The circadian clock and inflammation: A new insight

Gene expression of Decompression Sickness-resistant rats through a miRnome/transcriptome crossed approach

Susceptibility to decompression sickness (DCS) is characterized by a wide inter-individual variability, the origins of which are still poorly understood. We selectively bred rats with at least a 3-fold greater resistance to DCS than standard rats after 6 generations. In order to better understand DCS mechanisms, we compared the static genome expression of these resistant rats from the 10th generation to their counterparts of the initial non-resistant Wistar strain, by a microarray transcriptomic approach coupled and crossed with a PCR plates miRnome study. Thus, we identified differentially expressed genes on selected males and females, as well as gender differences in those genes, and we crossed these transcripts with the respective targets of the differentially expressed microRNAs. Our results highlight pathways involved in inflammatory responses, circadian clock, cell signaling and motricity, phagocytosis or apoptosis, and they confirm the importance of inflammation in DCS pathophysiology.

Biological Clock Genes are Crucial and Promising Biomarkers for the Therapeutic Targets and Prognostic Assessment in Gastric Cancer

BACKGROUND

Gastric cancer is one of the major public health problems worldwide. Circadian rhythm disturbances driven by circadian clock genes play a role in the development of cancer. However, whether circadian clock genes can serve as potential therapeutic targets and prognostic biomarkers for gastric cancer remains elusive.

METHODS

In this study, we comprehensively analyzed the potential relationship between circadian clock genes and gastric cancer using online bioinformatics databases such as GEPIA, cBioPortal, STRING, GeneMANIA, Metascape, TIMER, TRRUST, and GEDS.

RESULTS

Biological clock genes are expressed differently in human tumors. Compared with normal tissues, only PER1, CLOCK, and TIMELESS expression differences were statistically significant in gastric cancer (p < 0.05). PER1 (p = 0.0169) and CLOCK (p = 0.0414) were associated with gastric cancer pathological stage (p < 0.05). Gastric cancer patients with high expression of PER1 (p = 0.0028) and NR1D1 (p = 0.016) had longer overall survival, while those with high expression of PER1 (p = 0.042) and NR1D1 (p = 0.016) had longer disease-free survival. The main function of the biological clock gene is related to the circadian rhythms and melatonin metabolism and effects. CLOCK, NPAS2, and KAT2B were key transcription factors for circadian clock genes. In addition, we also found important correlations between circadian clock genes and various immune cells in the gastric cancer microenvironment.

CONCLUSIONS

This study may establish a new gastric cancer prognostic indicator based on the biological clock gene and develop new drugs for the treatment of gastric cancer using biological clock gene targets.

The association between circadian syndrome and chronic kidney disease in an aging population: a 4-year follow-up study

Introduction

Circadian syndrome (CircS) is proposed as a novel risk cluster based on reduced sleep duration, abdominal obesity, depression, hypertension, dyslipidemia and hyperglycemia. However, the association between CircS and chronic kidney disease (CKD) remains unclear. To investigate the cross-sectional and longitudinal association between CircS and CKD, this study was performed.

Methods

A national prospective cohort (China Health and Retirement Longitudinal Study, CHARLS) was used in this study. To define CKD, the estimated glomerular filtration rate (eGFR) was calculated based on the 2012 CKD-EPI creatinine-cystatin C equation. Participants with eGFR <60 mL.min-1/1.73/m2 were diagnosed with CKD. Multivariate binary logistic regression was used to assess the cross-sectional association between CircS and CKD. Subgroup and interactive analyses were performed to determine the interactive effects of covariates. In the sensitivity analysis, the obese population was excluded and another method for calculating the eGFR was used to verify the robustness of previous findings. In addition, participants without CKD at baseline were followed up for four years to investigate the longitudinal relationship between CircS and CKD.

Results

A total of 6355 participants were included in this study. In the full model, CircS was positively associated with CKD (OR = 1.28, 95% CI = 1.04-1.59, P < 0.05). As per one increase of CircS components, there was a 1.11-fold (95% CI = 1.04-1.18, P < 0.05) risk of prevalent CKD in the full model. A significant interactive effect of hyperuricemia in the CircS-CKD association (P for interaction < 0.01) was observed. Sensitivity analyses excluding the obese population and using the 2009 CKD-EPI creatinine equation to diagnose CKD supported the positive correlation between CircS and CKD. In the 2011-2015 follow-up cohort, the CircS group had a 2.18-fold risk of incident CKD (95% CI = 1.33-3.58, P < 0.01) in the full model. The OR was 1.29 (95% CI = 1.10-1.51, P < 0.001) with per one increase of CircS components.

Conclusion

CircS is a risk factor for CKD and may serve as a predictor of CKD for early identification and intervention.

A review for the impacts of circadian disturbance on urological cancers

Circadian rhythm is an internal timing system and harmonizes a variety of cellular, behavioral, and physiological processes to daily environment. Circadian disturbance caused by altered life style or disrupted sleep patterns inevitably contributes to various disorders. As the rapidly increased cancer occurrences and subsequent tremendous financial burdens, more researches focus on reducing the morbidity rather than treating it. Recently, many epidemiologic studies demonstrated that circadian disturbance was tightly related to the occurrence and development of cancers. For urinary system, numerous clinical researches observed the incidence and progress of prostate cancer were influenced by nightshift work, sleep duration, chronotypes, light exposure, and meal timing, this was also proved by many genetic and fundamental findings. Although the epidemiological studies regarding the relationship between circadian disturbance and kidney/bladder cancers were relative limited, some basic researches still claimed circadian disruption was closely correlated to these two cancers. The role of circadian chemotherapy on cancers of prostate, kidney, and bladder were also explored, however, it has not been regularly recommended considering the limited evidence and poor standard protocols. Finally, the researches for the impacts of circadian disturbance on cancers of adrenal gland, penis, testis were not found at present. In general, a better understanding the relationship between circadian disturbance and urological cancers might help to provide more scientific work schedules and rational lifestyles which finally saving health resource by reducing urological tumorigenesis, however, the underlying mechanisms are complex which need further exploration.

Circadian disturbance induces erectile dysfunction by impairing endothelial function

In order to explore the impact of circadian disturbance on erectile function, we randomly divided 24 adult male rats into groups of control (light on at 8:00 a.m. and off at 8:00 p.m.), dark/dark (DD; constant dark), light/light (LL; constant light), and shift dark/light (DL; light off at 8:00 a.m. and on at 8:00 p.m.). Four weeks later, erectile function was measured and corpora cavernosa were harvested for analysis. The maximum intracavernous pressure (mICP) and mICP/mean arterial pressure (MAP) ratio in the DD, LL, and DL groups were significantly lower than that in the control group. The LL and DL groups showed significantly attenuated endothelial nitric oxide synthase (eNOS), while DD, LL, and DL showed reduced neuronal nitric oxide synthase (nNOS) at both mRNA and protein levels. The production of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) was inhibited by altered light/dark cycles to varying degrees. Circadian disturbance impaired endothelial function and contributed to erectile dysfunction. For the core circadian elements, mRNA expression of circadian locomotor output cycles kaput ( Clock ) and brain/muscle aryl-hydrocarbon receptor nuclear translocator-like protein 1 ( Bmal1 ) was elevated in the DL group, but their protein expression was not significantly changed. DD, LL, and DL increased period 1 ( Per1 ) and Per3 levels, while LL and DL increased PER1 levels. No significant difference was found for Per2 levels, and PER2 and PER3 concentrations were not significantly changed. Moreover, LL and DL significantly increased cryptochrome-1 (CRY1) and CRY2 at both mRNA and protein levels. The altered light/dark rat model showed that circadian disturbance contributed to erectile dysfunction probably by impairing endothelial function. Meanwhile, the core circadian elements were detected in the corpora cavernosa, but these were disrupted. However, which circadian element regulates erectile function and how it works need further analysis.

Circadian clock gene expression and polymorphism in non-segmental vitiligo

BACKGROUND

Vitiligo is an acquired and progressive mucocutaneous disease with the damage of functioning epidermal melanocytes. Metabolic syndrome is associated with inflammatory skin diseases incorporating vitiligo. The circadian dysfunction triggers the pathogenesis of metabolic diseases, so our study aimed to determine the relationship between aryl hydrocarbon receptor nuclear translocator-like gene, a ligand-activated transcription factor and sensor of environmental chemicals, expression and polymorphism with non-segmental vitiligo, as well as its effect on lipid profile.

METHODS

This case-control study was handled on 50 non-segmental vitiligo patients (generalized (12) and localized type (focal; 24 and acrofacial; 14)) and 50 matched controls. Each subject was proposed for full history taking, clinical examinations, serum lipid profile, and measurement of BMAL1 gene expression in the blood, and BMAL1 rs2279287 polymorphism of DNA extract from whole blood by real time-PCR.

RESULTS

We identified that total cholesterol, triglyceride, and low-density lipoprotein were significantly higher, but high-density lipoprotein was significantly lower in non-segmental vitiligo patients than in the control group. A significant increase in circadian gene expression in non-segmental vitiligo patients was observed, with more detection of the BMAL1 T/C genotype (92%) than the T/T genotype. There was a significant positive relationship between the level of the circadian gene and the vitiligo patient's age, age of onset, and VIDA Score. The level of the circadian gene at Cutoff  ≥ 1.16 can predict the prognosis of vitiligo with a sensitivity of 78%, specificity of 84%, and accuracy of 81%.

CONCLUSION

The circadian gene has an active role in the progress of non-segmental vitiligo and targeting this gene could have a significant impact on its management.

Chronic Inflammation Disrupts Circadian Rhythms in Splenic CD4+ and CD8+ T Cells in Mice

Internal circadian clocks coordinate 24 h rhythms in behavior and physiology. Many immune functions show daily oscillations, and cellular circadian clocks can impact immune functions and disease outcome. Inflammation may disrupt circadian clocks in peripheral tissues and innate immune cells. However, it remains elusive if chronic inflammation impacts adaptive immune cell clock, e.g., in CD4+ and CD8+ T lymphocytes. We studied this in the experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis, as an established experimental paradigm for chronic inflammation. We analyzed splenic T cell circadian clock and immune gene expression rhythms in mice with late-stage EAE, CFA/PTx-treated, and untreated mice. In both treatment groups, clock gene expression rhythms were altered with differential effects for baseline expression and peak phase compared with control mice. Most immune cell marker genes tested in this study did not show circadian oscillations in either of the three groups, but time-of-day- independent alterations were observed in EAE and CFA/PTx compared to control mice. Notably, T cell effects were likely independent of central clock function as circadian behavioral rhythms in EAE mice remained intact. Together, chronic inflammation induced by CFA/PTx treatment and EAE immunization has lasting effects on circadian rhythms in peripheral immune cells.

The Physiological and Pharmacological Significance of the Circadian Timing of the HPA Axis: A Mathematical Modeling Approach

As a potent endogenous regulator of homeostasis, the circadian time-keeping system synchronizes internal physiology to periodic changes in the external environment to enhance survival. Adapting endogenous rhythms to the external time is accomplished hierarchically with the central pacemaker located in the suprachiasmatic nucleus (SCN) signaling the hypothalamus-pituitary-adrenal (HPA) axis to release hormones, notably cortisol, which help maintain the body's circadian rhythm. Given the essential role of HPA-releasing hormones in regulating physiological functions, including immune response, cell cycle, and energy metabolism, their daily variation is critical for the proper function of the circadian timing system. In this review, we focus on cortisol and key fundamental properties of the HPA axis and highlight their importance in controlling circadian dynamics. We demonstrate how systems-driven, mathematical modeling of the HPA axis complements experimental findings, enhances our understanding of complex physiological systems, helps predict potential mechanisms of action, and elucidates the consequences of circadian disruption. Finally, we outline the implications of circadian regulation in the context of personalized chronotherapy. Focusing on the chrono-pharmacology of synthetic glucocorticoids, we review the challenges and opportunities associated with moving toward personalized therapies that capitalize on circadian rhythms.

Sleep and circadian rhythm disturbance in kidney stone disease: a narrative review

The circadian rhythm generated by circadian clock genes functions as an internal timing system. Since the circadian rhythm controls abundant physiological processes, the circadian rhythm evolved in organisms is salient for adaptation to environmental change. A disturbed circadian rhythm is a trigger for numerous pathological events. Recently, accumulated data have indicated that kidney stone disease (KSD) is related to circadian rhythm disturbance. However, the mechanism between them has not been fully elucidated. In this narrative review, we summarized existing evidence to illustrate the possible association between circadian rhythm disturbance and KSD based on the epidemiological studies and risk factors that are linked to circadian rhythm disturbance and discuss some chronotherapies for KSD. In summary, KSD is associated with systemic disorders. Metabolic syndrome, inflammatory bowel disease, and microbiome dysbiosis are the major risk factors supported by sufficient data to cause KSD in patients with circadian rhythm disturbance, while others including hypertension, vitamin D deficiency, parathyroid gland dysfunction, and renal tubular damage/dysfunction need further investigation. Then, some chronotherapies for KSD were confirmed to be effective, but the molecular mechanism is still unclear.

New insights into the mechanisms of diabetic kidney disease: Role of circadian rhythm and Bmal1

It is common for diabetic kidney disease (DKD) to be complicated by abnormal blood glucose, blood lipids, and blood pressure rhythms. Thus, it is essential to examine diagnostic and treatment plans from the perspective of circadian disruption. This brief review discusses the clinical relevance of circadian rhythms in DKD and how the core clock gene encoding brain and muscle arnt-like protein 1 (BMAL1) functions owing to the importance of circadian rhythm disruption processes, including the excretion of urinary protein and irregular blood pressure, which occur in DKD. Exploring Bmal1 and its potential mechanisms and signaling pathways in DKD following contact with Sirt1 and NF-κB is novel and important. Finally, potential pharmacological and behavioral intervention strategies for DKD circadian rhythm disturbance are outlined. This review aids in unveiling novel, potential molecular targets for DKD based on circadian rhythms.

Disruptions of Circadian Genes in Cutaneous Melanoma-An In Silico Analysis of Transcriptome Databases

Circadian genes are a set of genes that regulate the body's internal clock and influence various physiological processes, including sleep-wake cycles, metabolism and immune function. Skin cutaneous melanoma (SKCM) is a type of skin cancer that arises from the pigment-producing cells in the skin and is the most deadly form of skin cancer. This study has investigated the relevance of circadian gene expression and immune infiltrations in the outcomes of cutaneous melanoma patients. In the present study, in silico methods based on the GEPIa, TIMER 2.0 and cBioPortal databases were performed, so as to investigate the transcript level and prognostic value of 24 circadian genes in SKCM and their relationship with the immune infiltration level. The in silico analysis showed that significantly more than half of the investigated circadian genes have an altered transcript pattern in cutaneous melanoma compared to normal skin. The mRNA levels of TIMELES and BHLHE41 were upregulated, whereas those of NFIL3, BMAL1, HLF, TEF, RORA, RORC, NR1D1, PER1, PER2, PER3, CRY2 and BHLHE40 were downregulated. The presented research shows that SKCM patients with at least one alteration of their circadian genes have decreased overall survival. Additionally, majority of the circadian genes are significantly corelated with the immune cells' infiltration level. The strongest correlation was found for neutrophils and was followed by circadian genes: NR1D2 r = 0.52 p < 0.0001, BMAL1 r = 0.509 p < 0.0001; CLOCK r = 0.45 p < 0.0001; CSNKA1A1 r = 0.45 p < 0.0001; RORA r = 0.44 p < 0.0001. The infiltration level of immune cells in skin tumors has been associated with patient prognosis and treatment response. Circadian regulation of immune cell infiltration may further contribute to these prognostic and predictive markers. Examining the correlation between circadian rhythm and immune cell infiltration can provide valuable insights into disease progression and guide personalized treatment decisions.

Time-dependent effect of REV-ERBα agonist SR9009 on nonalcoholic steatohepatitis and gut microbiota in mice

The circadian clock is involved in the pathogenesis of nonalcoholic steatohepatitis (NASH), and the target pathways of many NASH candidate drugs are controlled by the circadian clock. However, the application of chronopharmacology in NASH is little considered currently. Here, the time-dependent effect of REV-ERBα agonist SR9009 on diet-induced NASH and microbiota was investigated. C57BL/6J mice were fed a high-cholesterol and high-fat diet (CL) for 12 weeks to induce NASH and then treated with SR9009 either at Zeitgeber time 0 (ZT0) or ZT12 for another 6 weeks. Pharmacological activation of REV-ERBα by SR9009 alleviated hepatic steatosis, insulin resistance, liver inflammation, and fibrosis in CL diet-induced NASH mice. These effects were accompanied by improved gut barrier function and altered microbial composition and function in NASH mice, and the effect tended to be stronger when SR9009 was injected at ZT0. Moreover, SR9009 treatment at different time points resulted in a marked difference in the composition of the microbiota, with a stronger effect on the enrichment of beneficial bacteria and the diminishment of harmful bacteria when SR9009 was administrated at ZT0. Therefore, the time-dependent effect of REV-ERBα agonist on NASH was partly associated with the microbiota, highlighting the potential role of microbiota in the chronopharmacology of NASH and the possibility of discovering new therapeutic strategies for NASH.

Aryl hydrocarbon receptor (AhR) impairs circadian regulation: impact on the aging process

Circadian clocks control the internal sleep-wake rhythmicity of 24hours which is synchronized by the solar cycle. Circadian regulation of metabolism evolved about 2.5 billion years ago, i.e., the rhythmicity has been conserved from cyanobacteria and Archaea through to mammals although the mechanisms utilized have developed with evolution. While the aryl hydrocarbon receptor (AhR) is an evolutionarily conserved defence mechanism against environmental threats, it has gained many novel functions during evolution, such as the regulation of cell cycle, proteostasis, and many immune functions. There is robust evidence that AhR signaling impairs circadian rhythmicity, e.g., by interacting with the core BMAL1/CLOCK complex and disturbing the epigenetic regulation of clock genes. The maintenance of circadian rhythms is impaired with aging, disturbing metabolism and many important functions in aged organisms. Interestingly, it is known that AhR signaling promotes an age-related tissue degeneration, e.g., it is able to inhibit autophagy, enhance cellular senescence, and disrupt extracellular matrix. These alterations are rather similar to those induced by a long-term impairment of circadian rhythms. However, it is not known whether AhR signaling enhances the aging process by impairing circadian homeostasis. I will examine the experimental evidence indicating that AhR signaling is able to promote the age-related degeneration via a disruption of circadian rhythmicity.

The circadian rhythm gene Bmal1 ameliorates acute deoxynivalenol-induced liver damage

Deoxynivalenol (DON) is widely emerging in various grain crops, milk, and wine products, which can trigger different toxic effects on humans and animals by inhalation or ingestion. It also imposes a considerable financial loss on the agriculture and food industry each year. Previous studies have reported acute and chronic toxicity of DON in liver, and liver is not only the main detoxification organ for DON but also the circadian clock oscillator directly or indirectly regulates critical physiologically hepatic functions under different physiological and pathological conditions. However, researches on the association of circadian rhythm in DON-induced liver damage are limited. In the present study, mice were divided into four groups (CON, DON, Bmal1^OE, and Bmal1^OE + DON) and AAV8 was used to activate (Bmal1) expression in liver. Then mice were gavaged with 5 mg/kg bw/day DON or saline at different time points (ZT24 = 0, 4, 8, 12, 16, and 20 h) in 1 day and were sacrificed 30 min after oral gavage. The inflammatory cytokines, signal transducers, and activators of transcription Janus kinase/signal transducers and activator of transcription 3 (JAKs/STAT3) pathway and bile acids levels were detected by enzyme-linked immunosorbent assay (ELISA), western blotting, and target metabolomics, respectively. The DON group showed significantly elevated interleukin-1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-α (TNF-α) levels (P < 0.05 for both) and impaired liver function with rhythm disturbances compared to the CON and Bmal1^OE groups. At the molecular level, expressions of some circadian clock proteins were significantly downregulated (P < 0.05 for both) and JAKs/STAT3 pathway was activated during DON exposure, accompanied by indicated circadian rhythm disturbance and inflammatory damage. Importantly, Bmal1 overexpression attenuated DON-induced liver damage, while related hepatic bile acids such as cholic acid (CA) showed a decreasing trend in the DON group compared with the CON group. Our study demonstrates a novel finding that Bmal1 plays a critical role in attenuating liver damage by inhibiting inflammatory levels and maintaining bile acids levels under the DON condition. Therefore, Bmal1 may also be a potential molecular target for reducing the hepatotoxic effects of DON in future studies.

Irregular sleep and cardiometabolic risk: Clinical evidence and mechanisms

Sleep regularity is an essential part of the multidimensional sleep health framework. The phenomenon of irregular sleep patterns is widespread in contemporary lifestyles. This review synthesizes clinical evidence to summarize the measures of sleep regularity and discusses the role of different sleep regularity indicators in developing cardiometabolic diseases (coronary heart disease, hypertension, obesity, and diabetes). Existing literature has proposed several measurements to assess sleep regularity, mainly including the standard deviation (SD) of sleep duration and timing, sleep regularity index (SRI), interdaily stability (IS), and social jetlag (SJL). Evidence on associations between sleep variability and cardiometabolic diseases varies depending on the measure used to characterize variability in sleep. Current studies have identified a robust association between SRI and cardiometabolic diseases. In comparison, the association between other metrics of sleep regularity and cardiometabolic diseases was mixed. Meanwhile, the associations of sleep variability with cardiometabolic diseases differ across the population. SD of sleep characteristics or IS may be more consistently associated with HbA1c in patients with diabetes compared with the general population. The association between SJL and hypertension for patients with diabetes was more accordant than in the general population. Interestingly, the age-stratified association between SJL and metabolic factors was observed in the present studies. Furthermore, the relevant literature was reviewed to generalize the potential mechanisms through which irregular sleep increases cardiometabolic risk, including circadian dysfunction, inflammation, autonomic dysfunction, hypothalamic-pituitary-adrenal (HPA) axis disorder, and gut dysbiosis. Health-related practitioners should give more attention to the role of sleep regularity on human cardiometabolic in the future.

TNF-α Inhibitors from Natural Compounds: An Overview, CADD Approaches, and their Exploration for Anti-inflammatory Agents

Inflammation is a natural process that occurs in the organism in response to harmful external agents. Despite being considered beneficial, exaggerated cases can cause severe problems for the body. The main inflammatory manifestations are pain, increased temperature, edema, decreased mobility, and quality of life for affected individuals. Diseases such as arthritis, cancer, allergies, infections, arteriosclerosis, neurodegenerative diseases, and metabolic problems are mainly characterized by an exaggerated inflammatory response. Inflammation is related to two categories of substances: pro- and anti-inflammatory mediators. Among the pro-inflammatory mediators is Tumor Necrosis Factor-α (TNF-α). It is associated with immune diseases, cancer, and psychiatric disorders which increase its excretion. Thus, it becomes a target widely used in discovering new antiinflammatory drugs. In this context, secondary metabolites biosynthesized by plants have been used for thousands of years and continue to be one of the primary sources of new drug scaffolds against inflammatory diseases. To decrease costs related to the drug discovery process, Computer-Aided Drug Design (CADD) techniques are broadly explored to increase the chances of success. In this review, the main natural compounds derived from alkaloids, flavonoids, terpene, and polyphenols as promising TNF-α inhibitors will be discussed. Finally, we applied a molecular modeling protocol involving all compounds described here, suggesting that their interactions with Tyr⁵⁹, Tyr¹¹⁹, Tyr¹⁵¹, Leu⁵⁷, and Gly¹²¹ residues are essential for the activity. Such findings can be useful for research groups worldwide to design new anti-inflammatory TNF-α inhibitors.

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.

Integrative bioinformatics analysis to identify the effects of circadian rhythm on Crohn’s disease

Background: Crohn’s disease (CD) is a multifactorial inflammatory bowel disease characterized by complex aberrant autoimmune disorders. Currently, the involvement of the circadian rhythm in the pathogenesis of CD is unknown.

Methods: Bulk and single-cell RNA-seq data and associated clinical data from patients with CD were downloaded from the Gene Expression Omnibus (GEO). Single-sample gene set enrichment analysis was performed to calculate the enrichment score (ES) of circadian rhythm-related genes. Differential expression analysis was used to identify differentially expressed genes. Functional enrichment analysis was used to explore potential disease mechanisms. CIBERSORT was used to estimate immune cell abundance. Single-cell RNA-seq data were analyzed using the R package “Seurat.”

Results: The ES of circadian rhythm-related genes was lower in the CD tissue than in the normal tissue. Ubiquitin-specific protease 2 (USP2), a circadian rhythm-related gene, was identified as a potential modulator of CD pathogenesis. USP2 expression was reduced in CD and was associated with disease severity. Moreover, the analysis of bulk RNA-seq and single-cell RNA-seq data showed that monocyte and neutrophil abundance was elevated in CD and was negatively correlated with USP2 expression. It should be noted that USP2 expression in acinar cells was negatively correlated with monocyte and neutrophil abundance. Functional enrichment analysis revealed several canonical pathways to be enriched in CD, including the interleukin-17 signaling pathway, tumor necrosis factor signaling pathway, cytokine–cytokine receptor interaction, toll-like receptor signaling pathway, and nod-like receptor signaling pathway.

Conclusion: Aberrant expression of circadian rhythm-related genes is correlated with CD pathogenesis. USP2 might be related to crosstalk among the different cell types in CD. These findings provide insights into future chronotherapy for CD.

Regulation of Circadian Genes Nr1d1 and Nr1d2 in Sex-Different Manners during Liver Aging

Background: Circadian rhythm is associated with the aging process and sex differences; however, how age and sex can change circadian regulation systems remains unclear. Thus, we aimed to evaluate age- and sex-related changes in gene expression and identify sex-specific target molecules that can regulate aging. Methods: Rat livers were categorized into four groups, namely, young male, old male, young female, and old female, and the expression of several genes involved in the regulation of the circadian rhythm was confirmed by in silico and in vitro studies. Results: Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses showed that the expression of genes related to circadian rhythms changed more in males than in females during liver aging. In addition, differentially expressed gene analysis and quantitative real-time polymerase chain reaction/western blotting analysis revealed that Nr1d1 and Nr1d2 expression was upregulated in males during liver aging. Furthermore, the expression of other circadian genes, such as Arntl, Clock, Cry1/2, Per1/2, and Rora/c, decreased in males during liver aging; however, these genes showed various gene expression patterns in females during liver aging. Conclusions: Age-related elevation of Nr1d1/2 downregulates the expression of other circadian genes in males, but not females, during liver aging. Consequently, age-related upregulation of Nr1d1/2 may play a more crucial role in the change in circadian rhythms in males than in females during liver aging.

Effects of BMAL1 on dentinogenic differentiation of Dental Pulp Stem Cells via PI3K / Akt / mTOR pathway

AIM

The present study was aimed to investigate the effect of the circadian clock gene Bmal1 on dentinogenic differentiation of dental pulp stem cells (DPSCs) under inflammatory conditions.

METHODOLOGY

DPSCs were isolated from the pulp tissue of the healthy donor and were then stimulated with different concentrations of lipopolysaccharide (LPS) to mimic inflammatory conditions. Real-time polymerase chain reaction (PCR) was used to detect the gene expression of circadian clock genes Bmal1, Clock, Per1, Per2, Cry1, and Cry2. Western blot (WB) was applied to analyze the protein expression of circadian clock proteins (BMAL1, CLOCK) and dentinogenic differentiation related proteins (DSPP, DMP1). In addition, the apoptosis and osteogenic differentiation of DPSCs were also analyzed in the presence of different concentrations of LPS.

RESULTS

The expression of circadian clock genes of DPSCs significantly changed in an inflammatory environment. WB analysis shows that BMAL1 is relevant to the dentinogenic differentiation of DPSCs. In low concentrations of LPS-mimicked inflammatory condition, the expression of BMAL1 increased and promoted the dentinogenic differentiation of DPSCs. However, under high concentrations of LPS-mimicked inflammatory condition, the expression of BMAL1 decreased and inhibited the dentinogenic differentiation of DPSCs. Moreover, the effects of BMAL1 on dentinogenic differentiation of DPSCs may be through PI3K / Akt / mTOR pathway.

CONCLUSIONS

This study showed that the circadian clock gene Bmal1 affected dentinogenic differentiation of DPSCs, providing a new insight for clinical stem cell-based restorative dentinogenesis therapies.

Macrophage CD36 and TLR4 Cooperation Promotes Foam Cell Formation and VSMC Migration and Proliferation Under Circadian Oscillations

Circadian rhythm disorders can accelerate atherosclerosis. This study aimed to determine the role of circadian disordered macrophages in atherosclerotic development. Mice were divided into NC group (normal circadian rhythm), L24 group (constant light), D12L12 group (weekly shift light/dark cycle), and D24 group (constant dark). Atherosclerotic progression was significantly accelerated in L24, D12L12, and D24 groups. Peritoneal macrophages from circadian disruption groups exhibited enhanced cytokine secretion and foam cell formation. Migration and proliferation of vascular smooth muscle cells (VSMCs) were increased under the conditioned medium of circadian disordered macrophages. The blockade of CD36 markedly inhibited foam cell formation. Compared with blocking CD36 or TLR4 alone, the co-inhibition of CD36 and TLR4 in macrophages further reduced cytokine secretion and more effectively inhibited VSMC migration and proliferation. In conclusion, the activation of CD36 and TLR4 in circadian disordered macrophages promotes foam cell formation and cytokine secretion and enhances VSMC migration and proliferation. Circadian rhythm disorders promote lipid uptake and cytokine secretion of macrophages by regulating CD36 and TLR4, and enhance VSMC migration and proliferation through the paracrine effect of macrophages.

Potential Effect of the Circadian Clock on Erectile Dysfunction

The circadian rhythm is an internal timing system, which is generated by circadian clock genes. Because the circadian rhythm regulates numerous cellular, behavioral, and physiological processes, organisms have evolved with intrinsic biological rhythms to adapt the daily environmental changes. A variety of pathological events occur at specific times, while disturbed rhythms can lead to metabolic syndrome, vascular dysfunction, inflammatory disorders, and cancer. Therefore, the circadian clock is considered closely related to various diseases. Recently, accumulated data have shown that the penis is regulated by the circadian clock, while erectile function is impaired by an altered sleep-wake cycle. The circadian rhythm appears to be a novel therapeutic target for preventing and managing erectile dysfunction (ED), although research is still progressing. In this review, we briefly summarize the superficial interactions between the circadian clock and erectile function, while focusing on how disturbed rhythms contribute to risk factors of ED. These risk factors include NO/cGMP pathway, atherosclerosis, diabetes mellitus, lipid abnormalities, testosterone deficiency, as well as dysfunction of endothelial and smooth muscle cells. On the basis of recent findings, we discuss the potential role of the circadian clock for future therapeutic strategies on ED, although further relevant research needs to be performed.

The potential impacts of circadian rhythm disturbances on male fertility

A circadian rhythm is an internalized timing system that synchronizes the cellular, behavioral, and physiological processes of organisms to the Earth's rotation. Because all physiological activities occur at a specific time, circadian rhythm disturbances can lead to various pathological disorders and diseases. Growing evidence has shown that the circadian clock is tightly connected to male fertility, and circadian perturbations contribute to infertility. The night shiftwork, insufficient sleep, and poor sleep quality are common causes of circadian disturbances, and many studies have reported that they impair sperm quality and increase the risk of male infertility. However, research on the impacts of light, body temperature, and circadian/circannual rhythms is relatively lacking, although some correlations have been demonstrated. Moreover, as the index of sperm quality was diverse and study designs were non-uniform, the conclusions were temporarily inconsistent and underlying mechanisms remain unclear. A better understanding of whether and how circadian disturbances regulate male fertility will be meaningful, as more scientific work schedules and rational lifestyles might help improve infertility.

Expression Patterns of Clock Gene mRNAs and Clock Proteins in Human Psoriatic Skin Samples

Psoriasis is a systemic inflammatory skin disorder that can be associated with sleep disturbance and negatively influence the daily rhythm. The link between the pathomechanism of psoriasis and the circadian rhythm has been suggested by several previous studies. However, there are insufficient data on altered clock mechanisms in psoriasis to prove these theories. Therefore, we investigated the expression of the core clock genes in human psoriatic lesional and non-lesional skin and in human adult low calcium temperature (HaCaT) keratinocytes after stimulation with pro-inflammatory cytokines. Furthermore, we examined the clock proteins in skin biopsies from psoriatic patients by immunohistochemistry. We found that the clock gene transcripts were elevated in psoriatic lesions, especially in non-lesional psoriatic areas, except for rev-erbα, which was consistently downregulated in the psoriatic samples. In addition, the REV-ERBα protein showed a different epidermal distribution in non-lesional skin than in healthy skin. In cytokine-treated HaCaT cells, changes in the amplitude of the bmal1, cry1, rev-erbα and per1 mRNA oscillation were observed, especially after TNFα stimulation. In conclusion, in our study a perturbation of clock gene transcripts was observed in uninvolved and lesional psoriatic areas compared to healthy skin. These alterations may serve as therapeutic targets and facilitate the development of chronotherapeutic strategies in the future.

Effects of PM Exposure on the Methylation of Clock Genes in a Population of Subjects with Overweight or Obesity

The expression of clock genes, regulating the synchronization of metabolic and behavioral processes with environmental light/dark cycles, is regulated by methylation and might be influenced by short-term exposure to airborne particulate matter (PM), especially in individuals that are hypersensitive to proinflammatory cues. The present study aimed to evaluate the effects of PM2.5 and PM10 on the methylation profile of the clock genes ARNTL, CLOCK, CRY1, CRY2, PER1, PER2, and PER3 in a population of 200 women with obesity. A significant association between PM10 exposure and the methylation of clock genes was found, namely, this was negative for PER2 gene and positive for the CLOCK, CRY1, CRY2, and PER3 genes. PM2.5 was negatively associated with methylation of PER2 gene and positively with methylation of CRY2 gene. Evidence was observed for effect modification from body mass index (BMI) regarding the PER1 gene: as PM2.5/10 increases, DNA methylation increases significantly for relatively low BMI values (BMI = 25), while it decreases in participants with severe obesity (BMI = 51). PM may therefore alter the epigenetic regulation of clock genes, possibly affecting circadian rhythms. Future studies are needed to clarify how alterations in clock gene methylation are predictive of disease development and how obesity can modulate the adverse health effects of PM.

USP2-Related Cellular Signaling and Consequent Pathophysiological Outcomes

Ubiquitin specific protease (USP) 2 is a multifunctional deubiquitinating enzyme. USP2 modulates cell cycle progression, and therefore carcinogenesis, via the deubiquitination of cyclins and Aurora-A. Other tumorigenic molecules, including epidermal growth factor and fatty acid synthase, are also targets for USP2. USP2 additionally prevents p53 signaling. On the other hand, USP2 functions as a key component of the CLOCK/BMAL1 complex and participates in rhythmic gene expression in the suprachiasmatic nucleus and liver. USP2 variants influence energy metabolism by controlling hepatic gluconeogenesis, hepatic cholesterol uptake, adipose tissue inflammation, and subsequent systemic insulin sensitivity. USP2 also has the potential to promote surface expression of ion channels in renal and intestinal epithelial cells. In addition to modifying the production of cytokines in immune cells, USP2 also modulates the signaling molecules that are involved in cytokine signaling in the target cells. Usp2 knockout mice exhibit changes in locomotion and male fertility, which suggest roles for USP2 in the central nervous system and male genital tract, respectively. In this review, we summarize the cellular events with USP2 contributions and list the signaling molecules that are upstream or downstream of USP2. Additionally, we describe phenotypic differences found in the in vitro and in vivo experimental models.