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It has been reported that glyphosate, one of the most common herbicides used in agriculture, impairs locomotion and cognition. Glyphosate has a variable half-life in soil up to biotic and/or abiotic factors transform the molecule in metabolites such as the aminomethylphosphonic acid (AMPA) that has a longer half-life. In this study, female Sprague Dawley rats were acutely exposed to different doses of glyphosate or AMPA (i.e. 10, 56 or 100 mg/kg) and, subsequently, the acetylcholinesterase (AChE) activity was measured in the hippocampus, prefrontal cortex (PFC) and the gastrocnemius muscle. Both glyphosate and AMPA produced a similar decrease in the AChE activity in all the tissues tested. These results suggest that interference with normal cholinergic neurotransmission may be one of the mechanisms involved in glyphosate-induced motor alterations in rats. Moreover, our results highlight the biological importance of AMPA as a molecule with anticholinesterase action in brain and skeletal muscle. To our knowledge, this is the first report showing in vivo that AMPA, the major metabolite of glyphosate, behaves as an organophosphate.

This study aimed to explore the effects of S-nitrosylation on caspase-3 modification and its subsequent effects on beef myofibril degradation in vitro. Recombinant caspase-3 was reacted with different concentrations of S-nitrosoglutathione (GSNO, nitric oxide donor) at 37 °C for 30 min and subsequently incubated with purified myofibrillar protein from bovine semimembranosus muscle. Results indicated that the activity of caspase-3 was significantly reduced after GSNO treatments ( P < 0.05) and showed a dose-dependent inhibitory effect, which was attributed to the increased S-nitrosylation extent of caspase-3. LC-MS/MS analysis revealed that caspase-3 was S-nitrosylated at cysteine sites 116, 170, 184, 220, and 264. Moreover, the degradation of desmin and troponin-T was notably suppressed by S-nitrosylated caspase-3 ( P < 0.05). To conclude, protein S-nitrosylation could modify the cysteine residues of caspase-3, which accounts for the reduced caspase-3 activity and further represses its proteolytic ability on beef myofibrillar protein.

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., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Adult, lab-reared, highland deer mice acclimate to hypoxia by increasing reliance on carbohydrates to fuel exercise. Yet neither the underlying mechanisms for this shift in fuel use nor the impact of lifetime hypoxia exposure experienced in high alpine conditions, are fully understood. Thus, we assessed the use of fuel during exercise in wild highland deer mice running in their native environment. We examined a key step in muscle carbohydrate oxidation - the regulation of pyruvate dehydrogenase (PDH) - during exercise at altitude in wild highlanders and in first generation (G1) lab-born and -raised highlanders acclimated to normoxia or hypoxia. PDH activity was also determined in the gastrocnemius of G1 highlanders using an in situ muscle preparation. We found that wild highlanders had a high reliance on carbohydrates while running in their native environment, consistent with data from hypoxia-acclimated G1 highlanders. PDH activity in the gastrocnemius was similar post exercise between G1 and wild highlanders. However, when the gastrocnemius was stimulated at a light work rate in situ, PDH activity was higher in hypoxia-acclimated G1 highlanders and was associated with lower intramuscular lactate levels. These findings were supported by lower PDH kinase 2 protein production in hypoxia-acclimated G1 mice. Our findings indicate that adult phenotypic plasticity in response to low oxygen is sufficient to increase carbohydrate reliance during exercise in highland deer mice. Additionally, variation in PDH regulation with hypoxia acclimation contributes to shifts in whole-animal patterns of fuel use and is likely to improve exercise performance via elevated energy yield per mole of O2. ., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

The treatment of organophosphate (OP) anticholinesterases currently lacks an effective oxime reactivator of OP-inhibited acetylcholinesterase (AChE) which can penetrate the blood-brain barrier (BBB). Our laboratories have synthesized novel substituted phenoxyalkyl pyridinium oximes and tested them for their ability to promote survival of rats challenged with lethal doses of nerve agent surrogates. These previous studies demonstrated the ability of some of these oximes to promote 24-h survival to rats challenged with a lethal level of highly relevant surrogates for sarin and VX. The reactivation of OP-inhibited AChE in peripheral tissues was likely to be a major contributor to their efficacy in survival of lethal OP challenges. In the present study, twenty of these novel oximes were screened in vitro for reactivation ability for AChE in rat skeletal muscle and serum using two nerve agent surrogates: phthalimidyl isopropyl methylphosphonate (PIMP, a sarin surrogate) and 4-nitrophenyl ethyl methylphosphonate (NEMP, a VX surrogate). The oximes demonstrated a range of 23%-102% reactivation of AChE in vitro across both tissue types. Some of the novel oximes tested in the present study demonstrated the ability to more effectively reactivate AChE in serum than the currently approved oxime, 2-PAM. Therefore, some of these novel oximes have the potential to reverse AChE inhibition in peripheral target tissues and contribute to survival efficacy., (© 2024 Wiley Periodicals LLC.)

We previously showed that the transaminase inhibitor, aminooxyacetic acid, reduced respiration energized at complex II (succinate dehydrogenase, SDH) in mitochondria isolated from mouse hindlimb muscle. The effect required a reduction in membrane potential with resultant accumulation of oxaloacetate (OAA), a potent inhibitor of SDH. To specifically assess the effect of the mitochondrial transaminase, glutamic oxaloacetic transaminase (GOT2) on complex II respiration, and to determine the effect in intact cells as well as isolated mitochondria, we performed respiratory and metabolic studies in wildtype (WT) and CRISPR-generated GOT2 knockdown (KD) C2C12 myocytes. Intact cell respiration by GOT2KD cells versus WT was reduced by adding carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) to lower potential. In mitochondria of C2C12 KD cells, respiration at low potential generated by 1 µM FCCP and energized at complex II by 10 mM succinate + 0.5 mM glutamate (but not by complex I substrates) was reduced versus WT mitochondria. Although we could not detect OAA, metabolite data suggested that OAA inhibition of SDH may have contributed to the FCCP effect. C2C12 mitochondria differed from skeletal muscle mitochondria in that the effect of FCCP on complex II respiration was not evident with ADP addition. We also observed that C2C12 cells, unlike skeletal muscle, expressed glutamate dehydrogenase, which competes with GOT2 for glutamate metabolism. In summary, GOT2 KD reduced C2C12 respiration in intact cells at low potential. From differential substrate effects, this occurred largely at complex II. Moreover, C2C12 versus muscle mitochondria differ in complex II sensitivity to ADP and differ markedly in expression of glutamate dehydrogenase. NEW & NOTEWORTHY Impairment of the mitochondrial transaminase, GOT2, reduces complex II (succinate dehydrogenase, SDH)-energized respiration in C2C12 myocytes. This occurs only at low inner membrane potential and is consistent with inhibition of SDH. Incidentally, we observed that C2C12 mitochondria compared with muscle tissue mitochondria differ in sensitivity of complex II respiration to ADP and in the expression of glutamate dehydrogenase.

Objective: The objective of this study was to examine the relationship between creatine kinase (CK) concentration following official matches and the risk of subsequent muscle injury in professional male football (soccer) players., Methods: Blood samples were collected on the second post-match day for CK analysis over four consecutive seasons in a professional football club. Players were then followed for five days to observe any occurrence of indirect muscle injury (structural or functional in nature). Players exposed to at least 45 minutes in two consecutive matches within seven days were considered valid cases for analysis., Results: Eighty players participated in the study, generating 1,656 cases eligible for analysis, of which 229 resulted in muscle injuries. The hamstrings were the most frequently injured muscle group (54%), followed by the adductor (21%), triceps surae (19%), quadriceps (5%), and psoas (1%). While CK concentration was higher in muscle injury cases [783 ± 507 U/L (95%CI, 717 to 849; min-max, 105-2,800)] compared with uninjured cases [688 ± 446 U/L (95%CI, 665 to 711; min-max, 100-2,950)], it was not an accurate predictor of subsequent muscle injury risk in professional football players (sensitivity = 56%; specificity = 55%; odds ratio = 1.00; area under curve = 0.557)., Conclusion: CK concentration on the second post-match day cannot be used to effectively screen subsequent muscle injury risk in professional male football players.

Knowledge of the primary structure of neuronal NO synthase (nNOS) in skeletal muscle is still conflicting and needs further clarification. To elucidate the expression patterns of nNOS isoforms at both mRNA and protein level, systematic reverse transcription (RT)-PCR and epitope mapping by qualitative immunoblot analysis on skeletal muscle of C57/BL6 mice were performed. The ability of the nNOS isoforms to form aggregates was characterized by native low-temperature polyacrylamide electrophoresis (LT-PAGE). The molecular analysis was focused on the rectus femoris (RF) muscle, a skeletal muscle with a nearly balanced ratio of nNOS α- and β-isoforms. RT-PCR amplificates from RF muscles showed exclusive exon-1d mRNA expression, either with or without exon-μ. Epitope mapping demonstrated the simultaneous expression of the nNOS splice variants α/μ, α/non-μ, β/μ and β/non-μ. Furthermore, immunoblotting suggests that the transition between nNOS α- and β-isoforms lies within exon-3. In LT-PAGE, three protein nNOS associated aggregates were detected in homogenates of RF muscle and tibialis anterior muscle: a 320 kDa band containing nNOS α-isoforms, while 250 and 300 kDa bands consist of nNOS β-isoforms that form homodimers or heterodimers with non-nNOS proteins., (© 2024 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society.)

It is well known that preslaughter (antemortem) stress such as rough handling, transportation, a negative environment, physical discomfort, lack of consistent routine, and bad feed quality has a big impact on meat quality. The antemortem-induced poor meat quality is characterized by low pH, a pale and exudative appearance, and a soft texture. Previous studies indicate that antemortem stress plays a key role in regulating protein acetylation and glycolysis in postmortem (PM) muscle. However, the underlying molecular and biochemical mechanism is not clearly understood yet. In this study, we investigated the relationship between antemortem and protein acetylation and glycolysis using murine longissimus dorsi muscle isolated from ICR mice and murine muscle cell line C 2 C 12 treated with epinephrine hydrochloride. Because adrenaline secretion increases in stressed animals, epinephrine hydrochloride was intraperitoneally injected epinephrine into mice to simulate pre-slaughter stress in this study to facilitate experimental operations and save experimental costs. Our findings demonstrated that protein acetylation in pyruvate kinase M1 (PKM1) form is significantly reduced by antemortem, and the reduced acetylation subsequently leads to an increase in PKM1 enzymatic activity which causes increased glycolysis in PM muscle. By using molecular approaches, we identified lysine 141 in PKM1 as a critical residue for acetylation. Our results in this study provide useful insight for controlling or improving meat quality in the future., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The function of skeletal muscles can be markedly hampered by obesity. Ten-eleven translocation 2 (TET2) is an important therapeutic target for ameliorating skeletal muscle dysfunction. Our previous study revealed that punicalagin (PUN) regulated TET2 in obese mice; however, whether PUN can prevent obesity-induced skeletal muscle dysfunction by regulating TET2 remains unclear. In the present study, 40 male C57BL/6J mice were divided into four groups ( n = 10 per group): the control (CON) group, the high-fat-diet (HFD, negative control) group, the resveratrol (positive control) group, and the PUN group. The ratio of gastrocnemius weight to body weight (0.0097 ± 0.0016 vs. 0.0080 ± 0.0011), the grip strength (120.04 g ± 11.10 vs. 98.89 g ± 2.79), and the muscle fiber count (314.56 per visual field ± 92.73 vs. 236.44 per visual field ± 50.58) in the PUN group were higher than those in the HFD group. Moreover, the levels of the TET2 protein, 5-hydroxymethylcytosine (5hmC), and 5-formylcytosine (5fC) in skeletal muscles were significantly lower in the HFD group than those in the CON group; these levels increased after PUN treatment. Compared with the HFD group, the phosphorylation level of AMP-activated protein kinase (AMPK) α in the PUN group was higher, which effectively enhanced the stability of the TET2 protein. Besides, the ratio of (succinic acid + fumaric acid)/α-ketoglutarate in the PUN group was lower than that in the HFD group (43.21 ± 12.42 vs. 99.19 ± 37.07), and a lower ratio led to a higher demethylase activity of TET2 in the PUN group than in the HFD group. This study highlights that PUN supplementation protects against obesity-induced impairment of the skeletal muscle function via regulating the protein stability of TET2 and the enzymatic activity of TET2 demethylation.

Introduction/aims: Rapid-stretch nerve injuries represent a substantial treatment challenge. No study has examined motor neuron connection after rapid-stretch injury. Our objective in this study was to characterize the electrophysiological properties of graded rapid-stretch nerve injury and assess motor neuron health using retrograde labeling and muscle adenosine triphosphatase (ATPase) histology., Methods: Male C57BL/6 mice (n = 6 per group) were rapid-stretch injured at four levels of severity: sham injury, stretch within elastic modulus, inelastic deformation, and stretch rupture. Serial compound muscle action potential (CMAP) and motor unit number estimation (MUNE) measurements were made for 48 days, followed by retrograde labeling and muscle ATPase histology., Results: Elastic injuries showed no durable abnormalities. Inelastic injury demonstrated profound initial reduction in CMAP and MUNE (P < .036) on day 2, with partial recovery by day 14 after injury (CMAP: 40% baseline, P = .003; MUNE: 55% baseline, P = .033). However, at the experimental endpoint, CMAP had recovered to baseline with only limited improvement in MUNE. Inelastic injury led to reduced retrograde-labeled neurons and grouped fiber type histology. Rupture injury had severe and nonrecovering electrophysiological impairment, dramatically reducing labeled neurons (P = .005), and atrophic or type 1 muscle fibers. There was an excellent correlation between MUNE and retrograde-labeled tibial motor neurons across injury severities (R 2  = 0.96)., Discussion: There was no significant electrophysiological derangement in low-severity injuries but there was recoverable conduction block in inelastic injury with slow recovery, potentially due to collateral sprouting. Rupture injuries yielded permanent failure of injured axons to reinnervate. These results provide insight into the pathophysiology of clinical injuries and recovery., (© 2022 Wiley Periodicals LLC.)

Hummingbirds possess distinct metabolic adaptations to fuel their energy-demanding hovering flight, but the underlying genomic changes are largely unknown. Here, we generated a chromosome-level genome assembly of the long-tailed hermit and screened for genes that have been specifically inactivated in the ancestral hummingbird lineage. We discovered that FBP2 (fructose-bisphosphatase 2), which encodes a gluconeogenic muscle enzyme, was lost during a time period when hovering flight evolved. We show that FBP2 knockdown in an avian muscle cell line up-regulates glycolysis and enhances mitochondrial respiration, coincident with an increased mitochondria number. Furthermore, genes involved in mitochondrial respiration and organization have up-regulated expression in hummingbird flight muscle. Together, these results suggest that FBP2 loss was likely a key step in the evolution of metabolic muscle adaptations required for true hovering flight.

The sarco(endo)plasmic reticulum Ca 2+ ATPase (SERCA) pump is responsible for the transport of Ca 2+ from the cytosol into the sarcoplasmic reticulum at the expense of ATP, making it a regulator of both muscle relaxation and muscle-based energy expenditure. Neurogranin (Ng) is a small protein that negatively regulates calcineurin signaling. Calcineurin is Ca 2+ /calmodulin dependent phosphatase that promotes the oxidative fibre type in skeletal muscle and regulates muscle-based energy expenditure. A recent study has shown that calcineurin activation reduces SERCA Ca 2+ transport efficiency, ultimately raising energy expenditure. Since the biomedical view of obesity states that it arises as an imbalance between energy intake and expenditure which favors the former, we questioned whether heterozygous Ng deletion ( Ng +/- ) would reduce SERCA efficiency and increase energy expenditure in female mice fed a high-fat diet (HFD). Young (3-4-month-old) female wild type (WT) and Ng +/- mice were fed a HFD for 12 weeks with their metabolic profile being analyzed using metabolic cages and DXA scanning, while soleus SERCA efficiency was measured using SERCA specific Ca 2+ uptake and ATPase activity assays. Ng +/- mice showed significantly less cage ambulation compared to WT mice but this did not lead to any added weight gain nor changes in daily energy expenditure, glucose or insulin tolerance despite a similar level of food intake. Furthermore, we observed significant reductions in SERCA's apparent coupling ratio which were associated with significant reductions in SERCA1 and phospholamban content. Thus, our results show that Ng regulates SERCA pump efficiency, and future studies should further investigate the potential cellular mechanisms., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Braun, Ryoo, Goodwin, Copeland, Geromella, Baranowski, MacPherson and Fajardo.)

Glucose 6-P dehydrogenase (G6PD) is the first rate-limiting enzyme in pentose phosphate pathway (PPP), and it is proverbial that G6PD is absent in skeletal muscle. However, how and why G6PD is down-regulated during skeletal muscle development is unclear. In this study, we confirmed the expression of G6PD was down-regulated during myogenesis in vitro and in vivo. G6PD was absolutely silent in adult skeletal muscle. Histone H3 acetylation and DNA methylation act together on the expression of G6PD. Neither knock-down of G6PD nor over-expression of G6PD affects myogenic differentiation. Knock-down of G6PD significantly promotes the sensitivity and response of skeletal muscle cells to insulin; over-expression of G6PD significantly injures the sensitivity and response of skeletal muscle cells to insulin. High-fat diet treatment impairs insulin signaling by up-regulating G6PD, and knock-down of G6PD rescues the impaired insulin signaling and glucose uptake caused by high-fat diet treatment. Taken together, this study explored the importance of G6PD deficiency during myogenic differentiation, which provides new sight to treat insulin resistance and type-2 diabetes.

Sarco(endo)plasmic reticulum calcium (Ca 2+ ) ATPase (SERCA) transports Ca 2+ in muscle. Impaired SERCA activity may contribute to diabetic myopathy. Sirtuin (SIRT) 3 regulates muscle metabolism and function; however, it is unknown if SIRT3 regulates muscle SERCA activity or acetylation. We determined if SIRT3 overexpression enhances SERCA activity in mouse gastrocnemius muscle and if SIRT3 overexpression preserves gastrocnemius SERCA activity in a model of type 2 diabetes, induced by high fat - high sucrose (HFHS) feeding. We also determined if the acetylation status of SERCA proteins in mouse gastrocnemius is altered by SIRT3 overexpression or HFHS feeding. Wild-type (WT) and SIRT3 transgenic (SIRT3 TG ) mice, overexpressing SIRT3 in skeletal muscle, were fed a standard or HFHS diet for 4 months. SIRT3 TG and WT mice developed obesity and glucose intolerance after 4 months of HFHS feeding. SERCA V max was higher in gastrocnemius of SIRT3 TG mice compared with WT mice. HFHS-fed mice had lower SERCA1a protein levels and lower SERCA V max in their gastrocnemius than control-fed mice. The decrease in SERCA V max in gastrocnemius muscle due to HFHS feeding was attenuated by SIRT3 overexpression in HFHS-fed SIRT3 TG mice. SERCA1a and SERCA2a acetylation in mouse gastrocnemius was not altered by genotype or diet. These findings suggest SIRT3 overexpression improves SERCA function in mouse skeletal muscle.

Sarcolipin (SLN) is a small regulatory protein that inhibits the sarco(endo)plasmic reticulum Ca 2+ -ATPase (SERCA) pump. When bound to SERCA, SLN reduces the apparent Ca 2+ affinity of SERCA and uncouples SERCA Ca 2+ transport from its ATP consumption. As such, SLN plays a direct role in altering skeletal muscle relaxation and energy expenditure. Interestingly, the expression of SLN is dynamic during times of muscle adaptation, in that large increases in SLN content are found in response to development, atrophy, overload, and disease. Several groups have suggested that increases in SLN, especially in dystrophic muscle, are deleterious as it may reduce muscle function and exacerbate already abhorrent intracellular Ca 2+ levels. However, there is also significant evidence to show that increased SLN content is a beneficial adaptive mechanism that protects the SERCA pump and activates Ca 2+ signaling and adaptive remodeling during times of cell stress. In this review, we first discuss the role for SLN in healthy muscle during both development and overload, where SLN has been shown to activate Ca 2+ signaling to promote mitochondrial biogenesis, fiber-type shifts, and muscle hypertrophy. Then, with respect to muscle disease, we summarize the discrepancies in the literature as to whether SLN upregulation is adaptive or maladaptive in nature. This review is the first to offer the concept of SLN hormesis in muscle disease, wherein both too much and too little SLN are detrimental to muscle health. Finally, the underlying mechanisms which activate SLN upregulation are discussed, specifically acknowledging a potential positive feedback loop between SLN and Ca 2+ signaling molecules.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that shows progressive muscle weakness. A few treatments exist including symptomatic therapies, which can prolong survival or reduce a symptom; however, no fundamental therapies have been found. As a therapeutic strategy, enhancing muscle force is important for patients' quality of life. In this study, we focused on skeletal muscle-specific myosin regulatory light chain kinase (skMLCK), which potentially enhances muscle contraction, as overexpression of skMLCK was thought to improve muscle function. The adeno-associated virus serotype 6 encoding skMLCK (AAV6/skMLCK) and eGFP (control) was produced and injected intramuscularly into the lower limbs of SOD1 G37R mice, which are a familial ALS model. AAV6/skMLCK showed the successful expression of skMLCK in the muscle tissues. Although the control did not affect the muscle force in both of the WT and SOD1 G37R mice, AAV6/skMLCK enhanced the twitch force of SOD1 G37R mice and the tetanic force of WT and SOD1 G37R mice. These results indicate that overexpression of skMLCK can enhance the tetanic force of healthy muscle as well as rescue weakened muscle function. In conclusion, the gene transfer of skMLCK has the potential to be a new therapy for ALS as well as for other neuromuscular diseases.

Background: Skeletal muscle AMP deaminase (AMPD1) regulates the concentration of adenine nucleotides during muscle contraction. We previously provided evidence that rabbit AMPD1 is composed by two HPRG 73 kDa subunits and two 85 kDa catalytic subunits with a dinuclear zinc site with an average of two histidine residues at each metal site. AMPD1 is mainly expressed in fast twitching fibers and is inhibited by ATP. The limited trypsinization of the 95-residue N-terminal domain of rabbit AMPD1 desensitizes the enzyme towards ATP inhibition at the optimal pH 6.5, but not at pH 7.1., Methods: The modified residues of rabbit AMPD1 after incubation with radioactive diethyl pyrocarbonate ([ 14 C]DEP) causing the desensitization to inhibition by ATP at pH 7.1 have been identified by sequence analysis and MS analysis of the radioactive peptides liberated from the carbethoxylated enzyme by limited proteolysis with trypsin., Results: The study confirms the presence of a dinuclear zinc site in rabbit AMPD1 and shows that carbethoxylation of His-51 at the N-terminus of the catalytic subunit removes the inhibition of the enzyme by ATP at pH 7.1., Conclusions: The desensitization to ATP is due to the modification of His-51 of the Zn 2 coordination sphere which is transduced in a conformational change of the enzyme C-terminus, where an ATP-binding site has been localized., General Significance: The progress in the study of the complex regulation of rabbit AMPD1 that shares an identical amino acid sequence with the human enzyme is important in relation to the role of the enzyme during mammalian evolution., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Background: Animal handling practices are one of the factors majorly affecting animal metabolism prior to slaughter. This phenomenon increases the occurrence of meat quality defects such as dark cutting-beef, causing high economical losses in the meat industry. Under this framework, the assessment of apoptosis onset in post mortem muscle was proposed as a novel approach to reveal biochemical characteristics in several Spanish bovine breeds (Asturiana de los Valles, Retinta and Rubia Gallega) managed under different production systems (intensive versus semi-extensive) and transport/lairage conditions (mixing versus not mixing with unfamiliar animals). To do so, the activities of initiator caspase 9 and executioner caspases 3/7 were determined in Longissimus thoracis et lumborum muscle at three early post mortem times (2, 8, and 24 h)., Results: Breed effect and transport/lairage conditions were the most relevant factors that influenced both caspase activities over post mortem time, showing Rubia Gallega breed a completely different behavior compared to Asturiana de los Valles and Retinta breeds. Moreover, it is postulated that apoptosis cascade is initiated via the activation of caspase 9 under hypoxic or metabolic stress followed by the activation of executioner caspases 3/7., Conclusions: Assessment of apoptosis on post mortem muscle can be a novel approach to study the influence of animal handling on muscle metabolism and post mortem cell death and its consequences on meat quality traits. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry., (© 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.)

Skeletal muscle regeneration is triggered by local inflammation and is accompanied by phagocytosis of dead cells at the injury site. Efferocytosis regulates the inflammatory program in macrophages by initiating the conversion of their inflammatory phenotype into the healing one. While pro-inflammatory cytokines induce satellite cell proliferation and differentiation into myoblasts, growth factors, such as GDF3, released by healing macrophages drive myoblast fusion and myotube growth. Therefore, improper efferocytosis may lead to impaired muscle regeneration. Transglutaminase 2 (TG2) is a versatile enzyme participating in efferocytosis. Here, we show that TG2 ablation did not alter the skeletal muscle weights or sizes but led to the generation of small size myofibers and to decreased grip force in TG2 null mice. Following cardiotoxin-induced injury, the size of regenerating fibers was smaller, and the myoblast fusion was delayed in the tibialis anterior muscle of TG2 null mice. Loss of TG2 did not affect the efferocytic capacity of muscle macrophages but delayed their conversion to Ly6C - CD206 + , GDF3 expressing cells. Finally, TG2 promoted myoblast fusion in differentiating C2C12 myoblasts. These results indicate that TG2 expressed by both macrophages and myoblasts contributes to proper myoblast fusion, and its ablation leads to impaired muscle development and regeneration in mice.

Skeletal muscle regeneration is a complex process involving crosstalk between immune cells and myogenic precursor cells, i.e., satellite cells. In this scenario, macrophage recruitment in damaged muscles is a mandatory step for tissue repair since pro-inflammatory M1 macrophages promote the activation of satellite cells, stimulating their proliferation and then, after switching into anti-inflammatory M2 macrophages, they prompt satellite cells' differentiation into myotubes and resolve inflammation. Here, we show that acid sphingomyelinase (ASMase), a key enzyme in sphingolipid metabolism, is activated after skeletal muscle injury induced in vivo by the injection of cardiotoxin. ASMase ablation shortens the early phases of skeletal muscle regeneration without affecting satellite cell behavior. Of interest, ASMase regulates the balance between M1 and M2 macrophages in the injured muscles so that the absence of the enzyme reduces inflammation. The analysis of macrophage populations indicates that these events depend on the altered polarization of M1 macrophages towards an M2 phenotype. Our results unravel a novel role of ASMase in regulating immune response during muscle regeneration/repair and suggest ASMase as a supplemental therapeutic target in conditions of redundant inflammation that impairs muscle recovery.

Rho guanosine triphosphate hydrolases (GTPases) are molecular switches that cycle between an inactive guanosine diphosphate (GDP)-bound and an active guanosine triphosphate (GTP)-bound state during signal transduction. As such, they regulate a wide range of both cellular and physiological processes. In this review, we will summarize recent work on the role of Rho GTPase-regulated pathways in skeletal muscle development, regeneration, tissue mass homeostatic balance, and metabolism. In addition, we will present current evidence that links the dysregulation of these GTPases with diseases caused by skeletal muscle dysfunction. Overall, this information underscores the critical role of a number of members of the Rho GTPase subfamily in muscle development and the overall metabolic balance of mammalian species.

Purpose: This study investigated the effects of including sprints within low-intensity training (LIT) sessions during a 14-d training camp focusing on LIT, followed by 10-d recovery (Rec), on performance and performance-related measures in elite cyclists., Methods: During the camp, a sprint training group (SPR; n = 9) included 12 × 30-s maximal sprints during five LIT sessions, whereas a control group (CON; n = 9) performed distance-matched LIT only. Training load was equally increased in both groups by 48% ± 27% during the training camp and subsequently decreased by -56% ± 23% during the recovery period compared with habitual training. Performance tests were conducted before the training camp (Pre) and after Rec. Muscle biopsies, hematological measures, and stress/recovery questionnaires were collected Pre and after the camp (Post)., Results: Thirty-second sprint (SPR vs CON: 4% ± 4%, P < 0.01) and 5-min mean power (SPR vs CON: 4% ± 8%, P = 0.04) changed differently between groups. In muscle, Na+-K+ β1 protein content changed differently between groups, decreasing in CON compared with SPR (-8% ± 14%, P = 0.04), whereas other proteins showed similar changes. SPR and CON displayed similar increases in red blood cell volume (SPR: 2.6% ± 4.7%, P = 0.07; CON: 3.9% ± 4.5%, P = 0.02) and V˙O2 at 4 mmol·L-1 [BLa-] (SPR: 2.5% ± 3.3%, P = 0.03; CON: 2.2% ± 3.0%, P = 0.04). No changes were seen for V˙O2max, Wmax, hematological measures, muscle enzyme activity, and stress/recovery measures., Conclusions: Inclusion of 30-s sprints within LIT sessions during a high-volume training camp affected competition-relevant performance measures and Na+-K+ β1 protein content differently from LIT only, without affecting sport-specific stress/recovery or any other physiological measure in elite cyclists., (Copyright © 2021 by the American College of Sports Medicine.)

An extract from Artemisia dracunculus L. (termed PMI-5011) improves glucose homeostasis by enhancing insulin action and reducing ectopic lipid accumulation, while increasing fat oxidation in skeletal muscle tissue in obese insulin resistant male mice. A chalcone, DMC-2, in PMI-5011 is the major bioactive that enhances insulin signaling and activation of AKT. However, the mechanism by which PMI-5011 improves lipid metabolism is unknown. AMPK is the cellular energy and metabolic sensor and a key regulator of lipid metabolism in muscle. This study examined PMI-5011 activation of AMPK signaling using murine C2C12 muscle cell culture and skeletal muscle tissue. Findings show that PMI-5011 increases Thr172-phosphorylation of AMPK in muscle cells and skeletal muscle tissue, while hepatic AMPK activation by PMI-5011 was not observed. Increased AMPK activity by PMI-5011 affects downstream signaling of AMPK, resulting in inhibition of ACC and increased SIRT1 protein levels. Selective deletion of DMC-2 from PMI-5011 demonstrates that compounds other than DMC-2 in a "DMC-2 knock out extract" (KOE) are responsible for AMPK activation and its downstream effects. Compared to 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) and metformin, the phytochemical mixture characterizing the KOE appears to more efficiently activate AMPK in muscle cells. KOE-mediated AMPK activation was LKB-1 independent, suggesting KOE does not activate AMPK via LKB-1 stimulation. Through AMPK activation, compounds in PMI-5011 may regulate lipid metabolism in skeletal muscle. Thus, the AMPK-activating potential of the KOE adds therapeutic value to PMI-5011 and its constituents in treating insulin resistance or type 2 diabetes., (Copyright © 2021 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Calpains are a family of Ca 2+ ‑dependent cysteine proteases that participate in various cellular processes. Calpain 3 (CAPN3) is a classical calpain with unique N‑terminus and insertion sequence 1 and 2 domains that confer characteristics such as rapid autolysis, Ca 2+ ‑independent activation and Na + activation of the protease. CAPN3 is the only muscle‑specific calpain that has important roles in the promotion of calcium release from skeletal muscle fibers, calcium uptake of sarcoplasmic reticulum, muscle formation and muscle remodeling. Studies have indicated that recessive mutations in CAPN3 cause limb‑girdle muscular dystrophy (MD) type 2A and other types of MD; eosinophilic myositis, melanoma and epilepsy are also closely related to CAPN3. In the present review, the characteristics of CAPN3, its biological functions and roles in the pathogenesis of a number of disorders are discussed.

Skeletal muscle atrophy can result from a range of physiological conditions, including denervation, immobilization, hindlimb unweighting, and aging. To better characterize the molecular genetic events of atrophy, a microarray analysis revealed that FGGY carbohydrate kinase domain containing (Fggy) is expressed in skeletal muscle and is induced in response to denervation. Bioinformatic analysis of the Fggy gene locus revealed two validated isoforms with alternative transcription initiation sites that we have designated Fggy-L-552 and Fggy-S-387. Additionally, we cloned two novel alternative splice variants, designated Fggy-L-482 and Fggy-S-344, from cultured muscle cells suggesting that at least four Fggy splice variants are expressed in skeletal muscle. Quantitative RT-PCR was performed using RNA isolated from muscle cells and primers designed to distinguish the four alternative Fggy transcripts and found that the Fggy-L transcripts are more highly expressed during myoblast differentiation, while the Fggy-S transcripts show relatively stable expression in proliferating myoblasts and differentiated myotubes. Confocal fluorescent microscopy revealed that the Fggy-L variants appear to localize evenly throughout the cytoplasm, while the Fggy-S variants produce a more punctuate cytoplasmic localization pattern in proliferating muscle cells. Finally, ectopic expression of Fggy-L-552 and Fggy-S-387 resulted in inhibition of muscle cell differentiation and attenuation of the MAP kinase and Akt signaling pathways. The identification and characterization of novel genes such as Fggy helps to improve our understanding of the molecular and cellular events that lead to atrophy and may eventually result in the identification of new therapeutic targets for the treatment of muscle wasting., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Background: Children with mitochondrial disease undergo anesthesia for a wide array of surgical procedures. However, multiple medications used for their perioperative care can affect mitochondrial function. Defects in function of the mitochondrial electron transport chain (ETC) can lead to a profound hypersensitivity to sevoflurane in children. We studied the sensitivities to sevoflurane, during mask induction and maintenance of general anesthesia, in children presenting for muscle biopsies for diagnosis of mitochondrial disease., Methods: In this multicenter study, 91 children, aged 6 months to 16 years, presented to the operating room for diagnostic muscle biopsy for presumptive mitochondrial disease. General anesthesia was induced by a slow increase of inhaled sevoflurane concentration. The primary end point, end-tidal (ET) sevoflurane necessary to achieve a bispectral index (BIS) of 60, was recorded. Secondary end points were maximal sevoflurane used to maintain a BIS between 40 and 60 during the case, and maximum and minimum heart rate and blood pressures. After induction, general anesthesia was maintained according to the preferences of the providers directing the cases. Primary data were analyzed comparing data from patients with complex I deficiencies to other groups using nonparametric statistics in SPSS v.27., Results: The median sevoflurane concentration to reach BIS of 60 during inductions (ET sevoflurane % [BIS = 60]) was significantly lower for patients with complex I defects (0.98%; 95% confidence interval [CI], 0.5-1.4) compared to complex II (1.95%; 95% CI, 1.2-2.7; P < .001), complex III (2.0%; 95% CI, 0.7-3.5; P < .001), complex IV (2.0%; 95% CI, 1.7-3.2; P < .001), and normal groups (2.2%; 95% CI, 1.8-3.0; P < .001). The sevoflurane sensitivities of complex I patients did not reach significance when compared to patients diagnosed with mitochondrial disease but without an identifiable ETC abnormality (P = .172). Correlation of complex I activity with ET sevoflurane % (BIS = 60) gave a Spearman's coefficient of 0.505 (P < .001). The differences in sensitivities between groups were less during the maintenance of the anesthetic than during induction., Conclusions: The data indicate that patients with complex I dysfunction are hypersensitive to sevoflurane compared to normal patients. Hypersensitivity was less common in patients presenting with other mitochondrial defects or without a mitochondrial diagnosis., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2021 International Anesthesia Research Society.)

Patients with pulmonary emphysema often develop locomotor muscle dysfunction, which is independently associated with disability and higher mortality in that population. Muscle dysfunction entails reduced force generation capacity, which partially depends on fibers' oxidative potential, yet very little mechanistic research has focused on muscle respiration in pulmonary emphysema. Using a recently established animal model of pulmonary emphysema-driven skeletal muscle dysfunction, we found downregulation of SDHC (succinate dehydrogenase subunit C) in association with lower oxygen consumption and fatigue tolerance in locomotor muscles. Reduced SDH activity has been previously observed in muscles from patients with pulmonary emphysema, and we found that SDHC is required to support respiration in cultured muscle cells. Moreover, in vivo gain of SDH function in emphysema animals' muscles resulted in better oxygen consumption rate and fatigue tolerance. These changes correlated with a larger number of relatively more oxidative type 2-A and 2X fibers and a reduced amount of 2B fibers. Our data suggest that SDHC is a key regulator of respiration and fatigability in pulmonary emphysema-driven skeletal muscles, which could be impactful in developing strategies aimed at attenuating this comorbidity.

[Figure: see text].

The estimation of wound age and wound vitality is a recurring task in forensic routine work and has been subject of forensic research for a long time. By now, an unrestrictedly reliable marker or set of markers has not been found. In a study on myocardial infarctions, matrix metalloproteinases (MMP) 2 and 9 as well as tissue inhibitor of matrix metalloproteinases 1 (TIMP-1) were detected immunohistochemically in mechanically wounded myocardium (ECG electrodes, vessel ligations). Against this background, the potency of MMP-9, MMP-2, and TIMP-1 as markers for the estimation of wound age and wound vitality was tested in a broad approach with human tissue samples drawn during autopsies and with an animal model, the isolated perfused Langendorff heart. The study comprised samples of injured human skeletal muscle, injured human myocardium, rats' hearts with vital wounds, and rats' hearts with postmortem-inflicted wounds that were all stained immunohistochemically. The results showed great scattering, leading to the conclusion that MMP-2, MMP-9, and TIMP-1 are not suitable for wound age estimation. Merely the results for TIMP-1 suggested that this marker might be able to differentiate between vital and postmortem-inflicted wounds. With a view to the promising results of the preceding study, the results underline the necessity to test possible markers of wound age/wound vitality on a large and diverse sample set., (© 2021. The Author(s).)

H 2 O 2 is endogenously generated and its removal in the matrix of skeletal muscle mitochondria (SMM) is dependent on NADPH likely provided by NAD(P) + transhydrogenase (NNT) and isocitrate dehydrogenase (IDH2). Importantly, NNT activity is linked to mitochondrial protonmotive force. Here, we demonstrate the presence of NNT function in detergent-solubilized and intact functional SMM isolated from rats and wild type (Nnt +/+ ) mice, but not in SMM from congenic mice carrying a mutated NNT gene (Nnt -/- ). Further comparisons between SMM from both Nnt mouse genotypes revealed that the NADPH supplied by NNT supports up to 600 pmol/mg/min of H 2 O 2 removal under selected conditions. Surprisingly, SMM from Nnt -/- mice removed exogenous H 2 O 2 at wild-type levels and exhibited a maintained or even decreased net emission of endogenous H 2 O 2 when substrates that support Krebs cycle reactions were present (e.g., pyruvate plus malate or palmitoylcarnitine plus malate). These results may be explained by a compensation for the lack of NNT, since the total activities of concurrent NADP + -reducing enzymes (IDH2, malic enzymes and glutamate dehydrogenase) were ~70% elevated in Nnt -/- mice. Importantly, respiratory rates were similar between SMM from both Nnt genotypes despite differing NNT contributions to H 2 O 2 removal and their implications for an evolving concept in the literature are discussed. We concluded that NNT is capable of meaningfully sustaining NADPH-dependent H 2 O 2 removal in intact SMM. Nonetheless, if the available substrates favor non-NNT sources of NADPH, the H 2 O 2 removal by SMM is maintained in Nnt -/- mice SMM., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Duchenne muscular dystrophy (DMD) causes progressive skeletal muscle degeneration and currently there are few therapeutic options. The identification of new drug targets and their validation in model systems of DMD could be a promising approach to make progress in finding new treatments for this lethal disease. Histone deacetylases (HDACs) play key roles in myogenesis and the therapeutic approach targeting HDACs in DMD is in an advanced phase of clinical trial. Here, we show that the expression of HDAC8, one of the members of the HDAC family, is increased in DMD patients and dystrophic zebrafish. The selective inhibition of HDAC8 with the PCI-34051 inhibitor rescues skeletal muscle defects, similarly to the treatment with the pan-HDAC inhibitor Givinostat. Through acetylation profile of zebrafish with HDAC8 dysregulation, we identified new HDAC8 targets involved in cytoskeleton organization such as tubulin that, when acetylated, is a marker of stable microtubules. Our work provides evidence of HDAC8 overexpression in DMD patients and zebrafish and supports its specific inhibition as a new valuable therapeutic approach in the treatment of this pathology., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Objective: To investigate if PP2A plays a role in metformin-induced insulin sensitivity improvement in human skeletal muscle cells. Participants . Eight lean insulin-sensitive nondiabetic participants (4 females and 4 males; age: 21.0 ± 1.0 years; BMI: 22.0 ± 0.7 kg/m 2 ; 2-hour OGTT: 97.0 ± 6.0 mg/dl; HbA1c: 5.3 ± 0.1%; fasting plasma glucose: 87.0 ± 2.0 mg/dl; M value; 11.0 ± 1.0 mg/kgBW/min)., Design: A hyperinsulinemic-euglycemic clamp was performed to assess insulin sensitivity in human subjects, and skeletal muscle biopsy samples were obtained. Primary human skeletal muscle cells (shown to retain metabolic characteristics of donors) were cultured from these muscle biopsies that included 8 lean insulin-sensitive participants. Cultured cells were expanded, differentiated into myotubes, and treated with 50  μ M metformin for 24 hours before harvesting. PP2Ac activity was measured by a phosphatase activity assay kit (Millipore) according to the manufacturer's protocol., Results: The results indicated that metformin significantly increased the activity of PP2A in the myotubes for all 8 lean insulin-sensitive nondiabetic participants, and the average fold increase is 1.54 ± 0.11 ( P < 0.001)., Conclusions: These results provided the first evidence that metformin can activate PP2A in human skeletal muscle cells derived from lean healthy insulin-sensitive participants and may help to understand metformin's action in skeletal muscle in humans., Competing Interests: The authors declare no conflict of interest and have nothing to disclose., (Copyright © 2021 Aktham Mestareehi et al.)

Mechanical stimulation has benefits for muscle mass and function. Passive stretching is widely performed in clinical rehabilitation medicine. However, the hypertrophic effects of passive repetitive stretching on senescent skeletal muscles against muscle atrophy remain unknown. We used senescence-accelerated model SAM-P8 mice. The gastrocnemius muscle was passively repetitive stretched by manual ankle dorsiflexion for 15 min, 5 days a week for 2 weeks under deep anesthesia. We examined the effects of passive stretching on muscle mass, myofiber cross-sectional area, muscle fiber type composition, satellite cell and myonuclei content, signaling pathways involved in muscle protein synthesis, and myogenic regulatory factors. The gastrocnemius muscle weight and fiber cross-sectional area of the stretched side was found greater compared with that of the unstretched side. Passive repetitive stretching increased the mRNA expression level of Akt, p70S6K, 4E-BP1, Myf5, myogenin, MuRF1.The phosphorylation level of p70S6K significantly increased in the stretched muscles, whereas of Akt and 4E-BP1 remained unchanged, compared to the unstretched side. The Pax7+ cells and myonuclei content did not differ between the stretched and unstretched muscles. These findings suggest that the hypertrophic or suppressed atrophic observation in the stretched muscles are mainly attributable to the protein turnover provoked by stretching. These findings are applicable to clinical muscle strengthening and sarcopenia prevention., (© 2021. The Author(s).)

Duchenne muscular dystrophy (DMD) is a severe and progressive muscle wasting disorder, affecting one in 3500 to 5000 boys worldwide. The NO-sGC-cGMP pathway plays an important role in skeletal muscle function, primarily by improving blood flow and oxygen supply to the muscles during exercise. In fact, PDE5 inhibitors have previously been investigated as a potential therapy for DMD, however, a large-scale Phase III clinical trial did not meet its primary endpoint. Since the efficacy of PDE5i is dependent on sufficient endogenous NO production, which might be impaired in DMD, we investigated if NO-independent sGC stimulators, could have therapeutic benefits in a mouse model of DMD. Male mdx/mTR G2 mice aged six weeks were given food supplemented with the sGC stimulator, BAY-747 (150 mg/kg of food) or food alone (untreated) ad libitum for 16 weeks. Untreated C57BL6/J mice were used as wild type (WT) controls. Assessments of the four-limb hang, grip strength, running wheel and serum creatine kinase (CK) levels showed that mdx/mTR G2 mice had significantly reduced skeletal muscle function and severe muscle damage compared to WT mice. Treatment with BAY-747 improved grip strength and running speed, and these mice also had reduced CK levels compared to untreated mdx/mTR G2 mice. We also observed increased inflammation and fibrosis in the skeletal muscle of mdx/mTR G2 mice compared to WT. While gene expression of pro-inflammatory cytokines and some pro-fibrotic markers in the skeletal muscle was reduced following BAY-747 treatment, there was no reduction in infiltration of myeloid immune cells nor collagen deposition. In conclusion, treatment with BAY-747 significantly improves several functional and pathological parameters of the skeletal muscle in mdx/mTR G2 mice. However, the effect size was moderate and therefore, more studies are needed to fully understand the potential treatment benefit of sGC stimulators in DMD.

The balanced functionality of cellular proteostatic modules is central to both proteome stability and mitochondrial physiology; thus, the age-related decline of proteostasis also triggers mitochondrial dysfunction, which marks multiple degenerative disorders. Non-functional mitochondria are removed by mitophagy, including Parkin/Pink1-mediated mitophagy. A common feature of neuronal or muscle degenerative diseases, is the accumulation of damaged mitochondria due to disrupted mitophagy rates. Here, we exploit Drosophila as a model organism to investigate the functional role of Parkin/Pink1 in regulating mitophagy and proteostatic responses, as well as in suppressing degenerative phenotypes at the whole organism level. We found that Parkin or Pink1 knock down in young flies modulated proteostatic components in a tissue-dependent manner, increased cell oxidative load, and suppressed mitophagy in neuronal and muscle tissues, causing mitochondrial aggregation and neuromuscular degeneration. Concomitant to Parkin or Pink1 knock down cncC/Nrf2 overexpression, induced the proteostasis network, suppressed oxidative stress, restored mitochondrial function, and elevated mitophagy rates in flies' tissues; it also, largely rescued Parkin or Pink1 knock down-mediated neuromuscular degenerative phenotypes. Our in vivo findings highlight the critical role of the Parkin/Pink1 pathway in mitophagy, and support the therapeutic potency of Nrf2 (a druggable pathway) activation in age-related degenerative diseases.

Background: Previous studies have examined the relationship between external training load and creatine kinase (CK) response after soccer matches in adults. This study aimed to build training- and match-specific CK prediction models for elite youth national team soccer players., Hypothesis: Training and match load will have different effects on the CK response of elite youth soccer players, and there will be position-specific differences in the most influential external and internal load parameters on the CK response., Study Design: Prospective cohort study., Level of Evidence: Level 4., Methods: Forty-one U16-U17 youth national team soccer players were measured over an 18-month period. Training and match load were monitored with global positioning system devices. Individual CK values were measured from whole blood every morning in training camps. The dataset consisted of 1563 data points. Clustered prediction models were used to examine the relationship between external/internal load and consecutive CK changes. Clusters were built based on the playing position and activity type. The performance of the linear regression models was described by the R 2 and the root-mean-square error (RMSE, U/L for CK values)., Results: The prediction models fitted similarly during games and training sessions ( R 2 = 0.38-0.88 vs 0.6-0.77), but there were large differences based on playing positions. In contrast, the accuracy of the models was better during training sessions (RMSE = 81-135 vs 79-209 U/L). Position-specific differences were also found in the external and internal load parameters, which best explained the CK changes., Conclusion: The relationship between external/internal load parameters and CK changes are position specific and might depend on the type of session (training or match). Morning CK values also contributed to the next day's CK values., Clinical Relevance: The relationship between position-specific external/internal load and CK changes can be used to individualize postmatch recovery strategies and weekly training periodization with a view to optimize match performance.

We investigated ten pale, soft, and exudative (PSE), and ten normal meat samples from pig carcasses. The meat quality at 0, 5, 12, and 24 h post-mortem and the key enzyme activities at 0 and 24 h post-mortem were determined. We selected three PSE and three normal samples for proteomics analysis at 0 h and 24 h post-mortem. No remarkable differences in pyruvate kinase (PK) and lactate dehydrogenase (LDH) activity were observed between samples at 0 h post-mortem; however, creatine kinase (CK) activity was significantly higher in PSE meat. Hexokinase (HK) activity in PSE samples was higher than that in normal samples at 24 h post-mortem. Bioinformatics analysis of the proteome showed that PSE was related to glycolysis, TCA cycle, oxidative phosphorylation, muscle tissue structure, signal transduction, and molecular chaperones. This research found that proteins such as troponin T slow skeletal muscle isoform X, GADPH, L-lactate dehydrogenase A chain, and gamma-enolase isoform X1 might be responsible for PSE., (Copyright © 2020. Published by Elsevier Ltd.)

Sarcopenia has attracted interest due to its impact on various health problems. Chronic inflammation is an important contributor to sarcopenia. Thus, we aimed to investigate the association between serum alkaline phosphatase (ALP), which is a novel inflammatory marker, and muscle mass. This study included 15,579 adults from the 2008-2011 Korea National Health and Nutrition Survey. Low skeletal muscle mass index (LSMI) was defined as body mass index-adjusted appendicular skeletal muscle mass less than 0.789 for men and 0.512 for women. Multiple logistic regression revealed that the highest ALP tertile was significantly associated with LSMI compared with the lowest ALP tertile in both men [Odds ratio (OR): 1.41; 95% confidence interval (CI): 1.04-1.91] and women (OR: 1.45; 95% CI: 1.00-2.10) after adjusting for other confounders. On the receiver operating characteristic curve analysis, the predictive power was significantly higher for ALP levels than for white blood cell count in women ( p < 0.001), whereas the difference was not significant in men ( p = 0.515). Our findings suggest the potential use of serum ALP as an inflammatory marker and a predictor of sarcopenia.

Duchenne muscular dystrophy (DMD) is a muscular disease characterized by progressive muscle degeneration. Life expectancy is between 30 and 50 years, and death is correlated with cardiac or respiratory complications. Currently, there is no cure, so there is a great interest in new pharmacological targets. Sirtuin1 (SIRT1) seems to be a potential target for DMD. In muscle tissue, SIRT1 exerts anti-inflammatory and antioxidant effects. The aim of this study is to summarize all the findings of in vivo and in vitro literature studies about the potential role of SIRT1 in DMD. A systematic literature search was performed according to PRISMA guidelines. Twenty-three articles satisfied the eligibility criteria. It emerged that SIRT1 inhibition led to muscle fragility, while conversely its activation improved muscle function. Additionally, resveratrol, a SIRT1 activator, has brought beneficial effects to the skeletal, cardiac and respiratory muscles by exerting anti-inflammatory activity that leads to reduced myofiber wasting.

Purpose: Toll-like receptor 4 (TLR4) is an inflammatory receptor expressed ubiquitously in immune cells as well as skeletal muscle and other metabolic tissues. Skeletal muscle develops favorable inflammation-mediated metabolic adaptations from exercise training. Multiple inflammatory myokines, downstream from TLR4, are proposed links to the metabolic benefits of exercise. In addition, activation of TLR4 alters skeletal muscle substrate preference. The role of skeletal muscle TLR4 (mTLR4) in exercise metabolism has not previously been investigated. Herein, we aimed to specifically test the significance of mTLR4 to exercise-induced metabolic adaptations., Methods: We developed a novel muscle-specific TLR4 knockout (mTLR4-/-) mouse model on C57BL/6J background. Male mTLR4-/- mice and wild-type (WT) littermates were compared under sedentary (SED) and voluntary wheel running (WR) conditions for 4 wk., Results: mTLR4 deletion revealed marked reductions in downstream interleukin-1 receptor-associated kinase-4 (IRAK4) phosphorylation. In addition, the disruption of mTLR4 signaling prominently blunted the metabolic adaptations in WR-mTLR4-/- mice as opposed to substantial improvements exhibited by the WT counterparts. Voluntary WR in WT mice, relative to SED, resulted in significant increases in skeletal muscle fatty acid oxidation, glucose oxidation, and associated mitochondrial enzyme activities, all of which were not significantly changed in mTLR4-/- mice., Conclusions: This study introduces a novel mTLR4-/- mouse model and identifies mTLR4 as an immunomodulatory effector of exercise-induced metabolic adaptations in skeletal muscle., (Copyright © 2020 by the American College of Sports Medicine.)

Superoxide dismutase (SOD) is a major antioxidant enzyme for superoxide removal, and cytoplasmic SOD (SOD1) is expressed as a predominant isoform in all cells. We previously reported that renal SOD1 deficiency accelerates the progression of diabetic nephropathy (DN) via increasing renal oxidative stress. To evaluate whether the degree of SOD1 expression determines regeneration capacity and sarcopenic phenotypes of skeletal muscles under incipient and advanced DN conditions, we investigated the alterations of SOD1 expression, oxidative stress marker, inflammation, fibrosis, and regeneration capacity in cardiotoxin (CTX)-injured tibialis anterior (TA) muscles of two Akita diabetic mouse models with different susceptibility to DN, DN-resistant C57BL/6- Ins2 Akita and DN-prone KK/Ta- Ins2 Akita mice. Here, we report that KK/Ta- Ins2 Akita mice, but not C57BL/6- Ins2 Akita mice, exhibit delayed muscle regeneration after CTX injection, as demonstrated by the finding indicating significantly smaller average cross-sectional areas of regenerating TA muscle myofibers relative to KK/Ta-wild-type mice. Furthermore, we observed markedly reduced SOD1 expression in CTX-injected TA muscles of KK/Ta- Ins2 Akita mice, but not C57BL/6- Ins2 Akita mice, along with increased inflammatory cell infiltration, prominent fibrosis and superoxide overproduction. Our study provides the first evidence that SOD1 reduction and the following superoxide overproduction delay skeletal muscle regeneration through induction of overt inflammation and fibrosis in a mouse model of progressive DN.

Aims: Skeletal muscle mass and strength are reduced in asthma and contribute to compromised functional capacity in asthmatic patients. However, an effective pharmacological intervention remains elusive, partly because molecular mechanisms dictating muscle decline in asthma are not known., Materials: We investigated the potential contribution(s) of skeletal muscle sarcoplasmic reticulum Ca 2+ ATPase (SERCA) to muscle atrophy and weakness in asthmatic patients. Quadriceps muscle biopsies were taken from 58 to 72 years old male patients with mild and advanced asthma and the SERCA activity was analyzed in association with cellular redox environment and myonuclear domain (MND) size., Key Findings: Maximal SERCA activity was reduced in skeletal muscles of mild and advanced asthmatics and was associated with reduced expression of SERCA2 protein and upregulation of sarcolipin, a SERCA inhibitory lipoprotein. We also found downregulation of Ca 2+ release protein calstabin and upregulation of Ca 2+ buffer, calsequestrin in skeletal muscles of asthmatic patients. The atrophic single muscle fibers had smaller cytoplasmic domains per myonucleus possibly indicating the reduced transcriptional reserves of individual myonuclei. Plasma periostin and CAF22 levels were significantly elevated in asthmatic patients and showed a strong correlation with hand-grip strength. These changes were accompanied by substantially elevated markers of global oxidative stress including lipid peroxidation and mitochondrial ROS production., Conclusion: Taken together, our data suggest that muscle weakness and atrophy in asthma is in part driven by SERCA dysfunction and oxidative stress. The data propose SERCA dysfunction as a therapeutic intervention to address muscle decline in asthma., (Copyright © 2021 Elsevier Inc. All rights reserved.)

[Figure: see text].

The roles of nitrate and nitrite ions as nitric oxide (NO) sources in mammals, complementing NOS enzymes, have recently been the focus of much research. We previously reported that rat skeletal muscle serves as a nitrate reservoir, with the amount of stored nitrate being highly dependent on dietary nitrate availability, as well as its synthesis by NOS1 enzymes and its subsequent utilization. We showed that at conditions of increased NO need, this nitrate reservoir is used in situ to generate nitrite and NO, at least in part via the nitrate reductase activity of xanthine oxidoreductase (XOR). We now further investigate the dynamics of nitrate/nitrite fluxes in rat skeletal muscle after first increasing nitrate levels in drinking water and then returning to the original intake level. Nitrate/nitrite levels were analyzed in liver, blood and several skeletal muscle samples, and expression of proteins involved in nitrate metabolism and transport were also measured. Increased nitrate supply elevated nitrate and nitrite levels in all measured tissues. Surprisingly, after high nitrate diet termination, levels of both ions in liver and all muscle samples first declined to lower levels than the original baseline. During the course of the overall experiment there was a gradual increase of XOR expression in muscle tissue, which likely led to enhanced nitrate to nitrite reduction. We also noted differences in basal levels of nitrate in the different types of muscles. These findings suggest complex control of muscle nitrate levels, perhaps with multiple processes to preserve its intracellular levels., (Copyright © 2021 Elsevier Inc. All rights reserved.)

High-intensity unaccustomed eccentric contractions result in weakness and power loss because of fatigue and muscle damage. Through the repeated bout effect (RBE), adaptations occur, then damage and weakness are attenuated following a subsequent bout. However, it is unclear whether the RBE protects peak power output. We investigated the influence of the RBE on power production and estimated fatigue- and damage-induced neuromuscular impairments following repeated high-intensity eccentric contractions. Twelve healthy adult males performed 5 sets of 30 maximal eccentric elbow flexions and repeated an identical bout 4 weeks later. Recovery was tracked over 7 days following both bouts. Reduced maximum voluntary isometric contraction torque, and increased serum creatine kinase and self-reported soreness indirectly inferred muscle damage. Peak isotonic power, time-dependent measures - rate of velocity development (RVD) and rate of torque development (RTD) - and several electrophysiological indices of neuromuscular function were assessed. The RBE protected peak power, with a protective index of 66% 24 h after the second eccentric exercise bout. The protection of power also related to preserved RVD ( R 2 = 0.61, P < 0.01) and RTD ( R 2 = 0.39, P < 0.01). Furthermore, the RBE's protection against muscle damage permitted the estimation of fatigue-associated neuromuscular performance decrements following eccentric exercise. Novelty: The repeated bout effect protects peak isotonic power. Protection of peak power relates to preserved rates of torque and velocity development, but more so rate of velocity development. The repeated bout effect has little influence on indices of neuromuscular fatigue.

Glycogen phosphorylase (PG) is a key enzyme taking part in the first step of glycogenolysis. Muscle glycogen phosphorylase (PYGM) differs from other PG isoforms in expression pattern and biochemical properties. The main role of PYGM is providing sufficient energy for muscle contraction. However, it is expressed in tissues other than muscle, such as the brain, lymphoid tissues, and blood. PYGM is important not only in glycogen metabolism, but also in such diverse processes as the insulin and glucagon signaling pathway, insulin resistance, necroptosis, immune response, and phototransduction. PYGM is implicated in several pathological states, such as muscle glycogen phosphorylase deficiency (McArdle disease), schizophrenia, and cancer. Here we attempt to analyze the available data regarding the protein partners of PYGM to shed light on its possible interactions and functions. We also underline the potential for zebrafish to become a convenient and applicable model to study PYGM functions, especially because of its unique features that can complement data obtained from other approaches.