RESUMEN
Gain-of-function missense variants in the cardiac ryanodine receptor (RyR2) are linked to catecholaminergic polymorphic ventricular tachycardia (CPVT), whereas RyR2 loss-of-function missense variants cause Ca2+ release deficiency syndrome (CRDS). Recently, truncating variants in RyR2 have also been associated with ventricular arrhythmias (VAs) and sudden cardiac death. However, there are limited insights into the potential clinical relevance and in vitro functional impact of RyR2 truncating variants. We performed genetic screening of patients presenting with syncope, VAs, or unexplained sudden death and in vitro characterization of the expression and function of RyR2 truncating variants in HEK293 cells. We identified two previously unknown RyR2 truncating variants (Y4591Ter and R4663Ter) and one splice site variant predicted to result in a frameshift and premature termination (N4717 + 15Ter). These 3 new RyR2 truncating variants and a recently reported RyR2 truncating variant, R4790Ter, were generated and functionally characterized in vitro. Immunoprecipitation and immunoblotting analyses showed that all 4 RyR2 truncating variants formed heteromers with the RyR2-wildtype (WT) protein. Each of these C-terminal RyR2 truncations was non-functional and suppressed [3H]ryanodine binding to RyR2-WT and RyR2-WT mediated store overload induced spontaneous Ca2+ release activity in HEK293 cells. The expression of these RyR2 truncating variants in HEK293 cells was markedly reduced compared with that of the full-length RyR2 WT protein. Our data indicate that C-terminal RyR2 truncating variants are non-functional and can exert a dominant negative impact on the function of the RyR2 WT protein through formation of heteromeric WT/truncation complex.
Asunto(s)
Canal Liberador de Calcio Receptor de Rianodina , Taquicardia Ventricular , Humanos , Arritmias Cardíacas/genética , Calcio/metabolismo , Células HEK293 , Mutación , Fenotipo , Canal Liberador de Calcio Receptor de Rianodina/genética , Canal Liberador de Calcio Receptor de Rianodina/metabolismo , Taquicardia Ventricular/genética , Taquicardia Ventricular/metabolismoRESUMEN
RATIONALE: Mutations in the cardiac Ryanodine Receptor gene (RYR2) cause dominant catecholaminergic polymorphic ventricular tachycardia (CPVT), a leading cause of sudden death in apparently healthy individuals exposed to emotions or physical exercise. OBJECTIVE: We investigated the efficacy of allele-specific silencing by RNA interference to prevent CPVT phenotypic manifestations in our dominant CPVT mice model carriers of the heterozygous mutation R4496C in RYR2. METHODS AND RESULTS: We developed an in vitro mRNA and protein-based assays to screen multiple siRNAs for their ability to selectively silence mutant RYR2-R4496C mRNA over the corresponding wild-type allele. For the most performant of these siRNAs (siRYR2-U10), we evaluated the efficacy of an adeno-associated serotype 9 viral vector (AAV9) expressing miRYR2-U10 in correcting RyR2 (Ryanodine Receptor type 2 protein) function after in vivo delivery by intraperitoneal injection in neonatal and adult RyR2R4496C/+ (mice heterozygous for the R4496C mutation in the RyR2) heterozygous CPVT mice. Transcriptional analysis showed that after treatment with miRYR2-U10, the ratio between wild-type and mutant RYR2 mRNA was doubled (from 1:1 to 2:1) confirming the ability of miRYR2-U10 to selectively inhibit RYR2-R4496C mRNA, whereas protein quantification showed that total RyR2 was reduced by 15% in the heart of treated mice. Furthermore, AAV9-miRYR2-U10 effectively (1) reduced isoproterenol-induced delayed afterdepolarizations and triggered activity in infected cells, (2) reduced adrenergically mediated ventricular tachycardia in treated mice, (3) reverted ultrastructural abnormalities of junctional sarcoplasmic reticulum and transverse tubules, and (4) attenuated mitochondrial abnormalities. CONCLUSIONS: The study demonstrates that allele-specific silencing with miRYR2-U10 prevents life-threatening arrhythmias in CPVT mice, suggesting that the reduction of mutant RyR2 may be a novel therapeutic approach for CPVT.
Asunto(s)
Alelos , Arritmias Cardíacas/genética , Heterocigoto , Mutación/genética , ARN Mensajero/genética , Canal Liberador de Calcio Receptor de Rianodina/genética , Animales , Animales Recién Nacidos , Arritmias Cardíacas/patología , Arritmias Cardíacas/prevención & control , Células Cultivadas , Silenciador del Gen/fisiología , Células HEK293 , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Fenotipo , ARN Mensajero/ultraestructura , Canal Liberador de Calcio Receptor de Rianodina/deficiencia , Canal Liberador de Calcio Receptor de Rianodina/ultraestructuraRESUMEN
AIMS: Data on predictors of time-to-first appropriate implantable cardioverter-defibrillator (ICD) therapy in patients with Brugada Syndrome (BrS) and prophylactically implanted ICD's are scarce. METHODS AND RESULTS: SABRUS (Survey on Arrhythmic Events in BRUgada Syndrome) is an international survey on 678 BrS patients who experienced arrhythmic event (AE) including 252 patients in whom AE occurred after prophylactic ICD implantation. Analysis was performed on time-to-first appropriate ICD discharge regarding patients' characteristics. Multivariate logistic regression models were utilized to identify which parameters predicted time to arrhythmia ≤5 years. The median time-to-first appropriate ICD therapy was 24.8 ± 2.8 months. A shorter time was observed in patients from Asian ethnicity (P < 0.05), those with syncope (P = 0.001), and those with Class IIa indication for ICD (P = 0.001). A longer time was associated with a positive family history of sudden cardiac death (P < 0.05). Multivariate Cox regression revealed shorter time-to-ICD therapy in patients with syncope [odds ratio (OR) 1.65, P = 0.001]. In 193 patients (76.6%), therapy was delivered during the first 5 years. Factors associated with this time were syncope (OR 0.36, P = 0.001), spontaneous Type 1 Brugada electrocardiogram (ECG) (OR 0.5, P < 0.05), and Class IIa indication (OR 0.38, P < 0.01) as opposed to Class IIb (OR 2.41, P < 0.01). A near-significant trend for female gender was also noted (OR 0.13, P = 0.052). Two score models for prediction of <5 years to shock were built. CONCLUSION: First appropriate therapy in BrS patients with prophylactic ICD's occurred during the first 5 years in 76.6% of patients. Syncope and spontaneous Type 1 Brugada ECG correlated with a shorter time to ICD therapy.
Asunto(s)
Síndrome de Brugada , Muerte Súbita Cardíaca , Desfibriladores Implantables , Implantación de Prótesis , Síncope/diagnóstico , Adulto , Síndrome de Brugada/complicaciones , Síndrome de Brugada/cirugía , Muerte Súbita Cardíaca/etiología , Muerte Súbita Cardíaca/prevención & control , Electrocardiografía/métodos , Femenino , Humanos , Masculino , Pronóstico , Implantación de Prótesis/instrumentación , Implantación de Prótesis/métodos , Implantación de Prótesis/estadística & datos numéricos , Factores de Riesgo , Factores Sexuales , Encuestas y Cuestionarios , Factores de TiempoRESUMEN
Clinical narratives are a valuable source of information for both patient care and biomedical research. Given the unstructured nature of medical reports, specific automatic techniques are required to extract relevant entities from such texts. In the natural language processing (NLP) community, this task is often addressed by using supervised methods. To develop such methods, both reliably-annotated corpora and elaborately designed features are needed. Despite the recent advances on corpora collection and annotation, research on multiple domains and languages is still limited. In addition, to compute the features required for supervised classification, suitable language- and domain-specific tools are needed. In this work, we propose a novel application of recurrent neural networks (RNNs) for event extraction from medical reports written in Italian. To train and evaluate the proposed approach, we annotated a corpus of 75 cardiology reports for a total of 4365 mentions of relevant events and their attributes (e.g., the polarity). For the annotation task, we developed specific annotation guidelines, which are provided together with this paper. The RNN-based classifier was trained on a training set including 3335 events (60 documents). The resulting model was integrated into an NLP pipeline that uses a dictionary lookup approach to search for relevant concepts inside the text. A test set of 1030 events (15 documents) was used to evaluate and compare different pipeline configurations. As a main result, using the RNN-based classifier instead of the dictionary lookup approach allowed increasing recall from 52.4% to 88.9%, and precision from 81.1% to 88.2%. Further, using the two methods in combination, we obtained final recall, precision, and F1 score of 91.7%, 88.6%, and 90.1%, respectively. These experiments indicate that integrating a well-performing RNN-based classifier with a standard knowledge-based approach can be a good strategy to extract information from clinical text in non-English languages.
Asunto(s)
Minería de Datos/métodos , Registros Electrónicos de Salud , Procesamiento de Lenguaje Natural , Cardiopatías , Humanos , Italia , Redes Neurales de la Computación , SemánticaRESUMEN
Variant interpretation for the diagnosis of genetic diseases is a complex process. The American College of Medical Genetics and Genomics, with the Association for Molecular Pathology, have proposed a set of evidence-based guidelines to support variant pathogenicity assessment and reporting in Mendelian diseases. Cardiovascular disorders are a field of application of these guidelines, but practical implementation is challenging due to the genetic disease heterogeneity and the complexity of information sources that need to be integrated. Decision support systems able to automate variant interpretation in the light of specific disease domains are demanded. We implemented CardioVAI (Cardio Variant Interpreter), an automated system for guidelines based variant classification in cardiovascular-related genes. Different omics-resources were integrated to assess pathogenicity of every genomic variant in 72 cardiovascular diseases related genes. We validated our method on benchmark datasets of high-confident assessed variants, reaching pathogenicity and benignity concordance up to 83 and 97.08%, respectively. We compared CardioVAI to similar methods and analyzed the main differences in terms of guidelines implementation. We finally made available CardioVAI as a web resource (http://cardiovai.engenome.com/) that allows users to further specialize guidelines recommendations.
Asunto(s)
Enfermedades Cardiovasculares/genética , Variación Genética , Sociedades Médicas/organización & administración , Práctica Clínica Basada en la Evidencia , Pruebas Genéticas , Humanos , Guías de Práctica Clínica como Asunto , Programas InformáticosRESUMEN
PURPOSE OF REVIEW: The current article provides a concise summary of the possibilities and limitations of genotype-based risk stratification of cardiac arrhythmias. We will outline the most important findings of the recent years in the light of their chronological and conceptual development. RECENT FINDINGS: Genotype-phenotype association studies in families with single-gene disorders as well as in the general population led to the discovery of several DNA variants significantly associated with the risk of sudden death or life-threatening arrhythmias. In genetic (monogenic) diseases, the disease-causing mutations modulate the risk of events and response to antiarrhythmic therapy according to the specific gene involved, to their position of the mutation and to their functional effects. These causal relationships have been quite well characterized in the case of long QT syndrome but are still less defined in the case of other inherited conditions. Quantitatively, the risk associated with a single genetic variant is large for DNA variants that cause monogenic inherited arrhythmias. Much different is the case of more common variants associated with the risk of arrhythmias in the general population as they are generally associated with a small effect size. SUMMARY: Genetic profiling identifies arrhythmogenic risk even if a complete picture allowing high-granularity risk stratification is yet to come.
Asunto(s)
Arritmias Cardíacas , Estudios de Asociación Genética/métodos , Predisposición Genética a la Enfermedad , Pruebas Genéticas/métodos , Medición de Riesgo , Arritmias Cardíacas/complicaciones , Arritmias Cardíacas/diagnóstico , Arritmias Cardíacas/genética , Muerte Súbita Cardíaca/etiología , Humanos , Factores de RiesgoRESUMEN
Pharmacologic challenge with sodium channel blockers is part of the diagnostic workout in patients with suspected Brugada syndrome. The test is overall considered safe but both ajmaline and flecainide detain well known pro-arrhythmic properties. Moreover, the treatment of patients with life-threatening arrhythmias during these diagnostic procedures is not well defined. Current consensus guidelines suggest to adopt cautious protocols interrupting the sodium channel blockers as soon as any ECG alteration appears. Nevertheless, the risk of life-threatening arrhythmias persists, even adopting a safe and cautious protocol and in absence of major arrhythmic risk factors. The authors revise the main published case studies of sodium channel blockers challenge in adults and in children, and summarize three cases of untreatable ventricular arrhythmias discussing their management. In particular, the role of advanced cardiopulmonary resuscitation with extra-corporeal membrane oxygenation is stressed as it can reveal to be the only reliable lifesaving facility in prolonged cardiac arrest.
Asunto(s)
Síndrome de Brugada/diagnóstico , Reanimación Cardiopulmonar , Electrocardiografía , Oxigenación por Membrana Extracorpórea , Sistema de Conducción Cardíaco/efectos de los fármacos , Bloqueadores de los Canales de Sodio/efectos adversos , Taquicardia Ventricular/terapia , Fibrilación Ventricular/terapia , Potenciales de Acción/efectos de los fármacos , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Ajmalina/administración & dosificación , Ajmalina/efectos adversos , Síndrome de Brugada/fisiopatología , Niño , Femenino , Flecainida/administración & dosificación , Flecainida/efectos adversos , Paro Cardíaco/fisiopatología , Paro Cardíaco/terapia , Sistema de Conducción Cardíaco/fisiopatología , Frecuencia Cardíaca/efectos de los fármacos , Humanos , Masculino , Persona de Mediana Edad , Valor Predictivo de las Pruebas , Factores de Riesgo , Bloqueadores de los Canales de Sodio/administración & dosificación , Taquicardia Ventricular/inducido químicamente , Taquicardia Ventricular/diagnóstico , Taquicardia Ventricular/fisiopatología , Resultado del Tratamiento , Fibrilación Ventricular/inducido químicamente , Fibrilación Ventricular/diagnóstico , Fibrilación Ventricular/fisiopatología , Adulto JovenRESUMEN
BACKGROUND: The role of programmed ventricular stimulation in identifying patients with Brugada syndrome at the highest risk for sudden death is uncertain. METHODS AND RESULTS: We performed a systematic review and pooled analysis of prospective, observational studies of patients with Brugada syndrome without a history of sudden cardiac arrest who underwent programmed ventricular stimulation. We estimated incidence rates and relative hazards of cardiac arrest or implantable cardioverter-defibrillator shock. We analyzed individual-level data from 8 studies comprising 1312 patients who experienced 65 cardiac events (median follow-up, 38.3 months). A total of 527 patients were induced into arrhythmias with up to triple extrastimuli. Induction was associated with cardiac events during follow-up (hazard ratio, 2.66; 95% confidence interval [CI], 1.44-4.92, P<0.001), with the greatest risk observed among those induced with single or double extrastimuli. Annual event rates varied substantially by syncope history, presence of spontaneous type 1 ECG pattern, and arrhythmia induction. The lowest risk occurred in individuals without syncope and with drug-induced type 1 patterns (0.23%, 95% CI, 0.05-0.68 for no induced arrhythmia with up to double extrastimuli; 0.45%, 95% CI, 0.01-2.49 for induced arrhythmia), and the highest risk occurred in individuals with syncope and spontaneous type 1 patterns (2.55%, 95% CI, 1.58-3.89 for no induced arrhythmia; 5.60%, 95% CI, 2.98-9.58 for induced arrhythmia). CONCLUSIONS: In patients with Brugada syndrome, arrhythmias induced with programmed ventricular stimulation are associated with future ventricular arrhythmia risk. Induction with fewer extrastimuli is associated with higher risk. However, clinical risk factors are important determinants of arrhythmia risk, and lack of induction does not necessarily portend low ventricular arrhythmia risk, particularly in patients with high-risk clinical features.
Asunto(s)
Síndrome de Brugada/diagnóstico , Síndrome de Brugada/terapia , Desfibriladores Implantables/efectos adversos , Desfibriladores Implantables/normas , Humanos , Estudios Observacionales como Asunto , Estudios Prospectivos , Medición de Riesgo , Taquicardia Ventricular/diagnóstico , Taquicardia Ventricular/etiología , Fibrilación Ventricular/diagnóstico , Fibrilación Ventricular/etiologíaAsunto(s)
Tratamiento Farmacológico de COVID-19 , Hidroxicloroquina/farmacología , Síndrome de QT Prolongado/tratamiento farmacológico , Anciano , Anciano de 80 o más Años , COVID-19/epidemiología , COVID-19/virología , Electrocardiografía/métodos , Femenino , Humanos , Síndrome de QT Prolongado/epidemiología , Masculino , Persona de Mediana EdadRESUMEN
Short QT3 syndrome (SQT3S) is a cardiac disorder characterized by a high risk of mortality and associated with mutations in Kir2.1 (KCNJ2) channels. The molecular mechanisms leading to channel dysfunction, cardiac rhythm disturbances and neurodevelopmental disorders, potentially associated with SQT3S, remain incompletely understood. Here, we report on monozygotic twins displaying a short QT interval on electrocardiogram recordings and autism-epilepsy phenotype. Genetic screening identified a novel KCNJ2 variant in Kir2.1 that (i) enhanced the channel's surface expression and stability at the plasma membrane, (ii) reduced protein ubiquitylation and degradation, (iii) altered protein compartmentalization in lipid rafts by targeting more channels to cholesterol-poor domains and (iv) reduced interactions with caveolin 2. Importantly, our study reveals novel physiological mechanisms concerning wild-type Kir2.1 channel processing by the cell, such as binding to both caveolin 1 and 2, protein degradation through the ubiquitin-proteasome pathway; in addition, it uncovers a potential multifunctional site that controls Kir2.1 surface expression, protein half-life and partitioning to lipid rafts. The reported mechanisms emerge as crucial also for proper astrocyte function, suggesting the need for a neuropsychiatric evaluation in patients with SQT3S and offering new opportunities for disease management.
Asunto(s)
Arritmias Cardíacas/genética , Arritmias Cardíacas/patología , Trastorno Autístico/genética , Epilepsia/genética , Sistema de Conducción Cardíaco/anomalías , Cardiopatías Congénitas/genética , Cardiopatías Congénitas/patología , Canales de Potasio de Rectificación Interna/genética , Animales , Astrocitoma/metabolismo , Trastorno Autístico/patología , Caveolina 1/metabolismo , Caveolina 2/metabolismo , Línea Celular , Niño , Epilepsia/patología , Estudios de Asociación Genética , Células HEK293 , Sistema de Conducción Cardíaco/patología , Humanos , Masculino , Mutación , Fenotipo , Canales de Potasio de Rectificación Interna/metabolismo , Gemelos Monocigóticos , Xenopus laevis/embriologíaRESUMEN
INTRODUCTION: The 2013 HRS/EHRA/APHRS consensus statement recommends the use of V1 and V2 leads recorded in the second and third intercostal spaces (High-ICS) for diagnosis of Brugada syndrome (BrS) creating a new category of patients discovered only with modified leads. The clinical presentation and the arrhythmic risk in these patients are ill defined. This study was aimed at assessing the role of High-ICS in the analysis of BrS and the clinical profile of the patients diagnosed only when ECG leads are moved to upper intercostal spaces. METHODS AND RESULTS: We searched our Brugada syndrome registry and identified 300 subjects (age 36 ± 13 years), without a diagnostic coved ST-segment elevation in conventional V1 -V3 leads, both at baseline and after provocative drug challenge. Sixty-four subjects (21.3%, mean age at last follow-up 42 ± 11 years) were diagnosed with High-ICS. Diagnosis was possible at baseline only in 4 subjects while in 60 it was made after drug challenge with sodium channel blockers. Three subjects (4.7%) with spontaneous abnormal ECG experienced cardiac events with an annual event rate (0.11%) superimposable to that of the low risk category of BrS diagnosed in standard leads. CONCLUSION: This study demonstrates that the use of new diagnostic criteria for BrS allows increasing the diagnostic yield by 20% and that the arrhythmic risk is low when BrS can be established only in High-ICS. We also show that the prognostic value of spontaneous ECG pattern is confirmed in this subgroup.
Asunto(s)
Síndrome de Brugada/diagnóstico , Electrocardiografía , Sistema de Conducción Cardíaco/fisiopatología , Potenciales de Acción , Adulto , Síndrome de Brugada/fisiopatología , Síndrome de Brugada/terapia , Electrocardiografía/normas , Femenino , Frecuencia Cardíaca , Humanos , Masculino , Persona de Mediana Edad , Guías de Práctica Clínica como Asunto , Valor Predictivo de las Pruebas , Pronóstico , Sistema de Registros , Adulto JovenRESUMEN
Dysregulated intracellular Ca(2+) signaling is implicated in a variety of cardiac arrhythmias, including catecholaminergic polymorphic ventricular tachycardia. Spontaneous diastolic Ca(2+) release (DCR) can induce arrhythmogenic plasma membrane depolarizations, although the mechanism responsible for DCR synchronization among adjacent myocytes required for ectopic activity remains unclear. We investigated the synchronization mechanism(s) of DCR underlying untimely action potentials and diastolic contractions (DCs) in a catecholaminergic polymorphic ventricular tachycardia mouse model with a mutation in cardiac calsequestrin. We used a combination of different approaches including single ryanodine receptor channel recording, optical imaging (Ca(2+) and membrane potential), and contractile force measurements in ventricular myocytes and intact cardiac muscles. We demonstrate that DCR occurs in a temporally and spatially uniform manner in both myocytes and intact myocardial tissue isolated from cardiac calsequestrin mutation mice. Such synchronized DCR events give rise to triggered electrical activity that results in synchronous DCs in the myocardium. Importantly, we establish that synchronization of DCR is a result of a combination of abbreviated ryanodine receptor channel refractoriness and the preceding synchronous stimulated Ca(2+) release/reuptake dynamics. Our study reveals how aberrant DCR events can become synchronized in the intact myocardium, leading to triggered activity and the resultant DCs in the settings of a cardiac rhythm disorder.
Asunto(s)
Señalización del Calcio/fisiología , Calsecuestrina/genética , Corazón/fisiología , Canal Liberador de Calcio Receptor de Rianodina/genética , Taquicardia Ventricular/fisiopatología , Animales , Calcio/metabolismo , Calsecuestrina/fisiología , Diástole/fisiología , Modelos Animales de Enfermedad , Ventrículos Cardíacos/citología , Masculino , Ratones , Ratones Mutantes , Mutación , Miocitos Cardíacos/fisiología , Músculos Papilares/citología , Músculos Papilares/fisiología , Canal Liberador de Calcio Receptor de Rianodina/fisiología , Retículo Sarcoplasmático/fisiología , Taquicardia Ventricular/genética , Taquicardia Ventricular/metabolismoRESUMEN
BACKGROUND: Brugada syndrome (BrS) primarily associates with the loss of sodium channel function. Previous studies showed features consistent with sodium current (INa) deficit in patients carrying desmosomal mutations, diagnosed with arrhythmogenic cardiomyopathy (or arrhythmogenic right ventricular cardiomyopathy). Experimental models showed correlation between the loss of expression of desmosomal protein plakophilin-2 (PKP2) and reduced INa. We hypothesized that PKP2 variants that reduce INa could yield a BrS phenotype, even without overt structural features characteristic of arrhythmogenic right ventricular cardiomyopathy. METHODS AND RESULTS: We searched for PKP2 variants in the genomic DNA of 200 patients with a BrS diagnosis, no signs of arrhythmogenic cardiomyopathy, and no mutations in BrS-related genes SCN5A, CACNa1c, GPD1L, and MOG1. We identified 5 cases of single amino acid substitutions. Mutations were tested in HL-1-derived cells endogenously expressing NaV1.5 but made deficient in PKP2 (PKP2-KD). Loss of PKP2 caused decreased INa and NaV1.5 at the site of cell contact. These deficits were restored by the transfection of wild-type PKP2, but not of BrS-related PKP2 mutants. Human induced pluripotent stem cell cardiomyocytes from a patient with a PKP2 deficit showed drastically reduced INa. The deficit was restored by transfection of wild type, but not BrS-related PKP2. Super-resolution microscopy in murine PKP2-deficient cardiomyocytes related INa deficiency to the reduced number of channels at the intercalated disc and increased separation of microtubules from the cell end. CONCLUSIONS: This is the first systematic retrospective analysis of a patient group to define the coexistence of sodium channelopathy and genetic PKP2 variations. PKP2 mutations may be a molecular substrate leading to the diagnosis of BrS.
Asunto(s)
Síndrome de Brugada/genética , Síndrome de Brugada/metabolismo , Fenotipo , Placofilinas/genética , Canales de Sodio/deficiencia , Adulto , Animales , Síndrome de Brugada/fisiopatología , Línea Celular , Modelos Animales de Enfermedad , Femenino , Genotipo , Sistema de Conducción Cardíaco/fisiopatología , Humanos , Masculino , Ratones , Ratones Mutantes , Persona de Mediana Edad , Mutación Missense , Miocitos Cardíacos/metabolismo , Miocitos Cardíacos/patología , Canal de Sodio Activado por Voltaje NAV1.5/metabolismo , Técnicas de Placa-Clamp , Linaje , Estudios Retrospectivos , Canales de Sodio/metabolismoRESUMEN
BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia is an inherited arrhythmogenic disorder characterized by sudden cardiac death in children. Drug therapy is still insufficient to provide full protection against cardiac arrest, and the use of implantable defibrillators in the pediatric population is limited by side effects. There is therefore a need to explore the curative potential of gene therapy for this disease. We investigated the efficacy and durability of viral gene transfer of the calsequestrin 2 (CASQ2) wild-type gene in a catecholaminergic polymorphic ventricular tachycardia knock-in mouse model carrying the CASQ2(R33Q/R33Q) (R33Q) mutation. METHODS AND RESULTS: We engineered an adeno-associated viral vector serotype 9 (AAV9) containing cDNA of CASQ2 wild-type (AAV9-CASQ2) plus the green fluorescent protein (GFP) gene to infect newborn R33Q mice studied by in vivo and in vitro protocols at 6, 9, and 12 months to investigate the ability of the infection to prevent the disease and adult R33Q mice studied after 2 months to assess whether the AAV9-CASQ2 delivery could revert the catecholaminergic polymorphic ventricular tachycardia phenotype. In both protocols, we observed the restoration of physiological expression and interaction of CASQ2, junctin, and triadin; the rescue of electrophysiological and ultrastructural abnormalities in calcium release units present in R33Q mice; and the lack of life-threatening arrhythmias. CONCLUSIONS: Our data demonstrate that viral gene transfer of wild-type CASQ2 into the heart of R33Q mice prevents and reverts severe manifestations of catecholaminergic polymorphic ventricular tachycardia and that this curative effect lasts for 1 year after a single injection of the vector, thus posing the rationale for the design of a clinical trial.
Asunto(s)
Envejecimiento , Calsecuestrina/genética , Dependovirus/genética , Taquicardia Ventricular/terapia , Animales , Proteínas de Unión al Calcio/metabolismo , Calsecuestrina/metabolismo , Proteínas Portadoras/metabolismo , Modelos Animales de Enfermedad , Femenino , Terapia Genética , Masculino , Proteínas de la Membrana/metabolismo , Ratones , Ratones Noqueados , Oxigenasas de Función Mixta/metabolismo , Proteínas Musculares/metabolismo , Mutación/genética , Taquicardia Ventricular/metabolismo , Taquicardia Ventricular/patología , Resultado del TratamientoRESUMEN
RATIONALE: The recessive form of catecholaminergic polymorphic ventricular tachycardia is caused by mutations in the cardiac calsequestrin-2 gene; this variant of catecholaminergic polymorphic ventricular tachycardia is less well characterized than the autosomal-dominant form caused by mutations in the ryanodine receptor-2 gene. OBJECTIVE: We characterized the intracellular Ca²âº homeostasis, electrophysiological properties, and ultrastructural features of the Ca²âº release units in the homozygous calsequestrin 2-R33Q knock-in mouse model (R33Q) R33Q knock-in mouse model. METHODS AND RESULTS: We studied isolated R33Q and wild-type ventricular myocytes and observed properties not previously identified in a catecholaminergic polymorphic ventricular tachycardia model. As compared with wild-type cells, R33Q myocytes (1) show spontaneous Ca²âº waves unable to propagate as cell-wide waves; (2) show smaller Ca²âºsparks with shortened coupling intervals, suggesting a reduced refractoriness of Ca²âº release events; (3) have a reduction of the area of membrane contact, of the junctions between junctional sarcoplasmic reticulum and T tubules (couplons), and of junctional sarcoplasmic reticulum volume; (4) have a propensity to develop phase 2 to 4 afterdepolarizations that can elicit triggered beats; and (5) involve viral gene transfer with wild-type cardiac calsequestrin-2 that is able to normalize structural abnormalities and to restore cell-wide calcium wave propagation. CONCLUSIONS: Our data show that homozygous cardiac calsequestrin-2-R33Q myocytes develop spontaneous Ca²âº release events with a broad range of intervals coupled to preceding beats, leading to the formation of early and delayed afterdepolarizations. They also display a major disruption of the Ca²âº release unit architecture that leads to fragmentation of spontaneous Ca²âº waves. We propose that these 2 substrates in R33Q myocytes synergize to provide a new arrhythmogenic mechanism for catecholaminergic polymorphic ventricular tachycardia.
Asunto(s)
Señalización del Calcio/fisiología , Miocitos Cardíacos/ultraestructura , Taquicardia Ventricular/patología , Taquicardia Ventricular/fisiopatología , Remodelación Ventricular/fisiología , Potenciales de Acción/fisiología , Animales , Ratones , Ratones Transgénicos , Miocitos Cardíacos/patologíaRESUMEN
RATIONALE: Catecholaminergic polymorphic ventricular tachycardia is an inherited disease that predisposes to cardiac arrest and sudden death. The disease is associated with mutations in the genes encoding for the cardiac ryanodine receptor (RyR2) and cardiac calsequestrin (CASQ2). CASQ2 mutations lead to a major loss of CASQ2 monomers, possibly because of enhanced degradation of the mutant protein. The decrease of CASQ2 is associated with a reduction in the levels of Triadin (TrD) and Junctin (JnC), two proteins that form, with CASQ2 and RyR2, a macromolecular complex devoted to control of calcium release from the sarcoplasmic reticulum. OBJECTIVE: We intended to evaluate whether viral gene transfer of wild-type CASQ2 may rescue the broad spectrum of abnormalities caused by mutant CASQ2. METHODS AND RESULTS: We used an adeno-associated serotype 9 viral vector to express a green fluorescent protein-tagged CASQ2 construct. Twenty weeks after intraperitoneal injection of the vector in neonate CASQ2 KO mice, we observed normalization of the levels of calsequestrin, triadin, and junctin, rescue of electrophysiological and ultrastructural abnormalities caused by CASQ2 ablation, and lack of life-threatening arrhythmias. CONCLUSIONS: We have proven the concept that induction of CASQ2 expression in knockout mice reverts the molecular, structural, and electric abnormalities and prevents life-threatening arrhythmias in CASQ2-defective catecholaminergic polymorphic ventricular tachycardia mice. These data support the view that development of CASQ2 viral gene transfer could have clinical application.
Asunto(s)
Arritmias Cardíacas/genética , Arritmias Cardíacas/patología , Calsecuestrina/genética , Dependovirus/genética , Técnicas de Transferencia de Gen , Miocitos Cardíacos/ultraestructura , Fenotipo , Animales , Arritmias Cardíacas/metabolismo , Proteínas de Unión al Calcio/metabolismo , Calsecuestrina/metabolismo , Proteínas Portadoras/metabolismo , Células Cultivadas , Modelos Animales de Enfermedad , Electrocardiografía , Femenino , Ventrículos Cardíacos/patología , Masculino , Proteínas de la Membrana/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Oxigenasas de Función Mixta/metabolismo , Proteínas Musculares/metabolismo , Mutación/genética , Miocitos Cardíacos/metabolismo , Miocitos Cardíacos/patología , Canal Liberador de Calcio Receptor de Rianodina/metabolismo , Taquicardia Ventricular/genética , Taquicardia Ventricular/metabolismo , Taquicardia Ventricular/patologíaRESUMEN
BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia is characterized by stress-triggered syncope and sudden death. Patients with catecholaminergic polymorphic ventricular tachycardia manifest sinoatrial node (SAN) dysfunction, the mechanisms of which remain unexplored. METHODS AND RESULTS: We investigated SAN [Ca(2+)](i) handling in mice carrying the catecholaminergic polymorphic ventricular tachycardia-linked mutation of ryanodine receptor (RyR2(R4496C)) and their wild-type (WT) littermates. In vivo telemetric recordings showed impaired SAN automaticity in RyR2(R4496C) mice after isoproterenol injection, analogous to what was observed in catecholaminergic polymorphic ventricular tachycardia patients after exercise. Pacemaker activity was explored by measuring spontaneous [Ca(2+)](i) transients in SAN cells within the intact SAN by confocal microscopy. RyR2(R4496C) SAN presented significantly slower pacemaker activity and impaired chronotropic response under ß-adrenergic stimulation, accompanied by the appearance of pauses (in spontaneous [Ca(2+)](i) transients and action potentials) in 75% of the cases. Ca(2+) spark frequency was increased by 2-fold in RyR2(R4496C) SAN. Whole-cell patch-clamp experiments performed on isolated RyR2(R4496C) SAN cells showed that L-type Ca(2+) current (I(Ca,L)) density was reduced by ≈50%, an effect blunted by internal Ca(2+) buffering. Isoproterenol dramatically increased the frequency of Ca(2+) sparks and waves by ≈5 and ≈10-fold, respectively. Interestingly, the sarcoplasmic reticulum Ca(2+) content was significantly reduced in RyR2(R4496C) SAN cells in the presence of isoproterenol, which may contribute to stopping the "Ca(2+) clock" rhythm generation, originating SAN pauses. CONCLUSION: The increased activity of RyR2(R4496C) in SAN leads to an unanticipated decrease in SAN automaticity by a Ca(2+)-dependent decrease of I(Ca,L) and sarcoplasmic reticulum Ca(2+) depletion during diastole, identifying subcellular pathophysiological alterations contributing to the SAN dysfunction in catecholaminergic polymorphic ventricular tachycardia patients.
Asunto(s)
Calcio/metabolismo , Mutación/genética , Canal Liberador de Calcio Receptor de Rianodina/genética , Retículo Sarcoplasmático/metabolismo , Nodo Sinoatrial/fisiopatología , Taquicardia Ventricular/metabolismo , Taquicardia Ventricular/fisiopatología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Agonistas Adrenérgicos beta/farmacología , Adulto , Anciano , Animales , Señalización del Calcio/efectos de los fármacos , Modelos Animales de Enfermedad , Ejercicio Físico , Femenino , Humanos , Técnicas In Vitro , Isoproterenol/farmacología , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Mutantes , Persona de Mediana Edad , Técnicas de Placa-Clamp , Canal Liberador de Calcio Receptor de Rianodina/metabolismo , Retículo Sarcoplasmático/efectos de los fármacos , Nodo Sinoatrial/metabolismo , Nodo Sinoatrial/patología , Taquicardia Ventricular/genéticaRESUMEN
The L-type cardiac calcium channel (LTCC) plays a prominent role in the electric and mechanical function of the heart. Mutations in the LTCC have been associated with a number of inherited cardiac arrhythmia syndromes, including Timothy, Brugada, and early repolarization syndromes. Elucidation of the genetic defects associated with these syndromes has led to a better understanding of molecular and cellular mechanisms and the development of novel therapeutic approaches to dealing with the arrhythmic manifestations. This review provides an overview of the molecular structure and function of the LTCC, the genetic defects in these channels known to contribute to inherited disorders, and the underlying molecular and cellular mechanisms contributing to the development of life-threatening arrhythmias.
Asunto(s)
Arritmias Cardíacas/genética , Canales de Calcio Tipo L/genética , Mutación/genética , Arritmias Cardíacas/metabolismo , Arritmias Cardíacas/patología , Canales de Calcio Tipo L/metabolismo , Humanos , Miocardio/metabolismo , Miocardio/patología , FenotipoRESUMEN
RATIONALE: Flecainide prevents arrhythmias in catecholaminergic polymorphic ventricular tachycardia, but the antiarrhythmic mechanism remains unresolved. It is possible for flecainide to directly affect the cardiac ryanodine receptor (RyR2); however, an extracellular site of action is suggested because of the hydrophilic nature of flecainide. OBJECTIVE: To investigate the mechanism for the antiarrhythmic action of flecainide in a RyR2(R4496C+/-) knock-in mouse model of catecholaminergic polymorphic ventricular tachycardia. METHODS AND RESULTS: Flecainide prevented catecholamine-induced sustained ventricular tachycardia in RyR2(R4496C+/-) mice. Cellular studies were performed with isolated RyR2(R4496C+/-) myocytes. Isoproterenol caused the appearance of spontaneous Ca(2+) transients, which were unaffected by flecainide (6 µmol/L). Flecainide did not affect Ca(2+) transient amplitude, decay, or sarcoplasmic reticulum Ca(2+) content. Moreover, it did not affect the frequency of spontaneous Ca(2+) sparks in permeabilized myocytes. In contrast, flecainide effectively prevented triggered activity induced by isoproterenol. The threshold for action potential induction was increased significantly (P<0.01), which suggests a primary extracellular antiarrhythmic effect mediated by Na(+) channel blockade. CONCLUSIONS: Flecainide prevents catecholaminergic polymorphic ventricular tachycardia in RyR2(R4496C+/-) mice; however, at variance with previous reports, we observed minimal effects on intracellular Ca(2+) homeostasis. Our data suggest that the antiarrhythmic activity of the drug is caused by reduction of Na(+) channel availability and by an increase in the threshold for triggered activity.