Cell atlas of the foetal human heart and implications for autoimmune-mediated congenital heart block

Neonatal lupus erythematosus: an acquired autoimmune disease to be taken seriously

AIM

This review aims to summarize the epidemiology, pathogenesis, clinical features, management, prognosis and regression of Neonatal lupus erythematosus (NLE) with a view to providing directions for standardized diagnosis, treatment and further research.

METHODS

We conducted a comprehensive literature review of NLE. NLE-related peer-reviewed papers were searched through PubMed/Medline were searched up to November 2024.

RESULTS

NLE is a rare acquired autoimmune disease (AD) linked to organ damage from maternal autoantibodies crossing the placenta to the foetus. However, not all mothers have ADs or associated antibodies. The disease involves autoantibody-induced inflammation, apoptosis, fibrosis, calcium channel dysregulation in cardiomyocytes, and increased interferon expression. NLE incidence shows no sex difference, but there is a differential distribution of clinical features across ethnic groups. The frequency of organ involvement in NLE patients is more common in the cutaneous and cardiac. NLE also affects the haematological and hepatobiliary systems, and some patients may experience neurological and endocrinological involvement. Steroids and immunoglobulins can aid in the recovery of some patients. Proper use of antimalarials during prenatal and gestational periods may prevent or improve the prognosis of patients with congenital heart block (CHB). Implantation of a pacemaker is effective in maintaining cardiac function in children with complete atrioventricular block. Symptoms associated with NLE may improve with antibody depletion, but some patients may experience sequelae such as irreversible CHB, neuropsychiatric disorders and developmental delays. Universal screening for autoantibodies to Sjögren syndrome A or B autoantigens should be offered to women of childbearing age experiencing desiccation syndrome. Antibody-positive individuals require appropriate reproductive counselling and advice, along with close foetal monitoring starting at 16 weeks of gestation and postnatal prognostic follow-up.

CONCLUSION

Epidemiologic investigations and clinical studies on NLE are currently inadequate, and large-scale epidemiologic investigations, prospective clinical studies, and basic research are needed in the future to improve the understanding of the disease and the standardization of its clinical management.

Transcriptomic signatures of atheroresistance in the human atrium and ventricle highlight potential candidates for targeted atherosclerosis therapeutics

Atherosclerosis risk is not uniform throughout the cardiovascular system. This study therefore aimed to compare the transcriptomes of atheroresistant human atrium and ventricle with atheroprone coronary arteries to identify transcriptomic signatures of atheroresistance and potential targets for atherosclerosis therapeutics. Using publicly available gene read counts, differentially expressed genes between the atrium, ventricle, and coronary artery were identified for each contrast and validated against the Swiss Institute of Bioinformatics' Bgee database. Over-representation analysis and active-subnetwork-oriented enrichment assessment then identified enriched terms, which were grouped into endothelial dysfunction-related processes. Potential biological significance was further explored with pathway analysis. Among 21474 features, 12656 differentially expressed genes were identified across the three contrasts and associated with 1215 enriched terms. There were 315 down-regulated and 133 up-regulated genes associated with endothelial dysfunction-related processes across the contrasts, including immune modulators, cell adhesion molecules, and lipid metabolism- and coagulation-related molecules. Differentially expressed genes were associated with six down-regulated Kyoto Encyclopedia of Genes and Genomes pathways, related to immune cell and associated endothelium functions. Review of regulated genes associated with endothelial dysfunction-related processes and included in these pathways, indicate immune cell-associated B cell scaffold protein with ankyrin repeats 1, as well as arterial endothelial cell-associated vascular cell adhesion molecule 1 and cadherin 5, as potential atherosclerosis targets.

Identification of a rare variant in TNNT3 responsible for familial dilated cardiomyopathy through whole-exome sequencing and in silico analysis

BACKGROUND

Dilated cardiomyopathy (DCM) is a prevalent etiology of heart failure, distinguished by the gradual and frequently irreversible myocardial muscle impairment. Roughly 50% of DCM occurrences stem from hereditary rare variants. In this study, our aim was to identify the genetic cause of DCM in a pedigree with several affected individuals across four generations.

METHODS

Whole exome sequencing was performed on the proband, with variants filtered and analyzed using in silico tools. Co-segregation analysis was conducted using Sanger sequencing. Protein structure modeling and protein-protein interaction evaluations were performed using AlphaFold3 and HADDOCK2.4, respectively.

RESULTS

We identified a missense rare variant in the TNNT3 gene, leading to the p.Glu125Gly alteration in the Troponin T3 (TNNT3). This rare variant is strongly implicated as the causative factor for DCM in the pedigree. Several key factors underscore its significance: the rare variant co-segregates with the disease in the pedigree, is absent in 850 control samples, alters a conserved amino acid, is predicted to detrimentally affect protein function, and results in structural changes.

CONCLUSIONS

Our findings suggest that TNNT3 rare variants can induce DCM by weakening the binding energy between TNNT3 and Tropomyosin (TPM), leading to functional deficiencies in muscle contraction, as demonstrated by our structural modeling and docking studies. Troponin T is essential for the proper contraction of striated muscles and is related to cardiac development. Bioinformatics investigations have elucidated the involvement of TNNT3-related pathways, notably the Striated Muscle Contraction pathway and Cardiac Conduction. TNNT3 resides within loci previously implicated in cardiomyopathy. Given its crucial role in muscle contractile function, rare variants in TNNT3 hold the potential to be a significant contributing factor in the pathogenesis of DCM. A wealth of literature substantiates the correlation between troponin T and cardiac disorders. Our findings further corroborate this association.

SCIG: Machine learning uncovers cell identity genes in single cells by genetic sequence codes

Deciphering cell identity genes is pivotal to understanding cell differentiation, development, and cell identity dysregulation involving diseases. Here, we introduce SCIG, a machine-learning method to uncover cell identity genes in single cells. In alignment with recent reports that cell identity genes (CIGs) are regulated with unique epigenetic signatures, we found CIGs exhibit distinctive genetic sequence signatures, e.g. unique enrichment patterns of cis-regulatory elements. Using these genetic sequence signatures, along with gene expression information from single-cell RNA-seq data, SCIG uncovers the identity genes of a cell without a need for comparison to other cells. CIG score defined by SCIG surpassed expression value in network analysis to reveal the master transcription factors (TFs) regulating cell identity. Applying SCIG to the human endothelial cell atlas revealed that the tissue microenvironment is a critical supplement to master TFs for cell identity refinement. SCIG is publicly available at https://doi.org/10.5281/zenodo.14726426  , offering a valuable tool for advancing cell differentiation, development, and regenerative medicine research.

Single-cell transcriptomic analysis deciphers the inflammatory microenvironment characterized by CXCL9+ fibroblasts and ACKR1+ endothelial cells in immune-related myocarditis

BACKGROUND

Immune-related myocarditis induced by immune checkpoint inhibitors (ICIs) is a rare immune-related adverse event (irAE) but is characterized by a high mortality rate. However, the specific pathological mechanisms underlying immune-related myocarditis remain largely unclear. In this study, we aimed to elucidate the inflammatory microenvironment within cardiac tissues affected by immune-related myocarditis at the single-cell level to identify potential therapeutic targets.

METHODS

We performed single-cell RNA sequencing (scRNA-seq) on an endomyocardial biopsy specimen obtained from a patient with pancreatic neuroendocrine carcinoma who developed immune-related myocarditis following treatment with ICIs. Additionally, the scRNA-seq data of heart specimens from deceased donors without cardiovascular diseases were collected and applied as normal control. To validate our findings and assess their specificity to ICI-related pathology, we analyzed mouse scRNA-seq data, including controls, ICI-related myocarditis, viral myocarditis, and autoimmune myocarditis.

RESULTS

We found elevated proportions of lymphocytes, myeloid cells, and fibroblasts in the irAE group, suggesting an intensified inflammatory microenvironment in human immune-related myocarditis. Within the lymphocyte compartment, increased proportions of CD8 + T exhausted cells and CD8 + T proliferative cells were observed in the irAE group. The upregulated differentially expressed genes in myeloid cells in the irAE group were enriched in pro-inflammatory pathways, consistent with the observed metabolic shift from oxidative phosphorylation to glycolysis. CXCL9 + fibroblasts, characterized by the production of multiple pro-inflammatory cytokines and enriched in the JAK-STAT and TNFα signaling pathways, were predominantly found in the irAE group. Venous endothelial cells specifically expressing atypical chemokine receptor-1 (ACKR1) interacted with myeloid cells and CXCL9 + fibroblasts through the CXCL signaling pathway, facilitating chemokine transcytosis and leukocyte recruitment. Analysis of murine scRNA-seq data further supported these findings, revealing that exhausted CD8 + T cells and pro-inflammatory fibroblasts were uniquely enriched in ICI-related myocarditis, reflecting its distinct inflammatory microenvironment.

CONCLUSIONS

We elucidated the unique inflammatory microenvironment of immune-related myocarditis at the single-cell level. Our work revealed key cell subpopulations that were significantly implicated in inflammation, thus offering potential therapeutic targets.

Maternal Immune Activation: Implications for Congenital Heart Defects

Congenital heart defects (CHD) are the most common major birth defects and one of the leading causes of death from congenital defects after birth. CHD can arise in pregnancy from the combination of genetic and non-genetic factors. The maternal immune activation (MIA) hypothesis is widely implicated in embryonic neurodevelopmental abnormalities. MIA has been found to be associated with the development of asthma, diabetes mellitus, and other diseases in the offspring. Given the important role of cardiac immune cells and cytokines in embryonic heart development, it is hypothesized that MIA may play a significant role in embryonic heart development. This review aims to stimulate further investigation into the relationship between MIA and CHD and to highlight the gaps in the knowledge. It evaluates the impact of MIA on CHD in the context of pregnancy complications, immune-related diseases, infections, and environmental and lifestyle factors. The review outlines the mechanisms by which immune cells and their secretome indirectly regulate the immuno-microenvironment of the embryonic heart by influencing placental development. Furthermore, the inflammatory cytokines cross the placenta to induce related reactions including oxidative stress in the embryonic heart directly. This review delineates the role of MIA in CHD and underscores the impact of maternal factors, especially immune factors, as well as the embryonic cardiac immuno-microenvironment, on embryonic heart development. This review extends our understanding of the importance of MIA in the pathogenesis of CHD and provides important insights into prenatal prevention and treatment strategies for this congenital condition.

The future of cardiology: Integrating single-cell transcriptomics with multi-omics for enhanced cardiac disease insights

Recent advancements in single-cell transcriptome sequencing (scRNA-seq) have revolutionized our understanding of cellular heterogeneity in cardiovascular diseases, enabling the identification of novel therapeutic targets. This technology allows for high-resolution analysis of gene expression at the single-cell level, revealing the complex dynamics of human heart cell development and the diverse roles of cardiac cell types in health and disease. Despite its transformative potential, current applications of scRNA-seq face limitations, including challenges in data integration and the need for comprehensive multi-omic approaches to fully elucidate the mechanisms underlying cardiovascular pathologies. This review highlights the significant insights gained from scRNA-seq studies in the mammalian heart, emphasizing the importance of integrating spatial transcriptomics and other omics technologies to enhance our understanding of cardiac biology. Furthermore, it addresses the critical research gaps in the field, particularly in the context of personalized medicine and the need for improved methodologies to analyze rare cell populations. By exploring these challenges and opportunities, this review aims to pave the way for innovative diagnostic and therapeutic strategies that can ultimately improve outcomes for patients with cardiovascular diseases.

Neonatal lupus erythematosus presenting with congenital heart block: clinical characteristics and follow-up

OBJECTIVE

Congenital heart block (CHB) in patients with neonatal lupus erythematosus (NLE) is usually irreversible. Our study aimed to investigate the clinical characteristics and prognostic follow-up results of patients with NLE presenting with CHB and to provide a reference for the clinical treatment and management of such patients.

METHODS

Six patients with NLE and CHB at the Children's Hospital of Soochow University between January 1, 2011, and December 31, 2023, were retrospectively analyzed. Prenatal maternal data, clinical characteristics, laboratory investigations, treatments, and follow-ups were analyzed using descriptive statistics.

RESULTS

Six patients with NLE and CHB-four females, two males, and five preterm infants-were included. Three patients had degree III CHB, one had degree II CHB, and two had degree I CHB. The diagnostic gestational age for CHB was 23.6 ± 2.7 weeks. Four patients experienced varying degrees of bradycardia during the fetal period. Of the six pregnant mothers, three had systemic lupus erythematosus, one had Sjogren's syndrome, and one was positive for the anti-SSA/Ro autoantibody after the postpartum patient was seropositive. All pregnant mothers with autoimmune diseases were in remission and stable before delivery. One case of mildly active lupus in early pregnancy resolved after low-dose oral steroid hormone administration. All six patients with NLE-related manifestations, except CHB, showed improvement in systemic symptoms within 6 months. One patient was implanted with a pacemaker for exercise intolerance and complete atrioventricular block (CAVB) at the age of 1 year and 5 months and is now tolerating activity well without abnormal cardiac rhythms. One of the six patients had a global developmental delay, and two had a motor developmental delay.

CONCLUSIONS

Fetal echocardiography should be performed in high-risk pregnancies between 16 weeks of gestation and 1 month after birth. Patients with NLE and CHB are prone to varying degrees of growth retardation. Pacemaker implantation is an effective treatment for children with CAVB. Key Points • CHB in patients with NLE is usually irreversible. • Patients with NLE and CHB are prone to varying degrees of growth retardation. • Implantation of a pacemaker is an effective treatment for children with CAVB.

Cardiac Fibroblasts regulate myocardium and coronary vasculature development via the collagen signaling pathway

The fibroblast (FB), cardiomyocyte (CM), and vascular endothelial cell (Vas_EC) are the three major cell types in the heart, yet their relationships during development are largely unexplored. To address this gap, we employed RNA staining of the FB marker gene Col1a1 together with the CM marker gene Actn2 and the Vas_EC marker gene Cdh5 at different stages. This approach enabled us to discern the anatomical pattern of cardiac FBs and identify approximately one EC and four CMs directly interacting with each FB. Molecularly, through the analysis of single-cell mRNA sequencing (scRNA-seq) data, we unveiled collagen as the top signaling molecule derived from FBs influencing CM and Vas_EC development. Subsequently, we used a Pdgfra-CreER controlled diphtheria toxin A (DTA) system to ablate the FBs at different stages. We found that the ablation of FBs disrupted myocardium and vasculature development and led to embryonic heart defects. Using scRNA-seq, we further profiled the ablated hearts and identified molecular defects in their ventricular CMs and Vas_ECs compared to control hearts. Moreover, we identified a reduction of collagen in the ablated hearts and predicted collagen as the major signaling pathway regulating the differentially expressed genes in the ablated ventricular CMs. Finally, we performed both short-term and long-term fibroblast ablation at the neonatal stage. We found that short-term ablation caused a reduction in collagen and Vas_EC density, while long-term ablation may induce compensatory collagen expression without causing heart function reduction. In summary, our study has identified the function of fibroblasts in regulating myocardium and vasculature development and implicated an important role for the collagen pathway in this process.

Differential Regulation of Immune-Related Genes in the Developing Heart

In many congenital heart defects, it can be difficult to ascertain primary pathology from secondary consequences from altered flow through the developing heart. The molecular differences between the growing right and left ventricles (RV and LV, respectively) following the completion of septation and the impact of sex on these mechanisms have not been investigated. We analyzed RNA-seq data derived from twelve RV and LVs, one with Hypoplastic Left Heart Syndrome (HLHS), to compare the transcriptomic landscape between the ventricles during development. Differential gene expression analysis revealed a large proportion of genes unique to either the RV or LV as well as sex bias. Our GO enrichment and network analysis strategy highlighted the differential role of immune functions between the RV and LV in the developing heart. Comparatively, RNA-seq analysis of data from C57Bl6/J mice hearts collected at E14 resulted in the enrichment of similar processes related to T cells and leukocyte migration and activation. Differential gene expression analysis of an HLHS case highlighted significant downregulation of chromatin organization pathways and upregulation of genes involved in muscle organ development. This analysis also identified previously unreported upregulation of genes involved in IL-17 production pathways. In conclusion, differences exist between the gene expression profiles of RV versus LV with the expression of immune-related genes being significantly different between these two chambers. The pathogenesis of HLHS may involve alterations in the expression of chromatin and muscle gene organization as well as upregulation of the IL-17 response pathway.

Development and application of 3D cardiac tissues derived from human pluripotent stem cells

Recently human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have become an attractive platform to evaluate drug responses for cardiotoxicity testing and disease modeling. Moreover, three-dimensional (3D) cardiac models, such as engineered heart tissues (EHTs) developed by bioengineering approaches, and cardiac spheroids (CSs) formed by spherical aggregation of hPSC-CMs, have been established as useful tools for drug discovery and transplantation. These 3D models overcome many of the shortcomings of conventional 2D hPSC-CMs, such as immaturity of the cells. Cardiac organoids (COs), like other organs, have also been studied to reproduce structures that resemble a heart in vivo more closely and optimize various culture conditions. Heart-on-a-chip (HoC) developed by a microfluidic chip-based technology that enables real-time monitoring of contraction and electrical activity, provides multifaceted information that is essential for capturing natural tissue development in vivo. Recently, 3D experimental systems have been developed to study organ interactions in vitro. This review aims to discuss the developments and advancements of hPSC-CMs and 3D cardiac tissues.

Beyond the Heartbeat: Single-Cell Omics Redefining Cardiovascular Research

PURPOSE OF REVIEW

This review aims to explore recent advances in single-cell omics techniques as applied to various regions of the human heart, illuminating cellular diversity, regulatory networks, and disease mechanisms. We examine the contributions of single-cell transcriptomics, genomics, proteomics, epigenomics, and spatial transcriptomics in unraveling the complexity of cardiac tissues.

RECENT FINDINGS

Recent strides in single-cell omics technologies have revolutionized our understanding of the heart's cellular composition, cell type heterogeneity, and molecular dynamics. These advancements have elucidated pathological conditions as well as the cellular landscape in heart development. We highlight emerging applications of integrated single-cell omics, particularly for cardiac regeneration, disease modeling, and precision medicine, and emphasize the transformative potential of these technologies to advance cardiovascular research and clinical practice.

Organoids: development and applications in disease models, drug discovery, precision medicine, and regenerative medicine

Organoids are miniature, highly accurate representations of organs that capture the structure and unique functions of specific organs. Although the field of organoids has experienced exponential growth, driven by advances in artificial intelligence, gene editing, and bioinstrumentation, a comprehensive and accurate overview of organoid applications remains necessary. This review offers a detailed exploration of the historical origins and characteristics of various organoid types, their applications-including disease modeling, drug toxicity and efficacy assessments, precision medicine, and regenerative medicine-as well as the current challenges and future directions of organoid research. Organoids have proven instrumental in elucidating genetic cell fate in hereditary diseases, infectious diseases, metabolic disorders, and malignancies, as well as in the study of processes such as embryonic development, molecular mechanisms, and host-microbe interactions. Furthermore, the integration of organoid technology with artificial intelligence and microfluidics has significantly advanced large-scale, rapid, and cost-effective drug toxicity and efficacy assessments, thereby propelling progress in precision medicine. Finally, with the advent of high-performance materials, three-dimensional printing technology, and gene editing, organoids are also gaining prominence in the field of regenerative medicine. Our insights and predictions aim to provide valuable guidance to current researchers and to support the continued advancement of this rapidly developing field.

Single-cell RNA sequencing reveals the gene expression profile and cellular communication in human fetal heart development

The heart is the central organ of the circulatory system, and its proper development is vital to maintain human life. As fetal heart development is complex and poorly understood, we use single-cell RNA sequencing to profile the gene expression landscapes of human fetal hearts from the four-time points: 8, 10, 11, 17 gestational weeks (GW8, GW10, GW11, GW17), and identified 11 major types of cells: erythroid cells, fibroblasts, heart endothelial cells, ventricular cardiomyocytes, atrial cardiomyocytes, macrophage, DCs, smooth muscle, pericytes, neural cells, schwann cells. In addition, we identified a series of differentially expressed genes and signaling pathways in each cell type between different gestational weeks. Notably, we found that ANNEXIN, MIF, PTN, GRN signalling pathways were simple and fewer intercellular connections in GW8, however, they were significantly more complex and had more intercellular communication in GW10, GW11, and GW17. Notably, the interaction strength of OSM signalling pathways was gradually decreased during this period of time (from GW8 to GW17). Together, in this study, we presented a comprehensive and clear description of the differentiation processes of all the main cell types in the human fetal hearts, which may provide information and reference data for heart regeneration and heart disease treatment.

Protocol to achieve high-resolution single-cell transcriptomics of cardiomyocytes in multiple species

Single-cell RNA sequencing (scRNA-seq) remains state-of-the-art for transcriptomic cell-mapping. Here, we provide a protocol to generate high-resolution scRNA-seq of rare cardiomyocyte populations (e.g., regenerating/dividing, etc.) from mouse and zebrafish hearts as well as induced pluripotent stem cells, collected in time to achieve detailed transcriptomic insight. We describe the serial steps of viability staining, methanol fixation, storage, and cell sorting to preserve RNA integrity suited for scRNA-seq as well as the quality assessment of the data as shown by examples. For complete details on the use and execution of this protocol, please refer to Bak et al.1.

Machine Learning Uncovers Vascular Endothelial Cell Identity Genes by Expression Regulation Features in Single Cells

Deciphering cell identity genes is pivotal to understanding cell differentiation, development, and many diseases involving cell identity dysregulation. Here, we introduce SCIG, a machine-learning method to uncover cell identity genes in single cells. In alignment with recent reports that cell identity genes are regulated with unique epigenetic signatures, we found cell identity genes exhibit distinctive genetic sequence signatures, e.g., unique enrichment patterns of cis-regulatory elements. Using these genetic sequence signatures, along with gene expression information from single-cell RNA-seq data, enables SCIG to uncover the identity genes of a cell without a need for comparison to other cells. Cell identity gene score defined by SCIG surpassed expression value in network analysis to uncover master transcription factors regulating cell identity. Applying SCIG to the human endothelial cell atlas revealed that the tissue microenvironment is a critical supplement to master transcription factors for cell identity refinement. SCIG is publicly available at https://github.com/kaifuchenlab/SCIG , offering a valuable tool for advancing cell differentiation, development, and regenerative medicine research.

Early heart development: examining the dynamics of function-form emergence

During early embryonic development, the heart undergoes a remarkable and complex transformation, acquiring its iconic four-chamber structure whilst concomitantly contracting to maintain its essential function. The emergence of cardiac form and function involves intricate interplays between molecular, cellular, and biomechanical events, unfolding with precision in both space and time. The dynamic morphological remodelling of the developing heart renders it particularly vulnerable to congenital defects, with heart malformations being the most common type of congenital birth defect (∼35% of all congenital birth defects). This mini-review aims to give an overview of the morphogenetic processes which govern early heart formation as well as the dynamics and mechanisms of early cardiac function. Moreover, we aim to highlight some of the interplay between these two processes and discuss how recent findings and emerging techniques/models offer promising avenues for future exploration. In summary, the developing heart is an exciting model to gain fundamental insight into the dynamic relationship between form and function, which will augment our understanding of cardiac congenital defects and provide a blueprint for potential therapeutic strategies to treat disease.

Single-Cell RNA-Seq Analysis of Hearts in Patients with Fetal Tetralogy of Fallot

INTRODUCTION

To explore the cytological characteristics of tetralogy of Fallot (TOF), we collected samples and investigated the differences in the cytological classification between normal fetal hearts and fetal hearts with congenital defects. We then performed single-cell sequencing analysis to search for possible differential genes of disease markers.

METHODS

Here, the right ventricles of a heart sample with TOF and a healthy human fetal heart sample were analyzed through single-cell sequencing. Data quality control filtering, comparison, quantification, and identification of recovered cells on the raw data were performed using Cell Ranger, thereby ultimately obtaining gene expression matrices for each cell. Subsequently, Seurat was used for cell filtration, standardization, cell subgroup classification, differential expression gene analysis of each subgroup, and marker gene screening.

RESULTS

Bioinformatic analysis identified 9,979 and 15,224 cells from the healthy and diseased samples, respectively, with an average read depth of 25,000/cell. The cardiomyocyte cell populations, derived from the abnormal samples identified through the first-level graph-based analysis, were separated into six distinct cell clusters.

CONCLUSION

Our study provides some information on TOF in a fetus, which can offer a new reference for the early detection and treatment of TOF by comparing defective heart cells with normal heart cells.

Generation of human vascularized and chambered cardiac organoids for cardiac disease modelling and drug evaluation

Human induced pluripotent stem cell (hiPSC)-derived cardiac organoids (COs) have shown great potential in modelling human heart development and cardiovascular diseases, a leading cause of global death. However, several limitations such as low reproducibility, limited vascularization and difficulty in formation of cardiac chamber were yet to be overcome. We established a new method for robust generation of COs, via combination of methodologies of hiPSC-derived vascular spheres and directly differentiated cardiomyocytes from hiPSCs, and investigated the potential application of human COs in cardiac injury modelling and drug evaluation. The human COs we built displayed a vascularized and chamber-like structure, and hence were named vaschamcardioids (vcCOs). These vcCOs exhibited approximately 90% spontaneous beating ratio. Single-cell transcriptomics identified a total of six cell types in the vcCOs, including cardiomyocytes, cardiac precursor cells, endothelial cells, fibroblasts, etc. We successfully recaptured the processes of cardiac injury and fibrosis in vivo on vcCOs, and showed that the FDA-approved medication captopril significantly attenuated cardiac injury-induced fibrosis and functional disorders. In addition, the human vcCOs exhibited an obvious drug toxicity reaction to doxorubicin in a dose-dependent manner. We developed a three-step method for robust generation of chamber-like and vascularized complex vcCOs, and our data suggested that vcCOs might become a useful model for understanding pathophysiological mechanisms of cardiovascular diseases, developing intervention strategies and screening drugs.

Revisiting Cardiac Biology in the Era of Single Cell and Spatial Omics

Throughout our lifetime, each beat of the heart requires the coordinated action of multiple cardiac cell types. Understanding cardiac cell biology, its intricate microenvironments, and the mechanisms that govern their function in health and disease are crucial to designing novel therapeutical and behavioral interventions. Recent advances in single-cell and spatial omics technologies have significantly propelled this understanding, offering novel insights into the cellular diversity and function and the complex interactions of cardiac tissue. This review provides a comprehensive overview of the cellular landscape of the heart, bridging the gap between suspension-based and emerging in situ approaches, focusing on the experimental and computational challenges, comparative analyses of mouse and human cardiac systems, and the rising contextualization of cardiac cells within their niches. As we explore the heart at this unprecedented resolution, integrating insights from both mouse and human studies will pave the way for novel diagnostic tools and therapeutic interventions, ultimately improving outcomes for patients with cardiovascular diseases.

Aortic disease and cardiomyopathy in patients with a novel DNMT3A gene variant causing Tatton-Brown-Rahman syndrome

Tatton-Brown-Rahman syndrome (TBRS) is a rare congenital genetic disorder caused by autosomal dominant pathogenic variants in the DNA methyltransferase DNMT3A gene. Typical TBRS clinical features are overgrowth, intellectual disability, and minor facial anomalies. However, since the syndrome was first described in 2014, a widening spectrum of abnormalities is being described. Cardiovascular abnormalities are less commonly reported but can be a major complication of the syndrome. This article describes a family of three individuals diagnosed with TBRS in adulthood and highlights the variable expression of cardiovascular features. A 34-year-old proband presented with progressive aortic dilatation, mitral valve (MV) regurgitation, left ventricular (LV) dilatation, and ventricular arrhythmias. The affected family members (mother and brother) were diagnosed with MV regurgitation, LV dilatation, and arrhythmias. Exome sequencing and computational protein analysis suggested that the novel familial DNMT3A mutation Ser775Tyr is located in the methyltransferase domain, however, distant from the active site or DNA-binding loops. Nevertheless, this bulky substitution may have a significant effect on DNMT3A protein structure, dynamics, and function. Analysis of peripheral blood cfDNA and transcriptome showed shortened mononucleosome fragments and altered gene expression in a number of genes related to cardiovascular health and of yet undescribed function, including several lncRNAs. This highlights the importance of epigenetic regulation by DNMT3A on cardiovascular system development and function. From the clinical perspective, we suggest that new patients diagnosed with congenital DNMT3A variants and TBRS require close examination and follow-up for aortic dilatation and valvular disease because these conditions can progress rapidly. Moreover, personalized treatments, based on the specific DNMT3A variants and the different pathways of their function loss, can be envisioned in the future.

Primitive macrophages induce sarcomeric maturation and functional enhancement of developing human cardiac microtissues via efferocytic pathways

Yolk sac macrophages are the first to seed the developing heart, however we have no understanding of their roles in human heart development and function due to a lack of accessible tissue. Here, we bridge this gap by differentiating human embryonic stem cells (hESCs) into primitive LYVE1+ macrophages (hESC-macrophages) that stably engraft within contractile cardiac microtissues composed of hESC-cardiomyocytes and fibroblasts. Engraftment induces a human fetal cardiac macrophage gene program enriched in efferocytic pathways. Functionally, hESC-macrophages trigger cardiomyocyte sarcomeric protein maturation, enhance contractile force and improve relaxation kinetics. Mechanistically, hESC-macrophages engage in phosphatidylserine dependent ingestion of apoptotic cardiomyocyte cargo, which reduces microtissue stress, leading hESC-cardiomyocytes to more closely resemble early human fetal ventricular cardiomyocytes, both transcriptionally and metabolically. Inhibiting hESC-macrophage efferocytosis impairs sarcomeric protein maturation and reduces cardiac microtissue function. Taken together, macrophage-engineered human cardiac microtissues represent a considerably improved model for human heart development, and reveal a major beneficial role for human primitive macrophages in enhancing early cardiac tissue function.

Interferons and interferon-related pathways in heart disease

Interferons (IFNs) and IFN-related pathways play key roles in the defence against microbial infection. However, these processes may also be activated during the pathogenesis of non-infectious diseases, where they may contribute to organ injury, or function in a compensatory manner. In this review, we explore the roles of IFNs and IFN-related pathways in heart disease. We consider the cardiac effects of type I IFNs and IFN-stimulated genes (ISGs); the emerging role of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway; the seemingly paradoxical effects of the type II IFN, IFN-γ; and the varied actions of the interferon regulatory factor (IRF) family of transcription factors. Recombinant IFNs and small molecule inhibitors of mediators of IFN receptor signaling are already employed in the clinic for the treatment of some autoimmune diseases, infections, and cancers. There has also been renewed interest in IFNs and IFN-related pathways because of their involvement in SARS-CoV-2 infection, and because of the relatively recent emergence of cGAS-STING as a pattern recognition receptor-activated pathway. Whether these advances will ultimately result in improvements in the care of those experiencing heart disease remains to be determined.

Macrophage lineages in heart development and regeneration

During development, macrophage subpopulations derived from hematopoietic progenitors take up residence in the developing heart. Embryonic macrophages are detectable at the early stages of heart formation in the nascent myocardium, valves and coronary vasculature. The specific subtypes of macrophages present in the developing heart reflect the generation of hematopoietic progenitors in the yolk sac, aorta-gonad-mesonephros, fetal liver, and postnatal bone marrow. Ablation studies have demonstrated specific requirements for embryonic macrophages in valve remodeling, coronary and lymphatic vessel development, specialized conduction system maturation, and myocardial regeneration after neonatal injury. The developmental origins of macrophage lineages change over time, with embryonic lineages having more reparative and remodeling functions in comparison to the bone marrow derived myeloid lineages of adults. Here we review the contributions and functions of cardiac macrophages in the developing heart with potential regenerative and reparative implications for cardiovascular disease.

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.

Mapping Cell Atlases at the Single-Cell Level

Recent advancements in single-cell technologies have led to rapid developments in the construction of cell atlases. These atlases have the potential to provide detailed information about every cell type in different organisms, enabling the characterization of cellular diversity at the single-cell level. Global efforts in developing comprehensive cell atlases have profound implications for both basic research and clinical applications. This review provides a broad overview of the cellular diversity and dynamics across various biological systems. In addition, the incorporation of machine learning techniques into cell atlas analyses opens up exciting prospects for the field of integrative biology.

Fibroblasts and immune cells: at the crossroad of organ inflammation and fibrosis

The immune and fibrotic responses have evolved to work in tandem to respond to pathogen clearance and promote tissue repair. However, excessive immune and fibrotic responses lead to chronic inflammation and fibrosis, respectively, both of which are key pathological drivers of organ pathophysiology. Fibroblasts and immune cells are central to these responses, and evidence of these two cell types communicating through soluble mediators or adopting functions from each other through direct contact is constantly emerging. Here, we review complex junctions of fibroblast-immune cell cross talk, such as immune cell modulation of fibroblast physiology and fibroblast acquisition of immune cell-like functions, as well as how these systems of communication contribute to organ pathophysiology. We review the concept of antigen presentation by fibroblasts among different organs with different regenerative capacities, and then focus on the inflammation-fibrosis axis in the heart in the complex syndrome of heart failure. We discuss the need to develop anti-inflammatory and antifibrotic therapies, so far unsuccessful to date, that target novel mechanisms that sit at the crossroads of the fibrotic and immune responses.

Autoimmune congenital heart block: a case report and review of the literature related to pathogenesis and pregnancy management

Autoimmune congenital heart block (ACHB) is a passively acquired immune-mediated disease characterized by the presence of maternal antibodies against components of the Ro/SSA and La/SSB ribonucleoprotein complex that mainly affects the cardiac conducting system. ACHB occurs in 2% of women with positive anti-Ro/SSA and anti-La/SSB antibodies and causes a high risk of intrauterine fetal death, neonatal mortality, and long-term sequelae. In this review, we first describe a case of ACHB to provide preliminary knowledge. Then, we discuss the possible pathogenic mechanisms of ACHB; summarize the pregnancy management of patients with positive anti-Ro/SSA and anti-La/SSB antibodies and/or rheumatic diseases, the prevention of ACHB, and the treatment of ACHB fetuses; and propose routine screening of these antibodies for the general population. Careful follow-up, which consists of monitoring the fetal heart rate, is feasible and reassuring for pregnant women with positive anti-Ro/SSA and/or anti-La/SSB antibodies to lower the risk of ACHB in fetuses. Moreover, maternal administration of hydroxychloroquine may be useful in preventing ACHB in pregnant women with anti-Ro/SSA and/or anti-La/SSB antibodies.

Self-recruited neutrophils trigger over-activated innate immune response and phenotypic change of cardiomyocytes in fulminant viral myocarditis

Fulminant myocarditis (FM) is a life-threatening inflammatory disease. However, the mechanisms underlying its acute onset are unknown. By dynamic cardiac function measurement, we discovered that the initiation of sudden hemodynamic collapse was on day 4 in the mouse model of FM. Single-cell RNA-sequencing study revealed that healthy cardiomyocytes (CMs) lost their contractile and metabolic function and differentiated into pro-angiogenic and pro-inflammatory CMs. Meanwhile, neutrophils, the most expanded immune cells, exhibited a unique developmental trajectory only after migrating to the heart, where they continuously attracted peripheral neutrophils via Cxcl2/Cxcl3, resulting in the acute accumulation of neutrophils in the heart. Well-differentiated cardiac-infiltrating neutrophils, rather than viruses, induced phenotypic changes in CMs. Moreover, neutrophils could amplify cytokine storm by recruiting and activating pro-inflammatory monocytes. Blockade of the self-recruiting loop of neutrophils by targeting the Cxcl2/Cxcl3-Cxcr2 axis substantially alleviated FM in mice. Collectively, we provide a comprehensive single-cell atlas of immune cells and CMs in FM, elucidate the disease pathogenesis, and suggest potential therapeutic strategies.

Adapting to a new environment: postnatal maturation of the human cardiomyocyte

The postnatal mammalian heart undergoes remarkable developmental changes, which are stimulated by the transition from the intrauterine to extrauterine environment. With birth, increased oxygen levels promote metabolic, structural and biophysical maturation of cardiomyocytes, resulting in mature muscle with increased efficiency, contractility and electrical conduction. In this Topical Review article, we highlight key studies that inform our current understanding of human cardiomyocyte maturation. Collectively, these studies suggest that human atrial and ventricular myocytes evolve quickly within the first year but might not reach a fully mature adult phenotype until nearly the first decade of life. However, it is important to note that fetal, neonatal and paediatric cardiac physiology studies are hindered by a number of limitations, including the scarcity of human tissue, small sample size and a heavy reliance on diseased tissue samples, often without age-matched healthy controls. Future developmental studies are warranted to expand our understanding of normal cardiac physiology/pathophysiology and inform age-appropriate treatment strategies for cardiac disease.

Hydroxychloroquine improves pregnancy outcomes in patients undergoing frozen embryo transfer with positive serum autoantibodies

PROBLEM

Does hydroxychloroquine (HCQ) improve pregnancy outcomes after frozen embryo transfer (FET) cycles in patients who are positive for autoantibodies？ METHOD OF STUDY: This was a retrospective clinical study involving 128 patients who were positive for autoantibodies undergoing FET cycles between October 2017 and December 2022. Subjects were divided into two groups: a study group of 65 cycles with HCQ (HCQ was administered orally over 2 months before transplantation and continued during the first trimester) and a control group consisting of 63 cycles without HCQ (no HCQ was used throughout the FET cycle). Each patient was enrolled in the cohort only once. Then, we analyzed the clinical pregnancy outcomes between the two groups.

RESULTS

Analysis showed that HCQ was a factor that independently associated with clinical pregnancy rate (CPR) OR (Odds Ratio): 3.106; 95% confidence interval (CI): 1.458-6.616; p = .003. Furthermore, the implantation rate (IR), CPR and ongoing pregnancy rate (OPR) of the treatment group were significantly higher than those in the control group. The biochemical pregnancy rate (BPR) and early miscarriage rate (EMR) were significantly lower than that in the control group (p = .029, p < .001).

CONCLUSION

We found that HCQ improved clinical pregnancy outcomes and reduced the rate of first-trimester abortion in patients who were positive for autoantibodies during FET cycles.

ScRNA-seq and spatial transcriptomics: exploring the occurrence and treatment of coronary-related diseases starting from development

Single-cell RNA sequencing (scRNA-seq) is a new technology that can be used to explore molecular changes in complex cell clusters at the single-cell level. Single-cell spatial transcriptomic technology complements the cell-space location information lost during single-cell sequencing. Coronary artery disease is an important cardiovascular disease with high mortality rates. Many studies have explored the physiological development and pathological changes in coronary arteries from the perspective of single cells using single-cell spatial transcriptomic technology. This article reviews the molecular mechanisms underlying coronary artery development and diseases as revealed by scRNA-seq combined with spatial transcriptomic technology. Based on these mechanisms, we discuss the possible new treatments for coronary diseases.

Integrated bioinformatics and machine learning algorithms reveal the critical cellular senescence-associated genes and immune infiltration in heart failure due to ischemic cardiomyopathy

Heart failure (HF) is the final stage of many cardiovascular illnesses and the leading cause of death worldwide. At the same time, ischemic cardiomyopathy has replaced valvular heart disease and hypertension as the primary causes of heart failure. Cellular senescence in heart failure is currently receiving more attention. In this paper, we investigated the correlation between the immunological properties of myocardial tissue and the pathological mechanisms of cellular senescence during ischemic cardiomyopathy leading to heart failure (ICM-HF) using bioinformatics and machine learning methodologies. Our goals were to clarify the pathogenic causes of heart failure and find new treatment options. First, after obtaining GSE5406 from the Gene Expression Omnibus (GEO) database and doing limma analysis, differential genes (DEGs) among the ICM-HF and control groups were identified. We intersected these differential genes with cellular senescence-associated genes (CSAG) via the CellAge database to obtain 39 cellular senescence-associated DEGs (CSA-DEGs). Then, a functional enrichment analysis was performed to elucidate the precise biological processes by which the hub genes control cellular senescence and immunological pathways. Then, the respective key genes were identified by Random Forest (RF) method, LASSO (Least Absolute Shrinkage and Selection Operator) algorithms, and Cytoscape's MCODE plug-in. Three sets of key genes were taken to intersect to obtain three CSA-signature genes (including MYC, MAP2K1, and STAT3), and these three CSA-signature genes were validated in the test gene set (GSE57345), and Nomogram analysis was done. In addition, we assessed the relationship between these three CSA- signature genes and the immunological landscape of heart failure encompassing immunological infiltration expression profiles. This work implies that cellular senescence may have a crucial role in the pathogenesis of ICM-HF, which may be closely tied to its effect on the immune microenvironment. Exploring the molecular underpinnings of cellular senescence during ICM-HF is anticipated to yield significant advances in the disease's diagnosis and therapy.

Single-cell transcriptomics for the assessment of cardiac disease

Cardiovascular disease is the leading cause of death globally. An advanced understanding of cardiovascular disease mechanisms is required to improve therapeutic strategies and patient risk stratification. State-of-the-art, large-scale, single-cell and single-nucleus transcriptomics facilitate the exploration of the cardiac cellular landscape at an unprecedented level, beyond its descriptive features, and can further our understanding of the mechanisms of disease and guide functional studies. In this Review, we provide an overview of the technical challenges in the experimental design of single-cell and single-nucleus transcriptomics studies, as well as a discussion of the type of inferences that can be made from the data derived from these studies. Furthermore, we describe novel findings derived from transcriptomics studies for each major cardiac cell type in both health and disease, and from development to adulthood. This Review also provides a guide to interpreting the exhaustive list of newly identified cardiac cell types and states, and highlights the consensus and discordances in annotation, indicating an urgent need for standardization. We describe advanced applications such as integration of single-cell data with spatial transcriptomics to map genes and cells on tissue and define cellular microenvironments that regulate homeostasis and disease progression. Finally, we discuss current and future translational and clinical implications of novel transcriptomics approaches, and provide an outlook of how these technologies will change the way we diagnose and treat heart disease.

Endocardial Fibroelastosis as an Independent Predictor of Atrioventricular Valve Rupture in Maternal Autoimmune Antibody Exposed Fetus: A Systematic Review with Clinicopathologic Analysis

BACKGROUND

Neonatal lupus (NL) is a clinical syndrome that develops in the fetus as a result of maternal autoimmune antibodies. Congenital complete heart block (CHB) is the most common manifestation, while extranodal cardiac manifestations of NL, such as endocardial fibroelastosis (EFE) and myocarditis, are rare but more serious. Less is known about this atrioventricular valve rupture due to valvulitis as a consequence of maternal autoantibodies. We have described a case of cardiac neonatal lupus with an antenatally detected CHB patient who developed mitral and tricuspid valve chordal rupture at 45 days of age. We compared the cardiac histopathology and the fetal cardiac echocardiographic findings of this case with another fetus that was aborted after being antenatally diagnosed with CHB but without valvar rupture. A narrative analysis after a systematic review of the literature regarding atrioventricular valve apparatus rupture due to autoimmune etiology along with maternal characteristics, presentation, treatment, and outcome have been discussed in this article.

OBJECTIVES

To describe published data on atrioventricular valve rupture in neonatal lupus, including clinical presentation, diagnostic evaluation, management, and outcomes.

METHODS

We conducted a PRISMA-compliant descriptive systematic examination of case reports that included accounts of lupus during pregnancy or in the newborn period that resulted in an atrioventricular valve rupture. We gathered information on the patient's demographics, the details of the valve rupture and other comorbidities, the maternal therapy, the clinical course, and the results. We also used a standardized method to evaluate the cases' quality. A total of 12 cases were investigated, with 11 cases drawn from 10 case reports or case series and 1 from our own experience.

RESULTS

Tricuspid valve rupture (50%) is more common than mitral valve rupture (17%). Unlike mitral valve rupture, which occurs postnatally, the timing of tricuspid valve rupture is perinatal. A total of 33% of the patients had concomitant complete heart block, while 75% of the patients had endocardial fibroelastosis on an antenatal ultrasound. Antenatal changes pertaining to endocardial fibroelastosis can be seen as early as 19 weeks of gestation. Patients with both valve ruptures generally have a poor prognosis, especially if they occur at close intervals.

CONCLUSION

Atrioventricular valve rupture in neonatal lupus is rare. A majority of patients with valve rupture had antenatally detected endocardial fibroelastosis in the valvar apparatus. Appropriate and expedited surgical repair of ruptured atrioventricular valves is feasible and has a low mortality risk. Rupture of both atrioventricular valves occurring at close intervals carries a high mortality risk.

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.

Contribution of S100A4-expressing fibroblasts to anti-SSA/Ro-associated atrioventricular nodal calcification and soluble S100A4 as a biomarker of clinical severity

Background

Fibrosis and dystrophic calcification disrupting conduction tissue architecture are histopathological lesions characterizing cardiac manifestations of neonatal lupus (cardiac-NL) associated with maternal anti-SSA/Ro antibodies.

Objectives

Increased appreciation of heterogeneity in fibroblasts encourages re-examination of existing models with the consideration of multiple fibroblast subtypes (and their unique functional differences) in mind. This study addressed fibroblast heterogeneity by examining expression of α-Smooth Muscle Actin (myofibroblasts) and of S100 Calcium-Binding Protein A4 (S100A4).

Methods

Using a previously established model of rheumatic scarring/fibrosis in vitro, supported by the evaluation of cord blood from cardiac-NL neonates and their healthy (anti-SSA/Ro-exposed) counterparts, and autopsy tissue from fetuses dying with cardiac-NL, the current study was initiated to more clearly define and distinguish the S100A4-positive fibroblast in the fetal cardiac environment.

Results

S100A4 immunostaining was observed in 4 cardiac-NL hearts with positional identity in the conduction system at regions of dystrophic calcification but not fibrotic zones, the latter containing only myofibroblasts. In vitro, fibroblasts cultured with supernatants of macrophages transfected with hY3 (noncoding ssRNA) differentiated into myofibroblasts or S100A4+ fibroblasts. Myofibroblasts expressed collagen while S100A4+ fibroblasts expressed pro-angiogenic cytokines and proteases that degrade collagen. Cord blood levels of S100A4 in anti-SSA/Ro-exposed neonates tracked disease severity and, in discordant twins, distinguished affected from unaffected.

Conclusions

These findings position the S100A4+ fibroblast alongside the canonical myofibroblast in the pathogenesis of cardiac-NL. Neonatal S100A4 levels support a novel biomarker of poor prognosis.

Deciphering endothelial heterogeneity in health and disease at single-cell resolution: progress and perspectives

Endothelial cells (ECs) constitute the inner lining of vascular beds in mammals and are crucial for homeostatic regulation of blood vessel physiology, but also play a key role in pathogenesis of many diseases, thereby representing realistic therapeutic targets. However, it has become evident that ECs are heterogeneous, encompassing several subtypes with distinct functions, which makes EC targeting and modulation in diseases challenging. The rise of the new single-cell era has led to an emergence of studies aimed at interrogating transcriptome diversity along the vascular tree, and has revolutionized our understanding of EC heterogeneity from both a physiological and pathophysiological context. Here, we discuss recent landmark studies aimed at teasing apart the heterogeneous nature of ECs. We cover driving (epi)genetic, transcriptomic, and metabolic forces underlying EC heterogeneity in health and disease, as well as current strategies used to combat disease-enriched EC phenotypes, and propose strategies to transcend largely descriptive heterogeneity towards prioritization and functional validation of therapeutically targetable drivers of EC diversity. Lastly, we provide an overview of the most recent advances and hurdles in single EC OMICs.

Single-cell transcriptomes in the heart: when every epigenome counts

The response of an organ to stimuli emerges from the actions of individual cells. Recent cardiac single-cell RNA-sequencing studies of development, injury, and reprogramming have uncovered heterogeneous populations even among previously well-defined cell types, raising questions about what level of experimental resolution corresponds to disease-relevant, tissue-level phenotypes. In this review, we explore the biological meaning behind this cellular heterogeneity by undertaking an exhaustive analysis of single-cell transcriptomics in the heart (including a comprehensive, annotated compendium of studies published to date) and evaluating new models for the cardiac function that have emerged from these studies (including discussion and schematics that depict new hypotheses in the field). We evaluate the evidence to support the biological actions of newly identified cell populations and debate questions related to the role of cell-to-cell variability in development and disease. Finally, we present emerging epigenomic approaches that, when combined with single-cell RNA-sequencing, can resolve basic mechanisms of gene regulation and variability in cell phenotype.

Multi-species meta-analysis identifies transcriptional signatures associated with cardiac endothelial responses in the ischaemic heart

AIM

Myocardial infarction remains the leading cause of heart failure. The adult human heart lacks the capacity to undergo endogenous regeneration. New blood vessel growth is integral to regenerative medicine necessitating a comprehensive understanding of the pathways that regulate vascular regeneration. We sought to define the transcriptomic dynamics of coronary endothelial cells following ischaemic injuries in the developing and adult mouse and human heart and to identify new mechanistic insights and targets for cardiovascular regeneration.

METHODS AND RESULTS

We carried out a comprehensive meta-analysis of integrated single-cell RNA-sequencing data of coronary vascular endothelial cells from the developing and adult mouse and human heart spanning healthy and acute and chronic ischaemic cardiac disease. We identified species-conserved gene regulatory pathways aligned to endogenous neovascularization. We annotated injury-associated temporal shifts of the endothelial transcriptome and validated four genes: VEGF-C, KLF4, EGR1, and ZFP36. Moreover, we showed that ZFP36 regulates human coronary endothelial cell proliferation and defined that VEGF-C administration in vivo enhances clonal expansion of the cardiac vasculature post-myocardial infarction. Finally, we constructed a coronary endothelial cell meta-atlas, CrescENDO, to empower future in-depth research to target pathways associated with coronary neovascularization.

CONCLUSION

We present a high-resolution single-cell meta-atlas of healthy and injured coronary endothelial cells in the mouse and human heart, revealing a suite of novel targets with great potential to promote vascular regeneration, and providing a rich resource for therapeutic development.

Implications of CRISPR-Cas9 Genome Editing Methods in Atherosclerotic Cardiovascular Diseases

Today, new methods have been developed to treat or modify the natural course of cardiovascular diseases (CVDs), including atherosclerosis, by the clustered regularly interspaced short palindromic repeats-CRISPR-associated protein 9 (CRISPR-Cas9) system. Genome-editing tools are CRISPR-related palindromic short iteration systems such as CRISPR-Cas9, a valuable technology for achieving somatic and germinal genomic manipulation in model cells and organisms for various applications, including the creation of deletion alleles. Mutations in genomic deoxyribonucleic acid and new genes' placement have emerged. Based on World Health Organization fact sheets, 17.9 million people die from CVDs each year, an estimated 32% of all deaths worldwide. 85% of all CVD deaths are due to acute coronary events and strokes. This review discusses the applications of CRISPR-Cas9 technology throughout atherosclerotic disease research and the prospects for future in vivo genome editing therapies. We also describe several limitations that must be considered to achieve the full scientific and therapeutic potential of cardiovascular genome editing in the treatment of atherosclerosis.

Novel rare mutation in a conserved site of PTPRB causes human hypoplastic left heart syndrome

Hypoplastic left heart syndrome (HLHS) is a rare but fatal birth defect in which the left side of the heart is underdeveloped. HLHS accounts for 2% to 4% of congenital heart anomalies. Whole genome sequencing (WGS) was conducted for a family trio consisting of a proband and his parents. A homozygous rare variant was detected in the PTPRB (Protein Tyrosine Phosphatase Receptor Type B) gene of the proband by functional annotation and co-segregation analysis. Sanger sequencing was used to confirm genotypes of the variant. The in silico prediction tools, including Mutation Taster, SpliceAI, and CADD, were used to predict the impact of the mutation. The allele frequencies across populations were compared based on multiple databases, including "1000 genomes" and "gnomAD". We used two vectors (pcMINI and pcDNA3.1) to generate a minigene construct to validate the mutational effect at the transcriptional level. Family-based WGS analyses showed that only a homozygous splice acceptor variant (NC_000012.12: g.70636068T>G, NM_001109754.4: c.56-2A>C, NG_029940.2: g.6373A>C) at the exon-intron border of PTPRB gene associates with HLHS. This variant is also within the region with the enhancer activity based on UCSC genome annotation. Genotyping and Sanger sequencing revealed that the proband's parents are heterozygous for this variant. Evolutionary conservation analysis revealed that the site (NC_000012.12: g.70636068) is extremely conserved across species, supporting the evolutionary functional constraints of the ancestral wild type (T). In silico tools universally predicted a deleterious or disease-causing impact of the mutation from T to G. The mutation was not found in the 1000 genomes and gnomAD databases, which indicates that this mutation is very rare in most human populations. A splicing assay indicated that the mutated minigene caused aberrant splicing of mRNA, in which a 3 bp missing in the second exon resulted in the deletion of one amino acid (NP_001103224.1:p.Glu19del) compared to the normal protein of PRPTB (also the VE-PTP). Structure prediction revealed that the deletion occurred within the C-region of the signal peptide of VE-PTP, suggesting signal peptide-related defects as a potential mechanism for the HLHS cellular pathogeny. We report a rare homozygous variant with splicing error in PTPRB associated with HLHS. Previous model species studies revealed conserved functions of PTPRB in cardiovascular and heart development in mice and zebrafish. Our study is the first report to show the association between PTPRB and HLHS in humans.

Integrative single-cell analysis of cardiogenesis identifies developmental trajectories and non-coding mutations in congenital heart disease

To define the multi-cellular epigenomic and transcriptional landscape of cardiac cellular development, we generated single-cell chromatin accessibility maps of human fetal heart tissues. We identified eight major differentiation trajectories involving primary cardiac cell types, each associated with dynamic transcription factor (TF) activity signatures. We contrasted regulatory landscapes of iPSC-derived cardiac cell types and their in vivo counterparts, which enabled optimization of in vitro differentiation of epicardial cells. Further, we interpreted sequence based deep learning models of cell-type-resolved chromatin accessibility profiles to decipher underlying TF motif lexicons. De novo mutations predicted to affect chromatin accessibility in arterial endothelium were enriched in congenital heart disease (CHD) cases vs. controls. In vitro studies in iPSCs validated the functional impact of identified variation on the predicted developmental cell types. This work thus defines the cell-type-resolved cis-regulatory sequence determinants of heart development and identifies disruption of cell type-specific regulatory elements in CHD.

A single-cell comparison of adult and fetal human epicardium defines the age-associated changes in epicardial activity

Re-activating quiescent adult epicardium represents a potential therapeutic approach for human cardiac regeneration. However, the exact molecular differences between inactive adult and active fetal epicardium are not known. In this study, we combined fetal and adult human hearts using single-cell and single-nuclei RNA sequencing and compared epicardial cells from both stages. We found that a migratory fibroblast-like epicardial population only in the fetal heart and fetal epicardium expressed angiogenic gene programs, whereas the adult epicardium was solely mesothelial and immune responsive. Furthermore, we predicted that adult hearts may still receive fetal epicardial paracrine communication, including WNT signaling with endocardium, reinforcing the validity of regenerative strategies that administer or reactivate epicardial cells in situ. Finally, we explained graft efficacy of our human embryonic stem-cell-derived epicardium model by noting its similarity to human fetal epicardium. Overall, our study defines epicardial programs of regenerative angiogenesis absent in adult hearts, contextualizes animal studies and defines epicardial states required for effective human heart regeneration.

Defining cardiac cell populations and relative cellular composition of the early fetal human heart

While the adult human heart is primarily composed of cardiomyocytes, fibroblasts, endothelial and smooth muscle cells, the cellular composition during early development remains largely unknown. Reliable identification of fetal cardiac cell types using protein markers is critical to understand cardiac development and delineate the cellular composition of the developing human heart. This is the first study to use immunohistochemistry (IHC), flow cytometry and RT-PCR analyses to investigate the expression and specificity of commonly used cardiac cell markers in the early human fetal heart (8-12 post-conception weeks). The expression of previously reported protein markers for the detection of cardiomyocytes (Myosin Heavy Chain (MHC) and cardiac troponin I (cTnI), fibroblasts (DDR2, THY1, Vimentin), endothelial cells (CD31) and smooth muscle cells (α-SMA) were assessed. Two distinct populations of cTnI positive cells were identified through flow cytometry, with MHC positive cardiomyocytes showing high cTnI expression (cTnIHigh) while MHC negative non-myocytes showed lower cTnI expression (cTnILow). cTnI expression in non-myocytes was further confirmed by IHC and RT-PCR analyses, suggesting troponins are not cardiomyocyte-specific and may play distinct roles in non-muscle cells during early development. Vimentin (VIM) was expressed in cultured ventricular fibroblast populations and flow cytometry revealed VIMHigh and VIMLow cell populations in the fetal heart. MHC positive cardiomyocytes were VIMLow whilst CD31 positive endothelial cells were VIMHigh. Using markers investigated within this study, we characterised fetal human cardiac populations and estimate that 75-80% of fetal cardiac cells are cardiomyocytes and are MHC+/cTnIHigh/VIMLow, whilst non-myocytes comprise 20-25% of total cells and are MHC-/cTnILow/VIMHigh, with CD31+ endothelial cells comprising ~9% of this population. These findings show distinct differences from those reported for adult heart.

Case Report: A novel KNCH2 variant-induced fetal heart block and the advantages of fetal genomic sequencing in prenatal long-term dexamethasone exposure

Background: Fetal bradycardia is a common but severe condition. In addition to autoimmune-mediated fetal heart block, several types of channelopathies induce high-degree atrioventricular block (AVB). Long QT syndrome (LQTS) is a major cause of non-autoimmune-mediated fetal heart block. Due to the limitations of prenatal diagnostic technologies, LQTS is seldom identified unless fetal genetic screening is performed. Thus, long-term prenatal dexamethasone (DEX) exposure can become a challenge for these patients. We report on a rare case of a novel KCNH2 variant related to LQTS and associated with high-degree fetal AVB with long-term DEX exposure. This case led us to review our prenatal administration strategy for such patients.

Case Presentation: A fetus was identified with high-degree AVB (2:1 transduction at 28 + 2 gestational weeks). Typical tests of immune function in the pregnant woman were conducted including tests for thyroid function, rheumatic screening, autoimmune antibodies (such as anti-Ro/SSA and anti-La/SSB), and anti-nuclear antibodies (anti-ANA). Following the recommended protocol, the pregnant patient received DEX (0.75 mg/day) during pregnancy. Subsequently, the fetal AVB changed from 2:1 to prolonged AV intervals with ventricular tachycardia, which suggested a therapeutic benefit of DEX in some respects. However, a high-degree AVB with a significantly prolonged QTc interval was identified in the neonate following birth. Genetic testing revealed that a KCNH2 c.1868C&gt;A variant induced LQTS. The body length remained approximately -3.2 SD from the reference value after prenatal long-term DEX exposure, which indicated a developmental restriction. Additionally, the functional validation experiments were performed to demonstrate the prolonged duration of calcium transit both in depolarization and repolarization with the KCNH2 c.1868C&gt;A variant.

Conclusion: Genetic screening should be recommended in fetuses with autoimmune antibody negative high-degree AVB, especially for 2:1 transduction AVB and in fetuses with changes in fetal heart rhythm following initial DEX treatment. Genetic screening may help identify genetic variant–related channelopathies and avoid unexpected prenatal exposure of DEX and its possible long-term adverse postnatal complications.

Non-cardiomyocytes in the heart in embryo development, health, and disease, a single-cell perspective

Recent single-cell atlases of the heart gave unprecedented details about the diversity of cell types and states during heart development in health and disease conditions. Beyond a profiling tool, researchers also use single-cell analyses to dissect the mechanism of diseases in animal models. The new knowledge from these studies revealed that beating cardiomyocytes account for less than 50% of the total heart cell population. In contrast, non-cardiomyocytes (NCMs), such as cardiac fibroblasts, endothelial cells, and immune cells, make up the remaining proportion and have indispensable roles in structural support, homeostasis maintenance, and injury repair of the heart. In this review, we categorize the composition and characteristics of NCMs from the latest single-cell studies of the heart in various contexts and compare the findings from both human samples and mouse models. This information will enrich our understanding of the cellular basis of heart development and diseases and provide insights into the potential therapeutic targets in NCMs to repair the heart.

Advances in application of single-cell RNA sequencing in cardiovascular research

Single-cell RNA sequencing (scRNA-seq) provides high-resolution information on transcriptomic changes at the single-cell level, which is of great significance for distinguishing cell subtypes, identifying stem cell differentiation processes, and identifying targets for disease treatment. In recent years, emerging single-cell RNA sequencing technologies have been used to make breakthroughs regarding decoding developmental trajectories, phenotypic transitions, and cellular interactions in the cardiovascular system, providing new insights into cardiovascular disease. This paper reviews the technical processes of single-cell RNA sequencing and the latest progress based on single-cell RNA sequencing in the field of cardiovascular system research, compares single-cell RNA sequencing with other single-cell technologies, and summarizes the extended applications and advantages and disadvantages of single-cell RNA sequencing. Finally, the prospects for applying single-cell RNA sequencing in the field of cardiovascular research are discussed.