Modified Xiaoyao San reverses lipopolysaccharide-induced depression-like behavior through suppressing microglia M1 polarization via enhancing autophagy involved in PI3K/Akt/mTOR pathway in mice

Abstract

Ethnopharmacological relevance: Modified Xiaoyao San (MXYS), a clinical empirical modified formula based on famous traditional Chinese herbal prescription Xiaoyao San, according to the "yu syndrome" theory of traditional Chinese medicine. MXYS has been shown to be an excellent effective therapy for depression patients in clinic, but the antidepressant mechanisms remain unclear.

Aim of the study: A growing body of evidence indicates the microglia autophagy and M1 polarized microglia (proinflammatory phenotype)-mediated neuroinflammation act critical roles in the pathogenesis of depression. This study aimed to investigate whether MXYS exerts antidepressant efficacy through inhibition of M1 polarized microglia-mediated neuroinflammation and modulation of autophagy involved in PI3K/Akt/mTOR pathway.

Materials and methods: In present research, the lipopolysaccharide (LPS)-induced depressive mice and LPS-stimulated N9 microglia cell line were utilized. Behavioral tests (sucrose preference, tail suspension and open field tests) were carried out to evaluate the antidepressant effect of MXYS. The neuronal damage was measured by Nissl's staining in LPS-treated mice. The proinflammatory cytokine levels, the autophagic markers, microglia M1 polarization as well as the PI3K/Akt/mTOR pathway related proteins of MXYS treatment were analyzed by ELISA kits, Western blot and immunofluorescence staining in vivo and vitro. Finally, the influence of autophagy antagonist (3-MA) on the protective effect of MXYS-containing serum in the LPS-stimulated N9 microglia was investigated.

Results: Treatment of LPS-induced depressive mice with MXYS significantly reversed depression-like behaviors, accompanied by reduction of proinflammatory cytokine levels (TNF-α, IL-1β) and amelioration of neuronal damage in prefrontal cortex. MXYS suppressed microglia M1 polarization and promoted autophagy in prefrontal cortex and LPS-stimulated N9 cells. Importantly, the remarkable inhibitory effect of the MXYS-medicated serum on microglia M1 polarization was blocked by autophagy antagonist 3-MA in LPS-stimulated N9 cells. Meanwhile, the MXYS treatment exhibited an excellent inhibition effect of PI3K/Akt/mTOR pathway in vivo and vitro.

Conclusion: Our research suggests that the antidepressant effect of MXYS in LPS-induced depressive mice may be related to alleviate neuroinflammation through suppression of microglia M1 polarization via enhancing autophagy involved in inactivation of the PI3K/Akt/mTOR pathway.

Keywords: Antidepressant; Autophagy; M1 polarization; Modified Xiaoyao San; Neuroinflammation; PI3K/Akt/mTOR pathway.