Restricted Feeding Schedules Modulate in a Different Manner the Expression of Clock Genes in Rat Hypothalamic Nuclei

Exploration of sleep quality and rest-activity rhythms characteristics in Bilateral Vestibulopathy patients

Sleep and circadian timing systems are constantly regulated by both photic and non-photic signals. Connections between the vestibular nuclei and the biological clock raise the question of the effect of peripheral vestibular loss on daily rhythms, such as the sleep-wake cycle and circadian rhythm. To answer this question, we compared the sleep and rest-activity rhythm parameters of 15 patients with bilateral vestibulopathy (BVP) to those of 15 healthy controls. Sleep and rest-activity cycle were recorded by a device coupling actimetry with the heart rate and actigraphy at home over 7 days. Subjective sleep quality was assessed by the Pittsburgh Sleep Quality Index (PSQI). Sleep efficiency and subjective sleep quality were significantly reduced, and sleep fragmentation was increased in BVP patients compared to controls. BVP patients displayed a damped amplitude of the rest-activity rhythm and higher sleep fragmentation, reflected by a higher nocturnal activity compared to controls. These results suggest that both rest-activity and sleep cycles are impaired in BVP patients compared to healthy controls. BVP patients seem to have greater difficulty maintaining good sleep at night compared to controls. BVP pathology appears to affect the sleep-wake cycle and disturb the circadian rhythm synchronization. Nevertheless, these results need further investigation to be confirmed, particularly with larger sample sizes.

Reestablishment of ad libitum feeding following partial food deprivation: Impact on locomotor activity, visceral fat, food intake, and circadian glycemic curve

Food deprivation has been associated with the development of metabolic pathologies. Few studies have explored the repercussions of a partial food deprivation following the reestablishment of an ad libitum diet. This study investigates the impact of a partial food deprivation (an 8-hour food intake restriction coupled with a 4-hour feeding window during the active phase) and the subsequent return to ad libitum feeding on the glycemic curve, food intake, and locomotor behavior. Wistar rats aged 45 days were subjected to 6 weeks of a partial food deprivation followed by 6 weeks of ad libitum feeding. Body weight, visceral fat, food intake, circadian glycemia, oral glucose tolerance, and locomotor activity were evaluated. It was found that the partial food deprivation resulted in the reduction of both the body weight and food intake; however, it increased visceral fat by 60%. Circadian glycemic values were altered at all intervals during the light phase, and glucose sensitivity improved at 60 minutes in the oral glucose tolerance test (OGTT). In the food-deprived group, the locomotor activity rhythm was reduced, with an observed delay in the peak of activity, reduction in total activity, and a decrease in the rhythmicity percentage. After the reestablishment of the ad libitum feeding, there was recovery of body weight, no difference in visceral fat, normalization of the food intake pattern, circadian glycemia, and oral glucose tolerance. Additionally, the return to ad libitum feeding restored locomotor activity, although the duration required for its complete recovery warrants further investigation. In conclusion, partial food deprivation induces physio-metabolic changes in rats, most of which are reversed after reestablishing ad libitum feeding.

Time-restricted eating for chronodisruption-related chronic diseases

The circadian timing system enables organisms to adapt their physiology and behavior to the cyclic environmental changes including light-dark cycle or food availability. Misalignment between the endogenous circadian rhythms and external cues is known as chronodisruption and is closely associated with the development of metabolic and gastrointestinal disorders, cardiovascular diseases, and cancer. Time-restricted eating (TRE, in human) is an emerging dietary approach for weight management. Recent studies have shown that TRE or time-restricted feeding (TRF, when referring to animals) has several beneficial health effects, which, however, are not limited to weight management. This review summarizes the effects of TRE/TRF on regulating energy metabolism, gut microbiota and homeostasis, development of cardiovascular diseases and cancer. Furthermore, we will address the role of circadian clocks in TRE/TRF and propose ways to optimize TRE as a dietary strategy to obtain maximal health benefits.

Effects of low dose radiation on behavior rhythm of zebrafish (Danio rerio)

Biological rhythm refers to the internal regulation of various life activities of an organism, which are determined by the specific time structure sequences of each individual. Behavior rhythm is the most intuitive embodiment of biological rhythm. To study the effect of low dose radiation on behavioral rhythm, zebrafish (Danio rerio) was used as a model organism in this study. The early embryos of zebrafish were irradiated at doses of 0.01, 0.1, and 1 Gy to observe the changes in zebrafish development, circadian rhythm, key clock genes, related RNA and protein expression, and melatonin. The results revealed that 0.1 and 1 Gy radiation could lead to different degrees of telencephalic nerve cell apoptosis and the formation of vacuolar structures. 0.1 and 1 Gy radiation could reduce the hatching rate of zebrafish embryos at 72 hpf and delay embryo hatching. The analysis of circadian behavior at 120 hpf demonstrated that 1 Gy dose of radiation altered the circadian rhythm of zebrafish, as well as decreased the distance, amplitude, and phase of movement. RT-PCR analysis of the key clock genes (bmal1b, clock1a, per1b, per2, cry2, and nr1d1) involved in regulating circadian rhythm was performed. The results showed that 1 Gy radiation could interfere with the expression of clock genes in zebrafish embryos and upregulate bmal1b, clock1a, and per1b. Western blot experiments further verified the protein expression of key clock genes, bmal1b and clock. Detection of melatonin secretion at different time points over 24 h showed that radiation doses of 0.1 and 1 Gy could increase melatonin secretion. Based on these findings, it is speculated that a certain dose of radiation may affect melatonin secretion, which impacts the telencephalon structure and ontogeny of zebrafish, delays hatching, and changes the circadian rhythm. This effect is thought to be achieved through upregulating the expression of circadian rhythm genes, clock1a and per1b and related proteins, which may be responsible for the abnormal circadian rhythm caused by radiation.

The Circadian Axis and Cardiometabolic Syndrome

Circadian rhythm refers to the daily physiologically fluctuating patterns of systemic processes that occur within a circa 24-hour timeframe, independently of external factors. There is evidence that in time, external and internal cycle misalignment leads to severe health consequences, resulting in the development of cardiometabolic disturbances. Desynchronized hormonal fluctuations along with daily specific macronutrient utilization patterns are also discussed, which by consequence, are all predictors of metabolic syndrome. The aim of this paper is to provide insight on the circadian clock’s organization throughout the human body and to explain the underlying genetic background. By understanding these well-established molecular mechanisms and processes, we believe this paper will provide accuracy regarding the importance of the circadian clock’s integrity and will highlight its role in the etiopathology of cardiometabolic syndrome.

The circadian clock regulates metabolic responses to physical exercise

It has been proposed for years that physical exercise ameliorates metabolic diseases. Optimal exercise timing in humans and mammals has indicated that circadian clocks play a vital role in exercise and body metabolism. Skeletal muscle metabolism exhibits a robust circadian rhythm under the control of the suprachiasmatic nucleus of the hypothalamus. Clock genes also control the development, differentiation, and function of skeletal muscles. In this review, we aimed to clarify the relationship between exercise, skeletal muscles, and the circadian clock. Health benefits can be attained by the scheduling of exercise at the best circadian time. Exercise therapy for metabolic diseases and cardiovascular health is a key adjuvant method. This review highlights the importance of exercise timing in maintaining healthy metabolism and circadian clocks.

Restricted feeding modulates peripheral clocks and nutrient sensing pathways in rats

OBJECTIVE

Feeding restriction in rats alters the oscillators in suprachiasmatic, paraventricular, and arcuate nuclei, hypothalamic areas involved in food intake. In the present study, using the same animals and experimental protocol, we aimed to analyze if food restriction could reset clock genes (Clock, Bmal1) and genes involved in lipid metabolism (Pgc1a, Pparg, Ucp2) through nutrient-sensing pathways (Sirt1, Ampk, Nampt) in peripheral tissues.

METHODS

Rats were grouped according to food access: Control group (CG, food ad libitum), Restricted night-fed (RF-n, food access during 2 h at night), Restricted day-fed (RF-d, food access during 2 h in the daytime), and Day-fed (DF, food access during 12 h in the daytime). After 21 days, rats were decapitated at ZT3 (0900-1000 h), ZT11 (1700-1800 h), or ZT17 (2300-2400 h). Blood, liver, brown (BAT) and peri-epididymal (PAT) adipose tissues were collected. Plasma corticosterone and gene expression were evaluated by radioimmunoassay and qPCR, respectively.

RESULTS

In the liver, the expression pattern of Clock and Bmal1 shifted when food access was dissociated from rat nocturnal activity; this phenomenon was attenuated in adipose tissues. Daytime feeding also inverted the profile of energy-sensing and lipid metabolism-related genes in the liver, whereas calorie restriction induced a pre-feeding increased expression of these genes. In adipose tissues, Sirt1 expression was modified by daytime feeding and calorie restriction, with concomitant expression of Pgc1a, Pparg, and Ucp2 but not Ampk and Nampt.

CONCLUSION

Feeding restriction reset clock genes and genes involved in lipid metabolism through nutrient-sensing-related genes in rat liver, brown, and peri-epididymal adipose tissues.

The circadian clock and metabolic homeostasis: entangled networks

The circadian clock exerts an important role in systemic homeostasis as it acts a keeper of time for the organism. The synchrony between the daily challenges imposed by the environment needs to be aligned with biological processes and with the internal circadian clock. In this review, it is provided an in-depth view of the molecular functioning of the circadian molecular clock, how this system is organized, and how central and peripheral clocks communicate with each other. In this sense, we provide an overview of the neuro-hormonal factors controlled by the central clock and how they affect peripheral tissues. We also evaluate signals released by peripheral organs and their effects in the central clock and other brain areas. Additionally, we evaluate a possible communication between peripheral tissues as a novel layer of circadian organization by reviewing recent studies in the literature. In the last section, we analyze how the circadian clock can modulate intracellular and tissue-dependent processes of metabolic organs. Taken altogether, the goal of this review is to provide a systemic and integrative view of the molecular clock function and organization with an emphasis in metabolic tissues.

Circadian Rhythms of the Hypothalamus: From Function to Physiology

The nearly ubiquitous expression of endogenous 24 h oscillations known as circadian rhythms regulate the timing of physiological functions in the body. These intrinsic rhythms are sensitive to external cues, known as zeitgebers, which entrain the internal biological processes to the daily environmental changes in light, temperature, and food availability. Light directly entrains the master clock, the suprachiasmatic nucleus (SCN) which lies in the hypothalamus of the brain and is responsible for synchronizing internal rhythms. However, recent evidence underscores the importance of other hypothalamic nuclei in regulating several essential rhythmic biological functions. These extra-SCN hypothalamic nuclei also express circadian rhythms, suggesting distinct regions that oscillate either semi-autonomously or independent of SCN innervation. Concurrently, the extra-SCN hypothalamic nuclei are also sensitized to fluctuations in nutrient and hormonal signals. Thus, food intake acts as another powerful entrainer for the hypothalamic oscillators' mediation of energy homeostasis. Ablation studies and genetic mouse models with perturbed extra-SCN hypothalamic nuclei function reveal their critical downstream involvement in an array of functions including metabolism, thermogenesis, food consumption, thirst, mood and sleep. Large epidemiological studies of individuals whose internal circadian cycle is chronically disrupted reveal that disruption of our internal clock is associated with an increased risk of obesity and several neurological diseases and disorders. In this review, we discuss the profound role of the extra-SCN hypothalamic nuclei in rhythmically regulating and coordinating body wide functions.

Regulation and function of extra-SCN circadian oscillators in the brain

Most organisms evolved endogenous, so called circadian clocks as internal timekeeping mechanisms allowing them to adapt to recurring changes in environmental demands brought about by 24-hour rhythms such as the light-dark cycle, temperature variations or changes in humidity. The mammalian circadian clock system is based on cellular oscillators found in all tissues of the body that are organized in a hierarchical fashion. A master pacemaker located in the suprachiasmatic nucleus (SCN) synchronizes peripheral tissue clocks and extra-SCN oscillators in the brain with each other and with external time. Different time cues (so called Zeitgebers) such as light, food intake, activity and hormonal signals reset the clock system through the SCN or by direct action at the tissue clock level. While most studies on non-SCN clocks so far have focused on peripheral tissues, several extra-SCN central oscillators were characterized in terms of circadian rhythm regulation and output. Some of them are directly innervated by the SCN pacemaker, while others receive indirect input from the SCN via other neural circuits or extra-brain structures. The specific physiological function of these non-SCN brain oscillators as well as their role in the regulation of the circadian clock network remains understudied. In this review we summarize our current knowledge about the regulation and function of extra-SCN circadian oscillators in different brain regions and devise experimental approaches enabling us to unravel the organization of the circadian clock network in the central nervous system.

Differentiating external zeitgeber impact on peripheral circadian clock resetting

Circadian clocks regulate physiological functions, including energy metabolism, along the 24-hour day cycle. The mammalian clock system is organized in a hierarchical manner with a coordinating pacemaker residing in the hypothalamic suprachiasmatic nucleus (SCN). The SCN clock is reset primarily by the external light-dark cycle while other zeitgebers such as the timing of food intake are potent synchronizers of many peripheral tissue clocks. Under conflicting zeitgeber conditions, e.g. during shift work, phase synchrony across the clock network is disrupted promoting the development of metabolic disorders. We established a zeitgeber desynchrony (ZD) paradigm to quantify the differential contributions of the two main zeitgebers, light and food, to the resetting of specific tissue clocks and the effect on metabolic homeostasis in mice. Under 28-hour light-dark and 24-hour feeding-fasting conditions SCN and peripheral clock, as well as activity and hormonal rhythms showed specific periodicities aligning in-between those of the two zeitgebers. During ZD, metabolic homeostasis was cyclic with mice gaining weight under synchronous and losing weight under conflicting zeitgeber conditions. In summary, our study establishes an experimental paradigm to compare zeitgeber input in vivo and study the physiological consequences of chronodisruption.

Changes in Clock Genes Expression in Esophagus in Rat Reflux Esophagitis

BACKGROUND

Gastroesophageal reflux disease (GERD) is strongly associated with sleep disturbances. Clock genes harmonize circadian rhythms by their periodic expression and regulate several physiological functions. However, the association between clock genes and GERD is still unknown.

AIMS

We investigated whether reflux esophagitis affects circadian variability of clock genes in the esophagus and other organs using a rat reflux esophagitis model.

METHODS

Reflux esophagitis was induced in 7-week-old male Wistar rats. Sham-operated rats were used as controls. Rats were killed at 09:00 (light period) and 21:00 (dark period) 3 days (acute phase) and 21 days (chronic phase) after induction of esophagitis. The expression levels of clock gene mRNAs such as Per1, Per2, Per3, Cry1, Cry2, Arntl, and Clock in the esophagus were investigated by qPCR. Arntl expression was examined in stomach, small intestine, colon, and liver tissues. Serum melatonin and IL-6 levels were measured by ELISA.

RESULTS

Histological examination of reflux esophagitis mainly revealed epithelial defects with marked inflammatory cell infiltration in the acute phase and mucosal thickening with basal cell hyperplasia in the chronic phase. Circadian variability of clock genes, except Cry1, was present in the normal esophagus and was completely disrupted in reflux esophagitis during the acute phase. The circadian variability of Per2, Per3, and Arntl returned to normal, but disruption of Per1, Cry2, and Clock was present in the chronic phase. Disruption of circadian variability of Arntl was observed in the esophagus, as well as in the stomach, small intestine, and liver tissues in reflux esophagitis during the acute phase. There were no significant differences in serum melatonin and IL-6 levels between control and reflux esophagitis animals in both acute and chronic phases.

CONCLUSIONS

Disruption to circadian variability of clock genes may play a role in the pathogenesis of GERD.