Immobilization causing calf atrophy is due to which protein degradation pathway?

• A. Autophagy-lysosome degradation
• B. Polyubiquitination
• C. Apoptosis
• D. Necrosis

Answer: (B)

Disuse atrophy from immobilization mainly results from increased proteolysis of muscle proteins via the ubiquitin-proteasome system. Proteins targeted for degradation are marked with polyubiquitin chains, signaling them for destruction by the proteasome. This tagging and rapid breakdown of contractile proteins drives the calf muscle wasting seen with immobilization. Autophagy-lysosome degradation also contributes to turnover, but the specific process that labels proteins for proteasomal destruction in this situation is polyubiquitination. Apoptosis and necrosis are forms of cell death, not the primary pathways for degrading muscle proteins in disuse atrophy.