Effects of treadmill exercise and training frequency on anabolic signaling pathways in the skeletal muscle of aged rats

Exp Gerontol. 2012 Jan;47(1):23-8. doi: 10.1016/j.exger.2011.10.003. Epub 2011 Oct 12.

Abstract

Physical exercise is the most effective intervention against sarcopenia of aging; however, the cellular and molecular mechanisms mediating training-induced adaptations are not yet completely understood. Furthermore, it is unclear whether exercise training initiated late in life affects myocyte anabolic signaling in a dose-dependent manner. Hence, we sought to investigate the effects of treadmill exercise and training frequency on anabolic pathways, including insulin signaling, in the skeletal muscle of old rats. Aged (14-16-month-old) male Wistar rats were trained on a treadmill for 3 (EX3) or 5 days/week (EX5) during 8 weeks and compared with age-matched sedentary controls (SED). Four-month-old rats were used as young controls (YC). Protein expression levels of insulin receptor (IR), insulin receptor substrate 1 (IRS-1), activated (phosphorylated) mammalian target of rapamycin (p-mTOR) and glucose transporter GLUT4 were determined in quadriceps muscle extracts via immunoblotting. Mitochondrial cytochrome c oxidase (COX) activity was assessed by histochemical staining, while electron microscopy was employed to quantify the sarcomere volume (V(src)). Body weight (BW) increased, whereas muscle weight (MW) and V(src) decreased with age. EX5, but not EX3 increased MW and V(src), without affecting BW. The expression of IR and GLUT4 was higher in SED rats relative to the YC group. Conversely, protein levels of IRS-1 and p-mTOR as well as COX activity were reduced in advanced age. Compared with SED rats, EX3 animals displayed reduced IR expression and increased IRS-1 levels and COX activity. The expression of GLUT 4 and p-mTOR was unaffected by EX3. EX5 up-regulated IRS-1 and p-mTOR expression and COX activity, while decreasing GLUT4 levels, with no effect on IR expression. In summary, substantial impairments in muscle anabolic pathways, including insulin signaling, were detected in aged sedentary rats. These changes were ameliorated by exercise training, concomitant with improvements in muscle trophism. Benefits were more evident in rats trained for 5 days/week, suggesting that physical exercise initiated late in life affects anabolic signaling in a dose-dependent manner.

MeSH terms

  • Animals
  • Body Weight
  • Electron Transport Complex IV / metabolism
  • Glucose Transporter Type 4 / metabolism
  • Insulin Receptor Substrate Proteins / metabolism
  • Male
  • Microscopy, Electron
  • Mitochondria, Muscle / metabolism
  • Motor Activity / physiology
  • Physical Conditioning, Animal / physiology*
  • Quadriceps Muscle / metabolism
  • Quadriceps Muscle / physiology*
  • Quadriceps Muscle / ultrastructure
  • Rats
  • Rats, Wistar
  • Sarcopenia / metabolism
  • Sarcopenia / pathology
  • Sarcopenia / physiopathology*
  • Signal Transduction / physiology*
  • TOR Serine-Threonine Kinases / metabolism

Substances

  • Glucose Transporter Type 4
  • Insulin Receptor Substrate Proteins
  • Irs1 protein, rat
  • Slc2a4 protein, rat
  • Electron Transport Complex IV
  • TOR Serine-Threonine Kinases
  • mTOR protein, rat