Circadian dysfunction and cardio-metabolic disorders in humans.

The topic of human circadian rhythms is not only attracting the attention of clinical researchers from various fields but also sparking a growing public interest. The circadian system comprises the central clock, located in the suprachiasmatic nucleus of the hypothalamus, and the peripheral clocks in various tissues that are interconnected; together they coordinate many daily activities, including sleep and wakefulness, physical activity, food intake, glucose sensitivity and cardiovascular functions. Disruption of circadian regulation seems to be associated with metabolic disorders (particularly impaired glucose tolerance) and cardiovascular disease. Previous clinical trials revealed that disturbance of the circadian system, specifically due to shift work, is associated with an increased risk of type 2 diabetes mellitus. This review is intended to provide clinicians who wish to implement knowledge of circadian disruption in diagnosis and strategies to avoid cardio-metabolic disease with a general overview of this topic.

Circadian clock in choroid plexus is resistant to immune challenge but dampens in response to chronodisruption.

The choroid plexus (ChP) in the brain ventricles has a major influence on brain homeostasis. In this study, we aimed to determine whether the circadian clock located in ChP is affected by chronodisruption caused by misalignment with the external light/dark cycle and/or inflammation. Adult mPer2Luc mice were maintained in the LD12:12 cycle or exposed to one of two models of chronic chronodisruption - constant light for 22-25 weeks (cLL) or 6-hour phase advances of the LD12:12 cycle repeated weekly for 12 weeks (cLD-shifts). Locomotor activity was monitored before the 4th ventricle ChP and suprachiasmatic nuclei (SCN) explants were recorded in real time for PER2-driven population and single-cell bioluminescence rhythms. In addition, plasma immune marker concentrations and gene expression in ChP, prefrontal cortex, hippocampus and cerebellum were analyzed. cLL dampened the SCN clock but did not shorten the inactivity interval (sleep). cLD-shifts had no effect on the SCN clock, but transiently affected sleep duration and fragmentation. Both chronodisruption protocols dampened the ChP clock. Although immune markers were elevated in plasma and hippocampus, levels in ChP were unaffected, and unlike the liver clock, the ChP clock was resistant to lipopolysaccharide treatment. Importantly, both chronodisruption protocols reduced glucocorticoid signaling in ChP. The data demonstrate the high resistance of the ChP clock to inflammation, highlighting its role in protecting the brain from neuroinflammation, and on the other hand its high sensitivity to chronodisruption. Our results provide a novel link between human lifestyle-induced chronodisruption and the impairment of ChP-dependent brain homeostasis.

Population-representative study reveals cardiovascular and metabolic disease biomarkers associated with misaligned sleep schedules.

STUDY OBJECTIVES: Social jetlag manifests as a difference in sleep timing on workdays and free days. Social jetlag is often associated with shorter, lower-quality sleep, so it is unclear how much the chronic circadian misalignment contributes to observed negative health outcomes. We aimed to (1) investigate associations between social jetlag, chronotype (one of its determinants), and the levels of health markers, (2) describe factors associated with social jetlag, and (3) examine whether working from home can reduce social jetlag. METHODS: Adult respondents participated in a nationally representative longitudinal survey of Czech households (individuals in each wave: n2018/19/20 = 5132/1957/1533), which included Munich ChronoType Questionnaire to evaluate chronotype and social jetlag. A subset provided blood samples (n2019 = 1957) for detection of nine biomarkers and was surveyed in three successive years (social jetlag calculated for n2018/19/20 = 3930/1601/1237). Data were analyzed by nonparametric univariate tests and mixed effects multivariate regression with social jetlag, chronotype, sex, age, body-mass index, and reported diseases as predictors and biomarker levels as outcomes. RESULTS: Higher social jetlag (≥0.65 h) was significantly associated with increased levels of total cholesterol and low-density lipoprotein cholesterol, particularly in participants older than 50 years (Mann-Whitney, men: pCHL = 0.0005, pLDL = 0.0009; women: pCHL = 0.0079, pLDL = 0.0068). Extreme chronotypes were associated with cardiovascular disease risk markers regardless of social jetlag (Kruskal-Wallis, p < 0.0001). Commuting to work and time stress were identified as important contributors to social jetlag. Individual longitudinal data showed that working from home decreased social jetlag and prolonged sleep. CONCLUSIONS: We report significant associations between sleep phase preference, social jetlag, and cardio-metabolic biomarkers.

Lithium affects the circadian clock in the choroid plexus - A new role for an old mechanism.

Lithium is an effective mood stabilizer, but the mechanism of its therapeutic action is not well understood. We investigated the effect of lithium on the circadian clock located in the ventricle barrier complex containing the choroid plexus (CP), a part of the glymphatic system that influences gross brain function via the production of cerebrospinal fluid. The mPer2Luc mice were injected with lithium chloride (LiCl) or vehicle, and their effects on the clock gene Nr1d1 in CP were detected by RT qPCR. CP organotypic explants were prepared to monitor bioluminescence rhythms in real time and examine the responses of the CP clock to LiCl and inhibitors of glycogen synthase kinase-3 (CHIR-99021) and protein kinase C (chelerythrine). LiCl affected Nr1d1 expression levels in CP in vivo and dose-dependently delayed the phase and prolonged the period of the CP clock in vitro. LiCl and CHIR-99021 had different effects on 1] CP clock parameters (amplitude, period, phase), 2] dexamethasone-induced phase shifts of the CP clock, and 3] dynamics of PER2 degradation and de novo accumulation. LiCl-induced phase delays were significantly reduced by chelerythrine, suggesting the involvement of PKC activity. The effects on the CP clock may be involved in the therapeutic effects of lithium and hypothetically improve brain function in psychiatric patients by aligning the function of the CP clock-related glymphatic system with the sleep-wake cycle. Importantly, our data argue for personalized timing of lithium treatment in BD patients.

The rs10830963 Polymorphism of the MTNR1B Gene: Association With Abnormal Glucose, Insulin and C-peptide Kinetics.

Background: The MTNR1B gene encodes a receptor for melatonin, a hormone regulating biorhythms. Disruptions in biorhythms contribute to the development of type 2 diabetes mellitus (T2DM). Genetic studies suggest that variability in the MTNR1B gene affects T2DM development. Our aim was to compare the distribution of the genetic variant rs10830963 between persons differing in glucose tolerance in a sample of the Czech population (N=1206). We also evaluated possible associations of the polymorphism with insulin sensitivity, beta cell function, with the shape of glucose, insulin and C-peptide trajectories measured 7 times during a 3-hour oral glucose tolerance test (OGTT) and with glucagon response. In a subgroup of 268 volunteers we also evaluated sleep patterns and biorhythm. Results: 13 persons were diagnosed with T2DM, 119 had impaired fasting blood glucose (IFG) and/or impaired glucose tolerance (IGT). 1074 participants showed normal results and formed a control group. A higher frequency of minor allele G was found in the IFG/IGT group in comparison with controls. The GG constellation was present in 23% of diabetics, in 17% of IFG/IGT probands and in 11% of controls. Compared to CC and CG genotypes, GG homozygotes showed higher stimulated glycemia levels during the OGTT. Homozygous as well as heterozygous carriers of the G allele showed lower very early phase of insulin and C-peptide secretion with unchanged insulin sensitivity. These differences remained significant after excluding diabetics and the IFG/IGT group from the analysis. No associations of the genotype with the shape of OGTT-based trajectories, with glucagon or with chronobiological patterns were observed. However, the shape of the trajectories differed significantly between men and women. Conclusion: In a representative sample of the Czech population, the G allele of the rs10830963 polymorphism is associated with impaired early phase of beta cell function, and this is evident even in healthy individuals.

Misaligned feeding schedule elicits divergent circadian reorganizations in endo- and exocrine pancreas clocks.

Misaligned feeding may lead to pancreatic insufficiency, however, whether and how it affects circadian clock in the exocrine pancreas is not known. We exposed rats to a reversed restricted feeding regimen (rRF) for 10 or 20 days and analyzed locomotor activity, daily profiles of hormone levels (insulin, glucagon, and corticosterone) in plasma, and clock gene expression in the liver and endocrine and exocrine pancreas. In addition, we monitored responses of the exocrine pancreatic clock in organotypic explants of mPer2Luc mice in real time to acetylcholine, insulin, and glucocorticoids. rRF phase-reversed the clock in the endocrine pancreas, similar to the clock in the liver, but completely abolished clock gene rhythmicity and significantly downregulated the expression of Cpb1 and Cel in the exocrine pancreas. rRF desynchronized the rhythms of plasma insulin and corticosterone. Daily profiles of their receptor expression differed in the two parts of the pancreas and responded differently to rRF. Additionally, the pancreatic exocrine clock responded differently to treatments with insulin and the glucocorticoid analog dexamethasone in vitro. Mathematical simulation confirmed that the long-term misalignment between these two hormonal signals, as occurred under rRF, may lead to dampening of the exocrine pancreatic clock. In summary, our data suggest that misaligned meals impair the clock in the exocrine part of the pancreas by uncoupling insulin and corticosterone rhythms. These findings suggest a new mechanism by which adverse dietary habits, often associated with shift work in humans, may impair the clock in the exocrine pancreas and potentially contribute to exocrine pancreatic insufficiency.

Early rhythmicity in the fetal suprachiasmatic nuclei in response to maternal signals detected by omics approach.

The suprachiasmatic nuclei (SCN) of the hypothalamus harbor the central clock of the circadian system, which gradually matures during the perinatal period. In this study, time-resolved transcriptomic and proteomic approaches were used to describe fetal SCN tissue-level rhythms before rhythms in clock gene expression develop. Pregnant rats were maintained in constant darkness and had intact SCN, or their SCN were lesioned and behavioral rhythm was imposed by temporal restriction of food availability. Model-selecting tools dryR and CompareRhythms identified sets of genes in the fetal SCN that were rhythmic in the absence of the fetal canonical clock. Subsets of rhythmically expressed genes were assigned to groups of fetuses from mothers with either intact or lesioned SCN, or both groups. Enrichment analysis for GO terms and signaling pathways revealed that neurodevelopment and cell-to-cell signaling were significantly enriched within the subsets of genes that were rhythmic in response to distinct maternal signals. The findings discovered a previously unexpected breadth of rhythmicity in the fetal SCN at a developmental stage when the canonical clock has not yet developed at the tissue level and thus likely represents responses to rhythmic maternal signals.

High Sensitivity of the Circadian Clock in the Hippocampal Dentate Gyrus to Glucocorticoid- and GSK3-Beta-Dependent Signals.

AIMS: Circadian clocks in the hippocampus (HPC) align memory processing with appropriate time of day. Our study was aimed at ascertaining the specificity of glycogen synthase kinase 3-beta (GSK3ß)- and glucocorticoid (GC)-dependent pathways in the entrainment of clocks in individual HPC regions, CA1-3, and dentate gyrus (DG). METHODS: The role of GCs was addressed in vivo by comparing the effects of adrenalectomy (ADX) and subsequent dexamethasone (DEX) supplementation on clock gene expression profiles (Per1, Per2, Nr1d1, and Bmal1). In vitro the effects of DEX and the GSK3ß inhibitor, CHIR-99021, were assessed from recordings of bioluminescence rhythms in HPC organotypic explants of mPER2Luc mice. RESULTS: Circadian rhythms of clock gene expression in all HPC regions were abolished by ADX, and DEX injections to the rats rescued those rhythms in DG. The DEX treatment of the HPC explants significantly lengthened periods of the bioluminescence rhythms in all HPC regions with the most significant effect in DG. In contrast to DEX, CHIR-99021 significantly shortened the period of bioluminescence rhythm. Again, the effect was most significant in DG which lacks the endogenously inactivated (phosphorylated) form of GSK3ß. Co-treatment of the explants with CHIR-99021 and DEX produced the CHIR-99021 response. Therefore, the GSK3ß-mediated pathway had dominant effect on the clocks. CONCLUSION: GSK3ß- and GC-dependent pathways entrain the clock in individual HPC regions by modulating their periods in an opposite manner. The results provide novel insights into the mechanisms connecting the arousal state-relevant signals with temporal control of HPC-dependent memory and cognitive functions.

Targeted modification of the Per2 clock gene alters circadian function in mPer2luciferase (mPer2Luc) mice.

Modification of the Per2 clock gene in mPer2Luc reporter mice significantly alters circadian function. Behavioral period in constant dark is lengthened, and dissociates into two distinct components in constant light. Rhythms exhibit increased bimodality, enhanced phase resetting to light pulses, and altered entrainment to scheduled feeding. Mechanistic mathematical modelling predicts that enhanced protein interactions with the modified mPER2 C-terminus, combined with differential clock regulation among SCN subregions, can account for effects on circadian behavior via increased Per2 transcript and protein stability. PER2::LUC produces greater suppression of CLOCK:BMAL1 E-box activity than PER2. mPer2Luc carries a 72 bp deletion in exon 23 of Per2, and retains a neomycin resistance cassette that affects rhythm amplitude but not period. The results show that mPer2Luc acts as a circadian clock mutation illustrating a need for detailed assessment of potential impacts of c-terminal tags in genetically modified animal models.

Hormonal fine-tuning of clock in decidual region of mouse placenta by dopamine, melatonin, insulin, leptin and ghrelin.

INTRODUCTION: The maternal part of the rodent placenta harbors a circadian clock which robustly responds to glucocorticoids, however, its sensitivity to other hormones has not been elucidated. In this study, we tested five selected hormones (dopamine, melatonin, insulin, leptin and ghrelin) for their effectiveness to affect the clock in decidual region of mouse placenta in vitro. METHODS: We administered the hormones or corresponding vehicles at various time points over 24 h to organotypic placental explants of mPer2Luc mice containing the decidua basalis (DB) region and monitored their effects on amplitude, period, median expression level (mesor) and phase of PER2-driven bioluminescence rhythms. RESULTS: Dopamine significantly increased the amplitude, robustly dampened the mesor, and during a narrow time interval (corresponding to daytime) induced phase delays of the rhythms. In contrast, melatonin had no effect on amplitude, but induced phase advances of the rhythms at the opposite time window than dopamine (corresponding to nighttime). Leptin and ghrelin, but not insulin, slightly increased amplitudes and moderately modulated phase delays of the clock, suggesting that the DB clock, in contrast to other peripheral clocks, is rather resilient to abrupt changes in levels of feeding- and metabolism-related hormones. DISCUSSION: The results demonstrate for the first time that dopamine and melatonin exhibit delicate yet specific effects on parameters of the DB clock and may thus potentially contribute to fine-tuning of its phase under in vivo conditions. It also implies that dysregulation of their levels, which accompany various pathologies, may account for malfunction of the clock in DB.

Modulation of single cell circadian response to NMDA by diacylglycerol lipase inhibition reveals a role of endocannabinoids in light entrainment of the suprachiasmatic nucleus.

Suprachiasmatic nucleus (SCN) of the hypothalamus is the master clock that drives circadian rhythms in physiology and behavior and adjusts their timing to external cues. Neurotransmitter glutamate and glutamatergic receptors sensitive to N-methyl-d-aspartate (NMDA) play a dual role in the SCN by coupling astrocytic and neuronal single cell oscillators and by resetting their phase in response to light. Recent reports suggested that signaling by endogenous cannabinoids (ECs) participates in both of these functions. We have previously shown that ECs, such as 2-arachidonoylglycerol (2-AG), act via CB1 receptors to affect the SCN response to light-mimicking NMDA stimulus in a time-dependent manner. We hypothesized that this ability is linked to the circadian regulation of EC signaling. We demonstrate that circadian clock in the rat SCN regulates expression of 2-AG transport, synthesis and degradation enzymes as well as its receptors. Inhibition of the major 2-AG synthesis enzyme, diacylglycerol lipase, enhanced the phase delay and lowered the amplitude of explanted SCN rhythm in response to NMDAR activation. Using microscopic PER2 bioluminescence imaging, we visualized how individual single cell oscillators in different parts of the SCN respond to the DAGL inhibition/NMDAR activation and shape response of the whole pacemaker. Additionally, we present strong evidence that the zero amplitude behavior of the SCN in response to single NMDA stimulus in the middle of subjective night is the result of a loss of rhythm in individual SCN cells. The paper provides new insights into the modulatory role of endocannabinoid signaling during the light entrainment of the SCN.

Glucocorticoids reset circadian clock in choroid plexus via period genes.

The epithelial cells of choroid plexus (CP) in brain ventricles produce cerebrospinal fluid and act as the blood-cerebrospinal fluid barrier. In this study, we confirmed that CP in the 4th ventricle is composed of cellular oscillators that all harbor glucocorticoid receptors and are mutually synchronized to produce a robust clock gene expression rhythm detectable at the tissue level in vivo and in vitro. Animals lacking glucocorticoids (GCs) due to surgical removal of adrenal glands had Per1, Per2, Nr1d1 and Bmal1 clock gene rhythmicity in their CP significantly dampened, whereas subjecting them to daily bouts of synthetic GC analog, dexamethasone (DEX), reinforced those rhythms. We verified these in vivo effects using an in vitro model of organotypic CP explants; depending on the time of its application, DEX significantly increased the amplitude and efficiently reset the phase of the CP clock. The results are the first description of a PRC for a non-neuronal clock in the brain, demonstrating that CP clock shares some properties with the non-neuronal clocks elsewhere in the body. Finally, we found that DEX exhibited multiple synergic effects on the CP clock, including acute activation of Per1 expression and change of PER2 protein turnover rate. The DEX-induced shifts of the CP clock were partially mediated via PKA-ERK1/2 pathway. The results provide the first evidence that the GC rhythm strengthens and entrains the clock in the CP helping thus fine-tune the brain environment according to time of day.

Chronotype assessment via a large scale socio-demographic survey favours yearlong Standard time over Daylight Saving Time in central Europe.

Abandoning daylight saving time in Europe raises the topical issue of proper setting of yearlong social time, which needs mapping of various socio-demographic factors, including chronotype, in specific geographic regions. This study represents the first detailed large scale chronotyping in the Czech Republic based on data collected in the complex panel socio-demographic survey in households (total 8760 respondents) and the socio-physiological survey, in which chronotyped participants also provided blood samples (n = 1107). Chronotype assessment based on sleep phase (MCTQ questions and/or time-use diary) correlated with a self-assessed interval of best alertness. The mean chronotype of the Czech population defined as mid sleep phase (MSFsc) was 3.13 ± 0.02 h. Chronotype exhibited significant east-to-westward, north-to-southward, and settlement size-dependent gradients and was associated with age, sex, partnership, and time spent outdoors as previously demonstrated. Moreover, for subjects younger than 40 years, childcare was highly associated with earlier chronotype, while dog care was associated with later chronotype. Body mass index correlated with later chronotype in women whose extreme chronotype was also associated with lower plasma levels of protective HDL cholesterol. Based on the chronotype prevalence the results favour yearlong Standard Time as the best choice for this geographic region.

Withdrawn: Dexamethasone resets the circadian clock in hippocampus via multiple mechanisms involving lithium-independent GSK3ß signalling.

The above article from British Journal of Pharmacology, published online as an Accepted Article on 19 August 2019 in Wiley Online Library (wileyonlinelibrary.com), has been withdrawn by agreement between the authors, the journal Editor-in-Chief Professor Amrita Ahluwalia, and John Wiley & Sons Limited. The withdrawal has been agreed owing to new findings that necessitate re-interpretation of the results.

Circadian profiling reveals distinct regulation of endocannabinoid system in the rat plasma, liver and adrenal glands by light-dark and feeding cycles.

Circadian clocks coordinate physiological and behavioral rhythms that allow the organism to anticipate and adapt to daily changes in environment. The clock-driven cellular oscillations are highly tissue specific to efficiently fine-tune local signaling, manage energy use and segregate incompatible processes. In most peripheral tissues, food acts as the main cue that entrains the oscillations to external time. Food intake and energy balance are under control of endocannabinoid (EC) signaling. Despite this obvious link between the circadian and EC systems, evidence for their interaction started to emerge only recently. We used targeted lipidomics to analyze circadian variations in EC tone in rat plasma, liver and adrenal tissue. The results provide the evidence that ECs, monoacylglycerols, N-acylethanolamines and their precursors oscillate with a tissue-specific circadian phase in plasma and liver. We then identified a set of rhythmically expressed genes likely responsible for the variations in EC tissue tone. In contrast to the liver, EC levels did not oscillate in the adrenal glands. Instead, we revealed that local EC receptor genes are under circadian regulation. To explore the impact of metabolic signals on expression of these genes, we used daytime-restricted feeding schedule. We subsequently showed that daytime feeding strongly suppressed liver-expressed fatty acid binding protein 5 (Fabp5) and adrenal-expressed non-canonical endocannabinoid receptors Gpr55 and Trpv1, whereas it upregulated liver-expressed Trpv1 and glycerophosphodiester phosphodiesterase 1 (Gde1). Our results reveal tissue-specific mechanisms involved in interaction between endocannabinoid signaling, circadian system and metabolism.

Modulation of NMDA-Mediated Clock Resetting in the Suprachiasmatic Nuclei of mPer2 Luc Mouse by Endocannabinoids.

Light entrains the master circadian clock in the suprachiasmatic nucleus (SCN) predominantly through glutamatergic signaling via NMDA receptors. The magnitude and the direction of resulting phase shifts depend on timing of the photic stimulus. Previous reports based on behavioral and electrophysiological data suggested that endocannabinoids (EC) might reduce the ability of the SCN clock to respond to light. However, there is little direct evidence for the involvement of EC in entrainment of the rhythmic clock gene expression in the SCN. We have used luminescence recording of cultured SCN slices from mPer2 Luc mice to construct a complete phase response curve (PRC) for NMDA receptor activation. The results demonstrated that NMDA administration phase-shifts the PER2 rhythm in a time-specific manner. A stable "singularity," in the course of which the clock seemingly stops while the overall phase is caught between delays and advances, can occur in response to NMDA at a narrow interval during the PER2 level decrease. NMDA-induced phase delays were affected neither by the agonist (WIN 55,212-2 mesylate) nor by the antagonist (rimonabant hydrochloride) of EC receptors. However, the agonist significantly reduced the NMDA-induced phase advance of the clock, while the antagonist enhanced the phase advance, causing a shift in the sensitivity window of the SCN to NMDA. The modulation of EC signaling in the SCN had no effect by itself on the phase of the PER2 rhythm. The results provide evidence for a modulatory role of EC in photic entrainment of the circadian clock in the SCN.

Development and Entrainment of the Fetal Clock in the Suprachiasmatic Nuclei: The Role of Glucocorticoids.

The adult circadian clock in the suprachiasmatic nucleus (SCN) of the hypothalamus is resilient to glucocorticoids (GCs). The fetal rodent SCN resembles that of the adult in its organization of GC-sensitive peripheral tissues. We tested the hypothesis that the fetal SCN clock is sensitive to changes in GC levels. Maternal GCs must pass through the placenta to reach the fetal SCN. We show that the maternal but not the fetal part of the placenta harbors the autonomous circadian clock, which is reset by dexamethasone (DEX) and rhythmically expresses Hsd11b2. The results suggest the presence of a mechanism for rhythmic GC passage through the placental barrier, which is adjusted according to actual GC levels. GC receptors are expressed rhythmically in the laser-dissected fetal SCN samples. We demonstrate that hypothalamic explants containing the SCN of the mPer2 Luc mouse prepared at embryonic day (E)15 spontaneously develop rhythmicity within several days of culture, with dynamics varying among fetuses from the same litter. Culturing these explants in media enriched with DEX accelerates the development. At E17, treatment of the explants with DEX induces phase advances and phase delays of the rhythms depending on the timing of treatments, and the shifts are completely blocked by the GC receptor antagonist, mifepristone. The DEX-induced phase-response curve differs from that induced by the vehicle. The fetal SCN is sensitive to GCs in vivo because DEX administration to pregnant rats acutely downregulates c-fos expression specifically in the laser-dissected fetal SCN. Our results provide evidence that the rodent fetal SCN clock may respond to changes in GC levels.

The McGill Transgenic Rat Model of Alzheimer's Disease Displays Cognitive and Motor Impairments, Changes in Anxiety and Social Behavior, and Altered Circadian Activity.

The McGill-R-Thy1-APP transgenic rat is an animal model of the familial form of Alzheimer's disease (AD). This model mirrors several neuropathological hallmarks of the disease, including the accumulation of beta-amyloid and the formation of amyloid plaques (in homozygous animals only), neuroinflammation and the gradual deterioration of cognitive functions even prior to plaque formation, although it lacks the tauopathy observed in human victims of AD. The goal of the present study was a thorough characterization of the homozygous model with emphasis on its face validity in several domains of behavior known to be affected in AD patients, including cognitive functions, motor coordination, emotionality, sociability, and circadian activity patterns. On the behavioral level, we found normal locomotor activity in spontaneous exploration, but problems with balance and gait coordination, increased anxiety and severely impaired spatial cognition in 4-7 month old homozygous animals. The profile of social behavior and ultrasonic communication was altered in the McGill rats, without a general social withdrawal. McGill rats also exhibited changes in circadian profile, with a shorter free-running period and increased total activity during the subjective night, without signs of sleep disturbances during the inactive phase. Expression of circadian clock gene Bmal1 was found to be increased in the parietal cortex and cerebellum, while Nr1d1 expression was not changed. The clock-controlled gene Prok2 expression was found to be elevated in the parietal cortex and hippocampus, which might have contributed to the observed changes in circadian phenotype. We conclude that the phenotype in the McGill rat model is not restricted to the cognitive domain, but also includes gait problems, changes in emotionality, social behavior, and circadian profiles. Our findings show that the model should be useful for the development of new therapeutic approaches targeting not only memory decline but also other symptoms decreasing the quality of life of AD patients.

Alteration in glucose homeostasis and persistence of the pancreatic clock in aged mPer2Luc mice.

The physiological function of the pancreas is controlled by the circadian clock. The aim of this study was to determine whether aging-induced changes in glucose homeostasis affect properties of the circadian clock in the pancreas and/or its sensitivity to disturbances in environmental lighting conditions. mPer2Luc mice aged 24-26 months developed hyperinsulinemic hypoglycaemia, which was likely due to the Pclo-mediated insulin hyper-secretion and Slc2a2-mediated glucose transport impairment in the pancreas, and due to the alterations in Pp1r3c-related glycogen storage and Sgk1-related glucose transport in the liver. In the pancreatic tissue, aging affected clock gene expression only marginally, it upregulated Bmal1 and downregulated Clock expression. Whereas aging significantly impaired the circadian clock in lung explants, which were used as a control tissue, the properties of the pancreatic clock in vitro were not affected. The data suggest a non-circadian role of Bmal1 in changes of pancreatic function that occur during aging. Additionally, the pancreatic clock was more sensitive to exposure of animals to constant light conditions. These findings provide an explanation for the previously demonstrated relationship between disturbances in the circadian system and disordered glucose homeostasis, including diabetes mellitus type 2, in subjects exposed to long-term shift work.

Circadian alignment in a foster mother improves the offspring's pathological phenotype.

KEY POINTS: In mammals, the mother-offspring interaction is essential for health later in adulthood. The impact of altered timing and quality of maternal care on the offspring's circadian system was assessed using a cross-strain fostering approach. Better maternal care facilitated the development of amplitudes of Bmal1 clock gene expression in the central clock, as well as the clock-driven activity/rest rhythm, and also its entrainment to the external light/dark cycle. Worse maternal care impaired entrainment of the central clock parameters in the Wistar rat during the early developmental stages. Better maternal care remedied the dampened amplitudes of the colonic clock, as well as cardiovascular functions. The results provide compelling evidence that the circadian phenotype of a foster mother may affect the pathological symptoms of the offspring, even if they are genetically programmed. ABSTRACT: In mammals, the mother-offspring interaction is essential for health later in adulthood. Maternal care is determined by the circadian phenotype of the mother. The impact of altered timing and quality of maternal care on the circadian system was assessed using a cross-strain fostering approach, with 'abnormal' (i.e. circadian misaligned) care being represented by spontaneously hypertensive rats (SHR) and 'normal' care by Wistar rats. The SHR mothers worsened synchrony of the central clock in the suprachiasmatic nuclei with the light/dark cycle in Wistar rat pups, although this effect disappeared after weaning. The maternal care provided by Wistar rat mothers to SHR pups facilitated the development of amplitudes of the Bmal1 expression rhythm in the suprachiasmatic nuclei of the hypothalamus, as well as the clock-driven activity/rest rhythm and its entrainment to the external light/dark cycle. The peripheral clocks in the liver and colon responded robustly to cross-strain fostering; the circadian phenotype of the Wistar rat foster mother remedied the dampened amplitudes of the colonic clock in SHR pups and improved their cardiovascular functions. In general, the more intensive maternal care of the Wistar rat mothers improved most of the parameters of the abnormal SHR circadian phenotype in adulthood; conversely, the less frequent maternal care of the SHR mothers worsened these parameters in the Wistar rat during the early developmental stages. Altogether, our data provide compelling evidence that the circadian phenotype of a foster mother may positively and negatively affect the regulatory mechanisms of various physiological parameters, even if the pathological symptoms are genetically programmed.