Beta-Catenin downregulation attenuates ischemic cardiac remodeling through enhanced resident precursor cell differentiation

Evaluation of the Canonical Wnt Signaling Pathway in the Hearts of Hypertensive Rats of Various Etiologies

Wnt/β-catenin signaling dysregulation is associated with the pathogenesis of many human diseases, including hypertension and heart disease. The aim of this study was to immunohistochemically evaluate and compare the expression of the Fzd8, WNT1, GSK-3β, and β-catenin genes in the hearts of rats with spontaneous hypertension (SHRs) and deoxycorticosterone acetate (DOCA)-salt-induced hypertension. The myocardial expression of Fzd8, WNT1, GSK-3β, and β-catenin was detected by immunohistochemistry, and the gene expression was assessed with a real-time PCR method. In SHRs, the immunoreactivity of Fzd8, WNT1, GSK-3β, and β-catenin was attenuated in comparison to that in normotensive animals. In DOCA-salt-induced hypertension, the immunoreactivity of Fzd8, WNT1, GSK-3β, and β-catenin was enhanced. In SHRs, decreases in the expression of the genes encoding Fzd8, WNT1, GSK-3β, and β-catenin were observed compared to the control group. Increased expression of the genes encoding Fzd8, WNT1, GSK-3β, and β-catenin was demonstrated in the hearts of rats with DOCA-salt-induced hypertension. Wnt signaling may play an essential role in the pathogenesis of arterial hypertension and the accompanying heart damage. The obtained results may constitute the basis for further research aimed at better understanding the role of the Wnt/β-catenin pathway in the functioning of the heart.

Wnt signaling in cardiac development and heart diseases

The Wnt signaling pathway is a fundamental cellular communication system with extensive implications in various organs including the heart. In cardiac homeostasis, it governs essential processes like cellular proliferation, differentiation, and apoptosis, ensuring the heart's structural and functional integrity from embryonic stages and throughout life. Both canonical and non-canonical Wnt signaling pathways play a critical role during embryonic heart development in a region- and stage-specific manner. Canonical Wnt signaling also plays a significant role in heart diseases such as myocardial infarction and heart failure. However, the role of non-canonical Wnt signaling in heart diseases has not been fully elucidated. Wnt5a is a major ligand that activates non-canonical Wnt pathway, and recent studies start to clarify the role of the Wnt5a signaling axis in cardiac health and disease. In this review, we will briefly summarize the previous findings on the role of Wnt signaling pathways in heart development and diseases, and then focus on the role of Wnt5a signaling in heart failure progression. The multifaceted roles of the Wnt signaling pathway highlight its therapeutic potential for various types of heart diseases.

XAV939 Improves the Prognosis of Myocardial Infarction by Blocking the Wnt/β-Catenin Signalling Pathway

Myocardial infarction (MI) is closely related to the Wnt signalling pathway, but the role of XAV939 (a Wnt/β-catenin signalling pathway blocker) in MI has not been elucidated. The purpose of this study was to explore the role of XAV939 in mouse hearts and to provide a new and feasible treatment for improving the prognosis of MI. C57BL/6 (male, 8 weeks old, 20-25 g) mice were selected for our study. The MI model was made by ligating the left anterior descending coronary artery. On day 28 after the operation, cardiac function was examined by echocardiography. Infarct size, fibrosis, and angiogenesis were individually measured by TTC assays, Masson's trichrome staining, and CD31 analysis, respectively. Apoptosis was examined by TdT-mediated dUTP nick-end labelling (TUNEL) staining. The expression of Wnt, β-catenin, caspase 3, Bax, and Bcl-2 was determined by western blotting. XAV939 successfully blocked Wnt/β-catenin signalling pathway activation in cardiomyocytes after MI by promoting the degradation of β-catenin. XAV939 suppressed fibrosis and apoptosis, promoted angiogenesis, reduced myocardial infarct size and improved cardiac function after MI. XAV939 can reduce myocardial infarct size and improve cardiac function by blocking the Wnt/β-catenin signalling pathway, which may provide a new strategy for improving the prognosis of MI.

Peptidase Inhibitor 16 Attenuates Left Ventricular Injury and Remodeling After Myocardial Infarction by Inhibiting the HDAC1-Wnt3a-β-Catenin Signaling Axis

Background Myocardial infarction (MI) is a cardiovascular disease with high morbidity and mortality. PI16 (peptidase inhibitor 16), as a secreted protein, is highly expressed in heart diseases such as heart failure. However, the functional role of PI16 in MI is unknown. This study aimed to investigate the role of PI16 after MI and its underlying mechanisms. Methods and Results PI16 levels after MI were measured by enzyme-linked immunosorbent assay and immunofluorescence staining, which showed that PI16 was upregulated in the plasma of patients with acute MI and in the infarct zone of murine hearts. PI16 gain- and loss-of-function experiments were used to investigate the potential role of PI16 after MI. In vitro, PI16 overexpression inhibited oxygen-glucose deprivation-induced apoptosis in neonatal rat cardiomyocytes, whereas knockdown of PI16 exacerbated neonatal rat cardiomyocyte apoptosis. In vivo, left anterior descending coronary artery ligation was performed on PI16 transgenic mice, PI16 knockout mice, and their littermates. PI16 transgenic mice showed decreased cardiomyocyte apoptosis at 24 hours after MI and improved left ventricular remodeling at 28 days after MI. Conversely, PI16 knockout mice showed aggravated infract size and remodeling. Mechanistically, PI16 downregulated Wnt3a (wingless-type MMTV integration site family, member 3a)/β-catenin pathways, and the antiapoptotic role of PI16 was reversed by recombinant Wnt3a in oxygen-glucose deprivation-induced neonatal rat cardiomyocytes. PI16 also inhibited HDAC1 (class I histone deacetylase) expression, and overexpression HDAC1 abolished the inhibition of apoptosis and Wnt signaling of PI16. Conclusions In summary, PI16 protects against cardiomyocyte apoptosis and left ventricular remodeling after MI through the HDAC1-Wnt3a-β-catenin axis.

WNT/β-catenin pathway is a key regulator of cardiac function and energetic metabolism

The WNT/β-catenin pathway is a master regulator of cardiac development and growth, and its activity is low in healthy adult hearts. However, even this low activity is essential for maintaining normal heart function. Acute activation of the WNT/β-catenin signaling cascade is considered to be cardioprotective after infarction through the upregulation of prosurvival genes and reprogramming of metabolism. Chronically high WNT/β-catenin pathway activity causes profibrotic and hypertrophic effects in the adult heart. New data suggest more complex functions of β-catenin in metabolic maturation of the perinatal heart, establishing an adult pattern of glucose and fatty acid utilization. Additionally, low basal activity of the WNT/β-catenin cascade maintains oxidative metabolism in the adult heart, and this pathway is reactivated by physiological or pathological stimuli to meet the higher energy needs of the heart. This review summarizes the current state of knowledge of the organization of canonical WNT signaling and its function in cardiogenesis, heart maturation, adult heart function, and remodeling. We also discuss the role of the WNT/β-catenin pathway in cardiac glucose, lipid metabolism, and mitochondrial physiology.

The role of β-catenin in cardiac diseases

The Wnt/β-catenin signaling pathway is a classical Wnt pathway that regulates the stability and nuclear localization of β-catenin and plays an important role in adult heart development and cardiac tissue homeostasis. In recent years, an increasing number of researchers have implicated the dysregulation of this signaling pathway in a variety of cardiac diseases, such as myocardial infarction, arrhythmias, arrhythmogenic cardiomyopathy, diabetic cardiomyopathies, and myocardial hypertrophy. The morbidity and mortality of cardiac diseases are increasing, which brings great challenges to clinical treatment and seriously affects patient health. Thus, understanding the biological roles of the Wnt/β-catenin pathway in these diseases may be essential for cardiac disease treatment and diagnosis to improve patient quality of life. In this review, we summarize current research on the roles of β-catenin in human cardiac diseases and potential inhibitors of Wnt/β-catenin, which may provide new strategies for cardiac disease therapies.

The effects of β-catenin on cardiomyogenesis via Islet-1 and MLIP ubiquitination

Mesenchymal stem cells (MSCs) can treat myocardial injury-related diseases by differentiating into cardiomyocytes. Islet-1 plays an essential role in cardiac maturation. We have discovered that Islet-1 plays a crucial role in the histone acetylation regulation in this process. In addition, to increase GATA4/Nkx2.5 expression, Islet-1 may bind to Gcn5 and then guide Gcn5 to the GATA4/Nkx2.5 promoters, thereby facilitating the differentiation of MSCs into cardiomyocytes. Islet-1 is an important factor in the maturation of the heart. We have previously found that the pivotal factor in histone acetylation regulation in this process is Islet-1. Furthermore, Islet-1 and Gcn5 may boost GATA4/Nkx2.5 expression, which in turn promotes cardiomyocyte differentiation from MSCs. But the molecular mechanism of Islet-1 binding to GCN5 has not been elucidated. In this study, we found that the competitive binding relationship between Islet-1 and MLIP and GCN5 affected myocardial differentiation. The key enzymes of ubiquitination modification of MLIP and Islet-1 are UBE3C and WWP1, respectively. When short hairpin RNA (shRNA) was used to inhibit β-catenin expression, we found that the expression of UBE3C was upregulated, modifying MLIP ubiquitination and reducing its expression, and it upregulated Islet-1 by inhibiting the expression of WWP1. By using the chromatin immunoprecipitation (ChIP) and luciferase reporter system, we found that when MLIP binds to Islet-1, it significantly inhibits the transcriptional activity of Islet-1. In summary, our results show that decreasing β-catenin regulates the ubiquitination of Islet-1 and MLIP, affecting their expression, reducing the amount of Islet-1 binding to MLIP, and increasing the amount of binding to GCN5 in the nucleus. Therefore, the transcriptional activity of Islet-1 is significantly activated, inducing C3H10T1/2 cells to differentiate into myocytes. Further knowledge of biochemical pathways, including molecular signaling pathways, can provide more insights into the myocardial differentiation mechanism of MSCs.

Huoxin pill prevents excessive inflammation and cardiac dysfunction following myocardial infarction by inhibiting adverse Wnt/β‑catenin signaling activation

BACKGROUND

Myocardial infarction (MI) is the most common cause of cardiac injury, resulting in widespread and irreversible damage to the heart. The incidence of MI gives rise to the excessive production of inflammatory cytokines that further promotes myocardial dysfunction. Wnt/β-catenin signaling pathway is adversely activated during MI and plays an important role in the modulation of the inflammatory response following tissue injury. Huoxin pill (HXP) is a Traditional Chinese Medicine formulation that has been long used in the treatment of cardiovascular diseases, however its mechanisms of cardioprotection remain unclear.

METHODS

We performed murine models of MI in order to model myocardial ischemic damage and examine the effect and underlying mechanism of HXP in protecting against myocardial ischemic injury. We further constructed conditional cardiomyocyte-specific β-catenin knockout mice and induced surgical MI in order to better understand the role of Wnt/β-catenin signaling following myocardial infarction in the adult heart.

RESULTS

HXP administration strongly protected against cardiac ischemic injury, improved cardiac function, and markedly decreased the expression of pro-inflammatory cytokines following MI. Nuclear activation of β‑catenin resulted in significantly increased nuclear translocation and activation of NF-κB. In contrast, cardiomyocyte-specific deletion of β-catenin decreased NF-κB activation and exhibited beneficial effects following ischemic injury. Hence, HXP protected against MI-induced ischemic injury and excessive inflammatory response via inhibiting Wnt/β‑catenin signaling.

CONCLUSIONS

Our study elucidated the role of HXP in protecting against ischemic myocardial injury via preventing MI-induced inflammatory response, which was mediated by its ability to inhibit adverse Wnt/β‑catenin signaling activation. Thus, our study provides the basis for the implementation of HXP as an effective therapeutic strategy in protecting against myocardial ischemic diseases.

Wnt Signaling in Heart Development and Regeneration

PURPOSE OF REVIEW

Cardiovascular diseases are the leading cause of death worldwide, largely due to the limited regenerative capacity of the adult human heart. In contrast, teleost zebrafish hearts possess natural regeneration capacity by proliferation of pre-existing cardiomyocytes after injury. Hearts of mice can regenerate if injured in a few days after birth, which coincides with the transient capacity for cardiomyocyte proliferation. This review tends to elaborate the roles and mechanisms of Wnt/β-catenin signaling in heart development and regeneration in mammals and non-mammalian vertebrates.

RECENT FINDINGS

Studies in zebrafish, mice, and human embryonic stem cells demonstrate the binary effect for Wnt/β-catenin signaling during heart development. Both Wnts and Wnt antagonists are induced in multiple cell types during cardiac development and injury repair. In this review, we summarize composites of the Wnt signaling pathway and their different action routes, followed by the discussion of their involvements in cardiac specification, proliferation, and patterning. We provide overviews about canonical and non-canonical Wnt activity during heart homeostasis, remodeling, and regeneration. Wnt/β-catenin signaling exhibits biphasic and antagonistic effects on cardiac specification and differentiation depending on the stage of embryogenesis. Inhibition of Wnt signaling is beneficial for cardiac wound healing and functional recovery after injury. Understanding of the roles and mechanisms of Wnt signaling pathway in injured animal hearts will contribute to the development of potential therapeutics for human diseased hearts.

Recent Advances in Small Molecule Stimulation of Regeneration and Repair

Therapeutic approaches to stimulate regeneration and repair have the potential to transform healthcare and improve outcomes for patients suffering from numerous chronic degenerative diseases. To date most approaches have involved the transplantation of therapeutic cells, and while there have been a small number of clinical approvals, major hurdles exist to the routine adoption of such therapies. In recent years humans and other mammals have been shown to possess a regenerative capacity across multiple tissues and organs, and an innate regenerative and repair response has been shown to be activated in these organs in response to injury. These realisations have inspired a transformative approach in regenerative medicine: the development of new agents to directly target these innate regeneration and repair pathways. In this article we will review the current state of the art in the discovery of small molecule modulators of regeneration and their translation towards therapeutic agents, focussing specifically on the areas of neuroregeneration and cardiac regeneration.

Identification of IL-6 as a potential mediator of the myocardial fibrosis that occurs in response to surgery with cardiopulmonary bypass in children with Tetralogy of Fallot

BACKGROUND

Tetralogy of Fallot is a common CHD. Studies have shown a close link between heart failure and myocardial fibrosis. Interleukin-6 has been suggested to be a post-independent factor of heart failure. This study aimed to explore the relationship between IL-6 and myocardial fibrosis during cardiopulmonary bypass.

MATERIAL AND METHODS

We downloaded the expression profile dataset GSE132176 from Gene Expression Omnibus. After normalising the raw data, Gene Set Enrichment Analysis and differential gene expression analysis were performed using R. Further, a weighted gene correlation network analysis and a protein-protein interaction network analysis were used to identify HUB genes. Finally, we downloaded single-cell expression data for HUB genes using PanglaoDB.

RESULTS

There were 119 differentially expressed genes in right atrium tissues comparing the post-CPB group with the pre-CPB group. IL-6 was found to be significantly up-regulated in the post-CPB group. Six genes (JUN, FOS, ATF3, EGR1, IL-6, and PTGS2) were identified as HUB genes by a weighted gene correlation network analysis and a protein-protein interaction network analysis. Gene Set Enrichment Analysis showed that IL-6 affects the myocardium during CPB mainly through the JAK/STAT signalling pathway. Finally, we used PanglaoDB data to analyse the single-cell expression of the HUB genes.

CONCLUSION

Our findings suggest that high expression of IL-6 and the activation of the JAK/STAT signalling pathway during CPB maybe the potential mechanism of myocardial fibrosis. We speculate that the high expression of IL-6 might be an important factor leading to heart failure after ToF surgery. We expect that these findings will provide a basis for the development of targeted drugs.

Targeting cardiomyocyte proliferation as a key approach of promoting heart repair after injury

Cardiovascular diseases such as myocardial infarction (MI) is a major contributor to human mortality and morbidity. The mammalian adult heart almost loses its plasticity to appreciably regenerate new cardiomyocytes after injuries, such as MI and heart failure. The neonatal heart exhibits robust proliferative capacity when exposed to varying forms of myocardial damage. The ability of the neonatal heart to repair the injury and prevent pathological left ventricular remodeling leads to preserved or improved cardiac function. Therefore, promoting cardiomyocyte proliferation after injuries to reinitiate the process of cardiomyocyte regeneration, and suppress heart failure and other serious cardiovascular problems have become the primary goal of many researchers. Here, we review recent studies in this field and summarize the factors that act upon the proliferation of cardiomyocytes and cardiac repair after injury and discuss the new possibilities for potential clinical treatment strategies for cardiovascular diseases.

Cardiomyocyte-specific deletion of β-catenin protects mouse hearts from ventricular arrhythmias after myocardial infarction

Wnt/β-catenin signaling is activated in the heart after myocardial infarction (MI). This study aims to investigate if β-catenin deletion affects post-MI ion channel gene alterations and ventricular tachycardias (VT). MI was induced by permanent ligation of left anterior descending artery in wild-type (WT) and cardiomyocyte-specific β-catenin knockout (KO) mice. KO mice showed reduced susceptibility to VT (18% vs. 77% in WT) at 8 weeks after MI, associated with reduced scar size and attenuated chamber dilation. qPCR analyses of both myocardial tissues and purified cardiomyocytes demonstrated upregulation of Wnt pathway genes in border and infarct regions after MI, including Wnt ligands (such as Wnt4) and receptors (such as Fzd1 and Fzd2). At 1 week after MI, cardiac sodium channel gene (Scn5a) transcript was reduced in WT but not in KO hearts, consistent with previous studies showing Scn5a inhibition by Wnt/β-catenin signaling. At 8 weeks after MI when Wnt genes have declined, Scn5a returned to near sham levels and K⁺ channel gene downregulations were not different between WT and KO mice. This study demonstrated that VT susceptibility in the chronic phase after MI is reduced in mice with cardiomyocyte-specific β-catenin deletion primarily through attenuated structural remodeling, but not ion channel gene alterations.

Wnt/β-Catenin Antagonist Pyrvinium Exerts Cardioprotective Effects in Polymicrobial Sepsis Model by Attenuating Calcium Dyshomeostasis and Mitochondrial Dysfunction

Calcium dysregulation and mitochondrial dysfunction are key elements in the development of sepsis-induced cardiac dysfunction. Evidences have suggested that inhibition of Wnt/β-Catenin signalling prevents cardiac dysfunction and remodelling in surgical, hypertension and pressure overload models. The present study investigated the effects of Wnt/β-Catenin inhibitor on calcium overload and mitochondrial dysfunction in rat sepsis model of cardiomyopathy. Induction of sepsis by cecal ligation puncture (CLP) resulted in the up-regulation of cardiac β-catenin transcriptional levels and cardiac dysfunction depicted by increased serum lactate dehydrogenase, CK-MB levels reduced maximum (dp/dt max.) and minimum developed pressure (dp/dt min.), increased LVEsDP and relaxation constant tau values. Moreover, oxidative and inflammatory stress, immune cell infiltration, increased myeloperoxidase activity, enhanced caspase-3 activity and fibronectin protein levels were observed in septic rat's heart. Also, septic rat's heart displayed mitochondrial dysfunction due to mPTP opening, increased calcium up-regulation in left ventricular apex tissues and whole heart, increased collagen staining, necrosis and structural damage. Pre-treatment with Wnt/β-Catenin antagonist attenuated sepsis-induced serum and tissue biochemical changes, cardiac dysfunction and structural alterations by inhibiting mitochondrial mPTP opening and restricting calcium overloading in cardiac tissue.

LRP5 Regulates HIF-1α Stability via Interaction with PHD2 in Ischemic Myocardium

Low-density lipoprotein receptor-related protein 5 (LRP5) has been studied as a co-receptor for Wnt/β-catenin signaling. However, its role in the ischemic myocardium is largely unknown. Here, we show that LRP5 may act as a negative regulator of ischemic heart injury via its interaction with prolyl hydroxylase 2 (PHD2), resulting in hypoxia-inducible factor-1α (HIF-1α) degradation. Overexpression of LRP5 in cardiomyocytes promoted hypoxia-induced apoptotic cell death, whereas LRP5-silenced cardiomyocytes were protected from hypoxic insult. Gene expression analysis (mRNA-seq) demonstrated that overexpression of LRP5 limited the expression of HIF-1α target genes. LRP5 promoted HIF-1α degradation, as evidenced by the increased hydroxylation and shorter stability of HIF-1α under hypoxic conditions through the interaction between LRP5 and PHD2. Moreover, the specific phosphorylation of LRP5 at T1492 and S1503 is responsible for enhancing the hydroxylation activity of PHD2, resulting in HIF-1α degradation, which is independent of Wnt/β-catenin signaling. Importantly, direct myocardial delivery of adenoviral constructs, silencing LRP5 in vivo, significantly improved cardiac function in infarcted rat hearts, suggesting the potential value of LRP5 as a new target for ischemic injury treatment.

Wnt Signaling Plays a Key Role in the Regulation of the Immune Response and Cardiac Damage during Trypanosoma cruzi Infection

Chagas cardiomyopathy is the consequence of a compromised electrical and mechanical cardiac function, with parasite persistence, unbalanced inflammation, and pathological tissue remodelling, being intricately related to myocardial aggression and impaired function. Recent studies have shown that Wnt signaling pathways play a critical role in the pathogenesis of cardiac and vascular diseases. In addition, we have reported that Trypanosoma cruzi infection activates Wnt signaling to promote intracellular replication of the parasites in macrophages, with the treatment of mice with IWP-L6 (an inhibitor of the O-acyl-transferase, PORCN, responsible for the post-translational modifications necessary for Wnt protein secretion) being able to diminish parasitemia and tissue parasitism. Here, we show that inhibition of Wnt signaling during the acute phase of T. cruzi infection controls the parasite replication, inhibits the development of parasite-prone and fibrosis-prone Th2-type immune response, and prevents the development of cardiac abnormalities characteristics of chronic Chagas disease. Our results suggest that the Wnt signaling pathway might be a potential target to prevent the development of T. cruzi-induced cardiomyopathy.

Pygo1 regulates pathological cardiac hypertrophy via a β-catenin-dependent mechanism

Wnt/β-catenin signaling plays a key role in pathological cardiac remodeling in adults. The identification of a tissue-specific Wnt/β-catenin interaction factor may provide a tissue-specific clinical targeting strategy. Drosophila Pygo encodes the core interaction factor of Wnt/β-catenin. Two Pygo homologs (Pygo1 and Pygo2) have been identified in mammals. Different from the ubiquitous expression profile of Pygo2, Pygo1 is enriched in cardiac tissue. However, the role of Pygo1 in mammalian cardiac disease is yet to be elucidated. In this study, we found that Pygo1 was upregulated in human cardiac tissues with pathological hypertrophy. Cardiac-specific overexpression of Pygo1 in mice spontaneously led to cardiac hypertrophy accompanied by declined cardiac function, increased heart weight/body weight and heart weight/tibial length ratios, and increased cell size. The canonical β-catenin/T-cell transcription factor 4 (TCF4) complex was abundant in Pygo1-overexpressing transgenic (Pygo1-TG) cardiac tissue, and the downstream genes of Wnt signaling, that is, Axin2, Ephb3, and c-Myc, were upregulated. A tail vein injection of β-catenin inhibitor effectively rescued the phenotype of cardiac failure and pathological myocardial remodeling in Pygo1-TG mice. Furthermore, in vivo downregulated pygo1 during cardiac hypertrophic condition antagonized agonist-induced cardiac hypertrophy. Therefore, our study is the first to present in vivo evidence demonstrating that Pygo1 regulates pathological cardiac hypertrophy in a canonical Wnt/β-catenin-dependent manner, which may provide new clues for tissue-specific clinical treatment via targeting this pathway.NEW & NOTEWORTHY In this study, we found that Pygo1 is associated with human pathological hypertrophy. Cardiac-specific overexpression of Pygo1 in mice spontaneously led to cardiac hypertrophy. Meanwhile, cardiac function was improved when expression of Pygo1 was interfered in hypertrophy-model mice. Our study is the first to present in vivo evidence demonstrating that Pygo1 regulates pathological cardiac hypertrophy in a canonical Wnt/β-catenin-dependent manner, which may provide new clues for a tissue-specific clinical treatment targeting this pathway.

Discovering small molecules as Wnt inhibitors that promote heart regeneration and injury repair

There are intense interests in discovering proregenerative medicine leads that can promote cardiac differentiation and regeneration, as well as repair damaged heart tissues. We have combined zebrafish embryo-based screens with cardiomyogenesis assays to discover selective small molecules that modulate heart development and regeneration with minimal adverse effects. Two related compounds with novel structures, named as Cardiomogen 1 and 2 (CDMG1 and CDMG2), were identified for their capacity to promote myocardial hyperplasia through expansion of the cardiac progenitor cell population. We find that Cardiomogen acts as a Wnt inhibitor by targeting β-catenin and reducing Tcf/Lef-mediated transcription in cultured cells. CDMG treatment of amputated zebrafish hearts reduces nuclear β-catenin in injured heart tissue, increases cardiomyocyte (CM) proliferation, and expedites wound healing, thus accelerating cardiac muscle regeneration. Importantly, Cardiomogen can alleviate the functional deterioration of mammalian hearts after myocardial infarction. Injured hearts exposed to CDMG1 display increased newly formed CMs and reduced fibrotic scar tissue, which are in part attributable to the β-catenin reduction. Our findings indicate Cardiomogen as a Wnt inhibitor in enhancing injury-induced CM proliferation and heart regeneration, highlighting the values of embryo-based small molecule screens in discovery of effective and safe medicine leads.

Effect of Interventions in WNT Signaling on Healing of Cardiac Injury: A Systematic Review

The wound healing that follows myocardial infarction is a complex process involving multiple mechanisms, such as inflammation, angiogenesis and fibrosis. In the last two decades, the involvement of WNT signaling has been extensively studied and effects on virtually all aspects of this wound healing have been reported. However, as often is the case in a newly emerging field, inconsistent and sometimes even contradictory findings have been reported. The aim of this systematic review is to provide a comprehensive overview of studies in which the effect of interventions in WNT signaling were investigated in in vivo models of cardiac injury. To this end, we used different search engines to perform a systematic search of the literature using the key words "WNT and myocardial and infarction". We categorized the interventions according to their place in the WNT signaling pathway (ligand, receptor, destruction complex or nuclear level). The most consistent improvements of the wound healing response were observed in studies in which the acylation of WNT proteins was inhibited by administering porcupine inhibitors, by inhibiting of the downstream glycogen synthase kinase-3β (GSK3β) and by intervening in the β-catenin-mediated gene transcription. Interestingly, in several of these studies, evidence was presented for activation of cardiomyocyte proliferation around the infarct area. These findings indicate that inhibition of WNT signaling can play a valuable role in the repair of cardiac injury, thereby improving cardiac function and preventing the development of heart failure.

Sfrp1 protects against acute myocardial ischemia (AMI) injury in aged mice by inhibiting the Wnt/β-catenin signaling pathway

BACKGROUND

Aged patients suffering from acute myocardial ischemia (AMI) exhibit an increased mortality rate and worse prognosis, and a more effective treatment is currently in need. In the present study, we investigated potent targets related to Wnt/β-catenin pathway deregulation for AMI injury treatment.

METHODS

In the present study, AAV-Sfrp1 was transduced into the myocardium of aged mice, and an AMI model was established in these aged mice to study the effect and molecular mechanism of Sfrp1 overexpression on AMI-induced injury.

RESULTS

The results showed that Sfrp1 was successfully overexpressed in the myocardium of aged mice and remarkably reduced Wnt/β-catenin pathway activity in aged mice after AMI, effectively reducing the degree of myocardial fibrosis, inhibiting cardiomyocyte apoptosis, and improving cardiac function. We revealed that the exogenous introduction of Sfrp1 could be considered a promising strategy for improving post-AMI injury in aged mice by inhibiting Wnt/β-catenin pathway activity.

CONCLUSIONS

In conclusion, the Wnt/β-catenin pathway potentially represents a key target in AMI in aged mice. Sfrp1 might be used as a small molecule gene therapy drug to improve heart function, reduce the degree of myocardial fibrosis, inhibit cardiomyocyte apoptosis and reduce AMI injury in aged mice by inhibiting the Wnt/β-catenin pathway, thereby effectively protecting aged hearts from AMI injury.

Expression and Function of WNT6: From Development to Disease

WNT family member 6 (WNT6) is a member of the highly conserved WNT protein family. It plays an essential role in the normal development process, not only in embryonic morphogenesis, but also in post-natal homeostasis. WNT6 functions in mice and humans. This review summarizes the current findings on the biological functions of WNT6, describing its involvement in regulating embryogenesis, decidualization, and organ development. Aberrant WNT6 signaling is related to various pathologies, such as promoting cancer development, lung tuberculosis, and kidney fibrosis and improving the symptoms of Rett syndrome (RTT). Thus, due to its various functions, WNT6 has great potential for in-depth research. This work not only describes the signaling mechanism and function of WNT6 under physiological and pathological conditions, but also provides a theoretical basis for targeted therapy.

Differentiation of Human Cardiac Atrial Appendage Stem Cells into Adult Cardiomyocytes: A Role for the Wnt Pathway?

Human cardiac stem cells isolated from atrial appendages based on aldehyde dehydrogenase activity (CASCs) can be expanded in vitro and differentiate into mature cardiomyocytes. In this study, we assess whether Wnt activation stimulates human CASC proliferation, whereas Wnt inhibition induces cardiac maturation. CASCs were cultured as described before. Conventional PCR confirmed the presence of the Frizzled receptors. Small-molecule inhibitors (IWP2, C59, XAV939, and IWR1-endo) and activator (CHIR99021) of the Wnt/β -catenin signaling pathway were applied, and the effect on β-catenin and target genes for proliferation and differentiation was assessed by Western blot and RT-qPCR. CASCs express multiple early cardiac differentiation markers and are committed toward myocardial differentiation. They express several Frizzled receptors, suggesting a role for Wnt signaling in clonogenicity, proliferation, and differentiation. Wnt activation increases total and active β-catenin levels. However, this does not affect CASC proliferation or clonogenicity. Wnt inhibition upregulated early cardiac markers but could not induce mature myocardial differentiation. When CASCs are committed toward myocardial differentiation, the Wnt pathway is active and can be modulated. However, despite its role in cardiogenesis and myocardial differentiation of pluripotent stem-cell populations, our data indicate that Wnt signaling has limited effects on CASC clonogenicity, proliferation, and differentiation.

Wnt/β-catenin in ischemic myocardium: interactions and signaling pathways as a therapeutic target

Cardiovascular disease (CVD) is still a factor of mortality in the whole world. Through canonical and noncanonical pathways and with different receptors, the Wnt/β-catenin signaling pathway plays an essential role in response to heart injuries. Wnt regulates the mobilization and proliferation of cells in endothelium and epicardium in an infarcted heart. Therefore, with its profibrotic effects as well as its antagonism with other proteins, Wnt/β-catenin signaling pathway leads to beneficial effects on fibrosis and cardiac remodeling in myocardium. In addition, Wnt increases the proliferation and differentiation of cardiac progenitors in an ischemic heart. Complex interactions and dual activity of Wnt, the changes in its expression, and mutations that can change its activity during heart development have an adverse effect on cardiac myocardium after injury. However, targeting the Wnt in myocardium with cellular and molecular pathways can be suggested to improve and repair ischemic heart. Given these challenges, in this review article, we deal with the role of Wnt/β-catenin signaling pathway as well as its interactions with other cells and molecules in an ischemic myocardium.

Contribution of Increased Expression of Yin Yang 2 to Development of Cardiomyopathy

Yin Yang 2 (YY2) is a member of the Yin Yang family of transcription factors. Although the bioactivity of YY2 has been previously studied, its role in cardiovascular diseases is not known. We observed the increased expression of YY2 in failing human hearts compared with control hearts, raising the question of whether YY2 is involved in the pathogenesis of cardiomyopathy. To investigate the potential contribution of YY2 to the development of cardiomyopathy, we crossed two independent transgenic (Tg) mouse lines, pCAG-YY2-Tg+and alpha-myosin heavy chain-cre (α-MHC-Cre), to generate two independent double transgenic (dTg) mouse lines in which the conditional cardiomyocyte-specific expression of YY2 driven by the α-MHC promoter was mediated by Cre recombinase, starting at embryonic day 9.0. In dTg mice, we observed partial embryonic lethality and hearts with defective cardiomyocyte proliferation. Surviving dTg mice from both lines developed cardiomyopathy and heart failure that occurred with aging, showing different degrees of severity that were associated with the level of transgene expression. The development of cardiomyopathy was accompanied by increased levels of cardiac disease markers, apoptosis, and cardiac fibrosis. Our studies further revealed that the Cre-mediated cardiomyocyte-specific increase in YY2 expression led to increased levels of Beclin 1 and LC3II, indicating that YY2 is involved in mediating autophagic activity in mouse hearts in vivo. Also, compared with control hearts, dTg mouse hearts showed increased JNK activity. Because autophagy and JNK activity are important for maintaining cardiac homeostasis, the dysregulation of these signaling pathways may contribute to YY2-induced cardiomyopathy and heart failure in vivo.

Ageing-related changes in the levels of β-catenin, CacyBP/SIP, galectin-3 and immunoproteasome subunit LMP7 in the heart of men

Aging is a major risk factor for morbidity and mortality from cardiovascular causes in men. To better understand the cellular processes related to age-related cardiac complications, we undertook research aimed at comparative evaluation of genes expression and distribution of β-catenin, CacyBP/SIP, galectin-3 and LMP7 in the heart of healthy men in different age groups. The study was conducted on the hearts of 12 men (organ donors) without a history of cardiovascular disease, who were divided into two age groups: men under and men over 45 years of age. On paraffin sections, immunohistochemical reactions were performed to detect β-catenin, CacyBP/SIP, galectin-3 and immunoproteasome subunit LMP7. The expression of genes coding β-catenin, CacyBP/SIP, galectin-3 and LMP7 was also evaluated by real-time PCR method. In the heart of men over 45 years old, both gene expression and immunoreactivity of β-catenin, CacyBP/SIP, galectin-3 and LMP7 were stronger compared to younger individuals. The results of the presented studies suggest that β-catenin, CacyBP/SIP, galectin-3 and immunoproteasomes might be involved in the internal regulation of heart homeostasis during ageing.

Role of Sfrps in cardiovascular disease

Secreted frizzled-related proteins (Sfrps) are a family of secreted proteins that bind extracellularly to Wnt ligands and frizzled receptors. This binding modulates the Wnt signaling cascade, and Sfrps interact with their corresponding receptors. Sfrps are thought to play an important role in the pathological mechanism of cardiac disease such as myocardial infarction, cardiac remodeling, and heart failure. However, the overall role of Sfrps in cardiac disease is unknown. Some members of the Sfrps family modulate cellular apoptosis, angiogenesis, differentiation, the inflammatory process, and cardiac remodeling. In this review, we summarize the evidence of Sfrps association with cardiac disease. We also discuss how multiple mechanisms may underlie Sfrps being involved in such diverse pathologies.

The circular RNA ZNF292 alleviates OGD-induced injury in H9c2 cells via targeting BNIP3

The research aims to explore the roles and regulatory mechanisms of the circular RNA (circRNA) ZNF292 (circZNF292) in OGD-induced damage in H9c2 cells. The H9c2 cells were treated by OGD and/or transfected with circZNF292, si-circZNF292, pc-Bcl-2/adenovirus E1B-19 kDa-interacting protein 3 (BNIP3) or corresponding controls. Cell viability was detected with the CCK-8. The protein expression levels of the Bax, caspase-3, Beclin-1, p62, LC3, BNIP3, Wnt3a, β-catenin and mammalian target of rapamycin (mTOR) were individually determined via western blot. qRT-PCR was used to examine the circZNF292 expression level. The apoptotic rate was determined by the Annexin V-FITC/PI with flow cytometer. The production of the circZNF292 was promoted by OGD. Abundant circZNF292 released OGD-induced damage by up-regulating cell viability and Wnt3a/β-catenin or mTOR proteins, but down-regulating apoptosis and autophagy. circZNF292 had an opposite effect on these elements mentioned above. Besides, BNIP3 was negatively adjusted by the circZNF292. The BNIP3 overproduction destroyed the protective effect of circZNF292 on H9c2. circZNF292 released OGD-induced damage in the H9c2 cells by targeting the BNIP3 through Wnt/β-catenin and mTOR activation.

Interventions in WNT Signaling to Induce Cardiomyocyte Proliferation: Crosstalk with Other Pathways

Myocardial infarction is a frequent cardiovascular event and a major cause for cardiomyocyte loss. In adult mammals, cardiomyocytes are traditionally considered to be terminally differentiated cells, unable to proliferate. Therefore, the wound-healing response in the infarct area typically yields scar tissue rather than newly formed cardiomyocytes. In the last decade, several lines of evidence have challenged the lack of proliferative capacity of the differentiated cardiomyocyte: studies in zebrafish and neonatal mammals have convincingly demonstrated the regenerative capacity of cardiomyocytes. Moreover, multiple signaling pathways have been identified in these models that-when activated in adult mammalian cardiomyocytes-can reactivate the cell cycle in these cells. However, cardiomyocytes frequently exit the cell cycle before symmetric division into daughter cells, leading to polyploidy and multinucleation. Now that there is more insight into the reactivation of the cell cycle machinery, other prerequisites for successful symmetric division of cardiomyocytes, such as the control of sarcomere disassembly to allow cytokinesis, require more investigation. This review aims to discuss the signaling pathways involved in cardiomyocyte proliferation, with a specific focus on wingless/int-1 protein signaling. Comparing the conflicting results from in vitro and in vivo studies on this pathway illustrates that the interaction with other cells and structures around the infarct is likely to be essential to determine the outcome of these interventions. The extensive crosstalk with other pathways implicated in cardiomyocyte proliferation calls for the identification of nodal points in the cell signaling before cardiomyocyte proliferation can be moved forward toward clinical application as a cure of cardiac disease. SIGNIFICANCE STATEMENT: Evidence is mounting that proliferation of pre-existing cardiomyocytes can be stimulated to repair injury of the heart. In this review article, an overview is provided of the different signaling pathways implicated in cardiomyocyte proliferation with emphasis on wingless/int-1 protein signaling, crosstalk between the pathways, and controversial results obtained in vitro and in vivo.

The Hippo pathway in the heart: pivotal roles in development, disease, and regeneration

The Hippo-YAP (Yes-associated protein) pathway is an evolutionarily and functionally conserved regulator of organ size and growth with crucial roles in cell proliferation, apoptosis, and differentiation. This pathway has great potential for therapeutic manipulation in different disease states and to promote organ regeneration. In this Review, we summarize findings from the past decade revealing the function and regulation of the Hippo-YAP pathway in cardiac development, growth, homeostasis, disease, and regeneration. In particular, we highlight the roles of the Hippo-YAP pathway in endogenous heart muscle renewal, including the pivotal role of the Hippo-YAP pathway in regulating cardiomyocyte proliferation and differentiation, stress response, and mechanical signalling. The human heart lacks the capacity to self-repair; therefore, the loss of cardiomyocytes after injury such as myocardial infarction can result in heart failure and death. Despite substantial advances in the treatment of heart failure, an enormous unmet clinical need exists for alternative treatment options. Targeting the Hippo-YAP pathway has tremendous potential for developing therapeutic strategies for cardiac repair and regeneration for currently intractable cardiovascular diseases such as heart failure. The lessons learned from cardiac repair and regeneration studies will also bring new insights into the regeneration of other tissues with limited regenerative capacity.

A context-specific cardiac β-catenin and GATA4 interaction influences TCF7L2 occupancy and remodels chromatin driving disease progression in the adult heart

Chromatin remodelling precedes transcriptional and structural changes in heart failure. A body of work suggests roles for the developmental Wnt signalling pathway in cardiac remodelling. Hitherto, there is no evidence supporting a direct role of Wnt nuclear components in regulating chromatin landscapes in this process. We show that transcriptionally active, nuclear, phosphorylated(p)Ser675-β-catenin and TCF7L2 are upregulated in diseased murine and human cardiac ventricles. We report that inducible cardiomyocytes (CM)-specific pSer675-β-catenin accumulation mimics the disease situation by triggering TCF7L2 expression. This enhances active chromatin, characterized by increased H3K27ac and TCF7L2 occupancies to cardiac developmental and remodelling genes in vivo. Accordingly, transcriptomic analysis of β-catenin stabilized hearts shows a strong recapitulation of cardiac developmental processes like cell cycling and cytoskeletal remodelling. Mechanistically, TCF7L2 co-occupies distal genomic regions with cardiac transcription factors NKX2–5 and GATA4 in stabilized-β-catenin hearts. Validation assays revealed a previously unrecognized function of GATA4 as a cardiac repressor of the TCF7L2/β-catenin complex in vivo, thereby defining a transcriptional switch controlling disease progression. Conversely, preventing β-catenin activation post-pressure-overload results in a downregulation of these novel TCF7L2-targets and rescues cardiac function. Thus, we present a novel role for TCF7L2/β-catenin in CMs-specific chromatin modulation, which could be exploited for manipulating the ubiquitous Wnt pathway.

Association Between AXIN1 Gene Polymorphisms and Dilated Cardiomyopathy in a Chinese Han Population

Dilated cardiomyopathy (DCM) is a common type of cardiomyopathy. The pathogenesis of DCM remains unclear and involves varied genes. AXIN1 is a crucial gene in regulating various functions in cells, it encodes protein Axin1, which regulates the assembly and disassembly of β-catenin destruction complex. In addition, Wnt/β-catenin signaling pathway plays an important role in cardiogenesis. We aimed to detect whether AXIN1 polymorphisms contribute to the susceptibility and prognosis of DCM in a Chinese Han population. A total of 340 DCM patients and 430 controls were enrolled, and patients who had complete contact information were followed up for a median period of 49 months. Polymerase chain reaction-restriction fragment length polymorphism was carried out to genotype the two AXIN1 tag single nucleotide polymorphisms (SNPs) (rs12921862 and rs1805105). All data were analyzed using the statistical software package, SPSS 21.0. The frequencies of allele A in rs12921862 and allele C in rs1805015 were increased in DCM patients compared with healthy controls (p < 0.001). Genotypic frequencies of rs12921862 and rs1805105 were associated with the susceptibility of DCM in codominant, dominant, and overdominant models (p < 0.01). AA/AC and AC genotypes of rs12921862 in the dominant and the overdominant genetic models also presented a correlation with poor prognosis of DCM in both univariate (p < 0.01) and multivariate analyses (p < 0.01) after adjusting for age, gender, left ventricular (LV) end-diastolic diameter, and LV ejection fraction. Our results suggest that AXIN1 polymorphisms are associated with the susceptibility and prognosis of DCM in a Chinese Han population.

The role of Thymosin β4 in angiotensin II-induced cardiomyocytes growth

INTRODUCTION

Thymosin beta-4 (Tβ4) is an actin sequestering protein and is furthermore involved in diverse biological processes including cell proliferation, differentiation, wound healing, stem- or progenitor cell differentiation, and modulates inflammatory mediators. Tβ4 also attenuates fibrosis. However, the role of Tβ4 in cardiomyocytes hypertrophy is unknown.

AREAS COVERED

In this review, we will discuss the role of Tβ4 in cardiac remodeling that specifically includes cardiac hypertrophy and fibrosis only. Our review will further cover a new signaling pathway, the wingless and integrated-1 (Wnt) pathway in cardiac remodeling. In rat neonatal and adult cardiomyocytes stimulated with angiotensin II (Ang II), we showed that Tβ4 has the ability to reduce cell sizes, attenuate hypertrophy marker genes expression, along with a panel of WNT-associated gene expressions induced by Ang II. Selected target gene WNT1-inducible-signaling pathway protein 1 (WISP-1) was identified by Tβ4. Data further confirmed that WISP-1 overexpression promoted cardiomyocytes growth and was reversed by Tβ4 pretreatment.

EXPERT OPINION

Our data suggested that Tβ4 protects cardiomyocytes from hypertrophic response by targeting WISP-1. The new role of Tβ4 in cardiac hypertrophy advances our understanding, and the mechanism of action of Tβ4 may provide a solid foundation for the treatment of cardiac disease.

Comparative evaluation of CacyBP/SIP protein, β-catenin, and immunoproteasome subunit LMP7 in the heart of rats with hypertension of different etiology

Calcyclin-binding protein/Siah-1-interacting protein (CacyBP/SIP) is the recently discovered peptide, which participates in various intracellular processes. Recent reports indicated that CacyBP/SIP activates the ubiquitin ligases and promotes proteasomal degradation of proteins. One of the most important proteins degraded in CacyBP/SIP-dependent pathway is β-catenin. Considering the key importance of β-catenin in the functioning of the cardiovascular system and in the view of the close relationship between CacyBP/SIP, β-catenin, and proteasomal activity, we have decided to undertake research to identify and evaluate the distribution of CacyBP/SIP, β-catenin and the LMP7 subunit of the immunoproteasome in the heart of rats with hypertension of various etiology. The studies were carried out on the hearts of rats with spontaneous hypertension (SHR), renovascular hypertension, and DOCA-salt hypertension. The myocardial expression of CacyBP/SIP, β-catenin, and LMP7 was detected by immunohistochemistry using the EnVision method. The hypertension significantly increased the immunoreactivity to CacyBP/SIP and LMP-7, while weakening the β-catenin immunoreaction. The intensity of the observed changes depends on the type of hypertension. Our results show an innovative and important network of interactions between proteins potentially involved in the development and progression of heart problems in various types of hypertension. This report might contribute to deeper understanding of the role of the CacyBP/SIP protein, β-catenin, and immunoproteasomes in heart function, as well as to bringing new information concerning pathophysiologic mechanisms leading to cardiac dysfunction in the state of elevated blood pressure.

Impact statement

Despite extensive research into the pathogenesis of hypertension and disease-related end organ damage, the mechanisms leading to cardiac complications of hypertensive patients are still not fully elucidated. The aim of the presented research was immunodetection and evaluation of CacyBP/SIP, β-catenin, and proteasomes in the hearts of rats with hypertension of different etiology. Our results show an innovative and important network of interactions between proteins potentially involved in the development and progression of heart problems in various types of hypertension. This report might contribute to deeper understanding of the role of the CacyBP/SIP protein, β-catenin, and proteasomes in heart function. Our results might also bring new information concerning the intracellular processes and signal pathways involved in the regulation of cardiomyocytes functioning in hypertension state. In addition to cognitive significance, the results of presented studies may contribute to further successes in preventing and treatment of cardiac complications associated with hypertension.

Multipoint targeting of TGF-β/Wnt transactivation circuit with microRNA 384-5p for cardiac fibrosis

Cardiac fibrosis is a common precursor to ventricular dysfunction and eventual heart failure, and cardiac fibrosis begins with cardiac fibroblast activation. Here we have demonstrated that the TGF-β signaling pathway and Wnt signaling pathway formed a transactivation circuit during cardiac fibroblast activation and that miR-384-5p is a key regulator of the transactivation circuit. The results of in vitro study indicated that TGF-β activated an auto-positive feedback loop by increasing Wnt production in cardiac fibroblasts, and Wnt neutralizing antibodies disrupted the feedback loop. Also, we demonstrated that miR-384-5p simultaneously targeted the key receptors of the TGF-β/Wnt transactivation circuit and significantly attenuated both TGF-β-induced cardiac fibroblast activation and ischemia-reperfusion-induced cardiac fibrosis. In addition, small molecule that prevented pro-fibrogenic stimulus-induced downregulation of endogenous miR-384-5p significantly suppressed cardiac fibroblast activation and cardiac fibrosis. In conclusion, modulating a key endogenous miRNA targeting multiple components of the TGF-β/Wnt transactivation circuit can be an effective means to control cardiac fibrosis and has great therapeutic potential.

At the heart of inter- and intracellular signaling: the intercalated disc

Proper cardiac function requires the synchronous mechanical and electrical coupling of individual cardiomyocytes. The intercalated disc (ID) mediates coupling of neighboring myocytes through intercellular signaling. Intercellular communication is highly regulated via intracellular signaling, and signaling pathways originating from the ID control cardiomyocyte remodeling and function. Herein, we present an overview of the inter- and intracellular signaling that occurs at and originates from the intercalated disc in normal physiology and pathophysiology. This review highlights the importance of the intercalated disc as an integrator of signaling events regulating homeostasis and stress responses in the heart and the center of several pathophysiological processes mediating the development of cardiomyopathies.

The Mingle-Mangle of Wnt Signaling and Extracellular Vesicles: Functional Implications for Heart Research

Wnt signaling is an important pathway in health and disease and a key regulator of stem cell maintenance, differentiation, and proliferation. During heart development, Wnt signaling controls specification, proliferation and differentiation of cardiovascular cells. In this regard, the role of activated Wnt signaling in cardiogenesis is well defined. However, the knowledge about signaling transmission has been challenged. Recently, the packaging of hydrophobic Wnt proteins on extracellular vesicles (EVs) has emerged as a mechanism to facilitate their extracellular spreading and their functioning as morphogens. EVs spread systemically and therefore can have pleiotropic effects on very different cell types. They are heavily studied in tumor biology where they affect tumor growth and vascularization and can serve as biomarkers in liquid biopsies. In this review we will highlight recent discoveries of factors involved in the release of Wnts on EVs and its potential implications in the communication between physiological and pathological heart cells.

Wnt inhibition promotes vascular specification of embryonic cardiac progenitors

Several studies have demonstrated a multiphasic role for Wnt signaling during embryonic cardiogenesis and developed protocols that enrich for cardiac derivatives during in vitro differentiation of human pluripotent stem cells (hPSCs). However, few studies have investigated the role of Wnt signaling in the specification of cardiac progenitor cells (CPCs) toward downstream fates. Using transgenic mice and hPSCs, we tracked endothelial cells (ECs) that originated from CPCs expressing NKX2.5. Analysis of EC-fated CPCs at discrete phenotypic milestones during hPSC differentiation identified reduced Wnt activity as a hallmark of EC specification, and the enforced activation or inhibition of Wnt reduced or increased, respectively, the degree of vascular commitment within the CPC population during both hPSC differentiation and mouse embryogenesis. Wnt5a, which has been shown to exert an inhibitory influence on Wnt signaling during cardiac development, was dynamically expressed during vascular commitment of hPSC-derived CPCs, and ectopic Wnt5a promoted vascular specification of hPSC-derived and mouse embryonic CPCs.

WNT Signaling in Cardiac and Vascular Disease

WNT signaling is an elaborate and complex collection of signal transduction pathways mediated by multiple signaling molecules. WNT signaling is critically important for developmental processes, including cell proliferation, differentiation and tissue patterning. Little WNT signaling activity is present in the cardiovascular system of healthy adults, but reactivation of the pathway is observed in many pathologies of heart and blood vessels. The high prevalence of these pathologies and their significant contribution to human disease burden has raised interest in WNT signaling as a potential target for therapeutic intervention. In this review, we first will focus on the constituents of the pathway and their regulation and the different signaling routes. Subsequently, the role of WNT signaling in cardiovascular development is addressed, followed by a detailed discussion of its involvement in vascular and cardiac disease. After highlighting the crosstalk between WNT, transforming growth factor-β and angiotensin II signaling, and the emerging role of WNT signaling in the regulation of stem cells, we provide an overview of drugs targeting the pathway at different levels. From the combined studies we conclude that, despite the sometimes conflicting experimental data, a general picture is emerging that excessive stimulation of WNT signaling adversely affects cardiovascular pathology. The rapidly increasing collection of drugs interfering at different levels of WNT signaling will allow the evaluation of therapeutic interventions in the pathway in relevant animal models of cardiovascular diseases and eventually in patients in the near future, translating the outcomes of the many preclinical studies into a clinically relevant context.

The canonical way to make a heart: β-catenin and plakoglobin in heart development and remodeling

The main mediator of the canonical Wnt pathway, β-catenin, is a major effector of embryonic development, postnatal tissue homeostasis, and adult tissue regeneration. The requirement for β-catenin in cardiogenesis and embryogenesis has been well established. However, many questions regarding the molecular mechanisms by which β-catenin and canonical Wnt signaling regulate these developmental processes remain unanswered. An interesting question that emerged from our studies concerns how β-catenin signaling is modulated through interaction with other factors. Recent experimental data implicate new players in canonical Wnt signaling, particularly those which modulate β-catenin function in many its biological processes, including cardiogenesis. One of the interesting candidates is plakoglobin, a little-studied member of the catenin family which shares several mechanistic and functional features with its close relative, β-catenin. Here we have focused on the function of β-catenin in cardiogenesis. We also summarize findings on plakoglobin signaling function and discuss possible interplays between β-catenin and plakoglobin in the regulation of embryonic heart development. Impact statement Heart development, function, and remodeling are complex processes orchestrated by multiple signaling networks. This review examines our current knowledge of the role of canonical Wnt signaling in cardiogenesis and heart remodeling, focusing primarily on the mechanistic action of its effector β-catenin. We summarize the generally accepted understanding of the field based on experimental in vitro and in vivo data, and address unresolved questions in the field, specifically relating to the role of canonical Wnt signaling in heart maturation and regeneration. What are the modulators of canonical Wnt, and particularly what are the potential roles of plakoglobin, a close relative of β-catenin, in regulating Wnt signaling?Answers to these questions will enhance our understanding of the mechanism by which the canonical Wnt signaling regulates development of the heart and its regeneration after damage.

Synergistic role of 5-azacytidine and ascorbic acid in directing cardiosphere derived cells to cardiomyocytes in vitro by downregulating Wnt signaling pathway via phosphorylation of β-catenin

Background

Cardiosphere derived cells (CDCs) represent a valuable source in stem cell based therapy for cardiovascular diseases, yet poor differentiation rate hinders the transplantation efficiency. The aim of this study is to check the ability of 5-Azacytidine (Aza) alone and in combination with ascorbic acid (Aza+AA) in delineating CDCs to cardiomyogenesis and the underlying Wnt signaling mechanism in induced differentiation.

Methods

CDCs were treated with Aza and Aza+AA for a period of 14 days to examine the expression of cardiac specific markers and Wnt downstream regulators by immunofluorescence, real time PCR and western blot.

Results

Results revealed that Aza+AA induced efficient commitment of CDCs to cardiomyogenic lineage. Immunofluorescence analysis showed significant augment for Nkx 2.5, GATA 4 and α-Sarcomeric actinin markers in Aza+AA group than control group (p = 0.0118, p = 0.009 and p = 0.0091, respectively). Relative upregulation of cardiac markers, Nkx 2.5 (p = 0.0156), GATA 4 (p = 0.0087) and down regulation of Wnt markers, β-catenin (p = 0.0107) and Cyclin D1 (p = 0. 0116) in Aza+AA group was revealed by RNA expression analysis. Moreover, the Aza+AA induced prominent expression of GATA 4, α-Sarcomeric actinin and phospho β-catenin while non phospho β-catenin and Cyclin D1 expression was significantly suppressed as displayed in protein expression analysis. Generation of spontaneous beating in Aza+AA treated CDCs further reinforced that Aza+AA accelerates the cardiomyogenic potential of CDCs.

Conclusion

Combined treatment of Aza along with AA implicit in inducing cardiomyogenic potential of CDCs and is associated with down regulating Wnt signaling pathway. Altogether, CDCs represent a valuable tool for the treatment of cardiovascular disorders.

Increased β-catenin accumulation and nuclear translocation are associated with concentric hypertrophy in cardiomyocytes

Defective Wnt/β-Catenin signaling, activated under various pathological conditions, can result in cardiac and vascular abnormalities. In the present study, the possible role of β-catenin over expression during cardiac hypertrophy was investigated. Ten samples from hearts of human patients with acute infarction, and granulation tissue from 20 patients and 10 from normal ones were collected in order to investigate roles of β-catenin in cardiac hypertrophy. H9c2 cardiomyoblast cells and Wistar rat primary neonatal cardiomyocytes were overexpressed with β-catenin. Expression levels of β-catenin protein were increased in human acute infarction tissues and rat hypertension heart tissues. Overexpression of this transcription factor induced actin filament formation and increased hypertrophic marker protein levels via MAPK pathway. In addition, β-catenin overexpression also resulted in increased elevation of NFATc3 and p-GATA4. Therefore, acute infarction resulted in β-catenin overexpression mediated hypertrophy in cardiomyocytes regulated through MAPK pathway.

The Erythropoietin System Protects the Heart Upon Injury by Cardiac Progenitor Cell Activation

Erythropoietin (EPO) is a growth hormone, widely known for its role in erythropoiesis. The broad expression of erythropoietin receptor (EPOR) in adult organs suggested that EPO may also affect other cells besides late erythroid progenitors. In the embryonic heart, EPOR is expressed in all cells including the immature proliferating cardiomyocytes. In contrast to the embryonic heart in adulthood, EPOR expression is decreased and mainly detected in immature proliferating cells (i.e., resident cardiac progenitor cells) rather than in terminally differentiated cells (i.e., cardiomyocytes). Since cardiac progenitor cells are considered a regenerative cell source upon cardiac injury, the protective action of the EPO system was tested by creating an erythroid-rescued EPOR knockout mouse model. Although these mice appear to have less immature proliferating myocytes during embryogenesis, they reach adulthood without apparent morphological defects. However, upon ischemia reperfusion, these animals show a greater infarct size, suggesting that the EPO/EPOR protects the heart upon injury. Indeed preclinical studies showed that EPO administration postinfarction improves cardiac function via neoangiogenesis, antiapoptotic mechanisms, and/or CPC activation. Despite the promising preclinical data, large cohort clinical studies in humans failed to show a significant amelioration in cardiac function upon systemic injection of EPO in patients with myocardial infarctions. The discrepancy between preclinical and clinical trials may be due to differences between the doses, the way of delivery, the homogeneity of the cohorts, and last but not least the species differences. These data pinpoint the importance of carrying out preclinical studies in human models of disease as engineered human cardiac tissue that will provide a better understanding of the expression pattern of EPOR and the role of its ligand in human cardiac cells. Such studies may be able to bridge the gap between preclinical rodent data and human clinical trials and thus lead to the design of more successful clinical studies.

Dnmt3a-mediated inhibition of Wnt in cardiac progenitor cells improves differentiation and remote remodeling after infarction

Adult cardiac progenitor cells (CPCs) display a low capacity to differentiate into cardiomyocytes in injured hearts, strongly limiting the regenerative capacity of the mammalian myocardium. To identify new mechanisms regulating CPC differentiation, we used primary and clonally expanded Sca-1+ CPCs from murine adult hearts in homotypic culture or coculture with cardiomyocytes. Expression kinetics analysis during homotypic culture differentiation showed downregulation of Wnt target genes concomitant with increased expression of the Wnt antagonist, Wnt inhibitory factor 1 (Wif1), which is necessary to stimulate CPC differentiation. We show that the expression of the Wif1 gene is repressed by DNA methylation and regulated by the de novo DNA methyltransferase Dnmt3a. In addition, miR-29a is upregulated early during CPC differentiation and downregulates Dnmt3a expression, thereby decreasing Wif1 gene methylation and increasing the efficiency of differentiation of Sca-1+ CPCs in vitro. Extending these findings in vivo, transient silencing of Dnmt3a in CPCs subsequently injected in the border zone of infarcted mouse hearts improved CPC differentiation in situ and remote cardiac remodeling. In conclusion, miR-29a and Dnmt3a epigenetically regulate CPC differentiation through Wnt inhibition. Remote effects on cardiac remodeling support paracrine signaling beyond the local injection site, with potential therapeutic interest for cardiac repair.

Calcium/Calmodulin-Dependent Protein Kinase II Activity Persists During Chronic β-Adrenoceptor Blockade in Experimental and Human Heart Failure

BACKGROUND

Considerable evidence suggests that calcium/calmodulin-dependent protein kinase II (CaMKII) overactivity plays a crucial role in the pathophysiology of heart failure (HF), a condition characterized by excessive β-adrenoceptor (β-AR) stimulation. Recent studies indicate a significant cross talk between β-AR signaling and CaMKII activation presenting CaMKII as a possible downstream mediator of detrimental β-AR signaling in HF. In this study, we investigated the effect of chronic β-AR blocker treatment on CaMKII activity in human and experimental HF.

METHODS AND RESULTS

Immunoblot analysis of myocardium from end-stage HF patients (n=12) and non-HF subjects undergoing cardiac surgery (n=12) treated with β-AR blockers revealed no difference in CaMKII activity when compared with non-β-AR blocker-treated patients. CaMKII activity was judged by analysis of CaMKII expression, autophosphorylation, and oxidation and by investigating the phosphorylation status of CaMKII downstream targets. To further evaluate these findings, CaMKIIδC transgenic mice were treated with the β1-AR blocker metoprolol (270 mg/kg*d). Metoprolol significantly reduced transgene-associated mortality (n≥29; P<0.001), attenuated the development of cardiac hypertrophy (-14±6% heart weight/tibia length; P<0.05), and strongly reduced ventricular arrhythmias (-70±22% premature ventricular contractions; P<0.05). On a molecular level, metoprolol expectedly decreased protein kinase A-dependent phospholamban and ryanodine receptor 2 phosphorylation (-42±9% for P-phospholamban-S16 and -22±7% for P-ryanodine receptor 2-S2808; P<0.05). However, this was paralled neither by a reduction in CaMKII autophosphorylation, oxidation, and substrate binding nor a change in the phosphorylation of CaMKII downstream target proteins (n≥11). The lack of CaMKII modulation by β-AR blocker treatment was confirmed in healthy wild-type mice receiving metoprolol.

CONCLUSIONS

Chronic β-AR blocker therapy in patients and in a mouse model of CaMKII-induced HF is not associated with a change in CaMKII activity. Thus, our data suggest that the molecular effects of β-AR blockers are not based on a modulation of CaMKII. Directly targeting CaMKII may, therefore, further improve HF therapy in addition to β-AR blockade.

Cdon deficiency causes cardiac remodeling through hyperactivation of WNT/β-catenin signaling

On pathological stress, Wnt signaling is reactivated and induces genes associated with cardiac remodeling and fibrosis. We have previously shown that a cell surface receptor Cdon (cell-adhesion associated, oncogene regulated) suppresses Wnt signaling to promote neuronal differentiation however its role in heart is unknown. Here, we demonstrate a critical role of Cdon in cardiac function and remodeling. Cdon is expressed and predominantly localized at intercalated disk in both mouse and human hearts. Cdon-deficient mice develop cardiac dysfunction including reduced ejection fraction and ECG abnormalities. Cdon^-/- hearts exhibit increased fibrosis and up-regulation of genes associated with cardiac remodeling and fibrosis. Electrical remodeling was demonstrated by up-regulation and mislocalization of the gap junction protein, Connexin 43 (Cx43) in Cdon^-/- hearts. In agreement with altered Cx43 expression, functional analysis both using Cdon^-/- cardiomyocytes and shRNA-mediated knockdown in rat cardiomyocytes shows aberrant gap junction activities. Analysis of the underlying mechanism reveals that Cdon^-/- hearts exhibit hyperactive Wnt signaling as evident by β-catenin accumulation and Axin2 up-regulation. On the other hand, the treatment of rat cardiomyocytes with a Wnt activator TWS119 reduces Cdon levels and aberrant Cx43 activities, similarly to Cdon-deficient cardiomyocytes, suggesting a negative feedback between Cdon and Wnt signaling. Finally, inhibition of Wnt/β-catenin signaling by XAV939, IWP2 or dickkopf (DKK)1 prevented Cdon depletion-induced up-regulation of collagen 1a and Cx43. Taken together, these results demonstrate that Cdon deficiency causes hyperactive Wnt signaling leading to aberrant intercellular coupling and cardiac fibrosis. Cdon exhibits great potential as a target for the treatment of cardiac fibrosis and cardiomyopathy.