The mPer2 gene encodes a functional component of the mammalian circadian clock

Maternal Obesity during Pregnancy Alters Daily Activity and Feeding Cycles, and Hypothalamic Clock Gene Expression in Adult Male Mouse Offspring

An obesogenic diet adversely affects the endogenous mammalian circadian clock, altering daily activity and metabolism, and resulting in obesity. We investigated whether an obese pregnancy can alter the molecular clock in the offspring hypothalamus, resulting in changes to their activity and feeding rhythms. Female mice were fed a control (C, 7% kcal fat) or high fat diet (HF, 45% kcal fat) before mating and throughout pregnancy. Male offspring were fed the C or HF diet postweaning, resulting in four offspring groups: C/C, C/HF, HF/C, and HF/HF. Daily activity and food intake were monitored, and at 15 weeks of age were killed at six time-points over 24 h. The clock genes Clock, Bmal1, Per2, and Cry2 in the suprachiasmatic nucleus (SCN) and appetite genes Npy and Pomc in the arcuate nucleus (ARC) were measured. Daily activity and feeding cycles in the HF/C, C/HF, and HF/HF offspring were altered, with increased feeding bouts and activity during the day and increased food intake but reduced activity at night. Gene expression patterns and levels of Clock, Bmal1, Per2, and Cry2 in the SCN and Npy and Pomc in the ARC were altered in HF diet-exposed offspring. The altered expression of hypothalamic molecular clock components and appetite genes, together with changes in activity and feeding rhythms, could be contributing to offspring obesity.

Sex Differences in Adrenal Bmal1 Deletion-Induced Augmentation of Glucocorticoid Responses to Stress and ACTH in Mice

The circadian glucocorticoid (GC) rhythm is dependent on a molecular clock in the suprachiasmatic nucleus (SCN) and an adrenal clock that is synchronized by the SCN. To determine whether the adrenal clock modulates GC responses to stress, experiments used female and male Cyp11A1Cre/+::Bmal1Fl/Fl knockout [side-chain cleavage (SCC)-KO] mice, in which the core clock gene, Bmal1, is deleted in all steroidogenic tissues, including the adrenal cortex. Following restraint stress, female and male SCC-KO mice demonstrate augmented plasma corticosterone but not plasma ACTH. In contrast, following submaximal scruff stress, plasma corticosterone was elevated only in female SCC-KO mice. Adrenal sensitivity to ACTH was measured in vitro using acutely dispersed adrenocortical cells. Maximal corticosterone responses to ACTH were elevated in cells from female KO mice without affecting the EC50 response. Neither the maximum nor the EC50 response to ACTH was affected in male cells, indicating that female SCC-KO mice show a stronger adrenal phenotype. Parallel experiments were conducted using female Cyp11B2 (Aldosterone Synthase)Cre/+::Bmal1Fl/Fl mice and adrenal cortex-specific Bmal1-null (Ad-KO) mice. Plasma corticosterone was increased in Ad-KO mice following restraint or scruff stress, and in vitro responses to ACTH were elevated in adrenal cells from Ad-KO mice, replicating data from female SCC-KO mice. Gene analysis showed increased expression of adrenal genes in female SCC-KO mice involved in cell cycle control, cell adhesion-extracellular matrix interaction, and ligand receptor activity that could promote steroid production. These observations underscore a role for adrenal Bmal1 as an attenuator of steroid secretion that is most prominent in female mice.

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

OBJECTIVES

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.

DESIGN

Animal study.

SETTING

University experimental laboratory.

SUBJECTS

Wildtype, Per2 mice.

INTERVENTIONS

Midazolam, lipopolysaccharide (lipopolysaccharide), constant light, nobiletin, or sham-treated animals.

MEASUREMENTS AND MAIN RESULTS

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.

CONCLUSIONS

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.

The circadian gene, Per2, influences methamphetamine sensitization and reward through the dopaminergic system in the striatum of mice

Drug addiction is a chronic and relapsing brain disorder, influenced by complex interactions between endogenous and exogenous factors. Per2, a circadian gene, plays a role in drug addiction. Previous studies using Per2-knockout mice have shown a role for Per2 in cocaine, morphine and alcohol addiction. In the present study, we investigated the role of Per2 in methamphetamine (METH) addiction using Per2-overexpression and knockout mice. We observed locomotor sensitization responses to METH administration, and rewarding effects using a conditioned place preference test. In addition, we measured expression levels of dopamine and dopamine-related genes (monoamine oxidase A, DA receptor 1, DA receptor 2, DA active transporter, tyrosine hydroxylase and cAMP response element-binding protein 1) in the striatum of the mice after repeated METH treatments, using qRT-PCR. Per2-overexpressed mice showed decreased locomotor sensitization and rewarding effects of METH compared to the wildtype mice, whereas the opposite was observed in Per2 knockout mice. Both types of transgenic mice showed altered expression levels of dopamine-related genes after repeated METH administration. Specifically, we observed lower dopamine levels in Per2-overexpressed mice and higher levels in Per2-knockout mice. Taken together, Per2 expression levels may influence the addictive effects of METH through the dopaminergic system in the striatum of mice.

The period circadian clock 2 gene responds to glucocorticoids and regulates osteogenic capacity

Introduction

The central regulatory system that generates biological rhythms is regulated by circadian clock genes expressed by cells in the suprachiasmatic nucleus. Signals from this system are converted to adrenocortical hormones through the sympathetic nervous system and transmitted to peripheral organs. Another system releases glucocorticoids (GCs) in response to stress through the HPA-axis. Here we investigated the second messenger GC, which is shared by these systems and influences the expression of circadian clock genes of cells of the musculoskeletal system and in viable bone tissue.

Methods

We used mouse-derived cell lines, which differentiate into osteoblasts (MC3T3-E1, C2C12, and 10T1/2) as well as primary cultures of mouse osteoblasts to determine the expression levels of circadian clock genes that respond to GC. Mice (mPer2^m/m) with an inactivating mutation in the period circadian clock 2 gene (Per2) exhibit marked dysrhythmia. Here we compared the bone morphologies of mPer2^m/m mice with those of wild-type (WT) mice.

Results

The expression of major circadian clock genes was detected in each cell line, and their responsiveness to GC was confirmed. We focused on Per2, a negative regulator of the circadian clock and found that a Per2-loss-of-function mutation increased the proliferative capacity of osteoblasts. Treatment of mutant mice with slow-release GC and bisphosphonate affected the maturation of bone tissue, which reflects a tendency to retard calcification.

Conclusion

Our investigations of the mechanisms that regulate circadian rhythm function in tissues of the musculoskeletal system that respond to the stress hormone GC, reveal that Per2 is required for the maturation of bone tissue. Thus, the influences of the systems that control circadian rhythms and the responses to stress by regenerating tissue used for regenerative medicine must be considered and studied in greater detail.

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Circadian clock genes expressed in musculoskeletal cells respond to GCs.

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Per2, a negative regulatory gene, influences the proliferation of osteoblasts.

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Circadian rhythms and GCs affect bone maturation and may control regenerating tissues.

Circadian period 2: a missing beneficial factor in sickle cell disease by lowering pulmonary inflammation, iron overload, and mortality

The circadian clock is important for cellular and organ function. However, its function in sickle cell disease (SCD), a life-threatening hemolytic disorder, remains unknown. Here, we performed an unbiased microarray screen, which revealed significantly altered expression of circadian rhythmic genes, inflammatory response genes, and iron metabolic genes in SCD Berkeley transgenic mouse lungs compared with controls. Given the vital role of period 2 (Per2) in the core clock and the unrecognized role of Per2 in SCD, we transplanted the bone marrow (BM) of SCD mice to Per2^Luciferase mice, which revealed that Per2 expression was up-regulated in SCD mouse lung. Next, we transplanted the BM of SCD mice to period 1 (Per1)/Per2 double deficient [Per1/Per2 double knockout (dKO)] and wild-type mice, respectively. We discovered that Per1/Per2 dKO mice transplanted with SCD BM (SCD → Per1/Per2 dKO) displayed severe irradiation sensitivity and were more susceptible to an early death. Although we observed an increase of peripheral inflammatory cells, we did not detect differences in erythrocyte sickling. However, there was further lung damage due to elevated pulmonary congestion, inflammatory cell infiltration, iron overload, and secretion of IL-6 in lavage fluid. Overall, we demonstrate that Per1/Per2 is beneficial to counteract elevated systemic inflammation, lung tissue inflammation, and iron overload in SCD.-Adebiyi, M. G., Zhao, Z., Ye, Y., Manalo, J., Hong, Y., Lee, C. C., Xian, W., McKeon, F., Culp-Hill, R., D' Alessandro, A., Kellems, R. E., Yoo, S.-H., Han, L., Xia, Y. Circadian period 2: a missing beneficial factor in sickle cell disease by lowering pulmonary inflammation, iron overload, and mortality.

Non-coding cis-element of Period2 is essential for maintaining organismal circadian behaviour and body temperature rhythmicity

Non-coding cis-regulatory elements are essential determinants of development, but their exact impacts on behavior and physiology in adults remain elusive. Cis-element-based transcriptional regulation is believed to be crucial for generating circadian rhythms in behavior and physiology. However, genetic evidence supporting this model is based on mutations in the protein-coding sequences of clock genes. Here, we report generation of mutant mice carrying a mutation only at the E'-box cis-element in the promoter region of the core clock gene Per2. The Per2 E'-box mutation abolishes sustainable molecular clock oscillations and renders circadian locomotor activity and body temperature rhythms unstable. Without the E'-box, Per2 messenger RNA and protein expression remain at mid-to-high levels. Our work delineates the Per2 E'-box as a critical nodal element for keeping sustainable cell-autonomous circadian oscillation and reveals the extent of the impact of the non-coding cis-element in daily maintenance of animal locomotor activity and body temperature rhythmicity.

Circadian Analysis of the Mouse Cerebellum Proteome

The cerebellum contains a circadian clock, generating internal temporal signals. The daily oscillations of cerebellar proteins were investigated in mice using a large-scale two-dimensional difference in gel electrophoresis (2D-DIGE). Analysis of 2D-DIGE gels highlighted the rhythmic variation in the intensity of 27/588 protein spots (5%) over 24 h based on cosinor regression. Notably, the rhythmic expression of most abundant cerebellar proteins was clustered in two main phases (i.e., midday and midnight), leading to bimodal distribution. Only six proteins identified here to be rhythmic in the cerebellum are also known to oscillate in the suprachiasmatic nuclei, including two proteins involved in the synapse activity (Synapsin 2 [SYN2] and vesicle-fusing ATPase [NSF]), two others participating in carbohydrate metabolism (triosephosphate isomerase (TPI1] and alpha-enolase [ENO1]), Glutamine synthetase (GLUL), as well as Tubulin alpha (TUBA4A). Most oscillating cerebellar proteins were not previously identified in circadian proteomic analyses of any tissue. Strikingly, the daily accumulation of mitochondrial proteins was clustered to the mid-resting phase, as previously observed for distinct mitochondrial proteins in the liver. Moreover, a number of rhythmic proteins, such as SYN2, NSF and TPI1, were associated with non-rhythmic mRNAs, indicating widespread post-transcriptional control in cerebellar oscillations. Thus, this study highlights extensive rhythmic aspects of the cerebellar proteome.

Loss-of-function mutations with circadian rhythm regulator Per1/Per2 lead to premature ovarian insufficiency†

The mechanism underlying premature ovarian insufficiency remains incompletely understood. Here we report that mice with Per1m/m; Per2m/m double mutations display a decrease in female fertility starting approximately at 20 weeks old, with significantly less pups born from 32 weeks old onwards. Histological analysis revealed that a significant reduction of ovarian follicles was observed in the Per1/Per2 mutants compared with the littermate controls examined at 26 and 52 weeks old, while the difference was not statistically significant between the two groups at 3 and 8 weeks old. We further showed that vascular development including the ovarian follicle associated vascular growth appeared normal in the Per1/Per2 mutant mice, although clock genes were reported to regulate angiogenesis in zebrafish. The findings imply that loss-of-function mutations with Per1/Per2 result in a premature depletion of ovarian follicle reserve leading to the decline of reproductive capacity.

Chronotype Genetic Variant in PER2 is Associated with Intrinsic Circadian Period in Humans

The PERIOD2 (PER2) gene is a core molecular component of the circadian clock and plays an important role in the generation and maintenance of daily rhythms. Rs35333999, a missense variant of PER2 common in European populations, has been shown to associate with later chronotype. Chronotype relates to the timing of biological and behavioral activities, including when we sleep, eat, and exercise, and later chronotype is associated with longer intrinsic circadian period (cycle length), a fundamental property of the circadian system. Thus, we tested whether this PER2 variant was associated with circadian period and found significant associations with longer intrinsic circadian period as measured under forced desynchrony protocols, the 'gold standard' for intrinsic circadian period assessment. Minor allele (T) carriers exhibited significantly longer circadian periods when determinations were based on either core body temperature or plasma melatonin measurements, as compared to non-carriers (by 12 and 11 min, respectively; accounting for ~7% of inter-individual variance). These findings provide a possible underlying biological mechanism for inter-individual differences in chronotype, and support the central role of PER2 in the human circadian timing system.

The Circadian Protein Period2 Suppresses mTORC1 Activity via Recruiting Tsc1 to mTORC1 Complex

Although emerging evidence indicates an important role of the circadian clock in modulating the diurnal oscillation of mammalian target of rapamycin complex 1 (mTORC1) signaling, the underlying molecular mechanism remains elusive. Here we show that Period2 (Per2), a core clock protein, functions as a scaffold protein to tether tuberous sclerosis complex 1 (Tsc1), Raptor, and mTOR together to specifically suppress the activity of mTORC1 complex. Due to the loss of its inhibition of mTORC1, Per2 deficiency significantly enhances protein synthesis and cell proliferation but reduces autophagy. Furthermore, we find that the glucagon-Creb/Crtc2 signaling cascade induces Per2 expression, which mediates the suppression of mTORC1 in mouse liver during fasting. Our study not only uncovers a novel role of Per2 in regulating the mTORC1 pathway, but also sheds new light on the mechanism of fasting inhibition on mTORC1 in the liver.

Rosiglitazone reverses high fat diet-induced changes in BMAL1 function in muscle, fat, and liver tissue in mice

OBJECTIVE

Nutrient challenge in the form of a high fat (HF) diet causes a reversible reprogramming of the hepatic circadian clock. This depends in part on changes in the recruitment of the circadian transcription factor BMAL1 to genome targets, though the causes and extent of disruption to hepatic and extra-hepatic BMAL1 are unknown. The objective of the study was to determine whether HF diet-induced alterations in BMAL1 function occur across insulin-resistant tissues and whether this could be reversed by restoring whole body insulin sensitivity.

METHODS

BMAL1 subcellular localization and target recruitment was analyzed in several metabolically active peripheral tissues, including liver, muscle, and adipose tissue under conditions of diet-induced obesity. Animals made obese with HF diet were subsequently treated with rosiglitazone to determine whether resensitizing insulin-resistant tissues to insulin restored hepatic and extra-hepatic BMAL1 function.

RESULTS

These data reveal that both hepatic and extra-hepatic BMAL1 activity are altered under conditions of obesity and insulin resistance. Restoring whole body insulin sensitivity by treatment with the antidiabetic drug rosiglitazone is sufficient to restore changes in HF diet-induced BMAL1 recruitment and activity in several tissues.

CONCLUSIONS

This study reveals that a key mechanism by which HF diet interferes with clock function in peripheral tissues is via the development of insulin resistance.

Circadian oscillator proteins across the kingdoms of life: structural aspects

Circadian oscillators are networks of biochemical feedback loops that generate 24-hour rhythms in organisms from bacteria to animals. These periodic rhythms result from a complex interplay among clock components that are specific to the organism, but share molecular mechanisms across kingdoms. A full understanding of these processes requires detailed knowledge, not only of the biochemical properties of clock proteins and their interactions, but also of the three-dimensional structure of clockwork components. Posttranslational modifications and protein–protein interactions have become a recent focus, in particular the complex interactions mediated by the phosphorylation of clock proteins and the formation of multimeric protein complexes that regulate clock genes at transcriptional and translational levels. This review covers the structural aspects of circadian oscillators, and serves as a primer for this exciting realm of structural biology.

Coupling the Circadian Clock to Homeostasis: The Role of Period in Timing Physiology

A plethora of physiological processes show stable and synchronized daily oscillations that are either driven or modulated by biological clocks. A circadian pacemaker located in the suprachiasmatic nucleus of the ventral hypothalamus coordinates 24-hour oscillations of central and peripheral physiology with the environment. The circadian clockwork involved in driving rhythmic physiology is composed of various clock genes that are interlocked via a complex feedback loop to generate precise yet plastic oscillations of ∼24 hours. This review focuses on the specific role of the core clockwork gene Period1 and its paralogs on intra-oscillator and extra-oscillator functions, including, but not limited to, hippocampus-dependent processes, cardiovascular function, appetite control, as well as glucose and lipid homeostasis. Alterations in Period gene function have been implicated in a wide range of physical and mental disorders. At the same time, a variety of conditions including metabolic disorders also impact clock gene expression, resulting in circadian disruptions, which in turn often exacerbates the disease state.

Cell-based screen identifies a new potent and highly selective CK2 inhibitor for modulation of circadian rhythms and cancer cell growth

Compounds targeting the circadian clock have been identified as potential treatments for clock-related diseases, including cancer. Our cell-based phenotypic screen revealed uncharacterized clock-modulating compounds. Through affinity-based target deconvolution, we identified GO289, which strongly lengthened circadian period, as a potent and selective inhibitor of CK2. Phosphoproteomics identified multiple phosphorylation sites inhibited by GO289 on clock proteins, including PER2 S693. Furthermore, GO289 exhibited cell type-dependent inhibition of cancer cell growth that correlated with cellular clock function. The x-ray crystal structure of the CK2α-GO289 complex revealed critical interactions between GO289 and CK2-specific residues and no direct interaction of GO289 with the hinge region that is highly conserved among kinases. The discovery of GO289 provides a direct link between the circadian clock and cancer regulation and reveals unique design principles underlying kinase selectivity.

Hsp90 Heterocomplexes Regulate Steroid Hormone Receptors: From Stress Response to Psychiatric Disease

The hypothalamus-pituitary-adrenal (HPA) axis directly controls the stress response. Dysregulation of this neuroendocrine system is a common feature among psychiatric disorders. Steroid hormone receptors, like glucocorticoid receptor (GR), function as transcription factors of a diverse set of genes upon activation. This activity is regulated by molecular chaperone heterocomplexes. Much is known about the structure and function of these GR/heterocomplexes. There is strong evidence suggesting altered regulation of steroid receptor hormones by chaperones, particularly the 51 kDa FK506-binding protein (FKBP51), may work with environmental factors to increase susceptibility to various psychiatric illnesses including post-traumatic stress disorder (PTSD), major depressive disorder (MDD), and anxiety. This review highlights the regulation of steroid receptor dynamics by the 90kDa heat shock protein (Hsp90)/cochaperone heterocomplexes with an in depth look at how the structural regulation and imbalances in cochaperones can cause functional effects on GR activity. Links between the stress response and circadian systems and the development of novel chaperone-targeting therapeutics are also discussed.

Prospects for circadian treatment of mood disorders

Disruption of circadian clocks is strongly associated with mood disorders. Chronotherapies targeting circadian rhythms have been shown to be very effective treatments of mood disorders, but still are not widely used in clinical practice. The mechanisms by which circadian disruption leads to mood disorders are poorly characterized and, therefore, may not convince clinicians to apply chronotherapies. Hence, in this review, we describe specific potential mechanisms, in order to make this connection more credible to clinicians. We believe that four major features of disrupted clocks may contribute to the development of mood disorders: (1) loss of synchronization to environmental 24-h rhythms, (2) internal desynchronization among body clocks, (3) low rhythm amplitude, and (4) changes in sleep architecture. Discussing these attributes and giving plausible examples, we will discuss prospects for relatively simple chronotherapies addressing these features that are easy to implement in clinical practice. Key messages In this review, we describe specific potential mechanisms by which disrupted clocks may contribute to the development of mood disorders: (1) loss of synchronization to environmental 24-h rhythms, (2) internal desynchronization among body clocks, (3) low rhythm amplitude, and (4) changes in sleep architecture. We provide prospects for relatively simple chronotherapies addressing these features that are easy to implement in clinical practice.

Mutation of the gene encoding the circadian clock component PERIOD2 in oncogenic cells confers chemoresistance by up-regulating the Aldh3a1 gene

Disruption of circadian rhythms has been implicated in an increased risk for cancer development. The Period2 (Per2) gene encodes one of the major components of the mammalian circadian clock, which plays a key role in controlling the circadian rhythms in physiology and behavior. PER2 has also been reported to suppress the malignant transformation of cells, but its role in the regulation of cancer susceptibility to chemotherapeutic drugs remains unclear. In this study, we found that oncogene-transformed embryonic fibroblasts prepared from Per2-mutant (Per2^m/m ) mice, which are susceptible to both spontaneous and radiation-induced tumorigenesis, were resistant against common chemotherapeutic drugs and that this resistance is associated with up-regulation of the aldehyde dehydrogenase 3a1 (Aldh3a1) gene. Co-expression of the oncogenes H-ras^V12 and SV40 large T-antigen induced malignant transformation of both WT and Per2^m/m cells, but the cytotoxic effects of the chemotherapeutic agents methotrexate, gemcitabine, etoposide, vincristine, and oxaliplatin were significantly alleviated in the oncogene-transformed Per2^m/m cells. Although introduction of the two oncogenes increased the expression of Aldh3a1 in both WT and Per2^m/m cells, the ALDH3A1 protein levels in the Per2^m/m cells were ∼7-fold higher than in WT cells. The elevated ALDH3A1 levels in the oncogene-transformed Per2^m/m cells were sufficient to prevent chemotherapeutic drug-induced accumulation of reactive oxygen species. Consequently, shRNA-mediated suppression of Aldh3a1 expression relieved the chemoresistance of the Per2^m/m cells. These results suggest a role for mutated PER2 in the development of multiple drug resistance and may inform therapeutic strategies for cancer management.

Long non-coding RNAs have age-dependent diurnal expression that coincides with age-related changes in genome-wide facultative heterochromatin

Background

Disrupted diurnal rhythms cause accelerated aging and an increased incidence in age-related disease and morbidity. The circadian clock governs cell physiology and metabolism by controlling transcription and chromatin. The goal of this study is to further understand the mechanism of age-related changes to circadian chromatin with a focus on facultative heterochromatin and diurnal non-coding RNAs.

Results

We performed a combined RNA-seq and ChIP-seq at two diurnal time-points for three different age groups to examine the connection between age-related changes to circadian transcription and heterochromatin in neuronal tissue. Our analysis focused on uncovering the relationships between long non-coding RNA (lncRNA) and age-related changes to histone H3 lysine 9 tri-methylation (H3K9me3), in part because the Period (Per) complex can direct facultative heterochromatin and models of aging suggest age-related changes to heterochromatin and DNA methylation. Our results reveal that lncRNAs and circadian output change dramatically with age, but the core clock genes remain rhythmic. Age-related changes in clock-controlled gene (ccg) expression indicate there are age-dependent circadian output that change from anabolic to catabolic processes during aging. In addition, there are diurnal and age-related changes in H3K9me3 that coincide with changes in transcription.

Conclusions

The data suggest a model where some age-related changes in diurnal expression are partially attributed to age-related alterations to rhythmic facultative heterochromatin. The changes in heterochromatin are potentially mediated by changes in diurnal lncRNA creating an interlocked circadian-chromatin regulatory network that undergoes age-dependent metamorphosis.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5170-3) contains supplementary material, which is available to authorized users.

A suprachiasmatic-independent circadian clock(s) in the habenula is affected by Per gene mutations and housing light conditions in mice

For many years, the suprachiasmatic nucleus (SCN) was considered as the unique circadian pacemaker in the mammalian brain. Currently, it is known that other brain areas are able to oscillate in a circadian manner. However, many of them are dependent on, or synchronized by, the SCN. The Habenula (Hb), localized in the epithalamus, is a key nucleus for the regulation of monoamine activity (dopamine, serotonin) and presents circadian features; nonetheless, the clock properties of the Hb are not fully described. Here, we report, first, circadian expression of clock genes in the lateral habenula (LHb) under constant darkness (DD) condition in wild-type mice which is disturbed in double Per1^-/--Per2^Brdm1 clock-mutant mice. Second, using Per2::luciferase transgenic mice, we observed a self-sustained oscillatory ability (PER2::LUCIFERASE bioluminescence rhythmicity) in the rostral and caudal part of the Hb of arrhythmic SCN-ablated animals. Finally, in Per2::luciferase mice exposed to different lighting conditions (light-dark, constant darkness or constant light), the period or amplitude of PER2 oscillations, in both the rostral and caudal Hb, were similar. However, under DD condition or from SCN-lesioned mice, these two Hb regions were out of phase, suggesting an uncoupling of two putative Hb oscillators. Altogether, these results suggest that an autonomous clock in the rostral and caudal part of the Hb requires integrity of circadian genes to tick, and light information or SCN innervation to keep synchrony. The relevance of the Hb timing might reside in the regulation of circadian functions linked to motivational (reward) and emotional (mood) processes.

Ultradian calcium rhythms in the paraventricular nucleus and subparaventricular zone in the hypothalamus

Despite that the various functions in mammals fluctuate in the ultradian fashion, the origin and mechanism of the rhythm are largely unknown. In this study, we found synchronous ultradian calcium rhythms in the hypothalamic paraventricular nucleus (PVN), subparaventricular zone (SPZ), and suprachiasmatic nucleus (SCN). The ultradian rhythms were originated from the SPZ-PVN region and transmitted to the SCN. Neurochemical interventions revealed that the glutamatergic mechanism is critical for generation and a tetrodotoxin-sensitive neural network for synchrony of the ultradian rhythm. The GABAergic system could have a role in refining the circadian output signals. The study provides the first clue to understand the loci and mechanism of ultradian rhythm in the hypothalamus.

The suprachiasmatic nucleus (SCN), the master circadian clock in mammals, sends major output signals to the subparaventricular zone (SPZ) and further to the paraventricular nucleus (PVN), the neural mechanism of which is largely unknown. In this study, the intracellular calcium levels were measured continuously in cultured hypothalamic slices containing the PVN, SPZ, and SCN. We detected ultradian calcium rhythms in both the SPZ-PVN and SCN regions with periods of 0.5–4.0 hours, the frequency of which depended on the local circadian rhythm in the SPZ-PVN region. The ultradian rhythms were synchronous in the entire SPZ-PVN region and a part of the SCN. Because the ultradian rhythms were not detected in the SCN-only slice, the origin of ultradian rhythm is the SPZ-PVN region. In association with an ultradian bout, a rapid increase of intracellular calcium in a millisecond order was detected, the frequency of which determined the amplitude of an ultradian bout. The synchronous ultradian rhythms were desynchronized and depressed by a sodium channel blocker tetrodotoxin, suggesting that a tetrodotoxin-sensitive network is involved in synchrony of the ultradian bouts. In contrast, the ultradian rhythm is abolished by glutamate receptor blockers, indicating the critical role of glutamatergic mechanism in ultradian rhythm generation, while a GABA_A receptor blocker increased the frequency of ultradian rhythm and modified the circadian rhythm in the SCN. A GABAergic network may refine the circadian output signals. The present study provides a clue to unraveling the loci and network mechanisms of the ultradian rhythm.

A sleeping giant: Suvorexant for the treatment of alcohol use disorder?

There are currently 3 FDA approved treatments for alcohol use disorder (AUD) in the USA, opioid receptor antagonists such as naltrexone, disulfiram and acamprosate. To date, these have been largely inadequate at preventing relapse at a population level and this may be because they only target certain aspects of AUD. Recently, suvorexant, a dual orexin receptor antagonist, has been FDA approved for the treatment of insomnia. Importantly, sleep disruptions occur during both acute and prolonged alcohol exposure and sleep deprivation is a potent factor promoting relapse to alcohol use. In this mini review article, we explore the therapeutic potential of suvorexant for the treatment of AUD. In particular, we highlight that in addition to altering the motivational properties of alcohol, suvorexant may also address key physiological components associated with alcohol withdrawal and abstinence, such as sleep disruptions, which should in turn help reduce or prevent relapse.

Neurobiological Functions of the Period Circadian Clock 2 Gene, Per2

Most organisms have adapted to a circadian rhythm that follows a roughly 24-hour cycle, which is modulated by both internal (clock-related genes) and external (environment) factors. In such organisms, the central nervous system (CNS) is influenced by the circadian rhythm of individual cells. Furthermore, the period circadian clock 2 (Per2) gene is an important component of the circadian clock, which modulates the circadian rhythm. Per2 is mainly expressed in the suprachiasmatic nucleus (SCN) of the hypothalamus as well as other brain areas, including the midbrain and forebrain. This indicates that Per2 may affect various neurobiological activities such as sleeping, depression, and addiction. In this review, we focus on the neurobiological functions of Per2, which could help to better understand its roles in the CNS.

Circadian clock component PERIOD2 regulates diurnal expression of Na+/H+ exchanger regulatory factor-1 and its scaffolding function

A number of diverse cell-surface proteins are anchored to the cytoskeleton via scaffold proteins. Na⁺/H⁺ exchanger regulatory factor-1 (NHERF1), encoded by the Slc9a3r1 gene, functions as a scaffold protein, which is implicated in the regulation of membrane expression of various cell-surface proteins. Here, we demonstrate that the circadian clock component PERIOD2 (PER2) modulates transcription of the mouse Slc9a3r1 gene, generating diurnal accumulation of NHERF1 in the mouse liver. Basal expression of Slc9a3r1 was dependent on transcriptional activation by p65/p50. PER2 bound to p65 protein and prevented p65/p50-mediated transactivation of Slc9a3r1. The time-dependent interaction between PER2 and p65 underlay diurnal oscillation in the hepatic expression of Slc9a3r1/NHERF1. The results of immunoprecipitation experiments and liquid chromatography-mass spectrometry analysis of mouse liver revealed that NHERF1 time-dependently interacted with fatty acid transport protein-5 (FATP5). Temporary accumulation of NHERF1 protein stabilized plasmalemmal localization of FATP5, thereby enhancing hepatic uptake of fatty acids at certain times of the day. Our results suggest an unacknowledged role for PER2 in regulating the diurnal expression of NHERF1 in mouse liver. This machinery also contributed to diurnal changes in the ability of hepatic cells to uptake fatty acids.

Clock genes alterations and endocrine disorders

BACKGROUND

Various endocrine signals oscillate over the 24-hour period and so does the responsiveness of target tissues. These daily oscillations do not occur solely in response to external stimuli but are also under the control of an intrinsic circadian clock.

DESIGN

We searched the PubMed database to identify studies describing the associations of clock genes with endocrine diseases.

RESULTS

Various human single nucleotide polymorphisms of brain and muscle ARNT-like 1 (BMAL1) and Circadian Locomotor Output Cycles Kaput (CLOCK) genes exhibited significant associations with type 2 diabetes mellitus. ARNTL2 gene expression and upregulation of BMAL1 and PER1 were associated with the development of type 1 diabetes mellitus. Thyroid hormones modulated PER2 expression in a tissue-specific way, whereas BMAL1 regulated the expression of type 2 iodothyronine deiodinase in specific tissues. Adrenal gland and adrenal adenoma expressed PER1, PER2, CRY2, CLOCK and BMAL1 genes. Adrenal sensitivity to adrenocorticotrophin was also affected by circadian oscillations. A significant correlation between the expression of propio-melanocorticotrophin and PER 2, as well as between prolactin and CLOCK, was found in corticotroph and lactosomatotroph cells, respectively, in the pituitary. Clock genes and especially BMAL1 showed an important role in fertility, whereas oestradiol and androgens exhibited tissue-specific effects on clock gene expression. Metabolic disorders were also associated with circadian dysregulation according to studies in shift workers.

CONCLUSIONS

Clock genes are associated with various endocrine disorders through complex mechanisms. However, data on humans are scarce. Moreover, clock genes exhibit a tissue-specific expression representing an additional level of regulation. Their specific role in endocrine disorders and their potential implications remain to be further clarified.

Circadian clock-mediated regulation of blood pressure

Most bodily functions vary over the course of a 24h day. Circadian rhythms in body temperature, sleep-wake cycles, metabolism, and blood pressure (BP) are just a few examples. These circadian rhythms are controlled by the central clock in the suprachiasmatic nucleus (SCN) of the hypothalamus and peripheral clocks located throughout the body. Light and food cues entrain these clocks to the time of day and this synchronicity contributes to the regulation of a variety of physiological processes with effects on overall health. The kidney, brain, nervous system, vasculature, and heart have been identified through the use of mouse models and clinical trials as peripheral clock regulators of BP. The dysregulation of this circadian pattern of BP, with or without hypertension, is associated with increased risk for cardiovascular disease. The mechanism of this dysregulation is unknown and is a growing area of research. In this review, we highlight research of human and mouse circadian models that has provided insight into the roles of these molecular clocks and their effects on physiological functions. Additional tissue-specific studies of the molecular clock mechanism are needed, as well as clinical studies including more diverse populations (different races, female patients, etc.), which will be critical to fully understand the mechanism of circadian regulation of BP. Understanding how these molecular clocks regulate the circadian rhythm of BP is critical in the treatment of circadian BP dysregulation and hypertension.

Racing the clock: The role of circadian rhythmicity in addiction across the lifespan

Although potent effects of psychoactive drugs on circadian rhythms were first described over 30 years ago, research into the reciprocal relationship between the reward system and the circadian system - and the impact of this relationship on addiction - has only become a focus in the last decade. Nonetheless, great progress has been made in that short time toward understanding how drugs of abuse impact the molecular and physiological circadian clocks, as well as how disruption of normal circadian rhythm biology may contribute to addiction and ameliorate the efficacy of treatments for addiction. In particular, data have emerged demonstrating that disrupted circadian rhythms, such as those observed in shift workers and adolescents, increase susceptibility to addiction. Furthermore, circadian rhythms and addiction impact one another longitudinally - specifically from adolescence to the elderly. In this review, the current understanding of how the circadian clock interacts with substances of abuse within the context of age-dependent changes in rhythmicity, including the potential existence of a drug-sensitive clock, the correlation between chronotype and addiction vulnerability, and the importance of rhythmicity in the mesocorticolimbic dopamine system, is discussed. The primary focus is on alcohol addiction, as the preponderance of research is in this area, with references to other addictions as warranted. The implications of clock-drug interactions for the treatment of addiction will also be reviewed, and the potential of therapeutics that reset the circadian rhythm will be highlighted.

Predicted effect of circadian clock modulation of NHE3 of a proximal tubule cell on sodium transport

Major renal functions such as renal blood flow, glomerular filtration rate, and urinary excretion are known to exhibit circadian oscillations. However, the underlying mechanisms that govern these variations have yet to be fully elucidated. To better understand the impact of the circadian clock on renal solute and water transport, we have developed a computational model of the renal circadian clock and coupled that model to an epithelial transport model of the proximal convoluted cell of the rat kidney. The activity of the Na⁺-H⁺ exchanger 3 (NHE3) is assumed to be regulated by changes in transcription of the NHE3 mRNA due to regulation by circadian clock proteins. The model predicts the rhythmic oscillations in NHE3 activity, which gives rise to significant daily fluctuations in Na⁺ and water transport of the proximal tubule cell. Additionally, the model predicts that 1) mutation in period 2 (Per2) or cryptochrome 1 (Cry1) preserves the circadian rhythm and modestly raises Na⁺ reabsorption; 2) mutation in Bmal1 or CLOCK eliminates the circadian rhythm and modestly lowers Na⁺ reabsorption; 3) mutation in Rev-Erb or ROR-related orphan receptor (Ror) has minimal impact on the circadian oscillations. The model represents the first step in building a tool set aimed at increasing our understanding of how the molecular clock affects renal ion transport and renal function, which likely has important implications for kidney disease.

A point mutation in the ion conduction pore of AMPA receptor GRIA3 causes dramatically perturbed sleep patterns as well as intellectual disability

The discovery of genetic variants influencing sleep patterns can shed light on the physiological processes underlying sleep. As part of a large clinical sequencing project, WGS500, we sequenced a family in which the two male children had severe developmental delay and a dramatically disturbed sleep-wake cycle, with very long wake and sleep durations, reaching up to 106-h awake and 48-h asleep. The most likely causal variant identified was a novel missense variant in the X-linked GRIA3 gene, which has been implicated in intellectual disability. GRIA3 encodes GluA3, a subunit of AMPA-type ionotropic glutamate receptors (AMPARs). The mutation (A653T) falls within the highly conserved transmembrane domain of the ion channel gate, immediately adjacent to the analogous residue in the Grid2 (glutamate receptor) gene, which is mutated in the mouse neurobehavioral mutant, Lurcher. In vitro, the GRIA3(A653T) mutation stabilizes the channel in a closed conformation, in contrast to Lurcher. We introduced the orthologous mutation into a mouse strain by CRISPR-Cas9 mutagenesis and found that hemizygous mutants displayed significant differences in the structure of their activity and sleep compared to wild-type littermates. Typically, mice are polyphasic, exhibiting multiple sleep bouts of sleep several minutes long within a 24-h period. The Gria3^A653T mouse showed significantly fewer brief bouts of activity and sleep than the wild-types. Furthermore, Gria3^A653T mice showed enhanced period lengthening under constant light compared to wild-type mice, suggesting an increased sensitivity to light. Our results suggest a role for GluA3 channel activity in the regulation of sleep behavior in both mice and humans.

Clock gene Per2 as a controller of liver carcinogenesis

Environmental disruption of molecular clocks promoted liver carcinogenesis and accelerated cancer progression in rodents. We investigated the specific role of clock gene Period 2 (Per2) for liver carcinogenesis and clock-controlled cellular proliferation, genomic instability and inflammation. We assessed liver histopathology, and determined molecular and physiology circadian patterns in mice on chronic diethylnitrosamine (DEN) exposure according to constitutive Per2 mutation. First, we found that Per2^m/m liver displayed profound alterations in proliferation gene expression, including c-Myc derepression, phase-advanced Wee1, and arrhythmic Ccnb1 and K-ras mRNA expressions, as well as deregulated inflammation, through arrhythmic liver IL-6 protein concentration, in the absence of any DEN exposure. These changes could then make Per2^m/m mice more prone to subsequently develop liver cancers on DEN. Indeed, primary liver cancers were nearly fourfold as frequent in Per2^m/m mice as compared to wild-type (WT), 4 months after DEN exposure. The liver molecular clock was severely disrupted throughout the whole carcinogenesis process, including the initiation stage, i.e. within the initial 17 days on DEN. Per2^m/m further exhibited increased c-Myc and Ccnb1 mean 24h expressions, lack of P53 response, and arrhythmic ATM, Wee1 and Ccnb1 expressions. DEN-induced tumor related inflammation was further promoted through increased protein concentrations of liver IL-6 and TNF-α as compared to WT during carcinogenesis initiation. Per2 mutation severely deregulated liver gene or protein expressions related to three cancer hallmarks, including uncontrolled proliferation, genomic instability, and tumor promoting inflammation, and accelerated liver carcinogenesis several-fold. Clock gene Per2 acted here as a liver tumor suppressor from initiation to progression.

The Circadian Oscillator of the Cerebral Cortex: Molecular, Biochemical and Behavioral Effects of Deleting the Arntl Clock Gene in Cortical Neurons

A molecular circadian oscillator resides in neurons of the cerebral cortex, but its role is unknown. Using the Cre-LoxP method, we have here abolished the core clock gene Arntl in those neurons. This mouse represents the first model carrying a deletion of a circadian clock component specifically in an extrahypothalamic cell type of the brain. Molecular analyses of clock gene expression in the cerebral cortex of the Arntl conditional knockout mouse revealed disrupted circadian expression profiles, whereas clock gene expression in the suprachiasmatic nucleus was still rhythmic, thus showing that Arntl is required for normal function of the cortical circadian oscillator. Daily rhythms in running activity and temperature were not influenced, whereas the resynchronization response to experimental jet-lag exhibited minor though significant differences between genotypes. The tail-suspension test revealed significantly prolonged immobility periods in the knockout mouse indicative of a depressive-like behavioral state. This phenotype was accompanied by reduced norepinephrine levels in the cerebral cortex. Our data show that Arntl is required for normal cortical clock function and further give reason to suspect that the circadian oscillator of the cerebral cortex is involved in regulating both circadian biology and mood-related behavior and biochemistry.

The Circadian PER2 Enhancer Nobiletin Reverses the Deleterious Effects of Midazolam in Myocardial Ischemia and Reperfusion Injury

BACKGROUND

Recently, we identified the circadian rhythm protein Period 2 (PER2) in robust cardioprotection from myocardial ischemia (MI). Based on findings that perioperative MI is the most common major cardiovascular complication and that anesthetics can alter the expression of PER2, we hypothesized that an anesthesia mediated downregulation of PER2 could be detrimental if myocardial ischemia and reperfusion (IR) would occur.

METHODS AND RESULTS

We exposed mice to pentobarbital, fentanyl, ketamine, propofol, midazolam or isoflurane and determined cardiac Per2 mRNA levels. Unexpectedly, only midazolam treatment resulted in an immediate and significant downregulation of Per2 transcript levels. Subsequent studies in mice pretreated with midazolam using an in-situ mouse model for myocardial (IR)-injury revealed a significant and dramatic increase in infarct sizes or Troponin-I serum levels in the midazolam treated group when compared to controls. Using the recently identified flavonoid, nobiletin, as a PER2 enhancer completely abolished the deleterious effects of midazolam during myocardial IR-injury. Moreover, nobiletin treatment alone significantly reduced infarct sizes or Troponin I levels in wildtype but not in Per2-/- mice. Pharmacological studies on nobiletin like flavonoids revealed that only nobiletin and tangeritin, both found to enhance PER2, were cardioprotective in our murine model for myocardial IR-injury.

CONCLUSION

We identified midazolam mediated downregulation of cardiac PER2 as an underlying mechanism for a deleterious effect of midazolam pretreatment in myocardial IR-injury. These findings highlight PER2 as a cardioprotective mechanism and suggest the PER2 enhancers nobiletin or tangeritin as a preventative therapy for myocardial IR-injury in the perioperative setting where midazolam pretreatment occurs frequently.

Circadian clocks: from stem cells to tissue homeostasis and regeneration

The circadian clock is an evolutionarily conserved timekeeper that adapts body physiology to diurnal cycles of around 24 h by influencing a wide variety of processes such as sleep-to-wake transitions, feeding and fasting patterns, body temperature, and hormone regulation. The molecular clock machinery comprises a pathway that is driven by rhythmic docking of the transcription factors BMAL1 and CLOCK on clock-controlled output genes, which results in tissue-specific oscillatory gene expression programs. Genetic as well as environmental perturbation of the circadian clock has been implicated in various diseases ranging from sleep to metabolic disorders and cancer development. Here, we review the origination of circadian rhythms in stem cells and their function in differentiated cells and organs. We describe how clocks influence stem cell maintenance and organ physiology, as well as how rhythmicity affects lineage commitment, tissue regeneration, and aging.

Food-Anticipatory Behavior in Neonatal Rabbits and Rodents: An Update on the Role of Clock Genes

In mammals, the suprachiasmatic nucleus (SCN), the master circadian clock, is mainly synchronized to the environmental light/dark cycle. SCN oscillations are maintained by a molecular clockwork in which certain genes, Period 1-2, Cry1-2, Bmal1, and Clock, are rhythmically expressed. Disruption of these genes leads to a malfunctioning clockwork and behavioral and physiological rhythms are altered. In addition to synchronization of circadian rhythms by light, when subjects are exposed to food for a few hours daily, behavioral and physiological rhythms are entrained to anticipate mealtime, even in the absence of the SCN. The presence of anticipatory rhythms synchronized by food suggests the existence of an SCN-independent circadian pacemaker that might be dependent on clock genes. Interestingly, rabbit pups, unable to perceive light, suckle milk once a day, which entrains behavioral rhythms to anticipate nursing time. Mutations of clock genes, singly or in combination, affect diverse rhythms in brain activity and physiological processes, but anticipatory behavior and physiology to feeding time remains attenuated or unaffected. It had been suggested that compensatory upregulation of paralogs or subtypes genes, or even non-transcriptional mechanisms, are able to maintain circadian oscillations entrained to mealtime. In the present mini-review, we evaluate the current state of the role played by clock genes in meal anticipation and provide evidence for rabbit pups as a natural model of food-anticipatory circadian behavior.

Circadian clock regulates hepatic polyploidy by modulating Mkp1-Erk1/2 signaling pathway

Liver metabolism undergoes robust circadian oscillations in gene expression and enzymatic activity essential for liver homeostasis, but whether the circadian clock controls homeostatic self-renewal of hepatocytes is unknown. Here we show that hepatocyte polyploidization is markedly accelerated around the central vein, the site of permanent cell self-renewal, in mice deficient in circadian Period genes. In these mice, a massive accumulation of hyperpolyploid mononuclear and binuclear hepatocytes occurs due to impaired mitogen-activated protein kinase phosphatase 1 (Mkp1)-mediated circadian modulation of the extracellular signal-regulated kinase (Erk1/2) activity. Time-lapse imaging of hepatocytes suggests that the reduced activity of Erk1/2 in the midbody during cytokinesis results in abscission failure, leading to polyploidization. Manipulation of Mkp1 phosphatase activity is sufficient to change the ploidy level of hepatocytes. These data provide clear evidence that the Period genes not only orchestrate dynamic changes in metabolic activity, but also regulate homeostatic self-renewal of hepatocytes through Mkp1-Erk1/2 signaling pathway.

Circadian clock regulates hepatic gene expression and functions. Here Chao et al. show that alteration of circadian clock genes by Period deletion induces polyploidy in hepatocytes due to impaired regulation of Erk signaling by mitogen-activated protein kinase phosphatase 1.

Valproic acid disrupts the oscillatory expression of core circadian rhythm transcription factors

Valproic acid (VPA) is a well-established therapeutic used in treatment of seizure and mood disorders as well as migraines and a known hepatotoxicant. About 50% of VPA users experience metabolic disruptions, including weight gain, hyperlipidemia, and hyperinsulinemia, among others. Several of these metabolic abnormalities are similar to the effects of circadian rhythm disruption. In the current study, we examine the effect of VPA exposure on the expression of core circadian transcription factors that drive the circadian clock via a transcription-translation feedback loop. In cells with an unsynchronized clock, VPA simultaneously upregulated the expression of genes encoding core circadian transcription factors that regulate the positive and negative limbs of the feedback loop. Using low dose glucocorticoid, we synchronized cultured fibroblast cells to a circadian oscillatory pattern. Whether VPA was added at the time of synchronization or 12h later at CT12, we found that VPA disrupted the oscillatory expression of multiple genes encoding essential transcription factors that regulate circadian rhythm. Therefore, we conclude that VPA has a potent effect on the circadian rhythm transcription-translation feedback loop that may be linked to negative VPA side effects in humans. Furthermore, our study suggests potential chronopharmacology implications of VPA usage.

Impact of Time-Restricted Feeding and Dawn-to-Sunset Fasting on Circadian Rhythm, Obesity, Metabolic Syndrome, and Nonalcoholic Fatty Liver Disease

Obesity now affects millions of people and places them at risk of developing metabolic syndrome, nonalcoholic fatty liver disease (NAFLD), and even hepatocellular carcinoma. This rapidly emerging epidemic has led to a search for cost-effective methods to prevent the metabolic syndrome and NAFLD as well as the progression of NAFLD to cirrhosis and hepatocellular carcinoma. In murine models, time-restricted feeding resets the hepatic circadian clock and enhances transcription of key metabolic regulators of glucose and lipid homeostasis. Studies of the effect of dawn-to-sunset Ramadan fasting, which is akin to time-restricted feeding model, have also identified significant improvement in body mass index, serum lipid profiles, and oxidative stress parameters. Based on the findings of studies conducted on human subjects, dawn-to-sunset fasting has the potential to be a cost-effective intervention for obesity, metabolic syndrome, and NAFLD.

mPeriod2 Brdm1 and other single Period mutant mice have normal food anticipatory activity

Animals anticipate the timing of food availability via the food-entrainable oscillator (FEO). The anatomical location and timekeeping mechanism of the FEO are unknown. Several studies showed the circadian gene, Period 2, is critical for FEO timekeeping. However, other studies concluded that canonical circadian genes are not essential for FEO timekeeping. In this study, we re-examined the effects of the Per2^Brdm1 mutation on food entrainment using methods that have revealed robust food anticipatory activity in other mutant lines. We examined food anticipatory activity, which is the output of the FEO, in single Period mutant mice. Single Per1, Per2, and Per3 mutant mice had robust food anticipatory activity during restricted feeding. In addition, we found that two different lines of Per2 mutant mice (ldc and Brdm1) anticipated restricted food availability. To determine if FEO timekeeping persisted in the absence of the food cue, we assessed activity during fasting. Food anticipatory (wheel-running) activity in all Period mutant mice was also robust during food deprivation. Together, our studies demonstrate that the Period genes are not necessary for the expression of food anticipatory activity.

Circadian Rhythm Disturbances in Mood Disorders: Insights into the Role of the Suprachiasmatic Nucleus

Circadian rhythm disturbances are a common symptom among individuals with mood disorders. The suprachiasmatic nucleus (SCN), in the ventral part of the anterior hypothalamus, orchestrates physiological and behavioral circadian rhythms. The SCN consists of self-sustaining oscillators and receives photic and nonphotic cues, which entrain the SCN to the external environment. In turn, through synaptic and hormonal mechanisms, the SCN can drive and synchronize circadian rhythms in extra-SCN brain regions and peripheral tissues. Thus, genetic or environmental perturbations of SCN rhythms could disrupt brain regions more closely related to mood regulation and cause mood disturbances. Here, we review clinical and preclinical studies that provide evidence both for and against a causal role for the SCN in mood disorders.

Loss of the clock gene PER2 is associated with cancer development and altered expression of important tumor-related genes in oral cancer

Recent studies have demonstrated that abnormal expression of the clock gene PER2 is closely associated with the development of a variety of cancer types. However, the expression of PER2 in oral squamous cell carcinoma (OSCC), a common malignant tumor in humans, and its correlations with the clinicopathological parameters and survival time of OSCC patients and the altered expression of important tumor-related genes remain unclear. In the present study, we detected the mRNA and protein expression levels of PER2, PIK3CA, PTEN, P53, P14ARF and caspase‑8 in OSCC tissues and cancer-adjacent oral mucosa by reverse transcription-quantitative PCR (RT-qPCR), western blotting and immunohistochemistry. The results showed that the PER2, PTEN, P53, P14ARF and caspase‑8 mRNA and protein expression levels in OSCC were significantly reduced compared with those in cancer-adjacent tissues. Additionally, the PIK3CA protein expression level was significantly increased in OSCC tissues, whereas the mRNA level was not. Decreased expression of PER2 was significantly associated with advanced clinical stage and the presence of lymphatic metastasis in OSCC patients. Patients with PER2‑negative expression had a significantly shorter survival time than those with PER2‑positive expression. PER2 expression was negatively correlated with PIK3CA and P53 levels, and positively correlated with PTEN, P14ARF and caspase‑8 levels. In summary, the results of this study suggest that loss of PER2 expression is closely associated with the genesis and development of OSCC and that PER2 may be an important prognostic biomarker in OSCC. PER2 may serve an antitumor role via the P53/P14ARF, PIK3CA/AKT and caspase‑8 pathways.

Circadian Clock Protein Content and Daily Rhythm of Locomotor Activity Are Altered after Chronic Exposure to Lead in Rat

Lead exposure has been reported to produce many clinical features, including parkinsonism. However, its consequences on the circadian rhythms are still unknown. Here we aimed to examine the circadian rhythms of locomotor activity following lead intoxication and investigate the mechanisms by which lead may induce alterations of circadian rhythms in rats. Male Wistar rats were injected with lead or sodium acetate (10 mg/kg/day, i.p.) during 4 weeks. Both groups were tested in the “open field” to quantify the exploratory activity and in the rotarod to evaluate motor coordination. Then, animals were submitted to continuous 24 h recordings of locomotor activity under 14/10 Light/dark (14/10 LD) cycle and in complete darkness (DD). At the end of experiments, the clock proteins BMAL1, PER1-2, and CRY1-2 were assayed in the suprachiasmatic nucleus (SCN) using immunohistochemistry. We showed that lead significantly reduced the number of crossing in the open field, impaired motor coordination and altered the daily locomotor activity rhythm. When the LD cycle was advanced by 6 h, both groups adjusted their daily locomotor activity to the new LD cycle with high onset variability in lead-intoxicated rats compared to controls. Lead also led to a decrease in the number of immunoreactive cells (ir-) of BMAL1, PER1, and PER2 without affecting the number of ir-CRY1 and ir-CRY2 cells in the SCN. Our data provide strong evidence that lead intoxication disturbs the rhythm of locomotor activity and alters clock proteins expression in the SCN. They contribute to the understanding of the mechanism by which lead induce circadian rhythms disturbances.

Circadian repressors CRY1 and CRY2 broadly interact with nuclear receptors and modulate transcriptional activity

Nuclear hormone receptors (NRs) regulate physiology by sensing lipophilic ligands and adapting cellular transcription appropriately. A growing understanding of the impact of circadian clocks on mammalian transcription has sparked interest in the interregulation of transcriptional programs. Mammalian clocks are based on a transcriptional feedback loop featuring the transcriptional activators circadian locomotor output cycles kaput (CLOCK) and brain and muscle ARNT-like 1 (BMAL1), and transcriptional repressors cryptochrome (CRY) and period (PER). CRY1 and CRY2 bind independently of other core clock factors to many genomic sites, which are enriched for NR recognition motifs. Here we report that CRY1/2 serve as corepressors for many NRs, indicating a new facet of circadian control of NR-mediated regulation of metabolism and physiology, and specifically contribute to diurnal modulation of drug metabolism.

Implications of Circadian Rhythm in Dopamine and Mood Regulation

Mammalian physiology and behavior are regulated by an internal time-keeping system, referred to as circadian rhythm. The circadian timing system has a hierarchical organization composed of the master clock in the suprachiasmatic nucleus (SCN) and local clocks in extra-SCN brain regions and peripheral organs. The circadian clock molecular mechanism involves a network of transcription-translation feedback loops. In addition to the clinical association between circadian rhythm disruption and mood disorders, recent studies have suggested a molecular link between mood regulation and circadian rhythm. Specifically, genetic deletion of the circadian nuclear receptor Rev-erbα induces mania-like behavior caused by increased midbrain dopaminergic (DAergic) tone at dusk. The association between circadian rhythm and emotion-related behaviors can be applied to pathological conditions, including neurodegenerative diseases. In Parkinson's disease (PD), DAergic neurons in the substantia nigra pars compacta progressively degenerate leading to motor dysfunction. Patients with PD also exhibit non-motor symptoms, including sleep disorder and neuropsychiatric disorders. Thus, it is important to understand the mechanisms that link the molecular circadian clock and brain machinery in the regulation of emotional behaviors and related midbrain DAergic neuronal circuits in healthy and pathological states. This review summarizes the current literature regarding the association between circadian rhythm and mood regulation from a chronobiological perspective, and may provide insight into therapeutic approaches to target psychiatric symptoms in neurodegenerative diseases involving circadian rhythm dysfunction.

Circadian rhythm disruption impairs tissue homeostasis and exacerbates chronic inflammation in the intestine

Endogenous circadian clocks regulate 24-h rhythms of physiology and behavior. Circadian rhythm disruption (CRD) is suggested as a risk factor for inflammatory bowel disease. However, the underlying molecular mechanisms remain unknown. Intestinal biopsies from Per1/2 mutant and wild-type (WT) mice were investigated by electron microscopy, immunohistochemistry, and bromodeoxyuridine pulse-chase experiments. TNF-α was injected intraperitoneally, with or without necrostatin-1, into Per1/2 mice or rhythmic and externally desynchronized WT mice to study intestinal epithelial cell death. Experimental chronic colitis was induced by oral administration of dextran sodium sulfate. In vitro, caspase activity was assayed in Per1/2-specific small interfering RNA-transfected cells. Wee1 was overexpressed to study antiapoptosis and the cell cycle. Genetic ablation of circadian clock function or environmental CRD in mice increased susceptibility to severe intestinal inflammation and epithelial dysregulation, accompanied by excessive necroptotic cell death and a reduced number of secretory epithelial cells. Receptor-interacting serine/threonine-protein kinase (RIP)-3-mediated intestinal necroptosis was linked to increased mitotic cell cycle arrest via Per1/2-controlled Wee1, resulting in increased antiapoptosis via cellular inhibitor of apoptosis-2. Together, our data suggest that circadian rhythm stability is pivotal for the maintenance of mucosal barrier function. CRD increases intestinal necroptosis, thus rendering the gut epithelium more susceptible to inflammatory processes.-Pagel, R., Bär, F., Schröder, T., Sünderhauf, A., Künstner, A., Ibrahim, S. M., Autenrieth, S. E., Kalies, K., König, P., Tsang, A. H., Bettenworth, D., Divanovic, S., Lehnert, H., Fellermann, K., Oster, H., Derer, S., Sina, C. Circadian rhythm disruption impairs tissue homeostasis and exacerbates chronic inflammation in the intestine.

Analyses of the cellular clock gene expression in peripheral tissue, caudal fin, in the Japanese flounder, Paralichthys olivaceus

Understanding the systems for maintaining the circadian rhythms that give organisms the flexibility to adapt to environmental changes is important in both aquaculture and fish chronobiology, because nursery lighting conditions can affect the survival and growth rates of larvae. We previously demonstrated that in flounder, the suprachiasmatic nucleus (SCN) exhibits daily rhythm in per2 expression, in sharp contrast to zebrafish, in which the SCN does not exhibit clear per2 expression rhythm. To examine whether a hierarchy exists in systems that maintain the expression rhythm of peripheral clock genes in flounder, in the present study we analyzed the in vivo and in vitro expression of three clock genes, per2, per1, and cry1, in the caudal fin and the effects of cortisol and melatonin administration on the expression of each clock gene. In vivo, the fin maintained a daily expression rhythm of all three genes, even in 24-h darkness (DD) when shifted from 12-h light:12-h dark (LD) conditions, but fin explants lost the expression rhythm after a short time of tissue culture, even under LD conditions. Cortisol, but not melatonin, significantly upregulated the expression of the three clock genes in fin both in vitro and in vivo. Therefore, we hypothesize that the SCN-pituitary-adrenal cortex pathway plays a role in the oscillation of the peripheral clock in flounder. However, in vivo, peak expression of per2 and cry1 was shifted 2-4h earlier under DD conditions, and their expression was upregulated in response to short exposures to light when larvae were kept under DD conditions. Therefore, we also hypothesize that in addition to the SCN, a light-responsive coordinating factor also functions in photo-entrainment of the peripheral clock in flounder.