Effects of intermittent hypoxia preconditioning on autophagy protein expressions and related pathways in myocardium of exhaustive exercise rats

  AIM   To investigate the effects of intermittent hypoxia (IH) preconditioning on the expressions of autophagy-related proteins and the monophospho-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR)/uncoordinated 51 autophagy-activated kinase 1(ULK1) signaling pathways in cardiomyocytes of exhaustive exercise (EE) rats.

  METHODS   Sixty SD rats were randomly divided into blank group, control group, EE group, EE+1wIH group and EE+3wIH group. EE+1wIH group and EE+3wIH group were pretreated with 1w and 3w IH before constructing EE model, respectively. All groups, except blank group, received swimming training, and EE models were constructed in EE group, EE+1wIH group and EE+3wIH group. The levels of cardiac troponin I (cTnI) in plasma were detected by ELISA, the sensitivity and ischemia and hypoxia of rats were detected by C-2R staining, apoptosis was detected by TUNEL method and the number of autophagosomes in myocardial tissue was observed by electron microscopy. Immunohistochemistry was used to detect the expressions of antibody microtubule-associated protein 1 light chain 3 II (LC3 II) and Beclin 1 protein, and Western blot was used to detect the expression of AMPK-mTOR-ULK1 signaling pathway protein.

  RESULTS   In the blank group, the boundaries of all myocardium cells were clear and uniformly green. In the control group, myocardial cells had clear boundaries and only a small amount of red staining was scattered in the tissue. In the EE group, the boundary of some cardiomyocytes was not clear, and the majority of cardiomyocytes were red, while a few were green, indicating that most of the cardiomyocytes were affected by ischemia and hypoxia to varying degrees. The number of red stained cardiomyocytes in EE+1wIH and EE+3wIH groups was significantly lower than that in EE group. Compared with those in blank group, plasma cTnI level, C-2R average optical density (MOD), myocardial cell apoptosis rate, autophagy number of myocardial tissue, Beclin1, LC3 II, p-AMPK and ULK1 proteins were significantly increased in EE group, while p-mTOR protein was significantly decreased, with statistically significant differences (P<0.05). The above indicators were significantly improved in EE+1wIH group and EE+3wIH group and the difference was statistically significant (P<0.05).

  CONCLUSION   EE can significantly increase the level of cardiac autophagy in rats and IH may improve the level of cardiac autophagy induced by EE by regulating AMPK-mTOR-ULK1 signaling pathway.