Shikonin Attenuates Neuroinflammation and Depression-Like Behaviors by Regulating Microglial Polarization Through Inhibiting cGAS-STING/NF-κB Signaling and Lipid Droplet Accumulation.

BACKGROUND: Major depressive disorder is a disabling psychiatric illness with a growing global burden. Neuroinflammation, particularly microglial polarization, is increasingly recognized as a key pathogenic factor and is closely linked to lipid metabolic regulation. Shikonin, a bioactive naphthoquinone from Lithospermum erythrorhizon, exhibits anti-inflammatory and antioxidant properties, yet its antidepressant effects remain unclear. This study examined whether shikonin alleviates depressive-like behaviors by suppressing neuroinflammation.

METHODS: Mice were orally treated with shikonin for two weeks before the induction of learned helplessness (LH). A series of behavioral paradigms tail suspension test (TST), forced swim test (FST), sucrose preference test (SPT), and escapable shocks test (EST) was employed to evaluate depression-related behaviors. Following behavioral testing, inflammatory mediators, activation of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway, microglial lipid droplet accumulation, autophagic status, and M1/M2 polarization markers were evaluated. In vitro, mouse microglial cell line BV2 (BV2) microglia were activated by lipopolysaccharide (LPS). A cell counting kit-8 (CCK-8) assay was conducted to screen non-cytotoxic shikonin concentrations, with subsequent in vitro verification of in vivo outcomes. The role of lipophagy in microglial polarization was further examined through pharmacological modulation of autophagy using chloroquine and rapamycin.

RESULTS: Shikonin markedly alleviated depression-like behaviors in LH mice, accompanied by decreased interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) expression and inhibition of the cGAS-STING pathway. Mechanistically, shikonin suppressed M1 microglial polarization and lipid droplet accumulation in the hippocampus by restoring autophagic flux. Shikonin exerted anti-inflammatory effects in vitro by inhibiting cGAS-STING-dependent M1 polarization and restoring lipophagy in LPS-stimulated BV2 cells.

CONCLUSIONS: Our findings show that shikonin suppresses cGAS-STING activation, shifts microglia away from the M1 phenotype, and promotes autophagy, thereby reducing lipid droplet accumulation and alleviating neuroinflammation and depressive-like symptoms.