Hypercholesterolemia Causes Circadian Dysfunction: A Potential Risk Factor for Cardiovascular Disease

BMAL1 and CLOCK proteins exhibit differential association with mitochondrial dynamics, protein synthesis pathways and muscle strength in human muscle

Murine models lacking CLOCK/BMAL1 proteins in skeletal muscle (SkM) present muscle deterioration and mitochondria abnormalities. It is unclear whether humans with lower levels of these proteins in the SkM have similar alterations. Here we evaluated the association between BMAL1 and CLOCK protein mass with mitochondrial dynamics parameters and molecular and functional SkM quality markers in males. SkM biopsies were taken from the vastus lateralis of 16 male (non-athletes, non-obese and non-diabetic) subjects (8-9 a.m.). The morphology of mitochondria and their interaction with the sarcoplasmic reticulum (mitochondria-SR) were determined using transmission electron microscopy images. Additionally, protein abundance of the OXPHOS complex, mitochondria fusion/fission regulators, mitophagy and signalling proteins related to muscle protein synthesis were measured. To evaluate the quality of SkM, the cross-sectional area and maximal SkM strength were also measured. The results showed that BMAL1 protein mass was positively associated with mitochondria-SR distance, mitochondria size, mitochondria cristae density and mTOR protein mass. On the other hand, CLOCK protein mass was negatively associated with mitochondria-SR interaction, but positively associated with mitochondria complex III, OPA1 and DRP1 protein mass. Furthermore, CLOCK protein mass was positively associated with the protein synthesis signalling pathway (total mTOR, AKT and P70S6K protein mass) and SkM strength. These findings suggest that the BMAL1 and CLOCK proteins play different roles in regulating mitochondrial dynamics and SkM function in males, and that modulation of these proteins could be a potential therapeutic target for treating muscle diseases. KEY POINTS: In murine models, reductions in BMAL1 and CLOCK proteins lead to changes in mitochondria biology and a decline in muscle function. However, this association has not been explored in humans. We found that in human skeletal muscle, a decrease in BMAL1 protein mass is linked to smaller intermyofibrillar mitochondria, lower mitochondria cristae density, higher interaction between mitochondria and sarcoplasmic reticulum, and reduced mTOR protein mass. Additionally, we found that a decrease in CLOCK protein mass is associated with a higher interaction between mitochondria and sarcoplasmic reticulum, lower protein mass of OPA1 and DRP1, which regulates mitochondria fusion and fission, lower protein synthesis signalling pathway (mTOR, AKT and P70S6K protein mass), and decreased skeletal muscle strength. According to our findings in humans, which are supported by previous studies in animals, the mitochondrial dynamics and skeletal muscle function could be regulated differently by BMAL1 and CLOCK proteins. As a result, targeting the modulation of these proteins could be a potential therapeutic approach for treating muscle diseases and metabolic disorders related to muscle.

Circadian Mechanisms in Brain Fluid Biology

The brain is a complex organ, fundamentally changing across the day to perform basic functions like sleep, thought, and regulating whole-body physiology. This requires a complex symphony of nutrients, hormones, ions, neurotransmitters and more to be properly distributed across the brain to maintain homeostasis throughout 24 hours. These solutes are distributed both by the blood and by cerebrospinal fluid. Cerebrospinal fluid contents are distinct from the general circulation because of regulation at brain barriers including the choroid plexus, glymphatic system, and blood-brain barrier. In this review, we discuss the overlapping circadian (≈24-hour) rhythms in brain fluid biology and at the brain barriers. Our goal is for the reader to gain both a fundamental understanding of brain barriers alongside an understanding of the interactions between these fluids and the circadian timing system. Ultimately, this review will provide new insight into how alterations in these finely tuned clocks may lead to pathology.

Molecular mechanisms of artificial light at night affecting circadian rhythm disturbance

Artificial light at night (ALAN) pollution has been regarded as a global environmental concern. More than 80% of the global population is exposed to light pollution. Exacerbating this issue, artificially lit outdoor areas are growing by 2.2% per year, while continuously lit areas have brightened by 2.2% each year due to rapid population growth and expanding urbanization. Furthermore, the increasing prevalence of night shift work and smart device usage contributes to the inescapable influence of ALAN. Studies have shown that ALAN can disrupt endogenous biological clocks, resulting in a disturbance of the circadian rhythm, which ultimately affects various physiological functions. Up until now, scholars have studied various disease mechanisms caused by ALAN that may be related to the response of the circadian system to light. This review outlines the molecular mechanisms by which ALAN causes circadian rhythm abnormalities in sleep disorders, endocrine diseases, cardiovascular disease, cancer, immune impairment, depression, anxiety and cognitive impairments.

Insight on Cardiac Chronobiology and Latest Developments of Chronotherapeutic Antihypertensive Interventions for Better Clinical Outcomes

Cardiac circadian rhythms are an important regulator of body functions, including cardiac activities and blood pressure. Disturbance of circadian rhythm is known to trigger and aggravate various cardiovascular diseases. Thus, modulating the circadian rhythm can be used as a therapeutic approach to cardiovascular diseases. Through this work, we intend to discuss the current understanding of cardiac circadian rhythms, in terms of quantifiable parameters like BP and HR. We also elaborate on the molecular regulators and the molecular cascades along with their specific genetic aspects involved in modulating circadian rhythms, with specific reference to cardiovascular health and cardiovascular diseases. Along with this, we also presented the latest pharmacogenomic and metabolomics markers involved in chronobiological control of the cardiovascular system along with their possible utility in cardiovascular disease diagnosis and therapeutics. Finally, we reviewed the current expert opinions on chronotherapeutic approaches for utilizing the conventional as well as the new pharmacological molecules for antihypertensive chronotherapy.

MicroRNA-21 Controls Circadian Regulation of Apoptosis in Atherosclerotic Lesions

Background: The necrotic core partly formed by ineffective efferocytosis increases the risk of an atherosclerotic plaque rupture. microRNAs contribute to necrotic core formation by regulating efferocytosis and macrophage apoptosis. Atherosclerotic plaque rupture occurs at increased frequency in the early morning, indicating diurnal changes in plaque vulnerability. Although circadian rhythms play a role in atherosclerosis, the molecular clock output pathways that control plaque composition and rupture susceptibility are unclear. Methods: Circadian gene expression, necrotic core size, and apoptosis and efferocytosis in aortic lesions were investigated at different times of the day in Apoe^-/-Mir21^+/+ mice and Apoe^-/- Mir21^-/- mice after consumption of a high-fat diet for 12 weeks feeding. Genome-wide gene expression and lesion formation were analyzed in bone marrow (BM)-transplanted mice. Diurnal changes in apoptosis and clock gene expression were determined in human atherosclerotic lesions. Results: The expression of molecular clock genes, lesional apoptosis, and necrotic core size were diurnally regulated in Apoe^-/- mice. Efferocytosis did not match the diurnal increase in apoptosis at the beginning of the active phase. However, in parallel with apoptosis, expression levels of oscillating Mir21 strands decreased in the mouse atherosclerotic aorta. Mir21 knockout abolished circadian regulation of apoptosis and reduced necrotic core size, but did not affect core clock gene expression. Further, Mir21 knockout upregulated expression of pro-apoptotic XIAP associated factor 1 (Xaf1) in the atherosclerotic aorta, which abolished circadian expression of Xaf1. The anti-apoptotic effect of Mir21 was mediated by non-canonical targeting of Xaf1 through both Mir21 strands. Mir21 knockout in BM cells also reduced atherosclerosis and necrotic core size. Circadian regulation of clock gene expression was confirmed in human atherosclerotic lesions. Apoptosis oscillated diurnally in phase with XAF1 expression, demonstrating an early morning peak anti-phase to that of the Mir21 strands. Conclusions: Our findings suggest that the molecular clock in atherosclerotic lesions induces a diurnal rhythm of apoptosis regulated by circadian Mir21 expression in macrophages that is not matched by efferocytosis, thus increasing the size of the necrotic core.

Circadian clock genes as promising therapeutic targets for autoimmune diseases

Circadian rhythm is a natural, endogenous process whose physiological functions are controlled by a set of clock genes. Disturbance of the clock genes have detrimental effects on both innate and adaptive immunity, which significantly enhance pro-inflammatory responses and susceptibility to autoimmune diseases via strictly controlling the individual cellular components of the immune system that initiate and perpetuate the inflammation pathways. Autoimmune diseases, especially rheumatoid arthritis (RA), often exhibit substantial circadian oscillations, and circadian rhythm is involved in the onset and progression of autoimmune diseases. Mounting evidence indicate that the synthetic ligands of circadian clock genes have the property of reducing the susceptibility and clinical severity of subjects. This review supplies an overview of the roles of circadian clock genes in the pathology of autoimmune diseases, including BMAL1, CLOCK, PER, CRY, REV-ERBα, and ROR. Furthermore, summarized some circadian clock genes as candidate genes for autoimmune diseases and current advancement on therapy of autoimmune diseases with synthetic ligands of circadian clock genes. The existing body of knowledge demonstrates that circadian clock genes are inextricably linked to autoimmune diseases. Future research should pay attention to improve the quality of life of patients with autoimmune diseases and reduce the effects of drug preparation on the normal circadian rhythms.

The risks of using the chi-square periodogram to estimate the period of biological rhythms

The chi-square periodogram (CSP), developed over 40 years ago, continues to be one of the most popular methods to estimate the period of circadian (circa 24-h) rhythms. Previous work has indicated the CSP is sometimes less accurate than other methods, but understanding of why and under what conditions remains incomplete. Using simulated rhythmic time-courses, we found that the CSP is prone to underestimating the period in a manner that depends on the true period and the length of the time-course. This underestimation bias is most severe in short time-courses (e.g., 3 days), but is also visible in longer simulated time-courses (e.g., 12 days) and in experimental time-courses of mouse wheel-running and ex vivo bioluminescence. We traced the source of the bias to discontinuities in the periodogram that are related to the number of time-points the CSP uses to calculate the observed variance for a given test period. By revising the calculation to avoid discontinuities, we developed a new version, the greedy CSP, that shows reduced bias and improved accuracy. Nonetheless, even the greedy CSP tended to be less accurate on our simulated time-courses than an alternative method, namely the Lomb-Scargle periodogram. Thus, although our study describes a major improvement to a classic method, it also suggests that users should generally avoid the CSP when estimating the period of biological rhythms.

The chi-square periodogram is a popular method for estimating period length, one of the most important properties of the daily biological rhythms found throughout nature. In this study, we identify a major source of inaccuracy in the chi-square periodogram, and quantify the inaccuracy using a broad array of simulated and experimentally observed biological rhythms. Although we revise the chi-square periodogram calculation to improve its accuracy, we also show that the revised version is still less accurate than an alternative method, the Lomb-Scargle periodogram. Our work thus provides evidence on how to obtain better estimates of the period of biological rhythms.

A new activator of esterase D decreases blood cholesterol level through ESD/JAB1/ABCA1 pathway

Excessively high cholesterol content in the blood leads to nonalcohol fatty liver disease (NAFLD) and arteriosclerosis. Although there are increasing publications and patent applications to lower blood cholesterol with small chemical molecules, limited effective drugs can be available in clinic. It is necessary to uncover new targets and drugs to alleviate high cholesterol. Esterase D (ESD) is abundant in liver and it remains unknown about its role in cholesterol metabolism. Here we reported that small chemical molecule fluorescigenic pyrazoline derivative 5 (FPD5), a new ESD activator, could effectively reverse high blood cholesterol level and prevent fatty liver and arteriosclerosis in apoE^-/- mice fed the high-fat diet. We also observed that FPD5 could reduce oxidized low density lipoprotein (oxLDL)-induced formation of foam cells. To further investigate the mechanism of FPD5 action on blood cholesterol modulation, we found that ESD trigged by FPD5 was aggregated in lysosome and interacted with Jun activation domain binding protein 1 (JAB1). ESD served as a deacetylase to remove Thr89 acetylation of JAB1 and increased its activity; thus, promoting the ATP-binding cassette transporters A1 (ABCA1) to accelerate cholesterol efflux. Our findings demonstrate that FPD5 decreases blood cholesterol level to ameliorate NAFLD and arteriosclerosis through ESD/JAB1/ABCA1 pathway, and ESD functions as a novel nonclassical deacetylase that hydrolyzes serine/threonine acetyl group. Our findings not only highlight that FPD5 may be a pioneer drug for alleviating blood cholesterol but also indicate that ESD is a potential drug target that promotes cholesterol metabolism.

Does a high-fat diet affect the circadian clock, or is it the other way around? A systematic review

This paper reviews studies that addressed the influence of diet on circadian rhythmicity in mice and, in turn, circadian clock chronodisruption and its role in the development of metabolic disorders. Studies from the past 14 years were selected via a systematic search conducted using the PubMed electronic database. After applying the inclusion and exclusion criteria, 291 studies were selected, of which 13 were chosen using the following inclusion criteria: use of a high-fat diet for mice, evaluation of clock gene expression, and the association between chronodisruption and lipid metabolism disorders. These studies reported changes in animals' biological clock when they developed metabolic disorders by consuming a high-fat diet. It was also evident that some clock gene mutations or deletions triggered metabolic changes. Disturbances of clock gene machinery may play important roles in lipid metabolism and the development of atherosclerotic processes. However, many metabolic processes also affect the function of clock genes and circadian systems. In summary, this review's results may provide new insights into the reciprocal regulation of energy homeostasis and the biological clock.

Diel pattern in the structure and function of the gut microbial community in Lymantria dispar asiatica (Lepidoptera: Lymantriidae) larvae

In the present study, diel pattern in gut microbial communities in insects were evaluated. Lymantria dispar asiatica fourth instar larvae (72 ± 2 hr after molting) at noon (LdD) and midnight (LdN) were used for a comparative analysis of the gut microbial community. Ten bacterial operational taxonomic units (OTUs) were shared between LdD and LdN samples. One bacterial OTU was specific to LdD. The dominant gut microbes were OTU72 in LdD and OTU75 in LdN. A linear discriminant analysis effect size cladogram suggested that ten bacterial OTUs maintain significant differences in relative abundances between LdD and LdN. These results agreed with the discrete ellipses between LdD and LdN in principal coordinates analysis plots. Additionally, using phylogenetic investigation of communities by reconstruction of unobserved states, the gut microbial community was assigned to 23 functional terms, among which 22 exhibited significant differences between LdD and LdN. To conclude, the present study documented a diel pattern in the gut microbial community of L. dispar asiatica larvae.

Altered Circadian Timing System-Mediated Non-Dipping Pattern of Blood Pressure and Associated Cardiovascular Disorders in Metabolic and Kidney Diseases

The morning surge in blood pressure (BP) coincides with increased cardiovascular (CV) events. This strongly suggests that an altered circadian rhythm of BP plays a crucial role in the development of CV disease (CVD). A disrupted circadian rhythm of BP, such as the non-dipping type of hypertension (i.e., absence of nocturnal BP decline), is frequently observed in metabolic disorders and chronic kidney disease (CKD). The circadian timing system, controlled by the central clock in the suprachiasmatic nucleus of the hypothalamus and/or by peripheral clocks in the heart, vasculature, and kidneys, modulates the 24 h oscillation of BP. However, little information is available regarding the molecular and cellular mechanisms of an altered circadian timing system-mediated disrupted dipping pattern of BP in metabolic disorders and CKD that can lead to the development of CV events. A more thorough understanding of this pathogenesis could provide novel therapeutic strategies for the management of CVD. This short review will address our and others' recent findings on the molecular mechanisms that may affect the dipping pattern of BP in metabolic dysfunction and kidney disease and its association with CV disorders.

Loss of the clock gene PER2 is associated with cancer development and altered expression of important tumor-related genes in oral cancer

Recent studies have demonstrated that abnormal expression of the clock gene PER2 is closely associated with the development of a variety of cancer types. However, the expression of PER2 in oral squamous cell carcinoma (OSCC), a common malignant tumor in humans, and its correlations with the clinicopathological parameters and survival time of OSCC patients and the altered expression of important tumor-related genes remain unclear. In the present study, we detected the mRNA and protein expression levels of PER2, PIK3CA, PTEN, P53, P14ARF and caspase‑8 in OSCC tissues and cancer-adjacent oral mucosa by reverse transcription-quantitative PCR (RT-qPCR), western blotting and immunohistochemistry. The results showed that the PER2, PTEN, P53, P14ARF and caspase‑8 mRNA and protein expression levels in OSCC were significantly reduced compared with those in cancer-adjacent tissues. Additionally, the PIK3CA protein expression level was significantly increased in OSCC tissues, whereas the mRNA level was not. Decreased expression of PER2 was significantly associated with advanced clinical stage and the presence of lymphatic metastasis in OSCC patients. Patients with PER2‑negative expression had a significantly shorter survival time than those with PER2‑positive expression. PER2 expression was negatively correlated with PIK3CA and P53 levels, and positively correlated with PTEN, P14ARF and caspase‑8 levels. In summary, the results of this study suggest that loss of PER2 expression is closely associated with the genesis and development of OSCC and that PER2 may be an important prognostic biomarker in OSCC. PER2 may serve an antitumor role via the P53/P14ARF, PIK3CA/AKT and caspase‑8 pathways.