Clock regulation of dietary lipid absorption.

PURPOSE OF REVIEW: To summarize the new knowledge about the regulation of dietary lipid absorption by circadian locomotor output cycles kaput (Clock) and Nocturnin. RECENT
FINDINGS: Recent findings have shown that Clock and Nocturnin, proteins involved in circadian regulation, play an important role in the regulation of dietary lipid absorption. Clock deficiency increases, whereas Nocturnin deficiency decreases lipid absorption. Clock plays a role in turning off the genes involved in lipid absorption at the onset of the day. Molecular studies revealed that Clock binds to the promoter of small heterodimer partner to enhance its transcription. When levels are high, small heterodimer partner interacts with the transcription factors associated with the promoter of microsomal triglyceride transfer protein to repress transcription. Reduced microsomal triglyceride transfer protein levels are correlated with low intestinal lipid absorption and plasma lipid levels. In contrast, Nocturnin assists in lipid absorption by regulating their partitioning in different intracellular compartments.
SUMMARY: Clock and Nocturnin regulate lipid absorption involving different mechanisms. It is likely that other clock genes also modulate lipid absorption and plasma lipid levels.