Hepatic Clock Gene Expression Research Articles

Effects of Dim Light at Night on Food Intake and Body Mass in Developing Mice

Appropriately timed light is critical for circadian organization; exposure to dim light at night (dLAN) disrupts temporal organization of endogenous biological timing. Exposure to dLAN in adult mice is associated with elevated body mass and changes in metabolism putatively driven by voluntary changes in the time of food intake. We predicted that exposure of young mice to LAN could affect adult metabolic function. At 3 weeks (Experiment 1) or 5 weeks (Experiment 2) of age, mice were either maintained in standard light-dark (DARK) cycles or exposed to nightly dLAN (5 lux). In the first two experiments, food intake and locomotor activity were assessed after 4 weeks and a glucose tolerance test was administered after 6 weeks in experimental lighting conditions. In Experiment 3, tissues were collected around the clock at 6 h intervals to investigate rhythmic hepatic clock gene expression in mice exposed to dLAN from 3 or 5 weeks of age. Male and female mice exposed to dLAN beginning at 3 weeks of age displayed similar growth rates and body mass to DARK-reared offspring, despite increasing day-time food intake. Exposure to dLAN beginning at 5 weeks of age increased body mass and daytime food intake in male, but not female, mice. Consistent with the body mass phenotype, clock gene expression was unaltered in the liver. In contrast to adults, dLAN exposure during the development of the peripheral circadian system has sex- and development-dependent effects on body mass gain.

Pregnancy-induced changes in the circadian expression of hepatic clock genes: implications for maternal glucose homeostasis.

Adaptations in maternal carbohydrate metabolism are particularly important in pregnancy because glucose is the principal energy substrate used by the fetus. As metabolic homeostasis is intricately linked to the circadian system via the rhythmic expression of clock genes, it is likely that metabolic adaptations during pregnancy also involve shifts in maternal circadian function. We hypothesized that maternal adaptation in pregnancy involves changes in the hepatic expression of clock genes, which drive downstream shifts in circadian expression of glucoregulatory genes. Maternal liver and plasma (n = 6-8/group) were collected across 24-h periods (0800, 1200, 1600, 2000, 0000, 0400) from C57Bl/6J mice under isoflurane-nitrous oxide anesthesia prior to and on days 6, 10, 14 and 18 of pregnancy (term = day 19). Hepatic expression of clock genes and glucoregulatory genes was determined by RT-qPCR. Hepatic clock gene expression was substantially altered across pregnancy, most notably in late gestation when the circadian rhythmicity of several clock genes was attenuated (≤64% reduced amplitude on day 18). These changes were associated with a similar decline in rhythmicity of the key glucoregulatory genes Pck1, G6Pase, and Gk, and by day 18, Pck1 was no longer rhythmic. Overall, our data show marked adaptations in the liver clock during mouse pregnancy, changes that may contribute to the altered circadian variation in glucoregulatory genes near term. We propose that the observed reduction of daily oscillations in glucose metabolism ensure a sustained supply of glucose to meet the high demands of fetal growth.

Altered cellular redox status, sirtuin abundance and clock gene expression in a mouse model of developmentally primed NASH

BackgroundWe have previously shown that high fat (HF) feeding during pregnancy primes the development of non-alcoholic steatohepatits (NASH) in the adult offspring. However, the underlying mechanisms are unclear. AimsSince the endogenous molecular clock can regulate hepatic lipid metabolism, we investigated whether exposure to a HF diet during development could alter hepatic clock gene expression and contribute to NASH onset in later life. MethodsFemale mice were fed either a control (C, 7%kcal fat) or HF (45%kcal fat) diet. Offspring were fed either a C or HF diet resulting in four offspring groups: C/C, C/HF, HF/C and HF/HF. NAFLD progression, cellular redox status, sirtuin expression (Sirt1, Sirt3), and the expression of core clock genes (Clock, Bmal1, Per2, Cry2) and clock-controlled genes involved in lipid metabolism (Rev-Erbα, Rev-Erbβ, RORα, and Srebp1c) were measured in offspring livers. ResultsOffspring fed a HF diet developed NAFLD. However HF fed offspring of mothers fed a HF diet developed NASH, coupled with significantly reduced NAD+/NADH (p<0.05, HF/HF vs C/C), Sirt1 (p<0.001, HF/HF vs C/C), Sirt3 (p<0.01, HF/HF vs C/C), perturbed clock gene expression, and elevated expression of genes involved lipid metabolism, such as Srebp1c (p<0.05, C/HF and HF/HF vs C/C). ConclusionOur results suggest that exposure to excess dietary fat during early and post-natal life increases the susceptibility to develop NASH in adulthood, involving altered cellular redox status, reduced sirtuin abundance, and desynchronized clock gene expression.

Short-term circadian disruption impairs bile acid and lipid homeostasis in mice.

Background & AimsBile acids are physiologic detergents that also activate nuclear receptors to regulate glucose and lipid homeostasis. Cholesterol 7α-hydroxylase (Cyp7a1), the rate-limiting enzyme that converts cholesterol to bile acids, is transcriptionally regulated by bile acids and circadian rhythms. Fasting, nutrients, and the circadian clock critically control hepatic bile acid and lipid homeostasis, and circadian misalignment is associated with the metabolic syndrome in humans. To delineate these interactions, we employed a sleep disruption model to induce circadian disruption and examined hepatic metabolism with respect to bile acids, lipids, and clock gene expression.MethodsB6xC57 mice were maintained on chow or Western diet and were sleep disrupted for 6 hours/day for 5 days. Mice were sacrificed at 4-hour intervals over 24 hours. Hepatic metabolic genes were examined, and bile acid pool and lipid profiles were measured over 24 hours.ResultsSleep disruption significantly suppressed circadian expression of core clock genes, genes involved in lipid metabolism, and key regulators of Cyp7a1 as well as Cyp7a1 expression itself. Sleep disruption abolished the peak in serum cholesterol and increased liver and serum free fatty acids. Bile acid pool size was increased while liver bile acids were decreased. Chromatin immunoprecipitation assay revealed that hepatocyte nuclear factor 4α (HNF4α) and D-site binding protein (Dbp) occupancies were suppressed at the Cyp7a1 promoter in sleep-disrupted mice. When coupled with Western diet, sleep disruption abolished liver clock rhythms and elevated free fatty acids.ConclusionsEven short-term circadian disruption dramatically alters hepatic clock gene expression, bile acid metabolism, and lipid homeostasis to contribute to dyslipidemia.

Involvement of adenosine monophosphate–activated protein kinase in the influence of timed high-fat evening diet on the hepatic clock and lipogenic gene expression in mice

A high-fat diet may result in changes in hepatic clock gene expression, but potential mechanisms are not yet elucidated. Adenosine monophosphate–activated protein kinase (AMPK) is a serine/threonine protein kinase that is recognized as a key regulator of energy metabolism and certain clock genes. Therefore, we hypothesized that AMPK may be involved in the alteration of hepatic clock gene expression under a high-fat environment. This study aimed to examine the effects of timed high-fat evening diet on the activity of hepatic AMPK, clock genes, and lipogenic genes. Mice with hyperlipidemic fatty livers were induced by orally administering high-fat milk via gavage every evening (19:00-20:00) for 6 weeks. Results showed that timed high-fat diet in the evening not only decreased the hepatic AMPK protein expression and activity but also disturbed its circadian rhythm. Accordingly, the hepatic clock genes, including clock, brain-muscle-Arnt-like 1, cryptochrome 2, and period 2, exhibited prominent changes in their expression rhythms and/or amplitudes. The diurnal rhythms of the messenger RNA expression of peroxisome proliferator–activated receptorα, acetyl-CoA carboxylase 1α, and carnitine palmitoyltransferase 1 were also disrupted; the amplitude of peroxisome proliferator–activated receptorγcoactivator 1α was significantly decreased at 3 time points, and fatty liver was observed. These findings demonstrate that timed high-fat diet at night can change hepatic AMPK protein levels, activity, and circadian rhythm, which may subsequently alter the circadian expression of several hepatic clock genes and finally result in the disorder of hepatic lipogenic gene expression and the formation of fatty liver.

Crucial roles of mixed-lineage leukemia 3 and 4 as epigenetic switches of the hepatic circadian clock controlling bile acid homeostasis in mice.

The histone H3-lysine-4 methyltransferase mixed-lineage leukemia 3 (MLL3) and its closest homolog, MLL4 (aka KMT2D), belong to two homologous transcriptional coactivator complexes, named MLL3 and MLL4 complexes, respectively. MLL3 plays crucial roles in multiple metabolic processes. However, the physiological roles of MLL4 in metabolism and the relationship between MLL3 and MLL4 in metabolic gene regulation are unclear. To address these issues, we analyzed the phenotypes of newly generated MLL4 mutant mice, along with MLL3 mutant and MLL3;MLL4 compound mutant mice. We also performed comparative genome-wide transcriptome analyses in livers of MLL3, MLL4, and MLL3;MLL4 mutant mice. These analyses revealed that MLL3 and MLL4 complexes are key epigenetic regulators of common metabolic processes and the hepatic circadian clock. Subsequent mechanistic analyses uncovered that MLL3/4 complexes function as pivotal coactivators of the circadian transcription factors (TFs), retinoid-related orphan receptor (ROR)-α and -γ, in the hepatic circadian clock. Consistent with disturbed hepatic clock gene expression in MLL4 mutant mice, we found that rhythmic fluctuation of hepatic and serum bile acid (BA) levels over the circadian cycle is abolished in MLL4 mutant mice. Our analyses also demonstrate that MLL4 primarily impinges on hepatic BA production among several regulatory pathways to control BA homeostasis. Together, our results provide strong in vivo support for important roles of both MLL3 and MLL4 in similar metabolic pathways. Both MLL3 and MLL4 complexes act as major epigenetic regulators of diverse metabolic processes (including circadian control of bile acid homeostasis) and as critical transcriptional coactivators of the circadian TFs, RORs.

Long‐lived and Obesity Resistant Mice Exhibit 24 h Locomotor Circadian Rhythms at Young and Old Age

Ageing is associated with disruption of circadian homeostasis, including reduced entraiment to light‐dark cycles, reduced amplitude and desynchronization of circadian physiological rhythms, and shortening or lengthening of the endogenous circadian period length (tau). αMUPA mice carry a transgene encoding the urokinase‐type plasminogen activator, an extracellular protease implicated in fibrinolysis, tissue remodeling, and brain plasticity. Female αMUPA mice spontaneously eat ~25% less, live ~20% longer, and show high‐amplitude circadian rhythms in food intake, body temperature, and in hepatic clock gene expression levels, compared with WT mice. Herein we examined the tau of locomotor activity of mature (8‐month old) and aged (18‐month old) female αMUPA and WT mice under total darkness. We show that tau changed in WT mice from a period &lt;24 h at 8 months to a period &gt;;24 h at 18 months. However, tau of αMUPA mice was ~24 h at both ages. Deviation of tau from 24 h has shown to be inversely related to life span of rodents and nonhuman primates. Hence, our results suggest that the sustainable endogenous period of ~24 h in αMUPA mice may contribute to their longevity. These results support the hypothesis that although a non‐24‐h tau has an adaptive significance in allowing a better response to natural daylight changes, such a lack of resonance between tau and external period length entails a life‐shortening metabolic cost.

Feeding Cues and Injected Nutrients Induce Acute Expression of Multiple Clock Genes in the Mouse Liver

The circadian clock is closely associated with energy metabolism. The liver clock can rapidly adapt to a new feeding cycle within a few days, whereas the lung clock is gradually entrained over one week. However, the mechanism underlying tissue-specific clock resetting is not fully understood. To characterize the rapid response to feeding cues in the liver clock, we examined the effects of a single time-delayed feeding on circadian rhythms in the liver and lungs of Per2::Luc reporter knockin mice. After adapting to a night-time restricted feeding schedule, the mice were fed according to a 4, 8, or 13 h delayed schedule on the last day. The phase of the liver clock was delayed in all groups with delayed feeding, whereas the lung clock remained unaffected. We then examined the acute response of clock and metabolism-related genes in the liver using focused DNA-microarrays. Clock mutant mice were bred under constant light to attenuate the endogenous circadian rhythm, and gene expression profiles were determined during 24 h of fasting followed by 8 h of feeding. Per2 and Dec1 were significantly increased within 1 h of feeding. Real-time RT-PCR analysis revealed a similarly acute response in hepatic clock gene expression caused by feeding wild type mice after an overnight fast. In addition to Per2 and Dec1, the expression of Per1 increased, and that of Rev-erbα decreased in the liver within 1 h of feeding after fasting, whereas none of these clock genes were affected in the lung. Moreover, an intraperitoneal injection of glucose combined with amino acids, but not either alone, reproduced a similar hepatic response. Our findings show that multiple clock genes respond to nutritional cues within 1 h in the liver but not in the lung.

Circadian Variation in Placental and Hepatic Clock Genes in Rat Pregnancy

Clock genes drive circadian rhythms in a range of physiological processes both centrally and in peripheral tissues such as the liver. The aims of this study were to determine whether the two functionally-distinct zones of the rat placenta (junctional and labyrinth) differentially express clock genes and, if so, whether these exhibit circadian patterns. Rats were sampled from d 21 of pregnancy (term = d 23) and from diestrus I of the estrous cycle. Adult liver (all animals), fetal liver, and placental zones (pregnant animals) were collected at 0800, 1400, 2000, and 0200 h. Both zones of the rat placenta expressed all seven canonical clock genes (Clock, Bmal1, Per1, Per2, Per3, Cry1, and Cry2), but there were marked zonal differences and, unlike in maternal liver, circadian variation in placenta was limited. Similarly, placental expression of Vegf varied with zone but not time of day. Pregnancy also led to marked changes in hepatic clock gene expression, with peak levels of Per1, Cry1, and Cry2 all reduced, Per3 increased, and circadian variation in Clock expression lost. All clock genes were expressed in fetal liver, but there was less circadian variation than in maternal liver. Similarly, fetal corticosterone levels remained stable across the day, whereas maternal corticosterone showed clear circadian variation. In conclusion, our data show that the rat placenta expresses all canonical clock genes in a highly zone-specific manner but with relatively little circadian variation. Moreover, pregnancy alters the expression and circadian variation of clock genes in maternal liver, possibly contributing to maternal physiological adaptations.

Long-lived mice exhibit 24 h locomotor circadian rhythms at young and old age

αMUPA transgenic mice exhibit spontaneously reduced eating and increased life span compared with their wild type (WT) control FVB/N mice. αMUPA mice also show high-amplitude circadian rhythms in food intake, body temperature, and hepatic clock gene expression. Here we examined young and aged WT and αMUPA mice for the period of locomotor activity ( tau) under total darkness (DD). We show that tau changed in WT mice from a period < 24 h at 8 months to a period > 24 h at 18 months. However, the period of αMUPA mice was ~ 24 h at both 8 and 18 months. As deviation of tau from 24 h has been found to be inversely related to life span in a large number of rodents, our results suggest that the sustainable endogenous period of ~ 24 h in αMUPA mice may contribute to their prolonged life span.

Entrainment to Feeding but Not to Light: Circadian Phenotype of VPAC2Receptor-Null Mice

The master clock driving mammalian circadian rhythms is located in the suprachiasmatic nuclei (SCN) of the hypothalamus and entrained by daily light/dark cycles. SCN lesions abolish circadian rhythms of behavior and result in a loss of synchronized circadian rhythms of clock gene expression in peripheral organs (e.g., the liver) and of hormone secretion (e.g., corticosterone). We examined rhythms of behavior, hepatic clock gene expression, and corticosterone secretion in VPAC2 receptor-null (Vipr2-/-) mice, which lack a functional SCN clock. Unexpectedly, although Vipr2-/- mice lacked robust circadian rhythms of wheel-running activity and corticosterone secretion, hepatic clock gene expression was strongly rhythmic, but advanced in phase compared with that in wild-type mice. The timing of food availability is thought to be an important entrainment signal for circadian clocks outside the SCN. Vipr2-/- mice consumed food significantly earlier in the 24 h cycle than wild-type mice, consistent with the observed timing of peripheral rhythms of circadian gene expression. When restricted to feeding only during the daytime (RF), mice develop rhythms of activity and of corticosterone secretion in anticipation of feeding time, thought to be driven by a food-entrainable circadian oscillator, located outside the SCN. Under RF, mice of both genotypes developed food-anticipatory rhythms of activity and corticosterone secretion, and hepatic gene expression rhythms also became synchronized to the RF stimulus. Thus, food intake is an effective zeitgeber capable of coordinating circadian rhythms of behavior, peripheral clock gene expression, and hormone secretion, even in the absence of a functional SCN clock.