Mending a broken heart: In vitro, in vivo and in silico models of congenital heart disease

Spontaneously Corrected Hypoplastic Left Heart: A Case Report and Exceptional Opportunity to Discuss Etiology with Novel Therapeutic Vision

Hypoplastic left heart syndrome (HLHS) is a relatively prevalent fetal echocardiography finding in complex congenital heart diseases. Current studies indicate that intrinsic and extrinsic mechanisms could be involved in the development of left heart hypoplasia. Left ventricular inflow or outflow disorders may cause left heart hypoplasia. Prenatal aortic valvuloplasty has become more common as a therapeutic strategy. Our case presentation provides an opportunity for a new vision toward the etiology, prevention, and treatment of HLHS. In our patient, prenatal progressive left heart hypoplasia associated with restrictive foramen oval (FO) suggested the likelihood of a flow-mediated mechanism. Additionally, postnatal improvement of the hypoplastic left heart in the presence of a functional perimembranous ventricular septal defect (PM-VSD) reinforced the suspicion of an extrinsic mechanism. Pre- or postnatal interventional creation of an atrial septal defect (ASD) or VSD is our proposed method for HLHS in selected patients.

Interdependence of placenta and fetal cardiac development

The placenta and fetal heart undergo development concurrently during early pregnancy, and, while human studies have reported associations between placental abnormalities and congenital heart disease (CHD), the nature of this relationship remains incompletely understood. Evidence from animal studies suggests a plausible cause and effect connection between placental abnormalities and fetal CHD. Biomechanical models demonstrate the influence of mechanical forces on cardiac development, whereas genetic models highlight the role of confined placental mutations that can cause some forms of CHD. Similar definitive studies in humans are lacking; however, placental pathologies such as maternal and fetal vascular malperfusion and chronic deciduitis are frequently observed in pregnancies complicated by CHD. Moreover, maternal conditions such as diabetes and pre-eclampsia, which affect placental function, are associated with increased risk of CHD in offspring. Bridging the gap between animal models and human studies is crucial to understanding how placental abnormalities may contribute to human fetal CHD. The next steps will require new methodologies and multidisciplinary approaches combining innovative imaging modalities, comprehensive genomic testing, and histopathology. These studies may eventually lead to preventative strategies for some forms of CHD by targeting placental influences on fetal heart development.

Current genetic models for studying congenital heart diseases: Advantages and disadvantages

Congenital heart disease (CHD) encompasses a diverse range of structural and functional anomalies that affect the heart and the major blood vessels. Epidemiological studies have documented a global increase in CHD prevalence, which can be attributed to advancements in diagnostic technologies. Extensive research has identified a plethora of CHD-related genes, providing insights into the biochemical pathways and molecular mechanisms underlying this pathological state. In this review, we discuss the advantages and challenges of various In vitro and in vivo CHD models, including primates, canines, Xenopus frogs, rabbits, chicks, mice, Drosophila, zebrafish, and induced pluripotent stem cells (iPSCs). Primates are closely related to humans but are rare and expensive. Canine models are costly but structurally comparable to humans. Xenopus frogs are advantageous because of their generation of many embryos, ease of genetic modification, and cardiac similarity. Rabbits mimic human physiology but are challenging to genetically control. Chicks are inexpensive and simple to handle; however, cardiac events can vary among humans. Mice differ physiologically, while being evolutionarily close and well-resourced. Drosophila has genes similar to those of humans but different heart structures. Zebrafish have several advantages, including high gene conservation in humans and physiological cardiac similarities but limitations in cross-reactivity with mammalian antibodies, gene duplication, and limited embryonic stem cells for reverse genetic methods. iPSCs have the potential for gene editing, but face challenges in terms of 2D structure and genomic stability. CRISPR-Cas9 allows for genetic correction but requires high technical skills and resources. These models have provided valuable knowledge regarding cardiac development, disease simulation, and the verification of genetic factors. This review highlights the distinct features of various models with respect to their biological characteristics, vulnerability to developing specific heart diseases, approaches employed to induce particular conditions, and the comparability of these species to humans. Therefore, the selection of appropriate models is based on research objectives, ultimately leading to an enhanced comprehension of disease pathology and therapy.

Understanding the Genetic and Non-genetic Interconnections in the Aetiology of Isolated Congenital Heart Disease: An Updated Review: Part 1

PURPOSE OF REVIEW

Congenital heart disease (CHD) is the most frequently occurring birth defect. Majority of the earlier reviews focussed on the association of genetic factors with CHD. A few epidemiological studies provide convincing evidence for environmental factors in the causation of CHD. Although the multifactorial theory of gene-environment interaction is the prevailing explanation, explicit understanding of the biological mechanism(s) involved, remains obscure. Nonetheless, integration of all the information into one platform would enable us to better understand the collective risk implicated in CHD development.

RECENT FINDINGS

Great strides in novel genomic technologies namely, massive parallel sequencing, whole exome sequencing, multiomics studies supported by system-biology have greatly improved our understanding of the aetiology of CHD. Molecular genetic studies reveal that cardiac specific gene variants in transcription factors or signalling molecules, or structural proteins could cause CHD. Additionally, non-hereditary contributors such as exposure to teratogens, maternal nutrition, parental age and lifestyle factors also contribute to induce CHD. Moreover, DNA methylation and non-coding RNA are also correlated with CHD. Here, we inform that a complex combination of genetic, environmental and epigenetic factors interact to interfere with morphogenetic processes of cardiac development leading to CHD. It is important, not only to identify individual genetic and non-inherited risk factors but also to recognize which factors interact mutually, causing cardiac defects.

Emerging Roles of Cullin-RING Ubiquitin Ligases in Cardiac Development

Heart development is a spatiotemporally regulated process that extends from the embryonic phase to postnatal stages. Disruption of this highly orchestrated process can lead to congenital heart disease or predispose the heart to cardiomyopathy or heart failure. Consequently, gaining an in-depth understanding of the molecular mechanisms governing cardiac development holds considerable promise for the development of innovative therapies for various cardiac ailments. While significant progress in uncovering novel transcriptional and epigenetic regulators of heart development has been made, the exploration of post-translational mechanisms that influence this process has lagged. Culling-RING E3 ubiquitin ligases (CRLs), the largest family of ubiquitin ligases, control the ubiquitination and degradation of ~20% of intracellular proteins. Emerging evidence has uncovered the critical roles of CRLs in the regulation of a wide range of cellular, physiological, and pathological processes. In this review, we summarize current findings on the versatile regulation of cardiac morphogenesis and maturation by CRLs and present future perspectives to advance our comprehensive understanding of how CRLs govern cardiac developmental processes.

Step-by-step fabrication of heart-on-chip systems as models for cardiac disease modeling and drug screening

Cardiovascular diseases are caused by hereditary factors, environmental conditions, and medication-related issues. On the other hand, the cardiotoxicity of drugs should be thoroughly examined before entering the market. In this regard, heart-on-chip (HOC) systems have been developed as a more efficient and cost-effective solution than traditional methods, such as 2D cell culture and animal models. HOCs must replicate the biology, physiology, and pathology of human heart tissue to be considered a reliable platform for heart disease modeling and drug testing. Therefore, many efforts have been made to find the best methods to fabricate different parts of HOCs and to improve the bio-mimicry of the systems in the last decade. Beating HOCs with different platforms have been developed and techniques, such as fabricating pumpless HOCs, have been used to make HOCs more user-friendly systems. Recent HOC platforms have the ability to simultaneously induce and record electrophysiological stimuli. Additionally, systems including both heart and cancer tissue have been developed to investigate tissue-tissue interactions' effect on cardiac tissue response to cancer drugs. In this review, all steps needed to be considered to fabricate a HOC were introduced, including the choice of cellular resources, biomaterials, fabrication techniques, biomarkers, and corresponding biosensors. Moreover, the current HOCs used for modeling cardiac diseases and testing the drugs are discussed. We finally introduced some suggestions for fabricating relatively more user-friendly HOCs and facilitating the commercialization process.

Advancing clinical translation of cardiac biomechanics models: a comprehensive review, applications and future pathways

Cardiac mechanics models are developed to represent a high level of detail, including refined anatomies, accurate cell mechanics models, and platforms to link microscale physiology to whole-organ function. However, cardiac biomechanics models still have limited clinical translation. In this review, we provide a picture of cardiac mechanics models, focusing on their clinical translation. We review the main experimental and clinical data used in cardiac models, as well as the steps followed in the literature to generate anatomical meshes ready for simulations. We describe the main models in active and passive mechanics and the different lumped parameter models to represent the circulatory system. Lastly, we provide a summary of the state-of-the-art in terms of ventricular, atrial, and four-chamber cardiac biomechanics models. We discuss the steps that may facilitate clinical translation of the biomechanics models we describe. A well-established software to simulate cardiac biomechanics is lacking, with all available platforms involving different levels of documentation, learning curves, accessibility, and cost. Furthermore, there is no regulatory framework that clearly outlines the verification and validation requirements a model has to satisfy in order to be reliably used in applications. Finally, better integration with increasingly rich clinical and/or experimental datasets as well as machine learning techniques to reduce computational costs might increase model reliability at feasible resources. Cardiac biomechanics models provide excellent opportunities to be integrated into clinical workflows, but more refinement and careful validation against clinical data are needed to improve their credibility. In addition, in each context of use, model complexity must be balanced with the associated high computational cost of running these models.

The dimethadione-exposed rat fetus: an animal model for the prenatal ultrasound characterization of ventricular septal defect

BACKGROUND

Ventricular septal defect (VSD) is the most prevalent congenital heart disease (CHD) and is easily misdiagnosed or missed. An appropriate VSD animal model could be used to analyze the ultrasound characteristics and their related pathological bases, and provides the opportunity to further explore the pathogenesis of VSD. Currently, little is known about whether ultrahigh-frequency ultrasound biomicroscopy (UBM) is suitable to diagnose VSD of fetal rats. There is no research on whether a dimethadione (DMO)-induced fetal VSD model is suitable for the observation and analysis of imaging characteristics and the associated pathological basis.

METHODS

We used DMO to induce VSD. UBM was used to perform the prenatal ultrasound characterization. With the pathological results used as the gold standard, the ultrasound characteristics and their related pathological bases were analyzed.

RESULTS

The incidence of VSD in the DMO group was 42.05% and 39.71% (diagnosed by UBM and pathology, respectively, P > 0.05). The prenatal ultrasound findings and pathological basis of various diseases, including isolated VSD, complex CHD containing VSD, and extracardiac lesions, were detected and discussed. It was discovered that some fetuses showed features of noncompacted ventricular myocardium, and for the first time, clusters of red blood cell traversing the cardiomyocytes.

CONCLUSIONS

The DMO-induced VSD model is a low-cost model with a high success rate and is suitable for the observation and analysis of VSD. UBM is suitable for evaluating VSD.

Piglet cardiopulmonary bypass induces intestinal dysbiosis and barrier dysfunction associated with systemic inflammation

The intestinal microbiome is essential to human health and homeostasis, and is implicated in the pathophysiology of disease, including congenital heart disease and cardiac surgery. Improving the microbiome and reducing inflammatory metabolites may reduce systemic inflammation following cardiac surgery with cardiopulmonary bypass (CPB) to expedite recovery post-operatively. Limited research exists in this area and identifying animal models that can replicate changes in the human intestinal microbiome after CPB is necessary. We used a piglet model of CPB with two groups, CPB (n=5) and a control group with mechanical ventilation (n=7), to evaluate changes to the microbiome, intestinal barrier dysfunction and intestinal metabolites with inflammation after CPB. We identified significant changes to the microbiome, barrier dysfunction, intestinal short-chain fatty acids and eicosanoids, and elevated cytokines in the CPB/deep hypothermic circulatory arrest group compared to the control group at just 4 h after intervention. This piglet model of CPB replicates known human changes to intestinal flora and metabolite profiles, and can be used to evaluate gut interventions aimed at reducing downstream inflammation after cardiac surgery with CPB.

Accelerating Cardiovascular Research: Recent Advances in Translational 2D and 3D Heart Models

In vitro modelling the complex (patho-) physiological conditions of the heart is a major challenge in cardiovascular research. In recent years, methods based on three-dimensional (3D) cultivation approaches have steadily evolved to overcome the major limitations of conventional adherent monolayer cultivation (2D). These 3D approaches aim to study, reproduce or modify fundamental native features of the heart such as tissue organization and cardiovascular microenvironment. Therefore, these systems have great potential for (patient-specific) disease research, for the development of new drug screening platforms, and for the use in regenerative and replacement therapy applications. Consequently, continuous improvement and adaptation is required with respect to fundamental limitations such as cardiomyocyte maturation, scalability, heterogeneity, vascularization, and reproduction of native properties. In this review, 2D monolayer culturing and the 3D in vitro systems of cardiac spheroids, organoids, engineered cardiac microtissue and bioprinting as well as the ex vivo technique of myocardial slicing are introduced with their basic concepts, advantages, and limitations. Furthermore, recent advances of various new approaches aiming to extend as well as to optimize these in vitro and ex vivo systems are presented. This article is protected by copyright. All rights reserved.

Epigenetics and Congenital Heart Diseases

Congenital heart disease (CHD) is a frequent occurrence, with a prevalence rate of almost 1% in the general population. However, the pathophysiology of the anomalous heart development is still unclear in most patients screened. A definitive genetic origin, be it single-point mutation or larger chromosomal disruptions, only explains about 35% of identified cases. The precisely choreographed embryology of the heart relies on timed activation of developmental molecular cascades, spatially and temporally regulated through epigenetic regulation: chromatin conformation, DNA priming through methylation patterns, and spatial accessibility to transcription factors. This multi-level regulatory network is eminently susceptible to outside disruption, resulting in faulty cardiac development. Similarly, the heart is unique in its dynamic development: growth is intrinsically related to mechanical stimulation, and disruption of the intrauterine environment will have a direct impact on fetal embryology. These two converging axes offer new areas of research to characterize the cardiac epigenetic regulation and identify points of fragility in order to counteract its teratogenic consequences.

Disease Models & Mechanisms helps move heart failure to heart success

Heart failure affects ∼64 million people worldwide, resulting in high morbidity, mortality and societal cost. Current treatment strategies are primarily geared at slowing the progression to an advanced disease state, but do not reverse or cure heart failure. A more comprehensive understanding of the underlying biology and development of preclinical models of this heterogeneous group of disorders will improve diagnosis and treatment. Here, we summarise recent preclinical and translational research in this area published in Disease Models & Mechanisms. We also discuss how our Journal is propelling this field forward by launching a Special Issue and ongoing subject collection, ‘Moving Heart Failure to Heart Success: Mechanisms, Regeneration & Therapy’.

Computational Methods for Fluid-Structure Interaction Simulation of Heart Valves in Patient-Specific Left Heart Anatomies

Given the complexity of human left heart anatomy and valvular structures, the fluid–structure interaction (FSI) simulation of native and prosthetic valves poses a significant challenge for numerical methods. In this review, recent numerical advancements for both fluid and structural solvers for heart valves in patient-specific left hearts are systematically considered, emphasizing the numerical treatments of blood flow and valve surfaces, which are the most critical aspects for accurate simulations. Numerical methods for hemodynamics are considered under both the continuum and discrete (particle) approaches. The numerical treatments for the structural dynamics of aortic/mitral valves and FSI coupling methods between the solid Ωs and fluid domain Ωf are also reviewed. Future work toward more advanced patient-specific simulations is also discussed, including the fusion of high-fidelity simulation within vivo measurements and physics-based digital twining based on data analytics and machine learning techniques.

Drosophila Heart as a Model for Cardiac Development and Diseases

The Drosophila heart, also referred to as the dorsal vessel, pumps the insect blood, the hemolymph. The bilateral heart primordia develop from the most dorsally located mesodermal cells, migrate coordinately, and fuse to form the cardiac tube. Though much simpler, the fruit fly heart displays several developmental and functional similarities to the vertebrate heart and, as we discuss here, represents an attractive model system for dissecting mechanisms of cardiac aging and heart failure and identifying genes causing congenital heart diseases. Fast imaging technologies allow for the characterization of heartbeat parameters in the adult fly and there is growing evidence that cardiac dysfunction in human diseases could be reproduced and analyzed in Drosophila, as discussed here for heart defects associated with the myotonic dystrophy type 1. Overall, the power of genetics and unsuspected conservation of genes and pathways puts Drosophila at the heart of fundamental and applied cardiac research.

A mouse model of hypoplastic left heart syndrome demonstrating left heart hypoplasia and retrograde aortic arch flow

In hypoplastic left heart syndrome (HLHS), the mechanisms leading to left heart hypoplasia and their associated fetal abnormalities are largely unknown. Current animal models have limited utility in resolving these questions as they either do not fully reproduce the cardiac phenotype, do not survive to term and/or have very low disease penetrance. Here, we report the development of a surgically induced mouse model of HLHS that overcomes these limitations. Briefly, we microinjected the fetal left atrium of embryonic day (E)14.5 mice with an embolizing agent under high-frequency ultrasound guidance, which partially blocks blood flow into the left heart and induces hypoplasia. At term (E18.5), all positively embolized mice exhibit retrograde aortic arch flow, non-apex-forming left ventricles and hypoplastic ascending aortas. We thus report the development of the first mouse model of isolated HLHS with a fully penetrant cardiac phenotype and survival to term. Our method allows for the interrogation of previously intractable questions, such as determining the mechanisms of cardiac hypoplasia and fetal abnormalities observed in HLHS, as well as testing of mechanism-based therapies, which are urgently lacking.