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Circadian Rhythm of Clock Genes in Human Adipose Explants
Abstract
To analyze in severely obese women the circadian expression of the clock genes hPer2, hBmal1, and hCry1 in explants from subcutaneous (SAT) and visceral (VAT) adipose tissue (AT), in order to elucidate whether this circadian clockwork can oscillate accurately and independently of the suprachiasmatic nucleus (SCN) and if glucocorticoid metabolism-related genes such as glucocorticoid receptor (hGr) and 11beta-hydroxysteroid dehydrogenase 1 (h11 beta Hsd1) and the transcription factor peroxisome proliferator activated receptor gamma (hPPAR gamma) are part of the clock controlled genes. AT biopsies were obtained from morbid obese patients (BMI > or =40 kg/m(2)) (n = 7). Anthropometric variables were measured and fasting plasma lipids and lipoprotein concentrations were analyzed. In order to carry out rhythmic expression analysis, AT explants were cultured during 24 h and gene expression was performed at the following times (T): 0, 6, 12, and 18 h, with quantitative real-time PCR. Clock genes oscillated accurately and independently of the SCN in AT explants. Their intrinsic oscillatory mechanism regulated the timing of other genes such as hPPAR gamma and glucocorticoid-related genes. Circadian patterns differed between VAT and SAT. Correlation analyses between the genetic circadian oscillation and components of the metabolic syndrome (MetS) revealed that subjects with a higher sagittal diameter showed an increased circadian variability in hPer2 expression (r = 0.91; P = 0.031) and hBmal1 (r = 0.90; P = 0.040). Data demonstrate the presence of peripheral circadian oscillators in human AT independently of the central circadian control mechanism. This knowledge paves the way for a better understanding of the circadian contribution to medical conditions such as obesity and MetS.
... (Grill and Zhou, 1995;Shulman, 2000;Drosatos and Schulze, 2013) Predictably, the peripheral clock in adipose tissue from humans has been reported to exhibit robust patterns of circadian gene expression; also, these endogenous circadian rhythms persist following removal and short-term culture in vitro. (Fain et al., 2003;Phillips et al., 2008;Rogers et al., 2008;Gómez-Santos et al., 2009;Garaulet et al., 2011;Gómez-Abellán et al., 2012;Aubin et al., 2015;Wang et al., 2015) Thus, circadian patterns of gene expression in adipose tissue are highly relevant in physiological and pathophysiological states. ...
... Similar protocols have shown that human adipose tissue circadian clock gene and clock-controlled gene rhythms can be maintained without direct SCN signal. (Fain et al., 2003;Phillips et al., 2008;Rogers et al., 2008;Gómez-Santos et al., 2009;Garaulet et al., 2011;Gómez-Abellán et al., 2012;Aubin et al., 2015;Wang et al., 2015) Yet, to preserve the SCN-mediated imprint of endogenous entrainment of the peripheral circadian clock, the tissue was not serum shocked. ...
... In contrast, prior reports of Bmal1 acrophase preceded our report. (Gómez-Santos et al., 2009;Gómez-Abellán et al., 2012) However, in our current study we: 1) utilized no FBS serum shock, which allowed us to maintain the endogenous rhythmicity from each subject; 2) utilized base media of M199 instead of DMEM; and 3) utilized, in media, low insulin (1 nM) and very low dexamethasone treatment (40 nM) to support cell viability. For Dbp, the calculated acrophases were, respectively: 19:36, 19:58, 20:46, and 21:42 (Supplemental Figure 6). ...
A hallmark of biology is the cyclical nature of organismal physiology driven by networks of biological, including circadian, rhythms. Unsurprisingly, disruptions of the circadian rhythms through sleep curtailment or shift work have been connected through numerous studies to positive associations with obesity, insulin resistance, and diabetes. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) measures oscillation in messenger RNA expression, an essential foundation for the study of the physiological circadian regulatory network. Primarily, measured oscillations have involved the use of reference gene normalization. However, the validation and identification of suitable reference genes is a significant challenge across different biological systems. This study focuses on adipose tissue of premenopausal, otherwise healthy, morbidly obese women voluntarily enrolled after being scheduled for laparoscopic sleeve gastrectomy surgery. Acquisition of tissue was accomplished by aspiratory needle biopsies of subcutaneous adipose tissue 1 to 2 weeks prior to surgery and 12 to 13 weeks following surgery and an in-surgery scalpel-assisted excision of mesenteric adipose tissue. Each biopsy was sterile cultured ex vivo and serially collected every 4 h over approximately 36 h. The candidate reference genes that were tested were 18S rRNA, GAPDH, HPRT1, RPII, RPL13α, and YWHAZ. Three analytic tools were used to test suitability, and the candidate reference genes were used to measure oscillation in expression of a known circadian clock element (Dbp). No gene was deemed suitable as an individual reference gene control, which indicated that the optimal reference gene set was the geometrically averaged 3-gene panel composed of YWHAZ, RPL13α, and GAPDH. These methods can be employed to identify optimal reference genes in other systems.
... Extra. 4): [33][34][35][36][37][38] tejidos (3,17,21). Todo ello implica que el reloj de los mamíferos se trate de un mecanismo altamente complejo que presenta unos tiempos específicos a nivel de órganos y células (17). ...
... Dar quimioterapia en el momento adecuado parece atacar el tumor con menos efectos secundarios para el resto del órgano o del tejido que cuando está en horas de actividad, y para eso hay que conocer al detalle el ritmo de cada reloj biológico específico (7,24). Además, este reloj fisiológico también es de especial importancia en la fisiología del hambre/saciedad (33)(34)(35). ...
... Extra. 4): [33][34][35][36][37][38] sa y ácidos grasos en sangre y hormonas como el neuropéptido Y (NPY). Este neuropéptido forma parte del sistema lipoestabilizador, junto con la leptina y la hormona liberadora de corticotropina (CRH). ...
For centuries it has been observed in living beings the existence of endogenous rhythms that prepare and adapt the physiology of the organism to the different daily and seasonal phases. These internal clocks regulate an enormous variety of physiological systems that mark their activity. Because of this, these complex systems are subject to strict genetic and molecular regulations, which cause these repetitive patterns to be maintained in the absence of external stimuli. Circadian dysfunctions have been linked to sleep disorders, psychological problems, neurological diseases, metabolic disorders and obesity. Maintaining a daily routine related to rest, physical activity and food keeps these body clocks synchronized, helps control body weight and optimizes certain medical treatments. Diet is one of the external factors that most influences the synchrony of these endogenous clocks, so that a correct feeding at the right times can benefit our health.
... Excess hypertrophy can lead to cell lysis, at which time free FAs are released into the bloodstream, promoting ectopic lipid storage in other organs, which is thought to be a primary driver of insulin resistance. Interestingly, the molecular clock core is involved in the regulation of lipogenesis and lipolysis, as many of the key enzymes that are involved in lipolysis and lipogenesis are directly regulated by the CLOCK:BMAL1 transcriptional complex [9][10][11][12][13]. In fact, lipolysis has been reported to be highly rhythmic in WAT, resulting in daily fluctuations of free fatty acids (FA) and glycerol in the bloodstream [9]. ...
... The clock in adipocytes is highly rhythmic in rodents and humans alike, with similar phase oscillations for the core clock components in brown (BAT), subcutaneous (SAT), and visceral (VAT) adipose tissue [9,10,[13][14][15]. Interestingly, these oscillations are autonomous to the fat pad, as adipose tissue explant cultures which are devoid of signals coming from the central clock within the hypothalamic suprachiasmatic nucleus (SCN) can maintain rhythmicity ex vivo for some period of time [12]. Several circadian-disrupted genetic mouse models targeting core clock genes support the importance of the circadian clock in WAT [15]. ...
White adipose tissue (WAT) is a metabolic organ with flexibility to retract and expand based on energy storage and utilization needs, processes that are driven via the coordination of different cells within adipose tissue. WAT is comprised of mature adipocytes (MA) and cells of the stromal vascular cell fraction (SVF), which include adipose progenitor cells (APCs), adipose endothelial cells (AEC) and infiltrating immune cells. APCs have the ability to proliferate and undergo adipogenesis to form MA, the main constituents of WAT being predominantly composed of white, triglyceride-storing adipocytes with unilocular lipid droplets. While adiposity and adipose tissue health are controlled by diet and aging, the endogenous circadian (24-h) biological clock of the body is highly active in adipose tissue, from adipocyte progenitor cells to mature adipocytes, and may play a unique role in adipose tissue health and function. To some extent, 24-h rhythms in adipose tissue rely on rhythmic energy intake, but individual circadian clock proteins are also thought to be important for healthy fat. Here we discuss how and why the clock might be so important in this metabolic depot, and how temporal and qualitative aspects of energy intake play important roles in maintaining healthy fat throughout aging.
... In mice, for the precise determination of the period in vivo and ex vivo, transgenic animals can be used that express luciferase reporters under the control of clock gene promoters or reporters fused to clock proteins (20,21). Studying adipose rhythms in humans is more challenging and, so far, repeated biopsies, cultured primary adipocytes or explants that are sampled at different time points across the day and night have been necessary to analyze the rhythmic expression of circadian clock genes in AT (22). The precision of the assessment of period and phase of AT rhythms with these tools is considerably limited, as most of these experiments are performed within a 24 h timeframe with limited samples (typically, n # 6) and long intervals of several hours between sample time points (typically, $4 h). ...
... In general, expression experiments for human circadian rhythm analysis require a large amount of tissue or repeated invasive extractions from participants. In our own experience, for adipose tissue analysis, at least 12 g of tissue is needed to establish a reliable circadian expression profile (22,(25)(26)(27). In this case, the profile is obtained by taking AT samples at least every 4 h along a 24 h cycle with a total of 6 time points in the analysis. ...
Daily rhythms in physiology and behavior change with age. An unresolved question is to what extent such age‐related alterations in circadian organization are driven by the central clock in the suprachiasmatic nucleus (SCN), modifying timing signals to contributing peripheral tissue oscillators, and are mediated by underlying changes in the local cellular oscillators themselves. Using a bioluminescence reporter approach, we sought to determine whether circadian clock function in human adipocytes from subcutaneous (SAT) and visceral (VAT) adipose tissues changes with age. SAT and VAT biopsies were obtained from obese individuals during gastric bypass surgeries [n = 16; body mass index: 44.8 ± 11.4 kg/m²; age: 44 ± 9 yr (range: 30–58)]. Cells were isolated and transduced with a lentiviral circadian reporter construct [brain and muscle ary1 hydrocarbon receptor nuclear translocator‐like:luciferase (BMAL:LUC)], and bioluminescence was recorded over a period of 3 d. Human BMAL1:LUC adipocytes displayed a robust luminescence rhythm with comparable within‐individual periods in mature and preadipocytes (P > 0.05). With increasing age, the circadian period decreased in mature adipocytes (P = 0.005) (β = 4 min/yr; P < 0.05). Our ex vivo approach indicated that ageing changes the organization of endogenous circadian oscillators in human adipocytes, independent of SCN signaling.—Kolbe, I., Carrasco‐Benso, M. P., López‐Mínguez, J., Luján, J., Scheer, F. A. J. L., Oster, H., Garaulet, M. Circadian period of luciferase expression shortens with age in human mature adipocytes from obese patients. FASEB J. 33, 175–180 (2019). www.fasebj.org
... However, we are not alone in suggesting a more complicated interaction between central and peripheral clocks that could not happen without an assessment and integration of all zeitgeber signals, independently of their origin. The essential master clock role of the SCN has been questioned before, as studies have shown persistent circadian rhythms in explants of adipose tissue, lung, liver and kidney in the complete absence of SCN signalling (59,60). In addition, in rats and mice under DF, neuronal activity in SCN was observed to be reduced, allowing food anticipatory activity to occur during the passive, lights-on phase (47,61). ...
One of the main zeitgebers in the digestive system is food intake; however, little is known about organ- and sex-specific differences in food-driven circadian regulation. We placed male and female C57Bl/6 mice on time-restricted feeding (TRF), limiting food intake period to 8 hours. TRF was started either at dark (ZT12) or light (ZT0) onset and continued for 28 days, with or without an additional 4 hour forward shift on day 15.
TRF from ZT12 to ZT20 led to the highest weight gain in females, but the lowest weight gain in males, while improving intestinal transepithelial resistance (TEER) in both sexes. Unexpectedly, it also led to the disappearance of diurnal rhythmicity in several hepatic genes. Shifting the TRF start to ZT16 led to an increase in weight gain and a decrease in fasting plasma glucose levels in male mice, as well as to strong rhythmicity in nutrient metabolism-related hepatic and duodenal genes in both sexes. Surprisingly, food intake during ZT0-ZT8 caused only minor changes in physiological responses. However, it did lead to an overall downregulation of gene expression in the liver, an upregulation in the stomach and duodenum, and to flattened diurnal responses. Shifting the start of food intake to ZT4 was highly detrimental, causing an increase in fasting blood glucose levels, a decrease in TEER, and disrupting diurnal gene expression pattern in the liver and stomach. Despite this, in duodenum TRF from ZT4 to ZT12 acted as a potent zeitgeber.
These results demonstrate that the adjustment to food intake time in mice is highly sex- and organ-specific. Our chosen TRF regimes were not able to achieve full diurnal rhythm synchronization across the digestive system. Instead, we observed that the same food intake time might be a strong zeitgeber in one organ, and a rhythm disruptor in another.
... This review describes recent advancements in research, explores current questions, and identifies directions for future research. regulates lipid metabolism, including the diurnal rhythm of lipid absorption, storage, and transport [12,[16][17][18][19][20][21][22][23][24][25][26][27][28][29]. The mechanisms through which disruption of the circadian rhythm and circadian clock affects the rhythmic expression of lipid metabolism-associated apolipoprotein genes in various brain regions remain unclear. ...
The circadian rhythm is a 24 h internal clock within the body that regulates various factors, including sleep, body temperature, and hormone secretion. Circadian rhythm disruption is an important risk factor for many diseases including neurodegenerative illnesses. The central and peripheral oscillators’ circadian clock network controls the circadian rhythm in mammals. The clock genes govern the central clock in the suprachiasmatic nucleus (SCN) of the brain. One function of the circadian clock is regulating lipid metabolism. However, investigations of the circadian regulation of lipid metabolism-associated apolipoprotein genes in the brain are lacking. This review summarizes the rhythmic expression of clock genes and lipid metabolism-associated apolipoprotein genes within the SCN in Mus musculus. Nine of the twenty apolipoprotein genes identified from searching the published database (SCNseq and CircaDB) are highly expressed in the SCN. Most apolipoprotein genes (ApoE, ApoC1, apoA1, ApoH, ApoM, and Cln) show rhythmic expression in the brain in mice and thus might be regulated by the master clock. Therefore, this review summarizes studies on lipid-associated apolipoprotein genes in the SCN and other brain locations, to understand how apolipoproteins associated with perturbed cerebral lipid metabolism cause multiple brain diseases and disorders. This review describes recent advancements in research, explores current questions, and identifies directions for future research.
... This review describes recent advancements in research, explores current questions, and identifies directions for future research. regulates lipid metabolism, including the diurnal rhythm of lipid absorption, storage, and transport [12,[16][17][18][19][20][21][22][23][24][25][26][27][28][29]. The mechanisms through which disruption of the circadian rhythm and circadian clock affects the rhythmic expression of lipid metabolism-associated apolipoprotein genes in various brain regions remain unclear. ...
... Santos et al. evaluated the circadian expression of clock genes in subcutaneous and visceral adipose tissue cultures of female morbidly obese patients and found that the circadian rhythm was maintained ex vivo for a minimum of two circadian cycles following surgery, indicating the presence of the cellular circadian clock that controls individual cellular processes separate from the SCN. In addition, according to correlation analyses of the circadian rhythm and metabolic syndrome markers, having a larger sagittal abdominal diameter leads to an increase in circadian variability of Per2 and Bmal1 gene expression [165]. PER2 and NR1D1 expressions in subcutaneous adipose tissue of overweight subjects were shown to be increased after body weight loss with a caloric restriction [166]. ...
Essential for survival and reproduction, the circadian timing system (CTS) regulates adaptation to cyclical changes such as the light/dark cycle, temperature change, and food availability. The regulation of energy homeostasis possesses rhythmic properties that correspond to constantly fluctuating needs for energy production and consumption. Adipose tissue is mainly responsible for energy storage and, thus, operates as one of the principal components of energy homeostasis regulation. In accordance with its roles in energy homeostasis, alterations in adipose tissue’s physiological processes are associated with numerous pathologies, such as obesity and type 2 diabetes. These alterations also include changes in circadian rhythm. In the current review, we aim to summarize the current knowledge regarding the circadian rhythmicity of adipogenesis, lipolysis, adipokine secretion, browning, and non-shivering thermogenesis in adipose tissue and to evaluate possible links between those alterations and metabolic diseases. Based on this evaluation, potential therapeutic approaches, as well as clock genes as potential therapeutic targets, are also discussed in the context of chronotherapy.
... Adipose tissues also participated in regulating circadian clock network. Some glucocorticoid metabolism-related genes and the transcription factor peroxisome proliferator activated receptor γ (PPARγ), are part of the intrinsic clock controlled genes [35]. Besides, a large number of intestinal enzymes and hormones are also exhibited in a circadian manner and are synchronized by food [30]. ...
Background
Unhealthy lifestyle has been associated with obesity and type 2 diabetes. Whereas its association with vascular complications in patients with long-duration of type 2 diabetes is still uncertain.
Methods
A total of 1188 patients with long-duration of type 2 diabetes from the Taiwan Diabetes Registry (TDR) data were analyzed. We stratified the severity of unhealthy lifestyle via scoring three factors (sleep duration <7 or >9 h, sit duration ≥ 8h, and meal numbers ≥ with night snack) and analyzed their associations with the development of vascular complications using logistic regression analysis. Besides, we also included 3285 patients with newly diagnosed type 2 diabetes as the comparison.
Results
Increased numbers of factors that stand for unhealthy lifestyle were significantly associated with the development of cardiovascular disease, peripheral arterial occlusion disease (PAOD) and nephropathy in patients with long-duration of type 2 diabetes. After adjusting multiple covariables, having ≥ 2 factors of unhealthy lifestyle remained significant associations with cardiovascular disease and PAOD, with an odds ratio (OR) of 2.09 (95% confidence interval [CI] 1.18–3.69) and 2.68 (95% CI 1.21–5.90), respectively. Among individual factor for unhealthy lifestyle behaviors, we revealed that eating ≥ 4 meals per day with night snack increased the risk of cardiovascular disease and nephropathy after multivariable adjustment (OR of 2.60, 95% CI 1.28–5.30; OR of 2.54, 95% CI 1.52–4.26, respectively). Whereas sit duration for ≥ 8 h per day increased the risk of PAOD (OR of 4.32, 95% CI 2.38–7.84).
Conclusion
Unhealthy lifestyle is associated with increased prevalence of macro- and micro-vascular comorbidities in Taiwanese patients with long-duration type 2 diabetes.
... (eWAT)], (e) [F time(1, 16) = 2.735 / F group(1, 16) = 37.28], (g) [F time(1, 13) = 0.7485 / F group(1, 13) = 11.27], (h) [F time(1, 14) = 10.23 / F group(1,14) and also in subcutaneous adipose-derived stem cells4,55,56 . ...
Hyperplastic expansion of white adipose tissue (WAT) relies in part on the proliferation of adipocyte precursor cells residing in the stromal vascular cell fraction (SVF) of WAT. This study reveals a circadian clock- and feeding-induced diurnal pattern of cell proliferation in the SVF of visceral and subcutaneous WAT in vivo, with higher proliferation of visceral adipocyte progenitor cells subsequent to feeding in lean mice. Fasting or loss of rhythmic feeding eliminates this diurnal proliferation, while high fat feeding or genetic disruption of the molecular circadian clock modifies the temporal expression of proliferation genes and impinges on diurnal SVF proliferation in eWAT. Surprisingly, high fat diet reversal, sufficient to reverse elevated SVF proliferation in eWAT, was insufficient in restoring diurnal patterns of SVF proliferation, suggesting that high fat diet induces a sustained disruption of the adipose circadian clock. In conclusion, the circadian clock and feeding simultaneously impart dynamic, regulatory control of adipocyte progenitor proliferation, which may be a critical determinant of adipose tissue expansion and health over time.
... Comme expliquée au chapitre 1, l'horloge circadienne se synchronise à l'alternance jour/nuit, permettant ainsi à l'organisme de s'adapter au caractère périodique de l'environnement terrestre. Au niveau cellulaire, les oscillations se caractérisent par une variation périodique de certains constituants sur une période d'environ 24h [36]. Plusieurs modèles existent dans la littérature notamment basés sur des EDO. ...
Dans cette thèse, nous nous intéressons à l'analyse qualitative de la dynamique de deux cycles biologiques centraux dans les cellules eucaryotes, le cycle de division cellulaire et l'horloge circadienne. Nous utilisons pour cela des réseaux Booléens asynchrones, bien adaptés à une analyse qualitative. Dans ces réseaux, les cycles sont capturés par des attracteurs complexes, pouvant contenir des centaines d'états. Nous proposons une nouvelle méthode d'analyse de ces attracteurs complexes, basée sur la construction d'un graphe résumé. Cette méthode permet de comparer les trajectoires contenues l'attracteur avec les propriétés qualitatives du cycle biologique. Nous illustrons notre méthode sur un modèle du cycle cellulaire de la littérature et sur un modèle de l'horloge circadienne, que nous avons construit à partir d'un modèle continu existant. Dans ces deux modèles, notre méthode s'est montrée efficace pour visualiser la structure de l'attracteur complexe et le comparer avec un cycle biologique. En combinant le graphe résumé avec une chaîne de Markov, nous estimons les proportions de temps passé dans les phases décrites par les oscillations. En le combinant avec une méthode d'inférence Booléenne, nous montrons également comment ajuster localement la dynamique asymptotique du modèle, afin de forcer certaines propriétés dynamiques. Ces deux applications montrent l'intérêt de notre méthode pour la modélisation et l'analyse de réseaux de régulation cellulaire.
... Therefore, circadian disruption may alter the physiology of adipose tissue and thereby affect whole body energy homeostasis. The rhythmic expression of circadian genes in different white adipose depots in rodents [5,82,83] and humans [84][85][86] have been revealed by both in vitro and in vivo studies. In murine adipose tissue, approximately 10% of genes are expressed in circadian rhythm, which underlines the circadian control over the adipose tissue function [83]. ...
Obesity is a major risk factor for most metabolic and cardiovascular disorders. Adipose tissue is an important endocrine organ that modulates metabolic and cardiovascular health by secreting signaling molecules. Oxidative stress is a common mechanism associated with metabolic and cardiovascular complications including obesity, type 2 diabetes, and hypertension. Oxidative stress can cause adipose tissue dysfunction. Accumulating data from both humans and experimental animal models suggest that adipose tissue function and oxidative stress have an innate connection with the intrinsic biological clock. Circadian clock orchestrates biological processes in adjusting to daily environmental changes according to internal or external cues. Recent studies have identified the genes and molecular pathways exhibiting circadian expression patterns in adipose tissue. Disruption of the circadian rhythmicity has been suggested to augment oxidative stress and aberrate adipose tissue function and metabolism. Therefore, circadian machinery in the adipose tissue may be a novel therapeutic target for the prevention and treatment of metabolic and cardiovascular diseases. In this review, we summarize recent findings on circadian rhythm and oxidative stress in adipose tissue, dissect the key components that play a role in regulating the clock rhythm, oxidative stress and adipose tissue function, and discuss the potential use of antioxidant treatment on metabolic and cardiovascular diseases by targeting the adipose clock.
... The adipose tissue clock. WAT contains an autonomous circadian clock as shown in both rodent 58,59 and human 60,61 in vitro models (Fig. 6). Similar to the muscle clock, the WAT clock is synchronized by the SCN 62 and by signals resulting from food intake 63,64 . ...
... Poor eating habits and obesity alter circadian rhythms. For example, obesity in humans and animals is associated with sleep and circadian rhythms (Gómez-Santos et al. 2009;Laposky et al. 2008;Mistlberger et al. 1998). High-fat diet (HFD) alters free-running period (Kohsaka et al. 2007) and responses to light cues that help synchronize or entrain the circadian clock (Mendoza et al. 2008). ...
Altered circadian rhythms have negative consequences on health and behavior. Emerging evidence suggests genetics influences the physiological and behavioral responses to circadian disruption. We investigated the effects of a 21 h day (T = 21 cycle), with high-fat diet consumption, on locomotor activity, explorative behaviors, and health in male C57BL/6J and C57BL/6N mice. Mice were exposed to either a T = 24 or T = 21 cycle and given standard rodent chow (RC) or a 60% high-fat diet (HFD) followed by behavioral assays and physiological measures. We uncovered numerous strain differences within the behavioral and physiological assays, mainly that C57BL/6J mice exhibit reduced susceptibility to the obesogenic effects of (HFD) and anxiety-like behavior as well as increased circadian and novelty-induced locomotor activity compared to C57BL/6N mice. There were also substrain-specific differences in behavioral responses to the T = 21 cycle, including exploratory behaviors and circadian locomotor activity. Under the 21-h day, mice consuming RC displayed entrainment, while mice exposed to HFD exhibited a lengthening of activity rhythms. In the open-field and light-dark box, mice exposed to the T = 21 cycle had increased novelty-induced locomotor activity with no further effects of diet, suggesting daylength may affect mood-related behaviors. These results indicate that different circadian cycles impact metabolic and behavioral responses depending on genetic background, and despite circadian entrainment.
... 2 Soon after, the rhythmicity of the adipose tissue was established, showing the existence of an internal biological clock in the human adipose tissue. 19 From these reports, numerous studies have been carried out confirming the relationship between the alteration of biological rhythms and obesity. p0105 Today, the influence of chronobiology on the development of obesity is undeniable, and it is well known that both advancing or delaying these rhythms produces an alteration of glucoseeinsulin metabolism and a reduction of substrate oxidation levels (decrease in energy expenditure), so that eating outside our biological rhythms chronically favors the development of obesity. ...
... The ACE 'D' allele is associated with increased angiotensin II [36] which may further reduce the adiponectin levels. Further, the role of circadian rhythm has been implicated earlier in regulating metabolic processes of adipose tissue, and in the expression and secretion of adipokines [37,38]. The metabolic regulation is predicted to be mediated by the action of melatonin, a pineal gland hormone, on VAT receptors or via the sympathetic nervous system [39,40]. ...
Vaspin, an insulin-sensitizing adipokine, has been associated with type 2 diabetes (T2D). The present study aimed to investigate the distribution of genotypes and high-risk alleles of vaspin genetic variants (rs77060950 G/T and rs2236242 A/T), in Gujarat subpopulation (India). Genomic DNA isolated from PBMCs was used to genotype vaspin polymorphisms by PCR-RFLP and ARMS-PCR from 502 controls and 478 patients. RNA isolated from visceral adipose tissue (VAT) of 22 controls and 20 patients was used to assess vaspin transcript levels by qPCR while the vaspin titre of the subjects was assayed using ELISA. Phenotypic characteristics of Fasting Blood Glucose (FBG), BMI and plasma lipid profile were estimated and analyzed for the genotype-phenotype correlation. We identified a significant association of rs2236242 A/T with T2D as the TT genotype conferred a 3.087-fold increased risk. The TT genotype showed association with increased FBG, BMI and Triglycerides levels. Increased GA, GT and TA haplotype frequencies, decreased VAT transcript and vaspin protein levels in T2D patients was observed, which were further negatively correlated with FBG and BMI. In conclusion, rs2274907 A/T polymorphism is strongly associated with reduced vaspin transcript and protein levels, and related metabolic alterations that may play a role in the advancement of T2D.
... Dysregulation of blood glucose levels with the increased propensity towards T2D and diabetic complications have been shown to be associated with sleep disturbances [35]. Moreover, it has also been reported that circadian rhythms can influence metabolic processes of adipose tissue and also expression and secretion of adipokines [36,37]. Such regulation is likely to be mediated by melatonin by way of its action on VAT either through its membrane receptors or via an action on the sympathetic nervous system [38]. ...
Objective:
Omentin-1, an anti-inflammatory protein, is secreted by the visceral adipose tissue. Altered levels of Omentin-1 are associated with obesity and Type 2 Diabetes (T2D). Although Omentin-1 is implicated in the insulin signaling pathway, the relationship between the genetic variants of Omentin-1 and T2D is not yet explored. The current study evaluates the association of Omentin-1 polymorphisms (rs2274907 A/T and rs1333062 G/T), its transcript and protein levels, and genotype-phenotype correlation with metabolic parameters and T2D susceptibility.
Methods:
Plasma and Peripheral Blood Mononuclear Cells (PBMCs) were separated from venous blood taken from 250 controls and 250 T2D patients recruited from Gujarat, India. Genomic DNA was isolated from PBMCs and genotyping of Omentin-1 variants was performed by Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP). RNA was isolated from Visceral Adipose Tissue (VAT) samples of 12 controls and 10 patients, and transcript levels of Omentin-1 were assessed by qPCR. Plasma Omentin-1 levels were estimated by ELISA. Fasting Blood Glucose, Body Mass Index (BMI) and plasma lipid profile were considered for the genotype-phenotype correlation analysis.
Results:
Our study revealed no association of Omentin-1 genetic variants with T2D risk (p > 0.05). However, the AT genotype of Omentin-1 rs2274907 A/T polymorphism was associated with increased BMI (p = 0.0247). Plasma Omentin-1 levels were significantly decreased (p < 0.0001) however, increased VAT Omentin-1 transcript levels (p = 0.0127) were observed in T2D patients.
Conclusion:
Our findings suggest that decreased circulatory Omentin-1 levels could pose a risk towards T2D susceptibility.
... More often the symptoms and Table 1 Role of DNA methylation in circadian rhythms in various tissues and their associated experimental methods. diseases are associated with a drastic increase in body weight, arteriosclerosis, and diabetes as a result of compromised insulin sensitivity and rise in blood pressure [87][88][89]. In addition to that methylation studies in human female subjects show a strong correlation with the methylation levels of Clock gene CpGs with MetS characteristics (BMI, fat content, insulin resistance, and systolic pressure) [90]. ...
Over the course of evolution, nature has forced organisms under selection pressure to hardwire an internal time keeping device that defines 24 h of a daily cycle of physiological and behavioral rhythms, known as circadian rhythms. At the cellular level, the cycle is governed by significant fractions of transcriptomes, which are under the control of transcriptional and translational feedback loop of clock genes. Intriguingly, this feedback loop is regulated at multiple stratums such as at the transcriptional and translational levels, which direct a cell towards producing a robust rhythm by sustaining the repeated stoichiometry of protein products. Moreover, with the advent of state of the art paradigms, epigenetic regulation of circadian rhythms has been becoming more evident at present time. Light-induced recurring fluctuations in chromatin acetylation concurrent with the binding of RNA Pol II and integration of miRNAs monitor the chromatin modifiers or clock genes expression to drive temporal rhythmicity. Furthermore, CLOCK protein intrinsic histone acetyl transferase activity, the interaction of CLOCK-BMAL-1 with HAT enzymes, and the involvement of many histone deacetylases also maintain the rhythmic protein profile. Additionally, the critical role of the rhythmic methylation pattern of clock genes in battery of cancer and metabolic disorders also defines its importance. Therefore, in this review, we focused on accumulating all the present data available on epigenetics and circadian rhythms. Interestingly, we also gathered evidence from the available literature pinpointing towards the dynamic nature of chromatin architecture governed by long and short-range regulatory elements DNA contacts arising daily, that was thought to be steady otherwise.
... The adipose tissue clock. WAT contains an autonomous circadian clock as shown in both rodent 58,59 and human 60,61 in vitro models (Fig. 6). Similar to the muscle clock, the WAT clock is synchronized by the SCN 62 and by signals resulting from food intake 63,64 . ...
Insulin resistance is a main determinant in the development of type 2 diabetes mellitus and a major cause of morbidity and mortality. The circadian timing system consists of a central brain clock in the hypothalamic suprachiasmatic nucleus and various peripheral tissue clocks. The circadian timing system is responsible for the coordination of many daily processes, including the daily rhythm in human glucose metabolism. The central clock regulates food intake, energy expenditure and whole-body insulin sensitivity, and these actions are further fine-tuned by local peripheral clocks. For instance, the peripheral clock in the gut regulates glucose absorption, peripheral clocks in muscle, adipose tissue and liver regulate local insulin sensitivity, and the peripheral clock in the pancreas regulates insulin secretion. Misalignment between different components of the circadian timing system and daily rhythms of sleep–wake behaviour or food intake as a result of genetic, environmental or behavioural factors might be an important contributor to the development of insulin resistance. Specifically, clock gene mutations, exposure to artificial light–dark cycles, disturbed sleep, shift work and social jet lag are factors that might contribute to circadian disruption. Here, we review the physiological links between circadian clocks, glucose metabolism and insulin sensitivity, and present current evidence for a relationship between circadian disruption and insulin resistance. We conclude by proposing several strategies that aim to use chronobiological knowledge to improve human metabolic health.
... Additionally, a positive correlation of period length is observed between the circadian expression of fibroblasts and physiology (Pagani et al., 2010). A rhythmic expression of clock genes (hClock, hBMal1, hPer2, and hCry1) is observed with explants of human adipose tissue (Gomez-Santos et al., 2009), and further variation in glucocorticoid-associated circadian gene expression has been observed between visceral and subcutaneous explants of adipose tissues (Gomez-Abellan et al., 2012). In the process of understanding the human circadian system, RNA interference (RNAi) technology has been used to modulate the endogenous amplitude of gene expression for understanding the variation of circadian properties in the human circadian system using osteosarcoma cell lines (Zhang et al., 2009). ...
In the course of evolution, health is prioritized for human well‐being and economies. Epidemiological and experimental studies suggest that modern life habits, including eating habits, and living and working conditions, can deteriorate health through circadian misalignment. This has been most commonly observed with urban societies and working classes of non‐standard working schedules (NSWSs), such as shift work, night work, and overtime work. Poor health conditions with NSWSs generate economic burden for the modern society. Therefore, we attempt to provide a systematic approach to understanding the relations among the circadian clock, health, and economics. To understand these connections, we review the mechanisms of the human circadian clock and how modern living conditions can misalign the circadian system and associated health consequences. We also emphasize the importance of health for the modern economy and the economic costs of health disorders associated with circadian disruption and NSWSs.
... Clock genes compose the molecular systems of circadian rhythms. Clock genes are expressed in peripheral tissues and oscillate twenty four hour cycle by forming transcriptional and translational feedback loops 2,3) . ...
Tumor microenvironment is related to growth, survival, invasion, and metastasis of tumor cells. Several studies have proved that stromal fibroblasts play an important role in the tumor microenvironment to convert cancer-associated fibroblast （CAFs）. Clock genes are known to regulate circadian rhythms, angiogenesis, and immunoreaction. In addition, clock genes play an important role in cancer development. However, little has been shown about how these clock genes function in the tumor microenvironment. In the present study, we investigated to evaluate the effect of co-culture fibroblasts with oral cancer cells on the expression of clock genes. Following the coculture of human primary fibroblasts with human gingival carcinoma Ca9-22 cells, the expression levels of clock genes were analyzed by real-time quantitative PCR. We found that the rhythmic expression of clock genes were altered,enhanced, or disappeared by the co-culture. Such effect was observed not only in fibroblasts in the presence of Ca9-22 cells but also in Ca9-22 cells in the presence of fibroblasts. Our results suggested that clock genes might affect an important role in the tumor microenvironment.
... Different WAT depots have different functions, and increase and reduce their mass differentially, as illustrated by several metabolic disorders that result in loss of mainly subcutaneous or gain of mainly intra-abdominal (visceral) fat mass. Rhythmicity plays an important role in lipid metabolism, and clock gene rhythms have been described for some but not all WAT depots in rodents (17)(18)(19)(20) and in humans (21,22). We, therefore, hypothesized that differences in rhythmicity might explain differences in depot function and analyzed rhythmicity of gene expression in subcutaneous and different intra-abdominal WAT depots. ...
White adipose tissue (WAT) is present in different depots throughout the body. Although all depots are exposed to systemic humoral signals, they are not functionally identical. Studies in clock gene knockout animals and in shift workers suggest that daily rhythmicity may play an important role in lipid metabolism. Differences in rhythmicity between fat depots might explain differences in depot function; therefore, we measured mRNA expression of clock genes and metabolic genes on a 3-h interval over a 24-h period in the subcutaneous inguinal depot and in the intra-abdominal perirenal, epididymal, and mesenteric depots of male Wistar rats. We analyzed rhythmicity using CircWave software. Additionally, we measured plasma concentrations of glucose, insulin, corticosterone, and leptin. The clock genes (Bmal1/Per2/Cry1/Cry2/RevErbα/DBP) showed robust daily gene expression rhythms, which did not vary between WAT depots. Metabolic gene expression rhythms (SREBP1c/PPARα/PPARγ/FAS/LPL/Glut4/HSL/CPT1b/leptin/visfatin/resistin) were more variable between depots. However, no distinct differences between intra-abdominal and subcutaneous rhythms were found. Concluding, specific fat depots are not associated with differences in clock gene expression rhythms and, therefore, do not provide a likely explanation for the differences in metabolic function between different fat depots.
... Numerous studies have reported that clock genes are expressed in peripheral human tissues or cells. Clock genes in those cell function as peripheral oscillators of the circadian rhythm, [41][42][43][44][45][46]. In this respect, the existence of a circadian clock within nasal mucosa was anticipated because numerous studies reported circadian variations in the pathophysiological functions of nasal mucosa. ...
Numerous peripheral tissues possess self-sustaining daily biologic rhythms that are regulated at the molecular level by clock genes such as PER1, PER2, CLOCK, and BMAL1. Physiological function of nasal mucosa exhibits rhythmic variability to a day-night environmental cycle. Nevertheless, little is known of the expression and distribution pattern of clock genes in nasal mucosa. The present study investigates the expression level and distribution pattern of PER1, PER2, CLOCK, and BMAL1 genes in nasal mucosa of healthy controls, allergic rhinitis patients, and normal rats. In human and rat nasal mucosa, the levels of these genes are asymmetrically expressed in nasal mucosa derived from right and left cavities in normal controls, allergic patients, and rat. In human nasal mucosa, the expression levels of these genes were higher in the decongested side than the congested mucosa. In rat nasal mucosa, these clock genes are expressed in a rhythmic circadian manner under the regular light/dark cycles. The expression levels of MUC5AC, a key mucin genes produced in superficial epithelium, are higher in decongested side than that congested side in human nasal mucosa. In rat nasal mucosa, MUC5AC levels showed a circadian rhythm which was associated with different expression levels in nasal mucosa derived from the right and left nasal cavities. Taken together with these results, the present study shows that the clock genes such as PER1, PER2, CLOCK, and BMAL1 are present in human and rat nasal mucosa, and suggest that these clock genes may control the pathophysiological function of nasal mucosa as circadian oscillators and affect the maintenance of the nasal cycle.
... In addition, it is possible that a phase shift or change in amplitude in this local PVAT homeostatic control of BP during the resting phase may be associated with adverse cardiovascular outcomes in shift workers and individuals with jet lag. 66 Furthermore, the PVAT peripheral clock may be altered in the context of obesity, which is known to cause both PVAT dysfunction 67,68 and overall disruption of systemic circadian cycles. 69 Future studies should also address the molecular aspects of cross-communication between known drivers of systemic oscillation of BP and the synchronization of the local PVAT peripheral clock. ...
Background
-The perivascular adipose tissue (PVAT), surrounding vessels, constitutes a distinct functional integral layer of the vasculature required to preserve vascular tone under physiological conditions. However, there is little information regarding the relationship between PVAT and blood pressure regulation, including its potential contributions to circadian blood pressure variation.
Methods
-Using unique brown adipocyte-specific aryl hydrocarbon receptor nuclear translocator-like protein 1 (Bmal1) and angiotensinogen (Agt) knock out mice we determined the vasoactivity of homogenized PVAT in aortic rings and how brown-adipocyte peripheral expression of Bmal1 and Agt in PVAT regulate the amplitude of diurnal change in blood pressure in mice.
Results
-We uncovered a peripheral clock in PVAT and demonstrated that loss of Bmal1 in PVAT reduces blood pressure in mice during the resting phase leading to a super-dipper phenotype. PVAT extracts from wild type mice significantly induced contractility of isolated aortic ringsin vitroin an endothelium independent manner. This property was impaired in PVAT from brown adipocyte-selective Bmal1 deficient mice (BA-Bmal1-KO). The PVAT contractile properties are mediated by local angiotensin II (Ang II), operating through angiotensin II type 1 receptor-dependent signaling in the isolated vessels and is linked to PVAT circadian regulation of Agt. Indeed, Agt mRNA and Ang II levels in PVAT of BA-Bmal1-KO mice were significantly reduced. Systemic infusion of Ang II, in turn, reduced Bmal1 expression in PVAT while eliminating the hypotensive phenotype during the resting phase in BA-Bmal1-KOmice. Agt, highly expressed in PVAT, shows circadian expression in PVAT and selective deletion of Agt in brown adipocytes recapitulates the phenotype of selective deletion of Bmal1 in brown adipocytes. Furthermore, Agt is a transcriptional target of Bmal1 in PVAT.
Conclusions
-These data indicate that local Bmal1 in PVAT regulates Agt expression and the ensuing increase in Ang II, which acts on smooth muscle cells (SMCs) in the vessel walls to regulate vasoactivity and blood pressure on a circadian fashion during the resting phase. These findings will contribute to better understand cardiovascular complications of circadian disorders, alterations in the circadian dipping phenotype and the crosstalk between systemic and peripheral regulation of blood pressure.
... A wide range of melatonin physiological functions includes its anti-inflammatory and immunomodulatory actions, as well as its potent direct and indirect antioxidant properties [16,21,23]. Many metabolic processes in adipose tissue, including the expression and secretion of some adipokines, are under circadian control [24,25]. This regulation may be at least partly mediated by melatonin, which could have actions on WAT by means of its membrane receptors or via an action on the sympathetic nervous system [26,27]. ...
Obesity is one of the major global health problems. Melatonin deficiency has been demonstrated to correlate with obesity. The aim of the study was to estimate the effect of melatonin on oxidative stress and adipokine levels in obese patients on a calorie-restricted diet. Thirty obese patients were supplemented with a daily dose of 10 mg of melatonin ( n=15 ) or placebo ( n=15 ) for 30 days with a calorie-restricted diet. Serum levels of melatonin, 4-hydroxynonenal (HNE), adiponectin, omentin-1, leptin, and resistin, as well as erythrocytic malondialdehyde (MDA) concentration and Zn/Cu-superoxide dismutase, catalase, and glutathione peroxidase (GPx) activities, were measured at baseline and after supplementation. Significant body weight reduction was observed only in the melatonin group. After melatonin supplementation, the adiponectin and omentin-1 levels and GPx activities statistically increased, whereas the MDA concentrations were reduced. In the placebo group, a significant rise in the HNE and a drop in the melatonin concentrations were found. The results show evidence of increased oxidative stress accompanying calorie restriction. Melatonin supplementation facilitated body weight reduction, improved the antioxidant defense, and regulated adipokine secretion. The findings strongly suggest that melatonin should be considered in obesity management. This trial is registered with CTRI/2017/07/009093 .
... 253 Moreover, epidemiological studies show that shift work is associated with obesity, hypertriglyceridemia, low HDL-C, abdominal obesity, T2DM, and CVD. 254 Experiments performed in animal models and in tissue culture 255,256 are contributing to a deeper knowledge of the relationship between chronobiology and MetS. 257 Although there is an effect of the endogenous circadian clock on multiple human metabolic pathways, 258 modifications of sleep or other external synchronizers of the internal clock, such as light intensity, and changes from fasting to eating and from resting to activity may alter the circadian system. ...
The importance of metabolic syndrome (MetS) lies in its associated risk of cardiovascular disease and type 2 diabetes, as well as other harmful conditions such as nonalcoholic fatty liver disease. In this report, the available scientific evidence on the associations between lifestyle changes and MetS and its components is reviewed to derive recommendations for MetS prevention and management. Weight loss through an energy-restricted diet together with increased energy expenditure. © The Author(s) 2017. Published by Oxford University Press on behalf of the International Life Sciences Institute.
... In vitro and in vivo experiments reveal rhythmic expression of clock genes in different white adipose depots in rodents [16][17][18] and humans. [19][20][21][22][23][24] In line with this, several hundreds of genes display a diurnal expression rhythm in the adipose tissue of rodent 4,17,25,26 and human, 21 some of which are involved in core adipose functions such as lipolysis, adipogenesis, and metabolic inflammation (detailed genes are specified in Figure 2). 18,21,25 The role of the circadian clock machinery in adipocyte physiology has been described in both in vitro and in animal studies. ...
Most organisms adapt to the 24-h cycle of the Earth’s rotation by anticipating the time of day through light–dark processes. The biological clock is crucial for the survival of living organisms and environmental adaptation. Current research suggests that this periodicity comprises a multi-feedback loop of transcriptional and translational regulation of genes related to the biological clock, with a core mechanism regulating near 24-h rhythmic oscillations. With the rapid development of life sciences, epigenetic regulation has become a prominent area of research. During biological clock oscillations, gene expression is closely linked to epigenetic modifications of chromatin. In this review, we explore the molecular regulatory mechanisms of the biological clock and its impact on nutrient metabolism, focusing on the interplay between circadian biology and epigenetic modifications. We also highlight the effects of dysbiosis on human health.
The menstrual cycle is a loop involving the interplay of different organs and hormones, with the capacity to impact numerous physiological processes, including body temperature and heart rate, which in turn display menstrual rhythms. The advent of wearable devices that can continuously track physiological data opens the possibility of using these prolonged time series of skin temperature data to noninvasively detect the temperature variations that occur in ovulatory menstrual cycles. Here, we show that the menstrual skin temperature variation is better represented by a model of oscillation, the cosinor, than by a biphasic square wave model. We describe how applying a cosinor model to a menstrual cycle of distal skin temperature data can be used to assess whether the data oscillate or not, and in cases of oscillation, rhythm metrics for the cycle, including mesor, amplitude, and acrophase, can be obtained. We apply the method to wearable temperature data collected at a minute resolution each day from 120 female individuals over a menstrual cycle to illustrate how the method can be used to derive and present menstrual cycle characteristics, which can be used in other analyses examining indicators of female health. The cosinor method, frequently used in circadian rhythms studies, can be employed in research to facilitate the assessment of menstrual cycle effects on physiological parameters, and in clinical settings to use the characteristics of the menstrual cycles as health markers or to facilitate menstrual chronotherapy.
The effect of oleic acid (OA) on the regulation of the circadian rhythm present in human visceral (VAT) and subcutaneous (SAT) adipose tissue from patients with morbid obesity has not been analyzed yet. VAT and SAT explants from patients with morbid obesity were incubated with OA to analyze the circadian regulation of clock and other genes related to lipid metabolism (SREBP-1c, FAS, LPL and CPT1), and their association with baseline variables and the improvement of these patients after bariatric surgery. There were significant differences in amplitude and acrophase in VAT with respect to SAT. In VAT, body weight negatively correlated with BMAL1 and CRY1 amplitude, and REVERBα acrophase; body mass index (BMI) negatively correlated with REVERBα acrophase; and waist circumference negatively correlated with PER3 acrophase. In SAT, BMI negatively correlated with CLOCK amplitude, and CLOCK, REVERBα and CRY2 MESOR; and waist circumference negatively correlated with PER3 amplitude and acrophase. A greater short-term improvement of body weight, BMI and waist circumference in patients with morbid obesity after bariatric surgery was associated with a lower CRY1 and CRY2 amplitude and an earlier PER1 and PER3 acrophase in SAT. OA produced a more relevant circadian rhythm and increased the amplitude of most clock genes and lipid metabolism-related genes. OA regulated the acrophase of most clock genes in VAT and SAT, placing CLOCK/BMAL1 in antiphase with regard to the other genes. OA increased the circadian rhythmicity, although with slight differences between adipose tissues. These differences could determine its different behaviour in obesity.
Mammalian circadian rhythms are controlled by a master pacemaker located in the suprachiasmatic nuclei (SCN), which is synchronized to the environment by photic and nonphotic stimuli. One of the main functions of the SCN is to regulate peripheral oscillators to set temporal variations in the homeostatic control of physiology and metabolism. In this sense, the SCN coordinate the activity/rest and feeding/fasting rhythms setting the timing of food intake, energy expenditure, thermogenesis, and active and basal metabolism. One of the major time cues to the periphery is the nocturnal melatonin, which is synthesized and secreted by the pineal gland. Under SCN control, arylalkylamine N-acetyltransferase (AA-NAT)—the main enzyme regulating melatonin synthesis in vertebrates—is activated at night by sympathetic innervation that includes the superior cervical ganglia (SCG). Bilateral surgical removal of the superior cervical ganglia (SCGx) is considered a reliable procedure to completely prevent the nocturnal AA-NAT activation, irreversibly suppressing melatonin rhythmicity. In the present work, we studied the effects of SCGx on rat metabolic parameters and diurnal rhythms of feeding and locomotor activity. We found a significant difference between SCGx and sham-operated rats in metabolic variables such as an increased body weight/food intake ratio, increased adipose tissue, and decreased glycemia with a normal glucose tolerance. An analysis of locomotor activity and feeding rhythms showed an increased daytime (lights on) activity (including food consumption) in the SCGx group. These alterations suggest that superior cervical ganglia-related feedback mechanisms play a role in SCN-periphery phase coordination and that SCGx is a valid model without brain-invasive surgery to explore how sympathetic innervation affects daily (24 h) patterns of activity, food consumption and, ultimately, its role in metabolism homeostasis.
The circadian clock is a self-sustained molecular timekeeper that drives 24-hour (circadian) rhythms in animals. The clock governs important aspects of behavior and physiology including wake/sleep activity cycles that regulate the activity of metabolic and digestive systems. Light/dark cycles (photoperiod) and cycles in the time of feeding synchronize the circadian clock to the surrounding environment, providing an anticipatory benefit that promotes digestive health. The availability of animal models targeting the genetic components of the circadian clock has made it possible to investigate the circadian clock's role in cellular functions. Circadian clock genes have been shown to regulate the physiological function of hepatocytes, gastrointestinal cells, and adipocytes; disruption of the circadian clock leads to the exacerbation of liver diseases and liver cancer, inflammatory bowel disease and colorectal cancer, and obesity. Previous findings provide strong evidence that the circadian clock plays an integral role in digestive/metabolic disease pathogenesis, hence, the circadian clock is a necessary component in metabolic and digestive health and homeostasis. Circadian rhythms and circadian clock function provide an opportunity to improve the prevention and treatment of digestive and metabolic diseases by aligning digestive system tissue with the 24-hour day.
Circadian oscillators are the body’s biological clocks which exhibited in most of living organisms from bacteria to higher vertebrates. They are responsible for organizing a variety of biochemical and physiological cellular functions with a rhythmic period of a day cycle (24 h, circadian, repeat cycle in a day) even without any timing indicators. Any disruption in synchronization of circadian rhythm (chronodistruption) causes a wide range of complications which can be referred to as metabolic syndrome, obesity or type 2 diabetes mellitus (T2DM). Food intake can be stimulated because of its hedonic properties, although energy need is sufficiently provided. Addiction can be determined as excessive intake of either drug or food. Drug and food addiction shares some similar hedonic neuroadaptative properties in perception reward circuits. That could be as a result of childhood physical or psychological trauma by increasing neurotransmitter hypersensivity or dysregulation. Circadian clocks are key players of hormone synthesis and release, which cause cellular adaptations to the body environment. Ion channels are protein structured gate keepers located in the cell membrane, allowing charged ions to move across the membrane. They contribute and regulate many of cellular functions in the body. Ion channels act as an important player in circadian phases and also subsequent physiological functions by contributing in signaling pathway including homeostasis, gene expression, etc. Hence, this review focuses on the importance of chronobiology and its role on prevention of obesity, T2DM and regulation of the ion channels by circadian rhythm.
Adipose tissue (AT) is a key metabolic organ which functions are rhythmically regulated by an endogenous circadian clock. Feeding is a zeitgeber aligning the clock in AT with the external time but mechanisms of this regulation remain largely unclear. We tested the hypothesis that postprandial changes of the hormone insulin directly entrain circadian clocks in AT and investigated transcriptional-dependent mechanism of this regulation. We analysed gene expression in subcutaneous AT (SAT) of obese subjects collected before and after the hyperinsulinemic-euglycemic clamp (EC) or control saline infusion (SC). The expression of core clock gene PER2, PER3 and NR1D1 in SAT were differentially changed upon insulin and saline infusion suggesting insulin-dependent clock regulation. In human stem cell-derived adipocytes, mouse 3T3-L1 cells and AT explants from mPer2Luc knockin mice, insulin induced a transient increase of the Per2 mRNA and protein expression leading to the phase shift of circadian oscillations and showing similar effects for Per1 Insulin effects were dependent on the region between the -64 and -43 in the Per2 promoter, but not on CRE and E-box elements. Our results demonstrate that insulin directly regulates circadian clocks in AT and isolated adipocytes and thus represent a primary mechanism of feeding-induced AT clock entrainment.
Chrononutrition is the science that investigates the correlations between mealtimes, metabolism, physiology, and endogenous circadian rhythms, but it also outlines a diet in harmony with biological biorhythms, one of the main processes that is involved in healthiness, causing, if altered, many diseases and syndromes associated with the aging process. These rhythms originate in the hypothalamic suprachiasmatic nucleus (SCN), located in the anterior hypothalamus, and it is mainly controlled by the oscillations, an important type of cellular signaling characterized by the periodic change of the system over time. The oscillation originating in the suprachiasmatic nucleus (SCN) is known as the central oscillator, and all other similar signals are named peripheral oscillations. These rhythms are not only regulated by these endogenous signals, but it may be entrained by external signals named zeitgebers, such as light, exercise, and meal times. The worst outcome of the deregulation of the physiological circadian rhythms is chronodisruption, which consists of desynchronization of peripheral oscillators from the central one. Some causes of this phenomenon are night work and jet lag, including social jet lag, for example, the discrepancy in a person's sleep pattern between the weekday and the weekend which, if continued chronically, have been associated with an increased risk of metabolic syndrome, obesity, and cardiovascular disease, all pathological conditions associated with aging. Both a low-calorie diet and the regular use of functional and mimetic compounds could be the nutritional basis for promoting health in aging, obviously only together with all the other measures that characterize a correct lifestyle. The optimal diet model for that is the one inspired by the food choices typical of the Mediterranean model with oriental influences and adopt a calorie intake that, depending on the proposed diet, provides a quantity of calories that is between a range of 15%–20% around the basal metabolic rate in subjects with a low level of physical activity. Furthermore, an optimal diet should provide a protein content of around 0.95–1 g/kg body weight and follow all other recommendations published by international nutrition companies. This chapter discusses what is currently known about genetics and physiology of the circadian rhythms and zeitgebers, as well as the main evidence regarding the chronodisruption correlations with obesity, metabolic syndrome, and cardiovascular diseases. Furthermore, here we try to gather chrononutrition main aspects with the best dietary regime for ensuring a successful aging.
Background & Aims
We investigated whether oleic acid (OA), one of the main components of the Mediterranean diet, participates in the regulation of the intestinal circadian rhythm in patients with morbid obesity.
Methods
Stomach and jejunum explants from patients with morbid obesity were incubated with oleic acid to analyze the regulation of clock genes.
Results
Stomach explants showed an altered circadian rhythm in CLOCK, BMAL1, REVERBα, CRY1, and CRY2, and an absence in PER1, PER2, PER3 and ghrelin (p>0.05). OA led to the emergence of rhythmicity in PER1, PER2, PER3 and ghrelin (p<0.05). Jejunum explants showed an altered circadian rhythm in CLOCK, BMAL1, PER1 and PER3, and an absence in PER2, REVERBα, CRY1, CRY2 and GLP1 (p>0.05). OA led to the emergence of rhythmicity in PER2, REVERBα, CRY1 and GLP1 (p<0.05), but not in CRY2 (p>0.05). OA restored the rhythmicity of acrophase and increased the amplitude for most of the genes studied in stomach and jejunum explants. OA placed PER1, PER2, PER3, REVERBα, CRY1 and CRY2 in antiphase with regard to CLOCK and BMAL1.
Conclusions
There is an alteration in circadian rhythm in stomach and jejunum explants in morbid obesity. OA restored the rhythmicity of the genes related with circadian rhythm, ghrelin and GLP1, although with slight differences between tissues, which could determine a different behaviour of the explants from jejunum and stomach in obesity.
Introduction/aim: Circadian rhythm disruption is emerging as a risk factor for metabolic disorders and particularly, alterations in clock genes circadian expression have been shown to influence insulin sensitivity. Recently, the reciprocal interplay between the circadian clock machinery and HPA axis has been largely demonstrated: the circadian clock may control the physiological circadian endogenous glucocorticoids secretion and action; glucocorticoids, in turn, are potent regulator of the circadian clock and their inappropriate replacement has been associated with metabolic impairment. The aim of the current study was to investigate in vitro the interaction between the timing-of-the-day exposure to different hydrocortisone (HC) concentrations on muscle insulin sensitivity.
Methods: Serum-shock synchronized mouse skeletal muscle C2C12 cells were exposed to different HC concentrations recapitulating the circulating daily physiological cortisol profile (standard cortisol profile), the circulating daily cortisol profile that reached in adrenal insufficient (AI) patients treated with once-daily MR-HC (flat cortisol profile) and treated with thrice-daily of conventional IR-HC (steep cortisol profile). The 24 hrs spontaneous oscillation of the clock genes in synchronized C2C12 cells was used to align the timing for in vitro HC exposure (Bmal1 acrophase, midphase and bathyphase) with the reference times of cortisol peaks in AI treated with IR-HC (8 am, 1 pm, 6 pm). A panel of 84 insulin sensitivity related genes and intracellular insulin signaling proteins were analyzed by RT-qPCR and western blot, respectively.
Results: Only the steep profile, characterized by a higher HC exposure during Bmal1 bathyphase, produced significant downregulation in 21 insulin sensitivity-related genes. Among these, Insr, Irs1, Irs2, Pi3kca and Adipor2 were downregulated when compared the flat to the standard or steep profile. Reduced intracellular IRS1 Tyr608, AKT Ser473, AMPK Thr172 and ACC Ser79 phosphorylations were also observed.
Conclusions: The current study demonstrated that is late-in-the-day cortisol exposure that modulates insulin sensitivity-related genes expression and intracellular insulin signaling in skeletal muscle cells.
The interaction of the maternal and fetal circadian systems is recognized as a crucial crosstalk for fetal development, which may be a key factor determining fitting health in adulthood. Unfortunately, in our modern societies the relevance of regular light/dark cycles has been dangerously disregarded, generating a disarray of the internal temporal order of circadian physiological functions (i.e. chronodisruption). In fact, it is well established that gestational circadian misalignment negatively affects gestation progression; probably through alteration of maternal melatonin transfer to the fetus, given that melatonin is inhibited by light at night, therefore depriving the fetus of a maternal light/dark signal. Mounting evidence supports that the intermittent circadian rhythm of melatonin induced by gestational chronodisruption provides an anomalous adaptive frame to the fetus, programming abnormal metabolic function in the adult. Indeed, adult male offspring gestated under chronodisruption displays a circadian disarray and several metabolic abnormalities, like increased body weight and adipose tissue mass, together with abnormal responses to glucose and insulin; suggestive of white adipose tissue dysfunction. Thus, gestational chronodisruption is akin to other human and animal models of Developmental Origin of Health and Disease.
In the current review we will discuss the role played by maternal circadian rhythms in fetal development and the impact of fetal-maternal desynchronization on offspring’s health and disease; with special focus on metabolic disorders and the role played by adipose tissue in the metabolic unbalance induced by chronodisruption.
Phototherapy was applied to treat medical conditions since 3,500 years, when the ancient Egyptians and Indians used sunlight to treat various diseases. It was only with the invention of electric light in the late 19th century that an alternative emerged. From that time on, the use of phototherapy in the medical field grew, techniques were perfected and developed and eventually gained widespread acceptance. To date, over 2000 scientific articles have been published in PubMed focusing on the various physiological effects of red and NIR radiation. These wavelengths of light have been shown to penetrate through human tissues and to locally and systematically influence cell metabolism, cell signalling, inflammatory processes and growth. This treatment is now called "photobiomodulation" (PBM) therapy. Despite the numerous studies reported, variability in irradiation settings and parameters has led to inconsistent outcomes. The greatest lack of knowledge is related to the effects of low wavelengths of blue/green light. Compared to red/NIR light, blue light is used for a limited range of medical applications because of its inhibitory and cytotoxic effects. However blue light effects have rarely been reported in adipogenesis or lipogenesis studies on adipose tissue. Hence, the biomodulatory potential of blue light at 453 nm wavelength was tested on 3T3-L1 cells during and after the differentiation process with respect to adipogenesis/lipogenesis, metabolic processes, cell proliferation and transcriptome changes. PBM using blue light revealed dose dependent effects during preadipocytes 3T3-L1 differentiation. A single irradiation performed at the first day of induction (Day0) led to a slight effect with a reduced lipid accumulation and changes in the expression of adipogenic markers that appeared down-regulated already after one exposure. Also metabolism, reflecting mitochondria activity, was negatively affected by blue light since oxidative phosphorylation and ATP contents were decreased with effects that were long lasting until 24h. Tests with repeated irradiations for all differentiation period showed an enhanced inhibition in lipid accumulation and metabolism. This chronic exposure was supposed to rise the ROS amount leading to DNA damages that have had as consequence a cell cycle delay, reduced proliferation rate and cell death processes. Gene expression analysis supported this hypothesis by an up-regulation of the p53 pathway and for all the other genes involved in repair systems such as ATM, Chk1 and Claspin. The blue light spectrum, being close to the harmful UVs wavelength, seems to induce cell death mediated by oxidative stress and damages accumulation in differentiating preadipocytes. On the other hand mature adipocytes treated with 21.6 j/cm2 or 43.2 j/cm2 of blue light have proven to be less responsive. No significant differences were reported in metabolism, growth and lipid storage. Similarly apoptosis has not been deregulated and no changes in ROS levels or cellular damages have been observed. In conclusion adipocytes seem to be more sensitive to blue light exposure during early rather than in late differentiation phases. Furthermore, the high doses of irradiation chosen led to inhibitory effects on metabolism and differentiation promoting cell death in preadipocytes subjected to chronic exposure while no effects were recorded in irradiated mature adipocytes. The results indicated that an optimal choice of irradiation parameters, particularly the dose or irradiation time, is important. Too high doses can lead to expected inhibitory but also deleterious effects on cells. Though inhibitory effects in adipogenesis or proliferation are requested relating to the treatment of hyperplastic obesity or dysregulation of lipid accumulation during childhood, the formation of aberrant cells has to be avoided. Therefore additional studies are needed to promote or reject blue light application in these fields. If tetraploid or aneuploid cells formation is not observed, blue light could be a possible alternative to pharmacological or surgical solutions in some obese subjects. However, there is currently no evidence of a possible application in hypertrophic obesity condition.
Our modern society and global economy require individuals to work under non-standard schedules to provide twenty-four-hour coverage for a large number of essential services. Despite the importance of these non-standard work schedules for production and logistical demands, they have a significant negative impact on the health of workers. Shift work and night work are recognized as risk factors for the development of a myriad of health-related problems due to the misalignment of circadian rhythms, chronic sleep deprivation, and exposure to light at night. The aim of this review is to provide an overview of the factors contributing to the detrimental effects of shift work on health and to highlight targeted interventions aimed at re-synchronizing the circadian system of those who work under shift schedules.
The molecular circadian clock plays a role in metabolic homeostasis. We tested the hypothesis obesity and systemic factors associated with insulin resistance affect skeletal muscle clock gene expression. We determined clock gene expression in skeletal muscle of obese women (n=5) and men (n=18) before and 6 months after Roux-en-Y gastric bypass (RYGB) surgery and normal weight controls (women n=6, men n=8). Skeletal muscle clock gene expression was affected by obesity and weight loss. CRY1 mRNA (P=0.05) was increased and DBP mRNA (P<0.05) was decreased in obese versus normal weight women and restored to control levels after RYGB-induced weight loss. CLOCK, CRY1, CRY2 and DBP mRNA (P<0.05) was decreased in obese men as compared to normal weight men. Expression of all other clock genes was unaltered by obesity or weight loss in both cohorts. We correlated clock gene expression with clinical characteristics of the participants. Among the genes studied, DBP and PER3 expression was inversely correlated with plasma lipids in both cohorts. Circadian time-course studies revealed that core clock genes oscillate over time (P<0.05), with BMAL1, CIART, CRY2, DBP, PER1 and PER3 expression profiles altered by palmitate treatment. In conclusion, skeletal muscle clock gene expression and function is altered by obesity, coincident with changes in plasma lipid levels. Palmitate exposure disrupts clock gene expression in myotubes, indicating dyslipidemia directly alters the circadian program. Strategies to reduce lipid overload and prevent elevations in NEFA and cholesterol levels may sustain circadian clock signals in skeletal muscle.
Over the course of evolution, nature has forced organisms under selection pressure to hardwire an internal time keeping device that defines 24 h of daily cycle of physiological and behavioral rhythms, known as circadian rhythms. At the cellular level, the cycle is governed by significant fractions of transcriptomes, which are under the control of transcriptional and translational feedback loop of clock genes. Intriguingly, this feedback loop is regulated at multiple stratums such as at the transcriptional and translational levels, which direct a cell towards producing a robust rhythm by sustaining the repeated stoichiometry of protein products. Moreover, with the advent of state of the art paradigms, epigenetic regulation of circadian rhythms has been becoming more evident at present time. Light-induced recurring fluctuations in chromatin acetylation concurrent with binding of RNA Pol II and integration of miRNAs monitor the chromatin modifiers or clock genes expression to drive temporal rhythmicity. Furthermore, CLOCK protein-intrinsic histone acetyl transferase activity, interaction of CLOCK-BMAL-1 with HAT enzymes, and involvement of many histone deacetylases also maintain the rhythmic protein profile. Additionally, critical role of rhythmic methylation pattern of clock genes in battery of cancer and metabolic disorders also defines its importance. Therefore, in this review, we focused in accumulating all the present data available on epigenetics and circadian rhythms. Interestingly, we also gathered evidence from the available literature pinpointing towards the dynamic nature of chromatin architecture governed by long and short-range regulatory elements DNA contacts arising daily, that was thought to be steady otherwise.
A plethora of physiological processes show stable and synchronized daily oscillations that are either driven or modulated by biological clocks. A circadian pacemaker located in the suprachiasmatic nucleus (SCN) of the ventral hypothalamus coordinates 24-hour oscillations of central and peripheral physiology with the environment. The circadian clockwork involved in driving rhythmic physiology is composed of various clock genes that are interlocked via a complex feedback loop to generate precise yet plastic oscillations of about 24-hours. This review focuses on the specific role of the core clockwork gene Period1 (Per1) and its paralogs on intra- and extra-oscillator functions, including but not limited to hippocampus-dependent processes, cardiovascular function, appetite control as well as glucose and lipid homeostasis. Alterations in Per gene function have been implicated in a wide range of physical and mental disorders. At the same time, a variety of conditions including metabolic disorders also impact clock gene expression resulting in circadian disruptions, which in turn often exacerbates the disease state.
Obesity is a major risk factor for the development of illnesses, such as insulin resistance and hypertension and has become a serious public health problem. Mammals have developed a circadian clock located in the hypothalamic suprachiasmatic nuclei (SCN) that responds to the environmental light-dark cycle. Clocks similar to the one located in the SCN are found in peripheral tissues, such as the kidney, liver and adipose tissue. The circadian clock regulates metabolism and energy homeostasis in peripheral tissues by mediating activity and/or expression of key metabolic enzymes and transport systems. Knockouts or mutations in clock genes that lead to disruption of cellular rhythmicity have provided evidence to the tight link between the circadian clock and metabolism. In addition, key proteins play a dual role in regulating the core clock mechanism as well as adipose tissue metabolism and link circadian rhythms with lipogenesis and lipolysis. Adipose tissues are distinguished as white, brown and beige (or brite), each with unique metabolic characteristics. Recently, the role of the circadian clock in regulating the differentiation into the different adipose tissues has been investigated. In this review, the role of clock proteins and the downstream signaling pathways in white, brown and brite adipose tissue function and differentiation will be reviewed. In addition, chronodisruption and metabolic disorders and clinical aspects of circadian adiposity will be addressed.
Timing of eating is recognized as a significant contributor to body weight regulation. Disruption of sleep-wake cycles from a predominantly diurnal (daytime) to a delayed (evening) lifestyle leads to altered circadian rhythms and metabolic dysfunction. This article reviews current evidence for timed and delayed eating in individuals of normal weight and those with overweight or obesity: some findings indicate a benefit of eating earlier in the daytime on weight and/or metabolic outcomes, although the findings have not been uniformly consistent, and more rigorous and longer-duration studies are needed. We also review potential circadian mechanisms resulting from the metabolic- and weight-related impact of changes in timing of eating. Further identification of mechanisms using deep phenotyping is required to determine targets for medical interventions for obesity and for prevention of metabolic syndrome and diabetes, and to inform clinical guidelines regarding eating schedules for management of weight and metabolic disease.
Adipocyte differentiation is a highly controlled process that has been extensively studied for the last 25 years. Two different kinds of in vitro experimental models, essential in determining the mechanisms involved in adipocyte proliferation, differentiation and adipokine secretion, are currently available: preadipocyte cell lines, already committed to the adipocyte lineage, and multipotent stem cell lines, able to commit to different lineages including adipose, bone and muscle lineage. Many different events contribute to the commitment of a mesenchymal stem cell into the adipocyte lineage, including the coordination of a complex network of transcription factors, cofactors and signalling intermediates from numerous pathways. New fat cells constantly arise from a preexisting population of undifferentiated progenitor cells or through the dedifferentiation of adipocytes to preadipocytes, which then proliferate and redifferentiate into mature adipocytes. Analysis of adipocyte turnover has shown that adipocytes are a dynamic and highly regulated population of cells. Adipogenesis is a multi-step process involving a cascade of transcription factors and cell-cycle proteins regulating gene expression and leading to adipocyte development. Several positive and negative regulators of this network have been elucidated in recent years. This review is focused in the main molecular and cellular processes associated with adipocyte differentiation, including transcriptional factors and cofactors and extranuclear modulators. The role of epigenetic factors, microRNAs and chronobiology in adipogenesis is also summarized.
From the pineal gland to the endocrine pancreas, the circadian timing system drives rhythms of hormone synthesis and secretion. Observation of rhythmic hormone secretion stimulated discovery in the field of chronobiology for well over a century and continues to present new and exciting challenges. Much of what we know about the biological basis of timing in physiology is fruit born of an effort to characterize the basis of hormonal oscillations. The advent of applied molecular genetics in circadian biology ushered in a wave of discovery, leading to characterization of the molecular basis of circadian rhythms in mammals. With this discovery came the revelation that nearly every cell and tissue in mammals harbors a circadian clock: a self-regulating transcription based oscillator of genetic regulatory factors. This benchmark stimulated an explosion of interest in the role for the molecular clock in the timing and amplitude of cellular and organismal physiology. As a field, interest rapidly turned to the elegant and persistent rhythms of hormone secretion. With this renewed focus, the last 10–15 years have been a time of high-paced discovery. We now know a great deal about molecular clock function in each of the major endocrine organs, including the pituitary gland, adrenal gland, pineal gland, gonads, adipose tissue, and endocrine pancreas. The impact of altered clock function in these tissues on physiology suggests strong functional links between the timing and endocrine systems. Understanding the depth and breadth of this integration will allow us to appreciate the complex mechanisms of basic endocrine physiology and possibly provide new and exciting avenues for the treatment of devastating and complex endocrine disorders.
Many mammalian peripheral tissues have circadian clocks(1-4); endogenous oscillators that generate transcriptional rhythms thought to be important for the daily timing of physiological processes(5,6). The extent of circadian gene regulation in peripheral tissues is unclear, and to what degree circadian regulation in different tissues involves common or specialized pathways is unknown. Here we report a comparative analysis of circadian gene expression in vivo in mouse liver and heart using oligonucleotide arrays representing 12,488 genes. We find that peripheral circadian gene regulation is extensive (greater than or equal to8-10% of the genes expressed in each tissue), that the distributions of circadian phases in the two tissues are markedly different, and that very few genes show circadian regulation in both tissues. This specificity of circadian regulation cannot be accounted for by tissue-specific gene expression. Despite this divergence, the clock-regulated genes in liver and heart participate in overlapping, extremely diverse processes. A core set of 37 genes with similar circadian regulation in both tissues includes candidates for new clock genes and output genes, and it contains genes responsive to circulating factors with circadian or diurnal rhythms.
To analyze, in morbid obese patients, the expression of several human genes regulating cortisol metabolism, such as glucocorticoid receptor (GR), 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1), 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2), stearoyl-acute regulatory protein (StAR), 5alpha-reductase type I (5alpha-R) and peroxisome proliferator-activated receptor-gamma (PPARgamma) in two different adipose depots. A second objective was to characterize the circadian rhythmicity of these genes in both adipose tissue (AT) regions.
Visceral and subcutaneous abdominal AT biopsies were obtained from obese patients (body mass index >or=40 kg m(-2)). To carry out rhythmic expression analysis, AT explants were cultured for 24 h and gene expression at times (T) 0, 6, 12 and 18 h, was performed with quantitative real-time PCR.
GR, 11betaHSD1 and PPARgamma genes were highly expressed in both subcutaneous and visceral depots. StAR and 5alpha-R genes were detected at lower levels. The expression of 11betaHSD2 was quantified in both AT depots with a higher expression in the visceral depot (P=0.032). Both sexes had similar gene expression levels, except for 5alpha-R (P=0.002). The genes studied showed circadian rhythmicity being more robust in visceral than in subcutaneous AT. Genes ranged in anti-phase between both depots (P=0.002). This rhythmicity was maintained in an AT culture.
We have shown for the first time circadian rhythmicity in glucocorticoid-related gene expression in human AT ex vivo. These results may have potential therapeutic implications with respect to the pathogenesis and treatment of diseases, such as obesity, type 2 diabetes and cardiovascular diseases.
Rev-ErbA alpha (Rev-Erb) is a nuclear hormone receptor-related transcriptional activator that is encoded on the noncoding strand of the alpha-thyroid hormone receptor (TR) gene. The similarities between Rev-Erb and receptors for differentiating agents, as well as the abundance of Rev-Erb mRNA in fat, led us to study Rev-Erb gene expression during adipogenesis. Remarkably, Rev-Erb mRNA levels increased dramatically during the differentiation of 3T3-L1 cells into adipocytes. Rev-Erb was similarly induced in the related 3T3-F442A cell line but not in nondifferentiating 3T3-C2 cells. The time course of Rev-Erb induction was similar to that of C/EBP alpha, an important transcriptional regulator in adipocytes, and Rev-Erb mRNA was superinduced by cycloheximide. Nuclear run-on assays indicated that an increased rate of Rev-Erb mRNA synthesis accounted for the increased steady state mRNA levels; the half-life of Rev-Erb mRNA was indistinguishable in preadipocytes and adipocytes. Treatment of preadipocytes with retinoic acid inhibited adipocyte differentiation and also prevented Rev-Erb induction. Thus, there is a correlation between Rev-Erb gene expression and differentiation, and transcriptional regulation by Rev-Erb could play an important role in the generation and/or maintenance of the adipocyte phenotype. Interestingly, and possibly related to the overlap between the Rev-Erb gene and the exon specific for TR alpha 2, the induction of Rev-Erb was also associated with a 3-fold increase in the ratio of TR alpha 1 to TR alpha 2 mRNA levels, indicating that Rev-Erb expression has the potential to modulate adipocyte gene expression by multiple mechanisms.
Many mammalian peripheral tissues have circadian clocks; endogenous oscillators that generate transcriptional rhythms thought to be important for the daily timing of physiological processes. The extent of circadian gene regulation in peripheral tissues is unclear, and to what degree circadian regulation in different tissues involves common or specialized pathways is unknown. Here we report a comparative analysis of circadian gene expression in vivo in mouse liver and heart using oligonucleotide arrays representing 12,488 genes. We find that peripheral circadian gene regulation is extensive (> or = 8-10% of the genes expressed in each tissue), that the distributions of circadian phases in the two tissues are markedly different, and that very few genes show circadian regulation in both tissues. This specificity of circadian regulation cannot be accounted for by tissue-specific gene expression. Despite this divergence, the clock-regulated genes in liver and heart participate in overlapping, extremely diverse processes. A core set of 37 genes with similar circadian regulation in both tissues includes candidates for new clock genes and output genes, and it contains genes responsive to circulating factors with circadian or diurnal rhythms.
Proapoptotic drugs such as docetaxel displayed least toxicity and highest antitumor efficacy following dosing during the circadian rest phase in mice, suggesting that cell cycle and apoptotic processes could be regulated by the circadian clock. In study 1, mouse bone marrow and/or tumor were obtained every 4 h for 24 h in C3H/HeN mice with or without MA13/C mammary adenocarcinoma in order to determine the circadian patterns in cell-cycle phase distribution and BCL-2 anti-apoptotic protein expression. In study 2, mouse bone marrow from B6D2F1 mice was sampled every 3 h for 24 h in order to confirm the BCL-2 rhythm and to study its relation with 24 h changes in the expression of proapoptotic BCL-2-associated X protein (BAX) protein and clock genes mPer2, mBmal1, mClock, and mTim mRNAs. The rhythms in G1-, S- or G2/M-phase cells were shifted in tumor compared with bone marrow. In the tumor, the mean proportion of G2/M-phase cells increased by 75% from late rest to late activity span (P from cosinor = 0.001). No 24 h rhythm was found for BCL-2 in tumors. In contrast to this, in the bone marrow, mean BCL-2 expression varied 2.8-fold in B6D2F1 mice (P=0.025) and 3- or 4.5-fold in tumor-bearing and nontumor-bearing C3H/HeN mice, with a peak during the early rest span (P=0.024 and P<0.001, respectively). BAX varied fivefold during the 24 h span with a major peak occurring near mid-activity (P=0.007). The mean mRNAs of mPer2, mClock, and mBmal1 varied twofold to threefold over the 24 h, with high values during the activity span (P<0.05). In the tumor, the circadian organization in cell-cycle phase distribution was shifted and BCL2 rhythm was ablated. Conversely, a molecular circadian clock likely regulated BCL-2 and BAX expression in the bone marrow, increasing cellular protection against apoptosis during the rest span.
Various peripheral tissues show circadian rhythmicity, which is generated at the cellular level by their own core oscillators that are composed of transcriptional/translational feedback loops involving a set of clock genes. Although the circulating levels of some adipocytokines, i.e. bioactive substances secreted by adipocytes, are on a 24-h rhythmic cycle, it remains to be elucidated whether the clock gene system works in adipose tissue. To address this issue, we investigated the daily mRNA expression profiles of the clock genes and adipocytokines in mouse perigonadal adipose tissues. In C57BL/6J mice, all transcript levels of the clock genes (Bmal1, Per1, Per2, Cry1, Cry2, and Dbp) and adipocytokines (adiponectin, resistin, and visfatin) clearly showed 24-h rhythms. On the other hand, the rhythmic expression of these genes was mildly attenuated in obese KK mice and greatly attenuated in more obese, diabetic KK-A(y) mice. Obese diabetes also diminished the rhythmic expression of the clock genes in the liver. Interestingly, a 2-wk treatment of KK and KK-A(y) mice with pioglitazone impaired the 24-h rhythmicity of the mRNA expression of the clock genes and adipocytokines despite the antidiabetic effect of the drug. In contrast, pioglitazone improved the attenuated rhythmicity in the liver. These findings suggest that the intracellular clock gene system acts in visceral adipose tissues as well as liver and is influenced by the conditions of obesity/type 2 diabetes and pioglitazone treatment.
Mice deficient in the circadian transcription factor BMAL1 (brain and muscle ARNT-like protein) have impaired circadian behavior and demonstrate loss of rhythmicity in the expression of target genes. Here we report that Bmal1(-/-) mice have reduced lifespans and display various symptoms of premature aging including sarcopenia, cataracts, less subcutaneous fat, organ shrinkage, and others. The early aging phenotype correlates with increased levels of reactive oxygen species in some tissues of the Bmal1(-/- )animals. These findings, together with data on CLOCK/BMAL1-dependent control of stress responses, may provide a mechanistic explanation for the early onset of age-related pathologies in the absence of BMAL1.
Rev-Erbα (NR1D1) is an orphan nuclear receptor encoded on the opposite strand of the thyroid receptor α gene. Rev-Erbα mRNA
is induced during adipocyte differentiation of 3T3-L1 cells, and its expression is abundant in rat adipose tissue. Peroxisome
proliferator-activated receptor γ (PPARγ) (NR1C3) is a nuclear receptor controlling adipocyte differentiation and insulin
sensitivity. Here we show that Rev-Erbα expression is induced by PPARγ activation with rosiglitazone in rat epididymal and
perirenal adipose tissues in vivo as well as in 3T3-L1 adipocytes in vitro. Furthermore, activated PPARγ induces Rev-Erbα promoter activity by binding to the direct repeat (DR)-2 response element
Rev-DR2. Mutations of the 5′ or 3′ half-sites of the response element totally abrogated PPARγ binding and transcriptional
activation, identifying this site as a novel type of functional PPARγ response element. Finally, ectopic expression of Rev-Erbα
in 3T3-L1 preadipocytes potentiated adipocyte differentiation induced by the PPARγ ligand rosiglitazone. These results identify
Rev-Erbα as a target gene of PPARγ in adipose tissue and demonstrate a role for this nuclear receptor as a promoter of adipocyte
differentiation.
The discovery of an internal temporal clockwork that coordinates behavior and metabolism according to the rising and setting of the sun was first revealed in flies and plants. However, in the past decade, a molecular transcription-translation feedback loop with similar properties has also been identified in mammals. In mammals, this transcriptional oscillator programs 24-hour cycles in sleep, activity and feeding within the master pacemaker neurons of the suprachiasmatic nucleus of the hypothalamus. More recent studies have shown that the core transcription mechanism is also present in other locations within the brain, in addition to many peripheral tissues. Processes ranging from glucose transport to gluconeogenesis, lipolysis, adipogenesis and mitochondrial oxidative phosphorylation are controlled through overlapping transcription networks that are tied to the clock and are thus time sensitive. Because disruption of tissue timing occurs when food intake, activity and sleep are altered, understanding how these many tissue clocks are synchronized to tick at the same time each day, and determining how each tissue 'senses time' set by these molecular clocks might open new insight into human disease, including disorders of sleep, circadian disruption, diabetes and obesity.
Clock genes play a role in adipose tissue (AT) in animal experimental models. However, it remains to be elucidated whether these genes are expressed in human AT.
We investigated the expression of several clock genes, Bmal1, Per2 and Cry1, in human AT from visceral and subcutaneous abdominal depots. A second objective was to elucidate whether these clock genes expressions were related to the metabolic syndrome features.
Visceral and subcutaneous AT samples were obtained from morbid obese men (n=8), age: 42+/-13 years and body mass index>/=40 kg/m(2), undergoing laparoscopic surgery due to obesity. Biopsies were taken as paired samples at the beginning of the surgical process (1100 hour). Metabolic syndrome features such as waist circumference, plasma glucose, triglycerides, total cholesterol, high-density lipoprotein cholesterol and low-density lipoprotein (LDL) cholesterol were also studied. Homeostasis model assessment index of insulin resistance was also calculated. The expression of the different clock genes, hBmal1, hPer2 and hCry1, was determined by quantitative real-time PCR.
Clock genes were expressed in both human AT depots. hBmal1 expression was significantly lower than hPer2 and hCry1 in both AT (P<0.001). All genes were highly correlated to one another in the subcutaneous fat, while no correlation was found between Bmal1 and Per2 in the visceral AT. Clock genes AT expression was associated with the metabolic syndrome parameters: hPer2 expression level from visceral depot was inversely correlated to waist circumference (P<0.01), while the three clock genes studied were significantly and negatively correlated to total cholesterol and LDL cholesterol (P<0.01).
We have demonstrated for the first time in humans that clock genes are expressed in both subcutaneous and visceral fat. Their association with abdominal fat content and cardiovascular risk factors may be an indicator of the potential role of these clock genes in the metabolic syndrome disturbances.
The two most commonly used methods to analyze data from real-time, quantitative PCR experiments are absolute quantification and relative quantification. Absolute quantification determines the input copy number, usually by relating the PCR signal to a standard curve. Relative quantification relates the PCR signal of the target transcript in a treatment group to that of another sample such as an untreated control. The 2(-DeltaDeltaCr) method is a convenient way to analyze the relative changes in gene expression from real-time quantitative PCR experiments. The purpose of this report is to present the derivation, assumptions, and applications of the 2(-DeltaDeltaCr) method. In addition, we present the derivation and applications of two variations of the 2(-DeltaDeltaCr) method that may be useful in the analysis of real-time, quantitative PCR data. (C) 2001 Elsevier science.
Circadian rhythms are such an innate part of our lives that we rarely pause to speculate why they even exist. Recently, some studies have suggested that the disruption of the circadian system may be causal for the manifestations of metabolic syndrome (MetS). This review summarizes the latest evidence of the existing interaction among chronobiology, genetics and MetS.
Shift work, sleep deprivation and bright light exposure at night are related to increased adiposity and prevalence of MetS. Animal models have revealed that mice with circadian locomotor output cycles kaput (clock) gene disruption are prone to develop a phenotype resembling MetS. Moreover, studies in humans have shown that clock genes are expressed in adipose tissue, and that both their levels of expression and their genetic variants correlate with different components of the MetS. Current studies are illustrating the particular role of different clock gene variants and their predicted haplotypes in MetS.
The circadian system has an important impact on metabolic disturbances and vice versa. Although the precise mechanism linking the MetS to chronodisruption is not well known, hypotheses point to the internal desynchronization between different circadian rhythms. The novelty of this area of research is contributing to the development of new and intriguing studies, particularly those focused on the association between different clock genes polymorphisms and MetS traits.
The treatment of cultured rat-1 fibroblasts or H35 hepatoma cells with high concentrations of serum induces the circadian expression of various genes whose transcription also oscillates in living animals. Oscillating genes include rper1 and rper2 (rat homologs of the Drosophila clock gene period), and the genes encoding the transcription factors Rev-Erb alpha, DBP, and TEF. In rat-1 fibroblasts, up to three consecutive daily oscillations with an average period length of 22.5 hr could be recorded. The temporal sequence of the various mRNA accumulation cycles is the same in cultured cells and in vivo. The serum shock of rat-1 fibroblasts also results in a transient stimulation of c-fos and rper expression and thus mimics light-induced immediate-early gene expression in the suprachiasmatic nucleus.
In mammals, circadian oscillators reside not only in the suprachiasmatic nucleus of the brain, which harbors the central pacemaker,
but also in most peripheral tissues. Here, we show that the glucocorticoid hormone analog dexamethasone induces circadian
gene expression in cultured rat-1 fibroblasts and transiently changes the phase of circadian gene expression in liver, kidney,
and heart. However, dexamethasone does not affect cyclic gene expression in neurons of the suprachiasmatic nucleus. This enabled
us to establish an apparent phase-shift response curve specifically for peripheral clocks in intact animals. In contrast to
the central clock, circadian oscillators in peripheral tissues appear to remain responsive to phase resetting throughout the
day.
The two most commonly used methods to analyze data from real-time, quantitative PCR experiments are absolute quantification and relative quantification. Absolute quantification determines the input copy number, usually by relating the PCR signal to a standard curve. Relative quantification relates the PCR signal of the target transcript in a treatment group to that of another sample such as an untreated control. The 2(-Delta Delta C(T)) method is a convenient way to analyze the relative changes in gene expression from real-time quantitative PCR experiments. The purpose of this report is to present the derivation, assumptions, and applications of the 2(-Delta Delta C(T)) method. In addition, we present the derivation and applications of two variations of the 2(-Delta Delta C(T)) method that may be useful in the analysis of real-time, quantitative PCR data.
For many years, neurons of the suprachiasmatic nucleus (SCN) in the hypothalamus were thought to contain the unique mammalian clock controlling circadian rhythmicity of peripheral tissues via neural and humoral signals. Surprisingly, the cloning and characterisation of mammalian clock genes have revealed that they are expressed in a circadian manner throughout the body. It is generally accepted now that peripheral cells contain a circadian clock which is similar to the one present in SCN neurons, although only the latter seems to be self-sustained. It is still unclear how these peripheral clocks are synchronised by the central SCN clock, albeit humoral signals appear to be crucial. Interestingly, peripheral clocks can be uncoupled from the central clock in particular conditions such as restricted-feeding, allowing peripheral tissues to adapt themselves to cues incompatible to other cues perceived by the SCN (mainly the photoperiod). Whereas circadian clocks have been intensively dissected, little is known about the mechanisms by which these clocks regulate the expression of clock-controlled genes. Direct regulation for some of them by the products of clock genes was recently documented, but this probably represents the exception rather than the rule. We should soon be able to describe complete circadian transcriptional cascades from clock genes to enzymes and structural proteins. In addition to circadian humoral and neural signals, these cascades should help us to understand how gene expression, physiology and behaviour are influenced by the rotation of the Earth around its axis.
Time in the biological sense is measured by cycles that range from
milliseconds to years. Circadian rhythms, which measure time on a scale of
24 h, are generated by one of the most ubiquitous and well-studied
timing systems. At the core of this timing mechanism is an intricate molecular
mechanism that ticks away in many different tissues throughout the body.
However, these independent rhythms are tamed by a master clock in the brain,
which coordinates tissue-specific rhythms according to light input it receives
from the outside world.
The mammalian circadian timing system is composed of a central pacemaker in the suprachiasmatic nucleus (SCN) of the brain and subsidiary oscillators in most peripheral cell types. While oscillators in SCN neurons are known to function in a self-sustained fashion, peripheral oscillators have been thought to damp rapidly when disconnected from the control exerted by the SCN. Using two reporter systems, we monitored circadian gene expression in NIH3T3 mouse fibroblasts in real time and in individual cells. In conjunction with mathematical modeling and cell co-culture experiments, these data demonstrated that in vitro cultured fibroblasts harbor self-sustained and cell-autonomous circadian clocks similar to those operative in SCN neurons. Circadian gene expression in fibroblasts continues during cell division, and our experiments unveiled unexpected interactions between the circadian clock and the cell division clock. Specifically, the circadian oscillator gates cytokinesis to defined time windows, and mitosis elicits phase shifts in circadian cycles.
Circadian ( approximately 24 h) rhythms in physiology and behaviour are observed in all mammals, including humans. These rhythms are generated by circadian clocks located in the hypothalamus and also in most peripheral tissues. Clock genes are essential components of circadian clocks, and mutations or polymorphisms within several of them have been associated with circadian disorders in humans. However, information about human clock gene expression has remained very limited. Peripheral blood mononuclear cells (PBMCs) represent an ideal material to investigate non-invasively the human clock at the molecular level. In the present study, we analysed the expression of three key clock genes, PER2, BMAL1 and REV-ERBalpha in PBMCs from ten healthy humans over a 24-h cycle. PER2 and BMAL1 were found to oscillate throughout the light-dark cycle in all subjects. Interestingly, despite normal melatonin and cortisol secretion patterns, two groups of subjects could be distinguished with significantly different mean PER2 and BMAL1 acrophases. BMAL1 oscillated with approximately the same phase as PER2, instead of being anti-phasic as anticipated from data previously obtained in other peripheral tissues. Furthermore, this unusual phase relationship of PER2 and BMAL1 in human PBMCs was associated with a constant expression of REV-ERBalpha, a crucial regulator of BMAL1, which is highly rhythmic in many other systems. These results reveal the existence of different chronotypes of clock gene expression patterns and suggest specific regulatory mechanisms in human PBMCs.
The master mammalian pacemaker in the brain controls numerous diverse physiological and behavioral processes throughout the organism. Timing information is continually transmitted from the master clock to peripheral organs to synchronize rhythmic daily oscillations of clock gene transcripts and control local physiology. To investigate the presence of peripheral clocks in the horse, quantitative real-time RT-PCR assays were designed to detect levels of equine clock genes. Expression profiles for Per2, Bmal1 and Cry1 were first determined in a synchronized equine cell line. Subsequently, expression in equine whole blood and adipose tissue was assessed. Robust circadian oscillations of Per2, Bmal1 and Cry1 were observed in vitro. A synchronized molecular clock was also demonstrated in equine adipose tissue although oscillation of Bmal1 was less robust than that of Per2 and Cry1. In contrast to previous studies in humans and rats however, there was no evidence of synchronized clock gene expression in equine peripheral blood. These studies suggest that synchronous control of clock gene oscillation in equine peripheral blood is not as tightly regulated as in other species and may reflect the influence of different evolutionary challenges modifying the function of a peripheral clock.
To establish a unified working diagnostic tool for the metabolic syndrome (MetS) that is convenient to use in clinical practice and that can be used world-wide so that data from different countries can be compared. An additional aim was to highlight areas where more research into the MetS is needed.
The International Diabetes Federation (IDF) convened a workshop held 12-14 May 2004 in London, UK. The 21 participants included experts in the fields of diabetes, public health, epidemiology, lipidology, genetics, metabolism, nutrition and cardiology. There were participants from each of the five continents as well as from the World Health Organization (WHO) and the National Cholesterol Education Program-Third Adult Treatment Panel (ATP III). The workshop was sponsored by an educational grant from AstraZeneca Pharmaceuticals.
The consensus statement emerged following detailed discussions at the IDF workshop. After the workshop, a writing group produced a consensus statement which was reviewed and approved by all participants.
The IDF has produced a new set of criteria for use both epidemiologically and in clinical practice world-wide with the aim of identifying people with the MetS to clarify the nature of the syndrome and to focus therapeutic strategies to reduce the long-term risk of cardiovascular disease. Guidance is included on how to compensate for differences in waist circumference and in regional adipose tissue distribution between different populations. The IDF has also produced recommendations for additional criteria that should be included when studying the MetS for research purposes. Finally, the IDF has identified areas where more studies are currently needed; these include research into the aetiology of the syndrome.
Although a number of genes expressed in most tissues, including the liver, exhibit circadian regulation, gene expression profiles are usually examined only at one scheduled time each day. In this study, we investigated the effects of obese diabetes on the hepatic mRNA levels of various genes at 6-h intervals over a single 24-h period. Microarray analysis revealed that many genes are expressed rhythmically, not only in control KK mice but also in obese diabetic KK-A(y) mice. Real-time quantitative PCR verified that 19 of 23 putative circadianly expressed genes showed significant 24-h rhythmicity in both strains. However, obese diabetes attenuated these expression rhythms in 10 of 19 genes. More importantly, the effects of obese diabetes were observed throughout the day in only two genes. These results suggest that observation time influences the results of gene expression analyses of genes expressed circadianly.
Chronic stress is associated with a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis consisting on disturbances on the cortisol response and lipid metabolism.
To evaluate the HPA axis activity in women from a Mediterranean area, comparing three different measurements: daily cortisol secretory variability, postprandial cortisol secretion and glucocorticoid feedback sensitivity. In addition, HPA axis disturbance is correlated with dietary habits and plasma fatty acid profiles.
The participants were 41 women born during the first 6 months of 1960 and living in a Mediterranean area (Murcia, Spain). They were of normal weight, with a waist circumference of 80.5 +/- 9.3 cm. Their salivary cortisol levels, 7-day dietary record and plasma fatty acid profile were evaluated. Daily cortisol variability and postlunch cortisol secretion were recorded and a dexamethasone suppression test is performed in order to detect possible HPA disturbance.
Both the methods used for HPA axis evaluation were positively correlated (r = 0.448, P = 0.004). Subjects with normal diurnal curves (high cortisol variability) showed significantly higher cortisol values in the morning and postprandial cortisol secretion than women with pathological curves (medium and low variability). Cortisol variability was inversely correlated with waist circumference (r = -0.312, P = 0.047), suggesting that a disturbed HPA axis response may lead to an android pattern of body fat distribution. Dietary fat and saturated fatty acid intake were lower in the high cortisol variability group, while monounsaturated fatty acid intake was higher (P < 0.05). No major differences were reported in plasma fatty acid profile.
A disturbed HPA axis is associated with abdominal fat distribution and a higher content of fat and saturated fatty acids in the diet. Women who chose a dietary pattern closer to the Mediterranean diet, with high monounsaturated fatty acid intake, showed lower levels on HPA axis disturbance.
Obesity is one of the most profound public health problems today, and simplistic explanations based on excessive nutritional consumption or lack of physical activity are inadequate to account for this dramatic and literal growth in our world population. Recent reports have suggested that disruptions in sleep patterns, often linked to our '24-h' lifestyle, are associated with increased body fat and altered metabolism, although the cause-effect relationship for these associations has yet to be elucidated. Abnormal sleep/wake patterns likely alter intracellular circadian clocks, which are molecular mechanisms that enable the cell/tissue/organism to anticipate diurnal variations in its environment. The environment may include circulating levels of nutrients (e.g. glucose, fatty acids and triglycerides) and various hormones (e.g. insulin, glucocorticoids). As such, alterations in this molecular mechanism, in particular within the adipocyte, likely induce metabolic changes that may potentiate disrupted metabolism, adipose accumulation and/or obesity. Although diurnal variations in adipokines and adipose tissue metabolism have been observed, little is known regarding the molecular mechanisms that influence these events.
Circadian oscillators play an indispensable role in the coordination of physiological processes with the cyclic changes in the physical environment. A significant number of recent clinical and molecular studies suggest that circadian biology may play an important role in the regulation of adipose and other metabolic tissue functions. In this discussion, we present the hypothesis that circadian dysfunction may be involved in the pathogenesis of obesity, type 2 diabetes, and the metabolic syndrome.
Genes encoding the circadian transcriptional apparatus exhibit robust oscillatory expression in murine adipose tissues. This study tests the hypothesis that human subcutaneous adipose-derived stem cells (ASCs) provide an in vitro model in which to monitor the activity of the core circadian transcriptional apparatus.
Primary cultures of undifferentiated or adipocyte-differentiated ASCs were treated with dexamethasone, rosiglitazone, or 30% fetal bovine serum. The response of undifferentiated ASCs to dexamethasone was further evaluated in the presence of lithium chloride. Lithium inhibits glycogen synthase kinase 3, a key component of the circadian apparatus. Total RNA was harvested at 4-hour intervals over 48 hours and examined by real-time reverse transcription polymerase chain reaction (RT-PCR).
Adipocyte-differentiated cells responded more rapidly to treatments than their donor-matched undifferentiated controls; however, the period of the circadian gene oscillation was longer in the adipocyte-differentiated cells. Dexamethasone generated circadian gene expression patterns with mean periods of 25.4 and 26.7 hours in undifferentiated and adipocyte-differentiated ASCs, respectively. Both rosiglitazone and serum shock generated a significantly longer period in adipocyte-differentiated ASCs relative to undifferentiated ASCs. The Bmal1 profile was phase-shifted by approximately 8 to 12 hours relative to Per1, Per3, and Cry2, consistent with their expression in vivo. Lithium chloride inhibited adipogenesis and significantly lengthened the period of Per3 and Rev-erbalpha gene expression profiles by >5 hours in dexamethasone-activated undifferentiated ASCs.
These results support the initial hypothesis and validate ASCs as an in vitro model for the analysis of circadian biology in human adipose tissue.
Although a change in lifestyle is the first choice in controlling cardiovascular risk, lipid-lowering drugs are effective in normalizing different forms of atherogenic dyslipidemia. Although statins are a class of drugs which primarily lower low-density lipoprotein cholesterol, fibrates decrease triglycerides, normalize the low-density lipoprotein cholesterol profile, and increase high-density lipoprotein cholesterol. As lipids are important determinants for cardiovascular diseases, these drugs reduce cardiovascular morbidity. However, a number of recent studies indicate that, in addition to their lipid-normalizing activities, statins and fibrates exhibit pleiotropic actions, such as inhibit inflammation, improve endothelial function, suppress the production of reactive oxygen species, etc. Statins are competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate-limiting enzyme of cholesterol synthesis, whereas fibrates are activators of the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha). The similarity between the pleiotropic effects of statins and fibrates is remarkable and suggests a mechanistic link between these two classes of drugs. Here we discuss recent data on the cross-talk between statins and PPARalpha agonists and the mechanisms behind these actions.
Night and shift work might be risk factors for metabolic and cardiovascular disorders due to interference with diet, circadian metabolic rhythms, and lifestyle. The relationship between permanent night work and metabolic and cardiovascular risk factors was explored in a retrospective longitudinal study of workers employed in a large municipal enterprise in charge of street cleaning and domestic waste collection. All subjects who had worked night shifts between 1976 and 2007 as hand sweepers, motor sweepers, and delivery tricar drivers were compared with subjects who always worked the same jobs but on day shifts. From the periodical medical surveillance files, we identified 488 male workers who had been examined on average five times (minimum 2, maximum 14) during the study period, for a total of 2,328 medical examinations; 157 always had worked day shifts, 12 always the night shift, and 319 both (initially day and subsequently night shifts). Their age ranged from 22 to 62 yrs, and work experience varied from 1 to 28 yrs. Lifestyle habits (smoking, alcohol consumption), body mass index, serum glucose, total cholesterol, tryglicerides, hepatic enzymes, blood pressure, resting electrocardiogram, diabetes, coronary heart disease, hypertension, and related drugs were taken into consideration for the analysis. We used generalized estimating equations (GEE) models (exchangeable correlation matrix) to analyze the relationship between night work and health effects while accounting for within-subject correlations and adjusting for study period, job, age, and lifestyle variables. As a whole, night workers smoked more and had significantly higher BMI, serum total cholesterol, and triglycerides than day workers. Both the inter-individual comparison between day and night workers and the intra-individual comparison among the workers, who were day workers at the beginning of their employment and later became night workers, showed a significant increase in BMI, total cholesterol, and tryglicerides associated with night work. No consistent effect was seen on fasting glucose, hepatic enzymes, and blood pressure, whereas a higher incidence of coronary heart disease was recorded in night workers.
Early aging and age-related pathologies in mice deficient in BMAL1, the core componentof the circadian clock
- R V Kondratov
- A A Kondratova
- V Y Gorbacheva
- O V Vykhovanets
- M P Antoch
Kondratov RV, Kondratova AA, Gorbacheva VY, Vykhovanets OV,
Antoch MP. Early aging and age-related pathologies in mice deficient
in BMAL1, the core componentof the circadian clock. Genes Dev
2006;20:1868-1873.
Early aging and age-related pathologies in mice deficient in BMAL1, the core componentof the circadian clock
- Kondratov
Extensive and divergent circadian gene expression in liver and heart
- Storch
Coordination of circadian timing in mammals
- Reppert