Per2 Mice Research Articles

Per2 Expression Regulates the Spatial Working Memory of Mice through DRD1-PKA-CREB Signaling.

Several individuals worldwide show cognitive impairment due to various reasons, including a prolonged lifespan and an altered lifestyle. Various causes, such as broken circadian rhythms and dopamine-related factors, have been proposed to be involved in the development of cognitive impairment. However, the underlying pathways remain elusive. Humans with circadian misalignment often face cognitive impairments, and animals with mutations in circadian rhythm-related genes display impaired cognitive functions. To analyze this in detail, this study aimed to investigate the pathways potentially involved in cognitive impairment using Period2 (Per2) transgenic animals. Spatial working memory performance in Per2 knockout (KO) and wild-type mice was assessed using the Barnes maze and Y-maze. The dopamine-related protein expression levels in the hippocampus were measured by Western blotting and enzyme-linked immunosorbent assay (ELISA). Per2 KO mice exhibited impaired spatial working memory, and the expression levels of dopamine receptor D1 (DRD1), protein kinase A (PKA), and cAMP response element-binding protein (CREB) were higher in Per2 KO mice than in control mice. Additionally, DRD1 expression levels were inversely proportional to those of PER2. Thus, memory tests were again conducted after administration of the DRD1 antagonist SCH-23390. Per2 KO mice recovered from memory impairment, and the levels of PKA and CREB decreased after treatment. The effects of Aβ on memory in Per2 mice were also investigated, and we found the increased Aβ levels did not influence the memory performance of Per2 mice after SCH-23390 treatment. These results indicate that Per2 expression levels might influence spatial working memory performance via DRD1-PKA-CREB-dependent signaling.

The Period 2 Enhancer Nobiletin as Novel Therapy in Murine Models of Circadian Disruption Resembling Delirium.

Delirium occurs in approximately 30% of critically ill patients, and the risk of dying during admission doubles in those patients. Molecular mechanisms causing delirium are largely unknown. However, critical illness and the ICU environment consistently disrupt circadian rhythms, and circadian disruptions are strongly associated with delirium. Exposure to benzodiazepines and constant light are suspected risk factors for the development of delirium. Thus, we tested the functional role of the circadian rhythm protein Period 2 (PER2) in different mouse models resembling delirium. Animal study. University experimental laboratory. Wildtype, Per2 mice. Midazolam, lipopolysaccharide (lipopolysaccharide), constant light, nobiletin, or sham-treated animals. Midazolam significantly reduced the expression of PER2 in the suprachiasmatic nucleus and the hippocampus of wild-type mice. Behavioral tests following midazolam exposure revealed a robust phenotype including executive dysfunction and memory impairment suggestive of delirium. These findings indicated a critical role of hippocampal expressed PER2. Similar results were obtained in mice exposed to lipopolysaccharide or constant light. Subsequent studies in Per2 mice confirmed a functional role of PER2 in a midazolam-induced delirium-like phenotype. Using the small molecule nobiletin to enhance PER2 function, the cognitive deficits induced by midazolam or constant light were attenuated in wild-type mice. These experiments identify a novel role for PER2 during a midazolam- or constant light-induced delirium-like state, highlight the importance of hippocampal PER2 expression for cognitive function, and suggest the PER2 enhancer nobiletin as potential therapy in delirium-like conditions associated with circadian disruption.

Lack of Food Anticipation in Per2 Mutant Mice

Predicting time of food availability is key for survival in most animals. Under restricted feeding conditions, this prediction is manifested in anticipatory bouts of locomotor activity and body temperature. This process seems to be driven by a food-entrainable oscillator independent of the main, light-entrainable clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus . Although the SCN clockwork involves self-sustaining transcriptional and translational feedback loops based on rhythmic expression of mRNA and proteins of clock genes , the molecular mechanisms responsible for food anticipation are not well understood. Period genes Per1 and Per2 are crucial for the SCN's resetting to light . Here, we investigated the role of these genes in circadian anticipatory behavior by studying rest-activity and body-temperature rhythms of Per1 and Per2 mutant mice under restricted feeding conditions. We also monitored expression of clock genes in the SCN and peripheral tissues. Whereas wild-type and Per1 mutant mice expressed regular food-anticipatory activity, Per2 mutant mice did not show food anticipation. In peripheral tissues, however, phase shifts of clock-gene expression in response to timed food restriction were comparable in all genotypes. In conclusion, a mutation in Per2 abolishes anticipation of mealtime, without interfering with peripheral synchronization by feeding cycles.

035. Circadian rhythms and the early life programming of adult physiological systems

We are all familiar with the idea that the external environment influences many diverse physiological systems. For example, the level of nutrition can not only influence adult health directly, but also fetal development and subsequently many adult functions in the offspring. Maternal stress can affect fetal outcomes as can the administration of drugs during pregnancy. Until recently, however, the daily changes in environmental light have been considered to really only influence the time that we sleep and in many other species the optimal time to mate. The impact of circadian rhythms on life trajectory has had little attention. In the last 5 years it has become clear that circadian rhythmicity is entrenched in virtually every cell of our bodies. A suite of clock gene transcription factors that include Clock, Bmal1 and the period and cryptochrome genes, generate a robust daily cycle of transcription and translation of hundreds of proteins. This cellular clock system is synchronised with the external photoperiod through retinal light perception, the hypothalamic suprachiasmatic nucleus (SCN) and neural and hormonal pathways. Most importantly when the clock system in peripheral tissues is disrupted, a growing list of detrimental consequences are being uncovered. As an example, mice with mutations in either Clock or Bmal1 have non-rhythmic peripheral tissues and exhibit mild to severe reproductive failure and metabolic dysfunction. Null per2 mice have a higher incidence of salivary gland hyperplasia, teratomas and increased susceptibility to radiation induced lymphomas. It is also apparent that intrauterine insults (e.g. cocaine administration, poor nutrition and stress) can have long term effects on the central circadian timing system in the SCN. Whether this involves alterations in neural development or gene function is not known. Nevertheless it is time we paid more attention to the temporal nature of our environment as a possible contributor to lifetime disorders and diseases.

Big Ben Rings in a Lesson on Biological Clocks

There is a long history of experimental work seeking a connection between circadian clocks and the cell cycle. For some eukaryotic, unicellular systems, the evidence is quite good—photocycles that entrain circadian rhythms reset ∼24 hr rhythms of cell division that persist for many days in constant darkness or constant light (reviewed by Edmunds, 1988xEdmunds, L.N. Jr. See all ReferencesEdmunds, 1988). Are there comparable interactions in multicellular organisms, even mammals?Cheng Chi Lee produced a list of novel phenotypes in Per 2 mutant mice that indicate action of PER as a tumor suppressor, as a regulator of cell growth, and as a component of the DNA damage response (Fu et al., 2002xThe circadian gene Period2 plays an important role in tumor suppression and DNA damage response in vivo. Fu, L., Pelicano, H., Liu, J., Huang, P., and Lee, C. Cell. 2002; 111: 41–50Abstract | Full Text | Full Text PDF | PubMed | Scopus (690)See all References(Fu et al., 2002). First, there is a highly significant difference in the frequency of spontaneous and γ irradiation-induced tumors and hyperplasia in Per2 mice. In fact, all Per2 mice develop an otherwise rarely encountered, salivary gland hyperplasia by the age of 8 months. Per2 mice were also found to be unusually resistant to irradiation-induced apoptosis. This deficiency appears to be linked to reduced induction of p53 and associated cytochrome c regulation. Even more surprising, Lee's laboratory reports that genes composing the clock are induced by γ irradiation in wild-type but not Per2 mice, suggesting a possible role for the clock itself in the apoptotic response.Timed expression of several genes central to cell cycle control is altered in Per2 mice. For example, both cyclin A and cyclin D1 mRNAs accumulate in hepatocytes from wild-type mice with a circadian rhythm. The phase and amplitude of both rhythms appear to be substantially altered in Per2 mice (Fu et al., 2002xThe circadian gene Period2 plays an important role in tumor suppression and DNA damage response in vivo. Fu, L., Pelicano, H., Liu, J., Huang, P., and Lee, C. Cell. 2002; 111: 41–50Abstract | Full Text | Full Text PDF | PubMed | Scopus (690)See all References(Fu et al., 2002). Since cyclin D1 is a target for c-myc, the latter gene's regulation was also examined; c-myc too oscillates with a circadian rhythm that is significantly altered in Per2 mutants. Lee suggested that, in particular, strong upward swings in c-myc expression may underlie the salivary gland hyperplasia his laboratory sees in Per2 mice.Testing a focused proposal of this sort will be challenging because circadian clocks command such broad programs of timed gene expression. Recall that in the mouse, 24 hr clocks not only determine the sequential expression of hundreds of genes, but the list of clock-controlled targets is tissue specific, amplifying the complexity of the temporal code. Presumably, a Per2 mutant response ripples through the entire program of rhythmic expression in each tissue. Surely connections between individual clock-controlled genes and elements of the Per2 phenotype will remain speculative for awhile. These difficulties aside, the mouse Per2 study does remind us that a dominant mutation of this gene has been associated with FASPS, a familial sleep disorder in humans (Toh et al., 2001xAn hPer2 phosphorylation site mutation in familial advanced sleep phase syndrome. Toh, K.L., Jones, C.R., He, Y., Eide, E.J., Hinz, W.A., Virshup, D.M., Ptacek, L.J., and Fu, Y.H. Science. 2001; 291: 1040–1043Crossref | PubMed | Scopus (824)See all References(Toh et al., 2001). It would be fascinating to study the range of phenotypic effects associated with this Per2 mutation in transgenic mice.