Ganoderma lucidum polysaccharides ameliorated depression-like behaviors in the chronic social defeat stress depression model via modulation of Dectin-1 and the innate immune system

Major depressive disorder (MDD) is a prevalent, chronic, and recurrent disease. At least one-third of patients have treatment-resistant depression; therefore, there is an urgent need for novel drug development. Cumulative studies have suggested an inflammatory mechanism for the pathophysiology of MDD. Ganoderma lucidum polysaccharides (GLP) is an anti-inflammatory and immunomodulatory agent. Here, we found that an injection of GLP led to a rapid and robust antidepressant effect after 60 min in the tail suspension test. This antidepressant effect remained after 5 days of treatment with GLP in the forced swim test. Unlike psychostimulants, GLP did not show a hyperactive effect in the open field test. After 60 min or 5 days of treatment, GLP exhibited an antidepressant effect in a chronic social defeat stress (CSDS) depression animal model. Moreover, after 5 days of treatment, GLP attenuated the expression of the proinflammatory cytokines IL-1β and TNF-α, enhanced the expression of the anti-inflammatory cytokine IL-10 and the neurotrophic factor BDNF, and inhibited the activation of microglia and proliferation of astrocytes in the hippocampus of CSDS mice. In addition, after 5 days of treatment, GLP significantly enhanced GluA1 S845 phosphorylation as well as GluA1 and GluA2 expression levels in the hippocampus of CSDS mice. To determine whether the antidepressant effect was mediated by Dectin-1, we found that GLP treatment enhanced Dectin-1 expression in the hippocampus in CSDS mice, and the Dectin-1-specific inhibitor laminarin almost completely blocked the antidepressant effect of GLP. This study identified GLP, an agonist of Dectin-1, as a novel and rapid antidepressant with clinical potential and multiple beneficial mechanisms, particularly in regulating the neuroimmune system and, subsequently, AMPA receptor function.