Farnesoid X receptor (NR1H4) (FXR)

The Farnesoid X receptor (FXR), encoded by the NR1H4 gene, is a ligand-activated nuclear transcription factor that serves as the primary sensor for bile acids in the enterohepatic system. While highly expressed in both the liver and the intestine, intestinal FXR signaling plays a distinct and critical role in metabolic regulation by inducing the secretion of fibroblast growth factor 19 (FGF19). FGF19 acts as an endocrine hormone that travels to the liver to inhibit the rate-limiting enzyme of bile acid synthesis, CYP7A1, thereby preventing bile acid toxicity and maintaining homeostasis. Beyond bile acid regulation, intestinal FXR signaling is involved in lipid and glucose metabolism, as well as the maintenance of the intestinal epithelial barrier and the modulation of gut-associated immune responses. Dysregulation of this pathway is a hallmark of diseases such as nonalcoholic steatohepatitis (NASH), primary biliary cholangitis (PBC), and inflammatory bowel disease (IBD). Pharmacological activation of FXR using agonists like obeticholic acid has shown therapeutic efficacy in treating these conditions, although clinical use is often limited by side effects such as severe pruritus and adverse changes in serum lipid profiles.

Other names

Bile acid receptorBARNuclear receptor subfamily 1 group H member 4NR1H4FXR-alpha

Agonist; activates the receptor to regulate gene expression, notably inducing intestinal fibroblast growth factor 19 (FGF19) to suppress hepatic bile acid synthesis via the FGFR4/beta-Klotho complex.