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1
Jurdana, Mihaela, Maja Cemazar, Katarina Pegan e Tomaz Mars. "Effect of ionizing radiation on human skeletal muscle precursor cells". Radiology and Oncology 47, n. 4 (1 dicembre 2013): 376–81. http://dx.doi.org/10.2478/raon-2013-0058.
Testo completoAbstract (sommario):
Abstract Background. Long term effects of different doses of ionizing radiation on human skeletal muscle myoblast proliferation, cytokine signalling and stress response capacity were studied in primary cell cultures. Materials and methods. Human skeletal muscle myoblasts obtained from muscle biopsies were cultured and irradiated with a Darpac 2000 X-ray unit at doses of 4, 6 and 8 Gy. Acute effects of radiation were studied by interleukin - 6 (IL-6) release and stress response detected by the heat shock protein (HSP) level, while long term effects were followed by proliferation capacity and cell death. Results. Compared with non-irradiated control and cells treated with inhibitor of cell proliferation Ara C, myoblast proliferation decreased 72 h post-irradiation, this effect was more pronounced with increasing doses. Post-irradiation myoblast survival determined by measurement of released LDH enzyme activity revealed increased activity after exposure to irradiation. The acute response of myoblasts to lower doses of irradiation (4 and 6 Gy) was decreased secretion of constitutive IL-6. Higher doses of irradiation triggered a stress response in myoblasts, determined by increased levels of stress markers (HSPs 27 and 70). Conclusions. Our results show that myoblasts are sensitive to irradiation in terms of their proliferation capacity and capacity to secret IL-6. Since myoblast proliferation and differentiation are a key stage in muscle regeneration, this effect of irradiation needs to be taken in account, particularly in certain clinical conditions.
2
Quinn, LeBris S., Barbara G. Anderson e 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, n. 6 (dicembre 2007): E1538—E1551. http://dx.doi.org/10.1152/ajpendo.00160.2007.
Testo completoAbstract (sommario):
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.
3
Hicks, Michael R., Thanh V. Cao, David H. Campbell e Paul R. Standley. "Mechanical strain applied to human fibroblasts differentially regulates skeletal myoblast differentiation". Journal of Applied Physiology 113, n. 3 (1 agosto 2012): 465–72. http://dx.doi.org/10.1152/japplphysiol.01545.2011.
Testo completoAbstract (sommario):
Cyclic short-duration stretches (CSDS) such as those resulting from repetitive motion strain increase the risk of musculoskeletal injury. Myofascial release is a common technique used by clinicians that applies an acyclic long-duration stretch (ALDS) to muscle fascia to repair injury. When subjected to mechanical strain, fibroblasts within muscle fascia secrete IL-6, which has been shown to induce myoblast differentiation, essential for muscle repair. We hypothesize that fibroblasts subjected to ALDS following CSDS induce myoblast differentiation through IL-6. Fibroblast conditioned media and fibroblast-myoblast cocultures were used to test fibroblasts' ability to induce myoblast differentiation. The coculture system applies strain to fibroblasts only but still allows for diffusion of potential differentiation mediators to unstrained myoblasts on coverslips. To determine the role of IL-6, we utilized myoblast unicultures ± IL-6 (0–100 ng/ml) and cocultures ± α-IL-6 (0–200 μg/ml). Untreated uniculture myoblasts served as a negative control. After 96 h, coverslips ( n = 6–21) were microscopically analyzed and quantified by blinded observer for differentiation endpoints: myotubes per square millimeter (>3 nuclei/cell), nuclei/myotube, and fusion efficiency (%nuclei within myotubes). The presence of fibroblasts and fibroblast conditioned media significantly enhanced myotube number ( P < 0.05). However, in coculture, CSDS applied to fibroblasts did not reproduce this effect. ALDS following CSDS increased myotube number by 78% and fusion efficiency by 96% vs. CSDS alone ( P < 0.05). Fibroblasts in coculture increase IL-6 secretion; however, IL-6 secretion did not correlate with enhanced differentiation among strain groups. Exogenous IL-6 in myoblast uniculture failed to induce differentiation. However, α-IL-6 attenuated differentiation in all coculture groups ( P < 0.05). Fibroblasts secrete soluble mediators that have profound effects on several measures of myoblast differentiation. Specific biophysical strain patterns modify these outcomes, and suggest that myofascial release after repetitive strain increases myoblast differentiation and thus may improve muscle repair in vivo. Neutralization of IL-6 in coculture significantly reduced differentiation, suggesting fibroblast-IL-6 is necessary but not sufficient in this process.
4
Lee, Nicole K. L., Jarrod P. J. Skinner, Jeffrey D. Zajac e Helen E. MacLean. "Ornithine decarboxylase is upregulated by the androgen receptor in skeletal muscle and regulates myoblast proliferation". American Journal of Physiology-Endocrinology and Metabolism 301, n. 1 (luglio 2011): E172—E179. http://dx.doi.org/10.1152/ajpendo.00094.2011.
Testo completoAbstract (sommario):
The aim of this study is to determine if the Odc1 gene, which encodes ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, is directly regulated by the androgen receptor (AR) in skeletal muscle myoblasts and if Odc1 regulates myoblast proliferation and differentiation. We previously showed that expression of Odc1 is decreased in muscle from AR knockout male mice. In this study, we show in vivo that Odc1 expression is also decreased >60% in muscle from male muscle-specific AR knockout mice. In normal muscle homeostasis, Odc1 expression is regulated by age and sex, reflecting testosterone levels, as muscle of adult male mice expresses high levels of Odc1 compared with age-matched females and younger males. In vitro, expression of Odc1 is 10- and 1.5-fold higher in proliferating mouse C2C12 and human skeletal muscle myoblasts, respectively, than in differentiated myotubes. Dihydrotestosterone increases Odc1 levels 2.7- and 1.6-fold in skeletal muscle cell myoblasts after 12 and 24 h of treatment, respectively. Inhibition of ODC activity in C2C12 myoblasts by α-difluoromethylornithine decreases myoblast number by 40% and 66% following 48 and 72 h of treatment, respectively. In contrast, overexpression of Odc1 in C2C12 myoblasts results in a 27% increase in cell number vs. control when cells are grown under differentiation conditions for 96 h. This prolonged proliferation is associated with delayed differentiation, with reduced expression of the differentiation markers myogenin and Myf6 in Odc1-overexpressing cells. In conclusion, androgens act via the AR to upregulate Odc1 in skeletal muscle myoblasts, and Odc1 promotes myoblast proliferation and delays differentiation.
5
Rauen, Melanie, Dandan Hao, Aline Müller, Eva Mückter, Leo Cornelius Bollheimer e Mahtab Nourbakhsh. "Free Fatty Acid Species Differentially Modulate the Inflammatory Gene Response in Primary Human Skeletal Myoblasts". Biology 10, n. 12 (12 dicembre 2021): 1318. http://dx.doi.org/10.3390/biology10121318.
Testo completoAbstract (sommario):
Age-related loss of skeletal muscle is associated with obesity and inflammation. In animal models, intramuscular fat deposits compromise muscle integrity; however, the relevant fat components that mediate muscular inflammation are not known. Previously, we hypothesized that free fatty acids (FFAs) may directly induce inflammatory gene expression in skeletal muscle cells of obese rats. Here, we examined this hypothesis in primary human skeletal myoblasts (SkMs) using multiplex expression analysis of 39 inflammatory proteins in response to different FFA species. Multiplex mRNA quantification confirmed that the IL6, IL1RA, IL4, LIF, CXCL8, CXCL1, CXCL12 and CCL2 genes were differentially regulated by saturated and unsaturated C16 or C18 FFAs. Fluorescence staining revealed that only saturated C16 and C18 strongly interfere with myoblast replication independent of desmin expression, mitochondrial abundance and oxidative activity. Furthermore, we addressed the possible implications of 71 human receptor tyrosine kinases (RTKs) in FFA-mediated effects. Phosphorylated EphB6 and TNK2 were associated with impaired myoblast replication by saturated C16 and C18 FFAs. Our data suggest that abundant FFA species in human skeletal muscle tissue may play a decisive role in the progression of sarcopenic obesity by affecting inflammatory signals or myoblast replication.
6
Chen, Xiaoping, Zebin Mao, Shuhong Liu, Hong Liu, Xuan Wang, Haitao Wu, Yan Wu et al. "Dedifferentiation of Adult Human Myoblasts Induced by Ciliary Neurotrophic Factor In Vitro". Molecular Biology of the Cell 16, n. 7 (luglio 2005): 3140–51. http://dx.doi.org/10.1091/mbc.e05-03-0218.
Testo completoAbstract (sommario):
Ciliary neurotrophic factor (CNTF) is primarily known for its important cellular effects within the nervous system. However, recent studies indicate that its receptor can be highly expressed in denervated skeletal muscle. Here, we investigated the direct effect of CNTF on skeletal myoblasts of adult human. Surprisingly, we found that CNTF induced the myogenic lineage-committed myoblasts at a clonal level to dedifferentiate into multipotent progenitor cells—they not only could proliferate for over 20 passages with the expression absence of myogenic specific factors Myf5 and MyoD, but they were also capable of differentiating into new phenotypes, mainly neurons, glial cells, smooth muscle cells, and adipocytes. These “progenitor cells” retained their myogenic memory and were capable of redifferentiating into myotubes. Furthermore, CNTF could activate the p44/p42 MAPK and down-regulate the expression of myogenic regulatory factors (MRFs). Finally, PD98059, a specific inhibitor of p44/p42 MAPK pathway, was able to abolish the effects of CNTF on both myoblast fate and MRF expression. Our results demonstrate the myogenic lineage-committed human myoblasts can dedifferentiate at a clonal level and CNTF is a novel regulator of skeletal myoblast dedifferentiation via p44/p42 MAPK pathway.
7
Kagawa, Yuki, e Masahiro Kino-oka. "An in silico prediction tool for the expansion culture of human skeletal muscle myoblasts". Royal Society Open Science 3, n. 10 (ottobre 2016): 160500. http://dx.doi.org/10.1098/rsos.160500.
Testo completoAbstract (sommario):
Regenerative therapy using autologous skeletal myoblasts requires a large number of cells to be prepared for high-level secretion of cytokines and chemokines to induce good regeneration of damaged regions. However, myoblast expansion culture is hindered by a reduction in growth rate owing to cellular quiescence and differentiation, therefore optimization is required. We have developed a kinetic computational model describing skeletal myoblast proliferation and differentiation, which can be used as a prediction tool for the expansion process. In the model, myoblasts migrate, divide, quiesce and differentiate as observed during in vitro culture. We assumed cell differentiation initiates following cell–cell attachment for a defined time period. The model parameter values were estimated by fitting to several predetermined experimental datasets. Using an additional experimental dataset, we confirmed validity of the developed model. We then executed simulations using the developed model under several culture conditions and quantitatively predicted that non-uniform cell seeding had adverse effects on the expansion culture, mainly by reducing the existing ratio of proliferative cells. The proposed model is expected to be useful for predicting myoblast behaviours and in designing efficient expansion culture conditions for these cells.
8
Broholm, Christa, Matthew J. Laye, Claus Brandt, Radhika Vadalasetty, Henriette Pilegaard, Bente Klarlund Pedersen e Camilla Scheele. "LIF is a contraction-induced myokine stimulating human myocyte proliferation". Journal of Applied Physiology 111, n. 1 (luglio 2011): 251–59. http://dx.doi.org/10.1152/japplphysiol.01399.2010.
Testo completoAbstract (sommario):
The cytokine leukemia inhibitory factor (LIF) is expressed by skeletal muscle and induces proliferation of myoblasts. We hypothesized that LIF is a contraction-induced myokine functioning in an autocrine fashion to activate gene regulation of human muscle satellite cell proliferation. Skeletal muscle LIF expression, regulation, and action were examined in two models: 1) young men performing a bout of heavy resistance exercise of the quadriceps muscle and 2) cultured primary human satellite cells. Resistance exercise induced a ninefold increase in LIF mRNA content in skeletal muscle, but LIF was not detectable in plasma of the subjects. However, electrically stimulated cultured human myotubes produced and secreted LIF, suggesting that LIF is a myokine with local effects. The well established exercise-induced signaling molecules PI3K, Akt, and mTor contributed to the regulation of LIF in cultured human myotubes as chemical inhibition of PI3K and mTor and siRNA knockdown of Akt1 were independently sufficient to downregulate LIF. Human myoblast proliferation was increased by recombinant exogenous LIF and decreased by siRNA knockdown of the endogenous LIF receptor. Finally, the transcription factors JunB and c-Myc, which promote myoblast proliferation, were induced by LIF in cultured human myotubes. Indeed, both JunB and c-Myc were also increased in skeletal muscle following resistance exercise. Our data suggest that LIF is a contraction-induced myokine, potentially acting in an autocrine or paracrine fashion to promote satellite cell proliferation.
9
Zhang, Haifeng, Junfei Wen, Anne Bigot, Jiacheng Chen, Renjie Shang, Vincent Mouly e Pengpeng Bi. "Human myotube formation is determined by MyoD–Myomixer/Myomaker axis". Science Advances 6, n. 51 (dicembre 2020): eabc4062. http://dx.doi.org/10.1126/sciadv.abc4062.
Testo completoAbstract (sommario):
Myoblast fusion is essential for formations of myofibers, the basic cellular and functional units of skeletal muscles. Recent genetic studies in mice identified two long-sought membrane proteins, Myomaker and Myomixer, which cooperatively drive myoblast fusion. It is unknown whether and how human muscles, with myofibers of tremendously larger size, use this mechanism to achieve multinucleations. Here, we report an interesting fusion model of human myoblasts where Myomaker is sufficient to induce low-grade fusion, while Myomixer boosts its efficiency to generate giant myotubes. By CRISPR mutagenesis and biochemical assays, we identified MyoD as the key molecular switch of fusion that is required and sufficient to initiate Myomixer and Myomaker expression. Mechanistically, we defined the E-box motifs on promoters of Myomixer and Myomaker by which MyoD induces their expression for multinucleations of human muscle cells. Together, our study uncovered the key molecular apparatus and the transcriptional control mechanism underlying human myoblast fusion.
10
Badu-Mensah, Agnes, Paola Valinski, Hemant Parsaud, James J. Hickman e Xiufang Guo. "Hyperglycemia Negatively Affects IPSC-Derived Myoblast Proliferation and Skeletal Muscle Regeneration and Function". Cells 11, n. 22 (18 novembre 2022): 3674. http://dx.doi.org/10.3390/cells11223674.
Testo completoAbstract (sommario):
Diabetic myopathy is a co-morbidity diagnosed in most diabetes mellitus patients, yet its pathogenesis is still understudied, which hinders the development of effective therapies. This project aimed to investigate the effect of hyperglycemia on human myoblast physiology, devoid of other complicating factors, by utilizing human myoblasts derived from induced pluripotent stem cells (iPSCs), in a defined in vitro system. IPSC-derived myoblasts were expanded under three glucose conditions: low (5 mM), medium (17.5 mM) or high (25 mM). While hyperglycemic myoblasts demonstrated upregulation of Glut4 relative to the euglycemic control, myoblast proliferation demonstrated a glucose dose-dependent impedance. Further cellular analysis revealed a retarded cell cycle progression trapped at the S phase and G2/M phase and an impaired mitochondrial function in hyperglycemic myoblasts. Terminal differentiation of these hyperglycemic myoblasts resulted in significantly hypertrophic and highly branched myotubes with disturbed myosin heavy chain arrangement. Lastly, functional assessment of these myofibers derived from hyperglycemic myoblasts demonstrated comparatively increased fatigability. Collectively, the hyperglycemic myoblasts demonstrated deficient muscle regeneration capability and functionality, which falls in line with the sarcopenia symptoms observed in diabetic myopathy patients. This human-based iPSC-derived skeletal muscle hyperglycemic model provides a valuable platform for mechanistic investigation of diabetic myopathy and therapeutic development.
11
Gower, H. J., S. E. Moore, G. Dickson, V. L. Elsom, R. Nayak e F. S. Walsh. "Cloning and characterization of a myoblast cell surface antigen defined by 24.1D5 monoclonal antibody". Development 105, n. 4 (1 aprile 1989): 723–31. http://dx.doi.org/10.1242/dev.105.4.723.
Testo completoAbstract (sommario):
Monoclonal antibody 24.1D5 reacts specifically with an epitope expressed on the cell surface of mononucleate myoblasts in primary cultures of human skeletal muscle cells, but not with either multinucleate myotubes or fibroblasts. Polypeptides of 60 and 100 X 10(3) Mr were identified by immunoblotting with the McAb. Human muscle cDNAs encoding the 24.1D5 epitope were used to study further the structure and expression of 24.1D5 during skeletal muscle development. Two mRNA species of 3.0 and 2.5 kb were identified in primary cultures of human skeletal muscle and in mouse muscle cell lines. The levels of both transcripts decreased during myotube formation in vitro and were similarly decreased during myogenesis in the mouse embryo. 24.1D5 mRNAs were expressed by multipotential cells and myoblast derivatives of the mouse embryonic cell line C3H10T1/2, suggesting that 24.1D5 is expressed at an early stage during skeletal muscle development.
12
Mesmer, O. T., e T. C. Lo. "Hexose transport in human myoblasts". Biochemical Journal 262, n. 1 (15 agosto 1989): 15–24. http://dx.doi.org/10.1042/bj2620015.
Testo completoAbstract (sommario):
The present investigation reports on the hexose transport properties of human myoblasts isolated from normal subjects and from patients with Duchenne muscular dystrophy (DMD). Similar to rat myoblast L6, normal human myoblasts possess a high- (HAHT) and a low- (LAHT) affinity hexose transport system. The non-metabolizable hexose analogue, 2-deoxyglucose, is preferentially taken up by HAHT. The transport of this analogue is the rate-limiting step in the uptake process. This human myoblast HAHT is also similar to that of the rat myoblast in its substrate specificity and in response to the energy uncouplers, cytochalasin B and phloretin. The human myoblast LAHT resembles that of rat myoblast in its insensitivity to energy uncouplers, and in its transport affinity and capacity for 3-O-methyl-D-glucose. Although DMD myoblasts resemble their normal counterpart in their ability to differentiate, they differ significantly in their hexose transport properties. In addition to HAHT and LAHT present in normal human myoblast, DMD myoblasts contain a super-high-affinity hexose transport system (SHAHT). SHAHT can be detected only at very low substrate concentrations. It differs from HAHT not only in its much higher transport affinity, but also in its response to the traditional hexose transport inhibitors. For example, SHAHT can be activated by cytochalasin B and phlorizin, whereas it is more sensitive to inhibition by phloretin. Unlike HAHT, energy uncouplers are found to be ineffective in inhibiting SHAHT. It should be mentioned that SHAHT cannot be detected in myoblasts isolated from patients with other types of myopathy. The present study serves to demonstrate that more than one hexose transport system is operating in human skeletal muscle cells, as found in other cell types.
13
Fischer-Lougheed, Jacqueline, Jian-Hui Liu, Estelle Espinos, David Mordasini, Charles R. Bader, Dominique Belin e Laurent Bernheim. "Human Myoblast Fusion Requires Expression of Functional Inward Rectifier Kir2.1 Channels". Journal of Cell Biology 153, n. 4 (7 maggio 2001): 677–86. http://dx.doi.org/10.1083/jcb.153.4.677.
Testo completoAbstract (sommario):
Myoblast fusion is essential to skeletal muscle development and repair. We have demonstrated previously that human myoblasts hyperpolarize, before fusion, through the sequential expression of two K+ channels: an ether-à-go-go and an inward rectifier. This hyperpolarization is a prerequisite for fusion, as it sets the resting membrane potential in a range at which Ca2+ can enter myoblasts and thereby trigger fusion via a window current through α1H T channels.
14
Lucas, Lathan, e Thomas A. Cooper. "Insights into Cell-Specific Functions of Microtubules in Skeletal Muscle Development and Homeostasis". International Journal of Molecular Sciences 24, n. 3 (2 febbraio 2023): 2903. http://dx.doi.org/10.3390/ijms24032903.
Testo completoAbstract (sommario):
The contractile cells of skeletal muscles, called myofibers, are elongated multinucleated syncytia formed and maintained by the fusion of proliferative myoblasts. Human myofibers can be hundreds of microns in diameter and millimeters in length. Myofibers are non-mitotic, obviating the need for microtubules in cell division. However, microtubules have been adapted to the unique needs of these cells and are critical for myofiber development and function. Microtubules in mature myofibers are highly dynamic, and studies in several experimental systems have demonstrated the requirements for microtubules in the unique features of muscle biology including myoblast fusion, peripheral localization of nuclei, assembly of the sarcomere, transport and signaling. Microtubule-binding proteins have also been adapted to the needs of the skeletal muscle including the expression of skeletal muscle-specific protein isoforms generated by alternative splicing. Here, we will outline the different roles microtubules play in skeletal muscle cells, describe how microtubule abnormalities can lead to muscle disease and discuss the broader implications for microtubule function.
15
Miller, S. C., H. Ito, H. M. Blau e F. M. Torti. "Tumor necrosis factor inhibits human myogenesis in vitro". Molecular and Cellular Biology 8, n. 6 (giugno 1988): 2295–301. http://dx.doi.org/10.1128/mcb.8.6.2295-2301.1988.
Testo completoAbstract (sommario):
We examined the effects of human recombinant tumor necrosis factor-alpha (TNF) on human primary myoblasts. When added to proliferating myoblasts, TNF inhibited the expression of alpha-cardiac actin, a muscle-specific gene whose expression is observed at low levels in human myoblasts. TNF also inhibited muscle differentiation as measured by several parameters, including cell fusion and the expression of other muscle-specific genes, such as alpha-skeletal actin and myosin heavy chain. Muscle cells were sensitive to TNF in a narrow temporal window of differentiation. Northern (RNA) blot and immunofluorescence analyses revealed that human muscle gene expression became unresponsive to TNF coincident with myoblast differentiation. When TNF was added to differentiated myotubes, there was no effect on muscle gene expression. In contrast, TNF-inducible mRNAs such as interferon beta-2 still responded, suggesting that the signal mediated by TNF binding to its receptor had no effect on muscle-specific genes after differentiation.
16
Miller, S. C., H. Ito, H. M. Blau e F. M. Torti. "Tumor necrosis factor inhibits human myogenesis in vitro." Molecular and Cellular Biology 8, n. 6 (giugno 1988): 2295–301. http://dx.doi.org/10.1128/mcb.8.6.2295.
Testo completoAbstract (sommario):
We examined the effects of human recombinant tumor necrosis factor-alpha (TNF) on human primary myoblasts. When added to proliferating myoblasts, TNF inhibited the expression of alpha-cardiac actin, a muscle-specific gene whose expression is observed at low levels in human myoblasts. TNF also inhibited muscle differentiation as measured by several parameters, including cell fusion and the expression of other muscle-specific genes, such as alpha-skeletal actin and myosin heavy chain. Muscle cells were sensitive to TNF in a narrow temporal window of differentiation. Northern (RNA) blot and immunofluorescence analyses revealed that human muscle gene expression became unresponsive to TNF coincident with myoblast differentiation. When TNF was added to differentiated myotubes, there was no effect on muscle gene expression. In contrast, TNF-inducible mRNAs such as interferon beta-2 still responded, suggesting that the signal mediated by TNF binding to its receptor had no effect on muscle-specific genes after differentiation.
17
Fazeli, S., D. J. Wells, C. Hobbs e F. S. Walsh. "Altered secondary myogenesis in transgenic animals expressing the neural cell adhesion molecule under the control of a skeletal muscle alpha-actin promoter." Journal of Cell Biology 135, n. 1 (1 ottobre 1996): 241–51. http://dx.doi.org/10.1083/jcb.135.1.241.
Testo completoAbstract (sommario):
The majority of skeletal muscle fibers are generated through the process of secondary myogenesis. Cell adhesion molecules such as NCAM are thought to be intricately involved in the cell-cell interactions between developing secondary and primary myotubes. During secondary myogenesis, the expression of NCAM in skeletal muscle is under strict spatial and temporal control. To investigate the role of NCAM in the regulation of primary-secondary myotube interactions and muscle fusion in vivo, we have examined muscle development in transgenic mice expressing the 125-kD muscle-specific, glycosylphosphatidylinositol-anchored isoform of human NCAM, under the control of a human skeletal muscle alpha-actin promoter that is active from about embryonic day 15 onward. Analysis of developing muscle from transgenic animals revealed a significantly lower number of myofibers encased by basal lamina at postnatal day 1 compared with nontransgenic littermates, although the total number of developing myofibers was similar. An increase in muscle fiber size and decreased numbers of VCAM-1-positive secondary myoblasts at postnatal day 1 was also found, indicating enhanced secondary myoblast fusion in the transgenic animals. There was also a significant decrease in myofiber number but no increase in overall muscle size in adult transgenic animals; other measurements such as the number of nuclei per fiber and the size of individual muscle fibers were significantly increased, again suggesting increased secondary myoblast fusion. Thus the level of NCAM in the sarcolemma is a key regulator of cell-cell interactions occurring during secondary myogenesis in vivo and fulfills the prediction derived from transfection studies in vitro that the 125-kD NCAM isoform can enhance myoblast fusion.
18
Saini, Amarjit, Linda Björkhem-Bergman, Johan Boström, Mats Lilja, Michael Melin, Karl Olsson, Lena Ekström et al. "Impact of vitamin D and vitamin D receptor TaqI polymorphism in primary human myoblasts". Endocrine Connections 8, n. 7 (luglio 2019): 1070–81. http://dx.doi.org/10.1530/ec-19-0194.
Testo completoAbstract (sommario):
The CC genotype of the vitamin D receptor (VDR) polymorphism TaqI rs731236 has previously been associated with a higher risk of developing myopathy compared to TT carriers. However, the mechanistic role of this polymorphism in skeletal muscle is not well defined. The effects of vitamin D on patients genotyped for the VDR polymorphism TaqI rs731236, comparing CC and TT carriers were evaluated. Primary human myoblasts isolated from 4 CC carriers were compared with myoblasts isolated from four TT carriers and treated with vitamin D in vitro. A dose-dependent inhibitory effect on myoblast proliferation and differentiation was observed concurrent with modifications of key myogenic regulatory factors. RNA sequencing revealed a vitamin D dose–response gene signature enriched with a higher number of VDR-responsive elements (VDREs) per gene. Interestingly, the greater the expression of muscle differentiation markers in myoblasts, the more pronounced was the vitamin D-mediated response to suppress genes associated with myogenic fusion and myotube formation. This novel finding provides a mechanistic explanation to the inconsistency regarding previous reports of the role of vitamin D in myoblast differentiation. No effects in myoblast proliferation, differentiation or gene expression were related to CC vs TT carriers. Our findings suggest that the VDR polymorphism TaqI rs731236 comparing CC vs TT carriers did not influence the effects of vitamin D on primary human myoblasts and that vitamin D inhibits myoblast proliferation and differentiation through key regulators of cell cycle progression. Future studies need to employ strategies to identify the primary responses of vitamin D that drive the cellular response towards quiescence.
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Podbregar, Matej, Mitja Lainscak, Oja Prelovsek e Tomaz Mars. "Cytokine Response of Cultured Skeletal Muscle Cells Stimulated with Proinflammatory Factors Depends on Differentiation Stage". Scientific World Journal 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/617170.
Testo completoAbstract (sommario):
Myoblast proliferation and myotube formation are critical early events in skeletal muscle regeneration. The attending inflammation and cytokine signaling are involved in regulation of skeletal muscle cell proliferation and differentiation. Secretion of muscle-derived cytokines upon exposure to inflammatory factors may depend on the differentiation stage of regenerating muscle cells. Cultured human myoblasts and myotubes were exposed to 24-hour treatment with tumor necrosis factor (TNF)-αor lipopolysaccharide (LPS). Secretion of interleukin 6 (IL-6), a major muscle-derived cytokine, and interleukin 1 (IL-1), an important regulator of inflammatory response, was measured 24 hours after termination of TNF-αor LPS treatment. Myoblasts pretreated with TNF-αor LPS displayed robustly increased IL-6 secretion during the 24-hour period after removal of treatments, while IL-1 secretion remained unaltered. IL-6 secretion was also increased in myotubes, but the response was less pronounced compared with myoblasts. In contrast to myoblasts, IL-1 secretion was markedly stimulated in LPS-pretreated myotubes. We demonstrate that preceding exposure to inflammatory factors stimulates a prolonged upregulation of muscle-derived IL-6 and/or IL-1 in cultured skeletal muscle cells. Our findings also indicate that cytokine response to inflammatory factors in regenerating skeletal muscle partially depends on the differentiation stage of myogenic cells.
20
Cadaret, Caitlin N., Robert J. Posont, Kristin A. Beede, Hannah E. Riley, John Dustin Loy e Dustin T. Yates. "Maternal inflammation at midgestation impairs subsequent fetal myoblast function and skeletal muscle growth in rats, resulting in intrauterine growth restriction at term1". Translational Animal Science 3, n. 2 (1 marzo 2019): 867–76. http://dx.doi.org/10.1093/tas/txz037.
Testo completoAbstract (sommario):
Abstract Maternal inflammation induces intrauterine growth restriction (MI-IUGR) of the fetus, which compromises metabolic health in human offspring and reduces value in livestock. The objective of this study was to determine the effect of maternal inflammation at midgestation on fetal skeletal muscle growth and myoblast profiles at term. Pregnant Sprague-Dawley rats were injected daily with bacterial endotoxin (MI-IUGR) or saline (controls) from the 9th to the 11th day of gestational age (dGA; term = 21 dGA). At necropsy on dGA 20, average fetal mass and upper hindlimb cross-sectional areas were reduced (P < 0.05) in MI-IUGR fetuses compared with controls. MyoD+ and myf5+ myoblasts were less abundant (P < 0.05), and myogenin+ myoblasts were more abundant (P < 0.05) in MI-IUGR hindlimb skeletal muscle compared with controls, indicating precocious myoblast differentiation. Type I and Type II hindlimb muscle fibers were smaller (P < 0.05) in MI-IUGR fetuses than in controls, but fiber type proportions did not differ between experimental groups. Fetal blood plasma TNFα concentrations were below detectable amounts in both experimental groups, but skeletal muscle gene expression for the cytokine receptors TNFR1, IL6R, and FN14 was greater (P < 0.05) in MI-IUGR fetuses than controls, perhaps indicating enhanced sensitivity to these cytokines. Maternal blood glucose concentrations at term did not differ between experimental groups, but MI-IUGR fetal blood contained less (P < 0.05) glucose, cholesterol, and triglycerides. Fetal-to-maternal blood glucose ratios were also reduced (P < 0.05), which is indicative of placental insufficiency. Indicators of protein catabolism, including blood plasma urea nitrogen and creatine kinase, were greater (P < 0.05) in MI-IUGR fetuses than in controls. From these findings, we conclude that maternal inflammation at midgestation causes muscle-centric fetal programming that impairs myoblast function, increases protein catabolism, and reduces skeletal muscle growth near term. Fetal muscle sensitivity to inflammatory cytokines appeared to be enhanced after maternal inflammation, which may represent a mechanistic target for improving these outcomes in MI-IUGR fetuses.
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Langlois, Stéphanie, Xiao Xiang, Kelsey Young, Bryce J. Cowan, Silvia Penuela e Kyle N. Cowan. "Pannexin 1 and Pannexin 3 Channels Regulate Skeletal Muscle Myoblast Proliferation and Differentiation". Journal of Biological Chemistry 289, n. 44 (19 settembre 2014): 30717–31. http://dx.doi.org/10.1074/jbc.m114.572131.
Testo completoAbstract (sommario):
Pannexins constitute a family of three glycoproteins (Panx1, -2, and -3) forming single membrane channels. Recent work demonstrated that Panx1 is expressed in skeletal muscle and involved in the potentiation of contraction. However, Panxs functions in skeletal muscle cell differentiation, and proliferation had yet to be assessed. We show here that Panx1 and Panx3, but not Panx2, are present in human and rodent skeletal muscle, and their various species are differentially expressed in fetal versus adult human skeletal muscle tissue. Panx1 levels were very low in undifferentiated human primary skeletal muscle cells and myoblasts (HSMM) but increased drastically during differentiation and became the main Panx expressed in differentiated cells. Using HSMM, we found that Panx1 expression promotes this process, whereas it was impaired in the presence of probenecid or carbenoxolone. As for Panx3, its lower molecular weight species were prominent in adult skeletal muscle but very low in the fetal tissue and in undifferentiated skeletal muscle cells and myoblasts. Its overexpression (∼43-kDa species) induced HSMM differentiation and also inhibited their proliferation. On the other hand, a ∼70-kDa immunoreactive species of Panx3, likely glycosylated, sialylated, and phosphorylated, was highly expressed in proliferative myoblasts but strikingly down-regulated during their differentiation. Reduction of its endogenous expression using two Panx3 shRNAs significantly inhibited HSMM proliferation without triggering their differentiation. In summary, our results demonstrate that Panx1 and Panx3 are co-expressed in human skeletal muscle myoblasts and play a pivotal role in dictating the proliferation and differentiation status of these cells.
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Cheng, Cindy S., Yasser El-Abd, Khanh Bui, Young-Eun Hyun, Rebecca Harbuck Hughes, William E. Kraus e George A. Truskey. "Conditions that promote primary human skeletal myoblast culture and muscle differentiation in vitro". American Journal of Physiology-Cell Physiology 306, n. 4 (15 febbraio 2014): C385—C395. http://dx.doi.org/10.1152/ajpcell.00179.2013.
Testo completoAbstract (sommario):
Conditions under which skeletal myoblasts are cultured in vitro are critical to growth and differentiation of these cells into mature skeletal myofibers. We examined several culture conditions that promoted human skeletal myoblast (HSkM) culture and examined the effect of microRNAs and mechanical stimulation on differentiation. Culture conditions for HSkM are different from those that enable rapid C2C12 myoblast differentiation. Culture on a growth factor-reduced Matrigel (GFR-MG)-coated surface in 2% equine serum-supplemented differentiation medium to promote HSkM differentiation under static conditions was compared with culture conditions used for C2C12 cell differentiation. Such conditions led to a >20-fold increase in myogenic miR-1, miR-133a, and miR-206 expression, a >2-fold increase in myogenic transcription factor Mef-2C expression, and an increase in sarcomeric α-actinin protein. Imposing ±10% cyclic stretch at 0.5 Hz for 1 h followed by 5 h of rest over 2 wk produced a >20% increase in miR-1, miR-133a, and miR-206 expression in 8% equine serum and a >35% decrease in 2% equine serum relative to static conditions. HSkM differentiation was accelerated in vitro by inhibition of proliferation-promoting miR-133a: immunofluorescence for sarcomeric α-actinin exhibited accelerated development of striations compared with the corresponding negative control, and Western blotting showed 30% more α-actinin at day 6 postdifferentiation. This study showed that 100 μg/ml GFR-MG coating and 2% equine serum-supplemented differentiation medium enhanced HSkM differentiation and myogenic miR expression and that addition of antisense miR-133a alone can accelerate primary human skeletal muscle differentiation in vitro.
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Rudnicki, Michael A., Kenneth R. Reuhl e Michael W. McBurney. "A transfected H-ras oncogene does not inhibit differentiation of cardiac and skeletal muscle from embryonal carcinoma cells". Biochemistry and Cell Biology 67, n. 9 (1 settembre 1989): 590–96. http://dx.doi.org/10.1139/o89-091.
Testo completoAbstract (sommario):
P19 embryonal carcinoma (EC) cells can be induced to differentiate in vitro into a variety of cell types, including cardiac and skeletal myocytes. We have isolated P19 cells stably transformed with either the activated human H-ras oncogene or with a chimeric gene in which the H-ras oncogene was controlled by a muscle-specific promoter. These P19 lines exhibited ubiquitous and muscle-specific expression of the activated H-ras protein, respectively. In both lines of P19 cells, normal cardiac and skeletal muscle differentiation was observed. Since the activated H-ras prevents differentiation of myoblast cell lines, our results suggest that the EC-derived muscle progenitor cell differs from continuous myoblast cell lines, perhaps by lacking a complementing oncogene responsible for myoblast immortalization.Key words: embryonal carcinoma, oncogene, ras, differentiation, myogenesis.
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Fornaro, Mara, Aaron C. Hinken, Saul Needle, Erding Hu, Anne-Ulrike Trendelenburg, Angelika Mayer, Antonia Rosenstiel et al. "Mechano-growth factor peptide, the COOH terminus of unprocessed insulin-like growth factor 1, has no apparent effect on myoblasts or primary muscle stem cells". American Journal of Physiology-Endocrinology and Metabolism 306, n. 2 (15 gennaio 2014): E150—E156. http://dx.doi.org/10.1152/ajpendo.00408.2013.
Testo completoAbstract (sommario):
A splice form of IGF-1, IGF-1Eb, is upregulated after exercise or injury. Physiological responses have been ascribed to the 24-amino acid COOH-terminal peptide that is cleaved from the NH3-terminal 70-amino acid mature IGF-1 protein. This COOH-terminal peptide was termed “mechano-growth factor” (MGF). Activities claimed for the MGF peptide included enhancing muscle satellite cell proliferation and delaying myoblast fusion. As such, MGF could represent a promising strategy to improve muscle regeneration. Thus, at our two pharmaceutical companies, we attempted to reproduce the claimed effect of MGF peptides on human and mouse muscle myoblast proliferation and differentiation in vitro. Concentrations of peptide up to 500 ng/ml failed to increase the proliferation of C2C12 cells or primary human skeletal muscle myoblasts. In contrast, all cell types exhibited a proliferative response to mature IGF-1 or full-length IGF-1Eb. MGF also failed to inhibit the differentiation of myoblasts into myotubes. To address whether the response to MGF was lost in these tissue culture lines, we measured proliferation and differentiation of primary mouse skeletal muscle stem cells exposed to MGF. This, too, failed to demonstrate a significant effect. Finally, we tested whether MGF could alter a separate documented in vitro effect of the peptide, activation of p-ERK, but not p-Akt, in cardiac myocytes. Although a robust response to IGF-1 was observed, there were no demonstrated activating responses from the native or a stabilized MGF peptide. These results call in to question whether there is a physiological role for MGF.
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Rando, T. A., e H. M. Blau. "Primary mouse myoblast purification, characterization, and transplantation for cell-mediated gene therapy." Journal of Cell Biology 125, n. 6 (15 giugno 1994): 1275–87. http://dx.doi.org/10.1083/jcb.125.6.1275.
Testo completoAbstract (sommario):
The transplantation of cultured myoblasts into mature skeletal muscle is the basis for a new therapeutic approach to muscle and non-muscle diseases: myoblast-mediated gene therapy. The success of myoblast transplantation for correction of intrinsic muscle defects depends on the fusion of implanted cells with host myofibers. Previous studies in mice have been problematic because they have involved transplantation of established myogenic cell lines or primary muscle cultures. Both of these cell populations have disadvantages: myogenic cell lines are tumorigenic, and primary cultures contain a substantial percentage of non-myogenic cells which will not fuse to host fibers. Furthermore, for both cell populations, immune suppression of the host has been necessary for long-term retention of transplanted cells. To overcome these difficulties, we developed novel culture conditions that permit the purification of mouse myoblasts from primary cultures. Both enriched and clonal populations of primary myoblasts were characterized in assays of cell proliferation and differentiation. Primary myoblasts were dependent on added bFGF for growth and retained the ability to differentiate even after 30 population doublings. The fate of the pure myoblast populations after transplantation was monitored by labeling the cells with the marker enzyme beta-galactosidase (beta-gal) using retroviral mediated gene transfer. Within five days of transplantation into muscle of mature mice, primary myoblasts had fused with host muscle cells to form hybrid myofibers. To examine the immunobiology of primary myoblasts, we compared transplanted cells in syngeneic and allogeneic hosts. Even without immune suppression, the hybrid fibers persisted with continued beta-gal expression up to six months after myoblast transplantation in syngeneic hosts. In allogeneic hosts, the implanted cells were completely eliminated within three weeks. To assess tumorigenicity, primary myoblasts and myoblasts from the C2 myogenic cell line were transplanted into immunodeficient mice. Only C2 myoblasts formed tumors. The ease of isolation, growth, and transfection of primary mouse myoblasts under the conditions described here expand the opportunities to study muscle cell growth and differentiation using myoblasts from normal as well as mutant strains of mice. The properties of these cells after transplantation--the stability of resulting hybrid myofibers without immune suppression, the persistence of transgene expression, and the lack of tumorigenicity--suggest that studies of cell-mediated gene therapy using primary myoblasts can now be broadly applied to mouse models of human muscle and non-muscle diseases.
26
Nihashi, Yuma, Machi Yamamoto, Takeshi Shimosato e Tomohide Takaya. "Myogenetic Oligodeoxynucleotide Restores Differentiation and Reverses Inflammation of Myoblasts Aggravated by Cancer-Conditioned Medium". Muscles 1, n. 2 (9 settembre 2022): 111–20. http://dx.doi.org/10.3390/muscles1020012.
Testo completoAbstract (sommario):
Cancer cachexia is characterized by irreversible muscle loss which is a critical factor in the prognosis of cancer patients. Myoblasts are myogenic precursor cells that are required to maintain skeletal muscle tissue. Previous studies reported that cancer-released factors deteriorate myoblast differentiation, which is one of the causes of cachexia-associated muscle wasting. We recently identified the myogenetic oligodeoxynucleotide, iSN04, which serves as an anti-nucleolin aptamer and promotes myogenesis. The present study investigated the effects of iSN04 on human myoblasts exposed to a conditioned medium (CM) of cancer cells. CM of colon cancer cell lines LoVo and HCT-116 significantly impaired myogenic differentiation and the myotube formation of human myoblasts by inducing the expression of inflammatory cytokines such as interleukin (IL)-1β and tumor necrosis factor-α (TNF-α); however, the CM of the colon fibroblast cell line CCD-18Co did not. Intriguingly, iSN04 completely reversed the deterioration of myoblast differentiation by LoVo-CM by upregulating MyoD and myogenin, and downregulating myostatin, IL-1β, and TNF-α. TNF-α, of which a high level was produced in LoVo, alone inhibited myogenic differentiation and induced IL-1β, IL-6, and IL-8 transcriptions of myoblasts; however, pre-treatment with iSN04 reversed TNF-α-induced cachectic phenotypic features. The results indicate that iSN04 protects myoblasts against the effects of cancer-released factors and maintains their myogenic activity. This study provides a novel therapeutic strategy to prevent muscle loss associated with cancer cachexia.
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Goswami, Mansi V., Shefa M. Tawalbeh, Emily H. Canessa e Yetrib Hathout. "Temporal Proteomic Profiling During Differentiation of Normal and Dystrophin-Deficient Human Muscle Cells". Journal of Neuromuscular Diseases 8, s2 (30 novembre 2021): S205—S222. http://dx.doi.org/10.3233/jnd-210713.
Testo completoAbstract (sommario):
Background: Myogenesis is a dynamic process involving temporal changes in the expression of many genes. Lack of dystrophin protein such as in Duchenne muscular dystrophy might alter the natural course of gene expression dynamics during myogenesis. Objective: To gain insight into the dynamic temporal changes in protein expression during differentiation of normal and dystrophin deficient myoblasts to myotubes. Method: A super SILAC spike-in strategy in combination and LC-MS/MS was used for temporal proteome profiling of normal and dystrophin deficient myoblasts during differentiation. The acquired data was analyzed using Proteome Discoverer 2.2. and data clustering using R to define significant temporal changes in protein expression. Results: sFour major temporal protein clusters that showed sequential dynamic expression profiles during myogenesis of normal myoblasts were identified. Clusters 1 and 2, consisting mainly of proteins involved mRNA splicing and processing expression, were elevated at days 0 and 0.5 of differentiation then gradually decreased by day 7 of differentiation, then remained lower thereafter. Cluster 3 consisted of proteins involved contractile muscle and actomyosin organization. They increased in their expression reaching maximum at day 7 of differentiation then stabilized thereafter. Cluster 4 consisting of proteins involved in skeletal muscle development glucogenesis and extracellular remodeling had a lower expression during myoblast stage then gradually increased in their expression to reach a maximum at days 11–15 of differentiation. Lack of dystrophin expression in DMD muscle myoblast caused major alteration in temporal expression of proteins involved in cell adhesion, cytoskeleton, and organelle organization as well as the ubiquitination machinery. Conclusion: Time series proteome profiling using super SILAC strategy is a powerful method to assess temporal changes in protein expression during myogenesis and to define the downstream consequences of lack of dystrophin on these temporal protein expressions. Key alterations were identified in dystrophin deficient myoblast differentiation compared to normal myoblasts. These alterations could be an attractive therapeutic target.
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Zainul Azlan, Nurhazirah, Yasmin Anum Mohd Yusof, Ekram Alias e Suzana Makpol. "Chlorella vulgaris Improves the Regenerative Capacity of Young and Senescent Myoblasts and Promotes Muscle Regeneration". Oxidative Medicine and Cellular Longevity 2019 (4 giugno 2019): 1–16. http://dx.doi.org/10.1155/2019/3520789.
Testo completoAbstract (sommario):
Sarcopenia is characterized by the loss of muscle mass, strength, and function with ageing. With increasing life expectancy, greater attention has been given to counteracting the effects of sarcopenia on the growing elderly population. Chlorella vulgaris, a microscopic, unicellular, green alga with the potential for various pharmaceutical uses, has been widely studied in this context. This study is aimed at determining the effects of C. vulgaris on promoting muscle regeneration by evaluating myoblast regenerative capacity in vitro. Human skeletal myoblast cells were cultured and underwent serial passaging into young and senescent phases and were then treated with C. vulgaris, followed by the induction of differentiation. The ability of C. vulgaris to promote myoblast differentiation was analysed through cellular morphology, real-time monitoring, cell proliferation, senescence-associated β-galactosidase (SA-β-gal) expression, myogenic differentiation, myogenin expression, and cell cycle profiling. The results obtained showed that senescent myoblasts exhibited an enlarged and flattened morphology, with increased SA-β-gal expression, reduced myogenic differentiation, decreased expression of myogenin, and an increased percentage of cells in the G0/G1 phase. Treatment with C. vulgaris resulted in decreased SA-β-gal expression and promotion of myogenic differentiation, as observed via an increased fusion index, maturation index, myotube size, and surface area and an increased percentage of cells that stained positive for myogenin. In conclusion, C. vulgaris improves the regenerative capacity of young and senescent myoblasts and promotes myoblast differentiation, indicating its potential to promote muscle regeneration.
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McFarlane, Craig, Gu Zi Hui, Wong Zhi Wei Amanda, Hiu Yeung Lau, Sudarsanareddy Lokireddy, Ge XiaoJia, Vincent Mouly et al. "Human myostatin negatively regulates human myoblast growth and differentiation". American Journal of Physiology-Cell Physiology 301, n. 1 (luglio 2011): C195—C203. http://dx.doi.org/10.1152/ajpcell.00012.2011.
Testo completoAbstract (sommario):
Myostatin, a member of the transforming growth factor-β superfamily, has been implicated in the potent negative regulation of myogenesis in murine models. However, little is known about the mechanism(s) through which human myostatin negatively regulates human skeletal muscle growth. Using human primary myoblasts and recombinant human myostatin protein, we show here that myostatin blocks human myoblast proliferation by regulating cell cycle progression through targeted upregulation of p21. We further show that myostatin regulates myogenic differentiation through the inhibition of key myogenic regulatory factors including MyoD, via canonical Smad signaling. In addition, we have for the first time demonstrated the capability of myostatin to regulate the Notch signaling pathway during inhibition of human myoblast differentiation. Treatment with myostatin results in the upregulation of Hes1, Hes5, and Hey1 expression during differentiation; moreover, when we interfere with Notch signaling, through treatment with the γ-secretase inhibitor L-685,458, we find enhanced myotube formation despite the presence of excess myostatin. Therefore, blockade of the Notch pathway relieves myostatin repression of differentiation, and myostatin upregulates Notch downstream target genes. Immunoprecipitation studies demonstrate that myostatin treatment of myoblasts results in enhanced association of Notch1-intracellular domain with Smad3, providing an additional mechanism through which myostatin targets and represses the activity of the myogenic regulatory factor MyoD. On the basis of these results, we suggest that myostatin function and mechanism of action are very well conserved between species, and that myostatin regulation of postnatal myogenesis involves interactions with numerous downstream signaling mediators, including the Notch pathway.
30
D'Andrea, Paola, Deborah Civita, Michela Cok, Luisa Ulloa Severino, Francesca Vita, Denis Scaini, Loredana Casalis, Paola Lorenzon, Ivan Donati e Antonella Bandiera. "Myoblast Adhesion, Proliferation and Differentiation on Human Elastin-Like Polypeptide (HELP) Hydrogels". Journal of Applied Biomaterials & Functional Materials 15, n. 1 (26 gennaio 2017): 43–53. http://dx.doi.org/10.5301/jabfm.5000331.
Testo completoAbstract (sommario):
Background The biochemical, mechanical and topographic properties of extracellular matrix are crucially involved in determining skeletal muscle cell morphogenesis, proliferation and differentiation. Human elastin-like polypeptides (HELPs) are recombinant biomimetic proteins designed to mimic some properties of the native matrix protein; when employed as myoblast adhesion substrates, they stimulate in vitro myogenesis. Given the influence that the biophysical properties of extracellular matrix have on skeletal muscle cells, the aim of this work was to investigate the effects of HELP hydrogels on myoblasts’ viability and functions. Methods We recently synthesized a novel polypeptide, HELPc, by fusing the elastin-like backbone to a 41aa sequence present in the α2 chain of type IV collagen, containing two arginyl-glycyl-aspartic acid (RGD) motifs. To obtain hydrogels, the enzymatic cross-linking of the HELPc was accomplished by transglutaminase. Here, we employed both non-cross-linked HELPc glass coatings and cross-linked HELPc hydrogels at different monomer densities, as adhesion substrates for C2C12 cells, used as a myoblast model. Results By comparing cell adhesion, proliferation and differentiation, we revealed several striking differences. Depending on support rigidity, adhesion to HELPc substrates dictated cell morphology, spreading, focal adhesion formation and cytoskeletal organization. Hydrogels greatly stimulated cell proliferation, particularly in low-serum medium, and partially inhibited myogenic differentiation. Conclusions On the whole, the results underline the potential of these genetically engineered polypeptides as a tool for dissecting crucial steps in myogenesis.
31
Morton, Sarah U., Christopher R. Sefton, Huanqing Zhang, Manhong Dai, David L. Turner, Michael D. Uhler e Pankaj B. Agrawal. "microRNA-mRNA Profile of Skeletal Muscle Differentiation and Relevance to Congenital Myotonic Dystrophy". International Journal of Molecular Sciences 22, n. 5 (7 marzo 2021): 2692. http://dx.doi.org/10.3390/ijms22052692.
Testo completoAbstract (sommario):
microRNAs (miRNAs) regulate messenger RNA (mRNA) abundance and translation during key developmental processes including muscle differentiation. Assessment of miRNA targets can provide insight into muscle biology and gene expression profiles altered by disease. mRNA and miRNA libraries were generated from C2C12 myoblasts during differentiation, and predicted miRNA targets were identified based on presence of miRNA binding sites and reciprocal expression. Seventeen miRNAs were differentially expressed at all time intervals (comparing days 0, 2, and 5) of differentiation. mRNA targets of differentially expressed miRNAs were enriched for functions related to calcium signaling and sarcomere formation. To evaluate this relationship in a disease state, we evaluated the miRNAs differentially expressed in human congenital myotonic dystrophy (CMD) myoblasts and compared with normal control. Seventy-four miRNAs were differentially expressed during healthy human myocyte maturation, of which only 12 were also up- or downregulated in CMD patient cells. The 62 miRNAs that were only differentially expressed in healthy cells were compared with differentiating C2C12 cells. Eighteen of the 62 were conserved in mouse and up- or down-regulated during mouse myoblast differentiation, and their C2C12 targets were enriched for functions related to muscle differentiation and contraction.
32
Naidoo, P. "Em evidence of myoblast origin in regenerating human skeletal muscle explants". Cell Biology International 17, n. 9 (settembre 1993): 825–32. http://dx.doi.org/10.1006/cbir.1993.1144.
Testo completo
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Ng, Dominic C. H., Uda Y. Ho e Miranda D. Grounds. "Cilia, Centrosomes and Skeletal Muscle". International Journal of Molecular Sciences 22, n. 17 (4 settembre 2021): 9605. http://dx.doi.org/10.3390/ijms22179605.
Testo completoAbstract (sommario):
Primary cilia are non-motile, cell cycle-associated organelles that can be found on most vertebrate cell types. Comprised of microtubule bundles organised into an axoneme and anchored by a mature centriole or basal body, primary cilia are dynamic signalling platforms that are intimately involved in cellular responses to their extracellular milieu. Defects in ciliogenesis or dysfunction in cilia signalling underlie a host of developmental disorders collectively referred to as ciliopathies, reinforcing important roles for cilia in human health. Whilst primary cilia have long been recognised to be present in striated muscle, their role in muscle is not well understood. However, recent studies indicate important contributions, particularly in skeletal muscle, that have to date remained underappreciated. Here, we explore recent revelations that the sensory and signalling functions of cilia on muscle progenitors regulate cell cycle progression, trigger differentiation and maintain a commitment to myogenesis. Cilia disassembly is initiated during myoblast fusion. However, the remnants of primary cilia persist in multi-nucleated myotubes, and we discuss their potential role in late-stage differentiation and myofiber formation. Reciprocal interactions between cilia and the extracellular matrix (ECM) microenvironment described for other tissues may also inform on parallel interactions in skeletal muscle. We also discuss emerging evidence that cilia on fibroblasts/fibro–adipogenic progenitors and myofibroblasts may influence cell fate in both a cell autonomous and non-autonomous manner with critical consequences for skeletal muscle ageing and repair in response to injury and disease. This review addresses the enigmatic but emerging role of primary cilia in satellite cells in myoblasts and myofibers during myogenesis, as well as the wider tissue microenvironment required for skeletal muscle formation and homeostasis.
34
Hosoyama, Tohru, Hiroki Iida, Minako Kawai-Takaishi e Ken Watanabe. "Vitamin D Inhibits Myogenic Cell Fusion and Expression of Fusogenic Genes". Nutrients 12, n. 8 (23 luglio 2020): 2192. http://dx.doi.org/10.3390/nu12082192.
Testo completoAbstract (sommario):
Vitamin D, a fat-soluble vitamin, is an important nutrient for tissue homeostasis and is recently gaining attention for its role in sarcopenia. Although several studies have focused on the role of vitamin D in muscle homeostasis, the molecular mechanism underlying its action on skeletal muscle remains unclear. This study investigated the role of vitamin D in myogenesis and muscle fiber maintenance in an immortalized mouse myogenic cell line. A high concentration of active vitamin D, 1α,25(OH)2D3, decreased the expression of myogenic regulatory factors (MRFs), myf5 and myogenin in proliferating myoblasts. In addition, high concentration of vitamin D reduced myoblast-to-myoblast and myoblast-to-myotube fusion through the inhibition of Tmem8c (myomaker) and Gm7325 (myomerger), which encode muscle-specific fusion-related micropeptides. A similar inhibitory effect of vitamin D was also observed in immortalized human myogenic cells. A high concentration of vitamin D also induced hypertrophy of multinucleated myotubes by stimulating protein anabolism. The results from this study indicated that vitamin D had both positive and negative effects on muscle homeostasis, such as in muscle regeneration and myofiber maintenance. Elderly individuals face a higher risk of falling and suffering fractures; hence, administration of vitamin D for treating fractures in the elderly could actually promote fusion impairment and, consequently, severe defects in muscle regeneration. Therefore, our results suggest that vitamin D replacement therapy should be used for prevention of age-related muscle loss, rather than for treatment of sarcopenia.
35
Miroshnychenko, Olga, Wen-teh Chang e Jason L. Dragoo. "The Use of Platelet-Rich and Platelet-Poor Plasma to Enhance Differentiation of Skeletal Myoblasts: Implications for the Use of Autologous Blood Products for Muscle Regeneration". American Journal of Sports Medicine 45, n. 4 (27 dicembre 2016): 945–53. http://dx.doi.org/10.1177/0363546516677547.
Testo completoAbstract (sommario):
Background: Platelet-rich plasma (PRP) has been used to augment tissue repair and regeneration after musculoskeletal injury. However, there is increasing clinical evidence that PRP does not show a consistent clinical effect. Purpose/Hypothesis: This study aimed to compare the effects of the following non–neutrophil-containing (leukocyte-poor) plasma fractions on human skeletal muscle myoblast (HSMM) differentiation: (1) PRP, (2) modified PRP (Mod-PRP), in which transforming growth factor β1 (TGF-β1) and myostatin (MSTN) were depleted, and (3) platelet-poor plasma (PPP). The hypothesis was that leukocyte-poor PRP would lead to myoblast proliferation (not differentiation), whereas certain modifications of PRP preparations would increase myoblast differentiation, which is necessary for skeletal muscle regeneration. Study Design: Controlled laboratory study. Methods: Blood from 7 human donors was individually processed to simultaneously create leukocyte-poor fractions: PRP, Mod-PRP, PPP, and secondarily spun PRP and Mod-PRP (PRPss and Mod-PRPss, respectively). Mod-PRP was produced by removing TGF-β1 and MSTN from PRP using antibodies attached to sterile beads, while a second-stage centrifugal spin of PRP was performed to remove platelets. The biologics were individually added to cell culture groups. Analysis for induction into myoblast differentiation pathways included Western blot analysis, reverse-transcription polymerase chain reaction, and immunohistochemistry, as well as confocal microscopy to assess polynucleated myotubule formation. Results: HSMMs cultured with PRP showed an increase in proliferation but no evidence of differentiation. Western blot analysis confirmed that MSTN and TGF-β1 could be decreased in Mod-PRP using antibody-coated beads, but this modification mildly improved myoblast differentiation. However, cell culture with PPP, PRPss, and Mod-PRPss led to a decreased proliferation rate but a significant induction of myoblast differentiation verified by increased multinucleated myotubule formation and myosin heavy chain expression (mean 8-fold change in mRNA level; P < .05), which was comparable with 2% horse serum, the positive control. Conclusion: PPP and leukocyte-poor PRP preparations subjected to a second spin to remove the platelets led to induction of myoblast cells into the muscle differentiation pathway, whereas unmodified leukocyte-poor PRP led to myoblast proliferation. Clinical Relevance: These results indicate that traditionally formulated PRP may not be appropriate to induce muscle regeneration. Laboratory evidence suggests that PPP or non–neutrophil-containing PRPss, subjected to an additional spin to remove platelets, should be used to stimulate myoblast differentiation, which is necessary for skeletal muscle regeneration. Clinical studies will be required to confirm the effect of these biologics on muscle regeneration.
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Matheny, Ronald W., Melissa A. Riddle-Kottke, Luis A. Leandry, Christine M. Lynch, Mary N. Abdalla, Alyssa V. Geddis, David R. Piper e Jean J. Zhao. "Role of Phosphoinositide 3-OH Kinase p110β in Skeletal Myogenesis". Molecular and Cellular Biology 35, n. 7 (20 gennaio 2015): 1182–96. http://dx.doi.org/10.1128/mcb.00550-14.
Testo completoAbstract (sommario):
Phosphoinositide 3-OH kinase (PI3K) regulates a number of developmental and physiologic processes in skeletal muscle; however, the contributions of individual PI3K p110 catalytic subunits to these processes are not well-defined. To address this question, we investigated the role of the 110-kDa PI3K catalytic subunit β (p110β) in myogenesis and metabolism. In C2C12 cells, pharmacological inhibition of p110β delayed differentiation. We next generated mice with conditional deletion of p110β in skeletal muscle (p110β muscle knockout [p110β-mKO] mice). While young p110β-mKO mice possessed a lower quadriceps mass and exhibited less strength than control littermates, no differences in muscle mass or strength were observed between genotypes in old mice. However, old p110β-mKO mice were less glucose tolerant than old control mice. Overexpression of p110β accelerated differentiation in C2C12 cells and primary human myoblasts through an Akt-dependent mechanism, while expression of kinase-inactive p110β had the opposite effect. p110β overexpression was unable to promote myoblast differentiation under conditions of p110α inhibition, but expression of p110α was able to promote differentiation under conditions of p110β inhibition. These findings reveal a role for p110β during myogenesis and demonstrate that long-term reduction of skeletal muscle p110β impairs whole-body glucose tolerance without affecting skeletal muscle size or strength in old mice.
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Sacconi, S., D. Simkin, N. Arrighi, F. Chapon, M. M. Larroque, S. Vicart, D. Sternberg et al. "Mechanisms underlying Andersen's syndrome pathology in skeletal muscle are revealed in human myotubes". American Journal of Physiology-Cell Physiology 297, n. 4 (ottobre 2009): C876—C885. http://dx.doi.org/10.1152/ajpcell.00519.2008.
Testo completoAbstract (sommario):
Andersen's syndrome is a rare disorder that has been defined with a triad: periodic paralysis, cardiac arrhythmia, and development anomalies. Muscle weakness has been reported in two-thirds of the patients. KCNJ2 remains the only gene linked to Andersen's syndrome; this gene encodes for the α-subunit of the strong inward-rectifier K+ channel Kir2.1. Several studies have shown that Andersen's syndrome mutations lead to a loss of function of the K+ channel activity in vitro. However, ex vivo studies on isolated patient muscle tissue have not been reported. We have performed muscle biopsies of controls and patients presenting with clinically and genetically defined Andersen's syndrome disorder. Myoblasts were cultured and characterized morphologically and functionally using the whole cell patch-clamp technique. No morphological difference was observed between Andersen's syndrome and control myoblasts at each passage of the cell culture. Cellular proliferation and viability were quantified in parallel with direct cell counts and showed no difference between control and Andersen's syndrome patients. Moreover, our data show no significant difference in myoblast fusion index among Andersen's syndrome and control patients. Current recordings carried out on myotubes revealed the absence of an inwardly rectifying Ba2+-sensitive current in affected patient cells. One consequence of the Ik1 current loss in Andersen's syndrome myotubes is a shift of the resting membrane potential toward depolarizing potentials. Our data describe for the first time the functional consequences of Andersen's syndrome mutations ex vivo and provide clues to the K+ channel pathophysiology in skeletal muscle.
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Rochat, Anne, Anne Fernandez, Marie Vandromme, Jeàn-Pierre Molès, Triston Bouschet, Gilles Carnac e Ned J. C. Lamb. "Insulin and Wnt1 Pathways Cooperate to Induce Reserve Cell Activation in Differentiation and Myotube Hypertrophy". Molecular Biology of the Cell 15, n. 10 (ottobre 2004): 4544–55. http://dx.doi.org/10.1091/mbc.e03-11-0816.
Testo completoAbstract (sommario):
During ex vivo myoblast differentiation, a pool of quiescent mononucleated myoblasts, reserve cells, arise alongside myotubes. Insulin/insulin-like growth factor (IGF) and PKB/Akt-dependent phosphorylation activates skeletal muscle differentiation and hypertrophy. We have investigated the role of glycogen synthase kinase 3 (GSK-3) inhibition by protein kinase B (PKB)/Akt and Wnt/β-catenin pathways in reserve cell activation during myoblast differentiation and myotube hypertrophy. Inhibition of GSK-3 by LiCl or SB216763, restored insulin-dependent differentiation of C2ind myoblasts in low serum, and cooperated with insulin in serum-free medium to induce MyoD and myogenin expression in C2ind myoblasts, quiescent C2 or primary human reserve cells. We show that LiCl treatment induced nuclear accumulation of β-catenin in C2 myoblasts, thus mimicking activation of canonical Wnt signaling. Similarly to the effect of GSK-3 inhibitors with insulin, coculturing C2 reserve cells with Wnt1-expressing fibroblasts enhanced insulin-stimulated induction of MyoD and myogenin in reserve cells. A similar cooperative effect of LiCl or Wnt1 with insulin was observed during late ex vivo differentiation and promoted increased size and fusion of myotubes. We show that this synergistic effect on myotube hypertrophy involved an increased fusion of reserve cells into preexisting myotubes. These data reveal insulin and Wnt/β-catenin pathways cooperate in muscle cell differentiation through activation and recruitment of satellite cell-like reserve myoblasts.
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Crown, AL, XL He, JM Holly, SL Lightman e CE Stewart. "Characterisation of the IGF system in a primary adult human skeletal muscle cell model, and comparison of the effects of insulin and IGF-I on protein metabolism". Journal of Endocrinology 167, n. 3 (1 dicembre 2000): 403–15. http://dx.doi.org/10.1677/joe.0.1670403.
Testo completoAbstract (sommario):
In an attempt to address the complex and clinically challenging question of the causes of muscle wasting in patients with cachexia, we have developed a primary adult human skeletal muscle cell model. The cultured cells were characterised by immunocytochemistry using antibodies to the myofibrillar protein constituents desmin and titin. Myotube formation was confirmed biochemically by a fourfold increase in the activity of the muscle-specific enzyme creatinine kinase, and myoblast withdrawal from the cell cycle, which is essential for terminal differentiation, was associated with progressive retinoblastoma protein dephosphorylation. Having successfully confirmed the phenotype of these adult human muscle cells, we assessed their interaction with the insulin-like growth factor (IGF) system. IGF-I is known to stimulate myoblast survival, proliferation and differentiation in cell lines, and, like insulin, is a potent anabolic agent in the regulation of protein metabolism. We have shown that IGF-I stimulated both replication and differentiation of myoblasts, whilst fibroblast growth factor-2 stimulated replication but inhibited differentiation. Examining the IGF system during the process of terminal differentiation, we found that both myoblasts and myotubes expressed insulin, IGF-I and insulin-IGF-I hybrid receptors, with the levels of all three receptor types increasing on differentiation. The cells also produced a wide range of IGF binding proteins (IGFBPs) including IGFBP-2, IGFBP-4 and abundant IGFBP-3, which has not been shown to be produced by any other skeletal muscle cell line examined to date. Both insulin and IGF-I had anabolic effects on myotube protein metabolism at physiological concentrations. Insulin was more potent than IGF-I: use of the IGF analogue long R(3)IGF-I demonstrated that the effects of exogenous IGF-I on protein metabolism were not affected by the high levels of endogenous IGFBP production. In summary, we have developed and characterised a clinically relevant in vitro model with which to address the aetiology of muscle wasting associated with chronic catabolic conditions, and we anticipate that future work will enable the development of novel, effective therapeutic interventions.
40
Sente, Tahnee, An M. Van Berendoncks, Erik Fransen, Christiaan J. Vrints e Vicky Y. Hoymans. "Tumor necrosis factor-α impairs adiponectin signalling, mitochondrial biogenesis, and myogenesis in primary human myotubes cultures". American Journal of Physiology-Heart and Circulatory Physiology 310, n. 9 (1 maggio 2016): H1164—H1175. http://dx.doi.org/10.1152/ajpheart.00831.2015.
Testo completoAbstract (sommario):
Skeletal muscle metabolic changes are common in patients with chronic heart failure (HF). Previously, we demonstrated a functional skeletal muscle adiponectin resistance in HF patients with reduced left ventricular ejection fraction (HFrEF). We aimed to examine the impact of adiponectin receptor 1 (AdipoR1) deficiency and TNF-α treatment on adiponectin signaling, proliferative capacity, myogenic differentiation, and mitochondrial biogenesis in primary human skeletal muscle cells. Primary cultures of myoblasts and myotubes were initiated from the musculus vastus lateralis of 10 HFrEF patients (left ventricular ejection fraction; 31.30 ± 2.89%) and 10 age- and gender-matched healthy controls. Healthy control cultures were transfected with siAdipoR1 and/or exposed to TNF-α (10 ng/ml; 72 h). Primary cultures from HFrEF patients preserved the features of adiponectin resistance in vivo. AdipoR1 mRNA was negatively correlated with time to reach maximal cell index ( r = −0.7319, P = 0.003). SiRNA-mediated AdipoR1 silencing reduced pAMPK ( P < 0.01), AMPK activation ( P = 0.046), and myoblast proliferation rate (xCELLigence Real-Time Cellular Analysis; P < 0.0001). Moreover, TNF-α decreased the mRNA expression of genes involved in glucose (APPL1, P = 0.0002; AMPK, P = 0.021), lipid (PPARα, P = 0.025; ACADM, P = 0.003), and mitochondrial (FOXO3, P = 0.018) metabolism, impaired myogenesis (MyoD1, P = 0.053; myogenin, P = 0.048) and polarized cytokine secretion toward a growth-promoting phenotype (IL-10, IL-1β, IFN-γ, P < 0.05 for all; Meso Scale Discovery Technology). Major features of adiponectin resistance are retained in primary cultures from the skeletal muscle of HFrEF patients. In addition, our results suggest that an increased inflammatory constitution contributes to adiponectin resistance and confers alterations in skeletal muscle differentiation, growth, and function.
41
Gunning, P., E. Hardeman, R. Wade, P. Ponte, W. Bains, H. M. Blau e L. Kedes. "Differential patterns of transcript accumulation during human myogenesis". Molecular and Cellular Biology 7, n. 11 (novembre 1987): 4100–4114. http://dx.doi.org/10.1128/mcb.7.11.4100-4114.1987.
Testo completoAbstract (sommario):
We evaluated the extent to which muscle-specific genes display identical patterns of mRNA accumulation during human myogenesis. Cloned satellite cells isolated from adult human skeletal muscle were expanded in culture, and RNA was isolated from low- and high-confluence cells and from fusing cultures over a 15-day time course. The accumulation of over 20 different transcripts was compared in these samples with that in fetal and adult human skeletal muscle. The expression of carbonic anhydrase 3, myoglobin, HSP83, and mRNAs encoding eight unknown proteins were examined in human myogenic cultures. In general, the expression of most of the mRNAs was induced after fusion to form myotubes. However, several exceptions, including carbonic anhydrase and myoglobin, showed no detectable expression in early myotubes. Comparison of all transcripts demonstrated little, if any, identity of mRNA accumulation patterns. Similar variability was also seen for mRNAs which were also expressed in nonmuscle cells. Accumulation of mRNAs encoding alpha-skeletal, alpha-cardiac, beta- and gamma-actin, total myosin heavy chain, and alpha- and beta-tubulin also displayed discordant regulation, which has important implications for sarcomere assembly. Cardiac actin was the only muscle-specific transcript that was detected in low-confluency cells and was the major alpha-actin mRNA at all times in fusing cultures. Skeletal actin was transiently induced in fusing cultures and then reduced by an order of magnitude. Total myosin heavy-chain mRNA accumulation lagged behind that of alpha-actin. Whereas beta- and gamma-actin displayed a sharp decrease after initiation of fusion and thereafter did not change, alpha- and beta-tubulin were transiently induced to a high level during the time course in culture. We conclude that each gene may have its own unique determinants of transcript accumulation and that the phenotype of a muscle may not be determined so much by which genes are active or silent but rather by the extent to which their transcript levels are modulated. Finally, we observed that patterns of transcript accumulation established within the myotube cultures were consistent with the hypothesis that myoblasts isolated from adult tissue recapitulate a myogenic developmental program. However, we also detected a transient appearance of adult skeletal muscle-specific transcripts in high-confluence myoblast cultures. This indicates that the initial differentiation of these myoblasts may reflect a more complex process than simple recapitulation of development.
42
Gunning, P., E. Hardeman, R. Wade, P. Ponte, W. Bains, H. M. Blau e L. Kedes. "Differential patterns of transcript accumulation during human myogenesis." Molecular and Cellular Biology 7, n. 11 (novembre 1987): 4100–4114. http://dx.doi.org/10.1128/mcb.7.11.4100.
Testo completoAbstract (sommario):
We evaluated the extent to which muscle-specific genes display identical patterns of mRNA accumulation during human myogenesis. Cloned satellite cells isolated from adult human skeletal muscle were expanded in culture, and RNA was isolated from low- and high-confluence cells and from fusing cultures over a 15-day time course. The accumulation of over 20 different transcripts was compared in these samples with that in fetal and adult human skeletal muscle. The expression of carbonic anhydrase 3, myoglobin, HSP83, and mRNAs encoding eight unknown proteins were examined in human myogenic cultures. In general, the expression of most of the mRNAs was induced after fusion to form myotubes. However, several exceptions, including carbonic anhydrase and myoglobin, showed no detectable expression in early myotubes. Comparison of all transcripts demonstrated little, if any, identity of mRNA accumulation patterns. Similar variability was also seen for mRNAs which were also expressed in nonmuscle cells. Accumulation of mRNAs encoding alpha-skeletal, alpha-cardiac, beta- and gamma-actin, total myosin heavy chain, and alpha- and beta-tubulin also displayed discordant regulation, which has important implications for sarcomere assembly. Cardiac actin was the only muscle-specific transcript that was detected in low-confluency cells and was the major alpha-actin mRNA at all times in fusing cultures. Skeletal actin was transiently induced in fusing cultures and then reduced by an order of magnitude. Total myosin heavy-chain mRNA accumulation lagged behind that of alpha-actin. Whereas beta- and gamma-actin displayed a sharp decrease after initiation of fusion and thereafter did not change, alpha- and beta-tubulin were transiently induced to a high level during the time course in culture. We conclude that each gene may have its own unique determinants of transcript accumulation and that the phenotype of a muscle may not be determined so much by which genes are active or silent but rather by the extent to which their transcript levels are modulated. Finally, we observed that patterns of transcript accumulation established within the myotube cultures were consistent with the hypothesis that myoblasts isolated from adult tissue recapitulate a myogenic developmental program. However, we also detected a transient appearance of adult skeletal muscle-specific transcripts in high-confluence myoblast cultures. This indicates that the initial differentiation of these myoblasts may reflect a more complex process than simple recapitulation of development.
43
Pirkmajer, Sergej, Dragana Filipovic, Tomaz Mars, Katarina Mis e Zoran Grubic. "HIF-1α response to hypoxia is functionally separated from the glucocorticoid stress response in the in vitro regenerating human skeletal muscle". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 299, n. 6 (dicembre 2010): R1693—R1700. http://dx.doi.org/10.1152/ajpregu.00133.2010.
Testo completoAbstract (sommario):
Injury of skeletal muscle is followed by muscle regeneration in which new muscle tissue is formed from the proliferating mononuclear myoblasts, and by systemic response to stress that exposes proliferating myoblasts to increased glucocorticoid (GC) concentration. Because of its various causes, hypoxia is a frequent condition affecting skeletal muscle, and therefore both processes, which importantly determine the outcome of the injury, often proceed under hypoxic conditions. It is therefore important to identify and characterize in proliferating human myoblasts: 1) response to hypoxia which is generally organized by hypoxia-inducible factor-1α (HIF-1α); 2) response to GCs which is mediated through the isoforms of glucocorticoid receptors (GRs) and 11β-hydroxysteroid dehydrogenases (11β-HSDs), and 3) the response to GCs under the hypoxic conditions and the influence of this combination on the factors controlling myoblast proliferation. Using real-time PCR, Western blotting, and HIF-1α small-interfering RNA silencing, we demonstrated that cultured human myoblasts possess both, the HIF-1α-based response to hypoxia, and the GC response system composed of GRα and types 1 and 2 11β-HSDs. However, using combined dexamethasone and hypoxia treatments, we demonstrated that these two systems operate practically without mutual interactions. A seemingly surprising separation of the two systems that both organize response to hypoxic stress can be explained on the evolutionary basis: the phylogenetically older HIF-1α response is a protection at the cellular level, whereas the GC stress response protects the organism as a whole. This necessitates actions, like downregulation of IL-6 secretion and vascular endothelial growth factor, that might not be of direct benefit for the affected myoblasts.
44
Wang, Jian-Min, Hong Zheng, Mila Blaivas e Kotoku Kurachi. "Persistent Systemic Production of Human Factor IX in Mice by Skeletal Myoblast-Mediated Gene Transfer: Feasibility of Repeat Application to Obtain Therapeutic Levels". Blood 90, n. 3 (1 agosto 1997): 1075–82. http://dx.doi.org/10.1182/blood.v90.3.1075.
Testo completoAbstract (sommario):
Abstract Myoblast-mediated gene transfer and its repeated applications were tested for achieving a long-term stable systemic production of human factor IX (hFIX) at a therapeutic level in SCID mice. Primary skeletal myoblasts were stably transfected with a hFIX expression plasmid vector, pdLMe4βAhIXm1, which contains a hFIX minigene under the control of a β-actin promoter with muscle creatine kinase enhancers. Myotubes derived from the myoblasts produced 1,750 ng hFIX/106 cells/24 hours in culture. hFIX secretion by the myoblasts and thereof derived myotubes were equally efficient, and myotubes were shown to have a sufficient secretory capacity to handle a substantially elevated production of hFIX. After intramuscular injection of 5, 10, and 20 × 106 myoblasts, SCID mice stably produced hFIX into the systemic circulation proportional to the number of implanted cells, and the expression levels were maintained for at least up to 10 months (end of the experiment). Additional cell injections administered to animals that originally received 10 × 106 cells approximately 2 months later elevated the systemic hFIX levels to an average of 182 ± 21 ng/mL, a therapeutic level, which persisted for at least 8 months (end of the experiment). These results indicate that long-term, stable systemic production of hFIX at therapeutic levels can be achieved by repeated application of myoblast-mediated gene transfer.
45
Wang, Jian-Min, Hong Zheng, Mila Blaivas e Kotoku Kurachi. "Persistent Systemic Production of Human Factor IX in Mice by Skeletal Myoblast-Mediated Gene Transfer: Feasibility of Repeat Application to Obtain Therapeutic Levels". Blood 90, n. 3 (1 agosto 1997): 1075–82. http://dx.doi.org/10.1182/blood.v90.3.1075.1075_1075_1082.
Testo completoAbstract (sommario):
Myoblast-mediated gene transfer and its repeated applications were tested for achieving a long-term stable systemic production of human factor IX (hFIX) at a therapeutic level in SCID mice. Primary skeletal myoblasts were stably transfected with a hFIX expression plasmid vector, pdLMe4βAhIXm1, which contains a hFIX minigene under the control of a β-actin promoter with muscle creatine kinase enhancers. Myotubes derived from the myoblasts produced 1,750 ng hFIX/106 cells/24 hours in culture. hFIX secretion by the myoblasts and thereof derived myotubes were equally efficient, and myotubes were shown to have a sufficient secretory capacity to handle a substantially elevated production of hFIX. After intramuscular injection of 5, 10, and 20 × 106 myoblasts, SCID mice stably produced hFIX into the systemic circulation proportional to the number of implanted cells, and the expression levels were maintained for at least up to 10 months (end of the experiment). Additional cell injections administered to animals that originally received 10 × 106 cells approximately 2 months later elevated the systemic hFIX levels to an average of 182 ± 21 ng/mL, a therapeutic level, which persisted for at least 8 months (end of the experiment). These results indicate that long-term, stable systemic production of hFIX at therapeutic levels can be achieved by repeated application of myoblast-mediated gene transfer.
46
Lokireddy, Sudarsanareddy, Vincent Mouly, Gillian Butler-Browne, Peter D. Gluckman, Mridula Sharma, Ravi Kambadur e Craig McFarlane. "Myostatin promotes the wasting of human myoblast cultures through promoting ubiquitin-proteasome pathway-mediated loss of sarcomeric proteins". American Journal of Physiology-Cell Physiology 301, n. 6 (dicembre 2011): C1316—C1324. http://dx.doi.org/10.1152/ajpcell.00114.2011.
Testo completoAbstract (sommario):
Myostatin is a negative regulator of skeletal muscle growth and in fact acts as a potent inducer of “cachectic-like” muscle wasting in mice. The mechanism of action of myostatin in promoting muscle wasting has been predominantly studied in murine models. Despite numerous reports linking elevated levels of myostatin to human skeletal muscle wasting conditions, little is currently known about the signaling mechanism(s) through which myostatin promotes human skeletal muscle wasting. Therefore, in this present study we describe in further detail the mechanisms behind myostatin regulation of human skeletal muscle wasting using an in vitro human primary myotube atrophy model. Treatment of human myotube populations with myostatin promoted dramatic myotubular atrophy. Mechanistically, myostatin-induced myotube atrophy resulted in reduced p-AKT concomitant with the accumulation of active dephosphorylated Forkhead Box-O (FOXO1) and FOXO3. We further show that addition of myostatin results in enhanced activation of atrogin-1 and muscle-specific RING finger protein 1 (MURF1) and reduced expression of both myosin light chain (MYL) and myosin heavy chain (MYH). In addition, we found that myostatin-induced loss of MYL and MYH proteins is dependent on the activity of the proteasome and mediated via SMAD3-dependent regulation of FOXO1 and atrogin-1. Therefore, these data suggest that the mechanism through which myostatin promotes muscle wasting is very well conserved between species, and that myostatin-induced human myotube atrophy is mediated through inhibition of insulin-like growth factor (IGF)/phosphoinositide 3-kinase (PI3-K)/AKT signaling and enhanced activation of the ubiquitin-proteasome pathway and elevated protein degradation.
47
Zainul Azlan, Nurhazirah, Yasmin Anum Mohd Yusof, Ekram Alias e Suzana Makpol. "Chlorella vulgaris Modulates Genes and Muscle-Specific microRNAs Expression to Promote Myoblast Differentiation in Culture". Evidence-Based Complementary and Alternative Medicine 2019 (21 luglio 2019): 1–16. http://dx.doi.org/10.1155/2019/8394648.
Testo completoAbstract (sommario):
Background. Loss of skeletal muscle mass, strength, and function due to gradual decline in the regeneration of skeletal muscle fibers was observed with advancing age. This condition is known as sarcopenia. Myogenic regulatory factors (MRFs) are essential in muscle regeneration as its activation leads to the differentiation of myoblasts to myofibers. Chlorella vulgaris is a coccoid green eukaryotic microalga that contains highly nutritious substances and has been reported for its pharmaceutical effects. The aim of this study was to determine the effect of C. vulgaris on the regulation of MRFs and myomiRs expression in young and senescent myoblasts during differentiation in vitro. Methods. Human skeletal muscle myoblast (HSMM) cells were cultured and serial passaging was carried out to obtain young and senescent cells. The cells were then treated with C. vulgaris followed by differentiation induction. The expression of Pax7, MyoD1, Myf5, MEF2C, IGF1R, MYOG, TNNT1, PTEN, and MYH2 genes and miR-133b, miR-206, and miR-486 was determined in untreated and C. vulgaris-treated myoblasts on Days 0, 1, 3, 5, and 7 of differentiation. Results. The expression of Pax7, MyoD1, Myf5, MEF2C, IGF1R, MYOG, TNNT1, and PTEN in control senescent myoblasts was significantly decreased on Day 0 of differentiation (p<0.05). Treatment with C. vulgaris upregulated Pax7, Myf5, MEF2C, IGF1R, MYOG, and PTEN in senescent myoblasts (p<0.05) and upregulated Pax7 and MYOG in young myoblasts (p<0.05). The expression of MyoD1 and Myf5 in young myoblasts however was significantly decreased on Day 0 of differentiation (p<0.05). During differentiation, the expression of these genes was increased with C. vulgaris treatment. Further analysis on myomiRs expression showed that miR-133b, miR-206, and miR-486 were significantly downregulated in senescent myoblasts on Day 0 of differentiation which was upregulated by C. vulgaris treatment (p<0.05). During differentiation, the expression of miR-133b and miR-206 was significantly increased with C. vulgaris treatment in both young and senescent myoblasts (p<0.05). However, no significant change was observed on the expression of miR-486 with C. vulgaris treatment. Conclusions. C. vulgaris demonstrated the modulatory effects on the expression of MRFs and myomiRs during proliferation and differentiation of myoblasts in culture. These findings may indicate the beneficial effect of C. vulgaris in muscle regeneration during ageing thus may prevent sarcopenia in the elderly.
48
Coulton, G. R., B. Rogers, P. Strutt, M. J. Skynner e D. J. Watt. "In situ localisation of single-stranded DNA breaks in nuclei of a subpopulation of cells within regenerating skeletal muscle of the dystrophic mdx mouse". Journal of Cell Science 102, n. 3 (1 luglio 1992): 653–62. http://dx.doi.org/10.1242/jcs.102.3.653.
Testo completoAbstract (sommario):
Degeneration of muscle fibres during the early stages of Duchenne Muscular Dystrophy (DMD) is accompanied by muscle fibre regeneration where cell division and myoblast fusion to form multinucleate myotubes within the lesions appear to recapitulate the events of normal muscle development. The mechanisms that govern the expression of genes regulating differentiation of myoblasts in regenerating skeletal muscle are of great interest for the development of future therapies designed to stimulate muscle regeneration. We show here that single-stranded breaks in DNA are localised in nuclei, using an exogenously applied medium containing labelled deoxynucleotides and the Klenow fragment of DNA polymerase I. The nuclei of a sub-population of cells lying in the inflammatory infiltrate of lesions in the skeletal muscle of the muscular dystrophic mouse (mdx), a genetic homologue of DMD, were labelled in this fashion. By contrast, labelled cells were completely absent from the muscles of normal non-myopathic animals (C57BL/10) and non-lesioned areas of mdx muscles. Cells expressing the muscle-specific regulatory gene, myogenin, were also found within mononucleate cells and myotubes within similar mdx muscle lesions. While we cannot yet say that the cells labelled by the DNA polymerase reaction are in fact differentiating, they were found only in significant numbers within mdx muscle lesions where new muscle fibres appear, providing strong circumstantial evidence that they are intimately associated with the regenerative process. Using a range of nucleases and different DNA polymerases, we show that the DNA polymerase-labelling reaction observed was DNA-dependent and most probably due to infilling of naturally occurring single-stranded gaps in DNA. Since the regenerative process in human Duchenne Muscular Dystrophy is apparently less effective than that seen in mdx mice, continued study of single-stranded DNA breaks may help to elucidate further the mechanisms controlling the expression of genes that characterise the myogenic process during skeletal muscle regeneration. Such findings might be applied in the development of future therapies designed to stimulate muscle regeneration in human dystrophies.
49
Wilson, Magdalene O., Kathleen T. Scougall, Jarupa Ratanamart, Elizabeth A. McIntyre e James A. M. Shaw. "Tetracycline-regulated secretion of human (pro)insulin following plasmid-mediated transfection of human muscle". Journal of Molecular Endocrinology 34, n. 2 (aprile 2005): 391–403. http://dx.doi.org/10.1677/jme.1.01646.
Testo completoAbstract (sommario):
Long-term secretion of insulin by host muscle following transduction with an insulin gene construct offers the potential of gene therapy for diabetes without immunosuppression. Clinical implementation will be dependent on proof of principle in human tissue and a system for safely regulating basal insulin levels. Liposomal co-transfection with a tetracycline-responsive wild type human preproinsulin (pTRE-hppI1) or mutant construct (pTRE-hppI4), in which PC2 and PC3 cleavage sites were altered to form tetrabasic consensus sites for furin, together with pTet-off (coding for a transactivating protein) was evaluated in the C2C12 mouse myoblast cell line and human myoblasts following establishment in primary culture. In the absence of tetracycline, (pro)insulin secretion in C2C12 and human myoblasts transfected with tetracycline-responsive hppI1 and hppI4 constructs was comparable to that following transfection with equivalent constructs under the control of a constitutively active cytomegaloviral promoter. Percentage processing to mature insulin was <5% in C2C12 and human myoblasts transfected with pTet-off/pTRE-hppI1 but >90% in C2C12 cells and 45–60% in human myoblasts on transfection with pTet-off/pTRE-hppI4. Incremental dose-responsive suppression of proinsulin secretion was demonstrated in C2C12 and human myoblasts expressing pTet-off/pTRE-hppI1 following incubation with tetracycline (0–100 μg/ml) for up to 72 h. Reversibility was confirmed following tetracycline withdrawal. Dose-responsive tetracycline-inducible repression of mature insulin secretion was confirmed in C2C12 cells following transfection with pTet-off/pTRE-hppI4. Regulation of human proinsulin biosynthesis and secretion has been attained in vivo following plasmid-mediated gene transfer to rat skeletal muscle and oral tetracycline administration. In conclusion, processing to mature insulin has been confirmed following plasmid-mediated gene transfer to human muscle in addition to in vitro- and in vivo-regulated human proinsulin secretion employing the safe and well-tolerated antibiotic, tetracycline.
50
Morgan, Stuart A., Zaki K. Hassan-Smith, Craig L. Doig, Mark Sherlock, Paul M. Stewart e Gareth G. Lavery. "Glucocorticoids and 11β-HSD1 are major regulators of intramyocellular protein metabolism". Journal of Endocrinology 229, n. 3 (giugno 2016): 277–86. http://dx.doi.org/10.1530/joe-16-0011.
Testo completoAbstract (sommario):
The adverse metabolic effects of prescribed and endogenous glucocorticoid excess, ‘Cushing’s syndrome’, create a significant health burden. While skeletal muscle atrophy and resultant myopathy is a clinical feature, the molecular mechanisms underpinning these changes are not fully defined. We have characterized the impact of glucocorticoids upon key metabolic pathways and processes regulating muscle size and mass including: protein synthesis, protein degradation, and myoblast proliferation in both murine C2C12 and human primary myotube cultures. Furthermore, we have investigated the role of pre-receptor modulation of glucocorticoid availability by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in these processes. Corticosterone (CORT) decreased myotube area, decreased protein synthesis, and increased protein degradation in murine myotubes. This was supported by decreased mRNA expression of insulin-like growth factor (IGF1), decreased activating phosphorylation of mammalian target of rapamycin (mTOR), decreased phosphorylation of 4E binding protein 1 (4E-BP1), and increased mRNA expression of key atrophy markers including: atrogin-1, forkhead box O3a (FOXO3a), myostatin (MSTN), and muscle-ring finger protein-1 (MuRF1). These findings were endorsed in human primary myotubes, where cortisol also decreased protein synthesis and increased protein degradation. The effects of 11-dehydrocorticosterone (11DHC) (in murine myotubes) and cortisone (in human myotubes) on protein metabolism were indistinguishable from that of CORT/cortisol treatments. Selective 11β-HSD1 inhibition blocked the decrease in protein synthesis, increase in protein degradation, and reduction in myotube area induced by 11DHC/cortisone. Furthermore, CORT/cortisol, but not 11DHC/cortisone, decreased murine and human myoblast proliferative capacity. Glucocorticoids are potent regulators of skeletal muscle protein homeostasis and myoblast proliferation. Our data underscores the potential use of selective 11β-HSD1 inhibitors to ameliorate muscle-wasting effects associated with glucocorticoid excess.