Melatonin promotes proliferation and differentiation of neural stem cells subjected to hypoxia in vitro

Unveiling the Protective Roles of Melatonin on Glial Cells in the Battle Against Alzheimer's Disease-Insights from In Vivo and In Vitro Studies

Alzheimer's disease (AD) is a chronic, progressive neurodegenerative disorder that predominantly affects the elderly. Characterized by amyloid-beta (Aβ) plaques and neurofibrillary tangles, AD leads to memory loss, cognitive decline, and severe behavioral changes. As the most common form of dementia, AD imposes a significant global health burden, highlighting the need for interventions that address underlying disease mechanisms rather than only symptomatic treatment. Glial cells, including microglia and astrocytes, play a crucial role in AD progression by mediating neuroinflammatory responses and modulating Aβ clearance and neuronal health. Dysfunction in these cells can exacerbate neuroinflammation and neuronal damage, making glial cells an important target for therapeutic intervention. This review synthesizes findings from in vivo and in vitro studies on melatonin's effects on glial cell dysfunction in AD, emphasizing the multi-mechanistic nature of its neuroprotective properties. Recent studies highlight melatonin's potential as a therapeutic agent that addresses AD-related mechanisms through its interactions with glial cells. Melatonin has demonstrated protective effects, including reducing oxidative stress, apoptosis, and inflammation, inhibiting Aβ fibrillogenesis, and modulating amyloid precursor proteins. Additionally, its influence on glial cell activity, through melatonin receptor pathways, suggests it can alleviate neuroinflammation, a key component of AD progression. The collective evidence points to melatonin's promise as a therapeutic tool with potential roles in both preventive and adjunctive treatments for AD. However, further research is necessary to establish its efficacy and safety in clinical settings.

Exploring melatonin's multifaceted role in female reproductive health: From follicular development to lactation and its therapeutic potential in obstetric syndromes

BACKGROUND

Melatonin is mainly secreted by the pineal gland during darkness and regulates biological rhythms through its receptors in the suprachiasmatic nucleus of the hypothalamus. In addition, it also plays a role in the reproductive system by affecting the function of the hypothalamic-pituitary-gonadal axis, and by acting as a free radical scavenger thus contributing to the maintenance of the optimal physiological state of the gonads. Besides, melatonin can freely cross the placenta to influence fetal development. However, there is still a lack of overall understanding of the role of melatonin in the reproductive cycle of female mammals.

AIM OF REVIEW

Here we focus the role of melatonin in female reproduction from follicular development to delivery as well as the relationship between melatonin and lactation. We further summarize the potential role of melatonin in the treatment of preeclampsia, polycystic ovary syndrome, endometriosis, and ovarian aging.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Understanding the physiological role of melatonin in female reproductive processes will contribute to the advancement of human fertility and reproductive medicine research.

Melatonin Alleviates Albumin-Induced Tubular Cell Injury by Activating Clock-Controlled Nuclear Enriched Abundant Transcript 1-Mediated Proliferation

The pleiotropic and protective effects of melatonin have been demonstrated in a variety of animal models of renal injury. While coding RNAs regulated by melatonin in renal tissues are well identified, the functional involvement of long noncoding RNAs (lncRNAs) in melatonin signaling remains undefined. This study identified nuclear enriched abundant transcript 1 (NEAT1), a clock-controlled lncRNA that was upregulated by melatonin through the BMAL1/CLOCK heterodimer in renal tubular epithelial cells (TECs). Mechanistic studies showed that melatonin enhanced NEAT1 expression via increasing BMAL1 stability and thereby the enrichment of BMAL1 on NEAT1's promoter. Further studies have revealed that NEAT1 promotes the proliferation of TECs by increasing levels of H3K27ac and H3K4me1 at the promoter regions of the proliferation gene MKI67. Treatment of albumin-injured TECs with melatonin promoted proliferation by transactivating NEAT1 and restoring the expression levels of core clock genes and MKI67. Moreover, melatonin treatment ameliorated proteinuria, hypoalbuminemia, and fibrotic lesions, which was correlated with increased levels of core clock genes, H3K27ac, Mki67, and Neat1 in experimental MN kidneys. Melatonin mediates a novel regulatory axis, BMAL1-NEAT1-MKI67, in TEC proliferation, establishing potential therapeutic targets for MN and other renal diseases.

Melatonin Modulates Cell Cycle Dynamics and Promotes Hippocampal Cell Proliferation After Ischemic Injury in Neonatal Rats

Promoting neural cell proliferation may represent an important strategy for enhancing brain repair after developmental brain injury. The present study aimed to assess the effects of melatonin on cell proliferation after an ischemic injury in the developing hippocampus, focusing on cell cycle dynamics. After in vivo neonatal hypoxia-ischemia (HI), hippocampal cell cycle dynamics were assessed by flow cytometry, together with histological evaluation of dentate gyrus cellularity and proliferation. Melatonin significantly increased the number of proliferating cells in the G2/M phase as well as the proliferating cell nuclear antigen (PCNA) and doublecortin (DCX) labeling reduced by HI. In vivo BrdU labeling revealed a higher BrdU-positivity in the dentate gyrus of ischemic rats treated with melatonin, an effect followed by increased cellularity and preserved hippocampal tissue integrity. These results indicate that the protective effect of melatonin after ischemic injury in neonatal rats may rely on the modulation of cell cycle dynamics of newborn hippocampal cells and increased cell proliferation.

Experimental study on small molecule combinations inducing reprogramming of rat fibroblasts into functional neurons

OBJECTIVES

To establish a methodological system for reprogramming rat embryonic fibroblasts (REF) into chemically induced neurons (ciNCs) via small molecule compounds to provide safe and effective donor cells for treatment of neurodegenerative diseases.

METHODS

Based on the method established by PEI Gang's research group to directly reprogram human fibroblasts into neurons, the induction medium and maturation medium was optimized by replacing the coating solution, mitigating oxidative stress injury, adding neurogenic protective factors, adjusting the concentration of trichothecenes, performing small-molecule removal experiments, and carrying out immunofluorescence and Western blotting on cells at different stages of induction to validate the effect of induction.

RESULTS

When the original protocol was used for induction, the cell survival rate was (34.24±2.77)%. After replacing the coating solution gelatin with matrigel, the cell survival rate increased to (45.41±4.27)%; after adding melatonin, the cell survival rate increased to (67.95±5.61)% and (23.43±1.42)% were transformed into neural-like cells; after adding the small molecule P7C3-A20, the cell survival rate was further increased to (76.27±1.41)%, and (39.72±4.75)% of the cells were transformed into neural-like cells. When the concentration of trichothecene was increased to 30 μmol/L, the proportion of neural-like cells reached (55.79±1.90)%; after the removal of SP600125, (86.96±2.15)% of the cells survived, and the rate of neural-like cell production increased to (63.43±1.60)%. With the optimized protocol, REF could be successfully induced into ciNC through the neural precursor cell stage, in which the neural precursor cells were able to highly express the neural precursor cell markers SRY-related HMG-box gene 2 (Sox2) and paired box 6 (Pax6) as well as neuron-specific marker tubulin 1 (Tuj1), while the expression of fiber-associated protein vimentin was reduced. After two weeks of induction of neural precursor cells in a maturation medium, most cells displayed neuronal-like cell morphology. The induced ciNCs were able to highly express the mature neuronal surface markers Tuj1 and microtubule-associated protein 2 (MAP2), while the expression of vimentin was reduced.

CONCLUSIONS

The small molecule combinations optimized in this study can reprogram REF to ciNCs under normoxic conditions.

Effect of mesenchymal stem cells and melatonin on experimentally induced peripheral nerve injury in rats

Injury of a peripheral nerve (PNI) leads to both ischemic and inflammatory alterations. Sciatic nerve injury (SNI) represents the most widely used model for PNI. Mesenchymal stem cell-based therapy (MSCs) has convenient properties on PNI by stimulating the nerve regeneration. Melatonin has cytoprotective activity. The neuroprotective characteristics of MSCs and melatonin separately or in combination remain a knowledge need. In the rats-challenged SNI, therapeutic roles of intralesional MSCs and intraperitoneal melatonin injections were evaluated by functional assessment of peripheral nerve regeneration by walking track analysis involving sciatic function index (SFI) and two electrophysiological tests, electromyography and nerve conduction velocity, as well as measurement of antioxidant markers in serum, total antioxidant capacity (TAC) and malondialdehyde, and mRNA expression of brain derived neurotrophic factor (BDNF) in nerve tissues in addition to the histopathological evaluation of nerve tissue. Both individual and combination therapy with MSCs and melatonin therapies could effectively ameliorate this SNI and promote its regeneration as evidenced by improving the SFI and two electrophysiological tests and remarkable elevation of TAC with decline in lipid peroxidation and upregulation of BDNF levels. All of these led to functional improvement of the damaged nerve tissues and good recovery of the histopathological sections of sciatic nerve tissues suggesting multifactorial synergistic approach of the concurrent usage of melatonin and MSCs in PNI. The combination regimen has the most synergistic neuro-beneficial effects in PNI that should be used as therapeutic option in patients with PNI to boost their quality of life.

Melatonin promotes cell cycle progression of neural stem cells subjected to manganese via Nurr1

Excessive exposure to manganese (Mn) through drinking water and food during pregnancy significantly heightens the likelihood of neurodevelopmental damage in offspring. Multiple studies have indicated that melatonin (Mel) may help to relieve neurodevelopmental disorders caused by Mn, but potential mechanisms underlying this effect require further exploration. Here, we utilized primary neural stem cells (NSCs) as a model to elucidate the molecular mechanism underlying the protective function of Mel on Mn-induced cell proliferation dysfunction and cycle arrest. Our results showed that Mn disrupted the cell cycle in NSCs by suppressing positive regulatory proteins (CDK2, Cyclin A, Cyclin D1, and E2F1) and enhancing negative ones (p27KIP1 and p57KIP2), leading to cell proliferation dysfunction. Mel inhibited the Mn-dependent changes to these proteins and the cell cycle through nuclear receptor-related protein 1 (Nurr1), thus alleviating the proliferation dysfunction. Knockdown of Nurr1 using lentivirus-expressed shRNA in NSCs resulted in a diminished protective effect of Mel. We concluded that Mel mitigated Mn-induced proliferation dysfunction and cycle arrest in NSCs through Nurr1.

Melatonin alleviates valproic acid-induced neural tube defects by modulating Src/PI3K/ERK signaling and oxidative stress

Neural tube defects (NTDs) represent a developmental disorder of the nervous system that can lead to significant disability in children and impose substantial social burdens. Valproic acid (VPA), a widely prescribed first-line antiepileptic drug for epilepsy and various neurological conditions, has been associated with a 4-fold increase in the risk of NTDs when used during pregnancy. Consequently, urgent efforts are required to identify innovative prevention and treatment approaches for VPA-induced NTDs. Studies have demonstrated that the disruption in the delicate balance between cell proliferation and apoptosis is a crucial factor contributing to NTDs induced by VPA. Encouragingly, our current data reveal that melatonin (MT) significantly inhibits apoptosis while promoting the restoration of neuroepithelial cell proliferation impaired by VPA. Moreover, further investigations demonstrate that MT substantially reduces the incidence of neural tube malformations resulted from VPA exposure, primarily by suppressing apoptosis through the modulation of intracellular reactive oxygen species levels. In addition, the Src/PI3K/ERK signaling pathway appears to play a pivotal role in VPA-induced NTDs, with significant inhibition observed in the affected samples. Notably, MT treatment successfully reinstates Src/PI3K/ERK signaling, thereby offering a potential underlying mechanism for the protective effects of MT against VPA-induced NTDs. In summary, our current study substantiates the considerable protective potential of MT in mitigating VPA-triggered NTDs, thereby offering valuable strategies for the clinical management of VPA-related birth defects.

Autophagy Is Essential for Neural Stem Cell Proliferation Promoted by Hypoxia

Hypoxia as a microenvironment or niche stimulates proliferation of neural stem cells (NSCs). However, the underlying mechanisms remain elusive. Autophagy is a protective mechanism by which recycled cellular components and energy are rapidly supplied to the cell under stress. Whether autophagy mediates the proliferation of NSCs under hypoxia and how hypoxia induces autophagy remain unclear. Here, we report that hypoxia facilitates embryonic NSC proliferation through HIF-1/mTORC1 signaling pathway-mediated autophagy. Initially, we found that hypoxia greatly induced autophagy in NSCs, while inhibition of autophagy severely impeded the proliferation of NSCs in hypoxia conditions. Next, we demonstrated that the hypoxia core regulator HIF-1 was necessary and sufficient for autophagy induction in NSCs. Considering that mTORC1 is a key switch that suppresses autophagy, we subsequently analyzed the effect of HIF-1 on mTORC1 activity. Our results showed that the mTORC1 activity was negatively regulated by HIF-1. Finally, we provided evidence that HIF-1 regulated mTORC1 activity via its downstream target gene BNIP3. The increased expression of BNIP3 under hypoxia enhanced autophagy activity and proliferation of NSCs, which was mediated by repressing the activity of mTORC1. We further illustrated that BNIP3 can interact with Rheb, a canonical activator of mTORC1. Thus, we suppose that the interaction of BNIP3 with Rheb reduces the regulation of Rheb toward mTORC1 activity, which relieves the suppression of mTORC1 on autophagy, thereby promoting the rapid proliferation of NSCs. Altogether, this study identified a new HIF-1/BNIP3-Rheb/mTORC1 signaling axis, which regulates the NSC proliferation under hypoxia through induction of autophagy.

Bioinformatic analysis of the coding region of the melatonin receptor 1b gene as a reliable DNA marker to resolve interspecific mammal phylogenetic relationships

This research looks into the main DNA markers and the limits of their application in molecular phylogenetic analysis. Melatonin 1B (MTNR1B) receptor genes were analyzed from various biological sources. Based on the coding sequences of this gene, using the class Mammalia as example, phylogenetic reconstructions were made to study the potential of mtnr1b as a DNA marker for phylogenetic relationships investigating. The phylogenetic trees were constructed using NJ, ME and ML methods that establish the evolutionary relationships between different groups of mammals. The resulting topologies were generally in good agreement with topologies established on the basis of morphological and archaeological data as well as with other molecular markers. The present divergences provided a unique opportunity for evolutionary analysis. These results suggest that the coding sequence of the MTNR1B gene can be used as a marker to study the relationships of lower evolutionary levels (order, species) as well as to resolve deeper branches of the phylogenetic tree at the infraclass level.

Melatonin promotes the proliferation of primordial germ cell-like cells derived from porcine skin-derived stem cells: A mechanistic analysis

In vitro differentiation of stem cells into functional gametes remains of great interest in the biomedical field. Skin-derived stem cells (SDSCs) are an adult stem cells that provides a wide range of clinical applications without inherent ethical restrictions. In this paper, porcine SDSCs were successfully differentiated into primordial germ cell-like cells (PGCLCs) in conditioned media. The PGCLCs were characterized in terms of cell morphology, marker gene expression, and epigenetic properties. Furthermore, we also found that 25 μM melatonin (MLT) significantly increased the proliferation of the SDSC-derived PGCLCs while acting through the MLT receptor type 1 (MT1). RNA-seq results found the mitogen-activated protein kinase (MAPK) signaling pathway was more active when PGCLCs were cultured with MLT. Moreover, the effect of MLT was attenuated by the use of S26131 (MT1 antagonist), crenolanib (platelet-derived growth factor receptor inhibitor), U0126 (mitogen-activated protein kinase kinase inhibitor), or CCG-1423 (serum response factor transcription inhibitor), suggesting that MLT promotes the proliferation processes through the MAPK pathway. Taken together, this study highlights the role of MLT in promoting PGCLCs proliferation. Importantly, this study provides a suitable in vitro model for use in translational studies and could help to answer numerous remaining questions related to germ cell physiology.

Exogenous Melatonin Ameliorates the Negative Effect of Osmotic Stress in Human and Bovine Ovarian Stromal Cells

Ovarian tissue cryopreservation transplantation (OTCT) is the most flexible option to preserve fertility in women and children with cancer. However, OTCT is associated with follicle loss and an accompanying short lifespan of the grafts. Cryopreservation-induced damage could be due to cryoprotective agent (CPA) toxicity and osmotic shock. Therefore, one way to avoid this damage is to maintain the cell volume within osmotic tolerance limits (OTLs). Here, we aimed to determine, for the first time, the OTLs of ovarian stromal cells (OSCs) and their relationship with reactive oxygen species (ROS) and mitochondrial respiratory chain activity (MRCA) of OSCs. We evaluated the effect of an optimal dose of melatonin on OTLs, viability, MRCA, ROS and total antioxidant capacity (TAC) of both human and bovine OSCs in plated and suspended cells. The OTLs of OSCs were between 200 and 375 mOsm/kg in bovine and between 150 and 500 mOsm/kg in human. Melatonin expands OTLs of OSCs. Furthermore, melatonin significantly reduced ROS and improved TAC, MRCA and viability. Due to the narrow osmotic window of OSCs, it is important to optimize the current protocols of OTCT to maintain enough alive stromal cells, which are necessary for follicle development and graft longevity. The addition of melatonin is a promising strategy for improved cryopreservation media.

Melatonin and the Programming of Stem Cells

Melatonin interacts with various types of stem cells, in multiple ways that comprise stimulation of proliferation, maintenance of stemness and self-renewal, protection of survival, and programming toward functionally different cell lineages. These various properties are frequently intertwined but may not be always jointly present. Melatonin typically stimulates proliferation and transition to the mature cell type. For all sufficiently studied stem or progenitor cells, melatonin’s signaling pathways leading to expression of respective morphogenetic factors are discussed. The focus of this article will be laid on the aspect of programming, particularly in pluripotent cells. This is especially but not exclusively the case in neural stem cells (NSCs) and mesenchymal stem cells (MSCs). Concerning developmental bifurcations, decisions are not exclusively made by melatonin alone. In MSCs, melatonin promotes adipogenesis in a Wnt (Wingless-Integration-1)-independent mode, but chondrogenesis and osteogenesis Wnt-dependently. Melatonin upregulates Wnt, but not in the adipogenic lineage. This decision seems to depend on microenvironment and epigenetic memory. The decision for chondrogenesis instead of osteogenesis, both being Wnt-dependent, seems to involve fibroblast growth factor receptor 3. Stem cell-specific differences in melatonin and Wnt receptors, and contributions of transcription factors and noncoding RNAs are outlined, as well as possibilities and the medical importance of re-programming for transdifferentiation.

Hormesis and neural stem cells

This paper provides a detailed identification and assessment of hormetic dose responses in neural stem cells (NSCs) as identified in a number of animal models and human tissues, with particular emphasis on cell proliferation and differentiation. Hormetic dose responses were commonly observed following administration of a number of agents, including dietary supplements [e.g., berberine, curcumin, (-)-epigallocatechin-3-gallate (EGCG), Ginkgo Biloba, resveratrol], pharmaceuticals (e.g., lithium, lovastatin, melatonin), endogenous ligands [e.g., hydrogen sulfide (H₂S), magnesium, progesterone, taurine], environmental contaminants (e.g., arsenic, rotenone) and physical agents [e.g., hypoxia, ionizing radiation, electromagnetic radiation (EMF)]. These data indicate that numerous agents can induce hormetic dose responses to upregulate key functions of such as cell proliferation and differentiation in NSCs, and enhance resilience to inflammatory stresses. The paper assesses both putative mechanisms of hormetic responses in NSCs, and the potential therapeutic implications and application(s) of hormetic frameworks in clinical approaches to neurological injury and disease.

Hormesis and embryonic stem cells

This paper provides an identification and detailed assessment of hormetic dose responses of embryonic stem cells (ESCs) with particular emphasis on cell renewal (proliferation) and differentiation, underlying mechanistic foundations and potential therapeutic implications. Hormetic dose responses were commonly reported, being induced by a broad range of chemicals, including pharmaceuticals (e.g., atorvastatin, isoproterenol, lithium, nicotine, ouabain), dietary supplements (e.g., curcumin, multiple ginsenosides, resveratrol), endogenous agents (e.g., estrogen, hydrogen peroxide, melatonin), and physical stressor agents (e.g., hypoxia, ionizing radiation). ESC-hormetic dose responses are similar for other stem cell types (e.g., adipose-derived stem cells, apical papilla, bone marrow stem cells, dental pulp stem cells, endothelial stem cells, muscle stem cells, periodontal ligament stem cells, neural stem cells), indicating a high degree of generality for the hormetic-stem cells response. The widespread occurrence of hormetic dose responses shown by ESCs and other stem cells suggests that the hormetic dose response may represent a fundamental and highly conserved evolutionary strategy.

Effects of different doses of melatonin on rat adipose derived mesenchymal stem cells

OBJECTIVES

Stem cell treatment is based on Melatonin which is crucial for lots of pathological and physiological pathways. Our aim is determining the most appropriate dose of melatonin affecting the rat adipose tissue mesenchymal stem cells.

METHODS

Stem cells were isolated from male rat adipose tissue. Differentiation and characterization experiments were performed. Cell viability analyses in stem cells were used the XTT [2,3-Bis-(2-methoxy-4-Nitro-5-Sulfophenyl)-2H-Tetrazolium-5-Carboxanilide] assay. After 24 h incubation, different concentrations (0.5, 1, 5, 10, 50 µM) of extract were treated to the stem cells for 24 h, 48 and 72 h considering time and dose dependent manner. Total antioxidant status (TAS) and the total oxidant status (TOS) in control cells and melatonin treated cells (5, 10 µM) were determined Rel Assay commercial kits.

RESULTS

In 24 h, melatonin increased cell viability in all groups. When we evaluate the effect of melatonin in 48 h, the most proliferation increase was seen at 5, 10 µM doses. When the total oxidant activity melatonin was found to be significantly lower in 5 and 10 µM dose groups of melatonin.

CONCLUSIONS

Melatonin increases the survivor of stem cells and the most effective dose is 5 and 10 µM. The reduction of the oxidative stress index as a result of treating melatonin to mesenchymal stem cells showed that melatonin is a powerful antioxidant for stem cells.

The effect of melatonin on Hippo signaling pathway in dental pulp stem cells

Dental pulp stem cells (DPSCs) have a high capacity to differentiate into the neuronal cell lineage. Meanwhile, both Hippo signaling and melatonin are key regulators in neuronal differentiation of neuronal progenitor cells. Recently emerging evidences suggest the possible interaction between melatonin and Hippo signaling in different cell lines. But underlying mechanisms involved in the initiation or progression of neurogenic differentiation in DPSCs through this connection need to be explored. Therefore, the scope of this study is to investigate the effect of melatonin on Hippo signaling pathway through the expression of its downstream effector (YAP/p-YAP^Y357) after the neuronal differentiation of DPSCs. In regard with this, DPSCs were incubated with growth and dopaminergic neuronal differentiation medium with or without melatonin (10 μM) for 21 days. The morphological changes were followed by phase contrast microscopy and differentiation of DPSCs was evaluated by immunofluorescence labelling with NeuN, GFAP, and tyrosine hydroxylase. Furthermore, we evaluated the presence of neural progenitor cells by nestin immunoreactivity. Hippo signaling pathway was investigated by evaluating the immunoreactivity of YAP and p-YAP^Y357. Our results were also supported by western-blot analysis and SOX2, PCNA and caspase-3 were also evaluated. The positive immunoreactivity for NeuN, tyrosine hydroxylase and negative immunoreactivity for GFAP showed the successful differentiation of DPSCs to neurons, not glial cells. Melatonin addition to dopaminergic media induced tyrosine hydroxylase and decreased significantly nestin expression. The expressions of PCNA and caspase-3 were also decreased significantly with melatonin addition into growth media. Melatonin treatment induced phosphorylation of YAP^Y357 and reduced YAP expression. In conclusion, melatonin has potential to induce neuronal differentiation and reduce the proliferation of DPSCs by increasing phosphorylation of YAP^Y357 and eliminating the activity of YAP, which indicates the active state of Hippo signaling pathway.

Effects of melatonin in wound healing of dental pulp and periodontium: Evidence from in vitro, in vivo and clinical studies

INTRODUCTION

Database research has revealed that melatonin has beneficial effects in pulpal and periodontal regeneration. Several studies reported protective effects of melatonin against inflammation in several organs including the heart, brain, and teeth. In addition to inflammation reduction, melatonin has been involved in tissue regeneration and wound healing. The aim of this review is to summarize the evidence from in vitro, in vivo and clinical studies on the effects of melatonin in wound healing of dental pulp and periodontium. This review gives a thorough summary of the possible role of melatonin in wound healing of dental pulp and periodontium in connection with anti-inflammatory and antioxidant effects, cell proliferation, and cell differentiation. Any contradictory evidence is also assessed.

METHODS

The PubMed database was searched for all research articles published before April 2020 with the search terms "melatonin" and "dental pulp". Articles with the search terms "melatonin", "periodontal disease" and "bone" published before October 2019 were also included. Non-English articles were excluded.

RESULTS

Melatonin has been shown to reduce inflammation, inhibit cell proliferation and regulate differentiation of pulp cells. Melatonin increased odontoblast activities, resulting in the differentiation in the dental pulp. However, melatonin did not initiate differentiation in undifferentiated pulp cells but seemed to have beneficial effects in periodontitis by promoting periodontium's wound healing.

CONCLUSION

Those findings suggest that melatonin could have beneficial effects on pulpal and periodontal cells under inflammatory conditions. However, discrepancies remain between in vitro and in vivo findings regarding the effect of melatonin on dental pulp and periodontium.

Maternal pineal melatonin in gestation and lactation physiology, and in fetal development and programming

Pregnancy and lactation are reproductive processes that rely on physiological adaptations that should be timely and adequately triggered to guarantee both maternal and fetal health. Pineal melatonin is a hormone that presents daily and seasonal variations that synchronizes the organism's physiology to the different demands across time through its specific mechanisms and ways of action. The reproductive system is a notable target for melatonin as it actively participates on reproductive physiology and regulates the hypothalamus-pituitary-gonads axis, influencing gonadotropins and sexual hormones synthesis and release. For its antioxidant properties, melatonin is also vital for the oocytes and spermatozoa quality and viability, and for blastocyst development. Maternal pineal melatonin blood levels increase during pregnancy and triggers the maternal physiological alterations in energy metabolism both during pregnancy and lactation to cope with the energy demands of both periods and to promote adequate mammary gland development. Moreover, maternal melatonin freely crosses the placenta and is the only source of this hormone to the fetus. It importantly times the conceptus physiology and influences its development and programing of several functions that depend on neural and brain development, ultimately priming adult behavior and energy and glucose metabolism. The present review aims to explain the above listed melatonin functions, including the potential alterations observed in the progeny gestated under maternal chronodisruption and/or hypomelatoninemia.

Melatonin, aging, and COVID-19: Could melatonin be beneficial for COVID-19 treatment in the elderly?

The aim of this review is to summarize current studies on the relationship between melatonin and aging. Nowadays, age-related diseases come into prominence, and identifying age-related changes and developing proper therapeutic approaches are counted as some of the major issues regarding community health. Melatonin is the main hormone of the pineal gland. Melatonin is known to influence many biological processes in the body, including circadian rhythms, the immune system, and neuroendocrine and cardiovascular functions.Melatoninrhythms also reflect the biological process of aging. Aging is an extremely complex and multifactorial process. Melatonin levels decline considerably with aging and its decline is associated with several age-related diseases. Aging is closely associated with oxidative damage and mitochondrial dysfunction. Free radical reactions initiated by the mitochondria constitute the inherent aging process. Melatonin plays a pivotal role in preventing age-related oxidative stress. Coronavirus disease 2019 (COVID-19) fatality rates increase with chronic diseases and age, where melatonin levels decrease. For this reason, melatonin supplementation in elderly could be beneficial in COVID-19 treatment. Therefore, studies on the usage of melatonin in COVID-19 treatment are needed.

Protective Effects of Melatonin on Neurogenesis Impairment in Neurological Disorders and Its Relevant Molecular Mechanisms

Neurogenesis is the process by which functional new neurons are generated from the neural stem cells (NSCs) or neural progenitor cells (NPCs). Increasing lines of evidence show that neurogenesis impairment is involved in different neurological illnesses, including mood disorders, neurogenerative diseases, and central nervous system (CNS) injuries. Since reversing neurogenesis impairment was found to improve neurological outcomes in the pathological conditions, it is speculated that modulating neurogenesis is a potential therapeutic strategy for neurological diseases. Among different modulators of neurogenesis, melatonin is a particularly interesting one. In traditional understanding, melatonin controls the circadian rhythm and sleep-wake cycle, although it is not directly involved in the proliferation and survival of neurons. In the last decade, it was reported that melatonin plays an important role in the regulation of neurogenesis, and thus it may be a potential treatment for neurogenesis-related disorders. The present review aims to summarize and discuss the recent findings regarding the protective effects of melatonin on the neurogenesis impairment in different neurological conditions. We also address the molecular mechanisms involved in the actions of melatonin in neurogenesis modulation.

Oxidative Stress in Preterm Infants: Overview of Current Evidence and Future Prospects

Preterm birth (PTB), defined as parturition prior to 37 weeks of gestation, is the leading cause of morbidity and mortality in the neonatal population. The incidence and severity of complications of prematurity increase with decreasing gestational age and birthweight. The aim of this review study is to select the most current evidence on the role of oxidative stress in the onset of preterm complication prevention strategies and treatment options with pre-clinical and clinical trials. We also provide a literature review of primary and secondary studies on the role of oxidative stress in preterm infants and its eventual treatment in prematurity diseases. We conducted a systematic literature search of the Medline (Pubmed), Scholar, and ClinicalTrials.gov databases, retroactively, over a 7-year period. From an initial 777 articles identified, 25 articles were identified that met the inclusion and exclusion criteria. Of these, there were 11 literature reviews: one prospective cohort study, one experimental study, three case-control studies, three pre-clinical trials, and six clinical trials. Several biomarkers were identified as particularly promising, such as the products of the peroxidation of polyunsaturated fatty acids, those of the oxidation of phenylalanine, and the hydroxyl radicals that can attack the DNA chain. Among the most promising drugs, there are those for the prevention of neurological damage, such as melatonin, retinoid lactoferrin, and vitamin E. The microbiome also has an important role in oxidative stress. In conclusion, the most recent studies show that a strong relationship between oxidative stress and prematurity exists and that, unfortunately, there is still little therapeutic evidence reported in the literature.

Melatonin Promotes the Proliferation of Chicken Sertoli Cells by Activating the ERK/Inhibin Alpha Subunit Signaling Pathway

Melatonin influences physiological processes such as promoting proliferation and regulating cell development and function, and its effects on chicken Sertoli cells are unknown. Therefore, we investigated the effects of melatonin on cell proliferation and its underlying mechanisms in chicken Sertoli cells. Chicken Sertoli cells were exposed to varying melatonin concentrations (1, 10, 100, and 1000 nM), and the melatonin-induced effects on cell proliferation were measured by Cell Counting Kit 8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), real-time qPCR, and western blotting. We found that 1000 nM melatonin significantly (p < 0.05) promoted cell proliferation in chicken Sertoli cells. Furthermore, melatonin significantly (p < 0.05) increased the expression of inhibin alpha subunit (INHA), and the silencing of INHA reversed the melatonin-induced effects on Sertoli cell proliferation. We also found that melatonin activates the extracellular-regulated protein kinase (ERK) signaling pathway. To explore the role of the ERK signaling pathway in melatonin-induced cell proliferation, PD98059 (an inhibitor of EKR1/2) was used to pre-treat chicken Sertoli cells. The melatonin-induced proliferation of chicken Sertoli cells was reversed by PD98059, with decreased cell viability, weakened cell proliferation, and down-regulated expression of the proliferating cell nuclear antigen (PCNA), cyclin D1 (CCND1) and INHA. In summary, our results indicate that melatonin promotes the proliferation of chicken Sertoli cells by activating the ERK/inhibin alpha subunit signaling pathway.

Melatonin Protects Neural Stem Cells Against Tri-Ortho-Cresyl Phosphate-Induced Autophagy

Tri-ortho-cresyl phosphate (TOCP) is an extensively used organophosphate in industry. It has been proven to lead to toxicity in different organ systems, especially in the nervous system. Neural stem cells (NSCs) play important roles in both embryonic and adult nervous systems. However, whether TOCP induces cytotoxicity in embryonic NSCs remains unclear. In this study, mouse NSCs were exposed to different concentrations of TOCP for 24 h. The results showed that TOCP led to impaired proliferation of NSCs and induced the autophagy of NSCs by increasing the generation of intracellular reactive oxygen species (ROS) and decreasing the phosphorylation of extracellular regulated protein kinase (ERK1/2). Melatonin has been reported to exert neuroprotective effects via various mechanisms. Therefore, we further investigate whether melatonin has potential protective effects against TOCP-induced cytotoxicity on NSCs. Our data showed that melatonin pretreatment attenuated TOCP-induced autophagy by suppressing oxidative stress and restoring ERK1/2 phosphorylation consistently. Taken together, the results indicated that TOCP induced the autophagy in mouse NSCs, and melatonin may effectively protect NSCs against TOCP-induced autophagy.

Administration of melatonin for prevention of preterm birth and fetal brain injury associated with premature birth in a mouse model

PROBLEM

Maternal inflammation leads to preterm birth and perinatal brain injury. Melatonin, through its anti-inflammatory effects, has been shown to be protective against inflammation-induced perinatal adverse effects. However, the immunomodulatory effects of melatonin on preterm birth and prematurity-related morbidity remain unknown. We wanted to investigate the effects of maternally administered melatonin on preterm birth and perinatal brain injury in a mouse model of maternal inflammation.

METHOD OF STUDY

A model of maternal inflammation employing lipopolysaccharide (LPS) was used to mimic the most common clinical scenario of preterm birth, that of maternal inflammation. Mice were randomly divided into the following groups: control, LPS, and LPS with melatonin pre-treatment. Doppler ultrasonography was used to obtain fetal and maternal hemodynamic measurements in utero. Placenta and fetal brains were harvested and analyzed for proinflammatory markers and signs of perinatal brain injury, respectively. Surviving offspring were assessed for neuromotor outcomes.

RESULTS

Melatonin pre-treatment lowered the level of proinflammatory cytokines in the uterus and the placenta, significantly improved LPS-induced acute fetal neuroinflammation and perinatal brain injury, as well as significantly upregulated the SIRT1/Nrf2 signaling pathway to reduce LPS-induced inflammation. Melatonin also prevented adverse neuromotor outcomes in offspring exposed to maternal inflammation.

CONCLUSION

Maternally administered melatonin modulated immune responses to maternal inflammation and decreased preterm birth and perinatal brain injury. These results suggest that melatonin, a safe treatment during pregnancy, may be used as an experimental therapeutic in clinical trials.

Melatonin benefits to the growth of human annulus fibrosus cells through inhibiting miR-106a-5p/ATG7 signaling pathway

BACKGROUND

Disc degeneration (DD) is one of the common diseases worldwide, which deeply influences normal life and leads to excruciating pain. However, an effective treatment for DD is still not identified.

METHOD

The present study systemically examined the effect of melatonin on annulus fibrosus (AF) cells of patients with DD.

RESULTS

Melatonin had the effect of promoting proliferation, inducing autophagy, and suppressing apoptosis on AF cells of patients with DD. Moreover, melatonin contributed to the translation and transcription of autophagy-related protein ATG7 and inhibited the function of miR-106a-5p in AF cells. In addition, the results suggested that miR-106a-5p mediated the expression of ATG7 by directly binding to its 3'UTR in AF cells.

CONCLUSION

This research not only gained a deep insight of melatonin mode of action, but also indicated its potential target signaling pathway in AF cells.

TIGAR promotes neural stem cell differentiation through acetyl-CoA-mediated histone acetylation

Cellular metabolism plays a crucial role in controlling the proliferation, differentiation, and quiescence of neural stem cells (NSCs). The metabolic transition from aerobic glycolysis to oxidative phosphorylation has been regarded as a hallmark of neuronal differentiation. Understanding what triggers metabolism reprogramming and how glucose metabolism directs NSC differentiation may provide new insight into the regenerative potential of the brain. TP53 inducible glycolysis and apoptosis regulator (TIGAR) is an endogenous inhibitor of glycolysis and is highly expressed in mature neurons. However, its function in embryonic NSCs has not yet been explored. In this study, we aimed to investigate the precise roles of TIGAR in NSCs and the possible involvement of metabolic reprogramming in the TIGAR regulatory network. We observed that TIGAR is significantly increased during brain development as neural differentiation proceeds, especially at the peak of NSC differentiation (E14.5–E16.5). In cultured NSCs, knockdown of TIGAR reduced the expression of microtubule-associated protein 2 (MAP2), neuron-specific class III beta-tubulin (Tuj1), glial fibrillary acidic protein (GFAP), Ngn1, and NeuroD1, and enhanced the expression of REST, suggesting that TIGAR is an important regulator of NSC differentiation. Furthermore, TIGAR enhanced the expression of lactate dehydrogenase B (LDHB) and the mitochondrial biogenesis and oxidative phosphorylation (OXPHOS) markers, peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1α), nuclear respiratory factor (NRF1), and MitoNEET during NSC differentiation. TIGAR can decrease lactate production and accelerate oxygen consumption and ATP generation to maintain a high rate of OXPHOS in differentiated NSCs. Interestingly, knockdown of TIGAR decreased the level of acetyl-CoA and H3K9 acetylation at the promoters of Ngn1, Neurod1, and Gfap. Acetate, a precursor of acetyl-CoA, increased the level of H3K9 acetylation and rescued the effect of TIGAR deficiency on NSC differentiation. Together, our data demonstrated that TIGAR promotes metabolic reprogramming and regulates NSC differentiation through an epigenetic mechanism.

Melatonin Enhances Proliferation and Modulates Differentiation of Neural Stem Cells Via Autophagy in Hyperglycemia

Dysfunction of neural stem cells (NSCs) has been linked to fetal neuropathy, one of the most devastating complications of gestational diabetes. Several studies have demonstrated that melatonin (Mel) exerted neuroprotective actions in various stresses. However, the role of autophagy and the involvement of Mel in NSCs in hyperglycemia (HG) have not yet been fully established. Here, we found that HG increased autophagy and autophagic flux of NSCs as evidenced by increasing LC3B II/I ratio, Beclin-1 expression, and autophagosomes. Moreover, Mel enhanced NSCs proliferation and self-renewal in HG with decreasing autophagy and activated mTOR signaling. Consistently, inhibition of autophagy by 3-Methyladenine (3-Ma) could assist Mel effects above, and induction of autophagy by Rapamycin (Rapa) could diminish Mel effects. Remarkably, HG induced premature differentiation of NSCs into neurons (Map2 positive cells) and astrocytes (GFAP positive cells). Furthermore, Mel diminished HG-induced premature differentiation and assisted NSCs in HG differentiation as that in normal condition. Coincidentally, inhibiting of NSCs autophagy by 3-Ma assisted Mel to modulate differentiation. However, increasing NSCs autophagy by Rapa disturbed the Mel effects and retarded NSCs differentiation. These findings suggested that Mel supplementation could contribute to mimicking normal NSCs proliferation and differentiation in fetal central nervous system by inhibiting autophagy in the context of gestational diabetes. Stem Cells 2019;37:504-515.

Melatonin in Hypoxic-Ischemic Brain Injury in Term and Preterm Babies

Melatonin may serve as a potential therapeutic free radical scavenger and broad-spectrum antioxidant. It shows neuroprotective properties against hypoxic-ischemic brain injury in animal models. The authors review the studies focusing on the neuroprotective potential of melatonin and its possibility of treatment after perinatal asphyxia. Melatonin efficacy, low toxicity, and ability to readily cross through the blood-brain barrier make it a promising molecule. A very interesting thing is the difference between the half-life of melatonin in preterm neonates (15 hours) and adults (45-60 minutes). Probably, the use of synergic strategies-hypothermia coupled with melatonin treatment-may be promising in improving antioxidant action. The authors discuss and try to summarize the evidence surrounding the use of melatonin in hypoxic-ischemic events in term and preterm babies.

Potential effects and molecular mechanisms of melatonin on the dopaminergic neuronal differentiation of human amniotic fluid mesenchymal stem cells

Melatonin, a highly lipophilic molecule secreted by the pineal gland in the brain, plays a role in various biological functions. Previous studies reported that melatonin exerts its effect on mesenchymal stem cell (MSC) survival and differentiation into osteogenic- and adipogenic-lineage. However, the effect of melatonin in neurogenic differentiation in amniotic fluid (AF)-MSCs remains to be explored, thus we investigated the potential role of melatonin on dopaminergic neuron differentiation in AF-MSCs. The results showed that various concentrations of melatonin did not affect cell viability and proliferative effects of AF-MSCs. Increases in the levels of neuronal protein marker (βIII-tubulin) and dopaminergic neuronal markers (tyrosine hydroxylase, TH and NURR1), but decrease in the level of glial fibrillary acidic protein (GFAP), were observed in melatonin-treated AF-MSCs. Melatonin induced alteration in differential expression patterns of mesenchymal stem cell antigens by reducing CD29, CD45, CD73, CD90 and CD105, but no changing CD34 expressing cells. AF-MSCs were sequentially induced in neurobasal medium containing standard inducing cocktails (ST: bFGF, SHH, FGF8, BDNF), 1 μM melatonin, or a combination of ST and melatonin. The levels of TUJ1, TH, MAP2, NURR1 and dopamine transporter (DAT) were significantly increased in all treated groups when compared with control-untreated cells. Pretreated AF-MSCs with non-selective MT1/MT2 receptors antagonist, luzindole and selective MT2 receptor antagonist, 4-P-PDOT diminished melatonin-induced increase in dopaminergic neuronal markers and phosphorylated ERK but did not diminish increase in phosphorylated CaMKII by melatonin. Pretreatment with mitogen-activated protein kinase (MEK) inhibitor, PD98059 and CaMKII inhibitor, KN-93 were able to abolish increase in the levels of dopaminergic markers in melatonin-treated AF-MSCs. These findings suggest that melatonin promotes dopaminergic neuronal differentiation of AF-MSCs possibly via the induction in ERK and CaMKII pathways through melatonin receptor-dependent and -independent mechanisms, respectively.

The absence of maternal pineal melatonin rhythm during pregnancy and lactation impairs offspring physical growth, neurodevelopment, and behavior

Maternal melatonin provides photoperiodic information to the fetus and thus influences the regulation and timing of the offspring's internal rhythms and preparation for extra-uterine development. There is clinical evidence that melatonin deprivation of both mother and fetus during pregnancy, and of the neonate during lactation, results in negative long-term health outcomes. As a consequence, we hypothesized that the absence of maternal pineal melatonin might determine abnormal brain programming in the offspring, which would lead to long-lasting implications for behavior and brain function. To test our hypothesis, we investigated in rats the effects of maternal melatonin deprivation during gestation and lactation (MMD) to the offspring and the effects of its therapeutic replacement. The parameters evaluated were: (1) somatic, physical growth and neurobehavioral development of pups of both sexes; (2) hippocampal-dependent spatial learning and memory of the male offspring; (3) adult hippocampal neurogenesis of the male offspring. Our findings show that MMD significantly delayed male offspring's onset of fur development, pinna detachment, eyes opening, eruption of superior incisor teeth, testis descent and the time of maturation of palmar grasp, righting reflex, free-fall righting and walking. Conversely, female offspring neurodevelopment was not affected. Later on, male offspring show that MMD was able to disrupt both spatial reference and working memory in the Morris Water Maze paradigm and these deficits correlate with changes in the number of proliferative cells in the hippocampus. Importantly, all the observed impairments were reversed by maternal melatonin replacement therapy. In summary, we demonstrate that MMD delays the appearance of physical features, neurodevelopment and cognition in the male offspring, and points to putative public health implications for night shift working mothers.

Melatonin Rescues Mesenchymal Stem Cells from Senescence Induced by the Uremic Toxin p-Cresol via Inhibiting mTOR-Dependent Autophagy

p-Cresol, found at high concentrations in the serum of chronic kidney failure patients, is known to cause cell senescence and other complications in different parts of the body. p-Cresol is thought to mediate cytotoxic effects through the induction of autophagy response. However, toxic effects of p-cresol on mesenchymal stem cells have not been elucidated. Thus, we aimed to investigate whether p-cresol induces senescence of mesenchymal stem cells, and whether melatonin can ameliorate abnormal autophagy response caused by p-cresol. We found that p-cresol concentration-dependently reduced proliferation of mesenchymal stem cells. Pretreatment with melatonin prevented pro-senescence effects of p-cresol on mesenchymal stem cells. We found that by inducing phosphorylation of Akt and activating the Akt signaling pathway, melatonin enhanced catalase activity and thereby inhibited the accumulation of reactive oxygen species induced by p-cresol in mesenchymal stem cells, ultimately preventing abnormal activation of autophagy. Furthermore, preincubation with melatonin counteracted other pro-senescence changes caused by p-cresol, such as the increase in total 5′-AMP-activated protein kinase expression and decrease in the level of phosphorylated mechanistic target of rapamycin. Ultimately, we discovered that melatonin restored the expression of senescence marker protein 30, which is normally suppressed because of the induction of the autophagy pathway in chronic kidney failure patients by p-cresol. Our findings suggest that stem cell senescence in patients with chronic kidney failure could be potentially rescued by the administration of melatonin, which grants this hormone a novel therapeutic role.

Effects of Melatonin and Its Underlying Mechanism on Ethanol-Stimulated Senescence and Osteoclastic Differentiation in Human Periodontal Ligament Cells and Cementoblasts

The present study evaluated the protective effects of melatonin in ethanol (EtOH)-induced senescence and osteoclastic differentiation in human periodontal ligament cells (HPDLCs) and cementoblasts and the underlying mechanism. EtOH increased senescence activity, levels of reactive oxygen species (ROS) and the expression of cell cycle regulators (p53, p21 and p16) and senescence-associated secretory phenotype (SASP) genes (interleukin [IL]-1β, IL-6, IL-8 and tumor necrosis factor-α) in HPDLCs and cementoblasts. Melatonin inhibited EtOH-induced senescence and the production of ROS as well as the increased expression of cell cycle regulators and SASP genes. However, it recovered EtOH-suppressed osteoblastic/cementoblastic differentiation, as evidenced by alkaline phosphatase activity, alizarin staining and mRNA expression levels of Runt-related transcription factor 2 (Runx2) and osteoblastic and cementoblastic markers (glucose transporter 1 and cementum-derived protein-32) in HPDLCs and cementoblasts. Moreover, it inhibited EtOH-induced osteoclastic differentiation in mouse bone marrow⁻derived macrophages (BMMs). Inhibition of protein never in mitosis gene A interacting-1 (PIN1) by juglone or small interfering RNA reversed the effects of melatonin on EtOH-mediated senescence as well as osteoblastic and osteoclastic differentiation. Melatonin blocked EtOH-induced activation of mammalian target of rapamycin (mTOR), AMP-activated protein kinase (AMPK), mitogen-activated protein kinase (MAPK) and Nuclear factor of activated T-cells (NFAT) c-1 pathways, which was reversed by inhibition of PIN1. This is the first study to show the protective effects of melatonin on senescence-like phenotypes and osteoclastic differentiation induced by oxidative stress in HPDLCs and cementoblasts through the PIN1 pathway.

Melatonin promotes goat spermatogonia stem cells (SSCs) proliferation by stimulating glial cell line-derived neurotrophic factor (GDNF) production in Sertoli cells

Melatonin has been reported to be an important endogenous hormone for regulating neurogenesis, immunityand the biological clock. Recently, the effects of melatonin on neural stem cells (NSCs), mesenchymal stem cells(MSCs), and induced pluripotent stem cells(iPSCs) have been reported; however, the effects of melatonin on spermatogonia stem cells (SSCs) are not clear. Here, 1μM and 1nM melatonin was added to medium when goat SSCs were cultured in vitro, the results showed that melatonin could increase the formation and size of SSC colonies. Real-time quantitative PCR (QRT-PCR) and western blot analysis showed that the expression levels of SSC proliferation and self-renewal markers were up-regulated. Meanwhile, QRT-PCR results showed that melatonin inhibit the mRNA expression level of SSC differentiation markers. ELISA analysis showed an obvious increase in the concentration of GDNF (a niche factor secreted by Sertoli cells) in the medium when treated with melatonin. Meanwhile, the phosphorylation level of AKT, a downstream of GDNF-GFRa1-RET pathway was activated. In conclusion, melatonin promotes goat SSC proliferation by stimulating GDNF production in Sertoli cells.

Melatonin inhibits apoptotic cell death induced by Vibrio vulnificus VvhA via melatonin receptor 2 coupling with NCF-1

Melatonin, an endogenous hormone molecule, has a variety of biological functions, but a functional role of melatonin in the infection of Gram-negative bacterium Vibrio vulnificus has yet to be described. In this study, we investigated the molecular mechanism of melatonin in the apoptosis of human intestinal epithelial (HCT116) cells induced by the hemolysin (VvhA) produced by V. vulnificus. Melatonin (1 μM) significantly inhibited apoptosis induced by the recombinant protein (r) VvhA, which had been inhibited by the knockdown of MT₂. The rVvhA recruited caveolin-1, NCF-1, and Rac1 into lipid rafts to facilitate the production of ROS responsible for the phosphorylation of PKC and JNK. Interestingly, melatonin recruited NCF-1 into non-lipid rafts to prevent ROS production via MT₂ coupling with Gαq. Melatonin inhibited the JNK-mediated phosphorylation of c-Jun responsible for Bax expression, the release of mitochondrial cytochrome c, and caspase-3/-9 activation during its promotion of rVvhA-induced apoptotic cell death. In addition, melatonin inhibited JNK-mediated phosphorylation of Bcl-2 responsible for the release of Beclin-1 and Atg5 expression during its promotion of rVvhA-induced autophagic cell death. These results demonstrate that melatonin signaling via MT₂ triggers recruitment of NCF-1 into non-lipid rafts to block ROS production and JNK-mediated apoptotic and autophagic cell deaths induced by rVvhA in intestinal epithelial cells.

Brain injury and neural stem cells

Many therapies with potential for treatment of brain injury have been investigated. Few types of cells have spurred as much interest and excitement as stem cells over the past few decades. The multipotentiality and self-renewing characteristics of stem cells confer upon them the capability to regenerate lost tissue in ischemic or degenerative conditions as well as trauma. While stem cells have not yet proven to be clinically effective in many such conditions as was once hoped, they have demonstrated some effects that could be manipulated for clinical benefit. The various types of stem cells have similar characteristics, and largely differ in terms of origin; those that have differentiated to some extent may exhibit limited capability in differentiation potential. Stem cells can aid in decreasing lesion size and improving function following brain injury.

Melatonin Attenuates Histopathological Changes in the Hippocampus of Infantile Rats with Kaolin-Induced Hydrocephalus

OBJECTIVE/AIM

Hydrocephalus is defined as an incapacitating neurological disorder characterized by ventricular enlargement in children, but the effects of melatonin on this hydrocephalus have not yet been fully elucidated. In the present experiment, we attempted to investigate the effects of exogenous melatonin administration on hydrocephalus-induced hippocampal changes in infantile rats.

METHODS

In this study, we randomly divided 45 Swiss albino rats aged 2 weeks into 3 groups: group I, the control group received a sham injection with needle insertion only; groups II and III were given kaolin injections before treatment - group II, the hydrocephalus group, was treated with an isotonic NaCl solution, and group III, the hydrocephalus plus melatonin group, was treated with 0.5 mg/100 g body weight of exogenous melatonin. Both immunohistochemical and histological analyses were performed after hydrocephalus induction and melatonin administration. Immunohistochemical staining consisted anti-glial fibrillary acidic protein staining. The TUNEL technique was used for defining quantitate apoptosis.

RESULTS

Melatonin administration significantly attenuated chronic hydrocephalus-induced histopathological changes in the hippocampal subregions of infantile rats. Compared to hydrocephalic rats treated with saline solution, melatonin significantly decreased the number of apoptotic cells and pyknotic index values of each hippocampal subregion after the kaolin-induced hydrocephalus (p < 0.001).

CONCLUSION

The present results demonstrate that the chronic hydrocephalus-induced histopathological changes in the hippocampus were partially reversible with melatonin treatment, suggesting its neuroprotective effects in infantile rats. However, these findings need to be confirmed by further experimental studies and clinical trials.

Melatonin up-regulates the expression of the GATA-4 transcription factor and increases testosterone secretion from Leydig cells through RORα signaling in an in vitro goat spermatogonial stem cell differentiation culture system

Because androgen function is regulated by its receptors, androgen-androgen receptor signaling is crucial for regulating spermatogenesis. Androgen is mainly testosterone secreted by testis. Based on the results of early studies in goats, the administration of melatonin over an extended period of time increases steroid production, but the underlying mechanism remains unclear. Here, we report the expression of the melatonin membrane receptors MT1 and MT2 and the retinoic acid receptor-related orphan receptor-alpha (RORα) in the goat testis. An in vitro differentiation system using spermatogonial stem cells (SSCs) cultured in the presence of testicular somatic cells was able to support the formation of sperm-like cells with a single flagellum. The addition of 10^-7 M melatonin to the in vitro culture system increased RORα expression and considerably improved the efficiency of haploid cell differentiation, and the addition of the RORα agonist CGP52608 significantly increased the testosterone concentration and expression of GATA binding factor 4 (GATA-4). Furthermore, inhibitors of melatonin membrane receptors and a RORα antagonist (T0901317) also led to a considerable reduction in the efficiency of haploid spermatid formation, which was coupled with the suppression of GATA-4 expression. Based on these results, RORα may play a crucial role in enhancing melatonin-regulated GATA-4 transcription and steroid hormone synthesis in the goat spermatogonial stem cell differentiation culture system.

Effects of ginsenoside‑Rg1 on the proliferation and glial‑like directed differentiation of embryonic rat cortical neural stem cells in vitro

Ginsenoside-Rg1, the main active component of Panax notoginseng, exhibits a number of pharmacological functions, including promoting protein synthesis in the brain, increasing the number of synapses, improving memory and promoting recovery of brain function following injury. The effect of ginsenoside-Rg1 on proliferation and glial-like-directed differentiation in the cortical neural stem cells (NSCs) of embryonic rat brain was investigated. The present study used MTS assays to identify the optimum dose and window time of ginsenoside-Rg1 administration to stimulate the proliferation of cortical NSCs in the rat embryonic tissue. The oxygen glucose deprivation (OGD) set-up was used as a cell injury model. Immunofluorescent staining was used for identification of NSCs and subsequent observation of their proliferation and glial-like directed differentiation. Nestin expression was the marker for the presence of NSCs among the cortical cells of embryonic rat brain. The optimum dose of ginsenoside-Rg1 for proliferation of NSCs was 0.32 µg/ml. The optimum window time of 0.32 µg/ml ginsenoside-Rg1 administration on proliferation of NSCs was 6 h. Ginsenoside-Rg1 at 0.32 µg/ml concentration promoted incorporation of bromo-2-deoxyuridine, and expression of nestin and vimentin in primary and passaged NSCs, and NSCs following OGD. Ginsenoside-Rg1 had a role in promoting proliferation and glial-like-directed differentiation of cortical NSCs. The plausible explanation for these responses is that ginsenoside-Rg1 acts similarly to the growth factors to promote the proliferation and differentiation of NSCs.

Rapid modulation of the silent information regulator 1 by melatonin after hypoxia-ischemia in the neonatal rat brain

Increasing evidence indicates that melatonin possesses protective effects toward different kinds of damage in various organs, including the brain. In a neonatal model of hypoxia-ischemia (HI), melatonin was neuroprotective and preserved the expression of the silent information regulator 1 (SIRT1) 24 hours after the insult. This study aimed to gain more insight into the role of SIRT1 in the protective effect of melatonin after HI by studying the early (1 hour) modulation of SIRT1 and its downstream targets, and the consequences on necrosis, apoptosis, autophagy, and glial cell activation. We found that melatonin administered 5 minutes after the ischemic insult significantly reduced necrotic cell death assessed 1 hour after its administration. In parallel, we found a reduced activation of the early phases of intrinsic apoptosis, detected by reduced BAX translocation to the mitochondria and preservation of the mitochondrial expression of cytochrome C, indicating a reduced outer mitochondrial membrane permeabilization in the melatonin-treated ischemic animals. These effects were concomitant to increased expression and activity of SIRT1, reduced expression and acetylation of p53, and increased autophagy activation. Melatonin also reduced HI-induced glial cells activation. SIRT1 was expressed in neurons after HI and melatonin but not in reactive glial cells expressing GFAP. Colocalization between SIRT1 and GFAP was found in some cells in control conditions. In summary, our results provide more insight into the connection between SIRT1 and melatonin in neuroprotection. The possibility that melatonin-induced SIRT1 activity might contribute to differentiate neuronal progenitor cells during the neurodegenerative process needs to be further investigated.

Melatonin inhibits nucleus pulposus (NP) cell proliferation and extracellular matrix (ECM) remodeling via the melatonin membrane receptors mediated PI3K-Akt pathway

Pinealectomy in vertebrates accelerated intervertebral disk degeneration (IDD). However, the potential mechanisms, particularly melatonin's role, are still to be clarified. In this study, for first time, melatonin membrane receptors of MT1 and MT2 were found to be present in the human intervertebral disk tissues and nucleus pulposus (NP) cells, respectively. Melatonin treatment significantly inhibited NP cell proliferation in dose-dependent manner. Accordingly, melatonin down-regulated gene expression of cyclin D1, PCNA, matrix metallopeptidase-3, and matrix metallopeptidase-9 and upregulated gene expression of collagen type II alpha 1 chain and aggrecan in NP cells. These effects of melatonin were blocked by luzindole, a nonspecific melatonin membrane receptor antagonist. Signaling pathway analysis indicated that in the intervertebral disk tissues and NP cells, melatonin acted on MT1/2 and subsequently reduced phosphorylation of phosphoinositide 3-kinase p85 regulatory subunit, phosphoinositide-dependent kinase-1, and Akt. The results indicate that melatonin is a crucial regulator of NP cell function and plays a vital role in prevention of IDD.

Melatonin Increases Oligodendrocyte Differentiation in Cultured Neural Stem Cells

Neural stem cell (NSC) culture is a remarkable tool to investigate the potential therapeutic benefits of drugs in neurological diseases. The purpose of this study was to determine the effect of melatonin on proliferation and differentiation of NSCs in vitro. NSCs were isolated and expanded from mouse embryonic E14 cortex, and the effect of various concentrations of melatonin (0.05, 0.1, 0.5, 1, 5 and 10 μM) on NSC proliferation was assessed by MTT and neurosphere assay. Results showed that melatonin significantly increased NSC viability and NSC proliferation in a dose-dependent manner, in comparison to controls. Similarly, neurosphere formation frequency and cell counts increased significantly with increasing melatonin concentrations and reached its peak at 0.5 μM, in comparison to controls. Moreover, NSCs treated with either low (0.05 µM) or high concentrations (5 µM) of melatonin showed that the mean percentage of glial fibrillary acidic protein (GFAP) positive cells were not significantly different in PDGF or melatonin at 5 μM, in comparison to controls. However, low melatonin concentrations (0.05 µM) showed a slight significant increase in comparison to controls and PDGF. On the other hand, both concentrations of melatonin treatment significantly increased the percentage of myelin basic protein (MBP) positive cells (oligodendrocytes), in comparison to controls and to PDGF. Our results demonstrated, for the first time, that melatonin increased oligodendrocyte differentiation from NSCs. These results suggest that melatonin might have a potential therapeutic effect for some neurological diseases that involve oligodendrocyte and myelin pathologies.

Melatonin enhances neural stem cell differentiation and engraftment by increasing mitochondrial function

Neural stem cells (NSCs) are regarded as a promising therapeutic approach to protecting and restoring damaged neurons in neurodegenerative diseases (NDs) such as Parkinson's disease and Alzheimer's disease (PD and AD, respectively). However, new research suggests that NSC differentiation is required to make this strategy effective. Several studies have demonstrated that melatonin increases mature neuronal markers, which reflects NSC differentiation into neurons. Nevertheless, the possible involvement of mitochondria in the effects of melatonin during NSC differentiation has not yet been fully established. We therefore tested the impact of melatonin on NSC proliferation and differentiation in an attempt to determine whether these actions depend on modulating mitochondrial activity. We measured proliferation and differentiation markers, mitochondrial structural and functional parameters as well as oxidative stress indicators and also evaluated cell transplant engraftment. This enabled us to show that melatonin (25 μM) induces NSC differentiation into oligodendrocytes and neurons. These effects depend on increased mitochondrial mass/DNA/complexes, mitochondrial respiration, and membrane potential as well as ATP synthesis in NSCs. It is also interesting to note that melatonin prevented oxidative stress caused by high levels of mitochondrial activity. Finally, we found that melatonin enriches NSC engraftment in the ND mouse model following transplantation. We concluded that a combined therapy involving transplantation of NSCs pretreated with pharmacological doses of melatonin could efficiently restore neuronal cell populations in PD and AD mouse models depending on mitochondrial activity promotion.

Melatonin promotes circadian rhythm-induced proliferation through Clock/histone deacetylase 3/c-Myc interaction in mouse adipose tissue

Melatonin is synthesized in the pineal gland and controls circadian rhythm of peripheral adipose tissue, resulting in changes in body weight. Although core regulatory components of clock rhythmicity have been defined, insight into the mechanisms of circadian rhythm-mediated proliferation in adipose tissue is still limited. Here, we showed that melatonin (20 mg/kg/d) promoted circadian and proliferation processes in white adipose tissue. The circadian amplitudes of brain and muscle aryl hydrocarbon receptor nuclear translocator-like 1 (Bmal1, P<.05) and circadian locomotor output cycles kaput (Clock, P<.05), period 2 (Per2, P<.05), cyclin E (P<.05), and c-Myc (P<.05) were directly increased by melatonin in adipose tissue. Melatonin also promoted cell cycle and increased cell numbers (P<.05), which was correlated with the Clock expression (P<.05). Further analysis demonstrated that Clock bound to the E-box elements in the promoter region of c-Myc and then directly stimulated c-Myc transcription. Moreover, Clock physically interacted with histone deacetylase 3 (HDAC3) and formed a complex with c-Myc to promote adipocyte proliferation. Melatonin also attenuated circadian disruption and promoted adipocyte proliferation in chronic jet-lagged mice and obese mice. Thus, our study found that melatonin promoted adipocyte proliferation by forming a Clock/HDAC3/c-Myc complex and subsequently driving the circadian amplitudes of proliferation genes. Our data reveal a novel mechanism that links circadian rhythm to cell proliferation in adipose tissue. These findings also identify a new potential means for melatonin to prevent and treat sleep deprivation-caused obesity.

Melatonin alleviates acute spinal cord injury in rats through promoting on progenitor cells proliferation

The previous studies have shown that melatonin is beneficial for nervous system after spinal cord injury (SCI). After SCI, the endogenous neural stem/progenitor cells (eNSPCs) proliferate and differentiate into neurons and glial cells. In the present study, we examined the effect of melatonin on eNSPCs proliferation and differentiation in SCI rat model. SCI rat model was established by dropping a 10 g rod from the height of 25 mm. Then, the rats were randomly divided into the control group, the melatonin treated group, and the G3335 treated group. The Basso-Beattie-Bresnahan locomotor rating scale (BBB scale) was used to evaluate the recovery of locomotor function after SCI. Flow cytometry was used to evaluate eNSPCs proliferation and differentiation. The rats in the melatonin treated group demonstrated significantly faster locomotor function recovery and more eNSPCs proliferation and differentiation. However, these effects were abolished in the G3335 treated group. Melatonin can effectively promote locomotor function recovery via improving eNSPCs proliferation and differentiation after SCI.

Melatonin antagonizes interleukin-18-mediated inhibition on neural stem cell proliferation and differentiation

Neural stem cells (NSCs) are self‐renewing, pluripotent and undifferentiated cells which have the potential to differentiate into neurons, oligodendrocytes and astrocytes. NSC therapy for tissue regeneration, thus, gains popularity. However, the low survivals rate of the transplanted cell impedes its utilities. In this study, we tested whether melatonin, a potent antioxidant, could promote the NSC proliferation and neuronal differentiation, especially, in the presence of the pro‐inflammatory cytokine interleukin‐18 (IL‐18). Our results showed that melatonin per se indeed exhibited beneficial effects on NSCs and IL‐18 inhibited NSC proliferation, neurosphere formation and their differentiation into neurons. All inhibitory effects of IL‐18 on NSCs were significantly reduced by melatonin treatment. Moreover, melatonin application increased the production of both brain‐derived and glial cell‐derived neurotrophic factors (BDNF, GDNF) in IL‐18‐stimulated NSCs. It was observed that inhibition of BDNF or GDNF hindered the protective effects of melatonin on NSCs. A potentially protective mechanism of melatonin on the inhibition of NSC's differentiation caused IL‐18 may attribute to the up‐regulation of these two major neurotrophic factors, BNDF and GNDF. The findings indicate that melatonin may play an important role promoting the survival of NSCs in neuroinflammatory diseases.