Possible Involvement of Calcium Signaling Pathways in<scp>L</scp>-Leucine-Stimulated Protein Synthesis in L6 Myotubes

Miura, Yutaka; Nakazawa, Taro; Yagasaki, Kazumi

doi:10.1271/bbb.60081

Cited by 5 publications

(7 citation statements)

References 21 publications

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“…The positive effects of L‐Leu supplementation on protein synthesis have been widely studied in situations where the subjects were either in deficient or fasting conditions,8, 11, 12, 13, 14, 15 and therefore under a catabolic stimulus.…”

Section: Discussionmentioning

confidence: 99%

“…L-Leu stimulates protein synthesis in muscle cells through at least two distinct mechanisms: by stimulation of mRNA translation initiation machinery 13,35 and by activation of intracellular signalling pathways linked to mTOR. 6,36,37 The positive effects of L-Leu supplementation on protein synthesis have been widely studied in situations where the subjects were either in deficient or fasting conditions, 8,[11][12][13][14][15] and therefore under a catabolic stimulus.…”

Section: Discussionmentioning

confidence: 99%

“…1,2 Amino acids, particularly branched chain amino acids, are capable of increasing protein synthesis in skeletal muscle. [6][7][8][9] Their mechanism of action is dual; they provide substrates required for polypeptide synthesis and modulate signalling pathways responsible for translation initiation. 10,11 Among them, leucine is the most effective amino acid in stimulating protein synthesis through a direct activation of mTOR.…”

Section: Introductionmentioning

confidence: 99%

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Conversion of leucine to β-hydroxy-β-methylbutyrate by α-keto isocaproate dioxygenase is required for a potent stimulation of protein synthesis in L6 rat myotubes

Girón

Rienda

Salto

et al. 2015

Journal of Cachexia, Sarcopenia and Muscle

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BackgroundL‐Leu and its metabolite β‐hydroxy‐β‐methylbutyrate (HMB) stimulate muscle protein synthesis enhancing the phosphorylation of proteins that regulate anabolic signalling pathways. Alterations in these pathways are observed in many catabolic diseases, and HMB and L‐Leu have proven their anabolic effects in in vivo and in vitro models. The aim of this study was to compare the anabolic effects of L‐Leu and HMB in myotubes grown in the absence of any catabolic stimuli.MethodsStudies were conducted in vitro using rat L6 myotubes under normal growth conditions (non‐involving L‐Leu‐deprived conditions). Protein synthesis and mechanistic target of rapamycin signalling pathway were determined.ResultsOnly HMB was able to increase protein synthesis through a mechanism that involves the phosphorylation of the mechanistic target of rapamycin as well as its downstream elements, pS6 kinase, 4E binding protein‐1, and eIF4E. HMB was significantly more effective than L‐Leu in promoting these effects through an activation of protein kinase B/Akt. Because the conversion of L‐Leu to HMB is limited in muscle, L6 cells were transfected with a plasmid that codes for α‐keto isocaproate dioxygenase, the key enzyme involved in the catabolic conversion of α‐keto isocaproate into HMB. In these transfected cells, L‐Leu was able to promote protein synthesis and mechanistic target of rapamycin regulated pathway activation equally to HMB. Additionally, these effects of leucine were reverted to a normal state by mesotrione, a specific inhibitor of α‐keto isocaproate dioxygenase.ConclusionOur results suggest that HMB is an active L‐Leu metabolite able to maximize protein synthesis in skeletal muscle under conditions, in which no amino acid deprivation occurred. It may be proposed that supplementation with HMB may be very useful to stimulate protein synthesis in wasting conditions associated with chronic diseases, such as cancer or chronic heart failure.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Conversion of leucine to β-hydroxy-β-methylbutyrate by α-keto isocaproate dioxygenase is required for a potent stimulation of protein synthesis in L6 rat myotubes

Girón

Rienda

Salto

et al. 2015

Journal of Cachexia, Sarcopenia and Muscle

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“…(Raffaello, Mammucari, Gherardi, & Rizzuto, 2016). Miura et al (2006) recently observed in L6 myotubes that leucine stimulated protein synthesis was inhibited by ryanodine receptor antagonist or 2-APB, an IP 3 receptor antagonist. In our conditions, neither ryanodine nor 2-APB were able to prevent the rimonabant-induced protein synthesis in C2C12 myotubes.…”

Section: Discussionmentioning

confidence: 99%

Acute rimonabant treatment promotes protein synthesis in C2C12 myotubes through a CB1‐independent mechanism

Bacquer

Lanchais

Combe

et al. 2020

Journal Cellular Physiology

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Sarcopenia is an age‐related loss of muscle mass associated with changes in skeletal muscle protein homeostasis due to lipid accumulation and anabolic resistance; changes that are also commonly described in obesity. Activation of the endocannabinoid system is associated with the development of obesity and insulin resistance, and with the perturbed skeletal muscle development. Taken together this suggests that endocannabinoids could be regulators of skeletal muscle protein homeostasis. Here we report that rimonabant, an antagonist for the CB1 receptor, can prevent dexamethasone‐induced C2C12 myotube atrophy without affecting the mRNA expression of atrogin‐1/MAFbx (a marker of proteolysis), which suggests it is involved in the control of protein synthesis. Rimonabant alone stimulates protein synthesis in a time‐ and dose‐dependent manner through mTOR‐ and intracellular calcium‐dependent mechanisms. CB1 agonists are unable to modulate protein synthesis or prevent the effect of rimonabant. Using C2C12 cells stably expressing an shRNA directed against CB1, or HEK293 cells overexpressing HA‐tagged CB1, we demonstrated that the effect of rimonabant is unaffected by CB1 expression level. In summary, rimonabant can stimulate protein synthesis in C2C12 myotubes through a CB1‐independent mechanism. These results highlight the need to identify non‐CB1 receptor(s) mediating the pro‐anabolic effect of rimonabant as potential targets for the treatment of sarcopenia, and to design new side‐effect‐free molecules that consolidate the effect of rimonabant on skeletal muscle protein synthesis.

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“…L6 myoblasts established from rat skeletal muscle tissues are well known to grow rapidly, fuse spontaneously, differentiate into multinucleated myotubes [5], and are widely used in the studies on the effects of various biofactors on muscle functions in vitro. The stimulatory effect of leucine on protein synthesis has been demonstrated in differentiated L6 myocytes (myotubes) [6,7] through several signaling pathways. Leucine has been also demonstrated to stimulate glucose uptake (GU) in the soleus muscle of rats [8].…”

Section: Introductionmentioning

confidence: 99%

Antidiabetic Effect of Taxifolin in Cultured L6 Myotubes and Type 2 Diabetic Model KK-Ay/Ta Mice with Hyperglycemia and Hyperuricemia

Kondo

Adachi

Yoshizawa

et al. 2021

CIMB

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Muscle is the largest tissue in our body and plays an important role in glucose homeostasis and hence diabetes. In the present study, we examined the effects of taxifolin (TXF) on glucose metabolism in cultured L6 muscle cells (myotubes) and in type 2 diabetic (T2D) model KK-Ay/Ta mice. TXF dose-dependently increased glucose uptake (GU) in L6 myotubes under the condition of insulin absence. This increase in GU was partially, but significantly canceled by TXF treatment in combination with either LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3K), which phosphorylates protein kinase B (Akt) or Compound C, an inhibitor of 5’-adenosine monophosphate-activated protein kinase (AMPK). Furthermore, TXF was demonstrated to activate (=phosphorylate) both Akt and AMPK, and promote glucose transporter 4 (GLUT4) translocation to the plasma membrane from cytosol of L6 myotubes via both PI3K/Akt and AMPK signaling pathways. Based on these in vitro findings, we conducted an in vivo experiment in KK-Ay/Ta mice with hyperglycemia and hyperuricemia. Fasting plasma glucose, insulin, uric acid levels and an index of insulin resistance (HOMA-IR) increased significantly in the T2D model mice compared with normal ones. Such rises in the T2D state were significantly suppressed by oral administration of TXF for four weeks. These results suggest that TXF is a potent antihyperglycemic and antihyperuricemic phytochemical in the T2D state.

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Possible Involvement of Calcium Signaling Pathways inL-Leucine-Stimulated Protein Synthesis in L6 Myotubes

Cited by 5 publications

References 21 publications

Conversion of leucine to β-hydroxy-β-methylbutyrate by α-keto isocaproate dioxygenase is required for a potent stimulation of protein synthesis in L6 rat myotubes

Conversion of leucine to β-hydroxy-β-methylbutyrate by α-keto isocaproate dioxygenase is required for a potent stimulation of protein synthesis in L6 rat myotubes

Acute rimonabant treatment promotes protein synthesis in C2C12 myotubes through a CB1‐independent mechanism

Antidiabetic Effect of Taxifolin in Cultured L6 Myotubes and Type 2 Diabetic Model KK-Ay/Ta Mice with Hyperglycemia and Hyperuricemia

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