Metabolic remodeling and calcium handling abnormality in induced pluripotent stem cell-derived cardiomyocytes in dilated phase of hypertrophic cardiomyopathy with MYBPC3 frameshift mutation.

Hypertrophic cardiomyopathy (HCM) is an inherited disorder characterized by left ventricular hypertrophy and diastolic dysfunction, and increases the risk of arrhythmias and heart failure. Some patients with HCM develop a dilated phase of hypertrophic cardiomyopathy (D-HCM) and have poor prognosis; however, its pathogenesis is unclear and few pathological models exist. This study established disease-specific human induced pluripotent stem cells (iPSCs) from a patient with D-HCM harboring a mutation in MYBPC3 (c.1377delC), a common causative gene of HCM, and investigated the associated pathophysiological mechanisms using disease-specific iPSC-derived cardiomyocytes (iPSC-CMs). We confirmed the expression of pluripotent markers and the ability to differentiate into three germ layers in D-HCM patient-derived iPSCs (D-HCM iPSCs). D-HCM iPSC-CMs exhibited disrupted myocardial sarcomere structures and an increased number of damaged mitochondria. Ca2+ imaging showed increased abnormal Ca2+ signaling and prolonged decay time in D-HCM iPSC-CMs. Cell metabolic analysis revealed increased basal respiration, maximal respiration, and spare-respiratory capacity in D-HCM iPSC-CMs. RNA sequencing also showed an increased expression of mitochondrial electron transport system-related genes. D-HCM iPSC-CMs showed abnormal Ca2+ handling and hypermetabolic state, similar to that previously reported for HCM patient-derived iPSC-CMs. Although further studies are required, this is expected to be a useful pathological model for D-HCM.

MYH7 R453C induced cardiac remodelling via activating TGF-ß/Smad2/3, ERK1/2 and Nox4/ROS/NF-κB signalling pathways.

Hypertrophic cardiomyopathy (HCM) is a monogenic cardiac disorder commonly induced by sarcomere gene mutations. However, the mechanism for HCM is not well defined. Here, we generated transgenic MYH7 R453C and MYH6 R453C piglets and found both developed typical cardiac hypertrophy. Unexpectedly, we found serious fibrosis and cardiomyocyte loss in the ventricular of MYH7 R453C, not MYH6 R453C piglets, similar to HCM patients. Then, RNA-seq analysis and western blotting identified the activation of ERK1/2 and PI3K-Akt pathways in MYH7 R453C. Moreover, we observed an increased expression of fetal genes and an excess of reactive oxygen species (ROS) in MYH7 R453C piglet models, which was produced by Nox4 and subsequently induced inflammatory response. Additionally, the phosphorylation levels of Smad2/3, ERK1/2 and NF-kB p65 proteins were elevated in cardiomyocytes with the MYH7 R453C mutation. Furthermore, epigallocatechin gallate, a natural bioactive compound, could be used as a drug to reduce cell death by adjusting significant downregulation of the protein expression of Bax and upregulated Bcl-2 levels in the H9C2 models with MYH7 R453C mutation. In conclusion, our study illustrated that TGF-ß/Smad2/3, ERK1/2 and Nox4/ROS pathways have synergistic effects on cardiac remodelling and inflammation in MYH7 R453C mutation.

Integrating Clinical Phenotype With Multiomics Analyses of Human Cardiac Tissue Unveils Divergent Metabolic Remodeling in Genotype-Positive and Genotype-Negative Patients With Hypertrophic Cardiomyopathy.

BACKGROUND: Hypertrophic cardiomyopathy (HCM) is caused by sarcomere gene mutations (genotype-positive HCM) in ≈50% of patients and occurs in the absence of mutations (genotype-negative HCM) in the other half of patients. We explored how alterations in the metabolomic and lipidomic landscape are involved in cardiac remodeling in both patient groups. METHODS: We performed proteomics, metabolomics, and lipidomics on myectomy samples (genotype-positive N=19; genotype-negative N=22; and genotype unknown N=6) from clinically well-phenotyped patients with HCM and on cardiac tissue samples from sex- and age-matched and body mass index-matched nonfailing donors (N=20). These data sets were integrated to comprehensively map changes in lipid-handling and energy metabolism pathways. By linking metabolomic and lipidomic data to variability in clinical data, we explored patient group-specific associations between cardiac and metabolic remodeling. RESULTS: HCM myectomy samples exhibited (1) increased glucose and glycogen metabolism, (2) downregulation of fatty acid oxidation, and (3) reduced ceramide formation and lipid storage. In genotype-negative patients, septal hypertrophy and diastolic dysfunction correlated with lowering of acylcarnitines, redox metabolites, amino acids, pentose phosphate pathway intermediates, purines, and pyrimidines. In contrast, redox metabolites, amino acids, pentose phosphate pathway intermediates, purines, and pyrimidines were positively associated with septal hypertrophy and diastolic impairment in genotype-positive patients. CONCLUSIONS: We provide novel insights into both general and genotype-specific metabolic changes in HCM. Distinct metabolic alterations underlie cardiac disease progression in genotype-negative and genotype-positive patients with HCM.

Viral myocarditis in combination with genetic cardiomyopathy as a cause of sudden death. An autopsy series.

Sudden cardiac death (SCD) is a major public health issue worldwide. In the young (< 40 years of age), genetic cardiomyopathies and viral myocarditis, sometimes in combination, are the most frequent, but underestimated, causes of SCD. Molecular autopsy is essential for prevention. Several studies have shown an association between genetic cardiomyopathies and viral myocarditis, which is probably underestimated due to insufficient post-mortem investigations. We report on four autopsy cases illustrating the pathogenesis of these combined pathologies. In two cases, a genetic hypertrophic cardiomyopathy was diagnosed in combination with Herpes Virus Type 6 (HHV6) and/or Parvovirus-B19 (PVB19) in the heart. In the third case, autopsy revealed a dilated cardiomyopathy and virological analyses revealed acute myocarditis caused by three viruses: PVB19, HHV6 and Epstein-Barr virus. Genetic analyses revealed a mutation in the gene coding for desmin. The fourth case illustrated a channelopathy and a PVB19/HHV6 coinfection. Our four cases illustrate the highly probable deleterious role of cardiotropic viruses in the occurrence of SCD in subjects with genetic cardiomyopathies. We discuss the pathogenetic link between viral myocarditis and genetic cardiomyopathy. Molecular autopsy is essential in prevention of these SCD, and a close collaboration between cardiologists, pathologists, microbiologists and geneticians is mandatory.

Mechanisms of ischaemia-induced arrhythmias in hypertrophic cardiomyopathy: a large-scale computational study.

AIMS: Lethal arrhythmias in hypertrophic cardiomyopathy (HCM) are widely attributed to myocardial ischaemia and fibrosis. How these factors modulate arrhythmic risk remains largely unknown, especially as invasive mapping protocols are not routinely used in these patients. By leveraging multiscale digital twin technologies, we aim to investigate ischaemic mechanisms of increased arrhythmic risk in HCM. METHODS AND RESULTS: Computational models of human HCM cardiomyocytes, tissue, and ventricles were used to simulate outcomes of Phase 1A acute myocardial ischaemia. Cellular response predictions were validated with patch-clamp studies of human HCM cardiomyocytes (n = 12 cells, N = 5 patients). Ventricular simulations were informed by typical distributions of subendocardial/transmural ischaemia as analysed in perfusion scans (N = 28 patients). S1-S2 pacing protocols were used to quantify arrhythmic risk for scenarios in which regions of septal obstructive hypertrophy were affected by (i) ischaemia, (ii) ischaemia and impaired repolarization, and (iii) ischaemia, impaired repolarization, and diffuse fibrosis. HCM cardiomyocytes exhibited enhanced action potential and abnormal effective refractory period shortening to ischaemic insults. Analysis of ∼75 000 re-entry induction cases revealed that the abnormal HCM cellular response enabled establishment of arrhythmia at milder ischaemia than otherwise possible in healthy myocardium, due to larger refractoriness gradients that promoted conduction block. Arrhythmias were more easily sustained in transmural than subendocardial ischaemia. Mechanisms of ischaemia-fibrosis interaction were strongly electrophysiology dependent. Fibrosis enabled asymmetric re-entry patterns and break-up into sustained ventricular tachycardia. CONCLUSION: HCM ventricles exhibited an increased risk to non-sustained and sustained re-entry, largely dominated by an impaired cellular response and deleterious interactions with the diffuse fibrotic substrate.

Cardiac Magnetic Resonance Feature-Tracking Identifies Preclinical Abnormalities in Hypertrophic Cardiomyopathy Sarcomere Gene Mutation Carriers.

BACKGROUND: Assessing myocardial strain by cardiac magnetic resonance feature tracking (FT) has been found to be useful in patients with overt hypertrophic cardiomyopathy (HCM). Little is known, however, of its role in sarcomere gene mutation carriers without overt left ventricular hypertrophy (subclinical HCM). METHODS: Thirty-eight subclinical HCM subjects and 42 healthy volunteers were enrolled in this multicenter case-control study. They underwent a comprehensive cardiac magnetic resonance study. Two-dimensional global radial, circumferential, and longitudinal strain of the left ventricle (LV) were evaluated by FT analysis. RESULTS: The subclinical HCM sample was 41 (22-51) years old and 32% were men. FT analysis revealed a reduction in global radial strain (29±7.2 versus 47.9±7.4; P<0.0001), global circumferential strain (-17.3±2.6 -versus -20.8±7.4; P<0.0001) and global longitudinal strain (-16.9±2.4 versus -20.5±2.6; P<0.0001) in subclinical HCM compared with control subjects. The significant differences persisted when considering the 23 individuals free of all the structural and functional ECG and cardiac magnetic resonance abnormalities previously described. Receiver operating characteristic curve analyses showed that the differential diagnostic performances of FT in discriminating subclinical HCM from normal subjects were good to excellent (global radial strain with optimal cut-off value of 40.43%: AUC, 0.946 [95% CI, 0.93-1.00]; sensitivity 90.48%, specificity 94.44%; global circumferential strain with cut-off, -18.54%: AUC, 0.849 [95% CI, 0.76-0.94]; sensitivity, 88.10%; specificity, 72.22%; global longitudinal strain with cut-off, -19.06%: AUC, 0.843 [95% CI, 0.76-0.93]; sensitivity, 78.57%; specificity, 78.95%). Similar values were found for discriminating those subclinical HCM subjects without other phenotypic abnormalities from healthy volunteers (global radial strain with optimal cut-off 40.43%: AUC, 0.966 [95% CI, 0.92-1.00]; sensitivity, 90.48%; specificity, 95.45%; global circumferential strain with cut-off, -18.44%: AUC, 0.866 [95% CI, 0.76-0.96]; sensitivity, 92.86%; specificity, 77.27%; global longitudinal strain with cut-off, -17.32%: AUC, 0.838 [95% CI, 0.73-0.94]; sensitivity, 90.48%; specificity, 65.22%). CONCLUSIONS: Cardiac magnetic resonance FT-derived parameters are consistently lower in subclinical patients with HCM, and they could emerge as a good tool for discovering the disease during a preclinical phase.

Myosin inhibitor reverses hypertrophic cardiomyopathy in genotypically diverse pediatric iPSC-cardiomyocytes to mirror variant correction.

Pathogenic variants in MYH7 and MYBPC3 account for the majority of hypertrophic cardiomyopathy (HCM). Targeted drugs like myosin ATPase inhibitors have not been evaluated in children. We generate patient and variant-corrected iPSC-cardiomyocytes (CMs) from pediatric HCM patients harboring single variants in MYH7 (V606M; R453C), MYBPC3 (G148R) or digenic variants (MYBPC3 P955fs, TNNI3 A157V). We also generate CMs harboring MYBPC3 mono- and biallelic variants using CRISPR editing of a healthy control. Compared with isogenic and healthy controls, variant-positive CMs show sarcomere disorganization, higher contractility, calcium transients, and ATPase activity. However, only MYH7 and biallelic MYBPC3 variant-positive CMs show stronger myosin-actin binding. Targeted myosin ATPase inhibitors show complete rescue of the phenotype in variant-positive CMs and in cardiac Biowires to mirror isogenic controls. The response is superior to verapamil or metoprolol. Myosin inhibitors can be effective in genotypically diverse HCM highlighting the need for myosin inhibitor drug trials in pediatric HCM.

Post-hoc standardisation of parametric T1 maps in cardiovascular magnetic resonance imaging: a proof-of-concept.

BACKGROUND: In cardiovascular magnetic resonance imaging parametric T1 mapping lacks universally valid reference values. This limits its extensive use in the clinical routine. The aim of this work was the introduction of our self-developed Magnetic Resonance Imaging Software for Standardization (MARISSA) as a post-hoc standardisation approach. METHODS: Our standardisation approach minimises the bias of confounding parameters (CPs) on the base of regression models. 214 healthy subjects with 814 parametric T1 maps were used for training those models on the CPs: age, gender, scanner and sequence. The training dataset included both sex, eleven different scanners and eight different sequences. The regression model type and four other adjustable standardisation parameters were optimised among 240 tested settings to achieve the lowest coefficient of variation, as measure for the inter-subject variability, in the mean T1 value across the healthy test datasets (HTE, N = 40, 156 T1 maps). The HTE were then compared to 135 patients with left ventricular hypertrophy including hypertrophic cardiomyopathy (HCM, N = 112, 121 T1 maps) and amyloidosis (AMY, N = 24, 24 T1 maps) after applying the best performing standardisation pipeline (BPSP) to evaluate the diagnostic accuracy. FINDINGS: The BPSP reduced the COV of the HTE from 12.47% to 5.81%. Sensitivity and specificity reached 95.83% / 91.67% between HTE and AMY, 71.90% / 72.44% between HTE and HCM, and 87.50% / 98.35% between HCM and AMY. INTERPRETATION: Regarding the BPSP, MARISSA enabled the comparability of T1 maps independently of CPs while keeping the discrimination of healthy and patient groups as found in literature. FUNDING: This study was supported by the BMBF / DZHK.

Coronary microvascular dysfunction: prevalence and aetiology in patients with suspected myocardial ischaemia.

AIM: To evaluate the prevalence, aetiology, and corresponding morbidity of coronary microvascular dysfunction (CMD) in patients with suspected myocardial ischaemia. MATERIALS AND METHODS: The present study included 115 patients with suspected myocardial ischaemia who underwent stress perfusion cardiac magnetic resonance imaging. CMD was assessed visually based on the myocardial perfusion results. The CMR-derived myocardial perfusion reserve index (MPRI) and left ventricular (LV) strain parameters obtained using the post-processing software CVI42 were employed to evaluate LV myocardial perfusion and deformation. LV strain parameters included global longitudinal, circumferential, and radial strain (GLS, GCS, and GRS), global systolic/diastolic longitudinal, circumferential, and radial strain rates (SLSR, SCSR, SRSR, DLSR, DCSR, and DRSR). RESULTS: Of the 115 patients, 12 patients were excluded and 103 patients were finally included in the study. CMD was observed in 79 % (81 patients, aged 53 ± 12 years) of patients. Regarding aetiology, 91 (88 %) patients had non-obstructive coronary artery disease (CAD), eight (8 %) had obstructive CAD, and four (4 %) had hypertrophic cardiomyopathy (HCM). The incidence of CMD was highest (100 %) in patients with HCM, followed by those with non-obstructive CAD (up to 79 %). There were no statistical differences between CMD and non-CMD groups in GCS, GRS, GLS, SRSR, SCSR, SLSR, DCSR, DRSR and DLSR. CONCLUSION: The incidence of CMD was higher in patients with signs and symptoms of ischaemia. CMD occurred with non-obstructive CAD, obstructive CAD, and HCM, with the highest prevalence of CMD in HCM.

Genetic Testing Yield and Clinical Characteristics of Hypertrophic Cardiomyopathy in Understudied Ethnic Groups: Insights From a New Zealand National Registry.

BACKGROUND: Aotearoa/New Zealand has a multiethnic population. Patients with hypertrophic cardiomyopathy (HCM) are enrolled in the national Cardiac Inherited Diseases Registry New Zealand. Here, we report the characteristics of Cardiac Inherited Diseases Registry New Zealand HCM probands with and without pathogenic or likely pathogenic (P/LP) genetic variants for HCM, and assess genetic testing yield and variant spectrum by self-identified ethnicity. METHODS: Probands with HCM and enrolled in Cardiac Inherited Diseases Registry New Zealand who have undergone clinical genetic testing over a 17-year period were included. Clinical data, family history, and genetic test results were analyzed. RESULTS: Of 336 probands, 121 (36%) were women, 220 (66%) were European ethnicity, 41 (12%) were Maori, 26 (8%) were Pacific people, and 49 (15%) were other ethnicities. Thirteen probands (4%) presented with sudden death and 19 (6%) with cardiac arrest. A total of 134 (40%) had a P/LP variant identified; most commonly in the MYBPC3 gene (60%) followed by the MYH7 gene (24%). A P/LP variant was identified in 27% of Maori or Pacific probands versus 43% European or other ethnicity probands (P=0.022); 16% of Maori or Pacific probands had a variant of uncertain significance identified, compared with 9% of European or other ethnicity probands (P=0.092). Women more often had a P/LP variant identified than men (48% versus 35%; P=0.032), and variant-positive probands were younger at clinical diagnosis than variant of uncertain significance/variant-negative probands (39±17 versus 50±17 years; P<0.001) and more likely to have experienced cardiac arrest or sudden death events over their lifetime (P=0.002). CONCLUSIONS: Carriage of a P/LP variant in HCM probands is associated with presentation at younger age, and cardiac arrest or sudden death events. Maori or Pacific probands were less likely to have a P/LP variant identified than European or other ethnicity probands.

Genetic Testing in Hypertrophic Cardiomyopathy.

Genetic testing is an important tool in the diagnosis and management of patients and families with hypertrophic cardiomyopathy (HCM). Modern testing can identify causative variants in 30 to >60% of patients, with probability of a positive test varying with baseline characteristics such as known family history of HCM. Patients diagnosed with HCM should be offered genetic counseling and genetic testing as appropriate. Standard multigene panels evaluate sarcomeric genes known to cause HCM as well as genetic conditions that can mimic HCM but require different management. Positive genetic testing (finding a pathogenic or likely pathogenic variant) helps to clarify diagnosis and assists in family screening. If there is high confidence that an identified variant is the cause of HCM, at-risk family members can pursue predictive testing to determine if they are truly at risk or if they can be dismissed from serial screening based on whether they inherited the family's causative variant. Interpreting test results can be complex, and providers should make use of multidisciplinary teams as well as evidence-based resources to obtain the best possible understanding of pathogenicity.

Pathological causes of sudden death in autopsied children with reference to peculiar findings: An Egyptian perspective.

Childhood is a long period extending up to the age of 18 years. Childhood encompasses different developmental stages; each stage has specific characteristics. This 5-year study included 244 autopsied children who died unexpectedly due to natural causes. This study was conducted in the forensic pathology unit of the Egyptian Forensic Medicine Authority (EFMA). Pathological causes of death were diagnosed in 181 cases, representing nearly three-quarters (74.2 %) of cases. Males represented 60.8 % of these cases. More than half (51.4 %) of deaths due to natural disease occurred within the first month of life. The diagnosis was established for the first-time during autopsy in 58 % of cases. Prematurity complications and infections were the cause of death in 35.9 % and 30.4 % of deaths attributed to natural pathologies, respectively. Prematurity complications are the most common cause of death in perinatal (63.6) and neonatal (71.4 %) periods. Whereas infection is the most common cause of death during infancy (55 %), childhood (52.8 %), and adolescence (43.8 %). Pneumonia was the most common infection (61.8 %). This study highlighted cases with peculiar pathologies that include cardiomyopathies (idiopathic dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), and Arrhythmogenic right ventricular cardiomyopathy (ARVD)), Waterhouse-Friderichsen syndrome (WFS), ruptured cerebral cavernous hemangioma, and cerebellar medulloblastoma.

FARS2 Deficiency Causes Cardiomyopathy by Disrupting Mitochondrial Homeostasis and the Mitochondrial Quality Control System.

BACKGROUND: Hypertrophic cardiomyopathy (HCM) is a common heritable heart disease. Although HCM has been reported to be associated with many variants of genes involved in sarcomeric protein biomechanics, pathogenic genes have not been identified in patients with partial HCM. FARS2 (the mitochondrial phenylalanyl-tRNA synthetase), a type of mitochondrial aminoacyl-tRNA synthetase, plays a role in the mitochondrial translation machinery. Several variants of FARS2 have been suggested to cause neurological disorders; however, FARS2-associated diseases involving other organs have not been reported. We identified FARS2 as a potential novel pathogenic gene in cardiomyopathy and investigated its effects on mitochondrial homeostasis and the cardiomyopathy phenotype. METHODS: FARS2 variants in patients with HCM were identified using whole-exome sequencing, Sanger sequencing, molecular docking analyses, and cell model investigation. Fars2 conditional mutant (p.R415L) or knockout mice, fars2-knockdown zebrafish, and Fars2-knockdown neonatal rat ventricular myocytes were engineered to construct FARS2 deficiency models both in vivo and in vitro. The effects of FARS2 and its role in mitochondrial homeostasis were subsequently evaluated using RNA sequencing and mitochondrial functional analyses. Myocardial tissues from patients were used for further verification. RESULTS: We identified 7 unreported FARS2 variants in patients with HCM. Heart-specific Fars2-deficient mice presented cardiac hypertrophy, left ventricular dilation, progressive heart failure accompanied by myocardial and mitochondrial dysfunction, and a short life span. Heterozygous cardiac-specific Fars2R415L mice displayed a tendency to cardiac hypertrophy at age 4 weeks, accompanied by myocardial dysfunction. In addition, fars2-knockdown zebrafish presented pericardial edema and heart failure. FARS2 deficiency impaired mitochondrial homeostasis by directly blocking the aminoacylation of mt-tRNAPhe and inhibiting the synthesis of mitochondrial proteins, ultimately contributing to an imbalanced mitochondrial quality control system by accelerating mitochondrial hyperfragmentation and disrupting mitochondrion-related autophagy. Interfering with the mitochondrial quality control system using adeno-associated virus 9 or specific inhibitors mitigated the cardiac and mitochondrial dysfunction triggered by FARS2 deficiency by restoring mitochondrial homeostasis. CONCLUSIONS: Our findings unveil the previously unrecognized role of FARS2 in heart and mitochondrial homeostasis. This study may provide new insights into the molecular diagnosis and prevention of heritable cardiomyopathy as well as therapeutic options for FARS2-associated cardiomyopathy.

Morphological and Genetic Aspects for Post-Mortem Diagnosis of Hypertrophic Cardiomyopathy: A Systematic Review.

Hypertrophic cardiomyopathy (HCM) is one of the most common genetic cardiovascular diseases, and it shows an autosomal dominant pattern of inheritance. HCM can be clinically silent, and sudden unexpected death due to malignant arrhythmias may be the first manifestation. Thus, the HCM diagnosis could be performed at a clinical and judicial autopsy and offer useful findings on morphological features; moreover, it could integrate the knowledge on the genetic aspect of the disease. This review aims to systematically analyze the literature on the main post-mortem investigations and the related findings of HCM to reach a well-characterized and stringent diagnosis; the review was performed using PubMed and Scopus databases. The articles on the post-mortem evaluation of HCM by gross and microscopic evaluation, imaging, and genetic test were selected; a total of 36 studies were included. HCM was described with a wide range of gross findings, and there were cases without morphological alterations. Myocyte hypertrophy, disarray, fibrosis, and small vessel disease were the main histological findings. The post-mortem genetic tests allowed the diagnosis to be reached in cases without morpho-structural abnormalities; clinical and forensic pathologists have a pivotal role in HCM diagnosis; they contribute to a better definition of the disease and also provide data on the genotype-phenotype correlation, which is useful for clinical research.

Hypertrophic cardiomyopathy dysfunction mimicked in human engineered heart tissue and improved by sodium-glucose cotransporter 2 inhibitors.

AIMS: Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiomyopathy, often caused by pathogenic sarcomere mutations. Early characteristics of HCM are diastolic dysfunction and hypercontractility. Treatment to prevent mutation-induced cardiac dysfunction is lacking. Sodium-glucose cotransporter 2 inhibitors (SGLT2i) are a group of antidiabetic drugs that recently showed beneficial cardiovascular outcomes in patients with acquired forms of heart failure. We here studied if SGLT2i represent a potential therapy to correct cardiomyocyte dysfunction induced by an HCM sarcomere mutation. METHODS AND RESULTS: Contractility was measured of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) harbouring an HCM mutation cultured in 2D and in 3D engineered heart tissue (EHT). Mutations in the gene encoding ß-myosin heavy chain (MYH7-R403Q) or cardiac troponin T (TNNT2-R92Q) were investigated. In 2D, intracellular [Ca2+], action potential and ion currents were determined. HCM mutations in hiPSC-CMs impaired relaxation or increased force, mimicking early features observed in human HCM. SGLT2i enhance the relaxation of hiPSC-CMs, to a larger extent in HCM compared to control hiPSC-CMs. Moreover, SGLT2i-effects on relaxation in R403Q EHT increased with culture duration, i.e. hiPSC-CMs maturation. Canagliflozin's effects on relaxation were more pronounced than empagliflozin and dapagliflozin. SGLT2i acutely altered Ca2+ handling in HCM hiPSC-CMs. Analyses of SGLT2i-mediated mechanisms that may underlie enhanced relaxation in mutant hiPSC-CMs excluded SGLT2, Na+/H+ exchanger, peak and late Nav1.5 currents, and L-type Ca2+ current, but indicate an important role for the Na+/Ca2+ exchanger. Indeed, electrophysiological measurements in mutant hiPSC-CM indicate that SGLT2i altered Na+/Ca2+ exchange current. CONCLUSION: SGLT2i (canagliflozin > dapagliflozin > empagliflozin) acutely enhance relaxation in human EHT, especially in HCM and upon prolonged culture. SGLT2i may represent a potential therapy to correct early cardiac dysfunction in HCM.

Exploring the Connection Between Relaxed Myosin States and the Anrep Effect.

The Anrep effect is an adaptive response that increases left ventricular contractility following an acute rise in afterload. Although the mechanistic origin remains undefined, recent findings suggest a two-phase activation of resting myosin for contraction, involving strain-sensitive and posttranslational phases. We propose that this mobilization represents a transition among the relaxed states of myosin-specifically, from the super-relaxed (SRX) to the disordered-relaxed (DRX)-with DRX myosin ready to participate in force generation. This hypothesis offers a unified explanation that connects myosin's SRX-DRX equilibrium and the Anrep effect as parts of a singular phenomenon. We underscore the significance of this equilibrium in modulating contractility, primarily studied in the context of hypertrophic cardiomyopathy, the most common inherited cardiomyopathy associated with diastolic dysfunction, hypercontractility, and left ventricular hypertrophy. As we posit that the cellular basis of the Anrep effect relies on a two-phased transition of myosin from the SRX to the contraction-ready DRX configuration, any dysregulation in this equilibrium may result in the pathological manifestation of the Anrep phenomenon. For instance, in hypertrophic cardiomyopathy, hypercontractility is linked to a considerable shift of myosin to the DRX state, implying a persistent activation of the Anrep effect. These valuable insights call for additional research to uncover a clinical Anrep fingerprint in pathological states. Here, we demonstrate through noninvasive echocardiographic pressure-volume measurements that this fingerprint is evident in 12 patients with hypertrophic obstructive cardiomyopathy before septal myocardial ablation. This unique signature is characterized by enhanced contractility, indicated by a leftward shift and steepening of the end-systolic pressure-volume relationship, and a prolonged systolic ejection time adjusted for heart rate, which reverses post-procedure. The clinical application of this concept has potential implications beyond hypertrophic cardiomyopathy, extending to other genetic cardiomyopathies and even noncongenital heart diseases with complex etiologies across a broad spectrum of left ventricular ejection fractions.

Whole-exome sequencing reveals a likely pathogenic LMNA variant causing hypertrophic cardiomyopathy.

OBJECTIVE: We studied the clinical and molecular features of a family with hypertrophic cardiomyopathy (HCM). BACKGROUND: A very heterogeneous disease affecting the heart muscle, HCM is mostly caused by variants in the proteins of sarcomeres. The detection of HCM pathogenic variants can affect the handling of patients and their families. METHODS: Whole-exome sequencing (WES) was performed to assess the genetic cause(s) of HCM in a consanguineous Iranian family. RESULTS: Missense likely pathogenic variant c.1279C>T (p.Arg427Cys) within exon 7 of the LMNA gene (NM_170707) was found. The segregations were confirmed by polymerase chain reaction-based Sanger sequencing. CONCLUSIONS: Variant c.1279C>T (p.Arg427Cys) in the LMNA gene seemed to have been the cause of HCM in the family. A few LMNA gene variants related to HCM phenotypes have been recognized so far. Identifying HCM genetic basis confers significant opportunities to understand how the disease can develop and, by extension, how this progression can be arrested. Our study supports WES effectiveness for first-tier variant screening of HCM in a clinical setting.