Heg1 and Ccm1/2 proteins control endocardial mechanosensitivity during zebrafish valvulogenesis

Differential Development of the Chordae Tendineae and Anterior Leaflet of the Bovine Mitral Valve

There is increasing evidence that some adult mitral valve pathologies may have developmental origins involving errors in cell signaling and protein deposition during valvulogenesis. While early and late gestational stages are well-documented in zebrafish, chicks, and small mammalian models, longitudinal studies in large mammals with a similar gestational period to humans are lacking. Further, the mechanism of chordae tendineae formation and multiplication remains unclear. The current study presents a comprehensive examination of mitral anterior leaflet and chordae tendineae development in a bovine model (a large mammal with the same gestational period as humans). Remarkably distinct from small mammals, bovine development displayed early branched chordae, with increasing attachments only until birth, while the anterior leaflet grew both during gestation and postnatally. Chordae also exhibited accelerated collagen deposition, maturation, and crimp development during gestation. These findings suggest that the bovine anterior leaflet and chordae tendineae possess unique processes of development despite being a continuous collagenous structure and could provide greater insight into human valve development.

Convergence of coronary artery disease genes onto endothelial cell programs

Linking variants from genome-wide association studies (GWAS) to underlying mechanisms of disease remains a challenge1-3. For some diseases, a successful strategy has been to look for cases in which multiple GWAS loci contain genes that act in the same biological pathway1-6. However, our knowledge of which genes act in which pathways is incomplete, particularly for cell-type-specific pathways or understudied genes. Here we introduce a method to connect GWAS variants to functions. This method links variants to genes using epigenomics data, links genes to pathways de novo using Perturb-seq and integrates these data to identify convergence of GWAS loci onto pathways. We apply this approach to study the role of endothelial cells in genetic risk for coronary artery disease (CAD), and discover 43 CAD GWAS signals that converge on the cerebral cavernous malformation (CCM) signalling pathway. Two regulators of this pathway, CCM2 and TLNRD1, are each linked to a CAD risk variant, regulate other CAD risk genes and affect atheroprotective processes in endothelial cells. These results suggest a model whereby CAD risk is driven in part by the convergence of causal genes onto a particular transcriptional pathway in endothelial cells. They highlight shared genes between common and rare vascular diseases (CAD and CCM), and identify TLNRD1 as a new, previously uncharacterized member of the CCM signalling pathway. This approach will be widely useful for linking variants to functions for other common polygenic diseases.

Membranous Expression of Heart Development Protein with EGF-like Domain 1 Is Associated with a Good Prognosis in Patients with Bladder Cancer

OBJECTIVE

To investigate the correlation between total protein expression of heart development protein with EGF-like domain 1 (HEG1) and clinicopathological characteristics in patients with bladder cancer (BC) after radical cystectomy (RC).

PATIENTS AND METHODS

We retrospectively analyzed data from 110 patients who underwent RC at Kitasato University Hospital. And we prepared an anti-HEG1 monoclonal antibody W10B9, which can detect total HEG1 protein. HEG1 protein expression in tumor cells was evaluated separately for membrane and cytoplasmic staining using immunohistochemistry.

RESULTS

Membranous HEG1 expression was associated with absent lymphovascular invasion (p < 0.01) and low pT stage (p < 0.01). Kaplan-Meier analysis revealed that the membranous HEG1-positive group had significantly long recurrence-free survival (RFS) (p < 0.01) and cancer-specific survival (p = 0.01). Expression of membranous HEG1 was identified as an independent prognostic factor for RFS (p = 0.04). There were no significant differences between cytoplasmic HEG1 expression and clinicopathologic factors including prognosis.

CONCLUSION

The expression of membranous HEG1 could serve as a favorable prognostic indicator in patients with BC treated with RC.

Protein-protein interactions: developing small-molecule inhibitors/stabilizers through covalent strategies

The development of small-molecule inhibitors or stabilizers of selected protein-protein interactions (PPIs) of interest holds considerable promise for the development of research tools as well as candidate therapeutics. In this context, the covalent modification of selected residues within the target protein has emerged as a promising mechanism of action to obtain small-molecule modulators of PPIs with appropriate selectivity and duration of action. Different covalent labeling strategies are now available that can potentially allow for a rational, ground-up discovery and optimization of ligands as PPI inhibitors or stabilizers. This review article provides a synopsis of recent developments and applications of such tactics, with a particular focus on site-directed fragment tethering and proximity-enabled approaches.

KRIT1-mediated regulation of neutrophil adhesion and motility

Loss of Krev interaction-trapped-1 (KRIT1) expression leads to the development of cerebral cavernous malformations (CCM), a disease in which abnormal blood vessel formation compromises the structure and function of the blood-brain barrier. The role of KRIT1 in regulating endothelial function is well-established. However, several studies have suggested that KRIT1 could also play a role in regulating nonendothelial cell types and, in particular, immune cells. In this study, we generated a mouse model with neutrophil-specific deletion of KRIT1 in order to investigate the effect of KRIT1 deficiency on neutrophil function. Neutrophils isolated from adult Ly6Gtm2621(cre)Arte Krit1flox/flox mice had a reduced ability to attach and spread on the extracellular matrix protein fibronectin and exhibited a subsequent increase in migration. However, adhesion to and migration on ICAM-1 was unchanged. In addition, we used a monomeric, fluorescently-labelled fragment of fibronectin to show that integrin activation is reduced in the absence of KRIT1 expression, though β1 integrin expression appears unchanged. Finally, neutrophil migration in response to lipopolysaccharide-induced inflammation in the lung was decreased, as shown by reduced cell number and myeloperoxidase activity in lavage samples from Krit1PMNKO mice. Altogether, we show that KRIT1 regulates neutrophil adhesion and migration, likely through regulation of integrin activation, which can lead to altered inflammatory responses in vivo.

HEG1 as a novel potential biomarker for the prognosis of lung adenocarcinoma

BACKGROUND

Heart development protein with EGF-like domains 1 (HEG1), generally related to angiogenesis and embryonic development, was reported to participate in the occurrence and progression of some tumors recently. However, the role of HEG1 in lung adenocarcinoma (LUAD) is unclear.

PATIENTS AND METHODS

To explore the effect of HEG1 on LUAD, GEPIA platform and UALCAN database, as well as Kaplan-Meier plotter were adopted to analyze the association of HEG1 with clinicopathological characteristics and survival outcomes for LUAD firstly. And then the HEG1 in LUAD tissues, blood and cell lines were detected by qRT-PCR, western blot, immunofluorescence, immunohistochemistry, and ELISA. Gene set enrichment analysis (GSEA) was conducted to identify pathways that might be affected by HEG1 in LUAD.

RESULTS

In this study, HEG1 in lung tissues and cell lines of LUAD were significantly downregulated compared to benign pulmonary disease tissues and alveolar epithelial cells (p < 0.05). Moreover, compared with other groups, patients with advanced tumor stage had lower HEG1 mRNA expression levels (p = 0.025), which were negatively correlated with Ki67 index in tumor tissues (r = -0.427, p = 0.033). On the other hand, the LUAD patients with lower HEG1 had shorter overall survival (OS) (HR = 0.51, 95% CI: 0.40-0.65, p < 0.001) according to Kaplan-Meier plotter. In addition, HEG1 in serum of LUAD patients was negatively associated with CEA (r = -0.636, p < 0.001). GSEA showed that HEG1 was enriched in various metabolic-related pathways, including glucose metabolism, lipid metabolism, and nucleotide metabolism signaling.

CONCLUSIONS

HEG1 was downregulated in LUAD patients and associated with poor prognosis, which indicating HEG1 may serve as a potential biomarker for diagnosis and prognosis of LUAD.

Effects of different pharmaceutical residues on embryos of fish species native to Central Europe

Environmental concentrations of pharmacologically active substances are increasing dramatically throughout the world, to the point where they are now considered a serious threat to the aquatic environment. This high occurrence of pharmaceutical residues in the aquatic environment is due to an increase in i) the prescription and consumption of drugs, and ii) their subsequent discharge into wastewater and its imperfect purification in wastewater treatment plants. Recent surveys have clearly shown that such substances can have serious negative effects on non-target organisms. In the present study, we tested the effects of several commonly used pharmaceuticals, such as antidepressants, analgesics and antibiotics, on the embryonic stages of different fishes. Specifically, we applied concentration ranges of tramadol, enrofloxacin and nortriptylined on a common toxicological model organism, the zebrafish (Danio rerio), and other species native to Central European freshwaters, i.e. common carp (Cyprinus carpio), catfish (Silurus glanis) and tench (Tinca tinca). Our results show that, though malformation and negative impacts on hatching and mortality were only observed at the highest test concentrations, gene expression indicated that even low environmentally relevant concentrations (0.1 μg/L) can cause significant changes in early development of embryo.

Cardiac forces regulate zebrafish heart valve delamination by modulating Nfat signaling

In the clinic, most cases of congenital heart valve defects are thought to arise through errors that occur after the endothelial–mesenchymal transition (EndoMT) stage of valve development. Although mechanical forces caused by heartbeat are essential modulators of cardiovascular development, their role in these later developmental events is poorly understood. To address this question, we used the zebrafish superior atrioventricular valve (AV) as a model. We found that cellularized cushions of the superior atrioventricular canal (AVC) morph into valve leaflets via mesenchymal–endothelial transition (MEndoT) and tissue sheet delamination. Defects in delamination result in thickened, hyperplastic valves, and reduced heart function. Mechanical, chemical, and genetic perturbation of cardiac forces showed that mechanical stimuli are important regulators of valve delamination. Mechanistically, we show that forces modulate Nfatc activity to control delamination. Together, our results establish the cellular and molecular signature of cardiac valve delamination in vivo and demonstrate the continuous regulatory role of mechanical forces and blood flow during valve formation.

Why do developing zebrafish atrioventricular heart valves become hyperplastic under certain hemodynamic conditions? This study suggests that part of the answer lies in how the mechanosensitive Nfat pathway regulates the valve mesenchymal-to-endothelial transition.

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.

Bioelectric signaling and the control of cardiac cell identity in response to mechanical forces

[Figure: see text].

Mechanosensitive Notch-Dll4 and Klf2-Wnt9 signaling pathways intersect in guiding valvulogenesis in zebrafish

In the zebrafish embryo, the onset of blood flow generates fluid shear stress on endocardial cells, which are specialized endothelial cells that line the interior of the heart. High levels of fluid shear stress activate both Notch and Klf2 signaling, which play crucial roles in atrioventricular valvulogenesis. However, it remains unclear why only individual endocardial cells ingress into the cardiac jelly and initiate valvulogenesis. Here, we show that lateral inhibition between endocardial cells, mediated by Notch, singles out Delta-like-4-positive endocardial cells. These cells ingress into the cardiac jelly, where they form an abluminal cell population. Delta-like-4-positive cells ingress in response to Wnt9a, which is produced in parallel through an Erk5-Klf2-Wnt9a signaling cascade also activated by blood flow. Hence, mechanical stimulation activates parallel mechanosensitive signaling pathways that produce binary effects by driving endocardial cells toward either luminal or abluminal fates. Ultimately, these cell fate decisions sculpt cardiac valve leaflets.

Cerebral Cavernous Malformation: From Mechanism to Therapy

Cerebral cavernous malformations are acquired vascular anomalies that constitute a common cause of central nervous system hemorrhage and stroke. The past 2 decades have seen a remarkable increase in our understanding of the pathogenesis of this vascular disease. This new knowledge spans genetic causes of sporadic and familial forms of the disease, molecular signaling changes in vascular endothelial cells that underlie the disease, unexpectedly strong environmental effects on disease pathogenesis, and drivers of disease end points such as hemorrhage. These novel insights are the integrated product of human clinical studies, human genetic studies, studies in mouse and zebrafish genetic models, and basic molecular and cellular studies. This review addresses the genetic and molecular underpinnings of cerebral cavernous malformation disease, the mechanisms that lead to lesion hemorrhage, and emerging biomarkers and therapies for clinical treatment of cerebral cavernous malformation disease. It may also serve as an example for how focused basic and clinical investigation and emerging technologies can rapidly unravel a complex disease mechanism.

Inhibition of the HEG1-KRIT1 interaction increases KLF4 and KLF2 expression in endothelial cells

The transmembrane protein heart of glass1 (HEG1) directly binds to and recruits Krev interaction trapped protein 1 (KRIT1) to endothelial junctions to form the HEG1-KRIT1 protein complex that establishes and maintains junctional integrity. Genetic inactivation or knockdown of endothelial HEG1 or KRIT1 leads to the upregulation of transcription factors Krüppel-like factors 4 and 2 (KLF4 and KLF2), which are implicated in endothelial vascular homeostasis; however, the effect of acute inhibition of the HEG1-KRIT1 interaction remains incompletely understood. Here, we report a high-throughput screening assay and molecular design of a small-molecule HEG1-KRIT1 inhibitor to uncover acute changes in signaling pathways downstream of the HEG1-KRIT1 protein complex disruption. The small-molecule HEG1-KRIT1 inhibitor 2 (HKi2) was demonstrated to be a bona fide inhibitor of the interaction between HEG1 and KRIT1 proteins, by competing orthosterically with HEG1 through covalent reversible interactions with the FERM (4.1, ezrin, radixin, and moesin) domain of KRIT1. The crystal structure of HKi2 bound to KRIT1 FERM revealed that it occupies the same binding pocket on KRIT1 as the HEG1 cytoplasmic tail. In human endothelial cells (ECs), acute inhibition of the HEG1-KRIT1 interaction by HKi2 increased KLF4 and KLF2 mRNA and protein levels, whereas a structurally similar inactive compound failed to do so. In zebrafish, HKi2 induced expression of klf2a in arterial and venous endothelium. Furthermore, genome-wide RNA transcriptome analysis of HKi2-treated ECs under static conditions revealed that, in addition to elevating KLF4 and KLF2 expression, inhibition of the HEG1-KRIT1 interaction mimics many of the transcriptional effects of laminar blood flow. Furthermore, HKi2-treated ECs also triggered Akt signaling in a phosphoinositide 3-kinase (PI3K)-dependent manner, as blocking PI3K activity blunted the Akt phosphorylation induced by HKi2. Finally, using an in vitro colocalization assay, we show that HKi6, an improved derivative of HKi2 with higher affinity for KRIT1, significantly impedes recruitment of KRIT1 to mitochondria-localized HEG1 in CHO cells, indicating a direct inhibition of the HEG1-KRIT1 interaction. Thus, our results demonstrate that early events of the acute inhibition of HEG1-KRIT1 interaction with HKi small-molecule inhibitors lead to: (i) elevated KLF4 and KLF2 gene expression; and (ii) increased Akt phosphorylation. Thus, HKi's provide new pharmacologic tools to study acute inhibition of the HEG1-KRIT1 protein complex and may provide insights to dissect early signaling events that regulate vascular homeostasis.

The Zebrafish Cardiac Endothelial Cell-Roles in Development and Regeneration

In zebrafish, the spatiotemporal development of the vascular system is well described due to its stereotypical nature. However, the cellular and molecular mechanisms orchestrating post-embryonic vascular development, the maintenance of vascular homeostasis, or how coronary vessels integrate into the growing heart are less well studied. In the context of cardiac regeneration, the central cellular mechanism by which the heart regenerates a fully functional myocardium relies on the proliferation of pre-existing cardiomyocytes; the epicardium and the endocardium are also known to play key roles in the regenerative process. Remarkably, revascularisation of the injured tissue occurs within a few hours after cardiac damage, thus generating a vascular network acting as a scaffold for the regenerating myocardium. The activation of the endocardium leads to the secretion of cytokines, further supporting the proliferation of the cardiomyocytes. Although epicardium, endocardium, and myocardium interact with each other to orchestrate heart development and regeneration, in this review, we focus on recent advances in the understanding of the development of the endocardium and the coronary vasculature in zebrafish as well as their pivotal roles in the heart regeneration process.

Antagonistic Activities of Vegfr3/Flt4 and Notch1b Fine-tune Mechanosensitive Signaling during Zebrafish Cardiac Valvulogenesis

The formation of cardiac valves depends on mechanical forces exerted by blood flow. Endocardial cells lining the interior of the heart are sensitive to these stimuli and respond by rearranging into luminal cells subjected to shear stress and abluminal cells not exposed to it. The mechanisms by which endocardial cells sense these dynamic biomechanical stimuli and how they evoke different cellular responses are largely unknown. Here, we show that blood flow activates two parallel mechanosensitive pathways, one mediated by Notch and the other by Klf2a. Both pathways negatively regulate the angiogenesis receptor Vegfr3/Flt4, which becomes restricted to abluminal endocardial cells. Its loss disrupts valve morphogenesis and results in the occurrence of Notch signaling within abluminal endocardial cells. Our work explains how antagonistic activities by Vegfr3/Flt4 on the abluminal side and by Notch on the luminal side shape cardiac valve leaflets by triggering unique differences in the fates of endocardial cells.

Investigating gene methylation signatures for fetal intolerance prediction

Pregnancy is a complicated and long procedure during one or more offspring development inside a woman. A short period of oxygen shortage after birth is quite normal for most babies and does not threaten their health. However, if babies have to suffer from a long period of oxygen shortage, then this condition is an indication of pathological fetal intolerance, which probably causes their death. The identification of the pathological fetal intolerance from the physical oxygen shortage is one of the important clinical problems in obstetrics for a long time. The clinical syndromes typically manifest five symptoms that indicate that the baby may suffer from fetal intolerance. At present, liquid biopsy combined with high-throughput sequencing or mass spectrum techniques provides a quick approach to detect real-time alteration in the peripheral blood at multiple levels with the rapid development of molecule sequencing technologies. Gene methylation is functionally correlated with gene expression; thus, the combination of gene methylation and expression information would help in screening out the key regulators for the pathogenesis of fetal intolerance. We combined gene methylation and expression features together and screened out the optimal features, including gene expression or methylation signatures, for fetal intolerance prediction for the first time. In addition, we applied various computational methods to construct a comprehensive computational pipeline to identify the potential biomarkers for fetal intolerance dependent on the liquid biopsy samples. We set up qualitative and quantitative computational models for the prediction for fetal intolerance during pregnancy. Moreover, we provided a new prospective for the detailed pathological mechanism of fetal intolerance. This work can provide a solid foundation for further experimental research and contribute to the application of liquid biopsy in antenatal care.

A Missense Mutation in the KLF7 Gene Is a Potential Candidate Variant for Congenital Deafness in Australian Stumpy Tail Cattle Dogs

Congenital deafness is prevalent among modern dog breeds, including Australian Stumpy Tail Cattle Dogs (ASCD). However, in ASCD, no causative gene has been identified so far. Therefore, we performed a genome-wide association study (GWAS) and whole genome sequencing (WGS) of affected and normal individuals. For GWAS, 3 bilateral deaf ASCDs, 43 herding dogs, and one unaffected ASCD were used, resulting in 13 significantly associated loci on 6 chromosomes, i.e., CFA3, 8, 17, 23, 28, and 37. CFA37 harbored a region with the most significant association (−log₁₀(9.54 × 10⁻²¹) = 20.02) as well as 7 of the 13 associated loci. For whole genome sequencing, the same three affected ASCDs and one unaffected ASCD were used. The WGS data were compared with 722 canine controls and filtered for protein coding and non-synonymous variants, resulting in four missense variants present only in the affected dogs. Using effect prediction tools, two variants remained with predicted deleterious effects within the Heart development protein with EGF like domains 1 (HEG1) gene (NC_006615.3: g.28028412G>C; XP_022269716.1: p.His531Asp) and Kruppel-like factor 7 (KLF7) gene (NC_006619.3: g.15562684G>A; XP_022270984.1: p.Leu173Phe). Due to its function as a regulator in heart and vessel formation and cardiovascular development, HEG1 was excluded as a candidate gene. On the other hand, KLF7 plays a crucial role in the nervous system, is expressed in the otic placode, and is reported to be involved in inner ear development. 55 additional ASCD samples (28 deaf and 27 normal hearing dogs) were genotyped for the KLF7 variant, and the variant remained significantly associated with deafness in ASCD (p = 0.014). Furthermore, 24 dogs with heterozygous or homozygous mutations were detected, including 18 deaf dogs. The penetrance was calculated to be 0.75, which is in agreement with previous reports. In conclusion, KLF7 is a promising candidate gene causative for ASCD deafness.

Generation and Application of the Zebrafish heg1 Mutant as a Cardiovascular Disease Model

Cardiovascular disease (CVD) is the leading cause of global mortality, which has caused a huge burden on the quality of human life. Therefore, experimental animal models of CVD have become essential tools for analyzing the pathogenesis, developing drug screening, and testing potential therapeutic strategies. In recent decades, zebrafish has entered the field of CVD as an important model organism. HEG1, a heart development protein with EGF like domains 1, plays important roles in the development of vertebrate cardiovascular system. Loss of HEG1 will affect the stabilization of vascular endothelial cell connection and eventually lead to dilated cardiomyopathy (DCM). Here, we generated a heg1-specific knockout zebrafish line using CRISPR/Cas9 technology. Zebrafish heg1 mutant demonstrated severe cardiovascular malformations, including atrial ventricular enlargement, heart rate slowing, venous thrombosis and slow blood flow, which were similar to human heart failure and thrombosis phenotype. In addition, the expression of zebrafish cardiac and vascular markers was abnormal in heg1 mutants. In order to apply zebrafish heg1 mutant in cardiovascular drug screening, four Traditional Chinese Medicine (TCM) herbs and three Chinese herbal monomers were used to treat heg1 mutant. The pericardial area, the distance between sinus venosus and bulbus arteriosus (SV-BA), heart rate, red blood cells (RBCs) accumulation in posterior cardinal vein (PCV), and blood circulation in the tail vein were measured to evaluate the therapeutic effects of those drugs on DCM and thrombosis. Here, a new zebrafish model of DCM and thrombosis was established, which was verified to be suitable for drug screening of cardiovascular diseases. It provided an alternative method for traditional in vitro screening, and produced potential clinical related drugs in a rapid and cost-effective way.

HEG1 Is a Highly Specific and Sensitive Marker of Epithelioid Malignant Mesothelioma

Malignant mesothelioma can be difficult to distinguish from other malignancies, particularly non-small cell lung carcinomas (NSCLCs), without immunohistochemistry. However, conventional markers of mesothelial lineage all have variable degrees of cross-reactivity with other neoplasms, including NSCLCs, necessitating the use of multiple mesothelioma and carcinoma markers in every case for accurate diagnosis. A recently described monoclonal HEG homolog 1 (HEG1) antibody was proposed to be a specific marker for mesothelioma. Here we performed a large scale assessment of the SKM9-2 HEG1 antibody using tissue microarrays containing 69 epithelioid mesotheliomas, 32 sarcomatoid mesotheliomas, 167 NSCLCs, and 17 ovarian high-grade serous carcinomas. Strong membrane staining, usually diffuse, for HEG1 was seen in 65/69 (94%) epithelioid mesotheliomas, 0/60 pulmonary squamous cell carcinomas, 0/73 pulmonary adenocarcinomas, and 0/13 pulmonary large cell carcinomas. HEG1 showed staining in 14/32 (44%) sarcomatoid mesotheliomas compared with 0/21 sarcomatoid pulmonary carcinomas. Three of 17 (18%) high-grade serous carcinomas demonstrated membrane staining. Ten B3 thymoma whole sections were negative. On the microarrays, the conventional mesothelial markers calretinin, WT1, D2-40, and CK5/6 had sensitivities for epithelioid mesothelioma of 94%, 90%, 96%, and 91%, respectively. We conclude that HEG1 SKM9-2 antibody offers sensitivity comparable to conventional markers for epithelioid mesotheliomas, but provides considerably better specificity, such that the diagnosis of epithelioid mesothelioma versus NSCLC potentially could be confirmed with a combination of HEG1 and a suitable broad spectrum carcinoma marker such as claudin-4. HEG1 is specific but insensitive for separating sarcomatoid mesotheliomas from sarcomatoid lung carcinomas.

In Full Force. Mechanotransduction and Morphogenesis during Homeostasis and Tissue Regeneration

The interactions of form and function have been the focus of numerous studies in the context of development and more recently regeneration. Our understanding on how cells, tissues and organs sense and interpret external cues, such as mechanical forces, is becoming deeper as novel techniques in imaging are applied and the relevant signaling pathways emerge. These cellular responses can be found from bacteria to all multicellular organisms such as plants and animals. In this review, we focus on hemodynamic flow and endothelial shear stress during cardiovascular development and regeneration, where the interactions of morphogenesis and proper function are more prominent. In addition, we address the recent literature on the role of extracellular matrix and fibrotic response during tissue repair and regeneration. Finally, we refer to examples where the integration of multi-disciplinary approaches to understand the biomechanics of cellular responses could be utilized in novel medical applications.

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.

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.

Biomechanical Cues Direct Valvulogenesis

The vertebrate embryonic heart initially forms with two chambers, a ventricle and an atrium, separated by the atrioventricular junction. Localized genetic and biomechanical information guides the development of valves, which function to ensure unidirectional blood flow. If the valve development process goes awry, pathology associated with congenital valve defects can ensue. Congenital valve defects (CVD) are estimated to affect 1–2% of the population and can often require a lifetime of treatment. Despite significant clinical interest, molecular genetic mechanisms that direct valve development remain incompletely elucidated. Cells in the developing valve must contend with a dynamic hemodynamic environment. A growing body of research supports the idea that cells in the valve are highly sensitive to biomechanical forces, which cue changes in gene expression required for normal development or for maintenance of the adult valve. This review will focus on mechanotransductive pathways involved in valve development across model species. We highlight current knowledge regarding how cells sense physical forces associated with blood flow and pressure in the forming heart, and summarize how these changes are transduced into genetic and developmental responses. Lastly, we provide perspectives on how altered biomechanical cues may lead to CVD pathogenesis.

HEG1-responsive microRNA-23b regulates cell proliferation in malignant mesothelioma cells

Malignant mesothelioma (MM) is a fatal tumor, and the absence of a specific diagnostic marker and/or a pathogenic molecule-targeting drug is a major issue for its pathological diagnosis and for targeting therapy. The molecular target of MM has not been elucidated because of unknown survival, death, and cytotoxic signals in MM. HEG homolog 1 (HEG1) is a mucin-like membrane protein that contains epidermal growth factor-like domains, and it plays an important role in cancers through aberrant signaling, including that during cell adhesion, as well as through protection from invasion of tumor cells. HEG1 expression supports the survival and proliferation of MM cells. In this study, functional analysis of HEG1 and microRNAs using MM cell lines (H226, MESO4, H2052) was performed. The MTS assay revealed that cell proliferation was significantly reduced upon transient transfection with microRNA-23b (miR-23b) inhibitor and/or HEG1 siRNA. The Annexin V assay revealed that apoptosis was induced upon suppression of miR-23b and/or HEG1. Western blotting showed that the autophagy-related protein LC3-II was induced upon suppression of miR-23b and/or HEG1. These results revealed that miR-23b contributes to HEG1-dependent cell proliferation through evasion of cytotoxicity induced by apoptosis and autophagy in MM cells. HEG1-dependent/mediated miR-23b signaling may therefore be a potential target for MM diagnosis and therapy.

Blocking Signalopathic Events to Treat Cerebral Cavernous Malformations

Cerebral cavernous malformations (CCMs) are pathologies of the brain vasculature characterized by capillary-venous angiomas that result in recurrent cerebral hemorrhages. Familial forms are caused by a clonal loss of any of three CCM genes in endothelial cells, which causes the activation of a novel pathophysiological pathway involving mitogen-activated protein kinase and Krüppel-like transcription factor KLF2/4 signaling. Recent work has shown that cavernomas can undergo strong growth when CCM-deficient endothelial cells recruit wild-type neighbors through the secretion of cytokines. This suggests a treatment strategy based on targeting signalopathic events between CCM-deficient endothelial cells and their environment. Such approaches will have to consider recent evidence implicating 'third hits' from hypoxia-induced angiogenesis signaling or the microbiome in modulating the development of cerebral hemorrhages.

Nfatc1 Promotes Interstitial Cell Formation During Cardiac Valve Development in Zebrafish

RATIONALE

The transcription factor NFATC1 (nuclear factor of activated T-cell 1) has been implicated in cardiac valve formation in humans and mice, but we know little about the underlying mechanisms. To gain mechanistic understanding of cardiac valve formation at single-cell resolution and insights into the role of NFATC1 in this process, we used the zebrafish model as it offers unique attributes for live imaging and facile genetics.

OBJECTIVE

To understand the role of Nfatc1 in cardiac valve formation.

METHODS AND RESULTS

Using the zebrafish atrioventricular valve, we focus on the valve interstitial cells (VICs), which confer biomechanical strength to the cardiac valve leaflets. We find that initially atrioventricular endocardial cells migrate collectively into the cardiac jelly to form a bilayered structure; subsequently, the cells that led this migration invade the ECM (extracellular matrix) between the 2 endocardial cell monolayers, undergo endothelial-to-mesenchymal transition as marked by loss of intercellular adhesion, and differentiate into VICs. These cells proliferate and are joined by a few neural crest-derived cells. VIC expansion and a switch from a promigratory to an elastic ECM drive valve leaflet elongation. Functional analysis of Nfatc1 reveals its requirement during VIC development. Zebrafish nfatc1 mutants form significantly fewer VICs due to reduced proliferation and impaired recruitment of endocardial and neural crest cells during the early stages of VIC development. With high-speed microscopy and echocardiography, we show that reduced VIC formation correlates with valvular dysfunction and severe retrograde blood flow that persist into adulthood. Analysis of downstream effectors reveals that Nfatc1 promotes the expression of twist1b-a well-known regulator of epithelial-to-mesenchymal transition.

CONCLUSIONS

Our study sheds light on the function of Nfatc1 in zebrafish cardiac valve development and reveals its role in VIC formation. It also further establishes the zebrafish as a powerful model to carry out longitudinal studies of valve formation and function.

Immunofluorescence of Cell-Cell and Cell-Extracellular Matrix Adhesive Defects in In Vitro Endothelial CCM Model: Juxtacrine Role of Mutant Extracellular Matrix on Wild-Type Endothelial Cells

Endothelial cells lining cerebral cavernous malformations (CCM) present strong adhesive and mechanical defects. Increased cell contractility is a driver to the onset and the expansion of the CCM lesions. 2D in vitro endothelial models have been developed from either endothelial cells isolated from ccm1-3 knock-out mice or CCM1-3-silenced primary endothelial cells. These in vitro models faithfully recapitulate the adhesive and contractile defects of the CCM-deficient endothelial cells such as increased cell-extracellular matrix (ECM) adhesion through β1 integrin-anchored actin stress fibers, abnormal remodeling of the ECM, and destabilized VE-cadherin-dependent cell-cell junctions. Using such 2D in vitro CCM models, we have shown that the ECM remodeled by CCM-depleted endothelial cells can propagate CCM-like adhesive defects to wild-type endothelial cells, a process potentially pertinent to CCM lesion expansion. Here, we detail methods for studying the morphology of focal adhesions, actomyosin cytoskeleton, and VE-cadherin-dependent Adherens junctions by immunofluorescence and morphometric analyses. Moreover, we detail the protocols to produce and purify remodeled ECM and to test its effect on endothelial cell adhesion.

Zebrafish Vestigial Like Family Member 4b Is Required for Valvulogenesis Through Sequestration of Transcription Factor Myocyte Enhancer Factor 2c

A variety of cardiac transcription factors/cofactors, signaling pathways, and downstream structural genes integrate to form the regulatory hierarchies to ensure proper cardiogenesis in vertebrate. Major interaction proteins of the transcription cofactor vestigial like family member 4 (VGLL4) include myocyte enhancer factor 2 (MEF2) and TEA domain transcription factors (TEAD), both of which play important roles in embryonic cardiac development and in adulthood. In this study, we identified that the deficiency of zebrafish vgll4b paralog, a unique family member expressed in developing heart, led to an impaired valve development. Mechanistically, in vgll4b mutant embryos the disruption of Vgll4b-Mef2c complex, rather than that of Vgll4b-Tead complex, resulted in an aberrant expression of krüppel-like factor 2a (klf2a) in endocardium. Such misexpression of klf2a eventually evoked the valvulogenesis defects. Our findings suggest that zebrafish Vgll4b plays an important role in modulating the transcription activity of Mef2c on klf2a during valve development in a blood-flow-independent manner.

Reactivation of Notch signaling is required for cardiac valve regeneration

Cardiac Valve Disease is one of the most common heart disorders with an emerging epidemic of cardiac valve degeneration due to aging. Zebrafish can regenerate most of their organs, including their heart. We aimed to explore the regenerative potential of cardiac valves and the underlying molecular mechanisms involved. We used an inducible, tissue-specific system of chemogenetic ablation and showed that zebrafish can also regenerate their cardiac valves. Upon valvular damage at larval stages, the intracardiac flow pattern becomes reminiscent of the early embryonic stages, exhibiting an increase in the retrograde flow fraction through the atrioventricular canal. As a result of the altered hemodynamics, notch1b and klf2a expression are ectopically upregulated, adopting the expression pattern of earlier developmental stages. We find that Notch signaling is re-activated upon valvular damage both at larval and adult stages and that it is required during the initial regeneration phase of cardiac valves. Our results introduce an animal model of cardiac valve specific ablation and regeneration.

Blood Flow Suppresses Vascular Anomalies in a Zebrafish Model of Cerebral Cavernous Malformations

Rationale:

Pathological biomechanical signaling induces vascular anomalies including cerebral cavernous malformations (CCM), which are caused by a clonal loss of CCM1/KRIT1 (Krev interaction trapped protein 1), CCM2/MGC4607, or CCM3/PDCD10. Why patients typically experience lesions only in lowly perfused venous capillaries of the cerebrovasculature is completely unknown.

Objective:

In contrast, animal models with a complete loss of CCM proteins lack a functional heart and blood flow and exhibit vascular anomalies within major blood vessels as well. This finding raises the possibility that hemodynamics may play a role in the context of this vascular pathology.

Methods and Results:

Here, we used a genetic approach to restore cardiac function and blood flow in a zebrafish model of CCM1. We find that blood flow prevents cardiovascular anomalies including a hyperplastic expansion within a large Ccm1-deficient vascular bed, the lateral dorsal aorta.

Conclusions:

This study identifies blood flow as an important physiological factor that is protective in the cause of this devastating vascular pathology.

Mechanotransduction in cardiovascular morphogenesis and tissue engineering

Cardiovascular morphogenesis involves cell behavior and cell identity changes that are activated by mechanical forces associated with heart function. Recently, advances in in vivo imaging, methods to alter blood flow, and computational modelling have greatly advanced our understanding of how forces produced by heart contraction and blood flow impact different morphogenetic processes. Meanwhile, traditional genetic approaches have helped to elucidate how endothelial cells respond to forces at the cellular and molecular level. Here we discuss the principles of endothelial mechanosensitity and their interplay with cellular processes during cardiovascular morphogenesis. We then discuss their implications in the field of cardiovascular tissue engineering.

Mechanically activated piezo channels modulate outflow tract valve development through the Yap1 and Klf2-Notch signaling axis

Mechanical forces are well known for modulating heart valve developmental programs. Yet, it is still unclear how genetic programs and mechanosensation interact during heart valve development. Here, we assessed the mechanosensitive pathways involved during zebrafish outflow tract (OFT) valve development in vivo. Our results show that the hippo effector Yap1, Klf2, and the Notch signaling pathway are all essential for OFT valve morphogenesis in response to mechanical forces, albeit active in different cell layers. Furthermore, we show that Piezo and TRP mechanosensitive channels are important factors modulating these pathways. In addition, live reporters reveal that Piezo controls Klf2 and Notch activity in the endothelium and Yap1 localization in the smooth muscle progenitors to coordinate OFT valve morphogenesis. Together, this work identifies a unique morphogenetic program during OFT valve formation and places Piezo as a central modulator of the cell response to forces in this process.

Notch and interacting signalling pathways in cardiac development, disease, and regeneration

Cardiogenesis is a complex developmental process involving multiple overlapping stages of cell fate specification, proliferation, differentiation, and morphogenesis. Precise spatiotemporal coordination between the different cardiogenic processes is ensured by intercellular signalling crosstalk and tissue-tissue interactions. Notch is an intercellular signalling pathway crucial for cell fate decisions during multicellular organismal development and is aptly positioned to coordinate the complex signalling crosstalk required for progressive cell lineage restriction during cardiogenesis. In this Review, we describe the role of Notch signalling and the crosstalk with other signalling pathways during the differentiation and patterning of the different cardiac tissues and in cardiac valve and ventricular chamber development. We examine how perturbation of Notch signalling activity is linked to congenital heart diseases affecting the neonate and adult, and discuss studies that shed light on the role of Notch signalling in heart regeneration and repair after injury.

Epigenetics and Mechanobiology in Heart Development and Congenital Heart Disease

: Congenital heart disease (CHD) is the most common birth defect worldwide and the number one killer of live-born infants in the United States. Heart development occurs early in embryogenesis and involves complex interactions between multiple cell populations, limiting the understanding and consequent treatment of CHD. Furthermore, genome sequencing has largely failed to predict or yield therapeutics for CHD. In addition to the underlying genome, epigenetics and mechanobiology both drive heart development. A growing body of evidence implicates the aberrant regulation of these two extra-genomic systems in the pathogenesis of CHD. In this review, we describe the stages of human heart development and the heart defects known to manifest at each stage. Next, we discuss the distinct and overlapping roles of epigenetics and mechanobiology in normal development and in the pathogenesis of CHD. Finally, we highlight recent advances in the identification of novel epigenetic biomarkers and environmental risk factors that may be useful for improved diagnosis and further elucidation of CHD etiology.

HEG1 indicates poor prognosis and promotes hepatocellular carcinoma invasion, metastasis, and EMT by activating Wnt/β-catenin signaling

Heart development protein with EGF-like domains 1 (HEG1) plays critical roles in embryo development and angiogenesis, which are closely related to tumor progression. However, the role of HEG1 in hepatocellular carcinoma (HCC) remains unknown. In the present study, we explored the clinical significance, biological function and regulatory mechanisms of HEG1 in HCC and found that HEG1 is significantly up-regulated in HCC cell lines and primary tumor samples. Additionally, high HEG1 expression is correlated with aggressive clinicopathological features. Patients with high HEG1 expression had shorter overall survival (OS) and disease-free survival (DFS) than those with low HEG1 expression, which indicated that HEG1 is an independent factor for poor prognosis. Lentivirus-mediated HEG1 overexpression significantly promotes HCC cell migration, invasion and epithelial–mesenchymal transition (EMT) in vitro and promotes intrahepatic metastasis, lung metastasis and EMT in vivo. Opposing results are observed when HEG1 is silenced. Mechanistically, HEG1 promotes β-catenin expression and maintains its stability, leading to intracellular β-catenin accumulation, β-catenin nuclear translocation and Wnt signaling activation. Loss- and gain-of-function assays further confirmed that β-catenin is essential for HEG1-mediated promotion of HCC invasion, metastasis and EMT. In conclusion, HEG1 indicates poor prognosis; plays important roles in HCC invasion, metastasis and EMT by activating Wnt/β-catenin signaling; and can serve as a potentially valuable prognostic biomarker and therapeutic target for HCC.

A Role for Sensory end Organ-Derived Signals in Regulating Muscle Spindle Proprioceptor Phenotype

Proprioceptive feedback from Group Ia/II muscle spindle afferents and Group Ib Golgi tendon afferents is critical for the normal execution of most motor tasks, yet how these distinct proprioceptor subtypes emerge during development remains poorly understood. Using molecular genetic approaches in mice of either sex, we identified 24 transcripts that have not previously been associated with a proprioceptor identity. Combinatorial expression analyses of these markers reveal at least three molecularly distinct proprioceptor subtypes. In addition, we find that 12 of these transcripts are expressed well after proprioceptors innervate their respective sensory receptors, and expression of three of these markers, including the heart development molecule Heg1, is significantly reduced in mice that lack muscle spindles. These data reveal Heg1 as a putative marker for proprioceptive muscle spindle afferents. Moreover, they suggest that the phenotypic specialization of functionally distinct proprioceptor subtypes depends, in part, on extrinsic sensory receptor organ-derived signals.SIGNIFICANCE STATEMENT Sensory feedback from muscle spindle (MS) and Golgi tendon organ (GTO) sensory end organs is critical for normal motor control, but how distinct MS and GTO afferent sensory neurons emerge during development remains poorly understood. Using (bulk) transcriptome analysis of genetically identified proprioceptors, this work reveals molecular markers for distinct proprioceptor subsets, including some that appear selectively expressed in MS afferents. Detailed analysis of the expression of these transcripts provides evidence that MS/GTO afferent subtype phenotypes may, at least in part, emerge through extrinsic, sensory end organ-derived signals.

Fluid forces shape the embryonic heart: Insights from zebrafish

Heart formation involves a complex series of tissue rearrangements, during which regions of the developing organ expand, bend, converge, and protrude in order to create the specific shapes of important cardiac components. Much of this morphogenesis takes place while cardiac function is underway, with blood flowing through the rapidly contracting chambers. Fluid forces are therefore likely to influence the regulation of cardiac morphogenesis, but it is not yet clear how these biomechanical cues direct specific cellular behaviors. In recent years, the optical accessibility and genetic amenability of zebrafish embryos have facilitated unique opportunities to integrate the analysis of flow parameters with the molecular and cellular dynamics underlying cardiogenesis. Consequently, we are making progress toward a comprehensive view of the biomechanical regulation of cardiac chamber emergence, atrioventricular canal differentiation, and ventricular trabeculation. In this review, we highlight a series of studies in zebrafish that have provided new insight into how cardiac function can shape cardiac morphology, with a particular focus on how hemodynamics can impact cardiac cell behavior. Over the long-term, this knowledge will undoubtedly guide our consideration of the potential causes of congenital heart disease.

Recent advances in cerebral cavernous malformation research

Cerebral cavernous malformations (CCM) are manifested by microvascular lesions characterized by leaky endothelial cells with minimal intervening parenchyma predominantly in the central nervous system predisposed to hemorrhagic stroke, resulting in focal neurological defects. Till date, three proteins are implicated in this condition: CCM1 (KRIT1), CCM2 (MGC4607), and CCM3 (PDCD10). These multi-domain proteins form a protein complex via CCM2 that function as a docking site for the CCM signaling complex, which modulates many signaling pathways. Defects in the formation of this signaling complex have been shown to affect a wide range of cellular processes including cell-cell contact stability, vascular angiogenesis, oxidative damage protection and multiple biogenic events. In this review we provide an update on recent advances in structure and function of these CCM proteins, especially focusing on the signaling cascades involved in CCM pathogenesis and the resultant CCM cellular phenotypes in the past decade.

Cerebral Cavernous Malformation 1/2 complex controls ROCK1 and ROCK2 complementary functions for endothelial integrity

Endothelial integrity relies on a mechanical crosstalk between intercellular and cell-matrix interactions. This cross-talk is compromised in hemorrhagic vascular lesions of patients carrying loss-of-function mutations in CCM genes. RhoA/ROCK-dependent cytoskeletal remodeling is central to the disease as it causes unbalanced cell adhesion towards increased cell-extracellular matrix adhesions and destabilized cell-cell junctions. Our study reveals that CCM proteins directly orchestrate ROCK1 and ROCK2 complementary roles on the mechanics of the endothelium. CCM proteins act as a scaffold promoting ROCK2 interactions with VE-cadherin and limiting ROCK1 kinase activity. Loss of CCM1 produces excessive ROCK1-dependent actin stress fibers and destabilizes intercellular junctions. Silencing of ROCK1 but not ROCK2 restores the adhesive and mechanical homeostasis of CCM1/2-depleted endothelial monolayers and rescues cardiovascular defects of ccm1 mutant zebrafish embryos. Conversely, knocking down of Rock2 but not Rock1 in WT zebrafish embryos generates defects reminiscent of the ccm1 mutant phenotypes. Our study uncovers the role of the CCM complex in controlling ROCK1 and ROCK2 to preserve endothelial integrity and drive heart morphogenesis. Moreover, it identifies solely the ROCK1 isoform as therapeutic target for the CCM disease.