Skeletal muscle protein balance in mTOR heterozygous mice in response to inflammation and leucine

Charles H. Lang, Robert A. Frost, Sarah K. Bronson, Christopher J. Lynch, Thomas C. Vary

Research output: Contribution to journalArticle

42 Citations (Scopus)

Abstract

Sepsis and lipopolysaccharide (LPS) may decrease skeletal muscle protein synthesis by impairing mTOR (mammalian target of rapamycin) activity. The role of mTOR in regulating muscle protein synthesis was assessed in wild-type (WT) and mTOR heterozygous (+/-) mice under basal conditions and in response to LPS and/or leucine stimulation. No difference in body weight of mTOR+/- mice was observed compared with WT mice; whereas whole body lean body mass was reduced. Gastrocnemius weight was decreased in mTOR+/- mice, which was attributable in part to a reduced rate of basal protein synthesis. LPS decreased muscle protein synthesis in WT and mTOR+/- mice to the same extent. Reduced muscle protein synthesis in mTOR+/- mice under basal and LPS-stimulated conditions was associated with lower 4E-BP1 and S6K1 phosphorylation. LPS also decreased PRAS40 phosphorylation and increased phosphorylation of raptor and IRS-1 (Ser307) to the same extent in WT and mTOR+/- mice. Muscle atrogin-1 and MuRF1 mRNA content was elevated in mTOR+/- mice under basal conditions, implying increased ubiquitin-proteasome-mediated proteolysis, but the LPS-induced increase in these atrogenes was comparable between groups. Plasma insulin and IGF-I as well as tissue expression of TNFα, IL-6, or NOS2 did not differ between WT and mTOR+/- mice. Finally, whereas LPS impaired the ability of leucine to stimulate muscle protein synthesis and 4E-BP1 phosphorylation in WT mice, this inflammatory state rendered mTOR+/- mice leucine unresponsive. These data support the idea that the LPS-induced reduction in mTOR activity is relatively more important in regulating skeletal muscle mass in response to nutrient stimulation than under basal conditions.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Volume298
Issue number6
DOIs
StatePublished - Jun 1 2010

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Muscle Proteins
Sirolimus
Leucine
Skeletal Muscle
Inflammation
Lipopolysaccharides
Phosphorylation
Raptors
Proteasome Endopeptidase Complex
Ubiquitin
Insulin-Like Growth Factor I
Proteolysis
Interleukin-6
Sepsis
Body Weight
Insulin

All Science Journal Classification (ASJC) codes

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)

Cite this

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abstract = "Sepsis and lipopolysaccharide (LPS) may decrease skeletal muscle protein synthesis by impairing mTOR (mammalian target of rapamycin) activity. The role of mTOR in regulating muscle protein synthesis was assessed in wild-type (WT) and mTOR heterozygous (+/-) mice under basal conditions and in response to LPS and/or leucine stimulation. No difference in body weight of mTOR+/- mice was observed compared with WT mice; whereas whole body lean body mass was reduced. Gastrocnemius weight was decreased in mTOR+/- mice, which was attributable in part to a reduced rate of basal protein synthesis. LPS decreased muscle protein synthesis in WT and mTOR+/- mice to the same extent. Reduced muscle protein synthesis in mTOR+/- mice under basal and LPS-stimulated conditions was associated with lower 4E-BP1 and S6K1 phosphorylation. LPS also decreased PRAS40 phosphorylation and increased phosphorylation of raptor and IRS-1 (Ser307) to the same extent in WT and mTOR+/- mice. Muscle atrogin-1 and MuRF1 mRNA content was elevated in mTOR+/- mice under basal conditions, implying increased ubiquitin-proteasome-mediated proteolysis, but the LPS-induced increase in these atrogenes was comparable between groups. Plasma insulin and IGF-I as well as tissue expression of TNFα, IL-6, or NOS2 did not differ between WT and mTOR+/- mice. Finally, whereas LPS impaired the ability of leucine to stimulate muscle protein synthesis and 4E-BP1 phosphorylation in WT mice, this inflammatory state rendered mTOR+/- mice leucine unresponsive. These data support the idea that the LPS-induced reduction in mTOR activity is relatively more important in regulating skeletal muscle mass in response to nutrient stimulation than under basal conditions.",
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Skeletal muscle protein balance in mTOR heterozygous mice in response to inflammation and leucine. / Lang, Charles H.; Frost, Robert A.; Bronson, Sarah K.; Lynch, Christopher J.; Vary, Thomas C.

In: American Journal of Physiology - Endocrinology and Metabolism, Vol. 298, No. 6, 01.06.2010.

Research output: Contribution to journalArticle

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T1 - Skeletal muscle protein balance in mTOR heterozygous mice in response to inflammation and leucine

AU - Lang, Charles H.

AU - Frost, Robert A.

AU - Bronson, Sarah K.

AU - Lynch, Christopher J.

AU - Vary, Thomas C.

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N2 - Sepsis and lipopolysaccharide (LPS) may decrease skeletal muscle protein synthesis by impairing mTOR (mammalian target of rapamycin) activity. The role of mTOR in regulating muscle protein synthesis was assessed in wild-type (WT) and mTOR heterozygous (+/-) mice under basal conditions and in response to LPS and/or leucine stimulation. No difference in body weight of mTOR+/- mice was observed compared with WT mice; whereas whole body lean body mass was reduced. Gastrocnemius weight was decreased in mTOR+/- mice, which was attributable in part to a reduced rate of basal protein synthesis. LPS decreased muscle protein synthesis in WT and mTOR+/- mice to the same extent. Reduced muscle protein synthesis in mTOR+/- mice under basal and LPS-stimulated conditions was associated with lower 4E-BP1 and S6K1 phosphorylation. LPS also decreased PRAS40 phosphorylation and increased phosphorylation of raptor and IRS-1 (Ser307) to the same extent in WT and mTOR+/- mice. Muscle atrogin-1 and MuRF1 mRNA content was elevated in mTOR+/- mice under basal conditions, implying increased ubiquitin-proteasome-mediated proteolysis, but the LPS-induced increase in these atrogenes was comparable between groups. Plasma insulin and IGF-I as well as tissue expression of TNFα, IL-6, or NOS2 did not differ between WT and mTOR+/- mice. Finally, whereas LPS impaired the ability of leucine to stimulate muscle protein synthesis and 4E-BP1 phosphorylation in WT mice, this inflammatory state rendered mTOR+/- mice leucine unresponsive. These data support the idea that the LPS-induced reduction in mTOR activity is relatively more important in regulating skeletal muscle mass in response to nutrient stimulation than under basal conditions.

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