Lactate induces C2C12 myoblasts differentiation by mediating ROS/p38 MAPK signalling pathway

Lactate serves not merely as an energy substrate for skeletal muscle but also regulates myogenic differentiation, leading to an elevation of reactive oxygen species (ROS) levels. The present study was focused on exploring the effects of lactate and ROS/p38 MAPK in promoting C2C12 myoblasts differentiation. Our results demonstrated that lactate increased C2C12 myoblasts differentiation at a range of physiological concentrations, accompanied by enhanced ROS contents. We used n-acetylcysteine (NAC, a ROS scavenger) pretreatment and found that it delayed lactate-induced C2C12 myoblast differentiation by upregulating Myf5 expression on days 5 and 7 and lowering MyoD and MyoG expression. The finding implies that lactate accompanies ROS-dependent manner to promote C2C12 myoblast differentiation. Additionally, lactate significantly increased p38 MAPK phosphorylation to promote C2C12 cell differentiation, but pretreatment with SB203580 (p38 MAPK inhibitor) reduced lactate-induced C2C12 myoblasts differentiation. whereas lactate pretreatment with NAC inhibited p38 MAPK phosphorylation in C2C12 cells, demonstrating that lactate mediated ROS and regulated the p38 MAPK signalling pathway to promote C2C12 cell differentiation. In conclusion, our results suggest that the promotion of C2C12 myoblasts differentiation by lactate is dependent on ROS and the p38 MAPK signalling pathway. These observations reveal a beneficial role for lactate in increasing myogenesis through ROS-sensitive mechanisms as well as providing new ideas regarding the positive impact of ROS in improving the function of skeletal muscle.

Mechanism of Innate Immune Response Induced by Albizia julibrissin Saponin Active Fraction Using C2C12 Myoblasts

Albizia julibrissin saponin active fraction (AJSAF), is a prospective adjuvant with dual Th1/Th2 and Tc1/Tc2 potentiating activity. Its adjuvant activity has previously been proven to be strictly dependent on its spatial co-localization with antigens, highlighting the role of local innate immunity in its mechanisms. However, its potential targets and pathways remain unclear. Here, its intracellular molecular mechanisms of innate immune response were explored using mouse C2C12 myoblast by integrative analysis of the in vivo and in vitro transcriptome in combination with experimental validations. AJSAF elicited a temporary cytotoxicity and inflammation towards C2C12 cells. Gene set enrichment analysis demonstrated that AJSAF regulated similar cell death- and inflammatory response-related genes in vitro and in vivo through activating second messenger-MAPK-CREB pathways. AJSAF markedly enhanced the Ca2+, cAMP, and reactive oxygen species levels and accelerated MAPK and CREB phosphorylation in C2C12 cells. Furthermore, Ca2+ chelator, CREB inhibitor, and MAPK inhibitors dramatically blocked the up-regulation of IL-6, CXCL1, and COX2 in AJSAF-treated C2C12 cells. Collectively, these results demonstrated that AJSAF induced innate immunity via Ca2+-MAPK-CREB pathways. This study is beneficial for insights into the molecular mechanisms of saponin adjuvants.

The aminopeptidase LAP3 suppression accelerates myogenic differentiation via the AKT-TFE3 pathway in C2C12 myoblasts

Skeletal muscle maintenance depends largely on muscle stem cells (satellite cells) that supply myoblasts required for muscle regeneration and growth. The ubiquitin-proteasome system is the major intracellular protein degradation pathway. We previously reported that proteasome dysfunction in skeletal muscle significantly impairs muscle growth and development. Furthermore, the inhibition of aminopeptidase, a proteolytic enzyme that removes amino acids from the termini of peptides derived from proteasomal proteolysis, impairs the proliferation and differentiation ability of C2C12 myoblasts. However, no evidence has been reported on the role of aminopeptidases with different substrate specificities on myogenesis. In this study, therefore, we investigated whether the knockdown of aminopeptidases in differentiating C2C12 myoblasts affects myogenesis. The knockdown of the X-prolyl aminopeptidase 1, aspartyl aminopeptidase, leucyl-cystinyl aminopeptidase, methionyl aminopeptidase 1, methionyl aminopeptidase 2, puromycine-sensitive aminopeptidase, and arginyl aminopeptidase like 1 gene in C2C12 myoblasts resulted in defective myogenic differentiation. Surprisingly, the knockdown of leucine aminopeptidase 3 (LAP3) in C2C12 myoblasts promoted myogenic differentiation. We also found that suppression of LAP3 expression in C2C12 myoblasts resulted in the inhibition of proteasomal proteolysis, decreased intracellular branched-chain amino acid levels, and enhanced mTORC2-mediated AKT phosphorylation (S473). Furthermore, phosphorylated AKT induced the translocation of TFE3 from the nucleus to the cytoplasm, promoting myogenic differentiation through increased expression of myogenin. Overall, our study highlights the association of aminopeptidases with myogenic differentiation.

miR-100-5p Regulates Skeletal Muscle Myogenesis through the Trib2/mTOR/S6K Signaling Pathway

MicroRNAs (miRNAs) are endogenous small non-coding RNAs that play crucial regulatory roles in many biological processes, including the growth and development of skeletal muscle. miRNA-100-5p is often associated with tumor cell proliferation and migration. This study aimed to uncover the regulatory mechanism of miRNA-100-5p in myogenesis. In our study, we found that the miRNA-100-5p expression level was significantly higher in muscle tissue than in other tissues in pigs. Functionally, this study shows that miR-100-5p overexpression significantly promotes the proliferation and inhibits the differentiation of C2C12 myoblasts, whereas miR-100-5p inhibition results in the opposite effects. Bioinformatic analysis predicted that Trib2 has potential binding sites for miR-100-5p at the 3'UTR region. A dual-luciferase assay, qRT-qPCR, and Western blot confirmed that Trib2 is a target gene of miR-100-5p. We further explored the function of Trib2 in myogenesis and found that Trib2 knockdown markedly facilitated proliferation but suppressed the differentiation of C2C12 myoblasts, which is contrary to the effects of miR-100-5p. In addition, co-transfection experiments demonstrated that Trib2 knockdown could attenuate the effects of miR-100-5p inhibition on C2C12 myoblasts differentiation. In terms of the molecular mechanism, miR-100-5p suppressed C2C12 myoblasts differentiation by inactivating the mTOR/S6K signaling pathway. Taken together, our study results indicate that miR-100-5p regulates skeletal muscle myogenesis through the Trib2/mTOR/S6K signaling pathway.

Exosomes derived from inflammatory myoblasts promote M1 polarization and break the balance of myoblast proliferation/differentiation

BACKGROUND

Acute muscle injuries are one of the most common injuries in sports. Severely injured muscles are prone to re-injury due to fibrotic scar formation caused by prolonged inflammation. How to regulate inflammation and suppress fibrosis is the focus of promoting muscle healing. Recent studies have found that myoblasts and macrophages play important roles in the inflammatory phase following muscle injury; however, the crosstalk between these two types of cells in the inflammatory environment, particularly the exosome-related mechanisms, had not been well studied.

AIM

To evaluate the effects of exosomes from inflammatory C2C12 myoblasts (IF-C2C12-Exos) on macrophage polarization and myoblast proliferation/differentiation.

METHODS

A model of inflammation was established in vitro by lipopolysaccharide stimulation of myoblasts. C2C12-Exos were isolated and purified from the supernatant of myoblasts by gradient centrifugation. Multiple methods were used to identify the exosomes. Gradient concentrations of IF-C2C12-Exos were added to normal macrophages and myoblasts. PKH67 fluorescence tracing was used to identify the interaction between exosomes and cells. Microscopic morphology, Giemsa stain, and immunofluorescence were carried out for histological analysis. Additionally, ELISA assays, flow cytometry, and western blot were conducted to analyze molecular changes. Moreover, myogenic proliferation was assessed by the BrdU test, scratch assay, and CCK-8 assay.

RESULTS

We found that the PKH-67-marked C2C12-Exos can be endocytosed by both macrophages and myoblasts. IF-C2C12-Exos induced M1 macrophage polarization and suppressed the M2 phenotype in vitro. In addition, these exosomes also stimulated the inflammatory reactions of macrophages. Furthermore, we demonstrated that IF-C2C12-Exos disrupted the balance of myoblast proliferation/differentiation, leading to enhanced proliferation and suppressed fibrogenic/myogenic differentiation.

CONCLUSION

IF-C2C12-Exos can induce M1 polarization, resulting in a sustained and aggravated inflammatory environment that impairs myoblast differentiation, and leads to enhanced myogenic proliferation. These results demonstrate why prolonged inflammation occurs after acute muscle injury and provide a new target for the regulation of muscle regeneration.

Lnc-GD2H Promotes Proliferation by Forming a Feedback Loop With c-Myc and Enhances Differentiation Through Interacting With NACA to Upregulate Myog in C2C12 Myoblasts

In the present study, the roles of a novel long non-coding RNA (lncRNA), lnc-GD2H, in promoting C2C12 myoblast proliferation and differentiation and muscle regeneration were investigated by quantitative polymerase chain reaction, western blotting, Cell Counting Kit-8, 5-ethynyl-2′-deoxyuridine (EdU), immunofluorescence staining, luciferase reporter, mass spectrometry, pulldown, chromatin immunoprecipitation, RNA immunoprecipitation assay, wound healing assays, and cardiotoxin (CTX)-induced muscle injury assays. It was observed that lnc-GD2H promoted myoblast proliferation as evidenced by the enhancement of the proliferation markers c-Myc, CDK2, CDK4, and CDK6, percentage of EdU-positive cells, and rate of cell survival during C2C12 myoblast proliferation. Additional experiments confirmed that c-Myc bound to the lnc-GD2H promoter and regulated its transcription. lnc-GD2H promoted cell differentiation with enhanced MyHC immunostaining as well as increased expression of the myogenic marker genes myogenin (Myog), Mef2a, and Mef2c during myoblast differentiation. Additional assays indicated that lnc-GD2H interacted with NACA which plays a role of transcriptional regulation in myoblast differentiation, and the enrichment of NACA at the Myog promoter was impaired by lnc-GD2H. Furthermore, inhibition of lnc-GD2H impaired muscle regeneration after CTX-induced injury in mice. lnc-GD2H facilitated the expression of proliferating marker genes and formed a feedback loop with c-Myc during myoblast proliferation. In differentiating myoblasts, lnc-GD2H interacted with NACA to relieve the inhibitory effect of NACA on Myog, facilitating Myog expression to promote differentiation. The results provide evidence for the role of lncRNAs in muscle regeneration and are useful for developing novel therapeutic targets for muscle disorders.

A Split-Luciferase-Based Cell Fusion Assay for Evaluating the Myogenesis-Promoting Effects of Bioactive Molecules

A split-luciferase-based cell fusion assay enables high-throughput screening of myogenesis-promoting chemicals in chemical libraries. The assay consists of two C2C12 myoblast-derived cell lines (N- and C-cells), each of which stably expresses either an N- or C-terminal split-firefly luciferase (FLuc) fragment fused to a naturally split DnaE intein (N- and C-probes, respectively). The fusion of N- and C-cells during myogenesis induces bioluminescence (BL) in the cytosol due to a stable reconstitution of the split-FLuc. Thus, the myogenesis-promoting effects of a chemical compound can be determined through the enhanced BL intensity. Here, we describe the preparation of N- and C-cells and determination of the myogenesis-promoting effects of imatinib using a 96-well microplate-based assay.

The difference of castration timing of Korean Hanwoo bulls does not significantly affect the carcass characteristics

It is already well known that castration improves marbling quality but exact timing of castration is still highly debated in beef cattle production industry. After castration, blood hormonal changes occur in steer and objective of this study was to investigate the effects of growth hormone (GH) levels on adipocyte differentiation in stromal vascular cells (SVCs) and transdifferentiation into adipocytes in C2C12 myoblasts. Total GH concentrations were measured via enzyme-linked immunosorbent assay (ELISA) in 24 male calves and 4 female calves. Cell proliferation, cellular triglyceride (TG) accumulation, and the cell's lipolytic capability were measured in C2C12 myoblasts and SVCs. Myogenic, adipogenic, and brown adipocyte-specific gene expression was measured via real-time polymerase chain reaction (PCR) using SYBR green. Serum GH levels were the highest in late-castrated calves. Treatment with 5 ng/mL GH resulted in greater TG accumulation as well as increased CCAAT-enhancer-binding protein (C/EBP)α and peroxisome proliferator-activated receptor (PPAR)γ expression compared to that after treatment with 15 ng/mL GH. Treatment with 5 ng/mL GH also resulted in lower myogenin (myo)G and myoD expression compared to that after treatment with 15 ng/mL GH. The expression of bone morphogenetic protein (BMP) 7 after treatment with 5 ng/mL GH was higher than that after treatment with 15 ng/mL GH. But carcass characteristics data showed no significant difference between early and late castrated steers. Therefore, our results indicate that castration timing does not seem to be inevitable determinate of carcass qualities, particularly carcass weight and marbling score in Hanwoo beef cattle.

The Extract of Arctium lappa L. Fruit (Arctii Fructus) Improves Cancer-Induced Cachexia by Inhibiting Weight Loss of Skeletal Muscle and Adipose Tissue

Background: Cachexia induced by cancer is a systemic wasting syndrome and it accompanies continuous body weight loss with the exhaustion of skeletal muscle and adipose tissue. Cancer cachexia is not only a problem in itself, but it also reduces the effectiveness of treatments and deteriorates quality of life. However, effective treatments have not been found yet. Although Arctii Fructus (AF) has been studied about several pharmacological effects, there were no reports on its use in cancer cachexia. Methods: To induce cancer cachexia in mice, we inoculated CT-26 cells to BALB/c mice through subcutaneous injection and intraperitoneal injection. To mimic cancer cachexia in vitro, we used conditioned media (CM), which was CT-26 colon cancer cells cultured medium. Results: In in vivo experiments, AF suppressed expression of interleukin (IL)-6 and atrophy of skeletal muscle and adipose tissue. As a result, the administration of AF decreased mortality by preventing weight loss. In adipose tissue, AF decreased expression of uncoupling protein 1 (UCP1) by restoring AMP-activated protein kinase (AMPK) activation. In in vitro model, CM increased muscle degradation factors and decreased adipocytes differentiation factors. However, these tendencies were ameliorated by AF treatment in C2C12 myoblasts and 3T3-L1 cells. Conclusion: Taken together, our study demonstrated that AF could be a therapeutic supplement for patients suffering from cancer cachexia.

miR-324-5p Inhibits C2C12 cell Differentiation and Promotes Intramuscular Lipid Deposition through lncDUM and PM20D1

Skeletal muscle is an important metabolic organ of the body, and impaired skeletal muscle differentiation can result in a wide range of metabolic diseases. It has been shown that microRNAs (miRNAs) play an important role in skeletal muscle differentiation. The aim of this study was to investigate the role of mmu-miR-324-5p in the differentiation of C2C12 myoblasts and lipid droplet deposition in myotubes for future targeted therapies. We found that mmu-miR-324-5p was highly expressed in mouse skeletal muscle. Overexpression of miR-324-5p significantly inhibited C2C12 myoblast differentiation while promoting oleate-induced lipid accumulation and β-oxidation in C2C12 myoblasts. Conversely, inhibition of mmu-miR-324-5p promoted C2C12 myoblast differentiation and inhibited lipid deposition in myotubes. Mechanistically, mmu-miR-324-5p negatively regulated the expression of long non-coding Dum (lncDum) and peptidase M20 domain containing 1 (Pm20d1) in C2C12 myoblasts. Reduced lncDum expression was associated with a significant decrease in the expression of myogenesis-related genes. Knockdown of mmu-miR-324-5p increased the levels of lncDum and myogenesis-related gene expression. Following oleate-induced lipid deposition in C2C12 myoblasts, overexpression of mmu-miR-324-5p decreased the expression of Pm20d1 while increasing the expression of mitochondrial β-oxidation and long-chain fatty acid synthesis-related genes. In conclusion, we provide evidence that miR-324-5p inhibits C2C12 myoblast differentiation and promotes intramuscular lipid deposition by targeting lncDum and Pm20d1, respectively.

Data on the proliferation and differentiation of C2C12 myoblast treated with branched-chain ketoacid dehydrogenase kinase inhibitor

The catabolism of branched chain amino acids (BCAAs) is mainly carried out in skeletal muscle myofibers. It is mediated by branched chain aminotransferase 2 and branched chain alpha ketoacid dehydrogenase (BCKDH) in mitochondria for energy supply, especially during exercise. BCKDH kinase (BCKDK) is a negative regulator of BCAAs catabolism by its inhibitory phosphorylation of the BCKDH E1a subunit. The data presented in this article are related to the research article that we previously have reported entitled “Energy metabolism profile of the effects of amino acid treatment on skeletal muscle cells: Leucine inhibits glycolysis of myotubes” (Suzuki et al., 2020)[1]. In this report, we have demonstrated that 1hour treatment of BT2, an inhibitor of BCKDK, decreased the glycolysis of C2C12 differentiated myotubes compared to the control. Although BCAAs metabolism is basically assumed to be carried out in differentiated myofibers, BCKDK is expressed in both undifferentiated myoblasts and differentiated myotubes, and the biological and physiological significance of BCAAs metabolism in myoblasts is still unclear. Present data demonstrate an in vitro assessment of BT2 on C2C12 myoblasts proliferation and differentiation. The data suggest that activation of BCAAs catabolism by the BCKDK inhibitor BT2 impairs C2C12 myoblasts proliferation and differentiation.

Corylifol A from Psoralea corylifolia L. Enhances Myogenesis and Alleviates Muscle Atrophy

Inflammatory conditions caused by cancer, chronic diseases or aging can lead to skeletal muscle atrophy. We identified myogenic compounds from Psoralea corylifolia (PC), a medicinal plant that has been used for the treatment of inflammatory and skin diseases. C2C12 mouse skeletal myoblasts were differentiated in the presence of eight compounds isolated from PC to evaluate their myogenic potential. Among them, corylifol A showed the strongest transactivation of MyoD and increased expression of myogenic markers, such as MyoD, myogenin and myosin heavy chain (MHC). Corylifol A increased the number of multinucleated and MHC-expressing myotubes. We also found that the p38 MAPK signaling pathway is essential for the myogenic action of corylifol A. Atrophic condition was induced by treatment with dexamethasone. Corylifol A protected against dexamethasone-induced myotube loss by increasing the proportion of multinucleated MHC-expressing myotubes compared with dexamethasone-damaged myotubes. Corylifol A reduced the expression of muscle-specific ubiquitin-E3 ligases (MAFbx and MuRF1) and myostatin, while activating Akt. These dual effects of corylifol A, inhibition of catabolic and activation of anabolic pathways, protect myotubes against dexamethasone damage. In summary, corylifol A isolated from P. corylifolia alleviates muscle atrophic condition through activating myoblast differentiation and suppressing muscle degradation in atrophic conditions.

Enhancing effects of anagliptin on myoblast differentiation and the expression of mitochondrial biogenetic factors in C2C12 mouse skeletal muscle cells

To investigate the regulatory effects of anagliptin, a DPP-IV inhibitor used to treat type 2 diabetes mellitus (T2DM), on myoblast differentiation and mitochondrial biogenesis in C2C12 mouse skeletal muscle cells. C2C12 myoblasts were differentiated into myotubes and then treated with anagliptin (10, 25, and 50 μmol/L) for 24 hours. In C2C12 myotubes, anagliptin treatment was significantly increased the expression of MHC, PGC1α, Sirt-1, NRF-1, and TFAM and the phosphorylation of AMPK and ACC in a concentration-dependent manner. Anagliptin also significantly increased the total ATP levels in the myotubes. These results suggest that anagliptin can help prevent skeletal muscle dysfunction in T2DM by promotion of myoblast differentiation and enhancement of energy production via upregulation of mitochondrial biogenetic factors and activation of the AMPK/ACC signalling pathway.

Fibroblast growth factor 9 (FGF9) inhibits myogenic differentiation of C2C12 and human muscle cells

Osteoporosis and sarcopenia (osteosarcopenia (OS)) are twin-aging diseases. The biochemical crosstalk between muscle and bone seems to play a role in OS. We have previously shown that osteocytes produce soluble factors with beneficial effects on muscle and vice versa. Recently, enhanced FGF9 production was observed in the OmGFP66 osteogenic cell line. To test its role in myogenic differentiation, C2C12 myoblasts were treated with recombinant FGF9. FGF9 as low as 10 ng/mL inhibited myogenic differentiation, suggesting that FGF9 might be a potential inhibitory factor produced from bone cells with effects on muscle cells. FGF9 (10–50 ng/mL) significantly decreased mRNA expression of MyoG and Mhc while increasing the expression of Myostatin. Consistent with the phenotype, RT-qPCR array revealed that FGF9 (10 ng/mL) increased the expression of Icam1 while decreased the expression of Wnt1 and Wnt6 decreased, respectively. FGF9 decreased caffeine-induced Ca²⁺ release from the sarcoplasmic reticulum (SR) of C2C12 myotubes and reduced the expression of genes (i.e. Cacna1s, RyR2, Naftc3) directly associated with intracellular Ca²⁺ homeostasis. Myogenic differentiation in human skeletal muscle cells was similarly inhibited by FGF9 but required higher doses of 200 ng/mL FGF9. FGF9 was also shown to stimulate C2C12 myoblast proliferation. FGF2 and the FGF9 subfamily members FGF16 and FGF20 also inhibited C2C12 myoblast differentiation and enhanced proliferation. Intriguingly, the differentiation inhibition was independent of proliferation enhancement. These findings suggest that FGF9 may modulate myogenesis via a complex signaling mechanism.

Recombinant porcine myostatin propeptide generated by the Pichia pastoris elevates myoblast growth and ameliorates high-fat diet-induced glucose intolerance

Myostatin (MSTN) was identified as a negative regulator of skeletal muscle growth. MSTN inhibition by myostatin propeptide (MSPP) increased skeletal muscle mass, myofiber growth and muscle force. Thus, this study was designed to produce wild-type porcine MSPP (WT-MSPP) and its mutated form (D75A-MSPP) in yeast Pichia pastoris and to investigate its potential enhancement of myoblast growth and differentiation. In an in vitro study, C2C12 myoblasts were treated with the purified WT-MSPP or D75A-MSPP (10 μg/mL) in either a regular culture medium or in a differentiation medium for 72 h. In an animal trial, post-weaning C57BL/6 mice fed with a high-fat diet (HFD) were administered WT-MSPP or D75A-MSPP for 6 weeks. The results showed that C2C12 myoblasts treated with the purified WT-MSPP or D75A-MSPP could dramatically promote cell proliferation. Both myoD and myogenin were significantly increased (p < .05) after WT-MSPP or D75A-MSPP treatment. D75A-MSPP was particularly more effective than WT-MSPP in promoting myotube formation (p < .05). The post-weaning mice treated with D75A-MSPP significantly increased both body and muscle weights compared with the mock and WT-MSPP groups (p < .05). Furthermore, the mice treatment with D75A-MSPP could prevent increased glucose injection from inducing glucose elevation. Our data indicated that a mutant-type MSPP (D75A-MSPP) was superior to WT-MSPP in effectively enhancing myofiber growth due to the highly resistant to proteolytic cleavage by the bone morphogenetic protein-1/tolloid (BMP-1/TLD) and thus has potential applications for clinical muscle wasting diseases or for increasing muscle mass in meat-producing animals.

Application of black phosphorus nanodots to live cell imaging

BACKGROUND

Black phosphorus (BP) has emerged as a novel class of nanomaterials owing to its unique optical and electronic properties. BP, a two-dimensional (2D) nanomaterial, is a structure where phosphorenes are stacked together in layers by van der Waals interactions. However, although BP nanodots have many advantages, their biosafety and biological effect have not yet been elucidated as compared to the other nanomaterials. Therefore, it is particularly important to assess the cytotoxicity of BP nanodots for exploring their potentials as novel biomaterials.

METHODS

BP nanodots were prepared by exfoliation with a modified ultrasonication-assisted solution method. The physicochemical properties of BP nanodots were characterized by transmission electron microscopy, dynamic light scattering, Raman spectroscopy, and X-ray diffractometry. In addition, the cytotoxicity of BP nanodots against C2C12 myoblasts was evaluated. Moreover, their cell imaging potential was investigated.

RESULTS

Herein, we concentrated on evaluating the cytotoxicity of BP nanodots and investigating their cell imaging potential. It was revealed that the BP nanodots were cytocompatible at a low concentration, although the cell viability was decreased with increasing BP nanodot concentration. Furthermore, our results demonstrated that the cells took up the BP nanodots, and the BP nanodots exhibited green fluorescence.

CONCLUSIONS

In conclusion, our findings suggest that the BP nanodots have suitable biocompatibility, and are promising candidates as fluorescence probes for biomedical imaging applications.

The Major Lysosomal Membrane Proteins LAMP-1 and LAMP-2 Participate in Differentiation of C2C12 Myoblasts

Lysosomes are organelles that play a crucial role in the degradation of endocytosed molecules, phagocytosed macromolecules and autophagic substrates. The membrane of lysosomes contains several highly glycosylated membrane proteins, and lysosome-associated membrane protein (LAMP)-1 and LAMP-2 account for a major portion of the lysosomal membrane glycoproteins. Although it is well known that LAMP-2 deficiency causes Danon disease, which is characterized by cardiomyopathy, myopathy and mental retardation, the roles of lysosomal membrane proteins including LAMP-1 and LAMP-2 in myogenesis are not fully understood. In this study, to understand the role of LAMP proteins in the course of differentiation of myoblasts into myotubes, we used C2C12 myoblasts and found that the protein and mRNA levels of LAMP-1 and LAMP-2 were increased in the course of differentiation of C2C12 myoblasts into myotubes. Then, we investigated the effects of LAMP-1 or LAMP-2 knockdown on C2C12 myotube formation, and found that LAMP-1 or LAMP-2 depletion impaired the differentiation of C2C12 myoblasts and reduced the diameter of C2C12 myotubes. LAMP-2 knockdown more severely impaired C2C12 myotube formation compared with LAMP-1 knockdown, and knockdown of LAMP-1 did not exacerbate the suppressive effects of LAMP-2 knockdown on C2C12 myotube formation. In addition, knockdown of LAMP-1 or LAMP-2 decreased the expression levels of myogenic regulatory factors, MyoD and myogenin. These results demonstrate that both LAMP-1 and LAMP-2 are involved in C2C12 myotube formation and LAMP-2 may contribute dominantly to it.

Tomatidine inhibits tumor necrosis factor-α-induced apoptosis in C2C12 myoblasts via ameliorating endoplasmic reticulum stress

In this study, we examined the effect of tomatidine on tumor necrosis factor (TNF)-α-induced apoptosis in C₂C₁₂ myoblasts. TNF-α treatment increased cleaved caspase 3 and cleaved poly (ADP-ribose) polymerase (PARP) protein levels in a dose- and time-dependent manner. Pretreatment of cells with 10 μM tomatidine prevented TNF-α-induced apoptosis, caspase 3 cleavage, and PARP cleavage. Cells were treated with 100 ng/mL TNF-α for 24 h, and flow cytometry was utilized to assess apoptosis using annexin-V and 7-aminoactinomycin D. TNF-α up-regulated activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP) expression. This effect was suppressed by pretreatment with tomatidine. Pretreatment with 4-phenylbutyric acid (a chemical chaperone) also inhibited TNF-α-induced cleavage of caspase 3 and PARP and up-regulation of ATF4 and CHOP expression. In addition, tomatidine-mediated inhibition of phosphorylation of c-Jun amino terminal kinase (JNK) attenuated TNF-α-induced cleavage of PARP and caspase 3. However, tomatidine did not affect NF-κB activation in TNF-α-treated C₂C₁₂ myoblast cells. Taken together, the present study demonstrates that tomatidine attenuates TNF-α-induced apoptosis through down-regulation of CHOP expression and inhibition of JNK activation.

NMR-based metabolomic analysis for the effects of creatine supplementation on mouse myoblast cell line C2C12

Creatine (Cr) supplementation has drawn much attention from researchers owing to its widespread efficacy in sports, and more recently, in therapeutic fields. However, the underlying molecular mechanisms remain elusive. Here, we performed nuclear magnetic resonance-based metabolomic analysis to address the metabolic profile of aqueous extracts from the mouse myoblast cell line C2C12 exposed to 2 mM Cr for 24 h (the Cr-treated group). Results showed that Cr supplementation facilitated the proliferation of C2C12 myoblasts. Both pattern recognition and hierarchical cluster analyses demonstrated that the metabolic profiles of the Cr-treated and control groups were distinctly different. We identified 13 characteristic metabolites significantly responsible for the discrimination of metabolic profiles between the two groups, through orthogonal projection to latent structures discriminant analysis and independent samples t-test. We further verified the discrimination performances of these metabolites by conducting univariate receiver operating characteristic curve analysis. Compared with the control group, the Cr-treated group exhibited increased levels of Cr, phosphocreatine (PCr), glutathione (GSH), and glucose, but decreased levels of leucine, valine, isoleucine, phenylalanine, methionine, choline, O-phosphocholine, sn-glycero-3-phosphocholine, and glycerol. Our results demonstrated that Cr supplementation upregulated PCr and glucose, promoted trichloroacetic acid cycle anaplerotic flux and GSH-mediated antioxidant capacity, and stabilized lipid membranes through suppressing glycerophospholipid metabolism. Our work provides new clues to the molecular mechanisms underlying the pleiotropic effects of Cr in muscle cells.

Knockdown of subunit 3 of the COP9 signalosome inhibits C2C12 myoblast differentiation via NF-KappaB signaling pathway

Background

The COP9 signalosome (CSN) is a conserved protein complex composed of 8 subunits designated CSN1-CSN8. CSN3 represents the third subunit of the CSN and maintains the integrity of the complex. CSN3 binds to the striated muscle-specific β1D integrin tail, and its subcellular localization is altered in differentiated skeletal muscle cells. However, the role of CSN3 in skeletal muscle differentiation is unknown. The main goal of this study was to identify whether CSN3 participates in myoblast differentiation and the signalling mechanisms involved using C2C12 cells as a skeletal muscle cell model.

Methods

Small-hairpin (shRNA) was used to knockdown CSN3 in C2C12 cells. Differentiation was evaluated by immunostaining and confocal microscopy. Markers of differentiation, NF-κB signaling and CSN subunits expression, were assessed by immunoblotting and/or immunostaining. Cell proliferation was analysed by cell counting, flow cytometry and a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Data were analyzed by one or two-way analysis of variance (ANOVA) followed by post-hoc testing.

Results

Transduction of C2C12 cells with two distinct CSN3 shRNAs led to the production of two cells lines expressing 7% of CSN3 protein (shCSN3-Low) and 43% of CSN3 protein (CSN3-Med) compared to controls. Knockdown of CSN3 was accompanied by destabilization of several CSN subunits and increased nuclear NF-κB localization. shCSN3-Med cells expressed less myogenin and formed shorter and thinner myotubes. In contrast, the shCSN3-Low cells expressed higher levels of myogenin prior and during the differentiation and remained mononucleated throughout the differentiation period. Both CSN3 knockdown cell lines failed to express sarcomeric myosin heavy chain (MHC) protein during differentiation. The fusion index was significantly higher in control cells than in shCSN3-Med cells, whereas shCSN3-Low cells showed no cell fusion. Interestingly, CSN3 knockdown cells exhibited a significantly slower growth rate relative to the control cells. Cell cycle analysis revealed that CSN3 knockdowns delayed in S phase and had increased levels of nuclear p21/Cip1 and p27/Kip1.

Conclusions

This study clarifies the first step toward unrevealing the CSN3/CSN-mediated pathways that controls C2C12 differentiation and proliferation. Further in vivo characterization of CSN/CSN3 may lead to the discovery of novel therapeutic target of skeletal muscle diseases such as muscular dystrophies.

Characterization and optimization of actuating poly(ethylene glycol) diacrylate/acrylic acid hydrogels as artificial muscles

Large volume deficiencies in skeletal muscle tissue fail to heal with conservative treatments, and improved treatment methods are needed. Tissue engineered scaffolds for skeletal muscle need to mimic the optimal environment for muscle development by providing the proper electric, mechanical, and chemical cues. Electroactive polymers, polymers that change in size or shape in response to an electric field, may be able to provide the optimal environment for muscle growth. In this study, an electroactive polymer made from poly(ethylene glycol) diacrylate (PEGDA) and acrylic acid (AA) is characterized and optimized for movement and biocompatibility. Hydrogel sample thickness, overall polymer concentration, and the ratio of PEGDA to AA were found to significantly impact the actuation response. C2C12 mouse myoblast cells attached and proliferated on hydrogel samples with various ratios of PEGDA to AA. Future experiments will produce hydrogel samples combined with aligned guidance cues in the form of electrospun fibers to provide a favorable environment for muscle development.

Silencing myotubularin related protein 7 enhances proliferation and early differentiation of C2C12 myoblast

Myotubularin related protein 7 (MTMR7) is a key member of the highly conserved myotubularin related proteins (MTMRs) family, which has phosphatase activity. MTMR7 was increased during myoblast differentiation and exhibited high expression level at primary fibers formation stages in pigs. This suggests that MTMR7 may be involved in myogenesis. In our study, we investigated the roles of MTMR7 on proliferation and differentiation of C2C12 myoblasts. Knocking down MTMR7 not only enhanced myoblast early differentiation via altering the expression of Myf5, but also promoted myoblast proliferation through increasing cyclinA2 expression. The improved proliferation capacity was related to the increased phosphorylation of AKT. Taken together, our research demonstrates that MTMR7 plays an important role in proliferation and early differentiation of C2C12 myoblast.

The roles of supernatant of macrophage treated by excretory-secretory products from muscle larvae of Trichinella spiralis on the differentiation of C2C12 myoblasts

The excretory-secretory products (ESPs) released by the muscle-larvae (ML) stage of Trichinella spiralis have been suggested to be involved in nurse cell formation. However, the molecular mechanisms by which ML-ESPs modulate nurse cell formation remain unclear. Macrophages exert either beneficial or deleterious effects on tissue repair, depending on their activation/polarization state. They are crucial for skeletal muscle repair, notably, via their actions on myogenic precursor cells. However, these interactions during T. spiralis infection have not been characterized. In the present study, the ability of conditioned medium (CM) from J774A.1 macrophages treated with ML-ESPs to influence the differentiation of murine myoblasts, and the mechanisms of this influence, were investigated in vitro. The results showed that the expression of Myogenic Regulatory Factors (MRFs) MyoD and myogenin, myosin heavy chain (MyHC), and the p21 cyclin-dependent kinase inhibitor were reduced in CM treated cells compared to their expression in the control group. These findings indicated that CM inhibited myoblast differentiation. Conversely, CM promoted myoblast proliferation and increased cyclin D1 levels. Taken together, results of our study suggested that CM can indirectly influence myoblast differentiation and proliferation, which provides a new method for the elucidation of the complex mechanisms involved in cell-parasite and cell-cell interactions during T. spiralis infection.

Lipogenesis in myoblasts and its regulation of CTRP6 by AdipoR1/Erk/PPARγ signaling pathway

The induced lipogenesis and its regulation in C2C12 myoblasts remain largely unclear. Here, we found that the cocktail method could significantly induce lipogenesis through regulating lipid metabolic genes and Erk1/2 phosphorylation in myoblasts. Meanwhile, the expression and secretion of CTRP6 were increased during ectopic lipogenesis. Moreover, CTRP6 knockdown down-regulated the levels of lipogenic genes and phosphorylated Erk1/2 (p-Erk1/2) in the early lipogenic stage, whereas up-regulated p-Erk1/2 in the terminal differentiation. Interestingly, the effect of CTRP6 siRNA was attenuated by U0126 (a special p-Erk1/2 inhibitor) in myoblasts. Furthermore, AdipoR1, not AdipoR2, was first identified as a receptor of CTRP6 during the process of mitotic clonal expansion. Collectively, we suggest that CTRP6 mediates the ectopic lipogenesis through AdipoR1/Erk/PPARγ signaling pathway in myoblasts. Our findings will shed light on the novel biological function of CTRP6 during myoblast lipogenesis and provide a hopeful direction of improving meat quality of domestic animal by lipogenic regulation in skeletal muscle myoblasts.

PLLA/ZnO nanocomposites: Dynamic surfaces to harness cell differentiation

This work investigates the effect of the sequential availability of ZnO nanoparticles, (nanorods of ∼40nm) loaded within a degradable poly(lactic acid) (PLLA) matrix, in cell differentiation. The system constitutes a dynamic surface, in which nanoparticles are exposed as the polymer matrix degrades. ZnO nanoparticles were loaded into PLLA and the system was measured at different time points to characterise the time evolution of the physicochemical properties, including wettability and thermal properties. The micro and nanostructure were also investigated using AFM, SEM and TEM images. Cellular experiments with C2C12 myoblasts show that cell differentiation was significantly enhanced on ZnO nanoparticles-loaded PLLA, as the polymer degrades and the availability of nanoparticles become more apparent, whereas the release of zinc within the culture medium was negligible. Our results suggest PLLA/ZnO nanocomposites can be used as a dynamic system where nanoparticles are exposed during degradation, activating the material surface and driving cell differentiation.

Multiphoton imaging of myogenic differentiation in gelatin-based hydrogels as tissue engineering scaffolds

BACKGROUND

Hydrogels can serve as three-dimensional (3D) scaffolds for cell culture and be readily injected into the body. Recent advances in the image technology for 3D scaffolds like hydrogels have attracted considerable attention to overcome the drawbacks of ordinary imaging technologies such as optical and fluorescence microscopy. Multiphoton microscopy (MPM) is an effective method based on the excitation of two-photons. In the present study, C2C12 myoblasts differentiated in 3D gelatin hydroxyphenylpropionic acid (GHPA) hydrogels were imaged by using a custom-built multiphoton excitation fluorescence microscopy to compare the difference in the imaging capacity between conventional microscopy and MPM.

RESULTS

The physicochemical properties of GHPA hydrogels were characterized by using scanning electron microscopy and Fourier-transform infrared spectroscopy. In addition, the cell viability and proliferation of C2C12 myoblasts cultured in the GHPA hydrogels were analyzed by using Live/Dead Cell and CCK-8 assays, respectively. It was found that C2C12 cells were well grown and normally proliferated in the hydrogels. Furthermore, the hydrogels were shown to be suitable to facilitate the myogenic differentiation of C2C12 cells incubated in differentiation media, which had been corroborated by MPM. It was very hard to get clear images from a fluorescence microscope.

CONCLUSIONS

Our findings suggest that the gelatin-based hydrogels can be beneficially utilized as 3D scaffolds for skeletal muscle engineering and that MPM can be effectively applied to imaging technology for tissue regeneration.