Interventions in WNT Signaling to Induce Cardiomyocyte Proliferation: Crosstalk with Other Pathways

Adult cardiomyocytes-derived EVs for the treatment of cardiac fibrosis

Cardiac fibrosis is a common pathological feature of cardiovascular diseases that arises from the hyperactivation of fibroblasts and excessive extracellular matrix (ECM) deposition, leading to impaired cardiac function and potentially heart failure or arrhythmia. Extracellular vesicles (EVs) released by cardiomyocytes (CMs) regulate various physiological functions essential for myocardial homeostasis, which are disrupted in cardiac disease. Therefore, healthy CM-derived EVs represent a promising cell-free therapy for the treatment of cardiac fibrosis. To this end, we optimized the culture conditions of human adult CMs to obtain a large yield of EVs without compromising cellular integrity by using a defined combination of small molecules. EVs were isolated by ultracentrifugation, and their characteristics were analysed. Finally, their effect on fibrosis was tested. Treatment of TGFβ-activated human cardiac fibroblasts with EVs derived from CMs using our culture system resulted in a decrease in fibroblast activation markers and ECM accumulation. The rescued phenotype was associated with specific EV cargo, including multiple myocyte-specific and antifibrotic microRNAs, although their effect individually was not as effective as the EV treatment. Notably, pathway analysis showed that EV treatment reverted the transcription of activated fibroblasts and decreased several signalling pathways, including MAPK, mTOR, JAK/STAT, TGFβ, and PI3K/Akt, all of which are involved in fibrosis development. Intracardiac injection of CM-derived EVs in an animal model of cardiac fibrosis reduced fibrotic area and increased angiogenesis, which correlated with improved cardiac function. These findings suggest that EVs derived from human adult CMs may offer a targeted and effective treatment for cardiac fibrosis, owing to their antifibrotic properties and the specificity of cargo.

Cardiac regeneration: Pre-existing cardiomyocyte as the hub of novel signaling pathway

In the mammalian heart, cardiomyocytes are forced to withdraw from the cell cycle shortly after birth, limiting the ability of the heart to regenerate and repair. The development of multimodal regulation of cardiac proliferation has verified that pre-existing cardiomyocyte proliferation is an essential driver of cardiac renewal. With the continuous development of genetic lineage tracking technology, it has been revealed that cell cycle activity produces polyploid cardiomyocytes during the embryonic, juvenile, and adult stages of cardiogenesis, but newly formed mononucleated diploid cardiomyocytes also elevated sporadically during myocardial infarction. It implied that adult cardiomyocytes have a weak regenerative capacity under the condition of ischemia injury, which offers hope for the clinical treatment of myocardial infarction. However, the regeneration frequency and source of cardiomyocytes are still low, and the mechanism of regulating cardiomyocyte proliferation remains further explained. It is noteworthy to explore what force triggers endogenous cardiomyocyte proliferation and heart regeneration. Here, we focused on summarizing the recent research progress of emerging endogenous key modulators and crosstalk with other signaling pathways and furnished valuable insights into the internal mechanism of heart regeneration. In addition, myocardial transcription factors, non-coding RNAs, cyclins, and cell cycle-dependent kinases are involved in the multimodal regulation of pre-existing cardiomyocyte proliferation. Ultimately, awakening the myocardial proliferation endogenous modulator and regeneration pathways may be the final battlefield for the regenerative therapy of cardiovascular diseases.

XAV939 Improves the Prognosis of Myocardial Infarction by Blocking the Wnt/β-Catenin Signalling Pathway

Myocardial infarction (MI) is closely related to the Wnt signalling pathway, but the role of XAV939 (a Wnt/β-catenin signalling pathway blocker) in MI has not been elucidated. The purpose of this study was to explore the role of XAV939 in mouse hearts and to provide a new and feasible treatment for improving the prognosis of MI. C57BL/6 (male, 8 weeks old, 20-25 g) mice were selected for our study. The MI model was made by ligating the left anterior descending coronary artery. On day 28 after the operation, cardiac function was examined by echocardiography. Infarct size, fibrosis, and angiogenesis were individually measured by TTC assays, Masson's trichrome staining, and CD31 analysis, respectively. Apoptosis was examined by TdT-mediated dUTP nick-end labelling (TUNEL) staining. The expression of Wnt, β-catenin, caspase 3, Bax, and Bcl-2 was determined by western blotting. XAV939 successfully blocked Wnt/β-catenin signalling pathway activation in cardiomyocytes after MI by promoting the degradation of β-catenin. XAV939 suppressed fibrosis and apoptosis, promoted angiogenesis, reduced myocardial infarct size and improved cardiac function after MI. XAV939 can reduce myocardial infarct size and improve cardiac function by blocking the Wnt/β-catenin signalling pathway, which may provide a new strategy for improving the prognosis of MI.

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.

Human-induced pluripotent stem cell-atrial-specific cardiomyocytes and atrial fibrillation

Patient-specific human-induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCMs) may be produced, genome-edited, and differentiated into multiple cell types for regenerative medicine, disease modeling, drug testing, toxicity screening, and three-dimensional tissue fabrication. There is presently no complete model of atrial fibrillation (AF) available for studying human pharmacological responses and evaluating the toxicity of potential medication candidates. It has been demonstrated that hiPSC-aCMs can replicate the electrophysiological disease phenotype and genotype of AF. The hiPSC-aCMs, however, are immature and do not reflect the maturity of aCMs in the native myocardium. Numerous laboratories utilize a variety of methodologies and procedures to improve and promote aCM maturation, including electrical stimulation, culture duration, biophysical signals, and changes in metabolic variables. This review covers the current methods being explored for use in the maturation of patient-specific hiPSC-aCMs and their application towards a personalized approach to the pharmacologic therapy of AF.

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.

Carpaine Promotes Proliferation and Repair of H9c2 Cardiomyocytes after Oxidative Insults

Carpaine has long been identified as the major alkaloid in Carica papaya leaves that possess muscle relaxant properties. Limited study on the molecular signaling properties of carpaine urges us to conduct this study that aims to elucidate the mechanism underlying the cardioprotective effect of carpaine in embryonic cardiomyocytes of the H9c2 cell line. The 50% inhibitory concentration (IC₅₀) of carpaine was first determined using a colorimetric MTT assay to establish the minimum inhibitory concentration for the subsequent test. Using a 1 µM carpaine treatment, a significant increase in the H9c2 proliferation rate was observed following 24 and 48 h of incubation. A Western blot analysis also revealed that carpaine promotes the upregulation of the cell cycle marker proteins cyclin D1 and PCNA. Carpaine-induced H9c2 cell proliferation is mediated by the activation of the FAK-ERK1/2 and FAK-AKT signaling pathways. In the setting of ischemia-reperfusion injury (IRI), carpaine provided a significant protective role to recover the wounded area affected by the hydrogen peroxide (H₂O₂) treatment. Furthermore, the oxidative-stress-induced reduction in mitochondrial membrane potential (MMP) and overproduction of reactive oxygen species (ROS) were attenuated by carpaine treatment. The current study revealed a novel therapeutic potential of carpaine in promoting in vitro cardiomyocyte proliferation and repair following injury.

Cardiomyocyte Proliferation as a Source of New Myocyte Development in the Adult Heart

Cardiac diseases such as myocardial infarction (MI) can lead to adverse remodeling and impaired contractility of the heart due to widespread cardiomyocyte death in the damaged area. Current therapies focus on improving heart contractility and minimizing fibrosis with modest cardiac regeneration, but MI patients can still progress to heart failure (HF). There is a dire need for clinical therapies that can replace the lost myocardium, specifically by the induction of new myocyte formation from pre-existing cardiomyocytes. Many studies have shown terminally differentiated myocytes can re-enter the cell cycle and divide through manipulations of the cardiomyocyte cell cycle, signaling pathways, endogenous genes, and environmental factors. However, these approaches result in minimal myocyte renewal or cardiomegaly due to hyperactivation of cardiomyocyte proliferation. Finding the optimal treatment that will replenish cardiomyocyte numbers without causing tumorigenesis is a major challenge in the field. Another controversy is the inability to clearly define cardiomyocyte division versus myocyte DNA synthesis due to limited methods. In this review, we discuss several studies that induced cardiomyocyte cell cycle re-entry after cardiac injury, highlight whether cardiomyocytes completed cytokinesis, and address both limitations and methodological advances made to identify new myocyte formation.

Prolonged Transcriptional Consequences in Survivors of Sepsis

Survivors of sepsis often suffer from prolonged post-critical illness syndrome secondary to the immune system’s reprogramming. It is unclear if this process is static and pervasive due to methodological difficulties studying long-term outcomes of sepsis. The purpose of this study is to evaluate transcriptional profiles longitudinally in Drosophila melanogaster in the aftermath of sepsis to provide preliminary data for targets playing a role in post-sepsis immunostasis. Adult Drosophila melanogaster were infected with E. coli, and survivors were euthanized at 7, 14, and 21 days. Control flies were subjected to sham stress. Gene profiling was done with RNA-seq, and potential miRNA factors were computed. Profiling identified 55 unique genes at seven days, 61 unique genes at 14 days, and 78 genes at 21 days in sepsis survivors vs. sham control. Each post-sepsis timepoint had a distinctive transcriptional pattern with a signature related to oxidative stress at seven days, neuronal signal transduction at 14 days, and metabolism at 21 days. Several potential miRNA patterns were computed as potentially affecting several of the genes expressed in sepsis survivors. Our study demonstrated that post-sepsis changes in the transcriptome profile are dynamic and extend well into the Drosophila melanogaster natural life span.

WNT signaling in atrial fibrillation

The Wnt signaling pathway regulates physiological processes such as cell proliferation and differentiation, cell fate decisions, and stem cell maintenance and, thus, plays essential roles in embryonic development, but also in adult tissue homeostasis and repair. The Wnt signaling pathway has been associated with heart development and repair and has been shown to be crucially involved in proliferation and differentiation of progenitor cells into cardiomyocytes. The investigation of the role of the Wnt signaling pathway and the regulation of its expression/activity in atrial fibrillation has only just begun. The present minireview (I) provides original data regarding the expression of Wnt signaling components in atrial tissue of patients with atrial fibrillation or sinus rhythm and (II) summarizes the current state of knowledge of the regulation of Wnt signaling components' expression/activity and the contribution of the various levels of the Wnt signal transduction pathway to the processes of the development, maintenance, and progression of atrial fibrillation.

Effect of Interventions in WNT Signaling on Healing of Cardiac Injury: A Systematic Review

The wound healing that follows myocardial infarction is a complex process involving multiple mechanisms, such as inflammation, angiogenesis and fibrosis. In the last two decades, the involvement of WNT signaling has been extensively studied and effects on virtually all aspects of this wound healing have been reported. However, as often is the case in a newly emerging field, inconsistent and sometimes even contradictory findings have been reported. The aim of this systematic review is to provide a comprehensive overview of studies in which the effect of interventions in WNT signaling were investigated in in vivo models of cardiac injury. To this end, we used different search engines to perform a systematic search of the literature using the key words "WNT and myocardial and infarction". We categorized the interventions according to their place in the WNT signaling pathway (ligand, receptor, destruction complex or nuclear level). The most consistent improvements of the wound healing response were observed in studies in which the acylation of WNT proteins was inhibited by administering porcupine inhibitors, by inhibiting of the downstream glycogen synthase kinase-3β (GSK3β) and by intervening in the β-catenin-mediated gene transcription. Interestingly, in several of these studies, evidence was presented for activation of cardiomyocyte proliferation around the infarct area. These findings indicate that inhibition of WNT signaling can play a valuable role in the repair of cardiac injury, thereby improving cardiac function and preventing the development of heart failure.

Extracellular Vesicle-Associated Proteins in Tissue Repair

The administration of (stem) cell-derived extracellular vesicles (EVs) promotes tissue repair through management of different inflammatory, proliferative and remodeling processes in the body. Despite the widely observed biological and therapeutic roles of EVs in wound healing and tissue repair, knowledge on how EVs activate recipient cells and which EV cargo is responsible for the subsequent functional effects is limited. Recent studies hint toward an important role for proteins as functional EV cargo. Here, we provide an overview of how EV-associated proteins promote tissue repair processes and discuss current challenges in evaluating their contribution to EV function and future directions for translating fundamental insights into clinically relevant EV therapies.