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Lysine suppresses myofibrillar protein degradation by regulating the autophagic-lysosomal system through phosphorylation of Akt in C2C12 cells.

Sato T, Ito Y, Nagasawa T - Springerplus (2014)

Bottom Line: Lys suppressed the phosphorylation of AMPK, but this effect was also abolished by Akti.These results indicate that regulation of AMPK activity is not essential for the regulation of autophagy by Lys.Taken together, our results show that Lys suppresses myofibrillar protein degradation by the autophagic-lysosomal system through the phosphorylation of Akt in C2C12 cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioresources Science, The United Graduate School of Agricultural Sciences, Iwate University, Morioka, Iwate 020-8550 Japan.

ABSTRACT
The prevention of muscle wasting is important for maintaining quality of life, since loss of muscle mass can lead to a bedridden state and decreased resistance to diseases. The prevention of muscle wasting requires an increase in protein synthesis and a decrease in protein degradation in skeletal muscle. We previously showed that lysine (Lys) markedly suppressed myofibrillar protein degradation by inhibiting the autophagic-lysosomal system via the mammalian target of rapamycin (mTOR) and other signal molecules in C2C12 cells. In this study, we investigated the involvement of Akt and adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), two regulators of autophagy, on the suppressive effects of Lys on myofibrillar protein degradation in C2C12 cells. Lys induced the phosphorylation of Akt, but the suppressive effects of Lys on myofibrillar protein degradation and autophagy were completely abolished in the presence of Akt1/2 kinase inhibitor (Akti). Lys suppressed the phosphorylation of AMPK, but this effect was also abolished by Akti. On the other hand, AMPK activation by 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside (AICAR) did not affect either Akt activity or the autophagic-lysosomal system in C2C12 cells treated with Lys. These results indicate that regulation of AMPK activity is not essential for the regulation of autophagy by Lys. Taken together, our results show that Lys suppresses myofibrillar protein degradation by the autophagic-lysosomal system through the phosphorylation of Akt in C2C12 cells.

No MeSH data available.


Related in: MedlinePlus

Lys suppresses the autophagic-lysosomal system through activation of Akt in C2C12 myotubes. Cells were treated for 30 min with DMSO (C), 10 μM Akti (Ai), 10 mM Leu (L), 10 mM Leu and 10 μM Akti (AiL), 10 mM Lys (K), or 10 mM Lys and 10 μM Akti (AiK). The ratio of LC3-II to total LC3 (LC3-I + LC3-II) in the lysates was determined by Western blotting. Results are expressed as the level relative to the control group. Values are means with SE (n = 3–4). Different letters indicate significant differences among the groups (p < 0.05).
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Fig3: Lys suppresses the autophagic-lysosomal system through activation of Akt in C2C12 myotubes. Cells were treated for 30 min with DMSO (C), 10 μM Akti (Ai), 10 mM Leu (L), 10 mM Leu and 10 μM Akti (AiL), 10 mM Lys (K), or 10 mM Lys and 10 μM Akti (AiK). The ratio of LC3-II to total LC3 (LC3-I + LC3-II) in the lysates was determined by Western blotting. Results are expressed as the level relative to the control group. Values are means with SE (n = 3–4). Different letters indicate significant differences among the groups (p < 0.05).

Mentions: Light chain 3 (LC3) is a mammalian homolog of Apg8p, a protein that is essential for the autophagic-lysosomal system in yeast. LC3 has two forms: LC3-I and LC3-II. The ratio of LC3-II to total LC3 (LC3-I + LC3-II) was used as a marker of autophagy (Naito et al. 2013). We evaluated the involvement of Akt activation induced by Lys in the regulation of autophagic-lysosomal activity by the ratio of LC3-II to total LC3. The ratio of LC3-II to total LC3 was reduced in C2C12 cells treated with Lys (K), however, this reduction was abolished by treatment with Akt inhibitor (AiK). Similar results were observed when the cells were treated with Leu (Figure 3). These results suggest that the suppression of the autophagic-lysosomal system by Lys is dependent on the activation of Akt.Figure 3


Lysine suppresses myofibrillar protein degradation by regulating the autophagic-lysosomal system through phosphorylation of Akt in C2C12 cells.

Sato T, Ito Y, Nagasawa T - Springerplus (2014)

Lys suppresses the autophagic-lysosomal system through activation of Akt in C2C12 myotubes. Cells were treated for 30 min with DMSO (C), 10 μM Akti (Ai), 10 mM Leu (L), 10 mM Leu and 10 μM Akti (AiL), 10 mM Lys (K), or 10 mM Lys and 10 μM Akti (AiK). The ratio of LC3-II to total LC3 (LC3-I + LC3-II) in the lysates was determined by Western blotting. Results are expressed as the level relative to the control group. Values are means with SE (n = 3–4). Different letters indicate significant differences among the groups (p < 0.05).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4197202&req=5

Fig3: Lys suppresses the autophagic-lysosomal system through activation of Akt in C2C12 myotubes. Cells were treated for 30 min with DMSO (C), 10 μM Akti (Ai), 10 mM Leu (L), 10 mM Leu and 10 μM Akti (AiL), 10 mM Lys (K), or 10 mM Lys and 10 μM Akti (AiK). The ratio of LC3-II to total LC3 (LC3-I + LC3-II) in the lysates was determined by Western blotting. Results are expressed as the level relative to the control group. Values are means with SE (n = 3–4). Different letters indicate significant differences among the groups (p < 0.05).
Mentions: Light chain 3 (LC3) is a mammalian homolog of Apg8p, a protein that is essential for the autophagic-lysosomal system in yeast. LC3 has two forms: LC3-I and LC3-II. The ratio of LC3-II to total LC3 (LC3-I + LC3-II) was used as a marker of autophagy (Naito et al. 2013). We evaluated the involvement of Akt activation induced by Lys in the regulation of autophagic-lysosomal activity by the ratio of LC3-II to total LC3. The ratio of LC3-II to total LC3 was reduced in C2C12 cells treated with Lys (K), however, this reduction was abolished by treatment with Akt inhibitor (AiK). Similar results were observed when the cells were treated with Leu (Figure 3). These results suggest that the suppression of the autophagic-lysosomal system by Lys is dependent on the activation of Akt.Figure 3

Bottom Line: Lys suppressed the phosphorylation of AMPK, but this effect was also abolished by Akti.These results indicate that regulation of AMPK activity is not essential for the regulation of autophagy by Lys.Taken together, our results show that Lys suppresses myofibrillar protein degradation by the autophagic-lysosomal system through the phosphorylation of Akt in C2C12 cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioresources Science, The United Graduate School of Agricultural Sciences, Iwate University, Morioka, Iwate 020-8550 Japan.

ABSTRACT
The prevention of muscle wasting is important for maintaining quality of life, since loss of muscle mass can lead to a bedridden state and decreased resistance to diseases. The prevention of muscle wasting requires an increase in protein synthesis and a decrease in protein degradation in skeletal muscle. We previously showed that lysine (Lys) markedly suppressed myofibrillar protein degradation by inhibiting the autophagic-lysosomal system via the mammalian target of rapamycin (mTOR) and other signal molecules in C2C12 cells. In this study, we investigated the involvement of Akt and adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), two regulators of autophagy, on the suppressive effects of Lys on myofibrillar protein degradation in C2C12 cells. Lys induced the phosphorylation of Akt, but the suppressive effects of Lys on myofibrillar protein degradation and autophagy were completely abolished in the presence of Akt1/2 kinase inhibitor (Akti). Lys suppressed the phosphorylation of AMPK, but this effect was also abolished by Akti. On the other hand, AMPK activation by 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside (AICAR) did not affect either Akt activity or the autophagic-lysosomal system in C2C12 cells treated with Lys. These results indicate that regulation of AMPK activity is not essential for the regulation of autophagy by Lys. Taken together, our results show that Lys suppresses myofibrillar protein degradation by the autophagic-lysosomal system through the phosphorylation of Akt in C2C12 cells.

No MeSH data available.


Related in: MedlinePlus