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The Journal of General Physiology Jul 2021The July 2021 issue of is a collection of peer-reviewed articles focused on the function and dynamic regulation of contractile systems in muscle and non-muscle cells.
The July 2021 issue of is a collection of peer-reviewed articles focused on the function and dynamic regulation of contractile systems in muscle and non-muscle cells.
Topics: Myofibrils
PubMed: 34170286
DOI: 10.1085/jgp.202112972 -
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 -
The Journal of Biological Chemistry May 2019"Myosin" is famous as a component of muscle fibrils, but the majority of myosin family members act elsewhere with roles unrelated to muscle contraction. The biological...
"Myosin" is famous as a component of muscle fibrils, but the majority of myosin family members act elsewhere with roles unrelated to muscle contraction. The biological functions of a relatively new family of these unconventional myosins, myosins 18A and 18B, are poorly understood. New research from Horsthemke describes a new isoform (Myo18Aγ) that is essential for heart function and viability in mice. Their findings both support and contradict other work in the field and raise new questions about the roles of myosin 18 proteins .
Topics: Animals; Cytoskeleton; Mice; Myofibrils; Myosins
PubMed: 31053679
DOI: 10.1074/jbc.H119.008784 -
Biochimica Et Biophysica Acta Jul 2016Cells that constitute fully differentiated tissues are characterised by an architecture that makes them perfectly suited for the job they have to do. This is especially... (Review)
Review
Cells that constitute fully differentiated tissues are characterised by an architecture that makes them perfectly suited for the job they have to do. This is especially obvious for cardiomyocytes, which have an extremely regular shape and display a paracrystalline arrangement of their cytoplasmic components. This article will focus on the two major cytoskeletal multiprotein complexes that are found in cardiomyocytes, the myofibrils, which are responsible for contraction and the intercalated disc, which mediates mechanical and electrochemical contact between individual cardiomyocytes. Recent studies have revealed that these two sites are also crucial in sensing excessive mechanical strain. Signalling processes will be triggered that## lead to changes in gene expression and eventually lead to an altered cardiac cytoarchitecture in the diseased heart, which results in a compromised function. Thus, understanding these changes and the signals that lead to them is crucial to design treatment strategies that can attenuate these processes. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.
Topics: Animals; Cardiomyopathy, Dilated; Cell Communication; Gene Expression Regulation; Heart; Humans; Mechanotransduction, Cellular; Membrane Potentials; Myocardial Contraction; Myocardium; Myocytes, Cardiac; Myofibrils; Stress, Mechanical
PubMed: 26577135
DOI: 10.1016/j.bbamcr.2015.11.006 -
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 -
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 -
Proteomics. Clinical Applications Aug 2014Myofilaments are composed of thin and thick filaments that coordinate with each other to regulate muscle contraction and relaxation. PTMs together with genetic... (Review)
Review
Myofilaments are composed of thin and thick filaments that coordinate with each other to regulate muscle contraction and relaxation. PTMs together with genetic variations and alternative splicing of the myofilament proteins play essential roles in regulating cardiac contractility in health and disease. Therefore, a comprehensive characterization of the myofilament proteins in physiological and pathological conditions is essential for better understanding the molecular basis of cardiac function and dysfunction. Due to the vast complexity and dynamic nature of proteins, it is challenging to obtain a holistic view of myofilament protein modifications. In recent years, top-down MS has emerged as a powerful approach to study isoform composition and PTMs of proteins owing to its advantage of complete sequence coverage and its ability to identify PTMs and sequence variants without a priori knowledge. In this review, we will discuss the application of top-down MS to the study of cardiac myofilaments and highlight the insights it provides into the understanding of molecular mechanisms in contractile dysfunction of heart failure. Particularly, recent results of cardiac troponin and tropomyosin modifications will be elaborated. The limitations and perspectives on the use of top-down MS for myofilament protein characterization will also be briefly discussed.
Topics: Amino Acid Sequence; Animals; Health; Heart Failure; Humans; Mass Spectrometry; Molecular Sequence Data; Myofibrils; Proteomics
PubMed: 24945106
DOI: 10.1002/prca.201400043 -
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 -
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