A transgenic rabbit model for human hypertrophic cardiomyopathy

Incomplete-penetrant hypertrophic cardiomyopathy MYH7 G256E mutation causes hypercontractility and elevated mitochondrial respiration

Determining the pathogenicity of hypertrophic cardiomyopathy-associated mutations in the β-myosin heavy chain (MYH7) can be challenging due to its variable penetrance and clinical severity. This study investigates the early pathogenic effects of the incomplete-penetrant MYH7 G256E mutation on myosin function that may trigger pathogenic adaptations and hypertrophy. We hypothesized that the G256E mutation would alter myosin biomechanical function, leading to changes in cellular functions. We developed a collaborative pipeline to characterize myosin function across protein, myofibril, cell, and tissue levels to determine the multiscale effects on structure-function of the contractile apparatus and its implications for gene regulation and metabolic state. The G256E mutation disrupts the transducer region of the S1 head and reduces the fraction of myosin in the folded-back state by 33%, resulting in more myosin heads available for contraction. Myofibrils from gene-edited MYH7WT/G256E human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) exhibited greater and faster tension development. This hypercontractile phenotype persisted in single-cell hiPSC-CMs and engineered heart tissues. We demonstrated consistent hypercontractile myosin function as a primary consequence of the MYH7 G256E mutation across scales, highlighting the pathogenicity of this gene variant. Single-cell transcriptomic and metabolic profiling demonstrated upregulated mitochondrial genes and increased mitochondrial respiration, indicating early bioenergetic alterations. This work highlights the benefit of our multiscale platform to systematically evaluate the pathogenicity of gene variants at the protein and contractile organelle level and their early consequences on cellular and tissue function. We believe this platform can help elucidate the genotype-phenotype relationships underlying other genetic cardiovascular diseases.

New drug discovery of cardiac anti-arrhythmic drugs: insights in animal models

Cardiac rhythm regulated by micro-macroscopic structures of heart. Pacemaker abnormalities or disruptions in electrical conduction, lead to arrhythmic disorders may be benign, typical, threatening, ultimately fatal, occurs in clinical practice, patients on digitalis, anaesthesia or acute myocardial infarction. Both traditional and genetic animal models are: In-vitro: Isolated ventricular Myocytes, Guinea pig papillary muscles, Patch-Clamp Experiments, Porcine Atrial Myocytes, Guinea pig ventricular myocytes, Guinea pig papillary muscle: action potential and refractory period, Langendorff technique, Arrhythmia by acetylcholine or potassium. Acquired arrhythmia disorders: Transverse Aortic Constriction, Myocardial Ischemia, Complete Heart Block and AV Node Ablation, Chronic Tachypacing, Inflammation, Metabolic and Drug-Induced Arrhythmia. In-Vivo: Chemically induced arrhythmia: Aconitine antagonism, Digoxin-induced arrhythmia, Strophanthin/ouabain-induced arrhythmia, Adrenaline-induced arrhythmia, and Calcium-induced arrhythmia. Electrically induced arrhythmia: Ventricular fibrillation electrical threshold, Arrhythmia through programmed electrical stimulation, sudden coronary death in dogs, Exercise ventricular fibrillation. Genetic Arrhythmia: Channelopathies, Calcium Release Deficiency Syndrome, Long QT Syndrome, Short QT Syndrome, Brugada Syndrome. Genetic with Structural Heart Disease: Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia, Dilated Cardiomyopathy, Hypertrophic Cardiomyopathy, Atrial Fibrillation, Sick Sinus Syndrome, Atrioventricular Block, Preexcitation Syndrome. Arrhythmia in Pluripotent Stem Cell Cardiomyocytes. Conclusion: Both traditional and genetic, experimental models of cardiac arrhythmias' characteristics and significance help in development of new antiarrhythmic drugs.

Anti-fibrotic effects of statin drugs: a review of evidence and mechanisms

Fibrosis is a pathological repair process common among organs, that responds to damage by replacement of tissue with non-functional connective tissue. Despite the widespread prevalence of tissue fibrosis, manifesting in numerous disease states across myriad organs, therapeutic modalities to prevent or alleviate fibrosis are severely lacking in quantity and efficacy. Alongside development of new drugs, repurposing of existing drugs may be a complementary strategy to elect anti-fibrotic compounds for pharmacologic treatment of tissue fibrosis. Drug repurposing can provide key advantages to de novo drug discovery, harnessing the benefits of previously elucidated mechanisms of action and already existing pharmacokinetic profiles. One class of drugs a wealth of clinical data and extensively studied safety profiles is the statins, a class of antilipidemic drugs widely prescribed for hypercholesterolemia. In addition to these widely utilized lipid-lowering effects, increasing data from cellular, pre-clinical mammalian, and clinical human studies have also demonstrated that statins are able to alleviate tissue fibrosis originating from a variety of pathological insults via lesser-studied, pleiotropic effects of these drugs. Here we review literature demonstrating evidence for direct effects of statins antagonistic to fibrosis, as well as much of the available mechanistic data underlying these effects. A more complete understanding of the anti-fibrotic effects of statins may enable a clearer picture of their anti-fibrotic potential for various clinical indications. Additionally, more lucid comprehension of the mechanisms by which statins exert anti-fibrotic effects may aid in development of novel therapeutic agents that target similar pathways but with greater specificity or efficacy.

Multi-scale models reveal hypertrophic cardiomyopathy MYH7 G256E mutation drives hypercontractility and elevated mitochondrial respiration

Rationale

Over 200 mutations in the sarcomeric protein β-myosin heavy chain (MYH7) have been linked to hypertrophic cardiomyopathy (HCM). However, different mutations in MYH7 lead to variable penetrance and clinical severity, and alter myosin function to varying degrees, making it difficult to determine genotype-phenotype relationships, especially when caused by rare gene variants such as the G256E mutation.

Objective

This study aims to determine the effects of low penetrant MYH7 G256E mutation on myosin function. We hypothesize that the G256E mutation would alter myosin function, precipitating compensatory responses in cellular functions.

Methods

We developed a collaborative pipeline to characterize myosin function at multiple scales (protein to myofibril to cell to tissue). We also used our previously published data on other mutations to compare the degree to which myosin function was altered.

Results

At the protein level, the G256E mutation disrupts the transducer region of the S1 head and reduces the fraction of myosin in the folded-back state by 50.9%, suggesting more myosins available for contraction. Myofibrils isolated from hiPSC-CMs CRISPR-edited with G256E (MYH7 WT/G256E ) generated greater tension, had faster tension development and slower early phase relaxation, suggesting altered myosin-actin crossbridge cycling kinetics. This hypercontractile phenotype persisted in single-cell hiPSC-CMs and engineered heart tissues. Single-cell transcriptomic and metabolic profiling demonstrated upregulation of mitochondrial genes and increased mitochondrial respiration, suggesting altered bioenergetics as an early feature of HCM.

Conclusions

MYH7 G256E mutation causes structural instability in the transducer region, leading to hypercontractility across scales, perhaps from increased myosin recruitment and altered crossbridge cycling. Hypercontractile function of the mutant myosin was accompanied by increased mitochondrial respiration, while cellular hypertrophy was modest in the physiological stiffness environment. We believe that this multi-scale platform will be useful to elucidate genotype-phenotype relationships underlying other genetic cardiovascular diseases.

Animal Models to Study Cardiac Arrhythmias

Cardiac arrhythmias are a significant cause of morbidity and mortality worldwide, accounting for 10% to 15% of all deaths. Although most arrhythmias are due to acquired heart disease, inherited channelopathies and cardiomyopathies disproportionately affect children and young adults. Arrhythmogenesis is complex, involving anatomic structure, ion channels and regulatory proteins, and the interplay between cells in the conduction system, cardiomyocytes, fibroblasts, and the immune system. Animal models of arrhythmia are powerful tools for studying not only molecular and cellular mechanism of arrhythmogenesis but also more complex mechanisms at the whole heart level, and for testing therapeutic interventions. This review summarizes basic and clinical arrhythmia mechanisms followed by an in-depth review of published animal models of genetic and acquired arrhythmia disorders.

Genetically modified rabbit models for cardiovascular medicine

Genetically modified (GM) rabbits are outstanding animal models for studying human genetic and acquired diseases. As such, GM rabbits that express human genes have been extensively used as models of cardiovascular disease. Rabbits are genetically modified via prokaryotic microinjection. Through this process, genes are randomly integrated into the rabbit genome. Moreover, gene targeting in embryonic stem (ES) cells is a powerful tool for understanding gene function. However, rabbits lack stable ES cell lines. Therefore, ES-dependent gene targeting is not possible in rabbits. Nevertheless, the RNA interference technique is rapidly becoming a useful experimental tool that enables researchers to knock down specific gene expression, which leads to the genetic modification of rabbits. Recently, with the emergence of new genetic technology, such as zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), clustered regularly interspaced short palindromic repeats (CRISPR), and CRISPR-associated protein 9 (CRISPR/Cas9), major breakthroughs have been made in rabbit gene targeting. Using these novel genetic techniques, researchers have successfully modified knockout (KO) rabbit models. In this paper, we aimed to review the recent advances in GM technology in rabbits and highlight their application as models for cardiovascular medicine.

Inhibition of mTOR or MAPK ameliorates vmhcl/myh7 cardiomyopathy in zebrafish

Myosin heavy chain 7 (MYH7) is a major causative gene for hypertrophic cardiomyopathy, but the affected signaling pathways and therapeutics remain elusive. In this research, we identified ventricle myosin heavy chain like (vmhcl) as a zebrafish homolog of human MYH7, and we generated vmhcl frameshift mutants. We noted vmhcl-based embryonic cardiac dysfunction (VEC) in the vmhcl homozygous mutants and vmhcl-based adult cardiomyopathy (VAC) phenotypes in the vmhcl heterozygous mutants. Using the VEC model, we assessed 7 known cardiomyopathy signaling pathways pharmacologically and 11 candidate genes genetically via CRISPR/Cas9 genome editing technology based on microhomology-mediated end joining (MMEJ). Both studies converged on therapeutic benefits of mTOR or mitogen-activated protein kinase (MAPK) inhibition of VEC. While mTOR inhibition rescued the enlarged nuclear size of cardiomyocytes, MAPK inhibition restored the prolonged cell shape in the VEC model. The therapeutic effects of mTOR and MAPK inhibition were later validated in the VAC model. Together, vmhcl/myh7 loss of function is sufficient to induce cardiomyopathy in zebrafish. The VEC and VAC models in zebrafish are amenable to both efficient genetic and chemical genetic tools, offering a rapid in vivo platform for discovering candidate signaling pathways of MYH7 cardiomyopathy.

Abnormalities in sodium current and calcium homoeostasis as drivers of arrhythmogenesis in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common inherited monogenic disease with a prevalence of 1/500 in the general population, representing an important cause of arrhythmic sudden cardiac death (SCD), heart failure, and atrial fibrillation in the young. HCM is a global condition, diagnosed in >50 countries and in all continents. HCM affects people of both sexes and various ethnic and racial origins, with similar clinical course and phenotypic expression. The most unpredictable and devastating consequence of HCM is represented by arrhythmic SCD, most commonly caused by sustained ventricular tachycardia or ventricular fibrillation. Indeed, HCM represents one of the main causes of arrhythmic SCD in the young, with a marked preference for children and adults <30 years. SCD is most prevalent in patients with paediatric onset of HCM but may occur at any age. However, risk is substantially lower after 60 years, suggesting that the potential for ventricular tachyarrhythmias is mitigated by ageing. SCD had been linked originally to sports and vigorous activity in HCM patients. However, it is increasingly clear that the majority of events occurs at rest or during routine daily occupations, suggesting that triggers are far from consistent. In general, the pathophysiology of SCD in HCM remains unresolved. While the pathologic and physiologic substrates abound and have been described in detail, specific factors precipitating ventricular tachyarrhythmias are still unknown. SCD is a rare phenomenon in HCM cohorts (<1%/year) and attempts to identify patients at risk, while generating clinically useful algorithms for primary prevention, remain very inaccurate on an individual basis. One of the reasons for our limited understanding of these phenomena is that limited translational research exists in the field, while most efforts have focused on clinical markers of risk derived from pathology, instrumental patient evaluation, and imaging. Specifically, few studies conducted in animal models and human samples have focused on targeting the cellular mechanisms of arrhythmogenesis in HCM, despite potential implications for therapeutic innovation and SCD prevention. These studies found that altered intracellular Ca2+ homoeostasis and increased late Na+ current, leading to an increased likelihood of early and delayed after-depolarizations, contribute to generate arrhythmic events in diseased cardiomyocytes. As an array of novel experimental opportunities have emerged to investigate these mechanisms, including novel 'disease-in-the-dish' cellular models with patient-specific induced pluripotent stem cell-derived cardiomyocytes, important gaps in knowledge remain. Accordingly, the aim of the present review is to provide a contemporary reappraisal of the cellular basis of SCD-predisposing arrhythmias in patients with HCM and discuss the implications for risk stratification and management.

ESC working group on cardiac cellular electrophysiology position paper: relevance, opportunities, and limitations of experimental models for cardiac electrophysiology research

Cardiac arrhythmias are a major cause of death and disability. A large number of experimental cell and animal models have been developed to study arrhythmogenic diseases. These models have provided important insights into the underlying arrhythmia mechanisms and translational options for their therapeutic management. This position paper from the ESC Working Group on Cardiac Cellular Electrophysiology provides an overview of (i) currently available in vitro, ex vivo, and in vivo electrophysiological research methodologies, (ii) the most commonly used experimental (cellular and animal) models for cardiac arrhythmias including relevant species differences, (iii) the use of human cardiac tissue, induced pluripotent stem cell (hiPSC)-derived and in silico models to study cardiac arrhythmias, and (iv) the availability, relevance, limitations, and opportunities of these cellular and animal models to recapitulate specific acquired and inherited arrhythmogenic diseases, including atrial fibrillation, heart failure, cardiomyopathy, myocarditis, sinus node, and conduction disorders and channelopathies. By promoting a better understanding of these models and their limitations, this position paper aims to improve the quality of basic research in cardiac electrophysiology, with the ultimate goal to facilitate the clinical translation and application of basic electrophysiological research findings on arrhythmia mechanisms and therapies.

Transgenic rabbit models for cardiac disease research

To study the pathophysiology of human cardiac diseases and to develop novel treatment strategies, complex interactions of cardiac cells on cellular, tissue and on level of the whole heart need to be considered. As in vitro cell-based models do not depict the complexity of the human heart, animal models are used to obtain insights that can be translated to human diseases. Mice are the most commonly used animals in cardiac research. However, differences in electrophysiological and mechanical cardiac function and a different composition of electrical and contractile proteins limit the transferability of the knowledge gained. Moreover, the small heart size and fast heart rate are major disadvantages. In contrast to rodents, electrophysiological, mechanical and structural cardiac characteristics of rabbits resemble the human heart more closely, making them particularly suitable as an animal model for cardiac disease research. In this review, various methodological approaches for the generation of transgenic rabbits for cardiac disease research, such as pronuclear microinjection, the sleeping beauty transposon system and novel genome-editing methods (ZFN and CRISPR/Cas9)will be discussed. In the second section, we will introduce the different currently available transgenic rabbit models for monogenic cardiac diseases (such as long QT syndrome, short-QT syndrome and hypertrophic cardiomyopathy) in detail, especially in regard to their utility to increase the understanding of pathophysiological disease mechanisms and novel treatment options.

Genetically Modified Rabbits for Cardiovascular Research

Rabbits are one of the most used experimental animals for investigating the mechanisms of human cardiovascular disease and lipid metabolism because they are phylogenetically closer to human than rodents (mice and rats). Cholesterol-fed wild-type rabbits were first used to study human atherosclerosis more than 100 years ago and are still playing an important role in cardiovascular research. Furthermore, transgenic rabbits generated by pronuclear microinjection provided another means to investigate many gene functions associated with human disease. Because of the lack of both rabbit embryonic stem cells and the genome information, for a long time, it has been a dream for scientists to obtain knockout rabbits generated by homologous recombination-based genomic manipulation as in mice. This obstacle has greatly hampered using genetically modified rabbits to disclose the molecular mechanisms of many human diseases. The advent of genome editing technologies has dramatically extended the applications of experimental animals including rabbits. In this review, we will update genetically modified rabbits, including transgenic, knock-out, and knock-in rabbits during the past decades regarding their use in cardiovascular research and point out the perspectives in future.

Genetic Restrictive Cardiomyopathy: Causes and Consequences-An Integrative Approach

The sarcomere as the smallest contractile unit is prone to alterations in its functional, structural and associated proteins. Sarcomeric dysfunction leads to heart failure or cardiomyopathies like hypertrophic (HCM) or restrictive cardiomyopathy (RCM) etc. Genetic based RCM, a very rare but severe disease with a high mortality rate, might be induced by mutations in genes of non-sarcomeric, sarcomeric and sarcomere associated proteins. In this review, we discuss the functional effects in correlation to the phenotype and present an integrated model for the development of genetic RCM.

Transgenic Rabbit Models: Now and the Future

Transgenic rabbits have contributed to the progress of biomedical science as human disease models because of their unique features, such as the lipid metabolism system similar to humans and medium body size that facilitates handling and experimental manipulation. In fact, many useful transgenic rabbits have been generated and used in research fields such as lipid metabolism and atherosclerosis, cardiac failure, immunology, and oncogenesis. However, there have been long-term problems, namely that the transgenic efficiency when using pronuclear microinjection is low compared with transgenic mice and production of knockout rabbits is impossible owing to the lack of embryonic stem cells for gene targeting in rabbits. Despite these limitations, the emergence of novel genome editing technology has changed the production of genetically modified animals including the rabbit. We are finally able to produce both transgenic and knockout rabbit models to analyze gain- and loss-of-functions of specific genes. It is expected that the use of genetically modified rabbits will extend to various research fields. In this review, we describe the unique features of rabbits as laboratory animals, the current status of their development and use, and future perspectives of transgenic rabbit models for human diseases.

A Journey through Genetic Architecture and Predisposition of Coronary Artery Disease

Introduction

To halt the spread of coronary artery disease (CAD), the number one killer in the world, requires primary prevention. Fifty percent of all Americans are expected to experience a cardiac event; the challenge is identifying those at risk. 40 to 60% of predisposition to CAD is genetic. The first genetic risk variant, 9p21, was discovered in 2007. Genome-Wide Association Studies has since discovered hundreds of genetic risk variants. The genetic burden for CAD can be expressed as a single number, Genetic Risk Score (GRS). Assessment of GRS to risk stratify for CAD was superior to conventional risk factors in several large clinical trials assessing statin therapy, and more recently in a population of nearly 500,000 (UK Biobank). Studies were performed based on prospective genetic risk stratification for CAD. These studies showed that a favorable lifestyle was associated with a 46% reduction in cardiac events and programmed exercise, a 50% reduction in cardiac events. Genetic risk score is superior to conventional risk factors, and is markedly attenuated by lifestyle changes and drug therapy. Genetic risk can be determined at birth or any time thereafter.

Conclusion

Utilizing the GRS to risk stratify young, asymptomatic individuals could provide a paradigm shift in the primary prevention of CAD and significantly halt its spread.

Phenotypic variation and targeted therapy of hypertrophic cardiomyopathy using genetic animal models

Hypertrophic cardiomyopathy (HCM) has a variable clinical presentation due to the diversity of causative genetic mutations. Animal models allow in vivo study of genotypic expression through non-invasive imaging, pathologic sampling, and force analysis. This review focuses on the spontaneous and induced mutations in various animal models affecting mainly sarcomere proteins. The sarcomere is comprised of thick (myosin) filaments and related proteins including myosin heavy chain and myosin binding protein-C; thin (actin) filament proteins and their associated regulators including tropomyosin, troponin I, troponin C, and troponin T. The regulatory milieu including transcription factors and cell signaling also play a significant role. Animal models provide a layered approach of understanding beginning with the causative mutation as a foundation. The functional consequences of protein energy utilization and calcium sensitivity in vivo and ex vivo can be studied. Beyond pathophysiologic disruption of sarcomere function, these models demonstrate the clinical sequalae of diastolic dysfunction, heart failure, and arrhythmogenic death. Through this cascade of understanding the mutation followed by their functional significance, targeted therapies have been developed and are briefly discussed.

Advanced Evolution of Pathogenesis Concepts in Cardiomyopathies

Cardiomyopathy is a group of heterogeneous cardiac diseases that impair systolic and diastolic function, and can induce chronic heart failure and sudden cardiac death. Cardiomyopathy is prevalent in the general population, with high morbidity and mortality rates, and contributes to nearly 20% of sudden cardiac deaths in younger individuals. Genetic mutations associated with cardiomyopathy play a key role in disease formation, especially the mutation of sarcomere encoding genes and ATP kinase genes, such as titin, lamin A/C, myosin heavy chain 7, and troponin T1. Pathogenesis of cardiomyopathy occurs by multiple complex steps involving several pathways, including the Ras-Raf-mitogen-activated protein kinase-extracellular signal-activated kinase pathway, G-protein signaling, mechanotransduction pathway, and protein kinase B/phosphoinositide 3-kinase signaling. Excess biomechanical stress induces apoptosis signaling in cardiomyocytes, leading to cell loss, which can induce myocardial fibrosis and remodeling. The clinical features and pathophysiology of cardiomyopathy are discussed. Although several basic and clinical studies have investigated the mechanism of cardiomyopathy, the detailed pathophysiology remains unclear. This review summarizes current concepts and focuses on the molecular mechanisms of cardiomyopathy, especially in the signaling from mutation to clinical phenotype, with the aim of informing the development of therapeutic interventions.

INDUCED PLURIPOTENT STEM CELLS FOR MODELLING ENERGETIC ALTERATIONS IN HYPERTROPHIC CARDIOMYOPATHY

Hypertrophic cardiomyopathy (HCM) is one of the most commonly inherited cardiac disorders that manifests with increased ventricular wall thickening, cardiomyocyte hypertrophy, disarrayed myofibers and interstitial fibrosis. The major pathophysiological features include, diastolic dysfunction, obstruction of the left ventricular outflow tract and cardiac arrhythmias. Mutations in genes that encode mostly for sarcomeric proteins have been associated with HCM but, despite the abundant research conducted to decipher the molecular mechanisms underlying the disease, it remains unclear as to how a primary defect in the sarcomere could lead to secondary phenotypes such as cellular hypertrophy. Mounting evidence suggests energy deficiency could be an important contributor of disease pathogenesis as well. Various animal models of HCM have been generated for gaining deeper insight into disease pathogenesis, however species variation between animals and humans, as well as the limited availability of human myocardial samples, has encouraged researchers to seek alternative 'humanized' models. Using induced pluripotent stem cells (iPSCs), human cardiomyocytes (CMs) have been generated from patients with HCM for investigating disease mechanisms. While these HCM-iPSC models demonstrate most of the phenotypic traits, it is important to ascertain if they recapitulate all pathophysiological features, especially that of energy deficiency. In this review we discuss the currently established HCM-iPSC models with emphasis on altered energetics.

Hypertrophic cardiomyopathy R403Q mutation in rabbit β-myosin reduces contractile function at the molecular and myofibrillar levels

In 1990, the Seidmans showed that a single point mutation, R403Q, in the human β-myosin heavy chain (MHC) of heart muscle caused a particularly malignant form of familial hypertrophic cardiomyopathy (HCM) [Geisterfer-Lowrance AA, et al. (1990) Cell 62:999-1006.]. Since then, more than 300 mutations in the β-MHC have been reported, and yet there remains a poor understanding of how a single missense mutation in the MYH7 gene can lead to heart disease. Previous studies with a transgenic mouse model showed that the myosin phenotype depended on whether the mutation was in an α- or β-MHC backbone. This led to the generation of a transgenic rabbit model with the R403Q mutation in a β-MHC backbone. We find that the in vitro motility of heterodimeric R403Q myosin is markedly reduced, whereas the actin-activated ATPase activity of R403Q subfragment-1 is about the same as myosin from a nontransgenic littermate. Single myofibrils isolated from the ventricles of R403Q transgenic rabbits and analyzed by atomic force microscopy showed reduced rates of force development and relaxation, and achieved a significantly lower steady-state level of isometric force compared with nontransgenic myofibrils. Myofibrils isolated from the soleus gave similar results. The force-velocity relationship determined for R403Q ventricular myofibrils showed a decrease in the velocity of shortening under load, resulting in a diminished power output. We conclude that independent of whether experiments are performed with isolated molecules or with ordered molecules in the native thick filament of a myofibril, there is a loss-of-function induced by the R403Q mutation in β-cardiac myosin.

Hypertrophic Cardiomyopathy: Genetics, Pathogenesis, Clinical Manifestations, Diagnosis, and Therapy

Hypertrophic cardiomyopathy (HCM) is a genetic disorder that is characterized by left ventricular hypertrophy unexplained by secondary causes and a nondilated left ventricle with preserved or increased ejection fraction. It is commonly asymmetrical with the most severe hypertrophy involving the basal interventricular septum. Left ventricular outflow tract obstruction is present at rest in about one third of the patients and can be provoked in another third. The histological features of HCM include myocyte hypertrophy and disarray, as well as interstitial fibrosis. The hypertrophy is also frequently associated with left ventricular diastolic dysfunction. In the majority of patients, HCM has a relatively benign course. However, HCM is also an important cause of sudden cardiac death, particularly in adolescents and young adults. Nonsustained ventricular tachycardia, syncope, a family history of sudden cardiac death, and severe cardiac hypertrophy are major risk factors for sudden cardiac death. This complication can usually be averted by implantation of a cardioverter-defibrillator in appropriate high-risk patients. Atrial fibrillation is also a common complication and is not well tolerated. Mutations in over a dozen genes encoding sarcomere-associated proteins cause HCM. MYH7 and MYBPC3, encoding β-myosin heavy chain and myosin-binding protein C, respectively, are the 2 most common genes involved, together accounting for ≈50% of the HCM families. In ≈40% of HCM patients, the causal genes remain to be identified. Mutations in genes responsible for storage diseases also cause a phenotype resembling HCM (genocopy or phenocopy). The routine applications of genetic testing and preclinical identification of family members represents an important advance. The genetic discoveries have enhanced understanding of the molecular pathogenesis of HCM and have stimulated efforts designed to identify new therapeutic agents.

A One Health Approach to Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease in humans and results in significant morbidity and mortality. Research over the past 25 years has contributed enormous insight into this inherited disease particularly in the areas of genetics, molecular mechanisms, and pathophysiology. Our understanding continues to be limited by the heterogeneity of clinical presentations with various genetic mutations associated with HCM. Transgenic mouse models have been utilized especially studying the genotypic and phenotypic interactions. However, mice possess intrinsic cardiac and hemodynamic differences compared to humans and have limitations preventing their direct translation. Other animal models of HCM have been studied or generated in part to overcome these limitations. HCM in cats shows strikingly similar molecular, histopathological, and genetic similarities to human HCM, and offers an important translational opportunity for the study of this disease. Recently, inherited left ventricular hypertrophy in rhesus macaques was identified and collaborative investigations have been conducted to begin to develop a non-human primate HCM model. These naturally-occurring large-animal models may aid in advancing our understanding of HCM and developing novel therapeutic approaches to this disease. This review will highlight the features of HCM in humans and the relevant available and developing animal models of this condition.

Genomic Insights into Cardiomyopathies: A Comparative Cross-Species Review

In the global human population, the leading cause of non-communicable death is cardiovascular disease. It is predicted that by 2030, deaths attributable to cardiovascular disease will have risen to over 20 million per year. This review compares the cardiomyopathies in both human and non-human animals and identifies the genetic associations for each disorder in each species/taxonomic group. Despite differences between species, advances in human medicine can be gained by utilising animal models of cardiac disease; likewise, gains can be made in animal medicine from human genomic insights. Advances could include undertaking regular clinical checks in individuals susceptible to cardiomyopathy, genetic testing prior to breeding, and careful administration of breeding programmes (in non-human animals), further development of treatment regimes, and drugs and diagnostic techniques.

Murine Electrophysiological Models of Cardiac Arrhythmogenesis

Cardiac arrhythmias can follow disruption of the normal cellular electrophysiological processes underlying excitable activity and their tissue propagation as coherent wavefronts from the primary sinoatrial node pacemaker, through the atria, conducting structures and ventricular myocardium. These physiological events are driven by interacting, voltage-dependent, processes of activation, inactivation, and recovery in the ion channels present in cardiomyocyte membranes. Generation and conduction of these events are further modulated by intracellular Ca2+ homeostasis, and metabolic and structural change. This review describes experimental studies on murine models for known clinical arrhythmic conditions in which these mechanisms were modified by genetic, physiological, or pharmacological manipulation. These exemplars yielded molecular, physiological, and structural phenotypes often directly translatable to their corresponding clinical conditions, which could be investigated at the molecular, cellular, tissue, organ, and whole animal levels. Arrhythmogenesis could be explored during normal pacing activity, regular stimulation, following imposed extra-stimuli, or during progressively incremented steady pacing frequencies. Arrhythmic substrate was identified with temporal and spatial functional heterogeneities predisposing to reentrant excitation phenomena. These could arise from abnormalities in cardiac pacing function, tissue electrical connectivity, and cellular excitation and recovery. Triggering events during or following recovery from action potential excitation could thereby lead to sustained arrhythmia. These surface membrane processes were modified by alterations in cellular Ca2+ homeostasis and energetics, as well as cellular and tissue structural change. Study of murine systems thus offers major insights into both our understanding of normal cardiac activity and its propagation, and their relationship to mechanisms generating clinical arrhythmias.

Clinical Genetic Testing for the Cardiomyopathies and Arrhythmias: A Systematic Framework for Establishing Clinical Validity and Addressing Genotypic and Phenotypic Heterogeneity

Advances in DNA sequencing have made large, diagnostic gene panels affordable and efficient. Broad adoption of such panels has begun to deliver on the promises of personalized medicine, but has also brought new challenges such as the presence of unexpected results, or results of uncertain clinical significance. Genetic analysis of inherited cardiac conditions is particularly challenging due to the extensive genetic heterogeneity underlying cardiac phenotypes, and the overlapping, variable, and incompletely penetrant nature of their clinical presentations. The design of effective diagnostic tests and the effective use of the results depend on a clear understanding of the relationship between each gene and each considered condition. To address these issues, we developed simple, systematic approaches to three fundamental challenges: (1) evaluating the strength of the evidence suggesting that a particular condition is caused by pathogenic variants in a particular gene, (2) evaluating whether unusual genotype/phenotype observations represent a plausible expansion of clinical phenotype associated with a gene, and (3) establishing a molecular diagnostic strategy to capture overlapping clinical presentations. These approaches focus on the systematic evaluation of the pathogenicity of variants identified in clinically affected individuals, and the natural history of disease in those individuals. Here, we applied these approaches to the evaluation of more than 100 genes reported to be associated with inherited cardiomyopathies and arrhythmias including hypertrophic cardiomyopathy, dilated cardiomyopathy, arrhythmogenic right ventricular dysplasia or cardiomyopathy, long QT syndrome, short QT syndrome, Brugada, and catecholaminergic polymorphic ventricular tachycardia, and to a set of related syndromes such as Noonan Syndrome and Fabry disease. These approaches provide a framework for delivering meaningful and accurate genetic test results to individuals with hereditary cardiac conditions.

Cryo-EM structure of a human cytoplasmic actomyosin complex at near-atomic resolution

The interaction of myosin with actin filaments is the central feature of muscle contraction and cargo movement along actin filaments of the cytoskeleton. The energy for these movements is generated during a complex mechanochemical reaction cycle. Crystal structures of myosin in different states have provided important structural insights into the myosin motor cycle when myosin is detached from F-actin. The difficulty of obtaining diffracting crystals, however, has prevented structure determination by crystallography of actomyosin complexes. Thus, although structural models exist of F-actin in complex with various myosins, a high-resolution structure of the F-actin–myosin complex is missing. Here, using electron cryomicroscopy, we present the structure of a human rigor actomyosin complex at an average resolution of 3.9 Å. The structure reveals details of the actomyosin interface, which is mainly stabilized by hydrophobic interactions. The negatively charged amino (N) terminus of actin interacts with a conserved basic motif in loop 2 of myosin, promoting cleft closure in myosin. Surprisingly, the overall structure of myosin is similar to rigor-like myosin structures in the absence of F-actin, indicating that F-actin binding induces only minimal conformational changes in myosin. A comparison with pre-powerstroke and intermediate (Pi-release) states of myosin allows us to discuss the general mechanism of myosin binding to F-actin. Our results serve as a strong foundation for the molecular understanding of cytoskeletal diseases, such as autosomal dominant hearing loss and diseases affecting skeletal and cardiac muscles, in particular nemaline myopathy and hypertrophic cardiomyopathy.

Rabbit models as tools for preclinical cardiac electrophysiological safety testing: Importance of repolarization reserve

It is essential to more reliably assess the pro-arrhythmic liability of compounds in development. Current guidelines for pre-clinical and clinical testing of drug candidates advocate the use of healthy animals/tissues and healthy individuals and focus on the test compound's ability to block the hERG current and prolong cardiac ventricular repolarization. Also, pre-clinical safety tests utilize several species commonly used in cardiac electrophysiological studies. In this review, important species differences in cardiac ventricular repolarizing ion currents are considered, followed by the discussion on electrical remodeling associated with chronic cardiovascular diseases that leads to altered ion channel and transporter expression and densities in pathological settings. We argue that the choice of species strongly influences experimental outcome and extrapolation of results to human clinical settings. We suggest that based on cardiac cellular electrophysiology, the rabbit is a useful species for pharmacological pro-arrhythmic investigations. In addition to healthy animals and tissues, the use of animal models (e.g. those with impaired repolarization reserve) is suggested that more closely resemble subsets of patients exhibiting increased vulnerability towards the development of ventricular arrhythmias and sudden cardiac death.

Left Ventricular Hypertrophy in Rhesus Macaques (Macaca mulatta) at the California National Primate Research Center (1992-2014)

Necropsy records and associated clinical histories from the rhesus macaque colony at the California National Primate Research Center were reviewed to identify mortality related to cardiac abnormalities involving left ventricular hypertrophy (LVH). Over a 21-y period, 162 cases (female, 90; male, 72) of idiopathic LVH were identified. Macaques presented to necropsy with prominent concentric hypertrophy of the left ventricle associated with striking reduction of the ventricular lumen. Among all LVH cases, 74 macaques (female, 39; male, 35), mostly young adults, presented for spontaneous (sudden) death; more than 50% of these 74 cases were associated with a recent history of sedation or intraspecific aggression. The risk of sudden death in the 6- to 9-y-old age group was significantly higher in male macaques. Subtle histologic cardiac lesions included karyomegaly and increased cardiac myocyte diameter. Pedigree analyses based on rhesus macaque LVH probands suggested a strong genetic predisposition for the condition. In humans, hypertrophic cardiomyopathy (HCM) is defined by the presence of unexplained left ventricular hypertrophy, associated with diverse clinical outcomes ranging from asymptomatic disease to sudden death. Although the overall risk of disease complications such as sudden death, end-stage heart failure, and stroke is low (1% to 2%) in patients with HCM, the absolute risk can vary dramatically. Prima facie comparison of HCM and LVH suggest that further study may allow the development of spontaneously occurring LVH in rhesus macaques as a useful model of HCM, to better understand the pathogenesis of this remarkably heterogeneous disease.

Irreversible triggers for hypertrophic cardiomyopathy are established in the early postnatal period

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is caused by mutations in sarcomere protein genes, and left ventricular hypertrophy (LVH) develops as an adaptive response to sarcomere dysfunction. It remains unclear whether persistent expression of the mutant gene is required for LVH or whether early gene expression acts as an immutable inductive trigger.

OBJECTIVES

The aim of this study was to use a regulatable murine model of HCM to study the reversibility of pathological LVH.

METHODS

The authors generated a double-transgenic mouse model, tTAxαMHCR403Q, in which expression of the HCM-causing Arg403Gln mutation in the α-myosin heavy chain (MHC) gene is inhibited by doxycycline administration. Cardiac structure and function were evaluated in groups of mice that received doxycycline for varying periods from 0 to 40 weeks of age.

RESULTS

Untreated tTAxαMHCR403Q mice showed increased left ventricular (LV) mass, contractile dysfunction, myofibrillar disarray, and fibrosis. In contrast, mice treated with doxycycline from conception to 6 weeks had markedly less LVH and fibrosis at 40 weeks. Transgene inhibition from 6 weeks reduced fibrosis but did not prevent LVH or functional changes. There were no differences in LV parameters at 40 weeks between mice with transgene inhibition from 20 weeks and mice with continuous transgene expression.

CONCLUSIONS

These findings highlight the critical role of the early postnatal period in HCM pathogenesis and suggest that mutant sarcomeres manifest irreversible cardiomyocyte defects that induce LVH. In HCM, mutation-silencing therapies are likely to be ineffective for hypertrophy regression and would have to be administered very early in life to prevent hypertrophy development.

Rabbit models for the study of human atherosclerosis: from pathophysiological mechanisms to translational medicine

Laboratory animal models play an important role in the study of human diseases. Using appropriate animals is critical not only for basic research but also for the development of therapeutics and diagnostic tools. Rabbits are widely used for the study of human atherosclerosis. Because rabbits have a unique feature of lipoprotein metabolism (like humans but unlike rodents) and are sensitive to a cholesterol diet, rabbit models have not only provided many insights into the pathogenesis and development of human atherosclerosis but also made a great contribution to translational research. In fact, rabbit was the first animal model used for studying human atherosclerosis, more than a century ago. Currently, three types of rabbit model are commonly used for the study of human atherosclerosis and lipid metabolism: (1) cholesterol-fed rabbits, (2) Watanabe heritable hyperlipidemic rabbits, analogous to human familial hypercholesterolemia due to genetic deficiency of LDL receptors, and (3) genetically modified (transgenic and knock-out) rabbits. Despite their importance, compared with the mouse, the most widely used laboratory animal model nowadays, the use of rabbit models is still limited. In this review, we focus on the features of rabbit lipoprotein metabolism and pathology of atherosclerotic lesions that make it the optimal model for human atherosclerotic disease, especially for the translational medicine. For the sake of clarity, the review is not an attempt to be completely inclusive, but instead attempts to summarize substantial information concisely and provide a guideline for experiments using rabbits.

Hypertrophic cardiomyopathy: how do mutations lead to disease?

Hypertrophic cardiomyopathy (HCM) is the most common monogenic genetic cardiac disease, with an estimated prevalence of 1:500 in the general population. Clinically, HCM is characterized by hypertrophy of the left ventricle (LV) walls, especially the septum, usually asymmetric, in the absence of any cardiac or systemic disease that leads to a secondary hypertrophy. The clinical course of the disease has a large inter- and intrafamilial heterogeneity, ranging from mild symptoms of heart failure late in life to the onset of sudden cardiac death at a young age and is caused by a mutation in one of the genes that encode a protein from the sarcomere, Z-disc or intracellular calcium modulators. Although many genes and mutations are already known to cause HCM, the molecular pathways that lead to the phenotype are still unclear. This review focus on the molecular mechanisms of HCM, the pathways from mutation to clinical phenotype and how the disease's genotype correlates with phenotype.

Clinical Potentials of Cardiomyocytes Derived from Patient-Specific Induced Pluripotent Stem Cells

The lack of appropriate human cardiomyocyte-based experimental platform has largely hindered the study of cardiac diseases and the development of therapeutic strategies. To date, somatic cells isolated from human subjects can be reprogramed into induced pluripotent stem cells (iPSCs) and subsequently differentiated into functional cardiomyocytes. This powerful reprogramming technology provides a novel in vitro human cell-based platform for the study of human hereditary cardiac disorders. The clinical potential of using iPSCs derived from patients with inherited cardiac disorders for therapeutic studies have been increasingly highlighted. In this review, the standard procedures for generating patient-specific iPSCs and the latest commonly used cardiac differentiation protocols will be outlined. Furthermore, the progress and limitations of current applications of iPSCs and iPSCs-derived cardiomyocytes in cell replacement therapy, disease modeling, drug-testing and toxicology studies will be discussed in detail.

Small and large animal models in cardiac contraction research: advantages and disadvantages

The mammalian heart is responsible for not only pumping blood throughout the body but also adjusting this pumping activity quickly depending upon sudden changes in the metabolic demands of the body. For the most part, the human heart is capable of performing its duties without complications; however, throughout many decades of use, at some point this system encounters problems. Research into the heart's activities during healthy states and during adverse impacts that occur in disease states is necessary in order to strategize novel treatment options to ultimately prolong and improve patients' lives. Animal models are an important aspect of cardiac research where a variety of cardiac processes and therapeutic targets can be studied. However, there are differences between the heart of a human being and an animal and depending on the specific animal, these differences can become more pronounced and in certain cases limiting. There is no ideal animal model available for cardiac research, the use of each animal model is accompanied with its own set of advantages and disadvantages. In this review, we will discuss these advantages and disadvantages of commonly used laboratory animals including mouse, rat, rabbit, canine, swine, and sheep. Since the goal of cardiac research is to enhance our understanding of human health and disease and help improve clinical outcomes, we will also discuss the role of human cardiac tissue in cardiac research. This review will focus on the cardiac ventricular contractile and relaxation kinetics of humans and animal models in order to illustrate these differences.

Generation of knockout rabbits using transcription activator-like effector nucleases

Zinc-finger nucleases and transcription activator-like effector nucleases are novel gene-editing platforms contributing to redefine the boundaries of modern biological research. They are composed of a non-specific cleavage domain and a tailor made DNA-binding module, which enables a broad range of genetic modifications by inducing efficient DNA double-strand breaks at desired loci. Among other remarkable uses, these nucleases have been employed to produce gene knockouts in mid-size and large animals, such as rabbits and pigs, respectively. This approach is cost effective, relatively quick, and can produce invaluable models for human disease studies, biotechnology or agricultural purposes. Here we describe a protocol for the efficient generation of knockout rabbits using transcription activator-like effector nucleases, and a perspective of the field.

Genomics in cardiovascular disease

A paradigm shift toward biology occurred in the 1990s and was subsequently catalyzed by the sequencing of the human genome in 2000. The cost of deoxyribonucleic acid (DNA) sequencing has gone from millions to thousands of dollars with sequencing of one's entire genome costing only $1,000. Rapid DNA sequencing is being embraced for single gene disorders, particularly for sporadic cases and those from small families. Transmission of lethal genes such as associated with Huntington's disease can, through in vitro fertilization, avoid passing it on to one's offspring. DNA sequencing will meet the challenge of elucidating the genetic predisposition for common polygenic diseases, especially in determining the function of the novel common genetic risk variants and identifying the rare variants, which may also partially ascertain the source of the missing heritability. The challenge for DNA sequencing remains great, despite human genome sequences being 99.5% identical, the 3 million single nucleotide polymorphisms responsible for most of the unique features add up to 40 to 60 new mutations per person which, for 7 billion people, is 300 to 400 billion mutations. It is claimed that DNA sequencing has increased 10,000-fold while information storage and retrieval only 16-fold. The physician and health user will be challenged by the convergence of 2 major trends, whole genome sequencing, and the storage/retrieval and integration of the data.

Transgenic rabbit models for studying human cardiovascular diseases

Cardiovascular diseases involve the heart or blood vessels and remain a leading cause of morbidity and mortality in developed countries. A variety of animal models have been used to study cardiovascular diseases and have contributed to our understanding of their pathophysiology and treatment. However, mutations or abnormal expression of specific genes play important roles in the pathophysiology of some heart diseases, for which a closely similar animal model often is not naturally available. With the advent of techniques for specific genomic modification, several transgenic and knockout mouse models have been developed for cardiovascular conditions that result from spontaneous mutations. However, mouse and human heart show marked electrophysiologic differences. In addition, cardiac studies in mouse models are extremely difficult because of their small heart size and fast heart rate. Therefore, larger genetically engineered animal models are needed to overcome the limitations of the mouse models. This review summarizes the transgenic rabbit models that have been developed to study cardiovascular diseases.

DCM-related tropomyosin mutants E40K/E54K over-inhibit the actomyosin interaction and lead to a decrease in the number of cycling cross-bridges

Two DCM mutants (E40K and E54K) of tropomyosin (Tm) were examined using the thin-filament extraction/reconstitu­tion technique. The effects of the Ca²⁺, ATP, phos­phate (Pi), and ADP concentrations on isometric tension and its transients were studied at 25°C, and the results were com­pared to those for the WT protein. Our results indicate that both E40K and E54K have a significantly lower T_HC (high Ca²⁺ ten­sion at pCa 4.66) (E40K: 1.21±0.06 T_a, ±SEM, N = 34; E54K: 1.24±0.07 T_a, N = 28), a significantly lower T_LC (low- Ca²⁺ tension at pCa 7.0) (E40K: 0.07±0.02 T_a, N = 34; E54K: 0.06±0.02 T_a, N = 28), and a significantly lower T_act (Ca²⁺ activatable tension) (T_act = T_HC–T_LC, E40K: 1.15±0.08 T_a, N = 34; E54K: 1.18±0.06 T_a, N = 28) than WT (T_HC = 1.53±0.07 T_a, T_LC = 0.12±0.01 T_a, T_act = 1.40±0.07 T_a, N = 25). All tensions were normalized to T_a ( = 13.9±0.8 kPa, N = 57), the ten­sion of actin-filament reconstituted cardiac fibers (myocardium) under the standard activating conditions. The Ca²⁺ sensitivity (pCa₅₀) of E40K (5.23±0.02, N = 34) and E54K (5.24±0.03, N = 28) was similar to that of the WT protein (5.26±0.03, N = 25). The cooper­a­tivity increased significantly in E54K (3.73±0.25, N = 28) compared to WT (2.80±0.17, N = 25). Seven kinetic constants were deduced using sinusoidal analysis at pCa 4.66. These results enabled us to calculate the cross-bridge distribution in the strongly attached states, and thereby deduce the force/cross-bridge. The results indicate that the force/cross-bridge is ∼15% less in E54K than WT, but remains similar to that of the WT protein in the case of E40K. We conclude that over-inhibition of the actomyosin interaction by E40K and E54K Tm mutants leads to a decreased force-generating ability at systole, which is the main mechanism underlying the early pathogenesis of DCM.

A novel, minimally invasive, segmental myocardial infarction with a clear healed infarct borderzone in rabbits

Ventricular arrhythmias in the setting of a healed myocardial infarction have been studied to a much lesser degree than acute and subacute infarction, due to the pericardial scarring, which results from the traditional open-chest techniques used for myocardial infarction (MI) induction. We sought to develop a segmental MI with low perioperative mortality in the rabbit that allows optimal visualization and therefore improved study of the infarction borderzone. Rabbits underwent MI using endovascular coil occlusion of the first obtuse marginal artery. Three weeks postprocedure, we evaluated our model by echocardiography and electrophysiology studies, optical mapping of isolated hearts, and histological studies. Seventeen rabbits underwent the protocol (12 MI and 5 sham) with a 92% survival to completion of the study (11 MI and 5 sham). MI rabbits demonstrated wall motion abnormalities on echocardiography while shams did not. At electrophysiological study, two MI rabbits had inducible ventricular tachycardia and one had inducible ventricular fibrillation. Isolated hearts demonstrated no pericardial scarring with a smooth, easily identifiable infarct borderzone. Optical mapping of the borderzone region showed successful mapping of peri-infarct reentry formation, with ventricular fibrillation inducible in 11 of 11 MI hearts and 1 of 5 sham hearts. We demonstrate successful high resolution mapping in the borderzone, showing delayed conduction in this region corresponding to late deflections in the QRS on ECG. We report the successful development of a minimally invasive MI via targeted coil delivery to the obtuse marginal artery with an exceptionally high rate of procedural survival and an arrhythmogenic phenotype. This model mimics human post-MI on echocardiography, gross pathology, histology, and electrophysiology.

Therapeutic potential of c-Myc inhibition in the treatment of hypertrophic cardiomyopathy

Investigating the pathophysiological importance of the molecular and mechanical development of cardiomyopathy is critical to find new and broader means of protection against this disease that is increasing in prevalence and impact. The current available treatment options for cardiomyopathy mainly focus on treating symptoms and strive to make the patient more comfortable while preventing progression of disease and sudden death. The proto-oncogene c-Myc (Myc) has been shown to be increased in many different types of heart disease, including hypertrophic cardiomyopathy, before any signs of the disease are present. As the mechanisms of action and multiple pathways of dependent actions of Myc are being dissected by many research groups, inhibition of Myc is becoming an attractive paradigm for prevention and treatment of cardiomyopathy and heart failure. Elucidating the role Myc plays in the development, propagation and perpetuation of cardiomyopathy and heart failure will one day translate into potential therapeutics for cardiomyopathy.

Molecular biology of heart disease

Dr. Robert Roberts is currently Professor of Medicine and Director of the Ruddy Canadian Cardiovascular Genetics Centre along with being President and CEO of the University of Ottawa Heart Institute. Prior to this appointment, he was Chief of Cardiology for 23 years at Baylor College of Medicine, Houston, Texas. His original research was in cardiac enzymology which led to the development of the MBCK test which was the standard diagnostic assay for myocardial infarction for more than 3 decades. In the late 1970s, his research interests switched to molecular biology and the genetics of cardiomyopathies. He is regarded as one of the founders of molecular cardiology and has identified and sequenced more than 20 genes responsible for cardiovascular disorders. In the past 6 years, he has pursued genome-wide association studies to identify genes predisposing to coronary artery disease (CAD) and myocardial infarction. The first genetic variant for CAD, 9p21, was identified by Dr. Robert's laboratory and, in collaboration with the international consortium, CARDIoGRAM, has identified 13 novel genes for CAD.

Animal model of ascending aortic stenosis in rabbits without endotracheal intubation

BACKGROUND AND AIM

Experimental animal studies of left ventricular hypertrophy (LVH) usually involve endotracheal intubation, which is associated with a risk of serious tracheal injury and other significant negative sequelae. We developed an animal model of pressure overload hypertrophy caused by constriction of the ascending aorta in rabbits that does not require endotracheal intubation.

METHODS

New Zealand White rabbits of either sex (1.94 +/- 0.12 kg) were randomly assigned to the aortic banding (AB) group (n = 9) and the sham-operated group (n = 8). The sternum was carefully incised along the midline to avoid injury to the parietal pleura. Then, the intervention group underwent AB with three to zero Prolene proximal to the innominate artery without endotracheal intubation. To investigate the effects of the surgical procedure on physiological parameters, echocardiography, histology, and electron microscopy were performed to assess functional and structural hypertrophy at various time intervals.

RESULTS

Banding of the ascending aorta created the expected increases in both aortic velocity and the pressure gradient between proximal and distal aorta coarctation. The pressure overload resulted in a robust LVH assessed by transthoracic echocardiography and histology. The animals did not experience severe mechanical ventilatory impairment.

CONCLUSION

We developed a safe, efficient, and reproducible method of producing LVH in rabbits without the need for endotracheal intubation and mechanical ventilation. Ultimately, this model will facilitate focused study of the mechanisms involved with LVH progression.

Narrative review: harnessing molecular genetics for the diagnosis and management of hypertrophic cardiomyopathy

Unexplained cardiac hypertrophy, the diagnostic criterion for hypertrophic cardiomyopathy (HCM), occurs in 1 in 500 adults. Insights into the genetic cause and molecular pathophysiology of HCM are reshaping clinical paradigms for diagnosis and treatment of this common myocardial disorder. Human genetic studies have established that dominant mutations in the proteins that make up the contractile apparatus (the sarcomere) cause HCM. With the current availability of clinical gene-based diagnostics, pathogenic mutations in affected patients can be defined, which can suggest a clinical course and allow definitive preclinical identification of family members at risk for HCM. Genetic discoveries have also fostered mechanistic investigations in model organisms that are engineered to carry human HCM mutations. Novel therapeutic targets have emerged from these fundamental studies and are currently under clinical assessment in humans. The combination of contemporary gene-based diagnosis with new strategies to attenuate disease development and progression is changing the natural history of lifelong cardiac symptoms, arrhythmias, and heart failure from HCM.