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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

Immobilization induces fiber-type-dependent decreases in protein synthesis and fiber size that are not associated with the level of mTOR activity. Mice were subjected to unilateral hindlimb immobilization (IM) for 3 days, or a non-immobilized control condition (CNT), and injected with puromycin as in Fig. 1. (A) EDL muscles obtained from CNT and IM mice were frozen adjacent to one another and subjected to immunohistochemistry for different isoforms of myosin heavy chain (MHC; 1, yellow; 2A, blue; 2X, red; 2B, green) and puromycin-labeled peptides, phosphorylated (P)-S6 (S240/244), or total (T)-S6. (B-D) Fiber-type-specific measurements of (B) the fiber cross-sectional area (CSA) normalized to body weight (BW), (C) the puromycin staining intensity (i.e. protein synthesis), and (D) the ratio of P-S6 normalized to T-S6. All values were expressed relative to the values obtained in the fiber-type-matched CNT muscles and presented as the mean+s.e.m. (n=48-360 fibers per group from four independent pairs of muscles). * versus the fiber-type-matched CNT groups, a-d versus one another, P≤0.05.
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DMM019414F6: Immobilization induces fiber-type-dependent decreases in protein synthesis and fiber size that are not associated with the level of mTOR activity. Mice were subjected to unilateral hindlimb immobilization (IM) for 3 days, or a non-immobilized control condition (CNT), and injected with puromycin as in Fig. 1. (A) EDL muscles obtained from CNT and IM mice were frozen adjacent to one another and subjected to immunohistochemistry for different isoforms of myosin heavy chain (MHC; 1, yellow; 2A, blue; 2X, red; 2B, green) and puromycin-labeled peptides, phosphorylated (P)-S6 (S240/244), or total (T)-S6. (B-D) Fiber-type-specific measurements of (B) the fiber cross-sectional area (CSA) normalized to body weight (BW), (C) the puromycin staining intensity (i.e. protein synthesis), and (D) the ratio of P-S6 normalized to T-S6. All values were expressed relative to the values obtained in the fiber-type-matched CNT muscles and presented as the mean+s.e.m. (n=48-360 fibers per group from four independent pairs of muscles). * versus the fiber-type-matched CNT groups, a-d versus one another, P≤0.05.

Mentions: We have previously shown that the regulation of fiber size in response to mechanical overload and food deprivation varies among different fiber types, and that this variation is associated with similar fiber-type-dependent alterations in the rate of protein synthesis and mTOR activity as revealed by S6 (S240/244) phosphorylation (Goodman et al., 2012). Furthermore, in Fig. 2D, immobilization seemed to preferentially reduce the size of larger fibers. Hence, we wondered whether changes in fiber size and protein synthesis during immobilization are also fiber-type-dependent, and whether these changes are associated with similar alterations in the level of mTOR signaling. Specifically, we hypothesized that the magnitude of any fiber-type-dependent decreases in protein synthesis would be inversely correlated with the magnitude of mTOR activation. As shown in Fig. 6B, we first determined that immobilization decreases the size of fibers in EDL muscles with the following fiber-type-dependent order: 1≤2A<2X=2B. Interestingly, it was also found that immobilization decreases the rates of protein synthesis in a similar fiber-type-dependent fashion with type 1<2A<2X<2B (Fig. 6C) [note: similar results were also observed in tibialis anterior (TA) muscles; data not shown]. On the other hand, we were not able to detect an inverse correlation between the fiber-type-dependent regulation of protein synthesis and the level of mTOR signaling as revealed by S6 (S240/244) phosphorylation (Fig. 6D). Therefore, these results suggest that: (1) the regulation of protein synthesis during immobilization largely influences the extent of disuse atrophy, and (2) the fiber-type-dependent decreases in the rate of protein synthesis are not mediated through fiber-type-dependent differences in the regulation of mTOR signaling.Fig. 6.


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)

Immobilization induces fiber-type-dependent decreases in protein synthesis and fiber size that are not associated with the level of mTOR activity. Mice were subjected to unilateral hindlimb immobilization (IM) for 3 days, or a non-immobilized control condition (CNT), and injected with puromycin as in Fig. 1. (A) EDL muscles obtained from CNT and IM mice were frozen adjacent to one another and subjected to immunohistochemistry for different isoforms of myosin heavy chain (MHC; 1, yellow; 2A, blue; 2X, red; 2B, green) and puromycin-labeled peptides, phosphorylated (P)-S6 (S240/244), or total (T)-S6. (B-D) Fiber-type-specific measurements of (B) the fiber cross-sectional area (CSA) normalized to body weight (BW), (C) the puromycin staining intensity (i.e. protein synthesis), and (D) the ratio of P-S6 normalized to T-S6. All values were expressed relative to the values obtained in the fiber-type-matched CNT muscles and presented as the mean+s.e.m. (n=48-360 fibers per group from four independent pairs of muscles). * versus the fiber-type-matched CNT groups, a-d versus one another, P≤0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

DMM019414F6: Immobilization induces fiber-type-dependent decreases in protein synthesis and fiber size that are not associated with the level of mTOR activity. Mice were subjected to unilateral hindlimb immobilization (IM) for 3 days, or a non-immobilized control condition (CNT), and injected with puromycin as in Fig. 1. (A) EDL muscles obtained from CNT and IM mice were frozen adjacent to one another and subjected to immunohistochemistry for different isoforms of myosin heavy chain (MHC; 1, yellow; 2A, blue; 2X, red; 2B, green) and puromycin-labeled peptides, phosphorylated (P)-S6 (S240/244), or total (T)-S6. (B-D) Fiber-type-specific measurements of (B) the fiber cross-sectional area (CSA) normalized to body weight (BW), (C) the puromycin staining intensity (i.e. protein synthesis), and (D) the ratio of P-S6 normalized to T-S6. All values were expressed relative to the values obtained in the fiber-type-matched CNT muscles and presented as the mean+s.e.m. (n=48-360 fibers per group from four independent pairs of muscles). * versus the fiber-type-matched CNT groups, a-d versus one another, P≤0.05.
Mentions: We have previously shown that the regulation of fiber size in response to mechanical overload and food deprivation varies among different fiber types, and that this variation is associated with similar fiber-type-dependent alterations in the rate of protein synthesis and mTOR activity as revealed by S6 (S240/244) phosphorylation (Goodman et al., 2012). Furthermore, in Fig. 2D, immobilization seemed to preferentially reduce the size of larger fibers. Hence, we wondered whether changes in fiber size and protein synthesis during immobilization are also fiber-type-dependent, and whether these changes are associated with similar alterations in the level of mTOR signaling. Specifically, we hypothesized that the magnitude of any fiber-type-dependent decreases in protein synthesis would be inversely correlated with the magnitude of mTOR activation. As shown in Fig. 6B, we first determined that immobilization decreases the size of fibers in EDL muscles with the following fiber-type-dependent order: 1≤2A<2X=2B. Interestingly, it was also found that immobilization decreases the rates of protein synthesis in a similar fiber-type-dependent fashion with type 1<2A<2X<2B (Fig. 6C) [note: similar results were also observed in tibialis anterior (TA) muscles; data not shown]. On the other hand, we were not able to detect an inverse correlation between the fiber-type-dependent regulation of protein synthesis and the level of mTOR signaling as revealed by S6 (S240/244) phosphorylation (Fig. 6D). Therefore, these results suggest that: (1) the regulation of protein synthesis during immobilization largely influences the extent of disuse atrophy, and (2) the fiber-type-dependent decreases in the rate of protein synthesis are not mediated through fiber-type-dependent differences in the regulation of mTOR signaling.Fig. 6.

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