Exploration and Verification of MAPK Mechanism of Hypoxia Regulates Sarcolemma Injury after EIMD

Objective:To investigate and verify the effects of hypoxia on sarcolemma injury, and regulated mechanism by mitogen-activated protein kinases (MAPK) after exercise-induced muscle Damage (EIMD) . Methods:The male SD rats were randomly divided into control group, normoxia (24, 48 and 72 h group) and hypoxia group (24, 48 and 72 h group) . Rats were experienced intermittent downhill running according to EIMD model. And Rats were treated with intraperitoneal injection of Evans blue dye (EBD) after downhill running. Gastrocnemius muscle sample was isolated quickly and prepared to analyze. The positive ratio of cells (PRC) was observed by fluorescence microscope. To explore the hypoxia regulating mechanism of MAPK signal pathways in sarcolemma injury after EIMD, the m RNA, protein content and phosphylation of ERK1/2, JUN, p38 and BMK1 were tested by RT-q PCR and Western blot. Subsequently, inhibitor experiment was carried out so as to confirm the sarcolemma injury regulation mechanism of MAPK signal pathways in hypoxia.. Results:After EIMD, hypoxia and normoxia groups suffered a significant sarcolemma injury. The PRC showed a significant difference between hypoxia groups and normoxia groups (P<0.01) . The m RNA, protein expression and phosphorylation of ERK1, p38 and BMK1 in hypoxia groups were significantly higher than those in normoxia groups (P< 0.05) . In addition, protein expression and phosphorylation of JNK had no significant change (P>0.05) . The results of inhibitor experiment showed no significant changes of phosphorylation and PRC in inhibitor group (P> 0.05) . However, phosphorylation and PRC in inhibitor 24 h and 48 h BMK1 groups were significantly lower than placebo group (P<0.001) . And there were no significant difference between BMK1 inhibitor groups and placebo group (P>0.05) . Conclusions:1) The hypoxia exacerbates sarcolemma injury and causes the peak value shift forward after EIMD. 2) Inhibition of BMK1 phosphorylation can prevent sarcolemma injury. BMK1/ERK5 is the key signal pathway of MAPK mechanism in hypoxia regulates sarcolemma injury after EIMD.