Specific ablation of CD4+ T-cells promotes heart regeneration in juvenile mice

A cardiac fibroblast-enriched micropeptide regulates inflammation in ischemia/reperfusion injury

Inflammation is a critical pathological process in myocardial infarction. Although immunosuppressive therapies can mitigate inflammatory responses and improve outcomes in myocardial infarction, they also increase the risk of infections. Identifying novel regulators of local cardiac inflammation could provide safer therapeutic targets for myocardial ischemia/reperfusion injury. In this study, we identified a previously uncharacterized micropeptide, which we named Inflammation Associated MicroPeptide (IAMP). IAMP is predominantly expressed in cardiac fibroblasts, and its expression is closely associated with cardiac inflammation. Downregulation of IAMP promotes, whereas its overexpression prevents, the transformation of cardiac fibroblasts into a more inflammatory phenotype under stressed/stimulated conditions, as evidenced by changes in the expression and secretion of proinflammatory cytokines. Consequently, loss of IAMP function leads to uncontrolled inflammation and worsens cardiac injury following ischemia/reperfusion surgery. Mechanistically, IAMP promotes the degradation of HIF-1α by interacting with its stabilizing partner HSP90 and, thus, suppresses the transcription of proinflammatory genes downstream of HIF-1α. This study underscores the significance of fibroblast-mediated inflammation in cardiac ischemia/reperfusion injury and highlights the therapeutic potential of targeting micropeptides for myocardial infarction.

Immune-mediated cardiac development and regeneration

The complex interplay between the immune and cardiovascular systems during development, homeostasis and regeneration represents a rapidly evolving field in cardiac biology. Single cell technologies, spatial mapping and computational analysis have revolutionised our understanding of the diversity and functional specialisation of immune cells within the heart. From the earliest stages of cardiogenesis, where primitive macrophages guide heart tube formation, to the complex choreography of inflammation and its resolution during regeneration, immune cells emerge as central orchestrators of cardiac fate. Translating these fundamental insights into clinical applications represents a major challenge and opportunity for the field. In this Review, we decode the immunological blueprint of heart development and regeneration to transform cardiovascular disease treatment and unlock the regenerative capacity of the human heart.

Anti-inflammatory phenotypes of immune cells after myocardial infarction and prospects of therapeutic strategy

Often causing negative cardiac remodeling and heart failure, a major threat to human life and health, myocardial infarction (MI) is a cardiovascular disease with a high morbidity and fatality rate worldwide. Maintaining ordinary heart function depends significantly on the immune system. Necrotic cardiomyocyte signals promote specific immunity and activate general immunity as the disease progresses in MI. Complex immune cells play a key role in all stages of MI progression by removing necrotic cardiomyocytes and tissue and promoting the healing of damaged tissue cells. Immune cells can help to regrow injured heart muscle as well as enable both inflammation and cardiomyocyte death. Immune cells are essential elements that help the immune system carry out its protective function. There are two types of immunity: nonspecific immunity and specific immunity. Developed throughout the long-term evolution of species, nonspecific immunity (including macrophages, myeloid-derived suppressor cells MDSC, natural killer cells NK, neutrophils, and dendritic cells DC) offers immediate and conservative host defense that might destroy healthy tissues because of its nonspecific nature. Precisely acquired immunity, specific immunity helps humoral and cellular immunity mediated through B and T cells correspondingly. These findings offer crucial information needed for the creation of effective immunomodulatory treatment, as discussed in this article.

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.

Complex regulation of cardiac fibrosis: insights from immune cells and signaling pathways

Cardiac fibrosis is a physiological process that involves the formation of scar tissue in the heart in response to injury or damage. This process is initially a protective measure characterized by enhanced fibroblasts, which are responsible for producing extracellular matrix proteins that provide structural support to the heart. However, when fibrosis becomes excessive, it can lead to adverse outcomes, including increasing tissue stiffness and impaired cardiac function, which can ultimately result in heart failure with a poor prognosis. While fibroblasts are the primary cells involved in cardiac fibrosis, immune cells have also been found to play a vital role in its progression. Recent research has shown that immune cells exert multifaceted effects besides regulation of inflammatory response. Advanced research techniques such as single-cell sequencing and multiomics have provided insights into the specific subsets of immune cells involved in fibrosis and the complex regulation of the process. Targeted immunotherapy against fibrosis is gaining traction as a potential treatment option, but it is still unclear how immune cells achieve this regulation and whether distinct subsets are involved in different roles. To better understand the role of immune cells in cardiac fibrosis, it is essential to examine the classical signaling pathways that are closely related to fibrosis formation. We have also focused on the unique properties of diverse immune cells in cardiac fibrosis and their specific intercommunications. Therefore, this review will delve into the plasticity and heterogeneity of immune cells and their specific roles in cardiac fibrosis, which propose insights to facilitate the development of anti-fibrosis therapeutic strategies.

Clinical application and immune infiltration landscape of stemness-related genes in heart failure

BACKGROUND

Heart failure (HF) is the leading cause of morbidity and mortality worldwide. Stemness refers to the self-renewal and differentiation ability of cells. However, little is known about the heart's stemness properties. Thus, the current study aims to identify putative stemness-related biomarkers to construct a viable prediction model of HF and characterize the immune infiltration features of HF.

METHODS

HF datasets from the Gene Expression Omnibus (GEO) database were adopted as the training and validation cohorts while stemness-related genes were obtained from GeneCards and previously published papers. Feature selection was performed using two machine learning algorithms. Nomogram models were then constructed to predict HF risk based on the selected key genes. Moreover, the biological functions of the key genes were evaluated using Gene Ontology (GO) and Kyoto Encyclopedia of Genes Genomes (KEGG) pathway analyses, and gene set variation analysis (GSVA) and enrichment analysis (GSEA) were performed between the high- and low-risk groups. The immune infiltration landscape in HF was investigated, and the interaction network of key genes was analysed to predict potential targets and molecular mechanisms.

RESULTS

Seven key genes, namely SMOC2, LUM, FNDC1, SCUBE2, CD163, BLM and S1PR3, were included in the proposed nomogram. This nomogram showed good predictive performance for HF diagnosis in the training and validation sets. GO and KEGG analyses revealed that the key genes were primarily associated with ageing, inflammatory processes and DNA oxidation. GSEA and GSVA identified various inflammatory and immune signalling pathways that were enriched between the high- and low-risk groups. The infiltration of 15 immune cell subsets suggests that adaptive immunity has an important role in HF.

CONCLUSIONS

Our study identified a clinically significant stemness-related signature for predicting HF risk, with the potential to improve early disease diagnosis, optimize risk stratification and provide new strategies for treating patients with HF.

Cardiomyocyte S1PR1 promotes cardiac regeneration via AKT/mTORC1 signaling pathway

Aims: Lower vertebrates and some neonatal mammals are known to possess the ability to regenerate cardiomyocyte and fully recover after heart injuries within a limited period. Understanding the molecular mechanisms of heart regeneration and exploring new ways to enhance cardiac regeneration hold significant promise for therapeutic intervention of heart failure. Sphingosine 1-phospahte receptor 1 (S1PR1) is highly expressed in cardiomyocytes and plays a crucial role in heart development and pathological cardiac remodeling. However, the effect of cardiomyocyte-expressing S1PR1 on heart regeneration has not yet been elucidated. This study aims to investigate the role of cardiomyocyte S1PR1 in cardiac regeneration following heart injuries. Methods and Results: We generated cardiomyocyte (CM)-specific S1pr1 knock-out mice and demonstrated that CM-specific S1pr1 loss-of-function severely reduced cardiomyocyte proliferation and inhibited heart regeneration following apex resection in neonatal mice. Conversely, AAV9-mediated CM-specific S1pr1 gain-of-function significantly enhanced cardiac regeneration. We identified that S1PR1 activated the AKT/mTORC1/CYCLIN D1 and BCL2 signaling pathways to promote cardiomyocyte proliferation and inhibit apoptosis. Moreover, CM-targeted gene delivery system via AAV9 to overexpress S1PR1 significantly increased cardiomyocyte proliferation and improved cardiac functions following myocardial infarction in adult mice, suggesting a potential method to enhance cardiac regeneration and improve cardiac function in the injured heart. Conclusions: This study demonstrates that CM-S1PR1 plays an essential role in cardiomyocyte proliferation and heart regeneration. This research provides a potential strategy by CM-targeted S1PR1 overexpression as a new therapeutic intervention for heart failure.

Single-cell transcriptomic analysis of the senescent microenvironment in bone metastasis

Bone metastasis (BM) is a mortality-related event of late-stage cancer, with non-small cell lung cancer (NSCLC) being a common origin for BM. However, the detailed molecular profiling of the metastatic bone ecosystem is not fully understood, hindering the development of effective therapies for advanced patients. In this study, we examined the cellular heterogeneity between primary tumours and BM from tissues and peripheral blood by single-cell transcriptomic analysis, which was verified using multiplex immunofluorescence staining and public datasets. Our results demonstrate a senescent microenvironment in BM tissues of NSCLC. BM has a significantly higher infiltration of malignant cells with senescent characteristics relative to primary tumours, accompanied by aggravated metastatic properties. The endothelial-mesenchymal transition involved with SOX18 activation is related to the cellular senescence of vascular endothelial cells from BM. CD4Tstr cells, with pronounced stress and senescence states, are preferentially infiltrated in BM, indicating stress-related dysfunction contributing to the immunocompromised environment during tumour metastasis to bone. Moreover, we identify the SPP1 pathway-induced cellular crosstalk among T cells, vascular ECs and malignant cells in BM, which activates SOX18 and deteriorates patient survival. Our findings highlight the roles of cellular senescence in modulating the microenvironment of BM and implicate anti-senescence therapy for advanced NSCLC patients.

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.

The roles of Th cells in myocardial infarction

Myocardial infarction, commonly known as a heart attack, is a serious condition caused by the abrupt stoppage of blood flow to a part of the heart, leading to tissue damage. A significant aspect of this condition is reperfusion injury, which occurs when blood flow is restored but exacerbates the damage. This review first addresses the role of the innate immune system, including neutrophils and macrophages, in the cascade of events leading to myocardial infarction and reperfusion injury. It then shifts focus to the critical involvement of CD4+ T helper cells in these processes. These cells, pivotal in regulating the immune response and tissue recovery, include various subpopulations such as Th1, Th2, Th9, Th17, and Th22, each playing a unique role in the pathophysiology of myocardial infarction and reperfusion injury. These subpopulations contribute to the injury process through diverse mechanisms, with cytokines such as IFN-γ and IL-4 influencing the balance between tissue repair and injury exacerbation. Understanding the interplay between the innate immune system and CD4+ T helper cells, along with their cytokines, is crucial for developing targeted therapies to mitigate myocardial infarction and reperfusion injury, ultimately improving outcomes for cardiac patients.

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.

Structural, angiogenic, and immune responses influencing myocardial regeneration: a glimpse into the crucible

Complete cardiac regeneration remains an elusive therapeutic goal. Although much attention has been focused on cardiomyocyte proliferation, especially in neonatal mammals, recent investigations have unearthed mechanisms by which non-cardiomyocytes, such as endothelial cells, fibroblasts, macrophages, and other immune cells, play critical roles in modulating the regenerative capacity of the injured heart. The degree to which each of these cell types influence cardiac regeneration, however, remains incompletely understood. This review highlights the roles of these non-cardiomyocytes and their respective contributions to cardiac regeneration, with emphasis on natural heart regeneration after cardiac injury during the neonatal period.

The PD-1-PD-L1 pathway maintains an immunosuppressive environment essential for neonatal heart regeneration

The adult mouse heart responds to injury by scarring with consequent loss of contractile function, whereas the neonatal heart possesses the ability to regenerate. Activation of the immune system is among the first events upon tissue injury. It has been shown that immune response kinetics differ between regeneration and pathological remodeling, yet the underlying mechanisms of the distinct immune reactions during tissue healing remain unclear. Here we show that the immunomodulatory PD-1-PD-L1 pathway is highly active in regenerative neonatal hearts but rapidly silenced later in life. Deletion of the PD-1 receptor or inactivation of its ligand PD-L1 prevented regeneration of neonatal hearts after injury. Disruption of the pathway during neonatal cardiac injury led to increased inflammation and aberrant T cell activation, which ultimately impaired cardiac regeneration. Our findings reveal an immunomodulatory and cardioprotective role for the PD-1-PD-L1 pathway in heart regeneration and offer potential avenues for the control of adult tissue regeneration.

Single-cell RNA Sequencing (scRNA-seq): Advances and Challenges for Cardiovascular Diseases (CVDs)

Implementing Single-cell RNA sequencing (scRNA-seq) has significantly enhanced our comprehension of cardiovascular diseases (CVDs), providing new opportunities to strengthen the prevention of CVDs progression. Cardiovascular diseases continue to be the primary cause of death worldwide. Improving treatment strategies and patient risk assessment requires a deeper understanding of the fundamental mechanisms underlying these disorders. The advanced and widespread use of Single-cell RNA sequencing enables a comprehensive investigation of the complex cellular makeup of the heart, surpassing essential descriptive aspects. This enhances our understanding of disease causes and directs functional research. The significant advancement in understanding cellular phenotypes has enhanced the study of fundamental cardiovascular science. scRNA-seq enables the identification of discrete cellular subgroups, unveiling previously unknown cell types in the heart and vascular systems that may have relevance to different disease pathologies. Moreover, scRNA-seq has revealed significant heterogeneity in phenotypes among distinct cell subtypes. Finally, we will examine current and upcoming scRNA-seq studies about various aspects of the cardiovascular system, assessing their potential impact on our understanding of the cardiovascular system and offering insight into how these technologies may revolutionise the diagnosis and treatment of cardiac conditions.

Microbiota affects mitochondria and immune cell infiltrations via alternative polyadenylation during postnatal heart development

There is a growing body of evidence supporting the significant impact of microbiota on heart development. Alternative polyadenylation (APA) is a crucial mechanism for gene expression regulation and has been implicated in postnatal heart development. Nonetheless, whether microbiota can influence postnatal heart development through the regulation of APA remains unclear. Therefore, we conducted APA sequencing on heart tissues collected from specific pathogen-free (SPF) mice and germ-free (GF) mice at three different developmental stages: within the first 24 h after birth (P1), 7-day-old SPF mice, and 7-day-old GF mice. This approach allowed us to obtain a comprehensive genome-wide profile of APA sites in the heart tissue samples. In this study, we made a significant observation that GF mice exhibited noticeably longer 3' untranslated region (3' UTR) lengths. Furthermore, we confirmed significant alterations in the 3' UTR lengths of mitochondria-related genes, namely Rala, Timm13, and Uqcc3. Interestingly, the GF condition resulted in a marked decrease in mitochondrial cristae density and a reduction in the level of Tomm20 in postnatal hearts. Moreover, we discovered a connection between Rala and Src, which further implicated their association with other differentially expressed genes (DEGs). Notably, most of the DEGs were significantly downregulated in GF mice, with the exceptions being Thbs1 and Egr1. Importantly, the GF condition demonstrated a correlation with a lower infiltration of immune cells, whereby the levels of resting NK cells, Th17 cells, immature dendritic cells, and plasma cells in GF mice were comparable to those observed in P1 mice. Furthermore, we established significant correlations between these immune cells and Rala as well as the related DEGs. Our findings clearly indicated that microbiota plays a vital role in postnatal heart development by affecting APA switching, mitochondria and immune cell infiltrations.

Single-cell transcriptomics of Treg reveals hallmarks and trajectories of immunological aging

Age-related immunosenescence is characterized by progressive dysfunction of adaptive immune response and increased autoimmunity. Nevertheless, the impact of aging on CD4+ regulatory T cells that are master regulators of the immune system remains largely unclear. Here, we report cellular and molecular hallmarks of regulatory T cells derived from murine lymphoid and adipose tissues at 3, 18, and 24 mo of age, respectively, by analyzing their heterogeneity that displays dynamic changes in transcriptomic effector signatures at a single-cell resolution. Although the proportion of regulatory T cells among total Cd4+ T cells, as well as their expression levels of Foxp3, did not show any global change with time, we have identified 6 transcriptomically distinct clusters of regulatory T cells with cross-tissue conserved hallmarks of aging, including increased numbers of proinflammatory regulatory T cells, reduced precursor cells, increased immature and mature T follicular regulatory cells potentially supported by a metabolic switch from oxidative phosphorylation to glycolysis, a gradual loss of CD150hi regulatory T cells that support hematopoiesis, and increased adipose tissue-specific regulatory T cells that are associated with metabolic disease. To dissect the impact of immunosenescence on humoral immunity, we propose some potential mechanisms underlying T follicular regulatory cell-mediated dysfunction by interactome analysis on T follicular regulatory cells, T follicular helper cells, and B cells during aging. Lastly, spatiotemporal analysis further revealed trajectories of regulatory T-cell aging that demonstrate the most significant changes in marrow and adipose tissues that might contribute to the development of age-related immunosenescence and type 2 diabetes. Taken together, our findings could provide a better understanding of age-associated regulatory T-cell heterogeneity in lymphoid and adipose tissues, as well as regulatory T-cell hallmarks during progressive adaptation to aging that could be therapeutically targeted for rejuvenating the aging immune system in the future.

Cardiac Development at a Single-Cell Resolution

Mammalian cardiac development is a complex, multistage process. Though traditional lineage tracing studies have characterized the broad trajectories of cardiac progenitors, the advent and rapid optimization of single-cell RNA sequencing methods have yielded an ever-expanding toolkit for characterizing heterogeneous cell populations in the developing heart. Importantly, they have allowed for a robust profiling of the spatiotemporal transcriptomic landscape of the human and mouse heart, revealing the diversity of cardiac cells-myocyte and non-myocyte-over the course of development. These studies have yielded insights into novel cardiac progenitor populations, chamber-specific developmental signatures, the gene regulatory networks governing cardiac development, and, thus, the etiologies of congenital heart diseases. Furthermore, single-cell RNA sequencing has allowed for the exquisite characterization of distinct cardiac populations such as the hard-to-capture cardiac conduction system and the intracardiac immune population. Therefore, single-cell profiling has also resulted in new insights into the regulation of cardiac regeneration and injury repair. Single-cell multiomics approaches combining transcriptomics, genomics, and epigenomics may uncover an even more comprehensive atlas of human cardiac biology. Single-cell analyses of the developing and adult mammalian heart offer an unprecedented look into the fundamental mechanisms of cardiac development and the complex diseases that may arise from it.

Manganese Enhances the Osteogenic Effect of Silicon-Hydroxyapatite Nanowires by Targeting T Lymphocyte Polarization

Biomaterials encounter considerable challenges in extensive bone defect regeneration. The amelioration of outcomes may be attainable through the orchestrated modulation of both innate and adaptive immunity. Silicon-hydroxyapatite, for instance, which solely focuses on regulating innate immunity, is inadequate for long-term bone regeneration. Herein, extra manganese (Mn)-doping is utilized for enhancing the osteogenic ability by mediating adaptive immunity. Intriguingly, Mn-doping engenders heightened recruitment of CD4+ T cells to the bone defect site, concurrently manifesting escalated T helper (Th) 2 polarization and an abatement in Th1 cell polarization. This consequential immune milieu yields a collaborative elevation of interleukin 4, secreted by Th2 cells, coupled with attenuated interferon gamma, secreted by Th1 cells. This orchestrated interplay distinctly fosters the osteogenesis of bone marrow stromal cells and effectuates consequential regeneration of the mandibular bone defect. The modulatory mechanism of Th1/Th2 balance lies primarily in the indispensable role of manganese superoxide dismutase (MnSOD) and the phosphorylation of adenosine 5'-monophosphate-activated protein kinase (AMPK). In conclusion, this study highlights the transformative potential of Mn-doping in amplifying the osteogenic efficacy of silicon-hydroxyapatite nanowires by regulating T cell-mediated adaptive immunity via the MnSOD/AMPK pathway, thereby creating an anti-inflammatory milieu favorable for bone regeneration.

The Dynamic Landscapes of Circular RNAs in Axolotl, a Regenerative Medicine Model, with Implications for Early Phase of Limb Regeneration

Circular RNAs (circRNAs) are of relevance to regenerative medicine and play crucial roles in post-transcriptional and translational regulation of biological processes. circRNAs are a class of RNA molecules that are formed through a unique splicing process, resulting in a covalently closed-loop structure. Recent advancements in RNA sequencing technologies and specialized computational tools have facilitated the identification and functional characterization of circRNAs. These molecules are known to exhibit stability, developmental regulation, and specific expression patterns in different tissues and cell types across various organisms. However, our understanding of circRNA expression and putative function in model organisms for regeneration is limited. In this context, this study reports, for the first time, on the repertoire of circRNAs in axolotl, a widely used model organism for regeneration. We generated RNA-seq data from intact limb, wound, and blastema tissues of axolotl during limb regeneration. The analysis revealed the presence of 35,956 putative axolotl circRNAs, among which 5331 unique circRNAs exhibited orthology with human circRNAs. In silico data analysis underlined the potential roles of axolotl circRNAs in cell cycle, cell death, and cell senescence-related pathways during limb regeneration, suggesting the participation of circRNAs in regulation of diverse functions pertinent to regenerative medicine. These new observations help advance our understanding of the dynamic landscape of axolotl circRNAs, and by extension, inform future regenerative medicine research and innovation that harness this model organism.

Cardiac cellular diversity and functionality in cardiac repair by single-cell transcriptomics

Cardiac repair after myocardial infarction (MI) is orchestrated by multiple intrinsic mechanisms in the heart. Identifying cardiac cell heterogeneity and its effect on processes that mediate the ischemic myocardium repair may be key to developing novel therapeutics for preventing heart failure. With the rapid advancement of single-cell transcriptomics, recent studies have uncovered novel cardiac cell populations, dynamics of cell type composition, and molecular signatures of MI-associated cells at the single-cell level. In this review, we summarized the main findings during cardiac repair by applying single-cell transcriptomics, including endogenous myocardial regeneration, myocardial fibrosis, angiogenesis, and the immune microenvironment. Finally, we also discussed the integrative analysis of spatial multi-omics transcriptomics and single-cell transcriptomics. This review provided a basis for future studies to further advance the mechanism and development of therapeutic approaches for cardiac repair.

The origin, progress, and application of cell-based cardiac regeneration therapy

Cardiovascular disease (CVD) has become a severe threat to human health, with morbidity and mortality increasing yearly and gradually becoming younger. When the disease progresses to the middle and late stages, the loss of a large number of cardiomyocytes is irreparable to the body itself, and clinical drug therapy and mechanical support therapy cannot reverse the development of the disease. To explore the source of regenerated myocardium in model animals with the ability of heart regeneration through lineage tracing and other methods, and develop a new alternative therapy for CVDs, namely cell therapy. It directly compensates for cardiomyocyte proliferation through adult stem cell differentiation or cell reprogramming, which indirectly promotes cardiomyocyte proliferation through non-cardiomyocyte paracrine, to play a role in heart repair and regeneration. This review comprehensively summarizes the origin of newly generated cardiomyocytes, the research progress of cardiac regeneration based on cell therapy, the opportunity and development of cardiac regeneration in the context of bioengineering, and the clinical application of cell therapy in ischemic diseases.

Regeneration of the heart: from molecular mechanisms to clinical therapeutics

Heart injury such as myocardial infarction leads to cardiomyocyte loss, fibrotic tissue deposition, and scar formation. These changes reduce cardiac contractility, resulting in heart failure, which causes a huge public health burden. Military personnel, compared with civilians, is exposed to more stress, a risk factor for heart diseases, making cardiovascular health management and treatment innovation an important topic for military medicine. So far, medical intervention can slow down cardiovascular disease progression, but not yet induce heart regeneration. In the past decades, studies have focused on mechanisms underlying the regenerative capability of the heart and applicable approaches to reverse heart injury. Insights have emerged from studies in animal models and early clinical trials. Clinical interventions show the potential to reduce scar formation and enhance cardiomyocyte proliferation that counteracts the pathogenesis of heart disease. In this review, we discuss the signaling events controlling the regeneration of heart tissue and summarize current therapeutic approaches to promote heart regeneration after injury.

Depletion of Ly6G-Expressing Neutrophilic Cells Leads to Altered Peripheral T-Cell Homeostasis and Thymic Development in Neonatal Mice

Newborns and especially preterm infants are much more susceptible to infections than adults. Due to immature adaptive immunity, especially innate immune cells play an important role in a newborn's infection defense. Neonatal neutrophils exhibit profound differences in their functionality compared to neutrophils of adults. In particular, neonates possess a relevant population of suppressive neutrophils, which not only inhibit but also specifically modulate the function of T-cells. In this study, we investigated whether neonatal neutrophils are already involved in T-cell development in the thymus. For this purpose, we used a newly developed model of antibody-mediated immune cell depletion in which we administered a depleting antibody to pregnant and then lactating dams. Using this method, we were able to sufficiently deplete Ly6G-positive neutrophils in offspring. We demonstrated that the depletion of neutrophils in newborn mice resulted in altered peripheral T-cell homeostasis with a decreased CD4+/CD8+ T-cell ratio and decreased expression of CD62L. Neutrophil depletion even affected T-cell development in the thymus, with increased double positive thymocytes and a decreased CD4+/CD8+ single positive thymocyte ratio. Altogether, we demonstrated a previously unknown mechanism mediating neutrophils' immunomodulatory effects in newborns.

Single-cell and spatial transcriptomics: Advances in heart development and disease applications

Current transcriptomics technologies, including bulk RNA-seq, single-cell RNA sequencing (scRNA-seq), single-nucleus RNA-sequencing (snRNA-seq), and spatial transcriptomics (ST), provide novel insights into the spatial and temporal dynamics of gene expression during cardiac development and disease processes. Cardiac development is a highly sophisticated process involving the regulation of numerous key genes and signaling pathways at specific anatomical sites and developmental stages. Exploring the cell biological mechanisms involved in cardiogenesis also contributes to congenital heart disease research. Meanwhile, the severity of distinct heart diseases, such as coronary heart disease, valvular disease, cardiomyopathy, and heart failure, is associated with cellular transcriptional heterogeneity and phenotypic alteration. Integrating transcriptomic technologies in the clinical diagnosis and treatment of heart diseases will aid in advancing precision medicine. In this review, we summarize applications of scRNA-seq and ST in the cardiac field, including organogenesis and clinical diseases, and provide insights into the promise of single-cell and spatial transcriptomics in translational research and precision medicine.

Unlocking cardiomyocyte renewal potential for myocardial regeneration therapy

Cardiovascular disease remains the leading cause of mortality worldwide. Cardiomyocytes are irreversibly lost due to cardiac ischemia secondary to disease. This leads to increased cardiac fibrosis, poor contractility, cardiac hypertrophy, and subsequent life-threatening heart failure. Adult mammalian hearts exhibit notoriously low regenerative potential, further compounding the calamities described above. Neonatal mammalian hearts, on the other hand, display robust regenerative capacities. Lower vertebrates such as zebrafish and salamanders retain the ability to replenish lost cardiomyocytes throughout life. It is critical to understand the varying mechanisms that are responsible for these differences in cardiac regeneration across phylogeny and ontogeny. Adult mammalian cardiomyocyte cell cycle arrest and polyploidization have been proposed as major barriers to heart regeneration. Here we review current models about why adult mammalian cardiac regenerative potential is lost including changes in environmental oxygen levels, acquisition of endothermy, complex immune system development, and possible cancer risk tradeoffs. We also discuss recent progress and highlight conflicting reports pertaining to extrinsic and intrinsic signaling pathways that control cardiomyocyte proliferation and polyploidization in growth and regeneration. Uncovering the physiological brakes of cardiac regeneration could illuminate novel molecular targets and offer promising therapeutic strategies to treat heart failure.

The multifaceted nature of endogenous cardiac regeneration

Since the first evidence of cardiac regeneration was observed, almost 50 years ago, more studies have highlighted the endogenous regenerative abilities of several models following cardiac injury. In particular, analysis of cardiac regeneration in zebrafish and neonatal mice has uncovered numerous mechanisms involved in the regenerative process. It is now apparent that cardiac regeneration is not simply achieved by inducing cardiomyocytes to proliferate but requires a multifaceted response involving numerous different cell types, signaling pathways and mechanisms which must all work in harmony in order for regeneration to occur. In this review we will endeavor to highlight a variety of processes that have been identifed as being essential for cardiac regeneration.

Targeting immunoregulation for cardiac regeneration

Inducing endogenous cardiomyocyte proliferation and heart regeneration is a promising strategy to treat ischemic heart failure. The immune response has recently been considered critical in cardiac regeneration. Thus, targeting the immune response is a potent strategy to improve cardiac regeneration and repair after myocardial infarction. Here we reviewed the characteristics of the relationship between the postinjury immune response and heart regenerative capacity and summarized the latest studies focusing on inflammation and heart regeneration to identify potent targets of the immune response and strategies in the immune response to promote cardiac regeneration.

Murine neonatal cardiac B cells promote cardiomyocyte proliferation and heart regeneration

The irreversible loss of cardiomyocytes in the adult heart following cardiac injury leads to adverse cardiac remodeling and ventricular dysfunction. However, the role of B cells in cardiomyocyte proliferation and heart regeneration has not been clarified. Here, we found that the neonatal mice with B cell depletion showed markedly reduced cardiomyocyte proliferation, leading to cardiac dysfunction, fibrosis scar formation, and the complete failure of heart regeneration after apical resection. B cell depletion also significantly impaired heart regeneration and cardiac function in neonatal mice following myocardial infarction (MI). However, B cell depletion in adult mice suppressed tissue inflammation, inhibited myocardial fibrosis, and improved cardiac function after MI. Interestingly, B cell depletion partially restricted cardiomyocyte proliferation in adult mice post-MI. Single-cell RNA sequencing showed that cardiac B cells possessed a more powerful ability to inhibit inflammatory responses and enhance angiogenesis in the postnatal day 1 (P1) mice compared with P7 and adult mice. Besides, the proportion of cardioprotective B cell clusters with high expression levels of S100a6 (S100 calcium-binding protein A6) and S100a4 (S100 calcium-binding protein A4) was greatly decreased in adult heart tissues compared with neonatal mice after cardiac damage. Thus, our study discovers that cardiac B cells in neonatal mice are required for cardiomyocyte proliferation and heart regeneration, while adult B cells promote inflammation and impair cardiac function after myocardial injury.

The role of major immune cells in myocardial infarction

Myocardial infarction (MI) is a cardiovascular disease (CVD) with high morbidity and mortality worldwide, often leading to adverse cardiac remodeling and heart failure, which is a serious threat to human life and health. The immune system makes an important contribution to the maintenance of normal cardiac function. In the disease process of MI, necrotic cardiomyocytes release signals that activate nonspecific immunity and trigger the action of specific immunity. Complex immune cells play an important role in all stages of MI progression by removing necrotic cardiomyocytes and tissue and promoting the healing of damaged tissue cells. With the development of biomaterials, cardiac patches have become an emerging method of repairing MI, and the development of engineered cardiac patches through the construction of multiple animal models of MI can help treat MI. This review introduces immune cells involved in the development of MI, summarizes the commonly used animal models of MI and the newly developed cardiac patch, so as to provide scientific reference for the accurate diagnosis and effective treatment of MI.

Targeting regulatory T cells for cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of death and disability worldwide. The CVDs are accompanied by inflammatory progression, resulting in innate and adaptive immune responses. Regulatory T cells (Tregs) have an immunosuppressive function and are one of the subsets of CD4⁺T cells that play a crucial role in inflammatory diseases. Whether using Tregs as a biomarker for CVDs or targeting Tregs to exert cardioprotective functions by regulating immune balance, suppressing inflammation, suppressing cardiac and vascular remodeling, mediating immune tolerance, and promoting cardiac regeneration in the treatment of CVDs has become an emerging research focus. However, Tregs have plasticity, and this plastic Tregs lose immunosuppressive function and produce toxic effects on target organs in some diseases. This review aims to provide an overview of Tregs' role and related mechanisms in CVDs, and reports on the research of plasticity Tregs in CVDs, to lay a foundation for further studies targeting Tregs in the prevention and treatment of CVDs.

Adult T-cells impair neonatal cardiac regeneration

AIMS

Newborn mice and humans display transient cardiac regenerative potential that rapidly declines postnatally. Patients who survive a myocardial infarction (MI) often develop chronic heart failure due to the heart's poor regeneration capacity. We hypothesized that the cardiac 'regenerative-to-scarring' transition might be driven by the perinatal shifts observed in the circulating T-cell compartment.

METHODS AND RESULTS

Post-MI immune responses were characterized in 1- (P1) vs. 7-day-old (P7) mice subjected to left anterior descending artery ligation. Myocardial infarction induced robust early inflammatory responses (36 h post-MI) in both age groups, but neonatal hearts exhibited rapid resolution of inflammation and full functional recovery. The perinatal loss of myocardial regenerative capacity was paralleled by a baseline increase in αβ-T cell (CD4+ and CD8+) numbers. Strikingly, P1-infarcted mice reconstituted with adult T-cells shifted to an adult-like healing phenotype, marked by irreversible cardiac functional impairment and increased fibrosis. Infarcted neonatal mice harbouring adult T-cells also had more monocyte-derived macrophage recruitment, as typically seen in adults. At the transcriptome level, infarcted P1 hearts that received isolated adult T-cells showed enriched gene sets linked to fibrosis, inflammation, and interferon-gamma (IFN-γ) signalling. In contrast, newborn mice that received isolated Ifng-/- adult T-cells prior to MI displayed a regenerative phenotype that resembled that of its age-matched untreated controls.

CONCLUSION

Physiological T-cell development or adoptive transfer of adult IFN-γ-producing T-cells into neonates contributed to impaired cardiac regeneration and promoted irreversible structural and functional cardiac damage. These findings reveal a trade-off between myocardial regenerative potential and the development of T-cell competence.

Leukocyte-Mediated Cardiac Repair after Myocardial Infarction in Non-Regenerative vs. Regenerative Systems

Innate and adaptive leukocytes rapidly mobilize to ischemic tissues after myocardial infarction in response to damage signals released from necrotic cells. Leukocytes play important roles in cardiac repair and regeneration such as inflammation initiation and resolution; the removal of dead cells and debris; the deposition of the extracellular matrix and granulation tissue; supporting angiogenesis and cardiomyocyte proliferation; and fibrotic scar generation and resolution. By organizing and comparing the present knowledge of leukocyte recruitment and function after cardiac injury in non-regenerative to regenerative systems, we propose that the leukocyte response to cardiac injury differs in non-regenerative adult mammals such as humans and mice in comparison to cardiac regenerative models such as neonatal mice and adult zebrafish. Specifically, extensive neutrophil, macrophage, and T-cell persistence contributes to a lengthy inflammatory period in non-regenerative systems for adverse cardiac remodeling and heart failure development, whereas their quick removal supports inflammation resolution in regenerative systems for new contractile tissue formation and coronary revascularization. Surprisingly, other leukocytes have not been examined in regenerative model systems. With this review, we aim to encourage the development of improved immune cell markers and tools in cardiac regenerative models for the identification of new immune targets in non-regenerative systems to develop new therapies.

A human pluripotent stem cell-based model of SARS-CoV-2 infection reveals an ACE2-independent inflammatory activation of vascular endothelial cells through TLR4

To date, the direct causative mechanism of SARS-CoV-2-induced endotheliitis remains unclear. Here, we report that human ECs barely express surface ACE2, and ECs express less intracellular ACE2 than non-ECs of the lungs. We ectopically expressed ACE2 in hESC-ECs to model SARS-CoV-2 infection. ACE2-deficient ECs are resistant to the infection but are more activated than ACE2-expressing ones. The virus directly induces endothelial activation by increasing monocyte adhesion, NO production, and enhanced phosphorylation of p38 mitogen-associated protein kinase (MAPK), NF-κB, and eNOS in ACE2-expressing and -deficient ECs. ACE2-deficient ECs respond to SARS-CoV-2 through TLR4 as treatment with its antagonist inhibits p38 MAPK/NF-κB/ interleukin-1β (IL-1β) activation after viral exposure. Genome-wide, single-cell RNA-seq analyses further confirm activation of the TLR4/MAPK14/RELA/IL-1β axis in circulating ECs of mild and severe COVID-19 patients. Circulating ECs could serve as biomarkers for indicating patients with endotheliitis. Together, our findings support a direct role for SARS-CoV-2 in mediating endothelial inflammation in an ACE2-dependent or -independent manner.

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The majority of adult and fetal ECs rarely express surface ACE2

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ACE2 is dispensable for SARS-CoV-2-mediated endothelial activation

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SARS-CoV-2 directly induces endothelial inflammation through TLR4 activation

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ScRNA-seq reveals TLR4 pathway activation in circulating ECs of COVID-19 patients

Loss of m6A methyltransferase METTL3 promotes heart regeneration and repair after myocardial injury

AIMS

N6-Methyladenosine (m6A), one of the important epigenitic modifications, is very commom in messenger RNAs (mRNAs) of eukaryotes, and has been involved in various diseases. However, the role of m6A modification in heart regeneration after injury remains unclear. The study was conducted to investigate whether targeting methyltransferase-like 3 (METTL3) could replenish the loss of cardiomyocytes (CMs) and improve cardiac function after myocardial infarction (MI).

METHODS AND RESULTS

METTL3 knockout mouse line was generated. A series of functional experiments were carried out and the molecular mechanism was further explored. We identified that METTL3, a methyltransferase of m6A methylation, is upregulated in mouse hearts after birth, which is the opposite of the changes in CMs proliferation. Furthermore, both METTL3 heterozygous knockout mice and administration of METTL3 shRNA adenovirus in mice exhibited CMs cell cycle re-entered, infract size decreased and cardiac function improved after MI. Mechanically, the silencing of METTL3 promoted CMs proliferation by reducing primary miR-143 (pri-miR-143) m6A modificaiton, thereby inhibiting the pri-miR-143 into mature miR-143-3p. Moreover, we found that miR-143-3p has targeting effects on Yap and Ctnnd1 so as to regulate CMs proliferation.

CONCLUSION

METTL3 deficiency contributes to heart regeneration after MI via METTL3-pri-miR-143-(miR-143)-Yap/Ctnnd1 axis. This study provides new insights into the significance of RNA m6A modification in heart regeneration.

Immunomodulatory bioactive glasses for tissue regeneration

The regulatory functions of the immune response in tissue healing, repair, and regeneration have been evidenced in the last decade. Immune cells play central roles in immune responses toward inducing favorable tissue regenerative processes. Modulating and controlling the immune cell responses (particularly macrophages) is an emerging approach to enhance tissue regeneration. Bioactive glasses (BGs) are multifunctional materials exhibiting osteogenic, angiogenic, and antibacterial properties, being increasingly investigated for various tissue regeneration scenarios, including bone regeneration and wound healing. On the other hand, the immunomodulatory effects of BGs in relation to regenerating tissues have started to be understood, and key knowledge is emerging. This is the first review article summarizing the immunomodulatory effects of BGs for tissue repair and regeneration. The immune response to BGs is firstly introduced, discussing potential mechanisms regarding the immunomodulation effects induced by BGs. Moreover, the interactions between the immune cells involved in the immunomodulation process and BGs (dissolution products) are summarized in detail. Particularly, a well-regulated and timely switch of macrophage phenotype from pro-inflammatory to anti-inflammatory is crucial to constructive tissue regeneration through modulating osteogenesis, osteoclastogenesis, and angiogenesis. The influence of BG characteristics on macrophage responses is discussed. We highlight the strategies employed to harness macrophage responses for enhanced tissue regeneration, including the incorporation of active ions, surface functionalization, and controlled release of immunomodulatory molecules. Finally, we conclude with our perspectives on future research challenges and directions in the emerging field of immunomodulatory BGs for tissue regeneration. STATEMENT OF SIGNIFICANCE: Immunomodulatory effects of bioactive glasses (BGs) in relation to bone regeneration and wound healing have started to be understood. We summarize those studies which have focused on immunomodulatory BGs for tissue regeneration. We first introduce the potential mechanisms of the immunomodulation effects induced by BGs. Interactions between the cells involved in immunomodulation processes and BGs (and their dissolution products, biologically active ions) are elaborated. We highlight the strategies employed to modulate macrophage responses for enhancing tissue regeneration, including incorporation of active ions, surface functionalization, and controlled release of immunomodulatory agents. This is the first review article summarizing and outlining the immunomodulatory effects of BGs for tissue regeneration. We anticipate that increasing research efforts will start to emerge in the area of immunomodulatory BGs.

Cardiac macrophage subsets differentially regulate lymphatic network remodeling during pressure overload

The lymphatic network of mammalian heart is an important regulator of interstitial fluid compartment and immune cell trafficking. We observed a remodeling of the cardiac lymphatic vessels and a reduced lymphatic efficiency during heart hypertrophy and failure induced by transverse aortic constriction. The lymphatic endothelial cell number of the failing hearts was positively correlated with cardiac function and with a subset of cardiac macrophages. This macrophage population distinguished by LYVE-1 (Lymphatic vessel endothelial hyaluronic acid receptor-1) and by resident macrophage gene expression signature, appeared not replenished by CCR2 mediated monocyte infiltration during pressure overload. Isolation of macrophage subpopulations showed that the LYVE-1 positive subset sustained in vitro and in vivo lymphangiogenesis through the expression of pro-lymphangiogenic factors. In contrast, the LYVE-1 negative macrophage subset strongly expressed MMP12 and decreased the endothelial LYVE-1 receptors in lymphatic endothelial cells, a feature of cardiac lymphatic remodeling in failing hearts. The treatment of mice with a CCR2 antagonist during pressure overload modified the proportion of macrophage subsets within the pathological heart and preserved lymphatic network from remodeling. This study reports unknown and differential functions of macrophage subpopulations in the regulation of cardiac lymphatic during pathological hypertrophy and may constitute a key mechanism underlying the progression of heart failure.

Postnatal Right Ventricular Developmental Track Changed by Volume Overload

Background Current right ventricular (RV) volume overload (VO) is established in adult mice. There are no neonatal mouse VO models and how VO affects postnatal RV development is largely unknown. Methods and Results Neonatal VO was induced by the fistula between abdominal aorta and inferior vena cava on postnatal day 7 and confirmed by abdominal ultrasound, echocardiography, and hematoxylin and eosin staining. The RNA-sequencing results showed that the top 5 most enriched gene ontology terms in normal RV development were energy derivation by oxidation of organic compounds, generation of precursor metabolites and energy, cellular respiration, striated muscle tissue development, and muscle organ development. Under the influence of VO, the top 5 most enriched gene ontology terms were angiogenesis, regulation of cytoskeleton organization, regulation of vasculature development, regulation of mitotic cell cycle, and regulation of the actin filament-based process. The top 3 enriched signaling pathways for the normal RV development were PPAR signaling pathway, citrate cycle (Tricarboxylic acid cycle), and fatty acid degradation. VO changed the signaling pathways to focal adhesion, the PI3K-Akt signaling pathway, and pathways in cancer. The RNA sequencing results were confirmed by the examination of the markers of metabolic and cardiac muscle maturation and the markers of cell cycle and angiogenesis. Conclusions A neonatal mouse VO model was successfully established, and the main processes of postnatal RV development were metabolic and cardiac muscle maturation, and VO changed that to angiogenesis and cell cycle regulation.

Genetic, Epigenetic, and Post-Transcriptional Basis of Divergent Tissue Regenerative Capacities Among Vertebrates

Regeneration is widespread across the animal kingdom but varies vastly across phylogeny and even ontogeny. Adult mammalian regeneration in most organs and appendages is limited, while vertebrates such as zebrafish and salamanders are able to regenerate various organs and body parts. Here, we focus on the regeneration of appendages, spinal cord, and heart - organs and body parts that are highly regenerative among fish and amphibian species but limited in adult mammals. We then describe potential genetic, epigenetic, and post-transcriptional similarities among these different forms of regeneration across vertebrates and discuss several theories for diminished regenerative capacity throughout evolution.

Understanding the Adult Mammalian Heart at Single-Cell RNA-Seq Resolution

During the last decade, extensive efforts have been made to comprehend cardiac cell genetic and functional diversity. Such knowledge allows for the definition of the cardiac cellular interactome as a reasonable strategy to increase our understanding of the normal and pathologic heart. Previous experimental approaches including cell lineage tracing, flow cytometry, and bulk RNA-Seq have often tackled the analysis of cardiac cell diversity as based on the assumption that cell types can be identified by the expression of a single gene. More recently, however, the emergence of single-cell RNA-Seq technology has led us to explore the diversity of individual cells, enabling the cardiovascular research community to redefine cardiac cell subpopulations and identify relevant ones, and even novel cell types, through their cell-specific transcriptomic signatures in an unbiased manner. These findings are changing our understanding of cell composition and in consequence the identification of potential therapeutic targets for different cardiac diseases. In this review, we provide an overview of the continuously changing cardiac cellular landscape, traveling from the pre-single-cell RNA-Seq times to the single cell-RNA-Seq revolution, and discuss the utilities and limitations of this technology.

Navigating the Crossroads of Cell Therapy and Natural Heart Regeneration

Cardiovascular disease remains the leading cause of death worldwide despite significant advances in our understanding of the disease and its treatment. Consequently, the therapeutic potential of cell therapy and induction of natural myocardial regeneration have stimulated a recent surge of research and clinical trials aimed at addressing this challenge. Recent developments in the field have shed new light on the intricate relationship between inflammation and natural regeneration, an intersection that warrants further investigation.

From Autonomy to Integration, From Integration to Dynamically Balanced Integrated Co-existence: Non-aging as the Third Stage of Development

Reversible senescence at the cellular level emerged together with tissue specialization in Metazoans. However, this reversibility (ability to permanently rejuvenate) through recapitulation of early stages of development, was originally a part of ontogenesis, since the pressure of integrativeness was not dominant. The complication of specialization in phylogenesis narrowed this "freedom of maneuver", gradually "truncating" remorphogenesis to local epimorphosis and further up to the complete disappearance of remorphogenesis from the ontogenesis repertoire. This evolutionary trend transformed cellular senescence into organismal aging and any recapitulation of autonomy into carcinogenesis. The crown of specialization, Homo sapiens, completed this post-unicellular stage of development, while in the genome all the potential for the next stage of development, which can be called the stage of balanced coexistence of autonomous and integrative dominants within a single whole. Here, completing the substantiation of the new section of developmental biology, we propose to call it Developmental Biogerontology.

Macrophage Polarization in Cardiac Tissue Repair Following Myocardial Infarction

Cardiovascular disease is the leading cause of mortality and morbidity around the globe, creating a substantial socio-economic burden as a result. Myocardial infarction is a significant contributor to the detrimental impact of cardiovascular disease. The death of cardiomyocytes following myocardial infarction causes an immune response which leads to further destruction of tissue, and subsequently, results in the formation of non-contractile scar tissue. Macrophages have been recognized as important regulators and participants of inflammation and fibrosis following myocardial infarction. Macrophages are generally classified into two distinct groups, namely, classically activated, or M1 macrophages, and alternatively activated, or M2 macrophages. The phenotypic profile of cardiac macrophages, however, is much more diverse and should not be reduced to these two subsets. In this review, we describe the phenotypes and functions of macrophages which are present in the healthy, as well as the infarcted heart, and analyze them with respect to M1 and M2 polarization states. Furthermore, we discuss therapeutic strategies which utilize macrophage polarization towards an anti-inflammatory or reparative phenotype for the treatment of myocardial infarction.

Vertebrate cardiac regeneration: evolutionary and developmental perspectives

Cardiac regeneration is an ancestral trait in vertebrates that is lost both as more recent vertebrate lineages evolved to adapt to new environments and selective pressures, and as members of certain species developmentally progress towards their adult forms. While higher vertebrates like humans and rodents resolve cardiac injury with permanent fibrosis and loss of cardiac output as adults, neonates of these same species can fully regenerate heart structure and function after injury - as can adult lower vertebrates like many teleost fish and urodele amphibians. Recent research has elucidated several broad factors hypothesized to contribute to this loss of cardiac regenerative potential both evolutionarily and developmentally: an oxygen-rich environment, vertebrate thermogenesis, a complex adaptive immune system, and cancer risk trade-offs. In this review, we discuss the evidence for these hypotheses as well as the cellular participators and molecular regulators by which they act to govern heart regeneration in vertebrates.

Increased Expression of Ephrins on Immune Cells of Patients with Relapsing Remitting Multiple Sclerosis Affects Oligodendrocyte Differentiation

The effect of the inflammatory response on regenerative processes in the brain is complex. This complexity is even greater when the cause of the tissue damage is an autoimmune response. Multiple sclerosis (MS) is an immune-mediated disease in which demyelination foci are formed in the central nervous system. The degree of repair through oligodendrocyte regeneration and remyelination is insufficient. Ephrins are membrane-bound ligands activating tyrosine kinase signaling proteins that are known to have an inhibitory effect on oligodendrocyte regeneration. In this study, we examined the expression of ephrins on immune cells of 43 patients with relapsing-remitting (RR) MS compared to 27 matched healthy controls (HC). We found an increased expression of ephrin-A2, -A3 and -B3, especially on T cell subpopulations. We also showed overexpression of ephrins on immune cells of patients with RR-MS that increases the forward signaling pathway and that expression of ephrins on immune cells has an inhibitory effect on the differentiation of oligodendrocyte precursor cells (OPCs) in vitro. Our study findings support the concept that the immune activity of T cells in patients with RR-MS has an inhibitory effect on the differentiation capacity of OPCs through the expression and forward signaling of ephrins.

Ex uno, plures-From One Tissue to Many Cells: A Review of Single-Cell Transcriptomics in Cardiovascular Biology

Recent technological advances have revolutionized the study of tissue biology and garnered a greater appreciation for tissue complexity. In order to understand cardiac development, heart tissue homeostasis, and the effects of stress and injury on the cardiovascular system, it is essential to characterize the heart at high cellular resolution. Single-cell profiling provides a more precise definition of tissue composition, cell differentiation trajectories, and intercellular communication, compared to classical bulk approaches. Here, we aim to review how recent single-cell multi-omic studies have changed our understanding of cell dynamics during cardiac development, and in the healthy and diseased adult myocardium.

Cardiac cell type-specific responses to injury and contributions to heart regeneration

Heart disease is the leading cause of mortality worldwide. Due to the limited proliferation rate of mature cardiomyocytes, adult mammalian hearts are unable to regenerate damaged cardiac muscle following injury. Instead, injured area is replaced by fibrotic scar tissue, which may lead to irreversible cardiac remodeling and organ failure. In contrast, adult zebrafish and neonatal mammalian possess the capacity for heart regeneration and have been widely used as experimental models. Recent studies have shown that multiple types of cells within the heart can respond to injury with the activation of distinct signaling pathways. Determining the specific contributions of each cell type is essential for our understanding of the regeneration network organization throughout the heart. In this review, we provide an overview of the distinct functions and coordinated cell behaviors of several major cell types including cardiomyocytes, endocardial cells, epicardial cells, fibroblasts, and immune cells. The topic focuses on their specific responses and cellular plasticity after injury, and potential therapeutic applications.