Oxidative stress enhances myofibrillar protein degradation via calpain and caspase‐3

Oxidative stress has been shown to accelerate proteolysis and muscle fiber atrophy during periods of prolonged skeletal muscle inactivity. Currently, the mechanisms connecting oxidative stress to muscle protein degradation remain unknown. In this regard, calpain and caspase‐3 are proteases capable of degrading select myofilament proteins in skeletal muscle. However, it is unclear if oxidation of myofibrillar proteins increases recognition and degradation by these key proteases. Therefore, we tested the hypothesis that oxidative modification of myofibrillar proteins increases their susceptibility to degradation by calpain and caspase‐3. Myofibrillar proteins were isolated from skeletal muscle and exposed to in vitro oxidation to produce varying levels of protein modification. Modified proteins were then independently incubated with active calpain I, calpain II, or caspase‐3 and protein degradation was assessed via peptide mapping. Our results reveal that increased protein oxidation results in a stepwise escalation in the degradation of myofibrillar proteins by calpain I, calpain II, and caspase‐3. These findings provide a link to connect oxidative stress with accelerated proteolysis during disuse muscle atrophy. Supported by NIH RO1 HL087839 awarded to SKP