Vitamin D3 metabolites-enhanced hepatic VDR-FXR binding attenuates bile acid dysregulation diarrhea in weaned piglets

Hepatic bile acid (BA) dysregulation contributes to diarrhea and intestinal injury in weaned piglets. Although the farnesoid X receptor (FXR) is a central regulator of BA homeostasis and a promising therapeutic target, its agonist chenodeoxycholic acid (CDCA) may exacerbate diarrhea and gut damage, underscoring the need for safer FXR-targeting strategies. In this study, we identify ileal accumulation of 7-ketoLCA, which correlates with enterohepatic pathology, in naturally diarrheic piglets using BA metabolomics. Mouse oral gavage experiments confirm the direct pathogenic role of 7-ketoLCA. Mechanistically, utilizing AlphaFold3 prediction and Co-IP assays reveal a novel interaction between FXR and the vitamin D receptor (VDR) in porcine liver samples and TNF-a-stimulated AML12 hepatocytes. Dietary vitamin D3 metabolites alleviate diarrhea, reduce ileal 7-ketoLCA, and enhance intestinal barrier integrity in diarrheic piglets. Further analysis demonstrates that vitamin D3 metabolites enhance VDR-FXR binding, thereby potentiating FXR transactivity, which downregulates BA synthesis genes CYP7A1/CYP8B1 and upregulates export transporters BSEP/MRP2, ultimately restoring BA homeostasis and attenuating inflammation injury. These findings reveal a novel mechanism of BA regulation through VDR-FXR interaction and support vitamin D3 metabolites as a safe nutritional strategy against piglet diarrhea.