Taurine is a liver X receptor-alpha ligand and activates transcription of key genes in the reverse cholesterol transport without inducing hepatic lipogenesis

Abstract

Scope: Taurine, which is abundant in seafood, has antiatherogenic activities in both animals and humans; however, its molecular target has been elusive. We examined whether taurine could activate liver X receptor-alpha (LXR-alpha), a critical transcription factor in the regulation of reverse cholesterol transport in macrophages. Methods and results: Taurine bound directly to LXR-alpha in a reporter gene assay, time-resolved fluorescence resonance energy transfer analysis, and limited protease digestion experiment. Macrophage cells incubated with taurine showed reduced cellular cholesterol and induced medium cholesterol in a dose-dependent manner with the induction of ATP-binding cassette transporter A1 and G gene and protein expression. In hepatocytes, taurine significantly induced Insig-2a levels and delayed nuclear translocation of the sterol regulatory element-binding protein 1 (SREBP-1) protein, resulting in a dose-dependent reduction in the cellular lipid levels without inducing the expression of fatty acid synthesis genes. Conclusion: Taurine is a direct LXR-alpha ligand, represses cholesterol accumulation, and modulates the expression of genes involved in reverse cholesterol transport in macrophages, without inducing hepatic lipogenesis. The induction of Insig-2a suppressed the nuclear translocation of SREBP-1c.