Franklin H. Epstein Lecture. Cardiac development and implications for heart disease

The 14th International Podocyte Conference 2023: from podocyte biology to glomerular medicine

The 14th International Podocyte Conference took place in Philadelphia, Pennsylvania, USA from May 23 to 26, 2023. It commenced with an early-career researchers' meeting on May 23, providing young scientists with a platform to present and discuss their research findings. Throughout the main conference, 29 speakers across 9 sessions shared their insights on podocyte biology, glomerular medicine, novel technologic advancements, and translational approaches. Additionally, the event featured 3 keynote lectures addressing engineered chimeric antigen receptor T cell- and mRNA-based therapies and the use of biobanks for enhanced disease comprehension. Furthermore, 4 brief oral abstract sessions allowed scientists to present their findings to a broad audience. The program also included a panel discussion addressing the challenges of conducting human research within the American Black community. Remarkably, after a 5-year hiatus from in-person conferences, the 14th International Podocyte Conference successfully convened scientists from around the globe, fostering the presentation and discussion of crucial research findings, as summarized in this review. Furthermore, to ensure continuous and sustainable education, research, translation, and trial medicine related to podocyte and glomerular diseases for the benefit of patients, the International Society of Glomerular Disease was officially launched during the conference.

The Kir2.1E299V mutation increases atrial fibrillation vulnerability while protecting the ventricles against arrhythmias in a mouse model of short QT syndrome type 3

AIMS

Short QT syndrome type 3 (SQTS3) is a rare arrhythmogenic disease caused by gain-of-function mutations in KCNJ2, the gene coding the inward rectifier potassium channel Kir2.1. We used a multidisciplinary approach and investigated arrhythmogenic mechanisms in an in-vivo model of de-novo mutation Kir2.1E299V identified in a patient presenting an extremely abbreviated QT interval and paroxysmal atrial fibrillation.

METHODS AND RESULTS

We used intravenous adeno-associated virus-mediated gene transfer to generate mouse models, and confirmed cardiac-specific expression of Kir2.1WT or Kir2.1E299V. On ECG, the Kir2.1E299V mouse recapitulated the QT interval shortening and the atrial-specific arrhythmia of the patient. The PR interval was also significantly shorter in Kir2.1E299V mice. Patch-clamping showed extremely abbreviated action potentials in both atrial and ventricular Kir2.1E299V cardiomyocytes due to a lack of inward-going rectification and increased IK1 at voltages positive to -80 mV. Relative to Kir2.1WT, atrial Kir2.1E299V cardiomyocytes had a significantly reduced slope conductance at voltages negative to -80 mV. After confirming a higher proportion of heterotetrameric Kir2.x channels containing Kir2.2 subunits in the atria, in-silico 3D simulations predicted an atrial-specific impairment of polyamine block and reduced pore diameter in the Kir2.1E299V-Kir2.2WT channel. In ventricular cardiomyocytes, the mutation increased excitability by shifting INa activation and inactivation in the hyperpolarizing direction, which protected the ventricle against arrhythmia. Moreover, Purkinje myocytes from Kir2.1E299V mice manifested substantially higher INa density than Kir2.1WT, explaining the abbreviation in the PR interval.

CONCLUSION

The first in-vivo mouse model of cardiac-specific SQTS3 recapitulates the electrophysiological phenotype of a patient with the Kir2.1E299V mutation. Kir2.1E299V eliminates rectification in both cardiac chambers but protects against ventricular arrhythmias by increasing excitability in both Purkinje-fiber network and ventricles. Consequently, the predominant arrhythmias are supraventricular likely due to the lack of inward rectification and atrial-specific reduced pore diameter of the Kir2.1E299V-Kir2.2WT heterotetramer.

On the involvement of the second heart field in congenital heart defects

Congenital heart defects (CHD) affect 1 in 100 live births and result from defects in cardiac development. Growth of the early heart tube occurs by the progressive addition of second heart field (SHF) progenitor cells to the cardiac poles. The SHF gives rise to ventricular septal, right ventricular and outflow tract myocardium at the arterial pole, and atrial, including atrial septal myocardium, at the venous pole. SHF deployment creates the template for subsequent cardiac septation and has been implicated in cardiac looping and in orchestrating outflow tract development with neural crest cells. Genetic or environmental perturbation of SHF deployment thus underlies a spectrum of common forms of CHD affecting conotruncal and septal morphogenesis. Here we review the major properties of SHF cells as well as recent insights into the developmental programs that drive normal cardiac progenitor cell addition and the origins of CHD.

Cardiac Development and Animal Models of Congenital Heart Defects

The major events of cardiac development, including early heart formation, chamber morphogenesis and septation, and conduction system and coronary artery development, are briefly reviewed together with a short introduction to the animal species commonly used to study heart development and model congenital heart defects (CHDs).

Epigenetic regulator RNF20 underlies temporal hierarchy of gene expression to regulate postnatal cardiomyocyte polarization

Differentiated cardiomyocytes (CMs) must undergo diverse morphological and functional changes during postnatal development. However, the mechanisms underlying initiation and coordination of these changes remain unclear. Here, we delineate an integrated, time-ordered transcriptional network that begins with expression of genes for cell-cell connections and leads to a sequence of structural, cell-cycle, functional, and metabolic transitions in mouse postnatal hearts. Depletion of histone H2B ubiquitin ligase RNF20 disrupts this gene network and impairs CM polarization. Subsequently, assay for transposase-accessible chromatin using sequencing (ATAC-seq) analysis confirmed that RNF20 contributes to chromatin accessibility in this context. As such, RNF20 is likely to facilitate binding of transcription factors at the promoters of genes involved in cell-cell connections and actin organization, which are crucial for CM polarization and functional integration. These results suggest that CM polarization is one of the earliest events during postnatal heart development and provide insights into how RNF20 regulates CM polarity and the postnatal gene program.

Right ventricular systolic function and associated anatomic risk factors in fetuses with transposition of the great arteries: Evaluation by velocity vector imaging

Objectives

The aim of this study was to evaluate right ventricular (RV) systolic function in fetuses with transposition of the great arteries (TGA) using velocity vector imaging (VVI) and to investigate the impact of different factors on RV systolic function in TGA fetuses.

Methods

This was a retrospective cross-sectional study of fetuses referred to our tertiary center between 2015 and 2019. Maternal and fetal baseline characteristics and conventional echocardiographic and myocardial deformation indices were collected in fetuses with TGA at 20-28 weeks' gestation, which were compared with normal fetuses with comparable gestational age (GA). RV deformational parameters including global and regional longitudinal peak systolic strain, strain rate, and velocity were measured using off-line speckle tracking analysis. The univariate and multivariate linear regression analyses were established to evaluate the independent risk factors for RV global longitudinal systolic strain (RVGLSs) and strain rate (RVGLSRs).

Results

In total, 78 fetuses with TGA [including 49 fetuses with complete transposition of the great arteries (d-TGA) and 29 fetuses with Taussig-Bing anomaly (TBA)] and 49 normal fetuses were included. Compared with normal controls, global and most regional RV longitudinal systolic peak velocity, strain, and strain rate were lower in d-TGA and TBA fetuses (P < 0.05). Compared with normal controls, global and most regional RV longitudinal systolic strain was lower in d-TGA fetuses without pulmonary stenosis (PS) and ventricular septal defect (VSD), while RVGLSs and RVGLSRs were lower in TBA fetuses without PS. The VSD was an independent determinant of RVGLSRs (P = 0.024) in the d-TGA group. Additionally, PS was an independent determinant of RVGLSs and RVGLSRs (P = 0.012, P = 0.027) in the TBA group.

Conclusion

Early impairment of RV systolic function has already occurred in TGA fetuses during the 2nd trimester of pregnancy. PS, VSD, and foramen ovale (FO) were independent risk factors for decreased RV function.

The second heart field: the first 20 years

In 2001, three independent groups reported the identification of a novel cluster of progenitor cells that contribute to heart development in mouse and chicken embryos. This population of progenitor cells was designated as the second heart field (SHF), and a new research direction in heart development was launched. Twenty years have since passed and a comprehensive understanding of the SHF has been achieved. This review provides retrospective insights in to the contribution, the signaling regulatory networks and the epithelial properties of the SHF. It also includes the spatiotemporal characteristics of SHF development and interactions between the SHF and other types of cells during heart development. Although considerable efforts will be required to investigate the cellular heterogeneity of the SHF, together with its intricate regulatory networks and undefined mechanisms, it is expected that the burgeoning new technology of single-cell sequencing and precise lineage tracing will advance the comprehension of SHF function and its molecular signals. The advances in SHF research will translate to clinical applications and to the treatment of congenital heart diseases, especially conotruncal defects, as well as to regenerative medicine.

Morphologic Markers of Acute and Chronic Stress in Child Abuse

OBJECTIVES

To elucidate pathologic markers of acute and chronic stress found but rarely reported in chronic child abuse.

METHODS

Autopsies of 3 cases of fatal child abuse with well-documented chronic maltreatment are reported, with an emphasis on the nontraumatic findings of acute and chronic stress.

RESULTS

Besides the overwhelming physical injuries, all 3 children and 1 additional case obtained for consultation had telogen effluvium, a form of alopecia well known to be associated with stress in adults and some children but never reported in chronic abuse. All 3 had the microscopic findings of markedly involuted thymus, a well-known marker of physiologic stress in children but only occasionally referred to in child abuse. All 3 also had microscopic findings of myocardial necrosis associated with supraphysiologic levels of catecholamine, a well-documented finding associated with stress but rarely reported in fatalities associated with child abuse. Two of the 3 children also had Anitschkow-like nuclear changes in cardiac tissue, markers associated with prior, nonischemic myocardial pathologies that may be associated with prior episodes of acute stress.

CONCLUSIONS

Pathologists are urged to explore these markers as supportive evidence in their own investigations of possible child abuse fatalities, especially when associated with stress.

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

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

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

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Depletion of KDM1A isoforms impairs hESC differentiation into cardiac cells

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

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KDM1A isoforms exhibit enzymatic-independent divergent roles during cardiogenesis

Stage-specific regulation of signalling pathways to differentiate pluripotent stem cells to cardiomyocytes with ventricular lineage

Background

Pluripotent stem cells (PSCs) can be an ideal source of differentiation of cardiomyocytes in vitro and during transplantation to induce cardiac regeneration. However, differentiation of PSCs into a heterogeneous population is associated with an increased incidence of arrhythmia following transplantation. We aimed to design a protocol to drive PSCs to a ventricular lineage by regulating Wnt and retinoic acid (RA) signalling pathways.

Methods

Mouse embryonic stem cells were cultured either in monolayers or three-dimensional hanging drop method to form embryonic bodies (EBs) and exposed to different treatments acting on Wnt and retinoic acid signalling. Samples were collected at different time points to analyse cardiomyocyte-specific markers by RT-PCR, flow cytometry and immunofluorescence.

Results

Treatment of monolayer and EBs with Wnt and RA signalling pathways and ascorbic acid, as a cardiac programming enhancer, resulted in the formation of an immature non-contractile cardiac population that expressed many of the putative markers of cardiac differentiation. The population exhibited upregulation of ventricular specific markers while suppressing the expression of pro-atrial and pro-sinoatrial markers. Differentiation of EBs resulted in early foetal like non-contractile ventricular cardiomyocytes with an inherent propensity to contract when stimulated.

Conclusion

Our results provide the first evidence of in vitro differentiation that mimics the embryonic morphogenesis towards ventricular specific cardiomyocytes through regulation of Wnt and RA signalling pathways.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02845-9.

Impact of concomitant complex cardiac anatomy in nonsyndromic patients with complete atrioventricular septal defect

OBJECTIVE

We studied a cohort of patients with nonsyndromic complete atrioventricular septal defect with and without concomitant complex cardiac anatomy and compared the outcomes after surgical repair.

METHODS

Between 1993 and 2018, 62 nonsyndromic patients underwent complete atrioventricular septal defect repair. Sixteen patients (26%) had complex complete atrioventricular septal defect with variables representing concomitant cardiac anatomic complexity: tetralogy of Fallot, double outlet right ventricle, total anomalous pulmonary venous return, concomitant aortic arch reconstruction, multiple ventricular septal defects, staged repair of coarctation of the aorta, and a persisting left superior vena cava. The mean follow-up was 12.7 ± 7.9 years. Baseline variables were retrospectively evaluated and analyzed using univariable logistic regression. Survival was studied using Kaplan-Meier estimates, and group comparisons were performed using the log-rank test. A competing-risk analysis estimated the risk of reoperation with death as the competing event. A Gray's test was used to test equality of the cumulative incidence curves between groups.

RESULTS

The perioperative mortality was 3.2% (2/62). Actuarial survival was 100% versus 66.7% ± 14.9% at 10 years in the noncomplex and complex groups, respectively (P < .01). There was no significant difference in the overall reoperation rate between the noncomplex group (7/46; 15%) and the complex group (4/16; 25%) (odds ratio, 1.86; 95% confidence interval, 0.46-7.45; P = .30). The competing-risk analysis demonstrated no significant difference in reoperation between the groups (P = .28).

CONCLUSIONS

Our data show that nonsyndromic patients without complex cardiac anatomy have a good long-term survival and an acceptable risk of reoperation similar to contemporary outcomes for patients with complete atrioventricular septal defect with trisomy 21. However, the corresponding group of nonsyndromic patients with concomitant complex cardiac lesions are still a high-risk population, especially regarding mortality.

Reconstructing the heart using iPSCs: Engineering strategies and applications

Induced pluripotent stem cells (iPSCs) have emerged as a key component of cardiac tissue engineering, enabling studies of cardiovascular disease mechanisms, drug responses, and developmental processes in human 3D tissue models assembled from isogenic cells. Since the very first engineered heart tissues were introduced more than two decades ago, a wide array of iPSC-derived cardiac spheroids, organoids, and heart-on-a-chip models have been developed incorporating the latest available technologies and materials. In this review, we will first outline the fundamental biological building blocks required to form a functional unit of cardiac muscle, including iPSC-derived cells differentiated by soluble factors (e.g., small molecules), extracellular matrix scaffolds, and exogenous biophysical maturation cues. We will then summarize the different fabrication approaches and strategies employed to reconstruct the heart in vitro at varying scales and geometries. Finally, we will discuss how these platforms, with continued improvements in scalability and tissue maturity, can contribute to both basic cardiovascular research and clinical applications in the future.

DAND5 Inactivation Enhances Cardiac Differentiation in Mouse Embryonic Stem Cells

Deciphering the clues of a regenerative mechanism for the mammalian adult heart would save millions of lives in the near future. Heart failure due to cardiomyocyte loss is still one of the significant health burdens worldwide. Here, we show the potential of a single molecule, DAND5, in mouse pluripotent stem cell-derived cardiomyocytes specification and proliferation. Dand5 loss-of-function generated the double of cardiac beating foci compared to the wild-type cells. The early formation of cardiac progenitor cells and the increased proliferative capacity of Dand5 KO mESC-derived cardiomyocytes contribute to the observed higher number of derived cardiac cells. Transcriptional profiling sequencing and quantitative RT-PCR assays showed an upregulation of early cardiac gene networks governing cardiomyocyte differentiation, cell cycling, and cardiac regenerative pathways but reduced levels of genes involved in cardiomyocyte maturation. These findings prompt DAND5 as a key driver for the generation and expansion of pluripotent stem cell-derived cardiomyocytes systems with further clinical application purposes.

Heart defects and embryonic lethality in Asb2 knock out mice correlate with placental defects

Asb2, ankyrin repeat, and SOCS box protein 2 form an E3 ubiquitin ligase complex. Asb2 ubiquitin ligase activity drives the degradation of filamins, which have essential functions in humans. The placenta is a temporary organ that forms during pregnancy, and normal placentation is important for survival and growth of the fetus. Recent studies have shown that approximately 25-30% of knockout (KO) mice have non-viable offspring, and 68% of knockout lines exhibit placental dysmorphologies. There are very few studies on Asb2, with insufficient research on its role in placental development. Therefore, we generated Asb2 knockout mice and undertook to investigate Asb2 expression during organogenesis, and to identify its role in early embryonic and placental development. The external morphology of KO embryos revealed abnormal phenotypes including growth retardation, pericardial effusion, pale color, and especially heart beat defect from E 9.5. Furthermore, Asb2 expression was observed in the heart from E 9.5, indicating that it is specifically expressed during early heart formation, resulting in embryonic lethality. Histological analysis of E 10.5 KO heart showed malformations such as failure of chamber formation, reduction in trabeculated myocardium length, absence of mesenchymal cells, and destruction of myocardium wall. Moreover, the histological results of Asb2-deficient placenta showed abnormal phenotypes including small labyrinth and reduced vascular complexity, indicating that failure to establish mature circulatory pattern affects the embryonic development and results in early mortality. Collectively, our results demonstrate that Asb2 knockout mice have placental defects, that subsequently result in failure to form a normal cardiac septum, and thereby result in embryo mortality in utero at around E 9.5.

Smad4 regulates the nuclear translocation of Nkx2-5 in cardiac differentiation

Bmp plays an important role in cardiomyocyte differentiation, but the function of Smad4 in Bmp signaling remains elusive. Here, we show that disruption of the Smad4 gene in cardiac progenitors expressing Sfrp5 led to embryonic lethality with hypoplastic heart formation. Although the expression of Nkx2-5 is regulated by Bmp signaling, expression of Nkx2-5 was weakly detected in the mutant heart. However, the nuclear translocation of Nkx2-5 was impaired. Expression of CK2 or PP1, which could alter the phosphorylation status of the NLS of Nkx2-5, was not affected, but Nkx2-5 was found to bind to Smad4 by co-immunoprecipitation experiments. Introduction of Smad4 into cells derived from Smad4 conditional knockout embryonic hearts restored the nuclear localization of Nkx2-5, and exogenous Nkx2-5 failed to translocate into the nucleus of Smad4-depleted fibroblasts. These results suggest that Smad4 plays an essential role in cardiomyocyte differentiation by controlling not only transcription but also the nuclear localization of Nkx2-5.

Over-expression of Fgf8 in cardiac neural crest cells leads to persistent truncus arteriosus

During cardiogenesis, the outflow tract undergoes a complicated morphogenesis, including the re-alignment of the great blood vessels, and the separation of aorta and pulmonary trunk. The deficiency of FGF8 in the morphogenesis of outflow tract has been well studied, however, the effect of over-dosed FGF8 on the development of outflow tract remains unknown. In this study, Rosa26R-Fgf8 knock-in allele was constitutively activated by Wnt1-cre transgene in the mouse neural crest cells presumptive for the endocardial cushion of outflow tract. Surprisingly, Wnt1-cre; Rosa26R-Fgf8 mouse embryos exhibited persistent truncus arteriosus and died prior to E15.5. The cardiac neural crest cells in Wnt1-cre; Rosa26R-Fgf8 truncus arteriosus did not degenerate as in WT controls, but proliferated into a thickened endocardial cushion and then, blocked the blood outflow from cardiac chambers into the lungs, which resulted in the embryonic lethality. Although the spiral aorticopulmonary septum failed to form, the differentiaion of the endothelium and smooth muscle in the Wnt1-cre; Rosa26R-Fgf8 truncus arteriosus were impacted little. However, lineage tracing assay showed that the neural crest derived cells aggregated in the cushion layer, but failed to differentiate into the endothelium of Wnt1-cre; Rosa26R-Fgf8 truncus arteriosus. Further investigation displayed the reduced p-Akt and p-Erk immunostaining, and the decreased Bmp2 and Bmp4 transcription in the endothelium of Wnt1-cre; Rosa26R-Fgf8 truncus arteriosus. Our findings suggested that Fgf8 over-expression in cardiac neural crest impaired the formation of aorticopulmonary septum by suppressing the endothelial differentiation and stimulating the proliferation of endocardial cushion cells, which implicated a novel etiology of persistent truncus arteriosus.

Nkx2-5 Regulates the Proliferation and Migration of H9c2 Cells

Background

The protein NKX2–5 affects mammalian heart development. In mice, the disruption of Nkx2–5 has been associated with arrhythmias, abnormal myocardial contraction, abnormal cardiac morphogenesis, and death. However, the details of the mechanisms are unclear. This study was designed to investigate them.

Material/Methods

Rat cardiomyocytes from the H9c2 cell line were used in our study. First, we knocked down Nkx2–5 in the H9c2 cells and then validated consequent changes in cell proliferation and migration. We then used RNA sequencing to determine the changes in transcripts. Finally, we validated these results by quantitative reverse transcription-polymerase chain reaction.

Results

We confirmed that Nkx2–5 regulates the proliferation and migration of H9c2 cells. In our experiments, Nkx2–5 regulated the expression of genes related to proliferation, migration, heart development, and disease. Based on bioinformatics analysis, knockdown of Nkx2–5 caused differential expression of genes involved in cardiac development, calcium ion-related biological activity, the transforming growth factor (TGF)-β signaling pathway, pathways related to heart diseases, the MAPK signaling pathway, and other biological processes and signaling pathways.

Conclusions

Nkx2–5 may regulate proliferation and migration of the H9c2 cells through the genes Tgfb-2, Bmp10, Id2, Wt1, Hey1, and Cacna1g; rno-miR-1-3p; the TGF-β signaling pathway; the MAPK signaling pathway; as well as other genes and pathways.

Congenital heart defects associated with aneuploidy syndromes: New insights into familiar associations

The frequent occurrence of congenital heart defects (CHDs) in chromosome abnormality syndromes is well-known, and among aneuploidy syndromes, distinctive patterns have been delineated. We update the type and frequency of CHDs in the aneuploidy syndromes involving trisomy 13, 18, 21, and 22, and in several sex chromosome abnormalities (Turner syndrome, trisomy X, Klinefelter syndrome, 47,XYY, and 48,XXYY). We also discuss the impact of noninvasive prenatal screening (mainly, cell-free DNA analysis), critical CHD screening, and the growth of parental advocacy on their surgical management and natural history. We encourage clinicians to view the cardiac diagnosis as a "phenotype" which supplements the external dysmorphology examination. When detected prenatally, severe CHDs may influence decision-making, and postnatally, they are often the major determinants of survival. This review should be useful to geneticists, cardiologists, neonatologists, perinatal specialists, other pediatric specialists, and general pediatricians. As patients survive (and thrive) into adulthood, internists and related adult specialists will also need to be informed about their natural history and management.

Endothelial/Epithelial Mesenchymal Transition in Ascending Aortas of Patients With Bicuspid Aortic Valve

Thoracic aortic aneurysm (TAA) is the progressive enlargement of the aorta due to destructive changes in the connective tissue of the aortic wall. Aneurysm development is silent and often first manifested by the drastic events of aortic dissection or rupture. As yet, therapeutic agents that halt or reverse the process of aortic wall deterioration are absent, and the only available therapeutic recommendation is elective prophylactic surgical intervention. Being born with a bicuspid instead of the normal tricuspid aortic valve (TAV) is a major risk factor for developing aneurysm in the ascending aorta later in life. Although the pathophysiology of the increased aneurysm susceptibility is not known, recent studies are suggestive of a transformation of aortic endothelium into a more mesenchymal state i.e., an endothelial-to-mesenchymal transition in these individuals. This process involves the loss of endothelial cell features, resulting in junction instability and enhanced vascular permeability of the ascending aorta that may lay the ground for increased aneurysm susceptibility. This finding differentiates and further emphasizes the specific characteristics of aneurysm development in individuals with a bicuspid aortic valve (BAV). This review discusses the possibility of a developmental fate shared between the aortic endothelium and aortic valves. It further speculates about the impact of aortic endothelium phenotypic shift on aneurysm development in individuals with a BAV and revisits previous studies in the light of the new findings.

Cardiac Sca-1+ Cells Are Not Intrinsic Stem Cells for Myocardial Development, Renewal, and Repair

BACKGROUND

For more than a decade, Sca-1⁺ cells within the mouse heart have been widely recognized as a stem cell population with multipotency that can give rise to cardiomyocytes, endothelial cells, and smooth muscle cells in vitro and after cardiac grafting. However, the developmental origin and authentic nature of these cells remain elusive.

METHODS

Here, we used a series of high-fidelity genetic mouse models to characterize the identity and regenerative potential of cardiac resident Sca-1⁺ cells.

RESULTS

With these novel genetic tools, we found that Sca-1 does not label cardiac precursor cells during early embryonic heart formation. Postnatal cardiac resident Sca-1⁺ cells are in fact a pure endothelial cell population. They retain endothelial properties and exhibit minimal cardiomyogenic potential during development, normal aging and upon ischemic injury.

CONCLUSIONS

Our study provides definitive insights into the nature of cardiac resident Sca-1⁺ cells. The observations challenge the current dogma that cardiac resident Sca-1⁺ cells are intrinsic stem cells for myocardial development, renewal, and repair, and suggest that the mechanisms of transplanted Sca-1⁺ cells in heart repair need to be reassessed.

Differential expression of novel MicroRNAs from developing fetal heart of Gallus gallus domesticus implies a role in cardiac development

Heart development is a complex process regulated by multi-layered genetic as well epigenetic regulators many of which are still unknown. Besides their critical role during cardiac development, these molecular regulators emerge as key modulators of cardiovascular pathologies, where fetal cardiac genes' re-expression is witnessed. MicroRNAs have recently emerged as a crucial part of signalling cascade in both development and diseases. We aimed to identify, validate, and perform functional annotation of putative novel miRNAs using chicken as a cardiac development model system. Novel miRNAs were obtained through deep sequencing of small RNAs extracted from chicken embryonic cardiac tissue of different developmental stages. After filtering out real pre-miRNAs, their expression analysis, potential target gene's prediction and functional annotations were performed. Expression analysis revealed that miRNAs were differentially expressed during different developmental stages of chicken heart. The expression of selected putative novel miRNAs was further validated by real-time PCR. Our analysis indicated the presence of novel cardiac miRNAs that might be regulating critical cardiac development events such as cardiac cell growth, differentiation, cardiac action potential generation and signal transduction.

The interstitium in cardiac repair: role of the immune-stromal cell interplay

Cardiac regeneration, that is, restoration of the original structure and function in a damaged heart, differs from tissue repair, in which collagen deposition and scar formation often lead to functional impairment. In both scenarios, the early-onset inflammatory response is essential to clear damaged cardiac cells and initiate organ repair, but the quality and extent of the immune response vary. Immune cells embedded in the damaged heart tissue sense and modulate inflammation through a dynamic interplay with stromal cells in the cardiac interstitium, which either leads to recapitulation of cardiac morphology by rebuilding functional scaffolds to support muscle regrowth in regenerative organisms or fails to resolve the inflammatory response and produces fibrotic scar tissue in adult mammals. Current investigation into the mechanistic basis of homeostasis and restoration of cardiac function has increasingly shifted focus away from stem cell-mediated cardiac repair towards a dynamic interplay of cells composing the less-studied interstitial compartment of the heart, offering unexpected insights into the immunoregulatory functions of cardiac interstitial components and the complex network of cell interactions that must be considered for clinical intervention in heart diseases.

Maternal hyperglycemia and fetal cardiac development: Clinical impact and underlying mechanisms

Congenital heart disease (CHD) is the most common type of birth defect and is both a significant pediatric and adult health problem, in light of a growing population of survivors. The etiology of CHD has been considered to be multifactorial with genetic and environmental factors playing important roles. The combination of advances in cardiac developmental biology, which have resulted in the elucidation of molecular pathways regulating normal cardiac morphogenesis, and genome sequencing technology have allowed the discovery of numerous genetic contributors of CHD ranging from chromosomal abnormalities to single gene variants. Conversely, mechanistic details of the contribution of environmental factors to CHD remain unknown. Maternal diabetes mellitus (matDM) is a well-established and increasingly prevalent environmental risk factor for CHD, but the underlying etiologic mechanisms by which pregestational matDM increases the vulnerability of embryos to cardiac malformations remains largely elusive. Here, we will briefly discuss the multifactorial etiology of CHD with a focus on the epidemiologic link between matDM and CHD. We will describe the animal models used to study the underlying mechanisms between matDM and CHD and review the numerous cellular and molecular pathways affected by maternal hyperglycemia in the developing heart. Last, we discuss how this increased understanding may open the door for the development of novel prevention strategies to reduce the incidence of CHD in this high-risk population.

Epithelial Properties of the Second Heart Field

The vertebrate heart tube forms from epithelial progenitor cells in the early embryo and subsequently elongates by progressive addition of second heart field (SHF) progenitor cells from adjacent splanchnic mesoderm. Failure to maximally elongate the heart results in a spectrum of morphological defects affecting the cardiac poles, including outflow tract alignment and atrioventricular septal defects, among the most common congenital birth anomalies. SHF cells constitute an atypical apicobasally polarized epithelium with dynamic basal filopodia, located in the dorsal wall of the pericardial cavity. Recent studies have highlighted the importance of epithelial architecture and cell adhesion in the SHF, particularly for signaling events that control the progenitor cell niche during heart tube elongation. The 22q11.2 deletion syndrome gene Tbx1 regulates progenitor cell status through modulating cell shape and filopodial activity and is required for SHF contributions to both cardiac poles. Noncanonical Wnt signaling and planar cell polarity pathway genes control epithelial polarity in the dorsal pericardial wall, as progenitor cells differentiate in a transition zone at the arterial pole. Defects in these pathways lead to outflow tract shortening. Moreover, new biomechanical models of heart tube elongation have been proposed based on analysis of tissue-wide forces driving epithelial morphogenesis in the SHF, including regional cell intercalation, cell cohesion, and epithelial tension. Regulation of the epithelial properties of SHF cells is thus emerging as a key step during heart tube elongation, adding a new facet to our understanding of the mechanisms underlying both heart morphogenesis and congenital heart defects.

T-box genes and retinoic acid signaling regulate the segregation of arterial and venous pole progenitor cells in the murine second heart field

The arterial and venous poles of the mammalian heart are hotspots of congenital heart defects (CHD) such as those observed in 22q11.2 deletion (or DiGeorge) and Holt-Oram syndromes. These regions of the heart are derived from late differentiating cardiac progenitor cells of the Second Heart Field (SHF) located in pharyngeal mesoderm contiguous with the elongating heart tube. The T-box transcription factor Tbx1, encoded by the major 22q11.2 deletion syndrome gene, regulates SHF addition to both cardiac poles from a common progenitor population. Despite the significance of this cellular addition the mechanisms regulating the deployment of common progenitor cells to alternate cardiac poles remain poorly understood. Here we demonstrate that Tbx5, mutated in Holt-Oram syndrome and essential for venous pole development, is activated in Tbx1 expressing cells in the posterior region of the SHF at early stages of heart tube elongation. A subset of the SHF transcriptional program, including Tbx1 expression, is subsequently downregulated in Tbx5 expressing cells, generating a transcriptional boundary between Tbx1-positive arterial pole and Tbx5-positive venous pole progenitor cell populations. We show that normal downregulation of the definitive arterial pole progenitor cell program in the posterior SHF is dependent on both Tbx1 and Tbx5. Furthermore, retinoic acid (RA) signaling is required for Tbx5 activation in Tbx1-positive cells and blocking RA signaling at the time of Tbx5 activation results in atrioventricular septal defects at fetal stages. Our results reveal sequential steps of cardiac progenitor cell patterning and provide mechanistic insights into the origin of common forms of CHD.

Roles of Glycogen Synthase Kinase-3 (GSK-3) in Cardiac Development and Heart Disease

Glycogen synthase kinase-3 (GSK-3) is a cytoplasmic serine/threonine protein kinase which is known to regulate a variety of cellular processes through a number of signaling pathways important for cell proliferation, stem cell renewal, apoptosis and development. Although GSK-3 exists in a variety of tissues, this kinase plays very important roles in the heart to control its development through the formation of heart and cardiomyocyte proliferation. GSK-3 is also recognized as one of the main molecules that control cardiac hypertrophy and fibrosis. Therefore, GSK-3 could be an attractive target for the development of new drugs to cure cardiac diseases. The present review summarizes the roles of GSK-3 in the signaling pathways and the heart, and discusses the possibility of new drug development targeting this kinase.

'Heart development and morphogenesis' is a novel pathway for human ovarian granulosa cell differentiation during long‑term in vitro cultivation‑a microarray approach

Granulosa cells (GCs) have many functions in the endocrine system. Most notably, they produce progesterone following ovulation. However, it has recently been proven that GCs can change their properties when subjected to long-term culture. In the present study, GCs were collected from hyper-stimulated ovarian follicles during in vitro fertilization procedures. They were grown in vitro, in a long-term manner. RNA was collected following 1, 7, 15 and 30 days of culture. Expression microarrays were used for analysis, which allowed to identify groups of genes characteristic for particular cellular processes. In addition, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to validate the obtained results. Two ontological groups characteristic for processes associated with the development and morphogenesis of the heart were identified during the analyses: ‘Heart development’ and ‘heart morphogenesis’. The results of the microarrays revealed that the highest change in expression was demonstrated by the lysyl Oxidase, oxytocin receptor, nexilin F-actin binding protein, and cysteine-rich protein 3 genes. The lowest change was exhibited by odd-skipped related transcription factor 1, plakophilin 2, transcription growth factor-β receptor 1, and kinesin family member 3A. The direction of changes was confirmed by RT-qPCR results. In the present study, it was suggested that GCs may have the potential to differentiate towards other cell types under long-term in vitro culture conditions. Thus, genes belonging to the presented ontological groups can be considered as novel markers of proliferation and differentiation of GCs towards the heart muscle cells.

Good Things for Those Who Wait: Predictive Modeling Highlights Importance of Delay Discounting for Income Attainment

Income is a primary determinant of social mobility, career progression, and personal happiness. It has been shown to vary with demographic variables like age and education, with more oblique variables such as height, and with behaviors such as delay discounting, i.e., the propensity to devalue future rewards. However, the relative contribution of each these salary-linked variables to income is not known. Further, much of past research has often been underpowered, drawn from populations of convenience, and produced findings that have not always been replicated. Here we tested a large (n = 2,564), heterogeneous sample, and employed a novel analytic approach: using three machine learning algorithms to model the relationship between income and age, gender, height, race, zip code, education, occupation, and discounting. We found that delay discounting is more predictive of income than age, ethnicity, or height. We then used a holdout data set to test the robustness of our findings. We discuss the benefits of our methodological approach, as well as possible explanations and implications for the prominent relationship between delay discounting and income.

Gestational Hypoxia and Developmental Plasticity

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

Next-generation pacemakers: from small devices to biological pacemakers

Electrogenesis in the heart begins in the sinoatrial node and proceeds down the conduction system to originate the heartbeat. Conduction system disorders lead to slow heart rates that are insufficient to support the circulation, necessitating implantation of electronic pacemakers. The typical electronic pacemaker consists of a subcutaneous generator and battery module attached to one or more endocardial leads. New leadless pacemakers can be implanted directly into the right ventricular apex, providing single-chamber pacing without a subcutaneous generator. Modern pacemakers are generally reliable, and their programmability provides options for different pacing modes tailored to specific clinical needs. Advances in device technology will probably include alternative energy sources and dual-chamber leadless pacing in the not-too-distant future. Although effective, current electronic devices have limitations related to lead or generator malfunction, lack of autonomic responsiveness, undesirable interactions with strong magnetic fields, and device-related infections. Biological pacemakers, generated by somatic gene transfer, cell fusion, or cell transplantation, provide an alternative to electronic devices. Somatic reprogramming strategies, which involve transfer of genes encoding transcription factors to transform working myocardium into a surrogate sinoatrial node, are furthest along in the translational pipeline. Even as electronic pacemakers become smaller and less invasive, biological pacemakers might expand the therapeutic armamentarium for conduction system disorders.

Drug-induced cardiac abnormalities in premature infants and neonates

The Cardiac Safety Research Consortium (CSRC) is a transparent, public-private partnership that was established in 2005 as a Critical Path Program and formalized in 2006 under a Memorandum of Understanding between the United States Food and Drug Administration and Duke University. Our continuing goal is to advance paradigms for more efficient regulatory science related to the cardiovascular safety of new therapeutics, both in the United States and globally, particularly where such safety questions add burden to innovative research and development. This White Paper provides a summary of discussions by a cardiovascular committee cosponsored by the CSRC and the US Food and Drug Administration (FDA) that initially met in December 2014, and periodically convened at FDA's White Oak headquarters from March 2015 to September 2016. The committee focused on the lack of information concerning the cardiac effects of medications in the premature infant and neonate population compared with that of the older pediatric and adult populations. Key objectives of this paper are as follows: Provide an overview of human developmental cardiac electrophysiology, as well as the electrophysiology of premature infants and neonates; summarize all published juvenile animal models relevant to drug-induced cardiac toxicity; provide a consolidated source for all reported drug-induced cardiac toxicities by therapeutic area as a resource for neonatologists; present drugs that have a known cardiac effect in an adult population, but no reported toxicity in the premature infant and neonate populations; and summarize what is not currently known about drug-induced cardiac toxicity in premature infants and neonates, and what could be done to address this lack of knowledge. This paper presents the views of the authors and should not be construed to represent the views or policies of the FDA or Health Canada.

Clinical and molecular effects of CHD7 in the heart

Heart defects caused by loss-of-function mutations in CHD7 are a frequent cause of morbidity and mortality in CHARGE syndrome. Here we review the clinical and molecular aspects of CHD7 that are related to the cardiovascular manifestations of the syndrome. The types of heart defects found in patients with CHD7 mutations are variable, with an overrepresentation of atrioventricular septal defect and outflow tract defect including aortic arch anomalies compared to nonsyndromic heart defects. Chd7 haploinsufficiency in mouse is a good model for studying the heart effects seen in CHARGE syndrome, and mouse models reveal a role for Chd7 in multiple lineages during heart development. Formation of the great vessels requires Chd7 expression in the pharyngeal surface ectoderm, and this expression likely has an non-autonomous effect on neural crest cells. In the cardiogenic mesoderm, Chd7 is required for atrioventricular cushion development and septation of the outflow tract. Emerging knowledge about the function of CHD7 in the heart indicates that it may act in concert with transcription factors such as TBX1 and SMADs to regulate genes such as p53 and the cardiac transcription factor NKX2.5.

Coordinating Regulation of Gene Expression in Cardiovascular Disease: Interactions between Chromatin Modifiers and Transcription Factors

Cardiovascular disease is a leading cause of death with increasing economic burden. The pathogenesis of cardiovascular diseases is complex, but can arise from genetic and/or environmental risk factors. This can lead to dysregulated gene expression in numerous cell types including cardiomyocytes, endothelial cells, vascular smooth muscle cells, and inflammatory cells. While initial studies addressed transcriptional control of gene expression, epigenetics has been increasingly appreciated to also play an important role in this process through alterations in chromatin structure and gene accessibility. Chromatin-modifying proteins including enzymes that modulate DNA methylation, histone methylation, and histone acetylation can influence gene expression in numerous ways. These chromatin modifiers and their marks can promote or prevent transcription factor recruitment to regulatory regions of genes through modifications to DNA, histones, or the transcription factors themselves. This review will focus on the emerging question of how epigenetic modifiers and transcription factors interact to coordinately regulate gene expression in cardiovascular disease. While most studies have addressed the roles of either epigenetic or transcriptional control, our understanding of the integration of these processes is only just beginning. Interrogating these interactions is challenging, and improved technical approaches will be needed to fully dissect the temporal and spatial relationships between transcription factors, chromatin modifiers, and gene expression in cardiovascular disease. We summarize the current state of the field and provide perspectives on limitations and future directions. Through studies of epigenetic and transcriptional interactions, we can advance our understanding of the basic mechanisms of cardiovascular disease pathogenesis to develop novel therapeutics.

Epithelial tension in the second heart field promotes mouse heart tube elongation

Extension of the vertebrate heart tube is driven by progressive addition of second heart field (SHF) progenitor cells to the poles of the heart. Defects in this process cause a spectrum of congenital anomalies. SHF cells form an epithelial layer in splanchnic mesoderm in the dorsal wall of the pericardial cavity. Here we report oriented cell elongation, polarized actomyosin distribution and nuclear YAP/TAZ in a proliferative centre in the posterior dorsal pericardial wall during heart tube extension. These parameters are indicative of mechanical stress, further supported by analysis of cell shape changes in wound assays. Time course and mutant analysis identifies SHF deployment as a source of epithelial tension. Moreover, cell division and oriented growth in the dorsal pericardial wall align with the axis of cell elongation, suggesting that epithelial tension in turn contributes to heart tube extension. Our results implicate tissue-level forces in the regulation of heart tube extension.

Epithelial progenitor cell growth in the second heart field contributes to heart morphogenesis but how this is regulated at the tissue level is unclear. Here, the authors show that cell elongation, polarized actomyosin and nuclear YAP/TAZ drive epithelial growth and correlate with mechanical tension.

Autophagy-related polymorphisms predict hypertension in patients with metastatic colorectal cancer treated with FOLFIRI and bevacizumab: Results from TRIBE and FIRE-3 trials

PURPOSE

The most frequent bevacizumab-related side-effects are hypertension, proteinuria, bleeding and thromboembolism. To date, there is no biomarker that predicts anti-VEGF-associated toxicity. As autophagy inhibits angiogenesis, we hypothesised that single-nucleotide polymorphisms (SNPs) within autophagy-related genes may predict bevacizumab-mediated toxicity in patients with metastatic colorectal cancer (mCRC).

PATIENTS AND METHODS

Patients with mCRC treated with first-line FOLFIRI and bevacizumab in two phase III randomised trials, namely the TRIBE trial (n = 219, discovery cohort) and the FIRE-3 trial (n = 234, validation cohort) were included in this study. Patients receiving treatment with FOLFIRI and cetuximab (FIRE-3, n = 204) served as a negative control. 12 SNPs in eight autophagy-related genes (ATG3/5/8/13, beclin 1, FIP200, unc-51-like kinase 1, UVRAG) were analysed by PCR-based direct sequencing.

RESULTS

The FIP200 rs1129660 variant showed significant associations with hypertension in the TRIBE cohort. Patients harbouring any G allele of the FIP200 rs1129660 SNP showed a significantly lower rate of grade 2-3 hypertension compared with the A/A genotype (3% versus 15%, odds ratio [OR] 0.17; 95% confidence interval [CI], 0.02-0.73; P = 0.009). Similarly, G allele carriers of the FIP200 rs1129660 SNP were less likely to develop grade 2-3 hypertension than patients with an A/A genotype in the FIRE-3 validation cohort (9% versus 20%, OR 0.43; 95% CI, 0.14-1.11; P = 0.077), whereas this association could not be observed in the control cohort (12% versus 9%, OR 1.40; 95% CI, 0.45-4.04; P = 0.60).

CONCLUSION

This is the first report demonstrating that polymorphisms in the autophagy-related FIP200 gene may predict hypertension in patients with mCRC treated with FOLFIRI and bevacizumab.

Disruption of pdgfra alters endocardial and myocardial fusion during zebrafish cardiac assembly

Cardiac development in vertebrates is a finely tuned process regulated by a set of conserved signaling pathways. Perturbations of these processes are often associated with congenital cardiac malformations. Platelet-derived growth factor receptor α (PDGFRα) is a highly conserved tyrosine kinase receptor, which is essential for development and organogenesis. Disruption of Pdgfrα function in murine models is embryonic lethal due to severe cardiovascular defects, suggesting a role in cardiac development, thus necessitating the use of alternative models to explore its precise function. In this study, we generated a zebrafish pdgfra mutant line by gene trapping, in which the Pdgfra protein is truncated and fused with mRFP (Pdgfra-mRFP). Our results demonstrate that pdgfra mutants have defects in cardiac morphology as a result of abnormal fusion of myocardial precursors. Expression analysis of the developing heart at later stages suggested that Pdgfra-mRFP is expressed in the endocardium. Further examination of the endocardium in pdgfra mutants revealed defective endocardial migration to the midline, where cardiac fusion eventually occurs. Together, our data suggests that pdgfra is required for proper medial migration of both endocardial and myocardial precursors, an essential step required for cardiac assembly and development.

Summary: The molecular mechanisms regulating cardiac fusion are not well understood. Here, we show that platelet-derived growth factor receptor alpha is essential for normal endocardial and myocardial fusion during zebrafish development.

A Comprehensive TALEN-Based Knockout Library for Generating Human-Induced Pluripotent Stem Cell-Based Models for Cardiovascular Diseases

RATIONALE

Targeted genetic engineering using programmable nucleases such as transcription activator-like effector nucleases (TALENs) is a valuable tool for precise, site-specific genetic modification in the human genome.

OBJECTIVE

The emergence of novel technologies such as human induced pluripotent stem cells (iPSCs) and nuclease-mediated genome editing represent a unique opportunity for studying cardiovascular diseases in vitro.

METHODS AND RESULTS

By incorporating extensive literature and database searches, we designed a collection of TALEN constructs to knockout 88 human genes that are associated with cardiomyopathies and congenital heart diseases. The TALEN pairs were designed to induce double-strand DNA break near the starting codon of each gene that either disrupted the start codon or introduced a frameshift mutation in the early coding region, ensuring faithful gene knockout. We observed that all the constructs were active and disrupted the target locus at high frequencies. To illustrate the utility of the TALEN-mediated knockout technique, 6 individual genes (TNNT2, LMNA/C, TBX5, MYH7, ANKRD1, and NKX2.5) were knocked out with high efficiency and specificity in human iPSCs. By selectively targeting a pathogenic mutation (TNNT2 p.R173W) in patient-specific iPSC-derived cardiac myocytes, we demonstrated that the knockout strategy ameliorates the dilated cardiomyopathy phenotype in vitro. In addition, we modeled the Holt-Oram syndrome in iPSC-cardiac myocytes in vitro and uncovered novel pathways regulated by TBX5 in human cardiac myocyte development.

CONCLUSIONS

Collectively, our study illustrates the powerful combination of iPSCs and genome editing technologies for understanding the biological function of genes, and the pathological significance of genetic variants in human cardiovascular diseases. The methods, strategies, constructs, and iPSC lines developed in this study provide a validated, readily available resource for cardiovascular research.

Left and right ventricular hemodynamic forces in healthy volunteers and elite athletes assessed with 4D flow magnetic resonance imaging

Intracardiac blood flow is driven by hemodynamic forces that are exchanged between the blood and myocardium. Previous studies have been limited to 2D measurements or investigated only left ventricular (LV) forces. Right ventricular (RV) forces and their mechanistic contribution to asymmetric redirection of flow in the RV have not been measured. We therefore aimed to quantify 3D hemodynamic forces in both ventricles in a cohort of healthy subjects, using magnetic resonance imaging 4D flow measurements. Twenty five controls, 14 elite endurance athletes, and 2 patients with LV dyssynchrony were included. 4D flow data were used as input for the Navier-Stokes equations to compute hemodynamic forces over the entire cardiac cycle. Hemodynamic forces were found in a qualitatively consistent pattern in all healthy subjects, with variations in amplitude. LV forces were mainly aligned along the apical-basal longitudinal axis, with an additional component aimed toward the aortic valve during systole. Conversely, RV forces were found in both longitudinal and short-axis planes, with a systolic force component driving a slingshot-like acceleration that explains the mechanism behind the redirection of blood flow toward the pulmonary valve. No differences were found between controls and athletes when indexing forces to ventricular volumes, indicating that cardiac force expenditures are tuned to accelerate blood similarly in small and large hearts. Patients’ forces differed from controls in both timing and amplitude. Normal cardiac pumping is associated with specific force patterns for both ventricles, and deviation from these forces may be a sensitive marker of ventricular dysfunction. Reference values are provided for future studies.

NEW & NOTEWORTHY Biventricular hemodynamic forces were quantified for the first time in healthy controls and elite athletes (n = 39). Hemodynamic forces constitute a slingshot-like mechanism in the right ventricle, redirecting blood flow toward the pulmonary circulation. Force patterns were similar between healthy subjects and athletes, indicating potential utility as a cardiac function biomarker.

Rare novel variants in the ZIC3 gene cause X-linked heterotaxy

Variants in the ZIC3 gene are rare, but have demonstrated their profound clinical significance in X-linked heterotaxy, affecting in particular male patients with abnormal arrangement of thoracic and visceral organs. Several reports have shown relevance of ZIC3 gene variants in both familial and sporadic cases and with a predominance of mutations detected in zinc-finger domains. No studies so far have assessed the functional consequences of ZIC3 variants in an in vivo model organism. A study population of 348 patients collected over more than 10 years with a large variety of congenital heart disease including heterotaxy was screened for variants in the ZIC3 gene. Functional effects of three variants were assessed both in vitro and in vivo in the zebrafish. We identified six novel pathogenic variants (1,7%), all in either male patients with heterotaxy (n=5) or a female patient with multiple male deaths due to heterotaxy in the family (n=1). All variants were located within the zinc-finger domains or leading to a truncation before these domains. Truncating variants showed abnormal trafficking of mutated ZIC3 proteins, whereas the missense variant showed normal trafficking. Overexpression of wild-type and mutated ZIC protein in zebrafish showed full non-functionality of the two frame-shift variants and partial activity of the missense variant compared with wild-type, further underscoring the pathogenic character of these variants. Concluding, we greatly expanded the number of causative variants in ZIC3 and delineated the functional effects of three variants using in vitro and in vivo model systems.

Modulating microRNAs in cardiac surgery patients: Novel therapeutic opportunities?

This review focuses on microRNAs (miRs) in cardiac surgery, where they are emerging as potential targets for therapeutic intervention as well as novel clinical biomarkers. Identification of the up/down-regulation of specific miRs in defined groups of cardiac surgery patients can lead to the development of novel strategies for targeted treatment in order to maximise therapeutic results and minimise acute, delayed or chronic complications. MiRs could also be involved in determining the outcome independently of complications, for example in relation to myocardial perfusion and fibrosis. Because of their relevance in disease, their known sequence and pharmacological properties, miRs are attractive candidates for therapeutic manipulation. Pharmacological inhibition of individual miRs can be achieved by modified antisense oligonucleotides, referred to as antimiRs, while miR replacement can be achieved by miR mimics to increase the level of a specific miR. MiR mimics can restore the function of a lost or down-regulated miR, while antimiRs can inhibit the levels of disease-driving or aberrantly expressed miRs, thus de-repressing the expression of mRNAs targeted by the miR. The main delivery methods for miR therapeutics involve lipid-based vehicles, viral systems, cationic polymers, and intravenous or local injection of an antagomiR. Local delivery is particularly desirable for miR therapeutics and options include the development of devices specific for local delivery, light-induced antimiR, and vesicle-encapsulated miRs serving as therapeutic delivery agents able to improve intracellular uptake. Here, we discuss the potential therapeutic use of miRNAs in the context of cardiac surgery.

Transcriptomic Profiling Maps Anatomically Patterned Subpopulations among Single Embryonic Cardiac Cells

Embryonic gene expression intricately reflects anatomical context, developmental stage, and cell type. To address whether the precise spatial origins of cardiac cells can be deduced solely from their transcriptional profiles, we established a genome-wide expression database from 118, 949, and 1,166 single murine heart cells at embryonic day 8.5 (e8.5), e9.5, and e10.5, respectively. We segregated these cells by type using unsupervised bioinformatics analysis and identified chamber-specific genes. Using a random forest algorithm, we reconstructed the spatial origin of single e9.5 and e10.5 cardiomyocytes with 92.0% ± 3.2% and 91.2% ± 2.8% accuracy, respectively (99.4% ± 1.0% and 99.1% ± 1.1% if a ±1 zone margin is permitted) and predicted the second heart field distribution of Isl-1-lineage descendants. When applied to Nkx2-5^-/- cardiomyocytes from murine e9.5 hearts, we showed their transcriptional alteration and lack of ventricular phenotype. Our database and zone classification algorithm will enable the discovery of novel mechanisms in early cardiac development and disease.

The role of microRNAs in cardiac development and regenerative capacity

The mammalian heart has long been considered to be a postmitotic organ. It was thought that, in the postnatal period, the heart underwent a transition from hyperplasic growth (more cells) to hypertrophic growth (larger cells) due to the conversion of cardiomyocytes from a proliferative state to one of terminal differentiation. This hypothesis was gradually disproven, as data were published showing that the myocardium is a more dynamic tissue in which cardiomyocyte karyokinesis and cytokinesis produce new cells, leading to the hyperplasic regeneration of some of the muscle mass lost in various pathological processes. microRNAs have been shown to be critical regulators of cardiomyocyte differentiation and proliferation and may offer the novel opportunity of regenerative hyperplasic therapy. Here we summarize the relevant processes and recent progress regarding the functions of specific microRNAs in cardiac development and regeneration.

HEART DEVELOPMENT. Integration of Bmp and Wnt signaling by Hopx specifies commitment of cardiomyoblasts

Cardiac progenitor cells are multipotent and give rise to cardiac endothelium, smooth muscle, and cardiomyocytes. Here, we define and characterize the cardiomyoblast intermediate that is committed to the cardiomyocyte fate, and we characterize the niche signals that regulate commitment. Cardiomyoblasts express Hopx, which functions to coordinate local Bmp signals to inhibit the Wnt pathway, thus promoting cardiomyogenesis. Hopx integrates Bmp and Wnt signaling by physically interacting with activated Smads and repressing Wnt genes. The identification of the committed cardiomyoblast that retains proliferative potential will inform cardiac regenerative therapeutics. In addition, Bmp signals characterize adult stem cell niches in other tissues where Hopx-mediated inhibition of Wnt is likely to contribute to stem cell quiescence and to explain the role of Hopx as a tumor suppressor.

Semaphorin signaling in cardiovascular development

Semaphorins were originally identified as neuronal guidance molecules mediating their attractive or repulsive signals by forming complexes with plexin and neuropilin receptors. Subsequent research has identified functions for semaphorin signaling in many organs and tissues outside of the nervous system. Vital roles for semaphorin signaling in vascular patterning and cardiac morphogenesis have been demonstrated, and impaired semaphorin signaling has been associated with various human cardiovascular disorders, including persistent truncus arteriosus, sinus bradycardia and anomalous pulmonary venous connections. Here, we review the functions of semaphorins and their receptors in cardiovascular development and disease and highlight important recent discoveries in the field.

DOT1L-mediated H3K79me2 modification critically regulates gene expression during cardiomyocyte differentiation

Epigenetic changes on DNA and chromatin are implicated in cell differentiation and organogenesis. For the heart, distinct histone methylation profiles were recently linked to stage-specific gene expression programs during cardiac differentiation in vitro. However, the enzymes catalyzing these modifications and the genes regulated by them remain poorly defined. We therefore decided to identify the epigenetic enzymes that are potentially involved in cardiomyogenesis by analyzing the expression profile of the 85 genes encoding the epigenetic-related proteins in mouse cardiomyocytes (CMs), and then study how they affect gene expression during differentiation and maturation of this cell type. We show here with gene expression screening of epigenetic enzymes that the highly expressed H3 methyltransferase disruptor of telomeric silencing 1-like (DOT1L) drives a transitional pattern of di-methylation on H3 lysine 79 (H3K79) in CMs at different stages of differentiation in vitro and in vivo. Through a genome-wide chromatin-immunoprecipitation DNA-sequencing approach, we found H3K79me2 enriched at genes expressed during cardiac differentiation. Moreover, knockdown of Dot1L affected the expression of H3K79me2-enriched genes. Our results demonstrate that histone methylation, and in particular DOT1L-mediated H3K79me2 modification, drives cardiomyogenesis through the definition of a specific transcriptional landscape.

Directed differentiation of patient-specific induced pluripotent stem cells identifies the transcriptional repression and epigenetic modification of NKX2-5, HAND1, and NOTCH1 in hypoplastic left heart syndrome

The genetic basis of hypoplastic left heart syndrome (HLHS) remains unknown, and the lack of animal models to reconstitute the cardiac maldevelopment has hampered the study of this disease. This study investigated the altered control of transcriptional and epigenetic programs that may affect the development of HLHS by using disease-specific induced pluripotent stem (iPS) cells. Cardiac progenitor cells (CPCs) were isolated from patients with congenital heart diseases to generate patient-specific iPS cells. Comparative gene expression analysis of HLHS- and biventricle (BV) heart-derived iPS cells was performed to dissect the complex genetic circuits that may promote the disease phenotype. Both HLHS- and BV heart-derived CPCs were reprogrammed to generate disease-specific iPS cells, which showed characteristic human embryonic stem cell signatures, expressed pluripotency markers, and could give rise to cardiomyocytes. However, HLHS-iPS cells exhibited lower cardiomyogenic differentiation potential than BV-iPS cells. Quantitative gene expression analysis demonstrated that HLHS-derived iPS cells showed transcriptional repression of NKX2-5, reduced levels of TBX2 and NOTCH/HEY signaling, and inhibited HAND1/2 transcripts compared with control cells. Although both HLHS-derived CPCs and iPS cells showed reduced SRE and TNNT2 transcriptional activation compared with BV-derived cells, co-transfection of NKX2-5, HAND1, and NOTCH1 into HLHS-derived cells resulted in synergistic restoration of these promoters activation. Notably, gain- and loss-of-function studies revealed that NKX2-5 had a predominant impact on NPPA transcriptional activation. Moreover, differentiated HLHS-derived iPS cells showed reduced H3K4 dimethylation as well as histone H3 acetylation but increased H3K27 trimethylation to inhibit transcriptional activation on the NKX2-5 promoter. These findings suggest that patient-specific iPS cells may provide molecular insights into complex transcriptional and epigenetic mechanisms, at least in part, through combinatorial expression of NKX2-5, HAND1, and NOTCH1 that coordinately contribute to cardiac malformations in HLHS.