scholarly journals Increased mitochondrial nanotunneling activity, induced by calcium imbalance, affects intermitochondrial matrix exchanges

2017 ◽  
Vol 114 (5) ◽  
pp. E849-E858 ◽  
Author(s):  
Manuela Lavorato ◽  
V. Ramesh Iyer ◽  
Williams Dewight ◽  
Ryan R. Cupo ◽  
Valentina Debattisti ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Direct Contact ◽  
Fluorescent Proteins ◽  
Electron Tomography ◽  
Polymorphic Ventricular Tachycardia ◽  
Channel Activity ◽  
Isolated Cardiomyocytes ◽  
Contraction Coupling ◽  
Ryr2 Channel ◽  
Exchange Matrix

Exchanges of matrix contents are essential to the maintenance of mitochondria. Cardiac mitochondrial exchange matrix content in two ways: by direct contact with neighboring mitochondria and over longer distances. The latter mode is supported by thin tubular protrusions, called nanotunnels, that contact other mitochondria at relatively long distances. Here, we report that cardiac myocytes of heterozygous mice carrying a catecholaminergic polymorphic ventricular tachycardia-linked RyR2 mutation (A4860G) show a unique and unusual mitochondrial response: a significantly increased frequency of nanotunnel extensions. The mutation induces Ca2+imbalance by depressing RyR2 channel activity during excitation–contraction coupling, resulting in random bursts of Ca2+release probably due to Ca2+overload in the sarcoplasmic reticulum. We took advantage of the increased nanotunnel frequency in RyR2A4860G+/−cardiomyocytes to investigate and accurately define the ultrastructure of these mitochondrial extensions and to reconstruct the overall 3D distribution of nanotunnels using electron tomography. Additionally, to define the effects of communication via nanotunnels, we evaluated the intermitochondrial exchanges of matrix-targeted soluble fluorescent proteins, mtDsRed and photoactivable mtPA-GFP, in isolated cardiomyocytes by confocal microscopy. A direct comparison between exchanges occurring at short and long distances directly demonstrates that communication via nanotunnels is slower.

Mechanism of Destabilized RyR2 Channel in Catecholaminergic Polymorphic Ventricular Tachycardia

2010 ◽  
Vol 16 (9) ◽  
pp. S151
Author(s):  
Takeshi Suetomi ◽  
Masafumi Yano ◽  
Masakazu Fukuda ◽  
Akihiro Hino ◽  
Xiaojuan Xu ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Catecholaminergic Polymorphic Ventricular Tachycardia ◽  
Polymorphic Ventricular Tachycardia ◽  
Ryr2 Channel

P5025Structural insights into catecholaminergic polymorphic ventricular tachycardia-associated RyR2 mutant channels using a three-dimensional in silico model

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
J Gao ◽  
T Makiyama ◽  
S Ohno ◽  
Y Yamamoto ◽  
Y Wuriyanghai ◽  
...  
Keyword(s):  
Amino Acids ◽  
Ventricular Tachycardia ◽  
In Silico ◽  
Structural Model ◽  
Three Dimensional ◽  
Polymorphic Ventricular Tachycardia ◽  
In Silico Modeling ◽  
Ryr2 Channel ◽  
The Relationship ◽  
Inherited Arrhythmias

Abstract Background The cardiac ryanodine receptors (RyR2) are large tetrameric calcium-permeant ion channels found in cardiac muscle sarcoplasmic reticulum, which play an important role in the control of intracellular Ca2+ release and cardiac contraction. Mutations in the RYR2 gene are associated with lethal arrhythmia diseases including catecholaminergic polymorphic ventricular tachycardia (CPVT) resulting from increased diastolic Ca2+ leak from mutant channels. RyR2 is a huge protein that each subunit of tetramer is comprised of 4967 amino acids, which hampers the detailed in vitro analysis of RyR2 mutant channels. Purpose We aimed to analyze the structural features of RyR2 mutant channels identified in our cohort with inherited arrhythmias using RyR2 three-dimensional (3D) in silico model to reveal the arrhythmogenic mechanisms. Methods A targeted next-generation sequencing panel for inherited arrhythmias was employed for genetic diagnosis of the patients. Then, we mapped the identified mutations on RyR2 3D structural model developed by cryo-EM images (PDB: 5go9, 5goa, Peng Science 2016) and investigated the relationship between the location of the mutations and specific functional sites. Results As a result of genetic analysis, we identified 93 RYR2 mutations from 112 probands with CPVT (n=93) or long-QT syndrome (LQTS) (n=19).64 of 93 (69%) RYR2 mutations are located in three “hot-spot” area (N-terminal (residues 77–466), central (2246–2534), and channel (3778–4959) hotspot. RyR2 3D in silico modeling revealed that the mutations are regionally distributed mainly in three parts: N-terminal, periphery, and channel part (Figure A). In N-terminal part (1–642 amino acid), 9 of 13 mutations alter the charges of the amino acids (Figure B). Especially, R169L, R169Q, and G172E are close to the interface between two neighboring subunits (∼20Å). These mutations which change the amino acid charge may cause a complete disruption of the ionic pair network and result in largest structural changes, which facilitates RyR2 channel opening. In periphery part (643–3528aa), 22 of 33 mutations are close to the two predicted binding sites of FKBP12.6, a stabilizer of RyR2 (∼5–40Å, Figure C). The mutations are supposed to disturb the binding affinity to the FKBP12.6 resulting in RyR2 channel instability. In channel part (3613–4968aa), 16 of 40 mutations are located near two interface. (FigureD) 12 mutations are close to the Ca2+ sensor and the other 4 mutations are adjacent to the pore-forming segment. Especially, V4821I is just located on this segment and strongly expected to impair the channel function. Above all, RyR2 3D in silico modeling revealed that 63 of all 93 (68%) identified mutations are supposed to be pathogenic. Location of RYR2 mutations in 3D model Conclusion 3D structural model of RyR2 is useful for the investigation of the pathogenic mechanisms of CPVT-related mutations. Further studies are needed to elucidate the relationship between the location of the mutations and clinical phenotypes.

scholarly journals A Novel Mice Model of Catecholaminergic Polymorphic Ventricular Tachycardia Generated by CRISPR/Cas9

2021 ◽  
Author(s):  
cuilan hou ◽  
Xunwei jiang ◽  
Qingzhu Qiu ◽  
Junmin Zheng ◽  
Shujia Lin ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Induced Pluripotent Stem Cell ◽  
Catecholaminergic Polymorphic Ventricular Tachycardia ◽  
Calcium Handling ◽  
Polymorphic Ventricular Tachycardia ◽  
Mice Model ◽  
Isolated Cardiomyocytes ◽  
Therapeutic Targeting ◽  
Protein Levels ◽  
Induced Pluripotent

Catecholaminergic polymorphic ventricular tachycardia (CPVT) has been considered as one of the most important causes of children's sudden cardiac death. Mutations in the genes for RyR2 and CASQ2, two mainly subtypes of CPVT, have been identified. However, the mutation in the gene of TECRL was rarely reported, which could be another genetic cause of CPVT. We evaluated myocardial contractility, electrophysiology, calcium handling in Tecrl knockout (Tecrl KO) mice and human induced pluripotent stem cell-derived cardiomyocytes. Immediately after epinephrine plus caffeine injection, Tecrl KO mice showed much more multiple premature ventricular beats and ventricular tachycardia. The Tecrl KO mice demonstrate CPVT phenotypes. Mechanistically, intracellular calcium amplitude was reduced, while time to baseline of 50 was increased in acute isolated cardiomyocytes. RyR2 protein levels decreased significantly upon cycloheximide treatment in TECRL deficiency cardiomyocytes. Overexpression of TECRL and KN93 can partially reverse cardiomyocytes calcium dysfunction, and this is p-CaMKII/CaMKII dependent. Therefore, a new CPVT mouse model was constructed. We propose a previously unrecognized mechanism of TECRL and provide support for the therapeutic targeting of TECRL in treating CPVT

Abstract 795: Enhanced Sensitivity Of The Cardiac Ryanodine Receptor To Activation By Luminal Ca 2+ As A Primary Cause Of Catecholaminergic Polymorphic Ventricular Tachycardia

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Hitoshi Uchinoumi ◽  
Masafumi Yano ◽  
Makoto Ohno ◽  
Xiaojuan Xu ◽  
Hiroki Tateishi ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Ryanodine Receptor ◽  
Underlying Mechanism ◽  
Catecholaminergic Polymorphic Ventricular Tachycardia ◽  
Polymorphic Ventricular Tachycardia ◽  
Enhanced Sensitivity ◽  
Histological Abnormality ◽  
Ryr2 Channel ◽  
The Relationship ◽  
Cardiac Ryanodine Receptor

Mutations in cardiac ryanodine receptor (RyR2) was found to be linked with catecholaminergic polymorphic ventricular tachycardia (CPVT). To study the underlying mechanism of CPVT, we developed knock-in mice harboring the Arg-to-Ser (R2474S) mutation. The RyR2 R2474S/+ knock-in (KI) mice revealed no structural or histological abnormality in hearts. Echocardiography showed no contractile or relaxation dysfunction at rest. In all KI mice (n=6), bidirectional ventricular tachycardia (VT) was observed during or after exercise with treadmill, but never observed in wild-type (WT) mice (n=6). In intact cardiomyocytes, the frequency of Ca 2+ sparks (SpF; s −1 ·100μm −1 ) was significantly increased in KI mice, but not in WT mice (at 2 mM [Ca 2+ ]; KI:6.4±0.7, WT:0.9±0.08, p<0.01). To investigate the sensitivity of the RyR2 channel to activation by luminal Ca 2+ {[Ca 2+ ] in sarcoplasmic reticulum (SR)}, we measured cytoplasmic [Ca 2+ ] ([Ca 2+ ] C ) and luminal [Ca 2+ ] ([Ca 2+ ] L ) simultaneously in saponin-permeabilized cardiomyocytes, using Rhod-2 and Fluo-5N AM as Ca 2+ indicators, respectively. When [Ca 2+ ] C was buffered at 100 nM (by 1 mM EGTA), the spontaneous Ca 2+ sparks were frequently observed both in KI and WT cardiomyocyts (SpF: KI:22.1±0.9, WT:22.0±0.8, p=ns). When we added thapsigargin (1 μM) to the cardiomyocytes under this condition ([Ca 2+ ] C =100 nM), both SpF and [Ca 2+ ] L gradually decreased due to a decrease in SR Ca 2+ content caused by an inhibition of SR Ca 2+ ATPase. The relationship curve between SpF and [Ca 2+ ] L (SpF -[Ca 2+ ] L ) during the addition of thapsigargin was markedly shifted to the left in KI cardiomyocytes compared to WT cardiomyocytes, thereby lowering the threshold of [Ca 2+ ] L to induce Ca 2+ sparks to approximately one-fifth in KI cardiomyocytes. In conclusion, the enhanced sensitivity of the RyR2 channel to activation by [Ca 2+ ] L : i.e. decreased threshold [Ca 2+ ] L to induce spontaneous Ca 2+ release, may be a primary cause of CPVT.

scholarly journals Arrhythmogenesis in a catecholaminergic polymorphic ventricular tachycardia mutation that depresses ryanodine receptor function

2015 ◽  
Vol 112 (13) ◽  
pp. E1669-E1677 ◽  
Author(s):  
Yan-Ting Zhao ◽  
Carmen R. Valdivia ◽  
Georgina B. Gurrola ◽  
Patricia P. Powers ◽  
B. Cicero Willis ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Ryanodine Receptor ◽  
Single Channel ◽  
Ventricular Myocytes ◽  
Catecholaminergic Polymorphic Ventricular Tachycardia ◽  
Polymorphic Ventricular Tachycardia ◽  
Channel Activity ◽  
Loss Of Function ◽  
Human Patient ◽  
Essential Components

Current mechanisms of arrhythmogenesis in catecholaminergic polymorphic ventricular tachycardia (CPVT) require spontaneous Ca2+ release via cardiac ryanodine receptor (RyR2) channels affected by gain-of-function mutations. Hence, hyperactive RyR2 channels eager to release Ca2+ on their own appear as essential components of this arrhythmogenic scheme. This mechanism, therefore, appears inadequate to explain lethal arrhythmias in patients harboring RyR2 channels destabilized by loss-of-function mutations. We aimed to elucidate arrhythmia mechanisms in a RyR2-linked CPVT mutation (RyR2-A4860G) that depresses channel activity. Recombinant RyR2-A4860G protein was expressed equally as wild type (WT) RyR2, but channel activity was dramatically inhibited, as inferred by [3H]ryanodine binding and single channel recordings. Mice heterozygous for the RyR2-A4860G mutation (RyR2-A4860G+/−) exhibited basal bradycardia but no cardiac structural alterations; in contrast, no homozygotes were detected at birth, suggesting a lethal phenotype. Sympathetic stimulation elicited malignant arrhythmias in RyR2-A4860G+/− hearts, recapitulating the phenotype originally described in a human patient with the same mutation. In isoproterenol-stimulated ventricular myocytes, the RyR2-A4860G mutation decreased the peak of Ca2+ release during systole, gradually overloading the sarcoplasmic reticulum with Ca2+. The resultant Ca2+ overload then randomly caused bursts of prolonged Ca2+ release, activating electrogenic Na+-Ca2+ exchanger activity and triggering early afterdepolarizations. The RyR2-A4860G mutation reveals novel pathways by which RyR2 channels engage sarcolemmal currents to produce life-threatening arrhythmias.

scholarly journals Methadone-Induced Polymorphic Ventricular Tachycardia Complicated by Takotsubo Cardiomyopathy in a Malnourished Patient

2021 ◽  
Vol 9 ◽  
pp. 232470962110051
Author(s):  
Mohammed Ali ◽  
Omeralfaroug Adam ◽  
Ahmed Subahi ◽  
Abdalaziz Awadelkarim ◽  
Lubna Fatiwala ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Ventricular Tachycardia ◽  
Coronary Disease ◽  
Takotsubo Cardiomyopathy ◽  
Myocardial Dysfunction ◽  
Polymorphic Ventricular Tachycardia ◽  
Malnourished Patient

Takotsubo cardiomyopathy (TC) is a syndrome characterized by acute and transient regional systolic myocardial dysfunction. TC often mimics myocardial infarction without obstructive coronary disease. We present a case of a 48-year-old woman who developed TC following the onset of polymorphic ventricular tachycardia in the setting of methadone intoxication.

scholarly journals Catecholaminergic polymorphic ventricular tachycardia complicated by dilated cardiomyopathy: a case report

2020 ◽  
Author(s):  
Granitz Christina ◽  
Jirak Peter ◽  
Strohmer Bernhard ◽  
Pölzl Gerhard
Keyword(s):  
Heart Failure ◽  
Ventricular Tachycardia ◽  
Dilated Cardiomyopathy ◽  
Sinus Bradycardia ◽  
Clinical Care ◽  
Structural Heart Disease ◽  
Catecholaminergic Polymorphic Ventricular Tachycardia ◽  
Polymorphic Ventricular Tachycardia ◽  
Myocardial Inflammation ◽  
As Stress

Abstract Background  Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a severe genetic arrhythmogenic disorder characterized by adrenergically induced ventricular tachycardia manifesting as stress-induced syncope and sudden cardiac death. While CPVT is not associated with dilated cardiomyopathy (DCM) in most cases, the combination of both disease entities poses a major diagnostic and therapeutic challenge. Case summary  We present the case of a young woman with CPVT. The clinical course since childhood was characterized by repetitive episodes of exercise-induced ventricular arrhythmias and a brady-tachy syndrome due to rapid paroxysmal atrial fibrillation and sinus bradycardia. Medical treatment included propranolol and flecainide until echocardiography showed a dilated left ventricle with severely depressed ejection fraction when the patient was 32 years old. Cardiac magnetic resonance imaging revealed non-specific late gadolinium enhancement. Myocardial inflammation, however, was excluded by subsequent endomyocardial biopsy. Genetic analysis confirmed a mutation in the cardiac ryanodine receptor but no pathogenetic variant associated with DCM. Guideline-directed medical therapy for HFrEF was limited due to symptomatic hypotension. Over the next months, the patient developed progressive heart failure symptoms that were finally managed by heart transplantation. Discussion  Management in patients with CPVT and DCM is challenging, as Class I antiarrhythmic drugs are not recommended in structural heart disease and prophylactic internal cardioverter-defibrillator implantation without adjuvant antiarrhythmic therapy can be detrimental. Regular echocardiographic screening for DCM is recommendable in patients with CPVT. A multidisciplinary team of heart failure specialists, electrophysiologists, geneticists, and imaging specialists is needed to collaborate in the delivery of clinical care.

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