Oxidation enhances myofibrillar protein degradation via calpain and caspase-3

Resilience in life and death: Metabolism and proteolysis in Bos indicus muscle and meat

Bos indicus cattle are important to beef production in hot, humid climates, but they have a reputation for producing tougher beef with more variability. Reduced and delayed degradation of muscle proteins postmortem is a major reason underlying these tenderness challenges. Inherent muscle metabolic characteristics and processing conditions shape the early dynamics of postmortem metabolism and protein degradation after harvest, which impacts subsequent tenderization. Skeletal muscles exhibit diverse metabolic and contractile properties, and metabolic pathways are coordinated to regulate flux under variable working conditions. Considering how living muscles respond and adapt to cellular stress may enhance our understanding of muscle death and quality development. The aim of this review is to examine how muscle properties influence metabolism and cellular response in the context of early postmortem muscle to meat conversion, and specifically, their potential contribution to variation in proteolysis in Bos indicus beef.

Differential regulation of physicochemical properties and myofibrillar protein degradation of yak meat by interactions between reactive oxygen species and reactive nitrogen species during postmortem aging

BACKGROUND

This study aimed to explore how interactions between reactive oxygen species (ROS) and reactive nitrogen species (RNS) affect oxidative properties, nitrosative properties, and myofibrillar protein degradation during postmortem aging of yak meat.

RESULTS

Yak longissimus dorsi was incubated with saline, ROS activator (H2O2)/inhibitor N-Acetyl-L-cysteine (NAC) and RNS activator S-Nitrosoglutathione (GSNO)/inhibitor L-NAME hydrochloride (L-NAME) combined treatments at 4 °C for 12, 24, 72, 120, and 168 h. The results indicated that regardless of whether RNS was activated or inhibited, activated ROS played a dominant role in myofibrillar protein degradation by oxidative modification to increase carbonyl content, disulfide bonds, surface hydrophobicity, and dimerized tyrosine while decreasing sulfhydryl content, thereby degrading nebulin, titin, troponin-t and desmin. Notably, the Warner-Bratzler shear force (WBSF) of the H2O2 + L-NAME group was the smallest, whereas that of the NAC + GSNO group was smaller than that of the NAC + L-NAME group.

CONCLUSION

These findings provide new insights into meat tenderization patterns through the interaction between ROS and RNS. © 2024 Society of Chemical Industry.

Electrical stimulation to improve meat quality: Factors at interplay, underlying biochemical mechanisms and a second look into the molecular pathways using proteomics

Ensuring consistent beef eating quality is paramount for meeting consumer demands and sustaining the meat industry. Electrical stimulation (ES) is a post-slaughter intervention used to accelerate post-mortem glycolysis, to avoid cold shortening, to control the tenderization rate of meat through sophisticated physical, chemical and biochemical mechanisms including proteolysis, to improve beef tenderness and to achieve normal pHu that might lead to positive impact on color. This review comprehensively examines the multifaceted effects of ES on beef quality, encompassing factors and settings influencing its efficacy and the underlying biochemical mechanisms revealed using traditional biochemistry methods. It then delves into the molecular pathways modulated by ES, as unveiled by muscle proteomics, aiming to provide a second look and an unprecedented understanding of the underlying biochemical mechanisms through an integrative proteomics analysis of low-voltage ES (LVES) proteomics studies. The proteins changing as a result of ES were gathered in a compendium of 67 proteins, from which 14 were commonly identified across studies. In-depth bioinformatics of this compendium allowed a comprehensive overview of the molecular signatures and interacting biochemical pathways behind electrically stimulated beef muscles. The proteins belong to interconnected molecular pathways including the ATP metabolic process and glycolysis, muscle structure and contraction, heat shock proteins, oxidative stress, proteolysis and apoptosis. Understanding the intricate interplay of molecular pathways behind ES could improve the efficiency of beef production, ensuring consistent meat quality and meeting consumer expectations. The integrative analysis approach performed in this study holds promise for the meat industry's sustainability and competitiveness.

Hypoxia Tolerance of Two Killifish Species

Hypoxia tolerance in aquatic ectotherms involves a suite of behavioral and physiological responses at the organismal, tissue, and cellular levels. The current study evaluated two closely related killifish species (Fundulus heteroclitus, Fundulus majalis) to evaluate responses to acute moderate and acute severe hypoxia. Routine metabolic rate and loss of equilibrium were assessed, followed by analysis in skeletal muscle of markers of oxidative damage to proteins (2,4-DNPH), lipids (4-HNE), and DNA (8-OHdG), hypoxia signaling (HIF1α, HIF2α), cellular energy state (p-AMPK: AMPK), and protein degradation (Ubiquitin, LC3B, Calpain 2, Hsp70). Both species had a similar reduction in metabolic rate at low PO2. However, F. heteroclitus was the more hypoxia-tolerant species based on a lower PO2 at which there was loss of equilibrium, perhaps due in part to a lower oxygen demand at all oxygen tensions. Despite the differences in hypoxia tolerance between the species, skeletal muscle molecular markers were largely insensitive to hypoxia, and there were few differences in responses between the species. Thus, the metabolic depression observed at the whole animal level appears to limit perturbations in skeletal muscle in both species during the hypoxia treatments.

Ventilator-induced diaphragm dysfunction: phenomenology and mechanism(s) of pathogenesis

Mechanical ventilation (MV) is used to support ventilation and pulmonary gas exchange in patients during critical illness and surgery. Although MV is a life-saving intervention for patients in respiratory failure, an unintended side-effect of MV is the rapid development of diaphragmatic atrophy and contractile dysfunction. This MV-induced diaphragmatic weakness is labelled as 'ventilator-induced diaphragm dysfunction' (VIDD). VIDD is an important clinical problem because diaphragmatic weakness is a risk factor for the failure to wean patients from MV. Indeed, the inability to remove patients from ventilator support results in prolonged hospitalization and increased morbidity and mortality. The pathogenesis of VIDD has been extensively investigated, revealing that increased mitochondrial production of reactive oxygen species within diaphragm muscle fibres promotes a cascade of redox-regulated signalling events leading to both accelerated proteolysis and depressed protein synthesis. Together, these events promote the rapid development of diaphragmatic atrophy and contractile dysfunction. This review highlights the MV-induced changes in the structure/function of diaphragm muscle and discusses the cell-signalling mechanisms responsible for the pathogenesis of VIDD. This report concludes with a discussion of potential therapeutic opportunities to prevent VIDD and suggestions for future research in this exciting field.

Protein turnover in pigs: A review of interacting factors

Protein turnover defines the balance between two continuous and complex processes of protein metabolism, synthesis and degradation, which determine their deposition in tissues. Although the liver and intestine have been studied extensively for their important roles in protein digestion, absorption and metabolism, the study of protein metabolism has focused mainly on skeletal muscle tissue to understand the basis for its growth. Due to the high adaptability of skeletal muscle, its protein turnover is greatly affected by different internal and external factors, contributing to carcass lean-yield and animal growth. Amino acid (AA) labelling and tracking using isotope tracer methodology, together with the study of myofiber type profiling, signal transduction pathways and gene expression, has allowed the analysis of these mechanisms from different perspectives. Positive stimuli such as increased nutrient availability in the diet (e.g., AA), physical activity, the presence of certain hormones (e.g., testosterone) or a more oxidative myofiber profile in certain muscles or pig genotypes promote increased upregulation of translation and transcription-related genes, activation of mTORC1 signalling mechanisms and increased abundance of satellite cells, allowing for more efficient protein synthesis. However, fasting, animal aging, inactivity and stress, inflammation or sepsis produce the opposite effect. Deepening the understanding of modifying factors and their possible interaction may contribute to the design of optimal strategies to better control tissue growth and nutrient use (i.e., protein and AA), and thus advance the precision feeding strategy.

Heme oxygenase-1: A potential therapeutic target for improving skeletal muscle atrophy

Skeletal muscle atrophy is a common muscle disease that is directly caused by an imbalance in protein synthesis and degradation. At the histological level, it is mainly characterized by a reduction in muscle mass and fiber cross-sectional area (CSA). Patients with skeletal muscle atrophy present with reduced motor ability, easy fatigue, and poor life quality. Heme oxygenase-1 (HO-1) is an inducible enzyme that catalyzes the degradation of heme and has attracted much attention for its anti-oxidation effects. In addition, there is growing evidence that HO-1 plays an important role in anti-inflammatory, anti-apoptosis, pro-angiogenesis, and maintaining skeletal muscle homeostasis, making it a potential therapeutic target for improving skeletal muscle atrophy. Here, we review the pathogenesis of skeletal muscle atrophy, the biology of HO-1 and its regulation, and the biological function of HO-1 in skeletal muscle homeostasis, with a specific focus on the role of HO-1 in skeletal muscle atrophy, aiming to observe the therapeutic potential of HO-1 for skeletal muscle atrophy.

Research progress on the pathogenesis and treatment of ventilator-induced diaphragm dysfunction

Prolonged controlled mechanical ventilation (CMV) can cause diaphragm fiber atrophy and inspiratory muscle weakness, resulting in diaphragmatic contractile dysfunction, called ventilator-induced diaphragm dysfunction (VIDD). VIDD is associated with higher rates of in-hospital deaths, nosocomial pneumonia, difficulty weaning from ventilators, and increased costs. Currently, appropriate clinical strategies to prevent and treat VIDD are unavailable, necessitating the importance of exploring the mechanisms of VIDD and suitable treatment options to reduce the healthcare burden. Numerous animal studies have demonstrated that ventilator-induced diaphragm dysfunction is associated with oxidative stress, increased protein hydrolysis, disuse atrophy, and calcium ion disorders. Therefore, this article summarizes the molecular pathogenesis and treatment of ventilator-induced diaphragm dysfunction in recent years so that it can be better served clinically and is essential to reduce the duration of mechanical ventilation use, intensive care unit (ICU) length of stay, and the medical burden.

Mitochondrial dysfunction and skeletal muscle atrophy: Causes, mechanisms, and treatment strategies

Skeletal muscle, which accounts for approximately 40% of total body weight, is one of the most dynamic and plastic tissues in the human body and plays a vital role in movement, posture and force production. More than just a component of the locomotor system, skeletal muscle functions as an endocrine organ capable of producing and secreting hundreds of bioactive molecules. Therefore, maintaining healthy skeletal muscles is crucial for supporting overall body health. Various pathological conditions, such as prolonged immobilization, cachexia, aging, drug-induced toxicity, and cardiovascular diseases (CVDs), can disrupt the balance between muscle protein synthesis and degradation, leading to skeletal muscle atrophy. Mitochondrial dysfunction is a major contributing mechanism to skeletal muscle atrophy, as it plays crucial roles in various biological processes, including energy production, metabolic flexibility, maintenance of redox homeostasis, and regulation of apoptosis. In this review, we critically examine recent knowledge regarding the causes of muscle atrophy (disuse, cachexia, aging, etc.) and its contribution to CVDs. Additionally, we highlight the mitochondrial signaling pathways involvement to skeletal muscle atrophy, such as the ubiquitin-proteasome system, autophagy and mitophagy, mitochondrial fission-fusion, and mitochondrial biogenesis. Furthermore, we discuss current strategies, including exercise, mitochondria-targeted antioxidants, in vivo transfection of PGC-1α, and the potential use of mitochondrial transplantation as a possible therapeutic approach.

Intrinsic contractile dysfunction due to impaired sarcoplasmic reticulum Ca2+ release in compensatory hypertrophied muscle fibers following synergist ablation

Synergist ablation (SA) is an experimental procedure for the induction of hypertrophy. However, SA causes a decrease in specific force (i.e., force per cross-sectional area), likely due to excessive muscle use. Here, we investigated the mechanisms behind the SA-induced intrinsic contractile dysfunction, especially focusing on the excitation-contraction (EC) coupling. Male Wistar rats had unilateral surgical ablation of gastrocnemius and soleus muscles to induce compensatory hypertrophy in the plantaris muscles. Two weeks after SA, plantaris muscle was dissected from each animal and used for later analyses. SA significantly increased the mean fiber cross-sectional area (+18%). On the other hand, the ratio of depolarization-induced force to the maximum Ca2+-activated specific force, an indicator of sarcoplasmic reticulum (SR) Ca2+ release, was markedly reduced in mechanically skinned fibers from the SA group (-51%). These functional defects were accompanied by an extensive fragmentation of the SR Ca2+ release channel, the ryanodine receptor 1 (RyR1), and a decrease in the amount of other triad proteins (i.e., DHPR, STAC3, and junctophilin1). SA treatment also caused activation of calpain-1 and increased the amount of NADPH oxidase 2, endoplasmic reticulum (ER) stress proteins (i.e., Grp78, Grp94, PDI, and Ero1), and lipid peroxidation [i.e., 4-hydroxynonenal (4-HNE)] in SA-treated muscles. Our findings show that SA causes skeletal muscle weakness due to impaired EC coupling. This is likely to be induced by Ca2+-dependent degradation of triad proteins, which may result from Ca2+ leak from fragmented RyR1 triggered by increased oxidative stress.NEW & NOTEWORTHY Synergist ablation (SA) has widely been used to understand the mechanisms behind skeletal muscle hypertrophy. However, compensatory hypertrophied muscles display intrinsic contractile dysfunction, i.e., a hallmark of overuse. Here, we demonstrate that SA-induced compensatory hypertrophy is accompanied by muscle weakness due to impaired sarcoplasmic reticulum Ca2+ release. This dysfunction may be caused by the degradation of triad proteins due to the reciprocal amplification of reactive oxygen species and Ca2+ signaling at the junctional space microdomain.

Mitochondrial dysfunction: roles in skeletal muscle atrophy

Mitochondria play important roles in maintaining cellular homeostasis and skeletal muscle health, and damage to mitochondria can lead to a series of pathophysiological changes. Mitochondrial dysfunction can lead to skeletal muscle atrophy, and its molecular mechanism leading to skeletal muscle atrophy is complex. Understanding the pathogenesis of mitochondrial dysfunction is useful for the prevention and treatment of skeletal muscle atrophy, and finding drugs and methods to target and modulate mitochondrial function are urgent tasks in the prevention and treatment of skeletal muscle atrophy. In this review, we first discussed the roles of normal mitochondria in skeletal muscle. Importantly, we described the effect of mitochondrial dysfunction on skeletal muscle atrophy and the molecular mechanisms involved. Furthermore, the regulatory roles of different signaling pathways (AMPK-SIRT1-PGC-1α, IGF-1-PI3K-Akt-mTOR, FoxOs, JAK-STAT3, TGF-β-Smad2/3 and NF-κB pathways, etc.) and the roles of mitochondrial factors were investigated in mitochondrial dysfunction. Next, we analyzed the manifestations of mitochondrial dysfunction in muscle atrophy caused by different diseases. Finally, we summarized the preventive and therapeutic effects of targeted regulation of mitochondrial function on skeletal muscle atrophy, including drug therapy, exercise and diet, gene therapy, stem cell therapy and physical therapy. This review is of great significance for the holistic understanding of the important role of mitochondria in skeletal muscle, which is helpful for researchers to further understanding the molecular regulatory mechanism of skeletal muscle atrophy, and has an important inspiring role for the development of therapeutic strategies for muscle atrophy targeting mitochondria in the future.

Mitochondrial Apoptotic Signaling Involvement in Remodeling During Myogenesis and Skeletal Muscle Atrophy

Mitochondria play a major role in apoptotic signaling. In addition to its role in eliminating dysfunctional cells, mitochondrial apoptotic signaling is implicated as a key component of myogenic differentiation and skeletal muscle atrophy. For example, the activation of cysteine-aspartic proteases (caspases; CASP's) can aid in the initial remodeling stages of myogenic differentiation by cleaving protein kinases, transcription factors, and cytoskeletal proteins. Precise regulation of these signals is needed to prevent excessive cell disassemble and subsequent cell death. During skeletal muscle atrophy, the activation of CASP's and mitochondrial derived nucleases participate in myonuclear fragmentation, a potential loss of myonuclei, and cleavage of contractile structures within skeletal muscle. The B cell leukemia/lymphoma 2 (BCL2) family of proteins play a significant role in regulating myogenesis and skeletal muscle atrophy by governing the initiating steps of mitochondrial apoptotic signaling. This review discusses the role of mitochondrial apoptotic signaling in skeletal muscle remodeling during myogenic differentiation and skeletal muscle pathological states, including aging, disuse, and muscular dystrophy.

Chronic Intermittent Hypoxia-Induced Diaphragm Muscle Weakness Is NADPH Oxidase-2 Dependent

Chronic intermittent hypoxia (CIH)-induced redox alterations underlie diaphragm muscle dysfunction. We sought to establish if NADPH oxidase 2 (NOX2)-derived reactive oxygen species (ROS) underpin CIH-induced changes in diaphragm muscle, which manifest as impaired muscle performance. Adult male mice (C57BL/6J) were assigned to one of three groups: normoxic controls (sham); chronic intermittent hypoxia-exposed (CIH, 12 cycles/hour, 8 h/day for 14 days); and CIH + apocynin (NOX2 inhibitor, 2 mM) administered in the drinking water throughout exposure to CIH. In separate studies, we examined sham and CIH-exposed NOX2-null mice (B6.129S-Cybb^TM1Din/J). Apocynin co-treatment or NOX2 deletion proved efficacious in entirely preventing diaphragm muscle dysfunction following exposure to CIH. Exposure to CIH had no effect on NOX2 expression. However, NOX4 mRNA expression was increased following exposure to CIH in wild-type and NOX2 null mice. There was no evidence of overt CIH-induced oxidative stress. A NOX2-dependent increase in genes related to muscle regeneration, antioxidant capacity, and autophagy and atrophy was evident following exposure to CIH. We suggest that NOX-dependent CIH-induced diaphragm muscle weakness has the potential to affect ventilatory and non-ventilatory performance of the respiratory system. Therapeutic strategies employing NOX2 blockade may function as an adjunct therapy to improve diaphragm muscle performance and reduce disease burden in diseases characterised by exposure to CIH, such as obstructive sleep apnoea.

Degradation and evaluation of myofibril proteins induced by endogenous protease in aquatic products during storage: a review

Myofibril proteins degradation constitutes an important factor in quality deterioration, procedural activation or inhibition of endogenous protease potential regulates autolytic proteolysis-induced softening of post mortem fish muscle. Based on the brief introduction of myofibril proteins degradation in fish skeletal muscle, a detailed description of the main myofibril degradation properties and the distinct role played by endogenous proteases were proposed, which reflects the limitations and challenges of the current research on myofibril hydrolysis mechanisms based on the varied surrounding conditions. In addition, the latest researches on the evaluation method of myofibril proteins degradation were comprehensively reviewed. The potential use of label-free proteomics combined with bioinformatics was also emphasized and has become an important means to in-depth understand protein degradation mechanism.

Effects of heat stress on markers of skeletal muscle proteolysis in dairy cattle

Heat stress (HS) markedly affects postabsorptive energetics and protein metabolism. Circulating urea nitrogen increases in multiple species during HS and it has been traditionally presumed to stem from increased skeletal muscle proteolysis; however, this has not been empirically established. We hypothesized HS would increase activation of the calpain and proteasome systems as well as increase degradation of autophagosomes in skeletal muscle. To test this hypothesis, lactating dairy cows (∼139 d in milk; parity ∼2.4) were exposed to thermal neutral (TN) or HS conditions for 7 d (8 cows/environment). To induce HS, cattle were fitted with electric blankets for the duration of the heating period and the semitendinosus was biopsied on d 7. Heat stress increased rectal temperature (1.3°C) and respiratory rate (38 breaths per minute) while it decreased dry matter intake (34%) and milk yield (32%). Plasma urea nitrogen (PUN) peaked following 3 d (46%) and milk urea nitrogen (MUN) peaked following 4 d of environmental treatment and while both decreased thereafter, PUN and MUN remained elevated compared with TN (PUN: 20%; MUN: 27%) on d 7 of HS. Contrary to expectations, calpain I and II abundance and activation and calpain activity were similar between groups. Likewise, relative protein abundance of E3 ligases, muscle atrophy F-box protein/atrogin-1 and muscle ring-finger protein-1, total ubiquitinated proteins, and proteasome activity were similar between environmental treatments. Finally, autophagosome degradation was also unaltered by HS. Counter to our hypothesis, these results suggest skeletal muscle proteolysis is not increased following 7 d of HS and call into question the presumed dogma that elevated skeletal muscle proteolysis, per se, drives increased AA mobilization.

Role of the endoplasmic reticulum in the search for early biomarkers of meat quality

Defects in meat quality such as dark, firm and dry (DFD) beef have been related to high levels of oxidative stress that produce cellular alterations that may affect to the process of meat quality acquisition. Despite the important role of endoplasmic reticulum (ER) in the cellular response to oxidative stress, its function in the muscle-to-meat conversion process has not yet been studied. In this study, differences in muscular antioxidant defense and the unfolded protein response (UPR) of the ER in CONTROL (normal pH₂₄) and dark, firm, and dry (DFD, pH₂₄ ≥ 6.2) beef at 24 h post-mortem were analyzed to understand the changes in the muscle-to-meat conversion process related to meat quality defects. DFD meat showed poor quality, lower antioxidant activity (P < 0.05) and higher UPR activation (P < 0.05), which indicates higher oxidative stress what could partly explain the occurrence of meat quality defects. Therefore, the biomarkers of these cellular processes (IRE1α, ATF6α, and p-eIF2α) are putative biomarkers of meat quality.

Distinct myofibrillar sub-proteomic profiles are associated with the instrumental texture of aged pork loin

Fresh pork tenderness contributes to consumer satisfaction with the eating experience. Postmortem proteolysis of proteins within and between myofibrils has been closely linked with pork tenderness development. A clear understanding of the molecular features associated with pork tenderness development will provide additional targets and open the door to new solutions to improve and make pork tenderness development more consistent. Therefore, the objective was to utilize liquid chromatography and mass spectrometry with tandem mass tag (TMT) multiplexing to evaluate myofibrillar sub-proteome differences between pork chops of different instrumental star probe values. Pork loins (N = 120) were collected from a commercial harvest facility at 24 h postmortem. Quality and sensory attributes were evaluated at 24 h postmortem and after ~2 weeks of postmortem aging. Pork chops were grouped into 4 groups based on instrumental star probe value (group A,x¯ = 4.23 kg, 3.43 to 4.55 kg; group B,x¯ = 4.79 kg, 4.66 to 5.00 kg; group C,x¯ = 5.43 kg, 5.20 to 5.64 kg; group D,x¯ = 6.21 kg, 5.70 to 7.41 kg; n = 25 per group). Myofibrillar proteins from the samples aged ~2 wk were fractionated, washed, and solubilized in 8.3 M urea, 2 M thiourea, and 1% dithiothreitol. Proteins were digested with trypsin, labeled with 11-plex isobaric TMT reagents, and identified and quantified using a Q-Exactive Mass Spectrometer. Between groups A and D, 54 protein groups were differentially abundant (adjusted P < 0.05). Group A had a greater abundance of proteins related to the thick and thin filament and a lesser abundance of Z-line-associated proteins and metabolic enzymes than group D chops. These data highlight that distinct myofibrillar sub-proteomes are associated with pork chops of different tenderness values. Future research should evaluate changes immediately and earlier postmortem to further elucidate myofibrillar sub-proteome differences over the postmortem aging period.

Identification of the co-differentially expressed hub genes involved in the endogenous protective mechanism against ventilator-induced diaphragm dysfunction

BACKGROUND

In intensive care units (ICU), mechanical ventilation (MV) is commonly applied to save patients' lives. However, ventilator-induced diaphragm dysfunction (VIDD) can complicate treatment by hindering weaning in critically ill patients and worsening outcomes. The goal of this study was to identify potential genes involved in the endogenous protective mechanism against VIDD.

METHODS

Twelve adult male rabbits were assigned to either an MV group or a control group under the same anesthetic conditions. Immunostaining and quantitative morphometry were used to assess diaphragm atrophy, while RNA-seq was used to investigate molecular differences between the groups. Additionally, core module and hub genes were analyzed using WGCNA, and co-differentially expressed hub genes were subsequently discovered by overlapping the differentially expressed genes (DEGs) with the hub genes from WGCNA. The identified genes were validated by western blotting (WB) and quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

After a VIDD model was successfully built, 1276 DEGs were found between the MV and control groups. The turquoise and yellow modules were identified as the core modules, and Trim63, Fbxo32, Uchl1, Tmprss13, and Cst3 were identified as the five co-differentially expressed hub genes. After the two atrophy-related genes (Trim63 and Fbxo32) were excluded, the levels of the remaining three genes/proteins (Uchl1/UCHL1, Tmprss13/TMPRSS13, and Cst3/CST3) were found to be significantly elevated in the MV group (P < 0.05), suggesting the existence of a potential antiproteasomal, antiapoptotic, and antiautophagic mechanism against diaphragm dysfunction.

CONCLUSION

The current research helps to reveal a potentially important endogenous protective mechanism that could serve as a novel therapeutic target against VIDD.

Advances in application of ultrasound in meat tenderization: A review

Tenderness could measure the eating quality of meat. The mechanism of muscle tenderization is becoming more and more critical in the past decade. Since the transforming of muscle into edible meat requires a complex physiological and biochemical process, the related tenderization of meat can be beneficial to improving the meat quality. As a non-thermal processing technology with energy-saving, environmental protection, and intense penetration, ultrasonic treatment has been widely used in the tenderizing process of meat products. In this paper, the principle of meat tenderization, the ultrasonic technology, and the application of ultrasonic technology in meat tenderization is summarized. The effect of ultrasonic technology on the tenderization of meat products is discussed from different perspectives (muscle fibers and connective tissue properties).

Histological alterations and oxidative stress in adult zebrafish muscle after aluminium exposure

Aluminium (Al) is among the most abundant metals in nature, and its presence in the environment is further increasing by anthropogenic activities. In water bodies, the Al concentrations ranged between 0.001 and 50 mg/L, raising concerns about the health of aquatic organisms. For this reason, zebrafish was chosen as the model, since it is well suited for ecotoxicological studies. Adult specimens were exposed to 11 mg/L of Al for 10, 15 and 20 days to assess both the morphology and the oxidative state of muscle tissue. Considering the involvement of ROS, the activity of the main antioxidant enzymes, metallothioneins contents, but also oxidative damage and enzymes involved in energy consumption and neuromuscular transmission were assessed. Collected data showed an increase in the thickness of the endomysium and resorbed myofibrils in the organisms exposed to Al for 10 days, and an increase of myotomes' size in the organisms exposed to Al for 15 days. Moreover, the organisms exposed for less time to Al, it was evident an activation of anaerobic metabolism and the increased activity of antioxidant enzymes such as superoxide dismutase, glutathione peroxidase and glutathione S-transferases. However, these effects stabilized with increasing exposure time. In addition, only after 20 days of treatment did the oxidative damage to the proteins and the activity of acetylcholinesterase increase while the levels of metallothioneins and the lipid peroxidation were lower for all treated animals when compared to the control group. Overall, the biochemical and histological changes induced by aluminium exposure in the muscular tissue represent a relevant contribution to understanding the environmental risk due to the diffusion of this metal within the aquatic compartment.

Redox signaling regulates skeletal muscle remodeling in response to exercise and prolonged inactivity

Skeletal muscle fibers are malleable and undergo rapid remodeling in response to increased contractile activity (i.e., exercise) or prolonged periods of muscle inactivity (e.g., prolonged bedrest). Exploration of the cell signaling pathways regulating these skeletal muscle adaptations reveal that redox signaling pathways play a key role in the control of muscle remodeling during both exercise and prolonged muscle inactivity. In this regard, muscular exercise results in an acute increase in the production of reactive oxygen species (ROS) in the contracting fibers; however, this contraction-induced rise in ROS production rapidly declines when contractions cease. In contrast, prolonged muscle disuse results in a chronic elevation in ROS production within the inactive fibers. This difference in the temporal pattern of ROS production in muscle during exercise and muscle inactivity stimulates divergent cell-signaling pathways that activate both genomic and nongenomic mechanisms to promote muscle remodeling. This review examines the role that redox signaling plays in skeletal muscle adaptation in response to both prolonged muscle inactivity and endurance exercise training. We begin with a summary of the sites of ROS production in muscle fibers followed by a review of the cellular antioxidants that are responsible for regulation of ROS levels in the cell. We then discuss the specific redox-sensitive signaling pathways that promote skeletal muscle adaptation in response to both prolonged muscle inactivity and exercise. To stimulate future research, we close with a discussion of unanswered questions in this exciting field.

Effects of oxidation on the physicochemical properties and degradation of mutton myofibrillar proteins

Tenderness affects mutton quality and price, and the degradation of myofibrillar protein (MP) is critical to improve tenderness. We investigated the oxidative modification of mutton MP by hydroxyl radicals (OH) and the effects of this modification on the proteolysis of MP by µ-calpain. As the H₂ O₂ concentrations increased, the carbonyl and dityrosine contents and the surface hydrophobicity of MP all display an increasing trend, whereas the total sulfhydryl and intrinsic fluorescence intensity of MP declines significantly. SDS-PAGE electrophoresis indicates that disulfide bonds and other covalent bonds led to protein cross-linking and aggregation. After adding µ-calpain, with increasing oxidation, the degradation percentage of myosin heavy chain (MHC) increases considerably and actin degradation is promoted, while the proteolysis of troponin-T and desmin is inhibited. These data suggest that·OH can change MP physicochemical properties and its susceptibility to µ-calpain. Future investigations will focus on the effect of oxidation on the degradation of MP by other proteases, such as cathepsins and caspase and the effect of oxidation on these enzymes. PRACTICAL APPLICATION: The calpain system, particularly µ-calpain, plays a pivotal role in postmortem tenderization of meat. Protein oxidative modifications influence meat tenderness mainly by regulating proteolysis. An investigation of the effect of oxidation on the proteolytic susceptibility of MP to degradation by µ-calpain allows for the monitoring of the association between protein oxidation and meat tenderness.

High-Fat Diet Impairs Muscle Function and Increases the Risk of Environmental Heatstroke in Mice

Environmental heat-stroke (HS) is a life-threatening response often triggered by hot and humid weather. Several lines of evidence indicate that HS is caused by excessive heat production in skeletal muscle, which in turn is the result of abnormal Ca2+ leak from the sarcoplasmic reticulum (SR) and excessive production of oxidative species of oxygen and nitrogen. As a high fat diet is known to increase oxidative stress, the objective of the present study was to investigate the effects of 3 months of high-fat diet (HFD) on the HS susceptibility of wild type (WT) mice. HS susceptibility was tested in an environmental chamber where 4 months old WT mice were exposed to heat stress (41 °C for 1 h). In comparison with mice fed with a regular diet, mice fed with HFD showed: (a) increased body weight and accumulation of adipose tissue; (b) elevated oxidative stress in skeletal muscles; (c) increased heat generation and oxygen consumption during exposure to heat stress; and finally, (d) enhanced sensitivity to both temperature and caffeine of isolated muscles during in-vitro contracture test. These data (a) suggest that HFD predisposes WT mice to heat stress and (b) could have implications for guidelines regarding food intake during periods of intense environmental heat.

Linoleic Acid Attenuates Denervation-Induced Skeletal Muscle Atrophy in Mice through Regulation of Reactive Oxygen Species-Dependent Signaling

Muscle atrophy is a major muscle disease, the symptoms of which include decreased muscle volume leading to insufficient muscular support during exercise. One cause of muscle atrophy is the induction of oxidative stress by reactive oxygen species (ROS). This study aimed to identify the antioxidant mechanism of linoleic acid (LA) in muscle atrophy caused by oxidative stress. H2O2 has been used to induce oxidative stress in myoblasts in vitro. C2C12 myoblasts treated with H2O2 exhibited decreased viability and increased ROS synthesis. However, with LA treatment, the cells tended to recover from oxidative effects similar to those of the control groups. At the molecular level, the expression of superoxide dismutase 1 (SOD1), Bax, heat shock protein 70 (HSP70), and phosphorylated forkhead box protein O1 was increased by oxidative stress, causing apoptosis. LA treatment suppressed these changes. In addition, the expression of MuRF1 and Atrogin-1/MAFbx mRNA increased under oxidative stress but not in the LA-treated group. Sciatic denervation of C57BL/6 mice manifested as atrophy of the skeletal muscle in micro-computed tomography (micro-CT). The protein expression levels of SOD1, HSP70, and MuRF1 did not differ between the atrophied muscle tissues and C2C12 myoblasts under oxidative stress. With LA treatment, muscle atrophy recovered and protein expression was restored to levels similar to those in the control. Therefore, this study suggests that LA may be a candidate substance for preventing muscle atrophy.

The Role of Oxidative Stress in Skeletal Muscle Myogenesis and Muscle Disease

The contractile activity, high oxygen consumption and metabolic rate of skeletal muscle cause it to continuously produce moderate levels of oxidant species, such as reactive oxygen species (ROS) and reactive nitrogen species (RNS). Under normal physiological conditions, there is a dynamic balance between the production and elimination of ROS/RNS. However, when the oxidation products exceed the antioxidant defense capacity, the body enters a state of oxidative stress. Myogenesis is an important process to maintain muscle homeostasis and the physiological function of skeletal muscle. Accumulating evidence suggests that oxidative stress plays a key role in myogenesis and skeletal muscle physiology and pathology. In this review, we summarize the sources of reactive oxygen species in skeletal muscle and the causes of oxidative stress and analyze the key role of oxidative stress in myogenesis. Then, we discuss the relationship between oxidative stress and muscle homeostasis and physiopathology. This work systematically summarizes the role of oxidative stress in myogenesis and muscle diseases and provides targets for subsequent antioxidant therapy and repair of inflammatory damage in noninflammatory muscle diseases.

Current insights into cellular senescence and myotoxicity induced by doxorubicin

Doxorubicin is an anti-neoplasmic drug that prevents DNA replication but induces senescence and cellular toxicity. Intensive research has focused on strategies to alleviate the doxorubicin-induced skeletal myotoxicity. The aim of the present review is to critically discuss the relevant scientific evidence about the role of exercise and growth factor administration and offer novel insights about newly developed-tools to combat the adverse drug reactions of doxorubicin treatment on skeletal muscle. In the first part, we discuss current data and mechanistic details on the impact of doxorubicin on skeletal myotoxicity. We next, review key aspects about the role of regular exercise and the impact of growth factors either administered pharmacologically or via genetic interventions. Future strategies such as combination of exercise and growth factor administration remain to be established to combat the pharmacologically-induced myotoxicity.

Cancer-Related Cachexia: The Vicious Circle between Inflammatory Cytokines, Skeletal Muscle, Lipid Metabolism and the Possible Role of Physical Training

Cachexia is a multifactorial and multi-organ syndrome that is a major cause of morbidity and mortality in late-stage chronic diseases. The main clinical features of cancer-related cachexia are chronic inflammation, wasting of skeletal muscle and adipose tissue, insulin resistance, anorexia, and impaired myogenesis. A multimodal treatment has been suggested to approach the multifactorial genesis of cachexia. In this context, physical exercise has been found to have a general effect on maintaining homeostasis in a healthy life, involving multiple organs and their metabolism. The purpose of this review is to present the evidence for the relationship between inflammatory cytokines, skeletal muscle, and fat metabolism and the potential role of exercise training in breaking the vicious circle of this impaired tissue cross-talk. Due to the wide-ranging effects of exercise training, from the body to the behavior and cognition of the individual, it seems to be able to improve the quality of life in this syndrome. Therefore, studying the molecular effects of physical exercise could provide important information about the interactions between organs and the systemic mediators involved in the overall homeostasis of the body.

Cardiovasomobility: an integrative understanding of how disuse impacts cardiovascular and skeletal muscle health

Cardiovasomobility is a novel concept that encompasses the integration of cardiovascular and skeletal muscle function in health and disease with critical modification by physical activity, or lack thereof. Compelling evidence indicates that physical activity improves health while a sedentary, or inactive, lifestyle accelerates cardiovascular and skeletal muscle dysfunction and hastens disease progression. Identifying causative factors for vascular and skeletal muscle dysfunction, especially in humans, has proven difficult due to the limitations associated with cross-sectional investigations. Therefore, experimental models of physical inactivity and disuse, which mimic hospitalization, injury, and illness, provide important insight into the mechanisms and consequences of vascular and skeletal muscle dysfunction. This review provides an overview of the experimental models of disuse and inactivity and focuses on the integrated responses of the vasculature and skeletal muscle in response to disuse/inactivity. The time course and magnitude of dysfunction evoked by various models of disuse/inactivity are discussed in detail, and evidence in support of the critical roles of mitochondrial function and oxidative stress are presented. Lastly, strategies aimed at preserving vascular and skeletal muscle dysfunction during disuse/inactivity are reviewed. Within the context of cardiovasomobility, experimental manipulation of physical activity provides valuable insight into the mechanisms responsible for vascular and skeletal muscle dysfunction that limit mobility, degrade quality of life, and hasten the onset of disease.

Connecting Heat Tolerance and Tenderness in Bos indicus Influenced Cattle

Bos indicus cattle are widely utilized in tropical and subtropical climates. Their heat tolerance and parasite resistance are integral for beef production in these regions; however, a reputation for excitable temperaments, slower growth, and variation in tenderness has limited their use in commercial beef production. This suggests that there is antagonism between heat tolerance and meat production traits. Meat quality characteristics are determined by the properties of skeletal muscle as well as conditions during slaughter and processing. Thus, it is possible that adaptations related to heat tolerance in the living animal affect tenderness and other meat quality attributes. Since muscle represents a large proportion of body mass, relatively small changes at the cellular level could impact overall heat production of the animal. Specifically, protein degradation and mitochondria function are aspects of organ and cellular metabolism that may help limit heat production and also have a connection to tenderness. Protein degradation postmortem is critical to structural changes that enhance tenderness whereas mitochondria may influence tenderness through their roles in energy metabolism, calcium regulation, cell death signaling, and oxidative stress. This review explores potential relationships between cellular metabolism in vivo and beef quality development in Bos indicus and Bos indicus influenced cattle.

Identification of differentially expressed genes in mouse paraspinal muscle in response to microgravity

Lower back pain (LBP) is the primary reason leading to dyskinesia in patients, which can be experienced by people of all ages. Increasing evidence have revealed that paraspinal muscle (PSM) degeneration (PSMD) is a causative contributor to LBP. Current research revealed that fatty infiltration, tissue fibrosis, and muscle atrophy are the characteristic pathological alterations of PSMD, and muscle atrophy is associated with abnormally elevated oxidative stress, reactive oxygen species (ROS) and inflammation. Interestingly, microgravity can induce PSMD and LBP. However, studies on the molecular mechanism of microgravity in the induction of PSMD are strongly limited. This study identified 23 differentially expressed genes (DEGs) in the PSM (longissimus dorsi) of mice which were flown aboard the Bion M1 biosatellite in microgravity by bioinformatics analysis. Then, we performed protein-protein interaction, Gene Ontology function, and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis for the DEGs. We found that Il6ra, Tnfaip2, Myo5a, Sesn1, Lcn2, Lrg1, and Pik3r1 were inflammatory genes; Fbox32, Cdkn1a, Sesn1, and Mafb were associated with muscle atrophy; Cdkn1a, Sesn1, Lcn2, and Net1 were associated with ROS; and Sesn1 and Net1 were linked to oxidative stress. Furthermore, Lcn2, Fbxo32, Cdkn1a, Pik3r1, Sesn1, Net1, Il6ra, Myo5a, Lrg1, and Pfkfb3 were remarkably upregulated, whereas Tnfaip2 and Mafb were remarkably downregulated in PSMD, suggesting that they might play a significant role in regulating the occurrence and development of PSMD. These findings provide theoretical basis and therapeutic targets for the treatment of PSMD.

Shared and distinct mechanisms of skeletal muscle atrophy: A narrative review

Maintenance of skeletal muscle mass and function is an incredibly nuanced balance of anabolism and catabolism that can become distorted within different pathological conditions. In this paper we intend to discuss the distinct intracellular signaling events that regulate muscle protein atrophy for a given clinical occurrence. Aside from the common outcome of muscle deterioration, several conditions have at least one or more distinct mechanisms that creates unique intracellular environments that facilitate muscle loss. The subtle individuality to each of these given pathologies can provide both researchers and clinicians with specific targets of interest to further identify and increase the efficacy of medical treatments and interventions.

Redox Signaling and Sarcopenia: Searching for the Primary Suspect

Sarcopenia, the age-related decline in muscle mass and function, derives from multiple etiological mechanisms. Accumulative research suggests that reactive oxygen species (ROS) generation plays a critical role in the development of this pathophysiological disorder. In this communication, we review the various signaling pathways that control muscle metabolic and functional integrity such as protein turnover, cell death and regeneration, inflammation, organismic damage, and metabolic functions. Although no single pathway can be identified as the most crucial factor that causes sarcopenia, age-associated dysregulation of redox signaling appears to underlie many deteriorations at physiological, subcellular, and molecular levels. Furthermore, discord of mitochondrial homeostasis with aging affects most observed problems and requires our attention. The search for the primary suspect of the fundamental mechanism for sarcopenia will likely take more intense research for the secret of this health hazard to the elderly to be unlocked.

Meat tenderness: advances in biology, biochemistry, molecular mechanisms and new technologies

Meat tenderness is an important quality trait critical to consumer acceptance, and determines satisfaction, repeat purchase and willingness-to-pay premium prices. Recent advances in tenderness research from a variety of perspectives are presented. Our understanding of molecular factors influencing tenderization are discussed in relation to glycolysis, calcium release, protease activation, apoptosis and heat shock proteins, the use of proteomic analysis for monitoring changes, proteomic biomarkers and oxidative/nitrosative stress. Each of these structural, metabolic and molecular determinants of meat tenderness are then discussed in greater detail in relation to animal variation, postmortem influences, and changes during cooking, with a focus on recent advances. Innovations in postmortem technologies and enzymes for meat tenderization are discussed including their potential commercial application. Continued success of the meat industry relies on ongoing advances in our understanding, and in industry innovation. The recent advances in fundamental and applied research on meat tenderness in relation to the various sectors of the supply chain will enable such innovation.

Skeletal muscle atrophy: From mechanisms to treatments

Skeletal muscle is a crucial tissue for movement, gestural assistance, metabolic homeostasis, and thermogenesis. It makes up approximately 40% of the total body weight and 50% of total protein. However, several pathological abnormalities (e.g., chronic diseases, cancer, long-term infection, aging) can induce an imbalance in skeletal muscle protein synthesis and degradation, which triggers muscle wasting and even leads to atrophy. Skeletal muscle atrophy is characterized by weakening, shrinking, and decreasing muscle mass and fiber cross-sectional area at the histological level. It manifests as a reduction in force production, easy fatigue and decreased exercise capability, along with a lower quality of life. Mechanistically, there are several pathophysiological processes involved in skeletal muscle atrophy, including oxidative stress and inflammation, which then activate signal transduction, such as the ubiquitin proteasome system, autophagy lysosome system, and mTOR. Considering the great economic and social burden that muscle atrophy can inflict, effective prevention and treatment strategies are essential but still limited. Exercise is widely acknowledged as the most effective therapy for skeletal muscle atrophy; unfortunately, it is not applicable for all patients. Several active substances for skeletal muscle atrophy have been discovered and evaluated in clinical trials, however, they have not been marketed to date. Knowledge is being gained on the underlying mechanisms, highlighting more promising treatment strategies in the future. In this paper, the mechanisms and treatment strategies for skeletal muscle atrophy are briefly reviewed.

μ-Calpain oxidation and proteolytic changes on myofibrillar proteins from Coregonus Peled in vitro

The purpose of this study was to investigate the structural properties of μ-calpain induced by hydroxyl radical oxidation and its effect on the degradation of myofibrillar protein (MP) from the dorsal muscles of Coregonus peled. The carbonyl and sulfhydryl content of μ-calpain changed significantly after oxidation. The content of α-helix in the secondary structure decreased from 0.825 to 0.232 and the changes in intrinsic fluorescence and ultraviolet (UV) absorption spectra indicated that oxidation could cause the expansion and aggregation of µ-calpain molecules. Changes in µ-calpain structure could improve the activity of µ-calpain, reaching the highest value at 0.5 mM H₂O₂. The highest µ-calpain activity facilitate the degradation of unoxidized MP, while the degradation of oxidized MP was facilitated at the 1 mM H₂O₂. Thus, our results provide a scientific basis for the interaction mechanism among hydroxyl radical oxidation, µ-calpain, and MP degradation.

Mitochondrial Dysfunction Is a Common Denominator Linking Skeletal Muscle Wasting Due to Disease, Aging, and Prolonged Inactivity

Skeletal muscle is the most abundant tissue in the body and is required for numerous vital functions, including breathing and locomotion. Notably, deterioration of skeletal muscle mass is also highly correlated to mortality in patients suffering from chronic diseases (e.g., cancer). Numerous conditions can promote skeletal muscle wasting, including several chronic diseases, cancer chemotherapy, aging, and prolonged inactivity. Although the mechanisms responsible for this loss of muscle mass is multifactorial, mitochondrial dysfunction is predicted to be a major contributor to muscle wasting in various conditions. This systematic review will highlight the biochemical pathways that have been shown to link mitochondrial dysfunction to skeletal muscle wasting. Importantly, we will discuss the experimental evidence that connects mitochondrial dysfunction to muscle wasting in specific diseases (i.e., cancer and sepsis), aging, cancer chemotherapy, and prolonged muscle inactivity (e.g., limb immobilization). Finally, in hopes of stimulating future research, we conclude with a discussion of important future directions for research in the field of muscle wasting.

Methylarginine metabolites are associated with attenuated muscle protein synthesis in cancer-associated muscle wasting

Cancer cachexia is characterized by reductions in peripheral lean muscle mass. Prior studies have primarily focused on increased protein breakdown as the driver of cancer-associated muscle wasting. Therapeutic interventions targeting catabolic pathways have, however, largely failed to preserve muscle mass in cachexia, suggesting that other mechanisms might be involved. In pursuit of novel pathways, we used untargeted metabolomics to search for metabolite signatures that may be linked with muscle atrophy. We injected 7-week-old C57/BL6 mice with LLC1 tumor cells or vehicle. After 21 days, tumor-bearing mice exhibited reduced body and muscle mass and impaired grip strength compared with controls, which was accompanied by lower synthesis rates of mixed muscle protein and the myofibrillar and sarcoplasmic muscle fractions. Reductions in protein synthesis were accompanied by mitochondrial enlargement and reduced coupling efficiency in tumor-bearing mice. To generate mechanistic insights into impaired protein synthesis, we performed untargeted metabolomic analyses of plasma and muscle and found increased concentrations of two methylarginines, asymmetric dimethylarginine (ADMA) and N^G-monomethyl-l-arginine, in tumor-bearing mice compared with control mice. Compared with healthy controls, human cancer patients were also found to have higher levels of ADMA in the skeletal muscle. Treatment of C2C12 myotubes with ADMA impaired protein synthesis and reduced mitochondrial protein quality. These results suggest that increased levels of ADMA and mitochondrial changes may contribute to impaired muscle protein synthesis in cancer cachexia and could point to novel therapeutic targets by which to mitigate cancer cachexia.

Skeletal Muscle Energetics and Mitochondrial Function Are Impaired Following 10 Days of Bed Rest in Older Adults

Background

Older adults exposed to periods of inactivity during hospitalization, illness, or injury lose muscle mass and strength. This, in turn, predisposes poor recovery of physical function upon reambulation and represents a significant health risk for older adults. Bed rest (BR) results in altered skeletal muscle fuel metabolism and loss of oxidative capacity that have recently been linked to the muscle atrophy program. Our primary objective was to explore the effects of BR on mitochondrial energetics in muscle from older adults. A secondary objective was to examine the effect of β-hydroxy-β-methylbuturate (HMB) supplementation on mitochondrial energetics.

Methods

We studied 20 older adults before and after a 10-day BR intervention, who consumed a complete oral nutritional supplement (ONS) with HMB (3.0 g/d HMB, n = 11) or without HMB (CON, n = 9). Percutaneous biopsies of the vastus lateralis were obtained to determine mitochondrial respiration and H₂O₂ emission in permeabilized muscle fibers along with markers of content. RNA sequencing and lipidomics analyses were also conducted.

Results

We found a significant up-regulation of collagen synthesis and down-regulation of ribosome, oxidative metabolism and mitochondrial gene transcripts following BR in the CON group. Alterations to these gene transcripts were significantly blunted in the HMB group. Mitochondrial respiration and markers of content were both reduced and H₂O₂ emission was elevated in both groups following BR.

Conclusions

In summary, 10 days of BR in older adults causes a significant deterioration in mitochondrial energetics, while transcriptomic profiling revealed that some of these negative effects may be attenuated by an ONS containing HMB.

Differential protein metabolism and regeneration in hypertrophic diaphragm and atrophic gastrocnemius muscles in hibernating Daurian ground squirrels

NEW FINDINGS

What is the central question of this study? The aim was to investigate whether diaphragm hypertrophy and gastrocnemius atrophy during hibernation of Daurian ground squirrels involve differential regulation of protein metabolism and regeneration. What is the main finding and its importance? We clarified the differences in protein metabolism and muscle regenerative potential in the diaphragm and gastrocnemius of hibernating ground squirrels, reflecting the different adaptability of muscles.

ABSTRACT

Are differences in the regulation of protein metabolism and regeneration involved in the different phenotypic adaptation mechanisms of muscle hypertrophy and atrophy in hibernators? Two fast-type muscles (diaphragm and gastrocnemius) in summer active and hibernating Daurian ground squirrels were selected to detect changes in cross-sectional area (CSA) and protein expression indicative of protein synthesis metabolism (protein expression of P-Akt, P-mTORC1, P-S6K1 and P-4E-BP1), protein degradation metabolism (MuRF1, atrogin-1, calpain-1, calpain-2, calpastatin, desmin, troponin T, Beclin1 and LC3-II) and muscle regeneration (MyoD, myogenin and myostatin). In the hibernation group compared with the summer active group, the CSA of the diaphragm muscle increased significantly by 26.1%, whereas the CSA of the gastrocnemius muscle decreased significantly by 20.4%. Our study also indicated that increased protein synthesis, decreased protein degradation and increased muscle regenerative potential contributed to diaphragm muscle hypertrophy, whereas decreased protein synthesis, increased protein degradation and decreased muscle regenerative potential contributed to gastrocnemius muscle atrophy. In conclusion, the differences in muscle regeneration and regulatory pattern of protein metabolism might contribute to the different adaptive changes observed in the diaphragm and gastrocnemius muscles of ground squirrels.

Understanding the common mechanisms of heart and skeletal muscle wasting in cancer cachexia

Cachexia is a severe complication of cancer that adversely affects the course of the disease, with currently no effective treatments. It is characterized by a progressive atrophy of skeletal muscle and adipose tissue, resulting in weight loss, a reduced quality of life, and a shortened life expectancy. Although the cachectic condition primarily affects the skeletal muscle, a tissue that accounts for ~40% of total body weight, cachexia is considered a multi-organ disease that involves different tissues and organs, among which the cardiac muscle stands out for its relevance. Patients with cancer often experience severe cardiac abnormalities and manifest symptoms that are indicative of chronic heart failure, including fatigue, shortness of breath, and impaired exercise tolerance. Furthermore, cardiovascular complications are among the major causes of death in cancer patients who experienced cachexia. The lack of effective treatments for cancer cachexia underscores the need to improve our understanding of the underlying mechanisms. Increasing evidence links the wasting of the cardiac and skeletal muscles to metabolic alterations, primarily increased energy expenditure, and to increased proteolysis, ensuing from activation of the major proteolytic machineries of the cell, including ubiquitin-dependent proteolysis and autophagy. This review aims at providing an overview of the key mechanisms of cancer cachexia, with a major focus on those that are shared by the skeletal and cardiac muscles.

Aerobic exercise training attenuates doxorubicin-induced ultrastructural changes in rat ventricular myocytes

AIMS

To investigate the effects of aerobic exercise training on cardiomyocyte ultrastructure, oxidative stress, and activation of protein synthesis pathways in a model of cardiomyopathy induced by doxorubicin (Dox).

MAIN METHODS

Male Sprague Dawley rats were randomly assigned to Control (saline, sedentary), Dox/sedentary (DoxSed), or Dox/exercise (DoxEx) groups. Saline or Dox were injected i.p. for 10 days (1 mg/kg/d). Aerobic exercise training was performed for 9 wks (starting with drug administration) on a treadmill, 5 d/wk, 30 min/d at 60% of maximum velocity. After euthanasia, the left ventricle (LV) was dissected, and processed for microscopy or frozen for Western blot and kinetic measurement of antioxidant enzymes activity.

KEY FINDINGS

Dox resulted in a mortality of 31.2% of sedentary animals, whilst all animals from both Control and DoxEx groups survived. DoxSed animals presented increased LV connective tissue deposition alongside with massive sarcomeric disorganization with dissolution of myofibrils and wavy Z-lines. There was an increase in oxidative damage and a reduction in the activation of both Akt and ERK pathways in LV from DoxSed compared to Control group. Aerobic training caused notable changes in myocardial structure with reduced fibrosis and preservation of myofibrils integrity and sarcomere organization. This was associated with reduced LV oxidative damage and increased activity of antioxidant enzymes, and an increase in the activation of PI3K-Akt pathway.

SIGNIFICANCE

Aerobic exercise training was effective in preventing mortality caused by Dox and in preserving LV ultrastructure, partially via activation of the physiological protein synthesis pathway, PI3K-Akt, and reducing oxidative stress.

Calpains play an essential role in mechanical ventilation-induced diaphragmatic weakness and mitochondrial dysfunction

Mechanical ventilation (MV) is a life-saving intervention for many critically ill patients. Unfortunately, an unintended consequence of prolonged MV is the rapid development of diaphragmatic atrophy and contractile dysfunction, known as ventilator-induced diaphragm dysfunction (VIDD). Although the mechanism(s) responsible for VIDD are not fully understood, abundant evidence reveals that oxidative stress leading to the activation of the major proteolytic systems (i.e., autophagy, ubiquitin-proteasome, caspase, and calpain) plays a dominant role. Of the proteolytic systems involved in VIDD, calpain has received limited experimental attention due to the longstanding dogma that calpain plays a minor role in inactivity-induced muscle atrophy. Guided by preliminary experiments, we tested the hypothesis that activation of calpains play an essential role in MV-induced oxidative stress and the development of VIDD. This premise was rigorously tested by transgene overexpression of calpastatin, an endogenous inhibitor of calpains. Animals with/without transfection of the calpastatin gene in diaphragm muscle fibers were exposed to 12 h of MV. Results confirmed that overexpression of calpastatin barred MV-induced activation of calpain in diaphragm fibers. Importantly, deterrence of calpain activation protected the diaphragm against MV-induced oxidative stress, fiber atrophy, and contractile dysfunction. Moreover, prevention of calpain activation in the diaphragm forstalled MV-induced mitochondrial dysfunction and prevented MV-induced activation of caspase-3 along with the transcription of muscle specific E3 ligases. Collectively, these results support the hypothesis that calpain activation plays an essential role in the early development of VIDD. Further, these findings provide the first direct evidence that calpain plays an important function in inactivity-induced mitochondrial dysfunction and oxidative stress in skeletal muscle fibers.

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Inhibiting calpains during mechanical ventilation protects the diaphragm.

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Calpains play an important role in muscle atrophy and contractile dysfunction.

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Calpain inhibition during mechanical ventilation prevents mitochondrial dysfunction.

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Calpain-cleaved molecules may play important signaling roles.

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Calpain activation cross-talks with other proteolytic systems.

Modification of Neuromuscular Junction Protein Expression by Exercise and Doxorubicin

PURPOSE

Doxorubicin (DOX) is a highly effective antitumor agent widely used in cancer treatment. However, it is well established that DOX induces muscular atrophy and impairs force production. Although no therapeutic interventions exist to combat DOX-induced muscle weakness, endurance exercise training has been shown to reduce skeletal muscle damage caused by DOX administration. Numerous studies have attempted to identify molecular mechanisms responsible for exercise-induced protection against DOX myotoxicity. Nevertheless, the mechanisms by which endurance exercise protects against DOX-induced muscle weakness remain elusive. In this regard, impairments to the neuromuscular junction (NMJ) are associated with muscle wasting, and studies indicate that physical exercise can rescue NMJ fragmentation. Therefore, we tested the hypothesis that exercise protects against DOX-induced myopathy by preventing detrimental changes to key proteins responsible for maintenance of the NMJ.

METHODS

Female Sprague-Dawley rats were assigned to sedentary or exercise-trained groups. Exercise training consisted of a 5-d treadmill habituation period followed by 10 d of running (60 min·d, 30 m·min, 0% grade). After the last training bout, exercise-trained and sedentary animals were paired with either placebo (saline) or DOX (20 mg·kg i.p.) treatment. Two days after drug treatment, the soleus muscle was excised for subsequent analyses.

RESULTS

Our results indicate that endurance exercise training prevents soleus muscle atrophy and contractile dysfunction in DOX-treated animals. These adaptations were associated with the increased expression of the following neurotrophic factors: brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, nerve growth factor, and neurotrophin-3. In addition, exercise enhanced the expression of receptor-associated protein of the synapse and the acetylcholine receptor (AChR) subunits AChRβ, AChRδ, and AChRγ in DOX-treated animals.

CONCLUSION

Therefore, upregulating neurotrophic factor and NMJ protein expression may be an effective strategy to prevent DOX-induced skeletal muscle dysfunction.

Skeletal Muscle Recovery from Disuse Atrophy: Protein Turnover Signaling and Strategies for Accelerating Muscle Regrowth

Skeletal muscle fibers have a unique capacity to adjust their metabolism and phenotype in response to alternations in mechanical loading. Indeed, chronic mechanical loading leads to an increase in skeletal muscle mass, while prolonged mechanical unloading results in a significant decrease in muscle mass (muscle atrophy). The maintenance of skeletal muscle mass is dependent on the balance between rates of muscle protein synthesis and breakdown. While molecular mechanisms regulating protein synthesis during mechanical unloading have been relatively well studied, signaling events implicated in protein turnover during skeletal muscle recovery from unloading are poorly defined. A better understanding of the molecular events that underpin muscle mass recovery following disuse-induced atrophy is of significant importance for both clinical and space medicine. This review focuses on the molecular mechanisms that may be involved in the activation of protein synthesis and subsequent restoration of muscle mass after a period of mechanical unloading. In addition, the efficiency of strategies proposed to improve muscle protein gain during recovery is also discussed.

Pharmacological targeting of mitochondrial function and reactive oxygen species production prevents colon 26 cancer-induced cardiorespiratory muscle weakness

Cancer cachexia is a syndrome characterized by profound cardiac and diaphragm muscle wasting, which increase the risk of morbidity in cancer patients due to failure of the cardiorespiratory system. In this regard, muscle relies greatly on mitochondria to meet energy requirements for contraction and mitochondrial dysfunction can result in muscle weakness and fatigue. In addition, mitochondria are a major source of reactive oxygen species (ROS) production, which can stimulate increased rates of muscle protein degradation. Therefore, it has been suggested that mitochondrial dysfunction may be an underlying factor that contributes to the pathology of cancer cachexia. To determine if pharmacologically targeting mitochondrial dysfunction via treatment with the mitochondria-targeting peptide SS-31 would prevent cardiorespiratory muscle dysfunction, colon 26 (C26) adenocarcinoma tumor-bearing mice were administered either saline or SS-31 daily (3 mg/kg/day) following inoculation. C26 mice treated with saline demonstrated greater ROS production and mitochondrial uncoupling compared to C26 mice receiving SS-31 in both the heart and diaphragm muscle. In addition, saline-treated C26 mice exhibited a decline in left ventricular function which was significantly rescued in C26 mice treated with SS-31. In the diaphragm, muscle fiber cross-sectional area of C26 mice treated with saline was significantly reduced and force production was impaired compared to C26, SS-31-treated animals. Finally, ventilatory deficits were also attenuated in C26 mice treated with SS-31, compared to saline treatment. These data demonstrate that C26 tumors promote severe cardiac and respiratory myopathy, and that prevention of mitochondrial dysfunction is sufficient to preclude cancer cachexia-induced cardiorespiratory dysfunction.

Molecular signatures of beef tenderness: Underlying mechanisms based on integromics of protein biomarkers from multi-platform proteomics studies

Over the last two decades, proteomics have been employed to decipher the underlying factors contributing to variation in the quality of muscle foods, including beef tenderness. One such approach is the application of high-throughput protein analytical platforms in the identification of meat quality biomarkers. To broaden our understanding about the biological mechanisms underpinning meat tenderization across a large number of studies, an integromics study was performed to review the current status of protein biomarker discovery targeting beef tenderness. This meta-analysis is the first to gather and propose a comprehensive list of 124 putative protein biomarkers derived from 28 independent proteomics-based experiments, from which 33 robust candidates were identified worthy of evaluation using targeted or untargeted data-independent acquisition proteomic methods. We further provide an overview of the interconnectedness of the main biological pathways impacting tenderness determination after multistep analyses including Gene Ontology annotations, pathway and process enrichment and literature mining, and specifically discuss the major proteins and pathways most often reported in proteomics research.

Redox Control of Proteolysis During Inactivity-Induced Skeletal Muscle Atrophy

Significance: Skeletal muscles play essential roles in key body functions including breathing, locomotion, and glucose homeostasis; therefore, maintaining healthy skeletal muscles is important. Prolonged periods of muscle inactivity (e.g., bed rest, mechanical ventilation, or limb immobilization) result in skeletal muscle atrophy and weakness. Recent Advances: Disuse skeletal muscle atrophy occurs due to both accelerated proteolysis and decreased protein synthesis with proteolysis playing a leading role in some types of inactivity-induced atrophy. Although all major proteolytic systems are involved in inactivity-induced proteolysis in skeletal muscles, growing evidence indicates that both calpain and autophagy play an important role. Regulation of proteolysis in skeletal muscle is under complex control, but it is established that activation of both calpain and autophagy is directly linked to oxidative stress. Critical Issues: In this review, we highlight the experimental evidence that supports a cause and effect link between reactive oxygen species (ROS) and activation of both calpain and autophagy in skeletal muscle fibers during prolonged inactivity. We also review the sources of oxidant production in muscle fibers during inactivity-induced atrophy, and provide a detailed discussion on how ROS activates both calpain and autophagy during disuse muscle wasting. Future Directions: Future studies are required to delineate the specific mechanisms by which ROS activates both calpain and autophagy in skeletal muscles during prolonged periods of contractile inactivity. This knowledge is essential to develop the most effective strategies to protect against disuse muscle atrophy. Antioxid. Redox Signal. 33, 559-569.

TAK1 preserves skeletal muscle mass and mitochondrial function through redox homeostasis

Skeletal muscle atrophy is debilitating consequence of a large number of chronic disease states, aging, and disuse conditions. Skeletal muscle mass is regulated through coordinated activation of a number of signaling cascades. Transforming growth factor-β activated kinase 1 (TAK1) is a central kinase that mediates the activation of multiple signaling pathways in response to various growth factors, cytokines, and microbial products. Accumulating evidence suggests that TAK1 promotes skeletal muscle growth and essential for the maintenance of muscle mass in adults. Targeted inactivation of TAK1 leads to severe muscle wasting and kyphosis in mice. However, the mechanisms by which TAK1 prevents loss of muscle mass remain poorly understood. Through generation of inducible skeletal muscle-specific Tak1-knockout mice, we demonstrate that targeted ablation of TAK1 disrupts redox signaling leading to the accumulation of reactive oxygen species and loss of skeletal muscle mass and contractile function. Suppression of oxidative stress using Trolox improves muscle contractile function and inhibits the activation of catabolic signaling pathways in Tak1-deficient muscle. Moreover, Trolox inhibits the activation of ubiquitin-proteasome system and autophagy markers in skeletal muscle of Tak1-deficient mice. Furthermore, inhibition of oxidative stress using Trolox prevents the slow-to-fast type fiber transition and improves mitochondrial respiration in skeletal muscle of Tak1-deficient mice. Overall, our results demonstrate that TAK1 maintains skeletal muscle mass and health through redox homeostasis.