Regulates Cardiomyocyte Proliferation Research Articles

Delivery of SAV-siRNA via Exosomes from Adipose-Derived Stem Cells for the Treatment of Myocardial Infarction.

Myocardial infarction (MI) leads to cardiomyocyte death, poor cardiac remodeling, and heart failure, making it a major cause of mortality and morbidity. To restore cardiac pumping function, induction of cardiomyocyte regeneration has become a focus of academic interest. The Hippo pathway is known to regulate cardiomyocyte proliferation and heart size, and its inactivation allows adult cardiomyocytes to re-enter the cell cycle. In this study, we investigated whether exosomes from adipose-derived stem cells (ADSCs) could effectively transfer siRNA for the Hippo pathway regulator Salvador (SAV) into cardiomyocytes to induce cardiomyocyte regeneration in a mouse model of MI. Our results showed that exosomes loaded with SAV-siRNA effectively transferred siRNA into cardiomyocytes and induced cardiomyocyte re-entry into the cell cycle, while retaining the previously demonstrated therapeutic efficacy of ADSC-derived exosomes to improve post-infarction cardiac function through anti-fibrotic, pro-angiogenic, and other effects. Our findings suggest that siRNA delivery via ADSC-derived exosomes may be a promising approach for the treatment of MI.

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.

Two decades of heart regeneration research: Cardiomyocyte proliferation and beyond.

Interest in vertebrate cardiac regeneration has exploded over the past two decades since the discovery that adult zebrafish are capable of complete heart regeneration, contrasting the limited regenerative potential typically observed in adult mammalian hearts. Undercovering the mechanisms that both support and limit cardiac regeneration across the animal kingdom may provide unique insights in how we may unlock this capacity in adult humans. In this review, we discuss key discoveries in the heart regeneration field over the last 20 years. Initially, seminal findings revealed that pre-existing cardiomyocytes are the major source of regenerated cardiac muscle, drawing interest into the intrinsic mechanisms regulating cardiomyocyte proliferation. Moreover, recent studies have identified the importance of intercellular interactions and physiological adaptations, which highlight the vast complexity of the cardiac regenerative process. Finally, we compare strategies that have been tested to increase the regenerative capacity of the adult mammalian heart. This article is categorized under: Cardiovascular Diseases > Stem Cells and Development.

Abstract P1097: Foxk1 Is A Regulator Of Cardiomyocyte Proliferation And Heart Regeneration

While the adult mammalian heart has limited regenerative potential, the neonatal mouse heart has a remarkable regenerative capacity. Our goal focused on defining new factors and mechanisms that could enhance repair and regeneration in the adult mouse heart. FOXK1 is a transcription factor that regulates cell cycle kinetics, myogenic stem cell proliferation and skeletal muscle regeneration. During development, its expression is restricted to progenitors, somites and the heart. However, its role in neonatal heart regeneration is unknown and warrants investigation. Here, we describe a novel role for FOXK1 as a regulator of cardiomyocyte (CM) proliferation and regeneration. Using computational analysis of single nucleus RNAseq datasets of neonatal CMs, we determined that FOXK1 was expressed in CMs. qPCR analysis of P1 hearts from control or Foxk1 null mice demonstrated that the absence of FOXK1 led to the dysregulation of Ccne1 and p21 expression, suggesting that FOXK1 could play a role in cell cycle kinetics in the neonatal heart. Control or Foxk1 null mice were pulsed with EdU which demonstrated that the absence of FOXK1 led to a decrease in CM proliferation in vivo. We then engineered a transgenic mouse model that overexpressed FOXK1 using the muscle creatine kinase ( MCK-Foxk1 ) promoter and isolated and cultured control or MCK-Foxk1 CMs (72 hrs), and determined that overexpression of FOXK1 led to a significant increase in CM proliferation. Furthermore, EdU pulsing studies in adult control or MCK-Foxk1 mice demonstrated a significant increase in EdU incorporation in adult CMs of MCK-Foxk1 unperturbed mice compared to control. We then performed LAD ligation surgeries in control and MCK-Foxk1 adult mice. Echocardiography 2 months following LAD ligations showed a significant increase in both ejection fraction and fractional shortening in MCK-Foxk1 mice compared to controls. Single nucleus RNAseq analysis of control and MCK-Foxk1 adult hearts highlighted two distinct CM populations by UMAP analysis, with the latter demonstrating a higher expression of myoblast proliferative pathways. These results identify FOXK1 as a regulator of CM proliferation and heart regeneration by employing both knockout and transgenic mouse models.

Abstract P1089: Pontin Is Necessary And Sufficient For Driving Cardiomyocyte Proliferation In Zebrafish And Mice

A major barrier to human heart regeneration is the absence of cardiomyocyte (CM) cell division in the infarcted heart. Remarkably, injured hearts of adult zebrafish and neonatal mice are capable of robust heart regeneration achieved through CM proliferation. Pontin is an evolutionarily conserved member of the AAA+ ATPase superfamily of proteins that regulates transcription, chromatin remodeling, and cell cycle progression in many contexts. Nonetheless, the involvement of Pontin in regulating CM proliferation has not been assessed. Using loss- and gain-of-function models in zebrafish and mice, we have determined that Pontin is necessary and sufficient for driving CM proliferation. Zebrafish pontin mutants are devoid of CM proliferation during heart development, and CM-specific overexpression of Pontin ( pontin OE ) is sufficient to induce myocardial hyperplasia during heart development and regeneration. In mice, myocardial-specific deletion of Pontin dampens CM proliferation, leading to embryonic lethality at E12.5, while CM-specific overexpression of Pontin from P0 to P7 is sufficient to increase the CM mitotic index. To decipher the molecular mechanism by which pontin OE stimulates CM proliferation, we performed single-cell ATAC + RNA-sequencing analysis of hyperproliferative pontin OE CMs during zebrafish regeneration. We identified significant downregulation of several anti-proliferative genes, including three in the btg/tob family ( btg1 , btg2 , tob1b ). The btg2 and tob1b loci showed reduced chromatin accessibility, suggesting that they could be direct targets of Pontin’s chromatin remodeling activity. We are currently testing this hypothesis and determining if overexpression of Pontin in neonatal mice extends the regenerative window beyond P7. In conclusion, our data highlight Pontin as a novel regulator of CM proliferation, potentially by controlling the chromatin accessibility of anti-proliferative genes.

Abstract P1120: Chromobox 7 Represses Cardiomyocyte Proliferation, And Its Genetic Ablation Promotes Cardiac Regeneration Following Myocardial Injury

Background: Cardiomyocyte (CM) proliferation decreases after birth but the underlying mechanism is poorly understood. Chromobox 7 (CBX7) regulates the cell cycle but its role in CM proliferation is unknown. Methods: We profiled CBX7 expression in the mouse hearts via qRT-PCR, western blotting, and immunohistochemistry. We knocked down CBX7 by using constitutive and inducible conditional knockout mice (Tnnt2-cre;Cbx7 fl/+ and Myh6-MCM;Cbx7 fl/fl , respectively). We then measured CM proliferation by immunostaining. To examine the role of CBX7 in cardiac regeneration, we employed neonatal cardiac apical resection and adult myocardial infarction (MI) models. We examined the mechanism of CBX7-mediated repression of CM proliferation via co-immunoprecipitation, mass spectrometry, and other molecular techniques. Results: The mRNA expression of Cbx7 was increased at the perinatal stage and sustained in the postnatal heart. The haplodeficiency of Cbx7 (Tnnt2-Cre;Cbx7 fl/+ ) promoted proliferation of neonatal CMs in vivo , leading to increased myocardial wall thickness. Genetic deletion of Cbx7 in CMs ( Cbx7 iCKO, Myh6-MCM;Cbx7 fl/fl ) at P0 resulted in increased CM proliferation (% of Ki67 + CMs: vehicle, 9.5 vs. tamoxifen, 18.3, P < 0.01). In response to cardiac apical resection surgery at P7, Cbx7 iCKO mice exhibited better cardiac function (% of LVEF: vehicle, 44.1 vs. tamoxifen, 54.7, P < 0.05) and less fibrosis at P28 compared to the control. Following the MI surgery, adult (5-months-old) Cbx7 iCKO mice exhibited better cardiac function (% of LVEF: vehicle, 41.4 vs. tamoxifen, 51.5, P < 0.05) and less fibrosis at one month post-MI compared to the control. Mechanistically, CBX7 interacted with TARDBP and positively regulated its downstream target, RBM38, an inducer of the cell cycle arrest, in a TARDBP-dependent manner. Rbm38 was perinatally upregulated in the mouse hearts and overexpression of Rbm38 reduced proliferation of neonatal CMs. Conclusions: CBX7 expression is perinatally increased and inhibits proliferation of CMs by controlling TARDBP/Rbm38 pathway. Genetic ablation of Cbx7 promoted regeneration of neonatal and adult hearts. This is the first study to uncover the role of CBX7 in regulation of CM proliferation and cardiac regeneration.

Abstract P3041: Stage-specific Alternative Rna Splicing Attunes Cardiomyocyte Proliferation And Contraction

During heart development, cardiomyocytes display reduced proliferation and enhanced contractility to support cardiac functional maturation, but the mechanistic basis is not fully understood. Alternative RNA splicing is an important mechanism of RNA posttranscriptional modification and gene regulation in the heart. In studying a cardiac RNA binding protein, RBPMS (RNA-binding protein with multiple splicing), we found that RBPMS mediates distinct RNA splicing profiles in adult hearts versus neonatal hearts, indicating its stage-specific modulation of alternative RNA splicing. We showed that RBPMS regulates the splicing of cytoskeletal genes to enable proliferation of neonatal cardiomyocytes. In adult hearts, RBPMS regulates the splicing of sarcomere genes to support cardiac contraction. Cardiac-specific loss of RBPMS causes severe dilated cardiomyopathy and early lethality in adult mice. Using both in vivo and in vitro approaches, we found that the absence of RBPMS caused aberrant splicing of some key sarcomeric components, including Titin and Nexilin, causing cardiomyocyte contractile defects. Intriguingly, we also showed that RBPMS interacts with other cardiac RNA binding proteins, such as RBM20, suggesting their synergistic effects on cardiomyocyte physiology. Our work provides novel insights into how RNA binding proteins regulate cardiomyocyte proliferation and contraction by mediating alternative RNA splicing.

Melatonin attenuates inflammation and cardiac dysfunction in myocardial infarction by regulating the miRNA-200b-3p/high mobility group box chromosomal protein 1 axis.

Melatonin confers protection against myocardial injury by reducing inflammation and inhibiting apoptosis. In the present study, we investigated whether melatonin regulates cardiomyocyte proliferation and improves cardiac function in rats with myocardial infarction (MI). Two MI models were established in vitro (H9c2 cells were cultured under hypoxia) and in vivo (the left anterior descending coronary artery of rats was surgically ligated). miR-200b-3p and high mobility group box 1 (HMGB1) levels were detected. Cell proliferation and apoptosis were analyzed in vitro, and cardiac function, inflammatory cytokines, and myocardial injury markers in vivo were tested. The experimental results reported that melatonin promoted proliferation and impaired apoptosis of H9c2 cells cultured in hypoxia. In vivo, melatonin improved cardiac function and inhibited the inflammation and myocardial injury of rats with MI. miR-200b-3p was downregulated and HMGB1 was upregulated in MI, while melatonin could upregulate miR-200b-3p and downregulate HMGB1. The HMGB1 was targeted by miR-200b-3p. Upregulating miR-200b-3p or downregulating HMGB1 could further promote the therapeutic effect of melatonin, and downregulating miR-200b-3p or upregulating HMGB1 could abolish the therapeutic effect of melatonin. In conclusion, melatonin alleviates inflammation and cardiac dysfunction after MI by regulating the miR-200b-3p/HMGB1 axis, offering a new therapeutic strategy for MI.

The translation initiation factor homolog eif4e1c regulates cardiomyocyte metabolism and proliferation during heart regeneration.

The eIF4E family of translation initiation factors bind 5' methylated caps and act as the limiting step for mRNA translation. The canonical eIF4E1A is required for cell viability, yet other related eIF4E families exist and are utilized in specific contexts or tissues. Here, we describe a family called Eif4e1c, for which we find roles during heart development and regeneration in zebrafish. The Eif4e1c family is present in all aquatic vertebrates but is lost in all terrestrial species. A core group of amino acids shared over 500 million years of evolution forms an interface along the protein surface, suggesting that Eif4e1c functions in a novel pathway. Deletion of eif4e1c in zebrafish caused growth deficits and impaired survival in juveniles. Mutants surviving to adulthood had fewer cardiomyocytes and reduced proliferative responses to cardiac injury. Ribosome profiling of mutant hearts demonstrated changes in translation efficiency of mRNA for genes known to regulate cardiomyocyte proliferation. Although eif4e1c is broadly expressed, its disruption had most notable impact on the heart and at juvenile stages. Our findings reveal context-dependent requirements for translation initiation regulators during heart regeneration.

TMEM11 regulates cardiomyocyte proliferation and cardiac repair via METTL1-mediated m7G methylation of ATF5 mRNA

The mitochondrial transmembrane (TMEM) protein family has several essential physiological functions. However, its roles in cardiomyocyte proliferation and cardiac regeneration remain unclear. Here, we detected that TMEM11 inhibits cardiomyocyte proliferation and cardiac regeneration in vitro. TMEM11 deletion enhanced cardiomyocyte proliferation and restored heart function after myocardial injury. In contrast, TMEM11-overexpression inhibited neonatal cardiomyocyte proliferation and regeneration in mouse hearts. TMEM11 directly interacted with METTL1 and enhanced m7G methylation of Atf5 mRNA, thereby increasing ATF5 expression. A TMEM11-dependent increase in ATF5 promoted the transcription of Inca1, an inhibitor of cyclin-dependent kinase interacting with cyclin A1, which suppressed cardiomyocyte proliferation. Hence, our findings revealed that TMEM11-mediated m7G methylation is involved in the regulation of cardiomyocyte proliferation, and targeting the TMEM11-METTL1-ATF5-INCA1 axis may serve as a novel therapeutic strategy for promoting cardiac repair and regeneration.

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.

Polycomb Group Protein CBX7 Represses Cardiomyocyte Proliferation Through Modulation of the TARDBP/RBM38 Axis.

Shortly after birth, cardiomyocytes exit the cell cycle and cease proliferation. At present, the regulatory mechanisms for this loss of proliferative capacity are poorly understood. CBX7 (chromobox 7), a polycomb group (PcG) protein, regulates the cell cycle, but its role in cardiomyocyte proliferation is unknown. We profiled CBX7 expression in the mouse hearts through quantitative real-time polymerase chain reaction, Western blotting, and immunohistochemistry. We overexpressed CBX7 in neonatal mouse cardiomyocytes through adenoviral transduction. We knocked down CBX7 by using constitutive and inducible conditional knockout mice (Tnnt2-Cre;Cbx7fl/+ and Myh6-MCM;Cbx7fl/fl, respectively). We measured cardiomyocyte proliferation by immunostaining of proliferation markers such as Ki67, phospho-histone 3, and cyclin B1. To examine the role of CBX7 in cardiac regeneration, we used neonatal cardiac apical resection and adult myocardial infarction models. We examined the mechanism of CBX7-mediated repression of cardiomyocyte proliferation through coimmunoprecipitation, mass spectrometry, and other molecular techniques. We explored Cbx7 expression in the heart and found that mRNA expression abruptly increased after birth and was sustained throughout adulthood. Overexpression of CBX7 through adenoviral transduction reduced proliferation of neonatal cardiomyocytes and promoted their multinucleation. On the other hand, genetic inactivation of Cbx7 increased proliferation of cardiomyocytes and impeded cardiac maturation during postnatal heart growth. Genetic ablation of Cbx7 promoted regeneration of neonatal and adult injured hearts. Mechanistically, CBX7 interacted with TARDBP (TAR DNA-binding protein 43) and positively regulated its downstream target, RBM38 (RNA Binding Motif Protein 38), in a TARDBP-dependent manner. Overexpression of RBM38 inhibited the proliferation of CBX7-depleted neonatal cardiomyocytes. Our results demonstrate that CBX7 directs the cell cycle exit of cardiomyocytes during the postnatal period by regulating its downstream targets TARDBP and RBM38. This is the first study to demonstrate the role of CBX7 in regulation of cardiomyocyte proliferation, and CBX7 could be an important target for cardiac regeneration.

Foxm1 regulates cardiomyocyte proliferation in adult zebrafish after cardiac injury.

The regenerative capacity of the mammalian heart is poor, with one potential reason being that adult cardiomyocytes cannot proliferate at sufficient levels to replace lost tissue. During development and neonatal stages, cardiomyocytes can successfully divide under injury conditions; however, as these cells mature their ability to proliferate is lost. Therefore, understanding the regulatory programs that can induce post-mitotic cardiomyocytes into a proliferative state is essential to enhance cardiac regeneration. Here, we report that the forkhead transcription factor Foxm1 is required for cardiomyocyte proliferation after injury through transcriptional regulation of cell cycle genes. Transcriptomic analysis of injured zebrafish hearts revealed that foxm1 expression is increased in border zone cardiomyocytes. Decreased cardiomyocyte proliferation and expression of cell cycle genes in foxm1 mutant hearts was observed, suggesting it is required for cell cycle checkpoints. Subsequent analysis of a candidate Foxm1 target gene, cenpf, revealed that this microtubule and kinetochore binding protein is also required for cardiac regeneration. Moreover, cenpf mutants show increased cardiomyocyte binucleation. Thus, foxm1 and cenpf are required for cardiomyocytes to complete mitosis during zebrafish cardiac regeneration.

Malat1 deficiency prevents neonatal heart regeneration by inducing cardiomyocyte binucleation.

The adult mammalian heart has limited regenerative capacity, while the neonatal heart fully regenerates during the first week of life. Postnatal regeneration is mainly driven by proliferation of preexisting cardiomyocytes and supported by proregenerative macrophages and angiogenesis. Although the process of regeneration has been well studied in the neonatal mouse, the molecular mechanisms that define the switch between regenerative and nonregenerative cardiomyocytes are not well understood. Here, using in vivo and in vitro approaches, we identified the lncRNA Malat1 as a key player in postnatal cardiac regeneration. Malat1 deletion prevented heart regeneration in mice after myocardial infarction on postnatal day 3 associated with a decline in cardiomyocyte proliferation and reparative angiogenesis. Interestingly, Malat1 deficiency increased cardiomyocyte binucleation even in the absence of cardiac injury. Cardiomyocyte-specific deletion of Malat1 was sufficient to block regeneration, supporting a critical role of Malat1 in regulating cardiomyocyte proliferation and binucleation, a landmark of mature nonregenerative cardiomyocytes. In vitro, Malat1 deficiency induced binucleation and the expression of a maturation gene program. Finally, the loss of hnRNP U, an interaction partner of Malat1, induced similar features in vitro, suggesting that Malat1 regulates cardiomyocyte proliferation and binucleation by hnRNP U to control the regenerative window in the heart.

ABRO1 arrests cardiomyocyte proliferation and myocardial repair by suppressing PSPH

The role of Abraxas 2 (ABRO1 or KIAA0157), a component of the lysine63-linked deubiquitinating system, in the cardiomyocyte proliferation and myocardial regeneration is unknown. Here, we found that ABRO1 regulates cardiomyocyte proliferation and cardiac regeneration in the postnatal heart by targeting METTL3-mediated m6A methylation of Psph mRNA. The deletion of ABRO1 increased cardiomyocyte proliferation in hearts and restored the heart function after myocardial injury. On the contrary, ABRO1 overexpression significantly inhibited the neonatal cardiomyocyte proliferation and cardiac regeneration in mouse hearts. The mechanism by which ABRO1 regulates cardiomyocyte proliferation mainly involved METTL3-mediated Psph mRNA methylation and CDK2 phosphorylation. In the early postnatal period, METTL3-dependent m6A methylation promotes cardiomyocyte proliferation by hypermethylation of Psph mRNA and upregulating PSPH expression. PSPH dephosphorylates cyclin-dependent kinase 2 (CDK2), a positive regulator of cell cycle, at Thr14/Tyr15 and increases its activity. Upregulation of ABRO1 restricts METTL3 activity and halts the cardiomyocyte proliferation in the postnatal hearts. Thus, our study reveals that ABRO1 is an essential contributor in the cell cycle withdrawal and attenuation of proliferative response in the postnatal cardiomyocytes and could act as a potential target to accelerate cardiomyocyte proliferation and cardiac repair in the adult heart.

Renewal of embryonic and neonatal-derived cardiac-resident macrophages in response to environmental cues abrogated their potential to promote cardiomyocyte proliferation via Jagged-1–Notch1

Cardiac-resident macrophages (CRMs) play important roles in homeostasis, cardiac function, and remodeling. Although CRMs play critical roles in cardiac regeneration of neonatal mice, their roles are yet to be fully elucidated. Therefore, this study aimed to investigate the dynamic changes of CRMs during cardiac ontogeny and analyze the phenotypic and functional properties of CRMs in the promotion of cardiac regeneration. During mouse cardiac ontogeny, four CRM subsets exist successively: CX3CR1+CCR2-Ly6C-MHCII- (MP1), CX3CR1lowCCR2lowLy6C-MHCII- (MP2), CX3CR1-CCR2+Ly6C+MHCII- (MP3), and CX3CR1+CCR2-Ly6C-MHCII+ (MP4). MP1 cluster has different derivations (yolk sac, fetal liver, and bone marrow) and multiple functions population. Embryonic and neonatal-derived-MP1 directly promoted cardiomyocyte proliferation through Jagged-1-Notch1 axis and significantly ameliorated cardiac injury following myocardial infarction. MP2/3 subsets could survive throughout adulthood. MP4, the main population in adult mouse hearts, contributed to inflammation. During ontogeny, MP1 can convert into MP4 triggered by changes in the cellular redox state. These findings delineate the evolutionary dynamics of CRMs under physiological conditions and found direct evidence that embryonic and neonatal-derived CRMs regulate cardiomyocyte proliferation. Our findings also shed light on cardiac repair following injury.

Mechanical loading regulates cardiomyocyte proliferation

Mechanical loading regulates cardiomyocyte proliferation

Abstract 11817: Induced Pluripotent Stem Cell-Derived Cardiac Disease Modeling for Studying Mitogenic Cardiomyopathy in Alström Syndrome

Introduction: Cardiomyopathies are a prominent cause of heart failure and affect millions of people worldwide. We reported two case studies describing siblings with a mutation in the Alström 1 (ALMS1) gene causing Alström syndrome (ALMS), who developed mitogenic cardiomyopathy, characterized by delayed postnatal cardiomyocyte (CM) cell cycle arrest resulting in neonatal heart failure and death in early infancy. OBJECTIVES : To generate induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from ALMS patients and investigate molecular mechanisms of persistent CM proliferation in co-culture with ALMS1 fibroblasts. METHODS : We reprogrammed somatic cells from ALMS patients with mitogenic cardiomyopathy into iPSCs using Sendai virus technology and generated ALMS-specific iPSC-CMs using established in vitro differentiation protocols. We analyzed cell cycle progression by determining CM percentages in the G0/G1, S and G2/M phase using flow cytometry, and measured expression and secretion of periostin (POSTN) and collagens from ALMS1 fibroblasts in the extracellular matrix (ECM) using RT-QPCR and western blot. Finally, we investigated Hippo signaling by measuring expression and nuclear translocation of its downstream effectors YAP/TAZ using western blot and immunostaining. RESULTS : iPSC-CMs were successfully generated from ALMS patients and controls. ALMS1-deficient iPSC-CMs exhibited impaired ability to undergo cell cycle arrest, evidenced by a higher cell percentage in the G2/M phase. Furthermore, increased ECM levels of POSTN, a potent regulator of CM proliferation, were observed in co-cultures of ALMS1-deficient iPSC-CMs and ALMS1 fibroblasts. Finally, we found preliminary evidence of dysregulation of the Hippo pathway with altered cellular localization of YAP, and dysregulated total YAP and phosphorylated YAP. CONCLUSION : ALMS1-deficient iPSC-CMs recapitulate persistent postnatal proliferation observed in ALMS patients with mitogenic cardiomyopathy. Increased POSTN in the ECM and altered downstream Hippo signaling contribute to the mitogenic phenotype and suggest critical cues for future therapies aiming at stimulating CM turnover, a much-sought objective in cardiac repair to improve contractile function.

A large-scale functional high-throughput screening identifies miR-515 and miR-519e as potent inducers of human iPSC-cardiomyocyte proliferation

Abstract Introduction Ischemic heart failure persists as a global health problem despite optimized medical and adjunctive device therapies. Loss of cardiomyocytes in the absence of a proliferative response comprise a major contributor to pathological remodeling and death in this patient population. Experimental studies have shown that microRNAs (miRNAs) may be used as a therapeutic option to reinduce adult cardiomyocyte proliferation. Purpose This study thought to evaluate proliferative potential in human cardiomyocytes after overexpression and inhibition of 2019 miRNAs. Methods To identify miRNAs that regulate cardiomyocyte proliferation, we performed functional high-throughput screenings in human iPSC-derived cardiomyocytes (hiPSC-CM) after transient hypoxia. Herein, 2019 miRNA-mimics for overexpression and 2019 anti-miRs for inhibition were individually transfected to examine EdU-incorporation in hiPSC-CM. MiR-mimic-515 and miR-mimic-519e that induced the highest EdU-uptake, were further assessed by immunostaining and molecular methods for markers indicative of early and late mitosis. In addition, RNA-Sequencing in hiPSC-CM after overexpression of miR-515 and miR-519e was performed to examine differential gene expression and miRNA-modulated pathways involved in cardiomyocyte proliferation. Results Using a functional high-throughput screening, we assessed differential proliferative potential of 2019 miRNAs after transient hypoxia by transfecting both miR-inhibitor and miR-mimic libraries in human iPSC-derived cardiomyocytes (hiPSC-CM). Overexpression of 28 miRNAs substantially induced proliferative activity in hiPSC-CM, with an overrepresentation of miRNAs belonging to the C19MC-cluster and adjacent miR-371–373 family. Two of these miRNAs, miR-515 and miR-519e increased markers of early and late mitosis, with an additive cardiomyocyte turnover after transient hypoxia and substantially increased Aurora B-kinase activity in midbodies, indicative of cell division. These findings were supported by molecular studies using qRT-PCR, Western blot, and RNA-Sequencing after overexpression of miR-515 and miR-519e showing substantial alterations of signaling pathways relevant for cardiomyocytes proliferation in human iPSC-CM. Conclusion Collectively, these results support a critical role of miR-515 and miR-519e for induction of proliferation in human cardiomyocytes under hypoxic conditions, such as present in patients with ischemia-driven cardiomyopathy. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): This work was supported by the German Centre for Cardiovascular Research (DZHK), Deutsche Stiftung für Herzforschung (DSHF) and OPO Foundation.

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.