NR1H4 and inflammatory bowel disease: Potential mechanisms for this close association between PSC and IBD include alterations in gut flora leading to changes in immune responses that could affect biliary epithelia and alterations in bile acid composition and signaling (e.g. via farnesoid X receptor [FXR], TGR5, and/or FGF19-mediated pathways) by gut microbial populations that could have downstream effects on biliary epithelia.