Browsing by Author "Zhu, Haibo"

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    Diminished satellite cell fusion and S6K1 expression in myotubes derived from skeletal muscle of low birth weight neonatal pigs
    Chen, Ying; Zhu, Haibo; McCauley, Sydney R.; Zhao, Lidan; Johnson, Sally E.; Rhoads, Robert P.; El-Kadi, Samer Wassim (The American Physiological Society, 2017-02-09)
    Low birth weight (LBWT) is consistently associated with impaired postnatal muscle growth in mammals. Satellite cell (SC)‐mediated myonuclear incorporation precedes protein accumulation in the early stages of postnatal muscle development and growth. The objective of this study was to investigate proliferation and differentiation of SCs and the regulation of protein synthesis signaling in response to insulin‐like growth factor (IGF)‐I stimulation in SC‐derived myotubes of LBWT neonatal pigs. SCs isolated from Longissimus dorsi muscle of LBWT and NBWT pigs (3‐d‐old, n = 8) were cultured and induced to proliferate and differentiate to myotubes in vitro. On day 3 of differentiation, myotubes were fasted in serum‐free media for 3 h and treated with human recombinant R³‐insulin‐like growth factor‐I (rh IGF‐I) at 0, 25, and 50 ng × mL⁻¹ for 30 min. There was no difference in proliferation rates of SCs from LBWT and NBWT pigs. However, LBWT SC fusion was 15% lower (P ≤ 0.05) without a difference in MyoD or myogenin mRNA expression in comparison with NBWT pigs, suggesting SCs are not intrinsically different between the two groups. IGF‐Ι stimulation at physiological concentrations activated downstream effectors of mTOR similarly in myotubes from LBWT and NBWT pigs. However, abundance of ribosomal protein S6 kinase 1(S6K1) was lower in myotubes of LBWT compared to their NBWT siblings (P ≤ 0.05). These results indicate that the modest reduction in SC fusion and S6K1 expression are not the major contributors to the impaired postnatal muscle growth of LBWT pigs.
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    Muscle Growth and Development in Intrauterine Growth Restricted Pigs
    Zhu, Haibo (Virginia Tech, 2015-03-16)
    Intrauterine growth restriction causes impaired growth and development of mammalian fetus, and leads to long-term negative effect on postnatal growth. Among domestic animals, pigs exhibit the most severe naturally occurring IUGR and reduced postnatal muscle growth. The objectives of this research project were to: 1) determine muscle stem cell characteristics in IUGR pigs; 2) determine how intrauterine growth restriction alters protein deposition in skeletal muscle; 3) investigate whether branched-chain amino acids (BCAA) are able to enhance protein synthesis in intrauterine growth restricted (IUGR) pig muscle. Newborn piglets were considered normal body weight (NBWT) or IUGR when birth weight was within ± 0.5 SD and -2 SD of litter average respectively. Muscle satellite cell numbers, believed to be the major nuclei source for postnatal muscle growth, were lower in newborn IUGR pigs which could result in reduced muscle hypertrophy potential. In addition, cultures derived from IUGR muscle satellite cells had a lower fusion percentage. Fewer satellite cells and impaired differentiation ability may contributor to impaired muscle growth in these pigs. Protein synthesis rate was significantly lower in IUGR pig hindquarter in the first hour after feeding, but BCAA supplementation had no effect on protein synthesis in IUGR pigs. Further, eukaryotic translation initiation factor 4E (eIF4E) expression is down regulated in IUGR pig muscle. These results suggest that impaired translation initiation may provide a plausible explanation for the lower protein synthesis rates observed in IUGR pigs. Overall, reduced muscle stem cell number and changes in their activity, as well as impaired translation initiation may be important explanations for compromised postnatal muscle growth in intrauterine growth restricted pigs.