Building and re-building the heart by cardiomyocyte proliferation

The role of deubiquitinases in cardiovascular diseases: mechanisms and therapeutic implications

Cardiovascular diseases (CVDs) have become the leading cause of death globally, surpassing infectious diseases and other chronic illnesses. The incidence and mortality rates of CVDs are rising worldwide, posing a key challenge in public health. The ubiquitination system is a vast and complex. It is an important post-translational modification that plays a crucial role in various cellular processes. Deubiquitination is catalyzed by deubiquitinases (DUBs), which remove ubiquitin (Ub) from ubiquitinated proteins, thereby reversing the ubiquitination process. DUBs play an important role in many biological processes, such as DNA repair, cell metabolism, differentiation, epigenetic regulation, and protein stability control. They also participate in the regulation of many signaling pathways associated with the development and progression of CVDs. In this review, we primarily focus on the role of DUBs in various key pathological mechanisms of atherosclerosis (AS), such as foam cell formation, vascular remodeling (VR), endothelial-to-mesenchymal transition (End-MT), and clonal hematopoiesis (CH). In the heart, we summarize the involvement of DUBs in diseases and pathological processes, including heart failure (HF), myocardial infarction (MI), myocardial hypertrophy (MH) and ischemia/reperfusion (I/R) injury. Additionally, we also explore the diabetic cardiomyopathy (DCM) and the use of doxorubicin-induced cardiotoxicity in clinical settings. A comprehensive understanding of deubiquitination may provide new insights for the treatment and drug design of CVDs.

The Application of scRNA-Seq in Heart Development and Regeneration

Single-cell RNA sequencing (scRNA-seq) is a rapidly developing and useful technique for elucidating biological mechanisms and characterizing individual cells. Tens of millions of patients worldwide suffer from heart injuries and other types of heart disease. Neonatal mammalian hearts and certain adult vertebrate species, such as zebrafish, can fully regenerate after myocardial injury. However, the adult mammalian heart is unable to regenerate the damaged myocardium. scRNA-seq provides many new insights into pathological and normal hearts and facilitates our understanding of cellular responses to cardiac injury and repair at different stages, which may provide critical clues for effective therapies for adult heart regeneration. In this review, we summarize the application of scRNA-seq in heart development and regeneration and describe how important molecular mechanisms can be harnessed to promote heart regeneration.

Squamate ventricular cardiomyocytes: Ploidy, proliferation, and heart muscle cell size in the leopard gecko (Eublepharis macularius)

BACKGROUND

While heart function is broadly conserved across vertebrates, the cellular phenotype of muscle cells (cardiomyocytes) varies across taxa and throughout ontogeny. Emerging evidence suggests that some attributes may correlate with the capacity for spontaneous cardiomyocyte replacement following injury. For example, among non-regenerating taxa like adult mammals and birds, cardiomyocytes are polyploid, rarely proliferate, and are large in size. In contrast, in regeneration-competent zebrafish and amphibians, cardiomyocytes are diploid, spontaneously proliferate, and are comparatively small. For other species, less is known.

RESULTS

Here, we investigate these attributes in the squamate Eublepharis macularius, the leopard gecko. Using the nuclear counterstain DAPI to measure fluorescence intensity as a proxy for DNA content, we found that >90% of adult cardiomyocytes are diploid. Using serial histology and immunostaining for markers of DNA synthesis and mitosis, we determined that adult gecko cardiomyocytes spontaneously proliferate, albeit at significantly lower levels than previously reported in subadults. Furthermore, using wheat germ agglutinin, we found that the cross-sectional area is maintained across ontogeny and that gecko cardiomyocytes are 10× smaller than those of mice.

CONCLUSIONS

Taken together, our data show that gecko cardiomyocytes share several key cellular attributes with regeneration-competent species and that postnatal ventricular growth occurs via cardiomyocyte hyperplasia.

RNA-Binding Protein Signature in Proliferative Cardiomyocytes: A Cross-Species Meta-Analysis from Mouse, Pig, and Human Transcriptomic Profiling Data

In mammals, because cardiomyocytes withdraw from cell-cycle activities shortly after birth, the heart cannot repair the damage caused by a myocardial injury; thus, understanding how cardiomyocytes proliferate is among the most important topics in cardiovascular sciences. In newborn neonatal mammals, when a left ventricular injury is applied in hearts earlier than postnatal day 7, the cardiomyocytes actively proliferate and regenerate lost myocardium in the following weeks. The regulators promoting cardiomyocyte proliferation were discovered by analyzing transcriptomic data generated from models. Most of these regulators support the mRNA production of cell-cycle machinery, yet the mRNA requires translation into functional proteins under the regulation of RNA-binding proteins (RBPs). In this work, we performed a meta-analysis to study the relationship between RBP expression and cardiomyocyte proliferation. To identify RBPs associated with mouse and pig cardiomyocyte proliferation, the single-nuclei RNA sequencing (snRNA-seq) data from regenerating mouse and pig hearts were reanalyzed via an Autoencoder focusing on RBP expression. We also generated and analyzed new bulk RNA-seq from two human-induced pluripotent stem cell-derived (hiPSC) cardiomyocyte (hiPSC-CM) cell lines; the first cell line was harvested sixteen days after differentiation, when the cells still actively proliferated, and the second cell line was harvested one hundred and forty days after differentiation, when the cells ceased cell cycle activity. Then, the RBP associated with mouse, pig, and hiPSC-CM were compared across species. Twenty-one RBPs were found to be consistently upregulated, and six RBPs were downregulated in proliferating mouse, pig, and hiPSC-derived cardiomyocytes. Among upregulated RBPs across species, an immunofluorescence-based imaging analysis validated the significant increase in the proteins of DHX9, PTBP3, HNRNPUL1, and DDX6 in pig hearts with proliferating CMs. This meta-analysis in all species demonstrated a strong relationship between RBP expression and cardiomyocyte proliferation.

N-Cadherin promotes cardiac regeneration by potentiating pro-mitotic β-Catenin signaling in cardiomyocytes

Adult human hearts exhibit limited regenerative capacity. Post-injury cardiomyocyte (CM) loss can lead to myocardial dysfunction and failure. Although neonatal mammalian hearts can regenerate, the underlying molecular mechanisms remain elusive. Herein, comparative transcriptome analyses identify adherens junction protein N-Cadherin as a crucial regulator of CM proliferation/renewal. Its expression correlates positively with mitotic genes and shows an age-dependent reduction. N-Cadherin is upregulated in the neonatal mouse heart following injury, coinciding with increased CM mitotic activities. N-Cadherin knockdown reduces, whereas overexpression increases, the proliferation activity of neonatal mouse CMs and human induced pluripotent stem cell-derived CMs. Mechanistically, N-Cadherin binds and stabilizes pro-mitotic transcription regulator β-Catenin, driving CM self-renewal. Targeted N-Cadherin deletion in CMs impedes cardiac regeneration in neonatal mice, leading to excessive scarring. N-Cadherin overexpression, by contrast, promotes regeneration in adult mouse hearts following ischemic injury. N-Cadherin targeting presents a promising avenue for promoting cardiac regeneration and restoring function in injured adult human hearts.

Mechanisms and Therapeutic Potential of Multiple Forms of Cell Death in Myocardial Ischemia-Reperfusion Injury

Programmed cell death, especially programmed necrosis such as necroptosis, ferroptosis, and pyroptosis, has attracted significant attention recently. Traditionally, necrosis was thought to occur accidentally without signaling pathways, but recent discoveries have revealed that molecular pathways regulate certain forms of necrosis, similar to apoptosis. Accumulating evidence indicates that programmed necrosis is involved in the development of various diseases, including myocardial ischemia-reperfusion injury (MIRI). MIRI occurs when blood flow and oxygen return to an ischemic area, causing excessive production of reactive oxygen species. While this reperfusion is critical for treating myocardial infarction, it inevitably causes cellular damage via oxidative stress. Furthermore, this cellular damage triggers multiple forms of cardiomyocyte death, which is the primary cause of inflammation, cardiac tissue remodeling, and ensuing heart failure. Therefore, understanding the molecular mechanisms of various forms of cell death in MIRI is crucial for therapeutic target discovery. Developing therapeutic strategies to inhibit multiple cell death pathways simultaneously could provide effective protection against MIRI. In this paper, we review the fundamental molecular pathways and MIRI-specific mechanisms of apoptosis, necroptosis, ferroptosis, and pyroptosis. Additionally, we suggest that the simultaneous suppression of multiple cell death pathways could be an effective therapy and identify potential therapeutic targets for implementing this strategy.

Micropeptide MPM regulates cardiomyocyte proliferation and heart growth via the AKT pathway

The role of micropeptide in cardiomyocyte proliferation remains unknown. We found that MPM (micropeptide in mitochondria) was highly expressed in cardiomyocytes. Compared to MPM+/+ mice, MPM knockout (MPM-/-) mice exhibited reduction in left ventricular (LV) mass, myocardial thickness and LV fractional shortening. RNA-sequencing analysis in H9c2, a rat cardiomyocyte cell line, identified downregulation of cell cycle-promoting genes as the most significant alteration in MPM-silencing cells. Consistently, gain- and loss-of-function analyses in H9c2 cells revealed that cardiomyocyte proliferation was repressed by silencing MPM but was promoted by overexpressing MPM. Moreover, the cardiomyocytes in the hearts of MPM-/- mice displayed reduced proliferation rates. Mechanism investigations disclosed that MPM is crucial for AKT activation in cardiomyocytes. We also identified an interaction between MPM and PTPMT1, and found that silencing PTPMT1 attenuated the effect of MPM in activating the AKT pathway, whereas inhibition of the AKT pathway abrogated the role of MPM in promoting cardiomyocyte proliferation. Collectively, these results indicate that MPM may promote cardiomyocyte proliferation and thus heart growth by interacting with PTPMT1 to activate the AKT pathway. Our findings identify the novel function and regulatory network of MPM and highlight the importance of micropeptides in cardiomyocyte proliferation and heart growth.

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.

Distinct mechanisms regulate ventricular and atrial chamber wall formation

Tissues undergo distinct morphogenetic processes to achieve similarly shaped structures. In the heart, cardiomyocytes in both the ventricle and atrium build internal structures for efficient contraction. Ventricular wall formation (trabeculation) is initiated by cardiomyocyte delamination. How cardiomyocytes build the atrial wall is poorly understood. Using longitudinal imaging in zebrafish, we found that at least 25% of the atrial cardiomyocytes elongate along the long axis of the heart. These cell shape changes result in cell intercalation and convergent thickening, leading to the formation of the internal muscle network. We tested factors important for ventricular trabeculation including Nrg/ErbB and Notch signaling and found no evidence for their role in atrial muscle network formation. Instead, our data suggest that atrial cardiomyocyte elongation is regulated by Yap, which has not been implicated in trabeculation. Altogether, these data indicate that distinct cellular and molecular mechanisms build the internal muscle structures in the atrium and ventricle.

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.

Cardiac-specific deletion of heat shock protein 60 induces mitochondrial stress and disrupts heart development in mice

Congenital heart diseases are the most common birth defects around the world. Emerging evidence suggests that mitochondrial homeostasis is required for normal heart development. In mitochondria, a series of molecular chaperones including heat shock protein 60 (HSP60) are engaged in assisting the import and folding of mitochondrial proteins. However, it remains largely obscure whether and how these mitochondrial chaperones regulate cardiac development. Here, we generated a cardiac-specific Hspd1 deletion mouse model by αMHC-Cre and investigated the role of HSP60 in cardiac development. We observed that deletion of HSP60 in embryonic cardiomyocytes resulted in abnormal heart development and embryonic lethality, characterized by reduced cardiac cell proliferation and thinner ventricular walls, highlighting an essential role of cardiac HSP60 in embryonic heart development and survival. Our results also demonstrated that HSP60 deficiency caused significant downregulation of mitochondrial ETC subunits and induced mitochondrial stress. Analysis of gene expression revealed that P21 that negatively regulates cell proliferation is significantly upregulated in HSP60 knockout hearts. Moreover, HSP60 deficiency induced activation of eIF2α-ATF4 pathway, further indicating the underlying mitochondrial stress in cardiomyocytes after HSP60 deletion. Taken together, our study demonstrated that regular function of mitochondrial chaperones is pivotal for maintaining normal mitochondrial homeostasis and embryonic heart development.

Chlorogenic Acid Attenuates Isoproterenol Hydrochloride-Induced Cardiac Hypertrophy in AC16 Cells by Inhibiting the Wnt/β-Catenin Signaling Pathway

Cardiac hypertrophy (CH) is an important characteristic in heart failure development. Chlorogenic acid (CGA), a crucial bioactive compound from honeysuckle, is reported to protect against CH. However, its underlying mechanism of action remains incompletely elucidated. Therefore, this study aimed to explore the mechanism underlying the protective effect of CGA on CH. This study established a CH model by stimulating AC16 cells with isoproterenol (Iso). The observed significant decrease in cell surface area, evaluated through fluorescence staining, along with the downregulation of CH-related markers, including atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and β-myosin heavy chain (β-MHC) at both mRNA and protein levels, provide compelling evidence of the protective effect of CGA against isoproterenol-induced CH. Mechanistically, CGA induced the expression of glycogen synthase kinase 3β (GSK-3β) while concurrently attenuating the expression of the core protein β-catenin in the Wnt/β-catenin signaling pathway. Furthermore, the experiment utilized the Wnt signaling activator IM-12 to observe its ability to modulate the impact of CGA pretreatment on the development of CH. Using the Gene Expression Omnibus (GEO) database combined with online platforms and tools, this study identified Wnt-related genes influenced by CGA in hypertrophic cardiomyopathy (HCM) and further validated the correlation between CGA and the Wnt/β-catenin signaling pathway in CH. This result provides new insights into the molecular mechanisms underlying the protective effect of CGA against CH, indicating CGA as a promising candidate for the prevention and treatment of heart diseases.

Distinct epicardial gene regulatory programs drive development and regeneration of the zebrafish heart

Unlike the adult mammalian heart, which has limited regenerative capacity, the zebrafish heart fully regenerates following injury. Reactivation of cardiac developmental programs is considered key to successfully regenerating the heart, yet the regulation underlying the response to injury remains elusive. Here, we compared the transcriptome and epigenome of the developing and regenerating zebrafish epicardia. We identified epicardial enhancer elements with specific activity during development or during adult heart regeneration. By generating gene regulatory networks associated with epicardial development and regeneration, we inferred genetic programs driving each of these processes, which were largely distinct. Loss of Hif1ab, Nrf1, Tbx2b, and Zbtb7a, central regulators of the regenerating epicardial network, in injured hearts resulted in elevated epicardial cell numbers infiltrating the wound and excess fibrosis after cryoinjury. Our work identifies differences between the regulatory blueprint deployed during epicardial development and regeneration, underlining that heart regeneration goes beyond the reactivation of developmental programs.

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Gelatin methacrylate (GelMA) hydrogels have gained significant traction in diverse tissue engineering applications through the utilization of 3D printing technology. As an artificial hydrogel possessing remarkable processability, GelMA has emerged as a pioneering material in the advancement of tissue engineering due to its exceptional biocompatibility and degradability. The integration of 3D printing technology facilitates the precise arrangement of cells and hydrogel materials, thereby enabling the creation of in vitro models that simulate artificial tissues suitable for transplantation. Consequently, the potential applications of GelMA in tissue engineering are further expanded. In tissue engineering applications, the mechanical properties of GelMA are often modified to overcome the hydrogel material's inherent mechanical strength limitations. This review provides a comprehensive overview of recent advancements in enhancing the mechanical properties of GelMA at the monomer, micron, and nano scales. Additionally, the diverse applications of GelMA in soft tissue engineering via 3D printing are emphasized. Furthermore, the potential opportunities and obstacles that GelMA may encounter in the field of tissue engineering are discussed. It is our contention that through ongoing technological progress, GelMA hydrogels with enhanced mechanical strength can be successfully fabricated, leading to the production of superior biological scaffolds with increased efficacy for tissue engineering purposes.

Animal models to study cardiac regeneration

Permanent fibrosis and chronic deterioration of heart function in patients after myocardial infarction present a major health-care burden worldwide. In contrast to the restricted potential for cellular and functional regeneration of the adult mammalian heart, a robust capacity for cardiac regeneration is seen during the neonatal period in mammals as well as in the adults of many fish and amphibian species. However, we lack a complete understanding as to why cardiac regeneration takes place more efficiently in some species than in others. The capacity of the heart to regenerate after injury is controlled by a complex network of cellular and molecular mechanisms that form a regulatory landscape, either permitting or restricting regeneration. In this Review, we provide an overview of the diverse array of vertebrates that have been studied for their cardiac regenerative potential and discuss differential heart regeneration outcomes in closely related species. Additionally, we summarize current knowledge about the core mechanisms that regulate cardiac regeneration across vertebrate species.

Endothelial cells adopt a pro-reparative immune responsive signature during cardiac injury

Modulation of the heart's immune microenvironment is crucial for recovery after ischemic events such as myocardial infarction (MI). Endothelial cells (ECs) can have immune regulatory functions; however, interactions between ECs and the immune environment in the heart after MI remain poorly understood. We identified an EC-specific IFN responsive and immune regulatory gene signature in adult and pediatric heart failure (HF) tissues. Single-cell transcriptomic analysis of murine hearts subjected to MI uncovered an EC population (IFN-ECs) with immunologic gene signatures similar to those in human HF. IFN-ECs were enriched in regenerative-stage mouse hearts and expressed genes encoding immune responsive transcription factors (Irf7, Batf2, and Stat1). Single-cell chromatin accessibility studies revealed an enrichment of these TF motifs at IFN-EC signature genes. Expression of immune regulatory ligand genes by IFN-ECs suggests bidirectional signaling between IFN-ECs and macrophages in regenerative-stage hearts. Our data suggest that ECs may adopt immune regulatory signatures after cardiac injury to accompany the reparative response. The presence of these signatures in human HF and murine MI models suggests a potential role for EC-mediated immune regulation in responding to stress induced by acute injury in MI and chronic adverse remodeling in HF.

Thioredoxin-1 and its mimetic peptide improve systolic cardiac function and remodeling after myocardial infarction

Myocardial infarction (MI) is characterized by a significant loss of cardiomyocytes (CMs), and it is suggested that reactive oxygen species (ROS) are involved in cell cycle arrest, leading to impaired CM renewal. Thioredoxin-1 (Trx-1) scavenges ROS and may play a role in restoring CM renewal. However, the truncated form of Trx-1, Trx-80, can compromise its efficacy by exerting antagonistic effects. Therefore, a Trx-1 mimetic peptide called CB3 was tested as an alternative way to restore CMs. This study aimed to investigate the effects of Trx-1, Trx-80, and CB3 on mice with experimental MI and study the underlying mechanism of CB3 on CMs. Mouse cardiac parameters were quantified by echocardiography, and infarction size and fibrosis determined using Trichrome and Picro-Sirius Red staining. The study found that Trx-1 and CB3 improved mouse cardiac function, reduced the size of cardiac infarct and fibrosis, and decreased the expression of cardiac inflammatory markers. Furthermore, CB3 polarized macrophages into M2 phenotype, reduced apoptosis and oxidative stress after MI, and increased CM proliferation in cell culture and in vivo. CB3 effectively protected against myocardial infarction and could represent a new class of compounds for treating MI.

Cardiomyocyte maturation and its reversal during cardiac regeneration

Cardiovascular disease is a leading cause of death worldwide. Due to the limited proliferative and regenerative capacity of adult cardiomyocytes, the lost myocardium is not replenished efficiently and is replaced by a fibrotic scar, which eventually leads to heart failure. Current therapies to cure or delay the progression of heart failure are limited; hence, there is a pressing need for regenerative approaches to support the failing heart. Cardiomyocytes undergo a series of transcriptional, structural, and metabolic changes after birth (collectively termed maturation), which is critical for their contractile function but limits the regenerative capacity of the heart. In regenerative organisms, cardiomyocytes revert from their terminally differentiated state into a less mature state (ie, dedifferentiation) to allow for proliferation and regeneration to occur. Importantly, stimulating adult cardiomyocyte dedifferentiation has been shown to promote morphological and functional improvement after myocardial infarction, further highlighting the importance of cardiomyocyte dedifferentiation in heart regeneration. Here, we review several hallmarks of cardiomyocyte maturation, and summarize how their reversal facilitates cardiomyocyte proliferation and heart regeneration. A detailed understanding of how cardiomyocyte dedifferentiation is regulated will provide insights into therapeutic options to promote cardiomyocyte de-maturation and proliferation, and ultimately heart regeneration in mammals.

Perish in the Attempt: Regulated Cell Death in Regenerative and Nonregenerative Tissue

Significance: A cell plays its roles throughout its life span, even during its demise. Regulated cell death (RCD) is one of the key topics in modern biomedical studies. It is considered the main approach for removing stressed and/or damaged cells. Research during the past two decades revealed more roles of RCD, such as coordinating tissue development and driving compensatory proliferation during tissue repair. Recent Advances: Compensatory proliferation, initially identified in primitive organisms during the regeneration of lost tissue, is an evolutionarily conserved process that also functions in mammals. Among various types of RCD, apoptosis is considered the top candidate to induce compensatory proliferation in damaged tissue. Critical Issues: The roles of apoptosis in the recovery of nonregenerative tissue are still vague. The roles of other types of RCD, such as necroptosis and ferroptosis, have not been well characterized in the context of tissue regeneration. Future Directions: In this review article, we attempt to summarize the recent insights on the role of RCD in tissue repair. We focus on apoptosis, with expansion to ferroptosis and necroptosis, in primitive organisms with significant regenerative capacity as well as common mammalian research models. After gathering hints from regenerative tissue, in the second half of the review, we take a notoriously nonregenerative tissue, the myocardium, as an example to discuss the role of RCD in terminally differentiated quiescent cells. Antioxid. Redox Signal. 39, 1053-1069.

Implantable Triboelectric Nanogenerators for Self-Powered Cardiovascular Healthcare

Triboelectric nanogenerators (TENGs) have gained significant traction in recent years in the bioengineering community. With the potential for expansive applications for biomedical use, many individuals and research groups have furthered their studies on the topic, in order to gain an understanding of how TENGs can contribute to healthcare. More specifically, there have been a number of recent studies focusing on implantable triboelectric nanogenerators (I-TENGs) toward self-powered cardiac systems healthcare. In this review, the progression of implantable TENGs for self-powered cardiovascular healthcare, including self-powered cardiac monitoring devices, self-powered therapeutic devices, and power sources for cardiac pacemakers, will be systematically reviewed. Long-term expectations of these implantable TENG devices through their biocompatibility and other utilization strategies will also be discussed.

Cell Therapy in the Treatment of Coronary Heart Disease

Heart failure is a leading cause of death in patients who have suffered a myocardial infarction. Despite the timely use of modern reperfusion therapies such as thrombolysis, surgical revascularization and balloon angioplasty, they are sometimes unable to prevent the development of significant areas of myocardial damage and subsequent heart failure. Research efforts have focused on developing strategies to improve the functional status of myocardial injury areas. Consequently, the restoration of cardiac function using cell therapy is an exciting prospect. This review describes the characteristics of various cell types relevant to cellular cardiomyoplasty and presents findings from experimental and clinical studies investigating cell therapy for coronary heart disease. Cell delivery methods, optimal dosage and potential treatment mechanisms are discussed.

Hypoxia-induced signaling in the cardiovascular system: pathogenesis and therapeutic targets

Hypoxia, characterized by reduced oxygen concentration, is a significant stressor that affects the survival of aerobic species and plays a prominent role in cardiovascular diseases. From the research history and milestone events related to hypoxia in cardiovascular development and diseases, The "hypoxia-inducible factors (HIFs) switch" can be observed from both temporal and spatial perspectives, encompassing the occurrence and progression of hypoxia (gradual decline in oxygen concentration), the acute and chronic manifestations of hypoxia, and the geographical characteristics of hypoxia (natural selection at high altitudes). Furthermore, hypoxia signaling pathways are associated with natural rhythms, such as diurnal and hibernation processes. In addition to innate factors and natural selection, it has been found that epigenetics, as a postnatal factor, profoundly influences the hypoxic response and progression within the cardiovascular system. Within this intricate process, interactions between different tissues and organs within the cardiovascular system and other systems in the context of hypoxia signaling pathways have been established. Thus, it is the time to summarize and to construct a multi-level regulatory framework of hypoxia signaling and mechanisms in cardiovascular diseases for developing more therapeutic targets and make reasonable advancements in clinical research, including FDA-approved drugs and ongoing clinical trials, to guide future clinical practice in the field of hypoxia signaling in cardiovascular diseases.

Regulatory Mechanisms That Guide the Fetal to Postnatal Transition of Cardiomyocytes

Heart disease remains a global leading cause of death and disability, necessitating a comprehensive understanding of the heart's development, repair, and dysfunction. This review surveys recent discoveries that explore the developmental transition of proliferative fetal cardiomyocytes into hypertrophic postnatal cardiomyocytes, a process yet to be well-defined. This transition is key to the heart's growth and has promising therapeutic potential, particularly for congenital or acquired heart damage, such as myocardial infarctions. Although significant progress has been made, much work is needed to unravel the complex interplay of signaling pathways that regulate cardiomyocyte proliferation and hypertrophy. This review provides a detailed perspective for future research directions aimed at the potential therapeutic harnessing of the perinatal heart transitions.

Evaluation of quantitative biomarkers of aging in human PBMCs

Functional decline with age contributes significantly to the burden of disease in developed countries. There is growing interest in the development of therapeutic interventions which slow or even reverse aging. Time and cost constraints prohibit the testing of a large number of interventions for health and lifespan extension in model organisms. Cell-based models of aging could enable high throughput testing of potential interventions. Despite extensive reports in the literature of cell properties that correlate with donor age, few are robustly observed across different laboratories. This casts doubt on the extent that aging signatures are captured in cultured cells. We tested molecular changes previously reported to correlate with donor age in peripheral blood mononuclear cells (PBMCs) and evaluated their suitability for inclusion in a panel of functional aging measures. The tested measures spanned several pathways implicated in aging including epigenetic changes, apoptosis, proteostasis, and intracellular communication. Surprisingly, only two markers correlated with donor age. DNA methylation age accurately predicted donor age confirming this is a robust aging biomarker. Additionally, the apoptotic marker CD95 correlated with donor age but only within subsets of PBMCs. To demonstrate cellular rejuvenation in response to a treatment will require integration of multiple read-outs of cell function. However, building a panel of measures to detect aging in cells is challenging and further research is needed to identify robust predictors of age in humans.

Sinus venosus adaptation models prolonged cardiovascular disease and reveals insights into evolutionary transitions of the vertebrate heart

How two-chambered hearts in basal vertebrates have evolved from single-chamber hearts found in ancestral chordates remains unclear. Here, we show that the teleost sinus venosus (SV) is a chamber-like vessel comprised of an outer layer of smooth muscle cells. We find that in adult zebrafish nr2f1a mutants, which lack atria, the SV comes to physically resemble the thicker bulbus arteriosus (BA) at the arterial pole of the heart through an adaptive, hypertensive response involving smooth muscle proliferation due to aberrant hemodynamic flow. Single cell transcriptomics show that smooth muscle and endothelial cell populations within the adapting SV also take on arterial signatures. Bulk transcriptomics of the blood sinuses flanking the tunicate heart reinforce a model of greater equivalency in ancestral chordate BA and SV precursors. Our data simultaneously reveal that secondary complications from congenital heart defects can develop in adult zebrafish similar to those in humans and that the foundation of equivalency between flanking auxiliary vessels may remain latent within basal vertebrate hearts.

Neuronal migration prevents spatial competition in retinal morphogenesis

The concomitant occurrence of tissue growth and organization is a hallmark of organismal development1-3. This often means that proliferating and differentiating cells are found at the same time in a continuously changing tissue environment. How cells adapt to architectural changes to prevent spatial interference remains unclear. Here, to understand how cell movements that are key for growth and organization are orchestrated, we study the emergence of photoreceptor neurons that occur during the peak of retinal growth, using zebrafish, human tissue and human organoids. Quantitative imaging reveals that successful retinal morphogenesis depends on the active bidirectional translocation of photoreceptors, leading to a transient transfer of the entire cell population away from the apical proliferative zone. This pattern of migration is driven by cytoskeletal machineries that differ depending on the direction: microtubules are exclusively required for basal translocation, whereas actomyosin is involved in apical movement. Blocking the basal translocation of photoreceptors induces apical congestion, which hampers the apical divisions of progenitor cells and leads to secondary defects in lamination. Thus, photoreceptor migration is crucial to prevent competition for space, and to allow concurrent tissue growth and lamination. This shows that neuronal migration, in addition to its canonical role in cell positioning4, can be involved in coordinating morphogenesis.

Genetic recording of in vivo cell proliferation by ProTracer

The ability to experimentally measure cell proliferation is the basis for understanding the sources of cells that drive organ development, tissue regeneration and repair. Recently, we generated a genetic approach to detect cell proliferation: we used genetic lineage-tracing technologies to achieve seamless recording of in vivo cell proliferation in a tissue-specific manner. We provide a detailed protocol (generation of mouse lines, characterization of mouse lines, mouse line crossing and cell-proliferation tracing) for using this genetic system to study cell proliferation. This cell-proliferation tracing system, which we term 'ProTracer' (Proliferation Tracer), permits lifelong noninvasive monitoring of cell proliferation of specific cell lineages in live animals. Compared with other short-term strategies that require execution of animals, ProTracer does not require sampling or animal sacrifice for tissue processing. To highlight these features, we used ProTracer to study the proliferation of hepatocytes during liver homeostasis and after tissue injury in mice. We show that the protocol is applicable to study any in vivo cell proliferation, which takes ~9 months to finish from mouse generation to data analysis. This protocol can easily be carried out by researchers skilled in mouse-related experiments.

Nono deficiency impedes the proliferation and adhesion of H9c2 cardiomyocytes through Pi3k/Akt signaling pathway

Congenital heart disease (CHD) is the most common type of birth defect and the main noninfectious cause of death during the neonatal stage. The non-POU domain containing, octamer-binding gene, NONO, performs a variety of roles involved in DNA repair, RNA synthesis, transcriptional and post-transcriptional regulation. Currently, hemizygous loss-of-function mutation of NONO have been described as the genetic origin of CHD. However, essential effects of NONO during cardiac development have not been fully elucidated. In this study, we aim to understand role of Nono in cardiomyocytes during development by utilizing the CRISPR/Cas9 gene editing system to deplete Nono in the rat cardiomyocytes H9c2. Functional comparison of H9c2 control and knockout cells showed that Nono deficiency suppressed cell proliferation and adhesion. Furthermore, Nono depletion significantly affected the mitochondrial oxidative phosphorylation (OXPHOS) and glycolysis, resulting in H9c2 overall metabolic deficits. Mechanistically we demonstrated that the Nono knockout impeded the cardiomyocyte function by attenuating phosphatidyl inositol 3 kinase-serine/threonine kinase (Pi3k/Akt) signaling via the assay for transposase-accessible chromatin using sequencing in combination with RNA sequencing. From these results we propose a novel molecular mechanism of Nono to influence cardiomyocytes differentiation and proliferation during the development of embryonic heart. We conclude that NONO may represent an emerging possible biomarkers and targets for the diagnosis and treatment of human cardiac development defects.

Analysis of cardiac single-cell RNA-sequencing data can be improved by the use of artificial-intelligence-based tools

Single-cell RNA sequencing (scRNAseq) enables researchers to identify and characterize populations and subpopulations of different cell types in hearts recovering from myocardial infarction (MI) by characterizing the transcriptomes in thousands of individual cells. However, the effectiveness of the currently available tools for processing and interpreting these immense datasets is limited. We incorporated three Artificial Intelligence (AI) techniques into a toolkit for evaluating scRNAseq data: AI Autoencoding separates data from different cell types and subpopulations of cell types (cluster analysis); AI Sparse Modeling identifies genes and signaling mechanisms that are differentially activated between subpopulations (pathway/gene set enrichment analysis), and AI Semisupervised Learning tracks the transformation of cells from one subpopulation into another (trajectory analysis). Autoencoding was often used in data denoising; yet, in our pipeline, Autoencoding was exclusively used for cell embedding and clustering. The performance of our AI scRNAseq toolkit and other highly cited non-AI tools was evaluated with three scRNAseq datasets obtained from the Gene Expression Omnibus database. Autoencoder was the only tool to identify differences between the cardiomyocyte subpopulations found in mice that underwent MI or sham-MI surgery on postnatal day (P) 1. Statistically significant differences between cardiomyocytes from P1-MI mice and mice that underwent MI on P8 were identified for six cell-cycle phases and five signaling pathways when the data were analyzed via Sparse Modeling, compared to just one cell-cycle phase and one pathway when the data were analyzed with non-AI techniques. Only Semisupervised Learning detected trajectories between the predominant cardiomyocyte clusters in hearts collected on P28 from pigs that underwent apical resection (AR) on P1, and on P30 from pigs that underwent AR on P1 and MI on P28. In another dataset, the pig scRNAseq data were collected after the injection of CCND2-overexpression Human-induced Pluripotent Stem Cell-derived cardiomyocytes (^CCND2hiPSC) into injured P28 pig heart; only the AI-based technique could demonstrate that the host cardiomyocytes increase proliferating by through the HIPPO/YAP and MAPK signaling pathways. For the cluster, pathway/gene set enrichment, and trajectory analysis of scRNAseq datasets generated from studies of myocardial regeneration in mice and pigs, our AI-based toolkit identified results that non-AI techniques did not discover. These different results were validated and were important in explaining myocardial regeneration.

Measures of Fetal Growth and Cardiac Structure in Stillbirths With Placental Maternal Vascular Malperfusion: Evidence for Heart Weight Sparing and Structural Cardiac Alterations in Humans

BACKGROUND

Placental maternal vascular malperfusion (MVM) is associated with fetal growth restriction (FGR). While FGR increases the risk of cardiovascular disease, the impact of MVM on fetal cardiac structure is understudied.

METHODS

We utilized a cohort of autopsied stillbirths; 29 with MVM as the cause of death and 21 with a cause of death unrelated to MVM. Fetal and organ weights and heart measurements were standardized by gestational age and compared between MVM and non-MVM stillbirths. Differences in standardized fetal organ and cardiac measures as compared to standardized fetal body weight were calculated to account for body size.

RESULTS

MVM stillbirths had smaller organ and heart weights than non-MVM stillbirths; however, after accounting for gestational age, heart weight was the least affected among all organs. In an analysis of organ weights relative to body size, heart weights were 0.31 standard deviations (SD) larger than expected relative to body weight (95% CI: 0.04, 0.57). Right and left ventricle thicknesses and mitral valve circumference were also larger than expected relative to body weight.

CONCLUSION

Stillbirth due to MVM was associated with relative sparing of heart weight and other heart measurements. The significance of these findings in liveborn infants needs further study.

Purkinje Cardiomyocytes of the Adult Ventricular Conduction System Are Highly Diploid but Not Uniquely Regenerative

Adult hearts are characterized by inefficient regeneration after injury, thus, the features that support or prevent cardiomyocyte (CM) proliferation are important to clarify. Diploid CMs are a candidate cell type that may have unique proliferative and regenerative competence, but no molecular markers are yet known that selectively identify all or subpopulations of diploid CMs. Here, using the conduction system expression marker Cntn2-GFP and the conduction system lineage marker Etv1CreERT2, we demonstrate that Purkinje CMs that comprise the adult ventricular conduction system are disproportionately diploid (33%, vs. 4% of bulk ventricular CMs). These, however, represent only a small proportion (3%) of the total diploid CM population. Using EdU incorporation during the first postnatal week, we demonstrate that bulk diploid CMs found in the later heart enter and complete the cell cycle during the neonatal period. In contrast, a significant fraction of conduction CMs persist as diploid cells from fetal life and avoid neonatal cell cycle activity. Despite their high degree of diploidy, the Purkinje lineage had no enhanced competence to support regeneration after adult heart infarction.

Hyperglycaemia-induced impairment of the autorhythmicity and gap junction activity of mouse embryonic stem cell-derived cardiomyocyte-like cells

Diabetes mellitus with hyperglycaemia is a major risk factor for malignant cardiac dysrhythmias. However, the underlying mechanisms remain unclear, especially during the embryonic developmental phase of the heart. This study investigated the effect of hyperglycaemia on the pulsatile activity of stem cell-derived cardiomyocytes. Mouse embryonic stem cells (mESCs) were differentiated into cardiac-like cells through embryoid body (EB) formation, in either baseline glucose or high glucose conditions. Action potentials (APs) were recorded using a voltage-sensitive fluorescent dye and gap junction activity was evaluated using scrape-loading lucifer yellow dye transfer assay. Molecular components were detected using immunocytochemistry and immunoblot analyses. High glucose decreased the spontaneous beating rate of EBs and shortened the duration of onset of quinidine-induced asystole. Furthermore, it altered AP amplitude, but not AP duration, and had no impact on neither the expression of the hyperpolarisation-activated cyclic nucleotide-gated isoform 4 (HCN4) channel nor on the EB beating rate response to ivabradine nor isoprenaline. High glucose also decreased both the intercellular spread of lucifer yellow within an EB and the expression of the cardiac gap junction protein connexin 43 as well as upregulated the expression of transforming growth factor beta 1 (TGF-β1) and phosphorylated Smad3. High glucose suppressed the autorhythmicity and gap junction conduction of mESC-derived cardiomyocytes, via mechanisms probably involving TGF-β1/Smad3 signalling. The results allude to glucotoxicity related proarrhythmic effects, with potential clinical implications in foetal diabetic cardiac disease.

Targeting Epigenetic Regulation of Cardiomyocytes through Development for Therapeutic Cardiac Regeneration after Heart Failure

Cardiovascular diseases are the leading cause of death globally, with no cure currently. Therefore, there is a dire need to further understand the mechanisms that arise during heart failure. Notoriously, the adult mammalian heart has a very limited ability to regenerate its functional cardiac cells, cardiomyocytes, after injury. However, the neonatal mammalian heart has a window of regeneration that allows for the repair and renewal of cardiomyocytes after injury. This specific timeline has been of interest in the field of cardiovascular and regenerative biology as a potential target for adult cardiomyocyte repair. Recently, many of the neonatal cardiomyocyte regeneration mechanisms have been associated with epigenetic regulation within the heart. This review summarizes the current and most promising epigenetic mechanisms in neonatal cardiomyocyte regeneration, with a specific emphasis on the potential for targeting these mechanisms in adult cardiac models for repair after injury.

General consensus on multimodal functions and validation analysis of perinatal derivatives for regenerative medicine applications

Perinatal tissues, such as placenta and umbilical cord contain a variety of somatic stem cell types, spanning from the largely used hematopoietic stem and progenitor cells to the most recently described broadly multipotent epithelial and stromal cells. As perinatal derivatives (PnD), several of these cell types and related products provide an interesting regenerative potential for a variety of diseases. Within COST SPRINT Action, we continue our review series, revising and summarizing the modalities of action and proposed medical approaches using PnD products: cells, secretome, extracellular vesicles, and decellularized tissues. Focusing on the brain, bone, skeletal muscle, heart, intestinal, liver, and lung pathologies, we discuss the importance of potency testing in validating PnD therapeutics, and critically evaluate the concept of PnD application in the field of tissue regeneration. Hereby we aim to shed light on the actual therapeutic properties of PnD, with an open eye for future clinical application. This review is part of a quadrinomial series on functional/potency assays for validation of PnD, spanning biological functions, such as immunomodulation, anti-microbial/anti-cancer, anti-inflammation, wound healing, angiogenesis, and regeneration.

Overexpression of GATA binding protein 4 and myocyte enhancer factor 2C induces differentiation of mesenchymal stem cells into cardiac-like cells

BACKGROUND

Heart diseases are the primary cause of death all over the world. Following myocardial infarction, billions of cells die, resulting in a huge loss of cardiac function. Stem cell-based therapies have appeared as a new area to support heart regeneration. The transcription factors GATA binding protein 4 (GATA-4) and myocyte enhancer factor 2C (MEF2C) are considered prominent factors in the development of the cardiovascular system.

AIM

To explore the potential of GATA-4 and MEF2C for the cardiac differentiation of human umbilical cord mesenchymal stem cells (hUC-MSCs).

METHODS

hUC-MSCs were characterized morphologically and immunologically by the presence of specific markers of MSCs via immunocytochemistry and flow cytometry, and by their potential to differentiate into osteocytes and adipocytes. hUC-MSCs were transfected with GATA-4, MEF2C, and their combination to direct the differentiation. Cardiac differentiation was confirmed by semiquantitative real-time polymerase chain reaction and immunocytochemistry.

RESULTS

hUC-MSCs expressed specific cell surface markers CD105, CD90, CD44, and vimentin but lack the expression of CD45. The transcription factors GATA-4 and MEF2C, and their combination induced differentiation in hUC-MSCs with significant expression of cardiac genes i.e., GATA-4, MEF2C, NK2 homeobox 5 (NKX2.5), MHC, and connexin-43, and cardiac proteins GATA-4, NKX2.5, cardiac troponin T, and connexin-43.

CONCLUSION

Transfection with GATA-4, MEF2C, and their combination effectively induces cardiac differentiation in hUC-MSCs. These genetically modified MSCs could be a promising treatment option for heart diseases in the future.

Antenatal Glucocorticoid Administration Promotes Cardiac Structure and Energy Metabolism Maturation in Preterm Fetuses

Although the rate of preterm birth has increased in recent decades, a number of preterm infants have escaped death due to improvements in perinatal and neonatal care. Antenatal glucocorticoid (GC) therapy has significantly contributed to progression in lung maturation; however, its potential effects on other organs remain controversial. Furthermore, the effects of antenatal GC therapy on the fetal heart show both pros and cons. Translational research in animal models indicates that constant fetal exposure to antenatal GC administration is sufficient for lung maturation. We have established a premature fetal rat model to investigate immature cardiopulmonary functions in the lungs and heart, including the effects of antenatal GC administration. In this review, we explain the mechanisms of antenatal GC actions on the heart in the fetus compared to those in the neonate. Antenatal GCs may contribute to premature heart maturation by accelerating cardiomyocyte proliferation, angiogenesis, energy production, and sarcoplasmic reticulum function. Additionally, this review specifically focuses on fetal heart growth with antenatal GC administration in experimental animal models. Moreover, knowledge regarding antenatal GC administration in experimental animal models can be coupled with that from developmental biology, with the potential for the generation of functional cells and tissues that could be used for regenerative medical purposes in the future.

Non-coding RNAs to regulate cardiomyocyte proliferation: A new trend in therapeutic cardiac regeneration

Cardiovascular diseases remain the leading cause of death worldwide, particularly ischemic heart disease (IHD). It is also classified as incurable given the irreversible damage it causes to cardiomyocytes. Thus, myocardial tissue rejuvenation following ischemia is one of the global primary research concerns for scientists. Interestingly, the mammalian heart thrives after an injury during the embryonic or neonatal period; however, this ability disappears with increasing age. Previous studies have found that specific non-coding (nc) RNAs play a pivotal role in this process. Hence, the review herein summarizes the research on cardiomyocyte regenerative medicine in recent years and sets forth the biological functions and mechanisms of the micro (mi)RNA, long non-coding (lnc)RNA, and circular (circ)RNA in the posttranscriptional regulation of cardiomyocytes. In addition, this review summarizes the roles of ncRNAs in specific species while enumerating potential therapeutic strategies for myocardial infarction.

Development of an improved inhibitor of Lats kinases to promote regeneration of mammalian organs

The Hippo signaling pathway acts as a brake on regeneration in many tissues. This cascade of kinases culminates in the phosphorylation of the transcriptional cofactors Yap and Taz, whose concentration in the nucleus consequently remains low. Various types of cellular signals can reduce phosphorylation, however, resulting in the accumulation of Yap and Taz in the nucleus and subsequently in mitosis. We earlier identified a small molecule, TRULI, that blocks the final kinases in the pathway, Lats1 and Lats2, and thus elicits proliferation of several cell types that are ordinarily postmitotic and aids regeneration in mammals. In the present study, we present the results of chemical modification of the original compound and demonstrate that a derivative, TDI-011536, is an effective blocker of Lats kinases in vitro at nanomolar concentrations. The compound fosters extensive proliferation in retinal organoids derived from human induced pluripotent stem cells. Intraperitoneal administration of the substance to mice suppresses Yap phosphorylation for several hours and induces transcriptional activation of Yap target genes in the heart, liver, and skin. Moreover, the compound initiates the proliferation of cardiomyocytes in adult mice following cardiac cryolesions. After further chemical refinement, related compounds might prove useful in protective and regenerative therapies.

STEMIN and YAP5SA synthetic modified mRNAs regenerate and repair infarcted mouse hearts

Introduction

The adult heart lacks the regenerative capacity to self-repair. Serum response factor (SRF) is essential for heart organogenesis, sarcomerogenesis, and contractility. SRF interacts with co-factors, such as NKX2.5 and GATA4, required for cardiac specified gene activity. ETS factors such as ELK1 interact with SRF and drive cell replication. To weaken SRF interactions with NKX2.5 and GATA4, one mutant, SRF153(A3) named STEMIN, did not bind CArG boxes, yet induced stem cell factors such as NANOG and OCT4, cardiomyocyte dedifferentiation, and cell cycle reentry. The mutant YAP5SA of the Hippo pathway also promotes cardiomyocyte proliferation and growth.

Aim

Infarcted adult mouse hearts were injected with translatable STEMIN and YAP5SA mmRNA to evaluate their clinical potential.

Methods and Results

Mice were pulsed one day later with alpha-EDU and then heart sections were DAPI stained. Replicating cells were identified by immuno-staining against members of the DNA replisome pathway that mark entry to S phase of the cell cycle. Echocardiography was used to determine cardiac function following infarcts and mRNA treatment. To monitor cardiac wall repair, microscopic analysis was performed, and the extent of myocardial fibrosis was analyzed for immune cell infiltration. Injections of STEMIN and YAP5SA mmRNA into the left ventricles of infarcted adult mice promoted a greater than 17-fold increase in the DAPI stained and alpha-EDU marked cardiomyocyte nuclei, within a day. We observed de novo expression of phospho-histone H3, ORC2, MCM2, and CLASPIN. Cardiac function was significantly improved by four weeks post-infarct, and fibrosis and immune cell infiltration were diminished in hearts treated with STEMIN and YAP5SA mmRNA than each alone.

Conclusion

STEMIN and YAP5SA mmRNA improved cardiac function and myocardial fibrosis in left ventricles of infarcted adult mice. The combinatorial use of mmRNA encoding STEMIN and YAP5SA has the potential to become a powerful clinical strategy to treat human heart disease.

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.

Cytokine receptor gp130 promotes postnatal proliferation of cardiomyocytes required for the normal functional development of the heart

Mammalian ventricular cardiomyocytes are premature at birth and exhibit substantial phenotypic changes before weaning. Mouse ventricular myocytes undergo cell division several times after birth; however, the regulatory mechanisms and roles of cardiomyocyte division in postnatal heart development remain unclear. Here, we investigated the physiological role of gp130, the main subunit of multifunctional receptors for the IL-6 family of cytokines, in postnatal cardiomyocyte proliferation. Pharmacological inhibition of gp130 within the first month after birth induced significant systolic dysfunction of the left ventricle in mice. Consistently, mice with postnatal cardiomyocyte-specific gp130 depletion exhibited impaired left ventricular contractility compared to control mice. In these mice, cardiomyocytes exhibited a moderately decreased size and dramatically inhibited proliferation in the left ventricle but not in the right ventricle. Stereological analysis revealed that this change significantly decreased the number of cardiomyocytes in the left ventricle. Furthermore, IL-6 was mainly responsible for promoting ventricular cardiomyocyte proliferation by activating the JAK/STAT3 pathway. Taken together, the IL-6/gp130/JAK/STAT3 axis plays a crucial role in the physiological postnatal proliferation and hypertrophy of left ventricular cardiomyocytes to ensure normal cardiac functional development.

Stimulation of Cardiomyocyte Proliferation Is Dependent on Species and Level of Maturation

The heart is one of the least regenerative organs. This is in large part due to the inability of adult mammalian cardiomyocytes to proliferate and divide. In recent years, a number of small molecules and molecular targets have been identified to stimulate cardiomyocyte proliferation, including p38 inhibition, YAP-Tead activation, fibroblast growth factor 1 and Neuregulin 1. Despite these exciting initial findings, a therapeutic approach to enhance cardiomyocyte proliferation in vivo is still lacking. We hypothesized that a more comprehensive in vitro validation using live-cell imaging and assessment of the proliferative effects on various cardiomyocyte sources might identify the most potent proliferative stimuli. Here, we used previously published stimuli to determine their proliferative effect on cardiomyocytes from different species and isolated from different developmental timepoints. Although all stimuli enhanced DNA synthesis and Histone H3 phosphorylation in neonatal rat ventricular cardiomyocytes to similar degrees, these effects varied substantially in mouse cardiomyocytes and human iPSC-derived cardiomyocytes. Our results highlight p21 inhibition and Yap-Tead activation as potent proliferative strategies to induce cultured cardiomyocyte cell cycle activity across mouse, rat and human cardiomyocytes.

Inefficient development of syncytiotrophoblasts in the Atp11a-deficient mouse placenta

Plasma membranes are composed of a lipid bilayer in which phosphatidylserine (PtdSer) is confined to the inner leaflet by the action of flippase that translocates PtdSer from the outer to inner leaflets. Two P4-ATPases (ATP11A and ATP11C) work as flippase at plasma membranes. Here, we report that the mouse placenta expresses only ATP11A, and Atp11a-deficient mouse embryos die during embryogenesis due to inefficient formation of syncytiotrophoblasts in the placental labyrinth. The flippase-null mutation inactivates human choriocarcinoma BeWo cells to translocate PtdSer into the inner leaflet and undergo cell fusion. These findings highlight the importance of flippase to regulate the distribution of phospholipids for cell fusion, at least in trophoblast fusion.

The P4-ATPases ATP11A and ATP11C function as flippases at the plasma membrane to translocate phosphatidylserine from the outer to the inner leaflet. We herein demonstrated that Atp11a-deficient mouse embryos died at approximately E14.5 with thin-walled heart ventricles. However, the cardiomyocyte- or epiblast-specific Atp11a deletion did not affect mouse development or mortality. ATP11C may have compensated for the function of ATP11A in most of the cell types in the embryo. On the other hand, Atp11a, but not Atp11c, was expressed in the mouse placenta, and the Atp11a-null mutation caused poor development of the labyrinthine layer with an increased number of TUNEL-positive foci. Immunohistochemistry and electron microscopy revealed a disorganized labyrinthine layer with unfused trophoblasts in the Atp11a-null placenta. Human placenta-derived choriocarcinoma BeWo cells expressed the ATP11A and ATP11C genes. A lack of ATP11A and ATP11C eliminated the ability of BeWo cells to flip phosphatidylserine and fuse when treated with forskolin. These results indicate that flippases at the plasma membrane play an important role in the formation of syncytiotrophoblasts in placental development.

Metabolic Pathway of Cardiospecific Troponins: From Fundamental Aspects to Diagnostic Role (Comprehensive Review)

Many molecules of the human body perform key regulatory functions and are widely used as targets for the development of therapeutic drugs or as specific diagnostic markers. These molecules undergo a significant metabolic pathway, during which they are influenced by a number of factors (biological characteristics, hormones, enzymes, etc.) that can affect molecular metabolism and, as a consequence, the serum concentration or activity of these molecules. Among the most important molecules in the field of cardiology are the molecules of cardiospecific troponins (Tns), which regulate the processes of myocardial contraction/relaxation and are used as markers for the early diagnosis of ischemic necrosis of cardiomyocytes (CMC) in myocardial infarction (MI). The diagnostic value and diagnostic capabilities of cardiospecific Tns have changed significantly after the advent of new (highly sensitive (HS)) detection methods. Thus, early diagnostic algorithms of MI were approved for clinical practice, thanks to which the possibility of rapid diagnosis and determination of optimal tactics for managing patients with MI was opened. Relatively recently, promising directions have also been opened for the use of cardiospecific Tns as prognostic markers both at the early stages of the development of cardiovascular diseases (CVD) (arterial hypertension (AH), heart failure (HF), coronary heart disease (CHD), etc.), and in non-ischemic extra-cardiac pathologies that can negatively affect CMC (for example, sepsis, chronic kidney disease (CKD), chronic obstructive pulmonary disease (COPD), etc.). Recent studies have also shown that cardiospecific Tns are present not only in blood serum, but also in other biological fluids (urine, oral fluid, pericardial fluid, amniotic fluid). Thus, cardiospecific Tns have additional diagnostic capabilities. However, the fundamental aspects of the metabolic pathway of cardiospecific Tns are definitively unknown, in particular, specific mechanisms of release of Tns from CMC in non-ischemic extra-cardiac pathologies, mechanisms of circulation and elimination of Tns from the human body, mechanisms of transport of Tns to other biological fluids and factors that may affect these processes have not been established. In this comprehensive manuscript, all stages of the metabolic pathway are consistently and in detail considered, starting from release from CMC and ending with excretion (removal) from the human body. In addition, the possible diagnostic role of individual stages and mechanisms, influencing factors is analyzed and directions for further research in this area are noted.

The Importance of Cardiac Troponin Metabolism in the Laboratory Diagnosis of Myocardial Infarction (Comprehensive Review)

The study of the metabolism of endogenous molecules is not only of great fundamental significance but also of high practical importance, since many molecules serve as drug targets and/or biomarkers for laboratory diagnostics of diseases. Thus, cardiac troponin molecules have long been used as the main biomarkers for confirmation of diagnosis of myocardial infarction, and with the introduction of high-sensitivity test methods, many of our ideas about metabolism of these cardiac markers have changed significantly. In clinical practice, there are opening new promising diagnostic capabilities of cardiac troponins, the understanding and justification of which are closely connected with the fundamental principles of the metabolism of these molecules. Our current knowledge about the metabolism of cardiac troponins is insufficient and extremely disconnected from various literary sources. Thus, many researchers do not sufficiently understand the potential importance of cardiac troponin metabolism in the laboratory diagnosis of myocardial infarction. The purpose of this comprehensive review is to systematize information about the metabolism of cardiac troponins and during the discussion to focus on the potential impact of cTns metabolism on the laboratory diagnosis of myocardial infarction. The format of this comprehensive review includes a sequential consideration and analysis of the stages of the metabolic pathway, starting from possible release mechanisms and ending with elimination mechanisms. This will allow doctors and researchers to understand the significant importance of cTns metabolism and its impact on the laboratory diagnosis of myocardial infarction.

Biology of Cardiac Troponins: Emphasis on Metabolism

Understanding of the biology of endo- and exogenous molecules, in particular their metabolism, is not only of great theoretical importance, but also of high practical significance, since many molecules serve as drug targets or markers for the laboratory diagnostics of many human diseases. Thus, cardiac troponin (cTns) molecules have long been used as key markers for the confirmation of diagnosis of myocardial infarction (MI), and with the introduction of contemporary (high sensitivity) test methods, many of our concepts related to the biology of these cardiac markers have changed significantly. In current clinical practice, there are opening new promising diagnostic capabilities of cTns, the understanding and justification of which is closely connected with the theoretical principles of the metabolism of these molecules. However, today, the biology and metabolism of cTns have not been properly investigated; in particular, we do not know the precise mechanisms of release of these molecules from the myocardial cells (MCs) of healthy people and the mechanisms of circulation, and the elimination of cTns from the bloodstream. The main purpose of this manuscript is to systematize information about the biology of cTns, with an emphasis on the metabolism of cTns. The format of this paper, starting with the release of cTns in the blood and concluding with the metabolism/filtration of troponins, provides a comprehensive yet logically easy way for the readers to approach our current knowledge in the framework of understanding the basic mechanisms by which cTns are produced and processed. Conclusions. Based on the analysis of the current literature, the important role of biology and all stages of metabolism (release, circulation, removal) of cTns in laboratory diagnostics should be noted. It is necessary to continue studying the biology and metabolism of cTns, because this will improve the differential diagnosis of MI and i a new application of cTns immunoassays in current clinical practice.

Hippo-Yap/Taz signalling in zebrafish regeneration

The extent of tissue regeneration varies widely between species. Mammals have a limited regenerative capacity whilst lower vertebrates such as the zebrafish (Danio rerio), a freshwater teleost, can robustly regenerate a range of tissues, including the spinal cord, heart, and fin. The molecular and cellular basis of this altered response is one of intense investigation. In this review, we summarise the current understanding of the association between zebrafish regeneration and Hippo pathway function, a phosphorylation cascade that regulates cell proliferation, mechanotransduction, stem cell fate, and tumorigenesis, amongst others. We also compare this function to Hippo pathway activity in the regenerative response of other species. We find that the Hippo pathway effectors Yap/Taz facilitate zebrafish regeneration and that this appears to be latent in mammals, suggesting that therapeutically promoting precise and temporal YAP/TAZ signalling in humans may enhance regeneration and hence reduce morbidity.

Amino acid primed mTOR activity is essential for heart regeneration

Heart disease is the leading cause of death with no method to repair damaged myocardium due to the limited proliferative capacity of adult cardiomyocytes. Curiously, mouse neonates and zebrafish can regenerate their hearts via cardiomyocyte de-differentiation and proliferation. However, a molecular mechanism of why these cardiomyocytes can re-enter cell cycle is poorly understood. Here, we identify a unique metabolic state that primes adult zebrafish and neonatal mouse ventricular cardiomyocytes to proliferate. Zebrafish and neonatal mouse hearts display elevated glutamine levels, predisposing them to amino-acid-driven activation of TOR, and that TOR activation is required for zebrafish cardiomyocyte regeneration in vivo. Through a multi-omics approach with cellular validation we identify metabolic and mitochondrial changes during the first week of regeneration. These data suggest that regeneration of zebrafish myocardium is driven by metabolic remodeling and reveals a unique metabolic regulator, TOR-primed state, in which zebrafish and mammalian cardiomyocytes are regeneration competent.