Melatonin prevents the injury-induced decline of Akt/forkhead transcription factors phosphorylation

A FOX transcription factor phosphorylated for regulation of autophagy facilitates fruiting body development in Sclerotinia sclerotiorum

Autophagy is a recycling process by which eukaryotic cells degrade their own components, and the fruiting body (sexual structure) is a necessary structure for some plant pathogenic fungi to start the infection cycle. However, the transcriptional regulation of plant pathogenic fungal autophagy and autophagy regulating sexual reproduction remains elusive. Here, we provide the report linking autophagy transcription and fruiting body development in phytopathogenic fungi. The forkhead box transcription factor (FOX TF) SsFoxE2 in Sclerotinia sclerotiorum (Ss) binds to the promoters of ATG genes, thus promoting their transcription. SsFoxE2 is phosphorylated by AMP-activated protein kinase (AMPK) SsSnf1, and the phosphorylated SsFoxE2 interacts with (translationally controlled tumor protein) SsTctp1, leading to enhanced stability and ATG transcription activity of SsFoxE2. Importantly, the regulation of autophagy by SsFoxE2 affects the balance of the ubiquitination system and the early development of the fruiting body, which directly determines the occurrence and prevalence of plant disease. Furthermore, transcriptional binding of FOX TF to ATG gene promoters is conserved in phytopathogenic fungi. Taken together, our results bring new insights into pathogen initiation in phytopathogenic fungi and connect it to other autophagy-regulated processes in plant pathogens.

Systematic review of melatonin in cerebral ischemia-reperfusion injury: critical role and therapeutic opportunities

Cerebral ischemia-reperfusion (I/R) injury is the predominant causes for the poor prognosis of ischemic stroke patients after reperfusion therapy. Currently, potent therapeutic interventions for cerebral I/R injury are still very limited. Melatonin, an endogenous hormone, was found to be valid in preventing I/R injury in a variety of organs. However, a systematic review covering all neuroprotective effects of melatonin in cerebral I/R injury has not been reported yet. Thus, we perform a comprehensive overview of the influence of melatonin on cerebral I/R injury by collecting all available literature exploring the latent effect of melatonin on cerebral I/R injury as well as ischemic stroke. In this systematic review, we outline the extensive scientific studies and summarize the beneficial functions of melatonin, including reducing infarct volume, decreasing brain edema, improving neurological functions and attenuating blood-brain barrier breakdown, as well as its key protective mechanisms on almost every aspect of cerebral I/R injury, including inhibiting oxidative stress, neuroinflammation, apoptosis, excessive autophagy, glutamate excitotoxicity and mitochondrial dysfunction. Subsequently, we also review the predictive and therapeutic implications of melatonin on ischemic stroke reported in clinical studies. We hope that our systematic review can provide the most comprehensive introduction of current advancements on melatonin in cerebral I/R injury and new insights into personalized diagnosis and treatment of ischemic stroke.

Identification of significant modules and hub genes involved in hepatic encephalopathy using WGCNA

BACKGROUND

Hepatic encephalopathy (HE) is a reversible syndrome of brain dysfunction caused by advanced liver disease. Weighted gene co-expression network analysis (WGCNA) could establish a robust co-expression network to identify the hub genes and underlying biological functions. This study was aimed to explore the potential therapeutic targets in HE by WGCNA.

RESULTS

The green and brown modules were found to be significantly associated with the development of HE. Functional enrichment analyses suggested the neuroinflammation, neuroimmune, extracellular matrix (ECM), and coagulation cascade were involved in HE. CYBB and FOXO1 were calculated as hub genes, which were upregulated in the HE patients. Tamibarotene and vitamin E were suggested as possible drug candidates to alleviate HE.

CONCLUSIONS

It is the first time to analyze transcriptomic data of HE by WGCNA. Our study not only promoted the current understanding of neuroinflammation in HE, but also provided the first evidence that CYBB and FOXO1 played pivotal roles in the pathogenesis of HE, which might be potential biomarkers and therapeutic targets. Tamibarotene might be a novel drug compound against HE.

Role of Forkhead Box Protein O1 (FoxO1) in Stroke: A Literature Review

Stroke is one of the most prevalent causes of death around the world. When a stroke occurs, many cellular signaling cascades and regulators are activated, which results in severe cellular dysfunction and debilitating long-term disability. One crucial regulator of cell fate and function is mammalian Forkhead box protein O1 (FoxO1). Many studies have found FoxO1 to be implicated in many cellular processes, including regulating gluconeogenesis and glycogenolysis. During a stroke, modifications of FoxO1 have been linked to a variety of functions, such as inducing cell death and inflammation, inhibiting oxidative injury, affecting the blood brain barrier (BBB), and regulating hepatic gluconeogenesis. For these functions of FoxO1, different measures and treatments were applied to FoxO1 after ischemia. However, the subtle mechanisms of post-transcriptional modification and the role of FoxO1 are still elusive and even contradictory in the development of stroke. The determination of these mechanisms will lead to further enlightenment for FoxO1 signal transduction and the identification of targeted drugs. The regulation and function of FoxO1 may provide an important way for the prevention and treatment of diseases. Overall, the functions of FoxO1 are multifactorial, and this paper will summarize all of the significant pathways in which FoxO1 plays an important role during stroke damage and recovery.

Melatonin ameliorates diabetes-induced brain injury in rats

Diabetic brain is a serious complication of diabetes, and it is associated with oxidative stress and neuronal injury. This study investigated the protective effect of melatonin (MLT) on diabetes-induced brain injury. A rat model of type 2 diabetes mellitus was produced by intraperitoneal injection of nicotinamide 100 mg/kg, followed by intraperitoneal injection of streptozotocin 55 mg/kg. The diabetic rats were orally administered MLT 10 mg/kg of body weight for 15 days. MLT remarkably downregulated serum glucose levels. It also improved levels of the lipid peroxidation product 4-hydroxynonenal, improved levels of antioxidants including glutathione, glutathione peroxidase and glutathione reductase in the brains of the diabetic rats, and this is indicative of the antioxidant potential of MLT. MLT also prevented increase in homocysteine, amyloid-β42 and tau levels in diabetic rats, and this suggests that it can reduce the risk of dementia. This is associated with reduction in the levels of the dopamine, serotonin, and glutamate and is indicative of the regulatory effect of MLT on neurotransmitters. Treatment with MLT improved diabetes-induced structural alteration in the hippocampus and cerebral cortex. MLT significantly reduced caspase-3 and Bax as well as significantly increase Bcl-2 protein and GFAP-positive astrocytes indicating its anti-apoptotic effect. MLT showed remarkable ameliorative effect against biochemical and molecular alterations in the brains of diabetic rats most likely through its antioxidant property.

Daily and seasonal mitochondrial protection: Unraveling common possible mechanisms involving vitamin D and melatonin

From an evolutionary point of view, vitamin D and melatonin appeared very early and share functions related to defense mechanisms. In the current clinical setting, vitamin D is exclusively associated with phosphocalcic metabolism. Meanwhile, melatonin has chronobiological effects and influences the sleep-wake cycle. Scientific evidence, however, has identified new actions of both molecules in different physiological and pathological settings. The biosynthetic pathways of vitamin D and melatonin are inversely related relative to sun exposure. A deficiency of these molecules has been associated with the pathogenesis of cardiovascular diseases, including arterial hypertension, neurodegenerative diseases, sleep disorders, kidney diseases, cancer, psychiatric disorders, bone diseases, metabolic syndrome, and diabetes, among others. During aging, the intake and cutaneous synthesis of vitamin D, as well as the endogenous synthesis of melatonin are remarkably depleted, therefore, producing a state characterized by an increase of oxidative stress, inflammation, and mitochondrial dysfunction. Both molecules are involved in the homeostatic functioning of the mitochondria. Given the presence of specific receptors in the organelle, the antagonism of the renin-angiotensin-aldosterone system (RAAS), the decrease of reactive species of oxygen (ROS), in conjunction with modifications in autophagy and apoptosis, anti-inflammatory properties inter alia, mitochondria emerge as the final common target for melatonin and vitamin D. The primary purpose of this review is to elucidate the common molecular mechanisms by which vitamin D and melatonin might share a synergistic effect in the protection of proper mitochondrial functioning.

Melatonin's efficacy in stroke patients; a matter of dose? A systematic review

There is a lack of effective therapies for stroke patients; its treatment is even more difficult considering the unexpected onset of the disease. In the last decade, melatonin has emerged as a promising neuroprotective agent which is able to cross the blood-brain-barrier (BBB) and with a low toxicity profile. The aim of this systematic review was to summarize and critically review clinical and pre-clinical evidence related to melatonin's effectiveness as a stroke treatment. Together with a comparative dose extrapolation with those used in the selected randomized controlled trials (RCTs), and based on these data to discuss whether the administered doses correlate with those advisable in human patients. To address this purpose, we performed a systematic review of the available literature. A total of 529 records were screened with the selecting of six full articles containing RCTs that met the inclusion/exclusion criteria. The evidence drawn from these six reports was analyzed to identify remaining gaps, treatment efficacy, and to suggest future directions. The primary outcome reported was the reduction of the oxidative response; the secondary outcome was the increase of the survival rate of the patients in the intervention groups. Calculations derived from animal studies revealed that the translational doses to humans were substantially higher than those employed in the RCTs. The findings of this systematic review revealed that there are insufficient RCTs to prove melatonin's value in stroke patients. Nevertheless, the evidence is promising, and further clinical research may support the benefits of melatonin in stroke patients, if the adequate dose is administered.

Resveratrol modulates the Akt/GSK-3β signaling pathway in a middle cerebral artery occlusion animal model

Cerebral ischemia is a major cause of neurodegenerative disease. It induces neuronal vulnerability and susceptibility, and leads to neuronal cell death. Resveratrol is a polyphenolic compound that acts as an anti-oxidant. It exerts a neuroprotective effect against focal cerebral ischemic injury. Akt signaling pathway is accepted as a representative cell survival pathway, including proliferation, growth, and glycogen synthesis. This study investigated whether resveratrol regulates Akt/glycogen synthase kinase-3β (GSK-3β) pathway in a middle cerebral artery occlusion (MCAO)-induced ischemic brain injury. Adult male rats were intraperitoneally injected with vehicle or resveratrol (30 mg/kg) and cerebral cortices were isolated 24 h after MCAO. Neurological behavior test, corner test, brain edema measurment, and 2,3,5-triphenyltetrazolium chloride staining were performed to elucidate the neuroprotective effects of resveratrol. Phospho-Akt and phospho-GSK-3β expression levels were measured using Western blot analysis. MCAO injury led to severe neurobehavioral deficit, infraction, and histopathological changes in cerebral cortex. However, resveratrol treatment alleviated these changes caused by MCAO injury. Moreover, MCAO injury induced decreases in phospho-Akt and phospho-GSK-3β protein levels, whereas resveratrol attenuated these decreases. Phosphorylations of Akt and GSK-3β act as a critical role for the suppression of apoptotic cell death. Thus, our finding suggests that resveratrol attenuates neuronal cell death in MCAO-induced cerebral ischemia and Akt/GSK-3β signaling pathway contributes to the neuroprotective effect of resveratrol.

Comparing the Effects of Melatonin with Caloric Restriction in the Hippocampus of Aging Mice: Involvement of Sirtuin1 and the FOXOs Pathway

It has been suggested that age-related neurodegeneration might be associated with neuropeptide Y (NPY); sirtuin1 (SIRT1) and forkhead box transcription factors O subfamily (FOXOs) pathways. Melatonin, a hormone mainly secreted by the pineal gland, is another anti-aging agent associated with the SIRT1-FOXOs pathway. This study aimed to compare the effects of melatonin (Mel) and caloric restriction (CR) on the expression of Sirt1, FoxO1, FoxO3a and FOXOs target genes in the aging mouse hippocampus. Neuropeptide Y-knockout (NpyKO) and wild-type (WT) male mice aged 19 months were previously treated either with food ad libitum or CR for 16 months. WT old animals were divided into four groups: control, CR, Mel and CR+Mel treated groups. The Mel and CR+Mel were treated with melatonin 10 mg/kg, daily, subcutaneously for 7 consecutive days. Mel treatment upregulated the mRNA expression of Sirt1, FOXOs (FoxO1 and FoxO3a) target genes that regulated the cell cycle [e.g., cyclin-dependent kinase inhibitor 1B (p27)], Wingless and INT-1 (Wnt1) and inducible signaling pathway protein 1 (Wisp1) in the aged mouse hippocampus. CR treatment also showed the similar actions. However, the mRNA expression of Sirt1, FoxO1, FoxO3a, p27 or Wisp1 did not alter in the CR+Mel group when compared with CR or Mel group. Melatonin could not produce any additive effect on the CR treatment group, suggesting that both treatments mimicked the effect, possibly via the same pathway. NPY which mediates physiological adaptations to energy deficits is an essential link between CR and longevity in mice. In order to focus on the role of Npy in mediating the effects of melatonin, the gene expression between NpyKO and WT male mice were compared. Our data showed that, in the absence of Npy, melatonin could not mediate effects on those gene expressions, suggesting that Npy was required for melatonin to mediate the effect, possibly, on life extension.

Melatonin regulates the aging mouse hippocampal homeostasis via the sirtuin1-FOXO1 pathway

Sirtuin1 (SIRT1) and forkhead box transcription factor O subfamily 1 (FOXO1) play vital roles in the maintenance of hippocampal neuronal homeostasis during aging. Our previous study showed that melatonin, a hormone mainly secreted by the pineal gland, restored the impaired memory of aged mice. Age-related neuronal energy deficits contribute to the pathogenesis of several neurodegenerative disorders. An attempt has been made to determine whether the effect of melatonin is mediated through the SIRT1-FOXO1 pathways. The present results showed that aged mice (22 months old) exhibited significantly downregulated SIRT1, FOXO1, and melatonin receptors MT1 and MT2 protein expression but upregulated tumor suppressor protein 53 (p53), acetyl-p53 protein (Ac-p53), mouse double minute 2 homolog (MDM2), Dickkopf-1 (DKK1) protein expression in mouse hippocampus compared with the young group. Melatonin treatment (10 mg/kg, daily in drinking water for 6 months) in aged mice significantly attenuated the age-induced downregulation of SIRT1, FOXO1, MT1 and MT2 protein expression and attenuated the age-induced increase in p53, ac-p53, MDM2, and DKK1 protein and mRNA expression. Melatonin decreased p53 and MDM2 expression, which led to a decrease in FOXO1 degradation. These present results suggest that melatonin may help the hippocampal neuronal homeostasis by increasing SIRT1, FOXO1 and melatonin receptors expression while decreasing DKK1 expression in the aging hippocampus. DKK1 can be induced by the accumulation of amyloid β (Aβ) which is the major hallmark of Alzheimer's disease.

Ischemic brain injury: New insights on the protective role of melatonin

Stroke represents one of the most common causes of brain's vulnerability for many millions of people worldwide. The plethora of physiopathological events associated with brain ischemia are regulate through multiple signaling pathways leading to the activation of oxidative stress process, Ca²⁺ dyshomeostasis, mitochondrial dysfunction, proinflammatory mediators, excitotoxicity and/or programmed neuronal cell death. Understanding this cascade of molecular events is mandatory in order to develop new therapeutic strategies for stroke. In this review article, we have highlighted the pleiotropic effects of melatonin to counteract the multiple processes of the ischemic cascade. Additionally, experimental evidence supports its actions to ameliorate ischemic long-term behavioural and neuronal deficits, preserving the functional integrity of the blood-brain barrier, inducing neurogenesis and cell proliferation through receptor-dependent mechanism, as well as improving synaptic transmission. Consequently, the synthesis of melatonin derivatives designed as new multitarget-directed products has focused a great interest in this area. This latter has been reinforced by the low cost of melatonin and its reduced toxicity. Furthermore, its spectrum of usages seems to be wide and with the potential for improving human health. Nevertheless, the molecular and cellular mechanisms underlying melatonin´s actions need to be further exploration and accordingly, new clinical studies should be conducted in human patients with ischemic brain pathologies.

Melatonin and Nitrones As Potential Therapeutic Agents for Stroke

Stroke is a disease of aging affecting millions of people worldwide, and recombinant tissue-type plasminogen activator (r-tPA) is the only treatment approved. However, r-tPA has a low therapeutic window and secondary effects which limit its beneficial outcome, urging thus the search for new more efficient therapies. Among them, neuroprotection based on melatonin or nitrones, as free radical traps, have arisen as drug candidates due to their strong antioxidant power. In this Perspective article, an update on the specific results of the melatonin and several new nitrones are presented.

Melatonin protects against oxygen and glucose deprivation by decreasing extracellular glutamate and Nox-derived ROS in rat hippocampal slices

Therapeutic interventions on pathological processes involved in the ischemic cascade, such as oxidative stress, neuroinflammation, excitotoxicity and/or apoptosis, are of urgent need for stroke treatment. Melatonin regulates a large number of physiological actions and its beneficial properties have been reported. The aim of this study was to investigate whether melatonin mediates neuroprotection in rat hippocampal slices subjected to oxygen-glucose-deprivation (OGD) and glutamate excitotoxicity. Thus, we describe here that melatonin significantly reduced the amount of lactate dehydrogenase released in the OGD-treated slices, reverted neuronal injury caused by OGD-reoxygenation in CA1 and CA3 hippocampal regions, restored the reduction of GSH content of the hippocampal slices induced by OGD, and diminished the oxidative stress produced in the reoxygenation period. Furthermore, melatonin afforded maximum protection against glutamate-induced toxicity and reversed the glutamate released almost basal levels, at 10 and 30μM concentration, respectively. Consequently, we propose that melatonin might strongly and positively influence the outcome of brain ischemia/reperfusion.

Effects of rapamycin pretreatment on blood-brain barrier disruption in cerebral ischemia-reperfusion

The mammalian target of rapamycin (mTOR) pathway is essential in neuronal survival and repair in cerebral ischemia. Decreases in blood-brain barrier (BBB) disruption are associated with a decrease in neuronal damage in cerebral ischemia. This study was performed to investigate how pre-inhibition of the mTOR pathway with rapamycin would affect BBB disruption and the size of the infarcted cortical area in the early stage of focal cerebral ischemia-reperfusion using quantitative analysis of BBB disruption. Rats were treated with 20mg/kg of rapamycin i.p. once a day for 2days (Rapamycin Group) or vehicle (Control Group) before transient middle cerebral artery (MCA) occlusion. After one hour of MCA occlusion and two hours of reperfusion, the transfer coefficient (Ki) of (14)C-α-aminoisobutyric acid ((14)C-AIB) to measure the degree of BBB disruption and the size of the cortical infarct were determined. Ischemia-reperfusion increased the Ki in the Rapamycin treated (+15%) as well as in the untreated control group (+13%). However, rapamycin pretreatment moderately decreased Ki in the contralateral (-30%) as well as in the ischemic-reperfused (-29%) cortex when compared with the untreated control group. Rapamycin pretreatment substantially increased the percentage of cortical infarct compared with the control group (+56%). Our data suggest that activation of mTOR pathway is necessary for neuronal survival in the early stage of cerebral ischemia-perfusion and that the reason for the enlarged cortical infarct by rapamycin pretreatment may be related to its non-BBB effects on the mTOR pathway.

Melatonin regulates aging and neurodegeneration through energy metabolism, epigenetics, autophagy and circadian rhythm pathways

Brain aging is linked to certain types of neurodegenerative diseases and identifying new therapeutic targets has become critical. Melatonin, a pineal hormone, associates with molecules and signaling pathways that sense and influence energy metabolism, autophagy, and circadian rhythms, including insulin-like growth factor 1 (IGF-1), Forkhead box O (FoxOs), sirtuins and mammalian target of rapamycin (mTOR) signaling pathways. This review summarizes the current understanding of how melatonin, together with molecular, cellular and systemic energy metabolisms, regulates epigenetic processes in the neurons. This information will lead to a greater understanding of molecular epigenetic aging of the brain and anti-aging mechanisms to increase lifespan under healthy conditions.

Melatonin and the theories of aging: a critical appraisal of melatonin's role in antiaging mechanisms

The classic theories of aging such as the free radical theory, including its mitochondria-related versions, have largely focused on a few specific processes of senescence. Meanwhile, numerous interconnections have become apparent between age-dependent changes previously thought to proceed more or less independently. Increased damage by free radicals is not only linked to impairments of mitochondrial function, but also to inflammaging as it occurs during immune remodeling and by release of proinflammatory cytokines from mitotically arrested, DNA-damaged cells that exhibit the senescence-associated secretory phenotype (SASP). Among other effects, SASP can cause mutations in stem cells that reduce the capacity for tissue regeneration or, in worst case, lead to cancer stem cells. Oxidative stress has also been shown to promote telomere attrition. Moreover, damage by free radicals is connected to impaired circadian rhythmicity. Another nexus exists between cellular oscillators and metabolic sensing, in particular to the aging-suppressor SIRT1, which acts as an accessory clock protein. Melatonin, being a highly pleiotropic regulator molecule, interacts directly or indirectly with all the processes mentioned. These influences are critically reviewed, with emphasis on data from aged organisms and senescence-accelerated animals. The sometimes-controversial findings obtained either in a nongerontological context or in comparisons of tumor with nontumor cells are discussed in light of evidence obtained in senescent organisms. Although, in mammals, lifetime extension by melatonin has been rarely documented in a fully conclusive way, a support of healthy aging has been observed in rodents and is highly likely in humans.

Neuroprotective effect of melatonin: a novel therapy against perinatal hypoxia-ischemia

One of the most common causes of mortality and morbidity in children is perinatal hypoxia-ischemia (HI). In spite of the advances in neonatology, its incidence is not diminishing, generating a pediatric population that will require an extended amount of chronic care throughout their lifetime. For this reason, new and more effective neuroprotective strategies are urgently required, in order to minimize as much as possible the neurological consequences of this encephalopathy. In this sense, interest has grown in the neuroprotective possibilities of melatonin, as this hormone may help to maintain cell survival through the modulation of a wide range of physiological functions. Although some of the mechanisms by which melatonin is neuroprotective after neonatal asphyxia remain a subject of investigation, this review tries to summarize some of the most recent advances related with its use as a therapeutic drug against perinatal hypoxic-ischemic brain injury, supporting the high interest in this indoleamine as a future feasible strategy for cerebral asphyctic events.

Melatonin regulates the calcium-buffering proteins, parvalbumin and hippocalcin, in ischemic brain injury

Melatonin has anti-oxidant activity and it exerts a neuroprotective effects during ischemic brain injury. Calcium-buffering proteins including parvalbumin and hippocalcin are involved in neuronal differentiation and maturation through calcium signaling. This study investigated whether melatonin moderates parvalbumin and hippocalcin expression in cerebral ischemia and glutamate toxicity-induced neuronal cell death. Focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO). Male Sprague-Dawley rats were treated with vehicle or melatonin (5 mg/kg) prior to MCAO, and cerebral cortical tissues were collected 24 hr after MCAO. Parvalbumin and hippocalcin levels were decreased in vehicle-treated animal with MCAO, whereas melatonin prevented the ischemic injury-induced reduction in these proteins. In cultured hippocampal cells, glutamate toxicity decreased parvalbumin and hippocalcin levels, while melatonin treatment prevented the glutamate exposure-induced diminished in these proteins levels. Melatonin also attenuated the glutamate toxicity-induced increase in intracellular Ca(2+) levels. These results suggest that the maintenance of parvalbumin and hippocalcin levels by melatonin in ischemic injury contributes to the neuroprotective effect of melatonin against neuronal cell damage.

Melatonin attenuates decrease of protein phosphatase 2A subunit B in ischemic brain injury

Melatonin is an antioxidant that has neuroprotective functions in ischemic brain injury. Protein phosphatase 2A (PP2A) is a serine and threonine phosphatase that modulates cell metabolism and cell survival. This study investigated whether melatonin modulates PP2A subunit B in focal cerebral ischemia and glutamate toxicity-induced neuronal cell death in a rat model. Middle cerebral artery occlusion (MCAO) was performed to induce permanent cerebral ischemic injury. Adult male rats were treated with vehicle or melatonin (5 mg/kg) prior to MCAO, and cerebral cortex tissues were collected 24 hr after MCAO. A proteomic approach elucidated the decrease in PP2A subunit B in MCAO-operated animals. Melatonin treatment attenuated injury-induced reductions in PP2A subunit B levels. Western blot analyses indicated that melatonin prevents injury-induced decrease in PP2A subunit B levels. In neuronal cells, glutamate toxicity induced a lowering of PP2A subunit B, while melatonin treatment attenuated the glutamate exposure-induced decreases in PP2A subunit B. These results suggest that the maintenance of PP2A subunit B by melatonin in ischemic injury is critical to the neuroprotective function of melatonin during neuronal cell damage.

Melatonin prevents down-regulation of astrocytic phosphoprotein PEA-15 in ischemic brain injury

Melatonin functions as a free-radical scavenger and has a neuroprotective effect against ischemic brain damage. PEA-15 (phosphoprotein enriched in astrocytes 15) regulates various cellular processes including cell proliferation and apoptosis. In this study, we investigated whether melatonin regulates the levels of PEA-15 and the two phosphorylated forms of PEA-15 (Ser 104 and Ser 116) in a middle cerebral artery occlusion (MCAO)-induced injury model and neuronal cells exposed to glutamate. Adult male rats were treated with vehicle or melatonin (5 mg/kg) prior to MCAO, and cerebral cortex tissues were collected 24 h after MCAO. PEA-15 levels after ischemic brain injury were monitored using a proteomic approach. Melatonin pretreatment prevented the ischemic injury-induced reduction in PEA-15 levels. Moreover, Western blot analysis demonstrated that melatonin attenuated the ischemic injury-induced reduction in PEA-15, phospho-PEA-15 (Ser 104), and phospho-PEA-15 (Ser 116) levels. Neuronal cells exposed to glutamate showed decreased expression of PEA-15, phospho-PEA-15 (Ser 104), and phospho-PEA-15 (Ser 116), while melatonin pretreatment prevented the glutamate toxicity-induced decreases in the levels of these proteins. The reduction in the levels of phospho-PEA-15 proteins indicates the inhibition of anti-apoptotic function of PEA-15. Together, in vivo and in vitro results suggest that melatonin protects neurons against ischemic injury by maintaining levels of phospho-PEA-15 proteins.

The inhibition of apoptosis by melatonin in VSC4.1 motoneurons exposed to oxidative stress, glutamate excitotoxicity, or TNF-alpha toxicity involves membrane melatonin receptors

Loss of motoneurons may underlie some of the deficits in motor function associated with the central nervous system (CNS) injuries and diseases. We tested whether melatonin, a potent antioxidant and free radical scavenger, would prevent motoneuron apoptosis following exposure to toxins and whether this neuroprotection is mediated by melatonin receptors. Exposure of VSC4.1 motoneurons to either 50 microm H(2)O(2), 25 microm glutamate (LGA), or 50 ng/mL tumor necrosis factor-alpha (TNF-alpha) for 24 h caused significant increases in apoptosis, as determined by Wright staining and ApopTag assay. Analyses of mRNA and proteins showed increased expression and activities of stress kinases and cysteine proteases and loss of mitochondrial membrane potential during apoptosis. These insults also caused increases in intracellular free [Ca(2+)] and activities of calpain and caspases. Cells exposed to stress stimuli for 15 min were then treated with 200 nm melatonin. Post-treatment of cells with melatonin attenuated production of reactive oxygen species (ROS) and phosphorylation of p38, MAPK, and JNK1, prevented cell death, and maintained whole-cell membrane potential, indicating functional neuroprotection. Melatonin receptors (MT1 and MT2) were upregulated following treatment with melatonin. To confirm the involvement of MT1 and MT2 in providing neuroprotection, cells were post-treated (20 min) with 10 microm luzindole (melatonin receptor antagonist). Luzindole significantly attenuated melatonin-induced neuroprotection, suggesting that melatonin worked, at least in part, via its receptors to prevent VSC4.1 motoneuron apoptosis. Results suggest that neuroprotection rendered by melatonin to motoneurons is receptor mediated and melatonin may be an effective neuroprotective agent to attenuate motoneuron death in CNS injuries and diseases.

The antiapoptotic activity of melatonin in neurodegenerative diseases

Melatonin plays a neuroprotective role in models of neurodegenerative diseases. However, the molecular mechanisms underlying neuroprotection by melatonin are not well understood. Apoptotic cell death in the central nervous system is a feature of neurodegenerative diseases. The intrinsic and extrinsic apoptotic pathways and the antiapoptotic survival signal pathways play critical roles in neurodegeneration. This review summarizes the reports to date showing inhibition by melatonin of the intrinsic apoptotic pathways in neurodegenerative diseases including stroke, Alzheimer disease, Parkinson disease, Huntington disease, and amyotrophic lateral sclerosis. Furthermore, the activation of survival signal pathways by melatonin in neurodegenerative diseases is discussed.

Identification of proteins differentially expressed by melatonin treatment in cerebral ischemic injury--a proteomics approach

We previously reported that melatonin protects neuronal cells against ischemic brain damage. In this study, we identified proteins that were differentially expressed by melatonin treatment during ischemic brain injury. Rats were subjected to cerebral ischemia by middle cerebral artery occlusion (MCAO). Adult male rats were treated with melatonin (5 mg/kg) or vehicle prior to MCAO and brains were collected at 24 hr after MCAO. Proteins derived from the cerebral cortex were analyzed using two-dimensional gel electrophoresis. Protein spots with a greater than 2.5-fold change in intensity were identified by mass spectrometry. Among these proteins, gamma-enolase, stathmin, thioredoxin, peroxiredoxin-6, hippocalcin, protein phosphatase 2A, adenosylhomocysteinase, ubiquitin carboxy-terminal hydrolase L1, and NAD-specific isocitrate dehydrogenase subunit alpha were significantly decreased in the vehicle-treated group in comparison to the melatonin-treated group. The identified proteins consist of cell differentiation and stabilization proteins, as well as an antioxidant enzyme. In contrast, dehydroprimidinase-related protein 2 (DRP-2), a target of protein oxidation in neurodegeneration, was significantly increased in vehicle-treated animals, while melatonin prevented the injury-induced increase of DRP-2. Thus, the results of this study suggest that melatonin prevents cell death resulting from ischemic brain injury and that its neuroprotective effects are mediated by both the up- and down-regulation of various proteins.