Forkhead box O3 plays a role in skeletal muscle atrophy through expression of E3 ubiquitin ligases MuRF-1 and atrogin-1 in Cushing's syndrome

Identification of Peucedanum japonicum Thunb. extract components and their protective effects against dexamethasone-induced muscle atrophy

BACKGROUND

Peucedanum japonicum Thunb. (PJ) is a vegetable widely consumed in East Asia and is known to have anticancer and anti-inflammatory effects. However, the effect of PJ on muscle atrophy remains elusive.

PURPOSE

This study aimed to investigate the effect of PJ and its active compound on dexamethasone (DEX)-induced muscle atrophy.

METHODS

We performed qualitative and quantitative analysis of PJ using ultra-performance liquid chromatography-mass spectrometry tandem mass spectrometry (UPLC-MS/MS) and high-performance liquid chromatography (HPLC), respectively. The efficacy of PJ and its main compound 4-caffeoylquinic acid (CQA) on muscle atrophy was evaluated in DEX-induced myotube atrophy and DEX-induced muscle atrophy in mouse myoblasts (C2C12) and C57BL/6 mice, in vitro and in vivo, respectively.

RESULTS

The UPLC-MS/MS and HPLC data showed that the concentration of 4-CQA in PJ was 18.845 mg/g. PJ and 4-CQA treatments significantly inhibited DEX-induced myotube atrophy by decreasing protein synthesis and glucocorticoid translocation to the nucleus in C2C12 myotubes. In addition, PJ enhanced myogenesis by upregulating myogenin and myogenic differentiation 1 in C2C12 cells. PJ supplementation effectively increased muscle function and mass, downregulated atrogenes, and decreased proteasome activity in C57BL/6 mice. Additionally, PJ effectively decreased the nuclear translocation of forkhead transcription factor 3 alpha by inhibiting glucocorticoid receptor.

CONCLUSION

Overall, PJ and its active compound 4-CQA alleviated skeletal muscle atrophy by inhibiting protein degradation. Hence, our findings present PJ as a potential novel pharmaceutical candidate for the treatment of muscle atrophy.

Unlocking the Potential of Obestatin: A Novel Peptide Intervention for Skeletal Muscle Regeneration and Prevention of Atrophy

Obestatin is derived from the same gene as that of ghrelin and their functions were perceived to be antagonistic. Recent developments have shown that although they are known to have contradictory functions, effect of obestatin on skeletal muscle regeneration is similar to that of ghrelin. Obestatin works through a receptor called GPR39, a ghrelin and motilin family receptor and transduces signals in skeletal muscle similar to that of ghrelin. Not only there is a similarity in the receptor family, but also obestatin targets similar proteins and transcription factors as that of ghrelin (for example, FoxO family members) for salvaging skeletal muscle atrophy. Moreover, like ghrelin, obestatin also works by inducing the transcription of Pax7 which is required for muscle stem cell mobilisation. Hence, there are quite some evidences which points to the fact that obestatin can be purposed as a peptide intervention to prevent skeletal muscle wasting and induce myogenesis. This review elaborates these aspects of obestatin which can be further exploited and addressed to bring obestatin as a clinical intervention towards preventing skeletal muscle atrophy and sarcopenia.

Frontiers in sarcopenia: Advancements in diagnostics, molecular mechanisms, and therapeutic strategies

The onset of sarcopenia is intimately linked with aging, posing significant implications not only for individual patient quality of life but also for the broader societal healthcare framework. Early and accurate identification of sarcopenia and a comprehensive understanding of its mechanistic underpinnings and therapeutic targets paramount to addressing this condition effectively. This review endeavors to present a cohesive overview of recent advancements in sarcopenia research and diagnosis. We initially delve into the contemporary diagnostic criteria, specifically referencing the European Working Group on Sarcopenia in Older People (EWGSOP) 2 and Asian Working Group on Sarcopenia (AWGS) 2019 benchmarks. Additionally, we elucidate comprehensive assessment techniques for muscle strength, quantity, and physical performance, highlighting tools such as grip strength, chair stand test, dual-energy X-ray Absorptiometry (DEXA), bioelectrical impedance analysis (BIA), gait speed, and short physical performance battery (SPPB), while also discussing their inherent advantages and limitations. Such diagnostic advancements pave the way for early identification and unequivocal diagnosis of sarcopenia. Proceeding further, we provide a deep-dive into sarcopenia's pathogenesis, offering a thorough examination of associated signaling pathways like the Myostatin, AMP-activated protein kinase (AMPK), insulin/IGF-1 Signaling (IIS), and the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathways. Each pathway's role in sarcopenia mediation is detailed, underscoring potential therapeutic target avenues. From a mechanistic perspective, the review also underscores the pivotal role of mitochondrial dysfunction in sarcopenia, emphasizing elements such as mitochondrial oxidative overload, mitochondrial biogenesis, and mitophagy, and highlighting their therapeutic significance. At last, we capture recent strides made in sarcopenia treatment, ranging from nutritional and exercise interventions to potential pharmacological and supplementation strategies. In sum, this review meticulously synthesizes the latest scientific developments in sarcopenia, aiming to enhance diagnostic precision in clinical practice and provide comprehensive insights into refined mechanistic targets and innovative therapeutic interventions, ultimately contributing to optimized patient care and advancements in the field.

Gromwell ameliorates glucocorticoid-induced muscle atrophy through the regulation of Akt/mTOR pathway

BACKGROUND

Muscle atrophy is characterized by decreased muscle mass, function, and strength. Synthetic glucocorticoids, including dexamethasone (Dexa), are commonly used to treat autoimmune diseases. However, prolonged exposure of Dexa with high dose exerts severe side effects, including muscle atrophy. The purpose of this study was to investigate whether Gromwell root extract (GW) can prevent Dexa-induced muscle atrophy in C2C12 cells and mice and to characterize the composition of GW to identify bioactive compounds.

METHODS

For in vitro experiments, GW (0.5 and 1 µg/mL) or lithospermic acid (LA, 5 and 10 µM) was added to C2C12 myotubes on day 4 of differentiation and incubated for 24 h, along with 50 µM Dexa. For in vivo experiment, four-week-old male C57BL/6 mice were randomly divided into the four following groups (n = 7/group): Con group, Dexa group, GW0.1 group, and GW0.2 group. Mice were fed experimental diets of AIN-93 M with or without 0.1 or 0.2% GW for 4 weeks. Subsequently, muscle atrophy was induced by administering an intraperitoneal injection of Dexa at a dose of 15 mg/kg/day for 38 days, in conjunction with dietary intake.

RESULTS

In Dexa-induced myotube atrophy, treatment with GW increased myotube diameter, reduced the expression of muscle atrophy markers, and enhanced the expression of myosin heavy chain (MHC) isoforms in C2C12 cells. Supplementation with the GW improved muscle function and performance in mice with Dexa-induced muscle atrophy, evidenced in the grip strength and running tests. The GW group showed increased lean body mass, skeletal muscle mass, size, and myosin heavy chain isoform expression, along with reduced skeletal muscle atrophy markers in Dexa-injected mice. Supplementation with GW increased protein synthesis and decreased protein degradation through the Akt/mammalian target of rapamycin and glucocorticoid receptor/forkhead box O3 signaling pathways, respectively. We identified LA as a potential bioactive component of the GW. LA treatment increased myotube diameter and decreased the expression of muscle atrophy markers in Dexa-induced C2C12 cells.

CONCLUSIONS

These findings underscore the potential of the GW in preventing Dexa-induced skeletal muscle atrophy and highlight the contribution of LA to its effects.

Therapeutic Consequences of Targeting the IGF-1/PI3K/AKT/FOXO3 Axis in Sarcopenia: A Narrative Review

The high prevalence of sarcopenia in an aging population has an underestimated impact on quality of life by increasing the risk of falls and subsequent hospitalization. Unfortunately, the application of the major established key therapeutic-physical activity-is challenging in the immobile and injured sarcopenic patient. Consequently, novel therapeutic directions are needed. The transcription factor Forkhead-Box-Protein O3 (FOXO3) may be an option, as it and its targets have been observed to be more highly expressed in sarcopenic muscle. In such catabolic situations, Foxo3 induces the expression of two muscle specific ubiquitin ligases (Atrogin-1 and Murf-1) via the PI3K/AKT pathway. In this review, we particularly evaluate the potential of Foxo3-targeted gene therapy. Foxo3 knockdown has been shown to lead to increased muscle cross sectional area, through both the AKT-dependent and -independent pathways and the reduced impact on the two major downstream targets Atrogin-1 and Murf-1. Moreover, a Foxo3 reduction suppresses apoptosis, activates satellite cells, and initiates their differentiation into muscle cells. While this indicates a critical role in muscle regeneration, this mechanism might exhaust the stem cell pool, limiting its clinical applicability. As systemic Foxo3 knockdown has also been associated with risks of inflammation and cancer progression, a muscle-specific approach would be necessary. In this review, we summarize the current knowledge on Foxo3 and conceptualize a specific and targeted therapy that may circumvent the drawbacks of systemic Foxo3 knockdown. This approach presumably would limit the side effects and enable an activity-independent positive impact on skeletal muscle.

Targeting Epigenetic Regulators with HDAC and BET Inhibitors to Modulate Muscle Wasting

Epigenetic changes contribute to the profound alteration in the transcriptional program associated with the onset and progression of muscle wasting in several pathological conditions. Although HDACs and their inhibitors have been extensively studied in the field of muscular dystrophies, the potential of epigenetic inhibitors has only been marginally explored in other disorders associated with muscle atrophy, such as in cancer cachexia and sarcopenia. BET inhibitors represent a novel class of recently developed epigenetic drugs that display beneficial effects in a variety of diseases beyond malignancies. Based on the preliminary in vitro and preclinical data, HDACs and BET proteins contribute to the pathogenesis of cancer cachexia and sarcopenia, modulating processes related to skeletal muscle mass maintenance and/or metabolism. Thus, epigenetic drugs targeting HDACs and BET proteins may emerge as promising strategies to reverse the catabolic phenotype associated with cachexia and sarcopenia. Further preclinical studies are warranted to delve deeper into the molecular mechanisms associated with the functions of HDACs and BET proteins in muscle atrophy and to establish whether their epigenetic inhibitors represent a prospective therapeutic avenue to alleviate muscle wasting.

Mitigation of chronic glucotoxicity-mediated skeletal muscle atrophy by arachidonic acid

Toxicity caused by chronic hyperglycemia is a significant factor affecting skeletal muscle myogenesis, resulting in diabetic myopathy. Chronic and persistent hyperglycemia causes activation of the atrophy-related pathways in the skeletal muscles, which eventually results in inflammation and muscle degeneration. To counteract this process, various bioactive compound has been studied for their reversal or hypertrophic effect. In this study, we explored the molecular mechanisms associated with reversing glucotoxicity's effect in C2C12 cells by arachidonic acid (AA). We found a substantial increase in the pro-inflammatory cytokines and ROS production in hyperglycemic conditions, mitigated by AA supplementation. We found that AA supplementation restored protein synthesis that was downregulated under glucotoxicity conditions. AA enhanced myogenesis by suppressing high glucose induced inflammation and ROS production and enhancing protein synthesis. These results imply that AA has cytoprotective actions against hyperglycemia-induced cytotoxicity.

Resistance exercise alleviates dexamethasone-induced muscle atrophy via Sestrin2/MSTN pathway in C57BL/6J mice

AIM

It has long been recognized that resistance exercise can substantially increase skeletal muscle mass and strength, but whether it can protect against glucocorticoid-induced muscle atrophy and its potential mechanism is yet to be determined. This study aimed to investigate the protective effects of resistance exercise in dexamethasone-induced muscle atrophy and elucidate the possible function of exercise-induced protein Sestrin2 in this process.

METHODS

Eight-week-old male C57BL/6J mice carried out the incremental mouse ladder exercise for 11 weeks. Two weeks before the end of the intervention, mice were daily intraperitoneally injected with dexamethasone. Body composition, muscle mass, and exercise performance were examined to evaluate muscle atrophy. In vitro, C2C12 cells were used for RT-qPCR, Western Blot, and immunofluorescence experiments to elucidate the potential mechanism.

RESULTS

Our results showed that long-term resistance exercise is an effective intervention for dexamethasone-induced muscle atrophy. We also found that Sestrin2 plays a vital role in dexamethasone-induced muscle atrophy. In both animal (P = .0006) and cell models (P = .0266), dexamethasone intervention significantly reduced the protein expression of Sestrin2, which was increased (P = .0112) by resistance exercise. Inversely, overexpression of Sestrin2 improved (P < .0001) dexamethasone-induced myotube cell atrophy by reducing the activation of the ubiquitin-proteasome pathway via inhibiting Forkhead box O3 (FoxO3a) and myostatin (MSTN)/small mother against decapentaplegic (Smad) signaling pathways.

CONCLUSION

Taken together, our results indicated that Sestrin2 may serve as an effective molecule that mimics the protective effect of resistance exercise on dexamethasone-induced muscle atrophy.

The relationship between temporal muscle thickness and disease activity in Cushing's disease

OBJECTIVE

This study aimed to investigate the relationship between hypercortisolism and temporal muscle thickness (TMT) in Cushing's disease (CD).

METHODS

A retrospective review of medical records was conducted for patients with CD who presented to our clinic between 2012 and 2022. Biochemical data and TMT measurements from sella imaging were evaluated during diagnosis and the first postoperative year.

RESULTS

A total of 44 patients were included in the study, with an average age of 43.9 years, of which 38 were female. The mean TMT at the time of diagnosis was 19.07 ± 1.71 mm, with no significant difference between males and females (p = 0.097), and no correlation between the TMT and age at diagnosis (p = 0.497). There was an inverse relationship between TMT and serum cortisol levels, 24-h UFC, and midnight salivary cortisol at the time of diagnosis of CD (p < 0.05, for all). One year after surgery, TMT significantly increased in all patients compared to baseline (p < 0.001). Furthermore, patients who achieved postoperative remission had significantly higher TMT values compared to those who did not achieve remission (p = 0.043). Among the patients who achieved remission, those who achieved remission through surgery had significantly higher TMT compared to those who could not reach remission with surgery and patients who started medical treatment and achieved biochemical remission (p = 0.01). Patients with severe myopathy and sarcopenia had significantly lower TMT values than the others (p < 0.001).

CONCLUSION

Temporal muscle thickness was found to be associated with disease activity and disease control in Cushing's disease.

Silk Peptide Ameliorates Sarcopenia through the Regulation of Akt/mTOR/FoxO3a Signaling Pathways and the Inhibition of Low-Grade Chronic Inflammation in Aged Mice

As populations around the world age, interest in healthy aging is growing. One of the first physical changes that occurs with aging is the loss of muscle mass and strength, termed sarcopenia. Sarcopenia limits the activity of older people, reduces their quality of life, and increases the likelihood of their developing disease. In the present study, we aimed to evaluate the effects of the ingestion of acid-hydrolyzed silk peptide (SP) on the muscle mass and strength of mice of >22 months of age with naturally occurring sarcopenia, and to identify the mechanisms involved. The daily administration of SP for 8 weeks increased the activation of the Akt/mTOR/FoxO3a signaling pathways and increased the muscle mass and strength of the old mice. In addition, SP inhibited oxidative stress and inflammation in muscle, which are direct causes of sarcopenia. Therefore, SP represents a promising potential treatment for sarcopenia that may improve the healthy lifespan and quality of life of older people.

GABA Prevents Age-Related Sarcopenic Obesity in Mice with High-Fat-Diet-Induced Obesity

Sarcopenic obesity is characterized by concurrent obesity and muscle wasting (sarcopenia) and is common in the elderly. Sarcopenic obesity has steadily increased as the aging population has grown and is an increasing public health burden. Both obesity and sarcopenia independently increase health risks of the elderly, but sarcopenic obesity has a greater effect on metabolic disease than either obesity or sarcopenia alone. The metabolic mechanisms of obesity and sarcopenia are strongly interconnected, and obesity and sarcopenia form a vicious cycle, with each pathology exacerbating the other. The pathogenesis of sarcopenic obesity is more complex than either disease alone and remains incompletely understood, underscoring the significant unmet clinical need for effective sarcopenic obesity treatments. We aimed to determine the efficacy and underlying regulatory mechanisms of Gamma-aminobutyric acid (GABA) in sarcopenic obesity in high-fat-diet-fed obese aged mice and alterations in related mechanisms to determine the potential of GABA as a therapeutic modality for sarcopenic obesity. In this study, we used young (3 months) and aged (20 months) mice to evaluate age-related sarcopenic obesity. The daily administration of GABA for 8 weeks resulted in decreased fat mass and increased muscle mass and strength in aged mice. GABA also enhanced energy expenditure in both adipose tissue and skeletal muscle. In addition, GABA promoted muscle synthesis and decreased muscle degradation by activating the phosphatidylinositol-3-kinase (PI3K)/Akt pathway. These findings demonstrate that GABA has potential uses in preventing age-related sarcopenic obesity and related metabolic diseases.

Hesperidin Ameliorates Sarcopenia through the Regulation of Inflammaging and the AKT/mTOR/FoxO3a Signaling Pathway in 22-26-Month-Old Mice

Faced with a globally aging society, the maintenance of health and quality of life in older people is very important. The age-related loss of muscle mass and strength, known as sarcopenia, severely reduces quality of life and increases the risks of various diseases. In this study, we investigated the inhibitory effect of hesperidin (HES) on inflammaging, with the intention of evaluating its potential use as a treatment for sarcopenia. We studied 22-26-month-old mice, corresponding to humans aged ≥70 years, with aging-related sarcopenia, and young mice aged 3-6 months. The daily administration of HES for 8 weeks resulted in greater muscle mass and strength and increased the fiber size of the old mice. HES also restored the immune homeostasis that had been disrupted by aging, such as the imbalance in M1/M2 macrophage ratio. In addition, we found that HES ameliorated the sarcopenia by regulating AKT/mammalian target of rapamycin/forkhead box 3a signaling through an increase in insulin-like growth factor (IGF)-1 expression in the old mice. Therefore, HES represents a promising candidate inhibitor of sarcopenia in older people, and its effects are achieved through the maintenance of immune homeostasis.

A Phytomolecule Icariin Protects from Sarcopenia Partially by Suppressing Myosin Heavy Chain Degradation in Orchiectomized Rats

Treatments are lacking for sarcopenia, which is an age-related disease characterized by loss of skeletal muscle mass, strength, and/or physical performance. Icariin is a phytomolecule from herbal Epimedium, a traditional Chinese medicine widely used to treat musculoskeletal disorders for thousands of years. Here the effects of icariin against sarcopenia are investigated and the underlying mechanism is elucidated. A classic rat model of bilaterally orchiectomized (ORX) is used to induce sarcopenia. After administration for 8 weeks, compared to the control group, the forelimb grip strength, the specific tetanic forces of the soleus (SOL) and extensor digitorum longus muscle (EDL) are higher, and the fiber cross-sectional areas (CSAs) of the gastrocnemius and tibialis anterior muscle are larger in the icariin group. In addition, icariin promotes mRNA and protein expressions of myosin heavy chain (MyHC) both in SOL and EDL. Mechanistically, icariin significantly suppresses the mRNA and protein expressions of FOXO3a, atrogin-1, and MuRF-1, which are related to the degradation of myosin heavy chain. Collectively, icariin protects from sarcopenia in ORX rats characterized by enhancing grip strength and skeletal muscle contraction, as well as increasing skeletal muscle CSA by inhibiting the ubiquitination degradation of the MyHC in skeletal muscle fibers.

The accumulation of muscle RING finger-1 in regenerating myofibers: Implications for muscle repair in immune-mediated necrotizing myopathy

Background

Muscle RING finger-1 (MuRF-1) plays a key role in the degradation of skeletal muscle proteins. We hypothesize the involvement of MuRF-1 in immune-mediated necrotizing myopathy (IMNM).

Methods

Muscle biopsies from patients with IMNM (n = 37) were analyzed and compared to biopsies from patients with dermatomyositis (DM, n = 13), dysferlinopathy (n = 9) and controls (n = 7) using immunostaining.

Results

MuRF-1 staining could be observed in IMNM, DM and dysferlinopathy biopsies, whereas the percentage of MuRF-1 positive myofibers was significantly higher in IMNM than in dysferlinopathy (p = 0.0448), and positively correlated with muscle weakness and disease activity in IMNM and DM. Surprisingly, MuRF-1 staining predominantly presented in regenerating fibers but not in atrophic fibers. Moreover, MuRF-1-positive fibers tended to be distributed around necrotic myofibers and myofibers with sarcolemma membrane attack complex deposition. Abundant MuRF-1 expression in IMNM and DM was associated with rapid activation of myogenesis after muscle injury, whereas relatively low expression of MuRF-1 in dysferlinopathy may be attributed to damaged muscle regeneration.

Conclusions

MuRF-1 accumulated in regenerating myofibers, which may contribute to muscle injury repair in IMNM and DM. MuRF-1 staining may help clinicians differentiate IMNM and dysferlinopathy.

Exogenous Antioxidants in Remyelination and Skeletal Muscle Recovery

Inflammatory, oxidative, and autoimmune responses cause severe damage to the nervous system inducing loss of myelin layers or demyelination. Even though demyelination is not considered a direct cause of skeletal muscle disease there is extensive damage in skeletal muscles following demyelination and impaired innervation. In vitro and in vivo evidence using exogenous antioxidants in models of demyelination is showing improvements in myelin formation alongside skeletal muscle recovery. For instance, exogenous antioxidants such as EGCG stimulate nerve structure maintenance, activation of glial cells, and reduction of oxidative stress. Consequently, this evidence is also showing structural and functional recovery of impaired skeletal muscles due to demyelination. Exogenous antioxidants mostly target inflammatory pathways and stimulate remyelinating mechanisms that seem to induce skeletal muscle regeneration. Therefore, the aim of this review is to describe recent evidence related to the molecular mechanisms in nerve and skeletal muscle regeneration induced by exogenous antioxidants. This will be relevant to identifying further targets to improve treatments of neuromuscular demyelinating diseases.

Urotensin receptor acts as a novel target for ameliorating fasting-induced skeletal muscle atrophy

Urotensin receptor (UT) is a G-protein-coupled receptor, whose endogenous ligand is urotensin-II (U-II). Skeletal muscle mass is regulated by various conditions, such as nutritional status, exercise, and diseases. Previous studies have pointed out that the urotensinergic system is involved in skeletal muscle metabolism and function, but its mechanism remains unclear, especially given the lack of research on the effect and mechanism of fasting. In this study, UT receptor knockout mice were generated to evaluate whether UT has effects on fasting induced skeletal muscle atrophy. Furthermore, the UT antagonist palosuran (3, 10, 30mg/kg) was intraperitoneally administered daily for 5 days to clarify the therapeutic effect of UT antagonism. Our results found the mice that fasted for 48hours exhibited skeletal muscle atrophy, accompanied by enhanced U-II levels in both skeletal muscles and blood. UT receptor knockout effectively prevented fasting-induced skeletal muscle atrophy. The UT antagonist ameliorated fasting-induced muscle atrophy in mice as determined by increased muscle strengths, weights, and muscle fiber areas (including fast, slow, and mixed types). In addition, the UT antagonist reduced skeletal muscle atrophic markers, including F-box only protein 32 (FBXO32) and tripartite motif containing 63 (TRIM63). Moreover, the UT antagonist was also observed to enhance PI3K/AKT/mTOR while inhibiting autophagy signaling. In summary, our study provides the first evidence that UT antagonism may represent a novel therapeutic approach for the treatment of fasting-induced skeletal muscle atrophy.

Gardeniae Fructus Extract Alleviates Dexamethasone-Induced Muscle Atrophy in Mice

Muscle atrophy (MA) is a case in which protein degeneration occurs excessively due to an imbalance between protein synthesis and breakdown, and is characterized by decreased muscle mass and weakened muscle strength. Despite mounting concern about MA, the number of patients with MA is increasing every year. The aim of the present study was to assess the impact of Gardeniae Fructus (GF) hot water extract on dexamethasone (DEX)-induced MA in mice. C57BL/6N mice were grouped (n = 8) as follows: Normal mice (Normal), MA mice were treated with distilled water (Control), MA mice were treated with GF 100 mg/kg (GF100), MA mice were treated with GF 200 mg/kg (GF200). For 10 days, DEX (25 mg/kg body weight, i.p.) injection was used to induce MA, and GF was administered. GF treatment restored the muscle weight decreased due to MA, and in particular, the weights of EDL+TA and Sol were significantly increased in the GF200 group. Also, it was confirmed that the swimming time was improved in the GF200 group. In addition, the expression of NADPH oxidase related to oxidative stress was significantly reduced, and protective (insulin-like growth factor I/phosphoinositide 3-kinase/protein kinase B pathway) and catabolic (AMP-activated kinase [AMPK]/sirtuin 1 [SIRT1]/proliferator-activated receptor-gamma coactivator-1α (PGC-1α)-forkhead box O (FOXO) pathway) pathways were significantly modulated. These results demonstrate that GF regulates muscle protein synthesis and catabolic pathways, and in particular, it is judged to improve MA by regulating the proteolytic AMPK/SIRT1/PGC-1α-FOXO pathway.

PLOD3 contributes to HER-2 therapy resistance in gastric cancer through FoxO3/Survivin pathway

Human epidermal growth factor receptor 2 (HER-2), a famous therapeutic target for breast cancer, is also associated with an increased risk of recurrence and poor outcomes of other malignancies, including gastric cancer. Yet the mechanism of HER-2 therapy resistance remains controversial due to the heterogeneity of gastric adenocarcinoma. We know, Procollagen-Lysine,2-Oxoglutarate 5-Dioxygenase 3 (PLOD3), a key gene coding enzymes that catalyze the lysyl hydroxylation of extracellular matrix collagen, plays an important contributor to HER-2 targeting agent Trastuzumab resistance in gastric cancer. Herein, we analyzed clinical samples of gastric cancer patients and gastric cancer cell lines and identified PLOD3, unveiled that depletion of PLOD3 leads to decreased cell proliferation, tumor growth and Trastuzumab sensitivity in these Trastuzumab resistant GC cell lines. Clinically, increased PLOD3 expression correlates with decreased Trastuzumab therapy responsiveness in GC patients. Mechanistically, we show that PLOD3 represses tumor suppressor FoxO3 expression, therefore upregulating Survivin protein expression that contributes to Trastuzumab resistance in GC. Therefore, our study identifies a new signaling axis PLOD3-FoxO3- Survivin pathway that may be therapeutically targeted in HER-2 positive gastric cancer.

Network pharmacology-based analysis of the effects of puerarin on sarcopenia

Background

With the acceleration of population aging, sarcopenia will place a heavy burden on families and society. Thus, effective treatments urgently need to be developed to slow down the development of sarcopenia. This study adopted a network pharmacological approach to explore the possible mechanisms of puerarin in treating sarcopenia.

Methods

The potential therapeutic targets of puerarin were obtained from the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP) database, while the targets of sarcopenia were obtained from the GeneCards, DisGeNET, Online Mendelian Inheritance in Man (OMIM), and Therapeutic Target Database (TTD) databases. The protein-protein interaction (PPI) network was generated by BisoGenet, and core targets were identified by a topological analysis. To determine the potential targeting pathways, the core targets were further imported into the Metascape platform for the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. The results were visualized using an online bioinformatics tool.

Results

We identified 53 targets for puerarin and 129 targets for sarcopenia. A total of 206 core targets, which were considered potential therapeutic targets, were identified from the merged PPI network. Further, the GO and KEGG analyses revealed that the functions of the core targets and related pathways were mainly associated with the cell cycle, apoptosis, protein synthesis, and proteolysis.

Conclusions

Puerarin has the potential to treat sarcopenia through the regulation of the cell cycle, apoptosis, and protein homeostasis. Our study has laid a foundation for further studies on drug development and pharmacological experiments in the treatment of sarcopenia.

The Administration of Panax Ginseng Berry Extract Attenuates High-Fat-Diet-Induced Sarcopenic Obesity in C57BL/6 Mice

Sarcopenia and obesity are serious health problems that are highly related to several metabolic diseases. Sarcopenic obesity, a combined state of sarcopenia and obesity, results in higher risks of metabolic diseases and even mortality than sarcopenia or obesity alone. Therefore, the development of therapeutic agents for sarcopenic obesity is crucial. C57BL/6 mice were fed with a high-fat diet (HFD) for 9 weeks. Then, mice were administered with Panax ginseng berry extract (GBE) for an additional 4 weeks, with continuous HFD intake. GBE significantly decreased the food efficiency ratio, serum lipid and insulin levels, adipose tissue weights, and adipocyte size. It significantly increased the grip strength, muscle masses, and myofiber cross-sectional area. It deactivated the protein kinase C (PKC) theta and zeta, resulting in activation of the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway, which is known to regulate muscle synthesis and degradation. Furthermore, it inhibited the production of inflammatory cytokines in the muscle tissue. GBE attenuated both obesity and sarcopenia. Thus, GBE is a potential agent to prevent or treat sarcopenic obesity.

Antioxidant Activity of Valeriana fauriei Protects against Dexamethasone-Induced Muscle Atrophy

Skeletal muscle atrophy is defined as wasting or loss of muscle. Although glucocorticoids (GCs) are well-known anti-inflammatory drugs, their long-term or high-dose use induces skeletal muscle atrophy. Valeriana fauriei (VF) is used to treat restlessness, anxiety, and sleep disorders; however, its effects on skeletal muscle health have not been investigated. This study investigated whether Valeriana fauriei could ameliorate muscle atrophy. We induced muscle atrophy in vitro and in vivo, by treatment with dexamethasone (DEX), a synthetic GC. In DEX-induced myotube atrophy, Valeriana fauriei treatment increased the fusion index and decreased the expression of muscle atrophic genes such as muscle atrophy F-box (MAFbx/Atrogin-1) and muscle RING-finger protein 1 (MuRF1). In DEX-treated mice with muscle atrophy, Valeriana fauriei supplementation increased the ability to exercise, muscle weight, and cross-sectional area, whereas it inhibited myosin heavy chain isoform transition and the expression of muscle atrophy biomarkers. Valeriana fauriei treatment led to via the downregulation of muscle atrophic genes via inhibition of GC receptor translocation. Valeriana fauriei was also found to act as a reactive oxygen species (ROS) scavenger. Didrovaltrate (DI), an iridoid compound from Valeriana fauriei, was found to downregulate atrophic genes and decrease ROS in the DEX-induced myotube atrophy. Consolidated, our results indicate that Valeriana fauriei prevents DEX-induced muscle atrophy by inhibiting GC receptor translocation. Further, Valeriana fauriei acts as a ROS scavenger, and its functional compound is didrovaltrate. We suggest that Valeriana fauriei and its functional compound didrovaltrate possess therapeutic potentials against muscle atrophy.

Identification of a KLF5-dependent program and drug development for skeletal muscle atrophy

Skeletal muscle atrophy is caused by various conditions, including aging, disuse related to a sedentary lifestyle and lack of physical activity, and cachexia. Our insufficient understanding of the molecular mechanism underlying muscle atrophy limits the targets for the development of effective pharmacologic treatments and preventions. Here, we identified Krüppel-like factor 5 (KLF5), a zinc-finger transcription factor, as a key mediator of the early muscle atrophy program. KLF5 was up-regulated in atrophying myotubes as an early response to dexamethasone or simulated microgravity in vitro. Skeletal muscle-selective deletion of Klf5 significantly attenuated muscle atrophy induced by mechanical unloading in mice. Transcriptome- and genome-wide chromatin accessibility analyses revealed that KLF5 regulates atrophy-related programs, including metabolic changes and E3-ubiquitin ligase-mediated proteolysis, in coordination with Foxo1. The synthetic retinoic acid receptor agonist Am80, a KLF5 inhibitor, suppressed both dexamethasone- and microgravity-induced muscle atrophy in vitro and oral Am80 ameliorated disuse- and dexamethasone-induced atrophy in mice. Moreover, in three independent sets of transcriptomic data from human skeletal muscle, KLF5 expression significantly increased with age and the presence of sarcopenia and correlated positively with the expression of the atrophy-related ubiquitin ligase genes FBXO32 and TRIM63 These findings demonstrate that KLF5 is a key transcriptional regulator mediating muscle atrophy and that pharmacological intervention with Am80 is a potentially preventive treatment.

Polyphenols and Their Effects on Muscle Atrophy and Muscle Health

Skeletal muscle atrophy is the decrease in muscle mass and strength caused by reduced protein synthesis/accelerated protein degradation. Various conditions, such as denervation, disuse, aging, chronic diseases, heart disease, obstructive lung disease, diabetes, renal failure, AIDS, sepsis, cancer, and steroidal medications, can cause muscle atrophy. Mechanistically, inflammation, oxidative stress, and mitochondrial dysfunction are among the major contributors to muscle atrophy, by modulating signaling pathways that regulate muscle homeostasis. To prevent muscle catabolism and enhance muscle anabolism, several natural and synthetic compounds have been investigated. Recently, polyphenols (i.e., natural phytochemicals) have received extensive attention regarding their effect on muscle atrophy because of their potent antioxidant and anti-inflammatory properties. Numerous in vitro and in vivo studies have reported polyphenols as strongly effective bioactive molecules that attenuate muscle atrophy and enhance muscle health. This review describes polyphenols as promising bioactive molecules that impede muscle atrophy induced by various proatrophic factors. The effects of each class/subclass of polyphenolic compounds regarding protection against the muscle disorders induced by various pathological/physiological factors are summarized in tabular form and discussed. Although considerable variations in antiatrophic potencies and mechanisms were observed among structurally diverse polyphenolic compounds, they are vital factors to be considered in muscle atrophy prevention strategies.

Markers of muscle atrophy and impact of treatment with pergolide in horses with pituitary pars intermedia dysfunction and muscle atrophy

Pituitary pars intermedia dysfunction (PPID) is a common endocrine disorder of aged horses, with muscle atrophy as one of the clinical signs. We sought to compare muscle mass and regulation of skeletal muscle proteolysis between horses with PPID and muscle atrophy to older horses without PPID, and to assess the impact of treatment with pergolide (dopaminergic agonist) on PPID horses. We hypothesized that PPID-associated muscle atrophy is a result of increased proteolysis, and that markers of muscle atrophy and proteolysis would improve over time with pergolide treatment. Markers of muscle atrophy, adiposity, insulin regulation, skeletal muscle composition, and proteolysis (muscle atrophy F- box/atrogin 1 [MAFbx1], muscle RING finger 1 [MuRF1], Bcl2/adenovirus EIV 19kD interacting protein 3 [Bnip3], and microtubule-associated light chain 3 [LC3]) were compared between PPID and control horses. PPID horses were treated for 12 weeks with either pergolide or placebo. Dose of pergolide was adjusted based upon monthly measurement of adrenocorticotropin, and markers of muscle atrophy, adiposity, insulin regulation, skeletal muscle composition, and proteolysis were compared after 12 weeks of treatment. Horses with PPID exhibited increased transcript abundance of MuRF1 (P= 0.04) compared to control. However, no difference was observed in transcript abundance of markers of proteolysis with treatment (P ≥ 0.25). Pergolide treated horses lost weight (P = 0.02) and improved fasting insulin (P = 0.02), while placebo treated horses gained weight and rump fat thickness (P = 0.02). Findings from this study suggest that treatment with pergolide may promote weight loss and improve insulin regulation in horses with PPID, but does not impact muscle mass or markers of muscle proteolysis.

Cushing Syndrome Associated Myopathy: It Is Time for a Change

Cushing syndrome is the result of excessive levels of glucocorticoids. Endogenous Cushing syndrome is rare with an incidence of two to three cases per million per year. Clinically, the presentation consists of a characteristic phenotype including skin symptoms and metabolic manifestations. A frequent co-morbidity with high impact on quality of life is Cushing syndrome associated myopathy. It characteristically affects the proximal myopathy, impairing stair climbing and straightening up. The pathophysiology is complex and involves protein degradation via the forkhead box O3 (FOXO3) pathway, intramuscular fat accumulation, and inactivity-associated muscle atrophy. Surgical remission of Cushing syndrome is the most important step for recovery of muscle function. Restoration depends on age, co-morbidities and postoperative insulin-like growth factor concentrations. At average, functionality remains impaired during the long-term compared to age and sex matched control persons. Growth hormone therapy in individuals with impaired growth hormone secretion could be an option but has not been proved in a randomized trial.

The effect of repeated bouts of electrical stimulation-induced muscle contractions on proteolytic signaling in rat skeletal muscle

Mechanistic target of rapamycin complex 1 (mTORC1) plays a central role in muscle protein synthesis and repeated bouts of resistance exercise (RE) blunt mTORC1 activation. However, the changes in the proteolytic signaling when recurrent RE bouts attenuate mTORC1 activation are unclear. Using a RE model of electrically stimulated rat skeletal muscle, this study aimed to clarify the effect of repeated RE bouts on acute proteolytic signaling, particularly the calpain, autophagy‐lysosome, and ubiquitin‐proteasome pathway. p70S6K and rpS6 phosphorylation, indicators of mTORC1 activity, were attenuated by repeated RE bouts. Calpain 3 protein was decreased at 6 h post‐RE in all exercised groups regardless of the bout number. Microtubule‐associated protein 1 light chain 3 beta‐II, an indicator of autophagosome formation, was increased at 3 h and repeated RE bouts increased at 6 h, post‐RE. Ubiquitinated proteins were increased following RE, but these increases were independent of the number of RE bouts. These results suggest that the magnitude of autophagosome formation was increased following RE when mTORC1 activity was attenuated with repeated bouts of RE.

Mitochondrial Bioenergetics and Turnover during Chronic Muscle Disuse

Periods of muscle disuse promote marked mitochondrial alterations that contribute to the impaired metabolic health and degree of atrophy in the muscle. Thus, understanding the molecular underpinnings of muscle mitochondrial decline with prolonged inactivity is of considerable interest. There are translational applications to patients subjected to limb immobilization following injury, illness-induced bed rest, neuropathies, and even microgravity. Studies in these patients, as well as on various pre-clinical rodent models have elucidated the pathways involved in mitochondrial quality control, such as mitochondrial biogenesis, mitophagy, fission and fusion, and the corresponding mitochondrial derangements that underlie the muscle atrophy that ensues from inactivity. Defective organelles display altered respiratory function concurrent with increased accumulation of reactive oxygen species, which exacerbate myofiber atrophy via degradative pathways. The preservation of muscle quality and function is critical for maintaining mobility throughout the lifespan, and for the prevention of inactivity-related diseases. Exercise training is effective in preserving muscle mass by promoting favourable mitochondrial adaptations that offset the mitochondrial dysfunction, which contributes to the declines in muscle and whole-body metabolic health. This highlights the need for further investigation of the mechanisms in which mitochondria contribute to disuse-induced atrophy, as well as the specific molecular targets that can be exploited therapeutically.

Mountain ginseng inhibits skeletal muscle atrophy by decreasing muscle RING finger protein-1 and atrogin1 through forkhead box O3 in L6 myotubes

ETHNOPHARMACOLOGICAL RELEVANCE

Mountain ginseng (Panax ginseng C.A. Meyer) is a medicinal herb with immune effects, muscle damage protection and energy metabolism effects. However, the pharmacological role of mountain ginseng in dexamethasone (DEXA)-induced muscle atrophy through the forkhead box O (FOXO) family is not understood. Therefore, we hypothesized that mountain ginseng inhibits skeletal muscle atrophy by decreasing muscle RING finger protein-1 (MuRF1) and atrogin1 through FOXO3 in L6 myotubes.

METHODS

Rat myoblast (L6) cells or Sprague-Dawley (SD) rats were exposed to DEXA and mountain ginseng. The expressions of muscle atrophy targets such as MuRF1, atrogin1, MyHC (myosin heavy chain), HSP90, p-Akt, Akt, p-ERK1/2, ERK, FOXO3a, FOXO1, myostatin, and follistatin were analyzed by using Western blot analysis or real-time PCR. The diameter of myotubes was measured. Recruitment of glucocorticoid receptor (GR) or FOXO3a was analyzed by performing a chromatin immunoprecipitation (ChIP) assay.

RESULTS

Mountain ginseng treatment reduced muscle weight loss and collagen deposition in DEXA-induced rats. Mountain ginseng treatment led to decreases in MuRF1, atrogin1, p-ERK1/2, FOXO3a, FOXO1, and myostatin. Also, mountain ginseng treatment led to increases in the diameter of myotubes, MyHC, HSP90, p-Akt, and follistatin. Treatment with mountain ginseng reduced enrichment of GR, FOXO3a, and RNA polymerase II on the promoters.

CONCLUSIONS

These results suggest that mountain ginseng inhibits skeletal muscle atrophy by decreasing MuRF1 and atrogin1 through FOXO3a in L6 myotubes.

Daidzein alleviates cisplatin-induced muscle atrophy by regulating Glut4/AMPK/FoxO pathway

Cisplatin (DDP) is widely used in cancer treatment, but DDP can cause skeletal muscle atrophy and cachexia. This study explored the effect and mechanism of daidzein (DAI) in reducing DDP-induced skeletal muscle atrophy and cachexia in vivo and in vitro. DAI alleviated the weight, food intake, muscle, adipose tissue, kidney weight and forelimb grip of LLC tumour-bearing mice after DDP treatment, and did not affect the antitumour effect of DDP. DAI can reduce the decrease of the cross-sectional area of skeletal muscle fibre-induced by DDP and prevent the change of fibre type proportion. In skeletal muscle, it can inhibit Glut4/AMPK/FoxO pathway, down-regulate the expression of atrogin1 and MuRF1, and inhibit skeletal muscle protein degradation. In DDP treated C2C12 myotubes, DAI could inhibit Glut4/AMPK/FoxO pathway to reduce myotubes atrophy, while AMPK agonist MK-3903 could reverse the protective effect of DAI. These results suggest that DAI can alleviate DDP-induced skeletal muscle atrophy by downregulating the expression of Atrogin1 and MuRF1 through the regulation of Glut4/AMPK/FoxO pathway.

Regulation of the early expression of MAFbx/atrogin-1 and MuRF1 through membrane-initiated cortisol action in the skeletal muscle of rainbow trout

Glucocorticoids are key stress-related hormones in vertebrates, with cortisol being the main glucocorticoid in teleosts. Glucocorticoids exert their effects through two mechanisms of action: genomic/classic and membrane initiated. In mammals, cortisol-mediated stress has been found to be associated with increased expression of critical atrophy-related genes (atrogenes), such as MAFbx/atrogin-1 and murf1/trim63. However, the direct impact of cortisol on the early regulation of atrogene expression in teleost skeletal muscle and the contribution of membrane-initiated cortisol action to this process have not been identified. In this work, the mRNA levels of atrogin-1 and murf1 were assessed in isolated myotubes and skeletal muscle of rainbow trout administered with cortisol or cortisol-BSA. This latter compound is a membrane-impermeable cortisol analog that exclusively induces membrane-initiated effects. We found that cortisol (10 mg/kg) first decreased the expression of both atrogenes at 3 h of treatment and then increased their expression at 9 h of treatment in the skeletal muscle of rainbow trout. Additionally, the in vitro analysis suggested that membrane-initiated cortisol action regulates murf1 but not atrogin-1 in rainbow trout myotubes. Using RU486 to selectively block glucocorticoid receptor (GR), we found that early downregulation of murf1 is potentially mediated by membrane GR signaling in myotubes. Considering the results of both the in vivo and in vitro approaches, we suggest that membrane-initiated cortisol action regulates the early expression of atrophy-related processes in teleosts.

MuRF1/TRIM63, Master Regulator of Muscle Mass

The E3 ubiquitin ligase MuRF1/TRIM63 was identified 20 years ago and suspected to play important roles during skeletal muscle atrophy. Since then, numerous studies have been conducted to decipher the roles, molecular mechanisms and regulation of this enzyme. This revealed that MuRF1 is an important player in the skeletal muscle atrophy process occurring during catabolic states, making MuRF1 a prime candidate for pharmacological treatments against muscle wasting. Indeed, muscle wasting is an associated event of several diseases (e.g., cancer, sepsis, diabetes, renal failure, etc.) and negatively impacts the prognosis of patients, which has stimulated the search for MuRF1 inhibitory molecules. However, studies on MuRF1 cardiac functions revealed that MuRF1 is also cardioprotective, revealing a yin and yang role of MuRF1, being detrimental in skeletal muscle and beneficial in the heart. This review discusses data obtained on MuRF1, both in skeletal and cardiac muscles, over the past 20 years, regarding the structure, the regulation, the location and the different functions identified, and the first inhibitors reported, and aim to draw the picture of what is known about MuRF1. The review also discusses important MuRF1 characteristics to consider for the design of future drugs to maintain skeletal muscle mass in patients with different pathologies.

Generation of reporter cell lines for factors inducing muscle wasting in cancer cachexia

Rapidly identifying cachexia-inducing factors that directly induce muscle wasting is an existing challenge. We developed two reporter cell lines that allow swift detection of such factors in blood from patients. C2C12 myoblasts were used for the establishment of reporter cells. A luciferase reporter gene, driven by promoters of wasting genes, Muscle RING-finger protein-1 (MuRF1) and Muscle Atrophy F-Box Protein (MAFbx/Atrogin-1) were used for the construction of reporter constructs. Increased expression of these genes in muscle tissue under wasting conditions was shown in vivo and in vitro. We found these reporter cell lines could detect factors associated with cancer cachexia, such as myostatin (Mstn), activin A, and TNF-α. We further investigated the capacity to directly detect a cachectic state using plasma samples from cachectic mice and cancer patients. Activation of the reporter cell lines was observed by the addition of plasma from mice with cancer cachexia and serum samples from patients with pancreatic or colorectal cancer. These results indicate that the reporter cell lines are competent as a tool for screening cachexia-inducing factors and potentially distinguishing a cachectic state induced by cancer.

The Effects of Cold Water Immersion and Active Recovery on Molecular Factors That Regulate Growth and Remodeling of Skeletal Muscle After Resistance Exercise

Regular postexercise cooling attenuates muscle hypertrophy, yet its effects on the key molecular factors that regulate muscle growth and remodeling are not well characterized. In the present study, nine men completed two sessions of single-leg resistance exercise on separate days. On 1 day, they sat in cold water (10°C) up to their waist for 10 min after exercise. On the other day, they exercised at a low intensity for 10 min after exercise. Muscle biopsies were collected from the exercised leg before, 2, 24, and 48 h after exercise in both trials. These muscle samples were analyzed to evaluate changes in genes and proteins involved in muscle growth and remodeling. Muscle-specific RING finger 1 mRNA increased at 2 h after both trials (P < 0.05), while insulin-like growth factor (IGF)-1 Ec, IGF-1 receptor, growth arrest and DNA damage-inducible protein 45, collagen type I alpha chain A, collagen type III alpha chain 1, laminin and tissue inhibitor of metallopeptidase 1 mRNA increased 24−48 h after both trials (P < 0.05). By contrast, atrogin-1 mRNA decreased at all time points after both trials (P < 0.05). Protein expression of tenascin C increased 2 h after the active recovery trial (P < 0.05), whereas FoxO3a protein expression decreased after both trials (P < 0.05). Myostatin mRNA and ubiquitin protein expression did not change after either trial. These responses were not significantly different between the trials. The present findings suggest that regular cold water immersion attenuates muscle hypertrophy independently of changes in factors that regulate myogenesis, proteolysis and extracellular matrix remodeling in muscle after exercise.

4-Hydroxyderricin and xanthoangelol isolated from Angelica keiskei prevent dexamethasone-induced muscle loss

Since a decrease in muscle mass leads to an increased risk of mortality, the prevention of muscle wasting contributes to maintaining the quality of life. Recently, we reported that glabridin, a prenylated flavonoid in licorice, prevents dexamethasone-induced muscle loss. In this study, we focused on the other prenylated chalcones 4-hydroxyderricin and xanthoangelol in Ashitaba (Angelica keiskei) and investigated their prevention effect on dexamethasone-induced muscle loss. It was found that 4-hydroxyderricin and xanthoangelol significantly prevented dexamethasone-induced protein degradation in C2C12 myotubes by suppressing the expression of ubiquitin ligases, Cbl-b and MuRF-1. These prenylated chalcones acted as the antagonists of the glucocorticoid receptor and inhibited the binding of dexamethasone to this receptor and its subsequent nuclear translocation. In addition, the chalcones suppressed the phosphorylation of p38 and FoxO3a as the upstream factors for ubiquitin ligases. Dexamethasone-induced protein degradation and upregulation of Cbl-b were attenuated by the knockdown of the glucocorticoid receptor but not by the knockdown of p38. In male C57BL/6J mice, the Ashitaba extract, containing 4-hydroxyderricin and xanthoangelol, suppressed dexamethasone-induced muscle mass wasting accompanied by a decrease in the expression of ubiquitin ligases by inhibiting the nuclear translocation of the glucocorticoid receptor and phosphorylation of FoxO3a. In conclusion, 4-hydroxyderricin and xanthoangelol are effective compounds to inhibit steroid-induced muscle loss.

Imoxin prevents dexamethasone-induced promotion of muscle-specific E3 ubiquitin ligases and stimulates anabolic signaling in C2C12 myotubes

Muscle atrophy is the loss of skeletal muscle mass during several pathological conditions such as long-term fasting, aging, cancer, diabetes, sepsis and immune disorders. Glucocorticoids are known to trigger skeletal muscle atrophy. Dexamethasone (DEX), a synthetic glucocorticoid, induces skeletal muscle atrophy by suppression of protein synthesis and promotion of protein degradation. The double-stranded RNA (dsRNA)-activated protein kinase R (PKR) plays a significant role in mediating lipopolysaccharide-induced inflammation. However, pathological roles of PKR in muscle atrophy are not fully understood. The current study aimed to investigate the effect of imoxin, a PKR inhibitor, on DEX-induced muscle atrophy in C2C12 myotubes. Myotubes were incubated with imoxin at different concentrations with or without 5 μM DEX for 24 h. In the current study, imoxin treatment significantly reduced protein levels of MuRF1 and MAFbx induced by DEX by 88 ± 2% and MAFbx by 99 ± 0%, respectively. Moreover, 5 μM imoxin treatment reduced protein ubiquitination by 42 ± 4% and protein content of nuclear FoxO3α (77 ± 4%) in presence of DEX. Furthermore, 5 μM imoxin treatment stimulated Akt phosphorylation (195 ± 5%), mTOR phosphorylation (171 ± 21 %) and p70S6K1 phosphorylation (314 ± 31 %) under DEX-treated condition even though DEX treatment did not suppressed Akt/mTOR/p70S6K1 axis. These findings suggest that imoxin may protect against DEX-induced skeletal muscle atrophy by alleviating muscle specific E3 ubiquitin ligases and imoxin alone may promote protein synthesis via Akt/mTOR/S6K1 axis in muscle cells.

Protein Nutritional Support: The Classical and Potential New Mechanisms in the Prevention and Therapy of Sarcopenia

Sarcopenia commonly occurs in the elderly and patients with wasting diseases. The main reason is an imbalance in protein metabolism (protein degradation exceeding protein synthesis). It causes a serious decline in muscle strength and motion ability, even leading to long-term bed rest. Recent studies indicate that nutritional support is beneficial for ameliorating sarcopenia and restoring muscle function. This review will summarize the classical mechanisms of protein nutritional support for alleviating sarcopenia, such as modulating the ubiquitin-proteasome system, oxidative response, and cell autophagy, as well as the potential new mechanisms, including altering miRNA profiles and gut microbiota. In addition, the clinical application and outcome of protein nutritional support in the elderly and patients with wasting diseases are also introduced. Protein nutritional support is expected to provide new approaches for the prevention and adjuvant therapy of sarcopenia.

CircMRPS35 suppresses gastric cancer progression via recruiting KAT7 to govern histone modification

Background

Aberrant expression of circular RNAs contributes to the initiation and progression of cancers, but the underlying mechanism remains elusive.

Methods

RNA-seq and qRT-PCR were performed to screen differential expressed circRNAs between gastric cancer tissues and adjacent normal tissues. Candidate circRNA (circMRPS35) was screened out and validated by qRT-PCR. Cell proliferation and invasion ability were determined by CCK-8 and cell invasion assays. RNA-seq, GO-pathway, RNA pull-down and ChIRP were further applied to search for detailed mechanism.

Results

Here, a novel circRNA named circMRPS35, was screened out by RNA-seq in gastric cancer tissues, whose expression is related to clinicopathological characteristics and prognosis in gastric cancer patients. Biologically, circMRPS35 suppresses the proliferation and invasion of gastric cancer cells in vitro and in vivo. Mechanistically, circMRPS35 acts as a modular scaffold to recruit histone acetyltransferase KAT7 to the promoters of FOXO1 and FOXO3a genes, which elicits acetylation of H4K5 in their promoters. Particularly, circMRPS35 specifically binds to FOXO1/3a promoter regions directly. Thus, it dramatically activates the transcription of FOXO1/3a and triggers subsequent response of their downstream target genes expression, including p21, p27, Twist1 and E-cadherin, resulting in the inhibition of cell proliferation and invasion. Moreover, circMRPS35 expression positively correlates with that of FOXO1/3a in gastric cancer tissues.

Conclusions

Our findings not only reveal the pivotal roles of circMRPS35 in governing histone modification in anticancer treatment, but also advocate for triggering circMRPS35/KAT7/FOXO1/3a pathway to combat gastric cancer.

FOXO3a from the Nucleus to the Mitochondria: A Round Trip in Cellular Stress Response

Cellular stress response is a universal mechanism that ensures the survival or negative selection of cells in challenging conditions. The transcription factor Forkhead box protein O3 (FOXO3a) is a core regulator of cellular homeostasis, stress response, and longevity since it can modulate a variety of stress responses upon nutrient shortage, oxidative stress, hypoxia, heat shock, and DNA damage. FOXO3a activity is regulated by post-translational modifications that drive its shuttling between different cellular compartments, thereby determining its inactivation (cytoplasm) or activation (nucleus and mitochondria). Depending on the stress stimulus and subcellular context, activated FOXO3a can induce specific sets of nuclear genes, including cell cycle inhibitors, pro-apoptotic genes, reactive oxygen species (ROS) scavengers, autophagy effectors, gluconeogenic enzymes, and others. On the other hand, upon glucose restriction, 5′-AMP-activated protein kinase (AMPK) and mitogen activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) -dependent FOXO3a mitochondrial translocation allows the transcription of oxidative phosphorylation (OXPHOS) genes, restoring cellular ATP levels, while in cancer cells, mitochondrial FOXO3a mediates survival upon genotoxic stress induced by chemotherapy. Interestingly, these target genes and their related pathways are diverse and sometimes antagonistic, suggesting that FOXO3a is an adaptable player in the dynamic homeostasis of normal and stressed cells. In this review, we describe the multiple roles of FOXO3a in cellular stress response, with a focus on both its nuclear and mitochondrial functions.

Expression of aromatase and synthesis of sex steroid hormones in skeletal muscle following exercise training in ovariectomized rats

Age-related muscle wasting (sarcopenia) is accompanied by a decrease in estrogen levels which can compromise the health of aging women. Recent studies have shown that the key enzyme of estrogen synthesis (aromatase) is detected in the skeletal muscle. The purpose of this study was to investigate the effects of exercise on the expression of aromatase and the synthesis of sex steroid hormones in skeletal muscle following exercise training. Ovariectomized rats were divided into two groups, treadmill running group (25 m/min, 60 min/day, 6 days/week) and sedentary group. We found that in ovariectomized rats, exercise training significantly increased the soleus and plantar muscles mass. The level of aromatase expression and 17-β-estradiol (E2) were increased significantly in skeletal muscle following exercise training. In addition, activation of the down-stream Akt-FoxO1-MyoD signaling pathway was significantly increased in both soleus and plantaris muscles following exercise. These results demonstrate that exercise training increased the expression of aromatase and local estrogen production in skeletal muscle, which potentially influences skeletal muscle in ovariectomized rats through activation of the Akt-FoxO1-MyoD signaling pathway.

Polycystin-2 Is Required for Starvation- and Rapamycin-Induced Atrophy in Myotubes

Muscle atrophy involves a massive catabolism of intracellular components leading to a significant reduction in cellular and tissue volume. In this regard, autophagy, an intracellular mechanism that degrades proteins and organelles, has been implicated with muscle breakdown. Recently, it has shown that polycystin-2 (PC2), a membrane protein that belongs to the transient receptor potential (TRP) family, is required for the maintenance of cellular proteostasis, by regulating autophagy in several cell types. The role of PC2 in the control of atrophy and autophagy in skeletal muscle remains unknown. Here, we show that PC2 is required for the induction of atrophy in C2C12 myotubes caused by nutrient deprivation or rapamycin exposure. Consistently, overexpression of PC2 induces atrophy in C2C12 myotubes as indicated by decreasing of the myogenic proteins myogenin and caveolin-3. In addition, we show that inhibition of mTORC1, by starvation or rapamycin is inhibited in cells when PC2 is silenced. Importantly, even if PC2 regulates mTORC1, our results show that the regulation of atrophy by PC2 is independent of autophagy. This study provides novel evidence regarding the role of PC2 in skeletal muscle cell atrophy.

Increased Serpina3n release into circulation during glucocorticoid-mediated muscle atrophy

BACKGROUND

Glucocorticoids (GC) play a major role in muscle atrophy. As skeletal muscle is a secretory organ, characterization of the muscle secretome elicited by muscle atrophy should allow to better understand the cellular mechanisms and to identify circulating biomarkers of this condition. Our project aimed to identify the changes in the muscle secretome associated with GC-induced muscle atrophy and susceptible to translate into circulation.

METHODS

We have identified the GC-induced changes in the secretome of C₂ C₁₂ muscle cells by proteomic analysis, and then, we have determined how these changes translate into the circulation of mice or human subjects exposed to high concentrations of GC.

RESULTS

This approach led us to identify Serpina3n as one of the most markedly secreted protein in response to GC. Our original in vitro results were confirmed in vivo by an increased expression of Serpina3n in skeletal muscle (3.9-fold; P < 0.01) and in the serum (two-fold; P < 0.01) of mice treated with GC. We also observed increased levels of the human orthologue Serpina3 in the serum of Cushing's syndrome patients compared with healthy controls matched for age and sex (n = 9/group, 2.5-fold; P < 0.01). An increase of Serpina3n was also demonstrated in muscle atrophy models mediated by GC such as cancer cachexia (four-fold; P < 0.01), sepsis (12.5-fold; P < 0.001), or diabetes (two-fold; P < 0.01). In contrast, levels of Serpina3n both in skeletal muscle and in the circulation were reduced in several models of muscle hypertrophy induced by myostatin inhibition (P < 0.01). Furthermore, a cluster of data suggests that the regulation of muscle Serpina3n involves mTOR, an essential determinant of the muscle cell size.

CONCLUSIONS

Taken together, these data suggest that Serpina3n may represent a circulating biomarker of muscle atrophy associated to GC and, broadly, a reflection of dynamic changes in muscle mass.

Increasing Cardiomyocyte Atrogin-1 Reduces Aging-Associated Fibrosis and Regulates Remodeling in Vivo

The muscle-specific ubiquitin ligase atrogin-1 (MAFbx) has been identified as a critical regulator of pathologic and physiological cardiac hypertrophy; it regulates these processes by ubiquitinating transcription factors [nuclear factor of activated T-cells and forkhead box O (FoxO) 1/3]. However, the role of atrogin-1 in regulating transcription factors in aging has not previously been described. Atrogin-1 cardiomyocyte-specific transgenic (Tg⁺) adult mice (α-major histocompatibility complex promoter driven) have normal cardiac function and size. Herein, we demonstrate that 18-month-old atrogin-1 Tg⁺ hearts exhibit significantly increased anterior wall thickness without functional impairment versus wild-type mice. Histologic analysis at 18 months revealed atrogin-1 Tg⁺ mice had significantly less fibrosis and significantly greater nuclei and cardiomyocyte cross-sectional analysis. Furthermore, by real-time quantitative PCR, atrogin-1 Tg⁺ had increased Col 6a4, 6a5, 6a6, matrix metalloproteinase 8 (Mmp8), and Mmp9 mRNA, suggesting a role for atrogin-1 in regulating collagen deposits and MMP-8 and MMP-9. Because atrogin-1 Tg⁺ mice exhibited significantly less collagen deposition and protein levels, enhanced Mmp8 and Mmp9 mRNA may offer one mechanism by which collagen levels are kept in check in the aged atrogin-1 Tg⁺ heart. In addition, atrogin-1 Tg⁺ hearts showed enhanced FoxO1/3 activity. The present study shows a novel link between atrogin-1-mediated regulation of FoxO1/3 activity and reduced collagen deposition and fibrosis in the aged heart. Therefore, targeting FoxO1/3 activity via the muscle-specific atrogin-1 ubiquitin ligase may offer a muscle-specific method to modulate aging-related cardiac fibrosis.

Anti-cachectic effect of Antrodia cinnamomea extract in lung tumor-bearing mice under chemotherapy

Skeletal muscle atrophy, the most characteristic feature of cancer cachexia, often occurs in patients with cancer undergoing chemotherapy. Antrodia cinnamomea (AC) a widely used edible medical fungus, exhibits hepatoprotective, anti-inflammatory and anticancer activities. In this study, we investigated whether combined treatment with the ethonolic extract of AC ameliorates cachexia symptoms, especially muscle wasting, in lung tumor-bearing mice treated with chemotherapy. Our results revealed that gemcitabine and cisplatin-induced severe body weight loss and skeletal muscle atrophy in the mice with cancer were greatly attenuated after AC extract administration. The protection may be attributed to the inhibition of skeletal muscle proteolysis by suppressing myostatin and activin release, muscle wasting-related FoxO3/MuRF-1/MAFbx signaling, proteasomal enzyme activity, and pro-inflammatory cytokine production. A significant decrease in insulin-like growth factor 1 (IGF-1) expression and formation was observed in the atrophying muscle of the conventional chemotherapy treatment group (CGC), and this decrease was markedly reversed by AC treatment. Additionally, the anorexia, intestinal injury and dysfunction that occurred in the CGC group were mitigated by AC extract. Taken together, these results demonstrated that the AC extract has a protective effect against chemotherapy-induced muscle atrophy mainly by attenuating muscle proteolysis, pro-inflammatory cytokine production, and anorexia, and activating IGF-1-dependent protein synthesis.

α-Ketoglutarate prevents skeletal muscle protein degradation and muscle atrophy through PHD3/ADRB2 pathway

Skeletal muscle atrophy due to excessive protein degradation is the main cause for muscle dysfunction, fatigue, and weakening of athletic ability. Endurance exercise is effective to attenuate muscle atrophy, but the underlying mechanism has not been fully investigated. α-Ketoglutarate (AKG) is a key intermediate of tricarboxylic acid cycle, which is generated during endurance exercise. Here, we demonstrated that AKG effectively attenuated corticosterone-induced protein degradation and rescued the muscle atrophy and dysfunction in a Duchenne muscular dystrophy mouse model. Interestingly, AKG also inhibited the expression of proline hydroxylase 3 (PHD3), one of the important oxidoreductases expressed under hypoxic conditions. Subsequently, we identified the β2 adrenergic receptor (ADRB2) as a downstream target for PHD3. We found AKG inhibited PHD3/ADRB2 interaction and therefore increased the stability of ADRB2. In addition, combining pharmacologic and genetic approaches, we showed that AKG rescues skeletal muscle atrophy and protein degradation through a PHD3/ADRB2 mediated mechanism. Taken together, these data reveal a mechanism for inhibitory effects of AKG on muscle atrophy and protein degradation. These findings not only provide a molecular basis for the potential use of exercise-generated metabolite AKG in muscle atrophy treatment, but also identify PHD3 as a potential target for the development of therapies for muscle wasting.-Cai, X., Yuan, Y., Liao, Z., Xing, K., Zhu, C., Xu, Y., Yu, L., Wang, L., Wang, S., Zhu, X., Gao, P., Zhang, Y., Jiang, Q., Xu, P., Shu, G. α-Ketoglutarate prevents skeletal muscle protein degradation and muscle atrophy through PHD3/ADRB2 pathway.