Adipose circadian clocks: coordination of metabolic rhythms by clock genes, steroid hormones, and PPARs.

A central clock consisting of interconnected positive and negative feedback gene loops operates in the brain, tying rhythmic activity to the 24-h day. The central clock entrains similar feedback loops present in most peripheral tissues to coordinate metabolic gene expression among organs and with feeding activity for more efficient utilization of resources. Recent studies are beginning to elucidate the intricate feedback mechanisms among central and peripheral clocks and their roles in activity and metabolic homeostasis. Adipose tissue serves as a major energy storage organ and releases paracrine and endocrine hormones to signal energy status to other organs. Within the adipose tissue, the transcriptional feedback regulation between clock genes and nuclear hormone receptors, together with direct protein associations among these molecules, ensures the expression of metabolic genes at the appropriate time. This review will summarize the important components and mechanisms of adipose clock entrainment, particularly highlighting instructive studies carried out in mice. This research not only illustrates the intricate connections between clocks and metabolism but also provides potential mechanisms to correct abnormalities induced by disrupted sleep or poor diet.