Translation Initiation Signaling in Myotubes from Normal and Low Birth Weight Neonatal Pigs

Abstract

Skeletal muscle growth is impaired in low birth weight (LBWT) compared to normal birth weight (NBWT) neonates. Our previous studies showed that skeletal muscle protein synthesis is lower and IGF‐І receptor expression is higher in LBWT than NBWT neonatal pigs. The objective of the current study was to investigate the effect of IGF‐І stimulation on the regulation of translation initiation signaling in primary myotubes from LBWT and NBWT neonatal pigs. Primary satellite cells were isolated from Longissimus dorsi muscle of male LBWT and NBWT pigs (n = 4). Cells were allowed to proliferate to ~80% confluence, and differentiate to form myotubes. At 2.5 day of differentiation, myotubes were treated with IGF‐І at physiological levels (0, 25 and 50 ng/ml) after fasting in serum‐free media for 3 h. Myotubes were harvested in lysis buffer, and the expression of translation initiation signaling proteins were measured by Western blotting. IGF‐І stimulation significantly increased protein kinase B (PKB/Akt), eukaryotic initiation factor 4E binding protein (4EBP1) and ribosomal protein S6 kinase beta‐1 (S6K1) phosphorylation in myotubes from LBWT and NBWT pigs (P < 0.05). However, total S6K1 expression was significantly lower (P < 0.05) and 4EBP1 phosphorylation was higher (P = 0.09) in myotubes of LBWT compared with NBWT pigs. Our data suggest IGF‐І stimulation does not differentially regulate translation initiation signaling in myotubes from LBWT and NBWT pigs. S6K1 expression is reduced in primary myotubes from LBWT pigs, which likely indicates impaired translation initiation signaling in myotubes from LBWT compared with NBWT pigs.