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Sarcopenia and Androgens: A Link Between Pathology and Treatment
Published in Chad Cox, Clinical Nutrition and Aging, 2017
Carla Basualto-AlarcÓN, Diego Varela, Javier Duran, Rodrigo Maass, Manuel Estrada
The satellite cells are mononucleated cells that lie under or embedded in the basal lamina of the myofiber, which demonstrate close relationship with the mature myofiber (75). The satellite cells are myogenic precursors capable of regenerating skeletal muscle and demonstrate self-renewal properties. During development and regeneration, quiescent satellite cells are activated and start proliferating, at this point they are called myogenic precursor cells or myoblasts (76). Once muscle satellite cells are activated to become myoblasts, they enter the proliferative stage and differentiate into myotubes by expression of MyoD, whereas, the secondary myogenic regulatory factors (MRF) as myogenin and MRF4 regulate terminal differentiations. Myofibers derived from satellite cells show characteristic skeletal muscle markers such as sarcomeric striations, MHC, MyoD, and desmin expression (77).
Diseases of Muscle and the Neuromuscular Junction
Published in John W. Scadding, Nicholas A. Losseff, Clinical Neurology, 2011
Chris Turner, Anthony Schapira
Dominant mutations in the MYF6 and DNM2 genes cause later onset disease with a milder phenotype. Slow progression of muscle weakness is usual and patients are often wheelchair-bound by the sixth decade.
Protein and amino acids
Published in Jay R Hoffman, Dietary Supplementation in Sport and Exercise, 2019
As mentioned previously, NPB is a result of MPS and MPB. During resistance training, the goal is to increase MPS with as little effect on MPB as possible. The resulting protein accretion can lead to increases in muscle mass and strength over the course of resistance training. Since many tissues other than muscle also undergo synthesis and breakdown, this leads to the issue of whole-body protein turnover and can be increased due to catabolically-related conditions such as hypocalorism and exercise inflammation. However, it is common that ongoing high-intensity exercise (either aerobic or resistance exercise) in conjunction with inadequate daily calories will augment MPB so that the liberated amino acids can be used as a fuel source. As a result, these conditions are associated with physiological, and perhaps psychological, stress and cause an increase in the activity of the hypothalamic-pituitary-adrenal (HPA) axis. Inevitably this results in a release of cortisol from the cortical area of the adrenal gland into circulation. Cortisol is a lipophilic hormone and in muscle will diffuse across the sarcolemma where it can bind with the intracellular glucocorticoid receptor (GR). Once bound, the GR becomes an activated transcription factor with DNA binding properties and will translocate into the nucleus where it will bind enhancer elements in the regulatory promoter region within various proteolytic genes such as those associated with the ATP-dependent ubiquitin proteolytic pathway (Atrogin-1, MuRF-1 FoxO, ubiquitin) and myostatin (83). Conversely, the expression of various genes associated with up-regulating muscle hypertrophic processes, such as the myogenic regulatory factors (MyoD, myogenin, MRF4 and MYF5), are down-regulated. The overall catabolic process involving muscle proteolysis ultimately results in MPB and a subsequent release of amino acids into circulation. As previously mentioned, the goal during exercise training (especially resistance training) is to minimize this process as much as possible, which can be accomplished with proper post-exercise recovery practices, including adequate daily intake of protein and total calories.
Bidirectional regulation of genistein on the proliferation and differentiation of C2C12 myoblasts
Published in Xenobiotica, 2020
Mailin Gan, Dongli Yang, Yuan Fan, Jingjing Du, Linyuan Shen, Qiang Li, Yanzhi Jiang, Guoqing Tang, Mingzhou Li, Jinyong Wang, Xuewei Li, Shunhua Zhang, Li Zhu
C2C12 myoblast differentiation was promoted with the treatment of 10 µM/L genistein (p < 0.05), but it was inhibited at 20–100 µM/L genistein (p < 0.01) (Figure 2A and B). Except for 50 µM/L (p < 0.05), genistein had no significant effects on myotube length and diameter, and the 100 µM/L group had no observed myotubes (Figure 2C). The expression levels of the muscle-specific gene, myosin heavy chain (MyHC), demonstrated a trend similar to that of the myotube fusion index (Figure 2D). Furthermore, the expression levels of myogenic factors MyoG (myogenin), MyoD (myogenic differentiation antigen), and MRF4 (myogenic regulatory factor 4) were increased at the concentration that demonstrated a significant change in MyHC (10 µM/L; p < 0.01). However, MyoG, MyoD, and Myf5 (myogenic factor 5) were decreased after treatment with 100 µM/L genistein (p < 0.01) (Figure 2E). The expression of ERα (estrogen receptor-α), which is the binding substrate of genistein was increased after treatment with 10 µM/L genistein (p < 0.05), but ERα and IGF-1R (insulin-like growth factor 1 receptor), a typical receptor tyrosine kinase (RTK) were both decreased in 100 µM/L genistein (p < 0.01) (Figure 2F).
Synergistic effect of glucocorticoids and IGF-1 on myogenic differentiation through the Akt/GSK-3β pathway in C2C12 myoblasts
Published in International Journal of Neuroscience, 2020
Xiao-Bo Fang, Zu-Biao Song, Meng-Shu Xie, Yan-Mei Liu, Wei-Xi Zhang
Myogenesis, which is also known as myogenic differentiation, involves cellular activation, proliferation, and subsequent differentiation into myotubes [7,34,35]. This process is highly coordinated during development and involves two major stages. In the early stage of differentiation, MRFs, including MyoD, Myf5, myogenin and MRF4, are induced hierarchically as master regulatory factors, while muscle contractile or sarcomeric proteins (MyHC, MyLC) and muscle energy metabolism enzymes (MCK) are expressed in the late stage [34–36]. Therefore, our study selected MyoD and myogenin as early-stage markers and MyHC and MCK as late-stage markers. Our study revealed that DEX and IGF-1 cotreatment increased the protein expression of MyHC, MyoD and myogenin and upregulated MCK mRNA; this finding supports the hypothesis that MyoD plays a more important role in differentiation than myogenin [7]. IGF-1 plays a vital role in normal muscle growth and development and can stimulate both proliferation and differentiation; however, interestingly, IGF-1 promoted C2C12 proliferation rather than differentiation in the present study, which is inconsistent with the findings in previous reports. Contact inhibition is the likely explanation for this discrepancy, as differentiation of C2C12 myoblasts was induced in our study at 90% confluence, while most previous studies induced differentiation at 70%−80% confluence. When IGF-1 is added to 90% confluent C2C12 myoblasts, contact inhibition following initial cell proliferation can induce growth arrest [37].
Arsenic: an emerging role in adipose tissue dysfunction and muscle toxicity
Published in Toxin Reviews, 2022
Kaviyarasi Renu, Aditi Panda, Balachandar Vellingiri, Alex George, Abilash Valsala Gopalakrishnan
Myogenesis is a process classified into three major steps; withdrawal of myoblast from the cell cycle, expression of myotube-specific genes, and formation of multi-nucleated myotubes. The entire process of myogenesis is largely regulated by a group of transcription factors like Myogenic Differentiation Antigen (MyoD), myogenin, myogenic factor 5 (myf5), Muscle Regulatory Factor 4 (MRF4), myocyte enhancer factor which in turn regulates the expression of creatinine kinases and myosin heavy chain required for muscle production (Weintraub 1993, Lassar et al.1994, Olson et al.1995).