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Ca2+-mediated activation of thin filaments is a crucial step in initiating striated muscle contraction. To gain mechanistic insight into this regulatory process, thin filament (TF) components and myosin motors from diverse species and tissue sources are often combined in minimal in vitro systems. The contribution of tissue-specific TF composition with native myosin motors in generating contraction speed remains unclear. To examine TF-mediated regulation, we established a procedure to purify native TFs (nTF) and myosin motors (M-II) from the same cardiac tissue samples as low as 10 mg and investigated their influence on gliding speeds and Ca2+ sensitivity. The rabbit atrial and ventricular nTFs and M-II were assessed in in vitro nTF motility experiments under varying Ca2+ concentrations. The speed-pCa relationship yielded a maximum TF speed of 2.58 mm/s for atrial (aM-II) and 1.51 mm/s for ventricular myosin (vM-II), both higher than the respective unregulated actin filament gliding speeds. The Ca2+ sensitivity was different for both protein sources. After swapping the nTFs, the ventricular TFs increased their gliding speed on atrial myosin, while the atrial nTFs reduced their gliding speed on ventricular myosin. Swapping of the nTFs decreased the calcium sensitivity for both vM-II and aM-II, indicating a strong influence of the thin filament source. These studies suggest that the nTF-myosin combination is critical to understanding the Ca2+ sensitivity of the shortening speed. Our approach is highly relevant to studying precious human cardiac samples, that is, small myectomy samples, to address the alteration of contraction speed and Ca2+ sensitivity in cardiomyopathies. [ABSTRACT FROM AUTHOR]

Small Heat Shock Proteins are considered as the first line of defense when proteostasis fails. Among them, αB-crystallin is expressed in striated muscles in which it interacts with desmin intermediate filaments to stabilize them, maintaining cytoskeleton's integrity and muscular functionalities. Desmin is a key actor for muscle health; its targeting by αB-crystallin is thus crucial, especially in stress conditions. αB-crystallin is phosphorylated and O-GlcNAcylated. Its phosphorylation increases consecutively to various stresses, correlated with its recruitment for cytoskeleton's safeguarding. However, phosphorylation as unique signal for cytoskeleton translocation remains controversial; indeed, O-GlcNAcylation was also proposed to be involved. Thus, there are still some gaps for a deeper comprehension of how αB-crystallin functions are finely regulated by post-translational modifications. Furthermore, desmin also bears both post-translational modifications; while desmin phosphorylation is closely linked to desmin intermediates filaments turnover, it is unclear whereas its O-GlcNAcylation could impact its proper function. In the herein paper, we aim at identifying whether phosphorylation and/or O-GlcNAcylation are involved in αB-crystallin targeting towards cytoskeleton in proteotoxic stress induced by proteasome inhibition in C2C12 myotubes. We demonstrated that proteotoxicity led to αB-crystallin's phosphorylation and O-GlcNAcylation patterns changes, both presenting a dynamic interplay depending on protein subfraction. Importantly, both post-translational modifications showed a spatio-temporal variation correlated with αB-crystallin translocation towards cytoskeleton. In contrast, we did not detect any change of desmin phosphorylation and O-GlcNAcylation. All together, these data strongly support that αB-crystallin phosphorylation/O-GlcNAcylation interplay rather than changes on desmin is a key regulator for its cytoskeleton translocation, preserving it towards stress. [Display omitted] • Small Heat Shock Proteins (sHSPs) are the first line of defense when proteostasis failed in stressful conditions. • The MG132-induced proteotoxicity modifies O-GlcNAcylation/phosphorylation patterns of αB-crystallin. • The MG132-induced proteotoxicity does not modify the O-GlcNAcylation/phosphorylation patterns of desmin. • Phosphorylation/O-GlcNAcylation of αB-crystallin spatio-temporally varies along proteotoxic stress. • Phosphorylation/O-GlcNAcylation interplay is a key regulator of αB-crystallin cytoskeleton translocation. [ABSTRACT FROM AUTHOR]

Striated muscle cells, encompassing cardiac myocytes and skeletal muscle fibers, are fundamental to athletic performance, facilitating blood circulation and coordinated movement through contraction. Despite their distinct functional roles, these muscle types exhibit similarities in cytoarchitecture, protein expression, and excitation-contraction coupling. Both muscle types also undergo molecular remodeling in energy metabolism and cell size in response to acute and repeated exercise stimuli to enhance exercise performance. Reactive oxygen species (ROS) produced by NADPH oxidase (NOX) isoforms 2 and 4 have emerged as signaling molecules that regulate exercise adaptations. This review systematically compares NOX2 and NOX4 expression, regulation, and roles in cardiac and skeletal muscle responses across exercise modalities. We highlight the many gaps in our knowledge and opportunities to let future skeletal muscle research into NOX-dependent mechanisms be inspired by cardiac muscle studies and vice versa. Understanding these processes could enhance the development of exercise routines to optimize human performance and health strategies that capitalize on the advantages of physical activity. [Display omitted] • Striated muscle cells exhibit many redox-regulated similarities, including the expression of NOX2 and NOX4. • NOX2 and NOX4 are linked to responses to exercise in skeletal and cardiac muscles, influencing glucose metabolism and cell growth. • Further studies on NOX-dependent redox regulation of striated skeletal muscle may improve our understanding of the factors that limit human performance. [ABSTRACT FROM AUTHOR]

• aCGH is an important diagnostic tool for the genetic screening of early onset myopathies. • RALGAPA1 deficiency leads GLUT4 overexpression in human striated muscle cells. • GLUT4 overexpression is potentially linked to glycogen storage in muscle tissue. Early onset myopathies are a clinically and histologically heterogeneous monogenic diseases linked to approximately 90 genes. Molecular diagnosis is challenging, especially in patients with a mild phenotype. We describe a 26-year-old man with neonatal hypotonia, motor delay and seizures during infancy, and non-progressive, mild muscular weakness in adulthood. Serum Creatine kinase level was normal. Whole-body muscle MRI showed thin muscles, and brain MRI was unremarkable. A deltoid muscle biopsy showed glycogen storage. WGS revealed a de novo 1.4 Mb-deletion of chromosome 14, confirmed by Array-CGH. This microdeletion causes the loss of ten genes including RALGAPA1, encoding for RalA, a regulator of glucose transporter 4 (GLUT4) expression at the membrane of myofibers. GLUT4 was overexpressed in patient's muscle. Here we highlight the importance to search for chromosomal alterations in the diagnostic workup of early onset myopathies. [ABSTRACT FROM AUTHOR]

• Collaborating with patient organisations and including patients in the whole process is important to increase the impact of the research. • SML recommendations/guidelines are needed to improve the standard of care. • An International/European SML patient registry is highly recommended. • Natural history of SML still needs to be completely defined. • Emerging non-clinical biomarkers may be helpful for SML patients longitudinal evaluation. [ABSTRACT FROM AUTHOR]

For decades, sarcomeric myosin heavy chain proteins were assumed to be restricted to striated muscle where they function as molecular motors that contract muscle. However, MYH7b, an evolutionarily ancient member of this myosin family, has been detected in mammalian nonmuscle tissues, and mutations in MYH7b are linked to hereditary hearing loss in compound heterozygous patients. These mutations are the first associated with hearing loss rather than a muscle pathology, and because there are no homologous mutations in other myosin isoforms, their functional effects were unknown. We generated recombinant human MYH7b harboring the D515N or R1651Q hearing loss-associated mutation and studied their effects on motor activity and structural and assembly properties, respectively. The D515N mutation had no effect on steady-state actin-activated ATPase rate or load-dependent detachment kinetics but increased actin sliding velocity because of an increased displacement during the myosin working stroke. Furthermore, we found that the D515N mutation caused an increase in the proportion of myosin heads that occupy the disordered-relaxed state, meaning more myosin heads are available to interact with actin. Although we found no impact of the R1651Q mutation on myosin rod secondary structure or solubility, we observed a striking aggregation phenotype when this mutation was introduced into nonmuscle cells. Our results suggest that each mutation independently affects MYH7b function and structure. Together, these results provide the foundation for further study of a role for MYH7b outside the sarcomere. [ABSTRACT FROM AUTHOR]

Myosin heavy chain 7b (MYH7b) is an evolutionarily ancient member of the sarcomeric myosin family, which typically supports striated muscle function. However, in mammals, alternative splicing prevents MYH7b protein production in cardiac and most skeletal muscles and limits expression to a subset of specialized muscles and certain nonmuscle environments. In contrast, MYH7b protein is abundant in python cardiac and skeletal muscles. Although the MYH7b expression pattern diverges in mammals versus reptiles, MYH7b shares high sequence identity across species. So, it remains unclear how mammalian MYH7b function may differ from that of other sarcomeric myosins and whether human and python MYH7b motor functions diverge as their expression patterns suggest. Thus, we generated recombinant human and python MYH7b protein and measured their motor properties to investigate any species-specific differences in activity. Our results reveal that despite having similar working strokes, the MYH7b isoforms have slower actin-activated ATPase cycles and actin sliding velocities than human cardiac β-MyHC. Furthermore, python MYH7b is tuned to have slower motor activity than human MYH7b because of slower kinetics of the chemomechanical cycle. We found that the MYH7b isoforms adopt a higher proportion of myosin heads in the ultraslow, super-relaxed state compared with human cardiac β-MyHC. These findings are supported by molecular dynamics simulations that predict MYH7b preferentially occupies myosin active site conformations similar to those observed in the structurally inactive state. Together, these results suggest that MYH7b is specialized for slow and energy-conserving motor activity and that differential tuning of MYH7b orthologs contributes to species-specific biological roles. [ABSTRACT FROM AUTHOR]

Telethonin/titin-cap (TCAP) encodes a Z-disc protein that plays important roles in sarcomere/T-tubule interactions, stretch-sensing and signaling. Mutations in TCAP are associated with muscular dystrophy and cardiomyopathy; however, the complete etiology and its roles in myocardial infarction and regeneration are not fully understood. Here, we generated tcap gene knockout zebrafish with CRISPR/Cas9 technology and observed muscular dystrophy-like phenotypes and abnormal mitochondria in skeletal muscles. The stretch-sensing ability was inhibited in tcap ‐ / ‐ mutants. Moreover, Tcap deficiency led to alterations in cardiac morphology and function as well as increases in reactive oxygen species (ROS) and mitophagy. In addition, the cardiac regeneration and cardiomyocyte proliferation ability of tcap ‐ / ‐ mutants were impaired, but these impairments could be rescued by supplementation with ROS scavengers or autophagy inhibitors. Overall, our study demonstrates the essential roles of Tcap in striated muscle function and heart regeneration. Additionally, elevations in ROS and autophagy may account for the phenotypes resulting from Tcap deficiency and could serve as novel therapeutic targets for muscular dystrophy and cardiomyopathy. [ABSTRACT FROM AUTHOR]

Pompe disease is a metabolic lysosomal disease caused by mutations in the alpha 1,4-glucosidase (GAA) gene. Reduced GAA enzyme activity leads to accumulation of glycogen, particularly in striated muscle fibers. Dependent on the age of onset and residual GAA enzyme activity, Pompe disease is classified as infantile onset Pompe disease (IOPD) and late onset Pompe disease (LOPD). The clinical and morphological phenotype is highly variable and response to enzyme replacement therapy (ERT) can be difficult to predict. The aim of our study was to perform transcriptomic and proteomic studies on human skeletal muscle samples to obtain a deeper insight into the pathophysiological mechanisms underlying Pompe disease. In a retrospective study, mass spectrometry (MS) was performed on skeletal muscle biopsies from 21 LOPD patients (mean age 47.3y, 43% female) prior ERT and 11 non-diseased subjects (mean age 43.4y, 50% female). RNA-Seq analysis was conducted on 10 LOPD and 7 control samples. Samples with different degree of LOPD muscle pathology were included in the study and the muscle pathology was assessed by histological grading. Bioinformatic studies utilizing the GO and HALLMARK database, an overrepresentation pathway analysis and a gene set enrichment analysis were performed. Due to the large number of samples proteins associated with the degree of muscle pathology were identified by additional regression analysis. MS analysis identified a total of 830 proteins, and significant deregulation of 68 proteins in LOPD (44 downregulated and 24 upregulated proteins) compared to controls. RNA-Seq analysis revealed 20,171 genes, of which 22 showed significant down-regulation and 1 up-regulation in LOPD. Among others, sarcomere proteins associated with thin filaments (e.g. TPM3, TNNI2), thick filaments (e.g. MYL6B, MYH4), and z-discs (e.g. PDLIM3, NEB) were downregulated in LOPD. These findings were supported by transcriptomic analysis, which revealed that genes important for the structural integrity of the muscle fibers were systematically downregulated in LOPD. Correlation of MS data with the degree of muscle pathology unveiled a significant positive correlation of Vesicle-associated membrane associated protein B/C (VAPB), which is known to participate in the endoplasmic reticulum unfolded protein response (UPR), with increasing muscle pathology (p=0.024). Multiomic analysis of skeletal muscle biopsies from patients with LOPD revealed a significant deregulation of several proteins and genes involved in contractile muscle function. Whether these findings are dependent on intracellular glycogen accumulation needs to be investigated in further studies. In addition, the identification of proteins associated with the degree of muscle pathology may provide further insights into the clinical and morphological heterogeneity of LOPD. [ABSTRACT FROM AUTHOR]

Extreme heterogeneity exists in the hypersensitive fear response exhibited by the dystrophin-deficient mdx mouse model of Duchenne muscular dystrophy. Because fear hypersensitivity can impact dystrophic phenotypes, this research aimed to understand the central pathways driving this inter-individual variability. Male and female mdx mice were phenotypically stratified into "stress-resistant" or "stress-sensitive" groups based on their response to two stressors (scruff-restraint and forced treadmill exercise). Label-free quantitative proteomics of striated muscle (heart and tibialis anterior) revealed clustering of the proteome according to sex and stress sensitivity. In both muscles, stress-resistant females were most dissimilar from all other groups, with over 250 proteins differentially regulated between stress-resistant and stress-sensitive females in each muscle. Males showed less proteomic variation with stress sensitivity (70-90 proteins in each tissue) however these changes were associated with clear pathway enrichment. In the heart, stress-sensitive males had significant enrichment of pathways related to mitochondrial ATP synthesis, suggesting that increased cardio-metabolic capacity is associated with fear sensitivity in male mdx mice. Independent of striated muscle source or sex, fear sensitivity was associated with altered expression of beta-actin-like protein 2 (ACTBL2), an actin isoform critical for the formation of focal adhesions and cell motility. Stress-sensitive individuals had ∼6-fold higher expression of ACTBL2, indicative of altered cytoskeletal organisation and focal adhesion formation. Despite identifying proteomic signatures associated with fear sensitivity, no differences in the serum metabolome were detected acutely after a stressor. These data suggest that the heterogeneity in fear hypersensitivity in mdx mice is partially driven by cytoskeletal organisation, but that sex-specific cardio-metabolic reprogramming may play a role in this phenotype. [ABSTRACT FROM AUTHOR]

Loss of brain-specific dystrophin has been implicated in the heightened predisposition of patients and vertebrate models of Duchenne muscular dystrophy (DMD) to stressful stimuli. Using 18F-fluorodeoxyglucose uptake by positron emission tomography (18FDG PET) to assess metabolic tissue activity, we measured decreased 18FDG uptake in most brain regions and marginally increased uptake in skeletal muscle of wildtype mice following stress. By contrast, 18FDG uptake did not change in brain and decreased in striated muscle in the mdx mouse model of DMD in response to stress, suggesting dysfunctional glucose-insulin signalling. Glucose intolerance in mdx mice was exacerbated by stress and driven not by an insensitivity to insulin, but by an inability to synthesize insulin. Exogenous administration of naked insulin mitigated immediate stress-induced physical inactivity (indirect measure of stress sensitivity), lowered 18FDG uptake in brain and elevated 18FDG uptake in striated muscle of mdx mice in response to stress. These data indicate that during stress, dystrophin-deficiency impairs the ability of brain and striated muscle to respond metabolically appropriately. It also suggests that the hypersensitive stress phenotype of mdx mice is associated with dysfunctional glucose-insulin signalling that can be mitigated with exogenous insulin. [ABSTRACT FROM AUTHOR]

• Hydrogen rich water delays the onset of muscle fatigue and could prevent stress fractures. • Patches with H 2 release would have the same effect by repairing bone lesions. • These patches can also prevent the complications of stress fractures. As a result of the ability of hydrogen rich water to delay muscle fatigue, and considering that tired striated muscles do not sufficiently protect the bone from mechanical stress, the hypothetical mechanism according to which the consumption of the respective drink by athletes could reduce the incidence of stress fractures is discussed. The application of patches with transdermal release of molecular hydrogen in the areas where stress fractures occur frequently could strengthen this preventive action, due to the local anti-inflammatory and regenerative action established experimentally on the senescent bone, to which could be added the stimulation of osteogenesis, the inhibition of bone resorption and the prevention of fractures due to the antioxidant action. The hypothesis can be tested experimentally using the rabbit tibia as a model, or statistical studies can be done on the incidence of stress fractures in athletes who consume hydrogen rich water. Even baths in water saturated with molecular hydrogen can prevent stress fractures, because they reduce the perception of muscle fever, and the plasters could also prevent the complications of this type of fractures. [ABSTRACT FROM AUTHOR]

La maladie du foie gras non-alcoolique (en anglais, Non-Alcoholic Fatty Liver Disease , NAFLD) toucherait 26 % des hommes et 11 % des femmes, en France. La NAFLD est un continuum de lésions hépatiques allant de la stéatose simple à la stéatohépatite non-alcoolique (NASH), la NASH avec fibrose hépatique et parfois la cirrhose post NASH. La NAFLD est favorisée par un excès de poids (surpoids ou obésité) associé à des anomalies métaboliques systémiques touchant notamment le tissu adipeux et les muscles striés. Le traitement préventif et curatif de la NAFLD repose sur les mesures hygiéno-diététiques. Ces mesures ont prouvé leur efficacité en termes de résolution de la NASH et de stabilisation, voire de régression de la fibrose hépatique. La mise en place d'un programme d'activité physique adaptée (APA), par un professionnel compétent, contribue significativement à l'amélioration de l'état clinique indépendamment de la perte de poids. Au niveau moléculaire, la littérature actuelle souligne l'effet pléiotropique de cette prise en charge notamment par son action directe ou indirecte sur le métabolisme local (e.g. hépatique) et systémique, l'état inflammatoire systémique et l'activité rhéologique. Au-delà de ces répercussions physiopathologiques, le professionnel en APA accompagne le patient présentant une maladie chronique, ici la NAFLD, à induire un changement de mode de vie durable en s'axant sur son état motivationnel. Ces mesures sont bénéfiques tant chez l'adulte que chez l'enfant. Non-Alcoholic Fatty Liver Disease (NAFLD) is estimated to affect 26% of men and 11% of women in France. NAFLD is a continuum of liver damage ranging from, simple steatosis, to non-alcoholic steatohepatitis (NASH), NASH with liver fibrosis and sometimes post-NASH cirrhosis. NAFLD is favored by excess weight (overweight or obesity) associated with systemic metabolic abnormalities affecting particularly, adipose tissue and striated muscles. The preventive and curative treatment of NAFLD is based on hygienic and dietary measures. These measures have proven to be effective in terms of resolution of NASH and stabilization or even regression of liver fibrosis. The implementation of a program of adapted physical activity (APA), by a competent professional, contributes significantly to the improvement of the clinical state independently of weight loss. At the molecular level, the current literature emphazises the pleiotropic effect of this management, particularly through its direct or indirect action on local (e.g. hepatic) and systemic metabolism, the systemic inflammatory state and rheological activity. Beyond these pathophysiological repercussions, the APA professional accompanies the patient with a chronic disease, in this case NAFLD, to induce a sustainable lifestyle change by focusing on his or her motivational state. These measures appear to be beneficial for both adults and children. [ABSTRACT FROM AUTHOR]

Post-vaccinal sarcomas have been reported in cats and rarely in other domestic mammals, but not in birds. Three village weaver birds (Ploceus cucullatus) presented with poor flying ability and abnormal wing carriage attributable to large, unilateral pectoral masses. All had received at least one dose of autogenous Yersinia pseudotuberculosis vaccine into the affected pectoral muscle 74–408 days previously. Following euthanasia, gross post-mortem examination revealed locally invasive subcutaneous tumours extending through the sternum into the coelomic cavity. Cytology and histology revealed neoplasms of pleomorphic spindloid neoplastic cells with foci of coagulative necrosis and cavitation, sometimes containing faintly refractile non-polarizing granular material, both extracellularly and after phagocytosis by surrounding cells, including multinucleated giant cells. Immunohistochemistry in one bird supported a striated muscle cell origin. Findings of anaplastic sarcoma with intralesional foreign crystalline material resembled typical injection-site sarcomas in cats. This is the first report of presumptive vaccine-associated sarcoma in a non-mammalian species. [Display omitted] [ABSTRACT FROM AUTHOR]

Introduction and Hypothesis: The purpose of this study was to compare the muscle elasticity of the striated urethral sphincter (SUS) using real-time tissue elastography (RTE) as an evaluation of pelvic floor muscle (PFM) function between overactive bladder (OAB) patients and healthy women.Methods: The subjects were 8 healthy middle-aged women (healthy group; age range 57-65 years) and 9 female OAB patients (OAB group; age range 42-80 years). The target sites of elastography were the striated urethral sphincter (SUS) and adipose tissue as the reference site; muscle elasticity was calculated as the strain ratio (SR) of the SUS to the reference site. Evaluations were performed at rest and during PFM contraction. The OAB group completed OAB symptom and quality of life questionnaires. The SUS SR was compared between the groups. The SUS SR at rest and during PFM contraction was compared within groups using the t-test and Wilcoxon's test. The relationship between the questionnaire results and the SUS SR was evaluated by correlation analysis.Results: Intergroup comparisons between the healthy and OAB groups showed no significant differences in SUS SR at rest and during PFM contraction. On intragroup comparisons, the SUS SR was significantly higher during PFM contraction than at rest in the healthy group (p = 0.011); in the OAB group, there was no significant difference in the SUS SR between rest and PFM contraction. The SUS SR was not significantly correlated with questionnaire results for OAB symptoms.Conclusion: This study shows the potential to non-invasively confirm the inability of OAB patients to correctly perform PFM contraction using RTE. [ABSTRACT FROM AUTHOR]

Cardiac muscle myosin regulatory light chain (RLC) is constitutively phosphorylated at _0.4 mol phosphate/mol RLC in normal hearts, and phosphorylation is maintained by balanced activities of dedicated cardiac muscle--specific myosin light chain kinase and myosin light chain phosphatase (MLCP). Previously, the identity of the cardiac-MLCP was biochemically shown to be similar to the smooth muscle MLCP, which is a well-characterized trimeric protein comprising the regulatory subunit (MYPT1), catalytic subunit PP1cβ, and accessory subunit M20. In smooth muscles in vivo, MYPT1 and PP1cβ co-stabilize each other and are both necessary for normal smooth muscle contractions. In the cardiac muscle, MYPT1 and MYPT2 are both expressed, but contributions to physiological regulation of cardiac myosin dephosphorylation are unclear. We hypothesized that the main catalytic subunit for cardiac- MLCP is PP1cβ, and maintenance of RLC phosphorylation in vivo is dependent on regulation by striated muscle--specific MYPT2. Here, we used PP1cβ conditional knockout mice to biochemically define cardiac-MLCP proteins and developed a cardiac myofibrillar phosphatase assay to measure the direct contribution of MYPT-regulated and MYPT-independent phosphatase activities toward phosphorylated cardiac myosin. We report that (1) PP1cβ is the main isoform expressed in the cardiac myocyte, (2) cardiac muscle pathogenesis in PP1cβ knockout animals involve upregulation of total PP1cα in myocytes and non-muscle cells, (3) the stability of cardiac MYPT1 and MYPT2 proteins in vivo is not dependent on the PP1cβ expression, and (4) phosphorylated myofibrillar cardiac myosin is dephosphorylated by both myosin-targeted and soluble MYPT-independent PP1cβ activities. These results contribute to our understanding of the cardiac-MLCP in vivo. [ABSTRACT FROM AUTHOR]

Voice production has been an area of interest in science since ancient times, and although advancing research has improved our understanding of the anatomy and function of the larynx, there is still little general consensus on these two topics. This review aims to outline the main developments in this field and highlight the areas where further research is needed. The most important hypotheses are presented and discussed highlighting the four main lines of research in the anatomy of the human larynx and their most important findings: (1) the arrangement of the muscle fibers of the thyroarytenoid muscle is not parallel to the vocal folds in the internal part (vocalis muscle), leading to altered properties during contraction; (2) the histological structure of the human vocal cords differs from other striated muscles; (3) there is a specialized type of heavy myosin chains in the larynx; and (4) the neuromuscular system of the larynx has specific structures that form the basis of an intrinsic laryngeal nervous system. These approaches are discussed in the context of current physiological models of vocal fold vibration, and new avenues of investigation are proposed. [ABSTRACT FROM AUTHOR]

• Data on genitourinary and gastrointestinal systems in DM1 are scarce and conflicting. • Incontinence, erectile dysfunction, constipation and diarrhea were found highly prevalent. • Smooth and striated muscle impairments were described in small sample size studies. • There was limited evidence on treatment effects for these conditions. • High-quality studies using validated outcomes are lacking and should be conducted. Myotonic dystrophy type 1 (DM1) is a progressive neuromuscular disease affecting both smooth and striated muscles. It has been suggested that this multisystemic disease also impairs the genitourinary and lower gastrointestinal systems, but information is scattered and no systematic review has been conducted. The objectives of this systematic review were to document (1) symptoms and signs associated with genitourinary and lower gastrointestinal systems in the DM1 population; (2) impacts on quality of life and participation; and (3) efficacy of treatments available to treat those conditions. Among the 75 studies included, 30 articles presented genitourinary outcomes and 67, lower gastrointestinal outcomes. A wide range of symptoms was reported for both systems but most studies were of poor quality, using medical chart reviews without the use of standardized questionnaires. Urinary incontinence, erectile dysfunction, anal incontinence, constipation, diarrhea and abdominal pain were the most described symptoms. Smooth and striated muscle impairment has been documented in small sample size studies. No experimental study evaluated the efficacy of treatments for these conditions. Few descriptive studies described altered quality of life or participation related to these conditions. Further studies should use standardized questionnaires, provide a clear definition of symptoms and investigate treatment options. [ABSTRACT FROM AUTHOR]

Mutations in the titin (TTN) gene are among the most common genomic aberrations in ocular surface squamous neoplasia (OSSN), the most common cancer of the external eye. Further, TTN mutations are associated with resistance to standard therapy with topical interferon alpha-2b (IFN-α2b). However, it remains unclear how TTN mutations drive OSSN pathogenesis and treatment resistance. TTN encodes the largest protein in the human body and its best understood function is as a myofibril scaffold in striated muscle. However, recent evidence indicates that TTN has additional functions in non-muscle cells and in cancer. Here, we performed a disorder-based bioinformatics analysis which revealed that intrinsically disordered protein regions are abundant in TTN and provide mechanistic insights into its function as a nuclear protein in epithelial cells. Specific mutations found in OSSN are predicted to affect its intrinsically disordered protein regions (IDPRs), promoting chromosomal instability, oncogenesis, and altered response to IFN-α2b treatment. [ABSTRACT FROM AUTHOR]

The pelvic floor functions as a holistic entity. The organs, bladder, bowel, smooth and striated muscles, nerves, ligaments and other connective tissues are directed cortically and reflexly from various levels of the nervous system. Such holistic integration is essential for the system's multiple functions, for example, pelvic girdle stability, continence, voiding/defecation, and sexuality. Pelvic floor dysfunction (PFD) is related to a variety of pelvic pain syndromes and organ problems of continence and evacuation. Prior to treatment, it is necessary to understand which part(s) of the system may be causing the dysfunction (s) of Chronic Pelvic Pain Syndrome (CPPS), pelvic girdle pain, sexual problems, Lower Urinary Tract Symptoms (LUTS), dysfunctional voiding, constipation, prolapse and incontinence. The interpretation of pelvic floor biomechanics is complex and involves multiple theories. Non-surgical treatment of PFD requires correct diagnosis and correctly supervised pelvic floor training. The aims of this review are to analyze pelvic function and dysfunction. Because it is a holistic and entirely anatomically based system, we have accorded significant weight to the Integral Theory's explanations of function and dysfunction. [ABSTRACT FROM AUTHOR]

Striated muscle is intricately designed to provide efficient and powerful muscle contractions. Recently, a long sought-after missing component of the thin filament pointed-end machinery was discovered: cyclase-associated protein 2 (CAP2). CAP2 was identified as a crucial contributor to actin polymerization, striated muscle development, and severe muscle disease when mutated. [ABSTRACT FROM AUTHOR]

The theory proposed by Suga and Sagawa, encompassing the concepts of 'time-varying elastance', 'pressure-volume area' and 'isoefficiency', has been widely applied in cardiac research - albeit not without contention. In this Review, we commence with a brief history of striated muscle energetics as a prelude to re-visiting the Suga-Sagawa Theory. We conclude our discussion by including recent insights into the fundamental flaw underlying the metabolic component of the Theory. [ABSTRACT FROM AUTHOR]

• Normalized muscle volumes distinguish between wild type and DE50-MD dogs. • Global muscle T2 signal intensities discriminate between wild type and DE50-MD dogs. • Musculoskeletal changes detected by MRI reflect those seen in human DMD patients. • Musculoskeletal MRI in this model will be useful to assess treatment efficacy. The DE50-MD canine model of Duchenne muscular dystrophy (DMD) has a dystrophin gene splice site mutation causing deletion of exon 50, an out-of-frame transcript and absence of dystrophin expression in striated muscles. We hypothesized that the musculoskeletal phenotype of DE50-MD dogs could be detected using Magnetic Resonance Imaging (MRI), that it would progress with age and that it would reflect those in other canine models and DMD patients. 15 DE50-MD and 10 age-matched littermate wild type (WT) male dogs underwent MRI every 3 months from 3 to 18 months of age. Normalized muscle volumes, global muscle T2 and ratio of post- to pre-gadolinium T1-weighted SI were evaluated in 7 pelvic limb and 4 lumbar muscles bilaterally. DE50-MD dogs, compared to WT, had smaller volumes in all muscles, except the cranial sartorius; global muscle T2 was significantly higher in DE50-MD dogs compared to WT. Muscle volumes plateaued and global muscle T2 decreased with age. Normalized muscle volumes and global muscle T2 revealed significant differences between groups longitudinally and should be useful to determine efficacy of therapeutics in this model with suitable power and low sample sizes. Musculoskeletal changes reflect those of DMD patients and other dog models. [ABSTRACT FROM AUTHOR]

• Exertional Rhabdomyolysis (ERM) represents a potentially serious health condition. • ERM is common in military personnel, untrained and high-performance athletes. • The incidence of ERM is unknown mainly because of its highly variable presentation. • Genetic and environmental conditions may increase susceptibility to develop ERM. • Adequacy of exercise protocols is imperative to avoid ERM-costly hospitalization. Exertional rhabdomyolysis may occur when an individual is subjected to strenuous physical exercise. It is occasionally associated with myoglobinuria (i.e. "cola-colored" urine) alongside muscle pain and weakness. The pathophysiology of exertional rhabdomyolysis involves striated muscle damage and the release of cellular components into extracellular fluid and bloodstream. This can cause acute renal failure, electrolyte abnormalities, arrhythmias and potentially death. Exertional rhabdomyolysis is observed in high-performance athletes who are subjected to intense, repetitive and/or prolonged exercise but is also observed in untrained individuals and highly trained or elite groups of military personnel. Several risk factors have been reported to increase the likelihood of the condition in athletes, including: viral infection, drug and alcohol abuse, exercise in intensely hot and humid environments, genetic polymorphisms (e.g. sickle cell trait and McArdle disease) and epigenetic modifications. This article reviews several of these risk factors and proposes screening protocols to identify individual susceptibility to exertional rhabdomyolysis as well as the relevance of proteomics for the evaluation of potential biomarkers of muscle damage. [ABSTRACT FROM AUTHOR]

Many esophageal striated muscles of mammals are dually innervated by the vagal and enteric nerves. Recently, substance P (SP)-sensory nerve terminals with calcitonin gene-related peptide (CGRP) were found on a few striated muscle fibers in the rat esophagus, implying that these muscle fibers are triply innervated. In this study, we examined the localization and origin of CGRP-nerve endings in striated muscles to consider their possible roles in the esophagus regarding triple innervation. Wholemounts of the rat esophagus were immunolabeled to detect CGRP-nerve endings in striated muscles. Also, retrograde tracing was performed by injecting Fast Blue (FB) into the esophagus, and cryostat sections of the medulla oblongata, nodose ganglion (NG), and the tenth thoracic (T10) dorsal root ganglion (DRG) were immunostained to identify the origin of the CGRP-nerve endings. CGRP-fine, varicose nerve endings were localized in motor endplates on a few esophageal striated muscle fibers (4 %), most of which received nitric oxide (NO) synthase nerve terminals, and most of the CGRP nerve endings were SP- and transient receptor potential vanilloid member 1 (TRPV1)-positive. Retrograde tracing showed many FB-labeled CGRP-neurons positive for SP and TRPV1 in the NG and T10 DGR. This study suggests that the CGRP-varicose nerve endings containing SP and TRPV1 in motor endplates are sensory, and a few esophageal striated muscle fibers are triply innervated. The nerve endings may detect acetylcholine-derived acetic acid from the vagal motor nerve endings and NO from esophageal intrinsic nerve terminals in the motor endplates to regulate esophageal motility. [ABSTRACT FROM AUTHOR]

Sarcoglycanopathies are rare autosomal recessive diseases belonging to the family of limb-girdle muscular dystrophies. They are caused by mutations in the genes coding for α-, β-, γ-, and δ-sarcoglycan. The mutations impair the assembly of a key structural complex, which normally protects the sarcolemma of striated muscle from contraction-derived stress. Although heterogeneous, sarcoglycanopathies are characterized by progressive muscle degeneration, increased serum creatine kinase levels, loss of ambulation often during adolescence, and variable cardio-respiratory impairment. Genetic defects can impair sarcoglycan synthesis or produce a protein that is defective in folding. There is currently no effective treatment available; however, both gene replacement strategy and small molecule-based approaches show great promise and have entered or are starting to enter clinical trials. Therapeutic approaches for sarcoglycanopathies based on gene replacement and small molecules inducing either protein recovery or acting on secondary causes of the disease. Combined approaches are also envisaged. [Display omitted] • Sarcoglycanopathies are due to the loss of function of the sarcoglycan complex. • Different types of mutations are responsible for sarcoglycan complex disruption. • Gene replacement strategy is currently in the early phase of a clinical trial. • Compounds correcting the mutated sarcoglycan are at an advanced preclinical stage. [ABSTRACT FROM AUTHOR]

Forensic toolmark examiners have been comparing features observed in toolmarks to help determine their source for over a century. However, in the past decade, the holistic process of comparing toolmarks and presenting findings in court have faced intense scrutiny. This paper provides a summary of the voiced criticisms, primarily concerning the scientific reliability and validity of the comparison methods employed by examiners and the conclusions they testify to. The focus of this review is specifically on the examination of striated toolmarks. We assess the comparison methods and reporting practices currently in use, while also delving deeper into research aligned with current recommendations, such as PCAST (The President's Council of Advisors on Science and Technology). Throughout the review, we examine both the strengths and weaknesses of existing practices, aiming to assist practitioners in identifying key research needs and addressing the concerns raised by critics. By doing so, we seek to enhance the credibility and effectiveness of toolmark analysis in the field of forensic science. • Review of the response to organizations challenges. • Automatic methods: implementation and strengths. • The influence of the tool's use on the variability of marks. • Creating empirical and operational datasets. • The adoption of the probabilistic framework, the way forward. [ABSTRACT FROM AUTHOR]

We have studied the effects of hydrogen peroxide (H 2 O 2) on the differentiation and maintenance of C2C12 myoblasts. The effects of H 2 O 2 were evaluated by cell viability, total protein concentration, the relative amount of muscle-related proteins, sarcomere structure, and active tension generation. Oxidative stress is one of the major causes of myopathy after exercise and thus establishing the method to evaluate the effects on muscle function is essential. The primary function of striated muscle is to generate force, thus, the measurement of active tension is important in assessing the effect of chemicals on muscle. Among the indices we tested, the sarcomere structure was the most sensitive to the H 2 O 2 exposure while the cell viability was less sensitive. The effects of H 2 O 2 on active tension correlated with a decrease in the amount of muscle proteins. In this study, our results showed that the effect of chemicals on muscle should be measured in multiple ways, including active tension generation, for a better understanding of its physiological impact. [ABSTRACT FROM AUTHOR]

Chronic glucocorticoid exposure causes insulin resistance and muscle atrophy in skeletal muscle. We previously identified phosphoinositide-3-kinase regulatory subunit 1 (Pik3r1) as a primary target gene of skeletal muscle glucocorticoid receptors involved in the glucocorticoid-mediated suppression of insulin action. However, the in vivo functions of Pik3r1 remain unclear. Here, we generated striated muscle-specific Pik3r1 knockout (MKO) mice and treated them with a dexamethasone (DEX), a synthetic glucocorticoid. Treating wildtype (WT) mice with DEX attenuated insulin activated Akt activity in liver, epididymal white adipose tissue, and gastrocnemius (GA) muscle. This DEX effect was diminished in GA muscle of MKO mice, therefore, resulting in improved glucose and insulin tolerance in DEX-treated MKO mice. Stable isotope labeling techniques revealed that in WT mice, DEX treatment decreased protein fractional synthesis rates in GA muscle. Furthermore, histology showed that in WT mice, DEX treatment reduced GA myotube diameters. In MKO mice, myotube diameters were smaller than in WT mice, and there were more fast oxidative fibers. Importantly, DEX failed to further reduce myotube diameters. Pik3r1 knockout also decreased basal protein synthesis rate (likely caused by lower 4E-BP1 phosphorylation at Thr37/Thr46) and curbed the ability of DEX to attenuate protein synthesis rate. Finally, the ability of DEX to inhibit eIF2a phosphorylation and insulin-induced 4E-BP1 phosphorylation was reduced in MKO mice. Taken together, these results demonstrate the role of Pik3r1 in glucocorticoid-mediated effects on glucose and protein metabolism in skeletal muscle. [ABSTRACT FROM AUTHOR]

Membrane remodeling is required for dynamic cellular processes such as cell division, polarization, and motility. BAR domain proteins and dynamins are key molecules in membrane remodeling that work together for membrane deformation and fission. In striated muscles, sarcolemmal invaginations termed T-tubules are required for excitation-contraction coupling. BIN1 and DNM2, which encode a BAR domain protein BIN1 and dynamin 2, respectively, have been reported to be causative genes of centronuclear myopathy (CNM), a hereditary degenerative disease of skeletal muscle, and deformation of T-tubules is often observed in the CNM patients. However, it remains unclear how BIN1 and dynamin 2 are implicated in T-tubule biogenesis and how mutations in these molecules cause CNM to develop. Here, using an in cellulo reconstitution assay, we demonstrate that dynamin 2 is required for stabilization of membranous structures equivalent to T-tubules. GTPase activity of wild-type dynamin 2 is suppressed through interaction with BIN1, whereas that of the disease-associated mutant dynamin 2 remains active due to lack of the BIN1-mediated regulation, thus causing aberrant membrane remodeling. Finally, we show that in cellulo aberrant membrane remodeling by mutant dynamin 2 variants is correlated with their enhanced membrane fission activities, and the results can explain severity of the symptoms in patients. Thus, this study provides molecular insights into dysregulated membrane remodeling triggering the pathogenesis of DNM2-related CNM. [ABSTRACT FROM AUTHOR]

Crotamine and crotamine-like peptides are non-enzymatic polypeptides, belonging to the family of myotoxins, which are found in high concentration in the venom of the Crotalus genus. Helleramine was isolated and purified from the venom of the Southern Pacific rattlesnake, Crotalus oreganus helleri. This peptide had a similar, but unique, identity to crotamine and crotamine-like proteins isolated from other rattlesnakes species. The variability of crotamine-like protein amino acid sequences may allow different toxic effects on biological targets or optimize the action against the same target of different prey. Helleramine was capable of increasing intracellular Ca2+ in Chinese Hamster Ovary (CHO) cell line. It inhibited cell migration as well as cell viability (IC 50 = 11.44 μM) of C2C12, immortalized skeletal myoblasts, in a concentration dependent manner, and promoted early apoptosis and cell death under our experimental conditions. Skeletal muscle harvested from mice 24 h after helleramine injection showed contracted myofibrils and profound vacuolization that enlarged the subsarcolemmal space, along with loss of plasmatic and basal membrane integrity. The effects of helleramine provide further insights and evidence of myotoxic activities of crotamine-like peptides and their possible role in crotalid envenomings. • A new crotamine-like peptide was isolated from the Southern Pacific rattlesnake, which shared high identity with crotamine. • Helleramine promoted calcium influx into CHO cells. • Inhibited cell viability through apoptosis in myoblasts and induced toxicity in muscle tissue in vivo. • Helleramine may play a role in the myotoxicity induced by North American crotalid venoms. [ABSTRACT FROM AUTHOR]

Vertebrate striated muscle thin filaments are thought to be thermodynamically activated in response to an increase in Ca2+ concentration. We tested this hypothesis by measuring time intervals for gliding runs and pauses of individual skeletal muscle thin filaments in cycling myosin motility assays. A classic thermodynamic mechanism predicts that if chemical potential is constant, transitions between runs and pauses of gliding thin filaments will occur at constant rate as given by a Poisson distribution. In this scenario, rate is given by the odds of a pause, and hence, run times between pauses fit an exponential distribution that slopes negatively for all observable run times. However, we determined that relative density of observed run times fits an exponential only at low Ca2+ levels that activate filament gliding. Further titration with Ca2+, or adding excess regulatory proteins tropomyosin and troponin, shifted the relative density of short run times to fit the positive slope of a gamma distribution, which derives from waiting times between Poisson events. Events that arise during a run and prevent the chance of ending a run for a random interval of time account for the observed run time distributions, suggesting that the events originate with cycling myosin. We propose that regulatory proteins of the thin filament require the mechanical force of cycling myosin to achieve the transition state for activation. During activation, combinations of cycling myosin that contribute insufficient activation energy delay deactivation. [ABSTRACT FROM AUTHOR]

Recent proteomics studies of vertebrate striated muscle have identified lysine acetylation at several sites on actin. Acetylation is a reversible post-translational modification that neutralizes lysine's positive charge. Positively charged residues on actin, particularly Lys326 and Lys328, are predicted to form critical electrostatic interactions with tropomyosin (Tpm) that promote its binding to filamentous (F)-actin and bias Tpm to an azimuthal location where it impedes myosin attachment. The troponin (Tn) complex also influences Tpm's position along F-actin as a function of Ca2+ to regulate exposure of myosinbinding sites and, thus, myosin cross-bridge recruitment and force production. Interestingly, Lys326 and Lys328 are among the documented acetylated residues. Using an acetic anhydridebased labeling approach, we showed that excessive, nonspecific actin acetylation did not disrupt characteristic F-actin-Tpm binding. However, it significantly reduced Tpm-mediated inhibition of myosin attachment, as reflected by increased F-actin- Tpm motility that persisted in the presence of Tn and submaximal Ca2+. Furthermore, decreasing the extent of chemical acetylation, to presumptively target highly reactive Lys326 and Lys328, also resulted in less inhibited F-actin-Tpm, implying that modifying only these residues influences Tpm's location and, potentially, thin filament regulation. To unequivocally determine the residue-specific consequences of acetylation on Tn-Tpm-based regulation of actomyosin activity, we assessed the effects of K326Q and K328Q acetyl (Ac)-mimetic actin on Ca2+-dependent, in vitro motility parameters of reconstituted thin filaments (RTFs). Incorporation of K328Q actin significantly enhanced Ca2+ sensitivity of RTF activation relative to control. Together, our findings suggest that actin acetylation, especially Lys328, modulates muscle contraction via disrupting inhibitory Tpmpositioning. [ABSTRACT FROM AUTHOR]

Background: Prospective studies to guide the application of a gastrocnemius recession for Achilles tendinopathy are limited. Our aim was to prospectively evaluate patient reported outcomes and muscle performance.Methods: Patients with unilateral recalcitrant Achilles tendinopathy who received an isolated gastrocnemius recession (n=8) and a healthy control group (n=8) were included. Patient reported outcomes, ankle power during walking and stair ascent, and the heel rise limb symmetry index (total work) were collected.Results: Improvements in pain and self-reported function were observed (six months and two years). Sport participation scores reached 92% by two years. Patients demonstrated lower ankle power during stair ascent and decreased limb symmetry during heel rise six months following treatment (p≤.02).Conclusions: Study findings regarding long-term improvements in patient pain, self-reported function and sport participation, and early preservation of ankle function during walking, can help refine patient selection, anticipated outcomes, and rehabilitation strategies. [ABSTRACT FROM AUTHOR]

Ectomesenchymal chondromyxoid tumour (ECT) is an extremely rare intraoral mesenchymal tumour. Most of these tumours have been identified on the anterior aspect of the dorsal surface of the tongue. ECT is difficult to diagnose because of its rarity. We report a case of ECT arising on the lateral border of the tongue in a 67-year-old woman. The tumour, measuring 20 × 10 mm in size, was surgically removed. Histopathologically, the tumour was composed of small polygonal cells arranged in sheets, with a myxoid or hyalinized stroma. The tumour boundary was clear; however, the tumour showed a multinodular structure expanding along the tongue surface without obvious capsule. Careful examination revealed the tumour nodule to be spreading in a skip lesion-like fashion away from the main part of the tumour in the striated muscle layer. Although there was no evidence of recurrence at 18 months after the surgery, our observations suggest that surgery for ECT resection with a safety margin is more appropriate than enucleation. [ABSTRACT FROM AUTHOR]

It is well appreciated that autonomic neurons have a central role in the homeostatic regulation of organs and systems and participate to the pathogenesis of several disease conditions. As such, the function and signalling pathways activated by sympathetic neurons (SNs) in different cell types and organs have become a matter of intense investigation throughout the years of modern biomedical research. This review is focused on the methods used to address sympathetic innervation of cardiac and skeletal muscles which, quite surprisingly, has remained incompletely understood, mainly due to the technical limitations of the traditional methodologies. The current review provides a summary of the existing literature and, putting together the results obtained with different methodological approaches, provides a comprehensive view of the complexity of the SN network in striated muscles. [ABSTRACT FROM AUTHOR]

Changes in the incidence of porcine cysticercosis is used commonly in the assessment of efforts to control the transmission of Taenia solium , the cause of human neurocysticercosis. Although cysticerci may occasionally occur in tissues other than the striated muscles, particularly the brain, infection in pigs can be diagnosed reliably by assessment of muscle tissue alone. [ABSTRACT FROM AUTHOR]

Rhabdomyosarcoma is a rare malignant tumor originating from striated muscle cells. It accounts for only 3% of all soft tissue sarcomas in adults, and its metastases can also reach the central nervous system. Only sporadic cases of primary brain rhabdomyosarcoma (PBRMS) have been reported so far. We discuss the atypical presentation and diagnostic challenge of PBRMS in a 65-year-old man. He presented with a 3-day history of progressive right hemiparesis caused by an unspecific left frontoparietal heterogeneously enhancing lesion. Total body computed tomography and positron emission tomography scans performed at baseline did not reveal other secondarisms. The patient underwent radical excision of the lesion, which allowed to establish the diagnosis, with immunohistochemical staining positive for desmin and myogenin. Stereotactic radiotherapy guaranteed local disease control; nonetheless, the patient also required adjuvant chemotherapy when he developed large right lung metastases 6 months postoperatively. PBRMS can be hardly distinguished from other malignant brain tumors during preoperative radiologic workup; only histology can raise the suspicion of primary or metastatic rhabdomyosarcoma, depending on the presence of other distant lesions. Our review of the literature demonstrates that prognosis is poor: 44% of patients die within 1 year from diagnosis. Overall, survival seems to correlate with radical resection, tolerance of stereotactic or if necessary full neuraxis radiotherapy, and adjuvant chemotherapy. Given the high relapse rate, close monitoring and restaging are imperative. [ABSTRACT FROM AUTHOR]

Urinary incontinence is common after radical prostatectomy. Pelvic floor muscle training provides a plausible solution. Although early trials provided promising results, systematic reviews have questioned the efficacy of this intervention. A major consideration is that most clinical trials in men have applied principles developed for pelvic floor muscle training for stress urinary incontinence in women, despite differences in anatomy between sexes and differences in the mechanisms for continence/incontinence. Literature regarding continence control in men has been conflicting and often based on erroneous anatomy. New understanding of continence mechanisms in men, including the complex contribution of multiple layers of striated pelvic floor muscles, and detailed consideration of the impact of radical prostatectomy on continence anatomy and physiology, have provided foundations for a new approach to pelvic floor muscle training to prevent and treat incontinence after prostatectomy. An approach to training can be designed to target the pathophysiology of incontinence. This approach relies on principles of motor learning and exercise physiology, in a manner that is tailored to the individual patient. The aims of this review are to consider new understanding of continence control in men, the mechanisms for incontinence after radical prostatectomy, and to review the characteristics of a pelvic floor muscle training program designed to specifically target recovery of continence after prostatectomy. [ABSTRACT FROM AUTHOR]

The troponin complex regulates the Ca2+ activation of myofilaments during striated muscle contraction and relaxation. Troponin genes emerged 500-700 million years ago during early animal evolution. Troponin T (TnT) is the thin-filament-anchoring subunit of troponin. Vertebrate and invertebrate TnTs have conserved core structures, reflecting conserved functions in regulating muscle contraction, and they also contain significantly diverged structures, reflecting muscle type- and species-specific adaptations. TnT in insects contains a highly-diverged structure consisting of a long glutamic acid-rich C-terminal extension of ~70 residues with unknown function. We found here that C-terminally truncated Drosophila TnT (TpnT-CD70) retains binding of tropomyosin, troponin I, and troponin C, indicating a preserved core structure of TnT. However, the mutant TpnTCD70 gene residing on the X chromosome resulted in lethality in male flies. We demonstrate that this X-linked mutation produces dominant-negative phenotypes, including decreased flying and climbing abilities, in heterozygous female flies. Immunoblot quantification with a TpnT-specific mAb indicated expression of TpnT-CD70 in vivo and normal stoichiometry of total TnT in myofilaments of heterozygous female flies. Light and EM examinations revealed primarily normal sarcomere structures in female heterozygous animals, whereas Z-band streaming could be observed in the jump muscle of these flies. Although TpnT-CD70-expressing flies exhibited lower resistance to cardiac stress, their hearts were significantly more tolerant to Ca2+ overloading induced by high-frequency electrical pacing. Our findings suggest that the Glu-rich long C-terminal extension of insect TnT functions as a myofilament Ca2+ buffer/reservoir and is potentially critical to the high-frequency asynchronous contraction of flight muscles. [ABSTRACT FROM AUTHOR]

• External urethral sphincter-related (EUS-R) spinal neurons were labeled by transneuronal virus tracing. • One group of EUS-R neurons was identified in the L3-L4 spinal segments near the central canal. • Properties of L3-L4 EUS-R neurons were studied in spinal slices with patch clamp and intracellular filling methods. • EUS-R propriospinal neurons projecting into the ventral funiculus and interneurons were identified. • L3-L4 EUS-R neurons are thought to have a role in coordinating bladder and EUS function during voiding. Coordination of activity of external urethral sphincter (EUS) striated muscle and bladder (BL) smooth muscle is essential for efficient voiding. In this study we examined the morphological and electrophysiological properties of neurons in the L3/L4 spinal cord (SC) that are likely to have an important role in EUS-BL coordination in rats. EUS-related SC neurons were identified by retrograde transsynaptic tracing following injection of pseudorabies virus (PRV) co-expressing fluorescent markers into the EUS of P18-P20 male rats. Tracing revealed not only EUS motoneurons in L6/S1 but also interneurons in lamina X of the L6/S1 and L3/L4 SC. Physiological properties of fluorescently labeled neurons were assessed during whole-cell recordings in SC slices followed by reconstruction of biocytin-filled neurons. Reconstructions of neuronal processes from transverse or longitudinal slices showed that some L3/L4 neurons have axons projecting toward and into the ventro-medial funiculus (VMf) where axons extended caudally. Other neurons had axons projecting within laminae X and VII. Dendrites of L3/L4 neurons were distributed within laminae X and VII. The majority of L3/L4 neurons exhibited tonic firing in response to depolarizing currents. In transverse slices focal electrical stimulation (FES) in the VMf or in laminae X and VII elicited antidromic axonal spikes and/or excitatory synaptic responses in L3/L4 neurons; while in longitudinal slices FES elicited excitatory synaptic inputs from sites up to 400 μm along the central canal. Inhibitory inputs were rarely observed. These data suggest that L3/L4 EUS-related circuitry consists of at least two neuronal populations: segmental interneurons and propriospinal neurons projecting to L6/S1. [ABSTRACT FROM AUTHOR]

Hyperinsulinemia is the key feature of equine metabolic syndrome (EMS) which leads to debilitating sequelae. Hyperinsulinemia-associated laminitis (HAL) is one of the major sequelae of EMS, although the pathophysiological mechanisms are not well elucidated. Using an equine model, we hypothesized that expression of inflammatory markers would be increased in digital lamellae and striated muscle following prolonged hyperinsulinemia. Healthy Standardbred horses (5.4 ± 1.9 years) were alternately assigned to a prolonged euglycemic-hyperinsulinemic clamp (pEHC) or control group (n = 4 per group). Following a 48 h pEHC or a 48 h infusion of a balanced electrolyte solution (controls), biopsies were collected from digital lamellar tissue, skeletal muscle and cardiac muscle were obtained. All hyperinsulinemic horses developed laminitis regardless of previous health status at enrollment. Protein expression was quantified via Western blotting. A significant (P < 0.05) upregulation of the protein expression of heat shock protein 90 (HSP90), alpha 2 macroglobulin (A2M) and fibrinogen (α, β isoforms), as well as inflammatory cytokines including interleukin-1β were detected in digital lamellae following prolonged hyperinsulinemia. In contrast, protein expression of cytokines and acute phase proteins in heart and skeletal muscle was unchanged following hyperinsulinemia. Upregulation of inflammatory cytokines and acute phase proteins in digital lamellae during prolonged hyperinsulinemia may reveal potential biomarkers and novel therapeutic targets for equine endocrinopathic laminitis. Further, the lack of increase of inflammatory proteins and acute phase proteins in striated muscle following prolonged hyperinsulinemia may highlight potential anti-inflammatory and cardioprotective mechanisms in these insulin-sensitive tissues. • An equine hyperinsulinemia model was used to study tissue responses. • Acute phase proteins (APP) and cytokines were evaluated. • Increased APP and cytokine concentrations were found in digital lamellae. • Unchanged cytokine levels were found in skeletal muscle. • Cardiac muscle similarly showed a lack of inflammatory changes. [ABSTRACT FROM AUTHOR]

Aberrant regulation of myocardial force production represents an early biomechanical defect associated with sarcomeric cardiomyopathies, but the molecular mechanisms remain poorly defined. Here, we evaluated the pathogenicity of a previously unreported sarcomeric gene variant identified in a pediatric patient with sporadic dilated cardiomyopathy, and we determined a molecular mechanism. Trio whole-exome sequencing revealed a de novo missense variant in TNNC1 that encodes a p.I4M substitution in the N-terminal helix of cardiac troponinC (cTnC). Reconstitution of this human cTnC variant into permeabilized porcine cardiac muscle preparations significantly decreases the magnitude and rate of isometric force generation at physiological Ca2+-activation levels. Computational modeling suggests that this inhibitory effect can be explained by a decrease in the rates of cross-bridge attachment and detachment. For the first time, we show that cardiac troponin T (cTnT), in part through its intrinsically disordered C terminus, directly binds to WT cTnC, and we find that this cardiomyopathic variant displays tighter binding to cTnT. Steady-state fluorescence and NMR spectroscopy studies suggest that this variant propagates perturbations in cTnC structural dynamics to distal regions of the molecule. We propose that the intrinsically disordered C terminus of cTnT directly interacts with the regulatory N-domain of cTnC to allosterically modulate Ca2+ activation of force, perhaps by controlling the troponin I switching mechanism of striated muscle contraction. Alterations in cTnC-cTnT binding may compromise contractile performance and trigger pathological remodeling of the myocardium. [ABSTRACT FROM AUTHOR]

Striated muscle is activated by myosin- and actin-linked processes, with the latter being regulated through changes in the position of tropomyosin relative to the actin surface. The C-terminal region of cardiac troponin T (TnT), a tropomyosin-associated protein, is required for full TnT inactivation at low Ca2+ and for limiting its activation at saturating Ca2+. Here, we investigated whether basic residues in this TnT region are involved in these activities, whether the TnT C terminus undergoes Ca2+- dependent conformational changes, and whether these residues affect cardiac muscle contraction. We generated a human cardiac TnT variant in which we replaced seven C-terminal Lys and Arg residues with Ala and added a Cys residue at either position 289 or 275 to affix a fluorescent probe. At pCa 3.7, actin filaments containing high-alanine TnT had an elevated ATPase rate like that obtained when the last TnT 14 residues were deleted. Acrylodan-tropomyosin fluorescence changes and S1-actin binding kinetics revealed that at pCa 8, the high-alanine TnT-containing filaments did not enter the first inactive state. FRET analyses indicated that the C-terminal TnT region approached Cys-190 of tropomyosin as actin filaments transitioned to the inactive B state; that transition was abolished with high-alanine TnT. High-alanine TnT-containing cardiac muscle preparations had increased Ca2+ sensitivity of both steadystate isometric force and sinusoidal stiffness as well as increased maximum steady-state isometric force and sinusoidal stiffness. We conclude that C-terminal basic residues in cardiac TnT are critical for the regulation of cardiac muscle contraction. [ABSTRACT FROM AUTHOR]

• Late-onset Pompe disease is caused by multi-organ glycogen deposition. • We report four LOPD patients having a polyneuropathy of undetermined etiology. • Polyneuropathy could be an additional morbid condition in LOPD patients. • Polyneuropathy in LOPD patients needs specific additional care. Late-onset Pompe disease is caused by a glycogen deposition involving mainly striated muscle. It may also target many other tissues such as liver, smooth muscles or spine anterior horn. Glycogen accumulation in Schwann cells and in the perineurium of peripheral nerves was shown in Pompe's disease mouse models. Moreover two late-onset Pompe disease patients were reported as having a small fiber neuropathy. To the best of our knowledge an involvement of large nerve fibers was never depicted. We describe four late-onset Pompe disease patients having a concomitant polyneuropathy of undetermined etiology. Our observations reinforce the proof-of-concept supporting a potential involvement of peripheral nerves as additional organ targeted by late-onset Pompe disease. It has clinical care consequences since peripheral neuropathy in late-onset Pompe disease could worsen patient's disability and needs particular care such as proprioceptive physiotherapy. [ABSTRACT FROM AUTHOR]

• A novel flat sheet preparation of mouse abdominal muscles has been developed to study muscle afferents ex vivo. • Extracellular recordings identified a distinctive class of Group III muscle afferents (referred to as "CT3 muscle afferents"). • CT3 muscle afferents combined characteristics mechanosensitivity and metabosensitivity. • Biotinamide tracing showed that CT3 afferents had specialised branching endings in connective tissue between muscle layers. • CT3 afferents lacked CGRP immunoreactivity and capsaicin sensitivity. Group III/IV striated muscle afferents are small diameter sensory neurons that play important roles in reflexes and sensation. To date, the morphological features of physiologically characterised group III/IV muscular afferents have not been identified. Here, the electrophysiological and morphological characteristics of sensory neurons innervating striated muscles of the mouse abdominal wall were investigated, ex vivo. Extracellular recordings were made from subcostal nerve trunks innervating the muscles. A distinctive class of mechanosensitive afferents was identified by a combination of physiological features including sensitivity to local compression, saturating response to graded stretch and, in most cases, absence of spontaneous firing. Studies were restricted to these distinctive units. These units had conduction velocities averaging 14 ± 4 m/s (range: 8–20 m/s, n = 7); within the range of group III fibres in mice. Von Frey hairs were used to map receptive fields, which covered an area of 0.36 ± 0.18 mm2 (n = 7). In 7 preparations, biotinamide filling of recorded nerve trunks revealed a single axon in the marked receptive field, with distinctive axonal branching and terminations meandering through the connective tissue sandwiched between two closely associated muscle layers. These axons were not immunoreactive for CGRP (n = 7) and were not activated by application of capsaicin (1 µM, n = 14). All of these afferents were strongly activated by a "metabolite mix" containing lactate, adenosine triphosphate and reduced pH. Responses to mechanical stimuli and to metabolites were additive. We have characterised a distinctive class of mechano- and chemo-sensitive group III afferent endings associated with connective tissue close to muscle fibres. [ABSTRACT FROM AUTHOR]

Striated muscle myosins are encoded by a large gene family in all mammals, including humans. These isoforms define several of the key characteristics of the different striated muscle fiber types, including maximum shortening velocity. We have previously used recombinant isoforms of the motor domains of seven different human myosin isoforms to define the actin·myosin cross-bridge cycle in solution. Here, we present data on an eighth isoform, the perinatal, which has not previously been characterized. The perinatal is distinct from the embryonic isoform, appearing to have features in common with the adult fast-muscle isoforms, including weak affinity of ADP for actin·myosin and fast ADP release. We go on to use a recently developed modeling approach, MUSICO, to explore how well the experimentally defined cross-bridge cycles for each isoform in solution can predict the characteristics of muscle fiber contraction, including duty ratio, shortening velocity, ATP economy, and load dependence of these parameters. The work shows that the parameters of the cross-bridge cycle predict many of the major characteristics of each muscle fiber type and raises the question of what sequence changes are responsible for these characteristics. [ABSTRACT FROM AUTHOR]

For long-lived contractile cells, such as striated muscle cells, maintaining proteome integrity is a challenging task. These cells require hundreds of components that must be properly synthesized, folded, and incorporated into the basic contractile unit, the sarcomere. Muscle protein quality control in cells is mainly guaranteed by the ubiquitin-proteasome system (UPS), the lysosome-autophagy system, and various molecular chaperones. Recent studies establish the concept of dedicated UPS in the regulation of sarcomere assembly during development and in adult life to maintain the intricate and interwoven organization of protein complexes in muscle. Failure of sarcomere protein quality control often represents the basis of severe myopathies and cardiomyopathies in human, further highlighting its importance in producing and maintaining the contractile machinery of muscle cells in shape. A protein quality control (PQC) network ensures the maintenance and adaptation of the contractile unit, the sarcomere, in response to physiological stimuli and under stress conditions. The ubiquitin-proteasome system (UPS) is the main player in the PQC network and controls specific sarcomere element degradation, supporting the concept of specialized and dedicated protein turnover machinery. As with other UPS components, ubiquitin ligases act in a highly selective and timely controlled way to ensure the building, maintenance, and adaptation of sarcomeres at all stages of muscle lifespan. The interplay between PQC actors (UPS, chaperones, and autophagy) supports a fine-tuning regulation of the sarcomere quality control. The development of proteasome inhibitors and the discovery of small molecules targeting the UPS pave the way for future innovative therapy in striated muscle diseases. [ABSTRACT FROM AUTHOR]

Ingestion of large quantities of Geigeria species by sheep causes "vermeersiekte", an economically important poisoning in southern Africa. The toxic principles are several sesquiterpene lactones, such as vermeerin, geigerin and ivalin. These sesquitepene lactones are myotoxic and the disease is characterized by microscopic and ultrastructural lesions in skeletal and cardiac muscle. Murine myoblast cells (C2C12) were exposed to 2.0, 2.5 and 5.0 mM geigerin for 24, 48 and 72 h to evaluate its effect on cytoskeletal proteins and filaments using immunocytochemistry and immunofluorescence staining. A concentration-dependent cytotoxic response was observed in desmin-expressing murine myoblasts under the light microscope, evidenced by disorganization and dot-like perinuclear aggregation of desmin filaments in the cells. β-Tubulin, other desmin-associated proteins (αB-crystallin and synemin) as well as the microfilament F-actin were unaffected. The disorganization and aggregation of desmin following exposure to increasing geigerin concentrations is significant and can explain some of the striated muscle lesions observed in "vermeersiekte". • Geigerin induced disorganization of the cytoskeletal intermediate filament desmin in a murine myoblast cell line. • Perinuclear aggregation of desmin filaments in the myoblasts. • Synemin, another intermediate filament, was not affected. • αB-crystallin, β-tubulin and F-actin were also not affected. • Explains some of the striated muscle lesions observed in "vermeersiekte" (vomiting disease). [ABSTRACT FROM AUTHOR]

The roles of intrinsic neurons and the significance of the coinnervated striated muscles in the esophagus are unclear. We examined the number distribution of intrinsic neurons and coinnervated motor endplates on the striated muscles in the rat esophagus using immunohistochemistry to investigate whether these neurons and coinnervated striated muscles may be relevant to the local control of esophageal motility. The number of PGP9.5-positive neurons was higher in the cervical esophagus (segment 1) and gradually decreased toward the aboral, with a moderate increase in the abdominal (segment 5). This pattern was similar to that of NOS-positive neurons, while the number of ChAT-positive neurons decreased toward the aboral, but it was not significantly different among segments 3 to 5. The number of ChAT-positive motor endplates increased toward the aboral, with the highest number in segment 5. The proportion of coinnervated motor endplates was approximately 80% in segments 1 to 4, but approximately 66% in segment 5. NPY-IR was localized in some nerve terminals among the smooth muscles of the muscularis mucosa and some NOS- or ChAT-positive esophageal intrinsic neurons. ENK-8-IR was found in some NOS- or ChAT-positive intrinsic neurons, and nerve terminals surrounding intrinsic neurons in the esophagus, but not in motor neurons at the NA or DMV. This study suggests that regional variations in the number of intrinsic neurons and coinnervated striated muscles in the rat esophagus may be involved in local regulations of esophageal motility, and that the rat esophageal intrinsic neurons may contain, at least, motor neurons and interneurons. [ABSTRACT FROM AUTHOR]