RESUMO
Long QT syndrome (LQTS) is a disorder of cardiac electrophysiology resulting in life-threatening arrhythmias; nowadays, only a few drugs are available for the management of LQTS. Focusing our attention on LQT2, one of the most common subtypes of LQTS caused by mutations in the human ether-à-go-go-related gene (hERG), in the present work, the stereoselectivity of the recently discovered mexiletine-derived urea 8 was investigated on the hERG potassium channel. According to preliminary in silico predictions, in vitro studies revealed a stereoselective behavior, with the meso form showing the greatest hERG opening activity. In addition, functional studies on guinea pig isolated left atria, aorta, and ileum demonstrated that 8 does not present any cardiac or intestinal liability in our ex vivo studies. Due to its overall profile, (R,S)-8 paves the way for the design and development of a new series of compounds potentially useful in the treatment of both congenital and drug-induced forms of LQTS.
Assuntos
Síndrome do QT Longo , Mexiletina , Humanos , Animais , Cobaias , Mexiletina/farmacologia , Simulação de Acoplamento Molecular , Ureia , Relação Estrutura-Atividade , Canais de Potássio/metabolismo , Síndrome do QT Longo/genética , Síndrome do QT Longo/terapiaRESUMO
Industrial chemical PFAS are persistent pollutants. Long chain PFAS were taken out of production due to their risk for human health, however, new congeners PFAS have been introduced. The in vitro effects of the long-chain PFOA, the short-chain PFHxA and the new-generation C6O4 were evaluated in normal and in thyroid cancer cell lines in terms of cell viability and proliferation, and secretion of a pro-tumorigenic chemokine (CXCL8), both at the mRNA and at the protein level. The Nthy-ory 3-1 normal-thyroid cell line, the TPC-1 and the 8505C (RET/PTC rearranged and BRAFV600e mutated, respectively) thyroid-cancer cell lines were exposed to increasing concentrations of each PFAS in a time-course. We evaluated viability using WST-1 (confirmed by AnnexinV/PI) and proliferation using the cristal-violet test. To evaluate CXCL8 mRNA we used RT-PCR and measured CXCL8 in the supernatants by ELISA. The exposure to none PFAS did not affect thyroid cells viability (except for a reduction of 8505C cells viability after 144 h) or proliferation. Individual PFAS differently modulated CXCL8 mRNA and protein level. PFOA increased CXCL8 both at mRNA and protein level in the three cell lines; PFHxA increased CXCL8 mRNA in the three cell lines, but increased the protein only in TPC-1 cells; C6O4 increased the CXCL8 mRNA only in thyroid cancer cell lines, but never increased the CXCL8 protein. The results of the present study indicate that the in vitro exposure to different PFAS may modulate both at the mRNA and secreted protein levels of CXCL8 in normal and cancer thyroid cells. Strikingly different effects emerged according to the specific cell type and to the targeted analyte (CXCL8 mRNA or protein).
Assuntos
Fluorocarbonos , Neoplasias da Glândula Tireoide , Humanos , Linhagem Celular Tumoral , Sobrevivência Celular , Fluorocarbonos/farmacologia , Interleucina-8RESUMO
Glyphosate is a pesticide, which contaminates the environment and exposes workers and general population to its residues present in foods and waters. In soil, Glyphosate is degraded in metabolites, amino-methyl-phosphonic acid (AMPA) being the main one. Glyphosate is considered a potential cancerogenic and endocrine-disruptor agent, however its adverse effects on the thyroid were evaluated only in animal models and in vitro data are still lacking. Aim of this study was to investigate whether exposure to Glyphosate could exert adverse effects on thyroid cells in vitro. Two models (adherent-2D and spheroid-3D) derived from the same cell strain Fisher-rat-thyroid-cell line-5 (FRTL-5) were employed. After exposure to Glyphosate at increasing concentrations (0.0, 0.1-0.25- 0.5-1.0-2.0-10.0 mM) we evaluated cell viability by WST-1 (adherent and spheroids), results being confirmed by propidium-iodide staining (only for spheroids). Proliferation of adherent cells was assessed by crystal violet and trypan-blue assays, the increasing volume of spheroids was taken as a measure of proliferation. We also evaluated the ability of cells to form spheroids after Glyphosate exposure. We assessed changes of reactive-oxygen-species (ROS) by the cell-permeant H2DCFDA. Glyphosate-induced changes of mRNAs encoding for thyroid-related genes (TSHR, TPO, TG, NIS, TTF-1 and PAX8) were evaluated by RT-PCR. Glyphosate reduced cell viability and proliferation in both models, even if at different concentrations. Glyphosate at the highest concentration reduced the ability of FRTL-5 to form spheroids. An increased ROS production was found in both models after exposure to Glyphosate. Finally, Glyphosate increased the mRNA levels of some thyroid related genes (TSHR, TPO, TG and TTF-1) in both models, while it increased the mRNAs of PAX8 and NIS only in the adherent model. The present study supports an adverse effect of Glyphosate on cultured thyroid cells. Glyphosate reduced cell viability and proliferation and increased ROS production in thyroid cells.
Assuntos
Fatores de Transcrição Box Pareados , Glândula Tireoide , Ratos , Animais , Humanos , Fatores de Transcrição Box Pareados/genética , Fatores de Transcrição Box Pareados/metabolismo , Fatores de Transcrição Box Pareados/farmacologia , Espécies Reativas de Oxigênio/metabolismo , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Proteínas Nucleares/farmacologia , Fator de Transcrição PAX8/metabolismo , RNA Mensageiro/metabolismo , GlifosatoRESUMO
BACKGROUND: Evidence for the role of the CACNA1C gene, which encodes for the α-subunit of the cardiac L-type calcium channel CaV1.2, as a cause of the BrS3 variant of Brugada syndrome (BrS) is contradictory. OBJECTIVE: The purpose of this study was to define in a large BrS cohort the yield of molecular screening and to test whether appropriate patient selection could improve clinical utility. METHODS: A total of 709 patients were included in this study. BrS probands (n = 563, consecutively referred) underwent CACNA1C sequencing. Two matched cohorts where defined: discovery cohort (n = 200) and confirmation cohort (n = 363). In addition, the clinical phenotypes of a matched SCN5A-positive BrS cohort (n = 146) were included for comparative genotype-phenotype correlation. RESULTS: In the discovery cohort, we identified 11 different rare variants in 9 patients; 10 of the variants (5%) were considered potentially causative based on their frequency in the general population. However, American College of Medical Genetics criteria were unable to classify the majority (80%) of them, which eventually were labeled as variants of unknown significance (VUS). Functional studies revealed a loss of function for 9 variants, pointing to a prevalence of CACNA1C causative variants in 4% of the discovery cohort. Genotype-phenotype correlation showed that pathogenic variants are significantly more frequent in patients with shorter QTc (12.9% vs 2.2% in patients with QTc <390 ms). CONCLUSION: CACNA1C is an infrequent but definitive cause of BrS typically associated with short QT. Functional studies are highly relevant to improve variant interpretation.
Assuntos
Síndrome de Brugada , Síndrome de Brugada/diagnóstico , Síndrome de Brugada/epidemiologia , Síndrome de Brugada/genética , Canais de Cálcio Tipo L/genética , Testes Genéticos , Humanos , Mutação , Canal de Sódio Disparado por Voltagem NAV1.5/genética , Fenótipo , PrevalênciaRESUMO
INTRODUCTION: Angiotensin-converting-enzyme-2 (ACE-2) was demonstrated to be the receptor for cellular entry of SARS-CoV-2. ACE-2 mRNA was identified in several human tissues and recently also in thyroid cells in vitro. PURPOSE: Aim of the present study was to investigate the effect of pro-inflammatory cytokines on the ACE-2 mRNA levels in human thyroid cells in primary cultures. METHODS: Primary thyroid cell cultures were treated with IFN-γ and TNF-α alone or in combination for 24 h. ACE-2 mRNA levels were measured by RT-PCR. As a control, the levels of IFN-γ inducible chemokine (CXCL10) were measured in the respective cell culture supernatants. RESULTS: The mean levels of ACE-2 mRNA increased after treatment with IFN-γ and TNF-α in all the thyroid cell preparations, while the combination treatment did not consistently synergically increase ACE-2-mRNA. At difference, CXCL10 was consistently increased by IFN-γ and synergically further increased by the combination treatment with IFN-γ + TNF-α, with respect to IFN-γ alone. CONCLUSIONS: The results of the present study show that IFN-γ and, to a lesser extent TNF-α consistently increase ACE-2 mRNA levels in NHT primary cultures. More interestingly, the combined stimulation (proven to be effective according to the synergic effect registered for CXCL10) produces different responses in terms of ACE-2 mRNA modulation. These results would suggest that elevated levels of pro-inflammatory cytokines could facilitate the entering of the virus in cells by further increasing ACE-2 expression and/or account for the different degree of severity of SARS-COV-2 infection. This hypothesis deserves to be confirmed by further specific studies.
Assuntos
COVID-19 , Glândula Tireoide , Enzima de Conversão de Angiotensina 2 , Citocinas , Humanos , Projetos Piloto , RNA Mensageiro , SARS-CoV-2 , Fator de Necrose Tumoral alfaRESUMO
The hexafluoropropylene-oxide-dimer-acid (GenX) is a short-chain perfluoroalkyl substance that was recently introduced following the phase out of PFOA, as an alternative for the process of polymerization. GenX was detected at high concentrations in rivers, drinking water and in sera of exposed workers and recent findings suggested its potential dangerousness for human health. Aim of the study was to assess the consequences of GenX exposure on in vitro thyroid cells with particular attention to the effects on cell-viability, proliferation, DNA-damage and in the thyroid-related genes expression. FRTL-5 rat-thyroid cell line were incubated with increasing concentrations of GenX for 24 h, 48 h and 72 h to assess cell viability by WST-1. DNA-damage was assessed by comet assay and further confirmed by micronucleus assay. The proliferation of survived cells was measured by staining with crystal violet and evaluation of its optical density after incubation with SDS. Changes in TTF-1, Pax8, Tg, TSH-R, NIS and TPO genes expression were evaluated by RT-PCR. GenX exposure reduced FRTL-5 viability in a time and dose-dependent manner (24 h: ANOVA F = 22.286; p < 0.001; 48 h: F = 43.253, p < 0.001; 72 h: F = 49.708, p < 0.001). Moreover, GenX exerted a genotoxic effect, as assessed by comet assay (significant increase in tail-length, olive-tail-moment and percentage of tail-DNA) and micronucleus assay, both at cytotoxic and non-cytotoxic concentrations. Exposure to GenX at concentrations non-cytotoxic exerted a significant lowering of the expression of the regulatory gene TTF-1 (p < 0.05 versus untreated) and higher expression of Pax-8 (p < 0.05 versus untreated) and a down-regulation of NIS (p < 0.05 versus untreated). In addition, cells survived to GenX exposure showed a reduced re-proliferation ability (24 h: ANOVA F = 11,941; p < 0,001; 48 h: F = 93.11; p < 0.001; 72 h F = 21.65; p < 0.001). The exposure to GenX produces several toxic effects on thyroid cells in vitro. GenX is able to promote DNA-damage and to affect the expression of thyroid transcription-factor genes.
Assuntos
Proteínas Nucleares , Glândula Tireoide , Animais , Sobrevivência Celular , DNA , Humanos , Fatores de Transcrição Box Pareados , Ratos , TransativadoresRESUMO
Phenformin is a biguanide drug which, besides the original anti-diabetic effect, also exerts anti-cancer effects. The aim of this study was to further characterize these latter in terms of both cell-viability and modulation of the secretion of the pro-tumorigenic chemokine CXCL8. Normal human thyrocytes in primary cultures (NHT) and thyroid cancer cell lines, TPC-1 and 8505C (RET/PTC and BRAFV600E mutated, respectively) were treated with increasing concentrations of phenformin at different times. Cell-viability was assessed by WST-1 and further characterized by AnnexinV/PI staining and cell proliferation colony-assay. CXCL8 levels were measured in cell supernatants. Phenformin reduced cell-viability in TPC-1 and 8505C and their ability to form colonies. In NHT cells, phenformin affected cell-viability only at the maximal dose but interestingly it inhibited CXCL8 secretion at all the concentrations not affecting cell-viability. Phenformin had no effect on CXCL8 secretion in thyroid cancer cell lines. Thus, phenformin exerts anti-cancer effects on both cancer cells (cell death induction) and surrounding normal cells (inhibition of CXCL8 secretion). These results highlight that the anti-cancer effects of phenformin are multifaceted and effective on both solid and soluble components of the tumor-microenvironment.
RESUMO
CXCL8 is a chemokine secreted by normal and thyroid cancer cells with proven tumor-promoting effects. The presence of BRAFV600E mutation is associated with a more aggressive clinical behavior and increased ability to secrete CXCL8 by papillary-thyroid-cancer cells. Aim of this study was to test the effect of the BRAF-inhibitor (PLX4720) on the basal and TNF-α-induced CXCL8 secretions in BRAFV600E mutated (BCPAP, 8305C, 8505C), in RET/PTC rearranged (TPC-1) thyroid-cancer-cell-lines and in normal-human-thyrocytes (NHT). Cells were incubated with increasing concentrations of PLX4720 alone or in combination with TNF-α for 24-hours. CXCL8 concentrations were measured in the cell supernatants. PLX4720 dose-dependently inhibited the basal and the TNF-α-induced CXCL8 secretions in BCPAP (F: 14.3, p < 0.0001 for basal and F: 12.29 p < 0.0001 for TNF-α), 8305C (F: 407.9 p < 0.0001 for basal and F: 5.76 p < 0.0001 for TNF-α) and 8505C (F:55.24 p < 0.0001 for basal and F: 42.85 p < 0.0001 for TNF-α). No effect was found in TPC-1 (F: 1.8, p = 0.134 for basal; F: 1.6, p = 0.178 for TNF-α). In NHT an inhibitory effect was found only at the highest concentration of PLX4720 (F: 13.13 p < 0.001 for basal and F: 2.5 p < 0.01 for TNF-α). Cell migration assays showed that PLX4720 reduced both basal and CXCL8-induced cell migration in BCPAP, 8305C, 8505C and NHT but not in TPC-1 cells. These results constitutes the first demonstration that PLX4720 is able to inhibit the secretion of CXCL8 in BRAFV600E mutated thyroid cancer cells indicating that, at least some, of the anti-tumor activities of PLX4720 could be exerted through a lowering of CXCL8 in the thyroid-cancer-microenvironment.
Assuntos
Indóis/farmacologia , Interleucina-8/metabolismo , Proteínas Proto-Oncogênicas B-raf/antagonistas & inibidores , Proteínas Proto-Oncogênicas B-raf/genética , Sulfonamidas/farmacologia , Células Epiteliais da Tireoide/efeitos dos fármacos , Células Epiteliais da Tireoide/metabolismo , Linhagem Celular Tumoral , Movimento Celular/efeitos dos fármacos , Células Cultivadas , Humanos , Neoplasias da Glândula Tireoide/metabolismo , Fator de Necrose Tumoral alfa/farmacologia , Cicatrização/efeitos dos fármacosRESUMO
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.
Assuntos
Alelos , Arritmias Cardíacas/genética , Heterozigoto , Mutação/genética , RNA Mensageiro/genética , Canal de Liberação de Cálcio do Receptor de Rianodina/genética , Animais , Animais Recém-Nascidos , Arritmias Cardíacas/patologia , Arritmias Cardíacas/prevenção & controle , Células Cultivadas , Inativação Gênica/fisiologia , Células HEK293 , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Fenótipo , RNA Mensageiro/ultraestrutura , Canal de Liberação de Cálcio do Receptor de Rianodina/deficiência , Canal de Liberação de Cálcio do Receptor de Rianodina/ultraestruturaRESUMO
Catecholaminergic Polymorphic Ventricular Tachycardia type 2 (CPVT2) is a highly lethal recessive arrhythmogenic disease caused by mutations in the calsequestrin-2 (CASQ2) gene. We have previously demonstrated that viral transfer of the wild-type (WT) CASQ2 gene prevents the development of CPVT2 in a genetically induced mouse model of the disease homozygous carrier of the R33Q mutation. In the present study, we investigated the efficacy of the virally mediated gene therapy in cardiomyocytes (CMs) differentiated from induced pluripotent stem cells (iPSCs) obtained from a patient carrying the homozygous CASQ2-G112+5X mutation. To this end, we infected cells with an Adeno-Associated Viral vector serotype 9 (AAV9) encoding the human CASQ2 gene (AAV9-hCASQ2). Administration of the human WT CASQ2 gene was capable and sufficient to restore the physiological expression of calsequestrin-2 protein and to rescue functional defects of the patient-specific iPSC-derived CMs. Indeed, after viral gene transfer, we observed a remarkable decrease in the percentage of delayed afterdepolarizations (DADs) developed by the diseased CMs upon adrenergic stimulation, the calcium transient amplitude was re-established and the density and duration of calcium sparks were normalized. We therefore demonstrate the efficacy of the AAV9-mediated gene replacement therapy for CPVT2 in a human cardiac-specific model system, supporting the view that the gene-therapy tested is curative in models with different human mutations of CPVT.
Assuntos
Calsequestrina/genética , Catecolaminas/metabolismo , Dependovirus/metabolismo , Técnicas de Transferência de Genes , Genes Recessivos , Modelos Biológicos , Taquicardia Ventricular/terapia , Arritmias Cardíacas/metabolismo , Arritmias Cardíacas/patologia , Biópsia , Cálcio/metabolismo , Diferenciação Celular , Feminino , Humanos , Células-Tronco Pluripotentes Induzidas/metabolismo , Masculino , Miócitos Cardíacos/metabolismo , Miócitos Cardíacos/patologia , Linhagem , Fenótipo , Pele/patologia , Taquicardia Ventricular/patologia , Taquicardia Ventricular/fisiopatologiaRESUMO
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.
Assuntos
Envelhecimento , Calsequestrina/genética , Dependovirus/genética , Taquicardia Ventricular/terapia , Animais , Proteínas de Ligação ao Cálcio/metabolismo , Calsequestrina/metabolismo , Proteínas de Transporte/metabolismo , Modelos Animais de Doenças , Feminino , Terapia Genética , Masculino , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Knockout , Oxigenases de Função Mista/metabolismo , Proteínas Musculares/metabolismo , Mutação/genética , Taquicardia Ventricular/metabolismo , Taquicardia Ventricular/patologia , Resultado do TratamentoRESUMO
OBJECTIVES: This study sought to explore whether subclinical alterations of sarcoplasmic reticulum (SR) Ca(2+) release through cardiac ryanodine receptors (RyR2) aggravate cardiac remodeling in mice carrying a human RyR2(R4496C+/-) gain-of-function mutation in response to pressure overload. BACKGROUND: RyR2 dysfunction causes increased diastolic SR Ca(2+) release associated with arrhythmias and contractile dysfunction in inherited and acquired cardiac diseases, such as catecholaminergic polymorphic ventricular tachycardia and heart failure (HF). METHODS: Functional and structural properties of wild-type and catecholaminergic polymorphic ventricular tachycardia-associated RyR2(R4496C+/-) hearts were characterized under conditions of pressure overload induced by transverse aortic constriction (TAC). RESULTS: Wild-type and RyR2(R4496C+/-) hearts had comparable structural and functional properties at baseline. After TAC, RyR2(R4496C+/-) hearts responded with eccentric hypertrophy, substantial fibrosis, ventricular dilation, and reduced fractional shortening, ultimately resulting in overt HF. RyR2(R4496C+/-)-TAC cardiomyocytes showed increased incidence of spontaneous SR Ca(2+) release events, reduced Ca(2+) transient peak amplitude, and SR Ca(2+) content as well as reduced SR Ca(2+)-ATPase 2a and increased Na(+)/Ca(2+)-exchanger protein expression. HF phenotype in RyR2(R4496C+/-)-TAC mice was associated with increased mortality due to pump failure but not tachyarrhythmic events. RyR2-stabilizer K201 markedly reduced Ca(2+) spark frequency in RyR2(R4496C+/-)-TAC cardiomyocytes. Mini-osmotic pump infusion of K201 prevented deleterious remodeling and improved survival in RyR2(R4496C+/-)-TAC mice. CONCLUSIONS: The combination of subclinical congenital alteration of SR Ca(2+) release and pressure overload promoted eccentric remodeling and HF death in RyR2(R4496C+/-) mice, and pharmacological RyR2 stabilization prevented this deleterious interaction. These findings suggest potential clinical relevance for patients with acquired or inherited gain-of-function of RyR2-mediated SR Ca(2+) release.
Assuntos
Sinalização do Cálcio/genética , DNA/genética , Insuficiência Cardíaca/genética , Miócitos Cardíacos/metabolismo , Canal de Liberação de Cálcio do Receptor de Rianodina/genética , Retículo Sarcoplasmático/metabolismo , Remodelação Ventricular/genética , Animais , Análise Mutacional de DNA , Modelos Animais de Doenças , Progressão da Doença , Insuficiência Cardíaca/metabolismo , Insuficiência Cardíaca/fisiopatologia , Camundongos , Camundongos Knockout , Mutação , Miócitos Cardíacos/patologia , Canal de Liberação de Cálcio do Receptor de Rianodina/metabolismo , Pressão VentricularRESUMO
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.
Assuntos
Sinalização do Cálcio/fisiologia , Miócitos Cardíacos/ultraestrutura , Taquicardia Ventricular/patologia , Taquicardia Ventricular/fisiopatologia , Remodelação Ventricular/fisiologia , Potenciais de Ação/fisiologia , Animais , Camundongos , Camundongos Transgênicos , Miócitos Cardíacos/patologiaRESUMO
We describe a mutation (E299V) in KCNJ2, the gene that encodes the strong inward rectifier K(+) channel protein (Kir2.1), in an 11-y-old boy. The unique short QT syndrome type-3 phenotype is associated with an extremely abbreviated QT interval (200 ms) on ECG and paroxysmal atrial fibrillation. Genetic screening identified an A896T substitution in a highly conserved region of KCNJ2 that resulted in a de novo mutation E299V. Whole-cell patch-clamp experiments showed that E299V presents an abnormally large outward IK1 at potentials above -55 mV (P < 0.001 versus wild type) due to a lack of inward rectification. Coexpression of wild-type and mutant channels to mimic the heterozygous condition still resulted in a large outward current. Coimmunoprecipitation and kinetic analysis showed that E299V and wild-type isoforms may heteromerize and that their interaction impairs function. The homomeric assembly of E299V mutant proteins actually results in gain of function. Computer simulations of ventricular excitation and propagation using both the homozygous and heterozygous conditions at three different levels of integration (single cell, 2D, and 3D) accurately reproduced the electrocardiographic phenotype of the proband, including an exceedingly short QT interval with merging of the QRS and the T wave, absence of ST segment, and peaked T waves. Numerical experiments predict that, in addition to the short QT interval, absence of inward rectification in the E299V mutation should result in atrial fibrillation. In addition, as predicted by simulations using a geometrically accurate three-dimensional ventricular model that included the His-Purkinje network, a slight reduction in ventricular excitability via 20% reduction of the sodium current should increase vulnerability to life-threatening ventricular tachyarrhythmia.
Assuntos
Arritmias Cardíacas/metabolismo , Fibrilação Atrial/metabolismo , Cardiopatias Congênitas/metabolismo , Proteínas Musculares/metabolismo , Mutação de Sentido Incorreto , Canais de Potássio Corretores do Fluxo de Internalização/metabolismo , Multimerização Proteica , Substituição de Aminoácidos , Arritmias Cardíacas/genética , Arritmias Cardíacas/patologia , Arritmias Cardíacas/fisiopatologia , Fibrilação Atrial/genética , Fibrilação Atrial/patologia , Fibrilação Atrial/fisiopatologia , Criança , Simulação por Computador , Células HEK293 , Sistema de Condução Cardíaco/anormalidades , Sistema de Condução Cardíaco/metabolismo , Sistema de Condução Cardíaco/patologia , Sistema de Condução Cardíaco/fisiopatologia , Cardiopatias Congênitas/genética , Cardiopatias Congênitas/patologia , Cardiopatias Congênitas/fisiopatologia , Humanos , Masculino , Proteínas Musculares/genética , Miocárdio/metabolismo , Miocárdio/patologia , Canais de Potássio Corretores do Fluxo de Internalização/genéticaRESUMO
Regulation of calcium flux in the heart is a key process that affects cardiac excitability and contractility. Degenerative diseases, such as coronary artery disease, have long been recognized to alter the physiology of intracellular calcium regulation, leading to contractile dysfunction or arrhythmias. Since the discovery of the first gene mutation associated with catecholaminergic polymorphic ventricular tachycardia (CPVT) in 2001, a new area of interest in this field has emerged--the genetic abnormalities of key components of the calcium regulatory system. Such anomalies cause a variety of genetic diseases characterized by the development of life-threatening arrhythmias in young individuals. In this Review, we provide an overview of the structural organization and the function of calcium-handling proteins and describe the mechanisms by which mutations determine the clinical phenotype. Firstly, we discuss mutations in the genes encoding the ryanodine receptor 2 (RYR2) and calsequestrin 2 (CASQ2). These proteins are pivotal to the regulation of calcium release from the sarcoplasmic reticulum, and mutations can cause CPVT. Secondly, we review defects in genes encoding proteins that form the voltage-dependent L-type calcium channel, which regulates calcium entry into myocytes. Mutations in these genes cause various phenotypes, including Timothy syndrome, Brugada syndrome, and early repolarization syndrome. The identification of mutations associated with 'calcium-handling diseases' has led to an improved understanding of the role of calcium in cardiac physiology.
Assuntos
Arritmias Cardíacas/patologia , Canais de Cálcio , Canalopatias/patologia , Arritmias Cardíacas/genética , Transtorno Autístico , Síndrome de Brugada/genética , Síndrome de Brugada/patologia , Calsequestrina/genética , Canalopatias/genética , Sistema de Condução Cardíaco/anormalidades , Sistema de Condução Cardíaco/patologia , Cardiopatias Congênitas/genética , Cardiopatias Congênitas/patologia , Humanos , Síndrome do QT Longo/genética , Síndrome do QT Longo/patologia , Receptores Adrenérgicos beta/genética , Medição de Risco , Canal de Liberação de Cálcio do Receptor de Rianodina/genética , Sindactilia/genética , Sindactilia/patologiaRESUMO
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.
Assuntos
Arritmias Cardíacas/genética , Arritmias Cardíacas/patologia , Calsequestrina/genética , Dependovirus/genética , Técnicas de Transferência de Genes , Miócitos Cardíacos/ultraestrutura , Fenótipo , Animais , Arritmias Cardíacas/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Calsequestrina/metabolismo , Proteínas de Transporte/metabolismo , Células Cultivadas , Modelos Animais de Doenças , Eletrocardiografia , Feminino , Ventrículos do Coração/patologia , Masculino , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Oxigenases de Função Mista/metabolismo , Proteínas Musculares/metabolismo , Mutação/genética , Miócitos Cardíacos/metabolismo , Miócitos Cardíacos/patologia , Canal de Liberação de Cálcio do Receptor de Rianodina/metabolismo , Taquicardia Ventricular/genética , Taquicardia Ventricular/metabolismo , Taquicardia Ventricular/patologiaRESUMO
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.
Assuntos
Antiarrítmicos/farmacologia , Flecainida/farmacologia , Canal de Liberação de Cálcio do Receptor de Rianodina/fisiologia , Taquicardia Ventricular/tratamento farmacológico , Taquicardia Ventricular/prevenção & controle , Animais , Sinalização do Cálcio/efeitos dos fármacos , Sinalização do Cálcio/fisiologia , Modelos Animais de Doenças , Espaço Extracelular/efeitos dos fármacos , Espaço Extracelular/fisiologia , Técnicas de Introdução de Genes , Isoproterenol/farmacologia , Camundongos , Camundongos Mutantes , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/fisiologia , Técnicas de Patch-Clamp , Canal de Liberação de Cálcio do Receptor de Rianodina/genética , Retículo Sarcoplasmático/efeitos dos fármacos , Retículo Sarcoplasmático/fisiologia , Canais de Sódio/fisiologia , Simpatomiméticos/farmacologia , Taquicardia Ventricular/genéticaRESUMO
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disease characterized by life-threatening arrhythmias elicited by adrenergic activation. CPVT is caused by mutations in the cardiac ryanodine receptor gene (RyR2). In vitro studies demonstrated that RyR2 mutations respond to sympathetic activation with an abnormal diastolic Ca(2+) leak from the sarcoplasmic reticulum; however the pathways that mediate the response to adrenergic stimulation have not been defined. In our RyR2(R4496C+/-) knock-in mouse model of CPVT we tested the hypothesis that inhibition of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) counteracts the effects of adrenergic stimulation resulting in an antiarrhythmic activity. CaMKII inhibition with KN-93 completely prevented catecholamine-induced sustained ventricular tachyarrhythmia in RyR2(R4496C+/-) mice, while the inactive congener KN-92 had no effect. In ventricular myocytes isolated from the hearts of RyR2(R4496C+/-) mice, CaMKII inhibition with an autocamtide-2 related inhibitory peptide or with KN-93 blunted triggered activity and transient inward currents induced by isoproterenol. Isoproterenol also enhanced the activity of the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA), increased spontaneous Ca(2+) release and spark frequency. CaMKII inhibition blunted each of these parameters without having an effect on the SR Ca(2+) content. Our data therefore indicate that CaMKII inhibition is an effective intervention to prevent arrhythmogenesis (both in vivo and in vitro) in the RyR2(R4496C+/-) knock-in mouse model of CPVT. Mechanistically, CAMKII inhibition acts on several elements of the EC coupling cascade, including an attenuation of SR Ca(2+) leak and blunting catecholamine-mediated SERCA activation. CaMKII inhibition may therefore represent a novel therapeutic target for patients with CPVT.
Assuntos
Arritmias Cardíacas/metabolismo , Arritmias Cardíacas/prevenção & controle , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/antagonistas & inibidores , Canal de Liberação de Cálcio do Receptor de Rianodina/metabolismo , Taquicardia/metabolismo , Animais , Benzilaminas/farmacologia , Western Blotting , Cafeína/farmacologia , Cálcio/metabolismo , Eletrofisiologia , Epinefrina/farmacologia , Camundongos , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/metabolismo , Canal de Liberação de Cálcio do Receptor de Rianodina/genética , Sulfonamidas/farmacologiaRESUMO
Heterogeneous nuclear ribonucleoprotein-M (hnRNP-M) is an abundant nuclear protein that binds to pre-mRNA and is a component of the spliceosome complex. A direct interaction was detected in vivo between hnRNP-M and the human spliceosome proteins cell division cycle 5-like (CDC5L) and pleiotropic regulator 1 (PLRG1) that was inhibited during the heat-shock stress response. A central region in hnRNP-M is required for interaction with CDC5L/PLRG1. hnRNP-M affects both 5' and 3' alternative splice site choices, and an hnRNP-M mutant lacking the CDC5L/PLRG1 interaction domain is unable to modulate alternative splicing of an adeno-E1A mini-gene substrate.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Ribonucleoproteínas Nucleares Heterogêneas Grupo M/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas Nucleares/metabolismo , Sítios de Splice de RNA , Proteínas de Ligação a RNA/metabolismo , Sítios de Ligação , Proteínas de Ciclo Celular/química , Proteínas de Fluorescência Verde , Células HeLa , Resposta ao Choque Térmico , Ribonucleoproteínas Nucleares Heterogêneas Grupo M/química , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/química , Proteínas Nucleares/química , Ligação Proteica , Mapeamento de Interação de Proteínas , Estrutura Terciária de Proteína , Proteínas de Ligação a RNA/química , Proteínas Recombinantes de FusãoRESUMO
RATIONALE: Sodium channel blockers are used as gene-specific treatments in long-QT syndrome type 3, which is caused by mutations in the sodium channel gene (SCN5A). Response to treatment is influenced by biophysical properties of mutations. OBJECTIVE: We sought to investigate the unexpected deleterious effect of mexiletine in a mutation combining gain-of- function and trafficking abnormalities. METHODS AND RESULTS: A long-QT syndrome type 3 child experienced paradoxical QT prolongation and worsening of arrhythmias after mexiletine treatment. The SCN5A mutation F1473S expressed in HEK293 cells presented a right-ward shift of steady-state inactivation, enlarged window current, and huge sustained sodium current. Unexpectedly, it also reduced the peak sodium current by 80%. Immunostaining showed that mutant Nav1.5 is retained in the cytoplasm. Incubation with 10 micromol/L mexiletine rescued the trafficking defect of F1473S, causing a significant increase in peak current, whereas sustained current was unchanged. Using a Markovian model of the Na channel and a model of human ventricular action potential, we showed that simulated exposure of F1473S to mexiletine paradoxically increased action potential duration, mimicking QT prolongation seen in the index patient on mexiletine treatment. CONCLUSIONS: Sodium channel blockers are largely used to shorten QT intervals in carriers of SCN5A mutations. We provided evidence that these agents may facilitate trafficking of mutant proteins, thus exacerbating QT prolongation. These data suggest that caution should be used when recommending this class of drugs to carriers of mutations with undefined electrophysiological properties.