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. 2018 Oct 25;6(4):425–430. doi: 10.14218/JCTH.2018.00025

Fig. 2. Feedback regulation of bile acid (BA) synthesis through farnesoid X receptor (FXR).

Fig. 2.

Cytochrome P450 7A1 (CYP7A1) is the rate-limiting enzyme of BA synthesis. In the liver, BA binds to FXR to induce expression of small heterodimer partner (SHP), which inhibits transcriptional activity of hepatocyte nuclear factor 4α (HNF-4α) as well as liver-related homologue-1 (LRH-1), and down-regulates CYP7A1 transcription. In the intestine, BA binds to FXR to induce fibroblast growth factor 15 (FGF15), which is secreted into portal bloodstream and finally activates hepatic FGFR4/β-Klotho complex, initiating a regulatory cascade to repress CYP7A1 transcription.