Epicardial Epithelial-to-Mesenchymal Transition in Heart Development and Disease

Primary cilia-associated signalling in squamous cell carcinoma of head and neck region

Squamous cell carcinoma (SCC) of the head and neck originates from the mucosal lining of the upper aerodigestive tract, including the lip, tongue, nasopharynx, oropharynx, larynx and hypopharynx. In this review, we summarise what is currently known about the potential function of primary cilia in the pathogenesis of this disease. As primary cilia represent a key cellular structure for signal transduction and are related to cell proliferation, an understanding of their role in carcinogenesis is necessary for the design of new treatment approaches. Here, we introduce cilia-related signalling in head and neck squamous cell carcinoma (HNSCC) and its possible association with HNSCC tumorigenesis. From this point of view, PDGF, EGF, Wnt and Hh signalling are discussed as all these pathways were found to be dysregulated in HNSCC. Moreover, we review the clinical potential of small molecules affecting primary cilia signalling to target squamous cell carcinoma of the head and neck area.

Epicardial EMT and cardiac repair: an update

Epicardial epithelial-to-mesenchymal transition (EMT) plays a pivotal role in both heart development and injury response and involves dynamic cellular changes that are essential for cardiogenesis and myocardial repair. Specifically, epicardial EMT is a crucial process in which epicardial cells lose polarity, migrate into the myocardium, and differentiate into various cardiac cell types during development and repair. Importantly, following EMT, the epicardium becomes a source of paracrine factors that support cardiac growth at the last stages of cardiogenesis and contribute to cardiac remodeling after injury. As such, EMT seems to represent a fundamental step in cardiac repair. Nevertheless, endogenous EMT alone is insufficient to stimulate adequate repair. Redirecting and amplifying epicardial EMT pathways offers promising avenues for the development of innovative therapeutic strategies and treatment approaches for heart disease. In this review, we present a synthesis of recent literature highlighting the significance of epicardial EMT reactivation in adult heart disease patients.

Epigenetic determinants and non-myocardial signaling pathways contributing to heart growth and regeneration

Congenital heart disease is the most common birth defect worldwide. Defective cardiac myogenesis is either a major presentation or associated with many types of congenital heart disease. Non-myocardial tissues, including endocardium and epicardium, function as a supporting hub for myocardial growth and maturation during heart development. Recent research findings suggest an emerging role of epigenetics in nonmyocytes supporting myocardial development. Understanding how growth signaling pathways in non-myocardial tissues are regulated by epigenetic factors will likely identify new disease mechanisms for congenital heart diseases and shed lights for novel therapeutic strategies for heart regeneration.

Loss of developmentally derived Irf8+ macrophages promotes hyperinnervation and arrhythmia in the adult zebrafish heart

Recent developments in cardiac macrophage biology have broadened our understanding of the critical functions of macrophages in the heart. As a result, there is further interest in understanding the independent contributions of distinct subsets of macrophage to cardiac development and function. Here, we demonstrate that genetic loss of interferon regulatory factor 8 (Irf8)-positive embryonic-derived macrophages significantly disrupts cardiac conduction, chamber function, and innervation in adult zebrafish. At 4 months post-fertilization (mpf), homozygous irf8st96/st96 mutants have significantly shortened atrial action potential duration and significant differential expression of genes involved in cardiac contraction. Functional in vivo assessments via electro- and echocardiograms at 12 mpf reveal that irf8 mutants are arrhythmogenic and exhibit diastolic dysfunction and ventricular stiffening. To identify the molecular drivers of the functional disturbances in irf8 null zebrafish, we perform single cell RNA sequencing and immunohistochemistry, which reveal increased leukocyte infiltration, epicardial activation, mesenchymal gene expression, and fibrosis. Irf8 null hearts are also hyperinnervated and have aberrant axonal patterning, a phenotype not previously assessed in the context of cardiac macrophage loss. Gene ontology analysis supports a novel role for activated epicardial-derived cells (EPDCs) in promoting neurogenesis and neuronal remodeling in vivo. Together, these data uncover significant cardiac abnormalities following embryonic macrophage loss and expand our knowledge of critical macrophage functions in heart physiology and governing homeostatic heart health.

EMT and primary ciliogenesis: For better or worse in sickness and in health

Epithelial-mesenchymal transition (EMT) and primary ciliogenesis are two cell-biological programs that are essential for development of multicellular organisms and whose abnormal regulation results in many diseases (i.e., developmental anomalies and cancers). Emerging studies suggest an intricate interplay between these two processes. Here, we discuss physiological and pathological contexts in which their interconnections promote normal development or disease progression. We describe underlying molecular mechanisms of the interplay and EMT/ciliary signaling axes that influence EMT-related processes (i.e., stemness, motility and invasion). Understanding the molecular and cellular mechanisms of the relationship between EMT and primary ciliogenesis may provide new insights in the etiology of diseases related to EMT and cilia dysfunction.

Epicardium and Coronary Vessels

Congenital anomalies and acquired diseases of the coronary blood vessels are of great clinical relevance. The early diagnosis of these conditions remains, however, challenging. In order to improve our knowledge of these ailments, progress has to be achieved in the research of the molecular and cellular mechanisms that control development of the coronary vascular bed. The aim of this chapter is to provide a succint account of the key elements of coronary blood vessel development, especially in the context of the role played by the epicardium and epicardial cellular derivatives. We will discuss the importance of the epicardium in coronary blood vessel morphogenesis, from the contribution of the epicardially derived mesenchyme to these blood vessels to its role as an instructive signaling center, attempting to relate these concepts to the origin of coronary disease.

Elucidation of the genetic causes of bicuspid aortic valve disease

AIMS

The present study aims to characterize the genetic risk architecture of bicuspid aortic valve (BAV) disease, the most common congenital heart defect.

METHODS AND RESULTS

We carried out a genome-wide association study (GWAS) including 2236 BAV patients and 11 604 controls. This led to the identification of a new risk locus for BAV on chromosome 3q29. The single nucleotide polymorphism rs2550262 was genome-wide significant BAV associated (P = 3.49 × 10-08) and was replicated in an independent case-control sample. The risk locus encodes a deleterious missense variant in MUC4 (p.Ala4821Ser), a gene that is involved in epithelial-to-mesenchymal transformation. Mechanistical studies in zebrafish revealed that loss of Muc4 led to a delay in cardiac valvular development suggesting that loss of MUC4 may also play a role in aortic valve malformation. The GWAS also confirmed previously reported BAV risk loci at PALMD (P = 3.97 × 10-16), GATA4 (P = 1.61 × 10-09), and TEX41 (P = 7.68 × 10-04). In addition, the genetic BAV architecture was examined beyond the single-marker level revealing that a substantial fraction of BAV heritability is polygenic and ∼20% of the observed heritability can be explained by our GWAS data. Furthermore, we used the largest human single-cell atlas for foetal gene expression and show that the transcriptome profile in endothelial cells is a major source contributing to BAV pathology.

CONCLUSION

Our study provides a deeper understanding of the genetic risk architecture of BAV formation on the single marker and polygenic level.

Cre-loxP-mediated genetic lineage tracing: Unraveling cell fate and origin in the developing heart

The Cre-loxP-mediated genetic lineage tracing system is essential for constructing the fate mapping of single-cell progeny or cell populations. Understanding the structural hierarchy of cardiac progenitor cells facilitates unraveling cell fate and origin issues in cardiac development. Several prospective Cre-loxP-based lineage-tracing systems have been used to analyze precisely the fate determination and developmental characteristics of endocardial cells (ECs), epicardial cells, and cardiomyocytes. Therefore, emerging lineage-tracing techniques advance the study of cardiovascular-related cellular plasticity. In this review, we illustrate the principles and methods of the emerging Cre-loxP-based genetic lineage tracing technology for trajectory monitoring of distinct cell lineages in the heart. The comprehensive demonstration of the differentiation process of single-cell progeny using genetic lineage tracing technology has made outstanding contributions to cardiac development and homeostasis, providing new therapeutic strategies for tissue regeneration in congenital and cardiovascular diseases (CVDs).

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

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

Tbx18 Orchestrates Cytostructural Transdifferentiation of Cardiomyocytes to Pacemaker Cells by Recruiting the Epithelial-Mesenchymal Transition Program

Previously, we reported that heterologous expression of an embryonic transcription factor, Tbx18, reprograms ventricular cardiomyocytes into induced pacemaker cells (Tbx18-iPMs), though the key pathways are unknown. Here, we have used a tandem mass tag proteomic approach to characterize the impact of Tbx18 on neonatal rat ventricular myocytes. Tbx18 expression triggered vast proteome remodeling. Tbx18-iPMs exhibited increased expression of known pacemaker ion channels, including Hcn4 and Cx45 as well as upregulation of the mechanosensitive ion channels Piezo1, Trpp2 (PKD2), and TrpM7. Metabolic pathways were broadly downregulated, as were ion channels associated with ventricular excitation-contraction coupling. Tbx18-iPMs also exhibited extensive intracellular cytoskeletal and extracellular matrix remodeling, including 96 differentially expressed proteins associated with the epithelial-to-mesenchymal transition (EMT). RNAseq extended coverage of low abundance transcription factors, revealing upregulation of EMT-inducing Snai1, Snai2, Twist1, Twist2, and Zeb2. Finally, network diffusion mapping of >200 transcriptional regulators indicates EMT and heart development factors occupy adjacent network neighborhoods downstream of Tbx18 but upstream of metabolic control factors. In conclusion, transdifferentiation of cardiac myocytes into pacemaker cells entails massive electrogenic, metabolic, and cytostructural remodeling. Structural changes exhibit hallmarks of the EMT. The results aid ongoing efforts to maximize the yield and phenotypic stability of engineered biological pacemakers.

Polysaccharide-Polyplex Nanofilm Coatings Enhance Nanoneedle-Based Gene Delivery and Transfection Efficiency

Non-viral vectors represent versatile and immunologically safer alternatives for nucleic acid delivery. Nanoneedles and high-aspect ratio nanostructures are unconventional but interesting delivery systems, in which delivery is mediated by surface interactions. Herein, nanoneedles are synergistically combined with polysaccharide-polyplex nanofilms and enhanced transfection efficiency is observed, compared to polyplexes in suspension. Different polyplex-polyelectrolyte nanofilm combinations are assessed and it is found that transfection efficiency is enhanced when using polysaccharide-based polyanions, rather than being only specific for hyaluronic acid, as suggested in earlier studies. Moreover, results show that enhanced transfection is not mediated by interactions with the CD44 receptor, previously hypothesized as a major mechanism mediating enhancement via hyaluronate. In cardiac tissue, nanoneedles are shown to increase the transfection efficiency of nanofilms compared to flat substrates; while in vitro, high transfection efficiencies are observed in nanostructures where cells present large interfacing areas with the substrate. The results of this study demonstrate that surface-mediated transfection using this system is efficient and safe, requiring amounts of nucleic acid with an order of magnitude lower than standard culture transfection. These findings expand the spectrum of possible polyelectrolyte combinations that can be used for the development of suitable non-viral vectors for exploration in further clinical trials.

The negative regulation of gene expression by microRNAs as key driver of inducers and repressors of cardiomyocyte differentiation

Cardiac muscle damage-induced loss of cardiomyocytes (CMs) and dysfunction of the remaining ones leads to heart failure, which nowadays is the number one killer worldwide. Therapies fostering effective cardiac regeneration are the holy grail of cardiovascular research to stop the heart failure epidemic. The main goal of most myocardial regeneration protocols is the generation of new functional CMs through the differentiation of endogenous or exogenous cardiomyogenic cells. Understanding the cellular and molecular basis of cardiomyocyte commitment, specification, differentiation and maturation is needed to devise innovative approaches to replace the CMs lost after injury in the adult heart. The transcriptional regulation of CM differentiation is a highly conserved process that require sequential activation and/or repression of different genetic programs. Therefore, CM differentiation and specification have been depicted as a step-wise specific chemical and mechanical stimuli inducing complete myogenic commitment and cell-cycle exit. Yet, the demonstration that some microRNAs are sufficient to direct ESC differentiation into CMs and that four specific miRNAs reprogram fibroblasts into CMs show that CM differentiation must also involve negative regulatory instructions. Here, we review the mechanisms of CM differentiation during development and from regenerative stem cells with a focus on the involvement of microRNAs in the process, putting in perspective their negative gene regulation as a main modifier of effective CM regeneration in the adult heart.

Integrated Analysis of the microRNA–mRNA Network Predicts Potential Regulators of Atrial Fibrillation in Humans

Atrial fibrillation (AF) is a form of sustained cardiac arrhythmia and microRNAs (miRs) play crucial roles in the pathophysiology of AF. To identify novel miR–mRNA pairs, we performed RNA-seq from atrial biopsies of persistent AF patients and non-AF patients with normal sinus rhythm (SR). Differentially expressed miRs (11 down and 9 up) and mRNAs (95 up and 82 down) were identified and hierarchically clustered in a heat map. Subsequently, GO, KEGG, and GSEA analyses were run to identify deregulated pathways. Then, miR targets were predicted in the miRDB database, and a regulatory network of negatively correlated miR–mRNA pairs was constructed using Cytoscape. To select potential candidate genes from GSEA analysis, the top-50 enriched genes in GSEA were overlaid with predicted targets of differentially deregulated miRs. Further, the protein–protein interaction (PPI) network of enriched genes in GSEA was constructed, and subsequently, GO and canonical pathway analyses were run for genes in the PPI network. Our analyses showed that TNF-α, p53, EMT, and SYDECAN1 signaling were among the highly affected pathways in AF samples. SDC-1 (SYNDECAN-1) was the top-enriched gene in p53, EMT, and SYDECAN1 signaling. Consistently, SDC-1 mRNA and protein levels were significantly higher in atrial samples of AF patients. Among negatively correlated miRs, miR-302b-3p was experimentally validated to suppress SDC-1 transcript levels. Overall, our results suggested that the miR-302b-3p/SDC-1 axis may be involved in the pathogenesis of AF.

Fine-tuned KDM1A alternative splicing regulates human cardiomyogenesis through an enzymatic-independent mechanism

The histone demethylase KDM1A is a multi-faceted regulator of vital developmental processes, including mesodermal and cardiac tube formation during gastrulation. However, it is unknown whether the fine-tuning of KDM1A splicing isoforms, already shown to regulate neuronal maturation, is crucial for the specification and maintenance of cell identity during cardiogenesis. Here, we discovered a temporal modulation of ubKDM1A and KDM1A+2a during human and mice fetal cardiac development and evaluated their impact on the regulation of cardiac differentiation. We revealed a severely impaired cardiac differentiation in KDM1A^−/− hESCs that can be rescued by re-expressing ubKDM1A or catalytically impaired ubKDM1A-K661A, but not by KDM1A+2a or KDM1A+2a-K661A. Conversely, KDM1A+2a^−/− hESCs give rise to functional cardiac cells, displaying increased beating amplitude and frequency and enhanced expression of critical cardiogenic markers. Our findings prove the existence of a divergent scaffolding role of KDM1A splice variants, independent of their enzymatic activity, during hESC differentiation into cardiac cells.

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ubKDM1A and KDM1A+2a isoforms are fine-tuned during fetal cardiac development

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Depletion of KDM1A isoforms impairs hESC differentiation into cardiac cells

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KDM1A+2a ablation enhances the expression of key cardiac markers

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KDM1A isoforms exhibit enzymatic-independent divergent roles during cardiogenesis

CDH18 is a fetal epicardial biomarker regulating differentiation towards vascular smooth muscle cells

The epicardium is a mesothelial layer covering the myocardium serving as a progenitor source during cardiac development. The epicardium reactivates upon cardiac injury supporting cardiac repair and regeneration. Fine-tuned balanced signaling regulates cell plasticity and cell-fate decisions of epicardial-derived cells (EPCDs) via epicardial-to-mesenchymal transition (EMT). However, powerful tools to investigate epicardial function, including markers with pivotal roles in developmental signaling, are still lacking. Here, we recapitulated epicardiogenesis using human induced pluripotent stem cells (hiPSCs) and identified type II classical cadherin CDH18 as a biomarker defining lineage specification in human active epicardium. The loss of CDH18 led to the onset of EMT and specific differentiation towards cardiac smooth muscle cells. Furthermore, GATA4 regulated epicardial CDH18 expression. These results highlight the importance of tracing CDH18 expression in hiPSC-derived epicardial cells, providing a model for investigating epicardial function in human development and disease and enabling new possibilities for regenerative medicine.

Epicardial and endothelial cell activation concurs with extracellular matrix remodeling in atrial fibrillation

BACKGROUND

Improved understanding of the interconnectedness of structural remodeling processes in atrial fibrillation (AF) in patients could identify targets for future therapies.

METHODS

We present transcriptome sequencing of atrial tissues of patients without AF, with paroxysmal AF, and persistent AF (total n = 64). RNA expression levels were validated in the same and an independent cohort with qPCR. Biological processes were assessed with histological and immunohistochemical analyses.

RESULTS

In AF patients, epicardial cell gene expression decreased, contrasting with an upregulation of epithelial-to-mesenchymal transition (EMT) and mesenchymal cell gene expression. Immunohistochemistry demonstrated thickening of the epicardium and an increased proportion of (myo)fibroblast-like cells in the myocardium, supporting enhanced EMT in AF. We furthermore report an upregulation of endothelial cell proliferation, angiogenesis, and endothelial signaling. EMT and endothelial cell proliferation concurred with increased interstitial (myo)fibroblast-like cells and extracellular matrix gene expression including enhanced tenascin-C, thrombospondins, biglycan, and versican. Morphological analyses discovered increased and redistributed glycosaminoglycans and collagens in the atria of AF patients. Signaling pathways, including cell-matrix interactions, PI3K-AKT, and Notch signaling that could regulate mesenchymal cell activation, were upregulated.

CONCLUSION

Our results suggest that EMT and endothelial cell proliferation work in concert and characterize the (myo)fibroblast recruitment and ECM remodeling of AF. These processes could guide future research toward the discovery of targets for AF therapy.

Cellular dynamics of EMT: lessons from live in vivo imaging of embryonic development

Epithelial-mesenchymal transition (EMT) refers to a process in which epithelial cells lose apical-basal polarity and loosen cell-cell junctions to take on mesenchymal cell morphologies and invasive properties that facilitate migration through extracellular matrix. EMT-and the reverse mesenchymal-epithelial transition (MET)-are evolutionarily conserved processes that are used throughout embryonic development to drive tissue morphogenesis. During adult life, EMT is activated to close wounds after injury, but also can be used by cancers to promote metastasis. EMT is controlled by several mechanisms that depend on context. In response to cell-cell signaling and/or interactions with the local environment, cells undergoing EMT make rapid changes in kinase and adaptor proteins, adhesion and extracellular matrix molecules, and gene expression. Many of these changes modulate localization, activity, or expression of cytoskeletal proteins that mediate cell shape changes and cell motility. Since cellular changes during EMT are highly dynamic and context-dependent, it is ideal to analyze this process in situ in living organisms. Embryonic development of model organisms is amenable to live time-lapse microscopy, which provides an opportunity to watch EMT as it happens. Here, with a focus on functions of the actin cytoskeleton, I review recent examples of how live in vivo imaging of embryonic development has led to new insights into mechanisms of EMT. At the same time, I highlight specific developmental processes in model embryos-gastrulation in fly and mouse embryos, and neural crest cell development in zebrafish and frog embryos-that provide in vivo platforms for visualizing cellular dynamics during EMT. In addition, I introduce Kupffer's vesicle in the zebrafish embryo as a new model system to investigate EMT and MET. I discuss how these systems have provided insights into the dynamics of adherens junction remodeling, planar cell polarity signaling, cadherin functions, and cytoskeletal organization during EMT, which are not only important for understanding development, but also cancer progression. These findings shed light on mechanisms of actin cytoskeletal dynamics during EMT, and feature live in vivo imaging strategies that can be exploited in future work to identify new mechanisms of EMT and MET. Video Abstract.

The role of the Hippo pathway in heart disease

Heart disease, including coronary artery disease, myocardial infarction, heart failure, cardiac hypertrophy, and cardiomyopathies, is the leading causes of death worldwide. The Hippo pathway is a central controller for organ size and tissue growth, which plays a pivotal role in determining cardiomyocytes and nonmyocytes proliferation, regeneration, differentiation, and apoptosis. In this review, we summarize the effects of the Hippo pathway on heart disease and propose potential intervention targets. Especially, we discuss the molecular mechanisms of the Hippo pathway involved in maintaining cardiac homeostasis by regulating cardiomyocytes and nonmyocytes function in the heart. Based on this, we conclude that the Hippo pathway is a promising therapeutic target for cardiovascular therapy, which will bring new perspectives for their treatments.

Bioengineering strategies to control epithelial-to-mesenchymal transition for studies of cardiac development and disease

Epithelial-to-mesenchymal transition (EMT) is a process that occurs in a wide range of tissues and environments, in response to numerous factors and conditions, and plays a critical role in development, disease, and regeneration. The process involves epithelia transitioning into a mobile state and becoming mesenchymal cells. The investigation of EMT processes has been important for understanding developmental biology and disease progression, enabling the advancement of treatment approaches for a variety of disorders such as cancer and myocardial infarction. More recently, tissue engineering efforts have also recognized the importance of controlling the EMT process. In this review, we provide an overview of the EMT process and the signaling pathways and factors that control it, followed by a discussion of bioengineering strategies to control EMT. Important biological, biomaterial, biochemical, and physical factors and properties that have been utilized to control EMT are described, as well as the studies that have investigated the modulation of EMT in tissue engineering and regenerative approaches in vivo, with a specific focus on the heart. Novel tools that can be used to characterize and assess EMT are discussed and finally, we close with a perspective on new bioengineering methods that have the potential to transform our ability to control EMT, ultimately leading to new therapies.

Defective mesothelium and limited physical space are drivers of dysregulated lung development in a genetic model of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a developmental disorder associated with diaphragm defects and lung hypoplasia. The etiology of CDH is complex and its clinical presentation is variable. We investigated the role of the pulmonary mesothelium in dysregulated lung growth noted in the Wt1 knockout mouse model of CDH. Loss of WT1 leads to intrafetal effusions, altered lung growth, and branching defects prior to normal closure of the diaphragm. We found significant differences in key genes; however, when Wt1 null lungs were cultured ex vivo, growth and branching were indistinguishable from wild-type littermates. Micro-CT imaging of embryos in situ within the uterus revealed a near absence of space in the dorsal chest cavity, but no difference in total chest cavity volume in Wt1 null embryos, indicating a redistribution of pleural space. The altered space and normal ex vivo growth suggest that physical constraints are contributing to the CDH lung phenotype observed in this mouse model. These studies emphasize the importance of examining the mesothelium and chest cavity as a whole, rather than focusing on single organs in isolation to understand early CDH etiology.

Zinc finger E-box binding homeobox 1 and atherosclerosis: New insights and therapeutic potential

Zinc finger E-box binding homeobox 1 (ZEB1), an important transcription factor belonging to the ZEB family, plays a crucial role in regulating gene expression required for both normal physiological and pathological processes. Accumulating evidence has shown that ZEB1 participates in the initiation and progression of atherosclerotic cardiovascular disease. Recent studies suggest that ZEB1 protects against atherosclerosis by regulation of endothelial cell angiogenesis, endothelial dysfunction, monocyte-endothelial cell interaction, macrophage lipid accumulation, macrophage polarization, monocyte-vascular smooth muscle cell (VSMC) interaction, VSMC proliferation and migration, and T cell proliferation. In this review, we summarize the recent progress of ZEB1 in the pathogenesis of atherosclerosis and provide insights into the prevention and treatment of atherosclerotic cardiovascular disease.

Human cardiac fibroblasts expressing VCAM1 improve heart function in postinfarct heart failure rat models by stimulating lymphangiogenesis

Cardiovascular diseases are a leading cause of death worldwide. After an ischemic injury, the myocardium undergoes severe necrosis and apoptosis, leading to a dramatic degradation of function. Numerous studies have reported that cardiac fibroblasts (CFs) play a critical role in heart function even after injury. However, CFs present heterogeneous characteristics according to their development stage (i.e., fetal or adult), and the molecular mechanisms by which they maintain heart function are not fully understood. The aim of this study is to explore the hypothesis that a specific population of CFs can repair the injured myocardium in heart failure following ischemic infarction, and lead to a significant recovery of cardiac function. Flow cytometry analysis of CFs defined two subpopulations according to their relative expression of vascular cell adhesion molecule 1 (VCAM1). Whole-transcriptome analysis described distinct profiles for these groups, with a correlation between VCAM1 expression and lymphangiogenesis-related genes up-regulation. Vascular formation assays showed a significant stimulation of lymphatic cells network complexity by VCFs. Injection of human VCAM1-expressing CFs (VCFs) in postinfarct heart failure rat models (ligation of the left anterior descending artery) led to a significant restoration of the left ventricle contraction. Over the course of the experiment, left ventricular ejection fraction and fractional shortening increased by 16.65% ± 5.64% and 10.43% ± 6.02%, respectively, in VCF-treated rats. Histological examinations revealed that VCFs efficiently mobilized the lymphatic endothelial cells into the infarcted area. In conclusion, human CFs present heterogeneous expression of VCAM1 and lymphangiogenesis-promoting factors. VCFs restore the mechanical properties of ventricular walls by mobilizing lymphatic endothelial cells into the infarct when injected into a rat heart failure model. These results suggest a role of this specific population of CFs in the homeostasis of the lymphatic system in cardiac regeneration, providing new information for the study and therapy of cardiac diseases.

Spatiotemporal Analysis Reveals Overlap of Key Proepicardial Markers in the Developing Murine Heart

The embryonic epicardium, originating from the proepicardial organ (PEO), provides a source of multipotent progenitors for cardiac lineages, including pericytes, fibroblasts, and vascular smooth muscle cells. Maximizing the regenerative capacity of the adult epicardium depends on recapitulating embryonic cell fates. The potential of the epicardium to contribute coronary endothelium is unclear, due to conflicting Cre-based lineage trace data. Controversy also surrounds when epicardial cell fate becomes restricted. Here, we systematically investigate expression of five widely used epicardial markers, Wt1, Tcf21, Tbx18, Sema3d, and Scx, over the course of development. We show overlap of markers in all PEO and epicardial cells until E13.5, and find no evidence for discrete proepicardial sub-compartments that might contribute coronary endothelium via the epicardial layer. Our findings clarify a number of prevailing discrepancies and support the notion that epicardium-derived cell fate, to form fibroblasts or mural cells, is specified after epithelial-mesenchymal transition, not pre-determined within the PEO.

TETs Regulate Proepicardial Cell Migration through Extracellular Matrix Organization during Zebrafish Cardiogenesis

Ten-eleven translocation (Tet) enzymes (Tet1/2/3) mediate 5-methylcytosine (5mC) hydroxylation, which can facilitate DNA demethylation and thereby impact gene expression. Studied mostly for how mutant isoforms impact cancer, the normal roles for Tet enzymes during organogenesis are largely unknown. By analyzing compound mutant zebrafish, we discovered a requirement for Tet2/3 activity in the embryonic heart for recruitment of epicardial progenitors, associated with development of the atrial-ventricular canal (AVC). Through a combination of methylation, hydroxymethylation, and transcript profiling, the genes encoding the activin A subunit Inhbaa (in endocardium) and Sox9b (in myocardium) were implicated as demethylation targets of Tet2/3 and critical for organization of AVC-localized extracellular matrix (ECM), facilitating migration of epicardial progenitors onto the developing heart tube. This study elucidates essential DNA demethylation modifications that govern gene expression changes during cardiac development with striking temporal and lineage specificities, highlighting complex interactions in multiple cell populations during development of the vertebrate heart.

Lan et al. show that zebrafish larvae mutant for tet2 and tet3 fail to demethylate genes encoding Inhbaa (in endocardium) and Sox9b (in myocardium), leading to defects in ECM needed to form valves and to recruit epicardial progenitors onto the heart tube.

Cardiac progenitors and paracrine mediators in cardiogenesis and heart regeneration

The mammalian hearts have the least regenerative capabilities among tissues and organs. As such, heart regeneration has been and continues to be the ultimate goal in the treatment against acquired and congenital heart diseases. Uncovering such a long-awaited therapy is still extremely challenging in the current settings. On the other hand, this desperate need for effective heart regeneration has developed various forms of modern biotechnologies in recent years. These involve the transplantation of pluripotent stem cell-derived cardiac progenitors or cardiomyocytes generated in vitro and novel biochemical molecules along with tissue engineering platforms. Such newly generated technologies and approaches have been shown to effectively proliferate cardiomyocytes and promote heart repair in the diseased settings, albeit mainly preclinically. These novel tools and medicines give somehow credence to breaking down the barriers associated with re-building heart muscle. However, in order to maximize efficacy and achieve better clinical outcomes through these cell-based and/or cell-free therapies, it is crucial to understand more deeply the developmental cellular hierarchies/paths and molecular mechanisms in normal or pathological cardiogenesis. Indeed, the morphogenetic process of mammalian cardiac development is highly complex and spatiotemporally regulated by various types of cardiac progenitors and their paracrine mediators. Here we discuss the most recent knowledge and findings in cardiac progenitor cell biology and the major cardiogenic paracrine mediators in the settings of cardiogenesis, congenital heart disease, and heart regeneration.

Embryonic Chicken (Gallus gallus domesticus) as a Model of Cardiac Biology and Development

Cardiovascular disease remains one of the top contributors to morbidity and mortality in the United States. Increasing evidence suggests that many processes, pathways, and programs observed during development and organogenesis are recapitulated in adults in the face of disease. Therefore, a heightened understanding of cardiac development and organogenesis will help increase our understanding of developmental defects and cardiovascular diseases in adults. Chicks have long served as a model system in which to study developmental problems. Detailed descriptions of morphogenesis, low cost, accessibility, ease of manipulation, and the optimization of genetic engineering techniques have made chicks a robust model for studying development and make it a powerful platform for cardiovascular research. This review summarizes the cardiac developmental milestones of embryonic chickens, practical considerations when working with chicken embryos, and techniques available for use in chicks (including tissue chimeras, genetic manipulations, and live imaging). In addition, this article highlights examples that accentuate the utility of the embryonic chicken as model system in which to study cardiac development, particularly epicardial development, and that underscore the importance of how studying development informs our understanding of disease.

Mesothelium and Malignant Mesothelioma

The mesothelium is an epithelial structure derived from the embryonic mesoderm. It plays an important role in the development of a number of different organs, including the heart, lungs, and intestines. In this publication, we discuss aspects of the development of the mesothelium, where mesothelial structures can be found, and review molecular and cellular characteristics associated with the mesothelium. Furthermore, we discuss the involvement of the mesothelium in a number of disease conditions, in particular in the pathogenesis of mesotheliomas with an emphasis on malignant pleural mesothelioma (MPM)—a primary cancer developing in the pleural cavity.

The TRPV4-TAZ mechanotransduction signaling axis in matrix stiffness- and TGFβ1-induced epithelial-mesenchymal transition

Introduction

The implantation of biomaterials into soft tissue leads to the development of foreign body response, a non-specific inflammatory condition that is characterized by the presence of fibrotic tissue. Epithelial-mesenchymal transition (EMT) is a key event in development, fibrosis, and oncogenesis. Emerging data support a role for both a mechanical signal and a biochemical signal in EMT. We hypothesized that transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive channel, is a mediator of EMT.

Methods

Normal human primary epidermal keratinocytes (NHEKs) were seeded on collagen-coated plastic plates or varied stiffness polyacrylamide gels in the presence or absence of TGFβ1, Immunofluorescence, immunoblot, and polymerase chain reaction analysis were performed to determine expression level of EMT markers and signaling proteins. Knock-down of TRPV4 function was achieved by siRNA transfection or by GSK2193874 treatment.

Results

We found that knock-down of TRPV4 blocked both matrix stiffness- and TGFβ1-induced EMT in NHEKs. In a murine skin fibrosis model, TRPV4 deletion resulted in decreased expression of the mesenchymal marker, α-SMA, and increased expression of epithelial marker, E-cadherin. Mechanistically, our data showed that: i) TRPV4 was essential for the nuclear translocation of TAZ in response to matrix stiffness and TGFβ1; ii) Antagonism of TRPV4 inhibited both matrix stiffness-induced and TGFβ1-induced expression of TAZ proteins; and iii) TRPV4 antagonism suppressed both matrix stiffness-induced and TGFβ1-induced activation of Smad2/3, but not of AKT.

Conclusions

These data identify a novel role for TRPV4-TAZ mechanotransduction signaling axis in regulating EMT in NHEKs in response to both matrix stiffness and TGFβ1.

TRPV4 regulates matrix stiffness and TGFβ1-induced epithelial-mesenchymal transition

Substrate stiffness (or rigidity) of the extracellular matrix has important functions in numerous pathophysiological processes including fibrosis. Emerging data support a role for both a mechanical signal, for example, matrix stiffness, and a biochemical signal, for example, transforming growth factor β1 (TGFβ1), in epithelial‐mesenchymal transition (EMT), a process critically involved in fibrosis. Here, we report evidence showing that transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive channel, is the likely mediator of EMT in response to both TGFβ1 and matrix stiffness. Specifically, we found that: (a) genetic ablation or pharmacological inhibition of TRPV4 blocked matrix stiffness and TGFβ1‐induced EMT in normal mouse primary epidermal keratinocytes (NMEKs) as determined by changes in morphology, adhesion, migration and alterations of expression of EMT markers including E‐cadherin, N‐cadherin (NCAD) and α‐smooth muscle actin (α‐SMA), and (b) TRPV4 deficiency prevented matrix stiffness‐induced EMT in NMEKs over a pathophysiological range. Intriguingly, TRPV4 deletion in mice suppressed expression of mesenchymal markers, NCAD and α‐SMA, in a bleomycin‐induced murine skin fibrosis model. Mechanistically, we found that: (a) TRPV4 was essential for the nuclear translocation of YAP/TAZ (yes‐associated protein/transcriptional coactivator with PDZ‐binding motif) in response to matrix stiffness and TGFβ1, (b) TRPV4 deletion inhibited both matrix stiffness‐ and TGFβ1‐induced expression of YAP/TAZ proteins and (c) TRPV4 deletion abrogated both matrix stiffness‐ and TGFβ1‐induced activation of AKT, but not Smad2/3, suggesting a mechanism by which TRPV4 activity regulates EMT in NMEKs. Altogether, these data identify a novel role for TRPV4 in regulating EMT.

Hand Factors in Cardiac Development

Congenital heart defects account for 1% of infant mortality and 10% of in utero deaths. As the vertebrate embryo develops, multiple tissue types develop in tandem to morphologically pattern the functional heart. Underlying cardiac development is a network of transcription factors known to tightly control these morphological events. Members of the Twist family of basic helix-loop-helix transcription factors, Hand1 and Hand2, are essential to this process. The expression patterns and functional role of Hand factors in neural crest cells, endocardium, myocardium, and epicardium is indicative of their importance during cardiogenesis; however, to date, an extensive understanding of the transcriptional targets of Hand proteins and their overall mechanism of action remain unclear. In this review, we summarize the recent findings that further outline the crucial functions of Hand factors during heart development and in post-natal heart function. Anat Rec, 302:101-107, 2019. © 2018 Wiley Periodicals, Inc.

Desuppression of TGF-β signaling via nuclear c-Abl-mediated phosphorylation of TIF1γ/TRIM33 at Tyr-524, -610, and -1048

Protein-tyrosine kinases regulate a broad range of intracellular processes occurring primarily just beneath the plasma membrane. With the greatest care to prevent dephosphorylation, we have shown that nuclear tyrosine phosphorylation regulates global chromatin structural states. However, the roles for tyrosine phosphorylation in the nucleus are poorly understood. Here we identify transcriptional intermediary factor 1-γ (TIF1γ/TRIM33/Ectodermin), which suppresses transforming growth factor-β (TGF-β) signaling through the association with Smad2/3 transcription factor, as a new nuclear substrate of c-Abl tyrosine kinase. Replacement of the three tyrosine residues Tyr-524, -610, and -1048 with phenylalanine (3YF) inhibits c-Abl-mediated phosphorylation of TIF1γ and enhances TIF1γ's association with Smad3. Importantly, knockdown-rescue experiments show that 3YF strengthens TIF1γ's ability to suppress TGF-β signaling. Intriguingly, activation of c-Abl by epidermal growth factor (EGF) induces desuppression of TGF-β signaling via enhancing the tyrosine phosphorylation level of TIF1γ. TGF-β together with EGF synergistically provokes desuppressive responses of epithelial-to-mesenchymal transition through tyrosine phosphorylation of TIF1γ. These results suggest that nuclear c-Abl-mediated tyrosine phosphorylation of TIF1γ has a desuppressive role in TGF-β-Smad2/3 signaling.

The MELAS mutation m.3243A>G promotes reactivation of fetal cardiac genes and an epithelial-mesenchymal transition-like program via dysregulation of miRNAs

The pathomechanisms underlying oxidative phosphorylation (OXPHOS) diseases are not well-understood, but they involve maladaptive changes in mitochondria-nucleus communication. Many studies on the mitochondria-nucleus cross-talk triggered by mitochondrial dysfunction have focused on the role played by regulatory proteins, while the participation of miRNAs remains poorly explored. MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) is mostly caused by mutation m.3243A>G in mitochondrial tRNA^Leu(UUR) gene. Adverse cardiac and neurological events are the commonest causes of early death in m.3243A>G patients. Notably, the incidence of major clinical features associated with this mutation has been correlated to the level of m.3243A>G mutant mitochondrial DNA (heteroplasmy) in skeletal muscle. In this work, we used a transmitochondrial cybrid model of MELAS (100% m.3243A>G mutant mitochondrial DNA) to investigate the participation of miRNAs in the mitochondria-nucleus cross-talk associated with OXPHOS dysfunction. High-throughput analysis of small-RNA-Seq data indicated that expression of 246 miRNAs was significantly altered in MELAS cybrids. Validation of selected miRNAs, including miR-4775 and miR-218-5p, in patient muscle samples revealed miRNAs whose expression declined with high levels of mutant heteroplasmy. We show that miR-218-5p and miR-4775 are direct regulators of fetal cardiac genes such as NODAL, RHOA, ISL1 and RXRB, which are up-regulated in MELAS cybrids and in patient muscle samples with heteroplasmy above 60%. Our data clearly indicate that TGF-β superfamily signaling and an epithelial-mesenchymal transition-like program are activated in MELAS cybrids, and suggest that down-regulation of miRNAs regulating fetal cardiac genes is a risk marker of heart failure in patients with OXPHOS diseases.

Recapitulation of developmental mechanisms to revascularize the ischemic heart

Restoring blood flow after myocardial infarction (MI) is essential for survival of existing and newly regenerated tissue. Endogenous vascular repair processes are deployed following injury but are poorly understood. We sought to determine whether developmental mechanisms of coronary vessel formation are intrinsically reactivated in the adult mouse after MI. Using pulse-chase genetic lineage tracing, we establish that de novo vessel formation constitutes a substantial component of the neovascular response, with apparent cellular contributions from the endocardium and coronary sinus. The adult heart reverts to its former hypertrabeculated state and repeats the process of compaction, which may facilitate endocardium-derived neovascularization. The capacity for angiogenic sprouting of the coronary sinus vein, the adult derivative of the sinus venosus, may also reflect its embryonic origin. The quiescent epicardium is reactivated and, while direct cellular contribution to new vessels is minimal, it supports the directional expansion of the neovessel network toward the infarcted myocardium. Thymosin β4, a peptide with roles in vascular development, was required for endocardial compaction, epicardial vessel expansion, and smooth muscle cell recruitment. Insight into pathways that regulate endogenous vascular repair, drawing on comparisons with development, may reveal novel targets for therapeutically enhancing neovascularization.

Embryonic mechanisms are redeployed to revascularize the ischemic heart, with contributions primarily from the endocardium and coronary sinus and processes that require thymosin β4.

The Role and Mechanism of Epithelial-to-Mesenchymal Transition in Prostate Cancer Progression

In prostate cancer (PCa), similar to many other cancers, distant organ metastasis symbolizes the beginning of the end disease, which eventually leads to cancer death. Many mechanisms have been identified in this process that can be rationalized into targeted therapy. Among them, epithelial-to-mesenchymal transition (EMT) is originally characterized as a critical step for cell trans-differentiation during embryo development and now recognized in promoting cancer cells invasiveness because of high mobility and migratory abilities of mesenchymal cells once converted from carcinoma cells. Nevertheless, the underlying pathways leading to EMT appear to be very diverse in different cancer types, which certainly represent a challenge for developing effective intervention. In this article, we have carefully reviewed the key factors involved in EMT of PCa with clinical correlation in hope to facilitate the development of new therapeutic strategy that is expected to reduce the disease mortality.

Joint analysis of left ventricular expression and circulating plasma levels of Omentin after myocardial ischemia

BACKGROUND

Omentin-1, also known as Intelectin-1 (ITLN1), is an adipokine with plasma levels associated with diabetes, obesity, and coronary artery disease. Recent studies suggest that ITLN1 can mitigate myocardial ischemic injury but the expression of ITLN1 in the heart itself has not been well characterized. The purpose of this study is to discern the relationship between the expression pattern of ITLN1 RNA in the human heart and the level of circulating ITLN1 protein in plasma from the same patients following myocardial ischemia.

METHODS

A large cohort of patients (n = 140) undergoing elective cardiac surgery for aortic valve replacement were enrolled in this study. Plasma and left ventricular biopsy samples were taken at the beginning of cardiopulmonary bypass and after an average of 82 min of ischemic cross clamp time. The localization of ITLN1 in epicardial adipose tissue (EAT) was also further characterized with immunoassays and cell fate transition studies.

RESULTS

mRNA expression of ITLN1 decreases in left ventricular tissue after acute ischemia in human patients (mean difference 280.48, p = 0.001) whereas plasma protein levels of ITLN1 increase (mean difference 5.24, p < 0.001). Immunohistochemistry localized ITLN1 to the mesothelium or visceral pericardium of EAT. Epithelial to mesenchymal transition in mesothelial cells leads to a downregulation of ITLN1 expression.

CONCLUSIONS

Myocardial injury leads to a decrease in ITLN1 expression in the heart and a corresponding increase in plasma levels. These changes may in part be due to an epithelial to mesenchymal transition of the cells that express ITLN1 following ischemia. Trial Registration Clinicaltrials.gov ID: NCT00985049.

Proteomic characterization of epicardial-myocardial signaling reveals novel regulatory networks including a role for NF-κB in epicardial EMT

Signaling between the epicardium and underlying myocardium is crucial for proper heart development. The complex molecular interactions and regulatory networks involved in this communication are not well understood. In this study, we integrated mass spectrometry with bioinformatics to systematically characterize the secretome of embryonic chicken EPDC-heart explant (EHE) co-cultures. The 150-protein secretome dataset established greatly expands the knowledge base of the molecular players involved in epicardial-myocardial signaling. We identified proteins and pathways that are implicated in epicardial-myocardial signaling for the first time, as well as new components of pathways that are known to regulate the crosstalk between epicardium and myocardium. The large size of the dataset enabled bioinformatics analysis to deduce networks for the regulation of specific biological processes and predicted signal transduction nodes within the networks. We performed functional analysis on one of the predicted nodes, NF-κB, and demonstrate that NF-κB activation is an essential step in TGFβ2/PDGFBB-induced cardiac epithelial-to-mesenchymal transition. In summary, we have generated a global perspective of epicardial-myocardial signaling for the first time, and our findings open exciting new avenues for investigating the molecular basis of heart development and regeneration.

Epithelial-mesenchymal transition in tissue repair and fibrosis

The epithelial-mesenchymal transition (EMT) describes the global process by which stationary epithelial cells undergo phenotypic changes, including the loss of cell-cell adhesion and apical-basal polarity, and acquire mesenchymal characteristics that confer migratory capacity. EMT and its converse, MET (mesenchymal-epithelial transition), are integral stages of many physiologic processes and, as such, are tightly coordinated by a host of molecular regulators. Converging lines of evidence have identified EMT as a component of cutaneous wound healing, during which otherwise stationary keratinocytes (the resident skin epithelial cells) migrate across the wound bed to restore the epidermal barrier. Moreover, EMT plays a role in the development of scarring and fibrosis, as the matrix-producing myofibroblasts arise from cells of the epithelial lineage in response to injury but are pathologically sustained instead of undergoing MET or apoptosis. In this review, we summarize the role of EMT in physiologic repair and pathologic fibrosis of tissues and organs. We conclude that further investigation into the contribution of EMT to the faulty repair of fibrotic wounds might identify components of EMT signaling as common therapeutic targets for impaired healing in many tissues. Graphical Abstract Model for injury-triggered EMT activation in physiologic wound repair (left) and fibrotic wound healing (right).