Liberation of galactose from lactose by gut microbial β-galactosidase prevents uterine bacterial infection

Abstract Reproductive infection is closely associated with adverse reproductive outcomes, contributing to a reduced live birth rate per pregnancy and an elevated infertility rate. Nutrition is widely acknowledged as a fundamental determinant of human and animal health, as well as the etiopathogenesis of various diseases, with the gut microbiota playing an integral part in this process. Lactose, a disaccharide present in mammalian milk, has been identified as a potential prebiotic. Here, we found that lactose was able to mitigate the inflammatory response elicited by uterine bacterial infection, preserve the integrity of the endometrial epithelial barrier, and reduce the bacterial load in the uterus. The protective effects of lactose were found to be gut microbiota-dependent and fecal microbiota transplantation from lactose-treated mice to recipient mice also ameliorated E. coli-induced metritis. 16S rRNA gene amplicon sequencing revealed that lactose supplementation changed the gut microbiota, specifically increasing the abundance of Lactobacillus intestinalis (L. intestinalis). Whole-genome sequencing identified that L. intestinalis expressed β-galactosidase, a lactose-metabolizing enzyme. Inhibition or exogenous supplementation of β-galactosidase confirmed its essential role in mediating lactose’s protective effects against E. coli uterine infection. Furthermore, intragastric administration of [1-13Cgal]-lactose confirmed that galactose, a lactose metabolite, could translocate from the gut to the uterus. Mechanistically, galactose upregulated the CEBPB-dependent S100a8 expression after E. coli infection, and the protective effect could be blunted by S100a8 inhibition. Collectively, these findings highlight a nutrition-microbiota-host interaction that is stimulated by lactose supplementation, providing potential benefits for reproductive infection.