Antidepressant Effect Of Ganoderma Lucidum Polysaccharide And Its Mechanism

Background:Depression is a chronic disease that has a negative impact on people’s emotions and cognitions.It is characterized by depression,distress,insomnia,cognitive dysfunction,and anhedonia.Depression can damage cognitive and social functions,resulting in suffering from life.Particularly,Major depressive disorder（MDD）impairs cognitive and social functions,and develops suicidal thoughts.Therefore,many active components of traditional Chinese medicine show stable antidepressant effect,high effective rate,and mild adverse reactions and have attracted the attention of many scholars at home and abroad.Ganoderma lucidum is one of the top ten precious medicinal mushrooms in Yunnan,which has many beneficial and medicinal effects.It is found that Ganoderma lucidum polysaccharide（GLP）is one of the bioactive components extracted from Ganoderma lucidum,which has many pharmacological effects,such as anti-cancer,anti-oxidation,immune regulation,and so on.A number of studies show that ganoderma lucidum has strong neuro-protective effect on diseases of central nervous system（CNS）,such as Alzheimer’s disease,cerebral ischemia,epilepsy and so on.The anti-inflammatory and immunomodulatory effects of Ganoderma lucidum polysaccharide on depression has not been reported so far.This study intended to study its effect on the treatment of depression.Research methods:Male C57BL/6 J mice（5-6 weeks old）were used in this study,with saline as the negative control（Control,CON）,imipramine（Imipramine,IMI 15 mg/kg）as the positive control.The antidepressant effect of GLP was evaluated by three dose groups:1,5,and 12.5 mg/kg GLP.Sixty minutes after intraperitoneal injection,TST（Tail Suspension Test,TST）was performed,OFT（Open Field Test,OFT）was performed 3 days later and FST（Forced Swim Test,FST）was performed 5 days later.According to the results of the dose dependent curve,the optimal dose of GLP（5mg/kg）was selected and further used to treat depression model mice induced by chronic social defeat stress（CSDS）.After that,biochemical and molecular biology experiments were performed.Hippocampal protein extract from the mice were analyzed by Western blot analysis to detect the expression of Dectin-1,NLRP3,IL-1β,TNF-α,BDNF,ASC,NF-κBp65,IL-6,IL-10,caspase-1,and AMPAR.Immunofluorescence staining was used to detect the microglia and astrocytes in hippocampus.Finally,laminarin,a Dectin-1 receptor antagonist,was used to further study whether GLP could inhibit neuroinflammation and enhance synaptic plasticity by up-regulating Dectin-1 receptor in CSDS animal model.Results:（1）Compared with control group,GLP significantly reduced the immobility time of TST（P<0.05）and FST（P<0.001）in mice in a GLP dose-dependent manner.The immobility time of the GLP（5 mg/kg）group was the lowest,which indicated that this dose was the best dose for the antidepressant effect.The weight changes of the mice in each group after continuous injection of normal saline,imipramine,low,medium,and high doses of GLP within 5 days showed no significant difference during GLP administration.In the open field test,GLP did not induce hyperactivity in mice.（2）After 10 days of CSDS procedure,the susceptibility of C57BL/6J mice were determined by SPT.The CSDS model mice which lost the preference to the sucrose were identified as the depressed mice.By detecting the immobility time of mice in control group,CSDS model group,and the GLP administration group（the best dose of 5 mg/kg GLP+CSDS model mice）,the results of TST and FST showed that compared with control group,the immobility time of mice in CSDS model group increased significantly after 60 minutes or 5 days of intraperitoneal injection with saline.However,the immobility time of GLP treatment group was significantly reduced,showing a significant antidepressant effect,indicating that GLP has a rapid and stable antidepressant effect.（3）Western blot analysis showed that GLP significantly increased the expression of Dectin-1（P<0.001）.In addition,specific antagonist laminarin could effectively block the antidepressant effect of GLP（P<0.05）in TST.Moreover,compared with control group,the protein expression levels of NF-κBp65,NLRP3,ASC,caspase-1 and IL-1β in the hippocampus of CSDS model mice were significantly up-regulated.However,after GLP treatment,the protein expression levels of NF-κBp65,NLRP3,ASC,caspase-1 and IL-1β were down-regulated and restored to their normal levels.Compared with control group,the expression of IL-6（P<0.01）and TNF-α（P<0.01）in hippocampus of CSDS model group were increased,and GLP treatment reversed the up-regulation of IL-6 and TNF-α induced by CSDS and restored their normal expression level.The expression of IL-10（P<0.001）and BDNF（P<0.001）in hippocampus of CSDS model group was decreased.GLP reversed the down-regulation of anti-inflammatory cytokines IL-10（P<0.01）and BDNF（P<0.001）induced by CSDS.（4）Western blot analysis showed that the expression levels of pGluAlS845,GluA1,and GluA2 in the hippocampus of CSDS model mice were significantly decreased compared with the control group,while GLP treatment significantly increased the expression levels of pGluAlS845,GluA1,and GluA2 in the hippocampus of CSDS depression model mice.Immunofluorescence showed that the microglia cells in the hippocampus of mice in the CSDS model group were increased significantly compared with the control group.However,GLP treatment significantly reduced the increased number of microglia induced by CSDS.In addition,astrocytes showed the same trend.Conclusion:In this paper,we identified GLP as a polysaccharide compound with good potential for rapid and relatively safe antidepressant for the treatment of depression.GLP can inhibit neuroinflammation and enhance the function of AMPA receptors.This discovery will provide a novel target and potential candidate compound for the clinical treatment of MDD.