Regulates Cardiomyocyte Proliferation Research Articles

Screening lncRNAs essential for cardiomyocyte proliferation by integrative profiling of lncRNAs and mRNAs associated with heart development

BackgroundThe proliferation potential of mammalian cardiomyocytes declines markedly shortly after birth. Both long non-coding RNAs (lncRNAs) and mRNAs demonstrate altered expression patterns during cardiac development. However, the role of lncRNAs in the cell cycle arrest of cardiomyocytes remains inadequately understood. MethodThe expression pattern of lncRNAs and mRNAs was analyzed in mouse hearts exhibiting varying regenerative potentials on postnatal days (P) 1, 7, and 28. Weighted correlation network analysis (WGCNA) was employed to elucidate the co-expression relationship between lncRNAs and mRNAs. Protein-protein interaction (PPI) network was built using the STRING database, and hub lncRNAs were identified by CytoHubba. Molecular Complex Detection (MCODE) was used to screen core modules of the PPI network in Cytoscape. Upstream lncRNAs and miRNAs which may regulate mRNAs were predicted using miRTarBase and AnnoLnc2, respectively. Myocardial infarction (MI) was induced by ligation of the left anterior descending coronary artery. ResultsCompared with the P1 heart, 618 mRNAs and 414 lncRNAs displayed.transcriptional changes in the P7 heart, while 2358 mRNAs and 1290 lncRNAs showed from P7 to P28. Gene Ontology (GO) analysis revealed that module 1 in the both comparisons was enriched in the mitotic cell cycle process. 2810408I11Rik and 2010110K18Rik were identified as hub lncRNAs and their effects on the proliferation of cardiomyocytes were verified in vitro. Additionally, four lncRNA-miRNA-mRNA regulatory axes were predicted to explain the mechanism by which 2810408I11Rik and 2010110K18Rik regulate cardiomyocyte proliferation. Notably, the overexpression of 2810408I11Rik enhances cardiomyocyte proliferation and heart regeneration in the adult heart following MI. ConclusionThis study systematically analyzed the landscape of lncRNAs and mRNAs at P1, P7, and P28. These findings may enhance our understanding of the framework for heart development and could have significant implications for heart regeneration.

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

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

Abstract We032: FOXK1-Gli2 network regulates cardiomyocyte proliferation and heart regeneration

Unlike adult mammals, the neonatal mouse has an exceptional regenerative capacity following myocardial injury. Our goal was to decipher and define novel factors and mechanisms that have a role in regeneration of the injured 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. In these studies, we identified a novel role for FOXK1 as a regulator of cardiomyocyte (CM) proliferation and regeneration through the regulation of Gli2 . Analysis of single nucleus RNAseq datasets of neonatal hearts revealed that FOXK1 was expressed in neonatal CMs. qPCR analysis from P1 hearts of control and Foxk1 null mice confirmed this finding and demonstrated dysregulation of the cell cycle regulators, Ccne1 and p21 , in the absence of Foxk1 . Control and Foxk1 null mice were pulsed with EdU from P3 to P7 which demonstrated that the absence of Foxk1 led to a decrease in CM proliferation in-vivo. Then, using a transgenic mouse model that we engineered to overexpress FOXK1 in muscle ( MCK-Foxk1 ), we observed CM proliferation in adult MCK-Foxk1 mice, which showed increased incorporation of EdU and increased pH3 expression compared to control. Bulk RNA-seq analysis of P1, P7, and P14 hearts indicated increased CM proliferation in the MCK-Foxk1 mouse and revealed Gli2 as a potential downstream target of FOXK1. A gel shift assay was performed, which demonstrated that FOXK1 was able to bind to a FOXK1 motif upstream of the Gli2 gene. ChIP-PCR further verified that Gli2 was a direct downstream target of FOXK1 in the embryonic stem cell-embryoid body (ES-EB) system. We then performed ligation of the left anterior descending coronary artery (LAD) in adult control and MCK-Foxk1 mice. Echocardiography following the LAD-ligation injuries showed improved cardiac function in MCK-Foxk1 transgenic mice compared with controls. These results identify FOXK1 as a regulator of CM proliferation and heart regeneration and suggest that this function is mediated through the regulation of Gli2 gene expression.

Abstract We043: MYCN is a regulator of cardiomyocyte proliferation and regeneration in the mammalian heart

The identification of new factors and mechanisms that can promote the repair and regeneration of the adult injured mammalian heart are necessary as the adult heart has limited ability to repair itself. We identified MYCN as a downstream effector of the sonic hedgehog (SHH) signaling cascade during cardiomyocyte proliferation in the neonatal heart. Although the protooncogene, MYCN, has been shown to be an essential factor during embryonic heart development, its role in regenerating the adult heart has not been established. Here, we define MYCN as a critical regulator of cardiomyocyte (CM) proliferation and regeneration using genetic mouse models and in vivo modified RNA (modRNA) delivery. In these studies, we conditionally deleted Mycn in the neonatal heart (P0). Immunohistochemical (IHC) analysis of P3 neonatal hearts demonstrated significantly (p < 0.05) decreased expression of Ki67 and pH3 in the absence of Mycn compared to control (no 4-OHT) hearts. This observation was further validated in isolated CMs and neonatal P7 hearts pulsed with EdU which demonstrated a significant decrease in EdU+ CMs in the absence of Mycn compared to control. Single-nucleus RNA-sequencing results from control and Mycn CKO P4 ventricles revealed a severe depletion of the proliferative and regenerative cardiomyocyte population in the Mycn CKO hearts. We then ligated the left anterior descending coronary artery (LAD) to produce an ischemic cardiac injury in control and Mycn CKO P2 neonatal mice. Echocardiography one-month following the LAD surgeries demonstrated that the Mycn CKO failed to recover baseline cardiac function compared to their control counterparts who achieved complete recovery. RNAseq analysis of control and Mycn CKO hearts 1 month following LAD ligations demonstrated that muscle developmental pathways were significantly downregulated in the Mycn CKO group compared to the control. We then delivered either GFP (control) or Mycn modRNA intramuscularly into the border zone following LAD coronary artery ligation surgeries in adult (2-6 month old) mice. We observed that the Mycn modRNA treated mice had significantly improved cardiac function at one month and two months following injury/delivery compared to controls. These results identify MYCN as an important regulator of CM proliferation and heart regeneration.

Abstract We026: Foxk1 and Foxk2 Promote Cardiomyocyte Proliferation and Heart Regeneration

Background: The adult mammalian heart exhibits limited regenerative capacity due to restricted cardiomyocyte (CM) proliferation following injuries like ischemia. Foxk1 and Foxk2, members of the Foxk family, are pivotal in cell proliferation and metabolic regulation. However, the roles of Foxk1 and Foxk2 in CM proliferation and heart regeneration remain elusive. Hypothesis: We propose that Foxk1 and Foxk2 are master regulators of CM proliferation and heart regeneration. Methods: Three genetic mouse lines, Myh6-CreER , Foxk1 fl/fl , and Foxk2 fl/fl were used to generate CM-specific Foxk1 or Foxk2 deficient mice. Myocardial infarction was performed in neonatal and adult mice. Cleavage Under Targets and Tagmentation sequencing (CUT&Tag-seq), RNA sequencing (RNA-seq), qRT-PCR, Western blotting, immunostaining, and Seahorse metabolic assays were conducted to investigate the intrinsic mechanisms by which Foxk1 and Foxk2 regulate CM proliferation and heart regeneration. Masson’s staining and echocardiography were conducted to evaluate cardiac fibrosis and function, respectively. Results: Our results showed that the expression of Foxk1 and Foxk2 gradually decreased in CMs during postnatal heart development. CM-specific knockout of Foxk1 or Foxk2 inhibited neonatal heart regeneration after MI. AAV9-mediated CM-specific overexpression of Foxk1 or Foxk2 prolonged the postnatal proliferative window of CMs in mice. AAV9-mediated overexpression of Foxk1 or Foxk2 in adult mice improved heart regeneration by promoting endogenous CM proliferation after MI. Through joint analysis of RNA-Seq and CUT&Tag-seq, we found that Foxk1 and Foxk2 regulated Ccnb1 and Cdk1 transcription respectively. Knockdown of Ccnb1 hindered CM proliferation induced by Foxk1 overexpression, and the same effect was observed when Cdk1 was knocked down in Foxk2-overexpressing CMs. Additionally, Foxk1 and Foxk2 induced CM metabolic reprogramming, suppressing mitochondrial oxidative phosphorylation (OXPHOS) via Hif1α upregulation and reducing oxidative DNA damage, thereby modulating the cell cycle. Conclusions: Foxk1 and Foxk2 promote CM proliferation and heart regeneration. Mechanistically, Foxk1 and Foxk2 promote CM proliferation via dual effects that directly promote cell cycle gene transcription and induce metabolic reprogramming. Our findings suggest these transcription factors as potential novel targets in cardiac regeneration post-injury.

Abstract We131: Systems-Enabled Drug Repurposing to Regulate Cardiomyocyte Proliferation

Introduction: The inability of the adult heart to regenerate results in prevalent morbidity and mortality related to myocardial infarction and heart failure. This lack of cardiac regeneration is driven by the loss of cardiomyocytes (CMs), with limited supporting endogenous CM renewal. While many individual regulators of CM proliferation have been implicated, the field lacks strategies to identify druggable proliferative signaling pathways and prioritize candidate therapeutics. Our goal is to predict and experimentally validate FDA-approved drugs and their respective mechanisms that regulate CM proliferation. Methods: A logic-based differential equation model of CM proliferation signaling was integrated with drug-target interactions from a publicly available database (DrugBank) to simulate the effect of drugs on CM proliferation phenotypes (Binucleation, Cytokinesis, DNA Replication, Mitosis, and Polyploid). A virtual screen with knockdown combinations of regulators identified signaling mechanisms responsible for mediating the effect of drugs, and literature validation was performed against published experimental data investigating the drugs or the drug targets in CMs. Neonatal rat CMs were treated with the YAP-activating drug TT10 or drugs predicted to increase CM proliferation. Proliferation was measured by high-content microscopy and DNA replication and mitosis positive cells were identified from image analysis (CellProfiler) to discern CM proliferation from endoreplication. Results: We identified 16 unique drug-target interactions predicted to regulate CM proliferation phenotypes. Four drugs were predicted to increase CM phenotypic proliferation outputs. Experimental validation confirmed lithium, a GSK3beta-antagonist, induces cell cycle activity in neonatal rat CMs as evidenced by increased Ki67 expression in cardiac Troponin T positive cells. The model predicts cyclin D is critical in mediating this response and subsequent experiments measured changes in cyclin D expression in response to lithium treatment. Retrospective analysis of clinical data (TriNetX and AERSMine) indicates more adverse events of congenital cardiac disorders were reported in patients exposed to lithium. Conclusion: We identified lithium to promote DNA replication in CMs by upregulating cyclin D. This study advances the current knowledge of CM proliferation regulators by providing insight into new pathways targeted with existing drugs that can ultimately impact cardiac regeneration.

Exploring the Function of Epicardial Cells Beyond the Surface.

The epicardium, previously viewed as a passive outer layer around the heart, is now recognized as an essential component in development, regeneration, and repair. In this review, we explore the cellular and molecular makeup of the epicardium, highlighting its roles in heart regeneration and repair in zebrafish and salamanders, as well as its activation in young and adult postnatal mammals. We also examine the latest technologies used to study the function of epicardial cells for therapeutic interventions. Analysis of highly regenerative animal models shows that the epicardium is essential in regulating cardiomyocyte proliferation, transient fibrosis, and neovascularization. However, despite the epicardium's unique cellular programs to resolve cardiac damage, it remains unclear how to replicate these processes in nonregenerative mammalian organisms. During myocardial infarction, epicardial cells secrete signaling factors that modulate fibrotic, vascular, and inflammatory remodeling, which differentially enhance or inhibit cardiac repair. Recent transcriptomic studies have validated the cellular and molecular heterogeneity of the epicardium across various species and developmental stages, shedding further light on its function under pathological conditions. These studies have also provided insights into the function of regulatory epicardial-derived signaling molecules in various diseases, which could lead to new therapies and advances in reparative cardiovascular medicine. Moreover, insights gained from investigating epicardial cell function have initiated the development of novel techniques, including using human pluripotent stem cells and cardiac organoids to model reparative processes within the cardiovascular system. This growing understanding of epicardial function holds the potential for developing innovative therapeutic strategies aimed at addressing developmental heart disorders, enhancing regenerative therapies, and mitigating cardiovascular disease progression.

Upregulation of LncRNA UCA1 promotes cardiomyocyte proliferation by inhibiting the miR-128/SUZ12/P27 pathway

Enhancing cardiomyocyte proliferation is essential to reverse or slow down the heart failure progression in many cardiovascular diseases such as myocardial infarction (MI). Long non-coding RNAs (lncRNAs) have been reported to regulate cardiomyocyte proliferation. In particular, lncRNA urothelial carcinoma-associated 1 (lncUCA1) played multiple roles in regulating cell cycle progression and cardiovascular diseases, making lncUCA1 a potential target for promoting cardiomyocyte proliferation. However, the role of lncUCA1 in cardiomyocyte proliferation remains unknown. This study aimed at exploring the function and underlying molecular mechanism of lncUCA1 in cardiomyocyte proliferation. Quantitative RT-PCR showed that lncUCA1 expression decreased in postnatal hearts. Gain-and-loss-of-function experiments showed that lncUCA1 positively regulated cardiomyocyte proliferation in vitro and in vivo. The bioinformatics program identified miR-128 as a potential target of lncUCA1, and loss of miR-128 was reported to promote cardiomyocyte proliferation by inhibiting the SUZ12/P27 pathway. Luciferase reporter assay, qRT-PCR, western blotting, and immunostaining experiments further revealed that lncUCA1 acted as a ceRNA of miR-128 to upregulate its target SUZ12 and downregulate P27, thereby increasing cyclin B1, cyclin E, CDK1 and CDK2 expression to promote cardiomyocyte proliferation. In conclusion, upregulation of lncRNA UCA1 promoted cardiomyocyte proliferation by inhibiting the miR-128/SUZ12/P27 pathway. Our results indicated that lncUCA1 might be a new therapeutic target for stimulating cardiomyocyte proliferation.

Identification of circular RNAs regulating cardiomyocyte proliferation in neonatal pig hearts.

Little is known about the expression patterns and functions of circular RNAs (circRNAs) in the heart of large mammals. In this study, we examined the expression profiles of circRNAs, microRNAs (miRNAs), and messenger RNAs (mRNAs) in neonatal pig hearts. Pig heart samples collected on postnatal days 1 (P1), 3 (P3), 7 (P7), and 28 (P28) were sent for total RNA sequencing. Our data revealed a total of 7,000 circRNAs in the 24 pig hearts. Pathway enrichment analysis of hallmark gene sets demonstrated that differentially expressed circRNAs were engaged in different pathways. The most significant difference was observed between P1 and the other 3 groups (P3, P7, and P28) in pathways related to cell cycle and muscle development. Out of the 10 circRNAs that were validated through real-time quantitative PCR to verify their expression, 6 exhibited significant effects on cell cycle activity in human induced pluripotent stem cell-derived cardiomyocytes following small interfering RNA-mediated knockdown. circRNA-miRNA-mRNA networks were constructed to understand the potential mechanisms of circRNAs in the heart. In conclusion, our study provided a data set for exploring the roles of circRNAs in pig hearts. In addition, we identified several circRNAs that regulate cardiomyocyte cell cycle.

Dissecting signal transduction pathways that regulate cardiomyocyte proliferation

Abstract Funding Acknowledgements None. Introduction During cardiac development, the Notch, Hippo, and Wnt/β-catenin signalling pathways play a crucial role in the tuning of cardiomyocyte proliferation. The individual engagement of each of these pathways during the early postnatal life, however, is still unclear. Purpose We wanted to develop a method to visualize over time, both in vitro and in vivo, the topography of activation of the Notch, Wnt/β-catenin, and Hippo pathways and their crosstalk upon cardiomyocyte treatment with a series of pro-proliferative stimuli. Methods We obtained Adeno-Associated Virus (AAV) constructs expressing distinct fluorescent proteins (ECFP, GFP, mCherry, DsRed) under the control of promoters that are specifically activated downstream of the signalling cascades of interest (a synthetic promoter consisting of 12 CSL binding sites for Notch1, a synthetic promoter consisting of 8 TEAD binding sites for YAP, and a synthetic promoter containing 7 TCF/LEF1 binding sites for β-catenin). Results First, by high content microscopy we followed the time of the activation of the AAV vectors coding for fluorescent reporters, either alone or in combination. We observed that a crosstalk exists between Yap and Notch signalling in proliferating cardiomyocytes, as detected by the activation of their respective fluorescent reporters. We confirmed our data by gene expression analysis and co-immunoprecipitation using specific antibodies in fractionated cardiomyocyte extracts. Next, we observe that miR-1825, miR-199a-3p, and miR-590-3p – three pro-regenerative miRNAs in cardiomyocytes– specifically activate both Yap and Notch signalling. Finally we characterized the reporter systems in vivo, to dissect the intracellular signalling pathways that are active in the first week of postnatal life. Beta-catenin signalling was quite undetectable in any of the conditions tested. In contrast, both Notch and Yap showed significant activation, consistent with their role in regulating early postnatal cardiomyocyte proliferation. Conclusions The developed AAV-fluorescent reporters allow to efficiently and specifically visualize the pro-proliferative activation of Notch and Yap signalling both in vitro and in vivo. The results obtained are supportive of a crosstalk existing between Notch and Yap pathways in proliferating cardiomyocytes.

Identification of two miRNAs regulating cardiomyocyte proliferation in an Antarctic icefish

Identification of two miRNAs regulating cardiomyocyte proliferation in an Antarctic icefish

Metabolic Reprogramming: A Byproduct or a Driver of Cardiomyocyte Proliferation?

Defining mechanisms of cardiomyocyte proliferation should guide the understanding of endogenous cardiac regeneration and could lead to novel treatments for diseases such as myocardial infarction. In the neonatal heart, energy metabolic reprogramming (phenotypic alteration of glucose, fatty acid, and amino acid metabolism) parallels cell cycle arrest of cardiomyocytes. The metabolic reprogramming occurring shortly after birth is associated with alterations in blood oxygen levels, metabolic substrate availability, hemodynamic stress, and hormone release. In the adult heart, myocardial infarction causes metabolic reprogramming but these changes cannot stimulate sufficient cardiomyocyte proliferation to replace those lost by the ischemic injury. Some putative pro-proliferative interventions can induce the metabolic reprogramming. Recent data show that altering the metabolic enzymes PKM2 [pyruvate kinase 2], LDHA [lactate dehydrogenase A], PDK4 [pyruvate dehydrogenase kinase 4], SDH [succinate dehydrogenase], CPT1b [carnitine palmitoyl transferase 1b], or HMGCS2 [3-hydroxy-3-methylglutaryl-CoA synthase 2] is sufficient to partially reverse metabolic reprogramming and promotes adult cardiomyocyte proliferation. How metabolic reprogramming regulates cardiomyocyte proliferation is not clearly defined. The possible mechanisms involve biosynthetic pathways from the glycolysis shunts and the epigenetic regulation induced by metabolic intermediates. Metabolic manipulation could represent a new approach to stimulate cardiac regeneration; however, the efficacy of these manipulations requires optimization, and novel molecular targets need to be defined. In this review, we summarize the features, triggers, and molecular regulatory networks responsible for metabolic reprogramming and discuss the current understanding of metabolic reprogramming as a critical determinant of cardiomyocyte proliferation.

Mitochondrial-to-nuclear communications through multiple routes regulate cardiomyocyte proliferation

The regenerative capacity of the adult mammalian heart remains a formidable challenge in biological research. Despite extensive investigations into the loss of regenerative potential during evolution and development, unlocking the mechanisms governing cardiomyocyte proliferation remains elusive. Two recent groundbreaking studies have provided fresh perspectives on mitochondrial-to-nuclear communication, shedding light on novel factors that regulate cardiomyocyte proliferation. The studies identified two mitochondrial processes, fatty acid oxidation and protein translation, as key players in restricting cardiomyocyte proliferation. Inhibition of these processes led to increased cell cycle activity in cardiomyocytes, mediated by reduction in H3k4me3 levels through accumulated α-ketoglutarate (αKG), and activation of the mitochondrial unfolded protein response (UPRmt), respectively. In this research highlight, we discuss the novel insights into mitochondrial-to-nuclear communication presented in these studies, the broad implications in cardiomyocyte biology and cardiovascular diseases, as well as the intriguing scientific questions inspired by the studies that may facilitate future investigations into the detailed molecular mechanisms of cardiomyocyte metabolism, proliferation, and mitochondrial-to-nuclear communications.

MiR-431 promotes cardiomyocyte proliferation by targeting FBXO32 expression.

The induction of cardiomyocyte (CM) proliferation is a promising approach for cardiac regeneration following myocardial injury. MicroRNAs (miRNAs) have been reported to regulate CM proliferation. In particular, miR-431 expression decreases during cardiac development, according to Gene Expression Omnibus (GEO) microarray data. However, whether miR-431 regulates CM proliferation has not been thoroughly investigated. We used integrated bioinformatics analysis of GEO datasets to identify the most significantly differentially expressed miRNAs. Real-time quantitative PCR and fluorescence in situ hybridization were performed to determine the miRNA expression patterns in hearts. Gain- and loss-of-function assays were conducted to detect the role of miRNA in CM proliferation. Additionally, we detected whether miR-431 affected CM proliferation in a myocardial infarction model. The TargetScan, miRDB and miRWalk online databases were used to predict the potential target genes of miRNAs. Luciferase reporter assays were used to study miRNA interactions with the targeting mRNA. First, we found a significant reduction in miR-431 levels during cardiac development. Then, by overexpression and inhibition of miR-431, we demonstrated that miR-431 promotes CM proliferation in vitro and in vivo, as determined by immunofluorescence assays of 5-ethynyl-2'-deoxyuridine (EdU), pH3, Aurora B and CM count, whereas miR-431 inhibition suppresses CM proliferation. Then, we found that miR-431 improved cardiac function post-myocardial infarction. In addition, we identified FBXO32 as a direct target gene of miR-431, with FBXO32 mRNA and protein expression being suppressed by miR-431. FBXO32 inhibited CM proliferation. Overexpression of FBXO32 blocks the enhanced effect of miR-431 on CM proliferation, suggesting that FBXO32 is a functional target of miR-431 during CM proliferation. In summary, miR-431 promotes CM proliferation by targeting FBXO32, providing a potential molecular target for preventing myocardial injury.

PARP1 Promotes Heart Regeneration and Cardiomyocyte Proliferation.

Myocardial infarction causes cardiomyocyte loss, and depleted cardiomyocyte proliferative capacity after birth impinges the heart repair process, eventually leading to heart failure. This study aims to investigate the role of Poly(ADP-Ribose) Polymerase 1 (PARP1) in the regulation of cardiomyocyte proliferation and heart regeneration. Our findings demonstrated that PARP1 knockout impaired cardiomyocyte proliferation, cardiac function, and scar formation, while PARP1 overexpression improved heart regeneration in apical resection-operated mice. Mechanistically, we found that PARP1 interacts with and poly(ADP-ribosyl)ates Heat Shock Protein 90 Alpha Family Class B Member 1 (HSP90AB1) and increases binding between HSP90AB1 and Cell Division Cycle 37 (CDC37) and cell cycle kinase activity, thus activating cardiomyocyte cell cycle. Our results reveal that PARP1 promotes heart regeneration and cardiomyocyte proliferation via poly(ADP-ribosyl)ation of HSP90AB1 activating the cardiomyocyte cell cycle, suggesting that PARP1 may be a potential therapeutic target in treating cardiac injury.

RETRACTED: The novel antibody fusion protein rhNRG1-HER3i promotes heart regeneration by enhancing NRG1-ERBB4 signaling pathway

Stimulating cardiomyocyte proliferation in the adult heart has emerged as a promising strategy for cardiac regeneration following myocardial infarction (MI). The NRG1-ERBB4 signaling pathway has been implicated in the regulation of cardiomyocyte proliferation. However, the therapeutic potential of recombinant human NRG1 (rhNRG1) has been limited due to the low expression of ERBB4 in adult cardiomyocytes. Here, we investigated whether a fusion protein of rhNRG1 and an ERBB3 inhibitor (rhNRG1-HER3i) could enhance the affinity of NRG1 for ERBB4 and promote adult cardiomyocyte proliferation. In vitro and in vivo experiments were conducted using postnatal day 1 (P1), P7, and adult cardiomyocytes. Western blot analysis was performed to assess the expression and activity of ERBB4. Cardiomyocyte proliferation was evaluated using Ki67 and pH 3 immunostaining, while fibrosis was assessed using Masson staining. Our results indicate that rhNRG1-HER3i, but not rhNRG1, promoted P7 and adult cardiomyocyte proliferation. Furthermore, rhNRG1-HER3i improved cardiac function and reduced cardiac fibrosis in post-MI hearts. Administration of rhNRG1-HER3i inhibited ERBB3 phosphorylation while increasing ERBB4 phosphorylation in adult mouse hearts. Additionally, rhNRG1-HER3i enhanced angiogenesis following MI compared to rhNRG1. In conclusion, our findings suggest that rhNRG1-HER3i is a viable therapeutic approach for promoting adult cardiomyocyte proliferation and treating MI by enhancing NRG1-ERBB4 signaling pathway.

Hydrogel‐Based Delivery of antimiR‐195 Improves Cardiac Efficacy after Ischemic Injury

AbstractMicroRNAs (miRs) are potent regulators of biology and disease. The miR‐15 family is shown to regulate cardiomyocyte proliferation and antimiR‐based inhibition induces a cardioprotective effect after myocardial infarction in mice. However, systemic delivery of antimiRs leads to accumulation in kidneys and liver, with relatively poor cardiac exposure. Injectable hydrogels are proposed to serve as sustained‐release drug delivery depots and can potentially be used to improve cardiac efficacy of antimiR therapeutics. Here, the effect of a hydrogel‐formulated antimiR‐195 after myocardial infarction in mice is studied. For this, an injectable, pH‐switchable supramolecular hydrogel based on poly(ethylene glycol) (PEG) functionalized with hydrogen bonding ureido‐pyrimidinone (UPy) units is used. Intracardiac injections under baseline conditions of this UPy–PEG hydrogelator induce a transient inflammatory response that is no longer present 7 days postinjection. In vitro experiments show that antimiR‐195 is released from the gel, and induces microRNA inhibition leading to downstream cardiomyocyte proliferation. In vivo, intramyocardial delivery of antimiR‐195 in UPy–PEG enhances cardiac target derepression compared to phosphate‐buffered‐saline‐dissolved antimiR‐195, despite a low cardiac retention. After ischemic injury, this translates into a greater therapeutic effect by increasing both target derepression and cardiomyocyte proliferation. Intramyocardial injection of UPy–PEG‐formulated antimiR‐195 is sufficient to improve cardiac efficacy of antimiR‐195.

Epigenetic repression of Cend1 by lysine-specific demethylase 1 is essential for murine heart development

Epigenetic regulation of heart development remains incompletely understood. Here we show that LSD1, a histone demethylase, plays a crucial role in regulating cardiomyocyte proliferation during heart development. Cardiomyocyte-specific deletion of Lsd1 in mice inhibited cardiomyocyte proliferation, causing severe growth defect of embryonic and neonatal heart. Invivo RNA-seq and invitro functional studies identified Cend1 as a target suppressed by LSD1. Lsd1 loss resulted in elevated Cend1 transcription associated with increased active histone mark H3K4me2 at Cend1 promoter. Cend1 knockdown relieved the cell-cycle arrest and proliferation defect caused by LSD1 inhibition in primary rat cardiomyocytes. Moreover, genetic deletion of Cend1 rescued cardiomyocyte proliferation defect and embryonic lethality in Lsd1 null embryos. Consistently, LSD1 promoted the cell cycle of cardiomyocytes derived from human-induced pluripotent stem cells by repressing CEND1. Together, these findings reveal an epigenetic regulatory mechanism involving the LSD1-CEND1 axis that controls cardiomyocyte proliferation essential for murine heart development.

Abstract 17134: Mycn is a Regulator of Cardiomyocyte Proliferation and Regeneration in the Mammalian Heart

The adult mammalian heart has limited regeneration in response to injury. Therefore, we focused on defining new factors and mechanisms that could enhance repair and regeneration in the adult mouse heart. MYCN is a protooncogene that regulates embryonic heart development. We identified MYCN as a downstream effector of the sonic hedgehog (SHH) signaling cascade during cardiomyocyte proliferation. However, its role in heart regeneration is unknown and warrants further investigation. Here, we describe a novel role for MYCN as a regulator of cardiomyocyte (CM) proliferation and regeneration using genetic mouse models and in vivo modified RNA (modRNA) delivery. By crossing Mycn floxed mice with the Myh6 -MerCreMer mice ( Mycn CKO), we conditionally deleted Mycn in the neonatal heart following administration of 4-hydroxy-tamoxifen (4-OHT) starting at P0. Successful deletion of Mycn was demonstrated by qPCR analysis of P2 isolated CMs. Immunohistochemical (IHC) analyses of P3 neonatal hearts in the absence of MYCN demonstrated a significant decrease in Ki67 expression and pH3 detection. This observation was validated in isolated P7 CMs and hearts pulsed with EdU which demonstrated a significant decrease in EdU+ CMs in the absence of MYCN compared to control. We then performed LAD coronary artery ligation surgeries in control and Mycn CKO P2 neonatal mice. Echocardiography one month following LAD coronary artery ligations demonstrated that the Mycn CKO failed to recover baseline cardiac function compared to their control counterparts who achieved complete recovery measured by ejection fraction (EF) and fractional shortening (FS). RNAseq analysis of control and Mycn CKO hearts one month following LAD ligations demonstrated that muscle developmental pathways were significantly downregulated in the Mycn CKO group compared to the control. We then delivered either GFP (control) or Mycn modRNA intramuscularly into the border zone following LAD coronary artery ligation injuries in adult (2-6 month old) mice. We observed that the Mycn modRNA treated mice had significantly improved cardiac function at one month and two months following injury/delivery compared to controls. These results identify MYCN as a regulator of CM proliferation and heart regeneration.

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.