Mulberry Leaf Water Extract Ameliorates Impaired Glucose Tolerance via the Gut Microbiota/SCFAs/AMPKα1 Axis in Adipose Tissue

Background/Objectives: Impaired glucose tolerance (IGT) is a prediabetic condition affecting over 600 million adults worldwide. Mulberry leaf (Morus alba L.) has shown antidiabetic potential, but whether adipose AMPKα1 is required for its effects remains unclear. This study aimed to determine whether mulberry leaf water extract (MLE) ameliorates IGT through adipose AMPKα1-mediated gut microbiota modulation and thermogenesis. Methods: Adipose-specific AMPKα1 knockout (AKO) mice and floxed controls (Flox) were fed a high-fat diet for 12 weeks to establish IGT, then treated with MLE or short-chain fatty acids (SCFAs) for 10 weeks. Metabolic parameters, gut microbiota (16S rRNA sequencing), fecal SCFAs, and AMPKα1/SIRT1/PGC-1α pathway expression were assessed. Results: In Flox mice, MLE and SCFAs significantly improved glucose tolerance, reduced serum lipids and hepatic steatosis, and enhanced brown adipose tissue activation and white adipose browning. These effects were accompanied by gut microbiota remodeling, elevated fecal acetate/propionate/butyrate, and upregulation of the AMPKα1/SIRT1/PGC-1α pathway. All these metabolic and microbiota benefits were abrogated in AKO mice, in which MLE failed to improve any parameter, with only minimal and functionally insignificant thermogenic gene/protein upregulation. Conclusions: Adipose AMPKα1 is essential for MLE to improve IGT via gut microbiota/SCFAs and thermogenesis. These findings identify adipose AMPKα1 as a molecular target for dietary intervention in prediabetes.