Chronic Calorie Restriction Downregulates Skeletal Muscle mTORC1 Signaling Independent of Dietary Protein Level and Associated microRNA Expression in Male Rats
Abstract
Short‐term (5–10 days) calorie restriction downregulates muscle protein synthesis, with consumption of a high protein‐based diet attenuating this decline. Benefit with increased protein intake is likely due to maintenance of amino acid‐mediated anabolic signaling through the mechanistic target of rapamycin complex 1 (mTORC1) pathway. However, the effects of chronic caloric restriction and high protein diets on mTORC1 signaling and the expression of microRNA (miR) that regulates this pathway remain unclear. This study determined skeletal muscle mTORC1 and miR responses to a 16 week ad libitum (AL; ~25 g/d) or calorie restricted (CR; 40%; ~15 g/d) standard (10%; ~96 g/kg) or high (32%; ~327 g/kg) protein milk‐based diet in 12‐wk old male Sprague Dawley rats. Crude and clear mixed gastrocnemius homogenate protein concentrations (BSA Protein Assay) were used to calculate protein content, an index of hypertrophy. Immunoblotting was performed to quantify total protein and phosphorylation status of mTORC1 signaling proteins. Expression of miR‐99a‐5p, miR‐100‐5p, miR‐128a‐3p, miR‐133a‐3p, miR‐199a‐3p, and miR‐221‐3p were determined using RT‐qPCR. Data were expressed as fold change (mean ± SEM), compared to AL 10% as the study control. Protein content was higher (P P r = 0.611, r2 = 0.372, P Ser473, mTORSer2448, rpS6Ser235/236 and p70S6KThr389 were 1.72 ± 0.11, 1.41 ± 0.08, 3.47 ± 0.05, and 1.95 ± 0.05 fold lower (P < 0.05) for CR than for AL. No effects were observed for dietary protein level on mTORC1 signaling protein, and neither energy nor protein intake altered skeletal muscle miR expression. These data show that prolonged caloric restriction downregulates mTORC1 intracellular signaling, independent of skeletal muscle miR known to regulate mTORC1 protein expression. Consuming a high protein does not appear to attenuate the negative effects of chronic caloric restriction on the intracellular regulation of skeletal muscle mass.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Apr 01, 2016
- Source ID
- 10.1096/fasebj.30.1_supplement.1244.4
Entities
People
- Andrew J Young
- Donato A Rivas
- James P. Mcclung
- Lee M. Margolis
- Maria Berrone
- Roger A. Fielding
- Stefan M. Pasiakos
- Yassine Ezzyat
Organizations
- Tufts University
- United States Army Medical Research and Development Command
- United States Army Research Institute of Environmental Medicine
- United States Department of Agriculture