Journal articles: 'L6 myotubes'

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Sultan, Karim R., Birgit Henkel, Maarten Terlou, and Henk P. Haagsman. "Quantification of hormone-induced atrophy of large myotubes from C2C12 and L6 cells: atrophy-inducible and atrophy-resistant C2C12 myotubes." American Journal of Physiology-Cell Physiology 290, no. 2 (February 2006): C650—C659. http://dx.doi.org/10.1152/ajpcell.00163.2005.

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Myofiber atrophy is the final outcome of muscle wasting induced by catabolic factors such as glucocorticoids and thyroid hormones. We set up an in vitro system to define the catabolic reaction based on myotube atrophy. Both mouse C2C12 and rat L6 cells were used. C2C12 myotube formation was improved by replacing horse serum with the serum substitute Ultroser G. A new method was developed to quantify size changes of large (0.5–1 mm) myotubes only, excluding remaining myoblasts and small myotubes. Dexamethasone reduced myotube size by 30% in L6 but not in C2C12 myotubes. Expression of the glucocorticoid receptor was twofold higher in L6 myotubes than in C2C12 myotubes. In both cell lines, 3,3′,5-triiodo-l-thyronine (T3) did not induce a significant size reduction. Expression of the major T3 receptor (T3Rβ1) was higher in L6 myotubes. We investigated whether the changes in myotube size are related to changes in atrogin-1 expression, as this enzyme is thought to be a key factor in the initiation of muscle atrophy. Dexamethasone induced a twofold increase of atrogin-1 mRNA; again, only L6 myotubes were susceptible. Interestingly, atrogin-1 expression in Ultroser G-fused C2C12 myotubes was lower than that in horse serum-fused myotubes. Furthermore, dexamethasone treatment increased atrogin-1 expression only in horse serum-fused myotubes but not in Ultroser G-fused myotubes. Ultroser G-induced fusion may result in atrophy-resistant C2C12 myotubes. Therefore, C2C12 myotubes offer an ideal system in which to study skeletal muscle atrophy because, depending on differentiation conditions, C2C12 cells produce atrophy-inducible and atrophy-resistant myotubes.

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Yang, H., J. M. Egan, Y. Wang, C. D. Moyes, J. Roth, M. H. Montrose, and C. Montrose-Rafizadeh. "GLP-1 action in L6 myotubes is via a receptor different from the pancreatic GLP-1 receptor." American Journal of Physiology-Cell Physiology 275, no. 3 (September 1, 1998): C675—C683. http://dx.doi.org/10.1152/ajpcell.1998.275.3.c675.

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The incretin hormone glucagon-like peptide-1 (GLP-1)-(7—36) amide is best known for its antidiabetogenic actions mediated via a GLP-1 receptor present on pancreatic endocrine cells. To investigate the molecular mechanisms of GLP-1 action in muscle, we used cultured L6 myotubes. In L6 myotubes, GLP-1 enhanced insulin-stimulated glycogen synthesis by 140% while stimulating CO2 production and lactate formation by 150%. In the presence of IBMX, GLP-1 diminished cAMP levels to 83% of IBMX alone. In L6 myotubes transfected with pancreatic GLP-1 receptor, GLP-1 increased cAMP levels and inhibited glycogen synthesis by 60%. An antagonist of pancreatic GLP-1 receptor, exendin-4-(9—39), inhibited GLP-1-mediated glycogen synthesis in GLP-1 receptor-transfected L6 myotubes. However, in parental L6 myotubes, exendin-4-(9—39) and GLP-1-(1—36) amide, an inactive peptide on pancreatic GLP-1 receptor, displaced125I-labeled GLP-1 binding and stimulated glycogen synthesis by 186 and 130%, respectively. These results suggest that the insulinomimetic effects of GLP-1 in L6 cells are likely to be mediated by a receptor that is different from the GLP-1 receptor found in the pancreas.

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Robinson, Matthew M., Bergen K. Sather, Emily R. Burney, Sarah E. Ehrlicher, Harrison D. Stierwalt, Maria Clara Franco, and Sean A. Newsom. "Robust intrinsic differences in mitochondrial respiration and H2O2 emission between L6 and C2C12 cells." American Journal of Physiology-Cell Physiology 317, no. 2 (August 1, 2019): C339—C347. http://dx.doi.org/10.1152/ajpcell.00343.2018.

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Rat L6 and mouse C2C12 cell lines are commonly used to investigate myocellular metabolism. Mitochondrial characteristics of these cell lines remain poorly understood despite mitochondria being implicated in the development of various metabolic diseases. To address this need, we performed high-resolution respirometry to determine rates of oxygen consumption and H2O2 emission in suspended myoblasts during multiple substrate-uncoupler-inhibitor titration protocols. The capacity for oxidative phosphorylation supported by glutamate and malate, with and without succinate, or supported by palmitoyl-l-carnitine was lower in L6 compared with C2C12 myoblasts (all P < 0.01 for L6 vs. C2C12). Conversely, H2O2 emission during oxidative phosphorylation was greater in L6 than C2C12 myoblasts ( P < 0.01 for L6 vs. C2C12). Induction of noncoupled respiration revealed a significantly greater electron transfer capacity in C2C12 compared with L6 myoblasts, regardless of the substrate(s) provided. Mitochondrial metabolism was also investigated in differentiated L6 and C2C12 myotubes. Basal rates of oxygen consumption were not different between intact, adherent L6, and C2C12 myotubes; however, noncoupled respiration was significantly lower in L6 compared with C2C12 myotubes ( P = 0.01). In summary, L6 myoblasts had lower respiration rates than C2C12 myoblasts, including lesser capacity for fatty acid oxidation and greater electron leak toward H2O2. L6 cells also retain a lower capacity for electron transfer compared with C2C12 following differentiation to form fused myotubes. Intrinsic differences in mitochondrial metabolism between these cell lines should be considered when modeling and investigating myocellular metabolism.

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Abdelmoez, Ahmed M., Laura Sardón Puig, Jonathon A. B. Smith, Brendan M. Gabriel, Mladen Savikj, Lucile Dollet, Alexander V. Chibalin, Anna Krook, Juleen R. Zierath, and Nicolas J. Pillon. "Comparative profiling of skeletal muscle models reveals heterogeneity of transcriptome and metabolism." American Journal of Physiology-Cell Physiology 318, no. 3 (March 1, 2020): C615—C626. http://dx.doi.org/10.1152/ajpcell.00540.2019.

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Rat L6, mouse C2C12, and primary human skeletal muscle cells (HSMCs) are commonly used to study biological processes in skeletal muscle, and experimental data on these models are abundant. However, consistently matched experimental data are scarce, and comparisons between the different cell types and adult tissue are problematic. We hypothesized that metabolic differences between these cellular models may be reflected at the mRNA level. Publicly available data sets were used to profile mRNA levels in myotubes and skeletal muscle tissues. L6, C2C12, and HSMC myotubes were assessed for proliferation, glucose uptake, glycogen synthesis, mitochondrial activity, and substrate oxidation, as well as the response to in vitro contraction. Transcriptomic profiling revealed that mRNA of genes coding for actin and myosin was enriched in C2C12, whereas L6 myotubes had the highest levels of genes encoding glucose transporters and the five complexes of the mitochondrial electron transport chain. Consistently, insulin-stimulated glucose uptake and oxidative capacity were greatest in L6 myotubes. Insulin-induced glycogen synthesis was highest in HSMCs, but C2C12 myotubes had higher baseline glucose oxidation. All models responded to electrical pulse stimulation-induced glucose uptake and gene expression but in a slightly different manner. Our analysis reveals a great degree of heterogeneity in the transcriptomic and metabolic profiles of L6, C2C12, or primary human myotubes. Based on these distinct signatures, we provide recommendations for the appropriate use of these models depending on scientific hypotheses and biological relevance.

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Rajesh, P., and K. Balasubramanian. "Di(2-ethylhexyl)phthalate exposure impairs insulin receptor and glucose transporter 4 gene expression in L6 myotubes." Human & Experimental Toxicology 33, no. 7 (October 15, 2013): 685–700. http://dx.doi.org/10.1177/0960327113506238.

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Di(2-ethyl hexyl)-phthalate (DEHP) is an endocrine disrupter and is the most abundantly used phthalate derivative, which is suspected to be an inevitable environmental exposure contributing to the increasing incidence of type-2 diabetes in humans. Therefore, the present study was designed to address the dose-dependent effects of DEHP on insulin signaling molecules in L6 myotubes. L6 myotubes were exposed to different concentrations (25, 50, and 100 μM) of DEHP for 24 h. At the end of exposure, cells were utilized for assessing various parameters. Insulin receptor and glucose transporter4 (GLUT4) gene expression, insulin receptor protein concentration, glucose uptake and oxidation, and enzymatic and nonenzymatic antioxidants were significantly reduced, but glutamine fructose-6-phosphate amidotransferase, nitric oxide, lipid peroxidation, and reactive oxygen species levels were elevated in a dose-dependent manner in L6 myotubes exposed to DEHP. The present study in turn shows the direct adverse effect of DEHP on the expression of insulin receptor and GLUT4 gene, glucose uptake, and oxidation in L6 myotubes suggesting that DEHP exposure may have a negative influence on insulin signaling.

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Sarabia, Vivian, Toolsie Ramlal, and Amira Klip. "Glucose uptake in human and animal muscle cells in culture." Biochemistry and Cell Biology 68, no. 2 (February 1, 1990): 536–42. http://dx.doi.org/10.1139/o90-076.

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Human muscle cells were grown in culture from satellite cells present in muscle biopsies and fusion-competent clones were identified. Hexose uptake was studied in fused myotubes of human muscle cells in culture and compared with hexose uptake in myotubes of the rat L6 and mouse C2C12 muscle cell lines. Uptake of 2-deoxyglucose was saturable and showed an apparent Km of about 1.5 mM in myotubes of all three cell types. The Vmax of uptake was about 6000 pmol/(min∙mg protein) in human cells, 4000 pmol/(min∙mg protein) in mouse C2C12 muscle cells, and 500 pmol/(min∙mg protein) in L6 cells. Hexose uptake was inhibited ~90% by cytochalasin B in human, rat, and mouse muscle cell cultures. Insulin stimulated 2-deoxyglucose uptake in all three cultures. The hormone also stimulated transport of 3-O-methylglucose. The sensitivity to insulin was higher in human and C2C12 mouse myotubes (half-maximal stimulation observed at 3.5 × 10−9 M) than in rat L6 myotubes (half-maximal stimulation observed at 2.5 × 10−8 M). However, insulin (10−6 M) stimulated hexose uptake to a larger extent (2.37-fold) in L6 than in either human (1.58-fold) or mouse (1.39-fold) myotubes. It is concluded that human muscle cells grown in culture display carrier-mediated glucose uptake, with qualitatively similar characteristics to those of other muscle cells, and that insulin stimulates hexose uptake in human cells. These cultures will be instrumental in the study of human insulin resistance and in investigations on the mechanism of action of antidiabetic drugs.Key words: glucose uptake, insulin action, primary muscle cultures, L6 cells, C2 cells.

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Ryu, Yunkyoung, Donghyen Lee, Seung Hyo Jung, Kyung-Jin Lee, Hengzhe Jin, Su Jung Kim, Hwan Myung Lee, Bokyung Kim, and Kyung-Jong Won. "Sabinene Prevents Skeletal Muscle Atrophy by Inhibiting the MAPK–MuRF-1 Pathway in Rats." International Journal of Molecular Sciences 20, no. 19 (October 8, 2019): 4955. http://dx.doi.org/10.3390/ijms20194955.

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Chrysanthemum boreale Makino essential oil (CBMEO) has diverse biological activities including a skin regenerating effect. However, its role in muscle atrophy remains unknown. This study explored the effects of CBMEO and its active ingredients on skeletal muscle atrophy using in vitro and in vivo models of muscle atrophy. CBMEO reversed the size decrease of L6 myoblasts under starvation. Among the eight monoterpene compounds of CBMEO without cytotoxicity for L6 cells, sabinene induced predominant recovery of reductions of myotube diameters under starvation. Sabinene diminished the elevated E3 ubiquitin ligase muscle ring-finger protein-1 (MuRF-1) expression and p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase1/2 (ERK1/2) phosphorylations in starved myotubes. Moreover, sabinene decreased the increased level of reactive oxygen species (ROS) in myotubes under starvation. The ROS inhibitor antagonized expression of MuRF-1 and phosphorylation of MAPKs, which were elevated in starved myotubes. In addition, levels of muscle fiber atrophy and MuRF-1 expression in gastrocnemius from fasted rats were reduced after administration of sabinene. These findings demonstrate that sabinene, a bioactive component from CBMEO, may attenuate skeletal muscle atrophy by regulating the activation mechanism of ROS-mediated MAPK/MuRF-1 pathways in starved myotubes, probably leading to the reverse of reduced muscle fiber size in fasted rats.

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Li, Yiming, Van H. Tran, Nooshin Koolaji, Colin Duke, and Basil D. Roufogalis. "(S)-[6]-Gingerol enhances glucose uptake in L6 myotubes by activation of AMPK in response to [Ca²⁺]_i." Journal of Pharmacy & Pharmaceutical Sciences 16, no. 2 (July 10, 2013): 304. http://dx.doi.org/10.18433/j34g7p.

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PURPOSE. The aim of this study was to investigate the mechanism of (S)-[6]-gingerol in promoting glucose uptake in L6 skeletal muscle cells. METHODS. The effect of (S)-[6]-gingerol on glucose uptake in L6 myotubes was examined using 2-[1,2-3H]-deoxy-D-glucose. Intracellular Ca2+ concentration was measured using Fluo-4. Phosphorylation of AMPKα was determined by Western blotting analysis. RESULTS. (S)-[6]-Gingerol time-dependently enhanced glucose uptake in L6 myotubes. (S)-[6]-Gingerol elevated intracellular Ca2+ concentration and subsequently induced a dose- and time-dependent enhancement of threonine172 phosphorylated AMPKα in L6 myotubes via modulation by Ca2+/calmodulin-dependent protein kinase kinase. CONCLUSION. The results indicated that (S)-[6]-gingerol increased glucose uptake in L6 skeletal muscle cells by activating AMPK. (S)-[6]-gingerol, a major component of Zingiber officinale, may have potential for development as an antidiabetic agent. This article is open to POST-PUBLICATION REVIEW. Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page.

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Fernandez, C., and R. D. Sainz. "Pathways of Protein Degradation in L6 Myotubes." Experimental Biology and Medicine 214, no. 3 (March 1, 1997): 242–47. http://dx.doi.org/10.3181/00379727-214-44092.

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Yonemitsu, S., H. Nishimura, M. Shintani, R. Inoue, Y. Yamamoto, H. Masuzaki, Y. Ogawa, et al. "Troglitazone Induces GLUT4 Translocation in L6 Myotubes." Diabetes 50, no. 5 (May 1, 2001): 1093–101. http://dx.doi.org/10.2337/diabetes.50.5.1093.

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Yacoub Wasef, Sherif Z., Katherine A. Robinson, Mary N. Berkaw, and Maria G. Buse. "Glucose, dexamethasone, and the unfolded protein response regulate TRB3 mRNA expression in 3T3-L1 adipocytes and L6 myotubes." American Journal of Physiology-Endocrinology and Metabolism 291, no. 6 (December 2006): E1274—E1280. http://dx.doi.org/10.1152/ajpendo.00117.2006.

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Tribbles 3 (TRB3) is a recently recognized atypical inactive kinase that negatively regulates Akt activity in hepatocytes, resulting in insulin resistance. Recent reports link TRB3 to nutrient sensing and regulation of cell survival under stressful conditions. We studied the regulation of TRB3 by glucose, insulin, dexamethasone (Dex), and the unfolded protein response (UPR) in 3T3-L1 adipocytes and in L6 myotubes. In 3T3-L1 adipocytes, incubation in high glucose with insulin did not increase TRB3 mRNA expression. Rather, TRB3 mRNA increased fourfold with glucose deprivation and two- to threefold after incubation with tunicamcyin (an inducer of the UPR). Incubation of cells in no glucose or in tunicamcyin stimulated the expression of CCAAT/enhancer-binding protein homologous protein. In L6 myotubes, absent or low glucose induced TRB3 mRNA expression by six- and twofold, respectively. The addition of Dex to 5 mM glucose increased TRB3 mRNA expression twofold in 3T3-L1 adipocytes but decreased it 16% in L6 cells. In conclusion, TRB3 is not the mediator of high glucose or glucocorticoid-induced insulin resistance in 3T3-L1 adipocytes or L6 myotubes. TRB3 is induced by glucose deprivation in both cell types as a part of the UPR, where it may be involved in regulation of cell survival in response to glucose depletion.

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Ross, J. J., M. J. Duxson, and A. J. Harris. "Neural determination of muscle fibre numbers in embryonic rat lumbrical muscles." Development 100, no. 3 (July 1, 1987): 395–409. http://dx.doi.org/10.1242/dev.100.3.395.

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The generation and development of muscle cells in the IVth hindlimb lumbrical muscle of the rat was studied following total or partial denervation. Denervation was carried out by injection of beta-bungarotoxin (beta-BTX), a neurotoxin which binds to and destroys peripheral nerves. Primary myotubes were generated in denervated muscles and reached their normal stable number on embryonic day 17 (E17). This number was not maintained and denervated muscles examined on E19 or E21 contained many degenerating primary myotubes. Embryos injected with beta-bungarotoxin (beta-BTX) on E12 or E13 suffered a partial loss of motoneurones, resulting in a reduced number of axons in the L4 ventral root (the IVth lumbrical muscle is supplied by axons in L4, L5 and L6 ventral roots) and reduced numbers of nerve terminals in the intrinsic muscles of the hindfoot. Twitch tension measurements showed that all myotubes in partly innervated muscles examined on E21 contracted in response to nerve stimulation. Primary myotubes were formed and maintained at normal numbers in muscles with innervation reduced throughout development, but a diminished number of secondary myotubes formed by E21. The latter was correlated with a reduction in number of mononucleate cells within the muscles. If beta-BTX was injected on E18 to denervate muscles after primary myotube formation was complete, E21 embryo muscles contained degenerating primary myotubes. After injection to denervate muscles on E19, the day secondary myotubes begin to form, E21 muscles possessed normal numbers of primary myotubes. In both cases, secondary myotube formation had stopped about 1 day after the injection and the number of mononucleate cells was greatly reduced, indicating that cessation of secondary myotube generation was most probably due to exhaustion of the supply of competent myoblasts. We conclude that nerve terminals regulate the number of secondary myotubes by stimulating mitosis in a nerve-dependent population of myoblasts and that activation of these myoblasts requires the physical presence of nerve terminals as well as activation of contraction in primary myotubes.

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Yang, Hongmei, Wei Wei, Michael Menconi, and Per-Olof Hasselgren. "Dexamethasone-induced protein degradation in cultured myotubes is p300/HAT dependent." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 292, no. 1 (January 2007): R337—R334. http://dx.doi.org/10.1152/ajpregu.00230.2006.

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Muscle proteolysis during sepsis and other catabolic conditions is, at least in part, regulated by glucocorticoids. Dexamethasone-treated myotubes are a commonly used in vitro model of muscle wasting. We reported recently that treatment of cultured L6 myotubes with dexamethasone resulted in increased gene and protein expression of the nuclear cofactor p300 but it is not known whether glucocorticoids upregulate p300 histone acetyl transferase (HAT) activity in muscle and whether p300/HAT activity regulates glucocorticoid-induced muscle proteolysis. Here, we found that treatment of cultured L6 myotubes with dexamethasone resulted in increased nuclear p300/HAT activity. Treatment of myotubes with p300 siRNA or transfection of muscle cells with a plasmid expressing p300 that was mutated in its HAT activity domain blocked the dexamethasone-induced increase in protein degradation, supporting a role of p300/HAT in glucocortiocoid-induced muscle proteolysis. In addition to increased HAT activity, treatment of the myotubes with dexamethasone resulted in reduced nuclear expression and activity of histone deacetylases (HDACs) 3 and 6. When myotubes were treated with the HDAC inhibitor trichostatin A, protein degradation increased to the same degree as in dexamethasone-treated myotubes. The results suggest that glucocorticoids increase HAT and decrease HDAC activities in muscle, changes that both favor hyperacetylation. The results also provide evidence that dexamethasone-induced protein degradation in cultured myotubes is, at least in part, regulated by p300/HAT activity.

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Caron, Marc-André, Marie-Eve Thériault, Marie-Ève Paré, François Maltais, and Richard Debigaré. "Hypoxia alters contractile protein homeostasis in L6 myotubes." FEBS Letters 583, no. 9 (April 11, 2009): 1528–34. http://dx.doi.org/10.1016/j.febslet.2009.04.006.

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Ueyama, Atsunori, Karen L. Yaworsky, Qinghua Wang, Yousuke Ebina, and Amira Klip. "GLUT-4myc ectopic expression in L6 myoblasts generates a GLUT-4-specific pool conferring insulin sensitivity." American Journal of Physiology-Endocrinology and Metabolism 277, no. 3 (September 1, 1999): E572—E578. http://dx.doi.org/10.1152/ajpendo.1999.277.3.e572.

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Insulin stimulates glucose uptake into muscle and fat cells via recruitment of the glucose transporter 4 (GLUT-4) from intracellular store(s) to the cell surface. Robust stimulation of glucose uptake by insulin coincides with the expression of GLUT-4 during differentiation of muscle and fat cells, but it is not known if GLUT-4 expression suffices to confer insulin sensitivity to glucose uptake. We have therefore examined the effect of expression of a myc epitope-tagged GLUT-4 (GLUT-4myc) into L6 myoblasts, which do not express endogenous GLUT-4 until differentiated into myotubes. Ectopic expression of GLUT-4myc markedly improved insulin sensitivity of glucose uptake in L6 myoblasts. The GLUT-4myc protein distributed equally to the cell surface and intracellular compartments in myoblasts, and the intracellular fraction of GLUT-4myc further increased in myotubes. In myoblasts, the intracellular GLUT-4myc compartment contained the majority of the insulin-regulatable amino peptidase (IRAP) but less than half of the GLUT-1, suggesting segregation of GLUT-4myc and IRAP to a specific cellular locus. Insulin stimulation of phosphatidylinositol 3-kinase and protein kinase B-α activities was similar for L6-GLUT-4myc myoblasts and myotubes. At both stages, GLUT-4myc responded to insulin by translocating to the cell surface. These results suggest that GLUT-4myc segregates into a specific compartment in L6 myoblasts and confers insulin sensitivity to these cells. L6-GLUT-4myc myoblasts, which are easily transfectable with various constructs, are a useful resource to study insulin action.

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Sawyer, J. T., and R. A. Akeson. "Differential redistribution of lectin receptor classes on clonal rat myotubes and myoblasts." Journal of Cell Science 83, no. 1 (July 1, 1986): 181–96. http://dx.doi.org/10.1242/jcs.83.1.181.

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To evaluate the relative mobilities of cell surface glycoconjugates during myogenesis we have studied the redistribution of fluorescein-conjugated plant lectins on L6 rat myogenic cells. Previous experiments had demonstrated that the receptors for the lectins soybean agglutinin (SBA), wheat germ agglutinin, concanavalin A and Lens culinaris agglutinin all were relatively uniformly distributed on both myoblasts and myotubes, and that SBA receptors were capable of rapid redistribution on myotubes but not myoblasts at 4 degrees C (Sawyer & Akeson, 1983). Here we show that when SBA-labelled myoblasts are incubated at 37 degrees C, or for extended times at 4 degrees C, the lectin aggregates as on myotubes. So it appears that SBA-binding components show a quantitative rather than qualitative change in their mobility during L6 differentiation. In addition, the redistribution of the three other lectins on myoblasts and myotubes was either less prominent (i.e. showing fewer apparent surface clusters) or occurred less rapidly than with SBA. None of these three lectins showed striking differences in mobility between myoblasts and myotubes. Thus, it appears that SBA binds to a subset of surface glycoconjugates that is relatively highly mobile, and that this mobility is specifically enhanced with differentiation.

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Prakash, Shubha N., Jayakumari Shanthakumari, and Anitha Devanath. "Effect of Sucralose on Glucose Uptake in Rat L6 Myotubes." Indian journal of Medical Biochemistry 21, no. 2 (2017): 162–65. http://dx.doi.org/10.5005/jp-journals-10054-0042.

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ABSTRACT Introduction With growing awareness of the link between diet and health and the problem of obesity, public concern over sugar levels in the diet is forcing a worldwide trend toward cutting down on sugar by using artificial sweeteners (AS). Aim To study the effect of increasing concentrations of sucralose (an AS) on glucose uptake in rat L6 myotubes. Materials and methods The L6 cell line from American type cell culture (ATCC) was grown in Dulbecco's Modified Eagle's Medium (DMEM) and differentiated into myotubes. The wells were exposed to either 0, 1 nM, 1 μM, or 1 mM of sucralose alone or with 10 nM insulin for 24 hours. Glucose uptake was studied after this period. Results Significant decrease was seen between the insulin-stimulated basal glucose uptake and insulin-stimulated glucose uptake across all the concentrations of sucralose treatment. Conclusion Increased concentration of sucralose appears to decrease glucose uptake even on insulin stimulation. Clinical significance It may not be beneficial to use sucralose in certain groups of people who have insulin resistance or are prone to it. How to cite this article Prakash SN, Shanthakumari J, Devanath A. Effect of Sucralose on Glucose Uptake in Rat L6 Myotubes. Indian J Med Biochem 2017;21(2):162-165.

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Rachek, L. I., S. I. Musiyenko, S. P. LeDoux, and G. L. Wilson. "Palmitate Induced Mitochondrial Deoxyribonucleic Acid Damage and Apoptosis in L6 Rat Skeletal Muscle Cells." Endocrinology 148, no. 1 (January 1, 2007): 293–99. http://dx.doi.org/10.1210/en.2006-0998.

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A major characteristic of type 2 diabetes mellitus (T2DM) is insulin resistance in skeletal muscle. A growing body of evidence indicates that oxidative stress that results from increased production of reactive oxygen species and/or reactive nitrogen species leads to insulin resistance, tissue damage, and other complications observed in T2DM. It has been suggested that muscular free fatty acid accumulation might be responsible for the mitochondrial dysfunction and insulin resistance seen in T2DM, although the mechanisms by which increased levels of free fatty acid lead to insulin resistance are not well understood. To help resolve this situation, we report that saturated fatty acid palmitate stimulated the expression of inducible nitric oxide (NO) synthase and the production of reactive oxygen species and NO in L6 myotubes. Additionally, palmitate caused a significant dose-dependent increase in mitochondrial DNA (mtDNA) damage and a subsequent decrease in L6 myotube viability and ATP levels at concentrations as low as 0.5 mm. Furthermore, palmitate induced apoptosis, which was detected by DNA fragmentation, caspase-3 cleavage, and cytochrome c release. N-acetyl cysteine, a precursor compound for glutathione formation, aminoguanidine, an inducible NO synthase inhibitor, and 5,10,15,20-tetrakis(4-sulphonatophenyl) porphyrinato iron (III), a peroxynitrite inhibitor, all prevented palmitate-induced mtDNA damage and diminished palmitate-induced cytotoxicity. We conclude that exposure of L6 myotubes to palmitate induced mtDNA damage and triggered mitochondrial dysfunction, which caused apoptosis. Additionally, our findings indicate that palmitate-induced mtDNA damage and cytotoxicity in skeletal muscle cells were caused by overproduction of peroxynitrite.

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Karthikeyan, Gayathri, T. Lakshmi, S. Rajeshkumar, Anitha Roy, Deepa Gurunadhan, RV Geetha, and R. Pradeep Kumar. "Glucose Uptake Potential in L6 Myotubes by Ficus racemosa." Indian Journal of Public Health Research & Development 10, no. 11 (2019): 3527. http://dx.doi.org/10.5958/0976-5506.2019.04132.9.

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Cornelius, Peter, M. Douglas Lee, Melissa Marlowe, and Phillip H. Pekala. "Monokine regulation of glucose transporter mRNA in L6 myotubes." Biochemical and Biophysical Research Communications 165, no. 1 (November 1989): 429–36. http://dx.doi.org/10.1016/0006-291x(89)91088-7.

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Roeder, R. A., and J. M. Gunn. "Effects of zeranol on protein turnover in L6 myotubes." Domestic Animal Endocrinology 4, no. 1 (January 1987): 61–67. http://dx.doi.org/10.1016/0739-7240(87)90039-7.

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Muller, A., C. van Hardeveld, W. S. Simonides, and J. van Rijn. "Ca2+ homeostasis and fast-type sarcoplasmic reticulum Ca2+-ATPase expression in L6 muscle cells. Role of thyroid hormone." Biochemical Journal 283, no. 3 (May 1, 1992): 713–18. http://dx.doi.org/10.1042/bj2830713.

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The effect of thyroid hormone (L-tri-iodothyronine; T3) on the cytosolic free Ca2+ concentration ([Ca2+]i) in L6 myotubes was studied at rest and during activation to explore the possible mediating role of [Ca2+]i in the T3-induced net synthesis of fast-type sarcoplasmic reticulum (SR) Ca(2+)-ATPase. The mean [Ca2+]i at rest was approx. 115 nM in myoblasts, control myotubes and T3-treated myotubes. Therefore it is unlikely that the T3-induced elevation of Ca(2+)-ATPase levels is mediated by [Ca2+]i changes. To investigate the influence of the 4-fold higher Ca(2+)-ATPase levels in T3-treated myotubes (compared with controls) on [Ca2+]i, interventions with caffeine (10 mM) and a high extracellular K+ concentration ([K+]o) (30 mM) were applied which initially mobilize Ca2+ predominantly from the SR. The results showed a lower (caffeine) or not significantly different (high [K+]o) increase in [Ca2+]i in T3-treated myotubes compared with controls. No rise in [Ca2+]i was found in myoblasts with caffeine or high [K+]o. The role of [Ca2+]i in the regulation of Ca(2+)-ATPase levels was investigated by varying [Ca2+]i through exposure of cells to different concentrations of extracellular Ca2+ (0.2-1.8 mM) and ionomycin (0.1-0.25 microM). At subnormal [Ca2+]i (55 nM) the T3-induced net synthesis of Ca(2+)-ATPase was virtually abolished, and at supranormal [Ca2+]i (195 nM) it was greatly depressed. Intermediate stimulation of net Ca(2+)-ATPase synthesis was found at [Ca2+]i of 95 and 165 nM, with an optimum at approx. 125 nM. Similar but less pronounced effects were found for the basal Ca(2+)-ATPase levels. In contracting primary rat myotubes, Ca(2+)-ATPase levels were significantly lower than in tetrodotoxin-arrested myotubes. The same results were obtained in the presence of T3. Since the mean [Ca2+]i in contracting cells is higher than in resting cells, these data agree with those obtained in the L6 cells with ionomycin. A major conclusion of this study is the existence of a [Ca2+]i optimum, near resting levels, for the expression of the fast-type Ca(2+)-ATPase in the L6 muscle cell line.

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Quinn, LeBris S., Barbara G. Anderson, and Stephen R. Plymate. "Muscle-specific overexpression of the type 1 IGF receptor results in myoblast-independent muscle hypertrophy via PI3K, and not calcineurin, signaling." American Journal of Physiology-Endocrinology and Metabolism 293, no. 6 (December 2007): E1538—E1551. http://dx.doi.org/10.1152/ajpendo.00160.2007.

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The insulin-like growth factors (IGF-I and IGF-II), working through the type 1 IGF receptor (IGF-1R), are key mediators of skeletal muscle fiber growth and hypertrophy. These processes are largely dependent on stimulation of proliferation and differentiation of muscle precursor cells, termed myoblasts. It has not been rigorously determined whether the IGFs can also mediate skeletal muscle hypertrophy in a myoblast-independent fashion. Similarly, although the phosphatidylinositol 3-kinase (PI3K) and calcineurin signaling pathways have been implicated in skeletal muscle hypertrophy, these pathways are also involved in skeletal myoblast differentiation. To determine whether the IGFs can stimulate skeletal muscle hypertrophy in a myoblast-independent fashion, we developed and validated a retroviral expression vector that mediated overexpression of the human IGF-1R in rat L6 skeletal myotubes (immature muscle fibers), but not in myoblasts. L6 myotubes transduced with this vector accumulated significantly higher amounts of myofibrillar proteins, in a ligand- and receptor-dependent manner, than controls and demonstrated significantly increased rates of protein synthesis. Stimulation of myotube hypertrophy was independent of myoblast contributions, inasmuch as these cultures did not exhibit increased levels of myoblast proliferation or differentiation. Experiments with PI3K and calcineurin inhibitors indicated that myoblast-independent myotube hypertrophy was mediated by PI3K, but not calcineurin, signaling. This study demonstrates that IGF can mediate skeletal muscle hypertrophy in a myoblast-independent fashion and suggests that muscle-specific overexpression of the IGF-1R or stimulation of its signaling pathways could be used to develop strategies to ameliorate muscle wasting without stimulating proliferative pathways leading to carcinogenesis or other pathological sequelae.

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24

Herget, T., M. Burba, M. Schmoll, K. Zimmermann, and A. Starzinski-Powitz. "Regulated expression of nuclear protein(s) in myogenic cells that binds to a conserved 3' untranslated region in pro alpha 1 (I) collagen cDNA." Molecular and Cellular Biology 9, no. 7 (July 1989): 2828–36. http://dx.doi.org/10.1128/mcb.9.7.2828.

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We describe the identification and DNA-binding properties of nuclear proteins from rat L6 myoblasts which recognize an interspecies conserved 3' untranslated segment of pro alpha 1 (I) collagen cDNA. Levels of the two pro alpha 1 (I) collagen RNAs, present in L6 myoblasts, decreased drastically between 54 and 75 h after induction of myotube formation in serum-free medium. Both mRNAs contained a conserved sequence segment of 135 nucleotides (termed tame sequence) in the 3' untranslated region that had 96% homology to the human and murine pro alpha 1 (I) collagen genes. The cDNA of this tame sequence was specifically recognized by nuclear protein(s) from L6 myoblasts, as judged by gel retardation assays and DNase I footprints. The tame-binding protein(s) was able to recognize its target sequence on double-stranded DNA but bound also to the appropriate single-stranded oligonucleotide. Protein that bound to the tame sequence was undetectable in nuclear extracts of L6 myotubes that did not accumulate the two collagen mRNAs. Therefore, the activity of this nuclear protein seems to be linked to accumulation of the sequences that it recognizes in vitro. The collagen RNAs and the nuclear tame-binding proteins reappeared after a change of medium, which further suggests that the RNAs and the protein(s) are coordinately regulated.

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25

Herget, T., M. Burba, M. Schmoll, K. Zimmermann, and A. Starzinski-Powitz. "Regulated expression of nuclear protein(s) in myogenic cells that binds to a conserved 3' untranslated region in pro alpha 1 (I) collagen cDNA." Molecular and Cellular Biology 9, no. 7 (July 1989): 2828–36. http://dx.doi.org/10.1128/mcb.9.7.2828-2836.1989.

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We describe the identification and DNA-binding properties of nuclear proteins from rat L6 myoblasts which recognize an interspecies conserved 3' untranslated segment of pro alpha 1 (I) collagen cDNA. Levels of the two pro alpha 1 (I) collagen RNAs, present in L6 myoblasts, decreased drastically between 54 and 75 h after induction of myotube formation in serum-free medium. Both mRNAs contained a conserved sequence segment of 135 nucleotides (termed tame sequence) in the 3' untranslated region that had 96% homology to the human and murine pro alpha 1 (I) collagen genes. The cDNA of this tame sequence was specifically recognized by nuclear protein(s) from L6 myoblasts, as judged by gel retardation assays and DNase I footprints. The tame-binding protein(s) was able to recognize its target sequence on double-stranded DNA but bound also to the appropriate single-stranded oligonucleotide. Protein that bound to the tame sequence was undetectable in nuclear extracts of L6 myotubes that did not accumulate the two collagen mRNAs. Therefore, the activity of this nuclear protein seems to be linked to accumulation of the sequences that it recognizes in vitro. The collagen RNAs and the nuclear tame-binding proteins reappeared after a change of medium, which further suggests that the RNAs and the protein(s) are coordinately regulated.

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26

Kim, Ji H., Jung O. Lee, Ji W. Moon, Min J. Kang, Won S. Byun, Jeong A. Han, Su J. Kim, Sun H. Park, and Hyeon S. Kim. "Laminarin From Salicornia herbacea Stimulates Glucose Uptake Through AMPK-p38 MAPK Pathways in L6 Muscle Cells." Natural Product Communications 15, no. 3 (March 1, 2020): 1934578X2090140. http://dx.doi.org/10.1177/1934578x20901409.

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Laminarin is a component of brown seaweed, especially isolated from Salicornia herbacea. Laminarin was known to have various physiological functions, however, the molecular mechanism is still unclear. In this study, we report that laminarin stimulates an activation of AMP-activated protein kinase (AMPK) and increases glucose uptake in rat L6 myotubes. Laminarin also increases an intracellular calcium release. Inhibition of Ca2+ release, using with CaMKK inhibitor, STO-609, blocked laminarin-induced AMPK activity, indicating that laminarin stimulated AMPK activity via calcium. In addition, laminarin activates p38 mitogen-activated protein kinase (MAPK) signaling pathways depending on AMPK activity. Moreover, the inhibition of either AMPK or p38 MAPK blocked laminarin-induced glucose uptake in rat L6 myotubes. Taken together, these results demonstrate that the hypoglycemic effect of laminarin is caused by its ability to activate AMPK-p38 MAPK pathways in skeletal muscles.

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27

Rodriguez Lanzi, Cecilia, Diahann J. Perdicaro, Julián Gambarte Tudela, Victoria Muscia, Ariel R. Fontana, Patricia I. Oteiza, and Marcela A. Vazquez Prieto. "Grape pomace extract supplementation activates FNDC5/irisin in muscle and promotes white adipose browning in rats fed a high-fat diet." Food & Function 11, no. 2 (2020): 1537–46. http://dx.doi.org/10.1039/c9fo02463h.

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Grape pomace extract (GPE) and epicatechin up-regulate the expression and secretion of the myokine irisin in rats and in L6 myotubes via PGC-1α, respectively. GPE also promotes browning of white adipose tissue and prevent HFD-induce glucose intolerance.

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28

Lira, Vitor A., David S. Criswell, Quinlyn A. Soltow, Jenna L. Betters, and Jodi H. Long. "Nitric Oxide-dependent Regulation Of Glut4 Expression In L6 Myotubes." Medicine & Science in Sports & Exercise 37, Supplement (May 2005): S309. http://dx.doi.org/10.1249/00005768-200505001-01611.

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29

Lira, Vitor A., David S. Criswell, Quinlyn A. Soltow, Jenna L. Betters, and Jodi H. Long. "Nitric Oxide-dependent Regulation Of Glut4 Expression In L6 Myotubes." Medicine & Science in Sports & Exercise 37, Supplement (May 2005): S309. http://dx.doi.org/10.1097/00005768-200505001-01611.

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30

Gao, Dan, Helen R. Griffiths, and Clifford J. Bailey. "Oleate protects against palmitate-induced insulin resistance in L6 myotubes." British Journal of Nutrition 102, no. 11 (July 22, 2009): 1557. http://dx.doi.org/10.1017/s0007114509990948.

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31

Fang, X., J. Fetros, K. E. Dadson, A. Xu, and G. Sweeney. "Leptin prevents the metabolic effects of adiponectin in L6 myotubes." Diabetologia 52, no. 10 (July 28, 2009): 2190–200. http://dx.doi.org/10.1007/s00125-009-1462-0.

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32

Martins, Vitor F., Maedha Begur, Shivani Lakkaraju, Kristoffer Svensson, Ji Park, Byron Hetrick, Carrie E. McCurdy, and Simon Schenk. "Acute inhibition of protein deacetylases does not impact skeletal muscle insulin action." American Journal of Physiology-Cell Physiology 317, no. 5 (November 1, 2019): C964—C968. http://dx.doi.org/10.1152/ajpcell.00159.2019.

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Whether the histone deacetylase (HDAC) and sirtuin families of protein deacetylases regulate insulin-stimulated glucose uptake, independent of their transcriptional effects, has not been studied. Our objective was to determine the nontranscriptional role of HDACs and sirtuins in regulation of skeletal muscle insulin action. Basal and insulin-stimulated glucose uptake and signaling and acetylation were assessed in L6 myotubes and skeletal muscle from C57BL/6J mice that were treated acutely (1 h) with HDAC (trichostatin A, panobinostat, TMP195) and sirtuin inhibitors (nicotinamide). Treatment of L6 myotubes with HDAC inhibitors or skeletal muscle with a combination of HDAC and sirtuin inhibitors increased tubulin and pan-protein acetylation, demonstrating effective impairment of HDAC and sirtuin deacetylase activities. Despite this, neither basal nor insulin-stimulated glucose uptake or insulin signaling was impacted. Acute reduction of the deacetylase activity of HDACs and/or sirtuins does not impact insulin action in skeletal muscle.

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33

Faez, S., H. Muhajir, I. Amin, and A. Zainah. "Effects of Oil Palm (Elais guineensis) Fruit Extracts on Glucose Uptake Activity of Muscle, Adipose and Liver Cells." ASEAN Journal on Science and Technology for Development 31, no. 2 (December 20, 2015): 83. http://dx.doi.org/10.29037/ajstd.17.

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The effect of oil palm (Elaeis guineensis) fruit aqueous extract (OPF) on glucose uptake activity of three different cell lines was investigated. The cell lines were incubated with different concentrations of OPF to evaluate the stimulatory effect of OPF towards glucose uptake activity of L6 myotubes, 3T3F442A adipocytes and Chang liver cell line. The glucose uptake activities of all tested cells were enhanced in the presence of OPF extract (basal condition). Nevertheless in combination of OPF extract and 100 nM insulin, the glucose uptake activity was only significantly enhanced in L6 myotubes and 3T3F442A adipocytes cell lines. The extracts enhanced the glucose uptake into cells through either insulin-mimetic or insulin-sensitizing property or combination of these two properties. It can be suggested that the OPF extract exerts its antihyperglycemic action partly by mediated glucose uptake into the glucose-responsive disposal cells, muscle, adipose and liver.

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34

HYDE, Russell, Graham R. CHRISTIE, Gary J. LITHERLAND, Eric HAJDUCH, Peter M. TAYLOR, and Harinder S. HUNDAL. "Subcellular localization and adaptive up-regulation of the System A (SAT2) amino acid transporter in skeletal-muscle cells and adipocytes." Biochemical Journal 355, no. 3 (April 24, 2001): 563–68. http://dx.doi.org/10.1042/bj3550563.

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The recently cloned amino acid transporter SAT2 is ubiquitously expressed and confers Na+-dependent transport of short-chain neutral amino acids, characteristics of the functionally defined System A transporter. Here we report the presence of SAT2 mRNA and protein in both skeletal muscle and adipocytes, and the characterization of polyclonal antibodies directed against this transporter. SAT2 protein was present in both plasma-membrane and internal-membrane fractions derived from rat skeletal muscle and adipose tissue, L6 myotubes and 3T3-L1 adipocytes, having a localization similar to that of the glucose transporter GLUT4. Moreover, consistent with the adaptive up-regulation of System A activity following chronic amino acid deprivation, a time-dependent increase in SAT2 protein abundance was observed in amino-acid-deprived L6 myotubes and 3T3-L1 adipocytes. These studies provide the first evidence regarding the subcellular distribution and adaptive up-regulation of SAT2 protein and the characterization of molecular probes for this physiologically important transporter, the function of which is altered in several disease states.

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35

LaDu, Mary Jo, and Warren K. Palmer. "Expression of lipoprotein lipase during differentiation of cultured L6 muscle cells." Canadian Journal of Physiology and Pharmacology 72, no. 3 (March 1, 1994): 243–47. http://dx.doi.org/10.1139/y94-038.

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The presence of lipoprotein lipase (LPL) in L6 muscle cells is equivocal. Analysis of a 21-day time course indicates that these cells express both LPL activity and mRNA. Lipase activity peaked at 4 days after plating and decreased to a nadir at day 21 after plating. Characterization of lipase activity at 4 and 19 days after plating, corresponding to myoblasts and myotubes, respectively, indicated that most of the enzyme activity had the properties of LPL, including an alkaline pH optimum, a serum requirement, and inhibition by NaCl. LPL mRNA expression peaked at 7 days after plating and fell slightly (24%) at day 21. The primary LPL mRNA species in these cells is 3.7 kb in length. Lipase activity and LPL mRNA were highly correlated during the time course (r = +0.82), suggesting transcriptional regulation of the enzyme. These data clearly demonstrate that L6 cells express LPL during differentiation.Key words: myoblasts, myotubes, mRNA, total protein, total RNA.

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36

Sauro, V. S., and K. P. Strickland. "Changes in oleic acid oxidation and incorporation into lipids of differentiating L6 myoblasts cultured in normal or fatty acid-supplemented growth medium." Biochemical Journal 244, no. 3 (June 15, 1987): 743–48. http://dx.doi.org/10.1042/bj2440743.

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L6 myoblasts accumulate large stores of neutral lipid (predominantly triacylglycerol) when cultured in fatty acid-supplemented growth medium. No accumulation of neutral lipid was evident in myotubes (differentiated myoblasts) when treated similarly. Triacylglycerol accumulation was rapid and dependent on exogenous fatty acid concentration. Triacylglycerol content in myoblasts cultured in fatty acid-supplemented growth medium was approx. 3-fold higher than that in myotubes treated similarly and 2-3-fold higher than that in myoblasts cultured in normal growth medium. Incorporation studies using [I-14C]oleic acid showed that myoblasts and myotubes take up exogenous fatty acid at similar rates. However, cells cultured in fatty acid-supplemented growth medium remove more exogenous fatty acid than do cells cultured in normal growth medium. Over 90% of the incorporated label was found in phospholipid and triacylglycerol fractions in all situations studied. Myoblasts incorporated a more significant proportion (P less than 0.001) of label into triacylglycerol compared with that of myotubes. No differences in fatty acid oxidation rates were detected when differentiating L6 cells cultured in normal growth medium were compared with those cultured in fatty acid-supplemented growth medium. However, fatty acid oxidation rates were observed to increase 3-5-fold upon myoblast differentiation. We conclude that there is a marked change in the pattern of lipid metabolism when myoblasts (primarily triacylglycerol-synthesizing cells) differentiate into myotubes (primarily phospholipid-synthesizing cells). Understanding these changes, which coincide with normal muscle development, may be important, since a defect in this natural switch could explain the observed accumulation of lipid in muscle characteristic of some of the muscular dystrophies and other lipid-storage myopathies.

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37

Noipha, Kusumarn, and Putrada Ninla-Aesong. "Antidiabetic Activity of Zingiber officinale Roscoe Rhizome Extract: an In Vitro Study." HAYATI Journal of Biosciences 25, no. 4 (December 4, 2018): 160. http://dx.doi.org/10.4308/hjb.25.4.160.

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The potential roles of Zingiber officinale Roscoe (ginger) for treating and preventing diabetes have been investigated in both humans and experimental animals. However, the mode of its action has not yet been elucidated. This study aimed to investigate the effects of ginger extract on glucose uptake activity and its activation pathway in L6 myotubes. Cells were co-cultured for 24 h with a variable concentration of either ginger extract or 2 mM metformin or 200 nM insulin or 20 μM Troglitazone (TGZ), followed by a 10-min 2-[3H]-deoxy-D-glucose (2-DG) uptake. The levels of glucose transporters 1 (GLUT1) and GLUT4 protein and mRNA expression were determined. Ginger extract at 400 μg/ml significantly enhanced glucose uptake in L6 myotubes (208.03 ± 10.65% above basal value, p<0.05) after co-culture for 24 h. The ginger-enhancement of glucose uptake was inhibited by 3.5 μM cycloheximide, a protein synthesis inhibitor, 1 μM wortmannin (Phosphatidylinositol 3-Kinase (PI3 kinase) inhibitor) and 15 nM rapamycin (mammalian target of rapamycin (mTOR) inhibitor). The enhancement of glucose transport by ginger extract at 400 μg/ml was accompanied with the increased expression of GLUT1 protein (1.60 ± 0.20, 2.03 ± 0.19, and 2.25 ± 0.35 folds of basal at 4, 8, and 24 h, respectively p<0.05) and mRNA (1.22 ± 0.96, 1.45 ± 0.93, 1.91 ± 0.75, 2.32±0.92, and 2.20 ± 0.64 folds of basal at 1, 2, 4, 8, and 24 h, respectively p<0.05) in a time-dependent manner. Z. officinale Roscoe rhizome extract increase glucose transport activity of L6 myotubes by enhancing GLUT1 expression, the results of PI3-Kinase and 5’-AMP-activated kinase (AMPK) stimulation.

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Yin, Jun, Aamir Zuberi, Zhanguo Gao, Dong Liu, Zhijun Liu, and Jianping Ye. "Shilianhua extract inhibits GSK-3β and promotes glucose metabolism." American Journal of Physiology-Endocrinology and Metabolism 296, no. 6 (June 2009): E1275—E1280. http://dx.doi.org/10.1152/ajpendo.00092.2009.

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The extract of plant Shilianhua (SLH; Sinocrassula indica Berge) is a component in a commercial product for control of blood glucose. However, it remains to be investigated whether the SLH extract enhances insulin sensitivity in a model of type 2 diabetes. To address this question, the SLH crude extract was fractionated into four parts on the basis of polarity, and bioactivities of each part were tested in cells. One of the fractions, F100, exhibited a strong activity in the stimulation of glucose consumption in vitro. Glucose consumption was induced significantly by F100 in 3T3-L1 adipocytes, L6 myotubes, and H4IIE hepatocytes in the absence of insulin. F100 also increased insulin-stimulated glucose consumption in L6 myotubes and H4IIE hepatocytes. It increased insulin-independent glucose uptake in 3T3-L1 adipocytes and insulin-dependent glucose uptake in L6 cells. The glucose transporter-1 (GLUT1) protein was induced in 3T3-L1 cells, and the GLUT4 protein was induced in L6 cells by F100. Mechanism study indicated that F100 induced GSK-3β phosphorylation, which was comparable with that induced by insulin. Additionally, the transcriptional activity of NF-κB was inhibited by F100. In RAW 264.7 macrophages, mRNA expression of NF-κB target genes (TNFα and MCP-1) was suppressed by F100. In KK.Cg-Ay/+ mice, F100 decreased fasting insulin and blood glucose and improved insulin tolerance significantly. We conclude that the F100 may be a bioactive component in the SLH plant. It promotes glucose metabolism in vitro and in vivo. Inhibition of GSK-3β and NF-κB may be the potential mechanism.

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Sauro, V. S., H. J. Klamut, C. H. Lin, and K. P. Strickland. "Lysosomal triacylglycerol lipase activity in L6 myoblasts and its changes on differentiation." Biochemical Journal 227, no. 2 (April 15, 1985): 583–89. http://dx.doi.org/10.1042/bj2270583.

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L6 myoblasts, before fusion, accumulate large stores of neutral lipid when cultured in medium supplemented with fatty acid. Upon fusion to terminally differentiated myotubes, a noticeable decrease in these neutral-lipid stores was observed. Triacylglycerol lipase activity was examined in L6 myoblasts at various stages of cell differentiation to assess a possible role for this enzyme in the above phenomenon. In this first study to demonstrate lipolytic activity in cultured muscle cells, the activity was found to be totally dependent on the presence of a detergent, either Cutscum or Triton X-100, during homogenization. The inhibition by many thiol-specific reagents [N-ethylmaleimide, p-chloromercuribenzoate, iodoacetate, 5,5′-dithiobis-(2-nitrobenzoic acid)] suggest that a thiol group is at or near the active site. The observed acidic pH optimum (5.5-6.0), the acute inhibition by chlorpromazine (a lysosomal lipase inhibitor) and the distribution of lipolytic activity upon cell fractionation (which co-sediments with acid phosphatase, a lysosomal marker enzyme) suggest that the lipase may be of lysosomal origin. Under the optimal conditions described, the triacylglycerol lipase activity of L6 myoblasts was determined to be 2.9 +/- 0.4 nmol of oleic acid released/min per mg of DNA. This activity increased 3-fold, to 9.0 +/- 1.6 nmol/min per mg, in the myotube phase. This increase in lipolytic activity may be responsible for the observed decrease in neutral-lipid stores of differentiating myoblasts.

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40

Lee, Myung Sun, Chung Hee Kim, Duc Manh Hoang, Bo Yeon Kim, Cheon Bae Sohn, Mee Ree Kim, and Jong Seog Ahn. "Genistein-Derivatives from Tetracera scandens Stimulate Glucose-Uptake in L6 Myotubes." Biological & Pharmaceutical Bulletin 32, no. 3 (2009): 504–8. http://dx.doi.org/10.1248/bpb.32.504.

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41

Uranga, Selina, J. William Deever, Matthew Bird, Colleen Louise O'Reilly, Patrick J. Ryan, and James D. Fluckey. "Effect of Electrical Pulse Stimulation on Anabolic Signaling in L6 Myotubes." FASEB Journal 34, S1 (April 2020): 1. http://dx.doi.org/10.1096/fasebj.2020.34.s1.06622.

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42

Wang, Li, Guang-Ju Luo, Jing-Jing Wang, and Per-Olof Hasselgren. "DEXAMETHASONE STIMULATES PROTEASOME- AND CALCIUM-DEPENDENT PROTEOLYSIS IN CULTURED L6 MYOTUBES." Shock 10, no. 4 (October 1998): 298–306. http://dx.doi.org/10.1097/00024382-199810000-00011.

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Hatakeyama, Y., and PJ Scarpace. "Transcriptional regulation of uncoupling protein-2 gene expression in L6 myotubes." International Journal of Obesity 25, no. 11 (November 2001): 1619–24. http://dx.doi.org/10.1038/sj.ijo.0801812.

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Nankar, Rakesh P., and Mukesh Doble. "Ellagic acid potentiates insulin sensitising activity of pioglitazone in L6 myotubes." Journal of Functional Foods 15 (May 2015): 1–10. http://dx.doi.org/10.1016/j.jff.2015.03.010.

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45

Li, Chunmei, Bixia Ma, Junhong Chen, Yoonhwa Jeong, and Xiulong Xu. "Astaxanthin Inhibits p70 S6 Kinase 1 Activity to Sensitize Insulin Signaling." Marine Drugs 18, no. 10 (September 28, 2020): 495. http://dx.doi.org/10.3390/md18100495.

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Astaxanthin (AST) is a carotenoid with therapeutic values on hyperglycemia and diabetic complications. The mechanisms of action of AST remain incompletely understood. p70 S6 kinase 1 (S6K1) is a serine/threonine kinase that phosphorylates insulin receptor substrate 1 (IRS-1)S1101 and desensitizes the insulin receptor (IR). Our present study aims to determine if AST improves glucose metabolisms by targeting S6K1. Western blot analysis revealed that AST inhibited the phosphorylation of two S6K1 substrates, S6S235/236 and IRS-1S1101, but enhanced the phosphorylation of AKTT308, AKTS473, and S6K1T389 by feedback activation of the phosphatidylinositol-3 (PI-3) kinase in 3T3-L1 adipocytes and L6 myotubes. In vitro kinase assays revealed that AST inhibited S6K1 activity with an IC50 value of approximately 13.8 μM. AST increased insulin-induced IR tyrosine phosphorylation and IRS-1 binding to the p85 subunit of PI-3 kinase. Confocal microscopy revealed that AST increased the translocation of the glucose transporter 4 (GLUT4) to the plasma membrane in L6 cells. Glucose uptake assays using a fluorescent dye, 2-NBDG (2-N-(Nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose), revealed that AST increased glucose uptake in 3T3-L1 adipocytes and L6 myotubes under insulin resistance conditions. Our study identifies S6K1 as a previously unrecognized molecular target of AST and provides novel insights into the mechanisms of action of AST on IR sensitization.

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McConell, G. K., G. P. Y. Ng, M. Phillips, Z. Ruan, S. L. Macaulay, and G. D. Wadley. "Central role of nitric oxide synthase in AICAR and caffeine-induced mitochondrial biogenesis in L6 myocytes." Journal of Applied Physiology 108, no. 3 (March 2010): 589–95. http://dx.doi.org/10.1152/japplphysiol.00377.2009.

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5-Aminoimidazole-4-carboxamide-ribonucleoside (AICAR) and caffeine, which activate AMP-activated protein kinase (AMPK) and cause sarcoplasmic reticulum calcium release, respectively, have been shown to increase mitochondrial biogenesis in L6 myotubes. Nitric oxide (NO) donors also increase mitochondrial biogenesis. Since neuronal and endothelial NO synthase (NOS) are calcium dependent and are also phosphorylated by AMPK, we hypothesized that NOS inhibition would attenuate the activation of mitochondrial biogenesis in response to AICAR and caffeine. L6 myotubes either were not treated (control) or were exposed acutely or for 5 h/day over 5 days to 100 μM of NG-nitro-l-arginine methyl ester (l-NAME, NOS inhibitor), 100 μM S-nitroso- N-acetyl-penicillamine (SNAP) (NO donor) ± 100 μM l-NAME, 2 mM AICAR ± 100 μM l-NAME, or 5 mM caffeine ± 100 μM l-NAME ( n = 12/treatment). Acute AICAR administration increased ( P < 0.05) phospho- (P-)AMPK, but also increased P-CaMK, with resultant chronic increases in peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), cytochrome- c oxidase (COX)-1, and COX-4 protein expression compared with control cells. NOS inhibition, which had no effect on AICAR-stimulated P-AMPK, surprisingly increased P-CaMK and attenuated the AICAR-induced increases in COX-1 and COX-4 protein. Caffeine administration, which increased P-CaMK without affecting P-AMPK, increased COX-1, COX-4, PGC-1α, and citrate synthase activity. NOS inhibition, surprisingly, greatly attenuated the effect of caffeine on P-CaMK and attenuated the increases in COX-1 and COX-4 protein. SNAP increased all markers of mitochondrial biogenesis, and it also increased P-AMPK and P-CaMK. In conclusion, AICAR and caffeine increase mitochondrial biogenesis in L6 myotubes, at least in part, via interactions with NOS.

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Chamberlain, Wei, Patricia Gonnella, Nima Alamdari, Zaira Aversa, and Per-Olof Hasselgren. "Multiple muscle wasting-related transcription factors are acetylated in dexamethasone-treated muscle cells." Biochemistry and Cell Biology 90, no. 2 (April 2012): 200–208. http://dx.doi.org/10.1139/o11-082.

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Recent studies suggest that the expression and activity of the histone acetyltransferase p300 are upregulated in catabolic muscle allowing for acetylation of cellular proteins. The function of transcription factors is influenced by posttranslational modifications, including acetylation. It is not known if transcription factors involved in the regulation of muscle mass are acetylated in atrophying muscle. We determined cellular levels of acetylated C/EBPβ, C/EBPδ, FOXO1, FOXO3a, and NF-kB/p65 in dexamethasone-treated L6 muscle cells, a commonly used in vitro model of muscle wasting. The role of p300 in dexamethasone-induced transcription factor acetylation and myotube atrophy was examined by transfecting muscle cells with p300 siRNA. Treatment of L6 myotubes with dexamethasone resulted in increased cellular levels of acetylated C/EBPβ and δ, FOXO1 and 3a, and p65. Downregulation of p300 with p300 siRNA reduced acetylation of transcription factors and decreased dexamethasone-induced myotube atrophy and expression of the ubiquitin ligase MuRF1. The results suggest that several muscle wasting-related transcription factors are acetylated supporting the concept that posttranslational modifications of proteins regulating gene transcription may be involved in the loss of muscle mass. The results also suggest that acetylation of the transcription factors is at least in part regulated by p300 and plays a role in glucocorticoid-induced muscle atrophy. Targeting molecules that regulate acetylation of transcription factors may help reduce the impact of muscle wasting.

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48

Meadus, William J., and Jnanankur Bag. "The effect of inhibitors of DNA synthesis on 40-kilodalton polypeptide translation in rat L6 myoblasts." Biochemistry and Cell Biology 68, no. 4 (April 1, 1990): 716–22. http://dx.doi.org/10.1139/o90-103.

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Messenger RNA coding for a polypeptide of 40 kilodaltons (P40) was translated in proliferating rat L6 myoblasts but not in the terminally differentiated myotubes. The relationship between DNA synthesis, differentiation, and P40 mRNA translation was studied. Aphidicolin, a reversible inhibitor of DNA synthesis, was shown to block DNA synthesis in proliferating myoblasts without allowing these cells to differentiate. A second inhibitor, cytosine arabinoside, when added to dividing myoblasts also prevented differentiation. In the absence of biochemical differentiation P40 mRNA remained in the translated state. Translational repression of this mRNA was, therefore, linked to the biochemical differentiation of rat L6 myoblasts.Key words: translational control, DNA synthesis, aphidicolin, P40 mRNA, myogenesis.

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49

Khayat, Z. A., P. Tong, K. Yaworsky, R. J. Bloch, and A. Klip. "Insulin-induced actin filament remodeling colocalizes actin with phosphatidylinositol 3-kinase and GLUT4 in L6 myotubes." Journal of Cell Science 113, no. 2 (January 15, 2000): 279–90. http://dx.doi.org/10.1242/jcs.113.2.279.

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We examined the temporal reorganization of actin microfilaments by insulin and its participation in the localization of signaling molecules and glucose transporters in L6 myotubes expressing myc-tagged glucose transporter 4 (GLUT4myc). Scanning electron microscopy revealed a dynamic distortion of the dorsal cell surface (membrane ruffles) upon insulin treatment. In unstimulated cells, phalloidin-labeled actin filaments ran parallel to the longitudinal axis of the cell. Immunostaining of the p85 regulatory subunit of phosphatidylinositol 3-kinase was diffusely punctate, and GLUT4myc was perinuclear. After 3 minutes of insulin treatment, actin reorganized to form structures; these structures protruded from the dorsal surface of the myotubes by 10 minutes and condensed in the myoplasm into less prominent foci at 30 minutes. The p85 polypeptide colocalized with these structures at all time points. Actin remodeling and p85 relocalization to actin structures were prevented by cytochalasin D or latrunculin B. GLUT4myc recruitment into the actin-rich projections was also observed, but only after 10 minutes of insulin treatment. Irrespective of insulin stimulation, the majority of p85 and a portion (45%) of GLUT4 were recovered in the Triton X-100-insoluble material that was also enriched with actin. In contrast, vp165, a transmembrane aminopeptidase that morphologically colocalized with GLUT4 vesicles, was fully soluble in Triton X-100 extracts of both insulin-treated and control myotubes. Transient transfection of dominant inhibitory Rac1 (N17) into L6 myotubes prevented formation of dorsal actin structures and blocked insulin-induced GLUT4myc translocation to the cell surface. We propose that insulin-dependent formation of actin structures facilitates the association of PI3-K (p85) with GLUT4 vesicles and, potentially, the arrival of GLUT4 at the cell surface.

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50

Muller, A., C. van Hardeveld, W. S. Simonides, and J. van Rijn. "The elevation of sarcoplasmic reticulum Ca2+-ATPase levels by thyroid hormone in the L6 muscle cell line is potentiated by insulin-like growth factor-I." Biochemical Journal 275, no. 1 (April 1, 1991): 35–40. http://dx.doi.org/10.1042/bj2750035.

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Net synthesis of the fast-type sarcoplasmic reticulum (SR) Ca2(+)-ATPase was studied in the muscle cell line L6AM using an immunochemical assay (e.l.i.s.a.). In addition, Ca2+ uptake by SR was monitored in muscle cell homogenates by a method employing the fluorescent Ca2+ indicator fura-2. Measurements were done both in differentiating myoblasts and in myotubes. Ca2(+)-ATPase levels were low (1 pmol/mg of protein) in undifferentiated myoblasts (controls) and only doubled over a period of 8 days in the absence of thyroid hormone (L-triiodothyronine; T3). This corresponded to a similar increase in Ca2+ uptake activity. Only half of the myoblasts fused under these conditions. Fusion was not increased in the presence of T3 (5 nM), but Ca2(+)-ATPase levels increased 4-fold and the Ca2+ uptake activity doubled compared with controls. In contrast, insulin-like growth factor-I (IGF-I) induced almost complete myotube formation (greater than 90% fusion), but only slightly stimulated (50%) net Ca2(+)-ATPase synthesis above control levels. However, the doubling of the Ca2+ uptake stimulation by IGF-I was comparable with that caused by T3. The effects of T3 plus IGF-I on Ca2(+)-ATPase levels and Ca2+ uptake activity were more than additive. Furthermore, the temporal relationship between the induction of Ca2(+)-ATPase net synthesis and Ca2+ uptake activity was identical with the two hormones. Qualitatively similar results were obtained when T3 and IGF-I were added to maximally fused cell cultures. The enhanced effect of T3 on Ca2(+)-ATPase net synthesis and Ca2+ uptake activity in the presence of IGF-I cannot therefore be explained by an increased myotube formation stimulated by the latter. In both differentiating myoblasts and myotubes the effect of T3 was more prominent on Ca2(+)-ATPase net synthesis than on Ca2+ uptake activity, whereas in myotubes the opposite was observed for IGF-I. This could imply complementary actions of the two agents in the development of a functional SR.

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Journal articles on the topic 'L6 myotubes'

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