Deletion of the mammalian circadian clock gene BMAL1/Mop3 alters baseline sleep architecture and the response to sleep deprivation

Causal Associations Between Sleep Traits and Low Grip Strength: A Bidirectional Mendelian Randomization Study

Background

Sleep disorders and low grip strength often co-occur clinically and are geriatric symptoms that cause significant socioeconomic burden. Previous observational studies have found an association between sleep behaviors and grip strength, but the causal relationship remains unclear.

Purpose

With the Mendelian randomization (MR) approach, the study aimed to determine the causal association between sleep traits (sleep duration, insomnia, daytime napping, sleep-wake disorders, chronotype) and low grip strength.

Methods

The study used genetic variants from the genome-wide association study (GWAS) archived in UK Biobank and FinnGen. We assessed the potential causal relationship between sleep behaviors and grip strength using inverse variance weighting (IVW), weighted median (WM), and MR-Egger. Additionally, we performed sensitivity analyses using Cochran's Q test, MR Egger Intercept test, funnel plots, and leave-one-out method.

Results

We found that sleep duration is causally negatively associated with low grip strength (OR = 0.618, 95% CI = 0.424-0.900, P = 0.012). Sleep-wake disorders have a positive association with low grip strength (OR = 1.018, 95% CI = 1.002-1.034, P = 0.029). Reversely, high low grip strength risk was causally associated with increased daytime napping (OR = 1.018, 95% CI = 1.004-1.032, P = 0.011).

Conclusion

The study revealed causal associations between sleep duration, sleep-wake disorders, and low grip strength. Understanding their relationship helps in early clinical intervention to improve the life quality of the elderly.

Modulation of sleep/wake patterns by gephyrin phosphorylation status

Sleep/wake cycles intricately shape physiological activities including cognitive brain functions, yet the precise molecular orchestrators of sleep remain elusive. Notably, the clinical impact of benzodiazepine drugs underscores the pivotal role of GABAergic neurotransmission in sleep regulation. However, the specific contributions of distinct GABAA receptor subtypes and their principal scaffolding protein, gephyrin, in sleep dynamics remain unclear. The evolving role of synaptic phospho-proteome alterations at excitatory and inhibitory synapses suggests a potential avenue for modulating gephyrin and, consequently, GABAARs for sleep through on-demand kinase recruitment. Our study unveils the distinctive roles of two prevalent GABAA receptor subtypes, α1- and α2-GABAARs, in influencing sleep duration and electrical sleep activity. Notably, the absence of α1-GABAARs emerges as central in sleep regulation, manifesting significant alterations in both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep during dark or active phases, accompanied by altered electroencephalogram (EEG) patterns across various frequencies. Gephyrin proteomics analysis reveals sleep/wake-dependent interactions with a repertoire of known and novel kinases. Crucially, we identify the regulation of gephyrin interaction with ERK1/2, and phosphorylations at serines 268 and 270 are dictated by sleep/wake cycles. Employing AAV-eGFP-gephyrin or its phospho-null variant (S268A/S270A), we disrupt sleep either globally or locally to demonstrate gephyrin phosphorylation as a sleep regulator. In summary, our findings support the local cortical sleep hypothesis and we unveil a molecular mechanism operating at GABAergic synapses, providing critical insights into the intricate regulation of sleep.

Insomnia-related rodent models in drug discovery

Despite the widespread prevalence and important medical impact of insomnia, effective agents with few side effects are lacking in clinics. This is most likely due to relatively poor understanding of the etiology and pathophysiology of insomnia, and the lack of appropriate animal models for screening new compounds. As the main homeostatic, circadian, and neurochemical modulations of sleep remain essentially similar between humans and rodents, rodent models are often used to elucidate the mechanisms of insomnia and to develop novel therapeutic targets. In this article, we focus on several rodent models of insomnia induced by stress, diseases, drugs, disruption of the circadian clock, and other means such as genetic manipulation of specific neuronal activity, respectively, which could be used to screen for novel hypnotics. Moreover, important advantages and constraints of some animal models are discussed. Finally, this review highlights that the rodent models of insomnia may play a crucial role in novel drug development to optimize the management of insomnia.

The Genetics of Human Sleep and Sleep Disorders

Healthy sleep is vital for humans to achieve optimal health and longevity. Poor sleep and sleep disorders are strongly associated with increased morbidity and mortality. However, the importance of good sleep continues to be underrecognized. Mechanisms regulating sleep and its functions in humans remain mostly unclear even after decades of dedicated research. Advancements in gene sequencing techniques and computational methodologies have paved the way for various genetic analysis approaches, which have provided some insights into human sleep genetics. This review summarizes our current knowledge of the genetic basis underlying human sleep traits and sleep disorders. We also highlight the use of animal models to validate genetic findings from human sleep studies and discuss potential molecular mechanisms and signaling pathways involved in the regulation of human sleep.

High-frequency neural activity dysregulation is associated with sleep and psychiatric disorders in BMAL1-deficient animal models

Sleep disturbance led by BMAL1-deficiency has been recognized both in rodent and non-human primate models. Yet it remained unclear how their diurnal brain oscillations were affected upon BMAL1 ablation and what caused the discrepancy in the quantity of sleep between the two species. Here, we investigated diurnal electroencephalographs of BMAL1-deficient mice and cynomolgus monkeys at young adult age and uncovered a shared defect of dysregulated high-frequency oscillations by Kullback-Leibler divergence analysis. We found beta and gamma oscillations were significantly disturbed in a day versus night manner in BMAL1-deficient monkeys, while in mice the beta band difference was less evident. Notably, the dysregulation of beta oscillations was particularly associated with psychiatric behaviors in BMAL1-deficient monkeys, including the occurrence of self-injuring and delusion-like actions. As such psychiatric phenotypes were challenging to uncover in rodent models, our results offered a unique method to study the correlation between circadian clock dysregulation and psychiatric disorders.

Adaptive changes in BMAL2 with increased locomotion associated with the evolution of unihemispheric slow-wave sleep in mammals

Marine mammals, especially cetaceans, have evolved a very special form of sleep characterized by unihemispheric slow-wave sleep (USWS) and a negligible amount or complete absence of rapid-eye-movement sleep; however, the underlying genetic mechanisms remain unclear. Here, we detected unique, significant selection signatures in basic helix-loop-helix ARNT like 2 (BMAL2; also called ARNTL2), a key circadian regulator, in marine mammal lineages, and identified two nonsynonymous amino acid substitutions (K204E and K346Q) in the important PER-ARNT-SIM domain of cetacean BMAL2 via sequence comparison with other mammals. In vitro assays revealed that these cetacean-specific mutations specifically enhanced the response to E-box-like enhancer and consequently promoted the transcriptional activation of PER2, which is closely linked to sleep regulation. The increased PER2 expression, which was further confirmed both in vitro and in vivo, is beneficial for allowing cetaceans to maintain continuous movement and alertness during sleep. Concordantly, the locomotor activities of zebrafish overexpressing the cetacean-specific mutant bmal2 were significantly higher than the zebrafish overexpressing the wild-type gene. Subsequently, transcriptome analyses revealed that cetacean-specific mutations caused the upregulation of arousal-related genes and the downregulation of several sleep-promoting genes, which is consistent with the need to maintain hemispheric arousal during USWS. Our findings suggest a potential close relationship between adaptive changes in BMAL2 and the remarkable adaptation of USWS and may provide novel insights into the genetic basis of the evolution of animal sleep.

Excessive fat expenditure in MCT-induced heart failure rats is associated with BMAL1/REV-ERBα circadian rhythmic loop disruption

Fat loss predicts adverse outcomes in advanced heart failure (HF). Disrupted circadian clocks are a primary cause of lipid metabolic issues, but it's unclear if this disruption affects fat expenditure in HF. To address this issue, we investigated the effects of disruption of the BMAL1/REV-ERBα circadian rhythmic loop on adipose tissue metabolism in HF.50 Wistar rats were initially divided into control (n = 10) and model (n = 40) groups. The model rats were induced with HF via monocrotaline (MCT) injections, while the control group received equivalent solvent injections. After establishing the HF model, the model group was further subdivided into four groups: normal rhythm (LD), inverted rhythm (DL), lentivirus vector carrying Bmal1 short hairpin RNA (LV-Bmal1 shRNA), and empty lentivirus vector control (LV-Control shRNA) groups, each with 10 rats. The DL subgroup was exposed to a reversed light-dark cycle of 8 h: 16 h (dark: light), while the rest adhered to normal light-dark conditions (light: dark 12 h: 12 h). Histological analyses were conducted using H&E, Oil Red O, and Picrosirius red stains to examine adipose and liver tissues. Immunohistochemical staining, RT-qPCR, and Western blotting were performed to detect markers of lipolysis, lipogenesis, and beiging of white adipose tissue (WAT), while thermogenesis indicators were detected in brown adipose tissue (BAT). The LD group rats exhibited decreased levels of BMAL1 protein, increased levels of REV-ERBα protein, and disrupted circadian circuits in adipose tissue compared to controls. Additionally, HF rats showed reduced adipose mass and increased ectopic lipid deposition, along with smaller adipocytes containing lower lipid content and fibrotic adipose tissue. In the LD group WAT, expression of ATGL, HSL, PKA, and p-PKA proteins increased, alongside elevated mRNA levels of lipase genes (Hsl, Atgl, Peripilin) and FFA β-oxidation genes (Cpt1, acyl-CoA). Conversely, lipogenic gene expression (Scd1, Fas, Mgat, Dgat2) decreased, while beige adipocyte markers (Cd137, Tbx-1, Ucp-1, Zic-1) and UCP-1 protein expression increased. In BAT, HF rats exhibited elevated levels of PKA, p-PKA, and UCP-1 proteins, along with increased expression of thermogenic genes (Ucp-1, Pparγ, Pgc-1α) and lipid transportation genes (Cd36, Fatp-1, Cpt-1). Plasma NT-proBNP levels were higher in LD rats, accompanied by elevated NE and IL-6 levels in adipose tissue. Remarkably, morphologically, the adipocytes in the DL and LV-Bmal1 shRNA groups showed reduced size and lower lipid content, while lipid deposition in the liver was more pronounced in these groups compared to the LD group. At the gene/protein level, the BMAL1/REV-ERBα circadian loop exhibited severe disruption in LV-Bmal1 shRNA rats compared to LD rats. Additionally, there was increased expression of lipase genes, FFA β oxidation genes, and beige adipocyte markers in WAT, as well as higher expression of thermogenic genes and lipid transportation genes in BAT. Furthermore, plasma NT-proBNP levels and adipose tissue levels of NE and IL-6 were elevated in LV-Bmal1 shRNA rats compared with LD rats. The present study demonstrates that disruption of the BMAL1/REV-ERBα circadian rhythmic loop is associated with fat expenditure in HF. This result suggests that restoring circadian rhythms in adipose tissue may help counteract disorders of adipose metabolism and reduce fat loss in HF.

Interorgan rhythmicity as a feature of healthful metabolism

The finding that animals with circadian gene mutations exhibit diet-induced obesity and metabolic syndrome with hypoinsulinemia revealed a distinct role for the clock in the brain and peripheral tissues. Obesogenic diets disrupt rhythmic sleep/wake patterns, feeding behavior, and transcriptional networks, showing that metabolic signals reciprocally control the clock. Providing access to high-fat diet only during the sleep phase (light period) in mice accelerates weight gain, whereas isocaloric time-restricted feeding during the active period enhances energy expenditure due to circadian induction of adipose thermogenesis. This perspective focuses on advances and unanswered questions in understanding the interorgan circadian control of healthful metabolism.

A two-process model of Drosophila sleep reveals an inter-dependence between circadian clock speed and the rate of sleep pressure decay

Sleep is controlled by two processes-a circadian clock that regulates its timing and a homeostat that regulates the drive to sleep. Drosophila has been an insightful model for understanding both processes. For four decades, Borbély and Daan's two-process model has provided a powerful framework for understanding sleep regulation. However, the field of fly sleep has not employed such a model as a framework for the investigation of sleep. To this end, we have adapted the two-process model to the fly and established its utility by showing that it can provide empirically testable predictions regarding the circadian and homeostatic control of fly sleep. We show that the ultradian rhythms previously reported for loss-of-function clock mutants in the fly are robustly detectable and a predictable consequence of a functional sleep homeostat in the absence of a functioning circadian system. We find that a model in which the circadian clock speed and homeostatic rates act without influencing each other provides imprecise predictions regarding how clock speed influences the strength of sleep rhythms and the amount of daily sleep. We also find that quantitatively good fits between empirical values and model predictions were achieved only when clock speeds were positively correlated with rates of decay of sleep pressure. Our results indicate that longer sleep bouts better reflect the homeostatic process than the current definition of sleep as any inactivity lasting 5 minutes or more. This two-process model represents a powerful framework for work on the molecular and physiological regulation of fly sleep.

Childhood sleep: assessments, risk factors, and potential mechanisms

BACKGROUND

Sleep problem is a highly prevalent health issue among pediatric populations across the world. In this review, we aimed to identify risk factors contributing to sleep deficiency and poor sleep hygiene in children. Potential biological, psychosocial, and environmental mechanisms as well as research gaps in the literature are also discussed.

DATA SOURCES

A comprehensive search for relevant English language full-text, peer-reviewed publications was performed focusing on pediatric sleep studies from prenatal to childhood and adolescence in a variety of indexes in PubMed, SCOPUS, and Psych Info. Both relevant data based and systematic reviews are included.

RESULTS

This paper summarizes many risk factors for childhood sleep problems, including biological (e.g., genetics, gender, age and puberty, prenatal factors, postnatal factors); nutritional (e.g., macronutrients, micronutrients, omega-3 fatty acids, obesity); environmental (e.g., heavy metals, noise, light, air pollution); interpersonal (e.g., family, exposure to violence, screen media use, physical injury); and community/socioeconomic variables (e.g., racial/ethnicity and cultural factors, neighborhood conditions and socioeconomic status, school factors, public health disasters/emergencies), to better understand the development of sleep problems in children.

CONCLUSIONS

Poor childhood sleep is a multifactorial issue affected by a wide range of prenatal and early-life biological, environmental, and psychosocial risk factors and contributors. A better understanding of these risk factors and their mechanisms is an important first step to develop future research and prevention programs focusing on pediatric sleep problems.

Molecular crosstalk between circadian clock and NLRP3 inflammasome signaling in Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Research has recently found that both animal models and patients with PD have circadian dysfunction, accompanied by abnormal expression of circadian genes and proteins, which implies that the circadian clock plays a crucial role in PD etiopathogenesis. In addition, a strong relationship between NLRP3 inflammasome signaling and PD has been observed. Meanwhile, the activation of the NLRP3 inflammasome is highly relevant to dysfunctions of the molecular clock. Therefore, alleviating the neuroinflammation caused by NLRP3 inflammasome signaling by adjusting the abnormal molecular clock may be a potential strategy for preventing and treating PD. In this article, we have reviewed the potential or direct relationship between abnormalities of the circadian clock and NLRP3 inflammasome signaling in PD.

Sleep and circadian rhythmicity as entangled processes serving homeostasis

Sleep is considered essential for the brain and body. A predominant concept is that sleep is regulated by circadian rhythmicity and sleep homeostasis, processes that were posited to be functionally and mechanistically separate. Here we review and re-evaluate this concept and its assumptions using findings from recent human and rodent studies. Alterations in genes that are central to circadian rhythmicity affect not only sleep timing but also putative markers of sleep homeostasis such as electroencephalogram slow-wave activity (SWA). Perturbations of sleep change the rhythmicity in the expression of core clock genes in tissues outside the central clock. The dynamics of recovery from sleep loss vary across sleep variables: SWA and immediate early genes show an early response, but the recovery of non-rapid eye movement and rapid eye movement sleep follows slower time courses. Changes in the expression of many genes in response to sleep perturbations outlast the effects on SWA and time spent asleep. These findings are difficult to reconcile with the notion that circadian- and sleep-wake-driven processes are mutually independent and that the dynamics of sleep homeostasis are reflected in a single variable. Further understanding of how both sleep and circadian rhythmicity contribute to the homeostasis of essential physiological variables may benefit from the assessment of multiple sleep and molecular variables over longer time scales.

Predicting neurodegeneration from sleep related biofluid changes

Sleep-wake disturbances are common in neurodegenerative diseases and may occur years before the clinical diagnosis, potentially either representing an early stage of the disease itself or acting as a pathophysiological driver. Therefore, discovering biomarkers that identify individuals with sleep-wake disturbances who are at risk of developing neurodegenerative diseases will allow early diagnosis and intervention. Given the association between sleep and neurodegeneration, the most frequently analyzed fluid biomarkers in people with sleep-wake disturbances to date include those directly associated with neurodegeneration itself, such as neurofilament light chain, phosphorylated tau, amyloid-beta and alpha-synuclein. Abnormalities in these biomarkers in patients with sleep-wake disturbances are considered as evidence of an underlying neurodegenerative process. Levels of hormonal sleep-related biomarkers such as melatonin, cortisol and orexin are often abnormal in patients with clinical neurodegenerative diseases, but their relationships with the more standard neurodegenerative biomarkers remain unclear. Similarly, it is unclear whether other chronobiological/circadian biomarkers, such as disrupted clock gene expression, are causal factors or a consequence of neurodegeneration. Current data would suggest that a combination of fluid biomarkers may identify sleep-wake disturbances that are most predictive for the risk of developing neurodegenerative disease with more optimal sensitivity and specificity.

BMAL1 loss in oligodendroglia contributes to abnormal myelination and sleep

Myelination depends on the maintenance of oligodendrocytes that arise from oligodendrocyte precursor cells (OPCs). We show that OPC-specific proliferation, morphology, and BMAL1 are time-of-day dependent. Knockout of Bmal1 in mouse OPCs during development disrupts the expression of genes associated with circadian rhythms, proliferation, density, morphology, and migration, leading to changes in OPC dynamics in a spatiotemporal manner. Furthermore, these deficits translate into thinner myelin, dysregulated cognitive and motor functions, and sleep fragmentation. OPC-specific Bmal1 loss in adulthood does not alter OPC density at baseline but impairs the remyelination of a demyelinated lesion driven by changes in OPC morphology and migration. Lastly, we show that sleep fragmentation is associated with increased prevalence of the demyelinating disorder multiple sclerosis (MS), suggesting a link between MS and sleep that requires further investigation. These findings have broad mechanistic and therapeutic implications for brain disorders that include both myelin and sleep phenotypes.

Interaction of Bmal1 and eIF2α/ATF4 pathway was involved in Shuxie compound alleviation of circadian rhythm disturbance-induced hepatic endoplasmic reticulum stress

ETHNOPHARMACOLOGICAL RELEVANCE

Shuxie Compound (SX) combines the composition and efficacy of Suanzaoren decoction and Huanglian Wendan decoction. It can soothe the liver, regulate the qi, nourish the blood and calm the mind. It is used in the clinical treatment of sleep disorder with liver stagnation. Modern studies have proved that circadian rhythm disorder (CRD) can cause sleep deprivation and liver damage, which can be effectively ameliorated by traditional Chinese medicine to soothe the liver stagnation. However, the mechanism of SX is unclear.

AIM OF THE STUDY

This study was designed to demonstrate the impact of SX on CRD in vivo, and confirm the molecular mechanisms of SX in vitro.

MATERIALS AND METHODS

The quality of SX and drug-containing serum was controlled by UPLC-Q-TOF/MS, which were used in vivo and in vitro experiments, respectively. In vivo, a light deprivation mouse model was used. In vitro, a stable knockdown Bmal1 cell line was used to explore SX mechanism.

RESULTS

Low-dose SX (SXL) could restore (1) circadian activity pattern, (2) 24-h basal metabolic pattern, (3) liver injury, and (4) Endoplasmic reticulum (ER) stress in CRD mice. CRD decreased the liver Bmal1 protein at ZT15, which was reversed by SXL treatment. Besides, SXL decreased the mRNA expression of Grp78/ATF4/Chop and the protein expression of ATF4/Chop at ZT11. In vitro experiments, SX reduced the protein expression of thapsigargin (tg)-induced p-eIF2α/ATF4 pathway and increase the viability of AML12 cells by increasing the expression of Bmal1 protein.

CONCLUSIONS

SXL relieved CRD-induced ER stress and improve cell viability by up-regulating the expression of Bmal1 protein in the liver and then inhibiting the protein expression of p-eIF2α/ATF4.

FABP7: a glial integrator of sleep, circadian rhythms, plasticity, and metabolic function

Sleep and circadian rhythms are observed broadly throughout animal phyla and influence neural plasticity and cognitive function. However, the few phylogenetically conserved cellular and molecular pathways that are implicated in these processes are largely focused on neuronal cells. Research on these topics has traditionally segregated sleep homeostatic behavior from circadian rest-activity rhythms. Here we posit an alternative perspective, whereby mechanisms underlying the integration of sleep and circadian rhythms that affect behavioral state, plasticity, and cognition reside within glial cells. The brain-type fatty acid binding protein, FABP7, is part of a larger family of lipid chaperone proteins that regulate the subcellular trafficking of fatty acids for a wide range of cellular functions, including gene expression, growth, survival, inflammation, and metabolism. FABP7 is enriched in glial cells of the central nervous system and has been shown to be a clock-controlled gene implicated in sleep/wake regulation and cognitive processing. FABP7 is known to affect gene transcription, cellular outgrowth, and its subcellular localization in the fine perisynaptic astrocytic processes (PAPs) varies based on time-of-day. Future studies determining the effects of FABP7 on behavioral state- and circadian-dependent plasticity and cognitive processes, in addition to functional consequences on cellular and molecular mechanisms related to neural-glial interactions, lipid storage, and blood brain barrier integrity will be important for our knowledge of basic sleep function. Given the comorbidity of sleep disturbance with neurological disorders, these studies will also be important for our understanding of the etiology and pathophysiology of how these diseases affect or are affected by sleep.

Peripheral clock disruption and metabolic disease: moving beyond the anatomy to a functional approach

Sleep and circadian disruption are associated with an increased risk of metabolic disease, including obesity and diabetes. Mounting evidence indicates that misaligned and/or non-functional clock proteins in peripheral tissues critically contribute to the presentation of metabolic disease. Many of the foundational studies which led to this conclusion have focused on specific tissues such as the adipose, pancreas, muscle, and liver. While these studies have greatly advanced the field, the use of anatomical markers to manipulate tissue-specific molecular clocks may not be representative of the circadian disruption that occurs within the clinical population. In this manuscript, we argue that investigators can gain a better understanding of the consequences of sleep and circadian disruption by targeting groups of cells with a functional relationship, even if those cells go beyond anatomical boundaries. This approach is especially important when considering metabolic outcomes which rely on endocrine signaling molecules, such as leptin, that have multiple sites of action. Through the review of several studies, as well as our own work, this article reframes peripheral clock disruption from a functional approach. We additionally present new evidence that disruption of the molecular clock within all cells expressing the leptin receptor affects leptin sensitivity in a time-dependent manner. Taken together, this perspective aims to provide new insight into the mechanisms leading to metabolic disease associated with circadian disruption and various sleep disorders.

Analysis of circadian rhythm components in EEG/EMG data of aged mice

Aging disrupts circadian clocks, as evidenced by a reduction in the amplitude of circadian rhythms. Because the circadian clock strongly influences sleep-wake behavior in mammals, age-related alterations in sleep-wake patterns may be attributable, at least partly, to functional changes in the circadian clock. However, the effect of aging on the circadian characteristics of sleep architecture has not been well assessed, as circadian behaviors are usually evaluated through long-term behavioral recording with wheel-running or infrared sensors. In this study, we examined age-related changes in circadian sleep-wake behavior using circadian components extracted from electroencephalography (EEG) and electromyography (EMG) data. EEG and EMG were recorded from 12 to 17-week-old and 78 to 83-week-old mice for 3 days under light/dark and constant dark conditions. We analyzed time-dependent changes in the duration of sleep. Rapid eye movement (REM) and non-REM (NREM) sleep significantly increased during the night phase in old mice, whereas no significant change was observed during the light phase. The circadian components were then extracted from the EEG data for each sleep-wake stage, revealing that the circadian rhythm in the power of delta waves during NREM sleep was attenuated and delayed in old mice. Furthermore, we used machine learning to evaluate the phase of the circadian rhythm, with EEG data serving as the input and the phase of the sleep-wake rhythm (environmental time) as the output. The results indicated that the output time for the old mice data tended to be delayed, specifically at night. These results indicate that the aging process significantly impacts the circadian rhythm in the EEG power spectrum despite the circadian rhythm in the amounts of sleep and wake attenuated but still remaining in old mice. Moreover, EEG/EMG analysis is useful not only for evaluating sleep-wake stages but also for circadian rhythms in the brain.

Deletion of the Circadian Clock Gene Per2 in the Whole Body, but Not in Neurons or Astroglia, Affects Sleep in Response to Sleep Deprivation

The sleep-wake cycle is a highly regulated behavior in which a circadian clock times sleep and waking, whereas a homeostatic process controls sleep need. Both the clock and the sleep homeostat interact, but to what extent they influence each other is not understood. There is evidence that clock genes, in particular Period2 (Per2), might be implicated in the sleep homeostatic process. Sleep regulation depends also on the proper functioning of neurons and astroglial cells, two cell-types in the brain that are metabolically dependent on each other. In order to investigate clock-driven contributions to sleep regulation we non-invasively measured sleep of mice that lack the Per2 gene either in astroglia, neurons, or all body cells. We observed that mice lacking Per2 in all body cells (Per2^Brdm and TPer2 animals) display earlier onset of sleep after sleep deprivation (SD), whereas neuronal and astroglial Per2 knock-out animals (NPer2 and GPer2, respectively) were normal in that respect. It appears that systemic (whole body) Per2 expression is important for physiological sleep architecture expressed by number and length of sleep bouts, whereas neuronal and astroglial Per2 weakly impacts night-time sleep amount. Our results suggest that Per2 contributes to the timing of the regulatory homeostatic sleep response by delaying sleep onset after SD and attenuating the early night rebound response.

Myeloid deficiency of the intrinsic clock protein BMAL1 accelerates cognitive aging by disrupting microglial synaptic pruning

Aging is associated with loss of circadian immune responses and circadian gene transcription in peripheral macrophages. Microglia, the resident macrophages of the brain, also show diurnal rhythmicity in regulating local immune responses and synaptic remodeling. To investigate the interaction between aging and microglial circadian rhythmicity, we examined mice deficient in the core clock transcription factor, BMAL1. Aging Cd11bcre;Bmallox/lox mice demonstrated accelerated cognitive decline in association with suppressed hippocampal long-term potentiation and increases in immature dendritic spines. C1q deposition at synapses and synaptic engulfment were significantly decreased in aging Bmal1-deficient microglia, suggesting that BMAL1 plays a role in regulating synaptic pruning in aging. In addition to accelerated age-associated hippocampal deficits, Cd11bcre;Bmallox/lox mice also showed deficits in the sleep-wake cycle with increased wakefulness across light and dark phases. These results highlight an essential role of microglial BMAL1 in maintenance of synapse homeostasis in the aging brain.

Many faces of sleep regulation: beyond the time of day and prior wake time

The two-process model of sleep regulation posits two main processes regulating sleep: the circadian process controlled by the circadian clock and the homeostatic process that depends on the history of sleep and wakefulness. The model has provided a dominant conceptual framework for sleep research since its publication ~ 40 years ago. The time of day and prior wake time are the primary factors affecting the circadian and homeostatic processes, respectively. However, it is critical to consider other factors influencing sleep. Since sleep is incompatible with other behaviors, it is affected by the need for essential behaviors such as eating, foraging, mating, caring for offspring, and avoiding predators. Sleep is also affected by sensory inputs, sickness, increased need for memory consolidation after learning, and other factors. Here, we review multiple factors influencing sleep and discuss recent insights into the mechanisms balancing competing needs.

ISX-9 potentiates CaMKIIδ-mediated BMAL1 activation to enhance circadian amplitude

Circadian dysregulation associates with numerous diseases including metabolic dysfunction, sleep disorder, depression and aging. Given that declined circadian amplitude is a trait commonly found with compromised health, interventions that design in precluding circadian amplitude from dampening will aid to mitigate complex, circadian-related diseases. Here we identify a neurogenic small molecule ISX-9 that is able to support persistent and higher amplitude of circadian oscillations. ISX-9 improves diurnal metabolic rhythms in middle-aged mice. Moreover, the ISX-9-treated mice show better sleep homeostasis with increased delta power during the day time and higher locomotive activity in the dark period. ISX-9 augments CaMKIIδ expression and increases BMAL1 activity via eliciting CaMKIIδ-mediated phosphorylation on BMAL1 residues S513/S515/S516, accordingly composes a positive feedback effect on enhancing circadian amplitude. CaMKIIδ-targeting, and the use of ISX-9 may serve as decent choices for treating circadian-related disorders.

Circadian programming of the ellipsoid body sleep homeostat in Drosophila

Homeostatic and circadian processes collaborate to appropriately time and consolidate sleep and wake. To understand how these processes are integrated, we scheduled brief sleep deprivation at different times of day in Drosophila and find elevated morning rebound compared to evening. These effects depend on discrete morning and evening clock neurons, independent of their roles in circadian locomotor activity. In the R5 ellipsoid body sleep homeostat, we identified elevated morning expression of activity dependent and presynaptic gene expression as well as the presynaptic protein BRUCHPILOT consistent with regulation by clock circuits. These neurons also display elevated calcium levels in response to sleep loss in the morning, but not the evening consistent with the observed time-dependent sleep rebound. These studies reveal the circuit and molecular mechanisms by which discrete circadian clock neurons program a homeostatic sleep center.

Running skeletal muscle clocks on time- the determining factors

Circadian rhythms generate 24 h-long oscillations, which are key regulators of many aspects of behavior and physiology. Recent circadian transcriptome studies have discovered rhythmicity at the transcriptional level of hundreds of skeletal muscle genes, with roles in skeletal muscle growth, maintenance, and metabolic functions. These rhythms allow this tissue to perform molecular functions at the appropriate time of the day in order to anticipate environmental changes. However, while the last decade of research has characterized several aspects of the skeletal muscle molecular clock, many still are unexplored, including its functions, regulatory mechanisms, and interactions with other tissues. The central clock is believed to be located in the suprachiasmatic nucleus (SCN) of the brain hypothalamus, providing entrainment to peripheral organs through humoral and neuronal signals. However, these mechanisms of action are still unknown. Conversely, muscle tissue can be entrained through extrinsic, SCN-independent factors, such as feeding and physical activity. In this review, we provide an overview of the recent research about the extrinsic and intrinsic factors required for skeletal muscle clock regulation. Furthermore, we discuss the need for future studies to elucidate the mechanisms behind this regulation, which will in turn help dissect the role of circadian disruption at the onset of aging and diseases.

The Effects of Light and the Circadian System on Rhythmic Brain Function

Life on earth has evolved under the influence of regularly recurring changes in the environment, such as the 24 h light/dark cycle. Consequently, organisms have developed endogenous clocks, generating 24 h (circadian) rhythms that serve to anticipate these rhythmic changes. In addition to these circadian rhythms, which persist in constant conditions and can be entrained to environmental rhythms, light drives rhythmic behavior and brain function, especially in nocturnal laboratory rodents. In recent decades, research has made great advances in the elucidation of the molecular circadian clockwork and circadian light perception. This review summarizes the role of light and the circadian clock in rhythmic brain function, with a focus on the complex interaction between the different components of the mammalian circadian system. Furthermore, chronodisruption as a consequence of light at night, genetic manipulation, and neurodegenerative diseases is briefly discussed.

Conditional Knockout of Bmal1 in Corticotropin-Releasing Factor Neurons Does Not Alter Sleep–Wake Rhythm in Mice

Sleep and wakefulness are regulated by both the homeostatic mechanism and circadian clock. In mammals, the central circadian clock, the suprachiasmatic nucleus, in the hypothalamus plays a crucial role in the timing of physiology and behavior. Recently, we found that the circadian regulation of wakefulness was transmitted via corticotropin-releasing factor (CRF) neurons in the paraventricular nucleus of the hypothalamus to orexin neurons in the lateral hypothalamus. However, it is still unclear how the molecular clock in the CRF neurons contributes to the regulation of sleep and wakefulness. In the present study, we established CRF neuron-specific Bmal1-deficient mice and measured locomotor activity or electroencephalography and electromyography. We found that these mice showed normal circadian locomotor activity rhythms in both light–dark cycle and constant darkness. Furthermore, they showed normal daily patterns of sleep and wakefulness. These results suggest that Bmal1 in CRF neurons has no effect on either circadian locomotor activity or sleep and wakefulness.

Role of Sleep Restriction in Daily Rhythms of Expression of Hypothalamic Core Clock Genes in Mice

Lack of sleep time is a menace to modern people, and it leads to chronic diseases and mental illnesses. Circadian processes control sleep, but little is known about how sleep affects the circadian system. Therefore, we performed a 28-day sleep restriction (SR) treatment in mice. Sleep restriction disrupted the clock genes’ circadian rhythm. The circadian rhythms of the Cry1 and Per1/2/3 genes disappeared. The acrophase of the clock genes (Bmal1, Clock, Rev-erbα, and Rorβ) that still had a circadian rhythm was advanced, while the acrophase of negative clock gene Cry2 was delayed. Clock genes’ upstream signals ERK and EIFs also had circadian rhythm disorders. Accompanied by changes in the central oscillator, the plasma output signal (melatonin, corticosterone, IL-6, and TNF-α) had an advanced acrophase. While the melatonin mesor was decreased, the corticosterone, IL-6, and TNF-α mesor was increased. Our results indicated that chronic sleep loss could disrupt the circadian rhythm of the central clock through ERK and EIFs and affect the output signal downstream of the core biological clock.

Circadian Rhythm Effects on the Molecular Regulation of Physiological Systems

Nearly every system within the body contains an intrinsic cellular circadian clock. The circadian clock contributes to the regulation of a variety of homeostatic processes in mammals through the regulation of gene expression. Circadian disruption of physiological systems is associated with pathophysiological disorders. Here, we review the current understanding of the molecular mechanisms contributing to the known circadian rhythms in physiological function. This article focuses on what is known in humans, along with discoveries made with cell and rodent models. In particular, the impact of circadian clock components in metabolic, cardiovascular, endocrine, musculoskeletal, immune, and central nervous systems are discussed. © 2021 American Physiological Society. Compr Physiol 11:1-30, 2021.

NADH inhibition of SIRT1 links energy state to transcription during time-restricted feeding

In mammals, circadian rhythms are entrained to the light cycle and drive daily oscillations in levels of NAD+, a cosubstrate of the class III histone deacetylase sirtuin 1 (SIRT1) that associates with clock transcription factors. Although NAD+ also participates in redox reactions, the extent to which NAD(H) couples nutrient state with circadian transcriptional cycles remains unknown. Here we show that nocturnal animals subjected to time-restricted feeding of a calorie-restricted diet (TRF-CR) only during night-time display reduced body temperature and elevated hepatic NADH during daytime. Genetic uncoupling of nutrient state from NADH redox state through transduction of the water-forming NADH oxidase from Lactobacillus brevis (LbNOX) increases daytime body temperature and blood and liver acyl-carnitines. LbNOX expression in TRF-CR mice induces oxidative gene networks controlled by brain and muscle Arnt-like protein 1 (BMAL1) and peroxisome proliferator-activated receptor alpha (PPARα) and suppresses amino acid catabolic pathways. Enzymatic analyses reveal that NADH inhibits SIRT1 in vitro, corresponding with reduced deacetylation of SIRT1 substrates during TRF-CR in vivo. Remarkably, Sirt1 liver nullizygous animals subjected to TRF-CR display persistent hypothermia even when NADH is oxidized by LbNOX. Our findings reveal that the hepatic NADH cycle links nutrient state to whole-body energetics through the rhythmic regulation of SIRT1.

Circadian Clocks, Sleep, and Metabolism

A molecular circadian clock exists not only in the brain, but also in most cells of the body. Research over the past two decades has demonstrated that it directs daily rhythmicity of nearly every aspect of metabolism. It also consolidates sleep-wake behavior each day into an activity/feeding period and a sleep/fasting period. Otherwise, sleep-wake states are mostly controlled by hypothalamic and thalamic regulatory circuits in the brain that direct overall brain state. Recent evidence suggests that hypothalamic control of appetite and metabolism may be concomitant with sleep-wake regulation, and even share the same control centers. Thus, circadian control of metabolic pathways might be overlaid by sleep-wake control of the same pathways, providing a flexible and redundant system to modify metabolism according to both activity and environment.

Brain Clocks, Sleep, and Mood

The suprachiasmatic nucleus houses the master clock, but the genes which encode the circadian clock components are also expressed throughout the brain. Here, we review how circadian clock transcription factors regulate neuromodulator systems such as histamine, dopamine, and orexin that promote arousal. These circadian transcription factors all lead to repression of the histamine, dopamine, and orexin systems during the sleep period, so ensuring integration with the ecology of the animal. If these transcription factors are deleted or mutated, in addition to the global disturbances in circadian rhythms, this causes a chronic up-regulation of neuromodulators leading to hyperactivity, elevated mood, and reduced sleep, which have been suggested to be states resembling mania.

Peripheral Clock System Abnormalities in Patients With Parkinson's Disease

Objective: To evaluate the altered expression of peripheral clock genes, circulating melatonin levels, and their correlations with sleep-wake phenotypes including probable rapid eye movement sleep behavior disorder (pRBD) symptoms in a relatively large population of Parkinson’s disease (PD) patients.

Methods: We determined the expression profiles of five principal clock genes, BMAL1, CLOCK, CRY1, PER1, and PER2, in the peripheral blood mononuclear cells (PBMCs) of PD patients (n = 326), and healthy controls (HC, n = 314) using quantitative real-time PCR. Melatonin concentration in the plasma of two groups was evaluated by enzyme-linked immunosorbent assay. Then we performed comprehensive association analyses on the PBMCs clock gene expression, plasma melatonin levels and sleep characteristics.

Results: Our data showed that the expression levels of BMAL1, CLOCK, CRY1, PER1, and PER2 were significantly decreased in the PBMCs of PD as compared with that of HC (P < 0.05). PD patients had reduced plasma melatonin levels compared with HC (P < 0.0001). pRBD and excessive daytime sleepiness are common in these PD patients and are associated with the expression levels of all five clock genes (r = −0.344∼−0.789, P < 0.01) and melatonin concentration (r = −0.509∼−0.753, P < 0.01). Statistical analyses also revealed that a combination of five clock genes and melatonin could reach a high diagnostic performance (areas under the curves, 97%) for PD comorbid pRBD.

Conclusion: This case-control study demonstrates that peripheral BMAL1, CLOCK, CRY1, PER1, PER2, and melatonin levels are altered in PD patients and may serve as endogenous markers for sleep and wakefulness disturbances of PD.

Restoring the Molecular Clockwork within the Suprachiasmatic Hypothalamus of an Otherwise Clockless Mouse Enables Circadian Phasing and Stabilization of Sleep-Wake Cycles and Reverses Memory Deficits

The timing and quality of sleep-wake cycles are regulated by interacting circadian and homeostatic mechanisms. Although the suprachiasmatic nucleus (SCN) is the principal clock, circadian clocks are active across the brain and the respective sleep-regulatory roles of SCN and local clocks are unclear. To determine the specific contribution(s) of the SCN, we used virally mediated genetic complementation, expressing Cryptochrome1 (Cry1) to establish circadian molecular competence in the suprachiasmatic hypothalamus of globally clockless, arrhythmic male Cry1/Cry2-null mice. Under free-running conditions, the rest/activity behavior of Cry1/Cry2-null controls expressing EGFP (SCN^Con) was arrhythmic, whereas Cry1-complemented mice (SCN^Cry1) had coherent circadian behavior, comparable to that of Cry1,2-competent wild types (WTs). In SCN^Con mice, sleep-wakefulness, assessed by electroencephalography (EEG)/electromyography (EMG), lacked circadian organization. In SCN^Cry1 mice, however, it matched WTs, with consolidated vigilance states [wake, rapid eye movement sleep (REMS) and non-REMS (NREMS)] and rhythms in NREMS δ power and expression of REMS within total sleep (TS). Wakefulness in SCN^Con mice was more fragmented than in WTs, with more wake-NREMS-wake transitions. This disruption was reversed in SCN^Cry1 mice. Following sleep deprivation (SD), all mice showed a homeostatic increase in NREMS δ power, although the SCN^Con mice had reduced NREMS during the inactive (light) phase of recovery. In contrast, the dynamics of homeostatic responses in the SCN^Cry1 mice were comparable to WTs. Finally, SCN^Con mice exhibited poor sleep-dependent memory but this was corrected in SCN^Cry1mice. In clockless mice, circadian molecular competence focused solely on the SCN rescued the architecture and consolidation of sleep-wake and sleep-dependent memory, highlighting its dominant role in timing sleep.

SIGNIFICANCE STATEMENT The circadian timing system regulates sleep-wake cycles. The hypothalamic suprachiasmatic nucleus (SCN) is the principal circadian clock, but the presence of multiple local brain and peripheral clocks mean the respective roles of SCN and other clocks in regulating sleep are unclear. We therefore used virally mediated genetic complementation to restore molecular circadian functions in the suprachiasmatic hypothalamus, focusing on the SCN, in otherwise genetically clockless, arrhythmic mice. This initiated circadian activity-rest cycles, and circadian sleep-wake cycles, circadian patterning to the intensity of non-rapid eye movement sleep (NREMS) and circadian control of REMS as a proportion of total sleep (TS). Consolidation of sleep-wake established normal dynamics of sleep homeostasis and enhanced sleep-dependent memory. Thus, the suprachiasmatic hypothalamus, alone, can direct circadian regulation of sleep-wake.

Circadian NAD(P)(H) cycles in cell metabolism

Intrinsic circadian clocks are present in all forms of photosensitive life, enabling daily anticipation of the light/dark cycle and separation of energy storage and utilization cycles on a 24-h timescale. The core mechanism underlying circadian rhythmicity involves a cell-autonomous transcription/translation feedback loop that in turn drives rhythmic organismal physiology. In mammals, genetic studies have established that the core clock plays an essential role in maintaining metabolic health through actions within both brain pacemaker neurons and peripheral tissues and that disruption of the clock contributes to disease. Peripheral clocks, in turn, can be entrained by metabolic cues. In this review, we focus on the role of the nucleotide NAD(P)(H) and NAD⁺-dependent sirtuin deacetylases as integrators of circadian and metabolic cycles, as well as the implications for this interrelationship in healthful aging.

Sleep timing and the circadian clock in mammals: Past, present and the road ahead

Nearly all mammals display robust daily rhythms of physiology and behavior. These approximately 24-h cycles, known as circadian rhythms, are driven by a master clock in the suprachiasmatic nucleus (SCN) of the hypothalamus and affect biological processes ranging from metabolism to immune function. Perhaps the most overt output of the circadian clock is the sleep-wake cycle, the integrity of which is critical for health and homeostasis of the organism. In this review, we summarize our current understanding of the circadian regulation of sleep. We discuss the neural circuitry and molecular mechanisms underlying daily sleep timing, and the trajectory of circadian regulation of sleep across development. We conclude by proposing future research priorities for the field that will significantly advance our mechanistic understanding of the circadian regulation of sleep.

Sleep Timing and Risk of Dementia Among the Chinese Elderly in an Urban Community: The Shanghai Aging Study

Background: Growing evidence has suggested a link between poor sleep quality and increased risk of dementia. However, little is known about the association between sleep timing, an important behavior marker of circadian rhythms, and dementia risk in older adults, and whether this is independent of sleep duration or quality. Methods: We included data from 1,051 community-dwelling older men and women (aged≥ 60y) without dementia from the Shanghai Aging Study. At baseline, participants reported sleep timing, duration, and quality using the Chinese version of the Pittsburgh Sleep Quality Index (CPSQI). Dementia diagnosis over the following 7.3 years was determined by neurologists using DSM-IV criteria. We used Cox proportional hazards models to examine the association between bedtime (before 9 p.m., after 11 p.m. vs. 9-11 p.m.), rise time (before 6 a.m., after 8 a.m. vs. 6-8 a.m.), and risk of dementia. Results: A total of 238 (22.8%), 675 (64.5%), and 133 (12.7%) participants reported going to bed before 9 p.m., between 9 and 11 p.m., and after 11 p.m., respectively, while 272 (26%), 626 (59.9%), and 148 (14.2%) reported getting up before 6 a.m., between 6 and 8 a.m., and after 8 a.m., respectively. Participants who reported going to bed earlier had a lower education level, were less likely to be smokers, more likely to have hypertension or diabetes, and had longer sleep duration but poorer sleep quality compared to those who reported a later bedtime. We found 47 incidents of dementia among 584 participants followed up over an average of 7.3 years. After adjustment for demographics, education, income, body mass index, depressive symptoms, smoking, alcohol use, physical activity, comorbidities, APOE4 genotype, and baseline MMSE, those with a bedtime of before 9 p.m. were two times more likely to develop dementia [hazard ratio (HR)=2.16 (95%CI: 1.06-4.40)], compared to those going to bed between 9 and 11 p.m. Later bedtime (i.e., after 11 p.m.) showed the opposite but had a non-significant association with dementia risk (HR=0.15, 95%CI: 0.02-1.29). We did not find an association for rise time and risk of dementia. Conclusion: Earlier sleep timing in older adults without dementia was associated with an increased risk of dementia. Future studies should examine the underlying mechanisms of this association and explore the usefulness of sleep timing as a preclinical marker for dementia.

Deciphering the Interacting Mechanisms of Circadian Disruption and Alzheimer's Disease

Alzheimer's disease (AD) is one of the crucial causative factors for progressive dementia. Neuropathologically, AD is characterized by the extracellular accumulation of amyloid beta plaques and intracellular neurofibrillary tangles in cortical and limbic regions of the human brain. The circadian system is one of the many affected physiological processes in AD, the dysfunction of which may reflect in the irregularity of the sleep/wake cycle. The interplay of circadian and sleep disturbances inducing AD progression is bidirectional. Sleep-associated pathological alterations are frequently evident in AD. Understanding the interrelation between circadian disruption and AD may allow for earlier identification of AD pathogenesis as well as better suited approaches and potential therapies to combat dementia. In this article, we examine the existing literature related to the molecular mechanisms of the circadian clock and interacting mechanisms of circadian disruption and AD pathogenesis.

Sleep disturbance induces depressive behaviors and neuroinflammation by altering the circadian oscillations of clock genes in rats

Sleep loss leads to a spectrum of mood disorders such as anxiety disorders, bipolar disorder and depression in many individuals. However, the underlying mechanisms are largely unknown. In this study, sleep-disturbed animals were tested for anxiety and depressive behaviors. We then studied the effects of SD on hypothalamic-pituitary-adrenal (HPA) axis function by measuring serum and CSF levels of corticosterone (CORT), and at the end of the experiment, brains were collected to measure the circadian oscillations of clock genes expression in the hypothalamus, glial cell activation and inflammatory cytokine alterations. Our results indicated that SD for 3 days resulted in anxiety- and depressive-like behaviors. SD exaggerated cortisol response to HPA axis, significantly altered the circadian oscillations of clock genes, decreased the expression of tight junction protein ZO-1 and Claudin 5 and increased the number of GFAP-positive cells and Iba-1-positive cells and caused subsequent elevation of pro-inflammatory cytokines IL-6, IL-1β and TNFα. These findings demonstrated that SD for 3 days induced anxiety- and depression-like behaviors in rats in company with altering the circadian oscillations of clock genes and inducing neuroinflammation, indicating the underlying mechanism of sleep loss induced neuronal dysfunction.

Circadian Chimeric Mice Reveal an Interplay Between the Suprachiasmatic Nucleus and Local Brain Clocks in the Control of Sleep and Memory

Sleep is regulated by circadian and homeostatic processes. Whereas the suprachiasmatic nucleus (SCN) is viewed as the principal mediator of circadian control, the contributions of sub-ordinate local circadian clocks distributed across the brain are unknown. To test whether the SCN and local brain clocks interact to regulate sleep, we used intersectional genetics to create temporally chimeric CK1ε Tau mice, in which dopamine 1a receptor (Drd1a)-expressing cells, a powerful pacemaking sub-population of the SCN, had a cell-autonomous circadian period of 24 h whereas the rest of the SCN and the brain had intrinsic periods of 20 h. We compared these mice with non-chimeric 24 h wild-types (WT) and 20 h CK1ε Tau mutants. The periods of the SCN ex vivo and the in vivo circadian behavior of chimeric mice were 24 h, as with WT, whereas other tissues in the chimeras had ex vivo periods of 20 h, as did all tissues from Tau mice. Nevertheless, the chimeric SCN imposed its 24 h period on the circadian patterning of sleep. When compared to 24 h WT and 20 h Tau mice, however, the sleep/wake cycle of chimeric mice under free-running conditions was disrupted, with more fragmented sleep and an increased number of short NREMS and REMS episodes. Even though the chimeras could entrain to 20 h light:dark cycles, the onset of activity and wakefulness was delayed, suggesting that SCN Drd1a-Cre cells regulate the sleep/wake transition. Chimeric mice also displayed a blunted homeostatic response to 6 h sleep deprivation (SD) with an impaired ability to recover lost sleep. Furthermore, sleep-dependent memory was compromised in chimeras, which performed significantly worse than 24 h WT and 20 h Tau mice. These results demonstrate a central role for the circadian clocks of SCN Drd1a cells in circadian sleep regulation, but they also indicate a role for extra-SCN clocks. In circumstances where the SCN and sub-ordinate local clocks are temporally mis-aligned, the SCN can maintain overall circadian control, but sleep consolidation and recovery from SD are compromised. The importance of temporal alignment between SCN and extra-SCN clocks for maintaining vigilance state, restorative sleep and memory may have relevance to circadian misalignment in humans, with environmental (e.g., shift work) causes.

The influence of circadian rhythms and aerobic glycolysis in autism spectrum disorder

Intellectual abilities and their clinical presentations are extremely heterogeneous in autism spectrum disorder (ASD). The main causes of ASD remain unclear. ASD is frequently associated with sleep disorders. Biologic rhythms are complex systems interacting with the environment and controlling several physiological pathways, including brain development and behavioral processes. Recent findings have shown that the deregulation of the core clock neurodevelopmental signaling is correlated with ASD clinical presentation. One of the main pathways involved in developmental cognitive disorders is the canonical WNT/β-catenin pathway. Circadian clocks have a main role in some tissues by driving circadian expression of genes involved in physiologic and metabolic functions. In ASD, the increase of the canonical WNT/β-catenin pathway is enhancing by the dysregulation of circadian rhythms. ASD progression is associated with a major metabolic reprogramming, initiated by aberrant WNT/β-catenin pathway, the aerobic glycolysis. This review focuses on the interest of circadian rhythms dysregulation in metabolic reprogramming in ASD through the aberrant upregulation of the canonical WNT/β-catenin pathway.

Exercise Training Impacts Skeletal Muscle Clock Machinery in Prediabetes

PURPOSE

Disruption of the skeletal muscle molecular clock leads to metabolic disease, whereas exercise may be restorative, leading to improvements in metabolic health. The purpose of this study was to evaluate the effects of a 12-wk exercise intervention on skeletal muscle molecular clock machinery in adults with obesity and prediabetes, and determine whether these changes were related to exercise-induced improvements in metabolic health.

METHODS

Twenty-six adults (age, 66 ± 4.5 yr; body mass index (BMI), 34 ± 3.4 kg·m; fasting plasma glucose, 105 ± 15 mg·dL) participated in a 12-wk exercise intervention and were fully provided isoenergetic diets. Body composition (dual x-ray absorptiometry), abdominal adiposity (computed tomography scans), peripheral insulin sensitivity (euglycemic-hyperinsulinemic clamp), exercise capacity (maximal oxygen consumption), and skeletal muscle molecular clock machinery (vastus lateralis biopsy) were assessed at baseline and after intervention. Gene and protein expression of skeletal muscle BMAL1, CLOCK, CRY1/2, and PER 1/2 were measured by quantitative real-time polymerase chain reaction and Western blot, respectively.

RESULTS

Body composition (BMI, dual x-ray absorptiometry, computed tomography), peripheral insulin sensitivity (glucose disposal rate), and exercise capacity (maximal oxygen consumption) all improved (P < 0.005) with exercise training. Skeletal muscle BMAL1 gene (fold change, 1.62 ± 1.01; P = 0.027) and PER2 protein expression (fold change, 1.35 ± 0.05; P = 0.02) increased, whereas CLOCK, CRY1/2, and PER1 were unchanged. The fold change in BMAL1 correlated with post-glucose disposal rate (r = 0.43, P = 0.044), BMI (r = -0.44, P = 0.042), and body weight changes (r = -0.44, P = 0.039) expressed as percent delta.

CONCLUSIONS

Exercise training impacts skeletal muscle molecular clock machinery in a clinically relevant cohort of adults with obesity and prediabetes. Skeletal muscle BMAL1 gene expression may improve insulin sensitivity. Future studies are needed to determine the physiological significance of exercise-induced alterations in skeletal muscle clock machinery.

Sleep-length differences are associated with altered longevity in the fruit fly Drosophila melanogaster

Sleep deprivation has been shown to negatively impact health outcomes, leading to decreased immune responses, memory loss, increased activity of stress and inflammatory pathways, weight gain, and even behavioral changes. These observations suggest that sleep deprivation substantially interferes with important physiological functions, including metabolic pathways of energy utilization. Many of those phenotypes are correlated with age, suggesting that disrupted sleep may interfere with the aging process. However, little is known about how sleep disruption affects aging and longevity. Here, we investigate this relationship using eight representative fruit fly lines from the Sleep Inbred Panel (SIP). The SIP consists of 39 inbred lines that display extreme short- and long-sleep patterns, and constitutes a crucial Drosophila community resource for investigating the mechanisms of sleep regulation. Our data show that flies with short-sleep periods have ∼16% longer life span, as well as reduced aging rate, compared to flies with long-sleep. In contrast, disrupting normal circadian rhythm reduces fly longevity. Short-sleep SIP flies moreover show slight metabolic differences to long-sleep lines, and to flies with disrupted circadian rhythm. These data suggest that the inbred SIP lines engage sleep mechanisms that are distinct from the circadian clock system.

Impact of circadian and diurnal rhythms on cellular metabolic function and neurodegenerative diseases

The 24-h rotational period of the earth has driven evolution of biological systems that serve to synchronize organismal physiology and behavior to this predictable environmental event. In mammals, the circadian (circa, "about" and dia, "a day") clock keeps 24-h time at the organismal and cellular level, optimizing biological function for a given time of day. The most obvious circadian output is the sleep-wake cycle, though countless bodily functions, ranging from hormone levels to cognitive function, are influenced by the circadian clock. Here we discuss the regulation of metabolic pathways by the circadian clock, discuss the evidence implicating circadian and sleep disruption in neurodegenerative diseases, and suggest some possible connections between the clock, metabolism, and neurodegenerative disease.

Circadian and Sleep Metabolomics Across Species

Under normal circadian function, metabolic control is temporally coordinated across tissues and behaviors with a 24-h period. However, circadian disruption results in negative consequences for metabolic homeostasis including energy or redox imbalances. Yet, circadian disruption has become increasingly prevalent within today's society due to many factors including sleep loss. Metabolic consequences of both have been revealed by metabolomics analyses of circadian biology and sleep. Specifically, two primary analytical platforms, mass spectrometry and nuclear magnetic resonance spectroscopy, have been used to study molecular clock and sleep influences on overall metabolic rhythmicity. For example, human studies have demonstrated the prevalence of metabolic rhythms in human biology, as well as pan-metabolome consequences of sleep disruption. However, human studies are limited to peripheral metabolic readouts primarily through minimally invasive procedures. For further tissue- and organism-specific investigations, a number of model systems have been studied, based upon the conserved nature of both the molecular clock and sleep across species. Here we summarize human studies as well as key findings from metabolomics studies using mice, Drosophila, and zebrafish. While informative, a limitation in existing literature is a lack of interpretation regarding dynamic synthesis or catabolism within metabolite pools. To this extent, future work incorporating isotope tracers, specific metabolite reporters, and single-cell metabolomics may provide a means of exploring dynamic activity in pathways of interest.

Circadian rhythms in the absence of the clock gene Bmal1

Circadian (~24 hour) clocks have a fundamental role in regulating daily physiology. The transcription factor BMAL1 is a principal driver of a molecular clock in mammals. Bmal1 deletion abolishes 24-hour activity patterning, one measure of clock output. We determined whether Bmal1 function is necessary for daily molecular oscillations in skin fibroblasts and liver slices. Unexpectedly, in Bmal1 knockout mice, both tissues exhibited 24-hour oscillations of the transcriptome, proteome, and phosphoproteome over 2 to 3 days in the absence of any exogenous drivers such as daily light or temperature cycles. This demonstrates a competent 24-hour molecular pacemaker in Bmal1 knockouts. We suggest that such oscillations might be underpinned by transcriptional regulation by the recruitment of ETS family transcription factors, and nontranscriptionally by co-opting redox oscillations.

Perfect timing: circadian rhythms, sleep, and immunity - an NIH workshop summary

Recent discoveries demonstrate a critical role for circadian rhythms and sleep in immune system homeostasis. Both innate and adaptive immune responses - ranging from leukocyte mobilization, trafficking, and chemotaxis to cytokine release and T cell differentiation -are mediated in a time of day-dependent manner. The National Institutes of Health (NIH) recently sponsored an interdisciplinary workshop, "Sleep Insufficiency, Circadian Misalignment, and the Immune Response," to highlight new research linking sleep and circadian biology to immune function and to identify areas of high translational potential. This Review summarizes topics discussed and highlights immediate opportunities for delineating clinically relevant connections among biological rhythms, sleep, and immune regulation.