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Physiological Reviews Jan 2022Ca-release channels are giant membrane proteins that control the release of Ca from the endoplasmic and sarcoplasmic reticulum. The two members, ryanodine receptors... (Review)
Review
Ca-release channels are giant membrane proteins that control the release of Ca from the endoplasmic and sarcoplasmic reticulum. The two members, ryanodine receptors (RyRs) and inositol-1,4,5-trisphosphate receptors (IPRs), are evolutionarily related and are both activated by cytosolic Ca. They share a common architecture, but RyRs have evolved additional modules in the cytosolic region. Their massive size allows for the regulation by tens of proteins and small molecules, which can affect the opening and closing of the channels. In addition to Ca, other major triggers include IP for the IPRs and depolarization of the plasma membrane for a particular RyR subtype expressed in skeletal muscle. Their size has made them popular targets for study via electron microscopic methods, with current structures culminating near 3 Å. The available structures have provided many new mechanistic insights into the binding of auxiliary proteins and small molecules, how these can regulate channel opening, and the mechanisms of disease-associated mutations. They also help scrutinize previously proposed binding sites, as some of these are now incompatible with the structures. Many questions remain around the structural effects of posttranslational modifications, additional binding partners, and the higher order complexes these channels can make in situ. This review summarizes our current knowledge about the structures of Ca-release channels and how this informs on their function.
Topics: Animals; Calcium; Calcium Signaling; Cell Membrane; Humans; Muscle, Skeletal; Ryanodine Receptor Calcium Release Channel; Sarcoplasmic Reticulum
PubMed: 34280054
DOI: 10.1152/physrev.00033.2020 -
Cell Sep 2019Necrosis of infected macrophages constitutes a critical pathogenetic event in tuberculosis by releasing mycobacteria into the growth-permissive extracellular...
Necrosis of infected macrophages constitutes a critical pathogenetic event in tuberculosis by releasing mycobacteria into the growth-permissive extracellular environment. In zebrafish infected with Mycobacterium marinum or Mycobacterium tuberculosis, excess tumor necrosis factor triggers programmed necrosis of infected macrophages through the production of mitochondrial reactive oxygen species (ROS) and the participation of cyclophilin D, a component of the mitochondrial permeability transition pore. Here, we show that this necrosis pathway is not mitochondrion-intrinsic but results from an inter-organellar circuit initiating and culminating in the mitochondrion. Mitochondrial ROS induce production of lysosomal ceramide that ultimately activates the cytosolic protein BAX. BAX promotes calcium flow from the endoplasmic reticulum into the mitochondrion through ryanodine receptors, and the resultant mitochondrial calcium overload triggers cyclophilin-D-mediated necrosis. We identify ryanodine receptors and plasma membrane L-type calcium channels as druggable targets to intercept mitochondrial calcium overload and necrosis of mycobacterium-infected zebrafish and human macrophages.
Topics: Animals; Apoptosis; Calcium; Endoplasmic Reticulum; Humans; Lysosomes; Macrophages; Membrane Potential, Mitochondrial; Mitochondria; Mycobacterium Infections, Nontuberculous; Mycobacterium marinum; Mycobacterium tuberculosis; Necrosis; Reactive Oxygen Species; THP-1 Cells; Tuberculosis; Tumor Necrosis Factor-alpha; Zebrafish
PubMed: 31474371
DOI: 10.1016/j.cell.2019.08.004 -
Nature Reviews. Cardiology Nov 2020Ca is a fundamental second messenger in all cell types and is required for numerous essential cellular functions, including cardiac and skeletal muscle contraction. The... (Review)
Review
Ca is a fundamental second messenger in all cell types and is required for numerous essential cellular functions, including cardiac and skeletal muscle contraction. The intracellular concentration of free Ca ([Ca]) is regulated primarily by ion channels, pumps (ATPases), exchangers and Ca-binding proteins. Defective regulation of [Ca] is found in a diverse spectrum of pathological states that affect all the major organs. In the heart, abnormalities in the regulation of cytosolic and mitochondrial [Ca] occur in heart failure (HF) and atrial fibrillation (AF), two common forms of heart disease and leading contributors to morbidity and mortality. In this Review, we focus on the mechanisms that regulate ryanodine receptor 2 (RYR2), the major sarcoplasmic reticulum (SR) Ca-release channel in the heart, how RYR2 becomes dysfunctional in HF and AF, and its potential as a therapeutic target. Inherited RYR2 mutations and/or stress-induced phosphorylation and oxidation of the protein destabilize the closed state of the channel, resulting in a pathological diastolic Ca leak from the SR that both triggers arrhythmias and impairs contractility. On the basis of our increased understanding of SR Ca leak as a shared Ca-dependent pathological mechanism in HF and AF, a new class of drugs developed in our laboratory, known as rycals, which stabilize RYR2 channels and prevent Ca leak from the SR, are undergoing investigation in clinical trials.
Topics: Allosteric Regulation; Animals; Arrhythmias, Cardiac; Atrial Fibrillation; Calcium; Calcium Signaling; Diastole; Disease Progression; Excitation Contraction Coupling; Heart Failure; Humans; Mice; Mitochondria, Heart; Mutation; Myocytes, Cardiac; Oxidation-Reduction; Phosphorylation; Protein Stability; Ryanodine Receptor Calcium Release Channel; Sarcoplasmic Reticulum; Tacrolimus Binding Proteins
PubMed: 32555383
DOI: 10.1038/s41569-020-0394-8 -
Frontiers in Immunology 2020Myasthenia gravis (MG) is an autoimmune disease characterized by muscle weakness and fatiguability of skeletal muscles. It is an antibody-mediated disease, caused by... (Review)
Review
Myasthenia gravis (MG) is an autoimmune disease characterized by muscle weakness and fatiguability of skeletal muscles. It is an antibody-mediated disease, caused by autoantibodies targeting neuromuscular junction proteins. In the majority of patients (~85%) antibodies against the muscle acetylcholine receptor (AChR) are detected, while in 6% antibodies against the muscle-specific kinase (MuSK) are detected. In ~10% of MG patients no autoantibodies can be found with the classical diagnostics for AChR and MuSK antibodies (seronegative MG, SN-MG), making the improvement of methods for the detection of known autoantibodies or the discovery of novel antigenic targets imperative. Over the past years, using cell-based assays or improved highly sensitive immunoprecipitation assays, it has been possible to detect autoantibodies in previously SN-MG patients, including the identification of the low-density lipoprotein receptor-related protein 4 (LRP4) as a third MG autoantigen, as well as AChR and MuSK antibodies undetectable by conventional methods. Furthermore, antibodies against other extracellular or intracellular targets, such as titin, the ryanodine receptor, agrin, collagen Q, K1.4 potassium channels and cortactin have been found in some MG patients, which can be useful biomarkers. In addition to the improvement of diagnosis, the identification of the patients' autoantibody specificity is important for their stratification into respective subgroups, which can differ in terms of clinical manifestations, prognosis and most importantly their response to therapies. The knowledge of the autoantibody profile of MG patients would allow for a therapeutic strategy tailored to their MG subgroup. This is becoming especially relevant as there is increasing progress toward the development of antigen-specific therapies, targeting only the specific autoantibodies or immune cells involved in the autoimmune response, such as antigen-specific immunoadsorption, which have shown promising results. We will herein review the advances made by us and others toward development of more sensitive detection methods and the identification of new antibody targets in MG, and discuss their significance in MG diagnosis and therapy. Overall, the development of novel autoantibody assays is aiding in the more accurate diagnosis and classification of MG patients, supporting the development of advanced therapeutics and ultimately the improvement of disease management and patient quality of life.
Topics: Antibody Specificity; Autoantibodies; Humans; Myasthenia Gravis; Receptor Protein-Tyrosine Kinases; Receptors, Cholinergic; Ryanodine Receptor Calcium Release Channel
PubMed: 32117321
DOI: 10.3389/fimmu.2020.00212 -
Arrhythmia & Electrophysiology Review Apr 2022Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome characterised by adenergically mediated bidirectional and/or polymorphic... (Review)
Review
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome characterised by adenergically mediated bidirectional and/or polymorphic ventricular tachycardia. CPVT is a significant cause of autopsy-negative sudden death in children and adolescents, although it can also affect adults. It is often caused by pathogenic variants in the cardiac ryanodine receptor gene as well as other rarer genes. Early identification and risk stratification is of major importance. β-blockers are the cornerstone of therapy. Sodium channel blockers, specifically flecainide, have an additive role. Left cardiac sympathetic denervation is playing an increasing role in suppression of arrhythmia and symptoms. Concerns have been raised, however, about the efficacy of implantable cardioverter defibrillator therapy and the risk of catecholamine driven proarrhythmic storms. In this review, we summarise the clinical characteristics, genetics, and diagnostic and therapeutic strategies for CPVT and describe recent advances and challenges.
PubMed: 36644199
DOI: 10.15420/aer.2022.09 -
Acta Neuropathologica Jun 2020RYR1 encodes the type 1 ryanodine receptor, an intracellular calcium release channel (RyR1) on the skeletal muscle sarcoplasmic reticulum (SR). Pathogenic RYR1...
RYR1 encodes the type 1 ryanodine receptor, an intracellular calcium release channel (RyR1) on the skeletal muscle sarcoplasmic reticulum (SR). Pathogenic RYR1 variations can destabilize RyR1 leading to calcium leak causing oxidative overload and myopathy. However, the effect of RyR1 leak has not been established in individuals with RYR1-related myopathies (RYR1-RM), a broad spectrum of rare neuromuscular disorders. We sought to determine whether RYR1-RM affected individuals exhibit pathologic, leaky RyR1 and whether variant location in the channel structure can predict pathogenicity. Skeletal muscle biopsies were obtained from 17 individuals with RYR1-RM. Mutant RyR1 from these individuals exhibited pathologic SR calcium leak and increased activity of calcium-activated proteases. The increased calcium leak and protease activity were normalized by ex-vivo treatment with S107, a RyR stabilizing Rycal molecule. Using the cryo-EM structure of RyR1 and a new dataset of > 2200 suspected RYR1-RM affected individuals we developed a method for assigning pathogenicity probabilities to RYR1 variants based on 3D co-localization of known pathogenic variants. This study provides the rationale for a clinical trial testing Rycals in RYR1-RM affected individuals and introduces a predictive tool for investigating the pathogenicity of RYR1 variants of uncertain significance.
Topics: Animals; Calcium; Cytoplasm; Humans; Muscle, Skeletal; Muscular Diseases; Ryanodine Receptor Calcium Release Channel; Sarcoplasmic Reticulum
PubMed: 32236737
DOI: 10.1007/s00401-020-02150-w -
Annual Review of Biochemistry Jun 2023Muscles are essential for movement and heart function. Contraction and relaxation of muscles rely on the sliding of two types of filaments-the thin filament and the... (Review)
Review
Muscles are essential for movement and heart function. Contraction and relaxation of muscles rely on the sliding of two types of filaments-the thin filament and the thick myosin filament. The thin filament is composed mainly of filamentous actin (F-actin), tropomyosin, and troponin. Additionally, several other proteins are involved in the contraction mechanism, and their malfunction can lead to diverse muscle diseases, such as cardiomyopathies. We review recent high-resolution structural data that explain the mechanism of action of muscle proteins at an unprecedented level of molecular detail. We focus on the molecular structures of the components of the thin and thick filaments and highlight the mechanisms underlying force generation through actin-myosin interactions, as well as Ca-dependent regulation via the dihydropyridine receptor, the ryanodine receptor, and troponin. We particularly emphasize the impact of cryo-electron microscopy and cryo-electron tomography in leading muscle research into a new era.
Topics: Actins; Cryoelectron Microscopy; Muscle Contraction; Troponin; Myosins; Calcium
PubMed: 37001141
DOI: 10.1146/annurev-biochem-052521-042909 -
Channels (Austin, Tex.) Dec 2023Calcium ions (Ca) are the basis of a unique and potent array of cellular responses. Calmodulin (CaM) is a small but vital protein that is able to rapidly transmit... (Review)
Review
Calcium ions (Ca) are the basis of a unique and potent array of cellular responses. Calmodulin (CaM) is a small but vital protein that is able to rapidly transmit information about changes in Ca concentrations to its regulatory targets. CaM plays a critical role in cellular Ca signaling, and interacts with a myriad of target proteins. Ca-dependent modulation by CaM is a major component of a diverse array of processes, ranging from gene expression in neurons to the shaping of the cardiac action potential in heart cells. Furthermore, the protein sequence of CaM is highly evolutionarily conserved, and identical CaM proteins are encoded by three independent genes () in humans. Mutations within any of these three genes may lead to severe cardiac deficits including severe long QT syndrome (LQTS) and/or catecholaminergic polymorphic ventricular tachycardia (CPVT). Research into disease-associated CaM variants has identified several proteins modulated by CaM that are likely to underlie the pathogenesis of these calmodulinopathies, including the cardiac L-type Ca channel (LTCC) Ca1.2, and the sarcoplasmic reticulum Ca release channel, ryanodine receptor 2 (RyR2). Here, we review the research that has been done to identify calmodulinopathic CaM mutations and evaluate the mechanisms underlying their role in disease.
Topics: Humans; Calmodulin; Mutation; Tachycardia, Ventricular; Long QT Syndrome; Myocytes, Cardiac; Ryanodine Receptor Calcium Release Channel; Calcium
PubMed: 36629534
DOI: 10.1080/19336950.2023.2165278 -
Frontiers in Physiology 2022The sarcoplasmic reticulum (SR) plays the key role in cardiac function as the major source of Ca that activates cardiomyocyte contractile machinery. Disturbances in... (Review)
Review
The sarcoplasmic reticulum (SR) plays the key role in cardiac function as the major source of Ca that activates cardiomyocyte contractile machinery. Disturbances in finely-tuned SR Ca release by SR Ca channel ryanodine receptor (RyR2) and SR Ca reuptake by SR Ca-ATPase (SERCa2a) not only impair contraction, but also contribute to cardiac arrhythmia trigger and reentry. Besides being the main Ca storage organelle, SR in cardiomyocytes performs all the functions of endoplasmic reticulum (ER) in other cell types including protein synthesis, folding and degradation. In recent years ER stress has become recognized as an important contributing factor in many cardiac pathologies, including deadly ventricular arrhythmias. This brief review will therefore focus on ER stress mechanisms in the heart and how these changes can lead to pro-arrhythmic defects in SR Ca handling machinery.
PubMed: 36425292
DOI: 10.3389/fphys.2022.1041940