Dysregulation of Npas2 leads to altered metabolic pathways in a murine knockout model

Rhythm gene PER1 mediates ferroptosis and lipid metabolism through SREBF2/ALOX15 axis in polycystic ovary syndrome

OBJECTIVE

This work aimed to investigate the role of rhythm gene PER1 in mediating granulosa cell ferroptosis and lipid metabolism of polycystic ovary syndrome (PCOS).

METHODS

We injected dehydroepiandrosterone and Ferrostatin-1 (Fer-1) into mice to explore the mechanism of ferroptosis in PCOS. The effect of PER1 on ferroptosis-like changes in granulosa cells was explored by overexpression of PER1 plasmid transfection and Fer-1 treatment.

RESULTS

We found that Fer-1 ameliorated the characteristic polycystic ovary morphology, suppressed ferroptosis in the PCOS mice. PER1 and ALOX15 were highly expressed in PCOS, whereas SREBF2 was lowly expressed. Overexpression of PER1 decreased granulosa cell viability and inhibited proliferation. Meanwhile, overexpression of PER1 increased lipid reactive oxygen species, 4-Hydroxynonenal (4-HNE), Malondialdehyde (MDA), total Fe, and Fe2+ levels in granulosa cells and decreased Glutathione (GSH) content. Fer-1, SREBF2 overexpression, or ALOX15 silencing treatment reversed the effects of PER1 overexpression on granulosa cells. PER1 binds to the SREBF2 promoter and represses SREBF2 transcription. SREBF2 binds to the ALOX15 promoter and represses ALOX15 transcription. Correlation analysis of clinical trials showed that PER1 was positively correlated with total cholesterol, low-density lipoprotein cholesterol, luteinizing hormone, testosterone, 4-HNE, MDA, total Fe, Fe2+, and ALOX15. In contrast, PER1 was negatively correlated with SREBF2, high-density lipoprotein cholesterol, follicle-stimulating hormone, progesterone, and GSH.

CONCLUSION

This study demonstrates that the rhythm gene PER1 promotes ferroptosis and dysfunctional lipid metabolism in granulosa cells in PCOS by inhibiting SREBF2/ALOX15 signaling.

The Bayesian Regularized Quantile Varying Coefficient Model

The quantile varying coefficient (VC) model can flexibly capture dynamical patterns of regression coefficients. In addition, due to the quantile check loss function, it is robust against outliers and heavy-tailed distributions of the response variable, and can provide a more comprehensive picture of modeling via exploring the conditional quantiles of the response variable. Although extensive studies have been conducted to examine variable selection for the high-dimensional quantile varying coefficient models, the Bayesian analysis has been rarely developed. The Bayesian regularized quantile varying coefficient model has been proposed to incorporate robustness against data heterogeneity while accommodating the non-linear interactions between the effect modifier and predictors. Selecting important varying coefficients can be achieved through Bayesian variable selection. Incorporating the multivariate spike-and-slab priors further improves performance by inducing exact sparsity. The Gibbs sampler has been derived to conduct efficient posterior inference of the sparse Bayesian quantile VC model through Markov chain Monte Carlo (MCMC). The merit of the proposed model in selection and estimation accuracy over the alternatives has been systematically investigated in simulation under specific quantile levels and multiple heavy-tailed model errors. In the case study, the proposed model leads to identification of biologically sensible markers in a non-linear gene-environment interaction study using the NHS data.

Identification of the potential biomarkers associated with circadian rhythms in heart failure

Background

Heart failure (HF) is a syndrome with multiple clinical symptoms resulting from damage to the heart's structure and/or function with various pathogenic factors, which has developed as one of the most severe threats to human health. Approximately 13% of genes and about 8% of proteins contained in the heart are rhythmic, which could lead to HF if disrupted. Herein, we aimed to identify the circadian rhythms-related hub genes as potential biomarkers contributing to the identification and treatment of HF.

Methods

Expression data of ischemic and dilated cardiomyopathy samples with or without HF were collected from the GEO database. First, genes with differential expression in HF and healthy samples were identified, named as differentially expressed genes (DEGs), which were then intersected with circadian rhythms-related genes to identify circadian rhythms-related DEGs. A protein-protein interaction (PPI) network was established to screen hub genes. The performance of the hub genes to identify HF among healthy controls was assessed by referring to the receiver operating characteristic (ROC) curve. Additionally, quantitative real-time polymerase chain reaction (RT-PCR) was run to further validate the hub genes depending on clinical human peripheral blood samples.

Results

A total of 10,163 DEGs were determined, composed of 4,615 up-regulated genes and 5,548 down-regulated genes in HF patients in comparison to healthy controls. By overlapping the circadian rhythms-related genes in the Circadian Gene DataBase (CGDB), 723 circadian rhythms-related DEGs were obtained, mainly enriched in regulating lipid metabolic process, circadian rhythm and AMPK signaling pathway. Eight hub genes were screened out through the PPI network. The ROC curve indicated the high accuracy of five hub genes with AUC > 0.7, which also showed high accuracy validated by the external validation dataset. Furthermore, according to the results of quantitative RT-PCR, the HF group showed significantly increased relative mRNA expression of CRY2 and BHLHE41 while the decreased ARNTL and NPAS2 in comparison to controls, indicating the four hub genes as potential biomarkers of HF.

Conclusion

Our study validated that ARNTL, CRY2, BHLHE41 and NPAS2 could serve as potential biomarkers of circadian rhythm in HF. These results may provide a reference for employing novel markers or targets for the diagnosis and treatment of HF.

Identification of a Chromosome 1 Substitution Line B6-Chr1BLD as a Novel Hyperlipidemia Model via Phenotyping Screening

Hyperlipidemia is a chronic disease that seriously affects human health. Due to the fact that traditional animal models cannot fully mimic hyperlipidemia in humans, new animal models are urgently needed for basic drug research on hyperlipidemia. Previous studies have demonstrated that the genomic diversity of the wild mice chromosome 1 substitution lines was significantly different from that of laboratory mice, suggesting that it might be accompanied by phenotypic diversity. We first screened the blood lipid-related phenotype of chromosome 1 substitution lines. We found that the male HFD-fed B6-Chr1BLD mice showed more severe hyperlipidemia-related phenotypes in body weight, lipid metabolism and liver lesions. By RNA sequencing and whole-genome sequencing results of B6-Chr1BLD, we found that several differentially expressed single nucleotide polymorphism enriched genes were associated with lipid metabolism-related pathways. Lipid metabolism-related genes, mainly including Aida, Soat1, Scly and Ildr2, might play an initial and upstream role in the abnormal metabolic phenotype of male B6-Chr1BLD mice. Taken together, male B6-Chr1BLD mice could serve as a novel, polygenic interaction-based hyperlipidemia model. This study could provide a novel animal model for accurate clinical diagnosis and precise medicine of hyperlipidemia.

Circadian transcription factor NPAS2 and the NAD+ -dependent deacetylase SIRT1 interact in the mouse nucleus accumbens and regulate reward

Substance use disorders are associated with disruptions to both circadian rhythms and cellular metabolic state. At the molecular level, the circadian molecular clock and cellular metabolic state may be interconnected through interactions with the nicotinamide adenine dinucleotide (NAD⁺ )-dependent deacetylase, sirtuin 1 (SIRT1). In the nucleus accumbens (NAc), a region important for reward, both SIRT1 and the circadian transcription factor neuronal PAS domain protein 2 (NPAS2) are highly enriched, and both are regulated by the metabolic cofactor NAD⁺ . Substances of abuse, like cocaine, greatly disrupt cellular metabolism and promote oxidative stress; however, their effects on NAD⁺ in the brain remain unclear. Interestingly, cocaine also induces NAc expression of both NPAS2 and SIRT1, and both have independently been shown to regulate cocaine reward in mice. However, whether NPAS2 and SIRT1 interact in the NAc and/or whether together they regulate reward is unknown. Here, we demonstrate diurnal expression of Npas2, Sirt1 and NAD⁺ in the NAc, which is altered by cocaine-induced upregulation. Additionally, co-immunoprecipitation reveals NPAS2 and SIRT1 interact in the NAc, and cross-analysis of NPAS2 and SIRT1 chromatin immunoprecipitation sequencing reveals several reward-relevant and metabolic-related pathways enriched among shared gene targets. Notably, NAc-specific Npas2 knock-down or a functional Npas2 mutation in mice attenuates SIRT1-mediated increases in cocaine preference. Together, our data reveal an interaction between NPAS2 and SIRT1 in the NAc, which may serve to integrate cocaine's effects on circadian and metabolic factors, leading to regulation of drug reward.

Therapeutic downregulation of neuronal PAS domain 2 (Npas2) promotes surgical skin wound healing

Attempts to minimize scarring remain among the most difficult challenges facing surgeons, despite the use of optimal wound closure techniques. Previously, we reported improved healing of dermal excisional wounds in circadian clock neuronal PAS domain 2 (Npas2)-null mice. In this study, we performed high-throughput drug screening to identify a compound that downregulates Npas2 activity. The hit compound (Dwn1) suppressed circadian Npas2 expression, increased murine dermal fibroblast cell migration, and decreased collagen synthesis in vitro. Based on the in vitro results, Dwn1 was topically applied to iatrogenic full-thickness dorsal cutaneous wounds in a murine model. The Dwn1-treated dermal wounds healed faster with favorable mechanical strength and developed less granulation tissue than the controls. The expression of type I collagen, Tgfβ1, and α-smooth muscle actin was significantly decreased in Dwn1-treated wounds, suggesting that hypertrophic scarring and myofibroblast differentiation are attenuated by Dwn1 treatment. NPAS2 may represent an important target for therapeutic approaches to optimal surgical wound management.

Maternal and early life exposures and their potential to influence development of the microbiome

At the dawn of the twentieth century, the medical care of mothers and children was largely relegated to family members and informally trained birth attendants. As the industrial era progressed, early and key public health observations among women and children linked the persistence of adverse health outcomes to poverty and poor nutrition. In the time hence, numerous studies connecting genetics ("nature") to public health and epidemiologic data on the role of the environment ("nurture") have yielded insights into the importance of early life exposures in relation to the occurrence of common diseases, such as diabetes, allergic and atopic disease, cardiovascular disease, and obesity. As a result of these parallel efforts in science, medicine, and public health, the developing brain, immune system, and metabolic physiology are now recognized as being particularly vulnerable to poor nutrition and stressful environments from the start of pregnancy to 3 years of age. In particular, compelling evidence arising from a diverse array of studies across mammalian lineages suggest that modifications to our metagenome and/or microbiome occur following certain environmental exposures during pregnancy and lactation, which in turn render risk of childhood and adult diseases. In this review, we will consider the evidence suggesting that development of the offspring microbiome may be vulnerable to maternal exposures, including an analysis of the data regarding the presence or absence of a low-biomass intrauterine microbiome.

NPAS2 ameliorates myocardial ischaemia/reperfusion injury in rats via CX3CL1 pathways and regulating autophagy

BACKGROUND

Myocardial ischemia/reperfusion (I/R) injury is common during the treatment of cardiovascular diseases. Neuronal PAS Domain Protein 2 (NPAS2) is one of the core genes that control the rhythm of the biological clock. NPAS2 also regulates the biological rhythm.

RESULTS

The rat I/R model showed that the expression of NPAS2 decreased with the increase of reperfusion time. Overexpressing NPAS2 adenovirus (ad-NPAS2) was injected into IR rat which demonstrated that ad-NPAS2 ameliorated rats I/R injury. A hypoxia/reoxygenation (H/R) model in rat cardiomyocytes showed that ad-NPAS2 inhibited cardiomyocyte apoptosis. Co-Immunoprecipitation results showed that there is an interaction between NPAS2 and Cry2. Knockdown of Cry2 aggravated the cardiomyocyte apoptosis induced by H/R. Additionally, NPAS2 directly act on the promoter region of CX3CL1. Knockdown of CX3CL1 reverse the protective effect of ad-NPAS2 on rat myocardial ischemia-reperfusion injury and H/R-induced cardiomyocyte apoptosis. CX3CL1 also regulates autophagy through the downstream AKT/mTOR pathway.

CONCLUSIONS

research demonstrated that overexpression of NPAS2 interacts with Cry2 and promotes the transcriptional activity of CX3CL1. Moreover, overexpression of NPAS2 regulates the downstream AKT/mTOR pathway to inhibit autophagy in order to improve rat cardiac I/R injury.

Transcriptional Control of Circadian Rhythms and Metabolism: A Matter of Time and Space

All biological processes, living organisms, and ecosystems have evolved with the Sun that confers a 24-hour periodicity to life on Earth. Circadian rhythms arose from evolutionary needs to maximize daily organismal fitness by enabling organisms to mount anticipatory and adaptive responses to recurrent light-dark cycles and associated environmental changes. The clock is a conserved feature in nearly all forms of life, ranging from prokaryotes to virtually every cell of multicellular eukaryotes. The mammalian clock comprises transcription factors interlocked in negative feedback loops, which generate circadian expression of genes that coordinate rhythmic physiology. In this review, we highlight previous and recent studies that have advanced our understanding of the transcriptional architecture of the mammalian clock, with a specific focus on epigenetic mechanisms, transcriptomics, and 3-dimensional chromatin architecture. In addition, we discuss reciprocal ways in which the clock and metabolism regulate each other to generate metabolic rhythms. We also highlight implications of circadian biology in human health, ranging from genetic and environment disruptions of the clock to novel therapeutic opportunities for circadian medicine. Finally, we explore remaining fundamental questions and future challenges to advancing the field forward.

NPAS2 Contributes to Liver Fibrosis by Direct Transcriptional Activation of Hes1 in Hepatic Stellate Cells

Recently, emerging evidence shows that dysregulation of circadian genes is closely associated with liver fibrosis. However, how dysregulation of circadian genes promotes liver fibrosis is unknown. In this study, we show that neuronal PAS domain protein 2 (NPAS2), one of the core circadian molecules that has been shown to promote hepatocarcinoma cell proliferation, significantly contributed to liver fibrogenesis. NPAS2 is upregulated in hepatic stellate cells (HSCs) after fibrogenic injury, which subsequently contributes to the activation of HSCs. Mechanistically, NPAS2 plays a profibrotic role via direct transcriptional activation of hairy and enhancer of split 1 (Hes1), a critical transcriptor of Notch signaling for the fibrogenesis process, in HSCs. Our findings demonstrate that NPAS2 plays a critical role in liver fibrosis through direct transcriptional activation of Hes1, indicating that NPAS2 may serve as an important therapeutic target to reverse the progression of liver fibrosis.

E-cigarettes and Western Diet: Important Metabolic Risk Factors for Hepatic Diseases

The use of electronic nicotine delivery systems (ENDS), also known as e-cigarettes, with a variety of e-liquids/e-juices, is increasing at an alarming rate among adolescents who do not realize the potential harmful health effects. This study examines the harmful effects of ENDS on the liver. Apolipoprotein E null (ApoE-/-) mice on a western diet (WD) were exposed to saline or ENDS with 2.4% nicotine aerosol for 12 weeks using our mouse ENDS exposure model system, which delivers nicotine to mice and leads to equivalent serum cotinine levels found in human cigarette users. ApoE-/- mice on a WD exposed to ENDS exhibited a marked increase in hepatic lipid accumulation compared with ApoE-/- on a similar diet exposed to saline aerosol. The detrimental effects of ENDS on hepatic steatosis were associated with significantly greater oxidative stress, increased hepatic triglyceride levels, and increased hepatocyte apoptosis, independent of adenosine monophosphate-activated protein kinase signaling. In addition, hepatic RNA sequencing analysis revealed that 433 genes were differentially expressed in ENDS-exposed mice on WD compared with saline-exposed mice. Functional analysis indicates that genes associated with lipid metabolism, cholesterol biosynthesis, and circadian rhythm were most significantly altered in the liver in response to ENDS. Conclusion: These results demonstrate profound adverse effects of ENDS on the liver. This is important information for regulatory agencies as they regulate ENDS.

Neuronal PAS Domain 2 (Npas2)-Deficient Fibroblasts Accelerate Skin Wound Healing and Dermal Collagen Reconstruction

The circadian clock, which consists of endogenous self-sustained and cell-autonomous oscillations in mammalian cells, is known to regulate a wide range of peripheral tissues. The unique upregulation of a clock gene, neuronal PAS domain protein 2 (Npas2), observed along with fibroblast aging prompted us to investigate the role of Npas2 in the homeostasis of dermal structure using in vivo and in vitro wound healing models. Time-course healing of a full-thickness skin punched wound exhibited significantly faster wound closure in Npas2-/- mice than wild-type (WT) C57Bl/6J mice. Dorsal skin fibroblasts isolated from WT, Npas2+/-, and Npas2-/- mice exhibited consistent profiles of core clock gene expression except for Npas2 and Per2. In vitro behavioral characterizations of dermal fibroblasts revealed that Npas2-/- mutation was associated with increased proliferation, migration, and cell contraction measured by floating collagen gel contraction and single-cell force contraction assays. Npas2 knockout fibroblasts carrying sustained the high expression level of type XII and XIV FAICT collagens and synthesized dermis-like thick collagen fibers in vitro. Confocal laser scanning microscopy demonstrated the reconstruction of dermis-like collagen architecture in the wound healing area of Npas2-/- mice. This study indicates that the induced Npas2 expression in fibroblasts may interfere with skin homeostasis, wound healing, and dermal tissue reconstruction, providing a basis for novel therapeutic target and strategy. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc.

Chronic Maternal Low-Protein Diet in Mice Affects Anxiety, Night-Time Energy Expenditure and Sleep Patterns, but Not Circadian Rhythm in Male Offspring

Offspring of murine dams chronically fed a protein-restricted diet have an increased risk for metabolic and neurobehavioral disorders. Previously we showed that adult offspring, developmentally exposed to a chronic maternal low-protein (MLP) diet, had lower body and hind-leg muscle weights and decreased liver enzyme serum levels. We conducted energy expenditure, neurobehavioral and circadian rhythm assays in male offspring to examine mechanisms for the body-weight phenotype and assess neurodevelopmental implications of MLP exposure. C57BL/6J dams were fed a protein restricted (8%protein, MLP) or a control protein (20% protein, C) diet from four weeks before mating until weaning of offspring. Male offspring were weaned to standard rodent diet (20% protein) and single-housed until 8–12 weeks of age. We examined body composition, food intake, energy expenditure, spontaneous rearing activity and sleep patterns and performed behavioral assays for anxiety (open field activity, elevated plus maze [EPM], light/dark exploration), depression (tail suspension and forced swim test), sociability (three-chamber), repetitive (marble burying), learning and memory (fear conditioning), and circadian behavior (wheel-running activity during light-dark and constant dark cycles). We also measured circadian gene expression in hypothalamus and liver at different Zeitgeber times (ZT). Male offspring from separate MLP exposed dams had significantly greater body fat (P = 0.03), less energy expenditure (P = 0.004), less rearing activity (P = 0.04) and a greater number of night-time rest/sleep bouts (P = 0.03) compared to control. MLP offspring displayed greater anxiety-like behavior in the EPM (P<0.01) but had no learning and memory deficit in fear-conditioning assay (P = 0.02). There was an effect of time on Per1, Per 2 and Clock circadian gene expression in the hypothalamus but not on circadian behavior. Thus, transplacental and early developmental exposure of dams to chronic MLP reduces food intake and energy expenditure, increases anxiety like behavior and disturbs sleep patterns but not circadian rhythm in adult male offspring.

NPAS2 Compensates for Loss of CLOCK in Peripheral Circadian Oscillators

Heterodimers of CLOCK and BMAL1 are the major transcriptional activators of the mammalian circadian clock. Because the paralog NPAS2 can substitute for CLOCK in the suprachiasmatic nucleus (SCN), the master circadian pacemaker, CLOCK-deficient mice maintain circadian rhythms in behavior and in tissues in vivo. However, when isolated from the SCN, CLOCK-deficient peripheral tissues are reportedly arrhythmic, suggesting a fundamental difference in circadian clock function between SCN and peripheral tissues. Surprisingly, however, using luminometry and single-cell bioluminescence imaging of PER2 expression, we now find that CLOCK-deficient dispersed SCN neurons and peripheral cells exhibit similarly stable, autonomous circadian rhythms in vitro. In CLOCK-deficient fibroblasts, knockdown of Npas2 leads to arrhythmicity, suggesting that NPAS2 can compensate for loss of CLOCK in peripheral cells as well as in SCN. Our data overturn the notion of an SCN-specific role for NPAS2 in the molecular circadian clock, and instead indicate that, at the cellular level, the core loops of SCN neuron and peripheral cell circadian clocks are fundamentally similar.

In mammals, circadian clocks are based on a core transcriptional–translational feedback loop. BMAL1 and CLOCK activate the transcription of Per1-3 and Cry1/2. PER and CRY proteins inhibit BMAL1/CLOCK, and thus their own transcription. In Clock^-/- mice, NPAS2 can substitute for CLOCK in the suprachiasmatic nucleus (SCN), the major circadian pacemaker. However, peripheral tissues of Clock^-/- mice were reported to lack circadian rhythms. Since then, the protein CLOCK has been deemed essential for circadian rhythms in peripheral tissues. However, here we show that Clock^-/- peripheral cells and tissues exhibit stable, autonomous circadian rhythms. Furthermore, in Clock^-/- fibroblasts, knockdown of Npas2 leads to arrhythmicity, suggesting that NPAS2 can compensate for the loss of CLOCK in peripheral cells as well as in SCN. Our data overturn the notion of an SCN-specific role for NPAS2, and instead indicate that the core loops of SCN neuron and peripheral cell circadian clocks are fundamentally similar. This finding redefines a basic principle of molecular circadian clock regulation in peripheral organs which are essential for many metabolic processes. Disturbances of these rhythms lead to disorders like diabetes, obesity, and cancer. Thus, understanding the molecular basis of peripheral circadian oscillators is essential to develop treatments against clock-related disorders.

Chromosomal assignment of quantitative trait loci influencing baseline circulating total cholesterol level in male laboratory mice: report of a consomic strain survey and comparison with published results

Background

An important risk for atherosclerosis is a low level of HDL cholesterol. Baseline HDL cholesterol is under complex genetic and environmental control. Here we report on results of male mice from a consomic strain survey and the parental inbred strains for baseline circulating total cholesterol concentration, which is almost the same as HDL cholesterol in chow fed mice. The consomic strains have been derived from C57BL/6J (host strain) and A/J (donor strain) inbred lines. The work contributes to the value of the mouse as an animal model for studying the genetic background of differences in baseline circulating total and HDL cholesterol levels.

Results

The consomic strain survey suggested that mouse chromosomes 1, 7, 9, 14, 16, 17, 19, X, and Y contained at least one quantitative trait locus that is involved in baseline circulating total cholesterol concentration. All consomic lines, for which there is evidence that the substituted chromosome contains a quantitative trait locus, increase compared to the host strain baseline circulating total cholesterol concentration. Since there is evidence that ‘body weight’, ‘age at blood sampling’, ‘time of the day blood was collected’, and ‘season’ influence this phenotype, additional statistical analyses (with these variables as covariates) were performed. Now there is only evidence for quantitative trait loci on chromosomes 1, 8, 12, and Y. Taken the present results together with previous consomic strain surveys there is evidence that all mouse chromosomes carry quantitative trait loci that control baseline circulating total cholesterol levels. There was however little agreement between the present consomic strain results and previous sets of data. This might be explained by seasonal effects and differences in methodological variables such as age of the mice, fasting versus non-fasting, percentage of dietary fat, unanesthetized versus anesthetized mice, and the daily light–dark cycle.

Conclusions

The present findings, when compared with previous consomic strain surveys, clearly illustrate the complexity of the genetic-environmental architecture for the regulation of baseline circulating total cholesterol levels in mice. Different data can be obtained from different labs and it underscores that animal geneticists should present as accurate a picture as possible of the laboratory mouse’s environment.

Small heterodimer partner/neuronal PAS domain protein 2 axis regulates the oscillation of liver lipid metabolism

In mammals, circadian rhythms are essential for coordinating the timing of various metabolic processes. The Clock gene regulates diurnal plasma triglyceride fluctuation through nuclear receptor small heterodimer partner (Shp; Nr0b2). Given that SHP is a critical regulator of metabolism in the liver, it is unknown whether SHP is necessary to coordinate metabolism and circadian rhythms. Shp(+/+) and Shp(-/-) mice on a C57BL/6 background (n = 3-5/group) were fed a standard chow diet and water ad libitum. Serum and livers were collected at zeitgeber time 2, 6, 10, 14, 18, and 22. In vivo and in vitro assays included RNA sequencing, quantitative polymerase chain reaction, very-low-density lipoprotein production, adenovirus overexpression and small interfering RNA knockdown, serum parameters, circadian locomotor activity, Oil Red O staining, transient transfection, luciferase reporter assay, chromatin immunoprecipitation assay, gel-shift assay, coimmunoprecipitation, and western blottings. Shp deficiency had a robust global impact on major liver metabolic genes. Several components of the liver clock, including peroxisome proliferator-activated receptor-γ, coactivator 1 (Pgc-1α), neuronal PAS domain-containing protein 2 (Npas2), and retinoic acid-related orphan receptor (Ror)α/γ were sharply induced in Shp(-/-) liver. At the molecular level, SHP inhibited Npas2 gene transcription and promoter activity through interaction with Rorγ to repress Rorγ transactivation and by interacting with Rev-erbα to enhance its inhibition of Rorα activity. Conversely, Npas2 controlled the circadian rhythm of Shp expression by binding rhythmically to the Shp promoter, which was enhanced by nicotinamide adenine dinucleotide, but not nicotinamide adenine dinucleotide phosphate. Phenotypically, Npas2 deficiency induced severe steatosis in Shp(-/-) mice, which was attributed to the dysregulation of lipoprotein metabolism.

CONCLUSION

Shp and Npas2 crosstalk is essential to maintain hepatic lipid homeostasis.

Circadian gene variants in cancer

Humans as diurnal beings are active during the day and rest at night. This daily oscillation of behavior and physiology is driven by an endogenous circadian clock not environmental cues. In modern societies, changes in lifestyle have led to a frequent disruption of the endogenous circadian homeostasis leading to increased risk of various diseases including cancer. The clock is operated by the feedback loops of circadian genes and controls daily physiology by coupling cell proliferation and metabolism, DNA damage repair, and apoptosis in peripheral tissues with physical activity, energy homeostasis, immune and neuroendocrine functions at the organismal level. Recent studies have revealed that defects in circadian genes due to targeted gene ablation in animal models or single nucleotide polymorphism, deletion, deregulation and/or epigenetic silencing in humans are closely associated with increased risk of cancer. In addition, disruption of circadian rhythm can disrupt the molecular clock in peripheral tissues in the absence of circadian gene mutations. Circadian disruption has recently been recognized as an independent cancer risk factor. Further study of the mechanism of clock-controlled tumor suppression will have a significant impact on human health by improving the efficiencies of cancer prevention and treatment.

Diurnal regulation of lipid metabolism and applications of circadian lipidomics

The circadian timing system plays a key role in orchestrating lipid metabolism. In concert with the solar cycle, the circadian system ensures that daily rhythms in lipid absorption, storage, and transport are temporally coordinated with rest-activity and feeding cycles. At the cellular level, genes involved in lipid synthesis and fatty acid oxidation are rhythmically activated and repressed by core clock proteins in a tissue-specific manner. Consequently, loss of clock gene function or misalignment of circadian rhythms with feeding cycles (e.g., in shift work) results in impaired lipid homeostasis. Herein, we review recent progress in circadian rhythms research using lipidomics, i.e., large-scale profiling of lipid metabolites, to characterize circadian-regulated lipid pathways in mammals. In mice, novel regulatory circuits involved in fatty acid metabolism have been identified in adipose tissue, liver, and muscle. Extensive diversity in circadian regulation of plasma lipids has also been revealed in humans using lipidomics and other metabolomics approaches. In future studies, lipidomics platforms will be increasingly used to better understand the effects of genetic variation, shift work, food intake, and drugs on circadian-regulated lipid pathways and metabolic health.

Circadian rhythms and addiction: mechanistic insights and future directions

Circadian rhythms are prominent in many physiological and behavioral functions. Circadian disruptions either by environmental or molecular perturbation can have profound health consequences, including the development and progression of addiction. Both animal and humans studies indicate extensive bidirectional relationships between the circadian system and drugs of abuse. Addicted individuals display disrupted rhythms, and chronic disruption or particular chronotypes may increase the risk for substance abuse and relapse. Moreover, polymorphisms in circadian genes and an evening chronotype have been linked to mood and addiction disorders, and recent efforts suggest an association with the function of reward neurocircuitry. Animal studies are beginning to determine how altered circadian gene function results in drug-induced neuroplasticity and behaviors. Many studies suggest a critical role for circadian rhythms in reward-related pathways in the brain and indicate that drugs of abuse directly affect the central circadian pacemaker. In this review, we highlight key findings demonstrating the importance of circadian rhythms in addiction and how future studies will reveal important mechanistic insights into the involvement of circadian rhythms in drug addiction.