Nutrient sensing and the circadian clock

Advancing Chrononutrition for Cardiometabolic Health: A 2023 National Heart, Lung, and Blood Institute Workshop Report

The circadian system maintains optimal biological functions at the appropriate time of day, and the disruption of this organization can contribute to the pathogenesis of cardiometabolic disorders. The timing of eating is a prominent external time cue that influences the circadian system. "Chrononutrition" is an emerging dimension of nutrition and active area of research that examines how timing-related aspects of eating and nutrition impact circadian rhythms, biological processes, and disease pathogenesis. There is evidence to support chrononutrition as a form of chronotherapy, such that optimizing the timing of eating may serve as an actionable strategy to improve cardiometabolic health. This report summarizes key information from the National Heart, Lung, and Blood Institute's virtual workshop entitled "Chrononutrition: Elucidating the Role of Circadian Biology and Meal Timing in Cardiometabolic Health," which convened on May 2 to 3, 2023, to review current literature and identify critical knowledge gaps and research opportunities. The speakers presented evidence highlighting the impact on cardiometabolic health of earlier and shorter eating windows and more consistent day-to-day eating patterns. The multidimensionality of chrononutrition was a common theme, as it encompasses multiple facets of eating along with the timing of other behaviors including sleep and physical activity. Advancing the emerging field of chrononutrition will require: (1) standardization of terminology and metrics; (2) scalable and precise tools for real-world settings; (3) consideration of individual differences that may act as effect modifiers; and (4) deeper understanding of social, behavioral, and cultural influences. Ultimately, there is great potential for circadian-based dietary interventions to improve cardiometabolic health.

Circadian Dysfunction in the Skeletal Muscle Impairs Limb Perfusion and Muscle Regeneration in Peripheral Artery Disease

BACKGROUND

Peripheral artery disease (PAD), caused by atherosclerosis, leads to limb ischemia, muscle damage, and impaired mobility in the lower extremities. Recent studies suggest that circadian rhythm disruptions can hinder vascular repair during ischemia, but the specific tissues involved and the impact on muscle health remain unclear. This study investigates the role of the skeletal muscle circadian clock in muscle adaptation to ischemic stress using a surgical mouse model of hindlimb ischemia.

METHODS

We performed secondary analysis of publicly available RNA-sequencing data sets derived from patients with PAD to identify the differential expression of circadian-related genes in endothelial cells and ischemic limb skeletal muscles. We used mice with specific genetic loss of the circadian clock activator, BMAL1 (brain and muscle ARNT-like 1), in adult skeletal muscle tissues (Bmal1muscle). Bmal1muscle mice and controls underwent femoral artery ligation surgery to induce hindlimb ischemia. Laser Doppler imaging was used to assess limb perfusion at various time points after the surgery. Muscle tissues were analyzed with RNA sequencing and histological examination to investigate PAD-related muscle pathologies. Additionally, we studied the role of BMAL1 in muscle fiber adaptation to hypoxia using RNA and assay for transposase-accessible chromatin with sequencing analyses in primary myotube culture model.

RESULTS

Disrupted expression of circadian rhythm-related genes was observed in existing RNA-sequencing data sets from endothelial cells and ischemic limb skeletal muscles derived from patients with PAD. Genetic loss of Bmal1 specifically in adult mouse skeletal muscle tissues delayed reperfusion recovery following induction of hindlimb ischemia. Histological examination of muscle tissues showed reduced regenerated myofiber number and a decreased proportion of type IIB fast-twitch myofibers in Bmal1muscle mouse muscles in the ischemic limbs but not in their contralateral nonischemic limbs. Transcriptomic analysis revealed abrogated metabolic, angiogenic, and myogenic pathways relevant to hypoxia adaptation in Bmal1muscle mouse muscles. These changes were corroborated in Bmal1-deficient cultured primary myotubes cultured under hypoxic conditions.

CONCLUSIONS

Circadian clock in skeletal muscle is crucial for the muscle's response to hypoxia during hindlimb ischemia. Targeting the muscle circadian clock may have therapeutic potential for enhancing muscle response to reduced blood flow and promoting recovery in conditions such as PAD.

SIRT1: a novel regulator in colorectal cancer

The class-III histone deacetylase SIRT1 is the most extensively investigated sirtuin deacetylase. It is resistant to the broad deacetylase inhibitor trichostatin A and depends on oxidized nicotinamide adenine nucleotide (NAD+). SIRT1 plays a crucial role in the tumorigenesis of numerous types of cancers, including colorectal cancer (CRC). Accumulating evidence indicates that SIRT1 is a therapeutic target for CRC; however, the function and underlying mechanism of SIRT1 in CRC still need to be elucidated. Herein, we provide a detailed and updated review to illustrate that SIRT1 regulates many processes that go awry in CRC cells, such as apoptosis, autophagy, proliferation, migration, invasion, metastasis, oxidative stress, resistance to chemo-radio therapy, immune evasion, and metabolic reprogramming. Moreover, we closely link our review to the clinical practice of CRC treatment, summarizing the mechanisms and prospects of SIRT1 inhibitors in CRC therapy. SIRT1 inhibitors as monotherapy in CRC or in combination with chemotherapy, radiotherapy, and immune therapies are comprehensively discussed. From epigenetic regulation to its potential therapeutic effect, we hope to offer novel insights and a comprehensive understanding of SIRT1's role in CRC.

Avian migration clocks in a changing world

Avian long-distance migration requires refined programming to orchestrate the birds' movements on annual temporal and continental spatial scales. Programming is particularly important as long-distance movements typically anticipate future environmental conditions. Hence, migration has long been of particular interest in chronobiology. Captivity studies using a proxy, the shift to nocturnality during migration seasons (i.e., migratory restlessness), have revealed circannual and circadian regulation, as well as an innate sense of direction. Thanks to rapid development of tracking technology, detailed information from free-flying birds, including annual-cycle data and actograms, now allows relating this mechanistic background to behaviour in the wild. Likewise, genomic approaches begin to unravel the many physiological pathways that contribute to migration. Despite these advances, it is still unclear how migration programmes are integrated with specific environmental conditions experienced during the journey. Such knowledge is imminently important as temporal environments undergo rapid anthropogenic modification. Migratory birds as a group are not dealing well with the changes, yet some species show remarkable adjustments at behavioural and genetic levels. Integrated research programmes and interdisciplinary collaborations are needed to understand the range of responses of migratory birds to environmental change, and more broadly, the functioning of timing programmes under natural conditions.

Circadian timing of satellite cell function and muscle regeneration

Recent research has highlighted an important role for the molecular circadian machinery in the regulation of tissue-specific function and stress responses. Indeed, disruption of circadian function, which is pervasive in modern society, is linked to accelerated aging, obesity, and type 2 diabetes. Furthermore, evidence supporting the importance of the circadian clock within both the mature muscle tissue and satellite cells to regulate the maintenance of muscle mass and repair capacity in response injury has recently emerged. Here, we review the discovery of circadian clocks within the satellite cell (a.k.a. adult muscle stem cell) and how they act to regulate metabolism, epigenetics, and myogenesis during both healthy and diseased states.

Position statement on nutrition therapy for overweight and obesity: nutrition department of the Brazilian association for the study of obesity and metabolic syndrome (ABESO-2022)

Obesity is a chronic disease resulting from multifactorial causes mainly related to lifestyle (sedentary lifestyle, inadequate eating habits) and to other conditions such as genetic, hereditary, psychological, cultural, and ethnic factors. The weight loss process is slow and complex, and involves lifestyle changes with an emphasis on nutritional therapy, physical activity practice, psychological interventions, and pharmacological or surgical treatment. Because the management of obesity is a long-term process, it is essential that the nutritional treatment contributes to the maintenance of the individual's global health. The main diet-related causes associated with excess weight are the high consumption of ultraprocessed foods, which are high in fats, sugars, and have high energy density; increased portion sizes; and low intake of fruits, vegetables, and grains. In addition, some situations negatively interfere with the weight loss process, such as fad diets that involve the belief in superfoods, the use of teas and phytotherapics, or even the avoidance of certain food groups, as has currently been the case for foods that are sources of carbohydrates. Individuals with obesity are often exposed to fad diets and, on a recurring basis, adhere to proposals with promises of quick solutions, which are not supported by the scientific literature. The adoption of a dietary pattern combining foods such as grains, lean meats, low-fat dairy, fruits, and vegetables, associated with an energy deficit, is the nutritional treatment recommended by the main international guidelines. Moreover, an emphasis on behavioral aspects including motivational interviewing and the encouragement for the individual to develop skills will contribute to achieve and maintain a healthy weight. Therefore, this Position Statement was prepared based on the analysis of the main randomized controlled studies and meta-analyses that tested different nutrition interventions for weight loss. Topics in the frontier of knowledge such as gut microbiota, inflammation, and nutritional genomics, as well as the processes involved in weight regain, were included in this document. This Position Statement was prepared by the Nutrition Department of the Brazilian Association for the Study of Obesity and Metabolic Syndrome (ABESO), with the collaboration of dietitians from research and clinical fields with an emphasis on strategies for weight loss.

Physiological Rhythms and Biological Variation of Biomolecules: The Road to Personalized Laboratory Medicine

The concentration of biomolecules in living systems shows numerous systematic and random variations. Systematic variations can be classified based on the frequency of variations as ultradian (<24 h), circadian (approximately 24 h), and infradian (>24 h), which are partly predictable. Random biological variations are known as between-subject biological variations that are the variations among the set points of an analyte from different individuals and within-subject biological variation, which is the variation of the analyte around individuals’ set points. The random biological variation cannot be predicted but can be estimated using appropriate measurement and statistical procedures. Physiological rhythms and random biological variation of the analytes could be considered the essential elements of predictive, preventive, and particularly personalized laboratory medicine. This systematic review aims to summarize research that have been done about the types of physiological rhythms, biological variations, and their effects on laboratory tests. We have searched the PubMed and Web of Science databases for biological variation and physiological rhythm articles in English without time restrictions with the terms “Biological variation, Within-subject biological variation, Between-subject biological variation, Physiological rhythms, Ultradian rhythms, Circadian rhythm, Infradian rhythms”. It was concluded that, for effective management of predicting, preventing, and personalizing medicine, which is based on the safe and valid interpretation of patients’ laboratory test results, both physiological rhythms and biological variation of the measurands should be considered simultaneously.

Effect of the one-day fasting on cortisol and DHEA daily rhythm regarding sex, chronotype, and age among obese adults

Introduction

Physiological and biochemical processes in the human body occur in a specific order and show rhythmic variability. Time dependence characterizes the secretion of cortisol and dehydroepiandrosterone (DHEA). One-day fasting implies alternating fasting days and eating days. The study aimed to determine how 24-h fasting affects the daily rhythm of cortisol and DHEA levels in obese people while taking into account gender and chronotype.

Methods

Forty-nine obese patients (BMI 32.2-67.1 kg/m²; 25 women and 24 men) underwent a 3-week hospital-controlled calorie restriction diet to reduce body weight. During hospitalization, patients fasted for 1 day, during which only water could be consumed. Samples of whole mixed unstimulated saliva were collected at 2-3-h intervals over a 64-h period and analyzed for cortisol and DHEA by immunoassays. The individual chronotypes were assessed by the morning and evening questionnaire, according to Horne and Östberg. Three components of daily rhythm were evaluated: amplitude, acrophase, and the so-called MESOR.

Results

Cortisol rhythm showed differences in amplitude (p = 0.0127) and acrophase (p = 0.0005). The amplitude on the fasting day was 11% higher (p = 0.224) than the day after. The acrophase advanced on the day of fasting, 48 min earlier than the day before (p = 0.0064), and by 39 min to the day after fasting (p = 0.0005). In the rhythm of DHEA, differences were found in the MESOR (p = 0.0381). The MESOR on the fasting day increased.

Discussion

Our results obtained during 64 consecutive hours of saliva sampling suggest that one-day fasting may affect three components of cortisol and DHEA daily rhythm. Additionally, no differences were found in the daily rhythm between the morning and evening chronotypes and between females and males. Although aging did not influence daily cortisol rhythm, DHEA amplitude, MESOR, and acrophase changed with age. To the best of our knowledge, this is the first presentation of changes in DHEA rhythm during one-day fasting.

A comprehensive analysis of the circRNA-miRNA-mRNA network in osteocyte-like cell associated with Mycobacterium leprae infection

BACKGROUND

Bone formation and loss are the characteristic clinical manifestations of leprosy, but the mechanisms underlying the bone remodeling with Mycobacterium leprae (M. leprae) infection are unclear.

METHODOLOGY/PRINCIPAL FINDINGS

Osteocytes may have a role through regulating the differentiation of osteogenic lineages. To investigate osteocyte-related mechanisms in leprosy, we treated osteocyte-like cell with N-glycosylated muramyl dipeptide (N.g MDP). RNA-seq analysis showed 724 differentially expressed messenger RNAs (mRNAs) and 724 differentially expressed circular RNA (circRNAs). Of these, we filtered through eight osteogenic-related differentially expressed genes, according to the characteristic of competing endogenous RNA, PubMed databases, and bioinformatic analysis, including TargetScan, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes. Based on these results, we built a circRNA-microRNA (miRNA)-mRNA triple network. Quantitative reverse-transcription polymerase chain reaction and western blots analyses confirmed decreased Clock expression in osteocyte-like cell, while increased in bone mesenchymal stem cells (BMSCs), implicating a crucial factor in osteogenic differentiation. Immunohistochemistry showed obviously increased expression of CLOCK protein in BMSCs and osteoblasts in N.g MDP-treated mice, but decreased expression in osteocytes.

CONCLUSIONS/SIGNIFICANCE

This analytical method provided a basis for the relationship between N.g MDP and remodeling in osteocytes, and the circRNA-miRNA-mRNA triple network may offer a new target for leprosy therapeutics.

About gladiators and a sacred disease

In this special edition of the Biomedical Journal the reader gains an insight into drug-resistant epilepsy and according treatment approaches involving deep brain stimulation, the ketogenic diet and fecal microbiota transplant. Another emphasis is put on personalized medicine strategies, and covered in articles about the use of natriuretic peptides against cancer, along with an article about companion diagnostics involving extracellular vesicles. Recurrent infection with Clostridium difficile, associated risk factors and therapeutic options are discussed. We learn about a mechanism that helps Leishmania evade a host control mechanism, receive an update about human adenovirus and are presented with characteristic magnetic resonance neuroimaging in COVID-19 pediatric patients. An advanced assessment in pediatric septic shock and an improved model for a pediatric early warning system are proposed. Some of the genetic causes of renal hypomagnesemia are explored, the impact of air pollution on children is examined, and an antisiphon device is described for surgical treatment of hydrocephalus. The relation between energy metabolism, circadian rhythm and its influence on the ATPase in the SCN are investigated, and among others some of the genetics influencing smoking duration and lung cancer. Finally it is discussed how embryo quality can be improved in in vitro fertilization, and what impact high estradiol has on blastocyst implantation. The outcome of surgery to correct mandibular deficiency is assessed, and in two letters the inclusion of observational studies in the evaluation of clinical trials related to COVID-19 is elaborated.

Role of circadian rhythm and impact of circadian rhythm disturbance on the metabolism and disease

ABSTRACT

Molecular circadian clocks exist in almost all cells of the organism and operate for approximately 24 h, maintain the normal physiological and behavioral body processes and regulate metabolism of many cells related to a variety of disease states. Circadian rhythms regulate metabolism, mainly including neurotransmitters, hormones, amino acids and lipids. Circadian misalignment is related to metabolic syndromes, such as obesity, diabetes and hypertension, which have reached an alarming level in modern society. We reviewed the mechanism of the circadian clock and the interaction between circadian rhythm and metabolism, as well as circadian rhythm disturbance on the metabolism of hypertension, obesity and diabetes. Finally, we discuss how to use the circadian rhythm to prevent diseases. Thus, this review is a micro to macro discussion from the perspective of circadian rhythm and aims to provide basic ideas for circadian rhythm research and disease therapies.

Effects of the circadian rhythm on milk composition in dairy cows: Does day milk differ from night milk?

Metabolism in most organisms can show variations between the day and night. These variations may also affect the composition of products derived from livestock. The aim of the present study was to investigate the difference in composition between the day milk and night milk of dairy cows. Ten multiparous Holstein cows (milk yield = 25.2 ± 5.00 kg/d) were randomly selected during mid lactation. Milk samples were collected at 0500 h ("night milk") and 1500 h ("day milk") and analyzed to determine their composition. Mid-infrared spectroscopy was used to analyze macronutrient content of milk. Metabolomics and lipidomics were used to detect and analyze small molecules and fatty acids, respectively. An automatic biochemical analyzer and ELISA kits were used to determine biochemical indicators, as well as antioxidant and immune parameters in the milk. Though milk fat, protein, lactose, and total milk solids were not different between day milk and night milk, small molecules, metabolites and lipids, and hormones and cytokines differed between day milk and night milk. Regarding biochemical and immune-related indicators, the concentrations of malondialdehyde, HSP70, and HSP90 in night milk were lower than that in day milk. However, interferon-γ levels were higher in night milk. Additionally, night milk was naturally rich in melatonin. Lipidomics analyses showed that the levels of some lipids in night milk were higher than those in day milk. Metabolomics analyses identified 36 different metabolites between day milk and night milk. Higher concentrations of N-acetyl-d-glucosamine, cis-aconitate, and d-sorbitol were observed in day milk. However, the other 33 metabolites analyzed, including carbohydrates, lipids, AA, and aromatic compounds, showed lower concentrations in day milk than in night milk. The present findings show that the composition of night milk differs considerably from that of day milk. Notable changes in the circadian rhythm also altered milk composition. These results provide evidence to support the strategic use and classification of day milk and night milk.

Why do cancer cells break from host circadian rhythm? Insights from unicellular organisms

It is not clear why cancer cells choose to disrupt their circadian clock rhythms, and whether such disruption governs a selective fitness and a survival advantage. In this review, I focus on understanding the impacts of clock gene disruption on a simpler model, such as the unicellular cyanobacterium, in order to explain how cancer cells may alter the circadian rhythm to reprogram their metabolism based on their needs and status. It appears to be that the activation of the oxidative pentose phosphate pathway (OPPP) and production of NADPH, the preferred molecule for detoxification of reactive oxygen species, is a critical process for night survival in unicellular organisms. The circadian clock acts as a gatekeeper that controls how the organism will utilize its sugar, shifting sugar influx between glycolysis and OPPP. The circadian clock can thus act as a gatekeeper between an anabolic, proliferative mode and a homeostatic, survival mode.

PPARs in liver physiology

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors and transcriptional modulators with crucial functions in hepatic and whole-body energy homeostasis. Besides their well-documented roles in lipid and glucose metabolism, emerging evidence also implicate PPARs in the control of other processes such as inflammatory responses. Recent technological advances, such as single-cell RNA sequencing, have allowed to unravel an unexpected complexity in the regulation of PPAR expression, activity and downstream signaling. Here we provide an overview of the latest advances in the study of PPARs in liver physiology, with a specific focus on formerly neglected aspects of PPAR regulation, such as tissular zonation, cellular heterogeneity, circadian rhythms, sexual dimorphism and species-specific features.

Human torpor: translating insights from nature into manned deep space expedition

During a long-duration manned spaceflight mission, such as flying to Mars and beyond, all crew members will spend a long period in an independent spacecraft with closed-loop bioregenerative life-support systems. Saving resources and reducing medical risks, particularly in mental heath, are key technology gaps hampering human expedition into deep space. In the 1960s, several scientists proposed that an induced state of suppressed metabolism in humans, which mimics 'hibernation', could be an ideal solution to cope with many issues during spaceflight. In recent years, with the introduction of specific methods, it is becoming more feasible to induce an artificial hibernation-like state (synthetic torpor) in non-hibernating species. Natural torpor is a fascinating, yet enigmatic, physiological process in which metabolic rate (MR), body core temperature (T_b ) and behavioural activity are reduced to save energy during harsh seasonal conditions. It employs a complex central neural network to orchestrate a homeostatic state of hypometabolism, hypothermia and hypoactivity in response to environmental challenges. The anatomical and functional connections within the central nervous system (CNS) lie at the heart of controlling synthetic torpor. Although progress has been made, the precise mechanisms underlying the active regulation of the torpor-arousal transition, and their profound influence on neural function and behaviour, which are critical concerns for safe and reversible human torpor, remain poorly understood. In this review, we place particular emphasis on elaborating the central nervous mechanism orchestrating the torpor-arousal transition in both non-flying hibernating mammals and non-hibernating species, and aim to provide translational insights into long-duration manned spaceflight. In addition, identifying difficulties and challenges ahead will underscore important concerns in engineering synthetic torpor in humans. We believe that synthetic torpor may not be the only option for manned long-duration spaceflight, but it is the most achievable solution in the foreseeable future. Translating the available knowledge from natural torpor research will not only benefit manned spaceflight, but also many clinical settings attempting to manipulate energy metabolism and neurobehavioural functions.

The circadian machinery links metabolic disorders and depression: A review of pathways, proteins and potential pharmacological interventions

Circadian rhythms are responsible for regulating a number of physiological processes. The central oscillator is located within the suprachiasmatic nucleus (SCN) of the hypothalamus and the SCN synchronises the circadian clocks that are found in our peripheral organs through neural and humoral signalling. At the molecular level, biological clocks consist of transcription-translation feedback loops (TTFLs) and these pathways are influenced by transcription factors, post-translational modifications, signalling pathways and epigenetic modifiers. When disruptions occur in the circadian machinery, the activities of the proteins implicated in this network and the expression of core clock or clock-controlled genes (CCGs) can be altered. Circadian misalignment can also arise when there is desychronisation between our internal clocks and environmental stimuli. There is evidence in the literature demonstrating that disturbances in the circadian rhythm contribute to the pathophysiology of several diseases and disorders. This includes the metabolic syndrome and recently, it has been suggested that the 'circadian syndrome' may be a more appropriate term to use to not only describe the cardio-metabolic risk factors but also the associated comorbidities. Here we overview the molecular architecture of circadian clocks in mammals and provide insight into the effects of shift work, exposure to artificial light, food intake and stress on the circadian rhythm. The relationship between circadian rhythms, metabolic disorders and depression is reviewed and this is a topic that requires further investigation. We also describe how particular proteins involved in the TTFLs can be potentially modulated by small molecules, including pharmacological interventions and dietary compounds.

Does a high-fat diet affect the circadian clock, or is it the other way around? A systematic review

This paper reviews studies that addressed the influence of diet on circadian rhythmicity in mice and, in turn, circadian clock chronodisruption and its role in the development of metabolic disorders. Studies from the past 14 years were selected via a systematic search conducted using the PubMed electronic database. After applying the inclusion and exclusion criteria, 291 studies were selected, of which 13 were chosen using the following inclusion criteria: use of a high-fat diet for mice, evaluation of clock gene expression, and the association between chronodisruption and lipid metabolism disorders. These studies reported changes in animals' biological clock when they developed metabolic disorders by consuming a high-fat diet. It was also evident that some clock gene mutations or deletions triggered metabolic changes. Disturbances of clock gene machinery may play important roles in lipid metabolism and the development of atherosclerotic processes. However, many metabolic processes also affect the function of clock genes and circadian systems. In summary, this review's results may provide new insights into the reciprocal regulation of energy homeostasis and the biological clock.

PER1 interaction with GPX1 regulates metabolic homeostasis under oxidative stress

Metabolism serves mammalian feeding and active behavior, and is controlled by circadian clock. The molecular mechanism by which clock factors regulate metabolic homeostasis under oxidative stress is unclear. Here, we have characterized that the daily oxygen consumption rhythm was deregulated in Per1 deficient mice. Per1 deficiency impaired daily mitochondrial dynamics and deregulated cellular GPx-related ROS fluctuations in the peripheral organs. We identified that PER1 enhanced GPx activity through PER1/GPX1 interaction in cytoplasm, consequently improving the oxidative phosphorylation efficiency of mitochondria. Per1 expression was specifically elevated in the fasting peripheral organs for protecting mitochondrial from oxidation stress. These observations reveal that Per1-driven mitochondrial dynamics is a critical effector mechanism for the regulation of mitochondrial function in response to oxidation stress.

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PER1 regulates daily metabolic rhythm uncoupled from feeding oscillations.

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Per1 deficiency impairs mitochondrial dynamics and deregulates ROS fluctuations.

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PER1 interactions with GPX1 and increases mitochondrial ROS clearance.

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Fasting elevates Per1 expression to protect mitochondrial from oxidation stress.

The cacao procyanidin extract-caused anti-hyperglycemic effect was changed by the administration timings

Mammals have the biological clocks with approximately 24 h-rhythm. Energy metabolism including glucose metabolism is regulated by the biological clocks. Glucose metabolism is affected by not only meal volume and its energy but also meal timing. We have reported that cacao liquor procyanidin-rich extract (CLPr) ameliorated the postprandial hyperglycemia through AMP-activated protein kinase pathway. However, the effect of administration timing of CLPr on the postprandial hyperglycemia and its signaling pathway are still unclear. In the present study, we compared the effect of CLPr-administration at the rest-phase (light-period) and active-phase (dark-period) on glucose metabolism. Single oral administration of CLPr to ICR mice at the rest-phase, but not at the active-phase, promoted phosphorylation of AMP-activated protein kinase and its upstream liver kinase B1 and translocation of glucose transporter 4 to the plasma membrane in the skeletal muscle, resulting in reduced postprandial hyperglycemia. These results indicated that the intake of CLPr at the rest-phase more effectively suppressed postprandial hyperglycemia.

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.

Molecular Connections Between Circadian Clocks and Aging

The mammalian circadian clockwork has evolved as a timing system that allows the daily environmental changes to be anticipated so that behavior and tissue physiology can be adjusted accordingly. The circadian clock synchronizes the function of all cells within tissues in order to temporally separate preclusive and potentially harmful physiologic processes and to establish a coherent temporal organismal physiology. Thus, the proper functioning of the circadian clockwork is essential for maintaining cellular and tissue homeostasis. Importantly, aging reduces the robustness of the circadian clock, resulting in disturbed sleep-wake cycles, a lowered capacity to synchronize circadian rhythms in peripheral tissues, and reprogramming of the circadian clock output at the molecular function levels. These circadian clock-dependent behavioral and molecular changes in turn further accelerate the process of aging. Here we review the current knowledge about how aging affects the circadian clock, how the functional decline of the circadian clock affects aging, and how the circadian clock machinery and the molecular processes that underlie aging are intertwined.

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.

Consumption of out-of-season orange modulates fat accumulation, morphology and gene expression in the adipose tissue of Fischer 344 rats

PURPOSE

According to the xenohormesis theory, animals receive signals from plants that give clues about the changing environment, and thus, depending on the season of the year, animals develop physiological changes to adapt in advance to the seasonal changes. Our objective was to study how the same fruit cultivated during two different seasons could affect the adipose tissue of rats.

METHODS

Thirty-six Fischer 344 rats were acclimated for 4 weeks to long-day or short-day (SD) photoperiods. After adaptation, three groups (n = 6) from each photoperiod were supplemented either with orange from the northern (ON) or southern (OS) hemispheres harvested in the same month or a vehicle (VH) for 10 weeks. Biometric measurements, postprandial plasmatic parameters, gene expression of the inguinal white adipose tissue (IWAT) and brown adipose tissue (BAT), and the histology of the IWAT were analysed.

RESULTS

The OSSD group increased its fat content compared to the VHSD, while the ON groups showed no biometric differences. The OS groups were further studied, and the IWAT showed increased levels of Pparγ gene expression and a higher percentage of larger adipocytes compared to the VH group. The BAT showed down-regulation of Lpl, Cpt1b and Pparα in the OSSD group compared to that in the VHSD group, suggesting an inhibition of BAT activity, however, Ucp1 gene expression was up-regulated.

CONCLUSIONS

We observed a different effect from both fruits, with the OS promoting a phenotype prone to fat accumulation when consumed in an SD photoperiod, which might be explained by the xenohormesis theory.

Obesity programmed by prenatal dexamethasone and postnatal high-fat diet leads to distinct alterations in nutrition sensory signals and circadian-clock genes in visceral adipose tissue

BACKGROUND

Prenatal dexamethasone treatment has been shown to enhance the susceptibility of offspring to postnatal high-fat (HF) diet-induced programmed obesity. We investigated the metabolic phenotypes, nutrient-sensing signal and circadian-clock genes in adipose tissue that are programmed by prenatal dexamethasone exposure and postnatal HF diet.

METHODS

Male offspring of Sprague-Dawley rats were divided into four experimental groups: normal diet, prenatal dexamethasone exposure, postnatal HF diet, and prenatal dexamethasone plus postnatal HF diet. Postnatal HF diet was prescribed from weaning to 6 months of age.

RESULTS

Prenatal dexamethasone and postnatal HF diet exerted synergistic effects on body weight and visceral adiposity, whereas prenatal dexamethasone and postnatal HF diet altered the metabolic profile and caused leptin dysregulation. Prenatal dexamethasone and postnatal HF diet distinctly influenced nutrient-sensing molecules and circadian-clock genes in adipose tissue. The mRNA expression of mTOR, AMPK-α2, PPAR-α, and PPAR-γ was suppressed by prenatal dexamethasone but enhanced by postnatal HF diet.

CONCLUSION

Prenatal dexamethasone and postnatal HF treatment cause dysregulation of nutrient-sensing molecules and circadian-clock genes in visceral adipose tissue. Characterizing altered nutrient-sensing molecules and circadian-clock genes has potential therapeutic relevance with respect to the pathogenesis and treatment of prenatal stress and postnatal HF diet-related metabolic disorders.

Delayed first active-phase meal, a breakfast-skipping model, led to increased body weight and shifted the circadian oscillation of the hepatic clock and lipid metabolism-related genes in rats fed a high-fat diet

The circadian clock is closely related to human health, such as metabolic syndrome and cardiovascular disease. Our previous study revealed that irregular feeding induced abnormal lipid metabolism with disruption of the hepatic circadian clock. We hypothesized that breakfast skipping induces lipid abnormalities, such as adiposity, by altering the hepatic circadian oscillation of clock and lipid metabolism-related genes. Here, we established a delayed first active-phase meal (DFAM) protocol as a breakfast-skipping model. Briefly, rats were fed a high-fat diet during zeitgeber time (ZT) 12-24 in a control group and ZT 16-4 in the DFAM group. The DFAM group showed increased body weight gain and perirenal adipose tissue weight without a change in total food intake. The circadian oscillations of hepatic clock and de novo fatty acid synthesis genes were delayed by 2-4 h because of DFAM. The peaks of serum insulin, a synchronizer for the liver clock, bile acids, and non-esterified fatty acid (NEFA) were delayed by 4-6 h because of DFAM. Moreover, DFAM delayed the surge in body temperature by 4 h and may have contributed to the increase in body weight gain and adipose tissue weight because of decreased energy expenditure. These data indicated a potential molecular mechanism by which breakfast skipping induces abnormal lipid metabolism, which is related to the altered circadian oscillation of hepatic gene expression. The results also suggested that the delayed peaks of serum NEFA, bile acids, and insulin entrain the circadian rhythm of hepatic clock and lipid metabolism-related genes.

Analysing the Expression of Eight Clock Genes in Five Tissues From Fasting and Fed Sows

In a previous study, we observed that circadian clock genes are differentially expressed in the skeletal muscle of fasting and fed sows. The goal of the current work was to investigate if these genes are also differentially expressed in tissues containing the central (hypothalamus) and peripheral (duodenum, dorsal fat, muscle, and liver) clocks. As animal material, we used 12 sows that fasted 12 h before slaughtering (T0) and 12 sows that were fed ad libitum 7 h prior slaughtering (T2). Tissue samples were collected immediately after slaughter and total RNA was subsequently extracted. The expression of the ARNTL, BHLHE40, CRY2, NPAS2, NR1D1, PER1, PER2, and SIK1 genes was measured by quantitative reverse transcription PCR. The numbers of clock genes showing differential expression before and after feeding varied depending on the tissue i.e., four in dorsal fat and duodenum, six in skeletal muscle, and seven in the liver. In contrast, none of the eight analysed genes displayed a significant differential expression in hypothalamus, the tissue where the central clock resides. This result supports that the differential expression of clock genes in the four tissues mentioned above is probably induced by nutrition and not by the central clock entrained by light. Moreover, we have observed that the NPAS2 and ARNTL genes display positive log2(FC) values in the five tissues under analysis, whilst the CRY2, PER1 (except dorsal fat) and PER2 (except hypothalamus) genes generally show negative log2(FC) values. Such result might be explained by the existence of a negative feedback loop between the ARNTL/NPAS2 and CRY/PER genes. Collectively, these results support that nutrition plays an important role in modulating the timing of porcine peripheral circadian clocks. Such regulation could be essential for coordinating the subsequent metabolic response to nutrient supply.

Potential Mechanisms of Age Acceleration Caused by Estrogen Deprivation: Do Endocrine Therapies Carry the Same Risks?

Longer duration of endocrine therapy decreases breast cancer recurrence and mortality, but these benefits need to be weighed against potential risks to overall health. Notable side effects of endocrine therapy include cataracts, uterine cancer, thromboembolic events, osteoporosis and fracture risk, chronic musculoskeletal complaints, as well as vaginal dryness and discharge, and vasomotor symptoms. Estrogen deprivation in healthy women younger than 50 years undergoing bilateral oophorectomy has been shown to accelerate the development of diseases related to aging, including coronary artery disease, cardiac arrhythmias, stroke, dementia, and osteoporosis, raising concern that even less dramatic modulation of estrogen homeostasis may adversely affect health outcomes. Diminished available estrogen at the cellular and molecular level may facilitate mechanisms that underlie the aging process, often termed the hallmarks of aging. In this review, we describe estrogen's role in normal physiology across tissues, review the effects of estrogen deprivation on health outcomes in the setting of both surgical and natural menopause, and examine the hallmarks of aging with attention to the effects of estrogen and estrogen blockade on each molecular mechanism underlying the aging process.

Consumption of Cherry out of Season Changes White Adipose Tissue Gene Expression and Morphology to a Phenotype Prone to Fat Accumulation

The aim of this study was to determine whether the consumption of cherry out of its normal harvest photoperiod affects adipose tissue, increasing the risk of obesity. Fischer 344 rats were held over a long day (LD) or a short day (SD), fed a standard diet (STD), and treated with a cherry lyophilizate (CH) or vehicle (VH) (n = 6). Biometric measurements, serum parameters, gene expression in white (RWAT) and brown (BAT) adipose tissues, and RWAT histology were analysed. A second experiment with similar conditions was performed (n = 10) but with a cafeteria diet (CAF). In the STD experiment, Bmal1 and Cry1 were downregulated in the CHSD group compared to the VHSD group. Pparα expression was downregulated while Ucp1 levels were higher in the BAT of the CHSD group compared to the VHSD group. In the CAF-fed rats, glucose and insulin serum levels increased, and the expression levels of lipogenesis and lipolysis genes in RWAT were downregulated, while the adipocyte area increased and the number of adipocytes diminished in the CHSD group compared to the VHSD group. In conclusion, we show that the consumption of cherry out of season influences the metabolism of adipose tissue and promotes fat accumulation when accompanied by an obesogenic diet.

Postischemic application of estrogen ameliorates myocardial damage in an in vivo mouse model

BACKGROUND

Cardioprotection provided by estrogen has been recognized for many years. It is noteworthy that most of these studies employ a means of preinjury application in experimental research and the preventive usage in clinical studies. Compared to pretreatment, postischemic administration of estrogen will be more practical in treating myocardial ischemia. On the other hand, defect in circadian clock gene period2 (Per2) has been shown to aggravate ischemia-induced heart damage. Given that Per2 expression decreases as a consequence of menopause, in this study, we aim to determine (1) potential improvement of myocardial function by postischemic administration of 17β-estradiol (E2) using an in vivo mouse myocardial ischemia/reperfusion (I/R) model and (2) the role of E2 in regulating myocardial Per2 expression following I/R.

METHODS

Thirty-minute occlusion of left anterior descending artery followed by 24-h reperfusion was performed on adult C57BL ovariectomized female mice. Groups (n = 3-6/group) were as follows: (1) Sham, (2) I/R + vehicle, and (3) I/R + E2. Vehicle or 0.5 mg/kg of E2 was subcutaneously injected right after 30-min ischemia. Following 24-h reperfusion, myocardial function was determined. Heart tissue was collected for analysis of cleaved caspase-3 and Per2 expression by Western blotting, as well as proinflammatory cytokine production (IL-1β, IL-6, and TNF-α) by enzyme-linked immunosorbent assay.

RESULTS

I/R significantly impaired left ventricular function and increased myocardial levels of active caspase-3, IL-1β, and IL-6. Importantly, postischemic treatment of E2 markedly restored I/R-depressed myocardial function, reduced caspase-3 activation, and decreased proinflammatory cytokine production (IL-1β, IL-6, and TNF-α). Intriguingly, a trend of the decreased Per2 level was observed in ovariectomized female hearts subjected to I/R, whereas E2 treatment upregulated myocardial Per2 expression.

CONCLUSIONS

Our study represents the initial evidence that postischemic administration of E2 effectively preserves the myocardium against I/R injury and this protective effect of E2 may involve upregulation of Per2 in ischemic heart.

Potential Roles of Dec and Bmal1 Genes in Interconnecting Circadian Clock and Energy Metabolism

The daily rhythm of mammalian energy metabolism is subject to the circadian clock system, which is made up of the molecular clock machinery residing in nearly all cells throughout the body. The clock genes have been revealed not only to form the molecular clock but also to function as a mediator that regulates both circadian and metabolic functions. While the circadian signals generated by clock genes produce metabolic rhythms, clock gene function is tightly coupled to fundamental metabolic processes such as glucose and lipid metabolism. Therefore, defects in the clock genes not only result in the dysregulation of physiological rhythms but also induce metabolic disorders including diabetes and obesity. Among the clock genes, Dec1 (Bhlhe40/Stra13/Sharp2), Dec2 (Bhlhe41/Sharp1), and Bmal1 (Mop3/Arntl) have been shown to be particularly relevant to the regulation of energy metabolism at the cellular, tissue, and organismal levels. This paper reviews our current knowledge of the roles of Dec1, Dec2, and Bmal1 in coordinating the circadian and metabolic pathways.

Daily Gene Expression Rhythms in Rat White Adipose Tissue Do Not Differ Between Subcutaneous and Intra-Abdominal Depots

White adipose tissue (WAT) is present in different depots throughout the body. Although all depots are exposed to systemic humoral signals, they are not functionally identical. Studies in clock gene knockout animals and in shift workers suggest that daily rhythmicity may play an important role in lipid metabolism. Differences in rhythmicity between fat depots might explain differences in depot function; therefore, we measured mRNA expression of clock genes and metabolic genes on a 3-h interval over a 24-h period in the subcutaneous inguinal depot and in the intra-abdominal perirenal, epididymal, and mesenteric depots of male Wistar rats. We analyzed rhythmicity using CircWave software. Additionally, we measured plasma concentrations of glucose, insulin, corticosterone, and leptin. The clock genes (Bmal1/Per2/Cry1/Cry2/RevErbα/DBP) showed robust daily gene expression rhythms, which did not vary between WAT depots. Metabolic gene expression rhythms (SREBP1c/PPARα/PPARγ/FAS/LPL/Glut4/HSL/CPT1b/leptin/visfatin/resistin) were more variable between depots. However, no distinct differences between intra-abdominal and subcutaneous rhythms were found. Concluding, specific fat depots are not associated with differences in clock gene expression rhythms and, therefore, do not provide a likely explanation for the differences in metabolic function between different fat depots.

MicroRNAs modulate core-clock gene expression in pancreatic islets during early postnatal life in rats

AIMS/HYPOTHESIS

Evidence continues to emerge detailing a fine-tuning of the regulation of metabolic processes and energy homeostasis by cell-autonomous circadian clocks. Pancreatic beta cell functional maturation occurs after birth and implies transcriptional changes triggered by a shift in the nutritional supply that occurs at weaning, enabling the adaptation of insulin secretion. So far, the developmental timing and exact mechanisms involved in the initiation of the circadian clock in the growing pancreatic islets have never been addressed.

METHODS

Circadian gene expression was measured by quantitative RT-PCR in islets of rats at different postnatal ages up to 3 months, and by in vitro bioluminescence recording in newborn (10-day-old) and adult (3-month-old) islets. The effect of the microRNAs miR-17-5p and miR-29b-3p on the expression of target circadian genes was assessed in newborn rat islets transfected with microRNA antisense or mimic oligonucleotides, and luciferase reporter assays were performed on the rat insulin-secreting cell line INS832/13 to determine a direct effect. The global regulatory network between microRNAs and circadian genes was computationally predicted.

RESULTS

We found up to a sixfold-change in the 24 h transcriptional oscillations and overall expression of Clock, Npas2, Bmal1, Bmal2, Rev-erbα, Per1, Per2, Per3 and Cry2 between newborn and adult rat islets. Synchronisation of the clock machinery in cultured islet cells revealed a delayed cell-autonomous rhythmicity of about 1.5 h in newborn compared with adult rats. Computational predictions unveiled the existence of a complex regulatory network linking over 40 microRNAs displaying modifications in their expression profiles during postnatal beta cell maturation and key core-clock genes. In agreement with these computational predictions, we demonstrated that miR-17-5p and miR-29b-3p directly regulated circadian gene expression in the maturing islet cells of 10-day-old rats.

CONCLUSIONS/INTERPRETATION

These data show that the circadian clock is not fully operational in newborn islets and that microRNAs potently contribute to its regulation during postnatal beta cell maturation. Defects in this process may have long-term consequences on circadian physiology and pancreatic islet function, favouring the manifestation of metabolic diseases such as diabetes.

Protein malnutrition after weaning disrupts peripheral clock and daily insulin secretion in mice

Changes in nutritional state may alter circadian rhythms through alterations in expression of clock genes. Protein deficiency has a profound effect on body metabolism, but the effect of this nutrient restriction after weaning on biological clock has not been explored. Thus, this study aims to investigate whether the protein restriction affects the daily oscillation in the behavior and metabolic rhythms, as well as expression of clock genes in peripheral tissues. Male C57BL/6 J mice, after weaning, were fed a normal-protein (NP) diet or a low-protein (LP) diet for 8 weeks. Mice fed an LP diet did not show difference in locomotor activity and energy expenditure, but the food intake was increased, with parallel increased expression of the orexigenic neuropeptide Npy and disruption of the anorexigenic Pomc oscillatory pattern in the hypothalamus. LP mice showed disruption in the daily rhythmic patterns of plasma glucose, triglycerides and insulin. Also, the rhythmic expression of clock genes in peripheral tissues and pancreatic islets was altered in LP mice. In pancreatic islets, the disruption of clock genes was followed by impairment of daily glucose-stimulated insulin secretion and the expression of genes involved in exocytosis. Pharmacological activation of REV-ERBα could not restore the insulin secretion in LP mice. The present study demonstrates that protein restriction, leading to development of malnutrition, alters the peripheral clock and metabolic outputs, suggesting that this nutrient provides important entraining cues to regulate the daily fluctuation of biological clock.

Effects of intermittent fasting on glucose and lipid metabolism

Two intermittent fasting variants, intermittent energy restriction (IER) and time-restricted feeding (TRF), have received considerable interest as strategies for weight-management and/or improving metabolic health. With these strategies, the pattern of energy restriction and/or timing of food intake are altered so that individuals undergo frequently repeated periods of fasting. This review provides a commentary on the rodent and human literature, specifically focusing on the effects of IER and TRF on glucose and lipid metabolism. For IER, there is a growing evidence demonstrating its benefits on glucose and lipid homeostasis in the short-to-medium term; however, more long-term safety studies are required. Whilst the metabolic benefits of TRF appear quite profound in rodents, findings from the few human studies have been mixed. There is some suggestion that the metabolic changes elicited by these approaches can occur in the absence of energy restriction, and in the context of IER, may be distinct from those observed following similar weight-loss achieved via modest continuous energy restriction. Mechanistically, the frequently repeated prolonged fasting intervals may favour preferential reduction of ectopic fat, beneficially modulate aspects of adipose tissue physiology/morphology, and may also impinge on circadian clock regulation. However, mechanistic evidence is largely limited to findings from rodent studies, thus necessitating focused human studies, which also incorporate more dynamic assessments of glucose and lipid metabolism. Ultimately, much remains to be learned about intermittent fasting (in its various forms); however, the findings to date serve to highlight promising avenues for future research.

Circadian Clock Interaction with HIF1α Mediates Oxygenic Metabolism and Anaerobic Glycolysis in Skeletal Muscle

Circadian clocks are encoded by a transcription-translation feedback loop that aligns energetic processes with the solar cycle. We show that genetic disruption of the clock activator BMAL1 in skeletal myotubes and fibroblasts increased levels of the hypoxia-inducible factor 1α (HIF1α) under hypoxic conditions. Bmal1^-/- myotubes displayed reduced anaerobic glycolysis, mitochondrial respiration with glycolytic fuel, and transcription of HIF1α targets Phd3, Vegfa, Mct4, Pk-m, and Ldha, whereas abrogation of the clock repressors CRY1/2 stabilized HIF1α in response to hypoxia. HIF1α bound directly to core clock gene promoters, and, when co-expressed with BMAL1, led to transactivation of PER2-LUC and HRE-LUC reporters. Further, genetic stabilization of HIF1α in Vhl^-/- cells altered circadian transcription. Finally, induction of clock and HIF1α target genes in response to strenuous exercise varied according to the time of day in wild-type mice. Collectively, our results reveal bidirectional interactions between circadian and HIF pathways that influence metabolic adaptation to hypoxia.

Photoperiod Affects the Phenotype of Mitochondrial Complex I Mutants

Plant mutants for genes encoding subunits of mitochondrial complex I (CI; NADH:ubiquinone oxidoreductase), the first enzyme of the respiratory chain, display various phenotypes depending on growth conditions. Here, we examined the impact of photoperiod, a major environmental factor controlling plant development, on two Arabidopsis (Arabidopsis thaliana) CI mutants: a new insertion mutant interrupted in both ndufs8.1 and ndufs8.2 genes encoding the NDUFS8 subunit and the previously characterized ndufs4 CI mutant. In the long day (LD) condition, both ndufs8.1 and ndufs8.2 single mutants were indistinguishable from Columbia-0 at phenotypic and biochemical levels, whereas the ndufs8.1 ndufs8.2 double mutant was devoid of detectable holo-CI assembly/activity, showed higher alternative oxidase content/activity, and displayed a growth retardation phenotype similar to that of the ndufs4 mutant. Although growth was more affected in ndufs4 than in ndufs8.1 ndufs8.2 under the short day (SD) condition, both mutants displayed a similar impairment of growth acceleration after transfer to LD compared with the wild type. Untargeted and targeted metabolomics showed that overall metabolism was less responsive to the SD-to-LD transition in mutants than in the wild type. The typical LD acclimation of carbon and nitrogen assimilation as well as redox-related parameters was not observed in ndufs8.1 ndufs8 Similarly, NAD(H) content, which was higher in the SD condition in both mutants than in Columbia-0, did not adjust under LD We propose that altered redox homeostasis and NAD(H) content/redox state control the phenotype of CI mutants and photoperiod acclimation in Arabidopsis.

The metabolic sensor Sirt1 and the hypothalamus: Interplay between peptide hormones and pro-hormone convertases

The last decade had witnessed a tremendous progress in our understanding of the causes of metabolic diseases including obesity. Among the contributing factors regulating energy balance are nutrient sensors such as sirtuins. Sirtuin1 (Sirt1), a NAD + - dependent deacetylase is affected by diet, environmental stress, and also plays a critical role in metabolic health by deacetylating proteins in many tissues, including liver, muscle, adipose tissue, heart, endothelium, and in the complexity of the hypothalamus. Because of its dependence on NAD+, Sirt1 also functions as a nutrient/redox sensor, and new novel data show a function of this enzyme in the maturation of hypothalamic peptide hormones controlling energy balance either through regulation of specific nuclear transcription factors or by regulating specific pro-hormone convertases (PCs) involved in the post-translational processing of pro-hormones. The post-translational processing mechanism of pro-hormones is critical in the pathogenesis of obesity as recently shown that metabolic and physiological triggers affect the biosynthesis and processing of many peptides hormones. Specific regulation of pro-hormone processing is likely another key step where final amounts of bioactive peptides can be tightly regulated. Different factors stimulate or inhibit pro-hormones biosynthesis in concert with an increase in the PCs involved in the maturation of bioactive hormones. Adding more complexity to the system, the new studies describe here suggest that Sirt1 could also regulate the fate of peptide hormone biosynthesis. The present review summarizes the recent progress in hypothalamic SIRT1 research with a particular emphasis on the tissue-specific control of neuropeptide hormone maturation. The series of studies done in mouse and rat models strongly advocate for the first time that a deacetylating enzyme could be a regulator in the maturation of peptide hormones and their processing enzymes. These discoveries are the culmination of the first in-depth understanding of the metabolic role of Sirt1 in the brain. It suggests that Sirt1 behaves differently in the brain than in organs such as the liver and pancreas, where the enzyme has been more commonly studied.

The bear circadian clock doesn't 'sleep' during winter dormancy

Background

Most biological functions are synchronized to the environmental light:dark cycle via a circadian timekeeping system. Bears exhibit shallow torpor combined with metabolic suppression during winter dormancy. We sought to confirm that free-running circadian rhythms of body temperature (Tb) and activity were expressed in torpid grizzly (brown) bears and that they were functionally responsive to environmental light. We also measured activity and ambient light exposures in denning wild bears to determine if rhythms were evident and what the photic conditions of their natural dens were. Lastly, we used cultured skin fibroblasts obtained from captive torpid bears to assess molecular clock operation in peripheral tissues. Circadian parameters were estimated using robust wavelet transforms and maximum entropy spectral analyses.

Results

Captive grizzly bears housed in constant darkness during winter dormancy expressed circadian rhythms of activity and Tb. The rhythm period of juvenile bears was significantly shorter than that of adult bears. However, the period of activity rhythms in adult captive bears was virtually identical to that of adult wild denning bears as was the strength of the activity rhythms. Similar to what has been found in other mammals, a single light exposure during the bear’s active period delayed subsequent activity onsets whereas these were advanced when light was applied during the bear’s inactive period. Lastly, in vitro studies confirmed the expression of molecular circadian rhythms with a period comparable to the bear’s own behavioral rhythms.

Conclusions

Based on these findings we conclude that the circadian system is functional in torpid bears and their peripheral tissues even when housed in constant darkness, is responsive to phase-shifting effects of light, and therefore, is a normal facet of torpid bear physiology.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-016-0173-x) contains supplementary material, which is available to authorized users.

Small Heterodimer Partner (NR0B2) Coordinates Nutrient Signaling and the Circadian Clock in Mice

Circadian rhythm regulates multiple metabolic processes and in turn is readily entrained by feeding-fasting cycles. However, the molecular mechanisms by which the peripheral clock senses nutrition availability remain largely unknown. Bile acids are under circadian control and also increase postprandially, serving as regulators of the fed state in the liver. Here, we show that nuclear receptor Small Heterodimer Partner (SHP), a regulator of bile acid metabolism, impacts the endogenous peripheral clock by directly regulating Bmal1. Bmal1-dependent gene expression is altered in Shp knockout mice, and liver clock adaptation is delayed in Shp knockout mice upon restricted feeding. These results identify SHP as a potential mediator connecting nutrient signaling with the circadian clock.

Temporal Organization of the Sleep-Wake Cycle under Food Entrainment in the Rat

STUDY OBJECTIVES

To analyze the temporal organization of the sleep-wake cycle under food entrainment in the rat.

METHODS

Eighteen male Sprague-Dawley rats were chronically implanted for polysomnographic recording. During the baseline (BL) protocol, rats were recorded under a 12:12 light-dark (LD) schedule in individual isolation chambers with food and water ad libitum. Food entrainment was performed by means of a 4-h food restriction (FR) protocol starting at photic zeitgeber time 5. Eight animals underwent a 3-h phase advance of the FR protocol (A-FR). We compared the mean curves and acrophases of wakefulness, NREM sleep, and REM sleep under photic and food entrainment and after a phase advance in scheduled food delivery. We further evaluated the dynamics of REM sleep homeostasis and the NREM sleep EEG delta wave profile.

RESULTS

A prominent food-anticipatory arousal interval was observed after nine or more days of FR, characterized by increased wakefulness and suppression of REM sleep propensity and dampening of NREM sleep EEG delta activity. REM sleep exhibited a robust nocturnal phase preference under FR that was not explained by a nocturnal REM sleep rebound. The mean curve of sleep-wake states and NREM sleep EEG delta activity remained phase-locked to the timing of meals during the A-FR protocol.

CONCLUSIONS

Our results support the hypothesis that under food entrainment, the sleep-wake cycle is coupled to a food-entrainable oscillator (FEO). Our findings suggest an unexpected interaction between FEO output and NREM sleep EEG delta activity generators.

Glucocorticoid receptor isoforms direct distinct mitochondrial programs to regulate ATP production

The glucocorticoid receptor (GR), a nuclear receptor and major drug target, has a highly conserved minor splice variant, GRγ, which differs by a single arginine within the DNA binding domain. GRγ, which comprises 10% of all GR transcripts, is constitutively expressed and tightly conserved through mammalian evolution, suggesting an important non-redundant role. However, to date no specific role for GRγ has been reported. We discovered significant differences in subcellular localisation, and nuclear-cytoplasmic shuttling in response to ligand. In addition the GRγ transcriptome and protein interactome was distinct, and with a gene ontology signal for mitochondrial regulation which was confirmed using Seahorse technology. We propose that evolutionary conservation of the single additional arginine in GRγ is driven by a distinct, non-redundant functional profile, including regulation of mitochondrial function.

Chronobesity: role of the circadian system in the obesity epidemic

Although obesity is considered to result from an imbalance between energy uptake and energy expenditure, the strategy of dietary changes and physical exercise has failed to tackle the global obesity epidemic. In search of alternative and more adequate treatment options, research has aimed at further unravelling the mechanisms underlying this excessive weight gain. While numerous studies are focusing on the neuroendocrine alterations that occur after bariatric Roux-en-Y gastric bypass surgery, an increasing amount of chronobiological studies have started to raise awareness concerning the pivotal role of the circadian system in the development and exacerbation of obesity. This internal timekeeping mechanism rhythmically regulates metabolic and physiological processes in order to meet the fluctuating demands in energy use and supply throughout the 24-h day. This review elaborates on the extensive bidirectional interaction between the circadian system and metabolism and explains how disruption of body clocks by means of shift work, frequent time zone travelling or non-stop consumption of calorie-dense foods can evoke detrimental metabolic alterations that contribute to obesity. Altering the body's circadian rhythms by means of time-related dietary approaches (chrononutrition) or pharmacological substances (chronobiotics) may therefore represent a novel and interesting way to prevent or treat obesity and associated comorbidities.

Evidence for time dependent variation of glucagon secretion in mice

Glucose metabolism is subjected to diurnal variation, which might be mediated by alterations in the transcription pattern of clock genes and regulated by hormonal factors, as has been demonstrated for insulin. However, whether also glucagon is involved in the diurnal variation of glucose homeostasis is not known. We therefore examined glucagon secretion after meal ingestion (meal tolerance test) and during hypoglycemia (hyperinsulinemic hypoglycemic clamp at 2.5mmol/L glucose) and in vitro from isolated islets at ZT3 versus ZT15 in normal C57BL/6J mice and, furthermore, glucose levels and the insulin response to meal ingestion were also examined at these time points in glucagon receptor knockout mice (GCGR-/-) and their wildtype (wt) littermates. We found in normal mice that whereas the glucagon response to meal ingestion was not different between ZT3 and ZT15, the glucagon response to hypoglycemia was lower at ZT3 than at ZT15 and glucagon secretion from isolated islets was higher at ZT3 than at ZT15. GCGR-/- mice displayed lower basal glucose, a lower insulin response to meal and a higher insulin sensitivity than wt mice at ZT3 but not at ZT15. We conclude that there is a time dependent variation in glucagon secretion in normal mice, which is dependent both on intraislet and extraislet regulatory mechanisms and that the phenotype characteristics of a lower glucose and reduced insulin response to meal in GCGR-/- mice are evident only during the light phase. These findings suggest that glucagon signaling is a plausible contributor to the diurnal variation in glucose homeostasis which may explain that the phenotype of the GCGR-/- mice is dependent on the time of the day when it is examined.