Limits...
The role of mTOR signaling in the regulation of protein synthesis and muscle mass during immobilization in mice.

You JS, Anderson GB, Dooley MS, Hornberger TA - Dis Model Mech (2015)

Bottom Line: Unexpectedly, the effects of isometric contractions were also independent of eIF4F complex formation.Similar to isometric contractions, overexpression of Rheb in immobilized muscles enhanced mTOR signaling, cap-dependent translation and global protein synthesis, and prevented the reduction in fiber size.Furthermore, these results indicate that the activation of mTOR signaling is a viable target for therapies that are aimed at preventing muscle atrophy during periods of mechanical unloading.

View Article: PubMed Central - PubMed

Affiliation: Program in Cellular and Molecular Biology, University of Wisconsin - Madison, 2015 Linden Drive, Madison, WI 53706, USA Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin - Madison, 2015 Linden Drive, Madison, WI 53706, USA.

No MeSH data available.


Related in: MedlinePlus

In immobilized muscles, isometric contractions enhance mTOR signaling and rescue the decrease in protein synthesis via a rapamycin-sensitive mechanism. (A-C) Mice were subjected to unilateral hindlimb immobilization for 3 days (IM+), or a non-immobilized control condition (IM−), and then injected with rapamycin (RAP+) or the vehicle (RAP−) and puromycin (puro) at the indicated time points. Following the RAP−/+ injections, mice were subjected to a bout of isometric contractions (IC+) or the sham condition (IC−). Upon collection, EDL muscles were subjected to western blot analysis for (B) phosphorylated (P) and total (T) p70, T-S6 and (C) puromycin-labeled peptides (i.e. protein synthesis). (D,E) Mice were treated as in A except for the injections, and the EDL muscles were analyzed for (D) total RNA to muscle weight (MW) ratio and (E) 28S+18S rRNA content. The amount of P-p70, T-p70, puromycin-labeled peptides and 28S+18S rRNA was expressed relative to the values obtained in the IC−/IM−/RAP− groups. All values are presented as the mean (+s.e.m. in graphs, n=3-6 muscles per group). * versus the drug- and mobility-matched IC− groups, # versus the contraction-matched IM−/RAP− groups, † versus the contraction-matched IM+/RAP− groups, P≤0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4582099&req=5

DMM019414F3: In immobilized muscles, isometric contractions enhance mTOR signaling and rescue the decrease in protein synthesis via a rapamycin-sensitive mechanism. (A-C) Mice were subjected to unilateral hindlimb immobilization for 3 days (IM+), or a non-immobilized control condition (IM−), and then injected with rapamycin (RAP+) or the vehicle (RAP−) and puromycin (puro) at the indicated time points. Following the RAP−/+ injections, mice were subjected to a bout of isometric contractions (IC+) or the sham condition (IC−). Upon collection, EDL muscles were subjected to western blot analysis for (B) phosphorylated (P) and total (T) p70, T-S6 and (C) puromycin-labeled peptides (i.e. protein synthesis). (D,E) Mice were treated as in A except for the injections, and the EDL muscles were analyzed for (D) total RNA to muscle weight (MW) ratio and (E) 28S+18S rRNA content. The amount of P-p70, T-p70, puromycin-labeled peptides and 28S+18S rRNA was expressed relative to the values obtained in the IC−/IM−/RAP− groups. All values are presented as the mean (+s.e.m. in graphs, n=3-6 muscles per group). * versus the drug- and mobility-matched IC− groups, # versus the contraction-matched IM−/RAP− groups, † versus the contraction-matched IM+/RAP− groups, P≤0.05.

Mentions: Previous human studies have shown that electrically evoked contractions can prevent disuse-induced reductions in the rate of protein synthesis and muscle size (Gibson et al., 1988; Hirose et al., 2013). Although the molecular mechanisms behind this effect are not known, current evidence suggests that the activation of mTOR signaling might be involved. For instance, previous studies have shown that the activation of mTOR signaling positively correlates with contraction-induced increases in the rate of protein synthesis and training-induced increases in muscle mass (Baar and Esser, 1999; Kumar et al., 2009; Terzis et al., 2008). Therefore, we reasoned that a further activation of mTOR signaling during immobilization, via electrically evoked contractions, might alleviate the immobilization-induced decrease in protein synthesis. To test this, we treated control and 3-day-immobilized mice with or without an acute bolus of rapamycin and then subjected the mice to a bout of isometric contractions or a sham condition (Fig. 3A). As shown in Fig. 3B, isometric contractions enhanced the level of mTOR signaling in immobilized muscles, and rapamycin abolished this effect. Moreover, in immobilized muscles, isometric contractions enhanced the rate of protein synthesis and, again, this effect was completely abolished by rapamycin (Fig. 3C). Combined, these results indicate that isometric contractions can prevent the immobilization-induced decrease in protein synthesis and this effect is mediated by a rapamycin-sensitive/mTOR-dependent mechanism.Fig. 3.


The role of mTOR signaling in the regulation of protein synthesis and muscle mass during immobilization in mice.

You JS, Anderson GB, Dooley MS, Hornberger TA - Dis Model Mech (2015)

In immobilized muscles, isometric contractions enhance mTOR signaling and rescue the decrease in protein synthesis via a rapamycin-sensitive mechanism. (A-C) Mice were subjected to unilateral hindlimb immobilization for 3 days (IM+), or a non-immobilized control condition (IM−), and then injected with rapamycin (RAP+) or the vehicle (RAP−) and puromycin (puro) at the indicated time points. Following the RAP−/+ injections, mice were subjected to a bout of isometric contractions (IC+) or the sham condition (IC−). Upon collection, EDL muscles were subjected to western blot analysis for (B) phosphorylated (P) and total (T) p70, T-S6 and (C) puromycin-labeled peptides (i.e. protein synthesis). (D,E) Mice were treated as in A except for the injections, and the EDL muscles were analyzed for (D) total RNA to muscle weight (MW) ratio and (E) 28S+18S rRNA content. The amount of P-p70, T-p70, puromycin-labeled peptides and 28S+18S rRNA was expressed relative to the values obtained in the IC−/IM−/RAP− groups. All values are presented as the mean (+s.e.m. in graphs, n=3-6 muscles per group). * versus the drug- and mobility-matched IC− groups, # versus the contraction-matched IM−/RAP− groups, † versus the contraction-matched IM+/RAP− groups, P≤0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4582099&req=5

DMM019414F3: In immobilized muscles, isometric contractions enhance mTOR signaling and rescue the decrease in protein synthesis via a rapamycin-sensitive mechanism. (A-C) Mice were subjected to unilateral hindlimb immobilization for 3 days (IM+), or a non-immobilized control condition (IM−), and then injected with rapamycin (RAP+) or the vehicle (RAP−) and puromycin (puro) at the indicated time points. Following the RAP−/+ injections, mice were subjected to a bout of isometric contractions (IC+) or the sham condition (IC−). Upon collection, EDL muscles were subjected to western blot analysis for (B) phosphorylated (P) and total (T) p70, T-S6 and (C) puromycin-labeled peptides (i.e. protein synthesis). (D,E) Mice were treated as in A except for the injections, and the EDL muscles were analyzed for (D) total RNA to muscle weight (MW) ratio and (E) 28S+18S rRNA content. The amount of P-p70, T-p70, puromycin-labeled peptides and 28S+18S rRNA was expressed relative to the values obtained in the IC−/IM−/RAP− groups. All values are presented as the mean (+s.e.m. in graphs, n=3-6 muscles per group). * versus the drug- and mobility-matched IC− groups, # versus the contraction-matched IM−/RAP− groups, † versus the contraction-matched IM+/RAP− groups, P≤0.05.
Mentions: Previous human studies have shown that electrically evoked contractions can prevent disuse-induced reductions in the rate of protein synthesis and muscle size (Gibson et al., 1988; Hirose et al., 2013). Although the molecular mechanisms behind this effect are not known, current evidence suggests that the activation of mTOR signaling might be involved. For instance, previous studies have shown that the activation of mTOR signaling positively correlates with contraction-induced increases in the rate of protein synthesis and training-induced increases in muscle mass (Baar and Esser, 1999; Kumar et al., 2009; Terzis et al., 2008). Therefore, we reasoned that a further activation of mTOR signaling during immobilization, via electrically evoked contractions, might alleviate the immobilization-induced decrease in protein synthesis. To test this, we treated control and 3-day-immobilized mice with or without an acute bolus of rapamycin and then subjected the mice to a bout of isometric contractions or a sham condition (Fig. 3A). As shown in Fig. 3B, isometric contractions enhanced the level of mTOR signaling in immobilized muscles, and rapamycin abolished this effect. Moreover, in immobilized muscles, isometric contractions enhanced the rate of protein synthesis and, again, this effect was completely abolished by rapamycin (Fig. 3C). Combined, these results indicate that isometric contractions can prevent the immobilization-induced decrease in protein synthesis and this effect is mediated by a rapamycin-sensitive/mTOR-dependent mechanism.Fig. 3.

Bottom Line: Unexpectedly, the effects of isometric contractions were also independent of eIF4F complex formation.Similar to isometric contractions, overexpression of Rheb in immobilized muscles enhanced mTOR signaling, cap-dependent translation and global protein synthesis, and prevented the reduction in fiber size.Furthermore, these results indicate that the activation of mTOR signaling is a viable target for therapies that are aimed at preventing muscle atrophy during periods of mechanical unloading.

View Article: PubMed Central - PubMed

Affiliation: Program in Cellular and Molecular Biology, University of Wisconsin - Madison, 2015 Linden Drive, Madison, WI 53706, USA Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin - Madison, 2015 Linden Drive, Madison, WI 53706, USA.

No MeSH data available.


Related in: MedlinePlus