Adult neural stem cell activation in mice is regulated by the day/night cycle and intracellular calcium dynamics.

Neural stem cells (NSCs) in the adult brain transit from the quiescent state to proliferation to produce new neurons. The mechanisms regulating this transition in freely behaving animals are, however, poorly understood. We customized in vivo imaging protocols to follow NSCs for several days up to months, observing their activation kinetics in freely behaving mice. Strikingly, NSC division is more frequent during daylight and is inhibited by darkness-induced melatonin signaling. The inhibition of melatonin receptors affected intracellular Ca2+ dynamics and promoted NSC activation. We further discovered a Ca2+ signature of quiescent versus activated NSCs and showed that several microenvironmental signals converge on intracellular Ca2+ pathways to regulate NSC quiescence and activation. In vivo NSC-specific optogenetic modulation of Ca2+ fluxes to mimic quiescent-state-like Ca2+ dynamics in freely behaving mice blocked NSC activation and maintained their quiescence, pointing to the regulatory mechanisms mediating NSC activation in freely behaving animals.

Nomo1 deficiency causes autism-like behavior in zebrafish.

Patients with neuropsychiatric disorders often exhibit a combination of clinical symptoms such as autism, epilepsy, or schizophrenia, complicating diagnosis and development of therapeutic strategies. Functional studies of novel genes associated with co-morbidities can provide clues to understand the pathogenic mechanisms and interventions. NOMO1 is one of the candidate genes located at 16p13.11, a hotspot of neuropsychiatric diseases. Here, we generate nomo1-/- zebrafish to get further insight into the function of NOMO1. Nomo1 mutants show abnormal brain and neuronal development and activation of apoptosis and inflammation-related pathways in the brain. Adult Nomo1-deficient zebrafish exhibit multiple neuropsychiatric behaviors such as hyperactive locomotor activity, social deficits, and repetitive stereotypic behaviors. The Habenular nucleus and the pineal gland in the telencephalon are affected, and the melatonin level of nomo1-/- is reduced. Melatonin treatment restores locomotor activity, reduces repetitive stereotypic behaviors, and rescues the noninfectious brain inflammatory responses caused by nomo1 deficiency. These results suggest melatonin supplementation as a potential therapeutic regimen for neuropsychiatric disorders caused by NOMO1 deficiency.

Coordination of apicoplast transcription in a malaria parasite by internal and host cues.

The malaria parasite Plasmodium falciparum has a nonphotosynthetic plastid called the apicoplast, which contains its own genome. Regulatory mechanisms for apicoplast gene expression remain poorly understood, despite this organelle being crucial for the parasite life cycle. Here, we identify a nuclear-encoded apicoplast RNA polymerase σ subunit (sigma factor) which, along with the α subunit, appears to mediate apicoplast transcript accumulation. This has a periodicity reminiscent of parasite circadian or developmental control. Expression of the apicoplast subunit gene, apSig, together with apicoplast transcripts, increased in the presence of the blood circadian signaling hormone melatonin. Our data suggest that the host circadian rhythm is integrated with intrinsic parasite cues to coordinate apicoplast genome transcription. This evolutionarily conserved regulatory system might be a future target for malaria treatment.

Melatonin and vitamin D, two sides of the same coin, better to land on its edge to improve multiple sclerosis.

Previous studies revealed a latitudinal gradient of multiple sclerosis (MS) prevalence, increasing by moving from the equator to the poles. The duration and quality of an individual's exposure to sunlight vary with latitude. Skin exposure to sunlight activates vitamin D synthesis, while light absence, as perceived by the eyes, activates melatonin synthesis in the pineal gland. Vitamin D or melatonin deficiency/insufficiency or overdose can occur at any latitude due to specific lifestyles and diets. Moving away from the equator, especially beyond 37°, decreases vitamin D while raising melatonin. Furthermore, melatonin synthesis increases in cold habitats like northern countries. Since melatonin's beneficial role was shown in MS, it is expected that northern countries whose individuals have higher endogenous melatonin should show a lower MS prevalence; however, these are ranked with the highest scores. In addition, countries like the United States and Canada have uncontrolled over-the-counter usage. In high latitudes, vitamin D deficiency and a higher MS prevalence persist even though vitamin D is typically compensated for by supplementation and not sunlight. Recently, we found that prolonged darkness increased MS melatonin levels, mimicking the long-term increase in northern countries. This caused a reduction in cortisol and increased infiltration, inflammation, and demyelination, which were all rescued by constant light therapy. In this review, we explain melatonin and vitamin D's possible roles in MS prevalence. The possible causes in northern countries are then discussed. Finally, we suggest strategies to treat MS by manipulating vitamin D and melatonin, preferably with sunlight or darkness, not supplements.

Machine learning estimation of human body time using metabolomic profiling.

Circadian rhythms influence physiology, metabolism, and molecular processes in the human body. Estimation of individual body time (circadian phase) is therefore highly relevant for individual optimization of behavior (sleep, meals, sports), diagnostic sampling, medical treatment, and for treatment of circadian rhythm disorders. Here, we provide a partial least squares regression (PLSR) machine learning approach that uses plasma-derived metabolomics data in one or more samples to estimate dim light melatonin onset (DLMO) as a proxy for circadian phase of the human body. For this purpose, our protocol was aimed to stay close to real-life conditions. We found that a metabolomics approach optimized for either women or men under entrained conditions performed equally well or better than existing approaches using more labor-intensive RNA sequencing-based methods. Although estimation of circadian body time using blood-targeted metabolomics requires further validation in shift work and other real-world conditions, it currently may offer a robust, feasible technique with relatively high accuracy to aid personalized optimization of behavior and clinical treatment after appropriate validation in patient populations.

Selective Enhancement of REM Sleep in Male Rats through Activation of Melatonin MT1 Receptors Located in the Locus Ceruleus Norepinephrine Neurons.

Sleep disorders affect millions of people around the world and have a high comorbidity with psychiatric disorders. While current hypnotics mostly increase non-rapid eye movement sleep (NREMS), drugs acting selectively on enhancing rapid eye movement sleep (REMS) are lacking. This polysomnographic study in male rats showed that the first-in-class selective melatonin MT1 receptor partial agonist UCM871 increases the duration of REMS without affecting that of NREMS. The REMS-promoting effects of UCM871 occurred by inhibiting, in a dose-response manner, the firing activity of the locus ceruleus (LC) norepinephrine (NE) neurons, which express MT1 receptors. The increase of REMS duration and the inhibition of LC-NE neuronal activity by UCM871 were abolished by MT1 pharmacological antagonism and by an adeno-associated viral (AAV) vector, which selectively knocked down MT1 receptors in the LC-NE neurons. In conclusion, MT1 receptor agonism inhibits LC-NE neurons and triggers REMS, thus representing a novel mechanism and target for REMS disorders and/or psychiatric disorders associated with REMS impairments.

Melatonin confers tolerance to nitrogen deficiency through regulating MdHY5 in apple plants.

Nitrogen (N) is an essential nutrient for crop growth and development, significantly influencing both yield and quality. Melatonin (MT), a known enhancer of abiotic stress tolerance, has been extensively studied. However, its relationship with nutrient stress, particularly N deficiency, and the underlying regulatory mechanisms of MT on N absorption remain unclear. In this study, exogenous MT treatment was found to improve the tolerance of apple plants to N deficiency. Apple plants overexpressing the MT biosynthetic gene N-acetylserotonin methyltransferase 9 (MdASMT9) were used to further investigate the effects of endogenous MT on low-N stress. Overexpression of MdASMT9 improved the light harvesting and heat transfer capability of apple plants, thereby mitigating the detrimental effects of N deficiency on the photosynthetic system. Proteomic and physiological data analyses indicated that MdASMT9 overexpression enhanced the trichloroacetic acid cycle and positively modulated amino acid metabolism to counteract N-deficiency stress. Additionally, both exogenous and endogenous MT promoted the transcription of MdHY5, which in turn bound to the MdNRT2.1 and MdNRT2.4 promoters and activated their expression. Notably, MT-mediated promotion of MdNRT2.1 and MdNRT2.4 expression through regulating MdHY5, ultimately enhancing N absorption. Taken together, these findings shed light on the association between MdASMT9-mediated MT biosynthesis and N absorption in apple plants under N-deficiency conditions.

Multi-class plant hormone HILIC-MS/MS analysis coupled with high-throughput phenotyping to investigate plant-environment interactions.

Plant hormones are chemical signals governing almost every aspect of a plant's life cycle and responses to environmental cues. They are enmeshed within complex signaling networks that can only be deciphered by using broad-scale analytical methods to capture information about several plant hormone classes simultaneously. Methods used for this purpose are all based on reversed-phase (RP) liquid chromatography and mass spectrometric detection. Hydrophilic interaction chromatography (HILIC) is an alternative chromatographic method that performs well in analyses of biological samples. We therefore developed and validated a HILIC method for broad-scale plant hormone analysis including a rapid sample preparation procedure; moreover, derivatization or fractionation is not required. The method enables plant hormone screening focused on polar and moderately polar analytes including cytokinins, auxins, jasmonates, abscisic acid and its metabolites, salicylates, indoleamines (melatonin), and 1-aminocyclopropane-1-carboxylic acid (ACC), for a total of 45 analytes. Importantly, the major pitfalls of ACC analysis have been addressed. Furthermore, HILIC provides orthogonal selectivity to conventional RP methods and displays greater sensitivity, resulting in lower limits of quantification. However, it is less robust, so procedures to increase its reproducibility were established. The method's potential is demonstrated in a case study by employing an approach combining hormonal analysis with phenomics to examine responses of three Arabidopsis ecotypes toward three abiotic stress treatments: salinity, low nutrient availability, and their combination. The case study showcases the value of the simultaneous determination of several plant hormone classes coupled with phenomics data when unraveling processes involving complex cross-talk under diverse plant-environment interactions.

Melatonin and brain barriers: The protection conferred by melatonin to the blood-brain barrier and blood-cerebrospinal fluid barrier.

The blood-brain barrier and the blood-cerebrospinal fluid barrier separate the blood from brain tissue and cerebrospinal fluid. These brain barriers are important to maintain homeostasis and complex functions by protecting the brain from xenobiotics and harmful endogenous compounds. The disruption of brain barriers is a characteristic of neurologic diseases. Melatonin is a lipophilic hormone that is mainly produced by the pineal gland. The blood-brain barrier and the blood-cerebrospinal fluid barriers are melatonin-binding sites. Among the several melatonin actions, the most characteristic one is the regulation of sleep-wake cycles, melatonin has anti-inflammatory and antioxidant properties. Since brain barriers disruption can arise from inflammation and oxidative stress, knowing the influence of melatonin on the integrity of brain barriers is extremely important. Therefore, the objective of this review is to gather and discuss the available literature about the regulation of brain barriers by melatonin.

Melatonin facilitates oocyte growth in goats and mice through increased nutrient reserves and enhanced mitochondrial function.

Oogenesis involves two phases: initial volumetric growth driven by nutrient accumulation and subsequent nuclear maturation. While melatonin (MLT) has been employed as a supplement to enhance the quality of fully grown oocytes during nuclear maturation phase, its impact on oocyte growth remains poorly studied. Here, we provide in vivo evidence demonstrating that follicle-stimulating hormone increases MLT content in ovary. Administration of MLT improves oocyte growth and quality in mice and goats by enhancing nutrient reserves and mitochondrial function. Conversely, MLT-deficient mice have smaller oocytes and dysfunctional mitochondria. Exploring the clinical implications of MLT in promoting oocyte growth, we observe that a brief 2-day MLT treatment enhances oocyte quality and reproductive performance in older mice. These findings highlight the role of MLT in regulating oocyte growth and provide a specific treatment window for optimizing oocyte quality and reproductive performance in female animals.

Melatonin suppresses atherosclerosis by ferroptosis inhibition via activating NRF2 pathway.

Melatonin (MLT), a conserved small indole compound, exhibits anti-inflammatory and antioxidant properties, contributing to its cardioprotective effects. Lipoprotein-associated phospholipase A2 (Lp-PLA2) is associated with atherosclerosis disease risk, and is known as an atherosclerosis risk biomarker. This study aimed to investigate the impact of MLT on Lp-PLA2 expression in the atherosclerotic process and explore the underlying mechanisms involved. In vivo, ApoE-/- mice were fed a high-fat diet, with or without MLT administration, after which the plaque area and collagen content were assessed. Macrophages were pretreated with MLT combined with ox-LDL, and the levels of ferroptosis-related proteins, NRF2 activation, mitochondrial function, and oxidative stress were measured. MLT administration significantly attenuated atherosclerotic plaque progression, as evidenced by decreased plaque area and increased collagen. Compared with those in the high-fat diet (HD) group, the levels of glutathione peroxidase 4 (GPX4) and SLC7A11 (xCT, a cystine/glutamate transporter) in atherosclerotic root macrophages were significantly increased in the MLT group. In vitro, MLT activated the nuclear factor-E2-related Factor 2 (NRF2)/SLC7A11/GPX4 signaling pathway, enhancing antioxidant capacity while reducing lipid peroxidation and suppressing Lp-PLA2 expression in macrophages. Moreover, MLT reversed ox-LDL-induced ferroptosis, through the use of ferrostatin-1 (a ferroptosis inhibitor) and/or erastin (a ferroptosis activator). Furthermore, the protective effects of MLT on Lp-PLA2 expression, antioxidant capacity, lipid peroxidation, and ferroptosis were decreased in ML385 (a specific NRF2 inhibitor)-treated macrophages and in AAV-sh-NRF2 treated ApoE-/- mice. MLT suppresses Lp-PLA2 expression and atherosclerosis processes by inhibiting macrophage ferroptosis and partially activating the NRF2 pathway.

Disruption of central and peripheral circadian clocks and circadian controlled estrogen receptor rhythms in night shift nurses in working environments.

Chronic disruption of circadian rhythms by night shift work is associated with an increased breast cancer risk. However, little is known about the impact of night shift on peripheral circadian genes (CGs) and circadian-controlled genes (CCGs) associated with breast cancer. Hence, we assessed central clock markers (melatonin and cortisol) in plasma, and peripheral CGs (PER1, PER2, PER3, and BMAL1) and CCGs (ESR1 and ESR2) in peripheral blood mononuclear cells (PBMCs). In day shift nurses (n = 12), 24-h rhythms of cortisol and melatonin were aligned with day shift-oriented light/dark schedules. The mRNA expression of PER2, PER3, BMAL1, and ESR2 showed 24-h rhythms with peak values in the morning. In contrast, night shift nurses (n = 10) lost 24-h rhythmicity of cortisol with a suppressed morning surge but retained normal rhythmic patterns of melatonin, leading to misalignment between cortisol and melatonin. Moreover, night shift nurses showed disruption of rhythmic expressions of PER2, PER3, BMAL1, and ESR2 genes, resulting in an impaired inverse correlation between PER2 and BMAL1 compared to day shift nurses. The observed trends of disrupted circadian markers were recapitulated in additional day (n = 20) and night (n = 19) shift nurses by measurement at early night and midnight time points. Taken together, this study demonstrated the misalignment of cortisol and melatonin, associated disruption of PER2 and ESR2 circadian expressions, and internal misalignment in peripheral circadian network in night shift nurses. Morning plasma cortisol and PER2, BMAL1, and ESR2 expressions in PBMCs may therefore be useful biomarkers of circadian disruption in shift workers.

Circadian disturbances by altering the light-dark cycle negatively affects hematopoietic function of bone marrow in mice.

Circadian rhythms in metabolically active tissues are crucial for maintaining physical health. Circadian disturbance (CD) can cause various health issues, such as metabolic abnormalities and immune and cognitive dysfunctions. However, studies on the role of CD in immune cell development and differentiation, as well as the rhythmic expression of the core clock genes and their altered expression under CD, remain unclear. Therefore, we exposed C57bl/6j mice to repeated reversed light-dark cycles for 90 days to research the effects of CD on bone marrow (BM) hematopoietic function. We also researched the effects of CD on endogenous circadian rhythms, temporally dependent expression in peripheral blood and myeloid leukocytes, environmental homeostasis within BM, and circadian oscillations of hematopoietic-extrinsic cues. Our results confirmed that when the light and dark cycles around mice were frequently reversed, the circadian rhythmic expression of the two main circadian rhythm markers, the hypothalamic clock gene, and serum melatonin, was disturbed, indicating that the body was in a state of endogenous CD. Furthermore, CD altered the temporally dependent expression of peripheral blood and BM leukocytes and destroyed environmental homeostasis within the BM as well as circadian oscillations of hematopoietic-extrinsic cues, which may negatively affect BM hematopoiesis in mice. Collectively, these results demonstrate that circadian rhythms are vital for maintaining health and suggest that the association between CD and hematopoietic dysfunction warrants further investigation.

The specificities, influencing factors, and medical implications of bone circadian rhythms.

Physiological processes within the human body are regulated in approximately 24-h cycles known as circadian rhythms, serving to adapt to environmental changes. Bone rhythms play pivotal roles in bone development, metabolism, mineralization, and remodeling processes. Bone rhythms exhibit cell specificity, and different cells in bone display various expressions of clock genes. Multiple environmental factors, including light, feeding, exercise, and temperature, affect bone diurnal rhythms through the sympathetic nervous system and various hormones. Disruptions in bone diurnal rhythms contribute to the onset of skeletal disorders such as osteoporosis, osteoarthritis and skeletal hypoplasia. Conversely, these bone diseases can be effectively treated when aimed at the circadian clock in bone cells, including the rhythmic expressions of clock genes and drug targets. In this review, we describe the unique circadian rhythms in physiological activities of various bone cells. Then we summarize the factors synchronizing the diurnal rhythms of bone with the underlying mechanisms. Based on the review, we aim to build an overall understanding of the diurnal rhythms in bone and summarize the new preventive and therapeutic strategies for bone disorders.

Melatonin alleviates hyperoxia-induced lung injury through elevating MSC exosomal miR-18a-5p expression to repress PUM2 signaling.

Mesenchymal stem cells (MSC)-derived exosomes (Exo) are a possible option for hyperoxia-induced lung injury (HLI). We wanted to see if melatonin (MT)-pretreated MSC-derived exosomes (MT-Exo) were more effective against HLI, and we also tried to figure out the underlying mechanism. HLI models were established by hyperoxia exposure. HE staining was adopted to analyze lung pathological changes. MTT and flow cytometry were used to determine cell viability and apoptosis, respectively. The mitochondrial membrane potential (MMP) was analyzed using the JC-1 probe. LDH, ROS, SOD, and GSH-Px levels were examined by the corresponding kits. The interactions between miR-18a-5p, PUM2, and DUB3 were analyzed by molecular interaction experiments. MT-Exo could effectively inhibit hyperoxia-induced oxidative stress, inflammatory injury, and apoptosis in lung epithelial cells, while these effects of MT-Exo were weakened by miR-18a-5p knockdown in MSCs. miR-18a-5p reduced PUM2 expression in MLE-12 cells by directly targeting PUM2. In addition, PUM2 inactivated the Nrf2/HO-1 signaling pathway by promoting DUB3 mRNA decay post-transcriptionally. As expected, PUM2 overexpression or DUB3 knockdown abolished the protective effect of MT-Exo on hyperoxia-induced lung epithelial cell injury. MT-Exo carrying miR-18a-5p reduced hyperoxia-mediated lung injury in mice through activating Nrf2/HO-1 pathway. MT reduced PUM2 expression and subsequently activated the DUB3/Nrf2/HO-1 signal axis by increasing miR-18a-5p expression in MSC-derived exosomes to alleviate HLI.

Assessing the antiviral potential of melatonin: A comprehensive systematic review.

This review assesses the antiviral potential of melatonin through comprehensive analysis of studies across human subjects, animal models, cell cultures, and in-silico simulations. The search strategy targeted relevant research until 22 June 2023, resulting in 20 primary studies after screening and deduplication. The findings highlight strong evidence supporting antiviral properties of melatonin. In silico studies identify melatonin as a candidate against SARS-CoV-2, reducing cytokine storm-related respiratory responses. Cell culture experiments reveal its multifaceted effects on different viruses including respiratory syncytial virus, anti-dengue virus, transmissible gastroenteritis virus, and encephalomyocarditis virus. Animal studies show melatonin reduces mortality and viral replication in various infections such as Venezuelan equine encephalomyelitis and COVID-19. Clinical trials show how it could be evaluated, but with no conclusive evidence of efficacy and safety so far from large, double-blind placebo-controlled trials. These insights showcase the potential of melatonin as a versatile antiviral agent with immunomodulatory, antioxidant, anti-inflammatory and antiviral properties. In summary, our review highlights melatonin's promising antiviral properties across diverse settings. Melatonin's immunomodulatory and antiviral potential makes it a compelling candidate for further investigation, emphasising the need for rigorous clinical trials to establish its safety and efficacy against viral infections.

α-Synuclein reduces acetylserotonin O-methyltransferase mediated melatonin biosynthesis by microtubule-associated protein 1 light chain 3 beta-related degradation pathway.

Previous studies have demonstrated that α-synuclein (α-SYN) is closely associated with rapid eye movement sleep behavior disorder (RBD) related to several neurodegenerative disorders. However, the exact molecular mechanisms are still rarely investigated. In the present study, we found that in the α-SYNA53T induced RBD-like behavior mouse model, the melatonin level in the plasma and pineal gland were significantly decreased. To elucidate the underlying mechanism of α-SYN-induced melatonin reduction, we investigated the effect of α-SYN in melatonin biosynthesis. Our findings showed that α-SYN reduced the level and activity of melatonin synthesis enzyme acetylserotonin O-methyltransferase (ASMT) in the pineal gland and in the cell cultures. In addition, we found that microtubule-associated protein 1 light chain 3 beta (LC3B) as an important autophagy adapter is involved in the degradation of ASMT. Immunoprecipitation assays revealed that α-SYN increases the binding between LC3B and ASMT, leading to ASMT degradation and a consequent reduction in melatonin biosynthesis. Collectively, our results demonstrate the molecular mechanisms of α-SYN in melatonin biosynthesis, indicating that melatonin is an important molecule involved in the α-SYN-associated RBD-like behaviors, which may provide a potential therapeutic target for RBD of Parkinson's disease.

The spectral sensitivity of human circadian phase resetting and melatonin suppression to light changes dynamically with light duration.

Human circadian, neuroendocrine, and neurobehavioral responses to light are mediated primarily by melanopsin-containing intrinsically-photosensitive retinal ganglion cells (ipRGCs) but they also receive input from visual photoreceptors. Relative photoreceptor contributions are irradiance- and duration-dependent but results for long-duration light exposures are limited. We constructed irradiance-response curves and action spectra for melatonin suppression and circadian resetting responses in participants exposed to 6.5-h monochromatic 420, 460, 480, 507, 555, or 620 nm light exposures initiated near the onset of nocturnal melatonin secretion. Melatonin suppression and phase resetting action spectra were best fit by a single-opsin template with lambdamax at 481 and 483 nm, respectively. Linear combinations of melanopsin (ipRGC), short-wavelength (S) cone, and combined long- and medium-wavelength (L+M) cone functions were also fit and compared. For melatonin suppression, lambdamax was 441 nm in the first quarter of the 6.5-h exposure with a second peak at 550 nm, suggesting strong initial S and L+M cone contribution. This contribution decayed over time; lambdamax was 485 nm in the final quarter of light exposure, consistent with a predominant melanopsin contribution. Similarly, for circadian resetting, lambdamax ranged from 445 nm (all three functions) to 487 nm (L+M-cone and melanopsin functions only), suggesting significant S-cone contribution, consistent with recent model findings that the first few minutes of a light exposure drive the majority of the phase resetting response. These findings suggest a possible initial strong cone contribution in driving melatonin suppression and phase resetting, followed by a dominant melanopsin contribution over longer duration light exposures.

Melatonin promotes proliferation of Inner Mongolia cashmere goat hair follicle papilla cells through Wnt10b.

The study demonstrated that melatonin (MT) can induce the development of secondary hair follicles in Inner Mongolian cashmere goats through the Wnt10b gene, leading to secondary dehairing. However, the mechanisms underlying the expression and molecular function of Wnt10b in dermal papilla cells (DPC) remain unknown. This research aimed to investigate the impact of MT on DPC and the regulation of Wnt10b expression, function, and molecular mechanisms in DPC. The findings revealed that MT promotes DPC proliferation and enhances DPC activity. Co-culturing DPC with overexpressed Wnt10b and MT showed a significant growth promotion. Subsequent RNA sequencing (RNA-seq) of overexpressed Wnt10b and control groups unveiled the regulatory role of Wnt10b in DPC. Numerous genes and pathways, including developmental pathways such as Wnt and MAPK, as well as processes like hair follicle morphogenesis and hair cycle, were identified. These results suggest that Wnt10b promotes the growth of secondary hair follicles in Inner Mongolian cashmere goats by regulating crucial factors and pathways in DPC proliferation.

Melatonin partially rescues defects induced by tranexamic acid exposure during oocyte maturation in mice.

Tranexamic acid (TXA) is widely used among young women because of its ability to whiten skin and treat menorrhagia. Nevertheless, its potential effects on oocyte maturation and quality have not yet been clearly clarified. Melatonin (MT) is an endogenous hormone released by the pineal gland and believed to protect cells from oxidative stress injury. In the present study, we used an in vitro maturation model to investigate the toxicity of TXA and the protective role of MT in mouse oocytes. Compared with the control group, the TXA-exposed group had significantly lower nuclear maturation (57.72% vs. 94.08%, P < 0.001) and early embryo cleavage rates (38.18% vs. 87.66%, P < 0.001). Further study showed that spindle organization (52.56% vs. 18.77%, P < 0.01) and chromosome alignment (33.23% vs. 16.66%, P < 0.01) were also disrupted after TXA treatment. Mechanistically, we have demonstrated that TXA induced early apoptosis of oocytes (P < 0.001) by raising the level of reactive oxygen species (P < 0.001), which was consistent with an increase in mitochondrial damage (P < 0.01). Fortunately, all these effects except the spindle defect were successfully rescued by an appropriate level of MT. Collectively, our findings indicate that MT could partially reverse TXA-induced oocyte quality deterioration in mice by effectively improving mitochondrial function and reducing oxidative stress-mediated apoptosis.NEW & NOTEWORTHY Tranexamic acid is increasingly used to whiten skin, reverse dermal damages, and treat heavy menstrual bleeding in young women. However, its potential toxicity in mammalian oocytes is still unclear. Our study revealed that tranexamic acid exposure impaired the mouse oocyte quality and subsequent embryo development. Meanwhile, melatonin has been found to exert beneficial effects in reducing tranexamic acid-induced mitochondrial dysfunction and oxidative stress.