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FXR, a bile acid receptor and biological sensor
1Tularik Inc., South San Francisco, CA 94080, USA.
Abstract:
Bile acid synthesis is a major pathway for cholesterol disposal and thus represents a potential therapeutic target pathway for the treatment of hypercholesterolemia. Recently, the nuclear farnesoid X receptor (FXR) was identified as a bile acid receptor and biological sensor for the regulation of bile acid biosynthesis. FXR was shown to regulate cholesterol metabolism in two ways: (1) chenodeoxycholic acid (CDCA), a primary bile acid, binds directly to and activates FXR, which then mediates the feedback suppression by bile acids of cholesterol 7 alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in bile acid biosynthesis from cholesterol; and (2) FXR participates in the activation of intestinal bile acid binding protein (IBABP), which is involved in the enterohepatic circulation of bile acids. Thus FXR constitutes a potential therapeutic target that can be modulated to enhance the removal of cholesterol from the body.
Insights
The nuclear farnesoid X receptor (FXR) regulates bile acid synthesis, a key pathway for cholesterol removal. Modulating FXR offers a therapeutic strategy for treating high cholesterol levels.
Area of Science:
- Biochemistry
- Metabolic Regulation
- Pharmacology
Background:
- Bile acid synthesis is crucial for cholesterol homeostasis and a target for hypercholesterolemia treatment.
- The nuclear farnesoid X receptor (FXR) acts as a bile acid sensor, regulating bile acid biosynthesis.
- FXR influences cholesterol metabolism through feedback suppression of bile acid synthesis and regulation of enterohepatic circulation.
Purpose of the Study:
- To elucidate the role of FXR in regulating bile acid synthesis and cholesterol metabolism.
- To explore FXR as a potential therapeutic target for hypercholesterolemia.
Main Methods:
- Investigated the interaction between bile acids (e.g., CDCA) and FXR.
- Examined the effect of FXR activation on the expression of CYP7A1, the rate-limiting enzyme in bile acid synthesis.
- Assessed FXR's role in the regulation of intestinal bile acid binding protein (IBABP) and enterohepatic circulation.
Main Results:
- Chenodeoxycholic acid (CDCA) directly binds to and activates FXR.
- FXR activation mediates feedback suppression of cholesterol 7 alpha-hydroxylase (CYP7A1) by bile acids.
- FXR is involved in activating intestinal bile acid binding protein (IBABP), impacting bile acid circulation.
Conclusions:
- FXR is a critical regulator of bile acid biosynthesis and cholesterol metabolism.
- FXR represents a promising therapeutic target for modulating cholesterol levels and treating hypercholesterolemia.