Mouse C2C12 Myotubes Research Articles

Endurance exercise-induced histone methylation modification involved in skeletal muscle fiber type transition and mitochondrial biogenesis

Skeletal muscle is a highly heterogeneous tissue, and its contractile proteins are composed of different isoforms, forming various types of muscle fiber, each of which has its own metabolic characteristics. It has been demonstrated that endurance exercise induces the transition of muscle fibers from fast-twitch to slow-twitch muscle fiber type. Herein, we discover a novel epigenetic mechanism for muscle contractile property tightly coupled to its metabolic capacity during muscle fiber type transition with exercise training. Our results show that an 8-week endurance exercise induces histone methylation remodeling of PGC-1α and myosin heavy chain (MHC) isoforms in the rat gastrocnemius muscle, accompanied by increased mitochondrial biogenesis and an elevated ratio of slow-twitch to fast-twitch fibers. Furthermore, to verify the roles of reactive oxygen species (ROS) and AMPK in exercise-regulated epigenetic modifications and muscle fiber type transitions, mouse C2C12 myotubes were used. It was shown that rotenone activates ROS/AMPK pathway and histone methylation enzymes, which then promote mitochondrial biogenesis and MHC slow isoform expression. Mitoquinone (MitoQ) partially blocking rotenone-treated model confirms the role of ROS in coupling mitochondrial biogenesis with muscle fiber type. In conclusion, endurance exercise couples mitochondrial biogenesis with MHC slow isoform by remodeling histone methylation, which in turn promotes the transition of fast-twitch to slow-twitch muscle fibers. The ROS/AMPK pathway may be involved in the regulation of histone methylation enzymes by endurance exercise.

Jie-Du-Tong-Luo formula protects C2C12 myotubes against high glucose and palmitic acid injury by activating the PI3K/Akt/PPARγ pathway in vitro

IntroductionIn prior reports, Jie-Du-Tong-Luo (JDTL) was reported to help control insulin secretion and blood glucose in patients with diabetes, while also protecting liver and pancreatic islet cells against injury caused by exposure to high glucose (HG) levels. This study was thus developed to assess the effects of JDTL on HG and palmitic acid (PA)-induced muscle injury and to explore the mechanistic basis for these effects. MethodsA model of muscle injury was established using mouse C2C12 myotubes treated with HG + PA. A proteomics approach was used to assess changes in protein levels following JDTL treatment, after which Western immunoblotting was employed to validate significantly affected pathways. ResultsJDTL was able to protect against HG + PA-induced muscle cell injury in this experimental system, altering lipid metabolism and inflammatory activity in these injured C2C12 myotubes. Western blotting suggested that JDTL is capable of activating PI3K/Akt/PPARγ signaling to control lipid metabolism without any corresponding impact on the inflammatory NF-κB pathway. ConclusionsThese data highlight the ability of JDTL to protect against HG + PA-induced injury to muscle cells, and suggest that the underlying basis for such efficacy is related to the PI3K/Akt/PPARγ pathway-mediated modulation of lipid metabolism.

Profiling cells with DELs: Small molecule fingerprinting of cell surfaces

DNA-encoded small molecule library technology has recently emerged as a new paradigm for identifying ligands against drug targets. To date, it has been used to identify ligands against targets that are soluble or overexpressed on cell surfaces. Here, we report applying cell-based selection methods to profile surfaces of mouse C2C12 myoblasts and myotube cells in an unbiased, target agnostic manner. A panel of on-DNA compounds were identified and confirmed for cell binding selectivity. We optimized the cell selection protocol and employed a novel data analysis method to identify cell selective ligands against a panel of human B and T lymphocytes. We discuss the generality of using this workflow for DNA encoded small molecule library selection and data analysis against different cell types, and the feasibility of applying this method to profile cell surfaces for biomarker and target identification.

Myotube growth is associated with cancer-like metabolic reprogramming and is limited by phosphoglycerate dehydrogenase and pyruvate kinase M2

Skeletal myofiber size and oxidative metabolism are inversely related. Glycolytic fast type myofibers are larger than high high oxidative, slow type myofibers. Paradoxically, despite their lower capacity for protein synthesis (lower myonucluar density and RNA content), glycolytic, low oxidative are more responsive to an anabolic stimulus. We hypothesized that glycolytic myofibers may make use of a Warburg-like metabolic reprogramming in response to an anabolic stimulus. The Warburg effect links growth and glycolysis in tumor cells to generate glycolytic intermediates for synthesis of nucleotides and amino. The aim of this study was to test whether a similar ‘glycolysis-for-anabolism’ metabolic reprogramming also occurs in post-mitotic, hypertrophying myofibers. For this purpose, we first induced C2C12 myotube hypertrophy with IGF-1. We then added 14C glucose to the differentiation medium and measured radioactivity in isolated protein and RNA to establish whether 14C had entered anabolism. We found that especially protein became radioactive, suggesting a glucose → glycolytic intermediates → non-essential amino acid(s) → protein series of reactions, the rate of which was increased by IGF-1. Next, to investigate the importance of glycolytic flux and non-essential amino acid synthesis for myotube hypertrophy, we exposed C2C12 and primary mouse myotubes to the glycolysis inhibitor 2-Deoxy-D-glucose (2DG). We found that inhibiting glycolysis lowered C2C12 and primary myotube size. Similarly, siRNA silencing of PHGDH and PKM2, key enzymes of the Warburg-like metabolic reprogramming, reduced C2C12 and primary myotube growth; whereas retroviral PHGDH overexpression increased C2C12 myotube size. Together these results suggest that glycolysis is important for hypertrophying myotubes, which reprogramme their metabolism to facilitate anabolism, similar to cancer cells. Brendan M. Gabriel was supported by fellowships from the Novo Nordisk Foundation (NNF19OC0055072) & the Wenner-Gren Foundation, an Albert Renold Travel Fellowship from the European Foundation for the Study of Diabetes, and an Eric Reid Fund for Methodology from the Biochemical Society. Abdalla D. Mohamed was funded initially by Sarcoma UK (grant number SUK09.2015), then supported by funding from Postdoctoral Fellowship Program (Helmholtz Zentrum München, Germany), and currently by Cancer Research UK. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Differential effects of cholecalciferol and calcitriol on muscle proteolysis and oxidative stress in angiotensin II-induced C2C12 myotube atrophy.

Renin-angiotensin system activation contributes to skeletal muscle atrophy in aging individuals with chronic diseases. We aimed to explore the effects of cholecalciferol (VD3) and calcitriol (1,25VD3) on signaling of muscle proteolysis and oxidative stress in myotubes challenged with angiotensin II (AII). The mouse C2C12 myotubes were assigned to vehicle, AII, AII + VD3, AII + 1,25VD3, and AII + losartan groups. The expression levels of muscle-specific E3 ubiquitin ligase proteins, autophagy-related proteins, and oxidative stress markers were investigated. We demonstrated the diverse effects of VD3 and 1,25VD3 on AII-induced myotube atrophy. The myotube diameter was preserved by treatment with 100 nM VD3 and losartan, while 1 and 10 nM 1,25VD3 increased levels of FoxO3a, MuRF1, and atrogin-1 protein expression in myotubes exposed to AII. Treatment with AII + 10 nM 1,25VD3 resulted in the upregulation of LC3B-II, LC3B-II/LC3B-I, and mature cathepsin L, which are autophagic marker proteins. The p62/SQSTM1 protein was downregulated and vitamin D receptor was upregulated after treatment with AII + 10 nM 1,25VD3. A cellular redox imbalance was observed as AII + 10 nM 1,25VD3-induced reactive oxygen species and NADPH oxidase-2 overproduction, and these changes were associated with an inadequate response of antioxidant superoxide dismutase-1 and catalase proteins. Collectively, these findings provide a translational perspective on the role of vitamin D3 in alleviating muscle atrophy related to high levels of AII.

Direct Plasmid DNA Transfection into Differentiated Mouse C2C12 Myotubes

Direct Plasmid DNA Transfection into Differentiated Mouse C2C12 Myotubes

Myotube growth is associated with cancer-like metabolic reprogramming and is limited by phosphoglycerate dehydrogenase

The Warburg effect links growth and glycolysis in cancer. A key purpose of the Warburg effect is to generate glycolytic intermediates for anabolic reactions, such as nucleotides → RNA/DNA and amino acids → protein synthesis. The aim of this study was to investigate whether a similar ‘glycolysis-for-anabolism’ metabolic reprogramming also occurs in hypertrophying skeletal muscle. To interrogate this, we first induced C2C12 myotube hypertrophy with IGF-1. We then added 14C glucose to the differentiation medium and measured radioactivity in isolated protein and RNA to establish whether 14C had entered anabolism. We found that especially protein became radioactive, suggesting a glucose → glycolytic intermediates → non-essential amino acid(s) → protein series of reactions, the rate of which was increased by IGF-1. Next, to investigate the importance of glycolytic flux and non-essential amino acid synthesis for myotube hypertrophy, we exposed C2C12 and primary mouse myotubes to the glycolysis inhibitor 2-Deoxy-d-glucose (2DG). We found that inhibiting glycolysis lowered C2C12 and primary myotube size. Similarly, siRNA silencing of PHGDH, the key enzyme of the serine biosynthesis pathway, decreased C2C12 and primary myotube size; whereas retroviral PHGDH overexpression increased C2C12 myotube size. Together these results suggest that glycolysis is important for hypertrophying myotubes, which reprogram their metabolism to facilitate anabolism, similar to cancer cells.

CaMKK2 is not involved in contraction-stimulated AMPK activation and glucose uptake in skeletal muscle

ObjectiveThe AMP-activated protein kinase (AMPK) gets activated in response to energetic stress such as contractions and plays a vital role in regulating various metabolic processes such as insulin-independent glucose uptake in skeletal muscle. The main upstream kinase that activates AMPK through phosphorylation of α-AMPK Thr172 in skeletal muscle is LKB1, however some studies have suggested that Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2) acts as an alternative kinase to activate AMPK. We aimed to establish whether CaMKK2 is involved in activation of AMPK and promotion of glucose uptake following contractions in skeletal muscle. MethodsA recently developed CaMKK2 inhibitor (SGC-CAMKK2-1) alongside a structurally related but inactive compound (SGC-CAMKK2-1N), as well as CaMKK2 knock-out (KO) mice were used. In vitro kinase inhibition selectivity and efficacy assays, as well as cellular inhibition efficacy analyses of CaMKK inhibitors (STO-609 and SGC-CAMKK2-1) were performed. Phosphorylation and activity of AMPK following contractions (ex vivo) in mouse skeletal muscles treated with/without CaMKK inhibitors or isolated from wild-type (WT)/CaMKK2 KO mice were assessed. Camkk2 mRNA in mouse tissues was measured by qPCR. CaMKK2 protein expression was assessed by immunoblotting with or without prior enrichment of calmodulin-binding proteins from skeletal muscle extracts, as well as by mass spectrometry-based proteomics of mouse skeletal muscle and C2C12 myotubes. ResultsSTO-609 and SGC-CAMKK2-1 were equally potent and effective in inhibiting CaMKK2 in cell-free and cell-based assays, but SGC-CAMKK2-1 was much more selective. Contraction-stimulated phosphorylation and activation of AMPK were not affected with CaMKK inhibitors or in CaMKK2 null muscles. Contraction-stimulated glucose uptake was comparable between WT and CaMKK2 KO muscle. Both CaMKK inhibitors (STO-609 and SGC-CAMKK2-1) and the inactive compound (SGC-CAMKK2-1N) significantly inhibited contraction-stimulated glucose uptake. SGC-CAMKK2-1 also inhibited glucose uptake induced by a pharmacological AMPK activator or insulin. Relatively low levels of Camkk2 mRNA were detected in mouse skeletal muscle, but neither CaMKK2 protein nor its derived peptides were detectable in mouse skeletal muscle tissue. ConclusionsWe demonstrate that pharmacological inhibition or genetic loss of CaMKK2 does not affect contraction-stimulated AMPK phosphorylation and activation, as well as glucose uptake in skeletal muscle. Previously observed inhibitory effect of STO-609 on AMPK activity and glucose uptake is likely due to off-target effects. CaMKK2 protein is either absent from adult murine skeletal muscle or below the detection limit of currently available methods.

ODP201 Fyn regulates sarcopenia via autophagy

Abstract Sarcopenia is an important element that impairs daily activity. Sarcopenia is also linked to insulin resistance, and the number of diabetic patients also presenting sarcopenia is increasing. In recent years, autophagy has been identified as one of the novel mechanisms associated with sarcopenia. We previously reported that Fyn not only participates in the metabolic syndrome but also that autophagy-regulating sarcopenia was decreased in muscle specific Fyn transgenic mice through STAT3 regulation (Cell metabolism 2010, Cell Rep. 2012). More recently, we revealed Fyn-dependent STAT3 phosphorylation by IL6, which is involved in chronic inflammation and metabolic syndrome, using mouse C2C12 myotube cells expressing shRNA for Fyn. Furthermore, using WT mice with both the denervated and the hind limb suspension (HS) that promotes disuse atrophy by suspending the hind limb, not only both Fyn and IL6 gene expressions were increased but the expression and phosphorylation levels of STAT3 were also augmented, while the autophagic activity was decreased. To confirm those regulations are Fyn dependent, we took advantage of Fyn null mice (FynKO) with HS. Compare to WT mice with HS, all the muscles of FynKO were resistant for the loss of muscle mass induced by HS. The expressions of bothatrogin-1 and muRF-1,the key muscle specific E3 ubiquitin ligases as well as the markers for sarcopenia, were not changed in the muscles of FynKO with HS. Moreover, the STAT3 phosphorylation on tyrosine 705 was decreased in the muscle of FynKO compared to WT mice after hind limb suspension, while expression levels of STAT3 were not changed. IL-6mRNA expression levels were increased in the HS muscle of control mice, but were not changed in FynKO HS muscle. Finally, the autophagic activity, examined by both LC3-2 protein levels after intraperitoneal administration of colchicine andSQSTM1/p62 immunofluorescence in muscles, was retained in FynKO after HS. These results strongly suggest that Fyn is involved not only in the metabolic syndrome but also in the pathogenesis of sarcopenia, and may lead to a better understanding of the pathology of sarcopenia-associated obesity and the development of therapeutic methods. Presentation: No date and time listed

Cathelicidin-related antimicrobial peptide mediates skeletal muscle degeneration caused by injury and Duchenne muscular dystrophy in mice.

Cathelicidin, an antimicrobial peptide, plays a key role in regulating bacterial killing and innate immunity; however, its role in skeletal muscle function is unknown. We investigated the potential role of cathelicidin in skeletal muscle pathology resulting from acute injury and Duchenne muscular dystrophy (DMD) in mice. Expression changes and muscular localization of mouse cathelicidin-related antimicrobial peptide (Cramp) were examined in the skeletal muscle of normal mice treated with chemicals (cardiotoxin and BaCl2 ) or in dystrophic muscle of DMD mouse models (mdx, mdx/Utrn+/- and mdx/Utrn-/- ). Cramp penetration into myofibres and effects on muscle damage were studied by treating synthetic peptides to mouse skeletal muscles or C2C12 myotubes. Cramp knockout (KO) mice and mdx/Utrn/Cramp KO lines were used to determine whether Cramp mediates muscle degeneration. Muscle pathophysiology was assessed by histological methods, serum analysis, grip strength and lifespan. Molecular factors targeted by Cramp were identified by the pull-down assay and proteomic analysis. In response to acute muscle injury, Cramp was activated in muscle-infiltrating neutrophils and internalized into myofibres. Cramp treatments of mouse skeletal muscles or C2C12 myotubes resulted in muscle degeneration and myotube damage, respectively. Genetic ablation of Cramp reduced neutrophil infiltration and ameliorated muscle pathology, such as fibre size (P<0.001; n=6) and fibrofatty infiltration (P<0.05). Genetic reduction of Cramp in mdx/Utrn+/- mice not only attenuated muscle damage (35%, P<0.05; n=9-10), myonecrosis (53%, P<0.05), inflammation (37-65%, P<0.01) and fibrosis (14%, P<0.05) but also restored muscle fibre size (14%, P<0.05) and muscle force (18%, P<0.05). Reducing Cramp levels led to a 63% (male, P<0.05; n=10-14) and a 124% (female, P<0.001; n=20) increase in the lifespan of mdx/Utrn-/- mice. Proteomic and mechanistic studies revealed that Cramp cross-talks with Ca2+ signalling in skeletal muscle through sarcoplasmic/endoplasmic reticulum Ca2+ -ATPase1 (SERCA1). Cramp binds and inactivates SERCA1, leading to the activation of Ca2+ -dependent calpain proteases that exacerbate DMD progression. These findings identify Cramp as an immune cell-derived regulator of skeletal muscle degeneration and provide a potential therapeutic target for DMD.

L-Arginine increases AMPK phosphorylation and the oxidation of energy substrates in hepatocytes, skeletal muscle cells, and adipocytes.

Previous work has shown that dietary L-arginine (Arg) supplementation reduced white fat mass in obese rats. The present study was conducted with cell models to define direct effects of Arg on energy-substrate oxidation in hepatocytes, skeletal muscle cells, and adipocytes. BNL CL.2 mouse hepatocytes, C2C12 mouse myotubes, and 3T3-L1 mouse adipocytes were treated with different extracellular concentrations of Arg (0, 15, 50, 100 and 400µM) or 400µM Arg + 0.5mM NG-nitro-L-arginine methyl ester (L-NAME; an NOS inhibitor) for 48h. Increasing Arg concentrations in culture medium dose-dependently enhanced (P < 0.05) the oxidation of glucose and oleic acid to CO2 in all three cell types, lactate release from C2C12 cells, and the incorporation of oleic acid into esterified lipids in BNL CL.2 and 3T3-L1 cells. Arg at 400µM also stimulated (P < 0.05) the phosphorylation of AMP-activated protein kinase (AMPK) in all three cell types and increased (P < 0.05) NO production in C2C12 and BNL CL.2 cells. The inhibition of NOS by L-NAME moderately reduced (P < 0.05) glucose and oleic acid oxidation, lactate release, and the phosphorylation of AMPK and acetyl-CoA carboxylase (ACC) in BNL CL.2 cells, but had no effect (P > 0.05) on these variables inC2C12 or 3T3-L1 cells. Collectively, these results indicate that Arg increased AMPK activity and energy-substrate oxidation in BNL CL.2, C2C12, and 3T3-L1 cells through both NO-dependent and NO-independent mechanisms.

Hydrogen Peroxide Stimulates Dihydrotestosterone Release in C2C12 Myotubes: A New Perspective for Exercise-Related Muscle Steroidogenesis?

Skeletal muscle is a tissue that has recently been recognized for its ability to produce androgens under physiological conditions. The steroidogenesis process is known to be negatively influenced by reactive oxygen species (ROS) in reproductive Leydig and ovary cells, while their effect on muscle steroidogenesis is still an unexplored field. Muscle cells are continuously exposed to ROS, resulting from both their metabolic activity and the surrounding environment. Interestingly, the regulation of signaling pathways, induced by mild ROS levels, plays an important role in muscle fiber adaptation to exercise, in a process that also elicits a significant modulation in the hormonal response. The aim of the present study was to investigate whether ROS could influence steroidogenesis in skeletal muscle cells by evaluating the release of testosterone (T) and dihydrotestosterone (DHT), as well as the evaluation of the relative expression of the key steroidogenic enzymes 5α-reductase, 3β-hydroxysteroid dehydrogenase (HSD), 17β-HSD, and aromatase. C2C12 mouse myotubes were exposed to a non-cytotoxic concentration of hydrogen peroxide (H2O2), a condition intended to reproduce, in vitro, one of the main stimuli linked to the process of homeostasis and adaptation induced by exercise in skeletal muscle. Moreover, the influence of tadalafil (TAD), a phosphodiesterase 5 inhibitor (PDE5i) originally used to treat erectile dysfunction but often misused among athletes as a “performance-enhancing” drug, was evaluated in a single treatment or in combination with H2O2. Our data showed that a mild hydrogen peroxide exposure induced the release of DHT, but not T, and modulated the expression of the enzymes involved in steroidogenesis, while TAD treatment significantly reduced the H2O2-induced DHT release. This study adds a new piece of information about the adaptive skeletal muscle cell response to an oxidative environment, revealing that hydrogen peroxide plays an important role in activating muscle steroidogenesis.

Assessment of Sialic Acid Levels in an In Vitro Model of Muscle Atrophy

Muscular atrophy is a loss of muscle tissue that can occur due to inactivity or underlying disease processes. Studies have shown that muscle pathology may be linked to levels of sialic acid (SA), an essential glycan found capping extracellular glycan chains of muscle cells. This is particularly evident in GNE myopathy, a disease of muscle wasting in which the causative genetic mutation is linked to decreased SA production. However, the relationship between muscle atrophy and sialylation is poorly understood. Here, we have assessed SA levels in an in vitro model of atrophy in which C2C12 mouse myotubes were treated with dexamethasone. We have utilized lectins, glycan‐binding proteins, to probe linkage‐specific effects of atrophy on sialylation in this in vitro model. This work can help to elucidate the relationship between atrophy and muscle sialylation, and may inform future therapeutic development.

Identification of protein markers for skeletal muscle‐derived extracellular vesicles (SkM‐EVs) by quantitative proteomics reveals how SkM‐EVs function in vivo

BackgroundSkeletal muscle serves as a secretory organ; it releases various soluble factors called myokine. They act as mediators for cell‐cell communications in autocrine, paracrine, and endocrine fashions. Extracellular vesicles (EVs) have been proposed to be a partial paracrine and/or endocrine effectors by facilitating the exchange of biological cargoes among cells and tissue. Some in vitro study showed that skeletal muscle released EVs and skeletal muscle‐derived EVs (SkM‐EVs) could induce biological effects in recipient cells. However, whether the skeletal muscle actively releases EVs in vivo, how much proportion of plasma EVs are derived from this tissue, and where SkM‐EVs are delivered and exert their roles remain largely unknown. Here, we aimed to identify SkM‐EV marker proteins by quantitative proteomics on human and mouse myocyte‐derived EVs to evaluate SkM‐EVs abundance in vivo. In addition, we explored whether SkM‐EVs isolated from mice could exert biological functions.MethodsProteomic analysis of EVs released from mouse C2C12 myotubes and human iPS‐derived myocytes was performed to identify potential SkM‐EVs markers. The levels of SkM‐EVs in plasma and muscle interstitium were evaluated by the abundance of identified SkM‐EVs protein markers. Based on previous methods, we developed a modified protocol to isolated SkM‐EVs from muscle interstitium. We confirmed that muscle interstitium‐EVs were incorporated into C2C12 myoblast and investigated the expression levels of myogenesis‐related genes.Results&amp; DiscussionWe first determined proteomic profiles of EVs released from C2C12 myoblasts, C2C12 myotubes, and hiPSC‐derived myocytes and identified several proteins that serve as potential markers for SkM‐EVs. Among them, we identified ATP2A1, β‐enolase, and desmin as reliable SkM‐EV marker proteins. Using these protein markers, we confirmed that SkM‐EVs were present in muscle interstitium but little in the blood, which were supported by our electron microscopy. Unexpectedly, the abundance of SkM‐EVs present in plasma and muscle interstitium was not changed in response to acute exercise. Furthermore, we showed that SkM‐EVs accumulated in muscle interstitium space were incorporated into C2C12 myoblast and promoted muscle differentiation by regulating gene expression of Pax7 and myosin heavy chain at least partially through myomiRs (miRs‐1, ‐206, ‐431, and ‐486). We expect that molecular characterization and in vivo distribution of SkM‐EVs could provide a conceptually new basis how skeletal muscle EVs exert their functions.

Resveratrol Alleviates Skeletal Muscle Insulin Resistance by Downregulating Long Noncoding RNA.

Long noncoding RNA (lncRNA) is a crucial factor in the progression of insulin resistance (IR). Resveratrol (RSV) exhibits promising therapeutic potential for IR. However, there are few studies on whether RSV improves IR through lncRNA. This study aimed to determine whether RSV could influence the expression of lncRNA and to elucidate the underlying mechanism. Mice were divided into three groups: control group, high-fat diet (HFD) group, and HFD + RSV group. We conducted a high-throughput sequencing analysis to detect lncRNA and mRNA expression signatures and the ceRNA-network in the skeletal muscles of mice that were fed an HFD to induce IR. Hierarchical clustering, gene enrichment, and gene ceRNA-network analyses were subsequently conducted. Differentially expressed lncRNAs were selected and validated via reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The biological functions of the selected lncRNAs were investigated by silencing the target genes via lentivirus transfection of C2C12 mouse myotube cells. RSV treatment reversed the expression of 338 mRNAs and 629 lncRNAs in the skeletal muscles of mice with HFD-induced IR. The results of the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes database analyses indicated that the differentially expressed mRNAs modulated type II diabetes mellitus. After validating randomly selected lncRNAs via RT-qPCR, we identified a novel lncRNA, NONMMUT044897.2, which was upregulated in the HFD group and reversed with RSV treatment. Additionally, NONMMUT044897.2 was proven to function as a ceRNA of microRNA- (miR-) 7051-5p. Suppressor of Cytokine Signaling 1 (SOCS1) was confirmed as a target of miR-7051-5p. We further performed lentivirus transfection to knock down NONMMUT044897.2 in vitro and found that NONMMUT044897.2 silenced SOCS1 and potentiated the insulin signaling pathway. Hence, RSV mimicked the silencing effect of lentivirus transfection on NONMMUT044897.2. Our study revealed that RSV reduced IR in mouse skeletal muscles via the regulation of NONMMUT044897.2.

DIF-1 promotes glucose uptake in mouse C2C12 myotube cells

DIF-1 promotes glucose uptake in mouse C2C12 myotube cells

α-Hydroxyisocaproic Acid Decreases Protein Synthesis but Attenuates TNFα/IFNγ Co-Exposure-Induced Protein Degradation and Myotube Atrophy via Suppression of iNOS and IL-6 in Murine C2C12 Myotube.

There is ongoing debate as to whether or not α-hydroxyisocaproic acid (HICA) positively regulates skeletal muscle protein synthesis resulting in the gain or maintenance of skeletal muscle. We investigated the effects of HICA on mouse C2C12 myotubes under normal conditions and during cachexia induced by co-exposure to TNFα and IFNγ. The phosphorylation of AMPK or ERK1/2 was significantly altered 30 min after HICA treatment under normal conditions. The basal protein synthesis rates measured by a deuterium-labeling method were significantly lowered by the HICA treatment under normal and cachexic conditions. Conversely, myotube atrophy induced by TNFα/IFNγ co-exposure was significantly improved by the HICA pretreatment, and this improvement was accompanied by the inhibition of iNOS expression and IL-6 production. Moreover, HICA also suppressed the TNFα/IFNγ co-exposure-induced secretion of 3-methylhistidine. These results demonstrated that HICA decreases basal protein synthesis under normal or cachexic conditions; however, HICA might attenuate skeletal muscle atrophy via maintaining a low level of protein degradation under cachexic conditions.

Identifying a New Mechanism of Sarcopenia by Autophagy

Sarcopenia is one of the critical factors in reducing Activity of Daily Life and associated with morbidity and mortality. Sarcopenia has also been linked to metabolic syndrome. In recent years, it has been reported that autophagy is one of the mechanisms as a cause of sarcopenia. Therefore, we focused on autophagy as a system that can regulate both sarcopenia and metabolic syndrome in skeletal muscle and revealed that non-receptor tyrosine kinase Fyn not only participates in metabolic syndrome but also regulates autophagy regulating sarcopenia through STAT3 regulation, mainly using transgenic mice (Cell metabolism 2010, Cell Rep. 2012). However, since these were non-physiological studies, we proceeded with further studies and demonstrating that Fyn dependent STAT3 phosphorylation by IL6, which is involved in chronic inflammation and metabolic syndrome, was observed in mouse C2C12 myotube cells. Autophagy was decreased in those cells by both IL6 dependent and Fyn dependent mechanisms. Furthermore, in the denervated mouse model, not only both Fyn and IL6 gene expressions as well as the key muscle specific E3 ubiquitin ligases, Atrogin1 and MuRf1 were increased but the expression and phosphorylation levels of STAT3 were also augmented, while the autophagy activity was decreased. We believe that a denervated mouse model alone is not enough as a model for sarcopenia, thus we next introduced a hind limb suspension mouse model that promotes disuse atrophy by suspending the hind limb. Using this model, we found that muscle atrophy was observed mainly in the soleus muscle, tibialis anterior muscle, and the gastrocnemius muscle with Atrogin1 and MuRf1 increased. Increase of both IL6 and STAT3 expression/phosphorylation were also observed in the muscles of hind limb suspension mice. Autophagy activity, examined by intraperitoneal administration of colchicine, was decreased. These results strongly suggest that Fyn is involved not only in the metabolic syndrome but also in the pathogenesis of sarcopenia, and may lead to a better understanding of the pathology of sarcopenia obesity and the development of therapeutic methods.

\u03b22-adrenergic receptor agonist counteracts skeletal muscle atrophy and oxidative stress in uremic mice

In patients with chronic kidney disease, skeletal muscle dysfunction is associated with mortality. Uremic sarcopenia is caused by ageing, malnutrition, and chronic inflammation, but the molecular mechanism and potential therapeutics have not been fully elucidated yet. We hypothesize that accumulated uremic toxins might exert a direct deteriorative effect on skeletal muscle and explore the pharmacological treatment in experimental animal and culture cell models. The mice intraperitoneally injected with indoxyl sulfate (IS) after unilateral nephrectomy displayed an elevation of IS concentration in skeletal muscle and a reduction of instantaneous muscle strength, along with the predominant loss of fast-twitch myofibers and intramuscular reactive oxygen species (ROS) generation. The addition of IS in the culture media decreased the size of fully differentiated mouse C2C12 myotubes as well. ROS accumulation and mitochondrial dysfunction were also noted. Next, the effect of the β2-adrenergic receptor (β2-AR) agonist, clenbuterol, was evaluated as a potential treatment for uremic sarcopenia. In mice injected with IS, clenbuterol treatment increased the muscle mass and restored the tissue ROS level but failed to improve muscle weakness. In C2C12 myotubes stimulated with IS, although β2-AR activation also attenuated myotube size reduction and ROS accumulation as did other anti-oxidant reagents, it failed to augment the mitochondrial membrane potential. In conclusion, IS provokes muscular strength loss (uremic dynapenia), ROS generation, and mitochondrial impairment. Although the β2-AR agonist can increase the muscular mass with ROS reduction, development of therapeutic interventions for restoring skeletal muscle function is still awaited.

Possible involvement of CXC motif chemokine ligand 10 in exercise-induced collagen production of mouse dermal fibroblasts.

Evidence suggests that exercise can regulate skin functions such as promoting wound healing and inhibiting aging. Physical exercise modulates the secretion of proteins and peptides from skeletal muscles, called myokines, which play a role in transmitting exercise signals throughout the body. Therefore, exercise-regulated myokines may play a role in controlling skin functions; however, the precise mechanisms remain elusive. In this study, we focused on the recently identified CXC motif chemokine ligand 10 (CXCL10), an exercise-reduced myokine, and attempted to elucidate its role in regulating collagen synthesis in dermal fibroblasts. Mouse C2C12 myotubes were stimulated with or without electrical pulse stimulation (EPS) to induce contraction for 24 h, and conditioned medium was collected (EPS-CM or Ctrl-CM, respectively). The reduction in CXCL10 concentration by EPS was confirmed using ELISA. Next, mouse dermal fibroblasts were isolated from the dorsal skin of C57BL6/J mice (2 weeks old) and were stimulated with Ctrl-CM or EPS-CM for 24 h. EPS-CM treatment significantly increased collagen production compared to Ctrl-CM treatment. Even in the Ctrl-CM condition, the addition of an antagonist for CXCR3 (CXCL10 receptor) increased collagen production. In contrast, recombinant CXCL10 abolished EPS-CM-dependent collagen induction. Overall, this study raises the possibility that CXCL10 secretion from skeletal muscles may control collagen production in mouse dermal fibroblasts.