Crosstalk between components of circadian and metabolic cycles in mammals

Misregulation of Drosophila Myc Disrupts Circadian Behavior and Metabolism

Drosophila Myc (dMyc) is highly conserved and functions as a transcription factor similar to mammalian Myc. We previously found that oncogenic Myc disrupts the molecular clock in cancer cells. Here, we demonstrate that misregulation of dMyc expression affects Drosophila circadian behavior. dMyc overexpression results in a high percentage of arrhythmic flies, concomitant with increases in the expression of clock genes cyc, tim, cry, and cwo. Conversely, flies with hypomorphic mutations in dMyc exhibit considerable arrhythmia, which can be rescued by loss of dMnt, a suppressor of dMyc activity. Metabolic profiling of fly heads revealed that loss of dMyc and its overexpression alter steady-state metabolite levels and have opposing effects on histidine, the histamine precursor, which is rescued in dMyc mutants by ablation of dMnt and could contribute to effects of dMyc on locomotor behavior. Our results demonstrate a role of dMyc in modulating Drosophila circadian clock, behavior, and metabolism.

Diurnal Rhythmicity Programs of Microbiota and Transcriptional Oscillation of Circadian Regulator, NFIL3

Circadian rhythms are a very exquisite mechanism to influence on transcriptional levels and physiological activities of various molecules that affect cell metabolic pathways. Long-term alteration of circadian rhythms increases the risk of cardiovascular diseases, hypertension, hypertriglyceridemia, and metabolic syndrome. A drastic change in dietary patterns can affect synchronizing the circadian clock within the metabolic system. Therefore, the interaction between the host and the bacterial community colonizing the mammalian gastrointestinal tract has a great impact on the circadian clock in diurnal programs. Here, we propose that the microbiota regulates body composition through the transcriptional oscillation of circadian regulators. The transcriptional regulator, NFIL3 (also called E4BP4) is a good example. Compositional change of the commensal bacteria influences the rhythmic expression of NFIL3 in the epithelium, which subsequently controls obesity and insulin resistance. Therefore, control of circadian regulators would be a promising therapeutic target for metabolic diseases.

A role for alternative splicing in circadian control of exocytosis and glucose homeostasis

The circadian clock is encoded by a negative transcriptional feedback loop that coordinates physiology and behavior through molecular programs that remain incompletely understood. Here, we reveal rhythmic genome-wide alternative splicing (AS) of pre-mRNAs encoding regulators of peptidergic secretion within pancreatic β cells that are perturbed in Clock-/- and Bmal1-/- β-cell lines. We show that the RNA-binding protein THRAP3 (thyroid hormone receptor-associated protein 3) regulates circadian clock-dependent AS by binding to exons at coding sequences flanking exons that are more frequently skipped in clock mutant β cells, including transcripts encoding Cask (calcium/calmodulin-dependent serine protein kinase) and Madd (MAP kinase-activating death domain). Depletion of THRAP3 restores expression of the long isoforms of Cask and Madd, and mimicking exon skipping in these transcripts through antisense oligonucleotide delivery in wild-type islets reduces glucose-stimulated insulin secretion. Finally, we identify shared networks of alternatively spliced exocytic genes from islets of rodent models of diet-induced obesity that significantly overlap with clock mutants. Our results establish a role for pre-mRNA alternative splicing in β-cell function across the sleep/wake cycle.

The circadian clock gene Bmal1 facilitates cisplatin-induced renal injury and hepatization

Cisplatin is one of the most potent chemotherapy drugs to treat cancers, but its clinical application remains limited due to severe nephrotoxicity. Several approaches have been developed to minimize such side effects, notably including chronotherapy, a well-known strategy based on the circadian clock. However, the component of the circadian clock machinery that particularly responses to the cisplatin stimulation remains unknown, including its functions in cisplatin-induced renal injury. In our present study, we demonstrated that Bmal1, as a key clock gene, was induced by the cisplatin stimulation in the mouse kidney and cultured human HK-2 renal cells. Gain- and loss-of-function studies indicated that Bmal1 facilitated cisplatin-induced renal injury both in vivo and in vitro, by aggravating the cell apoptotic process. More importantly, RNA-seq analysis revealed that Bmal1 triggered the expression of hallmark genes involved in renal hepatization, a critical event accompanied by the injury. At the molecular level, Bmal1 activated the transcription of hepatization-associated genes through direct recruitment to the E-box motifs of their promoters. Our findings suggest that Bmal1, a pivotal mediator induced renal injury in response to cisplatin treatment, and the therapeutic intervention targeting Bmal1 in the kidney may be a promising strategy to minimize the toxic side-effects of cisplatin in its clinical applications.

Identifying Cattle Breed-Specific Partner Choice of Transcription Factors during the African Trypanosomiasis Disease Progression Using Bioinformatics Analysis

African Animal Trypanosomiasis (AAT) is a disease caused by pathogenic trypanosomes which affects millions of livestock every year causing huge economic losses in agricultural production especially in sub-Saharan Africa. The disease is spread by the tsetse fly which carries the parasite in its saliva. During the disease progression, the cattle are prominently subjected to anaemia, weight loss, intermittent fever, chills, neuronal degeneration, congestive heart failure, and finally death. According to their different genetic programs governing the level of tolerance to AAT, cattle breeds are classified as either resistant or susceptible. In this study, we focus on the cattle breeds N’Dama and Boran which are known to be resistant and susceptible to trypanosomiasis, respectively. Despite the rich literature on both breeds, the gene regulatory mechanisms of the underlying biological processes for their resistance and susceptibility have not been extensively studied. To address the limited knowledge about the tissue-specific transcription factor (TF) cooperations associated with trypanosomiasis, we investigated gene expression data from these cattle breeds computationally. Consequently, we identified significant cooperative TF pairs (especially DBP−PPARA and DBP−THAP1 in N’Dama and DBP−PAX8 in Boran liver tissue) which could help understand the underlying AAT tolerance/susceptibility mechanism in both cattle breeds.

Sobriety and Satiety: Is NAD+ the Answer?

Nicotinamide adenine dinucleotide (NAD+) is an essential pyridine nucleotide that has garnered considerable interest in the last century due to its critical role in cellular processes associated with energy production, cellular protection against stress and longevity. Research in NAD+ has been reinvigorated by recent findings that components of NAD+ metabolism and NAD-dependent enzymes can influence major signalling processes associated with the neurobiology of addiction. These studies implicate raising intracellular NAD+ levels as a potential target for managing and treating addictive behaviour and reducing cravings and withdrawal symptoms in patients with food addiction and/or substance abuse. Since clinical studies showing the use of NAD+ for the treatment of addiction are limited, this review provides literature evidence that NAD+ can influence the neurobiology of addiction and may have benefits as an anti-addiction intervention.

Circadian Rhythms in the Pathogenesis and Treatment of Fatty Liver Disease

Circadian clock proteins are endogenous timing mechanisms that control the transcription of hundreds of genes. Their integral role in coordinating metabolism has led to their scrutiny in a number of diseases, including nonalcoholic fatty liver disease (NAFLD). Discoordination between central and peripheral circadian rhythms is a core feature of nearly every genetic, dietary, or environmental model of metabolic syndrome and NAFLD. Restricting feeding to a defined daily interval (time-restricted feeding) can synchronize the central and peripheral circadian rhythms, which in turn can prevent or even treat the metabolic syndrome and hepatic steatosis. Importantly, a number of proteins currently under study as drug targets in NAFLD (sterol regulatory element-binding protein [SREBP], acetyl-CoA carboxylase [ACC], peroxisome proliferator-activator receptors [PPARs], and incretins) are modulated by circadian proteins. Thus, the clock can be used to maximize the benefits and minimize the adverse effects of pharmaceutical agents for NAFLD. The circadian clock itself has the potential for use as a target for the treatment of NAFLD.

Feeding Rhythms and the Circadian Regulation of Metabolism

The molecular circadian clock regulates metabolic processes within the cell, and the alignment of these clocks between tissues is essential for the maintenance of metabolic homeostasis. The possibility of misalignment arises from the differential responsiveness of tissues to the environmental cues that synchronize the clock (zeitgebers). Although light is the dominant environmental cue for the master clock of the suprachiasmatic nucleus, many other tissues are sensitive to feeding and fasting. When rhythms of feeding behavior are altered, for example by shift work or the constant availability of highly palatable foods, strong feedback is sent to the peripheral molecular clocks. Varying degrees of phase shift can cause the systemic misalignment of metabolic processes. Moreover, when there is a misalignment between the endogenous rhythms in physiology and environmental inputs, such as feeding during the inactive phase, the body's ability to maintain homeostasis is impaired. The loss of phase coordination between the organism and environment, as well as internal misalignment between tissues, can produce cardiometabolic disease as a consequence. The aim of this review is to synthesize the work on the mechanisms and metabolic effects of circadian misalignment. The timing of food intake is highlighted as a powerful environmental cue with the potential to destroy or restore the synchrony of circadian rhythms in metabolism.

Time of day is associated with paradoxical reductions in global signal fluctuation and functional connectivity

The brain exhibits substantial diurnal variation in physiology and function, but neuroscience studies rarely report or consider the effects of time of day. Here, we examined variation in resting-state functional MRI (fMRI) in around 900 individuals scanned between 8 AM and 10 PM on two different days. Multiple studies across animals and humans have demonstrated that the brain’s global signal (GS) amplitude (henceforth referred to as “fluctuation”) increases with decreased arousal. Thus, in accord with known circadian variation in arousal, we hypothesised that GS fluctuation would be lowest in the morning, increase in the midafternoon, and dip in the early evening. Instead, we observed a cumulative decrease in GS fluctuation as the day progressed. Although respiratory variation also decreased with time of day, control analyses suggested that this did not account for the reduction in GS fluctuation. Finally, time of day was associated with marked decreases in resting-state functional connectivity across the whole brain. The magnitude of decrease was significantly stronger than associations between functional connectivity and behaviour (e.g., fluid intelligence). These findings reveal time of day effects on global brain activity that are not easily explained by expected arousal state or physiological artefacts. We conclude by discussing potential mechanisms for the observed diurnal variation in resting brain activity and the importance of accounting for time of day in future studies.

The brain exhibits substantial diurnal variation in physiology and function. A large-scale fMRI study reveals that the brain’s global signal amplitude, typically elevated during drowsy states, unexpectedly reduces steadily as the day progresses.

Systems Level Understanding of Circadian Integration with Cell Physiology

The mammalian circadian clock regulates a wide variety of physiological and behavioral processes. In turn, its disruption is associated with sleep deficiency, metabolic syndrome, neurological and psychiatric disorders, and cancer. At the turn of the century, the circadian clock was determined to be regulated by a transcriptional negative feedback mechanism composed of a dozen core clock genes. More recently, large-scale genomic studies have expanded the clock into a complex network composed of thousands of gene outputs and inputs. A major task of circadian research is to utilize systems biological approaches to uncover the governing principles underlying cellular oscillatory behavior and advance understanding of biological functions at the genomic level with spatiotemporal resolution. This review focuses on the genes and pathways that provide inputs to the circadian clock. Several emerging examples include AMP-activated protein kinase AMPK, nutrient/energy sensor mTOR, NAD⁺-dependent deacetylase SIRT1, hypoxia-inducible factor HIF1α, oxidative stress-inducible factor NRF2, and the proinflammatory factor NF-κB. Among others that continue to be revealed, these input pathways reflect the extensive interplay between the clock and cell physiology through the regulation of core clock genes and proteins. While the scope of this crosstalk is well-recognized, precise molecular links are scarce, and the underlying regulatory mechanisms are not well understood. Future research must leverage genetic and genomic tools and technologies, network analysis, and computational modeling to characterize additional modifiers and input pathways. This systems-based framework promises to advance understanding of the circadian timekeeping system and may enable the enhancement of circadian functions through related input pathways.

The p75 neurotrophin receptor in AgRP neurons is necessary for homeostatic feeding and food anticipation

Networks of neurons control feeding and activity patterns by integrating internal metabolic signals of energy balance with external environmental cues such as time-of-day. Proper circadian alignment of feeding behavior is necessary to prevent metabolic disease, and thus it is imperative that molecular players that maintain neuronal coordination of energy homeostasis are identified. Here, we demonstrate that mice lacking the p75 neurotrophin receptor, p75NTR, decrease their feeding and food anticipatory behavior (FAA) in response to daytime, but not nighttime, restricted feeding. These effects lead to increased weight loss, but do not require p75NTR during development. Instead, p75NTR is required for fasting-induced activation of neurons within the arcuate hypothalamus. Indeed, p75NTR specifically in AgRP neurons is required for FAA in response to daytime restricted feeding. These findings establish p75NTR as a novel regulator gating behavioral response to food scarcity and time-of-day dependence of circadian food anticipation.

Saliva Samples as A Tool to Study the Effect of Meal Timing on Metabolic And Inflammatory Biomarkers

Meal timing affects metabolic regulation in humans. Most studies use blood samples for their investigations. Saliva, although easily available and non-invasive, seems to be rarely used for chrononutritional studies. In this pilot study, we tested if saliva samples could be used to study the effect of timing of carbohydrate and fat intake on metabolic rhythms. In this cross-over trial, 29 nonobese men were randomized to two isocaloric 4-week diets: (1) carbohydrate-rich meals until 13:30 and high-fat meals between 16:30 and 22:00 or (2) the inverse order of meals. Stimulated saliva samples were collected every 4 h for 24 h at the end of each intervention, and levels of hormones and inflammatory biomarkers were assessed in saliva and blood. Cortisol, melatonin, resistin, adiponectin, interleukin-6 and MCP-1 demonstrated distinct diurnal variations, mirroring daytime reports in blood and showing significant correlations with blood levels. The rhythm patterns were similar for both diets, indicating that timing of carbohydrate and fat intake has a minimal effect on metabolic and inflammatory biomarkers in saliva. Our study revealed that saliva is a promising tool for the non-invasive assessment of metabolic rhythms in chrononutritional studies, but standardisation of sample collection is needed in out-of-lab studies.

Resetting the Aging Clock: Implications for Managing Age-Related Diseases

Worldwide, individuals are living longer due to medical and scientific advances, increased availability of medical care and changes in public health policies. Consequently, increasing attention has been focused on managing chronic conditions and age-related diseases to ensure healthy aging. The endogenous circadian system regulates molecular, physiological and behavioral rhythms orchestrating functional coordination and processes across tissues and organs. Circadian disruption or desynchronization of circadian oscillators increases disease risk and appears to accelerate aging. Reciprocally, aging weakens circadian function aggravating age-related diseases and pathologies. In this review, we summarize the molecular composition and structural organization of the circadian system in mammals and humans, and evaluate the technological and societal factors contributing to the increasing incidence of circadian disorders. Furthermore, we discuss the adverse effects of circadian dysfunction on aging and longevity and the bidirectional interactions through which aging affects circadian function using examples from mammalian research models and humans. Additionally, we review promising methods for managing healthy aging through behavioral and pharmacological reinforcement of the circadian system. Understanding age-related changes in the circadian clock and minimizing circadian dysfunction may be crucial components to promote healthy aging.

The importance of being rhythmic: Living in harmony with your body clocks

Circadian rhythms have developed in all light-sensitive organisms, including humans, as a fundamental anticipatory mechanism that enables proactive adaptation to environmental changes. The circadian system is organized in a highly hierarchical manner, with clocks operative in most cells of the body ensuring the temporal coordination of physiological processes. Circadian misalignment, stemming from modern life style, draws increasing attention due to its tight association with the development of metabolic, cardiovascular, inflammatory and mental diseases as well as cancer. This review highlights recent findings emphasizing the role of the circadian system in the temporal orchestration of physiology, with a particular focus on implications of circadian misalignment in human pathologies.

Circadian Clock Regulation on Lipid Metabolism and Metabolic Diseases

The basic helix-loop-helix-PAS transcription factor (CLOCK, Circadian locomotor output cycles protein kaput) was discovered in 1994 as a circadian clock. Soon after its discovery, the circadian clock, Aryl hydrocarbon receptor nuclear translocator-like protein 1 (ARNTL, also call BMAL1), was shown to regulate adiposity and body weight by controlling on the brain hypothalamic suprachiasmatic nucleus (SCN). Farther, circadian clock genes were determined to exert several of lipid metabolic and diabetes effects, overall indicating that CLOCK and BMAL1 act as a central master circadian clock. A master circadian clock acts through the neurons and hormones, with expression in the intestine, liver, kidney, lung, heart, SCN of brain, and other various cell types of the organization. Among circadian clock genes, numerous metabolic syndromes are the most important in the regulation of food intake (via regulation of circadian clock genes or clock-controlled genes in peripheral tissue), which lead to a variation in plasma phospholipids and tissue phospholipids. Circadian clock genes affect the regulation of transporters and proteins included in the regulation of phospholipid metabolism. These genes have recently received increasing recognition because a pharmacological target of circadian clock genes may be of therapeutic worth to make better resistance against insulin, diabetes, obesity, metabolism syndrome, atherosclerosis, and brain diseases. In this book chapter, we focus on the regulation of circadian clock and summarize its phospholipid effect as well as discuss the chemical, physiology, and molecular value of circadian clock pathway regulation for the treatment of plasma lipids and atherosclerosis.

Is Neuronal Histamine Signaling Involved in Cancer Cachexia? Implications and Perspectives

In this paper, we present evidence in support of our hypothesis that the neuronal histaminergic system might be involved in cancer cachexia¹. To build our premise, we present the research and the reasonable inferences that can be drawn from it in a section by section approach starting from one of the key issues related to cachexia, increased resting energy expenditure (REE), and progressing to the other, anorexia. Based on an extensive survey of the literature and our own deliberations on the abovementioned topics, we investigate whether histamine signaling might be the mechanism used by a tumor to hijack the body's thermogenic machinery. Our hypothesis in short is that hypothalamic histaminergic neurons are stimulated by inputs from the parasympathetic nervous system (PSNS), which senses tumor traits early in cancer development. Histamine release in the preoptic area of the hypothalamus primarily activates brown adipose tissue (BAT), triggering a highly energy demanding mechanism. Chronic activation of BAT, which, in this context, refers to intermittent and/or low grade activation by the sympathetic nervous system, leads to browning of white adipose tissue and further enhances thermogenic potential. Aberrant histamine signaling not only triggers energy-consuming processes, but also anorexia. Moreover, since functions such as taste, smell, and sleep are governed by discrete structures of the brain, which are targeted by distinct histaminergic neuron populations even relatively minor symptoms of cachexia, such as sleep disturbances and taste and smell distortions, also might be ascribed to aberrant histamine signaling. In late stage cachexia, the sympathetic tone in skeletal muscle breaks down, which we hypothesize might be caused by a reduction in histamine signaling or by the interference of other cachexia related mechanisms. Histamine signaling thus might delineate distinct stages of cachexia progression, with the early phase marked by a PSNS-mediated increase in histamine signaling, increased sympathetic tone and symptomatic adipose tissue depletion, and the late phase characterized by reduced histamine signaling, decreased sympathetic tone and symptomatic muscle wasting. To support our hypothesis, we review the literature from across disciplines and highlight the many commonalities between the mechanisms underlying cancer cachexia and current research findings on the regulation of energy homeostasis (particularly as it relates to hypothalamic histamine signaling). Extrapolating from the current body of knowledge, we develop our hypothetical framework (based on experimentally falsifiable assumptions) about the role of a distinct neuron population in the pathophysiology of cancer cachexia. Our hope is that presenting our ideas will spark discussion about the pathophysiology of cachexia, cancer's devastating and intractable syndrome.

Purine Catabolism Shows a Dampened Circadian Rhythmicity in a High-fat Diet-Induced Mouse Model of Obesity

High-calorie diet, circadian rhythms and metabolic features are intimately linked. However, the mediator(s) between nutritional status, circadian rhythms and metabolism remain largely unknown. This article aims to clarify the key metabolic pathways bridging nutritional status and circadian rhythms based on a combination of metabolomics and molecular biological techniques. A mouse model of high-fat diet-induced obesity was established and serum samples were collected in obese and normal mice at different zeitgeber times. Gas chromatography/mass spectrometry, multivariate/univariate data analyses and metabolic pathway analysis were used to reveal changes in metabolism. Metabolites involved in the metabolism of purines, carbohydrates, fatty acids and amino acids were markedly perturbed in accordance with circadian related variations, among which purine catabolism showed a typical oscillation. What's more, the rhythmicity of purine catabolism dampened in the high-fat diet group. The expressions of clock genes and metabolic enzymes in the liver were measured. The mRNA expression of Xanthine oxidase (Xor) was highly correlated with the rhythmicity of Clock, Rev-erbα and Bmal1, as well as the metabolites involved in purine catabolism. These data showed that a high-fat diet altered the circadian rhythm of metabolic pathways, especially purine catabolism. It had an obvious circadian oscillation and a high-fat diet dampened its circadian rhythmicity. It was suggested that circadian rhythmicity of purine catabolism is related to circadian oscillations of expression of Xor, Uox and corresponding clock genes.

Phenotypic proteomic profiling identifies a landscape of targets for circadian clock-modulating compounds

This study provides comprehensive insights into the mechanism of action and cellular effects of circadian period–modulating compounds, which is critical for clearly defining molecular targets to modulate daily rhythms for therapeutic benefit.

Determining the exact targets and mechanisms of action of drug molecules that modulate circadian rhythms is critical to develop novel compounds to treat clock-related disorders. Here, we have used phenotypic proteomic profiling (PPP) to systematically determine molecular targets of four circadian period–lengthening compounds in human cells. We demonstrate that the compounds cause similar changes in phosphorylation and activity of several proteins and kinases involved in vital pathways, including MAPK, NGF, B-cell receptor, AMP-activated protein kinases (AMPKs), and mTOR signaling. Kinome profiling further indicated inhibition of CKId, ERK1/2, CDK2/7, TNIK, and MST4 kinases as a common mechanism of action for these clock-modulating compounds. Pharmacological or genetic inhibition of several convergent kinases lengthened circadian period, establishing them as novel circadian targets. Finally, thermal stability profiling revealed binding of the compounds to clock regulatory kinases, signaling molecules, and ubiquitination proteins. Thus, phenotypic proteomic profiling defines novel clock effectors that could directly inform precise therapeutic targeting of the circadian system in humans.

Indoor light pollution and progression of carotid atherosclerosis: A longitudinal study of the HEIJO-KYO cohort

Exposure to light at inappropriate times in relation to the solar cycle can disturb circadian endocrine and metabolic rhythms. Previous studies have suggested an association between light exposure at night (LAN) and obesity, an important risk factor of atherosclerosis, although it remains unclear whether LAN associates with progression of atherosclerosis. To evaluate the longitudinal association between bedroom LAN intensity and progression of carotid atherosclerosis, light intensity in the bedroom at baseline and carotid artery intima-media thickness (IMT) at baseline and follow-up were measured in 989 elderly participants (945 at baseline and 780 at a median follow-up time of 34 months). The mean age of the participants was 71.4 ± 6.9 years. The average mean and maximal carotid IMT at baseline were 0.88 ± 0.15 and 1.10 ± 0.32 mm, respectively. The median intensity of bedroom LAN was 0.68 lx (IQR, 0.07-3.29). In multivariable analysis adjusted for potential confounders, the highest LAN group exhibited a significant increase in mean carotid IMT (adjusted β, 0.028; 95% CI, 0.005-0.052; P = 0.019) compared with the lowest LAN quartile group. A similar relationship was found between LAN and maximal carotid IMT (adjusted β, 0.083; 95% CI, 0.037-0.129; P < 0.001). In conclusion, we found a clear and significant association between bedroom LAN intensity and progression of subclinical carotid atherosclerosis, which was independent of known risk factors for atherosclerosis, including age, obesity, smoking, economic status, hypertension, and diabetes. Indoor light pollution may be a potential risk factor for atherosclerosis in the general population.

Distinct metabolic adaptation of liver circadian pathways to acute and chronic patterns of alcohol intake

Binge drinking and chronic exposure to ethanol contribute to alcoholic liver diseases (ALDs). A potential link between ALDs and circadian disruption has been observed, though how different patterns of alcohol consumption differentially impact hepatic circadian metabolism remains virtually unexplored. Using acute versus chronic ethanol feeding, we reveal differential reprogramming of the circadian transcriptome in the liver. Specifically, rewiring of diurnal SREBP transcriptional pathway leads to distinct hepatic signatures in acetyl-CoA metabolism that are translated into the subcellular patterns of protein acetylation. Thus, distinct drinking patterns of alcohol dictate differential adaptation of hepatic circadian metabolism.

Oolong Tea Polyphenols Ameliorate Circadian Rhythm of Intestinal Microbiome and Liver Clock Genes in Mouse Model

Our present study focused on the regulating effect of oolong tea polyphenols (OTPs) on the circadian rhythm of liver and intestinal microbiome. OTP significantly alleviated the disrupted diurnal oscillation and phase shift of the specific intestinal microbiota and liver clock genes in mice induced by constant dark (CD) treatment. Transcriptomics revealed that 1114 genes in the control group and 647 genes in the CD group showed circadian rhythm while 723 genes were rhythmic in the CD-OTP group. The Gene Ontology (GO) database provided significant differences in differentially expressed genes (DEGs) in response to OTP treatment. In addition, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways enriched the most DEGs after OTP intervention including "Focal adhesion" (9 DEGs) and "PI3K-Akt signaling pathway" (9 DEGs). The present study provided a global view that OTP may alleviate the circadian rhythm disorder of the host, contributing to the improvement of microecology and health.

Circadian Regulation of Cardiac Physiology: Rhythms That Keep the Heart Beating

On Earth, all life is exposed to dramatic changes in the environment over the course of the day; consequently, organisms have evolved strategies to both adapt to and anticipate these 24-h oscillations. As a result, time of day is a major regulator of mammalian physiology and processes, including transcription, signaling, metabolism, and muscle contraction, all of which oscillate over the course of the day. In particular, the heart is subject to wide fluctuations in energetic demand throughout the day as a result of waking, physical activity, and food intake patterns. Daily rhythms in cardiovascular function ensure that increased delivery of oxygen, nutrients, and endocrine factors to organs during the active period and the removal of metabolic by-products are in balance. Failure to maintain these physiologic rhythms invariably has pathologic consequences. This review highlights rhythms that underpin cardiac physiology. More specifically, we summarize the key aspects of cardiac physiology that oscillate over the course of the day and discuss potential mechanisms that regulate these 24-h rhythms.

Exploration of tissue-specific gene expression patterns underlying timing of breeding in contrasting temperature environments in a song bird

BACKGROUND

Seasonal timing of breeding is a life history trait with major fitness consequences but the genetic basis of the physiological mechanism underlying it, and how gene expression is affected by date and temperature, is not well known. In order to study this, we measured patterns of gene expression over different time points in three different tissues of the hypothalamic-pituitary-gonadal-liver axis, and investigated specifically how temperature affects this axis during breeding. We studied female great tits (Parus major) from lines artificially selected for early and late timing of breeding that were housed in two contrasting temperature environments in climate-controlled aviaries. We collected hypothalamus, liver and ovary samples at three different time points (before and after onset of egg-laying). For each tissue, we sequenced whole transcriptomes of 12 pools (n = 3 females) to analyse gene expression.

RESULTS

Birds from the selection lines differed in expression especially for one gene with clear reproductive functions, zona pellucida glycoprotein 4 (ZP4), which has also been shown to be under selection in these lines. Genes were differentially expressed at different time points in all tissues and most of the differentially expressed genes between the two temperature treatments were found in the liver. We identified a set of hub genes from all the tissues which showed high association to hormonal functions, suggesting that they have a core function in timing of breeding. We also found ample differentially expressed genes with largely unknown functions in birds.

CONCLUSIONS

We found differentially expressed genes associated with selection line and temperature treatment. Interestingly, the latter mainly in the liver suggesting that temperature effects on egg-laying date may happen down-stream in the physiological pathway. These findings, as well as our datasets, will further the knowledge of the mechanisms of tissue-specific avian seasonality in the future.

Meal timing and obesity: interactions with macronutrient intake and chronotype

BACKGROUND

Timing of dietary intake may play a role in obesity. However, previous studies produced mixed findings possibly due to inconsistent approaches to characterize meal timing and not taking into account chronotype and macronutrients. To address the aforementioned limitations, we have defined meal timing relative to sleep/wake timing, investigated the relationship between meal timing and body mass index (BMI) dependent on chronotype, and examined the associations.

METHODS

BMI, chronotype, and dietary intakes were measured in 872 middle-to-older-aged adults by six 24-h dietary recalls in 1 year. We defined four time windows of intake relative to sleep timing: morning (within 2 h after getting out of bed), night (within 2 h before bedtime), and two midday periods in between (split by the midpoint of the waking period).

RESULTS

A higher percent of total daily energy intake consumed during the morning window was associated with lower odds of being overweight or obese (odds ratio (95% confidence intervals), 0.53 (0.31, 0.89)). This association was stronger in people with an earlier chronotype (0.32 (0.16, 0.66)). A higher percent of total daily energy intake consumed during the night window was associated with higher odds of being overweight or obese (1.82 (1.07, 3.08)), particularly in people with a later chronotype (4.94 (1.61, 15.14)). These associations were stronger for the intakes of carbohydrates and protein than for fat intake.

CONCLUSION

Our study suggests that higher dietary consumption after waking up and lower consumption close to bedtime associate with lower BMI, but the relationship differs by chronotype. Furthermore, the data demonstrate a clear relationship between the timing of carbohydrate and protein intake and obesity. Our findings highlight the importance of considering timing of intake relative to sleep timing when studying the associations of meal timing with obesity and metabolic health.

At the Interface of Lifestyle, Behavior, and Circadian Rhythms: Metabolic Implications

Nutrient metabolism is under circadian regulation. Disruption of circadian rhythms by lifestyle and behavioral choices such as work schedules, eating patterns, and social jetlag, seriously impacts metabolic homeostasis. Metabolic dysfunction due to chronic misalignment of an organism's endogenous rhythms is detrimental to health, increasing the risk of obesity, metabolic and cardiovascular disease, diabetes, and cancer. In this paper, we review literature on recent findings on the mechanisms that communicate metabolic signals to circadian clocks and vice versa, and how human behavioral changes imposed by societal and occupational demands affect the physiological networks integrating peripheral clocks and metabolism. Finally, we discuss factors possibly contributing to inter-individual variability in response to circadian changes in the context of metabolic (dys)function.

Angptl8 mediates food-driven resetting of hepatic circadian clock in mice

Diurnal light-dark cycle resets the master clock, while timed food intake is another potent synchronizer of peripheral clocks in mammals. As the largest metabolic organ, the liver sensitively responds to the food signals and secretes hepatokines, leading to the robust regulation of metabolic and clock processes. However, it remains unknown which hepatokine mediates the food-driven resetting of the liver clock independent of the master clock. Here, we identify Angptl8 as a hepatokine that resets diurnal rhythms of hepatic clock and metabolic genes in mice. Mechanistically, the resetting function of Angptl8 is dependent on the signal relay of the membrane receptor PirB, phosphorylation of kinases and transcriptional factors, and consequently transient activation of the central clock gene Per1. Importantly, inhibition of Angptl8 signaling partially blocks food-entrained resetting of liver clock in mice. We have thus identified Angptl8 as a key regulator of the liver clock in response to food.

The importance of determining circadian parameters in pharmacological studies

In mammals, most molecular and cellular processes show circadian changes, leading to daily variations in physiology and ultimately in behaviour. Such daily variations induce a temporal coordination of processes that is essential to ensure homeostasis and health. Thus, it is of no surprise that pharmacokinetics (PK) and pharmacodynamics (PD) of many drugs are also subject to circadian variations, profoundly affecting their efficacy and tolerability. Understanding how circadian rhythms influence drug PK, PD, and toxicity might significantly improve treatment efficacy and decrease related side effects. Therefore, it is essential to take circadian variations into account and to determine circadian parameters in pharmacological studies, especially when drugs have a short half-life or target rhythmic processes. This review provides an overview of the current knowledge on circadian rhythms and their relevance to the field of pharmacology. Methodologies to evaluate circadian rhythms in vitro, in rodent models and in humans, from experimental to computational approaches, are described and discussed. Lastly, we aim at alerting the scientific, medical, and regulatory communities to the relevance of the physiological time, as a key parameter to be considered when designing pharmacological studies. This will eventually lead to more successful preclinical and clinical trials and pave the way to a more personalized treatment to the benefit of the patients.

Hypothalamic leptin sensitivity and health benefits of time-restricted feeding are dependent on the time of day in male mice

Synchronization between biologic clocks and metabolism is crucial for most species. Here, we examined the ability of leptin, important in the control of energy metabolism, to induce leptin signaling at the molecular as well as the behavioral level throughout the 24-h day in mice fed either a control or a high-fat diet (HFD). Furthermore, we investigated the effects of time-restricted feeding (TRF; a limitation of HFD access to 6 h each day) on energy metabolism during different periods throughout the 24-h day. In control mice, molecular leptin sensitivity was highest at zeitgeber time (ZT)0 (lights on), declining during the light phase, and increasing during the dark phase. Surprisingly, leptin resistance in HFD-fed mice was only present from the middle of the dark to the middle of the light period. Specifically, when TRF occurred from ZT21 to ZT3 (when leptin resistance in HFD-fed mice was most profound), it resulted in a disruption of the daily rhythms of locomotor activity and energy expenditure and in increased plasma insulin levels compared with other TRF periods. These data provide evidence that leptin sensitivity is controlled by the circadian rhythm and that TRF periods may be most efficient when aligned with the leptin-sensitive period.-Boucsein, A., Rizwan, M. Z., Tups, A. Hypothalamic leptin sensitivity and health benefits of time-restricted feeding are dependent on the time of day in male mice.

Genome-wide discovery of the daily transcriptome, DNA regulatory elements and transcription factor occupancy in the monarch butterfly brain

The Eastern North American monarch butterfly, Danaus plexippus, is famous for its spectacular seasonal long-distance migration. In recent years, it has also emerged as a novel system to study how animal circadian clocks keep track of time and regulate ecologically relevant daily rhythmic activities and seasonal behavioral outputs. However, unlike in Drosophila and the mouse, little work has been undertaken in the monarch to identify rhythmic genes at the genome-wide level and elucidate the regulation of their diurnal expression. Here, we used RNA-sequencing and Assay for Transposase-Accessible Chromatin (ATAC)-sequencing to profile the diurnal transcriptome, open chromatin regions, and transcription factor (TF) footprints in the brain of wild-type monarchs and of monarchs with impaired clock function, including Cryptochrome 2 (Cry2), Clock (Clk), and Cycle-like loss-of-function mutants. We identified 217 rhythmically expressed genes in the monarch brain; many of them were involved in the regulation of biological processes key to brain function, such as glucose metabolism and neurotransmission. Surprisingly, we found no significant time-of-day and genotype-dependent changes in chromatin accessibility in the brain. Instead, we found the existence of a temporal regulation of TF occupancy within open chromatin regions in the vicinity of rhythmic genes in the brains of wild-type monarchs, which is disrupted in clock deficient mutants. Together, this work identifies for the first time the rhythmic genes and modes of regulation by which diurnal transcription rhythms are regulated in the monarch brain. It also illustrates the power of ATAC-sequencing to profile genome-wide regulatory elements and TF binding in a non-model organism for which TF-specific antibodies are not yet available.

With a rich biology that includes a clock-regulated migratory behavior and a circadian clock possessing mammalian clock orthologues, the monarch butterfly is an unconventional system with broad appeal to study circadian and seasonal rhythms. While clockwork mechanisms and rhythmic behavioral outputs have been studied in this species, the rhythmic genes that regulate rhythmic daily and seasonal activities remain largely unknown. Likewise, the mechanisms regulating rhythmic gene expression have not been explored in the monarch. Here, we applied genome-wide sequencing approaches to identify genes with rhythmic diurnal expression in the monarch brain, revealing the coordination of key pathways for brain function. We also identified the monarch brain open chromatin regions and provide evidence that regulation of rhythmic gene expression does not occur through temporal regulation of chromatin opening but rather by the time-of-day dependent binding of transcription factors in cis-regulatory elements. Together, our data extend our knowledge of the molecular rhythmic pathways, which may prove important in understanding the mechanisms underlying the daily and seasonal biology of the migratory monarch butterflies.

Bedroom lighting environment and incident diabetes mellitus: a longitudinal study of the HEIJO-KYO cohort

OBJECTIVES

Light information received by the brain influences human circadian timing and metabolism; low-level light at night (LAN) significantly increased body mass and led to prediabetes in mice. We hypothesized that LAN exposure increases the diabetes risk in humans. The aim of the present study was to evaluate a longitudinal association between LAN exposure and the incidence of diabetes in a general population.

METHODS

In our prospective cohort study, bedroom light intensity was measured at 1-min intervals in 678 elderly participants without diabetes at baseline. The average light intensity recorded between bedtimes and rise times over two consecutive nights was used in the analysis.

RESULTS

During follow-up (median, 42 months), 19 of the 678 participants (mean age, 70.6 years) developed diabetes. Poisson regression models revealed that the incidence rate for diabetes was significantly higher in the LAN group (average ≥ 5 lux, N = 128) than the dark group (average < 5 lux, N = 550) (incidence rate ratio, 3.74; 95% confidence interval (CI), 1.55-9.05; p = 0.003). Further propensity score adjustments in relation to LAN produced consistent results (incidence rate ratio, 3.19; 95% CI, 1.38-7.35; p = 0.007). When the cut-off value of LAN was decreased to 3 lux, the relationship remained significant (incidence rate ratio 2.74; 95% CI, 1.19-6.33; p = 0.018).

CONCLUSIONS

Our findings suggest that LAN exposure increases the incidence of diabetes in a general elderly population. Further research involving a large cohort with new-onset diabetes is warranted to elucidate these findings.

The circadian clock and liver function in health and disease

Each day, all organisms are subjected to changes in light intensity because of the Earth's rotation around its own axis. To anticipate this geo-physical variability, and to appropriately respond biochemically, most species, including mammals, have evolved an approximate 24-hour endogenous timing mechanism known as the circadian clock (CC). The 'clock' is self-sustained, cell autonomous and present in every cell type. At the core of the clock resides the CC-oscillator, an exquisitely crafted transcriptional-translational feedback system. Remarkably, components of the CC-oscillator not only maintain daily rhythmicity of their own synthesis, but also generate temporal variability in the expression levels of numerous target genes through transcriptional, post-transcriptional and post-translational mechanisms, thus, ensuring proper chronological coordination in the functioning of cells, tissues and organs, including the liver. Indeed, a variety of physiologically critical hepatic functions and cellular processes are CC-controlled. Thus, it is not surprising that modern lifestyle factors (e.g. travel and jet lag, night and rotating shift work), which force 'circadian misalignment', have emerged as major contributors to global health problems including obesity, non-alcoholic fatty liver disease and steatohepatitis. Herein, we provide an overview of the CC-dependent pathways which play critical roles in mediating several hepatic functions under physiological conditions, and whose deregulation is implicated in chronic liver diseases including non-alcoholic steatohepatitis and alcohol-related liver disease.

Time-Restricted Eating to Prevent and Manage Chronic Metabolic Diseases

Molecular clocks are present in almost every cell to anticipate daily recurring and predictable changes, such as rhythmic nutrient availability, and to adapt cellular functions accordingly. At the same time, nutrient-sensing pathways can respond to acute nutrient imbalance and modulate and orient metabolism so cells can adapt optimally to a declining or increasing availability of nutrients. Organismal circadian rhythms are coordinated by behavioral rhythms such as activity-rest and feeding-fasting cycles to temporally orchestrate a sequence of physiological processes to optimize metabolism. Basic research in circadian rhythms has largely focused on the functioning of the self-sustaining molecular circadian oscillator, while research in nutrition science has yielded insights into physiological responses to caloric deprivation or to specific macronutrients. Integration of these two fields into actionable new concepts in the timing of food intake has led to the emerging practice of time-restricted eating. In this paradigm, daily caloric intake is restricted to a consistent window of 8-12 h. This paradigm has pervasive benefits on multiple organ systems.

Nutrient-sensitive transcription factors TFEB and TFE3 couple autophagy and metabolism to the peripheral clock

Autophagy and energy metabolism are known to follow a circadian pattern. However, it is unclear whether autophagy and the circadian clock are coordinated by common control mechanisms. Here, we show that the oscillation of autophagy genes is dependent on the nutrient-sensitive activation of TFEB and TFE3, key regulators of autophagy, lysosomal biogenesis, and cell homeostasis. TFEB and TFE3 display a circadian activation over the 24-h cycle and are responsible for the rhythmic induction of genes involved in autophagy during the light phase. Genetic ablation of TFEB and TFE3 in mice results in deregulated autophagy over the diurnal cycle and altered gene expression causing abnormal circadian wheel-running behavior. In addition, TFEB and TFE3 directly regulate the expression of Rev-erbα (Nr1d1), a transcriptional repressor component of the core clock machinery also involved in the regulation of whole-body metabolism and autophagy. Comparative analysis of the cistromes of TFEB/TFE3 and REV-ERBα showed an extensive overlap of their binding sites, particularly in genes involved in autophagy and metabolic functions. These data reveal a direct link between nutrient and clock-dependent regulation of gene expression shedding a new light on the crosstalk between autophagy, metabolism, and circadian cycles.

Oxygen and Carbon Dioxide Rhythms Are Circadian Clock Controlled and Differentially Directed by Behavioral Signals

Daily rhythms in animal physiology are driven by endogenous circadian clocks in part through rest-activity and feeding-fasting cycles. Here, we examined principles that govern daily respiration. We monitored oxygen consumption and carbon dioxide release, as well as tissue oxygenation in freely moving animals to specifically dissect the role of circadian clocks and feeding time on daily respiration. We found that daily rhythms in oxygen and carbon dioxide are clock controlled and that time-restricted feeding restores their rhythmicity in clock-deficient mice. Remarkably, day-time feeding dissociated oxygen rhythms from carbon dioxide oscillations, whereby oxygen followed activity, and carbon dioxide was shifted and aligned with food intake. In addition, changes in carbon dioxide levels altered clock gene expression and phase shifted the clock. Collectively, our findings indicate that oxygen and carbon dioxide rhythms are clock controlled and feeding regulated and support a potential role for carbon dioxide in phase resetting peripheral clocks upon feeding.

CDK9 modulates circadian clock by attenuating REV-ERBα activity

Circadian clock and cell cycle are vital cellular programs acting in a timely-regulated, cyclic manner. The two cellular oscillators are coupled in various ways to facilitate biological processes. Here we report CDK9, a kinase belongs to the CDK family in regulating cell cycle and RNA Pol II activity, can serve as a modulator for circadian clock. We identified CDK inhibitor LY2857785 potently blocked PER2:LUC expression in MEFs from a screen of 17 commonly-used CDK inhibitors. We further analyzed the possible targets of LY2857785 by siRNA approach, and confirmed CDK9 as the main effector. LY2857785 treatment, as well as Cdk9 knock-down, led to lowered expression of Bmal1 in accordance with elevated expression of Rev-Erbα. CDK9 associated with REV-ERBα thus attenuated REV-ERBα binding to the RORE for Bmal1 suppression. To conform the circadian-modulating activity of CDK9 in vivo, we knocked down CDK9 in mice at the anterior hypothalamus covering the central oscillator SCN, and found the respiratory exchange ratio, daily activity and circadian period were altered in the Cdk9-knockdown mice. Together, our finding designated CDK9 as a novel modulator in circadian clock. CDK9 may serve as a vital basis to understand circadian- and cell cycle-misregulated ailments such as cancer.

The Circadian Clock Gene Bmal1 Controls Intestinal Exporter MRP2 and Drug Disposition

The intestinal exporter MRP2 plays an important role in disposition and elimination of a wide range of drugs. Here, we aimed to clarify the impact of circadian clock on intestinal MRP2, and to determine the molecular mechanisms for generation of diurnal MRP2 expression. Methods: The regulatory effects of Bmal1 on intestinal MRP2 expression were assessed using intestine-specific Bmal1 knockout (Bmal1iKO ) mice and colon cancer cells. The relative mRNA and protein levels were determined by qPCR and Western blotting, respectively. Everted gut sac, cell viability and in situ intestinal perfusion experiments were performed to evaluate intestinal efflux of the MRP2 substrate methotrexate (MTX). Toxicity and pharmacokinetic experiments were performed with Bmal1iKO mice and control littermates (Bmal1fl/fl mice) after oral gavage of MTX. Transcriptional gene regulation was investigated using luciferase reporter, mobility shift and chromatin immunoprecipitation (ChIP) assays. Results: Bmal1iKO mice were generated by inter-crossing the mice carrying a Bmal1 exon 8 floxed allele (Bmal1fl/fl ) with Villin-Cre mice. Intestinal MRP2 expression exhibited a diurnal oscillation in Bmal1fl/fl mice with a zenith value at ZT6. Bmal1 ablation caused reductions in Mrp2 mRNA and protein levels [as well as in transport activity (measured by MTX)], and blunted their diurnal rhythms. Intestinal ablation of Bmal1 abrogated circadian time-dependency of MTX pharmacokinetics and toxicity. Bmal1/BMAL1 regulation of rhythmic Mrp2/MRP2 expression was also confirmed in the colon cancer CT26 and Caco-2 cells. Based on a combination of luciferase reporter, mobility shift and ChIP assays, we found that Dbp activated and E4bp4 repressed Mrp2 transcription via specific binding to a same D-box (-100/-89 bp) element in promoter region. Further, Bmal1 directly activated the transcription of Dbp and Rev-erbα through the E-boxes, whereas it negatively regulated E4bp4 via the transcriptional repressor Rev-erbα. Positive regulation of Mrp2 by Rev-erbα was also observed, and attained through modulation of E4bp4. Conclusion: Bmal1 coordinates temporal expressions of DBP (a MRP2 activator), REV-ERBα (an E4BP4 repressor) and E4BP4 (a MRP2 repressor), generating diurnal MRP2 expression.

The Circadian Clock Protein CRY1 Is a Negative Regulator of HIF-1α

The circadian clock and the hypoxia-signaling pathway are regulated by an integrated interplay of positive and negative feedback limbs that incorporate energy homeostasis and carcinogenesis. We show that the negative circadian regulator CRY1 is also a negative regulator of hypoxia-inducible factor (HIF). Mechanistically, CRY1 interacts with the basic-helix-loop-helix domain of HIF-1α via its tail region. Subsequently, CRY1 reduces HIF-1α half-life and binding of HIFs to target gene promoters. This appeared to be CRY1 specific because genetic disruption of CRY1, but not CRY2, affected the hypoxia response. Furthermore, CRY1 deficiency could induce cellular HIF levels, proliferation, and migration, which could be reversed by CRISPR/Cas9- or short hairpin RNA-mediated HIF knockout. Altogether, our study provides a mechanistic explanation for genetic association studies linking a disruption of the circadian clock with hypoxia-associated processes such as carcinogenesis.

Influence of Eating Schedule on the Postprandial Response: Gender Differences

Ingestion of a meal induces conscious sensations depending of the characteristics of the meal and the predisposition of the eater. We hypothesized that the eating schedule plays a conditioning role, specifically, that an extemporaneous meal is less rewarding than when eaten at the habitual schedule. We conducted a randomized parallel trial in 10 women and 10 men comparing the responses to a consistent savoury lunch-type meal (stewed beans) eaten at the habitual afternoon schedule or at an unconventional time in the morning. Schedule and gender differences were analyzed by repeated measures analysis of covariance. In women, the sensory experience induced by the probe meal, particularly postprandial satisfaction, was weaker when eaten at an unconventional time for breakfast. Men were resilient to the schedule effect and experienced the same sensations regardless of the timing of ingestion; the effect of the eating schedule was significantly more pronounced in women for fullness (F(1,55) = 14.9; p < 0.001), digestive well-being (F(1,36.8) = 22.3; p < 0.001), mood (F(1,12.4) = 13.8; p < 0.001), and anxiety (F(1,11.9) = 10.9; p = 0.001). No differences in the physiological responses induced by the afternoon and morning meals were detected either in women or men. Our data indicate that women are more susceptible to changes in meal schedule than men.

Effect of ethanol on lipid metabolism

Hepatic lipid metabolism is a series of complex processes that control influx and efflux of not only hepatic lipid pools, but also organismal pools. Lipid homeostasis is usually tightly controlled by expression, substrate supply, oxidation and secretion that keep hepatic lipid pools relatively constant. However, perturbations of any of these processes can lead to lipid accumulation in the liver. Although it is thought that these responses are hepatic arms of the 'thrifty genome', they are maladaptive in the context of chronic fatty liver diseases. Ethanol is likely unique among toxins, in that it perturbs almost all aspects of hepatic lipid metabolism. This complex response is due in part to the large metabolic demand placed on the organ by alcohol metabolism, but also appears to involve more nuanced changes in expression and substrate supply. The net effect is that steatosis is a rapid response to alcohol abuse. Although transient steatosis is largely an inert pathology, the chronicity of alcohol-related liver disease seems to require steatosis. Better and more specific understanding of the mechanisms by which alcohol causes steatosis may therefore translate into targeted therapies to treat alcohol-related liver disease and/or prevent its progression.

Homeostasis of Glucose and Lipid in Non-Alcoholic Fatty Liver Disease

Industrialized society-caused dysregular human behaviors and activities such as overworking, excessive dietary intake, and sleep deprivation lead to perturbations in the metabolism and the development of metabolic syndrome. Non-alcoholic fatty liver disease (NAFLD), the most common chronic liver disease worldwide, affects around 30% and 25% of people in Western and Asian countries, respectively, which leads to numerous medical costs annually. Insulin resistance is the major hallmark of NAFLD and is crucial in the pathogenesis and for the progression from NAFLD to non-alcoholic steatohepatitis (NASH). Excessive dietary intake of saturated fats and carbohydrate-enriched foods contributes to both insulin resistance and NAFLD. Once NAFLD is established, insulin resistance can promote the progression to the more severe state of liver endangerment like NASH. Here, we review current and potential studies for understanding the complexity between insulin-regulated glycolytic and lipogenic homeostasis and the underlying causes of NAFLD. We discuss how disruption of the insulin signal is associated with various metabolic disorders of glucoses and lipids that constitute both the metabolic syndrome and NAFLD.

Circadian clock genes link photoperiodic signals to lipid accumulation during diapause preparation in the diapause-destined female cabbage beetles Colaphellus bowringi

Many organisms have evolved a series of adaptions, such as dormancy or diapause in insects that enable them to withstand seasonally adverse conditions. In insects, photoperiodic signals received during the diapause induction phase have irreversible effect on diapause initiation. Insects continue to be exposed to diapause-inducing photoperiod after the diapause induction phase during diapause preparation before they enter diapause. However, how photoperiodic signals experienced during the diapause preparation phase (DPP) regulate diapause remains largely unclear. In this paper, we investigate this in the cabbage beetle Colaphellus bowringi. The cabbage beetle is in many respects an ideal experimental model in which to investigate the effect of photoperiodic signals on the DPP because it has facultative reproductive diapause induced by long-day length and has differentiable diapause induction and preparation phases. We found that the lipid content of female cabbage beetles decreased after diapause-destined (DD) individuals were exposed to a diapause-inhibiting photoperiod during the DPP. Two circadian clock negative regulators, per and tim, were probably involved in the photoperiodic response of beetles during the DPP. Per and tim presented obvious oscillation of circadian rhythm and photoperiodic response during the DPP in DD females and knock-down of these genes in DD females caused their lipid content to decrease. Per and tim probably promote lipid accumulation by regulating the expression of genes that regulate lipogenesis and lipolysis. Moreover, decreased lipid accumulation caused by exposure to different photoperiods during the DPP was independent of juvenile hormone. In summary, these results suggest that photoperiodic signals received during the DPP influence lipid accumulation in DD insects. DD insects still have some ability to monitor photoperiodic changes during the DPP and per and tim are probably involved in regulating physiological responses to photoperiodic signals during diapause preparation. These results shed light on the relationship between photoperiodic signals and diapause preparation, and may provide new insights on both how to better utilize insects as resources and for pest management.

Copper in the suprachiasmatic circadian clock: A possible link between multiple circadian oscillators

The mammalian circadian clock in the suprachiasmatic nucleus (SCN) is very robust, able to coordinate our daily physiological and behavioral rhythms with exquisite accuracy. Simultaneously, the SCN clock is highly sensitive to environmental timing cues such as the solar cycle. This duality of resiliency and sensitivity may be sustained in part by a complex intertwining of three cellular oscillators: transcription/translation, metabolic/redox, and membrane excitability. We suggest here that one of the links connecting these oscillators may be forged from copper (Cu). Cellular Cu levels are highly regulated in the brain and peripherally, and Cu affects cellular metabolism, redox state, cell signaling, and transcription. We have shown that both Cu chelation and application induce nighttime phase shifts of the SCN clock in vitro and that these treatments affect glutamate, N-methyl-D-aspartate receptor, and associated signaling processes differently. More recently we found that Cu induces mitogen-activated protein kinase-dependent phase shifts, while the mechanisms by which Cu removal induces phase shifts remain unclear. Lastly, we have found that two Cu transporters are expressed in the SCN, and that one of these transporters (ATP7A) exhibits a day/night rhythm. Our results suggest that Cu homeostasis is tightly regulated in the SCN, and that changes in Cu levels may serve as a time cue for the circadian clock. We discuss these findings in light of the existing literature and current models of multiple coupled circadian oscillators in the SCN.

Circadian Disruptions in the Myshkin Mouse Model of Mania Are Independent of Deficits in Suprachiasmatic Molecular Clock Function

BACKGROUND

Alterations in environmental light and intrinsic circadian function have strong associations with mood disorders. The neural origins underpinning these changes remain unclear, although genetic deficits in the molecular clock regularly render mice with altered mood-associated phenotypes.

METHODS

A detailed circadian and light-associated behavioral characterization of the Na+/K+-ATPase α3 Myshkin (Myk/+) mouse model of mania was performed. Na+/K+-ATPase α3 does not reside within the core circadian molecular clockwork, but Myk/+ mice exhibit concomitant disruption in circadian rhythms and mood. The neural basis of this phenotype was investigated through molecular and electrophysiological dissection of the master circadian pacemaker, the suprachiasmatic nuclei (SCN). Light input and glutamatergic signaling to the SCN were concomitantly assessed through behavioral assays and calcium imaging.

RESULTS

In vivo assays revealed several circadian abnormalities including lengthened period and instability of behavioral rhythms, and elevated metabolic rate. Grossly aberrant responses to light included accentuated resetting, accelerated re-entrainment, and an absence of locomotor suppression. Bioluminescent recording of circadian clock protein (PERIOD2) output from ex vivo SCN revealed no deficits in Myk/+ molecular clock function. Optic nerve crush rescued the circadian period of Myk/+ behavior, highlighting that afferent inputs are critical upstream mediators. Electrophysiological and calcium imaging SCN recordings demonstrated changes in the response to glutamatergic stimulation as well as the electrical output indicative of altered retinal input processing.

CONCLUSIONS

The Myshkin model demonstrates profound circadian and light-responsive behavioral alterations independent of molecular clock disruption. Afferent light signaling drives behavioral changes and raises new mechanistic implications for circadian disruption in affective disorders.

A-to-I RNA editing enzyme ADAR2 regulates light-induced circadian phase-shift

In mammals, the central circadian clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus and it orchestrates peripheral clocks in the whole body to organize physiological and behavioral rhythms. Light-induced phase-shift of the SCN clock enables synchronization of the circadian clock system with 24-h environmental light/dark cycle. We previously found that adenosine deaminase acting on RNA 2 (Adar2), an A-to-I RNA editing enzyme catalyzing rhythmic A-to-I RNA editing, governs a wide range of mRNA rhythms in the mouse liver and regulates the circadian behavior. In brain, ADAR2-mediated A-to-I RNA editing was reported to occur in various transcripts encoding ion channels and neurotransmitter receptors, which could influence neuronal function of the SCN. Here we show that ADAR2 plays a crucial role for light-induced phase-shift of the circadian clock. Intriguingly, exposure of Adar2-knockout mice to a light pulse at late night caused an aberrant phase-advance of the locomotor rhythms. By monitoring the bioluminescence rhythms of the mutant SCN slices, we found that a phase-advance induced by treatment with pituitary adenylyl cyclase-activating polypeptide (PACAP) was markedly attenuated. The present study suggests that A-to-I RNA editing in the SCN regulates a proper phase response to light in the mouse circadian system.

Non-transcriptional processes in circadian rhythm generation

'Biological clocks' orchestrate mammalian biology to a daily rhythm. Whilst 'clock gene' transcriptional circuits impart rhythmic regulation to myriad cellular systems, our picture of the biochemical mechanisms that determine their circadian (∼24 hour) period is incomplete. Here we consider the evidence supporting different models for circadian rhythm generation in mammalian cells in light of evolutionary factors. We find it plausible that the circadian timekeeping mechanism in mammalian cells is primarily protein-based, signalling biological timing information to the nucleus by the post-translational regulation of transcription factor activity, with transcriptional feedback imparting robustness to the oscillation via hysteresis. We conclude by suggesting experiments that might distinguish this model from competing paradigms.