MicroRNA-23 Restricts Cardiac Valve Formation by Inhibiting Has2 and Extracellular Hyaluronic Acid Production

miR-194-3p regulates epithelial-mesenchymal transition in embryonic epicardial cells via p120/β-catenin signaling

The epicardium is integral to cardiac development and facilitates endogenous heart regeneration and repair. While miR-194-3p is associated with cellular migration and invasion, its impact on epicardial cells remains uncharted. In this work we use gain-of-function and loss-of-function methodologies to investigate the function of miR-194-3p in cardiac development. We culture embryonic epicardial cells in vitro and subject them to transforming growth factor β (TGF-β) treatment to induce epithelial-mesenchymal transition (EMT) and monitor miR-194-3p expression. In addition, the effects of miR-194-3p mimics and inhibitors on epicardial cell development and changes in EMT are investigated. To validate the binding targets of miR-194-3p and its ability to recover the target gene-phenotype, we produce a mutant vector p120-catenin-3'UTR-MUT. In epicardial cells, TGF-β-induced EMT results in a notable overexpression of miR-194-3p. The administration of miR-194-3p mimics promotes EMT, which is correlated with elevated levels of mesenchymal markers. Conversely, miR-194-3p inhibitor attenuates EMT. Further investigations reveal a negative correlation between miR-194-3p and p120-catenin, which influences β-catenin level in the cell adhesion pathway. The suppression of EMT caused by the miR-194-3p inhibitor is balanced by silencing of p120-catenin. In conclusion, miR-194-3p directly targets p120-catenin and modulates its expression, which in turn alters β-catenin expression, critically influencing the EMT process in the embryonic epicardial cells via the cell adhesion mechanism.

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.

Dynamically regulated focal adhesions coordinate endothelial cell remodelling in developing vasculature

The assembly of a mature vascular network involves coordinated endothelial cell (EC) shape changes, including the process of EC elongation. How EC elongation is dynamically regulated in vivo is not fully understood. Here, we have generated a zebrafish mutant that is deficient for the integrin adaptor protein Talin 1 (Tln1). Using a new focal adhesion (FA) marker line expressing endothelial Vinculinb-eGFP, we demonstrate that EC FAs function dynamically and are lost in our tln1 mutants, allowing us to uncouple the primary roles of FAs in EC morphogenesis from the secondary effects that occur due to systemic vessel failure or loss of blood flow. Tln1 loss led to compromised F-actin rearrangements, perturbed EC elongation and disrupted cell-cell junction linearisation in vessel remodelling. Finally, chemical induction of actin polymerisation restored actin dynamics and EC elongation during vascular morphogenesis. Together, we identify that FAs are essential for EC elongation and junction linearisation in flow-pressured vessels and that they influence actin polymerisation in cellular morphogenesis. These observations can explain the severely compromised vessel beds and vascular leakage observed in mutant models that lack integrin signalling. This article has an associated 'The people behind the papers' interview.

Hyaluronan synthase 2, a target of miR-200c, promotes carbon tetrachloride-induced acute and chronic liver inflammation via regulation of CCL3 and CCL4

Liver fibrosis occurs during wound healing after repeated liver injury and is characterized by extensive extracellular matrix deposition. We previously identified hyaluronan synthase 2 (HAS2) as a driver of liver fibrosis and hepatic stellate cell (HSC) activation. Developing strategies to suppress HSC activation is key to alleviating liver fibrosis, and HAS2 is an attractive candidate for intervention. To gain insight into the molecular function of HAS2, we investigated its posttranscriptional regulation. We found that miR-200c directly targets the 3' untranslated regions of HAS2. Moreover, miR-200c and HAS2 were inversely expressed in fibrotic human and mouse livers. After establishing the direct interaction between miR-200c and HAS2, we investigated the functional outcome of regulating HAS2 expression in three murine models: CCl₄-induced acute liver injury, CCl₄-induced chronic liver fibrosis, and bile duct ligation-induced liver fibrosis. Hepatic Has2 expression was induced by acute and chronic CCl₄ treatment. In contrast, miR-200c expression was decreased after CCl₄ treatment. HSC-specific Has2 deletion reduced the expression of inflammatory markers and infiltration of macrophages in the models. Importantly, hyaluronidase-2 (HYAL2) but not HYAL1 was overexpressed in fibrotic human and murine livers. HYAL2 is an enzyme that can cleave the extracellular matrix component hyaluronan. We found that low-molecular-weight hyaluronan stimulated the expression of inflammatory genes. Treatment with the HA synthesis inhibitor 4-methylumbelliferone alleviated bile duct ligation-induced expression of these inflammatory markers. Collectively, our results suggest that HAS2 is negatively regulated by miR-200c and contributes to the development of acute liver injury and chronic liver inflammation via hyaluronan-mediated immune signaling.

Cardiac Fibroblasts Promote Ferroptosis in Atrial Fibrillation by Secreting Exo-miR-23a-3p Targeting SLC7A11

The exact mechanism of atrial fibrillation (AF) has been not well elucidated. Ferroptosis is an iron-dependent cell death due to excessive accumulation of peroxidized polyunsaturated fatty acids. However, the molecular mechanism underlying AF and ferroptosis has never been reported. Here, we established the rapid pacing model in vivo and vitro to investigate the relationship between AF and ferroptosis. In canine model of rapid atrial pacing, the content of malondialdehyde and total ions in the atrial tissue of the Pacing group was significantly increased and the exosome inhibitor GW4869 reduced ferroptosis, fibrosis, and inflammation and improved histological and electrophysiological remodeling. In rapid pacing h9c2 cells, the expression of antioxidative stress genes associated with ferroptosis presented sequential changes and proteins involved in ferroptosis such as FTH1, SLC7A11, and GPX4 were gradually depleted. Furthermore, pacing cardiac fibroblast-derived exosomes (CF-exos) exacerbated ferroptosis in h9c2 cells and pretreated pacing-CF-exos with GW4869 alleviated injury to h9c2 cells. In mechanism, our results demonstrated that pacing-CF-exos highly expressed miR-23a-3p by informatics analysis and experimental verification. Inhibitor-miR-23a-3p protected h9c2 cells from ferroptosis accompanying with upregulation of SLC7A11. In addition, SLC7A11 was shown to be the target gene of miR-23a-3p. In conclusion, our results suggest that CF-exos-miR-23a-3p may promote ferroptosis. The development of AF in a persistent direction could be prevented by intervening with exosomal miRNAs to reduce oxidative stress injury and ferroptosis.

Post-Transcriptional Regulation of Molecular Determinants during Cardiogenesis

Cardiovascular development is initiated soon after gastrulation as bilateral precardiac mesoderm is progressively symmetrically determined at both sides of the developing embryo. The precardiac mesoderm subsequently fused at the embryonic midline constituting an embryonic linear heart tube. As development progress, the embryonic heart displays the first sign of left-right asymmetric morphology by the invariably rightward looping of the initial heart tube and prospective embryonic ventricular and atrial chambers emerged. As cardiac development progresses, the atrial and ventricular chambers enlarged and distinct left and right compartments emerge as consequence of the formation of the interatrial and interventricular septa, respectively. The last steps of cardiac morphogenesis are represented by the completion of atrial and ventricular septation, resulting in the configuration of a double circuitry with distinct systemic and pulmonary chambers, each of them with distinct inlets and outlets connections. Over the last decade, our understanding of the contribution of multiple growth factor signaling cascades such as Tgf-beta, Bmp and Wnt signaling as well as of transcriptional regulators to cardiac morphogenesis have greatly enlarged. Recently, a novel layer of complexity has emerged with the discovery of non-coding RNAs, particularly microRNAs and lncRNAs. Herein, we provide a state-of-the-art review of the contribution of non-coding RNAs during cardiac development. microRNAs and lncRNAs have been reported to functional modulate all stages of cardiac morphogenesis, spanning from lateral plate mesoderm formation to outflow tract septation, by modulating major growth factor signaling pathways as well as those transcriptional regulators involved in cardiac development.

The Role of Bmp- and Fgf Signaling Modulating Mouse Proepicardium Cell Fate

Bmp and Fgf signaling are widely involved in multiple aspects of embryonic development. More recently non coding RNAs, such as microRNAs have also been reported to play essential roles during embryonic development. We have previously demonstrated that microRNAs, i.e., miR-130, play an essential role modulating Bmp and Fgf signaling during early stages of cardiomyogenesis. More recently, we have also demonstrated that microRNAs are capable of modulating cell fate decision during proepicardial/septum transversum (PE/ST) development, since over-expression of miR-23 blocked while miR-125, miR-146, miR-223 and miR-195 enhanced PE/ST-derived cardiomyogenesis, respectively. Importantly, regulation of these microRNAs is distinct modulated by Bmp2 and Fgf2 administration in chicken. In this study, we aim to dissect the functional role of Bmp and Fgf signaling during mouse PE/ST development, their implication regulating post-transcriptional modulators such as microRNAs and their impact on lineage determination. Mouse PE/ST explants and epicardial/endocardial cell cultures were distinctly administrated Bmp and Fgf family members. qPCR analyses of distinct microRNAs, cardiomyogenic, fibrogenic differentiation markers as well as key elements directly epithelial to mesenchymal transition were evaluated. Our data demonstrate that neither Bmp2/Bmp4 nor Fgf2/Fgf8 signaling is capable of inducing cardiomyogenesis, fibrogenesis or inducing EMT in mouse PE/ST explants, yet deregulation of several microRNAs is observed, in contrast to previous findings in chicken PE/ST. RNAseq analyses in mouse PE/ST and embryonic epicardium identified novel Bmp and Fgf family members that might be involved in such cell fate differences, however, their implication on EMT induction and cardiomyogenic and/or fibrogenic differentiation is limited. Thus our data support the notion of species-specific differences regulating PE/ST cardiomyogenic lineage commitment.

Asymmetric Hapln1a drives regionalized cardiac ECM expansion and promotes heart morphogenesis in zebrafish development

AIMS

Vertebrate heart development requires the complex morphogenesis of a linear tube to form the mature organ, a process essential for correct cardiac form and function, requiring coordination of embryonic laterality, cardiac growth, and regionalized cellular changes. While previous studies have demonstrated broad requirements for extracellular matrix (ECM) components in cardiac morphogenesis, we hypothesized that ECM regionalization may fine tune cardiac shape during heart development.

METHODS AND RESULTS

Using live in vivo light sheet imaging of zebrafish embryos, we describe a left-sided expansion of the ECM between the myocardium and endocardium prior to the onset of heart looping and chamber ballooning. Analysis using an ECM sensor revealed the cardiac ECM is further regionalized along the atrioventricular axis. Spatial transcriptomic analysis of gene expression in the heart tube identified candidate genes that may drive ECM expansion. This approach identified regionalized expression of hapln1a, encoding an ECM cross-linking protein. Validation of transcriptomic data by in situ hybridization confirmed regionalized hapln1a expression in the heart, with highest levels of expression in the future atrium and on the left side of the tube, overlapping with the observed ECM expansion. Analysis of CRISPR-Cas9-generated hapln1a mutants revealed a reduction in atrial size and reduced chamber ballooning. Loss-of-function analysis demonstrated that ECM expansion is dependent upon Hapln1a, together supporting a role for Hapln1a in regionalized ECM modulation and cardiac morphogenesis. Analysis of hapln1a expression in zebrafish mutants with randomized or absent embryonic left-right asymmetry revealed that laterality cues position hapln1a-expressing cells asymmetrically in the left side of the heart tube.

CONCLUSION

We identify a regionalized ECM expansion in the heart tube which promotes correct heart development, and propose a novel model whereby embryonic laterality cues orient the axis of ECM asymmetry in the heart, suggesting these two pathways interact to promote robust cardiac morphogenesis.

Exosomes in Cardiovascular Diseases: Pathological Potential of Nano-Messenger

Cardiovascular diseases (CVDs) represent a major global health problem, due to their continued high incidences and mortality. The last few decades have witnessed new advances in clinical research which led to increased survival and recovery in CVD patients. Nevertheless, elusive and multifactorial pathophysiological mechanisms of CVD development perplexed researchers in identifying efficacious therapeutic interventions. Search for novel and effective strategies for diagnosis, prevention, and intervention for CVD has shifted research focus on extracellular vesicles (EVs) in recent years. By transporting molecular cargo from donor to recipient cells, EVs modulate gene expression and influence the phenotype of recipient cells, thus EVs prove to be an imperative component of intercellular signaling. Elucidation of the role of EVs in intercellular communications under physiological conditions implied the enormous potential of EVs in monitoring and treatment of CVD. The EVs secreted from the myriad of cells in the cardiovascular system such as cardiomyocytes, cardiac fibroblasts, cardiac progenitor cells, endothelial cells, inflammatory cells may facilitate the communication in physiological and pathological conditions. Understanding EVs-mediated cellular communication may delineate the mechanism of origin and progression of cardiovascular diseases. The current review summarizes exosome-mediated paracrine signaling leading to cardiovascular disease. The mechanistic role of exosomes in cardiovascular disease will provide novel avenues in designing diagnosis and therapeutic interventions.

Endothelial-Mesenchymal Transition in Cardiovascular Disease

Endothelial-to-mesenchymal transition is a dynamic process in which endothelial cells suppress constituent endothelial properties and take on mesenchymal cell behaviors. To begin the process, endothelial cells loosen their cell-cell junctions, degrade the basement membrane, and migrate out into the perivascular surroundings. These initial endothelial behaviors reflect a transient modulation of cellular phenotype, that is, a phenotypic modulation, that is sometimes referred to as partial endothelial-to-mesenchymal transition. Loosening of endothelial junctions and migration are also seen in inflammatory and angiogenic settings such that endothelial cells initiating endothelial-to-mesenchymal transition have overlapping behaviors and gene expression with endothelial cells responding to inflammatory signals or sprouting to form new blood vessels. Reduced endothelial junctions increase permeability, which facilitates leukocyte trafficking, whereas endothelial migration precedes angiogenic sprouting and neovascularization; both endothelial barriers and quiescence are restored as inflammatory and angiogenic stimuli subside. Complete endothelial-to-mesenchymal transition proceeds beyond phenotypic modulation such that mesenchymal characteristics become prominent and endothelial functions diminish. In proadaptive, regenerative settings the new mesenchymal cells produce extracellular matrix and contribute to tissue integrity whereas in maladaptive, pathologic settings the new mesenchymal cells become fibrotic, overproducing matrix to cause tissue stiffness, which eventually impacts function. Here we will review what is known about how TGF (transforming growth factor) β influences this continuum from junctional loosening to cellular migration and its relevance to cardiovascular diseases.

The ECM as a driver of heart development and repair

The developing heart is formed of two tissue layers separated by an extracellular matrix (ECM) that provides chemical and physical signals to cardiac cells. While deposition of specific ECM components creates matrix diversity, the cardiac ECM is also dynamic, with modification and degradation playing important roles in ECM maturation and function. In this Review, we discuss the spatiotemporal changes in ECM composition during cardiac development that support distinct aspects of heart morphogenesis. We highlight conserved requirements for specific ECM components in human cardiac development, and discuss emerging evidence of a central role for the ECM in promoting heart regeneration.

Sweet Control: MicroRNA Regulation of the Glycome

Glycosylation is a sophisticated informational system that controls specific biological functions at the cellular and organismal level. Dysregulation of glycosylation may underlie some of the most complex and common diseases of the modern era. In the past 5 years, microRNAs have come to the forefront as a critical regulator of the glycome. Herein, we review the current literature on miRNA regulation of glycosylation and how this work may point to a new way to identify the biological importance of glycosylation enzymes.

Non-coding RNA in endothelial-to-mesenchymal transition

Endothelial-to-mesenchymal transition (EndMT) is the process wherein endothelial cells lose their typical endothelial cell markers and functions and adopt a mesenchymal-like phenotype. EndMT is required for development of the cardiac valves, the pulmonary and dorsal aorta, and arterial maturation, but activation of the EndMT programme during adulthood is believed to contribute to several pathologies including organ fibrosis, cardiovascular disease, and cancer. Non-coding RNAs, including microRNAs, long non-coding RNAs, and circular RNAs, modulate EndMT during development and disease. Here, we review the mechanisms by which non-coding RNAs facilitate or inhibit EndMT during development and disease and provide a perspective on the therapeutic application of non-coding RNAs to treat fibroproliferative cardiovascular disease.

MiR-195 enhances cardiomyogenic differentiation of the proepicardium/septum transversum by Smurf1 and Foxp1 modulation

Cardiovascular development is a complex developmental process in which multiple cell lineages are involved, namely the deployment of first and second heart fields. Beside the contribution of these cardiogenic fields, extracardiac inputs to the developing heart are provided by the migrating cardiac neural crest cells and the proepicardial derived cells. The proepicardium (PE) is a transitory cauliflower-like structure located between the cardiac and hepatic primordia. The PE is constituted by an internal mesenchymal component surrounded by an external epithelial lining. With development, cells derived from the proepicardium migrate to the neighboring embryonic heart and progressive cover the most external surface, leading to the formation of the embryonic epicardium. Experimental evidence in chicken have nicely demonstrated that epicardial derived cells can distinctly contribute to fibroblasts, endothelial and smooth muscle cells. Surprisingly, isolation of the developing PE anlage and ex vivo culturing spontaneously lead to differentiation into beating cardiomyocytes, a process that is enhanced by Bmp but halted by Fgf administration. In this study we provide a comprehensive characterization of the developmental expression profile of multiple microRNAs during epicardial development in chicken. Subsequently, we identified that miR-125, miR-146, miR-195 and miR-223 selectively enhance cardiomyogenesis both in the PE/ST explants as well as in the embryonic epicardium, a Smurf1- and Foxp1-driven process. In addition we identified three novel long non-coding RNAs with enhanced expression in the PE/ST, that are complementary regulated by Bmp and Fgf administration and well as by microRNAs that selectively promote cardiomyogenesis, supporting a pivotal role of these long non coding RNAs in microRNA-mediated cardiomyogenesis of the PE/ST cells.

Functional Characterization and Expression Analyses Show Differential Roles of Maternal and Zygotic Dgcr8 in Early Embryonic Development

Dgcr8 is involved in the biogenesis of canonical miRNAs to process pri-miRNA into pre-miRNA. Previous studies have provided evidence that Dgcr8 plays an essential role in different biological processes. However, the function of maternal and zygotic Dgcr8 in early embryonic development remains largely unknown. Recently, we have reported a novel approach for generating germline-specific deletions in zebrafish. This germline knockout model offers an opportunity to investigate into the differential roles of maternal or zygotic Dgcr8. Although germline specific dgcr8 deletion has no influence on gonad development, maternal or zygotic dgcr8 is essential for embryonic development in the offspring. Both maternal dgcr8 (Mdgcr8) and maternal zygotic dgcr8 (MZdgcr8) mutants display multiple developmental defects and die within 1 week. Moreover, MZdcgr8 mutant displays more severe morphogenesis defects. However, when a miR-430 duplex (the most abundantly expressed miRNA in early embryonic stage) is used to rescue the maternal mutant phenotype, the Mdgcr8 embryos could be rescued successfully and grow into adulthood and achieve sexual maturation, whereas the MZdgcr8 embryos are only partially rescued and they all die within 1 week. The differential phenotypes between the Mdgcr8 and MZdgcr8 embryos provide us with an opportunity to study the roles of individual miRNAs during early development.

Dietary Suberic Acid Protects Against UVB-Induced Skin Photoaging in Hairless Mice

Ultraviolet (UV) radiation is a major cause of skin photoaging, which is mainly characterized by dryness and wrinkle formation. In the current study, we investigated the anti-photoaging effects of dietary suberic acid, a naturally occurring photochemical, using UVB-irradiated hairless mice. Mice were exposed to UVB three times weekly and fed diets containing three different suberic acid concentrations (0.05%, 0.1% and 0.2%) for 10 weeks. It was found that suberic acid inhibited UVB-induced skin dryness, wrinkle formation, and epidermal thickness in hairless mice. In parallel with phenotypic changes, suberic acid attenuated UVB-induced matrix metalloproteinase (MMP) genes (MMP1a, MMP1b, MMP3, and MMP9), while accelerating collagen genes including collagen type I alpha 1 chain (COL1A1), COL1A2, and COL3A1 and hyaluronic acid synthases genes (HAS1, HAS2 and HAS3). We further demonstrated that suberic acid upregulated the molecules involved in the transforming growth factor-β (TGF-β)/SMAD pathway, but downregulated the molecules participating in the mitogen-activated protein kinase (MAPK)/activator protein 1 (AP-1) signaling in UVB-irritated hairless mice. Collectively, we propose that suberic acid may be a promising agent for treating skin photoaging.

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.

Oct4 mediates Müller glia reprogramming and cell cycle exit during retina regeneration in zebrafish

The rapid induction of pluripotency-inducing factor Oct4 in the injured retina necessitates the de novo induction of stem cells and their subsequent cell cycle exit.

Octamer-binding transcription factor 4 (Oct4, also known as Pou5F3) is an essential pluripotency-inducing factor, governing a plethora of biological functions during cellular reprogramming. Retina regeneration in zebrafish involves reprogramming of Müller glia (MG) into a proliferating population of progenitors (MGPCs) with stem cell–like characteristics, along with up-regulation of pluripotency-inducing factors. However, the significance of Oct4 during retina regeneration remains elusive. In this study, we show an early panretinal induction of Oct4, which is essential for MG reprogramming through the regulation of several regeneration-associated factors such as Ascl1a, Lin28a, Sox2, Zeb, E-cadherin, and various miRNAs, namely, let-7a, miR-200a/miR-200b, and miR-143/miR-145. We also show the crucial roles played by Oct4 during cell cycle exit of MGPCs in collaboration with members of nucleosome remodeling and deacetylase complex such as Hdac1. Notably, Oct4 regulates Tgf-β signaling negatively during MG reprogramming, and positively to cause cycle exit of MGPCs. Our study reveals unique mechanistic involvement of Oct4, during MG reprogramming and cell cycle exit in zebrafish, which may also account for the inefficient retina regeneration in mammals.

Integrative Analysis of miRNA and mRNA Expression Profiles Associated With Human Atrial Aging

Background

Limited findings have been reported to systematically study miRNA and mRNA expression profiles in aged human atria. In this study, we aimed to identify miRNAs, genes, and miRNA-mRNA interaction networks for human atrial aging (AA).

Methods

Right atrial appendages from twelve patients who received aortic valve replacement were subjected to miRNA-seq and RNA-seq. All the patients were in sinus rhythm (SR) and stratified by age into four groups. Differential expression analysis was carried out to identify miRNAs and genes for human AA. The miRNA-mRNA interactions for human AA were identified by Pearson correlation analysis and miRNA target prediction programs.

Results

Seven miRNAs (4 upregulation and 3 downregulation) and 42 genes (23 upregulation and 19 downregulation) were differentially expressed in human right atrial tissues between older samples and younger samples. Bioinformatic analysis identified 114 pairs of putative miRNA-mRNA interactions on AA and four types of correlation. Pathway enrichment analysis identified over 40 significant pathways and the top three pathways included rhythmic process (P = 7.5 × 10^–5, Q = 0.034), senescence and autophagy in cancer (P = 9.0 × 10^–5, Q = 0.034), and positive regulation of cytokine biosynthetic process (P = 1.1 × 10^–4, Q = 0.034).

Conclusion

Our study revealed novel miRNA-mRNA interaction networks and signaling pathways for AA, providing novel insights into the development of human AA. Future studies are needed to investigate the potential significance of these miRNA-mRNA interactions in human AA or AA-related cardiovascular diseases.

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.

Endothelial to Mesenchymal Transition: Role in Physiology and in the Pathogenesis of Human Diseases

Numerous studies have demonstrated that endothelial cells are capable of undergoing endothelial to mesenchymal transition (EndMT), a newly recognized type of cellular transdifferentiation. EndMT is a complex biological process in which endothelial cells adopt a mesenchymal phenotype displaying typical mesenchymal cell morphology and functions, including the acquisition of cellular motility and contractile properties. Endothelial cells undergoing EndMT lose the expression of endothelial cell-specific proteins such as CD31/platelet-endothelial cell adhesion molecule, von Willebrand factor, and vascular-endothelial cadherin and initiate the expression of mesenchymal cell-specific genes and the production of their encoded proteins including α-smooth muscle actin, extra domain A fibronectin, N-cadherin, vimentin, fibroblast specific protein-1, also known as S100A4 protein, and fibrillar type I and type III collagens. Transforming growth factor-β1 is considered the main EndMT inducer. However, EndMT involves numerous molecular and signaling pathways that are triggered and modulated by multiple and often redundant mechanisms depending on the specific cellular context and on the physiological or pathological status of the cells. EndMT participates in highly important embryonic development processes, as well as in the pathogenesis of numerous genetically determined and acquired human diseases including malignant, vascular, inflammatory, and fibrotic disorders. Despite intensive investigation, many aspects of EndMT remain to be elucidated. The identification of molecules and regulatory pathways involved in EndMT and the discovery of specific EndMT inhibitors should provide novel therapeutic approaches for various human disorders mediated by EndMT.

Estrogen-Mediated MicroRNA-101-3p Expression Represses Hyaluronan Synthase 2 in Synovial Fibroblasts From Idiopathic Condylar Resorption Patients

PURPOSE

Idiopathic condylar resorption (ICR) is an aggressive form of osteoarthritis that is frequently observed in adolescent female patients. We hypothesized that an estrogen-mediated pathway may contribute to ICR development.

MATERIALS AND METHODS

An enzyme-linked immunosorbent assay was used to detect the levels of estradiol (E2) and hyaluronan in synovial fluid. Immunohistochemistry, real-time polymerase chain reaction, and Western blotting were used to detect the expression of microRNAs (miRNAs) and related genes after transfection of miRNA-101-3p mimics, inhibitor, or short interfering RNA into synovial fibroblasts. Dual-luciferase activity was determined to identify the direct effect of miRNA-101-3p on hyaluronan synthase 2 (HAS2). Linear regression analysis, the nonparametric Mann-Whitney U test, the Student t test, and 1-way analysis of variance were carried out to analyze the results of each group.

RESULTS

The relationship between hyaluronan and E2 was negatively correlated in synovial fluid (Pearson r = -0.3179, P = .0230). Among the screened miRNAs, miRNA-101-3p was the most overexpressed in ICR. E2 mostly upregulated the expression of miRNA-101-3p at a dose of 10 nmol/L 12 hours after transfection in synovial fibroblasts of patients with ICR. However, E2 induction of miRNA-101-3p expression was significantly repressed by estrogen receptor α interference (P = 0.0286). The dual-luciferase assay showed that miRNA-101-3p regulated the expression of HAS2 by directly targeting its 3' untranslated region.

CONCLUSIONS

We speculate that E2 regulates HAS2 expression by targeting miRNA-101-3p in synovial fibroblasts of patients with ICR. Thus, the E2-miRNA-101-3p-HAS2 pathway might play an important role in the pathogenesis of ICR.

Focal adhesions are essential to drive zebrafish heart valve morphogenesis

Gunawan et al. analyze at single-cell resolution collective endocardial cell migration into the extracellular matrix and the cellular rearrangements forming leaflets during zebrafish heart valve formation. They show that focal adhesion activity driven by Integrin α5β1 and Talin1 are essential to drive cardiac valve morphogenesis in zebrafish.

Elucidating the morphogenetic events that shape vertebrate heart valves, complex structures that prevent retrograde blood flow, is critical to understanding valvular development and aberrations. Here, we used the zebrafish atrioventricular (AV) valve to investigate these events in real time and at single-cell resolution. We report the initial events of collective migration of AV endocardial cells (ECs) into the extracellular matrix (ECM), and their subsequent rearrangements to form the leaflets. We functionally characterize integrin-based focal adhesions (FAs), critical mediators of cell–ECM interactions, during valve morphogenesis. Using transgenes to block FA signaling specifically in AV ECs as well as loss-of-function approaches, we show that FA signaling mediated by Integrin α5β1 and Talin1 promotes AV EC migration and overall shaping of the valve leaflets. Altogether, our investigation reveals the critical processes driving cardiac valve morphogenesis in vivo and establishes the zebrafish AV valve as a vertebrate model to study FA-regulated tissue morphogenesis.

The mir-200 family regulates key pathogenic events in ascending aortas of individuals with bicuspid aortic valves

BACKGROUND

An individual with a bicuspid aortic valve (BAV) runs a substantially higher risk of developing aneurysm in the ascending aorta compared to the normal population with tricuspid aortic valves (TAV). Aneurysm formation in patients with BAV and TAV is known to be distinct at the molecular level but the underlying mechanisms are undefined. Here, we investigated the still incompletely described role of microRNAs (miRNAs), important post-transcriptional regulators of gene expression, in such aortic disease of patients with BAV as compared with TAV.

METHODS AND RESULTS

Using a system biology approach, based on data obtained from proteomic analysis of non-dilated aortas from BAV and TAV patients, we constructed a gene-interaction network of regulatory microRNAs associated with the observed differential protein signature. The miR-200 family was the highest ranked miRNA, hence potentially having the strongest effect on the signalling network associated with BAV. Further, qRT-PCR and ChIP analyses showed lower expression of miR-200c, higher expression of miR-200 target genes, ZEB1/ZEB2 transcription factors, and higher chromatin occupancy of the miR-200c promoter by ZEB1/ZEB2 in BAV patients, indicating a miR-200c/ZEBs negative feedback loop and induction of endothelial/epithelial mesenchymal transition (EndMT/EMT).

CONCLUSION

We propose that a miR-200-dependent process of EndMT/EMT is a plausible biological mechanism rendering the BAV ascending aorta more prone to aneurysm development. Although initially supported by a miR-200c/ZEB feedback loop, this process is most probably advanced by cooperation of other miRNAs.

MicroRNAs as critical regulators of the endothelial to mesenchymal transition in vascular biology

The endothelial to mesenchymal transition (EndMT) is a newly recognized, fundamental biological process involved in development and tissue regeneration, as well as pathological processes such as the complications of diabetes, fibrosis and pulmonary arterial hypertension. The EndMT process is tightly controlled by diverse signaling networks, similar to the epithelial to mesenchymal transition. Accumulating evidence suggests that microRNAs (miRNAs) are key regulators of this network, with the capacity to target multiple messenger RNAs involved in the EndMT process as well as in the regulation of disease progression. Thus, it is highly important to understand the molecular basis of miRNA control of EndMT. This review highlights the current fund of knowledge regarding the known links between miRNAs and the EndMT process, with a focus on the mechanism that regulates associated signaling pathways and discusses the potential for the EndMT as a therapeutic target to treat many diseases.

Molecular Analysis of Endothelial-mesenchymal Transition Induced by Transforming Growth Factor-β Signaling

Phenotypic plasticity of endothelial cells underlies cardiovascular system development, cardiovascular diseases, and various conditions associated with organ fibrosis. In these conditions, differentiated endothelial cells acquire mesenchymal-like phenotypes. This process is called endothelial-mesenchymal transition (EndMT) and is characterized by downregulation of endothelial markers, upregulation of mesenchymal markers, and morphological changes. EndMT is induced by several signaling pathways, including transforming growth factor (TGF)-β, Wnt, and Notch, and regulated by molecular mechanisms similar to those of epithelial-mesenchymal transition (EMT) important for gastrulation, tissue fibrosis, and cancer metastasis. Understanding the mechanisms of EndMT is important to develop diagnostic and therapeutic approaches targeting EndMT. Robust induction of EndMT in vitro is useful to characterize common gene expression signatures, identify druggable molecular mechanisms, and screen for modulators of EndMT. Here, we describe an in vitro method for induction of EndMT. MS-1 mouse pancreatic microvascular endothelial cells undergo EndMT after prolonged exposure to TGF-β and show upregulation of mesenchymal markers and morphological changes as well as induction of multiple inflammatory chemokines and cytokines. Methods for the analysis of microRNA (miRNA) modulation are also included. These methods provide a platform to investigate mechanisms underlying EndMT and the contribution of miRNAs to EndMT.

EndMT: A promising and controversial field

The endothelial to mesenchymal transition (EndMT) is the process by which endothelial cells lose a portion of their cellular features and obtain certain characteristics of mesenchymal cells, including loss of tight junctions, increased motility, and increased secretion of extracellular matrix proteins. EndMT is involved in cardiac development and a variety of diseases processes, such as vascular or tissue fibrosis and tumor. However, its role in specific diseases remains under debate. This review summarizes EndMT-related diseases, existing controversies, different types of EndMT, and molecules and signaling pathways associated with the process.

Mediator complex subunit Med12 regulates cardiac jelly development and AV valve formation in zebrafish

The molecular mechanism essential for the formation of heart valves involves complex interactions of signaling molecules and transcription factors. The Mediator Complex (MC) functions as multi-subunit machinery to orchestrate gene transcription, especially for tissue-specific fine-tuning of transcriptional processes during development, also in the heart. Here, we analyzed the role of the MC subunit Med12 during atrioventricular canal (AVC) development and endocardial cushion formation, using the Med12-deficient zebrafish mutant trapped (tpd). Whereas primary heart formation was only slightly affected in tpd, we identified defects in AVC development and cardiac jelly formation. We found that although misexpression of bmp4 and versican in tpd hearts can be restored by overexpression of a modified version of the Sox9b transcription factor (harboring VP16 transactivation domain) that functions independent of its co-activator Med12, endocardial cushion development in tpd was not reconstituted. Interestingly, expression of tbx2b and its target hyaluronan synthase 2 (has2) - the synthase of hyaluronan (HA) in the heart - was absent in both uninjected and Sox9b-VP16 overexpressing tpd hearts. HA is a major ECM component of the cardiac jelly and required for endocardial cushion formation. Furthermore, we found secreted phosphoprotein 1 (spp1), an endocardial marker of activated AV endocardial cells, completely absent in tpd hearts, suggesting that crucial steps of the transformation of AV endocardial cells into endocardial cushions is blocked. We demonstrate that Med12 controls cardiac jelly formation Sox9-independently by regulating tbx2b and has2 expression and therefore the production of the glycosaminoglycan HA at the AVC to guarantee proper endocardial cushion development.

MicroRNA Control of TGF-β Signaling

Transcriptional and post-transcriptional regulation shapes the transcriptome and proteome changes induced by various cellular signaling cascades. MicroRNAs (miRNAs) are small regulatory RNAs that are approximately 22 nucleotides long, which direct the post-transcriptional regulation of diverse target genes and control cell states. Transforming growth factor (TGF)-β family is a multifunctional cytokine family, which plays many regulatory roles in the development and pathogenesis of diverse diseases, including fibrotic disease, cardiovascular disease and cancer. Previous studies have shown that the TGF-β pathway includes the miRNA pathway as an important component of its downstream signaling cascades. Multiple studies of epithelial–mesenchymal transition (EMT)-related miRNAs have highlighted that miRNAs constitute the intrinsic bistable molecular switches of cell states by forming double negative feedback loops with EMT-inducing transcription factors. This may be important for understanding the reversibility of EMT at the single-cell level, the presence of distinct EMT transition states and the intra- and inter-tumor heterogeneity of cancer cell phenotypes. In the present review, I summarize the connection between TGF-β signaling and the miRNA pathway, placing particular emphasis on the regulation of miRNA expression by TGF-β signaling, the modulation of TGF-β signaling by miRNAs, the miRNA-mediated modulation of EMT and endothelial–mesenchymal transition as well as the crosstalk between miRNA and TGF-β pathways in the tumor microenvironment.

At the heart of programming: the role of micro-RNAs

Epidemiological and experimental observations tend to prove that environment, lifestyle or nutritional challenges influence heart functions together with genetic factors. Furthermore, when occurring during sensitive windows of heart development, these environmental challenges can induce an 'altered programming' of heart development and shape the future heart disease risk. In the etiology of heart diseases driven by environmental challenges, epigenetics has been highlighted as an underlying mechanism, constituting a bridge between environment and heart health. In particular, micro-RNAs which are involved in each step of heart development and functions seem to play a crucial role in the unfavorable programming of heart diseases. This review describes the latest advances in micro-RNA research in heart diseases driven by early exposure to challenges and discusses the use of micro-RNAs as potential targets in the reversal of the pathophysiology.

Functional Role of Non-Coding RNAs during Epithelial-To-Mesenchymal Transition

Epithelial-to-mesenchymal transition (EMT) is a key biological process involved in a multitude of developmental and pathological events. It is characterized by the progressive loss of cell-to-cell contacts and actin cytoskeletal rearrangements, leading to filopodia formation and the progressive up-regulation of a mesenchymal gene expression pattern enabling cell migration. Epithelial-to-mesenchymal transition is already observed in early embryonic stages such as gastrulation, when the epiblast undergoes an EMT process and therefore leads to the formation of the third embryonic layer, the mesoderm. Epithelial-to-mesenchymal transition is pivotal in multiple embryonic processes, such as for example during cardiovascular system development, as valve primordia are formed and the cardiac jelly is progressively invaded by endocardium-derived mesenchyme or as the external cardiac cell layer is established, i.e., the epicardium and cells detached migrate into the embryonic myocardial to form the cardiac fibrous skeleton and the coronary vasculature. Strikingly, the most important biological event in which EMT is pivotal is cancer development and metastasis. Over the last years, understanding of the transcriptional regulatory networks involved in EMT has greatly advanced. Several transcriptional factors such as Snail, Slug, Twist, Zeb1 and Zeb2 have been reported to play fundamental roles in EMT, leading in most cases to transcriptional repression of cell⁻cell interacting proteins such as ZO-1 and cadherins and activation of cytoskeletal markers such as vimentin. In recent years, a fundamental role for non-coding RNAs, particularly microRNAs and more recently long non-coding RNAs, has been identified in normal tissue development and homeostasis as well as in several oncogenic processes. In this study, we will provide a state-of-the-art review of the functional roles of non-coding RNAs, particularly microRNAs, in epithelial-to-mesenchymal transition in both developmental and pathological EMT.

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

Endothelial cells respond to different levels of fluid shear stress through adaptations of their mechanosensitivity. Currently, we lack a good understanding of how this contributes to sculpting of the cardiovascular system. Cerebral cavernous malformation (CCM) is an inherited vascular disease that occurs when a second somatic mutation causes a loss of CCM1/KRIT1, CCM2, or CCM3 proteins. Here, we demonstrate that zebrafish Krit1 regulates the formation of cardiac valves. Expression of heg1, which encodes a binding partner of Krit1, is positively regulated by blood-flow. In turn, Heg1 stabilizes levels of Krit1 protein, and both Heg1 and Krit1 dampen expression levels of klf2a, a major mechanosensitive gene. Conversely, loss of Krit1 results in increased expression of klf2a and notch1b throughout the endocardium and prevents cardiac valve leaflet formation. Hence, the correct balance of blood-flow-dependent induction and Krit1 protein-mediated repression of klf2a and notch1b ultimately shapes cardiac valve leaflet morphology.

Engagement of circular RNA HECW2 in the nonautophagic role of ATG5 implicated in the endothelial-mesenchymal transition

Endothelial-mesenchymal transition (EndoMT) is associated with damage to blood-brain barrier (BBB) integrity. Circular RNAs (circRNAs) are highly expressed in the brain and are involved in brain diseases; however, whether circRNAs regulate the EndoMT in the brain remains unknown. Our study demonstrated that circHECW2 regulated the EndoMT by directly binding to MIR30D, a significantly downregulated miRNA from miRNA profiling, which subsequently caused an increased expression of ATG5. These findings shed new light on the understanding of the noncanonical role of ATG5 in the EndoMT induced by methamphetamine (Meth) or lipopolysaccharide (LPS). The in vivo relevance was confirmed as microinjection of circHecw2 siRNA lentivirus into the mouse hippocampus suppressed the EndoMT induced by LPS. These findings provide novel insights regarding the contribution of circHECW2 to the nonautophagic role of ATG5 in the EndoMT process in the context of drug abuse and the broad range of neuroinflammatory disorders.

Circular RNA DLGAP4 Ameliorates Ischemic Stroke Outcomes by Targeting miR-143 to Regulate Endothelial-Mesenchymal Transition Associated with Blood-Brain Barrier Integrity

Circular RNAs (circRNAs) are highly expressed in the CNS and regulate physiological and pathophysiological processes. However, the potential role of circRNAs in stroke remains largely unknown. Here, we show that the circRNA DLGAP4 (circDLGAP4) functions as an endogenous microRNA-143 (miR-143) sponge to inhibit miR-143 activity, resulting in the inhibition of homologous to the E6-AP C-terminal domain E3 ubiquitin protein ligase 1 expression. circDLGAP4 levels were significantly decreased in the plasma of acute ischemic stroke patients (13 females and 13 males) and in a mouse stroke model. Upregulation of circDLGAP4 expression significantly attenuated neurological deficits and decreased infarct areas and blood-brain barrier damage in the transient middle cerebral artery occlusion mouse stroke model. Endothelial-mesenchymal transition contributes to blood-brain barrier disruption and circDLGAP4 overexpression significantly inhibited endothelial-mesenchymal transition by regulating tight junction protein and mesenchymal cell marker expression. Together, the results of our study are illustrative of the involvement of circDLGAP4 and its coupling mechanism in cerebral ischemia, providing translational evidence that circDLGAP4 serves as a novel therapeutic target for acute cerebrovascular protection.SIGNIFICANCE STATEMENT Circular RNAs (circRNAs) are involved in the regulation of physiological and pathophysiological processes. However, whether circRNAs are involved in ischemic injury, particularly cerebrovascular disorders, remains largely unknown. Here, we demonstrate a critical role for circular RNA DLGAP4 (circDLGAP4), a novel circular RNA originally identified as a sponge for microRNA-143 (miR-143), in ischemic stroke outcomes. Overexpression of circDLGAP4 significantly attenuated neurological deficits and decreased infarct areas and blood-brain barrier damage in the transient middle cerebral artery occlusion mouse stroke model. To our knowledge, this is the first report describing the efficacy of circRNA injection in an ischemic stroke model. Our investigation suggests that circDLGAP4 may serve as a novel therapeutic target for acute ischemic injury.

MicroRNA-574 suppresses oocyte maturation via targeting hyaluronan synthase 2 in porcine cumulus cells

MicroRNAs (miRNAs) have been established as important regulators of gene expression in the mammalian ovary. A previous screen of small RNA in the porcine ovary identified the downregulation of miR-574 during oocyte maturation, although its role during this process was not established. Here, we found that miR-574 directly targets the transcript for hyaluronan synthase 2 protein (HAS2), a key enzyme in the production of extracellular matrix by the surrounding cumulus cells. Inhibiting this miRNA during in vitro maturation (IVM) increased HAS2 levels along with several markers of oocyte quality. Furthermore, inhibiting miR-574 increased oocyte meiotic progression. We then stably overexpressed miR-574 using a lentiviral vector to transduce cumulus cells during IVM. This gain-of-function approach resulted in a 50% decrease in HAS2 expression and nearly 20% reduction in oocyte progression through meiosis. To confirm the specific targeting of HAS2 by miR-574, we constructed several luciferase vectors harboring the HAS2 3'-untranslated region. Cotransfection of the reporter and miR-574 attenuated luciferase activity. After mutating the putative miR-574 binding site, however, this effect was abolished and luciferase activity remained high. Our results show that the direct targeting of HAS2 by miR-574 negatively impacts oocyte quality during IVM and that inhibiting miR-574 derepresses HAS2 expression and subsequently improves oocyte maturation. Taken together, we help to elucidate a mechanism of posttranscriptional regulation by miRNA in the mammalian ovary.

Dysregulation of hyaluronan homeostasis during aortic valve disease

Aortic valve disease (AVD) is one of the leading causes of cardiovascular mortality. Abnormal expression of hyaluronan (HA) and its synthesizing/degrading enzymes have been observed during latent AVD however, the mechanism of impaired HA homeostasis prior to and after the onset of AVD remains unexplored. Transforming growth factor beta (TGFβ) pathway defects and biomechanical dysfunction are hallmarks of AVD, however their association with altered HA regulation is understudied. Expression of HA homeostatic markers was evaluated in diseased human aortic valves and TGFβ1-cultured porcine aortic valve tissues using histology, immunohistochemistry and Western blotting. Further, porcine valve interstitial cell cultures were stretched (using Flexcell) and simultaneously treated with exogenous TGFβ1±inhibitors for activated Smad2/3 (SB431542) and ERK1/2 (U0126) pathways, and differential HA regulation was assessed using qRT-PCR. Pathological heavy chain HA together with abnormal regional expression of the enzymes HAS2, HYAL1, KIAA1199, TSG6 and IαI was demonstrated in calcified valve tissues identifying the collapse of HA homeostatic machinery during human AVD. Heightened TSG6 activity likely preceded the end-stage of disease, with the existence of a transitional, pre-calcific phase characterized by HA dysregulation. TGFβ1 elicited a fibrotic remodeling response in porcine aortic valves similar to human disease pathology, with increased collagen and HYAL to HAS ratio, and site-specific abnormalities in the expression of CD44 and RHAMM receptors. Further in these porcine valves, expression of HAS2 and HYAL1 was found to be differentially regulated by the Smad2/3 and ERK1/2 pathways, and CD44 expression was highly responsive to biomechanical strain. Leveraging the regulatory pathways that control both HA maintenance in normal valves and early postnatal dysregulation of HA homeostasis during disease may identify new mechanistic insight into AVD pathogenesis.

Regulation of TGF-β-mediated endothelial-mesenchymal transition by microRNA-27

Multiple microRNAs (miRNAs) regulate epithelial-mesenchymal transition and endothelial-mesenchymal transition (EndMT). Here we report that microRNA-27b (miR-27b) positively regulates transforming growth factor-β (TGF-β)-induced EndMT of MS-1 mouse pancreatic microvascular endothelial cells. TGF-β induced miR-23b/24-1/27b expression, and inhibition of miR-27 suppressed TGF-β-mediated induction of mesenchymal genes. Genome-wide miRNA target analysis revealed that miR-27 targets Elk1, which acts as a competitive inhibitor of myocardin-related transcription factor-serum response factor signalling and as a myogenic repressor. miR-27b was also found to regulate several semaphorin receptors including Neuropilin 2, Plexin A2 and Plexin D1. These results suggest important roles of miR-27 in TGF-β-driven EndMT.

Exosomes: A Rising Star in Falling Hearts

Although exosomes were previously recognized as a mechanism for discharging useless cellular components, growing evidence has elucidated their roles in conveying information between cells. They contribute to cell-cell communication by carrying nucleic acids, proteins and lipids that can, in turn, regulate behavior of the target cells. Recent research suggested that exosomes extensively participate in progression of diverse cardiovascular diseases (CVDs), such as myocardial infarction, cardiomyopathy, pulmonary arterial hypertension and others. Here, we summarize effects of exosome-derived molecules (mainly microRNAs and proteins) on cardiac function, to examine their potential applications as biomarkers or therapeutics in CVDs.

Tmem2 Regulates Embryonic Vegf Signaling by Controlling Hyaluronic Acid Turnover

Angiogenesis is responsible for tissue vascularization during development, as well as in pathological contexts, including cancer and ischemia. Vascular endothelial growth factors (VEGFs) regulate angiogenesis by acting through VEGF receptors to induce endothelial cell signaling. VEGF is processed in the extracellular matrix (ECM), but the complexity of ECM control of VEGF signaling and angiogenesis remains far from understood. In a forward genetic screen, we identified angiogenesis defects in tmem2 zebrafish mutants that lack both arterial and venous Vegf/Vegfr/Erk signaling. Strikingly, tmem2 mutants display increased hyaluronic acid (HA) surrounding developing vessels. Angiogenesis in tmem2 mutants was rescued, or restored after failed sprouting, by degrading this increased HA. Furthermore, oligomerized HA or overexpression of Vegfc rescued angiogenesis in tmem2 mutants. Based on these data, and the known structure of Tmem2, we find that Tmem2 regulates HA turnover to promote normal Vegf signaling during developmental angiogenesis.

MicroRNA-23a regulates epithelial-to-mesenchymal transition in endometrial endometrioid adenocarcinoma by targeting SMAD3

BACKGROUND

To investigate the role of total cellular microRNA (miRNA) in regulating epithelial-to-mesenchymal transition (EMT) during human endometrial endometrioid adenocarcinoma (EEC).

METHODS

A miRCURY LNA microRNA array was used to evaluate the miRNA profiles of human EEC tissues and corresponding nontumorous endometriums. An in vitro model of TGF-β induced EMT in HEC-1-A cells was used to investigate the role of miRNAs in the EEC during EMT. The expression of SMAD3, SMAD5, and a panel of EMT markers was detected by Western blot and quantitative PCR.

RESULTS

The results of miRNA profiling in human EEC tissues and corresponding nontumorous endometriums demonstrated that miR-23a expression was down-regulated. Using bioinformatics, we identified SMAD3 or SMAD5 maybe as a predicted target of miR-23a. The results of luciferase reporter assay showed miR-23a directly targets and down-regulates human SMAD3 protein levels, not SMAD5 protein levels. Furthermore, overexpression of miR-23a in HEC-1-A cells increased E-cadherin expression and decreased the expression of vimentin and alpha smooth muscle actin, markers of mesenchymal cellular phenotype.

CONCLUSIONS

Our data provide firm evidence of a role for miR-23a in the direct regulation of EMT through its targeting of SMAD3. Due to its ability to repress the EMT, miR-23a may be a novel target for EER therapeutic intervention.

miR-23a/b regulates the balance between osteoblast and adipocyte differentiation in bone marrow mesenchymal stem cells

Age-related osteoporosis is associated with the reduced capacity of bone marrow mesenchymal stem cells (BMSCs) to differentiate into osteoblasts instead of adipocytes. However, the molecular mechanisms that decide the fate of BMSCs remain unclear. In our study, microRNA-23a, and microRNA-23b (miR-23a/b) were found to be markedly downregulated in BMSCs of aged mice and humans. The overexpression of miR-23a/b in BMSCs promoted osteogenic differentiation, whereas the inhibition of miR-23a/b increased adipogenic differentiation. Transmembrane protein 64 (Tmem64), which has expression levels inversely related to those of miR-23a/b in aged and young mice, was identified as a major target of miR-23a/b during BMSC differentiation. In conclusion, our study suggests that miR-23a/b has a critical role in the regulation of mesenchymal lineage differentiation through the suppression of Tmem64.

The force within: endocardial development, mechanotransduction and signalling during cardiac morphogenesis

Endocardial cells are cardiac endothelial cells that line the interior of the heart tube. Historically, their contribution to cardiac development has mainly been considered from a morphological perspective. However, recent studies have begun to define novel instructive roles of the endocardium, as a sensor and signal transducer of biophysical forces induced by blood flow, and as an angiocrine signalling centre that is involved in myocardial cellular morphogenesis, regeneration and reprogramming. In this Review, we discuss how the endocardium develops, how endocardial-myocardial interactions influence the developing embryonic heart, and how the dysregulation of blood flow-responsive endocardial signalling can result in pathophysiological changes.

klf2a couples mechanotransduction and zebrafish valve morphogenesis through fibronectin synthesis

The heartbeat and blood flow signal to endocardial cell progenitors through mechanosensitive proteins that modulate the genetic program controlling heart valve morphogenesis. To date, the mechanism by which mechanical forces coordinate tissue morphogenesis is poorly understood. Here we use high-resolution imaging to uncover the coordinated cell behaviours leading to heart valve formation. We find that heart valves originate from progenitors located in the ventricle and atrium that generate the valve leaflets through a coordinated set of endocardial tissue movements. Gene profiling analyses and live imaging reveal that this reorganization is dependent on extracellular matrix proteins, in particular on the expression of fibronectin1b. We show that blood flow and klf2a, a major endocardial flow-responsive gene, control these cell behaviours and fibronectin1b synthesis. Our results uncover a unique multicellular layering process leading to leaflet formation and demonstrate that endocardial mechanotransduction and valve morphogenesis are coupled via cellular rearrangements mediated by fibronectin synthesis.

Functions of miRNAs during Mammalian Heart Development

MicroRNAs (miRNAs) play essential roles during mammalian heart development and have emerged as attractive therapeutic targets for cardiovascular diseases. The mammalian embryonic heart is mainly derived from four major cell types during development. These include cardiomyocytes, endocardial cells, epicardial cells, and neural crest cells. Recent data have identified various miRNAs as critical regulators of the proper differentiation, proliferation, and survival of these cell types. In this review, we briefly introduce the contemporary understanding of mammalian cardiac development. We also focus on recent developments in the field of cardiac miRNAs and their functions during the development of different cell types.

Strategies for analyzing cardiac phenotypes in the zebrafish embryo

The molecular mechanisms underlying cardiogenesis are of critical biomedical importance due to the high prevalence of cardiac birth defects. Over the past two decades, the zebrafish has served as a powerful model organism for investigating heart development, facilitated by its powerful combination of optical access to the embryonic heart and plentiful opportunities for genetic analysis. Work in zebrafish has identified numerous factors that are required for various aspects of heart formation, including the specification and differentiation of cardiac progenitor cells, the morphogenesis of the heart tube, cardiac chambers, and atrioventricular canal, and the establishment of proper cardiac function. However, our current roster of regulators of cardiogenesis is by no means complete. It is therefore valuable for ongoing studies to continue pursuit of additional genes and pathways that control the size, shape, and function of the zebrafish heart. An extensive arsenal of techniques is available to distinguish whether particular mutations, morpholinos, or small molecules disrupt specific processes during heart development. In this chapter, we provide a guide to the experimental strategies that are especially effective for the characterization of cardiac phenotypes in the zebrafish embryo.