Regulation of antioxidant enzyme gene expression in response to oxidative stress and during differentiation of mouse skeletal muscle

Various properties of skeletal muscle, including high metabolic activity an d high levels of heme-containing proteins, render it particularly susceptib le to free radical injury. Indeed, cellular injury from reactive oxygen spe cies (ROS) has been implicated in many muscle disorders. Thus muscle cell s urvival is critically dependent on the ability of the cell to respond to pe riods of oxidative stress. To investigate this important homeostatic respon se, we studied the effect of oxidative challenges on the expression of gene s encoding the antioxidant enzymes Cu,Zn-superoxide dismutase (CuZnSOD), Mn -superoxide dismutase (MnSOD), glutathione peroxidase (GPx), and catalase ( CAT) in myotube cultures. Using Northern blot analysis, we found that treat ment with the pro-oxidant paraquat resulted in time- and dose-dependent inc reases of transcript levels that were greatest for GPx and CAT (similar to 4-5 fold). CuZnSOD and MnSOD transcripts were also increased, albeit more m odestly (similar to 2-3 fold). Transcript levels were also induced by treat ment of the cells with two other pro-oxidants, menadione and H2O2, and corr elated with the level of oxidative injury to the cells, measured as protein carbonyl group formation. Activities of all of the enzymes increased in re sponse to the oxidative challenges, although the magnitudes of the increase s were less robust than the increases of the respective transcript levels. In studying the effect of cellular differentiation on antioxidant gene expr ession and susceptibility to oxidative stress, we found that pro-oxidant tr eatment resulted in greater oxidative injury to differentiated myotubes tha n to undifferentiated myoblasts. Furthermore, the increased susceptibility of myotubes correlated with decreased antioxidant defenses-as muscle cells differentiated, both transcript and activity levels of antioxidant enzymes decreased. These data suggest that muscle cells regulate antioxidant defens es in response to oxidative stress and cellular differentiation. (C) 1999 E lsevier Science Inc.