Aim. Cardiac arrhythmias comprise a major health and economic burden and are associated with significant morbidity and mortality, including cardiac failure, stroke and sudden cardiac death (SCD). ...Development of efficient preventive and therapeutic strategies is hampered by incomplete knowledge of disease mechanisms and pathways. Our aim is to identify novel mechanisms underlying cardiac arrhythmia and SCD using an unbiased approach.
Methods and Results. We employed a phenotype-driven N-ethyl-N-nitrosourea (ENU) mutagenesis screen and identified a mouse line with a high incidence of sudden death at young age (6-9 weeks) in the absence of prior symptoms. Affected mice were found to be homozygous for the nonsense mutation Bcat2p.Q300*/p.Q300* in the Bcat2 gene encoding branched chain amino acid transaminase 2. At the age of 4-5 weeks, Bcat2p.Q300*/p.Q300* mice displayed drastic increase of plasma levels of branch chain amino acids (BCAAs – leucine, isoleucine, valine) due to the incomplete catabolism of BCAAs, in addition to inducible arrhythmias ex vivo as well as cardiac conduction and repolarization disturbances. In line with these findings, plasma BCAA levels were positively correlated to ECG indices of conduction and repolarization in the German community-based KORA F4 Study. Isolated cardiomyocytes from Bcat2p.Q300*/p.Q300* mice revealed action potential (AP) prolongation, pro-arrhythmic events (early and late afterdepolarizations, triggered APs) and dysregulated calcium homeostasis. Incubation of human pluripotent stem cell-derived cardiomyocytes with elevated concentration of BCAAs induced similar calcium dysregulation and pro-arrhythmic events which were prevented by rapamycin, demonstrating the crucial involvement of mTOR pathway activation.
Conclusions. Our findings identify for the first time a causative link between elevated BCAAs and arrhythmia, which has implications for arrhythmogenesis in conditions associated with BCAA metabolism dysregulation such as diabetes, metabolic syndrome and heart failure. Translational perspectives. Development of efficient anti-arrhythmic strategies is hampered by incomplete knowledge of disease mechanisms. Using an unbiased approach, we here identified for the first time a pro-arrhythmic effect of increased levels of branched chain amino acids (BCAAs). This is of particular relevance for conditions associated with BCAA dysregulation and increased arrhythmia risk, including heart failure, obesity and diabetes, as well as for athletes supplementing their diet with BCAAs. Such metabolic dysregulation is potentially modifiable through dietary interventions, paving the way for novel preventive strategies. Our findings furthermore identify mTOR inhibition as a potential anti-arrhythmic strategy in patients with metabolic syndrome.
Complex molecular programs in specific cell lineages govern human heart development. Hypoplastic left heart syndrome (HLHS) is the most common and severe manifestation within the spectrum of left ...ventricular outflow tract obstruction defects occurring in association with ventricular hypoplasia. The pathogenesis of HLHS is unknown, but hemodynamic disturbances are assumed to play a prominent role.
To identify perturbations in gene programs controlling ventricular muscle lineage development in HLHS, we performed whole-exome sequencing of 87 HLHS parent-offspring trios, nuclear transcriptomics of cardiomyocytes from ventricles of 4 patients with HLHS and 15 controls at different stages of heart development, single cell RNA sequencing, and 3D modeling in induced pluripotent stem cells from 3 patients with HLHS and 3 controls.
Gene set enrichment and protein network analyses of damaging de novo mutations and dysregulated genes from ventricles of patients with HLHS suggested alterations in specific gene programs and cellular processes critical during fetal ventricular cardiogenesis, including cell cycle and cardiomyocyte maturation. Single-cell and 3D modeling with induced pluripotent stem cells demonstrated intrinsic defects in the cell cycle/unfolded protein response/autophagy hub resulting in disrupted differentiation of early cardiac progenitor lineages leading to defective cardiomyocyte subtype differentiation/maturation in HLHS. Premature cell cycle exit of ventricular cardiomyocytes from patients with HLHS prevented normal tissue responses to developmental signals for growth, leading to multinucleation/polyploidy, accumulation of DNA damage, and exacerbated apoptosis, all potential drivers of left ventricular hypoplasia in absence of hemodynamic cues.
Our results highlight that despite genetic heterogeneity in HLHS, many mutations converge on sequential cellular processes primarily driving cardiac myogenesis, suggesting novel therapeutic approaches.
Several arrhythmia syndromes that for long were considered idiopathic are now known to have a genetic basis and are caused by mutations in genes primarily encoding ion channels.Mutations in cardiac ...ion channels lead to abnormal ionic current characteristics via mechanisms, such as defective channel gating or reduction in sarcolemmal channel expression. This results in the electrocardiogram (ECG) features or arrhythmogenesis in the inherited arrhythmia syndromes.The genetic basis for most arrhythmia syndromes is heterogeneous (a given disorder may be caused by mutations in different genes) and evidence for further genetic heterogeneity exists.It is becoming increasingly clear that therapy should take the type of gene affected into consideration (gene-specific therapy).Considerable heterogeneity may exist in disease manifestation (both in severity as well as differences in disease features) among family members carrying the same mutation.
IntroductionThe recently discovered association between Calmodulin (CaM) mutations and diverse conditions associated with life-threatening arrhythmias, ranging from long QT syndrome (LQTS), to ...catecholaminergic polymorphic ventricular tachycardia (CPVT), to idiopathic ventricular fibrillation (IVF), has led to the definition of a new clinical entity called calmodulinopathy. Only a few reports based on small numbers are available so far. To define the natural history and response to therapy we have established an international calmodulinopathy registry (ICaMR).MethodsICaMR is an observational multi-center study enrolling patients (pts) with a mutation in one of the 3 CaM genes, which will be followed prospectively for 10 years. Genetic and clinical data are collected through a dedicated form sent to centers in Europe, North America and Japan.ResultsAt this time the ICaMR includes 49 55% females, median age 10 years heterozygous CALM1(n=32), CALM2 (n=12) or CALM3 (n=5) mutation-positive subjects. Cardiac events occurred in 41 pts (84%) at a median age of 4 years (IQR 1.5-9). Cardiac arrests (CA) or sudden deaths (SD), occurred in 30 (61%). In 29% of patients there was a fetal/perinatal presentation of LQTS, with a mean QTc of 650 ms, bradycardia, 2:1 AV block and/or T wave alternans. There are 2 main phenotypes1) CaM-LQTS (18 individuals in 18 families); 2) CaM-CPVT (19 subjects in 5 families). The remaining cases include 2 families with IVF, 4 with SD and 2 with overlapping LQTS/CPVT. In 80% of the probands the mutation was de novo. A mutation in the EF-hand IV was found in 13/18 (72%) CaM-LQTS, and in none of the 19 CaM-CPVT (p<0.0001), suggesting a correlation between mutation location and phenotype. Seven pts had SD without therapy; among 34 pts known to be treated with beta-blockers, mexiletine, left sympathectomy and/or implantable devices, 18 (53%) had recurrences, including 4 SD and 5 appropriate ICD shocks.ConclusionsData from the ICaMR confirm the malignant course of calmodulinopathy, unveil a large spectrum of phenotypic features and provide preliminary insights into mutation-site specific clinical manifestation. The Registry will provide data for understanding the natural history and for guiding a rational approach to therapy.
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