scholarly journals Notch Inhibition via GSI Treatment Elevates Protein Synthesis in C2C12 Myotubes

Biology ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 115
Author(s):  
Joshua R. Huot ◽  
Joseph S. Marino ◽  
Michael J. Turner ◽  
Susan T. Arthur
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Notch Signaling ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
C2c12 Cells ◽  
Skeletal Muscle Regeneration ◽  
C2c12 Myotubes ◽  
Myonuclear Domain ◽  
Myotube Hypertrophy

The role of Notch signaling is widely studied in skeletal muscle regeneration but little is known about its influences on muscle protein synthesis (MPS). The purpose of this study was to investigate whether Notch signaling is involved in the regulation of MPS. C2C12 cells were treated with a γ-secretase inhibitor (GSI), to determine the effect of reduced Notch signaling on MPS and anabolic signaling markers. GSI treatment increased myotube hypertrophy by increasing myonuclear accretion (nuclei/myotube: p = 0.01) and myonuclear domain (myotube area per fusing nuclei: p < 0.001) in differentiating C2C12 cells. GSI treatment also elevated myotube hypertrophy in differentiated C2C12s (area/myotube; p = 0.01). In concert, GSI treatment augmented pmTOR Ser2448 (p = 0.01) and protein synthesis (using SUnSET method) in myotubes (p < 0.001). Examining protein expression upstream of mTOR revealed reductions in PTEN (p = 0.04), with subsequent elevations in pAKT Thr308 (p < 0.001) and pAKT Ser473 (p = 0.05). These findings reveal that GSI treatment elevates myotube hypertrophy through both augmentation of fusion and MPS. This study sheds light on the potential multifaceted roles of Notch within skeletal muscle. Furthermore, we have demonstrated that Notch may modulate the PTEN/AKT/mTOR pathway.

scholarly journals GSI Treatment Preserves Protein Synthesis in C2C12 Myotubes

Cells ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1786
Author(s):  
Joshua R. Huot ◽  
Brian Thompson ◽  
Charlotte McMullen ◽  
Joseph S. Marino ◽  
Susan T. Arthur
Keyword(s):  
Protein Synthesis ◽  
Notch Signaling ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Mtor Signaling ◽  
C2c12 Cells ◽  
C2c12 Myotubes ◽  
Myotube Formation ◽  
Mediated Effects ◽  
Secretase Inhibitor

It has been demonstrated that inhibiting Notch signaling through γ-secretase inhibitor (GSI) treatment increases myogenesis, AKT/mTOR signaling, and muscle protein synthesis (MPS) in C2C12 myotubes. The purpose of this study was to determine if GSI-mediated effects on myogenesis and MPS are dependent on AKT/mTOR signaling. C2C12 cells were assessed for indices of myotube formation, anabolic signaling, and MPS following GSI treatment in combination with rapamycin and API-1, inhibitors of mTOR and AKT, respectively. GSI treatment increased several indices of myotube fusion and MPS in C2C12 myotubes. GSI-mediated effects on myotube formation and fusion were completely negated by treatment with rapamycin and API-1. Meanwhile, GSI treatment was able to rescue MPS in C2C12 myotubes exposed to rapamycin or rapamycin combined with API-1. Examination of protein expression revealed that GSI treatment was able to rescue pGSK3β Ser9 despite AKT inhibition by API-1. These findings demonstrate that GSI treatment is able to rescue MPS independent of AKT/mTOR signaling, possibly via GSK3β modulation.

scholarly journals Syncytin-1 Expression is Increased in Skeletal Muscle of Humans with Obesity and is Inversely Correlated to Muscle Protein Synthesis

2021 ◽  
Author(s):  
Jayachandran Ravichandran ◽  
Lori R Roust ◽  
Christos Katsanos
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Protein Metabolism ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
C2c12 Cell ◽  
C2c12 Cells ◽  
Anabolic Hormone ◽  
Lower Protein ◽  
Potential Link

Abstract Background: Various pathophysiological conditions alter protein metabolism in skeletal muscle, with obesity being one of them. Obesity impairs regeneration of skeletal muscle, and the same biological mechanism(s) may adversely affect protein metabolism in the muscle of these individuals. Methods: We used C2C12 cell line to evaluate the effects of the anabolic hormone insulin on the expression of protein syncytin-1, which regulates regeneration of muscle, and in the presence of fatty acids whose metabolism is altered in obesity. We used muscle biopsy samples from obese humans with lower muscle protein synthesis and lean controls to evaluate expression of syncytin-1 in obesity and its correlation with protein synthesis in muscle. Results: Insulin upregulated syncytin-1 expression in C2C12 cells and this response was impaired in the presence of the fatty acid palmitate, but not oleate. Expression of the protein 4E-BP1, which signals increase in protein synthesis in muscle, showed response similar to that of syncytin-1. Humans with obesity characterized by lower muscle protein synthesis had higher expression of syncytin-1 in muscle compared to lean humans (P < 0.01). The rate of synthesis of protein in skeletal muscle across humans subjects correlated inversely (r = -0.51; P = 0.03) with the expression of syncytin-1 in muscle. Conclusions: Our studies provide novel insights in the regulation of syncytin-1 in skeletal muscle, and describe potential link between syncytin-1 expression and protein metabolism in skeletal muscle of humans. Altered syncytin-1 expression in muscle may mediate lower protein turnover in muscle of humans with obesity.

scholarly journals Mechanisms of IGF-1-Mediated Regulation of Skeletal Muscle Hypertrophy and Atrophy

Cells ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 1970 ◽  
Author(s):  
Tadashi Yoshida ◽  
Patrice Delafontaine
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Growth Factor ◽  
Muscle Atrophy ◽  
Muscle Regeneration ◽  
Muscle Hypertrophy ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Skeletal Muscle Regeneration ◽  
Skeletal Muscle Atrophy

Insulin-like growth factor-1 (IGF-1) is a key growth factor that regulates both anabolic and catabolic pathways in skeletal muscle. IGF-1 increases skeletal muscle protein synthesis via PI3K/Akt/mTOR and PI3K/Akt/GSK3β pathways. PI3K/Akt can also inhibit FoxOs and suppress transcription of E3 ubiquitin ligases that regulate ubiquitin proteasome system (UPS)-mediated protein degradation. Autophagy is likely inhibited by IGF-1 via mTOR and FoxO signaling, although the contribution of autophagy regulation in IGF-1-mediated inhibition of skeletal muscle atrophy remains to be determined. Evidence has suggested that IGF-1/Akt can inhibit muscle atrophy-inducing cytokine and myostatin signaling via inhibition of the NF-κΒ and Smad pathways, respectively. Several miRNAs have been found to regulate IGF-1 signaling in skeletal muscle, and these miRs are likely regulated in different pathological conditions and contribute to the development of muscle atrophy. IGF-1 also potentiates skeletal muscle regeneration via activation of skeletal muscle stem (satellite) cells, which may contribute to muscle hypertrophy and/or inhibit atrophy. Importantly, IGF-1 levels and IGF-1R downstream signaling are suppressed in many chronic disease conditions and likely result in muscle atrophy via the combined effects of altered protein synthesis, UPS activity, autophagy, and muscle regeneration.

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

Nutrients ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 2391
Author(s):  
Koichiro Sumi ◽  
Misato Sakuda ◽  
Kinuyo Munakata ◽  
Kentaro Nakamura ◽  
Kinya Ashida
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Protein Degradation ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Skeletal Muscle Atrophy ◽  
C2c12 Myotubes ◽  
Skeletal Muscle Protein ◽  
Deuterium Labeling ◽  
Skeletal Muscle Protein Synthesis

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

Adaptation to prolonged starvation in the rat: curtailment of skeletal muscle proteolysis

1981 ◽  
Vol 241 (4) ◽  
pp. E321-E327 ◽  
Author(s):  
M. N. Goodman ◽  
M. A. McElaney ◽  
N. B. Ruderman
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Early Event ◽  
Body Protein ◽  
Fed State ◽  
Prolonged Starvation ◽  
Obese Rats ◽  
Old Rats

Previous studies have established that 16-wk-old nonobese and obese rats conserve body protein during prolonged starvation. To determine the basis for this, protein synthesis and degradation in skeletal muscle were evaluated in the isolated perfused hindquarters of these rats, in the fed state and when starved for 2, 5, 10, and 11 days. Rats aged 4 and 8 wk were used as a comparison. The results indicate that the response to starvation depends on several factors: the age of the rat, its degree of adiposity, and the duration of the fast. An early event in starvation was a decline in muscle protein synthesis. This occurred in all groups, albeit this reduction occurred more slowly in the older rats. A later response to starvation was an increase in muscle proteolysis. This occurred between 2 and 5 days in the 8-wk-old rats. In 16-wk-old rats it did not occur until between 5 and 10 days, and it was preceded by a period of decreased proteolysis. In 16-wk-old obese rats, a decrease in proteolysis persisted for upwards of 10 days and the secondary increase was not noted during the period of study. The data suggest that the ability of older and more obese rats to conserve body protein during starvation is due, in part, to a curtailment of muscle proteolysis. This adaptation seems to correlate with the availability of lipid fuels.

scholarly journals Resistance exercise maintains skeletal muscle protein synthesis during bed rest

1997 ◽  
Vol 82 (3) ◽  
pp. 807-810 ◽  
Author(s):  
Arny A. Ferrando ◽  
Kevin D. Tipton ◽  
Marcas M. Bamman ◽  
Robert R. Wolfe
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Resistance Training ◽  
Resistance Exercise ◽  
Lean Body Mass ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Bed Rest ◽  
Skeletal Muscle Protein ◽  
Skeletal Muscle Protein Synthesis

Ferrando, Arny A., Kevin D. Tipton, Marcas M. Bamman, and Robert R. Wolfe. Resistance exercise maintains skeletal muscle protein synthesis during bed rest. J. Appl. Physiol. 82(3): 807–810, 1997.—Spaceflight results in a loss of lean body mass and muscular strength. A ground-based model for microgravity, bed rest, results in a loss of lean body mass due to a decrease in muscle protein synthesis (MPS). Resistance training is suggested as a proposed countermeasure for spaceflight-induced atrophy because it is known to increase both MPS and skeletal muscle strength. We therefore hypothesized that scheduled resistance training throughout bed rest would ameliorate the decrease in MPS. Two groups of healthy volunteers were studied during 14 days of simulated microgravity. One group adhered to strict bed rest (BR; n = 5), whereas a second group engaged in leg resistance exercise every other day throughout bed rest (BREx; n = 6). MPS was determined directly by the incorporation of infusedl-[ ring-13C6]phenylalanine into vastus lateralis protein. After 14 days of bed rest, MPS in the BREx group did not change and was significantly greater than in the BR group. Thus moderate-resistance exercise can counteract the decrease in MPS during bed rest.

Growth hormone acutely stimulates forearm muscle protein synthesis in normal humans

1991 ◽  
Vol 260 (3) ◽  
pp. E499-E504 ◽  
Author(s):  
D. A. Fryburg ◽  
R. A. Gelfand ◽  
E. J. Barrett
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Growth Hormone ◽  
Protein Synthesis ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Skeletal Muscle Protein ◽  
Skeletal Muscle Protein Synthesis ◽  
Igf I ◽  
Normal Humans

The short-term effects of growth hormone (GH) on skeletal muscle protein synthesis and degradation in normal humans are unknown. We studied seven postabsorptive healthy men (age 18-23 yr) who received GH (0.014 micrograms.kg-1.min-1) via intrabrachial artery infusion for 6 h. The effects of GH on forearm amino acid and glucose balances and on forearm amino acid kinetics [( 3H]Phe and [14C]Leu) were determined after 3 and 6 h of the GH infusion. Forearm deep vein GH rose to 35 +/- 6 ng/ml in response to GH, whereas systemic levels of GH, insulin, and insulin-like growth factor I (IGF-I) were unchanged. Forearm glucose uptake did not change during the study. After 6 h, GH suppressed forearm net release (3 vs. 6 h) of Phe (P less than 0.05), Leu (P less than 0.01), total branched-chain amino acids (P less than 0.025), and essential neutral amino acids (0.05 less than P less than 0.1). The effect on the net balance of Phe and Leu was due to an increase in the tissue uptake for Phe (71%, P less than 0.05) and Leu (37%, P less than 0.005) in the absence of any significant change in release of Phe or Leu from tissue. In the absence of any change in systemic GH, IGF-I, or insulin, these findings suggest that locally infused GH stimulates skeletal muscle protein synthesis. These findings have important physiological implications for both the role of daily GH pulses and the mechanisms through which GH can promote protein anabolism.

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