Dim light at night disrupts molecular circadian rhythms and increases body weight

Microglia, circadian rhythm and lifestyle factors

Microglia, a vital homeostasis-keeper of the central nervous system, perform critical functions such as synaptic pruning, clearance of cellular debris, and participation in neuroinflammatory processes. Recent research has shown that microglia exhibit strong circadian rhythms that not only actively regulate their own immune activity, but also affect neuronal function. Disruptions of the circadian clock have been linked to a higher risk of developing a variety of diseases. In this article we will provide an overview of how lifestyle factors impact microglial function, with a focus on disruptions caused by irregular sleep-wake patterns, reduced physical activity, and eating at the wrong time-of-day. We will also discuss the potential connection between these lifestyle factors, disrupted circadian rhythms, and the role of microglia in keeping brain health. This article is part of the Special Issue on "Microglia".

Short-term exposure to indoor artificial light at night during sleep impairs cardiac autonomic function of young healthy adults in China

The artificial light at night (ALAN) exposure has emerged as a significant environmental and public health concern globally. However, there is far less evidence on the health effects of indoor ALAN than on outdoor ALAN. Moreover, evidence on cardiovascular effects of indoor ALAN is more limited. To evaluate the association between short-term exposure to ALAN during sleep with heart rate variability (HRV) in young healthy adults, as well as the mediating role of blood oxygen saturation (SpO2), and to further explore the intervention effects of shading habits, this prospective repeated measurement study was conducted among 81 adults with 150 nights (1324h) of HRV monitoring. HRV and SpO2 were monitored during sleep, concurrently with the measurement of indoor and outdoor ALAN. Shading habits were defined as whether to wear blindfolds or draw bed curtains during sleep, and were collected by questionnaires. Linear mixed-effect model was conducted to assess the association between ALAN exposure and HRV indices. The role of SpO2 in the association was analyzed using mediation analyses. We found that indoor ALAN exposure reduced parasympathetic activity and imbalanced cardiac autonomic function. We also found that the use of outdoor ALAN may underestimate or misestimate the potential health effects of ALAN. A significant mediation effects were observed on standard deviation of normal-to-normal intervals (SDNN; p-value for ACME = 0.014) and the ratio of low frequency power to high frequency power (LF/HF; p-value for ACME = 0.026) through minimum SpO2 after indoor ALAN exposure. The association between indoor ALAN and HRV was more pronounced among participants without shading habits during sleep. This study provides general population-based evidence that short-term exposure to indoor ALAN was significantly associated with impaired HRV, and SpO2 partially mediated the association. Improve shading habits during sleep may mitigate the adverse effects of indoor ALAN.

Exposure to light at night (LAN) and risk of overweight/obesity, hypertension, and diabetes: a systematic review and meta-analysis

Current studies have presented conflicting findings regarding the associations between light at night (LAN) exposure and the risk of overweight/obesity, hypertension, and diabetes. Our study systematically summarized the evidence of the association between LAN exposure and the risk of overweight/obesity, hypertension, and diabetes. We searched five databases (PubMed, Web of Science, Embase, Scopus, and Cochrane) for observational studies published up to 1 August 2023. The pooled odds ratio (ORs) and 95% confidence intervals (CIs) were estimated by random-effects models for the association. Eighteen studies were included in the meta-analysis. Compared with the group with the lowest level of LAN, the group with the highest level of LAN is associated with an increased risk of overweight/obesity (pooled OR = 1.19, 95%CI: 1.13-1.26), hypertension (pooled OR: 1.86, 95% CI:1.28-2.72), and diabetes (pooled OR = 1.21, 95%CI: 1.07-1.31). Our meta-analysis demonstrated LAN exposure is associated with increased risk of overweight/obesity, hypertension, and diabetes.

Dim light at night shifts microglia to a pro-inflammatory state after cerebral ischemia, altering stroke outcome in mice

Circadian rhythms are endogenous biological cycles that regulate physiology and behavior and are set to precisely 24-h by light exposure. Light at night (LAN) dysregulates physiology and function including immune response; a critical component that contributes to stroke pathophysiological progression of neuronal injury and may impair recovery from injury. The goal of this study is to explore the effects of dim LAN (dLAN) in a murine model of ischemic stroke to assess how nighttime lighting from hospital settings can affect stroke outcome. Further, this study sought to identify mechanisms underlying pathophysiological changes to immune response after circadian disruption. Male and female adult Swiss Webster (CFW) mice were subjected to transient or permanent focal cerebral ischemia, then were subsequently placed into either dark night conditions (LD) or one night of dLAN (5 lx). 24 h post-stroke, sensorimotor impairments and infarct sizes were quantified. A single night of dLAN following MCAO increased infarct size and sensorimotor deficits across both sexes and reduced survival in males after 24 h. Flow cytometry was performed to assess microglial phenotypes after MCAO, and revealed that dLAN altered the percentage of microglia that express pro-inflammatory markers (MHC II+ and IL-6) and microglia that express CD206 and IL-10 that likely contributed to poor ischemic outcomes. Following these results, microglia were reduced in the brain using Plexxikon 5622 (PLX 5622) a CSFR1 inhibitor, then the mice received an MCAO and were exposed to LD or dLAN conditions for 24 h. Microglial depletion by PLX5622 resulted in infarct sizes that were comparable between lighting conditions. This study provides supporting evidence that environmental lighting exacerbates ischemic injury and post-stroke mortality by a biological mechanism that exposure to dLAN causes a fundamental shift of activated microglial phenotypes from beneficial to detrimental at an early time point after stroke, resulting in irreversible neuronal death.

Artificial light at night affects the daily profile of pulse pressure and protein expression in the thoracic aorta of rats

Artificial light at night (ALAN) disrupts 24-h variability of blood pressure, but the molecular mechanisms underlying these effects are unknown. Therefore, we analysed the daily variability of pulse pressure, the maximum value of acceleration rate of aortic pressure (dP/dt(max)) measured by telemetry and protein expression in the thoracic aorta of normotensive male rats exposed to ALAN (1-2 lx) for 3 weeks. Daily, 24-h variability of pulse pressure and dP/dt(max) was observed during a regular light/dark regimen with higher values during the dark compared to the light phase of the day. ALAN suppressed 24-h variability and enhanced ultradian (<12-h) periods of pulse pressure and dP/dt(max) in duration-dependent manners. From beat-to-beat blood pressure variability, ALAN decreased low-frequency bands (a sympathetic marker) and had minimal effects on high-frequency bands. At the molecular level, ALAN decreased angiotensin II receptor type 1 expression and reduced 24-h variability. ALAN caused the appearance of 12-h oscillations in transforming growth factor β1 and fibulin 4. Expression of sarco/endoplasmic reticulum Ca2+-ATPase type 2 was increased in the middle of the light and dark phase of the day, and ALAN did not affect its daily and 12-h variability. In conclusion, ALAN suppressed 24-h variability of pulse pressure and dP/dt(max), decreased the power of low-frequency bands and differentially affected the expression of specific proteins in the rat thoracic aorta. Suppressed 24-h oscillations by ALAN underline the pulsatility of individual endocrine axes with different periods, disrupting the cardiovascular control of central blood pressure.

Effects of chronic light cycle disruption during adolescence on circadian clock, neuronal activity rhythms, and behavior in mice

The advent of artificial lighting, particularly during the evening and night, has significantly altered the predictable daily light and dark cycles in recent times. Altered light environments disrupt the biological clock and negatively impact mood and cognition. Although adolescents commonly experience chronic changes in light/dark cycles, our understanding of how the adolescents' brain adapts to altered light environments remains limited. Here, we investigated the impact of chronic light cycle disruption (LCD) during adolescence, exposing adolescent mice to 19 h of light and 5 h of darkness for 5 days and 12 L:12D for 2 days per week (LCD group) for 4 weeks. We showed that LCD exposure did not affect circadian locomotor activity but impaired memory and increased avoidance response in adolescent mice. Clock gene expression and neuronal activity rhythms analysis revealed that LCD disrupted local molecular clock and neuronal activity in the dentate gyrus (DG) and in the medial amygdala (MeA) but not in the circadian pacemaker (SCN). In addition, we characterized the photoresponsiveness of the MeA and showed that somatostatin neurons are affected by acute and chronic aberrant light exposure during adolescence. Our research provides new evidence highlighting the potential consequences of altered light environments during pubertal development on neuronal physiology and behaviors.

Exploring the metabolic implications of blue light exposure during daytime in rats

Excessive exposure to light is a global issue. Artificial light pollution has been shown to disrupt the body's natural circadian rhythm. To investigate the impacts of light on metabolism, we studied Sprague-Dawley rats chronically exposed to red or blue light during daytime or nighttime. Rats in the experimental group were exposed to extended light for 4 hours during daytime or nighttime to simulate the effects of excessive light usage. Strikingly, we found systemic metabolic alterations only induced by blue light during daytime. Furthermore, we conducted metabolomic analyses of the cerebrospinal fluid, serum, heart, liver, spleen, adrenal, cerebellum, pituitary, prostate, spermatophore, hypothalamus and kidney from rats in the control and blue light exposure during daytime. Significant changes in metabolites have been observed in cerebrospinal fluid, serum, hypothalamus and kidney of rats exposed to blue light during daytime. Metabolic alterations observed in rats encompassing pyruvate metabolism, glutathione metabolism homocysteine degradation, phosphatidylethanolamine biosynthesis, and phospholipid biosynthesis, exhibit analogous patterns to those inherent in specific physiological processes, notably neurodevelopment, cellular injury, oxidative stress, and autophagic pathways. Our study provides insights into tissue-specific metabolic changes in rats exposed to blue light during the daytime and may help explain potential mechanisms of photopathogenesis.

Lights at night mediate depression-like behavioral and molecular phenotypes in a glucocorticoid-dependent manner in male rats

Nocturnal light pollution, an underappreciated mood manipulator, disturbs the circadian rhythms of individuals in modern society. Preclinical and clinical studies have suggested that exposure to lights at night (LANs) results in depression-like phenotypes. However, the mechanism underlying the action of LANs remains unclear. Therefore, this study explored the potential influence of LANs on depression-related brain regions by testing brain-derived neurotrophic factor (BDNF), synaptic transmission, and plasticity in male Sprague-Dawley rats. Depression-related behavioral tests, enzyme-linked immunosorbent assays, and intracellular and extracellular electrophysiological recordings were performed. Resultantly, rats exposed to either white or blue LAN for 5 or 21 days exhibited depression-like behaviors. Both white and blue LANs reduced BDNF expression in the medial prefrontal cortex (mPFC) and ventrolateral periaqueductal gray (vlPAG). Moreover, both lights at night (LANs) elevated the plasma corticosterone levels. Pharmacologically, the activation of glucocorticoid receptors mimics the LAN-mediated effects on depression-like behaviors and reduces BDNF levels, whereas the inhibition of glucocorticoid receptors blocks LAN-mediated behavioral and molecular actions. Electrophysiologically, both LANs attenuated the stimulation-response curve, increased the paired-pulse ratio, and decreased the frequency and amplitude of miniature excitatory postsynaptic currents in the vlPAG. In the mPFC, LANs attenuate long-term potentiation and long-term depression. Collectively, these results suggested that white and blue LANs disturbed BDNF expression, synaptic transmission, and plasticity in the vlPAG and mPFC in a glucocorticoid-dependent manner. The results of the present study provide a theoretical basis for understanding the effects of nocturnal light exposure on depression-like phenotypes.

Melatonin restores hepatic lipid metabolic homeostasis disrupted by blue light at night in high-fat diet-fed mice

Artificial light at night (ALAN) is an emerging environmental pollutant that threatens public health. Recently, ALAN has been identified as a risk factor for obesity; however, the role of ALAN and its light wavelength in hepatic lipid metabolic homeostasis remains undetermined. We showed that chronic dim (~5 lx) ALAN (dLAN) exposure significantly promoted hepatic lipid accumulation in obese or diabetic mice, with the most severe effect of blue light and little effect of green or red light. These metabolic phenotypes were attributed to blue rather than green or red dLAN interfering with hepatic lipid metabolism, especially lipogenesis and lipolysis. Further studies found that blue dLAN disrupted hepatic lipogenesis and lipolysis processes by inhibiting hepatic REV-ERBs. Mechanistically, feeding behavior mediated the regulation of dLAN on hepatic REV-ERBs. In addition, different effects of light wavelengths at night on liver REV-ERBs depended on the activation of the corticosterone (CORT)/glucocorticoid receptor (GR) axis. Blue dLAN could activate the CORT/GR axis significantly while other wavelengths could not. Notably, we demonstrated that exogenous melatonin could effectively inhibit hepatic lipid accumulation and restore the hepatic GR/REV-ERBs axis disrupted by blue dLAN. These findings demonstrate that dLAN promotes hepatic lipid accumulation in mice via a short-wavelength-dependent manner, and exogenous melatonin is a potential therapeutic approach. This study strengthens the relationship between ALAN and hepatic lipid metabolism and provides insights into directing ambient light.

Effects of dim light at night in C57BL/6 J mice on recovery after spinal cord injury

Spinal cord injury (SCI) can cause long-lasting locomotor deficits, pain, and mood disorders. Anatomical and functional outcomes are exacerbated by inflammation after SCI, which causes secondary damage. One promising target after SCI is manipulating the circadian system, which optimizes biology and behavior for time of day - including neuroimmune responses and mood-related behaviors. Circadian disruption after SCI is likely worsened by a disruptive hospital environment, which typically includes dim light-at-night (dLAN). Here, we hypothesized that mice subjected to SCI, then placed in dLAN, would exhibit worsened locomotor deficits, pain-like behavior, and anxiety-depressive-like symptoms compared to mice maintained in light days with dark nights (LD). C57BL/6 J mice received sham surgery or moderate T9 contusion SCI, then were placed permanently in LD or dLAN. dLAN after SCI did not worsen locomotor deficits; rather, SCI-dLAN mice showed slight improvement in open-field locomotion at the final timepoint. Although dLAN did not alter SCI-induced heat hyperalgesia, SCI-dLAN mice exhibited an increase in mechanical allodynia at 13 days post-SCI compared to SCI-LD mice. SCI-LD and SCI-dLAN mice had similar outcomes using sucrose preference (depressive-like) and open-field (anxiety-like) tests. At 21 dpo, SCI-dLAN mice had reduced preference for a novel juvenile compared to SCI-LD, implying that dLAN combined with SCI may worsen this mood-related behavior. Finally, lesion size was similar between SCI-LD and SCI-dLAN mice. Therefore, newly placing C57BL/6 J mice in dLAN after SCI had modest effects on locomotor, pain-like, and mood-related behaviors. Future studies should consider whether clinically-relevant circadian disruptors, alone or in combination, could be ameliorated to enhance outcomes after SCI.

Artificial light at night suppresses the day-night cardiovascular variability: evidence from humans and rats

Artificial light at night (ALAN) affects most of the population. Through the retinohypothalamic tract, ALAN modulates the activity of the central circadian oscillator and, consequently, various physiological systems, including the cardiovascular one. We summarised the current knowledge about the effects of ALAN on the cardiovascular system in diurnal and nocturnal animals. Based on published data, ALAN reduces the day-night variability of the blood pressure and heart rate in diurnal and nocturnal animals by increasing the nocturnal values of cardiovascular variables in diurnal animals and decreasing them in nocturnal animals. The effects of ALAN on the cardiovascular system are mainly transmitted through the autonomic nervous system. ALAN is also considered a stress-inducing factor, as glucocorticoid and glucose level changes indicate. Moreover, in nocturnal rats, ALAN increases the pressure response to load. In addition, ALAN induces molecular changes in the heart and blood vessels. Changes in the cardiovascular system significantly depend on the duration of ALAN exposure. To some extent, alterations in physical activity can explain the changes observed in the cardiovascular system after ALAN exposure. Although ALAN acts differently on nocturnal and diurnal animals, we can conclude that both exhibit a weakened circadian coordination among physiological systems, which increases the risk of future cardiovascular complications and reduces the ability to anticipate stress.

Light: An Extrinsic Factor Influencing Animal-based Research

Light is an environmental factor that is extrinsic to animals themselves and that exerts a profound influence on the regulation of circadian, neurohormonal, metabolic, and neurobehavioral systems of all animals, including research animals. These widespread biologic effects of light are mediated by distinct photoreceptors-rods and cones that comprise the conventional visual system and melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) of the nonvisual system that interact with the rods and cones. The rods and cones of the visual system, along with the ipRGCs of the nonvisual system, are species distinct in terms of opsins and opsin concentrations and interact with one another to provide vision and regulate circadian rhythms of neurohormonal and neurobehavioral responses to light. Here, we review a brief history of lighting technologies, the nature of light and circadian rhythms, our present understanding of mammalian photoreception, and current industry practices and standards. We also consider the implications of light for vivarium measurement, production, and technological application and provide simple recommendations on artificial lighting for use by regulatory authorities, lighting manufacturers, designers, engineers, researchers, and research animal care staff that ensure best practices for optimizing animal health and well-being and, ultimately, improving scientific outcomes.

What happens when the lights are left on? Transcriptomic and phenotypic habituation to light pollution

Artificial light at night (ALAN) is a ubiquitous pollutant worldwide. Exposure can induce immediate behavioral and physiological changes in animals, sometimes leading to severe health consequences. Nevertheless, many organisms persist in light-polluted environments and may have mechanisms of habituating, reducing responses to repeated exposure over time, but this has yet to be tested experimentally. Here, we tested whether zebra finches (Taeniopygia guttata) can habituate to dim (0.3 lux) ALAN, measuring behavior, physiology (oxidative stress and telomere attrition), and gene expression in a repeated measures design, over 6 months. We present evidence of tolerance to chronic exposure, persistent behavioral responses lasting 8 weeks post-exposure, and attenuation of responses to re-exposure. Oxidative stress decreased under chronic ALAN. Changes in the blood transcriptome revealed unique responses to past exposure and re-exposure. Results demonstrate organismal resilience to chronic stressors and shed light on the capacity of birds to persist in an increasingly light-polluted world.

Association between outdoor light at night and hypertension and high-normal blood pressure: A nationwide cross-sectional study among Chinese adults

The authors aimed to investigate the association between outdoor light at night (LAN) intensity and blood pressure. The study included 13 507 participants aged 45 and above from the 2011-2012 China Health and Retirement Longitudinal Study baseline survey. Blood pressure measurements were obtained by averaging the last two readings recorded (three measurements with an interval of 45-60 s between each measurement) during the survey. Outdoor LAN intensity was assessed using Defense Meteorological Satellite Program data. The study categorized participants based on quartiles of outdoor LAN intensity and employed statistical methods like linear regression, restricted cubic splines, and logistic models to analyze the connections. After adjusting for potential confounding factors, higher levels of outdoor LAN intensity were associated with increase in systolic blood pressure (0.592 mmHg/interquartile range [IQR], 95% confidence interval [CI]: 0.027,1.157), diastolic blood pressure (0.853 mmHg/IQR, 95% CI: 0.525,1.180) and mean arterial pressure (0.766 mmHg/IQR, 95% CI: 0.385,1.147). Interestingly, the relationship between LAN intensity and odds of hypertension followed a non-linear pattern, resembling a reverse "L" shape on cubic splines. Participants with the highest quartile of outdoor LAN intensity had 1.31-fold increased odds of hypertension (95% CI: 1.08-1.58) compared to the lowest quartile. Additionally, there was an observable trend of rising odds for high-normal blood pressure with higher levels of LAN intensity in the crude model, but no statistically significant differences were observed after adjusting for confounding factors. In conclusion, this study underscores a significant connection between outdoor LAN intensity and the prevalence of hypertension.

Blue Light and Temperature Actigraphy Measures Predicting Metabolic Health Are Linked to Melatonin Receptor Polymorphism

This study explores the relationship between the light features of the Arctic spring equinox and circadian rhythms, sleep and metabolic health. Residents (N = 62) provided week-long actigraphy measures, including light exposure, which were related to body mass index (BMI), leptin and cortisol. Lower wrist temperature (wT) and higher evening blue light exposure (BLE), expressed as a novel index, the nocturnal excess index (NEIbl), were the most sensitive actigraphy measures associated with BMI. A higher BMI was linked to nocturnal BLE within distinct time windows. These associations were present specifically in carriers of the MTNR1B rs10830963 G-allele. A larger wake-after-sleep onset (WASO), smaller 24 h amplitude and earlier phase of the activity rhythm were associated with higher leptin. Higher cortisol was associated with an earlier M10 onset of BLE and with our other novel index, the Daylight Deficit Index of blue light, DDIbl. We also found sex-, age- and population-dependent differences in the parametric and non-parametric indices of BLE, wT and physical activity, while there were no differences in any sleep characteristics. Overall, this study determined sensitive actigraphy markers of light exposure and wT predictive of metabolic health and showed that these markers are linked to melatonin receptor polymorphism.

Circadian Clock Dysregulation and Prostate Cancer: A Molecular and Clinical Overview

Circadian clock dysregulation has been implicated in various types of cancer and represents an area of growing research. However, the role of the circadian clock in prostate cancer has been relatively unexplored. This literature review will highlight the potential role of circadian clock dysregulation in prostate cancer by examining molecular, epidemiologic, and clinical data. The influence of melatonin, light, night shift work, chronotherapy, and androgen independence are discussed as they relate to the existing literature on their role in prostate cancer.

Effects of Blue Light on Puberty and Ovary in Female Rats

Objective

This study was designed to examine the effect of blue light exposure and exposure time on puberty in an animal model.

Methods

Eighteen 21-day-old female Sprague Dawley rats were divided into three equal groups which were: control group (CG); blue light-6 hours (BL-6); and blue light-12 hours (BL-12). CG rats were maintained with 12/12-hour light-dark cycles. The animals in BL-6 and BL-12 were exposed to blue light of wavelength 450-470 nm and intensity of 0.03 uW/cm2 for 6 and 12 hours, respectively. Exposure to blue light continued until the first signs of puberty. Serum follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol, testosterone, dehydroepiandrosterone sulfate (DHEA-S), leptin and melatonin were measured. Subsequently the ovaries and uterus were examined histomorphologically.

Results

The median day of puberty start was 38, 32 and 30 for the CG, BL-6, and BL-12 groups, respectively (p=0.001). FSH, testosterone, DHEA-S, and leptin concentrations of all groups were similar. However, LH and estradiol concentrations in BL-6 were higher compared to CG (p=0.02). There was a negative correlation between blue light exposure, exposure time, and melatonin concentrations (r=-0.537, p=0.048). Ovarian tissue was compatible with puberty in all groups. As blue light exposure time increased, capillary dilatation and edema in the ovarian tissue increased. Prolonged exposure was associated with polycystic ovary-like (PCO) morphological changes and apoptosis in granulosa cells.

Conclusion

These results suggest that exposure to blue light and the duration of exposure induced earlier puberty in female rats. As the duration of blue light exposure increased, PCO-like inflammation, and apoptosis were detected in the ovaries.

Microglia depletion ameliorates neuroinflammation, anxiety-like behavior, and cognitive deficits in a sex-specific manner in Rev-erbα knockout mice

The circadian system is an evolutionarily adaptive system that synchronizes biological and physiological activities within the body to the 24 h oscillations on Earth. At the molecular level, circadian clock proteins are transcriptional factors that regulate the rhythmic expression of genes involved in numerous physiological processes such as sleep, cognition, mood, and immune function. Environmental and genetic disruption of the circadian clock can lead to pathology. For example, global deletion of the circadian clock gene Rev-erbα (RKO) leads to hyperlocomotion, increased anxiety-like behaviors, and cognitive impairments in male mice; however, the mechanisms underlying behavioral changes remain unclear. Here we hypothesized that RKO alters microglia function leading to neuroinflammation and altered mood and cognition, and that microglia depletion can resolve neuroinflammation and restore behavior. We show that microglia depletion (CSF1R inhibitor, PLX5622) in 8-month-old RKO mice ameliorated hyperactivity, memory impairments, and anxiety/risky-like behaviors. RKO mice exhibited striking increases in expression of pro-inflammatory cytokines (e.g., IL-1β and IL-6). Surprisingly, these increases were only fully reversed by microglia depletion in the male but not female RKO hippocampus. In contrast, male RKO mice showed greater alterations in microglial morphology and phagocytic activity than females. In both sexes, microglia depletion reduced microglial branching and decreased CD68 production without altering astrogliosis. Taken together, we show that male and female RKO mice exhibit unique perturbations to the neuroimmune system, but microglia depletion is effective at rescuing aspects of behavioral changes in both sexes. These results demonstrate that microglia are involved in Rev-erbα-mediated changes in behavior and neuroinflammation.

Outdoor Light at Night and Children's Body Mass: A Cross-Sectional Analysis in the Fr1da Study

BACKGROUND

Emerging evidence supports an association between light at night (LAN) exposure with obesity or overweight in adults. However, effects of LAN exposure during childhood have yet to be further investigated.

OBJECTIVE

In this study, we aimed to determine whether LAN exposure is associated with body mass in young children.

RESEARCH DESIGN AND METHOD

We used data from the Fr1da cohort study which screened children for early-stage islet autoimmunity in Bavaria, Germany from February 2015 to March 2019. A total of 62,212 children aged <11 years with complete residential information was included in the analysis. Self-reported weight and height were used to calculate age- and sex-specific body mass index (BMI) z-scores. LAN exposure was based on remotely sensed images from Visible Infrared Imaging Radiometer Suite and assigned to the children's residencies. We used generalized additive models to estimate the associations between LAN exposure and BMI adjusting for potential confounders.

RESULTS

We observed an increase in BMI z-scores of 34.0% (95% confidence interval (CI): 25.4-42.6) per 10 nW/cm2/sr increment in LAN exposure at baseline (2015) and of 32.6% (24.3-41.0) for LAN exposure one year prior to screening, both adjusted for age and sex. Similar associations were observed after adjustment for socioeconomic status and urbanization degree.

CONCLUSION

Our findings suggest that outdoor light exposure may be a risk factor for weight gain during childhood.

The effect of voluntary exercise on light cycle stress-induced metabolic resistance

PURPOSE

Disruption of circadian genes affects metabolic homeostasis. Regular exercise programs prevent metabolic dysfunction and alter circadian gene expression In this study, we investigated whether exercise affects light stress-induced circadian rhythm derangement and metabolic resistance.

METHODS

A circadian rhythm derangement mouse model was designed by extending the light exposure by two hours (14 L/10 D) for three weeks. Nine-weekold male mice were single-caged and divided into four groups: sedentary groups with or without light stress, and voluntary wheel-trained groups with or without light stress. In addition, differentiated myotubes were cultured in the presence of dexamethasone with or without 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR). The comprehensive laboratory animal monitoring system was used to analyze the metabolic changes in mice. Moreover, reverse transcription-polymerase chain reaction (RT-PCR) was used to quantify the mRNA expression levels of circadian genes in animal and cell culture models.

RESULTS

Three weeks of light stress reduced the running distance and increased the weight of mice. In addition, VO2 consumption and heat production were increased during the night cycle under non-stress conditions but not under stress conditions. PCR analysis revealed that exercise and stress altered the expression levels of circadian genes in the hypothalamus and quadriceps muscles. mRNA expression levels of period circadian regulator 1 were downregulated in the quadriceps muscles of the stressed sedentary group compared to that in muscles of the non-stressed sedentary group. Furthermore, differentiated myotube cells cultured in the presence of dexamethasone, with or without AICAR, showed distinct oscillation patterns at various time points.

CONCLUSION

Our study demonstrates that exercise partially prevents metabolic disruption by regulating the circadian gene expression in skeletal muscles.

Optimised Stable Lighting Strengthens Circadian Clock Gene Rhythmicity in Equine Hair Follicles

Hair follicles (HF) represent a useful tissue for monitoring the circadian clock in mammals. Irregular light exposure causes circadian disruption and represents a welfare concern for stabled horses. We aimed to evaluate the impact of two stable lighting regimes on circadian clock gene rhythmicity in HF from racehorses. Two groups of five Thoroughbred racehorses in training at a commercial racehorse yard were exposed to standard incandescent light or a customized LED lighting system. The control group received light from incandescent bulbs used according to standard yard practice. The treatment group received timed, blue-enriched white LED light by day and dim red LED light at night. On weeks 0 and 20, mane hairs were collected at 4 h intervals for 24 h. Samples were stored in RNAlater at -20 °C. RNA was isolated and samples interrogated by quantitative PCR for the core clock genes: ARNTL, CRY1, PER1, PER2, NR1D2, and the clock-controlled gene DBP. Cosinor analyses revealed 24 h rhythmicity for NR1D2 and PER2 and approached significance for CRY1 (p = 0.013, p = 0.013, and p = 0.051, respectively) in week 20 in the treatment group only. No rhythmicity was detected in week 0 or in week 20 in the HF of control horses. Results suggest that lighting practices in racehorse stables may be improved to better stimulate optimum functioning of the circadian system.

Acute Circadian Disruption Due to Constant Light Promotes Caspase 1 Activation in the Mouse Hippocampus

In mammals, the circadian system controls various physiological processes to maintain metabolism, behavior, and immune function during a daily 24 h cycle. Although driven by a cell-autonomous core clock in the hypothalamus, rhythmic activities are entrained to external cues, such as environmental lighting conditions. Exposure to artificial light at night (ALAN) can cause circadian disruption and thus is linked to an increased occurrence of civilization diseases in modern society. Moreover, alterations of circadian rhythms and dysregulation of immune responses, including inflammasome activation, are common attributes of neurodegenerative diseases, including Alzheimer', Parkinson's, and Huntington's disease. Although there is evidence that the inflammasome in the hippocampus is activated by stress, the direct effect of circadian disruption on inflammasome activation remains poorly understood. In the present study, we aimed to analyze whether exposure to constant light (LL) affects inflammasome activation in the mouse hippocampus. In addition to decreased circadian power and reduced locomotor activity, we found cleaved caspase 1 significantly elevated in the hippocampus of mice exposed to LL. However, we did not find hallmarks of inflammasome priming or cleavage of pro-interleukins. These findings suggest that acute circadian disruption leads to an assembled "ready to start" inflammasome, which may turn the brain more vulnerable to additional aversive stimuli.

The role of daylight exposure on body mass in male mice

Physiology and behavior are synchronized to the external environment by endogenous circadian rhythms that are set to precisely 24 h by exposure to bright light early in the day. Exposure to artificial light outside of the typical solar day, such as during the night, may impair aspects of physiology and behavior in human and non-human animals. Both the intensity and the wavelength of light are important in mediating these effects. The present report is the result of an unplanned change in our vivarium lighting conditions, which led to the observation that dim light during the daytime affects body mass similarly to dim nighttime light exposure in male Swiss Webster mice. Mice exposed to bright days (≥125 lux) with dark nights (0 lux) gained significantly less weight than those exposed to bright days with dim light at night (5 lux) or dim days (≤60 lux) with either dark nights or dim light at night. Notably, among the mice exposed to dim daytime light, no weight gain differences were observed between dark nights and dim light at night exposure; however dim light at night exposure shifted food intake to the inactive phase as previously reported. The mechanisms mediating these effects remain unspecified, but it appears that dimly illuminated days may have similar adverse metabolic effects as exposure to artificial light at night.

Emotionally clocked out: cell-type specific regulation of mood and anxiety by the circadian clock system in the brain

Circadian rhythms are self-sustained oscillations of biological systems that allow an organism to anticipate periodic changes in the environment and optimally align feeding, sleep, wakefulness, and the physiological and biochemical processes that support them within the 24 h cycle. These rhythms are generated at a cellular level by a set of genes, known as clock genes, which code for proteins that inhibit their own transcription in a negative feedback loop and can be perturbed by stress, a risk factor for the development of mood and anxiety disorders. A role for circadian clocks in mood and anxiety has been suggested for decades on the basis of clinical observations, and the dysregulation of circadian rhythms is a prominent clinical feature of stress-related disorders. Despite our understanding of central clock structure and function, the effect of circadian dysregulation in different neuronal subtypes in the suprachiasmatic nucleus (SCN), the master pacemaker region, as well as other brain systems regulating mood, including mesolimbic and limbic circuits, is just beginning to be elucidated. In the brain, circadian clocks regulate neuronal physiological functions, including neuronal activity, synaptic plasticity, protein expression, and neurotransmitter release which in turn affect mood-related behaviors via cell-type specific mechanisms. Both animal and human studies have revealed an association between circadian misalignment and mood disorders and suggest that internal temporal desynchrony might be part of the etiology of psychiatric disorders. To date, little work has been conducted associating mood-related phenotypes to cell-specific effects of the circadian clock disruptions. In this review, we discuss existing literature on how clock-driven changes in specific neuronal cell types might disrupt phase relationships among cellular communication, leading to neuronal circuit dysfunction and changes in mood-related behavior. In addition, we examine cell-type specific circuitry underlying mood dysfunction and discuss how this circuitry could affect circadian clock. We provide a focus for future research in this area and a perspective on chronotherapies for mood and anxiety disorders.

Night fasting as an alternative to improve nutritional support and glycaemic control in hospitalised patients with exclusive enteral nutrition

BACKGROUND

Enteral nutrition (EN) assists in the nutritional status of hospitalised patients unable to feed orally. The aim of this study was to determine which method-continuous EN or discontinuous EN, a diet in which the infusion is discontinued for 4h during the night,-is more effective in meeting nutrient recommendations and improving glycaemic control and biochemical parameters related to protein anabolism.

METHODS

Patients were divided into two groups: discontinuous (EN administered in mL/h, 18h/day, 4-h night fasting) and continuous (EN administered in mL/h, 22h/day). All patients with EN receive the diet over a 22-h daily period, in which the diet is suspended for two hours/day for daily hospital routines such as bathing, and physiotherapy, and followed for seven days. Evaluated data: prescribed and administered volume, calories, protein, and fibre; capillary blood glucose; erythrogram; serum albumin.

RESULTS

52 patients were followed-up, with 23 (44.2%) in the discontinuous group and 29 (55.8%) in the continuous group. Compared with the continuous group, the discontinuous group received volumes closer to those prescribed, equal or higher calories, and more protein. The capillary glucose values were within the reference range in the discontinuous group, while the continuous group presented elevated values. Both groups presented hypoalbuminaemia, haemoglobin, and haematocrit below the reference values; however, in the discontinuous group, the serum albumin values improved during hospitalisation relative to the continuous.

CONCLUSIONS

The method involving discontinuation of EN for 4h was more effective in meeting nutrient recommendations compared with the continuous method. Additionally, in the discontinuous group, we observed a better control of glycaemia when compared to that of the continuous group.

Circadian regulation of mTORC1 signaling via Per2 dependent mechanism disrupts folliculogenesis and oocyte maturation in female mice

mTOR (mammalian target of Rapamycin) is an important signaling pathway involved in several crucial ovarian functions including folliculogenesis and oocyte maturation. The circadian rhythm regulates multiple physiological processes and PER2 is one of the core circadian rhythm components. mTOR is regulated by the circadian clock and in turn, the rhythmic mTOR activities strengthen the clock function. Our current study aims to investigate a possible interconnection between the circadian clock and the mTORC1 signaling pathway in folliculogenesis and oocyte maturation. Here we demonstrate that the circadian system regulates mTORC1 signaling via Per2 dependent mechanism in the mouse ovary. To investigate the effect of constant light on ovarian and oocyte morphology, animals were housed 12:12 h L:D group in standard lightening conditions and the 12:12 h L:L group in constant light for one week. Food intake and body weight changes were measured. Ovarian morphology, follicle counting, and oocyte aging were evaluated. Afterward, western blot for mTOR, p-mTOR, p70S6K, p-p70S6K, PER2, and Caspase-3 protein levels was performed. The study demonstrated that circadian rhythm disruption caused an alteration in their food intake and decrease in primordial follicle numbers and an increase in the number of atretic follicles. It caused an increase in oxidative stress and a decrease in ZP3 expression in oocytes. Decreased protein levels of mTOR, p-mTOR, p70S6K, and PER2 were shown. The results showed that the circadian clock regulates mTORC1 through PER2 dependent mechanism and that decreased mTORC1 activity can contribute to premature aging of mouse ovary. In conclusion, these results suggest that the circadian clock may control ovarian aging by regulating mTOR signaling pathway through Per2 expression.

Understanding light pollution: Recent advances on its health threats and regulations

The prevalence of artificial lights not only improves the lighting conditions for modern society, but also poses kinds of health threats to human health. Although there are regulations and standards concerning light pollution, few of them are based on the potential contribution of improper lighting to diseases. Therefore, a better understanding of the health threats induced by light pollution may promote risk assessment and better regulation of artificial lights, thereby a healthy lighting environment. This review is based on a careful collection of the latest papers from 2018 to 2022 about the health threats of light pollution, both epidemiologically and experimentally. In addition to summing up the novel associations of light pollution with obesity, mental disorders, cancer, etc., we highlight the toxicological mechanism of light pollution via circadian disruption, since light pollution directly interferes with the natural light-dark cycles, and damages the circadian photoentrainment of organisms. And by reviewing the alternations of clock genes and disturbance of melatonin homeostasis induced by artificial lights, we aim to excavate the profound impacts of light pollution based on accumulating studies, thus providing perspectives for future research and guiding relevant regulations and standards.

Light at night in older age is associated with obesity, diabetes, and hypertension

Light at night (LAN) has been associated with negative health consequences and metabolic risk factors. Little is known about the prevalence of LAN in older adults in the United States and its association with CVD risk factors. We tested the hypothesis that LAN in older age is associated with higher prevalence of individual CVD risk factors. Five hundred and fifty-two community-dwelling adults aged 63-84 years underwent an examination of CVD risk factor profiles and 7-day actigraphy recording for activity and light measures. Associations between actigraphy-measured LAN, defined as no light vs. light within the 5-hour nadir (L5), and CVD risk factors, including obesity, diabetes, hypertension, and hypercholesterolemia, were examined, after adjusting for age, sex, race, season of recording, and sleep variables. LAN exposure was associated with a higher prevalence of obesity (multivariable-adjusted odds ratio [OR] 1.82 [95% CI 1.26-2.65]), diabetes (OR 2.00 [1.19-3.43]), and hypertension (OR 1.74 [1.21-2.52]) but not with hypercholesterolemia. LAN was also associated with (1) later timing of lowest light exposure (L5-light) and lowest activity (L5-activity), (2) lower inter-daily stability and amplitude of light exposure and activity, and (3) higher wake after sleep onset. Habitual LAN in older age is associated with concurrent obesity, diabetes, and hypertension. Further research is needed to understand long-term effects of LAN on cardiometabolic risks.

Artificial Light-at-Night Exposure and Overweight and Obesity across GDP Levels among Chinese Children and Adolescents

BACKGROUND

Evidence in adults suggests that exposure to artificial light-at-night (ALAN) leads to obesity. However, little is known about whether this effect exists in children and adolescents. We aimed to investigate whether ALAN exposure was associated with overweight and obesity in school-aged children and adolescents and whether this association varied with socioeconomic status.

METHODS

Data on the height and weight of 129,500 children and adolescents aged 10-18 years from 72 cities were extracted from the 2014 Chinese National Survey on Students' Constitution and Health (CNSSCH). The ALAN area percentage and average ALAN intensity were calculated using the Visible/Infrared Imager/Radiometer Suite. The subjects were separated into three categories based on the cities' gross domestic product per capita (GDPPC). A mixed-effect logistic regression model and generalized additive model (GAM) were utilized to evaluate the association between ALAN exposure and overweight and obesity in children and adolescents stratified by municipal GDPPC.

RESULTS

Both ALAN area (OR = 1.194, 95% CI: 1.175-1.212) and ALAN intensity (OR = 1.019, 95% CI: 1.017-1.020) were positively associated with overweight and obesity in children and adolescents, and the associations remained robust after adjusting for covariates. ORs for overweight and obesity and ALAN area decreased as GDPPC level increased (first tertile: OR = 1.457, 95% CI: 1.335-1.590; second tertile: OR = 1.350, 95% CI: 1.245-1.464; third tertile: OR = 1.100, 95% CI: 1.081-1.119). Similar results were observed for ALAN intensity. In the GAM models, thresholds existed in almost all these spline trends, indicating that ALAN might have a nonlinear association with overweight and obesity.

CONCLUSIONS

ALAN contributed to the development of overweight and obesity in children and adolescents and this effect differed with GDPPC. Future longitudinal studies should confirm the causal relationship between ALAN and obesity. Moreover, reducing unnecessary exposure to artificial light at night may have beneficial implications for controlling childhood and adolescent obesity, particularly in low-income areas.

Aging, circadian disruption and neurodegeneration: Interesting interplay

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

Light modulates glucose metabolism by a retina-hypothalamus-brown adipose tissue axis

Public health studies indicate that artificial light is a high-risk factor for metabolic disorders. However, the neural mechanism underlying metabolic modulation by light remains elusive. Here, we found that light can acutely decrease glucose tolerance (GT) in mice by activation of intrinsically photosensitive retinal ganglion cells (ipRGCs) innervating the hypothalamic supraoptic nucleus (SON). Vasopressin neurons in the SON project to the paraventricular nucleus, then to the GABAergic neurons in the solitary tract nucleus, and eventually to brown adipose tissue (BAT). Light activation of this neural circuit directly blocks adaptive thermogenesis in BAT, thereby decreasing GT. In humans, light also modulates GT at the temperature where BAT is active. Thus, our work unveils a retina-SON-BAT axis that mediates the effect of light on glucose metabolism, which may explain the connection between artificial light and metabolic dysregulation, suggesting a potential prevention and treatment strategy for managing glucose metabolic disorders.

Photoperiodic Remodeling of Adiposity and Energy Metabolism in Non-Human Mammals

Energy homeostasis and metabolism in mammals are strongly influenced by seasonal changes. Variations in photoperiod patterns drive adaptations in body weight and adiposity, reflecting changes in the regulation of food intake and energy expenditure. Humans also show distinct patterns of energy balance depending on the season, being more susceptible to gaining weight during a specific time of the year. Changes in body weight are mainly reflected by the adipose tissue, which is a key metabolic tissue and is highly affected by circannual rhythms. Mostly, in summer-like (long-active) photoperiod, adipocytes adopt a rather anabolic profile, more predisposed to store energy, while food intake increases and energy expenditure is reduced. These metabolic adaptations involve molecular modifications, some of which have been studied during the last years and are summarized in this review. In addition, there is a bidirectional relation between obesity and the seasonal responses, with obesity disrupting some of the seasonal responses observed in healthy mammals, and altered seasonality being highly associated with increased risk of developing obesity. This suggests that changes in photoperiod produce important metabolic alterations in healthy organisms. Biological rhythms impact the regulation of metabolism to different extents, some of which are already known, but further research is needed to fully understand the relationship between energy balance and seasonality.

Long wavelength light reduces the negative consequences of dim light at night

Many patients with autism spectrum disorders (ASD) show disturbances in their sleep/wake cycles, and they may be particularly vulnerable to the impact of circadian disruptors. We have previously shown that a 2-weeks exposure to dim light at night (DLaN) disrupts diurnal rhythms, increases repetitive behaviors and reduces social interactions in contactin-associated protein-like 2 knock out (Cntnap2 KO) mice. The deleterious effects of DLaN may be mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing the photopigment melanopsin, which is maximally sensitive to blue light (480 nm). In this study, the usage of a light-emitting diode array enabled us to shift the spectral properties of the DLaN while keeping the intensity of the illumination at 10 lx. First, we confirmed that the short-wavelength enriched lighting produced strong acute suppression of locomotor activity (masking), robust light-induced phase shifts, and cFos expression in the suprachiasmatic nucleus in wild-type (WT) mice, while the long-wavelength enriched lighting evoked much weaker responses. Opn4DTA mice, lacking the melanopsin expressing ipRGCs, were resistant to DLaN effects. Importantly, shifting the DLaN stimulus to longer wavelengths mitigated the negative impact on the activity rhythms and 'autistic' behaviors (i.e. reciprocal social interactions, repetitive grooming) in the Cntnap2 KO as well as in WT mice. The short-, but not the long-wavelength enriched, DLaN triggered cFos expression in in the basolateral amygdala (BLA) as well as in the peri-habenula region raising that possibility that these cell populations may mediate the effects. Broadly, our findings are consistent with the recommendation that spectral properties of light at night should be considered to optimize health in neurotypical as well as vulnerable populations.

Vivarium Lighting as an Important Extrinsic Factor Influencing Animal-based Research

Light is an extrinsic factor that exerts widespread influence on the regulation of circadian, physiologic, hormonal, metabolic, and behavioral systems of all animals, including those used in research. These wide-ranging biologic effects of light are mediated by distinct photoreceptors, the melanopsin-containing intrinsically photosensitive retinal ganglion cells of the nonvisual system, which interact with the rods and cones of the conventional visual system. Here, we review the nature of light and circadian rhythms, current industry practices and standards, and our present understanding of the neurophysiology of the visual and nonvisual systems. We also consider the implications of this extrinsic factor for vivarium measurement, production, and technological application of light, and provide simple recommendations on artificial lighting for use by regulatory authorities, lighting manufacturers, designers, engineers, researchers, and research animal care staff that ensure best practices for optimizing animal health and wellbeing and, ultimately, improving scientific outcomes.

Chronic exposure to dim light at night disrupts cell-mediated immune response and decreases longevity in aged female mice

Circadian rhythms are endogenous biological cycles that regulate physiology and behavior for optimal adaptive function and survival; they are synchronized to precisely 24 hours by daily light exposure. Disruption of the daily light-dark (LD) cycle by exposure to artificial light at night (ALAN) dysregulates core clock genes and biological function. Exposure to ALAN has been associated with increased health risks in humans, and elderly individuals are at elevated risk for poor outcome from disease and often experience elevated exposure to ALAN due to increased care requirements. The role of disrupted circadian rhythms in healthy, aged animals remains unspecified; thus, we hypothesized that disrupted circadian rhythms via chronic exposure to dim ALAN (dLAN) impair immune response and survival in aged mice. Twenty-month-old C57BL/6 male and female mice were exposed to 24 weeks of LD conditions or dLAN (5 lux); then, cell-mediated immune response was assessed using a delayed-type hypersensitivity test. Aged female mice exposed to dLAN displayed dysregulated hypersensitivity and inflammation as a measure of cell-mediated immune response and decreased lifespan compared to females housed in dark nights. Nighttime lighting did not affect cell-mediated immune response or lifespan in males but dysregulated body mass and increased adrenal mass after immune challenge after chronic exposure to dLAN. Together, these data indicate that chronic exposure to dLAN affects lifespan in aged females and suggest that females are more susceptible to the detrimental consequences of disrupted circadian rhythms.

Artificial Dim Light at Night during Pregnancy Can Affect Hormonal and Metabolic Rhythms in Rat Offspring

Artificial light at night (ALAN) is considered an environmental risk factor that can interfere with the circadian control of the endocrine system and metabolism. We studied the impact of ALAN during pregnancy on the hormonal and biochemical parameters in rat pups at postnatal (P) days P3, P10, and P20. Control dams (CTRL) were kept in a standard light-dark regime, and ALAN dams were exposed to dim ALAN (<2 lx) during the whole pregnancy. A plasma melatonin rhythm was found in all CTRL groups, whereas in ALAN pups, melatonin was not rhythmic at P3, and its amplitude was lowered at P10; no differences were found between groups at P20. Plasma corticosterone was rhythmic at P20 in both groups, with decreased mesor in ALAN pups. Plasma thyroid hormones exhibited an inconsistent developmental pattern, and vasopressin levels were suppressed at the beginning of the dark phase at P20 in ALAN compared to CTRL. Glucose and cholesterol showed significant daily rhythms in CTRL but not in ALAN offspring at P3. Exposure to ALAN during pregnancy disturbed the development of daily rhythms in measured hormones and metabolites, suggesting that ALAN during pregnancy can act as an endocrine disruptor that can interfere with the normal development of the progeny.

Different levels of circadian (de)synchrony -- where does it hurt?

A network of cellular timers ensures the maintenance of homeostasis by temporal modulation of physiological processes across the day. These so-called circadian clocks are synchronized to geophysical time by external time cues (or zeitgebers). In modern societies, natural environmental cycles are disrupted by artificial lighting, around-the-clock availability of food or shift work. Such contradictory zeitgeber input promotes chronodisruption, i.e., the perturbation of internal circadian rhythms, resulting in adverse health outcomes. While this phenomenon is well described, it is still poorly understood at which level of organization perturbed rhythms impact on health and wellbeing. In this review, we discuss different levels of chronodisruption and what is known about their health effects. We summarize the results of disrupted phase coherence between external and internal time vs. misalignment of tissue clocks amongst each other, i.e., internal desynchrony. Last, phase incoherence can also occur at the tissue level itself. Here, alterations in phase coordination can emerge between cellular clocks of the same tissue or between different clock genes within the single cell. A better understanding of the mechanisms of circadian misalignment and its effects on physiology will help to find effective tools to prevent or treat disorders arising from modern-day chronodisruptive environments.

Circadian Disruption and Consequences on Innate Immunity and Inflammatory Response

Circadian rhythms control almost all aspects of physiology and behavior, allowing temporal synchrony of these processes between each other, as well as with the external environment. In the immune system, daily rhythms of leukocyte functions can determine the strength of the immune response, thereby regulating the efficiency of defense mechanisms to cope with infections or tissue injury. The natural light/dark cycle is the prominent synchronizing agent perceived by the circadian clock, but this role of light is highly compromised by irregular working schedules and unintentional exposure to artificial light at night (ALAN). The primary concern is disrupted circadian control of important physiological processes, underlying potential links to adverse health effects. Here, we first discuss the immune consequences of genetic circadian disruption induced by mutation or deletion of specific clock genes. Next, we evaluate experimental research into the effects of disruptive light/dark regimes, particularly light-phase shifts, dim ALAN, and constant light on the innate immune mechanisms under steady state and acute inflammation, and in the pathogenesis of common lifestyle diseases. We suggest that a better understanding of the mechanisms by which circadian disruption influences immune status can be of importance in the search for strategies to minimize the negative consequences of chronodisruption on health.

Mood phenotypes in rodent models with circadian disturbances

Many physiological functions with approximately 24-h rhythmicity (circadian rhythms) are generated by an internal time-measuring system of the circadian clock. While sleep/wake cycles, feeding patterns, and body temperature are the most widely known physiological functions under the regulation of the circadian clock, physiological regulation by the circadian clock extends to higher brain functions. Accumulating evidence suggests strong associations between the circadian clock and mood disorders such as depression, but the underlying mechanisms of the functional relationship between them are obscure. This review overviews rodent models with disrupted circadian rhythms on depression-related responses. The animal models with circadian disturbances (by clock gene mutations and artifactual interventions) will help understand the causal link between the circadian clock and depression.

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The molecular mechanisms of the mammalian circadian rhythm are systematically overviewed.

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We overview how genetic and pharmacological manipulations of clock (related) genes are linked to mood phenotypes.

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We overview how artificial perturbations, such as SCN lesions and aberrant light, affect circadian rhythm and mood.

The role of light pollution in mammalian metabolic homeostasis and its potential interventions: A critical review

Irregular or unnatural artificial light causes severe environmental stress on the survival and health of organisms, which is rapidly becoming a widespread new type of environmental pollution. A series of disruptive behaviors to body homeostasis brought about by light pollution, including metabolic abnormalities, are likely to be the result of circadian rhythm disturbances. Recently, the proposed role of light pollution in metabolic dysregulation has accelerated it into an emerging field. Hence, the regulatory role of light pollution in mammalian metabolic homeostasis is reviewed in this contribution. Light at night is the most widely affected type of light pollution, which disrupts metabolic homeostasis largely due to its disruption of daily food intake patterns, alterations of hormone levels such as melatonin and glucocorticoids, and changes in the rhythm of inflammatory factor production. Besides, light pollution impairs mammalian metabolic processes in an intensity-, photoperiod-, and wavelength-dependent manner, and is also affected by species, gender, and diets. Nevertheless, metabolic disorders triggered by light pollution are not irreversible to some extent. Potential interventions such as melatonin supplementation, recovery to the LD cycle, time-restricted feeding, voluntary exercise, wearing blue light-shied goggles, and bright morning light therapy open a bright avenue to prevent light pollution. This work will help strengthen the relationship between light information and metabolic homeostasis and provide new insights for the better prevention of metabolic disorders and light pollution.

A broken circadian clock: The emerging neuro-immune link connecting depression to cancer

Circadian clocks orchestrate daily rhythms in many organisms and are essential for optimal health. Circadian rhythm disrupting events, such as jet-lag, shift-work, night-light exposure and clock gene alterations, give rise to pathologic conditions that include cancer and clinical depression. This review systemically describes the fundamental mechanisms of circadian clocks and the interacting relationships among a broken circadian clock, cancer and depression. We propose that this broken clock is an emerging link that connects depression and cancer development. Importantly, broken circadian clocks, cancer and depression form a vicious feedback loop that threatens systemic fitness. Arresting this harmful loop by restoring normal circadian rhythms is a potential therapeutic strategy for treating both cancer and depression.

Daytime restriction of feeding prevents illuminated night-induced impairment of metabolism and sleep in diurnal zebra finches

We investigated whether nocturnal eating was causal to the impairment of metabolism and sleep disruption in diurnal animals exposed to illuminated nights. Adult zebra finches hatched and raised in 12 h light: 12 h darkness (LD) were exposed to 5-lux dim light at night (dLAN, two groups), with a control group maintained on LD. For the next 3 weeks, the food availability to one of the dLAN groups was restricted to the 12 h light period (dLAN -F); the other dLAN (dLAN +F) and LD groups were continued on ad lib feeding. In spite of similar food intakes, dLAN +F condition led to the fat accumulation and weight gain. These birds showed concurrent changes in hepatic expression of genes associated with carbohydrate and lipid metabolism, suggesting an enhanced gluconeogenesis and impaired fatty acids synthesis. Increased sirt1 mRNA levels indicated the activation of molecular mechanisms to counter-balance the metabolic damage under dLAN +F. Furthermore, reduced bout length and total duration of the nocturnal sleep suggested a poorer sleep in dLAN +F condition. Negative sleep effects of dLAN were supported by the lower hypothalamic expression of sleep promoting sik3 and camkii genes, and higher mRNA expression of awake promoting achm3 gene in dLAN +F, compared to the LD condition. Importantly, dLAN-induced negative effects in metabolism and sleep were alleviated in the dLAN -F group. These results suggest the role of timed feeding in alleviating the negative impact of illuminated nights in metabolism and sleep in diurnal zebra finches.

Exposure to dim light at night alters daily rhythms of glucose and lipid metabolism in rats

Nocturnal light pollution has been rapidly increasing during the last decades and even though dim artificial light at night (ALAN) has been associated with metabolic diseases, its mechanism is still far from clear. Therefore, the aim of our study was to thoroughly analyze the effects of ALAN on energy metabolism, metabolites, metabolic hormones, and gene expression. Male Wistar rats were kept in either the standard light:dark (12:12) cycle or exposed to ALAN (∼2 lx) during the whole 12-h dark phase for 2 weeks. Energy metabolism was measured in metabolic cages. In addition, we measured plasma and hepatic metabolites, clock and metabolic gene expression in the liver and epididymal adipose tissue, and plasma hormone levels. In ALAN rats, we observed an unexpected transitory daytime peak of locomotor activity and a suppression of the peak in locomotor activity at the beginning of the dark period. These changes were mirrored in the respiratory exchange ratio. Plasma metabolites became arrhythmic, and plasma and hepatic cholesterol levels were increased. Lost rhythmicity of metabolites was associated with disrupted behavioral rhythms and expression of metabolic genes. In the liver, the rhythms of metabolic sensors were either phase-advanced (Ppara, Pgc1a, Nampt) or arrhythmic (Sirt1, Lxra) after ALAN. The rhythmic pattern of Ppara and Sirt1 was abolished in the adipose tissue. In the liver, the amplitude of the daily rhythm in glycogen content was attenuated, the Glut2 rhythm was phase-advanced and Foxo1 lost its daily rhythmicity. Moreover, hepatic Foxo1 and Gck were up-regulated after ALAN. Interestingly, several parameters of lipid metabolism gained rhythmicity (adiponectin, Hmgcs2, Lpl, Srebf1c) in the liver, whereas Noct became arrhythmic in the adipose tissue. Peripheral clock genes maintained their robust oscillations with small shifts in their acrophases. Our data show that even a low level of ALAN can induce changes in the daily pattern of behavior and energy metabolism, and disturb daily rhythms of genes encoding key metabolic sensors and components of metabolic pathways in the liver and adipose tissue. Disturbed metabolic rhythms by ALAN could represent a serious risk factor for the development and progression of metabolic diseases.

Associations of chronotype and sleep patterns with metabolic syndrome in the Hispanic community health study/study of Latinos

Sleep duration, sleep efficiency, and sleep timing have been shown to have potential effects on metabolic functions relevant to circadian rhythms. It is not clear if the impact of sleep patterns on metabolic risk factors is through sociocultural and environmental factors or circadian misalignment. We investigated the associations of sleep patterns, chronotype, and social jet lag with metabolic syndrome among non-shift worker Hispanic/Latino adults. We used cross-sectional data from the Sueño Ancillary Study of The Hispanic Community Health Study/Study of Latinos (HCHS/SOL). Data from a subsample of 2189 participants aged 18-64 years were used in the analysis. Mean nightly sleep duration, mean sleep onset time, mean sleep offset time, mean sleep midpoint time, sleep efficiency, sleep variability (standard deviation (SD) of sleep duration, and SD of sleep midpoint), and time spent above light exposure threshold (1000 lux) in a day were assessed by wrist actigraphy (Acti-watch Spectrum). Chronotype was determined by the reduced Morningness-Eveningness Questionnaire. Medical conditions including dyslipidemia, hypertension, and diabetes mellitus were determined from a fasting blood specimen and physical exam at the baseline visit. To determine whether sleep patterns, light levels, chronotype, and social jetlag are associated with metabolic syndrome, multivariable logistic regression models were fitted, including variables with P < .15 in the univariate analysis. The results of the multivariable analysis demonstrated that in participants older than 40 years, intermediate chronotype (vs early) was significantly associated with a higher risk of metabolic syndrome (Odds ratio (95%CI): 1.33 (1.04,1.7)), while later chronotype (vs. early) in participants younger than 40 years was significantly associated with a lower risk of metabolic syndrome (Odds ratio (95%CI): 0.37 (0.14, 0.96)). Also, higher sleep efficiency was significantly associated with decreased odds of metabolic syndrome (Odds ratio (95%CI): 0.98 (0.96, 0.99)). Nightly sleep duration was not significantly different between two groups of participants with and without metabolic syndrome in multivariable analyses. There was no significant association between social jet lag and metabolic syndrome in multivariable analysis (p = .286). Moreover, there was no significant association between chronotype and social jet lag in multivariable analysis. The association between metabolic syndrome and chronotype is age-dependent. While early chronotype is associated with metabolic syndrome in younger individuals, it tended to be associated with lower odds for metabolic syndrome in older individuals.

Sex Differences in Circadian Rhythms

Sex as a biological variable is the focus of much literature and has been emphasized by the National Institutes of Health, in part, to remedy a long history of male-dominated studies in preclinical and clinical research. We propose that time-of-day is also a crucial biological variable in biomedical research. In common with sex differences, time-of-day should be considered in analyses and reported to improve reproducibility of studies and to provide the appropriate context to the conclusions. Endogenous circadian rhythms are present in virtually all living organisms, including bacteria, plants, invertebrates, and vertebrates. Virtually all physiological and behavioral processes display daily fluctuations in optimal performance that are driven by these endogenous circadian clocks; importantly, many of those circadian rhythms also show sex differences. In this review, we describe some of the documented sex differences in circadian rhythms.

Dim Blue Light at Night Induces Spatial Memory Impairment in Mice by Hippocampal Neuroinflammation and Oxidative Stress

Light pollution is one of the most serious public problems, especially the night light. However, the effect of dim blue light at night (dLAN-BL) on cognitive function is unclear. In this study, we evaluated the effects of exposure to dLAN-BL in C57BL/6J mice for 4 consecutive weeks. Our results showed dLAN-BL significantly impaired spatial learning and memory and increased plasma corticosterone level in mice. Consistent with these changes, we observed dLAN-BL significantly increased the numbers and activation of microglia and the levels of oxidative stress product MDA in the hippocampus, decreased the levels of antioxidant enzymes Glutathione peroxidase (GSH-Px), Superoxide dismutase (SOD), Gluathione reductase (Gsr), total antioxidants (T-AOC) and the number of neurons in the hippocampus, up-regulated the mRNA expression levels of IL6, TNF-α and the protein expression levels of iNOS, COX2, TLR4, p-p65, Cleaved-Caspase3 and BAX, and down-regulated the mRNA expression levels of IL4, IL10, Psd95, Snap25, Sirt1, Dcx and the protein expression level of BCL2. In vitro results further showed corticosterone (10uM)-induced BV2 cell activation and up-regulated content of IL6, TNF-α in the cell supernatant and the protein expression levels of iNOS, COX2, p-p65 in BV2 cells. Our findings suggested dLAN-BL up-regulated plasma corticosterone level and hippocampal microglia activation, which in turn caused oxidative stress and neuroinflammation, leading to neuronal loss and synaptic dysfunction, ultimately leading to spatial learning and memory dysfunction in mice.

Prediction of suicidal ideation in shift workers compared to non-shift workers using machine learning techniques

BACKGROUND

Shift work can affect sleep and increase the risk of suicide. This study attempted to predict suicidal ideation according to shift work by using machine learning techniques.

METHODS

We analyzed a total of 43,095 data conducted by using the 10-year Korean National Health and Nutrition Examination Survey (KHANES). Shift workers and daytime workers were categorized and analyzed using random forest (RF) and decision tree (DT) techniques of machine learning techniques.

RESULTS

Shift workers were more than twice as likely to have suicidal ideation as daytime workers. The RF model showed an accuracy of 91.6% for shift workers and 98% for daytime workers. In the DT technique, the rate of suicidal ideation was the highest among shift workers (82.7%) when they were depressed and had an EuroQol-5 Dimension (EQ-5D) score of less than 0.71.

LIMITATIONS

Shift work type was evaluated questionnaire and based on screening data, it was not possible to reflect recent changes in the work type and we evaluated for only suicidal ideation for suicide risk factors.

CONCLUSION

The variables influencing the suicide risk of shift workers and daytime workers differ. In the case of shift workers, negative factors such as depression and low quality of life are risk factors for suicide. Efforts are needed to reduce risk factors through administrative and policy interventions to manage workers' health by early screening.

The Ventral Tegmental Area and Nucleus Accumbens as Circadian Oscillators: Implications for Drug Abuse and Substance Use Disorders

Circadian rhythms convergently evolved to allow for optimal synchronization of individuals’ physiological and behavioral processes with the Earth’s 24-h periodic cycling of environmental light and temperature. Whereas the suprachiasmatic nucleus (SCN) is considered the primary pacemaker of the mammalian circadian system, many extra-SCN oscillatory brain regions have been identified to not only exhibit sustainable rhythms in circadian molecular clock function, but also rhythms in overall region activity/function and mediated behaviors. In this review, we present the most recent evidence for the ventral tegmental area (VTA) and nucleus accumbens (NAc) to serve as extra-SCN oscillators and highlight studies that illustrate the functional significance of the VTA’s and NAc’s inherent circadian properties as they relate to reward-processing, drug abuse, and vulnerability to develop substance use disorders (SUDs).