Increased PINK1/Parkin-mediated mitophagy explains the improved brain protective effects of slow rewarming following hypothermia after cardiac arrest in rats

Abstract

Cerebral ischemia-reperfusion (I/R) after cardiac arrest (CA) induces mitochondrial dysfunction, and the timely removal of damaged mitochondria by mitophagy is reported to protect against cerebral I/R injury. Therapeutic hypothermia (TH) has become an important component of postresuscitation care for patients who return to spontaneous circulation after CA. Previous studies have shown that TH can activate mitophagy and can contribute a protective effect; however, the optimal rewarming rate and underlying mechanism of rewarming following TH remain largely unexplained. Here, we investigated the effects of different rewarming rates and whether mitophagy is involved in rewarming. After 5 min of asphyxial CA following 4 h of cooling, Sprague-Dawley rats were randomized into the normothermia, hypothermia, slow rewarming (0.5 °C/h) and fast rewarming (4 °C/h) groups. The hypothermia group was kept cool until tissue harvest, the rewarming duration for the slow rewarming group and fast rewarming group was 6 h and 45 min, respectively. We found that slowly rewarmed rats had better survival at 72 h than normothermic rats and fast-rewarmed rats (70%, 25.71%, and 50%, respectively) and higher neurological deficit scores (NDSs), in which the medians were 57.33, 26, and 28.83, respectively. In addition, we explored the underlying mechanism during this process and found that PINK1/Parkin-mediated mitophagy was activated during hypothermia in the slow rewarming group but was inhibited in the fast rewarming group. Further inhibition of mitophagy in the slowly rewarmed rats resulted in severe apoptosis and decreased the mean NDS from 58.39 to 33.11, indicating the protective role of mitophagy. Moreover, the fast rewarming group exhibited deficiencies in PINK1 expression and mitophagy activity and marked accumulation of reactive oxygen species (ROS). Overall, our results highlighted a neuroprotective role of PINK1/Parkin-mediated mitophagy during slow rewarming after hypothermia.