Expression Of MuRF1 Research Articles

Neuron-derived neurotrophic factor protects against dexamethasone-induced skeletal muscle atrophy

Skeletal muscle atrophy caused by various conditions including aging, nerve damage, and steroid administration, is a serious health problem worldwide. We recently reported that neuron-derived neurotrophic factor (NDNF) functions as a muscle-derived secreted factor, also known as myokine, which exerts protective actions on endothelial cell and cardiomyocyte function. Here, we investigated whether NDNF regulates skeletal muscle atrophy induced by steroid administration and sciatic denervation.NDNF-knockout (KO) mice and age-matched wild-type (WT) mice were subjected to continuous dexamethasone (DEX) treatment or sciatic denervation. NDNF-KO mice exhibited decreased gastrocnemius muscle weight and reduced cross sectional area of myocyte fiber after DEX treatment or sciatic denervation compared with WT mice. Administration of an adenoviral vector expressing NDNF (Ad-NDNF) or recombinant NDNF protein to gastrocnemius muscle of WT mice increased gastrocnemius muscle weight after DEX treatment. NDNF-KO mice showed increased expression of ubiquitin E3-ligases, including atrogin-1 and MuRF-1, in gastrocnemius muscle after DEX treatment, whereas Ad-NDNF reduced expression of atrogin-1 and MuRF-1 in gastrocnemius muscle of WT mice after DEX treatment. Pretreatment of cultured C2C12 myocytes with NDNF protein reversed reduced myotube diameter and increased expression of atrogin-1 and MuRF-1 after DEX stimulation. Treatment of C2C12 myocytes increased Akt phosphorylation. Pretreatment of C2C12 myotubes with the PI3-kinase/Akt inhibitor reversed NDNF-induced increase in myotube fiber diameter after DEX treatment. In conclusion, our findings indicated that NDNF prevents skeletal muscle atrophy in vivo and in vitro through reduction of ubiquitin E3-ligases expression, suggesting that NDNF could be a novel therapeutic target of muscle atrophy.

A new therapeutic effect of fenofibrate in Duchenne muscular dystrophy: The promotion of myostatin degradation.

Duchenne muscular dystrophy (DMD) is a degenerative muscle disease with no effective drug treatment. This study investigated the positive effects of fenofibrate on dystrophic muscles. Myostatin expression in serum and muscle tissue from patients with Duchenne muscular dystrophy and mdx mice were tested. Primary myoblasts isolated from mdx mice were challenged with an inflammatory stimulus and treated with fenofibrate. In animal experiments, 6-week-old male mdx mice were treated with fenofibrate (100 mg kg-1 ) administered orally once per day for 6weeks. Effects of fenofibrate were evaluated by tests of muscle function plus histology and biochemical analyses of serum. Expression of myostatin, MuRF1, and atrogin-1 in skeletal muscle was evaluated by western blotting and real-time PCR. Total and oxidative myosin heavy chain (MHC) were assessed via immunofluorescence. Expression of myostatin protein was increased in dystrophic muscle of patients with Duchenne muscular dystrophy and mdx mice. Fenofibrate enhanced myofibre differentiation by down-regulating the expression of myostatin protein but not mRNA in primary myoblasts of mdx mice. Fenofibrate significantly improved muscle function while ameliorating muscle damage in mdx mice. These benefits were accompanied by an anti-inflammatory effect. Fenofibrate treatment returned myofibre function by inhibiting the expressions of myostatin, MuRF1, and atrogin-1 protein in the gastrocnemius muscle and diaphragm, while leaving the mRNA level of myostatin unaffected. Fenofibrate substantially slows muscle dystrophy by promoting the degradation of myostatin protein, which may indicate a new therapeutic focus for patients with Duchenne muscular dystrophy.

Ovarian cancer ascites induces skeletal muscle wasting in vitro and reflects sarcopenia in patients.

BackgroundCachexia‐associated skeletal muscle wasting or ‘sarcopenia’ is highly prevalent in ovarian cancer and contributes to poor outcome. Drivers of cachexia‐associated sarcopenia in ovarian cancer remain elusive, underscoring the need for novel and better models to identify tumour factors inducing sarcopenia. We aimed to assess whether factors present in ascites of sarcopenic vs. non‐sarcopenic ovarian cancer patients differentially affect protein metabolism in skeletal muscle cells and to determine if these effects are correlated to cachexia‐related patient characteristics.MethodsFifteen patients with an ovarian mass and ascites underwent extensive physical screening focusing on cachexia‐related parameters. Based on computed tomography‐based body composition imaging, six cancer patients were classified as sarcopenic and six were not; three patients with a benign condition served as an additional non‐sarcopenic control group. Ascites was collected, and concentrations of cachexia‐associated factors were assessed by enzyme‐linked immunosorbent assay. Subsequently, ascites was used for in vitro exposure of C2C12 myotubes followed by measurements of protein synthesis and breakdown by radioactive isotope tracing, qPCR‐based analysis of atrophy‐related gene expression, and NF‐κB activity reporter assays.ResultsC2C12 protein synthesis was lower after exposure to ascites from sarcopenic patients (sarcopenia 3.1 ± 0.1 nmol/h/mg protein vs. non‐sarcopenia 5.5 ± 0.2 nmol/h/mg protein, P < 0.01), and protein breakdown rates tended to be higher (sarcopenia 31.2 ± 5.2% vs. non‐sarcopenia 20.9 ± 1.9%, P = 0.08). Ascites did not affect MuRF1, Atrogin‐1, or REDD1 expression of C2C12 myotubes, but NF‐κB activity was specifically increased in cells exposed to ascites from sarcopenic patients (sarcopenia 2.2 ± 0.4‐fold compared with control vs. non‐sarcopenia 1.2 ± 0.2‐fold compared with control, P = 0.01). Protein synthesis and breakdown correlated with NF‐κB activity (r s = −0.60, P = 0.03 and r s = 0.67, P = 0.01, respectively). The skeletal muscle index of the ascites donors was also correlated to both in vitro protein synthesis (r s = 0.70, P = 0.005) and protein breakdown rates (r s = −0.57, P = 0.04).ConclusionsAscites of sarcopenic ovarian cancer patients induces pronounced skeletal muscle protein metabolism changes in C2C12 cells that correlate with clinical muscle measures of the patient and that are characteristic of cachexia. The use of ascites offers a new experimental tool to study the impact of both tumour‐derived and systemic factors in various cachexia model systems, enabling identification of novel drivers of tissue wasting in ovarian cancer.

Differential Regulation of Myocardial E3 Ligases and Deubiquitinases in Ischemic Heart Failure.

The pathological changes of ubiquitination and deubiquitination following myocardial infarction (MI) and chronic heart failure (CHF) have been sparsely examined. We investigated the expression of muscle-specific E3 ubiquitin ligases and deubiquitinases in MI and CHF. Therefore, mice were assigned to coronary artery ligation for 3 days or 10 weeks as well as for sham operation (each n = 10). Expression of E3 ligases (MAFBX, MURF1, CHIP, ITCH, MDM2) and deubiquitinases (A20, CYLD, UCH-L1, USP14, USP19) was determined. After MI and in CHF, the mRNA expression of MURF1, CHIP and MDM2 (all p < 0.05) was decreased. Protein expression analyses revealed that ITCH expression decreased in CHF (p = 0.01), whereas MDM2 expression increased in MI (p = 0.02) and decreased in CHF (p = 0.02). Except for USP19 mRNA expression that decreased at 3 days and 10 weeks (both p < 0.01), the expression of other deubiquitinases remained unaffected after MI and CHF. The expression of myocardial E3 ligases is differentially regulated following MI, raising the question of whether an upstream regulation exists that is activated by MI for tissue protection or whether the downregulation of E3 ligases enables myocardial hypertrophy following MI.

Fermented Oyster Extract Attenuated Dexamethasone-Induced Muscle Atrophy by Decreasing Oxidative Stress.

It is well known that oxidative stress induces muscle atrophy, which decreases with the activation of Nrf2/HO-1. Fermented oyster extracts (FO), rich in γ-aminobutyric acid (GABA) and lactate, have shown antioxidative effects. We evaluated whether FO decreased oxidative stress by upregulating Nrf2/HO-1 and whether it decreased NF-κB, leading to decreased IL-6 and TNF-α. Decreased oxidative stress led to the downregulation of Cbl-b ubiquitin ligase, which increased IGF-1 and decreased FoxO3, atrogin1, and Murf1, and eventually decreased muscle atrophy in dexamethasone (Dexa)-induced muscle atrophy animal model. For four weeks, mice were orally administered with FO, GABA, lactate, or GABA+Lactate, and then Dexa was subcutaneously injected for ten days. During Dexa injection period, FO, GABA, lactate, or GABA+Lactate were also administered, and grip strength test and muscle harvesting were performed on the day of the last Dexa injection. We compared the attenuation effect of FO with GABA, lactate, and GABA+lactate treatment. Nrf2 and HO-1 expressions were increased by Dexa but decreased by FO; SOD activity and glutathione levels were decreased by Dexa but increased by FO; NADPH oxidase activity was increased by Dexa but decreased by FO; NF-κB, IL-6, and TNF-α activities were increased by Dexa were decreased by FO; Cbl-b expression was increased by Dexa but restored by FO; IGF-1 expression was decreased by Dexa but increased by FO; FoxO3, Atrogin-1, and MuRF1 expressions were increased by Dexa but decreased by FO. The gastrocnemius thickness and weight were decreased by Dexa but increased by FO. The cross-sectional area of muscle fiber and grip strength were decreased by Dexa but increased by FO. In conclusion, FO decreased Dexa-induced oxidative stress through the upregulation of Nrf2/HO-1. Decreased oxidative stress led to decreased Cbl-b, FoxO3, atrogin1, and MuRF1, which attenuated muscle atrophy.

Pharmacological Inhibition of HMGB1 Prevents Muscle Wasting.

Background: Cachexia is a multifactorial disorder characterized by weight loss and muscle wasting, making up for about 20% of cancer-related death. However, there are no effective drugs to combat cachexia at present. Methods: In this study, the effect of CT26 exosomes on C2C12 myotubes was observed. We compared serum HMGB1 level in cachexia and non-cachexia colon cancer patients. We further explored HMGB1 expression level in CT26 exosome. We added recombinant HMGB1 to C2C12 myotubes to observe the effects of HMGB1 on C2C12 myotubes and detected the expression level of the muscle atrophy-related proteins. Then, we used the HMGB1 inhibitor glycyrrhizin to reverse the effects of HMGB1 on C2C12 myotubes. Finally, HMGB1 inhibitor glycyrrhizin was utilized to relieve cachexia in CT26 cachexia mouse model. Results: Exosomes containing HMGB1 led to muscle atrophy with significantly decreased myotube diameter and increased expression of muscle atrophy-related proteins Atrogin1 and MuRF1. Further, we detected that HMGB1 induced the muscle atrophy mainly via TLR4/NF-κB pathway. Administration of the HMGB1 inhibitor glycyrrhizin could relieve muscle wasting in vitro and attenuate the progression of cachexia in vivo. Conclusion: These findings demonstrate the cachectic role of HMGB1, whether it is soluble form of HMGB1 or secreted from tumor cells as part of exosomes. HMGB1 inhibitor glycyrrhizin might be a promising drug in colon cancer cachexia.

Protein source affects apparent digestibility of feed ingredients and protein metabolism in Chinese perch ( Siniperca chuatsi )

In previous studies of apparent digestibility coefficients (ADCs), the association between apparent digestion and protein metabolism from different protein sources has long been ignored. To develop nutritionally adequate diets, this study evaluated the effects of different protein sources (fermented soybean meal [FSM], rapeseed meal [RSM], Antarctic krill powder [AKP] and fish protein hydrolysate [FPH]) on the growth performance, ADCs and expression of genes related to protein metabolism in Chinese perch. The experimental feed was composed of 300g kg-1 test ingredients and 700g kg-1 reference feed (RF). After the feeding trial, FPH was found to achieve the best growth performance of Chinese perch and had significantly higher ADCs of dry matter and gross energy than all other ingredients. Besides, FPH was the only ingredient with crude protein ADC exceeding 90% and the highest crude lipid ADC, while RSM had the lowest crude protein and crude lipid ADC. FPH showed the highest ADC of amino acids except for serine and tyrosine, and RSM showed the lowest amino acid ADC except for methionine. FPH resulted in the lowest expression of mtor, s6k, murf1, mafbx, pept2 and lat2 and the highest expression of gdh and ast in the muscle. The transcription level of cat significantly increased in the gut of the FSM group compared with that in the RF group. These findings imply that FPH may be a promising ingredient to be incorporated into the formulated diet of Chinese perch.

Effect of Cisatracurium to Intensify Diaphragmatic Atrophy in Mechanically Ventilated Rats

To investigate the role of cisatracurium in diaphragm atrophy in mechanically ventilated (MV) rats and its possible mechanism. 30 adult male Sprague-Dawley (SD) rats were randomly assigned to 5 groups: Rats in the control (CON) group ( n=6) were fasted for 30 h without any other intervention; rats in the MV group ( n=6) were fasted for 6 h, and then mechanically ventilated for 24 h while receiving continuous infusion of sodium pentobarbital and 0.9% NaCl; rats in the MV+cisatracurium (MVC) group ( n=6) were fasted for 6 h, and then mechanically ventilated for 24 h while receiving continuous infusion of sodium pentobarbital and cisatracurium; rats in the MV+chloroquine (QMV) group ( n=6) and rats in the MV+cisatracurium+chloroquine (QMVC) group ( n=6) received intraperitoneal injection of chloroquine (30 mg/kg), an autophagy inhibitor, at 24 h and 30 min prior to MV in addition to the treatments given to the MV group and the MVC group, respectively. The rats in each group were sacrificed 30 hours later, and costal diaphragm muscle specimens were collected. The cross-sectional area (CSA) of the diaphragm fibers was observed through HE staining, and the colocalizations of TOM20 and LC3 were assessed by immunofluorescence staining. The expression levels of PINK1, Parkin, P62 and LC3, the mitophagy-related proteins, and the expression levels of MAFbx and MURF-1, muscular-atrophy-related proteins, were evaluated by Western blot. Respective comparisons of the MV group with the CON group and the MVC group with the MV group showed that the CSA decreased ( P<0.05), the expression of MURF-1, MAFbx, PINK1, Parkin and LC3Ⅱ/Ⅰproteins increased ( P<0.05), the number of co-expressed mitochondria of TOM20 and LC3 and the expression of LC3 increased and the expression of P62 protein decreased ( P<0.05) in the MV and MVC groups. Respective comparisons of the QMV group with the MV group and the QMVC group with the MVC group showed that the CSA increased ( P<0.05), the expression of MURF-1, MAFbx, PINK1, Parkin and LC3Ⅱ/Ⅰ proteins increased ( P<0.05), the number of co-expressed mitochondria of TOM20 and LC3 and the expression of LC3 decreased and the expression of P62 protein decreased ( P<0.05) in the QMV and QMVC group. Mechanical ventilation for 24 h caused diaphragm atrophy in SD rats. Cisatracurium may aggravate diaphragm atrophy in mechanically ventilated rats through the autophagy-lysosome (AL) pathway, a process that may be related to the PINK1/Parkin-mediated mitophagy, and chloroquine may reduce diaphragmatic atrophy induced by cisatracurium by blocking the AL pathway.

Naringenin alleviates cisplatin induced muscle atrophy by regulating RIPK1/AMPK/NF-κB pathway

Cisplatin (DDP) is a commonly used chemotherapy drug, but DDP can cause skeletal muscle atrophy and cachexia. This study combined the DDP-induced C2C12 myotube atrophy model and the LLC tumour-bearing mouse cachexia model under DDP treatment to explore the effect and mechanism of naringenin (NAR) in alleviating skeletal muscle atrophy and cachexia. NAR alleviated the decreases in body weight, food intake, muscle, adipose tissue and kidney weight and forelimb grip strength in LLC tumour-bearing mice under DDP treatment and reduced the serum level of TNF-α. High dose NAR also enhanced the antitumour effect of DDP. NAR can prevent the cross-sectional area reduction of skeletal muscle fibres and prevent the change in fibre type ratio induced by DDP. NAR intervention inhibits the RIPK1/AMPK/NF-κB pathway in skeletal muscle, downregulates the expression of Atrogin1 and MuRF1, and inhibits the degradation of skeletal muscle protein. In C2C12 myotubes treated with DDP, NAR inhibited the RIPK1/AMPK/NF-κB pathway to reduce myotube cell atrophy, and the overexpression of RIPK1 reversed the therapeutic effect of NAR. These results indicate that NAR downregulates the expression of Atrogin1 and MuRF1 by regulating the RIPK1/AMPK/NF-κB pathway and alleviates DDP-induced skeletal muscle atrophy.

Mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force.

The hypoxia-inducible nuclear-encoded mitochondrial protein NADH dehydrogenase (ubiquinone) 1 alpha subcomplex, 4-like 2 (NDUFA4L2) has been demonstrated to decrease oxidative phosphorylation and production of reactive oxygen species in neonatal cardiomyocytes, brain tissue and hypoxic domains of cancer cells. Prolonged local hypoxia can negatively affect skeletal muscle size and tissue oxidative capacity. Although skeletal muscle is a mitochondrial rich, oxygen sensitive tissue, the role of NDUFA4L2 in skeletal muscle has not previously been investigated. Here we ectopically expressed NDUFA4L2 in mouse skeletal muscles using adenovirus-mediated expression and in vivo electroporation. Moreover, femoral artery ligation (FAL) was used as a model of peripheral vascular disease to induce hind limb ischemia and muscle damage. Ectopic NDUFA4L2 expression resulted in reduced mitochondrial respiration and reactive oxygen species followed by lowered AMP, ADP, ATP, and NAD+ levels without affecting the overall protein content of the mitochondrial electron transport chain. Furthermore, ectopically expressed NDUFA4L2 caused a ~20% reduction in muscle mass that resulted in weaker muscles. The loss of muscle mass was associated with increased gene expression of atrogenes MurF1 and Mul1, and apoptotic genes caspase 3 and Bax. Finally, we showed that NDUFA4L2 was induced by FAL and that the Ndufa4l2 mRNA expression correlated with the reduced capacity of the muscle to generate force after the ischemic insult. These results show, for the first time, that mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force. Specifically, induced NDUFA4L2 reduces mitochondrial activity leading to lower levels of important intramuscular metabolites, including adenine nucleotides and NAD+ , which are hallmarks of mitochondrial dysfunction and hence shows that dysfunctional mitochondrial activity may drive muscle wasting.

L-carnitine ameliorates the muscle wasting of cancer cachexia through the AKT/FOXO3a/MaFbx axis

BackgroundRecent studies suggest potential benefits of applying L-carnitine in the treatment of cancer cachexia, but the precise mechanisms underlying these benefits remain unknown. This study was conducted to determine the mechanism by which L-carnitine reduces cancer cachexia.MethodsC2C12 cells were differentiated into myotubes by growing them in DMEM for 24 h (hrs) and then changing the media to DMEM supplemented with 2% horse serum. Differentiated myotubes were treated for 2 h with TNF-α to establish a muscle atrophy cell model. After treated with L-carnitine, protein expression of MuRF1, MaFbx, FOXO3, p-FOXO3a, Akt, p-Akt, p70S6K and p-p70S6K was determined by Western blotting. Then siRNA-Akt was used to determine that L-carnitine ameliorated cancer cachexia via the Akt/FOXO3/MaFbx. In vivo, the cancer cachexia model was established by subcutaneously transplanting CT26 cells into the left flanks of the BALB/c nude mice. After treated with L-carnitine, serum levels of IL-1, IL-6 and TNF-α, and the skeletal muscle content of MuRF1, MaFbx, FOXO3, p-FOXO3a, Akt, p-Akt, p70S6K and p-p70S6K were measured.ResultsL-carnitine increased the gastrocnemius muscle (GM) weight in the CT26-bearing cachexia mouse model and the cross-sectional fiber area of the GM and myotube diameters of C2C12 cells treated with TNF-α. Additionally, L-carnitine reduced the protein expression of MuRF1, MaFbx and FOXO3a, and increased the p-FOXO3a level in vivo and in vitro. Inhibition of Akt, upstream of FOXO3a, reversed the effects of L-carnitine on the FOXO3a/MaFbx pathway and myotube diameters, without affecting FOXO3a/MuRF-1. In addition to regulating the ubiquitination of muscle proteins, L-carnitine also increased the levels of p-p70S6K and p70S6K, which are involved in protein synthesis. Akt inhibition did not reverse the effects of L-carnitine on p70S6K and p-p70S6K. Hence, L-carnitine ameliorated cancer cachexia via the Akt/FOXO3/MaFbx and p70S6K pathways. Moreover, L-carnitine reduced the serum levels of IL-1 and IL-6, factors known to induce cancer cachexia. However, there were minimal effects on TNF-α, another inducer of cachexia, in the in vivo model.ConclusionThese results revealed a novel mechanism by which L-carnitine protects muscle cells and reduces inflammation related to cancer cachexia.

Leucine did not stimulate growth and accretion in either stressed or unstressed Atlantic salmon

The aim of the current trial was to test whether leucine affected growth and accretion including test any effects on leucine upon stress. Quadruplicate tanks each containing 50 Atlantic salmon (Salmo salar) (mean start body weight of 524 ± 28 g) were fed diets containing 27.3, 30.0, 35.0 and 41.0 g leucine/kg diet for 74 days. Two tanks per dietary group were exposed to a stressor (5 min chasing) three days a week to test whether enriched leucine diet aid coping with chronic stress, while two tanks per dietary groups were left unstressed. The stressed fish consumed less feed and grew less than the unstressed fish, irrespective of diet. Leucine inclusion did not affect protein accretion, but leucine retention declined with increasing dietary leucine in both stressed and unstressed fish. No difference between the stressed or unstressed fish was present. Leucine did not affect relative liver size, but unstressed fish had slightly higher relative liver size compared with stressed fish (p = 0.05). Free leucine in the muscle and liver was not affected by dietary leucine, but unstressed fish had higher concentration of valine and isoleucine in the muscle compared with the stressed fish. Muscle of fish fed elevated leucine had lower mRNA expression of murf1 (p = 0.037) and higher expression of ppara (p = 0.012). Muscle of stressed fish had higher expression of the oxydative genes mnsod (p = 0.049) and catalase (p = 0.037) compared with the fish left unstressed, while in liver, there were no differences of expression of any of the genes tested. In conclusion, diets enriched in leucine had minor effects and neither protein accretion nor growth was affected in either stressed or unstressed fish.

Preventive effect of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) against endotoxin-induced muscle atrophy

Muscle atrophy is a public health issue and inflammation is a major cause of muscle atrophy. While docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which are typical ω-3 polyunsaturated fatty acids, are reported to have anti-inflammatory effects on endotoxin-induced inflammatory responses, their effects on inflammatory muscle atrophy have not been clarified. In this study, we aimed to investigate the effects of DHA and EPA on inflammatory muscle atrophy. DHA or EPA was added to C2C12 myotubes at a concentration of 25, 50, or 100μM, and 1h later, lipopolysaccharide (LPS) was added at a concentration of 1μg/mL. Two hours after the first LPS addition, mRNA expression of atrogin-1 and Murf-1 in C2C12 myotubes was measured. The second LPS addition was performed 24h after the first LPS addition, and myotube diameter, myofibrillar protein, and cell viability were measured. One-way ANOVA and Tukey's multiple comparison test were used for statistical processing of the results, and the significance level was set to less than 5%. The LPS-added group significantly decreased the myotube diameter and the myofibrillar protein content compared to the control group. The myotube diameter was significantly higher in the 25μM, 50μM DHA and 25μM EPA-added groups compared to the LPS group. In the 25μM DHA and EPA-added groups, the myofibrillar protein content was significantly higher than that in the LPS group. The mRNA expression levels of atrogin-1 and murf-1 were significantly suppressed in the 25μM DHA and EPA-added groups compared to the LPS group. The cell viability did not change by the addition of LPS, DHA, and EPA. The addition of DHA or EPA suppressed the decrease in myotube diameter and myofibrillar protein content and suppressed the increase in atrogin-1 and murf-1 induced by LPS. This study showed the preventive effect of DHA and EPA on endotoxin-induced muscle atrophy.

Role of Pannexin 1 ATP-Permeable Channels in the Regulation of Signaling Pathways during Skeletal Muscle Unloading.

Skeletal muscle unloading results in atrophy. We hypothesized that pannexin 1 ATP-permeable channel (PANX1) is involved in the response of muscle to unloading. We tested this hypothesis by blocking PANX1, which regulates efflux of ATP from the cytoplasm. Rats were divided into six groups (eight rats each): non-treated control for 1 and 3 days of the experiments (1C and 3C, respectively), 1 and 3 days of hindlimb suspension (HS) with placebo (1H and 3H, respectively), and 1 and 3 days of HS with PANX1 inhibitor probenecid (PRB; 1HP and 3HP, respectively). When compared with 3C group there was a significant increase in ATP in soleus muscle of 3H and 3HP groups (32 and 51%, respectively, p < 0.05). When compared with 3H group, 3HP group had: (1) lower mRNA expression of E3 ligases MuRF1 and MAFbx (by 50 and 38% respectively, p < 0.05) and MYOG (by 34%, p < 0.05); (2) higher phosphorylation of p70S6k and p90RSK (by 51 and 35% respectively, p < 0.05); (3) lower levels of phosphorylated eEF2 (by 157%, p < 0.05); (4) higher level of phosphorylated GSK3β (by 189%, p < 0.05). In conclusion, PANX1 ATP-permeable channels are involved in the regulation of muscle atrophic processes by modulating expression of E3 ligases, and protein translation and elongation processes during unloading.

Maslinic Acid Attenuates Denervation-Induced Loss of Skeletal Muscle Mass and Strength.

Maslinic acid (MA) is a pentacyclic triterpene abundant in olive peels. MA reportedly increases skeletal muscle mass and strength in older adults; however, the underlying mechanism is unknown. This study aimed to investigate the effects of MA on denervated muscle atrophy and strength and to explore the underlying molecular mechanism. Mice were fed either a control diet or a 0.27% MA diet. One week after intervention, the sciatic nerves of both legs were cut to induce muscle atrophy. Mice were examined 14 days after denervation. MA prevented the denervation-induced reduction in gastrocnemius muscle mass and skeletal muscle strength. Microarray gene expression profiling in gastrocnemius muscle demonstrated several potential mechanisms for muscle maintenance. Gene set enrichment analysis (GSEA) revealed different enriched biological processes, such as myogenesis, PI3/AKT/mTOR signaling, TNFα signaling via NF-κB, and TGF-β signaling in MA-treated mice. In addition, qPCR data showed that MA induced Igf1 expression and suppressed the expressions of Atrogin-1, Murf1 and Tgfb. Altogether, our results suggest the potential of MA as a new therapeutic and preventive dietary ingredient for muscular atrophy and strength.

Bcaa Alleviates Rats Skeletal Muscle Protein Degradation After Eccentric Exercise By Reducing KLF15 Expression

PURPOSE: Exercise-induced muscle damage after high-intensity eccentric exercise can lead to degradation of skeletal muscle protein, thereby affecting the training effect. The purpose of this study is to explore the effect of branched-chain amino acid (BCAA) supplementation on muscle damage caused by one-time eccentric exercise, and the regulation of KLF15-mediated proteolytic pathways in the process. METHODS: 64 male SD rats were randomly divided into eight groups: placebo + control group (PC, n = 8), placebo + immediately after exercise group (PE, n = 8), placebo +6 h after exercise group (PE6, n = 8), placebo +12 h after exercise group (PE12, n = 8), BCAA + control group (BC, n = 8), BCAA + immediately after exercise group (BE, n = 8), BCAA +6 h after exercise group (BE6, n = 8), BCAA +12 h after exercise group (BE12, n = 8). Rats in BCAA groups were supplied BCAA (1 g/kg/day) 3 times before exercise. The placebo groups were supplied the same volume of distilled water. Rats in exercise groups underwent a bout of 2 h eccentric exercise on treadmill (-16° slope, a speed of 16 m/min). Blood and gastrocnemius were collected immediately after exercise in PE and BE, 6 h after exercise in PE6 and BE6, and 12 h after exercise in PE12 and BE12. The expression of 3-MH in blood was detected by ELISA. RT-qPCR was used to measure the mRNA expression of KLF15, Atrogin-1, MuRF-1 and MHC-II in gastrocnemius. RESULTS: The mRNA expression of MHC-II (P < 0.05), KLF15 (P < 0.05), Atrogin-1 (P < 0.05), MuRF-1 (P < 0.01) in PE were higher than those in PC, MHC-II (P < 0.05) in PE6 and Atrogin-1 (P < 0.05) in PE12 were higher than in PC. MHC-II (P < 0.05) was higher in BE6 than in BE. Compared with PE, the mRNA expression of KLF15 (P < 0.01), Atrogin-1(P < 0.05), MuRF-1 (P < 0.01) in BE were significantly lower, Atrogin-1 (P < 0.05) in BE12 was lower than that in PE12. 3-MH (P < 0.05) content was higher in PE12 than in PC, 3-MH (P < 0.01) content was lower in BE and BE6 than in BC, 3-MH (P < 0.01) content was higher in BC than in PC. CONCLUSIONS: BCAA may reduce skeletal muscle proteolysis by lowering the level of gene transcription in the KLF15-related protein degradation pathway, which occurs immediately after exercise.

Association between serum tumor necrosis factor-α and sarcopenia in liver cirrhosis.

Background/AimsSarcopenia is an independent prognostic factor of liver cirrhosis (LC). However, the association between LC-related systemic inflammation and sarcopenia is unclear.MethodsSprague-Dawley rats were treated with thioacetamide (TAA) or saline as a control. Rifaximin was administered to TAA-induced LC rats. Enzyme-linked immunosorbent assay was performed to measure inflammatory mediators in rat serum. RT-PCR was performed to measure the molecular expression in tissues. Hematoxylin and eosin (H&E) staining and immunohistochemistry were performed to investigate tissue pathology. Serum tumor necrosis factor-α levels, liver stiffness (LS), and the L3 skeletal muscle index (L3SMI) were measured in 60 patients with chronic liver disease.ResultsLC and sarcopenia were successfully induced by TAA. Serum TNF-α levels were increased in LC rats and correlated with myostatin expression, muscle weight, and myofiber diameter. The expression of intestinal occludin and zona occludens-1 was reduced in LC rats and associated with serum TNF-α levels and sarcopenia. In patients with LS ≥7 kPa or sarcopenia, serum TNF-α levels were significantly increased, which was also confirmed when we raised the LS cutoff to 10 kPa. The L3SMI was inversely correlated with serum TNF-α levels in patients with LS ≥7 kPa. TNF-α was reduced by rifaximin, which might have resulted in reduced expression of muscular MuRF1 and myostatin and improvements in myofiber diameters within muscle tissues.ConclusionsThese results suggest that serum TNF-α is associated with LC-related sarcopenia. Rifaximin might be effective in reducing serum TNF-α levels and improving sarcopenia in LC, but these results need to be validated in future studies.

Administration of tauroursodeoxycholic acid attenuates dexamethasone-induced skeletal muscle atrophy

Glucocorticoids are known to induce skeletal muscle atrophy by suppressing protein synthesis and promoting protein degradation. Tauroursodeoxycholic acid (TUDCA) has beneficial effects in several diseases, such as hepatobiliary disorders, hindlimb ischemia and glucocorticoid-induced osteoporosis. However, the effects of TUDCA on glucocorticoid -induced skeletal muscle atrophy remains unknown. Therefore, in the present research, we explored the effects of TUDCA on dexamethasone (DEX)-induced loss and the potential mechanisms involved. We found TUDCA alleviated DEX-induced muscle wasting in C2C12 myotubes, identified by improved myotube differentiation index and expression of myogenin and MHC. And it showed that TUDCA activated the Akt/mTOR/S6K signaling pathway and inhibited FoxO3a transcriptional activity to decreased expression of MuRF1 and Atrogin-1, while blocking Akt by MK2206 blocked these effects of TUDCA on myotubes. Besides, TUDCA also attenuated DEX-induced apoptosis of myotubes. Furthermore, TUDCA was administrated to the mouse model of DEX-induced skeletal muscle atrophy. The results showed that TUDCA improved DEX-induced skeletal muscle atrophy and weakness (identified by increased grip strength and prolonged running exhaustive time) in mice by suppression of apoptosis, reduction of protein degradation and promotion of protein synthesis. Taken together, our research proved for the first time that TUDCA protected against DEX-induced skeletal muscle atrophy not only by improving myogenic differentiation and protein synthesis, but also through decreasing protein degradation and apoptosis of skeletal muscle.

Eriocitrin Contained in Lemon Peel Ameliorates Disuse Muscle Atrophy by Suppressing the Expression of Atrogin-1 and MuRF-1 in Denervated Mice.

Unloading stress enhances oxidative stress, which in turn induces disuse muscle atrophy. This study evaluated the suppressive effect of lemon peel extract containing eriocitrin on muscle atrophy. Both lemon peel extract and eriocitrin suppressed weight loss in the gastrocnemius muscle under denervation in C57BL/6 mice. The mRNA level of ubiquitin ligases and their transcription factor were downregulated by eriocitrin. Eriocitrin inhibited the increase in lipid peroxidation and the ratio of glutathione disulfide/glutathione. These data suggest that eriocitrin ameliorated disuse muscle atrophy by suppressing the expression of ubiquitin ligase genes by its antioxidative effect.

Histone Deacetylase 2 Suppresses Skeletal Muscle Atrophy and Senescence via NF-κB Signaling Pathway in Cigarette Smoke-Induced Mice with Emphysema.

BackgroundExposure to cigarette smoke (CS) is the main risk factor for chronic obstructive pulmonary disease (COPD). CS not only causes chronic airway inflammation and lung damage but also is involved in skeletal muscle dysfunction (SMD). Previous studies have shown that histone deacetylase 2 (HDAC2) plays an important role in the progression of COPD. The aim of this study was to determine the role of HDAC2 in CS-induced skeletal muscle atrophy and senescence.MethodsGastrocnemius muscle weight and cross-sectional area (CSA) were measured in mice with CS-induced emphysema, and changes in the expression of atrophy-related markers and senescence-related markers were detected. In addition, the relationship between HDAC2 expression and skeletal muscle atrophy and senescence was also investigated.ResultsMice exposed to CS for 24 weeks developed emphysema and gastrocnemius atrophy and exhibited a decrease in gastrocnemius weight and skeletal muscle cross-sectional area. In addition, the HDAC2 protein levels were significantly decreased while the levels of atrophy-associated markers, including MURF1 and MAFbx, and senescence-associated markers, including P53 and P21, were significantly increased in the gastrocnemius muscle. In vitro, the exposure of C2C12 cells to cigarette smoke extract (CSE) significantly increased the MAFbx and MURF1 protein levels and decreased the HDAC2 protein levels. Moreover, overexpression of HDAC2 significantly ameliorated CSE-induced atrophy and senescence and reversed the increased MURF1, MAFbx, P53, and P21 expression in C2C12 cells. In addition, CSE treatment significantly increased the IKK and NF-κB p65 protein levels, and PTDC (an NF-kB inhibitor) ameliorated atrophy and senescence.ConclusionOur findings suggest that HDAC2 plays an important role in CS-induced skeletal muscle atrophy and senescence, possibly through the NF-κB pathway.