Melatonin feedback on clock genes: a theory involving the proteasome

Revealing Melatonin's Mysteries: Receptors, Signaling Pathways, and Therapeutics Applications

Melatonin (5-methoxy-acetyl tryptamine) is a sleep-inducing hormone, and the pineal gland produces it in response to the circadian clock of darkness. In the body, MT1 and MT2 receptors are mostly found, having an orthosteric pocket and ligand binding determinants. Melatonin acts by binding on melatonin receptors, intracellular proteins, and orphan nuclear receptors. It inhibits adenyl cyclase and activates phospholipase C, resulting in gene expression and an intracellular alteration environment. Melatonin signaling pathways are also associated with other intracellular signaling pathways, i. e., cAMP/PKA and MAPK/ERK pathways. Relative expression of different proteins depends on the coupling profile of G protein, accounting pharmacology of the melatonin receptor bias system, and mediates action in a Gi-dependent manner. It shows antioxidant, antitumor, antiproliferative, and neuroprotective activity. Different types of melatonin agonists have been synthesized for the treatment of sleeping disorders. Researchers have developed therapeutics that target melatonin signaling, which could benefit a wide range of medical conditions. This review focuses on melatonin receptors, pharmacology, and signaling cascades; it aims to provide basic mechanical aspects of the receptor's pharmacology, melatonin's functions in cancer and neurodegenerative diseases, and any treatments and drugs designed for these diseases. This will allow a basic comparison between the receptors in question, highlighting any parallels and differences that may exist and providing fundamental knowledge about these receptors to future researchers.

Melatonin: a ferroptosis inhibitor with potential therapeutic efficacy for the post-COVID-19 trajectory of accelerated brain aging and neurodegeneration

The unprecedented pandemic of COVID-19 swept millions of lives in a short period, yet its menace continues among its survivors in the form of post-COVID syndrome. An exponentially growing number of COVID-19 survivors suffer from cognitive impairment, with compelling evidence of a trajectory of accelerated aging and neurodegeneration. The novel and enigmatic nature of this yet-to-unfold pathology demands extensive research seeking answers for both the molecular underpinnings and potential therapeutic targets. Ferroptosis, an iron-dependent cell death, is a strongly proposed underlying mechanism in post-COVID-19 aging and neurodegeneration discourse. COVID-19 incites neuroinflammation, iron dysregulation, reactive oxygen species (ROS) accumulation, antioxidant system repression, renin-angiotensin system (RAS) disruption, and clock gene alteration. These events pave the way for ferroptosis, which shows its signature in COVID-19, premature aging, and neurodegenerative disorders. In the search for a treatment, melatonin shines as a promising ferroptosis inhibitor with its repeatedly reported safety and tolerability. According to various studies, melatonin has proven efficacy in attenuating the severity of certain COVID-19 manifestations, validating its reputation as an anti-viral compound. Melatonin has well-documented anti-aging properties and combating neurodegenerative-related pathologies. Melatonin can block the leading events of ferroptosis since it is an efficient anti-inflammatory, iron chelator, antioxidant, angiotensin II antagonist, and clock gene regulator. Therefore, we propose ferroptosis as the culprit behind the post-COVID-19 trajectory of aging and neurodegeneration and melatonin, a well-fitting ferroptosis inhibitor, as a potential treatment.

Melatonin: the placental antioxidant and anti-inflammatory

Melatonin (N-acetyl-5-methoxytryptamine) is an indolamine hormone with many physiological and biological roles. Melatonin is an antioxidant, anti-inflammatory, free radical scavenger, circadian rhythm regulator, and sleep hormone. However, its most popular role is the ability to regulate sleep through the circadian rhythm. Interestingly, recent studies have shown that melatonin is an important and essential hormone during pregnancy, specifically in the placenta. This is primarily due to the placenta's ability to synthesize its own melatonin rather than depending on the pineal gland. During pregnancy, melatonin acts as an antioxidant and anti-inflammatory, which is necessary to ensure a stable environment for both the mother and the fetus. It is an essential antioxidant in the placenta because it reduces oxidative stress by constantly scavenging for free radicals, i.e., maintain the placenta's integrity. In a healthy pregnancy, the maternal immune system is constantly altered to accommodate the needs of the growing fetus, and melatonin acts as a key anti-inflammatory by regulating immune homeostasis during early and late gestation. This literature review aims to identify and summarize melatonin's role as a powerful antioxidant and anti-inflammatory that reduces oxidative stress and inflammation to maintain a favorable homeostatic environment in the placenta throughout gestation.

Melatonin: a modulator in metabolic rewiring in T-cell malignancies

Melatonin, (N-acetyl-5-methoxytryptamine) an indoleamine exerts multifaced effects and regulates numerous cellular pathways and molecular targets associated with circadian rhythm, immune modulation, and seasonal reproduction including metabolic rewiring during T cell malignancy. T-cell malignancies encompass a group of hematological cancers characterized by the uncontrolled growth and proliferation of malignant T-cells. These cancer cells exhibit a distinct metabolic adaptation, a hallmark of cancer in general, as they rewire their metabolic pathways to meet the heightened energy requirements and biosynthesis necessary for malignancies is the Warburg effect, characterized by a shift towards glycolysis, even when oxygen is available. In addition, T-cell malignancies cause metabolic shift by inhibiting the enzyme pyruvate Dehydrogenase Kinase (PDK) which in turn results in increased acetyl CoA enzyme production and cellular glycolytic activity. Further, melatonin plays a modulatory role in the expression of essential transporters (Glut1, Glut2) responsible for nutrient uptake and metabolic rewiring, such as glucose and amino acid transporters in T-cells. This modulation significantly impacts the metabolic profile of T-cells, consequently affecting their differentiation. Furthermore, melatonin has been found to regulate the expression of critical signaling molecules involved in T-cell activations, such as CD38, and CD69. These molecules are integral to T-cell adhesion, signaling, and activation. This review aims to provide insights into the mechanism of melatonin's anticancer properties concerning metabolic rewiring during T-cell malignancy. The present review encompasses the involvement of oncogenic factors, the tumor microenvironment and metabolic alteration, hallmarks, metabolic reprogramming, and the anti-oncogenic/oncostatic impact of melatonin on various cancer cells.

From Chronodisruption to Sarcopenia: The Therapeutic Potential of Melatonin

Sarcopenia is an age-related condition that involves a progressive decline in muscle mass and function, leading to increased risk of falls, frailty, and mortality. Although the exact mechanisms are not fully understood, aging-related processes like inflammation, oxidative stress, reduced mitochondrial capacity, and cell apoptosis contribute to this decline. Disruption of the circadian system with age may initiate these pathways in skeletal muscle, preceding the onset of sarcopenia. At present, there is no pharmacological treatment for sarcopenia, only resistance exercise and proper nutrition may delay its onset. Melatonin, derived from tryptophan, emerges as an exceptional candidate for treating sarcopenia due to its chronobiotic, antioxidant, and anti-inflammatory properties. Its impact on mitochondria and organelle, where it is synthesized and crucial in aging skeletal muscle, further highlights its potential. In this review, we discuss the influence of clock genes in muscular aging, with special reference to peripheral clock genes in the skeletal muscle, as well as their relationship with melatonin, which is proposed as a potential therapy against sarcopenia.

Crosstalk Between Aging, Circadian Rhythm, and Melatonin

Circadian rhythms (CRs) are 24-hour periodic oscillations governed by an endogenous circadian pacemaker located in the suprachiasmatic nucleus (SCN), which organizes the physiology and behavior of organisms. Circadian rhythm disruption (CRD) is also indicative of the aging process. In mammals, melatonin is primarily synthesized in the pineal gland and participates in a variety of multifaceted intracellular signaling networks and has been shown to synchronize CRs. Endogenous melatonin synthesis and its release tend to decrease progressively with advancing age. Older individuals experience frequent CR disruption, which hastens the process of aging. A profound understanding of the relationship between CRs and aging has the potential to improve existing treatments and facilitate development of novel chronotherapies that target age-related disorders. This review article aims to examine the circadian regulatory mechanisms in which melatonin plays a key role in signaling. We describe the basic architecture of the molecular circadian clock and its functional decline with age in detail. Furthermore, we discuss the role of melatonin in regulation of the circadian pacemaker and redox homeostasis during aging. Moreover, we also discuss the protective effect of exogenous melatonin supplementation in age-dependent CR disruption, which sheds light on this pleiotropic molecule and how it can be used as an effective chronotherapeutic medicine.

Circadian Regulation of the Neuroimmune Environment Across the Lifespan: From Brain Development to Aging

Circadian clocks confer 24-h periodicity to biological systems, to ultimately maximize energy efficiency and promote survival in a world with regular environmental light cycles. In mammals, circadian rhythms regulate myriad physiological functions, including the immune, endocrine, and central nervous systems. Within the central nervous system, specialized glial cells such as astrocytes and microglia survey and maintain the neuroimmune environment. The contributions of these neuroimmune cells to both homeostatic and pathogenic demands vary greatly across the day. Moreover, the function of these cells changes across the lifespan. In this review, we discuss circadian regulation of the neuroimmune environment across the lifespan, with a focus on microglia and astrocytes. Circadian rhythms emerge in early life concurrent with neuroimmune sculpting of brain circuits and wane late in life alongside increasing immunosenescence and neurodegeneration. Importantly, circadian dysregulation can alter immune function, which may contribute to susceptibility to neurodevelopmental and neurodegenerative diseases. In this review, we highlight circadian neuroimmune interactions across the lifespan and share evidence that circadian dysregulation within the neuroimmune system may be a critical component in human neurodevelopmental and neurodegenerative diseases.

Day-night fluctuations in choroid plexus transcriptomics and cerebrospinal fluid metabolomics

The cerebrospinal fluid (CSF) provides mechanical protection for the brain and serves as a brain dispersion route for nutrients, hormones, and metabolic waste. The CSF secretion rate is elevated in the dark phase in both humans and rats, which could support the CSF flow along the paravascular spaces that may be implicated in waste clearance. The similar diurnal CSF dynamics pattern observed in the day-active human and the nocturnal rat suggests a circadian regulation of this physiological variable, rather than sleep itself. To obtain a catalog of potential molecular drivers that could provide the day-night-associated modulation of the CSF secretion rate, we determined the diurnal fluctuation in the rat choroid plexus transcriptomic profile with RNA-seq and in the CSF metabolomics with ultraperformance liquid chromatography combined with mass spectrometry. We detected significant fluctuation of 19 CSF metabolites and differential expression of 2,778 choroid plexus genes between the light and the dark phase, the latter of which encompassed circadian rhythm-related genes and several choroid plexus transport mechanisms. The fluctuating components were organized with joint pathway analysis, of which several pathways demonstrated diurnal regulation. Our results illustrate substantial transcriptional and metabolic light-dark phase-mediated changes taking place in the rat choroid plexus and its encircling CSF. The combined data provide directions toward future identification of the molecular pathways governing the fluctuation of this physiological process and could potentially be harnessed to modulate the CSF dynamics in pathology.

Effects of astaxanthin on depressive and sleep symptoms: A narrative mini-review

Major depressive disorder (MDD) is a prevalent psychiatric condition that results in persistent feelings of sadness and loss of interest, imposing a significant economic burden on health systems and society. Impaired sleep is both a symptom and a risk factor for depression. Natural astaxanthin (AST), a carotenoid primarily derived from algae and aquatic animals, possesses multiple pharmacological properties such as anti-inflammatory, anti-apoptotic, and antioxidant stress effects. Prior research suggests that AST may have antidepressant properties. This mini-review highlights the potential mechanisms by which AST can prevent depression, providing novel insights into drug research for depression treatment. Specifically, this mechanism suggests that astaxanthin may improve sleep and thus potentially aid in the treatment of depression.

Melatonin-related dysfunction in chronic restraint stress triggers sleep disorders in mice

Stress may trigger sleep disorders and are also risk factors for depression. The study explored the melatonin-related mechanisms of stress-associated sleep disorders on a mouse model of chronic stress by exploring the alteration in sleep architecture, melatonin, and related small molecule levels, transcription and expression of melatonin-related genes as well as proteins. Mice undergoing chronic restraint stress modeling for 28 days showed body weight loss and reduced locomotor activity. Sleep fragmentation, circadian rhythm disorders, and insomnia exhibited in CRS-treated mice formed sleep disorders. Tryptophan and 5-hydroxytryptamine levels were increased in the hypothalamus, while melatonin level was decreased. The transcription and expression of melatonin receptors were reduced, and circadian rhythm related genes were altered. Expression of downstream effectors to melatonin receptors was also affected. These results identified sleep disorders in a mice model of chronic stress. The alteration of melatonin-related pathways was shown to trigger sleep disorders.

The impact of biological clock and sex hormones on the risk of disease

Molecular clocks are responsible for defining 24-h cycles of behaviour and physiology that are called circadian rhythms. Several structures and tissues are responsible for generating these circadian rhythms and are named circadian clocks. The suprachiasmatic nucleus of the hypothalamus is believed to be the master circadian clock receiving light input via the optic nerve and aligning internal rhythms with environmental cues. Studies using both in vivo and in vitro methodologies have reported the relationship between the molecular clock and sex hormones. The circadian system is directly responsible for controlling the synthesis of sex hormones and this synthesis varies according to the time of day and phase of the estrous cycle. Sex hormones also directly interact with the circadian system to regulate circadian gene expression, adjust biological processes, and even adjust their own synthesis. Several diseases have been linked with alterations in either the sex hormone background or the molecular clock. So, in this chapter we aim to summarize the current understanding of the relationship between the circadian system and sex hormones and their combined role in the onset of several related diseases.

Brain washing and neural health: role of age, sleep, and the cerebrospinal fluid melatonin rhythm

The brain lacks a classic lymphatic drainage system. How it is cleansed of damaged proteins, cellular debris, and molecular by-products has remained a mystery for decades. Recent discoveries have identified a hybrid system that includes cerebrospinal fluid (CSF)-filled perivascular spaces and classic lymph vessels in the dural covering of the brain and spinal cord that functionally cooperate to remove toxic and non-functional trash from the brain. These two components functioning together are referred to as the glymphatic system. We propose that the high levels of melatonin secreted by the pineal gland directly into the CSF play a role in flushing pathological molecules such as amyloid-β peptide (Aβ) from the brain via this network. Melatonin is a sleep-promoting agent, with waste clearance from the CNS being highest especially during slow wave sleep. Melatonin is also a potent and versatile antioxidant that prevents neural accumulation of oxidatively-damaged molecules which contribute to neurological decline. Due to its feedback actions on the suprachiasmatic nucleus, CSF melatonin rhythm functions to maintain optimal circadian rhythmicity, which is also critical for preserving neurocognitive health. Melatonin levels drop dramatically in the frail aged, potentially contributing to neurological failure and dementia. Melatonin supplementation in animal models of Alzheimer's disease (AD) defers Aβ accumulation, enhances its clearance from the CNS, and prolongs animal survival. In AD patients, preliminary data show that melatonin use reduces neurobehavioral signs such as sundowning. Finally, melatonin controls the mitotic activity of neural stem cells in the subventricular zone, suggesting its involvement in neuronal renewal.

Effects of fluoxetine on fish: What do we know and where should we focus our efforts in the future?

Fluoxetine is one of the most studied and detected selective serotonin reuptake inhibitors in the aquatic environment, found at concentrations ranging from ng/L to μg/L. Its presence in this environment can induce effects on aquatic organisms that may compromise their fitness. Several experimental studies have demonstrated that fluoxetine can induce neurotoxicity, genetic and biochemical changes, and cause behavioral dysfunction in a wide range of fish species. However, contradictory results can be found. There is thus the need for a comprehensive review of the current state of knowledge on the effects of fluoxetine on fish at different levels of biological organization, highlighting inclusive patterns and discussing the potential causes for the contradictory results, that can be found in the available literature. This review also aims to explore and identify the main gaps in knowledge and areas for future research. We conclude that environmentally relevant concentrations of fluoxetine (e.g., from 0.00345 μg/L) produced adverse effects and often this concentration range is not addressed in conventional environmental risk assessment strategies. Its environmental persistence and ionizable properties reinforce the need for standardized testing with representative aquatic models, targeting endpoints sensitive to the specific mode of action of fluoxetine, in order to assess and rank its actual environmental risk to aquatic ecosystems.

Role of Melatonin in Cancer: Effect on Clock Genes

The circadian clock is a regulatory system, with a periodicity of approximately 24 h, that generates rhythmic changes in many physiological processes. Increasing evidence links chronodisruption with aberrant functionality in clock gene expression, resulting in multiple diseases, including cancer. In this context, tumor cells have an altered circadian machinery compared to normal cells, which deregulates the cell cycle, repair mechanisms, energy metabolism and other processes. Melatonin is the main hormone produced by the pineal gland, whose production and secretion oscillates in accordance with the light:dark cycle. In addition, melatonin regulates the expression of clock genes, including those in cancer cells, which could play a key role in the numerous oncostatic effects of this hormone. This review aims to describe and clarify the role of clock genes in cancer, as well as the possible mechanisms of the action of melatonin through which it regulates the expression of the tumor's circadian machinery, in order to propose future anti-neoplastic clinical treatments.

Melatonin as a Chronobiotic with Sleep-promoting Properties

The use of exogenous melatonin (exo-MEL) as a sleep-promoting drug has been under extensive debate due to the lack of consistency of its described effects. In this study, we conduct a systematic and comprehensive review of the literature on the chronobiotic, sleep-inducing, and overall sleep-promoting properties of exo-MEL. To this aim, we first describe the possible pharmacological mechanisms involved in the sleep-promoting properties and then report the corresponding effects of exo-MEL administration on clinical outcomes in: a) healthy subjects, b) circadian rhythm sleep disorders, c) primary insomnia. Timing of administration and doses of exo-MEL received particular attention in this work. The exo-MEL pharmacological effects are hereby interpreted in view of changes in the physiological properties and rhythmicity of endogenous melatonin. Finally, we discuss some translational implications for the personalized use of exo-MEL in the clinical practice.

Melatonin as a Harmonizing Factor of Circadian Rhythms, Neuronal Cell Cycle and Neurogenesis: Additional Arguments for Its Therapeutic Use in Alzheimer's Disease

The synthesis and release of melatonin in the brain harmonize various physiological functions. The apparent decline in melatonin levels with advanced aging is an aperture to the neurodegenerative processes. It has been indicated that down regulation of melatonin leads to alterations of circadian rhythm components, which further causes a desynchronization of several genes and results in an increased susceptibility to develop neurodegenerative diseases. Additionally, as circadian rhythms and memory are intertwined, such rhythmic disturbances influence memory formation and recall. Besides, cell cycle events exhibit a remarkable oscillatory system, which is downstream of the circadian phenomena. The linkage between the molecular machinery of the cell cycle and complex fundamental regulatory proteins emphasizes the conjectural regulatory role of cell cycle components in neurodegenerative disorders such as Alzheimer's disease. Among the mechanisms intervening long before the signs of the disease appear, the disturbances of the circadian cycle, as well as the alteration of the machinery of the cell cycle and impaired neurogenesis, must hold our interest. Therefore, in the present review, we propose to discuss the underlying mechanisms of action of melatonin in regulating the circadian rhythm, cell cycle components and adult neurogenesis in the context of AD pathogenesis with the view that it might further assist to identify new therapeutic targets.

Novel Therapeutics for Treating Sleep Disorders: New Perspectives on Maydis stigma

Sleep is a restorative period that plays a crucial role in the physiological functioning of the body, including that of the immune system, memory processing, and cognition. Sleep disturbances can be caused by various physical, mental, and social problems. Recently, there has been growing interest in sleep. Maydis stigma (MS, corn silk) is a female maize flower that is traditionally used as a medicinal plant to treat many diseases, including hypertension, edema, and diabetes. It is also used as a functional food in tea and other supplements. β-Sitosterol (BS) is a phytosterol and a natural micronutrient in higher plants, and it has a similar structure to cholesterol. It is a major component of MS and has anti-inflammatory, antidepressive, and sedative effects. However, the potential effects of MS on sleep regulation remain unclear. Here, we investigated the effects of MS on sleep in mice. The effects of MS on sleep induction were determined using pentobarbital-induced sleep and caffeine-induced sleep disruption mouse models. MS extracts decreased sleep latency and increased sleep duration in both the pentobarbital-induced sleep induction and caffeine-induced sleep disruption models compared to the positive control, valerian root extract. The butanol fraction of MS extracts decreased sleep latency time and increased sleep duration. In addition, β-sitosterol enhances sleep latency and sleep duration. Both MS extract and β-sitosterol increased alpha activity in the EEG analysis. We measured the mRNA expression of melatonin receptors 1 and 2 (MT1/2) using qRT-PCR. The mRNA expression of melatonin receptors 1 and 2 was increased by MS extract and β-sitosterol treatment in rat primary cultured neurons and the brain. In addition, MS extract increased the expression of clock genes including per1/2, cry1/2, and Bmal1 in the brain. MS extract and β-sitosterol increased the phosphorylation of ERK1/2 and αCaMKII. Our results demonstrate for the first time that MS has a sleep-promoting effect via melatonin receptor expression, which may provide new scientific evidence for its use as a potential therapeutic agent for the treatment and prevention of sleep disturbance.

Circadian clock-mediated nuclear receptors in cancer

Circadian system coordinates the daily periodicity of physiological and biochemical functions to adapt to environmental changes. Circadian disruption has been identified to increase the risk of cancer and promote cancer progression, but the underlying mechanism remains unclear. And further mechanistic understanding of the crosstalk between clock components and cancer is urgent to achieve clinical anticancer benefits from chronochemotherapy. Recent studies discover that several nuclear receptors regulating circadian clock, also play crucial roles in mediating multiple cancer processes. In this review, we aim to summarize the latest developments of clock-related nuclear receptors in cancer biology and dissect mechanistic insights into how nuclear receptors coordinate with circadian clock to regulate tumorigenesis and cancer treatment. A better understanding of circadian clock-related nuclear receptors in cancer could help prevent tumorigenesis and improve anticancer efficacy.

The therapeutic effect and mechanism of melatonin on osteoarthritis: From the perspective of non-coding RNAs

Osteoarthritis (OA) is a slowly progressing and irreversible joint disease. The existing non-surgical treatment can only delay its progress, making the early treatment of OA a research hotspot in recent years. Melatonin, a neurohormone mainly secreted by the pineal gland, has a variety of regulatory functions in different organs, and numerous studies have confirmed its therapeutic effect on OA. Non-coding RNAs (ncRNAs) constitute the majority of the human transcribed genome. Various ncRNAs show significant differentially expressed between healthy people and OA patients. ncRNAs play diverse roles in many cellular processes and have been implicated in many pathological conditions, especially OA. Interestingly, the latest research found a close interaction between ncRNAs and melatonin in regulating the pathogenesis of OA. This review discusses the current understanding of the melatonin-mediated modulation of ncRNAs in the early stage of OA. We also delineate the potential link between rhythm genes and ncRNAs in chondrocytes. This review will serve as a solid foundation to formulate ideas for future mechanistic studies on the therapeutic potential of melatonin and ncRNAs in OA and better explore the emerging functions of the ncRNAs.

Neuroprotective therapies in the NICU in term infants: present and future

Outcomes of neonatal encephalopathy (NE) have improved since the widespread implementation of therapeutic hypothermia (TH) in high-resource settings. While TH for NE in term and near-term infants has proven beneficial, 30-50% of infants with moderate-to-severe NE treated with TH still suffer death or significant impairments. There is therefore a critical need to find additional pharmacological and non-pharmacological interventions that improve the outcomes for these children. There are many potential candidates; however, it is unclear whether these interventions have additional benefits when used with TH. Although primary and delayed (secondary) brain injury starting in the latent phase after HI are major contributors to neurodisability, the very late evolving effects of tertiary brain injury likely require different interventions targeting neurorestoration. Clinical trials of seizure management and neuroprotection bundles are needed, in addition to current trials combining erythropoietin, stem cells, and melatonin with TH. IMPACT: The widespread use of therapeutic hypothermia (TH) in the treatment of neonatal encephalopathy (NE) has reduced the associated morbidity and mortality. However, 30-50% of infants with moderate-to-severe NE treated with TH still suffer death or significant impairments. This review details the pathophysiology of NE along with the evidence for the use of TH and other beneficial neuroprotective strategies used in term infants. We also discuss treatment strategies undergoing evaluation at present as potential adjuvant treatments to TH in NE.

The role of solar and geomagnetic activity in endothelial activation and inflammation in the NAS cohort

This study investigated the associations between solar and geomagnetic activity and circulating biomarkers of systemic inflammation and endothelial activation in the Normative Aging Study (NAS) cohort. Mixed effects models with moving day averages from day 0 to day 28 were used to study the associations between solar activity (sunspot number (SSN), interplanetary magnetic field (IMF)), geomagnetic activity (planetary K index (K_p index), and various inflammatory and endothelial markers. Biomarkers included intracellular adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVCAM-1), C-reactive protein (CRP), and fibrinogen. After adjusting for demographic and meteorological variables, we observed significant positive associations between sICAM-1 and sVCAM-1 concentrations and solar and geomagnetic activity parameters: IMF, SSN, and K_p. Additionally, a negative association was observed between fibrinogen and K_p index and a positive association was observed for CRP and SSN. These results demonstrate that solar and geomagnetic activity might be upregulating endothelial activation and inflammation.

New Insights into the Diurnal Rhythmicity of Gut Microbiota and Its Crosstalk with Host Circadian Rhythm

Simple Summary

There is a growing consensus that the gut microbiota exhibits diurnal oscillation. The rhythmicity of gut microbiota has fundamental implications for host physiology, metabolism, and health. Further, the gut microbiota rhythmicity can regulate the host’s circadian rhythm. Therefore, in this review, we aimed to highlight the rhythmic phenomenon of the gut microbiota and elucidate its fundamental roles in host physiology, metabolism, and health, and illuminate the possible interactions between the gut microbiota rhythmicity and host circadian rhythm. Insights into these questions facilitate the development of chronotherapy.

Abstract

Unlike the strictly hierarchical organization in the circadian clock system, the gut microbiota rhythmicity has a more complex multilayer network of all taxonomic levels of microbial taxa and their metabolites. However, it is worth noting that the functionality of the gut microbiota rhythmicity is highly dependent on the host circadian clock and host physiological status. Here, we discussed the diurnal rhythmicity of the gut microbiota; its crucial role in host physiology, health, and metabolism; and the crosstalk between the gut microbial rhythmicity and host circadian rhythm. This knowledge lays the foundation for the development of chronotherapies targeting the gut microbiota. However, the formation mechanism, its beneficial effects on the host of gut microbial rhythmicity, and the dynamic microbial–host crosstalk are not yet clear and warrant further research.

Fluoxetine modifies circadian rhythm by reducing melatonin content in zebrafish

Fluoxetine (FLX), a selective serotonin reuptake inhibitor (SSRI), increases the serotonin levels in the brain to treat depression. Antidepressants have been demonstrated to modulate circadian rhythm, but the underlying mechanisms by which antidepressants regulate circadian rhythm require more research. This study aimed to investigate the role of FLX on circadian rhythm by analyzing the movement behavior and internal circadian oscillations in zebrafish. The results showed that the expression of clock genes clock1a and bmal1b was significantly down-regulated, and the amplitude reduction and phase shift were observed after FLX treatment. Furthermore, FLX exposure inhibited the expression of aanat2, which led to a decrease in nocturnal melatonin secretion. aanat2^-/- larvae showed disrupted circadian rhythm. These findings may help reveal the effect of FLX exposure on the circadian rhythm and locomotor activity. It may provide theoretical data for the clinical application of FLX.

Age and Chronodisruption in Mouse Heart: Effect of the NLRP3 Inflammasome and Melatonin Therapy

Age and age-dependent inflammation are two main risk factors for cardiovascular diseases. Aging can also affect clock gene-related impairments such as chronodisruption and has been linked to a decline in melatonin synthesis and aggravation of the NF-κB/NLRP3 innate immune response known as inflammaging. The molecular drivers of these mechanisms remain unknown. This study investigated the impact of aging and NLRP3 expression on the cardiac circadian system, and the actions of melatonin as a potential therapy to restore daily rhythms by mitigating inflammaging. We analyzed the circadian expression and rhythmicity of clock genes in heart tissue of wild-type and NLRP3-knockout mice at 3, 12, and 24 months of age, with and without melatonin treatment. Our results support that aging, NLRP3 inflammasome, and melatonin affected the cardiac clock genes expression, except for Rev-erbα, which was not influenced by genotype. Aging caused small phase changes in Clock, loss of rhythmicity in Per2 and Rorα, and mesor dampening of Clock, Bmal1, and Per2. NLRP3 inflammasome influenced the acrophase of Clock, Per2, and Rorα. Melatonin restored the acrophase and the rhythm of clock genes affected by age or NLRP3 activation. The administration of melatonin re-established murine cardiac homeostasis by reversing age-associated chronodisruption. Altogether, these results highlight new findings about the effects aging and NLRP3 inflammasome have on clock genes in cardiac tissue, pointing to continuous melatonin as a promising therapy to placate inflammaging and restore circadian rhythm in heart muscle. Additionally, light microscopy analysis showed age-related morphological impairments in cardiomyocytes, which were less severe in mice lacking NLRP3. Melatonin supplementation preserved the structure of cardiac muscle fibers in all experimental groups.

Ubiquitin proteasome system in circadian rhythm and sleep homeostasis: Lessons from Drosophila

Sleep is regulated by two main processes: the circadian clock and sleep homeostasis. Circadian rhythms have been well studied at the molecular level. In the Drosophila circadian clock neurons, the core clock proteins are precisely regulated by post-translational modifications and degraded via the ubiquitin-proteasome system (UPS). Sleep homeostasis, however, is less understood; nevertheless, recent reports suggest that proteasome-mediated degradation of core clock proteins or synaptic proteins contributes to the regulation of sleep amount. Here, we review the molecular mechanism of the UPS and summarize the role of protein degradation in the regulation of circadian clock and homeostatic sleep in Drosophila. Moreover, we discuss the potential interaction between circadian clock and homeostatic sleep regulation with a prime focus on E3 ubiquitin ligases.

Restoring the dampened expression of the core clock molecule BMAL1 protects against compression-induced intervertebral disc degeneration

The circadian clock participates in maintaining homeostasis in peripheral tissues, including intervertebral discs (IVDs). Abnormal mechanical loading is a known risk factor for intervertebral disc degeneration (IDD). Based on the rhythmic daily loading pattern of rest and activity, we hypothesized that abnormal mechanical loading could dampen the IVD clock, contributing to IDD. Here, we investigated the effects of abnormal loading on the IVD clock and aimed to inhibit compression-induced IDD by targeting the core clock molecule brain and muscle Arnt-like protein-1 (BMAL1). In this study, we showed that BMAL1 KO mice exhibit radiographic features similar to those of human IDD and that BMAL1 expression was negatively correlated with IDD severity by systematic analysis based on 149 human IVD samples. The intrinsic circadian clock in the IVD was dampened by excessive loading, and BMAL1 overexpression by lentivirus attenuated compression-induced IDD. Inhibition of the RhoA/ROCK pathway by Y-27632 or melatonin attenuated the compression-induced decrease in BMAL1 expression. Finally, the two drugs partially restored BMAL1 expression and alleviated IDD in a diurnal compression model. Our results first show that excessive loading dampens the circadian clock of nucleus pulposus tissues via the RhoA/ROCK pathway, the inhibition of which potentially protects against compression-induced IDD by preserving BMAL1 expression. These findings underline the importance of the circadian clock for IVD homeostasis and provide a potentially effective therapeutic strategy for IDD.

Targeting Oxidative Stress as a Therapeutic Approach for Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic interstitial lung disease characterized by an abnormal reepithelialisation, an excessive tissue remodelling and a progressive fibrosis within the alveolar wall that are not due to infection or cancer. Oxidative stress has been proposed as a key molecular process in pulmonary fibrosis development and different components of the redox system are altered in the cellular actors participating in lung fibrosis. To this respect, several activators of the antioxidant machinery and inhibitors of the oxidant species and pathways have been assayed in preclinical in vitro and in vivo models and in different clinical trials. This review discusses the role of oxidative stress in the development and progression of IPF and its underlying mechanisms as well as the evidence of oxidative stress in human IPF. Finally, we analyze the mechanism of action, the efficacy and the current status of different drugs developed to inhibit the oxidative stress as anti-fibrotic therapy in IPF.

Melatonin stabilizes age-dependent alterations in erythrocyte membrane induced by 'Artificial Light at Night' in a chronodisrupted model of rat

Growing evidence has shown that Artificial light at night (ALAN) is one of the threatening risk factors which disrupt circadian homeodynamics of cellular processes. The chronobiological role of melatonin seems to represent an important aspect of its contribution to healthy aging. In the present study, we examined the age dependent effect of melatonin on erythrocyte membrane transporters and oxidative stress biomarkers against ALAN to understand the degree of photo-oxidative damage in chronodisrupted rat model. Young (3 months) and old (24 months) male Wistar rats were subdivided in the following four young groups (n = 4) ; (i) control (ii) melatonin (10 mg/kg) (iii) ALAN (500 lx) (iv) ALAN (500 lx) + melatonin (10 mg/kg) and four old groups (n = 4); (v) control (vi) melatonin (10 mg/kg) (vii) ALAN (500 lx) (viii) ALAN (500 lx) + melatonin (10 mg/kg) to the experimental conditions for 10 days. Our findings demonstrated that ALAN significantly enhanced erythrocyte membrane lipid hydroperoxides (LHPs), protein carbonyl (PCO) while reduced total thiol (T-SH), and sialic acid (SA) level with higher amplitude in old ALAN group is restored by exogenous supplementation of melatonin. Activity of membrane transporters, sodium potassium ATPase (NKA) and plasma membrane calcium ion ATPase (PMCA) is significantly reduced meanwhile sodium hydrogen exchanger (NHE) activity is enhanced under the influence of ALAN with higher extent in old groups is effectively ameliorated by melatonin treatment. Further melatonin reduced osmotic fragility of erythrocyte in both young and old rats. It has been concluded from results that ALAN provoked redox insult and disrupt transporters activity more prominently in erythrocyte membrane of aged groups. Exogenous supplementation of melatonin is one of the possible therapeutic approaches to reinforce circadian modulations against ALAN in aged populations.

Melatonin supplementation in the culture medium rescues impaired glucose metabolism in IVF mice offspring

Increasing evidence suggests that in vitro fertilization (IVF) may be associated with an increased risk of developing obesity and metabolic diseases later in life in the offspring. Notably, the addition of melatonin to culture medium may improve embryo development and prevent cardiovascular dysfunction in IVF adult mice. This study aimed to determine if melatonin supplementation in the culture medium can reverse impaired glucose metabolism in IVF mice offspring and the underlying mechanisms. Blastocysts used for transfer were generated by natural mating (control group) or IVF with or without melatonin (10^-6  M) supplementation (mIVF and IVF group, respectively) in clinical-grade culture media. Here, we first report that IVF decreased hepatic expression of Fbxl7, which was associated with impaired glucose metabolism in mice offspring. Melatonin addition reversed the phenotype by up-regulating the expression of hepatic Fbxl7. In vitro experiments showed that Fbxl7 enhanced the insulin signaling pathway by degrading RhoA through ubiquitination and was up-regulated by transcription factor Foxa2. Specific knockout of Fbxl7 in the liver of adult mice, through tail intravenous injection of recombinant adeno-associated virus, impaired glucose tolerance, while overexpression of hepatic Fbxl7 significantly improved glucose tolerance in adult IVF mice. Thus, the data suggest that Fbxl7 plays an important role in maintaining glucose metabolism of mice, and melatonin supplementation in the culture medium may rescue the long-term risk of metabolic diseases in IVF offspring.

Melatonin, Clock Genes, and Mammalian Reproduction: What Is the Link?

Physiological processes and behaviors in many mammals are rhythmic. Recently there has been increasing interest in the role of circadian rhythmicity in the control of reproductive function. The circadian rhythm of the pineal hormone melatonin plays a role in synchronizing the reproductive responses of animals to environmental light conditions. There is some evidence that melatonin may have a role in the biological regulation of circadian rhythms and reproduction in humans. Moreover, circadian rhythms and clock genes appear to be involved in optimal reproductive performance. These rhythms are controlled by an endogenous molecular clock within the suprachiasmatic nucleus (SCN) in the hypothalamus, which is entrained by the light/dark cycle. The SCN synchronizes multiple subsidiary oscillators (clock genes) existing in various tissues throughout the body. The basis for maintaining the circadian rhythm is a molecular clock consisting of transcriptional/translational feedback loops. Circadian rhythms and clock genes appear to be involved in optimal reproductive performance. This mini review summarizes the current knowledge regarding the interrelationships between melatonin and the endogenous molecular clocks and their involvement in reproductive physiology (e.g., ovulation) and pathophysiology (e.g., polycystic ovarian syndrome).

Melatonin and Pathological Cell Interactions: Mitochondrial Glucose Processing in Cancer Cells

Melatonin is synthesized in the pineal gland at night. Since melatonin is produced in the mitochondria of all other cells in a non-circadian manner, the amount synthesized by the pineal gland is less than 5% of the total. Melatonin produced in mitochondria influences glucose metabolism in all cells. Many pathological cells adopt aerobic glycolysis (Warburg effect) in which pyruvate is excluded from the mitochondria and remains in the cytosol where it is metabolized to lactate. The entrance of pyruvate into the mitochondria of healthy cells allows it to be irreversibly decarboxylated by pyruvate dehydrogenase (PDH) to acetyl coenzyme A (acetyl-CoA). The exclusion of pyruvate from the mitochondria in pathological cells prevents the generation of acetyl-CoA from pyruvate. This is relevant to mitochondrial melatonin production, as acetyl-CoA is a required co-substrate/co-factor for melatonin synthesis. When PDH is inhibited during aerobic glycolysis or during intracellular hypoxia, the deficiency of acetyl-CoA likely prevents mitochondrial melatonin synthesis. When cells experiencing aerobic glycolysis or hypoxia with a diminished level of acetyl-CoA are supplemented with melatonin or receive it from another endogenous source (pineal-derived), pathological cells convert to a more normal phenotype and support the transport of pyruvate into the mitochondria, thereby re-establishing a healthier mitochondrial metabolic physiology.

Hibernation with rhythmicity: the circadian clock and hormonal adaptations of the hibernating Asiatic toads (Bufo gargarizans)

Hibernation is one of the fundamental strategies in response to cold environmental temperatures. During hibernation, the endocrine and circadian systems ensure minimal expenditure of energy for survival. The circadian rhythms of key hormones, melatonin (MT), corticosterone (CORT), triiodothyronine (T₃ ), and thyroxine (T₄ ), and the underlying molecular regulatory mechanisms of hibernation have been well determined in mammals but not in ectotherms. Here, a terrestrial hibernating species, Asiatic toad (Bufo gargarizans), was employed to investigate the plasma CORT, MT, T₃ , and T₄ ; and the retina, brain, and liver mRNA expression of the core clock genes, including circadian locomotor output cycles kaput (Clock), brain and muscle ARNT-like 1 (Bmal1), cryptochrome (Cry) 1 and 2, and period (Per) 1 and 2, at 7-time points over a 24-h period under acute cold (1 day at 4°C), and hibernation (45 days at 4°C). Our results showed that the circadian rhythms of the core clock genes were rather unaffected by acute cold exposure in the retina, unlike the brain and liver. In contrast, during hibernation, the liver clock genes displayed significant circadian oscillations, while those in the retina and brain stopped ticking. Furthermore, plasma CORT expressed circadian oscillations in both groups, and T₃ in acute cold exposure group, whereas T₄ and MT did not. Our results reveal that the plasma CORT and the liver sustain rhythmicity when the brain was not, indicating that the liver clock along with the adrenal clock synergistically maintains the metabolic requirements to ensure basic survival in hibernating Asiatic toads.

Dopamine D1 Receptor-Mediated Regulation of Per1, Per2, CLOCK, and BMAL1 Expression in the Suprachiasmatic Nucleus in Adult Male Rats

Photic and non-photic inputs are reported to affect clock gene expressions and behavioral activities in the SCN. However, it is not known whether dopaminergic input mediates these regulatory effects on clock genes. The present study examined the molecular effects of dopamine D1 agonist on Per1, Per2, CLOCK, and Bmal1 expressions in the SCN and its effect on behavioral activities to determine the role of dopamine D1 receptor in regulation of these gene expressions and behavioral activities in adult male Wistar rats. To examine the molecular effects of dopamine D1 agonist day and night, we injected 20 mg/kg SKF38393 to the first group of rats at 6 a.m. and the second group at 6 p.m. We also injected saline to the third and fourth groups of rats at 6 a.m. and 6 p.m. as control groups. All rats were sacrificed 2 h following the injections. The real-time PCR technique was used to evaluate the clock gene expression. In addition, to examine the effects of dopamine D1 agonists on behavioral activities, we injected 20 mg/kg SKF38393 to SKF receiving group and saline to control group. The behavioral activities of the rats were monitored on the running wheel for 21 days, 1 week following the injections. SKF injections increased the Per2 and CLOCK expressions in the daytime and significantly decreased the Per1 and Bmal1 expressions. However, at night, SKF injections increased only Per2 expressions significantly and decreased the Per1, CLOCK, and Bmal1 genes expressions. Both saline receiving groups showed that all gene expressions were significantly higher except Per2 during nighttime. SKF injection increased the running wheel activity during nighttime significantly. Based on the obtained result, clock gene expression and behavioral activities in adult male Wistar rats may be altered or monitored by administration of exogenous dopamine.

Potentiating the Benefits of Melatonin through Chemical Functionalization: Possible Impact on Multifactorial Neurodegenerative Disorders

Although melatonin is an astonishing molecule, it is possible that chemistry will help in the discovery of new compounds derived from it that may exceed our expectations regarding antioxidant protection and perhaps even neuroprotection. This review briefly summarizes the significant amount of data gathered to date regarding the multiple health benefits of melatonin and related compounds. This review also highlights some of the most recent directions in the discovery of multifunctional pharmaceuticals intended to act as one-molecule multiple-target drugs with potential use in multifactorial diseases, including neurodegenerative disorders. Herein, we discuss the beneficial activities of melatonin derivatives reported to date, in addition to computational strategies to rationally design new derivatives by functionalization of the melatonin molecular framework. It is hoped that this review will promote more investigations on the subject from both experimental and theoretical perspectives.

Chronic sleep deprivation altered the expression of circadian clock genes and aggravated Alzheimer's disease neuropathology

Circadian disruption is prevalent in Alzheimer's disease (AD) and may contribute to cognitive impairment, psychological symptoms, and neurodegeneration. This study aimed to evaluate the effects of environmental and genetic factors on the molecular clock and to establish a link between circadian rhythm disturbance and AD. We investigated the pathological effects of chronic sleep deprivation (CSD) in the APP^swe/PS1^ΔE9 transgenic mice and their wild‐type (WT) littermates for 2 months and evaluated the expression levels of clock genes in the circadian rhythm‐related nuclei. Our results showed that CSD impaired learning and memory, and further exaggerated disease progression in the AD mice. Furthermore, CSD caused abnormal expression of Bmal1, Clock, and Cry1 in the circadian rhythm‐related nuclei of experimental mice, and these changes are more significant in AD mice. Abnormal expression of clock genes in AD mice suggested that the expression of clock genes is affected by APP/PS1 mutations. In addition, abnormal tau phosphorylation was found in the retrosplenial cortex, which was co‐located with the alteration of BMAL1 protein level. Moreover, the level of tyrosine hydroxylase in the locus coeruleus of AD and WT mice was significantly increased after CSD. There may be a potential link between the molecular clock, Aβ pathology, tauopathy, and the noradrenergic system. The results of this study provided new insights into the potential link between the disruption of circadian rhythm and the development of AD.

Pan-cancer analyses reveal genomics and clinical characteristics of the melatonergic regulators in cancer

Melatonin, an endogenous hormone, plays protective roles in cancer. In addition to regulating circadian rhythms, sleep, and neuroendocrine activity, melatonin functions in various survival pathways. However, the mechanisms of melatonin regulation in cancer remain unknown. In the present study, we performed a comprehensive characterization of melatonin regulators in 9125 tumor samples across 33 cancer types using multi-omic data from The Cancer Genome Atlas and Cancer Cell Line Encyclopedia. In the genomic landscape, we identified the heterozygous amplification of AANAT and GPR50, and heterozygous deletion of PER3, CYP2C19, and MTNR1A as the dominant alteration events. Expression analysis revealed methylation-mediated downregulation of melatonergic regulator expression. In addition, we found that melatonergic regulator expression could be used to predict patient survival in various cancers. In depth, microRNA (miRNA) analysis revealed an miRNA-mRNA interaction network, and the deregulated miRNAs were involved in melatonin secretion and metabolism by targeting circadian clock genes. Pathway analysis showed that melatonergic regulators were associated with inhibition of apoptosis, the cell cycle, the DNA damage response, and activation of RAS/MAPK and RTK signaling pathways. Importantly, by mining the Genomics of Drug Sensitivity in Cancer database, we discovered a number of potential drugs that might target melatonergic regulators. In summary, this study revealed the genomic alteration and clinical characteristics of melatonergic regulators across 33 cancers, which might clarify the relationship between melatonin and tumorigenesis. Our findings also might provide a novel approach for the clinical treatment of cancers.

Melatonin modulates nitric oxide-regulated WNK-SPAK/OSR1-NKCC1 signaling in dorsal raphe nucleus of rats

The sleep-wake cycle is regulated by the alternating activity of sleep- and wake-promoting neurons. The dorsal raphe nucleus (DRN) secretes 5-hydroxytryptamine (5-HT, serotonin), promoting wakefulness. Melatonin secreted from the pineal gland also promotes wakefulness in rats. Our laboratory recently demonstrated that daily changes in nitric oxide (NO) production regulates a signaling pathway involving with-no-lysine kinase (WNK), Ste20-related proline alanine rich kinase (SPAK)/oxidative stress response kinase 1 (OSR1), and cation-chloride co-transporters (CCC) in rat DRN serotonergic neurons. This study was designed to investigate the effect of melatonin on NO-regulated WNK-SPAK/OSR1-CCC signaling in wake-inducing DRN neurons to elucidate the mechanism underlying melatonin's wake-promoting actions in rats. Ex vivo treatment of DRN slices with melatonin suppressed neuronal nitric oxide synthase (nNOS) expression and increased WNK4 expression without altering WNK1, 2, or 3. Melatonin increased phosphorylation of OSR1 and the expression of sodium-potassium-chloride co-transporter 1 (NKCC1), while potassium-chloride cotransporter 2 (KCC2) remained unchanged. Melatonin increased the expression of tryptophan hydroxylase 2 (TPH2, serotonin-synthesizing enzyme). The present study suggests that melatonin may promote its wakefulness by modulating NO-regulated WNK-SPAK/OSR1-KNCC1 signaling in rat DRN serotonergic neurons.

The association of minerals intake in three meals with cancer and all-cause mortality: the U.S. National Health and Nutrition Examination Survey, 2003-2014

BACKGROUND

Intake time of diet has recently been demonstrated to be associated with the internal clock and circadian pattern. However, whether and how the intake time of minerals would influence the natural course of cancer was largely unknown.

METHODS

This study aimed to assess the association of mineral intake at different periods with cancer and all-cause mortality. A total of 27,455 participants aged 18-85 years old in the National Health and Nutrition Examination Survey were recruited. The main exposures were the mineral intakes in the morning, afternoon and evening, which were categorized into quintiles, respectively. The main outcomes were mortality of cancer and all causes.

RESULTS

During the 178,182 person-years of follow-up, 2680 deaths, including 601 deaths due to cancer, were documented. After adjusting for potential confounders, compared to the participants who were in the lowest quintile(quintile-1) of mineral intakes at dinner, the participants in the highest quintile intake(quintile-5) of dietary potassium, calcium and magnesium had lower mortality risks of cancer (HRpotassium = 0.72, 95% CI:0.55-0.94, P for trend = 0.023; HRcalcium = 0.74, 95% CI:0.57-0.98, P for trend = 0.05; HRmagnesium = 0.75, 95% CI:0.56-0.99, P for trend = 0.037) and all-cause (HRpotassium = 0.83, 95% CI:0.73-0.94, P for trend = 0.012; HRcalcium = 0.87, 95% CI:0.76-0.99, P for trend = 0.025; HRmagnesium = 0.85, 95% CI:0.74-0.97, P for trend = 0.011; HRcopper = 0.80, 95%CI: 0.68-0.94, P for trend = 0.012). Further, equivalently replacing 10% of dietary potassium, calcium and magnesium consumed in the morning with those in the evening were associated with lower mortality risk of cancer (HRpotassium = 0.94, 95%CI:0.91-0.97; HRcalcium = 0.95, 95%CI:0.92-0.98; HRmagnesium = 0.95, 95%CI: 0.92-0.98).

CONCLUSIONS

This study demonstrated that the optimal intake time of potassium, calcium and magnesium for reducing the risk of cancer and all-cause mortality was in the evening.

cAMP/PKA/CREB signaling pathway-mediated effects of melatonin receptor genes on clock gene expression in Bactrian camel ovarian granulosa cells

The cAMP/PKA/CREB pathway is involved in the regulation of melatonin during important physiological activities in mammals. However, the regulation of circadian clock genes in ovarian granulosa cells remains unclear. Herein, we determined the relationship between melatonin and biological clock genes using cultured Bactrian camel ovarian granulosa cells. The enzyme-linked immunosorbent assays showed that the cAMP content was reduced when melatonin receptor (MT) genes or cryptochrome (Cry) genes were overexpressed; the quantitative polymerase chain reaction and western blot analyses revealed that the expression levels of all circadian clock genes (GNB2, PKA, CREB, Per1/2/3, and Clock) except Cry1/2 decreased significantly at 24 h. Cellular immunolocalization analysis showed that melatonin receptors were localized in the cell membrane and cytoplasm; the CRY protein was mainly localized in the nucleus. Overall, our findings indicated that the rhythmic regulation of ovarian granulosa cells was consistent with the regulatory action of the central circadian clock.

Pinealectomy and gonadectomy modulate amplitude, but not photoperiodic modulation of Clock gene expression in the Syrian hamster suprachiasmatic nuclei

The duration of daytime light phase (photoperiod) controls reproduction in seasonal mammals. Syrian hamsters are sexually active when exposed to long photoperiod, while gonadal atrophy is observed after exposure to short photoperiod. The photorefractory period, or photorefractoriness, is a particular state of spontaneous recrudescence of sexual activity that occurs after a long-term exposure to short photoperiod. Expression of core clock genes in the master circadian clock contained in the suprachiasmatic nuclei depends on photoperiodic conditions. Interestingly, the expression of the Clock gene is also modified in photorefractory Syrian hamsters. Since melatonin and testosterone levels in seasonal species are dependent on photoperiod, photoperiodic variations of Clock mRNA levels in the suprachiasmatic clock could be a consequence of these hormonal changes. To test this hypothesis, we analysed the effects of pinealectomy on Clock mRNA changes due to long to short photoperiod transition and of gonadectomy on Clock mRNA levels in photorefractory period. Our data show that the suprachiasmatic integration of the short photoperiod (assessed by a rhythmic expression profile of Clock) is independent of the presence of melatonin. Furthermore, constitutively low expression of Clock observed during the photorefractory period does not require the presence of either melatonin or testosterone. However, we show that both hormones provide positive feedback on average levels of Clock expression. Thus, our data support the hypothesis that daily variations of Clock levels in the suprachiasmatic nuclei are influenced by photoperiodic changes and the time spent in short photoperiod, independently of seasonal modifications of melatonin or testosterone levels.

Expression characteristics of pineal miRNAs at ovine different reproductive stages and the identification of miRNAs targeting the AANAT gene

Background

Many recent studies have shown that miRNAs play important roles in the regulation of animal reproduction, including seasonal reproduction. The pineal gland is a crucial hub in the regulation of seasonal reproduction. However, little is known about the expression characteristics of pineal miRNAs in different reproductive seasons (anestrus and breeding season). Therefore, the expression profiles and regulatory roles of ovine pineal miRNAs were investigated during different reproductive stages using Solexa sequencing technology and dual luciferase reporter assays.

Results

A total of 427 miRNAs were identified in the sheep pineal gland. Significant differences in miRNA expression were demonstrated between anestrus and the breeding season in terms of the frequency distributions of miRNA lengths, number of expressed miRNAs, and specifically and highly expressed miRNAs in each reproductive stage. KEGG analysis of the differentially expressed (DE) miRNAs between anestrus and the breeding season indicated that they are significantly enriched in pathways related to protein synthesis, secretion and uptake. Furthermore, transcriptome analysis revealed that many target genes of DE miRNAs in the ribosome pathway showed relatively low expression in the breeding season. On the other hand, analyses combining miRNA-gene expression data with target relationship validation in vitro implied that miR-89 may participate in the negative regulation of aralkylamine N-acetyltransferase (AANAT) mRNA expression by targeting its 3’UTR at a unique binding site.

Conclusions

Our results provide new insights into the expression characteristics of sheep pineal miRNAs at different reproductive stages and into the negative regulatory effects of pineal miRNAs on AANAT mRNA expression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07536-y.

Melatonin and Cancer: A Polyhedral Network Where the Source Matters

Melatonin is one of the most phylogenetically conserved signals in biology. Although its original function was probably related to its antioxidant capacity, this indoleamine has been “adopted” by multicellular organisms as the “darkness signal” when secreted in a circadian manner and is acutely suppressed by light at night by the pineal gland. However, melatonin is also produced by other tissues, which constitute its extrapineal sources. Apart from its undisputed chronobiotic function, melatonin exerts antioxidant, immunomodulatory, pro-apoptotic, antiproliferative, and anti-angiogenic effects, with all these properties making it a powerful antitumor agent. Indeed, this activity has been demonstrated to be mediated by interfering with various cancer hallmarks, and different epidemiological studies have also linked light at night (melatonin suppression) with a higher incidence of different types of cancer. In 2007, the World Health Organization classified night shift work as a probable carcinogen due to circadian disruption, where melatonin plays a central role. Our aim is to review, from a global perspective, the role of melatonin both from pineal and extrapineal origin, as well as their possible interplay, as an intrinsic factor in the incidence, development, and progression of cancer. Particular emphasis will be placed not only on those mechanisms related to melatonin’s antioxidant nature but also on the recently described novel roles of melatonin in microbiota and epigenetic regulation.

Melatonin and its Relationships with Diabetes and Obesity: A Literature Review

BACKGROUND

Obesity is an important clinical entity, causing many public health issues. Around two billion people in the world are overweight and obese. Almost 40% of American adults are obese and Brazil has about 18 million obese people. Nowadays, 415 million people have diabetes, around 1 in every 11 adults. These numbers will rise to 650 million people within 20 years. Melatonin shows a positive profile on the regulation of the metabolism of the human body.

OBJECTIVE

This study aimed to carry out a broad narrative review of the metabolic profile and associations between melatonin, diabetes and obesity.

METHODS

Article reviews, systematic reviews, prospective studies, retrospective studies, randomized, double-blind, and placebo-controlled trials in humans recently published were selected and analyzed. A total of 368 articles were collated and submitted to the eligibility analysis. Subsequently, 215 studies were selected to compose the content part of the paper, and 153 studies composed the narrative review.

RESULTS

Studies suggest a possible role of melatonin in metabolic diseases such as obesity, T2DM and metabolic syndrome. Intervention studies using this hormone in metabolic diseases are still unclear regarding the possible benefit of it. There is so far no consensus about the possible role of melatonin as an adjuvant in the treatment of metabolic diseases. More studies are necessary to define possible risks and benefits of melatonin as a therapeutic agent.

Central and peripheral actions of melatonin on reproduction in seasonal and continuous breeding mammals

Under field conditions, especially for mammals that inhabit high latitudes, the regulation of seasonal breeding activity to ensure delivery of the young at the time most conducive to their survival is essential. This is most frequently accomplished by the annual reproductive cycle being linked to seasonal photoperiod changes which determine the nocturnal duration of the pineal melatonin signal. Mating can occur during any season that ensures spring/early summer delivery of the offspring. Thus, the season of mating is determined by the duration of pregnancy. The precise hormonal control of the annual cycle of reproduction by melatonin is accomplished at the level of the hypothalamo-pituitary axis which, in turn, determines the physiological state of the gonad and adnexa due to the regulation of pituitary gonadotrophin release. Many species are continuous rather than seasonal breeders. In these species, melatonin has a minor hormonal influence on the central regulation of reproduction but, nevertheless, its antioxidant functions at the level of the gonads support optimal reproductive physiology. Possibly like all cells, those in the ovary, e.g., granulosa cells and oocytes (less is known about melatonin synthesis by the testes or spermatogenic cells), synthesize melatonin which is used locally to combat free radicals and reactive nitrogen species which would otherwise cause oxidative/nitrosative stress to these critically important cells. Oxidative damage to the oocyte, zygote, blastocyst, etc., results in an abnormal fetus which is either sloughed or gives rise to an unhealthy offspring. The importance of the protection of the gametes (both oocytes and sperm) from oxidative molecular mutilation cannot be overstated. Fortunately, as a highly effective free radical scavenger and indirect antioxidant (by upregulating antioxidant enzyme), locally-produced melatonin is in the optimal location to protect the reproductive system from such damage.

Role of melatonin in UV-B signaling pathway and UV-B stress resistance in Arabidopsis thaliana

Melatonin (N-acetyl-5-methoxytryptamine) plays important roles in plant defences against a variety of biotic and abiotic stresses, including UV-B stress. Molecular mechanisms underlying functions of melatonin in plant UV-B responses are poorly understood. Here, we show that melatonin effect on molecular signalling pathways, physiological changes and UV-B stress resistance in Arabidopsis. Both exogenous and endogenous melatonin affected expression of UV-B signal transduction pathway genes. Experiments using UV-B signalling component mutants cop1-4 and hy5-215 revealed that melatonin not only acts as an antioxidant to promote UV-B stress resistance, but also regulates expression of several key components of UV-B signalling pathway, including ubiquitin-degrading enzyme (COP1), transcription factors (HY5, HYH) and RUP1/2. Our findings indicate that melatonin delays and subsequently enhances expression of COP1, HY5, HYH and RUP1/2, which act as central effectors in UV-B signalling pathway, thus regulating their effects on antioxidant systems to protect the plant from UV-B stress.

The in vitro effects of melatonin and Cry gene on the secretion of estradiol from camel ovarian granulosa cells

Bactrian camel as endemic economic species to the Northwest of China, its seasonal reproduction severely limits litter rates. In addition to melatonin, seasonal reproduction of animals is also regulated by the biological clock, but the specific molecular mechanism is not clear. To investigate the effects of melatonin and Cryptochrome (Cry) genes on seasonal reproduction, they were placed in ovarian granulosa cells, and their effects on reproduction were determined by measuring the concentrations of estradiol. Immunohistochemistry revealed that melatonin receptor protein (MT) was expressed in the cytosol and membrane of the ovarian granulosa cells, and the highest levels of CRY were expressed in the nuclei. The concentrations of estradiol in the cell culture supernatant were increased after the addition of exogenous melatonin or overexpression of MT, but these were decreased after MT was over expressed, and exogenous melatonin was added to the cells. In addition, there was a significant increase in the concentrations of estradiol after the Cry genes were overexpressed; however, the estradiol concentrations were decreased after the Cry genes were silenced. Our findings demonstrate that the MT and Cry genes play important roles in ovarian granulosa cell production of estradiol in a seasonally breeding species.

The role of melatonin and Tryptophan-5-hydroxylase-1 in different abiotic stressors in Apis cerana cerana

Tryptophan-5-hydroxylase-1 (T5H-1) is the rate-limiting enzyme in the biosynthesis of serotonin, which is involved in the biosynthesis of melatonin (Mel). Mel, a biological hormone, plays crucial roles in stressors tolerance, such as cold, hot, Ultraviolet (UV) and pesticide tolerance. However, the direct correlation between T5H-1 and Mel and the underlying mechanism in organisms remains elusive. Mel-mediated cold tolerance was studied extensively in plants and somewhat in insects, including bees. The present study isolated the Mel synthesis gene T5H-1 from Apis cerana cerana for the first time. qRT-PCR analysis indicated that AccT5H-1 played vital roles during some adverse conditions, including 4 °C, 8 °C, 10 °C, 45 °C, UV, cyhalothrin, abamectin, paraquat and bifenthrin exposure. Knockdown of AccT5H-1 using RNA interference (RNAi) technology upregulated most antioxidant genes. Additionally, an enzyme activity assay revealed higher contents of Malondialdehyde (MDA) and Hydrogen peroxide (H₂O₂), lower content of Vitamin C (VC), and higher activities of Glutathione S-transferase (GST), Superoxide dismutase (SOD), Catalase (CAT) and Peroxidase (POD) in the AccT5H-1 silenced group than the control group. These results suggest that AccT5H-1 is involved in the response to different oxidative stressors in A. cerana cerana. The survival rate of A. cerana cerana exposed to low temperature treatment revealed that the optimal concentration of Mel in the diet was 10 µg/mL. We also found that the antioxidant enzyme (GST, SOD, POD and CAT) concentrations at 10 µg/mL Mel increased to different degrees, and the content of oxidizing substances (MDA and H₂O₂) decreased, the content of VC increased, and the content of substances that promote cold resistance (glycerol and glycogen) increased. Mel increased the resistance of A. cerana cerana exposed to low temperatures. The expression of AccT5H-1 decreased after the feeding of exogenous Mel to bees. These results provide a reference for other insect studies on Mel and T5H-1.

Physiological and pharmacological roles of melatonin in the pathophysiological components of cellular injury after ischemic stroke

Apart from its metabolic or physiological functions, melatonin has a potent cytoprotective activity in the physiological and pathological conditions. It is synthetized by the pineal gland and released into the blood circulation but particularly cerebrospinal fluid in a circadian manner. It can also easily diffuse through cellular membranes due its small size and lipophilic structure. Its cytoprotective activity has been linked to its potent free radical scavenger activity with the desirable characteristics of a clinically- reliable antioxidant. Melatonin detoxifies oxygen and nitrogen-based free radicals and oxidizing agents, including the highly toxic hydroxyl-and peroxynitrite radicals, initiating cellular damage. However, the cytoprotective activity of melatonin is complex and cannot be solely limited to its free radical scavenger activity. It regulates cellular signaling pathways through receptor– dependent and independent mechanisms. Most of these downstream molecules, such as PI3K/AKT pathway components, also contribute to the cytoprotective effects of melatonin. In this term, melatonin is a promising molecule for the treatment of neurodegenerative disorders, such as ischemic stroke, which melatonin reduces ischemic brain injury in animal models of ischemic stroke. It regulates also circadian rhythm proteins after ischemic stroke, playing roles in cellular survival. In this context, present article summarizes the possible role of melatonin in the pathophysiological events after ischemic stroke.