Cardiac myocyte cell cycle control in development, disease, and regeneration

Targeting cardiomyocyte cell cycle regulation in heart failure

Heart failure continues to be a significant global health concern, causing substantial morbidity and mortality. The limited ability of the adult heart to regenerate has posed challenges in finding effective treatments for cardiac pathologies. While various medications and surgical interventions have been used to improve cardiac function, they are not able to address the extensive loss of functioning cardiomyocytes that occurs during cardiac injury. As a result, there is growing interest in understanding how the cell cycle is regulated and exploring the potential for stimulating cardiomyocyte proliferation as a means of promoting heart regeneration. This review aims to provide an overview of current knowledge on cell cycle regulation and mechanisms underlying cardiomyocyte proliferation in cases of heart failure, while also highlighting established and novel therapeutic strategies targeting this area for treatment purposes.

A Meta-Analysis Approach to Gene Regulatory Network Inference Identifies Key Regulators of Cardiovascular Diseases

Cardiovascular diseases (CVDs) represent a major concern for global health, whose mechanistic understanding is complicated by a complex interplay between genetic predisposition and environmental factors. Specifically, heart failure (HF), encompassing dilated cardiomyopathy (DC), ischemic cardiomyopathy (ICM), and hypertrophic cardiomyopathy (HCM), is a topic of substantial interest in basic and clinical research. Here, we used a Partial Correlation Coefficient-based algorithm (PCC) within the context of a meta-analysis framework to construct a Gene Regulatory Network (GRN) that identifies key regulators whose activity is perturbed in Heart Failure. By integrating data from multiple independent studies, our approach unveiled crucial regulatory associations between transcription factors (TFs) and structural genes, emphasizing their pivotal roles in regulating metabolic pathways, such as fatty acid metabolism, oxidative stress response, epithelial-to-mesenchymal transition, and coagulation. In addition to known associations, our analysis also identified novel regulators, including the identification of TFs FPM315 and OVOL2, which are implicated in dilated cardiomyopathies, and TEAD1 and TEAD2 in both dilated and ischemic cardiomyopathies. Moreover, we uncovered alterations in adipogenesis and oxidative phosphorylation pathways in hypertrophic cardiomyopathy and discovered a role for IL2 STAT5 signaling in heart failure. Our findings underscore the importance of TF activity in the initiation and progression of cardiac disease, highlighting their potential as pharmacological targets.

Long Non-Coding RNA-Cardiac-Inducing RNA 6 Mediates Repair of Infarcted Hearts by Inducing Mesenchymal Stem Cell Differentiation into Cardiogenic Cells through Cyclin-Dependent Kinase 1

This study aims to investigate the induction effect of LncRNA-CIR6 on MSC differentiation into cardiogenic cells in vitro and in vivo. In addition to pretreatment with Ro-3306 (a CDK1 inhibitor), LncRNA-CIR6 was transfected into BMSCs and hUCMSCs using jetPRIME. LncRNA-CIR6 was further transfected into the hearts of C57BL/6 mice via 100 μL of AAV9-cTnT-LncRNA-CIR6-ZsGreen intravenous injection. After three weeks of transfection followed by AMI surgery, hUCMSCs (5 × 105/100 μL) were injected intravenously one week later. Cardiac function was evaluated using VEVO 2100 and electric mapping nine days after cell injection. Immunofluorescence, Evans blue-TTC, Masson staining, FACS, and Western blotting were employed to determine relevant indicators. LncRNA-CIR6 induced a significant percentage of differentiation in BMSCs (83.00 ± 0.58)% and hUCMSCs (95.43 ± 2.13)% into cardiogenic cells, as determined by the expression of cTnT using immunofluorescence and FACS. High cTNT expression was observed in MSCs after transfection with LncRNA-CIR6 by Western blotting. Compared with the MI group, cardiac contraction and conduction function in MI hearts treated with LncRNA-CIR6 or combined with MSCs injection groups were significantly increased, and the areas of MI and fibrosis were significantly lower. The transcriptional expression region of LncRNA-CIR6 was on Chr17 from 80209290 to 80209536. The functional region of LncRNA-CIR6 was located at nucleotides 0-50/190-255 in the sequence. CDK1, a protein found to be related to the proliferation and differentiation of cardiomyocytes, was located in the functional region of the LncRNA-CIR6 secondary structure (from 0 to 17). Ro-3306 impeded the differentiation of MSCs into cardiogenic cells, while MSCs transfected with LncRNA-CIR6 showed a high expression of CDK1. LncRNA-CIR6 mediates the repair of infarcted hearts by inducing MSC differentiation into cardiogenic cells through CDK1.

Cardiac lipidomic profiles in mice undergo changes from fetus to adult

AIMS

Lipids are essential cellular components with many important biological functions. Disturbed lipid biosynthesis and metabolism has been shown to cause cardiac developmental abnormality and cardiovascular diseases. In this study, we aimed to investigate the composition and the molecular profiles of lipids in mammalian hearts between embryonic and adult stages and uncover the underlying links between lipid and cardiac development and maturation.

MATERIALS AND METHODS

We collected mouse hearts at the embryonic day 11.5 (E11.5), E15.5, and the age of 2 months, 4 months and 10 months, and performed lipidomic analysis to determine the changes of the composition, molecular species, and relative abundance of cardiac lipids between embryonic and adult stages. Additionally, we also performed the electronic microscopy and RNA sequencing in both embryonic and adult mouse hearts.

KEY FINDINGS

The relative abundances of certain phospholipids and sphingolipids including cardiolipin, phosphatidylglycerol, phosphatidylethanolamine, and ceramide, are different between embryonic and adult hearts. Such lipidomic changes are accompanied with increased densities of mitochondrial membranes and elevated expression of genes related to mitochondrial formation in adult mouse hearts. We also analyzed individual molecular species of phospholipids and sphingolipids, and revealed that the composition and distribution of lipid molecular species in hearts also change with development.

SIGNIFICANCE

Our study provides not only a lipidomic view of mammalian hearts when developing from the embryonic to the adult stage, but also a potential pool of lipid indicators for cardiac cell development and maturation.

Myoglobin modulates the Hippo pathway to promote cardiomyocyte differentiation

The endogenous mechanisms that propagate cardiomyocyte differentiation and prevent de-differentiation remain unclear. While the expression of the heme protein myoglobin increases by over 50% during cardiomyocyte differentiation, a role for myoglobin in regulating cardiomyocyte differentiation has not been tested. Here, we show that deletion of myoglobin in cardiomyocyte models decreases the gene expression of differentiation markers and stimulates cellular proliferation, consistent with cardiomyocyte de-differentiation. Mechanistically, the heme prosthetic group of myoglobin catalyzes the oxidation of the Hippo pathway kinase LATS1, resulting in phosphorylation and inactivation of yes-associated protein (YAP). In vivo, myoglobin-deficient zebrafish hearts show YAP dephosphorylation and accelerated cardiac regeneration after apical injury. Similarly, myoglobin knockdown in neonatal murine hearts shows increased YAP dephosphorylation and cardiomyocyte cycling. These data demonstrate a novel role for myoglobin as an endogenous driver of cardiomyocyte differentiation and highlight myoglobin as a potential target to enhance cardiac development and improve cardiac repair and regeneration.

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.

Toxoplasma gondii Me49 and NED strains arrest host cell cycle progression and alter chromosome segregation in a strain-independent manner

Toxoplasma gondii is an obligate intracellular parasite that modulates a broad range of host cell functions to guarantee its intracellular development and replication. T. gondii includes three classical clonal lineages exhibiting different degrees of virulence. Regarding the genetic diversity of T. gondii circulating in Europe, type II strains and, to a lesser extent, type III strains are the dominant populations, both in humans and animals. Infections with the type I strain led to widespread parasite dissemination and death in mice, while type III is considered avirulent. Previously, we demonstrated that primary endothelial cells infected with the T. gondii RH strain (haplotype I) were arrested in the G2/M-phase transition, triggering cytokinesis failure and chromosome missegregation. Since T. gondii haplotypes differ in their virulence, we here studied whether T. gondii-driven host cell cycle perturbation is strain-dependent. Primary endothelial cells were infected with T. gondii Me49 (type II strain) or NED (type III strain), and their growth kinetics were compared up to cell lysis (6-30 h p. i.). In this study, only slight differences in the onset of full proliferation were observed, and developmental data in principle matched those of the RH strain. FACS-based DNA quantification to estimate cell proportions experiencing different cell cycle phases (G0/1-, S-, and G2/M-phase) revealed that Me49 and NED strains both arrested the host cell cycle in the S-phase. Cyclins A2 and B1 as key molecules of S- and M-phase were not changed by Me49 infection, while NED infection induced cyclin B1 upregulation. To analyze parasite-driven alterations during mitosis, we demonstrated that both Me49 and NED infections led to impaired host cellular chromosome segregation and irregular centriole overduplication. Moreover, in line with the RH strain, both strains boosted the proportion of binucleated cells within infected endothelial cell layers, thereby indicating enhanced cytokinesis failure. Taken together, we demonstrate that all parasite-driven host cell cycle arrest, chromosome missegregation, and binucleated phenotypes are T. gondii-specific but strain independent.

MicroRNA205: A Key Regulator of Cardiomyocyte Transition from Proliferative to Hypertrophic Growth in the Neonatal Heart

The mammalian myocardium grows rapidly during early development due to cardiomyocyte proliferation, which later transitions to cell hypertrophy to sustain the heart's postnatal growth. Although this cell transition in the postnatal heart is consistently preserved in mammalian biology, little is known about the regulatory mechanisms that link proliferation suppression with hypertrophy induction. We reasoned that the production of a micro-RNA(s) could serve as a key bridge to permit changes in gene expression that control the changed cell fate of postnatal cardiomyocytes. We used sequential expression analysis to identify miR205 as a micro-RNA that was uniquely expressed at the cessation of cardiomyocyte growth. Cardiomyocyte-specific miR205 deletion animals showed a 35% increase in heart mass by 3 months of age, with commensurate changes in cell cycle and Hippo pathway activity, confirming miR205's potential role in controlling cardiomyocyte proliferation. In contrast, overexpression of miR205 in newborn hearts had little effect on heart size or function, indicating a complex, probably redundant regulatory system. These findings highlight miR205's role in controlling the shift from cardiomyocyte proliferation to hypertrophic development in the postnatal period.

Engineered cocultures of iPSC-derived atrial cardiomyocytes and atrial fibroblasts for modeling atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia treatable with antiarrhythmic drugs; however, patient responses remain highly variable. Human induced pluripotent stem cell-derived atrial cardiomyocytes (iPSC-aCMs) are useful for discovering precision therapeutics, but current platforms yield phenotypically immature cells and are not easily scalable for high-throughput screening. Here, primary adult atrial, but not ventricular, fibroblasts induced greater functional iPSC-aCM maturation, partly through connexin-40 and ephrin-B1 signaling. We developed a protein patterning process within multiwell plates to engineer patterned iPSC-aCM and atrial fibroblast coculture (PC) that significantly enhanced iPSC-aCM structural, electrical, contractile, and metabolic maturation for 6+ weeks compared to conventional mono-/coculture. PC displayed greater sensitivity for detecting drug efficacy than monoculture and enabled the modeling and pharmacological or gene editing treatment of an AF-like electrophysiological phenotype due to a mutated sodium channel. Overall, PC is useful for elucidating cell signaling in the atria, drug screening, and modeling AF.

The miR-17-92 cluster in cardiac health and disease

MicroRNAs (miRs) are small noncoding RNAs that play important roles in both physiological and pathological processes through post-transcriptional regulation. The miR-17-92 cluster includes six individual members: miR-17, miR-18a, miR-19a, miR-19b-1, miR-20a, and miR-92a-1. The miR-17-92 cluster has been extensively studied and reported to broadly function in cancer biology, immunology, neurology, pulmonology, and cardiology. This review focuses on its roles in heart development and cardiac diseases. We briefly introduce the nature of the miR-17-92 cluster and its crucial roles in both normal development and the pathogenesis of various diseases. We summarize the recent progress in understanding the versatile roles of miR-17-92 during cardiac development, regeneration, and aging. Additionally, we highlight the indispensable roles of the miR-17-92 cluster in pathogenesis and therapeutic potential in cardiac birth defects and adult cardiac diseases.

Role of the CASZ1 transcription factor in tissue development and disease

The zinc finger transcription factor gene, CASZ1/Castor (Castor zinc finger 1), initially identified in Drosophila, plays a critical role in neural, cardiac, and cardiovascular development, exerting a complex, multifaceted influence on cell fate and tissue morphogenesis. During neurogenesis, CASZ1 exhibits dynamic expression from early embryonic development to the perinatal period, constituting a key regulator in this process. Additionally, CASZ1 controls the transition between neurogenesis and gliomagenesis. During human cardiovascular system development, CASZ1 is essential for cardiomyocyte differentiation, cardiac morphogenesis, and vascular morphology homeostasis and formation. The deletion or inactivation of CASZ1 mutations can lead to human developmental diseases or tumors, including congenital heart disease, cardiovascular disease, and neuroblastoma. CASZ1 can be used as a biomarker for disease prevention and diagnosis as well as a prognostic indicator for cancer. This review explores the unique functions of CASZ1 in tissue morphogenesis and associated diseases, offering new insights for elucidating the molecular mechanisms underlying diseases and identifying potential therapeutic targets for disease prevention and treatment.

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.

Binucleated Myocytes and Heart Weight: A Preliminary Study Linking Cardiac Hypertrophy and Myocyte Hypertrophy

ABSTRACT

Hypertrophy of the heart is assessed by heart weight (and dimensions) and myocyte hypertrophy. Establishing an association between the two may be useful in assessing hypertrophy in cases where there are limitations in assessing the heart weight. This preliminary study explored the association between the number of binucleated myocytes (a feature of myocyte hypertrophy) in a randomly chosen single high-power field of the left ventricular free wall and heart weight in an adult White population. It also compared the number of binucleated myocytes between cases with increased heart weight (>400 g in female and >500 g in male) and cases with normal heart weight. Heart weight and number of binucleated myocytes correlated significantly in male only. Increased heart weight had a significantly higher number of binucleated myocytes, with 8.5 binucleated myocytes being able to segregate cases with increased heart weight (74% sensitivity and 79% specificity). The results of this study showed the number of binucleated myocytes may have a complementary role in assessing hypertrophy of the heart.

Cardiac function evaluated by two-dimensional speckle tracking imaging in fetuses with congenital heart disease of ventricular afterload increase

AIMS

To study myocardial deformation in fetuses with ventricular afterload increase compared with gestational age-matched controls using speckle tracking echocardiography.

METHODS AND RESULTS

Eighty-nine fetuses were retrospectively selected from the pregnancy screen by echocardiography. There are 41 fetuses with gestational age-matched normal heart served as the control group, 25 fetuses with congenital heart disease (CHD) leading to left ventricular (LV) afterload increase as group LVA and 23 fetuses with CHD leading to right ventricular(RV) afterload increases as group RVA. LV and RV fractional shortening (FS) were measured by conventional methods. The longitudinal strain (LS) and strain rate (LSr) were analyzed by EchoPac software. Group LVA and RVA compared with control group, the LV FS was no significant difference, but LS and LSr values of LV were lower in fetuses with LVA compared to the control group (LS:-15.97(-12.50,-22.52)vs -27.53(-24.33,-29.16) %, p < .01; systolic strain rate (SRs):-1.34(-1.12,-2.16) vs -2.55(-2.28,-2.92) 1/sec, p < .01; early diastolic strain rate (SRe):1.70 ± 0.57 vs 2.46 ± 0.61 1/sec, p < 0.01; late diastolic strain rate (SRa):1.62 ± 0.82 vs 2.39 ± 0.81 1/sec, p < .01). LS and LSr values of LV or RV were lower in fetuses with RVA compared to the control group (LV: LS:-21.52 ± 6.68 vs -26.79 ± 3.22%, p < .01; SRs:-2.11 ± 0.78 vs -2.56 ± 0.43 1/sec; p = .02; RV: LS:-17.64 ± 7.58 vs -26.38 ± 3.97%, p < .01; SRs:-1.62 ± 0.67 vs -2.37 ± 0.44 1/sec; p < .01).

CONCLUSION

The results of this study showed that the ventricular LS, LSr, SRs, SRe, SRa values were lower in fetuses with LV or RV afterload increasing CHD estimated by speckle tracking imaging but LV and RV FS were normal,which indicated the strain imaging is feasible in evaluating cardiac function of fetus, and may be more sensitive.

Cardiac growth and metabolism of the fetal sheep are not vulnerable to a 10 day increase in fetal glucose and insulin concentrations during late gestation

Aims

To evaluate the effects of fetal glucose infusion in late gestation on the mRNA expression and protein abundance of molecules involved in the regulation of cardiac growth and metabolism.

Main methods

Either saline or glucose was infused into fetal sheep from 130 to 140 days (d) gestation (term, 150 d). At 140 d gestation, left ventricle tissue samples were collected. Quantitative real-time RT-PCR and Western blot were used to determine the mRNA expression and protein abundance of key signalling molecules within the left ventricle of the fetal heart.

Key findings

Although intra-fetal glucose infusion increased fetal plasma glucose and insulin concentrations, there was no change in the expression of molecules within the signalling pathways that regulate proliferation, hypertrophy, apoptosis or fibrosis in the fetal heart. Cardiac Solute carrier family 2 member 1 (SLC2A1) mRNA expression was decreased by glucose infusion. Glucose infusion increased cardiac mRNA expression of both Peroxisome proliferator activated receptor alpha (PPARA) and peroxisome proliferator activated receptor gamma (PPARG). However, there was no change in the mRNA expression of PPAR cofactors or molecules with PPAR response elements. Furthermore, glucose infusion did not impact the protein abundance of the 5 oxidative phosphorylation complexes of the electron transport chain.

Significance

Despite a 10-day doubling of fetal plasma glucose and insulin concentrations, the present study suggests that within the fetal left ventricle, the mRNA and protein expression of the signalling molecules involved in cardiac growth, development and metabolism are relatively unaffected.

Alternative polyadenylation regulation in cardiac development and cardiovascular disease

Cleavage and polyadenylation of pre-mRNAs is a necessary step for gene expression and function. Majority of human genes exhibit multiple polyadenylation sites, which can be alternatively used to generate different mRNA isoforms from a single gene. Alternative polyadenylation (APA) of pre-mRNAs is important for the proteome and transcriptome landscape. APA is tightly regulated during development and contributes to tissue-specific gene regulation. Mis-regulation of APA is linked to a wide range of pathological conditions. APA-mediated gene regulation in the heart is emerging as a new area of research. Here, we will discuss the impact of APA on gene regulation during heart development and in cardiovascular diseases. First, we will briefly review how APA impacts gene regulation and discuss molecular mechanisms that control APA. Then, we will address APA regulation during heart development and its dysregulation in cardiovascular diseases. Finally, we will discuss pre-mRNA targeting strategies to correct aberrant APA patterns of essential genes for the treatment or prevention of cardiovascular diseases. The RNA field is blooming due to advancements in RNA-based technologies. RNA-based vaccines and therapies are becoming the new line of effective and safe approaches for the treatment and prevention of human diseases. Overall, this review will be influential for understanding gene regulation at the RNA level via APA in the heart and will help design RNA-based tools for the treatment of cardiovascular diseases in the future.

Imaging Early Life Cardiovascular Phenotype

The growing epidemics of obesity, hypertension, and diabetes, in addition to worsening environmental factors such as air pollution, water scarcity, and climate change, have fueled the continuously increasing prevalence of cardiovascular diseases (CVDs). This has caused a markedly increasing burden of CVDs that includes mortality and morbidity worldwide. Identification of subclinical CVD before overt symptoms can lead to earlier deployment of preventative pharmacological and nonpharmacologic strategies. In this regard, noninvasive imaging techniques play a significant role in identifying early CVD phenotypes. An armamentarium of imaging techniques including vascular ultrasound, echocardiography, magnetic resonance imaging, computed tomography, noninvasive computed tomography angiography, positron emission tomography, and nuclear imaging, with intrinsic strengths and limitations can be utilized to delineate incipient CVD for both clinical and research purposes. In this article, we review the various imaging modalities used for the evaluation, characterization, and quantification of early subclinical cardiovascular diseases.

Cardiomyocyte Ploidy, Metabolic Reprogramming and Heart Repair

The adult heart is made up of cardiomyocytes (CMs) that maintain pump function but are unable to divide and form new myocytes in response to myocardial injury. In contrast, the developmental cardiac tissue is made up of proliferative CMs that regenerate injured myocardium. In mammals, CMs during development are diploid and mononucleated. In response to cardiac maturation, CMs undergo polyploidization and binucleation associated with CM functional changes. The transition from mononucleation to binucleation coincides with unique metabolic changes and shift in energy generation. Recent studies provide evidence that metabolic reprogramming promotes CM cell cycle reentry and changes in ploidy and nucleation state in the heart that together enhances cardiac structure and function after injury. This review summarizes current literature regarding changes in CM ploidy and nucleation during development, maturation and in response to cardiac injury. Importantly, how metabolism affects CM fate transition between mononucleation and binucleation and its impact on cell cycle progression, proliferation and ability to regenerate the heart will be discussed.

An Immunohistochemical Study of Proliferation of Human Fetal Heart Cardiomyocyte With Phospho-Histone H3 Antibody

The rapid proliferation of cardiomyocytes in mammals occurs during fetal life. But in postnatal life, this capacity of proliferation is reduced or lost as they exit the cell cycle. However, the cardiomyocytes don't show the same activity for different species. In human fetuses or in adult life, the capacity of the proliferation of cardiomyocytes and their response to an injury are not understood yet. In this study, we have done an immunohistochemical study using phospho-histone H3 (PHH3) to observe human fetal cardiomyocytes' proliferative activity. The heart specimens from the fetal autopsy of spontaneously aborted and stillborn human fetuses were subjected to immunohistochemical study using PHH3 antibody, and comparison between the PHH3 index (number of PHH3 positive cells per 1000 number of cardiomyocytes/high power field [HPF]) of myocardial regions was done using appropriate statistical tests. A total of 17 fetal hearts were included in our study. In the left ventricle, right ventricle, right atrium, and interventricular septum, the PHH3 index of myocardium was significantly higher over the pericardial region (p-value 0.002, p-value <0.001, <0.001, and 0.009 respectively) as compared to the region of over the endocardium and the middle part of the myocardium. The PHH3 index of the pericardial region of the left ventricle was significantly correlated with the maximum thickness of the left ventricle.

IGF2BP3 promotes adult myocardial regeneration by stabilizing MMP3 mRNA through interaction with m6A modification

Myocardial infarction that causes damage to heart muscle can lead to heart failure. The identification of molecular mechanisms promoting myocardial regeneration represents a promising strategy to improve cardiac function. Here we show that IGF2BP3 plays an important role in regulating adult cardiomyocyte proliferation and regeneration in a mouse model of myocardial infarction. IGF2BP3 expression progressively decreases during postnatal development and becomes undetectable in the adult heart. However, it becomes upregulated after cardiac injury. Both gain- and loss-of-function analyses indicate that IGF2BP3 regulates cardiomyocyte proliferation in vitro and in vivo. In particular, IGF2BP3 promotes cardiac regeneration and improves cardiac function after myocardial infarction. Mechanistically, we demonstrate that IGF2BP3 binds to and stabilizes MMP3 mRNA through interaction with N⁶-methyladenosine modification. The expression of MMP3 protein is also progressively downregulated during postnatal development. Functional analyses indicate that MMP3 acts downstream of IGF2BP3 to regulate cardiomyocyte proliferation. These results suggest that IGF2BP3-mediated post-transcriptional regulation of extracellular matrix and tissue remodeling contributes to cardiomyocyte regeneration. They should help to define therapeutic strategy for ameliorating myocardial infarction by inducing cell proliferation and heart repair.

Targeting neuro-immune systems to achieve cardiac tissue repair following myocardial infarction: A review of therapeutic approaches from in-vivo preclinical to clinical studies

Myocardial healing following myocardial infarction (MI) toward either functional tissue repair or excessive scarring/heart failure, may depend on a complex interplay between nervous and immune system responses, myocardial ischemia/reperfusion injury factors, as well as genetic and epidemiological factors. Hence, enhancing cardiac repair post MI may require a more patient-specific approach targeting this complex interplay and not just the heart, bearing in mind that the dysregulation or modulation of just one of these systems or some of their mechanisms may determine the outcome either toward functional repair or toward heart failure. In this review we have elected to focus on existing preclinical and clinical in-vivo studies aimed at testing novel therapeutic approaches targeting the nervous and immune systems to trigger myocardial healing toward functional tissue repair. To this end, we have only selected clinical and preclinical in-vivo studies reporting on novel treatments targeting neuro-immune systems to ultimately treat MI. Next, we have grouped and reported treatments under each neuro-immune system. Finally, for each treatment we have assessed and reported the results of each clinical/preclinical study and then discussed their results collectively. This structured approach has been followed for each treatment discussed. To keep this review focused, we have deliberately omitted to cover other important and related research areas such as myocardial ischemia/reperfusion injury, cell and gene therapies as well as any ex-vivo and in-vitro studies. The review indicates that some of the treatments targeting the neuro-immune/inflammatory systems appear to induce beneficial effects remotely on the healing heart post MI, warranting further validation. These remote effects on the heart also indicates the presence of an overarching synergic response occurring across the nervous and immune systems in response to acute MI, which appear to influence cardiac tissue repair in different ways depending on age and timing of treatment delivery following MI. The cumulative evidence arising from this review allows also to make informed considerations on safe as opposed to detrimental treatments, and within the safe treatments to ascertain those associated with conflicting or supporting preclinical data, and those warranting further validation.

A change of heart: understanding the mechanisms regulating cardiac proliferation and metabolism before and after birth

Mammalian cardiomyocytes undergo major maturational changes in preparation for birth and postnatal life. Immature cardiomyocytes contribute to cardiac growth via proliferation and thus the heart has the capacity to regenerate. To prepare for postnatal life, structural and metabolic changes associated with increased cardiac output and function must occur. This includes exit from the cell cycle, hypertrophic growth, mitochondrial maturation and sarcomeric protein isoform switching. However, these changes come at a price: the loss of cardiac regenerative capacity such that damage to the heart in postnatal life is permanent. This is a significant barrier to the development of new treatments for cardiac repair and contributes to heart failure. The transitional period of cardiomyocyte growth is a complex and multifaceted event. In this review, we focus on studies that have investigated this critical transition period as well as novel factors that may regulate and drive this process. We also discuss the potential use of new biomarkers for the detection of myocardial infarction and, in the broader sense, cardiovascular disease.

Mitochondria-derived damage-associated molecular patterns and inflammation in the ischemic-reperfused heart

Cardiac cell death after myocardial infarction release endogenous structures termed damage-associated molecular patterns (DAMPs) that trigger the innate immune system and initiate a sterile inflammation in the myocardium. Cardiomyocytes are energy demanding cells and 30% of their volume are mitochondria. Mitochondria are evolutionary endosymbionts originating from bacteria containing molecular patterns similar to bacteria, termed mitochondrial DAMPs (mDAMPs). Consequently, mitochondrial debris may be particularly immunogenic and damaging. However, the role of mDAMPs in myocardial infarction is not clarified. Identifying the most harmful mDAMPs and inhibiting their early inflammatory signaling may reduce infarct size and the risk of developing post-infarct heart failure. The focus of this review is the role of mDAMPs in the immediate pro-inflammatory phase after myocardial infarction before arrival of immune cells in the myocardium. We discuss different mDAMPs, their role in physiology and present knowledge regarding their role in the inflammatory response of acute myocardial infarction.

Epigenetic Modification Factors and microRNAs Network Associated with Differentiation of Embryonic Stem Cells and Induced Pluripotent Stem Cells toward Cardiomyocytes: A Review

More research is being conducted on myocardial cell treatments utilizing stem cell lines that can develop into cardiomyocytes. All of the forms of cardiac illnesses have shown to be quite amenable to treatments using embryonic (ESCs) and induced pluripotent stem cells (iPSCs). In the present study, we reviewed the differentiation of these cell types into cardiomyocytes from an epigenetic standpoint. We also provided a miRNA network that is devoted to the epigenetic commitment of stem cells toward cardiomyocyte cells and related diseases, such as congenital heart defects, comprehensively. Histone acetylation, methylation, DNA alterations, N6-methyladenosine (m⁶a) RNA methylation, and cardiac mitochondrial mutations are explored as potential tools for precise stem cell differentiation.

Ectopic Acsl6 Overexpression Partially Improves Isoproterenol-Induced Cardiac Hypertrophy In Vivo and Cardiomyocyte Hypertrophy In Vitro

ABSTRACT

The increase in cardiac myocyte size is a critical issue in cardiac hypertrophy development. In this study, 61 differentially expressed genes between hypertrophic rats and normal controls were enriched in the positive modulation of fatty acid uptake, fatty acid metabolism and degradation, cardiac conduction, and the oxidation of carbohydrates and other processes. Acsl6 was significantly downregulated in hypertrophic rat and mouse hearts according to online data. Based on the experimental data, Acsl6 was underexpressed in ISO-induced cardiac hypertrophy mouse model and isoproterenol (ISO)-induced cardiomyocyte hypertrophy cell model. In vivo, Acsl6 overexpression partially attenuated ISO-induced increases in the cross-sectional area and cardiac hypertrophy, elevated hypertrophic markers, and caused impairment of cardiac function. In vitro, Acsl6 overexpression partially attenuated ISO-induced cardiomyocyte hypertrophy and increased hypertrophic markers. Conclusively, Ascl6 is downregulated in ISO-induced cardiac hypertrophy mouse model and ISO-induced cardiomyocyte hypertrophy cell model. Acsl6 overexpression could partially improve cardiac hypertrophy in vivo and cardiomyocyte hypertrophy in vitro, possibly through the regulation of HIF-1α/Hippo pathway.

A comprehensive review of computational and image analysis techniques for quantitative evaluation of striated muscle tissue architecture

Unbiased evaluation of morphology is crucial to understanding development, mechanics, and pathology of striated muscle tissues. Indeed, the ability of striated muscles to contract and the strength of their contraction is dependent on their tissue-, cellular-, and cytoskeletal-level organization. Accordingly, the study of striated muscles often requires imaging and assessing aspects of their architecture at multiple different spatial scales. While an expert may be able to qualitatively appraise tissues, it is imperative to have robust, repeatable tools to quantify striated myocyte morphology and behavior that can be used to compare across different labs and experiments. There has been a recent effort to define the criteria used by experts to evaluate striated myocyte architecture. In this review, we will describe metrics that have been developed to summarize distinct aspects of striated muscle architecture in multiple different tissues, imaged with various modalities. Additionally, we will provide an overview of metrics and image processing software that needs to be developed. Importantly to any lab working on striated muscle platforms, characterization of striated myocyte morphology using the image processing pipelines discussed in this review can be used to quantitatively evaluate striated muscle tissues and contribute to a robust understanding of the development and mechanics of striated muscles.

Mesentery AjFGF4-AjFGFR2-ERK pathway modulates intestinal regeneration via targeting cell cycle in echinoderms

OBJECTIVES

The purpose of the study aims to understand the regeneration process and its cytology mechanism in economic echinoderms.

MATERIALS AND METHODS

The intestine regeneration process of Apostichopus japonicus was investigated by immunohistochemistry and the cell proliferation was detected by immunofluorescence and flow cytometry. Fibroblast growth factor 4 of A. japonicus (AjFGF4) was screened by RNA-seq analysis and validated to regulate cell proliferation by siAjFGF4 and recombinant-AjFGF4 treatment. The binding and co-localization of AjFGF4 and AjFGFR2 were verified by Co-IP, GST-pull down, and immunofluorescence. Then, the AjFGF4-AjFGFR2-ERK-cell cycle axis was examined by western blot, immunofluorescence, and flow cytometry techniques.

RESULTS

The mesentery was served as the epicenter of intestinal regeneration via activating cell proliferation and other cellular events. Mechanically, AjFGF4-mediated cell proliferation was dependent on the binding to its receptor AjFGFR2, and then triggered the conserved ERK-MAPK pathway but not JNK and p38 pathway. The activated ERK-MAPK subsequently mediated the expression of cell cycle regulatory proteins of CDK2, Cyclin A, and Cyclin B to promote cell proliferation.

CONCLUSIONS

We provide the first functional evidence that AjFGF4-AjFGFR2-ERK-cell cycle axis mediated cell proliferation was the engine for mesentery-derived intestine regeneration in echinoderms.

Loss of Rbl2 (Retinoblastoma-Like 2) Exacerbates Myocardial Ischemia/Reperfusion Injury

Background The postmitotic state of adult cardiomyocytes, maintained by the cell cycle repressor Rbl2 (retinoblastoma-like 2), is associated with considerable resistance to apoptosis. However, whether Rbl2 regulates cardiomyocyte apoptosis remains unknown. Methods and Results Here, we show that ablation of Rbl2 increased cardiomyocyte apoptosis following acute myocardial ischemia/reperfusion injury, leading to diminished cardiac function and exaggerated ventricular remodeling in the long term. Mechanistically, ischemia/reperfusion induced expression of the proapoptotic protein BCL2 interacting protein 3 (Bnip3), which was augmented by deletion of Rbl2. Because the Bnip3 promoter contains an adenoviral early region 2 binding factor (E2F)-binding site, we further showed that loss of Rbl2 upregulated the transcriptional activator E2F1 but downregulated the transcriptional repressor E2F4. In cultured cardiomyocytes, treatment with H₂O₂ markedly increased the levels of E2F1 and Bnip3, resulting in mitochondrial depolarization and apoptosis. Depletion of Rbl2 significantly augmented H₂O₂-induced mitochondrial damage and apoptosis in vitro. Conclusions Rbl2 deficiency enhanced E2F1-mediated Bnip3 expression, resulting in aggravated cardiomyocyte apoptosis and ischemia/reperfusion injury. Our results uncover a novel antiapoptotic role for Rbl2 in cardiomyocytes, suggesting that the cell cycle machinery may directly regulate apoptosis in postmitotic cardiomyocytes. These findings may be exploited to develop new strategies to limit ischemia/reperfusion injury in the treatment of acute myocardial infarction.

Energy Metabolism on Mitochondrial Maturation and Its Effects on Cardiomyocyte Cell Fate

Alterations in energy metabolism play a major role in the lineage of cardiomyocytes, such as the dramatic changes that occur in the transition from neonate to newborn. As cardiomyocytes mature, they shift from a primarily glycolytic state to a mitochondrial oxidative metabolic state. Metabolic intermediates and metabolites may have epigenetic and transcriptional roles in controlling cell fate by increasing mitochondrial biogenesis. In the maturing cardiomyocyte, such as in the postnatal heart, fatty acid oxidation increases in conjunction with increased mitochondrial biogenesis driven by the transcriptional coregulator PGC1-α. PGC1-α is necessary for mitochondrial biogenesis in the heart at birth, with deficiencies leading to postnatal cardiomyopathy. While stem cell therapy as a treatment for heart failure requires further investigation, studies suggest that adult stem cells may secrete cardioprotective factors which may regulate cardiomyocyte differentiation and survival. This review will discuss how metabolism influences mitochondrial biogenesis and how mitochondrial biogenesis influences cell fate, particularly in the context of the developing cardiomyocyte. The implications of energy metabolism on stem cell differentiation into cardiomyocytes and how this may be utilized as a therapy against heart failure and cardiovascular disease will also be discussed.

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.

The insulin receptor family in the heart: new light on old insights

Insulin was discovered over 100 years ago. Whilst the first half century defined many of the physiological effects of insulin, the second emphasised the mechanisms by which it elicits these effects, implicating a vast array of G proteins and their regulators, lipid and protein kinases and counteracting phosphatases, and more. Potential growth-promoting and protective effects of insulin on the heart emerged from studies of carbohydrate metabolism in the 1960s, but the insulin receptors (and the related receptor for insulin-like growth factors 1 and 2) were not defined until the 1980s. A related third receptor, the insulin receptor-related receptor remained an orphan receptor for many years until it was identified as an alkali-sensor. The mechanisms by which these receptors and the plethora of downstream signalling molecules confer cardioprotection remain elusive. Here, we review important aspects of the effects of the three insulin receptor family members in the heart. Metabolic studies are set in the context of what is now known of insulin receptor family signalling and the role of protein kinase B (PKB or Akt), and the relationship between this and cardiomyocyte survival versus death is discussed. PKB/Akt phosphorylates numerous substrates with potential for cardioprotection in the contractile cardiomyocytes and cardiac non-myocytes. Our overall conclusion is that the effects of insulin on glucose metabolism that were initially identified remain highly pertinent in managing cardiomyocyte energetics and preservation of function. This alone provides a high level of cardioprotection in the face of pathophysiological stressors such as ischaemia and myocardial infarction.

PKN2 deficiency leads both to prenatal congenital cardiomyopathy and defective angiotensin II stress responses

The protein kinase PKN2 is required for embryonic development and PKN2 knockout mice die as a result of failure in the expansion of mesoderm, cardiac development and neural tube closure. In the adult, cardiomyocyte PKN2 and PKN1 (in combination) are required for cardiac adaptation to pressure-overload. The specific role of PKN2 in contractile cardiomyocytes during development and its role in the adult heart remain to be fully established. We used mice with cardiomyocyte-directed knockout of PKN2 or global PKN2 haploinsufficiency to assess cardiac development and function using high resolution episcopic microscopy, MRI, micro-CT and echocardiography. Biochemical and histological changes were also assessed. Cardiomyocyte-directed PKN2 knockout embryos displayed striking abnormalities in the compact myocardium, with frequent myocardial clefts and diverticula, ventricular septal defects and abnormal heart shape. The sub-Mendelian homozygous knockout survivors developed cardiac failure. RNASeq data showed up-regulation of PKN2 in patients with dilated cardiomyopathy, suggesting an involvement in adult heart disease. Given the rarity of homozygous survivors with cardiomyocyte-specific deletion of PKN2, the requirement for PKN2 in adult mice was explored using the constitutive heterozygous PKN2 knockout. Cardiac hypertrophy resulting from hypertension induced by angiotensin II was reduced in these haploinsufficient PKN2 mice relative to wild-type littermates, with suppression of cardiomyocyte hypertrophy and cardiac fibrosis. It is concluded that cardiomyocyte PKN2 is essential for heart development and the formation of compact myocardium and is also required for cardiac hypertrophy in hypertension. Thus, PKN signalling may offer therapeutic options for managing congenital and adult heart diseases.

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.

The non-canonical nuclear functions of key players of the PI3K-AKT-MTOR pathway

The PI3K-AKT-MTOR signal transduction pathway is one of the essential signalling cascades within the cell due to its involvement in many vital functions. The pathway initiates with the recruitment of phosphatidylinositol-3 kinases (PI3Ks) onto the plasma membrane, generating phosphatidylinositol-3,4,5-triphosphate [PtdIns(3,4,5)P₃ ] and subsequently activating AKT. Being the central node of the PI3K network, AKT activates the mechanistic target of rapamycin kinase complex 1 (MTORC1) via Tuberous sclerosis complex 2 inhibition in the cytoplasm. Although the cytoplasmic role of the pathway has been widely explored for decades, we now know that most of the effector molecules of the PI3K axis diverge from the canonical route and translocate to other cell organelles including the nucleus. The presence of phosphoinositides (PtdIns) inside the nucleus itself indicates the existence of a nuclear PI3K signalling. The nuclear localization of these signaling components is evident in regulating many nuclear processes like DNA replication, transcription, DNA repair, maintenance of genomic integrity, chromatin architecture, and cell cycle control. Here, our review intends to present a comprehensive overview of the nuclear functions of the PI3K-AKT-MTOR signaling biomolecules.

Mitochondrial Membrane Potential Identifies a Subpopulation of Mesenchymal Progenitor Cells to Promote Angiogenesis and Myocardial Repair

Identifying effective donor cells is one of obstacles that limits cell therapy for heart disease. In this study, we sorted a subpopulation of human mesenchymal progenitor cells (hMPCs) from the right atrial appendage using the low mitochondrial membrane potential. Compared to the non-sorted cells, hMPCs hold the capacity for stemness and enrich mesenchymal stem cell markers. The hMPCs display better ability for survival, faster proliferation, less production of reactive oxygen species (ROS), and greater release of cytoprotective cytokines. The hMPCs exhibit decreased expression of senescence genes and increased expression of anti-apoptotic and antioxidant genes. Intramyocardial injection of hMPCs into the infarcted heart resulted in increased left ventricular ejection fraction and reduced cardiac remodeling and infarct size in the group of animals receiving hMPCs. Both in vitro and in vivo studies indicated hMPCs have the potential to differentiate into endothelial cells and smooth muscle cells. Immunohistochemistry staining showed that cell therapy with hMPCs enhances cardiac vascular regeneration and cardiac proliferation, and decreases cardiac cell apoptosis, which is associated with the increased secretion of cytoprotective and pro-angiogenic cytokines. Overall, we discovered a subpopulation of human mesenchymal progenitor cells via their low mitochondrial membrane potential, which might provide an alternative donor cell source for cellular therapy for ischemic heart disease.

Dynamic Involvement of Telocytes in Modulating Multiple Signaling Pathways in Cardiac Cytoarchitecture

Cardiac interstitium is a complex and dynamic environment, vital for normal cardiac structure and function. Telocytes are active cellular players in regulating main events that feature myocardial homeostasis and orchestrating its involvement in heart pathology. Despite the great amount of data suggesting (microscopically, proteomically, genetically, etc.) the implications of telocytes in the different physiological and reparatory/regenerative processes of the heart, understanding their involvement in realizing the heart's mature cytoarchitecture is still at its dawn. Our scrutiny of the recent literature gave clearer insights into the implications of telocytes in the WNT signaling pathway, but also TGFB and PI3K/AKT pathways that, inter alia, conduct cardiomyocytes differentiation, maturation and final integration into heart adult architecture. These data also strengthen evidence for telocytes as promising candidates for cellular therapies in various heart pathologies.

Development and Characterization of Furfuryl-Gelatin Electrospun Scaffolds for Cardiac Tissue Engineering

In this study, three types of electrospun scaffolds, including furfuryl-gelatin (f-gelatin) alone, f-gelatin with polycaprolactone (PCL) in a 1:1 ratio, and coaxial scaffolds with PCL (core) and f-gelatin (sheath), were developed for tissue engineering applications. Scaffolds were developed through single nozzle electrospinning and coaxial electrospinning, respectively, to serve as scaffolds for cardiac tissue engineering. Uniform fibrous structures were revealed in the scaffolds with significantly varying average fiber diameters of 760 ± 80 nm (f-gelatin), 420 ± 110 nm [f-gelatin and PCL (1:1)], and 810 ± 60 nm (coaxial f-gelatin > PCL) via scanning electron microscopy. The distinction between the core and the sheath of the fibers of the coaxial f-gelatin > PCL electrospun fibrous scaffolds was revealed by transmission electron microscopy. Thermal analysis and Fourier transformed infrared (FTIR) spectroscopy revealed no interactions between the polymers in the blended electrospun scaffolds. The varied blending methods led to significant differences in the elastic moduli of the electrospun scaffolds with the coaxial f-gelatin > PCL revealing the highest elastic modulus of all scaffolds (164 ± 3.85 kPa). All scaffolds exhibited excellent biocompatibility by supporting the adhesion and proliferation of human AC16 cardiomyocytes cells. The biocompatibility of the coaxial f-gelatin > PCL scaffolds with superior elastic modulus was assessed further through adhesion and functionality of human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes, thereby demonstrating the potential of the coaxially spun scaffolds as an ideal platform for developing cardiac tissue-on-a-chip models. Our results demonstrate a facile approach to produce visible light cross-linkable, hybrid, biodegradable nanofibrous scaffold biomaterials, which can serve as platforms for cardiac tissue engineered models.

The Cardiac Sarcomere and Cell Cycle

PURPOSE OF REVIEW

The lack of adult human cardiomyocyte proliferative capacity impairs cardiac regeneration such as after myocardial injury. The sarcomere, a specialized actin cytoskeletal structure that is essential for twitch contraction in cardiomyocytes, has been considered a critical factor limiting adult human cardiomyocyte proliferation through incompletely understood mechanisms.

RECENT FINDINGS

This review summarizes known and emerging regulatory mechanisms connecting the human cardiomyocyte sarcomere to cell cycle regulation including structural and signaling mechanisms. Cardiac regeneration could be augmented through targeting the inhibitory effects of the sarcomere on cardiomyocyte proliferation.

Monocyte subpopulation profiling indicates CDK6-derived cell differentiation and identifies subpopulation-specific miRNA expression sets in acute and stable coronary artery disease

Coronary artery disease (CAD) is a long-lasting inflammatory disease characterized by monocyte migration into the vessel wall leading to clinical events like myocardial infarction (MI). However, the role of monocyte subsets, especially their miRNA-driven differentiation in this scenario is still in its infancy. Here, we characterized monocyte subsets in controls and disease phenotypes of CAD and MI patients using flow cytometry and miRNA and mRNA expression profiling using RNA sequencing. We observed major differences in the miRNA profiles between the classical (CD14⁺⁺CD16⁻) and nonclassical (CD14⁺CD16⁺⁺) monocyte subsets irrespective of the disease phenotype suggesting the Cyclin-dependent Kinase 6 (CDK6) to be an important player in monocyte maturation. Between control and MI patients, we found a set of miRNAs to be differentially expressed in the nonclassical monocytes and targeting CCND2 (Cyclin D2) that is able to enhance myocardial repair. Interestingly, miRNAs as miR-125b playing a role in vascular calcification were differentially expressed in the classical subset in patients suffering from CAD and not MI in comparison to control samples. In conclusion, our study describes specific peculiarities of monocyte subset miRNA expression in control and diseased samples and provides basis to further functional analysis and to identify new cardiovascular disease treatment targets.

Characterization and Validation of ceRNA-Mediated Pathway–Pathway Crosstalk Networks Across Eight Major Cardiovascular Diseases

Pathway analysis is considered as an important strategy to reveal the underlying mechanisms of diseases. Pathways that are involved in crosstalk can regulate each other and co-regulate downstream biological processes. Furthermore, some genes in the pathways can function with other genes via the relationship of the competing endogenous RNA (ceRNA) mechanism, which has also been demonstrated to play key roles in cellular biology. However, the comprehensive analysis of ceRNA-mediated pathway crosstalk is lacking. Here, we constructed the landscape of the ceRNA-mediated pathway–pathway crosstalk of eight major cardiovascular diseases (CVDs) based on sequencing data from ∼2,800 samples. Some common features shared by numerous CVDs were uncovered. A fraction of the pathway–pathway crosstalk was conserved in multiple CVDs and a core pathway–pathway crosstalk network was identified, suggesting the similarity of pathway–pathway crosstalk among CVDs. Experimental evidence also demonstrated that the pathway crosstalk was functioned in CVDs. We split all hub pathways of each pathway–pathway crosstalk network into three categories, namely, common hubs, differential hubs, and specific hubs, which could highlight the common or specific biological mechanisms. Importantly, after a comparison analysis of the hub pathways of networks, ∼480 hub pathway-induced common modules were identified to exert functions in CVDs broadly. Moreover, we performed a random walk algorithm on the hub pathway-induced sub-network and identified 23 potentially novel CVD-related pathways. In summary, our study revealed the potential molecular regulatory mechanisms of ceRNA crosstalk in pathway–pathway crosstalk levels and provided a novel routine to investigate the pathway–pathway crosstalk in cardiology. All CVD pathway–pathway crosstalks are provided in http://www.licpathway.net/cepathway/index.html.

Cardiomyocyte BRAF and type 1 RAF inhibitors promote cardiomyocyte and cardiac hypertrophy in mice in vivo

The extracellular signal-regulated kinase 1/2 (ERK1/2) cascade promotes cardiomyocyte hypertrophy and is cardioprotective, with the three RAF kinases forming a node for signal integration. Our aims were to determine if BRAF is relevant for human heart failure, whether BRAF promotes cardiomyocyte hypertrophy, and if Type 1 RAF inhibitors developed for cancer (that paradoxically activate ERK1/2 at low concentrations: the 'RAF paradox') may have the same effect. BRAF was up-regulated in heart samples from patients with heart failure compared with normal controls. We assessed the effects of activated BRAF in the heart using mice with tamoxifen-activated Cre for cardiomyocyte-specific knock-in of the activating V600E mutation into the endogenous gene. We used echocardiography to measure cardiac dimensions/function. Cardiomyocyte BRAFV600E induced cardiac hypertrophy within 10 d, resulting in increased ejection fraction and fractional shortening over 6 weeks. This was associated with increased cardiomyocyte size without significant fibrosis, consistent with compensated hypertrophy. The experimental Type 1 RAF inhibitor, SB590885, and/or encorafenib (a RAF inhibitor used clinically) increased ERK1/2 phosphorylation in cardiomyocytes, and promoted hypertrophy, consistent with a 'RAF paradox' effect. Both promoted cardiac hypertrophy in mouse hearts in vivo, with increased cardiomyocyte size and no overt fibrosis. In conclusion, BRAF potentially plays an important role in human failing hearts, activation of BRAF is sufficient to induce hypertrophy, and Type 1 RAF inhibitors promote hypertrophy via the 'RAF paradox'. Cardiac hypertrophy resulting from these interventions was not associated with pathological features, suggesting that Type 1 RAF inhibitors may be useful to boost cardiomyocyte function.

Restoring Ravaged Heart: Molecular Mechanisms and Clinical Application of miRNA in Heart Regeneration

Human heart development is a complex and tightly regulated process, conserving proliferation, and multipotency of embryonic cardiovascular progenitors. At terminal stage, progenitor cell type gets suppressed for terminal differentiation and maturation. In the human heart, most cardiomyocytes are terminally differentiated and so have limited proliferation capacity. MicroRNAs (miRNAs) are non-coding single-stranded RNA that regulate gene expression and mRNA silencing at the post-transcriptional level. These miRNAs play a crucial role in numerous biological events, including cardiac development, and cardiomyocyte proliferation. Several cardiac cells specific miRNAs have been discovered. Inhibition or overexpression of these miRNAs could induce cardiac regeneration, cardiac stem cell proliferation and cardiomyocyte proliferation. Clinical application of miRNAs extends to heart failure, wherein the cell cycle arrest of terminally differentiated cardiac cells inhibits the heart regeneration. The regenerative capacity of the myocardium can be enhanced by cardiomyocyte specific miRNAs controlling the cell cycle. In this review, we focus on cardiac-specific miRNAs involved in cardiac regeneration and cardiomyocyte proliferation, and their potential as a new clinical therapy for heart regeneration.

Cell cycle defects underlie childhood-onset cardiomyopathy associated with Noonan syndrome

Childhood-onset myocardial hypertrophy and cardiomyopathic changes are associated with significant morbidity and mortality in early life, particularly in patients with Noonan syndrome, a multisystemic genetic disorder caused by autosomal dominant mutations in genes of the Ras-MAPK pathway. Although the cardiomyopathy associated with Noonan syndrome (NS-CM) shares certain cardiac features with the hypertrophic cardiomyopathy caused by mutations in sarcomeric proteins (HCM), such as pathological myocardial remodeling, ventricular dysfunction, and increased risk for malignant arrhythmias, the clinical course of NS-CM significantly differs from HCM. This suggests a distinct pathophysiology that remains to be elucidated. Here, through analysis of sarcomeric myosin conformational states, histopathology, and gene expression in left ventricular myocardial tissue from NS-CM, HCM, and normal hearts complemented with disease modeling in cardiomyocytes differentiated from patient-derived PTPN11 N308S/+ induced pluripotent stem cells, we demonstrate distinct disease phenotypes between NS-CM and HCM and uncover cell cycle defects as a potential driver of NS-CM.

CRISPR activation of endogenous genes reprograms fibroblasts into cardiovascular progenitor cells for myocardial infarction therapy

Fibroblasts can be reprogrammed into cardiovascular progenitor cells (CPCs) using transgenic approaches, although the underlying mechanism remains unclear. We determined whether activation of endogenous genes such as Gata4, Nkx2.5, and Tbx5 can rapidly establish autoregulatory loops and initiate CPC generation in adult extracardiac fibroblasts using a CRISPR activation system. The induced fibroblasts (>80%) showed phenotypic changes as indicated by an Nkx2.5 cardiac enhancer reporter. The progenitor characteristics were confirmed by colony formation and expression of cardiovascular genes. Cardiac sphere induction segregated the early and late reprogrammed cells that can generate functional cardiomyocytes and vascular cells in vitro. Therefore, they were termed CRISPR-induced CPCs (ciCPCs). Transcriptomic analysis showed that cell cycle and heart development pathways were important to accelerate CPC formation during the early reprogramming stage. The CRISPR system opened the silenced chromatin locus, thereby allowing transcriptional factors to access their own promoters and eventually forming a positive feedback loop. The regenerative potential of ciCPCs was assessed after implantation in mouse myocardial infarction models. The engrafted ciCPCs differentiated into cardiovascular cells in vivo but also significantly improved contractile function and scar formation. In conclusion, multiplex gene activation was sufficient to drive CPC reprogramming, providing a new cell source for regenerative therapeutics.

Mitochondrial-cell cycle cross-talk drives endoreplication in heart disease

[Figure: see text].

Diverging targets mediate the pathological roleof miR-199a-5p and miR-199a-3p by promoting cardiac hypertrophy and fibrosis

MicroRNA-199a-5p (miR-199a-5p) and -3p are enriched in the myocardium, but it is unknown whether miR-199a-5p and -3p are co-expressed in cardiac remodeling and what roles they have in cardiac hypertrophy and fibrosis. We show that miR-199a-5p and -3p are co-upregulated in the mouse and human myocardium with cardiac remodeling and in Ang-II-treated neonatal mouse ventricular cardiomyocytes (NMVCs) and cardiac fibroblasts (CFs). miR-199a-5p and -3p could aggravate cardiac hypertrophy and fibrosis in vivo and in vitro. PPAR gamma coactivator 1 alpha (Ppargc1a) and sirtuin 1 (Sirt1) were identified as target genes to mediate miR-199a-5p in promoting both cardiac hypertrophy and fibrosis. However, miR-199a-3p aggravated cardiac hypertrophy and fibrosis through targeting RB transcriptional corepressor 1 (Rb1) and Smad1, respectively. Serum response factor and nuclear factor κB p65 participated in the upregulation of miR-199a-5p and -3p in Ang-II-treated NMVCs and mouse CFs, and could be conversely elevated by miR-199a-5p and -3p. Together, Ppargc1a and Sirt1, Rb1 and Smad1 mediated the pathological effect of miR-199a-5p and -3p by promoting cardiac hypertrophy and fibrosis, respectively. This study suggests a possible new strategy for cardiac remodeling therapy by inhibiting miR-199a-5p and -3p.

Cardiac structure and function in very preterm-born adolescents compared to term-born controls: A longitudinal cohort study

BACKGROUND

There is emerging evidence of differences in cardiac structure and function in preterm-born adults and increased risk of heart failure. However, there is a paucity of data in populations who have been exposed to modern intensive care and the impact of perinatal factors is unclear.

AIMS

To compare echocardiographic measures of cardiac structure and function in a regional cohort of 17-year-olds born very preterm compared to term-born peers and the influence of perinatal factors.

STUDY DESIGN

Observational longitudinal cohort study.

SUBJECTS

A regional cohort of ninety-one 17-year-olds born at <32 weeks gestation compared to sixty-two term-born controls.

OUTCOME MEASURES

Echocardiographic measures of cardiac structure and function.

RESULTS

Left ventricular and right atrial volume and left ventricular mass, indexed to body surface area, were significantly smaller in preterm-born adolescents compared to term-born controls even when adjusted for sex. There were no between group differences in cardiac function. Within those born preterm we found a significant association between gestational age and birthweight z-score and measures of cardiac function at 17 years. Within the preterm group, those with a diagnosis of bronchopulmonary dysplasia had higher left ventricular posterior wall thickness, higher mitral deceleration time and lower left atrial area and tricuspid annular plane of systolic excursion.

CONCLUSIONS

Adolescents born very prematurely, who have received modern intensive care, have measurable differences in heart structure compared to their term-born peers but heart function is preserved. For those born preterm, gestational age, birthweight and bronchopulmonary dysplasia are associated with differences in cardiac function.