Multimodal Regulation of Cardiac Myocyte Proliferation

Cdk1 Deficiency Extends the Postnatal Window of Cardiomyocyte Proliferation and Restores Cardiac Function after Myocardial Infarction

Cyclin-dependent kinase 1 (Cdk1) is a master regulator of the G2-M transition between DNA replication and cell division. This study investigates the regulation of cardiomyocyte (CM) proliferation during the early neonatal period and following ischemic injury in adult mice. We analyzed cell cycle dynamics with the assessment of DNA synthesis, and cytokinesis in murine hearts during the first 15 days after birth. A distinct proliferative block was observed at 1 day, followed by a second wave of DNA synthesis at 4 days, leading to CM binucleation (CMBN) by day 5. Genome-wide mRNA profiling revealed the differential expression of cell cycle regulatory genes during this period, with a downregulation of factors involved in cell division and mitosis. The loss of Cdk1 impaired CMBN but extended the neonatal CM proliferation window until day 10 post-birth. In adult hearts, the cardiac-specific ablation of Cdk1 triggered CM proliferation post-myocardial-infarction (MI) in specific zones, driven by the activation of EGFR1 signaling and suppression of the anti-proliferative p38 and p53 signaling. This was accompanied by restoration of fractional shortening, mitochondrial function, and decreased reactive oxygen species. Additionally, cardiac hypertrophy was mitigated, and survival rates post-MI were increased in Cdk1-knockout mice. These findings reveal a novel role of Cdk1 in regulating cell cycle exit and re-entry in differentiated CMs and offer insights into potential strategies for cardiac repair.

Cardiomyocyte proliferation and regeneration in congenital heart disease

Despite advances in prenatal screening and a notable decrease in mortality rates, congenital heart disease (CHD) remains the most prevalent congenital disorder in newborns globally. Current therapeutic surgical approaches face challenges due to the significant rise in complications and disabilities. Emerging cardiac regenerative therapies offer promising adjuncts for CHD treatment. One novel avenue involves investigating methods to stimulate cardiomyocyte proliferation. However, the mechanism of altered cardiomyocyte proliferation in CHD is not fully understood, and there are few feasible approaches to stimulate cardiomyocyte cell cycling for optimal healing in CHD patients. In this review, we explore recent progress in understanding genetic and epigenetic mechanisms underlying defective cardiomyocyte proliferation in CHD from development through birth. Targeting cell cycle pathways shows promise for enhancing cardiomyocyte cytokinesis, division, and regeneration to repair heart defects. Advancements in human disease modeling techniques, CRISPR-based genome and epigenome editing, and next-generation sequencing technologies will expedite the exploration of abnormal machinery governing cardiomyocyte differentiation, proliferation, and maturation across diverse genetic backgrounds of CHD. Ongoing studies on screening drugs that regulate cell cycling are poised to translate this nascent technology of enhancing cardiomyocyte proliferation into a new therapeutic paradigm for CHD surgical interventions.

Promotion of maturation of human pluripotent stem cell-derived cardiomyocytes via treatment with the peroxisome proliferator-activated receptor alpha agonist Fenofibrate

As research on in vitro cardiotoxicity assessment and cardiac disease modeling becomes more important, the demand for human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) is increasing. However, it has been reported that differentiated hPSC-CMs are in a physiologically immature state compared to in vivo adult CMs. Since immaturity of hPSC-CMs can lead to poor drug response and loss of acquired heart disease modeling, various approaches have been attempted to promote maturation of CMs. Here, we confirm that peroxisome proliferator-activated receptor alpha (PPARα), one of the representative mechanisms of CM metabolism and cardioprotective effect also affects maturation of CMs. To upregulate PPARα expression, we treated hPSC-CMs with fenofibrate (Feno), a PPARα agonist used in clinical hyperlipidemia treatment, and demonstrated that the structure, mitochondria-mediated metabolism, and electrophysiology-based functions of hPSC-CMs were all mature. Furthermore, as a result of multi electrode array (MEA)-based cardiotoxicity evaluation between control and Feno groups according to treatment with arrhythmia-inducing drugs, drug response was similar in a dose-dependent manner. However, main parameters such as field potential duration, beat period, and spike amplitude were different between the 2 groups. Overall, these results emphasize that applying matured hPSC-CMs to the field of preclinical cardiotoxicity evaluation, which has become an essential procedure for new drug development, is necessary.

Anticancer drugs and cardiotoxicity: the role of cardiomyocyte and non-cardiomyocyte cells

Cardiotoxicity can be defined as "chemically induced heart disease", which can occur with many different drug classes treating a range of diseases. It is the primary cause of drug attrition during pre-clinical development and withdrawal from the market. Drug induced cardiovascular toxicity can result from both functional effects with alteration of the contractile and electrical regulation in the heart and structural changes with morphological changes to cardiomyocytes and other cardiac cells. These adverse effects result in conditions such as arrhythmia or a more serious reduction in left ventricular ejection fraction (LVEF), which can lead to heart failure and death. Anticancer drugs can adversely affect cardiomyocyte function as well as cardiac fibroblasts and cardiac endothelial cells, interfering in autocrine and paracrine signalling between these cell types and ultimately altering cardiac cellular homeostasis. This review aims to highlight potential toxicity mechanisms involving cardiomyocytes and non-cardiomyocyte cells by first introducing the physiological roles of these cells within the myocardium and secondly, identifying the physiological pathways perturbed by anticancer drugs in these cells.

Tudor-SN promotes cardiomyocyte proliferation and neonatal heart regeneration through regulating the phosphorylation of YAP

BACKGROUND

The neonatal mammalian heart exhibits considerable regenerative potential following injury through cardiomyocyte proliferation, whereas mature cardiomyocytes withdraw from the cell cycle and lose regenerative capacities. Therefore, investigating the mechanisms underlying neonatal cardiomyocyte proliferation and regeneration is crucial for unlocking the regenerative potential of adult mammalian heart to repair damage and restore contractile function following myocardial injury.

METHODS

The Tudor staphylococcal nuclease (Tudor-SN) transgenic (TG) or cardiomyocyte-specific knockout mice (Myh6-Tudor-SN -/-) were generated to investigate the role of Tudor-SN in cardiomyocyte proliferation and heart regeneration following apical resection (AR) surgery. Primary cardiomyocytes isolated from neonatal mice were used to assess the influence of Tudor-SN on cardiomyocyte proliferation in vitro. Affinity purification and mass spectrometry were employed to elucidate the underlying mechanism. H9c2 cells and mouse myocardia with either overexpression or knockout of Tudor-SN were utilized to assess its impact on the phosphorylation of Yes-associated protein (YAP), both in vitro and in vivo.

RESULTS

We previously identified Tudor-SN as a cell cycle regulator that is highly expressed in neonatal mice myocardia but downregulated in adults. Our present study demonstrates that sustained expression of Tudor-SN promotes and prolongs the proliferation of neonatal cardiomyocytes, improves cardiac function, and enhances the ability to repair the left ventricular apex resection in neonatal mice. Consistently, cardiomyocyte-specific knockout of Tudor-SN impairs cardiac function and retards recovery after injury. Tudor-SN associates with YAP, which plays important roles in heart development and regeneration, inhibiting phosphorylation at Ser 127 and Ser 397 residues by preventing the association between Large Tumor Suppressor 1 (LATS1) and YAP, correspondingly maintaining stability and promoting nuclear translocation of YAP to enhance the proliferation-related genes transcription.

CONCLUSION

Tudor-SN regulates the phosphorylation of YAP, consequently enhancing and prolonging neonatal cardiomyocyte proliferation under physiological conditions and promoting neonatal heart regeneration after injury.

Comparative effectiveness of myocardial patches and intramyocardial injections in treating myocardial infarction with a MitoQ/hydrogel system

In cardiac tissue engineering, myocardial surface patches and hydrogel intramyocardial injections represent the two primary hydrogel-based strategies for myocardial infarction (MI) treatment. However, the comparative effectiveness of these two treatments remains uncertain. Therefore, this study aimed to compare the effects of the two treatment modalities by designing a simple and reproducible hydrogel cross-linked with γ-PGA and 4-arm-PEG-SG. To improve mitochondrial damage in cardiomyocytes (CMs) during early MI, we incorporated the mitochondria-targeting antioxidant MitoQ into the hydrogel network. The hydrogel exhibited excellent biodegradability, biocompatibility, adhesion, and injectability in vitro. The hydrogel was utilized for rat MI treatment through both patch adhesion and intramyocardial injections. In vivo results demonstrated that the slow release of MitoQ peptide from the hydrogel hindered ROS production in CM, alleviated mitochondrial damage, and enhanced CM activity within 7 days, effectively inhibiting MI progression. Both hydrogel intramyocardial injections and patches exhibited positive therapeutic effects, with intramyocardial injections demonstrating superior efficacy in terms of cardiac function and structure in equivalent treatment cycles. In conclusion, we developed a MitoQ/hydrogel system that is easily prepared and can serve as both a myocardial patch and an intramyocardial injection for MI treatment, showing significant potential for clinical applications.

Transient induction of actin cytoskeletal remodeling associated with dedifferentiation, proliferation, and redifferentiation stimulates cardiac regeneration

The formation of new and functional cardiomyocytes requires a 3-step process: dedifferentiation, proliferation, and redifferentiation, but the critical genes required for efficient dedifferentiation, proliferation, and redifferentiation remain unknown. In our study, a circular trajectory using single-nucleus RNA sequencing of the pericentriolar material 1 positive (PCM1+) cardiomyocyte nuclei from hearts 1 and 3 days after surgery-induced myocardial infarction (MI) on postnatal Day 1 was reconstructed and demonstrated that actin remodeling contributed to the dedifferentiation, proliferation, and redifferentiation of cardiomyocytes after injury. We identified four top actin-remodeling regulators, namely Tmsb4x, Tmsb10, Dmd, and Ctnna3, which we collectively referred to as 2D2P. Transiently expressed changes of 2D2P, using a polycistronic non-integrating lentivirus driven by Tnnt2 (cardiac-specific troponin T) promoters (Tnnt2-2D2P-NIL), efficiently induced transiently proliferative activation and actin remodeling in postnatal Day 7 cardiomyocytes and adult hearts. Furthermore, the intramyocardial delivery of Tnnt2-2D2P-NIL resulted in a sustained improvement in cardiac function without ventricular dilatation, thickened septum, or fatal arrhythmia for at least 4 months. In conclusion, this study highlights the importance of actin remodeling in cardiac regeneration and provides a foundation for new gene-cocktail-therapy approaches to improve cardiac repair and treat heart failure using a novel transient and cardiomyocyte-specific viral construct.

Histone demethylase KDM5 regulates cardiomyocyte maturation by promoting fatty acid oxidation, oxidative phosphorylation, and myofibrillar organization

AIMS

Human pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) provide a platform to identify and characterize factors that regulate the maturation of CMs. The transition from an immature foetal to an adult CM state entails coordinated regulation of the expression of genes involved in myofibril formation and oxidative phosphorylation (OXPHOS) among others. Lysine demethylase 5 (KDM5) specifically demethylates H3K4me1/2/3 and has emerged as potential regulators of expression of genes involved in cardiac development and mitochondrial function. The purpose of this study is to determine the role of KDM5 in iPSC-CM maturation.

METHODS AND RESULTS

KDM5A, B, and C proteins were mainly expressed in the early post-natal stages, and their expressions were progressively downregulated in the post-natal CMs and were absent in adult hearts and CMs. In contrast, KDM5 proteins were persistently expressed in the iPSC-CMs up to 60 days after the induction of myogenic differentiation, consistent with the immaturity of these cells. Inhibition of KDM5 by KDM5-C70 -a pan-KDM5 inhibitor, induced differential expression of 2372 genes, including upregulation of genes involved in fatty acid oxidation (FAO), OXPHOS, and myogenesis in the iPSC-CMs. Likewise, genome-wide profiling of H3K4me3 binding sites by the cleavage under targets and release using nuclease assay showed enriched of the H3K4me3 peaks at the promoter regions of genes encoding FAO, OXPHOS, and sarcomere proteins. Consistent with the chromatin and gene expression data, KDM5 inhibition increased the expression of multiple sarcomere proteins and enhanced myofibrillar organization. Furthermore, inhibition of KDM5 increased H3K4me3 deposits at the promoter region of the ESRRA gene and increased its RNA and protein levels. Knockdown of ESRRA in KDM5-C70-treated iPSC-CM suppressed expression of a subset of the KDM5 targets. In conjunction with changes in gene expression, KDM5 inhibition increased oxygen consumption rate and contractility in iPSC-CMs.

CONCLUSION

KDM5 inhibition enhances maturation of iPSC-CMs by epigenetically upregulating the expressions of OXPHOS, FAO, and sarcomere genes and enhancing myofibril organization and mitochondrial function.

Chemokine CCL2 promotes cardiac regeneration and repair in myocardial infarction mice via activation of the JNK/STAT3 axis

Stimulation of adult cardiomyocyte proliferation is a promising strategy for treating myocardial infarction (MI). Earlier studies have shown increased CCL2 levels in plasma and cardiac tissue both in MI patients and mouse models. In present study we investigated the role of CCL2 in cardiac regeneration and the underlying mechanisms. MI was induced in adult mice by permanent ligation of the left anterior descending artery, we showed that the serum and cardiac CCL2 levels were significantly increased in MI mice. Intramyocardial injection of recombinant CCL2 (rCCL2, 1 μg) immediately after the surgery significantly promoted cardiomyocyte proliferation, improved survival rate and cardiac function, and diminished scar sizes in post-MI mice. Alongside these beneficial effects, we observed an increased angiogenesis and decreased cardiomyocyte apoptosis in post-MI mice. Conversely, treatment with a selective CCL2 synthesis inhibitor Bindarit (30 μM) suppressed both CCL2 expression and cardiomyocyte proliferation in P1 neonatal rat ventricle myocytes (NRVMs). We demonstrated in NRVMs that the CCL2 stimulated cardiomyocyte proliferation through STAT3 signaling: treatment with rCCL2 (100 ng/mL) significantly increased the phosphorylation levels of STAT3, whereas a STAT3 phosphorylation inhibitor Stattic (30 μM) suppressed rCCL2-induced cardiomyocyte proliferation. In conclusion, this study suggests that CCL2 promotes cardiac regeneration via activation of STAT3 signaling, underscoring its potential as a therapeutic agent for managing MI and associated heart failure.

Maternal androgen excess inhibits fetal cardiomyocytes proliferation through RB-mediated cell cycle arrest and induces cardiac hypertrophy in adulthood

PURPOSE

Maternal hyperandrogenism during pregnancy is associated with adverse gestational outcomes and chronic non-communicable diseases in offspring. However, few studies are reported to demonstrate the association between maternal androgen excess and cardiac health in offspring. This study aimed to explore the relation between androgen exposure in utero and cardiac health of offspring in fetal and adult period. Its underlying mechanism is also illustrated in this research.

METHODS

Pregnant mice were injected with dihydrotestosterone (DHT) from gestational day (GD) 16.5 to GD18.5. On GD18.5, fetal heart tissue was collected for metabolite and morphological analysis. The hearts from adult offspring were also collected for morphological and qPCR analysis. H9c2 cells were treated with 75 μM androsterone. Immunofluorescence, flow cytometry, qPCR, and western blot were performed to observe cell proliferation and explore the underlying mechanism.

RESULTS

Intrauterine exposure to excessive androgen led to thinner ventricular wall, decreased number of cardiomyocytes in fetal offspring and caused cardiac hypertrophy, compromised cardiac function in adult offspring. The analysis of steroid hormone metabolites in fetal heart tissue by ultra performance liquid chromatography and tandem mass spectrometry showed that the content of androgen metabolite androsterone was significantly increased. Mechanistically, H9c2 cells treated with androsterone led to a significant decrease in phosphorylated retinoblastoma protein (pRB) and cell cycle-related protein including cyclin-dependent kinase 2 (CDK2), cyclin-dependent kinase 4 (CDK4), and cyclin D1 (CCND1) in cardiomyocytes. This resulted in cell cycle arrest at G1-S phase, which in turn inhibited cardiomyocyte proliferation.

CONCLUSION

Taken together, our results indicate that in utero exposure to DHT, its metabolite androsterone could directly decrease cardiomyocytes proliferation through cell cycle arrest, which has a life-long-lasting effect on cardiac health. Our study highlights the importance of monitoring sex hormones in women during pregnancy and the follow-up of cardiac function in offspring with high risk of intrauterine androgen exposure.

Perlecan (HSPG2) promotes structural, contractile, and metabolic development of human cardiomyocytes

Perlecan (HSPG2), a heparan sulfate proteoglycan similar to agrin, is key for extracellular matrix (ECM) maturation and stabilization. Although crucial for cardiac development, its role remains elusive. We show that perlecan expression increases as cardiomyocytes mature in vivo and during human pluripotent stem cell differentiation to cardiomyocytes (hPSC-CMs). Perlecan-haploinsuffient hPSCs (HSPG2+/-) differentiate efficiently, but late-stage CMs have structural, contractile, metabolic, and ECM gene dysregulation. In keeping with this, late-stage HSPG2+/- hPSC-CMs have immature features, including reduced ⍺-actinin expression and increased glycolytic metabolism and proliferation. Moreover, perlecan-haploinsuffient engineered heart tissues have reduced tissue thickness and force generation. Conversely, hPSC-CMs grown on a perlecan-peptide substrate are enlarged and display increased nucleation, typical of hypertrophic growth. Together, perlecan appears to play the opposite role of agrin, promoting cellular maturation rather than hyperplasia and proliferation. Perlecan signaling is likely mediated via its binding to the dystroglycan complex. Targeting perlecan-dependent signaling may help reverse the phenotypic switch common to heart failure.

MiR-431 promotes cardiomyocyte proliferation by targeting FBXO32 expression

BACKGROUND

The induction of cardiomyocyte (CM) proliferation is a promising approach for cardiac regeneration following myocardial injury. MicroRNAs (miRNAs) have been reported to regulate CM proliferation. In particular, miR-431 expression decreases during cardiac development, according to Gene Expression Omnibus (GEO) microarray data. However, whether miR-431 regulates CM proliferation has not been thoroughly investigated.

METHODS

We used integrated bioinformatics analysis of GEO datasets to identify the most significantly differentially expressed miRNAs. Real-time quantitative PCR and fluorescence in situ hybridization were performed to determine the miRNA expression patterns in hearts. Gain- and loss-of-function assays were conducted to detect the role of miRNA in CM proliferation. Additionally, we detected whether miR-431 affected CM proliferation in a myocardial infarction model. The TargetScan, miRDB and miRWalk online databases were used to predict the potential target genes of miRNAs. Luciferase reporter assays were used to study miRNA interactions with the targeting mRNA.

RESULTS

First, we found a significant reduction in miR-431 levels during cardiac development. Then, by overexpression and inhibition of miR-431, we demonstrated that miR-431 promotes CM proliferation in vitro and in vivo, as determined by immunofluorescence assays of 5-ethynyl-2'-deoxyuridine (EdU), pH3, Aurora B and CM count, whereas miR-431 inhibition suppresses CM proliferation. Then, we found that miR-431 improved cardiac function post-myocardial infarction. In addition, we identified FBXO32 as a direct target gene of miR-431, with FBXO32 mRNA and protein expression being suppressed by miR-431. FBXO32 inhibited CM proliferation. Overexpression of FBXO32 blocks the enhanced effect of miR-431 on CM proliferation, suggesting that FBXO32 is a functional target of miR-431 during CM proliferation.

CONCLUSION

In summary, miR-431 promotes CM proliferation by targeting FBXO32, providing a potential molecular target for preventing myocardial injury.

The characteristics of proliferative cardiomyocytes in mammals

Better understanding of the mechanisms regulating the proliferation of pre-existing cardiomyocyte (CM) should lead to better options for regenerating injured myocardium. The absence of a perfect research model to definitively identify newly formed mammalian CMs is lacking. However, methodologies are being developed to identify and enrich proliferative CMs. These methods take advantages of the different proliferative states of CMs during postnatal development, before and after injury in the neonatal heart. New approaches use CMs labeled in lineage tracing animals or single cell technique-based CM clusters. This review aims to provide a timely update on the characteristics of the proliferative CMs, including their structural, functional, genetic, epigenetic and metabolic characteristics versus non-proliferative CMs. A better understanding of the characteristics of proliferative CMs should lead to the mechanisms for inducing endogenous CMs to self-renew, which is a promising therapeutic strategy to treat cardiac diseases that cause CM death in humans.

Altered Peripheral Blood Gene Expression in Childhood Cancer Survivors With Anthracycline-Induced Cardiomyopathy - A COG-ALTE03N1 Report

Background Anthracycline-induced cardiomyopathy is a leading cause of premature death in childhood cancer survivors, presenting a need to understand the underlying pathogenesis. We sought to examine differential blood-based mRNA expression profiles in anthracycline-exposed childhood cancer survivors with and without cardiomyopathy. Methods and Results We designed a matched case-control study (Children's Oncology Group-ALTE03N1) with mRNA sequencing on total RNA from peripheral blood in 40 anthracycline-exposed survivors with cardiomyopathy (cases) and 64 matched survivors without (controls). DESeq2 identified differentially expressed genes. Ingenuity Pathway Analyses (IPA) and Gene Set Enrichment Analyses determined the potential roles of altered genes in biological pathways. Functional validation was performed by gene knockout in human-induced pluripotent stem cell-derived cardiomyocytes using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9) technology. Median age at primary cancer diagnosis for cases and controls was 8.2 and 9.7 years, respectively. Thirty-six differentially expressed genes with fold change ≥±2 were identified; 35 were upregulated. IPA identified "hepatic fibrosis" and "iron homeostasis" pathways to be significantly modulated by differentially expressed genes, including toxicology functions of myocardial infarction, cardiac damage, and cardiac dilation. Leading edge analysis from Gene Set Enrichment Analyses identified lactate dehydrogenase A (LDHA) and cluster of differentiation 36 (CD36) genes to be significantly upregulated in cases. Interleukin 1 receptor type 1, 2 (IL1R1, IL1R2), and matrix metalloproteinase 8, 9 (MMP8, MMP9) appeared in multiple canonical pathways. LDHA-knockout human-induced pluripotent stem cell-derived cardiomyocytes showed increased sensitivity to doxorubicin. Conclusions We identified differential mRNA expression profiles in peripheral blood of anthracycline-exposed childhood cancer survivors with and without cardiomyopathy. Upregulation of LDHA and CD36 genes suggests metabolic perturbations in a failing heart. Dysregulation of proinflammatory cytokine receptors IL1R1 and IL1R2 and matrix metalloproteinases, MMP8 and MMP9 indicates structural remodeling that accompanies the clinical manifestation of symptomatic cardiotoxicity.

Inhibition of fatty acid oxidation enables heart regeneration in adult mice

Postnatal maturation of cardiomyocytes is characterized by a metabolic switch from glycolysis to fatty acid oxidation, chromatin reconfiguration and exit from the cell cycle, instating a barrier for adult heart regeneration1,2. Here, to explore whether metabolic reprogramming can overcome this barrier and enable heart regeneration, we abrogate fatty acid oxidation in cardiomyocytes by inactivation of Cpt1b. We find that disablement of fatty acid oxidation in cardiomyocytes improves resistance to hypoxia and stimulates cardiomyocyte proliferation, allowing heart regeneration after ischaemia-reperfusion injury. Metabolic studies reveal profound changes in energy metabolism and accumulation of α-ketoglutarate in Cpt1b-mutant cardiomyocytes, leading to activation of the α-ketoglutarate-dependent lysine demethylase KDM5 (ref. 3). Activated KDM5 demethylates broad H3K4me3 domains in genes that drive cardiomyocyte maturation, lowering their transcription levels and shifting cardiomyocytes into a less mature state, thereby promoting proliferation. We conclude that metabolic maturation shapes the epigenetic landscape of cardiomyocytes, creating a roadblock for further cell divisions. Reversal of this process allows repair of damaged hearts.

Amending the injured heart by in vivo reprogramming

Ischemic heart injury causes death of cardiomyocyte (CM), formation of a fibrotic scar, and often adverse cardiac remodeling, resulting in chronic heart failure. Therapeutic interventions have lowered myocardial damage and improved heart function, but pharmacological treatment of heart failure has only shown limited progress in recent years. Over the past two decades, different approaches have been pursued to regenerate the heart, by transplantation of newly generated CMs derived from pluripotent stem cells, generation of new CMs by reprogramming of cardiac fibroblasts, or by activating proliferation of preexisting CMs. Here, we summarize recent progress in the development of strategies for in situ generation of new CMs, review recent advances in understanding the underlying mechanisms, and discuss the challenges and future directions of the field.

Quantitative proteomics reveals PPAR signaling pathway regulates the cardiomyocyte activity of neonatal mouse heart

Cardiovascular diseases (CVDs) are among the most morbid and deadly types of diseases worldwide, while the existing therapeutic approaches all have their limitations. Mouse heart undergoes a very complex postnatal developmental process, including the 1-week window in which cardiomyocytes (CMs) maintain relatively high cell activity. The underlying mechanism provides an attractive direction for CVDs treatment. Herein, we collected ventricular tissues from mice of different ages from E18.5D to P8W and performed iTRAQ-based quantitative proteomics to characterize the atlas of cardiac development. A total of 3422 proteins were quantified at all selected time points, revealing critical proteomic changes related to cardiac developmental events such as the metabolic transition from glycolysis to beta-oxidation. A cluster of significantly dysregulated proteins containing proteins that have already been reported to be associated with cardiac regeneration (Erbb2, Agrin, and Hmgb) was identified. Meanwhile, the peroxisome proliferator-activated receptor (PPAR) signaling pathway (Cpt1α, Hmgcs2, Plin2, and Fabp4) was also found specifically enriched. We further revealed that bezafibrate, a pan-activator of PPAR signaling pathway markedly enhanced H9C2 cardiomyocyte activity via enhancing Cpt1α expression. This work provides new hint that activation of PPAR signaling pathway could potentially be a therapeutic strategy for the treatment of CVDs.

miRNAs Epigenetic Tuning of Wall Remodeling in the Early Phase after Myocardial Infarction: A Novel Epidrug Approach

Myocardial infarction (MI) is one of the leading causes of death in Western countries. An early diagnosis decreases subsequent severe complications such as wall remodeling or heart failure and improves treatments and interventions. Novel therapeutic targets have been recognized and, together with the development of direct and indirect epidrugs, the role of non-coding RNAs (ncRNAs) yields great expectancy. ncRNAs are a group of RNAs not translated into a product and, among them, microRNAs (miRNAs) are the most investigated subgroup since they are involved in several pathological processes related to MI and post-MI phases such as inflammation, apoptosis, angiogenesis, and fibrosis. These processes and pathways are finely tuned by miRNAs via complex mechanisms. We are at the beginning of the investigation and the main paths are still underexplored. In this review, we provide a comprehensive discussion of the recent findings on epigenetic changes involved in the first phases after MI as well as on the role of the several miRNAs. We focused on miRNAs function and on their relationship with key molecules and cells involved in healing processes after an ischemic accident, while also giving insight into the discrepancy between males and females in the prognosis of cardiovascular diseases.

The heterocellular heart: identities, interactions, and implications for cardiology

The heterocellular nature of the heart has been receiving increasing attention in recent years. In addition to cardiomyocytes as the prototypical cell type of the heart, non-myocytes such as endothelial cells, fibroblasts, or immune cells are coming more into focus. The rise of single-cell sequencing technologies enables  identification of ever more subtle differences and has reignited the question of what defines a cell's identity. Here we provide an overview of the major cardiac cell types, describe their roles in homeostasis, and outline recent findings on non-canonical functions that may be of relevance for cardiology. We highlight modes of biochemical and biophysical interactions between different cardiac cell types and discuss the potential implications of the heterocellular nature of the heart for basic research and therapeutic interventions.

Histone demethylase KDM5 regulates cardiomyocyte maturation by promoting fatty acid oxidation, oxidative phosphorylation, and myofibrillar organization

Rationale

Human pluripotent stem cell-derived CMs (iPSC-CMs) are a valuable tool for disease modeling, cell therapy and to reconstruct the CM maturation process and identify, characterize factors that regulate maturation. The transition from immature fetal to adult CM entails coordinated regulation of the mature gene programming, which is characterized by the induction of myofilament and OXPHOS gene expression among others. Recent studies in Drosophila , C. elegans, and C2C12 myoblast cell lines have implicated the histone H3K4me3 demethylase KDM5 and its homologs, as a potential regulator of developmental gene program and mitochondrial function. We speculated that KDM5 may potentiate the maturation of iPSC-CMs by targeting a conserved epigenetic program that encompass mitochondrial OXPHOS and other CM specific maturation genes.

Objectives

The purpose of this study is to determine the role of KDM5 in iPSC-CM maturation.

Methods and Results

Immunoblot analysis revealed that KDM5A, B, and C expression was progressively downregulated in postnatal cardiomyocytes and absent in adult hearts and CMs. Additionally, KDM5 proteins were found to be persistently expressed in iPSC-CMs up to 60 days after the onset of myogenic differentiation, consistent with the immaturity of these cells. Inhibition of KDM5 by KDM5-C70 -a pan-KDM5 inhibitor-resulted in differential regulation of 2,372 genes including upregulation of Fatty acid oxidation (FAO), OXPHOS, and myogenic gene programs in iPSC-CMs. Likewise, genome-wide profiling of H3K4me3 binding sites by the CUT&RUN assay revealed enriched H3K4me3 peaks at the promoter regions of FAO, OXPHOS, and sarcomere genes. Consistent with the chromatin and gene expression data, KDM5 inhibition led to increased expression of multiple sarcomere proteins, enhanced myofibrillar organization and improved calcium handling. Furthermore, inhibition of KDM5 increased H3K4me3 deposits at the promoter region of the ESRRA gene, which is known to regulate OXPHOS and cardiomyocyte maturation, and resulted in its increased RNA and protein levels. Finally, KDM5 inhibition increased baseline, peak, and spare oxygen consumption rates in iPSC-CMs.

Conclusions

KDM5 regulates the maturation of iPSC-CMs by epigenetically regulating the expression of ESRRA, OXPHOS, FAO, and sarcomere genes and enhancing myofibril organization and mitochondrial function.

Developmental Aspects of Cardiac Adaptation to Increased Workload

The heart is capable of extensive adaptive growth in response to the demands of the body. When the heart is confronted with an increased workload over a prolonged period, it tends to cope with the situation by increasing its muscle mass. The adaptive growth response of the cardiac muscle changes significantly during phylogenetic and ontogenetic development. Cold-blooded animals maintain the ability for cardiomyocyte proliferation even in adults. On the other hand, the extent of proliferation during ontogenetic development in warm-blooded species shows significant temporal limitations: whereas fetal and neonatal cardiac myocytes express proliferative potential (hyperplasia), after birth proliferation declines and the heart grows almost exclusively by hypertrophy. It is, therefore, understandable that the regulation of the cardiac growth response to the increased workload also differs significantly during development. The pressure overload (aortic constriction) induced in animals before the switch from hyperplastic to hypertrophic growth leads to a specific type of left ventricular hypertrophy which, in contrast with the same stimulus applied in adulthood, is characterized by hyperplasia of cardiomyocytes, capillary angiogenesis and biogenesis of collagenous structures, proportional to the growth of myocytes. These studies suggest that timing may be of crucial importance in neonatal cardiac interventions in humans: early definitive repairs of selected congenital heart disease may be more beneficial for the long-term results of surgical treatment.

Genome-wide association and multi-trait analyses characterize the common genetic architecture of heart failure

Heart failure is a leading cause of cardiovascular morbidity and mortality. However, the contribution of common genetic variation to heart failure risk has not been fully elucidated, particularly in comparison to other common cardiometabolic traits. We report a multi-ancestry genome-wide association study meta-analysis of all-cause heart failure including up to 115,150 cases and 1,550,331 controls of diverse genetic ancestry, identifying 47 risk loci. We also perform multivariate genome-wide association studies that integrate heart failure with related cardiac magnetic resonance imaging endophenotypes, identifying 61 risk loci. Gene-prioritization analyses including colocalization and transcriptome-wide association studies identify known and previously unreported candidate cardiomyopathy genes and cellular processes, which we validate in gene-expression profiling of failing and healthy human hearts. Colocalization, gene expression profiling, and Mendelian randomization provide convergent evidence for the roles of BCKDHA and circulating branch-chain amino acids in heart failure and cardiac structure. Finally, proteome-wide Mendelian randomization identifies 9 circulating proteins associated with heart failure or quantitative imaging traits. These analyses highlight similarities and differences among heart failure and associated cardiovascular imaging endophenotypes, implicate common genetic variation in the pathogenesis of heart failure, and identify circulating proteins that may represent cardiomyopathy treatment targets.

Dynamics of metabolism and regulation of epigenetics during cardiomyocytes maturation

Maturation is the last step of heart growth that prepares the organ over the lifetime of the mammal for powerful, effective, and sustained pumping. Structural, gene expression, physiological, and functional specialties of cardiomyocytes describe this mechanism as the heart transits from fetus to adult phases. The main cornerstones of maturation of cardiomyocytes are reviewed and primary regulatory mechanisms are summarized to facilitate and organize these cellular activities. During embryonic development, cardiomyocytes proliferate rigorously but leave the cell cycle permanently immediately after the parturition of the child and experience terminal differentiation. The activation of a host of genes specific for the mature heart is correlated with the exit from the cell cycle. Even when exposed to mitogenic stimuli, the bulk of mature cardiomyocytes do not re-join the cell cycle. The reason for this permanent exit from the cell cycle is shown to be linked with stable switching off of the genes of the cell cycle directly involved in the G2/M transition phase and cytokinesis development. Researchers also trying to explain the molecular mechanism involved in stable inhibition of the gene and described structural changes (epigenetic and chromatin) in this mechanism. Substantial developments in the future with advances in the scientific platforms used for cardiomyocyte maturation research will broaden our understanding of this mechanism and result in better maturation of cardiomyocyte-derived pluripotent stem cells and effective treatment approaches for cardiovascular diseases.

LDHA-mediated metabolic reprogramming promoted cardiomyocyte proliferation by alleviating ROS and inducing M2 macrophage polarization

Aims

Metabolic switching during heart development contributes to postnatal cardiomyocyte (CM) cell cycle exit and loss of regenerative capacity in the mammalian heart. Metabolic control has potential for developing effective CM proliferation strategies. We sought to determine whether lactate dehydrogenase A (LDHA) regulated CM proliferation by inducing metabolic reprogramming.

Methods and results

LDHA expression was high in P1 hearts and significantly decreased during postnatal heart development. CM-specific LDHA knockout mice were generated using CRISPR/Cas9 technology. CM-specific LDHA knockout inhibited CM proliferation, leading to worse cardiac function and a lower survival rate in the neonatal apical resection model. In contrast, CM-specific overexpression of LDHA promoted CM proliferation and cardiac repair post-MI. The α-MHC-H2B-mCh/CAG-eGFP-anillin system was used to confirm the proliferative effect triggered by LDHA on P7 CMs and adult hearts. Metabolomics, proteomics and Co-IP experiments indicated that LDHA-mediated succinyl coenzyme A reduction inhibited succinylation-dependent ubiquitination of thioredoxin reductase 1 (Txnrd1), which alleviated ROS and thereby promoted CM proliferation. In addition, flow cytometry and western blotting showed that LDHA-driven lactate production created a beneficial cardiac regenerative microenvironment by inducing M2 macrophage polarization.

Conclusions

LDHA-mediated metabolic reprogramming promoted CM proliferation by alleviating ROS and inducing M2 macrophage polarization, indicating that LDHA might be an effective target for promoting cardiac repair post-MI.

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Succinylation-dependent ubiquitination of Txnrd1 is a new mechanism involved in LDHA-mediated ROS alleviation during cardiomyocyte proliferation.

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LDHA-driven lactate production created a beneficial cardiac regenerative microenvironment by inducing M2 macrophage polarization.

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LDHA-mediated metabolic reprogramming promoted cardiomyocyte proliferation, indicating that LDHA might be a therapeutic target to promote cardiac repair post-MI.

Ablation of cardiomyocyte-derived BDNF during development causes myocardial degeneration and heart failure in the adult mouse heart

Objective

Brain-derived neurotrophic factor (BDNF) and its receptor TrkB-T1 were recently found to be expressed in cardiomyocytes. However, the functional role of cardiomyocyte-derived BDNF in heart pathophysiology is not yet fully known. Recent studies revealed that BDNF-TrkB pathway plays a critical role to maintain integrity of cardiac structure and function, cardiac pathology and regeneration of myocardial infarction (MI). Therefore, the BDNF-TrkB pathway may be a novel target for myocardial pathophysiology in the adult heart.

Approach and results

In the present study, we established a cardiomyocyte-derived BDNF conditional knockout mouse in which BDNF expression in developing cardiomyocytes is ablated under the control of the Myosin heavy chain 6 (MYH6) promoter. The results of the present study show that ablation of cardiomyocyte-derived BDNF during development does not impair survival, growth or reproduction; however, in the young adult heart, it causes cardiomyocyte death, degeneration of the myocardium, cardiomyocyte hypertrophy, left atrial appendage thrombosis, decreased cardiac function, increased cardiac inflammation and ROS activity, and metabolic disorders, leading to heart failure (HF) in the adult heart and eventually resulting in a decrease in the one-year survival rate. In addition, ablation of cardiomyocyte-derived BDNF during the developmental stage leads to exacerbation of cardiac dysfunction and poor regeneration after MI in adult hearts.

Conclusion

Cardiomyocyte-derived BDNF is irreplaceable for maintaining the integrity of cardiac structure and function in the adult heart and regeneration after MI. Therefore, the BDNF-TrkB pathway will be a novel target for myocardial pathophysiology in the adult heart.

N6-methyladenosine modulates long non-coding RNA in the developing mouse heart

Long non-coding RNAs (lncRNAs) were reported to potentially play a regulatory role in the process of myocardial regeneration in the neonatal mouse. N6-methyladenosine (m⁶A) modification may play a key role in myocardial regeneration in mice and regulates a variety of biological processes through affecting the stability of lncRNAs. However, the map of m⁶A modification of lncRNAs in mouse cardiac development still remains unknown. We aimed to investigate the differences in the m⁶A status of lncRNAs during mouse cardiac development and reveal a potential role of m⁶A modification modulating lncRNAs in cardiac development and myocardial regeneration during cardiac development in mice. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing (RNA-seq) of the heart tissue in C57BL/6 J mice at postnatal day 1 (P1), P7 and P28 were performed to produce stagewise cardiac lncRNA m⁶A-methylomes in a parallel timeframe with the established loss of an intrinsic cardiac regeneration capacity and early postnatal development. There were significant differences in the distribution and abundance of m⁶A modifications in lncRNAs in the P7 vs P1 mice. In addition, the functional role of m⁶A in regulating lncRNA levels was established for selected transcripts with METTL3 silencing in neonatal cardiomyocytes in vitro. Based on our MeRIP-qPCR experiment data, both lncGm15328 and lncRNA Zfp597, that were not previously associated with cardiac regeneration, were found to be the most differently methylated at P1-P7. These two lncRNAs sponged several miRNAs which further regulated multiple mRNAs, including some of which have previously been linked with cardiac regeneration ability. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis revealed that differential m⁶A modifications were more enriched in functions and cellular signalling pathways related to cardiomyocyte proliferation. Our data suggested that the m⁶A modification on lncRNAs may play an important role in the regeneration of myocardium and cardiac development.

The graphical abstract of the potential mechanism of m⁶A modulates long non-coding RNA in the developing mouse heart.

Defining the molecular underpinnings controlling cardiomyocyte proliferation

Shortly after birth, mammalian cardiomyocytes (CM) exit the cell cycle and cease to proliferate. The inability of adult CM to replicate renders the heart particularly vulnerable to injury. Restoration of CM proliferation would be an attractive clinical target for regenerative therapies that can preserve contractile function and thus prevent the development of heart failure. Our review focuses on recent progress in understanding the tight regulation of signaling pathways and their downstream molecular mechanisms that underly the inability of CM to proliferate in vivo. In this review, we describe the temporal expression of cell cycle activators e.g., cyclin/Cdk complexes and their inhibitors including p16, p21, p27 and members of the retinoblastoma gene family during gestation and postnatal life. The differential impact of members of the E2f transcription factor family and microRNAs on the regulation of positive and negative cell cycle factors is discussed. This review also highlights seminal studies that identified the coordination of signaling mechanisms that can potently activate CM cell cycle re-entry including the Wnt/Ctnnb1, Hippo, Pi3K-Akt and Nrg1-Erbb2/4 pathways. We also present an up-to-date account of landmark studies analyzing the effect of various genes such as Argin, Dystrophin, Fstl1, Meis1, Pitx2 and Pkm2 that are responsible for either inhibition or activation of CM cell division. All these reports describe bona fide therapeutically targets that could guide future clinical studies toward cardiac repair.

Cardiomyocyte Proliferation from Fetal- to Adult- and from Normal- to Hypertrophy and Failing Hearts

Simple Summary

Death from injury to the heart from a variety of causes remains a major cause of mortality worldwide. The cardiomyocyte, the major contracting cell of the heart, is responsible for pumping blood to the rest of the body. During fetal development, these immature cardiomyocytes are small and rapidly divide to complete development of the heart by birth when they develop structural and functional characteristics of mature cells which prevent further division. All further growth of the heart after birth is due to an increase in the size of cardiomyocytes, hypertrophy. Following the loss of functional cardiomyocytes due to coronary artery occlusion or other causes, the heart is unable to replace the lost cells. One of the significant research goals has been to induce adult cardiomyocytes to reactivate the cell cycle and repair cardiac injury. This review explores the developmental, structural, and functional changes of the growing cardiomyocyte, and particularly the sarcomere, responsible for force generation, from the early fetal period of reproductive cell growth through the neonatal period and on to adulthood, as well as during pathological response to different forms of myocardial diseases or injury. Multiple issues relative to cardiomyocyte cell-cycle regulation in normal or diseased conditions are discussed.

Abstract

The cardiomyocyte undergoes dramatic changes in structure, metabolism, and function from the early fetal stage of hyperplastic cell growth, through birth and the conversion to hypertrophic cell growth, continuing to the adult stage and responding to various forms of stress on the myocardium, often leading to myocardial failure. The fetal cell with incompletely formed sarcomeres and other cellular and extracellular components is actively undergoing mitosis, organelle dispersion, and formation of daughter cells. In the first few days of neonatal life, the heart is able to repair fully from injury, but not after conversion to hypertrophic growth. Structural and metabolic changes occur following conversion to hypertrophic growth which forms a barrier to further cardiomyocyte division, though interstitial components continue dividing to keep pace with cardiac growth. Both intra- and extracellular structural changes occur in the stressed myocardium which together with hemodynamic alterations lead to metabolic and functional alterations of myocardial failure. This review probes some of the questions regarding conditions that regulate normal and pathologic growth of the heart.

Pentachloronitrobenzene Reduces the Proliferative Capacity of Zebrafish Embryonic Cardiomyocytes via Oxidative Stress

Pentachloronitrobenzene (PCNB) is an organochlorine protective fungicide mainly used as a soil and seed fungicide. Currently, there are few reports on the toxicity of PCNB to zebrafish embryo. Here, we evaluated the toxicity of PCNB in aquatic vertebrates using a zebrafish model. Exposure of zebrafish embryos to PCNB at concentrations of 0.25 mg/L, 0.5 mg/L, and 0.75 mg/L from 6 hpf to 72 hpf resulted in abnormal embryonic development, including cardiac malformation, pericardial edema, decreased heart rate, decreased blood flow velocity, deposition at yolk sac, shortened body length, and increased distance between venous sinus and arterial bulb (SV-BA). The expression of genes related to cardiac development was disordered. However, due to the unstable embryo status in the 0.75 mg/L exposure concentration group, the effect of PCNB on the expression levels of cardiac-related genes was not concentration-dependent. We found that PCNB increased reactive oxygen species stress levels in zebrafish, increased malondialdehyde (MDA) content and catalase (CAT) activity, and decreased superoxide dismutase (SOD) activity. The increased level of oxidative stress reduced the proliferation ability of zebrafish cardiomyocytes, and the expressions of zebrafish proliferation-related genes such as cdk-2, cdk-6, ccnd1, and ccne1 were significantly down-regulated. Astaxanthin (AST) attenuates PCNB-induced reduction in zebrafish cardiomyocyte proliferation by reducing oxidative stress levels. Our study shows that PCNB can cause severe oxidative stress in zebrafish, thereby reducing the proliferative capacity of cardiomyocytes, resulting in zebrafish cardiotoxicity.

Prolonged Myocardial Regenerative Capacity in Neonatal Opossum

BACKGROUND

Early neonates of both large and small mammals are able to regenerate the myocardium through cardiomyocyte proliferation for only a short period after birth. This myocardial regenerative capacity declines in parallel with withdrawal of cardiomyocytes from the cell cycle in the first few postnatal days. No mammalian species examined to date has been found capable of a meaningful regenerative response to myocardial injury later than 1 week after birth.

METHODS

We examined cardiomyocyte proliferation in neonates of the marsupial opossum (Monodelphis domestica) by immunostaining at various times after birth. The regenerative capacity of the postnatal opossum myocardium was assessed after either apex resection or induction of myocardial infarction at postnatal day 14 or 29, whereas that of the postnatal mouse myocardium was assessed after myocardial infarction at postnatal day 7. Bioinformatics data analysis, immunofluorescence staining, and pharmacological and genetic intervention were applied to determine the role of AMPK (5'-AMP-activated protein kinase) signaling in regulation of the mammalian cardiomyocyte cell cycle.

RESULTS

Opossum neonates were found to manifest cardiomyocyte proliferation for at least 2 weeks after birth at a frequency similar to that apparent in early neonatal mice. Moreover, the opossum heart at postnatal day 14 showed substantial regenerative capacity both after apex resection and after myocardial infarction injury, whereas this capacity had diminished by postnatal day 29. Transcriptomic and immunofluorescence analyses indicated that AMPK signaling is activated in postnatal cardiomyocytes of both opossum and mouse. Pharmacological or genetic inhibition of AMPK signaling was sufficient to extend the postnatal window of cardiomyocyte proliferation in both mouse and opossum neonates as well as of cardiac regeneration in neonatal mice.

CONCLUSIONS

The marsupial opossum maintains cardiomyocyte proliferation and a capacity for myocardial regeneration for at least 2 weeks after birth. As far as we are aware, this is the longest postnatal duration of such a capacity among mammals examined to date. AMPK signaling was implicated as an evolutionarily conserved regulator of mammalian postnatal cardiomyocyte proliferation.

Epicardium-derived cells organize through tight junctions to replenish cardiac muscle in salamanders

The contribution of the epicardium, the outermost layer of the heart, to cardiac regeneration has remained controversial due to a lack of suitable analytical tools. By combining genetic marker-independent lineage-tracing strategies with transcriptional profiling and loss-of-function methods, we report here that the epicardium of the highly regenerative salamander species Pleurodeles waltl has an intrinsic capacity to differentiate into cardiomyocytes. Following cryoinjury, CLDN6+ epicardium-derived cells appear at the lesion site, organize into honeycomb-like structures connected via focal tight junctions and undergo transcriptional reprogramming that results in concomitant differentiation into de novo cardiomyocytes. Ablation of CLDN6+ differentiation intermediates as well as disruption of their tight junctions impairs cardiac regeneration. Salamanders constitute the evolutionarily closest species to mammals with an extensive ability to regenerate heart muscle and our results highlight the epicardium and tight junctions as key targets in efforts to promote cardiac regeneration.

Ultrasound-targeted microbubble destruction (UTMD)-mediated miR-150-5p attenuates oxygen and glucose deprivation-induced cardiomyocyte injury by inhibiting TTC5 expression

BACKGROUND

Cardiomyocyte injury is a typical feature in cardiovascular diseases. Changes in cardiomyocytes strongly affect the progression of cardiovascular diseases. This work aimed to investigate the biological function and potential mechanism of action of miR-150-5p in cardiomyocytes.

METHODS AND RESULTS

A myocardial ischemia (MI) injury rat model was constructed to detect miR-150-5p and tetratricopeptide repeat domain 5 (TTC5) expression during heart ischemia injury. Primary cardiomyocytes were isolated for in vitro study. CCK-8 assays were used to detect cardiomyocyte viability. Western blots were used to detect TTC5 and P53 expression. qPCR was utilized to measure RNA expression of miR-150-5p and TTC5. The TUNEL assay was used to determine cell apoptosis. ELISA was used to determine cytokine (TNF-α, IL-1β, IL-6, and IL-8) levels in heart tissues and cell culture supernatants. A dual-luciferase reporter assay was carried out to verify the binding ability between miR-150-5p and TTC5. Oxygen-glucose deprivation (OGD) treatment significantly inhibited cell viability. Ultrasound-targeted microbubble destruction (UTMD)-mediated uptake of miR-150-5p inverted these results. Additionally, UTMD-mediated uptake of miR-150-5p retarded the effects of OGD treatment on cell apoptosis. Besides, UTMD-mediated uptake of miR-150-5p counteracted the effects of OGD treatment on the inflammatory response by regulating cytokine (TNF-α, IL-1β, IL-6, and IL-8) levels. For the mechanism of the protective effect on the heart, we predicted and confirmed that miR-150-5p bound to TTC5 and inhibited TTC5 expression.

CONCLUSIONS

UTMD-mediated uptake of miR-150-5p attenuated OGD-induced primary cardiomyocyte injury by inhibiting TTC5 expression. This discovery contributes toward further understanding the progression of primary cardiomyocyte injury.

Histone deacetylase 1 controls cardiomyocyte proliferation during embryonic heart development and cardiac regeneration in zebrafish

In contrast to mammals, the zebrafish maintains its cardiomyocyte proliferation capacity throughout adulthood. However, neither the molecular mechanisms that orchestrate the proliferation of cardiomyocytes during developmental heart growth nor in the context of regeneration in the adult are sufficiently defined yet. We identified in a forward genetic N-ethyl-N-nitrosourea (ENU) mutagenesis screen the recessive, embryonic-lethal zebrafish mutant baldrian (bal), which shows severely impaired developmental heart growth due to diminished cardiomyocyte proliferation. By positional cloning, we identified a missense mutation in the zebrafish histone deacetylase 1 (hdac1) gene leading to severe protein instability and the loss of Hdac1 function in vivo. Hdac1 inhibition significantly reduces cardiomyocyte proliferation, indicating a role of Hdac1 during developmental heart growth in zebrafish. To evaluate whether developmental and regenerative Hdac1-associated mechanisms of cardiomyocyte proliferation are conserved, we analyzed regenerative cardiomyocyte proliferation after Hdac1 inhibition at the wound border zone in cryoinjured adult zebrafish hearts and we found that Hdac1 is also essential to orchestrate regenerative cardiomyocyte proliferation in the adult vertebrate heart. In summary, our findings suggest an important and conserved role of Histone deacetylase 1 (Hdac1) in developmental and adult regenerative cardiomyocyte proliferation in the vertebrate heart.

Heart disease is one of the most common causes of death in all developed countries. While zebrafish cardiomyocytes are able to proliferate throughout adulthood, mammalian cardiomyocytes lose this ability during early development, and therefore are not capable to replace and renew cardiomyocytes after injury. The underlying mechanisms of cardiomyocyte proliferation are still not completely resolved. Understanding how zebrafish cardiomyocytes preserve their proliferating state, would be a valuable information to foster cardiac regeneration, e.g. after myocardial infarction in patients. Knowledge of the signaling pathways that need to be activated, or deactivated in order to induce cardiomyocyte proliferation after acute or chronic injury will pave the way for the development of genetic and/or pharmacological treatment options. In an ENU-mutagenesis screen, we identified the zebrafish mutant baldrian, which shows reduced embryonic cardiomyocyte proliferation. As genetic cause of the observed phenotype, we identified a missense mutation in the hdac1 gene. By treatment of heart-injured adult fish with the HDAC1 inhibitor Mocetinostat, we were able to show a reduced rate of cardiomyocyte proliferation also in the adult zebrafish heart in vivo, suggesting a role of Hdac1 in embryonic heart growth and adult regenerative cardiomyocyte proliferation in zebrafish.

METTL3 improves cardiomyocyte proliferation upon myocardial infarction via upregulating miR-17-3p in a DGCR8-dependent manner

Myocardial infarction (MI), one of the most severe types of heart attack, exerts a strong negative effect on heart muscle by causing a massive and rapid loss of cardiomyocytes. However, the existing therapies do little to improve cardiac regeneration. Due to the role of methyltransferase-like 3 (METTL3) in the physiological proliferation of cardiomyocytes, we aimed to determine whether METTL3 could also promote cardiomyocyte proliferation under pathological conditions and to elucidate the underlying mechanism. The effects of METTL3 on cardiomyocyte proliferation and apoptosis were investigated in an in vivo rat model of MI and in an in vitro model of neonatal rat cardiomyocytes (NRCMs) exposed to hypoxia. We found that METTL3 expression was downregulated in hypoxia-exposed NRCMs and MI-induced rats. Furthermore, METTL3 pretreatment enhanced cardiomyocyte proliferation and inhibited cardiomyocyte apoptosis under hypoxic or MI conditions, and silencing METTL3 had the opposite effects. Additionally, METTL3 overexpression upregulated miR-17-3p expression. The miR-17-3p agomir mimicked the pro-proliferative and antiapoptotic effects of METTL3 in hypoxia-exposed cells or rats with MI, while the miR-17-3p antagomir blocked these effects. Additionally, pretreatment with the RNA-binding protein DGCR8 also hampered the protective role of METTL3 in hypoxia-exposed cells. Overall, the current study indicated that METTL3 could improve cardiomyocyte proliferation and subsequently ameliorate MI in rats by upregulating proliferation-related miR-17-3p in a DGCR8-dependent pri-miRNA-processing manner.

Arteriovenous Fistula-induced Cardiac Remodeling Shows Cardioprotective Features in Mice

Objective

Arteriovenous fistulae (AVF) placed for hemodialysis have high flow rates that can stimulate left ventricular (LV) hypertrophy. LV hypertrophy generally portends poor cardiac outcomes, yet clinical studies point to superior cardiac-specific outcomes for patients with AVF when compared with other dialysis modalities. We hypothesize that AVF induce physiologic cardiac hypertrophy with cardioprotective features.

Methods

We treated 9- to 11-week-old C57Bl/6 male and female mice with sham laparotomy or an aortocaval fistula via a 25G needle. Cardiac chamber size and function were assessed with serial echocardiography, and cardiac computed tomography angiography. Hearts were harvested at 5 weeks postoperatively, and the collagen content was assessed with Masson's trichrome. Bulk messenger RNA sequencing was performed from LV of sham and AVF mice at 10 days. Differentially expressed genes were analyzed using Ingenuity Pathway Analysis (Qiagen) to identify affected pathways and predict downstream biological effects.

Results

Mice with AVF had similar body weight and wet lung mass, but increased cardiac mass compared with sham-operated mice. AVF increased cardiac output while preserving LV systolic and diastolic function, as well as indices of right heart function; all four cardiac chambers were enlarged, with a slight decrement in the relative LV wall thickness. Histology showed preserved collagen density within each of the four chambers without areas of fibrosis. RNA sequencing captured 19 384 genes, of which 857 were significantly differentially expressed, including transcripts from extracellular matrix-related genes, ion channels, metabolism, and cardiac fetal genes. The top upstream regulatory molecules predicted include activation of angiogenic (Vegf, Akt1), procardiomyocyte survival (Hgf, Foxm1, Erbb2, Lin9, Areg), and inflammation-related (CSF2, Tgfb1, TNF, Ifng, Ccr2, IL6) genes, as well as the inactivation of cardiomyocyte antiproliferative factors (Cdkn1a, FoxO3, α-catenin). The predicted downstream effects include a decrease in heart damage, and increased arrhythmia, angiogenesis, and cardiogenesis. There were no significant sex-dependent differences in the AVF-stimulated cardiac adaptation.

Conclusions

AVF stimulate adaptive cardiac hypertrophy in wild-type mice without heart failure or pathologic fibrosis. Transcriptional correlates suggest AVF-induced cardiac remodeling has some cardioprotective, although also arrhythmogenic features. (JVS–Vascular Science 2021;2:110-28.)

Clinical Relevance

Arteriovenous fistulae (AVF) are commonly used as access for hemodialysis in patients with end-stage renal disease. AVF induce a high-output state that is associated with long-term structural cardiac remodeling, including left ventricle hypertrophy, but this element has uncertain clinical significance. Although left ventricle hypertrophy has traditionally been associated with an increased risk of cardiovascular disease, clinical studies have suggested that cardiac-specific outcomes of patients with end-stage renal disease were better with AVF compared with other dialysis modalities. This study uses a mouse model of AVF to study the structural, functional, and molecular correlates of AVF-induced cardiac remodeling. It finds that AVF causes an adaptive cardiac hypertrophy without functional decline or fibrosis. Transcriptional correlates suggest an electrical remodeling and the upregulation of proangiogenic, procardiogenic, and prosurvival factors, implying that AVF-induced cardiac hypertrophy is potentially cardioprotective, but also arrhythmogenic.

San1 deficiency leads to cardiomyopathy due to excessive R-loop-associated DNA damage and cardiomyocyte hypoplasia

R-loops are naturally occurring transcriptional intermediates containing RNA/DNA hybrids. Excessive R-loops cause genomic instability, DNA damage, and replication stress. Senataxin-associated exonuclease (San1) is a protein that interacts with Senataxin (SETX), a helicase resolving R-loops. It remains unknown if R-loops-induced DNA damage plays a role in the heart, especially in the proliferative neonatal cardiomyocytes (CMs). San1-/- mice were generated using the CRISPR/Cas9 technique. The newborn San1-/- mice show no overt phenotype, but their hearts were smaller with larger, yet fewer CMs. CM proliferation was impaired with reduced cell cycle-related transcripts and proteins. S9.6 staining revealed that excessive R-loops accumulated in the nucleus of neonatal San1-/- CMs. Increased γH2AX staining on newborn and adult heart sections exhibited increased DNA damage. Similarly, San1-/- AC16-cardiomyocytes showed cumulative R-loops and DNA damage, leading to the activation of cell cycle checkpoint kinase ATR and PARP1 hyperactivity, arresting G2/M cell-cycle and CM proliferation. Together, the present study uncovers an essential role of San1 in resolving excessive R-loops that lead to DNA damage and repressing CM proliferation, providing new insights into a novel biological function of San1 in the neonatal heart. San1 may serve as a novel therapeutic target for the treatment of hypoplastic cardiac disorders.

DAND5 Inactivation Enhances Cardiac Differentiation in Mouse Embryonic Stem Cells

Deciphering the clues of a regenerative mechanism for the mammalian adult heart would save millions of lives in the near future. Heart failure due to cardiomyocyte loss is still one of the significant health burdens worldwide. Here, we show the potential of a single molecule, DAND5, in mouse pluripotent stem cell-derived cardiomyocytes specification and proliferation. Dand5 loss-of-function generated the double of cardiac beating foci compared to the wild-type cells. The early formation of cardiac progenitor cells and the increased proliferative capacity of Dand5 KO mESC-derived cardiomyocytes contribute to the observed higher number of derived cardiac cells. Transcriptional profiling sequencing and quantitative RT-PCR assays showed an upregulation of early cardiac gene networks governing cardiomyocyte differentiation, cell cycling, and cardiac regenerative pathways but reduced levels of genes involved in cardiomyocyte maturation. These findings prompt DAND5 as a key driver for the generation and expansion of pluripotent stem cell-derived cardiomyocytes systems with further clinical application purposes.

Inhibiting the Pkm2/b-catenin axis drives in vivo replication of adult cardiomyocytes following experimental MI

Adult mammalian cardiomyocytes (CM) are postmitotic, differentiated cells that cannot re-enter the cell cycle after any appreciable injury. Therefore, understanding the factors required to induce CM proliferation for repair is of great clinical importance. While expression of muscle pyruvate kinase 2 (Pkm2), a cytosolic enzyme catalyzing the final step in glycolysis, is high in end-stage heart failure (HF), the loss of Pkm2 promotes proliferation in some cellular systems, in vivo. We hypothesized that in the adult heart CM proliferation may require low Pkm2 activity. Thus, we investigated the potential for Pkm2 to regulate CM proliferation in a mouse model of myocardial infarction (MI) employing inducible, cardiac-specific Pkm2 gene knockout (Pkm2KOi) mice. We found a lack of cardiac hypertrophy or expression of the fetal gene program in Pkm2KOi mice post MI, as compared to vehicle control animals (P < 0.01), correlating with smaller infarct size, improved mitochondrial (mt) function, enhanced angiogenesis, reduced degree of CM apoptosis, and reduced oxidative stress post MI. There was significantly higher numbers of dividing CM in the infarct zone between 3-9 days post MI (P < 0.001). Mechanistically, we determined that Pkm2 interacts with β-catenin (Ctnnb1) in the cytoplasm of CM, inhibiting Ctnnb1 phosphorylation at serine 552 and tyrosine 333, by Akt. In the absence of Pkm2, Ctnnb1 translocates to the nucleus leading to transcriptional activation of proliferation-associated target genes. All these effects are abrogated by genetic co-deletion of Pkm2 and Ctnnb1. Collectively, this work supports a novel antiproliferative function for Pkm2 in CM through the sequestration of Ctnnb1 in the cytoplasm of CM whereas loss of Pkm2 is essential for CM proliferation. Reducing cardiac Pkm2 expression may provide a useful strategy for cardiac repair after MI in patients.

Infarct in the Heart: What's MMP-9 Got to Do with It?

Over the past three decades, numerous studies have shown a strong connection between matrix metalloproteinase 9 (MMP-9) levels and myocardial infarction (MI) mortality and left ventricle remodeling and dysfunction. Despite this fact, clinical trials using MMP-9 inhibitors have been disappointing. This review focuses on the roles of MMP-9 in MI wound healing. Infiltrating leukocytes, cardiomyocytes, fibroblasts, and endothelial cells secrete MMP-9 during all phases of cardiac repair. MMP-9 both exacerbates the inflammatory response and aids in inflammation resolution by stimulating the pro-inflammatory to reparative cell transition. In addition, MMP-9 has a dual effect on neovascularization and prevents an overly stiff scar. Here, we review the complex role of MMP-9 in cardiac wound healing, and highlight the importance of targeting MMP-9 only for its detrimental actions. Therefore, delineating signaling pathways downstream of MMP-9 is critical.

Comprehensive Analysis of the Transcriptome-Wide m6A Methylome of Heart via MeRIP After Birth: Day 0 vs. Day 7

Aim: To systematically classify the profile of the RNA m6A modification landscape of neonatal heart regeneration.

Materials and Methods: Cardiomyocyte proliferation markers were detected via immunostaining. The expression of m6A modification regulators was detected using quantitative real-time PCR (qPCR) and Western blotting. Genome-wide profiling of methylation-modified transcripts was conducted with methylation-modified RNA immunoprecipitation sequencing (m6A-RIP-seq) and RNA sequencing (RNA-seq). The Gene Expression Omnibus database (GEO) dataset was used to verify the hub genes.

Results: METTL3 and the level of m6A modification in total RNA was lower in P7 rat hearts than in P0 ones. In all, 1,637 methylation peaks were differentially expressed using m6A-RIP-seq, with 84 upregulated and 1,553 downregulated. Furthermore, conjoint analyses of m6A-RIP-seq, RNA-seq, and GEO data generated eight potential hub genes with differentially expressed hypermethylated or hypomethylated m6A levels.

Conclusion: Our data provided novel information on m6A modification changes between Day 0 and Day 7 cardiomyocytes, which identified that increased METTL3 expression may enhance the proliferative capacity of neonatal cardiomyocytes, providing a theoretical basis for future clinical studies on the direct regulation of m6A in the proliferative capacity of cardiomyocytes.

Mitochondria and metabolic transitions in cardiomyocytes: lessons from development for stem cell-derived cardiomyocytes

Current methods to differentiate cardiomyocytes from human pluripotent stem cells (PSCs) inadequately recapitulate complete development and result in PSC-derived cardiomyocytes (PSC-CMs) with an immature or fetal-like phenotype. Embryonic and fetal development are highly dynamic periods during which the developing embryo or fetus is exposed to changing nutrient, oxygen, and hormone levels until birth. It is becoming increasingly apparent that these metabolic changes initiate developmental processes to mature cardiomyocytes. Mitochondria are central to these changes, responding to these metabolic changes and transitioning from small, fragmented mitochondria to large organelles capable of producing enough ATP to support the contractile function of the heart. These changes in mitochondria may not simply be a response to cardiomyocyte maturation; the metabolic signals that occur throughout development may actually be central to the maturation process in cardiomyocytes. Here, we review methods to enhance maturation of PSC-CMs and highlight evidence from development indicating the key roles that mitochondria play during cardiomyocyte maturation. We evaluate metabolic transitions that occur during development and how these affect molecular nutrient sensors, discuss how regulation of nutrient sensing pathways affect mitochondrial dynamics and function, and explore how changes in mitochondrial function can affect metabolite production, the cell cycle, and epigenetics to influence maturation of cardiomyocytes.

Low-dose Dasatinib Ameliorates Hypertrophic Cardiomyopathy in Noonan Syndrome with Multiple Lentigines

Purpose

Noonan syndrome with multiple lentigines (NSML) is an autosomal dominant disorder presenting with hypertrophic cardiomyopathy (HCM). Up to 85% of NSML cases are caused by mutations in the PTPN11 gene that encodes for the Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 2 (SHP2). We previously showed that low-dose dasatinib protects from the development of cardiac fibrosis in a mouse model of NSML harboring a Ptpn11^Y279C mutation. This study is performed to determine the pharmacokinetic (PK) and pharmacodynamic (PD) properties of a low-dose of dasatinib in NSML mice and to determine its effectiveness in ameliorating the development of HCM.

Methods

Dasatinib was administered intraperitoneally into NSML mice with doses ranging from 0.05 to 0.5 mg/kg. PK parameters of dasatinib in NSML mice were determined. PD parameters were obtained for biochemical analyses from heart tissue. Dasatinib-treated NSML mice (0.1 mg/kg) were subjected to echocardiography and assessment of markers of HCM by qRT-PCR. Transcriptome analysis was performed from the heart tissue of low-dose dasatinib-treated mice.

Results

Low-dose dasatinib exhibited PK properties that were linear across doses in NSML mice. Dasatinib treatment of between 0.05 and 0.5 mg/kg in NSML mice yielded an exposure-dependent inhibition of c-Src and PZR tyrosyl phosphorylation and inhibited AKT phosphorylation. We found that doses as low as 0.1 mg/kg of dasatinib prevented HCM in NSML mice. Transcriptome analysis identified differentially expressed HCM-associated genes in the heart of NSML mice that were reverted to wild type levels by low-dose dasatinib administration.

Conclusion

These data demonstrate that low-dose dasatinib exhibits desirable therapeutic PK properties that is sufficient for effective target engagement to ameliorate HCM progression in NSML mice. These data demonstrate that low-dose dasatinib treatment may be an effective therapy against HCM in NSML patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10557-021-07169-z.

Hypertension, BMI, and cardiovascular and cerebrovascular diseases

Hypertension is associated with body mass index (BMI) and cardiovascular and cerebrovascular diseases (CCDs). Whether hypertension modifies the relationship between BMI and CCDs is still unclear. We examined the association between BMI and CCDs and tested whether effect measure modification was present by hypertension. We identified a population-based sample of 3,942 participants in Shuncheng, Fushun, Liaoning, China. Hypertension was defined as any past use of antihypertensive medication or having a measured systolic/diastolic blood pressure ≥130/80 mm Hg. BMI was calculated from measured body weight and body height. Data on diagnosed CCDs were self-reported and validated in the medical records. We used logistic regression models to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for associations between BMI and CCDs. Higher BMI was associated with increased odds of having CCDs (OR = 1.19, 95% CI: 1.07–1.31). This association was significantly modified by hypertension (P for interaction <0.001), with positive associations observed among hypertensive individuals (OR = 1.28, 95% CI: 1.14–1.42). Age, sex, and diabetic status did not modify the relationship between BMI and CCDs (all P for interaction >0.10). Although higher BMI was associated with increased odds of CCDs, the relationship was mainly limited to hypertensive patients.

A loss-of-function mutation p.T256M in NDRG4 is implicated in the pathogenesis of pulmonary atresia with ventricular septal defect (PA/VSD) and tetralogy of Fallot (TOF)

Pulmonary atresia with ventricular septal defect (PA/VSD) is a rare congenital heart disease (CHD) characterized by a lack of luminal continuity and blood flow from either the right ventricle or the pulmonary artery, together with VSDs. The prevalence of PA/VSD is about 0.2% of live births and approximately 2% of CHDs. PA/VSD is similar to tetralogy of Fallot (TOF) in terms of structural and pathological characteristics. The pathogenesis of these two CHDs remains incompletely understood. It was previously reported that N‐myc downstream‐regulated gene (NDRG)4 is required for myocyte proliferation during early cardiac development. In the present study, we enrolled 80 unrelated patients with PA/VSD or TOF and identified a probably damaging variant p.T256M of NDRG4. The p.T256M variant impaired the proliferation ability of human cardiac myocytes (hCM). Furthermore, the p.T256M variant resulted in G1 and G2 arrest of hCM, followed by an increase in p27 and caspase‐9 expression. Our results provide evidence that the p.T256M variant in NDRG4 is a pathogenic variant associated with impaired hCM proliferation and cell‐cycle arrest and likely contributes towards the pathogenesis of PA/VSD and TOF.

miR‑449a‑5p suppresses CDK6 expression to inhibit cardiomyocyte proliferation

Induction of cardiomyocyte (CM) proliferation is a promising approach for cardiac regeneration following myocardial injury. MicroRNAs (miRs) have been reported to regulate CM proliferation. In particular, miR‑449a‑5p has been identified to be associated with CM proliferation in previous high throughput functional screening data. However, whether miR‑449a‑5p regulates CM proliferation has not been thoroughly investigated. This study aimed to explore whether miR‑449a‑5p modulates CM proliferation and to identify the molecular mechanism via which miR‑449a‑5p regulates CM proliferation. The current study demonstrated that miR‑449a‑5p expression levels were significantly increased during heart development. Furthermore, the results suggested that miR‑449a‑5p mimic inhibited CM proliferation <em>in vitro</em> as determined via immunofluorescence for ki67 and histone H3 phosphorylated at serine 10 (pH3), as well as the numbers of CMs. However, miR‑449a‑5p knockdown promoted CM proliferation. CDK6 was identified as a direct target gene of miR‑449a‑5p, and CDK6 mRNA and protein expression was suppressed by miR‑449a‑5p. Moreover, CDK6 gain‑of‑function increased CM proliferation. Overexpression of CDK6 also blocked the inhibitory effect of miR‑449a‑5p on CM proliferation, indicating that CDK6 was a functional target of miR‑449a‑5p in CM proliferation. In conclusion, miR‑449a‑5p inhibited CM proliferation by targeting CDK6, which provides a potential molecular target for preventing myocardial injury.

Progesterone, via yes-associated protein, promotes cardiomyocyte proliferation and cardiac repair

Objectives

The mechanisms responsible for the postnatal loss of mammalian cardiac regenerative capacity are not fully elucidated. The aim of the present study is to investigate the role of progesterone in cardiac regeneration and explore underlying mechanism.

Materials and Methods

Effect of progesterone on cardiomyocyte proliferation was analysed by immunofluorescent staining. RNA sequencing was performed to screen key target genes of progesterone, and yes‐associated protein (YAP) was knocked down to demonstrate its role in pro‐proliferative effect of progesterone. Effect of progesterone on activity of YAP promoter was measured by luciferase assay and interaction between progesterone receptor and YAP promoter by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP). Adult mice were subjected to myocardial infarction, and then, effects of progesterone on adult cardiac regeneration were analysed.

Results

Progesterone supplementation enhanced cardiomyocyte proliferation in a progesterone receptor‐dependent manner. Progesterone up‐regulated YAP expression and knockdown of YAP by small interfering RNA reduced progesterone‐mediated cardiomyocyte proliferative effect. Progesterone receptor interacted with the YAP promoter, determined by ChIP and EMSA; progesterone increased luciferase activity of YAP promoter and up‐regulated YAP target genes. Progesterone administration also promoted adult cardiomyocyte proliferation and improved cardiac function in myocardial infarction.

Conclusion

Our data uncover a role of circulating progesterone withdrawal as a novel mechanism for the postnatal loss of mammalian cardiac regenerative potential. Progesterone promotes both neonatal and adult cardiomyocyte proliferation by up‐regulating YAP expression.