Alleviative Effect of <i>Stropharia rugosoannulata</i> Exopolysaccharide on <scp>d</scp> ‐Galactose‐Induced Gut Inflammation and Oxidative Stress by Modulating Gut Microbiota

The exopolysaccharide SREP-1, purified from the fermentation broth of Stropharia rugosoannulata, exhibited antiaging potential. As aging significantly alters gut structure and function, protective effect of SREP-1 was investigated using a d-galactose-induced aging mouse model. SREP-1 administration reversed D-galactose-induced body weight loss and colon damage, as evidenced by improved histopathology. SREP-1 mitigated weight loss and colon damage, enhanced the activities of antioxidants (SOD, GSH-Px, and CAT), and reduced the level of MDA. It decreased proinflammatory cytokines (TNF-α, IL-1β, and IL-6) and elevated IL-10 in colon tissue, while boosting serum immunoglobulins (IgG and IgM). Crucially, these effects were abolished by antibiotic pretreatment, highlighting the role of gut microbiota in SREP-1 bioactivity. This role was further confirmed through fecal microbiota transplantation (FMT) and fecal supernatant transplantation (FST) experiments. Based on 16S rRNA sequencing, SREP-1 restored gut microbial diversity, increased beneficial genera (e.g., Faecalibacterium, Akkermansia, Lactobacillus, and Bacteroides), and decreased harmful bacteria (e.g., Escherichia-Shigella and Collinsella). Furthermore, short-chain fatty acids (SCFAs) levels were elevated in the SREP-1 group, which might regulate GPCRs/NF-κB/Nrf2 signaling pathways and exert biological activity. This study revealed the potential of SREP-1 to alleviate aging-related intestinal dysfunction and underscored the crucial role of gut microbiota in mediating these effects.