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Objective: Cell aging is one of the most important and fundamental step in cellular behavior and reduces muscle mass and myofibrils. This study aims to investigate the effect of resistance exercise along with vitamin C consumption on the expression of Telomerase Reverse Transcriptase (TERT) and Telomere Repeat Binding Factor-2 (TRF2) genes and the diameter and number of skeletal muscle myofibrils in old male Wistar rats. Methods: This is an experimental study using control groups. Twenty-five male Wistar rats (280-320 g and aged 24 weeks) were randomly divided into five groups of young control, old+resistance exercise, old+vitamin intake, old+resistance exercise+vitamin intake, and old control. In the supplementation groups, rats received liposomal vitamin C daily by gavage per body weight. Weight attached to the tail gradually increased during 8 weeks of exercise (weeks 1 and 2 by 50%; weeks 3 and 4 by 50%; weeks 5 and 6 by 75%; weeks 7 and 8 by 100% of total body weight). Exercises were performed at 3-5 sets of 8-12 repetitions, 3 or 4 days a week. The Quantitative polymerase chain reaction method was used to evaluate the expression of TERT and TRF2 genes in muscle tissue. One-way ANOVA was used to examine the difference between the groups and Tukey’s post hoc test was used to determine between which groups the difference was significant. Results: Aging significantly reduced the expression of TERT, TRF2 genes and the diameter and number of myofibrils in skeletal muscle of rats (P=0.001). Resistance exercise along with vitamin C intake had no significant effect on TERT and TRF2 expression (P≥0.05), but caused a significant increase in the diameter and number of myofibrils (P= 0.001). Conclusion: Eight weeks of resistance exercise along with vitamin C supplementation can significantly increase the number and diameter of skeletal muscle myofibrils in old rats.

The effects of xanthan gum (0 % and 0.3 %) on the quality of low sodium (2.0 %, 2.4 %, 2.8 %, 3.2 %, 3.6 % and 4.0 %) salted beef and property of myofibril proteins (MP) extracted from salted beef were researched. Changes in the salting absorptivity, cooking loss, shear force, color and sensory analysis showed that xanthan gum had a positive effect on the quality of salted beef with low salinity (2.0 %, 2.4 % and 2.8 %). MP of salted beef treated with xanthan gum had higher solubility, lower hydrogen bond than that without it (P < 0.05). The decrease of surface hydrophobicity and intrinsic fluorescence intensity indicated that the chromophore of protein was brought into a hydrophobic environment in the presence of xanthan gum. The electrophoresis showed that xanthan gum could improve the concentration of myosin heavy chain, paramyosin and actin after tumble-salting. The data suggested that salted beef and its MP treated with xanthan gum and 2.8 % salt (XS3) had the best properties. Together, xanthan gum could be considered as a sodium salt substitute for the development of low sodium meat products.

Phosphorylation post-translational modification plays an important role in postmortem muscle quality traits. Adenosine triphosphate (ATP) is an energy source and a key substrate of phosphorylation which provides the phosphatase groups to proteins in the presence of protein kinases. However, in postmortem muscle, the effects of ATP content on phosphorylation are poorly studied. The study investigated the effect of ATP on protein phosphorylation and degradation in postmortem ovine muscle. The ground muscle with/without additional ATP were treated/control groups and stored at 25 and 4°C, respectively. The ATP content led to different changes of pH value between the ATP-treated and control groups. The phosphorylation level of myofibrillar proteins was higher (P

When handling meat, processing it with low temperatures is widely used - cooling and freezing. Processing meat with subzero temperatures leads to the formation of microscopic ice crystals inside muscle cells and in the intercellular space, which disrupts the structure of muscle tissue and destroys individual myofibrils. As a result of single and double defrosting of turkey meat, morphological changes in the structure of muscle tissue are observed. The integrity of muscle fibers is impaired; in histological preparations of meat, their ruptures, vacuolization, and thickening of myofibrils are found. As a result of histological studies of parts of turkey carcasses, it was found that the number of thickening of myofibrils in defrosted products is 4.79 ± 0.14, which is 1.86 times more than in chilled meat; in re-defrosted meat - 12.23 ± 0.51, 4.74 times more than in chilled meat. The number of voids inside and between muscle fibers in defrosted turkey meat is 3.03 ± 0.17, 2.66 times higher than the value in chilled, and 8.71 ± 0.38, 7.64 times more in redefrosted meat ... The number of muscle fiber breaks in defrosted meat was 37.44 ± 1.07, which exceeds this value for chilled products by 13.66 times; redefrosted - 57.69 ± 1.62, which is 21.05 times higher than in chilled products. The obtained values are statistically significant - p

Typical skeletal muscles are composed of mixed muscle fiber types, which are classified as slow-twitch (type I) and fast-twitch (type II) fibers, whereas pectoralis major muscles (PMs) in broiler chickens are 100% composed of type IIb fast-twitch fibers. Since metabolic properties differ among muscle fiber types, the combination of muscle fiber types is involved in physiological functions and pathological conditions in skeletal muscles. In this study, using serial block-face scanning electron microscopy, we compared three-dimensional (3D) mitochondrial properties in type IIb fibers in broiler PMs and those in type I fibers of broiler gastrocnemius muscles (GMs) heterogeneously composed of slow- and fast-twitch muscle fibers. In type I fibers in the GMs, elongated mitochondria with numerous interconnections to form a substantial network among myofibrils were observed. Along with lipid droplets sandwiched by mitochondria, these features are an adaptation to effective oxidative respiration and constant oxidative damage in slow-twitch muscle fibers. In contrast, type IIb fibers in the PMs showed small and ellipsoid-shaped mitochondria with few interconnections and no lipid droplets, forming a sparse network. The mitochondrial spatial network comprises of active mitochondrial dynamics to reduce mitochondrial damage; therefore, type IIb fibers possess physiologically low capacity to maintain mitochondrial wellness due to static mitochondrial dynamics. Based on 3D mitochondrial properties, we discussed the contrasting physiological functions between type I and IIb fibers and proposed a high contractile power and low stress resistance as unique physiological properties of broiler PMs.

Microbial load, protein oxidation, myofibrillar protein changes and quality characteristics (meat color and water retentiveness including centrifugal loss (CeL) and water-holding capacity (WHC)) of post-rigor tan mutton exposed to different high-pressure treatments (200 MPa/500 MPa for 15 min at 18°C) during chilled storage for 7 days (4°C) were evaluated. High-pressure applications of 200 MPa and 500 MPa significantly reduced the number of Total Viable Counts (TVC) during storage (P 0.05) and better texture characteristics than untreated samples. ANOVA with Partial Least Squares Regression (APLSR) confirmed the relationshipS between these variations in quality characteristics induced by high-pressure treatments and protein oxidation and key myofibrillar skeleton proteins.

Collagen is the central structural component of extracellular connective tissue, which provides elastic qualities to tissues. For skeletal muscle, extracellular connective tissue transmits contractile force to the tendons and bones. Connective tissue proteins are in a constant state of remodeling and have been shown to express a high level of plasticity. Dietary-protein ingestion increases muscle protein synthesis rates. High-quality, rapidly digestible proteins are generally considered the preferred protein source to maximally stimulate myofibrillar (contractile) protein synthesis rates. In contrast, recent evidence demonstrates that protein ingestion does not increase muscle connective tissue protein synthesis. The absence of an increase in muscle connective tissue protein synthesis after protein ingestion may be explained by insufficient provision of glycine and/or proline. Dietary collagen contains large amounts of glycine and proline and, therefore, has been proposed to provide the precursors required to facilitate connective tissue protein synthesis. This literature review provides a comprehensive evaluation of the current knowledge on the proposed benefits of dietary collagen consumption to stimulate connective tissue remodeling to improve health and functional performance.

The objective of this study was to reveal the effects of boiling processing on the texture of scallop adductor muscle (SAM) and its mechanism. Compared to the fresh sample, all the texture indicators, including the hardness, chewiness, springiness, resilience, cohesiveness, and shear force of 30-s- and 3-min-boiled SAMs increased time-dependently (p < 0.05). As the boiling time increased further to 15 min, the shear force and cohesiveness still increased significantly (p < 0.05), and the resilience and hardness were maintained (p > 0.05), but the springiness and chewiness decreased significantly (p < 0.05). The overall increase in the texture indicators of the boiled SAMs was due to the boiling-induced protein denaturation, aggregation, and increased hydrophobicity, resulting in the longitudinal contraction and lateral expansion of myofibrils, the longitudinal contraction and lateral cross-linked aggregation of muscle fibers, and the loss of free water. However, the decreasing springiness and chewiness of the 15-min-boiled SAMs was due to the significant degradation of proteins (especially collagen), resulting in the destruction of the connective tissue between the muscle fiber clusters. Both from a subjective sensory point of view and from the objective point of view of protein denaturation and degradation, 3-min-boiled SAMs are recommended. The quality improvement of thermally processed products by controlled, moderate cooking is of practical value from the perspective of food consumption.

Background Poor recovery from periods of disuse accelerates age‐related muscle loss, predisposing individuals to the development of secondary adverse health outcomes. Exercise prior to disuse (prehabilitation) may prevent muscle deterioration during subsequent unloading. The present study aimed to investigate the effect of short‐term resistance exercise training (RET) prehabilitation on muscle morphology and regulatory mechanisms during 5 days of bed rest in older men. Methods Ten healthy older men aged 65–80 years underwent four bouts of high‐volume unilateral leg RET over 7 days prior to 5 days of inpatient bed rest. Physical activity and step‐count were monitored over the course of RET prehabilitation and bed rest, whilst dietary intake was recorded throughout. Prior to and following bed rest, quadriceps cross‐sectional area (CSA), and hormone/lipid profiles were determined. Serial muscle biopsies and dual‐stable isotope tracers were used to determine integrated myofibrillar protein synthesis (iMyoPS) over RET prehabilitation and bed rest phases, and acute postabsorptive and postprandial myofibrillar protein synthesis (aMyoPS) rates at the end of bed rest. Results During bed rest, daily step‐count and light and moderate physical activity time decreased, whilst sedentary time increased when compared with habitual levels (P

Striated preferentially expressed gene (SPEG), a member of the myosin light chain kinase family, is localized at the level of triad surrounding myofibrils in skeletal muscles. In humans, SPEG mutations are associated with centronuclear myopathy and cardiomyopathy. Using a striated muscle-specific Speg-knockout (KO) mouse model, we have previously shown that SPEG is critical for triad maintenance and calcium handling. Here, we further examined the molecular function of SPEG and characterized the effects of SPEG deficiency on triad and focal adhesion proteins. We used yeast two-hybrid assay, and identified desmin, an intermediate filament protein, to interact with SPEG and confirmed this interaction by co-immunoprecipitation. Using domain-mapping assay, we defined that Ig-like and fibronectin III domains of SPEG interact with rod domain of desmin. In skeletal muscles, SPEG depletion leads to desmin aggregates in vivo and a shift in desmin equilibrium from soluble to insoluble fraction. We also profiled the expression and localization of triadic proteins in Speg-KO mice using western blot and immunofluorescence. The amount of RyR1 and triadin were markedly reduced, whereas DHPRα1, SERCA1 and triadin were abnormally accumulated in discrete areas of Speg-KO myofibers. In addition, Speg-KO muscles exhibited internalized vinculin and β1 integrin, both of which are critical components of the focal adhesion complex. Further, β1 integrin was abnormally accumulated in early endosomes of Speg-KO myofibers. These results demonstrate that SPEG-deficient skeletal muscles exhibit several pathological features similar to those seen in MTM1 deficiency. Defects of shared cellular pathways may underlie these structural and functional abnormalities in both types of diseases.

The problem of iodine deficiency is becoming increasingly important in Ukraine. According to the United Nations Children’s Fund (UNICEF), each and all regions of Ukraine suffer from “hidden hunger”. The World Health Assembly has stated that the elimination of iodine deficiency will be as much a triumph for health care system as the eradication of smallpox and poliomyelitis. The goal of this study was to establish the peculiarities of structural organization of the masticatory muscles of rats in experimentally induced iodine deficiency. The research material involved masticatory muscle of 36 white outbred male rats, which were divided into groups: group І – intact animals; group ІІ – kept in iodine deficiency condition; group III – exposed to iodine deficiency with the addition of goitriferous food. All manipulations with test animals were performed in agreement with the regulations on the protection of vertebrate animals. The methods used in the study included: biochemical, histological, histochemical, submicroscopic, morphometric and statistical research methods. It has been established that under the conditions of iodine deficiency the lumen of arterial vessels in masticatory muscles becomes narrowed, the vascular vessels become thickened due to membrane oedema. The number of hemocapillaries per unit area of muscle fibre goes down in all the studied muscles. The number of muscle fibres with intermediate succinate dehydrogenase activity decreases with the simultaneous increase in muscle fibres with low succinate dehydrogenase activity. Furthermore, the oedematous changes are the most prominent in muscle fibres with low succinate dehydrogenase activity. In conditions of iodine deficiency with the addition of goitriferous products, we can observe the progression of luminal narrowing of the artery and wall thickening in masticatory muscles where oedematous-dystrophic changes are considerably marked. There is a tendency in the growth in haemocapillaries number per 1 μm2. Histostructurally, the loss of cross striation is quite noticeable. The cross-section diameter increases, especially in muscle fibres with low succinate dehydrogenase activity and muscle fibres with high succinate dehydrogenase activity in the masticatory muscle proper of immature animals. Ultrastructurally, the oedematous-dystrophic changes of myofibrils and mitochondria were revealed. Thus, under the conditions of iodine deficient diet the lumen of arterial vessels narrows in the masticatory muscles, their wall thickens due to oedema of the membranes, which progresses in iodine deficient diet with the addition of goitriferous products. The number of hemocapillaries per unit area of muscle fibre decreases in both study groups. Changes in vascular bed lead to the redistribution of the number of muscle fibres and their significant oedema.

The expression of some structural and regulatory muscle protein genes as well as the activity of the main intracellular proteases (calpains, proteasomes) in caged rainbow trout in the periods favorable for growth and under hyperthermia were estimated. Intense growth of fish was accompanied by high transcriptional activity of the myosin heavy chain (MyHC) gene with the constraining influence of myostatin, high protein turnover rate, and stable levels of myogenic factors, MyoG and MyoD1b. Trout growth retardation in response to summer increase in water temperature was associated with a decrease in gene expression of the main protein of myofibrils, myosin. In hyperthermia, proteolytic activity of calpains and proteasomes, which determine the level of protein degradation in muscle and thereby regulate the intensity of protein accumulation and overall growth, also decreased. Thus, changes in the intensity of myofibrillar protein synthesis, myogenesis, and protein degradation in rainbow trout during periods favorable for growth and under hyperthermia occur in a coordinated manner indicating a relationship of these processes.

Aims Dilated cardiomyopathy (DCM) is associated with mutations in many genes encoding sarcomere proteins. Truncating mutations in the titin gene TTN are the most frequent. Proteomic and functional characterizations are required to elucidate the origin of the disease and the pathogenic mechanisms of TTN-truncating variants. Methods and results We isolated myofibrils from DCM hearts carrying truncating TTN mutations and measured the Ca2+ sensitivity of force and its length dependence. Simultaneous measurement of force and adenosine triphosphate (ATP) consumption in skinned cardiomyocytes was also performed. Phosphorylation levels of troponin I (TnI) and myosin binding protein-C (MyBP-C) were manipulated using protein kinase A and λ phosphatase. mRNA sequencing was employed to overview gene expression profiles. We found that Ca2+ sensitivity of myofibrils carrying TTN mutations was significantly higher than in myofibrils from donor hearts. The length dependence of the Ca2+ sensitivity was absent in DCM myofibrils with TTN-truncating variants. No significant difference was found in the expression level of TTN mRNA between the DCM and donor groups. TTN exon usage and splicing were also similar. However, we identified down-regulation of genes encoding Z-disk proteins, while the atrial-specific regulatory myosin light chain gene, MYL7, was up-regulated in DCM patients with TTN-truncating variants. Conclusion Titin-truncating mutations lead to decreased length-dependent activation and increased elasticity of myofibrils. Phosphorylation levels of TnI and MyBP-C seen in the left ventricles are essential for the length-dependent changes in Ca2+ sensitivity in healthy donors, but they are reduced in DCM patients with TTN-truncating variants. A decrease in expression of Z-disk proteins may explain the observed decrease in myofibril passive stiffness and length-dependent activation., Graphical Abstract

In this study, different ultrasound frequencies, including 20 kHz, 23 kHz, and 20/23 kHz, were applied for the treatment of myofibrillar protein (MP) with different protein concentrations (20, 40, and 60 mg/mL). The structures and emulsifying properties of the treated and untreated MPs were compared. The MP structural changes were confirmed based on the active sulfhydryl content (ASC), surface hydrophobicity (SUH), particle size, and turbidity, and the degree of change decreased in the order of 20/23 kHz > 20 kHz ≈ 23 kHz > control (CON). Moreover, the MP emulsifying properties, determined based on the emulsifying activity index (EAI), emulsion stability index (ESI), and creaming stability, were in accordance with the structural changes. Notably, frequency superposition provided more external force through the resonance of cavitation bubbles to induce stronger stress response of myosin in MP, thereby promoting the change of protein structure and emulsifying properties. Results implied that MPs treated with different ultrasound frequencies, especially the superposition of two frequencies, have the potential for wide applications in emulsified-type meat products.

The study investigated the effects of three active components in Eucommia ulmoides on growth, flesh quality and muscle transcriptomics of grass carp (Ctenopharyngodon idella). Quercetin (QC), chlorogenic acid (CGA) and geniposide (GP) were individually supplemented into basal diet (control) at 400 mg/kg, and then, the four diets were fed to grass carp (18.50 ± 0.40 g) for 60 days. The results indicated that dietary CGA rather than QC and GP significantly improved growth performance. Compared to the control, dietary QC decreased the flesh centrifugal loss and thawing loss, and increased hardness and free amino acid level (p

De novo assembly of myofibrils in vertebrate cross-striated muscles progresses in three distinct steps, first from a minisarcomeric alignment of several nonmuscle and muscle proteins in premyofibrils, followed by insertions of additional proteins and increased organization in nascent myofibrils, ending with mature contractile myofibrils. In a search for controls of the process of myofibril assembly, we discovered that the transition from nascent to mature myofibrils could be halted by inhibitors of three distinct functions of the ubiquitin proteasome system (UPS). First, inhibition of pathway to E3 Cullin ligases that ubiquitinate proteins led to an arrest of myofibrillogenesis at the nascent myofibril stage. Second, inhibition of p97 protein extractions of ubiquitinated proteins led to a similar arrest of myofibrillogenesis at the nascent myofibril stage. Third, inhibitors of proteolytic action by proteasomes also blocked nascent myofibrils from transitioning to mature myofibrils. In contrast, inhibitors of autophagy or lysosomes did not affect myofibrillogenesis. To probe for differences in the effects of UPS inhibitors during myofibrillogenesis, we analyzed by fluorescence recovery after photobleaching the exchange rates of two selected sarcomeric proteins (muscle myosin II heavy chains and light chains). In the presence of p97 and proteasomal inhibitors, the dynamics of each of these two myosin proteins decreased in the nascent myofibril stage, but were unaffected in the mature myofibril stage. The increased stability of myofibrils occurring in the transition from nascent to mature myofibril assembly indicates the importance of dynamics and selective destruction in the muscle myosin II proteins for the remodeling of nascent to mature myofibrils.

Aim. — Unaccustomed physical exercise, particularly repeated eccentric muscle contractions,induces muscle soreness and alterations on muscle cellular structure. An increase in myofibrillarprotein accretion can occur in the early post-exercise period and be potentiated by essentialamino acid ingestion. We hypothesized that essential amino acid supplementation could reducethe efflux of indirect markers of muscle damage and delay the onset of muscular soreness inthe week following a heavy-load eccentric training session.Methods. — Twenty-three randomly assigned young males performed a bench press exerciseunder eccentric condition. They were subdivided into a placebo group (n = 11) and an essential amino acids group (n = 12). The effect of the training session was assessed by analysingtwo indirect markers of muscle damage, namely plasma concentrations of creatine kinase andmyoglobin measured before, immediately after, and post-workout day 1, 2, 3, 4 and 7. Musclesoreness was evaluated by a visual analogy scale at the same time point as the markers ofmuscle damage., info:eu-repo/semantics/published

The coordinated generation of mechanical forces by cardiac myocytes is required for proper heart function. Myofibrils are the functional contractile units of force production within individual cardiac myocytes. At the molecular level, myosin motors form cross-bridges with actin filaments and use ATP to convert chemical energy into mechanical forces. The energetic efficiency of the cross-bridge cycle is influenced by the viscous damping of myofibril contraction. The viscoelastic response of myofibrils is an emergent property of their individual mechanical components. Previous studies have implicated titin-actin interactions, cell-ECM adhesion, and microtubules as regulators of the viscoelastic response of myofibrils. Here we probed the viscoelastic response of myofibrils using laser-assisted dissection. As a proof-of-concept, we found actomyosin contractility was required to endow myofibrils with their viscoelastic response, with blebbistatin treatment resulting in decreased myofibril tension and viscous damping. Focal adhesion kinase (FAK) is a key regulator of cell-ECM adhesion, microtubule stability, and myofibril assembly. We found inhibition of FAK signaling altered the viscoelastic properties of myofibrils. Specifically, inhibition of FAK resulted in increased viscous damping of myofibril retraction following laser ablation. This damping was not associated with acute changes in the electrophysiological properties of cardiac myocytes. These results implicate FAK as a regulator of mechanical properties of myofibrils.

Background Congenital heart disease is one of the most common cardiac malformation-related diseases worldwide. Some causative genes have been identified but can explain only a small proportion of all cases; therefore, the discovery of novel susceptibility genes and/or modifier genes for abnormal cardiac development remains a major challenge. Methods We used a single nucleotide polymorphism (SNP) array, and next-generation sequencing (NGS) was conducted to screen and quickly identify candidate genes. KIAA0196 knockout zebrafish and mice were generated by CRISPR/Cas9 to detect whether or how KIAA0196 deficiency would influence cardiac development. Results Homozygous, but not heterozygous, zebrafish and mice showed early embryonic lethality. At the embryonic stage, microscopic examination and dissection revealed pericardial edema and ventricle enlargement in homozygous zebrafish and obviously delayed cardiac development in heterozygous mice, while echocardiography and tissue staining showed that significantly decreased cardiac function, ventricle enlargement, myofibril loss, and significantly reduced trabecular muscle density were observed in adult heterozygous zebrafish and mice. Most importantly, immunostaining and electron microscopy showed that there was a significant increase in sarcomere structural disorganization and myofibril structural integrity loss in KIAA0196 mutants. Furthermore, substantial downregulation in other sarcomeric genes and proteins was detected and verified in a mouse model via transcriptome and proteomics analyses; these changes especially affected the myosin heavy or light chain (MYH or MYL) family genes. Conclusion We identified KIAA0196 for the first time as a susceptibility gene for abnormal cardiac development. KIAA0196 deficiency may cause abnormal heart development by influencing the structural integrity of myofibrils.

The purpose of this study was to investigate the endogenous cathepsin activity in each subcellular fraction and the effect of this activity on myofibrillar protein and texture during refrigeration and partial freezing storage of northern pike (Esox lucius) fillets. The results showed that fillets stored under the refrigerated condition were more susceptible to oxidation than partial freezing. Endogenous cathepsin activity indicated that partial freezing destroys the integrity of lysosomes more effectively than refrigeration and inhibits the increase in cathepsin B and B + L in lysosomes. The activity of cathepsin B and B + L in lysosomes, mitochondria and myofibrils under the partial freezing conditions was always lower than that under refrigeration. Texture analysis showed that refrigeration had a negative impact on hardness and springiness. In conclusion, the cathepsin activity in each subcellular fraction was effectively inhibited and better textural characteristics were obtained with partial freezing than refrigeration. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10068-020-00781-z) contains supplementary material, which is available to authorized users.

In the last decades the term Store-operated Ca2+ entry (SOCE) has been used in the scientific literature to describe an ubiquitous cellular mechanism that allows recovery of calcium (Ca2+) from the extracellular space. SOCE is triggered by a reduction of Ca2+ content (i.e. depletion) in intracellular stores, i.e. endoplasmic or sarcoplasmic reticulum (ER and SR). In skeletal muscle the mechanism is primarily mediated by a physical interaction between stromal interaction molecule-1 (STIM1), a Ca2+ sensor located in the SR membrane, and ORAI1, a Ca2+-permeable channel of external membranes, located in transverse tubules (TTs), the invaginations of the plasma membrane (PM) deputed to propagation of action potentials. It is generally accepted that in skeletal muscle SOCE is important to limit muscle fatigue during repetitive stimulation. We recently discovered that exercise promotes the assembly of new intracellular junctions that contains colocalized STIM1 and ORAI1, and that the presence of these new junctions increases Ca2+ entry via ORAI1, while improving fatigue resistance during repetitive stimulation. Based on these findings we named these new junctions Ca2+ Entry Units (CEUs). CEUs are dynamic organelles that assemble during muscle activity and disassemble during recovery thanks to the plasticity of the SR (containing STIM1) and the elongation/retraction of TTs (bearing ORAI1). Interestingly, similar structures described as SR stacks were previously reported in different mouse models carrying mutations in proteins involved in Ca2+ handling (calsequestrin-null mice; triadin and junctin null mice, etc.) or associated to microtubules (MAP6 knockout mice). Mutations in Stim1 and Orai1 (and calsequestrin-1) genes have been associated to tubular aggregate myopathy (TAM), a muscular disease characterized by: (a) muscle pain, cramping, or weakness that begins in childhood and worsens over time, and (b) the presence of large accumulations of ordered SR tubes (tubular aggregates, TAs) that do not contain myofibrils, mitochondria, nor TTs. Interestingly, TAs are also present in fast twitch muscle fibers of ageing mice. Several important issues remain un-answered: (a) the molecular mechanisms and signals that trigger the remodeling of membranes and the functional activation of SOCE during exercise are unclear; and (b) how dysfunctional SOCE and/or mutations in Stim1, Orai1 and calsequestrin (Casq1) genes lead to the formation of tubular aggregates (TAs) in aging and disease deserve investigation.

Actin stress fibers (SFs), a contractile apparatus in nonmuscle cells, possess a contractile unit that is apparently similar to the sarcomere of myofibrils in muscles. The function of SFs has thus often been addressed based on well-characterized properties of muscles. However, unlike the fixed number of myosin molecules in myofibrils, the number of nonmuscle myosin II (NMII) within the contractile sarcomeric unit in SFs is quite low and variable for some reason. Here we address what factors may determine the specific number of NMII in SFs. We suggest with a theoretical model that the number lies just in between the function of SFs for bearing cellular tension under static conditions and for promptly disintegrating upon forced cell shortening. We monitored shortening-induced disintegration of SFs in human osteosarcoma U2OS cells expressing mutants of myosin regulatory light chain that virtually regulates the interaction of NMII with actin filaments, and the behaviors observed were indeed consistent with the theoretical consequences. This situation-specific nature of SFs may allow nonmuscle cells to respond adaptively to mechanical stress to circumvent activation of pro-inflammatory signals as previously indicated, i.e., a behavior distinct from that of muscles that are basically specialized for exhibiting contractile activity.

Objectives Cardiac damage in patient with diphtheritic myocarditis is reported as the leading cause of mortality. Diphtheria toxin (DTx) is a well-known bacterial toxin inducing various cytotoxic effects. Mainly, catalytic fragment inhibits protein synthesis, induces cytotoxicity, and depolymerizes actin filaments. In this study, we aimed to demonstrate the extent of myofibrillar damage under DTx treatment to porcine cardiac tissue samples. Methods Tissue samples were incubated with DTx for 1–3 h in culture conditions. To analyze whole toxin (both fragments) distribution, conjugation of DTx with FITC was performed. Measurements were carried out with fluorescence spectrophotometer before and after dialysis. Immunofluorescence microscopy was used to show localization of DTx-FITC (15 nM) on cardiac tissue incubated for 2 h. Ultrastructural characterization of cardiac tissue samples treated with DTx (15 or 150 nM) was performed with transmission electron microscopy. Results DTx exerts myofibrillar disorganization. Myofilament degeneration, mitochondrial damage, vacuolization, and abundant lipid droplets were determined with 150 nM of DTx treatment. Conclusions This finding is an addition to depolymerization of actin filaments as a result of the DTx-actin interactions in in vitro conditions, indicating that myofilament damage can occur with DTx directly besides protein synthesis inhibition. Ultrastructural results support the importance of filamentous actin degeneration at diphtheritic myocarditis.

Muscle contraction is regulated by the movement of end-to-end-linked troponin−tropomyosin complexes over the thin filament surface, which uncovers or blocks myosin binding sites along F-actin. The N-terminal half of troponin T (TnT), TNT1, independently promotes tropomyosin-based, steric inhibition of acto-myosin associations, in vitro. Recent structural models additionally suggest TNT1 may restrain the uniform, regulatory translocation of tropomyosin. Therefore, TnT potentially contributes to striated muscle relaxation; however, the in vivo functional relevance and molecular basis of this noncanonical role remain unclear. Impaired relaxation is a hallmark of hypertrophic and restrictive cardiomyopathies (HCM and RCM). Investigating the effects of cardiomyopathy-causing mutations could help clarify TNT1’s enigmatic inhibitory property. We tested the hypothesis that coupling of TNT1 with tropomyosin’s end-to-end overlap region helps anchor tropomyosin to an inhibitory position on F-actin, where it deters myosin binding at rest, and that, correspondingly, cross-bridge cycling is defectively suppressed under diastolic/low Ca(2+) conditions in the presence of HCM/RCM lesions. The impact of TNT1 mutations on Drosophila cardiac performance, rat myofibrillar and cardiomyocyte properties, and human TNT1’s propensity to inhibit myosin-driven, F-actin−tropomyosin motility were evaluated. Our data collectively demonstrate that removing conserved, charged residues in TNT1’s tropomyosin-binding domain impairs TnT’s contribution to inhibitory tropomyosin positioning and relaxation. Thus, TNT1 may modulate acto-myosin activity by optimizing F-actin−tropomyosin interfacial contacts and by binding to actin, which restrict tropomyosin’s movement to activating configurations. HCM/RCM mutations, therefore, highlight TNT1’s essential role in contractile regulation by diminishing its tropomyosin-anchoring effects, potentially serving as the initial trigger of pathology in our animal models and humans.

This study examined the effects on conformation and oxidation of myofibrillar protein in largemouth bass by different thawing methods. The conventional thawing, microwave thawing, microwave (MVT) or ultrasound combined with vacuum thawing, microwave or far-infrared thawing (FMT) combined with magnetic nanoparticles were used in this experiment. The physicochemical changes were analyzed by differential scanning calorimetry and dynamic rheology. The protein structure changes were measured by Raman, intrinsic fluorescence, and second-derivative ultraviolet spectrometry. The degree of protein aggregation was evaluated by surface hydrophobicity, particle size, and zeta-potential measurements. Total sulfhydryl content, protein carbonyl content, Ca2+ -ATPase activity, and SDS-PAGE were used to analyze the degree of protein oxidation. Results showed that MVT and FMT samples had better thermal stability, more stable protein conformation, and a lower degree of protein oxidation. Thus, these two methods would be beneficial to sustain the quality of thawed fillets. PRACTICAL APPLICATIONS: In the market circulation, largemouth bass (Micropterus salmoides) need to be frozen. The thawing methods can directly affect the quality of frozen fish, thus causing the changes in the conformation of the myofibrillar protein in fish, and also affecting the degree of protein oxidation. The results showed that the microwave combined with vacuum and the magnetic nanoparticles combined with far-infrared thawing had less effect on myofibrillar protein of fish and were a better thawing method.

In skeletal muscle fibers, mitochondria are densely packed adjacent to myofibrils because adenosine triphosphate (ATP) is needed to fuel sarcomere shortening. However, despite this close physical and biochemical relationship, the effects of mitochondrial dynamics on skeletal muscle contractility are poorly understood. In this study, we analyzed the effects of Mitochondrial Division Inhibitor 1 (mdivi-1), an inhibitor of mitochondrial fission, on the structure and function of both mitochondria and myofibrils in skeletal muscle tissues engineered on micromolded gelatin hydrogels. Treatment with mdivi-1 did not alter myotube morphology, but did increase the mitochondrial turbidity and oxidative capacity, consistent with reduced mitochondrial fission. Mdivi-1 also significantly increased basal, twitch, and tetanus stresses, as measured using the Muscular Thin Film (MTF) assay. Finally, mdivi-1 increased sarcomere length, potentially due to mdivi-1-induced changes in mitochondrial volume and compression of myofibrils. Together, these results suggest that mdivi-1 increases contractile stress generation, which may be caused by an increase in maximal respiration and/or sarcomere length due to increased volume of individual mitochondria. These data reinforce that mitochondria have both biochemical and biomechanical roles in skeletal muscle and that mitochondrial dynamics can be manipulated to alter muscle contractility.

Aims: Both left ventricular (LV) and left atrial (LA) dysfunction and remodelling contribute to adverse outcomes in heart failure with reduced ejection fraction (HFrEF). Danicamtiv is a novel, cardiac myosin activator that enhances cardiomyocyte contraction.Methods and results: We studied the effects of danicamtiv on LV and LA function in non-clinical studies (ex vivo: skinned muscle fibres and myofibrils; in vivo: dogs with heart failure) and in a randomized, double-blind, single- and multiple-dose phase 2a trial in patients with stable HFrEF (placebo, n = 10; danicamtiv, n = 30; 50–100 mg twice daily for 7 days). Danicamtiv increased ATPase activity and calcium sensitivity in LV and LA myofibrils/muscle fibres. In dogs with heart failure, danicamtiv improved LV stroke volume (+10.6 mL, P < 0.05) and LA emptying fraction (+10.7%, P < 0.05). In patients with HFrEF (mean age 60 years, 25% women, ischaemic heart disease 48%, mean LV ejection fraction 32%), treatment-emergent adverse events, mostly mild, were reported in 17 patients (57%) receiving danicamtiv and 4 patients (40%) receiving placebo. Danicamtiv (at plasma concentrations ≥2000 ng/mL) increased stroke volume (up to +7.8 mL, P < 0.01), improved global longitudinal (up to −1.0%, P < 0.05) and circumferential strain (up to −3.3%, P < 0.01), decreased LA minimal volume index (up to −2.4 mL/m2, P < 0.01) and increased LA function index (up to 6.1, P < 0.01), when compared with placebo.Conclusions: Danicamtiv was well tolerated and improved LV systolic function in patients with HFrEF. A marked improvement in LA volume and function was also observed in patients with HFrEF, consistent with pre-clinical findings of direct activation of LA contractility.

Low-load blood flow restricted resistance exercise (BFRRE) can stimulate whole-muscle growth and improve muscle function. However, limited knowledge exists on the effects at the myocellular level. We hypothesize that BFRRE has the ability to produce concurrent skeletal muscle myofibrillar, mitochondrial, and microvascular adaptations, thus offering an alternative strategy to counteract decay in skeletal muscle health and function in clinical populations.

Myofibril is contributing to gel-forming. Every species of fish have different myofibril concentration. Pacific codfish has white flesh which is expected to make surimi. The objective of this research was to analyze the characteristics of surimi prepared from Pacific codfish myofibril (SPM). The method of this research was used ionic strength by using NaCl. The observe parameters of this research were protein solubility, color, microstructure, molecular weight,and texture.the results showed that SPM have 3-dimensional network with rigid and porous structure than other surimi gels. The major molecular weights were 150 kDa (zetalin) and 40 kDa (tropomyosin). The hardness, cohesiveness and adhesiveness of SPM were 0.071338 N/cm2, 0.259 gf/sec and 116 gf.mm respectively. These results were shown that Pacific codfish was suitable to be used as surimi raw material because it can make a good gel to form surimi.

Postexercise protein ingestion can elevate rates of myofibrillar protein synthesis (MyoPS), mTORC1 activity, and mTOR translocation/protein-protein interactions. However, it is unclear if leucine-enriched essential amino acids (LEAA) can similarly facilitate intracellular mTOR trafficking in humans after exercise. The purpose of this study was to determine the effect of postexercise LEAA (4 g total EAAs, 1.6 g leucine) on acute MyoPS and mTORC1 translocation and signaling. Recreationally active men performed lower-body resistance exercise (5 × 8–10 leg press and leg extension) to volitional failure. Following exercise participants consumed LEAA (n = 8) or an isocaloric carbohydrate drink (PLA; n = 10). MyoPS was measured over 1.5–4 h of recovery by oral pulse of l-[ring-(2)H(5)]-phenylalanine. Phosphorylation of proteins in the mTORC1 pathway were analyzed via immunoblotting and mTORC1-LAMP2/WGA/Rheb colocalization via immunofluorescence microscopy. There was no difference in MyoPS between groups (LEAA = 0.098 ± 0.01%/h; PL = 0.090 ± 0.01%/h; P > 0.05). Exercise increased (P < 0.05) rpS6(Ser240/244)(LEAA = 35.3-fold; PLA = 20.6-fold), mTOR(Ser2448)(LEAA = 1.8-fold; PLA = 1.2-fold) and 4EBP1(Thr37/46)(LEAA = 1.5-fold; PLA = 1.4-fold) phosphorylation irrespective of nutrition (P > 0.05). LAT1 and SNAT2 protein expression were not affected by exercise or nutrient ingestion. mTOR-LAMP2 colocalization was greater in LEAA preexercise and decreased following exercise and supplement ingestion (P < 0.05), yet was unchanged in PLA. mTOR-WGA (cell periphery marker) and mTOR-Rheb colocalization was greater in LEAA compared with PLA irrespective of time-point (P < 0.05). In conclusion, the postexercise consumption of 4 g of LEAA maintains mTOR in peripheral regions of muscle fibers, in closer proximity to its direct activator Rheb, during prolonged recovery independent of differences in MyoPS or mTORC1 signaling compared with PLA ingestion. This intracellular localization of mTOR may serve to “prime” the kinase for future anabolic stimuli. NEW & NOTEWORTHY This is the first study to investigate whether postexercise leucine-enriched amino acid (LEAA) ingestion elevates mTORC1 translocation and protein-protein interactions in human skeletal muscle. Here, we observed that although LEAA ingestion did not further elevate postexercise MyoPS or mTORC1 signaling compared with placebo, mTORC1 peripheral location and interaction with Rheb were maintained. This may serve to “prime” mTORC1 for subsequent anabolic stimuli.

Massage is a viable mechanotherapy to improve protein turnover during disuse atrophy and improve muscle regrowth during recovery from disuse atrophy in adult muscle. Therefore, we investigated whether massage can cause beneficial adaptations in skeletal muscle from aged rats during normal weight-bearing (WB) conditions, hindlimb suspension (HS), or reloading (RE) following HS. Aged (30 months) male Fischer 344/Brown Norway rats were divided into two experiments: (1) WB for 7 days (WB, n = 8), WB with massage (WBM, n = 8), HS for 7 days (HS7, n = 8), or HS with massage (HSM, n = 8), and (2) WB for 14 days (WB14, n = 8), HS for 14 days (HS14, n = 8), reloading (RE, n = 10), or reloading with massage (REM, n = 10) for 7 days following HS. Deuterium oxide (D(2)O) labeling was used to assess dynamic protein and ribosome turnover in each group and anabolic signaling pathways were assessed. Massage did have an anabolic benefit during RE or WB. In contrast, massage during HS enhanced myofibrillar protein turnover in both the massaged limb and contralateral non-massaged limb compared with HS, but this did not prevent muscle loss. Overall, the data demonstrate that massage is not an effective mechanotherapy for prevention of atrophy during muscle disuse or recovery of muscle mass during reloading in aged rats. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s11357-020-00215-y) contains supplementary material, which is available to authorized users.

In order to investigate the effect of NaCl levels (1.5%, 3.5%, 5.5% and 13%) on the taste and texture of dry-cured ham, TPA, myofibril ultrastructure, proteolysis index and free amino acids were evaluated. The proteolysis index (30.76% ± 2.05–11.88% ± 1.90), cohesiveness (0.74 ± 0.04–0.60 ± 0.01), springiness (0.83 ± 0.03–0.71 ± 0.04), and the total free amino acids (9885.3 mg/100 g ± 677.98–3505.15 mg/100 g ± 378.20) decreased with the increase of salt addition, while the hardness (8701.99 g ± 513.37–12057.53 g ± 783.89) and adhesiveness (− 15.73 ± 2.53 to − 32.01 ± 4.95) increased with the increase of salt addition. The myofibril ultrastructure indicated that hams with higher proteolysis index (> 20%) showed more obvious degradation of M-line and Z-disk, and more disordered fiber structure, which was closely related to the degradation of myofibrillar proteins (actin, desmin and troponin-T). Among four groups, the dry-cured ham with 5.5% salt had the highest levels of moisture (45.73% ± 1.13) and umami amino acids (1422.77 mg/100 g ± 119.87), as well as the lowest chewiness (3346.89 ± 121.19). The ham with 5.5% salt also had higher sensory scores of texture (4.83 ± 0.1), taste (5.50 ± 0.2) and overall acceptance (5.51 ± 0.09) as compared to the ham added with other salt levels. These results indicated that 5.5% NaCl treatment showed positive effects on the texture and taste of dry-cured ham, which meets the consumer's demand for dry-cured meat products.

BACKGROUND Sturgeon is popular for its nutritious value and its taste. However, sturgeon fillets are traditionally heated in 100 °C boiling water, resulting in unfavorable taste and with a negative effect on the quality. This study considered the effect of combinations of vacuum and low-temperature treatments (LTVH groups) on sturgeon fillets compared with the traditional heat treatment (TC groups). RESULTS The results show that the LTVH groups had lower cooking-loss rates. All LTVH fillets were changed to a white color, and appeared 'done', as did the TC fillets. The LTVH and TC methods gave rise to significant differences in texture: the springiness of the LTVH groups decreased with heating time, and decreased rapidly in the TC groups (P