The Mechanism Of NLRP3 Gene Knockout Ameliorate Memory Impairment In Chronic Stress Induced Depression Mice

Background and purpose: Alzheimer’s disease(AD),as one of the most common neurodegenerative diseases and the most frequently encountered type of dementia,is characterized by progressive cognitive decline and mental symptoms.The two most common pathological characteristics of AD are extracellular A β plaque deposition and neurofibrillary tangles caused by intracellular tau protein phosphorylation.Recently,a hypothesis stipulating that neuroinflammation might play an important role in the pathophysiological development of AD has been increasingly explored.Clinical studies have shown that stress and mental illnesses such as depression represent risk factors for AD.Animal experiments have also confirmed that chronic stress can activate the hypothalamus-pituitary-adrenal axis.Therefore,activating microglia and leading to the secretion of inflammatory cytokines.The initiation of the inflammatory response by microglia involves the multiprotein complexes termed inflammasomes.Comprising a cytosolic multiprotein platform,the inflammasome enables the activation of pro-inflammatory caspases,mainly caspase-1.NACHT-,LRR-,and pyrin(PYD)-domain-containing protein 3(NLRP3)inflammasome is the best-characterized and most widely implicated regulator of IL-1β and IL-18.Some studies have found that NLRP3 inflammatory bodies mediate stress-induced depression-like behavior in mice by regulating neuroinflammation.Our previous study found that chronic stress mice showed not only depression-like behavior but also spatial learning and memory impairment.However,whether NLRP3 inflammatory body mediated neuroinflammation plays a role in chronic stress-induced cognitive impairment is unclear.The purpose of this study was to investigate the effect of chronic stress on the NLRP3-Caspase-1-IL-1β signaling pathway in microglia and its relationship with cognitive function and to assess whether inhibition of NLRP3-Caspase-1-IL-1β signaling pathway activation in microglia can improve the effect of chronic stress on cognitive function.Methods: Experimental groups: WT,WT+CUMS,NLRP3 KO,NLRP3 KO+CUMS,Chronic Unpredicted Stress(CUMS)in 4-month-old male wild-type and NLRP3 KO(including 1min tail clamping,5 min hot water swimming,5min ice water swimming,overnight lighting,1h bondage,24h fasting and water deprivation,12h in 45 ° inclined cage and 18h in a wet cage,two kinds of stress modes were given randomly every day,with different stimulation for two consecutive days).After 8W,the depression level of mice was assessed by the sucrose intake test(TSI),open field test(OFT),and the force swimming test(FST).Meanwhile,the new object recognition test(NORT)and the Morris water maze(MWM)were used to evaluate mice’s memory ability and spatial learning memory.Blood was collected from the heart of the animals under general anesthesia after the behavioral tests,and all experimental subjects were decapitated for sampling.Western blot,were used to detect stress and cognition related indexes.Results:1.Compared with the wild type control group,the wild type chronic stress group had a significantly decreased sugar water intake,central activity time in the open field,and a significantly prolonged immobility time during the forced swimming.However,there was no significant difference between the NLRP3 gene knockout group and the control group in the sugar water intake,the central activity time of the open field,and the immobility time of forced swimming.2.Compared with the control group,the time of exploring new things in the wild-type chronic stress group was significantly reduced,while the time of exploring new things in the NLRP3 gene knockout experimental group was not different from that in the control group.3.The water maze test showed that compared with the control group,the incubation period of finding the hidden platform in the wild-type chronic stress group was significantly longer,the dwelling time in the quadrant where the platform was located was significantly reduced,and learning and memory functions were significantly impaired.There was no significant difference in latency time and platform quadrant stay time between the NLRP3 knockout group and the control group.4.Compared with the control group,NLRP3,caspase-1,IL-1β,total tau,and p-tau were significantly increased in the hippocampus of the wild type chronic stress group,while there was no significant difference in total tau and p-tau between the NLRP3 gene knockout group and the control group.In addition,the expression of synapsin and PSD95 of hippocampal synapse related proteins in chronic stress mice was significantly reduced,while the expression of synapsin and PSD95 in chronic stress mice was significantly improved after NLRP3 gene knockout.5.Golgi staining results showed that the number of hippocampal dendritic spines in wild-type chronic stress mice was significantly reduced compared with that in wild-type mice,while the number of hippocampal dendritic spines in NLRP3 knockout mice was significantly improved.Conclusions: Chronic stress can not only lead to depression-like behavior in mice but also lead to damages of spatial learning and memory.Additionally,it can significantly increase the levels of NLRP3,caspase-1,IL-1 β total tau,and p-tau in the hippocampus of stressed rodents.However,inhibition of the NLRP3-Caspase-1-IL-1β signal pathway can not only improve the depression-like behavior but also improve the ability of spatial learning and memory in mice.The mechanism might be through the activation of microglia leading to the activation of the NLRP3-Caspase-1-IL-1β signal pathway in vivo.Thus,regulating the pathological changes of tau protein in mouse hippocampus.