Repetitive Hypoxic Preconditioning Attenuates Renal Ischemia/Reperfusion Induced Oxidative Injury via Upregulating HIF-1α-Dependent bcl-2 Signaling

Background. In response to ischemic/hypoxic preconditioning, tissues/organs exhibit protective responses to subsequent and severe ischemic stress. We hypothesized that repetitive hypoxic preconditioning (RHP) may provide long-lasting protection than single preconditioning against ischemia/reperfusion injury in rat kidneys through hypoxia-induced factor (HIF)-1-dependent pathway. Methods. For RHP induction, female Wistar rats were Subjected to intermittent hypoxic exposure (380 Torr) 15 hr/day for 28 days. Results. RHP increased renal HIF-1 alpha mRNA and protein expression and triggered HIF-1 alpha-dependent renal Bcl-2 protein expression in a time-dependent manner. When returning to normoxia, increased RHP exposure prolonged renal Bcl-2 expression. Forty-five minutes of renal ischemia with 4 hr of reperfusion enhanced O-2(-center dot) levels and proapoptotic mechanisms, including enhanced cytosolic Bax translocation to mitochondria, release of cytochrome c to cytosol, activation of caspase 3, poly-(ADP-ribose)-polymerase fragments, tubular apoptosis, blood urea nitrogen, and creatinine level. RHP treatment depressed renal O-2(-center dot) production, mitochondrial Bax translocation and cytochrome c release, and tubular apoptosis. In the primary tubular cultures from RHP-treated kidneys, antisense oligodeoxyribonucleotides of bcl-2 abrogated this protection. Conclusions. RHP activates an HIF-1 alpha-dependent signaling cascade leading to an increase in Bcl-2 protein expression, an inhibition in cytosolic Bax and mitochondrial cytochrome c translocation, and a hypoxic/ischemia tolerance against renal ischemia/reperfusion injury.