Which signaling molecule is activated by free radical signaling and regulates expression of muscle proteins and antioxidant enzymes?

• A. Nuclear factor kappa B
• B. Mitogen activated protein kinase
• C. AMPK
• D. PGC-1α

Answer: (A)

Free radical signaling acts as a stress cue in muscle and activates NF-κB, a transcription factor sensitive to reactive species. When ROS rise, the IKK complex phosphorylates IκB, marking it for degradation. Freed NF-κB then moves into the nucleus and binds to κB sites in DNA, turning on genes that increase the production of antioxidant enzymes (like MnSOD and other defenses) and also regulate muscle proteins involved in remodeling and turnover. This dual action helps muscle adapt to oxidative stress from exercise by boosting antioxidant capacity while coordinating changes in muscle protein content. While other pathways respond to stress or energy status and support adaptation in different ways, NF-κB’s redox-driven transcriptional program directly links free radical signals to both antioxidant enzyme expression and muscle protein regulation.