Effects of cold induced RNA binding protein on hippocampal neurons and mitochondrial damage after mild hypothermia in a rat model of cardiac arrest / 医学研究生学报

ABSTRACT

ObjectiveMild hypothermia was an effective way of cerebral resuscitation after cardiac arrest. The expression of cold-induced RNA binding protein (CIRP) was significantly enhanced when the temperature was lowered. This study was to evaluate the effects and the mechanisms of CIRP inhibition on hippocampal neurological and mitochondria function after mild hypothermia in a rat model of cardiac arrest.MethodsFive male Sprague-Dawley rats were injected with AAV9 in the hippocampus, 1 μL on each side, speeding 0.2 μL/min. The expression of GFP was observed by fluorescence microscopy after 2w. Sixty rats were randomly divided into 5 groups (n= 12 for each group) sham operation group, model group, mild hypothermia group, mild hypothermia + CIRP inhibition group and mild hypothermia + normal control group. Injection of AAV9 was performed on mild hypothermia + CIRP inhibition group, same amount of empty vector on mild hypothermia + normal control group, while normal saline on the other groups. Animal models of global cerebral IR were established by transesophageal cardiac pacing inducing cardiac arrest followed by cardiopulmonary resuscitation at 2w after injection. Cooling to 32-34℃ was initiated and the temperature was maintained for 6h on mild hypothermia groups. NDS score, HE staining and pyramidal cell counting on hippocampal CA1 area were performed at 72h after reperfusion. At 24h after reperfusion, mitochondrial structure of pyramidal cells in hippocampal CA1 was observed under electronic microscope and the expressions of CIRP, dynamin-related protein 1 (Drp1) and cytochrome C (Cyt-C) were detected by Western blot.ResultsThe NDS score of model group was decreased, the number of pyramidal cells was reduced, and the mitochondria were severely damaged. The NDS score of mild hypothermia group was increased, and the number of pyramidal cells was increased (all P<0.05), and mitochondrial damage was reduced compared with model group. In mild hypothermia + CIRP inhibition group, the NDS score was no significant difference compared with mild hypothermia + normal control group and model group, and the number of pyramidal cells was lower than that in mild hypothermia + normal control group [(27.2±4.9) vs (50.2±4.4), P<0.05], similar to model group (25.2±3.8), the damage of mitochondria was severe. After 2 weeks of AAV9 injection, GFP was widely expressed in the hippocampus. The expression of CIRP in mild hypothermia + CIRP inhibition group was respectively small compared with sham operation group [(0.14±0.03) vs (0.03±0.01),P<0.05], which was successfully inhibited by injection of AAV9. The expression of CIRP in model group (0.25±0.05) was significantly higher than that in sham operation group. The expression of CIRP in mild hypothermia group (0.37±0.08) and mild hypothermia + normal control group (0.39±0.04) were higher than that in model group (all P<0.05). The trends of Drp1 and Cyt-C expression were the same, in model group was higher than that in sham operation group, in mild hypothermia group was lower than that in model group, in mild hypothermia + CIRP inhibition group was higher than in mild hypothermia + normal control group (all P<0.05); There were no significant differences between model group and mild hypothermia + CIRP inhibition group, and between mild hypothermia group and mild hypothermia + normal control group.ConclusionInhibition of CIRP expression in hippocampus can weaken the protective effects of mild hypothermia on neurons in a rat model of cardiac arrest. The mechanism of those effects might be association with mitochondrial division.