Role Of TRPV1 On Microglia Activation And Depressive-like Behaviour Of Mice Induced By LPS

Microglia are immune cells in the central nervous system.Over-activation of mi-croglia lead to imbalance of inflammatory cytokines and damage the neural circuits in the central nervous system,which is related to the pathogenesis of depression.Transient receptor potential vanilloid type 1 channel?TRPV1?is a cationic channel that mainly mediates the influx of Ca²⁺,which may promote the overactivation of microglia.Previ-ous studies have shown that TRPV1 is associated with depressive-like behavior,but the underlying mechanism is still not clear.Therefore,the purpose of this study is to clarify the relationship between TRPV1 and microglial activation and its role in the occurrence of depressive-like behaviors.This research was divided into three parts:1)in order to explore the role of TRPV1 in mediating stress resistance in mice,LPS was injected into wild-type mice and TRPV1 gene deficient(TRPV1^-/-)mice and their depressive-like behaviors were measured.The results showed that TRPV1^-/-mice presented longer la-tency time and shorter immobility time in forced swimming test and tail suspension test than wild type mice,showing corresponding stress resistance.2)in order to determine the changes of TRPV1 on microglia during overactivation,immunofluorescence stain-ing was used to analyze the expression of TRPV1 in microglia and correlation analysis.The results showed that the fluorescence expression of TRPV1 protein on microglia was higher than that on astrocytes under physiological condition,and the expression of TRPV1 protein in microglia was significantly up-regulated under stress,indicating that the TRPV1 on microglia was involved in the rapid response to stress.3)in order to ex-plore the specific mechanism of TRPV1 involved in microglia activation,flow cytome-try,PCR and Western blot were used to determine the downstream signal pathway of TRPV1 on microglia.The results of flow cytometry showed that when primary micro-glia of TRPV1^-/-mice were used or TRPV1 ion channel were blocked pharmacological-ly,both showed protective effect on mitochondrial damage induced by LPS and reduced mitochondrial oxidative stress.The results of Western blot and real-time quantitative PCR analysis showed that there was no difference in the gene transcription level of the three components of NLRP3 inflammasome between TRPV1^-/-mice and wild-type mice,indicating that TRPV1 ion channels did not affect NLRP3 inflammasome at the tran-scriptional level.Furthermore,the protein expression level of IL-1?was analyzed,the downstream product of NLRP3 inflammasome,and the results showed that the expres-sion of IL-1?protein was significantly decreased in TRPV1^-/-mice,which revealed that the assembly of NLRP3 inflammasome was weakened in TRPV1^-/-mice.These results suggest that the TRPV1 ion channel of microglia participates in the assembly of NLRP3inflammasome and the production of inflammatory cytokines IL-1?was mediated by Ca²⁺influx,thus affecting the depressive-like behavior of mice.These studies also pro-vide us with a new anti-depressant strategy based on TRPV1 ion channel.