The Role And Mechanism Of NLRP3 Inflammasome In Cognitive Impairment In Depression

Background and Objective:With the rapid development of economy and society,and changes in lifestyle,people are under increasing pressure from work and life.Long-term high levels of pressure and stress can increase the risk of developing anxiety,depression,and other mental disorders.Depression is one of the most common psychiatric diseases.Its main clinical features are low mood,thinking retardation,less motivation and activity,and can be accompanied by cognitive impairment and a series of autonomic nervous dysfunction,such as:insomnia,fatigue,loss of appetite,etc.Cognitive impairment is one of the most common residual symptoms of depression,which is manifested as a decline in attention,executive function,working memory,and information processing speed.Most patients cannot return to premorbid cognitive levels even in remission stage.In addition,the cognitive impairment of depression may also have an impact on the long-term neurological function of patients with depression.Depression can significantly increase the risk of Alzheimer’s disease(AD)late in life.At present,the pathogenesis of cognitive impairment in depression is still unclear.And there is currently no specific drug for the treatment of cognitive impairment in depression.A large number of clinical and basic studies have shown that depression and AD may share a common pathophysiological basis,and a variety of pathogenic factors are involved.Chronic inflammatory response plays a central role in the pathological mechanisms of both depression and AD,and may be the key pathological mechanism shared by depression and AD.The pro-inflammatory cytokine IL-1β is one of the main mediators of neuroinflammatory response.The level of IL-1β in peripheral blood of patients with depression is much higher than that of normal people,and the higher the level of IL-1β,the worse the cognitive function of patients with depression.The level of IL-1β in peripheral blood of AD patients is also significantly higher than that of normal people.IL-1β can mediate inflammatory response induced cognitive decline by inhibiting the long-term potentiation of the hippocampus and affecting hippocampal neurogenesis.The mature activation of IL-1β is dependent on its upstream molecule,the NLRP3 inflammasome.The inflammasome effector protein Caspase-1 can cleave the IL-1βprecursor Pro-IL-1β,making it into biologically active IL-1β,which drives the proinflammatory response.The NLRP3 inflammasome is an important component of the innate immune system.Cognitive impairment caused by various diseases is associated with the activation of NLRP3 inflammasome.In animal models of cognitive impairment caused by some diseases,the application of NLRP3 inflammasome inhibitors or RNA knockdown technology(siRNA-NLRP3)can restore the expression of inflammasomes to normal and significantly improve cognitive function.Numerous studies have found that inhibiting the expression of NLRP3 inflammasome can significantly improve depressive-like behavior in acute and chronic stress model mice,but the research on its effect on cognitive impairment in depression and its mechanism is still lacking.Besides,there is little basic research about how depression increases the risk of Alzheimer’s disease.There is also a lack of treatment drugs and objective diagnostic indicators for cognitive impairment in depression in clinic.This study aimed to explore the role and mechanism of NLRP3 inflammasome in cognitive impairment in depression.This is of great significance for exploring new depression treatment targets,formulating personalized diagnosis and treatment plans,promoting comprehensive recovery of depression patients,and reducing social burden.Methods:1.Chronic stress induced depressive-like behavior and cognitive impairment in miceChronic unpredictable mild stress(CUMS)was used to build a depression mouse model.After 5 weeks of stress,depressive-like behaviors were detected in all mice,cognitive function and serum IL-1β levels were detected in a group of mice.The CUMS process was stopped after 5 weeks,and then the mice in the stress group were kept in the same environment as the mice in the control group.After 1,2,and 4 weeks of stress,the cognitive function of the mice was detected,and the depressive-like behaviors were re-tested.Transcriptome sequencing was performed on the hippocampus of mice in the stress-stopped group and the mice in the control group.2.The role of NLRP3 inflammasome in CUMS-induced cognitive impairment in depressionCUMS was used to establish a depression model.The NLRP3 inflammasome-specific inhibitor MCC950 and the classic antidepressant fluoxetine were used as interventions.Then we detected the depressive-like behavior and cognitive function of the model mice,the situation of neurons and glial cells,the NLRP3 inflammasome activation pathway in the hippocampus of mice,the changes of AD physiological indicators.3.Effects of NLRP3 inflammasome activation on AD-related pathway proteins in vitroIn vitro,the LPS+ATP was used to activate the NLRP3 inflammasome in mouse microglia(BV2),and the inflammasome inhibitor MCC950 was used as an intervene.Then we detected the activation of the NLRP3 inflammasome and its related pathway proteins,and the expression of Aβ metabolism-related proteins.Subsequently,the activated BV2 cells were co-cultured with primary neurons.The phosphorylation of tau protein and the activation of protein kinases in primary neurons were detected.Results:1.Chronic stress induced depressive-like behavior,cognitive impairment and related transcriptome sequencing in mice1.1 After 5 weeks of CUMS,model mice displayed depressive-like behavior and cognitive impairment.1.2 CUMS up-regulated the expression of serum IL-1β in mice.The expression of IL1β was positively correlated with the severity of depressive-like behavior in mice,and negatively correlated with the level of cognitive function.1.3 When the stress stopped,the depressive-like behaviors and cognitive functions of the CUMS-induced mice were partially relieved after 1 week of recovery.After 2-week cessation of stress,depressive-like behaviors of mice were restored,but symptoms of cognitive impairment remained.After 4-week cessation of stress,the depressive-like behaviors did not relapse,but cognitive function was still not fully restored in mice.1.4 The results of transcriptome sequencing enrichment analysis showed that CUMSinduced cognitive impairment may be related to AD pathway activation.2.The role of NLRP3 inflammasome in cognitive impairment in depression2.1 Both MCC950 and fluoxetine improved CUMS-induced depressive-like behavior in mice,while MCC950 improved CUMS-induced cognitive impairment,and fluoxetine partially improved cognitive function in mice.2.2 CUMS induced the activation of microglia,the decline in the number of immature neurons,and the decreased activity of neurons in the hippocampus of mice.MCC950 intervention had obvious protective effect.Fluoxetine could inhibit the activation of microglia and the decline of neuronal activity.There was no significant difference in the expression of astrocyte markers among the groups.2.3 CUMS activated the NLRP3 inflammasome and its pathway.Both MCC950 and fluoxetine inhibited the activation of the pathway.2.4 CUMS activated the expression of Aβ metabolic pathway related proteins,which could be significantly inhibited by MCC950 and fluoxetine intervention.However,there was no significant difference in the deposition of amyloid-beta among the groups.2.5 CUMS up-regulated the phosphorylation level of tau protein and activated related protein kinases.Both MCC950 and fluoxetine intervention had protective effects.Total tau protein levels were not significantly changed.3.Molecular mechanism of NLRP3 inflammasome mediating cognitive impairment in depression3.1 LPS(1 μg/mL)+ATP(1mM)activated the expression of NLRP3 inflammasome and IL-1β in BV2 cells in vitro.MCC950 could effectively inhibit the expression of NLRP3 inflammasome pathway.3.2 LPS+ATP activated the Aβ metabolic pathway,and the intervention of MCC950 could improve the abnormal expression of Aβ metabolism-related proteins.3.3 MCC950 was applied as an intervention in advance.BV2 cells were stimulated by LPS+ATP in vitro.After BV2 cells were activated,they were co-cultured with primary neurons.The activated BV2 cells promoted neuronal tau protein phosphorylation and activated related protein kinases.MCC950 could play an inhibitory effect.Conclusions:Collectively,the NLRP3 inflammasome played an important role in the development of cognitive impairment in depression.Inhibition of NLRP3 inflammasome could alleviate CUMS-induced depressive-like behaviors and cognitive impairment in mice,and inhibit the activation of AD physiological indicators.This study deepened the understanding of the relationship between cognitive impairment in depression and AD and provided a new target for the treatment of cognitive impairment in depression.