[Role of hypoxia-inducible factor-1alpha in the prevention of cardiomyocyte injury induced by hypoxic preconditioning].

In order to understand the intracellular mechanism of preconditioning, we investigated the relationship among activities of extracellular signal-regulated protein kinases (ERKs), the expression of hypoxia-inducible factor -1alpha (HIF-1alpha) and the effect of hypoxic preconditioning (HPC) on cell injury induced by hypoxia-reoxygenation in cultured neonatal rat cardiomyocytes 24 h after brief hypoxia. Cultured cardiomyocytes of neonatal Sprague-Dawley rats were divided into four groups: hypoxia/reoxygenation (H/R), hypoxia preconditioning (HPC), hypoxia preconditioning + mitogen-activated protein kinase (MAPK) inhibitor PD98059 (HPC+PD98059), and control (C). We measured the survival rate and apoptosis rate of cardiomyocytes at 6 or 12 h after hypoxia/reoxygenation, activities of extracellular signal-regulated protein kinases (ERKs), and expression of hypoxia-inducible factor-1alpha (HIF-1alpha). We found that the survival rate of cardiomyocytes in hypoxic preconditioning group increased by 6.08% and 7.91% at 6 and 12 h after hypoxia/reoxygenation (n=6, P<0.05), respectively, and the apoptotic rate decreased by 10.92% and 14.34% (n=6, P<0.05) respectively. Hypoxic preconditioning increased the abundance of phospho-ERK1/2 by 3-folds and expression of HIF-1alpha by 1-fold in whole cell extracts from hypoxic preconditioned cardiomyocytes. PD98059, an inhibitor of the upstream kinase of ERKs, abolished the anti-injury effect, ERKs activation, and expression of HIF-1alpha induced by hypoxic preconditioning. Statistical analysis indicated that there was negative correlation between apoptotic rate and activities of ERKs or expression of HIF-1alpha, and positive correlation between activities of ERKs and expression of HIF-1alpha. It is concluded that hypoxic preconditioning protects cardiomyocytes from hypoxia/reoxygenation-induced injury and that upregulation of HIF-1alpha through ERKs pathway mediates the cardioprotection of hypoxic preconditioning.