A scenario of unhealthy life cycle: The role of circadian rhythms in health.

Circadian rhythms are oscillations in physiology and behavior caused by the circadian regulator. Cryptochromes, Periods, and Bmal1 are circadian clock genes that have been linked to aging and cancer. Human pathologies alter circadian clock gene expression, and transgenic rats with clock gene defects progress to cancer and age prematurely. In the growth of age-linked pathologies and carcinogenesis, cell proliferation and genome integrity play critical roles. The relationship concerning the cell cycle regulation and circadian clock is discussed in this article. The circadian clock controls the behavior and countenance of many main cell cycle and cell cycle check-point proteins, and cell cycle-associated proteins, in turn, control the activity and expression of circadian clock proteins. The circadian clock can be reset by DNA disruption, providing a molecular mechanism for mutual control amid the cell cycle and the clock. This circadian clock-dependent regulation of cell proliferation, composed with other circadian clock-dependent physiological functions including metabolism control, genotoxic and oxidative stress response, and DNA repair, unlocks new avenues for studying the processes of aging and carcinogenesis.