Exploring the role of circadian clock gene and association with cancer pathophysiology

ABSTRACT

Most of the processes that occur in the mind and body follow natural rhythms. Those with a cycle length of about one day are called circadian rhythms. These rhythms are driven by a system of self-sustained clocks and are entrained by environmental cues such as light-dark cycles as well as food intake. In mammals, the circadian clock system is hierarchically organized such that the master clock in the suprachiasmatic nuclei of the hypothalamus integrates environmental information and synchronizes the phase of oscillators in peripheral tissues.

The circadian system is responsible for regulating a variety of physiological and behavioral processes, including feeding behavior and energy metabolism. Studies revealed that the circadian clock system consists primarily of a set of clock genes. Several genes control the biological clock, including BMAL1, CLOCK (positive regulators), CRY1, CRY2, PER1, PER2, and PER3 (negative regulators) as indicators of the peripheral clock.

Circadian has increasingly become an important area of medical research, with hundreds of studies pointing to the body’s internal clocks as a factor in both health and disease. Thousands of biochemical processes from sleep and wakefulness to DNA repair are scheduled and dictated by these internal clocks. Cancer is an example of health problems where chronotherapy can be used to improve outcomes and deliver a higher quality of care to patients.

In this article, we will discuss knowledge about molecular mechanisms of the circadian clock and the role of clocks in physiology and pathophysiology of concerns.     

Does the compromised sleep and circadian disruption of night and shiftworkers make them highly vulnerable to 2019 coronavirus disease (COVID-19)?

ABSTRACT

Rotating and permanent night shiftwork schedules typically result in acute and sometimes chronic sleep deprivation plus acute and sometimes chronic disruption of the circadian time structure. Immune system processes and functionalities are organized as circadian rhythms, and they are also strongly influenced by sleep status. Sleep is a vital behavioral state of living beings and a modulator of immune function and responsiveness. Shiftworkers show increased risk for developing viral infections due to possible compromise of both innate and acquired immunity responses. Short sleep and sleep loss, common consequences of shiftwork, are associated with altered integrity of the immune system. We discuss the possible excess risk for COVID-19 infection in the context of the common conditions among shiftworkers, including nurses, doctors, and first responders, among others of high exposure to the contagion, of sleep imbalance and circadian disruption.     

Phenotypic effects of genetic variability in human clock genes on circadian and sleep parameters

Circadian rhythms and sleep are two separate but intimately related processes. Circadian rhythms are generated through the precisely controlled, cyclic expression of a number of genes designated clock genes. Genetic variability in these genes has been associated with a number of phenotypic differences in circadian as well as sleep parameters, both in mouse models and in humans. Diurnal preferences as determined by the selfreported Horne-Östberg (HÖ) questionnaire, has been associated with polymorphisms in the human genes CLOCK, PER1, PER2 and PER3. Circadian rhythm-related sleep disorders have also been associated with mutations and polymorphisms in clock genes, with the advanced type cosegrating in an autosomal dominant inheritance pattern with mutations in the genes PER2 and CSNK1D, and the delayed type associating without discernible Mendelian inheritance with polymorphisms in CLOCK and PER3. Several mouse models of clock gene null alleles have been demonstrated to have affected sleep homeostasis. Recent findings have shown that the variable number tandem polymorphism in PER3, previously linked to diurnal preference, has profound effects on sleep homeostasis and cognitive performance following sleep loss, confirming the close association between the processes of circadian rhythms and sleep at the genetic level.     

Ultradian rhythmicity (circa 90 min) in physiologic processes ‐ evidence for multioscillatory phenomena

Abstract

Data accumulated in recent years have shown the existence of multiple about 90 min ultradian rhythms in gastric motility, urine flow and osmolality and physiologic indices of arousal. While these data support Kleitman's hypothesis that the REM‐NONREM sleep cycles are only fragments of a 24‐h rhythm (Basic Rest‐Activity Cycle) which is manifested in wakefulness in recurrent fluctuations in arousal, it further indicates that both the sleep and the waking rhythms are part of a more complex multioscillatory system with a dominant periodicity centered at 90 min.     

Expression profiles of PERIOD1, 2, and 3 in peripheral blood mononuclear cells from older subjects

AimsCircadian clocks regulate daily rhythms of behavior and physiology such as the sleep–wake cycle and hormonal secretion. Numerous characteristics of the behavioral and physiological processes change with age. In this study, we evaluated the circadian clockwork in older people by measuring daily profiles of PERIOD (PER) gene expression in peripheral blood mononuclear cells (PBMCs).Main methodsBlood samples were collected from 6 healthy older subjects (mean age 62 years) at 2-h intervals over a 24-h period under a semi-constant routine condition where masking effects are minimized. PBMCs were isolated from whole blood and temporal mRNA expression profiles of PER1, PER2, and PER3 were determined by RT-PCR. Phases of the PER rhythms, and times of sleep onset and offset were determined using data from those subjects who showed significant 24-h rhythms. The values for the parameters were compared between the older subjects and 8 young control subjects (mean age 21 years).Key findingsProminent daily rhythms of PER1, PER2, and PER3 mRNA levels, advanced sleep–wake timing and advanced phases of PER rhythms were observed in the older subjects compared to the young controls. There was no significant age-related phase difference in PER1 or PER2 rhythm with respect to sleep timing; however, PER3 expression pattern was altered in the older subjects.SignificanceThis preliminary study shows that human circadian clockwork in PBMCs remains intact at least until the presenile stage and suggests that the altered PER3 expression pattern may reflect decreased homeostatic sleep drive in older people.     

Seasonal Effect on Infants' Sleep Regulation: A Preliminary Study in a Mediterranean Climate

Infants' sleep-wake rhythms are influenced by multiple factors, including developmental and contextual aspects, as well as circadian cycles. Empirical studies that address the seasonal impact on infants' sleep are scarce. The present study examined aspects of sleep schedule and quality, comparing summer and winter months in a Mediterranean climate. This report is based on a convenience sample of 34 healthy 7-mo-olds, an age in which sleep is well consolidated and regulated compared with the first few months of life. Sleep was measured with actigraphy, in the home context. It was found that compared with winter, in the summer months, sleep onset occurred at a later hour, and more motor activity during sleep was detected. Although the overall sleep quality, as defined by sleep efficiency score, was similar in the two seasons, in the summer, more active sleep was observed. The authors discuss the finding in terms of circadian rhythms, developmental characteristics, as well as possible environmental factors and family routines, and call for more studies, in different climates and geographical zones, and in different developmental periods. (Author correspondence: cohen.dini@gmail.com or anats@edu.haifa.ac.il)     

The effect of consecutive transmeridian flights on alertness,sleep–wake cycles and sleepiness: A case study

ABSTRACT

Travel across time zones disrupts circadian rhythms causing increased daytime sleepiness, impaired alertness and sleep disturbance. However, the effect of repeated consecutive transmeridian travel on sleep–wake cycles and circadian dynamics is unknown. The aim of this study was to investigate changes in alertness, sleep–wake schedule and sleepiness and predict circadian and sleep dynamics of an individual undergoing demanding transmeridian travel. A 47-year-old healthy male flew 16 international flights over 12 consecutive days. He maintained a sleep–wake schedule based on Sydney, Australia time (GMT + 10?h). The participant completed a sleep diary and wore an Actiwatch before, during and after the flights. Subjective alertness, fatigue and sleepiness were rated 4 hourly (08:00–00:00), if awake during the flights. A validated physiologically based mathematical model of arousal dynamics was used to further explore the dynamics and compare sleep time predictions with observational data and to estimate circadian phase changes. The participant completed 191?h and 159 736?km of flying and traversed a total of 144 time-zones. Total sleep time during the flights decreased (357.5?min actigraphy; 292.4?min diary) compared to baseline (430.8?min actigraphy; 472.1?min diary), predominately due to restricted sleep opportunities. The daily range of alertness, sleepiness and fatigue increased compared to baseline, with heightened fatigue towards the end of the flight schedule. The arousal dynamics model predicted sleep/wake states during and post travel with 88% and 95% agreement with sleep diary data. The circadian phase predicted a delay of only 34?min over the 16 transmeridian flights. Despite repeated changes in transmeridian travel direction and flight duration, the participant was able to maintain a stable sleep schedule aligned with the Sydney night. Modelling revealed only minor circadian misalignment during the flying period. This was likely due to the transitory time spent in the overseas airports that did not allow for resynchronisation to the new time zone. The robustness of the arousal model in the real-world was demonstrated for the first time using unique transmeridian travel.     

FAILURE OF EXTRAOCULAR LIGHT TO FACILITATE CIRCADIAN RHYTHM REENTRAINMENT IN HUMANS

Although extraocular light can entrain the circadian rhythms of invertebrates and nonmammalian vertebrates, almost all studies show that the mammalian circadian system can only be affected by light to the eyes. The exception is a recent study by Campbell and Murphy that reported phase shifts in humans to bright light applied with fiber-optic pads behind the knees (popliteal region). We tested whether this extraocular light stimulus could accelerate the entrainment of circadian rhythms to a shift of the sleep schedule, as occurs in shift work or jet lag. In experiment 1, the sleep/dark episodes were delayed 8h from baseline for 2 days, and 3h light exposures were timed to occur before the temperature minimum to help delay circadian rhythms. There were three groups: (1) bright (about 13,000 lux) extraocular light from fiber-optic pads, (2) control (dim light, 10–20 lux), and (3) medium-intensity (about 1000 lux) ocular light from light boxes. In experiment 2, the sleep/dark episodes were inverted, and extraocular light was applied either before the temperature minimum to help delay circadian rhythms or after the temperature minimum to help advance rhythms. Circadian phase markers were the salivary dim light melatonin onset (DLMO) and the rectal temperature minimum. There was no evidence that the popliteal extraocular light had a phase-shifting effect in either experiment. Possible reasons for phase shifts in the Campbell and Murphy study and not the current study include the many differences between the protocols. In the current study, there was substantial sleep deprivation before the extraocular light was applied. There was a large shift in the sleep/dark schedule, rather than allowing subjects to sleep each day from midnight to noon, as in the Campbell and Murphy study. Also, when extraocular light was applied in the current protocol, subjects did not experience a change from sleeping to awake, a change in posture (from lying in bed to sitting in a chair), or a change in ocular light (from dark to dim light). Further research is necessary to determine the conditions under which extraocular light might produce phase shifts in human circadian rhythms. (Chronobiology International, 17(6), 807–826, 2000).     

Lithium and bipolar disorder: Impacts from molecular to behavioural circadian rhythms

Bipolar disorder (BD) is a severe and common psychiatric disorder. BD pathogenesis, clinical manifestations and relapses are associated with numerous circadian rhythm abnormalities. Lithium (Li) is the first-line treatment in BD, and its therapeutic action has been related to its ability to alter circadian rhythms. We systematically searched the PubMed database until January 2016, aiming to critically examine published studies investigating direct and indirect effects of Li on circadian rhythms. The results, from the 95 retained studies, indicated that Li: acts directly on the molecular clocks; delays the phase of sleep–wakefulness rhythms and the peak elevation of diurnal cycle body temperature; reduces the amplitude and shortens the duration of activity rhythms and lengthens free-running rhythms. Chronic Li treatment stabilizes free-running activity rhythms, by improving day-to-day rhythmicity of the activity, with effects that appear to be dose related. Pharmacogenetics demonstrate several associations of Li’s response with circadian genes (NR1D1, GSK3β, CRY1, ARNTL, TIM, PER2). Finally, Li acts on the retinal-hypothalamic pineal pathway, influencing light sensitivity and melatonin secretion. Li is a highly investigated chronobiologic agent, and although its chronobiological effects are not completely understood, it seems highly likely that they constitute an inherent component of its therapeutic action in the treatment of mood disorders.     

Loss of dexras1 Alters Nonphotic Circadian Phase Shifts and Reveals a Role for the Intergeniculate Leaflet (IGL) in Gene-Targeted Mice

Loss of Dexras1 in gene-targeted mice impairs circadian entrainment to light cycles and produces complex changes to phase-dependent resetting responses (phase shifts) to light. The authors now describe greatly enhanced and phase-specific nonphotic responses induced by arousal in dexras1^?/? mice. In constant conditions, mutant mice exhibited significant arousal-induced phase shifts throughout the subjective day. Unusual phase advances in the late subjective night were also produced when arousal has little effect in mice. Bilateral lesions of the intergeniculate leaflet (IGL) completely eliminated both the nonphotic as well as the light-induced phase shifts of circadian locomotor rhythms during the subjective day, but had no effect on nighttime phase shifts. The expression of FOS-like protein in the suprachiasmatic nucleus (SCN) was not affected by either photic or nonphotic stimulation in the subjective day in either genotype. Therefore, the loss of Dexras1 (1) enhances nonphotic phase shifts in a phase-dependent manner, and (2) demonstrates that the IGL in mice is a primary mediator of circadian phase-resetting responses to both photic and nonphotic events during the subjective day, but plays a different functional role in the subjective night. Furthermore, (3) the change in FOS level does not appear to be a critical step in the entrainment pathways for either light or arousal during the subjective day. The cumulative evidence suggests that Dexras1 regulates multiple photic and nonphotic signal-transduction pathways, thereby playing an essential role modulating species-specific characteristics of circadian entrainment. (Author correspondence: ralph@psych.utoronto.ca)     

Astronomical cycles

Abstract

Talorchestia quoyana, a sand beach amphipod, shows a rhythm of locomotor activity controlled by a circadian clock and an inhibitory circatidal clock. This article reports on an investigation of the entrainment of the circadian dock to skeleton photoperiods. Four important mathematical models for circadian rhythms are examined with respect to the results of the entrainment experiments and to predictions from the phase response curve for Talorchestia. Significant differences between the models are described, and properties of circadian rhythms not accounted for by present models are outlined.     

RETINAL CIRCADIAN RHYTHMS IN HUMANS*

Circadian rhythms in the retina may reflect intrinsic rhythms in the eye. Previous reports on circadian variability in electrophysiological human retinal measures have been scanty, and the results have been somewhat inconsistent. We studied the circadian variation of the electrooculography (EOG), electroretinography (ERG), and visual threshold (VTH) in subjects undergoing a 36h testing period. We used an ultrashort sleep-wake cycle to balance effects of sleep and light-dark across circadian cycles. Twelve healthy volunteers (10 males, 2 females; mean age 26.3 years, standard deviation [SD] 8.0 years, range 19–40 years) participated in the study. The retinal functions and oral temperature were measured every 90 min. The EOG was measured in the light, whereas the ERG and the VTH were measured in the dark. Sleep was inferred from activity detected by an Actillume monitor. The EOG peak-to-peak responses followed a circadian rhythm, with the peak occurring late in the morning (acrophase 12:22). The ERG b-wave implicit time peaked in the early morning (acrophase 06:46). No statistically significant circadian rhythms could be demonstrated in the ERG a-wave implicit time or peak-to-peak amplitude. The VTH rhythm peaked in the early morning (acrophases 07:59 for blue and 07:32 for red stimuli). All retinal rhythms showed less-consistent acrophases than the temperature and sleep rhythms. This study demonstrated several different circadian rhythms in retinal electrophysiological and psychophysical measures of healthy subjects. As the retinal rhythms had much poorer signal-to-noise ratios than the temperature rhythm, these measures cannot be recommended as circadian markers. (Chronobiology International, 18(6), 957–971, 2001)     

Human sleep‐wake cycles in the high arctic: Effects of unusual photoperiodicity in a natural setting

Abstract

Studies of human circadian rhythms are typically conducted in artificial environments that are low in ecological validity. In the current study, six subjects and the field director lived in temporal isolation in a completely natural environment with constant daylight (a high Arctic research camp) for six weeks. Detailed daily sleep logs were kept. In keeping with past findings, five of the six subjects developed a free‐running sleep‐wake cycle longer than 24 hours. Unlike past results, the isolated subjects did not exhibit any synchronicity in their rhythms. There was a high degree of intersubject variability in circadian patterns. The findings have important implications for the comparison of the results of laboratory and field investigations of sleep‐wake cycles.     

Behavioral and Serotonergic Regulation of Circadian Rhythms

Endogenous depression is often accompanied by alterations in core parameters of circadian rhythms, and antidepressant treatments, including serotonergic drugs, sleep deprivation and exercise, alter circadian phase or period in humans or animal models. Antidepressants may act in part through the circadian system, and behavioral antidepressants through a common serotonergic path to the clock. This review evaluates the evidence from animal models that serotonin (5-HT) mediates phase-shifting effects of behavioral stimuli on circadian rhythms. In rodents, 'exercise' stimulated during the rest phase of the rest-activity cycle induces large phase shifts of circadian rhythms. These shifts can be mimicked by short-term sleep deprivation without intense activity. During wheel running or sleep deprivation, 5-HT release in the suprachiasmatic nucleus (SCN) circadian clock is significantly elevated. Lesions of 5-HT afferents to the SCN attenuate phase shifts or entrainment induced by activity in response to some stimuli (e.g., triazolam injections in hamsters, treadmill running in mice) but not others (e.g., novel wheel confinement in hamsters). Antagonists selective to 5HT_{1, 2} or ₇ receptors do not attenuate shifts induced by wheel running, although 5-HT_2/7 antagonists do partially block shifts to saline injections. 5-HT agonists (e.g., 8-OH-DPAT) induce large shifts in vitro, but much smaller shifts in vivo, particularly if administered directly to the SCN. Procedures for inducing 5-HT supersensitivity in vivo result in larger shifts to 8-OH-DPAT. 5-HT stimuli may affect the clock by direct and indirect pathways, particularly through the thalamic intergeniculate leaflet, and the role of these pathways may differ across species. At the level of the SCN, 5-HT likely acts through 5-HT₇ receptors on neurons and possibly also glial cells. These receptors may be useful targets for the development of antidepressant drugs. In aggregate, the literature provides mixed support for the hypothesis that exercise or behavioral arousal shift the circadian clock by a 5-HT pathway; the role of indirect pathways, interactions with other transmitters, cellular adaptations to denervation, glial cells, and species differences remain to be more fully clarified. Serotonergic and behavioral stimuli provide an intriguing route to elucidate the circadian clockworks and their possible role in depression.     

The circadian program of algae

The endogenous circadian program enables organisms to cope with the temporal ecology of their environment. It is driven by a molecular pacemaker, which is found in animals as well as plants at the level of the single cell. Unicellular organisms are, therefore, ideal model systems for the study of circadian systems because rhythms can be investigated in single cells at the molecular, physiological, behavioral and environmental level. In this review, we discuss the possible driving forces for the evolution of circadian rhythmicity in unicellular marine organisms. The current knowledge about the cellular and molecular mechanisms involved in the different components of the circadian system (input, oscillator and output) are described primarily with reference to the marine dinoflagellate,Gonyaulax polyedra. Light is the most important and best described environmental signal synchronizing the endogenous rhythms to the 24-hour solar day. However, little is known about the nature of circadian light receptors, which appear to be distinct from those that control behavioral light responses such as phototaxis. It has recently been shown inGonyaulaxthat nutrients, namely nitrate, can act as a non-photic zeitgeber for the circadian system. In this alga, bioluminescence is under circadian control, and the molecular mechanisms of this circadian output have been investigated in detail. The circadian program turns out to be more complex than simply consisting of an input pathway, a pacemaker and the driven rhythms. Different rhythms appear to be controlled by separate pacemakers, even in single cells, and both circadian inputs and outputs contain feedback loops. The functional advantages of this complexity are discussed. Finally, we outline the differences between the circadian program under laboratory and natural conditions.