Regulation of the clock gene expression in human adipose tissue by weight loss

Circadian disruption, clock genes, and metabolic health

A growing body of research has identified circadian-rhythm disruption as a risk factor for metabolic health. However, the underlying biological basis remains complex, and complete molecular mechanisms are unknown. There is emerging evidence from animal and human research to suggest that the expression of core circadian genes, such as circadian locomotor output cycles kaput gene (CLOCK), brain and muscle ARNT-Like 1 gene (BMAL1), period (PER), and cyptochrome (CRY), and the consequent expression of hundreds of circadian output genes are integral to the regulation of cellular metabolism. These circadian mechanisms represent potential pathophysiological pathways linking circadian disruption to adverse metabolic health outcomes, including obesity, metabolic syndrome, and type 2 diabetes. Here, we aim to summarize select evidence from in vivo animal models and compare these results with epidemiologic research findings to advance understanding of existing foundational evidence and potential mechanistic links between circadian disruption and altered clock gene expression contributions to metabolic health-related pathologies. Findings have important implications for the treatment, prevention, and control of metabolic pathologies underlying leading causes of death and disability, including diabetes, cardiovascular disease, and cancer.

Chronomedicine Insights: Evaluating the Impact of Time-Restricted Meal Intake on Lipid Profile Parameters Among Individuals With Type 2 Diabetes in Northern India

INTRODUCTION

Time-restricted meal intake (TRM) has shown potential benefits such as enhanced insulin sensitivity, lowered blood sugar levels, and possible weight loss in individuals with type 2 diabetes mellitus (T2DM). Our study aimed to investigate the impact of TRM on lipid profile parameters such as total cholesterol (TC), triglycerides (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), and very low-density lipoprotein (VLDL) in fasting conditions in T2DM patients.

METHODS

In total, 400 patients from the endocrinology department at King George's Medical University (KGMU), Lucknow were enrolled in this study, adhering to the guidelines of the American Diabetes Association (ADA). Male and female patients with recently diagnosed T2DM (in the past five years), aged between 25 to 60 years, on oral anti-diabetic therapy excluding insulin, expressing willingness to provide written consent and to adhere to TRM were included in the TRM group. It was a longitudinal study as diabetic dyslipidemia is primarily caused by insulin resistance and nutritional reasons and we wanted to assess the effect of TRM on lipid profile in T2DM patients. Patients were enrolled via simple random sampling using the random number table method (computerized). The TRM group had an early dinner at 7 pm whereas the control group was of non-TRM/late-night eaters. TRM group was given comprehensive guidance including strategies to manage hunger, permissible beverage options (water and prescribed medication) during the fasting period, and daily maintenance of a diary documenting their timing, type, and quantity of food intake which they were requested to bring fortnightly. Emphasis was placed on recording even minor dietary items consumed throughout the day. The TRM group consumed food ad libitum during a 12-hour eating window from breakfast at 7 am to dinner at 7 pm. Data distribution was non-parametric. Mann-Whitney U test compared TRM and control group using mean values at baseline and follow-ups. Analysis used GraphPad Prism 9.2.0 software (GraphPad Inc., La Jolla, CA). A p-value less than 0.05 (p < 0.05) was considered statistically significant.

RESULTS

A total of 127 patients were lost to follow-up, resulting in 273 patients who completed the study. The mean value of TC in the TRM and non-TRM groups using the Mann-Whitney U test registered a highly significant p-value <0.0001 at 18 months, with a decrease of 14.17% from baseline in the TRM group and a decrease of 1.53% from baseline in the non-TRM group. The TRM group had a decrease of 24.75% in TG from a baseline value of 145.4±41.9, whereas the non-TRM group showed a decrease of 2.2% from a baseline value of 154.7±37.30 (p-value <0.0001). The TRM group showed an increase of 9.25% in HDL from a baseline value of 50.14±8.58; the non-TRM group showed an increase of 0.82% from a baseline value of 48.62±9.31 (p-value <0.0001). TRM group showed a decrease of 8.62% in LDL from a baseline value of 68.20±16.2 while the non-TRM group showed an increase of 1.54% from a baseline value of 65.38±19.3 (p-value <0.0002). The TRM group showed a decrease of 13.97% in VLDL from a baseline value of 32.20±18.7; the non-TRM group showed an increase of 4% from a baseline value of 30.16±24.2 (p-value <0.0001).

CONCLUSION

Our study's promising results underscore the potential of TRM as an effective strategy for managing dyslipidemia in individuals with T2DM, even over prolonged periods.

White adipose tissue: Distribution, molecular insights of impaired expandability, and its implication in fatty liver disease

We are far behind the 2025 World Health Organization (WHO) goal of a zero increase in obesity. Close to 360 million people in Latin America and the Caribbean are overweight, with the highest rates observed in the Bahamas, Mexico, and Chile. To achieve relevant progress against the obesity epidemic, scientific research is essential to establish uniform practices in the study of obesity pathophysiology (using pre-clinical and clinical models) that ensure accuracy, reproducibility, and transcendent outcomes. The present review focuses on relevant aspects of white adipose tissue (WAT) expansion, underlying mechanisms of inefficient expandability, and its repercussion in ectopic lipid accumulation in the liver during nutritional abundance. In addition, we highlight the potential role of disrupted circadian rhythm in WAT metabolism. Since genetic factors also play a key role in determining an individual's predisposition to weight gain, we describe the most relevant genes associated with obesity in the Mexican population, underlining that most of them are related to appetite control.

Subcutaneous adipose tissue circadian gene expression: Relationship with insulin sensitivity, obesity, and the effect of weight-reducing dietary intervention

OBJECTIVE

The circadian rhythms are controlled by the central clock in the hypothalamic suprachiasmatic nuclei and by the peripheral clocks in tissues, including adipose tissue. The adipose tissue circadian clock may be associated with the regulation of insulin action; however, human data are limited. The aim of this study was to analyze the expression of subcutaneous adipose tissue circadian genes as they relate to obesity and insulin sensitivity before and after diet-induced weight loss.

METHODS

The study group comprised 38 individuals who were overweight or obese. The individuals completed a 12-wk dietary intervention program. Hyperinsulinemic-euglycemic clamp and subcutaneous adipose tissue biopsy were performed before and after the program. Sixteen normal weight individuals were examined at baseline and served as a control group.

RESULTS

At baseline, individuals who were overweight/obese had lower adipose tissue expression of NR1D1, NR1D2, DBP, PER1, and PER2 than normal weight individuals. The expression of ARNTL, CLOCK, and CRY did not differ between the groups. A weight-reducing dietary intervention resulted in an increase in the expression of adipose tissue NR1D2 and DBP, which was positively related to insulin sensitivity both before (in the entire study group and in the subgroup of overweight/obese individuals) and after the dietary intervention.

CONCLUSIONS

Adipose tissue circadian gene expression is decreased in obesity and this decrease may be partially reversed by dietary intervention. Among circadian genes, NR1D2 and DBP seem to be specifically associated with insulin action.

Circadian Dysfunction in Adipose Tissue: Chronotherapy in Metabolic Diseases

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.

Multiple sclerosis and circadian rhythms: Can diet act as a treatment?

Multiple sclerosis (MS) is an autoimmune inflammatory and neurodegenerative disease of the central nervous system (CNS) with increasing incidence and prevalence. MS is associated with inflammatory and metabolic disturbances that, as preliminary human and animal data suggest, might be mediated by disruption of circadian rhythmicity. Nutrition habits can influence the risk for MS, and dietary interventions may be effective in modulating MS disease course. Chronotherapeutic approaches such as time-restricted eating (TRE) may benefit people with MS by stabilizing the circadian clock and restoring immunological and metabolic rhythms, thus potentially counteracting disease progression. This review provides a summary of selected studies on dietary intervention in MS, circadian rhythms, and their disruption in MS, including clock gene variations, circadian hormones, and retino-hypothalamic tract changes. Furthermore, we present studies that reported diurnal variations in MS, which might result from circadian disruption. And lastly, we suggest how chrononutritive approaches like TRE might counteract MS disease activity.

Acute and long-term exercise adaptation of adipose tissue and skeletal muscle in humans: a matched transcriptomics approach after 8-week training-intervention

BACKGROUND

Exercise exerts many health benefits by directly inducing molecular alterations in physically utilized skeletal muscle. Molecular adaptations of subcutaneous adipose tissue (SCAT) might also contribute to the prevention of metabolic diseases.

AIM

To characterize the response of human SCAT based on changes in transcripts and mitochondrial respiration to acute and repeated bouts of exercise in comparison to skeletal muscle.

METHODS

Sedentary participants (27 ± 4 yrs) with overweight or obesity underwent 8-week supervised endurance exercise 3×1h/week at 80% VO2peak. Before, 60 min after the first and last exercise bout and 5 days post intervention, biopsies were taken for transcriptomic analyses and high-resolution respirometry (n = 14, 8 female/6 male).

RESULTS

In SCAT, we found 37 acutely regulated transcripts (FC > 1.2, FDR < 10%) after the first exercise bout compared to 394, respectively, in skeletal muscle. Regulation of only 5 transcripts overlapped between tissues highlighting their differential response. Upstream and enrichment analyses revealed reduced transcripts of lipid uptake, storage and lipogenesis directly after exercise in SCAT and point to β-adrenergic regulation as potential major driver. The data also suggest an exercise-induced modulation of the circadian clock in SCAT. Neither term was associated with transcriptomic changes in skeletal muscle. No evidence for beigeing/browning was found in SCAT along with unchanged respiration.

CONCLUSIONS

Adipose tissue responds completely distinct from adaptations of skeletal muscle to exercise. The acute and repeated reduction in transcripts of lipid storage and lipogenesis, interconnected with a modulated circadian rhythm, can counteract metabolic syndrome progression toward diabetes.

Circadian stabilization loop: the regulatory hub and therapeutic target promoting circadian resilience and physiological health

The circadian clock is a fundamental biological mechanism that orchestrates essential cellular and physiological processes to optimize fitness and health. The basic functional unit is the cell-autonomous oscillator, consisting of intersecting negative feedback loops. Whereas the core loop is primarily responsible for rhythm generation, auxiliary loops, most notably the secondary or stabilization loop, play pivotal roles to confer temporal precision and molecular robustness. The stabilization loop contains opposing nuclear receptor subfamilies REV-ERBs and retinoic acid receptor-related orphan receptors (RORs), competing to modulate rhythmic expression of the basic helix-loop-helix ARNT like 1 ( Bmal1) genes in the core loop as well as other clock-controlled genes. Therefore, REV-ERBs and RORs are strategically located to interface the oscillator and the global transcriptomic network, promoting cellular homeostasis and physiological fitness throughout lifespan. Disruption of REV-ERB and ROR functions has been linked with diseases and aging, and pharmacological manipulation of these factors has shown promise in various mouse disease models. Nobiletin is a natural compound that directly binds to and activates RORα/γ, modulating circadian rhythms, and shows robust in vivo efficacies to combat clock-associated pathophysiologies and age-related decline. Results from several studies demonstrate an inverse relation between nobiletin efficacy and clock functional state, where nobiletin elicits little effect in young and healthy mice with growing efficacy as the clock is perturbed by environmental and genetic challenges. This mode of action is consistent with the function of the stabilization loop to promote circadian and physiological resilience. Future studies should further investigate the function and mechanism of REV-ERBs and RORs, and test strategies targeting these factors against disease and aging.

Circadian stabilization loop: the regulatory hub and therapeutic target promoting circadian resilience and physiological health

The circadian clock is a fundamental biological mechanism that orchestrates essential cellular and physiological processes to optimize fitness and health. The basic functional unit is the cell-autonomous oscillator, consisting of intersecting negative feedback loops. Whereas the core loop is primarily responsible for rhythm generation, auxiliary loops, most notably the secondary or stabilization loop, play pivotal roles to confer temporal precision and molecular robustness. The stabilization loop contains opposing nuclear receptor subfamilies REV-ERBs and retinoic acid receptor-related orphan receptors (RORs), competing to modulate rhythmic expression of the basic helix-loop-helix ARNT like 1 ( Bmal1) genes in the core loop as well as other clock-controlled genes. Therefore, REV-ERBs and RORs are strategically located to interface the oscillator and the global transcriptomic network, promoting cellular homeostasis and physiological fitness throughout lifespan. Disruption of REV-ERB and ROR functions has been linked with diseases and aging, and pharmacological manipulation of these factors has shown promise in various mouse disease models. Nobiletin is a natural compound that directly binds to and activates RORα/γ, modulating circadian rhythms, and shows robust in vivo efficacies to combat clock-associated pathophysiologies and age-related decline. Results from several studies demonstrate an inverse relation between nobiletin efficacy and clock functional state, where nobiletin elicits little effect in young and healthy mice with growing efficacy as the clock is perturbed by environmental and genetic challenges. This mode of action is consistent with the function of the stabilization loop to promote circadian and physiological resilience. Future studies should further investigate the function and mechanism of REV-ERBs and RORs, and test strategies targeting these factors against disease and aging.

Role of Circadian Transcription Factor Rev-Erb in Metabolism and Tissue Fibrosis

Circadian rhythms significantly affect metabolism, and their disruption leads to cardiometabolic diseases and fibrosis. The clock repressor Rev-Erb is mainly expressed in the liver, heart, lung, adipose tissue, skeletal muscles, and brain, recognized as a master regulator of metabolism, mitochondrial biogenesis, inflammatory response, and fibrosis. Fibrosis is the response of the body to injuries and chronic inflammation with the accumulation of extracellular matrix in tissues. Activation of myofibroblasts is a key factor in the development of organ fibrosis, initiated by hormones, growth factors, inflammatory cytokines, and mechanical stress. This review summarizes the importance of Rev-Erb in ECM remodeling and tissue fibrosis. In the heart, Rev-Erb activation has been shown to alleviate hypertrophy and increase exercise capacity. In the lung, Rev-Erb agonist reduced pulmonary fibrosis by suppressing fibroblast differentiation. In the liver, Rev-Erb inhibited inflammation and fibrosis by diminishing NF-κB activity. In adipose tissue, Rev- Erb agonists reduced fat mass. In summary, the results of multiple studies in preclinical models demonstrate that Rev-Erb is an attractive target for positively influencing dysregulated metabolism, inflammation, and fibrosis, but more specific tools and studies would be needed to increase the information base for the therapeutic potential of these substances interfering with the molecular clock.

The Shades of Grey in Adipose Tissue Reprogramming

The adipose tissue (AT) has a major role in contributing to obesity-related pathologies through regulating systemic immunometabolism. The pathogenicity of the AT is underpinned by its remarkable plasticity to be reprogrammed during obesity, in the perspectives of tissue morphology, extracellular matrix (ECM) composition, angiogenesis, immunometabolic homoeostasis and circadian rhythmicity. Dysregulation in these features escalates the pathogenesis conferred by this endometabolic organ. Intriguingly, the potential to be reprogrammed appears to be an Achilles’ heel of the obese AT that can be targeted for the management of obesity and its associated comorbidities. Here, we provide an overview of the reprogramming processes of white AT (WAT), with a focus on their dynamics and pleiotropic actions over local and systemic homoeostases, followed by a discussion of potential strategies favouring therapeutic reprogramming. The potential involvement of AT remodelling in the pathogenesis of COVID-19 is also discussed.

Effects of Early vs. Late Time-Restricted Eating on Cardiometabolic Health, Inflammation, and Sleep in Overweight and Obese Women: A Study Protocol for the ChronoFast Trial

Background: Time-restricted eating is a promising dietary strategy for weight loss, glucose and lipid metabolism improvements, and overall well-being. However, human studies demonstrated contradictory results for the restriction of food intake to the beginning (early TRE, eTRE) or to the end of the day (late TRE, lTRE) suggesting that more carefully controlled studies are needed.

Objective: The aim of the ChronoFast trial study is to determine whether eTRE or lTRE is a better dietary approach to improve cardiometabolic health upon minimized calorie deficits and nearly stable body weight.

Methods: Here, we present the study protocol of the randomized cross-over ChronoFast clinical trial comparing effects of 2 week eTRE (8:00 to 16:00 h) and lTRE (13:00 to 21:00 h) on insulin sensitivity and other glycemic traits, blood lipids, inflammation, and sleep quality in 30 women with overweight or obesity and increased risk of type 2 diabetes. To ensure timely compliance and unchanged dietary composition, and to minimize possible calorie deficits, real-time monitoring of dietary intake and body weight using a smartphone application, and extensive nutritional counseling are performed. Continuous glucose monitoring, oral glucose tolerance test, 24 h activity tracking, questionnaires, and gene expression analysis in adipose tissue and blood monocytes will be used for assessment of study outcomes.

Discussion: The trial will determine whether eTRE or lTRE is more effective to improve cardiometabolic health, elucidate underlying mechanisms, and contribute to the development of recommendations for medical practice and the wider population.

Clinical Trial Registration:www.ClinicalTrials.gov, Identifier [NCT04351672]

Insulin Directly Regulates the Circadian Clock in Adipose Tissue

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 a transcriptional-dependent mechanism of this regulation. We analyzed gene expression in subcutaneous AT (SAT) of obese subjects collected before and after the hyperinsulinemic-euglycemic clamp or control saline infusion (SC). The expressions of core clock genes 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 mPer2^Luc knockin mice, insulin induced a transient increase of the Per2 mRNA and protein expression, leading to the phase shift of circadian oscillations, with similar effects for Per1 Insulin effects were dependent on the region between -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, thus representing a primary mechanism of feeding-induced AT clock entrainment.

Transcriptomic analysis to elucidate the effects of high stocking density on grass carp (Ctenopharyngodon idella)

Background

Grass carp (Ctenopharyngodon idella) is one of the most widely cultivated fishes in China. High stocking density can reportedly affect fish growth and immunity. Herein we performed PacBio long-read single-molecule real-time (SMRT) sequencing and Illumina RNA sequencing to evaluate the effects of high stocking density on grass carp transcriptome.

Results

SMRT sequencing led to the identification of 33,773 genes (14,946 known and 18,827 new genes). From the structure analysis, 8,009 genes were detected with alternative splicing events, 10,219 genes showed alternative polyadenylation sites and 15,521 long noncoding RNAs. Further, 1,235, 962, and 213 differentially expressed genes (DEGs) were identified in the intestine, muscle, and brain tissues, respectively. We performed functional enrichment analyses of DEGs, and they were identified to be significantly enriched in nutrient metabolism and immune function. The expression levels of several genes encoding apolipoproteins and activities of enzymes involved in carbohydrate enzymolysis were found to be upregulated in the high stocking density group, indicating that lipid metabolism and carbohydrate decomposition were accelerated. Besides, four isoforms of grass carp major histocompatibility complex class II antigen alpha and beta chains in the aforementioned three tissue was showed at least a 4-fold decrease.

Conclusions

The results suggesting that fish farmed at high stocking densities face issues associated with the metabolism and immune system. To conclude, our results emphasize the importance of maintaining reasonable density in grass carp aquaculture.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07924-4.

Seasonal differences in clock gene expression levels in buccal epithelial cells of obese men: a pilot study

Various biological processes show seasonal variations in humans, including important metabolic pathways. Seasonal changes in gene expression may affect annual differences in human immunity. We hypothesized that seasonal changes occur in clock gene expression levels that are associated with body mass index. Six non-obese men and five obese men participated in summer and winter. Two milliliters of saliva were collected, and total RNA was isolated from buccal epithelial cells in saliva. The clock gene expression levels of CLOCK, BMAL1, PER1, CRY2, REV-ERB-α, and REV-ERB-ß were examined by real-time PCR. Blood samples were measured HbA1c, glucose, insulin, adiponectin, IL-6, and TNF-α. Participants were asked about their sleeping hours and seasonal pattern. In the present study, CLOCK, BMAL1, and REV-ERB-β gene expression levels were significantly lower in winter than in summer; BMAL1 expression level was significantly lower in obese men than in non-obese. Concentrations of adiponectin and insulin were significantly different between obese and non-obese. No significant seasonal effects were observed in HbA1c, glucose, insulin, adiponectin, IL-6, or TNF-α concentrations. Sleep duration did not significantly differ between summer and winter. The short photoperiod during winter might contribute to seasonal alterations in the expression of clock genes in men. In the present results, revealed seasonal differences in clock gene expression levels might be associated with obesity. These results also showed the potential for measuring clock gene expression in a non-invasive manner using saliva samples.

Circadian clock dysfunction in human omental fat links obesity to metabolic inflammation

To unravel the pathogenesis of obesity and its complications, we investigate the interplay between circadian clocks and NF-κB pathway in human adipose tissue. The circadian clock function is impaired in omental fat from obese patients. ChIP-seq analyses reveal that the core clock activator, BMAL1 binds to several thousand target genes. NF-κB competes with BMAL1 for transcriptional control of some targets and overall, BMAL1 chromatin binding occurs in close proximity to NF-κB consensus motifs. Obesity relocalizes BMAL1 occupancy genome-wide in human omental fat, thereby altering the transcription of numerous target genes involved in metabolic inflammation and adipose tissue remodeling. Eventually, clock dysfunction appears at early stages of obesity in mice and is corrected, together with impaired metabolism, by NF-κB inhibition. Collectively, our results reveal a relationship between NF-κB and the molecular clock in adipose tissue, which may contribute to obesity-related complications.

Oleic acid restores the rhythmicity of the disrupted circadian rhythm found in gastrointestinal explants from patients with morbid obesity

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.

Time Restricted Eating: A Dietary Strategy to Prevent and Treat Metabolic Disturbances

Time-restricted eating (TRE), a dietary approach limiting the daily eating window, has attracted increasing attention in media and research. The eating behavior in our modern society is often characterized by prolonged and erratic daily eating patterns, which might be associated with increased risk of obesity, diabetes, and cardiovascular diseases. In contrast, recent evidence suggests that TRE might support weight loss, improve cardiometabolic health, and overall wellbeing, but the data are controversial. The present work reviews how TRE affects glucose and lipid metabolism based on clinical trials published until June 2021. A range of trials demonstrated that TRE intervention lowered fasting and postprandial glucose levels in response to a standard meal or oral glucose tolerance test, as well as mean 24-h glucose and glycemic excursions assessed using continuous glucose monitoring. In addition, fasting insulin decreases and improvement of insulin sensitivity were demonstrated. These changes were often accompanied by the decrease of blood triglyceride and cholesterol levels. However, a number of studies found that TRE had either adverse or no effects on glycemic and lipid traits, which might be explained by the different study designs (i.e., fasting/eating duration, daytime of eating, changes of calorie intake, duration of intervention) and study subject cohorts (metabolic status, age, gender, chronotype, etc.). To summarize, TRE represents an attractive and easy-to-adapt dietary strategy for the prevention and therapy of glucose and lipid metabolic disturbances. However, carefully controlled future TRE studies are needed to confirm these effects to understand the underlying mechanisms and assess the applicability of personalized interventions.

Intermittent Fasting Does Not Uniformly Impact Genes Involved in Circadian Regulation in Women with Obesity

OBJECTIVE

This study aimed to examine the effects of intermittent fasting (IF) on mRNA levels of peripheral clock genes in skeletal muscle and subcutaneous adipose tissue (SAT) in women with obesity.

METHODS

Women were randomized to one of two IF protocols and provided with all foods at 100% or 70% of calculated weekly energy requirements for 8 weeks. Breakfast was consumed before a 24-hour fast, which was initiated on three nonconsecutive days per week. Muscle and SAT biopsies were performed at 8 am after an overnight fast at baseline and at week 8 on a refed day and again following a 24-hour fast at week 8 for analysis of the mRNA levels of key genes involved in circadian regulation.

RESULTS

A group-by-time interaction was observed in Per2 in muscle (F = 3.497, P = 0.044) and SAT (F = 6.686, P = 0.008), but significance was lost upon post hoc adjustment. A time effect was observed in Rorα in muscle, which was decreased by refeeding in both groups (F = 7.225, P = 0.003).

CONCLUSIONS

There was no universal effect of IF to alter peripheral clocks, which may be partly because of the alignment of the fasting/feeding cycle with the biological clock. Optimizing intermittent fasting protocols could be important to prevent circadian misalignment in humans.

Comparative Transcriptomic Analysis of Subcutaneous Adipose Tissue from Local Pig Breeds

When compared to modern lean-type breeds, Portuguese local Alentejano (AL) and Bísaro (BI) pig breeds present a high potential for subcutaneous and intramuscular fat (IMF) deposition which contributes for better meat quality. The aim of this work was to explore the genome function to better understand the underlying physiological mechanisms associated with body fat accretion. Dorsal subcutaneous fat samples were collected at slaughter from adult animals (n = 4 for each breed) with ~150 kg body weight. Total RNA was obtained and sequenced for transcriptome analysis using DESeq2. A total of 458 differentially expressed (DE) genes (q-value < 0.05) were identified, with 263 overexpressed in AL and 195 in BI. Key genes involved in de novo fatty acid biosynthesis, elongation and desaturation were upregulated in AL such as ACLY, FASN, ME1, ELOVL6 and SCD. A functional enrichment analysis of the DE genes was performed using Ingenuity Pathway Analysis. Cholesterol synthesis is suggested to be higher in AL via SREBF2, SCAP and PPARG, while lipolytic activity may be more active in BI through GH and AMPK signalling. Increased signalling of CD40 together with the predicted activation of INSIG1 and INSIG2 in BI suggests that this breed is more sensitive to insulin whereas the AL is less sensitive like the Iberian breed.

Targeting REV-ERBα for therapeutic purposes: promises and challenges

REV-ERBα (NR1D1) is a circadian clock component that functions as a transcriptional repressor. Due to its role in direct modulation of metabolic genes, REV-ERBα is regarded as an integrator of cell metabolism with circadian clock. Accordingly, REV-ERBα is first proposed as a drug target for treating sleep disorders and metabolic syndromes (e.g., dyslipidaemia, hyperglycaemia and obesity). Recent years of studies uncover a rather broad role of REV-ERBα in pathological conditions including local inflammatory diseases, heart failure and cancers. Moreover, REV-ERBα is involved in regulation of circadian drug metabolism that has implications in chronopharmacology. In the meantime, recent years have witnessed discovery of an array of new REV-ERBα ligands most of which have pharmacological activities in vivo. In this article, we review the regulatory role of REV-ERBα in various types of diseases and discuss the underlying mechanisms. We also describe the newly discovered ligands and the old ones together with their targeting potential. Despite well-established pharmacological effects of REV-ERBα ligands in animals (preclinical studies), no progress has been made regarding their translation to clinical trials. This implies certain challenges associated with drug development of REV-ERBα ligands. In particular, we discuss the potential challenges related to drug safety (or adverse effects) and bioavailability. For new drug development, it is advocated that REV-ERBα should be targeted to treat local diseases and a targeting drug should be locally distributed, avoiding the adverse effects on other tissues.

Physiological mechanisms underlying children's circannual growth patterns and their contributions to the obesity epidemic in elementary school age children

Several studies since the 1990s have demonstrated that children increase their body mass index at a faster rate during summer months compared with the school year, leading some to conclude that the out-of-school summer environment is responsible. Other studies, however, have suggested that seasonality may play a role in children's height and weight changes across the year. This article reviews evidence for seasonal differences in the rate of children's height and weight gain and proposes potential physiological mechanisms that may explain these seasonal variations.

The circadian rhythm in intervertebral disc degeneration: an autophagy connection

There is one circadian clock in the central nervous system and another in the peripheral organs, and the latter is driven by an autoregulatory molecular clock composed of several core clock genes. The height, water content, osmotic pressure and mechanical characteristics of intervertebral discs (IVDs) have been demonstrated to exhibit a circadian rhythm (CR). Recently, a molecular clock has been shown to exist in IVDs, abolition of which can lead to stress in nucleus pulposus cells (NPCs), contributing to intervertebral disc degeneration (IDD). Autophagy is a fundamental cellular process in eukaryotes and is essential for individual cells or organs to respond and adapt to changing environments; it has also been demonstrated to occur in human NPCs. Increasing evidence supports the hypothesis that autophagy is associated with CR. Thus, we review the connection between CR and autophagy and the roles of these mechanisms in IDD.

Influence of obesity, weight loss, and free fatty acids on skeletal muscle clock gene expression

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 mo 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 vs. 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 compared with 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 that dyslipidemia directly alters the circadian program. Strategies to reduce lipid overload and prevent elevations in nonesterified fatty acid and cholesterol levels may sustain circadian clock signals in skeletal muscle.

Boolean function network analysis of time course liver transcriptome data to reveal novel circadian transcriptional regulators in mammals

BACKGROUND

Many biological processes in mammals are subject to circadian control at the molecular level. Disruption of circadian rhythms has been demonstrated to be associated with a wide range of diseases, such as diabetes mellitus, mental disorders, and cancer. Although the core circadian genes are well established, there are multiple reports of novel peripheral circadian regulators. The goal of this study was to provide a comprehensive computational analysis to identify novel potential circadian transcriptional regulators.

METHODS

To fulfill the aforementioned goal, we applied a Boolean function network method to analyze the microarray time course mouse and rat liver datasets available in the literature. The inferred direct pairwise relations were further investigated using the functional annotation tool. This approach generated a list of transcription factors (TFs) and cofactors, which were associated with significantly enriched circadian gene ontology (GO) categories.

RESULTS

As a result, we identified 93 transcriptional circadian regulators in mouse and 95 transcriptional circadian regulators in rat. Of these, 19 regulators in mouse and 21 regulators in rat were known, whereas the rest were novel. Furthermore, we validated novel circadian TFs with bioinformatics databases, previous large-scale circadian studies, and related small-scale studies. Moreover, according to predictions inferred from ChIP-Seq experiments reported in the database, 40 of our candidate circadian regulators were confirmed to have circadian genes as direct regulatory targets. In addition, we annotated candidate circadian regulators with disorders that were often associated with disruptions of circadian rhythm in the literature.

CONCLUSION

In summary, our computational analysis, which was followed by an extensive verification by means of a literature review, can contribute to translational study from endocrinology to cancer research and provide insights for future investigation.

Meal Timing, Aging, and Metabolic Health

A growing body of evidence suggests that meal timing is an important factor for metabolic regulation and that the circadian clock tightly interacts with metabolic functions. The proper functioning of the circadian clock is critical for maintaining metabolic health. Therefore, chrononutrition, a novel discipline which investigates the relation between circadian rhythms, nutrition, and metabolism, has attracted increasing attention in recent years. Circadian rhythms are strongly affected by obesity, type 2 diabetes, and other dietary-induced metabolic diseases. With increasing age, the circadian system also undergoes significant changes which contribute to the dysregulation of metabolic rhythms. Metabolic diseases are a major health concern, particularly in light of a growing aging population, and effective approaches for their prevention and treatment are urgently needed. Recently, animal studies have impressively shown beneficial effects of several dietary patterns (e.g., caloric restriction or time-restricted feeding) on circadian rhythms and metabolic outcomes upon nutritional challenges. Whether these dietary patterns show the same beneficial effects in humans is, however, less well studied. As indicated by recent studies, dietary approaches might represent a promising, attractive, and easy-to-adapt strategy for the prevention and therapy of circadian and metabolic disturbances in humans of different age.

Interrelation of chemerin and TNF-α with mtDNA copy number in adipose tissues and blood cells in obese patients with and without type 2 diabetes

BACKGROUND

Inflammatory response plays a key role in the development of insulin resistance (IR) in obesity. Oxidative stress triggers the replication of the mitochondrial genome and division of the organelle. The purpose of this study was to identify the relationship of chemerin and TNF-α with mitochondrial DNA (mtDNA) copy number in subcutaneous adipose tissue (SAT) and visceral adipose tissue (mesentery of the small intestine (Mes), greater omentum (GO) and blood mononuclear cells (MNCs)) in patients with obesity with/without type 2 diabetes mellitus (T2DM).

METHODS

The study included 142 obese patients and 34 healthy donors. The samples used for the study were peripheral venous blood (MNCs) and ATs (SAT, Mes and GO). The measurement of mtDNA copy number was done by droplet digital PCR. Quantitative determination of insulin, adiponectin, TNF-α and chemerin in serum/plasma was performed by flow-through fluorometry and commercial ELISA kit. Statistical analysis and graphs were obtained in R Statistical Software (version 3.3.1).

RESULTS

The increase in body mass index (BMI) was accompanied by an increase in TNF-α production, an increase in mtDNA copy number in SAT and a decrease in mtDNA copy number in MNCs. The negative association between plasma chemerin and mtDNA copy number in the Mes, as well as between mtDNA copy number and chemerin expression in the Mes, in the group with BMI > 40 kg/m2 without T2DM demonstrates the protective effect of chemerin against the development of IR via the regulation of mtDNA copy number in adipose tissues.

CONCLUSIONS

We thus speculated the existence of a compensatory mechanism in which leads to the increased number of mtDNA copies under the influence of proinflammatory factors. Based on the obtained data, we propose that reducing mtDNA copy number in cases of morbid obesity without T2DM has a positive effect on carbohydrate metabolism, which may help maintain glucose levels within reference values. Obesity, type 2 diabetes, mtDNA, cytokines, TNF-a, chemerin.

Coupling the Circadian Clock to Homeostasis: The Role of Period in Timing Physiology

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 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 ∼24 hours. This review focuses on the specific role of the core clockwork gene Period1 and its paralogs on intra-oscillator 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 Period 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.

Interplay between diet, exercise and the molecular circadian clock in orchestrating metabolic adaptations of adipose tissue

Disruption of circadian rhythmicity induced by prolonged light exposure, altered sleep patterns and shift work is associated with the development of obesity and related metabolic disorders, including type 2 diabetes and cardiovascular diseases. White and brown adipose tissue activity shows circadian rhythmicity, with daily variations in the regulation of metabolic processes such as lipolysis, glucose and lipid uptake, and adipokine secretion. The role of the circadian clock in the regulation of energy homeostasis has raised interest in clock-related strategies to mitigate metabolic disturbances associated with type 2 diabetes, including 'resynchronizing' metabolism through diet or targeting a particular time of a day to potentiate the effect of a pharmacological or physiological treatment. Exercise is an effective intervention to prevent insulin resistance and type 2 diabetes. Beyond its effect on skeletal muscle, exercise training also has a profound effect on adipose tissue. Adipose tissue partly mediates the beneficial effect of exercise on glucose and energy homeostasis, via its metabolic and endocrine function. The interaction between zeitgeber time and diet or exercise is likely to influence the metabolic response of adipose tissue and therefore impact the whole-body phenotype. Understanding the impact of circadian clock systems on human physiology and how this is regulated by exercise in a tissue-specific manner will yield new insights for the management of metabolic disorders.

Melatonin as a Hormone: New Physiological and Clinical Insights

Melatonin is a ubiquitous molecule present in almost every live being from bacteria to humans. In vertebrates, besides being produced in peripheral tissues and acting as an autocrine and paracrine signal, melatonin is centrally synthetized by a neuroendocrine organ, the pineal gland. Independently of the considered species, pineal hormone melatonin is always produced during the night and its production and secretory episode duration are directly dependent on the length of the night. As its production is tightly linked to the light/dark cycle, melatonin main hormonal systemic integrative action is to coordinate behavioral and physiological adaptations to the environmental geophysical day and season. The circadian signal is dependent on its daily production regularity, on the contrast between day and night concentrations, and on specially developed ways of action. During its daily secretory episode, melatonin coordinates the night adaptive physiology through immediate effects and primes the day adaptive responses through prospective effects that will only appear at daytime, when melatonin is absent. Similarly, the annual history of the daily melatonin secretory episode duration primes the central nervous/endocrine system to the seasons to come. Remarkably, maternal melatonin programs the fetuses' behavior and physiology to cope with the environmental light/dark cycle and season after birth. These unique ways of action turn melatonin into a biological time-domain-acting molecule. The present review focuses on the above considerations, proposes a putative classification of clinical melatonin dysfunctions, and discusses general guidelines to the therapeutic use of melatonin.

Chronotype and social jetlag influence human circadian clock gene expression

We examined the relationships between chronotype or social jetlag and clock gene expression. Twenty-four young men [Chronotype: morningness, n = 8; intermediate, n = 8, eveningness, n = 8], aged 27 ± 2 years old (mean ± SE), completed two trials in a randomized order: (1) a Friday trial and (2) a Monday trial. In both trials, hair follicle cells were collected to evaluate the expression of clock genes over a 24-hour period at 4-hour intervals. There was a significant main effect of time on the expression of NR1D1, NR1D2, and PER3 (P < 0.001) in the morningness group, but not in the eveningness group. Changes in the peak time of expression of NR1D1 (r = 0.434, P = 0.034), NR1D2 (r = 0.481, P = 0.017), and PER3 (r = 0.457, P = 0.025) from the Friday to Monday trials were positively correlated with social jetlag (SJL) time. Our findings indicate that there was no change in the patterns of clock gene expression between workdays and the day after the holiday in the morningness group, and that SJL time influences the peak time of clock gene expression, moving it from the early to late workday, after a holiday.

Clock genes alterations and endocrine disorders

BACKGROUND

Various endocrine signals oscillate over the 24-hour period and so does the responsiveness of target tissues. These daily oscillations do not occur solely in response to external stimuli but are also under the control of an intrinsic circadian clock.

DESIGN

We searched the PubMed database to identify studies describing the associations of clock genes with endocrine diseases.

RESULTS

Various human single nucleotide polymorphisms of brain and muscle ARNT-like 1 (BMAL1) and Circadian Locomotor Output Cycles Kaput (CLOCK) genes exhibited significant associations with type 2 diabetes mellitus. ARNTL2 gene expression and upregulation of BMAL1 and PER1 were associated with the development of type 1 diabetes mellitus. Thyroid hormones modulated PER2 expression in a tissue-specific way, whereas BMAL1 regulated the expression of type 2 iodothyronine deiodinase in specific tissues. Adrenal gland and adrenal adenoma expressed PER1, PER2, CRY2, CLOCK and BMAL1 genes. Adrenal sensitivity to adrenocorticotrophin was also affected by circadian oscillations. A significant correlation between the expression of propio-melanocorticotrophin and PER 2, as well as between prolactin and CLOCK, was found in corticotroph and lactosomatotroph cells, respectively, in the pituitary. Clock genes and especially BMAL1 showed an important role in fertility, whereas oestradiol and androgens exhibited tissue-specific effects on clock gene expression. Metabolic disorders were also associated with circadian dysregulation according to studies in shift workers.

CONCLUSIONS

Clock genes are associated with various endocrine disorders through complex mechanisms. However, data on humans are scarce. Moreover, clock genes exhibit a tissue-specific expression representing an additional level of regulation. Their specific role in endocrine disorders and their potential implications remain to be further clarified.

The impact of BMI on sperm parameters and the metabolite changes of seminal plasma concomitantly

The development of male infertility increased rapidly worldwide, which coinciding with the epidemic of obesity. However, the impact of weight abnormalities on sperm quality is still contestable. To assess the correlation between BMI and sperm parameters, we searched relevant articles in PubMed, Embase, Web of science, and Wanfang database published until June 2015 without language restriction. Otherwise, we also recruited some participants who attended fertility clinic as well as some general populations in this report. We performed a systematic review and meta-analysis about BMI and sperm parameters containing total sperm count, concentration, semen volume and sperm motility (overall and progressive). Metabolomic analysis of seminal plasma was performed to explore the mechanism from a new perspective. This study found standardized weighted mean differences (SMD) in sperm parameters (total sperm count, sperm concentration, and semen volume) of abnormal weight groups decreased to different degree compared to normal weight. Dose-response analysis found SMD of sperm count, sperm concentration and semen volume respectively fell 2.4%, 1.3% and 2.0% compared with normal weight for every 5-unit increase in BMI. Metabolomic analysis of seminal plasma showed that spermidine and spermine were likely to play a vital role in the spermatogenesis progress. This systematic review with meta-analysis has confirmed there was a relationship between BMI and sperm quality, suggesting obesity may be a detrimental factor of male infertility.

Visceral adiposity and expression of clock genes in peripheral blood mononuclear cells: A pilot study

Increasing evidence suggests a close interrelationship between disrupted circadian rhythms and obesity and metabolic disturbances. In particular, abdominal obesity, which contributes to the pathogenesis of metabolic disease, is associated with disrupted clock gene expression. However, little is known about the relationship between clock gene expression and accurate computed tomography (CT)-based measurements of visceral adiposity. Therefore, we examined the relationship between expression of clock genes in peripheral blood mononuclear cells (PBMCs) with visceral and subcutaneous adiposity in 75 healthy overweight or obese individuals. PBMCs were obtained from blood samples collected at 8 AM, and gene expression was analyzed by real-time reverse transcription polymerase chain reaction. Visceral and subcutaneous adiposity were measured by CT. Our results showed that visceral fat area was significantly positively correlated with BMAL1 and CRY1 mRNA levels and significantly negatively correlated with CLOCK, PER2, PER3 and CRY2 mRNA levels. In contrast, subcutaneous fat area was not correlated with the expression of any of the clock genes analyzed. After adjusting for multiple variables, visceral fat area was significantly associated with the expression of BMAL1, PER2 and CRY1. Taken together, our results indicate that visceral adiposity, but not subcutaneous adiposity, correlates with expression of clock genes in PBMCs.

Adipose tissue NAD+ biology in obesity and insulin resistance: From mechanism to therapy

Nicotinamide adenine dinucleotide (NAD⁺ ) biosynthetic pathway, mediated by nicotinamide phosphoribosyltransferase (NAMPT), a key NAD⁺ biosynthetic enzyme, plays a pivotal role in controlling many biological processes, such as metabolism, circadian rhythm, inflammation, and aging. Over the past decade, NAMPT-mediated NAD⁺ biosynthesis, together with its key downstream mediator, namely the NAD⁺ -dependent protein deacetylase SIRT1, has been demonstrated to regulate glucose and lipid metabolism in a tissue-dependent manner. These discoveries have provided novel mechanistic and therapeutic insights into obesity and its metabolic complications, such as insulin resistance, an important risk factor for developing type 2 diabetes and cardiovascular disease. This review will focus on the importance of adipose tissue NAMPT-mediated NAD⁺ biosynthesis and SIRT1 in the pathophysiology of obesity and insulin resistance. We will also critically explore translational and clinical aspects of adipose tissue NAD⁺ biology.

Positive association between physical activity and PER3 expression in older adults

The circadian clock regulates many physiological functions including physical activity and feeding patterns. In addition, scheduled exercise and feeding themselves can affect the circadian clock. The purpose of the present study was to investigate the relationship between physical/feeding activity and expression of clock genes in hair follicle cells in older adults. Twenty adult men (age, 68 ± 7 years, mean ± SE) were examined in this cross-sectional study. Prior to hair follicle cell collection, the participants were asked to wear a uniaxial accelerometer for one week. The timings of breakfast, lunch, and dinner were also recorded. Hair follicle cells were then collected over a 24 h period at 4 h intervals. The amplitude of PER3 expression was positively correlated with moderate and vigorous physical activity (r = 0.582, p = 0.007) and peak oxygen uptake (r = 0.481, p = 0.032), but these correlations were not observed for NR1D1 or NR1D2. No association was noted between meal times and the amplitude or the acrophase for any of these three clock genes. These findings suggest that rhythmic expression of the circadian clock gene PER3 is associated with the amount of daily physical activity and physical fitness in older adults.

Nutrition and the circadian system

The human circadian system anticipates and adapts to daily environmental changes to optimise behaviour according to time of day and temporally partitions incompatible physiological processes. At the helm of this system is a master clock in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus. The SCN are primarily synchronised to the 24-h day by the light/dark cycle; however, feeding/fasting cycles are the primary time cues for clocks in peripheral tissues. Aligning feeding/fasting cycles with clock-regulated metabolic changes optimises metabolism, and studies of other animals suggest that feeding at inappropriate times disrupts circadian system organisation, and thereby contributes to adverse metabolic consequences and chronic disease development. 'High-fat diets' (HFD) produce particularly deleterious effects on circadian system organisation in rodents by blunting feeding/fasting cycles. Time-of-day-restricted feeding, where food availability is restricted to a period of several hours, offsets many adverse consequences of HFD in these animals; however, further evidence is required to assess whether the same is true in humans. Several nutritional compounds have robust effects on the circadian system. Caffeine, for example, can speed synchronisation to new time zones after jetlag. An appreciation of the circadian system has many implications for nutritional science and may ultimately help reduce the burden of chronic diseases.