The Antidepressant Mechanism Of Ganoderic Acid A Via Regulation Of FXR Receptor And NLRP3 Inflammasome

Background:Depression is a mental disease characterized by significant and lasting depression.At present,the existing drugs have no efficacy on one third of patients,so it is urgent to develop drugs with new mechanisms.Ganoderic Acid A（GAA）,as an important component of Ganoderma lucidum triterpenoids,is the effective component of Ganoderma lucidum.Its main functions include anti-inflammatory and anti-tumor effects,and recent studies have reported that GAA has the neuroprotective effects.Farnesoid X receptor（FXR）,a nuclear receptor of bile acid,has been pointed out to play an important role in regulating metabolic diseases and abnormal immune function.We found that GAA and FXR have the molecular affinity through a computational docking study.Therefore,based on the animal and clinical research,this study systematically explored and verified the antidepressant effect of Ganoderic Acid A on regulating the expression of FXR receptor,improving neuroimmune function and synaptic plasticity in the despair model of depression like behavior,LPS injection model,and chronic social defeat stress（CSDS）model.Methods:1.The mechanism of antidepressant effect of GAA.In this study,the tail suspension and forced swimming tests were used as the behavioral tests to observe whether GAA treatment for 60 minutes and 5 days could improve the depression-like behavior of mice.A computational docking study was used to detect whether GAA and FXRshowed promising binding affinity.Then,immunofluorescence and western blot were used to detect whether the GAA directly inhibited the activity of the NLRP3inflammasome,and activated thephosphorylation and expression of the AMPA receptor by modulating FXR in the prefrontal cortex of mice.We used FXR receptor specific inhibitor z-gugglesterone（GS）and FXR knockout mice to detect if the antidepressant effects inducedby GAA were dependent on FXR.Finally,we used behavioral test,Western blot analysis and immunofluorescence staining to further confirm that if the mechanism of antidepressant effects of GAA disappeard in FXR^-/-mice.2.Explore whether GAA treatment can improve LPS depression model.LPS model mice were treated with GAA to confirmits antidepressant effects.Immunofluorescence staining was used to determine whether GAA treatment under LPS model could inhibited the activity of the NLRP3 inflammasome,microglia and astrocytes.HE staining was used to confirm whether GAA could affect inflammatory cell infiltration in LPS model.3.Explore the role of GAA in chronic social defeat stress（CSDS）model.TST and FST were used to confirm whether GAA treatment could change the depression-like behavior of CSDS mice.Immunofluorescence and western blot were used to determine whether GAA treatment affected the expression levels of FXR receptor,NLRP3inflammasome and AMPA receptor,neurons,microglia and astrocytes in the prefrontal cortex.4.To investigate the antidepressant effect of FXR receptor agonist chenodeoxycholic acid（CDCA）.Clinical investigation was used to detect the change of plasma CDCA level in patients with depression.TST and FST were used to observe whether CDCA treatment could improve the depression-like behavior of CSDS model mice.Western blots were used to determine whether CDCA treatment could regulate the expression levels of FXR receptor,NLRP3 inflammasome and AMPA receptor subunits in CSDS models.Results:1.GAA demonstrated antidepressant effects on depression-like animal behaviors（1）Behavioral tests showed that GAA demonstrated the antidepressanteffects,and the antidepressant effect was blocked by FXR inhibitor GS.（2）GAA enhanced the expression of FXR receptor,inhibited the expression of NLRP3 inflammasome,and up-regulated the expression of AMPA receptor subunit.（3）FXR knockoutblocked GAA’s up-regulation of FXR receptor expression,inhibited NLRP3 inflammasome and up-regulated AMPA receptor subunit expression.2.GAA treatment improved LPS model of depression.（1）GAAsignificantly improved the depression-like behavior induced by LPS;（2）GAA significantly inhibited the up-regulated expression of Caspase-1 and IL-1βinduced by LPS;（3）GAA significantly inhibited LPS-induced activation of microglia and astrocytes;（4）GAA significantly reduced the inflammatory cell infiltration induced by LPS.3.GAAimproved CSDS depression model.（1）GAA significantly improved the depression-like behavior induced by CSDS;（2）GAA significantly up-regulated FXR receptor expression in CSDS model;（3）GAA significantly improved CSDS-induced reduction of neurons and activation of microglia and astrocytes.（4）GAA significantly down-regulated NLRP3 inflammasome related protein expression in CSDS animal model;（5）GAA significantly increased the expression of AMPA receptor subunit in CSDS model.4.FXR receptor agonist CDCA showd antidepressant effect.（1）Clinical studies showed that the plasma levels of CDCA in patients with depression were significantly decreased;（2）CDCA treatment significantly improved depression-like behavior in animal models;（3）CDCA treatment significantly up-regulated the expression of FXR in CSDS animal model;（4）CDCA treatment significantly inhibited NLRP3 inflammasome related protein expression in CSDS model;（5）CDCAsignificantly increased the expression of AMPA receptor subunit in CSDS model.Conclusion:This study found that GAA inhibited neuroimmune dysfunction and regulate synaptic plasticity by up-regulating FXR receptor expression,thus playing animportant role in antidepressant effect.It provides a novel mechanism for the treatment and new drug development of depression.