Protein turnover during skeletal muscle hypertrophy

Area of Science:

• Physiology
• Molecular Biology
• Exercise Science

Background:

• Skeletal muscle hypertrophy is a complex adaptation to mechanical stimuli.
• Previous research suggested increased protein synthesis and decreased degradation drive hypertrophy.
• The role of protein turnover and isotope recycling in hypertrophy requires clarification.

Purpose of the Study:

• To re-evaluate the mechanisms underlying skeletal muscle hypertrophy.
• To investigate the contribution of protein synthesis and degradation to muscle growth.
• To assess the impact of isotope recycling on turnover measurements during hypertrophy.

Main Methods:

• Analysis of protein turnover rates in various hypertrophy models (denervation, increased work, weight addition).
• Utilizing isotope labeling techniques to measure protein synthesis and degradation.
• Examining models such as rat soleus and plantaris, denervated hemidiaphragm, and chicken anterior latissimus dorsi.

Main Results:

• Early interpretations of increased synthesis and decreased degradation were likely inaccurate due to isotope recycling.
• Both protein synthesis and degradation are significantly increased during muscle hypertrophy.
• In chicken anterior latissimus dorsi, increased turnover accounts for up to two-thirds of elevated synthesis, with only one-third contributing to net growth.

Conclusions:

• Skeletal muscle hypertrophy involves a substantial increase in both protein synthesis and degradation.
• Isotope recycling complicates the interpretation of protein turnover measurements.
• A significant portion of increased protein synthesis during hypertrophy is associated with elevated turnover rather than net protein accretion.