The microglial state transition as a novel mechanism by which fresh Baihe Dihuang decoction prevents depression by regulating SIRT1/HMGB1 signaling

Abstract

Background: Fresh Baihe Dihuang decoction (FBD) is a classic Traditional Chinese Medicine (TCM) formula used to treat depression. However, its underlying molecular mechanisms in treating depression still need further exploration.

Purpose: In this study, we investigated whether FBD could prevent depressive-like behaviors by remodeling the microglial state transition via the inhibition of SIRT1/HMGB1 signaling in vivo and in vitro.

Study design and methods: In vivo, adult male C57BL/6 J mice were subjected to chronic unpredictable mild stress (CUMS) for 6 weeks to investigate whether FBD could produce antidepressant-like behavioral effects. At 9 weeks of age, EX527, a SIRT1 inhibitor, was injected intraperitoneally 30 min before the intragastric administration of FBD, Flx or vehicle daily until 12 weeks of age, and the effects of alterations in SIRT1/HMGB1 signaling on CUMS-mediated depression were investigated. In vitro, the anti-depressive mechanism of FBD was further investigated using BV-2 cells (a microglial cell line) and primary PFC neurons. We examined depression-like behaviors using behavioral tests. Serum and supernatants samples were collected and interleukin-1β (IL-1β), IL-6 and tumor necrosis factor-α (TNF-α) levels were measured using enzyme-linked immunosorbent assays (ELISAs). Prefrontal cortical (PFC) tissues, BV-2 cells and PFC neurons were collected to detect neuronal apoptosis, the microglial state or proteins in the silent information regulator 2 homolog 1 (SIRT1)/high mobility group box 1 (HMGB1) signaling pathway via flow cytometry, immunohistochemical staining, immunofluorescence staining,TUNEL staining or western blot analysis.

Results: The administration of FBD ameliorated the depressive-like behaviors induced by CUMS. In addition, FBD supplementation promoted the transition from a proinflammatory microglial phenotype to an anti-inflammatory microglial phenotype. The FBD-mediated inhibition of HMGB1 expression and its nucleocytoplasmic translocation were identified as likely due to increased SIRT1 activity, effectively inhibiting the subsequent inflammatory response. Furthermore, our findings revealed that FBD notably attenuated neuronal apoptosis in the PFC. In contrast, the SIRT1 inhibitor EX527 counteracted the antidepressant effect of FBD while also reversing the expression of brain-derived neurotrophic factor (BDNF), NeuN, cleaved caspase-3, bax, and bcl-2 proteins.

Conclusions: This study showed that FBD prevents depression by mediating a microglial state transition via the SIRT1/HMGB1 signaling pathway, providing a promising and novel antidepressant therapeutic strategy.

Keywords: Fresh baihe dihuang decoction; Microglial state transition; SIRT1/HMGB1 signaling.