Constant Darkness Is a Mammalian Biological Signal

Lee, Cheng‐Chi

doi:10.1101/sqb.2007.72.051

Cited by 10 publications

(10 citation statements)

References 17 publications

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“…Cd73 is regarded as the key enzyme in the formation of adenosine from 5 0 -AMP, which is an inducer of procolipase expression (40,41). The increased mRNA levels of Cd73 may downregulate 5 0 -AMP levels, thus subsequently inhibiting pancreatic lipase/procolipase expression, and negatively regulating fat absorption by the small intestine.…”

Section: Discussionmentioning

confidence: 99%

Gender Disparity of Hepatic Lipid Homoeostasis Regulated by the Circadian Clock

Yang

Zhang

Esterly

et al. 2009

Journal of Biochemistry

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The mammalian clock regulates major aspects of energy metabolism, including glucose and lipid homoeostasis as well as mitochondrial oxidative metabolism. This study is to identify specific patterns of circadian rhythms for lipid homoeostasis in both female and male mouse livers, and to clarify gender disparity in coupling the peripheral circadian clock to lipid metabolic outputs by nuclear receptors. To achieve this, profiling the diurnal hepatic expression of genes encoding circadian clocks, nuclear receptors and lipid metabolic enzymes was performed. Hepatic lipid levels including cholesterol, triglyceride and non-esterified fatty acids (NEFAs) were monitored over a 24-h period. The cosinor analysis revealed that several genes encoding nuclear receptors and enzymes involved in the lipid metabolic pathway were rhythmically expressed in liver in phase with the peripheral clocks, which were correlated with the diurnal changes of hepatic lipid levels. Gender disparity was observed for circadian characteristics including mesor and amplitude values, accompanied with advances in acrophases in female mouse livers. Accordingly, gender differences were also observed in diurnal lipid homoeostasis. The identification of cycling patterns for lipid metabolic pathways in both female and male mouse livers may shed light on the development of gender-based treatment for human diseases related to the coordination of the cellular clock and control of lipid homoeostasis.Key words: Circadian rhythm, gender, lipid homoeostasis, liver, nuclear receptor.Abbreviations: Bmal1, brain and muscle Arnt-like protein 1; Clock, circadian locomotor output cycles kaput; Cry, cryptochrome; LXR, liver X receptor; Mesor, midline estimating statistic of rhythm; NEFA, nonesterified fatty acids; Per, period; PGC1, PPARg coactivator 1; PPAR, peroxisome proliferator-activated receptor; ROR, retinoid-related orphan receptor; RORE, ROR response element.Circadian rhythms are daily cycles of multiple molecular, biochemical, physiological and behavioural processes that are driven by an endogenous clock with an approximate 24-h periodicity. Circadian rhythms in mammals are governed substantially by the main time-keeping system, called the central circadian clock, located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Circadian clocks also exist in most peripheral tissues and even in cultured cells. It is believed that the master circadian clock synchronizes the peripheral clocks through both neural and humoral factors, allowing animals to adapt their feeding, activity and metabolism to predictable rhythmic cycles. Environmental light is the predominant Zeitgeber (time-giver) to reset the intrinsic clocks. In addition, other cyclic inputs such as temperature, food, noise or social cues may also influence the phase of clocks (1-3).The central and peripheral clocks share common molecular circuitry. The circadian clockwork consists of two auto-regulatory feedback loops connected by a central pair of basic-helix-loop-helix (bHLH)-PAS (PER-ARNT-SIM)-cont...

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Section: Discussionmentioning

confidence: 99%

Gender Disparity of Hepatic Lipid Homoeostasis Regulated by the Circadian Clock

Yang

Zhang

Esterly

et al. 2009

Journal of Biochemistry

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“…Conversely, Gluck et al (2006) reported that ghrelin administration increased torpor in mice, although this eVect was countered by ablation of the ghrelin-rich area of the hypothalamus. A period of constant darkness modulates many of the enzymes associated with metabolism, inducing torpor and hibernation (Lee 2007), possibly through secretion of a speciWc hibernation hormone (Kondo 2007) involved in the orexigenic neuropeptide Y (NPY) signalling pathway (Chen et al 2004).…”

Section: Comparative Physiologymentioning

confidence: 99%

Seasonal variations in physical activity and implications for human health

2009

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This review explores the implications of seasonal changes in physical activity for fitness and human health. Photosensitivity and nutrient shortages mediate animal hibernation via the hypothalamus and changes in leptin and ghrelin concentrations. Opportunities for hunting and crop cultivation determine seasonal activity in under-developed human societies, but in developed societies temperature and rainfall are dominant influences, usually over-riding innate rhythms. Both questionnaire data and objective measurements show that many groups from children to the elderly increase their physical activity from winter to spring or summer. Measurements of maximal oxygen intake and muscle strength commonly show parallel seasonal changes. However, potential effects upon body mass and body fat may be counteracted by changes of food intake; subsistence agriculturists sometimes maintain or increase physical activity at the expense of a decrease in body mass. In developed societies, body fat commonly increases during the winter, with parallel changes in blood lipids, blood pressure and blood coagulability; moreover, these changes are not always fully reversed the following summer. Most developed societies show increased all-cause and cardiac mortalities in the winter. Health consequences of seasonal variations in physical activity including an increased vulnerability to cardiac catastrophe and a year-by-year increase in total body fat seem most likely if the average level of physical activity for the year is low. Public health recommendations should underline the importance of maintaining physical activity during adverse environmental conditions by adapting clothing, modifying behaviour and exploiting any available air-conditioned indoor facilities.

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“…However, under the constant light or dark conditions, a rhythm still persists [16]. Three models are often used to perform circadian researches: light-dark conditions (12 h light:12 h dark, LD), constant darkness (DD), and constant light (LL) [17,18]. Although most clock researches are carried out using the LD model, several studies described circadian rhythm under the DD condition where the time is referred as CT units, different from Zeitgeber Time (ZT) [17,[19][20][21].…”

Section: Introductionmentioning

confidence: 99%

“…In the DD model, animals are shielded from light to eliminate entrainment effects on the circadian clock, known as "free running rhythm", which is regarded as mammalian biological signal in metabolism [18,22]. Under DD condition, wheel-running experiment was performed to monitor the rhythm of locomotor activity [23].…”

Section: Introductionmentioning

confidence: 99%

Endogenous circadian time genes expressions in the liver of mice under constant darkness

Zhang

et al. 2020

BMC Genomics

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Background: The circadian rhythms regulate physiological functions and metabolism. Circadian Time (CT) is a unit to quantify the rhythm of endogenous circadian clock, independent of light influence. To understand the gene expression changes throughout CT, C57BL/6 J mice were maintained under constant darkness (DD) for 6 weeks, and the liver samples were collected starting at 9:00 AM (CT1), and every 4 h in a 24-h cycle (CT5, CT9, CT13, CT17 and CT21). Total RNA was extracted and subjected to RNA-Seq data (deposited as GSE 133342, L-DD). To compare gene oscillation pattern under normal light-dark condition (LD, GSE114400) and short time (2 days) dark-dark condition (S-DD, GSE70497), these data were retried from GEO database, and the trimmed mean of M-values normalization was used to normalize the three RNA-seq data followed by MetaCycle analysis. Results: Approximate 12.1% of the genes under L-DD exhibited significant rhythmically expression. The top 5 biological processes enriched in L-DD oscillation genes were mRNA processing, aromatic compound catabolic process, mitochondrion organization, heterocycle catabolic process and cellular nitrogen compound mitotic catabolic process. The endogenous circadian rhythms of clock genes, P450 genes and lipid metabolism genes under L-DD were further compared with LD and S-DD. The oscillation patterns were similar but the period and amplitude of those oscillation genes were slightly altered. RT-qPCR confirmed the selected RNA sequence findings. Conclusions: This is the first study to profile oscillation gene expressions under L-DD. Our data indicate that clock genes, P450 genes and lipid metabolism genes expressed rhythmically under L-DD. Light was not the necessary factor for persisting circadian rhythm but influenced the period and amplitude of oscillation genes.

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Constant Darkness Is a Mammalian Biological Signal

Cited by 10 publications

References 17 publications

Gender Disparity of Hepatic Lipid Homoeostasis Regulated by the Circadian Clock

Gender Disparity of Hepatic Lipid Homoeostasis Regulated by the Circadian Clock

Seasonal variations in physical activity and implications for human health

Endogenous circadian time genes expressions in the liver of mice under constant darkness

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