The interaction protein of SORBS2 in myocardial tissue to find out the pathogenic mechanism of LVNC disease.

BACKGROUND: Left ventricular noncompaction cardiomyopathy (LVNC) is a cardiac disorder characterized by an excessive trabecular meshwork of deep intertrabecular recesses within the ventricular myocardium. Sorbin and SH3 domain-containing protein 2 (SORBS2) converges on the actin and microtubule cytoskeleton. Here, we investigated the proteins interacting with SORBS2 to elucidate the pathogenic mechanism of LVNC. As reported in previous studies, SORBS2 enhances the occurrence of LVNC by potentiating heart failure, but the specific mechanism remains unclear. METHODS: Building from our previous finding of elevated SORBS2 levels in LVNC hearts, we screened for proteins interacting with SORBS2 by proteomics and conducting IP experiments. Co-IP and immunofluorescence were used to verify the effects. RESULTS: We selected several proteins with high scores and high coverage that could be closely related to SORBS2 according to earlier reports showing a correlation with LVNC for verification. We finally obtained several proteins that were related to the pathogenesis of LVNC and also interacted with SORBS2, such as α-actinin, ß-tubulin, MYH7, FLNA, MYBPC3, YWHAQ and DES, and YWHAQ was the most associated. CONCLUSIONS: We focused on the YWHAQ protein, and we identified a novel mechanism through which SORBS2 interacts with YWHAQ, having a negative effect on the cell cycle, potentially leading to LVNC.

Early Lethal Noncompaction Cardiomyopathy in Siblings With Compound Heterozygous RYR2 Variant.

Two siblings presented with early lethal noncompaction cardiomyopathy (NCCM). Both carry compound heterozygous variants in the ryanodine receptor gene (RYR2). Evolving animal and human data have begun to implicate a role for RYR2 dysfunction in the development of NCCM. The identified RYR2 variants are therefore likely causative for this early lethal NCCM phenotype. Further research is needed to understand the role of RYR2 in the heart compaction process.

Elevated myocardial SORBS2 and the underlying implications in left ventricular noncompaction cardiomyopathy.

BACKGROUND: Left ventricular noncompaction cardiomyopathy (LVNC) is a hereditary heart disease characterized by an excessive trabecular meshwork of deep intertrabecular recesses within the ventricular myocardium. The guidelines for management of LVNC patients aim to improve quality of life by preventing cardiac heart failure. However, the mechanism underlying LVNC-associated heart failure remains poorly understood. METHODS: Using protein mass spectrometry analysis, we established that Sorbin And SH3 Domain Containing 2 (SORBS2) is up-regulated in LVNC hearts without changes to structure proteins. We conducted in vivo experiments wherein the heart tissues of wild-type mice were injected with an AAV9 vector to overexpress SORBS2, followed by analysis using echocardiography, T-tubule analysis and Ca2+ imaging to identify functional and morphological changes. In addition, we analyzed the function and structure of SORBS2 overexpressing human embryonic stem cell (hESC) derived cardiomyocytes (hESC-CM) via immunoblotting, immunohistochemistry, immunofluorescence, and confocal Ca2+ imaging. FINDINGS: LVNC myocardial tissues feature strongly elevated expression of SORBS2, microtubule densification and redistribution of Junctophilin 2 (JP2). SORBS2 interacts with ß-tubulin, promoting its polymerization in 293T cells and hESC-derived CMs. In vivo, cardiac dysfunction, ß-tubulin densification, JP2 translocation, T-tubule disorganization and Ca2+ handling dysfunction were observed in mice overexpressing SORBS2. INTERPRETATION: We identified a novel mechanism through which SORBS2 interacts with ß-tubulin and promotes microtubule densification, eventually effecting JP2 distribution and T-tubule, potentially contributing to heart failure in LVNC disease. FUND: This work was supported by a CAMS Initiative for Innovative Medicine grant (CAMS-I2M, 2016-I2M-1-015 to Y.J.Wei).

Multiple genetic variants in adolescent patients with left ventricular noncompaction cardiomyopathy.

BACKGROUND: Left ventricular noncompaction cardiomyopathy (LVNC) is a primary cardiomyopathy with an unclear aetiology. The clinical symptoms range from asymptomatic to heart failure, arrhythmias and sudden cardiac death. This study aimed to characterize the genetic features and clinical outcomes of LVNC who underwent heart transplantation (HTx) to reveal the potential genetic pathogenesis. METHODS AND RESULTS: We recruited 16 cases who underwent HTx in our hospital. Exome-sequencing was performed to reveal genetic background. Clinical information and histopathology features of patients were investigated. Gene expression profiling of tissue fibrosis were evaluated by quantitative PCR. The median age of patients was 21 years. Of the 16 patients, 14 harboured multiple gene variants involved in LVNC. Ten of the patients harboured biallelic variants and/or truncating variants. Young patients (<18) with biallelic variants and/or truncating variants and lower LVEF (<45%) at initial symptom deteriorated quickly. Except for noncompaction myocardium, myocardial fibrosis was a remarkable pathological feature, and gene profiles related to immune inflammation and extracellular matrix remodelling were upregulated. CONCLUSIONS: This study showed that multiple pathologic variants were underlie genetic mechanism of LVNC who in high risks, suggesting that genetic screening should be applied to the diagnosis of LVNC. LVNC patient with multiple variants should be considered carefully follow-up. Genetics involved in the phenotype and cardiac fibrosis, and is the major causing for LVNC.

Co-Phenotype of Left Ventricular Non-Compaction Cardiomyopathy and Atypical Catecholaminergic Polymorphic Ventricular Tachycardia in Association With R169Q, a Ryanodine Receptor Type 2 Missense Mutation.

BACKGROUND: Left ventricular non-compaction (LVNC) is a cardiomyopathy characterized by prominent trabeculae and intertrabecular recesses. We present the cases of 3 girls with the sameryanodine receptor type 2(RYR2) mutation who had phenotypes of both catecholaminergic polymorphic ventricular tachycardia (CPVT) and LVNC .Methods and Results:Clinical characteristics and genetic background of the 3 patients were analyzed retrospectively. Age at onset was 5, 6, and 7 years, respectively. Clinical presentation included syncope during exercise in all 3 patients and cardiac arrest in 2 patients. LVNC diagnosis was confirmed on echocardiography according to previously defined criteria. Exercise stress testing provoked ventricular arrhythmia in two of the patients. Beta-blockers (n=3) and flecainide (n=2) were given, and an implantable cardioverter defibrillator was used in 1 patient. Genotyping identified the sameRYR2-R169Q missense mutation and no other CPVT- or LVNC-related gene mutations. Functional analysis of the mutation using HEK293 cells with single-cell Ca2+imaging and [3H]ryanodine binding analysis, indicated a gain of function: a reduced threshold for overload-induced Ca2+release from the sarcoplasmic reticulum and increased fractional Ca2+release. CONCLUSIONS: The rare association of LVNC and CPVT phenotypes withRYR2mutations is less likely to be coincidental. Screening for life-threatening arrhythmias using exercise or pharmacologic stress tests is recommended in LVNC patients to prevent sudden cardiac death in those with preserved LV function.

Familial Left Ventricular Non-Compaction Is Associated With a Rare p.V407I Variant in Bone Morphogenetic Protein 10.

BACKGROUND: Left ventricular non-compaction (LVNC) is a heritable cardiomyopathy characterized by hypertrabeculation, inter-trabecular recesses and thin compact myocardium, but the genetic basis and mechanisms remain unclear. This study identified novel LVNC-associated mutations inNOTCH-dependent genes and investigated their mutational effects.Methods and Results:High-resolution melting screening was performed in 230 individuals with LVNC, followed by whole exome and Sanger sequencing of available family members. Dimerization of bone morphogenetic protein 10 (BMP10) and its binding to BMP receptors (BMPRs) were evaluated. Cellular differentiation, proliferation and tolerance to mechanical stretch were assessed in H9C2 cardiomyoblasts, expressing wild-type (WT) or mutant BMP10 delivered by adenoviral vectors. Rare variants, p.W143*-NRG1and p.V407I-BMP10, were identified in 2 unrelated probands and their affected family members. Although dimerization of mutant V407I-BMP10 was preserved like WT-BMP10, V407I-BMP10 pulled BMPR1a and BMPR2 receptors more weakly compared with WT-BMP10. On comparative gene expression and siRNA analysis, expressed BMPR1a and BMPR2 receptors were responsive to BMP10 treatment in H9C2 cardiomyoblasts. Expression of V407I-BMP10 resulted in a significantly lower rate of proliferation in H9C2 cells compared with WT-BMP10. Cyclic stretch resulted in destruction and death of V407I-BMP10 cells. CONCLUSIONS: The W143*-NRG1and V470I-BMP10variants are associated with LVNC. Impaired BMPR-binding ability, perturbed proliferation and differentiation processes and intolerance to stretch in V407I-BMP10 mutant cardiomyoblasts may underlie myocardial non-compaction.

Cardiomyopathies Due to Left Ventricular Noncompaction, Mitochondrial and Storage Diseases, and Inborn Errors of Metabolism.

The normal function of the human myocardium requires the proper generation and utilization of energy and relies on a series of complex metabolic processes to achieve this normal function. When metabolic processes fail to work properly or effectively, heart muscle dysfunction can occur with or without accompanying functional abnormalities of other organ systems, particularly skeletal muscle. These metabolic derangements can result in structural, functional, and infiltrative deficiencies of the heart muscle. Mitochondrial and enzyme defects predominate as disease-related etiologies. In this review, left ventricular noncompaction cardiomyopathy, which is often caused by mutations in sarcomere and cytoskeletal proteins and is also associated with metabolic abnormalities, is discussed. In addition, cardiomyopathies resulting from mitochondrial dysfunction, metabolic abnormalities, storage diseases, and inborn errors of metabolism are described.

Combination of Whole Genome Sequencing, Linkage, and Functional Studies Implicates a Missense Mutation in Titin as a Cause of Autosomal Dominant Cardiomyopathy With Features of Left Ventricular Noncompaction.

BACKGROUND: High throughput next-generation sequencing techniques have made whole genome sequencing accessible in clinical practice; however, the abundance of variation in the human genomes makes the identification of a disease-causing mutation on a background of benign rare variants challenging. METHODS AND RESULTS: Here we combine whole genome sequencing with linkage analysis in a 3-generation family affected by cardiomyopathy with features of autosomal dominant left ventricular noncompaction cardiomyopathy. A missense mutation in the giant protein titin is the only plausible disease-causing variant that segregates with disease among the 7 surviving affected individuals, with interrogation of the entire genome excluding other potential causes. This A178D missense mutation, affecting a conserved residue in the second immunoglobulin-like domain of titin, was introduced in a bacterially expressed recombinant protein fragment and biophysically characterized in comparison to its wild-type counterpart. Multiple experiments, including size exclusion chromatography, small-angle x ray scattering, and circular dichroism spectroscopy suggest partial unfolding and domain destabilization in the presence of the mutation. Moreover, binding experiments in mammalian cells show that the mutation markedly impairs binding to the titin ligand telethonin. CONCLUSIONS: Here we present genetic and functional evidence implicating the novel A178D missense mutation in titin as the cause of a highly penetrant familial cardiomyopathy with features of left ventricular noncompaction. This expands the spectrum of titin's roles in cardiomyopathies. It furthermore highlights that rare titin missense variants, currently often ignored or left uninterpreted, should be considered to be relevant for cardiomyopathies and can be identified by the approach presented here.

A novel lamin A/C gene missense mutation (445 V > E) in immunoglobulin-like fold associated with left ventricular non-compaction.

AIMS: Two LMNA mutations (R644C and R190W) have been associated with familial and sporadic left ventricular non-compaction (LVNC). However, the mechanisms underlying these associations have not been elucidated. METHODS AND RESULTS: Genomic DNA was isolated from peripheral blood leucocytes and analysed by direct sequencing. Human embryonic kidney 293 cells were transfected with either wild type or mutant LMNA and SCN5A for whole-cell patch-clamp experiment and fluorescence microscopy. Point mutation modeling for mutant LMNA was also performed. One novel LVNC-associated mutation (V445E) in ß2 sheet of immunoglobulin (Ig)-like fold was found in the proband and his father. We also found that the peak current of sodium channel was markedly reduced in mutant LMNA compared with WT while the activation, inactivation, and recovery curves were not significantly altered. The mutant lamin A/C were aggregated into multiple highlighted particles. Three ß sheets and multiple side chains in Ig-like fold were altered due to the replacement of a valine by glutamic acid. CONCLUSION: Our data associated a novel lamin A/C mutation (V445E) with a sudden death form of familial LVNC. The reduced sodium current in mutant LMNA may account for the advent of malignant ventricular arrhythmias. The altered structures of three ß sheets and side chains may partially explain the aggregation of lamin A/C protein subjacent to the nuclear envelope.

Improving the diagnosis of LV non-compaction with cardiac magnetic resonance imaging.

BACKGROUND: Current diagnostic criteria for left ventricular non-compaction (LVNC) poorly correlate with clinical outcomes. We aimed to develop a cardiac magnetic resonance (CMR) based semi-automated technique for quantification of non-compacted (NC) and compacted (C) masses and to ascertain their relationships to global and regional LV function. METHODS: We analysed CMR data from 30 adults with isolated LVNC and 20 controls. NC and C masses were measured using relative signal intensities of myocardium and blood pool. Global and regional LVNC masses was calculated and correlated with both global and regional LV systolic function as well as occurrence of arrhythmia. RESULTS: LVNC patients had significantly higher end-systolic (ES) and end-diastolic (ED) NC:C ratios compared to controls (ES 0.21 [SD 0.09] vs. 0.12 [SD 0.02], p<0.001; ED 0.39 [SD 0.08] vs. 0.26 [SD 0.05], p<0.001). NC:C ratios correlated inversely with global ejection fraction, with a stronger correlation in ES vs. ED (r=-0.58, p<0.001 vs. r=-0.30, p=0.03). ES basal, mid and apical NC:C ratios also showed a significant inverse correlation with global LV ejection fraction (ES basal r=-0.29, p=0.04; mid-ventricular r=-0.50, p<0.001 and apical r=-0.71, p<0.001). Upon ROC testing, an ES NC:C ratio of 0.16 had a sensitivity of 70% and a specificity of 95% for detection of significant LVNC. Patients with sustained ventricular tachycardia had a significantly higher ES NC:C ratio (0.31 [SD 0.18] vs. 0.20 [SD 0.06], p=0.02). CONCLUSIONS: The NC:C ratio derived from relative signal intensities of myocardium and blood pool improves the ability to detect clinically relevant NC compared to previous CMR techniques.

A left ventricular noncompaction in a patient with long QT syndrome caused by a KCNQ1 mutation: a case report.

A 5-year-old girl developed cardiopulmonary arrest after crying. From the electrocardiogram and echocardiography, a left ventricular noncompaction (LVNC) with long QT syndrome (LQT) was suspected as the cause of the cardiopulmonary arrest, and treatment with a ß-blocker and a calcium antagonist was then begun. A genetic screening of LQT-related genes revealed a previously reported heterozygous KCNQ1 mutation. The association of LVNC and LQT is an extremely rare condition, and long-term treatment based on the characteristics of both disorders is required. Also, the association of cardiomyopathy and LQT could become a new clinical entity in the future.

Noncompaction myocardium in association with type Ib glycogen storage disease.

Noncompaction myocardium is a rare disorder assumed to occur as an arrest of the compaction process during the normal development of the heart. Left ventricular noncompaction has been reported to be associated with a variety of cardiac and extracardiac, especially neuromuscular abnormalities. Moreover, it has been suggested that metabolic alterations could be responsible for the noncompaction. However, no association of noncompaction myocardium with type Ib glycogen storage disease (GSD) has been reported so far. Type Ib GSD is due to a defect of a transmembrane protein which results, similar to type Ia GSD, in hypoglycemia, a markedly enlarged liver and, additionally, in neutropenia, recurrent infections, and inflammatory bowel disease. Until now, no muscular or cardiac involvement has been described in type Ib GSD patients. The present case represents the first report of a noncompaction myocardium in a child with type Ib GSD who died of sudden clinical deterioration at the age of four.