Developmental regulation of the activation of signaling components leading to translation initiation in skeletal muscle of neonatal pigs

Am J Physiol Endocrinol Metab. 2006 Oct;291(4):E849-59. doi: 10.1152/ajpendo.00069.2006. Epub 2006 Jun 6.


The rapid growth of neonates is driven by high rates of skeletal muscle protein synthesis. This high rate of protein synthesis, which is induced by feeding, declines with development. Overnight-fasted 7- and 26-day-old pigs either remained fasted or were refed, and the abundance and phosphorylation of growth factor- and nutrient-induced signaling components that regulate mRNA translation initiation were measured in skeletal muscle and liver. In muscle, but not liver, the activation of inhibitors of protein synthesis, phosphatase and tensin homolog deleted on chromosome 10, protein phosphatase 2A, and tuberous sclerosis complex 1/2 increased with age. Serine/threonine phosphorylation of the insulin receptor and insulin receptor substrate-1, which downregulates insulin signaling, and the activation of AMP-activated protein kinase, an inhibitor of protein synthesis, were unaffected by age and feeding in muscle and liver. Activation of positive regulators of protein synthesis, mammalian target of rapamycin (mTOR), ribosomal protein S6 kinase 1 (S6K1), and eIF4E-binding protein-1 (4E-BP1) decreased with age in muscle but not liver. Feeding enhanced mTOR, S6K1, and 4E-BP1 activation in muscle, and this response decreased with age. In liver, activation of S6K1 and 4E-BP1, but not mTOR, was increased by feeding but was unaffected by age. Raptor abundance and the association between raptor and mTOR were greater in 7- than in 26-day-old pigs. The results suggest that the developmental decline in skeletal muscle protein synthesis is due in part to developmental regulation of the activation of growth factor and nutrient-signaling components.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • AMP-Activated Protein Kinases
  • Age Factors
  • Animals
  • Animals, Newborn
  • Immunoblotting
  • Insulin / metabolism*
  • Insulin Receptor Substrate Proteins
  • Liver / metabolism
  • Multienzyme Complexes / metabolism
  • Muscle Proteins / biosynthesis
  • Muscle Proteins / metabolism*
  • Muscle, Skeletal / metabolism
  • Muscle, Skeletal / physiology*
  • PTEN Phosphohydrolase / metabolism
  • Phosphoprotein Phosphatases / metabolism
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Protein Biosynthesis / physiology*
  • Protein Kinases / metabolism
  • Protein Phosphatase 2
  • Protein Serine-Threonine Kinases / metabolism
  • Receptor, Insulin / metabolism
  • Ribosomal Protein S6 Kinases / metabolism
  • Signal Transduction / physiology*
  • Swine / metabolism
  • Swine / physiology*
  • TOR Serine-Threonine Kinases
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins / metabolism


  • Insulin
  • Insulin Receptor Substrate Proteins
  • Multienzyme Complexes
  • Muscle Proteins
  • Phosphoproteins
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins
  • Protein Kinases
  • Receptor, Insulin
  • Protein Serine-Threonine Kinases
  • Ribosomal Protein S6 Kinases
  • TOR Serine-Threonine Kinases
  • AMP-Activated Protein Kinases
  • Phosphoprotein Phosphatases
  • Protein Phosphatase 2
  • PTEN Phosphohydrolase