Polygonatum cyrtonema saponin supplementation ameliorated DSS-induced intestinal barrier injury via targeting the PI3K/AKT/mTOR-mediated autophagy/microbiota axis

Abstract

Autophagy is pivotal for the management of intestinal homeostasis, modulation of intestinal immunity response and anti-microbial protection. Previous studies have documented the protective function of Polygonatum cyrtonema Saponin (PCS) against intestinal injury, but whether PCS modulated autophagy and its associated responses remained unknown. A model of dextran sodium sulfate (DSS)- elicited intestinal injury was employed to confirm this hypothesis. The results showed that PCS effectively relieved the typical symptoms of DSS-induced weight reduction, shortened colon length, and augmented disease activity index score, down-regulated organ indices, reduced hepatic oxidative stress, and inhibited excessive inflammatory mediators. Meanwhile, PCS intervention ameliorated the intestinal barrier dysfunction via promoting the differentiation of goblet cells and augmenting the expression of tight junction proteins (TJs). It also suppressed apoptosis in intestinal cells by altering the Bcl-2/Bax ratios and diminishing the expressions of Caspase-9 and Caspase-3. Additionally, PCS remarkably enhanced autophagy by modulating the PI3K/AKT/mTOR signal pathway. More importantly, the classical autophagy inducer rapamycin augmented the beneficial effects of PCS. In contrast, the autophagy inhibitor 3-methyladenine essentially eliminated the above effects, revealing a role for autophagy in the response. Further studies have demonstrated that PCS intervention improved the diversities of the intestinal flora, increased occupancy of beneficial bacteria in Lachnospiraceaeae and Akkermansia, which was closely associated with autophagy. Taken together, these findings demonstrated that PCS is a potential supplier of prebiotics by modulating immunity, repairing intestinal mucosal injury, regulating autophagy and intestinal flora, and autophagy is a key target for PCS-mediated intestinal barrier protection.