MicroRNA‑mediated regulation of muscular atrophy: Exploring molecular pathways and therapeutics (Review)

Muscular atrophy, which results in loss of muscle mass and strength, is a significant concern for patients with various diseases. It is crucial to comprehend the molecular mechanisms underlying this condition to devise targeted treatments. MicroRNAs (miRNAs) have emerged as key regulators of gene expression, serving vital roles in numerous cellular processes, including the maintenance of muscle stability. An intricate network of miRNAs finely regulates gene expression, influencing pathways related to muscle protein production, and muscle breakdown and regeneration. Dysregulation of specific miRNAs has been linked to the development of muscular atrophy, affecting important signaling pathways including the protein kinase B/mTOR and ubiquitin‑proteasome systems. The present review summarizes recent work on miRNA patterns associated with muscular atrophy under various physiological and pathological conditions, elucidating its intricate regulatory networks. In conclusion, the present review lays a foundation for the development of novel treatment options for individuals affected by muscular atrophy, and explores other regulatory pathways, such as autophagy and inflammatory signaling, to ensure a comprehensive overview of the multifarious nature of muscular atrophy. The objective of the present review was to elucidate the complex molecular pathways involved in muscular atrophy, and to facilitate the development of innovative and specific therapeutic strategies for the prevention or reversal of muscular atrophy in diverse clinical scenarios.

The role of mitochondrial dynamics and mitophagy in skeletal muscle atrophy: from molecular mechanisms to therapeutic insights

Skeletal muscle is the largest metabolic organ of the human body. Maintaining the best quality control and functional integrity of mitochondria is essential for the health of skeletal muscle. However, mitochondrial dysfunction characterized by mitochondrial dynamic imbalance and mitophagy disruption can lead to varying degrees of muscle atrophy, but the underlying mechanism of action is still unclear. Although mitochondrial dynamics and mitophagy are two different mitochondrial quality control mechanisms, a large amount of evidence has indicated that they are interrelated and mutually regulated. The former maintains the balance of the mitochondrial network, eliminates damaged or aged mitochondria, and enables cells to survive normally. The latter degrades damaged or aged mitochondria through the lysosomal pathway, ensuring cellular functional health and metabolic homeostasis. Skeletal muscle atrophy is considered an urgent global health issue. Understanding and gaining knowledge about muscle atrophy caused by mitochondrial dysfunction, particularly focusing on mitochondrial dynamics and mitochondrial autophagy, can greatly contribute to the prevention and treatment of muscle atrophy. In this review, we critically summarize the recent research progress on mitochondrial dynamics and mitophagy in skeletal muscle atrophy, and expound on the intrinsic molecular mechanism of skeletal muscle atrophy caused by mitochondrial dynamics and mitophagy. Importantly, we emphasize the potential of targeting mitochondrial dynamics and mitophagy as therapeutic strategies for the prevention and treatment of muscle atrophy, including pharmacological treatment and exercise therapy, and summarize effective methods for the treatment of skeletal muscle atrophy.

Satellite Cell-Derived Exosomes: A Novel Approach to Alleviate Skeletal Muscle Atrophy and Fibrosis

Skeletal muscle atrophy coincides with extensive fibrous tissue hyperplasia in muscle-atrophied patients, and fibrous tissue plays a vital role in skeletal muscle function and hinders muscle fiber regeneration. However, effective drugs to manage skeletal muscle atrophy and fibrosis remain elusive. This study isolated and characterized exosomes derived from skeletal muscle satellite cells (MuSC-Exo). The study investigated their effects on denervated skeletal muscle atrophy and fibrosis in Sprague Dawley (SD) rats via intramuscular injection. MuSC-Exo demonstrated the potential to alleviate skeletal muscle atrophy and fibrosis. The underlying mechanism using single-cell RNA sequencing data and functional analysis are analyzed. Mechanistic studies reveal close associations between fibroblasts and myoblasts, with the transforming growth factor β1 (TGF-β1)-Smad3-Pax7 axis governing fibroblast activation in atrophic skeletal muscle. MuSC-Exo intervention inhibited the TGF-β1/Smad3 pathway and improved muscle atrophy and fibrosis. In conclusion, MuSC-Exo-based therapy may represent a novel strategy to alleviate skeletal muscle atrophy and reduce excessive fibrotic tissue by targeting Pax7 through the TGF-β1/Smad3 pathway.

Effects of exercise, metformin, and combination treatments on type 2 diabetic mellitus-induced muscle atrophy in db/db mice: Crosstalk between autophagy and the proteasome

Both exercise and metformin are common effective clinical treatments of type 2 diabetic mellitus. This study investigated the functional role of exercise, metformin, and combination treatment on type 2 diabetic mellitus-induced muscle atrophy. In this experiment, a total of 10 BKS mice were set as the control group. A total of 40 BKS-db/db mice were randomly divided into the control group (db/db); the exercise intervention group (db/db + Ex), which ran on a treadmill at 7-12 m/min, 30-40 min/day, 5 days/week; the metformin administration group (db/db + Met), which was administered 300 mg/kg of metformin solution by gavage daily; and the exercise combined with metformin administration group (db/db + Ex + Met). After 8 weeks of intervention, their tibialis anterior muscles were removed. The levels of insulin signaling pathway proteins, ubiquitin proteasome, and autophagic lysosome-associated proteins were detected using western blot, the expression of MuRF1 and Atrogin-1 was detected using immunohistochemical staining, and the degradation of autophagosomes was detected using double-labeled immunofluorescence. The db/db mice exhibited reduced insulin sensitivity and inhibition of the autophagic-lysosome system, the ubiquitin-proteasome system was activated, and protein degradation was exacerbated, leading to skeletal muscle atrophy. Exercise and metformin and their combined interventions can increase insulin sensitivity, whereas exercise alone showed more effective in inhibiting the ubiquitin-proteasome system, improving autophagy levels, and alleviating skeletal muscle atrophy. Compared with metformin, exercise demonstrated superior improvement of muscle atrophy by promoting the synthesis and degradation of autophagy through the AMPK/ULK1 pathway. However, the combination treatment exhibits no synergistic effect on muscle atrophy.

Electroacupuncture Promotes Skeletal Muscle Myogenic Differentiation and Protein Synthesis by Reducing Let-7c-5p Levels

Objective

Acupuncture with low-frequency electrical stimulation (Acu-LFES) can attenuate muscle atrophy. Previous studies have found that Acu-LFES reduces the let-7 family in serum exosomes. This study explored the effects of let-7c-5p in chronic kidney disease (CKD) muscle atrophy.

Methods

A total of 24 mice were randomly divided into control group, Acu-LFES group, CKD group, and CKD/Acu-LFES group (n = 6/group). The 5/6 nephrectomy was performed to establish the CKD model in mice. After 20 weeks, the Acu-LFES group and CKD/Acu-LFES group were treated with electroacupuncture at the "Zu San Li" and "Yang Ling Quan" bilaterally points for 15 minutes once. Surface sensing of translation (SUnSET), Reverse Transcription-quantitative PCR(RT-qPCR), immunofluorescence staining, and Western blot were performed to examine each group's state of protein production and myogenic differentiation. we knocked down or exogenously expressed let-7c-5p in C2C12 myoblast, RT-qPCR, and Western blot were performed to examine protein synthesis and myogenic differentiation.

Results

The protein expressions of MyoD and Myogenin (MyoG) were decreased in the CKD group (P = .029 and P = .026) concomitant with a decrease in the muscle fiber cross-sectional area. Acu-LFES prevented muscle atrophy in CKD mice. The protein expressions of MyoD and MyoG were increased in the CKD/Acu-LFES group (P = .006 and P = .001). In muscle of CKD mice, IGF1, IGF1R, IRS1, phosphorylated mTOR and P70S6K proteins were decreased compared with control muscle (P = .001, P = .007, P < .001, P < .001 and P < .001), whereas atrogin-1/MAFbx and MuRF1 were dramatically increased (P < .001). Acu-LFES reversed these phenomena, indicating IGF1/mTOR signaling pathway was induced to promote muscle protein synthesis and myogenic differentiation. Meanwhile, Acu-LFES caused a decrease of let-7c-5p in skeletal muscle of CKD mice (P = .034). Inhibiting let-7c-5p promoted C2C12 myogenic differentiation (P = .002 and P = .001) and increased IGF1, IGF1R, IRS1 levels while upregulating mTOR and P70S6K phosphorylation (P < .001, P = .002, P = .009, P < .001 and P = .007). It is interesting to observe that the abundance of atrogin-1/MAFbx and MuRF-1 was unaffected by let-7c-5p (P > .05).

Conclusions

Acu-LFES-reduced expression of let-7c-5p can ameliorate CKD-induced skeletal muscle atrophy by upregulating the IGF1/mTOR signaling pathway, which enhances skeletal muscle protein synthesis and myogenic differentiation. Let-7c-5p may be a potential regulator for the treatment of muscle atrophy.

Effect of ST36 electroacupuncture on the switch of skeletal muscle fibres in mice with sciatic nerve dissociation

Skeletal muscle is striated muscle that moves autonomously and is innervated by peripheral nerves. Peripheral nerve injury is very common in clinical treatment. However, the commonly used treatment methods often focus on the regeneration of the injured nerve but overlook the pathological changes in the injured skeletal muscle. Acupuncture, as the main treatment for denervated skeletal muscle atrophy, is used extensively in clinical practice. In the present study, a mouse model of lower limb sciatic nerve detachment was constructed and treated with electroacupuncture Stomach 36 to observe the atrophy of lower limb skeletal muscle and changes in skeletal muscle fibre types before and after electroacupuncture Stomach 36 treatment. Mice with skeletal muscle denervation showed a decrease in the proportion of IIa muscle fibres and an increase in the proportion of IIb muscle fibres, after electroacupuncture Stomach 36. The changes were reversed by specific activators of p38 MAPK, which increased IIa myofibre ratio. The results suggest that electroacupuncture Stomach 36 can reverse the change of muscle fibre type from IIb to IIa after denervation of skeletal muscle by inhibiting p38 MAPK. The results provide an important theoretical basis for the treatment of clinical peripheral nerve injury diseases with electroacupuncture, in addition to novel insights that could facilitate the study of pathological changes of denervated skeletal muscle.

Deliberation on debilitating condition of cancer cachexia: Skeletal muscle wasting

BACKGROUND

Cancer cachexia is a debilitating syndrome associated with marked body loss because of muscular atrophy and fat loss. There are several mechanisms contributing to the pathogenesis of cachexia. The presence of the tumor releases cytokines from inflammatory and immune cells, which play a significant role in activating and deactivating certain pathways associated with protein, carbohydrate, and lipid metabolism. This review focuses on various cascades involving an imbalance between protein synthesis and degradation in the skeletal muscles.

OBJECTIVES

This study aimed to elucidate the mechanisms involved in skeletal muscle wasting phenomenon over the last few years.

METHODS

This article briefly overviews different pathways responsible for muscle atrophy in cancer cachexia. Studies published up to April 2023 were included. Important findings and study contributions were chosen and compiled using several databases including PubMed, Google Scholar, Science Direct, and ClinicalTrials.gov using relevant keywords.

RESULTS

Cancer cachexia is a complex disease involving multiple factors resulting in atrophy of skeletal muscles. Systemic inflammation, altered energy balance and carbohydrate metabolism, altered lipid and protein metabolism, and adipose tissue browning are some of the major culprits in cancer cachexia. Increased protein degradation and decreased protein synthesis lead to muscle atrophy. Changes in signaling pathway like ubiquitin-proteasome, autophagy, mTOR, AMPK, and IGF-1 also lead to muscle wasting. Physical exercise, nutritional supplementation, steroids, myostatin inhibitors, and interventions targeting on inflammation have been investigated to treat cancer cachexia. Some therapy showed positive results in preclinical and clinical settings, although more research on the efficacy and safety of the treatment should be done.

CONCLUSION

Muscle atrophy in cancer cachexia is the result of multiple complex mechanisms; as a result, a lot more research has been done to describe the pathophysiology of the disease. Targeted therapy and multimodal interventions can improve clinical outcomes for patients.

Impacts of whole-body vibration on denervated skeletal-muscle atrophy in rats

Whole-body vibration has been considered as a countermeasure against muscle atrophy. However, its effects on muscle atrophy are poorly understood. We evaluated the effects of whole-body vibration on denervated skeletal muscle atrophy. Whole-body vibration was performed on rats from Day 15 to 28 after denervation injury. Motor performance was evaluated using an inclined-plane test. Compound muscle action potentials of the tibial nerve were examined. Muscle wet weight and muscle fiber cross-sectional area were measured. Myosin heavy chain isoforms were analyzed in both muscle homogenates and single myofibers. Whole-body vibration resulted in a significantly decreased inclination angle and muscle weight, but not muscle fiber cross-sectional area of fast-twitch gastrocnemius compared to denervation only. In denervated gastrocnemius, a fast-to-slow shift was observed in myosin heavy chain isoform composition following whole-body vibration. There were no significant changes in muscle weight, muscle fiber cross-sectional area, and myosin heavy chain isoform composition in denervated slow-twitch soleus. These results imply that whole-body vibration does not promote recovery of denervation-induced muscle atrophy.

Electrical stimulation mitigates muscle degradation shift in gene expressions during 12-h mechanical ventilation

Ventilator-induced diaphragm dysfunction (VIDD), a dysfunction of the diaphragm muscle caused by prolonged mechanical ventilation (MV), is an important factor that hinders successful weaning from ventilation. We evaluated the effects of electrical stimulation of the diaphragm muscle (pulsed current with off-time intervals) on genetic changes during 12 h of MV (E-V12). Rats were divided into four groups: control, 12-h MV, sham operation, and E-V12 groups. Transcriptome analysis using an RNA microarray revealed that 12-h MV caused upregulation of genes promoting muscle atrophy and downregulation of genes facilitating muscle synthesis, suggesting that 12-h MV is a reasonable method for establishing a VIDD rat model. Of the genes upregulated by 12-h MV, 18 genes were not affected by the sham operation but were downregulated by E-V12. These included genes related to catabolic processes, inflammatory cytokines, and skeletal muscle homeostasis. Of the genes downregulated by 12-h MV, 6 genes were not affected by the sham operation but were upregulated by E-V12. These included genes related to oxygen transport and mitochondrial respiration. These results suggested that 12-h MV shifted gene expression in the diaphragm muscle toward muscle degradation and that electrical stimulation counteracted this shift by suppressing catabolic processes and increasing mitochondrial respiration.

Effects of electroacupuncture at "Jiaji" (EX-B 2) combined with neurodynamic mobilization on gastrocnemius muscle atrophy and expression of NF-κB and MuRF1 in rabbits after sciatic nerve injury

OBJECTIVES

To observe the effects of electroacupuncture (EA) at "Jiaji" (EX-B 2) combined with neurodynamic mobilization (NM) on the cross-sectional area of the gastrocnemius muscle fibers after sciatic nerve injury in rabbits, and the expression of nuclear factor κB (NF-κB) and muscle-specific ring-finger protein 1 (MuRF1).

METHODS

A total of 180 common-grade New Zealand rabbits (half male and half female) were randomly divided into five groups, i.e. a normal control group, a model control group, a NM group, an EA group and a combined intervention group, 36 rabbits in each group. Except in the normal control group, clipping method was used to prepare the model of sciatic nerve injury in the rest groups. On the 3rd day of successful modeling, NM was delivered in the NM group. In the EA group, EA was exerted at bilateral "Jiaji" (EX-B 2) of L4 to L6, stimulated with disperse-dense wave and the frequency of 2 Hz/100 Hz. In the combined intervention group, after EA delivered at bilateral "Jiaji" (EX-B 2) of L4 to L6 , NM was operated. The intervention in each group was delivered once daily, for 6 days a week, and lasted 1, 2 or 4 weeks according to the collection time of sample tissue. After 1, 2 and 4 weeks of intervention, in each group, the toe tension reflex score and the modified Tarlov test score were observed; the morphology of the gastrocnemius muscle was observed by HE staining and the cross-sectional area of muscular fiber was measured; using Western blot method, the expression of NF-κB and MuRF1 of the gastrocnemius muscle was detected.

RESULTS

After 1, 2 and 4 weeks of intervention, the toe tension reflex scores and the modified Tarlov scores in the model control group were lower than those of the normal control group (P<0.05), and these two scores in the NM group, the EA group and the combined intervention group were all higher than those of the model control group (P<0.05); the scores in the combined intervention group were higher than those in the EA group and the NM group (P<0.05). The gastrocnemius fibers were well arranged and the myocyte morphology was normal in the normal control group. In the model control group, the gastrocnemius fibers were disarranged, the myocytes were irregular in morphology and the inflammatory cells were infiltrated in the local. In the NM group, the EA group and the combined intervention group, the muscle fibers were regularly arranged when compared with the model control group. After 1, 2 and 4 weeks of intervention, the cross-sectional areas of the gastrocnemius muscle fibers in the model control group were smaller than those of the normal control group (P<0.05). The cross-sectional areas in the NM group, the EA group and the combined intervention group were larger than those of the model control group (P<0.05), and the cross-sectional areas in the combined intervention group were larger than those in the NM group and the EA group (P<0.05). After intervention for 1, 2 and 4 weeks, the protein expressions of NF-κB and MuRF1 in the gastrocnemius muscle were higher in the model control group in comparison of those in the normal control group (P<0.05). In the NM group, the EA group and the combined intervention group, the expressions of NF-κB after intervention for 1, 2 and 4 weeks and the expressions of MuRF1 after 2 and 4 weeks of intervention were lower when compared with those in the model control group (P<0.05). In the combined intervention group, the protein expressions of NF-κB after intervention for 1, 2 and 4 weeks and the expressions of MuRF1 after 2 and 4 weeks of intervention were decreased when compared with those in the NM group and the EA group (P<0.05).

CONCLUSIONS

Electroacupuncture at "Jiaji" (EX-B 2) combined with NM may increase the muscle strength and sciatic function and alleviate gastrocnemius muscle atrophy in the rabbits with sciatic nerve injury. The underlying mechanism is related to the inhibition of NF-κB and MuRF1 expression.

Skeletal muscle atrophy, regeneration, and dysfunction in heart failure: Impact of exercise training

This review highlights some established and some more contemporary mechanisms responsible for heart failure (HF)-induced skeletal muscle wasting and weakness. We first describe the effects of HF on the relationship between protein synthesis and degradation rates, which determine muscle mass, the involvement of the satellite cells for continual muscle regeneration, and changes in myofiber calcium homeostasis linked to contractile dysfunction. We then highlight key mechanistic effects of both aerobic and resistance exercise training on skeletal muscle in HF and outline its application as a beneficial treatment. Overall, HF causes multiple impairments related to autophagy, anabolic-catabolic signaling, satellite cell proliferation, and calcium homeostasis, which together promote fiber atrophy, contractile dysfunction, and impaired regeneration. Although both wasting and weakness are partly rescued by aerobic and resistance exercise training in HF, the effects of satellite cell dynamics remain poorly explored.

Weight bearing training alleviates muscle atrophy and pyroptosis of middle-aged rats

Background

Age-related muscle atrophy and adipose accumulation begin to occur in young and middle-aged individuals, and exercise at an early age improves body composition. Pyroptosis may play an essential role in age-related low-grade inflammation. This study aimed to explore the alleviation of muscle atrophy by weight-bearing training with increasing age via inhibition of pyroptosis.

Methods

Ninety 8-month-old male SD rats were randomly divided into three groups: (1) normal baseline group (N group, n = 10), sacrificed after adaptive feeding; control group (C group, n = 40); and weight-bearing running group (R group, n = 40). Blood samples, adipose tissue (AT), and extensor digitorum longus (EDL) were collected after 8, 16, 24, and 32-weeks intervention.

Results

The body weight, muscle mass, fat mass, plasma lipid, AT wet weight, adipocyte cross-sectional area (CSA), and apoptosis rates of AT and EDL were increased, while the muscle mass, wet weight, and fiber CSA of EDL were decreased by aging, which were reversed by exercise. Weight-bearing training promoted protein synthesis in EDL, inhibited protein degradation in EDL, and expression of pyroptotic key proteins in EDL and AT in rats.

Conclusion

Weight-bearing training improves body composition and alleviates age-related muscle atrophy in rats, and its mechanism may be related to the inhibition of pyroptosis in the EDL and AT and the improvement of muscle protein metabolism.

Polydeoxyribonucleotide and Shock Wave Therapy Sequence Efficacy in Regenerating Immobilized Rabbit Calf Muscles

This study primarily aimed to investigate the combined effects of polydeoxyribonucleotide (PDRN) and extracorporeal shock wave therapy (ESWT) sequences on the regenerative processes in atrophied animal muscles. Thirty male New Zealand rabbits, aged 12 weeks, were divided into five groups: normal saline (Group 1), PDRN (Group 2), ESWT (Group 3), PDRN injection before ESWT (Group 4), and PDRN injection after ESWT (Group 5). After 2 weeks of cast immobilization, the respective treatments were administered to the atrophied calf muscles. Radial ESWT was performed twice weekly. Calf circumference, tibial nerve compound muscle action potential (CMAP), and gastrocnemius (GCM) muscle thickness after 2 weeks of treatment were evaluated. Histological and immunohistochemical staining, as well as Western blot analysis, were conducted 2 weeks post-treatment. Staining intensity and extent were assessed using semi-quantitative scores. Groups 4 and 5 demonstrated significantly greater calf muscle circumference, GCM muscle thickness, tibial nerve CMAP, and GCM muscle fiber cross-sectional area (type I, type II, and total) than the remaining three groups (p < 0.05), while they did not differ significantly in these parameters. Groups 2 and 3 showed higher values for all the mentioned parameters than Group 1 (p < 0.05). Group 4 had the greatest ratio of vascular endothelial growth factor (VEGF) to platelet endothelial cell adhesion molecule-1 (PECAM-1) in the GCM muscle fibers compared to the other four groups (p < 0.05). Western blot analysis revealed significantly higher expression of angiogenesis cytokines in Groups 4 and 5 than in the other groups (p < 0.05). The combination of ESWT and PDRN injection demonstrated superior regenerative efficacy for atrophied calf muscle tissue in rabbit models compared to these techniques alone or saline. In particular, administering ESWT after PDRN injection yielded the most favorable outcomes in specific parameters.

Mesenchymal stem cells alleviate dexamethasone-induced muscle atrophy in mice and the involvement of ERK1/2 signalling pathway

BACKGROUND

High dosage of dexamethasone (Dex) is an effective treatment for multiple diseases; however, it is often associated with severe side effects including muscle atrophy, resulting in higher risk of falls and poorer life quality of patients. Cell therapy with mesenchymal stem cells (MSCs) holds promise for regenerative medicine. In this study, we aimed to investigate the therapeutic efficacy of systemic administration of adipose-derived mesenchymal stem cells (ADSCs) in mitigating the loss of muscle mass and strength in mouse model of DEX-induced muscle atrophy.

METHODS

3-month-old female C57BL/6 mice were treated with Dex (20 mg/kg body weight, i.p.) for 10 days to induce muscle atrophy, then subjected to intravenous injection of a single dose of ADSCs ([Formula: see text] cells/kg body weight) or vehicle control. The mice were killed 7 days after ADSCs treatment. Body compositions were measured by animal DXA, gastrocnemius muscle was isolated for ex vivo muscle functional test, histological assessment and Western blot, while tibialis anterior muscles were isolated for RNA-sequencing and qPCR. For in vitro study, C2C12 myoblast cells were cultured under myogenic differentiation medium for 5 days following 100 [Formula: see text]M Dex treatment with or without ADSC-conditioned medium for another 4 days. Samples were collected for qPCR analysis and Western blot analysis. Myotube morphology was measured by myosin heavy chain immunofluorescence staining.

RESULTS

ADSC treatment significantly increased body lean mass (10-20%), muscle wet weight (15-30%) and cross-sectional area (CSA) (~ 33%) in DEX-induced muscle atrophy mice model and down-regulated muscle atrophy-associated genes expression (45-65%). Hindlimb grip strength (~ 37%) and forelimb ex vivo muscle contraction property were significantly improved (~ 57%) in the treatment group. Significant increase in type I fibres (~ 77%) was found after ADSC injection. RNA-sequencing results suggested that ERK1/2 signalling pathway might be playing important role underlying the beneficial effect of ADSC treatment, which was confirmed by ERK1/2 inhibitor both in vitro and in vivo.

CONCLUSIONS

ADSCs restore the pathogenesis of Dex-induced muscle atrophy with an increased number of type I fibres, stronger muscle strength, faster recovery rate and more anti-fatigue ability via ERK1/2 signalling pathway. The inhibition of muscle atrophy-associated genes by ADSCs offered this treatment as an intervention option for muscle-associated diseases. Taken together, our findings suggested that adipose-derived mesenchymal stem cell therapy could be a new treatment option for patient with Dex-induced muscle atrophy.

Printed dry electrode for neuromuscular electrical stimulation (NMES) for e-textile

Muscle atrophy is a well-known consequence of immobilization and critical illness, leading to prolonged rehabilitation and increased mortality. In this study, we develop a solution to preserve muscle mass using customized biocompatible neuromuscular electrical stimulation (NMES) device. Commercially available NMES solutions with gel-based electrodes often lead to skin irritation. We demonstrate the printing of conducting electrodes on a compressive stocking textile that can be used for more than seven days without observing any inflammation. This solution consists of a dry and biocompatible electrode directly integrated into the textile with good mechanical compatibility with skin (Young's modulus of 0.39 MPa). The surface roughness of the underlying substrate plays a significant role in obtaining good print quality. Electrochemical Impedance Spectroscopy (EIS) analysis showed that the printed electrode showed better performance than the commercial ones based on a matched interfacial performance and improved series resistance. Furthermore, we investigated our NMES solution in a hospital setting to evaluate its effectiveness on muscle atrophy, with promising results.

Acute effect of electrical stimulation on muscle protein synthesis and break-down in the soleus muscle of hindlimb unloaded rats

Electrical stimulation (ES) is effective for disuse-induced muscle atrophy. However, the acute effect of ES on muscle protein synthesis (MPS) and muscle protein breakdown (MPB) remains unclear. We investigated the effect of a single-session ES treatment on mTORC1 signaling, MPS, and MPB in the soleus muscle of 2-week hindlimb unloaded rats. Sprague Dawley rats (n = 12 male) were randomly divided into control (CON) and hindlimb unloaded (HU) groups. After 2 weeks, the right soleus muscle was percutaneously stimulated and underwent supramaximal isometric contractions. The left soleus muscle served as an internal control. We collected soleus muscle samples 6 h after ES. Two weeks of HU decreased p70S6K and S6rp activation, downstream factors for mTORC1 signaling, and SUnSET method-assessed MPS, but increased the LC3-II/I ratio, an indicator of autophagy. ES on disused muscle successfully activated mTORC1 signaling but did not affect MPS. Contrary, ES decreased ubiquitinated proteins expression and LC3B-II/I ratio. HU might affect mTORC1 activation and MPS differently in response to acute ES possibly due to excessive ROS production caused by ES. Our findings suggest that ES applied to disused skeletal muscles may suppress MPB, but its effect on MPS appears to be attenuated.

Extracellular Vesicles for Muscle Atrophy Treatment

Skeletal muscle atrophy is a progressive chronic disease associated with various conditions, such as aging, cancer, and muscular dystrophy. Interleukin-6 (IL-6) is highly correlated with or plays a crucial role in inducing skeletal muscle atrophy. Extracellular vehicles (EVs), including exosomes, mediate cell-cell communication, and alterations in the genetic material contained in EVs during muscle atrophy may impair muscle cell signaling. Transplantation of muscle progenitor cell-derived EVs (MPC-EVs) is a promising approach for treating muscle diseases such as Duchenne muscular dystrophy (DMD). Moreover, stem cell-derived EVs with modification of microRNAs (e.g., miR-26 and miR-29) have been reported to attenuate muscle atrophy. Unbiased RNA-Seq analysis suggests that MPC-EVs may exert an inhibitory effect on IL-6 pathway. Here, we review the latest advances concerning the mechanisms of stem cell/progenitor cell-derived EVs in alleviating muscle atrophy, including anti-inflammatory and anti-fibrotic effects. We also discuss the clinical application of EVs in the treatment of muscle atrophy.

Integrated Application of Low-Intensity Pulsed Ultrasound in Diagnosis and Treatment of Atrophied Skeletal Muscle Induced in Tail-Suspended Rats

Long-term exposure to microgravity leads to muscle atrophy, which is primarily characterized by a loss of muscle mass and strength and reduces one′s functional capability. A weightlessness-induced muscle atrophy model was established using the tail suspension test to evaluate the intervention or therapeutic effect of low-intensity pulsed ultrasound (LIPUS) on muscle atrophy. The rats were divided into five groups at random: the model group (B), the normal control group (NC), the sham-ultrasound control group (SUC), the LIPUS of 50 mW/cm2 radiation group (50 UR), and the LIPUS of 150 mW/cm2 radiation group (150 UR). Body weight, gastrocnemius weight, muscle force, and B-ultrasound images were used to evaluate muscle atrophy status. Results showed that the body weight, gastrocnemius weight, and image entropy of the tail suspension group were significantly lower than those of the control group (p < 0.01), confirming the presence of muscle atrophy. Although the results show that the muscle force and two weights of the rats stimulated by LIPUS are still much smaller than those of the NC group, they are significantly different from those of the pure tail suspension B group (p < 0.01). On day 14, the gastrocnemius forces of the rats exposed to 50 mW/cm2 and 150 mW/cm2 LIPUS were 150% and 165% of those in the B group. The gastrocnemius weights were both 135% of those in the B group. This suggests that ultrasound can, to a certain extent, prevent muscular atrophy.

Electrical stimulated GLUT4 signalling attenuates critical illness-associated muscle wasting

BACKGROUND

Critical illness myopathy (CIM) is a debilitating condition characterized by the preferential loss of the motor protein myosin. CIM is a by-product of critical care, attributed to impaired recovery, long-term complications, and mortality. CIM pathophysiology is complex, heterogeneous and remains incompletely understood; however, loss of mechanical stimuli contributes to critical illness-associated muscle atrophy and weakness. Passive mechanical loading and electrical stimulation (ES) therapies augment muscle mass and function. While having beneficial outcomes, the mechanistic underpinning of these therapies is less known. Therefore, here we aimed to assess the mechanism by which chronic supramaximal ES ameliorates CIM in a unique experimental rat model of critical care.

METHODS

Rats were subjected to 8 days of critical care conditions entailing deep sedation, controlled mechanical ventilation, and immobilization with and without direct soleus ES. Muscle size and function were assessed at the single cell level. RNAseq and western blotting were employed to understand the mechanisms driving ES muscle outcomes in CIM.

RESULTS

Following 8 days of controlled mechanical ventilation and immobilization, soleus muscle mass, myosin : actin ratio, and single muscle fibre maximum force normalized to cross-sectional area (CSA; specific force) were reduced by 40-50% (P < 0.0001). ES significantly reduced the loss of soleus muscle fibre CSA and myosin : actin ratio by approximately 30% (P < 0.05) yet failed to effect specific force. RNAseq pathway analysis revealed downregulation of insulin signalling in the soleus muscle following critical care, and GLUT4 trafficking was reduced by 55% leading to an 85% reduction of muscle glycogen content (P < 0.01). ES promoted phosphofructokinase and insulin signalling pathways to control levels (P < 0.05), consistent with the maintenance of GLUT4 translocation and glycogen levels. AMPK, but not AKT, signalling pathway was stimulated following ES, where the downstream target TBC1D4 increased 3 logFC (P = 0.029) and AMPK-specific P-TBC1D4 levels were increased approximately two-fold (P = 0.06). Reduction of muscle protein degradation rather than increased synthesis promoted soleus CSA, as ES reduced E3 ubiquitin proteins, Atrogin-1 (P = 0.006) and MuRF1 (P = 0.08) by approximately 50%, downstream of AMPK-FoxO3.

CONCLUSIONS

ES maintained GLUT4 translocation through increased AMPK-TBC1D4 signalling leading to improved muscle glucose homeostasis. Soleus CSA and myosin content was promoted through reduced protein degradation via AMPK-FoxO3 E3 ligases, Atrogin-1 and MuRF1. These results demonstrate chronic supramaximal ES reduces critical care associated muscle wasting, preserved glucose signalling, and reduced muscle protein degradation in CIM.

Secreted Protein Acidic and Rich in Cysteine as an Exercise-Induced Gene: Towards Novel Molecular Therapies for Immobilization-Related Muscle Atrophy in Elderly Patients

Long periods of immobilization, among other etiologies, would result is muscle atrophy. Exercise is the best approach to reverse this atrophy. However, the limited or the non-ability to perform the required physical activity for such patients and the limited pharmacological options make developing novel therapeutic approaches a necessity. Within this context, secreted protein acidic and rich in cysteine (SPARC) has been characterized as an exercise-induced gene. Whereas the knock-out of this gene leads to a phenotype that mimics number of the ageing-induced and sarcopenia-related changes including muscle atrophy, overexpressing SPARC in mice or adding it to muscular cell culture produces similar effects as exercise including enhanced muscle mass, strength and metabolism. Therefore, this piece of writing aims to provide evidence supporting the potential use of SPARC/SPARC as a molecular therapy for muscle atrophy in the context of immobilization especially for elderly patients.

Age-Related Susceptibility to Muscle Damage Following Mechanotherapy in Rats Recovering From Disuse Atrophy

The inability to fully recover lost muscle mass following periods of disuse atrophy predisposes older adults to lost independence and poor quality of life. We have previously shown that mechanotherapy at a moderate load (4.5 N) enhances muscle mass recovery following atrophy in adult, but not older adult rats. We propose that elevated transverse stiffness in aged muscle inhibits the growth response to mechanotherapy and hypothesize that a higher load (7.6 N) will overcome this resistance to mechanical stimuli. F344/BN adult and older adult male rats underwent 14 days of hindlimb suspension, followed by 7 days of recovery with (RE + M) or without (RE) mechanotherapy at 7.6 N on gastrocnemius muscle. The 7.6 N load was determined by measuring transverse passive stiffness and linearly scaling up from 4.5 N. No differences in protein turnover or mean fiber cross-sectional area were observed between RE and RE + M for older adult rats or adult rats at 7.6 N. However, there was a higher number of small muscle fibers present in older adult, but not adult rats, which was explained by a 16-fold increase in the frequency of small fibers expressing embryonic myosin heavy chain. Elevated central nucleation, satellite cell abundance, and dystrophin-/laminin+ fibers were present in older adult rats only following 7.6 N, while 4.5 N did not induce damage at either age. We conclude that age is an important variable when considering load used during mechanotherapy and age-related transverse stiffness may predispose older adults to damage during the recovery period following disuse atrophy.

Preventive effect and possible mechanisms of ultrashort wave diathermy on myogenic contracture in a rabbit model

The purpose of this study was to determine the preventive effect of ultrashort wave diathermy on immobilization-induced myogenic contracture and to explore its underlying mechanisms. Forty-two rabbits were randomly assigned into control (Group C), immobilization (Group I, which was further divided into one week, Group I-1; two weeks, Group I-2; and four weeks, Group I-4, subgroups by the length of immobilization) and ultrashort wave prevention (Group U, which was further divided into one week, Group U-1; two weeks, Group U-2; and four weeks, Group U-4, by time of treatment) groups. Intervention effects were assessed by evaluating rectus femoris cross-sectional area (CSA), knee range of motion, and the protein levels for myogenic differentiation (MyoD) and muscle atrophy F-box (MAFbx-1) in the rectus femoris. Compared with those of Group C, in Groups I and U, total contracture, myogenic contracture, MyoD and MAFbx-1 levels were significantly elevated, and CSA was significantly smaller (p < 0.05). Compared with those of Group I at each time point, MyoD levels were significantly elevated, MAFbx-1 levels were significantly lower, CSA was significantly larger, and myogenic contracture was significantly alleviated in Group U (p < 0.05). In the early stages of contracture, ultrashort wave diathermy reduces muscle atrophy and delays the process of myogenic contracture during joint immobilization; the mechanism of this may be explained as increased expression of MyoD triggered by suppression of the MAFbx-1-mediated ubiquitin-proteasome pathway.

Endoplasmic Reticulum Stress and Autophagy Markers in Soleus Muscle Disuse-Induced Atrophy of Rats Treated with Fish Oil

Endoplasmic reticulum stress (ERS) and autophagy pathways are implicated in disuse muscle atrophy. The effects of high eicosapentaenoic (EPA) or high docosahexaenoic (DHA) fish oils on soleus muscle ERS and autophagy markers were investigated in a rat hindlimb suspension (HS) atrophy model. Adult Wistar male rats received daily by gavage supplementation (0.3 mL per 100 g b.w.) of mineral oil or high EPA or high DHA fish oils (FOs) for two weeks. Afterward, the rats were subjected to HS and the respective treatments concomitantly for an additional two-week period. After four weeks, we evaluated ERS and autophagy markers in the soleus muscle. Results were analyzed using two-way analysis of variance (ANOVA) and Bonferroni post hoc test. Gastrocnemius muscle ω-6/ω-3 fatty acids (FAs) ratio was decreased by both FOs indicating the tissue incorporation of omega-3 fatty acids. HS altered (p < 0.05) the protein content (decreasing total p38 and BiP and increasing p-JNK2/total JNK2 ratio, and caspase 3) and gene expressions (decreasing BiP and increasing IRE1 and PERK) of ERS and autophagy (decreasing Beclin and increasing LC3 and ATG14) markers in soleus. Both FOs attenuated (p < 0.05) the increase in PERK and ATG14 expressions induced by HS. Thus, both FOs could potentially attenuate ERS and autophagy in skeletal muscles undergoing atrophy.

Cancer-Mediated Muscle Cachexia: Etiology and Clinical Management

Muscle cachexia has a major detrimental impact on cancer patients, being responsible for 30% of all cancer deaths. It is characterized by a debilitating loss in muscle mass and function, which ultimately deteriorates patients' quality of life and dampens therapeutic treatment efficacy. Muscle cachexia stems from widespread alterations in whole-body metabolism as well as immunity and neuroendocrine functions and these global defects often culminate in aberrant signaling within skeletal muscle, causing muscle protein breakdown and attendant muscle atrophy. This review summarizes recent landmark discoveries that significantly enhance our understanding of the molecular etiology of cancer-driven muscle cachexia and further discuss emerging therapeutic approaches seeking to simultaneously target those newly discovered mechanisms to efficiently curb this lethal syndrome.

Efficient ssODN-Mediated Targeting by Avoiding Cellular Inhibitory RNAs through Precomplexed CRISPR-Cas9/sgRNA Ribonucleoprotein

Combined with CRISPR-Cas9 technology and single-stranded oligodeoxynucleotides (ssODNs), specific single-nucleotide alterations can be introduced into a targeted genomic locus in induced pluripotent stem cells (iPSCs); however, ssODN knockin frequency is low compared with deletion induction. Although several Cas9 transduction methods have been reported, the biochemical behavior of CRISPR-Cas9 nuclease in mammalian cells is yet to be explored. Here, we investigated intrinsic cellular factors that affect Cas9 cleavage activity in vitro. We found that intracellular RNA, but not DNA or protein fractions, inhibits Cas9 from binding to single guide RNA (sgRNA) and reduces the enzymatic activity. To prevent this, precomplexing Cas9 and sgRNA before delivery into cells can lead to higher genome editing activity compared with Cas9 overexpression approaches. By optimizing electroporation parameters of precomplexed ribonucleoprotein and ssODN, we achieved efficiencies of single-nucleotide correction as high as 70% and loxP insertion up to 40%. Finally, we could replace the HLA-C1 allele with the C2 allele to generate histocompatibility leukocyte antigen custom-edited iPSCs.

Regenerative medicine for skeletal muscle loss: a review of current tissue engineering approaches

Skeletal muscle is capable of regeneration following minor damage, more significant volumetric muscle loss (VML) however results in permanent functional impairment. Current multimodal treatment methodologies yield variable functional recovery, with reconstructive surgical approaches restricted by limited donor tissue and significant donor morbidity. Tissue-engineered skeletal muscle constructs promise the potential to revolutionise the treatment of VML through the regeneration of functional skeletal muscle. Herein, we review the current status of tissue engineering approaches to VML; firstly the design of biocompatible tissue scaffolds, including recent developments with electroconductive materials. Secondly, we review the progenitor cell populations used to seed scaffolds and their relative merits. Thirdly we review in vitro methods of scaffold functional maturation including the use of three-dimensional bioprinting and bioreactors. Finally, we discuss the technical, regulatory and ethical barriers to clinical translation of this technology. Despite significant advances in areas, such as electroactive scaffolds and three-dimensional bioprinting, along with several promising in vivo studies, there remain multiple technical hurdles before translation into clinically impactful therapies can be achieved. Novel strategies for graft vascularisation, and in vitro functional maturation will be of particular importance in order to develop tissue-engineered constructs capable of significant clinical impact.

Monocarboxylate Transporter 8 Deficiency: From Pathophysiological Understanding to Therapy Development

Genetic defects in the thyroid hormone transporter monocarboxylate transporter 8 (MCT8) result in MCT8 deficiency. This disorder is characterized by a combination of severe intellectual and motor disability, caused by decreased cerebral thyroid hormone signalling, and a chronic thyrotoxic state in peripheral tissues, caused by exposure to elevated serum T3 concentrations. In particular, MCT8 plays a crucial role in the transport of thyroid hormone across the blood-brain-barrier. The life expectancy of patients with MCT8 deficiency is strongly impaired. Absence of head control and being underweight at a young age, which are considered proxies of the severity of the neurocognitive and peripheral phenotype, respectively, are associated with higher mortality rate. The thyroid hormone analogue triiodothyroacetic acid is able to effectively and safely ameliorate the peripheral thyrotoxicosis; its effect on the neurocognitive phenotype is currently under investigation. Other possible therapies are at a pre-clinical stage. This review provides an overview of the current understanding of the physiological role of MCT8 and the pathophysiology, key clinical characteristics and developing treatment options for MCT8 deficiency.

In vivo testing of an injectable matrix gel for the treatment of shoulder cuff muscle fatty degeneration

INTRODUCTION

Extracellular matrix (ECM) gels have shown efficacy for the treatment of damaged tissues, most notably cardiac muscle. We hypothesized that the ECM gel prepared from skeletal muscle could be used as a treatment strategy for fatty shoulder cuff muscle degeneration.

METHODS

We conducted experiments to (1) evaluate host biocompatibility to ECM gel injection using a rat model and (2) examine the effect of ECM gel injection on muscle recovery after delayed repair of a released supraspinatus (SSP) tendon using a rabbit model.

RESULTS

The host biocompatibility to the ECM gel was characterized by a transient rise (first 2 weeks only) in several genes associated with macrophage infiltration, matrix deposition, and inflammatory cytokine production. By 8 weeks all genes had returned to baseline levels and no evidence of fibrosis or chronic inflammation was observed from histology. When gel injection was combined with SSP tendon repair, we observed a significant reduction (7%) in SSP muscle atrophy (24 + 3% reduction from uninjured) when compared with treatment with tendon repair only (31 + 7% reduction). Although fatty degeneration was elevated in both treatment groups, fat content trended lower (2%) in response to combined tendon repair and intramuscular ECM injection (4.1 + 2.1%) when compared with tendon repair only (6.1 + 2.9%). Transcriptome analysis revealed adipogenesis and osteoarthritis pathway activation in the repair only group. These key pathways were abrogated in response to treatment using combined repair plus gel.

DISCUSSION

The findings suggest that ECM injection had a modest but positive effect on muscle mass, fatty degeneration, and key cellular signaling pathways.

Cachexia, a Systemic Disease beyond Muscle Atrophy

Cachexia is a complication of dismal prognosis, which often represents the last step of several chronic diseases. For this reason, the comprehension of the molecular drivers of such a condition is crucial for the development of management approaches. Importantly, cachexia is a syndrome affecting various organs, which often results in systemic complications. To date, the majority of the research on cachexia has been focused on skeletal muscle, muscle atrophy being a pivotal cause of weight loss and the major feature associated with the steep reduction in quality of life. Nevertheless, defining the impact of cachexia on other organs is essential to properly comprehend the complexity of such a condition and potentially develop novel therapeutic approaches.

Daily Oral Administration of Protease-Treated Royal Jelly Protects Against Denervation-Induced Skeletal Muscle Atrophy

Honeybees produce royal jelly (RJ) from their cephalic glands. Royal jelly is a source of nutrition for the queen honey bee throughout its lifespan and is also involved in fertility and longevity. Royal jelly has long been considered beneficial to human health. We recently observed that RJ delayed impairment of motor function during aging, affecting muscle fiber size. However, how RJ affects skeletal muscle metabolism and the functional component of RJ is as of yet unidentified. We demonstrate that feeding mice with RJ daily prevents a decrease in myofiber size following denervation without affecting total muscle weight. RJ did not affect atrophy-related genes but stimulated the expression of myogenesis-related genes, including IGF-1 and IGF receptor. Trans-10-hydroxy-2-decenoic acid (10H2DA) and 10-hydroxydecanoic acid (10HDAA), two major fatty acids contained in RJ. After ingestion, 10H2DA and 10HDAA are metabolized into 2-decenedioic acid (2DA) and sebacic acid (SA) respectively. We found that 10H2DA, 10HDAA, 2DA, and SA all regulated myogenesis of C2C12 cells, murine myoblast cells. These novel findings may be useful for potential preventative and therapeutic applications for muscle atrophy disease included in Sarcopenia, an age-related decline in skeletal muscle mass and strength.

[Effects of electroacupuncture combined with passive stretch exercise on disused muscle atrophy and expression of skeletal troponin in mice]

OBJECTIVE

To observe the efficacy of electroacupuncture (EA) plus passive stretch exercise in the treatment of disused atrophy of gastrocnemius and soleus muscles in mice.

METHODS

Fifty C57BL/6 mice were randomly and equally divided into 5 groups: blank control, model, passive stretch exercise (exercise), EA and EA+exercise groups. The muscular atrophy model was established by fixing the gastrocnemius and soleus muscles with plaster immobilization (by putting the right leg into a plastic vial and then twining the vial with medical plaster bandage from the ankle upwards to the thigh and groin to maintain the knee-joint flexion and ankle joint plantar flexion for 7 days). EA (2 Hz/100 Hz, 1 mA)was applied to bilateral "Zusanli"(ST36) for 10 min, once a day for 4 weeks. For mice with the passive exercise, the plastic vial was removed first, followed by pulling out the hindleg to seize the toes to stretch them until the right hindleg is fully extended, then, pushed the leg towards the body. The procedures were repeated once again and again for 10 min. The exercise was conducted once daily, for 4 weeks. The cross-sectional area of fast and slow muscle fibers of the soleus and gastrocnemius was measured under electronic microscope after ATPase histochemical stain and the expression of slow skeletal muscle troponin (TNNI1) and fast skeletal muscle troponin (TNNI2) in the soleus and gastrocnemius was detected by Western blot.

RESULTS

Compared with the blank control group, the cross-sectional areas of the fast and slow muscle fibers of the soleus and gastrocnemius muscles were significantly decreased in the model group (P<0.05, P<0.01). Following the interventions, the cross-sectional areas of the fast and slow muscle fibers of soleus muscle in the EA+exercise group, and those of the fast and slow muscle fibers of the gastrocnemius muscle in the EA and EA+exercise groups, and the expression levels of TNNI1 and TNNI2 proteins in the gastrocnemius muscle of the EA+exercise group were significantly increased in comparison with the model group (P<0.05, P<0.01).

CONCLUSION

EA combined with passive stretch exercise can promote the recovery of the soleus and gastrocnemius muscles in disused muscle atrophy mice, which may be related to its effect in up-regulating the expression of TNNI1 and TNNI2 proteins.

An in vitro study to assess the effect of hyaluronan-based gels on muscle-derived cells: Highlighting a new perspective in regenerative medicine

Hyaluronan (HA) is a nonsulfated glycosaminoglycan that has been widely used for biomedical applications. Here, we have analyzed the effect of HA on the rescue of primary cells under stress as well as its potential to recover muscle atrophy and validated the developed model in vitro using primary muscle cells derived from rats. The potentials of different HAs were elucidated through comparative analyses using pharmaceutical grade a) high (HHA) and b) low molecular weight (LHA) hyaluronans, c) hybrid cooperative complexes (HCC) of HA in three experimental set-ups. The cells were characterized based on the expression of myogenin, a muscle-specific biomarker, and the proliferation was analyzed using Time-Lapse Video Microscopy (TLVM). Cell viability in response to H₂O₂ challenge was evaluated by 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, and the expression of the superoxide dismutase enzyme (SOD-2) was assessed by western blotting. Additionally, in order to establish an in vitro model of atrophy, muscle cells were treated with tumor necrosis factor-alpha (TNF-α), along with hyaluronans. The expression of Atrogin, MuRF-1, nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-kB), and Forkhead-box-(Fox)-O-3 (FoxO3a) was evaluated by western blotting to elucidate the molecular mechanism of atrophy. The results showed that HCC and HHA increased cell proliferation by 1.15 and 2.3 folds in comparison to un-treated cells (control), respectively. Moreover, both pre- and post-treatments of HAs restored the cell viability, and the SOD-2 expression was found to be reduced by 1.5 fold in HA-treated cells as compared to the stressed condition. Specifically in atrophic stressed cells, HCC revealed a noteworthy beneficial effect on the myogenic biomarkers indicating that it could be used as a promising platform for tissue regeneration with specific attention to muscle cell protection against stressful agents.

The clinical relevance and mechanism of skeletal muscle wasting

Skeletal muscle wasting occurs in both chronic and acute diseases. Increasing evidence has shown this debilitating process is associated with short- and long-term outcomes in critical, cancer and surgical patients. Both muscle quantity and quality, as reflected by the area and density of a given range of attenuation in CT scan, impact the patient prognosis. In addition, ultrasound and bioelectrical impedance analysis (BIA) are also widely used in the assessment of body composition due to their bedside viability and no radioactivity. Mechanism researches have revealed complicated pathways are involved in muscle wasting, which include altered IGF1-Akt-FoxO signaling, elevated levels of myostatin and activin A, activation of NF-κB pathway and glucocorticoid effects. Particularly, central nervous system (CNS) has been proven to participate in regulating muscle wasting in various conditions, such as infection and tumor. Several promising therapeutic agents have been under developing in the treatment of muscle atrophy, such as myostatin antagonist, ghrelin analog, non-steroidal selective androgen receptor modulators (SARMs). Notably, nutritional therapy is still the fundamental support in combating muscle wasting. However, the optimizing and tailored nutrition regimen relies on accurate metabolism measurement and large clinical trials in the future. Here, we will discuss the current understanding of muscle wasting and potential treatment in clinical practice.

Pre-innervated tissue-engineered muscle promotes a pro-regenerative microenvironment following volumetric muscle loss

Volumetric muscle loss (VML) is the traumatic or surgical loss of skeletal muscle beyond the inherent regenerative capacity of the body, generally leading to severe functional deficit. Formation of appropriate somato-motor innervations remains one of the biggest challenges for both autologous grafts as well as tissue-engineered muscle constructs. We aim to address this challenge by developing pre-innervated tissue-engineered muscle comprised of long aligned networks of spinal motor neurons and skeletal myocytes on aligned nanofibrous scaffolds. Motor neurons led to enhanced differentiation and maturation of skeletal myocytes in vitro. These pre-innervated tissue-engineered muscle constructs when implanted in a rat VML model significantly increased satellite cell density, neuromuscular junction maintenance, graft revascularization, and muscle volume over three weeks as compared to myocyte-only constructs and nanofiber scaffolds alone. These pro-regenerative effects may enhance functional neuromuscular regeneration following VML, thereby improving the levels of functional recovery following these devastating injuries.

Evaluation on the effect of acupuncture on patients with sepsis-induced myopathy (ACU-SIM pilot study): A single center, propensity-score stratified, assessor-blinded, prospective pragmatic controlled trial

BACKGROUND

Sepsis-induced myopathy (SIM) is a disease that causes motor dysfunction in patients with sepsis. There is currently no targeted treatment for this disease. Acupuncture has shown considerable efficacy in the treatment of sepsis and muscle weakness. Therefore, our research aims to explore the effects of acupuncture on the improvement of muscle structure and function in SIM patients and on activities of daily living.

METHODS

The ACU-SIM pilot study is a single-center, propensity-score stratified, assessor-blinded, prospective pragmatic controlled trial (pCT) with a 1-year follow-up period. This study will be deployed in a multi-professional critical care department at a tertiary teaching hospital in Guangzhou, China. Ninety-eight intensive care unit subjects will be recruited and assigned to either the control group or the acupuncture group. Both groups will receive basic treatment for sepsis, and the acupuncture group will additionally receive acupuncture treatment. The primary outcomes will be the rectus femoris cross-sectional area, the Medical Research Council sum-score and time-to-event (defined as all-cause mortality or unplanned readmission to the intensive care unit due to invasive ventilation). The activities of daily living will be accessed by the motor item of the Functional Independence Measure. Recruitment will last for 2 years, and each patient will have a 1-year follow-up after the intervention.

DISCUSSION

There is currently no research on the therapeutic effects of acupuncture on SIM. The results of this study may contribute to new knowledge regarding early muscle atrophy and the treatment effect of acupuncture in SIM patients, and the results may also direct new approaches and interventions in these patients. This trial will serve as a pilot study for an upcoming multicenter real-world study.

TRIAL REGISTRATION

Chinese Clinical Trials Registry: ChiCTR-1900026308, registered on September 29th, 2019.

CRISPR/Cas9-Mediated miR-29b Editing as a Treatment of Different Types of Muscle Atrophy in Mice

Muscle atrophy is the loss of skeletal muscle mass and strength in response to diverse catabolic stimuli. At present, no effective treatments except exercise have been shown to reduce muscle atrophy clinically. Here, we report that CRISPR/Cas9-mediated genome editing through local injection into gastrocnemius muscles or tibialis anterior muscle efficiently targets the biogenesis processing sites in pre-miR-29b. In vivo, this CRISPR-based treatment prevented the muscle atrophy induced by angiotensin II (AngII), immobilization, and denervation via activation of the AKT-FOXO3A-mTOR signaling pathway and protected against AngII-induced myocyte apoptosis in mice, leading to significantly increased exercise capacity. Our work establishes CRISPR/Cas9-based gene targeting on miRNA as a potential durable therapy for the treatment of muscle atrophy and expands the strategies available interrogating miRNA function in vivo.

An update on nutrient modulation in the management of disease-induced muscle wasting: evidence from human studies

PURPOSE OF REVIEW

Skeletal muscle has many essential roles in maintaining human health, not only being crucial for locomotion, but further as a metabolically important organ. Muscle wasting in disease (cachexia) is highly prevalent, associated with poor clinical outcomes and is not fully reversible with nutritional interventions. Understanding proteostasis in diseased states is of great importance to design novel, effective nutritional/nutraceutical strategies aimed at alleviating muscle wasting. In this review, we will provide an update on muscle kinetics in disease and the effects of nutritional interventions.

RECENT FINDINGS

Whole body and skeletal muscle kinetics are commonly shown to be imbalanced in disease, promoting overall catabolism that underlies the development of cachexia. However, recent advancements in defining the effectiveness of nutritional interventions on muscle anabolism are clouded by heterogenous patient populations and a lack of direct incorporation stable isotope techniques. Current recommendations are focused on combating malnutrition, with increased protein intake (high in EAA) demonstrating promise.

SUMMARY

Recent progress in understanding catabolic states in cachexia across disease is minimal. Further, studies investigating muscle-specific protein turnover along with nutritional interventions are scarce. As such, there is a significant requirement for strong RCT's investigating both acute and chronic nutritional interventions and their impact on skeletal muscle in individual disease states.

The first reported case of Beaulieu-Boycott-Innes syndrome caused by two novel mutations in THOC6 gene in a Chinese infant

RATIONALE

This case report expands the mutation and phenotypic spectra of Beaulieu-Boycott-Innes syndrome (BBIS), and will be valuable for mutation-based pre- and post-natal screening of BBIS when conducting a genetic diagnosis.

PATIENT CONCERNS

A 4-year old boy from Guilin City, Guangxi Zhuang Autonomous Region, China, was referred to our clinic for clarification of his diagnosis because he showed moderate intellectual disability.

DIAGNOSIS

Two novel compound heterozygous mutations of THOC6, c.664T>C (p.Trp222Arg) and c.945+1 G>A were identified in this patient by whole exome sequencing. The two mutations were evaluated as pathogenic and likely pathogenic respectively according to the American College of Medical Genetics guidelines. This is the first case displaying the BBIS phenotype reported in the Chinese population. These two mutations have not been reported previously.

INTERVENTIONS

Symptomatic treatment and rehabilitation training for patients.

OUTCOMES

The genetic cause of the disease was identified. The family received scientific genetic counseling.

LESSONS

BBIS is a rare syndromic autosomal recessive disease with intellectual disability and it is normally difficult for clinicians to recognize it. Whole exome sequencing is an efficient way to identify the gene which causes a particular disease in patients.

Metabolic aspects of muscle wasting during critical illness

PURPOSE OF REVIEW

Skeletal muscle wasting during critical illness is the result of disturbed metabolism. No proven effective interventions targeting skeletal muscle mass and function during critical illness currently exist. This review summarizes recent advances regarding the complexity of metabolic factors involved and the challenge of establishing the clinical effects of metabolic interventions targeting the muscle.

RECENT FINDINGS

Although the catabolic state is limited to the acute phase of critical illness, its subsequent impact on muscle mass and function persists long after ICU discharge. Immobilization, inflammation and disturbed muscle energy and nutrient metabolism are key drivers of muscle protein loss. Current research focuses on the effects of enhanced protein provision, specific substrate delivery and physical exercise. Whilst some interventions have been successful at improving muscle mass, these effects do not always carry over into muscle function or strength.

SUMMARY

Increased understanding of metabolic derangements during critical illness provides new potential targets for treatment. The potential of dietary protein to attenuate the muscle protein catabolic state has yet to be established in clinical trials. Basic research should focus on ways to further improve the anabolic potential of nutrition by unravelling mechanisms that regulate anabolic and catabolic pathways and energy metabolism.

IL-13-driven pulmonary emphysema leads to skeletal muscle dysfunction attenuated by endurance exercise

Patients with chronic obstructive pulmonary disease (COPD) usually develop skeletal muscle dysfunction, which represents a major comorbidity in these patients and is strongly associated with mortality and other poor outcomes. Although clinical data indicates that accelerated protein degradation and metabolic disruption are common associations of muscle dysfunction in COPD, there is very limited data on the mechanisms regulating the process, in part, due to the lack of research performed on a validated animal model of pulmonary emphysema. This model deficiency complicates the translational value of data generated with highly reductionist settings. Here, we use an established transgenic animal model of COPD based on inducible IL-13-driven pulmonary emphysema (IL-13TG) to interrogate the mechanisms of skeletal muscle dysfunction. Skeletal muscles from these emphysematous mice develop most features present in COPD patients, including atrophy, decreased oxygen consumption, and reduced force-generation capacity. Analysis of muscle proteome indicates downregulation of succinate dehydrogenase C (SDH-C), which correlates with reduced enzymatic activity, also consistent with previous clinical observations. Ontology terms identified with human data, such as ATP binding/bioenergetics are also downregulated in this animal's skeletal muscles. Moreover, chronic exercise can partially restore muscle mass, metabolic and force-generation capacity, and SDH activity in COPD mice. We conclude that this animal model of COPD/emphysema is an adequate platform to further investigate mechanisms of muscle dysfunction in this setting and demonstrates multiple approaches that can be used to address specific mechanisms regulating this process.NEW & NOTEWORTHY Skeletal muscle dysfunction is a relevant comorbidity in patients with chronic obstructive pulmonary disease (COPD). Mechanistic research in the area has so far been accomplished with models based on specific exposures to otherwise healthy animals, and no investigation using an established and validated animal model of COPD has been accomplished. We present an animal model of COPD that was previously shown to recapitulate pulmonary functional and histologic features present in patients with COPD, and demonstrates most of the features present in patients with pulmonary emphysema-associated muscle dysfunction, which we proposed as an adequate tool to develop mechanistic research in the area.

Extracellular vesicles from human umbilical cord mesenchymal stem cells improve nerve regeneration after sciatic nerve transection in rats

Peripheral nerve injury results in limited nerve regeneration and severe functional impairment. Mesenchymal stem cells (MSCs) are a remarkable tool for peripheral nerve regeneration. The involvement of human umbilical cord MSC-derived extracellular vesicles (hUCMSC-EVs) in peripheral nerve regeneration, however, remains unknown. In this study, we evaluated functional recovery and nerve regeneration in rats that received hUCMSC-EV treatment after nerve transection. We observed that hUCMSC-EV treatment promoted the recovery of motor function and the regeneration of axons; increased the sciatic functional index; resulted in the generation of numerous axons and of several Schwann cells that surrounded individual axons; and attenuated the atrophy of the gastrocnemius muscle. hUCMSC-EVs aggregated to rat nerve defects, down-regulated interleukin (IL)-6 and IL-1β, up-regulated IL-10 and modulated inflammation in the injured nerve. These effects likely contributed to the promotion of nerve regeneration. Our findings indicate that hUCMSC-EVs can improve functional recovery and nerve regeneration by providing a favourable microenvironment for nerve regeneration. Thus, hUCMSC-EVs have considerable potential for application in the treatment of peripheral nerve injury.

Effects of combined treatment with blood flow restriction and low-intensity electrical stimulation on diabetes mellitus-associated muscle atrophy in rats

BACKGROUND

Diabetes mellitus (DM) results in decreased muscle mass and harmful complications. Blood flow restriction (Bfr) and electrical stimulation (ES) increase muscle protein synthesis. We hypothesized that combined Bfr and low-intensity ES may be more effective in preventing diabetes-associated muscle atrophy by inhibiting the downregulation of protein synthesis-related pathways. In this study, the effects of combined Bfr and low-intensity ES on diabetes-associated muscle atrophy were investigated by evaluating advanced glycation end-products (AGEs) and receptor for AGEs (RAGE) in rats.

METHODS

Twenty-four Goto-Kakizaki (GK) rats were randomly divided into four treatment groups: sedentary DM, DM + Bfr (pressure cuffs placed around the thigh), DM + ES, and DM + Bfr + ES. Six Wistar rats were used as an age-matched control. Levels of AGEs and the expression of RAGE, extracellular signal-regulated kinase (ERK), and ribosomal protein S6 (rpS6) were determined in plantaris muscles.

RESULTS

Diabetes resulted in a loss of muscle mass and upregulation of AGEs and RAGE in the plantaris muscle compared with the control group. Treatment with Bfr and ES alone failed to attenuate diabetes-associated loss of muscle mass, and could not prevent the upregulation of AGEs. However, the combination of Bfr and ES prevented the diabetes-associated decrease in muscle mass and upregulation of AGEs. In addition, the combination treatment prevented diabetes-associated decreases in the expression of phosphorylated rpS6.

CONCLUSIONS

Combination treatment with Bfr and ES may prevent diabetes-associated muscle atrophy by upregulating inhibition of AGEs, which leads to the activation of protein synthesis.

Contraction and nutrition interaction promotes anabolism in cachectic muscle

PURPOSE OF REVIEW

Cachexia is a disease-related multifactorial syndrome characterized by inflammation, massive muscle protein catabolism and carbohydrate and lipid metabolism disorder.Several studies tried to define the impact of either nutrition or physical exercise (single approach strategy) or their combination (multimodal approach strategy) on prevention and/or treatment of muscle wasting in cachectic patients.

RECENT FINDINGS

Single approach strategies (i.e. nutrition or physical exercise) have the potential of preventing and improving features of the cachexia syndrome possibly with a differential impact according to the underlying disease. Limited information is available on the beneficial effect of multimodal approach strategies.

SUMMARY

Multimodal approaches appear to be more effective than those based on single interventions in physiological condition and in cachectic patients with COPD or chronic kidney disease. Further studies, however, are required in cachexia induced by heart failure, cancer and critical illness.

Implications of low muscle mass across the continuum of care: a narrative review

Abnormalities in body composition can occur at any body weight. Low muscle mass is a predictor of poor morbidity and mortality and occurs in several populations. This narrative review provides an overview of the importance of low muscle mass on health outcomes for patients in inpatient, outpatient and long-term care clinical settings. A one-year glimpse at publications that showcases the rapidly growing research of body composition in clinical settings is included. Low muscle mass is associated with outcomes such as higher surgical and post-operative complications, longer length of hospital stay, lower physical function, poorer quality of life and shorter survival. As such, the potential clinical benefits of preventing and reversing this condition are likely to impact patient outcomes and resource utilization/health care costs. Clinically viable tools to measure body composition are needed for routine screening and intervention. Future research studies should elucidate the effectiveness of multimodal interventions to counteract low muscle mass for optimal patient outcomes across the healthcare continuum. Key messages Low muscle mass is associated with several negative outcomes across the healthcare continuum. Techniques to identify and counteract low muscle mass in clinical settings are needed.

Long Noncoding RNA lncMUMA Reverses Established Skeletal Muscle Atrophy following Mechanical Unloading

Reversing established muscle atrophy following mechanical unloading is of great clinical challenge. Long noncoding RNAs (lncRNAs) have been demonstrated to play important roles in myogenesis. Here we identified a lncRNA (mechanical unloading-induced muscle atrophy-related lncRNA [lncMUMA]) enriched in muscle, which was the most downregulated lncRNA during muscle atrophy development in hindlimb suspension (HLS) mice. The in vitro and in vivo data demonstrated that the decreased expression levels of lncMUMA closely associated with a reduction of myogenesis during mechanical unloading. Mechanistically, lncMUMA promoted myogenic differentiation by functioning as a miR-762 sponge to regulate the core myogenic regulator MyoD in vitro. The enforced expression of lncMUMA relieved the decreases in MyoD protein and muscle mass in miR-762 knockin mice. Therapeutically, the enforced expression of lncMUMA improved the in vitro myogenic differentiation of myoblasts under microgravity simulation, prevented the muscle atrophy development, and reversed the established muscle atrophy in HLS mice. These findings identify lncMUMA as an anabolic regulator to reverse established muscle atrophy following mechanical unloading.

Day-Night Oscillation of Atrogin1 and Timing-Dependent Preventive Effect of Weight-Bearing on Muscle Atrophy

BACKGROUND

Atrogin1, which is one of the key genes for the promotion of muscle atrophy, exhibits day-night variation. However, its mechanism and the role of its day-night variation are largely unknown in a muscle atrophic context.

METHODS

The mice were induced a muscle atrophy by hindlimb-unloading (HU). To examine a role of circadian clock, Wild-type (WT) and Clock mutant mice were used. To test the effects of a neuronal effects, an unilateral ablation of sciatic nerve was performed in HU mice. To test a timing-dependent effects of weight-bearing, mice were released from HU for 4 h in a day at early or late active phase (W-EAP and W-LAP groups, respectively).

FINDINGS

We found that the day-night oscillation of Atrogin1 expression was not observed in Clock mutant mice or in the sciatic denervated muscle. In addition, the therapeutic effects of weight-bearing were dependent on its timing with a better effect in the early active phase.

INTERPRETATION

These findings suggest that the circadian clock controls the day-night oscillation of Atrogin1 expression and the therapeutic effects of weight-bearing are dependent on its timing. FUND: Council for Science, Technology, and Innovation, SIP, "Technologies for creating next-generation agriculture, forestry, and fisheries".

Determinants of muscle preservation in individuals with cerebral palsy across the lifespan: a narrative review of the literature

In individuals with cerebral palsy (CP), smaller muscle and atrophy are present at young age. Many people with CP also experience a decline in gross motor function as they age, which might be explained by the loss of muscle mass. The clinical observation of muscle wasting has prompted a comparison with sarcopenia in older adults, and the term accelerated musculoskeletal ageing is often used to describe the hallmark phenotype of CP through the lifespan. However, there has been very little research emphasis on the natural history of ageing with CP and even less with respect to the determinants or prevention of muscle loss with CP. Considering the burgeoning interest in the science of muscle preservation, this paper aims to (i) describe the characteristics of accelerated musculoskeletal ageing in people with CP, (ii) describe the pathophysiology of sarcopenia and parallels with CP, and (iii) discuss possible therapeutic approaches, based on established approaches for sarcopenia.

Chronic Brachial Plexus Neuritis That Developed into Typical Neuralgic Amyotrophy and Positively Responded to Immunotherapy

Based on the hypothesis that autoimmunity plays a role in the pathogenesis of neuralgic amyotrophy (NA), immunotherapy is sometimes administered. Early intervention is recommended for a good prognosis. We herein report the case of a 55-year-old man who presented with neuralgia, weakness, and muscle atrophy in his right shoulder girdle and upper arm, which progressed for ten months following a marine sports accident. The patient was diagnosed with NA. His neurological deficits gradually improved after several courses of immunotherapy, suggesting that in addition to being effective for treating early-stage disease, immunotherapy may be effective for treating chronic cases.

Enhanced skeletal muscle regrowth and remodelling in massaged and contralateral non-massaged hindlimb

KEY POINTS

Muscle fibre cross sectional area is enhanced with massage in the form of cyclic compressive loading during regrowth after atrophy. Massage enhances protein synthesis of the myofibrillar and cytosolic, but not the mitochondrial fraction, in muscle during regrowth. Focal adhesion kinase activation and satellite cell number are elevated in muscles undergoing massage during regrowth. Muscle fibre cross sectional area and protein synthesis of the myofibrillar fraction, but not DNA synthesis, are elevated in muscle of the contralateral non-massaged limb. Massage in the form of cyclic compressive loading is a potential anabolic intervention during muscle regrowth after atrophy.

ABSTRACT

Massage, in the form of cyclic compressive loading (CCL), is associated with multiple health benefits, but its potential anabolic effect on atrophied muscle has not been investigated. We hypothesized that the mechanical activity associated with CCL induces an anabolic effect in skeletal muscle undergoing regrowth after a period of atrophy. Fischer-Brown Norway rats at 10 months of age were hindlimb unloaded for a period of 2 weeks. The rats were then allowed reambulation with CCL applied at a 4.5 N load at 0.5 Hz frequency for 30 min every other day for four bouts during a regrowth period of 8 days. Muscle fibre cross sectional area was enhanced by 18% with massage during regrowth compared to reloading alone, and this was accompanied by elevated myofibrillar and cytosolic protein as well as DNA synthesis. Focal adhesion kinase phosphorylation indicated that CCL increased mechanical stimulation, while a higher number of Pax7+ cells likely explains the elevated DNA synthesis. Surprisingly, the contralateral non-massaged limb exhibited a comparable 17% higher muscle fibre size compared to reloading alone, and myofibrillar protein synthesis, but not DNA synthesis, was also elevated. We conclude that massage in the form of CCL induces an anabolic response in muscles regrowing after an atrophy-inducing event. We suggest that massage can be used as an intervention to aid in the regrowth of muscle lost during immobilization.

The Molecular Mechanisms and Prevention Principles of Muscle Atrophy in Aging

Muscle atrophy in aging is characterized by progressive loss of muscle mass and function. Muscle mass is determined by the balance of synthesis and degradation of protein, which are regulated by several signaling pathways such as ubiquitin-proteasome system, autophagy-lysosome systems, oxidative stress, proinflammatory cytokines, hormones, and so on. Sufficient nutrition can enhance protein synthesis, while exercise can improve the quality of life in the elderly. This chapter will discuss the epidemiology, pathogenesis, as well as the current treatment for aging-induced muscular atrophy.