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Nature Medicine Nov 2020Ribonucleoprotein (RNP) granules are biomolecular condensates-liquid-liquid phase-separated droplets that organize and manage messenger RNA metabolism, cell signaling,...
Ribonucleoprotein (RNP) granules are biomolecular condensates-liquid-liquid phase-separated droplets that organize and manage messenger RNA metabolism, cell signaling, biopolymer assembly, biochemical reactions and stress granule responses to cellular adversity. Dysregulated RNP granules drive neuromuscular degenerative disease but have not previously been linked to heart failure. By exploring the molecular basis of congenital dilated cardiomyopathy (DCM) in genome-edited pigs homozygous for an RBM20 allele encoding the pathogenic R636S variant of human RNA-binding motif protein-20 (RBM20), we discovered that RNP granules accumulated abnormally in the sarcoplasm, and we confirmed this finding in myocardium and reprogrammed cardiomyocytes from patients with DCM carrying the R636S allele. Dysregulated sarcoplasmic RBM20 RNP granules displayed liquid-like material properties, docked at precisely spaced intervals along cytoskeletal elements, promoted phase partitioning of cardiac biomolecules and fused with stress granules. Our results link dysregulated RNP granules to myocardial cellular pathobiology and heart failure in gene-edited pigs and patients with DCM caused by RBM20 mutation.
Topics: Alleles; Animals; Cardiomyopathy, Dilated; Cellular Reprogramming; Disease Models, Animal; Female; Gene Editing; Humans; Male; Mutation; Myocardium; Myocytes, Cardiac; RNA, Messenger; RNA-Binding Proteins; Ribonucleoproteins; Sarcoplasmic Reticulum; Secretory Vesicles; Swine
PubMed: 33188278
DOI: 10.1038/s41591-020-1087-x -
Romanian Journal of Morphology and... 2012We present the case of a female patient, aged 12 years, with fatigability and exertional myalgias, progressively developed within the last two years. Negative family...
We present the case of a female patient, aged 12 years, with fatigability and exertional myalgias, progressively developed within the last two years. Negative family history, as well as negative personal medical history, were found. At physical examination, short stature, proximal muscle weakness and mild hepatomegaly were noted. Urine ketones level was slightly decreased, serum transaminases, creatine kinase and lactate dehydrogenase levels were increased. Electromyographical examination showed a myopathic non-specific pattern. Deltoid muscle biopsy revealed: small, clear vesicles are present on Hematoxylin-Eosin and modified Gömöri trichrome stains; modified Gömöri trichrome stain also revealed muscle fibers (especially type I of muscle fibers) having mild to moderate mitochondrial proliferation (red rim and speckled sarcoplasm). The lipid storage has been well demonstrated by Sudan Black stain, which revealed small lipid droplets in type I muscle fibers. Abnormal internal architecture with a punctate pattern was showed by adenine dinucleotide tetrazolium reductase and succinate dehydrogenase stains. Electron microscopy showed small inter-myofibrillar accumulations of round, amorphous, homogeneous acellular substances that are not membrane bounded. These features indicate that these are neutral fat (lipid) droplets. Subsarcolemmal accumulations of mitochondria were also revealed. The differential diagnosis of this case is discussed, and the up to date general data concerning carnitine deficiency are presented. The aim of our case-report is to emphasize the role of muscle biopsy in carnitine deficiency, as well as to remind the necessity of keeping in mind such metabolic disorders when doing the differential diagnostic of a muscular weakness.
Topics: Biopsy; Carnitine; Child; Diagnosis, Differential; Disease Progression; Electromyography; Female; Hepatomegaly; Humans; Lipids; Microscopy, Electron; Mitochondria; Muscle Weakness; Muscles; Muscular Diseases
PubMed: 22395524
DOI: No ID Found -
Structure (London, England : 1993) Mar 2022In this issue of Structure, Reddy et al. present details about the structure, topology, and dynamics of the small membrane protein DWORF, a regulin that activates the...
In this issue of Structure, Reddy et al. present details about the structure, topology, and dynamics of the small membrane protein DWORF, a regulin that activates the Ca pump SERCA. State-of-the art oriented solid-state NMR spectroscopy in combination with molecular dynamics simulations reveal the structure of this cardiac muscle protein.
Topics: Calcium-Binding Proteins; Magnetic Resonance Spectroscopy; Membrane Proteins; Molecular Dynamics Simulation; Sarcoplasmic Reticulum Calcium-Transporting ATPases
PubMed: 35245434
DOI: 10.1016/j.str.2022.02.006 -
The Journal of General Physiology Feb 2021JGP study reveals that insufficient reuptake of calcium into the sarcoplasmic reticulum underlies arrhythmogenic variations in cardiac calcium transients.
JGP study reveals that insufficient reuptake of calcium into the sarcoplasmic reticulum underlies arrhythmogenic variations in cardiac calcium transients.
Topics: Arrhythmias, Cardiac; Calcium; Calcium Signaling; Humans; Myocytes, Cardiac; Sarcoplasmic Reticulum
PubMed: 33443569
DOI: 10.1085/jgp.202112862 -
Biomolecules Mar 2022The sarcoplasmic reticulum of skeletal muscle cells is a highly ordered structure consisting of an intricate network of tubules and cisternae specialized for regulating... (Review)
Review
The sarcoplasmic reticulum of skeletal muscle cells is a highly ordered structure consisting of an intricate network of tubules and cisternae specialized for regulating Ca homeostasis in the context of muscle contraction. The sarcoplasmic reticulum contains several proteins, some of which support Ca storage and release, while others regulate the formation and maintenance of this highly convoluted organelle and mediate the interaction with other components of the muscle fiber. In this review, some of the main issues concerning the biology of the sarcoplasmic reticulum will be described and discussed; particular attention will be addressed to the structure and function of the two domains of the sarcoplasmic reticulum supporting the excitation-contraction coupling and Ca-uptake mechanisms.
Topics: Calcium; Muscle Contraction; Muscle Fibers, Skeletal; Muscle, Skeletal; Organelles; Sarcoplasmic Reticulum
PubMed: 35454077
DOI: 10.3390/biom12040488 -
The Journal of Physiology Sep 19731. During the first 2 hr washout of (24)Na from rat extensor digitorum longus muscle fits a sum of two exponentials, neither of which represents loss of extracellular...
1. During the first 2 hr washout of (24)Na from rat extensor digitorum longus muscle fits a sum of two exponentials, neither of which represents loss of extracellular tracer. This implies a model with two intracellular components.2. Results of suitably designed experiments indicate that the two components are bidirectionally connected to each other as well as to extracellular space. These results are incompatible with a model in which every fibre is homogeneous with respect to Na concentration and flux, but in which there is a distribution of these properties among fibres.3. Results are consistent with identification of the more slowly exchanging component as sarcoplasm and the more rapidly exchanging component as sarcoplasmic reticulum (SR).4. Parameters of the general model include six transport coefficients, two volumes, and contents of two Na pools. The number of equations is inadequate to yield unique solutions by which the values of these parameters can be calculated. However, we derive inequalities that place upper and lower limits on the parameters.5. If the model is correct, the rate constant for Na efflux from SR to extracellular space is at least five times greater than that across sarcolemma. Under standard conditions flux (per muscle weight) from SR is at least 100 times greater than that from sarcoplasm.6. Under standard conditions, only 2-4% of intracellular Na, or 0.5-0.9 m-equiv/kg wet wt., is in sarcoplasm, and the rest is in SR.7. Bounds on fluid volumes of sarcoplasm and SR under standard conditions are calculated with the assumption that Na concentration in SR is the same as in extracellular space. According to the calculations, fluid volume of sarcoplasm is 0.54 ml./g wet wt. Fluid volume of SR is about 0.124 ml./g wet wt., or 14.3% of fibre volume, in agreement with Peachey's estimate (1965) of volume of SR in frog muscle.8. Three tests are applied to the model, with the following results: (a) volume of sarcoplasm increases in hypotonic solution and decreases in hypertonic solutions, as predicted for an osmometer. Volume of SR tends to change in the opposite direction, in agreement with results of Birks & Davey (1969) from electron microscopy on frog muscle; (b) the major effect of partial substitution of external Na by Li is a reduction in Na content of SR, with no significant change in that of sarcoplasm or in volume of either component; (c) the major effect of 10(-5)M ouabain is an increase in Na content of sarcoplasm, with no demonstrable change in that of SR or in volume of either component.9. These results support the model, particularly our identification of the slowly exchanging component as sarcoplasm, identification of the rapidly exchanging component as SR, and the assumption that Na concentration in SR is close to that in extracellular fluid.
Topics: Animals; Biological Transport, Active; Carbon Isotopes; Extracellular Space; Female; In Vitro Techniques; Kinetics; Lithium; Male; Models, Biological; Muscles; Osmolar Concentration; Osmotic Pressure; Ouabain; Rats; Sarcoplasmic Reticulum; Sodium; Spectrophotometry, Atomic; Time Factors; Water
PubMed: 4747228
DOI: 10.1113/jphysiol.1973.sp010307 -
BMB Reports May 2013Heart failure is one of the leading causes of sudden death in developed countries. While current therapies are mostly aimed at mitigating associated symptoms, novel... (Review)
Review
Heart failure is one of the leading causes of sudden death in developed countries. While current therapies are mostly aimed at mitigating associated symptoms, novel therapies targeting the subcellular mechanisms underlying heart failure are emerging. Failing hearts are characterized by reduced contractile properties caused by impaired Ca(2+) cycling between the sarcoplasm and sarcoplasmic reticulum (SR). Sarcoplasmic/ endoplasmic reticulum Ca(2+)ATPase 2a (SERCA2a) mediates Ca(2+) reuptake into the SR in cardiomyocytes. Of note, the expression level and/or activity of SERCA2a, translating to the quantity of SR Ca(2+) uptake, are significantly reduced in failing hearts. Normalization of the SERCA2a expression level by gene delivery has been shown to restore hampered cardiac functions and ameliorate associated symptoms in pre-clinical as well as clinical studies. SERCA2a activity can be regulated at multiple levels of a signaling cascade comprised of phospholamban, protein phosphatase 1, inhibitor-1, and PKCα. SERCA2 activity is also regulated by post-translational modifications including SUMOylation and acetylation. In this review, we will highlight the molecular mechanisms underlying the regulation of SERCA2a activity and the potential therapeutic modalities for the treatment of heart failure.
Topics: Animals; Calcium; Calcium-Binding Proteins; Cardiovascular Agents; Gene Expression Regulation, Enzymologic; Genetic Therapy; Heart Failure; Humans; Myocardial Contraction; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Signal Transduction
PubMed: 23710633
DOI: 10.5483/bmbrep.2013.46.5.077 -
BMB Reports Mar 2010Calumenin is a multiple EF-hand Ca2+-binding protein located in the endo/sarcoplasmic reticulum of mammalian hearts. Calumenin belongs to the CREC family of Ca2+-binding... (Review)
Review
Calumenin is a multiple EF-hand Ca2+-binding protein located in the endo/sarcoplasmic reticulum of mammalian hearts. Calumenin belongs to the CREC family of Ca2+-binding proteins having multiple EF-hands. Ca2+ homeostasis in the sarcoplasmic reticulum (SR) of mammalian hearts is maintained by RyR2, SERCA2 and other associated SR resident proteins. Evidence suggests that calumenin interacts with RyR2 and SERCA2, and therefore changes in the expression of calumenin could alter Ca2+ cycling in mouse heart. In this review, current knowledge of the biochemical and functional roles of calumenin in mouse heart is described.
Topics: Animals; Calcium-Binding Proteins; Mice; Myocardium; Polymorphism, Genetic; Ryanodine Receptor Calcium Release Channel; Sarcoplasmic Reticulum; Sarcoplasmic Reticulum Calcium-Transporting ATPases
PubMed: 20356454
DOI: 10.5483/bmbrep.2010.43.3.158 -
IUBMB Life Oct 2011The cytosolic calcium concentration ([Ca(2+)](c)) is key for the regulation of many cellular processes, such cell signaling and proliferation, metabolism, and muscle... (Review)
Review
The cytosolic calcium concentration ([Ca(2+)](c)) is key for the regulation of many cellular processes, such cell signaling and proliferation, metabolism, and muscle contraction. In cardiomyocytes, Ca(2+) is an important regulator in many cellular functions such electrophysiological processes, excitation-contraction coupling, regulation of contractile proteins activity, energy metabolism, cell death, and transcriptional regulation by the activation of Ca(2+)-dependent transcriptional pathways. In cardiomyocytes, the two main Ca(2+) -dependent pathways are the Ca(2+)/calmodulin-calcineurin-NFAT and the Ca(2+) /calmodulin-dependent kinases-MEF2. Both pathways are involved in the transcriptional control of many cardiac genes. Cardiac hypertrophy (CH) and heart failure (HF) are characterized by alterations in calcium handling such a low sarcoplasmic reticulum Ca(2+) content, decreased rate of Ca(2+) removal from the sarcoplasm, increased diastolic [Ca(2+)](c), and decreased systolic [Ca(2+)](c), all of them contributing to diminished contractibility and force generation in failing heart. At gene expression level, there are also many changes such decreased levels of SERCA2a and activation of a fetal gene expression program in cardiomyocytes. A variety of Ca(2+)-dependent signaling pathways have been implicated in CH and HF, but whether these pathways are interrelated and whether there is specificity among them are still unclear and under investigation. The focus of this review is to make an analysis of the current knowledge about the role of Ca(2+) signaling pathways in the regulation of cardiac gene expression making special emphasis in novel strategies to correct Ca(2+) handling alterations by means of SERCA2a gene therapy.
Topics: Calcineurin; Calcium; Calcium Signaling; Calsequestrin; Cardiomegaly; Energy Metabolism; Gene Expression Regulation; Heart Failure; Humans; MADS Domain Proteins; MEF2 Transcription Factors; Models, Biological; Myocardial Contraction; Myocytes, Cardiac; Myogenic Regulatory Factors; NFATC Transcription Factors; Sarcoplasmic Reticulum; Sarcoplasmic Reticulum Calcium-Transporting ATPases
PubMed: 21901815
DOI: 10.1002/iub.545