-
Science Advances Jun 2024The suprachiasmatic nucleus (SCN) sets the phase of oscillation throughout the brain and body. Anatomical evidence reveals a portal system linking the SCN and the...
The suprachiasmatic nucleus (SCN) sets the phase of oscillation throughout the brain and body. Anatomical evidence reveals a portal system linking the SCN and the organum vasculosum of the lamina terminalis (OVLT), begging the question of the direction of blood flow and the nature of diffusible signals that flow in this specialized vasculature. Using a combination of anatomical and in vivo two-photon imaging approaches, we unequivocally show that blood flows unidirectionally from the SCN to the OVLT, that blood flow rate displays daily oscillations with a higher rate at night than in the day, and that circulating vasopressin can access portal vessels. These findings highlight a previously unknown central nervous system communication pathway, which, like that of the pituitary portal system, could allow neurosecretions to reach nearby target sites in OVLT, avoiding dilution in the systemic blood. In both of these brain portal pathways, the target sites relay signals broadly to both the brain and the rest of the body.
Topics: Suprachiasmatic Nucleus; Animals; Mice; Hypothalamus; Brain; Portal System; Male; Vasopressins; Cerebrovascular Circulation; Circadian Rhythm
PubMed: 38905332
DOI: 10.1126/sciadv.adn8350 -
Frontiers in Molecular Biosciences 2024All organisms have various circadian, behavioral, and physiological 24-h periodic rhythms, which are controlled by the circadian clock. The circadian clock controls... (Review)
Review
All organisms have various circadian, behavioral, and physiological 24-h periodic rhythms, which are controlled by the circadian clock. The circadian clock controls various behavioral and physiological rhythms. In mammals, the primary circadian clock is present in the suprachiasmatic nucleus of the hypothalamus. The rhythm of the circadian clock is controlled by the interaction between negative and positive feedback loops, consisting of crucial clock regulators (including Bmal1 and Clock), three cycles (mPer1, mPer2, and mPer3), and two cryptochromes (Cry1 and Cry2). The development of early mammalian embryos is an ordered and complex biological process that includes stages from fertilized eggs to blastocysts and undergoes important morphological changes, such as blastocyst formation, cell multiplication, and compaction. The circadian clock affects the onset and timing of embryonic development. The circadian clock affects many biological processes, including eating time, immune function, sleep, energy metabolism, and endocrinology, therefore, it is also crucial for overall health, growth and development after birth. This review summarized the effects of the circadian clock in the body's physiological activities. A new strategy is proposed for the prevention of malformations or diseases by regulating the circadian clock or changing circadian rhythms.
PubMed: 38903177
DOI: 10.3389/fmolb.2024.1387576 -
International Journal of Molecular... May 2024The circadian clock regulates biological cycles across species and is crucial for physiological activities and biochemical reactions, including cancer onset and... (Review)
Review
The circadian clock regulates biological cycles across species and is crucial for physiological activities and biochemical reactions, including cancer onset and development. The interplay between the circadian rhythm and cancer involves regulating cell division, DNA repair, immune function, hormonal balance, and the potential for chronotherapy. This highlights the importance of maintaining a healthy circadian rhythm for cancer prevention and treatment. This article investigates the complex relationship between the circadian rhythm and cancer, exploring how disruptions to the internal clock may contribute to tumorigenesis and influence cancer progression. Numerous databases are utilized to conduct searches for articles, such as NCBI, MEDLINE, and Scopus. The keywords used throughout the academic archives are "circadian rhythm", "cancer", and "circadian clock". Maintaining a healthy circadian cycle involves prioritizing healthy sleep habits and minimizing disruptions, such as consistent sleep schedules, reduced artificial light exposure, and meal timing adjustments. Dysregulation of the circadian clock gene and cell cycle can cause tumor growth, leading to the need to regulate the circadian cycle for better treatment outcomes. The circadian clock components significantly impact cellular responses to DNA damage, influencing cancer development. Understanding the circadian rhythm's role in tumor diseases and their therapeutic targets is essential for treating and preventing cancer. Disruptions to the circadian rhythm can promote abnormal cell development and tumor metastasis, potentially due to immune system imbalances and hormonal fluctuations.
Topics: Humans; Neoplasms; Circadian Rhythm; Animals; Circadian Clocks
PubMed: 38892035
DOI: 10.3390/ijms25115846 -
Frontiers in Genetics 2024Circadian rhythms, essential 24-hour cycles guiding biological functions, synchronize organisms with daily environmental changes. These rhythms, which are evolutionarily... (Review)
Review
Circadian rhythms, essential 24-hour cycles guiding biological functions, synchronize organisms with daily environmental changes. These rhythms, which are evolutionarily conserved, govern key processes like feeding, sleep, metabolism, body temperature, and endocrine secretion. The central clock, located in the suprachiasmatic nucleus (SCN), orchestrates a hierarchical network, synchronizing subsidiary peripheral clocks. At the cellular level, circadian expression involves transcription factors and epigenetic remodelers, with environmental signals contributing flexibility. Circadian disruption links to diverse diseases, emphasizing the urgency to comprehend the underlying mechanisms. This review explores the communication between the environment and chromatin, focusing on histone post-translational modifications. Special attention is given to the significance of histone methylation in circadian rhythms and metabolic control, highlighting its potential role as a crucial link between metabolism and circadian rhythms. Understanding these molecular intricacies holds promise for preventing and treating complex diseases associated with circadian disruption.
PubMed: 38818037
DOI: 10.3389/fgene.2024.1343030 -
Frontiers in Endocrinology 2024This article discusses data showing that mammals, including humans, have two sources of melatonin that exhibit different functions. The best-known source of melatonin,... (Review)
Review
This article discusses data showing that mammals, including humans, have two sources of melatonin that exhibit different functions. The best-known source of melatonin, herein referred to as Source #1, is the pineal gland. In this organ, melatonin production is circadian with maximal synthesis and release into the blood and cerebrospinal fluid occurring during the night. Of the total amount of melatonin produced in mammals, we speculate that less than 5% is synthesized by the pineal gland. The melatonin rhythm has the primary function of influencing the circadian clock at the level of the suprachiasmatic nucleus (the CSF melatonin) and the clockwork in all peripheral organs (the blood melatonin) via receptor-mediated actions. A second source of melatonin (Source # 2) is from multiple tissues throughout the body, probably being synthesized in the mitochondria of these cells. This constitutes the bulk of the melatonin produced in mammals and is concerned with metabolic regulation. This review emphasizes the action of melatonin from peripheral sources in determining re-dox homeostasis, but it has other critical metabolic effects as well. Extrapineal melatonin synthesis does not exhibit a circadian rhythm and it is not released into the blood but acts locally in its cell of origin and possibly in a paracrine matter on adjacent cells. The factors that control/influence melatonin synthesis at extrapineal sites are unknown. We propose that the concentration of melatonin in these cells is determined by the subcellular redox state and that melatonin synthesis may be inducible under stressful conditions as in plant cells.
Topics: Melatonin; Humans; Animals; Circadian Rhythm; Pineal Gland; Suprachiasmatic Nucleus
PubMed: 38808108
DOI: 10.3389/fendo.2024.1414463 -
Fluids and Barriers of the CNS May 2024Choroid plexus (ChP), the brain structure primarily responsible for cerebrospinal fluid production, contains a robust circadian clock, whose role remains to be...
Choroid plexus (ChP), the brain structure primarily responsible for cerebrospinal fluid production, contains a robust circadian clock, whose role remains to be elucidated. The aim of our study was to [1] identify rhythmically controlled cellular processes in the mouse ChP and [2] assess the role and nature of signals derived from the master clock in the suprachiasmatic nuclei (SCN) that control ChP rhythms. To accomplish this goal, we used various mouse models (WT, mPer2, ChP-specific Bmal1 knockout) and combined multiple experimental approaches, including surgical lesion of the SCN (SCNx), time-resolved transcriptomics, and single cell luminescence microscopy. In ChP of control (Ctrl) mice collected every 4 h over 2 circadian cycles in darkness, we found that the ChP clock regulates many processes, including the cerebrospinal fluid circadian secretome, precisely times endoplasmic reticulum stress response, and controls genes involved in neurodegenerative diseases (Alzheimer's disease, Huntington's disease, and frontotemporal dementia). In ChP of SCNx mice, the rhythmicity detected in vivo and ex vivo was severely dampened to a comparable extent as in mice with ChP-specific Bmal1 knockout, and the dampened cellular rhythms were restored by daily injections of dexamethasone in mice. Our data demonstrate that the ChP clock controls tissue-specific gene expression and is strongly dependent on the presence of a functional connection with the SCN. The results may contribute to the search for a novel link between ChP clock disruption and impaired brain health.
Topics: Animals; Suprachiasmatic Nucleus; Choroid Plexus; Circadian Clocks; Mice; Mice, Inbred C57BL; Circadian Rhythm; Male; Mice, Knockout; ARNTL Transcription Factors
PubMed: 38802875
DOI: 10.1186/s12987-024-00547-3 -
Neuropharmacology Sep 2024Feeding, like many other biological functions, displays a daily rhythm. This daily rhythmicity is controlled by the circadian timing system of which the central master... (Review)
Review
Feeding, like many other biological functions, displays a daily rhythm. This daily rhythmicity is controlled by the circadian timing system of which the central master clock is located in the hypothalamic suprachiasmatic nucleus (SCN). Other brain areas and tissues throughout the body also display rhythmic functions and contain the molecular clock mechanism known as peripheral oscillators. To generate the daily feeding rhythm, the SCN signals to different hypothalamic areas with the lateral hypothalamus, paraventricular nucleus and arcuate nucleus being the most prominent. With respect to the rewarding aspects of feeding behavior, the dopaminergic system is also under circadian influence. However the SCN projects only indirectly to the different reward regions, such as the ventral tegmental area where dopamine neurons are located. In addition, high palatable, high caloric diets have the potential to disturb the normal daily rhythms of physiology and have been shown to alter for example meal patterns. Around a meal several hormones and peptides are released that are also under circadian influence. For example, the release of postprandial insulin and glucagon-like peptide following a meal depend on the time of the day. Finally, we review the effect of deletion of different clock genes on feeding behavior. The most prominent effect on feeding behavior has been observed in Clock mutants, whereas deletion of Bmal1 and Per1/2 only disrupts the day-night rhythm, but not overall intake. Data presented here focus on the rodent literature as only limited data are available on the mechanisms underlying daily rhythms in human eating behavior.
Topics: Animals; Feeding Behavior; Circadian Rhythm; Humans; Suprachiasmatic Nucleus
PubMed: 38795953
DOI: 10.1016/j.neuropharm.2024.110007 -
Chrono-Endocrinology in Clinical Practice: A Journey from Pathophysiological to Therapeutic Aspects.Life (Basel, Switzerland) Apr 2024This review was aimed at collecting the knowledge on the pathophysiological and clinical aspects of endocrine rhythms and their implications in clinical practice,... (Review)
Review
This review was aimed at collecting the knowledge on the pathophysiological and clinical aspects of endocrine rhythms and their implications in clinical practice, derived from the published literature and from some personal experiences on this topic. We chose to review, according to the PRISMA guidelines, the results of original and observational studies, reviews, meta-analyses and case reports published up to March 2024. Thus, after summarizing the general aspects of biological rhythms, we will describe the characteristics of several endocrine rhythms and the consequences of their disruption, paying particular attention to the implications in clinical practice. Rhythmic endocrine secretions, like other physiological rhythms, are genetically determined and regulated by a central hypothalamic CLOCK located in the suprachiasmatic nucleus, which links the timing of the rhythms to independent clocks, in a hierarchical organization for the regulation of physiology and behavior. However, some environmental factors, such as daily cycles of light/darkness, sleep/wake, and timing of food intake, may influence the rhythm characteristics. Endocrine rhythms are involved in important physiological processes and their disruption may cause several disorders and also cancer. Thus, it is very important to prevent disruptions of endocrine rhythms and to restore a previously altered rhythm by an early corrective chronotherapy.
PubMed: 38792568
DOI: 10.3390/life14050546 -
Clinical and Experimental Hepatology Mar 2024The biological rhythm is a fundamental aspect of an organism, regulating many physiological processes. This study focuses on the analysis of the molecular basis of... (Review)
Review
The biological rhythm is a fundamental aspect of an organism, regulating many physiological processes. This study focuses on the analysis of the molecular basis of circadian rhythms and its impact on the functioning of the liver. The regulation of biological rhythms is carried out by the clock system, which consists of the central clock and peripheral clocks. The central clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus and is regulated by signals received from the retinal pathway. The SCN regulates the circadian rhythm of the entire body through its indirect influence on the peripheral clocks. In turn, the peripheral clocks can maintain their own rhythm, independent of the SCN, by creating special feedback loops between transcriptional and translational factors. The main protein families involved in these processes are CLOCK, BMAL, PER and CRY. Disorders in the expression of these factors have a significant impact on the functioning of the liver. In such cases lipid metabolism, cholesterol metabolism, bile acid metabolism, alcohol metabolism, and xenobiotic detoxification can be significantly affected. Clock dysfunctions contribute to the pathogenesis of various disorders, including fatty liver disease, liver cirrhosis and different types of cancer. Therefore understanding circadian rhythm can have significant implications for the therapy of many liver diseases, as well as the development of new preventive and treatment strategies.
PubMed: 38765904
DOI: 10.5114/ceh.2024.136220 -
Frontiers in Endocrinology 2024The topic of human circadian rhythms is not only attracting the attention of clinical researchers from various fields but also sparking a growing public interest. The... (Review)
Review
The topic of human circadian rhythms is not only attracting the attention of clinical researchers from various fields but also sparking a growing public interest. The circadian system comprises the central clock, located in the suprachiasmatic nucleus of the hypothalamus, and the peripheral clocks in various tissues that are interconnected; together they coordinate many daily activities, including sleep and wakefulness, physical activity, food intake, glucose sensitivity and cardiovascular functions. Disruption of circadian regulation seems to be associated with metabolic disorders (particularly impaired glucose tolerance) and cardiovascular disease. Previous clinical trials revealed that disturbance of the circadian system, specifically due to shift work, is associated with an increased risk of type 2 diabetes mellitus. This review is intended to provide clinicians who wish to implement knowledge of circadian disruption in diagnosis and strategies to avoid cardio-metabolic disease with a general overview of this topic.
Topics: Humans; Circadian Rhythm; Cardiovascular Diseases; Metabolic Diseases; Diabetes Mellitus, Type 2; Chronobiology Disorders
PubMed: 38742195
DOI: 10.3389/fendo.2024.1328139