Farnesoid X receptor (FXR; NR1H4), a member of the nuclear receptor (NR) superfamily, was identified as a receptor of bile acids (BAs).  As a ligand-activated transcription factor, FXR binds to DNA (i.e., FXR response elements) as a monomer or as a heterodimer with a common partner for NRs, retinoid X receptor (RXR; NR2B1), in order to regulate the expression of the diverse genes involved in the metabolism of BAs, lipids, and carbohydrates. There are two known FXR genes (i.e., FXRα (NR1H4) and FXRβ (NR1H5)). A single FXRα gene in human and rodents encodes four different isoforms (FXRα1, FXRα2, FXRα3, and FXRα4), resulting from different promoters and RNA splicing. FXR is mainly expressed in various tissues including the liver, intestine, kidney, and adrenal gland, with much lesser extents in the adipose tissue and heart.  FXR has been identified as a promising therapeutic target for the management of liver and/or metabolic diseases, allowing the pharmacological approaches to develop FXR modulators.


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