Tissue-specific effect of recombinant porcine growth hormone on expression of growth-related genes in the pig

Expression of GHR and PGC-lα in association with changes of MyHC isof orm types in longissimus muscle of Erhualian and Large White pigs (Sus scrofa) during postnatal growth

Myofibre composition in longissimus dorsi (LD) muscle of Erhualian (EHL) and Large White (LW) pigs was investigated by determining the ratios of mRNA abundances of four myosin heavy chain (MyHC) isoforms (MyHC I, MyHC 2a, MyHC 2x and MyHC 2b) using multiplex RT-PCR. The relationship between expression of growth hormone receptor (GHR) and peroxisome proliferator-activated receptor α coactivator-lα (PGC-lα) mRNAs and changes ofmyofibre type composition during postnatal growth from 3 to 180 days of age were analysed. At 3 days of age, proportions of MyHC I, 2a and 2x fibres were high while only a few MyHC 2b fibres were differentiated. Dramatic changes were observed from day 3 to day 20 with significantly decreased MyHC I, 2a and 2x fibres but abrupt increases in MyHC 2b fibres in both breeds of pigs. Breed difference was exhibited only from day 90, with higher MyHC 2b but less MyHC I and 2a expression in LW pigs. Developmental pattern of GHR mRNA expression in LD muscle coincided with that of MyHC 2b, with LW pigs expressing higher abundance of GHR mRNA. PGC-lα mRNA expression followed distinct patterns in the two breeds of pigs, a higher level of PGC-lα mRNA being expressed in LD muscle of EHL pigs, the breed that possessed more oxidative fibres (MyHC I and MyHC 2a).

Muscle type-specific responses of myoD and calpain 3 expression to recombinant porcine growth hormone in the pig

Sixteen castrated male Large White × Landrace pigs were employed to investigate the muscle type-specific changes of gene expression in response to recombinant porcine growth hormone (rpGH) administration. Pigs were injected intramuscularly with rpGH (4 mg/day, n = 8) or saline (n = 8) for 28 days. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the mRNA abundance of genes related to muscle growth in longissimus dorsi (LD) and semitendinosus (ST) muscles. Myofibre-type composition was characterised by the ratio of the expression of myosin heavy chain (MyHC) 1, 2a or 2b relative to 2x. The results showed that the relative myofibre-type composition of neither LD nor ST was affected by rpGH administration. rpGH administration did not induce significant changes in the abundances of myostatin and myogenin mRNA in both types of muscle. MyoD and calpain 3 mRNA were significantly increased after rpGH treatment in ST muscle, whereas the difference was not significant in LD muscle. A tendency of down-regulation was observed for PGC-1α mRNA expression in ST muscle of rpGH-treated group (P = 0.16). These results suggest that myoD, calpain 3 and probably PGC-1α may be involved in the mechanism of exogenous GH action on skeletal muscle growth; rpGH up-regulates mRNA expression of myoD and calpain 3 in a muscle type-specific manner, being more remarkable in ST than in LD, whereas no influences of rpGH on the mRNA expression of myostatin and myogenin were detected.