Farnesoid X receptor–Bile salt export pump pathway (FXR-BSEP pathway)

The Farnesoid X receptor–Bile salt export pump (FXR-BSEP) pathway is a fundamental regulatory axis in the liver and intestine responsible for maintaining bile acid homeostasis. The Farnesoid X receptor (FXR), a member of the nuclear receptor superfamily, serves as the primary sensor for endogenous bile acids; upon activation, it directly upregulates the expression of the Bile Salt Export Pump (BSEP), an ATP-binding cassette transporter that mediates the rate-limiting step of bile acid secretion into the bile canaliculi. This pathway is essential for the enterohepatic circulation of bile acids and protects hepatocytes from the detergent-like toxicity of accumulated bile salts. Dysregulation of the FXR-BSEP axis is a hallmark of various cholestatic and metabolic liver diseases, including primary biliary cholangitis (PBC) and nonalcoholic steatohepatitis (NASH). Therapeutic strategies targeting this pathway primarily utilize FXR agonists, such as obeticholic acid, to enhance bile acid efflux and suppress bile acid synthesis. However, clinical use of these agents is often limited by side effects such as dose-dependent pruritus and adverse changes in the plasma lipid profile, specifically elevations in LDL cholesterol.

Other names

FXR-BSEP axisNR1H4-ABCB11 pathwayBile acid-FXR-BSEP signalingFarnesoid X receptor-BSEP signaling axis

FXR agonists activate the Farnesoid X receptor (NR1H4), which then heterodimerizes with the Retinoid X receptor (RXR) and binds to the IR-1 element in the promoter of the ABCB11 gene. This induces the transcription and expression of the Bile Salt Export Pump (BSEP), which facilitates the ATP-dependent efflux of bile acids from hepatocytes into the bile canaliculi, thereby reducing intrahepatic bile acid concentrations and preventing hepatotoxicity.