Cannabinoid Receptor-2 Attenuates Surgery With Anesthesia Induced Neuroinflammation Via Microglial Polarization And Its Mechanism

Background: Surgical trauma can cause inflammatory factors to cross the blood brain barrier and enter the brain,resulting neuroinflammation.Neuroinflammation in hippocampus contributes to postoperative cognitive dysfunction(POCD).The process of microglial polarization to pro-inflammatory M1 or anti-inflammatory M2 phenotypes during brain inflammation is considered to be one of major immunomodulatory manners.Endocannabinoids is a compound with anti-inflammatory effects.There are two main types of physiological ligands.Previous studies show that the activation of Cannabinoid Receptor-2(CB2R)attenuates microglial activation and brain inflammation in mice after surgery.However,it is unclear whether the activation of CB2 R affects microglial polarization after surgery.Our study mainly investigated the role of CB2 R activation in microglial polarization after surgery.Methods: Healthy male C57/6 mice of 4 months were randomly divided into 4 groups including control group,surgery group,surgery + JWH133 group and surgery + AM630 group.Mice were subjected to intramedullary fixation surgery for tibial fracture under sevoflurane anesthesia.CB2 R agonist(JWH133)or CB2 R antagonist(AM630)was administered intraperitoneally after recovery and repeated every 24 hours.The animals were sacrificed 1 and 3 days after surgery,and the expression of CB2 R in prefrontal cortex and hippocampus was detected by western blot(n=24).The expression levels of IL-1β,IL-6,TNF-α were investigated by ELISA on postoperative days1 and 3(n=24).RT-q PCR was used to amplify the m RNA of M1 microglia marker genes CD68,CD86 and M2 microglia marker genes CD206 and YM-1(n=24).To test this hypothesis in vivo,we performed double staining for the microglia marker Iba1 and M1-associated marker proteins in the prefrontal cortex and hippocampus on postoperative days1 and 3(n = 24).Results: The expression of IL-1β,IL-6 and TNF-α in the prefrontal cortex and hippocampus were increased significantly on postoperative days1 and 3.JWH133 treatment reduced the expression of TNF-α in the prefrontal cortex on postoperative days1 and the expression of three inflammatory factors both in the prefrontal cortex and hippocampus on postoperative days1 and 3.Compared with the control group,the expression of CB2 R in the prefrontal cortex increased on postoperative days1,and the expression of CB2 R in the prefrontal cortex and hippocampus increased on postoperative days 3.However,CB2 R was downregulated by postoperative treatment with JWH133,while AM630 treatment increased the CB2 R expression.RT-q PCR results showed that the m RNA expression of M1 microglia was increased on postoperative days 1and 3,and the activation of CB2 R could increase the M2-like m RNA expression.Similarly,cells labeled with the M1 marker CD68 in the CA1 area of the hippocampus and prefrontal cortex were increased following surgery and decreased by postoperative treatment with JWH133.Conclusion: These findings indicate that surgery results the high levels of inflammation in the prefrontal cortex and hippocampus,and the activation of CB2 R probably suppresses neuroinflammation by regulating the M1 to M2 microglia phenotypical conversion.