Implications of Circadian Rhythms on Metabolic Disorders

A vital role of circadian rhythms is to enable an organism to predict or adapt to environmental oscillations, including internal and external cues. These physiological and behavioral circadian rhythmicities are exhibited by all mammals and are generated by intracellular levels of circadian oscillators, which are composed of transcriptional/translational feedback loops involving a set of circadian-clock genes. These circadian-clock genes play important roles in regulating not only circadian rhythms but also energy homeostasis and metabolism. Increasing evidence shows that mutations or knockouts of circadian-clock genes or disruptions of the circadian rhythm initiate metabolic disorders. Similarly, high-nutrient diets influence the expression levels of circadian-clock genes in the liver. Changes in the cellular redox potential affect the activity of circadianclock gene transcription factors and the expressions and functions of circadian-clock genes, which regulate energy metabolism. The characterizations of circadian-clock genes have potential therapeutic relevance with respect to the pathogenesis and treatment of obesity-related metabolic diseases including type 2 diabetes and metabolic syndrome.