Identification and characterization of novel splice variants of human farnesoid X receptor

Area of Science:

• Molecular biology
• Hepatology
• Nuclear receptor signaling

Background:

• Farnesoid X receptor (FXR) regulates key metabolic pathways, including bile acid, lipid, and glucose metabolism.
• FXR is a validated drug target for liver diseases like primary biliary cholangitis and non-alcoholic steatohepatitis.
• Previous research identified four FXR splice variants, suggesting functional diversity through alternative promoter usage and splicing.

Purpose of the Study:

• To systematically analyze human hepatic FXR splice variants.
• To identify novel FXR isoforms and characterize their functional properties.
• To investigate the potential impact of these variants on FXR activity and liver disease.

Main Methods:

• Systematic analysis of human hepatic FXR splice variants.
• Identification of novel splice variants through exon skipping events.
• Functional characterization including DNA binding, transactivation, heterodimerization, coactivator recruitment, and ligand binding assays.
• Molecular dynamics simulations to explain molecular behavior.
• Analysis of tissue expression levels.

Main Results:

• Identification of four novel human hepatic FXR splice variants (FXRα5-8) resulting from exon skipping.
• All newly identified isoforms exhibited diminished DNA binding and impaired transactivation.
• FXRα5 demonstrated dominant-negative activity by suppressing the function of the canonical FXRα2 isoform.
• FXRα5 showed deficiencies in heterodimerization, coactivator recruitment, and ligand binding, explained by molecular dynamics.
• FXRα5 displayed low, uniform expression across human tissues.

Conclusions:

• The study identified four novel, functionally deficient FXR splice variants in human hepatocytes.
• FXRα5 possesses dominant-negative activity, potentially influencing FXR signaling.
• The roles of these novel FXR isoforms in human liver diseases warrant further investigation.