Activation of Sirt6 by icariside Ⅱ alleviates depressive behaviors in mice with poststroke depression by modulating microbiota-gut-brain axis

Sirt6-mediated gut microbiota plays a vital role in poststroke depression (PSD). Icariside Ⅱ (ICS Ⅱ) is a naturally-occurring neuroprotectant with Sirt6 induction potency. However, it is unknown whether ICS Ⅱ protects against PSD through modulation of gut microbiota. This study aimed to reveal the effect and potential mechanisms of ICS Ⅱ on PSD, and the role of the microbiota-gut-brain axis was investigated. Using middle cerebral artery occlusion (MCAO) and chronic unpredictable mild stress (CUMS) to establish post-stroke depression (PSD) mice, we assessed anti-depressant effects of ICS Ⅱ via behavioral tests, immunohistochemistry, and western blot. Transcriptome profiling, molecular docking, and surface plasmon resonance were used to identify key targets. 16S rDNA genomic-derived taxonomic profiling and fecal microbiota transplantation (FMT) were conducted to figure out the mechanistic role of the gut microbiota and short-chain fatty acids (SCFAs). ICS Ⅱ ameliorated depressive-like behaviors in PSD mice as evidenced by sucrose preference test, forced swimming test and tail suspension test. ICS Ⅱ restored mitochondrial function, reduced oxidative damage and pro-inflammatory cytokines both in brain and intestine through regulation of Sirt6/NF-κB pathway. ICS Ⅱ significantly increased the abundance of gut microbiota (such asAkkermansia and Ligilactobacillus), enhanced SCFAs concentrations, repaired intestinal barrier integrity and upreglated the tight junction protein expression. FMT from ICS II-treated mice replicated these benefits, confirming gut microbiota's role. Mechanistically, ICS Ⅱ directly bound to Sirt6 and enhanced its activity. However, ICS Ⅱ-mediated neuroprotection was neutralized in PSD mice or hydrogen peroxide-induced enteric glial cells when Sirt6 was absent. Our findings expand the pharmacological properties of ICS II by demonstrating its ability to ameliorate PSD through modulation of the microbiota-gut-brain axis. ICS Ⅱ, as a novel Sirt6 activator, could be translated into an alternative microbiota-targeted avenue for coping with PSD.