Sex differences in gallstone formation in mice on a lithogenic diet are driven by gut microbiota-mediated bile acid metabolism.

Sex differences in gallstone formation involve the gut microbiota, but the specific mediating mechanisms remain unclear. This study established gallstone and pseudo-germ-free mouse models and found that male mice maintained higher gut microbiota diversity, whereas females showed an increased Firmicutes/Bacteroidota ratio, with enrichment of Clostridium_sensu_stricto_13 and Lactobacillus. This shift led to increased production of toxic secondary bile acids-deoxycholic acid and lithocholic acid-resulting in elevated bile hydrophobicity and higher cholesterol saturation, which significantly increased gallstone susceptibility in females. Following antibiotic-induced microbiota depletion, male mice exhibited higher levels of glycodeoxycholic acid and taurodeoxycholic acid, along with reduced hepatic Cyp7a1 expression. These changes promoted cholesterol absorption and impaired bile acid synthesis, thereby increasing gallstone risk in males compared to females. Gut microbiota eradication further revealed that hepatic Abcc4, Sult2a5, Slco1a1, and Slco1a4 are regulated not only by sex hormones but also exhibit sex-specific responses to microbial modulation. Collectively, these results highlight gut microbiota-mediated bile acid metabolism as a key modifiable driver of sex differences in gallstone formation under a lithogenic diet.