The multifaceted role of Notch in cardiac development and disease

Molecular basis of functional myogenic specification of Bona Fide multipotent adult cardiac stem cells

Ischemic Heart Disease (IHD) remains the developed world's number one killer. The improved survival from Acute Myocardial Infarction (AMI) and the progressive aging of western population brought to an increased incidence of chronic Heart Failure (HF), which assumed epidemic proportions nowadays. Except for heart transplantation, all treatments for HF should be considered palliative because none of the current therapies can reverse myocardial degeneration responsible for HF syndrome. To stop the HF epidemic will ultimately require protocols to reduce the progressive cardiomyocyte (CM) loss and to foster their regeneration. It is now generally accepted that mammalian CMs renew throughout life. However, this endogenous regenerative reservoir is insufficient to repair the extensive damage produced by AMI/IHD while the source and degree of CM turnover remains strongly disputed. Independent groups have convincingly shown that the adult myocardium harbors bona-fide tissue specific cardiac stem cells (CSCs). Unfortunately, recent reports have challenged the identity and the endogenous myogenic capacity of the c-kit expressing CSCs. This has hampered progress and unless this conflict is settled, clinical tests of repair/regenerative protocols are unlikely to provide convincing answers about their clinical potential. Here we review recent data that have eventually clarified the specific phenotypic identity of true multipotent CSCs. These cells when coaxed by embryonic cardiac morphogens undergo a precisely orchestrated myogenic commitment process robustly generating bona-fide functional cardiomyocytes. These data should set the path for the revival of further investigation untangling the regenerative biology of adult CSCs to harness their potential for HF prevention and treatment.

Endocardial Hippo signaling regulates myocardial growth and cardiogenesis

The Hippo signaling pathway has been implicated in control of cell and organ size, proliferation, and endothelial-mesenchymal transformation. This pathway impacts upon two partially redundant transcription cofactors, Yap and Taz, that interact with other factors, including members of the Tead family, to affect expression of downstream genes. Yap and Taz have been shown to regulate, in a cell-autonomous manner, myocardial proliferation, myocardial hypertrophy, regenerative potential, and overall size of the heart. Here, we show that Yap and Taz also play an instructive, non-cell-autonomous role in the endocardium of the developing heart to regulate myocardial growth through release of the paracrine factor, neuregulin. Without endocardial Yap and Taz, myocardial growth is impaired causing early post-natal lethality. Thus, the Hippo signaling pathway regulates cell size via both cell-autonomous and non-cell-autonomous mechanisms. Furthermore, these data suggest that Hippo may regulate organ size via a sensing and paracrine function in endothelial cells.

Beyond cardiomyocyte loss: Role of Notch in cardiac aging

The knowledge of the cellular events occurring in the aging heart has dramatically expanded in the last decade and is expected to further grow in years to come. It is now clear that impaired function and loss of cardiomyocytes are major features of cardiac aging, but other events are likewise important. In particular, accumulating experimental evidence highlights the importance of fibroblast and cardiac progenitor cell (CPC) dysfunction. The Notch pathway regulates cardiomyocyte, fibroblast, and CPC activity and, thus, may be critically involved in heart disease associated with advanced age, especially heart failure. In a translational perspective, thorough investigation of the Notch system in the aging myocardium may lead to the identification of molecular targets for novel therapies for age-related cardiac disease.

Combining cell and gene therapy to advance cardiac regeneration

INTRODUCTION

The characterization of multipotent endogenous cardiac stem cells (eCSCs) and the breakthroughs of somatic cell reprogramming to boost cardiomyocyte replacement have fostered the prospect of achieving functional heart repair/regeneration.

AREAS COVERED

Allogeneic CSC therapy through its paracrine stimulation of the endogenous resident reparative/regenerative process produces functional meaningful myocardial regeneration in pre-clinical porcine myocardial infarction models and is currently tested in the first-in-man human trial. The in vivo test of somatic reprogramming and cardioregenerative non-coding RNAs revived the interest in gene therapy for myocardial regeneration. The latter, together with the advent of genome editing, has prompted most recent efforts to produce genetically-modified allogeneic CSCs that secrete cardioregenerative factors to optimize effective myocardial repair.

EXPERT OPINION

The current war against heart failure epidemics in western countries seeks to find effective treatments to set back the failing hearts prolonging human lifespan. Off-the-shelf allogeneic-genetically-modified CSCs producing regenerative agents are a novel and evolving therapy set to be affordable, safe, effective and available at all times for myocardial regeneration to either prevent or treat heart failure.

Glycerophosphodiesterase GDE2/GDPD5 affects pancreas differentiation in zebrafish

Notch signaling plays an essential role in the proliferation, differentiation and cell fate determination of various tissues, including the developing pancreas. One regulator of the Notch pathway is GDE2 (or GDPD5), a transmembrane ecto-phosphodiesterase that cleaves GPI-anchored proteins at the plasma membrane, including a Notch ligand regulator. Here we report that Gdpd5-knockdown in zebrafish embryos leads to developmental defects, particularly, impaired motility and reduced pancreas differentiation, as shown by decreased expression of insulin and other pancreatic markers. Exogenous expression of human GDE2, but not catalytically dead GDE2, similarly leads to developmental defects. Human GDE2 restores insulin expression in Gdpd5a-depleted zebrafish embryos. Importantly, zebrafish Gdpd5 orthologues localize to the plasma membrane where they show catalytic activity against GPI-anchored GPC6. Thus, our data reveal functional conservation between zebrafish Gdpd5 and human GDE2, and suggest that strict regulation of GDE2 expression and catalytic activity is critical for correct embryonic patterning. In particular, our data uncover a role for GDE2 in regulating pancreas differentiation.

MicroRNA-34a modulates the Notch signaling pathway in mice with congenital heart disease and its role in heart development

The objective of the study was to elucidate the mechanism by which microRNA-34a (miR-34a) influences heart development and participates in the pathogenesis of congenital heart disease (CHD) by targeting NOTCH-1 through the Notch signaling pathway. Forty D7 pregnant mice were recruited for the purposes of the study and served as the CHD (n=20, successfully established as CHD model) and normal (n=20) groups. The positive expression of the NOTCH-1 protein was evaluated by means of immunohistochemistry. Embryonic endocardial cells (ECCs) were assigned into the normal, blank, negative control (NC), miR-34a mimics, miR-34a inhibitors, miR-34a inhibitors+siRNA-NOTCH-1, siRNA-NOTCH-1, miR-34a mimics+NOTCH-1 OE and miR-34a mimics+crispr/cas9 (mutant NOTCH-1) groups. The expressions of miR-34a, NOTCH-1, Jagged1, Hes1, Hey2 and Csx in cardiac tissues and ECCs were determined by both RT-qPCR and western blotting methods. MTT assay and flow cytometry were conducted for cell proliferation and apoptosis measurement. A dual luciferase reporter assay was applied to demonstrate that NOTCH-1 was the target gene of miR-34a. In comparison to the normal group, the expressions of miR-34a, Jagged1, Hes1 and Hey2 displayed up-regulated levels, while the expressions of NOTCH-1 and Csx were down-regulated in the CHD group. Compared with the blank and NC groups, the miR-34a mimics and siRNA-NOTCH-1 groups displayed reduced expressions of NOTCH-1 and Csx as well as a decreased proliferation rate, higher miR-34a, Jagged1, Hes1 and Hey2 expressions and an increased rate of apoptosis; while an reverse trend was observed in the miR-34a inhibitors group. The expressions of MiR-34a recorded increased levels in the miR-34a mimics+NOTCH-1 OE and miR-34a mimics+crispr/cas9 (mutant NOTCH-1) groups, however no changes in the expressions of NOTCH-1, Jagged1, Hes1, Hey2, Csx, as well as cell proliferation and apoptosis were observed when compared to the blank and NC groups. The results of our study demonstrated that miR-34a increases the risk of CHD through its downregulation of NOTCH-1 by modulating the Notch signaling pathway.

Relaxin ameliorates high glucose-induced cardiomyocyte hypertrophy and apoptosis via the Notch1 pathway

The present study aimed to investigate the role of relaxin (RLX) on high glucose (HG)-induced cardiomyocyte hypertrophy and apoptosis, as well as the possible molecular mechanism. H9c2 cells were exposed to 33 mmol/l HG with or without RLX (100 nmol/ml). Cell viability, apoptosis, oxidative stress, cell hypertrophy and the levels of Notch1, hairy and enhancer of split 1 (hes1), atrial natriuretic polypeptide (ANP), brain natriuretic peptide (BNP), manganese superoxide dismutase (MnSOD), cytochrome C and caspase-3 were assessed in cardiomyocytes. Compared with the HG group, the viability of H9c2 cells was increased by RLX in a time- and dose-dependent manner, and was accompanied with a significant reduction in apoptosis. Furthermore, RLX significantly suppressed the formation of reactive oxygen species and malondialdehyde, and enhanced the activity of SOD. In addition, the levels of ANP, BNP, cytochrome C and caspase-3 were increased and Notch1, hes1 and MnSOD were inhibited in the HG group compared with those in the normal group. However, the Notch inhibitor DAPT almost abolished the protective effects of RLX. These results suggested that RLX protected cardiomyocytes from HG-induced hypertrophy and apoptosis partly through a Notch1-dependent pathway, which may be associated with reducing oxidative stress.

Essentiality of Regulator of G Protein Signaling 6 and Oxidized Ca2+/Calmodulin-Dependent Protein Kinase II in Notch Signaling and Cardiovascular Development

Background

Congenital heart defects are the most common birth defects worldwide. Although defective Notch signaling is the major cause of mouse embryonic death from cardiovascular defects, how Notch signaling is regulated during embryonic vasculogenesis and heart development is poorly understood.

Methods and Results

Regulator of G protein signaling 6 (RGS6)^−/−/Ca²⁺/calmodulin‐dependent protein kinase II (CaMKII)^VV double mutant mice were developed by crossing RGS6^−/− mice with mice expressing an oxidation‐resistant CaMKIIδ (CaMKII^VV), and the resulting embryonic defects/lethality were investigated using E7.5 to E15.5 embryos. While loss of either RGS6 or oxidized CaMKIIδ does not alter embryogenesis, their combined loss causes defective Notch signaling, severe cardiovascular defects, and embryonic lethality (≈E10.5–11.5). Embryos lacking RGS6 and expressing oxidation‐resistant CaMKIIδ exhibit reduced myocardial wall thickness, abnormal trabeculation, and arterial specification defects. Double mutants show vascular remodeling defects, including reduced neurovascularization, delayed neural tube maturation, and small dorsal aortae. These striking cardiovascular defects were accompanied by placental and yolk sac defects in angiogenesis, hematopoiesis, and vascular remodeling similar to what is seen with defective Notch1 signaling. Double mutant hearts, embryos, and yolk sacs exhibit profound downregulation of Notch1, Jagged 1, and Notch downstream target genes Hey1, Hey2, and Hey1L as well as impaired Notch1 signaling in embryos/hearts.

Conclusions

RGS6 and oxidized CaMKIIδ together function as novel critical upstream modulators of Notch signaling required for normal cardiovascular development and embryo survival. Their combined need indicates that they function in parallel pathways needed for Notch1 signaling in yolk sac, placenta and embryos. Thus, dysregulated embryonic RGS6 expression and oxidative activation of CaMKII may potentially contribute to congenital heart defects.

Notch signaling pathway and gene expression profiles during early in vitro differentiation of liver-derived mesenchymal stromal cells to osteoblasts

Notch signaling is a key signaling pathway for cell proliferation and differentiation. Therefore, we formulated a working hypothesis that Notch signaling can be used to detect early osteoblastic differentiation of mesenchymal stromal cells. Changes in expression and distribution of Notch 1, 2, 3, and Delta1 in the cytoplasm and nuclei of rat liver-derived mesenchymal stromal cells differentiating into osteoblasts were investigated, together with the displacement of intracellular domains (ICDs) of the receptors. In addition, an oligonucleotide microarray was used to determine the expression of genes known to be linked to selected signaling pathways. Statistically significant changes in the number of cells expressing Notch1, Notch2, and Delta1, but not Notch3, and their activated forms were detected within 24 h of culture under osteogenic conditions. Although the number of cells expressing Notch3 remained unchanged, the number of cells with the activated receptor was significantly elevated. The number of cells positive for Notch3 was higher than that for the other Notch receptors even after 48 h of differentiation; however, a smaller fraction of cells contained activated Notch3. Culture mineralization was detected on day 4 of differentiation, and all analyzed receptors were present in the cells at that time, but only Delta1 was activated in twice as many cells than that before differentiation. Thus, the three analyzed receptors and ligand can serve as markers of very early stages of osteogenesis in stromal cells. These early changes in activation of the Notch signaling pathway were correlated with the transcription of several genes linked to osteogenesis, such as Bmps, Mmps, and Egfr, and with the regulation of cell cycle and apoptosis.

A method to quantify mechanobiologic forces during zebrafish cardiac development using 4-D light sheet imaging and computational modeling

Blood flow and mechanical forces in the ventricle are implicated in cardiac development and trabeculation. However, the mechanisms of mechanotransduction remain elusive. This is due in part to the challenges associated with accurately quantifying mechanical forces in the developing heart. We present a novel computational framework to simulate cardiac hemodynamics in developing zebrafish embryos by coupling 4-D light sheet imaging with a stabilized finite element flow solver, and extract time-dependent mechanical stimuli data. We employ deformable image registration methods to segment the motion of the ventricle from high resolution 4-D light sheet image data. This results in a robust and efficient workflow, as segmentation need only be performed at one cardiac phase, while wall position in the other cardiac phases is found by image registration. Ventricular hemodynamics are then quantified by numerically solving the Navier-Stokes equations in the moving wall domain with our validated flow solver. We demonstrate the applicability of the workflow in wild type zebrafish and three treated fish types that disrupt trabeculation: (a) chemical treatment using AG1478, an ErbB2 signaling inhibitor that inhibits proliferation and differentiation of cardiac trabeculation; (b) injection of gata1a morpholino oligomer (gata1aMO) suppressing hematopoiesis and resulting in attenuated trabeculation; (c) weak-atriumm58 mutant (wea) with inhibited atrial contraction leading to a highly undeveloped ventricle and poor cardiac function. Our simulations reveal elevated wall shear stress (WSS) in wild type and AG1478 compared to gata1aMO and wea. High oscillatory shear index (OSI) in the grooves between trabeculae, compared to lower values on the ridges, in the wild type suggest oscillatory forces as a possible regulatory mechanism of cardiac trabeculation development. The framework has broad applicability for future cardiac developmental studies focused on quantitatively investigating the role of hemodynamic forces and mechanotransduction during morphogenesis.

A tissue-specific, Gata6-driven transcriptional program instructs remodeling of the mature arterial tree

Connection of the heart to the systemic circulation is a critical developmental event that requires selective preservation of embryonic vessels (aortic arches). However, why some aortic arches regress while others are incorporated into the mature aortic tree remains unclear. By microdissection and deep sequencing in mouse, we find that neural crest (NC) only differentiates into vascular smooth muscle cells (SMCs) around those aortic arches destined for survival and reorganization, and identify the transcription factor Gata6 as a crucial regulator of this process. Gata6 is expressed in SMCs and its target genes activation control SMC differentiation. Furthermore, Gata6 is sufficient to promote SMCs differentiation in vivo, and drive preservation of aortic arches that ought to regress. These findings identify Gata6-directed differentiation of NC to SMCs as an essential mechanism that specifies the aortic tree, and provide a new framework for how mutations in GATA6 lead to congenital heart disorders in humans.

Notch signaling modulates the electrical behavior of cardiomyocytes

Notch receptor signaling is active during cardiac development and silenced in myocytes after birth. Conversely, outward K⁺ Kv currents progressively appear in postnatal myocytes leading to shortening of the action potential (AP) and acquisition of the mature electrical phenotype. In the present study, we tested the possibility that Notch signaling modulates the electrical behavior of cardiomyocytes by interfering with Kv currents. For this purpose, the effects of Notch receptor activity on electrophysiological properties of myocytes were evaluated using transgenic mice with inducible expression of the Notch1 intracellular domain (NICD), the functional fragment of the activated Notch receptor, and in neonatal myocytes after inhibition of the Notch transduction pathway. By patch clamp, NICD-overexpressing cells presented prolonged AP duration and reduced upstroke amplitude, properties that were coupled with reduced rapidly activating Kv and fast Na⁺ currents, compared with cells obtained from wild-type mice. In cultured neonatal myocytes, inhibition of the proteolitic release of NICD with a γ-secretase antagonist increased transcript levels of the Kv channel-interacting proteins 2 (KChIP2) and enhanced the density of Kv currents. Collectively, these results indicate that Notch signaling represents an important regulator of the electrophysiological behavior of developing and adult myocytes by repressing, at least in part, repolarizing Kv currents. NEW & NOTEWORTHY We investigated the effects of Notch receptor signaling on the electrical properties of cardiomyocytes. Our results indicate that the Notch transduction pathway interferes with outward K⁺ Kv currents, critical determinants of the electrical repolarization of myocytes.

Uncontrolled angiogenic precursor expansion causes coronary artery anomalies in mice lacking Pofut1

Coronary artery anomalies may cause life-threatening cardiac complications; however, developmental mechanisms underpinning coronary artery formation remain ill-defined. Here we identify an angiogenic cell population for coronary artery formation in mice. Regulated by a DLL4/NOTCH1/VEGFA/VEGFR2 signaling axis, these angiogenic cells generate mature coronary arteries. The NOTCH modulator POFUT1 critically regulates this signaling axis. POFUT1 inactivation disrupts signaling events and results in excessive angiogenic cell proliferation and plexus formation, leading to anomalous coronary arteries, myocardial infarction and heart failure. Simultaneous VEGFR2 inactivation fully rescues these defects. These findings show that dysregulated angiogenic precursors link coronary anomalies to ischemic heart disease.Though coronary arteries are crucial for heart function, the mechanisms guiding their formation are largely unknown. Here, Wang et al. identify a unique, endocardially-derived angiogenic precursor cell population for coronary artery formation in mice and show that a DLL4/NOTCH1/VEGFA/VEGFR2 signaling axis is key for coronary artery development.

Automated Segmentation of Light-Sheet Fluorescent Imaging to Characterize Experimental Doxorubicin-Induced Cardiac Injury and Repair

This study sought to develop an automated segmentation approach based on histogram analysis of raw axial images acquired by light-sheet fluorescent imaging (LSFI) to establish rapid reconstruction of the 3-D zebrafish cardiac architecture in response to doxorubicin-induced injury and repair. Input images underwent a 4-step automated image segmentation process consisting of stationary noise removal, histogram equalization, adaptive thresholding, and image fusion followed by 3-D reconstruction. We applied this method to 3-month old zebrafish injected intraperitoneally with doxorubicin followed by LSFI at 3, 30, and 60 days post-injection. We observed an initial decrease in myocardial and endocardial cavity volumes at day 3, followed by ventricular remodeling at day 30, and recovery at day 60 (P < 0.05, n = 7-19). Doxorubicin-injected fish developed ventricular diastolic dysfunction and worsening global cardiac function evidenced by elevated E/A ratios and myocardial performance indexes quantified by pulsed-wave Doppler ultrasound at day 30, followed by normalization at day 60 (P < 0.05, n = 9-20). Treatment with the γ-secretase inhibitor, DAPT, to inhibit cleavage and release of Notch Intracellular Domain (NICD) blocked cardiac architectural regeneration and restoration of ventricular function at day 60 (P < 0.05, n = 6-14). Our approach provides a high-throughput model with translational implications for drug discovery and genetic modifiers of chemotherapy-induced cardiomyopathy.

Transient HES5 Activity Instructs Mesodermal Cells toward a Cardiac Fate

Notch signaling plays a role in specifying a cardiac fate but the downstream effectors remain unknown. In this study we implicate the Notch downstream effector HES5 in cardiogenesis. We show transient Hes5 expression in early mesoderm of gastrulating embryos and demonstrate, by loss and gain-of-function experiments in mouse embryonic stem cells, that HES5 favors cardiac over primitive erythroid fate. Hes5 overexpression promotes upregulation of the cardiac gene Isl1, while the hematopoietic regulator Scl is downregulated. Moreover, whereas a pulse of Hes5 instructs cardiac commitment, sustained expression after lineage specification impairs progression of differentiation to contracting cardiomyocytes. These findings establish a role for HES5 in cardiogenesis and provide insights into the early cardiac molecular network.

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Hes5 is expressed in the nascent mesoderm of gastrulating mouse embryos

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Hes5 knockdown enhances primitive erythropoiesis in mESCs

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A stage-specific pulse of Hes5 instructs preferential cardiac fate in mESCs

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Sustained Hes5 activation impairs differentiation to contracting cardiomyocytes

GARLIC: a bioinformatic toolkit for aetiologically connecting diseases and cell type-specific regulatory maps

Genome-wide association studies (GWAS) have emerged as a powerful tool to uncover the genetic basis of human common diseases, which often show a complex, polygenic and multi-factorial aetiology. These studies have revealed that 70–90% of all single nucleotide polymorphisms (SNPs) associated with common complex diseases do not occur within genes (i.e. they are non-coding), making the discovery of disease-causative genetic variants and the elucidation of the underlying pathological mechanisms far from straightforward. Based on emerging evidences suggesting that disease-associated SNPs are frequently found within cell type-specific regulatory sequences, here we present GARLIC (GWAS-based Prediction Toolkit for Connecting Diseases and Cell Types), a user-friendly, multi-purpose software with an associated database and online viewer that, using global maps of cis-regulatory elements, can aetiologically connect human diseases with relevant cell types. Additionally, GARLIC can be used to retrieve potential disease-causative genetic variants overlapping regulatory sequences of interest. Overall, GARLIC can satisfy several important needs within the field of medical genetics, thus potentially assisting in the ultimate goal of uncovering the elusive and complex genetic basis of common human disorders.

Human fetal heart specific coexpression network involves congenital heart disease/defect candidate genes

Heart development is a complex process requiring dynamic transcriptional regulation. Disturbance of this process will lead to severe developmental defects such as congenital heart disease/defect (CHD). CHD is a group of complex disorder with high genetic heterogeneity, common pathways associated with CHD remains largely unknown. In the manuscript, we focused on the tissue specific genes in human fetal heart samples to explore such pathways. We used the RNA microarray dataset of human fetal tissues from ENCODE project to identify genes with heart tissue specific expression. A transcriptional network was constructed for these genes based on the Pearson correlation coefficients of their expression levels. Function, selective constraints and disease associations of these genes were then examined. Our analysis identified a network consisted of 316 genes with human fetal heart specific expression. The network was highly co-regulated and showed evolutionary conserved tissue expression pattern in tetrapod. Genes in this network are enriched in CHD specific genes and disease mutations. Using the transcriptomic data, we discovered a highly concerted gene network that might reflect a common pathway associated with the etiology of CHD. Such analysis should be helpful for disease associated gene identification in clinical studies.

Inhibition of miR-363 protects cardiomyocytes against hypoxia-induced apoptosis through regulation of Notch signaling

Cardiomyocyte apoptosis contributes to the pathological process of ischemic heart diseases, such as myocardial infarction. Emerging evidence suggests that microRNAs (miRNAs) play critical roles in the pathological process of myocardial infarction by regulating cardiomyocyte apoptosis. Previous studies have reported that miR-363 is an apoptosis-related miRNA. However, whether miR-363 is involved in regulating cardiomyocyte apoptosis remains unclear. This study aimed to investigate the potential role of miR-363 in the regulation of hypoxia-induced cardiomyocyte apoptosis. We found that miR-363 expression was significantly increased in hypoxic cardiomyocytes and that inhibition of miR-363 effectively protected cardiomyocytes against hypoxia-induced apoptosis. Bioinformatics analysis predicted that Notch1 is a potential target gene of miR-363. This finding was validated by dual-luciferase reporter assay, real-time quantitative polymerase chain reaction, and Western blot analysis. miR-363 inhibition significantly promoted the activation of Notch signaling in hypoxic cardiomyocytes. However, knockdown of Notch1 markedly reversed the protective effects induced by miR-363 inhibition. Furthermore, blocking the Notch signaling also significantly abrogated the protective effects of miR-363 inhibition. Overall, these findings suggest that inhibition of miR-363 protects cardiomyocytes against hypoxia-induced apoptosis through promotion of Notch1 expression and activation of Notch signaling. Our study provides a novel understanding of the molecular basis of hypoxia-induced cardiomyocyte apoptosis and suggests a potential therapeutic target for myocardial infarction.

Notch Signaling in Ischemic Damage and Fibrosis: Evidence and Clues from the Heart

Notch signaling is a major intercellular coordination mechanism highly conserved throughout evolution. In vertebrates, Notch signaling is physiologically involved in embryo development, including mesenchymal cell commitment, formation of heart tissues and angiogenesis. In post-natal life, Notch signaling is maintained as a key mechanism of cell–cell communication and its dysregulations have been found in pathological conditions such as ischemic and fibrotic diseases. In the heart, Notch takes part in the protective response to ischemia, being involved in pre- and post-conditioning, reduction of reperfusion-induced oxidative stress and myocardial damage, and cardiomyogenesis. Conceivably, the cardioprotective effects of Notch may depend on neo-angiogenesis, thus blunting lethal myocardial ischemia, as well as on direct stimulation of cardiac cells to increase their resistance to injury. Another post-developmental adaptation of Notch signaling is fibrosis: being involved in the orientation of mesenchymal cell fate, Notch can modulate the differentiation of pro-fibrotic myofibroblasts, e.g., by reducing the effects of the profibrotic cytokine TGF-β. In conclusion, Notch can regulate the interactions between heart muscle and stromal cells and switch cardiac repair from a pro-fibrotic default pathway to a pro-cardiogenic one. These features make Notch signaling a suitable target for new cardiotropic therapies.

Characterization of an Immunogenic Mutation in a Patient with Metastatic Triple-Negative Breast Cancer

Purpose: The administration of autologous tumor-infiltrating lymphocytes (TILs) can mediate durable tumor regressions in patients with melanoma likely based on the recognition of immunogenic somatic mutations expressed by the cancer. There are limited data regarding the immunogenicity of mutations in breast cancer. We sought to identify immunogenic nonsynonymous mutations in a patient with triple-negative breast cancer (TNBC) to identify and isolate mutation-reactive TILs for possible use in adoptive cell transfer.Experimental Design: A TNBC metastasis was resected for TIL generation and whole-exome sequencing. Tandem minigenes or long 25-mer peptides encoding selected mutations were electroporated or pulsed onto autologous antigen-presenting cells, and reactivity of TIL was screened by upregulation of CD137 and IFNγ ELISPOT. The nature of the T-cell response against a unique nonsynonymous mutation was characterized.Results: We identified 72 nonsynonymous mutations from the tumor of a patient with TNBC. CD4⁺ and HLA-DRB1*1501-restricted TILs isolated from this tumor recognized a single mutation in RBPJ (recombination signal binding protein for immunoglobulin kappa J region). Analysis of 16 metastatic sites revealed that the mutation was ubiquitously present in all samples.Conclusions: Breast cancers can express naturally processed and presented unique nonsynonymous mutations that are recognized by a patient's immune system. TILs recognizing these immunogenic mutations can be isolated from a patient's tumor, suggesting that adoptive cell transfer of mutation-reactive TILs could be a viable treatment option for patients with breast cancer. Clin Cancer Res; 23(15); 4347-53. ©2017 AACR.

14-3-3epsilon controls multiple developmental processes in the mouse heart

BACKGROUND

14-3-3ε plays an important role in the maturation of the compact ventricular myocardium by modulating the cardiomyocyte cell cycle via p27kip1 . However, additional cardiac defects are possible given the ubiquitous expression pattern of this protein.

RESULTS

Germ line deletion of 14-3-3ε led to malalignment of both the outflow tract (OFT) and atrioventricular (AV) cushions, with resulting tricuspid stenosis and atresia, mitral valve abnormalities, and perimembranous ventricular septal defects (VSDs). We confirmed myocardial non-compaction and detected a spongy septum with muscular VSDs and blebbing of the epicardium. These defects were associated with abnormal patterning of p27kip1 expression in the subendocardial and possibly the epicardial cell populations. In addition to abnormal pharyngeal arch artery patterning, we found deep endocardial recesses and paucity of intramyocardial coronary vasculature as a result of defective coronary plexus remodeling.

CONCLUSIONS

The malalignment of both endocardial cushions provides a new explanation for tricuspid and mitral valve defects, while myocardial non-compaction provides the basis for the abnormal coronary vasculature patterning. These abnormalities might arise from p27kip1 dysregulation and a resulting defect in epithelial-to-mesenchymal transformation. These data suggest that 14-3-3ε, in addition to left ventricular non-compaction (LVNC), might be linked to different forms of congenital heart disease (CHD). Developmental Dynamics 245:1107-1123, 2016. © 2016 Wiley Periodicals, Inc.

Family Based Whole Exome Sequencing Reveals the Multifaceted Role of Notch Signaling in Congenital Heart Disease

Left-ventricular outflow tract obstructions (LVOTO) encompass a wide spectrum of phenotypically heterogeneous heart malformations which frequently cluster in families. We performed family based whole-exome and targeted re-sequencing on 182 individuals from 51 families with multiple affected members. Central to our approach is the family unit which serves as a reference to identify causal genotype-phenotype correlations. Screening a multitude of 10 overlapping phenotypes revealed disease associated and co-segregating variants in 12 families. These rare or novel protein altering mutations cluster predominantly in genes (NOTCH1, ARHGAP31, MAML1, SMARCA4, JARID2, JAG1) along the Notch signaling cascade. This is in line with a significant enrichment (Wilcoxon, p< 0.05) of variants with a higher pathogenicity in the Notch signaling pathway in patients compared to controls. The significant enrichment of novel protein truncating and missense mutations in NOTCH1 highlights the allelic and phenotypic heterogeneity in our pediatric cohort. We identified novel co-segregating pathogenic mutations in NOTCH1 associated with left and right-sided cardiac malformations in three independent families with a total of 15 affected individuals. In summary, our results suggest that a small but highly pathogenic fraction of family specific mutations along the Notch cascade are a common cause of LVOTO.

Left-ventricular outflow tract obstructions comprise a group of developmental heart disorders that are genetically and phenotypically heterogeneous, with no single gene accounting for the majority of cases. In order to identify mutations contributing to disease, we selected patients from 51 families with a history of congenital cardiac malformations. We interrogated the entire coding sequences of 106 patients and identified a small but highly pathogenic fraction of mutations that are likely to contribute to disease in 12 families (23.5%). Furthermore, we present a strategy for identifying candidate mutations based on familial segregation in a genetically heterogeneous disorder.

Embryonic Ethanol Exposure Dysregulates BMP and Notch Signaling, Leading to Persistent Atrio-Ventricular Valve Defects in Zebrafish

Fetal alcohol spectrum disorder (FASD), birth defects associated with ethanol exposure in utero, includes a wide spectrum of congenital heart defects (CHDs), the most prevalent of which are septal and conotruncal defects. Zebrafish FASD model was used to dissect the mechanisms underlying FASD-associated CHDs. Embryonic ethanol exposure (3–24 hours post fertilization) led to defects in atrio-ventricular (AV) valvulogenesis beginning around 37 hpf, a morphogenetic event that arises long after ethanol withdrawal. Valve leaflets of the control embryos comprised two layers of cells confined at the compact atrio-ventricular canal (AVC). Ethanol treated embryos had extended AVC and valve forming cells were found either as rows of cells spanning the AVC or as unorganized clusters near the AV boundary. Ethanol exposure reduced valve precursors at the AVC, but some ventricular cells in ethanol treated embryos exhibited few characteristics of valve precursors. Late staged larvae and juvenile fish exposed to ethanol during embryonic development had faulty AV valves. Examination of AVC morphogenesis regulatory networks revealed that early ethanol exposure disrupted the Bmp signaling gradient in the heart during valve formation. Bmp signaling was prominent at the AVC in controls, but ethanol-exposed embryos displayed active Bmp signaling throughout the ventricle. Ethanol exposure also led to mislocalization of Notch signaling cells in endocardium during AV valve formation. Normally, highly active Notch signaling cells were organized at the AVC. In ethanol-exposed embryos, highly active Notch signaling cells were dispersed throughout the ventricle. At later stages, ethanol-exposed embryos exhibited reduced Wnt/β-catenin activity at the AVC. We conclude that early embryonic ethanol exposure alters Bmp, Notch and other signaling activities during AVC differentiation leading to faulty valve morphogenesis and valve defects persist in juvenile fish.

Pulling on my heartstrings: mechanotransduction in cardiac development and function

PURPOSE OF REVIEW

Endothelial cells line the surface of the cardiovascular system and display a large degree of heterogeneity due to developmental origin and location. Despite this heterogeneity, all endothelial cells are exposed to wall shear stress (WSS) imparted by the frictional force of flowing blood, which plays an important role in determining the endothelial cell phenotype. Although the effects of WSS have been greatly studied in vascular endothelial cells, less is known about the role of WSS in regulating cardiac function and cardiac endothelial cells.

RECENT FINDINGS

Recent advances in genetic and imaging technologies have enabled a more thorough investigation of cardiac hemodynamics. Using developmental models, shear stress sensing by endocardial endothelial cells has been shown to play an integral role in proper cardiac development including morphogenesis and formation of the conduction system. In the adult, less is known about hemodynamics and endocardial endothelial cells, but a clear role for WSS in the development of coronary and valvular disease is increasingly appreciated.

SUMMARY

Future research will further elucidate a role for WSS in the developing and adult heart, and understanding this dynamic relationship may represent a potential therapeutic target for the treatment of cardiomyopathies.

Specification and function of hemogenic endothelium during embryogenesis

Hemogenic endothelium is a specialized subset of developing vascular endothelium that acquires hematopoietic potential and can give rise to multilineage hematopoietic stem and progenitor cells during a narrow developmental window in tissues such as the extraembryonic yolk sac and embryonic aorta-gonad-mesonephros. Herein, we review current knowledge about the historical and developmental origins of hemogenic endothelium, the molecular events that govern hemogenic specification of vascular endothelial cells, the generation of multilineage hematopoietic stem and progenitor cells from hemogenic endothelium, and the potential for translational applications of knowledge gained from further study of these processes.

Mice Lacking Platelet-Derived Growth Factor D Display a Mild Vascular Phenotype

Platelet-derived growth factor D (PDGF-D) is the most recently discovered member of the PDGF family. PDGF-D signals through PDGF receptor β, but its biological role remains largely unknown. In contrast to other members of the PDGF family of growth factors, which have been extensively investigated using different knockout approaches in mice, PDGF-D has until now not been characterized by gene inactivation in mice. Here, we present the phenotype of a constitutive Pdgfd knockout mouse model (Pdgfd^-/-), carrying a LacZ reporter used to visualize Pdgfd promoter activity. Inactivation of the Pdgfd gene resulted in a mild phenotype in C57BL/6 mice, and the offspring was viable, fertile and generally in good health. We show that Pdgfd reporter gene activity was consistently localized to vascular structures in both postnatal and adult tissues. The expression was predominantly arterial, often localizing to vascular bifurcations. Endothelial cells appeared to be the dominating source for Pdgfd, but reporter gene activity was occasionally also found in subpopulations of mural cells. Tissue-specific analyses of vascular structures revealed that NG2-expressing pericytes of the cardiac vasculature were disorganized in Pdgfd^-/- mice. Furthermore, Pdgfd^-/- mice also had a slightly elevated blood pressure. In summary, the vascular expression pattern together with morphological changes in NG2-expressing cells, and the increase in blood pressure, support a function for PDGF-D in regulating systemic arterial blood pressure, and suggests a role in maintaining vascular homeostasis.

4-Dimensional light-sheet microscopy to elucidate shear stress modulation of cardiac trabeculation

Hemodynamic shear forces are intimately linked with cardiac development, during which trabeculae form a network of branching outgrowths from the myocardium. Mutations that alter Notch signaling also result in trabeculation defects. Here, we assessed whether shear stress modulates trabeculation to influence contractile function. Specifically, we acquired 4D (3D + time) images with light sheets by selective plane illumination microscopy (SPIM) for rapid scanning and deep axial penetration during zebrafish morphogenesis. Reduction of blood viscosity via gata1a morpholino oligonucleotides (MO) reduced shear stress, resulting in downregulation of Notch signaling and attenuation of trabeculation. Arrest of cardiomyocyte contraction either by troponin T type 2a (tnnt2a) MO or in weak atriumm58 (wea) mutants resulted in reduced shear stress and downregulation of Notch signaling and trabeculation. Integrating 4D SPIM imaging with synchronization algorithm demonstrated that coinjection of neuregulin1 mRNA with gata1 MO rescued trabeculation to restore contractile function in association with upregulation of Notch-related genes. Crossbreeding of Tg(flk:mCherry) fish, which allows visualization of the vascular system with the Tg(tp1:gfp) Notch reporter line, revealed that shear stress-mediated Notch activation localizes to the endocardium. Deleting endocardium via the clochesk4 mutants downregulated Notch signaling, resulting in nontrabeculated ventricle. Subjecting endothelial cells to pulsatile flow in the presence of the ADAM10 inhibitor corroborated shear stress-activated Notch signaling to modulate trabeculation.

Stability and function of adult vasculature is sustained by Akt/Jagged1 signalling axis in endothelium

The signalling pathways operational in quiescent, post-development vasculature remain enigmatic. Here we show that unlike neovascularization, endothelial Akt signalling in established vasculature is crucial not for endothelial cell (EC) survival, but for sustained interactions with pericytes and vascular smooth muscle cells (VSMCs) regulating vascular stability and function. Inducible endothelial-specific Akt1 deletion in adult global Akt2KO mice triggers progressive VSMC apoptosis. In hearts, this causes a loss of arteries and arterioles and, despite a high capillary density, diminished vascular patency and severe cardiac dysfunction. Similarly, endothelial Akt deletion induces retinal VSMC loss and basement membrane deterioration resulting in vascular regression and retinal atrophy. Mechanistically, the Akt/mTOR axis controls endothelial Jagged1 expression and, thereby, Notch signalling regulating VSMC maintenance. Jagged1 peptide treatment of Akt1ΔEC;Akt2KO mice and Jagged1 re-expression in Akt-deficient endothelium restores VSMC coverage. Thus, sustained endothelial Akt1/2 signalling is critical in maintaining vascular stability and homeostasis, thereby preserving tissue and organ function.

The Akt pathway integrates multiple signals, but whether it affects vasculature function is debatable. Here the authors show that Akt pathway shutdown in adult mouse endothelium causes destabilization of vasculature leading to cardiac and retinal dysfunction, due to decreased levels of Jagged1 and impaired Notch signaling.

Systems-based technologies in profiling the stem cell molecular framework for cardioregenerative medicine

Over the last decade, advancements in stem cell biology have yielded a variety of sources for stem cell-based cardiovascular investigation. Stem cell behavior, whether to maintain its stable state of pluripotency or to prime toward the cardiovascular lineage is governed by a set of coordinated interactions between epigenetic, transcriptional, and translational mechanisms. The science of incorporating genes (genomics), RNA (transcriptomics), proteins (proteomics), and metabolites (metabolomics) data in a specific biological sample is known as systems biology. Integrating systems biology in progression with stem cell biologics can contribute to our knowledge of mechanisms that underlie pluripotency maintenance and guarantee fidelity of cardiac lineage specification. This review provides a brief summarization of OMICS-based strategies including transcriptomics, proteomics, and metabolomics used to understand stem cell fate and to outline molecular processes involved in heart development. Additionally, current efforts in cardioregeneration based on the "one-size-fits-all" principle limit the potential of individualized therapy in regenerative medicine. Here, we summarize recent studies that introduced systems biology into cardiovascular clinical outcomes analysis, allowing for predictive assessment for disease recurrence and patient-specific therapeutic response.

Endosomal sorting of Notch receptors through COMMD9-dependent pathways modulates Notch signaling

COMMD protein family member COMMD9 regulates the endosome to plasma membrane trafficking of Notch through a unique COMMD–CCDC22–CCDC93 (CCC) complex.

Notch family members are transmembrane receptors that mediate essential developmental programs. Upon ligand binding, a proteolytic event releases the intracellular domain of Notch, which translocates to the nucleus to regulate gene transcription. In addition, Notch trafficking across the endolysosomal system is critical in its regulation. In this study we report that Notch recycling to the cell surface is dependent on the COMMD–CCDC22–CCDC93 (CCC) complex, a recently identified regulator of endosomal trafficking. Disruption in this system leads to intracellular accumulation of Notch2 and concomitant reduction in Notch signaling. Interestingly, among the 10 copper metabolism MURR1 domain containing (COMMD) family members that can associate with the CCC complex, only COMMD9 and its binding partner, COMMD5, have substantial effects on Notch. Furthermore, Commd9 deletion in mice leads to embryonic lethality and complex cardiovascular alterations that bear hallmarks of Notch deficiency. Altogether, these studies highlight that the CCC complex controls Notch activation by modulating its intracellular trafficking and demonstrate cargo-specific effects for members of the COMMD protein family.

A Three-Way Interaction among Maternal and Fetal Variants Contributing to Congenital Heart Defects

Congenital heart defects (CHDs) develop through a complex interplay between genetic variants, epigenetic modifications, and maternal environmental exposures. Genetic studies of CHDs have commonly tested single genetic variants for association with CHDs. Less attention has been given to complex gene-by-gene and gene-by-environment interactions. In this study, we applied a recently developed likelihood-ratio Mann-Whitney (LRMW) method to detect joint actions among maternal variants, fetal variants, and maternal environmental exposures, allowing for high-order statistical interactions. All subjects are participants from the National Birth Defect Prevention Study, including 623 mother-offspring pairs with CHD-affected pregnancies and 875 mother-offspring pairs with unaffected pregnancies. Each individual has 872 single nucleotide polymorphisms encoding for critical enzymes in the homocysteine, folate, and trans-sulfuration pathways. By using the LRMW method, three variants (fetal rs625879, maternal rs2169650, and maternal rs8177441) were identified with a joint association to CHD risk (nominal P-value = 1.13e-07). These three variants are located within genes BHMT2, GSTP1, and GPX3, respectively. Further examination indicated that maternal SNP rs2169650 may interact with both fetal SNP rs625879 and maternal SNP rs8177441. Our findings suggest that the risk of CHD may be influenced by both the intragenerational interaction within the maternal genome and the intergenerational interaction between maternal and fetal genomes.

Heart Development, Angiogenesis, and Blood-Brain Barrier Function Is Modulated by Adhesion GPCRs

The cardiovascular system in adult organisms forms a network of interconnected endothelial cells, supported by mural cells and displaying a high degree of hierarchy: arteries emerging from the heart ramify into arterioles and then capillaries, which return to the venous systems through venules and veins. The cardiovascular system allows blood circulation, which in turn is essential for hemostasis through gas diffusion, nutrient distribution, and cell trafficking. In this chapter, we have summarized the current knowledge on how adhesion GPCRs (aGPCRs) impact heart development, followed by their role in modulating vascular angiogenesis.

A Switch in Akt Isoforms Is Required for Notch-Induced Snail1 Expression and Protection from Cell Death

Notch activation in aortic endothelial cells (ECs) takes place at embryonic stages during cardiac valve formation and induces endothelial-to-mesenchymal transition (EndMT). Using aortic ECs, we show here that active Notch expression promotes EndMT, resulting in downregulation of vascular endothelial cadherin (VE-cadherin) and upregulation of mesenchymal genes such as those for fibronectin and Snail1/2. In these cells, transforming growth factor β1 exacerbates Notch effects by increasing Snail1 and fibronectin activation. When Notch-downstream pathways were analyzed, we detected an increase in glycogen synthase kinase 3β (GSK-3β) phosphorylation and inactivation that facilitates Snail1 nuclear retention and protein stabilization. However, the total activity of Akt was downregulated. The discrepancy between Akt activity and GSK-3β phosphorylation is explained by a Notch-induced switch in the Akt isoforms, whereby Akt1, the predominant isoform expressed in ECs, is decreased and Akt2 transcription is upregulated. Mechanistically, Akt2 induction requires the stimulation of the β-catenin/TCF4 transcriptional complex, which activates the Akt2 promoter. Active, phosphorylated Akt2 translocates to the nucleus in Notch-expressing cells, resulting in GSK-3β inactivation in this compartment. Akt2, but not Akt1, colocalizes in the nucleus with lamin B in the nuclear envelope. In addition to promoting GSK-3β inactivation, Notch downregulates Forkhead box O1 (FoxO1), another Akt2 nuclear substrate. Moreover, Notch protects ECs from oxidative stress-induced apoptosis through an Akt2- and Snail1-dependent mechanism.

Endocardial Notch Signaling in Cardiac Development and Disease

The Notch signaling pathway is an ancient and highly conserved signaling pathway that controls cell fate specification and tissue patterning in the embryo and in the adult. Region-specific endocardial Notch activity regulates heart morphogenesis through the interaction with multiple myocardial-, epicardial-, and neural crest-derived signals. Mutations in NOTCH signaling elements cause congenital heart disease in humans and mice, demonstrating its essential role in cardiac development. Studies in model systems have provided mechanistic understanding of Notch function in cardiac development, congenital heart disease, and heart regeneration. Notch patterns the embryonic endocardium into prospective territories for valve and chamber formation, and later regulates the signaling processes leading to outflow tract and valve morphogenesis and ventricular trabeculae compaction. Alterations in NOTCH signaling in the endocardium result in congenital structural malformations that can lead to disease in the neonate and adult heart.

VEGF Gene Polymorphisms are Associated with Risk of Tetralogy of Fallot

BACKGROUND

The aim of this study was to investigate associations of 3 common polymorphisms in the VEGF gene, -2578C>A, -634C>G, and 936C>T, with risk of tetralogy of Fallot (TOF) in Chinese Han children.

MATERIAL AND METHODS

From January 2010 to June 2013, a total of 400 pediatric subjects were recruited, including 160 cases with TOF (TOF group) and 240 healthy controls (control group). The genotypes of 3 common VEGF polymorphisms, -2578C>A, -634C>G, and 936C>T, were analyzed by polymerase chain reaction restriction fragment length polymorphism. All data were analyzed with SPSS 18.0 software.

RESULTS

No significant differences were observed in body mass index or sex between TOF patients and controls (both P>0.05), but significant differences in age and family history of TOF were observed between the 2 groups (both P<0.05). The AA genotype in -2578C>A of VEGF was correlated with a significantly increased risk of TOF, and TOF risk in A allele carrier was 1.54-fold higher than that of C allele carrier (OR=1.54, 95%CI=1.14-2.09, P=0.005); the statistical significance was still present after Bonferroni correction (Pc=0.045). GG genotype in -634C>G of VEGF gene was also associated with an increased risk of TOF, and TOF risk in patients with G allele was 1.62-fold higher compared to patients with C allele (OR=1.62, 95%CI=1.19-2.21, P=0.002); the statistical significance was still present after Bonferroni correction (Pc=0.018). Interestingly, T allele in VEGF 936C>T polymorphism is associated with a decreased TOF risk (OR=0.65, 95%CI=0.49-0.87, P=0.003, the statistical significance was still present after Bonferroni correction (Pc=0.027). The result of logistic regression analysis revealed that -2578C>A, -634C>G, and 936C>T genotypes are independently related to the prevalence of TOF (all P<0.05).

CONCLUSIONS

Our results confirmed that VEGF genetic polymorphisms, -2578C>A and -634C>G, may be associated with an increased TOF risk, while 936C>T polymorphism may be associated with decreased TOF risk.

Neural crest cell-autonomous roles of fibronectin in cardiovascular development

The chemical and mechanical properties of extracellular matrices (ECMs) modulate diverse aspects of cellular fates; however, how regional heterogeneity in ECM composition regulates developmental programs is not well understood. We discovered that fibronectin 1 (Fn1) is expressed in strikingly non-uniform patterns during mouse development, suggesting that regionalized synthesis of the ECM plays cell-specific regulatory roles during embryogenesis. To test this hypothesis, we ablated Fn1 in the neural crest (NC), a population of multi-potent progenitors expressing high levels of Fn1. We found that Fn1 synthesized by the NC mediated morphogenesis of the aortic arch artery and differentiation of NC cells into vascular smooth muscle cells (VSMCs) by regulating Notch signaling. We show that NC Fn1 signals in an NC cell-autonomous manner through integrin α5β1 expressed by the NC, leading to activation of Notch and differentiation of VSMCs. Our data demonstrate an essential role of the localized synthesis of Fn1 in cardiovascular development and spatial regulation of Notch signaling.

Jagged1 (JAG1): Structure, expression, and disease associations

Jagged1 (JAG1) is one of the 5 cell surface ligands that functions primarily in the highly conserved Notch signaling pathway. Notch signaling plays a critical role in cellular fate determination and is active throughout development and across many organ systems. The classic JAG1-NOTCH interaction leads to a cascade of proteolytic cleavages resulting in the NOTCH intracellular domain being transported into the nucleus where it functions to activate downstream transcription of target genes. JAG1 mutations have been associated with several disorders including the multi-system dominant disorder Alagille syndrome, and some cases of tetralogy of Fallot (although these may represent variable expressivity of Alagille syndrome). In addition, variations in JAG1 have been found to be associated with multiple types of cancer including breast cancer and adrenocortical carcinoma. Alagille syndrome, which primarily affects the liver, heart, skeleton, eye, face, kidney and vasculature is caused by loss of function mutations in JAG1, demonstrating that haploinsufficiency for JAG1 is disease causing, at least in these tissues. Expression and conditional gene knockout studies of JAG1 (Jag1) have correlated with tissue-specific disease phenotypes and have provided insight into both disease pathogenesis and human development.

MicroRNA-375 overexpression influences P19 cell proliferation, apoptosis and differentiation through the Notch signaling pathway

Our previous study reported that microRNA-375 (miR-375) is significantly upregulated in ventricular septal myocardial tissues from 22‑week‑old fetuses with ventricular septal defect as compared with normal controls. In the present study, the specific effects of miR‑375 on P19 cell differentiation into cardiomyocyte‑like cells were investigated. Stable P19 cell lines overexpressing miR‑375 or containing empty vector were established, which could be efficiently induced into cardiomyocyte‑like cells in the presence of dimethyl sulfoxide in vitro. miR‑375 overexpression was verified using reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). Cell proliferation was determined according to total cell counts; cell cycle distribution and apoptosis levels were examined using flow cytometry. Apoptosis‑related morphological changes were observed using Hoechst staining and fluorescence microscopy. During P19 cell differentiation, the cardiomyogenesis‑related mRNAs (cardiac troponin T, GATA binding protein 4, myocyte‑specific enhancer factor 2C) and mRNAs involved in the Notch signaling pathway (Notch2, Delta‑like 1 and hes family bHLH transcription factor 1) were detected at days 0, 4, 6 and 10. Their differential expression was examined using RT‑qPCR; the apoptosis‑related genes BAX and Bcl‑2 were also detected using this method. The corresponding proteins were evaluated by western blotting. Compared with the control group, miR‑375 overexpression inhibited proliferation but promoted apoptosis in P19 cells, and the associated mRNAs and proteins were decreased during differentiation. miR‑375 has an important role in cardiomyocyte differentiation, and can disrupt this process via the Notch signaling pathway. The present findings contribute to the understanding of the mechanisms of congenital heart disease and facilitate the development of new gene therapies.

Fibronectin signals through integrin α5β1 to regulate cardiovascular development in a cell type-specific manner

Fibronectin (Fn1) is an evolutionarily conserved extracellular matrix glycoprotein essential for embryonic development. Global deletion of Fn1 leads to mid-gestation lethality from cardiovascular defects. However, severe morphogenetic defects that occur early in embryogenesis in these embryos precluded assigning a direct role for Fn1 in cardiovascular development. We noticed that Fn1 is expressed in strikingly non-uniform patterns during mouse embryogenesis, and that its expression is particularly enriched in the pharyngeal region corresponding with the pharyngeal arches 3, 4, and 6. This region bears a special importance for the developing cardiovascular system, and we hypothesized that the localized enrichment of Fn1 in the pharyngeal region may be essential for cardiovascular morphogenesis. To test this hypothesis, we ablated Fn1 using the Isl1(Cre) knock-in strain of mice. Deletion of Fn1 using the Isl1(Cre) strain resulted in defective formation of the 4th pharyngeal arch arteries (PAAs), aberrant development of the cardiac outflow tract (OFT), and ventricular septum defects. To determine the cell types responding to Fn1 signaling during cardiovascular development, we deleted a major Fn1 receptor, integrin α5 using the Isl1(Cre) strain, and observed the same spectrum of abnormalities seen in the Fn1 conditional mutants. Additional conditional mutagenesis studies designed to ablate integrin α5 in distinct cell types within the Isl1(+) tissues and their derivatives, suggested that the expression of integrin α5 in the pharyngeal arch mesoderm, endothelium, surface ectoderm and the neural crest were not required for PAA formation. Our studies suggest that an (as yet unknown) integrin α5-dependent signal extrinsic to the pharyngeal endothelium mediates the formation of the 4th PAAs.

DNA-Methylation Patterns in Trisomy 21 Using Cells from Monozygotic Twins

DNA methylation is essential in mammalian development. We have hypothesized that methylation differences induced by trisomy 21 (T21) contribute to the phenotypic characteristics and heterogeneity in Down syndrome (DS). In order to determine the methylation differences in T21 without interference of the interindividual genomic variation, we have used fetal skin fibroblasts from monozygotic (MZ) twins discordant for T21. We also used skin fibroblasts from MZ twins concordant for T21, normal MZ twins without T21, and unrelated normal and T21 individuals. Reduced Representation Bisulfite Sequencing (RRBS) revealed 35 differentially methylated promoter regions (DMRs) (Absolute methylation differences = 25%, FDR < 0.001) in MZ twins discordant for T21 that have also been observed in comparison between unrelated normal and T21 individuals. The identified DMRs are enriched for genes involved in embryonic organ morphogenesis (FDR = 1.60 e -03) and include genes of the HOXB and HOXD clusters. These DMRs are maintained in iPS cells generated from this twin pair and are correlated with the gene expression changes. We have also observed an increase in DNA methylation level in the T21 methylome compared to the normal euploid methylome. This observation is concordant with the up regulation of DNA methyltransferase enzymes (DNMT3B and DNMT3L) and down regulation of DNA demethylation enzymes (TET2 and TET3) observed in the iPSC of the T21 versus normal twin. Altogether, the results of this study highlight the epigenetic effects of the extra chromosome 21 in T21 on loci outside of this chromosome that are relevant to DS associated phenotypes.

Relaxin inhibits cardiac fibrosis and endothelial-mesenchymal transition via the Notch pathway

BACKGROUND

Relaxin (RLX) can prevent cardiac fibrosis. We aimed to investigate the possible mechanism and signal transduction pathway of RLX inhibiting cardiac fibrosis.

METHODS

Isoproterenol (5 mg·kg(-1)·d(-1)) was used to establish the cardiac fibrosis model in rats, which were administered RLX. The cardiac function, related targets of cardiac fibrosis, and endothelial-mesenchymal transition (EndMT) were measured. Transforming growth factor β (TGF-β) was used to induce EndMT in human umbilical vein endothelial cells, which were pretreated with RLX, 200 ng·mL(-1), then with the inhibitor of Notch. Transwell cell migration was used to evaluate cell migration. CD31 and vimentin content was determined by immunofluorescence staining and Western blot analysis. Notch protein level was examined by Western blot analysis.

RESULTS

RLX improved cardiac function in rats with cardiac fibrosis; it reduced the content of collagen I and III, increased the microvascular density of the myocardium, and suppressed the EndMT in heart tissue. In vitro, RLX decreased the mobility of human umbilical vein endothelial cells induced by TGF-β, increased the expression of endothelial CD31, and decreased vimentin content. Compared to TGF-β and RLX co-culture alone, TGF-β + RLX + Notch inhibitor increased cell mobility and the EndMT, but decreased the levels of Notch-1, HES-1, and Jagged-1 proteins.

CONCLUSION

RLX may inhibit the cardiac fibrosis via EndMT by Notch-mediated signaling.

Hippo signaling is required for Notch-dependent smooth muscle differentiation of neural crest

Notch signaling has well-defined roles in the assembly of arterial walls and in the development of the endothelium and smooth muscle of the vasculature. Hippo signaling regulates cellular growth in many tissues, and contributes to regulation of organ size, in addition to other functions. Here, we show that the Notch and Hippo pathways converge to regulate smooth muscle differentiation of the neural crest, which is crucial for normal development of the aortic arch arteries and cranial vasculature during embryonic development. Neural crest-specific deletion of the Hippo effectors Yap and Taz produces neural crest precursors that migrate normally, but fail to produce vascular smooth muscle, and Notch target genes such as Jagged1 fail to activate normally. We show that Yap is normally recruited to a tissue-specific Jagged1 enhancer by directly interacting with the Notch intracellular domain (NICD). The Yap-NICD complex is recruited to chromatin by the DNA-binding protein Rbp-J in a Tead-independent fashion. Thus, Hippo signaling can modulate Notch signaling outputs, and components of the Hippo and Notch pathways physically interact. Convergence of Hippo and Notch pathways by the mechanisms described here might be relevant for the function of these signaling cascades in many tissues and in diseases such as cancer.

The pathology and pathobiology of bicuspid aortic valve: State of the art and novel research perspectives

Bicuspid aortic valve is the most prevalent cardiac valvular malformation. It is associated with a high rate of long‐term morbidity including development of calcific aortic valve disease, aortic regurgitation and concomitant thoracic aortic aneurysm and dissection. Recently, basic and translational studies have identified some key processes involved in the development of bicuspid aortic valve and its morbidity. The development of aortic valve disease and thoracic aortic aneurysm and dissection is the result of complex interactions between genotypes, environmental risk factors and specific haemodynamic conditions created by bicuspid aortic valve anatomy. Herein, we review the pathobiology of bicuspid aortic valve with a special emphasis on translational aspects of these basic findings. Important but unresolved problems in the pathology of bicuspid aortic valve and thoracic aortic aneurysm and dissection are discussed, along with the molecular processes involved.

Notch1 Mutation Leads to Valvular Calcification Through Enhanced Myofibroblast Mechanotransduction

OBJECTIVE

Calcific aortic valve disease (CAVD) is a significant cardiovascular disorder, and controversy exists as to whether it is primarily a dystrophic or osteogenic process in vivo. In this study, we sought to clarify the mechanism of CAVD by assessing a genetic mutation, Notch1 heterozygosity, which leads to CAVD with 100% penetrance in humans.

APPROACH AND RESULTS

Murine immortalized Notch1(+/-) aortic valve interstitial cells (AVICs) were isolated and expanded in vitro. Molecular signaling of wild-type and Notch1(+/-) AVICs were compared to identify changes in pathways that have been linked to CAVD-transforming growth factor-β1/bone morphogenetic protein, mitogen-activated protein kinase, and phosphoinositide 3-kinase/protein kinase B-and assessed for calcification potential. Additionally, AVIC mechanobiology was studied in a physiologically relevant, dynamic mechanical environment (10% cyclic strain) to investigate differences in responses between the cell types. We found that Notch1(+/-) AVICs resembled a myofibroblast-like phenotype expressing higher amounts of cadherin-11, a known mediator of dystrophic calcification, and decreased Runx2, a known osteogenic marker. We determined that cadherin-11 expression is regulated by Akt activity, and inhibition of Akt phosphorylation significantly reduced cadherin-11 expression. Moreover, in the presence of cyclic strain, Notch1(+/-) AVICs exhibited significantly upregulated phosphorylation of Akt at Ser473 and smooth muscle α-actin expression, indicative of a fully activated myofibroblast. Finally, these Notch1-mediated alterations led to enhanced dystrophic calcific nodule formation.

CONCLUSIONS

This study presents novel insights in our understanding of Notch1-mediated CAVD by demonstrating that the mutation leads to AVICs that are fully activated myofibroblasts, resulting in dystrophic, but not osteogenic, calcification.

Haploinsufficiency of the NOTCH1 Receptor as a Cause of Adams-Oliver Syndrome With Variable Cardiac Anomalies

BACKGROUND

Adams-Oliver syndrome (AOS) is a rare disorder characterized by congenital limb defects and scalp cutis aplasia. In a proportion of cases, notable cardiac involvement is also apparent. Despite recent advances in the understanding of the genetic basis of AOS, for the majority of affected subjects, the underlying molecular defect remains unresolved. This study aimed to identify novel genetic determinants of AOS.

METHODS AND RESULTS

Whole-exome sequencing was performed for 12 probands, each with a clinical diagnosis of AOS. Analyses led to the identification of novel heterozygous truncating NOTCH1 mutations (c.1649dupA and c.6049_6050delTC) in 2 kindreds in which AOS was segregating as an autosomal dominant trait. Screening a cohort of 52 unrelated AOS subjects, we detected 8 additional unique NOTCH1 mutations, including 3 de novo amino acid substitutions, all within the ligand-binding domain. Congenital heart anomalies were noted in 47% (8/17) of NOTCH1-positive probands and affected family members. In leukocyte-derived RNA from subjects harboring NOTCH1 extracellular domain mutations, we observed significant reduction of NOTCH1 expression, suggesting instability and degradation of mutant mRNA transcripts by the cellular machinery. Transient transfection of mutagenized NOTCH1 missense constructs also revealed significant reduction in gene expression. Mutant NOTCH1 expression was associated with downregulation of the Notch target genes HEY1 and HES1, indicating that NOTCH1-related AOS arises through dysregulation of the Notch signaling pathway.

CONCLUSIONS

These findings highlight a key role for NOTCH1 across a range of developmental anomalies that include cardiac defects and implicate NOTCH1 haploinsufficiency as a likely molecular mechanism for this group of disorders.