J Physiol. 2003 Feb 15;547(Pt 1):2.
Expression of IGF-I splice variants in young and old human skeletal muscle after high resistance exercise.
Hameed M, Orrell RW, Cobbold M, Goldspink G, Harridge SD.
Department of Physiology, Royal Free and University College Medical School, Rowland Hill Street, London NW3 2PF, UK.
The mRNA expression of two splice variants of the insulin-like growth factor-I (IGF-I) gene, IGF-IEa and mechano growth factor (MGF), were studied in human skeletal muscle. Subjects (eight young, aged 25-36 years, and seven elderly, aged 70-82 years) completed 10 sets of six repetitions of single legged knee extensor exercise at 80 % of their one repetition maximum. Muscle biopsy samples were obtained from the quadriceps muscle of both the control and exercised legs 2.5 h after completion of the exercise bout. Expression levels of the IGF-I mRNA transcripts were determined using real-time quantitative RT-PCR with specific primers. The resting levels of MGF were significantly (approximately 100-fold) lower than those of the IGF-IEa isoform. No difference was observed between the resting levels of the two isoforms between the two subject groups. High resistance exercise resulted in a significant increase in MGF mRNA in the young, but not in the elderly subjects. No changes in IGF-IEa mRNA levels were observed as a result of exercise in either group. The mRNA levels of the transcription factor MyoD were greater at rest in the older subjects (P < 0.05), but there was no significant effect of the exercise bout. Electrophoretic separation of myosin heavy chain (MHC) isoforms showed the older subjects to have a lower (P < 0.05) percentage of MHC-II isoforms than the young subjects. However, no association was observed between the composition of the muscle and changes in the IGF-I isoforms with exercise. The data from this study show an attenuated MGF response to high resistance exercise in the older subjects, indicative of age-related desensitivity to mechanical loading. The data in young subjects indicate that the MGF and IGF-IEa isoforms are differentially regulated in human skeletal muscle.
PMID: 12562960 [PubMed - indexed for MEDLINE]
Eur J Appl Physiol. 2008 Feb;102(3):253-63. Epub 2007 Oct 17. Links
Mechanical stimuli of skeletal muscle: implications on mTOR/p70s6k and protein synthesis.
Zanchi NE, Lancha AH Jr.
Laboratory of Applied Nutrition and Metabolism, Physical Education and Sport School, University of São Paulo, Av. Prof. Mello Moraes, 65, PO Box 05508-900, São Paulo, SP, Brazil. neloz@ig.com.br
The skeletal muscle is a tissue with adaptive properties which are essential to the survival of many species. When mechanically stimulated it is liable to undergo remodeling, namely, changes in its mass/volume resulting mainly from myofibrillar protein accumulation. The mTOR pathway (mammalian target of rapamycin) via its effector p70s6k (ribosomal protein kinase S6) has been reported to be of importance to the control of skeletal muscle mass, particularly under mechanical stimulation. However, not all mechanical stimuli are capable of activating this pathway, and among those who are, there are differences in the activation magnitude. Likewise, not all skeletal muscle fibers respond to the same extent to mechanical stimulation. Such evidences suggest specific mechanical stimuli through appropriate cellular signaling to be responsible for the final physiological response, namely, the accumulation of myofibrillar protein. Lately, after the mTOR signaling pathway has been acknowledged as of importance for remodeling, the interest for the mechanical/chemical mediators capable of activating it has increased. Apart from the already known MGF (mechano growth factor), some other mediators such as phosphatidic acid (PA) have been identified. This review article comprises and discusses relevant information on the mechano-chemical transduction of the pathway mTOR, with special emphasis on the muscle prote
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Response of growth and myogenic factors in human skeletal muscle to strength training.
Liu Y, Heinichen M, Wirth K, Schmidtbleicher D, Steinacker JM.
Section of Sports and Rehabilitation Medicine, Department of Cardiology, University of Ulm, Ulm, Germany. yuefei.liu@uniklinik-ulm.de
OBJECTIVE: To investigate the response to different strength training techniques of growth and myogenic factors in human skeletal muscle, with particular emphasis on satellite cell (SC) activation. METHODS: 24 volunteers were divided into two groups and performed a 6-week strength training (group A trained with maximum contraction and group B had training combined with maximum contractions, ballistic movement and stretching-shortening cycles). Muscle biopsies were obtained from triceps brachii 3 days before and 7 days after training. For estimating gene expression of insulin-like growth factor (IGF-1), mechano growth factor (MGF), MyoD and myogenin, real-time RT-PCR was performed. RESULTS: In group A, there was an increase in the 1 repeat maximum (1RM), but no change in V(max) (maximum movement velocity) and an increase in MHC (myosin heavy chain) IIa and a decrease in MHC IIx; in group B both 1RM and V(max) increased significantly along with an increase in MHC IIa and a decrease in MHC I. The MGF gene expression increased significantly in both groups (by 1160% and 59%, respectively), and IGF-1 increased only in group A (by 335%). MyoD and myogenin gene expression increased in group A (by 107% and 94%, respectively) but did not change in group B. CONCLUSIONS: Response of growth and myogenic factors occurs during muscular adaptation to a prolonged training, and strength training with different strategies caused different responses with respect to gene expression of these factors. These results suggest that SC activation is involved in the muscular adaptation process to training and might be attributed to MHC isoform transition.
PMID: 18308879 [PubMed - indexed for MEDLINE
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