Asperosaponin VI Ameliorates The CMS-Induced Depressive-Like Behaviors By Inducing A Neuroprotective Microglial Phenotype To Restore Hippocampal Synaptic Plasticity Via PPAR-γ Pathway

Abstract

Background: The natural compound asperosaponin VI has shown potential as an antidepressant, but how it works is unclear. Here we explored its effects on mice exposed to chronic mild stress (CMS) and the underlying molecular pathways.Methods: Mice were exposed to CMS for three weeks followed by asperosaponin VI (40 mg/kg) or imipramine (20 mg/kg) for another three weeks. Depression-like behaviors were assessed in the forced swimming test, sucrose preference test, tail suspension test, open field test and novelty-suppressed feeding test. Microglial phenotype and synaptic plasticity were evaluated using immunofluorescence staining, real-time quantitative PCR and enzyme-linked immunosorbent assays in hippocampus of mice. In some experiments, stressed animals were treated with the PPAR-γ antagonist GW9622 to examine its involvement in the effects of asperosaponin VI.Results: Asperosaponin VI ameliorated depression-like behaviors of CMS mice based on all three behavioral tests, and this was associated with a switch of hippocampal microglia from a pro-inflammatory (iNOS+-Iba1+) to neuroprotective (Arg-1+-Iba1+) phenotype. The natural compound also promoted interactions between hippocampal microglia and neurons by enhancing CX3CL1/CX3CR1 and CD200/CD200R, and preserved synaptic plasticity based on PSD95 and CamKIIa levels. These effects of asperosaponin VI were blocked by GW9662. Conclusion: CMS in mice induces a proinflammatory microglial phenotype, disrupting neuron-microglia communication and synaptic function in hippocampus, ultimately leading to depression-like behaviors. Asperosaponin VI may ameliorate the effects of CMS by inducing microglia to adopt a PPAR-γ-dependent neuroprotective phenotype.