Heart valve development: regulatory networks in development and disease

Multiscale structure and function of the aortic valve apparatus

Whereas studying the aortic valve in isolation has facilitated the development of life-saving procedures and technologies, the dynamic interplay of the aortic valve and its surrounding structures is vital to preserving their function across the wide range of conditions encountered in an active lifestyle. Our view is that these structures should be viewed as an integrated functional unit, here referred to as the aortic valve apparatus (AVA). The coupling of the aortic valve and root, left ventricular outflow tract, and blood circulation is crucial for AVA's functions: unidirectional flow out of the left ventricle, coronary perfusion, reservoir function, and support of left ventricular function. In this review, we explore the multiscale biological and physical phenomena that underlie the simultaneous fulfillment of these functions. A brief overview of the tools used to investigate the AVA, such as medical imaging modalities, experimental methods, and computational modeling, specifically fluid-structure interaction (FSI) simulations, is included. Some pathologies affecting the AVA are explored, and insights are provided on treatments and interventions that aim to maintain quality of life. The concepts explained in this article support the idea of AVA being an integrated functional unit and help identify unanswered research questions. Incorporating phenomena through the molecular, micro, meso, and whole tissue scales is crucial for understanding the sophisticated normal functions and diseases of the AVA.

Update on the genetic profile of mitral valve development and prolapse

The purpose of this review is to present a comprehensive overview of the literature published up to February 2024 on the PubMed database regarding the development of mitral valve disease, with detailed reference to mitral valve prolapse, from embryology to a genetic profile. Out of the 3291 publications that deal with mitral valve embryology, 215 refer to mitral valve genetics and 83 were selected for further analysis. After reviewing these data, we advocate for the importance of a gene-based therapy that should be available soon, to prevent or treat non-invasively the valvular degeneration.

Integrated single-cell RNA-seq analysis reveals mitochondrial calcium signaling as a modulator of endothelial-to-mesenchymal transition

Endothelial cells (ECs) are highly plastic, capable of differentiating into various cell types. Endothelial-to-mesenchymal transition (EndMT) is crucial during embryonic development and contributes substantially to vascular dysfunction in many cardiovascular diseases (CVDs). While targeting EndMT holds therapeutic promise, understanding its mechanisms and modulating its pathways remain challenging. Using single-cell RNA sequencing on three in vitro EndMT models, we identified conserved gene signatures. We validated original regulators in vitro and in vivo during embryonic heart development and peripheral artery disease. EndMT induction led to global expression changes in all EC subtypes rather than in mesenchymal clusters. We identified mitochondrial calcium uptake as a key driver of EndMT; inhibiting mitochondrial calcium uniporter (MCU) prevented EndMT in vitro, and conditional Mcu deletion in ECs blocked mesenchymal activation in a hind limb ischemia model. Tissues from patients with critical limb ischemia with EndMT features exhibited significantly elevated endothelial MCU. These findings highlight MCU as a regulator of EndMT and a potential therapeutic target.

Increased endothelial sclerostin caused by elevated DSCAM mediates multiple trisomy 21 phenotypes

Trisomy 21 (T21), a recurrent aneuploidy occurring in 1:800 births, predisposes to congenital heart disease (CHD) and multiple extracardiac phenotypes. Despite a definitive genetic etiology, the mechanisms by which T21 perturbs development and homeostasis remain poorly understood. We compared the transcriptome of CHD tissues from 49 patients with T21 and 226 with euploid CHD (eCHD). We resolved cell lineages that misexpressed T21 transcripts by cardiac single-nucleus RNA sequencing and RNA in situ hybridization. Compared with eCHD samples, T21 samples had increased chr21 gene expression; 11-fold-greater levels (P = 1.2 × 10-8) of SOST (chr17), encoding the Wnt inhibitor sclerostin; and 1.4-fold-higher levels (P = 8.7 × 10-8) of the SOST transcriptional activator ZNF467 (chr7). Euploid and T21 cardiac endothelial cells coexpressed SOST and ZNF467; however, T21 endothelial cells expressed 6.9-fold more SOST than euploid endothelial cells (P = 2.7 × 10-27). Wnt pathway genes were downregulated in T21 endothelial cells. Expression of DSCAM, residing within the chr21 CHD critical region, correlated with SOST (P = 1.9 × 10-5) and ZNF467 (P = 2.9 × 10-4). Deletion of DSCAM from T21 endothelial cells derived from human induced pluripotent stem cells diminished sclerostin secretion. As Wnt signaling is critical for atrioventricular canal formation, bone health, and pulmonary vascular homeostasis, we concluded that T21-mediated increased sclerostin levels would inappropriately inhibit Wnt activities and promote Down syndrome phenotypes. These findings imply therapeutic potential for anti-sclerostin antibodies in T21.

Directed Differentiation of Human Induced Pluripotent Stem Cells to Heart Valve Cells

BACKGROUND

A main obstacle in current valvular heart disease research is the lack of high-quality homogeneous functional heart valve cells. Human induced pluripotent stem cells (hiPSCs)-derived heart valve cells may help with this dilemma. However, there are no well-established protocols to induce hiPSCs to differentiate into functional heart valve cells, and the networks that mediate the differentiation have not been fully elucidated.

METHODS

To generate heart valve cells from hiPSCs, we sequentially activated the Wnt, BMP4, VEGF (vascular endothelial growth factor), and NFATc1 signaling pathways using CHIR-99021, BMP4, VEGF-165, and forskolin, respectively. The transcriptional and functional similarity of hiPSC-derived heart valve cells compared with primary heart valve cells were characterized. Longitudinal single-cell RNA sequencing was used to uncover the trajectory, switch genes, pathways, and transcription factors of the differentiation.

RESULTS

An efficient protocol was developed to induce hiPSCs to differentiate into functional hiPSC-derived valve endothelial-like cells and hiPSC-derived valve interstitial-like cells. After 6-day differentiation and CD144 magnetic bead sorting, ≈70% CD144+ cells and 30% CD144- cells were obtained. On the basis of single-cell RNA sequencing data, the CD144+ cells and CD144- cells were found to be highly similar to primary heart valve endothelial cells and primary heart valve interstitial cells in gene expression profile. Furthermore, CD144+ cells had the typical function of primary heart valve endothelial cells, including tube formation, uptake of low-density lipoprotein, generation of endothelial nitric oxide synthase, and response to shear stress. Meanwhile, CD144- cells could secret collagen and matrix metalloproteinases, and differentiate into osteogenic or adipogenic lineages like primary heart valve interstitial cells. Therefore, we identified CD144+ cells and CD144- cells as hiPSC-derived valve endothelial-like cells and hiPSC-derived valve interstitial-like cells, respectively. Using single-cell RNA sequencing analysis, we demonstrated that the trajectory of heart valve cell differentiation was consistent with embryonic valve development. We identified the main switch genes (NOTCH1, HEY1, and MEF2C), signaling pathways (TGF-β, Wnt, and NOTCH), and transcription factors (MSX1, SP5, and MECOM) that mediated the differentiation. Finally, we found that hiPSC-derived valve interstitial-like cells might derive from hiPSC-derived valve endothelial-like cells undergoing endocardial-mesenchymal transition.

CONCLUSIONS

In summary, this is the first study to report an efficient strategy to generate functional hiPSC-derived valve endothelial-like cells and hiPSC-derived valve interstitial-like cells from hiPSCs, as well as to elucidate the differentiation trajectory and transcriptional dynamics of hiPSCs differentiated into heart valve cells.

Downregulation of Wtap causes dilated cardiomyopathy and heart failure

RNA binding proteins have been shown to regulate heart development and cardiac diseases. However, the detailed molecular mechanisms is not known. In this study, we identified Wilms' tumor 1-associating protein (WTAP, a key regulatory protein of the m6A RNA methyltransferase complex) as a key regulator of heart function and cardiac diseases. WTAP is associated with heart development, and its expression is downregulated in both human and mice with heart failure. Cardiomyocyte-specific knockout of Wtap (Wtap-CKO) induces dilated cardiomyopathy, heart failure and neonatal death. Although WTAP deficiency in the heart decreases METTL3 (methyltransferase-like 3) protein levels, cardiomyocyte-specific overexpression of Mettl3 in Wtap-CKO mice does not rescue the phenotypes of Wtap-CKO mice. Instead, WTAP deficiency in the heart decreases chromatin accessibility in the promoter regions of Mef2a (myocyte enhancer factor-2α) and Mef2c, leading to reduced mRNA and protein levels of these genes and lower expression of their target genes. Conversely, WTAP directly binds to the promoter of the Mef2c gene and increases its promoter luciferase activity and expression. These data demonstrate that WTAP plays a key role in heart development and cardiac function by maintaining the chromatin accessibility of cardiomyocyte specific genes.

Spatiotemporal development and the regulatory mechanisms of cardiac resident macrophages: Contribution in cardiac development and steady state

Cardiac resident macrophages (CRMs) are integral components of the heart and play significant roles in cardiac development, steady-state, and injury. Advances in sequencing technology have revealed that CRMs are a highly heterogeneous population, with significant differences in phenotype and function at different developmental stages and locations within the heart. In addition to research focused on diseases, recent years have witnessed a heightened interest in elucidating the involvement of CRMs in heart development and the maintenance of cardiac function. In this review, we primarily concentrated on summarizing the developmental trajectories, both spatial and temporal, of CRMs and their impact on cardiac development and steady-state. Moreover, we discuss the possible factors by which the cardiac microenvironment regulates macrophages from the perspectives of migration, proliferation, and differentiation under physiological conditions. Gaining insight into the spatiotemporal heterogeneity and regulatory mechanisms of CRMs is of paramount importance in comprehending the involvement of macrophages in cardiac development, injury, and repair, and also provides new ideas and therapeutic methods for treating heart diseases.

Understanding the cell fate and behavior of progenitors at the origin of the mouse cardiac mitral valve

Congenital heart malformations include mitral valve defects, which remain largely unexplained. During embryogenesis, a restricted population of endocardial cells within the atrioventricular canal undergoes an endothelial-to-mesenchymal transition to give rise to mitral valvular cells. However, the identity and fate decisions of these progenitors as well as the behavior and distribution of their derivatives in valve leaflets remain unknown. We used single-cell RNA sequencing (scRNA-seq) of genetically labeled endocardial cells and microdissected mouse embryonic and postnatal mitral valves to characterize the developmental road. We defined the metabolic processes underlying the specification of the progenitors and their contributions to subtypes of valvular cells. Using retrospective multicolor clonal analysis, we describe specific modes of growth and behavior of endocardial cell-derived clones, which build up, in a proper manner, functional valve leaflets. Our data identify how both genetic and metabolic mechanisms specifically drive the fate of a subset of endocardial cells toward their distinct clonal contribution to the formation of the valve.

27-Hydroxycholesterol activates the GSK-3β/β-catenin signaling pathway resulting in intestinal fibrosis by inducing oxidative stress: effect of dietary interventions

OBJECTIVE

Intestinal fibrosis, a common and serious complication of inflammatory bowel disease (IBD), results from chronic inflammation. A high-cholesterol diet may be a risk factor for IBD and 27-hydroxylcholesterol (27HC) is the main human cholesterol metabolite. This study investigated whether 27HC can induce intestinal fibrosis.

METHODS

The effects of cholesterol and 27HC on intestinal fibrosis were assessed in zebrafish and human intestinal epithelial Caco-2 cells.

RESULTS

Cholesterol and 27HC induced intestinal inflammation and collagen deposition, inhibited E-cadherin (E-ca) expression in the intestinal epithelium, and promoted nuclear translocation of β-catenin in zebrafish. Cholesterol and 27HC up-regulated expression of COL-1, α-SMA, CTGF, TIMP1, N-cadherin, vimentin, glycogen synthesis kinase-3β (GSK-3β) and β-catenin, but inhibited E-ca, in Caco-2 cells. The expression of these proteins was inhibited by CYP27A1 knockdown and β-catenin knockdown. 27HC-induced nuclear translocation of β-catenin occurs in Caco-2 cells. p38, ERK, and AKT activate β-catenin and thereby participate in 27HC-induced epithelia-mesenchymal transition (EMT) and fibrosis. 27HC-increased oxidative stress and the fibrosis and EMT markers, the nuclear translocation of β-catenin, and the up-regulation of p-cell kinase proteins promoted by 27HC were inhibited by N-acetyl-L-cysteine (NAC). Folic acid (FA), resveratrol (RES), and NAC all ameliorated the 27HC-induced effects in Caco-2 cells and zebrafish.

CONCLUSION

A high-cholesterol diet caused intestinal fibrosis in zebrafish, mediated by a major cholesterol metabolite, 27HC. 27HC increased oxidative stress and activated p38, ERK, AKT, and β-catenin, leading to EMT of epithelial cells and intestinal fibrosis. FA and RES both ameliorated intestinal fibrosis by restraining 27HC-induced β-catenin activation.

Aortic Valve Embryology, Mechanobiology, and Second Messenger Pathways: Implications for Clinical Practice

During the Renaissance, Leonardo Da Vinci was the first person to successfully detail the anatomy of the aortic root and its adjacent structures. Ever since, novel insights into morphology, function, and their interplay have accumulated, resulting in advanced knowledge on the complex functional characteristics of the aortic valve (AV) and root. This has shifted our vision from the AV as being a static structure towards that of a dynamic interconnected apparatus within the aortic root as a functional unit, exhibiting a complex interplay with adjacent structures via both humoral and mechanical stimuli. This paradigm shift has stimulated surgical treatment strategies of valvular disease that seek to recapitulate healthy AV function, whereby AV disease can no longer be seen as an isolated morphological pathology which needs to be replaced. As prostheses still cannot reproduce the complexity of human nature, treatment of diseased AVs, whether stenotic or insufficient, has tremendously evolved, with a similar shift towards treatments options that are more hemodynamically centered, such as the Ross procedure and valve-conserving surgery. Native AV and root components allow for an efficient Venturi effect over the valve to allow for optimal opening during the cardiac cycle, while also alleviating the left ventricle. Next to that, several receptors are present on native AV leaflets, enabling messenger pathways based on their interaction with blood and other shear-stress-related stimuli. Many of these physiological and hemodynamical processes are under-acknowledged but may hold important clues for innovative treatment strategies, or as potential novel targets for therapeutic agents that halt or reverse the process of valve degeneration. A structured overview of these pathways and their implications for cardiothoracic surgeons and cardiologists is lacking. As such, we provide an overview on embryology, hemodynamics, and messenger pathways of the healthy and diseased AV and its implications for clinical practice, by relating this knowledge to current treatment alternatives and clinical decision making.

Feeder-free generation and characterization of endocardial and cardiac valve cells from human pluripotent stem cells

Valvular heart disease presents a significant health burden, yet advancements in valve biology and therapeutics have been hindered by the lack of accessibility to human valve cells. In this study, we have developed a scalable and feeder-free method to differentiate human induced pluripotent stem cells (iPSCs) into endocardial cells, which are transcriptionally and phenotypically distinct from vascular endothelial cells. These endocardial cells can be challenged to undergo endothelial-to-mesenchymal transition (EndMT), after which two distinct populations emerge-one population undergoes EndMT to become valvular interstitial cells (VICs), while the other population reinforces their endothelial identity to become valvular endothelial cells (VECs). We then characterized these populations through bulk RNA-seq transcriptome analyses and compared our VIC and VEC populations to pseudobulk data generated from normal valve tissue of a 15-week-old human fetus. By increasing the accessibility to these cell populations, we aim to accelerate discoveries for cardiac valve biology and disease.

Lineage Tracing Identifies Dynamic Contribution of Endothelial Cells to Cardiac Valve Mesenchyme During Development

Heart valve disease is an important cause of morbidity and mortality among cardiac patients worldwide. However, the pathogenesis of heart valve disease is not clear, and a growing body of evidence hints at the importance of the genetic basis and developmental origins of heart valve disease. Therefore, understanding the developmental mechanisms that underlie the formation of heart valves has important implications for the diagnosis, prevention, and treatment of congenital heart disease. Endothelial to mesenchymal transition is a key step in initiating cardiac valve development. The dynamic changes in the relative localization and proportion of different cell sources in the heart valve mesenchymal population are still not fully understood. Here, we used the Cdh5-CreER;R26R-tdTomato mouse line to trace endocardial cushion-derived endothelial cells to explore the dynamic contribution of these cells to each layer of the valve during valve development. This is beneficial for elaborating on the role of endocardial cells in the process of valve remodeling from a precise angle.

Capturing heart valve development with Gene Ontology

Introduction: The normal development of all heart valves requires highly coordinated signaling pathways and downstream mediators. While genomic variants can be responsible for congenital valve disease, environmental factors can also play a role. Later in life valve calcification is a leading cause of aortic valve stenosis, a progressive disease that may lead to heart failure. Current research into the causes of both congenital valve diseases and valve calcification is using a variety of high-throughput methodologies, including transcriptomics, proteomics and genomics. High quality genetic data from biological knowledge bases are essential to facilitate analyses and interpretation of these high-throughput datasets. The Gene Ontology (GO, http://geneontology.org/) is a major bioinformatics resource used to interpret these datasets, as it provides structured, computable knowledge describing the role of gene products across all organisms. The UCL Functional Gene Annotation team focuses on GO annotation of human gene products. Having identified that the GO annotations included in transcriptomic, proteomic and genomic data did not provide sufficient descriptive information about heart valve development, we initiated a focused project to address this issue. Methods: This project prioritized 138 proteins for GO annotation, which led to the curation of 100 peer-reviewed articles and the creation of 400 heart valve development-relevant GO annotations. Results: While the focus of this project was heart valve development, around 600 of the 1000 annotations created described the broader cellular role of these proteins, including those describing aortic valve morphogenesis, BMP signaling and endocardial cushion development. Our functional enrichment analysis of the 28 proteins known to have a role in bicuspid aortic valve disease confirmed that this annotation project has led to an improved interpretation of a heart valve genetic dataset. Discussion: To address the needs of the heart valve research community this project has provided GO annotations to describe the specific roles of key proteins involved in heart valve development. The breadth of GO annotations created by this project will benefit many of those seeking to interpret a wide range of cardiovascular genomic, transcriptomic, proteomic and metabolomic datasets.

Valvulogenesis of a living, innervated pulmonary root induced by an acellular scaffold

Heart valve disease is a major cause of mortality and morbidity worldwide with no effective medical therapy and no ideal valve substitute emulating the extremely sophisticated functions of a living heart valve. These functions influence survival and quality of life. This has stimulated extensive attempts at tissue engineering "living" heart valves. These attempts utilised combinations of allogeneic/ autologous cells and biological scaffolds with practical, regulatory, and ethical issues. In situ regeneration depends on scaffolds that attract, house and instruct cells and promote connective tissue formation. We describe a surgical, tissue-engineered, anatomically precise, novel off-the-shelf, acellular, synthetic scaffold inducing a rapid process of morphogenesis involving relevant cell types, extracellular matrix, regulatory elements including nerves and humoral components. This process relies on specific material characteristics, design and "morphodynamism".

Crk and Crkl Are Required in the Endocardial Lineage for Heart Valve Development

Background Endocardial cells are a major progenitor population that gives rise to heart valves through endocardial cushion formation by endocardial to mesenchymal transformation and the subsequent endocardial cushion remodeling. Genetic variants that affect these developmental processes can lead to congenital heart valve defects. Crk and Crkl are ubiquitously expressed genes encoding cytoplasmic adaptors essential for cell signaling. This study aims to explore the specific role of Crk and Crkl in the endocardial lineage during heart valve development. Methods and Results We deleted Crk and Crkl specifically in the endocardial lineage. The resultant heart valve morphology was evaluated by histological analysis, and the underlying cellular and molecular mechanisms were investigated by immunostaining and quantitative reverse transcription polymerase chain reaction. We found that the targeted deletion of Crk and Crkl impeded the remodeling of endocardial cushions at the atrioventricular canal into the atrioventricular valves. We showed that apoptosis was temporally increased in the remodeling atrioventricular endocardial cushions, and this developmentally upregulated apoptosis was repressed by deletion of Crk and Crkl. Loss of Crk and Crkl also resulted in altered extracellular matrix production and organization in the remodeling atrioventricular endocardial cushions. These morphogenic defects were associated with altered expression of genes in BMP (bone morphogenetic protein), connective tissue growth factor, and WNT signaling pathways, and reduced extracellular signal-regulated kinase signaling activities. Conclusions Our findings support that Crk and Crkl have shared functions in the endocardial lineage that critically regulate atrioventricular valve development; together, they likely coordinate the morphogenic signals involved in the remodeling of the atrioventricular endocardial cushions.

β-Catenin regulates endocardial cushion growth by suppressing p21

Endocardial cushion formation is essential for heart valve development and heart chamber separation. Abnormal endocardial cushion formation often causes congenital heart defects. β-Catenin is known to be essential for endocardial cushion formation; however, the underlying cellular and molecular mechanisms remain incompletely understood. Here, we show that endothelial-specific deletion of β-catenin in mice resulted in formation of hypoplastic endocardial cushions due to reduced cell proliferation and impaired cell migration. By using a β-catenin DM allele in which the transcriptional function of β-catenin is selectively disrupted, we further reveal that β-catenin regulated cell proliferation and migration through its transcriptional and non-transcriptional function, respectively. At the molecular level, loss of β-catenin resulted in increased expression of cell cycle inhibitor p21 in cushion endocardial and mesenchymal cells in vivo. In vitro rescue experiments with HUVECs and pig aortic valve interstitial cells confirmed that β-catenin promoted cell proliferation by suppressing p21. In addition, one savvy negative observation is that β-catenin was dispensable for endocardial-to-mesenchymal fate change. Taken together, our findings demonstrate that β-catenin is essential for cell proliferation and migration but dispensable for endocardial cells to gain mesenchymal fate during endocardial cushion formation. Mechanistically, β-catenin promotes cell proliferation by suppressing p21. These findings inform the potential role of β-catenin in the etiology of congenital heart defects.

Localized Prox1 Regulates Aortic Valve Endothelial Cell Diversity and Extracellular Matrix Stratification in Mice

BACKGROUND

Specialized valve endothelial cell (VEC) populations are localized oriented to blood flow in developing aortic and mitral valves, but their roles in valve development and disease are unknown. In the aortic valve (AoV), a population of VECs on the fibrosa side expresses the transcription factor Prox1 together with genes found in lymphatic ECs. In this study, we examine Prox1's role in regulating a lymphatic-like gene network and promoting VEC diversity required for the development of the stratified trilaminar extracellular matrix (ECM) of murine AoV leaflets.

METHODS

To determine whether disruption of Prox1 localization affects heart valve development, we generated mice (NFATc1enCre Prox1 gain-of-function) in which Prox1 is overexpressed on the ventricularis side of the AoV beginning in embryonic development. To identify potential targets of Prox1, we performed cleavage under targets and release using nuclease on wild-type and NFATc1enCre Prox1 gain-of-function AoVs with validation by colocalization in vivo using RNA in situ hybridization in NFATc1enCre Prox1 gain-of-function AoVs. Natural induction of Prox1 and target gene expression was evaluated in myxomatous AoVs in a mouse model of Marfan syndrome (Fbn1C1039G/+).

RESULTS

The overexpression of Prox1 is sufficient to cause enlargement of AoVs by postnatal day (P)0, as well as a decrease in ventricularis-specific gene expression and disorganized interstitial ECM layers at P7. We identified potential targets of Prox1 known to play roles in lymphatic ECs including Flt1, Efnb2, Egfl7, and Cx37. Ectopic Prox1 colocalized with induced Flt1, Efnb2, and Cx37 expression in NFATc1enCre Prox1 gain-of-function AoVs. Moreover, in Marfan syndrome myxomatous AoVs, endogenous Prox1, and its identified targets, were ectopically induced in ventricularis side VECs.

CONCLUSIONS

Our results support a role for Prox1 in localized lymphatic-like gene expression on the fibrosa side of the AoV. Furthermore, localized VEC specialization is required for development of the stratified trilaminar ECM critical for AoV function and is dysregulated in congenitally malformed valves.

SOX7 deficiency causes ventricular septal defects through its effects on endocardial-to-mesenchymal transition and the expression of Wnt4 and Bmp2

SOX7 is a transcription factor-encoding gene located in a region on chromosome 8p23.1 that is recurrently deleted in individuals with ventricular septal defects (VSDs). We have previously shown that Sox7-/- embryos die of heart failure around E11.5. Here, we demonstrate that these embryos have hypocellular endocardial cushions with severely reduced numbers of mesenchymal cells. Ablation of Sox7 in the endocardium also resulted in hypocellular endocardial cushions, and we observed VSDs in rare E15.5 Sox7flox/-;Tie2-Cre and Sox7flox/flox;Tie2-Cre embryos that survived to E15.5. In atrioventricular explant studies, we showed that SOX7 deficiency leads to a severe reduction in endocardial-to-mesenchymal transition (EndMT). RNA-seq studies performed on E9.5 Sox7-/- heart tubes revealed severely reduced Wnt4 transcript levels. Wnt4 is expressed in the endocardium and promotes EndMT by acting in a paracrine manner to increase the expression of Bmp2 in the myocardium. Both WNT4 and BMP2 have been previously implicated in the development of VSDs in individuals with 46,XX sex reversal with dysgenesis of kidney, adrenals and lungs (SERKAL) syndrome and in individuals with short stature, facial dysmorphism and skeletal anomalies with or without cardiac anomalies 1 (SSFSC1) syndrome, respectively. We now show that Sox7 and Wnt4 interact genetically in the development of VSDs through their additive effects on endocardial cushion development with Sox7+/-;Wnt4+/- double heterozygous embryos having hypocellular endocardial cushions and perimembranous and muscular VSDs not seen in their Sox7+/- and Wnt4+/- littermates. These results provide additional evidence that SOX7, WNT4 and BMP2 function in the same pathway during mammalian septal development and that their deficiency can contribute to the development of VSDs in humans.

Biology of mitral valve prolapse: from general mechanisms to advanced molecular patterns-a narrative review

Mitral valve prolapse (MVP) represents the most frequent cause of primary mitral regurgitation. For several years, biological mechanisms underlying this condition attracted the attention of investigators, trying to identify the pathways responsible for such a peculiar condition. In the last ten years, cardiovascular research has moved from general biological mechanisms to altered molecular pathways activation. Overexpression of TGF-β signaling, for instance, was shown to play a key role in MVP, while angiotensin-II receptor blockade was found to limit MVP progression by acting on the same signaling pathway. Concerning extracellular matrix organization, the increased valvular interstitial cells density and dysregulated production of catalytic enzymes (matrix metalloproteinases above all) altering the homeostasis between collagen, elastin and proteoglycan components, have been shown to possibly provide a mechanistic basis contributing to the myxomatous MVP phenotype. Moreover, it has been observed that high levels of osteoprotegerin may contribute to the pathogenesis of MVP by increasing collagen deposition in degenerated mitral leaflets. Although MVP is believed to represent the result of multiple genetic pathways alterations, it is important to distinguish between syndromic and non-syndromic conditions. In the first case, such as in Marfan syndrome, the role of specific genes has been clearly identified, while in the latter a progressively increasing number of genetic loci have been thoroughly investigated. Moreover, genomics is gaining more interest as potential disease-causing genes and loci possibly associated with MVP progression and severity have been identified. Animal models could be of help in better understanding the molecular basis of MVP, possibly providing sufficient information to tackle specific mechanisms aimed at slowing down MVP progression, therefore developing non-surgical therapies impacting on the natural history of this condition. Although continuous progress has been made in this field, further translational studies are advocated to improve our knowledge of biological mechanisms underlying MVP development and progression.

Induced Pluripotent Stem Cell-Based Modeling of Single-Ventricle Congenital Heart Diseases

PURPOSE OF REVIEW

Congenital heart disease includes a wide variety of structural cardiac defects, the most severe of which are single ventricle defects (SVD). These patients suffer from significant morbidity and mortality; however, our understanding of the developmental etiology of these conditions is limited. Model organisms offer a window into normal and abnormal cardiogenesis yet often fail to recapitulate complex congenital heart defects seen in patients. The use of induced pluripotent stem cells (iPSCs) derived from patients with single-ventricle defects opens the door to studying SVD in patient-derived cardiomyocytes (iPSC-CMs) in a variety of different contexts, including organoids and chamber-specific cardiomyocytes. As the genetic and cellular causes of SVD are not well defined, patient-derived iPSC-CMs hold promise for uncovering mechanisms of disease development and serve as a platform for testing therapies. The purpose of this review is to highlight recent advances in iPSC-based models of SVD.

RECENT FINDINGS

Recent advances in patient-derived iPSC-CM differentiation, as well as the development of both chamber-specific and non-myocyte cardiac cell types, make it possible to model the complex genetic and molecular architecture involved in SVD development. Moreover, iPSC models have become increasingly complex with the generation of 3D organoids and engineered cardiac tissues which open the door to new mechanistic insight into SVD development. Finally, iPSC-CMs have been used in proof-of-concept studies that the molecular underpinnings of SVD may be targetable for future therapies. While each platform has its advantages and disadvantages, the use of patient-derived iPSC-CMs offers a window into patient-specific cardiogenesis and SVD development. Advancement in stem-cell based modeling of SVD promises to revolutionize our understanding of the developmental etiology of SVD and provides a tool for developing and testing new therapies.

Metals and Trace Elements in Calcified Valves in Patients with Acquired Severe Aortic Valve Stenosis: Is There a Connection with the Degeneration Process?

BACKGROUND

Acquired calcified aortic valve stenosis is the most common valve disease in adulthood. In the etiopathogenesis of this complex pathology, the importance of inflammation is mentioned, in which non-infectious influences represented by the biological effects of metal pollutants may participate. The main goal of the study was to determine the concentration of 21 metals and trace elements-aluminium (Al), barium (Ba), cadmium (Cd), calcium (Ca), chrome (Cr), cobalt (Co), copper (Cu), gold (Au), lead (Pb), magnesium (Mg), mercury (Hg), molybdenum (Mo), nickel (Ni), phosphorus (P), selenium (Se), strontium (Sr), sulfur (S), tin (Sn), titanium (Ti), vanadium (V) and zinc (Zn)-in the tissue of calcified aortic valves and to compare them with the concentrations of the same elements in the tissue of healthy aortic valves in the control group.

MATERIAL AND METHODS

The study group consisted of 49 patients (25 men, mean age: 74) with acquired, severe, calcified aortic valve stenosis with indicated heart surgery. The control group included 34 deceased (20 men, median age: 53) with no evidence of heart disease. Calcified valves were explanted during cardiac surgery and deep frozen. Similarly, the valves of the control group were removed. All valves were lyophilized and analyzed by inductively coupled plasma mass spectrometry. The concentrations of selected elements were compared by means of standard statistical methods.

RESULTS

Calcified aortic valves contained significantly higher (p < 0.05) concentrations of Ba, Ca, Co, Cr, Mg, P, Pb, Se, Sn, Sr and Zn and-in contrast-lower concentrations of Cd, Cu, Mo, S and V than valves of the control group. Significant positive correlations of concentrations between the pairs Ca-P, Cu-S and Se-S and strong negative correlations between the elements Mg-Se, P-S and Ca-S were found in the affected valves.

CONCLUSION

Aortic valve calcification is associated with increased tissue accumulation of the majority of the analyzed elements, including metal pollutants. Some exposure factors may increase their accumulation in the valve tissue. A relationship between exposure to environmental burden and the aortic valve calcification process cannot be ruled out. Advances in histochemical and imaging techniques allowing imaging of metal pollutants directly in valve tissue may represent an important future perspective.

Using a zebrafish xenograft tumor model to compare the efficacy and safety of VEGFR-TKIs

PURPOSE

We constructed a zebrafish xenograft tumor model to compare and quantify the antiangiogenic efficacy and safety of nine vascular endothelial growth factor receptor-tyrosine kinase inhibitors (VEGFR-TKIs), axitinib, lenvatinib, pazopanib, apatinib, cabozantinib, sunitinib, semaxanib, sorafenib, and regorafenib, in parallel.

METHODS

CT26 and GL261 tumor cells were implanted into the perivitelline space of Tg (flk1: eGFP) zebrafish to construct a xenograft tumor model. VEGFR-TKIs' antiangiogenic efficacy was quantified using AngioTool software, and the median effective dose (ED50) was calculated. The toxicity was evaluated by calculating the median lethal dose (LD50) and gross morphological changes. Cardiac toxicity was further assessed by heart rate, heart rhythm, the distance between the sinus venosus (SV) and bulbus arteriosus (BA), and pericardial edema.

RESULTS

Using the zebrafish xenograft tumor model, we found that all nine VEGFR-TKIs exhibited antiangiogenic abilities, but the effectiveness of semaxanib was worse than that of other VEGFR-TKIs. Meanwhile, the zebrafish toxicity assay showed that all tested VEGFR-TKIs were associated with cardiac-related toxicity, especially apatinib and axitinib, which caused serious pericardial edema in zebrafish at relatively low concentrations. A narrow therapeutic window was found for most VEGFR-TKIs, and the simultaneous occurrence of toxic effects of semaxanib was recognized.

CONCLUSION

Our findings showed the potential of using a zebrafish xenograft tumor model to accelerate VEGFR-TKI screening and further the development of more efficient and less toxic VEGFR-TKIs.

Human Heart Morphogenesis: A New Vision Based on In Vivo Labeling and Cell Tracking

Despite the extensive information available on the different genetic, epigenetic, and molecular features of cardiogenesis, the origin of congenital heart defects remains unknown. Most genetic and molecular studies have been conducted outside the context of the progressive anatomical and histological changes in the embryonic heart, which is one of the reasons for the limited knowledge of the origins of congenital heart diseases. We integrated the findings of descriptive studies on human embryos and experimental studies on chick, rat, and mouse embryos. This research is based on the new dynamic concept of heart development and the existence of two heart fields. The first field corresponds to the straight heart tube, into which splanchnic mesodermal cells from the second heart field are gradually recruited. The overall aim was to create a new vision for the analysis, diagnosis, and regionalized classification of congenital defects of the heart and great arteries. In addition to highlighting the importance of genetic factors in the development of congenital heart disease, this study provides new insights into the composition of the straight heart tube, the processes of twisting and folding, and the fate of the conus in the development of the right ventricle and its outflow tract. The new vision, based on in vivo labeling and cell tracking and enhanced by models such as gastruloids and organoids, has contributed to a better understanding of important errors in cardiac morphogenesis, which may lead to several congenital heart diseases.

First Trimester Tricuspid Regurgitation: Clinical Significance

Tricuspid regurgitation is a cardiac valvular anomaly that consists of the return of blood to the right atrium during systole due to incomplete valve closure. This structure can be visualized on ultrasound between 11 and 14 weeks of gestation in most cases. Despite being a common finding, even in healthy fetuses, the presence of tricuspid regurgitation may be associated with chromosomal and structural abnormalities. The evaluation of tricuspid flow and the presence of regurgitation on first-trimester ultrasound has shown promising results regarding its role in the early detection of aneuploidies, congenital heart defects, and other adverse perinatal outcomes. This review article aims to demonstrate the importance of tricuspid regurgitation as a secondary marker, and consequently, significant benefits of its early detection when added to the combined first-trimester screening. Its value will be discussed, namely its sensitivity and specificity, alone and together with other current markers in the fetal assessment performed in the first-trimester ultrasound.

Congenital aortic valve stenosis: from pathophysiology to molecular genetics and the need for novel therapeutics

Congenital aortic valve stenosis (AVS) is one of the most common valve anomalies and accounts for 3%-6% of cardiac malformations. As congenital AVS is often progressive, many patients, both children and adults, require transcatheter or surgical intervention throughout their lives. While the mechanisms of degenerative aortic valve disease in the adult population are partially described, the pathophysiology of adult AVS is different from congenital AVS in children as epigenetic and environmental risk factors play a significant role in manifestations of aortic valve disease in adults. Despite increased understanding of genetic basis of congenital aortic valve disease such as bicuspid aortic valve, the etiology and underlying mechanisms of congenital AVS in infants and children remain unknown. Herein, we review the pathophysiology of congenitally stenotic aortic valves and their natural history and disease course along with current management strategies. With the rapid expansion of knowledge of genetic origins of congenital heart defects, we also summarize the literature on the genetic contributors to congenital AVS. Further, this increased molecular understanding has led to the expansion of animal models with congenital aortic valve anomalies. Finally, we discuss the potential to develop novel therapeutics for congenital AVS that expand on integration of these molecular and genetic advances.

Protective Role of Endothelial Fibulin-4 in Valvulo-Arterial Integrity

Background Homeostasis of the vessel wall is cooperatively maintained by endothelial cells (ECs), smooth muscle cells, and adventitial fibroblasts. The genetic deletion of fibulin-4 (Fbln4) in smooth muscle cells (SMKO) leads to the formation of thoracic aortic aneurysms with the disruption of elastic fibers. Although Fbln4 is expressed in the entire vessel wall, its function in ECs and relevance to the maintenance of valvulo-arterial integrity are not fully understood. Methods and Results Gene silencing of FBLN4 was conducted on human aortic ECs to evaluate morphological changes and gene expression profile. Fbln4 double knockout (DKO) mice in ECs and smooth muscle cells were generated and subjected to histological analysis, echocardiography, Western blotting, RNA sequencing, and immunostaining. An evaluation of the thoracic aortic aneurysm phenotype and screening of altered signaling pathways were performed. Knockdown of FBLN4 in human aortic ECs induced mesenchymal cell-like changes with the upregulation of mesenchymal genes, including TAGLN and MYL9. DKO mice showed the exacerbation of thoracic aortic aneurysms when compared with those of SMKO and upregulated Thbs1, a mechanical stress-responsive molecule, throughout the aorta. DKO mice also showed progressive aortic valve thickening with collagen deposition from postnatal day 14, as well as turbulent flow in the ascending aorta. Furthermore, RNA sequencing and immunostaining of the aortic valve revealed the upregulation of genes involved in endothelial-to-mesenchymal transition, inflammatory response, and tissue fibrosis in DKO valves and the presence of activated valve interstitial cells. Conclusions The current study uncovers the pivotal role of endothelial fibulin-4 in the maintenance of valvulo-arterial integrity, which influences thoracic aortic aneurysm progression.

Angiopoietin-like 2 is essential to aortic valve development in mice

Aortic valve (AoV) abnormalities during embryogenesis are a major risk for the development of aortic valve stenosis (AVS) and cardiac events later in life. Here, we identify an unexpected role for Angiopoietin-like 2 (ANGPTL2), a pro-inflammatory protein secreted by senescent cells, in valvulogenesis. At late embryonic stage, mice knocked-down for Angptl2 (Angptl2-KD) exhibit a premature thickening of AoV leaflets associated with a dysregulation of the fine balance between cell apoptosis, senescence and proliferation during AoV remodeling and a decrease in the crucial Notch signalling. These structural and molecular abnormalities lead toward spontaneous AVS with elevated trans-aortic gradient in adult mice of both sexes. Consistently, ANGPTL2 expression is detected in human fetal semilunar valves and associated with pathways involved in cell cycle and senescence. Altogether, these findings suggest that Angptl2 is essential for valvulogenesis, and identify Angptl2-KD mice as an animal model to study spontaneous AVS, a disease with unmet medical need.

Perspectives on pediatric congenital aortic valve stenosis: Extracellular matrix proteins, post translational modifications, and proteomic strategies

In heart valve biology, organization of the extracellular matrix structure is directly correlated to valve function. This is especially true in cases of pediatric congenital aortic valve stenosis (pCAVS), in which extracellular matrix (ECM) dysregulation is a hallmark of the disease, eventually leading to left ventricular hypertrophy and heart failure. Therapeutic strategies are limited, especially in pediatric cases in which mechanical and tissue engineered valve replacements may not be a suitable option. By identifying mechanisms of translational and post-translational dysregulation of ECM in CAVS, potential drug targets can be identified, and better bioengineered solutions can be developed. In this review, we summarize current knowledge regarding ECM proteins and their post translational modifications (PTMs) during aortic valve development and disease and contributing factors to ECM dysregulation in CAVS. Additionally, we aim to draw parallels between other fibrotic disease and contributions to ECM post-translational modifications. Finally, we explore the current treatment options in pediatrics and identify how the field of proteomics has advanced in recent years, highlighting novel characterization methods of ECM and PTMs that may be used to identify potential therapeutic strategies relevant to pCAVS.

Glycosaminoglycans affect endothelial to mesenchymal transformation, proliferation, and calcification in a 3D model of aortic valve disease

Calcific nodules form in the fibrosa layer of the aortic valve in calcific aortic valve disease (CAVD). Glycosaminoglycans (GAGs), which are normally found in the valve spongiosa, are located local to calcific nodules. Previous work suggests that GAGs induce endothelial to mesenchymal transformation (EndMT), a phenomenon described by endothelial cells’ loss of the endothelial markers, gaining of migratory properties, and expression of mesenchymal markers such as alpha smooth muscle actin (α-SMA). EndMT is known to play roles in valvulogenesis and may provide a source of activated fibroblast with a potential role in CAVD progression. In this study, a 3D collagen hydrogel co-culture model of the aortic valve fibrosa was created to study the role of EndMT-derived activated valvular interstitial cell behavior in CAVD progression. Porcine aortic valve interstitial cells (PAVIC) and porcine aortic valve endothelial cells (PAVEC) were cultured within collagen I hydrogels containing the GAGs chondroitin sulfate (CS) or hyaluronic acid (HA). The model was used to study alkaline phosphatase (ALP) enzyme activity, cellular proliferation and matrix invasion, protein expression, and calcific nodule formation of the resident cell populations. CS and HA were found to alter ALP activity and increase cell proliferation. CS increased the formation of calcified nodules without the addition of osteogenic culture medium. This model has applications in the improvement of bioprosthetic valves by making replacements more micro-compositionally dynamic, as well as providing a platform for testing new pharmaceutical treatments of CAVD.

Healing the Broken Hearts: A Glimpse on Next Generation Therapeutics

Cardiovascular diseases are the leading cause of death worldwide, accounting for 32% of deaths globally and thus representing almost 18 million people according to WHO. Myocardial infarction, the most prevalent adult cardiovascular pathology, affects over half a million people in the USA according to the last records of the AHA. However, not only adult cardiovascular diseases are the most frequent diseases in adulthood, but congenital heart diseases also affect 0.8–1.2% of all births, accounting for mild developmental defects such as atrial septal defects to life-threatening pathologies such as tetralogy of Fallot or permanent common trunk that, if not surgically corrected in early postnatal days, they are incompatible with life. Therefore, both congenital and adult cardiovascular diseases represent an enormous social and economic burden that invariably demands continuous efforts to understand the causes of such cardiovascular defects and develop innovative strategies to correct and/or palliate them. In the next paragraphs, we aim to briefly account for our current understanding of the cellular bases of both congenital and adult cardiovascular diseases, providing a perspective of the plausible lines of action that might eventually result in increasing our understanding of cardiovascular diseases. This analysis will come out with the building blocks for designing novel and innovative therapeutic approaches to healing the broken hearts.

Modeling human multi-lineage heart field development with pluripotent stem cells

The cardiomyocyte (CM) subtypes in the mammalian heart derive from distinct lineages known as the first heart field (FHF), the anterior second heart field (aSHF), and the posterior second heart field (pSHF) lineages that are specified during gastrulation. We modeled human heart field development from human pluripotent stem cells (hPSCs) by using single-cell RNA-sequencing to delineate lineage specification and progression. Analyses of hPSC-derived and mouse mesoderm transcriptomes enabled the identification of distinct human FHF, aSHF, and pSHF mesoderm subpopulations. Through staged manipulation of signaling pathways identified from transcriptomics, we generated myocyte populations that display molecular characteristics of key CM subtypes. The developmental trajectory of the human cardiac lineages recapitulated that of the mouse, demonstrating conserved cardiovascular programs. These findings establish a comprehensive landscape of human embryonic cardiogenesis that provides access to a broad spectrum of cardiomyocytes for modeling congenital heart diseases and chamber-specific cardiomyopathies as well as for developing new therapies to treat them.

Differential requirement for DICER1 activity during the development of mitral and tricuspid valves

Mitral and tricuspid valves are essential for unidirectional blood flow in the heart. They are derived from similar cell sources, and yet congenital dysplasia affecting both valves is clinically rare, suggesting the presence of differential regulatory mechanisms underlying their development. Here, we specifically inactivated Dicer1 in the endocardium during cardiogenesis and found that Dicer1 deletion caused congenital mitral valve stenosis and regurgitation, whereas it had no impact on other valves. We showed that hyperplastic mitral valves were caused by abnormal condensation and extracellular matrix (ECM) remodeling. Our single-cell RNA sequencing analysis revealed impaired maturation of mesenchymal cells and abnormal expression of ECM genes in mutant mitral valves. Furthermore, expression of a set of miRNAs that target ECM genes was significantly lower in tricuspid valves compared to mitral valves, consistent with the idea that the miRNAs are differentially required for mitral and tricuspid valve development. We thus reveal miRNA-mediated gene regulation as a novel molecular mechanism that differentially regulates mitral and tricuspid valve development, thereby enhancing our understanding of the non-association of inborn mitral and tricuspid dysplasia observed clinically.

Wnt Signaling in Heart Development and Regeneration

PURPOSE OF REVIEW

Cardiovascular diseases are the leading cause of death worldwide, largely due to the limited regenerative capacity of the adult human heart. In contrast, teleost zebrafish hearts possess natural regeneration capacity by proliferation of pre-existing cardiomyocytes after injury. Hearts of mice can regenerate if injured in a few days after birth, which coincides with the transient capacity for cardiomyocyte proliferation. This review tends to elaborate the roles and mechanisms of Wnt/β-catenin signaling in heart development and regeneration in mammals and non-mammalian vertebrates.

RECENT FINDINGS

Studies in zebrafish, mice, and human embryonic stem cells demonstrate the binary effect for Wnt/β-catenin signaling during heart development. Both Wnts and Wnt antagonists are induced in multiple cell types during cardiac development and injury repair. In this review, we summarize composites of the Wnt signaling pathway and their different action routes, followed by the discussion of their involvements in cardiac specification, proliferation, and patterning. We provide overviews about canonical and non-canonical Wnt activity during heart homeostasis, remodeling, and regeneration. Wnt/β-catenin signaling exhibits biphasic and antagonistic effects on cardiac specification and differentiation depending on the stage of embryogenesis. Inhibition of Wnt signaling is beneficial for cardiac wound healing and functional recovery after injury. Understanding of the roles and mechanisms of Wnt signaling pathway in injured animal hearts will contribute to the development of potential therapeutics for human diseased hearts.

The Role of Transforming Growth Factor-β Signaling in Myxomatous Mitral Valve Degeneration

Mitral valve prolapse (MVP) due to myxomatous degeneration is one of the most important chronic degenerative cardiovascular diseases in people and dogs. It is a common cause of heart failure leading to significant morbidity and mortality in both species. Human MVP is usually classified into primary or non-syndromic, including Barlow’s Disease (BD), fibro-elastic deficiency (FED) and Filamin-A mutation, and secondary or syndromic forms (typically familial), such as Marfan syndrome (MFS), Ehlers-Danlos syndrome, and Loeys–Dietz syndrome. Despite different etiologies the diseased valves share pathological features consistent with myxomatous degeneration. To reflect this common pathology the condition is often called myxomatous mitral valve degeneration (disease) (MMVD) and this term is universally used to describe the analogous condition in the dog. MMVD in both species is characterized by leaflet thickening and deformity, disorganized extracellular matrix, increased transformation of the quiescent valve interstitial cell (qVICs) to an activated state (aVICs), also known as activated myofibroblasts. Significant alterations in these cellular activities contribute to the initiation and progression of MMVD due to the increased expression of transforming growth factor-β (TGF-β) superfamily cytokines and the dysregulation of the TGF-β signaling pathways. Further understanding the molecular mechanisms of MMVD is needed to identify pharmacological manipulation strategies of the signaling pathway that might regulate VIC differentiation and so control the disease onset and development. This review briefly summarizes current understanding of the histopathology, cellular activities, molecular mechanisms and pathogenesis of MMVD in dogs and humans, and in more detail reviews the evidence for the role of TGF-β.

The harder the climb the better the view: The impact of substrate stiffness on cardiomyocyte fate

The quest for novel methods to mature human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for cardiac regeneration, modelling and drug testing has emphasized a need to create microenvironments with physiological features. Many studies have reported on how cardiomyocytes sense substrate stiffness and adapt their morphological and functional properties. However, these observations have raised new biological questions and a shared vision to translate it into a tissue or organ context is still elusive. In this review, we will focus on the relevance of substrates mimicking cardiac extracellular matrix (cECM) rigidity for the understanding of the biomechanical crosstalk between the extracellular and intracellular environment. The ability to opportunely modulate these pathways could be a key to regulate in vitro hiPSC-CM maturation. Therefore, both hiPSC-CM models and substrate stiffness appear as intriguing tools for the investigation of cECM-cell interactions. More understanding of these mechanisms may provide novel insights on how cECM affects cardiac cell function in the context of genetic cardiomyopathies.

A Systematic Review of Ebstein’s Anomaly with Left Ventricular Noncompaction

Traditional definitions of Ebstein’s anomaly (EA) and left ventricular noncompaction (LVNC), two rare congenital heart defects (CHDs), confine disease to either the right or left heart, respectively. Around 15–29% of patients with EA, which has a prevalence of 1 in 20,000 live births, commonly manifest with LVNC. While individual EA or LVNC literature is extensive, relatively little discussion is devoted to the joint appearance of EA and LVNC (EA/LVNC), which poses a higher risk of poor clinical outcomes. We queried PubMed, Medline, and Web of Science for all peer-reviewed publications from inception to February 2022 that discuss EA/LVNC and found 58 unique articles written in English. Here, we summarize and extrapolate commonalities in clinical and genetic understanding of EA/LVNC to date. We additionally postulate involvement of shared developmental pathways that may lead to this combined disease. Anatomical variation in EA/LVNC encompasses characteristics of both CHDs, including tricuspid valve displacement, right heart dilatation, and left ventricular trabeculation, and dictates clinical presentation in both age and severity. Disease treatment is non-specific, ranging from symptomatic management to invasive surgery. Apart from a few variant associations, mainly in sarcomeric genes MYH7 and TPM1, the genetic etiology and pathogenesis of EA/LVNC remain largely unknown.

Expanding genotypic and phenotypic spectrums of LTBP3 variants in dental anomalies and short stature syndrome

Mutations in LTBP3 are associated with Dental Anomalies and Short Stature syndrome (DASS; MIM 601216), which is characterized by hypoplastic type amelogenesis imperfecta, hypodontia, underdeveloped maxilla, short stature, brachyolmia, aneurysm and dissection of the thoracic aorta. Here we report a novel (p.Arg545ProfsTer22) and a recurrent (c.3107-2A > G) LTBP3 variants, in a Turkish family affected with DASS. The proband, who carried compound heterozygous variant c.3107-2A > G, p.Arg545ProfsTer22, was most severely affected with DASS. The proband's father, who carried the heterozygous variant c.3107-2A > G had short stature and prognathic mandible. The mother and brother of the proband carried the heterozygous variant p.Arg545ProfsTer22, but only the mother showed any DASS characteristics. The c.3107-2A > G and the p.Arg545ProfsTer22 variants are expected to result in abnormal LTPB3 protein, failure of TGFβ-LAP-LTBP3 complex formation, and subsequent disruption of TGFβ secretion and activation. This is the first report of heterozygous carriers of LTBP3 variants showing phenotypes. The new findings of DASS found in this family include taurodontism, single-rooted molars, abnormal dentin, calcified dental pulp blood vessels, prognathic mandible, failure of mandibular tooth eruption, interatrial septal aneurysm, secundum atrial septal defect, tricuspid valve prolapse, and a recurrent glenohumeral joint dislocation.

Sex-Differences in Aortic Stenosis: Mechanistic Insights and Clinical Implications

Objective

We aim to analyse sex-specific differences in aortic valves (AVs) and valve interstitial cells (VICs) from aortic stenosis (AS) patients.

Approach and Results

238 patients with severe AS undergoing surgical valve replacement were recruited. Two hundred and two AVs (39.1% women) were used for ex vivo analyses and 36 AVs (33.3% women) for in vitro experiments. AVs from men presented increased levels of the inflammatory molecules interleukin (IL)-1β, IL-6, Rantes, and CD45. Oxidative stress (eNOS, myeloperoxidase, malondialdehyde and nitrotyrosine) was upregulated in male AVs. Concerning fibrosis, similar levels of collagen type I, decreased levels of collagen type III and enhanced fibronectin, active Lox-1 and syndecan-1 expressions were found in AVs from men compared with women. Extracellular matrix (ECM) remodeling was characterized by reduced metalloproteinase-1 and 9 expression and increased tissue inhibitor of metalloproteinase-2 expression in male AVs. Importantly, osteogenic markers (bone morphogenetic protein-9, Rank-L, osteopontin, periostin, osteocalcin and Sox-9) and apoptosis (Bax, Caspase 3, p53, and PARP1) were enhanced in AVs from men as compared to women. Isolated male VICs presented higher myofibroblast-like phenotype than female VICs. Male VICs exhibited increased inflammatory, oxidative stress, fibrotic, apoptosis and osteogenic differentiation markers.

Conclusions

Our results suggest that the mechanisms driving the pathogenesis of AS could be different in men and women. Male AVs and isolated VICs presented more inflammation, oxidative stress, ECM remodeling and calcification as compared to those from women. A better knowledge of the pathophysiological pathways in AVs and VICs will allow the development of sex-specific options for the treatment of AS.

ERp44 is required for endocardial cushion development by regulating VEGFA secretion in myocardium

OBJECTIVES

Endocardial cushions are precursors of the valve septum complex that separates the four heart chambers. Several genes have been implicated in the development of endocardial cushions. Specifically, ERp44 has been found to play a role in the early secretory pathway, but its function in heart development has not been well studied.

MATERIALS AND METHODS

In this study, we established conditional and tissue-specific knockout mouse models. The morphology, survival rate, the development of heart and endocardial cushion were under evaluation. The relationship between ERp44 and VEGFA was investigated by transcriptome, qPCR, WB, immunofluorescence and immunohistochemistry.

RESULTS

ERp44 knockout (KO) mice were smaller in size, and most mice died during early postnatal life. KO hearts exhibited the typical phenotypes of congenital heart diseases, such as abnormal heart shapes and severe septal and valvular defects. Similar phenotypes were found in cTNT-Cre+/- ; ERp44fl / fl mice, which indicated that myocardial ERp44 principally controls endocardial cushion formation. Further studies demonstrated that the deletion of ERp44 significantly decreased the proliferation of cushion cells and impaired the endocardial-mesenchymal transition (EndMT), which was followed by endocardial cushion dysplasia. Finally, we found that ERp44 was directly bound to VEGFA and controlled its release, further regulating EndMT.

CONCLUSION

We demonstrated that ERp44 plays a specific role in heart development. ERp44 contributes to the development of the endocardial cushion by affecting VEGFA-mediated EndMT.

Local fluid shear stress operates a molecular switch to drive fetal semilunar valve extension

BACKGROUND

While much is known about the genetic regulation of early valvular morphogenesis, mechanisms governing fetal valvular growth and remodeling remain unclear. Hemodynamic forces strongly influence morphogenesis, but it is unknown whether or how they interact with valvulogenic signaling programs. Side-specific activity of valvulogenic programs motivates the hypothesis that shear stress pattern-specific endocardial signaling controls the elongation of leaflets.

RESULTS

We determined that extension of the semilunar valve occurs via fibrosa sided endocardial proliferation. Low OSS was necessary and sufficient to induce canonical Wnt/β-catenin activation in fetal valve endothelium, which in turn drives BMP receptor/ligand expression, and pSmad1/5 activity essential for endocardial proliferation. In contrast, ventricularis endocardial cells expressed active Notch1 but minimal pSmad1/5. Endocardial monolayers exposed to LSS attenuate Wnt signaling in a Notch1 dependent manner.

CONCLUSIONS

Low OSS is transduced by endocardial cells into canonical Wnt signaling programs that regulate BMP signaling and endocardial proliferation. In contrast, high LSS induces Notch signaling in endocardial cells, inhibiting Wnt signaling and thereby restricting growth on the ventricular surface. Our results identify a novel mechanically regulated molecular switch, whereby fluid shear stress drives the growth of valve endothelium, orchestrating the extension of the valve in the direction of blood flow.

Computational estimates of annular diameter reveal genetic determinants of mitral valve function and disease

The fibrous annulus of the mitral valve plays an important role in valvular function and cardiac physiology, while normal variation in the size of cardiovascular anatomy may share a genetic link with common and rare disease. We derived automated estimates of mitral valve annular diameter in the 4-chamber view from 32,220 MRI images from the UK Biobank at ventricular systole and diastole as the basis for GWAS. Mitral annular dimensions corresponded to previously described anatomical norms, and GWAS inclusive of 4 population strata identified 10 loci, including possibly novel loci (GOSR2, ERBB4, MCTP2, MCPH1) and genes related to cardiac contractility (BAG3, TTN, RBFOX1). ATAC-Seq of primary mitral valve tissue localized multiple variants to regions of open chromatin in biologically relevant cell types and rs17608766 to an algorithmically predicted enhancer element in GOSR2. We observed strong genetic correlation with measures of contractility and mitral valve disease and clinical correlations with heart failure, cerebrovascular disease, and ventricular arrhythmias. Polygenic scoring of mitral valve annular diameter in systole was predictive of risk mitral valve prolapse across 4 cohorts. In summary, genetic and clinical studies of mitral valve annular diameter revealed genetic determinants of mitral valve biology, while highlighting clinical associations. Polygenic determinants of mitral valve annular diameter may represent an independent risk factor for mitral prolapse. Overall, computationally estimated phenotypes derived at scale from medical imaging represent an important substrate for genetic discovery and clinical risk prediction.

Development of the Human Arterial Valves: Understanding Bicuspid Aortic Valve

Abnormalities in the arterial valves are some of the commonest congenital malformations, with bicuspid aortic valve (BAV) occurring in as many as 2% of the population. Despite this, most of what we understand about the development of the arterial (semilunar; aortic and pulmonary) valves is extrapolated from investigations of the atrioventricular valves in animal models, with surprisingly little specifically known about how the arterial valves develop in mouse, and even less in human. In this review, we summarise what is known about the development of the human arterial valve leaflets, comparing this to the mouse where appropriate.

Longitudinal Impact of WTC Dust Inhalation on Rat Cardiac Tissue Transcriptomic Profiles

First responders (FR) exposed to the World Trade Center (WTC) Ground Zero air over the first week after the 9/11 disaster have an increased heart disease incidence compared to unexposed FR and the general population. To test if WTC dusts were causative agents, rats were exposed to WTC dusts (under isoflurane [ISO] anesthesia) 2 h/day on 2 consecutive days; controls received air/ISO or air only. Hearts were collected 1, 30, 240, and 360 d post-exposure, left ventricle total RNA was extracted, and transcription profiles were obtained. The data showed that differentially expressed genes (DEG) for WTC vs. ISO rats did not reach any significance with a false discovery rate (FDR) < 0.05 at days 1, 30, and 240, indicating that the dusts did not impart effects beyond any from ISO. However, at day 360, 14 DEG with a low FDR were identified, reflecting potential long-term effects from WTC dust alone, and the majority of these DEG have been implicated as having an impact on heart functions. Furthermore, the functional gene set enrichment analysis (GSEA) data at day 360 showed that WTC dust could potentially impact the myocardial energy metabolism via PPAR signaling and heart valve development. This is the first study showing that WTC dust could significantly affect some genes that are associated with the heart/CV system, in the long term. Even > 20 years after the 9/11 disaster, this has potentially important implications for those FR exposed repeatedly at Ground Zero over the first week after the buildings collapsed.

Myocardial Afterload Is a Key Biomechanical Regulator of Atrioventricular Myocyte Differentiation in Zebrafish

Heart valve development is governed by both genetic and biomechanical inputs. Prior work has demonstrated that oscillating shear stress associated with blood flow is required for normal atrioventricular (AV) valve development. Cardiac afterload is defined as the pressure the ventricle must overcome in order to pump blood throughout the circulatory system. In human patients, conditions of high afterload can cause valve pathology. Whether high afterload adversely affects embryonic valve development remains poorly understood. Here we describe a zebrafish model exhibiting increased myocardial afterload, caused by vasopressin, a vasoconstrictive drug. We show that the application of vasopressin reliably produces an increase in afterload without directly acting on cardiac tissue in zebrafish embryos. We have found that increased afterload alters the rate of growth of the cardiac chambers and causes remodeling of cardiomyocytes. Consistent with pathology seen in patients with clinically high afterload, we see defects in both the form and the function of the valve leaflets. Our results suggest that valve defects are due to changes in atrioventricular myocyte signaling, rather than pressure directly acting on the endothelial valve leaflet cells. Cardiac afterload should therefore be considered a biomechanical factor that particularly impacts embryonic valve development.

Valvular Endothelial Cell Response to the Mechanical Environment-A Review

Heart valve leaflets are complex structures containing valve endothelial cells, interstitial cells, and extracellular matrix. Heart valve endothelial cells sense mechanical stimuli, and communicate amongst themselves and the surrounding cells and extracellular matrix to maintain tissue homeostasis. In the presence of abnormal mechanical stimuli, endothelial cell communication is triggered in defense and such processes may eventually lead to cardiac disease progression. This review focuses on the role of mechanical stimuli on heart valve endothelial surfaces-from heart valve development and maintenance of tissue integrity to disease progression with related signal pathways involved in this process.

The Individual and Combined Effects of Shear, Tension, and Flexure on Aortic Heart Valve Endothelial Cells in Culture

PURPOSE

The necessity of living engineered heart valves to treat patients with severe heart disease poses a challenge to tissue engineers. To reach such goal it is crucial to fully understand the role and the activities of valvular endothelial cells (VECs) when they face different types of mechanical stimuli. This study focuses on decomposing the roles of different mechanical stimuli on heart valve endothelial surfaces and the response of VECs in terms of morphology and phenotype change.

METHODS

This study utilizes soft hydrogel-based scaffolds to use as a substrate for cell culture to mimic heart valve tissue leaflet. VECs were cultured as a monolayer on the gel surface and different types of mechanical stimuli were applied. Finally, the response of cells was investigated in terms of morphology and protein expression changes.

RESULTS

Single stimuli introduces actin fibers reorganization in VECs, change in cell morphology, and higher mesenchymal protein expression. On the other hand, combined stimuli application has lower impact on actin fibers reorganization and cell morphology change, with lower mesenchymal protein expression.

CONCLUSIONS

When VECs face a single mechanical stimuli, they undergo transdifferentiation and transform into mesenchymal cells. However, when these cells face a combination of mechanical stimuli, the rate of transformation decreases compared to single stimuli applications. This indicates that a single stimulus induces endothelial to mesenchymal transition in VECs while the process is slower under the combination of multiple mechanical stimuli.

OCT4-mediated inflammation induces cell reprogramming at the origin of cardiac valve development and calcification

Cell plasticity plays a key role in embryos by maintaining the differentiation potential of progenitors. Whether postnatal somatic cells revert to an embryonic-like naïve state regaining plasticity and redifferentiate into a cell type leading to a disease remains intriguing. Using genetic lineage tracing and single-cell RNA sequencing, we reveal that Oct4 is induced by nuclear factor κB (NFκB) at embyronic day 9.5 in a subset of mouse endocardial cells originating from the anterior heart forming field at the onset of endocardial-to-mesenchymal transition. These cells acquired a chondro-osteogenic fate. OCT4 in adult valvular aortic cells leads to calcification of mouse and human valves. These calcifying cells originate from the Oct4 embryonic lineage. Genetic deletion of Pou5f1 (Pit-Oct-Unc, OCT4) in the endocardial cell lineage prevents aortic stenosis and calcification of ApoE^−/− mouse valve. We established previously unidentified self-cell reprogramming NFκB- and OCT4-mediated inflammatory pathway triggering a dose-dependent mechanism of valve calcification.