The circadian rhythm of glucocorticoids is regulated by a gating mechanism residing in the adrenal cortical clock

A brain-body feedback loop driving HPA-axis dysfunction in breast cancer

Breast cancer patients often exhibit disrupted circadian rhythms in circulating glucocorticoids (GCs), such as cortisol. This disruption correlates with reduced quality of life and higher cancer mortality 1-3 . The exact cause of this phenomenon - whether due to treatments, stress, age, co-morbidities, lifestyle factors, or the cancer itself remains unclear. Here, we demonstrate that primary breast cancer alone blunts host GC rhythms by disinhibiting neurons in the hypothalamus, and that circadian phase-specific neuromodulation of these neurons can attenuate tumor growth by enhancing anti-tumor immunity. We find that mice with mammary tumors exhibit blunted GC rhythms before tumors are palpable, alongside increased activity in paraventricular hypothalamic neurons expressing corticotropin-releasing hormone (i.e., PVN CRH neurons). Tumor-bearing mice have fewer inhibitory synapses contacting PVN CRH neurons and reduced miniature inhibitory post-synaptic current (mIPSC) frequency, leading to net excitation. Tumor-bearing mice experience impaired negative feedback on GC production, but adrenal and pituitary gland functions are largely unaffected, indicating that alterations in PVN CRH neuronal activity are likely a primary cause of hypothalamic-pituitary-adrenal (HPA) axis dysfunction in breast cancer. Using chemogenetics (hM3Dq) to stimulate PVN CRH neurons at different circadian phases, we show that stimulation just before the light-to-dark transition restores normal GC rhythms and reduces tumor progression. These mice have significantly more effector T cells (CD8+) within the tumor than non-stimulated controls, and the anti-tumor effect of PVN CRH neuronal stimulation is absent in mice lacking CD8+ T cells. Our findings demonstrate that breast cancer distally regulates neurons in the hypothalamus that control output of the HPA axis and provide evidence that therapeutic targeting of these neurons could mitigate tumor progression.

Glucocorticoid chrono-pharmacology unveils novel targets for the cardiomyocyte-specific GR-KLF15 axis in cardiac glucose metabolism

Circadian time-of-intake gates the cardioprotective effects of glucocorticoid administration in both healthy and infarcted hearts. The cardiomyocyte-specific glucocorticoid receptor (GR) and its co-factor, Krüppel-like factor (Klf15), play critical roles in maintaining normal heart function in the long-term and serve as pleiotropic regulators of cardiac metabolism. Despite this understanding, the cardiomyocyte-autonomous metabolic targets influenced by the concerted epigenetic action of GR-Klf15 axis remain undefined. Here, we demonstrate the critical roles of the cardiomyocyte-specific GR and Klf15 in orchestrating a circadian-dependent glucose oxidation program within the heart. Combining integrated transcriptomics and epigenomics with cardiomyocyte-specific inducible ablation of GR or Klf15, we identified their synergistic role in the activation of adiponectin receptor expression (Adipor1) and the mitochondrial pyruvate complex (Mpc1/2), thereby enhancing insulin-stimulated glucose uptake and pyruvate oxidation. Furthermore, in obese diabetic (db/db) mice exhibiting insulin resistance and impaired glucose oxidation, light-phase prednisone administration, as opposed to dark-phase prednisone dosing, effectively restored cardiomyocyte glucose oxidation and improved diastolic function towards control-like levels in a sex-independent manner. Collectively, our findings uncover novel cardiomyocyte-autonomous metabolic targets of the GR-Klf15 axis. This study highlights the circadian-dependent cardioprotective effects of glucocorticoids on cardiomyocyte glucose metabolism, providing critical insights into chrono-pharmacological strategies for glucocorticoid therapy in cardiovascular disease.

Effect of circadian clock disruption on type 2 diabetes

Introduction

Type 2 diabetes (T2D) is the predominant form of diabetes mellitus and is among the leading causes of death with an increasing prevalence worldwide. However, the pathological mechanism underlying T2D remains complex and unclear. An increasing number of studies have suggested an association between circadian clock disruption and high T2D prevalence.

Method

This review explores the physiological and genetic evidence underlying T2D symptoms associated with circadian clock disturbances, including insulin secretion and glucose metabolism.

Results and Discussion

Notably, circadian clock disruption reduces insulin secretion and insulin sensitivity and negatively affects glucose homeostasis. The circadian clock regulates the hypothalamic-pituitary-adrenal axis, an important factor that regulates glucose metabolism and influences T2D progression. Therefore, circadian clock regulation is an attractive, novel therapeutic approach for T2D, and various circadian clock stabilizers play therapeutic roles in T2D. Lastly, this review suggests novel therapeutic and preventive approaches using circadian clock regulators for T2D.

Circadian rhythm disruption and endocrine-related tumors

This review delved into the intricate relationship between circadian clocks and physiological processes, emphasizing their critical role in maintaining homeostasis. Orchestrated by interlocked clock genes, the circadian timekeeping system regulates fundamental processes like the sleep-wake cycle, energy metabolism, immune function, and cell proliferation. The central oscillator in the hypothalamic suprachiasmatic nucleus synchronizes with light-dark cycles, while peripheral tissue clocks are influenced by cues such as feeding times. Circadian disruption, linked to modern lifestyle factors like night shift work, correlates with adverse health outcomes, including metabolic syndrome, cardiovascular diseases, infections, and cancer. We explored the molecular mechanisms of circadian clock genes and their impact on metabolic disorders and cancer pathogenesis. Specific associations between circadian disruption and endocrine tumors, spanning breast, ovarian, testicular, prostate, thyroid, pituitary, and adrenal gland cancers, are highlighted. Shift work is associated with increased breast cancer risk, with PER genes influencing tumor progression and drug resistance. CLOCK gene expression correlates with cisplatin resistance in ovarian cancer, while factors like aging and intermittent fasting affect prostate cancer. Our review underscored the intricate interplay between circadian rhythms and cancer, involving the regulation of the cell cycle, DNA repair, metabolism, immune function, and the tumor microenvironment. We advocated for integrating biological timing into clinical considerations for personalized healthcare, proposing that understanding these connections could lead to novel therapeutic approaches. Evidence supports circadian rhythm-focused therapies, particularly chronotherapy, for treating endocrine tumors. Our review called for further research to uncover detailed connections between circadian clocks and cancer, providing essential insights for targeted treatments. We emphasized the importance of public health interventions to mitigate lifestyle-related circadian disruptions and underscored the critical role of circadian rhythms in disease mechanisms and therapeutic interventions.

The circadian clock in the choroid plexus drives rhythms in multiple cellular processes under the control of the suprachiasmatic nucleus

Choroid plexus (ChP), the brain structure primarily responsible for cerebrospinal fluid production, contains a robust circadian clock, whose role remains to be elucidated. The aim of our study was to [1] identify rhythmically controlled cellular processes in the mouse ChP and [2] assess the role and nature of signals derived from the master clock in the suprachiasmatic nuclei (SCN) that control ChP rhythms. To accomplish this goal, we used various mouse models (WT, mPer2Luc, ChP-specific Bmal1 knockout) and combined multiple experimental approaches, including surgical lesion of the SCN (SCNx), time-resolved transcriptomics, and single cell luminescence microscopy. In ChP of control (Ctrl) mice collected every 4 h over 2 circadian cycles in darkness, we found that the ChP clock regulates many processes, including the cerebrospinal fluid circadian secretome, precisely times endoplasmic reticulum stress response, and controls genes involved in neurodegenerative diseases (Alzheimer's disease, Huntington's disease, and frontotemporal dementia). In ChP of SCNx mice, the rhythmicity detected in vivo and ex vivo was severely dampened to a comparable extent as in mice with ChP-specific Bmal1 knockout, and the dampened cellular rhythms were restored by daily injections of dexamethasone in mice. Our data demonstrate that the ChP clock controls tissue-specific gene expression and is strongly dependent on the presence of a functional connection with the SCN. The results may contribute to the search for a novel link between ChP clock disruption and impaired brain health.

Daily glucocorticoids promote glioblastoma growth and circadian synchrony to the host

Glioblastoma (GBM) is the most common primary brain tumor in adults with a poor prognosis despite aggressive therapy. A recent, retrospective clinical study found that administering Temozolomide in the morning increased patient overall survival by 6 months compared to evening. Here, we tested the hypothesis that daily host signaling regulates tumor growth and synchronizes circadian rhythms in GBM. We found daily Dexamethasone promoted or suppressed GBM growth depending on time of day of administration and on the clock gene, Bmal1. Blocking circadian signals, like VIP or glucocorticoids, dramatically slowed GBM growth and disease progression. Finally, mouse and human GBM models have intrinsic circadian rhythms in clock gene expression in vitro and in vivo that entrain to the host through glucocorticoid signaling, regardless of tumor type or host immune status. We conclude that GBM entrains to the circadian circuit of the brain, which modulates its growth through clockcontrolled cues, like glucocorticoids.

Simulated Chronic Jet Lag Affects the Structural and Functional Complexity of Hippocampal Neurons in Mice

There has been a long history that chronic circadian disruption such as jet lag or shift work negatively affects brain and body physiology. Studies have shown that circadian misalignment act as a risk factor for developing anxiety and mood-related depression-like behavior. Till date, most studies focused on simulating jet lag in model animals under laboratory conditions by repeated phase advances or phase delay only, while the real-life conditions may differ. In the present study, adult male mice were subjected to simulated chronic jet lag (CJL) by alternately advancing and delaying the ambient light-dark (LD) cycle by 9 h every 2 days, thereby covering a total of 24 days. The effect of CJL was then examined for a range of stress and depression-related behavioral and physiological responses. The results showed that mice exposed to CJL exhibited depression-like behavior, such as anhedonia. In the open field and elevated plus maze test, CJL-exposed mice showed increased anxiety behavior compared to LD control. In addition, CJL-exposed mice showed an increased level of serum corticosterone and proinflammatory cytokine, TNF-α in both serum and hippocampus. Moreover, CJL-exposed mice exhibited a reduction in structural complexity of hippocampal CA1 neurons along with decreased expression of neurotrophic growth factors, BDNF and NGF in the hippocampus compared to LD control. Taken together, our findings suggest that simulated chronic jet lag adversely affects structural and functional complexity in hippocampal neurons along with interrelated endocrine and inflammatory responses, ultimately leading to stress, anxiety, and depression-like behavior in mice.

Circadian Mechanisms in Brain Fluid Biology

The brain is a complex organ, fundamentally changing across the day to perform basic functions like sleep, thought, and regulating whole-body physiology. This requires a complex symphony of nutrients, hormones, ions, neurotransmitters and more to be properly distributed across the brain to maintain homeostasis throughout 24 hours. These solutes are distributed both by the blood and by cerebrospinal fluid. Cerebrospinal fluid contents are distinct from the general circulation because of regulation at brain barriers including the choroid plexus, glymphatic system, and blood-brain barrier. In this review, we discuss the overlapping circadian (≈24-hour) rhythms in brain fluid biology and at the brain barriers. Our goal is for the reader to gain both a fundamental understanding of brain barriers alongside an understanding of the interactions between these fluids and the circadian timing system. Ultimately, this review will provide new insight into how alterations in these finely tuned clocks may lead to pathology.

Timed receptor tyrosine kinase signaling couples the central and a peripheral circadian clock in Drosophila

Circadian clocks impose daily periodicities to behavior, physiology, and metabolism. This control is mediated by a central clock and by peripheral clocks, which are synchronized to provide the organism with a unified time through mechanisms that are not fully understood. Here, we characterized in Drosophila the cellular and molecular mechanisms involved in coupling the central clock and the peripheral clock located in the prothoracic gland (PG), which together control the circadian rhythm of emergence of adult flies. The time signal from central clock neurons is transmitted via small neuropeptide F (sNPF) to neurons that produce the neuropeptide Prothoracicotropic Hormone (PTTH), which is then translated into daily oscillations of Ca2+ concentration and PTTH levels. PTTH signaling is required at the end of metamorphosis and transmits time information to the PG through changes in the expression of the PTTH receptor tyrosine kinase (RTK), TORSO, and of ERK phosphorylation, a key component of PTTH transduction. In addition to PTTH, we demonstrate that signaling mediated by other RTKs contributes to the rhythmicity of emergence. Interestingly, the ligand to one of these receptors (Pvf2) plays an autocrine role in the PG, which may explain why both central brain and PG clocks are required for the circadian gating of emergence. Our findings show that the coupling between the central and the PG clock is unexpectedly complex and involves several RTKs that act in concert and could serve as a paradigm to understand how circadian clocks are coordinated.

Circadian clock in choroid plexus is resistant to immune challenge but dampens in response to chronodisruption

The choroid plexus (ChP) in the brain ventricles has a major influence on brain homeostasis. In this study, we aimed to determine whether the circadian clock located in ChP is affected by chronodisruption caused by misalignment with the external light/dark cycle and/or inflammation. Adult mPer2Luc mice were maintained in the LD12:12 cycle or exposed to one of two models of chronic chronodisruption - constant light for 22-25 weeks (cLL) or 6-hour phase advances of the LD12:12 cycle repeated weekly for 12 weeks (cLD-shifts). Locomotor activity was monitored before the 4th ventricle ChP and suprachiasmatic nuclei (SCN) explants were recorded in real time for PER2-driven population and single-cell bioluminescence rhythms. In addition, plasma immune marker concentrations and gene expression in ChP, prefrontal cortex, hippocampus and cerebellum were analyzed. cLL dampened the SCN clock but did not shorten the inactivity interval (sleep). cLD-shifts had no effect on the SCN clock, but transiently affected sleep duration and fragmentation. Both chronodisruption protocols dampened the ChP clock. Although immune markers were elevated in plasma and hippocampus, levels in ChP were unaffected, and unlike the liver clock, the ChP clock was resistant to lipopolysaccharide treatment. Importantly, both chronodisruption protocols reduced glucocorticoid signaling in ChP. The data demonstrate the high resistance of the ChP clock to inflammation, highlighting its role in protecting the brain from neuroinflammation, and on the other hand its high sensitivity to chronodisruption. Our results provide a novel link between human lifestyle-induced chronodisruption and the impairment of ChP-dependent brain homeostasis.

Coupling allows robust mammalian redox circadian rhythms despite heterogeneity and noise

Circadian clocks are endogenous oscillators present in almost all cells that drive daily rhythms in physiology and behavior. There are two mechanisms that have been proposed to explain how circadian rhythms are generated in mammalian cells: through a transcription-translation feedback loop (TTFL) and based on oxidation/reduction reactions, both of which are intrinsically stochastic and heterogeneous at the single cell level. In order to explore the emerging properties of stochastic and heterogeneous redox oscillators, we simplify a recently developed kinetic model of redox oscillations to an amplitude-phase oscillator with 'twist' (period-amplitude correlation) and subject to Gaussian noise. We show that noise and heterogeneity alone lead to fast desynchronization, and that coupling between noisy oscillators can establish robust and synchronized rhythms with amplitude expansions and tuning of the period due to twist. Coupling a network of redox oscillators to a simple model of the TTFL also contributes to synchronization, large amplitudes and fine-tuning of the period for appropriate interaction strengths. These results provide insights into how the circadian clock compensates randomness from intracellular sources and highlight the importance of noise, heterogeneity and coupling in the context of circadian oscillators.

Ontogeny of the circadian system: a multiscale process throughout development

The 24 h (circadian) timing system develops in mammals during the perinatal period. It carries out the essential task of anticipating daily recurring environmental changes to identify the best time of day for each molecular, cellular, and systemic process. Although significant knowledge has been acquired about the organization and function of the adult circadian system, relatively little is known about its ontogeny. During the perinatal period, the circadian system progressively gains functionality under the influence of the early environment. This review explores current evidence on the development of the circadian clock in mammals, highlighting the multilevel complexity of the process and the importance of gaining a better understanding of its underlying biology.

Circadian Rhythm Changes in Healthy Aging and Mild Cognitive Impairment

Disruptions in circadian rhythms can occur in healthy aging; however, these changes are more severe and pervasive in individuals with age-related and neurodegenerative diseases, such as dementia. Circadian rhythm alterations are also present in preclinical stages of dementia, for example, in patients with mild cognitive impairments (MCI); thus, providing a unique window of opportunity for early intervention in neurodegenerative disorders. Nonetheless, there is a lack of studies examining the association between relevant changes in circadian rhythms and their relationship with cognitive dysfunctions in MCI individuals. In this review, circadian system alterations occurring in MCI patients are examined compared to healthy aging individuals while also considering their association with MCI neurocognitive alterations. The main findings are that abnormal circadian changes in rest-activity, core body temperature, melatonin, and cortisol rhythms appear in the MCI stage and that these circadian rhythm disruptions are associated with some of the neurocognitive deficits observed in MCI patients. In addition, preliminary evidence indicates that interventions aimed at restoring regular circadian rhythms may prevent or halt the progress of neurodegenerative diseases and mitigate their related cognitive impairments. Future longitudinal studies with repeated follow-up assessments are needed to establish the translational potential of these findings in clinical practice.

Timing Matters: The Interplay between Early Mealtime, Circadian Rhythms, Gene Expression, Circadian Hormones, and Metabolism-A Narrative Review

Achieving synchronization between the central and peripheral body clocks is essential for ensuring optimal metabolic function. Meal timing is an emerging field of research that investigates the influence of eating patterns on our circadian rhythm, metabolism, and overall health. This narrative review examines the relationship between meal timing, circadian rhythm, clock genes, circadian hormones, and metabolic function. It analyzes the existing literature and experimental data to explore the connection between mealtime, circadian rhythms, and metabolic processes. The available evidence highlights the importance of aligning mealtime with the body's natural rhythms to promote metabolic health and prevent metabolic disorders. Specifically, studies show that consuming meals later in the day is associated with an elevated prevalence of metabolic disorders, while early time-restricted eating, such as having an early breakfast and an earlier dinner, improves levels of glucose in the blood and substrate oxidation. Circadian hormones, including cortisol and melatonin, interact with mealtimes and play vital roles in regulating metabolic processes. Cortisol, aligned with dawn in diurnal mammals, activates energy reserves, stimulates appetite, influences clock gene expression, and synchronizes peripheral clocks. Consuming meals during periods of elevated melatonin levels, specifically during the circadian night, has been correlated with potential implications for glucose tolerance. Understanding the mechanisms of central and peripheral clock synchronization, including genetics, interactions with chronotype, sleep duration, and hormonal changes, provides valuable insights for optimizing dietary strategies and timing. This knowledge contributes to improved overall health and well-being by aligning mealtime with the body's natural circadian rhythm.

Effects of the neonatal intensive care environment on circadian health and development of preterm infants

The circadian system in mammals ensures adaptation to the light-dark cycle on Earth and imposes 24-h rhythmicity on metabolic, physiological and behavioral processes. The central circadian pacemaker is located in the brain and is entrained by environmental signals called Zeitgebers. From here, neural, humoral and systemic signals drive rhythms in peripheral clocks in nearly every mammalian tissue. During pregnancy, disruption of the complex interplay between the mother's rhythmic signals and the fetal developing circadian system can lead to long-term health consequences in the offspring. When an infant is born very preterm, it loses the temporal signals received from the mother prematurely and becomes totally dependent on 24/7 care in the Neonatal Intensive Care Unit (NICU), where day/night rhythmicity is usually blurred. In this literature review, we provide an overview of the fetal and neonatal development of the circadian system, and short-term consequences of disruption of this process as occurs in the NICU environment. Moreover, we provide a theoretical and molecular framework of how this disruption could lead to later-life disease. Finally, we discuss studies that aim to improve health outcomes after preterm birth by studying the effects of enhancing rhythmicity in light and noise exposure.

Hyperglycemia-activated 11β-hydroxysteroid dehydrogenase type 1 increases endoplasmic reticulum stress and skin barrier dysfunction

The diabetes mellitus (DM) skin shows skin barrier dysfunction and skin lipid abnormality, similar to conditions induced by systemic or local glucocorticoid excess and aged skin. Inactive glucocorticoid (GC) is converted into active glucocorticoid by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Hyperglycemia in DM and excessive GC are known to increase endoplasmic reticulum (ER) stress. We hypothesized that hyperglycemia affects systemic GC homeostasis and that the action of skin 11β-HSD1 and GC contributes to increased ER stress and barrier defects in DM. We compared 11β-HSD1, active GC, and ER stress between hyperglycemic and normoglycemic conditions in normal human keratinocytes and db/db mice. 11β-HSD1 and cortisol increased with time in keratinocyte culture under hyperglycemic conditions. 11β-HSD1 siRNA-transfected cells did not induce cortisol elevation in hyperglycemic condition. The production of 11β-HSD1 and cortisol was suppressed in cell culture treated with an ER stress-inhibitor. The 14-week-old db/db mice showed higher stratum corneum (SC) corticosterone, and skin 11β-HSD1 levels than 8-week-old db/db mice. Topical 11β-HSD1 inhibitor application in db/db mice decreased SC corticosterone levels and improved skin barrier function. Hyperglycemia in DM may affect systemic GC homeostasis, activate skin 11β-HSD1, and induce local GC excess, which increases ER stress and adversely affects skin barrier function.

Functional interaction of Clock genes and bone morphogenetic proteins in the adrenal cortex

The bone morphogenetic protein (BMP) system in the adrenal cortex plays modulatory roles in the control of adrenocortical steroidogenesis. BMP-6 enhances aldosterone production by modulating angiotensin (Ang) II-mitogen-activated protein kinase (MAPK) signaling, whereas activin regulates the adrenocorticotropin (ACTH)-cAMP cascade in adrenocortical cells. A peripheral clock system in the adrenal cortex was discovered and it has been shown to have functional roles in the adjustment of adrenocortical steroidogenesis by interacting with the BMP system. It was found that follistatin, a binding protein of activin, increased Clock mRNA levels, indicating an endogenous function of activin in the regulation of Clock mRNA expression. Elucidation of the interrelationships among the circadian clock system, the BMP system and adrenocortical steroidogenesis regulated by the hypothalamic-pituitary-adrenal (HPA) axis would lead to an understanding of the pathophysiology of adrenal disorders and metabolic disorders and the establishment of better medical treatment from the viewpoint of pharmacokinetics.

Identification of a novel class of cortisol biosynthesis inhibitors and its implications in a therapeutic strategy for hypercortisolism

AIMS

Dysregulation of adrenocortical steroid (corticosteroids) biosynthesis leads to pathological conditions such as Cushing's syndrome. Although several classes of steroid biosynthesis inhibitors have been developed to treat cortisol overproduction, limitations such as insufficient efficacy, adverse effects, and/or tolerability still remain. The present study aimed to develop a new class of small molecules that inhibit cortisol production, and investigated their putative modes of action.

MAIN METHODS

We screened an in-house chemical library with drug-like chemical scaffolds using human adrenocortical NCI-H295R cells. We then evaluated and validated the effects of the selected compounds at multiple regulatory steps of the adrenal steroidogenic pathway. Finally, genome-wide RNA expression analysis coupled with gene enrichment analysis was conducted to infer possible action mechanisms.

KEY FINDINGS

A subset of benzimidazolylurea derivatives, including a representative compound (designated as CJ28), inhibited both basal and stimulated production of cortisol and related intermediate steroids. CJ28 attenuated the mRNA expression of multiple genes involved in steroidogenesis and cholesterol biosynthesis. Furthermore, CJ28 significantly attenuated de novo cholesterol biosynthesis, which contributed to its suppression of cortisol production.

SIGNIFICANCE

We identified a novel chemical scaffold that exerts inhibitory effects on cortisol and cholesterol biosynthesis via coordinated transcriptional silencing of gene expression networks. Our findings also reveal an additional adrenal-directed pharmacological strategy for hypercortisolism involving a combination of inhibitors targeting steroidogenesis and de novo cholesterol biosynthesis.

Circadian glucocorticoids throughout development

Glucocorticoids (GCs) are essential drivers of mammalian tissue growth and maturation during one of the most critical developmental windows, the perinatal period. The developing circadian clock is shaped by maternal GCs. GC deficits, excess, or exposure at the wrong time of day leads to persisting effects later in life. During adulthood, GCs are one of the main hormonal outputs of the circadian system, peaking at the beginning of the active phase (i.e., the morning in humans and the evening in nocturnal rodents) and contributing to the coordination of complex functions such as energy metabolism and behavior, across the day. Our article discusses the current knowledge on the development of the circadian system with a focus on the role of GC rhythm. We explore the bidirectional interaction between GCs and clocks at the molecular and systemic levels, discuss the evidence of GC influence on the master clock in the suprachiasmatic nuclei (SCN) of the hypothalamus during development and in the adult system.

The Circadian Clock of Polarized Microglia and Its Interaction with Mouse Brain Oscillators

The activity of the immune system is controlled by circadian clocks present in different immune cells. The brain-resident subtype of immune cells, microglia, exhibits a wide range of functional phenotypes depending on the signaling molecules in their microenvironment. The exact role of microglia in the hypothalamic suprachiasmatic nuclei (SCN), the central circadian clock, has not been known. Therefore, the aim of this study was to determine (1) whether microenvironment-induced changes in microglial polarization affect circadian clocks in these cells and (2) whether the presence of microglia contributes to SCN clock function. Microglial and SCN clocks were monitored using PER2-driven bioluminescence rhythms at the tissue and single-cell levels. We found that polarization of resting microglia to a pro-inflammatory (M1) or anti-inflammatory (M2) state significantly altered the period and amplitude of their molecular circadian clock; importantly, the parameters changed plastically with the repolarization of microglia. This effect was reflected in specific modulations of the expression profiles of individual clock genes in the polarized microglia. Depletion of microglia significantly reduced the amplitude of the SCN clock, and co-cultivation of the SCN explants with M2-polarized microglia specifically improved the amplitude of the SCN clock. These results demonstrate that the presence of M2-polarized microglia has beneficial effects on SCN clock function. Our results provide new insight into the mutual interaction between immune and circadian systems in the brain.

Frank Beach Award Winner: The centrality of the hypothalamic-pituitary-adrenal axis in dealing with environmental change across temporal scales

Understanding if and how individuals and populations cope with environmental change is an enduring question in evolutionary ecology that has renewed importance given the pace of change in the Anthropocene. Two evolutionary strategies of coping with environmental change may be particularly important in rapidly changing environments: adaptive phenotypic plasticity and/or bet hedging. Adaptive plasticity could enable individuals to match their phenotypes to the expected environment if there is an accurate cue predicting the selective environment. Diversifying bet hedging involves the production of seemingly random phenotypes in an unpredictable environment, some of which may be adaptive. Here, I review the central role of the hypothalamic-pituitary-adrenal (HPA) axis and glucocorticoids (GCs) in enabling vertebrates to cope with environmental change through adaptive plasticity and bet hedging. I first describe how the HPA axis mediates three types of adaptive plasticity to cope with environmental change (evasion, tolerance, recovery) over short timescales (e.g., 1-3 generations) before discussing how the implications of GCs on phenotype integration may depend upon the timescale under consideration. GCs can promote adaptive phenotypic integration, but their effects on phenotypic co-variation could also limit the dimensions of phenotypic space explored by animals over longer timescales. Finally, I discuss how organismal responses to environmental stressors can act as a bet hedging mechanism and therefore enhance evolvability by increasing genetic or phenotypic variability or reducing patterns of genetic and phenotypic co-variance. Together, this emphasizes the crucial role of the HPA axis in understanding fundamental questions in evolutionary ecology.

Diurnal variation in declarative memory and the involvement of SCOP in cognitive functions in nonhuman primates

Cognitive functions depend on the time of day in various organisms. Previously, we found that 24-h recognition memory performance of nocturnal mice changes diurnally through SCOP protein-dependent regulation. It remains unknown whether diurnal change and SCOP-dependent regulation of memory performance are conserved across species with diurnal/nocturnal habits. We tested whether the memory performance of diurnal Japanese macaques depends on the time of day. The memory association between bitter taste of drinking water and the nozzle color of the water bottle was established during the light period of the day to evaluate of memory performance for macaques. Here we found diurnal variation of declarative memory in Japanese macaques. The middle of the daytime is the most effective time for memory performance during the light period. To assess whether SCOP is involved in declarative memory performance, we interfered with SCOP expression by using lentiviral vector expressing shRNA against Scop in the hippocampus of Japanese macaques. Scop knockdown in the hippocampus abrogated the memory performance in the middle of the daytime. Our results implicate that SCOP in the hippocampus is necessary for the diurnal rhythm of the memory system and that the SCOP-dependent memory regulation system may be conserved in mammals.

Basic Concepts and Hormonal Regulators of the Stress System

BACKGROUND

Human organisms have to cope with a large number of external or internal stressful stimuli that threaten - or are perceived as threatening - their internal dynamic balance or homeostasis. To face these disturbing forces, or stressors, organisms have developed a complex neuroendocrine system, the stress system, which consists of the hypothalamic-pituitary-adrenal axis and the locus caeruleus/norepinephrine-autonomic nervous system.

SUMMARY

Upon exposure to stressors beyond a certain threshold, the activation of the stress system leads to a series of physiological and behavioral adaptations that help achieve homeostasis and increase the chances of survival. When, however, the stress response to stressors is inadequate, excessive, or prolonged, the resultant maladaptation may lead to the development of several stress-related pathologic conditions. Adverse environmental events, especially during critical periods of life, such as prenatal life, childhood, and puberty/adolescence, in combination with the underlying genetic background, may leave deep, long-term epigenetic imprints in the human expressed genome.

KEY MESSAGES

In this review, we describe the components of the stress system and its functional interactions with other homeostatic systems of the organism; we present the hormonal regulators of the stress response, and we discuss the development of stress-related pathologies.

Cortisol: Analytical and clinical determinants

Cortisol, the main human glucocorticoid, is synthesized from cholesterol in the adrenal cortex and predominantly metabolized by the liver. Interpretation of quantitative results from the analysis of serum, urine and saliva is complicated by variation in circadian rhythm, response to stress as well as the presence of protein-bound and free forms. Interestingly, cortisol is the only hormone routinely measured in serum, urine, and saliva. Preanalytical and analytical challenges arise in each matrix and are further compounded by the use of various stimulation and suppression tests commonly employed in clinical practice. Although not yet included in clinical guidelines, measurement of cortisol in hair may be of interest in specific situations. Immunoassays are the most widely used methods in clinical laboratories to measure cortisol, but they are susceptible to interference from synthetic and endogenous steroids, generally producing a variable overestimation of true cortisol results, especially in urine. Analysis by mass spectrometry provides higher specificity and allows simultaneous measurement of multiple steroids including synthetic steroids, thus reducing diagnostic uncertainty. An integrated review of cortisol in various disease states is also addressed.

Circadian gene expression in mouse renal proximal tubule

Circadian variability in kidney function is well recognized but is often ignored as a potential confounding variable in physiological experiments. Here, we have created a data resource consisting of expression levels for mRNA transcripts in microdissected proximal tubule segments from mice as a function of the time of day. Small-sample RNA sequencing was applied to microdissected S1 proximal convoluted tubules and S2 proximal straight tubules. After stringent filtering, the data were analyzed using JTK-Cycle to detect periodicity. The data set is provided as a user-friendly webpage at https://esbl.nhlbi.nih.gov/Databases/Circadian-Prox2/. In proximal convoluted tubules, 234 transcripts varied in a circadian manner (4.0% of the total). In proximal straight tubules, 334 transcripts varied in a circadian manner (5.3%). Transcripts previously known to be associated with corticosteroid action and with increased flow were found to be overrepresented among circadian transcripts peaking during the "dark" portion of the day [zeitgeber time (ZT)14-22], corresponding to peak levels of corticosterone and glomerular filtration rate in mice. To ask whether there is a time-of-day dependence of protein abundances in the kidney, we carried out LC-MS/MS-based proteomics in whole mouse kidneys at ZT12 and ZT0. The full data set (n = 6,546 proteins) is available at https://esbl.nhlbi.nih.gov/Databases/Circadian-Proteome/. Overall, 293 proteins were differentially expressed between ZT12 and ZT0 (197 proteins greater at ZT12 and 96 proteins greater at ZT0). Among the regulated proteins, only nine proteins were found to be periodic in the RNA-sequencing analysis, suggesting a high level of posttranscriptional regulation of protein abundances.NEW & NOTEWORTHY Circadian variation in gene expression can be an important determinant in the regulation of kidney function. The authors used RNA-sequencing transcriptomics and LC-MS/MS-based proteomics to identify gene products expressed in a periodic manner. The data were used to construct user-friendly web resources.

Circadian rhythm in prostate cancer: time to take notice of the clock

The circadian clock is an evolutionary molecular product that is associated with better adaptation to changes in the external environment. Disruption of the circadian rhythm plays a critical role in tumorigenesis of many kinds of cancers, including prostate cancer (PCa). Integrating circadian rhythm into PCa research not only brings a closer understanding of the mechanisms of PCa but also provides new and effective options for the precise treatment of patients with PCa. This review begins with patterns of the circadian clock, highlights the role of the disruption of circadian rhythms in PCa at the epidemiological and molecular levels, and discusses possible new approaches to PCa therapy that target the circadian clock.

Circadian Rhythms Disrupted by Light at Night and Mistimed Food Intake Alter Hormonal Rhythms and Metabolism

Availability of artificial light and light-emitting devices have altered human temporal life, allowing 24-hour healthcare, commerce and production, and expanding social life around the clock. However, physiology and behavior that evolved in the context of 24 h solar days are frequently perturbed by exposure to artificial light at night. This is particularly salient in the context of circadian rhythms, the result of endogenous biological clocks with a rhythm of ~24 h. Circadian rhythms govern the temporal features of physiology and behavior, and are set to precisely 24 h primarily by exposure to light during the solar day, though other factors, such as the timing of meals, can also affect circadian rhythms. Circadian rhythms are significantly affected by night shift work because of exposure to nocturnal light, electronic devices, and shifts in the timing of meals. Night shift workers are at increased risk for metabolic disorder, as well as several types of cancer. Others who are exposed to artificial light at night or late mealtimes also show disrupted circadian rhythms and increased metabolic and cardiac disorders. It is imperative to understand how disrupted circadian rhythms alter metabolic function to develop strategies to mitigate their negative effects. In this review, we provide an introduction to circadian rhythms, physiological regulation of homeostasis by the suprachiasmatic nucleus (SCN), and SCN-mediated hormones that display circadian rhythms, including melatonin and glucocorticoids. Next, we discuss circadian-gated physiological processes including sleep and food intake, followed by types of disrupted circadian rhythms and how modern lighting disrupts molecular clock rhythms. Lastly, we identify how disruptions to hormones and metabolism can increase susceptibility to metabolic syndrome and risk for cardiovascular diseases, and discuss various strategies to mitigate the harmful consequences associated with disrupted circadian rhythms on human health.

Circadian modulation of microglial physiological processes and immune responses

Microglia is considered the central nervous system (CNS) resident macrophages that establish an innate immune response against pathogens and toxins. However, the recent studies have shown that microglial gene and protein expression follows a circadian pattern; several immune activation markers and clock genes are expressed rhythmically without the need for an immune stimulus. Furthermore, microglia responds to an immune challenge with different magnitudes depending on the time of the day. This review examines the circadian control of microglia function and the possible physiological implications. For example, we discuss that synaptic prune is performed in the cortex at a certain moment of the day. We also consider the implications of daily microglial function for maintaining biological rhythms like general activity, body temperature, and food intake. We conclude that the developmental stage, brain region, and pathological state are not the only factors to consider for the evaluation of microglial functions; instead, emerging evidence indicates that circadian time as an essential aspect for a better understanding of the role of microglia in CNS physiology.

Perfecting the Life Clock: The Journey from PTO to TTFL

The ubiquity of biological rhythms in life implies that it results from selection in the evolutionary process. The origin of the biological clock has two possible hypotheses: the selective pressure hypothesis of the oxidative stress cycle and the light evasion hypothesis. Moreover, the biological clock gives life higher adaptability. Two biological clock mechanisms have been discovered: the negative feedback loop of transcription-translation (TTFL) and the post-translational oscillation mechanism (PTO). The TTFL mechanism is the most classic and relatively conservative circadian clock oscillation mechanism, commonly found in eukaryotes. We have introduced the TTFL mechanism of the classical model organisms. However, the biological clock of prokaryotes is based on the PTO mechanism. The Peroxiredoxin (PRX or PRDX) protein-based PTO mechanism circadian clock widely existing in eukaryotic and prokaryotic life is considered a more conservative oscillation mechanism. The coexistence of the PTO and TTFL mechanisms in eukaryotes prompted us to explain the relationship between the two. Finally, we speculated that there might be a driving force for the evolution of the biological clock. The biological clock may have an evolutionary trend from the PTO mechanism to the TTFL mechanism, resulting from the evolution of organisms adapting to the environment.

Spatiotemporal Metabolic Liver Zonation and Consequences on Pathophysiology

Hepatocytes are the main workers in the hepatic factory, managing metabolism of nutrients and xenobiotics, production and recycling of proteins, and glucose and lipid homeostasis. Division of labor between hepatocytes is critical to coordinate complex complementary or opposing multistep processes, similar to distributed tasks at an assembly line. This so-called metabolic zonation has both spatial and temporal components. Spatial distribution of metabolic function in hepatocytes of different lobular zones is necessary to perform complex sequential multistep metabolic processes and to assign metabolic tasks to the right environment. Moreover, temporal control of metabolic processes is critical to align required metabolic processes to the feeding and fasting cycles. Disruption of this complex spatiotemporal hepatic organization impairs key metabolic processes with both local and systemic consequences. Many metabolic diseases, such as nonalcoholic steatohepatitis and diabetes, are associated with impaired metabolic liver zonation. Recent technological advances shed new light on the spatiotemporal gene expression networks controlling liver function and how their deregulation may be involved in a large variety of diseases. We summarize the current knowledge about spatiotemporal metabolic liver zonation and consequences on liver pathobiology.

Glucocorticoids coordinate the bladder peripheral clock and diurnal micturition pattern in mice

Peripheral clocks function to regulate each organ and are synchronized though various molecular and behavioral signals. However, signals that entrain the bladder clock remain elusive. Here, we show that glucocorticoids are a key cue for the bladder clock in vitro and in vivo. A pBmal1-dLuc human urothelial cell-line showed significant shifts in gene expression after cortisol treatment. In vivo, rhythmic bladder clock gene expression was unchanged by bilateral adrenalectomy but shifted 4 h forward by corticosterone administration at the inactive phase. Moreover, the bladder clock shifted 8-12 h in mice that underwent both bilateral adrenalectomy and corticosterone administration at the inactive phase. These mice showed decreases in the diurnal rhythm of volume voided per micturition, while maintaining diurnal activity rhythms. These results indicate that the diurnal rhythm of glucocorticoid signaling is a zeitgeber that overcomes other bladder clock entrainment factors and coordinates the diurnal rhythm of volume voided per micturition.

Epigenetic insight into effects of prenatal alcohol exposure on stress axis development: Systematic review with meta-analytic approaches

We conducted a systematic review with meta-analytic elements using publicly available Gene Expression Omnibus (GEO) datasets to determine the role of epigenetic mechanisms in prenatal alcohol exposure (PAE)-induced hypothalamic-pituitary-adrenal (HPA) axis dysfunctions in offspring. Several studies have demonstrated that PAE has long-term consequences on HPA axis functions in offspring. Some studies determined that alcohol-induced epigenetic alterations during fetal development persist in adulthood. However, additional research is needed to understand the major epigenetic events leading to alcohol-induced teratogenesis of the HPA axis. Our network analysis of GEO datasets identified key pathways relevant to alcohol-mediated histone modifications, DNA methylation, and miRNA involvement associated with PAE-induced alterations of the HPA axis. Our analysis indicated that PAE perturbated the epigenetic machinery to activate corticotrophin-releasing hormone, while it suppressed opioid, glucocorticoid receptor, and circadian clock genes. These results help to further our understanding of the epigenetic basis of alcohol's effects on HPA axis development.

Development of the circadian system in early life: maternal and environmental factors

In humans, an adaptable internal biological system generates circadian rhythms that maintain synchronicity of behavior and physiology with the changing demands of the 24-h environment. Development of the circadian system begins in utero and continues throughout the first few years of life. Maturation of the clock can be measured through sleep/wake patterns and hormone secretion. Circadian rhythms, by definition, can persist in the absence of environmental input; however, their ability to adjust to external time cues is vital for adaptation and entrainment to the environment. The significance of these external factors that influence the emergence of a stable circadian clock in the first years of life remain poorly understood. Infants raised in our post-modern world face adverse external circadian signals, such as artificial light and mistimed hormonal cues via breast milk, which may increase interference with the physiological mechanisms that promote circadian synchronization. This review describes the very early developmental stages of the clock and common circadian misalignment scenarios that make the developing circadian system more susceptible to conflicting time cues and temporal disorder between the maternal, fetal, infant, and peripheral clocks.

Fast dynamics in the HPA axis: Insight from mathematical and experimental studies

The activity of the hypothalamic-pituitary-adrenal (HPA) axis is characterised by complex dynamics spanning several timescales. This ranges from slow circadian rhythms in blood hormone concentration to faster ultradian pulses of hormone secretion and even more rapid oscillations in electrical and calcium activity in neuroendocrine cells of the hypothalamus and pituitary gland. Here, we focus on the system's oscillations on the short timescale. We highlight some of the mathematical modelling and experimental work that has been carried out to characterise the mechanisms regulating this highly dynamic mode of neuroendocrine signalling and discuss some future directions that may be explored to enhance understanding of HPA function.

Different levels of circadian (de)synchrony -- where does it hurt?

A network of cellular timers ensures the maintenance of homeostasis by temporal modulation of physiological processes across the day. These so-called circadian clocks are synchronized to geophysical time by external time cues (or zeitgebers). In modern societies, natural environmental cycles are disrupted by artificial lighting, around-the-clock availability of food or shiftwork. Such contradictory zeitgeber input promotes chronodisruption, i.e., the perturbation of internal circadian rhythms, resulting in adverse health outcomes. While this phenomenon is well described, it is still poorly understood at which level of organization perturbed rhythms impact on health and wellbeing. In this review, we discuss different levels of chronodisruption and what is known about their health effects. We summarize the results of disrupted phase coherence between external and internal time vs. misalignment of tissue clocks amongst each other, i.e., internal desynchrony. Last, phase incoherence can also occur at the tissue level itself. Here, alterations in phase coordination can emerge between cellular clocks of the same tissue or between different clock genes within the single cell. A better understanding of the mechanisms of circadian misalignment and its effects on physiology will help to find effective tools to prevent or treat disorders arising from modern-day chronodisruptive environments.

Different levels of circadian (de)synchrony -- where does it hurt?

A network of cellular timers ensures the maintenance of homeostasis by temporal modulation of physiological processes across the day. These so-called circadian clocks are synchronized to geophysical time by external time cues (or zeitgebers). In modern societies, natural environmental cycles are disrupted by artificial lighting, around-the-clock availability of food or shift work. Such contradictory zeitgeber input promotes chronodisruption, i.e., the perturbation of internal circadian rhythms, resulting in adverse health outcomes. While this phenomenon is well described, it is still poorly understood at which level of organization perturbed rhythms impact on health and wellbeing. In this review, we discuss different levels of chronodisruption and what is known about their health effects. We summarize the results of disrupted phase coherence between external and internal time vs. misalignment of tissue clocks amongst each other, i.e., internal desynchrony. Last, phase incoherence can also occur at the tissue level itself. Here, alterations in phase coordination can emerge between cellular clocks of the same tissue or between different clock genes within the single cell. A better understanding of the mechanisms of circadian misalignment and its effects on physiology will help to find effective tools to prevent or treat disorders arising from modern-day chronodisruptive environments.

Genetic and environmental circadian disruption induce weight gain through changes in the gut microbiome

OBJECTIVE

Internal clocks time behavior and physiology, including the gut microbiome, in a circadian (∼24 h) manner. Mismatch between internal and external time, e.g. during shift work, disrupts circadian system coordination promoting the development of obesity and type 2 diabetes (T2D). Conversely, body weight changes induce microbiota dysbiosis. The relationship between circadian disruption and microbiota dysbiosis in metabolic diseases, however, remains largely unknown.

METHODS

Core and accessory clock gene expression in different gastrointestinal (GI) tissues were determined by qPCR in two different models of circadian disruption - mice with Bmal1 deficiency in the circadian pacemaker, the suprachiasmatic nucleus (Bmal1^SCNfl/-), and wild-type mice exposed to simulated shift work (SSW). Body composition and energy balance were evaluated by nuclear magnetic resonance (NMR), bomb calorimetry, food intake and running-wheel activity. Intestinal permeability was measured in an Ussing chamber. Microbiota composition and functionality were evaluated by 16S rRNA gene amplicon sequencing, PICRUST2.0 analysis and targeted metabolomics. Finally, microbiota transfer was conducted to evaluate the functional impact of SSW-associated microbiota on the host's physiology.

RESULTS

Both chronodisruption models show desynchronization within and between peripheral clocks in GI tissues and reduced microbial rhythmicity, in particular in taxa involved in short-chain fatty acid (SCFA) fermentation and lipid metabolism. In Bmal1SCNfl/- mice, loss of rhythmicity in microbial functioning associates with previously shown increased body weight, dysfunctional glucose homeostasis and adiposity. Similarly, we observe an increase in body weight in SSW mice. Germ-free colonization experiments with SSW-associated microbiota mechanistically link body weight gain to microbial changes. Moreover, alterations in expression of peripheral clock genes as well as clock-controlled genes (CCGs) relevant for metabolic functioning of the host were observed in recipients, indicating a bidirectional relationship between microbiota rhythmicity and peripheral clock regulation.

CONCLUSIONS

Collectively, our data suggest that loss of rhythmicity in bacteria taxa and their products, which likely originates in desynchronization of intestinal clocks, promotes metabolic abnormalities during shift work.

Deficiency of the circadian clock gene Rev-erbα induces mood disorder-like behaviours and dysregulation of the serotonergic system in mice

Mood disorders such as depression, anxiety, and bipolar disorder are highly associated with disrupted daily rhythms of activity, which are often observed in shift work and sleep disturbance in humans. Recent studies have proposed the REV-ERBα protein as a key circadian nuclear receptor that links behavioural rhythms to mood regulation. However, how the Rev-erbα gene participates in the regulation of mood remains poorly understood. Here, we show that the regulation of the serotonergic (5-HTergic) system, which plays a central role in stress-induced mood behaviours, is markedly disrupted in Rev-erbα^-/- mice. Rev-erbα^-/- mice exhibit both negative and positive behavioural phenotypes, including anxiety-like and mania-like behaviours, when subjected to a stressful environment. Importantly, Rev-erbα^-/- mice show a significant decrease in the expression of a gene that encodes the rate-limiting enzyme of serotonin (5-HT) synthesis in the raphe nuclei (RN). In addition, 5-HT levels in Rev-erbα^-/- mice are significantly reduced in the prefrontal cortex, which receives strong inputs from the RN and controls stress-related behaviours. Our findings indicate that Rev-erbα plays an important role in controlling the 5-HTergic system and thus regulates mood and behaviour.

Circadian clock controls rhythms in ketogenesis by interfering with PPARα transcriptional network

Ketone bodies are energy-rich metabolites and signaling molecules whose production is mainly regulated by diet. Caloric restriction (CR) is a dietary intervention that improves metabolism and extends longevity across the taxa. We found that CR induced high-amplitude daily rhythms in blood ketone bodies (beta-hydroxybutyrate [βOHB]) that correlated with liver βOHB level. Time-restricted feeding, another periodic fasting-based diet, also led to rhythmic βOHB but with reduced amplitude. CR induced strong circadian rhythms in the expression of fatty acid oxidation and ketogenesis genes in the liver. The transcriptional factor peroxisome-proliferator-activated-receptor α (PPARα) and its transcriptional target hepatokine fibroblast growth factor 21 (FGF21) are primary regulators of ketogenesis. Fgf21 expression and the PPARα transcriptional network became highly rhythmic in the CR liver, which implicated the involvement of the circadian clock. Mechanistically, the circadian clock proteins CLOCK, BMAL1, and cryptochromes (CRYs) interfered with PPARα transcriptional activity. Daily rhythms in the blood βOHB level and in the expression of PPARα target genes were significantly impaired in circadian clock-deficient Cry1,2^-/- mice. These data suggest that blood βOHB level is tightly controlled and that the circadian clock is a regulator of diet-induced ketogenesis.

Fitness consequences of chronic exposure to different light pollution wavelengths in nocturnal and diurnal rodents

Use of artificial at night (ALAN) exposes the world to continuously increasing levels and distribution of light pollution. Our understanding of the adverse effects of ALAN is based mostly on observational or laboratory studies, and its effects are probably underestimated. Demonstration of direct experimental fitness consequences of ALAN on mammals is missing. We studied the effects of chronic light pollution at different wavelengths on fitness and glucocorticoid hormone levels under semi-natural conditions in two closely related species: the nocturnal common spiny mouse (Acomys cahirinus) and the diurnal golden spiny mouse (Acomys russatus). Our results clearly demonstrate the adverse effects of ALAN exposure on the fitness of both nocturnal and diurnal species, manifested by changes in cortisol levels and reproductive timing, reduced reproductive output and reduced survival, which differed between species and wavelengths. In A. russatus exposure to blue ALAN had the strongest effect on fitness, followed by white and yellow ALAN exposure. In A. cahirinus the results are more complex and suggest it suffered from the combined effects of ALAN and competition. Our research shows that light pollution presents a real threat to both nocturnal and diurnal species, affecting the species fitness directly and through interspecific interactions. Worryingly, these effects are probably not limited to spiny mice. The clear adverse effects we documented, as well as the differences between wave lengths, contribute to our ability to present science-based recommendations to decision makers regarding the use of artificial light at night. Such information and guidelines are highly important nowadays when lighting systems are being replaced to promote energy efficiency.

Molecular Derangements and the Diagnosis of ACTH-Dependent Cushing's Syndrome

Endogenous Cushing's syndrome (CS) is associated with morbidities (diabetes, hypertension, clotting disorders) and shortens life because of infections, pulmonary thromboembolism, and cardiovascular disease. Its clinical presentation is immensely variable, and diagnosis and treatment are often delayed. Thus, there are many opportunities for basic and clinical research leading to better tests, faster diagnosis, and optimized medical treatments. This review focuses on CS caused by excessive adrenocorticotropin (ACTH) production. It describes current concepts of the regulation of ACTH synthesis and secretion by normal corticotropes and mechanisms by which dysregulation occurs in corticotrope (termed "Cushing's disease") and noncorticotrope (so-called ectopic) ACTH-producing tumors. ACTH causes adrenal gland synthesis and pulsatile release of cortisol; the excess ACTH in these forms of CS leads to the hypercortisolism of endogenous CS. Again, the differences between healthy individuals and those with CS are highlighted. The clinical presentations and their use in the interpretation of CS screening tests are described. The tests used for screening and differential diagnosis of CS are presented, along with their relationship to cortisol dynamics, pathophysiology, and negative glucocorticoid feedback regulation in the two forms of ACTH-dependent CS. Finally, several gaps in current understanding are highlighted in the hope of stimulating additional research into this challenging disorder.

Acute sleep deprivation disrupts emotion, cognition, inflammation, and cortisol in young healthy adults

Chronic sleep deprivation has been demonstrated to diminish cognitive performance, alter mood states, and concomitantly dysregulate inflammation and stress hormones. At present, however, there is little understanding of how an acute sleep deprivation may collectively affect these factors and alter functioning. The present study aimed to determine the extent to which 24-h of sleep deprivation influences inflammatory cytokines, stress hormones, cognitive processing across domains, and emotion states. To that end, 23 participants (mean age = 20.78 years, SD = 2.87) filled out clinical health questionnaires measured by the Pittsburgh Sleep Quality Index, Morningness Eveningness Questionnaire, and Center for Epidemiological Studies Depression Scale. Actigraph was worn for seven days across testing to record sleep duration. At each session participants underwent a series of measures, including saliva and blood samples for quantification of leptin, ghrelin, IL-1β, IL-6, CRP, and cortisol levels, they completed a cognitive battery using an iPad, and an emotion battery. We found that an acute sleep deprivation, limited to a 24 h period, increases negative emotion states such as anxiety, fatigue, confusion, and depression. In conjunction, sleep deprivation results in increased inflammation and decreased cortisol levels in the morning, that are accompanied by deficits in vigilance and impulsivity. Combined, these results suggest that individuals who undergo 24 h sleep deprivation will induce systemic alterations to inflammation and endocrine functioning, while concomitantly increasing negative emotions.

Circadian Regulation of Hormonal Timing and the Pathophysiology of Circadian Dysregulation

Circadian rhythms are endogenously generated, daily patterns of behavior and physiology that are essential for optimal health and disease prevention. Disruptions to circadian timing are associated with a host of maladies, including metabolic disease and obesity, diabetes, heart disease, cancer, and mental health disturbances. The circadian timing system is hierarchically organized, with a master circadian clock located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus and subordinate clocks throughout the CNS and periphery. The SCN receives light information via a direct retinal pathway, synchronizing the master clock to environmental time. At the cellular level, circadian rhythms are ubiquitous, with rhythms generated by interlocking, autoregulatory transcription-translation feedback loops. At the level of the SCN, tight cellular coupling maintains rhythms even in the absence of environmental input. The SCN, in turn, communicates timing information via the autonomic nervous system and hormonal signaling. This signaling couples individual cellular oscillators at the tissue level in extra-SCN brain loci and the periphery and synchronizes subordinate clocks to external time. In the modern world, circadian disruption is widespread due to limited exposure to sunlight during the day, exposure to artificial light at night, and widespread use of light-emitting electronic devices, likely contributing to an increase in the prevalence, and the progression, of a host of disease states. The present overview focuses on the circadian control of endocrine secretions, the significance of rhythms within key endocrine axes for typical, homeostatic functioning, and implications for health and disease when dysregulated. © 2022 American Physiological Society. Compr Physiol 12: 1-30, 2022.

Circadian rhythms and pancreas physiology: A review

Type 2 diabetes mellitus, obesity and metabolic syndrome are becoming more prevalent worldwide and will present an increasingly challenging burden on healthcare systems. These interlinked metabolic abnormalities predispose affected individuals to a plethora of complications and comorbidities. Furthermore, diabetes is estimated by the World Health Organization to have caused 1.5 million deaths in 2019, with this figure projected to rise in coming years. This highlights the need for further research into the management of metabolic diseases and their complications. Studies on circadian rhythms, referring to physiological and behavioral changes which repeat approximately every 24 hours, may provide important insight into managing metabolic disease. Epidemiological studies show that populations who are at risk of circadian disruption such as night shift workers and regular long-haul flyers are also at an elevated risk of metabolic abnormalities such as insulin resistance and obesity. Aberrant expression of circadian genes appears to contribute to the dysregulation of metabolic functions such as insulin secretion, glucose homeostasis and energy expenditure. The potential clinical implications of these findings have been highlighted in animal studies and pilot studies in humans giving rise to the development of circadian interventions strategies including chronotherapy (time-specific therapy), time-restricted feeding, and circadian molecule stabilizers/analogues. Research into these areas will provide insights into the future of circadian medicine in metabolic diseases. In this review, we discuss the physiology of metabolism and the role of circadian timing in regulating these metabolic functions. Also, we review the clinical aspects of circadian physiology and the impact that ongoing and future research may have on the management of metabolic disease.

Adiponectin regulates the circadian rhythm of glucose and lipid metabolism

Adiponectin is a cytokine secreted from adipocytes and regulates metabolism. Although serum adiponectin levels show diurnal variations, it is not clear if the effects of adiponectin are time-dependent. Therefore, this study conducted locomotor activity analyses and various metabolic studies using the adiponectin knockout (APN (-/-)) and the APN (+/+) mice to understand whether adiponectin regulates the circadian rhythm of glucose and lipid metabolism. We observed that the adiponectin gene deficiency does not affect the rhythmicity of core circadian clock genes expression in several peripheral tissues. In contrast, the adiponectin gene deficiency alters the circadian rhythms of liver and serum lipid levels and results in the loss of the time dependency of very-low-density lipoprotein-triglyceride secretion from the liver. In addition, the whole-body glucose tolerance of the APN (-/-) mice was normal at CT10 but reduced at CT22, compared to the APN (+/+) mice. The decreased glucose tolerance at CT22 was associated with insulin hyposecretion in vivo. In contrast, the gluconeogenesis activity was higher in the APN (-/-) mice than in the APN (+/+) mice throughout the day. These results indicate that adiponectin regulates part of the circadian rhythm of metabolism in the liver.

Circadian regulation of digestive and metabolic tissues

The circadian clock is a self-sustained molecular timekeeper that drives 24-h (circadian) rhythms in animals. The clock governs important aspects of behavior and physiology including wake/sleep activity cycles that regulate the activity of metabolic and digestive systems. Light/dark cycles (photoperiod) and cycles in the time of feeding synchronize the circadian clock to the surrounding environment, providing an anticipatory benefit that promotes digestive health. The availability of animal models targeting the genetic components of the circadian clock has made it possible to investigate the circadian clock's role in cellular functions. Circadian clock genes have been shown to regulate the physiological function of hepatocytes, gastrointestinal cells, and adipocytes; disruption of the circadian clock leads to the exacerbation of liver diseases and liver cancer, inflammatory bowel disease and colorectal cancer, and obesity. Previous findings provide strong evidence that the circadian clock plays an integral role in digestive/metabolic disease pathogenesis, hence, the circadian clock is a necessary component in metabolic and digestive health and homeostasis. Circadian rhythms and circadian clock function provide an opportunity to improve the prevention and treatment of digestive and metabolic diseases by aligning digestive system tissue with the 24-h day.

Impact of circadian time of dosing on cardiomyocyte-autonomous effects of glucocorticoids

OBJECTIVE

Mitochondrial capacity is critical to adapt the high energy demand of the heart to circadian oscillations and diseased states. Glucocorticoids regulate the circadian cycle of energy metabolism, but little is known about how circadian timing of exogenous glucocorticoid dosing directly regulates heart metabolism through cardiomyocyte-autonomous mechanisms. While chronic once-daily intake of glucocorticoids promotes metabolic stress and heart failure, we recently discovered that intermittent once-weekly dosing of exogenous glucocorticoids promoted muscle metabolism in normal and obese skeletal muscle. However, the effects of glucocorticoid intermittence on heart metabolism and heart failure remain unknown. Here we investigated the extent to which circadian time of dosing regulates the effects of the glucocorticoid prednisone in heart metabolism and function in conditions of single pulse or chronic intermittent dosing.

METHODS AND RESULTS

In WT mice, we found that prednisone improved cardiac content of NAD+ and ATP with light-phase dosing (ZT0), while the effects were blocked by dark-phase dosing (ZT12). The drug effects on mitochondrial function were cardiomyocyte-autonomous, as shown by inducible cardiomyocyte-restricted glucocorticoid receptor (GR) ablation, and depended on an intact cardiomyocyte clock, as shown by inducible cardiomyocyte-restricted ablation of Brain and Muscle ARNT-like 1 (BMAL1). Conjugating time-of-dosing with chronic intermittence, we found that once-weekly prednisone improved metabolism and function in heart after myocardial injury dependent on circadian time of intake, i.e. with light-phase but not dark-phase dosing.

CONCLUSIONS

Our study identifies cardiac-autonomous mechanisms through which circadian-specific intermittent dosing reconverts glucocorticoid drugs to metabolic boosters for the heart.

Association of social jetlag with gestational diabetes: Qazvin Maternal and Neonatal Metabolic Study

The association of social jetlag (SJL), as a quantitative measure of circadian misalignment, with insulin resistance and metabolic syndrome has been reported. The present study was designed to investigate the association of SJL with gestational diabetes mellitus (GDM). Pregnant women with gestational age ≤14 weeks were enrolled in this longitudinal study. The participants with pre-GDM, shift workers and those who used alarms for waking up on free days were excluded from the study. SJL as well as behavioral and psychological parameters were evaluated at enrollment. The participants were categorized based on each 1-h increment of SJL. The association of SJL with the occurrence of GDM in the late second trimester was evaluated using univariate and multivariate methods. In total, 821 pregnant women entered the study, and after omitting individuals with excluding criteria, analyses were performed on 557 participants. The frequencies of SJL < 1 h,1 ≤ SJL < 2 h and SJL ≥ 2 h were 44.7%, 37.2% and 18.1%, respectively. Average sleep duration was higher in SJL < 1 h compared with the two other groups (p < 0.001). During follow-up, 90 (16.1%) women with GDM were identified. SJL ≥ 2 h was associated with a 4.4-5.6 times higher risk of GDM in different models of adjustment (p < 0.05). Pregnant women with high SJL are at a higher risk of GDM. Further studies for evaluating the mechanisms by which SJL affects GDM are warranted.

Mutual Shaping of Circadian Body-Wide Synchronization by the Suprachiasmatic Nucleus and Circulating Steroids

Background

Steroids are lipid hormones that reach bodily tissues through the systemic circulation, and play a major role in reproduction, metabolism, and homeostasis. All of these functions and steroids themselves are under the regulation of the circadian timing system (CTS) and its cellular/molecular underpinnings. In health, cells throughout the body coordinate their daily activities to optimize responses to signals from the CTS and steroids. Misalignment of responses to these signals produces dysfunction and underlies many pathologies.

Questions Addressed

To explore relationships between the CTS and circulating steroids, we examine the brain clock located in the suprachiasmatic nucleus (SCN), the daily fluctuations in plasma steroids, the mechanisms producing regularly recurring fluctuations, and the actions of steroids on their receptors within the SCN. The goal is to understand the relationship between temporal control of steroid secretion and how rhythmic changes in steroids impact the SCN, which in turn modulate behavior and physiology.

Evidence Surveyed

The CTS is a multi-level organization producing recurrent feedback loops that operate on several time scales. We review the evidence showing that the CTS modulates the timing of secretions from the level of the hypothalamus to the steroidogenic gonadal and adrenal glands, and at specific sites within steroidogenic pathways. The SCN determines the timing of steroid hormones that then act on their cognate receptors within the brain clock. In addition, some compartments of the body-wide CTS are impacted by signals derived from food, stress, exercise etc. These in turn act on steroidogenesis to either align or misalign CTS oscillators. Finally this review provides a comprehensive exploration of the broad contribution of steroid receptors in the SCN and how these receptors in turn impact peripheral responses.

Conclusion

The hypothesis emerging from the recognition of steroid receptors in the SCN is that mutual shaping of responses occurs between the brain clock and fluctuating plasma steroid levels.

Misaligned feeding schedule elicits divergent circadian reorganizations in endo- and exocrine pancreas clocks

Misaligned feeding may lead to pancreatic insufficiency, however, whether and how it affects circadian clock in the exocrine pancreas is not known. We exposed rats to a reversed restricted feeding regimen (rRF) for 10 or 20 days and analyzed locomotor activity, daily profiles of hormone levels (insulin, glucagon, and corticosterone) in plasma, and clock gene expression in the liver and endocrine and exocrine pancreas. In addition, we monitored responses of the exocrine pancreatic clock in organotypic explants of mPer2Luc mice in real time to acetylcholine, insulin, and glucocorticoids. rRF phase-reversed the clock in the endocrine pancreas, similar to the clock in the liver, but completely abolished clock gene rhythmicity and significantly downregulated the expression of Cpb1 and Cel in the exocrine pancreas. rRF desynchronized the rhythms of plasma insulin and corticosterone. Daily profiles of their receptor expression differed in the two parts of the pancreas and responded differently to rRF. Additionally, the pancreatic exocrine clock responded differently to treatments with insulin and the glucocorticoid analog dexamethasone in vitro. Mathematical simulation confirmed that the long-term misalignment between these two hormonal signals, as occurred under rRF, may lead to dampening of the exocrine pancreatic clock. In summary, our data suggest that misaligned meals impair the clock in the exocrine part of the pancreas by uncoupling insulin and corticosterone rhythms. These findings suggest a new mechanism by which adverse dietary habits, often associated with shift work in humans, may impair the clock in the exocrine pancreas and potentially contribute to exocrine pancreatic insufficiency.