Which degradation pathway is primarily responsible for disuse muscle atrophy leading to muscle protein loss?

Which degradation pathway is primarily responsible for disuse muscle atrophy leading to muscle protein loss?

• A. Autophagy-lysosome pathway
• B. Apoptosis
• C. Necrosis
• D. Ubiquitin-proteasome pathway

Answer: (D)

The degradation pathway most responsible for disuse muscle atrophy is the ubiquitin-proteasome system. When muscles are unused, signaling through the IGF-1/AKT pathway declines, allowing FoxO transcription factors to enter the nucleus and upregulate muscle-specific E3 ubiquitin ligases such as MuRF1 and atrogin-1. These ligases tag contractile proteins and other sarcomeric proteins with ubiquitin, marking them for destruction by the 26S proteasome and leading to loss of muscle proteins and fiber atrophy. The autophagy-lysosome pathway also participates in protein turnover, but for disuse atrophy the ubiquitin-proteasome pathway is the primary driver. Apoptosis and necrosis are cell death processes, not the main mechanism of muscle protein loss in disuse.

The degradation pathway most responsible for disuse muscle atrophy is the ubiquitin-proteasome system. When muscles are unused, signaling through the IGF-1/AKT pathway declines, allowing FoxO transcription factors to enter the nucleus and upregulate muscle-specific E3 ubiquitin ligases such as MuRF1 and atrogin-1. These ligases tag contractile proteins and other sarcomeric proteins with ubiquitin, marking them for destruction by the 26S proteasome and leading to loss of muscle proteins and fiber atrophy. The autophagy-lysosome pathway also participates in protein turnover, but for disuse atrophy the ubiquitin-proteasome pathway is the primary driver. Apoptosis and necrosis are cell death processes, not the main mechanism of muscle protein loss in disuse.