Research priorities in hypertrophic cardiomyopathy: report of a Working Group of the National Heart, Lung, and Blood Institute

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.

Transcatheter Ablation of Atrial Fibrillation in Patients With Hypertrophic Cardiomyopathy: A Multicenter Propensity Score-Based Analysis

Background

The prognostic impact of catheter ablation (CA) of atrial fibrillation (AF) in hypertrophic cardiomyopathy (HCM) patients has not yet been satisfactorily elucidated.

Objectives

The aim of the study was to assess the impact of CA of AF on clinical outcomes in a large cohort of HCM patients.

Methods

In this retrospective multicenter study, 555 HCM patients with AF were enrolled, 140 undergoing CA and 415 receiving medical therapy. 1:1 propensity score matching led to the inclusion of 226 patients (113 medical group, 113 intervention group) in the final analysis. The primary outcome was a composite of all-cause mortality, heart transplant and acute heart failure exacerbations. Secondary outcomes included AF recurrence and transition to permanent AF. Additionally, an inverse probability weighted (IPW) model was examined.

Results

At propensity score matching analysis, after a median follow-up of 58.1 months, the primary endpoint occurred in 29 (25.7%) patients in intervention group vs 42 (37.2%) in medical group (P = 0.9). Thromboembolic strokes and major arrhythmic events in intervention vs medical group were 9.7% vs 7.1% (P = 0.144) and 4.4 vs 8.0% (P = 0.779), respectively. Fewer patients in intervention vs medical group experienced AF recurrences (63.7% vs 84.1%, P = 0.001) and transition to permanent AF pattern (20.4% vs 33.6%, P = 0.026). IPW analysis showed consistent results. Severe complications related to CA were uncommon (0.7%).

Conclusions

After 5 years of follow-up, CA did not improve major adverse cardiac outcomes in a large cohort of patients with HCM and AF. Nevertheless, CA seems to facilitate the maintenance of sinus rhythm and slow the progression to permanent AF, without significant safety concerns.

Rationale and design of a randomised trial of trientine in patients with hypertrophic cardiomyopathy

AIMS

Hypertrophic cardiomyopathy (HCM) is characterised by left ventricular hypertrophy (LVH), myocardial fibrosis, enhanced oxidative stress and energy depletion. Unbound/loosely bound tissue copper II ions are powerful catalysts of oxidative stress and inhibitors of antioxidants. Trientine is a highly selective copper II chelator. In preclinical and clinical studies in diabetes, trientine is associated with reduced LVH and fibrosis, and improved mitochondrial function and energy metabolism. Trientine was associated with improvements in cardiac structure and function in an open-label study in patients with HCM.

METHODS

The Efficacy and Mechanism of Trientine in Patients with Hypertrophic Cardiomyopathy (TEMPEST) trial is a multicentre, double-blind, parallel group, 1:1 randomised, placebo-controlled phase II trial designed to evaluate the efficacy and mechanism of action of trientine in patients with HCM. Patients with a diagnosis of HCM according to the European Society of Cardiology Guidelines and in New York Heart Association classes I-III are randomised to trientine or matching placebo for 52 weeks. Primary outcome is change in left ventricular (LV) mass indexed to body surface area, measured using cardiovascular magnetic resonance. Secondary efficacy objectives will determine whether trientine improves exercise capacity, reduces arrhythmia burden, reduces cardiomyocyte injury, improves LV and atrial function, and reduces LV outflow tract gradient. Mechanistic objectives will determine whether the effects are mediated by cellular or extracellular mass regression and improved myocardial energetics.

CONCLUSION

TEMPEST will determine the efficacy and mechanism of action of trientine in patients with HCM.

TRIAL REGISTRATION NUMBERS

NCT04706429 and ISRCTN57145331.

Left Ventricular Hypertrophy: Etiology-Based Therapeutic Options

Determining the etiologies of left ventricular hypertrophy (LVH) can be challenging due to the similarities of the different manifestations in clinical presentation and morphological features. Depending on the underlying cause, not only left ventricular mass but also left ventricular cavity size, or both, may increase. Patients with LVH remain asymptomatic for a few years, but disease progression will lead to the development of systolic or diastolic dysfunction and end-stage heart failure. As hypertrophied cardiac muscle disrupts normal conduction, LVH predisposes to arrhythmias. Distinguishing individuals with treatable causes of LVH is important for prevention of cardiovascular events and mortality. Athletic’s heart with physiological LVH does not require treatment. Frequent causes of hypertrophy include etiologies due to pressure/volume overload, such as systemic hypertension, hypertrophic cardiomyopathy, or infiltrative cardiac processes such as amyloidosis, Fabry disease, and sarcoidosis. Hypertension and aortic valve stenosis are the most common causes of LVH. Management of LVH involves lifestyle changes, medications, surgery, and implantable devices. In this review we systematically summarize treatments for the different patterns of cardiac hypertrophy and their impacts on outcomes while informing clinicians on advances in the treatment of LVH due to Fabry disease, cardiac amyloidosis, and hypertrophic cardiomyopathy.

Sex differences in clinical outcomes for obstructive hypertrophic cardiomyopathy in the USA: a retrospective observational study of administrative claims data

OBJECTIVES

To evaluate sex differences in demographic and clinical characteristics, treatments and outcomes for patients with diagnosed obstructive hypertrophic cardiomyopathy (oHCM) in the USA.

SETTING

Retrospective observational study of administrative claims data from MarketScan Commercial Claims and Encounters Database from IBM Watson Health.

PARTICIPANTS

Of the 28 million covered employees and family members in MarketScan, 9306 patients with oHCM were included in this analysis.

MAIN OUTCOME MEASURES

oHCM-related outcomes included heart failure, atrial fibrillation, ventricular tachycardia/ fibrillation, sudden cardiac death, septal myectomy, alcohol septal ablation (ASA) and heart transplant.

RESULTS

Among 9306 patients with oHCM, the majority were male (60.5%, p<0.001) and women were of comparable age to men (50±15 vs 49±15 years, p<0.001). Women were less likely to be prescribed beta blockers (42.7% vs 45.2%, p=0.017) and undergo an implantable cardioverter-defibrillator (1.7% vs 2.6%, p=0.005). Septal reduction therapy was performed slightly more frequently in women (ASA: 0.08% vs 0.05%, p=0.600; SM: 0.35% vs 0.18%, p=0.096), although not statistically significant. Women were less likely to have atrial fibrillation (6.7% vs 9.9%, p<0.001).

CONCLUSION

Women were less likely to be prescribed beta blockers, ACE inhibitors, anticoagulants, undergo implantable cardioverter-defibrillator and have ventricular tachycardia/fibrillation. Men were more likely to have atrial fibrillation. Future research using large, clinical real-world data are warranted to understand the root cause of these potential treatment disparities in women with oHCM.

Gender Related Differences in the Clinical Presentation of Hypertrophic Cardiomyopathy—An Analysis from the SILICOFCM Database

Background and Objectives: Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease that affects approximately 1 in 500 people. Due to an incomplete disease penetrance associated with numerous factors, HCM is not manifested in all carriers of genetic mutation. Although about two-thirds of patients are male, it seems that female gender is associated with more severe disease phenotype and worse prognosis. The objective of this study was to evaluate the gender related differences in HCM presentation. Materials and Methods: This study was conducted as a part of the international multidisciplinary SILICOFCM project. Clinical information, laboratory analyses, electrocardiography, echocardiography, and genetic testing data were collected for 362 HCM patients from four clinical centers (Florence, Newcastle, Novi Sad, and Regensburg). There were 33% female patients, and 67% male patients. Results: Female patients were older than males (64.5 vs. 53.5 years, p < 0.0005). The male predominance was present across all age groups until the age of 70, when gender distribution became comparable. Females had higher number of symptomatic individuals then males (69% vs. 52%, p = 0.003), most frequently complaining of dyspnea (50% vs. 30%), followed by chest pain (30% vs. 17%), fatigue (26% vs. 13%), palpitations (22% vs. 13%), and syncope (13% vs. 8%). The most common rhythm disorder was atrial fibrillation which was present in a similar number of females and males (19% vs. 13%, p = 0.218). Levels of N-terminal pro-brain natriuretic peptide were comparable between the genders (571 vs. 794 ng/L, p = 0.244). Echocardiography showed similar thickness of interventricular septum (18 vs. 16 mm, p = 0.121) and posterolateral wall (13 vs. 12 mm, p = 0.656), however, females had a lower number of systolic anterior motion (8% vs. 16%, p = 0.020) and other mitral valve abnormalities. Conclusions: Female patients are underrepresented but seem to have a more pronounced clinical presentation of HCM. Therefore, establishing gender specific diagnostic criteria for HCM should be considered.

Copper chelation in patients with hypertrophic cardiomyopathy

BACKGROUND

Disturbances of copper (Cu) homeostasis can lead to hypertrophic cardiac phenotypes (eg, Wilson's disease). We previously identified abnormal Cu homeostasis in patients with hypertrophic cardiomyopathy (HCM) and, therefore, hypothesised that Cu²⁺-selective chelation with trientine dihydrochloride may slow or reverse disease progression in HCM. The aim of this study was, therefore to explore the clinical efficacy, safety and tolerability of trientine in HCM.

METHODS

In this medicines and healthcare products regulatory agency (MHRA) registered open-label pilot study, we treated 20 HCM patients with trientine for 6 months. Patients underwent a comprehensive assessment schedule including separate cardiac magnetic resonance imaging (CMR) and CMR ³¹P-spectroscopy at baseline and end of therapy. Predefined end points included changes in left ventricular mass (LVM), markers of LV fibrosis, markers of LV performance and myocardial energetics. Ten matched patients with HCM were studied as controls.

RESULTS

Trientine treatment was safe and tolerated. Trientine caused a substantial increase in urinary copper excretion (0.42±0.2 vs 2.02±1.0, p=0.001) without affecting serum copper concentrations. Treatment was associated with significant improvements in total atrial strain and global longitudinal LV strain using both Echo and CMR. LVM decreased significantly in the treatment arm compared with the control group (-4.2 g v 1.8 g, p=0.03). A strong trend towards an absolute decrease in LVM was observed in the treatment group (p=0.06). These changes were associated with a significant change in total myocardial volume driven by a significant reduction in extracellular matrix (ECM) volume (43.83±18.42 mL vs 41.49±16.89 mL, p=0.04) as opposed to pure cellular mass reduction and occurred against a background of significant ECM volume increase in the control group (44.59±16.50 mL vs 47.48±19.30 mL, p=0.02). A non-significant 10% increase in myocardial phosphocreatine/adenosine triphosphate (PCr/ATP) ratio with trientine therapy (1.27±0.44 vs 1.4±0.39) was noted.

CONCLUSIONS

Cu²⁺-selective chelation with trientine in a controlled environment is safe and a potential future therapeutic target. A phase 2b trial is now underway.

Mavacamten, a Novel Therapeutic Strategy for Obstructive Hypertrophic Cardiomyopathy

PURPOSE OF REVIEW

Pharmacological treatment options for hypertrophic cardiomyopathy (HCM) are currently limited and comprise non-disease specific therapies such as β-blockers, non-dihydropyridine calcium channel blockers, and disopyramide. These agents that offer a variable degree of symptomatic relief, often suboptimal, are often limited by side-effects and fail to address the key molecular abnormalities of the disease.

RECENT FINDINGS

Mavacamten is a novel, first-in-class, allosteric inhibitor of cardiac myosin ATPase, which reduces actin-myosin cross-bridge formation, thereby reducing myocardial contractility and improving myocardial energetic consumption in experimental HCM models. Following a successful Phase 2 study, the recently published phase III, placebo-controlled, randomized EXPLORER-HCM trial demonstrated the efficacy and safety of mavacamten in reducing left ventricular outflow tract obstruction and ameliorating exercise capacity, New York Heart Association functional class and health status in patients with obstructive HCM. Mavacamten represents the first agent specifically developed for HCM successfully tested in a Phase III trial, to be registered soon for clinical use, representing a radical change of paradigm in the pharmacological treatment of HCM.

The p.Ala2430Val mutation in filamin C causes a "hypertrophic myofibrillar cardiomyopathy"

Hypertrophic cardiomyopathy (HCM) often leads to heart failure. Mutations in sarcomeric proteins are most frequently the cause of HCM but in many patients the gene defect is not known. Here we report on a young man who was diagnosed with HCM shortly after birth. Whole exome sequencing revealed a mutation in the FLNC gene (c.7289C > T; p.Ala2430Val) that was previously shown to cause aggregation of the mutant protein in transfected cells. Myocardial tissue from patients with this mutation has not been analyzed before and thus, the underlying etiology is not well understood. Myocardial tissue of our patient obtained during myectomy at the age of 23 years was analyzed in detail by histochemistry, immunofluorescence staining, electron microscopy and western blot analysis. Cardiac histology showed a pathology typical for myofibrillar myopathy with myofibril disarray and abnormal protein aggregates containing BAG3, desmin, HSPB5 and filamin C. Analysis of sarcomeric and intercalated disc proteins showed focally reduced expression of the gap junction protein connexin43 and Xin-positive sarcomeric lesions in the cardiomyocytes of our patient. In addition, autophagy pathways were altered with upregulation of LC3-II, WIPI1 and HSPB5, 6, 7 and 8. We conclude that the p.Ala2430Val mutation in FLNC most probably is associated with HCM characterized by abnormal intercalated discs, disarray of myofibrils and aggregates containing Z-disc proteins similar to myofibrillar myopathy, which supports the pathological effect of the mutation.

A Perspective on Personalized Therapies in Hypertrophic Cardiomyopathy

ABSTRACT

A dominant mechanism of sudden cardiac death in the young is the progression of maladaptive responses to genes encoding proteins linked to hypertrophic cardiomyopathy. Most are mutant sarcomere proteins that trigger the progression by imposing a biophysical defect on the dynamics and levels of myofilament tension generation. We discuss approaches for personalized treatments that are indicated by recent advanced understanding of the progression.

Genetic determinants of clinical phenotype in hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disease that affects approximately one in 500 people. HCM is a recognized genetic disorder most often caused by mutations involving myosin-binding protein C (MYBPC3) and β-myosin heavy chain (MYH7) which are responsible for approximately three-quarters of the identified mutations.

METHODS

As a part of the international multidisciplinary SILICOFCM project ( www.silicofcm.eu ) the present study evaluated the association between underlying genetic mutations and clinical phenotype in patients with HCM. Only patients with confirmed single pathogenic mutations in either MYBPC3 or MYH7 genes were included in the study and divided into two groups accordingly. The MYBPC3 group was comprised of 48 patients (76%), while the MYH7 group included 15 patients (24%). Each patient underwent clinical examination and echocardiography.

RESULTS

The most prevalent symptom in patients with MYBPC3 was dyspnea (44%), whereas in patients with MYH7 it was palpitations (33%). The MYBPC3 group had a significantly higher number of patients with a positive family history of HCM (46% vs. 7%; p = 0.014). There was a numerically higher prevalence of atrial fibrillation in the MYH7 group (60% vs. 35%, p = 0.085). Laboratory analyses revealed normal levels of creatinine (85.5 ± 18.3 vs. 81.3 ± 16.4 µmol/l; p = 0.487) and blood urea nitrogen (10.2 ± 15.6 vs. 6.9 ± 3.9 mmol/l; p = 0.472) which were similar in both groups. The systolic anterior motion presence was significantly more frequent in patients carrying MYH7 mutation (33% vs. 10%; p = 0.025), as well as mitral leaflet abnormalities (40% vs. 19%; p = 0.039). Calcifications of mitral annulus were registered only in MYH7 patients (20% vs. 0%; p = 0.001). The difference in diastolic function, i.e. E/e' ratio between the two groups was also noted (MYBPC3 8.8 ± 3.3, MYH7 13.9 ± 6.9, p = 0.079).

CONCLUSIONS

Major findings of the present study corroborate the notion that MYH7 gene mutation patients are presented with more pronounced disease severity than those with MYBPC3.

EvaLuation Using Cardiac Insertable Devices And TelephonE in Hypertrophic Cardiomyopathy (ELUCIDATE HCM): A prospective observational study on incidence of arrhythmias

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a heterogeneous disease associated with arrhythmias. Non-sustained ventricular tachycardia (NSVT) is a risk factor for sudden cardiac death and part of the current risk stratification. Furthermore, atrial fibrillation (AF), which increases the risk of stroke, is believed to be common in HCM patients. Routine ambulatory monitoring captures the rhythm only periodically over 24-48 h; thus, the true burden of arrhythmia is unknown. The insertable cardiac monitor (ICM) should help determine a more realistic arrhythmia assessment in HCM patients.

OBJECTIVE

The purpose of this study was to ascertain the incidence of NSVT, AF, and bradycardia in unselected HCM patients by the use of an ICM.

METHODS

Thirty adults, mean age 49.9 ± 12.3 years, 25 (83.3%) males were implanted with a Confirm Rx ICM. The monitoring application was installed on the patient's smartphone, which allowed for patient activation in case of symptoms. The ICM was programmed as follows: ventricular tachycardia (VT) ≥ 160 beats per minute (bpm) for ≥8 intervals, AF ≥ 2 min of duration, and bradycardia ≤ 40 bpm or pause ≥ 3.0 s.

RESULTS

The mean calculated 5-year risk was 2.3%, and 29/30 of the patients had a risk <4%. During follow-up, AF was found in nine patients (30.0%). At least one episode of NSVT was detected in seven patients (23.3%). In 13 patients (43.3%), sinoatrial block/sinus arrest/sinus bradycardia were seen. No arrhythmia was detected in nine patients (30.0%).

CONCLUSION

In this first prospective study using an ICM, the arrhythmia burden in HCM patients yielded 30.0% AF and 23.3% NSVT.

Design of the SILICOFCM study: Effect of sacubitril/valsartan vs lifestyle intervention on functional capacity in patients with hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disease with a broad spectrum of disease severity. HCM ranges from a benign course to a progressive disorder characterized by angina, heart failure, malignant arrhythmia, syncope, or sudden cardiac death. So far, no medical treatment has reliably shown to halt or reverse progression of HCM or to alleviate its symptoms. While the angiotensin receptor neprilysin inhibitor sacubitril/valsartan has shown to reduce mortality and hospitalization in heart failure with reduced ejection fraction, data on its effect on HCM are sparse.

HYPOTHESIS

A 4-month pharmacological (sacubitril/valsartan) or lifestyle intervention will significantly improve exercise tolerance (ie, peak oxygen consumption) in patients with nonobstructive HCM compared to the optimal standard therapy (control group).

METHODS

SILICOFCM is a prospective, multicenter, open-label, randomized, controlled, three-arm clinical trial (NCT03832660) that will recruit 240 adult patients with a confirmed diagnosis of nonobstructive HCM. Eligible patients are randomized to sacubitril/valsartan, lifestyle intervention (physical activity and dietary supplementation with inorganic nitrate), or optimal standard therapy alone (control group). The primary endpoint is the change in functional capacity (ie, peak oxygen consumption). Secondary endpoints include: (a) Change in cardiac structure and function as assessed by transthoracic echocardiography and cardiac magnetic resonance (MRI imaging), (b) change in biomarkers (ie, CK, CKMB, and NT-proBNP), (c) physical activity, and (d) quality of life.

RESULTS

Until December 2019, a total of 41 patients were recruited into the ongoing SILICOFCM study and were allocated to the study groups and the control group. There was no significant difference in key baseline characteristics between the three groups.

CONCLUSION

The SILICOFCM study will provide novel evidence about the effect of sacubitril/valsartan or lifestyle intervention on functional capacity, clinical phenotype, injury and stretch activation markers, physical activity, and quality of life in patients with nonobstructive HCM.

New perspectives in the pharmacological treatment of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is an inherited cardiac disease and a major cause of heart failure and sudden death. Even though it was described more than 50 years ago, sarcomeric hypertrophic cardiomyopathy still lacks a disease-specific treatment. The drugs routinely used alleviate symptoms but do not prevent or revert the phenotype. With recent advances in the knowledge about the genetics and pathophysiology of hypertrophic cardiomyopathy, new genetic and pharmacological approaches have been recently discovered and studied that, by influencing different pathways involved in this disease, have the potential to function as disease-modifying therapies. These promising new pharmacological and genetic therapies will be the focus of this review.

Hypertrophic cardiomyopathy: the future of treatment

Hypertrophic cardiomyopathy (HCM) is a heterogeneous genetic disorder most often caused by sarcomeric mutations resulting in left ventricular hypertrophy, fibrosis, hypercontractility, and reduced compliance. It is the most common inherited monogenic cardiac condition, affecting 0.2% of the population. Whereas currently available therapies for HCM have been effective in reducing morbidity, there remain important unmet needs in the treatment of both the obstructive and non-obstructive phenotypes. Novel pharmacotherapies directly target the molecular underpinnings of HCM, while innovative procedural techniques may soon offer minimally-invasive alternatives to current septal reduction therapy. With the advent of embryonic gene editing, there now exists the potential to correct underlying genetic mutations that may result in disease. This article details the recent developments in the treatment of HCM including pharmacotherapy, septal reduction procedures, mitral valve manipulation, and gene-based therapies.

Baseline Characteristics of the VANISH Cohort

BACKGROUND

The VANISH trial (Valsartan for Attenuating Disease Evolution in Early Sarcomeric Hypertrophic Cardiomyopathy) targeted young sarcomeric gene mutation carriers with early-stage hypertrophic cardiomyopathy (HCM) to test whether valsartan can modify disease progression. We describe the baseline characteristics of the VANISH cohort and compare to previous trials evaluating angiotensin receptor blockers.

METHODS

Applying a randomized, double-blinded, placebo-controlled design, 178 participants with nonobstructive HCM (age, 23.3±10.1 years; 61% men) were randomized in the primary cohort and 34 (age, 16.5±4.9 years; 50% men) in the exploratory cohort of sarcomeric mutation carriers without left ventricular hypertrophy.

RESULTS

In the primary cohort, maximal left ventricular wall thickness was 17±4 mm for adults and Z score 7.0±4.5 for children. Nineteen percent had late gadolinium enhancement on cardiac magnetic resonance. Mean peak oxygen consumption was 33 mL/kg per minute, and 92% of participants were New York Heart Association functional class I. New York Heart Association class II was associated with older age, MYH7 variants, and more prominent imaging abnormalities. Six previous trials of angiotensin receptor blockers in HCM enrolled a median of 24 patients (range, 19-133) with mean age of 51.2 years; 42% of patients were in New York Heart Association class ≥II, and sarcomeric mutations were not required.

CONCLUSIONS

The VANISH cohort is much larger, younger, less heterogeneous, and has less advanced disease than prior angiotensin receptor blocker trials in HCM. Participants had relatively normal functional capacity and mild HCM features. New York Heart Association functional class II symptoms were associated with older age, more prominent imaging abnormalities, and MYH7 variants, suggesting both phenotype and genotype contribute to disease manifestations.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT01912534.

Small molecule studies: the fourth wave of muscle research

The study of muscle and contractility is an unusual scientific endeavour since it has from the start been focussed on one problem-What makes muscle work?-and yet has needed a vast range of different approaches and techniques to study it. Its uniqueness lies in the fundamental fascination of a large scale molecular machine that converts chemical energy into mechanical energy at ambient temperature and with high efficiency that is also controlled by an exquisitely intricate yet utterly reliable regulatory system and is an essential component of animal life. The investigation of muscle is as innovative as any other field of research. As soon as one approach appears to be played out another comes along. It is instructive to consider this as a series of waves of novel and heightened activity starting in the 1950s. The thesis of this article is that we are approaching the fourth wave with the recent rise of interest in small molecules as research tools and possible therapies for muscle diseases.

Moving Beyond the Sarcomere to Explain Heterogeneity in Hypertrophic Cardiomyopathy: JACC Review Topic of the Week

Hypertrophic cardiomyopathy (HCM) has been considered a heterogeneous cardiac disease ascribed solely to single sarcomere gene mutations. However, limitations of this hypothesis suggest that sarcomere mutations alone do not adequately explain all HCM clinical and pathobiological features. Disease-causing sarcomere mutations are absent in ∼70% of patients with established disease, and sarcomere gene carriers can live to advanced ages without developing HCM. Some features of HCM are also inconsistent with the single sarcomere gene hypothesis, such as regional left ventricular hypertrophy and myocardial fibrosis, as well as structurally abnormal elongated mitral valve leaflets and remodeled intramural coronary arterioles, which involve tissue types that do not express cardiomyocyte sarcomere proteins. It is timely to expand the HCM research focus beyond a single molecular event toward more inclusive models to explain this disease in its entirety. The authors chart paths forward addressing this knowledge gap using novel analytical approaches, particularly network medicine, to unravel the pathobiological complexity of HCM.

Family Relationships Associated With Communication and Testing for Inherited Cardiac Conditions

The purpose of this study was to identify characteristics of family relationships associated with communication of genetic risk and testing behaviors among at-risk relatives in families with an inherited cardiac condition. Data were collected from 53 patients and parents of children with an inherited cardiac condition through interviews, pedigrees, and surveys. Associations were examined among family relationship characteristics and whether at-risk relatives were informed about their risk and tested for disease. Of 1,178 at-risk relatives, 52.5% were informed about their risk and 52.1% of those informed were tested. Emotional closeness, relationship quality, and communication frequency had significant bivariate associations with genetic risk communication. Communication frequency was associated with genetic risk communication and testing in multivariate models. This study provides new insight into the extent of genetic risk communication and testing in families with inherited cardiac conditions. Family relationships, especially communication frequency, are critical factors in family communication of genetic risk.

Pathogenic troponin T mutants with opposing effects on myofilament Ca2+ sensitivity attenuate cardiomyopathy phenotypes in mice

Mutations in cardiac troponin T (TnT) associated with hypertrophic cardiomyopathy generally lead to an increase in the Ca²⁺ sensitivity of contraction and susceptibility to arrhythmias. In contrast, TnT mutations linked to dilated cardiomyopathy decrease the Ca²⁺ sensitivity of contraction. Here we tested the hypothesis that two TnT disease mutations with opposite effects on myofilament Ca²⁺ sensitivity can attenuate each other's phenotype. We crossed transgenic mice expressing the HCM TnT-I79N mutation (I79N) with a DCM knock-in mouse model carrying the heterozygous TnT-R141W mutation (HET). The results of the Ca²⁺ sensitivity in skinned cardiac muscle preparations ranked from highest to lowest were as follow: I79N > I79N/HET > NTg > HET. Echocardiographic measurements revealed an improvement in hemodynamic parameters in I79N/HET compared to I79N and normalization of left ventricular dimensions and volumes compared to both I79N and HET. Ex vivo testing showed that the I79N/HET mouse hearts had reduced arrhythmia susceptibility compared to I79N mice. These results suggest that two disease mutations in TnT that have opposite effects on the myofilament Ca²⁺ sensitivity can paradoxically ameliorate each other's disease phenotype. Normalizing myofilament Ca²⁺ sensitivity may be a promising new treatment approach for a variety of diseases.

Telomere shortening is a hallmark of genetic cardiomyopathies

This study demonstrates that significantly shortened telomeres are a hallmark of cardiomyocytes (CMs) from individuals with end-stage hypertrophic cardiomyopathy (HCM) or dilated cardiomyopathy (DCM) as a result of heritable defects in cardiac proteins critical to contractile function. Positioned at the ends of chromosomes, telomeres are DNA repeats that serve as protective caps that shorten with each cell division, a marker of aging. CMs are a known exception in which telomeres remain relatively stable throughout life in healthy individuals. We found that, relative to healthy controls, telomeres are significantly shorter in CMs of genetic HCM and DCM patient tissues harboring pathogenic mutations: TNNI3, MYBPC3, MYH7, DMD, TNNT2, and TTN Quantitative FISH (Q-FISH) of single cells revealed that telomeres were significantly reduced by 26% in HCM and 40% in DCM patient CMs in fixed tissue sections compared with CMs from age- and sex-matched healthy controls. In the cardiac tissues of the same patients, telomere shortening was not evident in vascular smooth muscle cells that do not express or require the contractile proteins, an important control. Telomere shortening was recapitulated in DCM and HCM CMs differentiated from patient-derived human-induced pluripotent stem cells (hiPSCs) measured by two independent assays. This study reveals telomere shortening as a hallmark of genetic HCM and DCM and demonstrates that this shortening can be modeled in vitro by using the hiPSC platform, enabling drug discovery.

Genetic basis of hypertrophic cardiomyopathy in children

BACKGROUND

Previous investigations assessing the genetic cause of pediatric hypertrophic cardiomyopathy (HCM) found underlying genetic mutations in 50-60% of cases. The purpose of our study was to analyze whether this number can be augmented by applying next-generation sequencing and directing further diagnostics by discussing unsolved cases in a multidisciplinary board.

METHODS AND RESULTS

42 patients with the diagnoses of HCM made before age 18 years were treated in our center from 2000 to 2016. Genetic analysis was performed in 36 subjects, a genetic defect was detected in 29 (78%) patients. 15 individuals (42%) had pathogenic variants in genes encoding sarcomere proteins, and 5 (14%) in genes coding for components of the RAS/MAPK signaling pathway. 4 subjects (11%) had mutations in the GAA gene (Pompe disease), and 3 (8%) had Frataxin repeat expansions (Friedreich's ataxia). One patient each showed a mutation in BAG3 and LMNA. Discussion of unsolved HCM cases after performing next-generation sequencing (28 genes) in an interdisciplinary board unraveled the genetic cause in 9 subjects (25%).

CONCLUSION

A definite genetic diagnosis can be reached in nearly 80% with HCM of childhood onset. Next-generation sequencing in conjunction with a multidisciplinary cooperation can enhance the diagnostic yield substantially. This may be important for risk stratification, treatment planning and genetic counseling.

Development of apical hypertrophic cardiomyopathy with age in a transgenic mouse model carrying the cardiac actin E99K mutation

In both humans and mice, the Glu-99-Lys (E99K) mutation in the cardiac actin gene (ACTC) results in little understood apical hypertrophic cardiomyopathy (AHCM). To determine how cross-bridge kinetics change with AHCM development, we applied sinusoidal length perturbations to skinned papillary muscle fibres from 2- and 5-month old E99K transgenic (Tg) and non-transgenic (NTg) mice, and studied tension and its transients. These age groups were chosen because our preliminary studies indicated that AHCM develops with age. Fibres from 5-month old E99K mice showed significant decreases in tension, stiffness, the rate of the medium-speed exponential process and its magnitude compared to non-transgenic control. The nucleotide association constants increased with age, and they were significantly larger in E99K compared to NTg. However, there were no large differences in the rates of the cross-bridge detachment step, the rates of the force generation step, or the phosphate association constant. Our result on force/cross-bridge demonstrates that the decreased active tension of E99K fibres was caused by a decreased amount of force generated per each cross-bridge. The effects were generally less or insignificant at 2 months. A pCa-tension study showed increased Ca²⁺-sensitivity (pCa₅₀) with age in both the E99K and NTg sample groups, and pCa₅₀ was significantly larger (but only for 0.05-0.06 pCa units) in E99K than in NTg groups. A significant decrease in cooperativity (n_H) was observed only in 5-month old E99K mice. We conclude that the AHCM-causing ACTC E99K mutation is associated with progressive alterations in biomechanical parameters, with changes smaller at 2 months but larger at 5 months, correlating with the development of AHCM.

Successful knock-in of Hypertrophic Cardiomyopathy-mutation R723G into the MYH7 gene mimics HCM pathology in pigs

Familial Hypertrophic Cardiomyopathy (HCM) is the most common inherited cardiac disease. About 30% of the patients are heterozygous for mutations in the MYH7 gene encoding the ß-myosin heavy chain (MyHC). Hallmarks of HCM are cardiomyocyte disarray and hypertrophy of the left ventricle, the symptoms range from slight arrhythmias to sudden cardiac death or heart failure. To gain insight into the underlying mechanisms of the diseases' etiology we aimed to generate genome edited pigs with an HCM-mutation. We used TALEN-mediated genome editing and successfully introduced the HCM-point mutation R723G into the MYH7 gene of porcine fibroblasts and subsequently cloned pigs that were heterozygous for the HCM-mutation R723G. No off-target effects were determined in the R723G-pigs. Surprisingly, the animals died within 24 h post partem, probably due to heart failure as indicated by a shift in the a/ß-MyHC ratio in the left ventricle. Most interestingly, the neonatal pigs displayed features of HCM, including mild myocyte disarray, malformed nuclei, and MYH7-overexpression. The finding of HCM-specific pathology in neonatal R723G-piglets suggests a very early onset of the disease and highlights the importance of novel large animal models for studying causative mechanisms and long-term progression of human cardiac diseases.

Short telomeres - A hallmark of heritable cardiomyopathies

Cardiovascular diseases are the leading cause of death worldwide and the incidence increases with age. Genetic testing has taught us much about the pathogenic pathways that drive heritable cardiomyopathies. Here we discuss an unexpected link between shortened telomeres, a molecular marker of aging, and genetic cardiomyopathy. Positioned at the ends of chromosomes, telomeres are DNA repeats which serve as protective caps that shorten with each cell division in proliferative tissues. Cardiomyocytes are an anomaly, as they are largely non-proliferative post-birth and retain relatively stable telomere lengths throughout life in healthy individuals. However, there is mounting evidence that in disease states, cardiomyocyte telomeres significantly shorten. Moreover, this shortening may play an active role in the development of mitochondrial dysfunction central to the etiology of dilated and hypertrophic cardiomyopathies. Elucidation of the mechanisms that underlie the telomere-mitochondrial signaling axis in the heart will provide fresh insights into our understanding of genetic cardiomyopathies, and could lead to the identification of previously uncharacterized modes of therapeutic intervention.

EvaLuation Using Cardiac Insertable Devices And TelephonE in Hypertrophic Cardiomyopathy (ELUCIDATE HCM)-rationale and design: a prospective observational study on incidence of arrhythmias in Sweden

INTRODUCTION

Hypertrophic cardiomyopathy (HCM) is a heterogeneous disease associated with sudden cardiac death (SCD) mainly due to ventricular tachycardia (VT) or fibrillation even though life-threatening bradycardia occurs. Risk stratification takes several variables into consideration including non-sustained VT (NSVT). An implantable cardioverter defibrillator effectively prevents SCD.Atrial fibrillation (AF) is common among patients with HCM and warrants anticoagulation even without conventional risk factors according to European guidelines. Routinely, the evaluation of arrhythmias using a 48-hour ambulatory external monitor takes place every 6-24 months if patients do not report palpitations. The remaining time the potential burden arrhythmia is unknown. Therefore, the aim of the present study is to assess NSVT and AF incidence during 18 months by an insertable cardiac monitor (ICM).

METHODS

Adult patients, aged 18-65 years, with a validated diagnosis of HCM are eligible for the study. The study sample is planned to include 30 patients. A Confirm Rx is implanted at the level of the fourth rib on the left side subcutaneously after local anaesthesia. The application for monitoring is installed in the patients' smartphone and symptoms registered by the patient activation and VT detection programmed as 160 bpm during ≥8 intervals. An AF episode is recorded based on ≥2 min duration. Bradycardia is recorded at ≤40 bpm or pause ≥3.0 s. The patients are followed during 18 months before explant.

ETHICS AND DISSEMINATION

The study was approved by The Regional Ethical Committee in Umeå (protocol number 2017/13-31). The study protocol, including variables and prespecified research questions, the study was registered at Clinical Trial Registration NCT03259113. Each patient is informed about the study in both oral and written form by a physician and included after written consent.

Routinely collected health data to study inherited heart disease: a systematic review (2000-2016)

Objective

Our understanding of inherited heart disease is predominantly based on retrospective specialised clinic cohorts, which have inherent selection bias. Population-based routinely collected data can provide insight into unbiased, large-scale patterns of treatment and care but may be limited by the granularity of clinical information available. We sought to synthesise the global literature to determine whether we can identify patients with inherited heart diseases using routinely collected health data.

Methods

Medline, Embase, CINAHL, PreMEDLINE and Google Scholar citation databases were searched for relevant articles published between 1 January 2000 and 31 October 2016.

Results

A total of 5641 titles/abstracts were screened and 46 full-text articles were retrieved. Twelve peer-reviewed, English-language manuscripts met our inclusion criteria. Studies predominantly focused on Marfan syndrome (41%) or hypertrophic cardiomyopathy (29%). All studies used International Classification of Disease diagnosis codes to define inherited heart disease populations; three studies also used procedure codes. Nine of the 17 definitions for inherited heart disease were repeated across studies.

Conclusions

Inherited heart disease populations can be identified using routinely collected health data, though challenges relate to existing diagnosis codes. This is an underutilised resource with the potential to inform patterns of care, patient outcomes and overall disease burden.

Myosin Rod Hypophosphorylation and CB Kinetics in Papillary Muscles from a TnC-A8V KI Mouse Model

The cardiac troponin C (TnC)-A8V mutation is associated with hypertrophic and restrictive cardiomyopathy (HCM and RCM) in human and mice. The residue affected lies in the N-helix, a region known to affect Ca²⁺-binding affinity to the N-terminal domain. Here we report on the functional effects of this mutation in skinned papillary muscle fibers from homozygous knock-in TnC-A8V mice. Muscle fibers from left ventricle were activated at 25°C under the ionic conditions of working cardiomyocytes. The pCa-tension relationship showed a 3× increase in Ca²⁺-sensitivity and a decrease (0.8×) in cooperativity (n_H) in mutant fibers. The elementary steps of the cross-bridge (CB) cycle were investigated by sinusoidal analysis. The ATP study revealed that there is no significant change in the affinity of ATP (K₁) for the myosin head. In TnC-A8V mutant fibers, the CB detachment rate (k₂) and its equilibrium constant (K₂) increased (1.5×). The phosphate study revealed that rate constant of the force-generation step (k₄) decreased (0.5×), reversal step (k_-4) increased (2×), and the phosphate-release step (1/K₅) increased (2×). Pro-Q Diamond staining of the skinned fibers samples revealed no significant changes in total phosphorylation of multiple sarcomeric proteins. Further investigation using liquid chromatography-tandem mass spectrometry revealed hypophosphorylation of the rod domain of myosin heavy chain in TnC-A8V mutant fibers compared to wild-type. Immunoblotting confirmed the results observed in the mass spectrometry analysis. The results suggest perturbed CB kinetics-possibly caused by changes in the α-myosin heavy chain phosphorylation profile-as a novel mechanism, to our knowledge, by which a mutation in TnC can have rippling effects in the myofilament and contribute to the pathogenesis of HCM/RCM.

Remodeling of repolarization and arrhythmia susceptibility in a myosin-binding protein C knockout mouse model

Hypertrophic cardiomyopathy (HCM) is one of the most common genetic cardiac diseases and among the leading causes of sudden cardiac death (SCD) in the young. The cellular mechanisms leading to SCD in HCM are not well known. Prolongation of the action potential (AP) duration (APD) is a common feature predisposing hypertrophied hearts to SCD. Previous studies have explored the roles of inward Na⁺ and Ca²⁺ in the development of HCM, but the role of repolarizing K⁺ currents has not been defined. The objective of this study was to characterize the arrhythmogenic phenotype and cellular electrophysiological properties of mice with HCM, induced by myosin-binding protein C (MyBPC) knockout (KO), and to test the hypothesis that remodeling of repolarizing K⁺ currents causes APD prolongation in MyBPC KO myocytes. We demonstrated that MyBPC KO mice developed severe hypertrophy and cardiac dysfunction compared with wild-type (WT) control mice. Telemetric electrocardiographic recordings of awake mice revealed prolongation of the corrected QT interval in the KO compared with WT control mice, with overt ventricular arrhythmias. Whole cell current- and voltage-clamp experiments comparing KO with WT mice demonstrated ventricular myocyte hypertrophy, AP prolongation, and decreased repolarizing K⁺ currents. Quantitative RT-PCR analysis revealed decreased mRNA levels of several key K⁺ channel subunits. In conclusion, decrease in repolarizing K⁺ currents in MyBPC KO ventricular myocytes contributes to AP and corrected QT interval prolongation and could account for the arrhythmia susceptibility.NEW & NOTEWORTHY Ventricular myocytes isolated from the myosin-binding protein C knockout hypertrophic cardiomyopathy mouse model demonstrate decreased repolarizing K⁺ currents and action potential and QT interval prolongation, linking cellular repolarization abnormalities with arrhythmia susceptibility and the risk for sudden cardiac death in hypertrophic cardiomyopathy.

Ranolazine Prevents Phenotype Development in a Mouse Model of Hypertrophic Cardiomyopathy

BACKGROUND

Current therapies are ineffective in preventing the development of cardiac phenotype in young carriers of mutations associated with hypertrophic cardiomyopathy (HCM). Ranolazine, a late Na⁺ current blocker, reduced the electromechanical dysfunction of human HCM myocardium in vitro.

METHODS AND RESULTS

To test whether long-term treatment prevents cardiomyopathy in vivo, transgenic mice harboring the R92Q troponin-T mutation and wild-type littermates received an oral lifelong treatment with ranolazine and were compared with age-matched vehicle-treated animals. In 12-months-old male R92Q mice, ranolazine at therapeutic plasma concentrations prevented the development of HCM-related cardiac phenotype, including thickening of the interventricular septum, left ventricular volume reduction, left ventricular hypercontractility, diastolic dysfunction, left-atrial enlargement and left ventricular fibrosis, as evaluated in vivo using echocardiography and magnetic resonance. Left ventricular cardiomyocytes from vehicle-treated R92Q mice showed marked excitation-contraction coupling abnormalities, including increased diastolic [Ca²⁺] and Ca²⁺ waves, whereas cells from treated mutants were undistinguishable from those from wild-type mice. Intact trabeculae from vehicle-treated mutants displayed inotropic insufficiency, increased diastolic tension, and premature contractions; ranolazine treatment counteracted the development of myocardial mechanical abnormalities. In mutant myocytes, ranolazine inhibited the enhanced late Na⁺ current and reduced intracellular [Na⁺] and diastolic [Ca²⁺], ultimately preventing the pathological increase of calmodulin kinase activity in treated mice.

CONCLUSIONS

Owing to the sustained reduction of intracellular Ca²⁺ and calmodulin kinase activity, ranolazine prevented the development of morphological and functional cardiac phenotype in mice carrying a clinically relevant HCM-related mutation. Pharmacological inhibitors of late Na⁺ current are promising candidates for an early preventive therapy in young phenotype-negative subjects carrying high-risk HCM-related mutations.

The structural basis of alpha-tropomyosin linked (Asp230Asn) familial dilated cardiomyopathy

Recently, linkage analysis of two large unrelated multigenerational families identified a novel dilated cardiomyopathy (DCM)-linked mutation in the gene coding for alpha-tropomyosin (TPM1) resulting in the substitution of an aspartic acid for an asparagine (at residue 230). To determine how a single amino acid mutation in α-tropomyosin (Tm) can lead to a highly penetrant DCM we generated a novel transgenic mouse model carrying the D230N mutation. The resultant mouse model strongly phenocopied the early onset of cardiomyopathic remodeling observed in patients as significant systolic dysfunction was observed by 2months of age. To determine the precise cellular mechanism(s) leading to the observed cardiac pathology we examined the effect of the mutation on Ca²⁺ handling in isolated myocytes and myofilament activation in vitro. D230N-Tm filaments exhibited a reduced Ca²⁺ sensitivity of sliding velocity. This decrease in sensitivity was coupled to increase in the peak amplitude of Ca²⁺ transients. While significant, and consistent with other DCMs, these measurements are comprised of complex inputs and did not provide sufficient experimental resolution. We then assessed the primary structural effects of D230N-Tm. Measurements of the thermal unfolding of D230N-Tm vs WT-Tm revealed an increase in stability primarily affecting the C-terminus of the Tm coiled-coil. We conclude that the D230N-Tm mutation induces a decrease in flexibility of the C-terminus via propagation through the helical structure of the protein, thus decreasing the flexibility of the Tm overlap and impairing its ability to regulate contraction. Understanding this unique structural mechanism could provide novel targets for eventual therapeutic interventions in patients with Tm-linked cardiomyopathies.

Troponin C Mutations Partially Stabilize the Active State of Regulated Actin and Fully Stabilize the Active State When Paired with Δ14 TnT

Striated muscle contraction is regulated by the actin-associated proteins tropomyosin and troponin. The extent of activation of myosin ATPase activity is lowest in the absence of both Ca²⁺ and activating cross-bridges (i.e., S1-ADP or rigor S1). Binding of activating species of myosin to actin at a saturating Ca²⁺ concentration stabilizes the most active state (M state) of the actin-tropomyosin-troponin complex (regulated actin). Ca²⁺ binding alone produces partial stabilization of the active state. The extent of stabilization at a saturating Ca²⁺ concentration depends on the isoform of the troponin subunits, the phosphorylation state of troponin, and, in the case of cardiac muscle, the presence of hypertrophic cardiomyopathy-producing mutants of troponin T and troponin I. Cardiac dysfunction is also associated with mutations of troponin C (TnC). Troponin C mutants A8V, C84Y, and D145E increase the Ca²⁺ sensitivity of ATPase activity. We show that these mutants change the distribution of regulated actin states. The A8V and C84Y TnC mutants decreased the inactive B state distribution slightly at low Ca²⁺ concentrations, but the D145E mutants had no effect on that state. All TnC mutants increased the level of the active M state compared to that of the wild type, at a saturating Ca²⁺ concentration. Troponin complexes that contained two mutations that stabilize the active M state, A8V TnC and Δ14 TnT, appeared to be completely in the active state in the presence of only Ca²⁺. Because Ca²⁺ gives full activation, in this situation, troponin must be capable of positioning tropomyosin in the active M state without the need for rigor myosin binding.

Hypertrophic Cardiomyopathy Cardiac Troponin C Mutations Differentially Affect Slow Skeletal and Cardiac Muscle Regulation

Mutations in TNNC1-the gene encoding cardiac troponin C (cTnC)-that have been associated with hypertrophic cardiomyopathy (HCM) and cardiac dysfunction may also affect Ca2+-regulation and function of slow skeletal muscle since the same gene is expressed in both cardiac and slow skeletal muscle. Therefore, we reconstituted rabbit soleus fibers and bovine masseter myofibrils with mutant cTnCs (A8V, C84Y, E134D, and D145E) associated with HCM to investigate their effects on contractile force and ATPase rates, respectively. Previously, we showed that these HCM cTnC mutants, except for E134D, increased the Ca2+ sensitivity of force development in cardiac preparations. In the current study, an increase in Ca2+ sensitivity of isometric force was only observed for the C84Y mutant when reconstituted in soleus fibers. Incorporation of cTnC C84Y in bovine masseter myofibrils reduced the ATPase activity at saturating [Ca2+], whereas, incorporation of cTnC D145E increased the ATPase activity at inhibiting and saturating [Ca2+]. We also tested whether reconstitution of cardiac fibers with troponin complexes containing the cTnC mutants and slow skeletal troponin I (ssTnI) could emulate the slow skeletal functional phenotype. Reconstitution of cardiac fibers with troponin complexes containing ssTnI attenuated the Ca2+ sensitization of isometric force when cTnC A8V and D145E were present; however, it was enhanced for C84Y. In summary, although the A8V and D145E mutants are present in both muscle types, their functional phenotype is more prominent in cardiac muscle than in slow skeletal muscle, which has implications for the protein-protein interactions within the troponin complex. The C84Y mutant warrants further investigation since it drastically alters the properties of both muscle types and may account for the earlier clinical onset in the proband.

Pathogenesis of depression- and anxiety-like behavior in an animal model of hypertrophic cardiomyopathy

Cardiovascular dysfunction is highly comorbid with mood disorders, such as anxiety and depression. However, the mechanisms linking cardiovascular dysfunction with the core behavioral features of mood disorder remain poorly understood. In this study, we used mice bearing a knock-in sarcomeric mutation, which is exhibited in human hypertrophic cardiomyopathy (HCM), to investigate the influence of HCM over the development of anxiety and depression. We employed behavioral, MRI, and biochemical techniques in young (3-4 mo) and aged adult (7-8 mo) female mice to examine the effects of HCM on the development of anxiety- and depression-like behaviors. We focused on females because in both humans and rodents, they experience a 2-fold increase in mood disorder prevalence vs. males. Our results showed that young and aged HCM mice displayed echocardiographic characteristics of the heart disease condition, yet only aged HCM females displayed anxiety- and depression-like behaviors. Electrocardiographic parameters of sympathetic nervous system activation were increased in aged HCM females vs. controls and correlated with mood disorder-related symptoms. In addition, when compared with controls, aged HCM females exhibited adrenal gland hypertrophy, reduced volume in mood-related brain regions, and reduced hippocampal signaling proteins, such as brain-derived neurotrophic factor and its downstream targets vs. controls. In conclusion, prolonged systemic HCM stress can lead to development of mood disorders, possibly through inducing structural and functional brain changes, and thus, mood disorders in patients with heart disease should not be considered solely a psychologic or situational condition.-Dossat, A. M., Sanchez-Gonzalez, M. A., Koutnik, A. P., Leitner, S., Ruiz, E. L., Griffin, B., Rosenberg, J. T., Grant, S. C., Fincham, F. D., Pinto, J. R. Kabbaj, M. Pathogenesis of depression- and anxiety-like behavior in an animal model of hypertrophic cardiomyopathy.

Sex-related differences in the associations between plasma free fatty acid levels and clinical features in patients with hypertrophic cardiomyopathy

Background

Previous studies have indicated that inefficient energy utilization may play a pivotal role in hypertrophic cardiomyopathy (HCM). However, whether plasma free fatty acid (FFA), a main energy substrate of heart, has an effect on HCM remains unclear. Besides, several studies have suggested sex-related differences in HCM features and FFA metabolism. Here, we aimed to explore the association between plasma FFA levels and HCM and potential effects of sex on this relation.

Methods

A total of 412 patients (age 47.8 ± 12.7 years, 243 males (59.0%)) with HCM were recruited. Complete medical history was collected. Echocardiography and cardiovascular magnetic resonance imaging (CMRI) were performed. Fasting plasma FFA was determined by clinical laboratory. Left ventricular mass (LVM), maximum wall thickness (MWT), and left atrium diameter (LAD) were assessed with CMRI.

Results

The median FFA levels were 0.38 (interquartile range (IQR) 0.27–0.52) mmol/L in men and 0.40 (IQR 0.30–0.59) mmol/L in women. The FFA levels were significantly lower in men compared with those in women (p = 0.005). Compared with women, men had greater LVM index (LVMI) (96.8 ± 37.6 vs. 78.6 ± 31.5 g/m², p < 0.001). FFA levels in male patients correlated positively with LVM, LVMI, LAD, cholesterol levels, high-density lipoprotein-cholesterol (HDL-C) levels, heart rate, and systolic blood pressure (SBP). However, none of these variables were significantly associated with sqrt (FFA) in female patients except a borderline correlation of LAD (p = 0.050). Multiple linear regression analysis was performed in male patients and revealed that HDL-C (β = 0.191, p = 0.002), heart rate (β = 0.182, p = 0.004), SBP (β = 0.167, p = 0.007), LVMI (β = 0.132, p = 0.032), and LAD (β = 0.165, p = 0.009) were independently associated with increasing FFA levels.

Conclusions

In patients with HCM, LVMI, LAD, HDL-C, SBP, and heart rate were independently associated with increasing plasma FFA levels in males, whereas not in females. These results suggest that sex may affect the pathogenesis of HCM through influencing FFA metabolism. And these sex-related differences should be taken into account in therapeutic approaches to influence myocardial FFA metabolism in HCM.

Human-based approaches to pharmacology and cardiology: an interdisciplinary and intersectorial workshop

Both biomedical research and clinical practice rely on complex datasets for the physiological and genetic characterization of human hearts in health and disease. Given the complexity and variety of approaches and recordings, there is now growing recognition of the need to embed computational methods in cardiovascular medicine and science for analysis, integration and prediction. This paper describes a Workshop on Computational Cardiovascular Science that created an international, interdisciplinary and inter-sectorial forum to define the next steps for a human-based approach to disease supported by computational methodologies. The main ideas highlighted were (i) a shift towards human-based methodologies, spurred by advances in new in silico, in vivo, in vitro, and ex vivo techniques and the increasing acknowledgement of the limitations of animal models. (ii) Computational approaches complement, expand, bridge, and integrate in vitro, in vivo, and ex vivo experimental and clinical data and methods, and as such they are an integral part of human-based methodologies in pharmacology and medicine. (iii) The effective implementation of multi- and interdisciplinary approaches, teams, and training combining and integrating computational methods with experimental and clinical approaches across academia, industry, and healthcare settings is a priority. (iv) The human-based cross-disciplinary approach requires experts in specific methodologies and domains, who also have the capacity to communicate and collaborate across disciplines and cross-sector environments. (v) This new translational domain for human-based cardiology and pharmacology requires new partnerships supported financially and institutionally across sectors. Institutional, organizational, and social barriers must be identified, understood and overcome in each specific setting.

Novel Approach Targeting the Complex Pathophysiology of Hypertrophic Cardiomyopathy: The Impact of Late Sodium Current Inhibition on Exercise Capacity in Subjects with Symptomatic Hypertrophic Cardiomyopathy (LIBERTY-HCM) Trial

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disorder, with an overall prevalence of at least 1:500 in the adult population although only a fraction of affected patients come to clinical recognition. It is also the most common cause of sudden cardiac death in young adults and a major cause of morbidity caused by chronic heart failure symptoms. However, more than half a century since the original description of the disease, there is no currently approved therapy for the treatment of patients with HCM, and to date there have been only 5 randomized studies of medical therapies in HCM. As such, unmet medical need in HCM has been highlighted by the National Heart, Lung, and Blood Institute (NHLBI) as a research priority. Encouragingly, the infrastructure needed to conduct rigorous clinical trials in HCM has recently emerged because of the heightened awareness and understanding of the disease, development of clinical centers of excellence, and advances in diagnostic imaging. In this article, we will discuss the complex pathophysiology of HCM, review the current therapeutic landscape, describe new mechanistic insights into the central role of the late sodium current in HCM, and introduce the scientific rationale and execution of the Impact of Late Sodium Current Inhibition on Exercise Capacity in Subjects with Symptomatic Hypertrophic Cardiomyopathy (LIBERTY-HCM) trial, the largest randomized, double-blind, placebo controlled clinical trial, now underway, designed to evaluate the effect of a novel pharmacological approach in patients with symptomatic HCM.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02291237.

Downregulation of GSTK1 Is a Common Mechanism Underlying Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is characterized by left ventricular hypertrophy and is associated with a number of potential outcomes, including impaired diastolic function, heart failure, and sudden cardiac death. Various etiologies have been described for HCM, including pressure overload and mutations in sarcomeric and non-sarcomeric genes. However, the molecular pathogenesis of HCM remains incompletely understood. In this study, we performed comparative transcriptome analysis to identify dysregulated genes common to five mouse HCM models of differing etiology: (i) mutation of myosin heavy chain 6, (ii) mutation of tropomyosin 1, (iii) expressing human phospholamban on a null background, (iv) knockout of frataxin, and (v) transverse aortic constriction. Gene-by-gene comparison identified five genes dysregulated in all five HCM models. Glutathione S-transferase kappa 1 (Gstk1) was significantly downregulated in the five models, whereas myosin heavy chain 7 (Myh7), connective tissue growth factor (Ctgf), periostin (Postn), and reticulon 4 (Rtn4) were significantly upregulated. Gene ontology comparison revealed that 51 cellular processes were significantly enriched in genes dysregulated in each transcriptome dataset. Among them, six processes (oxidative stress, aging, contraction, developmental process, cell differentiation, and cell proliferation) were related to four of the five genes dysregulated in all HCM models. GSTK1 was related to oxidative stress only, whereas the other four genes were related to all six cell processes except MYH7 for oxidative stress. Gene–gene functional interaction network analysis suggested correlative expression of GSTK1, MYH7, and actin alpha 2 (ACTA2). To investigate the implications of Gstk1 downregulation for cardiac function, we knocked out gstk1 in zebrafish using the clustered regularly interspaced short palindromic repeats/Cas9 system. We found that expression of the zebrafish homologs of MYH7, ACTA2, and actin alpha 1 were increased in the gstk1-knockout zebrafish. In vivo imaging of zebrafish expressing a fluorescent protein in cardiomyocytes showed that gstk1 deletion significantly decreased the end diastolic volume and, to a lesser extent, end systolic volume. These results suggest that downregulation of GSTK1 may be a common mechanism underlying HCM of various etiologies, possibly through increasing oxidative stress and the expression of sarcomere genes.

Enhanced troponin I binding explains the functional changes produced by the hypertrophic cardiomyopathy mutation A8V of cardiac troponin C

Higher affinity for TnI explains how troponin C (TnC) carrying a causative hypertrophic cardiomyopathy mutation, TnC(A8V), sensitizes muscle cells to Ca(2+). Muscle fibers reconstituted with TnC(A8V) require ∼2.3-fold less [Ca(2+)] to achieve 50% maximum-tension compared to fibers reconstituted with wild-type TnC (TnC(WT)). Binding measurements rule out a significant change in N-terminus Ca(2+)-affinity of isolated TnC(A8V), and TnC(A8V) binds the switch-peptide of troponin-I (TnI(sp)) ∼1.6-fold more strongly than TnC(WT); thus we model the TnC-TnI(sp) interaction as competing with the TnI-actin interaction. Tension data are well-fit by a model constrained to conditions in which the affinity of TnC(A8V) for TnI(sp) is 1.5-1.7-fold higher than that of TnC(WT) at all [Ca(2+)]. Mean ATPase rates of reconstituted cardiac myofibrils is greater for TnC(A8V) than TnC(WT) at all [Ca(2+)], with statistically significant differences in the means at higher [Ca(2+)]. To probe TnC-TnI interaction in low Ca(2+), displacement of bis-ANS from TnI was monitored as a function of TnC. Whereas Ca(2+)-TnC(WT) displaces significantly more bis-ANS than Mg(2+)-TnC(WT), Ca(2+)-TnC(A8V) displaces probe equivalently to Mg(2+)-TnC(A8V) and Ca(2+)-TnC(WT), consistent with stronger Ca(2+)-independent TnC(A8V)-TnI(sp). A Matlab program for computing theoretical activation is reported. Our work suggests that contractility is constantly above normal in hearts made hypertrophic by TnC(A8V).

MicroRNA: A new therapeutic strategy for cardiovascular diseases

Myocardial infarction, atherosclerosis, and hypertension are the most common heart-related diseases that affect both the heart and the blood vessels. Multiple independent risk factors have been shown to be responsible for cardiovascular diseases. The combination of a healthy diet, exercise, and smoking cessation keeps these risk factors in check and helps maintain homeostasis. The dynamic monolayer endothelial cell integrity and cell-cell communication are the fundamental mechanisms in maintaining homeostasis. Recently, it has been revealed that small noncoding RNAs (ncRNAs) play a critical role in regulation of genes involved in either posttranscriptional or pretranslational modifications. They also control diverse biological functions like development, differentiation, growth, and metabolism. Among ncRNAs, the short interfering RNAs (siRNAs), and microRNAs (miRNAs) have been extensively studied, but their specific functions remain largely unknown. In recent years, miRNAs are efficiently studied as one of the important candidates for involvement in most biological processes and have been implicated in many human diseases. Thus, the identification and the respective targets of miRNAs may provide novel molecular insight and new therapeutic strategies to treat diseases. This review summarizes the recent developments and insight on the role of miRNAs in cardiovascular disease prognosis, diagnostic and clinical applications.

Mimics of Hypertrophic Cardiomyopathy - Diagnostic Clues to Aid Early Identification of Phenocopies

Hypertrophic cardiomyopathy (HCM) is the most common genetic cause of cardiomyopathy worldwide. Significant advances and widespread availability of genetic testing have improved detection of the sarcomeric mutations that cause HCM, but have also highlighted the significance of inborn errors of metabolism (IEM) or metabolic storage disorders that can mimic HCM ('HCM phenocopies'). These conditions cannot always be reliably differentiated on the basis of imaging alone. Whilst HCM phenocopies are relatively rare, it is crucial to distinguish these conditions at an early stage as their natural history, management and prognosis vary significantly from that of HCM with sarcomeric mutations. This review illustrates the salient features of HCM phenocopies and stresses the need for a high level of suspicion for these conditions in the assessment of cardiac hypertrophy.

Novel insights on the relationship between T-tubular defects and contractile dysfunction in a mouse model of hypertrophic cardiomyopathy

Abnormalities of cardiomyocyte Ca^2 + homeostasis and excitation–contraction (E–C) coupling are early events in the pathogenesis of hypertrophic cardiomyopathy (HCM) and concomitant determinants of the diastolic dysfunction and arrhythmias typical of the disease. T-tubule remodelling has been reported to occur in HCM but little is known about its role in the E–C coupling alterations of HCM. Here, the role of T-tubule remodelling in the electro-mechanical dysfunction associated to HCM is investigated in the Δ160E cTnT mouse model that expresses a clinically-relevant HCM mutation. Contractile function of intact ventricular trabeculae is assessed in Δ160E mice and wild-type siblings. As compared with wild-type, Δ160E trabeculae show prolonged kinetics of force development and relaxation, blunted force-frequency response with reduced active tension at high stimulation frequency, and increased occurrence of spontaneous contractions. Consistently, prolonged Ca^2 + transient in terms of rise and duration are also observed in Δ160E trabeculae and isolated cardiomyocytes. Confocal imaging in cells isolated from Δ160E mice reveals significant, though modest, remodelling of T-tubular architecture. A two-photon random access microscope is employed to dissect the spatio-temporal relationship between T-tubular electrical activity and local Ca^2 + release in isolated cardiomyocytes. In Δ160E cardiomyocytes, a significant number of T-tubules (> 20%) fails to propagate action potentials, with consequent delay of local Ca^2 + release. At variance with wild-type, we also observe significantly increased variability of local Ca^2 + transient rise as well as higher Ca^2 +-spark frequency. Although T-tubule structural remodelling in Δ160E myocytes is modest, T-tubule functional defects determine non-homogeneous Ca^2 + release and delayed myofilament activation that significantly contribute to mechanical dysfunction.

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Contraction and Ca^2 + transient kinetics are impaired in myocardial preparations from mice carrying the cardiac troponin T ∆ 160E mutation.

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T-tubules architecture is mildly altered in ∆160E cardiomyocytes.

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20% of T-tubules fail to propagate action potential and produce delay of local Ca^2 + rise.

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Higher spatio-temporal variability of local Ca^2 + rise and increased Ca^2 + sparks frequency are found in ∆160E cardiomyocytes.