Versican Promotes Cardiomyocyte Proliferation and Cardiac Repair

Fibroblast-derived versican exacerbates periodontitis progression by regulating macrophage migration and inflammatory cytokine secretion

OBJECTIVE

Versican (VCAN), a prominent extracellular matrix component upregulated in inflammatory diseases, demonstrates context-specific regulatory mechanisms. Periodontitis, a chronic inflammatory disease leading to periodontal tissue destruction and tooth loss, the pathological role of it remains poorly defined. Our study aims to examine VCAN-mediated mechanisms in periodontitis.

METHODS

We conducted a comprehensive analysis of bulk RNA sequencing and single-cell RNA sequencing data to examine VCAN expression level and source in periodontitis. Functional and correlation analyses were used to explore its biological functions. We then validated VCAN expression using quantitative real-time polymerase chain reaction, immunohistochemical staining, and immunofluorescence staining in animal models and investigated its biological functions in inflammation through in vitro experiments.

RESULTS

Our findings reveal that VCAN is mainly generated by fibroblast in periodontitis, and its expression significantly upregulated at both mRNA and protein levels. Using VCAN-overexpressing L929 cells, we demonstrated enhanced proliferative capacity and inflammatory potential. Co-culture experiments with RAW264.7 cells showed promoted migration, adhesion, M1 polarization, and mitogen-activated protein kinase (MAPK) pathway activation.

CONCLUSION

VCAN enhances fibroblast proliferation and migration, and upregulates inflammatory cytokines expression. Furthermore, fibroblast-derived VCAN not only induces macrophage chemotaxis, migration, adhesion, and polarization toward the proinflammatory M1 phenotype, but also activates MAPK signaling of macrophage, which may amplify inflammatory cascades to exacerbate periodontal tissue destruction. Targeted regulation of VCAN expression may become a promising precision treatment strategy for periodontitis.

Indole-3-lactic acid derived from tryptophan metabolism promotes trophoblast migration and invasion by activating the AhR/VCAN pathway

BACKGROUND

Preeclampsia (PE) is a life-threatening condition that is unique to human pregnancy, and it is a leading cause of maternal and neonatal morbidity and mortality. Currently, the only definitive treatment for PE is delivery of the placenta. Several studies have suggested that the gut microbiota and its derived metabolites may be associated with PE. Our previous work indicated that the level of indole-3-lactic acid (ILA), which is a metabolite derived from tryptophan (Trp) metabolism in the gut, is increased in PE patients. However, the effects of ILA on trophoblast function and its underlying mechanisms remain largely unknown.

METHODS

Transwell assays were conducted to assess the effects of ILA on trophoblast migration and invasion. Moreover, the aryl hydrocarbon receptor (AhR) signaling pathway was examined by qRT-PCR, western blotting and siRNA transfection. Additionally, RNA-seq analysis was performed to explore the mechanism underlying the ILA-mediated effects on trophoblast function. Finally, in vivo trophoblast invasion was evaluated through immunohistochemical analysis.

RESULTS

Our data demonstrated that ILA promoted HTR-8/SVneo cell migration and invasion through AhR signaling pathway activation. Mechanistically, VCAN upregulation played a key role in mediating the effects of ILA on trophoblasts after AhR activation. Notably, ILA supplementation improved spiral artery remodeling and increased trophoblast invasion in PE-like mice, primarily by increasing VCAN levels.

CONCLUSIONS

These data strongly suggest that elevated ILA in PE serve as a protective mechanism against trophoblast dysfunction. Therefore, we propose that ILA may be a novel and promising therapeutic approach for treating PE by enhancing trophoblast functions.

PTMA controls cardiomyocyte proliferation and cardiac repair by enhancing STAT3 acetylation

The adult mammalian heart has limited regenerative capacity due to the low proliferative ability of cardiomyocytes, whereas embryonic cardiomyocytes exhibit robust proliferative potential. Using single-cell RNA sequencing of embryonic hearts, we identified prothymosin α (PTMA) as a key factor driving cardiomyocyte proliferation. Overexpression of PTMA in primary mouse and rat cardiomyocytes significantly promoted cardiomyocyte proliferation and similarly enhanced proliferation in human iPSC-derived cardiomyocytes. Conditional knockout of Ptma in cardiomyocytes impaired neonatal heart regeneration. AAV9-mediated overexpression of Ptma extended the neonatal proliferative window and showed therapeutic promise for enhancing adult heart regeneration. Mechanistically, PTMA interacted with MBD3, inhibiting its deacetylation activity within the MBD3/HDAC1 NuRD complex. This inhibition increased STAT3 acetylation, which positively regulated STAT3 phosphorylation and activation of its target genes. These findings establish PTMA as a critical regulator of heart regeneration and suggest its potential as a therapeutic target for ischemic myocardial injury.

Arbutin improves post-myocardial infarction cardiac dysfunction by inhibiting cardiac fibroblast activation

BACKGROUND

Arbutin exhibits multiple effects, including anti-inflammatory, antioxidant, and scavenging of free radicals, yet its research within the cardiovascular system remains limited.

PURPOSE

This study aims to investigate the effects of arbutin on myocardial infarction induced by left anterior descending (LAD) ligation in mice.

METHODS

The possible mechanism of arbutin's effect on myocardial infarction was predicted through network pharmacology studies. To evaluate the impact of arbutin on cardiac function in myocardial infarction, TTC staining of the heart was performed, and echocardiography was conducted on mice at different time points. Furthermore, Western blot analysis was utilized not only to detect αSMA, Collagen I, and Collagen III, aiming to investigate the impact of arbutin on myocardial fibrosis but also to detect the influence of arbutin on the phosphorylation level of ERK1/2, thereby elucidating its potential mechanism of action.

RESULTS

Network pharmacology data suggest that arbutin may exert a beneficial effect on myocardial infarction by modulating the ERK1/2 signaling pathway. In vivo experimental results indicate that after myocardial infarction, arbutin can alleviate myocardial fibrosis and cardiac hypertrophy, significantly improving cardiac function. Further in vitro experiments confirm that arbutin markedly reduces fibrosis-related indicators, and this process is partially achieved through the regulation of ERK1/2 phosphorylation.

CONCLUSION

In conclusion, this study reveals that arbutin exerts a significant protective effect by acting on the ERK1/2 signaling pathway, effectively inhibiting myocardial fibrosis, and subsequently attenuating myocardial infarction induced by LAD ligation.

ALDH2 delays ventricular pressure overload-induced heart failure by promoting cardiomyocyte proliferation in mice

The adult mammalian heart is a terminally differentiated organ in which the majority of cardiomyocytes are in a state of cell cycle arrest, rendering them incapable of effectively proliferating to replace damaged cells. ALDH2, an enzyme known for alleviating oxidative stress, has been demonstrated to play a critical role in cardiac protection. However, whether ALDH2 regulates cardiomyocyte proliferation has not been conclusively established. We found that activation of ALDH2 activity significantly promotes cardiomyocyte proliferation and extends the proliferation window during early postnatal development in neonatal mice. Furthermore, administration of Alda-1 to activate ALDH2 in adult mice subjected to transverse aortic constriction markedly enhanced cardiomyocyte proliferation and delayed the onset of pressure overload-induced heart failure. In summary, our findings identify ALDH2 as a potential target for regulating cardiomyocyte proliferation and offer a novel therapeutic approach for treating heart failure.

Cardiac regeneration: Unraveling the complex network of intercellular crosstalk

The heart is composed of multiple cell types, including cardiomyocytes, endothelial/endocardial cells, fibroblasts, resident immune cells and epicardium and crosstalk between these cell types is crucial for proper cardiac function and homeostasis. In response to cardiac injury or disease, cell-cell interactions and intercellular crosstalk contribute to remodeling to compensate reduced heart function. In some vertebrates, the heart can regenerate following cardiac injury. While cardiomyocytes play a crucial role in this process, additional cell types are necessary to create a pro-regenerative microenvironment in the injured heart. Here, we review recent literature regarding the importance of cellular crosstalk in promoting cardiac regeneration and provide insight into emerging technologies to investigate cell-cell interactions in vivo. Lastly, we explore recent studies highlighting the importance of inter-organ communication in response to injury and promotion of cardiac regeneration. Importantly, understanding how intercellular and inter-organ crosstalk promote cardiac regeneration is essential for the development of therapeutic strategies to stimulate regeneration in the human heart.

Endothelial-Mesenchymal Transition and Possible Role of Cytokines in Streptozotocin-Induced Diabetic Heart

Background: Although endothelial mesenchymal transition (EndMT) has been characterized as a basic process in embryogenesis, EndMT is the mechanism that accelerates the development of cardiovascular diseases, including heart failure, aging, and complications of diabetes or hypertension as well. Endothelial cells lose their distinct markers and take on a mesenchymal phenotype during EndMT, expressing distinct products. Methods: In this study, type 1 Diabetes mellitus (T1DM) was induced in rats with streptozotocin (STZ) by intraperitoneal injection at a 60 mg/kg dose. Diabetic rats were randomly divided into two groups, namely, control and diabetic rats, for 4 weeks. Heart, aorta, and plasma samples were collected at the end of 4 weeks. Sequentially, biochemical parameters, cytokines, reactive oxygen species (ROS), protein expression of EndMT markers (Chemokine C-X-C motif ligand-1 (CXCL-1), vimentin, citrullinated histone H3 (H3Cit), α-smooth muscle actin (α-SMA), and transforming growth factor beta (TGF-β) and versican), components of the extracellular matrix (matrix metalloproteinase 2 (MMP-2), tissue inhibitor of metalloproteinase-1(TIMP-1), and discoidin domain tyrosine kinase receptor 2 (DDR-2)) were detected by ELISA or Western blot, respectively. Results: Cytokines and ROS were increased in diabetic hearts, which induced partial EndMT. Among EndMT markers, histone citrullination, α-SMA, and CXCL-1 were increased; vimentin was decreased in DM. The endothelial marker endothelin-1 was significantly higher in the aortas of DM rats. Interestingly, TGF-β showed a significant decrease in the diabetic heart, plasma, and aorta. Additionally, MMP-2/TIMP-1 levels also decreased in DM. Conclusions: To sum up, the identification of molecules and regulatory pathways involved in EndMT provided novel therapeutic approaches for cardiac pathophysiological conditions.

Timestamp calibration for time-series single cell RNA-seq expression data

Timestamp automatic annotation (TAA) is a crucial procedure for analyzing time-series scRNA-seq data, as they unveil dynamic biological developments and cell regeneration processes. However, current TAA methods heavily rely on manual timestamps, often overlooking their reliability. This oversight can significantly degrade the performance of timestamp automatic annotation due to noisy timestamps. Nevertheless, the current approach for addressing this issue tends to select less critical cleaned samples for timestamp calibration. To tackle this challenge, we have developed a novel timestamp calibration model called ScPace for handling noisy labeled time-series scRNA-seq data. This approach incorporates a latent variable indicator within a base classifier instead of probability sampling to detect noisy samples effectively. To validate our proposed method, we conducted experiments on both simulated and real time-series scRNA-seq datasets. Cross validation experiments with different artificial mislabeling rates demonstrate that ScPace outperforms previous approaches. Furthermore, after calibrating the timestamps of the original time-series scRNA-seq data using our method, we performed supervised pseudotime analysis, revealing that ScPace enhances its performance significantly. These findings suggest that ScPace is an effective tool for timestamp calibration by enabling reclassification and deletion of detected noisy labeled samples while maintaining robustness across diverse ranges of time-series scRNA-seq datasets. The source code is available at https://github.com/OPUS-Lightphenexx/ScPace.

Resveratrol suppresses growth and VCAN expression in a Cancer-associated fibroblast-breast Cancer hybrid organoid

BACKGROUND

Cancer-associated fibroblast (CAF) is a major component of the tumor microenvironment (TME) and promotes breast cancer (BC) progression and drug resistance. Two-dimensional cell culture is insufficient to simulate the protective effects of CAFs on tumors, resulting in experimental bias in drug efficacy assays. CAF-organoid co-culture model applied in this study may help solve this problem. Resveratrol (Res) has been found to suppresses BC growth, yet its effects on CAF-protected BC remain unknown.

METHODS

Surgical resected BC tissues were harvested and established for BC organoids (BCOs, identified with pathological examination) and isolated for CAFs (identified with immunofluorescence) respectively. BCO-CAF co-culture system was established and was measured for the protection effects of CAFs on BCOs. The system was then treated with Res and tested for EdU proliferation assay and calcein-AM/PI viable/non-viable cell labeling. Biogenic analysis was performed and showed that VCAN from CAFs may be important in this process. Versican (VCAN) expression levels in CAFs with or without Res treatment were evaluated by immunohistochemistry, qRT-PCR, and Western blotting.

RESULTS

19 BCO cases were successfully cultured and confirmed with pathological examination. Res showed inhibitory effects on 15 of the 19 BCO cases (78.95 %). Although CAFs facilitated organoid growth of BCOs by 69.75 ± 14.78 %, Res treatment eliminated this effect and caused extensive cell death (84.97 % ±5.06 %) in CAF-coated BCOs, accompanied by a decrease in VCAN and TGF-β expression in CAFs.

CONCLUSIONS

The anti-BC value of Res was further proved by showing its promising suppressive effects on BCOs with or without the presence of CAFs.

Molecular gatekeepers of endogenous adult mammalian cardiomyocyte proliferation

Irreversible cardiac fibrosis, cardiomyocyte death and chronic cardiac dysfunction after myocardial infarction pose a substantial global health-care challenge, with no curative treatments available. To regenerate the injured heart, cardiomyocytes must proliferate to replace lost myocardial tissue - a capability that adult mammals have largely forfeited to adapt to the demanding conditions of life. Using various preclinical models, our understanding of cardiomyocyte proliferation has progressed remarkably, leading to the successful reactivation of cell cycle induction in adult animals, with functional recovery after cardiac injury. Central to this success is the targeting of key pathways and structures that drive cardiomyocyte maturation after birth - nucleation and ploidy, sarcomere structure, developmental signalling, chromatin and epigenetic regulation, the microenvironment and metabolic maturation - forming a complex regulatory framework that allows efficient cellular contraction but restricts cardiomyocyte proliferation. In this Review, we explore the molecular pathways underlying these core mechanisms and how their manipulation can reactivate the cell cycle in cardiomyocytes, potentially contributing to cardiac repair.

The Application of scRNA-Seq in Heart Development and Regeneration

Single-cell RNA sequencing (scRNA-seq) is a rapidly developing and useful technique for elucidating biological mechanisms and characterizing individual cells. Tens of millions of patients worldwide suffer from heart injuries and other types of heart disease. Neonatal mammalian hearts and certain adult vertebrate species, such as zebrafish, can fully regenerate after myocardial injury. However, the adult mammalian heart is unable to regenerate the damaged myocardium. scRNA-seq provides many new insights into pathological and normal hearts and facilitates our understanding of cellular responses to cardiac injury and repair at different stages, which may provide critical clues for effective therapies for adult heart regeneration. In this review, we summarize the application of scRNA-seq in heart development and regeneration and describe how important molecular mechanisms can be harnessed to promote heart regeneration.

Decoding the regulatory roles of circular RNAs in cardiac fibrosis

Cardiovascular diseases (CVDs) are the primary cause of death globally. The evolution of nearly all types of CVDs is characterized by a common theme: the emergence of cardiac fibrosis. The precise mechanisms that trigger cardiac fibrosis are still not completely understood. In recent years, a type of non-coding regulatory RNA molecule known as circular RNAs (circRNAs) has been reported. These molecules are produced during back splicing and possess significant biological capabilities, such as regulating microRNA activity, serving as protein scaffolds and recruiters, competing with mRNA, forming circR-loop structures to modulate transcription, and translating polypeptides. Furthermore, circRNAs exhibit a substantial abundance, notable stability, and specificity of tissues, cells, and time, endowing them with the potential as biomarkers, therapeutic targets, and therapeutic agents. CircRNAs have garnered growing interest in the field of CVDs. Recent investigations into the involvement of circRNAs in cardiac fibrosis have yielded encouraging findings. This study aims to provide a concise overview of the existing knowledge about the regulatory roles of circRNAs in cardiac fibrosis.

Medium from human iPSC-derived primitive macrophages promotes adult cardiomyocyte proliferation and cardiac regeneration

Heart injury has been characterized by the irreversible loss of cardiomyocytes comprising the contractile tissues of the heart and thus strategies enabling adult cardiomyocyte proliferation are highly desired for treating various heart diseases. Here, we test the ability of human induced pluripotent stem cell-derived primitive macrophages (hiPMs) and their conditioned medium (hiPM-cm) to promote human cardiomyocyte proliferation and enhance cardiac regeneration in adult mice. We find that hiPMs promote human cardiomyocyte proliferation, which is recapitulated by hiPM-cm through the activation of multiple pro-proliferative pathways, and a secreted proteome analysis identifies five proteins participating in this activation. Subsequent in vivo experiments show that hiPM-cm promotes adult cardiomyocyte proliferation in mice. Lastly, hiPM-cm enhances cardiac regeneration and improves contractile function in injured adult mouse hearts. Together, our study demonstrates the efficacy of using hiPM-cm in promoting adult cardiomyocyte proliferation and cardiac regeneration to serve as an innovative treatment for heart disease.

Extracellular matrix in cardiac morphogenesis, fibrosis, and regeneration

The extracellular matrix (ECM) plays a crucial role in providing structural integrity and regulating cell communication essential for organ development, homeostasis, and regeneration, including hearts. Evidence indicates that disruptions in the spatiotemporal expression or alterations in ECM components lead to cardiac malformations, including a wide range of congenital heart diseases (CHDs). Furthermore, research on injured hearts across various vertebrate species, some of which show effective regeneration while others experience irreversible fibrosis, underscores the significance of ECM molecules in cardiac regeneration. This review presents an overview of heart development and the dynamics of ECM during cardiac morphogenesis, beginning with the formation of the contractile heart tube and advancing to the development of distinct chambers separated by valves to facilitate unidirectional blood flow. Furthermore, we discuss research emphasizing the multifaceted roles of secreted molecules in mediating fibrosis and regeneration following myocardial injury.

Foxk1 and Foxk2 promote cardiomyocyte proliferation and heart regeneration

Promoting endogenous cardiomyocyte proliferation is a promising strategy for cardiac repair. Identifying key factors that regulate cardiomyocyte proliferation can advance the development of novel therapies for heart regeneration. Here, we identify Foxk1 and Foxk2 as key regulators of cardiomyocyte proliferation, whose expression declines during postnatal heart development. Cardiomyocyte-specific knockout of Foxk1 or Foxk2 impairs neonatal heart regeneration after myocardial infarction (MI) injury. AAV9-mediated Foxk1 or Foxk2 overexpression extends the postnatal cardiomyocyte proliferative window and enhances cardiac repair in adult mice after MI. Mechanistically, Foxk1 and Foxk2 drive cardiomyocyte cell cycle progression by directly activating CCNB1 and CDK1 expression, forming the CCNB1/CDK1 complex that facilitates G2/M transition. Moreover, Foxk1 and Foxk2 promote cardiomyocyte proliferation by upregulating HIF1α expression, which enhances glycolysis and the pentose phosphate pathway (PPP), which further favors cardiomyocyte proliferation. These findings establish Foxk1 and Foxk2 as promising therapeutic targets for cardiac injury.

The Role of the MAPK Signaling Pathway in Cardiovascular Disease: Pathophysiological Mechanisms and Clinical Therapy

Cardiovascular disease (CVD) is a serious global health issue with high mortality rates worldwide. Despite the numerous advancements in the study of CVD pathogenesis in recent years, further summarization and elaboration of specific molecular pathways are required. An extensive body of research has been conducted to elucidate the association between the MAPK signaling pathway, which is present in all eukaryotic organisms, and the pathogenesis of cardiovascular disease. This review aims to provide a comprehensive summary of the research conducted on MAPK and CVD over the past five years. The primary focus is on four specific diseases: heart failure, atherosclerosis, myocardial ischemia-reperfusion injury, and cardiac hypertrophy. The review will also address the pathophysiological mechanisms of MAPK in cardiovascular diseases, with the objective of proposing novel clinical treatment strategies for CVD.

Targeting the E Prostanoid Receptor EP4 Mitigates Cardiac Fibrosis Induced by β-Adrenergic Activation

Sustained β-adrenergic activation induces cardiac fibrosis characterized by excessive deposition of extracellular matrix (ECM). Prostaglandin E2 (PGE2) receptor EP4 is essential for cardiovascular homeostasis. This study aims to investigate the roles of cardiomyocyte (CM) and cardiac fibroblast (CF) EP4 in isoproterenol (ISO)-induced cardiac fibrosis. By crossing the EP4f/f mice with α-MyHC-Cre or S100A4-Cre mice, this work obtains the CM-EP4 knockout (EP4f/f-α-MyHCCre+) or CF-EP4 knockout (EP4f/f-S100A4Cre+) mice. The mice of both genders are subcutaneously injected with ISO (5 mg kg-1 day-1) for 7 days. Compared to the control mice, both EP4f/f-α-MyHCCre+ and EP4f/f-S100A4Cre+ mice show a significant improvement in cardiac diastolic function and fibrosis as assessed by echocardiography and histological staining, respectively. In the CMs, inhibition of EP4 suppresses ISO-induced TGF-β1 expression via blocking the cAMP/PKA pathway. In the CFs, inhibition of EP4 reversed TGF-β1-triggers production of ECM via preventing the formation of the TGF-β1/TGF-β receptor complex and blocks CF proliferation via suppressing the ERK1/2 pathway. Furthermore, double knockout of the CM- and CF-EP4 or administration of EP4 antagonist, grapiprant, markedly improves ISO-induced cardiac diastolic dysfunction and fibrosis. Collectively, this study demonstrates that both CM-EP4 and CF-EP4 contribute to β-adrenergic activation-induced cardiac fibrosis. Targeting EP4 may offer a novel therapeutic approach for cardiac fibrosis.

ADAMTS4 Reduction Contributes to Extracellular Matrix Deposition and Impaired Myogenesis in the Skeletal Muscle of Cigarette Smoke-Exposed Mice

Background: The extracellular matrix (ECM) plays a critical role in the proper regeneration of skeletal muscle. ECM remodeling has been reported in the skeletal muscle of chronic obstructive pulmonary disease (COPD), while the mechanisms remain poorly understood. Methods: In this study, we examined the dynamic interplay between ECM components and ECM enzymes in COPD skeletal muscle and cigarette smoke (CS) extract-treated C2C12 cells. C2C12 cells were further used to evaluate the role of a disintegrin and metalloproteinase with thrombospondin motif 4 (ADAMTS4) in ECM remodeling and myogenesis. Results: Chronic CS exposure induced the development of COPD and comorbid sarcopenia in C57BL/6J mice. Muscle fibrosis was observed in the gastrocnemius muscle of CS-exposed mice, accompanied by an upregulation of protein expression but a downregulation of mRNA levels of fibronectin and versican. We found that the discrepancy of mRNA and protein expression was attributed to the aberrant secretion of some ECM enzymes belonging to matrix metalloproteinases and ADAMTS proteases, especially ADAMTS4. CS exposure reduced ADAMTS4 expression in gastrocnemius muscles and C2C12 cells, and Adamts4 knockdown induced fibronectin and versican accumulation and impeded myogenic process. Conclusions: Considering that recent studies have indicated an impaired skeletal muscle regeneration in COPD, we suggested that the restrained production of ADAMTS4 in response to CS could be involved in the damaged muscle regeneration through regulating skeletal muscle ECM in COPD. Targeting ECM enzymes may benefit the rehabilitation of COPD-related sarcopenia.

The role of the extracellular matrix in cardiac regeneration

The extracellular matrix (ECM) is a complex and dynamic three-dimensional network that functions as an architectural scaffold to maintain cardiac homeostasis. Important biochemical and mechanical signals associated with cell‒cell communication are provided via the reciprocal interaction between cells and the ECM. By converting mechanical cues into biochemical signals, the ECM regulates many cell processes, including migration, adhesion, growth, differentiation, proliferation, and apoptosis. Moreover, the ECM facilitates the replacement of dead cells and preserves the structural integrity of the heart, making it essential in conditions such as myocardial infarction and other pathological states. When excessive ECM deposition or abnormal production of ECM components occurs, the heart undergoes fibrosis, leading to cardiac dysfunction and heart failure. However, emerging evidence suggests that the ECM may contribute to heart regeneration following cardiac injury. The present review offers a complete overview of the existing information and novel discoveries regarding the involvement of the ECM in heart regeneration from both mechanical and biochemical perspectives. Understanding the ECM and its involvement in mechanotransduction holds significant potential for advancing therapeutic approaches in heart repair and regeneration.

Enhanced fibrotic potential of COL1A1hiNR4A1low fibroblasts in ischemic heart revealed by transcriptional dynamics heterogeneity analysis at both bulk and single-cell levels

Background

Fibroblasts in the fibrotic heart exhibit a heterogeneous biological behavior. The specific subsets of fibroblasts that contribute to progressive cardiac fibrosis remain unrevealed. Our aim is to identify the heart fibroblast (FB) subsets that most significantly promote fibrosis and the related critical genes as biomarkers for ischemic heart disease.

Methods

The single nuclei RNA sequencing (snRNA-seq) and bulk RNA sequencing datasets used in this study were obtained from the Gene Expression Omnibus (GEO). The activity of gene sets related to progressive fibrosis was quantified for each FB cluster using the AddmoleculeScore function. Differentially expressed genes (DEGs) for the specific cell cluster with the highest fibrotic transcription dynamics were identified and integrated with bulk RNA sequencing data for analysis. Multiple machine learning models were employed to identify the optimal gene panel for diagnosing ischemic heart disease (IHD) based on the intersected DEGs. The effectiveness and robustness of the gene-derived diagnostic tool were validated using two independent IHD cohorts.Subsequently, we validated the signature genes using a rat post-myocardial infarction heart failure model.

Results

We conducted an analysis on high-quality snRNA-seq data obtained from 3 IHD and 4 cardiac sarcoidosis heart samples, resulting in the identification of 16 FB clusters. Cluster2 exhibited the highest gene activity in terms of fibrosis-related transcriptome dynamics. The characteristic gene expression profile of this FB subset indicated a specific upregulation of COL1A1 and several pro-fibrotic factors, including CCDC102B, GUCY1A3, TEX41, NREP, TCAP, and WISP, while showing a downregulation of NR4A1, an endogenous inhibitor of the TGF-β pathway. Consequently, we designated this subgroup as COL1A1hiNR4A1low FB. Gene set enrichment analysis (GSEA) shows that the gene expression pattern of COL1A1hiNR4A1low FB was closer to pathways associated with cardiac fibrosis. Through machine learning, ten feature genes from COL1A1hiNR4A1low FB were selected to construct a diagnostic tool for IHD. The robustness of this new tool was validated using an independent cohort and heart failure rats.

Conclusion

COL1A1hiNR4A1low FB possess heightened capability in promoting cardiac fibrosis. Additionally, it offers molecular insights into the mechanisms underlying the regulation of the TGF-β pathway. Furthermore, the characteristic genes of COL1A1hiNR4A1 FB could serve as valuable tools for diagnosing of IHD.

The highly conserved PIWI-interacting RNA CRAPIR antagonizes PA2G4-mediated NF110-NF45 disassembly to promote heart regeneration in mice

Targeting the cardiomyocyte cell cycle is a promising strategy for heart repair following injury. Here, we identify a cardiac-regeneration-associated PIWI-interacting RNA (CRAPIR) as a regulator of cardiomyocyte proliferation. Genetic ablation or antagomir-mediated knockdown of CRAPIR in mice impairs cardiomyocyte proliferation and reduces heart regenerative potential. Conversely, overexpression of CRAPIR promotes cardiomyocyte proliferation, reduces infarct size and improves heart function after myocardial infarction. Mechanistically, CRAPIR promotes cardiomyocyte proliferation by competing with NF110 for binding to the RNA-binding protein PA2G4, thereby preventing the interaction of PA2G4 with the NF110-NF45 heterodimer and reducing NF110 degradation. The ability of CRAPIR to promote proliferation was confirmed in human embryonic stem cell-derived cardiomyocytes. Notably, CRAPIR serum levels are lower in individuals with ischemic heart disease and negatively correlate with levels of N-terminal pro-brain natriuretic peptide. These findings position CRAPIR both as a potential diagnostic marker for cardiac injury and as a therapeutic target for heart regeneration through the PA2G4-NF110-NF45 signaling axis.

Myocardial fibrosis from the perspective of the extracellular matrix: Mechanisms to clinical impact

Fibrosis is defined by the excessive accumulation of extracellular matrix (ECM) and constitutes a central pathophysiological process that underlies tissue dysfunction, across organs, in multiple chronic diseases and during aging. Myocardial fibrosis is a key contributor to dysfunction and failure in numerous diseases of the heart and is a strong predictor of poor clinical outcome and mortality. The excess structural and matricellular ECM proteins deposited by cardiac fibroblasts, is found between cardiomyocytes (interstitial fibrosis), in focal areas where cardiomyocytes have died (replacement fibrosis), and around vessels (perivascular fibrosis). Although myocardial fibrosis has important clinical prognostic value, access to cardiac tissue biopsies for histological evaluation is limited. Despite challenges with sensitivity and specificity, cardiac magnetic resonance imaging (CMR) is the most applicable diagnostic tool in the clinic, and the scientific community is currently actively searching for blood biomarkers reflecting myocardial fibrosis, to complement the imaging techniques. The lack of mechanistic insights into specific pro- and anti-fibrotic molecular pathways has hampered the development of effective treatments to prevent or reverse myocardial fibrosis. Development and implementation of anti-fibrotic therapies is expected to improve patient outcomes and is an urgent medical need. Here, we discuss the importance of the ECM in the heart, the central role of fibrosis in heart disease, and mechanistic pathways likely to impact clinical practice with regards to diagnostics of myocardial fibrosis, risk stratification of patients, and anti-fibrotic therapy.

Matricellular proteins: From cardiac homeostasis to immune regulation

Tissue repair after myocardial injury is a complex process involving changes in all aspects of the myocardial tissue, including the extracellular matrix (ECM). The ECM is composed of large structural proteins such as collagen and elastin and smaller proteins with major regulatory properties called matricellular proteins. Matricellular cell proteins exert their functions and elicit cellular responses by binding to structural proteins not limited to interactions with cell surface receptors, cytokines, or proteases. At the same time, matricellular proteins act as the "bridge" of information exchange between cells and ECM, maintaining the integrity of the cardiac structure and regulating the immune environment, which is a key factor in determining cardiac homeostasis. In this review, we present an overview of the identified matricellular proteins and summarize the current knowledge regarding their roles in maintaining cardiac homeostasis and regulating the immune system.

Transcriptome Sequencing-Based Screening of Key Melatonin-Related Genes in Ischemic Stroke

Ischemic stroke (IS) is a complex syndrome of neurological deficits due to stenosis or occlusion of the carotid and vertebral arteries for which there is still no effective treatment. Melatonin, a hormone secreted by the pineal gland, has multiple biological effects, such as antioxidant and anti-inflammatory properties, circadian rhythm regulation, and tissue regeneration, demonstrating potential applications in the treatment of IS. The aim of this study was to investigate key melatonin-regulated genes associated with IS using transcriptome sequencing and bioinformatics analyses and to explore their potential mechanisms of action in the disease process. We obtained gene expression data related to ischemic stroke (IS) from the Gene Expression Omnibus (GEO) database and identified candidate genes using machine learning algorithms. We then assessed the predictive power of these genes using PPI network analysis and diagnostic models. Finally, a series of enrichment analyses identified four key genes: ADM, PTGS2, MMP9, and VCAN. In addition, we determined the mRNA levels of these four key genes in an IS rat model using qPCR and found that all of these genes were significantly upregulated in the IS model compared to the control group, which is consistent with the results of previous analyses. Meanwhile, these genes have biological functions such as regulating vascular tone, participating in the inflammatory response, influencing tissue remodeling, and regulating cell adhesion and proliferation, playing key roles in the pathogenesis of IS. Therefore, we suggest that these four key genes may serve as prospective biomarkers for IS and help predict the risk of developing IS. In conclusion, this study elucidates for the first time the potential role of melatonin in the pathogenesis of IS and lays the foundation for in-depth studies on the functions of these key genes in the pathophysiology of IS and their potential applications in clinical diagnosis and treatment.

From Cell to Gene: Deciphering the Mechanism of Heart Failure With Single-Cell Sequencing

Heart failure (HF) is a prevalent cardiovascular disease with significant morbidity and mortality rates worldwide. Due to the intricate structure of the heart, diverse cell types, and the complex pathogenesis of HF, further in-depth investigation into the underlying mechanisms  is required. The elucidation of the heterogeneity of cardiomyocytes and the intercellular communication network is particularly important. Traditional high-throughput sequencing methods provide an average measure of gene expression, failing to capture the "heterogeneity" between cells and impacting the accuracy of gene function knowledge. In contrast, single-cell sequencing techniques allow for the amplification of the entire genome or transcriptome at the individual cell level, facilitating the examination of gene structure and expression with unparalleled precision. This approach offers valuable insights into disease mechanisms, enabling the identification of changes in cellular components and gene expressions during hypertrophy associated with HF. Moreover, it reveals distinct cell populations and their unique roles in the HF microenvironment, providing a comprehensive understanding of the cellular landscape that underpins HF pathogenesis. This review focuses on the insights provided by single-cell sequencing techniques into the mechanisms underlying HF and discusses the challenges encountered in current cardiovascular research.

Circular RNA IGF1R Promotes Cardiac Repair via Activating β-Catenin Signaling by Interacting with DDX5 in Mice after Ischemic Insults

The potential of circular RNAs (circRNAs) as biomarkers and therapeutic targets is becoming increasingly evident, yet their roles in cardiac regeneration and myocardial renewal remain largely unexplored. Here, we investigated the function of circIGF1R and related mechanisms in cardiac regeneration. Through analysis of circRNA sequencing data from neonatal and adult cardiomyocytes, circRNAs associated with regeneration were identified. Our data showed that circIGF1R expression was high in neonatal hearts, decreased with postnatal maturation, and up-regulated after cardiac injury. The elevation was validated in patients diagnosed with acute myocardial infarction (MI) within 1 week. In human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and myocardial tissue from mice after apical resection and MI, we observed that circIGF1R overexpression enhanced cardiomyocyte proliferation, reduced apoptosis, and mitigated cardiac dysfunction and fibrosis, while circIGF1R knockdown impeded endogenous cardiac renewal. Mechanistically, we identified circIGF1R binding proteins through circRNA precipitation followed by mass spectrometry. RNA pull-down Western blot and RNA immunoprecipitation demonstrated that circIGF1R directly interacted with DDX5 and augmented its protein level by suppressing ubiquitin-dependent degradation. This subsequently triggered the β-catenin signaling pathway, leading to the transcriptional activation of cyclin D1 and c-Myc. The roles of circIGF1R and DDX5 in cardiac regeneration were further substantiated through site-directed mutagenesis and rescue experiments. In conclusion, our study highlights the pivotal role of circIGF1R in facilitating heart regeneration and repair after ischemic insults. The circIGF1R/DDX5/β-catenin axis emerges as a novel therapeutic target for enhancing myocardial repair after MI, offering promising avenues for the development of regenerative therapies.

CircNCX1 modulates cardiomyocyte proliferation through promoting ubiquitination of BRG1

In mammal, the myocardium loss cannot be recovered spontaneously due to the negligible proliferation ability of mature mammalian cardiomyocyte. However, accumulated evidence has shown that terminally differentiated mammalian cardiomyocyte also has proliferation potency, which can be mediated by several mechanisms. Here, we reported that circNCX1, the most abundant circular RNA in mammalian hearts, can affect the proliferation of murine cardiomyocytes. The level of circNCX1 is significantly elevated during heart development. Forced expression of circNCX1 inhibits cardiomyocyte proliferation, while silencing of endogenous circNCX1 in cardiomyocyte shows reversed effect in vitro. Mechanistically, circNCX1 functions via negatively regulating transcription activator BRG1. It bridges BRG1 and FBXW7 to enhance the ubiquitination and degradation of BRG1, decreasing the expression of BMP10 to lead cell cycle arrest. In summary, our study first revealed that circNCX1 is a modulator of cardiomyocyte proliferation.

Identification and Validation of Diagnostic Model Based on Angiogenesis- and Epithelial Mesenchymal Transition-Related Genes in Myocardial Infarction

Background

Myocardial infarction (MI) is a chronic cardiovascular disease. This study aims to discern potentially angiogenesis- and epithelial mesenchymal transition (EMT)-related genes as biomarkers for MI diagnosis through bioinformatics.

Methods

All datasets and angiogenesis- and EMT-related genes were collected from the public database. The differentially expressed genes (DEGs) of MI and MI-related genes were acquired. DEGs, MI-related genes, and angiogenesis- and EMT-related genes were intersected to obtain hub genes. Functional enrichment, immune microenvironment, and transcription factors (TFs)-hub genes regulatory network analysis were performed. The diagnostic markers and models were developed and validated. Drug prediction and molecular docking were performed. Finally, diagnostic markers expressions were validated using RT-qPCR.

Results

A total of 224 angiogenesis- and EMT-related genes, 2,897 DEGs, 1,217 MI-related genes, and 9 hub genes were acquired. The immune infiltration levels of plasma cells, T cells CD4 memory activated, monocytes, macrophages M0, mast cells resting, and neutrophils were higher in patients with MI. LRPAP1, COLGALT1, QSOX1, THBD, VCAN, PLOD1, and PLAUR as the diagnostic markers were identified and used to construct diagnostic models, which can distinguish MI from controls well. Then, 9 drugs were screened, and the binding energies ranged from -7.08 to -5.21 kcal/mol. RT-qPCR results showed that the expression of LRPAP1, PLAUR, and PLOD1 was significantly increased in the MI group.

Conclusion

The 7 diagnostic markers may play potential roles in MI and could contribute to improved future diagnostics.

Effects and mechanisms of the myocardial microenvironment on cardiomyocyte proliferation and regeneration

The adult mammalian cardiomyocyte has a limited capacity for self-renewal, which leads to the irreversible heart dysfunction and poses a significant threat to myocardial infarction patients. In the past decades, research efforts have been predominantly concentrated on the cardiomyocyte proliferation and heart regeneration. However, the heart is a complex organ that comprises not only cardiomyocytes but also numerous noncardiomyocyte cells, all playing integral roles in maintaining cardiac function. In addition, cardiomyocytes are exposed to a dynamically changing physical environment that includes oxygen saturation and mechanical forces. Recently, a growing number of studies on myocardial microenvironment in cardiomyocyte proliferation and heart regeneration is ongoing. In this review, we provide an overview of recent advances in myocardial microenvironment, which plays an important role in cardiomyocyte proliferation and heart regeneration.

Tudor-SN promotes cardiomyocyte proliferation and neonatal heart regeneration through regulating the phosphorylation of YAP

BACKGROUND

The neonatal mammalian heart exhibits considerable regenerative potential following injury through cardiomyocyte proliferation, whereas mature cardiomyocytes withdraw from the cell cycle and lose regenerative capacities. Therefore, investigating the mechanisms underlying neonatal cardiomyocyte proliferation and regeneration is crucial for unlocking the regenerative potential of adult mammalian heart to repair damage and restore contractile function following myocardial injury.

METHODS

The Tudor staphylococcal nuclease (Tudor-SN) transgenic (TG) or cardiomyocyte-specific knockout mice (Myh6-Tudor-SN -/-) were generated to investigate the role of Tudor-SN in cardiomyocyte proliferation and heart regeneration following apical resection (AR) surgery. Primary cardiomyocytes isolated from neonatal mice were used to assess the influence of Tudor-SN on cardiomyocyte proliferation in vitro. Affinity purification and mass spectrometry were employed to elucidate the underlying mechanism. H9c2 cells and mouse myocardia with either overexpression or knockout of Tudor-SN were utilized to assess its impact on the phosphorylation of Yes-associated protein (YAP), both in vitro and in vivo.

RESULTS

We previously identified Tudor-SN as a cell cycle regulator that is highly expressed in neonatal mice myocardia but downregulated in adults. Our present study demonstrates that sustained expression of Tudor-SN promotes and prolongs the proliferation of neonatal cardiomyocytes, improves cardiac function, and enhances the ability to repair the left ventricular apex resection in neonatal mice. Consistently, cardiomyocyte-specific knockout of Tudor-SN impairs cardiac function and retards recovery after injury. Tudor-SN associates with YAP, which plays important roles in heart development and regeneration, inhibiting phosphorylation at Ser 127 and Ser 397 residues by preventing the association between Large Tumor Suppressor 1 (LATS1) and YAP, correspondingly maintaining stability and promoting nuclear translocation of YAP to enhance the proliferation-related genes transcription.

CONCLUSION

Tudor-SN regulates the phosphorylation of YAP, consequently enhancing and prolonging neonatal cardiomyocyte proliferation under physiological conditions and promoting neonatal heart regeneration after injury.

Triiodothyronine induces a proinflammatory monocyte/macrophage profile and impedes cardiac regeneration

Neonatal mouse hearts can regenerate post-injury, unlike adult hearts that form fibrotic scars. The mechanism of thyroid hormone signaling in cardiac regeneration warrants further study. We found that triiodothyronine impairs cardiomyocyte proliferation and heart regeneration in neonatal mice after apical resection. Single-cell RNA-Sequencing on cardiac CD45-positive leukocytes revealed a pro-inflammatory phenotype in monocytes/macrophages after triiodothyronine treatment. Furthermore, we observed that cardiomyocyte proliferation was inhibited by medium from triiodothyronine-treated macrophages, while triiodothyronine itself had no direct effect on the cardiomyocytes in vitro. Our study unveils a novel role of triiodothyronine in mediating the inflammatory response that hinders heart regeneration.

Targeting cardiomyocyte cell cycle regulation in heart failure

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

Activation of CD14+ Monocytes via the IFN-γ Signaling Pathway Is Associated with Immune-Related Adverse Events in Hepatocellular Carcinoma Patients Receiving PD-1 Inhibition Combination Therapy

(1) Background: Immune-related adverse events (irAEs) are a series of unique organ-specific inflammatory toxicities observed in patients with hepatocellular carcinoma (HCC) undergoing PD-1 inhibition combination therapy. The specific underlying mechanisms remain unclear. (2) Methods: We recruited 71 patients with HCC undergoing PD-1 inhibition combination therapy. These patients were then divided into two groups based on irAE occurrence: 34 had irAEs and 37 did not. Using Olink proteomics, we analyzed the aberrant inflammation-related proteins (IRPs) in these patient groups. For single-cell RNA sequencing (scRNA-seq) analysis, we collected peripheral blood mononuclear cells (PBMCs) from two representative patients at the pretreatment, irAE occurrence, and resolution stages. (3) Results: Our study revealed distinct plasma protein signatures in HCC patients experiencing irAEs after PD-1 inhibition combination therapy. We clarified the relationship between monocyte activation and irAEs, identified a strongly associated CD14-MC-CCL3 monocyte subset, and explored the role of the IFN-γ signaling pathway in monocyte activation during irAEs. (4) Conclusions: The activation of monocytes induced by the IFN-γ signaling pathway is an important mechanism underlying the occurrence of irAEs in HCC patients receiving PD-1 inhibition combination therapy.

Epigenetic determinants and non-myocardial signaling pathways contributing to heart growth and regeneration

Congenital heart disease is the most common birth defect worldwide. Defective cardiac myogenesis is either a major presentation or associated with many types of congenital heart disease. Non-myocardial tissues, including endocardium and epicardium, function as a supporting hub for myocardial growth and maturation during heart development. Recent research findings suggest an emerging role of epigenetics in nonmyocytes supporting myocardial development. Understanding how growth signaling pathways in non-myocardial tissues are regulated by epigenetic factors will likely identify new disease mechanisms for congenital heart diseases and shed lights for novel therapeutic strategies for heart regeneration.

Deconvoluting nitric oxide-protein interactions with spatially resolved multiplex imaging

Simultaneous imaging of nitric oxide (NO) and its proximal proteins should facilitate the deconvolution of NO-protein interactions. While immunostaining is a primary assay to localize proteins in non-genetically manipulated samples, NO imaging probes with immunostaining-compatible signals remain unexplored. Herein, probe NOP-1 was developed with an NO-triggered proximal protein labeling capacity and fluorogenic signals. The trick is to fuse the native chemical ligation of acyl benzotriazole with the protein-conjugation-induced fluorogenic response of Si-rhodamine fluorophore. NOP-1 predominantly existed in the non-fluorescent spirocyclic form. Yet, its acyl o-phenylenediamine moiety was readily activated by NO into acyl benzotriazole to conjugate proximal proteins, providing a fluorogenic response and translating the transient cellular NO signal into a permanent stain compatible with immunostaining. NOP-1 was utilized to investigate NO signaling in hypoglycemia-induced neurological injury, providing direct evidence of NO-induced apoptosis during hypoglycemia. Mechanistically, multiplex imaging revealed the overlap of cellular NOP-1 fluorescence with immunofluorescence for α-tubulin and NO2-Tyr. Importantly, α-tubulin was resolved from NOP-1 labeled proteins. These results suggest that NO played a role in hypoglycemia-induced apoptosis, at least in part, through nitrating α-tubulin. This study fills a crucial gap in current imaging probes, providing a valuable tool for unraveling the complexities of NO signaling in biological processes.

Cardiomyocyte senescence and the potential therapeutic role of senolytics in the heart

Cellular senescence in cardiomyocytes, characterized by cell cycle arrest, resistance to apoptosis, and the senescence-associated secretory phenotype, occurs during aging and in response to various stresses, such as hypoxia/reoxygenation, ischemia/reperfusion, myocardial infarction (MI), pressure overload, doxorubicin treatment, angiotensin II, diabetes, and thoracic irradiation. Senescence in the heart has both beneficial and detrimental effects. Premature senescence of myofibroblasts has salutary effects during MI and pressure overload. On the other hand, persistent activation of senescence in cardiomyocytes precipitates cardiac dysfunction and adverse remodeling through paracrine mechanisms during MI, myocardial ischemia/reperfusion, aging, and doxorubicin-induced cardiomyopathy. Given the adverse roles of senescence in many conditions, specific removal of senescent cells, i.e., senolysis, is of great interest. Senolysis can be achieved using senolytic drugs (such as Navitoclax, Dasatinib, and Quercetin), pharmacogenetic approaches (including INK-ATTAC and AP20187, p16-3MR and Ganciclovir, p16 ablation, and p16-LOX-ATTAC and Cre), and immunogenetic interventions (CAR T cells or senolytic vaccination). In order to enhance the specificity and decrease the off-target effects of senolytic approaches, investigation into the mechanisms through which cardiomyocytes develop and/or maintain the senescent state is needed.

Extracellular Matrix Interactome in Modulating Vascular Homeostasis and Remodeling

The ECM (extracellular matrix) is a major component of the vascular microenvironment that modulates vascular homeostasis. ECM proteins include collagens, elastin, noncollagen glycoproteins, and proteoglycans/glycosaminoglycans. ECM proteins form complex matrix structures, such as the basal lamina and collagen and elastin fibers, through direct interactions or lysyl oxidase-mediated cross-linking. Moreover, ECM proteins directly interact with cell surface receptors or extracellular secreted molecules, exerting matricellular and matricrine modulation, respectively. In addition, extracellular proteases degrade or cleave matrix proteins, thereby contributing to ECM turnover. These interactions constitute the ECM interactome network, which is essential for maintaining vascular homeostasis and preventing pathological vascular remodeling. The current review mainly focuses on endogenous matrix proteins in blood vessels and discusses the interaction of these matrix proteins with other ECM proteins, cell surface receptors, cytokines, complement and coagulation factors, and their potential roles in maintaining vascular homeostasis and preventing pathological remodeling.

Single-cell RNA sequencing analysis identifies one subpopulation of endothelial cells that proliferates and another that undergoes the endothelial-mesenchymal transition in regenerating pig hearts

Background: In our previous work, we demonstrated that when newborn pigs undergo apical resection (AR) on postnatal day 1 (P1), the animals' hearts were completely recover from a myocardial infarction (MI) that occurs on postnatal day 28 (P28); single-nucleus RNA sequencing (snRNAseq) data suggested that this recovery was achieved by regeneration of pig cardiomyocyte subpopulations in response to MI. However, coronary vasculature also has a key role in promoting cardiac repair. Method: Thus, in this report, we used autoencoder algorithms to analyze snRNAseq data from endothelial cells (ECs) in the hearts of the same animals. Main results: Our results identified five EC clusters, three composed of vascular ECs (VEC1-3) and two containing lymphatic ECs (LEC1-2). Cells from VEC1 expressed elevated levels of each of five cell-cyclespecific markers (Aurora Kinase B [AURKB], Marker of Proliferation Ki-67 [MKI67], Inner Centromere Protein [INCENP], Survivin [BIRC5], and Borealin [CDCA8]), as well as a number of transcription factors that promote EC proliferation, while (VEC3 was enriched for genes that regulate intercellular junctions, participate in transforming growth factor β (TGFβ), bone morphogenic protein (BMP) signaling, and promote the endothelial mesenchymal transition (EndMT). The remaining VEC2 did not appear to participate directly in the angiogenic response to MI, but trajectory analyses indicated that it may serve as a reservoir for the generation of VEC1 and VEC3 ECs in response to MI. Notably, only the VEC3 cluster was more populous in regenerating (i.e., ARP1MIP28) than non-regenerating (i.e., MIP28) hearts during the 1-week period after MI induction, which suggests that further investigation of the VEC3 cluster could identify new targets for improving myocardial recovery after MI. Histological analysis of KI67 and EndMT marker PDGFRA demonstrated that while the expression of proliferation of endothelial cells was not significantly different, expression of EndMT markers was significantly higher among endothelial cells of ARP1MIP28 hearts compared to MIP28 hearts, which were consistent with snRNAseq analysis of clusters VEC1 and VEC3. Furthermore, upregulated secrete genes by VEC3 may promote cardiomyocyte proliferation via the Pi3k-Akt and ERBB signaling pathways, which directly contribute to cardiac muscle regeneration. Conclusion: In regenerative heart, endothelial cells may express EndMT markers, and this process could contribute to regeneration via a endothelial-cardiomyocyte crosstalk that supports cardiomyocyte proliferation.