Muscle-specific RING Finger Protein Research Articles

Potential of Lycii Radicis Cortex as an Ameliorative Agent for Skeletal Muscle Atrophy.

Lycii Radicis Cortex (LRC) is a traditional medicine in East Asia with various beneficial effects, including antioxidant, anti-inflammatory, anti-tumor, anti-diabetic, and anti-depressant properties. However, its potential effects on skeletal muscle atrophy have not been studied. In this study, the protective effects of LRC extract (LRCE) on dexamethasone (DEX)-induced muscle atrophy were investigated in C2C12 myotubes and mice. We evaluated the effect of LRCE on improving muscle atrophy using a variety of methods, including immunofluorescence staining, quantitative polymerase chain reaction (qPCR), Western blot, measurements of oxidative stress, apoptosis, ATP levels, and muscle tissue analysis. The results showed that LRCE improved myotube diameter, fusion index, superoxide dismutase (SOD) activity, mitochondrial content, ATP levels, expression of myogenin and myosin heavy chain (MHC), and reduced reactive oxygen species (ROS) production in dexamethasone-induced C2C12 myotubes. LRCE also enhanced protein synthesis and reduced protein degradation in the myotubes. In mice treated with DEX, LRCE restored calf thickness, decreased mRNA levels of muscle-specific RING finger protein 1 (MuRF1) and atrogin-1, and increased insulin-like growth factor 1 (IGF-1) mRNA level. Moreover, LRCE also repaired gastrocnemius muscle atrophy caused by DEX. Although human studies are not available, various preclinical studies have identified potential protective effects of LRCE against muscle atrophy, suggesting that it could be utilized in the prevention and treatment of muscle atrophy.

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

To observe the effects of electroacupuncture (EA) at "Jiaji" (EX-B 2) combined with neurodynamic mobilization (NM) on the cross-sectional area of the gastrocnemius muscle fibers after sciatic nerve injury in rabbits, and the expression of nuclear factor κB (NF-κB) and muscle-specific ring-finger protein 1 (MuRF1). A total of 180 common-grade New Zealand rabbits (half male and half female) were randomly divided into five groups, i.e. a normal control group, a model control group, a NM group, an EA group and a combined intervention group, 36 rabbits in each group. Except in the normal control group, clipping method was used to prepare the model of sciatic nerve injury in the rest groups. On the 3rd day of successful modeling, NM was delivered in the NM group. In the EA group, EA was exerted at bilateral "Jiaji" (EX-B 2) of L4 to L6, stimulated with disperse-dense wave and the frequency of 2 Hz/100 Hz. In the combined intervention group, after EA delivered at bilateral "Jiaji" (EX-B 2) of L4 to L6 , NM was operated. The intervention in each group was delivered once daily, for 6 days a week, and lasted 1, 2 or 4 weeks according to the collection time of sample tissue. After 1, 2 and 4 weeks of intervention, in each group, the toe tension reflex score and the modified Tarlov test score were observed; the morphology of the gastrocnemius muscle was observed by HE staining and the cross-sectional area of muscular fiber was measured; using Western blot method, the expression of NF-κB and MuRF1 of the gastrocnemius muscle was detected. After 1, 2 and 4 weeks of intervention, the toe tension reflex scores and the modified Tarlov scores in the model control group were lower than those of the normal control group (P<0.05), and these two scores in the NM group, the EA group and the combined intervention group were all higher than those of the model control group (P<0.05); the scores in the combined intervention group were higher than those in the EA group and the NM group (P<0.05). The gastrocnemius fibers were well arranged and the myocyte morphology was normal in the normal control group. In the model control group, the gastrocnemius fibers were disarranged, the myocytes were irregular in morphology and the inflammatory cells were infiltrated in the local. In the NM group, the EA group and the combined intervention group, the muscle fibers were regularly arranged when compared with the model control group. After 1, 2 and 4 weeks of intervention, the cross-sectional areas of the gastrocnemius muscle fibers in the model control group were smaller than those of the normal control group (P<0.05). The cross-sectional areas in the NM group, the EA group and the combined intervention group were larger than those of the model control group (P<0.05), and the cross-sectional areas in the combined intervention group were larger than those in the NM group and the EA group (P<0.05). After intervention for 1, 2 and 4 weeks, the protein expressions of NF-κB and MuRF1 in the gastrocnemius muscle were higher in the model control group in comparison of those in the normal control group (P<0.05). In the NM group, the EA group and the combined intervention group, the expressions of NF-κB after intervention for 1, 2 and 4 weeks and the expressions of MuRF1 after 2 and 4 weeks of intervention were lower when compared with those in the model control group (P<0.05). In the combined intervention group, the protein expressions of NF-κB after intervention for 1, 2 and 4 weeks and the expressions of MuRF1 after 2 and 4 weeks of intervention were decreased when compared with those in the NM group and the EA group (P<0.05). Electroacupuncture at "Jiaji" (EX-B 2) combined with NM may increase the muscle strength and sciatic function and alleviate gastrocnemius muscle atrophy in the rabbits with sciatic nerve injury. The underlying mechanism is related to the inhibition of NF-κB and MuRF1 expression.

Protective Role of Ethanol Extract of Cibotium barometz (Cibotium Rhizome) against Dexamethasone-Induced Muscle Atrophy in C2C12 Myotubes.

Sarcopenia is a progressive muscle disease characterized by the loss of skeletal muscle mass, strength, function, and physical performance. Since the disease code was assigned, attention has been focused on natural products that can protect against muscle atrophy. Cibotium barometz (Cibotium Rhizome) has been used as an herbal medicine for the treatment of bone or joint diseases in Asian countries. However, no studies have identified the mechanism of action of Cibotium Rhizome on muscle atrophy related to sarcopenia at the site of myotubes. The aim of this study was to investigate the improvement effect of the ethanol extract of Cibotium Rhizome (ECR) on dexamethasone-induced muscle atrophy in an in vitro cell model, i.e., the C2C12 myotubes. High-performance liquid chromatography was performed to examine the phytochemicals in ECR. Seven peaks in the ECR were identified, corresponding to the following compounds: protocatechuic acid, (+)-catechin hydrate, p-coumaric acid, ellagic acid, chlorogenic acid, caffeic acid, and ferulic acid. In atrophy-like conditions induced by 100 μM dexamethasone for 24 h in C2C12, ECR increased the expression of the myosin heavy chain, p-Akt, the p-mammalian target of rapamycin (mTOR), p-p70S6K, and repressed the expression of regulated in development and DNA damage responses 1 (REDD1), kruppel-like factor 15 (KLF 15), muscle atrophy F-box, and muscle-specific RING finger protein-1 in C2C12. In addition, ECR alleviated dexamethasone-induced muscle atrophy by repressing REDD1 and KLF15 transcription in C2C12 myotubes, indicating the need for further studies to provide a scientific basis for the development of useful therapeutic agents using ECR to alleviate the effects of skeletal muscle atrophy or sarcopenia.

A Mixture of Morus alba and Angelica keiskei Leaf Extracts Improves Muscle Atrophy by Activating the PI3K/Akt/mTOR Signaling Pathway and Inhibiting FoxO3a In Vitro and In Vivo.

Muscle atrophy, which is defined as a decrease in muscle mass and strength, is caused by an imbalance between the anabolism and catabolism of muscle proteins. Thus, modulating the homeostasis between muscle protein synthesis and degradation represents an efficient treatment approach for this condition. In the present study, the protective effects against muscle atrophy of ethanol extracts of Morus alba L. (MA) and Angelica keiskei Koidz. (AK) leaves and their mixtures (MIX) were evaluated in vitro and in vivo. Our results showed that MIX increased 5-aminoimidazole-4-carboxamide ribonucleotide-induced C2C12 myotube thinning, and enhanced soleus and gastrocnemius muscle thickness compared to each extract alone in dexamethasone-induced muscle atrophy Sprague Dawley rats. In addition, although MA and AK substantially improved grip strength and histological changes for dexamethasone-induced muscle atrophy in vivo, the efficacy was superior in the MIX-treated group. Moreover, MIX further increased the expression levels of myogenic factors (MyoD and myogenin) and decreased the expression levels of E3 ubiquitin ligases (atrogin-1 and muscle-specific RING finger protein-1) in vitro and in vivo compared to the MA- and AK-alone treatment groups. Furthermore, MIX increased the levels of phosphorylated phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), and mammalian target of rapamycin (mTOR) that were reduced by dexamethasone, and downregulated the expression of forkhead box O3 (FoxO3a) induced by dexamethasone. These results suggest that MIX has a protective effect against muscle atrophy by enhancing muscle protein anabolism through the activation of the PI3K/Akt/mTOR signaling pathway and attenuating catabolism through the inhibition of FoxO3a.

Limosilactobacillus fermentum MG5091 and Lactococcus lactis MG4668 and MG5474 Suppress Muscle Atrophy by Regulating Apoptosis in C2C12 Cells

Muscular atrophy is a chronic muscle disease characterized by a loss of muscle mass and muscle weakness due to excessive protein breakdown relative to protein synthesis. Apoptosis is a major factor in sarcopenia and the final stage of muscle atrophy that occurs via various mechanisms. In this study, we evaluated the protective effects of cell-free supernatants (CFSs) from different lactic acid bacteria (LAB) strains in dexamethasone (DEX)-treated C2C12 cells, followed by probiotic properties. We found that Limosilactobacillus fermentum (L. fermentum) MG4263 and MG5091 and Lactococcus lactis (Lc. lactis) MG4668 and MG5474 inhibited muscle atrophy F-box (atrogin-1) and muscle-specific RING-finger protein-1 (MuRF-1) in DEX-treated C2C12 cells. In addition, LAB strains inhibited the expression of apoptotic proteins, such as Bcl-2-associated X (Bax)/Bcl-2 and caspase-3 in DEX-treated C2C12 cells. L. fermentum MG5091, Lc. lactis MG4668, and MG5474 showed high survival rates in gastrointestinal (GIT) conditions and high adhesion rate to HT-29 cells. The LAB strains were also assessed for hemolysis and toxicity in HT-29 cells to confirm their stability. The LAB strains showed no hemolytic activity and toxicity to HT-29 cells. Therefore, L. fermentum MG5091, Lc. lactis MG4668, and MG5474 suggest their potential as probiotics to be used as functional foods for the inhibition of muscular atrophy.

Glycine Regulates Protein Turnover by Activating Protein Kinase B/Mammalian Target of Rapamycin and by Inhibiting MuRF1 and Atrogin-1 Gene Expression in C2C12 Myoblasts

Background: The regulation of protein turnover in skeletal muscle is essential for the maintenance of integrity, growth, and function of this tissue. We recently reported that glycine enhances skeletal muscle growth in young pigs. However, the underlying mechanisms remain unknown.Objective: This study was conducted with a mouse myoblast cell line, C2C12, to test the hypothesis that glycine activates protein kinase B/mammalian target of rapamycin (Akt/mTOR), as well as inhibits 5′-adenosine monophosphate-activated protein kinase (AMPK) and the expression of genes for proteolysis.Methods: C2C12 myoblasts were cultured with 0, 0.25 (physiologic concentration in mouse plasma), 0.5, or 1.0 mmol glycine/L. Cell proliferation, activation of mammalian target of rapamycin complex 1 (mTORC1), AMPK signaling, mRNA levels of atrogin-1 and muscle-specific ring finger protein 1 (MuRF1), and protein synthesis and degradation were measured in the absence or presence of an Akt inhibitor, LY294002, or an AMPK activator, 5-aminoimidazole-4-carboxyamide ribonucleoside (AICAR).Results: Compared with control cells, 0.25–1.0 mmol glycine/L enhanced cell growth (by 12–15%) after 24 h (P < 0.05). Glycine treatment led to increased DNA replication (by 70–80%) while enhancing mTORC1 activation by upregulating Akt and inhibiting AMPK signaling (P < 0.05). Accordingly, glycine exposure increased (P < 0.05) the rate of protein synthesis (by 20–80%) and inhibited (P < 0.05) the rate of protein degradation (by 15–30%) in a concentration-dependent manner in C2C12 cells. These observations were validated by the use of an Akt inhibitor, LY294002, or an AMPK activator, AICAR. Moreover, glycine addition resulted in decreased mRNA levels for atrogin-1 and MuRF1 (by 20–40% and 30–50%, respectively; P < 0.05). The repressing effect of glycine on the expression of MuRF1, instead of atrogin-1, was abolished by LY294002 (P < 0.05).Conclusions: These findings indicate that glycine plays a previously unrecognized role in enhancing protein synthesis and inhibiting protein degradation in C2C12 cells. Glycine regulates protein turnover by activating mTORC1 and by inhibiting the expression of genes for proteolysis. Our results indicate that glycine is a functional amino acid that improves muscle cell growth.

Ginsenoside Rd ameliorates muscle wasting by suppressing the signal transducer and activator of transcription 3 pathway.

The effects of some drugs, aging, cancers, and other diseases can cause muscle wasting. Currently, there are no effective drugs for treating muscle wasting. In this study, the effects of ginsenoside Rd (GRd) on muscle wasting were studied. Tumour necrosis factor-alpha (TNF-α)/interferon-gamma (IFN-γ)-induced myotube atrophy in mouse C2C12 and human skeletal myoblasts (HSkM) was evaluated based on cell thickness. Atrophy-related signalling, reactive oxygen species (ROS) level, mitochondrial membrane potential, and mitochondrial number were assessed. GRd (10mg/kg body weight) was orally administered to aged mice (23-24months old) and tumour-bearing (Lewis lung carcinoma [LLC1] or CT26) mice for 5weeks and 16days, respectively. Body weight, grip strength, inverted hanging time, and muscle weight were assessed. Histological analysis was also performed to assess the effects of GRd. The evolutionary chemical binding similarity (ECBS) approach, molecular docking, Biacore assay, and signal transducer and activator of transcription (STAT) 3 reporter assay were used to identify targets of GRd. GRd significantly induced hypertrophy in the C2C12 and HSkM myotubes (average diameter 50.8±2.6% and 49.9%±3.7% higher at 100nM, vs. control, P≤0.001). GRd treatment ameliorated aging- and cancer-induced (LLC1 or CT26) muscle atrophy in mice, which was evidenced by significant increases in grip strength, hanging time, muscle mass, and muscle tissue cross-sectional area (1.3-fold to 4.6-fold, vs. vehicle, P≤0.05; P≤0.01; P≤0.001). STAT3 was found to be a possible target of GRd by the ECBS approach and molecular docking assay. Validation of direct interaction between GRd and STAT3 was confirmed through Biacore analysis. GRd also inhibited STAT3 phosphorylation and STAT3 reporter activity, which led to the inhibition of STAT3 nuclear translocation and the suppression of downstream targets of STAT3, such as atrogin-1, muscle-specific RING finger protein (MuRF-1), and myostatin (MSTN) (29.0±11.2% to 84.3±30.5%, vs. vehicle, P≤0.05; P≤0.01; P≤0.001). Additionally, GRd scavenged ROS (91.7±1.4% reduction at 1nM, vs. vehicle, P≤0.001), inhibited TNF-α-induced dysregulation of ROS level, and improved mitochondrial integrity (P≤0.05; P≤0.01; P≤0.001). GRd ameliorates aging- and cancer-induced muscle wasting. Our findings suggest that GRd may be a novel therapeutic agent or adjuvant for reversing muscle wasting.

Ubiquitin E3 ligase Atrogin-1 protein is regulated via the rapamycin-sensitive mTOR-S6K1 signaling pathway in C2C12 muscle cells

Atrogin-1 and Muscle-specific RING finger protein 1 (MuRF1) are highly expressed in multiple conditions of skeletal muscle atrophy. The phosphoinositide 3-kinase (PI3K)/Akt/forkhead box (FoxO) signaling pathway is well known to regulate Atrogin-1 and MuRF1 gene expressions. However, Akt activation also activates the mechanistic target of rapamycin complex 1 (mTORC1), which induces skeletal muscle hypertrophy. Whether mTORC1-dependent signaling has a role in regulating Atrogin-1 and/or MuRF1 gene and protein expression is currently unclear. In this study, we showed that activation of insulin-mediated Akt signaling suppresses both Atrogin-1 and MuRF1 protein contents and that inhibition of Akt increases both Atrogin-1 and MuRF1 protein contents in C2C12 myotubes. Interestingly, inhibition of mTORC1 with a specific mTORC1 inhibitor, rapamycin, increased Atrogin-1, but not MuRF1, protein content. Furthermore, activation of AMP-activated protein kinase (AMPK), a negative regulator of the mTORC1 signaling pathway, also showed distinct time-dependent changes between Atrogin-1 and MuRF1 protein contents, suggesting differential regulatory mechanisms between Atrogin-1 and MuRF1 protein content. To further explore the downstream of mTORC1 signaling, we employed a specific S6K1 inhibitor, PF-4708671. We found that Atrogin-1 protein content was dose-dependently increased with PF-4708671 treatment, whereas MuRF1 protein content was decreased at 50 μM of PF-4708671 treatment. However, MuRF1 protein content was unexpectedly increased by PF-4708671 treatment for a longer period. Overall, our results indicate that Atrogin-1 and MuRF1 protein contents are regulated by different mechanisms, the downstream of Akt, and that Atrogin-1 protein content can be regulated by the rapamycin-sensitive mTOR-S6K1-dependent signaling pathway.

Acute cold stress induces transient MuRF1 upregulation in the skeletal muscle of zebrafish

Cryotherapy is one of the most common treatments for trauma or fatigue in the field of sports medicine. However, the molecular biological effects of acute cold exposure on skeletal muscle remain unclear. Therefore, we used zebrafish, which have recently been utilized as an animal model for skeletal muscle, to comprehensively investigate and selectively clarify the time-course changes induced by cryotherapy. Zebrafish were exposed intermittently to cold stimulation three times for 15 min each. Thereafter, skeletal muscle samples were collected after 15 min and 1, 2, 4, and 6 h. mRNA sequencing revealed the involvement of trim63a, fbxo32, fbxo30a, and klhl38b in “protein ubiquitination” from the top 10 most upregulated genes. Subsequently, we examined the time-course changes of the four genes by quantitative PCR, and their expression peaked 2 h after cryotherapy and returned to baseline after 6 h. Moreover, the proteins encoded by trim63a and fbxo32 (muscle-specific RING finger protein 1 [MuRF1] and muscle atrophy F-box, respectively), which are known to be major genes encoding E3 ubiquitin ligases, were examined by western blotting, and MuRF1 expression displayed similar temporal changes as trim63a expression. These findings suggest that acute cold exposure transiently upregulates E3 ubiquitin ligases, especially MuRF1; thus, cryotherapy may contribute to the treatment of trauma or fatigue by promoting protein processing.

Saturated fatty acids intake is associated with muscle atrophy in rheumatoid arthritis

AbstractBackgroundRheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease characterized by joint inflammation, abnormal body composition, and an increased risk for sarcopenia. Muscle wasting in turn increases the risk of infection, morbidity, and premature mortality, but little is known of the relation between nutrient intake and sarcopenia in RA.MethodsA prospective cohort study with follow‐up for 1 year examined body composition and diet in female outpatients with RA. We performed logistic regression analysis to assess which factors might have contributed to this loss of muscle mass. Multivariate logistic regression analysis with a forward–backward stepwise selection was also analysed. SKG/Jcl mice, which develop RA spontaneously, were fed normal chow or a high‐fat diet (HFD) and evaluated for inflammation and muscle mass.ResultsA total 53 female patients were included. The median age was 57.0 years, with an interquartile range (IQR) of 49.5 to 62.0 years, and the median disease duration was 4.0 years, with an IQR of 2.0 to 9.0 years. Fourteen patients (26.4%) had skeletal muscle mass index below the cut‐off for sarcopenia (≤5.7 kg/m2) as defined by the Asia Working Group for Sarcopenia. Multiple logistic regression analysis revealed that the intake of saturated fatty acids was associated with a &gt;5% decrease in skeletal muscle index of RA patients over 1 year [odds ratio 95% confidence interval 1.431 (1.082–1.894), P = 0.012]. In 9 weeks old SKG/Jcl mice, HFD feeding precipitated the onset of RA and exacerbated rheumatoid synovitis in association with the induction of T helper 17 cell differentiation. The serum concentrations of inflammatory cytokines including IL‐6 and TNF‐α were significantly higher in HFD‐fed RA mice than in normal chow (NC)‐fed RA mice or in HFD‐fed control mice (IL‐6; 3.8 vs. 32.2 pg/mL, P &lt; 0.05). Moreover, the HFD increased expression of the genes for the ubiquitin ligases atrogin‐1 and muscle‐specific RING‐finger protein‐1 (MuRF‐1) in skeletal muscle and elicited a marked loss of muscle mass in these mice (atrogin‐1; 1.72‐fold, MuRF‐1; 1.24‐fold in HFD‐fed mice). HFD‐fed RA mice showed a significant decrease in the weight of gastrocnemius and extensor digitorum longus and muscle volume of the lower limbs compared with NC‐fed RA mice or HFD‐fed control mice at 14 weeks of age.ConclusionsOur findings suggest that the consumption of saturated fat may be related to muscle loss in RA patients, and they may therefore provide a basis for a new dietary intervention strategy to prevent muscle wasting associated with this disease.

Roles of adenosine monophosphate activated protein kinase in skeletal muscle atrophy in rats with severe scald

Objective: To investigate the expression and phosphorylation level change of adenosine monophosphate activated protein kinase (AMPK) in skeletal muscle of severely scald rats and its roles in skeletal muscle atrophy in severely scalded rats. Methods: The experimental research method was applied. Totally 100 6-week-old male Wistar rats were divided into sham injury group and scald group according to the random number table, with 50 rats in each group. After weighing the body weight, rats in scald group were inflicted with full-thickness scald of 30% total body surface area on the back, and rats in sham injury group were simulated with scald. At 6 h and on 1, 3, 5, and 7 d post injury, 10 rats in each group were taken to measure their body weights and weights of extensor digitorum longus and soleus muscle. At 6 h and on 1, 3, 5, and 7 d post injury, the tibialis anterior muscles were collected, the mRNA expressions of muscle atrophy F-box protein (MAFbx) and muscle-specific RING finger protein 1 (MuRF1) were detected by real-time fluorescent quantitative reverse transcription polymerase chain reaction; the content of adenosine monophosphate (AMP), adenosine diphosphate, and adenosine triphosphate (ATP) were detected by high performance liquid chromatography, and AMP/ATP ratio and energy charge were calculated; the protein expressions of AMPK-α and phosphorylated AMPK-α (p-AMPK-α) were detected by Western blotting, and the p-AMPK-α/AMPK-α ratio was calculated, with sample number of 4 in each time point of each group. Data were statistically analyzed with analysis of variance for factorial design and least significant difference test. Results: The body weights of rats in 2 groups before injury and at each time point post injury were close (P>0.05). At 6 h post injury, the weight of extensor digitorum longus of rats in scald group was (0.107±0.007) g, which was significantly heavier than (0.086±0.0607) g of sham injury group (P<0.01). On 3 d post injury, the weight of extensor digitorum longus of rats in scald group was (0.083±0.016) g, which was significantly lighter than (0.102±0.005) g of sham injury group (P<0.01). The weight of soleus of rats in 2 groups were close at each time point post injury (P>0.05). Compared with those of sham injury group, the mRNA expression of MAFbx in tibialis anterior muscle of rats in scald group was significantly up-regulated at 6 h post injury (P<0.01), and the mRNA expressions of MuRF1 in tibial anterior muscle of rats in scald group were significantly up-regulated at 6 h and on 1 d post injury (P<0.01). At 6 h and on 7 d post injury, compared with those of false injury group, the AMP/ATP ratios of the tibial anterior muscle of rats in scald group were significantly increased (P<0.05 or P<0.01), and energy charges of the tibial anterior muscle of rats in scald group were significantly decreased (P<0.01). At each time point post injury, the protein expressions of AMPK-α of the tibial anterior muscle of rats in 2 groups were close (P>0.05). The p-AMPK-α/AMPK-α ratios of the tibial anterior muscle of rats in scald group at 6 h and on 7 d post injury were significantly higher than those in sham injury group (P<0.05 or P<0.01). Conclusions: The decrease in energy charge and increase in AMP/ATP ratio of skeletal muscle of rats after severe scald activate AMPK. The activation of AMPK in the early stage of injury is consistent with the up-regulation of MAFbx and MuRF1 expressions and down-regulation of skeletal muscle weight. The above-mentioned changes may be one of the molecular mechanisms of skeletal muscle atrophy in rats with severe scald.

Proteasome activity and expression of mammalian target of rapamycin signaling factors in skeletal muscle of dairy cows supplemented with conjugated linoleic acids during early lactation

The mammalian target of rapamycin (mTOR) is a major regulator of protein synthesis via its main downstream effectors, ribosomal protein S6 kinase (S6K1) and eukaryotic initiation factor 4E binding protein (4EBP1). The ubiquitin-proteasome system (UPS) is the main proteolytic pathway in muscle, and the muscle-specific ligases tripartite motif containing 63 (TRIM63; also called muscle-specific ring-finger protein 1, MuRF-1) and F-box only protein 32 (FBXO32; also called atrogin-1) are important components of the UPS. We investigated 20S proteasome activity and mRNA expression of key components of mTOR signaling and UPS in skeletal muscle of dairy cows during late gestation and early lactation and tested the effects of dietary supplementation (from d 1 in milk) with conjugated linoleic acids (sCLA; 100 g/d; n = 11) compared with control fat-supplemented cows (CTR; n = 10). Blood and muscle tissue (semitendinosus) samples were collected on d -21, 1, 21, and 70 relative to parturition. Dry matter intake increased with time of lactation in both groups. It was lower in sCLA than in CTR on d 21, which resulted in a reduced calculated metabolizable protein balance. Most serum and muscle concentrations of AA followed time-related changes but were unaffected by CLA supplementation. In both groups, serum and muscle 3-methylhistidine (3-MH) concentrations and the ratio of 3-MH:creatinine increased from d -21 to d 1, followed by a decline on d 21. The mRNA abundance of MTOR on d 21 and 70 was greater in sCLA than in CTR. The abundance of 4EBP1 mRNA did not differ between groups but was upregulated in both on d 1. The mRNA abundance of S6K1 on d 70 was greater in CTR than in sCLA, but remained unchanged over time in both groups. The mRNA abundance of FBXO32 (encoding atrogin-1) on d 21 was greater in sCLA than in CTR. The mRNA abundance of TRIM63 (also known as MuRF1) showed a similar pattern as FBXO32 in both groups: an increase from d -21 to d 1, followed by a decline. The mRNA for the α (BCKDHA) and β (BCKDHB) polypeptide of branched-chain α-keto acid dehydrogenase was elevated in sCLA and CTR cows on d 21, respectively, suggesting a role of CLA in determining the metabolic fate of branched-chain AA. For the mTOR protein, no group differences were observed. The abundance of S6K1 protein was greater across all time points in sCLA versus CTR. The antepartum 20S proteasome activity in muscle was elevated in both groups compared with postpartum, probably reflecting the start of protein mobilization before parturition. Plasma insulin concentrations decreased in both groups postpartum but to a greater extent in CTR than in sCLA, resulting in greater insulin concentrations in sCLA than in CTR. Thus, the greater abundance of MTOR mRNA and S6K1 protein in sCLA compared with CTR might be mediated by the greater plasma insulin postpartum. The upregulation of MTOR mRNA in sCLA cows on d 21, despite greater FBXO32 mRNA abundance, may reflect a simultaneous activation of both anabolic and catabolic signaling pathways, likely resulting in greater protein turnover.

Effects of exogenous ghrelin on muscle atrophy in elderly mice

Objective To investigate the effects of acylated ghrelin and des-acylated ghrelin on skeletal muscle atrophy in elderly mice. Methods Eighteen-month-old wild type(WT)mice and ghrelin-/- mice were selected to perform body composition analysis and wheel-running test under conditions of feeding versus fasting.The gene expressions of myogenic regulatory factors including muscle differentiation factor MyoD, myogenin, atrogin-1, muscle-specific RING finger protein 1(muRF-1), and insulin growth factor 1(IGF-1)in mice gastrocnemius muscle were detected by realtime polymerase chain reaction(PCR). Results The locomotor activity during the wheel-running test were significantly lower in elderly ghrelin-/- mice than in elderly WT mice(3 929±263 times/h vs.5359±601 times/h, t=4.87, P 0.05). After 48 h fasting, the decrements of body weight, fat and muscle weight were more in ghrelin-/- mice than in WT mice(P<0.05). In fasting old ghrelin-/- mice, the gene expressions of MyoD and myogenin were increased(improved)(t=232.00 and 121.00, P<0.05), and the gene expressions of atrogin-1 and muRF-1 were decreased(improved)(t=30.40 and 54.00, P<0.05)after treatment with both acylated ghrelin and desacylated ghrelin. Conclusions The acylated ghrelin and desacylated ghrelin may play protective roles in age-related muscle atrophy. Key words: Ghrelin; Muscular atrophy

Generation of MuRF-GFP transgenic zebrafish models for investigating murf gene expression and protein localization in Smyd1b and Hsp90α1 knockdown embryos.

Muscle-specific RING-finger proteins (MuRFs) are E3 ubiquitin ligases that play important roles in protein quality control in skeletal and cardiac muscles. Here we characterized murf gene expression and protein localization in zebrafish embryos. We found that the zebrafish genome contains six murf genes, including murf1a, murf1b, murf2a, murf2b, murf3 and a murf2-like gene that are specifically expressed in skeletal and cardiac muscles of zebrafish embryos. To analyze the subcellular localization, we generated transgenic zebrafish models expressing MurF1a-GFP or MuRF2a-GFP fusion proteins. MuRF1a-GFP and MuRF2a-GFP showed distinct patterns of subcellular localization. MuRF1a-GFP displayed a striated pattern of localization in myofibers, whereas MuRF2a-GFP mainly exhibited a random pattern of punctate distribution. The MuRF1a-GFP signal appeared as small dots aligned along the M-lines of the sarcomeres in skeletal myofibers. To determine whether knockdown of smyd1b or hsp90α1 that increased myosin protein degradation could alter murf gene expression or MuRF protein localization, we knocked down smyd1b or hsp90α1 in wild type, Tg(ef1a:MurF1a-GFP) and Tg(ef1a:MuRF2a-GFP) transgenic zebrafish embryos. Knockdown of smyd1b or hsp90α1 had no effect on murf gene expression. However, the sarcomeric distribution of MuRF1a-GFP was abolished in the knockdown embryos. This was accompanied by an increased random punctate distribution of MuRF1a-GFP in muscle cells of zebrafish embryos. Collectively, these studies demonstrate that MuRFs are specifically expressed in developing muscles of zebrafish embryos. The M-line localization MuRF1a is altered by sarcomere disruption in smyd1b or hsp90α1 knockdown embryos.

DCAF8, a novel MuRF1 interaction partner, promotes muscle atrophy.

The muscle-specific RING-finger protein MuRF1 (also known as TRIM63) constitutes a bona fide ubiquitin ligase that routes proteins like several different myosin heavy chain proteins (MyHC) to proteasomal degradation during muscle atrophy. In two unbiased screens, we identified DCAF8 as a new MuRF1-binding partner. MuRF1 physically interacts with DCAF8 and both proteins localize to overlapping structures in muscle cells. Importantly, similar to what is seen for MuRF1, DCAF8 levels increase during atrophy, and the downregulation of either protein substantially impedes muscle wasting and MyHC degradation in C2C12 myotubes, a model system for muscle differentiation and atrophy. DCAF proteins typically serve as substrate receptors for cullin 4-type (Cul4) ubiquitin ligases (CRL), and we demonstrate that DCAF8 and MuRF1 associate with the subunits of such a protein complex. Because genetic downregulation of DCAF8 and inhibition of cullin activity also impair myotube atrophy in C2C12 cells, our data imply that the DCAF8 promotes muscle wasting by targeting proteins like MyHC as an integral substrate receptor of a Cul4A-containing ring ubiquitin ligase complex (CRL4A).This article has an associated First Person interview with the first author of the paper.

Acute estradiol treatment reduces skeletal muscle protein breakdown markers in early- but not late-postmenopausal women

ObjectivesMenopause and decline in estradiol (E2) may contribute to sarcopenia (i.e., age-related decline in muscle mass and strength) in women. E2 may directly impact skeletal muscle protein breakdown via estrogen receptor (ER) signaling, primarily ERα. It is not yet known whether: 1) E2 regulates pathways of skeletal muscle protein breakdown; 2) E2-mediated changes in protein breakdown markers are associated with ERα activation and insulin sensitivity; and 3) the effects of E2 on protein breakdown markers differ by increasing time since menopause. Study designWe studied 27 women who were ≤6 years past menopause (early postmenopausal, EPM; n = 13) or ≥10 years past menopause (late postmenopausal, LPM; n = 14). Fasted skeletal muscle samples were collected following 1 week of transdermal E2 or placebo treatment in a randomized cross-over design. Main outcome measuresWe analyzed for cytosolic protein content of the: 1) structural proteins myosin heavy chain (MHC) and tropomyosin; and 2) protein regulatory markers: protein kinase B (Akt), muscle-specific ring finger protein1 (MuRF1), atrogin1, and forkhead box O3 (FOXO3) using Western blot. ResultsIn response to acute E2, FOXO3 activation (dephosphorylation) and MuRF1 protein expression decreased in EPM but increased in LPM women (p < 0.05). ERα activation was not associated with these protein breakdown markers, but FOXO3 activation tended to be inversely correlated (r = −0.318, p = 0.065) to insulin sensitivity. ConclusionsThese preliminary studies suggest the effects of E2 on skeletal muscle protein breakdown markers were dependent on time since menopause, which is consistent with our previous study on insulin sensitivity.

Effect of electroacupuncture on degradation of myosin heavy chain of gastrocnemius muscle in diabetes rats

To explore the effect of electroacupuncture（EA）on the expression of muscle-specific ring finger protein 1（MuRF1/Trim63），F-box only protein 32（Fbxo32），myosin heavy chain-IIa（Myh2），myosin heavy chain-IIb（Myh4）and myosin heavy chain-I（Myh7）in diabetes rats. Thirty-six male Wistar rats were equally randomized into control, model and EA groups. The diabetes model was established by intraperitoneal injection of 0.1% Streptozocin (STZ) solution (50 mg/kg). After that, EA (2 Hz, 1 mA) was applied to bilateral "Zusanli" (ST36), "Yinlingquan" (SP9) and "Shenshu" (BL23) for 10 min, once a day, 6 times a week for 2 weeks. The fasting blood glucose (FBG) and fasting serum insulin (FINS) contents were assayed by using ELISA, and the homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. The body weight, and wet weight of bilateral gastrocnemius muscles were measured. The cross-sectional area (CSA) of the gastrocnemius muscle was measured after H.E. stai-ning. The expression of MuRF1, Fbxo32, Myh2, Myh4 and Myh7 mRNAs in the gastrocnemius tissue was tested using quantitative real time-PCR. Compared with the control group, the FBG and HOMA-IR were significantly higher (P<0.05), and the FINS, body weight were significantly lower (P<0.05) after intravenous injection of STZ for 1, 2, 3, 4, 5 weeks respectively. Following EA treatment and compared with the model group, the FBG and HOMA-IR were significantly down-regulated (P<0.05), and the FINS and body weight were considerably increased (P<0.05). Following modeling and compared with the control group, the wet weight of gastrocnemius muscle, CSA, and expression levels of Myh2, Myh4 and Myh7 mRNAs were obviously decreased, and the expression of MuRF1 and Fbxo32 mRNA was obviously increased in the model group (P<0.05). After EA treatment, the gastrocnemius muscle wet weight, CSA, expression levels of Myh2, Myh4 and Myh7 mRNA were significantly up-regulated (P<0.05), and the expression levels of MuRF1 and Fbxo32 mRNA were markedly down-regulated in comparison with those of the model group (P<0.05). EA treatment can delay the atrophy of gastrocnemius muscle (skeletal muscle) in diabetes rats possibly by improving the degradation of myosin heavy chain via regulating the expression of muscular MuRF1, Fbxo32, Myh2, Myh4 and Myh7 mRNAs.

Perturbation of the titin/MURF1 signaling complex is associated with hypertrophic cardiomyopathy in a fish model and in human patients.

ABSTRACTHypertrophic cardiomyopathy (HCM) is a hereditary disease characterized by cardiac hypertrophy with diastolic dysfunction. Gene mutations causing HCM have been found in about half of HCM patients, while the genetic etiology and pathogenesis remain unknown for many cases of HCM. To identify novel mechanisms underlying HCM pathogenesis, we generated a cardiovascular-mutant medaka fish, non-spring heart (nsh), which showed diastolic dysfunction and hypertrophic myocardium. The nsh homozygotes had fewer myofibrils, disrupted sarcomeres and expressed pathologically stiffer titin isoforms. In addition, the nsh heterozygotes showed M-line disassembly that is similar to the pathological changes found in HCM. Positional cloning revealed a missense mutation in an immunoglobulin (Ig) domain located in the M-line–A-band transition zone of titin. Screening of mutations in 96 unrelated patients with familial HCM, who had no previously implicated mutations in known sarcomeric gene candidates, identified two mutations in Ig domains close to the M-line region of titin. In vitro studies revealed that the mutations found both in medaka fish and in familial HCM increased binding of titin to muscle-specific ring finger protein 1 (MURF1) and enhanced titin degradation by ubiquitination. These findings implicate an impaired interaction between titin and MURF1 as a novel mechanism underlying the pathogenesis of HCM.

Excessive glucocorticoid-induced muscle MuRF1 overexpression is independent of Akt/FoXO1 pathway.

The ubiquitin-proteasome system (UPS)-dependent proteolysis plays a major role in the muscle catabolic action of glucocorticoids (GCs). Atrogin-1 and muscle-specific RING finger protein 1 (MuRF1), two E3 ubiquitin ligases, are uniquely expressed in muscle. It has been previously demonstrated that GC treatment induced MuRF1 and atrogin-1 overexpression. However, it is yet unclear whether the higher pharmacological dose of GCs induced muscle protein catabolism through MuRF1 and atrogin-1. In the present study, the role of atrogin-1 and MuRF1 in C2C12 cells protein metabolism during excessive dexamethasone (DEX) was studied. The involvement of Akt/forkhead box O1 (FoXO1) signaling pathway and the cross-talk between anabolic regulator mammalian target of rapamycin (mTOR) and catabolic regulator FoXO1 were investigated. High concentration of DEX increased MuRF1 protein level in a time-dependent fashion (P<0.05), while had no detectable effect on atrogin-1 protein (P>0.05). FoXO1/3a (Thr24/32) phosphorylation was enhanced (P<0.05), mTOR phosphorylation was suppressed (P<0.05), while Akt protein expression was not affected (P>0.05) by DEX. RU486 treatment inhibited the DEX-induced increase of FoXO1/3a phosphorylation (P<0.05) and MuRF1 protein; LY294002 (LY) did not restore the stimulative effect of DEX on the FoXO1/3a phosphorylation (P>0.05), but inhibited the activation of MuRF1 protein induced by DEX (P<0.05); rapamycin (RAPA) inhibited the stimulative effect of DEX on the FoXO1/3a phosphorylation and MuRF1 protein (P<0.05).

Age-related external anal sphincter muscle dysfunction and fibrosis: possible role of Wnt/β-catenin signaling pathways.

Studies show an age-related increase in the prevalence of anal incontinence and sphincter muscle atrophy. The Wnt/β-catenin signaling pathway has been recently recognized as the major molecular pathway involved in age-related skeletal muscle atrophy and fibrosis. The goals of our study were to 1) evaluate the impact of normal aging on external anal sphincter (EAS) muscle length-tension (L-T) function and morphology and 2) specifically examine the role of Wnt signaling pathways in anal sphincter muscle fibrosis. New Zealand White female rabbits [6 young (6 mo of age) and 6 old (36 mo of age)] were anesthetized, and anal canal pressure was measured to determine the L-T function of EAS. Animals were killed at the end of the study, and the anal canal was harvested and processed for histochemical studies (Masson trichrome stain for muscle/connective tissue) as well as for molecular markers for fibrosis and atrophy [collagen I, β-catenin, transforming growth factor-β (TGF-β), atrogin-1, and muscle-specific RING finger protein-1 (MuRF-1)]. The L-T was significantly impaired in older animals compared with young animals. Anal canal sections stained with trichrome showed a significant decrease in the muscle content (52% in old compared with 70% in young) and an increase in the connective tissue/collagen content in the old animals. An increased protein and mRNA expression of all the fibrosis markers was seen in the older animals. Aging EAS muscle exhibits impairment of function and increase in connective tissue. Upregulation of atrophy and profibrogenic proteins with aging may be the reason for the age-related decrease in anal sphincter muscle thickness and function.NEW & NOTEWORTHY Our studies using a female rabbit model show age-related alterations in the structure and function of the external anal sphincter (EAS) muscle. We used endoluminal ultrasound to measure age-related changes in EAS muscle thickness. We employed Western blot and quantitative PCR to demonstrate age-related changes in the levels of important fibrogenic as well as atrophy markers. Our findings may have significant clinical implications, i.e., use of specific antagonists to prevent age-related EAS muscle dysfunction.