Cerebral ischemic post-conditioning induces autophagy inhibition and a HMGB1 secretion attenuation feedback loop to protect against ischemia reperfusion injury in an oxygen glucose deprivation cellular model

Cerebral ischemic postconditioning (IPOC) has been demonstrated to be neuroprotective against cerebral ischemia reperfusion injury. The present study aimed to determine whether IPOC could inhibit autophagy and high mobility group box 1 (HMGB1) release in a PC12 cell oxygen glucose deprivation/reperfusion (OGD/R) model. An 8 h OGD and 24 h reperfusion cellular model was developed to mimic cerebral ischemia reperfusion injury, with 3 cycles of 10 min OGD/5 min reperfusion treatment to imitate IPOC. Cell viability was determined to demonstrate the efficiency of OGD/R, IPOC and autophagy activator, rapamycin (RAP), treatment. Transmission electron microscopy was performed to observe the formation of autophagosomes, and immunofluorescence, western blot and co-immunoprecipitation were used to examine the expression of autophagy-associated proteins and HMGB1. Enzyme-linked immunosorbent assay analysis was conducted to examine the level of HMGB1 in cell supernatants. Additionally, PC12 cells were treated with RAP to examine the effect of autophagy on HMGB1 release, and the effect of recombinant human HMGB1 and Beclin1 small interfering RNA on autophagy was investigated. The present study confirmed that IPOC inhibited autophagy and HMGB1 secretion, autophagy inhibition induced a decrease in HMGB1 secretion, and HMGB1 secretion attenuation caused autophagy inhibition in return, as demonstrated by immunofluorescence and western blot analyses. Autophagy inhibition and HMGB1 secretion attenuation were, therefore, demonstrated to form a feedback loop under IPOC. These mechanisms illustrated the protective effects of IPOC and may accelerate the clinical use of IPOC.