Undernutrition Shapes the Gut Microbiota and Bile Acid Profile in Association with Altered Gut-Liver FXR Signaling in Weaning Pigs.

Bile acids, synthesized in the liver and metabolized by microbiota, have emerged as important signaling molecules regulating immune responses and cell proliferation. However, the crosstalk among nutrition, microbiota, and bile acids remains unclear. Our study indicated that undernutrition in weaning piglets led to intestinal atrophy, increased colonic production, and systemic accumulation of lithocholic acid (LCA), deoxycholic acid (DCA), or their conjugated forms, which might be associated with decreased Lactobacillus abundance. Moreover, undernutrition led to increased portal fibroblast growth factor 19 ( FGF19) level, upregulated hepatic heterodimer partner ( SHP), and downregulated cholesterol 7a-hydroxylase ( CYP7A1) expression. The detrimental effects of DCA and LCA on proliferation and barrier function were confirmed in porcine enterocytes, whereas their roles in weaning piglets warrant further research. In summary, undernutrition in weaning piglets led to increased secondary bile acids production, which might be related to altered gut microbiome and enhanced farnesoid X receptor (FXR) signaling while CYP7A1 expression was suppressed.