The function of LncRNA-H19 in cardiac hypertrophy.

Increasing evidence illustrated that H19, by acting as a molecular sponge or interacting with various proteins to regulate gene expression, could play an essential role in the complex network that regulates pathological hypertrophy progression, which includes intracellular calcium transition, fibrosis, angiogenesis, etc. These results indicate that H19 is a potential marker or a promising target for the treatment of CH. Nevertheless, there are still some questions to answer about the pathological mechanisms of CH. Thus, it is desirable to explore the molecular mechanisms and cellular pathways controlled by H19 in CH.

The goal of HCM therapy is to alleviate symptoms and prevent sudden death by the prohibition of competitive sports participation, septal alcohol ablation, septal myectomy, the implantation of cardioverter-defibrillators (ICDs) if needed, and cardiac transplantation [ 12 ]. With the elucidation of the underlying mechanism of pathological hypertrophy, many new perspectives for the targeted therapy of CH have been proposed. Mavacamten, named MYK-461, as an orally administered, small-molecule modulator of cardiac myosin, could selectively attenuate the activity of myosin ATPase to improve exercise capacity, left ventricular outflow tract obstruction, and health status in patients with obstructive hypertrophic cardiomyopathy [ 163 ]. Compared with most lncRNAs, H19 is a locus with a high degree of sequence conservation in mammals, which means that H19 has important functions and may be a potential therapeutic possibility as a targeting molecule in HCM. Overexpression of H19 could reduce cardiomyocyte size in response to phenylephrine [ 67 ]. Moreover, to evaluate the effect of H19 on myocardium, Viereck et al. established a cardiomyocyte-specific H19 gene therapy approach [ 68 ]. These authors used cardiomyocyte-related adeno-associated virus 9 (AAV9) as a vector and the cardiomyocyte-specific TNNT2 promoter to inhibit H19 expression in cardiomyocytes. Interestingly, echocardiography assessment showed that both murine and human H19 overexpression stall hypertrophy progression. These findings indicate that H19 is highly conserved and dysregulated in hypertrophic hearts of pigs and humans. This emphasizes that H19 is a promising therapeutic target for pathological CH. All these studies show that lncRNAs play a crucial role in the occurrence and progression of heart disease and will become a new hot spot and focus of cardiovascular basic and clinical research. Regulation of H19 expression provides a new direction for future treatment of CH. However, further research is warranted to clarify the following issues: (i) What processes regulates the H19 levels in the oncogenesis, development, and progression of CH? (ii) Accumulating data suggest that H19 is expressed in almost every human cancer [ 164 , 165 ], so could H19 lead to unpredictable toxicity and side effects during the process of influencing CH? (iii) How does H19 participate in different pathways to regulate CH? (iv) Does H19 act on both myocardial cells and fibroblasts to regulate myocardial hypertrophy? (v) What are other H19 targets involved in regulating CH? Therefore, further research is needed to understand the functions of H19 that are widely involved in cardiac homeostasis, diseases and therapeutics, but toxic effects and other side effects must be considered.

Myocardial infarction (MI) remains the leading cause of morbidity and mortality worldwide, despite significant progress in the treatment and prevention of the disease [ 152 ]. In addition to acute myocardial ischemic damage and reperfusion injury, heart failure triggered by the ensuing maladaptive ventricular remodeling can be a truly difficult issue to address [ 153 ]. Dynamic regulation of H19 post-MI is involved in multiple pathways of different cardiac cell types, including cardiomyocyte apoptosis and cardiac inflammation. Recently, aberrant expression of H19 has been detected in acute myocardial infarction (AMI) patients [ 154 ]. Intriguingly, Choong et al. observed that H19 is slowly upregulated and reaches an exceptionally high level and a significant increase in heart weight at day 4 post-MI [ 125 ]. Furthermore, the size of cardiomyocytes increased in H19-overexpressing mice at day 4 post-MI, suggesting that the overexpression of H19 indeed has an effect on cardiac hypertrophy. Further study found H19 competes with COL1A1 promoter to form the H19-YB-1 complex. The function of YB-1 as a suppressor of COL1A1 is abolished, and the expression of Col1a1 is increased and promotes the development of cardiac hypertrophy. In contrast, the study results were inconsistent with other studies, which concluded that H19 has antihypertrophic functions. Viereck et al. unraveled that H19 exerts its antihypertrophic functions by targeting the pro-hypertrophic nuclear factor of activated T cells (NFAT) signaling [ 68 ]. More recently, H19 could inhibit CYP1B1 expression in a PBX3-dependent manner to suppress cell apoptosis and promote cell proliferation, thus attenuating myocardial infarction [ 155 ]. Zhang and colleagues found that forced H19 expression could dramatically reduce myocardial infarction size, improve cardiac performance and alleviate cardiac fibrosis by mitigating myocardial apoptosis and decreasing inflammation [ 156 ]. Subsequent molecular mechanism experiments verified that H19 could function as an endogenous sponge to competitively bind to miR-22-3p to ameliorate MI-induced myocardial damage by upregulating the expression of KDM3A, which participated in left ventricular hypertrophy in response to pressure overload [ 157 ]. A potential explanation for this discrepancy is that lncRNAs can be differentially expressed in different cell types to exert distinct cell type-specific functions [ 22 , 158 ]. As a result, H19 regulates cardiac remodeling through different mechanisms, such as transcriptional regulation, and serves as a microRNA sponge to inhibit microRNA function to attenuate myocardial infarction and MI-induced myocardial damage. However, further research is required to investigate whether there are other mechanisms that link H19 and the pathological process of AMI. By genetic analysis, a recent study suggested a significant association between H19 gene variants and HCM [ 159 ], which requires validation in other large cohorts and functional studies to define the biological effect of these nucleotide changes. In addition, CH is also accompanied by changes in metabolism [ 160 ], oxidative stress [ 161 ], mitochondrial homeostasis [ 162 ], etc. However, whether H19 regulates these processes is still largely unknown, and the mechanism needs to be further elucidated.

Hypertrophic cardiomyopathy (HCM) is a common inherited disease characterized by an increase in the thickness of the ventricular wall (≥ 1.5 cm) in the absence of increased afterload, and it is recognized as an important cause of sudden cardiac death among young adults and competitive athletes [ 1 ]. In recent years, abundant data have revealed that HCM occurs at a rate of approximately 1/500 in the general population [ 2 ], but other data indicate a prevalence of HCM and genetic carriers of 1/200 [ 3 ]. Cardiac hypertrophy (CH), characterized by an increase in cardiomyocyte size, rather than an increase in their number, is initially a compensatory response to cope with biomechanical stresses and facilitate the maintenance of proper cardiac output and homeostasis [ 4 , 5 ]. CH has been categorized as either pathological or physiological hypertrophy. Physiological CH is generally caused by normal growth, pregnancy, or exercise. Pathological CH is the heart’s maladaptive reaction to various pathological stimuli, such as high blood pressure, myocardial infarction, and many more [ 6 ]. Pathological CH is related to myocardial fibrosis, calcium (Ca 2+ ) dysregulation, increased inflammatory cytokine, and epigenetic changes, which lead to maladaptive cardiac remodeling, heart failure (HF), and death [ 7 , 8 ]. The progression of both physiological and pathological hypertrophy depends on upstream stimuli and signaling mechanisms rather than cardiac stress [ 9 – 11 ]. The current efficiency of CH treatment is improving rapidly, but the mortality rate of HF remains at approximately 50% 5 years after diagnosis [ 12 ]. Therefore, identifying the fundamental molecular mechanisms underlying CH is a vital challenge for HF treatment. In the past decade, numerous studies have found that some regulatory mechanisms, including cellular metabolism [ 13 ], proliferation [ 6 ], miRNAs [ 14 – 16 ], immune responses [ 17 , 18 ], translational regulation [ 19 ], and epigenetic modifications [ 20 , 21 ], positively or negatively regulate CH. Global transcriptome analyses have identified a few lncRNAs that are critically involved in CH [ 22 – 24 ]. Recently, long noncoding RNAs (lncRNAs), which are more than 200 nucleotides in length and lack protein-coding capacity [ 25 ], have been shown to be involved in many cellular processes and the development of various diseases [ 26 , 27 ]. By interacting with RNA, DNA and proteins, lncRNAs can regulate the expression of genes involved in many biological activities [ 28 , 29 ], such as RNA processing [ 30 ], apoptosis [ 31 ], genome rearrangement and chromatin modification [ 32 , 33 ], and competing endogenous RNAs (ceRNAs) [ 34 , 35 ], at multiple levels. Therefore, lncRNAs are dynamically expressed in a range of differentiation processes, including those of embryonic stem cells [ 36 , 37 ], vascular smooth muscle cells [ 38 ], muscles [ 39 ], T cells [ 40 ], breast tissues [ 41 ] and neurons [ 42 ], as well as in cancer [ 42 , 43 ] and other diseases [ 44 , 45 ]. Moreover, many studies have shown that lncRNAs are important regulators in many pathophysiological processes of heart development and diseases [ 22 , 46 , 47 ], such as cardiac organogenesis [ 48 ], atherosclerosis [ 49 – 51 ], hypertension [ 38 , 52 , 53 ], pulmonary arterial hypertension [ 54 ], coronary artery disease [ 55 , 56 ], ischemia/reperfusion-induced apoptosis [ 57 ], HF [ 58 ], and CH (Table  1 ). All these results suggest that lncRNAs play a central role in the occurrence of human diseases, including cardiovascular diseases. Table 1 Anti- and pro-hypertrophic lncRNAs and their regulated genes LncRNA Regulated genes References Anti-hypertrophic lncRNAs  Plscr4 miR-214‐Mfn2 Lv et al. [ 59 ]  Ahit SUZ12/PRC2-MEF2A Yu et al. [ 60 ]  Uc.323 EZH2-CPT1b Sun et al. [ 61 ]  TINCR EZH2- CaMKII Cai et al. [ 62 ]  XIST miR-330-3p/S100B Chen et al. [ 63 ]  SNHG1 miR-15a-5p/HMGA1 Yan et al. [ 64 ]  Mhrt miR-145a‐5p/KLF4/myocardin Xu et al. [ 65 ]  Mhrt Brg1 Han et al. [ 66 ]  H19 miR-675/CaMKIId Liu et al. [ 67 ]  H19 PCR2- NFAT Viereck et al. [ 68 ]  HOTAIR miRi19/PTEN Lai et al. [ 69 ]  MAGI1-IT1 miR-302e/DKK1/Wnt/β-catenin Zhang et al. [ 70 ]  TUG1 miR-29b-3p Zou et al. [ 71 ]  Kcnq1ot1 miR-30e-5p/ADAM9 Wang et al. [ 72 ]   AK045171 SP1/MG53 Xu et al. [ 73 ] Pro-hypertrophic lncRNAs  Chaer PRC2 Wang et al. [ 21 ]  Chast Plekhm1 Viereck et al. [ 74 ]  MEG3 miR-361-5p/HDAC9 Zhang et al. [ 75 ]  DACH1 SERCA2a Frey et al. [ 76 ]  XIST miR-101/TLR2 Xiao et al. [ 77 ]  CHRF miR-489/ ;Myd88/NF-κB Wang et al. [ 78 ]  CHRF miR-93/Akt3 Wo et al. [ 79 ]  SYNE1-AS1 miR-525-5p/SP1 Wang et al. [ 80 ]  CASC15 miR-432-5p/TLR4 ;axis Li et al. [ 81 ]  MIAT miR1505p/P300 Li et al. [ 82 ]  SNHG14 miR-322‐5p/miR‐384‐5p/PCDH17 Long et al. [ 83 ]  SNHG16 miR-182-5p/IGF1 Wang et al. [ 84 ]  CASC15 miR-432-5p/TLR4 Li et al. [ 81 ]  PEG10 PEG10 Wen et al. [ 85 ]  ROR miR-133 Jiang et al. [ 86 ] The evidence described above indicates that a large number of lncRNAs are positively or negatively correlated with CH. These lncRNAs participate in complex networks in the pathological process of CH by interacting with contractile protein expression, calcium processing, and mitochondrial function. Among these lncRNAs, lncRNA H19 (hereafter called H19) has attracted our great interest Anti- and pro-hypertrophic lncRNAs and their regulated genes The evidence described above indicates that a large number of lncRNAs are positively or negatively correlated with CH. These lncRNAs participate in complex networks in the pathological process of CH by interacting with contractile protein expression, calcium processing, and mitochondrial function. Among these lncRNAs, lncRNA H19 (hereafter called H19) has attracted our great interest H19, which is a maternally expressed and paternally imprinted 2.7-kb gene, is localized near the telomeric region of chromosome 11p15.5 and is reciprocally imprinted and regulated with its neighboring gene, insulin-like growth factor 2 (IGF2) [ 28 , 87 , 88 ]. H19 is highly evolutionarily conserved, suggesting that it may have some crucial biological functions [ 89 ]. Intriguingly, H19 is most highly expressed in skeletal muscle and exhibits an ~ tenfold enrichment in cardiac tissue over all other mouse tissues (such as brain, lung, kidney, and many more) [ 68 ]. Emerging evidence shows that diverse cells, such as hematopoietic stem cells [ 90 ] and neurons [ 91 , 92 ], and cellular processes, including abdominal aortic aneurysm [ 93 ], diabetic nephropathy [ 94 ], hepatocyte proliferation [ 95 , 96 ], tumorigenesis [ 97 , 98 ], acute promyelocytic leukemia [ 99 ], ulcerative colitis [ 100 ], senescence [ 101 ], and endometriosis [ 102 ], are regulated by H19. Moreover, accumulating evidence indicates that H19 is a powerful regulator of cardiac development and pathophysiology, such as endothelial aging [ 103 ], mineralization of aortic valves [ 104 ], ischemia/reperfusion injury [ 105 , 106 ], and atherosclerosis [ 107 ]. All these studies show that H19 plays a crucial role in the occurrence and development of heart disease and will become a new hot spot and focus of cardiovascular basic and clinical research. H19 expression is dynamically regulated, and it is involved in multiple pathways of different cardiac cell types to exert distinct cell type-specific effects. In different stages of CH, H19 expression is different. During the process of heart maturation after birth and with age, the expression of H19 gradually decreases [ 67 ] but increases within 2 weeks after transverse aortic constriction (TAC, a surgical procedure that induces CH) in a mouse model [ 67 , 108 ]. Nonetheless, H19 expression was significantly decreased during the progression from the compensated stage to the decompensated stage of HF (4–6 weeks after TAC) and remained low until the experimental endpoint 13 weeks after TAC [ 68 ]. Of note, due to differences in mean age between patients with diseased and healthy hearts, lower levels of H19 expression in human heart tissues may be partially attributed to an age-related reduction. During the pathogenesis of CH, intracellular signals, such as calcium regulation, are regulated to promote the translocation of the hypertrophy-related transcription factor NFAT to regulate the expression of downstream hypertrophy genes. These signals promote myocardial fibrosis and CH. The long-term presence of stress promotes angiogenesis, inflammation, and then apoptosis, ultimately leading to heart failure. Numerous investigations have shown that H19 is involved in some of these pathophysiologies. Herein, we summarized the current studies on H19 in CH-related pathophysiological processes (Fig.  1 ) to explain the potential therapeutic value of H19 in HCM and provide a basis for further investigation. Fig. 1 The role of H19 and its targets in CH-related pathophysiological processes and the potential mechanisms. AMPK adenosine 5′-monophosphate (AMP)-activated protein kinase, CaMKIIδ Ca 2+ /calmodulin-dependent protein kinase IIδ, CN calcineurin, CTGF connective tissue growth factor, DUSP5 dual-specificity phosphatase 5, E2F1 E2F transcription factor 1, EZH2 enhancer of zeste homolog 2, FADD fas-associated protein with death domain, HIF-1α hypoxia-inducible factor 1α, ICAM-1 intercellular adhesion molecule 1, JNK jun n-terminal kinases, KDM3A Lysine (K)-specific demethylase 3 A, MDM2 mouse 3T3 cell double minute 2, NFAT nuclear factor of activated T cell, PA2G4 proliferation-associated protein 2G4, PRC2 polycomb suppression complex 2, RIPK receptor-interacting serine/threonine-protein kinase 1 and 3, STAT3 signal transducer and activator of transcription 3, VCAM-1 vascular cell adhesion molecule 1, VDAC1 voltage-dependent anion channel 1,  YB-1 Y-box-binding protein-1 The role of H19 and its targets in CH-related pathophysiological processes and the potential mechanisms. AMPK adenosine 5′-monophosphate (AMP)-activated protein kinase, CaMKIIδ Ca 2+ /calmodulin-dependent protein kinase IIδ, CN calcineurin, CTGF connective tissue growth factor, DUSP5 dual-specificity phosphatase 5, E2F1 E2F transcription factor 1, EZH2 enhancer of zeste homolog 2, FADD fas-associated protein with death domain, HIF-1α hypoxia-inducible factor 1α, ICAM-1 intercellular adhesion molecule 1, JNK jun n-terminal kinases, KDM3A Lysine (K)-specific demethylase 3 A, MDM2 mouse 3T3 cell double minute 2, NFAT nuclear factor of activated T cell, PA2G4 proliferation-associated protein 2G4, PRC2 polycomb suppression complex 2, RIPK receptor-interacting serine/threonine-protein kinase 1 and 3, STAT3 signal transducer and activator of transcription 3, VCAM-1 vascular cell adhesion molecule 1, VDAC1 voltage-dependent anion channel 1,  YB-1 Y-box-binding protein-1