The role of circadian clocks in cancer:Mechanisms and clinical implications

Circadian rhythm refers to the inherent 24-h cycle oscillation of biochemical,phys-iological and behavioral functions,which is almost universal in eukaryotes.At least 14 core clock genes have been reported to form multiple chain feedback loops that confer intrinsic circadian rhythmicity onto the molecular clock.Accumulating evidence has shown that the circadian gene dysfunction resulted from single nucleotide polymorphisms(SNPs),deletions,epigenetic modification,and deregulation is strongly associated with cancer risk.In the pre-sent review,we describe the composition of circadian rhythm system.We highlight the func-tion and mechanism of clock genes in cancer pathogenesis and progression.Moreover,their potential clinical implications as prognostic biomarkers and therapeutic targets have been ad-dressed.

Decoding the nexus:branched-chain amino acids and their connection with sleep,circadian rhythms,and cardiometabolic health

The sleep-wake cycle stands as an integrative process essential for sustaining optimal brain function and,either directly or indirectly,overall body health,encompassing metabolic and cardiovascular well-being.Given the heightened metabolic activity of the brain,there exists a considerable demand for nutrients in comparison to other organs.Among these,the branched-chain amino acids,comprising leucine,isoleucine,and valine,display distinctive significance,from their contribution to protein structure to their involvement in overall metabolism,especially in cerebral processes.Among the first amino acids that are released into circulation post-food intake,branched-chain amino acids assume a pivotal role in the regulation of protein synthesis,modulating insulin secretion and the amino acid sensing pathway of target of rapamycin.Branched-chain amino acids are key players in influencing the brain's uptake of monoamine precursors,competing for a shared transporter.Beyond their involvement in protein synthesis,these amino acids contribute to the metabolic cycles ofγ-aminobutyric acid and glutamate,as well as energy metabolism.Notably,they impact GABAergic neurons and the excitation/inhibition balance.The rhythmicity of branchedchain amino acids in plasma concentrations,observed over a 24-hour cycle and conserved in rodent models,is under circadian clock control.The mechanisms underlying those rhythms and the physiological consequences of their disruption are not fully understood.Disturbed sleep,obesity,diabetes,and cardiovascular diseases can elevate branched-chain amino acid concentrations or modify their oscillatory dynamics.The mechanisms driving these effects are currently the focal point of ongoing research efforts,since normalizing branched-chain amino acid levels has the ability to alleviate the severity of these pathologies.In this context,the Drosophila model,though underutilized,holds promise in shedding new light on these mechanisms.Initial findings indicate its potential to introduce novel concepts,particularly in elucidating the intricate connections between the circadian clock,sleep/wake,and metabolism.Consequently,the use and transport of branched-chain amino acids emerge as critical components and orchestrators in the web of interactions across multiple organs throughout the sleep/wake cycle.They could represent one of the so far elusive mechanisms connecting sleep patterns to metabolic and cardiovascular health,paving the way for potential therapeutic interventions.

Hypothalamic circuits and aging:keeping the circadian clock updated

Over the past century,age-related diseases,such as cancer,type-2 diabetes,obesity,and mental illness,have shown a significant increase,negatively impacting overall quality of life.Studies on aged animal models have unveiled a progressive discoordination at multiple regulatory levels,including transcriptional,translational,and post-translational processes,resulting from cellular stress and circadian derangements.The circadian clock emerges as a key regulator,sustaining physiological homeostasis and promoting healthy aging through timely molecular coordination of pivotal cellular processes,such as stem-cell function,cellular stress responses,and inter-tissue communication,which become disrupted during aging.Given the crucial role of hypothalamic circuits in regulating organismal physiology,metabolic control,sleep homeostasis,and circadian rhythms,and their dependence on these processes,strategies aimed at enhancing hypothalamic and circadian function,including pharmacological and non-pharmacological approaches,offer systemic benefits for healthy aging.Intranasal brain-directed drug administration represents a promising avenue for effectively targeting specific brain regions,like the hypothalamus,while reducing side effects associated with systemic drug delivery,thereby presenting new therapeutic possibilities for diverse age-related conditions.

Flowering-time regulation by the circadian clock:From Arabidopsis to crops

Precise timing of flowering in plants is critical for their growth and reproductive processes.One factor controlling flowering time is the cycle of light and darkness within a day,known as the photoperiod.Plants are classified into long-day,short-day,and day-neutral plants based on light requirements for floral initiation.Although the molecular mechanisms that govern this differentiation remain incompletely understood,studies have consistently shown that the circadian clock plays a central role in regulating photoperiod response across diverse plant species.However,there is a scarcity of reviews describing the regulatory network linking the circadian clock with photoperiodic flowering.This review summarizes that regulatory network,focusing on the distinct roles of clock genes in long-day and short-day plants.We also discuss the strategies of clock gene mutations contributing to geographic variation in longday and short-day crops.

Piperine regulates the circadian rhythms of hepatic clock gene expressions and gut microbiota in high-fat diet-induced obese rats

The interplay between the host circadian clock and microbiota has significant influences on host metabolism processes,and circadian desynchrony triggered by high-fat diet(HFD)is closely related to metabolic disorders.In this study,the modulatory effects of piperine(PIP)on lipid metabolism homeostasis,gut microbiota community and circadian rhythm of hepatic clock gene expressions in obese rats were investigated.The Sprague-Dawley(SD)rats were fed with normal diet(ND),HFD and HFD supplemented with PIP,respectively.After 9 weeks,rats were sacrificed with tissue and fecal samples collected for circadian analysis.Results showed that chronic PIP administration ameliorated the obesity-induced alterations in lipid metabolism and dysregulation of hepatic clock gene expressions in obese rats.The gut microbial communities studied through 16S rRNA sequencing showed that PIP ameliorated the imbalanced nicrobiota and recovered the circadian rhythm of Lactobacillaceae,Desulfovibrionaceae,Paraprevotellaceae,and Lachnospiraceae.The fecal metabolic profiles indicated that 3-dehydroshikimate,cytidine and lithocholyltaurine were altered,which were involved in the amino acid and fatty acid metabolism process.These findings could provide theoretical basis for PIP to work as functional food to alleviate the lipid metabolism disorder,circadian rhythm misalignment,and gut microbiota dysbiosis with wide applications in the food and pharmaceutic industries.

Diff erences in pigment circadian rhythmicity in greenand red-leafed tree species in the sun and shade

Light fl ux and quality are crucial factor for setting endogenous plant circadian rhythms.Evaluating the daily rhythmicity of leaf chlorophyll content is an eff ective method to monitor the plant physiological endogenous clock in response to environmental signals such as light availability/quality.Here,we used a leaf-clip sensor to monitor diurnal rhythms in the content of chlorophyll and fl avonoids such as fl avonols and anthocyanins in three green-(Ailanthus altissima,Tilia platyphyllos and Platanus×acerifolia)and two red-leafed(Acer platanoides cv.Crimson King and Prunus cerasifera var.pissardii)tree species,adapted to sun(L)or shade(S).Signifi cant diff erences in chlorophyll content(Chl)and its variations during the day were observed among treatments in all the analyzed species.S-plants had more Chl than L-plants irrespective of leaf color,and Chl variations were more distinct during the day than in L-plants.In particular,contents were lowest in the morning(9:00)and in the middle of the day(at 12:00 and 15:00),and the highest at dusk(21:00).The less evident trends in Chl variation in L-plants were attributed to a decrease in Chl content in high light,which likely masked any increases in the shaded counterparts during the afternoon.Daily fl avonol levels did not vary no notably during the day.In sun-exposed red leaves,anthocyanins partially screened mesophyll cells from incident light,and its levels were similar to the Chl dynamics in the shaded counterparts.This study provides new bases for further work on endogenous rhythms of plant pigments and improves our understanding of plant physiology in the context of day/night rhythmicity.

Major roles of the circadian clock in cancer

Circadian rhythms are natural rhythms that widely exist in all creatures,and regulate the processes and physiological functions of various biochemical reactions.The circadian clock is critical for cancer occurrence and progression.Its function is regulated by metabolic activities,and the expression and transcription of various genes.This review summarizes the composition of the circadian clock;the biological basis for its function;its relationship with,and mechanisms in,cancer;its various functions in different cancers;the effects of anti-tumor treatment;and potential therapeutic targets.Research in this area is expected to advance understanding of circadian locomotor output cycles kaput(CLOCK)and brain and muscle ARNT-like protein 1(BMAL1)in tumor diseases,and contribute to the development of new anti-tumor treatment strategies.

Circadian misalignment on submarines and other non-24-h environments – from research to application

Circadian clocks have important physiological and behavioral functions in humans and other organisms, which enable organisms to anticipate and respond to periodic environmental changes. Disturbances in circadian rhythms impair sleep, metabolism, and behavior. People with jet lag, night workers and shift workers are vulnerable to circadian misalignment. In addition, non-24-h cycles influence circadian rhythms and cause misalignment and disorders in different species, since these periods are beyond the entrainment ranges. In certain special conditions, e.g., on submarines and commercial ships, non-24-h watch schedules are often employed, which have also been demonstrated to be deleterious to circadian rhythms. Personnel working under such conditions suffer from circadian misalignment with their on-watch hours, leading to increased health risks and decreased cognitive performance. In this review, we summarize the research progress and knowledge concerning circadian rhythms on submarines and other environments in which non-24-h watch schedules are employed.

Molecular insights into the circadian clock in marine diatoms

The circadian clock is a fundamental endogenous mechanism of adaptation that coordinates the physiology and behavior of most organisms with diel variations in the external environment to maintain temporal homeostasis.Diatoms are the major primary producers in the ocean.However,little is known about the circadian clock in marine diatoms compared with other organisms.Here,we investigated circadian clock genes,their expression patterns,and responses to environmental stimuli such as light,nitrogen and phosphorus in two marine diatoms,Skeletonema costatum and Phaeodactylum tricornutum,using a combination of q RT-PCR and bioinformatic analysis.We identified 17 and 18 circadian clock genes in P.tricornutum and S.costatum,respectively.Despite significant evolutionary differences,these genes were similar to those of the higher plant Arabidopsis.We also established a molecular model for the marine diatom circadian clock comprising an input pathway,core oscillator,output pathway,and valve effector.Notably,the expression patterns of core clock genes(circadian clock associated 1(CCA1),late elongated hypocotyl(LHY)and timing of cab 1(TOC1))in both species differed from those of terrestrial plants.Furthermore,the expression of these genes was influenced by variations in ambient light,nitrogen and phosphorus availability.Although marine diatoms and higher plants share common circadian clock components,their clock genes have diverged throughout evolution,likely as a result of adapting to contrasting environments.

A new mammalian circadian oscillator model including the cAMP module

In this paper, we develop a new mathematical model for the mammalian circadian clock, which incorporates both transcriptional/translational feedback loops （TTFLs） and a cAMP-mediated feedback loop. The model shows that TTFLs and cAMP signalling cooperatively drive the circadian rhythms. It reproduces typical experimental observations with qualitative similarities, e.g. circadian oscillations in constant darkness and entrainment to light dark cycles. In addition, it can explain the phenotypes of cAMP-mutant and Rev-erba^-/^- -mutant mice, and help us make an experimentally-testable prediction： oscillations may be rescued when arrhythmic mice with constitutively low concentrations of cAMP are crossed with Rev-erba^-/- mutant mice. The model enhances our understanding of the mammalian circadian clockwork from the viewpoint of the entire cell.

Dynamic behavior of the cyanobacterial circadian clock with regulation of CikA

Cyanobacteria are the simplest organisms to have circadian clocks.The central oscillator in cyanobacteria is composed by a transcriptional/translational feedback loop(TTFL)and a post-translational oscillator(PTO).The PTO is a core pacemaker which consists of three proteins KaiA,KaiB and KaiC.KaiA stimulates the phosphorylation of KaiC,while KaiB inhibits the activity of KaiA.The cyanobacterial circadian clock is an interesting topic for researchers and many mathematical models have been constructed.However,the current mathematical models of the cyanobacterial circadian clock have been made only considering the interactions between Kai proteins.CikA,as an input pathway component,plays an essential role in the circadian clock,whose mutation results in abnormal rhythms.The regulation mechanism of CikA remains unclear.In this paper,we develop a detailed mathematical model for the cyanobacterial circadian clock with incorporation CikA-regulation.Based on numerical simulations,we explore the dynamic properties of the circadian clock regulated by CikA.The results show that the regulation of CikA makes the system more sensitive.In detail,CikA strengthens the central role of PTO and improves the adaptability of the circadian clock against the change of environment.With CikA,the system is able to modulate its period more easily to face environmental perturbation.CikA also enhances slightly the fitness of cyanobacteria.The findings of this paper can supplement the biological research and may help us more clearly understand the cyanobacterial circadian clock regulated by other proteins.

Entrainment mechanism of the cyanobacterial circadian clock induced by oxidized quinone

The circadian clock is a self-sustained biological oscillator which can be entrained by environmental signals.The cyanobacteria circadian clock is the simplest one,which is composed of the proteins KaiA,KaiB and KaiC.The phosphorylation/dephosphorylation state of KaiC exhibits a circadian oscillator.KaiA and KaiB activate KaiC phosphorylation and dephosphorylation respectively.CikA competing with KaiA for the same binding site on KaiB affects the phosphorylation state of KaiC.Quinone is a signaling molecule for entraining the cyanobacterial circadian clock which is oxidized at the onset of darkness and reduced at the onset of light,reflecting the environmental light-dark cycle.KaiA and CikA can sense external signals by detecting the oxidation state of quinone.However,the entrainment mechanism is far from clear.We develop an enhanced mathematical model including oxidized quinone sensed by KaiA and CikA,with which we present a detailed study on the entrainment of the cyanobacteria circadian clock induced by quinone signals.We find that KaiA and CikA sensing oxidized quinone pulse are related to phase advance and delay,respectively.The time of oxidized quinone pulse addition plays a key role in the phase shifts.The combination of KaiA and CikA is beneficial to the generation of entrainment,and the increase of signal intensity reduces the entrainment phase.This study provides a theoretical reference for biological research and helps us understand the dynamical mechanisms of cyanobacteria circadian clock.

Core clock component MtLUX controls shoot architecture through repression of MtTB1/MtTCP1A in Medicago truncatula

Plants are capable of regulating their shoot architecture in response to diverse internal and external environments.The circadian clock is an adaptive mechanism that integrates information from internal and ambient conditions to help plants cope with recurring environmental fluctuations.Despite the current understanding of plant circadian clock and genetic framework underlying plant shoot architecture,the intricate connection between these two adaptive mechanisms remains largely unclear.In this study,we elucidated how the core clock gene LUX ARRHYTHMO(LUX)regulates shoot architecture in the model legume plant Medicago truncatula.We show that mtlux mutant displays increased main stem height,reduced lateral shoot length,and decreased the number of lateral branches and biomass yield.Gene expression analysis revealed that Mt LUX regulated shoot architecture by repressing the expression of strigolactone receptor MtD14 and MtTB1/MtTCP1A,a TCP gene that functions centrally in modulating shoot architecture.In vivo and in vitro experiments showed that Mt LUX directly binds to a cis-element in the promoter of MtTB1/MtTCP1A,suggesting that Mt LUX regulates branching by rhythmically suppressing MtTB1/MtTCP1A.This work demonstrates the regulatory effect of the circadian clock on shoot architecture,offering a new understanding underlying the genetic basis towards the flexibility of plant shoot architecture.

The Circadian System Is Essential for the Crosstalk of VEGF-Notch-mediated Endothelial Angiogenesis in Ischemic Stroke

Ischemic stroke is a major public health problem worldwide.Although the circadian clock is involved in the process of ischemic stroke,the exact mechanism of the circadian clock in regulating angiogenesis after cerebral infarction remains unclear.In the present study,we determined that environmental circadian disruption(ECD)increased the stroke severity and impaired angiogenesis in the rat middle cerebral artery occlusion model,by measuring the infarct volume,neurological tests,and angiogenesis-related protein.We further report that Bmal1 plays an irreplaceable role in angiogenesis.Overexpression of Bmal1 promoted tube-forming,migration,and wound healing,and upregulated the vascular endothelial growth factor(VEGF)and Notch pathway protein levels.This promoting effect was reversed by the Notch pathway inhibitor DAPT,according to the results of angiogenesis capacity and VEGF pathway protein level.In conclusion,our study reveals the intervention of ECD in angiogenesis in ischemic stroke and further identifies the exact mechanism by which Bmal1 regulates angiogenesis through the VEGF-Notch1 pathway.

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

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

Clock component OsPRR59 delays heading date by repressing transcription of Ehd3 in rice

Heading date(or flowering time),an important agronomic trait in crop species,is closely associated with regional adaptation and yield.Members of the Pseudo-Response Regulator(PRR)family play key roles in regulating flowering.However,their role and molecular mechanism controlling heading date in rice is not very clear.Here,we identified rice OsPRR protein,OsPRR59,which delayed heading under longday conditions.OsPRR59 positively regulates yield by affecting plant height,secondary branches number per panicle,grain number per panicle,seed setting rate,and grain weight per plant.OsPRR59 is expressed in most tissues and its protein is localized to the nucleus.We also found that OsPRR59 directly binds to the promoter of Ehd3 to inhibit its expression.Compared with the WT,osprr59 ehd3 showed a significantly delayed heading phenotype,as did the ehd3 mutant.This was opposite to the phenotype of the osprr59 mutant,confirming that Ehd3 acted downstream of OsPRR59 in regulating rice flowering.Our results identified a direct regulator of Ehd3,and revealed a novel molecular mechanism of clock component OsPRR proteins in regulating heading date and provide a new genetic resource for fine-tuning heading date in rice.

Role of the ACTH/MC2R System in the Hair Cycle in Mice

Adrenocorticotropin hormone (ACTH), which is secreted in response to psychological stress, plays an important role in the hair cycle. This study examined the mechanism by which ACTH affects the hair cycle using mice deficient in melanocortin receptor-2(MC2R-/-), which is a main receptor for ACTH. We observed the hair cycle using female MC2R-/- mice at 15 weeks old and five days old to determine whether there were any age-dependent differences. The 15-week-old MC2R-/- mice showed the anagen phase for all mice. On the other hand, all of the MC2R+/+ mice showed the telogen phase at the same age. Moreover, in the five-day-old mice, the hair growth of the MC2R-/- mice occurred earlier than in the MC2R+/+ mice. Both the 15-week-old and five-day-old MC2R-/- mice had higher levels of ACTH and alpha-melanocyte stimulating hormone in the blood than did the MC2R+/+ mice. In addition, in the 15-week-old MC2R-/- mice, the hair cycle shifted to the telogen phase following the administration of a cyclic guanosine monophosphate (cGMP) inhibitor and MC1R/MC5R inhibitor. In the five-day-old MC2R-/- mice, the hair growth was slowed by the administration of corticosterone. These results suggest that the ACTH/MC2R system has an important role in the hair cycle.

The circadian clock of anti-tumor immunity

Immunotherapy has revolutionized cancer treatment by leveraging the intrinsic immune system.Although tremendous attention has focused on developing a new class of drugs enhancing or normalizing anti-tumor immunity,little effort was devoted to considering their time-of-day difference of administration in therapeutic efficacy.

Coordinated regulation of the mitochondrial retrograde response by circadian clock regulators and ANAC017

Mitochondrial retrograde signaling(MRS)supports photosynthetic function under a variety of conditions.Induction of mitochondrial dysfunction with myxothiazol(a specific inhibitor of the mitochondrial bc1 complex)or antimycin A(an inhibitor of the mitochondrial bc1 complex and cyclic electron transport in the chloroplast under light conditions)in the light and dark revealed diurnal control of MRS.This was evidenced by(1)significantly enhanced binding of ANAC017 to promoters in the light compared with the dark in Arabidopsis plants treated with myxothiazol(but not antimycin A),(2)overlap in the experimentally determined binding sites for ANAC017 and circadian clock regulators in the promoters of ANAC013 and AOX1a,(3)a diurnal expression pattern for ANAC017 and transcription factors it regulates,(4)altered expression of ANAC017-regulated genes in circadian clock mutants with and without myxothiazol treatment,and(5)a decrease in the magnitude of LHY and CCA1 expression in an ANAC017-overexpressing line and protein–protein interaction between ANAC017 and PIF4.This study also shows a large difference in transcriptome responses to antimycin A and myxothiazol in the dark:these responses are ANAC017 independent,observed in shoots and roots,similar to biotic challenge and salicylic acid responses,and involve ERF and ZAT transcription factors.This suggests that antimycin A treatment stimulates a second MRS pathway that is mediated or converges with salicylic acid signaling and provides a merging point with chloroplast retrograde signaling.

Temporal transcriptome reveals that circadian clock is invoived in the dynamic regulation of immune response to bacterial infection in Bombyx mori

The circadian clock plays a critical role in the regulation of host immune defense.However,the mechanistic basis for this regulation is largely unknown.Herein,the core clock gene cryptochromel(cryl)knockout line in Bombyx mori,an invertebrate animal model,was constructed to obtain the silkworm with dysfunctional molecular clock,and the dynamic regulation of the circadian clock on the immune responsiveness within 24h of Staphylococcus aureus infection was analyzed.We found that deletion of cryl decreased viability of silkworms and significantly reduced resistance of larvae to S.aureus.Time series RNA-seq analysis identified thousands of rhythmically expressed genes,including immune response genes,in the larval immune tissue,fat bodies.Uninfected cry1 knockout silkworms exhibited expression patterns of rhythmically expressed genes similar to wild-type(WT)silkworms infected with S.aureus.However,cry knockout silkworms exhibited a seriously weakened response to S.aureus infection.The immune response peaked at 6 and 24 h after infection,during which“transcription storms”occurred,and the expression levels of the immune response genes,PGRP and antimicrobial peptides(AMPs),were significantly upregulated in WT.In contrast,cry I knockout did not effectively activate Toll,Imd,or NF-κB signaling pathways during the immune adjustment period from 12 to 18 h after infection,resulting in failure to initiate the immune responsiveness peak at 24 h after infection.This may be related to inhibited silkworm fat body energy metabolism.These results demonstrated the dynamic regulation of circadian clock on silkworm immune response to bacterial infection and provided important insights into hostantimicrobial defensemechanisms.