Glucocorticoid receptor and ubiquitin expression after repeated eccentric exercise

Area of Science:

• Exercise Physiology
• Muscle Biology
• Molecular Biology

Background:

• Eccentric exercise induces muscle proteolysis, a process that breaks down muscle proteins.
• Repeated bouts of exercise may attenuate this muscle damage response.
• Understanding the molecular mechanisms is key to mitigating exercise-induced muscle injury.

Purpose of the Study:

• To investigate the impact of repeated eccentric exercise bouts on key molecular markers of muscle proteolysis.
• To determine if prior eccentric exercise exposure reduces subsequent muscle damage and strength loss.
• To examine changes in ubiquitin (UBI), E2 conjugating enzyme, 20S proteasome, and glucocorticoid receptor (GR) expression.

Main Methods:

• Nine male participants performed two identical eccentric exercise bouts (BT1 and BT2) separated by three weeks.
• Muscle biopsies and blood samples were collected pre- and post-exercise (6 and 24 hours).
• Muscle strength, soreness, caspase-3 activity, and molecular markers were assessed.

Main Results:

• Both exercise bouts caused strength decrements and soreness, but BT1 effects were more pronounced.
• Serum cortisol (CORT) and skeletal muscle troponin-I (sTnI) levels increased post-exercise, with higher elevations after BT1.
• UBI, E2, 20S, and GR mRNA and protein levels, as well as caspase-3 activity, increased post-exercise, particularly after BT1.

Conclusions:

• An initial bout of eccentric exercise leads to muscle strength loss and myofibrillar protein reduction, potentially via apoptosis and GR-mediated UBI-proteolytic pathway activation.
• A repeated bout of eccentric exercise appears to temper these negative effects, indicating an adaptation to exercise stress.
• These findings highlight the protective effect of prior eccentric exercise exposure on skeletal muscle.