Transient induction of actin cytoskeletal remodeling associated with dedifferentiation,proliferation,and redifferentiation stimulates cardiac regeneration

The formation of new and functional cardiomyocytes requires a 3-step process:dedifferentiation,proliferation,and redifferentiation,but the critical genes required for efficient dedifferentiation,proliferation,and redifferentiation remain unknown.In our study,a circular trajectory using single-nucleus RNA sequencing of the pericentriolar material 1 positive(PCM1^(+))cardiomyocyte nuclei from hearts 1 and 3 days after surgery-induced myocardial infarction(MI)on postnatal Day 1 was reconstructed and demonstrated that actin remodeling contributed to the dedifferentiation,proliferation,and redifferentiation of cardiomyocytes after injury.We identified four top actin-remodeling regulators,namely Tmsb4x,Tmsb10,Dmd,and Ctnna3,which we collectively referred to as 2D2P.Transiently expressed changes of 2D2P,using a polycistronic non-integrating lentivirus driven by Tnnt2(cardiac-specific troponin T)promoters(Tnnt2-2D2P-NIL),efficiently induced transiently proliferative activation and actin remodeling in postnatal Day 7 cardiomyocytes and adult hearts.Furthermore,the intramyocardial delivery of Tnnt2-2D2P-NIL resulted in a sustained improvement in cardiac function without ventricular dilatation,thickened septum,or fatal arrhythmia for at least 4 months.In conclusion,this study highlights the importance of actin remodeling in cardiac regeneration and provides a foundation for new gene-cocktail-therapy approaches to improve cardiac repair and treat heart failure using a novel transient and cardiomyocyte-specific viral construct.

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.

Hippo pathway-manipulating neutrophil-mimic hybrid nanoparticles for cardiac ischemic injury via modulation of local immunity and cardiac regeneration

The promise of regeneration therapy for restoration of damaged myocardium after cardiac ischemic injury relies on targeted delivery of proliferative molecules into cardiomyocytes whose healing benefits are still limited owing to severe immune microenvironment due to local high concentration of proinflammatory cytokines.Optimal therapeutic strategies are therefore in urgent need to both modulate local immunity and deliver proliferative molecules.Here,we addressed this unmet need by developing neutrophil-mimic nanoparticles NM@miR,fabricated by coating hybrid neutrophil membranes with artificial lipids onto mesoporous silica nanoparticles(MSNs)loaded with microRNA-10b.The hybrid membrane could endow nanoparticles with strong capacity to migrate into infammatory sites and neutralize proinfammatory cytokines and increase the delivery efficiency of microRNA-1Ob into adult mammalian cardiomyocytes(CMs)by fusing with cell membranes and leading to the release of MSNs-miR into cytosol.Upon NM@miR administration,this nanoparticle could home to the injured myocardium,restore the local immunity,and efficiently deliver microRNA-1Ob to cardiomyocytes,which could reduce the activation of Hippo-YAP pathway mediated by excessive cytokines and exert the best proliferative effect of miR-1Ob.This combination therapy could finally improve cardiac function and mitigate ventricular remodeling.Consequently,this work offers a combination strategy of immunity modulation and proliferative molecule delivery to boost cardiac regeneration after injury.

microRNAs in cardiac regeneration and cardiovascular disease

microRNAs(miRNAs)are a class of small non-coding RNAs,which have been shown important to a wide range of biological process by post-transcriptionally regulating the expression of protein-coding genes.miRNAs have been demonstrated essential to normal cardiac development and function.Recently,numerous studies indicate miRNAs are involved in cardiac regeneration and cardiac disease,including cardiac hypertrophy,myocardial infarction and cardiac arrhythmia.These observations suggest miRNAs play important roles in cardiology.In this review,we summarize the recent progress of studying miRNAs in cardiac regeneration and cardiac disease.We also discuss the diagnostic and therapeutic potential of miRNAs in heart disease.

Clinical cardiac regenerative studies in children

Although the incidence of pediatric heart failure is low, the mortality is relatively high, with severe clinical symptoms requiring repeated hospitalization or intensive care treatment in the surviving patients. Cardiac biopsy specimens have revealed a higher number of resident human cardiac progenitor cells, with greater proliferation and differentiation capacity, in the neonatal period as compared with adults, demonstrating the regeneration potential of the young heart, with rising interest in cardiac regeneration therapy in critically ill pediatric patients. We review here the available literature data, searching the MEDLINE, Google Scholar and EMBASE database for completed, and www.clinicaltrials.gov homepage for ongoing studies involving pediatric cardiac regeneration reports. Because of difficulties conducting randomized blinded clinical trials in pediatric patients, mostly case reports or cohort studies with a limited number of individuals have been published in the field of pediatric regenerative cardiology. The majority of pediatric autologous cell transplantations into the cardiac tissue have been performed in critically ill children with severe or terminal heart failure. Congenital heart disease, myocarditis, and idiopathic hypertrophic or dilated cardiomyopathy leading to congestive heart failure are some possible areas of interest for pediatric cardiac regeneration therapy. Autologous bone marrow mononuclear cells, progenitor cells, or cardiospheres have been applied either intracoronary or percutaneously intramyocardially in severely ill children, leading to a reported clinical benefit of cell-based cardiac therapies. In conclusion, compassionate use of autologous stem cell administration has led to at least short-term improvement in heart function and clinical stability in the majority of the critically ill pediatric patients.

Pursuing meaningful end-points for stem cell therapy assessment in ischemic cardiac disease

Despite optimal interventional and medical therapy, ischemic heart disease is still an important cause of morbidity and mortality worldwide. Although not included in standard of care rehabilitation, stem cell therapy(SCT) could be a solution for prompting cardiac regeneration. Multiple studies have been published from the beginning of SCT until now, but overall no unanimous conclusion could be drawn in part due to the lack of appropriate endpoints. In order to appreciate the impact of SCT, multiple markers from different categories should be considered: Structural, biological, functional, physiological, but also major adverse cardiac events or quality of life. Imaging end-points are among the most used-especially left ventricle ejection fraction(LVEF) measured through different methods. Other imaging parameters are infarct size, myocardial viability and perfusion. The impact of SCT on all of the aforementioned end-points is controversial and debatable. 2 D-echocardiography is widely exploited, but new approaches such as tissue Doppler, strain/strain rate or 3 D-echocardiography are more accurate, especially since the latter one is comparable with the MRI gold standard estimation of LVEF. Apart from the objective parameters, there are also patient-centered evaluations to reveal the benefits of SCT, such as quality of life and performance status, the most valuable from the patient point of view. Emerging parameters investigating molecular pathways such as non-coding RNAs or inflammation cytokines have a high potential as prognostic factors. Due to the disadvantages of current techniques, new imaging methods with labelled cells tracked along their lifetime seem promising, but until now only pre-clinical trials have been conducted in humans. Overall, SCT is characterized by high heterogeneity not only in preparation, administration and type of cells, but also in quantification of therapy effects.

A protease-activated receptor 1 antagonist protects against global cerebral ischemia/reperfusion injury after asphyxial cardiac arrest in rabbits

Cerebral ischemia/reperfusion injury is partially mediated by thrombin, which causes brain damage through protease-activated receptor 1（PAR1）. However, the role and mechanisms underlying the effects of PAR1 activation require further elucidation. Therefore, the present study investigated the effects of the PAR1 antagonist SCH79797 in a rabbit model of global cerebral ischemia induced by cardiac arrest. SCH79797 was intravenously administered 10 minutes after the model was established. Forty-eight hours later, compared with those administered saline, rabbits receiving SCH79797 showed markedly decreased neuronal damage as assessed by serum neuron specific enolase levels and less neurological dysfunction as determined using cerebral performance category scores. Additionally, in the hippocampus, cell apoptosis, polymorphonuclear cell infiltration, and c-Jun levels were decreased, whereas extracellular signal-regulated kinase phosphorylation levels were increased. All of these changes were inhibited by the intravenous administration of the phosphoinositide 3-kinase/Akt pathway inhibitor LY29004（3 mg/kg） 10 minutes before the SCH79797 intervention. These findings suggest that SCH79797 mitigates brain injury via anti-inflammatory and anti-apoptotic effects, possibly by modulating the extracellular signal-regulated kinase, c-Jun N-terminal kinase/c-Jun and phosphoinositide 3-kinase/Akt pathways.

Fifteen years of bone marrow mononuclear cell therapy in acute myocardial infarction

In spite of modern treatment, acute myocardial infarction(AMI) still carries significant morbidity and mortality worldwide. Even though standard of care therapy improves symptoms and also long-term prognosis of patients with AMI, it does not solve the critical issue, specifically the permanent damage of cardiomyocytes. As a result, a complex process occurs, namely cardiac remodeling, which leads to alterations in cardiac size, shape and function. This is what has driven the quest for unconventional therapeutic strategies aiming to regenerate the injured cardiac and vascular tissue. One of the latest breakthroughs in this regard is stem cell(SC) therapy. Based on favorable data obtained in experimental studies, therapeutic effectiveness of this innovative therapy has been investigated in clinical settings. Of various cell types used in the clinic, autologous bone marrow derived SCs were the first used to treat an AMI patient, 15 years ago. Since then, we have witnessed an increasing body of data as regards this cutting-edge therapy. Although feasibility and safety of SC transplant have been clearly proved, it's efficacy is still under dispute. Conducted studies and meta-analysis reported conflicting results, but there is hope for conclusive answer to be provided by the largest ongoing trial designed to demonstrate whether this treatment saves lives. In the meantime, strategies to enhance the SCs regenerative potential have been applied and/or suggested, position papers and recommendations have been published. But what have we learned so far and how can we properly use the knowledge gained? This review will analytically discuss each of the above topics, summarizing the current state of knowledge in the field.

Effects of cannabinoid receptor type 2 on endogenous myocardial regeneration by activating cardiac progenitor cells in mouse infarcted heart

Cannabinoid receptor type 2(CB2)activation is recently reported to promote proliferation of some types of resident stem cells(e.g.,hematopoietic stem/progenitor cell or neural progenitor cell).Resident cardiac progenitor cell(CPC)activation and proliferation are crucial for endogenous cardiac regeneration and cardiac repair after myocardial infarction(MI).This study aims to explore the role and possible mechanisms of CB2receptor activation in enhancing myocardial repair.Our results revealed that CB2receptor agonist AM1241 can significantly increase CPCs by c-kit and Runx1 staining in ischemic myocardium as well as improve cardiomyocyte proliferation.AM1241 also decreased serum levels of MDA,TNF-αand IL-6 after MI.In addition,AM1241 can ameliorate left ventricular ejection fraction and fractional shortening,and reduce fibrosis.Moreover,AM1241 treatment markedly increased p-Akt and HO-1 expression,and promoted Nrf-2 nuclear translocation.However,PI3K inhibitor wortmannin eliminated these cardioprotective roles of AM1241.In conclusion,AM1241 could induce myocardial regeneration and improve cardiac function,which might be associated with PI3K/Akt/Nrf2 signaling pathway activation.Our findings may provide a promising strategy for cardiac endogenous regeneration after MI.

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.

Cellular polyploidy in organ homeostasis and regeneration

Polyploid cells,which contain more than one set of chromosome pairs,are very common in nature.Polyploidy can provide cells with several potential benefits over their diploid counterparts,including an increase in cell size,contributing to organ growth and tissue homeostasis,and improving cellular robustness via increased tolerance to genomic stress and apoptotic signals.Here,we focus on why polyploidy in the cell occurs and which stress responses and molecular signals trigger cells to become polyploid.Moreover,we discuss its crucial roles in cell growth and tissue regeneration in the heart,liver,and other tissues.

Distinct mononuclear diploid cardiac subpopulation with minimal cell-cell communications persists in embryonic and adult mammalian heart

A small proportion of mononuclear diploid cardiomyocytes(MNDCMs),with regeneration potential,could persist in adult mammalian heart.However,the heterogeneity of MNDCMs and changes during development remains to be illuminated.To this end,12645 cardiac cells were generated from embryonic day 17.5 and postnatal days 2 and 8 mice by single-cell RNA sequencing.Three cardiac developmental paths were identified:two switching to cardiomyocytes(CM)maturation with close CM–fibroblast(FB)communications and one maintaining MNDCM status with least CM–FB communications.Proliferative MNDCMs having interactions with macrophages and non-proliferative MNDCMs(non-pMNDCMs)with minimal cell–cell communications were identified in the third path.The non-pMNDCMs possessed distinct properties:the lowest mitochondrial metabolisms,the highest glycolysis,and high expression of Myl4 and Tnni1.Single-nucleus RNA sequencing and immunohistochemical staining further proved that the Myl4^(+)Tnni1+MNDCMs persisted in embryonic and adult hearts.These MNDCMs were mapped to the heart by integrating the spatial and single-cell transcriptomic data.In conclusion,a novel non-pMNDCM subpopulation with minimal cell–cell communications was unveiled,highlighting the importance of microenvironment contribution to CM fate during maturation.These findings could improve the understanding of MNDCM heterogeneity and cardiac development,thus providing new clues for approaches to effective cardiac regeneration.

Overlapping Cardiac Programs in Heart Development and Regeneration

Gaining cellular and molecular insights into heart development and regeneration will likely provide new therapeutic targets and opportunities for cardiac regenerative medicine,one of the most urgent clinical needs for heart failure.Here we present a review on zebrafish heart development and regeneration,with a particular focus on early cardiac progenitor development and their contribution to building embryonic heart,as well as cellular and molecular programs in adult zebrafish heart regeneration.We attempt to emphasize that the signaling pathways shaping cardiac progenitors in heart development may also be redeployed during the progress of adult heart regeneration.A brief perspective highlights several important and promising research areas in this exciting field.

Molecular regulation of myocardial proliferation and regeneration

Heart regeneration is a fascinating and complex biological process. Decades of intensive studies have revealed asophisticated molecular network regulating cardiac regeneration in the zebrafish and neonatal mouse heart. Here,we review both the classical and recent literature on the molecular and cellular mechanisms underlying heartregeneration, with a particular focus on how injury triggers the cell-cycle re-entry of quiescent cardiomyocytes toreplenish their massive loss after myocardial infarction or ventricular resection. We highlight several importantsignaling pathways for cardiomyocyte proliferation and propose a working model of how these injury-inducedsignals promote cardiomyocyte proliferation. Thus, this concise review provides up-to-date research progresses onheart regeneration for investigators in the field of regeneration biology.