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Journal of Muscle Research and Cell... Jun 2021Appropriate organization of cytoskeletal components are required for normal distribution and intracellular localization of different ion channels and proteins involved... (Review)
Review
Appropriate organization of cytoskeletal components are required for normal distribution and intracellular localization of different ion channels and proteins involved in calcium homeostasis, signal transduction, and contractile function of striated muscle. Proteins of the contractile system are in direct or indirect connection with the extrasarcomeric cytoskeleton. A number of other molecules which have essential role in regulating stretch-, voltage-, and chemical signal transduction from the surface into the cytoplasm or other intracellular compartments are already well characterized. Sarcomere, the basic contractile unit, is comprised of a precisely organized system of thin (actin), and thick (myosin) filaments. Intermediate filaments connect the sarcomeres and other organelles (mitochondria and nucleus), and are responsible for the cellular integrity. Interacting proteins have a very diverse function in coupling of the intracellular assembly components and regulating the normal physiological function. Despite the more and more intense investigations of a new cytoskeletal protein family, the septins, only limited information is available regarding their expression and role in striated, especially in skeletal muscles. In this review we collected basic and specified knowledge regarding this protein group and emphasize the importance of this emerging field in skeletal muscle biology.
Topics: Cytoskeleton; Muscle, Skeletal; Muscle, Striated; Sarcomeres; Septins
PubMed: 31955380
DOI: 10.1007/s10974-020-09573-8 -
International Journal of Molecular... Jul 2023Myofibrillar myopathies (MFMs) are a group of hereditary neuromuscular disorders sharing common histological features, such as myofibrillar derangement, Z-disk...
Myofibrillar myopathies (MFMs) are a group of hereditary neuromuscular disorders sharing common histological features, such as myofibrillar derangement, Z-disk disintegration, and the accumulation of degradation products into protein aggregates. They are caused by mutations in several genes that encode either structural proteins or molecular chaperones. Nevertheless, the mechanisms by which mutated genes result in protein aggregation are still unknown. To unveil the role of myotilin and αB-crystallin in the pathogenesis of MFM, we injected zebrafish fertilized eggs at the one-cell stage with expression plasmids harboring cDNA sequences of human wildtype or mutated (p.Ser95Ile) and human wildtype or mutated (p.Gly154Ser). We evaluated the effects on fish survival, motor behavior, muscle structure and development. We found that transgenic zebrafish showed morphological defects that were more severe in those overexpressing mutant genes. which developed a myopathic phenotype consistent with that of human myofibrillar myopathy, including the formation of protein aggregates. Results indicate that pathogenic mutations in myotilin and αB-crystallin genes associated with MFM cause a structural and functional impairment of the skeletal muscle in zebrafish, thereby making this non-mammalian organism a powerful model to dissect disease pathogenesis and find possible druggable targets.
Topics: Animals; Humans; alpha-Crystallin B Chain; Crystallins; Muscle, Skeletal; Mutation; Myofibrils; Myopathies, Structural, Congenital; Protein Aggregates; Zebrafish
PubMed: 37511242
DOI: 10.3390/ijms241411483 -
Journal of Muscle Research and Cell... Sep 2023Early x-ray diffraction studies of muscle revealed spacings larger than the basic thick filament lattice spacing and led to a number of speculations on the mutual... (Review)
Review
Early x-ray diffraction studies of muscle revealed spacings larger than the basic thick filament lattice spacing and led to a number of speculations on the mutual rotations of the filaments in the myosin lattice. The nature of the arrangements of the filaments was resolved by John Squire and Pradeep Luther using careful electron microscopy and image analysis. The intriguing disorder in the rotations, that they termed the myosin superlattice, remained a curiosity, until work with Rick Millane and colleagues showed a connection to "geometric frustration," a well-known phenomenon in statistical and condensed matter physics. In this review, we describe how this connection gives a satisfying physical basis for the myosin superlattice, and how recent work has shown relationships to muscle mechanical behaviour.
Topics: Animals; Frustration; Vertebrates; Myosins; Cytoskeleton; Sarcomeres
PubMed: 37173591
DOI: 10.1007/s10974-023-09642-8 -
Journal of Biomechanics Dec 2021Understanding passive skeletal muscle mechanics is critical in defining structure-function relationships in skeletal muscle and ultimately understanding pathologically... (Review)
Review
Understanding passive skeletal muscle mechanics is critical in defining structure-function relationships in skeletal muscle and ultimately understanding pathologically impaired muscle. In this systematic review, we performed an exhaustive literature search using PRISMA guidelines to quantify passive muscle mechanical properties, summarized the methods used to create these data, and make recommendations to standardize future studies. We screened over 7500 papers and found 80 papers that met the inclusion criteria. These papers reported passive muscle mechanics from single muscle fiber to whole muscle across 16 species and 54 distinct muscles. We found a wide range of methodological differences in sample selection, preparation, testing, and analysis. The systematic review revealed that passive muscle mechanics is species and scale dependent-specifically within mammals, the passive mechanics increases non-linearly with scale. However, a detailed understanding of passive mechanics is still unclear because the varied methodologies impede comparisons across studies, scales, species, and muscles. Therefore, we recommend the following: smaller scales may be maintained within storage solution prior to testing, when samples are tested statically use 2-3 min of relaxation time, stress normalization at the whole muscle level be to physiologic cross-sectional area, strain normalization be to sarcomere length when possible, and an exponential equation be used to fit the data. Additional studies using these recommendations will allow exploration of the multiscale relationship of passive force within and across species to provide the fundamental knowledge needed to improve our understanding of passive muscle mechanics.
Topics: Animals; Muscle Fibers, Skeletal; Muscle, Skeletal; Sarcomeres
PubMed: 34736082
DOI: 10.1016/j.jbiomech.2021.110839 -
The Journal of Clinical Investigation Jan 2024Heterozygous (HET) truncating variant mutations in the TTN gene (TTNtvs), encoding the giant titin protein, are the most common genetic cause of dilated cardiomyopathy...
Heterozygous (HET) truncating variant mutations in the TTN gene (TTNtvs), encoding the giant titin protein, are the most common genetic cause of dilated cardiomyopathy (DCM). However, the molecular mechanisms by which TTNtv mutations induce DCM are controversial. Here, we studied 127 clinically identified DCM human cardiac samples with next-generation sequencing (NGS), high-resolution gel electrophoresis, Western blot analysis, and super-resolution microscopy in order to dissect the structural and functional consequences of TTNtv mutations. The occurrence of TTNtv was found to be 15% in the DCM cohort. Truncated titin proteins matching, by molecular weight, the gene sequence predictions were detected in the majority of the TTNtv+ samples. Full-length titin was reduced in TTNtv+ compared with TTNtv- samples. Proteomics analysis of washed myofibrils and stimulated emission depletion (STED) super-resolution microscopy of myocardial sarcomeres labeled with sequence-specific anti-titin antibodies revealed that truncated titin was structurally integrated into the sarcomere. Sarcomere length-dependent anti-titin epitope position, shape, and intensity analyses pointed at possible structural defects in the I/A junction and the M-band of TTNtv+ sarcomeres, which probably contribute, possibly via faulty mechanosensor function, to the development of manifest DCM.
Topics: Humans; Cardiomyopathy, Dilated; Connectin; Heart; Sarcomeres
PubMed: 37962957
DOI: 10.1172/JCI169753 -
Methods in Molecular Biology (Clifton,... 2021The more recent studies of human pathologies have essentially revealed the complexity of the interactions involved at the different levels of integration in organ...
The more recent studies of human pathologies have essentially revealed the complexity of the interactions involved at the different levels of integration in organ physiology. Integrated organ thus reveals functional properties not predictable by underlying molecular events. It is therefore obvious that current fine molecular analyses of pathologies should be fruitfully combined with integrative approaches of whole organ function. It follows that an important issue in the comprehension of the link between molecular events in pathologies and whole organ function/dysfunction is the development of new experimental strategies aimed at the study of the integrated organ physiology. Cardiovascular diseases are a good example as heart submitted to ischemic conditions has to cope both with a decreased supply of nutrients and oxygen, and the necessary increased activity required to sustain whole body-including the heart itself-oxygenation.By combining the principles of control analysis with noninvasive P NMR measurement of the energetic intermediates and simultaneous measurement of heart contractile activity, we developed MoCA (for Modular Control and regulation Analysis), an integrative approach designed to study in situ control and regulation of cardiac energetics during contraction in intact beating perfused isolated heart (Diolez et al., Am J Physiol Regul Integr Comp Physiol 293(1):R13-R19, 2007). Because it gives real access to integrated organ function, MoCA brings out a new type of information-the "elasticities," referring to integrated internal responses to metabolic changes-that may be a key to the understanding of the processes involved in pathologies. MoCA can potentially be used not only to detect the origin of the defects associated with the pathology, but also to provide the quantitative description of the routes by which these defects-or also drugs-modulate global heart function, therefore opening therapeutic perspectives. This review presents selected examples of the applications to isolated intact beating heart that evidence different modes of energetic regulation of cardiac contraction. We also discuss the clinical application by using noninvasive P cardiac energetics examination under clinical conditions for detection of heart pathologies.
Topics: Animals; Calcium; Cardiotonic Agents; Energy Metabolism; Epinephrine; Guinea Pigs; Heart; Homeostasis; Humans; Magnetic Resonance Spectroscopy; Male; Mitochondria, Heart; Myocardial Contraction; Myocardium; Myofibrils; Organ Culture Techniques; Rats; Simendan
PubMed: 34080165
DOI: 10.1007/978-1-0716-1270-5_25 -
JCI Insight Sep 2023Pediatric cardiomyopathy (CM) represents a group of rare, severe disorders that affect the myocardium. To date, the etiology and mechanisms underlying pediatric CM are...
Pediatric cardiomyopathy (CM) represents a group of rare, severe disorders that affect the myocardium. To date, the etiology and mechanisms underlying pediatric CM are incompletely understood, hampering accurate diagnosis and individualized therapy development. Here, we identified biallelic variants in the highly conserved flightless-I (FLII) gene in 3 families with idiopathic, early-onset dilated CM. We demonstrated that patient-specific FLII variants, when brought into the zebrafish genome using CRISPR/Cas9 genome editing, resulted in the manifestation of key aspects of morphological and functional abnormalities of the heart, as observed in our patients. Importantly, using these genetic animal models, complemented with in-depth loss-of-function studies, we provided insights into the function of Flii during ventricular chamber morphogenesis in vivo, including myofibril organization and cardiomyocyte cell adhesion, as well as trabeculation. In addition, we identified Flii function to be important for the regulation of Notch and Hippo signaling, crucial pathways associated with cardiac morphogenesis and function. Taken together, our data provide experimental evidence for a role for FLII in the pathogenesis of pediatric CM and report biallelic variants as a genetic cause of pediatric CM.
Topics: Animals; Cell Adhesion; Microfilament Proteins; Myocytes, Cardiac; Myofibrils; Zebrafish; Trans-Activators; Cardiomyopathies
PubMed: 37561591
DOI: 10.1172/jci.insight.168247 -
American Journal of Physiology. Heart... Mar 2024The impaired ability of the heart to relax and stretch to accommodate venous return is generally understood to represent a state of "diastolic dysfunction" and often... (Review)
Review
The impaired ability of the heart to relax and stretch to accommodate venous return is generally understood to represent a state of "diastolic dysfunction" and often described using the all-purpose noun "stiffness." Despite the now common qualitative usage of this term in fields of cardiac patho/physiology, the specific quantitative concept of stiffness as a molecular and biophysical entity with real practical interpretation in healthy and diseased hearts is sometimes obscure. The focus of this review is to characterize the concept of cardiomyocyte stiffness and to develop interpretation of "stiffness" attributes at the cellular and molecular levels. Here, we consider "stiffness"-related terminology interpretation and make links between cardiomyocyte stiffness and aspects of functional and structural cardiac performance. We discuss cross bridge-derived stiffness sources, considering the contributions of diastolic myofilament activation and impaired relaxation. This includes commentary relating to the role of cardiomyocyte Ca flux and Ca levels in diastole, the troponin-tropomyosin complex role as a Ca effector in diastole, the myosin ADP dissociation rate as a modulator of cross bridge attachment and regulation of cross-bridge attachment by myosin binding protein C. We also discuss non-cross bridge-derived stiffness sources, including the titin sarcomeric spring protein, microtubule and intermediate filaments, and cytoskeletal extracellular matrix interactions. As the prevalence of conditions involving diastolic heart failure has escalated, a more sophisticated understanding of the molecular, cellular, and tissue determinants of cardiomyocyte stiffness offers potential to develop imaging and molecular intervention tools.
Topics: Humans; Myocytes, Cardiac; Myocardium; Cardiomyopathies; Myofibrils; Diastole; Myosins; Connectin
PubMed: 38180448
DOI: 10.1152/ajpheart.00334.2023 -
Biochimica Et Biophysica Acta.... Oct 2020Muscle atrophy is an inevitable sequel of fasting, denervation, aging, exposure to microgravity, and many human diseases including, cancer, type-2 diabetes, and renal... (Review)
Review
Muscle atrophy is an inevitable sequel of fasting, denervation, aging, exposure to microgravity, and many human diseases including, cancer, type-2 diabetes, and renal failure. During atrophy the destruction of the muscle's fundamental contractile machinery, the myofibrils, is accelerated leading to a reduction in muscle mass, weakness, frailty, and physical disability. Recent findings indicate that atrophy can be a major cause of death in affected individuals, and inhibition of muscle wasting is likely to prolong survival. Major advances in our understanding of the mechanisms for myofibril breakdown in atrophy include the discovery of biological pathways and key components that play prominent roles. On fasting or denervation, degradation of myofibrillar proteins requires an initial dissociation of the desmin cytoskeleton, whose integrity is critical for myofibril stability. This loss of desmin filaments involves phosphorylation, ubiquitination, and subsequent depolymerization by calpain-1, and appears to reduce myofibrils integrity and facilitate their destruction. Consequently, depolymerization of desmin filament in atrophy seems to be an early key event for overall proteolysis. A focus of this review is to discuss these new insights and the specific role of calpain-1 in promoting desmin filaments loss, and to highlight important key questions that merit further study.
Topics: Animals; Calpain; Desmin; Humans; Muscular Atrophy; Myofibrils; Polymerization; Ubiquitination
PubMed: 32603758
DOI: 10.1016/j.bbamcr.2020.118788 -
Medicine and Science in Sports and... Oct 2019Carnosine (β-alanyl-L-histidine) plays an important role in exercise performance and skeletal muscle homeostasis. Dietary supplementation with the rate-limiting... (Review)
Review
Carnosine (β-alanyl-L-histidine) plays an important role in exercise performance and skeletal muscle homeostasis. Dietary supplementation with the rate-limiting precursor β-alanine leads to an increase in skeletal muscle carnosine content, which further potentiates its effects. There is significant interest in carnosine and β-alanine across athletic and clinical populations. Traditionally, attention has been given to performance outcomes with less focus on the underlying mechanism(s). Putative physiological roles in human skeletal muscle include acting as an intracellular pH buffer, modulating energy metabolism, regulating Ca handling and myofilament sensitivity, and scavenging of reactive species. Emerging evidence shows that carnosine could also act as a cytoplasmic Ca-H exchanger and form stable conjugates with exercise-induced reactive aldehydes. The enigmatic nature of carnosine means there is still much to learn regarding its actions and applications in exercise, health, and disease. In this review, we examine the research relating to each physiological role attributed to carnosine, and its precursor β-alanine, in exercising human skeletal muscle.
Topics: Calcium; Carnosine; Dietary Supplements; Energy Metabolism; Exercise; Glycolysis; Humans; Hydrogen-Ion Concentration; Muscle Cells; Muscle Contraction; Muscle, Skeletal; Myofibrils; Oxidation-Reduction; Reactive Oxygen Species; beta-Alanine
PubMed: 31083045
DOI: 10.1249/MSS.0000000000002033