-
The Journal of Physiology Jan 2020
Topics: Connectin; Muscle, Skeletal; Muscle, Striated; Sarcomeres
PubMed: 31829438
DOI: 10.1113/JP279314 -
Zoological Science Aug 2022The effects of mechanical stress on cultured muscle cells were examined with particular interest in myofibril assembly by using a cell-stretching system. We observed...
The effects of mechanical stress on cultured muscle cells were examined with particular interest in myofibril assembly by using a cell-stretching system. We observed that formation and maintenance of cross-striated myofibrils in chick muscle cell cultures was suppressed in the media containing higher concentration of KCl, tetrodotoxin, or ML-9 (an inhibitor of myosin light chain kinase), but periodic stretching of myotubes for several days enabled formation of striated myofibrils just as in standard muscle cultures. However, ryanodine (a blocker of the Ca channel in sarcoplasmic reticulum) and BDM (an inhibitor of myosin-actin interaction) suppressed the stretch-induced myofibrillogenesis. We further found that stretching of myotubes causes quick and transient elevation of the intracellular Ca concentration and this elevation is disturbed by inhibition of Ca channels of sarcoplasmic reticulum and suppression of Ca influx from culture medium. These observations indicate that periodic stretching induces elevation of intracellular Ca concentration and that this elevation may be due to release of Ca from sarcoplasmic reticulum and Ca influx from outside of the cells. The increased Ca may activate actin-myosin interaction by interacting with troponin that is located along actin filaments and/or inducing phosphorylation of myosin light chains and thereby promote myofibril assembly.
Topics: Actins; Animals; Cells, Cultured; Muscle Development; Muscle Fibers, Skeletal; Myofibrils; Myosins
PubMed: 35960030
DOI: 10.2108/zs220015 -
Quarterly Reviews of Biophysics Jan 2023The cardiac sarcomere is a cellular structure in the heart that enables muscle cells to contract. Dozens of proteins belong to the cardiac sarcomere, which work in... (Review)
Review
The cardiac sarcomere is a cellular structure in the heart that enables muscle cells to contract. Dozens of proteins belong to the cardiac sarcomere, which work in tandem to generate force and adapt to demands on cardiac output. Intriguingly, the majority of these proteins have significant intrinsic disorder that contributes to their functions, yet the biophysics of these intrinsically disordered regions (IDRs) have been characterized in limited detail. In this review, we first enumerate these myofilament-associated proteins with intrinsic disorder (MAPIDs) and recent biophysical studies to characterize their IDRs. We secondly summarize the biophysics governing IDR properties and the state-of-the-art in computational tools toward MAPID identification and characterization of their conformation ensembles. We conclude with an overview of future computational approaches toward broadening the understanding of intrinsic disorder in the cardiac sarcomere.
Topics: Myofibrils; Actin Cytoskeleton; Sarcomeres; Computer Simulation; Molecular Conformation
PubMed: 36628457
DOI: 10.1017/S003358352300001X -
Development (Cambridge, England) Mar 2023Proper muscle contraction requires the assembly and maintenance of sarcomeres and myofibrils. Although the protein components of myofibrils are generally known, less is...
Proper muscle contraction requires the assembly and maintenance of sarcomeres and myofibrils. Although the protein components of myofibrils are generally known, less is known about the mechanisms by which they individually function and together synergize for myofibril assembly and maintenance. For example, it is unclear how the disruption of actin filament (F-actin) regulatory proteins leads to the muscle weakness observed in myopathies. Here, we show that knockdown of Drosophila Tropomodulin (Tmod), results in several myopathy-related phenotypes, including reduction of muscle cell (myofiber) size, increased sarcomere length, disorganization and misorientation of myofibrils, ectopic F-actin accumulation, loss of tension-mediating proteins at the myotendinous junction, and misshaped and internalized nuclei. Our findings support and extend the tension-driven self-organizing myofibrillogenesis model. We show that, like its mammalian counterpart, Drosophila Tmod caps F-actin pointed-ends, and we propose that this activity is crucial for cellular processes in different locations within the myofiber that directly and indirectly contribute to the maintenance of muscle function. Our findings provide significant insights to the role of Tmod in muscle development, maintenance and disease.
Topics: Animals; Actins; Tropomodulin; Microfilament Proteins; Drosophila; Myofibrils; Actin Cytoskeleton; Sarcomeres; Mammals
PubMed: 36806912
DOI: 10.1242/dev.201194 -
International Journal of Molecular... Jan 2023Phospholamban () is a major regulator of cardiac contractility, and human mutations in this gene give rise to inherited cardiomyopathies. The deletion of Arginine 14 is...
Phospholamban () is a major regulator of cardiac contractility, and human mutations in this gene give rise to inherited cardiomyopathies. The deletion of Arginine 14 is the most-prevalent cardiomyopathy-related mutation, and it has been linked to arrhythmogenesis and early death. Studies in -humanized mutant mice indicated an increased propensity to arrhythmias, but the underlying cellular mechanisms associated with R14del- cardiac dysfunction in the absence of any apparent structural remodeling remain unclear. The present study addressed the specific role of myofilaments in the setting of R14del- and the long-term effects of R14del- in the heart. Maximal force was depressed in skinned cardiomyocytes from both left and right ventricles, but this effect was more pronounced in the right ventricle of R14del- mice. In addition, the Ca sensitivity of myofilaments was increased in both ventricles of mutant mice. However, the depressive effects of R14del- on contractile parameters could be reversed with the positive inotropic drug omecamtiv mecarbil, a myosin activator. At 12 months of age, corresponding to the mean symptomatic age of R14del- patients, contractile parameters and Ca transients were significantly depressed in the right ventricular R14del- cardiomyocytes. Echocardiography did not reveal any alterations in cardiac function or remodeling, although histological and electron microscopy analyses indicated subtle alterations in mutant hearts. These findings suggest that both aberrant myocyte calcium cycling and aberrant contractility remain specific to the right ventricle in the long term. In addition, altered myofilament activity is an early characteristic of R14del- mutant hearts and the positive inotropic drug omecamtiv mecarbil may be beneficial in treating R14del- cardiomyopathy.
Topics: Humans; Mice; Animals; Myofibrils; Cardiomyopathies; Calcium-Binding Proteins; Arrhythmias, Cardiac; Calcium
PubMed: 36768995
DOI: 10.3390/ijms24032675 -
Meat Science Apr 2023The effect of pre-rigor temperature incubation on the activity and distribution in sarcoplasmic and myofibrillar fractions of calpains, and meat quality attributes was...
The effect of pre-rigor temperature incubation on the activity and distribution in sarcoplasmic and myofibrillar fractions of calpains, and meat quality attributes was investigated. Porcine longissimus thoracis muscles were incubated pre-rigor at 14, 22, 30 and 38 °C to 6 h postmortem, followed by another 2 h incubation at 14 °C. Thereafter, muscles were stored at 2 °C for 1 or 4 days. With higher pre-rigor temperature, sarcoplasmic Ca concentration, purge loss and myofibril-bound calpain-1 content increased, while shear force declined. Water-holding capacity of isolated myofibrils was lower after pre-rigor incubation at 38 °C. Desmin and troponin T degradation, and myofibril fragmentation was greater upon incubation of isolated myofibrils with added Ca in the order 800 μM Ca > 40 μM Ca > no Ca, suggesting that calpain-1 and calpain-2 were associated to myofibrils and proteolytically active with sufficient Ca. Activity of myofibril-bound calpain-1 in muscle incubated pre-rigor at 22 and 30 °C were higher than when incubated at 14 and 38 °C. These results indicate that calpains translocate from the sarcoplasm onto myofibrils with higher pre-rigor temperature to 30 °C and the proteolytic potential of myofibril-associated calpains is thereby increased.
Topics: Swine; Animals; Proteolysis; Myofibrils; Calpain; Red Meat; Pork Meat; Temperature; Muscle, Skeletal; Meat
PubMed: 36608417
DOI: 10.1016/j.meatsci.2022.109094 -
Biophysical Journal Jan 2022FiberSim is a flexible open-source model of myofilament-level contraction. The code uses a spatially explicit technique, meaning that it tracks the position and status...
FiberSim is a flexible open-source model of myofilament-level contraction. The code uses a spatially explicit technique, meaning that it tracks the position and status of each contractile molecule within the lattice framework. This allows the model to simulate some of the mechanical effects modulated by myosin-binding protein C, as well as the dose dependence of myotropes and the effects of varying isoform expression levels. This paper provides a short introduction to FiberSim and presents simulations of tension-pCa curves with and without regulation of thick and thin filament activation by myosin-binding protein C. A myotrope dose-dependent response as well as slack/re-stretch maneuvers to assess rates of tension recovery are also presented. The software was designed to be flexible (the user can define their own model and/or protocol) and computationally efficient (simulations can be performed on a regular laptop). We hope that other investigators will use FiberSim to explore myofilament level mechanisms and to accelerate research focusing on the contractile properties of sarcomeres.
Topics: Actin Cytoskeleton; Calcium; Muscle Contraction; Myocardial Contraction; Myofibrils; Sarcomeres
PubMed: 34932957
DOI: 10.1016/j.bpj.2021.12.021 -
Proceedings of the National Academy of... Jun 2023Missense variant Ile79Asn in human cardiac troponin T (cTnT-I79N) has been associated with hypertrophic cardiomyopathy and sudden cardiac arrest in juveniles. cTnT-I79N...
Missense variant Ile79Asn in human cardiac troponin T (cTnT-I79N) has been associated with hypertrophic cardiomyopathy and sudden cardiac arrest in juveniles. cTnT-I79N is located in the cTnT N-terminal (TnT1) loop region and is known for its pathological and prognostic relevance. A recent structural study revealed that I79 is part of a hydrophobic interface between the TnT1 loop and actin, which stabilizes the relaxed (OFF) state of the cardiac thin filament. Given the importance of understanding the role of TnT1 loop region in Ca regulation of the cardiac thin filament along with the underlying mechanisms of cTnT-I79N-linked pathogenesis, we investigated the effects of cTnT-I79N on cardiac myofilament function. Transgenic I79N (Tg-I79N) muscle bundles displayed increased myofilament Ca sensitivity, smaller myofilament lattice spacing, and slower crossbridge kinetics. These findings can be attributed to destabilization of the cardiac thin filament's relaxed state resulting in an increased number of crossbridges during Ca activation. Additionally, in the low Ca-relaxed state (pCa8), we showed that more myosin heads are in the disordered-relaxed state (DRX) that are more likely to interact with actin in cTnT-I79N muscle bundles. Dysregulation of the myosin super-relaxed state (SRX) and the SRX/DRX equilibrium in cTnT-I79N muscle bundles likely result in increased mobility of myosin heads at pCa8, enhanced actomyosin interactions as evidenced by increased active force at low Ca, and increased sinusoidal stiffness. These findings point to a mechanism whereby cTnT-I79N weakens the interaction of the TnT1 loop with the actin filament, which in turn destabilizes the relaxed state of the cardiac thin filament.
Topics: Humans; Myofibrils; Troponin T; Actins; Mutation; Actin Cytoskeleton; Myosins; Calcium
PubMed: 37252999
DOI: 10.1073/pnas.2221244120 -
Cardiovascular Research May 2024Human pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) provide a platform to identify and characterize factors that regulate the maturation of CMs. The transition...
AIMS
Human pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) provide a platform to identify and characterize factors that regulate the maturation of CMs. The transition from an immature foetal to an adult CM state entails coordinated regulation of the expression of genes involved in myofibril formation and oxidative phosphorylation (OXPHOS) among others. Lysine demethylase 5 (KDM5) specifically demethylates H3K4me1/2/3 and has emerged as potential regulators of expression of genes involved in cardiac development and mitochondrial function. The purpose of this study is to determine the role of KDM5 in iPSC-CM maturation.
METHODS AND RESULTS
KDM5A, B, and C proteins were mainly expressed in the early post-natal stages, and their expressions were progressively downregulated in the post-natal CMs and were absent in adult hearts and CMs. In contrast, KDM5 proteins were persistently expressed in the iPSC-CMs up to 60 days after the induction of myogenic differentiation, consistent with the immaturity of these cells. Inhibition of KDM5 by KDM5-C70 -a pan-KDM5 inhibitor, induced differential expression of 2372 genes, including upregulation of genes involved in fatty acid oxidation (FAO), OXPHOS, and myogenesis in the iPSC-CMs. Likewise, genome-wide profiling of H3K4me3 binding sites by the cleavage under targets and release using nuclease assay showed enriched of the H3K4me3 peaks at the promoter regions of genes encoding FAO, OXPHOS, and sarcomere proteins. Consistent with the chromatin and gene expression data, KDM5 inhibition increased the expression of multiple sarcomere proteins and enhanced myofibrillar organization. Furthermore, inhibition of KDM5 increased H3K4me3 deposits at the promoter region of the ESRRA gene and increased its RNA and protein levels. Knockdown of ESRRA in KDM5-C70-treated iPSC-CM suppressed expression of a subset of the KDM5 targets. In conjunction with changes in gene expression, KDM5 inhibition increased oxygen consumption rate and contractility in iPSC-CMs.
CONCLUSION
KDM5 inhibition enhances maturation of iPSC-CMs by epigenetically upregulating the expressions of OXPHOS, FAO, and sarcomere genes and enhancing myofibril organization and mitochondrial function.
Topics: Humans; Cell Differentiation; Cells, Cultured; Fatty Acids; Gene Expression Regulation, Developmental; Histones; Induced Pluripotent Stem Cells; Mitochondria, Heart; Myocytes, Cardiac; Myofibrils; Oxidation-Reduction; Oxidative Phosphorylation; Promoter Regions, Genetic; Retinoblastoma-Binding Protein 2
PubMed: 38230606
DOI: 10.1093/cvr/cvae014 -
Meat Science Jul 2022The development of myofibrillar proteins drinks (MPDs) can provide meat protein nutrition to specific groups of people. However, one major challenge is that myofibrillar... (Review)
Review
The development of myofibrillar proteins drinks (MPDs) can provide meat protein nutrition to specific groups of people. However, one major challenge is that myofibrillar proteins (MPs) are insoluble in solutions with a low ionic strength. Another functional constraint is the susceptibility of MPs to heat-induced aggregation. Currently, the primary approach used to improve the water solubility of MPs is to inhibit the assembly of myofilaments. Increasing the thermostability of MPs primarily inhibits the aggregation of myosin or oxidizes myosin to soluble substances. This review focuses on the description of several chemical and physical strategies, with an emphasis on the advantages, disadvantages, and recent progress. Under the myosin filament assembly process and the cross-linking aggregation mechanism, this summary helps improve our understanding of the solution and thermostability of MPs in low-ionic-strength solutions, thus providing new ideas to the development of MPDs.
Topics: Humans; Solubility; Myosins; Myofibrils; Osmolar Concentration
PubMed: 35413661
DOI: 10.1016/j.meatsci.2022.108822