Yap1 is required for endothelial to mesenchymal transition of the atrioventricular cushion

Interplay between Skeletal Muscle Catabolism and Remodeling of Arteriovenous Fistula by Yes-Associated Protein 1 (YAP1) Signaling

Key Points

Atrophied muscle–derived myostatin stimulated mesenchymal stem cell differentiation and adverse arteriovenous (AV) fistula remodeling through yes-associated protein 1 (YAP1) activation. Treatment with myostatin peptibody inhibited muscle wasting and blocked mesenchymal stem cell activation and AV fistula fibrosis. A light-sensitive drug-release strategy was engineered for the periadventitial delivery of verteporfin to improve AV fistula patency.

Background

Arteriovenous (AV) fistulas are the preferred access for dialysis but have a high incidence of failure. The aim of this study was to understand the crosstalk between skeletal muscle catabolism and AV fistula maturation failure.

Methods

Skeletal muscle metabolism and AV fistula maturation were evaluated in mice with CKD. The roles of myostatin and yes-associated protein 1 (YAP1) in regulating the transdifferentiation of adventitial mesenchymal stem cells (MSCs) and intima hyperplasia in AV fistula were investigated. Nanoparticles carrying a YAP1 inhibitor, verteporfin, with light irradiation–controlled release were synthesized and applied to AV fistula.

Results

Increased trichrome signals and stenosis were observed in AV fistulas from mice treated with myostatin and from mice with CKD. By contrast, blocking myostatin function with an anti-myostatin peptibody not only improved body weight and muscle size in CKD mice but also decreased neointima formation in AV fistulas. In cultured MSCs, myostatin induced YAP1 expression, promoting the differentiation of MSCs into myofibroblasts and inducing extracellular matrix deposition. Red light irradiation–controlled release of verteporfin from nanoparticles blocked YAP1 activation and alleviated myostatin-induced MSC activation. Periadventitial application and red light irradiation of nanoparticles carrying verteporfin significantly suppressed stiffening and neointima formation in AV fistula.

Conclusions

CKD induced muscle wasting, leading to increased production of myostatin, which stimulated MSC activation and vascular fibrosis linked to AV fistula stenosis. YAP1 signaling was activated in these processes. Red light irradiation–controlled release of verteporfin offered a feasible approach for local vascular drug intervention to improve AV fistula maturation.

UFMylation maintains YAP stability to promote vascular endothelial cell senescence

Endothelial cell (EC) senescence is an accomplice for vascular aging, which leads to cardiovascular diseases (CVDs). Evidences showed that Hippo-Yes-associated protein (YAP) signaling pathway plays an essential role in aging-associated CVDs. Here, we reported that YAP was elevated in senescent human umbilical vein endothelial cells (HUVECs) and inhibition of YAP could attenuate HUVECs senescence. Besides, our findings revealed that the activity of UFMylation and the level of YAP were both elevated in senescent cells. Furthermore, UFM1-modified YAP was upregulated in senescent ECs, and increased the stability of YAP. Importantly, we found that compound 8.5, an inhibitor of E1 of UFMylation, can alleviate vascular aging in aged mice. Together, our finding provides molecular mechanism by which UFMylation maintains YAP stability and exerts an important role in promoting cell senescence, and identified that a previously unrecognized UFMylation is a potential therapeutic target for anti-aging.

The molecular mechanisms of cardiac development and related diseases

Cardiac development is a complex and intricate process involving numerous molecular signals and pathways. Researchers have explored cardiac development through a long journey, starting with early studies observing morphological changes and progressing to the exploration of molecular mechanisms using various molecular biology methods. Currently, advancements in stem cell technology and sequencing technology, such as the generation of human pluripotent stem cells and cardiac organoids, multi-omics sequencing, and artificial intelligence (AI) technology, have enabled researchers to understand the molecular mechanisms of cardiac development better. Many molecular signals regulate cardiac development, including various growth and transcription factors and signaling pathways, such as WNT signaling, retinoic acid signaling, and Notch signaling pathways. In addition, cilia, the extracellular matrix, epigenetic modifications, and hypoxia conditions also play important roles in cardiac development. These factors play crucial roles at one or even multiple stages of cardiac development. Recent studies have also identified roles for autophagy, metabolic transition, and macrophages in cardiac development. Deficiencies or abnormal expression of these factors can lead to various types of cardiac development abnormalities. Nowadays, congenital heart disease (CHD) management requires lifelong care, primarily involving surgical and pharmacological treatments. Advances in surgical techniques and the development of clinical genetic testing have enabled earlier diagnosis and treatment of CHD. However, these technologies still have significant limitations. The development of new technologies, such as sequencing and AI technologies, will help us better understand the molecular mechanisms of cardiac development and promote earlier prevention and treatment of CHD in the future.

YAP-LAMB3 axis dictates cellular resistance of pancreatic ductal adenocarcinoma cells to gemcitabine

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive tumors with poor prognosis and inadequate response to treatment, such as gemcitabine (Gem), the first-line chemotherapeutic drug. Understanding the molecular determinants that control drug resistance to Gem is critical to predict potentially responsive patients and improve the benefits of Gem therapy. Emerging evidence suggests that certain developmental pathways, such as Hippo signaling, are aberrated and play important roles in Gem resistance in cancers. Although Hippo signaling has been reported to play a role in chemoresistance in cancers, it has not been clarified which specific target gene(s) functionally mediates the effect. In the present study, we found that YAP serves as a potent barrier for the cellular sensitivity of PDAC cells to Gem. We then identified and characterized laminin subunit beta 3 (LAMB3) as a bona fide target of YAP-TEAD4 to amplify YAP signaling via a feedback loop. Such a YAP-LAMB3 axis is critical to induce epithelial-mesenchymal transition and mediate Gem resistance. Taken together, we uncovered that YAP-LAMB3 axis is an important regulator of Gem, thus providing potential therapeutic targets for overcoming Gem resistance in PDAC.

Hippo and PI5P4K signaling intersect to control the transcriptional activation of YAP

Phosphoinositides are essential signaling molecules. The PI5P4K family of phosphoinositide kinases and their substrates and products, PI5P and PI4,5P2, respectively, are emerging as intracellular metabolic and stress sensors. We performed an unbiased screen to investigate the signals that these kinases relay and the specific upstream regulators controlling this signaling node. We found that the core Hippo pathway kinases MST1/2 phosphorylated PI5P4Ks and inhibited their signaling in vitro and in cells. We further showed that PI5P4K activity regulated several Hippo- and YAP-related phenotypes, specifically decreasing the interaction between the key Hippo proteins MOB1 and LATS and stimulating the YAP-mediated genetic program governing epithelial-to-mesenchymal transition. Mechanistically, we showed that PI5P interacted with MOB1 and enhanced its interaction with LATS, thereby providing a signaling connection between the Hippo pathway and PI5P4Ks. These findings reveal how these two important evolutionarily conserved signaling pathways are integrated to regulate metazoan development and human disease.

The determinants of metabolic discrepancies in aerobic glycolysis: Providing potential targets for breast cancer treatment

Altered aerobic glycolysis is the robust mechanism to support cancer cell survival and proliferation beyond the maintenance of cellular energy metabolism. Several investigators portrayed the important role of deregulated glycolysis in different cancers, including breast cancer. Breast cancer is the most ubiquitous form of cancer and the primary cause of cancer death in women worldwide. Breast cancer with increased glycolytic flux is hampered to eradicate with current therapies and can result in tumor recurrence. In spite of the low order efficiency of ATP production, cancer cells are highly addicted to glycolysis. The glycolytic dependency of cancer cells provides potential therapeutic strategies to preferentially kill cancer cells by inhibiting glycolysis using antiglycolytic agents. The present review emphasizes the most recent research on the implication of glycolytic enzymes, including glucose transporters (GLUTs), hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), lactate dehydrogenase-A (LDHA), associated signalling pathways and transcription factors, as well as the antiglycolytic agents that target key glycolytic enzymes in breast cancer. The potential activity of glycolytic inhibitors impinges cancer prevalence and cellular resistance to conventional drugs even under worse physiological conditions such as hypoxia. As a single agent or in combination with other chemotherapeutic drugs, it provides the feasibility of new therapeutic modalities against a wide spectrum of human cancers.

A Meta-Analysis Approach to Gene Regulatory Network Inference Identifies Key Regulators of Cardiovascular Diseases

Cardiovascular diseases (CVDs) represent a major concern for global health, whose mechanistic understanding is complicated by a complex interplay between genetic predisposition and environmental factors. Specifically, heart failure (HF), encompassing dilated cardiomyopathy (DC), ischemic cardiomyopathy (ICM), and hypertrophic cardiomyopathy (HCM), is a topic of substantial interest in basic and clinical research. Here, we used a Partial Correlation Coefficient-based algorithm (PCC) within the context of a meta-analysis framework to construct a Gene Regulatory Network (GRN) that identifies key regulators whose activity is perturbed in Heart Failure. By integrating data from multiple independent studies, our approach unveiled crucial regulatory associations between transcription factors (TFs) and structural genes, emphasizing their pivotal roles in regulating metabolic pathways, such as fatty acid metabolism, oxidative stress response, epithelial-to-mesenchymal transition, and coagulation. In addition to known associations, our analysis also identified novel regulators, including the identification of TFs FPM315 and OVOL2, which are implicated in dilated cardiomyopathies, and TEAD1 and TEAD2 in both dilated and ischemic cardiomyopathies. Moreover, we uncovered alterations in adipogenesis and oxidative phosphorylation pathways in hypertrophic cardiomyopathy and discovered a role for IL2 STAT5 signaling in heart failure. Our findings underscore the importance of TF activity in the initiation and progression of cardiac disease, highlighting their potential as pharmacological targets.

Temporal gene expression profiling during early-stage traumatic temporomandibular joint bony ankylosis in a sheep model

BACKGROUND

Investigating the molecular biology underpinning the early-stage of traumatic temporomandibular joint (TMJ) ankylosis is crucial for discovering new ways to prevent the disease. This study aimed to explore the dynamic changes of transcriptome from the intra-articular hematoma or the newly generated ankylosed callus during the onset and early progression of TMJ ankylosis.

METHODS

Based on a well-established sheep model of TMJ bony ankylosis, the genome-wide microarray data were obtained from samples at postoperative Days 1, 4, 7, 9, 11, 14 and 28, with intra-articular hematoma at Day 1 serving as controls. Fold changes in gene expression values were measured, and genes were identified via clustering based on time series analysis and further categorised into three major temporal classes: increased, variable and decreased expression groups. The genes in these three temporal groups were further analysed to reveal pathways and establish their biological significance.

RESULTS

Osteoblastic and angiogenetic genes were found to be significantly expressed in the increased expression group. Genes linked to inflammation and osteoclasts were found in the decreased expression group. The various biological processes and pathways related to each temporal expression group were identified, and the increased expression group comprised genes exclusively involved in the following pathways: Hippo signaling pathway, Wnt signaling pathway and Rap 1 signaling pathway. The decreased expression group comprised genes exclusively involved in immune-related pathways and osteoclast differentiation. The variable expression group consisted of genes associated with DNA replication, DNA repair and DNA recombination. Significant biological pathways and transcription factors expressed at each time point postoperatively were also identified.

CONCLUSIONS

These data, for the first time, presented the temporal gene expression profiling and reveal the important process of molecular biology in the early-stage of traumatic TMJ bony ankylosis. The findings might contributed to identifying potential targets for the treatment of TMJ ankylosis.

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.

Cooperative Response to Endocardial Notch Reveals Interaction With Hippo Pathway

BACKGROUND

The endocardium is a crucial signaling center for cardiac valve development and maturation. Genetic analysis has identified several human endocardial genes whose inactivation leads to bicuspid aortic valve formation and calcific aortic valve disease, but knowledge is very limited about the role played in valve development and disease by noncoding endocardial regulatory regions and upstream factors.

METHODS

We manipulated Notch signaling in mouse embryonic endocardial cells by short-term and long-term coculture with OP9 stromal cells expressing Notch ligands and inhibition of Notch activity. We examined the transcriptional profile and chromatin accessibility landscape for each condition, integrated transcriptomic, transcription factor occupancy, chromatin accessibility, and proteomic datasets. We generated in vitro and in vivo models with CRISPR-Cas9-edited deletions of various noncoding regulatory elements and validated their regulatory potential.

RESULTS

We identified primary and secondary transcriptional responses to Notch ligands in the mouse embryonic endocardium, and a NOTCH-dependent transcriptional signature in valve development and disease. By defining the changes in the chromatin accessibility landscape and integrating with the landscape in developing mouse endocardium and adult human valves, we identify potential noncoding regulatory elements, validated selected candidates, propose interacting cofactors, and define the timeframe of their regulatory activity. Additionally, we found cooperative transcriptional repression with Hippo pathway by inhibiting nuclear Yap (Yes-associated protein) activity in the endocardium during cardiac valve development.

CONCLUSIONS

Sequential Notch-dependent transcriptional regulation in the embryonic endocardium involves multiple factors. Notch activates certain noncoding elements through these factors and simultaneously suppresses elements that could hinder cardiac valve development and homeostasis. Biorxviv: https://www.biorxiv.org/content/10.1101/2023.03.23.533882v1.full.

Hippo Signaling Mediates TGFβ-Dependent Transcriptional Inputs in Cardiac Cushion Mesenchymal Cells to Regulate Extracellular Matrix Remodeling

The transforming growth factor beta (TGFβ) and Hippo signaling pathways are evolutionarily conserved pathways that play a critical role in cardiac fibroblasts during embryonic development, tissue repair, and fibrosis. TGFβ signaling and Hippo signaling are also important for cardiac cushion remodeling and septation during embryonic development. Loss of TGFβ2 in mice causes cardiac cushion remodeling defects resulting in congenital heart disease. In this study, we used in vitro molecular and pharmacologic approaches in the cushion mesenchymal cell line (tsA58-AVM) and investigated if the Hippo pathway acts as a mediator of TGFβ2 signaling. Immunofluorescence staining showed that TGFβ2 induced nuclear translocation of activated SMAD3 in the cushion mesenchymal cells. In addition, the results indicate increased nuclear localization of Yes-associated protein 1 (YAP1) following a similar treatment of TGFβ2. In collagen lattice formation assays, the TGFβ2 treatment of cushion cells resulted in an enhanced collagen contraction compared to the untreated cushion cells. Interestingly, verteporfin, a YAP1 inhibitor, significantly blocked the ability of cushion cells to contract collagen gel in the absence or presence of exogenously added TGFβ2. To confirm the molecular mechanisms of the verteporfin-induced inhibition of TGFβ2-dependent extracellular matrix (ECM) reorganization, we performed a gene expression analysis of key mesenchymal genes involved in ECM remodeling in heart development and disease. Our results confirm that verteporfin significantly decreased the expression of α-smooth muscle actin (Acta2), collagen 1a1 (Col1a1), Ccn1 (i.e., Cyr61), and Ccn2 (i.e., Ctgf). Western blot analysis indicated that verteporfin treatment significantly blocked the TGFβ2-induced activation of SMAD2/3 in cushion mesenchymal cells. Collectively, these results indicate that TGFβ2 regulation of cushion mesenchymal cell behavior and ECM remodeling is mediated by YAP1. Thus, the TGFβ2 and Hippo pathway integration represents an important step in understanding the etiology of congenital heart disease.

Vasculature is getting Hip(po): Hippo signaling in vascular development and disease

The Hippo signaling pathway regulates developmental organ growth, regeneration, and cell fate decisions. Although the role of the Hippo pathway, and its transcriptional effectors YAP and TAZ, has been well documented in many cell types and species, only recently have the roles for this pathway come to light in vascular development and disease. Experiments in mice, zebrafish, and in vitro have uncovered roles for the Hippo pathway, YAP, and TAZ in vasculogenesis, angiogenesis, and lymphangiogenesis. In addition, the Hippo pathway has been implicated in vascular cancers and cardiovascular diseases, thus identifying it as a potential therapeutic target for the treatment of these conditions. However, despite recent advances, Hippo's role in the vasculature is still underappreciated compared with its role in epithelial tissues. In this review, we appraise our current understanding of the Hippo pathway in blood and lymphatic vessel development and highlight the current knowledge gaps and opportunities for further research.

Shear and hydrostatic stress regulate fetal heart valve remodeling through YAP-mediated mechanotransduction

Clinically serious congenital heart valve defects arise from improper growth and remodeling of endocardial cushions into leaflets. Genetic mutations have been extensively studied but explain less than 20% of cases. Mechanical forces generated by beating hearts drive valve development, but how these forces collectively determine valve growth and remodeling remains incompletely understood. Here, we decouple the influence of those forces on valve size and shape, and study the role of YAP pathway in determining the size and shape. The low oscillatory shear stress promotes YAP nuclear translocation in valvular endothelial cells (VEC), while the high unidirectional shear stress restricts YAP in cytoplasm. The hydrostatic compressive stress activated YAP in valvular interstitial cells (VIC), whereas the tensile stress deactivated YAP. YAP activation by small molecules promoted VIC proliferation and increased valve size. Whereas YAP inhibition enhanced the expression of cell-cell adhesions in VEC and affected valve shape. Finally, left atrial ligation was performed in chick embryonic hearts to manipulate the shear and hydrostatic stress in vivo. The restricted flow in the left ventricle induced a globular and hypoplastic left atrioventricular (AV) valves with an inhibited YAP expression. By contrast, the right AV valves with sustained YAP expression grew and elongated normally. This study establishes a simple yet elegant mechanobiological system by which transduction of local stresses regulates valve growth and remodeling. This system guides leaflets to grow into proper sizes and shapes with the ventricular development, without the need of a genetically prescribed timing mechanism.

Clinical Signs of Kawasaki Disease from the Perspective of Epithelial-to-Mesenchymal Transition Recruiting Erythrocytes: A Literature Review

Kawasaki disease (KD) is a systemic vasculitis affecting children younger than 5 years of age. Early period in life is marked by rapid somatic growth with cell proliferation and immaturity of the immunity with dominant innate immune system. Coronary complications in KD are the most common acquired heart disease in children, yet the diagnosis of KD still depends on the clinical diagnostic criteria. Glossy red lips and conjunctival injection are characteristic signs enabling pediatricians to make the initial diagnosis of KD; however, little is known why these are so characteristic. The diagnostic criteria of KD seem to be scattered in seemingly irrelevant body systems such as the eyes, lips, skin, and heart. KD is classified as a connective tissue disease. Recently, red blood cells (RBCs) have emerged as important modulators in innate immune response. RBCs are reported to participate in extracellular matrix remodeling and upregulating matrix metalloproteinase (MMP) expression in dermal fibroblasts. Also, fibroblast growth factors and microRNAs associated with fibrosis are drawing attention in KD. The cardinal signs of KD appear at the border of muco-cutaneous junction. Head and neck regions are abundant in tissues undergoing epithelial-to-mesenchymal transition (EMT). Interstitial carditis and valve insufficiency as well as coronary arterial lesions may complicate KD, and these lesions present in tissues that originated from epicardial progenitor cells by EMT. Having reviewed the recent research on KD, we presume that the signs of KD present at borders between keratinized and non-keratinized stratified squamous epithelium where the EMT is still ongoing for the rapid somatic growth where RBCs are recruited as an innate immune response and to prevent excessive fibrosis in mucosa. KD presents scarcely in adults with somatic growth and immune maturation completed. In this review, we attempted to explain the reasons for the clinical manifestations of KD and to search for a link among the diagnostic clues in the perspective of EMT during the somatic growth and immune system maturation in children with KD.

Future prospects in the tissue engineering of heart valves: a focus on the role of stem cells

INTRODUCTION

Heart valve disease is a growing burden on the healthcare system. Current solutions are insufficient for young patients and do not offer relief from reintervention. Tissue engineered heart valves (TEHVs) offer a solution that grows and responds to the native environment in a similar way to a healthy valve. Stem cells hold potential to populate these valves as a malleable source that can adapt to environmental cues.

AREAS COVERED

This review covers current methods of recapitulating features of native heart valves with tissue engineering through use of stem cell populations with in situ and in vitro methods.

EXPERT OPINION

In the field of TEHVs, we see a variety of approaches in cell source, biomaterial, and maturation methods. Choosing appropriate cell populations may be very patient specific; consistency and predictability will be key to long-term success. In situ methods are closer to translation but struggle with consistent cellularization. In vitro culture requires specialized methods but may recapitulate native valve cell populations with higher fidelity. Understanding how cell populations react to valve conditions and immune response is vital for success. Detrimental valve pathologies have proven to be difficult to avoid in early translation attempts.

Automated endocardial cushion segmentation and cellularization quantification in developing hearts using optical coherence tomography

Of all congenital heart defects (CHDs), anomalies in heart valves and septa are among the most common and contribute about fifty percent to the total burden of CHDs. Progenitors to heart valves and septa are endocardial cushions formed in looping hearts through a multi-step process that includes localized expansion of cardiac jelly, endothelial-to-mesenchymal transition, cell migration and proliferation. To characterize the development of endocardial cushions, previous studies manually measured cushion size or cushion cell density from images obtained using histology, immunohistochemistry, or optical coherence tomography (OCT). Manual methods are time-consuming and labor-intensive, impeding their applications in cohort studies that require large sample sizes. This study presents an automated strategy to rapidly characterize the anatomy of endocardial cushions from OCT images. A two-step deep learning technique was used to detect the location of the heart and segment endocardial cushions. The acellular and cellular cushion regions were then segregated by K-means clustering. The proposed method can quantify cushion development by measuring the cushion volume and cellularized fraction, and also map 3D spatial organization of the acellular and cellular cushion regions. The application of this method to study the developing looping hearts allowed us to discover a spatial asymmetry of the acellular cardiac jelly in endocardial cushions during these critical stages, which has not been reported before.

Depletion of VGLL4 Causes Perinatal Lethality without Affecting Myocardial Development

Congenital heart disease is one of the leading causes of pediatric morbidity and mortality, thus highlighting the importance of deciphering the molecular mechanisms that control heart development. As the terminal transcriptional effectors of the Hippo-YAP pathway, YAP and TEAD1 form a transcriptional complex that regulates the target gene expression and depletes either of these two genes in cardiomyocytes, thus resulting in cardiac hypoplasia. Vestigial-like 4 (VGLL4) is a transcriptional co-factor that interacts with TEAD and suppresses the YAP/TEAD complex by competing against YAP for TEAD binding. To understand the VGLL4 function in the heart, we generated two VGLL4 loss-of-function mouse lines: a germline Vgll4 depletion allele and a cardiomyocyte-specific Vgll4 depletion allele. The whole-body deletion of Vgll4 caused defective embryo development and perinatal lethality. The analysis of the embryos at day 16.5 revealed that Vgll4 knockout embryos had reduced body size, malformed tricuspid valves, and normal myocardium. Few whole-body Vgll4 knockout pups could survive up to 10 days, and none of them showed body weight gain. In contrast to the whole-body Vgll4 knockout mutants, cardiomyocyte-specific Vgll4 knockout mice had no noticeable heart growth defects and had normal heart function. In summary, our data suggest that VGLL4 is required for embryo development but dispensable for myocardial growth.

Endocardial Regulation of Cardiac Development

The endocardium is a specialized form of endothelium that lines the inner side of the heart chambers and plays a crucial role in cardiac development. While comparatively less studied than other cardiac cell types, much progress has been made in understanding the regulation of and by the endocardium over the past two decades. In this review, we will summarize what is currently known regarding endocardial origin and development, the relationship between endocardium and other cardiac cell types, and the various lineages that endocardial cells derive from and contribute to. These processes are driven by key molecular mechanisms such as Notch and BMP signaling. These pathways in particular have been well studied, but other signaling pathways and mechanical cues also play important roles. Finally, we will touch on the contribution of stem cell modeling in combination with single cell sequencing and its potential translational impact for congenital heart defects such as bicuspid aortic valves and hypoplastic left heart syndrome. The detailed understanding of cellular and molecular processes in the endocardium will be vital to further develop representative stem cell-derived models for disease modeling and regenerative medicine in the future.

Hippo signaling in cardiac fibroblasts during development, tissue repair, and fibrosis

The evolutionarily conserved Hippo signaling pathway plays key roles in regulating the balance between cell proliferation and apoptosis, cell differentiation, organ size control, tissue repair, and regeneration. Recently, the Hippo pathway has been shown to regulate heart fibrosis, defined as excess extracellular matrix (ECM) deposition and increased tissue stiffness. Cardiac fibroblasts (CFs) are the primary cell type that produces, degrades, and remodels the ECM during homeostasis, aging, inflammation, and tissue repair and regeneration. Here, we review the available evidence from the current literature regarding how the Hippo pathway regulates the formation and function of CFs during heart development and tissue repair.

Elevated H3K4me3 Through MLL2-WDR82 upon Hyperglycemia Causes Jagged Ligand Dependent Notch Activation to Interplay with Differentiation State of Endothelial Cells

Endothelial-to-mesenchymal transition (EndMT) is a hallmark of diabetes-associated vascular complications. Epigenetic mechanisms emerged as one of the key pathways to regulate diabetes-associated complications. In the current study, we aimed to determine how abrupt changes in histone 3 lysine 4 tri-methylation (H3K4me3) upon hyperglycemia exposure reprograms endothelial cells to undergo EndMT. Through in vitro studies, we first establish that intermittent high-glucose exposure to EC most potently induced partial mesenchyme-like characteristics compared with transient or constant high-glucose-challenged endothelial cells. In addition, glomerular endothelial cells of BTBR Ob/Ob mice also exhibited mesenchymal-like characteristics. Intermittent hyperglycemia-dependent induction of partial mesenchyme-like phenotype of endothelial cells coincided with an increase in H3K4me3 level in both macro- and micro-vascular EC due to selective increase in MLL2 and WDR82 protein of SET1/COMPASS complex. Such an endothelial-specific heightened H3K4me3 level was also detected in intermittent high-glucose-exposed rat aorta and in kidney glomeruli of Ob/Ob mice. Elevated H3K4me3 enriched in the promoter regions of Notch ligands Jagged1 and Jagged2, thus causing abrupt expression of these ligands and concomitant activation of Notch signaling upon intermittent hyperglycemia challenge. Pharmacological inhibition and/or knockdown of MLL2 in cells in vitro or in tissues ex vivo normalized intermittent high-glucose-mediated increase in H3K4me3 level and further reversed Jagged1 and Jagged2 expression, Notch activation and further attenuated acquisition of partial mesenchyme-like phenotype of endothelial cells. In summary, the present study identifies a crucial role of histone methylation in hyperglycemia-dependent reprograming of endothelial cells to undergo mesenchymal transition and indicated that epigenetic pathways contribute to diabetes-associated vascular complications.

Mechanical control of nuclear import by Importin-7 is regulated by its dominant cargo YAP

Mechanical forces regulate multiple essential pathways in the cell. The nuclear translocation of mechanoresponsive transcriptional regulators is an essential step for mechanotransduction. However, how mechanical forces regulate the nuclear import process is not understood. Here, we identify a highly mechanoresponsive nuclear transport receptor (NTR), Importin-7 (Imp7), that drives the nuclear import of YAP, a key regulator of mechanotransduction pathways. Unexpectedly, YAP governs the mechanoresponse of Imp7 by forming a YAP/Imp7 complex that responds to mechanical cues through the Hippo kinases MST1/2. Furthermore, YAP behaves as a dominant cargo of Imp7, restricting the Imp7 binding and the nuclear translocation of other Imp7 cargoes such as Smad3 and Erk2. Thus, the nuclear import process is an additional regulatory layer indirectly regulated by mechanical cues, which activate a preferential Imp7 cargo, YAP, which competes out other cargoes, resulting in signaling crosstalk.

The translation of mechanical cues into gene expression changes is dependent on the nuclear import of mechanoresponsive transcriptional regulators. Here the authors identify that Importin-7 drives the nuclear import of one such regulator YAP while YAP then controls Importin-7 response to mechanical cues and restricts Importin-7 binding to other cargoes.

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.

Hydrostatic Pressure Controls Angiogenesis Through Endothelial YAP1 During Lung Regeneration

Pulmonary artery (PA) pressure increases during lung growth after unilateral pneumonectomy (PNX). Mechanosensitive transcriptional co-activator, yes-associated protein (YAP1), in endothelial cells (ECs) is necessary for angiogenesis during post-PNX lung growth. We investigate whether increases in PA pressure following PNX control-angiogenesis through YAP1. When hydrostatic pressure is applied to human pulmonary arterial ECs (HPAECs), the expression of YAP1, transcription factor TEAD1, and angiogenic factor receptor Tie2 increases, while these effects are inhibited when HPAECs are treated with YAP1 siRNA or YAP1S94A mutant that fails to bind to TEAD1. Hydrostatic pressure also stimulates DNA synthesis, cell migration, and EC sprouting in HPAECs, while YAP1 knockdown or YAP1S94A mutant inhibits the effects. Gene enrichment analysis reveals that the levels of genes involved in extracellular matrix (ECM), cell adhesion, regeneration, or angiogenesis are altered in post-PNX mouse lung ECs, which interact with YAP1. Exosomes are known to promote tissue regeneration. Proteomics analysis reveals that exosomes isolated from conditioned media of post-PNX mouse lung ECs contain the higher levels of ECM and cell-adhesion proteins compared to those from sham-operated mouse lung ECs. Recruitment of host lung ECs and blood vessel formation are stimulated in the fibrin gel containing exosomes isolated from post-PNX mouse lung ECs or pressurized ECs, while YAP1 knockdown inhibits the effects. These results suggest that increases in PA pressure stimulate angiogenesis through YAP1 during regenerative lung growth.

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.

Inhibition of the proliferation, invasion, migration, and epithelial-mesenchymal transition of prostate cancer cells through the action of ATP1A2 on the TGF-β/Smad pathway

BACKGROUND

Prostate cancer (PC) is one of the major male malignancies worldwide. Because Na+-K+-ATPase is widely involved in various pathological processes, but the action of its α2 subtype (ATP1A2) in PC is unclear, we investigated the role of ATP1A2 in the invasion and migration of PC cells.

METHODS

We measured the expression levels of ATP1A2 in human normal prostate epithelial cell line (RWPE-1) and PC cell lines (PC-3 and DU145) by quantitative real-time PCR (qRT-PCR) and western blot. Cell proliferation, apoptosis, migration, and invasion of PC-3 and DU145 cells were investigated through clone formation assay, EdU assay, flow cytometry and transwell assay, respectively. The effect of ATP1A2 on a tumor-inhibitory pathway [transforming growth factor-β (TGF-β)/Smad] was assessed using western blot. In addition, tumor formation was detected using in vivo xenograft model in male BALB/c nude mice.

RESULTS

The Cancer Genome Atlas (TCGA) analysis showed that ATP1A2 expression was reduced in PC patients (P<0.05), and patients with low ATP1A2 expression had a lower survival rate (P<0.05). ATP1A2 levels were significantly reduced in PC-3 and DU145 cells, compared with RWPE-1 cells (P<0.01). We also demonstrated that overexpression of ATP1A2 significantly inhibited the proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) of PC-3 and DU145 cells (P<0.01) and promoted apoptosis (P<0.01). However, silencing ATP1A2 had the opposite effect (P<0.01). In addition, overexpression of ATP1A2 significantly inhibited the TGF-β/Smad pathway (P<0.01), whereas silencing ATP1A2 activated the TGF-β/Smad pathway (P<0.01). Meanwhile, the effect of ATP1A2 silencing on the proliferation, apoptosis, migration and invasion was reversed by TGF-β/Smad pathway inhibitor (LY364947). Furthermore, ATP1A2 inhibited tumor growth in vivo.

CONCLUSIONS

ATP1A2 inhibited proliferation, apoptosis, migration, invasion, and EMT in PC by inhibiting the TGF-β/Smad pathway.

Sculpting the heart: Cellular mechanisms shaping valves and trabeculae

The transformation of the heart from a simple tube to a complex organ requires the orchestration of several morphogenetic processes. Two structures critical for cardiac function, the cardiac valves and the trabecular network, are formed through extensive tissue morphogenesis-endocardial cell migration, deadhesion and differentiation into fibroblast-like cells during valve formation, and cardiomyocyte delamination and apico-basal depolarization during trabeculation. Here, we review current knowledge of how these specialized structures acquire their shape by focusing on the underlying cellular behaviors and molecular mechanisms, highlighting findings from in vivo models and briefly discussing the recent advances in cardiac cell culture and organoids.

Role of endothelial cells in pulmonary fibrosis via SREBP2 activation

Idiopathic pulmonary fibrosis (IPF) is a progressive lung disease with limited treatment options. Despite endothelial cells (ECs) comprising 30% of the lung cellular composition, the role of EC dysfunction in pulmonary fibrosis (PF) remains unclear. We hypothesize that sterol regulatory element-binding protein 2 (SREBP2) plays a critical role in the pathogenesis of PF via EC phenotypic modifications. Transcriptome data demonstrate that SREBP2 overexpression in ECs led to the induction of the TGF, Wnt, and cytoskeleton remodeling gene ontology pathways and the increased expression of mesenchymal genes, such as snail family transcriptional repressor 1 (snai1), α-smooth muscle actin, vimentin, and neural cadherin. Furthermore, SREBP2 directly bound to the promoter regions and transactivated these mesenchymal genes. This transcriptomic change was associated with an epigenetic and phenotypic switch in ECs, leading to increased proliferation, stress fiber formation, and ECM deposition. Mice with endothelial-specific transgenic overexpression of SREBP2 (EC-SREBP2[N]-Tg mice) that were administered bleomycin to induce PF demonstrated exacerbated vascular remodeling and increased mesenchymal transition in the lung. SREBP2 was also found to be markedly increased in lung specimens from patients with IPF. These results suggest that SREBP2, induced by lung injury, can exacerbate PF in rodent models and in human patients with IPF.

Control of tissue homeostasis, tumorigenesis, and degeneration by coupled bidirectional bistable switches

The Hippo-YAP/TAZ signaling pathway plays a critical role in tissue homeostasis, tumorigenesis, and degeneration disorders. The regulation of YAP/TAZ levels is controlled by a complex regulatory network, where several feedback loops have been identified. However, it remains elusive how these feedback loops contain the YAP/TAZ levels and maintain the system in a healthy physiological state or trap the system in pathological conditions. Here, a mathematical model was developed to represent the YAP/TAZ regulatory network. Through theoretical analyses, three distinct states that designate the one physiological and two pathological outcomes were found. The transition from the physiological state to the two pathological states is mechanistically controlled by coupled bidirectional bistable switches, which are robust to parametric variation and stochastic fluctuations at the molecular level. This work provides a mechanistic understanding of the regulation and dysregulation of YAP/TAZ levels in tissue state transitions.

Tissue development and homeostasis require well-controlled cell proliferation. Lack of this control could lead to degenerative or tumorigenic diseases. Signaling pathways have been explored in promoting or inhibiting these diseases. The Hippo signaling pathway is one of these, which has been found to control tissue homeostasis and organ size through cell proliferation and apoptosis, as evidenced by extensive experimental data. However, the question remains of how tissue can transition from a homeostatic state to either a degenerative or tumorigenic state. By theoretically analyzing a mathematical model of its regulatory network, we present a mechanism that underlies Hippo signaling to control tissue transition from a homeostatic state to a disease state. This provides us with a mechanistic understanding of how the parts of the regulatory network are coordinated for the transitions between the homeostasis state and the disease states. In addition, we looked at the role of system noise and found that it could promote the transition to one of the disease states. Our model allows for experimental hypotheses to be generated and could lead to the development of therapeutic strategies by targeting the Hippo signaling pathway.

Substrate stiffness modulates endothelial cell function via the YAP-Dll4-Notch1 pathway

Endothelial cells adapt their functions as a consequence of sensing extracellular substrate stiffness; these alterations allow them to maintain their vascular structure and function. Substrate stiffness-mediated yes-associated protein 1 (YAP) activation plays an important role in mechano-transduction and pro-angiogenic phenotype of endothelial cells, and Delta-like ligand 4 (Dll4)-Notch1 signaling is closely related to angiogenesis; however, the impact of substrate stiffness-mediated interrelation of these pathways on endothelial cell functions remains elusive. We confirmed that endothelial cells on softer substrates not only elongate cellular aspects but also attenuate YAP activation compared to cells on stiffer substrates. Endothelial cells on softer substrates also upregulate the vascular endothelial growth factor receptor 1 (VEGFR1) and VEGFR2 mRNA expression that is enhanced by VEGF stimulation. We determined that endothelial cells on softer substrates increased Dll4 expression, but not Notch1 expression, via YAP signaling. Moreover, endothelial cells on soft substrates induced not only VEGFRs upregulation but also suppression of pro-inflammatory interleukin-6 and plasminogen activator inhibitor-1 mRNA expression and the facilitation of anti-coagulant thrombomodulin and pro-coagulant tissue factor mRNA expression. Our results suggest that endothelial cells activate the YAP-Dll4-Notch signaling pathway in response to substrate stiffness and dictate cellular function.

The role of caveolae in endothelial dysfunction

Caveolae, the specialized cell-surface plasma membrane invaginations which are abundant in endothelial cells, play critical roles in regulating various cellular processes, including cholesterol homeostasis, nitric oxide production, and signal transduction. Endothelial caveolae serve as a membrane platform for compartmentalization, modulation, and integration of signal events associated with endothelial nitric oxide synthase, ATP synthase β, and integrins, which are involved in the regulation of endothelial dysfunction and related cardiovascular diseases, such as atherosclerosis and hypertension. Furthermore, these dynamic microdomains on cell membrane are modulated by various extracellular stimuli, including cholesterol and flow shear stress. In this brief review, we summarize the critical roles of caveolae in the orchestration of endothelial function based on recent findings as well as our work over the past two decades.

Hippo/yes-associated protein signaling functions as a mechanotransducer in regulating vascular homeostasis

Cells are constantly exposed to various mechanical forces, including hydrostatic pressure, cyclic stretch, fluid shear stress, and extracellular matrix stiffness. Mechanical cues can be translated into the cell-specific transcriptional process by a cellular mechanic-transducer. Evidence suggests that mechanical signals assist activated intracellular signal transduction pathways and the relative phenotypic adaptation to coordinate cell behavior and disease appropriately. The Hippo/yes-associated protein (YAP) signaling pathway is regulated in response to numerous mechanical stimuli. It plays an important role in the mechanotransduction mechanism, which converts mechanical forces to cascades of molecular signaling to modulate gene expression. This review summarizes the recent findings relevant to the Hippo/YAP pathway-based mechanotransduction in cell behavior and maintaining blood vessels, as well as cardiovascular disease.

MiR-200c-3p promotes ox-LDL-induced endothelial to mesenchymal transition in human umbilical vein endothelial cells through SMAD7/YAP pathway

BACKGROUND

Endothelial to mesenchymal transition (EndMT) participates in the progression of atherosclerosis (AS). MiR-200c-3p has been implicated in EndMT. However, the functional role of miR-200c-3p in AS remains largely unknown. Here, we demonstrated the critical role of miR-200c-3p in regulating EndMT in AS.

METHODS

ApoE-/- mice were fed with high-fat diet to establish AS mouse model, and human umbilical vein endothelial cells (HUVECs) were treated with oxidized low-density lipoprotein (ox-LDL) to mimic AS cell model. The expression of miR-200c-3p, SMAD7 and YAP in ApoE-/- mice and HUVECs was detected by quantitative real-time PCR. Rhodamine phalloidin staining and Western blot were performed to observe cell morphology and EndMT marker expression of HUVECs. Luciferase reporter assay and Co-Immunoprecipitation were performed to verify the relationship among miR-200c-3p, SMAD7, and YAP.

RESULTS

MiR-200c-3p was highly expressed, and SMAD7 and YAP were down-regulated in the aortic tissues of ApoE-/- mice and ox-LDL-treated HUVECs. MiR-200c-3p overexpression promoted the transformation of ox-LDL-treated HUVECs from cobblestone-like epithelial phenotype to a spindle-like mesenchymal phenotype. Meanwhile, miR-200c-3p up-regulation repressed the expression of endothelial markers CD31 and vWF and promoted the expression of mesenchymal markers α-SMA and vimentin in the ox-LDL-treated HUVECs. MiR-200c-3p inhibited SMAD7 and YAP expression by interacting with 3' untranslated region of SMAD7. Moreover, miR-200c-3p promoted EndMT in ox-LDL-treated HUVECs by inhibiting SMAD7/YAP pathway.

CONCLUSION

This work demonstrated that MiR-200c-3p promoted ox-LDL-induced EndMT in HUVECs through SMAD7/YAP pathway, which may be important for the onset of atherosclerosis.

Strong as a Hippo's Heart: Biomechanical Hippo Signaling During Zebrafish Cardiac Development

The heart is comprised of multiple tissues that contribute to its physiological functions. During development, the growth of myocardium and endocardium is coupled and morphogenetic processes within these separate tissue layers are integrated. Here, we discuss the roles of mechanosensitive Hippo signaling in growth and morphogenesis of the zebrafish heart. Hippo signaling is involved in defining numbers of cardiac progenitor cells derived from the secondary heart field, in restricting the growth of the epicardium, and in guiding trabeculation and outflow tract formation. Recent work also shows that myocardial chamber dimensions serve as a blueprint for Hippo signaling-dependent growth of the endocardium. Evidently, Hippo pathway components act at the crossroads of various signaling pathways involved in embryonic zebrafish heart development. Elucidating how biomechanical Hippo signaling guides heart morphogenesis has direct implications for our understanding of cardiac physiology and pathophysiology.

Endocytic Protein Defects in the Neural Crest Cell Lineage and Its Pathway Are Associated with Congenital Heart Defects

Endocytic trafficking is an under-appreciated pathway in cardiac development. Several genes related to endocytic trafficking have been uncovered in a mutagenic ENU screen, in which mutations led to congenital heart defects (CHDs). In this article, we review the relationship between these genes (including LRP1 and LRP2) and cardiac neural crest cells (CNCCs) during cardiac development. Mice with an ENU-induced Lrp1 mutation exhibit a spectrum of CHDs. Conditional deletion using a floxed Lrp1 allele with different Cre drivers showed that targeting neural crest cells with Wnt1-Cre expression replicated the full cardiac phenotypes of the ENU-induced Lrp1 mutation. In addition, LRP1 function in CNCCs is required for normal OFT lengthening and survival/expansion of the cushion mesenchyme, with other cell lineages along the NCC migratory path playing an additional role. Mice with an ENU-induced and targeted Lrp2 mutation demonstrated the cardiac phenotype of common arterial trunk (CAT). Although there is no impact on CNCCs in Lrp2 mutants, the loss of LRP2 results in the depletion of sonic hedgehog (SHH)-dependent cells in the second heart field. SHH is known to be crucial for CNCC survival and proliferation, which suggests LRP2 has a non-autonomous role in CNCCs. In this article, other endocytic trafficking proteins that are associated with CHDs that may play roles in the NCC pathway during development, such as AP1B1, AP2B1, FUZ, MYH10, and HECTD1, are reviewed.

A dual role of YAP in driving TGFβ-mediated endothelial-to-mesenchymal transition

Endothelial-to-mesenchymal transition (EndMT) is the biological process through which endothelial cells transdifferentiate into mesenchymal cells. During embryo development, EndMT regulates endocardial cushion formation via TGFβ/BMP signaling. In adults, EndMT is mainly activated during pathological conditions. Hence, it is necessary to characterize molecular regulators cooperating with TGFβ signaling in driving EndMT, to identify potential novel therapeutic targets to treat these pathologies. Here, we studied YAP, a transcriptional co-regulator involved in several biological processes, including epithelial-to-mesenchymal transition (EMT). As EndMT is the endothelial-specific form of EMT, and YAP (herein referring to YAP1) and TGFβ signaling cross-talk in other contexts, we hypothesized that YAP contributes to EndMT by modulating TGFβ signaling. We demonstrate that YAP is required to trigger TGFβ-induced EndMT response, specifically contributing to SMAD3-driven EndMT early gene transcription. We provide novel evidence that YAP acts as SMAD3 transcriptional co-factor and prevents GSK3β-mediated SMAD3 phosphorylation, thus protecting SMAD3 from degradation. YAP is therefore emerging as a possible candidate target to inhibit pathological TGFβ-induced EndMT at early stages.

Summary: A new crucial role for YAP as a co-activator of early pathological TGFβ-mediated endothelial-to-mesenchymal transition program and characterization of the underlying molecular mechanism.

Modulation of EndMT by Hydrogen Sulfide in the Prevention of Cardiovascular Fibrosis

Endothelial mesenchymal transition (EndMT) has been described as a fundamental process during embryogenesis; however, it can occur also in adult age, underlying pathological events, including fibrosis. Indeed, during EndMT, the endothelial cells lose their specific markers, such as vascular endothelial cadherin (VE-cadherin), and acquire a mesenchymal phenotype, expressing specific products, such as α-smooth muscle actin (α-SMA) and type I collagen; moreover, the integrity of the endothelium is disrupted, and cells show a migratory, invasive and proliferative phenotype. Several stimuli can trigger this transition, but transforming growth factor (TGF-β1) is considered the most relevant. EndMT can proceed in a canonical smad-dependent or non-canonical smad-independent manner and ultimately regulate gene expression of pro-fibrotic machinery. These events lead to endothelial dysfunction and atherosclerosis at the vascular level as well as myocardial hypertrophy and fibrosis. Indeed, EndMT is the mechanism which promotes the progression of cardiovascular disorders following hypertension, diabetes, heart failure and also ageing. In this scenario, hydrogen sulfide (H₂S) has been widely described for its preventive properties, but its role in EndMT is poorly investigated. This review is focused on the evaluation of the putative role of H₂S in the EndMT process.

Endothelial connexin-integrin crosstalk in vascular inflammation

Cardiovascular diseases including blood vessel disorders represent a major cause of death globally. The essential roles played by local and systemic vascular inflammation in the pathogenesis of cardiovascular diseases have been increasingly recognized. Vascular inflammation triggers the aberrant activation of endothelial cells, which leads to the functional and structural abnormalities in vascular vessels. In addition to humoral mediators such as pro-inflammatory cytokines and prostaglandins, the alteration of physical and mechanical microenvironment - including vascular stiffness and shear stress - modify the gene expression profiles and metabolic profiles of endothelial cells via mechano-transduction pathways, thereby contributing to the pathogenesis of vessel disorders. Notably, connexins and integrins crosstalk each other in response to the mechanical stress, and, thereby, play an important role in regulating the mechano-transduction of endothelial cells. Here, we provide an overview on how the inter-play between connexins and integrins in endothelial cells unfold during the mechano-transduction in vascular inflammation.

Role of the Epicardium in the Development of the Atrioventricular Valves and Its Relevance to the Pathogenesis of Myxomatous Valve Disease

This paper is dedicated to the memory of Dr. Adriana "Adri" Gittenberger-de Groot and in appreciation of her work in the field of developmental cardiovascular biology and the legacy that she has left behind. During her impressive career, Dr. Gittenberger-de Groot studied many aspects of heart development, including aspects of cardiac valve formation and disease and the role of the epicardium in the formation of the heart. In this contribution, we review some of the work on the role of epicardially-derived cells (EPDCs) in the development of the atrioventricular valves and their potential involvement in the pathogenesis of myxomatous valve disease (MVD). We provide an overview of critical events in the development of the atrioventricular junction, discuss the role of the epicardium in these events, and illustrate how interfering with molecular mechanisms that are involved in the epicardial-dependent formation of the atrioventricular junction leads to a number of abnormalities. These abnormalities include defects of the AV valves that resemble those observed in humans that suffer from MVD. The studies demonstrate the importance of the epicardium for the proper formation and maturation of the AV valves and show that the possibility of epicardial-associated developmental defects should be taken into consideration when determining the genetic origin and pathogenesis of MVD.

The transcription factor Sox7 modulates endocardiac cushion formation contributed to atrioventricular septal defect through Wnt4/Bmp2 signaling

Cardiac septum malformations account for the largest proportion in congenital heart defects. The transcription factor Sox7 has critical functions in the vascular development and angiogenesis. It is unclear whether Sox7 also contributes to cardiac septation development. We identified a de novo 8p23.1 deletion with Sox7 haploinsufficiency in an atrioventricular septal defect (AVSD) patient using whole exome sequencing in 100 AVSD patients. Then, multiple Sox7 conditional loss-of-function mice models were generated to explore the role of Sox7 in atrioventricular cushion development. Sox7 deficiency mice embryos exhibited partial AVSD and impaired endothelial to mesenchymal transition (EndMT). Transcriptome analysis revealed BMP signaling pathway was significantly downregulated in Sox7 deficiency atrioventricular cushions. Mechanistically, Sox7 deficiency reduced the expressions of Bmp2 in atrioventricular canal myocardium and Wnt4 in endocardium, and Sox7 binds to Wnt4 and Bmp2 directly. Furthermore, WNT4 or BMP2 protein could partially rescue the impaired EndMT process caused by Sox7 deficiency, and inhibition of BMP2 by Noggin could attenuate the effect of WNT4 protein. In summary, our findings identify Sox7 as a novel AVSD pathogenic candidate gene, and it can regulate the EndMT involved in atrioventricular cushion morphogenesis through Wnt4-Bmp2 signaling. This study contributes new strategies to the diagnosis and treatment of congenital heart defects.

Twist1 signaling in age-dependent decline in angiogenesis and lung regeneration

Angiogenesis – the formation of new blood capillaries- is impaired in aging animals and contributes to the pathogenesis of age-related diseases. A transcription factor, Twist1, contributes to the pathogenesis of age- and angiogenesis-related diseases such as pulmonary fibrosis and atherosclerosis. However, the mechanism by which Twist1 controls age-dependent decline in angiogenesis remains unclear. In this report, we have demonstrated that the levels of Twist1 are higher, while the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) that stimulates angiogenesis, is lower in endothelial cells (ECs) isolated from aged human adipose tissues and mouse lungs compared to those from young tissues. Knockdown of Twist1 in aged human ECs increases the levels of PGC1α and angiogenic factor receptor, vascular endothelial growth factor receptor (VEGFR2), and restores EC proliferation and migration, while inhibition of PGC1α suppresses these effects. Knockdown of Twist1 in supplemented aged ECs also restores vascular networks in the subcutaneously implanted gel, while these effects are abrogated by knockdown of PGC1α. Age-dependent inhibition of post-pneumonectomy (PNX) lung growth is suppressed in Tie2-specific Twist1 conditional knockout mouse lungs, in which VEGFR2 expression increases after PNX. These results suggest that upregulation of endothelial Twist1 mediates age-dependent decline in angiogenesis and regenerative lung growth.

Endothelial to Mesenchymal Transition in the Cardiogenesis and Cardiovascular Diseases

Today, cardiovascular diseases remain a leading cause of morbidity and mortality worldwide. Endothelial to mesenchymal transition (EndMT) does not only play a major role in the course of development but also contributes to several cardiovascular diseases in adulthood. EndMT is characterized by down-regulation of the endothelial proteins and highly up-regulated fibrotic specific genes and extracellular matrix-forming proteins. EndMT is also a transforming growth factor-β-driven (TGF-β) process in which endothelial cells lose their endothelial characteristics and acquire a mesenchymal phenotype with expression of α-smooth muscle actin (α-SMA), fibroblast-specific protein 1, etc. EndMT is a vital process during cardiac development, thus disrupted EndMT gives rise to the congenital heart diseases, namely septal defects and valve abnormalities. In this review, we have discussed the main signaling pathways and mechanisms participating in the process of EndMT such as TGF-β and Bone morphogenetic protein (BMP), Wnt^#, and Notch signaling pathway and also studied the role of EndMT in physiological cardiovascular development and pathological conditions including myocardial infarction, pulmonary arterial hypertension, congenital heart defects, cardiac fibrosis, and atherosclerosis. As a perspective view, having a clear understanding of involving cellular and molecular mechanisms in EndMT and conducting Randomized controlled trials (RCTs) with a large number of samples for involving pharmacological agents may guide us into novel therapeutic approaches of congenital disorders and heart diseases.

Context-dependent roles of YAP/TAZ in stem cell fates and cancer

Hippo effectors YAP and TAZ control cell fate and survival through various mechanisms, including transcriptional regulation of key genes. However, much of this research has been marked by conflicting results, as well as controversy over whether YAP and TAZ are redundant. A substantial portion of the discordance stems from their contradictory roles in stem cell self-renewal vs. differentiation and cancer cell survival vs. apoptosis. In this review, we present an overview of the multiple context-dependent functions of YAP and TAZ in regulating cell fate decisions in stem cells and organoids, as well as their mechanisms of controlling programmed cell death pathways in cancer.

Endothelial YAP/TAZ Signaling in Angiogenesis and Tumor Vasculature

Solid tumors are dependent on vascularization for their growth. The hypoxic, stiff, and pro-angiogenic tumor microenvironment induces angiogenesis, giving rise to an immature, proliferative, and permeable vasculature. The tumor vessels promote tumor metastasis and complicate delivery of anti-cancer therapies. In many types of tumors, YAP/TAZ activation is correlated with increased levels of angiogenesis. In addition, endothelial YAP/TAZ activation is important for the formation of new blood and lymphatic vessels during development. Oncogenic activation of YAP/TAZ in tumor cell growth and invasion has been studied in great detail, however the role of YAP/TAZ within the tumor endothelium remains insufficiently understood, which complicates therapeutic strategies aimed at targeting YAP/TAZ in cancer. Here, we overview the upstream signals from the tumor microenvironment that control endothelial YAP/TAZ activation and explore the role of their downstream targets in driving tumor angiogenesis. We further discuss the potential for anti-cancer treatments and vascular normalization strategies to improve tumor therapies.

VGLL4 Protects against Oxidized-LDL-Induced Endothelial Cell Dysfunction and Inflammation by Activating Hippo-YAP/TEAD1 Signaling Pathway

Vestigial-like 4 (VGLL4) has been found to have multiple functions in tumor development; however, its role in cardiovascular disease is unknown. The aim of this study was to investigate the effect of VGLL4 on the dysfunction and inflammatory response of Ox-LDL-induced human umbilical vein endothelial cells (HUVECs) and its mechanism, so as to provide a new theoretical basis for the diagnosis and treatment of atherosclerosis. In the present study, the protective activity of VGLL4 inhibiting Ox-LDL-induced apoptosis, oxidative stress, inflammation, and injury as well as its molecular mechanisms was examined using human umbilical vein endothelial cells (HUVECs). The results showed that the expression of VGLL4 was decreased with the increase of Ox-LDL concentration in HUVECs. In addition, the functional study found that VGLL4 overexpression alleviated Ox-LDL-induced oxidative stress, inflammation, and dysfunction and inhibited apoptosis. Further research found that VGLL4 regulated Hippo-YAP/TEAD1 signaling pathway, and the Hippo-YAP/TEAD1 signaling pathway was involved in the protective mechanism of VGLL4 on HUVECs. In conclusion, it suggests that VGLL4 protects against oxidized-LDL-induced endothelial cell dysfunction by activating the Hippo-YAP/TEAD1 signaling pathway.

The Mesenchymal Cap of the Atrial Septum and Atrial and Atrioventricular Septation

In this publication, dedicated to Professor Robert H. Anderson and his contributions to the field of cardiac development, anatomy, and congenital heart disease, we will review some of our earlier collaborative studies. The focus of this paper is on our work on the development of the atrioventricular mesenchymal complex, studies in which Professor Anderson has played a significant role. We will revisit a number of events relevant to atrial and atrioventricular septation and present new data on the development of the mesenchymal cap of the atrial septum, a component of the atrioventricular mesenchymal complex which, thus far, has received only moderate attention.

New Concepts in the Development and Malformation of the Arterial Valves

Although in many ways the arterial and atrioventricular valves are similar, both being derived for the most part from endocardial cushions, we now know that the arterial valves and their surrounding structures are uniquely dependent on progenitors from both the second heart field (SHF) and neural crest cells (NCC). Here, we will review aspects of arterial valve development, highlighting how our appreciation of NCC and the discovery of the SHF have altered our developmental models. We will highlight areas of research that have been particularly instructive for understanding how the leaflets form and remodel, as well as those with limited or conflicting results. With this background, we will explore how this developmental knowledge can help us to understand human valve malformations, particularly those of the bicuspid aortic valve (BAV). Controversies and the current state of valve genomics will be indicated.

Llgl1 regulates zebrafish cardiac development by mediating Yap stability in cardiomyocytes

The Hippo-Yap pathway regulates multiple cellular processes in response to mechanical and other stimuli. In Drosophila, the polarity protein Lethal (2) giant larvae [L(2)gl], negatively regulates Hippo-mediated transcriptional output. However, in vertebrates, little is known about its homolog Llgl1. Here, we define a novel role for vertebrate Llgl1 in regulating Yap stability in cardiomyocytes, which impacts heart development. In contrast to the role of Drosophila L(2)gl, Llgl1 depletion in cultured rat cardiomyocytes decreased Yap protein levels and blunted target gene transcription without affecting Yap transcript abundance. Llgl1 depletion in zebrafish resulted in larger and dysmorphic cardiomyocytes, pericardial effusion, impaired blood flow and aberrant valvulogenesis. Cardiomyocyte Yap protein levels were decreased in llgl1 morphants, whereas Notch, which is regulated by hemodynamic forces and participates in valvulogenesis, was more broadly activated. Consistent with the role of Llgl1 in regulating Yap stability, cardiomyocyte-specific overexpression of Yap in Llgl1-depleted embryos ameliorated pericardial effusion and restored blood flow velocity. Altogether, our data reveal that vertebrate Llgl1 is crucial for Yap stability in cardiomyocytes and its absence impairs cardiac development.

Fluid flow as a driver of embryonic morphogenesis

Fluid flow is a powerful morphogenic force during embryonic development. The physical forces created by flowing fluids can either create morphogen gradients or be translated by mechanosensitive cells into biological changes in gene expression. In this Primer, we describe how fluid flow is created in different systems and highlight the important mechanosensitive signalling pathways involved for sensing and transducing flow during embryogenesis. Specifically, we describe how fluid flow helps establish left-right asymmetry in the early embryo and discuss the role of flow of blood, lymph and cerebrospinal fluid in sculpting the embryonic cardiovascular and nervous system.

Mechanisms of heart valve development and disease

The valves of the heart are crucial for ensuring that blood flows in one direction from the heart, through the lungs and back to the rest of the body. Heart valve development is regulated by complex interactions between different cardiac cell types and is subject to blood flow-driven forces. Recent work has begun to elucidate the important roles of developmental pathways, valve cell heterogeneity and hemodynamics in determining the structure and function of developing valves. Furthermore, this work has revealed that many key genetic pathways involved in cardiac valve development are also implicated in diseased valves. Here, we review recent discoveries that have furthered our understanding of the molecular, cellular and mechanosensitive mechanisms of valve development, and highlight new insights into congenital and acquired valve disease.