Quercetin alleviates depression in CUMS rats via modulating immune plasticity in the choroid plexus to inhibit hippocampal microglial activation

Abstract

Purpose: To elucidate the antidepressant effects of Quercetin in a rat model of Chronic Unpredictable Mild Stress (CUMS), explore the underlying mechanisms of Quercetin, and offer novel insights into developing antidepressant agents derived from substances with both medicinal and nutritional applications.

Methods: Herein, 75 male rats were sourced and randomly assigned to three groups: Control, CUMS, and Quercetin (50 mg/kg/day). Except for the control group, all rats were exposed to social isolation and chronic stress for eight weeks. The Sucrose Preference Test (SPT), Elevated Plus Maze Test (EPMT), Three-Chamber Social Interaction Test (TCT), and Forced Swimming Test (FST) were used to assess the antidepressant effects of Quercetin on CUMS-exposed rats. Flow cytometry, Immunofluorescence (IF) staining, and Western Blotting (WB) were employed to quantify CD4⁺ T cells and detect their protein expression in the Choroid Plexus (CP), Cerebrospinal Fluid (CSF), plasma, and hippocampus. The IL-1β, IL-6, IL-4, and IL-10 cytokine levels were measured using the Enzyme-Linked Immunosorbent Assay (ELISA). The expressions of ionized calcium-binding adapter molecule 1 (Iba-1), inducible Nitric Oxide Synthase (iNOS), and Arginase-1 in hippocampal tissue were analyzed using IF and WB. Additionally, the CP was examined for ZO-1, CCL5, CCL11, CXCL9, CXCL10, ICAM-1, and VCAM-1 expression through IF. In vitro, HAPI microglial cells were treated with the CSF from the three groups (CON-CSF, CUMS-CSF, and Quercetin-CSF) and cell viability was assessed using the CCK-8 assay. The expressions of Iba-1, iNOS, and Arginase-1 in HAPI microglial cells were also assessed using IF.

Results: As demonstrated by the SPT, FST, EPMT, and TCT behavioral tests, Quercetin significantly improved depressive and anxiety-like behaviors, as well as social deficits in CUMS rats. It also upregulated ZO-1, chemokines (CCL5, CCL11, and CXCL10), and adhesion molecules (ICAM-1) in the CP of CUMS rats. Additionally, Quercetin facilitated moderate recruitment of CD4⁺ T lymphocytes to the CP, suppressed the production of pro-inflammatory cytokines (IL-1β, IL-6), reduced hippocampal microglial cell density, and inhibited M1-type microglial polarization.

Conclusion: Herein, Quercetin moderately promoted the recruitment of CD4⁺ T lymphocytes to the CP, enhanced the Immune Microenvironment (IME) of the CP-CSF-hippocampal axis, and influenced microglial polarization in the hippocampus, highlighting some of the potential mechanisms underlying its antidepressant effects. In light of the current limitations of conventional antidepressants, including suboptimal efficacy and Adverse Reactions (AR), our findings underscore the potential value of Quercetin as an effective antidepressant with both medicinal and nutritional applications.

Keywords: Choroid plexus; Depression; Hippocampal; Microglial activation; Quercetin.