Effects Of Hypoxia On Dystrophin In Rat Skeletal Muscle After Eccentric Exercise

Objective:The purpose of this study was firstly to explore the effects of hypoxia on Dystrophin and related signal pathways after acute eccentric exercise; and secondly to validate whether hypoxia regulates Dystrophin by this signal pathway. The results would provide an important reference for the HiLo.Methods:Study I:70 male Sprague-Dawley rats were randomly divided into 7 groups including sedentary group、normoxia rested for 24H、48H、72H groups after eccentric exercise and hypoxia exposed for 24H、48H、72H groups after eccentric exercise with 12.7% 02. All exercise groups went through different recovery protocols after an acute eccentric exercise. Study II:72 male Sprague-Dawley rats were randomly divided into 9 groups including sedentary group, ERK inhibitor used for 24H、48H groups, ERK placebo used for 24H、48H groups, AKT inhibitor used for 24H、48H groups and AKT placebo used for 24H、48H groups. Except the sedentary group, all the other groups were exposed for hypoxia after acute eccentric exercise, both studies were used immunohistochemistry、Western blot and qRT-PCR to measure the Dystrophin level and related signal pathway factors in each group.Results:(1) in hypoxia exposed groups, The ratio of EBD-positive cell were significantly higher, lower, and higher by comparing with normoxia rested groups at 24H,48H, and 72H respectively. (2) The expression of Dystrophin protein was not statistically different after acute eccentric exercise in all groups. The expression of Dystrophin mRNA was significantly decreased after exercise, and the expression in hypoxia exposed groups were lower than that of normoxia rested groups. There were significant differences in ERK and AKT/mTOR pathways, and the proteins and phosphorylation of ERK pathway in hypoxic exposed group showed the same trend as Dystrophin mRNA. (3) Injecting MEK target inhibitors blocked ERK pathway at 48H after exercise, and it can offset the regulation of hypoxia on Dystrophin mRNA expression by ERK1/2 signal pathway. Injecting AKT target inhibitors blocked AKT pathway at 24H after exercise, it didn’ t change the expression of Dystrophin and Dystrophin mRNA significantly.Conclusion:(1) After eccentric exercise, the acute hypoxic exposure can aggravate the damage of sarcolemma. with the extension of hypoxic exposure time, the body adapted to the situation for a short time and a part of the integrity of sarcolemma was recovered. (2) Whether in normoxia or hypoxic, the protein content of Dystrophin was not significantly changed after eccentric exercise, but the Dystrophin mRNA was decreased significantly. (3) Hypoxia regulated the effect of hypoxic on Dystrophin mRNA and protein expression though ERKl/2 signal pathway. ERKl/2 signal pathway was a negative regulator in Dystrophin mRNA expression. (4) The AKT/mTOR signal pathway was not a dominant pathway in regulating the Dystrophin protein expression under hypoxia.