Myofibrillar proteolysis in chick myotubes during oxidative stress

Changes in protein conformation and proteolysis in chick myotubes in response to the induction of oxidative stress by H2O2 treatment were studied. Myotubes were treated for 1 h with H2O2. After this treatment, the H2O2 was removed and the cells were cultured in serum-free medium for 6 and 24 h. Protein carbonyl content, as an index of protein modification, was increased at 6 and 24 h after H2O2 treatment. N(tau)-methylhistidine release, as an index of myofibrillar proteolysis, was also increased at 6 and 24 h after H2O2 treatment. Calpain and cathepsin (B+L and D) activities were increased at 24 but not 6 h after H2O2 treatment. Proteasome activity was increased at 6 and 24 h after H2O2 treatment. These results indicate that oxidative stress increased proteasome activity and caused an increase in myofibrillar proteolysis during short-term incubation, whereas it increased calpain, proteasome and cathepsin activities during long-term incubation, finally resulting in an increase of myofibrillar proteolysis in chick myotubes.