Dr Daan van der Veen

Metabolic rhythms include rapid, ultradian (hourly) dynamics, but it remains unclear what their relationship to circadian metabolic rhythms is, and what role meal timing plays in coordinating these ultradian rhythms in metabolism. Here, we characterized widespread ultradian rhythms under ad libitum feeding conditions in the plasma metabolome of the vole, the gold standard animal model for behavioral ultradian rhythms, naturally expressing similar to 2-h foraging rhythms throughout the day and night. These ultradian metabolite rhythms co-expressed with diurnal 24-h rhythms in the same metabolites and did not align with food intake patterns. Specifically, under light-dark entrained conditions we showed twice daily entrainment of phase and period of ultradian behavioral rhythms associated with phase adjustment of the ultradian cycle around the light-dark and dark-light transitions. These ultradian activity patterns also drove an ultradian feeding pattern. We used a unique approach to map this behavioral activity/feeding status to high temporal resolution (every 90 min) measures of plasma metabolite profiles across the 24-h light-dark cycle. A total of 148 known metabolites were detected in vole plasma. Supervised, discriminant analysis did not group metabolite concentration by feeding status, instead, unsupervised clustering of metabolite time courses revealed clusters of metabolites that exhibited significant ultradian rhythms with periods different from the feeding cycle. Two clusters with dissimilar ultradian dynamics, one lipid-enriched (period = 3.4 h) and one amino acid-enriched (period = 4.1 h), both showed co-expression with diurnal cycles. A third cluster solely comprised of glycerophospholipids (specifically ether-linked phosphatidylcholines) expressed an 11.9 h ultradian rhythm without co-expressed diurnal rhythmicity. Our findings show coordinated co-expression of diurnal metabolic rhythms with rapid dynamics in feeding and metabolism. These findings reveal that ultradian rhythms are integral to biological timing of metabolic regulation, and will be important in interpreting the impact of circadian desynchrony and meal timing on metabolic rhythms.

Intrinsically driven ultradian rhythms in the hourly range are often co-expressed with circadian rhythms in various physiological processes including metabolic processes such as feeding behaviour, gene expression and cellular metabolism. Several behavioural observations show that reduced energy intake or increased energy expenditure leads to a re-balancing of ultradian and circadian timing, favouring ultradian feeding and activity patterns when energy availability is limited. This suggests a close link between ultradian rhythmicity and metabolic homeostasis, but we currently lack models to test this hypothesis at a cellular level. We therefore transduced 3T3-L1 pre-adipocyte cells with a reporter construct that drives a destabilised luciferase via the Pdcd5 promotor, a gene we previously showed to exhibit robust ultradian rhythms in vitro . Ultradian rhythmicity in Pdcd5 promotor driven bioluminescence was observed in >80% of all cultures that were synchronised with dexamethasone, whereas significantly lower numbers exhibited ultradian rhythmicity in non-synchronised cultures (∼11%). Cosine fits to ultradian bioluminescence rhythms in cells cultured and measured in low glucose concentrations (2 mM and 5 mM), exhibited significantly higher amplitudes than all other cultures, and a shorter period (6.9 h vs. 8.2 h, N = 12). Our findings show substantial ultradian rhythmicity in Pdcd5 promotor activity in cells in which the circadian clocks have been synchronised in vitro , which is in line with observations of circadian synchronisation of behavioural ultradian rhythms. Critically, we show that the amplitude of ultradian rhythms is enhanced in low glucose conditions, suggesting that low energy availability enhances ultradian rhythmicity at the cellular level in vitro .

Circadian rhythms, metabolism, and nutrition are closely linked.1 Timing of a 3-meal daily feeding pattern synchronises some human circadian rhythms.2 Despite animal data showing anticipation of food availability, linked to a Food Entrainable Oscillator3, it is unknown whether human physiology predicts mealtimes and restricted food availability. In a controlled laboratory protocol, we tested the hypothesis that the human circadian system anticipates large meals. Twenty-four male participants undertook an 8-day laboratory study, with strict sleep-wake schedules, light-dark schedules, and food intake. For six days, participants consumed either hourly small meals throughout the waking period, or two large daily meals (7.5 and 14.5-h after wake-up). All participants then undertook a 37-hour constant routine. Interstitial glucose was measured every 15 minutes throughout the protocol. Hunger was assessed hourly during waking periods. Saliva melatonin was measured in the constant routine. During the 6-day feeding pattern, both groups exhibited increasing glucose concentration early each morning. In the small meal group, glucose concentrations continued to increase across the day. However, in the large meal group, glucose concentrations decreased from 2-h after waking until the first meal. Average 24-h glucose concentration did not differ between groups. In the constant routine, there was no difference in melatonin onset between groups, but antiphasic glucose rhythms were observed, with low glucose at the time of previous meals in the large meal group. Moreover, in the large meal group, constant routine hunger scores increased before the predicted meal times. These data support the existence of human food anticipation.

Microbiota assembly in the infant gut is influenced by diet. Breastfeeding and human breastmilk oligosaccharides promote the colonization of beneficial bifidobacteria. Infant formulas are supplemented with bifidobacteria or complex oligosaccharides, notably galacto-oligosaccharides (GOS), to mimic breast milk. To compare microbiota development across feeding modes, this randomized controlled intervention study (German Clinical Trial DRKS00012313) longitudinally sampled infant stool during the first year of life, revealing similar fecal bacterial communities between formula- and breast-fed infants (N = 210) but differences across age. Infant formula containing GOS sustained high levels of bifidobacteria compared with formula containing B. longum and B. breve or placebo. Metabolite and bacterial profiling revealed 24-h oscillations and circadian networks. Rhythmicity in bacterial diversity, specific taxa, and functional pathways increased with age and was strongest following breastfeeding and GOS supplementation. Circadian rhythms in dominant taxa were further maintained ex vivo in a chemostat model. Hence, microbiota rhythmicity develops early in life and is impacted by diet.

The Asian malaria vector Anopheles stephensi is invading Africa, requiring it to adapt to novel climates and ecosystems. In part, this may be facilitated by An. stephensi's poorly understood seasonal behavioural plasticity in flight timing, leading to earlier biting activity in cold Asian winters and later biting times in the warm summer. Changes in behavioural timing could be directly imposed by seasonal variation in ambient light and temperature levels or result from altered entrainment of intrinsically expressed circadian rhythms by these factors. We demonstrate that An. stephensi entrained flight activity timing is phase-locked to dawn and is not affected by constant ambient temperature, which cannot explain earlier biting activity in colder winters with later dawn. Instead, we show that where night temperatures are the colder part of daily temperature cycle; the entrained phase-angle between dawn and flight activity is altered, hereby increasingly colder, winter-like nights progressively advance flight activity onset. We propose that seasonal timing plasticity optimizes behaviour to warmer daytime in winter, and colder nights in summer, providing protection against both heat-desiccation and cold immobility. The adaptive advantage of this plasticity could be relevant to the successful invasion and survival of An. stephensi in African climates, and changing climate worldwide. This article is part of the Theo Murphy meeting issue, 'Circadian rhythms in infection and immunity'.

Bile acids are trans-genomic molecules arising from the concerted metabolism of the human host and the intestinal microbiota and are important for digestion, energy homeostasis and metabolic regulation. While diurnal variation has been demonstrated in the enterohepatic circulation and the gut microbiota, existing human data are poorly resolved, and the influence of the host circadian system has not been determined. Using entrained laboratory protocols, we demonstrate robust daily rhythms in the circulating bile acid pool in healthy male participants. We identify temporal relationships between bile acids and plasma lipids and show that these relationships are lost following sleep deprivation. We also highlight that bile acid rhythmicity is predominantly lost when environmental timing cues are held constant. Here we show that the environment is a stronger determinant of these temporal dynamics than the intrinsic circadian system of the host. This has significance for the intimate relationship between circadian timing and metabolism.Bile acids are important for digestion, energy homeostasis and metabolic regulation. Here the authors show daily rhythms in the circulating bile acid pool which are lost when environmental timing cues are held constant indicating that environment is a stronger determinant of these dynamics than the circadian system.

Angiogenesis, the formation of new capillaries from existing ones, is a fundamental process in regenerative medicine and tissue engineering. While it is known to be affected by circadian rhythms in vivo, its peripheral regulation within the vasculature and the role it performs in regulating the interplay between vascular cells have not yet been investigated. Peripheral clocks within the vasculature have been described in the endothelium and in smooth muscle cells. However, to date, scarce evidence has been presented regarding pericytes, a perivascular cell population deeply involved in the regulation of angiogenesis and vessel maturation, as well as endothelial function and homeostasis. More crucially, pericytes are also a promising source of cells for cell therapy and tissue engineering. Here, we established that human primary pericytes express key circadian genes and proteins in a rhythmic fashion, upon synchronization. Conversely, we did not detect the same patterns in cultured endothelial cells. In line with these results, pericytes’ viability was disproportionately affected by circadian cycle disruption, as compared to endothelial cells. Interestingly, endothelial cells’ rhythm could be induced following exposure to synchronized pericytes in a contact co-culture. We propose that this mechanism could be linked to the altered release/uptake pattern of lactate, a known mediator of cell-cell interaction which was specifically altered in pericytes by the knockout of the key circadian regulator Bmal1. In an angiogenesis assay, the maturation of vessel-like structures was affected only when both endothelial cells and pericytes did not express Bmal1, indicating some compensation system. In a 3D tissue engineering scaffold, a synchronized clock supported a more structured organization of cells around the scaffold pores, and a maturation of vascular structures. Our results demonstrate that pericytes play a critical role in regulating the circadian rhythms in endothelial cells, and that silencing this system disproportionately affect their pro-angiogenic function. In particular in the context of tissue engineering and regenerative medicine, considering the effect of circadian rhythms may be critical for the development of mature vascular structures and to obtain the maximal reparative effect.

Low indoor light in urban housing can dis-rupt health and wellbeing, especially in older adultswho experience reduced light sensitivity and sleep/cir-cadian disruptions with natural aging. While controlledstudies suggest that enhancing indoor lighting mayalleviate the negative effects of reduced light sensitiv-ity, evidence for this to be effective in the real world islacking. This study investigates the effects of two lightconditions on actigraphic rest-activity rhythms and sub-jective sleep in healthy older adults (≥ 60 years) livingat home. Two photon-matched lights were compared; acontrol white light (4000 K) and a blue-enriched whitelight (17000 K) at two different intensities (300–450 lxand 1100–1200 lx respectively). Participants (n = 36, 25female) completed an 11-week randomized, cross-overstudy, comprising 1 week of baseline, 3 weeks of self-administered light exposure (2 h in the morning and 2 hin the evening), and 2 weeks of washout for each lightcondition. Participants completed sleep diaries, worea wrist actigraph and a light sensor necklace, and col-lected urine to measure 6-sulphatoxymelatonin. Longerduration of morning blue-enriched light significantlyimproved rest-activity rhythm stability and decreasedsleep fragmentation. More time spent above 2500 lxincreased actigraphy amplitude, daytime activity, andadvanced bedtime. Evening light exposure, however,increased sleep latency and lowered sleep efficiency.Our findings show morning blue-enriched light is ben-eficial whereas evening light should be avoided. Optimaltiming of self-administered light interventions thus mayoffer a promising strategy to improve sleep and rest-activity rhythms in older adults in real-world settings.

An. stephensi mosquitoes have remarkable inter-animal differences in onset time and free running period length. (A) Example actograms of four mated females showing range of onset timing under 12:12 light:dark entrained conditions between individual mosquitoes. (B) Free running period (FRP) under constant dark conditions does not differ between mosquitoes expressing different onset times. Each scatter point represents a given mosquito’s measured FRP (only observed in constant dark conditions) and onset (only observed in light:dark conditions) (n = 100). The orange bars are a histogram representing onset and FRP distribution.

Rapid, ultradian biological rhythms are only partly comparable to circadian (24-h) rhythms. Often, the ensuing expectations from this comparison are that 1) ultradian rhythms should be driven by discrete oscillators, 2) they are biochemically buffered, and 3) they must be functionally linked to extrinsic events and cycles. These three expectations are not always met, but perhaps there is an adaptive benefit to ultradian rhythms not meeting these expectations, which sets them functionally apart from circadian rhythms. In view of the extensive descriptions of the manifold types of ultradian rhythms across all biological levels (e.g., see papers in this research topic), it seems important to ask whether we should actively create a new set of definitions and expectations. To make a start, we here lay out some important questions we need to ask about ultradian rhythms. We then illustrate how these questions highlight one key area of exploration: the linked expression of ultradian rhythms in metabolism and behaviour and the role this plays in addressing a negative energy balance.

Chemostat systems can be used to cultivate complex intestinal microbial communities ex vivo. Here, we present a protocol to transfer bacteria from human fecal material into chemostat systems as well as settings to simulate infant or adult colonic conditions. We describe the experimental setup, media design, donor selection, 16S rRNA amplicon sequencing, and circadian analysis of bacterial abundance. This protocol enables the investigation of changes in microbial community composition and bacteria-derived metabolites upon exposure to different dietary components. For complete details on the use and execution of this protocol, please refer to Heppner et al.1 [Display omitted] •Details of chemostat setup for continuous ex vivo cultivation of intestinal microbiota•Characterization of nutrient-microbiota interactions ex vivo•Versatile applications to simulate different intestinal conditions•Circadian analysis to determine rhythmic changes in microbiota composition and function Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics. Chemostat systems can be used to cultivate complex intestinal microbial communities ex vivo. Here, we present a protocol to transfer bacteria from human fecal material into chemostat systems as well as settings to simulate infant or adult colonic conditions. We describe the experimental setup, media design, donor selection, 16S rRNA amplicon sequencing, and circadian analysis of bacterial abundance. This protocol enables the investigation of changes in microbial community composition and bacteria-derived metabolites upon exposure to different dietary components.

Indoor light levels are low in urban housing, disrupting health and wellbeing. Low light intensities are associated with poor light entrainment and decreased daily rhythms' amplitude, which is associated with an increased risk of metabolic disturbances, cancers, and mood. This problem is exacerbated in older adults who are likely more impacted by mistimed exposure to indoor lights. Importantly, the age-related attenuation of circadian rhythms and reduction in transmission of short-wavelength light may underlie circadian/sleep alterations in older adults. However, studies indicate that improving indoor light conditions can alleviate age-related sleep/circadian disturbances. Here, we aim to assess the real-world impact of indoor light supplementation during daytime on activity-rest rhythms, wellbeing, and personal light exposure of older adults. In three cities (Bologna, Amsterdam, Tartu), 1,500 older adults (500 for each city) will be recruited in this population-based epidemiological design. Out of the 500 participants, 250 will be randomly selected to be exposed to indoor, blue-enriched light for 12 weeks and compared to 250 participants that will not have any indoor light intervention (control). A 2-week baseline will be carried out to assess daily activity patterns, sleep, and light exposure through wrist-worn actigraphy and wearable light sensors. In addition, participants will complete an activity diary in which they are asked when they eat, sleep, and are outdoors. Additionally, we will collect subjective measures of sleep quality, chronotype, and mood. After 12 weeks of light supplementation, the same measures will be re-assessed again for a 2-week period, allowing the quantification of the effects of the 12-week experimental lighting change. The results from this study will generate a scientific evidence base to support effective lighting guidelines aimed at improving citizens' health and wellbeing.

Chemotherapy-induced peripheral neurotoxicity (CIPN) is one of the most common dose-limiting side-effects of paclitaxel (PTX) treatment. Many age-related changes have been hypothesized to underlie susceptibility to damage or impaired regeneration/repair after nerve injury. The results of these studies, however, are inconclusive and other potential biomarkers of nerve impairment need to be investigated. Twenty-four young (2 months) and 24 adult (9 months) Wistar male rats were randomized to either PTX treatment (10 mg/kg i.v. once/week for 4 weeks) or vehicle administration. Neurophysiological and behavioral tests were performed at baseline, after 4 weeks of treatment and 2-week follow-up. Skin biopsies and nerve specimens collected from sacrificed animals were examined for intraepidermal nerve fiber (IENF) density assessment and nerve morphology/morphometry. Blood and liver samples were collected for targeted metabolomics analysis. At the end of treatment, the neurophysiological studies revealed a reduction in sensory nerve action potential amplitude (p 

Parkinson’s disease (PD) is a chronic disorder that presents a range of premotor signs, such as sleep disturbances and cognitive decline, which are key non-motor features of the disease. Increasing evidence of a possible association between sleep disruption and the neurodegenerative process suggests that sleep impairment could produce a detectable metabolic signature on the disease. In order to integrate neurocognitive and metabolic parameters, we performed untargeted and targeted metabolic profiling of the rotenone PD model in a chronic sleep restriction (SR) (6 h/day for 21 days) condition. We found that SR combined with PD altered several behavioural (reversal of locomotor activity impairment; cognitive impairment; delay of rest-activity rhythm) and metabolic parameters (branched-chain amino acids, tryptophan pathway, phenylalanine, and lipoproteins, pointing to mitochondrial impairment). If combined, our results bring a plethora of parameters that represents reliable early-phase PD biomarkers which can easily be measured and could be translated to human studies.

Circadian rhythms enable organisms to synchronise the processes underpinning survival and reproduction to anticipate daily changes in the external environment. Recent work shows that daily (circadian) rhythms also enable parasites to maximise fitness in the context of ecological interactions with their hosts. Because parasite rhythms matter for their fitness, understanding how they are regulated could lead to innovative ways to reduce the severity and spread of diseases. Here, we examine how host circadian rhythms influence rhythms in the asexual replication of malaria parasites. Asexual replication is responsible for the severity of malaria and fuels transmission of the disease, yet, how parasite rhythms are driven remains a mystery. We perturbed feeding rhythms of hosts by 12 hours (i.e. diurnal feeding in nocturnal mice) to desynchronise the hosts' peripheral oscillators from the central, light-entrained oscillator in the brain and their rhythmic outputs. We demonstrate that the rhythms of rodent malaria parasites in day-fed hosts become inverted relative to the rhythms of parasites in night-fed hosts. Our results reveal that the hosts' peripheral rhythms (associated with the timing of feeding and metabolism), but not rhythms driven by the central, light-entrained circadian oscillator in the brain, determine the timing (phase) of parasite rhythms. Further investigation reveals that parasite rhythms correlate closely with blood glucose rhythms. In addition, we show that parasite rhythms resynchronise to the altered host feeding rhythms when food availability is shifted, which is not mediated through rhythms in the host immune system. Our observations suggest that parasites actively control their developmental rhythms. Finally, counter to expectation, the severity of disease symptoms expressed by hosts was not affected by desynchronisation of their central and peripheral rhythms. Our study at the intersection of disease ecology and chronobiology opens up a new arena for studying host-parasite-vector coevolution and has broad implications for applied bioscience.

Biological oscillations with an ultradian time scale of 1 to several hours include cycles in behavioral arousal, episodic glucocorticoid release, and gene expression. Ultradian rhythms are thought to have an extrinsic origin because of a perceived absence of ultradian rhythmicity in vitro and a lack of known molecular ultradian oscillators. We designed a novel, non–spectral-analysis method of separating ultradian from circadian components and applied it to a published gene expression dataset with an ultradian sampling resolution. Ultradian rhythms in mouse hepatocytes in vivo have been published, and we validated our approach using this control by confirming 175 of 323 ultradian genes identified in a prior study and found 862 additional ultradian genes. For the first time, we now report ultradian expression of >900 genes in vitro. Sixty genes exhibited ultradian transcriptional rhythmicity, both in vivo and in vitro, including 5 genes involved in the cell cycle. Within these 60 genes, we identified significant enrichment of specific DNA motifs in the 1000 bp proximal promotor, some of which associate with known transcriptional factors. These findings are in strong support of instrinsically-driven ultradian rhythms and expose potential molecular mechanisms and functions underlying ultradian rhythms that remain unknown.

The aim of this study was to analyse the circadian behavioural responses of mice carrying a functional knockout of the Per3 gene (𝑃𝑒𝑟3−/−) to different light : dark (L : D) cycles. Male adult wild-type (WT) and 𝑃𝑒𝑟3−/− mice were kept under 12-hour light : 12- hour dark conditions (12L : 12D) and then transferred to either a short or long photoperiod and subsequently released into total darkness. All mice were exposed to both conditions, and behavioural activity data were acquired through running wheel activity and analysed for circadian characteristics during these conditions. We observed that, during the transition from 12L : 12D to 16L : 8D, 𝑃𝑒𝑟3−/− mice take approximately one additional day to synchronise to the new L : D cycle compared to WT mice. Under these long photoperiod conditions, 𝑃𝑒𝑟3−/− mice were more active in the light phase. Our results suggest that 𝑃𝑒𝑟3−/− mice are less sensitive to light. The data presented here provides further evidence that Per3 is involved in the suppression of behavioural activity in direct response to light.

Objective. Circadian rhythms in cartilage homeostasis are hypothesized to temporally segregate and synchronize the activities of chondrocytes to different times of the day, and thus may provide an efficient mechanism by which articular cartilage can recover following physical activity. While the circadian clock is clearly involved in chondrocyte homeostasis in health and disease, it is unclear as to what roles it may play during early chondrogenesis. Design. The purpose of this study was to determine whether the rhythmic expression of the core circadian clock was detectable at the earliest stages of chondrocyte differentiation, and if so, whether a synchronized expression pattern of chondrogenic transcription factors and developing cartilage matrix constituents was present during cartilage formation. Results. Following serum shock, embryonic limb bud–derived chondrifying micromass cultures exhibited synchronized temporal expression patterns of core clock genes involved in the molecular circadian clock. We also observed that chondrogenic marker genes followed a circadian oscillatory pattern. Clock synchronization significantly enhanced cartilage matrix production and elevated SOX9, ACAN, and COL2A1 gene expression. The observed chondrogenesis-promoting effect of the serum shock was likely attributable to its synchronizing effect on the molecular clockwork, as co-application of small molecule modulators (longdaysin and KL001) abolished the stimulating effects on extracellular matrix production and chondrogenic marker gene expression. Conclusions. Results from this study suggest that a functional molecular clockwork plays a positive role in tissue homeostasis and histogenesis during early chondrogenesis.

Metabolic profiling of individuals with type 2 diabetes mellitus (T2DM) has previously been limited to single-time-point samples, ignoring time-of-day variation. Here, we tested our hypothesis that body mass and T2DM affect daily rhythmicity and concentrations of circulating metabolites across a 24-h day in 3 age-matched, male groups—lean, overweight/obese (OW/OB), and OW/OB with T2DM—in controlled laboratory conditions, which were not confounded by large meals. By using targeted liquid chromatography/mass spectrometry metabolomics, we quantified 130 plasma metabolites every 2 h over 24 h, and we show that average metabolite concentrations were significantly altered by increased body mass (90 of 130) and T2DM (56 of 130). Thirty-eight percent of metabolites exhibited daily rhythms in at least 1 study group, and where a metabolite was rhythmic in >1 group, its peak time was comparable. The optimal time of day was assessed to provide discriminating biomarkers. This differed between metabolite classes and study groups—for example, phospholipids showed maximal difference at 5:00 AM (lean vs. OW/OB) and at 5:00 PM (OW/OB vs. T2DM). Metabolites that were identified with both robust 24-h rhythms and significant concentration differences between study groups emphasize the importance of controlling the time of day for diagnosis and biomarker discovery, offering a significant improvement over current single sampling.—Isherwood, C. M., Van der Veen, D. R., Johnston, J. D., Skene, D. J. Twenty-four-hour rhythmicity of circulating metabolites: effect of body mass and type 2 diabetes. It is widely accepted that obesity is the main risk factor for type 2 diabetes mellitus (T2DM) (1). The progression from obesity to T2DM is largely a result of comorbidities, such as systemic inflammation and insulin resistance. Metabolic profiling by using targeted metabolomics, which enables the quantification of more than 100 low-MW intermediates of metabolism, is increasingly used to characterize (pre)diabetic phenotypes and has identified differences in metabolite profiles between those individuals who are obese and those with T2DM (2–5). Recent work by our group and others has shown a 24-h variation in the human metabolome in healthy individuals, analyzed by using a range of analytical platforms (6–12), which has demonstrated that an estimated 15–20% of the metabolome is rhythmic in blood (6, 7). Transgenic mice that carry targeted genetic manipulation of circadian clock genes also exhibit a phenotype that involves defective metabolism, and associations between the circadian timing system and metabolic responses have been reported in humans (13). Reviews of these studies, including the higher incidence of obesity, T2DM, and related disorders in shift workers, have recently been published (14, 15). Existing metabolomics studies in T2DM have been restricted to the analysis of single-time-point, mostly fasting, samples, which cannot characterize the effect of increased body mass and T2DM on rhythmic metabolites. Characterizing 24-h metabolite rhythms in T2DM compared with age- and body mass–matched controls may therefore provide novel insights into the etiology and progression of T2DM. Identification of the optimal time of day for blood sampling—when metabolite levels show the biggest difference between T2DM and controls—would also provide more discriminating diagnostic biomarkers, rather than taking a single morning fasting sample. We thus assessed the effect of increased body mass [overweight/obese (OW/OB)] and T2DM on 24-h rhythms of circulating metabolites in men by using a quantitative targeted liquid chromatography/mass spectrometry (LC/MS) metabolomics approach. As T2DM is often accompanied by obesity, we set out to distinguish the effects of T2DM from those of increased body mass by incorporating both a lean and an OW/OB control group into the current study design.

Currently, cell separation occurs almost exclusively by density gradient methods and by fluorescence- and magnetic-activated cell sorting (FACS/MACS). These variously suffer from lack of specificity, high cell loss, use of labels, and high capital/operating cost. We present a dielectrophoresis (DEP)-based cell separation method, using 3D electrodes on a low-cost disposable chip; one cell type is allowed to pass through the chip whilst the other is retained and subsequently recovered. The method advances usability and throughput of DEP separation by orders of magnitude in throughput, efficiency, purity, recovery (cells arriving in the correct output fraction), cell losses (those which are unaccounted for at the end of the separation) and cost. The system was evaluated using three example separations; live and dead yeast; human cancer cells/red blood cells; and rodent fibroblasts/red blood cells. A single-pass protocol can enrich cells with cell recovery of up to 91.3% at over 300,000 cells/second with >3% cell loss. A two-pass protocol can process 300,000,000 cells in under 30 minutes, with cell recovery of up to 96.4% and cell losses below 5%, an effective processing rate >160,000 cells/second. A three-step protocol is shown to be effective for removal of 99.1% of RBCs spiked with 1% cancer cells, whilst maintaining a processing rate of ~170,000 cells/second. Furthermore, the self-contained and low-cost nature of the separator device means that it has potential application in low-contamination applications such as cell therapies, where GMP compatibility is of paramount importance. Significance statement. Cell separation is a fundamental process in biomedicine, but is presently complicated, cumbersome and expensive. We present a technique that can sort cells at a rate equivalent to or faster than gold-standard techniques such as FACS and MACs, but can do label-free and with very low cell loss. The system uses dielectrophoresis (DEP) to sort cells electrostatically, using a novel electrode chip that eschews microfabrication in favour of a laminate drilled with 397 electrode-bearing wells. This high level of parallelisation makes the system immune to the bubbles that limit labs-on-chip, whilst also increasing capacity and throughput to unprecedented levels, whilst the chip is cheap enough to be disposable, preventing inter-separation contamination.

Infection can dramatically alter behavioural and physiological traits as hosts become sick and subsequently return to health. Such “sickness behaviours” include disrupted circadian rhythms in both locomotor activity and body temperature. Host sickness behaviours vary in pathogen species-specific manners but the influence of pathogen intraspecific variation is rarely studied. We examine how infection with the murine malaria parasite, Plasmodium chabaudi, shapes sickness in terms of parasite genotype-specific effects on host circadian rhythms. We reveal that circadian rhythms in host locomotor activity patterns and body temperature become differentially disrupted and in parasite genotype-specific manners. Locomotor activity and body temperature in combination provide more sensitive measures of health than commonly used virulence metrics for malaria (e.g. anaemia). Moreover, patterns of host disruption cannot be explained simply by variation in replication rate across parasite genotypes or the severity of anaemia each parasite genotype causes. It is well known that disruption to circadian rhythms is associated with non-infectious diseases, including cancer, type 2 diabetes, and obesity. Our results reveal that disruption of host circadian rhythms is a genetically variable virulence trait of pathogens with implications for host health and disease tolerance.

Circadian organization of the mammalian transcriptome is achieved by rhythmic recruitment of key modifiers of chromatin structure and transcriptional and translational processes. These rhythmic processes, together with posttranslational modification, constitute circadian oscillators in the brain and peripheral tissues, which drive rhythms in physiology and behavior, including the sleep-wake cycle. In humans, sleep is normally timed to occur during the biological night, when body temperature is low and melatonin is synthesized. Desynchrony of sleep-wake timing and other circadian rhythms, such as occurs in shift work and jet lag, is associated with disruption of rhythmicity in physiology and endocrinology. However, to what extent mistimed sleep affects the molecular regulators of circadian rhythmicity remains to be established. Here, we show that mistimed sleep leads to a reduction of rhythmic transcripts in the human blood transcriptome from 6.4% at baseline to 1.0% during forced desynchrony of sleep and centrally driven circadian rhythms. Transcripts affected are key regulators of gene expression, including those associated with chromatin modification (methylases and acetylases), transcription (RNA polymerase II), translation (ribosomal proteins, initiation, and elongation factors), temperature-regulated transcription (cold inducible RNA-binding proteins), and core clock genes including CLOCK and ARNTL (BMAL1). We also estimated the separate contribution of sleep and circadian rhythmicity and found that the sleep-wake cycle coordinates the timing of transcription and translation in particular. The data show that mistimed sleep affects molecular processes at the core of circadian rhythm generation and imply that appropriate timing of sleep contributes significantly to the overall temporal organization of the human transcriptome.

The aim of this handbook is to present an overview of the work on learning, written by leading scholars from all these different perspectives and disciplines.

The biomechanical environment plays a key role in regulating cartilage formation, but the current understanding of mechanotransduction pathways in chondrogenic cells is incomplete. Among the combination of external factors that control chondrogenesis are temporal cues that are governed by the cell-autonomous circadian clock. However, mechanical stimulation has not yet directly been proven to modulate chondrogenesis via entraining the circadian clock in chondroprogenitor cells. The purpose of this study was to establish whether mechanical stimuli entrain the core clock in chondrogenic cells, and whether augmented chondrogenesis caused by mechanical loading was at least partially mediated by the synchronised, rhythmic expression of the core circadian clock genes, chondrogenic transcription factors, and cartilage matrix constituents at both transcript and protein levels. We report here, for the first time, that cyclic uniaxial mechanical load applied for 1 h for a period of 6 days entrains the molecular clockwork in chondroprogenitor cells during chondrogenesis in limb bud-derived micromass cultures. In addition to the several core clock genes and proteins, the chondrogenic markers SOX9 and ACAN also followed a robust sinusoidal rhythmic expression pattern. These rhythmic conditions significantly enhanced cartilage matrix production and upregulated marker gene expression. The observed chondrogenesis-promoting effect of the mechanical environment was at least partially attributable to its entraining effect on the molecular clockwork, as co-application of the small molecule clock modulator longdaysin attenuated the stimulatory effects of mechanical load. This study suggests that an optimal biomechanical environment enhances tissue homoeostasis and histogenesis during chondrogenesis at least partially through entraining the molecular clockwork.

Introduction: Individual differences in response to sleep loss have been described in various settings including driver sleepiness. A potential biological marker for this differential vulnerability is a PERIOD3 (PER3) Variable Number (4 or 5) Tandem Repeat polymorphism (rs57875989), for which homozygosity for the 5 repeat (PER35/5) has been associated with increased homeostatic sleep pressure and cognitive performance deficits in laboratory conditions. This is the first study so far experimentally investigating the effect of this polymorphism on sleepiness and performance outside the laboratory. Methods: 18 PER3 4/4 homozygotes and 10 PER3 5/5 homozygotes drove during day, evening and night for approximately 90 minutes on real roads. Subjective sleepiness was measured every 5th minute, physiological sleepiness (blink duration, delay of eyelid reopening) was measured continuously. Driving performance was averaged over the whole condition.Statistical analyses were conducted using multilevel mixed effects regression modelling. Results: Subjective sleepiness showed a steeper rise during evening and night conditions in PER3 5/5 individuals. The PER3 polymorphism was also associated with individual differences observed in one of the physiological sleepiness indicators (delay of eyelid reopening). While the standard deviation of lateral position and blink duration showed clear effects of condition and time on task, PER3 genotype was not significantly related to individual differences in these measures. Conclusion: The PER3 VNTR polymorphism contributed significantly to individual differences in subjective and physiological sleepiness during real road driving; yet observed individual differences were still pronounced.

Electrical correlates of the physiological state of a cell, such as membrane conductance and capacitance, as well as cytoplasm conductivity, contain vital information about cellular function, ion transport across the membrane, and propagation of electrical signals. They are, however, difficult to measure; gold-standard techniques are typically unable to measure more than a few cells per day, making widespread adoption difficult and limiting statistical reproducibility. We have developed a dielectrophoretic platform using a disposable 3D electrode geometry that accurately (r2>0.99) measures mean electrical properties of populations of ~20,000 cells, by taking parallel ensemble measurements of cells at 20 frequencies up to 45 MHz, in (typically) ten seconds. This allows acquisition of ultra-high-resolution (100-point) DEP spectra in under two minutes. Data acquired from a wide range of cells – from platelets to large cardiac cells - benchmark well with patch-clamp-data. These advantages are collectively demonstrated in a longitudinal (same-animal) study of rapidly-changing phenomena such as ultradian (2-3 hour) rhythmicity in whole blood samples of the common vole (Microtus arvalis), taken from 10 µl tail-nick blood samples and avoiding sacrifice of the animal that is typically required in these studies.

Adipocytes are energy stores of the body which also play a role in physiological regulation and homeostasis through their endocrine activity. Adipocyte circadian clocks drive rhythms in gene expression, and dysregulation of these circadian rhythms associates with pathological conditions such as diabetes. However, although the role of circadian rhythms in adipose cells and related tissues has been studied from phsyiological and molecular perspectives, they have not yet been explored from an electrical perspective. Research into electro-chronobiology has revealed that electrical properties have important roles in peripheral clock regulation independently of transcription–translation feedback loops. We have used dielectrophoresis to study electrophysiological rhythms in pre-adipocytes – representing an adipocyte precursor and nucleated cell-based model, using serum shocking as the cellular method of clock entrainment. The results revealed significant electrophysiological rhythms, culminating in circadian (ca. 24 hourly) cycles in effective membrane capacitance and radius properties, whereas effective membrane conductance was observed to express ultradian (ca. 14 hourly) rhythms. These data shed new light into pre-adipocyte electrical behaviour and present a potential target for understanding and manipulation of metabolic physiology.

Electrical correlates of the physiological state of a cell, such as membrane conductance and capacitance, as well as cytoplasm conductivity, contain vital information about cellular function, ion transport across the membrane, and propagation of electrical signals. They are, however, difficult to measure; gold-standard techniques are typically unable to measure more than a few cells per day, making widespread adoption difficult and limiting statistical reproducibility. We have developed a dielectrophoretic platform using a disposable 3D electrode geometry that accurately (r2 > 0.99) measures mean electrical properties of populations of ~20,000 cells, by taking parallel ensemble measurements of cells at 20 frequencies up to 45 MHz, in (typically) ten seconds. This allows acquisition of ultra-high-resolution (100-point) DEP spectra in under two minutes. Data acquired from a wide range of cells – from platelets to large cardiac cells - benchmark well with patch-clamp-data. These advantages are collectively demonstrated in a longitudinal (same-animal) study of rapidly-changing phenomena such as ultradian (2–3 hour) rhythmicity in whole blood samples of the common vole (Microtus arvalis), taken from 10 µl tail-nick blood samples and avoiding sacrifice of the animal that is typically required in these studies.

Under natural conditions, many aspects of the abiotic and biotic environment vary with time of day, season or even era, whilst these conditions are typically kept constant in laboratory settings. The timing information contained within the environment serve as critical timing cues for the internal biological timing system, but how this system drives daily rhythms in behaviour and physiology may also depend on the internal state of the animal. The disparity between timing of these cues in natural and laboratory conditions can result in substantial differences in the scheduling of behaviour and physiology under these conditions. In nature, temporal coordination of biological processes is critical to maximise fitness because they optimise the balance between reproduction, foraging, and predation risk. Here we focus on the role of peripheral circadian clocks, and the rhythms that they drive, in enabling adaptive phenotypes. We discuss how reproduction, endocrine activity and metabolism interact with peripheral clocks, and outline the complex phenotypes arising from changes in this system. We conclude that peripheral timing is critical to adaptive plasticity of circadian organisation in the field, and that we must abandon standard laboratory conditions to understand the mechanisms that underlie this plasticity which maximises fitness under natural conditions.

Background: Circadian organisation of behavioural and physiological rhythms in mammals is largely driven by the clock in the suprachiasmatic nuclei (SCN) of the hypothalamus. In this clock, a molecular transcriptional repression and activation mechanism generates near 24 hour rhythms. One of the outputs of the molecular clock in specific SCN neurons is arginine-vasopressin (AVP), which is responsive to transcriptional activation by clock gene products. As negative regulators, the protein products of theperiodgenes are thought to repress transcriptional activity of the positive limb after heterodimerisation with CRYPTOCHROME. When both thePer1andPer2genes are dysfunctional by targeted deletion of the PAS heterodimer binding domain, mice lose circadian organization of behaviour upon release into constant environmental conditions. To which degree the period genes are involved in the control of AVP output is unknown. Methods: Using anin vitroslice culture setup, SCN-AVP release of cultures made of 10 wildtype and 9Per1/2double-mutant mice was assayed. Mice were sacrificed in either the early light phase of the light-dark cycle, or in the early subjective day on the first day of constant dark. Results: Here we report that in arrhythmic homozygousPer1/2double-mutant mice there is still a diurnal peak inin vitroAVP release from the SCN similar to that of wildtypes but distinctively different from the release pattern from the paraventricular nucleus. Such a modulation of AVP release is unexpected in mice where the circadian clockwork is thought to be disrupted. Conclusion: Our results suggest that the circadian clock in these animals, although deficient in (most) behavioural and molecular rhythms, may still be (partially) functional, possibly as an hourglass mechanism. The level of perturbation of the clock inPer1/2double mutants may therefore be less than was originally thought.

Using positron emission tomography, we measured in vivo uptake of (18)F-fluorodeoxyglucose (FDG) in the brain and heart of C57Bl/6 mice at intervals across a 24-hour light-dark cycle. Our data describe a significant, high amplitude rhythm in FDG uptake throughout the whole brain, peaking at the mid-dark phase of the light-dark cycle, which is the active phase for nocturnal mice. Under these conditions, heart FDG uptake did not vary with time of day, but did show biological variation throughout the 24-hour period for measurements within the same mice. FDG uptake was scanned at different times of day within an individual mouse, and also compared to different times of day between individuals, showing both biological and technical reproducibility of the 24-hour pattern in FDG uptake. Regional analysis of brain FDG uptake revealed especially high amplitude rhythms in the olfactory bulb and cortex, while low amplitude rhythms were observed in the amygdala, brain stem and hypothalamus. Low amplitude 24-hour rhythms in regional FDG uptake may be due to multiple rhythms with different phases in a single brain structure, quenching some of the amplitude. Our data show that the whole brain exhibits significant, high amplitude daily variation in glucose uptake in living mice. Reports applying the 2-deoxy-D[(14)C]-glucose method for the quantitative determination of the rates of local cerebral glucose utilization indicate only a small number of brain regions exhibiting a day versus night variation in glucose utilization. In contrast, our data show 24-hour patterns in glucose uptake in most of the brain regions examined, including several regions that do not show a difference in glucose utilization. Our data also emphasizes a methodological requirement of controlling for the time of day of scanning FDG uptake in the brain in both clinical and pre-clinical settings, and suggests waveform normalization of FDG measurements at different times of the day.

The suprachiasmatic nuclei of the hypothalamus (SCN) are the master circadian clock in mammals. Transcriptional activity in this master clock has a marker in the immediate‐early gene c‐Fos. Within the SCN, distinct differences in c‐Fos in the ventrolateral and the dorsomedial SCN have been reported for rodent species such as rats, mice, and hamsters. We studied C‐FOS expression in the common vole (Microtus arvalis) SCN under LD 12∶12 h and under constant dim light conditions. In the vole dorsomedial SCN, rhythmic C‐FOS expression was seen in LD with a clear peak in the middle of the light period. Under constant dim light, we report constitutive, non‐rhythmic expression of C‐FOS in the dorsomedial SCN. This pattern is consistent with the circadian organization of behavioral activity, which is weak in voles and may be lost under constant dim-light conditions. In the ventrolateral SCN, we observed a rise in C‐FOS expression under LD conditions prior to lights‐on, followed by peak expression at lights‐on. Another peak was seen at lights‐off. In an additional experiment, we subjected animals to LD 16∶8 to test the hypothesis that the dawn and dusk peaks in ventrolateral C‐FOS expression change phase along with the photoperiod. The peak in C‐FOS expression did not shift with the time of lights on, but remained at the same external time 6. The results are consistent with the interpretation that in the vole, c‐Fos expression reports transcriptional activity associated more likely with an internal, gating process than with an external effect of light.

Industrialisation greatly increased human night-time exposure to artificial light, which in animal models is a known cause of depressive phenotypes. Whilst many of these phenotypes are ‘direct’ effects of light on affect, an ‘indirect’ pathway via altered sleep-wake timing has been suggested. We have previously shown that the Period3 gene, which forms part of the biological clock, is associated with altered sleep-wake patterns in response to light. Here, we show that both wild-type and Per3-/- mice showed elevated levels of circulating corticosterone and increased hippocampal Bdnf expression after 3 weeks of exposure to dim light at night, but only mice deficient for the PERIOD3 protein (Per3-/-) exhibited a transient anhedonia-like phenotype, observed as reduced sucrose preference, in weeks 2-3 of dim light at night, whereas WT mice did not. Per3-/- mice also exhibited a significantly smaller delay in behavioural timing than WT mice during weeks 1, 2 and 4 of dim light at night exposure. When treated with imipramine, neither Per3-/- nor WT mice exhibited an anhedonia-like phenotype, and neither genotypes exhibited a delay in behavioural timing in responses to dLAN. While the association between both Per3-/- phenotypes remains unclear, both are alleviated by imipramine treatment during dim night-time light.

Background and Objectives Narcolepsy type 1 (NT1) is an orphan brain disorder caused by the irreversible destruction of orexin neurons. Metabolic disturbances are common in patients with NT1 who have a body mass index (BMI) 10% to 20% higher than the general population, with one-third being obese (BMI >30 kg/m2). Besides the destruction of orexin neurons in NT1, the metabolic alterations in obese and nonobese patients with NT1 remain unknown. The aim of this study was to identify possible differences in plasma metabolic profiles between patients with NT1 and controls as a function of their BMI status. Methods We used a targeted liquid chromatography–mass spectrometry metabolomics approach to measure 141 circulating, low-molecular-weight metabolites in drug-free fasted plasma samples from 117 patients with NT1 (including 41 obese individuals) compared with 116 BMI-matched controls (including 57 obese individuals). Results Common metabolites driving the difference between patients with NT1 and controls, regardless of BMI, were identified, namely sarcosine, glutamate, nonaylcarnitine (C9), 5 long-chain lysophosphatidylcholine acyls, 1 sphingolipid, 12 phosphatidylcholine diacyls, and 11 phosphatidylcholine acyl-akyls, all showing increased concentrations in NT1. Metabolite concentrations significantly affected by NT1 (n = 42) and BMI category (n = 40) showed little overlap (n = 5). Quantitative enrichment analysis revealed common metabolic pathways that were implicated in the NT1/control differences in both normal BMI and obese comparisons, namely glycine and serine, arachidonic acid, and tryptophan metabolism. The metabolites driving these differences were glutamate, sarcosine, and ornithine (glycine and serine metabolism); glutamate and PC aa C34:4 (arachidonic acid metabolism); and glutamate, serotonin, and tryptophan (tryptophan metabolism). Linear metabolite-endophenotype regression analyses highlight that as part of the NT1 metabolic phenotype, most of the relationships between the sleep parameters (i.e., slow-wave sleep duration, sleep latency, and periodic leg movement) and metabolite concentrations seen in the controls were lost. Discussion These results represent the most comprehensive metabolic profiling of patients with NT1 as a function of BMI and propose some metabolic diagnostic biomarkers for NT1, namely glutamate, sarcosine, serotonin, tryptophan, nonaylcarnitine, and some phosphatidylcholines. The metabolic pathways identified offer, if confirmed, possible targets for treatment of obesity in NT1. Classification of Evidence This study provides Class II evidence that a distinct metabolic profile can differentiate patients with NT1 from patients without the disorder.

The unique structure and composition of articular cartilage is critical for its physiological function. However, this architecture may get disrupted by degeneration or trauma. Due to the low intrinsic regeneration properties of the tissue, the healing response is generally poor. Low-grade inflammation in patients with osteoarthritis advances cartilage degradation, resulting in pain, immobility, and reduced quality of life. Generating neocartilage using advanced tissue engineering approaches may address these limitations. The biocompatible microenvironment that is suitable for cartilage regeneration may not only rely on cells and scaffolds, but also on the spatial and temporal features of biomechanics. Cell-autonomous biological clocks that generate circadian rhythms in chondrocytes are generally accepted to be indispensable for normal cartilage homeostasis. While the molecular details of the circadian clockwork are increasingly well understood at the cellular level, the mechanisms that enable clock entrainment by biomechanical signals, which are highly relevant in cartilage, are still largely unknown. This narrative review outlines the role of the biomechanical microenvironment to advance cartilage tissue engineering via entraining the molecular circadian clockwork, and highlights how application of this concept may enhance the development and successful translation of biomechanically relevant tissue engineering interventions.

Circadian organization of the mammalian transcriptome is achieved by rhythmic recruitment of key modifiers of chromatin structure and transcriptional and translational processes. These rhythmic processes, together with posttranslational modification, constitute circadian oscillators in the brain and peripheral tissues, which drive rhythms in physiology and behavior, including the sleep–wake cycle. In humans, sleep is normally timed to occur during the biological night, when body temperature is low and melatonin is synthesized. Desynchrony of sleep–wake timing and other circadian rhythms, such as occurs in shift work and jet lag, is associated with disruption of rhythmicity in physiology and endocrinology. However, to what extent mistimed sleep affects the molecular regulators of circadian rhythmicity remains to be established. Here, we show that mistimed sleep leads to a reduction of rhythmic transcripts in the human blood transcriptome from 6.4% at baseline to 1.0% during forced desynchrony of sleep and centrally driven circadian rhythms. Transcripts affected are key regulators of gene expression, including those associated with chromatin modification (methylases and acetylases), transcription (RNA polymerase II), translation (ribosomal proteins, initiation, and elongation factors), temperature-regulated transcription (cold inducible RNA-binding proteins), and core clock genes including CLOCK and ARNTL (BMAL1). We also estimated the separate contribution of sleep and circadian rhythmicity and found that the sleep–wake cycle coordinates the timing of transcription and translation in particular. The data show that mistimed sleep affects molecular processes at the core of circadian rhythm generation and imply that appropriate timing of sleep contributes significantly to the overall temporal organization of the human transcriptome.

In most mammals, daily rhythms in physiology are driven by a circadian timing system composed of a master pacemaker in the suprachiasmatic nucleus (SCN) and peripheral oscillators in most body cells. The SCN clock, which is phase-entrained by light–dark cycles, is thought to synchronize subsidiary oscillators in peripheral tissues, mainly by driving cyclic feeding behavior. Here, we examined the expression of circadian clock genes in the SCN and the liver of the common vole Microtus arvalis, a rodent with ultradian activity and feeding rhythms. In these animals, clock-gene mRNAs accumulate with high circadian amplitudes in the SCN but are present at nearly constant levels in the liver. Interestingly, high-amplitude circadian liver gene expression can be elicited by subjecting voles to a circadian feeding regimen. Moreover, voles with access to a running wheel display a composite pattern of circadian and ultradian behavior, which correlates with low-amplitude circadian gene expression in the liver. Our data indicate that, in M. arvalis, the amplitude of circadian liver gene expression depends on the contribution of circadian and ultradian components in activity and feeding rhythms.

Light is the main entraining signal of the central circadian clock, which drives circadian organization of activity. When food is made available during only certain parts of the day, it can entrain the clock in the liver without changing the phase of the central circadian clock. Although a hallmark of food entrainment is a behavioral anticipation of food availability, the extent of behavioral alterations in response to food availability has not been fully characterized. The authors have investigated interactions between light and temporal food availability in the timing of activity in the common vole. Temporally restricted food availability enhanced or attenuated re-entrainment to a phase advance in light entrainment when it was shifted together with the light or remained at the same time of day, respectively. When light-entrained behavior was challenged with temporal food availability cycles with a different period, two distinct activity components were observed. More so, the present data indicate that in the presence of cycles of different period length of food and light, an activity component emerged that appeared to be driven by a free-running (light-entrainable) clock. Because the authors have previously shown that in the common vole altering activity through running-wheel availability can alter the effectiveness of food availability to entrain the clock in the liver, the authors included running-wheel availability as a parameter that alters the circadian/ultradian balance in activity. In the current protocols, running-wheel availability enhanced the entraining potential of both light and food availability in a differential way. The data presented here show that in the vole activity is a complex of individually driven components and that this activity is, itself, an important modulator of the effectiveness of entraining signals such as light and food.

Sleep homeostasis and circadian rhythmicity interact to determine the timing of behavioral activity. Circadian clock genes contribute to circadian rhythmicity centrally and in the periphery, but some also have roles within sleep regulation. The clock gene Period3 (Per3) has a redundant function within the circadian system and is associated with sleep homeostasis in humans. This study investigated the role of PER3 in sleep/wake activity and sleep homeostasis in mice by recording wheel running activity under baseline conditions in wild-type (WT; n = 54) and in PER3-deficient (Per3(-/-); n = 53) mice, as well as EEG-assessed sleep before and after 6 hours of sleep deprivation in WT (n = 7) and Per3(-/-) (n = 8) mice. Whereas total activity and vigilance states did not differ between the genotypes, the temporal distribution of wheel running activity, vigilance states, and EEG delta activity was affected by genotype. In Per3(-/-) mice, running wheel activity was increased and REM sleep and NREM sleep were reduced in the middle of the dark phase, and delta activity was enhanced at the end of the dark phase. At the beginning of the baseline light period, there was less wakefulness and more REM and NREM in Per3(-/-) mice. Per3(-/-) mice spent less time in wakefulness and more time in NREM sleep in the light period immediately after sleep deprivation and REM sleep accumulated more slowly during the recovery dark phase. These data confirm a role for PER3 in sleep/wake timing and sleep homeostasis.

Objectives: Previously, we reported a light-dependant phenotype incircadian regulation in PER3 knockout (Per3-/-) mice. These mice also showed altered sleep architecture and elevated activity levels inthe second half of the dark period. In humans, a polymorphism inPER3 has been associated with diurnal preference, sleep homeo-stasis, and cognitive decline in response to sleep loss. We generated humanised knock-in (KI) mice expressing two variants of the human polymorphism and investigated activity patterns in response to different photoperiods. We also further investigated gene expression profiles of Per3-/- and KI mice during an ultradian light exposure paradigm. Methods: Male and female C57Bl/6 mice, expressing either the 4- or 5- repeat of the human variable number tandem repeat in PER3 (Per34/4 and Per35/5) were exposed to short (8 h), intermediate (12 h) and long (16 h) photoperiods, as well as constant light.Transitions between the conditions were mixed between animals,such that the response to a new photoperiod could be analysed,taking into account different light-histories. Behavioural activity was recorded as running wheel revolutions. In addition, we subjected Per3-/- and KI mice to an ultradian light-dark cycle (3.5 h L–3.5 h D) and analysed whole genome RNA expression at CT 16, in an ultradian light episode. Results: Significant differences between male and female activity were seen. Female mice showed more activity in the second half of the dark period, and overall 24-h activity levels were more than 1.5-fold higher in females. These differences were seen in all genotypes. In constant darkness, both male and female Per34/4 mice showed increased activity in the second half of the dark period, compared toWT and Per35/5 mice. The behavioural responses to photoperiods were diverse, with KI mice appearing to adjust more rapidly to a new photoperiod. Whole genome RNA expression in Per3-/-and KI mice was altered compared to WT mice, and similar pathways were affected in both Per3-/-and KI mice. Conclusion: Here we show behavioural data on a novel humanised mouse model of PER3. In mice, this polymorphism associates with altered activity, especially in the transition between photic conditions.We also observed a consistent difference between male and female activity. This emphasizes the need to not only use transgenic mice but also to include both sexes in animal models of human conditions.

Polymorphisms in the human circadian clock gene PERIOD3 (PER3) are associated with a wide variety of phenotypes such as diurnal preference, delayed sleep phase disorder, sleep homeostasis, cognitive performance, bipolar disorder, type 2 diabetes, cardiac regulation, cancer, light sensitivity, hormone and cytokine secretion, and addiction. However, the molecular mechanisms underlying these phenotypic associations remain unknown. Per3 knockout mice (Per3

A functional knockout of Period3 in mice (mPer3— /—) results in a mildly altered circadian phenotype, and mPer3 shows a redundant role within the circadian clock. In this study, the authors reevaluated the Per3—/ — behavioral phenotype on a C57Bl/6J background and report altered responses to light. In constant light, free-running activity period was shorter than that of wild-type, whereas in constant darkness, no difference was observed between genotypes. The effect of light was parametric, and the difference in free-running period between genotypes increased under constant light with increasing light intensity. An attenuated response to light in Per3—/— mice was also demonstrated through reduced negative masking in activity in an ultradian protocol and a slower reentrainment to a shifted light-dark cycle when activity falls in the light period of the new light-dark cycle. Behavioral phase-shifts in response to a single delaying or advancing light pulse in the Per3—/— mouse were not compromised. This demonstrates that the mPer3— /— phenotype is characterized predominantly by altered sensitivity to light and not by the ability of the circadian system to respond to light. In addition to its redundant role within the molecular clock, these data suggest a new role for Per3 outside of the circadian clock and contributing to light input pathways.

In humans, a primate-specific variable-number tandem-repeat (VNTR) polymorphism (4 or 5 repeats 54 nt in length) in the circadian gene PER3 is associated with differences in sleep timing and homeostatic responses to sleep loss. We investigated the effects of this polymorphism on circadian rhythmicity and sleep homeostasis by introducing the polymorphism into mice and assessing circadian and sleep parameters at baseline and during and after 12 h of sleep deprivation (SD). Microarray analysis was used to measure hypothalamic and cortical gene expression. Circadian behavior and sleep were normal at baseline. The response to SD of 2 electrophysiological markers of sleep homeostasis, electroencephalography (EEG) θ power during wakefulness and δ power during sleep, were greater in the Per3(5/5) mice. During recovery, the Per3(5/5) mice fully compensated for the SD-induced deficit in δ power, but the Per3(4/4) and wild-type mice did not. Sleep homeostasis-related transcripts (e.g., Homer1, Ptgs2, and Kcna2) were differentially expressed between the humanized mice, but circadian clock genes were not. These data are in accordance with the hypothesis derived from human data that the PER3 VNTR polymorphism modifies the sleep homeostatic response without significantly influencing circadian parameters.-Hasan, S., van der Veen, D. R., Winsky-Sommerer, R., Hogben, A., Laing, E. E., Koentgen, F., Dijk, D.-J., Archer, S. N. A human sleep homeostasis phenotype in mice expressing a primate-specific PER3 variable-number tandem-repeat coding-region polymorphism.

Circadian rhythms in cardiac function are apparent in e.g., blood pressure, heart rate, and acute adverse cardiac events. A circadian clock in heart tissue has been identified, but entrainment pathways of this clock are still unclear. We cultured tissues of mice carrying bioluminescence reporters of the core clock genes, period 1 or 2 (per1(luc) or PER2(LUC)) and compared in vitro responses of atrium to treatment with medium and a synthetic glucocorticoid (dexamethasone [DEX]) to that of the suprachiasmatic nucleus (SCN) and liver. We observed that PER2(LUC), but not per1(luc) is rhythmic in atrial tissue, while both per1(luc) and PER2(LUC) exhibit rhythmicity in other cultured tissues. In contrast to the SCN and liver, both per1(luc) and PER2(LUC) bioluminescence amplitudes were increased in response to DEX treatment, and the PER2(LUC) amplitude response was dependent on the time of treatment. Large phase-shift responses to both medium and DEX treatments were observed in the atrium, and phase responses to medium treatment were not attributed to serum content but the treatment procedure itself. The phase-response curves of atrium to both DEX and medium treatments were found to be different to the liver. Moreover, the time of day of the culturing procedure itself influenced the phase of the circadian clock in each of the cultured tissues, but the magnitude of this response was uniquely large in atrial tissue. The current data describe novel entrainment signals for the atrial circadian clock and specifically highlight entrainment by mechanical treatment, an intriguing observation considering the mechanical nature of cardiac tissue.