Autophagy and circadian rhythms:interactions and clinical implications

Autophagy is a widespread biological process that controls cellular growth,survival,development,and death.Circadian rhythm is a recurring reaction of living organisms and behaviors to variations in surrounding brightness and obscurity.Most of the fundamental physiological processes in mammals,such as the sleep-wake pattern and the rhythm of nutrition and energy metabolism,are governed by circadian rhythms.Research has indicated that autophagy exhibits a specific circadian pattern in both normal and abnormal conditions.Autophagy can modulate circadian rhythms by breaking down proteins that regulate the circadian clock.The potential regulatory connection between the two has been a popular subject of clinical and fundamental research.Understanding the interaction between circadian rhythm and autophagy could potentially lead to the development of novel approaches for disease treatment in the future.The present analysis presented a summary of the molecular processes implicated in the interplay between autophagy and circadian rhythm,as well as the pathological importance of the disrupted regulatory association between these two phenomena.

Corneal and intraocular pressure changes associated to the circadian rhythms:a narrative review

AIM:To synthesize the current body of research regarding the diurnal variations in intraocular pressure(IOP)and corneal biomechanical and morphological parameters,highlighting their significance in various eye conditions.METHODS:A comprehensive review of studies on the diurnal variations of IOP and corneal parameters was conducted.Tonometry findings from various studies were assessed,including the Goldmann applanation tonometry(GAT)and non-contact tonometers.Data on the variations in central corneal thickness(CCT),corneal curvature,and corneal biomechanics measured by the Ocular Response Analyzer system across different population groups was extracted and analyzed.RESULTS:In both healthy subjects and those with Fuchs dystrophy,IOP and CCT demonstrate marked diurnal declines.GAT remains the gold standard for tonometry,with the highest reliability.However,its measurements are influenced by CCT.Keratoconus patients and those with pseudoexfoliation showed significant diurnal variations in IOP.The biomechanical parameters,especially corneal hysteresis(CH)and the corneal resistance factor(CRF),largely remain stable throughout the day for most of eye conditions,with some exceptions.Notably,the corneal morphology diurnal variation,particularly curvature,yielded mixed conclusions across studies.CONCLUSION:Circadian rhythms significantly influence various corneal parameters,most notably IOP and CCT.Further studies should emphasize standardized approaches larger sample sizes,and delve deeper into less-explored areas,such as the effects of orthokeratology lenses on diurnal biomechanical shifts.

Circadian rhythm disruption and retinal dysfunction:a bidirectional link in Alzheimer’s disease?

Dysfunction in circadian rhythms is a common occurrence in patients with Alzheimer’s disease.A predominant function of the retina is circadian synchronization,carrying information to the brain through the retinohypothalamic tract,which projects to the suprachiasmatic nucleus.Notably,Alzheimer’s disease hallmarks,including amyloid-β,are present in the retinas of Alzheimer’s disease patients,followed/associated by structural and functional disturbances.However,the mechanistic link between circadian dysfunction and the pathological changes affecting the retina in Alzheimer’s disease is not fully understood,although some studies point to the possibility that retinal dysfunction could be considered an early pathological process that directly modulates the circadian rhythm.

Probiotics administration alleviates cognitive impairment and circadian rhythm disturbance induced by sleep deprivation

Gut microbiome is indispensable for maintaining normal brain function.Specifically,gut microbiota plays a causal role in sleep deprivation(SD)-induced cognitive impairment.In this study,neurobehavioral effects of the Bifidobacterium breve strain(CCFM1025)were assessed in sleep-deprived mice.CCFM1025 improved the body weight and food and water intake of the mice.It also alleviated SD-induced cognitive behavioural abnormalities(in the novel object recognition test),but did not show beneficial effects on mood-and spatial memory-related behaviours.CCFM1025 significantly altered the gut microbial composition and genome function.Key microbial metabolites that may regulate sleep function were also identified,such as isovaleric acid andγ-aminobutyric acid in the gut and purine metabolites in the serum.Those metabolites may participate in gutbrain communication by acting on the striatal melatonin system,for example to increase melatonin levels,and by regulating the expression of circadian clock genes such as those encoding the adenosine A2A receptor and period circadian regulator 1.Collectively,administration of probiotics alleviated cognitive impairment and circadian rhythm disturbance induced by SD via modulation of gut microbiome and its metabolites.These findings may help guide the treatment of insomnia or other sleep disorders via dietary strategies.

Unraveling links between aging,circadian rhythm and cancer:Insights from evidence-based analysis

Aging and circadian rhythms have been connected for decades,but their molecular interaction has remained unknown,especially for cancers.In this situation,we summarized the current research actuality and problems in this field using the bibliometric analysis.Publications in the PubMed and Web of Science databases were retrieved.Overall,there is a rising trend in the publication volume regarding aging and circadian rhythms in the field of cancer.Researchers from USA,Germany,Italy,China and England have greater studies than others.Top three publication institutions are University of California System,UDICE-French Research Universities and University of Texas System.Current research hotspots include oxidative stress,breast cancer,melatonin,cell cycle,calorie restriction,prostate cancer and NF-κB.In conclusion,results generated by bibliometric analysis indicate that many approaches involve in the complex interactions between aging and circadian rhythm in cancer.These established and emerging research directions guide our exploration of the regulatory mechanisms of aging and circadian rhythms in cancer and provide a reference for developing new research avenues.

Capsaicin alleviates the hepatic clock gene disruption and gut microbiota dysbiosis in circadian rhythm disorder mouse model

As the body’s internal clock,the circadian rhythm regulates the energy expenditure,appetite,and sleep.There exists a close relationship between the host circadian rhythm and gut microbiota.In this work,a circadian disorder mouse model induced by constant darkness(CD)was constructed to investigate the regulating effects of capsaicin(CAP)on disturbances of metabolism homeostasis and gut microbiota in the respect of circadian rhythm-related mechanisms.Our results indicated that CAP reduced weight gain induced by circadian rhythm disorder in mice by inhibiting fat accumulation in liver and adipose tissue.The rhythmic expressions of circadian clock genes and lipid-metabolism related genes in liver were also recovered by CAP.Microbial study using 16S rRNA sequencing revealed that CAP modulated the gut microbiota richness,diversity and composition,and restored diurnal oscillations of gut microbes at the phylum and family level.These results indicated that CAP could alleviate CD-induced hepatic clock gene disruption and gut microbiota dysbiosis in mice,providing theoretical basis for CAP to be used as a muti-functional ingredient with great healthpromoting effects.

The modulatory effect of oolong tea polyphenols on intestinal flora and hypothalamus gene expression in a circadian rhythm disturbance mouse model

The interaction between host circadian rhythm and gut microbes through the gut-brain axis provides new clues for tea polyphenols to improve host health.Our present research showed that oolong tea polyphenols(OTP)improved the structural disorder of the intestinal flora caused by continuous darkness,thereby modulating the production of metabolites related to pyruvate metabolism,glycolysis/gluconeogenesis,and tryptophan metabolism to alleviate the steady-state imbalance.After fecal microbiota transplantation from the OTP group,the single-cell transcriptomic analysis revealed that OTP significantly increased the number of hypothalamus cell clusters,up-regulated the number of astrocytes and fibroblasts,and enhanced the expression of circadian rhythm genes Cry2,Per3,Bhlhe41,Nr1d1,Nr1d2,Dbp and Rorb in hypothalamic cells.Our results confirmed that OTP can actively improve the intestinal environmental state as well as internal/peripheral circadian rhythm disorders and cognitive impairment,with potential prebiotic functional characteristics to notably contribute to host health.

The Regulatory Role and Mechanism of Circadian Rhythm in Hemoglobin Co-cultured Neurovascular Unit

Objective Intracranial hemorrhage(ICH),the second most common subtype of stroke,exacerbates the disruption of the blood-brain barrier(BBB),leading to vasogenic edema,plasma protein extravasation,and infiltration of neurotoxic substances.The clearance capacity of the brain plays a crucial role in maintaining BBB homeostasis and facilitating patient recovery after hemorrhage.This study aimed to investigate the effect of circadian rhythms on BBB function,neuronal damage,and clearance capabilities.Methods The transwell model and hemoglobin were co-cultured to simulate the BBB environment after ICH.After intervention with different light groups,neuronal apoptosis was determined,glial phagocytosis was analyzed,the expression of endogenous clearing-related proteins aquaporin 4(AQP4)and low-density lipoprotein receptor-related protein 1(LRP1)was detected by western blotting and immunofluorescence dual standard method,and the expression of the tight junction protein occludin and melatonin receptor 1A(MTNR1A)was quantitatively analyzed.Results Circadian rhythms play a key role in maintaining the integrity of the BBB,reducing oxidative stress-induced neuronal damage,and improving microglial phagocytosis.Meanwhile,the expression of occludin and MTNR1A in neurovascular unit(NVU)co-cultured with hemoglobin improved the expression of AQP4 and LRP1,the key proteins in the NVU's endogenous brain clearance system.Conclusion Circadian rhythm(alternating black and white light)protects the NVU BBB function after ICH,promotes the expression of proteins related to the clearance of the hematoma,provides new evidence for the clinical treatment of patients recovering from ICH,and improves the circadian rhythm to promote brain metabolism and hematoma clearance.

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 homeo-stasis.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,infec-tions,and cancer.We explored the molecular mechanisms of circadian clock genes and their impact on metabolic disorders and cancer pathogenesis.Specific associ-ations 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 microenvir-onment.We advocated for integrating biological timing into clinical consider-ations for personalized healthcare,proposing that understanding these connec-tions 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.

Circadian rhythms in the pathogenesis of gastrointestinal diseases

The etiology of digestive pathologies such as irritable bowel syndrome(IBS), inflammatory bowel diseases(IBD) and cancer is not yet fully understood. In recent years, several studies have evidenced circadian variations in mechanisms involved in digestive health. In situations of disturbed circadian rhythms(chronodisruption) where the central clock and the peripheral clocks receive incoherent signals, the synchronicity is lost producing implications for health. This lack of coordination could alter the tissue function and cause long term damage to the organs. Life habits such as sleep, physical exercise, social interaction, and feeding times are determinants for stability and integrity of circadian rhythms. In recent years, experimental and clinical studies have consistently evidenced that the alteration of circadian rhythms is associated with the development of digestive pathologies mainly linked to dismotility or changes in microbiota composition. Likewise, it seems reasonable to deep into the importance of chronodisruption as a factor that may participate in the development of pathologies such as IBS, IBD and digestive cancers. Moreover, life habits respecting circadian rhythms should be promoted for the prevention of these diseases. Further studies will allow us a better understanding of the mechanisms acting at molecular level, and the development of new therapeutic targets.

Circadian rhythms in the growth and reproduction of the brown alga Undaria pinnatifida and gametogenesis under different photoperiods

Circadian growth rhythm of the juvenile sporophyte of the brown alga Undaria pinnatifida was measured with the computer-aided image analysis system in constant florescent white light under constant temperature （ 10 ℃ ）. The growth rhythm persisted for 4 d in constant light with a free-running period of 25.6 h. Egg release from filamentous gametophytes pre-cultured in the light - dark regime was evaluated for six consecutive days at fixed time intervals in constant white light and 12 h light per day. Egg release rhythm persisted for 3 d in both regimes, indicating the endogenous nature. Temporal scale of egg release and gametogenesis in 18, 16, 12 and 8 h light per day were evaluated respectively using vegetatively propagated filamentous gametophytes. Egg release occurred 2 h after the onset of dark phase and peaked at midnight. Evaluation of the rates of oogonium formation, egg release or fertilization revealed no significant differences in four light-dark regimes, indicating the great plasticity of sexual reproduction. No photoperiodic effect in gametogenesis in terms of oogonium formation and egg release was found, but fertilization in short days was significantly higher than in long days. Results of this investigation further confirmed the general occurrence of circadian rhythms in intertidal seaweed species.

The Clock gene clone and its circadian rhythms in Pelteobagrus vachelli

The Clock gene,a key molecule in circadian systems,is widely distributed in the animal kingdom. We isolated a 936-bp partial c DNA sequence of the C lock gene( Pva- clock) from the darkbarbel catfish P elteobagrus vachelli that exhibited high identity with C lock genes of other species of fish and animals(65%–88%). The putative domains included a basic helix-loop-helix(b HLH) domain and two period-ARNT-single-minded(PAS) domains,which were also similar to those in other species of fish and animals. P va- Clock was primarily expressed in the brain,and was detected in all of the peripheral tissues sampled. Additionally,the pattern of P va- Clock expression over a 24-h period exhibited a circadian rhythm in the brain,liver and intestine,with the acrophase at zeitgeber time 21:35,23:00,and 23:23,respectively. Our results provide insight into the function of the molecular C lock of P. vachelli.

Irisin/BDNF signaling in the muscle-brain axis and circadian system: A review

In mammals,the timing of physiological,biochemical and behavioral processes over a 24-h period is controlled by circadian rhythms.To entrain the master clock located in the suprachiasmatic nucleus of the hypothalamus to a precise 24-h rhythm,environmental zeitgebers are used by the circadian system.This is done primarily by signals from the retina via the retinohypothalamic tract,but other cues like exercise,feeding,temperature,anxiety,and social events have also been shown to act as non-photic zeitgebers.The recently identified myokine irisin is proposed to serve as an entraining non-photic signal of exercise.Irisin is a product of cleavage and modification from its precursor membrane fibronectin typeⅢdomain-containing protein 5(FNDC5)in response to exercise.Apart from well-known peripheral effects,such as inducing the"browning"of white adipocytes,irisin can penetrate the blood-brain barrier and display the effects on the brain.Experimental data suggest that FNDC5/irisin mediates the positive effects of physical activity on brain functions.In several brain areas,irisin induces the production of brain-derived neurotrophic factor(BDNF).In the master clock,a significant role in gating photic stimuli in the retinohypothalamic synapse for BDNF is suggested.However,the brain receptor for irisin remains unknown.In the current review,the interactions of physical activity and the irisin/BDNF axis with the circadian system are reconceptualized.

Effects of constant light and dark conditions on the locomotor activity,body mass,and body temperature rhythms of Eurasian Tree Sparrows(Passer montanus)

Light is an essential environmental cue influencing the endogenous circadian clocks that regulate behavioral and physiological processes in animals.Despite extensive research on the circadian rhythms of avian behavior and physiology,the mechanisms by which they adapt and adjust to abnormal photoperiod conditions,such as artificial light,have yet to be fully elucidated.Here,the circadian rhythms of the body mass,activity,and core and peripheral body temperatures of the Eurasian Tree Sparrow(Passer montanus,ETS)-a diurnal passerine-were examined under three different lighting conditions:constant light(LL),constant darkness(DD),and normal light-dark cycles(LD).Our results showed that the activity,body mass,core,tarsometatarsus,and eye temperatures of the ETSs varied significantly with treatment,time,and the interaction between treatment and time;however,there was no significant change in body mass in response to the interaction between time and treatment.Under LD conditions,the ETSs exhibited significant circadian rhythms in activity and core,tarsometatarsus,and eye temperatures.Under LL conditions,only the core temperature exhibited significant rhythmicity.Under DD conditions,there were no significant circadian rhythms in activity,body mass,and eye temperature;however,the core and tarsometatarsus temperatures remained rhythmic.Our results indicate that the core body temperature rhythm of ETS is endogenous and can be maintained under abnormal photoperiods.In contrast,the activity and body surface temperature,uncoupled from the core body temperature under abnormal photoperiod conditions,strongly depend on light.These results differ from those of other diurnal avian species,suggesting a unique coping mechanism of ETS in response to an abnormal photoperiod.

The role of pineal microRNA-325 in regulating circadian rhythms after neonatal hypoxic-ischemic brain damage

Circadian rhythm disorder is a common,but often neglected,consequence of neonatal hypoxic-ischemic brain damage(HIBD).However,the underlying molecular mechanisms remain largely unknown.We previously showed that,in a rat model of HIBD,up-regulation of microRNA-325(miR-325)in the pineal gland is responsible for the suppression of Aanat,a key enzyme involved in melatonin synthesis and circadian rhythm regulation.To better understand the mechanism by which miR-325 affects circadian rhythms in neonates with HIBD,we compared clinical samples from neonates with HIBD and samples from healthy neonates recruited from the First Affiliated Hospital of Soochow University(Dushuhu Branch)in 2019.We found that circulating miR-325 levels correlated positively with the severity of sleep and circadian rhythm disorders in neonates with HIBD.Furthermore,a luciferase reporter gene assay revealed that LIM homeobox 3(LHX3)is a novel downstream target of miR-325.In addition,in miR-325 knock-down mice,the transcription factor LHX3 exhibited an miR-325-dependent circadian pattern of expression in the pineal gland.We established a neonatal mouse model of HIBD by performing doublelayer ligation of the left common carotid artery and exposing the pups to a low-oxygen environment for 2 hours.Lhx3 mRNA expression was significantly down-regulated in these mice and partially rescued in miR-325 knockout mice subjected to the same conditions.Finally,we showed that improvement in circadian rhythm-related behaviors in animals with HIBD was dependent on both miR-325 and LHX3.Taken together,our findings suggest that the miR-325-LHX3 axis is responsible for regulating circadian rhythms and provide novel insights into the identification of potential therapeutic targets for circadian rhythm disorders in patients with neonatal HIBD.The clinical trial was approved by Institutional Review Board of Children’s Hospital of Soochow University(approval No.2015028)on July 20,2015.Animal experiments were approved by Animal Care and Use Committee,School of Medicine,Soochow University,China(approval No.XD-2016-1)on January 15,2016.

Potential Power of the Pyramidal Structure VII: Effects of Pyramid Power and Bio-Entanglement on the Circadian Rhythm of Biosensors

We have demonstrated the existence of a pyramid power and have revealed its characteristics by strictly scientific experiments using biosensors. We also revealed the existence of a Bio-Entanglement, an entangled relationship between biosensors. A parallel study of biosensors (edible cucumber slices) had also been conducted, and we found that the circadian rhythm of gas concentrations emitted from biosensors changes seasonally. The pyramid power and Bio-Entanglement did not change the number of cycles in the periodic approximation curve representing circadian rhythm. Therefore, in this paper we analyzed the influence of the pyramid power and Bio-Entanglement, i.e., their influence on the phase, amplitude, and correlation coefficient of the periodic approximation curve representing the circadian rhythm of emitted gas concentrations. The main results are as follows. 1) The pyramid power shifted the phase of the periodic approximation curve representing the circadian rhythm by 43 minutes. 2) The amplitude of the periodic approximation curve changed with the pyramid power and the Bio-Entanglement. The effect on the lower and upper sections of the biosensors stacked in two layers was different, with a tendency to increase the amplitude of the lower layer and decrease the amplitude of the upper layer. 3) The pyramid power and the Bio-Entanglement affected the correlation coefficient between gas concentration and the periodic approximation curve representing the circadian rhythm of gas concentration. The effect on the lower and upper layers of the biosensors was different, with a tendency for the lower layer correlation coefficient to be larger and the upper layer correlation coefficient to be smaller. Previously we demonstrated that the pyramid power and the Bio-Entanglement affect the ratio of gas concentration, i.e., psi index Ψ. In this paper we demonstrate for the first time that the pyramid power and the Bio-Entanglement affect time, i.e., phase difference.

Circadian Rhythm of Childbirths and Maternal and Neonatal Prognosis at the YaoundéCentral Hospital

Background: The circadian variation of childbirths has been described by several authors around the globe. De Graaf showed that hospital childbirths at night were associated with increased perinatal mortality and adverse perinatal outcome. To improve obstetric care, we carried out this study to evaluate the circadian rhythm of childbirths and to assess the outcome following variations in the time of childbirths during the day. Methods: It was a cross-sectional descriptive study at the Yaoundé Central Hospital (YCH), over a two years period. We collected data from files of women who delivered from the 1st of January 2017 to 31st December 2018. We included files of women who delivered at least at 28 weeks of pregnancy. We excluded files of those who delivered by elective caesarean section, those whose hour of delivery was not noted and those who delivered before reaching the hospital. Sociodemographic, obstetrical characteristics, and immediate prognosis were recorded. Data were entered into excel, then analysed with SPSS v23 software. Tools used to appreciate our results were means, median, number, percentage, P, and OR with its 95% confidence interval. The difference in p is significant if p is less than 5%. Results: We analyzed 6041 files bearing the time of birth. Childbirths took place at all hours of the day, but the times of the day where the highest numbers of births were recorded were 10, 11, 12, 13 (that’s 1pm), 14 (that’s 2 pm), 15 (that’s 3 pm), 16 (that’s 4 pm), 17 (that’s 5 pm) and 23 (that’s 11 pm) hours, with respectively 224 (3.7%), 277 (4.6%), 256 (4.2%), 265 (4.4%), 207 (3.4%), 255 (4.2%), 228 (3.8%), 216 (3.6%) and 226 (3.7%) births. The peak of births was at 11 am while the time of day where the lowest number of births was recorded was 6 pm, with 175 (2.9%) births. The mean age of participants was 27.34 ± 6.03 years with extremes of 13 and 49, with 87.6% between 20 to 39 years. Sociodemographic characteristics of participants, prematurity and bleeding during delivery, had no dependence on the time of delivery. Perineal tear, duration of observation, Apgar score of the newborn, birthweight, delivery mode, health personnel who performed the delivery, and episiotomyseemed to be influenced by the time of delivery. Daily shifts were not independently associated with the poor Apgar score (0 - 6) at 5 mins, when adjusted for all other factors (p = 0.109). Conclusion: Childbirths were more frequent between 10 am and 5 pm. The period where episiotomy was most performed is the same as when there was macrosomia childbirth. Tears of the perineum are more frequent between 2 pm and 10 pm. There was no independent association between Daily shifts and poor Apgar score. The poor APGAR score would be more related to low birth weight.

Effects of Exposure to Extremely Low Frequency Electro-magnetic Fields on Circadian Rhythms and Distribution of Some Leukocyte Differentiation Antigens in Dairy Cows

Objective To investigate the effects of extremely low frequency magnetic and electric fields （ELFEMFs） emitted from 380 kV transmission lines on some leukocyte differentiation antigens in dairy cows. Methods The study was carded out in 5 cows exposed to 1.98-3.28 μT of ELFEMFs and in 5 control cows exposed to 0.2-0.7 μT of ELFEMFs. Following haematological and immunologic parameters were measured in both groups： WBC, CD45R, CD6, CD4, CD8, CD21, and CD11B leukocyte antigen expression. Results Some of the haematological and immunologic parameters under investigation were similar in both groups. However, CD8 （T lymphocyte surface antigen） was higher in the exposed group （1.35 ±0.120 vs 0.50 ±0.14×10^3/mL）. Furthermore, the CD4/CD8 ratio （0.84 ±0.05 and 2.19±0.16 for exposed and not exposed cows respectively） and circadian rhythm were different between the two groups. Conclusion Exposure to ELFEMFs is responsible of the abnormal temporal variations and distribution of some haematological and immunological parameters in dairy cows.

Circadian rhythms of hormone secretion and obesity

The adipose tissue homeostasis is profoundly affected by circadian rhythms of corticosteroid secretion and chronic loss of hormonal oscillations is associated with obesity. How adipose tissue differentially responds to pulsatile vs continuous presence of glucocorticoids is poorly defined. To address this question, Bahrami-Nejad et al studied differentiation of pre-adipocytes, containing endogenously tagged CCAAT/enhancer binding protein and peroxisome proliferator-activated receptor(PPAR) γ(key regulators of adipocyte differentiation), in response to corticosteroids that were delivered either in an oscillatory fashion or continuously. The authors show that the bi-stable state of differentiation of pre-adipocytes and adipocytes was regulated by a combination of fast and slow positive feedback networks, that determined unique threshold of PPARγ in these cells. Evidently, pre-adipocytes used the fast feedback loop to reject differentiation cues of oscillating pulses of glucocorticoids and failed to differentiate into fat cells. In contrast, when glucocorticoids were delivered continuously, precursor cells exploited the slow feedback loop to embark on a path of maximal differentiation. This differential differentiation response of pre-adipocytes to pulsatile vs continuous exposure to glucocorticoids was corroborated in vivo. Thus, mice receiving non-oscillating doses of exogenous glucocorticoids, for 21 d, elicited excessive accumulation of visceral and subcutaneous fat. These data shed new light on the mechanisms of obesity caused by putative misalignment of circadian secretion of glucocorticoids or their persistently high levels due to chronic stress or Cushing's disease.

Nobiletin protects against metabolic syndrome by enhancing circadian rhythms

OBJECTIVE Dysregulation of circadian rhythms is associated with metabolic dysfunction,yet it is unclear whether enhancing clock function by small molecules can ameliorate metabolic disorders.METHODS We used an unbiased chemical screen in fibroblasts expressing PER2::Luc to identify the Clock amplitude-Enhancing Small Mole⁃cule.In diet-induced obese mice and DB/DB mutant mice,we evaluated the effects of the Clock amplitude-Enhancing small Molecule on metabolic syndrome and locomotor activity.RESULTS We identified Nobiletin(NOB),a natural poly⁃methoxylated flavone,as a Clock amplitude-Enhancing Small Molecule by an unbiased chemical screen.In diet-induced obese mice,NOB strongly improved metabolic syndrome and enhanced locomotor activity in a Clock gene-dependent manner.Moreover,the clock is also required for the beneficial effects of NOB on metabolic disorders in DB/DB mutant mice.Notably,NOB enhanced clock protein levels and reprogramed metabolic gene expressions in the liver.Finally,we revealed retinoid acid receptor-related orphan receptors(RORα/γ)as direct targets of NOB.CONCLUSION Altogether,our results demonstrate that a pharmacological intervention that enhances circadian rhythms by small molecule may be as a novel strategy for combating metabolic disease.