H sub(2)O sub(2) Exposure Affects Myotube Stiffness and Actin Filament Polymerization

Skeletal muscles often experience oxidative stress in anaerobic metabolism and ischemia-reperfusion. This paper reports how oxidative stress affects the stiffness of cultured murine myotubes and their actin filaments polymerization dynamics. H sub(2)O sub(2) was applied as an extrinsic oxidant to C2C12 myotubes. Atomic force microscopy results showed that short exposures to H sub(2)O sub(2) apparently increased the stiffness of myotubes, but that long exposures made the cells softer. The turning point seemed to take place somewhere between 1 and 2 h of H sub(2)O sub(2) exposure. We found that the stiffness change was probably due to actin filaments being favored for depolymerization after prolong H sub(2)O sub(2) treatments, especially when the exposure duration exceeded 1 h and the exposure concentration reached 1.0 mM. Such depolymerization effect was associated with the down-regulation of thymosin beta 4, as well as the up-regulation of both cofilin2 and profilin1 after prolong H sub(2)O sub(2) treatments.