Effects of resistance training on expression of IGF-I splice variants in younger and older men

Abstract

Insulin-like growth factor-I (IGF-I) and its splice variants Insulin-like growth factor-I isoform Ea (IGF-IEa) and mechano growth factor (MGF) may play an important role in muscular adaptations to resistance training (RT) that may be modulated by ageing. It has been suggested that IGF-I induces cellular responses via AKT8 virus oncogene cellular homolog (Akt) and Extracellular signal-regulated kinase (Erk) signalling pathways. Therefore, resistance exercise-induced changes in skeletal muscle IGF-IEa and MGF messenger ribonucleic acid (mRNA), and MGF, Erk1/2, Akt and p70S6K protein expression were investigated before and after 21 weeks of RT in younger (YM, 20–34 yrs., n = 7) and older men (OM, 51–71 yrs., n = 10). Experimental resistance exercises (RE) of 5 × 10 repetition maximum leg presses were performed pre- and post-RT. Muscle biopsies were obtained before and 48 h after REs, to study the late response to muscle loading. The muscle proteins or mRNAs of interest were not systematically influenced by the REs or RT, except for MGF mRNA expression which was increased (p < .01) following RE before RT in OM. No differences were observed between YM and OM in any variables. This study demonstrated that basal levels or RE-induced responses in skeletal muscle MGF, Erk1/2, Akt and p70S6K protein levels or IGF-IEa and MGF mRNA expression did not differ between YM and OM, nor change systematically due to RT. Thus, ageing appears not to effect expression of the present signalling molecules involved in skeletal muscle hypertrophy.

Keywords:

• Mechano growth factor
• muscle hypertrophy
• gene expression
• cell signalling
• ageing

Acknowledgements

The authors thank Mr. Risto Puurtinen and Mrs. Aila Ollikainen for their help in data collection and analysis. We also thank Dr. Koutsilieris Lab (Department of Experimental Physiology, Medical School, National and Kapodistrian University of Athens, Greece) for providing the MGF (IGF-IEc) antibody and the very dedicated group of subjects and research assistants who made this project possible.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The Finnish Ministry of Education and Culture supported this research.