Department of Physiological Sciences

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Browsing Department of Physiological Sciences by browse.metadata.advisor "Durcan, Peter J."

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    Investigation of myostatin and relevant regulators during muscle regeneration after an acute bout of eccentric exercise
    (Stellenbosch : Stellenbosch University, 2014-12) Conradie, Johannes David; Myburgh, Kathryn H.; Durcan, Peter J.; Stellenbosch University. Faculty of Science. Dept. of Physiological Sciences.
    ENGLISH ABSTRACT: The aim of this study was to investigate the powerful muscle regulator, myostatin, and its regulators in response to an acute bout of plyometric training. The participants were recruited and screened by characterization by means of isometric force production tests, baseline blood creatine kinase levels and VO2 max results. The selected individuals (n=15) were subjected to a baseline muscle biopsy for comparative purposes. The study made use of plyometric jumping, as source of eccentric exercise, to serve as an exercise intervention after which muscle biopsies (4 hours post and 24 hours post) and blood draw (4 hours post, 24 hours post and 48 hours post) samples were taken. Maximal voluntary isometric contractions of the knee extensors were also measured immediately after the exercise protocol and after 1 week recovery. Creatine kinase (CK) analysis on the serum samples was used to conclude muscle damage. The muscle biopsy samples were used for protein quantification (Western blot) and gene expression assessment (semi-quantitative and real-time PCR). The results showed decreased force production immediately after eccentric exercise (p < 0.05), while returning back to baseline values at 1 week post exercise and CK results showed a significant increases at 4 hours (p<0.05), 24 hours (p<0.001) and 48 hours (p<0.01) after exercise. There were no significant differences in myostatin precursor protein (43 kDa), phosphorylated Smad2,3, Smad7 or activin receptor IIb in response to eccentric exercise. However, the follistatin protein was increased at both 4 hours and 24 hours after exercise (p<0.01). RNA analysis of the extracellular matrix (ECM) protein, decorin, revealed the existence of the splice variants A1 and A2 in human skeletal muscle. The RT-PCR analysis (n=4) of these variants showed no significant difference when comparing pre- to post-exercise. The decorin core protein was also investigated by means of antibody probing and results revealed the need for ABC chondroitinase enzyme treatment before immunoblotting of human skeletal muscle samples. The results concerning knee extensor force reduction and circulating creatine kinase showed the effectiveness of plyometric jumping in producing skeletal muscle damage in the lower limbs of unfit individuals, unaccustomed to eccentric exercise. In conclusion, myostatin, and its associated signalling cascade, are not activated in early muscle regeneration, but follistatin is increased during this phase possibly aiding and initiating the muscle repair process. Future studies: Variants of decorin are expressed in human skeletal muscle, increasing the complexity that should be taken into account in studies concerning the regulation of decorin in a human model. Investigation into myostatin protein at different post-translational levels needs more clarification. Published methods and materials used in different laboratories are not consistent and investigators should attempt to standardise protocols in order to compare results between studies more effectively. Of importance, these results show that the myostatin at protein level report different results compared to mRNA analysis and that more investigation into myostatin regulatory factors, with special reference to follistatin and decorin, is needed in future human models.