Melatonin rescues zebrafish embryos from the parkinsonian phenotype restoring the parkin/PINK1/DJ-1/MUL1 network

Modulation of autophagy by melatonin and its receptors: implications in brain disorders

Autophagy plays a crucial role in maintaining neuronal homeostasis and function, and its disruption is linked to various brain diseases. Melatonin, an endogenous hormone that primarily acts through MT1 and MT2 receptors, regulates autophagy via multiple pathways. Growing evidence indicates that melatonin's ability to modulate autophagy provides therapeutic and preventive benefits in brain disorders, including neurodegenerative and affective diseases. In this review, we summarize the key mechanisms by which melatonin affects autophagy and explore its therapeutic potential in the treatment of brain disorders.

Therapeutic potential of Parkin and its regulation in Parkinson's disease

Parkinson's disease (PD) is a debilitating neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the midbrain substantia nigra, resulting in motor and non-motor symptoms. While the exact etiology of PD remains elusive, a growing body of evidence suggests that dysfunction in the parkin protein plays a pivotal role in the pathogenesis of the disease. Parkin is an E3 ubiquitin ligase that ubiquitinates substrate proteins to control a number of crucial cellular processes including protein catabolism, immune response, and cellular apoptosis.While autosomal recessive mutations in the PARK2 gene, which codes for parkin, are linked to an inherited form of early-onset PD, heterozygous mutations in PARK2 have also been reported in the more commonly occurring sporadic PD cases. Impairment of parkin's E3 ligase activity is believed to play a pathogenic role in both familial and sporadic forms of PD.This article provides an overview of the current understanding of the mechanistic basis of parkin's E3 ligase activity, its major physiological role in controlling cellular functions, and how these are disrupted in familial and sporadic PD. The second half of the manuscript explores the currently available and potential therapeutic strategies targeting parkin structure and/or function in order to slow down or mitigate the progressive neurodegeneration in PD.

Co-exposure effect of different colour of LED lights and increasing temperature on zebrafish larvae (Danio rerio): Immunohistochemical, metabolomics, molecular and behaviour approaches

Although there are studies in the literature on the effects of different coloured light-emitting diodes (LEDs) on different organisms, there is limited information on how these effects change with temperature increase. In this study, the effects of blue, green, red and white LED lights on the early development process of zebrafish (Danio rerio (Hamilton, 1822)) were comprehensively investigated. In addition, to simulate global warming, it was examined how a one-degree temperature increase affects this process. For this purpose, zebrafish embryos, which were placed at 4 hpf (hours post fertilization) in an incubator whose interior was divided into four areas, were kept at three different temperatures (28, 29 and 30 °C) for 120 h. The group kept in a dark environment was chosen as the control. The temperature of the control group was also increased at the same rate as the other groups. The results showed that at the end of the exposure period, temperature and light colour caused an increase in body malformations. Histopathological damage and immunopositive signals of HSP 70 and 8-OHdG biomarkers in larval brains, increase in free oxygen radicals, apoptotic cells and lipid accumulation throughout the body, increase in locomotor activity, decrease in heart rate and blood flow, and significant changes in more than thirty metabolite levels were detected. In addition, it has been determined that many metabolic pathways are affected, especially glutathione, vitamin B6 and pyrimidine metabolism. Moreover, it has been observed that a one-degree temperature increase worsens this negative effect. It was concluded that blue light was the closest light to the control group and was less harmful than other light colours. The study revealed that blue light produced results that were most similar to those seen in the control group.

Dysfunctional mitochondria in age-related neurodegeneration: Utility of melatonin as an antioxidant treatment

Mitochondria functionally degrade as neurons age. Degenerative changes cause inefficient oxidative phosphorylation (OXPHOS) and elevated electron leakage from the electron transport chain (ETC) promoting increased intramitochondrial generation of damaging reactive oxygen and reactive nitrogen species (ROS and RNS). The associated progressive accumulation of molecular damage causes an increasingly rapid decline in mitochondrial physiology contributing to aging. Melatonin, a multifunctional free radical scavenger and indirect antioxidant, is synthesized in the mitochondrial matrix of neurons. Melatonin reduces electron leakage from the ETC and elevates ATP production; it also detoxifies ROS/RNS and via the SIRT3/FOXO pathway it upregulates activities of superoxide dismutase 2 and glutathione peroxidase. Melatonin also influences glucose processing by neurons. In neurogenerative diseases, neurons often adopt Warburg-type metabolism which excludes pyruvate from the mitochondria causing reduced intramitochondrial acetyl coenzyme A production. Acetyl coenzyme A supports the citric acid cycle and OXPHOS. Additionally, acetyl coenzyme A is a required co-substrate for arylalkylamine-N-acetyl transferase, which rate limits melatonin synthesis; therefore, melatonin production is diminished in cells that experience Warburg-type metabolism making mitochondria more vulnerable to oxidative stress. Moreover, endogenously produced melatonin diminishes during aging, further increasing oxidative damage to mitochondrial components. More normal mitochondrial physiology is preserved in aging neurons with melatonin supplementation.

Characterizing the adult zebrafish model of Parkinson's disease: a systematic review of dynamic changes in behavior and physiology post-MPTP administration

Introduction

Adult zebrafish are increasingly used in Parkinson's disease (PD) research due to their well-characterized dopaminergic system. Among the toxin-based models, the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is widely utilized to induce parkinsonism in adult zebrafish. Therefore, this review presents an overview of the procedures and the dynamic changes in behavior and physiology observed in the adult zebrafish PD model following a single intraperitoneal injection of MPTP.

Methods

A systematic literature search in the PubMed and Google Scholar databases was conducted to identify relevant articles. Of the 165 articles identified, 9 were included in this review. These chosen articles are original works published before March 2024, all of which utilized adult zebrafish induced with MPTP as the model for PD. Other articles were excluded based on factors such as limited relevance, utilization of zebrafish embryos or larvae instead of adults, and variations in MPTP deliveries.

Results

Studies indicated that the ideal model entails the utilization of mixed gender zebrafish aged between 4 and 6 months from the wild-type strain. The acceptable MPTP doses ranges between 20 μg/g (lowest) and 225 μg/g (highest) and doses above 292 μg/g are lethal. Furthermore, noticeable parkinsonian symptoms appear 1 day after administration and persist for more than 1 week.

Discussion

Mitochondrial dysfunction precedes dopaminergic neurodegeneration within this experimental regime. A single administration of MPTP effectively induces PD in adult zebrafish. This study aids in crafting the adult zebrafish PD model, outlining the progressive behavioral and physiological changes ensuing from MPTP administration.

Retinoschisin Is Required for Pineal Gland Calcification and Cellular Communication in Pinealocytes of Rats and Mice

Retinoschisin (RS1) is a secretory protein specifically localized to the extracellular domains in both the lateral retina and the pineal gland (PG). However, the functions of RS1 in the pineal body are poorly understood. To address this knowledge gap, in this study, we undertook histochemical, ultrastructural, and Western blotting analyses of the PG in rats and RS1-knock-in transgenic. We found that RS1 plays a key role in pineal gland calcification (PGC) in mice through both extracellular and intracellular pathways. RS1 was clustered around the cell membrane or intracellularly in pinealocytes, actively participating in the exchange of calcium and thereby mediating PGC. Additionally, RS1 deposition is essential for maintaining PGC architecture in the intercellular space of the adult PG. In RS1-knock-in mice with a nonsense mutation (p.Y65X) in the Rs1-domain of RS1, the Rs1-domain is chaotically dispersed in pinealocytes and the intercellular region of the PG. This prevents RS1 from binding calcified spots and forming calcified nodules, ultimately leading to the accumulation of calcareous lamellae in microvesicles. Additionally, RS1 was observed to colocalize with connexin-36, thereby modulating intercellular communication in the PG of both rats and mice. Our study revealed for the first time that RS1 is essential for maintaining PGC architecture and that it colocalizes with connexin 36 to modulate intercellular communication in the PG. These findings provide novel insights into the function of the RS1 gene in the PG.

Mitochondrial dynamics dysfunction: Unraveling the hidden link to depression

Depression is a common mental disorder and its pathogenesis is not fully understood. However, more and more evidence shows that mitochondrial dynamics dysfunction may play an important role in the occurrence and development of depression. Mitochondria are the centre of energy production in cells, and are also involved in important processes such as apoptosis and oxidative stress. Studies have found that there are abnormalities in mitochondrial function in patients with depression, including mitochondrial morphological changes, mitochondrial dynamics disorders, mitochondrial DNA damage, and impaired mitochondrial respiratory chain function. These abnormalities may cause excessive free radicals and oxidative stress in mitochondria, which further damage cells and affect the balance of neurotransmitters, causing or aggravating depressive symptoms. Studies have shown that mitochondrial dynamics dysfunction may participate in the occurrence and development of depression by affecting neuroplasticity, inflammation and neurotransmitters. This article reviews the effects of mitochondrial dynamics dysfunction on the pathogenesis of depression and its potential molecular pathway. The restorers for the treatment of depression by regulating the function of mitochondrial dynamics were summarized and the possibility of using mitochondrial dynamics as a biomarker of depression was discussed.

Enriched Environment Enhances Sociability Through the Promotion of ESyt1-Related Synaptic Formation in the Medial Prefrontal Cortex

Sociability stands as a crucial factor in the evolutionary success of all mammalian species. Notably, enriched environment (EE) housing has been shown to enhance sociability in mice. However, the precise underlying molecular mechanism remains elusive. In this study, we established an EE paradigm, housing mice for a 14-day period. Both enhanced sociability and an increased spine density in the medial prefrontal cortex (mPFC) of mice subjected to EE were detected. To elucidate the potential molecular pathway, we conducted high-performance liquid chromatography tandem mass spectrometry (HPLC-MS) analysis of the entire mPFC from both EE and home-caged (HC) housed mice. Our analysis identified 16 upregulated and 20 downregulated proteins in the EE group. Among them, Extended Synaptotagmin 1 (ESyt1), an activity-dependent endoplasmic reticulum (ER)-plasma membrane (PM) tethering protein associated with synaptic function and growth, emerged as a potentially key player in the increased synapse formation and enhanced sociability observed in EE-housed mice. Further investigation, involving the knockdown of ESyt1 expression via sh ESyt1 lentivirus in the mPFC, revealed that ESyt1 is crucial for increased spine density of mPFC and enhanced sociability of mice in an enriched environment but not in normal condition. Overall, our findings uncover a novel mechanistic insight into the positive influence of environmental enrichment on social behavior via ESyt1-mediated pathways.

Mitophagy in neurodegenerative disease pathogenesis

Mitochondria are critical cellular energy resources and are central to the life of the neuron. Mitophagy selectively clears damaged or dysfunctional mitochondria through autophagic machinery to maintain mitochondrial quality control and homeostasis. Mature neurons are postmitotic and consume substantial energy, thus require highly efficient mitophagy pathways to turn over damaged or dysfunctional mitochondria. Recent evidence indicates that mitophagy is pivotal to the pathogenesis of neurological diseases. However, more work is needed to study mitophagy pathway components as potential therapeutic targets. In this review, we briefly discuss the characteristics of nonselective autophagy and selective autophagy, including ERphagy, aggrephagy, and mitophagy. We then introduce the mechanisms of Parkin-dependent and Parkin-independent mitophagy pathways under physiological conditions. Next, we summarize the diverse repertoire of mitochondrial membrane receptors and phospholipids that mediate mitophagy. Importantly, we review the critical role of mitophagy in the pathogenesis of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Last, we discuss recent studies considering mitophagy as a potential therapeutic target for treating neurodegenerative diseases. Together, our review may provide novel views to better understand the roles of mitophagy in neurodegenerative disease pathogenesis.

Melatonin-Loaded Nanoparticles Augment Mitophagy to Retard Parkinson's Disease

The molecular pathways that melatonin follows as a Parkinson's disease (PD) antagonist remain poorly elucidated, despite it being a safe and a potential neurotherapeutic drug with a few limitations such as less bioavailability, premature oxidation, brain delivery, etc. Here, we used a biocompatible protein (HSA) nanocarrier for the delivery of melatonin to the brain. This nanomelatonin showed better antioxidative and neuroprotective properties, and it not only improves mitophagy to remove unhealthy mitochondria but also improves mitochondrial biogenesis to counteract rotenone-induced toxicity in an in vitro PD model. We also showed BMI1, a member of the PRC1 complex that regulates mitophagy, whose protein expression was enhanced after nanomelatonin dosage. These effects were translated to a rodent model, where nanomelatonin improves the TH+ve neuron population in SNPC and protects against rotenone-mediated toxicity. Our findings highlight the significantly better in vitro and in vivo neuroprotective effect of nanomelatonin as well as the molecular/cellular dynamics it influences to regulate mitophagy as a measure of the potential therapeutic candidate for PD.

Developing Peripheral Biochemical Biomarkers of Brain Disorders: Insights from Zebrafish Models

High prevalence of human brain disorders necessitates development of the reliable peripheral biomarkers as diagnostic and disease-monitoring tools. In addition to clinical studies, animal models markedly advance studying of non-brain abnormalities associated with brain pathogenesis. The zebrafish (Danio rerio) is becoming increasingly popular as an animal model organism in translational neuroscience. These fish share some practical advantages over mammalian models together with high genetic homology and evolutionarily conserved biochemical and neurobehavioral phenotypes, thus enabling large-scale modeling of human brain diseases. Here, we review mounting evidence on peripheral biomarkers of brain disorders in zebrafish models, focusing on altered biochemistry (lipids, carbohydrates, proteins, and other non-signal molecules, as well as metabolic reactions and activity of enzymes). Collectively, these data strongly support the utility of zebrafish (from a systems biology standpoint) to study peripheral manifestations of brain disorders, as well as highlight potential applications of biochemical biomarkers in zebrafish models to biomarker-based drug discovery and development.

Involvement of Plasma Melatonin in Medication-Overuse Headache: A Cross-Sectional Study

OBJECTIVES

Patients with medication-overuse headache (MOH) are often complicated with anxiety, depression, and sleep disorders and are associated with dependence behavior and substance abuse. Melatonin has physiological properties including analgesia, regulation of circadian rhythms, soporific, and antidepressant and affects drug preference and addiction. This study aimed to investigate the role of melatonin in MOH compared with episodic migraine (EM) and healthy controls and to verify the relationship between plasma melatonin levels and psychiatric symptoms.

METHODS

Thirty patients affected by MOH, 30 patients with EM, and 30 matched healthy controls were enrolled. All subjects completed a detailed headache questionnaire and scales including the Hospital Anxiety and Depression Scale (HADS), the Pittsburgh Sleep Quality Index, the Leeds Dependence Questionnaire. Melatonin levels in plasma samples were measured by enzyme immunoassay method.

RESULTS

The levels of plasma melatonin were significantly different among 3 groups of subjects (MOH, 7.74 [5.40-9.89]; EM, 9.79 [8.23-10.62]; Control, 10.16 [8.60-17.57]; H = 13.433; P = 0.001). Significantly lower levels of melatonin were found in MOH patients compared with healthy controls ( P = 0.001). The level of plasma melatonin inversely correlated with the scores of HADS-Anxiety ( r = -0.318, P = 0.002), HADS-Depression ( r = -0.368, P < 0.001), Pittsburgh Sleep Quality Index ( r = -0.303, P = 0.004), and Leeds Dependence Questionnaire ( r = -0.312, P = 0.003).

CONCLUSIONS

This study innovatively detects the plasma melatonin levels in MOH patients and explores the association between melatonin levels and psychiatric symptoms. Melatonin may be potential complementary therapy in the treatment of MOH considering its comprehensive role in multiple aspects of MOH.

Advances in Zebrafish as a Comprehensive Model of Mental Disorders

As an important part in international disease, mental disorders seriously damage human health and social stability, which show the complex pathogenesis and increasing incidence year by year. In order to analyze the pathogenesis of mental disorders as soon as possible and to look for the targeted drug treatment for psychiatric diseases, a more reasonable animal model is imperious demands. Benefiting from its high homology with the human genome, its brain tissue is highly similar to that of humans, and it is easy to realize whole-body optical visualization and high-throughput screening; zebrafish stands out among many animal models of mental disorders. Here, valuable qualified zebrafish mental disorders models could be established through behavioral test and sociological analysis, which are simulated to humans, and combined with molecular analyses and other detection methods. This review focuses on the advances in the zebrafish model to simulate the human mental disorders; summarizes the various behavioral characterization means, the use of equipment, and operation principle; sums up the various mental disorder zebrafish model modeling methods; puts forward the current challenges and future development trend, which is to contribute the theoretical supports for the exploration of the mechanisms and treatment strategies of mental disorders.

Experimental models of chemically induced Parkinson's disease in zebrafish at the embryonic larval stage: a systematic review

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra that results in a decrease in dopamine levels, resulting in motor-type disturbances. Different vertebrate models, such as rodents and fish, have been used to study PD. In recent decades, Danio rerio (zebrafish) has emerged as a potential model for the investigation of neurodegenerative diseases due to its homology to the nervous system of humans. In this context, this systematic review aimed to identify publications that reported the utilization of neurotoxins as an experimental model of parkinsonism in zebrafish embryos and larvae. Ultimately, 56 articles were identified by searching three databases (PubMed, Web of Science, and Google Scholar). Seventeen studies using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 4 1-methyl-4-phenylpyridinium (MPP+), 24 6-hydroxydopamine (6-OHDA), 6 paraquat/diquat, 2 rotenone, and 6 articles using other types of unusual neurotoxins to induce PD were selected. Neurobehavioral function, such as motor activity, dopaminergic neuron markers, oxidative stress biomarkers, and other relevant parameters in the zebrafish embryo-larval model were examined. In summary, this review provides information to help researchers determine which chemical model is suitable to study experimental parkinsonism, according to the effects induced by neurotoxins in zebrafish embryos and larvae.

Melatonin as mitochondria-targeted drug

Oxidative damage is associated to numerous diseases as well as aging development. Mitochondria found in most eukaryotic organisms to create the energy of the cell, generate free radicals during its action and they are chief targets of the oxidants. Mitochondrial activities outspread outside the borders of the cell and effect human physiology by modulating interactions among cells and tissues. Therefore, it has been implicated in several human disorders and conditions. Melatonin (MLT) is an endogenously created indole derivative that modifies several tasks, involving mitochondria-associated activities. These possessions make MLT a powerful defender against a selection of free radical-linked disorders. MLT lessens mitochondrial anomalies causing from extreme oxidative stress and may improve mitochondrial physiology. It is a potent and inducible antioxidant for mitochondria. MLT is produced in mitochondria of conceivably of all cells and it also appears to be a mitochondria directed antioxidant which has related defensive properties as the synthesized antioxidant molecules. This chapter summarizes the suggestion that MLT is produced in mitochondria as well as disorders of mitochondrial MLT production that may associate to a number of mitochondria-linked diseases. MLT as a mitochondria-targeted drug is also discussed.

Chronodisruption and Loss of Melatonin Rhythm, Associated with Alterations in Daily Motor Activity and Mitochondrial Dynamics in Parkinsonian Zebrafish, Are Corrected by Melatonin Treatment

Beyond sleep/wake, clock genes regulate the daily rhythms of melatonin production, motor activity, innate immunity, and mitochondrial dynamics, among others. All these rhythms are affected in Parkinson's disease (PD), suggesting that chronodisruption may be an early stage of the disease. The aim of this study was to evaluate the connection between clock genes and these rhythms in PD, and whether melatonin administration reestablished the normal clock function. Parkinsonism was induced with 600 μM MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) in 24-120 h post fertilization (hpf) zebrafish embryos and melatonin was administered at a dose of 1 μM. Day-night melatonin rhythm disappeared in MPTP-treated embryos, which showed an advance in the activity phase in parallel with changes in the rhythm of clock genes. An alteration in the fission-to-fusion mitochondrial dynamics was also detected in parkinsonian embryos, increasing the former and leading to apoptosis. Melatonin administration to MPTP-treated embryos fully restored the circadian system, including the rhythms of clock genes, motor activity, melatonin rhythm, and mitochondrial dynamics, and decreasing apoptosis. Because clock-controlled rhythms such as sleep/wake alterations are early events in PD, the data here reported may point to chronodisruption as one initial pathophysiological event of the disease.

Proteomic profiling reveals the potential mechanisms and regulatory targets of sirtuin 4 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson's mouse model

Introduction

Parkinson's disease (PD), as a common neurodegenerative disease, currently has no effective therapeutic approaches to delay or stop its progression. There is an urgent need to further define its pathogenesis and develop new therapeutic targets. An increasing number of studies have shown that members of the sirtuin (SIRT) family are differentially involved in neurodegenerative diseases, indicating their potential to serve as targets in therapeutic strategies. Mitochondrial SIRT4 possesses multiple enzymatic activities, such as deacetylase, ADP ribosyltransferase, lipoamidase, and deacylase activities, and exhibits different enzymatic activities and target substrates in different tissues and cells; thus, mitochondrial SIRT4 plays an integral role in regulating metabolism. However, the role and mechanism of SIRT4 in PD are not fully understood. This study aimed to investigate the potential mechanism and possible regulatory targets of SIRT4 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice.

Methods

The expression of the SIRT4 protein in the MPTP-induced PD mouse mice or key familial Parkinson disease protein 7 knockout (DJ-1 KO) rat was compared against the control group by western blot assay. Afterwards, quantitative proteomics and bioinformatics analyses were performed to identify altered proteins in the vitro model and reveal the possible functional role of SIRT4. The most promising molecular target of SIRT4 were screened and validated by viral transfection, western blot assay and reverse transcription quantitative PCR (RT-qPCR) assays.

Results

The expression of the SIRT4 protein was found to be altered both in the MPTP-induced PD mouse mice and DJ-1KO rats. Following the viral transfection of SIRT4, a quantitative proteomics analysis identified 5,094 altered proteins in the vitro model, including 213 significantly upregulated proteins and 222 significantly downregulated proteins. The results from bioinformatics analyses indicated that SIRT4 mainly affected the ribosomal pathway, propionate metabolism pathway, peroxisome proliferator-activated receptor (PPAR) signaling pathway and peroxisome pathway in cells, and we screened 25 potential molecular targets. Finally, only fatty acid binding protein 4 (FABP4) in the PPAR signaling pathway was regulated by SIRT4 among the 25 molecules. Importantly, the alterations in FABP4 and PPARγ were verified in the MPTP-induced PD mouse model.

Discussion

Our results indicated that FABP4 in the PPAR signaling pathway is the most promising molecular target of SIRT4 in an MPTP-induced mouse model and revealed the possible functional role of SIRT4. This study provides a reference for future drug development and mechanism research with SIRT4 as a target or biomarker.

Dopamine Release Impairments Accompany Locomotor and Cognitive Deficiencies in Rotenone-Treated Parkinson's Disease Model Zebrafish

In this work, we carried out neurochemical and behavioral analysis of zebrafish (Danio rerio) treated with rotenone, an agent used to chemically induce a syndrome resembling Parkinson's disease (PD). Dopamine release, measured with fast-scan cyclic voltammetry (FSCV) at carbon-fiber electrodes in acutely harvested whole brains, was about 30% of that found in controls. Uptake, represented by the first order rate constant (k) and the half-life (t1/2) determined by nonlinear regression modeling of the stimulated release plots, was also diminished. Behavioral analysis revealed that rotenone treatment increased the time required for zebrafish to reach a reward within a maze by more than 50% and caused fish to select the wrong pathway, suggesting that latent learning was impaired. Additionally, zebrafish treated with rotenone suffered from diminished locomotor activity, swimming shorter distances with lower mean velocity and acceleration. Thus, the neurochemical and behavioral approaches, as applied, were able to resolve rotenone-induced differences in key parameters. This approach may be effective for screening therapies in this and other models of neurodegeneration.

Neurotoxicity of sanguinarine via inhibiting mitophagy and activating apoptosis in zebrafish and PC12 cells

Sanguinarine, a plant-derived phytoalexin, displays various biological activities, such as insecticidal, antimicrobial, anti-inflammatory, anti-angiogenesis and antitumor effects. But its potential neurotoxicity and the underlying mechanisms has rarely been investigated. Therefore, we aimed to assess the neurotoxicity of sanguinarine using zebrafish model and PC12 cells in this study. The results showed that sanguinarine induced the reduction of the length of dopamine neurons and inhibited the blood vessel in the head area of the zebrafish. Further studies demonstrated that the behavioral phenotype of the larval zebrafish was changed by sanguinarine. In addition, there were more apoptotic cells in the larval zebrafish head area. The mRNA expression levels of β-syn, th, pink1 and parkin, closely related to the nervous function, were changed after sanguinarine treatment. The in vitro studies show that notably increases of ROS and apoptosis levels in PC12 cells were observed after sanguinarine treatment. Moreover, the protein expression of Caspase3, Parp, Bax, Bcl2, α-Syn, Th, PINK1 and Parkin were also altered by sanguinarine. Our data indicated that the inhibition of mitophagy, ROS elevation and apoptosis were involved in the neurotoxicity of sanguinarine. These findings will be useful to understand the toxicity induced by sanguinarine.

Melatonin attenuates polystyrene microplastics induced motor neurodevelopmental defect in zebrafish (Danio rerio) by activating nrf2 - isl2a Axis

Microplastics, a new type of ecological pollutant, have now become a major environmental concern worldwide. Polystyrene microplastics (PS), one of the most abundant form of microplastics, cause deleterious effects across species. Melatonin (MT), which is secreted by pineal gland, exhibits protective role against pollutant-induced damage. However, whether MT could ameliorate PS-induced neurodevelopmental toxicity remain unclear. In our study, zebrafish embryos were treated with PS (0.5, 25 mg/L) in the presence or absence of MT (1 μM) from 4 h post-fertilization (hpf) to 144 hpf. Locomotion behavior, oxidative stress, apoptosis, proliferation and development of caudal primary (Cap) motoneuron axon were analyzed. Gene expression was determined by qRT-PCR or whole-mount in situ hybridization. Results showed that PS exposure significantly reduced swimming speed of zebrafish larvae and induced excessive reactive oxygen species (ROS), apoptosis and aberrant proliferation. In addition, PS treatment markedly shortened the length of Cap motoneuron axons and decreased expression of neurodevelopment related genes. While, MT administration considerably rescued the neurodevelopmental toxicity of PS. Mechanistically, MT activated nrf2 (nuclear factor-E2-related factor 2) - isl2a (ISL LIM homeobox 2a) axis to antagonize the side effects of PS. In all, our findings suggest that PS exposure during early life lead to aberrant neurodevelopment of zebrafish, and MT might be a therapeutic option for protecting such disorder.

Melatonin-related signaling pathways and their regulatory effects in aging organisms

Melatonin is a tryptophan-derived ancestral molecule evolved in bacteria. According to the endosymbiotic theory, eukaryotic cells received mitochondria, plastids, and other organelles from bacteria by internalization. After the endosymbiosis, bacteria evolved into organelles and retained their ability of producing melatonin. Melatonin is a small, evolutionarily conserved indole with multiple receptor-mediated, receptor-dependent, and independent actions. Melatonin's initial function was likely a radical scavenger in bacteria that's why there was high intensity of free radicals on primitive atmosphere in the ancient times, and hormetic functions of melatonin, which are effecting through the level of gene expression via prooxidant and antioxidant redox pathways, are developed in throughout the eukaryotic evolution. In the earlier stages of life, endosymbiotic events between mitochondria and other downstream organelles continue with mutual benefits. However, this interaction gradually deteriorates as a result of the imperfection of both mitochondrial and extramitochondrial endosymbiotic crosstalk with the advancing age of eukaryotic organisms. Throughout the aging process melatonin levels tend to reduce and as a manifestation of this, many symptoms in organisms' homeostasis, such as deterioration in adjustment of cellular clocks, are commonly seen. In addition, due to deterioration in mitochondrial integrity and functions, immunity decreases, and lower levels of melatonin renders older individuals to be more susceptible to impaired redox modulation and age-related diseases. Our aim in this paper is to focus on the several redox modulation mechanisms in which melatonin signaling has a central role, to discuss melatonin's gerontological aspects and to provide new research ideas with researchers.

The Zebrafish, an Outstanding Model for Biomedical Research in the Field of Melatonin and Human Diseases

The zebrafish has become an excellent model for the study of human diseases because it offers many advantages over other vertebrate animal models. The pineal gland, as well as the biological clock and circadian rhythms, are highly conserved in zebrafish, and melatonin is produced in the pineal gland and in most organs and tissues of the body. Zebrafish have several copies of the clock genes and of aanat and asmt genes, the latter involved in melatonin synthesis. As in mammals, melatonin can act through its membrane receptors, as with zebrafish, and through mechanisms that are independent of receptors. Pineal melatonin regulates peripheral clocks and the circadian rhythms of the body, such as the sleep/wake rhythm, among others. Extrapineal melatonin functions include antioxidant activity, inducing the endogenous antioxidants enzymes, scavenging activity, removing free radicals, anti-inflammatory activity through the regulation of the NF-κB/NLRP3 inflammasome pathway, and a homeostatic role in mitochondria. In this review, we introduce the utility of zebrafish to analyze the mechanisms of action of melatonin. The data here presented showed that the zebrafish is a useful model to study human diseases and that melatonin exerts beneficial effects on many pathophysiological processes involved in these diseases.

Mitochondrial E3 ubiquitin ligase 1 (MUL1) as a novel therapeutic target for diseases associated with mitochondrial dysfunction

Mitochondrial E3 ubiquitin ligase 1 (MUL1) is a mitochondrial outer membrane-anchored protein-containing transmembrane domain in its N- and C-terminal regions, where both are exposed to the cytosol. Interestingly the C-terminal region has a RING finger domain responsible for its E3 ligase activity, as ubiquitin or in SUMOylation, interacting with proteins related to mitochondrial fusion and fission, cell survival, and tumor suppressor process, such as Akt. Therefore, MUL1 is involved in various cellular processes, such as mitochondrial dynamics, inter-organelle communication, proliferation, mitophagy, immune response, inflammation and cell apoptosis. MUL1 is expressed at a higher basal level in the heart, immune system organs, and blood. Here, we discuss the role of MUL1 in mitochondrial dynamics and its function in various pathological models, both in vitro and in vivo. In this context, we describe the role of MUL1 in: (1) the inflammatory response, by regulating NF-κB activity; (2) cancer, by promoting cell death and regulating exonuclear function of proteins, such as p53; (3) neurological diseases, by maintaining communication with other organelles and interacting with proteins to eliminate damaged organelles and; (4) cardiovascular diseases, by maintaining mitochondrial fusion/fission homeostasis. In this review, we summarize the latest advances in the physiological and pathological functions of MUL1. We also describe the different substrates of MUL1, acting as a positive or negative regulator in various pathologies associated with mitochondrial dysfunction. In conclusion, MUL1 could be a potential key target for the development of therapies that focus on ensuring the functionality of the mitochondrial network and, furthermore, the quality control of intracellular components by synchronously modulating the activity of different cellular mechanisms involved in the aforementioned pathologies. This, in turn, will guide the development of targeted therapies.

Zebrafish, Medaka and Turquoise Killifish for Understanding Human Neurodegenerative/Neurodevelopmental Disorders

In recent years, small fishes such as zebrafish and medaka have been widely recognized as model animals. They have high homology in genetics and tissue structure with humans and unique features that mammalian model animals do not have, such as transparency of embryos and larvae, a small body size and ease of experiments, including genetic manipulation. Zebrafish and medaka have been used extensively in the field of neurology, especially to unveil the mechanisms of neurodegenerative diseases such as Parkinson's and Alzheimer's disease, and recently, these fishes have also been utilized to understand neurodevelopmental disorders such as autism spectrum disorder. The turquoise killifish has emerged as a new and unique model animal, especially for ageing research due to its unique life cycle, and this fish also seems to be useful for age-related neurological diseases. These small fishes are excellent animal models for the analysis of human neurological disorders and are expected to play increasing roles in this field. Here, we introduce various applications of these model fishes to improve our understanding of human neurological disorders.

Anticonvulsant activity of melatonin and its success in ameliorating epileptic comorbidity-like symptoms in zebrafish

Epilepsy is one of common neurological disorders, greatly distresses the well-being of the sufferers. Melatonin has been used in clinical anti-epileptic studies, but its effect on epileptic comorbidities is unknown, and the underlying mechanism needs further investigation. Herein, by generating PTZ-induced zebrafish seizure model, we carried out interdisciplinary research using neurobehavioral assays, bioelectrical detection, molecular biology, and network pharmacology to investigate the activity of melatonin as well as its pharmacological mechanisms. We found melatonin suppressed seizure-like behavior by using zebrafish regular locomotor assays. Zebrafish freezing and bursting activity assays revealed the ameliorative effect of melatonin on comorbidity-like symptoms. The preliminary screening results of neurobehavioral assays were further verified by the expression of key genes involved in neuronal activity, neurodevelopment, depression and anxiety, as well as electrical signal recording from the midbrain of zebrafish. Subsequently, network pharmacology was introduced to identify potential targets of melatonin and its pathways. Real-time qPCR and protein-protein interaction (PPI) were conducted to confirm the underlying mechanisms associated with glutathione metabolism. We also found that melatonin receptors were involved in this process, which were regulated in response to melatonin exposure before PTZ treatment. The antagonists of melatonin receptors affected anticonvulsant activity of melatonin. Overall, current study revealed the considerable ameliorative effects of melatonin on seizure and epileptic comorbidity-like symptoms and unveiled the underlying mechanism. This study provides an animal model for the clinical application of melatonin in the treatment of epilepsy and its comorbidities.

Cerebroventricular Microinjections of MPTP on Adult Zebrafish Induces Dopaminergic Neuronal Death, Mitochondrial Fragmentation, and Sensorimotor Impairments

Mitochondria are dynamic organelles that mediate the energetic supply to cells and mitigate oxidative stress through the intricate balance of fission and fusion. Mitochondrial dysfunction is a prominent feature within Parkinson disease (PD) etiologies. To date, there have been conflicting studies of neurotoxin impact on dopaminergic cell death, mitochondrial function and behavioral impairment using adult zebrafish. Here, we performed cerebroventricular microinjections (CVMIs) of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on adult transgenic zebrafish that resulted in significant reductions in dopaminergic neurons within the telencephalon and olfactory bulbs (OB) of Tg(dat:eGFP) fish. Visualization of mCherry and mitochondrial gene expression analysis in Tg(dat:tom20 MLS:mCherry) fish reveal that MPTP induces mitochondrial fragmentation in dopaminergic neurons and the activation of the pink1/parkin pathway involved mitophagy. Moreover, the loss of dopaminergic neurons translated into a transient locomotor and olfactory phenotype. Taken together, these data can contribute to a better understanding of the mitochondrial impact on dopaminergic survivability.

Melatonin Alleviates Radiculopathy Against Apoptosis and NLRP3 Inflammasomes Via the Parkin-Mediated Mitophagy Pathway

STUDY DESIGN

Animal experimental study with intervention.

OBJECTIVE

To investigate the effect of melatonin on rat radiculopathy model and dorsal root ganglion (DRG) cells, and to elucidate the underlying mechanism.

SUMMARY OF BACKGROUND DATA

Melatonin has a well-documented efficacy in intervertebral disc degeneration (IVDD) and low back pain. IVDD can also lead to other complications such as disc herniation which will cause radiculopathy. Herniated nucleus pulposus (NP) induced apoptosis and NLR pyrin domain containing 3 (NLRP3) activation in DRG. However, the effect and underlying mechanism of melatonin on radiculopathy and DRG cells are still unclear.

METHODS

Rat radiculopathy model was induced by implanting NP tissue from the tail disc of the same rat into the left L4/5 inter-laminar space near the left DRG. Melatonin was injected intraperitoneally in the treated group to test its function. Apoptosis was determined by Tunnel staining and flow cytometry. NLRP3 inflammasome activation was determined by levels of NLRP3, ASC, GSMDM-N, IL-1β, and Caspase-1. Mitophagy was determined by levels of Parkin, Beclin-1, p62, and LCB-II. Mitophagy was blocked by treatment with Parkin-si or cyclosporine A (CsA).

RESULTS

NLRP3 was significantly upregulated in DRG of rat radiculopathy model; moreover, melatonin markedly decreased pain behavior in rat radiculopathy model. Furthermore, melatonin treatment decreases the incidence of apoptosis in DRG cells. Melatonin also promotes mitophagy and inhibits NLRP3 inflammasomes in DRG cells. In addition, mitophagy was blocked by treatment with Parkin-si and CsA. Both Parkin-si and CsA attenuated melatonin's inhibitory effect on apoptosis and the NLRP3 inflammasome, indicating that the beneficial effects of melatonin in DRG cells are mediated through the Parkin-mediated mitophagy.

CONCLUSION

Melatonin alleviates radiculopathy against apoptosis and NLRP3 inflammasomes by promoting Parkin-mediated mitophagy, which may help us provide a potential target for the treatment of radiculopathy.Level of Evidence: N/A.

Advances of Zebrafish in Neurodegenerative Disease: From Models to Drug Discovery

Neurodegenerative disease (NDD), including Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis, are characterized by the progressive loss of neurons which leads to the decline of motor and/or cognitive function. Currently, the prevalence of NDD is rapidly increasing in the aging population. However, valid drugs or treatment for NDD are still lacking. The clinical heterogeneity and complex pathogenesis of NDD pose a great challenge for the development of disease-modifying therapies. Numerous animal models have been generated to mimic the pathological conditions of these diseases for drug discovery. Among them, zebrafish (Danio rerio) models are progressively emerging and becoming a powerful tool for in vivo study of NDD. Extensive use of zebrafish in pharmacology research or drug screening is due to the high conserved evolution and 87% homology to humans. In this review, we summarize the zebrafish models used in NDD studies, and highlight the recent findings on pharmacological targets for NDD treatment. As high-throughput platforms in zebrafish research have rapidly developed in recent years, we also discuss the application prospects of these new technologies in future NDD research.

DJ-1 in neurodegenerative diseases: Pathogenesis and clinical application

Neurodegenerative diseases (NDs) are one of the major health threats to human characterized by selective and progressive neuronal loss. The mechanisms of NDs are still not fully understood. The study of genetic defects and disease-related proteins offers us a window into the mystery of it, and the extension of knowledge indicates that different NDs share similar features, mechanisms, and even genetic or protein abnormalities. Among these findings, PARK7 and its production DJ-1 protein, which was initially found implicated in PD, have also been found altered in other NDs. PARK7 mutations, altered expression and posttranslational modification (PTM) cause DJ-1 abnormalities, which in turn lead to downstream mechanisms shared by most NDs, such as mitochondrial dysfunction, oxidative stress, protein aggregation, autophagy defects, and so on. The knowledge of DJ-1 derived from PD researches might apply to other NDs in both basic research and clinical application, and might yield novel insights into and alternative approaches for dealing with NDs.

Long-term exposure to 2-amino-3-methylimidazo[4,5-f]quinoline can trigger a potential risk of Parkinson's disease

Humans are exposed to heterocyclic amines (HCAs) from a wide range of sources, such as protein-rich thermally processed foods, cigarette smoke, contaminated river water, the atmosphere, soil, and forest fire ash. Although the carcinogenic and mutagenic hazards of HCAs have been widely studied, the potential neurotoxicity of these compounds still needs to be further elucidated. Here, we studied the neurotoxicity of the HCA 2-amino-3-methylimidazole[4,5-f]quinoline (IQ) in vivo by utilizing a zebrafish model. After 35 days of exposure at 8, 80, and 800 ng/mL, zebrafish exploratory behavior and locomotor activity were significantly inhibited, and light/dark preference behaviors were also disturbed. Moreover, the expression of Parkinson's disease (PD)-related genes and proteins, dopamine-related genes, neuroplasticity-related genes, antioxidant enzyme genes and inflammatory cytokine genes in the zebrafish brain was significantly affected. The numbers of NeuN neurons in the midbrain were decreased in exposed zebrafish, while the numbers of apoptotic cells were increased. In summary, our research suggests that IQ is neurotoxic and significantly associated with PD and that long-term exposure to IQ may contribute to PD risk. This risk may be related to IQ-mediated effects on mitochondrial homeostasis and induction of oxidative stress and inflammation.

Mitophagy in Human Diseases

Mitophagy is a selective autophagic process, essential for cellular homeostasis, that eliminates dysfunctional mitochondria. Activated by inner membrane depolarization, it plays an important role during development and is fundamental in highly differentiated post-mitotic cells that are highly dependent on aerobic metabolism, such as neurons, muscle cells, and hepatocytes. Both defective and excessive mitophagy have been proposed to contribute to age-related neurodegenerative diseases, such as Parkinson's and Alzheimer's diseases, metabolic diseases, vascular complications of diabetes, myocardial injury, muscle dystrophy, and liver disease, among others. Pharmacological or dietary interventions that restore mitophagy homeostasis and facilitate the elimination of irreversibly damaged mitochondria, thus, could serve as potential therapies in several chronic diseases. However, despite extraordinary advances in this field, mainly derived from in vitro and preclinical animal models, human applications based on the regulation of mitochondrial quality in patients have not yet been approved. In this review, we summarize the key selective mitochondrial autophagy pathways and their role in prevalent chronic human diseases and highlight the potential use of specific interventions.

Melatonin alleviates sepsis-induced heart injury through activating the Nrf2 pathway and inhibiting the NLRP3 inflammasome

Melatonin improved the outcome of septic cardiomyopathy by inhibiting NLRP3 priming induced by reactive oxygen species. To get insights into these events, we studied the melatonin/Nrf2 antioxidant pathways during sepsis in the heart of NLRP3-deficient mice. Sepsis was induced by cecal ligation and puncture and melatonin was given at a dose of 30 mg/kg. Nuclear turnover of Nrf2 and p-Ser40 Nrf2 and expression of ho-1 were enhanced in nlrp3+/+ and nlrp3-/- mice during sepsis. Sepsis caused higher mitochondria impairment, apoptotic and autophagic events in nlrp3+/+ mice than in nlrp3-/- animals. These findings were accompanied by greater levels of Parkin and PINK-1, and lower Mfn2/Drp-1 ratio in nlrp3+/+ than in nlrp3-/- mice during sepsis, supporting less mitophagy in the latter. Ultrastructural analysis of myocardial tissue further confirmed these observations. The activation of NLRP3 inflammasome accounted for most of the deleterious effects of sepsis, whereas the Nrf2-dependent antioxidative response activation in response to sepsis was unable to neutralize these events. In turn, melatonin further enhanced the Nrf2 response in both mice strains and reduced the NLRP3 inflammasome activation in nlrp3+/+ mice, restoring myocardial homeostasis. The data support that the anti-inflammatory efficacy of melatonin against sepsis depends, at least in part, on Nrf2 activation.

Antioxidants and Neuron-Astrocyte Interplay in Brain Physiology: Melatonin, a Neighbor to Rely on

This manuscript is a review focused onto the role of astrocytes in the protection of neurons against oxidative stress and how melatonin can contribute to the maintenance of brain homeostasis. The first part of the review is dedicated to the dependence of neurons on astrocytes by terms of survival under oxidative stress conditions. Additionally, the effects of melatonin against oxidative stress in the brain and its putative role in the protection against diseases affecting the brain are highlighted. The effects of melatonin on the physiology of neurons and astrocytes also are reviewed.

FUNDC1-dependent mitophagy induced by tPA protects neurons against cerebral ischemia-reperfusion injury

Autophagy of mitochondria, termed mitophagy, plays an important role in cerebral ischemia-reperfusion (IR) injury, but the mechanism is not yet clear. Tissue-type plasminogen activator (tPA) is the most important thrombolytic drug in the clinical treatment of ischemic stroke and has neuroprotective effects. Here, we explored the effects of tPA on neuronal apoptosis and mitophagy following IR. We found that knocking out the tPA gene significantly aggravated brain injury and increased neuronal apoptosis and mitochondrial damage. Exposure of neurons to tPA reduced injury severity and protected mitochondria. Further studies demonstrated that this protective effect of tPA was achieved via regulation of FUNDC1-mediated mitophagy. Furthermore, we found that tPA enhanced the expression level of FUNDC1 by activating the phosphorylation of AMPK. In summary, our results confirm that tPA exerts neuroprotective effects by increasing the phosphorylation of AMPK and the expression of FUNDC1, thereby inhibiting apoptosis and improving mitochondrial function.

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After cerebral ischemia, tPA released by neurons has a neuroprotective effect.

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tPA modulates mitophagy to decrease oxidative stress and inhibit apoptosis.

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The mitochondrial membrane protein FUNDC1 and the AMPK signaling pathway are involved in the neuroprotective process of tPA.

Environment-Sensitive Probes for Illuminating Amyloid Aggregation In Vitro and in Zebrafish

The aberrant aggregation of certain peptides and proteins, forming extracellular plaques of fibrillar material, is one of the hallmarks of amyloid diseases, such as Alzheimer's and Parkinson's. Herein, we have designed a new family of solvatochromic dyes based on the 9-amino-quinolimide moiety capable of reporting during the early stages of amyloid fibrillization. We have rationally improved the photophysical properties of quinolimides by placing diverse amino groups at the 9-position of the quinolimide core, leading to higher solvatochromic and fluorogenic character and higher lifetime dependence on the hydrophobicity of the environment, which represent excellent properties for the sensitive detection of prefibrillar aggregates. Among the different probes prepared, the 9-azetidinyl-quinolimide derivative showed striking performance in the following β-amyloid peptide (Aβ) aggregation in solution in real time and identifying the formation of different types of early oligomers of Aβ, the most important species linked to cytotoxicity, using novel, multidimensional fluorescence microscopy, with one- or two-photon excitation. Interestingly, the new dye allowed the visualization of proteinaceous inclusion bodies in a zebrafish model with neuronal damage induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Our results support the potential of the novel fluorophores as powerful tools to follow amyloid aggregation using fluorescence microscopy in vivo, revealing heterogeneous populations of different types of aggregates and, more broadly, to study protein interactions.

Melatonin ameliorates excessive PINK1/Parkin-mediated mitophagy by enhancing SIRT1 expression in granulosa cells of PCOS

Mitochondrial injury in granulosa cells is associated with the pathogenesis of polycystic ovary syndrome (PCOS). However, the protective effects of melatonin against mitochondrial injury in the granulosa cells of PCOS remain unclear. In this study, decreased mitochondrial membrane potential and mtDNA content, increased number of autophagosomes were found in the granulosa cells of PCOS patients and the dihydrotestosterone (DHT)-treated KGN cells, with decreased protein level of the autophagy substrate p62 and increased levels of the cellular autophagy markers Beclin 1 and LC3B-II, while the protein levels of PTEN-induced kinase-1 (PINK1) and Parkin were increased and the level of sirtuin 1 (SIRT1) was decreased. DHT-induced PCOS-like mice also showed enhanced mitophagy and decreased SIRT1 mRNA expression. Melatonin treatment significantly increased the protein level of SIRT1 and decreased the levels of PINK1/Parkin, whereas it ameliorated the mitochondrial dysfunction and PCOS phenotype in vitro and in vivo. However, when the KGN cells were treated with SIRT1 siRNA to knock down SIRT1 expression, melatonin treatment failed to repress the excessive mitophagy. In conclusion, melatonin protects against mitochondrial injury in granulosa cells of PCOS by enhancing SIRT1 expression to inhibit excessive PINK1/Parkin-mediated mitophagy.

Rosmarinic acid protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurotoxicity in zebrafish embryos

Rosmarinic acid (RA) is an extract that can be obtained from Lamiaceae herbs and the Boraginaceae family. This study aimed to evaluate the effect of RA on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity in zebrafish embryos. Embryos were challenged with MPTP and then were treated with RA or brusatol (a Nrf2 inhibitor). Locomotor activity of zebrafish was recorded using a video camera. The swimming distance was analyzed with SMART 3.0 software. Tyrosine hydroxylase (TH) immunohistochemistry, reactive oxygen species (ROS), glutathione (GSH), and malondialdehyde (MDA) contents were evaluated. The expressions of proteins in the DJ-1/Akt/Nrf2 signaling pathway were measured. The results showed that RA not only prevented MPTP-induced dopaminergic neuron loss, but also attenuated the deficit in locomotor behavior. RA attenuated the increases of ROS and MDA induced by MPTP. Treatment with RA augmented expression of glutamate cysteine ligase catalytic subunit, glutamate cysteine ligase modifier subunit, and GSH. Furthermore, RA increased the expression of DJ-1, p-Akt, Nuclear-Nrf2, HO-1 and inhibited the expression of PTEN. Brusatol partially abolished the neuroprotective effect of RA in MPTP-induced Parkinson's disease (PD) model of zebrafish embryos. The results of this study indicate that RA exerts neuroprotective effects on MPTP-induced neurotoxicity in dopaminergic neurons of a zebrafish PD model. The mechanism underlying the effects of RA is associated with promotion of antioxidant gene expression via regulation of the DJ-1/Akt/Nrf2 signaling pathway.

Melatonin/polydopamine nanostructures for collective neuroprotection-based Parkinson's disease therapy

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons in the substantia nigra and localized deposition of cytoplasmic fibrillary inclusions as Lewy bodies in the brain. The aberrant phosphorylation of α-synuclein at serine 129 is the key process on its early onset, which alters the cellular conformation to oligomers and insoluble aggregates, underpinning cellular oxidative stress and mitochondrial dysfunction, leading to devastating PD synucleinopathy. The multiple neuroprotective roles of dopamine and melatonin are often demonstrated separately; however, this approach suffers from low and short bioavailability and is associated with side-effects upon overdosing. Herein, highly pleiotropic melatonin-enriched polydopamine nanostructures were fabricated, which showed efficient brain tissue retention, sustainable and prolonged melatonin release, and prevented neuroblastoma cell death elicited by Parkinson's disease-associated and mitochondrial damaging stimuli. The synergistic neuroprotection re-established the mitochondrial membrane potential, reduced the generation of cellular reactive oxygen species (ROS), inhibited the activation of both the caspase-dependent and independent apoptotic pathways, and exhibited an anti-inflammatory effect. At the molecular level, it suppressed α-synuclein phosphorylation at Ser 129 and reduced the cellular deposition of high molecular weight oligomers. The therapeutic assessment on ex vivo organotypic brain slice culture, and in vivo experimental PD model confirmed the superior brain targeting, collective neuroprotection on dopaminergic neurons with reduced alpha-synuclein phosphorylation and deposition in the hippocampal and substantia nigra region of the brain. Thus, nature-inspired melatonin-enriched polydopamine nanostructures conferring collective neuroprotective effects attributes activation of anti-oxidative, anti-inflammatory, and anti-apoptotic pathways may be superior for application in a nanomedicine-based PD therapy.

Melatonin and Parkinson Disease: Current Status and Future Perspectives for Molecular Mechanisms

Parkinson disease (PD) is a chronic and neurodegenerative disease with motor and nonmotor symptoms. Multiple pathways are involved in the pathophysiology of PD, including apoptosis, autophagy, oxidative stress, inflammation, α-synuclein aggregation, and changes in the neurotransmitters. Preclinical and clinical studies have shown that melatonin supplementation is an appropriate therapy for PD. Administration of melatonin leads to inhibition of some pathways related to apoptosis, autophagy, oxidative stress, inflammation, α-synuclein aggregation, and dopamine loss in PD. In addition, melatonin improves some nonmotor symptom in patients with PD. Limited studies, however, have evaluated the role of melatonin on molecular mechanisms and clinical symptoms in PD. This review summarizes what is known regarding the impact of melatonin on PD in preclinical and clinical studies.

The role of melatonin on doxorubicin-induced cardiotoxicity: A systematic review

PURPOSE

Doxorubicin, as an effective chemotherapeutic drug, is commonly used for combating various solid and hematological tumors. However, doxorubicin-induced cardiotoxicity is considered as a serious adverse effect, and it limits the clinical use of this chemotherapeutic drug. The use of melatonin can lead to a decrease in the cardiotoxic effect induced by doxorubicin. The aim of this review was to evaluate the potential role of melatonin in the prevention of doxorubicin-induced cardiotoxicity.

METHODS

This review was conducted by a full systematic search strategy based on PRISMA guidelines for the identification of relevant literature in the electronic databases of PubMed, Web of Science, Embase, and Scopus up to January 2019 using search terms in the titles and abstracts. 286 articles were screened in accordance with our inclusion and exclusion criteria. Finally, 28 articles were selected in this systematic review.

RESULTS

The findings demonstrated that doxorubicin-treated groups had increased mortality, decreased body weight and heart weight, and increased ascites compared to the control groups; the co-administration of melatonin revealed an opposite pattern compared to the doxorubicin-treated groups. Also, this chemotherapeutic agent can lead to biochemical and histopathological changes; as for most of the cases, these alterations were reversed near to normal levels (control groups) by melatonin co-administration. Melatonin exerts these protection effects through mechanisms of anti-oxidant, anti-apoptosis, anti-inflammatory, and mitochondrial function.

CONCLUSION

The results of this systematic review indicated that co-administration of melatonin ameliorates the doxorubicin-induced cardiotoxicity.

Fishing in the Cell Powerhouse: Zebrafish as A Tool for Exploration of Mitochondrial Defects Affecting the Nervous System

The zebrafish (Danio rerio) is a small vertebrate ideally suited to the modeling of human diseases. Large numbers of genetic alterations have now been modeled and could be used to study organ development by means of a genetic approach. To date, limited attention has been paid to the possible use of the zebrafish toolbox in studying human mitochondrial disorders affecting the nervous system. Here, we review the pertinent scientific literature discussing the use of zebrafish in modeling gene mutations involved in mitochondria-related neurological human diseases. A critical analysis of the literature suggests that the zebrafish not only lends itself to exploration of the pathological consequences of mitochondrial energy output on the nervous system but could also serve as an attractive platform for future drugs in an as yet untreatable category of human disorders.

Fishing for Parkinson's Disease: A review of the literature

Parkinson's disease (PD), the second most common neurodegenerative disorder in the world, is due to the damage or death of cells that produce dopamine in the region called the substantia nigra (SN). Model organisms are important tools in PD research. Zebrafish (Danio rerio), a small tropical freshwater fish, entered the scientific world through developmental biology studies and today has become a popular model organism for human diseases. This review will provide information on the current knowledge about the use of zebrafish in PD research.

Model organism data evolving in support of translational medicine

Model organism databases (MODs) have been collecting and integrating biomedical research data for 30 years and were designed to meet specific needs of each model organism research community. The contributions of model organism research to understanding biological systems would be hard to overstate. Modern molecular biology methods and cost reductions in nucleotide sequencing have opened avenues for direct application of model organism research to elucidating mechanisms of human diseases. Thus, the mandate for model organism research and databases has now grown to include facilitating use of these data in translational applications. Challenges in meeting this opportunity include the distribution of research data across many databases and websites, a lack of data format standards for some data types, and sustainability of scale and cost for genomic database resources like MODs. The issues of widely distributed data and application of data standards are some of the challenges addressed by FAIR (Findable, Accessible, Interoperable, and Re-usable) data principles. The Alliance of Genome Resources is now moving to address these challenges by bringing together expertly curated research data from fly, mouse, rat, worm, yeast, zebrafish, and the Gene Ontology consortium. Centralized multi-species data access, integration, and format standardization will lower the data utilization barrier in comparative genomics and translational applications and will provide a framework in which sustainable scale and cost can be addressed. This article presents a brief historical perspective on how the Alliance model organisms are complementary and how they have already contributed to understanding the etiology of human diseases. In addition, we discuss four challenges for using data from MODs in translational applications and how the Alliance is working to address them, in part by applying FAIR data principles. Ultimately, combined data from these animal models are more powerful than the sum of the parts.

Melatonin Ameliorates the Progression of Atherosclerosis via Mitophagy Activation and NLRP3 Inflammasome Inhibition

The NLRP3 (nucleotide-binding domain and leucine-rich repeat pyrin domain containing 3) inflammasome-mediated inflammatory responses are critically involved in the progression of atherosclerosis (AS), which is the essential cause for cardiovascular diseases. Melatonin has anti-inflammatory properties. However, little is known about the potential effects of melatonin in the pathological process of AS. Herein, we demonstrate that melatonin suppressed prolonged NLRP3 inflammasome activation in atherosclerotic lesions by reactive oxygen species (ROS) scavenging via mitophagy in macrophages. The atherosclerotic mouse model was induced with a high-fat diet using ApoE^−/− mice. Melatonin treatment markedly attenuated AS plaque size and vulnerability. Furthermore, melatonin decreased NLRP3 inflammasome activation and the consequent IL-1β secretion within atherosclerotic lesions. Despite the unchanged protein expression, the silent information regulator 3 (Sirt3) activity was elevated in the atherosclerotic lesions in melatonin-treated mice. In ox-LDL-treated macrophages, melatonin attenuated the NLRP3 inflammasome activation and the inflammatory factors secretion, while this protective effect was abolished by either Sirt3 silence or autophagy inhibitor 3-MA. Mitochondrial ROS (mitoROS), which was a recognized inducer for NLRP3 inflammasome, was attenuated by melatonin through the induction of mitophagy. Both Sirt3-siRNA and autophagy inhibitor 3-MA partially abolished the beneficial effects of melatonin on mitoROS clearance and NLRP3 inflammasome activation, indicating the crucial role of Sirt3-mediated mitophagy. Furthermore, we demonstrated that melatonin protected against AS via the Sirt3/FOXO3a/Parkin signaling pathway. In conclusion, the current study demonstrated that melatonin prevented atherosclerotic progression, at least in part, via inducing mitophagy and attenuating NLRP3 inflammasome activation, which was mediated by the Sirt3/FOXO3a/Parkin signaling pathway. Collectively, our study provides insight into melatonin as a new target for therapeutic intervention for AS.

Ameliorating mitochondrial dysfunction restores carbon ion-induced cognitive deficits via co-activation of NRF2 and PINK1 signaling pathway

Carbon ion therapy is a promising modality in radiotherapy to treat tumors, however, a potential risk of induction of late normal tissue damage should still be investigated and protected. The aim of the present study was to explore the long-term cognitive deficits provoked by a high-linear energy transfer (high-LET) carbon ions in mice by targeting to hippocampus which plays a crucial role in memory and learning. Our data showed that, one month after 4 Gy carbon ion exposure, carbon ion irradiation conspicuously resulted in the impaired cognitive performance, neurodegeneration and neuronal cell death, as well as the reduced mitochondrial integrity, the disrupted activities of tricarboxylic acid cycle flux and electron transport chain, and the depressed antioxidant defense system, consequently leading to a decline of ATP production and persistent oxidative damage in the hippocampus region. Mechanistically, we demonstrated the disruptions of mitochondrial homeostasis and redox balance typically characterized by the disordered mitochondrial dynamics, mitophagy and glutathione redox couple, which is closely associated with the inhibitions of PINK1 and NRF2 signaling pathway as the key regulators of molecular responses in the context of neurotoxicity and neurodegenerative disorders. Most importantly, we found that administration with melatonin as a mitochondria-targeted antioxidant promoted the PINK1 accumulation on the mitochondrial membrane, and augmented the NRF2 accumulation and translocation. Moreover, melatonin pronouncedly enhanced the molecular interplay between NRF2 and PINK1. Furthermore, in the mouse hippocampal neuronal cells, overexpression of NRF2/PINK1 strikingly protected the hippocampal neurons from carbon ion-elicited toxic insults. Thus, these data suggest that alleviation of the sustained mitochondrial dysfunction and oxidative stress through co-modulation of NRF2 and PINK1 may be in charge of restoration of the cognitive impairments in a mouse model of high-LET carbon ion irradiation.

Melatonin improves cardiac and mitochondrial function during doxorubicin-induced cardiotoxicity: A possible role for peroxisome proliferator-activated receptor gamma coactivator 1-alpha and sirtuin activity?

Mitochondrial dysfunction is a central element in the development of doxorubicin (DXR)-induced cardiotoxicity. In this context, melatonin is known to influence mitochondrial homeostasis and function. This study aimed to investigate the effects of melatonin on cardiac function, tumor growth, mitochondrial fission and fusion, PGC1-α and sirtuin activity in an acute model of DXR-induced cardiotoxicity. During the in vitro study, H9c2 rat cardiomyoblasts were pre-treated with melatonin (10 μM, 24 h) followed by DXR exposure (3 μM, 24 h). Following treatment, cellular ATP levels and mitochondrial morphology were assessed. In the in vivo study, female Sprague Dawley rats (16 weeks old), were inoculated with a LA7 rat mammary tumor cell line and tumors were measure daily. Animals were injected with DXR (3 × 4 mg/kg) and/or received melatonin (6 mg/kg) for 14 days in their drinking water. Rat hearts were used to conduct isolated heart perfusions to assess cardiac function and thereafter, heart tissue was used for immunoblot analysis. DXR treatment increased cell death and mitochondrial fission which were reduced with melatonin treatment. Cardiac output increased in rats treated with DXR + melatonin compared to DXR-treated rats. Tumor volumes was significantly reduced in DXR + melatonin-treated rats on Day 8 in comparison to DXR-treated rats. Furthermore, DXR + melatonin treatment increased cellular ATP levels, PGC1-α and SIRT1 expression which was attenuated by DXR treatment. These results indicate that melatonin treatment confers a dual cardio-protective and oncostatic effect by improving mitochondrial function and cardiac function whilst simultaneously retarding tumor growth during DXR-induced cardiotoxicity.

Liraglutide repairs the infarcted heart: The role of the SIRT1/Parkin/mitophagy pathway

Liraglutide is glucagon‑like peptide‑1 receptor agonist used for treating patients with type 2 diabetes mellitus. The present study aimed to investigate the role and mechanism of liraglutide in repairing the infarcted heart following myocardial infarction. The results of the present study demonstrated that amplification of the dose of liraglutide for ~28 days was able to reduce cardiac fibrosis, inflammatory responses and myocardial death in the post‑infarcted heart. In vitro, liraglutide protected cardiomyocyte mitochondria against the chronic hypoxic damage, inhibiting the mitochondrial apoptosis pathways. Mechanistically, liraglutide elevated the expression of NAD‑dependent protein deacetylase sirtuin‑1 (SIRT1), which increased the expression of Parkin, leading to mitophagy activation. Protective mitophagy reversed cellular adenosine 5'‑triphosphate production, reduced cellular oxidative stress and balanced the redox response, sustaining mitochondrial homeostasis. Notably, following blockade of glucagon‑like peptide 1 receptor or knockdown of Parkin, the beneficial effects of liraglutide on mitochondria disappeared. In conclusion, the results of the present study illustrated the protective role of liraglutide in repairing the infarcted heart via regulation of the SIRT1/Parkin/mitophagy pathway.

Mitochondria: Central Organelles for Melatonin's Antioxidant and Anti-Aging Actions

Melatonin, along with its metabolites, have long been known to significantly reduce the oxidative stress burden of aging cells or cells exposed to toxins. Oxidative damage is a result of free radicals produced in cells, especially in mitochondria. When measured, melatonin, a potent antioxidant, was found to be in higher concentrations in mitochondria than in other organelles or subcellular locations. Recent evidence indicates that mitochondrial membranes possess transporters that aid in the rapid uptake of melatonin by these organelles against a gradient. Moreover, we predicted several years ago that, because of their origin from melatonin-producing bacteria, mitochondria likely also synthesize melatonin. Data accumulated within the last year supports this prediction. A high content of melatonin in mitochondria would be fortuitous, since these organelles produce an abundance of free radicals. Thus, melatonin is optimally positioned to scavenge the radicals and reduce the degree of oxidative damage. In light of the "free radical theory of aging", including all of its iterations, high melatonin levels in mitochondria would be expected to protect against age-related organismal decline. Also, there are many age-associated diseases that have, as a contributing factor, free radical damage. These multiple diseases may likely be deferred in their onset or progression if mitochondrial levels of melatonin can be maintained into advanced age.