The role of oxysterols in cholesterol homeostasis.

Cholesterol biosynthesis is regulated by transcription factors named steroid regulatory element-binding proteins. A newly discovered transcription factor, LXR, regulates the catabolic degradation of cholesterol by activation of the gene controlling cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme in the formation of bile acids. Excessive dietary cholesterol leads to increased oxysterol formation. Oxysterol binds to LXR and thereby induces transcription of cholesterol 7 alpha-hydroxylase, thus increasing the removal of cholesterol as bile acids.