Chronic circadian misalignment results in reduced longevity and large-scale changes in gene expression in Drosophila

How does a fly die? Insights into ageing from the pathophysiology of Drosophila mortality

The fruit fly Drosophila melanogaster is a common animal model in ageing research. Large populations of flies are used to study the impact of genetic, nutritional and pharmacological interventions on survival. However, the processes through which flies die and their relative prevalence in Drosophila populations are still comparatively unknown. Understanding the causes of death in an animal model is essential to dissect the lifespan-extending interventions that are organism- or disease-specific from those broadly applicable to ageing. Here, we review the pathophysiological processes that can lead to fly death and discuss their relation to ageing.

Circadian Control of Lipid Metabolism

To ensure optimum health and performance, lipid metabolism needs to be temporally aligned to other body processes and to daily changes in the environment. Central and peripheral circadian clocks and environmental signals such as light provide internal and external time cues to the body. Importantly, each of the key organs involved in insect lipid metabolism contains a molecular clockwork which ticks with a varying degree of autonomy from the central clock in the brain. In this chapter, we review our current knowledge about peripheral clocks in the insect fat body, gut and oenocytes, and light- and circadian-driven diel patterns in lipid metabolites and lipid-related transcripts. In addition, we highlight selected neuroendocrine signaling pathways that are or may be involved in the temporal coordination and control of lipid metabolism.

The importance of sleep regularity: a consensus statement of the National Sleep Foundation sleep timing and variability panel

OBJECTIVE

To develop and present consensus findings of the National Sleep Foundation sleep timing and variability panel regarding the impact of sleep timing variability on health and performance.

METHODS

The National Sleep Foundation assembled a panel of sleep and circadian experts to evaluate the scientific evidence and conduct a formal consensus and voting procedure. A systematic literature review was conducted using the NIH National Library of Medicine PubMed database, and panelists voted on the appropriateness of 3 questions using a modified Delphi RAND/UCLA Appropriateness Method with 2 rounds of voting.

RESULTS

The literature search and panel review identified 63 full text publications to inform consensus voting. Panelists achieved consensus on each question: (1) is daily regularity in sleep timing important for (a) health or (b) performance? and (2) when sleep is of insufficient duration during the week (or work days), is catch-up sleep on weekends (or non-work days) important for health? Based on the evidence currently available, panelists agreed to an affirmative response to all 3 questions.

CONCLUSIONS

Consistency of sleep onset and offset timing is important for health, safety, and performance. Nonetheless, when insufficient sleep is obtained during the week/work days, weekend/non-work day catch-up sleep may be beneficial.

The circadian clock is required for rhythmic lipid transport in Drosophila in interaction with diet and photic condition

Modern lifestyle is often at odds with endogenously driven rhythmicity, which can lead to circadian disruption and metabolic syndrome. One signature for circadian disruption is a reduced or altered metabolite cycling in the circulating tissue reflecting the current metabolic status. Drosophila is a well-established model in chronobiology, but day-time dependent variations of transport metabolites in the fly circulation are poorly characterized. Here, we sampled fly hemolymph throughout the day and analyzed diacylglycerols (DGs), phosphoethanolamines (PEs) and phosphocholines (PCs) using LC-MS. In wild-type flies kept on sugar-only medium under a light-dark cycle, all transport lipid species showed a synchronized bimodal oscillation pattern with maxima at the beginning and end of the light phase which were impaired in period01 clock mutants. In wild-type flies under constant dark conditions, the oscillation became monophasic with a maximum in the middle of the subjective day. In strong support of clock-driven oscillations, levels of the targeted lipids peaked once in the middle of the light phase under time-restricted feeding independent of the time of food intake. When wild-type flies were reared on full standard medium, the rhythmic alterations of hemolymph lipid levels were greatly attenuated. Our data suggest that the circadian clock aligns daily oscillations of DGs, PEs, and PCs in the hemolymph to the anabolic siesta phase, with a strong influence of light on phase and modality.

Circadian clock disruption promotes the degeneration of dopaminergic neurons in male Drosophila

Sleep and circadian rhythm disruptions are frequent comorbidities of Parkinson's disease (PD), a disorder characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra. However, the causal role of circadian clocks in the degenerative process remains uncertain. We demonstrated here that circadian clocks regulate the rhythmicity and magnitude of the vulnerability of DA neurons to oxidative stress in male Drosophila. Circadian pacemaker neurons are presynaptic to a subset of DA neurons and rhythmically modulate their susceptibility to degeneration. The arrhythmic period (per) gene null mutation exacerbates the age-dependent loss of DA neurons and, in combination with brief oxidative stress, causes premature animal death. These findings suggest that circadian clock disruption promotes dopaminergic neurodegeneration.

Light modulates Drosophila lifespan via perceptual systems independent of circadian rhythms

Across taxa, sensory perception modulates aging in response to important ecological cues, including food, sex, and danger. The range of sensory cues involved, and their mechanism of action, are largely unknown. We therefore sought to better understand how one potential cue, that of light, impacts aging in Drosophila melanogaster. In accordance with recently published data, we found that flies lived significantly longer in constant darkness. Extended lifespan was not accompanied by behavioral changes that might indirectly slow aging such as activity, feeding, or fecundity, nor were circadian rhythms necessary for the effect. The lifespans of flies lacking eyes or photoreceptor neurons were unaffected by light kept at normal housing conditions, and transgenic activation of these same neurons was sufficient to phenocopy the effects of environmental light on lifespan. The relationship between light and lifespan was not correlated with its intensity, duration, nor the frequency of light-dark transitions. Furthermore, high-intensity light reduced lifespan in eyeless flies, indicating that the effects we observed were largely independent of the known, non-specific damaging effects associated with light. Our results suggest that much like other environmental cues, light may act as a sensory stimulus to modulate aging.

Deciphering clock genes as emerging targets against aging

The old people often suffer from circadian rhythm disturbances, which in turn accelerate aging. Many aging-related degenerative diseases such as Alzheimer's disease, Parkinson's disease, and osteoarthritis have an inextricable connection with circadian rhythm. In light of the predominant effects of clock genes on regulating circadian rhythm, we systematically present the elaborate network of roles that clock genes play in aging in this review. First, we briefly introduce the basic background regarding clock genes. Second, we systemically summarize the roles of clock genes in aging and aging-related degenerative diseases. Third, we discuss the relationship between clock genes polymorphisms and aging. In summary, this review is intended to clarify the indispensable roles of clock genes in aging and sheds light on developing clock genes as anti-aging targets.

Dietary restriction and the transcription factor clock delay eye aging to extend lifespan in Drosophila Melanogaster

Many vital processes in the eye are under circadian regulation, and circadian dysfunction has emerged as a potential driver of eye aging. Dietary restriction is one of the most robust lifespan-extending therapies and amplifies circadian rhythms with age. Herein, we demonstrate that dietary restriction extends lifespan in Drosophila melanogaster by promoting circadian homeostatic processes that protect the visual system from age- and light-associated damage. Altering the positive limb core molecular clock transcription factor, CLOCK, or CLOCK-output genes, accelerates visual senescence, induces a systemic immune response, and shortens lifespan. Flies subjected to dietary restriction are protected from the lifespan-shortening effects of photoreceptor activation. Inversely, photoreceptor inactivation, achieved via mutating rhodopsin or housing flies in constant darkness, primarily extends the lifespan of flies reared on a high-nutrient diet. Our findings establish the eye as a diet-sensitive modulator of lifespan and indicates that vision is an antagonistically pleiotropic process that contributes to organismal aging.

Associations between circadian misalignment and telomere length in BD: an actigraphy study

BACKGROUND

Life expectancy is significantly decreased in bipolar disorder (BD). This is associated with accelerated cellular aging which can be estimated by telomere length (TL). However, specific determinants of shorter TL in BD are under-explored. This study examines whether circadian misalignment (i.e. mismatch between preferred and actual phase of circadian activity rhythms) is associated with shorter TL in BD.

METHODS

Euthymic individuals with BD (n = 101) undertook 21 consecutive days of actigraphy recording and completed the Composite Scale of Morningness (CSM) to assess phase preference for activities (chronotype). Polymerase chain reaction was used to measure TL in blood. Cluster analysis identified circadian aligned/misaligned subgroups as defined by preferred (CSM score) and actual phases of activity (actigraphically determined onset of active and inactive periods). We tested for any associations between TL and clusters, with adjustments for between-cluster differences in socio-demographic and illness factors.

RESULTS

We identified three clusters: an "Aligned Morning" cluster (n = 31) with preferred and actual timing of activity in the morning, an "Aligned Evening" cluster (n = 37) with preferred and actual timing of activity in the evening and a "Misaligned" cluster (n = 32) with an evening chronotype, but an earlier objective onset of active periods. After adjustment for confounders, we found that TL was significantly associated with circadian misalignment and older age.

CONCLUSIONS

Circadian misalignment may partly explain shorter TL in BD and could contribute to accelerated aging in these individuals.

First transcriptome profiling of D. melanogaster after development in a deep underground low radiation background laboratory

Natural background radiation is a permanent multicomponent factor. It has an influence on biological organisms, but effects of its deprivation still remain unclear. The aim of our work was to study for the first time responses of D. melanogaster to conditions of the Deep Underground Low-Background Laboratory DULB-4900 (BNO, INR, RAS, Russia) at the transcriptome level by RNA-seq profiling. Overall 77 transcripts demonstrated differential abundance between flies exposed to low and natural background radiation. Enriched biological process functional categories were established for all genes with differential expression. The results showed down-regulation of primary metabolic processes and up-regulation of both the immune system process and the response to stimuli. The comparative analysis of our data and publicly available transcriptome data on D. melanogaster exposed to low and high doses of ionizing radiation did not reveal common DEGs in them. We hypothesize that the observed changes in gene expression can be explained by the influence of the underground conditions in DULB-4900, in particular, by the lack of stimuli. Thus, our study challenges the validity of the LNT model for the region of background radiation doses below a certain level (~16.4 nGy h-1) and the presence of a dose threshold for D. melanogaster.

Constant Light and Frequent Schedule Changes Do Not Impact Resistance to Parasites in Monarch Butterflies

Organisms have evolved internal biological clocks to regulate their activities based on external environmental cues, such as light, temperature, and food. Environmental disruption of these rhythms, such as caused by constant light or frequent light schedule changes, has been shown to impair development, reduce survival, and increase infection susceptibility and disease progression in numerous organisms. However, the precise role of the biological clock in host-parasite interactions is understudied and has focused on unnatural host-parasite combinations in lab-adapted inbred models. Here, we use the natural interaction between monarch butterflies (Danaus plexippus) and their virulent protozoan parasite, Ophryocystis elektroscirrha, to investigate the effects of constant light and frequent light schedule changes on development, survival, and parasite susceptibility. We show that constant light exposure slows the monarchs' rate of development but does not increase susceptibility to parasitic infection. Furthermore, frequent schedule changes decrease parasite growth, but have no effect on egg-to-adult survival of infected monarchs. Interestingly, these conditions are usually disruptive to the biological clock, but do not significantly impact the clock of monarch larvae. These unexpected findings show that constant light and frequent schedule changes can uncouple host and parasite performance and highlight how natural relationships are needed to expand our understanding of clocks in host-parasite interactions.

Aging with rhythmicity. Is it possible? Physical exercise as a pacemaker

Aging is associated with gradual decline in numerous physiological processes, including a reduction in metabolic functions and immunological system. The circadian rhythm plays a vital role in health, and prolonged clock disruptions are associated with chronic diseases. The relationships between clock genes, aging, and immunosenescence are not well understood. Inflammation is an immune response triggered in living organisms in response to the danger associated with pathogens and injury. The term 'inflammaging' has been used to describe the chronic low-grade-inflammation that develops with advancing age and predicts susceptibility to age-related pathologies. Equilibrium between pro-and anti-inflammatory cytokines is needed for healthy aging and longevity. Sedentary and poor nutrition style life indices a disruption in circadian rhythm promoting an increase in pro-inflammatory factors or leads for chronic low-grade inflammation. Moreover, signals mediated by pro-inflammatory cytokines, such as tumor necrosis factor-alpha and interleukin-6, might accentuate of the muscle loss during aging. Circadian clock is important to maintain the physiological functions, as maintenance of immune system. A strategy for imposes rhythmicity in the physiological systems may be adopted of exercise training routine. The lifelong regular practice of physical exercise decelerates the processes of aging, providing better quality and prolongation of life. Thus, in this review, we will focus on how aging affects circadian rhythms and its relationship to inflammatory processes (inflammaging), as well as the role of physical exercise as a regulator of the circadian rhythm, promoting aging with rhythmicity.

Resetting the Aging Clock: Implications for Managing Age-Related Diseases

Worldwide, individuals are living longer due to medical and scientific advances, increased availability of medical care and changes in public health policies. Consequently, increasing attention has been focused on managing chronic conditions and age-related diseases to ensure healthy aging. The endogenous circadian system regulates molecular, physiological and behavioral rhythms orchestrating functional coordination and processes across tissues and organs. Circadian disruption or desynchronization of circadian oscillators increases disease risk and appears to accelerate aging. Reciprocally, aging weakens circadian function aggravating age-related diseases and pathologies. In this review, we summarize the molecular composition and structural organization of the circadian system in mammals and humans, and evaluate the technological and societal factors contributing to the increasing incidence of circadian disorders. Furthermore, we discuss the adverse effects of circadian dysfunction on aging and longevity and the bidirectional interactions through which aging affects circadian function using examples from mammalian research models and humans. Additionally, we review promising methods for managing healthy aging through behavioral and pharmacological reinforcement of the circadian system. Understanding age-related changes in the circadian clock and minimizing circadian dysfunction may be crucial components to promote healthy aging.

Transcription-based circadian mechanism controls the duration of molecular clock states in response to signaling inputs

The molecular oscillator of the mammalian circadian clock consists in a dynamical network of genes and proteins whose main regulatory mechanisms occur at the transcriptional level. From a dynamical point of view, the mechanisms leading to an oscillatory solution with an orderly protein peak expression and a clear day/night phase distinction remain unclear. Our goal is to identify the essential interactions needed to generate phase opposition between the activating CLOCK:BMAL1 and the repressing PER:CRY complexes and to better distinguish these two main clock molecular phases relating to rest/activity and fast/feeding cycles. To do this, we develop a transcription-based mathematical model centered on linear combinations of the clock controlled elements (CCEs): E-box, R-box and D-box. Each CCE is responsive to activators and repressors. After model calibration with single-cell data, we explore entrainment and period tuning via interplay with metabolism. Variation of the PER degradation rate γ_p, relating to the tau mutation, results in asymmetric changes in the duration of the different clock molecular phases. Time spent at the state of high PER/PER:CRY decreases with γ_p, while time spent at the state of high BMAL1 and CRY1, both proteins with activity in promoting insulin sensitivity, remains constant. This result suggests a possible mechanism behind the altered metabolism of tau mutation animals. Furthermore, we expose the clock system to two regulatory inputs, one relating to the fast/feeding cycle and the other to the light-dependent synchronization signaling. We observe the phase difference between these signals to also affect the relative duration of molecular clock states. Simulated circadian misalignment, known to correlate with insulin resistance, leads to decreased duration of BMAL1 expression. Our results reveal a possible mechanism for clock-controlled metabolic homeostasis, whereby the circadian clock controls the relative duration of different molecular (and metabolic) states in response to signaling inputs.

Evidence for Internal Desynchrony Caused by Circadian Clock Resetting

Circadian disruption has been linked to markers for poor health outcomes in humans and animal models. What is it about circadian disruption that is problematic? One hypothesis is that phase resetting of the circadian system, which occurs in response to changes in environmental timing cues, leads to internal desynchrony within the organism. Internal desynchrony is understood as acute changes in phase relationships between biological rhythms from different cell groups, tissues, or organs within the body. Do we have strong evidence for internal desynchrony associated with or caused by circadian clock resetting? Here we review the literature, highlighting several key studies from measures of gene expression in laboratory rodents. We conclude that current evidence offers strong support for the premise that some protocols for light-induced resetting are associated with internal desynchrony. It is important to continue research to test whether internal desynchrony is necessary and/or sufficient for negative health impact of circadian disruption.