Disuse-Induced Muscle Fatigue: Facts and Assumptions.

Skeletal muscle unloading occurs during a wide range of conditions, from space flight to bed rest. The unloaded muscle undergoes negative functional changes, which include increased fatigue. The mechanisms of unloading-induced fatigue are far from complete understanding and cannot be explained by muscle atrophy only. In this review, we summarize the data concerning unloading-induced fatigue in different muscles and different unloading models and provide several potential mechanisms of unloading-induced fatigue based on recent experimental data. The unloading-induced changes leading to increased fatigue include both neurobiological and intramuscular processes. The development of intramuscular fatigue seems to be mainly contributed by the transformation of soleus muscle fibers from a fatigue-resistant, "oxidative" "slow" phenotype to a "fast" "glycolytic" one. This process includes slow-to-fast fiber-type shift and mitochondrial density decline, as well as the disruption of activating signaling interconnections between slow-type myosin expression and mitochondrial biogenesis. A vast pool of relevant literature suggests that these events are triggered by the inactivation of muscle fibers in the early stages of muscle unloading, leading to the accumulation of high-energy phosphates and calcium ions in the myoplasm, as well as NO decrease. Disturbance of these secondary messengers leads to structural changes in muscles that, in turn, cause increased fatigue.

Comparison of Muscle Regeneration Effects at Different Melittin Concentrations in Rabbit Atrophied Muscle.

This research aimed to explore the healing impacts of Melittin treatment on gastrocnemius muscle wasting caused by immobilization with a cast in rabbits. Twenty-four rabbits were randomly allocated to four groups. The procedures included different injections: 0.2 mL of normal saline to Group 1 (G1-NS); 4 µg/kg of Melittin to Group 2 (G2-4 µg/kg Melittin); 20 µg/kg of Melittin to Group 3 (G3-20 µg/kg Melittin); and 100 µg/kg of Melittin to Group 4 (G4-100 µg/kg Melittin). Ultrasound was used to guide the injections into the rabbits' atrophied calf muscles following two weeks of immobilization via casting. Clinical measurements, including the length of the calf, the compound muscle action potential (CMAP) of the tibial nerve, and the gastrocnemius muscle thickness, were assessed. Additionally, cross-sectional slices of gastrocnemius muscle fibers were examined, and immunohistochemistry and Western blot analyses were performed following two weeks of therapy. The mean regenerative changes, as indicated by clinical parameters, in Group 4 were significantly more pronounced than in the other groups (p < 0.05). Furthermore, the cross-sectional area of the gastrocnemius muscle fibers and immunohistochemical indicators in Group 4 exceeded those in the remaining groups (p < 0.05). Western blot analysis also showed a more significant presence of anti-inflammatory and angiogenic cytokines in Group 4 compared to the others (p < 0.05). Melittin therapy at a higher dosage can more efficiently activate regeneration in atrophied gastrocnemius muscle compared to lower doses of Melittin or normal saline.

Protective role of pretreatment with Anisodamine against sepsis-induced diaphragm atrophy via inhibiting JAK2/STAT3 pathway.

There is an increasing tendency for sepsis patients to suffer from diaphragm atrophy as well as mortality. Therefore, reducing diaphragm atrophy could benefit sepsis patients' prognoses. Studies have shown that Anisodamine (Anis) can exert antioxidant effects when blows occur. However, the role of Anisodamine in diaphragm atrophy in sepsis patients has not been reported. Therefore, this study investigated the antioxidant effect of Anisodamine in sepsis-induced diaphragm atrophy and its mechanism. We used cecal ligation aspiration (CLP) to establish a mouse septic mode and stimulated the C2C12 myotube model with lipopolysaccharide (LPS). After treatment with Anisodamine, we measured the mice's bodyweight, diaphragm weight, fiber cross-sectional area and the diameter of C2C12 myotubes. The malondialdehyde (MDA) levels in the diaphragm were detected using the oxidative stress kit. The expression of MuRF1, Atrogin1 and JAK2/STAT3 signaling pathway components in the diaphragm and C2C12 myotubes was measured by RT-qPCR and Western blot. The mean fluorescence intensity of ROS in C2C12 myotubes was measured by flow cytometry. Meanwhile, we also measured the levels of Drp1 and Cytochrome C (Cyt-C) in vivo and in vitro by Western blot. Our study revealed that Anisodamine alleviated the reduction in diaphragmatic mass and the loss of diaphragmatic fiber cross-sectional area and attenuated the atrophy of the C2C12 myotubes by inhibiting the expression of E3 ubiquitin ligases. In addition, we observed that Anisodamine inhibited the JAK2/STAT3 signaling pathway and protects mitochondrial function. In conclusion, Anisodamine alleviates sepsis-induced diaphragm atrophy, and the mechanism may be related to inhibiting the JAK2/STAT3 signaling pathway.

Caffeic acid alleviates skeletal muscle atrophy in 5/6 nephrectomy rats through the TLR4/MYD88/NF-kB pathway.

Skeletal muscle atrophy is a common complication of chronic kidney disease (CKD) that affects the quality of life and prognosis of patients. We aimed to investigate the effects and mechanisms of caffeic acid (CA), a natural phenolic compound, on skeletal muscle atrophy in CKD rats. Male Sprague-Dawley rats underwent 5/6 nephrectomy (NPM) and were treated with CA (20, 40, or 80 mg/kg/day) for 10 weeks. The body and muscle weights, renal function, hemoglobin, and albumin were measured. The histological, molecular, and biochemical changes in skeletal muscles were evaluated using hematoxylin-eosin staining, quantitative real-time PCR, malondialdehyde/catalase/superoxide dismutase/glutathione level detection, and enzyme-linked immunosorbent assay. Western blotting and network pharmacology were applied to identify the potential targets and pathways of CA, CKD, and muscle atrophy. The results showed that CA significantly improved NPM-induced muscle-catabolic effects, reduced the expression of muscle atrophy-related proteins (muscle atrophy F-box and muscle RING finger 1) and proinflammatory cytokines (interleukin [IL]-6, tumor necrosis factor-alpha, and IL-1ß), and attenuated muscle oxidative stress. Network pharmacology revealed that CA modulated the response to oxidative stress and nuclear factor kappa B (NF-κB) signaling pathway and that Toll-like receptor 4 (TLR4) was a key target. In vivo experiment confirmed that CA inhibited the TLR4/myeloid differentiation primary response 88 (MYD88)/NF-kB signaling pathway, reduced muscle iron levels, and restored glutathione peroxidase 4 activity, thereby alleviating ferroptosis and inflammation in skeletal muscles. Thus, CA might be a promising therapeutic agent for preventing and treating skeletal muscle atrophy in CKD by modulating the TLR4/MYD88/NF-κB pathway and ferroptosis.

The crosstalk between macrophages and cancer cells potentiates pancreatic cancer cachexia.

With limited treatment options, cachexia remains a major challenge for patients with cancer. Characterizing the interplay between tumor cells and the immune microenvironment may help identify potential therapeutic targets for cancer cachexia. Herein, we investigate the critical role of macrophages in potentiating pancreatic cancer induced muscle wasting via promoting TWEAK (TNF-like weak inducer of apoptosis) secretion from the tumor. Specifically, depletion of macrophages reverses muscle degradation induced by tumor cells. Macrophages induce non-autonomous secretion of TWEAK through CCL5/TRAF6/NF-κB pathway. TWEAK promotes muscle atrophy by activating MuRF1 initiated muscle remodeling. Notably, tumor cells recruit and reprogram macrophages via the CCL2/CCR2 axis and disrupting the interplay between macrophages and tumor cells attenuates muscle wasting. Collectively, this study identifies a feedforward loop between pancreatic cancer cells and macrophages, underlying the non-autonomous activation of TWEAK secretion from tumor cells thereby providing promising therapeutic targets for pancreatic cancer cachexia.

Taurine Rescues Cancer-induced Atrophy in Human Skeletal Muscle Cells via Ameliorating the Inflammatory Tumor Microenvironment.

BACKGROUND/AIM: Cancer cachexia is a wasting syndrome that has a devastating impact on the prognosis of patients with cancer. It is well-documented that pro-inflammatory cytokines are involved in the progression of this disorder. Therefore, this study was conducted to investigate the protective effect of taurine, an essential nonprotein amino acid with great anti-inflammatory properties, in attenuating muscle atrophy induced by cancer. MATERIALS AND METHODS: Conditioned media (CM) derived from T24 human bladder carcinoma cells with or without 5 mM taurine were incubated with human skeletal muscle cells (HSkMCs) and their differentiation was examined. The intracellular reactive oxygen species (ROS), morphology, and the catabolic pathway were monitored. RESULTS: T24-derived CM with high levels of TNF-α and IL-6 caused aberrant ROS accumulation and formation of atrophic myotubes by HSkMCs. In T24 cancer cells, taurine significantly inhibited the production of TNF-α and IL-6. In HSkMCs, taurine increased ROS clearance during differentiation and preserved the myotube differentiation ability impaired by the inflammatory tumor microenvironment. In addition, taurine ameliorated myotube atrophy by regulating the Akt/FoxO1/MuRF1 and MAFbx signaling pathways. CONCLUSION: Taurine rescues cancer-induced atrophy in human skeletal muscle cells by ameliorating the inflammatory tumor microenvironment. Taurine supplementation may be a promising approach for intervening with the progression of cancer cachexia.

Photobiomodulation therapy moderates cancer cachexia-associated muscle wasting through activating PI3K/AKT/FoxO3a pathway.

Cancer cachexia-associated muscle wasting as a multifactorial wasting syndrome, is an important factor affecting the long-term survival rate of tumor patients. Photobiomodulation therapy (PBMT) has emerged as a promising tool to cure and prevent many diseases. However, the effect of PBMT on skeletal muscle atrophy during cancer progression has not been fully demonstrated yet. Here, we found PBMT alleviated the atrophy of myotube diameter induced by cancer cells in vitro, and prevented cancer-associated muscle atrophy in mice bearing tumor. Mechanistically, the alleviation of muscle wasting by PBMT was found to be involved in inhibiting E3 ubiquitin ligases MAFbx and MuRF-1. In addition, transcriptomic analysis using RNA-seq and GSEA revealed that PI3K/AKT pathway might be involved in PBMT-prevented muscle cachexia. Next, we showed the protective effect of PBMT against muscle cachexia was totally blocked by AKT inhibitor in vitro and in vivo. Moreover, PBMT-activated AKT promoted FoxO3a phosphorylation and thus inhibiting the nucleus entry of FoxO3a. Lastly, in cisplatin-treated muscle cachexia model, PBMT had also been shown to ameliorate muscle atrophy through enhancing PI3K/AKT pathway to suppress MAFbx and MuRF-1 expression. These novel findings revealed that PBMT could be a promising therapeutic approach in treating muscle cachexia induced by cancer.

Mechanism of muscle atrophy in a normal-weight rat model of type 2 diabetes established by using a soft-pellet diet.

Dietary factors such as food texture affect feeding behavior and energy metabolism, potentially causing obesity and type 2 diabetes. We previously found that rats fed soft pellets (SPs) were neither hyperphagic nor overweight but demonstrated glucose intolerance, insulin resistance, and hyperplasia of pancreatic ß-cells. In the present study, we investigated the mechanism of muscle atrophy in rats that had been fed SPs on a 3-h time-restricted feeding schedule for 24 weeks. As expected, the SP rats were normal weight; however, they developed insulin resistance, glucose intolerance, and fat accumulation. In addition, skeletal muscles of SP rats were histologically atrophic and demonstrated disrupted insulin signaling. Furthermore, we learned that the muscle atrophy of the SP rats developed via the IL-6-STAT3-SOCS3 and ubiquitin-proteasome pathways. Our data show that the dietary habit of consuming soft foods can lead to not only glucose intolerance or insulin resistance but also muscle atrophy.

IL-33-ST2 signaling in fibro-adipogenic progenitors alleviates immobilization-induced muscle atrophy in mice.

BACKGROUND: The regenerative and adaptive capacity of skeletal muscles reduces with age, leading to severe disability and frailty in the elderly. Therefore, development of effective therapeutic interventions for muscle wasting is important both medically and socioeconomically. In the present study, we aimed to elucidate the potential contribution of fibro-adipogenic progenitors (FAPs), which are mesenchymal stem cells in skeletal muscles, to immobilization-induced muscle atrophy. METHODS: Young (2-3 months), adult (12-14 months), and aged (20-22 months) mice were used for analysis. Muscle atrophy was induced by immobilizing the hind limbs with a steel wire. FAPs were isolated from the hind limbs on days 0, 3, and 14 after immobilization for transcriptome analysis. The expression of ST2 and IL-33 in FAPs was evaluated by flow cytometry and immunostaining, respectively. To examine the role of IL-33-ST2 signaling in vivo, we intraperitoneally administered recombinant IL-33 or soluble ST2 (sST2) twice a week throughout the 2-week immobilization period. After 2-week immobilization, the tibialis anterior muscles were harvested and the cross-sectional area of muscle fibers was evaluated. RESULTS: The number of FAPs increased with the progression of muscle atrophy after immobilization in all age-groups. Transcriptome analysis of FAPs collected before and after immobilization revealed that Il33 and Il1rl1 transcripts, which encode the IL-33 receptor ST2, were transiently induced in young mice and, to a lesser extent, in aged mice. The number of FAPs positive for ST2 increased after immobilization in young mice. The number of ST2-positive FAPs also increased after immobilization in aged mice, but the difference from the baseline was not statistically significant. Immunostaining for IL-33 in the muscle sections revealed a significant increase in the number of FAPs expressing IL-33 after immobilization. Administration of recombinant IL-33 suppressed immobilization-induced muscle atrophy in aged mice but not in young mice. CONCLUSIONS: Our data reveal a previously unknown protective role of IL-33-ST2 signaling against immobilization-induced muscle atrophy in FAPs and suggest that IL-33-ST2 signaling is a potential new therapeutic target for alleviating disuse muscle atrophy, particularly in older adults.

Targeting Molecular Mechanisms of Obesity- and Type 2 Diabetes Mellitus-Induced Skeletal Muscle Atrophy with Nerve Growth Factor.

Skeletal muscle plays a critical role in metabolic diseases, such as obesity and type 2 diabetes mellitus (T2DM). Muscle atrophy, characterized by a decrease in muscle mass and function, occurs due to an imbalance between the rates of muscle protein synthesis and degradation. This study aimed to investigate the molecular mechanisms that lead to muscle atrophy in obese and T2DM mouse models. Additionally, the effect of nerve growth factor (NGF) on the protein synthesis and degradation pathways was examined. Male mice were divided into three groups: a control group that was fed a standard chow diet, and two experimental groups that were fed a Western diet. After 8 weeks, the diabetic group was injected with streptozotocin to induce T2DM. Each group was then further divided into NGF-treated or non-treated control group. In the gastrocnemius muscles of the Western diet group, increased expressions of myostatin, autophagy markers, and ubiquitin ligases were observed. Skeletal muscle tissue morphology indicated signs of muscle atrophy in both obese and diabetic mice. The NGF-treated group showed a prominent decrease in the protein levels of myostatin and autophagy markers. Furthermore, the NGF-treated group showed an increased Cyclin D1 level. Western diet-induced obesity and T2DM may be linked to muscle atrophy through upregulation of myostatin and subsequent increase in the ubiquitin and autophagy systems. Moreover, NGF treatment may improve muscle protein synthesis and cell cycling.

Combination of Parenteral Amino Acid Infusion and Intermittent Loading Exercise Ameliorates Progression of Postoperative Sarcopenia in Rat Model.

Postoperative sarcopenia is associated with poor outcomes in hospitalized patients. However, few studies have focused on short-term postoperative sarcopenia. Furthermore, the influence of nutritional management using amino acids (AAs) comprising a peripheral parenteral nutrition (PPN) solution and its combination with exercise (Exc) is unclear. Hence, we established a postoperative sarcopenic rat model to evaluate the effects of parenteral AA infusion combined with Exc on skeletal muscles and investigate the underlying mechanisms involved in the amelioration of muscle atrophy. Male F344 rats underwent surgery followed by hindlimb suspension (HS) for 5 days. The rats were divided into AA (-), AA (+), AA (-)-Exc, and AA (+)-Exc groups. They were continuously administered a PPN solution with or without AA at 98 kcal/kg/day. The Exc groups were subjected to intermittent loading for 1 h per day. Postoperative sarcopenic rats exhibited decreased muscle strength and mass and an upregulated ubiquitin-proteasome system, autophagy-lysosome system, and fast-twitch fiber-related genes, especially in the AA (-) group. The AA (+)-Exc group exhibited attenuated decreased muscle strength, increased gastrocnemius mass, and a suppressed upregulation of muscle atrophy- and fast-twitch fiber-related genes. Therefore, parenteral AA infusion combined with Exc may be effective in preventing postoperative sarcopenia in hospitalized patients.

Exosomes in the pathogenesis and treatment of cancer-related cachexia.

Cancer-related cachexia is a metabolic syndrome characterized by weight loss, adipose tissue decomposition, and progressive skeletal muscle atrophy. It is a major complication of many advanced cancers and seriously affects the quality of life and survival of cancer patients. However, the specific molecules that mediate cancer-related cachexia remain elusive, and the fundamental cellular and molecular mechanisms associated with muscle atrophy and lipidolysis in cancer patients still need to be investigated. Exosomes, a newly discovered class of small extracellular vesicles that facilitate intercellular communication, have a significant role in the onset and development of various cancers. Studies have shown that exosomes play a role in the onset and progression of cancer-related cachexia by transporting active molecules such as nucleic acids and proteins. This review aimed to provide an overview of exosome developments in cancer-induced skeletal muscle atrophy and adipose tissue degradation. More importantly, exosomes were shown to have potential as diagnostic markers or therapeutic strategies for cachexia and were prospected, providing novel strategies for the diagnosis and treatment of cancer-related cachexia.

Assessment of fatty infiltration of the hamstring muscles in chronic proximal hamstring ruptures and effect on clinical outcomes after surgical repair: a novel application of the Goutallier classification.

INTRODUCTION: Increased time to surgery has been previously associated with poorer clinical outcomes after surgical treatment of proximal hamstring ruptures, though the etiology remains unclear. The purpose of this study was to evaluate whether degree of muscle atrophy, as assessed using the Goutallier classification system, is associated with worse outcomes following surgical treatment of chronic proximal hamstring ruptures. MATERIALS AND METHODS: This was a retrospective case series of patients who underwent repair of proximal hamstring ruptures from 2012 to 2020 with minimum 2-year follow-up. Patients were included if they underwent primary repair of a proximal hamstring rupture ≥ 6 weeks after the date of injury and had accessible preoperative magnetic resonance imaging (MRI). Exclusion criteria were allograft reconstruction, endoscopic repair, or prior ipsilateral hip surgery. Patients were administered validated surveys: the modified Harris Hip Score (mHHS) and Perth Hamstring Assessment Tool (PHAT). Fatty atrophy on preoperative MRI was independently graded by two musculoskeletal radiologists using the Goutallier classification. Multivariate regression analysis was performed to evaluate associations of preoperative characteristics with muscle atrophy, as well as mHHS and PHAT scores. RESULTS: Complete data sets were obtained for 27 patients. A majority of this cohort was male (63.0%), with a mean age of 51.5 ± 11.8 years and BMI of 26.3 ± 3.8. The mean follow-up time was 62.6 ± 23.1 months, and the mean time from injury-to-surgery was 20.4 ± 15.3 weeks. The Goutallier grading inter-reader weighted kappa coefficient was 0.655. Regression analysis demonstrated that atrophy was not significantly associated with PHAT (p = 0.542) or mHHS (p = 0.574) at latest follow-up. Increased age was significantly predictive of muscle atrophy (ß = 0.62, p = 0.005) and was also found to be a significant predictor of poorer mHHS (ß = - 0.75; p = 0.037). CONCLUSIONS: The degree of atrophy was not found to be an independent predictor of clinical outcomes following repair of chronic proximal hamstring ruptures. Increasing age was significantly predictive of increased atrophy and poorer patient-reported outcomes.

Association between nutritional risk status and both diaphragmatic dysfunction and diaphragm atrophy in medical intensive care unit patients.

Introduction: Aim: critical illness often leads to malnutrition and diaphragmatic dysfunction (DD), common in intensive care units (ICU). Ultrasonography (US) is a potent tool for detecting DD. This study examines the connection between malnutrition risk and DD in ICU patients using ultrasonographic diaphragm measurements in medical ICU patients. Methods: we assessed nutritional risk using risk screening tools and mid-upper arm circumference measurements (MUAC). Diaphragm atrophy (DA) and DD were evaluated by measuring diaphragmatic excursion (DE), thickness, and thickening fraction (TF) by US. We then compared these diaphragmatic measurements in patients based on their nutritional risk scores. Results: of the fifty patients studied, 54 % to 78 % were at risk of malnutrition, 28 % exhibited diaphragm atrophy (DA), and 24 % showed DD upon ICU admission. Malnutrition risk diagnosed by all nutritional risk screening tools was significantly more frequent in patients with DD, while diagnosed by MUAC was considerably higher in patients with DA. A total of 16 patients (32 %) died during their ICU stay, with DD, DA, and malnutrition risks (as identified by the mNUTRIC Score) being more prevalent among non-survivors (p < 0.05). Malnutrition risk (as determined by the mNUTRIC Score) was an independent risk factor for DD [OR (95 % CI): 6.6 (1.3-34), p = 0.03]. Conclusion: malnutrition risk may be significantly associated with DD and DA in medical ICU patients upon ICU admission.

Introducción: Objetivo: las enfermedades graves a menudo conducen a desnutrición y disfunción diafragmática (DD), comunes en las unidades de cuidados intensivos (UCI). La ultrasonografía (US) es una herramienta poderosa para detectar la DD. Este estudio examina la conexión entre riesgo de desnutrición y DD en pacientes de UCI utilizando mediciones ultrasonográficas del diafragma. Métodos: evaluamos el riesgo nutricional utilizando herramientas de evaluación de riesgos y mediciones de la circunferencia del brazo en su punto medio superior (MUAC). La atrofia del diafragma (DA) y la DD se evaluaron midiendo la excursión diafragmática (DE), el grosor y la fracción de engrosamiento (TF) por ecografía. Luego, comparamos estas mediciones diafragmáticas en pacientes según sus puntuaciones de riesgo nutricional. Resultados: de los cincuenta pacientes estudiados, entre el 54 % y el 78 % estaban en riesgo de desnutrición, el 28 % presentaban atrofia del diafragma (DA) y el 24 % mostraban DD al ingreso en la UCI. El riesgo de desnutrición diagnosticado por todas las herramientas de evaluación del riesgo nutricional fue significativamente más frecuente en los pacientes con DD, mientras que el diagnosticado por el MUAC fue considerablemente mayor en los pacientes con DA. Un total de 16 pacientes (32 %) fallecieron durante su estancia en la UCI, siendo la DD, la DA y los riesgos de desnutrición (según lo identificado por la puntuación mNUTRIC) más prevalentes entre los no sobrevivientes (p < 0,05). El riesgo de desnutrición (según lo determinado por la puntuación mNUTRIC) fue un factor de riesgo independiente de la DD [OR (95 % CI): 6,6 (1,3-34), p = 0,03]. Conclusión: en este estudio se encontró una asociación significativa entre el riesgo de desnutrición y la disfunción diafragmática, así como con la atrofia diafragmática al ingreso en la UCI.

Whey Peptide Alleviates Muscle Atrophy by Strongly Regulating Myocyte Differentiation in Mice.

Background and Objectives: Muscle atrophy occurs when protein degradation exceeds protein synthesis, resulting in imbalanced protein homeostasis, compromised muscle contraction, and a reduction in muscle mass. The incidence of muscle atrophy is increasingly recognized as a significant worldwide public health problem. The aim of the current study was to evaluate the effect of whey peptide (WP) on muscle atrophy induced by dexamethasone (DEX) in mice. Materials and Methods: C57BL/6 mice were divided into six groups, each consisting of nine individuals. WPs were orally administered to C57BL/6 mice for 6 weeks. DEX was administered for 5-6 weeks to induce muscle atrophy (intraperitoneal injection, i.p.). Results: Microcomputer tomography (CT) analysis confirmed that WP significantly increased calf muscle volume and surface area in mice with DEX-induced muscle atrophy, as evidenced by tissue staining. Furthermore, it increased the area of muscle fibers and facilitated greater collagen deposition. Moreover, WP significantly decreased the levels of serum biomarkers associated with muscle damage, kidney function, and inflammatory cytokines. WP increased p-mTOR and p-p70S6K levels through the IGF-1/PI3K/Akt pathway, while concurrently decreasing protein catabolism via the FOXO pathway. Furthermore, the expression of proteins associated with myocyte differentiation increased noticeably. Conclusions: These results confirm that WP reduces muscle atrophy by regulating muscle protein homeostasis. Additionally, it is believed that it helps to relieve muscle atrophy by regulating the expression of myocyte differentiation factors. Therefore, we propose that WP plays a significant role in preventing and treating muscle wasting by functioning as a supplement to counteract muscle atrophy.

Celecoxib attenuates hindlimb unloading-induced muscle atrophy via suppressing inflammation, oxidative stress and ER stress by inhibiting STAT3.

Improving inflammation may serve as useful therapeutic interventions for the hindlimb unloading-induced disuse muscle atrophy. Celecoxib is a selective non-steroidal anti-inflammatory drug. We aimed to determine the role and mechanism of celecoxib in hindlimb unloading-induced disuse muscle atrophy. Celecoxib significantly attenuated the decrease in soleus muscle mass, hindlimb muscle function and the shift from slow- to fast-twitch muscle fibers caused by hindlimb unloading in rats. Importantly, celecoxib inhibited the increased expression of inflammatory factors, macrophage infiltration in damaged soleus muscle. Mechanistically, Celecoxib could significantly reduce oxidative stress and endoplasmic reticulum stress in soleus muscle of unloaded rats. Furthermore, celecoxib inhibited muscle proteolysis by reducing the levels of MAFbx, MuRF1, and autophagy related proteins maybe by inhibiting the activation of pro-inflammatory STAT3 pathway in vivo and in vitro. This study is the first to demonstrate that celecoxib can attenuate disuse muscle atrophy caused by hindlimb unloading via suppressing inflammation, oxidative stress and endoplasmic reticulum stress probably, improving target muscle function and reversing the shift of muscle fiber types by inhibiting STAT3 pathways-mediated inflammatory cascade. This study not only enriches the potential molecular regulatory mechanisms, but also provides new potential therapeutic targets for disuse muscle atrophy.

Belt electrode tetanus muscle stimulation reduces denervation-induced atrophy of rat multiple skeletal muscle groups.

Belt electrode-skeletal muscle electrical stimulation (B-SES) involves the use of belt-shaped electrodes to contract multiple muscle groups simultaneously. Twitch contractions have been demonstrated to protect against denervation-induced muscle atrophy in rats, possibly through mitochondrial biosynthesis. This study examined whether inducing tetanus contractions with B-SES suppresses muscle atrophy and identified the underlying molecular mechanisms. We evaluated the effects of acute (60 Hz, 5 min) and chronic (60 Hz, 5 min, every alternate day for one week) B-SES on the tibialis anterior (TA) and gastrocnemius (GAS) muscles in Sprague-Dawley rats using belt electrodes attached to both ankle joints. After acute stimulation, a significant decrease in the glycogen content was observed in the left and right TA and GAS, suggesting that B-SES causes simultaneous contractions in multiple muscle groups. B-SES enhanced p70S6K phosphorylation, an indicator of the mechanistic target of rapamycin complex 1 activity. During chronic stimulations, rats were divided into control (CONT), denervation-induced atrophy (DEN), and DEN + electrically stimulated with B-SES (DEN + ES) groups. After seven days of treatment, the wet weight (n = 8-11 for each group) and muscle fiber cross-sectional area (CSA, n = 6 for each group) of the TA and GAS muscles were reduced in the DEN and DEN + ES groups compared with that in the CON group. The DEN + ES group showed significantly higher muscle weight and CSA than those in the DEN group. Although RNA-seq and pathway analysis suggested that mitochondrial biogenesis is a critical event in this phenomenon, mitochondrial content showed no difference. In contrast, ribosomal RNA 28S and 18S (n = 6) levels in the DEN + ES group were higher than those in the DEN group, even though RNA-seq showed that the ribosome biogenesis pathway was reduced by electrical stimulation. The mRNA levels of the muscle proteolytic molecules atrogin-1 and MuRF1 were significantly higher in DEN than those in CONT. However, they were more suppressed in DEN + ES than those in DEN. In conclusion, tetanic electrical stimulation of both ankles using belt electrodes effectively reduced denervation-induced atrophy in multiple muscle groups. Furthermore, ribosomal biosynthesis plays a vital role in this phenomenon.

Plasma beta-hydroxy-beta-methylbutyrate availability after enteral administration during critical illness after trauma: An exploratory study.

BACKGROUND: During critical illness skeletal muscle wasting occurs rapidly. Although beta-hydroxy-beta-methylbutyrate (HMB) is a potential treatment to attenuate this process, the plasma appearance and muscle concentration is uncertain. METHODS: This was an exploratory study nested within a blinded, parallel group, randomized clinical trial in which critically ill patients after trauma received enteral HMB (3 g daily) or placebo. Plasma samples were collected at 0, 60, and 180 min after study supplement administration on day 1. Needle biopsies of the vastus lateralis muscle were collected (baseline and day 7 of the HMB treatment intervention period). An external standard curve was used to calculate HMB concentrations in plasma and muscle. RESULTS: Data were available for 16 participants (male n = 12 (75%), median [interquartile range] age 50 [29-58] years) who received placebo and 18 participants (male n = 14 (78%), age 49 [34-55] years) who received HMB. Plasma HMB concentrations were similar at baseline but increased after HMB (T = 60 min: placebo 0.60 [0.44-1.31] µM; intervention 51.65 [22.76-64.72] µM). Paired muscle biopsies were collected from 11 participants (placebo n = 7, HMB n = 4). Muscle HMB concentrations were similar at baseline between groups (2.35 [2.17-2.95]; 2.07 [1.78-2.31] µM). For participants in the intervention group who had the repeat biopsy within 4 h of HMB administration, concentrations were greater (7.2 and 12.3 µM) than those who had the repeat biopsy >4 h after HMB (2.7 and 2.1 µM). CONCLUSION: In this exploratory study, enteral HMB administration increased plasma HMB availability. The small sample size limits interpretation of the muscle HMB findings.

IGF-1 Regulates Skeletal Muscle Degradation and Remolding in Ventilator-Induced Diaphragmatic Dysfunction by Mediating FOXO1 Expression.

BACKGROUND: Mechanical ventilation (MV) sustains life in critically ill patients by providing adequate alveolar ventilation. However, prolonged MV could induce inspiratory muscle atrophy known as ventilator-induced diaphragmatic dysfunction (VIDD). Insulin-like growth factor (IGF)-1 has been proven to play crucial roles in regulating skeletal muscle size and function. Meanwhile, the forkhead box protein O1 (FOXO1) has been linked to muscle atrophy. This study aimed to explore the effect of IGF-1 on muscle degradation and remodeling in VIDD and delved into the association of the underlying mechanism involving FOXO1. METHODS: VIDD models were established by treating rats with MV. Adeno-associated virus (AAV) was used for transfection to construct IGF-1 and/or FOXO1 overexpressed rats. There were four groups in this study: normal rats (NC), normal rats with MV treatment (MV), IGF-1-overexpressed rats with MV treatment (MV+IGF-1), and rats overexpressing both IGF-1 and FOXO1 with MV treatment (MV+IGF-1+FOXO1). Protein levels were measured by western blot or enzyme-linked immunosorbent assay (ELISA), and mRNA levels were detected by real-time reverse transcriptase-polymerase chain reaction (RT-qPCR). IGF-1 and FOXO1 expression were validated by detecting mRNA and protein levels. Diaphragmatic muscle contractility and morphometry were tested using stimulating electrodes in conjunction with hematoxylin and eosin (H&E) staining. Interleukin (IL)-6 and carbonylated protein were used for evaluating muscle atrophy and oxidation, respectively. Protein degradation was determined by troponin-I level and tyrosine release. Apoptosis was assessed using the terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate (UTP) nick-end labeling (TUNEL) assay, alongside markers like Bax, B-cell lymphoma 2 (BCL-2), and Cleaved Caspase-3. Atrogin-1, muscle RING finger 1 (MURF1), neuronally expressed developmentally downregulated 4 (NEDD4), muscle ubiquitin ligase of SCF complex in atrophy-1 (MUSA1), and ubiquitinated protein was used to determine proteolysis. Additionally, protein synthesis was measured by assessing the rates of mixed muscle protein (MMP) and myosin heavy chain (MHC). RESULTS: MV treatment caused IGF-1 downregulation (p < 0.01) and FOXO1 upregulation (p < 0.01). The IGF-1 upregulation downregulated FOXO1 in the MV+IGF-1 group (p < 0.001) while IGF-1 and FOXO1 were both upregulated in the MV+IGF-1+FOXO1 group (p < 0.001). The treatment of MV decreased muscle contractility and cross-sectional areas of diaphragm muscle fibers (p < 0.01). Additionally, IL-6, troponin-1, tyrosine release, carbonylated protein, TUNEL positive nuclei, Bax, Cleaved Caspase-3, Atrogin-1, MURF1, neuronally expressed developmentally downregulated 4 (NEDD4), MUSA1, and ubiquitinated protein levels increased significantly in MV group (p < 0.001) while levels of BCL-2, fractional synthetic rate of MMP and MHC, and type I and type II MHC protein mRNA expression decreased in MV group (p < 0.001). All of these alterations were reversed in the MV+IGF-1 group (p < 0.01), while the IGF-1-induced reversion was disrupted in the MV+IGF-1+FOXO1 group (p < 0.01). CONCLUSIONS: IGF-1 may protect diaphragmatic muscles from VIDD-induced structural damage and function loss by downregulating FOXO1. This action suppresses muscle breakdown and facilitates muscle remodeling in diaphragmatic muscles affected by VIDD.

Chronic hypoxia impairs skeletal muscle repair via HIF-2α stabilization.

BACKGROUND: Chronic hypoxia and skeletal muscle atrophy commonly coexist in patients with COPD and CHF, yet the underlying physio-pathological mechanisms remain elusive. Muscle regeneration, driven by muscle stem cells (MuSCs), holds therapeutic potential for mitigating muscle atrophy. This study endeavours to investigate the influence of chronic hypoxia on muscle regeneration, unravel key molecular mechanisms, and explore potential therapeutic interventions. METHODS: Experimental mice were exposed to prolonged normobaric hypoxic air (15% pO2, 1 atm, 2 weeks) to establish a chronic hypoxia model. The impact of chronic hypoxia on body composition, muscle mass, muscle strength, and the expression levels of hypoxia-inducible factors HIF-1α and HIF-2α in MuSC was examined. The influence of chronic hypoxia on muscle regeneration, MuSC proliferation, and the recovery of muscle mass and strength following cardiotoxin-induced injury were assessed. The muscle regeneration capacities under chronic hypoxia were compared between wildtype mice, MuSC-specific HIF-2α knockout mice, and mice treated with HIF-2α inhibitor PT2385, and angiotensin converting enzyme (ACE) inhibitor lisinopril. Transcriptomic analysis was performed to identify hypoxia- and HIF-2α-dependent molecular mechanisms. Statistical significance was determined using analysis of variance (ANOVA) and Mann-Whitney U tests. RESULTS: Chronic hypoxia led to limb muscle atrophy (EDL: 17.7%, P < 0.001; Soleus: 11.5% reduction in weight, P < 0.001) and weakness (10.0% reduction in peak-isometric torque, P < 0.001), along with impaired muscle regeneration characterized by diminished myofibre cross-sectional areas, increased fibrosis (P < 0.001), and incomplete strength recovery (92.3% of pre-injury levels, P < 0.05). HIF-2α stabilization in MuSC under chronic hypoxia hindered MuSC proliferation (26.1% reduction of MuSC at 10 dpi, P < 0.01). HIF-2α ablation in MuSC mitigated the adverse effects of chronic hypoxia on muscle regeneration and MuSC proliferation (30.9% increase in MuSC numbers at 10 dpi, P < 0.01), while HIF-1α ablation did not have the same effect. HIF-2α stabilization under chronic hypoxia led to elevated local ACE, a novel direct target of HIF-2α. Notably, pharmacological interventions with PT2385 or lisinopril enhanced muscle regeneration under chronic hypoxia (PT2385: 81.3% increase, P < 0.001; lisinopril: 34.6% increase in MuSC numbers at 10 dpi, P < 0.05), suggesting their therapeutic potential for alleviating chronic hypoxia-associated muscle atrophy. CONCLUSIONS: Chronic hypoxia detrimentally affects skeletal muscle regeneration by stabilizing HIF-2α in MuSC and thereby diminishing MuSC proliferation. HIF-2α increases local ACE levels in skeletal muscle, contributing to hypoxia-induced regenerative deficits. Administration of HIF-2α or ACE inhibitors may prove beneficial to ameliorate chronic hypoxia-associated muscle atrophy and weakness by improving muscle regeneration under chronic hypoxia.