Hypoxic preconditioning reinforces HIF-alpha-dependent HSP70 signaling to reduce ischemic renal failure-induced renal tubular apoptosis and autophagy

Aims: Repetitive hypoxic preconditioning (RHP) may provide more efficient protection than single hypoxic preconditioning against renal ischemia/reperfusion-induced injury via hypoxia-induced factor 1α (HIF-1α)-dependent heat shock protein 70 (HSP70) pathways. Main methods: Wistar rats were subjected to intermittent hypoxic exposure (15h/day), whereas controls were kept at sea level. We evaluated renal expression of HIF-1α, HSP70, the endoplasmic reticulum stress protein GRP78, caspase 12, Beclin-1, and poly-(ADP-ribose)-polymerase (PARP) with western blotting. Renal apoptosis determined by terminal transferase dUTP nick end labeling (TUNEL), Beclin-1-dependent autophagy, and monocyte/macrophage (ED-1) infiltration were evaluated by immunocytochemistry. Renal function was determined with blood urea nitrogen (BUN) and plasma creatinine levels. HIF-1α inhibitors and Deoxyribonucleotide (DNA) or Ribonucleotide (RNA) interference of HSP70 were used to evaluate their possible roles in this process. Key findings: Renal HIF-1α and HSP70 expression were enhanced by hypoxic preconditioning and inhibited by the HIF-1α inhibitor, YC-1, as well as phosphatidylinositol 3-kinase (PI3K)/Akt inhibitors. After the return to normoxia, renal HSP70 protein levels were maintained for one week in the RHP group, but they decayed after one day in the single hypoxic preconditioning group. Ischemia/reperfusion significantly increased renal TUNEL-apoptosis, Beclin-1-dependent autophagy, ED-1 infiltration, expression of GRP78, caspase 12, Beclin-1, PARP, and BUN and plasma creatinine levels in control rats. RHP significantly decreased all ischemia/reperfusion-enhanced parameters. Intraperitoneal pretreatment with YC-1 and quercetin (an inhibitor of HSP70 induction) eliminated RHP-induced protection. Anti-sense oligodeoxyribonucleotides or interference RNA targeting HSP70 abrogated the protection against hypoxia/reoxygenation-induced oxidative injury in RHP-treated proximal tubules. Significance: We demonstrate that RHP promotes HIF-1α-dependent HSP70 signaling to reduce renal ischemia/reperfusion injury.