Circadian aspects of energy metabolism and aging

Circadian-driven tissue specificity is constrained under caloric restricted feeding conditions

Tissue specificity is a fundamental property of an organ that affects numerous biological processes, including aging and longevity, and is regulated by the circadian clock. However, the distinction between circadian-affected tissue specificity and other tissue specificities remains poorly understood. Here, using multi-omics data on circadian rhythms in mice, we discovered that approximately 35% of tissue-specific genes are directly affected by circadian regulation. These circadian-affected tissue-specific genes have higher expression levels and are associated with metabolism in hepatocytes. They also exhibit specific features in long-reads sequencing data. Notably, these genes are associated with aging and longevity at both the gene level and at the network module level. The expression of these genes oscillates in response to caloric restricted feeding regimens, which have been demonstrated to promote longevity. In addition, aging and longevity genes are disrupted in various circadian disorders. Our study indicates that the modulation of circadian-affected tissue specificity is essential for understanding the circadian mechanisms that regulate aging and longevity at the genomic level.

Targeting the blood-brain barrier to delay aging-accompanied neurological diseases by modulating gut microbiota, circadian rhythms, and their interplays

The blood-brain barrier (BBB) impairment plays a crucial role in the pathological processes of aging-accompanied neurological diseases (AAND). Meanwhile, circadian rhythms disruption and gut microbiota dysbiosis are associated with increased morbidity of neurological diseases in the accelerated aging population. Importantly, circadian rhythms disruption and gut microbiota dysbiosis are also known to induce the generation of toxic metabolites and pro-inflammatory cytokines, resulting in disruption of BBB integrity. Collectively, this provides a new perspective for exploring the relationship among circadian rhythms, gut microbes, and the BBB in aging-accompanied neurological diseases. In this review, we focus on recent advances in the interplay between circadian rhythm disturbances and gut microbiota dysbiosis, and their potential roles in the BBB disruption that occurs in AAND. Based on existing literature, we discuss and propose potential mechanisms underlying BBB damage induced by dysregulated circadian rhythms and gut microbiota, which would serve as the basis for developing potential interventions to protect the BBB in the aging population through targeting the BBB by exploiting its links with gut microbiota and circadian rhythms for treating AAND.

Skeletal muscle gene expression dysregulation in long-term spaceflights and aging is clock-dependent

The circadian clock regulates cellular and molecular processes in mammals across all tissues including skeletal muscle, one of the largest organs in the human body. Dysregulated circadian rhythms are characteristic of aging and crewed spaceflight, associated with, for example, musculoskeletal atrophy. Molecular insights into spaceflight-related alterations of circadian regulation in skeletal muscle are still missing. Here, we investigated potential functional consequences of clock disruptions on skeletal muscle using published omics datasets obtained from spaceflights and other clock-altering, external (fasting and exercise), or internal (aging) conditions on Earth. Our analysis identified alterations of the clock network and skeletal muscle-associated pathways, as a result of spaceflight duration in mice, which resembles aging-related gene expression changes observed in humans on Earth (e.g., ATF4 downregulation, associated with muscle atrophy). Furthermore, according to our results, external factors such as exercise or fasting lead to molecular changes in the core-clock network, which may compensate for the circadian disruption observed during spaceflights. Thus, maintaining circadian functioning is crucial to ameliorate unphysiological alterations and musculoskeletal atrophy reported among astronauts.

Cellular rejuvenation: molecular mechanisms and potential therapeutic interventions for diseases

The ageing process is a systemic decline from cellular dysfunction to organ degeneration, with more predisposition to deteriorated disorders. Rejuvenation refers to giving aged cells or organisms more youthful characteristics through various techniques, such as cellular reprogramming and epigenetic regulation. The great leaps in cellular rejuvenation prove that ageing is not a one-way street, and many rejuvenative interventions have emerged to delay and even reverse the ageing process. Defining the mechanism by which roadblocks and signaling inputs influence complex ageing programs is essential for understanding and developing rejuvenative strategies. Here, we discuss the intrinsic and extrinsic factors that counteract cell rejuvenation, and the targeted cells and core mechanisms involved in this process. Then, we critically summarize the latest advances in state-of-art strategies of cellular rejuvenation. Various rejuvenation methods also provide insights for treating specific ageing-related diseases, including cellular reprogramming, the removal of senescence cells (SCs) and suppression of senescence-associated secretory phenotype (SASP), metabolic manipulation, stem cells-associated therapy, dietary restriction, immune rejuvenation and heterochronic transplantation, etc. The potential applications of rejuvenation therapy also extend to cancer treatment. Finally, we analyze in detail the therapeutic opportunities and challenges of rejuvenation technology. Deciphering rejuvenation interventions will provide further insights into anti-ageing and ageing-related disease treatment in clinical settings.

BMAL1/FOXA2-induced rhythmic fluctuations in IL-6 contribute to nocturnal asthma attacks

The circadian clock is closely associated with inflammatory reactions. Increased inflammatory cytokine levels have been detected in the airways of nocturnal asthma. However, the mechanisms that contribute to the nocturnal increase in inflammatory responses and the relationship with circadian clock remain unknown.

Methods

Inflammatory cytokine levels were measured in asthma patients with and without nocturnal symptoms. Allergic airway disease was induced in mice by ovalbumin (OVA), and different periods of light/dark cycles were used to induce circadian rhythm disorders. Serum shock was used to stimulate the rhythmic expression in human bronchial epidermal cells (16HBE). The expression and oscillation of circadian clock genes and inflammatory cytokines in 16HBE cells subjected to brain and muscle ARNT-like protein-1 (BMAL1) and Forkhead Box A2 (FOXA2) knockdown and treatment with a FOXA2 overexpression plasmid were assessed.

Results

Serum IL-6 was found to be significantly higher in asthmatic patients with nocturnal symptoms than those without nocturnal symptoms. The OVA-induced asthma model with a circadian rhythm disorder and 16HBE cells treated with serum shock showed an increase in IL-6 levels and a negative correlation with BMAL1 and FOXA2. The knockdown of BMAL1 resulted in a lower correlation between IL-6 and other rhythm clock genes. Furthermore, knockdown of the BMAL1 and FOXA2 in 16HBE cells reduced the expression and rhythmic fluctuations of IL-6.

Conclusions

Our findings suggest that there are increased IL-6 levels in nocturnal asthma resulting from inhibition of the BMAL1/FOXA2 signalling pathway in airway epithelial cells.

Circadian Control of Mitochondria in Reactive Oxygen Species Homeostasis

Significance: Mitochondria produce most of the cellular ATP through the process of oxidative phosphorylation. Energy metabolism in the mitochondria is associated with the production of reactive oxygen species (ROS). Excessive ROS production leads to oxidative stress and compromises cellular physiology. Energy metabolism in the mitochondria depends on nutrient flux and cellular metabolic needs, which are in turn connected with the feeding/fasting cycle. In animals, the feeding/fasting cycle is controlled by the circadian clock that generates 24-h rhythms in behavior, metabolism, and signaling. Recent Advances: Here, we discuss the role of the circadian clock and rhythms in mitochondria on ROS homeostasis. The circadian clock is involved in mitochondrial ROS production and detoxification through the control of nutrient flux and oxidation, uncoupling, antioxidant defense, and mitochondrial dynamics. Critical Issues: Little is known on the molecular mechanisms of circadian control of mitochondrial functions. The circadian clock regulates the expression and activity of mitochondrial metabolic and antioxidant enzymes. The regulation involves a direct transcriptional control by Circadian Locomotor Output Cycles Kaput/brain and muscle ARNT-like 1(CLOCK/BMAL1), nuclear factor erythroid-2-related factor 2 (NRF2) transcriptional network, and sirtuin-dependent posttranslational protein modifications. Future Perspectives: We hypothesize that the circadian clock orchestrates mitochondrial physiology to synchronize it with the feeding/fasting cycle. Circadian coordination of mitochondrial function couples energy metabolism with diets and contributes to antioxidant defense to prevent metabolic diseases and delay aging. Antioxid. Redox Signal. 37, 647-663.

Circadian alignment of early onset caloric restriction promotes longevity in male C57BL/6J mice

Caloric restriction (CR) prolongs lifespan, yet the mechanisms by which it does so remain poorly understood. Under CR, mice self-impose chronic cycles of 2-hour-feeding and 22-hour-fasting, raising the question whether calories, fasting, or time of day are causal. We show that 30%-CR is sufficient to extend lifespan 10%; however, a daily fasting interval and circadian-alignment of feeding act together to extend lifespan 35% in male C57BL/6J mice. These effects are independent of body weight. Aging induces widespread increases in gene expression associated with inflammation and decreases in expression of genes encoding components of metabolic pathways in liver from ad lib fed mice. CR at night ameliorates these aging-related changes. Thus, circadian interventions promote longevity and provide a perspective to further explore mechanisms of aging.

Timed caloric restriction at night enhances longevity.

Importance of circadian timing for aging and longevity

Dietary restriction (DR) decreases body weight, improves health, and extends lifespan. DR can be achieved by controlling how much and/or when food is provided, as well as by adjusting nutritional composition. Because these factors are often combined during DR, it is unclear which are necessary for beneficial effects. Several drugs have been utilized that target nutrient-sensing gene pathways, many of which change expression throughout the day, suggesting that the timing of drug administration is critical. Here, we discuss how dietary and pharmacological interventions promote a healthy lifespan by influencing energy intake and circadian rhythms.

Circadian clocks link physiologic processes to environmental conditions and a mismatch between internal and external rhythms has negative effects on organismal health. In this review, the authors discuss the interactions between circadian clocks and dietary interventions targeted to promote healthy aging.

Clock Gene Disruption Is an Initial Manifestation of Inflammatory Bowel Diseases

BACKGROUND & AIMS

Sleep disruption modifies the immune system and can trigger flares of inflammatory bowel diseases (IBD). Changes in expression of clock genes have been reported in patients with IBD. We investigated whether a change in the circadian clock is an early event in development of IBD.

METHODS

We performed a prospective study of patients younger than 21 years old who underwent diagnostic endoscopies at the pediatric and adult gastroenterology units at the Tel Aviv Sourasky Medical Center from August 2016 through August 2017. Questionnaires were completed by 32 patients with IBD (8-21 years old) and 18 healthy individuals (controls) that provided data on demographics, sleep, disease activity scores. We also obtained data on endoscopic scores, anthropometric parameters, blood level of C-reactive protein (CRP), and fecal level of calprotectin. Peripheral blood and intestinal mucosa samples were analyzed for expression levels of clock gene (CLOCK, BMAL1, CRY1, CRY2, PER1, and PER2).

RESULTS

Levels of CRP and fecal calprotectin were significantly higher in patients with IBD compared with controls (P<.05). Expression levels of clock genes (CLOCK, CRY1, CRY2, PER1, and PER2) were significantly lower in inflamed intestinal mucosa from patients compared with intestinal mucosa from controls (P<.05). Expression levels of all clock genes except for PER2, were also significantly lower in non-inflamed intestinal mucosal tissues from patients compared with controls (P<.05). Expression levels of clock genes (CLOCK, BMAL1, CRY1, CRY2, PER1 and PER2) were lower in white blood cells from patients with IBD compared with controls. This reduction was greater in white blood cells from patients with ulcerative colitis than in patients with Crohn's disease.

CONCLUSION

Young, newly diagnosed, untreated patients with IBD have reduced expression of clock genes in inflamed and non-inflamed intestinal mucosal samples, and also in blood cells, compared with healthy individuals. Alterations in expression of clock genes might be an early event in IBD pathogenesis. ClinicalTrials.gov Identifier: NCT03662646.

Molecular Connections Between Circadian Clocks and Aging

The mammalian circadian clockwork has evolved as a timing system that allows the daily environmental changes to be anticipated so that behavior and tissue physiology can be adjusted accordingly. The circadian clock synchronizes the function of all cells within tissues in order to temporally separate preclusive and potentially harmful physiologic processes and to establish a coherent temporal organismal physiology. Thus, the proper functioning of the circadian clockwork is essential for maintaining cellular and tissue homeostasis. Importantly, aging reduces the robustness of the circadian clock, resulting in disturbed sleep-wake cycles, a lowered capacity to synchronize circadian rhythms in peripheral tissues, and reprogramming of the circadian clock output at the molecular function levels. These circadian clock-dependent behavioral and molecular changes in turn further accelerate the process of aging. Here we review the current knowledge about how aging affects the circadian clock, how the functional decline of the circadian clock affects aging, and how the circadian clock machinery and the molecular processes that underlie aging are intertwined.

Calorie restriction reprograms diurnal rhythms in protein translation to regulate metabolism

Calorie restriction (CR) delays aging and affects the circadian clocks by reprogramming circadian rhythms in gene expression. To expand on the circadian mechanisms in CR, we assayed rhythms in the protein translation by analyzing polysome-associated mRNAs in the liver of mice fed ad libitum (AL) and CR diets. Global comparison of the diets revealed that <1% of transcripts were differentially abundant in the polysomes. In contrast, the large differential, up to 10%, was detected when CR and AL diets were compared at individual times throughout the day. Most transcripts that were rhythmic under AL lost their rhythms, and many new transcripts gained rhythms under CR. Only a small fraction of transcripts, including the circadian clock genes, were rhythmic under both diets. Thus, CR strongly reprograms translation. CR affected translation of enzymes regulating long-chain acetyl-coenzyme A (Acyl-CoA) metabolism. The expression of the Acyl-CoA thioesterase (ACOT) family was induced upon CR, leading to the increased transcriptional activity of peroxisome proliferator-activated receptor α, the transcriptional factor regulated by the ACOT products. We propose that the differential translation induced by CR leads to a temporal partition and reprogramming of metabolic processes and provides a link between CR, lipid metabolism, and the circadian clock.-Makwana, K., Gosai, N., Poe, A., Kondratov, R. V. Calorie restriction reprograms diurnal rhythms in protein translation to regulate metabolism.

Disruptions in gut microbial-host co-metabolism and the development of metabolic disorders

The microbial-mammalian metabolic axis has become recognized as an important component governing the overall homeostatic balance of the mammalian host. Disruption of the state of homeostasis among the gut microbiota has been shown to be causally linked to the development of host metabolic diseases including obesity, cardiovascular, diabetes, and fatty liver disease. This disruption is often referred to as gut dysbiosis. Gut dysbiosis leads to altered metabolic products derived from the microbiota and these in turn, typically shift the homeostatic metabolic balance of the host towards a low-grade chronic inflammation, a hallmark of metabolic syndrome. The primary objective of this review is to examine and discuss some very current research that has been done to study the effect of bacterial metabolites on host metabolism, sometimes referred to as microbiota-host co-metabolism. The metabolic conditions reviewed here include obesity, a known risk factor for all of the other metabolic conditions, as well as, cardiovascular disease, diabetes and nonalcoholic fatty liver disease. Only by further understanding the cause and result of gut dysbiosis will an adequate solution be found for metabolic disease, a viewpoint shared by many.

Association between Sleep Patterns and Health in Families with Exceptional Longevity

BACKGROUND

Sleep patterns such as longer sleep duration or napping are associated with poor health outcomes. Although centenarians and their offspring demonstrate a delayed onset of age-related diseases, it is not known whether they have healthier sleep patterns or are protected against the negative effects of sleep disturbances.

METHODS

Data on sleep patterns and health history were collected from Ashkenazi Jewish subjects of the Longevity Genes Project using standardized questionnaires. Participants included individuals with exceptional longevity (centenarians) with preserved cognition (n = 348, median age 97 years), their offspring (n = 513, median age 69 years), and controls (n = 199) age-matched to the offspring. Centenarians reported on their sleep patterns at age 70, while the offspring and controls on their current sleep patterns. Biochemical parameters were measured at baseline. Models were adjusted for age, sex, BMI, and use of sleep medication.

RESULTS

The offspring and controls reported similar sleep patterns, with 33% sleeping ≥8 h and 17% napping in each group. At age 70, centenarians were more likely to have slept ≥8 h (55%) and to have napped (28%) compared with offspring and controls, p < 0.01. Among centenarians, no association was noted between sleep patterns and health outcomes. Sleeping for ≥8 h was associated with lower high-density lipoprotein cholesterol levels in the offspring and controls, and with insulin resistance in the offspring, but not with diabetes. Napping was associated with insulin resistance among the controls (p < 0.01), but not the offspring. Controls, but not offspring, who napped were 2.79 times more likely to have one or more of the following diseases: hypertension, myocardial infarction, stroke, or diabetes (OR 2.79, 95% CI 1.08-7.21, p = 0.04).

CONCLUSION

Despite being more likely to exhibit risky sleep patterns at age 70 compared with the offspring and controls, the centenarians were protected from age-related morbidities. The offspring of centenarians did exhibit metabolic disturbances in association with less healthy sleep patterns; however, unlike the controls, they were much less likely to manifest age-related diseases. This suggests that offspring may have inherited resilience genotypes from their centenarian parents that protect them against the harmful effects of sleep disturbances.

Physiological links of circadian clock and biological clock of aging

Circadian rhythms orchestrate biochemical and physiological processes in living organisms to respond the day/night cycle. In mammals, nearly all cells hold self-sustained circadian clocks meanwhile couple the intrinsic rhythms to systemic changes in a hierarchical manner. The suprachiasmatic nucleus (SCN) of the hypothalamus functions as the master pacemaker to initiate daily synchronization according to the photoperiod, in turn determines the phase of peripheral cellular clocks through a variety of signaling relays, including endocrine rhythms and metabolic cycles. With aging, circadian desynchrony occurs at the expense of peripheral metabolic pathologies and central neurodegenerative disorders with sleep symptoms, and genetic ablation of circadian genes in model organisms resembled the aging-related features. Notably, a number of studies have linked longevity nutrient sensing pathways in modulating circadian clocks. Therapeutic strategies that bridge the nutrient sensing pathways and circadian clock might be rational designs to defy aging.

Desynchronization of Circadian Clocks in Cancer: A Metabolic and Epigenetic Connection

Circadian clocks are innate oscillators that drive daily rhythms in metabolism, physiology, and behavior. 24-h rhythms in gene expression, driven by core clock transcription factors, reflect the epigenetic state of the cell, which in turn is dictated by the metabolic environment. Cancer cells alter their metabolic state and gene expression and therefore are likely to tweak circadian clock function in their favor. Over the past decade, we have witnessed an extraordinary increase in systems-level studies that suggest intricate mechanistic links between the cellular metabolome and the circadian epigenome. In parallel, reprogramming of cellular clock function in cancers is increasingly evident and the role of clock genes in the development of hematological tumors, as well as their pathophysiological effects on tissues distal to the tumor, has been described. Furthermore, the interplay between components of the circadian clock, metabolic enzymes, and oncogenes is starting to be better understood, such as the close association between overexpression of the Myc oncogene and perturbation of circadian and metabolic rhythms, thus opening new avenues to treat cancers. This review article explores current knowledge on the circadian metabolome and the molecular pathways they control, with a focus on their involvement in the development of hematopoietic malignancies.

Circadian clock regulation of mRNA translation through eukaryotic elongation factor eEF-2

The circadian clock has a profound effect on gene regulation, controlling rhythmic transcript accumulation for up to half of expressed genes in eukaryotes. Evidence also exists for clock control of mRNA translation, but the extent and mechanisms for this regulation are not known. In Neurospora crassa, the circadian clock generates daily rhythms in the activation of conserved mitogen-activated protein kinase (MAPK) pathways when cells are grown in constant conditions, including rhythmic activation of the well-characterized p38 osmosensing (OS) MAPK pathway. Rhythmic phosphorylation of the MAPK OS-2 (P-OS-2) leads to temporal control of downstream targets of OS-2. We show that osmotic stress in N. crassa induced the phosphorylation of a eukaryotic elongation factor-2 (eEF-2) kinase, radiation sensitivity complementing kinase-2 (RCK-2), and that RCK-2 is necessary for high-level phosphorylation of eEF-2, a key regulator of translation elongation. The levels of phosphorylated RCK-2 and phosphorylated eEF-2 cycle in abundance in wild-type cells but not in cells deleted for OS-2 or the core clock component FREQUENCY (FRQ). Translation extracts from cells grown in constant conditions show decreased translational activity in the late subjective morning, coincident with the peak in eEF-2 phosphorylation, and rhythmic translation of glutathione S-transferase (GST-3) from constitutive mRNA levels in vivo is dependent on circadian regulation of eEF-2 activity. In contrast, rhythms in phosphorylated eEF-2 levels are not necessary for rhythms in accumulation of the clock protein FRQ, indicating that clock control of eEF-2 activity promotes rhythmic translation of specific mRNAs.

Genetic and Environmental Models of Circadian Disruption Link SRC-2 Function to Hepatic Pathology

Circadian rhythmicity is a fundamental process that synchronizes behavioral cues with metabolic homeostasis. Disruption of daily cycles due to jet lag or shift work results in severe physiological consequences including advanced aging, metabolic syndrome, and even cancer. Our understanding of the molecular clock, which is regulated by intricate positive feedforward and negative feedback loops, has expanded to include an important metabolic transcriptional coregulator, Steroid Receptor Coactivator-2 (SRC-2), that regulates both the central clock of the suprachiasmatic nucleus (SCN) and peripheral clocks including the liver. We hypothesized that an environmental uncoupling of the light-dark phases, termed chronic circadian disruption (CCD), would lead to pathology similar to the genetic circadian disruption observed with loss of SRC-2 We found that CCD and ablation of SRC-2 in mice led to a common comorbidity of metabolic syndrome also found in humans with circadian disruption, non-alcoholic fatty liver disease (NAFLD). The combination of SRC-2(-/-) and CCD results in a more robust phenotype that correlates with human non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC) gene signatures. Either CCD or SRC-2 ablation produces an advanced aging phenotype leading to increased mortality consistent with other circadian mutant mouse models. Collectively, our studies demonstrate that SRC-2 provides an essential link between the behavioral activities influenced by light cues and the metabolic homeostasis maintained by the liver.

Constructing the suprachiasmatic nucleus: a watchmaker's perspective on the central clockworks

The circadian system constrains an organism's palette of behaviors to portions of the solar day appropriate to its ecological niche. The central light-entrained clock in the suprachiasmatic nucleus (SCN) of the mammalian circadian system has evolved a complex network of interdependent signaling mechanisms linking multiple distinct oscillators to serve this crucial function. However, studies of the mechanisms controlling SCN development have greatly lagged behind our understanding of its physiological functions. We review advances in the understanding of adult SCN function, what has been described about SCN development to date, and the potential of both current and future studies of SCN development to yield important insights into master clock function, dysfunction, and evolution.