Hypertrophic cardiomyopathy in man and cats

Feline hypertrophic cardiomyopathy: Does the microRNA-mRNA regulatory network contribute to heart sarcomeric protein remodelling?

Feline primary hypertrophic cardiomyopathy (HCM) is an intrinsic myocardial disease characterized by concentric hypertrophy of the left ventricle. In the present study, we investigated the microRNA-mRNA regulatory network in feline myocardial tissue affected by primary (HCMI) and secondary HCM (HCMII). MRNA expression levels of sarcomeric genes, including, TNNT2, TNNI3, MYH7, MYBPC3, TPM1 and ACTC1 were assessed in the FFPE myocardial tissues. FFPE tissues from healthy cats were sequenced by the NGS, to explore, in the entire non-deposited miRNome, the expression level of microRNAs targeting the complementary sequences of selected sarcomeric mRNAs. The sarcomeric genes TNNT2, MYH7, MYBPC3 and TPM1 showed a statistically significant upregulation in HCMI compared to HCMII (p < .01), except ACTC1 which was downregulated (p < .01); TNNI3 showed no statistically significant difference. In HCMII miR-122-5p, miR-338-3p, miR-484, miR-370-3p, miR-92b-3p, miR-375 and miR-370-3p showed a significant upregulation (p < .01) compared to control. The exception was miR-30a-5p which showed downregulation. Worthy of note is the 4-fold higher expression of miR-370-3p, a key regulator of MYBPC3, in HMCI compared to HMCII. This research does not solve the aetiological mystery of HCM, but it may help to find a way to help diagnose and define the prognosis of HCM in cats.

The Unseen Side of Feline Hypertrophic Cardiomyopathy: Diagnostic and Prognostic Utility of Electrocardiography and Holter Monitoring

Hypertrophic cardiomyopathy (HCM) is a common heart disease in cats, characterized by regional or diffuse hypertrophy of the left ventricular walls, with an uncertain etiology and heterogenous natural history. Several types of rhythm disturbances are often associated with the disease. This study conducts a comprehensive review of the current literature, in order to evaluate the diagnostic and prognostic effectiveness of electrocardiography and Holter monitoring in the management of feline hypertrophic cardiomyopathy. The main subjects of discussion will include general information about HCM and its connection to arrhythmias. We will explore the rhythm disturbances documented in the current literature on Holter monitoring, as well as the techniques used for Holter monitoring. Additionally, the review will cover classical electrocardiography (ECG) and its diagnostic utility. Prognostic indicators and anti-arrhythmic therapy will also be discussed in detail. The findings highlight the importance of understanding arrhythmias in feline HCM for accurate diagnosis, risk assessment, and therapeutic intervention. ECG and Holter monitoring may offer valuable insights into managing feline HCM.

Classification of feline hypertrophic cardiomyopathy-associated gene variants according to the American College of Medical Genetics and Genomics guidelines

Introduction

The correct labeling of a genetic variant as pathogenic is important as breeding decisions based on incorrect DNA tests can lead to the unwarranted exclusion of animals, potentially compromising the long-term health of a population. In human medicine, the American college of Medical Genetics (ACMG) guidelines provide a framework for variant classification. This study aims to apply these guidelines to six genetic variants associated with hypertrophic cardiomyopathy (HCM) in certain cat breeds and to propose a modified criterion for variant classification.

Methods

Genetic samples were sourced from five cat breeds: Maine Coon, Sphynx, Ragdoll, Devon Rex, and British Short- and Longhair. Allele frequencies were determined, and in the subset with phenotypes available, odds ratios to determine the association with HCM were calculated. In silico evaluation followed with joint evidence and data from other publications assisting in the classification of each variant.

Results

Two variants, MYBPC3:c.91G > C [A31P] and MYBPC3:c.2453C > T [R818W], were designated as pathogenic. One variant, MYH7:c.5647G > A [E1883K], was found likely pathogenic, while the remaining three were labeled as variants of unknown significance.

Discussion

Routine genetic testing is advised solely for the MYBPC3:c.91G > C [A31P] in the Maine Coon and MYBPC3:c.2453C > T [R818W] in the Ragdoll breed. The human ACMG guidelines serve as a suitable foundational tool to ascertain which variants to include; however, refining them for application in veterinary medicine might be beneficial.

Exploration of Mediators Associated with Myocardial Remodelling in Feline Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) affects both humans and cats and exhibits considerable interspecies similarities that are exemplified by underlying pathological processes and clinical presentation to the extent that developments in the human field may have direct relevance to the feline disease. Characteristic changes on histological examination include cardiomyocyte hypertrophy and interstitial and replacement fibrosis. Clinically, HCM is characterised by significant diastolic dysfunction due to a reduction in ventricular compliance and relaxation associated with extracellular matrix (ECM) remodelling and the development of ventricular hypertrophy. Studies in rodent models and human HCM patients have identified key protein mediators implicated in these pathological changes, including lumican, lysyl oxidase and TGF-β isoforms. We therefore sought to quantify and describe the cellular location of these mediators in the left ventricular myocardium of cats with HCM and investigate their relationship with the quantity and structural composition of the ECM. We identified increased myocardial content of lumican, LOX and TGF-β2 mainly attributed to their increased expression within cardiomyocytes in HCM cats compared to control cats. Furthermore, we found strong correlations between the expressions of these mediators that is compatible with their role as important components of cellular pathways promoting remodelling of the left ventricular myocardium. Fibrosis and hypertrophy are important pathological changes in feline HCM, and a greater understanding of the mechanisms driving this pathology may facilitate the identification of potential therapies.

Hypertrophic cardiomyopathy in purpose-bred cats with the A31P mutation in cardiac myosin binding protein-C

We sought to establish a large animal model of inherited hypertrophic cardiomyopathy (HCM) with sufficient disease severity and early penetrance for identification of novel therapeutic strategies. HCM is the most common inherited cardiac disorder affecting 1 in 250-500 people, yet few therapies for its treatment or prevention are available. A research colony of purpose-bred cats carrying the A31P mutation in MYBPC3 was founded using sperm from a single heterozygous male cat. Cardiac function in four generations was assessed by periodic echocardiography and measurement of blood biomarkers. Results showed that HCM penetrance was age-dependent, and that penetrance occurred earlier and was more severe in successive generations, especially in homozygotes. Homozygosity was also associated with progression from preclinical to clinical disease. A31P homozygous cats represent a heritable model of HCM with early disease penetrance and a severe phenotype necessary for interventional studies aimed at altering disease progression. The occurrence of a more severe phenotype in later generations of cats, and the occasional occurrence of HCM in wildtype cats suggests the presence of at least one gene modifier or a second causal variant in this research colony that exacerbates the HCM phenotype when inherited in combination with the A31P mutation.

Induced pluripotent stem cells in companion animals: how can we move the field forward?

Following a one medicine approach, the development of regenerative therapies for human patients leads to innovative treatments for animals, while pre-clinical studies on animals provide knowledge to advance human medicine. Among many different biological products under investigation, stem cells are among the most prominent. Mesenchymal stromal cells (MSCs) are extensively investigated, but they present challenges such as senescence and limited differentiation ability. Embryonic stem cells (ESCs) are pluripotent cells with a virtually unlimited capacity for self-renewal and differentiation, but the use of embryos carries ethical concerns. Induced pluripotent stem cells (iPSCs) can overcome all of these limitations, as they closely resemble ESCs but are derived from adult cells by reprogramming in the laboratory using pluripotency-associated transcription factors. iPSCs hold great potential for applications in therapy, disease modeling, drug screening, and even species preservation strategies. However, iPSC technology is less developed in veterinary species compared to human. This review attempts to address the specific challenges associated with generating and applying iPSCs from companion animals. Firstly, we discuss strategies for the preparation of iPSCs in veterinary species and secondly, we address the potential for different applications of iPSCs in companion animals. Our aim is to provide an overview on the state of the art of iPSCs in companion animals, focusing on equine, canine, and feline species, as well as to identify which aspects need further optimization and, where possible, to provide guidance on future advancements. Following a "step-by-step" approach, we cover the generation of iPSCs in companion animals from the selection of somatic cells and the reprogramming strategies, to the expansion and characterization of iPSCs. Subsequently, we revise the current applications of iPSCs in companion animals, identify the main hurdles, and propose future paths to move the field forward. Transferring the knowledge gained from human iPSCs can increase our understanding in the biology of pluripotent cells in animals, but it is critical to further investigate the differences among species to develop specific approaches for animal iPSCs. This is key for significantly advancing iPSC application in veterinary medicine, which at the same time will also allow gaining pre-clinical knowledge transferable to human medicine.

QT interval instability and QRS interval dispersion in healthy cats and cats with a hypertrophic cardiomyopathy phenotype

OBJECTIVES

Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats. Electrocardiographic (ECG) analysis can help with the diagnosis of HCM and also in the investigation of the secondary consequences of the disease. This study investigated ECG markers of QT interval variability (total instability [TI], short-term instability [STI], long-term instability [LTI], QT variance [QTv]), mean QT interval (QTa) and QT interval corrected for heart rate (QTac), as well as the duration (QRSd) and dispersion (QRSv) of the QRS interval in healthy cats and in those with HCM.

METHODS

Data were collected from 63 domestic cats: 40 in the control group and 23 in the HCM group. Fifty consecutive QT intervals were recorded for all cats and then QTa, QTac, QTv, TI, LTI and STI were calculated. QRSd and QRSv were also obtained for all animals. A Mann-Whitney U-test was used for group comparison. Receiver operating characteristic curves were plotted to evaluate the sensitivity and specificity of all markers for HCM. Logistic regression analysis was performed to assess the risks of cats having HCM, based on the studied indexes.

RESULTS

QTa (P <0.01), QTac (P <0.01), QRSd (P <0.01) and STI (P = 0.02) were higher in the HCM group. QTa >158.8 ms, QTac >27.4 ms and QRSd >0.045 s had an accuracy of 77.4%, 68.2% and 80.9%, respectively, in detecting HCM. Logistic regression showed that cats with QTa >158 ms, QTac >27.4 ms and QRSd >0.045 s had a 1.58-, 1,23- and 6.5-fold higher risk, respectively, of developing HCM.

CONCLUSIONS AND RELEVANCE

Cats with HCM had higher ventricular instability as assessed by STI and showed a prolongation of the QT and QRS intervals via the QTa, QTac and QRSd markers. These markers show potential as ancillary screening tools for identifying the presence of HCM.

Pharmacokinetics of a single dose of Aficamten (CK-274) on cardiac contractility in a A31P MYBPC3 hypertrophic cardiomyopathy cat model

Hypertrophic cardiomyopathy (HCM) is the most prevalent cardiac disease in cats and lacks efficacious preclinical pharmacologic intervention, prompting investigation of novel therapies. Genetic mutations encoding sarcomeric proteins are implicated in the development of HCM and small molecule myosin inhibitors are an emerging class of therapeutics designed to target the interaction of actin and myosin to alleviate the detrimental effects of inappropriate contractile protein interactions. The purpose of this study was to characterize the pharmacodynamic effects of a single oral dose of the novel cardiac myosin inhibitor aficamten (CK-274) on cardiac function in purpose bred cats with naturally occurring A31P MYBPC3 mutation and a clinical diagnosis of HCM with left ventricular outflow tract obstruction (LVOTO). Five purpose bred cats were treated with aficamten (2 mg/kg) or vehicle and echocardiographic evaluations were performed at 0, 6, 24, and 48 h post-dosing. High dose aficamten (2 mg/kg) reduced left ventricular fractional shortening (LVFS%) by increasing the LV systolic internal dimension (LVIDs) and reduced isovolumic relaxation time (IVRT) compared with baseline without significant adverse effects. The marked reduction in systolic function and reduced IVRT coupled with an increased heart rate in treated cats, suggest a lower dose may be optimal. Further studies to determine optimal dosing of aficamten are indicated.

Feline myocardial transcriptome in health and in hypertrophic cardiomyopathy-A translational animal model for human disease

Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats, characterized by primary left ventricular hypertrophy. Feline HCM closely resembles human HCM and is suggested as translational animal model for the human disease. A genetic cause is established in humans and suspected for cats, but little is known about the gene expression and pathways involved in the pathogenesis of HCM. To investigate the myocardial transcriptome changes in HCM, RNA sequencing was conducted on left ventricle (LV) and left atrium (LA) samples of healthy cats and cats with HCM (each n = 5; 20 samples). Ingenuity Pathway Analysis was used to determine functional pathways, regulators, and networks. Distinct gene expression profiles were identified in the LV and LA of the feline healthy and HCM myocardium. Analysis of differentially expressed mRNAs (>2 fold; FDR < 0.01) found chamber-specific (LV vs. LA) expression in both healthy and HCM groups, with higher transcriptional activity in the LA. Genes that contribute to the distinct structure and function of each chamber in health and HCM were identified in the regional comparison. The gene expression profiles of HCM compared to healthy hearts revealed disease related genes, including THBS4 and KLHL33 (LV), FAM177B and THRSP (LA), the latter 3 have not been reported for the myocardium so far, as the top differently expressed genes in the HCM heart. Differently expressed genes and functional pathways found in the HCM heart are associated with cardiac remodeling and fibrosis, inflammation, microvascular changes, calcium signaling and cardiac metabolism, with some regional differences. RhoGDI-RhoGTPase signaling, integrin and ILK signaling pathways, the LXR/RXR pathway in the LA, and the PPARα/RXRα, HIF1α and CXCR4 pathways in the LV might be of particular importance in the HCM disease process. This study identified region-specific myocardial gene transcription patterns as well as novel genes and pathways associated with HCM.

Bacterial Cellulose and ECM Hydrogels: An Innovative Approach for Cardiovascular Regenerative Medicine

Cardiovascular diseases are considered the leading cause of death in the world, accounting for approximately 85% of sudden death cases. In dogs and cats, sudden cardiac death occurs commonly, despite the scarcity of available pathophysiological and prevalence data. Conventional treatments are not able to treat injured myocardium. Despite advances in cardiac therapy in recent decades, transplantation remains the gold standard treatment for most heart diseases in humans. In veterinary medicine, therapy seeks to control clinical signs, delay the evolution of the disease and provide a better quality of life, although transplantation is the ideal treatment. Both human and veterinary medicine face major challenges regarding the transplantation process, although each area presents different realities. In this context, it is necessary to search for alternative methods that overcome the recovery deficiency of injured myocardial tissue. Application of biomaterials is one of the most innovative treatments for heart regeneration, involving the use of hydrogels from decellularized extracellular matrix, and their association with nanomaterials, such as alginate, chitosan, hyaluronic acid and gelatin. A promising material is bacterial cellulose hydrogel, due to its nanostructure and morphology being similar to collagen. Cellulose provides support and immobilization of cells, which can result in better cell adhesion, growth and proliferation, making it a safe and innovative material for cardiovascular repair.

Heart rhythm characterization during sudden cardiac death in dogs

INTRODUCTION/OBJECTIVES

Inherited or acquired arrhythmic disorders and cardiac disease have been associated with sudden cardiac death (SCD) in dogs. The electrical mechanism related to death in most of these cases is unknown. This retrospective study aimed to describe arrhythmic events in dogs that experienced SCD during Holter monitoring.

ANIMALS, MATERIALS AND METHODS

Nineteen client-owned dogs that experienced SCD during Holter examination were included. Clinical records from a Holter service database were reviewed, and both the rhythm preceding death and the dominant rhythm causing SCD were analysed. Clinical data, Holter diaries and echocardiographic diagnosis were also evaluated.

RESULTS

Structural heart disease was identified in 12/19 dogs (dilated cardiomyopathy in five dogs, arrhythmogenic right ventricular cardiomyopathy in four dogs, myxomatous mitral valve disease in two dogs, and suspected myocarditis in one dog), five of which had concurrent congestive heart failure. Sudden cardiac death was related to ventricular premature complexes or monomorphic ventricular tachycardia degenerating into ventricular fibrillation in 42% of dogs, polymorphic ventricular tachycardia, or torsade de pointes-like inducing ventricular fibrillation in 21%, and asystole or presumptive agonal pulseless electrical activity triggered by malignant bradyarrhythmias in 37%.

CONCLUSIONS

The most common rhythm associated with SCD in our population of dogs was ventricular tachycardia leading to ventricular fibrillation, although bradyarrhythmia-related SCD, possibly related to inappropriate vagal reflexes, was also a notable cause.

Sudden cardiac death: A comparative review of humans, dogs and cats

Sudden death is one of the most common causes of death in humans in Western countries. Approximately 85% of these cases are of cardiac origin. In dogs and cats, sudden cardiac death (SCD) also commonly occurs, but fewer pathophysiological and prevalence data are available. Both structural, primarily 'electrical' and ischemic heart diseases are known to cause SCD, many of which share similar underlying arrhythmogenic mechanisms between humans and companion animals. As for underlying genetics, numerous mutations on multiple loci have been related to SCD in humans, but only a few mutations associated with dilated cardiomyopathy and SCD have been identified in dogs, e.g. in the phospholamban and titin genes. Information published from human medicine can therefore inform future veterinary studies, but also dogs and cats could act as spontaneous models of SCD in humans. Further research in both fields is therefore warranted to better understand the pathophysiology, genetics, and prevention of SCD.

Cardiomyopathy Associated With Coronary Arteriosclerosis in Free-Ranging Eurasian Lynx (Lynx lynx carpathicus)

The Eurasian lynx (subspecies Lynx lynx carpathicus) was reintroduced to Switzerland in the 1970's. Health monitoring of the reintroduced population started in the late 1980's. Since then, six lynx have been found affected by a myocardial disease. The earliest case was an animal that died after a field anesthesia. Two lynx were found dead, two were euthanized/culled because of disease signs, and one was hit by car. Two had a heart murmur at clinical examination. At necropsy, the first animal showed only lung edema but the other five had cardiomegaly associated with myocardial fibrosis. Three had multisystemic effusions. Histological examination of all six lynx showed mild to severe, multifocal, myocardial interstitial and perivascular fibrosis along with multifocal myocyte degeneration and loss, and replacement fibrosis. Moderate to severe multifocal arteriosclerosis with associated luminal stenosis of the small and medium-sized intramural coronary arteries and the presence of Anitschkow cells was also observed. The heart lesions may have led to sudden death in the first case and to a chronic right-sided heart failure in the remaining. None of the lynx showed lesions or signs suggestive of an acute or subacute infection. Given the common geographic origin of these animals and the severe loss of heterozygocity in this population, a genetic origin of the disease is hypothesized.

Association of diet with left ventricular wall thickness, troponin I and IGF-1 in cats with subclinical hypertrophic cardiomyopathy

BACKGROUND

Cats with subclinical hypertrophic cardiomyopathy (sHCM) have elevated serum insulin and serum amyloid A concentrations correlating with the degree of cardiac hypertrophy. Diet might affect these and other cardiac variables.

OBJECTIVE

Evaluate the effect of a complete, balanced diet with restricted starch and supplemented with eicosapentaenoic acid + docosahexaenoic acid (EPA + DHA) on echocardiographic variables and cardiac biomarkers in cats with sHCM.

ANIMALS

Forty-four client-owned cats with sHCM.

METHODS

A prospective, randomized, double-blind, multicenter study enrolled cats with end-diastole interventricular septum thickness (IVSd) or left ventricular wall thickness (LVWd) ≥6 mm, or both. Nonsedated, fasted cats were examined at baseline and after 6 and 12 months of Test (restricted starch and EPA + DHA supplements) (n = 23) or Control (unrestricted starch without EPA + DHA supplementation) (n = 21) diet. Assessments included auscultation, body weight, body condition score, echocardiography and blood analysis. Linear and generalized mixed models analyzed diet, time and diet * time interactions (5% significance level).

RESULTS

No differences between diet groups were significant for any variable at any timepoint. There were significant decreases in the Test but not Control group in maximum IVSd (P = .03), maximum LVWd (P = .02) and insulin-like growth factor-1 levels (P = .04) after 12 months, and in ultrasensitive cardiac troponin I (cTnI) (P = .001) after 6 months; effect sizes (95% confidence interval) were 0.53 (0.09; 0.99), 0.63 (0.18; 1.09), 0.61 (0.16; 1.07), and 0.37 (-0.06; 0.8), respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

Cats with sHCM fed Test diet had significant decreases in echocardiographic variables of sHCM and in cTnI and IGF-1.

Large Animal Models in Regenerative Medicine and Tissue Engineering: To Do or Not to Do

Rapid developments in Regenerative Medicine and Tissue Engineering has witnessed an increasing drive toward clinical translation of breakthrough technologies. However, the progression of promising preclinical data to achieve successful clinical market authorisation remains a bottleneck. One hurdle for progress to the clinic is the transition from small animal research to advanced preclinical studies in large animals to test safety and efficacy of products. Notwithstanding this, to draw meaningful and reliable conclusions from animal experiments it is critical that the species and disease model of choice is relevant to answer the research question as well as the clinical problem. Selecting the most appropriate animal model requires in-depth knowledge of specific species and breeds to ascertain the adequacy of the model and outcome measures that closely mirror the clinical situation. Traditional reductionist approaches in animal experiments, which often do not sufficiently reflect the studied disease, are still the norm and can result in a disconnect in outcomes observed between animal studies and clinical trials. To address these concerns a reconsideration in approach will be required. This should include a stepwise approach using in vitro and ex vivo experiments as well as in silico modeling to minimize the need for in vivo studies for screening and early development studies, followed by large animal models which more closely resemble human disease. Naturally occurring, or spontaneous diseases in large animals remain a largely untapped resource, and given the similarities in pathophysiology to humans they not only allow for studying new treatment strategies but also disease etiology and prevention. Naturally occurring disease models, particularly for longer lived large animal species, allow for studying disorders at an age when the disease is most prevalent. As these diseases are usually also a concern in the chosen veterinary species they would be beneficiaries of newly developed therapies. Improved awareness of the progress in animal models is mutually beneficial for animals, researchers, human and veterinary patients. In this overview we describe advantages and disadvantages of various animal models including domesticated and companion animals used in regenerative medicine and tissue engineering to provide an informed choice of disease-relevant animal models.

Genetics of feline hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is characterized by an abnormal increase in myocardial mass that affects cardiac structure and function. HCM is the most common inherited cardiovascular disease in humans (0.2%) and the most common cardiovascular disease in cats (14.7%). Feline HCM phenotype is very similar to the phenotype found in humans, but the time frame for the development of the disease is significantly shorter. Similar therapeutic agents are used in its treatment and it has the same complications, such as heart failure, thromboembolism and sudden cardiac death. In contrast to humans, in whom thousands of genetic variants have been identified, genetic studies in cats have been limited to fragment analysis of two sarcomeric genes identifying two variants in MYBPC3 and one in MYH7. Two of these variants have also been associated with human disease. The high prevalence of the reported variants in non-affected cats hinders the assumption of their pathogenicity in heterozygotes. An in-depth review of the literature about genetic studies on feline HCM in comparison with the same disease in humans is presented here. The close similarity in the phenotype and genotype between cats and humans makes the cat an excellent model for the pathophysiological study of the disease and future therapeutic agents.

Plasma growth differentiation factors 8 and 11 levels in cats with congestive heart failure secondary to hypertrophic cardiomyopathy

OBJECTIVES

Growth differentiation factor (GDF) 11 has been shown to reduce cardiac hypertrophy in mice. Low levels of GDF-11 are associated with cardiac hypertrophy in humans. The authors hypothesized that plasma GDF-11 level is decreased in cats with hypertrophic cardiomyopathy (HCM). Given the close homology between GDF-11 and myostatin/GDF-8, GDF-8 levels were also assessed.

ANIMALS

Thirty-seven client-owned cats were enrolled, including cats with normal cardiac structure (n = 16), cats with HCM or hypertrophic obstructive cardiomyopathy (HOCM; n = 14), and cats with HCM and congestive heart failure (CHF; n = 7).

METHODS

Plasma samples were analyzed for GDF-8 and GDF-11 using liquid chromatography tandem-mass spectrometry. Levels of GDF-8 and GDF-11 were compared between cats with normal cardiac structure, HCM or HOCM, and CHF.

RESULTS

No differences in GDF-11 concentrations were found between cats with normal cardiac structure and cats with HCM/HOCM, with or without history of CHF. Decreased GDF-8 concentrations were detected in cats with CHF compared to cats with HCM/HOCM without history of CHF (p=0.031) and cats with normal cardiac structure (p=0.027). Growth differentiation factor 8 was higher in cats with HOCM compared to those with CHF (p=0.002). No statistical difference was noted in GDF-8 level as a function of age, weight, or body condition score.

CONCLUSIONS

Plasma GDF-11 was not different between cats with HCM/HOCM and cats with normal cardiac structure regardless of age. Plasma GDF-8 was decreased in cats with CHF compared to cats with normal cardiac structure and cats with asymptomatic HCM/HOCM, suggesting a possible role in CHF development.

Inducing Pluripotency in the Domestic Cat (Felis catus)

Domestic cats suffer from a range of inherited genetic diseases, many of which display similarities with equivalent human conditions. Developing cellular models for these inherited diseases would enable drug discovery, benefiting feline health and welfare as well as enhancing the potential of cats as relevant animal models for translation to human medicine. Advances in our understanding of these diseases at the cellular level have come from the use of induced pluripotent stem cells (iPSCs). iPSCs can differentiate into virtually any cell type and can be derived from adult somatic cells, therefore overcoming the ethical implications of destroying embryos to obtain embryonic stem cells. No studies, however, report the generation of iPSCs from domestic cats [feline iPSCs (fiPSCs)]. Feline adipose-derived fibroblasts were infected with amphotropic retrovirus containing the coding sequences for human Oct4, Sox2, Klf4, cMyc, and Nanog. Isolated iPSC clones were expanded on inactivated mouse embryonic fibroblasts in the presence of feline leukemia inhibitory factor (fLIF). Retroviral delivery of human pluripotent genes gave rise to putative fiPSC colonies within 5-7 days. These iPS-like cells required fetal bovine serum and fLIF for maintenance. Colonies were domed with refractile edges, similar to mouse iPSCs. Immunocytochemistry demonstrated positive staining for stem cell markers: alkaline phosphatase, Oct4, Sox2, Nanog, and SSEA1. Cells were negative for SSEA4. Expression of endogenous feline Nanog was confirmed by quantitative polymerase chain reaction. The cells were able to differentiate in vitro into cells representative of the three germ layers. These results confirm the first generation of induced pluripotent stem cells from domestic cats. These cells will provide valuable models to study genetic diseases and explore novel therapeutic strategies.

A feline orthologue of the human MYH7 c.5647G>A (p.(Glu1883Lys)) variant causes hypertrophic cardiomyopathy in a Domestic Shorthair cat

Hypertrophic cardiomyopathy (HCM) is the most common inherited human heart disease. The same disease has a high prevalence in cats, where it is also suspected to be inherited. More than 1500 variants in MYBPC3, MYH7 and other sarcomeric genes are associated with human HCM, while in cats, only two causative variants in MYBPC3 are currently known. Here, we describe an adult Domestic Shorthair cat with arterial thromboembolism and heart failure that was diagnosed with HCM on necropsy. Sequencing of the coding regions of MYBPC3 and MYH7 revealed 21 variants, of which the MYH7 c.5647G>A (p.(Glu1883Lys)) variant was further analysed, because its orthologous variant had already been reported in a human patient with HCM, but with limited causal evidence. This variant affects the highly conserved assembly competence domain, is predicted in silico to be damaging and was found only once in population databases. Recently, functional studies have confirmed its predicted damaging effect and a paralogous variant in MYH6 has been associated with cardiac disease in humans as well. This report of an orthologous variant in a cat with HCM and its absence in 200 additional cats provides further evidence for its disease-causing nature. As the first report of feline HCM caused by a variant in MYH7, this study also emphasises this gene as a candidate gene for future studies in cats and highlights the similarity between human and feline HCM.

Left atrial size and volume in cats with primary cardiomyopathy with and without congestive heart failure

INTRODUCTION/OBJECTIVES

Myocardial diseases are the most common acquired cardiac diseases in cats and may result in left atrial enlargement and congestive heart failure (CHF). Volume calculations have replaced linear measurements for chamber quantification in humans but are not commonly measured in cats. The aims of this retrospective study were to compare the left atrial (LA) size by two-dimensional linear measurements to two-dimensional LA volumes (LAV).

ANIMALS

One hundred sixty-two client-owned cats were included.

MATERIALS AND METHODS

Cats with complete echocardiographic examinations were included and categorized into one of the three groups: healthy, cardiomyopathy (CM), and CHF. Seven measurements of the LA size were performed including minimal and maximal LA-to-aortic ratio (LA:Ao) and LAV and also maximal left atrial diameter (LAD).

RESULTS

Cats were classified as healthy (n = 56), CM (n = 62), and CHF (n = 44). The minimal LA:Ao (LA:Ao_min) and minimal LAV from the left apical view (LAV_min-LAP) best differentiated the CM and CHF groups. The LA:Ao_min value with the optimal sensitivity and specificity to distinguish CM and CHF cats was 1.64 (sensitivity 84% and specificity 75%).

CONCLUSIONS

Left atrial volumes were not superior to linear measurements of LA size in distinguishing CM and CHF cats in this study. Minimal LA size and volumes resulted in a larger area under the curve than each corresponding maximal value. Minimum LA size may be a better prognostic factor of CHF in cats with CM.

Holter monitoring demonstrates that ventricular arrhythmias are common in cats with decompensated and compensated hypertrophic cardiomyopathy

Arrhythmias can complicate cardiac disease in cats and are a potential cause of sudden death. The aim of this study was to evaluate the presence and nature of cardiac arrhythmias, and the potential correlation between plasma serum troponin I (cTnI) concentrations and the presence or severity of arrhythmias in cats with decompensated (dHCM) and compensated hypertrophic cardiomyopathy (cHCM). Forty one client-owned cats were studied: 16 with cHCM, 15 with dHCM and 10 healthy control cats. Physical examination, echocardiography, cTnI and 24-h Holter recordings were obtained in all cats and thoracic radiographs in cats with dHCM. Cats in both HCM groups were followed for 1 year after their initial Holter examination. The median (range) number of ventricular premature complexes (VPCs) over 24h was 867 (1-35,160) in cats with dHCM, 431 (0-18,919) in cats with cHCM and 2 (0-13) in healthy control cats. The median number of episodes of ventricular tachycardia (VTach) was 0 (0-1497) in dHCM and 0.5 (0-91) in cats with cHCM. The number of VPCs, VTach episodes and heart rate was not different between the HCM groups. Plasma serum troponin I was highest in the cats with dHCM, but there was no correlation between cTnI concentration and the number of arrhythmias. Thirteen of 31 cats with HCM died, but an association with the presence and complexity of ventricular arrhythmias was not observed. Compared to healthy cats, ventricular arrhythmias were common in cats with cHCM and dHCM, but neither presence nor complexity of arrhythmias could be linked to prognosis.

Inherited cardiomyopathies in veterinary medicine

Comparative and translation medicine is of particular value within the field of inherited cardiomyopathies. Despite massive advances in understanding the functional role of mutations in human cardiomyopathies, these advances have frequently failed to translate into medical discoveries that alter patient care. One potential explanation for this failure lies in the lack of suitable translational models that adequately recapitulate human cardiovascular physiology and disease expression. The vast genetic heterogeneity that complicates human cardiomyopathy research is potentially alleviated through the study of naturally occurring large animal models of disease, where incredibly homogenous populations, like those seen in a single breed of dog or cat, may exist (Kol et al., Sci Transl Med 7:308-321, 2015; Ueda and Stern, Yale J Biol Med 90:433-448, 2017). Veterinary medicine is in a unique position to provide research resources and information that may be readily applied to human disease (Kol et al., Sci Transl Med 7:308-321, 2015). Many inherited cardiomyopathies of humans are phenotypically and genotypically similar in veterinary species and ongoing research holds promise for aiding veterinary and human patients alike (Basso et al., Circulation 109:1180-1185, 2004; Fox et al., Cardiovasc Pathol 23:28-34, 2014; Fox et al., Circulation 102:1863-1870, 2000; Kittleson et al., J Vet Cardiol 17 Suppl 1:S53-73, 2015; Ueda and Stern, Yale J Biol Med 90:433-448, 2017). This article presents the current knowledge of inherited cardiomyopathies in dogs, cats, and non-human primates, with a goal of identifying areas of translational research and future directions.

International collaborative study to assess cardiovascular risk and evaluate long-term health in cats with preclinical hypertrophic cardiomyopathy and apparently healthy cats: The REVEAL Study

Background

Hypertrophic cardiomyopathy is the most prevalent heart disorder in cats and principal cause of cardiovascular morbidity and mortality. Yet, the impact of preclinical disease is unresolved.

Hypothesis/Objectives

Observational study to characterize cardiovascular morbidity and survival in cats with preclinical nonobstructive (HCM) and obstructive (HOCM) hypertrophic cardiomyopathy and in apparently healthy cats (AH).

Animals

One thousand seven hundred and thirty client‐owned cats (430 preclinical HCM; 578 preclinical HOCM; 722 AH).

Methods

Retrospective multicenter, longitudinal, cohort study. Cats from 21 countries were followed through medical record review and owner or referring veterinarian interviews. Data were analyzed to compare long‐term outcomes, incidence, and risk for congestive heart failure (CHF), arterial thromboembolism (ATE), and cardiovascular death.

Results

During the study period, CHF, ATE, or both occurred in 30.5% and cardiovascular death in 27.9% of 1008 HCM/HOCM cats. Risk assessed at 1, 5, and 10 years after study entry was 7.0%/3.5%, 19.9%/9.7%, and 23.9%/11.3% for CHF/ATE, and 6.7%, 22.8%, and 28.3% for cardiovascular death, respectively. There were no statistically significant differences between HOCM compared with HCM for cardiovascular morbidity or mortality, time from diagnosis to development of morbidity, or cardiovascular survival. Cats that developed cardiovascular morbidity had short survival (mean ± standard deviation, 1.3 ± 1.7 years). Overall, prolonged longevity was recorded in a minority of preclinical HCM/HOCM cats with 10% reaching 9‐15 years.

Conclusions and Clinical Importance

Preclinical HCM/HOCM is a global health problem of cats that carries substantial risk for CHF, ATE, and cardiovascular death. This finding underscores the need to identify therapies and monitoring strategies that decrease morbidity and mortality.

Time spent with cats is never wasted: Lessons learned from feline acromegalic cardiomyopathy, a naturally occurring animal model of the human disease

BACKGROUND

In humans, acromegaly due to a pituitary somatotrophic adenoma is a recognized cause of increased left ventricular (LV) mass. Acromegalic cardiomyopathy is incompletely understood, and represents a major cause of morbidity and mortality. We describe the clinical, echocardiographic and histopathologic features of naturally occurring feline acromegalic cardiomyopathy, an emerging disease among domestic cats.

METHODS

Cats with confirmed hypersomatotropism (IGF-1>1000ng/ml and pituitary mass; n = 67) were prospectively recruited, as were two control groups: diabetics (IGF-1<800ng/ml; n = 24) and healthy cats without known endocrinopathy or cardiovascular disease (n = 16). Echocardiography was performed in all cases, including after hypersomatotropism treatment where applicable. Additionally, tissue samples from deceased cats with hypersomatotropism, hypertrophic cardiomyopathy and age-matched controls (n = 21 each) were collected and systematically histopathologically reviewed and compared.

RESULTS

By echocardiography, cats with hypersomatotropism had a greater maximum LV wall thickness (6.5mm, 4.1-10.1mm) than diabetic (5.9mm, 4.2-9.1mm; Mann Whitney, p<0.001) or control cats (5.2mm, 4.1-6.5mm; Mann Whitney, p<0.001). Left atrial diameter was also greater in cats with hypersomatotropism (16.6mm, 13.0-29.5mm) than in diabetic (15.4mm, 11.2-20.3mm; Mann Whitney, p<0.001) and control cats (14.0mm, 12.6-17.4mm; Mann Whitney, p<0.001). After hypophysectomy and normalization of IGF-1 concentration (n = 20), echocardiographic changes proved mostly reversible. As in humans, histopathology of the feline acromegalic heart was dominated by myocyte hypertrophy with interstitial fibrosis and minimal myofiber disarray.

CONCLUSIONS

These results demonstrate cats could be considered a naturally occurring model of acromegalic cardiomyopathy, and as such help elucidate mechanisms driving cardiovascular remodeling in this disease.

Time spent with cats is never wasted: Lessons learned from feline acromegalic cardiomyopathy, a naturally occurring animal model of the human disease

Background

In humans, acromegaly due to a pituitary somatotrophic adenoma is a recognized cause of increased left ventricular (LV) mass. Acromegalic cardiomyopathy is incompletely understood, and represents a major cause of morbidity and mortality. We describe the clinical, echocardiographic and histopathologic features of naturally occurring feline acromegalic cardiomyopathy, an emerging disease among domestic cats.

Methods

Cats with confirmed hypersomatotropism (IGF-1>1000ng/ml and pituitary mass; n = 67) were prospectively recruited, as were two control groups: diabetics (IGF-1<800ng/ml; n = 24) and healthy cats without known endocrinopathy or cardiovascular disease (n = 16). Echocardiography was performed in all cases, including after hypersomatotropism treatment where applicable. Additionally, tissue samples from deceased cats with hypersomatotropism, hypertrophic cardiomyopathy and age-matched controls (n = 21 each) were collected and systematically histopathologically reviewed and compared.

Results

By echocardiography, cats with hypersomatotropism had a greater maximum LV wall thickness (6.5mm, 4.1–10.1mm) than diabetic (5.9mm, 4.2–9.1mm; Mann Whitney, p<0.001) or control cats (5.2mm, 4.1–6.5mm; Mann Whitney, p<0.001). Left atrial diameter was also greater in cats with hypersomatotropism (16.6mm, 13.0–29.5mm) than in diabetic (15.4mm, 11.2–20.3mm; Mann Whitney, p<0.001) and control cats (14.0mm, 12.6–17.4mm; Mann Whitney, p<0.001). After hypophysectomy and normalization of IGF-1 concentration (n = 20), echocardiographic changes proved mostly reversible. As in humans, histopathology of the feline acromegalic heart was dominated by myocyte hypertrophy with interstitial fibrosis and minimal myofiber disarray.

Conclusions

These results demonstrate cats could be considered a naturally occurring model of acromegalic cardiomyopathy, and as such help elucidate mechanisms driving cardiovascular remodeling in this disease.

Investigations into the Sarcomeric Protein and Ca2+-Regulation Abnormalities Underlying Hypertrophic Cardiomyopathy in Cats (Felix catus)

Hypertrophic cardiomyopathy (HCM) is the most common single gene inherited cardiomyopathy. In cats (Felix catus) HCM is even more prevalent and affects 16% of the outbred population and up to 26% in pedigree breeds such as Maine Coon and Ragdoll. Homozygous MYBPC3 mutations have been identified in these breeds but the mutations in other cats are unknown. At the clinical and physiological level feline HCM is closely analogous to human HCM but little is known about the primary causative mechanism. Most identified HCM causing mutations are in the genes coding for proteins of the sarcomere. We therefore investigated contractile and regulatory proteins in left ventricular tissue from 25 cats, 18 diagnosed with HCM, including a Ragdoll cat with a homozygous MYBPC3 R820W, and 7 non-HCM cats in comparison with human HCM (from septal myectomy) and donor heart tissue. Myofibrillar protein expression was normal except that we observed 20-44% MyBP-C haploinsufficiency in 5 of the HCM cats. Troponin extracted from 8 HCM and 5 non-HCM cat hearts was incorporated into thin filaments and studied by in vitro motility assay. All HCM cat hearts had a higher (2.06 ± 0.13 fold) Ca²⁺-sensitivity than non-HCM cats and, in all the HCM cats, Ca²⁺-sensitivity was not modulated by troponin I phosphorylation. We were able to restore modulation of Ca²⁺-sensitivity by replacing troponin T with wild-type protein or by adding 100 μM Epigallocatechin 3-gallate (EGCG). These fundamental regulatory characteristics closely mimic those seen in human HCM indicating a common molecular mechanism that is independent of the causative mutation. Thus, the HCM cat is a potentially useful large animal model.

Investigations into the Sarcomeric Protein and Ca2+-Regulation Abnormalities Underlying Hypertrophic Cardiomyopathy in Cats (Felix catus)

Hypertrophic cardiomyopathy (HCM) is the most common single gene inherited cardiomyopathy. In cats (Felix catus) HCM is even more prevalent and affects 16% of the outbred population and up to 26% in pedigree breeds such as Maine Coon and Ragdoll. Homozygous MYBPC3 mutations have been identified in these breeds but the mutations in other cats are unknown. At the clinical and physiological level feline HCM is closely analogous to human HCM but little is known about the primary causative mechanism. Most identified HCM causing mutations are in the genes coding for proteins of the sarcomere. We therefore investigated contractile and regulatory proteins in left ventricular tissue from 25 cats, 18 diagnosed with HCM, including a Ragdoll cat with a homozygous MYBPC3 R820W, and 7 non-HCM cats in comparison with human HCM (from septal myectomy) and donor heart tissue. Myofibrillar protein expression was normal except that we observed 20–44% MyBP-C haploinsufficiency in 5 of the HCM cats. Troponin extracted from 8 HCM and 5 non-HCM cat hearts was incorporated into thin filaments and studied by in vitro motility assay. All HCM cat hearts had a higher (2.06 ± 0.13 fold) Ca²⁺-sensitivity than non-HCM cats and, in all the HCM cats, Ca²⁺-sensitivity was not modulated by troponin I phosphorylation. We were able to restore modulation of Ca²⁺-sensitivity by replacing troponin T with wild-type protein or by adding 100 μM Epigallocatechin 3-gallate (EGCG). These fundamental regulatory characteristics closely mimic those seen in human HCM indicating a common molecular mechanism that is independent of the causative mutation. Thus, the HCM cat is a potentially useful large animal model.

Naturally Occurring Biventricular Noncompaction in an Adult Domestic Cat

A definitively diagnosed case of left ventricular noncompaction (LVNC) has not been previously reported in a non-human species. We describe a Maine Coon cross cat with echocardiographically and pathologically documented LVNC. The cat was from a research colony and was heterozygous for the cardiac myosin binding protein C mutation associated with hypertrophic cardiomyopathy (HCM) in Maine Coon cats (A31P). The cat had had echocardiographic examinations performed every 6 months until 6 years of age at which time the cat died of an unrelated cause. Echocardiographic findings consistent with LVNC (moth-eaten appearance to the inner wall of the mid- to apical region of the left ventricle (LV) in cross section and trabeculations of the inner LV wall that communicated with the LV chamber) first were identified at 2 years of age. At necropsy, pathologic findings of LVNC were verified and included the presence of noncompacted myocardium that consisted of endothelial-lined trabeculations and sinusoids that constituted more than half of the inner part of the LV wall. The right ventricular (RV) wall also was affected. Histopathology identified myofiber disarray, which is characteristic of HCM, although heart weight was normal and LV wall thickness was not increased.

A Small Molecule Inhibitor of Sarcomere Contractility Acutely Relieves Left Ventricular Outflow Tract Obstruction in Feline Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an inherited disease of the heart muscle characterized by otherwise unexplained thickening of the left ventricle. Left ventricular outflow tract (LVOT) obstruction is present in approximately two-thirds of patients and substantially increases the risk of disease complications. Invasive treatment with septal myectomy or alcohol septal ablation can improve symptoms and functional status, but currently available drugs for reducing obstruction have pleiotropic effects and variable therapeutic responses. New medical treatments with more targeted pharmacology are needed, but the lack of preclinical animal models for HCM with LVOT obstruction has limited their development. HCM is a common cause of heart failure in cats, and a subset exhibit systolic anterior motion of the mitral valve leading to LVOT obstruction. MYK-461 is a recently-described, mechanistically novel small molecule that acts at the sarcomere to specifically inhibit contractility that has been proposed as a treatment for HCM. Here, we use MYK-461 to test whether direct reduction in contractility is sufficient to relieve LVOT obstruction in feline HCM. We evaluated mixed-breed cats in a research colony derived from a Maine Coon/mixed-breed founder with naturally-occurring HCM. By echocardiography, we identified five cats that developed systolic anterior motion of the mitral valve and LVOT obstruction both at rest and under anesthesia when provoked with an adrenergic agonist. An IV MYK-461 infusion and echocardiography protocol was developed to serially assess contractility and LVOT gradient at multiple MYK-461 concentrations. Treatment with MYK-461 reduced contractility, eliminated systolic anterior motion of the mitral valve and relieved LVOT pressure gradients in an exposure-dependent manner. Our findings provide proof of principle that acute reduction in contractility with MYK-461 is sufficient to relieve LVOT obstruction. Further, these studies suggest that feline HCM will be a valuable translational model for the study of disease pathology, particularly LVOT obstruction.

Left Ventricular Apical Aneurysm in a Cat With Primary Cardiomyopathy

A 13-year-old female Persian cat died suddenly after severe respiratory distress. At necropsy, the changes were compatible with congestive heart failure. The heart was enlarged with a flabby and puckered sac-like aneurysm at the apex of the left ventricle. The apical zone showed a thin muscular wall arising from the free wall of the left ventricle connected to a bulged saccular area through a wide communication. Microscopically, the wall of the aneurysm was composed of fibrous connective tissue with neovascularization and sparse atrophied myocardial cells at the margins. A few isolated cardiomyocytes in the lesion stained positively for desmin, and the inner lining of the aneurysm had immunoreactivity to von Willebrand factor and CD31. Mature fibrous connective tissue was interspersed with degenerated and disorganized cardiomyocytes elsewhere in the myocardium, and many small myocardial arteries were tortuous and thickened. In this case of sudden death, the diagnosis was primary cardiomyopathy, with formation of a left ventricular apical aneurysm within an area of marked myocardial fibrosis and cardiomyocyte atrophy.