Cysteine Suppresses Oxidative Stress-Induced Myofibrillar Proteolysis in Chick Myotubes

The effects of cysteine as an antioxidant nutrient on change in protein modification and myofibrillar proteolysis in chick myotubes by induction of oxidative stress by H2O2 treatment were investigated. Myotubes were treated for 1 h with H2O2 (1 mM). After this treatment, the H2O2 was removed and the cells were cultured in cysteine (0.1 and 1 mM) containing serum-free medium for 24 h. Protein carbonyl content as an index of protein modification and Nτ-methylhistidine release as an index of myofibrillar proteolysis were increased at 24 h after H2O2 treatment, and the increment was reduced by cysteine. Calpain, proteasome and cathepsin (B+L and D) activities were increased at 24 h after H2O2 treatment, and the increment was also reduced by cysteine. These results indicate that cysteine suppresses protein modification by oxidative stress, resulting in a decrease of protease acitivities, finally resulting in a decrease in myofibrillar proteolysis in chick myotubes.