Microglial Elimination And Repopulation Ameliorates Postoperative Cognitive Dysfunction Impairment By Altering Neutrophil Infiltration

Objective:Microglia are a key immune-competent cell type that involve in surgery-induced cognitive impairment.This study aimed to investigate the effects of acute microglial elimination,followed by microglial repopulation on surgery-induced cognitive impairment and the potential mechanism in a C57BL/6J mice model of postoperative cognitive dysfunction(POCD).PLX5622 is a receptor antagonist of colony-stimulating factor 1(C-X-C motif ligand 1,CXCL1).Activated microglia can be removed with PLX5622,and the number and function of microglia cells can be quickly recovered after drug withdrawal.Mounting evidence supports the protective role of microglial repopulation in neurological diseases.Neutrophils are important immune cells in the Central Nervous System(CNS),they are involved in the activation of CNS inflammation.The aim of this study was to investigate the effect of microglial repopulation on POCD recovery and to further investigate the association between deplete and repopulate microglia and neutrophil infiltration.Methods:Partial hepatectomy was performed as a model of POCD.In the first part of the study,aged mice were divided into control group,microglial depletion group and microglial repopulation group.In the microglial depletion group,PLX5622 was injected and feed daily 17 days to deplete microglia.In the microglial repopulation group,PLX5622 was injected and feed daily 17 days to deplete microglia.PLX5622was withdrawn for 7 days after microglial depletion to allow microglial repopulation.In the second part of the study,aged mice were divided into control group,surgery group,surgery+microglial depletion group and surgery+microglial repopulation group.In the surgery+microglial depletion group,PLX5622 was injected and feed daily from 17 days before surgery to the day of postoperative sampling to deplete microglia.In the surgery+microglial repopulation group,PLX5622 was withdrawn for 7 days after microglial depletion to allow microglial repopulation.In the third part,aged mice were divided into control group,surgery group and surgery+Ly6G~-group.Ly6G Antibody was injected intraperitoneally at 24h before surgery to determine the role of neutrophils infiltration in surgery-induced cognitive impairment.Behavioral performance was evaluated by Morris Water Maze and Novel Object Recognition Test.The number of neutrophils and microglia was detected by flow cytometry at 3 and 7 days after operation.The levels of IL-4,TNF-αand chemokines were detected by Western blot,PCR and Elisa.To explore its underlying mechanism,we detected the amount of ZEB1 and TGF-βin hippocampus using Western blot.Results:After 17 days of PLX5622 treatment,the number of microglia was significantly reduced in the microglial depletion group,and after 7 days of drug withdrawal,the number of microglia was significantly increased in the microglial repopulation group.Anesthesia and surgery lead to spatial learning and memory impairment in aged rats on days 3 and 7 after surgery.Anesthesia stimulation can increase the number of neutrophils,reduce the anti-inflammatory factor IL-4,increase the pro-inflammatory factor TNF-α,and reduce the expression of related protein ZEB1.Depletion of microglia could not improve the behavioral abnormalities caused by surgery,but the depletion of microglia could shorten the latency period and increase the discrimination index on the 3rd and 7th day after surgery.The repopulation of microglia reduced the infiltration of neutrophils,increased the expression of IL-4,decreased the expression of TNF-αand chemokines,and increased the expression of ZEB1.After surgical stimulation,the neutrophil depleted mice showed decreased latency and increased discrimination index on day 3 and day7 after surgery.Neutrophil infiltration was reduced in neutrophil depleted mice after surgery,and the expression of related proteins ZEB1 and Tgf-βdid not change.These results indicate that the repopulation of microglial reverses the behavioral abnormalities and inflammation caused by POCD and that this process is driven by reduced neutrophil infiltration.ZEB1 may be involved in this phenomenon.Conclusion:Microglial depletion and subsequent repopulation inhibited neutrophil infiltration and resulted in a reversal of behavioral impairment following surgery challenge.This process may be related to the protein ZEB1.Targeting microglia may be a viable strategy for the prevention and treatment of POCD.