, such as H3 serines 10 and 28 and H2B serine 32, have been linked to transcriptional regulation [112,113,114]. However, the role of phosphorylation on transcription regulation is not yet understood since some studies showed that phosphorylation of histones leads to recruitment of additional histone modification enzymes but others were not able to connect histone modification with the degree of phosphorylation [115,116,117]. Histones, just like DNA, can also be methylated in order to regulate their expression. During methylation, the lysines and arginines of the histones can be conjugated without affecting the charge of the amino acids that are being methylated [118]. Unlike acetylation and phosphorylation, that only have one possible conjugation site, methylation can occur at multiple sites on the amino acids [119], in a process that is mediated by histone methyltransferases (HMTs) [120]. Methylation of histones can either enhance or inhibit transcription, depending on the number of methylated lysine/arginine sites per amino acid. For example, a monomethylated lysine leads to increased gene expression while a tri-methylated lysin represses gene expression [121,122]. A schematic overview of the regulation of chromatin remodeling by DNA methylation and major histone modifications is provided in Figure 2. 2.2. Chromatin Modifications in PAH Chromatin modifications are able to regulate change gene expression and have gained much research interest initially due to their potential role in developmental biology [123,124,125]. Since gene expression is strongly associated to disease, is not a surprise that chromatin remodeling has also been studied in the context of PAH. HDAC class I activity was shown to increase during hypoxia-induced but in vivo HDAC inhibition resulted in decreased pulmonary remodeling during PAH [126]. Furthermore, in a rat model of PAH, inhibition of class I HDACs decreased proliferation and migration of PASMCs [127,128]. Other studies have involved HDACs in PAH-induced oxidative stress by showing reduced ROS and NAPDH oxidative (Nox) levels after HDAC inhibition [129]. Furthermore, histone methylation has recently also been implicated in PAH, more specifically in hypoxia-induced PAH, where megakaryocytic leukemia 1 (MKL1) is upregulated and leads to an increase in the recruitment of the H3K4-specific complex components, ASH2 and WDR5 [130,131]. Knocking out of the methylation complex in vivo resulted in improved vascular remodeling, compared to healthy controls [130]. DNA methylation has been described for the superoxide dismutase 2 (SOD2) gene, found to be downregulated in PASMCs of PAH patients [132]. A profiling study also revealed that vasculature-related genes are hypermethylated in PAH, showing that dysregulation of vascular maintenance is not only regulated through the three main signaling pathways discussed earlier, but also through epigenetic inheritance [133]. Since the leading cause of death during PAH is RV failure, therapies targeting PAH will also reduce pathological RV remodeling. There is, however, a distinct epigenetic roadmap for the different cardiac chambers [134] which accounts for contrasting results. There have also been studies observing that broad HDAC inhibitor trichostatin A (TSA) lead to worsening [135] while valproic acid (VPA) and MGCD0103 have positive effects on RV remodeling [126,128]. VPA is a known HDAC I inhibitor and in vivo shows reduced proliferation of adventitial fibroblasts while MGCD0103 inhibits proliferation of PASMCs. Both VPA and MGCD0103 function by inhibiting HDACs and their subsequent target FoxO3a. However, MGDC0103 is also able to reduce inflammation and apoptosis in the RV, leading to an increased functionality during disease [126]. While the mechanism of action behind HDAC inhibitors in PAH and RV remodeling has not yet been fully elucidated, unraveling it might help in achieving more specific therapies for the both PAH and RV failure (RVF). 2.3. Non-Coding RNAs Until relatively recently, the central dogma of molecular biology assumed genomic DNA to be transcribed into messenger RNA (mRNA), which in turn would be translated into functional proteins [136]. Current knowledge reveals that only 2% of our genome is actually translated into proteins while the majority is composed of non-coding genetic information [137], non-coding transcripts (ncRNAs) that, for long, were described as transcriptional noise. However, multiple ncRNAs have been found to exert a regulatory effect in cellular pathways and therefore, being able to modulate disease onset and progression [138,139,140]. ncRNAs are classified based on their size and function, into miRNAs, circular RNAs (circRNAs) and long non-coding RNAs (lncRNAs). 2.3.1. MicroRNAs miRNAs are short strands of RNA, between 20 and 24 nucleotides long, that regulate target mRNAs through sequence complementarity followed by either strand degradation or translational inhibition [141]. The first discovered miRNA, in C. elegans, in 1993, was described as an anti-sense RNA strand for the lin-14 gene regulating the LIN-14 protein expression [142]. Nowadays we know that miRNAs are highly conserved among species, hinting at key regulatory functions [143]. Biogenesis of miRNAs starts with RNA polymerase II/III transcribing genomic DNA into a primary miRNA double-strand loop (pri-miRNA) that is then cleaved by the ribonuclease III enzyme DROSHA and RNA binding protein DiGeorge syndrome critical region 8 (DGCR8) complex into a pre-miRNA stem-loop, known as hairpin [144]. The pre-miRNA hairpin is then transported from the nucleus into the cytoplasm by two proteins, EXPORTIN5 and RanGTP. In the cytoplasm, cleavage by DICER, an RNase III endonuclease, into a mature miRNA duplex gives rise to two single strands, the 5p and 3p strand originating from the 5′ and 3′ ends of the hairpin [145]. One strand, the least stable, is thought to be degraded while the other strand is stabilized by the Argonaut complex. However, a recent study suggests that the least stable miRNA strand is shuttled out of the cells via extracellular vesicles and may play a role in cell-to-cell communication during disease progression [146]. The miRNA strand is then loaded into the RNA-induced silencing complex (RISC) where it will bind the 3′ untranslated region (UTR) of the target mRNA leading to either mRNA degradation or translational repression, depending on the complementarity between the two RNA strands [147]. The RISC includes the proteins Argonaut 2, DICER, TRBP, GW182 and PACT. While TRBP assists DICER in processing pre-miRNA, TRBP and PACT assist Argonaut 2 with binding to and stabilizing double stranded RNAs. Finally, GW182 helps Argonaut 2 in guiding the miRNA to ensure gene silencing [148]. 2.3.2. Circular RNAs The first circRNA was discovered in 1976 by Sänger et al. when investigating viroids, uncoated circular RNA pathogens for plants [149]. However, it was not before 1990 that the first functional circRNA was described while investigating a tumor repressor gene [150]. Transcription of circRNAs is also initiated by RNA polymerase II to form a linear pre-mRNA strand. While multiple biogenesis routes are proposed, the most common method of circularization is when a 5′ splice donor and 3′ splice acceptor ends join. Both sites are usually flanked by large introns with repetitive sequences that that form a looping structure. Branchpoint nucleophilic attack during splicing allows for RNA circularization through 5′-3′ linkages, assisted by RNA binding proteins, such as Muscleblind or Quaking, or through complementary Alu sequences, short DNA sequences utilized by the restriction enzyme Arthrobacter luteus (Alu) [151,152]. The function of circRNAs can differ depending on their sequence and subcellular localization. When in the nucleus, circRNAs can either enhance or inhibit transcription of parental genes [153,154]. circRNAs are also able to sponge miRNAs in the cytoplasm to prevent target mRNA degradation as it was shown for the conserved ciRS-7, with more than seventy miR-7 binding sites [155]. The study showed that when overexpressing ciRS-7 in vitro, addition of miR-7 resulted in lower silencing efficiency of known targets. Similarly, in zebrafish, an increase in ciRS-7 leads to an impairment in the midbrain, similar to what was observed when knocking out miR-7 [156]. Another circRNA, sex-determining region Y (Sry), was shown to function as a sponge for miR-138 in vitro with similar results as ciRS-7 when increased in vitro [155]. Furthermore, circRNAs are able to interact with RNA binding proteins and create a scaffold for enhanced RBP-RNA interactions, Argonaute being one example for this interaction [153,155]. A study performed on ciRS-7 showed that it does not only have miR-7 binding sites, but also contains binding sites used by Argonaute 2, assisting with the gene silencing induced by miR-7 [156]. While circRNAs are classified as non-coding, recent studies show that they are able to produce proteins and peptides. Such examples are circZNF609 which translates into a protein and polypeptides with a currently unknown function, and circβ-catenin which translates into a novel β-catenin isoform that stabilizes the full-length linear β-catenin by inhibiting GSK3β-mediated degradation [157,158,159]. 2.3.3. Long Non-Coding RNAs lncRNAs, named according to their length of a minimum of 200 nucleotides, were first described in 1990 with H19 being the first lncRNA to be characterized, followed by X-inactive specific transcript (XIST) in 1992 [160,161,162]. lncRNAs are associated with a plethora of functions related to regulation of transcription and/or translation, cell cycle homeostasis, cell differentiation and cell senescence [163,164,165,166,167]. In the nucleus, lncRNAs regulate gene expression through chromatin remodeling by providing protein scaffolds to guide enzymes such as acetylases, histone and DNA methyltransferases, towards specific locations in the genomic DNA [168,169]. They can also enhance a specific gene promoter by recruiting RNA binding proteins or act as co-factors for specific transcription factors [170,171]. While regulation of gene transcription is a potent mechanism to control gene expression, post-transcriptional modifications should not be overlooked. lncRNAs function through multiple ways to interact and affect gene expression post-transcriptionally, for example by sponging local miRNAs to prevent mRNA degradation, or by hosting specific miRNAs to increase their levels in the cell [172,173]. The lncRNA Xist, originating from the X-inactivation center (XIC), is able to inactivate one X-chromosome in female mammalian embryos [174]. Xist coats the chromosome in cis by activating polycomb-groups (PcGs), a group of DNA methyltransferases, that will induce H3K27 trimethylation by interacting with the 5′ end of Xist, containing an A-repeat. This eventually leads to formation of heterochromatin and subsequent silencing of the chromosome. Xist itself is regulated by Tsix, a lncRNA overlapping with Xist but translated antisense, in cis [175]. An overview of the classes of ncRNA, their biogenesis and cellular function is provided in Figure 3. 2.4. Non-Coding RNAs Involved in PAH ncRNAs have been associated with a prominent role in disease progression [176,177,178,179] and multiple studies revealed differential miRNA expression during the development of PAH. Multiple miRNAs were found to be dysregulated among different vascular cell types, allowing for clustering per cell class [180]. In VSMCs, the miR-17~92 cluster, miR-21, miR-145 and miR-210 are upregulated while miR-124 and miR-204 are downregulated. In ECs, the miR-17~92 cluster and miR-27a are upregulated but miR-21, miR-424 and miR-503 are downregulated. miR-340-5p was shown to be downregulated after acute pulmonary embolism and its overexpression in vivo prevented the development of PAH in a rat model of embolism through direct targeting of both interleukin-6 (IL-6) and interleukin-1β (IL-1β) and subsequent activation of nuclear factor κβ (NF-κβ) in PASCMs [181]. miR-138-5p is upregulated in PASMCs from PAH patients as well from rats subjected to MCT-induced PAH and its inhibition restores KCNK3 and Solute carrier family 45-member 3 (SLC45A3) expression and ameliorates PAH and RV function [182]. While SLC45A3′s function in PAH is not yet elucidated, KCNK3 inhibitions leads to increased proliferation, inflammation and subsequent vasoconstriction of the pulmonary artery [183]. In PAH patients, PASMC function is also tightly controlled by upregulated miR-18a-5p, through targeting of Notch2. While in PAH patients, miR-18a-5p influences PASMC proliferation and migration [184]. In MCT-treated rat PASMCs metabolism is affected by miR-125a-5p, through targeting of hexokinase 2 (HK2) and subsequent decrease in glycolysis [185]. However, not only SMCs are affected during PAH. Pulmonary fibroblasts are also affected during PAH but show only one miRNA to be downregulated, miR-124 [180]. With a plethora of miRNAs available, multiple therapeutic approaches are possible and some have already been tested. Studies where miR-145 was silenced, showed promising results by reducing pulmonary and subsequent RV remodeling in a hypoxia model [186]. Furthermore, circulating miRNAs have been investigated as biomarkers for PAH, and miRNAs such as miR-21-5p, miR-22-3p and miR-451a have been established as potential diagnostic tools to assess the development and/or progression of PH [187]. To date, only one circRNA, hsa_circ_0016070, has been involved in the pathophysiology of PAH. PASMCs transfected with hsa_circ_0016070 showed an increase in proliferation by inhibition of cell cycle arrest. It should be noted that in vivo validation of these results are lacking [188]. However, recently, increased levels of CircATP2B4 were detected in serum of PAH patients and associated with SMCs proliferation and migration. Bioinformatics and in vitro testing showed that CircATP2B4 is able to sponge miR-223, leading to an increase of the ATR protein, increased PASMC proliferation/migration and decreased apoptosis [189]. Further studies are expected to identify many other circRNAs involved in PAH and pulmonary arterial remodeling. lncRNAs have also been investigated as possible regulatory players during PAH-induced remodeling and multiple profiling studies have been performed to elucidate the role of lncRNAs in PAH [190,191,192,193,194]. In MCT rat models, the developed inflammatory response leads to an increase of H19 in the lungs and subsequent vascular remodeling. Increased H19 is able to sponge the let-7b leading to an increase of its downstream target, Angiotensin II receptor type 1 (AT1R), ensuing an increase in PASMC proliferation. This was confirmed by in vivo studies where a H19 null mice was subjected to MCT-induced PAH and reduced arterial remodeling was observed [190]. More recently, LncRNA-TCONS_00034812 was detected in the pulmonary artery of rats exposed to chronic hypoxia and by being downregulated in PASMCs it increases their proliferative capacity while reducing apoptosis, through decreased phosphorylation of p-ERK, p-JNK and p-p38 [191]. Another lncRNA, lnc-Ang362, was discovered to be upregulated together with miR-221 and miR-222 in the lung vasculature from patients suffering from PAH. Further in vitro studies showed that lnc-Ang362 regulates both miR-221 and miR-222 expression with its knockdown resulting in downregulation of miR-221 and miR-222 in PASMCs. Upregulation of lnc-Ang362 leads to increased PASMCs proliferation and migration which was reduced when miR-221 or miR-222 were inhibited through lnc-Ang362 overexpression [193]. Another lncRNA, lincRNA-Cox2, has been described as a regulator of inflammation, involved in atherosclerosis, and also found to be involved in PASCM migration and proliferation. LincRNA-Cox2 sponges miR-let-7a and leads to an increase in STAT3 [195]. In patient peripheral blood samples, lincRNA-Cox2 is upregulated, which is also observed in vitro in hypoxic PASMCs, and its silencing leads to decreased cell proliferation and migration. Furthermore, PASMCs derived from iPAH patients showed an increase in TYKRIL, a lncRNA playing a role in pericyte survival and vascular remodeling through regulation of Platelet-derived growth factor receptor beta (PDGFRβ) [196]. Another lncRNA that is upregulated in PAH patients and in vivo models and shown to be involved in vascular remodeling is lncRNA-SMILR. By sponging miR-141, lncRNA-SMILR leads to increased expression of RhoA/ROCK [197] and alterations in the proliferative and migratory capacity of PASMCs. An overview of the different ncRNAs that were associated with PAH is represented in Figure 4. While the studies by Wang et al. and Lei et al. were performed using patient material, most studies so far have not been validated in patients. While it remains to be proven that lncRNA expression patterns and function is conserved towards humans by being a new and upcoming field, there is a plethora of ncRNAs detected differentially expressed in PAH that might lead to a better understanding of this deadly disease, as well as to the development of more efficient therapeutic strategies. 2.5. Non-Coding RNAs in Right Ventricular Remodeling Looking more specifically at RV hypertrophy, not much is known about specific ncRNAs involved in RV remodeling compared to the information available for LV remodeling. Most studies remain descriptive by merely showing differences either between LV and RV or healthy and disease RV [198,199,200]. Some miRNAs involved in RV hypertrophy such as miR-21, miR-140-5p and -3p, miR-187-5p, miR-199b-5p, miR-221-3p, miR-222-3p, miR-702-3p, miR-887 and miR-1298 appear to have ventricle specific responses to pressure overload and remodeling [201,202,203]. For example, while in the LV miR-21 exerts a protective role during ventricle remodeling, increased miR-21 levels during RV remodeling correlate with severity of RV hypertrophy [201,202]. In turn, miR-199b is upregulated in both ventricles under pressure overload, but its target genes are differentially affected with DYRKA1 being downregulated in the LV while not being altered in the RV [204,205]. Furthermore, miR-1-5p has been described to be decreased in RV hypertrophy with its target, transforming growth factor beta receptor I (TGFβR1) being upregulated in a MCT rat model. However, in vivo studies including modulation of either miR-1-5p or TGFβR1 in MCT rats to validate the importance of the miR-1-5p during RVH are still lacking [206]. Figure 4 depicts the specific ncRNAs that were found to play a role in RV remodeling. While therapeutic intervention targeting RV-specific miRNAs as not yet been achieved, researchers have been focusing on pulmonary specific miRNAs, reducing the triggers for RV remodeling [207]. In the past decade, interest in RV-specific lncRNAs has increased as reflected by the several profiling studies performed on patient material and/or animal models [198,207,208]. Although one study has compared the role of H19, in both LV and RV remodeling induced by pressure overload and shown that of H19 in the LV protects against hypertrophic remodeling while in the RV H19 exacerbates the hypertrophic response [209,210], most studies remains descriptive. Without focusing on the mechanisms, the contribution of such lncRNAs towards the development and progression of the disease will remain unclear. 3. Future Perspectives Over the last two decades many improvements have been made towards treatment and symptom management of PAH patients but nevertheless, no cure has been found yet. Therefore, by exploring new fields such as epigenetic regulation, may help in better understanding the disease mechanisms as well as in developing new diagnostic and therapeutic strategies. However, many questions still remain: is ncRNA function conserved in humans and does it change in a similar way towards disease progression? If so, can we target specific cell types or tissue? Among many other questions that hopefully we will be able to answer in the upcoming decade. Another possibility may be that we do not focus on PAH itself but rather on its clinical outcome, RVF. We currently know that while both ventricles share the same cellular composition, intracellular signaling pathways are different within these two cardiac chambers, but it is not yet understood whether this is a result of the cell’s regulatory machinery or imprinting during embryonic development [211]. Finally, it is safe to say that a very exciting and exploratory field remains to be unveiled to further elucidate the mechanisms behind cardiac hypertrophy in general and the RV remodeling in response to PAH specifically. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Author Contributions J.M.M.K.: Conceptualization, investigation, resources, writing—original draft preparation; P.A.d.C.M.: Conceptualization, writing—review and editing, supervision, project administration and funding acquisition. All authors have read and agreed to the published version of the manuscript. Funding J.M.M.K. and P.A.d.C.M. were supported by the Dutch CardioVascular Alliance (DCVA) awarded to the Phaedra consortium as well as the Impulse Grant 2018 awarded to the Phaedra IMPACT consortium (CVON-2018-29). P.A.d.C.M. is further supported by Portuguese Foundation for Science and Technology Grant (PTDC/BIM-MEC/4578/2014) and a Dutch Heart Foundation grant (NHS2015T066). Conflicts of Interest Paula A. da Costa Martins is a cofounder of Mirabilis Therapeutics. Jordy M. M. Kocken declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Abbreviations 5caC 5-Carboxylcytosine 5fC 5-Formylcytosine 5hmC 5-Carboxylmethylcytosine ADD ATRX-DNMT3-DNMT3L Alu Arthrobacter luteus AT1R Angiotensin II Receptor Type 1 ATP Adenosine triphosphate ATP13A3 Probable cation-transporting ATPase 13A3 ACVRL1 Serine/threonine-protein kinase receptor R3 AQP1 Aquaporin 1 BMPR2 Bone morphogenetic protein receptor type II cAMP Cyclic adenosine monophosphate CAV1 Caveolin cGMP Cyclic 3′,5′ guanosine monophosphate circRNA Circular RNA CM Cardiomyocyte DGCR8 DiGeorge Syndrome Critical Region 8 DNMT1 DNA methyltransferases 1 DNMT3A DNA methyltransferases 3A DNMT3B DNA methyltransferases 3B ECs Endothelial cells EIF2AK4 Eukaryotic translation initiation factor 2-alpha kinase 4 eNOS Endothelial nitric oxide synthase EPAC1 Exchange factor directly activated by cAMP ERK1/2 Extracellular signal-regulated kinases 1/2 ET-1 Endothelin-1 FBs Fibroblasts FFA Free fatty acid GDF2 Growth differentiation factor 2 GLUT1 Glucose transporter 1 GLUT4 Glucose transporter 4 GNAT Gcn5-related N-acetyltransferases GPCRs G-coupled protein receptor H3K4me3 Histone 3 Lys4 trimethylation HAT Histone acetyltransferase HDAC Histone deacetylase HIF-1α Hypoxia-inducible factor 1-alpha HK2 Hexokinase-II HMTs Histone methyltransferase hPAH Hereditary pulmonary artery hypertension IL-1 Interleukin-1 IL-1β Interleuking-1β IL-6 Interleuking-6 IP Prostaglandin receptors JNK c-Jun N-terminal kinase KCNK3 Potassium two pore domain channel subfamily K member 3 lncRNA lncRNA LSH Lymphocyte-specific-helicase LV Left ventricle MCT Monocrotaline miRNA MicroRNA MKL1 Megakaryocytic leukemia 1 mPAP Mean pulmonary arterial pressure mRNA messenger RNA MTase Methyltransferase MYST Moz, Ybf2/Sas3, Sas2 and Tip60 ncRNA Non-coding RNA NF-κβ Nuclear Factor κ β NO Nitric oxide Nox NAPDH oxidative p300/CRBP p300/CREB-binding protein PAB Pulmonary artery banding PAH Pulmonary Artery Hypertension PASMCs Pulmonary artery smooth muscle cells PcGs Polycomb-groups PCWP Pulmonary capillary wedge pressure PDE5 Phosphodiesterase type 5 PDGFRβ Platelet-Derived Growth Factor Receptor beta PDH Pyruvate dehydrogenase PGI2 Prostacyclin PH Pulmonary hypertension PKA Protein Kinase A PKC Protein Kinase C PKD Pyruvate dehydrogenase kinases PLC Phospholipase C pri-miRNA Primary miRNA double-strand loop PVR Pulmonary vascular resistance RHF Right heart failure RhoA/ROCK RhoA/Rho-Kinase RISC RNA Induced Silencing Complex ROS Reactive oxygen species RV Right ventricle RVF Right ventricle failure RVH Right ventricle hypertrophy SETD2 SET Domain containing 2 sGC Soluble guanylate SLC45A3 Solute Carrier Family 45 Member 3 SMAD1 Mothers against decapentaplegic homolog 1 SMAD4 Mothers against decapentaplegic homolog 4 SMAD9 Mothers against decapentaplegic homolog 9 SMCs Smooth muscle cells SOD2 Superoxide dismutase 2 SOX17 SRY-box 17 Sry Sex-determining region Y TBX4 T-box transcription factor 4 TDG Thymine DNA glycosylase TET Ten-eleven translocation TGF-β Transforming growth factor beta TGF-βR1 Transforming growth factor beta receptor I TNF-α Tumor necrotic factor alpha TSA Trichostatin A UHRF1 Ubiquitin-line, containing PHD and RING finger domains, 1 UTR Untranslated region VPA Valproic acid XIC X-inactivation center XIST X-inactive specific transcript Figure 1 PAH induced pulmonary artery and subsequent RV remodeling and the ncRNAs involved in the process. During PAH, the pulmonary artery undergoes extensive remodeling due to increased proliferation and apoptosis resistance. The number of ECs and PASCMs increases which narrows the artery, decreasing the blood flow and increasing the pressure. Subsequently, the RV undergoes adaptive remodeling to overcome the increased PA pressure; during this adaptive remodeling, contractility, CM size, neoangiogenesis, metabolic stress and inflammation increases. During prolong PAH, the pulmonary artery continues to remodel with continuous proliferation, apoptosis resistance, blood pressure, and adventitial thickening while the blood flow decreases even further. Meanwhile, the RV can no longer sustain its output to overcome the pressure overload leading to a decoupling and maladaptive remodeling. This is marked by an increase in metabolic stress and further inflammation while contractility and RV output are decreased. The red arrows depict an increase of the mentioned change in homeostasis while a blue arrow signifies a decrease. Arrow thickness shows the severity of the change. Figure 2 Epigenetic regulation and chromatin remodeling. Chromatin remodeling can be mediated by different DNA and/or histone modifications such as methylation, acetylation, and ubiquitination. Methylation of DNA is mediated mainly by DNMT3A and DNMT3B in cytosine rich locations. Methylated sites are seen as being transcriptionally inactive. In turn, histones can be either methylated, acetylated, or ubiquitinated. While methylation of DNA is a sign of transcription inhibition, methylation of histones by HMTs can either inhibit or enhance transcription depending on the amount of methylation occurring on the histones. Furthermore, acetylation of histone amino acids is a sign of transcriptional activation. HATs acetylate lysines while HDACs deacylated lysine, influencing transcription by increasing (acetylation) or decreasing (deacetylation) accessibility of genes. Ubiquitination of histones is another process that regulates gene expression. Ubiquitination occurs on both histone 2A lysine 199 and histone 3B lysine 200. The effect of ubiquitination on gene expression is depending on its location, histone 2A lysine 199 has a repressing effect while histone 2B 200 ubiquitination activates gene expression. Figure 3 Different ncRNA species: their transcription from the eukaryotic genome and respective functions. Exons in protein-coding genes can be transcribed into lncRNAs (blue) and circRNAs (purple), normally after intron exclusion by the spliceosome (orange). miRNAs (green), in turn, can derive from intronic sequences or intergenic regions. LncRNAs are a large class of transcribed RNA molecules with a length of more than 200 nucleotides that are mostly located exclusively in the nucleus. They are often transcribed as whole or partial antisense transcripts to coding genes and can structurally resemble mRNAs. They exert their function by binding DNA, RNA, or proteins, to regulate gene expression at multiple levels via base pairing or secondary structure formation, respectively. LncRNAs, by acting as either signals, decoys, guides, and/or scaffolds, can recruit epigenetic factors to change patterns of chromatin organization, activate or repress the gene transcription by interacting with specific regulatory regions or transcription factors and manipulate mRNA function by regulating alternative splicing. At a posttranscriptional level lncRNAs can act as competing endogenous RNA, by base pairing with miRNAs and interfering with their inhibitory effects, but they can also affect mRNA translation and can modify mRNA and proteins, playing key roles in protein-protein interactions, protein activity and localization. While many different circRNAs can be generated from a single genomic locus, all of them are generated through backsplicing, a non-canonical splicing process in which a downstream splice donor is joined to an upstream splice acceptor. The roles of circRNAs are poorly described and remain therefore limited to inhibition of a linear, functional mRNA formation and microRNA sponging. They have been shown to also interact with proteins and although the exact function of such interactions remains unclear, they are speculated to be involved in either protein transport, protein sequestration and/or protein regulation. miRNAs are transcribed from intronic sequences and form a double stranded loop primary miRNA (pri-miRNA). Further processing generates precursor miRNA molecules (pre-miRNA) which once in the cytoplasm will produce mature miRNA molecules. Association of the miRNA with large protein complexes (RISC) allows for contact with target mRNA sequences. miRNAs will inhibit mRNA translation when a near-perfect pairing occurs or induce full mRNA cleavage with a perfect pairing. Figure 4 ncRNAs involved in PAH-induced pulmonary artery and RV remodeling. During disease progression, multiple ncRNAs are dysregulated in the different vascular and cardiac cell types, and compared to healthy tissues. miRNAs are depicted in red, lncRNAs in blue and circRNAs in green. Red and blue arrows represent gene up- or downregulation, respectively, in either the pulmonary artery or the RV. ==== Refs References 1. Galiè N. Humbert M. Vachiery J.L. Gibbs S. Lang I. Torbicki A. Simonneau G. Peacock A. Vonk Noordegraaf A. Beghetti M. 2015 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension: The Joint Task Force for the Diagnosis and Treatment of Pulmonary Hypertension of the European Society of Cardiology (ESC) and the European Respiratory Society (ERS): Endorsed by: Association for European Paediatric and Congenital Cardiology (AEPC), International Society for Heart and Lung Transplantation (ISHLT) Eur. Heart J. 2016 37 67 119 10.1093/eurheartj/ehv317 26320113 2. Evans J.D.W. Girerd B. Montani D. Wang X.J. Galiè N. Austin E.D. Elliott G. Asano K. Grünig E. Yan Y. BMPR2 mutations and survival in pulmonary arterial hypertension: An individual participant data meta-analysis Lancet Respir. Med. 2016 4 129 137 10.1016/S2213-2600(15)00544-5 26795434 3. Lan N.S.H. Massam B.D. Kulkarni S.S. Lang C.C. Pulmonary Arterial Hypertension: Pathophysiology and Treatment Diseases 2018 6 38 10.3390/diseases6020038 29772649 4. Simonneau G. Montani D. Celermajer D.S. Denton C.P. Gatzoulis M.A. Krowka M. Williams P.G. Souza R. Haemodynamic definitions and updated clinical classification of pulmonary hypertension Eur. Respir. J. 2018 53 1801913 10.1183/13993003.01913-2018 5. Prins K.W. Thenappan T. World Health Organization Group I Pulmonary Hypertension: Epidemiology and Pathophysiology Cardiol. Clin. 2016 34 363 374 10.1016/j.ccl.2016.04.001 27443134 6. Wijeratne D.T. Lajkosz K. Brogly S.B. Lougheed M.D. Jiang L. Housin A. Barber D. Johnson A. Doliszny K.M. Archer S.L. Increasing Incidence and Prevalence of World Health Organization Groups 1 to 4 Pulmonary Hypertension Circ. Cardiovasc. Qual. Outcomes 2018 11 e003973 10.1161/CIRCOUTCOMES.117.003973 29444925 7. Reis A. Santos M. Vicente M. Furtado I. Cruz C. Melo A. Carvalho L. Gonçalves F. Sa-Couto P. Almeida L. Health-Related Quality of Life in Pulmonary Hypertension and Its Clinical Correlates: A Cross-Sectional Study Biomed. Res. Int. 2018 2018 3924517 10.1155/2018/3924517 29750153 8. Sikirica M. Iorga S.R. Bancroft T. Potash J. The economic burden of pulmonary arterial hypertension (PAH) in the US on payers and patients BMC Health Serv. Res. 2014 14 676 10.1186/s12913-014-0676-0 25539602 9. Rich J.D. Rich S. Clinical Diagnosis of Pulmonary Hypertension Circulation 2014 130 1820 1830 10.1161/CIRCULATIONAHA.114.006971 25385937 10. Lau E.M. Humbert M. Celermajer D.S. Early detection of pulmonary arterial hypertension Nat. Rev. Cardiol. 2015 12 143 155 10.1038/nrcardio.2014.191 25421168 11. Condon D.F. Nickel N.P. Anderson R. Mirza S. de Jesus Perez V.A. The 6th World Symposium on Pulmonary Hypertension: What’s old is new F1000Research 2019 8 F1000 10.12688/f1000research.18811.1 12. Morrell N.W. Aldred M.A. Chung W.K. Elliott C.G. Nichols W.C. Soubrier F. Trembath R.C. Loyd J.E. Genetics and genomics of pulmonary arterial hypertension Eur. Respir. J. 2019 53 1801899 10.1183/13993003.01899-2018 30545973 13. Tuder R.M. Voelkel N.F. Plexiform lesion in severe pulmonary hypertension: Association with glomeruloid lesion Am. J. Pathol. 2001 159 382 383 10.1016/S0002-9440(10)61705-1 11438486 14. Masri F.A. Xu W. Comhair S.A.A. Asosingh K. Koo M. Vasanji A. Drazba J. Anand-Apte B. Erzurum S.C. Hyperproliferative apoptosis-resistant endothelial cells in idiopathic pulmonary arterial hypertension Am. J. Physiol. Lung Cell Mol. Physiol. 2007 293 L548 L554 10.1152/ajplung.00428.2006 17526595 15. Lee S.D. Shroyer K.R. Markham N.E. Cool C.D. Voelkel N.F. Tuder R.M. Monoclonal endothelial cell proliferation is present in primary but not secondary pulmonary hypertension J. Clin. Investig. 1998 101 927 934 10.1172/JCI1910 9486960 16. Atkinson C. Stewart S. Upton P.D. Machado R. Thomson J.R. Trembath R.C. Morrell N.W. Primary Pulmonary Hypertension Is Associated with Reduced Pulmonary Vascular Expression of Type II Bone Morphogenetic Protein Receptor Circulation 2002 105 1672 1678 10.1161/01.CIR.0000012754.72951.3D 11940546 17. Negi V. Chan S.Y. Discerning functional hierarchies of microRNAs in pulmonary hypertension JCI Insight 2017 2 e91327 10.1172/jci.insight.91327 28289720 18. Durrington H.J. Upton P.D. Hoer S. Boname J. Dunmore B.J. Yang J. Crilley T.K. Butler L.M. Blackbourn D.J. Nash G.B. Identification of a lysosomal pathway regulating degradation of the bone morphogenetic protein receptor type II J. Biol. Chem. 2010 285 37641 37649 10.1074/jbc.M110.132415 20870717 19. Dalvi P. O’Brien-Ladner A. Dhillon N.K. Downregulation of bone morphogenetic protein receptor axis during HIV-1 and cocaine-mediated pulmonary smooth muscle hyperplasia: Implications for HIV-related pulmonary arterial hypertension Arterioscler. Thromb. Vasc. Biol. 2013 33 2585 2595 10.1161/ATVBAHA.113.302054 24008158 20. Sztrymf B. Coulet F. Girerd B. Yaici A. Jais X. Sitbon O. Montani D. Souza R. Simonneau G. Soubrier F. Clinical Outcomes of Pulmonary Arterial Hypertension in Carriers of BMPR2 Mutation Am. J. Respir. Crit. Care Med. 2008 177 1377 1383 10.1164/rccm.200712-1807OC 18356561 21. Elliott C.G. Glissmeyer E.W. Havlena G.T. Carlquist J. McKinney J.T. Rich S. McGoon M.D. Scholand M.B. Kim M. Jensen R.L. Relationship of BMPR2 Mutations to Vasoreactivity in Pulmonary Arterial Hypertension Circulation 2006 113 2509 2515 10.1161/CIRCULATIONAHA.105.601930 16717148 22. Hoeper M.M. Kramer T. Pan Z. Eichstaedt C.A. Spiesshoefer J. Benjamin N. Olsson K.M. Meyer K. Vizza C.D. Vonk-Noordegraaf A. Mortality in pulmonary arterial hypertension: Prediction by the 2015 European pulmonary hypertension guidelines risk stratification model Eur. Respir. J. 2017 50 1700740 10.1183/13993003.00740-2017 28775047 23. Hurdman J. Condliffe R. Elliot C.A. Davies C. Hill C. Wild J.M. Capener D. Sephton P. Hamilton N. Armstrong I.J. ASPIRE registry: Assessing the Spectrum of Pulmonary hypertension Identified at a REferral centre Eur. Respir. J. 2012 39 945 955 10.1183/09031936.00078411 21885399 24. Oudiz R.J. Death in pulmonary arterial hypertension Am. J. Respir. Crit. Care Med. 2013 188 269 270 10.1164/rccm.201305-0898ED 23905521 25. Tuder R.M. Archer S.L. Dorfmüller P. Erzurum S.C. Guignabert C. Michelakis E. Rabinovitch M. Schermuly R. Stenmark K.R. Morrell N.W. Relevant issues in the pathology and pathobiology of pulmonary hypertension J. Am. Coll. Cardiol. 2013 62 D4 D12 10.1016/j.jacc.2013.10.025 24355640 26. Giaid A. Saleh D. Reduced Expression of Endothelial Nitric Oxide Synthase in the Lungs of Patients with Pulmonary Hypertension N. Engl. J. Med. 1995 333 214 221 10.1056/NEJM199507273330403 7540722 27. Fagan K.A. Fouty B.W. Tyler R.C. Morris K.G. Jr. Hepler L.K. Sato K. LeCras T.D. Abman S.H. Weinberger H.D. Huang P.L. The pulmonary circulation of homozygous or heterozygous eNOS-null mice is hyperresponsive to mild hypoxia J. Clin. Investig. 1999 103 291 299 10.1172/JCI3862 9916141 28. He H. Venema V.J. Gu X. Venema R.C. Marrero M.D. Caldwell R.B. Vascular Endothelial Growth Factor Signals Endothelial Cell Production of Nitric Oxide and Prostacyclin through Flk-1/KDR Activation of c-Src J. Biol. Chem. 1999 274 25130 25135 10.1074/jbc.274.35.25130 10455194 29. Tielemans B. Delcroix M. Belge C. Quarck R. TGFβ and BMPRII signalling pathways in the pathogenesis of pulmonary arterial hypertension Drug Discov. Today 2019 24 703 716 10.1016/j.drudis.2018.12.001 30529762 30. Gajecki D. Gawrys J. Szahidewicz-Krupska E. Doroszko A. Novel Molecular Mechanisms of Pulmonary Hypertension: A Search for Biomarkers and Novel Drug Targets—From Bench to Bed Site Oxidative Med. Cell. Longev. 2020 2020 7265487 10.1155/2020/7265487 31. Palmer R.M.J. Rees D.D. Ashton D.S. Moncada S. L-arginine is the physiological precursor for the formation of nitric oxide in endothelium-dependent relaxation Biochem. Biophys. Res. Commun. 1988 153 1251 1256 10.1016/S0006-291X(88)81362-7 3390182 32. Murad F. The nitric oxide-cyclic GMP signal transduction system for intracellular and intercellular communication Recent. Prog. Horm. Res. 1994 49 239 248 7511827 33. Lehners M. Dobrowinski H. Feil S. Feil R. cGMP Signaling and Vascular Smooth Muscle Cell Plasticity J. Cardiovasc. Dev. Dis. 2018 5 20 10.3390/jcdd5020020 34. Xue C. Johns R.A. Endothelial Nitric Oxide Synthase in the Lungs of Patients with Pulmonary Hypertension N. Engl. J. Med. 1995 333 1642 1644 7477212 35. Salguero K.L. Cummings J.J. Inhaled Nitric Oxide and Methemoglobin in Full-Term Infants with Persistent Pulmonary Hypertension of the Newborn Pulm. Pharmacol. Ther. 2002 15 1 5 10.1006/pupt.2001.0311 11969358 36. Chen C. Watson G. Zhao L. Cyclic guanosine monophosphate signalling pathway in pulmonary arterial hypertension Vasc. Pharmacol. 2013 58 211 218 10.1016/j.vph.2012.09.001 22982057 37. Leuchte H.H. Schwaiblmair M. Baumgartner R.A. Neurohr C.F. Kolbe T. Behr J. Hemodynamic Response to Sildenafil, Nitric Oxide, and Iloprost in Primary Pulmonary Hypertension Chest 2004 125 580 586 10.1378/chest.125.2.580 14769741 38. Faisal M. Siddiqi F. Alkaddour A. Bajwa A.A. Shujaat A. Effect of PAH specific therapy on pulmonary hemodynamics and six-minute walk distance in portopulmonary hypertension: A systematic review and meta-analysis Pulm. Med. 2014 2014 528783 10.1155/2014/528783 25478223 39. Lang I.M. Gaine S.P. Recent advances in targeting the prostacyclin pathway in pulmonary arterial hypertension Eur. Respir. Rev. 2015 24 630 641 10.1183/16000617.0067-2015 26621977 40. Clapp L.H. Finney P. Turcato S. Tran S. Rubin L.J. Tinker A. Differential Effects of Stable Prostacyclin Analogs on Smooth Muscle Proliferation and Cyclic AMP Generation in Human Pulmonary Artery Am. J. Respir. Cell Mol. Biol. 2002 26 194 201 10.1165/ajrcmb.26.2.4695 11804870 41. Hewer R.C. Sala-Newby G.B. Wu Y.J. Newby A.C. Bond M. PKA and Epac synergistically inhibit smooth muscle cell proliferation J. Mol. Cell. Cardiol. 2011 50 87 98 10.1016/j.yjmcc.2010.10.010 20971121 42. Murray F.S. Suda R.Y. Kwon O. Li X. Remillard C.V. Thistlethwaite P.A. Yuan J.X. Insel P.A. Decreased Expression and Activity of Epac (Exchange Protein Directly Activated by cAMP) in Pulmonary Arterial Hypertension Am. J. Respir. Crit. Care Med. 2020 201 A1804 43. Barnes H. Yeoh H.L. Fothergill T. Burns A. Humbert M. Williams T. Prostacyclin for pulmonary arterial hypertension Cochrane Database Syst. Rev. 2019 5 CD012785 10.1002/14651858.CD012785.pub2 31042010 44. Flora L.M. Monica M. Maria A.P. Endothelin-1: The Yin and Yang on Vascular Function Curr. Med. Chem. 2006 13 1655 1665 16787211 45. Frelin C. Guedin D. Why are circulating concentrations of endothelin-1 so low? Cardiovasc. Res. 1994 28 1613 1622 10.1093/cvr/28.11.1613 7842453 46. Gray G.A. Webb D.J. The endothelin system and its potential as a therapeutic target in cardiovascular disease Pharmacol. Ther. 1996 72 109 148 10.1016/S0163-7258(96)00101-5 8981573 47. Pollock D.M. Keith T.L. Highsmith R.F. Endothelin receptors and calcium signaling FASEB J. 1995 9 1196 1204 10.1096/fasebj.9.12.7672512 7672512 48. Ringvold H.C. Khalil R.A. Protein Kinase C as Regulator of Vascular Smooth Muscle Function and Potential Target in Vascular Disorders Adv. Pharmacol. 2017 78 203 301 28212798 49. Hirata Y. Emori T. Eguchi S. Kanno K. Imai T. Ohta K. Marumo F. Endothelin receptor subtype B mediates synthesis of nitric oxide by cultured bovine endothelial cells J. Clin. Investig. 1993 91 1367 1373 10.1172/JCI116338 7682570 50. Fox B. Langleben D. Hirsch A.M. Schlesinger R.D. Eisenberg M.J. Joyal D. Blenkhorn F. Lesenko L. Hemodynamic Stability after Transitioning between Endothelin Receptor Antagonists in Patients with Pulmonary Arterial Hypertension Can. J. Cardiol. 2013 29 672 677 10.1016/j.cjca.2012.05.013 22819360 51. Lee Y.H. Song G.G. Meta-analysis of randomized controlled trials of bosentan for treatment of pulmonary arterial hypertension Korean J. Intern. Med. 2013 28 701 707 10.3904/kjim.2013.28.6.701 24307846 52. Rubin L.J. Badesch D.B. Barst R.J. Galie N. Black C.M. Keogh A. Pulido T. Frost A. Roux S. Leconte I. Bosentan Therapy for Pulmonary Arterial Hypertension N. Engl. J. Med. 2002 346 896 903 10.1056/NEJMoa012212 11907289 53. Pulido T. Adzerikho I. Channick R.N. Delcroix M. Galiè N. Ghofrani H.A. Jansa P. Jing Z.C. Le Brun F.O. Mehta S. Macitentan and Morbidity and Mortality in Pulmonary Arterial Hypertension N. Engl. J. Med. 2013 369 809 818 10.1056/NEJMoa1213917 23984728 54. Galiè N. Olschewski H. Oudiz R.J. Torres F. Frost A. Ghofrani H.A. Badesch D.B. McGoon M.D. McLaughlin V.V. Roecker E.B. Ambrisentan for the Treatment of Pulmonary Arterial Hypertension Circulation 2008 117 3010 3019 10.1161/CIRCULATIONAHA.107.742510 18506008 55. Xu S.W. Denton C.P. Dashwood M.R. Holmes A.M. Bou-Gharios G. Pearson J.D. Black C.M. Abraham D.J. Fibroblast Matrix Gene Expression and Connective Tissue Remodeling: Role of Endothelin-1 J. Investig. Dermatol. 2001 116 417 425 10.1046/j.1523-1747.2001.01256.x 11231316 56. Shimony A. Eisenberg M.J. Rudski L.G. Schlesinger R. Afilalo J. Joyal D. Dragatakis L. Hirsch A. Boutet K. Fox B.D. Prevalence and Impact of Coronary Artery Disease in Patients with Pulmonary Arterial Hypertension Am. J. Cardiol. 2011 108 460 464 10.1016/j.amjcard.2011.03.066 21600533 57. Kolb T.M. Peabody J. Baddoura P. Fallica J. Mock J.R. Singer B.D. D’Alessio F.R. Damarla M. Damico R.L. Hassoun P.M. Right Ventricular Angiogenesis is an Early Adaptive Response to Chronic Hypoxia-Induced Pulmonary Hypertension Microcirculation 2015 22 724 736 10.1111/micc.12247 26352923 58. Avazmohammadi R. Mendiola E. Li D. Vanderslice P. Dixon R. Sacks M. Interactions between Structural Remodeling and Hypertrophy in the Right Ventricle in Response to Pulmonary Arterial Hypertension J. Biomech. Eng. 2019 141 0910161 09101613 10.1115/1.4044174 59. Reddy S. Bernstein D. Molecular Mechanisms of Right Ventricular Failure Circulation 2015 132 1734 1742 10.1161/CIRCULATIONAHA.114.012975 26527692 60. Huusko J. Lottonen L. Merentie M. Gurzeler E. Anisimov A. Miyanohara A. Alitalo K. Tavi P. Ylä-Herttuala S. AAV9-mediated VEGF-B Gene Transfer Improves Systolic Function in Progressive Left Ventricular Hypertrophy Mol. Ther. J. Am. Soc. Gene Ther. 2012 20 2212 2221 10.1038/mt.2012.145 61. Tello K. Gall H. Richter M. Ghofrani A. Schermuly R. Right ventricular function in pulmonary (arterial) hypertension Herz 2019 44 509 516 10.1007/s00059-019-4815-6 31101945 62. Lorell B.H. Carabello B.A. Left Ventricular Hypertrophy Circulation 2000 102 470 479 10.1161/01.CIR.102.4.470 10908222 63. Tuomainen T. Tavi P. The role of cardiac energy metabolism in cardiac hypertrophy and failure Exp. Cell Res. 2017 360 12 18 10.1016/j.yexcr.2017.03.052 28344054 64. Do E. Baudet S. Verdys M. Touzeau C. Bailly F. Lucas-Héron B. Sagniez M. Rossi A. Noireaud J. Energy metabolism in normal and hypertrophied right ventricle of the ferret heart J. Mol. Cell. Cardiol. 1997 29 1903 1913 10.1006/jmcc.1997.0429 9236144 65. Nascimben L. Ingwall J.S. Lorell B.H. Pinz I. Schultz V. Tornheim K. Tian R. Mechanisms for Increased Glycolysis in the Hypertrophied Rat Heart Hypertension 2004 44 662 667 10.1161/01.HYP.0000144292.69599.0c 15466668 66. Piao L. Marsboom G. Archer S.L. Mitochondrial metabolic adaptation in right ventricular hypertrophy and failure J. Mol. Med. 2010 88 1011 1020 10.1007/s00109-010-0679-1 20820751 67. Jeoung N.H. Pyruvate Dehydrogenase Kinases: Therapeutic Targets for Diabetes and Cancers Diabetes Metab. J. 2015 39 188 197 10.4093/dmj.2015.39.3.188 26124988 68. Semenza G.L. Hypoxia-inducible factor 1: Regulator of mitochondrial metabolism and mediator of ischemic preconditioning Biochimica. Biophysica. Acta. 2011 1813 1263 1268 10.1016/j.bbamcr.2010.08.006 69. Redout E.M. Wagner M.J. Zuidwijk M.J. Boer C. Musters R.J.P. van Hardeveld C. Paulus W.J. Simonides W.S. Right-ventricular failure is associated with increased mitochondrial complex II activity and production of reactive oxygen species Cardiovasc. Res. 2007 75 770 781 10.1016/j.cardiores.2007.05.012 17582388 70. Moris D. Spartalis M. Spartalis E. Karachaliou G.S. Karaolanis G.I. Tsourouflis G. Tsilimigras D.I. Tzatzaki E. Theocharis S. The role of reactive oxygen species in the pathophysiology of cardiovascular diseases and the clinical significance of myocardial redox Ann. Transl. Med. 2017 5 326 10.21037/atm.2017.06.27 28861423 71. Zhu T.T. Zhang W.F. Luo P. Qian Z.X. Li F. Zhang Z. Hu C.P. LOX-1 promotes right ventricular hypertrophy in hypoxia-exposed rats Life Sci. 2017 174 35 42 10.1016/j.lfs.2017.02.016 28259654 72. Cowley P.M. Wang G. Swigart P.M. Raghunathan A. Reddy N. Dulam P. Lovett D.H. Simpson P.C. Baker A.J. Reversal of right ventricular failure by chronic alpha1A-subtype adrenergic agonist therapy Am. J. Physiol. Heart Circ. Physiol. 2019 316 H224 H232 10.1152/ajpheart.00507.2018 30412439 73. Power A.S. Norman R. Jones T.L.M. Hickey A.J. Ward M.L. Mitochondrial function remains impaired in the hypertrophied right ventricle of pulmonary hypertensive rats following short duration metoprolol treatment PLoS ONE 2019 14 e0214740 10.1371/journal.pone.0214740 30964911 74. Gomez-Arroyo J. Mizuno S. Szczepanek K. Van Tassell B. Natarajan R. dos Remedios C.G. Drake J.I. Farkas L. Kraskauskas D. Wijesinghe D.S. Metabolic Gene Remodeling and Mitochondrial Dysfunction in Failing Right Ventricular Hypertrophy Secondary to Pulmonary Arterial Hypertension Circ. Heart Fail. 2013 6 136 144 10.1161/CIRCHEARTFAILURE.111.966127 23152488 75. Tsutsui H. Ide T. Hayashidani S. Suematsu N. Utsumi H. Nakamura R. Egashira K. Takeshita A. Greater susceptibility of failing cardiac myocytes to oxygen free radical-mediated injury Cardiovasc. Res. 2001 49 103 109 10.1016/S0008-6363(00)00197-8 11121801 76. Forrester S.J. Kikuchi D.S. Hernandes M.S. Xu Q. Griendling K.K. Reactive Oxygen Species in Metabolic and Inflammatory Signaling Circ. Res. 2018 122 877 902 10.1161/CIRCRESAHA.117.311401 29700084 77. Nergui S. Fukumoto Y. Do Z.E. Nakajima S. Shimizu T. Ikeda S. Elias-Al-Mamun M. Shimokawa H. Role of Endothelial Nitric Oxide Synthase and Collagen Metabolism in Right Ventricular Remodeling due to Pulmonary Hypertension Circ. J. 2014 78 1465 1474 10.1253/circj.CJ-13-1586 24705390 78. Campian M.E. Hardziyenka M. de Bruin K. van Eck-Smit B.L.F. de Bakker J.M.T. Verberne H.J. Tan H.L. Early inflammatory response during the development of right ventricular heart failure in a rat model Eur. J. Heart Fail. 2010 12 653 658 10.1093/eurjhf/hfq066 20495202 79. Rondelet B. Dewachter C. Kerbaul F. Kang X. Fesler P. Brimioulle S. Naeije R. Dewachter L. Prolonged overcirculation-induced pulmonary arterial hypertension as a cause of right ventricular failure Eur. Heart J. 2011 33 1017 1026 10.1093/eurheartj/ehr111 21606077 80. Patten M. Krämer E. Bünemann J. Wenck C. Thoenes M. Wieland T. Long C. Endotoxin and cytokines alter contractile protein expression in cardiac myocytes in vivo Pflügers Arch. 2001 442 920 927 11680626 81. Moe G.W. Marin-Garcia J. Konig A. Goldenthal M. Lu X. Feng Q. In vivo TNF-α inhibition ameliorates cardiac mitochondrial dysfunction, oxidative stress, and apoptosis in experimental heart failure Am. J. Physiol. Heart Circ. Physiol. 2004 287 H1813 H1820 10.1152/ajpheart.00036.2004 15205165 82. Arrigo M. Huber L.C. Winnik S. Mikulicic F. Guidetti F. Frank M. Flammer A.J. Ruschitzka F. Right Ventricular Failure: Pathophysiology, Diagnosis and Treatment Card. Fail. Rev. 2019 5 140 146 10.15420/cfr.2019.15.2 31768270 83. Hoeper M.M. Benza R.L. Corris P. de Perrot M. Fadel E. Keogh A.M. Kühn C. Savale L. Klepetko W. Intensive care, right ventricular support and lung transplantation in patients with pulmonary hypertension Eur. Respir. J. 2019 53 1801906 10.1183/13993003.01906-2018 30545979 84. Waddington C.H. The Epigenotype Int. J. Epidemiol. 2012 41 10 13 10.1093/ije/dyr184 22186258 85. Russo V.E.A. Martienssen R.A. Riggs A.D. Epigenetic Mechanisms of Gene Regulation Cold Spring Harbor Laboratory Press New York, NY, USA 1996 86. Okano M. Bell D.W. Haber D.A. Li E. DNA Methyltransferases Dnmt3a and Dnmt3b Are Essential for De Novo Methylation and Mammalian Development Cell 1999 99 247 257 10.1016/S0092-8674(00)81656-6 10555141 87. Piunti A. Shilatifard A. Epigenetic balance of gene expression by Polycomb and COMPASS families Science 2016 352 aad9780 10.1126/science.aad9780 27257261 88. Zhang Y. Jurkowska R. Soeroes S. Rajavelu A. Dhayalan A. Bock I. Rathert P. Brandt O. Reinhardt R. Fischle W. Chromatin methylation activity of Dnmt3a and Dnmt3a/3L is guided by interaction of the ADD domain with the histone H3 tail Nucleic Acids Res. 2010 38 4246 4253 10.1093/nar/gkq147 20223770 89. Bewick A.J. Ji L. Niederhuth C.E. Willing E.M. Hofmeister B.T. Shi X. Wang L. Lu Z. Rohr N.A. Hartwig B. On the origin and evolutionary consequences of gene body DNA methylation Proc. Natl. Acad. Sci. USA 2016 113 9111 9116 10.1073/pnas.1604666113 27457936 90. Suzuki S. Murakami Y. Takahata S. H3K36 methylation state and associated silencing mechanisms Transcription 2017 8 26 31 10.1080/21541264.2016.1246076 27723431 91. Bostick M. Kim J.K. Estève P.O. Clark A. Pradhan S. Jacobsen S.E. UHRF1 Plays a Role in Maintaining DNA Methylation in Mammalian Cells Science 2007 317 1760 1764 10.1126/science.1147939 17673620 92. Rothbart S.B. Dickson B.M. Ong M.S. Krajewski K. Houliston S. Kireev D.B. Arrowsmith C.H. Strahl B.D. Multivalent histone engagement by the linked tandem Tudor and PHD domains of UHRF1 is required for the epigenetic inheritance of DNA methylation Genes Dev. 2013 27 1288 1298 10.1101/gad.220467.113 23752590 93. Kohli R.M. Zhang Y. TET enzymes, TDG and the dynamics of DNA demethylation Nature 2013 502 472 479 10.1038/nature12750 24153300 94. Hashimoto H. Liu Y. Upadhyay A.K. Chang Y. Howerton S.B. Vertino P.M. Zhang X. Cheng X. Recognition and potential mechanisms for replication and erasure of cytosine hydroxymethylation Nucleic Acids Res. 2012 40 4841 4849 10.1093/nar/gks155 22362737 95. Otani J. Kimura H. Sharif J. Endo T.A. Mishima Y. Kawakami T. Koseki H. Shirakawa M. Suetake I. Tajima S. Cell cycle-dependent turnover of 5-hydroxymethyl cytosine in mouse embryonic stem cells PLoS ONE 2013 8 e82961 10.1371/journal.pone.0082961 24340069 96. Stadler M.B. Murr R. Burger L. Ivanek R. Lienert F. Schöler A. van Nimwegen E. Wirbelauer C. Oakeley E.J. Gaidatzis D. DNA-binding factors shape the mouse methylome at distal regulatory regions Nature 2011 480 490 495 10.1038/nature10716 22170606 97. Ando M. Saito Y. Xu G. Bui N.Q. Medetgul-Ernar K. Pu M. Fisch K. Ren S. Sakai A. Fukusumi T. Chromatin dysregulation and DNA methylation at transcription start sites associated with transcriptional repression in cancers Nat. Commun. 2019 10 2188 10.1038/s41467-019-09937-w 31097695 98. Miranda T.B. Jones P.A. DNA methylation: The nuts and bolts of repression J. Cell Physiol. 2007 213 384 390 10.1002/jcp.21224 17708532 99. Allfrey V.G. Faulkner R. Mirsky A.E. Acetylation and methylation of histones and their possible role in the regulation of RNA synthesis Proc. Natl. Acad. Sci. USA 1964 51 786 794 10.1073/pnas.51.5.786 14172992 100. Krajewski W.A. Becker P.B. Reconstitution of hyperacetylated, DNase I-sensitive chromatin characterized by high conformational flexibility of nucleosomal DNA Proc. Natl. Acad. Sci. USA 1998 95 1540 1545 10.1073/pnas.95.4.1540 9465051 101. Hebbes T.R. Clayton A.L. Thorne A.W. Crane-Robinson C. Core histone hyperacetylation co-maps with generalized DNase I sensitivity in the chicken beta-globin chromosomal domain EMBO J. 1994 13 1823 1830 10.1002/j.1460-2075.1994.tb06451.x 8168481 102. Verdone L. Agricola E. Caserta M. Mauro E.D. Histone acetylation in gene regulation Brief. Funct. Genom. 2006 5 209 221 10.1093/bfgp/ell028 16877467 103. Hodawadekar S.C. Marmorstein R. Chemistry of acetyl transfer by histone modifying enzymes: Structure, mechanism and implications for effector design Oncogene 2007 26 5528 5540 10.1038/sj.onc.1210619 17694092 104. Berndsen C.E. Albaugh B.N. Tan S. Denu J.M. Catalytic mechanism of a MYST family histone acetyltransferase Biochemistry 2007 46 623 629 10.1021/bi602513x 17223684 105. Dancy B.M. Cole P.A. Protein lysine acetylation by p300/CBP Chem. Rev. 2015 115 2419 2452 10.1021/cr500452k 25594381 106. Kim H.J. Bae S.C. Histone deacetylase inhibitors: Molecular mechanisms of action and clinical trials as anti-cancer drugs Am. J. Transl. Res. 2011 3 166 179 21416059 107. Seto E. Yoshida M. Erasers of histone acetylation: The histone deacetylase enzymes Cold Spring Harbor Perspect. Biol. 2014 6 a018713 10.1101/cshperspect.a018713 108. Wang F. Wang C. Wang J. Zou Y. Chen X. Liu T. Li Y. Zhao Y. Li Y. He B. N-acetyl lysine derivatives with zinc binding groups as novel HDAC inhibitors R. Soc. Open Sci. 2019 6 190338 10.1098/rsos.190338 31312496 109. Blander G. Guarente L. The Sir2 Family of Protein Deacetylases Annu. Rev. Biochem. 2004 73 417 435 10.1146/annurev.biochem.73.011303.073651 15189148 110. Bannister A.J. Kouzarides T. Regulation of chromatin by histone modifications Cell Res. 2011 21 381 395 10.1038/cr.2011.22 21321607 111. Rossetto D. Avvakumov N. Côté J. Histone phosphorylation: A chromatin modification involved in diverse nuclear events Epigenetics 2012 7 1098 1108 10.4161/epi.21975 22948226 112. Lau A.T.Y. Lee S.Y. Xu Y.M. Zheng D. Cho Y.Y. Zhu F. Kim H.G. Li S.Q. Zhang Z. Bode A.M. Phosphorylation of histone H2B serine 32 is linked to cell transformation J. Biol. Chem. 2011 286 26628 26637 10.1074/jbc.M110.215590 21646345 113. Choi H.S. Choi B.Y. Cho Y.Y. Mizuno H. Kang B.S. Bode A.M. Dong Z. Phosphorylation of histone H3 at serine 10 is indispensable for neoplastic cell transformation Cancer Res. 2005 65 5818 5827 10.1158/0008-5472.CAN-05-0197 15994958 114. Sawicka A. Seiser C. Histone H3 phosphorylation-a versatile chromatin modification for different occasions Biochimie 2012 94 2193 2201 10.1016/j.biochi.2012.04.018 22564826 115. Lo W.S. Trievel R.C. Rojas J.R. Duggan L. Hsu J.Y. Allis C.D. Marmorstein R. Berger S.L. Phosphorylation of Serine 10 in Histone H3 Is Functionally Linked In Vitro and In Vivo to Gcn5-Mediated Acetylation at Lysine 14 Mol. Cell 2000 5 917 926 10.1016/S1097-2765(00)80257-9 10911986 116. Thomson S. Clayton A.L. Mahadevan L.C. Independent Dynamic Regulation of Histone Phosphorylation and Acetylation during Immediate-Early Gene Induction Mol. Cell 2001 8 1231 1241 10.1016/S1097-2765(01)00404-X 11779499 117. Cheung P. Tanner K.G. Cheung W.L. Sassone-Corsi P. Denu J.M. Allis C.D. Synergistic Coupling of Histone H3 Phosphorylation and Acetylation in Response to Epidermal Growth Factor Stimulation Mol. Cell 2000 5 905 915 10.1016/S1097-2765(00)80256-7 10911985 118. Lanouette S. Mongeon V. Figeys D. Couture J.F. The functional diversity of protein lysine methylation Mol. Syst. Biol. 2014 10 724 10.1002/msb.134974 24714364 119. Jambhekar A. Dhall A. Shi Y. Roles and regulation of histone methylation in animal development Nat. Rev. Mol. Cell Biol. 2019 20 625 641 10.1038/s41580-019-0151-1 31267065 120. Rea S. Eisenhaber F. O’Carroll D. Strahl B.D. Sun Z.W. Schmid M. Opravil S. Mechtler K. Ponting C.P. Allis C.D. Regulation of chromatin structure by site-specific histone H3 methyltransferases Nature 2000 406 593 599 10.1038/35020506 10949293 121. Wang Z. Zang C. Rosenfeld J.A. Schones D.E. Barski A. Cuddapah S. Cui K. Roh T.Y. Peng W. Zhang M.Q. Combinatorial patterns of histone acetylations and methylations in the human genome Nat. Genet. 2008 40 897 903 10.1038/ng.154 18552846 122. Araki Y. Wang Z. Zang C. Wood W.H. 3rd Schones D. Cui K. Roh T.Y. Lhotsky B. Wersto R.P. Peng W. Genome-wide analysis of histone methylation reveals chromatin state-based regulation of gene transcription and function of memory CD8+ T cells Immunity 2009 30 912 925 10.1016/j.immuni.2009.05.006 19523850 123. de la Serna I.L. Ohkawa Y. Imbalzano A.N. Chromatin remodelling in mammalian differentiation: Lessons from ATP-dependent remodellers Nat. Rev. Genet. 2006 7 461 473 10.1038/nrg1882 16708073 124. Müller C. Leutz A. Chromatin remodeling in development and differentiation Curr. Opin. Genet. Dev. 2001 11 167 174 10.1016/S0959-437X(00)00175-1 11250140 125. Machida Y. Murai K. Miyake K. Iijima S. Expression of Chromatin Remodeling Factors during Neural Differentiation J. Biochem. 2001 129 43 49 10.1093/oxfordjournals.jbchem.a002834 11134956 126. Cavasin M.A. Demos-Davies K. Horn T.R. Walker L.A. Lemon D.D. Birdsey N. Weiser-Evans M.C.M. Harral J. Irwin D.C. Anwar A. Selective class I histone deacetylase inhibition suppresses hypoxia-induced cardiopulmonary remodeling through an antiproliferative mechanism Circ. Res. 2012 110 739 748 10.1161/CIRCRESAHA.111.258426 22282194 127. Galletti M. Cantoni S. Zambelli F. Valente S. Palazzini M. Manes A. Pasquinelli G. Mai A. Galiè N. Ventura C. Dissecting histone deacetylase role in pulmonary arterial smooth muscle cell proliferation and migration Biochem. Pharmacol. 2014 91 181 190 10.1016/j.bcp.2014.07.011 25063234 128. Zhao L. Chen C.N. Hajji N. Oliver E. Cotroneo E. Wharton J. Wang D. Li M. McKinsey T.A. Stenmark K.R. Histone deacetylation inhibition in pulmonary hypertension: Therapeutic potential of valproic acid and suberoylanilide hydroxamic acid Circulation 2012 126 455 467 10.1161/CIRCULATIONAHA.112.103176 22711276 129. Chen F. Li X. Aquadro E. Haigh S. Zhou J. Stepp D.W. Weintraub N.L. Barman S.A. Fulton D.J.R. Inhibition of histone deacetylase reduces transcription of NADPH oxidases and ROS production and ameliorates pulmonary arterial hypertension Free Radic. Biol. Med. 2016 99 167 178 10.1016/j.freeradbiomed.2016.08.003 27498117 130. Chen D. Yang Y. Cheng X. Fang F. Xu G. Yuan Z. Xia J. Kong H. Xie W. Wang H. Megakaryocytic Leukemia 1 Directs a Histone H3 Lysine 4 Methyltransferase Complex to Regulate Hypoxic Pulmonary Hypertension Hypertension 2015 65 821 833 10.1161/HYPERTENSIONAHA.114.04585 25646298 131. Yang Y. Cheng X. Tian W. Zhou B. Wu X. Xu H. Fang F. Fang M. Xu Y. MRTF-A steers an epigenetic complex to activate endothelin-induced pro-inflammatory transcription in vascular smooth muscle cells Nucleic Acids Res. 2014 42 10460 10472 10.1093/nar/gku776 25159611 132. Archer S.L. Marsboom G. Kim G.H. Zhang H.J. Toth P.T. Svensson E.C. Dyck J.R.B. Gomberg-Maitland M. Thébaud B. Husain A.N. Epigenetic attenuation of mitochondrial superoxide dismutase 2 in pulmonary arterial hypertension: A basis for excessive cell proliferation and a new therapeutic target Circulation 2010 121 2661 2671 10.1161/CIRCULATIONAHA.109.916098 20529999 133. Zhang L. Tang L. Wei J. Lao L. Gu W. Hu Q. Lv Y. Fu L. Du L. Extrauterine growth restriction on pulmonary vascular endothelial dysfunction in adult male rats: The role of epigenetic mechanisms J. Hypertens. 2014 32 2188 2198 10.1097/HJH.0000000000000309 25105456 134. Mathiyalagan P. Chang L. Du X.J. El-Osta A. Cardiac ventricular chambers are epigenetically distinguishable Cell Cycle 2010 9 612 617 10.4161/cc.9.3.10612 20090419 135. Bogaard H.J. Mizuno S. Al Hussaini A.A. Toldo S. Abbate A. Kraskauskas D. Kasper M. Natarajan R. Voelkel N.F. Suppression of Histone Deacetylases Worsens Right Ventricular Dysfunction after Pulmonary Artery Banding in Rats Am. J. Respir. Crit. Care Med. 2011 183 1402 1410 10.1164/rccm.201007-1106OC 21297075 136. Crick F.H. On protein synthesis Symp. Soc. Exp. Biol. 1958 12 138 163 13580867 137. Lander E.S. Initial impact of the sequencing of the human genome Nature 2011 470 187 197 10.1038/nature09792 21307931 138. Macfarlane L.A. Murphy P.R. MicroRNA: Biogenesis, Function and Role in Cancer Curr. Genom. 2010 11 537 561 10.2174/138920210793175895 139. Xiao M.S. Ai Y. Wilusz J.E. Biogenesis and Functions of Circular RNAs Come into Focus Trends Cell Biol. 2020 30 226 240 10.1016/j.tcb.2019.12.004 31973951 140. Khalil A.M. Guttman M. Huarte M. Garber M. Raj A. Morales D.R. Thomas K. Presser A. Bernstein B.E. van Oudenaarden A. Many human large intergenic noncoding RNAs associate with chromatin-modifying complexes and affect gene expression Proc. Natl. Acad. Sci. USA 2009 106 11667 11672 10.1073/pnas.0904715106 19571010 141. Pillai R.S. MicroRNA function: Multiple mechanisms for a tiny RNA? RNA N. Y. 2005 11 1753 1761 10.1261/rna.2248605 142. Lee R.C. Feinbaum R.L. Ambros V. The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14 Cell 1993 75 843 854 10.1016/0092-8674(93)90529-Y 8252621 143. Altuvia Y. Landgraf P. Lithwick G. Elefant N. Pfeffer S. Aravin A. Brownstein M.J. Tuschl T. Margalit H. Clustering and conservation patterns of human microRNAs Nucleic Acids Res. 2005 33 2697 2706 10.1093/nar/gki567 15891114 144. Denli A.M. Tops B.B.J. Plasterk R.H.A. Ketting R.F. Hannon G.J. Processing of primary microRNAs by the Microprocessor complex Nature 2004 432 231 235 10.1038/nature03049 15531879 145. Okada C. Yamashita E. Lee S.J. Shibata S. Katahira J. Nakagawa A. Yoneda Y. Tsukihara T. A high-resolution structure of the pre-microRNA nuclear export machinery Science 2009 326 1275 1279 10.1126/science.1178705 19965479 146. Bang C. Batkai S. Dangwal S. Gupta S.K. Foinquinos A. Holzmann A. Just A. Remke J. Zimmer K. Zeug A. Cardiac fibroblast-derived microRNA passenger strand-enriched exosomes mediate cardiomyocyte hypertrophy J. Clin. Investig. 2014 124 2136 2146 10.1172/JCI70577 24743145 147. Jonas S. Izaurralde E. Towards a molecular understanding of microRNA-mediated gene silencing Nat. Rev. Genet. 2015 16 421 433 10.1038/nrg3965 26077373 148. Zhang R. Jing Y. Zhang H. Niu Y. Liu C. Wang J. Zen K. Zhang C.Y. Li D. Comprehensive Evolutionary Analysis of the Major RNA-Induced Silencing Complex Members Sci. Rep. 2018 8 14189 10.1038/s41598-018-32635-4 30242207 149. Sanger H.L. Klotz G. Riesner D. Gross H.J. Kleinschmidt A.K. Viroids are single-stranded covalently closed circular RNA molecules existing as highly base-paired rod-like structures Proc. Natl. Acad. Sci. USA 1976 73 3852 3856 10.1073/pnas.73.11.3852 1069269 150. Nigro J.M. Cho K.R. Fearon E.R. Kern S.E. Ruppert J.M. Oliner J.D. Kinzler K.W. Vogelstein B. Scrambled exons Cell 1991 64 607 613 10.1016/0092-8674(91)90244-S 1991322 151. Ashwal-Fluss R. Meyer M. Pamudurti N.R. Ivanov A. Bartok O. Hanan M. Evantal N. Memczak S. Rajewsky N. Kadener S. circRNA Biogenesis Competes with Pre-mRNA Splicing Mol. Cell 2014 56 55 66 10.1016/j.molcel.2014.08.019 25242144 152. Hsiao K.Y. Sun H.S. Tsai S.J. Circular RNA – New member of noncoding RNA with novel functions Exp. Biol. Med. 2017 242 1136 1141 10.1177/1535370217708978 28485684 153. Li Z. Huang C. Bao C. Chen L. Lin M. Wang X. Zhong G. Yu B. Hu W. Dai L. Exon-intron circular RNAs regulate transcription in the nucleus Nat. Struct. Mol. Biol. 2015 22 256 264 10.1038/nsmb.2959 25664725 154. Zhang Y. Huang C. Bao C. Chen L. Lin M. Wang X. Zhong G. Yu B. Hu W. Dai L. Circular Intronic Long Noncoding RNAs Mol. Cell 2013 51 792 806 10.1016/j.molcel.2013.08.017 24035497 155. Hansen T.B. Jensen T.I. Clausen B.H. Bramsen J.B. Finsen B. Damgaard C.K. Kjems J. Natural RNA circles function as efficient microRNA sponges Nature 2013 495 384 388 10.1038/nature11993 23446346 156. Memczak S. Jens M. Elefsinioti A. Torti F. Krueger J. Rybak A. Maier L. Mackowiak S.D. Gregersen L.H. Munschauer M. Circular RNAs are a large class of animal RNAs with regulatory potency Nature 2013 495 333 338 10.1038/nature11928 23446348 157. Legnini I. Timoteo G.D. Rossi F. Morlando M. Briganti F. Sthandier O. Fatica A. Santini T. Andronache A. Wade M. Circ-ZNF609 Is a Circular RNA that Can Be Translated and Functions in Myogenesis Mol. Cell 2017 66 22 37.e9 10.1016/j.molcel.2017.02.017 28344082 158. Pamudurti N.R. Bartok O. Jens M. Ashwal-Fluss R. Stottmeister C. Ruhe L. Hanan M. Wyler E. Perez-Hernandez D. Ramberger E. Translation of CircRNAs Mol. Cell 2017 66 9 21.e7 10.1016/j.molcel.2017.02.021 28344080 159. Liang W.C. Wong W.C. Liang P.P. Shi M. Cao Y. Rao S.T. Tsui S.K.W. Waye M.M.Y. Zhang Q. Fu W.M. Translation of the circular RNA circβ-catenin promotes liver cancer cell growth through activation of the Wnt pathway Genome Biol. 2019 20 84 10.1186/s13059-019-1685-4 31027518 160. Brockdorff N. Ashworth A. Kay G.F. McCabe V.M. Norris D.P. Cooper P.J. Swift S. Rastan S. The product of the mouse Xist gene is a 15 kb inactive X-specific transcript containing no conserved ORF and located in the nucleus Cell 1992 71 515 526 10.1016/0092-8674(92)90519-I 1423610 161. Brown C.J. Hendrich D.B. Rupert J.L. Lafrenière R.G. Xing Y. Lawrence J. Willard H.F. The human XIST gene: Analysis of a 17 kb inactive X-specific RNA that contains conserved repeats and is highly localized within the nucleus Cell 1992 71 527 542 10.1016/0092-8674(92)90520-M 1423611 162. Brannan C.I. Dees E.C. Ingram R.S. Tilghman S.M. The product of the H19 gene may function as an RNA Mol. Cell. Biol. 1990 10 28 36 10.1128/MCB.10.1.28 1688465 163. Vance K.W. Ponting C.P. Transcriptional regulatory functions of nuclear long noncoding RNAs Trends Genet. 2014 30 348 355 10.1016/j.tig.2014.06.001 24974018 164. Dinger M.E. Amaral P.P. Mercer T.R. Pang K.C. Bruce S.J. Gardiner B.B. Askarian-Amiri M.E. Ru K. Soldà G. Simons C. Long noncoding RNAs in mouse embryonic stem cell pluripotency and differentiation Genome Res. 2008 18 1433 1445 10.1101/gr.078378.108 18562676 165. Maenner S. Muller M. Becker P.B. Roles of long, non-coding RNA in chromosome-wide transcription regulation: Lessons from two dosage compensation systems Biochimie 2012 94 1490 1498 10.1016/j.biochi.2011.12.026 22239950 166. Kitagawa M. Kitagawa K. Kotake Y. Niida H. Ohhata T. Cell cycle regulation by long non-coding RNAs Cell Mol. Life Sci. 2013 70 4785 4794 10.1007/s00018-013-1423-0 23880895 167. Grammatikakis I. Panda A.C. Abdelmohsen K. Gorospe M. Long noncoding RNAs(lncRNAs) and the molecular hallmarks of aging Aging (Albany N. Y.) 2014 6 992 1009 10.18632/aging.100710 168. Han P. Chang C.P. Long non-coding RNA and chromatin remodeling RNA Biol. 2015 12 1094 1098 10.1080/15476286.2015.1063770 26177256 169. Saxena A. Carninci P. Long non-coding RNA modifies chromatin: Epigenetic silencing by long non-coding RNAs BioEssays News Rev. Mol. Cell. Dev. Biol. 2011 33 830 839 10.1002/bies.201100084 170. Wang X. Arai S. Song X. Reichart D. Du K. Pascual G. Tempst P. Rosenfeld M.G. Glass C.K. Kurokawa R. Induced ncRNAs allosterically modify RNA-binding proteins in cis to inhibit transcription Nature 2008 454 126 130 10.1038/nature06992 18509338 171. Feng J. Bi C. Clark B.S. Mady R. Shah P. Kohtz J.D. The Evf-2 noncoding RNA is transcribed from the Dlx-5/6 ultraconserved region and functions as a Dlx-2 transcriptional coactivator Genes Dev. 2006 20 1470 1484 10.1101/gad.1416106 16705037 172. Xu F. Zhang J. Long non-coding RNA HOTAIR functions as miRNA sponge to promote the epithelial to mesenchymal transition in esophageal cancer Biomed. Pharmacother. 2017 90 888 896 10.1016/j.biopha.2017.03.103 28441714 173. Dhir A. Dhir S. Proudfoot N.J. Jopling C.L. Microprocessor mediates transcriptional termination of long noncoding RNA transcripts hosting microRNAs Nat. Struct. Mol. Biol. 2015 22 319 327 10.1038/nsmb.2982 25730776 174. Ogawa Y. Sun B.K. Lee J.T. Intersection of the RNA interference and X-inactivation pathways Science 2008 320 1336 1341 10.1126/science.1157676 18535243 175. Caley D.P. Pink R.C. Trujillano D. Carter D.R.F. Long noncoding RNAs, chromatin, and development Sci. World J. 2010 10 90 102 10.1100/tsw.2010.7 176. Anastasiadou E. Jacob L.S. Slack F.J. Non-coding RNA networks in cancer Nat. Rev. Cancer 2018 18 5 18 10.1038/nrc.2017.99 29170536 177. Poller W. Dimmeler S. Heymans S. Zeller T. Haas J. Karakas M. Leistner D.M. Jakob P. Nakagawa S. Blankenberg S. Non-coding RNAs in cardiovascular diseases: Diagnostic and therapeutic perspectives Eur. Heart J. 2018 39 2704 2716 10.1093/eurheartj/ehx165 28430919 178. Jiang S.D. Lu J. Deng Z.H. Li Y.S. Lei G.H. Long noncoding RNAs in osteoarthritis Joint Bone Spine 2017 84 553 556 10.1016/j.jbspin.2016.09.006 27919571 179. Tan L. Yu J.T. Hu N. Tan L. Non-coding RNAs in Alzheimer’s Disease Mol. Neurobiol. 2013 47 382 393 10.1007/s12035-012-8359-5 23054683 180. Zhou G. Chen T. Raj J.U. MicroRNAs in pulmonary arterial hypertension Am. J. Respir. Cell Mol. Biol. 2015 52 139 151 10.1165/rcmb.2014-0166TR 25192340 181. Ou M. Zhang C. Chen J. Zhao S. Cui S. Tu J. Overexpression of MicroRNA-340-5p Inhibits Pulmonary Arterial Hypertension Induced by APE by Downregulating IL-1β and IL-6 Mol. Ther. Nucleic Acids 2020 21 542 554 10.1016/j.omtn.2020.05.022 32712318 182. Le Ribeuz H. Courboulin A. Ghigna M.R. Lambert M. Hautefort A. Humbert M. Montani D. Cohen-Kaminsky S. Perros F. Antigny F. In vivo miR-138-5p inhibition alleviates monocrotaline-induced pulmonary hypertension and normalizes pulmonary KCNK3 and SLC45A3 expression Respir. Res. 2020 21 186 10.1186/s12931-020-01444-7 32678044 183. Antigny F. Hautefort A. Meloche J. Belacel-Ouari M. Manoury B. Rucker-Martin C. Péchoux C. Potus F. Nadeau V. Tremblay E. Potassium Channel Subfamily K Member 3 (KCNK3) Contributes to the Development of Pulmonary Arterial Hypertension Circulation 2016 133 1371 1385 10.1161/CIRCULATIONAHA.115.020951 26912814 184. Miao R. Liu W. Qi C. Song Y. Zhang Y. Fu Y. Liu W. Lang Y. Zhang Y. Zhang Z. MiR-18a-5p contributes to enhanced proliferation and migration of PASMCs via targeting Notch2 in pulmonary arterial hypertension Life Sci. 2020 257 117919 10.1016/j.lfs.2020.117919 32585247 185. Luo L. Xiao L. Lian G. Wang H. Xie L. miR-125a-5p inhibits glycolysis by targeting hexokinase-II to improve pulmonary arterial hypertension Aging (Albany N. Y.) 2020 12 9014 9030 10.18632/aging.103163 186. Caruso P. Dempsie Y. Stevens H.C. McDonald R.A. Long L. Lu R. White K. Mair K.M. McClure J.D. Southwood M. A Role for miR-145 in Pulmonary Arterial Hypertension Circ. Res. 2012 111 290 300 10.1161/CIRCRESAHA.112.267591 22715469 187. Grunig G. Eichstaedt C.A. Verweyen J. Durmus N. Saxer S. Krafsur G. Stenmark K. Ulrich S. Grünig E. Pylawka S. Circulating MicroRNA Markers for Pulmonary Hypertension in Supervised Exercise Intervention and Nightly Oxygen Intervention Front. Physiol. 2018 9 955 10.3389/fphys.2018.00955 30090067 188. Zhou S. Jiang H. Li M. Wu P. Sun L. Liu Y. Zhu K. Zhang B. Sun G. Cao C. Circular RNA hsa_circ_0016070 Is Associated with Pulmonary Arterial Hypertension by Promoting PASMC Proliferation. Molecular therapy Nucleic Acids 2019 18 275 284 10.1016/j.omtn.2019.08.026 31593832 189. Guo J. Zhang L. Lian L. Hao M. Chen S. Hong Y. CircATP2B4 promotes hypoxia-induced proliferation and migration of pulmonary arterial smooth muscle cells via the miR-223/ATR axis Life Sci. 2020 262 118420 10.1016/j.lfs.2020.118420 32926932 190. Su H. Xu X. Yan C. Shi Y. Hu Y. Dong L. Ying S. Ying K. Zhang R. LncRNA H19 promotes the proliferation of pulmonary artery smooth muscle cells through AT1R via sponging let-7b in monocrotaline-induced pulmonary arterial hypertension Respir. Res. 2018 19 254 10.1186/s12931-018-0956-z 30547791 191. Liu Y. Sun Z. Zhu J. Xiao B. Dong J. Li X. LncRNA-TCONS_00034812 in cell proliferation and apoptosis of pulmonary artery smooth muscle cells and its mechanism J. Cell. Physiol. 2018 233 4801 4814 10.1002/jcp.26279 29150946 192. Sun Z. Liu Y. Yu F. Xu Y. Yanli L. Liu N. Long non-coding RNA and mRNA profile analysis of metformin to reverse the pulmonary hypertension vascular remodeling induced by monocrotaline Biomed. Pharmacother. 2019 115 108933 10.1016/j.biopha.2019.108933 31060005 193. Wang H. Qin R. Cheng Y. LncRNA-Ang362 Promotes Pulmonary Arterial Hypertension by Regulating miR-221 and miR-222 Shock 2019 53 723 729 10.1097/SHK.0000000000001410 194. Wang D. Xu H. Wu B. Jiang S. Pan H. Wang R. Chen J. Long non-coding RNA MALAT1 sponges miR-124–3p.1/KLF5 to promote pulmonary vascular remodeling and cell cycle progression of pulmonary artery hypertension Int. J. Mol. Med. 2019 44 871 884 10.3892/ijmm.2019.4256 31257528 195. Cheng G. He L. Zhang Y. LincRNA-Cox2 promotes pulmonary arterial hypertension by regulating the let-7a-mediated STAT3 signaling pathway Mol. Cell. Biochem. 2020 475 239 247 10.1007/s11010-020-03877-6 32803651 196. Zehendner C.M. Valasarajan C. Werner A. Boeckel J.N. Bischoff F.C. John D. Weirick T. Glaser S.F. Rossbach O. Jaé N. Long Noncoding RNA TYKRIL Plays a Role in Pulmonary Hypertension via the p53-Mediated Regulation of PDGFRβ Am. J. Respir. Crit. Care. Med. 2020 202 1445 1457 10.1164/rccm.201910-2041OC 32634060 197. Lei S. Peng F. Li M.L. Duan W.B. Peng C.Q. Wu S.J. LncRNA-SMILR modulates RhoA/ROCK signaling by targeting miR-141 to regulate vascular remodeling in pulmonary arterial hypertension Am. J. Physiol. Heart Circ. Physiol. 2020 319 H377 H391 10.1152/ajpheart.00717.2019 32559140 198. Johnson E.K. Matkovich S.J. Nerbonne J.M. Regional Differences in mRNA and lncRNA Expression Profiles in Non-Failing Human Atria and Ventricles Sci. Rep. 2018 8 13919 10.1038/s41598-018-32154-2 30224797 199. Di Salvo T.G. Guo Y. Su Y.R. Clark T. Brittain E. Absi T. Maltais S. Hemnes A. Right ventricular long noncoding RNA expression in human heart failure Pulm. Circ. 2015 5 135 161 10.1086/679721 25992278 200. Thum T. Batkai S. MicroRNAs in right ventricular (dys)function (2013 Grover Conference series) Pulm. Circ. 2014 4 185 190 10.1086/675981 25006437 201. Qin Y. Yu Y. Dong H. Bian X. Guo X. Dong S. MicroRNA 21 inhibits left ventricular remodeling in the early phase of rat model with ischemia-reperfusion injury by suppressing cell apoptosis Int. J. Med. Sci. 2012 9 413 423 10.7150/ijms.4514 22859901 202. Chang W.T. Hsu C.H. Huang T.L. Tsai Y.C. Chiang C.Y. Chen Z.C. Shih J.Y. MicroRNA-21 is Associated with the Severity of Right Ventricular Dysfunction in Patients with Hypoxia-Induced Pulmonary Hypertension Acta. Cardiologica. Sinica. 2018 34 511 517 30449992 203. Joshi S.R. Dhagia V. Gairhe S. Edwards J.G. McMurtry I.F. Gupte S.A. MicroRNA-140 is elevated and mitofusin-1 is downregulated in the right ventricle of the Sugen5416/hypoxia/normoxia model of pulmonary arterial hypertension Am. J. Physiol. Heart Circ. Physiol. 2016 311 H689 H698 10.1152/ajpheart.00264.2016 27422986 204. da Costa Martins P.A. Salic K. Gladka M.M. Armand A.S. Leptidis S. el Azzouzi H. Hansen A. Coenen-de Roo C.J. Bierhuizen M.F. van der Nagel R. MicroRNA-199b targets the nuclear kinase Dyrk1a in an auto-amplification loop promoting calcineurin/NFAT signalling Nat. Cell Biol. 2010 12 1220 1227 10.1038/ncb2126 21102440 205. Koop A.M.C. Duygu B. Ottaviani L. Poels E. Van De Kolk K.W. Du Marchie Sarvaas G.J. Bartelds B. Lourenco A.P. Nascimento D.S. Pinto-Do-O P. Contribution of miR-199b to right ventricular remodelling due to pressure overload Eur. Heart J. 2018 39 Suppl. 1 ehy566.4929 10.1093/eurheartj/ehy566.4929 206. Connolly M. Garfield B.E. Crosby A. Morrell N.W. Wort S.J. Kemp P.R. miR-1–5p targets TGF-βR1 and is suppressed in the hypertrophying hearts of rats with pulmonary arterial hypertension PLoS ONE 2020 15 e0229409 10.1371/journal.pone.0229409 32109943 207. Batkai S. Bär C. Thum T. MicroRNAs in right ventricular remodelling Cardiovasc. Res. 2017 113 1433 1440 10.1093/cvr/cvx153 28957533 208. Cao Y. Yang Y. Wang L. Li L. Zhang J. Gao X. Dai S. Zhang Y. Guo Q. Peng Y.G. Analyses of long non-coding RNA and mRNA profiles in right ventricle myocardium of acute right heart failure in pulmonary arterial hypertension rats Biomed. Pharmacother. 2018 106 1108 1115 10.1016/j.biopha.2018.07.057 30119177 209. Liu L. An X. Li Z. Song Y. Li L. Zuo S. Liu N. Yang G. Wang H. Cheng X. The H19 long noncoding RNA is a novel negative regulator of cardiomyocyte hypertrophy Cardiovasc. Res. 2016 111 56 65 10.1093/cvr/cvw078 27084844 210. Omura J. Habbout K. Martineau S. Breuils-Bonnet S. Nadeau V. Potus F. Archer S.L. Paulin R. Provencher S. Boucherat O. Long Non-coding RNA H19 in Right Ventricular Failure associated with Pulmonary Arterial Hypertension Eur. Respir. J. 2019 54 PA5040 211. Kelly R.G. Buckingham M.E. Moorman A.F. Heart fields and cardiac morphogenesis Cold Spring Harbor Perspect. Med. 2014 4 a015750 10.1101/cshperspect.a015750