Circadian time signatures of fitness and disease

Chronic jetlag accelerates pancreatic neoplasia in conditional Kras-mutant mice

Misalignment of the circadian clock compared to environmental cues causes circadian desynchrony, which is pervasive in humans. Clock misalignment can lead to various pathologies including obesity and diabetes, both of which are associated with pancreatic ductal adenocarcinoma - a devastating cancer with an 80% five-year mortality rate. Although circadian desynchrony is associated with an increased risk of several solid-organ cancers, the correlation between clock misalignment and pancreas cancer is unclear. Using a chronic jetlag model, we investigated the impact of clock misalignment on pancreas cancer initiation in mice harboring a pancreas-specific activated Kras mutation. We found that chronic jetlag accelerated the development of pancreatic cancer precursor lesions, with a concomitant increase in precursor lesion grade. Cell-autonomous knock-out of the clock in pancreatic epithelial cells of Kras-mutant mice demonstrated no acceleration of precursor lesion formation, indicating non-cell-autonomous clock dysfunction was responsible for the expedited tumor development. Therefore, we applied single-cell RNA sequencing over time and identified fibroblasts as the cell population manifesting the greatest clock-dependent changes, with enrichment of specific cancer-associated fibroblast pathways due to circadian misalignment.

Adrenalectomy prevents the effects of social defeat stress on PER2 rhythms in some peripheral tissues in male mice

While stress does not affect the phase or period of the central pacemaker in the suprachiasmatic nucleus, it can shift clocks in peripheral tissues. Our previous studies showed significant delays of the PER2 rhythms in lung and kidney following social defeat stress. The mechanism underlying these effects is not fully understood, but might involve glucocorticoids (GC) released during the stressor. In the present study, we performed social defeat stress in adrenalectomized (ADX) mice to see if the induction of endogenous GC is necessary for the stress-induced phase shifts of peripheral clocks. We used mice that carry a luciferase reporter gene fused to the circadian clock gene Period2 (PER2::LUC) to examine daily rhythms of PER2 expression in various peripheral tissues. Mice were exposed to 5 consecutive daily social defeat stress in the late dark phase (ZT21-22). Running wheel rotations were recorded during 7 baseline and 5 social defeat days, which showed that social defeat stress suppressed locomotor activity without affecting the phase of the rhythm. This suppression of activity was not prevented by ADX. One hour after the last stressor, tissue samples from the liver, kidney and lung were collected and cultured for ex vivo bioluminescence recordings. In the liver, PER2 rhythms were not affected by social defeat stress or ADX. In the kidney, social defeat stress caused a > 4 h phase delay of the PER2 rhythm, which was prevented by ADX, supporting the hypothesis of a crucial role of GC in this stress effect. In the lung, social defeat stress caused an 8 h phase delay, but, surprisingly, a similar phase delay was seen in ADX animals independent of defeat. The latter indicates complex effects of stress and stress hormones on the lung clock. In conclusion, the findings show that repeated social defeat stress in the dark phase can shift PER2 rhythms in some tissues (lung, kidney) and not others (liver). Moreover, the social defeat stress effect in some tissues appears to be mediated by glucocorticoids (kidney) whereas the mechanism in other tissues is more complex (lung).

A dynamically coherent pattern of rhythms that matches between distant species across the evolutionary scale

We address the temporal organization of circadian and ultradian rhythms, crucial for understanding biological timekeeping in behavior, physiology, metabolism, and alignment with geophysical time. Using a newly developed five-steps wavelet-based approach to analyze high-resolution time series of metabolism in yeast cultures and spontaneous movement, metabolism, and feeding behavior in mice, rats, and quails, we describe a dynamically coherent pattern of rhythms spanning over a broad range of temporal scales (hours to minutes). The dynamic pattern found shares key features among the four, evolutionary distant, species analyzed. Specifically, a branching appearance given by splitting periods from 24 h into 12 h, 8 h and below in mammalian and avian species, or from 14 h down to 0.07 h in yeast. Scale-free fluctuations with long-range correlations prevail below ~ 4 h. Synthetic time series modeling support a scenario of coexisting behavioral rhythms, with circadian and ultradian rhythms at the center of the emergent pattern observed.

Single nucleotide polymorphisms (SNPs) in circadian genes: Impact on gene function and phenotype

Circadian rhythm is an endogenous timing system that allows an organism to anticipate and adapt to daily changes and regulate various physiological variables such as the sleep-wake cycle. This rhythm is governed by a molecular circadian clock mechanism, generated by a transcriptional and translational feedback loop (TTFL) mechanism. In mammals, TTFL is determined by the interaction of four main clock proteins: BMAL1, CLOCK, Cryptochromes (CRY), and Periods (PER). BMAL1 and CLOCK form dimers and initiate the transcription of clock-controlled genes (CCG) by binding an E-box element with the promotor genes. Among CCGs, PERs and CRYs accumulate in the cytosol and translocate into the nucleus, where they interact with the BMAL1/CLOCK dimer and inhibit its activity. Several epidemiological and genetic studies have revealed that circadian rhythm disruption causes various types of disease. In this chapter, we summarize the effect of core clock gene SNPs on circadian rhythm and diseases in humans.

Light at night and cause-specific mortality risk in Mainland China: a nationwide observational study

BACKGROUND

While epidemiological studies have found correlations between light at night (LAN) and health effects, none has so far investigated the impacts of LAN on population mortality yet. We aimed to estimate the relative risk for mortality from exposure to LAN in Mainland China.

METHODS

This time-stratified case-crossover nationwide study used NPP-VIIRS to obtain daily LAN data of Mainland China between 2015 and 2019. The daily mortality data were obtained from the Disease Surveillance Point System in China. Conditional Poisson regression models were applied to examine the relative risk (RR) for mortality along daily LAN in each county, then meta-analysis was performed to combine the county-specific estimates at the national or regional level.

RESULTS

A total of 579 counties with an average daily LAN of 4.39 (range: 1.02-35.46) were included in the main analysis. The overall RRs per 100 nW/cm²/sr increases in daily LAN were 1.08 (95%CI: 1.05-1.11) for all-cause mortality and 1.08 (95%CI: 1.05-1.11) for natural-cause mortality. A positive association between LAN and all natural cause-specific mortality was observed, of which the strongest effect was observed on mortality caused by neuron system disease (RR = 1.32, 95%CI: 1.14-1.52). The results were robust in both younger and old, as well as in males and females. The more pronounced effect of LAN was observed in median LAN-level regions. Combined with an exposure-response curve, our study suggests a non-linear association between LAN and mortality in China.

CONCLUSIONS

Our study shows LAN is associated with mortality in China, particularly for neuron system disease-related mortality. These findings have important implications for public health policy establishment to minimize the health consequences of light pollution.

The circadian regulation of extracellular ATP

Extracellular ATP is a potent signaling molecule released from various cells throughout the body and is intimately involved in the pathophysiological functions of the nervous system and immune system by activating P2 purinergic receptors. Recent increasingly studies showed that extracellular ATP exhibits circadian oscillation with an approximately 24-h periodicity, which participates in regulatory pathways of central oscillator suprachiasmatic nucleus and peripheral oscillator bladder, respectively. Oscillators modulate the protein expression of ATP release channels and ectonucleotidase activity through clock genes; indeed, real-time alterations of ATP release and degradation determine outcomes of temporal character on extracellular ATP rhythm. The regulatory pathways on extracellular ATP rhythm are different in central and peripheral systems. In this review, we summarize the circadian rhythm of extracellular ATP and discuss several circadian regulatory pathways in different organs via ATP release and degradation, to provide a new understanding for purinergic signaling in the regulatory mechanism of circadian rhythm and a potential target to research the circadian regulation of extracellular ATP in other circadian oscillators.

Beyond circadian rhythms: emerging roles of ultradian rhythms in control of liver functions

The mammalian liver must cope with various metabolic and physiological changes that normally recur every day and primarily stem from daily cycles of rest-activity and fasting-feeding. Although a large body of evidence supports the reciprocal regulation of circadian rhythms and liver function, the research on the hepatic ultradian rhythms have largely been lagging behind. However, with the advent of more cost-effective high-throughput omics technologies, high-resolution time-lapse imaging, and more robust and powerful mathematical tools, several recent studies have shed new light on the presence and functions of hepatic ultradian rhythms. In this review, we will first very briefly discuss the basic principles of circadian rhythms, and then cover in greater details the recent literature related to ultradian rhythms. Specifically, we will highlight the prevalence and mechanisms of hepatic 12-h rhythms, and 8-h rhythms, which cycle at the second and third harmonics of circadian frequency. Finally, we also refer to ultradian rhythms with other frequencies and examine the limitations of the current approaches as well as the challenges related to identifying ultradian rhythm and addressing their molecular underpinnings.

Circadian disruption: from mouse models to molecular mechanisms and cancer therapeutic targets

The circadian clock is a timekeeping system for numerous biological rhythms that contribute to the regulation of numerous homeostatic processes in humans. Disruption of circadian rhythms influences physiology and behavior and is associated with adverse health outcomes, especially cancer. However, the underlying molecular mechanisms of circadian disruption-associated cancer initiation and development remain unclear. It is essential to construct good circadian disruption models to uncover and validate the detailed molecular clock framework of circadian disruption in cancer development and progression. Mouse models are the most widely used in circadian studies due to their relatively small size, fast reproduction cycle, easy genome manipulation, and economic practicality. Here, we reviewed the current mouse models of circadian disruption, including suprachiasmatic nuclei destruction, genetic engineering, light disruption, sleep deprivation, and other lifestyle factors in our understanding of the crosstalk between circadian rhythms and oncogenic signaling, as well as the molecular mechanisms of circadian disruption that promotes cancer growth. We focused on the discoveries made with the nocturnal mouse, diurnal human being, and cell culture and provided several circadian rhythm-based cancer therapeutic strategies.

When should I eat: A circadian view on food intake and metabolic regulation

The circadian clock is a hierarchical timing system regulating most physiological and behavioral functions with a period of approximately 24 h in humans and other mammalian species. The circadian clock drives daily eating rhythms that, in turn, reinforce the circadian clock network itself to anticipate and orchestrate metabolic responses to food intake. Eating is tightly interconnected with the circadian clock and recent evidence shows that the timing of meals is crucial for the control of appetite and metabolic regulation. Obesity results from combined long-term dysregulation in food intake (homeostatic and hedonic circuits), energy expenditure, and energy storage. Increasing evidence supports that the loss of synchrony of daily rhythms significantly impairs metabolic homeostasis and is associated with obesity. This review presents an overview of mechanisms regulating food intake (homeostatic/hedonic) and focuses on the crucial role of the circadian clock on the metabolic response to eating, thus providing a fundamental research axis to maintain a healthy eating behavior.

Aging, circadian disruption and neurodegeneration: Interesting interplay

The circadian system is an intricate molecular network of coordinating circadian clocks that organize the internal synchrony of the organism in response to the environment. These rhythms are maintained by genetically programmed positive and negative auto-regulated transcriptional and translational feedback loops that sustain 24-hour oscillations in mRNA and protein components of the endogenous circadian clock. Since inter and intracellular activity of the central pacemaker appears to reduce with aging, the interaction between the circadian clock and aging continues to elude our understanding. In this review article, we discuss circadian clock components at the molecular level and how aging adversely affects circadian clock functioning in rodents and humans. The natural decline in melatonin levels with aging strongly contributes to circadian dysregulation resulting in the development of neurological anomalies. Additionally, inappropriate environmental conditions such as Artificial Light at Night (ALAN) can cause circadian disruption or chronodisruption (CD) which can result in a variety of pathological diseases, including premature aging. Furthermore, we summarize recent evidence suggesting that CD may also be a predisposing factor for the development of age-related neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), although more investigation is required to prove this link. Finally, certain chrono-enhancement approaches have been offered as intervention strategies to prevent, alleviate, or mitigate the impacts of CD. This review thus aims to bring together recent advancements in the chronobiology of the aging process, as well as its role in NDDs.

Role of Melatonin in Daily Variations of Plasma Insulin Level and Pancreatic Clock Gene Expression in Chick Exposed to Monochromatic Light

To clarify the effect of monochromatic light on circadian rhythms of plasma insulin level and pancreatic clock gene expression and its mechanism, 216 newly hatched chicks were divided into three groups (intact, sham operation and pinealectomy) and were raised under white (WL), red (RL), green (GL) or blue (BL) light for 21 days. Their plasma and pancreas were sampled at six four-hour intervals. For circadian rhythm analysis, measurements of plasma melatonin, insulin, and clock gene expression (cClock, cBmal1, cBmal2, cCry1, cCry2, cPer2, and cPer3) were made. Plasma melatonin, insulin, and the pancreatic clock gene all expressed rhythmically in the presence of monochromatic light. Red light reduced the mesor and amplitude of plasma melatonin in comparison to green light. The mesor and amplitude of the pancreatic clock gene in chickens exposed to red light were dramatically reduced, which is consistent with the drop in plasma melatonin levels. Red light, on the other hand, clearly raised the level of plasma insulin via raising the expression of cVamp2, but not cInsulin. After the pineal gland was removed, the circadian expressions of plasma melatonin and pancreatic clock gene were significantly reduced, but the plasma insulin level and the pancreatic cVamp2 expression were obviously increased, resulting in the disappearance of differences in insulin level and cVamp2 expression in the monochromatic light groups. Therefore, we hypothesize that melatonin may be crucial in the effect of monochromatic light on the circadian rhythm of plasma insulin level by influencing the expression of clock gene in chicken pancreas.

Chemotherapy delivery time affects treatment outcomes of female patients with diffuse large B cell lymphoma

BACKGROUNDChronotherapy is a drug intervention at specific times of the day to optimize efficacy and minimize adverse effects. Its value in hematologic malignancy remains to be explored, in particular in adult patients.METHODSWe performed chronotherapeutic analysis using 2 cohorts of patients with diffuse large B cell lymphoma (DLBCL) undergoing chemotherapy with a dichotomized schedule (morning or afternoon). The effect of a morning or afternoon schedule of rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) on survival and drug tolerability was evaluated in a survival cohort (n = 210) and an adverse event cohort (n = 129), respectively. Analysis of about 14,000 healthy individuals followed to identify the circadian variation in hematologic parameters.RESULTSBoth progression-free survival (PFS) and overall survival (OS) of female, but not male, patients were significantly shorter when patients received chemotherapy mostly in the morning (PFS HR 0.357, P = 0.033; and OS HR 0.141, P = 0.032). The dose intensity was reduced in female patients treated in the morning (cyclophosphamide 10%, P = 0.002; doxorubicin 8%, P = 0.002; and rituximab 7%, P = 0.003). This was mainly attributable to infection and neutropenic fever: female patients treated in the morning had a higher incidence of infections (16.7% vs. 2.4%) and febrile neutropenia (20.8% vs. 9.8%) as compared with those treated in the afternoon. The sex-specific chronotherapeutic effects can be explained by the larger daily fluctuation of circulating leukocytes and neutrophils in female than in male patients.CONCLUSIONIn female DLBCL patients, R-CHOP treatment in the afternoon can reduce toxicity while it improves efficacy and survival outcome.FUNDINGNational Research Foundation of Korea (NRF) grant funded by the Korean government (grant number NRF-2021R1A4A2001553), Institute for Basic Science IBS-R029-C3, and Human Frontiers Science Program Organization Grant RGY0063/2017.

Brain nuclear receptors and cardiovascular function

Brain-heart interaction has raised up increasing attentions. Nuclear receptors (NRs) are abundantly expressed in the brain, and emerging evidence indicates that a number of these brain NRs regulate multiple aspects of cardiovascular diseases (CVDs), including hypertension, heart failure, atherosclerosis, etc. In this review, we will elaborate recent findings that have established the physiological relevance of brain NRs in the context of cardiovascular function. In addition, we will discuss the currently available evidence regarding the distinct neuronal populations that respond to brain NRs in the cardiovascular control. These findings suggest connections between cardiac control and brain dynamics through NR signaling, which may lead to novel tools for the treatment of pathological changes in the CVDs.

Circadian regulation of cardiac muscle function and protein degradation

The circadian clock plays a fundamental role in physiology. In particular, the heart is a target organ where the clock orchestrates various aspects of cardiac function. At the molecular level, the clock machinery governs daily rhythms of gene expression. Such circadian regulation is in tune with the dynamic nature of heart structure and function, and provides the foundation for chronotherapeutic applications in cardiovascular diseases. In comparison, a regulatory role of the clock in cardiac protein degradation is poorly documented. Sarcomere is the structural and functional unit responsible for cardiac muscle contraction, and sarcomere components are closely regulated by protein folding and proteolysis. Emerging evidence supports a role of the circadian clock in governing sarcomere integrity and function. Particularly, recent studies uncovered a circadian regulation of a core sarcomere component TCAP. It is possible that circadian regulation of the cardiac muscle protein turnover is a key regulatory mechanism underlying cardiac remodeling in response to physiological and environmental stimuli. While the detailed regulatory mechanisms and the molecular links to cardiac (patho)physiology remain to be further studied, therapeutic strategies targeting circadian control in the heart may markedly enhance intervention outcomes against cardiovascular disease.

Circadian stabilization loop: the regulatory hub and therapeutic target promoting circadian resilience and physiological health

The circadian clock is a fundamental biological mechanism that orchestrates essential cellular and physiological processes to optimize fitness and health. The basic functional unit is the cell-autonomous oscillator, consisting of intersecting negative feedback loops. Whereas the core loop is primarily responsible for rhythm generation, auxiliary loops, most notably the secondary or stabilization loop, play pivotal roles to confer temporal precision and molecular robustness. The stabilization loop contains opposing nuclear receptor subfamilies REV-ERBs and retinoic acid receptor-related orphan receptors (RORs), competing to modulate rhythmic expression of the basic helix-loop-helix ARNT like 1 ( Bmal1) genes in the core loop as well as other clock-controlled genes. Therefore, REV-ERBs and RORs are strategically located to interface the oscillator and the global transcriptomic network, promoting cellular homeostasis and physiological fitness throughout lifespan. Disruption of REV-ERB and ROR functions has been linked with diseases and aging, and pharmacological manipulation of these factors has shown promise in various mouse disease models. Nobiletin is a natural compound that directly binds to and activates RORα/γ, modulating circadian rhythms, and shows robust in vivo efficacies to combat clock-associated pathophysiologies and age-related decline. Results from several studies demonstrate an inverse relation between nobiletin efficacy and clock functional state, where nobiletin elicits little effect in young and healthy mice with growing efficacy as the clock is perturbed by environmental and genetic challenges. This mode of action is consistent with the function of the stabilization loop to promote circadian and physiological resilience. Future studies should further investigate the function and mechanism of REV-ERBs and RORs, and test strategies targeting these factors against disease and aging.

Circadian stabilization loop: the regulatory hub and therapeutic target promoting circadian resilience and physiological health

The circadian clock is a fundamental biological mechanism that orchestrates essential cellular and physiological processes to optimize fitness and health. The basic functional unit is the cell-autonomous oscillator, consisting of intersecting negative feedback loops. Whereas the core loop is primarily responsible for rhythm generation, auxiliary loops, most notably the secondary or stabilization loop, play pivotal roles to confer temporal precision and molecular robustness. The stabilization loop contains opposing nuclear receptor subfamilies REV-ERBs and retinoic acid receptor-related orphan receptors (RORs), competing to modulate rhythmic expression of the basic helix-loop-helix ARNT like 1 ( Bmal1) genes in the core loop as well as other clock-controlled genes. Therefore, REV-ERBs and RORs are strategically located to interface the oscillator and the global transcriptomic network, promoting cellular homeostasis and physiological fitness throughout lifespan. Disruption of REV-ERB and ROR functions has been linked with diseases and aging, and pharmacological manipulation of these factors has shown promise in various mouse disease models. Nobiletin is a natural compound that directly binds to and activates RORα/γ, modulating circadian rhythms, and shows robust in vivo efficacies to combat clock-associated pathophysiologies and age-related decline. Results from several studies demonstrate an inverse relation between nobiletin efficacy and clock functional state, where nobiletin elicits little effect in young and healthy mice with growing efficacy as the clock is perturbed by environmental and genetic challenges. This mode of action is consistent with the function of the stabilization loop to promote circadian and physiological resilience. Future studies should further investigate the function and mechanism of REV-ERBs and RORs, and test strategies targeting these factors against disease and aging.

Modelling metabolic diseases and drug response using stem cells and organoids

Metabolic diseases, including obesity, diabetes mellitus and cardiovascular disease, are a major threat to health in the modern world, but efforts to understand the underlying mechanisms and develop rational treatments are limited by the lack of appropriate human model systems. Notably, advances in stem cell and organoid technology allow the generation of cellular models that replicate the histological, molecular and physiological properties of human organs. Combined with marked improvements in gene editing tools, human stem cells and organoids provide unprecedented systems for studying mechanisms of metabolic diseases. Here, we review progress made over the past decade in the generation and use of stem cell-derived metabolic cell types and organoids in metabolic disease research, especially obesity and liver diseases. In particular, we discuss the limitations of animal models and the advantages of stem cells and organoids, including their application to metabolic diseases. We also discuss mechanisms of drug action, understanding the efficacy and toxicity of existing therapies, screening for new treatments and pursuing personalized therapies. We highlight the potential of combining stem cell-derived organoids with gene editing and functional genomics to revolutionize the approach to finding treatments for metabolic diseases.

Low intensity near-infrared light promotes bone regeneration via circadian clock protein cryptochrome 1

Bone regeneration remains a great clinical challenge. Low intensity near-infrared (NIR) light showed strong potential to promote tissue regeneration, offering a promising strategy for bone defect regeneration. However, the effect and underlying mechanism of NIR on bone regeneration remain unclear. We demonstrated that bone regeneration in the rat skull defect model was significantly accelerated with low-intensity NIR stimulation. In vitro studies showed that NIR stimulation could promote the osteoblast differentiation in bone mesenchymal stem cells (BMSCs) and MC3T3-E1 cells, which was associated with increased ubiquitination of the core circadian clock protein Cryptochrome 1 (CRY1) in the nucleus. We found that the reduction of CRY1 induced by NIR light activated the bone morphogenetic protein (BMP) signaling pathways, promoting SMAD1/5/9 phosphorylation and increasing the expression levels of Runx2 and Osterix. NIR light treatment may act through sodium voltage-gated channel Scn4a, which may be a potential responder of NIR light to accelerate bone regeneration. Together, these findings suggest that low-intensity NIR light may promote in situ bone regeneration in a CRY1-dependent manner, providing a novel, efficient and non-invasive strategy to promote bone regeneration for clinical bone defects.

The circadian E3 ligase FBXL21 regulates myoblast differentiation and sarcomere architecture via MYOZ1 ubiquitination and NFAT signaling

Numerous molecular and physiological processes in the skeletal muscle undergo circadian time-dependent oscillations in accordance with daily activity/rest cycles. The circadian regulatory mechanisms underlying these cyclic processes, especially at the post-transcriptional level, are not well defined. Previously, we reported that the circadian E3 ligase FBXL21 mediates rhythmic degradation of the sarcomere protein TCAP in conjunction with GSK-3β, and Psttm mice harboring an Fbxl21 hypomorph allele show reduced muscle fiber diameter and impaired muscle function. To further elucidate the regulatory function of FBXL21 in skeletal muscle, we investigated another sarcomere protein, Myozenin1 (MYOZ1), that we identified as an FBXL21-binding protein from yeast 2-hybrid screening. We show that FBXL21 binding to MYOZ1 led to ubiquitination-mediated proteasomal degradation. GSK-3β co-expression and inhibition were found to accelerate and decelerate FBXL21-mediated MYOZ1 degradation, respectively. Previously, MYOZ1 has been shown to inhibit calcineurin/NFAT signaling important for muscle differentiation. In accordance, Fbxl21 KO and MyoZ1 KO in C2C12 cells impaired and enhanced myogenic differentiation respectively compared with control C2C12 cells, concomitant with distinct effects on NFAT nuclear localization and NFAT target gene expression. Importantly, in Psttm mice, both the levels and diurnal rhythm of NFAT2 nuclear localization were significantly diminished relative to wild-type mice, and circadian expression of NFAT target genes associated with muscle differentiation was also markedly dampened. Furthermore, Psttm mice exhibited significant disruption of sarcomere structure with a considerable excess of MYOZ1 accumulation in the Z-line. Taken together, our study illustrates a pivotal role of FBXL21 in sarcomere structure and muscle differentiation by regulating MYOZ1 degradation and NFAT2 signaling.

Potential Role of the Circadian Clock in the Regulation of Cancer Stem Cells and Cancer Therapy

Circadian rhythms, including sleep/wake cycles as well as hormonal, immune, metabolic, and cell proliferation rhythms, are fundamental biological processes driven by a cellular time-keeping system called the circadian clock. Disruptions in these rhythms due to genetic alterations or irregular lifestyles cause fundamental changes in physiology, from metabolism to cellular proliferation and differentiation, resulting in pathological consequences including cancer. Cancer cells are not uniform and static but exist as different subtypes with phenotypic and functional differences in the tumor microenvironment. At the top of the heterogeneous tumor cell hierarchy, cancer stem cells (CSCs), a self-renewing and multi-potent cancer cell type, are most responsible for tumor recurrence and metastasis, chemoresistance, and mortality. Phenotypically, CSCs are associated with the epithelial-mesenchymal transition (EMT), which confers cancer cells with increased motility and invasion ability that is characteristic of malignant and drug-resistant stem cells. Recently, emerging studies of different cancer types, such as glioblastoma, leukemia, prostate cancer, and breast cancer, suggest that the circadian clock plays an important role in the maintenance of CSC/EMT characteristics. In this review, we describe recent discoveries regarding how tumor intrinsic and extrinsic circadian clock-regulating factors affect CSC evolution, highlighting the possibility of developing novel chronotherapeutic strategies that could be used against CSCs to fight cancer.

SR9009 inhibits lethal prostate cancer subtype 1 by regulating the LXRα/FOXM1 pathway independently of REV-ERBs

Perturbations of the circadian clock are linked to multiple diseases, including cancers. Pharmacological activation of REV-ERB nuclear receptors, the core components of the circadian clock, has antitumor effects on various malignancies, while the impact of SR9009 on prostate cancer (PCa) remains unknown. Here, we found that SR9009 was specifically lethal to PCa cell lines but had no cytotoxic effect on prostate cells. SR9009 significantly inhibited colony formation, the cell cycle, and cell migration and promoted apoptosis in PCa cells. SR9009 treatment markedly inhibited prostate cancer subtype 1 (PCS1), the most lethal and aggressive PCa subtype, through FOXM1 pathway blockade, while it had no impacts on PCS2 and PCS3. Seven representative genes, including FOXM1, CENPA, CENPF, CDK1, CCNB1, CCNB2, and BIRC5, were identified as the shared genes involved in the FOXM1 pathway and PCS1. All of these genes were upregulated in PCa tissues, associated with worse clinicopathological outcomes and downregulated after SR9009 treatment. Nevertheless, knockdown or knockout of REV-ERB could not rescue the anticancer effect of SR9009 in PCa. Further analysis confirmed that it was LXRα rather than REV-ERBs which has been activated by SR9009. The expression levels of these seven genes were changed correspondingly after LXRα knockdown and SR9009 treatment. An in vivo study validated that SR9009 restrained tumor growth in 22RV1 xenograft models and inhibited FOXM1 and its targeted gene expression. In summary, SR9009 can serve as an effective treatment option for highly aggressive and lethal PCS1 tumors through mediating the LXRα/FOXM1 pathway independently of REV-ERBs.

The Cytoskeletal Transport Protein, Secretagogin, Is Essential for Diurnal Glucagon-like Peptide-1 Secretion in Mice

The intestinal L-cell incretin, glucagon-like peptide-1 (GLP-1), exhibits a circadian pattern of secretion, thereby entraining diurnal insulin release. Secretagogin (Scgn), an actin-binding regulatory protein, is essential for the temporal peak of GLP-1 secretion in vitro. To interrogate the role of Scgn in diurnal GLP-1 secretion in vivo, peak and trough GLP-1 release were evaluated in knockout mice (Scgn-/-, Gcg-CreERT2/+; Scgnfl/fl and Vil-CreERT2/+; Scgnfl/fl), and RNA sequencing (RNA-Seq) was conducted in Scgn knockdown L-cells. All 3 knockout models demonstrated loss of the diurnal rhythm of GLP-1 secretion in response to oral glucose. Gcg-CreERT2/+; Scgnfl/fl mice also lost the normal pattern in glucagon secretion, while Scgn-/- and Vil-CreERT2/+; Scgnfl/fl animals demonstrated impaired diurnal secretion of the related incretin, glucose-dependent insulinotrophic polypeptide. RNA-Seq of mGLUTag L-cells showed decreased pathways regulating vesicle transport, transport and binding, and protein-protein interaction at synapse, as well as pathways related to proteasome-mediated degradation including chaperone-mediated protein complex assembly following Scgn knockdown. Scgn is therefore essential for diurnal L-cell GLP-1 secretion in vivo, likely mediated through effects on secretory granule dynamics.

CRY2 isoform selectivity of a circadian clock modulator with antiglioblastoma efficacy

The mammalian cryptochrome isoforms, CRY1 and CRY2, are core circadian clock regulators that work redundantly. Recent studies revealed distinct roles of these closely related homologs in clock output pathways. Isoform-selective control of CRY1 and CRY2 is critical for further understanding their redundant and distinct roles. KL001 was the first identified small-molecule CRY modulator that activates both CRY1 and CRY2. SHP656 is an orally available KL001 derivative and has shown efficacy in blood glucose control and inhibition of glioblastoma stem cell (GSC) growth in animal models. However, CRY isoform selectivity of SHP656 was uncharacterized, limiting understanding of the roles of CRY1 and CRY2. Here, we report the elucidation of CRY2 selectivity of SHP656. SHP656 lengthened cellular circadian period in a CRY2-dependent manner and selectively interacted with CRY2. By determining the X-ray crystal structure of CRY2 in complex with SHP656 and performing molecular dynamics simulations, we elucidated compound interaction mechanisms. SHP656 binding was compatible with the intrinsic CRY2 gatekeeper W417 "in" orientation and also a close "further in" conformation. Perturbation of W417 interaction with the lid loop resulted in a reduced effect of SHP656 on CRY2, supporting an important role of gatekeeper orientation in isoform selectivity. We also identified the R form of SHP656 (called SHP1703) as the active isomer. Treatment with SHP1703 effectively reduced GSC viability. Our results suggest a direct role of CRY2 in glioblastoma antitumorigenesis and provide a rationale for the selective modulation of CRY isoforms in the therapeutic treatment of glioblastoma and other circadian clock-related diseases.

mTOR-AKT Signaling in Cellular Clock Resetting Triggered by Osmotic Stress

Aims: The circadian clock oscillates in a cell-autonomous manner with a period of ∼24 h, and the phase is regulated by various time cues such as light and temperature through multiple clock input pathways. We previously found that osmotic and oxidative stress strongly affected the circadian period and phase of cellular rhythms, and triple knockout of apoptosis signal-regulating kinase (ASK) family members, Ask1, Ask2, and Ask3, abolished the phase shift (clock resetting) induced by hyperosmotic pulse treatment. We aimed at exploring a key molecule(s) and signaling events in the clock input pathway dependent on ASK kinases. Results: The phase shift of the cellular clock induced by the hyperosmotic pulse treatment was significantly reduced by combined deficiencies of the clock(-related) genes, Dec1, Dec2, and E4 promoter-binding protein 4 (also known as Nfil3) (E4bp4). In addition, liquid chromatography mass/mass spectrometry (LC-MS/MS)-based proteomic analysis identified hyperosmotic pulse-induced phosphorylation of circadian locomotor output cycles caput (CLOCK) Ser845 in an AKT-dependent manner. We found that AKT kinase was phosphorylated at Ser473 (i.e., activated) in response to the hyperosmotic pulse experiments. Inhibition of mechanistic target of rapamycin (mTOR) kinase by Torin 1 treatment completely abolished the AKT activation, suppressed the phosphorylation of CLOCK Ser845, and blocked the clock resetting induced by the hyperosmotic pulse treatment. Innovation and Conclusions: We conclude that mTOR-AKT signaling is indispensable for the CLOCK Ser845 phosphorylation, which correlates with the clock resetting induced by the hyperosmotic pulse treatment. Immediate early induction of the clock(-related) genes and CLOCK carboxyl-terminal (C-terminal) region containing Ser845 also play important roles in the clock input pathway through redox-sensitive ASK kinases. Antioxid. Redox Signal. 37, 631-646.

A high-fat diet disrupts the hepatic and adipose circadian rhythms and modulates the diurnal rhythm of gut microbiota-derived short-chain fatty acids in gestational mice

The prevalence of gestational obesity has reached epidemic proportions. Evidence supported that the interactions between the gut microbiota and circadian clocks far reached, affecting host metabolism. Our study aimed to investigate the effect of a high-fat diet (HF) on the hepatic and adipose circadian rhythms in gestational mice and to explore the role of gut microbiota-derived short-chain fatty acids (SCFAs) in mediating the effects. C57BL/6 female mice were randomly fed a standard chow diet (Ctr) or HF prior to and during pregnancy. Samples were collected every 4 h over 24 h (six time points), and 16S rRNA and metabonomics were carried out. Rhythmic patterns were identified and compared using CircaCompare. The results showed that the HF before and during pregnancy significantly induced obesity and worsen glucose tolerance, insulin sensitivity, and lipid metabolism in the gestational mice. Furthermore, the HF significantly disrupted the rhythmic pattern of hepatic and adipose circadian clock genes and downstream metabolic genes. Importantly, our results revealed that the HF altered the diurnal rhythm of the gut microbiota in a diverse manner, which was assessed across three categories: phase shift, loss rhythmicity, and gained rhythmicity. We report here, for the first time, a parallel alteration of the rhythmic phase of butyric acid and butyrate-producing Clostridiaceae_1, which was confirmed by a positive correlation between them. Overall, our research emphasized the importance of the rhythmicity of gut microbiota-derived SCFAs in mediating circadian disruption in response to the HF in gestational mice, which may provide novel insights into the prevention and treatment of gestational obesity.

Neurodegenerative diseases and blood pressure variability: A comprehensive review from HOPE Asia

Asia has an enormous number of older people and is the primary contributor to the rise in neurodegenerative diseases such as Alzheimer's and Parkinson's disease. The therapy of many neurodegenerative diseases has not yet progressed to the point where it is possible to alter the course of the disease. Mid-life hypertension is an important predictor of later-life cognitive impairment and brain neurodegenerative conditions. These findings highlight the pivotal role of preventing and managing hypertension as a risk factor for neurodegenerative disease. Autonomic dysfunction, neuropsychiatric and sleep disturbances can arise in neurodegenerative diseases, resulting in blood pressure variability (BPV). The BPV itself can worsen the progression of the disease. In older people with neurodegenerative disease and hypertension, it is critical to consider 24-h blood pressure monitoring and personalized blood pressure therapy.

Disrupted and Elevated Circadian Secretion of Glucagon-Like Peptide-1 in a Murine Model of Type 2 Diabetes

Metabolism and circadian rhythms are intimately linked, with circadian glucagon-like peptide-1 (GLP-1) secretion by the intestinal L-cell entraining rhythmic insulin release. GLP-1 secretion has been explored in the context of obesogenic diets, but never in a rodent model of type 2 diabetes (T2D). There is also considerable disagreement regarding GLP-1 levels in human T2D. Furthermore, recent evidence has demonstrated decreased expression of the β-cell exocytotic protein secretagogin (SCGN) in T2D. To extend these findings to the L-cell, we administered oral glucose tolerance tests at 6 time points in 4-hour intervals to the high-fat diet/streptozotocin (HFD-STZ) mouse model of T2D. This revealed a 10-fold increase in peak GLP-1 secretion with a phase shift of the peak from the normal feeding period into the fasting-phase. This was accompanied by impairments in the rhythms of glucose, glucagon, mucosal clock genes (Arntl and Cry2), and Scgn. Immunostaining revealed that L-cell GLP-1 intensity was increased in the HFD-STZ model, as was the proportion of L-cells that expressed SCGN; however, this was not found in L-cells from humans with T2D, which exhibited decreased GLP-1 staining but maintained their SCGN expression. Gcg expression in isolated L-cells was increased along with pathways relating to GLP-1 secretion and electron transport chain activity in the HFD-STZ condition. Further investigation into the mechanisms responsible for this increase in GLP-1 secretion may give insights into therapies directed toward upregulating endogenous GLP-1 secretion.

Circadian clock disruptions link oxidative stress and systemic inflammation to metabolic syndrome in obstructive sleep apnea patients

Objectives: Obstructive sleep apnea (OSA) is an independent risk factor for metabolic syndrome (MetS). Recent studies have indicated that circadian clock genes were dysregulated in OSA. In addition, it is clear that the impairment of circadian clocks drives the progression of MetS. Therefore, we hypothesized that circadian rhythm disruption links OSA with MetS.

Methods: A total of 118 participants, who underwent polysomnography (PSG) and were diagnosed as healthy snorers (control, n = 29) or OSA (n = 89) patients based on the apnea–hypopnea index (AHI), were enrolled in the present study. General information, anthropometric data, blood biochemical indicators, clock gene expressions, and levels of oxidative and inflammatory indicators were collected, determined, and compared in all the participants.

Results: We found that Brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein 1 (Bmal1) and Differentiated embryo chondrocyte 1 (Dec1) were upregulated, while Period 1 (Per1) was reduced in OSA patients. In addition, these changing trends were closely associated with the hypoxia indicator of AHI and have a significant impact on the presence of MetS components, such as hyperglycemia (Dec1 and Per1, p < 0.05 and 0.001, respectively), hypertension (Bmal1 and Dec1, p < 0.001 and 0.01, respectively), hyperlipidemia (Dec1, p < 0.01), and obesity (Dec1, p < 0.05). Notably, expressions of Dec1 correlated with IR and predicted the presence of MetS in OSA patients. Finally, we also observed that Dec1 expression was interrelated with levels of both oxidative indicators and inflammatory biomarkers (IL-6) in OSA.

Conclusion: This study concluded that circadian clock disruptions, especially Dec1, link OSA with MetS in an oxidative and inflammatory-related manner. Circadian clock Dec1 can be used as a specific biomarker (p < 0.001) and therapeutic target in OSA combined with Mets patients.

Chrono-Aerobic Exercise Optimizes Metabolic State in DB/DB Mice through CLOCK–Mitophagy–Apoptosis

Although the benefits of aerobic exercise on obesity and type 2 diabetes are well-documented, the pathogenesis of type 2 diabetes and the intervention mechanism of exercise remain ambiguous. The correlation between mitochondrial quality and metabolic diseases has been identified. Disruption of the central or peripheral molecular clock can also induce chronic metabolic diseases. In addition, the interactive effects of the molecular clock and mitochondrial quality have attracted extensive attention in recent years. Exercise and a high-fat diet have been considered external factors that may change the molecular clock and metabolic state. Therefore, we utilized a DB/DB (BSK.Cg-Dock7m +/+ Leprdb/JNju) mouse model to explore the effect of chrono-aerobic exercise on the metabolic state of type 2 diabetic mice and the effect of timing exercise as an external rhythm cue on liver molecular clock-mitochondrial quality. We found that two differently timed exercises reduced the blood glucose and serum cholesterol levels in DB/DB mice, and compared with night exercise (8:00 p.m., the active period of mice), morning exercise (8:00 a.m., the sleeping period of mice) significantly improved the insulin sensitivity in DB/DB mice. In contrast, type 2 diabetes mellitus (T2DM) increased the expression of CLOCK and impaired the mitochondrial quality (mitochondrial networks, OPA1, Fis1, and mitophagy), as well as induced apoptosis. Both morning and night exercise ameliorated impaired mitochondrial quality and apoptosis induced by diabetes. However, compared with morning exercise, night exercise not only decreased the protein expression of CLOCK but also decreased excessive apoptosis. In addition, the expression of CLOCK was negatively correlated with the expression of OPA1 and Fis1. In summary, our research suggests that morning exercise is more beneficial for increasing insulin sensitivity and promoting glucose transport in T2DM, whereas night exercise may improve lipid infiltration and mitochondrial abnormalities through CLOCK–mitophagy–apoptosis in the liver, thereby downregulating glucose and lipid disorders. In addition, CLOCK-OPA1/Fis1–mitophagy might be novel targets for T2DM treatment.

Disruption of the circadian clock drives Apc loss of heterozygosity to accelerate colorectal cancer

An alarming rise in young onset colorectal cancer (CRC) has been reported; however, the underlying molecular mechanism remains undefined. Suspected risk factors of young onset CRC include environmental aspects, such as lifestyle and dietary factors, which are known to affect the circadian clock. We find that both genetic disruption and environmental disruption of the circadian clock accelerate Apc-driven CRC pathogenesis in vivo. Using an intestinal organoid model, we demonstrate that clock disruption promotes transformation by driving Apc loss of heterozygosity, which hyperactivates Wnt signaling. This up-regulates c-Myc, a known Wnt target, which drives heightened glycolytic metabolism. Using patient-derived organoids, we show that circadian rhythms are lost in human tumors. Last, we identify that variance between core clock and Wnt pathway genes significantly predicts the survival of patients with CRC. Overall, our findings demonstrate a previously unidentified mechanistic link between clock disruption and CRC, which has important implications for young onset cancer prevention.

Data-driven modelling captures dynamics of the circadian clock of Neurospora crassa

Eukaryotic circadian clocks are based on self-sustaining, cell-autonomous oscillatory feedback loops that can synchronize with the environment via recurrent stimuli (zeitgebers) such as light. The components of biological clocks and their network interactions are becoming increasingly known, calling for a quantitative understanding of their role for clock function. However, the development of data-driven mathematical clock models has remained limited by the lack of sufficiently accurate data. Here we present a comprehensive model of the circadian clock of Neurospora crassa that describe free-running oscillations in constant darkness and entrainment in light-dark cycles. To parameterize the model, we measured high-resolution time courses of luciferase reporters of morning and evening specific clock genes in WT and a mutant strain. Fitting the model to such comprehensive data allowed estimating parameters governing circadian phase, period length and amplitude, and the response of genes to light cues. Our model suggests that functional maturation of the core clock protein Frequency causes a delay in negative feedback that is critical for generating circadian rhythms.

Circadian rhythms are endogenous autonomous clocks that emancipate daily rhythms in physiology and behavior. Lately, a large body of research has contributed to our understanding of clocks’ genetic and mechanistic basis across kingdoms of life, i.e., mammals, fungi, plants, and bacteria. Several mathematical models have made key contributions to our current understanding of the design principles of the Neurospora crassa circadian clock and conditions for self-sustained oscillations. However, previous models uncovered and described the principle properties of the clock in generic manner due to a lack of experimental data. In this study, we developed a mathematical model based on systems of differential equations to describe the core clock components and estimated model parameters from luciferase data that capture experimental observations. We demonstrate the model predictive control simulation emphasizing the importance of functional maturation of the core clock protein Frequency in generating circadian rhythms.

Adaptive and Pathological Outcomes of Radiation Stress-Induced Redox Signaling

Significance: Ionizing radiation can damage cells either directly or through oxidative damage caused by ionization. Although radiation exposure from natural sources is very limited, ionizing radiation in nuclear disaster zones and long spaceflights causes inconspicuous, yet measurable physiological effects in men and animals, whose significance remains poorly known. Understanding the physiological impacts of ionizing radiation has a wide importance due to the increased use of medical imaging and radiotherapy. Recent Advances: Radiation exposure has been traditionally investigated from the perspective of DNA damage and its consequences. However, recent studies from Chernobyl as well as spaceflights have provided interesting insights into oxidative stress-induced metabolic alterations and disturbances in the circadian regulation. Critical Issues: In this review, we discuss the physiological consequences of radiation exposure in the light of oxidative stress signaling. Radiation exposure likely triggers many converging or interconnecting signaling pathways, some of which mimic mitochondrial dysfunction and might explain the observed metabolic changes. Future Directions: Better understanding of the different radiation-induced signaling pathways might help to devise strategies for mitigation of the long-term effects of radiation exposure. The utility of fibroblast growth factor 21 (FGF21) as a radiation exposure biomarker and the use of radiation hormesis as a method to protect astronauts on a prolonged spaceflight, such as a mission to Mars, should be investigated. Antioxid. Redox Signal. 37, 336-348.

Circadian regulation of digestive and metabolic tissues

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

The Role of Circadian Clock Genes in Critical Illness: The Potential Role of Translational Clock Gene Therapies for Targeting Inflammation, Mitochondrial Function, and Muscle Mass in Intensive Care

The Earth's 24-h planetary rotation, with predictable light and heat cycles, has driven profound evolutionary adaptation, with prominent impacts on physiological mechanisms important for surviving critical illness. Pathways of interest include inflammation, mitochondrial function, energy metabolism, hypoxic signaling, apoptosis, and defenses against reactive oxygen species. Regulation of these by the cellular circadian clock (BMAL-1 and its network) has an important influence on pulmonary inflammation; ventilator-associated lung injury; septic shock; brain injury, including vasospasm; and overall mortality in both animals and humans. Whether it is cytokines, the inflammasome, or mitochondrial biogenesis, circadian medicine represents exciting opportunities for translational therapy in intensive care, which is currently lacking. Circadian medicine also represents a link to metabolic determinants of outcome, such as diabetes and cardiovascular disease. More than ever, we are appreciating the problem of circadian desynchrony in intensive care. This review explores the rationale and evidence for the importance of the circadian clock in surviving critical illness.

Motivational and Valence-Related Modulation of Sleep/Wake Behavior are Mediated by Midbrain Dopamine and Uncoupled from the Homeostatic and Circadian Processes

Motivation and its hedonic valence are powerful modulators of sleep/wake behavior, yet its underlying mechanism is still poorly understood. Given the well-established role of midbrain dopamine (mDA) neurons in encoding motivation and emotional valence, here, neuronal mechanisms mediating sleep/wake regulation are systematically investigated by DA neurotransmission. It is discovered that mDA mediates the strong modulation of sleep/wake states by motivational valence. Surprisingly, this modulation can be uncoupled from the classically employed measures of circadian and homeostatic processes of sleep regulation. These results establish the experimental foundation for an additional new factor of sleep regulation. Furthermore, an electroencephalographic marker during wakefulness at the theta range is identified that can be used to reliably track valence-related modulation of sleep. Taken together, this study identifies mDA signaling as an important neural substrate mediating sleep modulation by motivational valence.

Récepteurs nucléaires et rythmes circadiens

L’horloge circadienne programme l’ensemble des processus physiologiques, dont l’activité du système immunitaire, à des moments précis de la journée. Elle permet d’optimiser les fonctions de l’organisme en anticipant les changements quotidiens tels que les cycles jour/nuit. Nos habitudes de vie comme l’exposition à la lumière artificielle ou une prise alimentaire irrégulière désynchronisent cependant cette horloge et provoquent des maladies, par exemple inflammatoires. Au niveau moléculaire, elle consiste en un réseau de facteurs de transcription dont certains sont des récepteurs nucléaires, activables par des ligands. Une meilleure compréhension des rythmes biologiques et du rôle des récepteurs nucléaires de l’horloge circadienne permettrait d’ouvrir un champ thérapeutique nouveau. La chronothérapie qui consiste en l’administration d’un composé pharmacologique au moment de la journée le plus propice, permettrait, en ciblant ces récepteurs, d’optimiser l’efficacité du traitement et d’en réduire les possibles effets secondaires.

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.

Genetic Variations within the Bovine CRY2 Gene Are Significantly Associated with Carcass Traits

As an important part of the circadian rhythm, the circadian regulation factor 2 of cryptochrome (CRY2), regulates many physiological functions. Previous studies have reported that CRY2 is involved in growth and development. However, the relationship between CRY2 gene polymorphism and cattle carcass traits remains unclear. The aim of this study was to detect the possible variations of the CRY2 gene and elucidate the association between the CRY2 gene and carcass traits in the Shandong Black Cattle Genetic Resource (SDBCGR) population (n = 705). We identified a 24-bp deletion variation (CRY2-P6) and a 6-bp insertion variation (CRY2-P7) in the bovine CRY2 gene. The frequency of the homozygous II genotype is higher than the heterozygous ID genotype in both two loci. In addition, CRY2-P6 was consistent with HWE (p > 0.05). Importantly, the CRY2-P6 variant was significantly associated with 12 carcass traits, including gross weight, ribeye, high rib, thick flank, etc. and the II was the dominant genotype. The CRY2-P7 site was also significantly correlated with five traits (gross weight, beef-tongue, etc.). Collectively, these outcomes indicated that the two Indel loci in the CRY2 gene could be used for marker-assisted selection of cattle carcass traits.

Orthogonal Control of Neuronal Circuits and Behavior Using Photopharmacology

Over the last decades, photopharmacology has gone far beyond its proof-of-concept stage to become a bona fide approach to study neural systems in vivo. Indeed, photopharmacological control has expanded over a wide range of endogenous targets, such as receptors, ion channels, transporters, kinases, lipids, and DNA transcription processes. In this review, we provide an overview of the recent progresses in the in vivo photopharmacological control of neuronal circuits and behavior. In particular, the use of small aquatic animals for the in vivo screening of photopharmacological compounds, the recent advances in optical modulation of complex behaviors in mice, and the development of adjacent techniques for light and drug delivery in vivo are described.

Why Do We Care More About Disease than Health?

Modern Western biomedical research and clinical practice are primarily focused on disease. This disease-centric approach has yielded an impressive amount of knowledge around what goes wrong in illness. However, in comparison, researchers and physicians know little about health. What is health? How do we quantify it? And how do we improve it? We currently do not have good answers to these questions. Our lack of fundamental knowledge about health is partly driven by three main factors: (i) a lack of understanding of the dynamic processes that cause variations in health/disease states over time, (ii) an excessive focus on genes, and (iii) a pervasive psychological bias towards additive solutions. Here I briefly discuss potential reasons why scientists and funders have generally adopted a gene- and disease-centric framework, how medicine has ended up practicing "diseasecare" rather than healthcare, and present cursory evidence that points towards an alternative energetic view of health. Understanding the basis of human health with a similar degree of precision that has been deployed towards mapping disease processes could bring us to a point where we can actively support and promote human health across the lifespan, before disease shows up on a scan or in bloodwork.

Chronic Cold Exposure Leads to Daytime Preference in the Circadian Expression of Hepatic Metabolic Genes

Circadian control allows organisms to anticipate and adapt to environmental changes through changes in physiology and behavior. The circadian system timing is entrained by cues, such as light, food, and temperature. An ambient temperature dramatically impacts the sleep-wake cycle and metabolic rhythmicity. As endotherms, mammals rely on tissues such as the liver to provide fuel for thermogenesis to maintain body temperature. The adaptive response of the circadian rhythm of liver metabolism to chronic cold exposure remains largely unexplored. Here, we investigated the circadian rhythm adaptation of hepatic metabolism in response to environmental cold stress using a mouse model of chronic cold exposure. We analyzed metabolites and transcripts of mouse livers at 24 h and found that long-term low-temperature exposure resulted in a synergistic and phase synchronization of transcriptional rhythms of many genes associated with metabolic pathways. Notably, transcription peaked in the early light phase when the body temperature was relatively low. Our results suggest that chronic cold does not alter the rhythmic expression of essential core clock genes in the liver, so the rewiring of clock control gene expression is another mechanism that optimizes the circadian rhythm of liver metabolism to meet the energy requirements of animal thermogenesis.

The Oscillating Gut Microbiome and Its Effects on Host Circadian Biology

The microbial community colonizing the gastrointestinal tract, collectively termed the gut microbiota, is an important element of the host organism due to its impact on multiple aspects of health. The digestion of food, secretion of immunostimulatory molecules, performance of chemical reactions in the intestine, and production of metabolites by the microbiota contribute to host homeostasis and disease. Recent discoveries indicate that these major functions are not constantly performed over the course of a day, but rather undergo diurnal fluctuations due to compositional and biogeographical oscillations in the microbiota. Here, we summarize the characteristics and origins of diurnal microbiome rhythms as well as their functional consequences for the circadian biology of the host. We describe the major known pathways of circadian host-microbiome communication and discuss possible implications of altered diurnal microbiome rhythms for human disease. Expected final online publication date for the Annual Review of Nutrition, Volume 42 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Circadian alignment of early onset caloric restriction promotes longevity in male C57BL/6J mice

Caloric restriction (CR) prolongs lifespan, yet the mechanisms by which it does so remain poorly understood. Under CR, mice self-impose chronic cycles of 2-hour-feeding and 22-hour-fasting, raising the question whether calories, fasting, or time of day are causal. We show that 30%-CR is sufficient to extend lifespan 10%; however, a daily fasting interval and circadian-alignment of feeding act together to extend lifespan 35% in male C57BL/6J mice. These effects are independent of body weight. Aging induces widespread increases in gene expression associated with inflammation and decreases in expression of genes encoding components of metabolic pathways in liver from ad lib fed mice. CR at night ameliorates these aging-related changes. Thus, circadian interventions promote longevity and provide a perspective to further explore mechanisms of aging.

Timed caloric restriction at night enhances longevity.

Nobiletin ameliorates high fat-induced disruptions in rhythmic glucagon-like peptide-1 secretion

The incretin hormone glucagon-like peptide-1 (GLP-1) is secreted by the intestinal L cell in response to nutrient intake. However, GLP-1 secretion also follows a circadian rhythm which is disrupted by the saturated fatty acid palmitate in vitro and high-fat diet (HFD) feeding in vivo. The flavonoid nobiletin is a clock enhancer which improves metabolic homeostasis. Therefore, the aim of this study was to elucidate whether and how nobiletin mitigates the negative effects of palmitate and HFD-feeding on rhythmic GLP-1 release. Pre-treatment of murine GLUTag L cells with palmitate dampened the GLP-1 secretory response at the normal peak of secretion, while nobiletin co-treatment restored GLP-1 secretion and upregulated the ‘metabolic pathway’ transcriptome. Mice fed a HFD also lost their GLP-1 secretory rhythm in association with markedly increased GLP-1 levels and upregulation of L cell transcriptional pathways related to ‘sensing’ and ‘transducing’ cellular stimuli at the normal peak of GLP-1 release. Nobiletin co-administration reduced GLP-1 levels to more physiological levels and upregulated L cell ‘oxidative metabolism’ transcriptional pathways. Furthermore, nobiletin improved colonic microbial 16S rRNA gene diversity and reduced the levels of Proteobacteria in HFD-fed mice. Collectively, this study establishes that nobiletin improves the normal rhythm in GLP-1 secretion following fat-induced disruption.

Chronic inflammatory arthritis drives systemic changes in circadian energy metabolism

Chronic inflammation underpins many human diseases. Morbidity and mortality associated with chronic inflammation are often mediated through metabolic dysfunction. Inflammatory and metabolic processes vary through circadian time, suggesting an important temporal crosstalk between these systems. Using an established mouse model of rheumatoid arthritis, we show that chronic inflammatory arthritis results in rhythmic joint inflammation and drives major changes in muscle and liver energy metabolism and rhythmic gene expression. Transcriptional and phosphoproteomic analyses revealed alterations in lipid metabolism and mitochondrial function associated with increased EGFR-JAK-STAT3 signaling. Metabolomic analyses confirmed rhythmic metabolic rewiring with impaired β-oxidation and lipid handling and revealed a pronounced shunt toward sphingolipid and ceramide accumulation. The arthritis-related production of ceramides was most pronounced during the day, which is the time of peak inflammation and increased reliance on fatty acid oxidation. Thus, our data demonstrate that localized joint inflammation drives a time-of-day–dependent build-up of bioactive lipid species driven by rhythmic inflammation and altered EGFR-STAT signaling.

Comprehensive Analysis Identified the Circadian Clock and Global Circadian Gene Expression in Human Corneal Endothelial Cells

Purpose

To investigate circadian clock oscillation and circadian global gene expression in cultured human corneal endothelial cells (cHCECs) to elucidate and assess the potential function of circadian regulation in HCECs.

Methods

In this study, we introduced a circadian bioluminescence reporter, Bmal1:luciferase (Bmal1:luc), into cHCECs and subsequently monitored real-time bioluminescence rhythms. RNA-sequencing data analysis was then performed using sequential time-course samples of the cHCECs to obtain a comprehensive understanding of the circadian gene expression rhythms. The potential relevance of rhythmically expressed genes was then assessed by systematic approaches using functional clustering and individual gene annotations.

Results

Bmal1:luc bioluminescence exhibited clear circadian oscillation in the cHCECs. The core clock genes and clock-related genes showed high-amplitude robust circadian messenger RNA (mRNA) expression rhythms in cHCECs after treatment with dexamethasone, and 329 genes that exhibited circadian mRNA expression rhythms were identified (i.e., genes involved in various physiological processes including glycolysis, mitochondrial function, antioxidative systems, hypoxic responses, apoptosis, and extracellular matrix regulation, which represent the physiological functions of HCECs).

Conclusions

Our findings revealed that cHCECs have a robust and functional circadian clock, and our discovery that a large number of genes exhibit circadian mRNA expression rhythms in cHCECs suggests a potential contribution of circadian regulation to fine-tune HCEC functions for daily changes in the environment.

Noise reduction by upstream open reading frames

Gene expression is prone to burst production, making it a highly noisy process that requires additional controls. Upstream open reading frames (uORFs) are widely present in the 5' leader sequences of 30-50% of eukaryotic messenger RNAs^1-3. The translation of uORFs can repress the translation efficiency of the downstream main coding sequences. Whether the low translation efficiency leads to a different variation, or noise, in gene expression has not been investigated, nor has the direct biological impact of uORF-repressed translation. Here we show that uORFs achieve low but precise protein production in plant cells, possibly by reducing the protein production rate. We also demonstrate that, by buffering a stable TIMING OF CAB EXPRESSION 1 (TOC1) protein production level, uORFs contribute to the robust operation of the plant circadian clock. Our results provide both an action model and the biological impact of uORFs in translational control to mitigate transcriptional noise for precise protein production.

Circadian Regulation of Gene Expression and Metabolism in the Liver

Circadian rhythms are approximately 24-hour cycles of variation in physiological processes, gene expression, and behavior. They result from the interplay of internal biological clocks with daily environmental rhythms, including light/dark and feeding/fasting. Note that 24-hour rhythms of liver metabolic processes have been known for almost 100 years. Modern studies reveal that, like metabolism, hepatic gene expression is highly rhythmic. Genetic or environmental changes can disrupt the circadian rhythms of the liver, leading to metabolic disorders and hepatocellular carcinoma. In this review, we summarize the current understanding of mechanisms regulating rhythmic gene expression in the liver, highlighting the roles of transcription factors that comprise the core clock molecular as well as noncanonical regulators. We emphasize the plasticity of circadian rhythms in the liver as it responds to multiple inputs from the external and internal environments as well as the potential of circadian medicine to impact liver-related diseases.