Constant Darkness Is a Mammalian Biological Signal

  1. C. C. Lee
  1. Department of Biochemistry and Molecular Biology, University of Texas Health Science Center, Houston, Texas 77030

Abstract

Environmental light is a potent modulator of mammalian circadian rhythm and expression of clock genes. Constant darkness (DD) is regarded as a “free-running” circadian state. In nature, hibernating mammals encounter constant darkness (DD) seasonally. Circadian expression of enzymes involved in fat catabolism, procolipase (CLP) and pancreatic-lipase-related protein 2 (PLRP2), were identified in many peripheral organs of mice during DD but not during regular light/dark (LD) cycles. Circulating 5′-adenosine monophosphate (5′-AMP) was associated with DD-activated gene expression. Synthetic 5′-AMP, when injected into LD mice, activated procolipase expression in their peripheral organs and the animals become severely hypothermic, both key features of hibernating mammals. These findings identified a circadian-regulated metabolic cycle in mammals that may be associated with hypometabolic behaviors such as hibernation and torpor.

Footnotes

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