The adaptive response of ribosome content to aerobic and resistance exercise training

Abstract

Ribosomes are the essential machinery for cellular protein synthesis. Ribosome content is hypothesized to support muscle growth and is suggested that those with more ribosomes may better respond to resistance training. Aerobic training also elicits distinct physiological adaptations; however, no direct measures of ribosome content following aerobic training have been measured. Ribosomes interact with mitochondria for mitochondrial protein synthesis and import. Mitochondria may also provide cellular energy to ribosomes. We hypothesized that aerobic and resistance training would increase ribosome content and that ribosome content following aerobic training would correspond to changes in mitochondrial-related protein content and gene expression. Fourteen young men and women performed 6 weeks of single-legged aerobic followed by 10 weeks of bilateral resistance training. Muscle biopsies were taken following aerobic (Pre RT) and resistance training (Post RT) in the aerobically trained (EX) and control (CTL) legs. Pre RT, EX had greater COXIV staining intensity in Type 1 (1.17-fold; p=0.020) and Type 2 (1.22-fold; p=0.015) fibres compared to CTL; however, no differences in whole-muscle mitochondrial-related protein content or gene expression were observed (p>0.05). No differences in regulatory (UBF, Cyclin D1, TIF-1A, POLR-1B), cytosolic (45S, 5.8S, 18S, 28S rRNAs) or mitochondrial (12S rRNA) ribosome-related gene expression were observed (p>0.05), except for c-Myc (CTL>EX; p=0.034) and 5S rRNA (Pre RT CTL<Pre RT EX; p=0.076). When stratified for leg-lean soft tissue mass (LLSTM), legs with greater LLSTM had lower expression in 3/13 ribosome-related genes (p<0.10). When stratified for ΔLLSTM following resistance training, legs with the greatest ΔLLSTM had lower expression in 11/13 ribosome-related genes prior to (p<0.10) and less change or decrease in expression in 9/13 genes following resistance training (p<0.05). These results indicate that baseline ribosome content was sufficient to support aerobic adaptations (capillarization, VO2 peak) that were previously observed and that ribosome’s efficiency, rather than content, is likely more important to support increases in muscle hypertrophy following resistance training.