Probiotic Combination of Limosilactobacillus fermentum HF07 and Lactococcus lactis HF08 Targeting Gut Microbiota–Secondary Bile Acid Metabolism Ameliorates Inflammation and Intestinal Barrier Dysfunction in Aging Colitis

This study investigated the intestinal protective effects of a probiotic mixture (PM) composed of Limosilactobacillus fermentum HF07 and Lactococcus lactis HF08 on d-gal/DSS-induced aging colitis in mice. The PM alleviated age-related colitis symptoms including weight loss, increased disease activity index scores, colonic shortening, and tissue damage. PM supplementation reshaped the gut microbiota by restoring the relative abundances of Lactobacillus, Dubosiella, Odoribacter, and Clostridia_UCG-014, thereby enhancing levels of bile acids (BAs) such as alpha-muricholic acid, isolithocholic acid, and ursodeoxycholic acid. Moreover, transcriptomic analysis revealed that PM administration activated the cAMP pathway through the gut microbiota–secondary BAs axis. Western blot analysis further demonstrated that the effects of anti-inflammatory and intestinal barrier repair induced by PM were associated with downregulation of key proteins in the NLRP3 and RhoA/ROCK pathways, both of which are downstream of the cAMP pathway. Additionally, the role of gut metabolites in mediating these effects via G protein-coupled receptor 5 (TGR5) activation was confirmed through in vitro experiments using Caco-2 cells. These findings provided a comprehensive understanding of how probiotics target intestinal metabolites and leverage the gut microbiota-BAs axis to mitigate age-related gastrointestinal diseases.