title: Constant darkness is a mammalian biological signal.
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.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas Health Science Center, Houston, Texas 77030, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Lee
mesh_terms: D000249:Adenosine Monophosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D003089:Colipases / Q000235:genetics / Q000378:metabolism; D003624:Darkness; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D006605:Hibernation / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D008049:Lipase / Q000378:metabolism; D051379:Mice; D017440:Photoperiod; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012621:Seasons; D015398:Signal Transduction / Q000502:physiology
chemical_list: D003089:Colipases; D004792:Enzyme Precursors; D012333:RNA, Messenger; D000249:Adenosine Monophosphate; C037107:procolipase; D008049:Lipase; C075988:pancreatic lipase related protein 2