Therapeutic effects of melatonin on cerebral ischemia reperfusion injury: Role of Yap-OPA1 signaling pathway and mitochondrial fusion

Exploring the intricacies of calcium dysregulation in ischemic stroke: Insights into neuronal cell death and therapeutic strategies

Calcium ion (Ca2+) dysregulation is one of the main causes of neuronal cell death and brain damage after cerebral ischemia. During ischemic stroke, the ability of neurons to maintain Ca2+ homeostasis is compromised. Ca2+ regulates various functions of the nervous system, including neuronal activity and adenosine triphosphate (ATP) production. Disruptions in Ca2+ homeostasis can trigger a cascade of events, including activation of the unfolded protein response (UPR) pathway, which is associated with endoplasmic reticulum (ER) stress and mitochondrial dysfunction. This response occurs when the cell is unable to manage protein folding within the ER due to various stressors, such as a high influx of Ca2+. Consequently, the UPR is initiated to restore ER function and alleviate stress, but prolonged activation can lead to mitochondrial dysfunction and, ultimately, cell death. Hence, precise regulation of Ca2+ within the cell is mandatory. The ER and mitochondria are two such organelles that maintain intracellular Ca2+ homeostasis through various calcium-operating channels, including ryanodine receptors (RyRs), inositol trisphosphate receptors (IP3Rs), sarco/endoplasmic reticulum calcium ATPases (SERCAs), the mitochondrial Na+/Ca2+ exchanger (NCLX), the mitochondrial calcium uniporter (MCU) and voltage-dependent anion channels (VDACs). These channels utilize Ca2+ sequestering and release mechanisms to maintain intracellular Ca2+ homeostasis and ensure proper cellular function and survival. The present review critically evaluates the significance of Ca2+ and its physiological role in cerebral ischemia. We have compiled recent findings on calcium's role and emerging treatment strategies, particularly targeting mitochondria and the endoplasmic reticulum, to address Ca2+ overload in cerebral ischemia.

Hippo (YAP)-autophagy axis protects against hepatic ischemia-reperfusion injury through JNK signaling

BACKGROUND

Hepatic ischemia-reperfusion injury (HIRI) remains a common complication during liver transplantation (LT) in patients. As a key downstream effector of the Hippo pathway, Yes-associated protein (YAP) has been reported to be involved in various physiological and pathological processes. However, it remains elusive whether and how YAP may control autophagy activation during ischemia-reperfusion.

METHODS

Human liver tissues from patients who had undergone LT were obtained to evaluate the correlation between YAP and autophagy activation. Both an in vitro hepatocyte cell line and in vivo liver-specific YAP knockdown mice were used to establish the hepatic ischemia-reperfusion models to determine the role of YAP in the activation of autophagy and the mechanism of regulation.

RESULTS

Autophagy was activated in the post-perfusion liver grafts during LT in patients, and the expression of YAP positively correlated with the autophagic level of hepatocytes. Liver-specific knockdown of YAP inhibited hepatocytes autophagy upon hypoxia-reoxygenation and HIRI ( P <0.05). YAP deficiency aggravated HIRI by promoting the apoptosis of hepatocytes both in the in vitro and in vivo models ( P <0.05). Attenuated HIRI by overexpression of YAP was diminished after the inhibition of autophagy with 3-methyladenine. In addition, inhibiting autophagy activation by YAP knockdown exacerbated mitochondrial damage through increasing reactive oxygen species ( P <0.05). Moreover, the regulation of autophagy by YAP during HIRI was mediated by AP1 (c-Jun) N-terminal kinase (JNK) signaling through binding to the transcriptional enhanced associate domain (TEAD).

CONCLUSIONS

YAP protects against HIRI by inducing autophagy via JNK signaling that suppresses the apoptosis of hepatocytes. Targeting Hippo (YAP)-JNK-autophagy axis may provide a novel strategy for the prevention and treatment of HIRI.

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.

A review for the correlation between optic atrophy 1-dependent mitochondrial fusion and cardiovascular disorders

Mitochondrial dynamics homeostasis is sustained by continuous and balanced fission and fusion, which are determinants of morphology, abundance, biogenesis and mitophagy of mitochondria. Optic atrophy 1 (OPA1), as the only inner mitochondrial membrane fusion protein, plays a key role in stabilizing mitochondrial dynamics. The disturbance of mitochondrial dynamics contributes to the pathophysiological progress of cardiovascular disorders, which are the main cause of death worldwide in recent decades and result in tremendous social burden. In this review, we describe the latest findings regarding OPA1 and its role in mitochondrial fusion. We summarize the post-translational modifications (PTMs) for OPA1 and its regulatory role in mitochondrial dynamics. Then the diverse cell fates caused by OPA1 expression during cardiovascular disorders are discussed. Moreover, cardiovascular disorders (such as heart failure, myocardial ischemia/reperfusion injury, cardiomyopathy and cardiac hypertrophy) relevant to OPA1-dependent mitochondrial dynamics imbalance have been detailed. Finally, we highlight the potential that targeting OPA1 to impact mitochondrial fusion may be used as a novel strategy against cardiovascular disorders.

Non-Excitatory Amino Acids, Melatonin, and Free Radicals: Examining the Role in Stroke and Aging

The aim of this review is to explore the relationship between melatonin, free radicals, and non-excitatory amino acids, and their role in stroke and aging. Melatonin has garnered significant attention in recent years due to its diverse physiological functions and potential therapeutic benefits by reducing oxidative stress, inflammation, and apoptosis. Melatonin has been found to mitigate ischemic brain damage caused by stroke. By scavenging free radicals and reducing oxidative damage, melatonin may help slow down the aging process and protect against age-related cognitive decline. Additionally, non-excitatory amino acids have been shown to possess neuroprotective properties, including antioxidant and anti-inflammatory in stroke and aging-related conditions. They can attenuate oxidative stress, modulate calcium homeostasis, and inhibit apoptosis, thereby safeguarding neurons against damage induced by stroke and aging processes. The intracellular accumulation of certain non-excitatory amino acids could promote harmful effects during hypoxia-ischemia episodes and thus, the blockade of the amino acid transporters involved in the process could be an alternative therapeutic strategy to reduce ischemic damage. On the other hand, the accumulation of free radicals, specifically mitochondrial reactive oxygen and nitrogen species, accelerates cellular senescence and contributes to age-related decline. Recent research suggests a complex interplay between melatonin, free radicals, and non-excitatory amino acids in stroke and aging. The neuroprotective actions of melatonin and non-excitatory amino acids converge on multiple pathways, including the regulation of calcium homeostasis, modulation of apoptosis, and reduction of inflammation. These mechanisms collectively contribute to the preservation of neuronal integrity and functions, making them promising targets for therapeutic interventions in stroke and age-related disorders.

An update on the role of Hippo signaling pathway in ischemia-associated central nervous system diseases

The most frequent reason of morbidity and mortality in the world, cerebral ischemia sets off a chain of molecular and cellular pathologies that associated with some central nervous system (CNS) disorders mainly including ischemic stroke, Alzheimer's disease (AD), Parkinson's disease (PD), epilepsy and other CNS diseases. In recent times, despite significant advancements in the treatment of the pathological processes underlying various neurological illnesses, effective therapeutic approaches that are specifically targeted to minimizing the damage of such diseases remain absent. Hippo signaling pathway, characterized by enzyme linked reactions between MSTI/2, LAST1/2, and YAP or TAZ proteins, controls cell division, survival, and differentiation, as well as being engaged in a variety of biological activities, such as the development and transformation of the nervous system. Recently, accumulating studies demonstrated that Hippo pathway takes part in the processes of ischemic stroke, AD, PD, etc., including but not limited to oxidative stress, inflammatory response, blood-brain barrier damage, mitochondrial disorders, and neural cells death. Thus, it's crucial to understand the molecular basis of the Hippo signaling pathway for determining potential new therapeutic targets against ischemia-associated CNS diseases. Here, we discuss latest advances in the deciphering of the Hippo signaling pathway and highlight the therapeutic potential of targeting the pathway in treating ischemia-associated CNS diseases.

Mitochondrial dysfunctions induce PANoptosis and ferroptosis in cerebral ischemia/reperfusion injury: from pathology to therapeutic potential

Ischemic stroke (IS) accounts for more than 80% of the total stroke, which represents the leading cause of mortality and disability worldwide. Cerebral ischemia/reperfusion injury (CI/RI) is a cascade of pathophysiological events following the restoration of blood flow and reoxygenation, which not only directly damages brain tissue, but also enhances a series of pathological signaling cascades, contributing to inflammation, further aggravate the damage of brain tissue. Paradoxically, there are still no effective methods to prevent CI/RI, since the detailed underlying mechanisms remain vague. Mitochondrial dysfunctions, which are characterized by mitochondrial oxidative stress, Ca²⁺ overload, iron dyshomeostasis, mitochondrial DNA (mtDNA) defects and mitochondrial quality control (MQC) disruption, are closely relevant to the pathological process of CI/RI. There is increasing evidence that mitochondrial dysfunctions play vital roles in the regulation of programmed cell deaths (PCDs) such as ferroptosis and PANoptosis, a newly proposed conception of cell deaths characterized by a unique form of innate immune inflammatory cell death that regulated by multifaceted PANoptosome complexes. In the present review, we highlight the mechanisms underlying mitochondrial dysfunctions and how this key event contributes to inflammatory response as well as cell death modes during CI/RI. Neuroprotective agents targeting mitochondrial dysfunctions may serve as a promising treatment strategy to alleviate serious secondary brain injuries. A comprehensive insight into mitochondrial dysfunctions-mediated PCDs can help provide more effective strategies to guide therapies of CI/RI in IS.

Circadian Factors in Stroke: A Clinician's Perspective

Stroke remains one of the leading causes of mortality and long-term and permanent disability worldwide despite technological innovations and developments in pharmacotherapy. In the last few decades, the growing data have evidenced the role of the circadian system in brain vulnerability to damage, the development and evolution of stroke, and short-term and long-term recovery. On the other hand, the stroke itself can affect the circadian system via direct injury of specific brain structures involved in circadian regulation (i.e., hypothalamus, retinohypothalamic tracts, etc.) and impairment of endogenous regulatory mechanisms, metabolic derangement, and a neurogenic inflammatory response in acute stroke. Moreover, the disruption of circadian rhythms can occur or exacerbate as a result of exogenous factors related to hospitalization itself, the conditions in the intensive care unit and the ward (light, noise, etc.), medication (sedatives and hypnotics), and loss of external factors entraining the circadian rhythms. In the acute phase of stroke, patients demonstrate abnormal circadian variations in circadian biomarkers (melatonin, cortisol), core body temperature, and rest-activity patterns. The approaches aimed at the restoration of disrupted circadian patterns include pharmacological (melatonin supplementation) and non-medication (bright light therapy, shifting feeding schedules, etc.) interventions; however, their effects on short- and long-term recovery after stroke are not well understood.

Neuropilin-1 promotes mitochondrial structural repair and functional recovery in rats with cerebral ischemia

OBJECTIVES

Available literature documents that ischemic stroke can disrupt the morphology and function of mitochondria and that the latter in other disease models can be preserved by neuropilin-1 (NRP-1) via oxidative stress suppression. However, whether NRP-1 can repair mitochondrial structure and promote functional recovery after cerebral ischemia is still unknown. This study tackled this very issue and explored the underlying mechanism.

METHODS

Adeno-associated viral (AAV)-NRP-1 was stereotaxically inoculated into the cortex and ipsilateral striatum posterior of adult male Sprague-Dawley (SD) rats before a 90-min transient middle cerebral artery occlusion (tMCAO) and subsequent reperfusion. Lentivirus (LV)-NRP-1 was transfected into rat primary cortical neuronal cultures before a 2-h oxygen-glucose deprivation and reoxygenation (OGD/R) injury to neurons. The expression and function of NRP-1 and its specific protective mechanism were investigated by Western Blot, immunofluorescence staining, flow cytometry, magnetic resonance imaging, transmission electron microscopy, etc. The binding was detected by molecular docking and molecular dynamics simulation.

RESULTS

Both in vitro and in vivo models of cerebral ischemia/reperfusion (I/R) injury presented a sharp increase in NRP-1 expression. The expression of AAV-NRP-1 markedly ameliorated the cerebral I/R-induced damage to the motor function and restored the mitochondrial morphology. The expression of LV-NRP-1 alleviated mitochondrial oxidative stress and bioenergetic deficits. AAV-NRP-1 and LV-NRP-1 treatments increased the wingless integration (Wnt)-associated signals and β-catenin nuclear localization. The protective effects of NRP-1 were reversed by the administration of XAV-939.

CONCLUSIONS

NRP-1 can produce neuroprotective effects against I/R injury to the brain by activating the Wnt/β-catenin signaling pathway and promoting mitochondrial structural repair and functional recovery, which may serve as a promising candidate target in treating ischemic stroke.

Melatonin-mediated malic enzyme 2 orchestrates mitochondrial fusion and respiratory functions to promote odontoblastic differentiation during tooth development

Tooth development is a complex process that is tightly controlled by circadian rhythm. Melatonin (MT) is a major hormonal regulator of the circadian rhythm, and influences dentin formation and odontoblastic differentiation during tooth development; however, the underlying mechanism remains elusive. This study investigated how MT regulates odontoblastic differentiation, with a special focus on its regulation of mitochondrial dynamics. In rat dental papilla cells (DPCs), we found that MT promotes odontoblastic differentiation concurrently with enhanced mitochondrial fusion, while disruption of mitochondrial fusion by depleting optic atrophy 1 (OPA1) impairs MT-mediated differentiation and mitochondrial respiratory functions. Through RNA sequencing, we discovered that MT significantly upregulated malic enzyme 2 (ME2), a mitochondrial NAD(P)⁺ -dependent enzyme, and identified ME2 as a critical MT downstream effector that orchestrates odontoblastic differentiation, mitochondrial fusion, and respiration functions. By detecting the spatiotemporal expression of ME2 in developing tooth germs, and using tooth germ reconstituted organoids, we also provided in vivo and ex vivo evidence that ME2 promotes dentin formation, indicating a possible involvement of ME2 in MT-modulated tooth development. Collectively, our findings offer novel understandings regarding the molecular mechanism by which MT affects cell differentiation and organogenesis, meanwhile, the critical role of ME2 in MT-regulated mitochondrial functions is also highlighted.

Mechanistic study of optic atrophy 1 in ischemia-reperfusion disease

Mitochondria consist of the inner mitochondrial membrane and the outer mitochondrial membrane, which maintain mitochondrial homeostasis through continuous fission and fusion to ensure a healthy mitochondrial network and thus regulate normal cellular function, namely mitochondrial dynamics. The imbalance between mitochondrial fusion and fission results in abnormal mitochondrial structure and eventually mitochondrial dysfunction, which is involved in the pathological process of ischemia-reperfusion injury (IRI). Optic atrophy 1 (OPA1) is a key protein that regulates mitochondrial inner membrane fusion and ensures normal mitochondrial function by balancing mitochondrial dynamics, participating in various processes such as mitochondrial fusion, oxidative stress, and apoptosis. Ischemia-induced changes in mitochondrial dynamics may be a key factor in limiting the recanalization time window and exacerbating reperfusion injury, and the mechanisms of these changes deserve further attention. Therefore, targeting OPA1-related mitochondrial fusions, thereby balancing mitochondrial dynamics and improving mitochondrial dysfunction, is a promising therapeutic strategy for ischemia-reperfusion diseases. This review will elaborate on the structure and function of OPA1 and the role of OPA1 in IRI to provide promising therapeutic targets for the treatment of ischemia-reperfusion diseases.

Melatonin attenuates manganese-induced mitochondrial fragmentation by suppressing the Mst1/JNK signaling pathway in primary mouse neurons

Manganese (Mn) toxicity is mainly caused by excessive Mn content in drinking water and occupational exposure. Moreover, overexposure to Mn can impair mental, cognitive, memory, and motor capacities. Although melatonin (Mel) can protect against Mn-induced neuronal damage and mitochondrial fragmentation, the underlying mechanism remains elusive. Here, we examined the related molecular mechanisms underlying Mel attenuating Mn-induced mitochondrial fragmentation through the mammalian sterile 20-like kinase-1 (Mst1)/JNK signaling path. To test the role of Mst1 in mitochondrial fragmentation, we treated mouse primary neurons overexpressing Mst1 with Mel and Mn stimulation. In normal neurons, 10 μM Mel reduced the effects of Mn (200 μM) on Mst1 expression at the mRNA and protein levels and on phosphorylation of JNK and Drp1, Drp1 mitochondrial translocation, and mitochondrial fragmentation. Conversely, overexpression of Mst1 hindered the protective effect of Mel (10 μM) against Mn-induced mitochondrial fragmentation. Anisomycin (ANI), an activator of JNK signaling, was similarly found to inhibit the protective effect of Mel on mitochondria, while Mst1 levels were not significantly changed. Thus, our results demonstrated that 10 μM Mel negatively regulated the Mst1-JNK pathway, thereby reducing excessive mitochondrial fission, maintaining the mitochondrial network, and alleviating Mn-induced mitochondrial dysfunction.

Neuroprotective Effect of Polyphenol Extracts from Terminalia chebula Retz. against Cerebral Ischemia-Reperfusion Injury

Current therapies for ischemic stroke are insufficient due to the lack of specific drugs. This study aimed to investigate the protective activity of polyphenol extracts from Terminalia chebula against cerebral ischemia-reperfusion induced damage. Polyphenols of ethyl acetate and n-butanol fractions were extracted from T. chebula. BV2 microglial cells exposed to oxygen-glucose deprivation/reoxygenation and mice subjected to middle cerebral artery occlusion/reperfusion were treated by TPE and TPB. Cell viability, cell morphology, apoptosis, mitochondrial membrane potential, enzyme activity and signaling pathway related to oxidative stress were observed. We found that TPE and TPB showed strong antioxidant activity in vitro. The protective effects of TPE and TPB on cerebral ischemia-reperfusion injury were demonstrated by enhanced antioxidant enzyme activities, elevated level of the nucleus transportation of nuclear factor erythroid 2-related factor 2 and expressions of antioxidant proteins, with a simultaneous reduction in cell apoptosis and reactive oxygen species level. In conclusion, TPE and TPB exert neuroprotective effects by stimulating the Nrf2 signaling pathway, thereby inhibiting apoptosis.

Calenduloside E alleviates cerebral ischemia/reperfusion injury by preserving mitochondrial function

Calenduloside E (CE) isolated from Aralia elata (Miq.) Seem. is a natural triterpenoid saponin that can reportedly ameliorate myocardial ischemia/reperfusion injury. However, its potential roles and mechanism in cerebral ischemia/reperfusion injury are barely understood. In this study, we established an oxygen-glucose deprivation/reoxygenation (OGD/R) model in HT22 cells. We found that CE significantly attenuated the OGD/R-induced inhibition of cell viability and apoptotic cell death in HT22 cells. Moreover, CE treatment significantly ameliorated OGD/R-induced mitochondrial fission by inhibiting mitochondrial dynamin-related protein 1 (Drp1) recruitment and increasing Drp1 phosphorylation at Ser637. CE treatment significantly ameliorated OGD/R-induced mitochondrial dysfunction by increasing the mitochondrial membrane potential and reducing the mitochondrial ROS and cellular calcium accumulation. Moreover, CE treatment significantly inhibited the OGD/R-induced release of mitochondrial Cytochrome C and increase in Bax, Cleaved-caspase3 and Cleaved-caspase9 protein levels, whereas CE treatment significantly reversed the OGD/R-induced decrease in Bcl-2 and full length of caspase3 and caspase9 protein levels. In vivo, we found that CE treatment significantly ameliorated ischemic/hypoxic-induced brain infarct volume, neurological deficits, and neuronal apoptosis in mice after middle cerebral artery occlusion and reperfusion. CE treatment also significantly ameliorated the mitochondrial transmembrane potential, decreased Cytochrome C release, and reversed the increase in Bax, Cleaved-caspase3 and Cleaved-caspase9 protein levels and the decrease in Bcl-2 and full length of caspase3 and caspase9 protein levels induced by cerebral ischemia/reperfusion (I/R). All these results indicated that CE treatment exerted a neuroprotective effect by ameliorating mitochondrial dysfunction during cerebral I/R injury.

Intertwined Relation between the Endoplasmic Reticulum and Mitochondria in Ischemic Stroke

In ischemic stroke (IS), accumulation of the misfolded proteins in the endoplasmic reticulum (ER) and mitochondria-induced oxidative stress (OS) has been identified as the indispensable inducers of secondary brain injury. With the increasing recognition of an association between ER stress and OS with ischemic stroke and with the improved understanding of the underlying molecular mechanism, novel targets for drug therapy and new strategies for therapeutic interventions are surfacing. This review discusses the molecular mechanism underlying ER stress and OS response as both causes and consequences of ischemic stroke. We also summarize the latest advances in understanding the importance of ER stress and OS in the pathogenesis of ischemic stroke and discuss potential strategies and clinical trials explicitly aiming to restore mitochondria and ER dynamics after IS.

Mitochondrial dynamics in the neonatal brain - a potential target following injury?

The impact of birth asphyxia and its sequelae, hypoxic–ischaemic (HI) brain injury, is long-lasting and significant, both for the infant and for their family. Treatment options are limited to therapeutic hypothermia, which is not universally successful and is unavailable in low resource settings. The energy deficits that accompany neuronal death following interruption of blood flow to the brain implicate mitochondrial dysfunction. Such HI insults trigger mitochondrial outer membrane permeabilisation leading to release of pro-apoptotic proteins into the cytosol and cell death. More recently, key players in mitochondrial fission and fusion have been identified as targets following HI brain injury. This review aims to provide an introduction to the molecular players and pathways driving mitochondrial dynamics, the regulation of these pathways and how they are altered following HI insult. Finally, we review progress on repurposing or repositioning drugs already approved for other indications, which may target mitochondrial dynamics and provide promising avenues for intervention following brain injury. Such repurposing may provide a mechanism to fast-track, low-cost treatment options to the clinic.

Mitochondrial Quality Control: A Pathophysiological Mechanism and Therapeutic Target for Stroke

Stroke is a devastating disease with high mortality and disability rates. Previous research has established that mitochondria, as major regulators, are both influenced by stroke, and further regulated the development of poststroke injury. Mitochondria are involved in several biological processes such as energy generation, calcium homeostasis, immune response, apoptosis regulation, and reactive oxygen species (ROS) generation. Meanwhile, mitochondria can evolve into various quality control systems, including mitochondrial dynamics (fission and fusion) and mitophagy, to maintain the homeostasis of the mitochondrial network. Various activities of mitochondrial fission and fusion are associated with mitochondrial integrity and neurological injury after stroke. Additionally, proper mitophagy seems to be neuroprotective for its effect on eliminating the damaged mitochondria, while excessive mitophagy disturbs energy generation and mitochondria-associated signal pathways. The balance between mitochondrial dynamics and mitophagy is more crucial than the absolute level of each process. A neurovascular unit (NVU) is a multidimensional system by which cells release multiple mediators and regulate diverse signaling pathways across the whole neurovascular network in a way with a high dynamic interaction. The turbulence of mitochondrial quality control (MQC) could lead to NVU dysfunctions, including neuron death, neuroglial activation, blood–brain barrier (BBB) disruption, and neuroinflammation. However, the exact changes and effects of MQC on the NVU after stroke have yet to be fully illustrated. In this review, we will discuss the updated mechanisms of MQC and the pathophysiology of mitochondrial dynamics and mitophagy after stroke. We highlight the regulation of MQC as a potential therapeutic target for both ischemic and hemorrhagic stroke.

Melatonin ameliorates cerebral ischemia-reperfusion injury in diabetic mice by enhancing autophagy via the SIRT1-BMAL1 pathway

Diabetic brains are more vulnerable to ischemia-reperfusion injury. Previous studies have proved that melatonin could protect against cerebral ischemia-reperfusion (CIR) injury in non-diabetic stroke models; however, its roles and the underlying mechanisms against CIR injury in diabetic mice remain unknown. Streptozotocin-induced diabetic mice and high-glucose-cultured HT22 cells were exposed to melatonin, with or without administration of the autophagy inhibitor 3-methyladenine (3-MA) and the specifically silent information regulator 1 (SIRT1) inhibitor EX527, and then subjected to CIR or oxygen-glucose deprivation/reperfusion operation. We found that diabetic mice showed aggravated brain damage, increased apoptosis and oxidative stress, and deficient autophagy following CIR compared with non-diabetic counterparts. Melatonin treatment exhibited improved histological damage, neurological outcomes, and cerebral infarct size. Intriguingly, melatonin markedly increased cell survival, anti-oxidative and anti-apoptosis effects, and significantly enhanced autophagy. However, these effects were largely attenuated by 3-MA or EX527. Additionally, our cellular experiments demonstrated that melatonin increased the SIRT1-BMAL1 pathway-related proteins' expression in a dose-dependent manner. In conclusion, these results indicate that melatonin treatment can protect against CIR-induced brain damage in diabetic mice, which may be achieved by the autophagy enhancement mediated by the SIRT1-BMAL1 pathway.

Mitochondrial quality control in acute ischemic stroke

Mitochondria play a central role in the pathophysiological processes of acute ischemic stroke. Disruption of the cerebral blood flow during acute ischemic stroke interrupts oxygen and glucose delivery, leading to the dysfunction of mitochondrial oxidative phosphorylation and cellular bioenergetic stress. Cells can respond to such stress by activating mitochondrial quality control mechanisms, including the mitochondrial unfolded protein response, mitochondrial fission and fusion, mitophagy, mitochondrial biogenesis, and intercellular mitochondrial transfer. Collectively, these adaptive response strategies contribute to retaining the integrity and function of the mitochondrial network, thereby helping to recover the homeostasis of the neurovascular unit. In this review, we focus on mitochondrial quality control mechanisms occurring in acute ischemic stroke. A better understanding of how these regulatory pathways work in maintaining mitochondrial homeostasis will provide a rationale for developing innovative neuroprotectants when these mechanisms fail in acute ischemic stroke.

P2RY2 Alleviates Cerebral Ischemia-Reperfusion Injury by Inhibiting YAP Phosphorylation and Reducing Mitochondrial Fission

P2Y purinoceptor 2 (P2RY2) is involved in the regulation of cell proliferation and apoptosis. The aim of this study was to explore the effects of P2RY2 on cerebral ischemia/reperfusion (I/R) injury and its molecular mechanism. Middle cerebral artery occlusion (MCAO) model in rats and OXYGEN and oxygen-glucose deprivation/reoxygenation (OGD/R) model in PC12 cells were established. P2RY2 expressions in I/R injury model in vitro and in vivo were up-regulated. In the OGD/R group, ROS level, cyto-CytC and mitochondrial fission factors expressions and cell apoptosis were increased, while SOD activity, mito-CytC and mitochondrial fusion factors expressions were decreased. P2RY2 overexpression could reverse these results. Up-regulated P2RY2 expression decreased Yes-associated protein (YAP) phosphorylation level, promote the nuclear translocation of YAP, and inhibit cell apoptosis, which can be reversed by YAP inhibitor verteporfin. The addition of PI3K/AKT inhibitor LY294002 could reverse the decrease of YAP phosphorylation level and cell apoptosis, and the increase of nuclear translocation caused by P2RY2 overexpression. Further in vivo studies validated that interference with P2RY2 increased the cerebral infarction area, decreased AKT expression, enhanced YAP phosphorylation, and inhibited the nuclear translocation of YAP. In conclusion, P2RY2 can alleviate cerebral I/R injury by inhibiting YAP phosphorylation and reducing mitochondrial fission.

Mitochondrial Dynamics: A Potential Therapeutic Target for Ischemic Stroke

Stroke is one of the leading causes of death and disability worldwide. Brain injury after ischemic stroke involves multiple pathophysiological mechanisms, such as oxidative stress, mitochondrial dysfunction, excitotoxicity, calcium overload, neuroinflammation, neuronal apoptosis, and blood-brain barrier (BBB) disruption. All of these factors are associated with dysfunctional energy metabolism after stroke. Mitochondria are organelles that provide adenosine triphosphate (ATP) to the cell through oxidative phosphorylation. Mitochondrial dynamics means that the mitochondria are constantly changing and that they maintain the normal physiological functions of the cell through continuous division and fusion. Mitochondrial dynamics are closely associated with various pathophysiological mechanisms of post-stroke brain injury. In this review, we will discuss the role of the molecular mechanisms of mitochondrial dynamics in energy metabolism after ischemic stroke, as well as new strategies to restore energy homeostasis and neural function. Through this, we hope to uncover new therapeutic targets for the treatment of ischemic stroke.

Mitochondrial Quality Control in Cerebral Ischemia-Reperfusion Injury

Ischemic stroke is one of the leading causes of death and also a major cause of adult disability worldwide. Revascularization via reperfusion therapy is currently a standard clinical procedure for patients with ischemic stroke. Although the restoration of blood flow (reperfusion) is critical for the salvage of ischemic tissue, reperfusion can also, paradoxically, exacerbate neuronal damage through a series of cellular alterations. Among the various theories postulated for ischemia/reperfusion (I/R) injury, including the burst generation of reactive oxygen species (ROS), activation of autophagy, and release of apoptotic factors, mitochondrial dysfunction has been proposed to play an essential role in mediating these pathophysiological processes. Therefore, strict regulation of the quality and quantity of mitochondria via mitochondrial quality control is of great importance to avoid the pathological effects of impaired mitochondria on neurons. Furthermore, timely elimination of dysfunctional mitochondria via mitophagy is also crucial to maintain a healthy mitochondrial network, whereas intensive or excessive mitophagy could exacerbate cerebral I/R injury. This review will provide a comprehensive overview of the effect of mitochondrial quality control on cerebral I/R injury and introduce recent advances in the understanding of the possible signaling pathways of mitophagy and potential factors responsible for the double-edged roles of mitophagy in the pathological processes of cerebral I/R injury.

Melatonin protects against focal cerebral ischemia-reperfusion injury in diabetic mice by ameliorating mitochondrial impairments: involvement of the Akt-SIRT3-SOD2 signaling pathway

Diabetic patients are more vulnerable to cerebral ischemia-reperfusion (CIR) injury and have a worse prognosis and higher mortality after ischemic stroke than non-diabetic counterparts. Melatonin can exert neuroprotective effects against CIR injury in nondiabetic animal models. However, its effects on diabetic CIR injury and the underlying mechanisms remain unclarified. Herein, we found that melatonin administration improved neurological deficit, cerebral infarct volume, brain edema, and cell viability, reduced mitochondrial swelling, reactive oxygen species generation, and cytoplasmic cytochrome C release, and increased mitochondrial antioxidant enzymes activities, adenosine triphosphate production, and mitochondrial membrane potential in both streptozotocin-induced diabetic mice and high glucose-treated HT22 cells. Importantly, melatonin also activated protein kinase B (Akt) and sirtuin 3 (SIRT3)/superoxide dismutase 2 (SOD2) signaling and upregulated mitochondrial biogenesis-related transcription factors. However, these effects were largely attenuated by LY294002 (a specific Akt signaling blocker) administration. Additionally, 3-TYP (a selective SIRT3 inhibitor) and SIRT3 siRNA inhibited the above protective effects of melatonin as well as the upregulation of SIRT3 and the decrease of SOD2 acetylation but did not affect the p-Akt/Akt ratio. Overall, we demonstrate that melatonin can alleviate CIR injury in diabetic mice by activating Akt-SIRT3-SOD2 signaling and subsequently improving mitochondrial damage.

Insight into the effects of melatonin on endoplasmic reticulum, mitochondrial function, and their cross-talk in the stroke

Ischemic stroke has remained a principal cause of mortality and neurological disabilities worldwide. Blood flow resumption, reperfusion, in the cerebral ischemia prompts a cascade in the brain characterized by various cellular mechanisms like mitochondrial dysfunction, oxidative stresses, endoplasmic reticulum (ER) stress, and excitotoxicity, finally resulting in programmed cell death. Any changes in the ER-mitochondria axis are probably responsible for both the onset and progression of central nervous system diseases. Melatonin, a neurohormone secreted by the pineal gland, has antioxidative, anti-inflammatory, and anti-apoptotic properties. Most studies have shown that it exerts neuroprotective effects against ischemic stroke. It was observed that melatonin therapy after the stroke not only leads to reduce mitochondrial dysfunction but also cause to alleviate ER stress and inflammation. This review discusses the impact of melatonin on mitochondrial, ER function, and on the crosstalk between two organelles as a therapeutic target for stroke. Given that the influences of melatonin on each organelle separately, its effects on mechanisms of crosstalk between ER and mitochondria are discussed.

Potential Role of Melatonin as an Adjuvant for Atherosclerotic Carotid Arterial Stenosis

Carotid artery stenosis (CAS) is an atherosclerotic disease characterized by a narrowing of the artery lumen and a high risk of ischemic stroke. Risk factors of atherosclerosis, including smoking, hypertension, hyperglycemia, hyperlipidemia, aging, and disrupted circadian rhythm, may potentiate atherosclerosis in the carotid artery and further reduce the arterial lumen. Ischemic stroke due to severe CAS and cerebral ischemic/reperfusion (I/R) injury after the revascularization of CAS also adversely affect clinical outcomes. Melatonin is a pluripotent agent with potent anti-inflammatory, anti-oxidative, and neuroprotective properties. Although there is a shortage of direct clinical evidence demonstrating the benefits of melatonin in CAS patients, previous studies have shown that melatonin may be beneficial for patients with CAS in terms of reducing endothelial damage, stabilizing arterial plaque, mitigating the harm from CAS-related ischemic stroke and cerebral I/R injury, and alleviating the adverse effects of the related risk factors. Additional pre-clinical and clinical are required to confirm this speculation.

Irisin Contributes to Neuroprotection by Promoting Mitochondrial Biogenesis After Experimental Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating form of stroke, which poses a series of intractable challenges to clinical practice. Imbalance of mitochondrial homeostasis has been thought to be the crucial pathomechanism in early brain injury (EBI) cascade after SAH. Irisin, a protein related to metabolism and mitochondrial homeostasis, has been reported to play pivotal roles in post-stroke neuroprotection. However, whether this myokine can exert neuroprotection effects after SAH remains unknown. In the present study, we explored the protective effects of irisin and the underlying mechanisms related to mitochondrial biogenesis in a SAH animal model. Endovascular perforation was used to induce SAH, and recombinant irisin was administered intracerebroventricularly. Neurobehavioral assessments, TdT-UTP nick end labeling (TUNEL) staining, dihydroethidium (DHE) staining, immunofluorescence, western blot, and transmission electron microscopy (TEM) were performed for post-SAH assessments. We demonstrated that irisin treatment improved neurobehavioral scores, reduced neuronal apoptosis, and alleviated oxidative stress in EBI after SAH. More importantly, the administration of exogenous irisin conserved the mitochondrial morphology and promoted mitochondrial biogenesis. The protective effects of irisin were partially reversed by the mitochondrial uncoupling protein-2 (UCP-2) inhibitor. Taken together, irisin may have neuroprotective effects against SAH via improving the mitochondrial biogenesis, at least in part, through UCP-2 related targets.

MicroRNA-670 aggravates cerebral ischemia/reperfusion injury via the Yap pathway

Apoptosis is an important programmed cell death process involved in ischemia/reperfusion injury. MicroRNAs are considered to play an important role in the molecular mechanism underlying the regulation of cerebral ischemia and reperfusion injury. However, whether miR-670 can regulate cell growth and death in cerebral ischemia/reperfusion and the underlying mechanism are poorly understood. In this study, we established mouse models of transient middle artery occlusion and Neuro 2a cell models of oxygen-glucose deprivation and reoxygenation to investigate the potential molecular mechanism by which miR-670 exhibits its effects during cerebral ischemia/reperfusion injury both in vitro and in vivo. Our results showed that after ischemia/reperfusion injury, miR-670 expression was obviously increased. After miR-670 expression was inhibited with an miR-670 antagomir, cerebral ischemia/reperfusion injury-induced neuronal death was obviously reduced. When miR-670 overexpression was induced by an miR-670 agomir, neuronal apoptosis was increased. In addition, we also found that miR-670 could promote Yap degradation via phosphorylation and worsen neuronal apoptosis and neurological deficits. Inhibition of miR-670 reduced neurological impairments after cerebral ischemia/reperfusion injury. These results suggest that microRNA-670 aggravates cerebral ischemia/reperfusion injury through the Yap pathway, which may be a potential target for treatment of cerebral ischemia/reperfusion injury. The present study was approved by the Institutional Animal Care and Use Committee of China Medical University on February 27, 2017 (IRB No. 2017PS035K).

The Neuroprotective Effect of Irisin in Ischemic Stroke

Irisin is a PGC-1α-dependent myokine that causes increased energy expenditure by driving the development of white adipose tissue into brown fat-like tissue. Exercise can improve irisin levels and lead to its release into the blood. In ischemic stroke, neurons are always sensitive to energy supply; after a series of pathophysiological processes, reactive oxygen species that are detrimental to cell survival via mitochondrial dysfunction are generated in large quantities. As a protein associated with exercise, irisin can alleviate brain injury in the pathogenesis of ischemic stroke. It is thought that irisin can upregulate the levels of brain-derived neurotrophic factor (BDNF), which protects nerve cells from injury during ischemic stroke. Furthermore, the release of irisin into the blood via exercise influences the mitochondrial dynamics crucial to maintaining the normal function of nerve cells. Consequently, we intended to summarize the known effects of irisin during ischemic stroke.

Mitochondrial Fusion and Fission in Neuronal Death Induced by Cerebral Ischemia-Reperfusion and Its Clinical Application: A Mini-Review

Mitochondria are highly dynamic organelles which are joined by mitochondrial fusion and divided by mitochondrial fission. The balance of mitochondrial fusion and fission plays a critical role in maintaining the normal function of neurons, of which the processes are both mediated by several proteins activated by external stimulation. Cerebral ischemia-reperfusion (I/R) injury can disrupt the balance of mitochondrial fusion and fission through regulating the expression and post-translation modification of fusion- and fission-related proteins, thereby destroying homeostasis of the intracellular environment and causing neuronal death. Furthermore, human intervention in fusion- and fission-related proteins can influence the function of neurons and change the outcomes of cerebral I/R injury. In recent years, researchers have found that mitochondrial dysfunction was one of the main factors involved in I/R, and mitochondria is an attractive target in I/R neuroprotection. Therefore, mitochondrial-targeted therapy of the nervous system for I/R gradually started from basic study to clinical application. In the present review, we highlight recent progress in mitochondria fusion and fission in neuronal death induced by cerebral I/R to help understanding the regulatory factors and signaling networks of aberrant mitochondrial fusion and fission contributing to neuronal death during I/R, as well as the potential neuroprotective therapeutics targeting mitochondrial dynamics, which may help clinical treatment and development of relevant dugs.

It takes two to tango: coupling of Hippo pathway and redox signaling in biological process

Hippo pathway is a chain of kinases consists of a series of protein kinases and transcription factors. Meanwhile, oxidative stress is a condition of elevated concentrations of reactive oxygen species (ROS) that cause molecular damage to vital structures and functions. Both of them are key regulators in cell proliferation, survival, and development. These processes are strictly regulated by highly coordinated mechanisms, including c-Jun n-terminal kinase (JNK) pathway, mTOR pathway and a number of extrinsic and intrinsic factors. Recently, emerging evidence suggests that Hippo pathway is involved in the responses to cellular stresses, including mechanic stress, DNA damage, and oxidative stress, to mediate biological process, such as apoptosis, pyroptosis, and metastasis. But the exact mechanism remains to be further explored. Therefore, the purpose of this review is to summarize recent findings and discuss how Hippo pathway, oxidative stress, and the crosstalk between them regulate some biological process which determines cell fate.

Melatonin for prevention of fetal lung injury associated with intrauterine inflammation and for improvement of lung maturation

Inflammation is associated with injury to immature lungs, and melatonin administration to preterm newborns with acute respiratory distress improves pulmonary outcomes. We hypothesized that maternally administered melatonin may reduce inflammation, oxidative stress, and structural injury in fetal lung and help fetal lung maturation in a mouse model of intrauterine inflammation (IUI). Mice were randomized to the following groups: control (C), melatonin (M), lipopolysaccharide (LPS; a model of IUI) (L), and LPS with melatonin (ML). Pro-inflammatory cytokines, components of the Hippo pathway, and Yap1/Taz were analyzed in the fetal lung at E18 by real-time RT-qPCR. Confirmatory histochemistry and immunohistochemical analyses (surfactant protein B, vimentin, HIF-1β, and CXCR2) were performed. The gene expression of IL1β in the fetal lung was significantly increased in L compared to C, M, and ML. Taz expression was significantly decreased in L compared to C and M. Taz gene expression in L was significantly decreased compared with those in ML. Immunohistochemical analyses showed that the expression of HIF-1β and CXCR2 was significantly increased in L compared to C, M, and ML. The area of surfactant protein B and vimentin were significantly decreased in L than C, M, or ML in the fetal and neonatal lung. Antenatal maternally administered melatonin appears to prevent fetal lung injury induced by IUI and to help lung maturation. The results from this study results suggest that melatonin could serve as a novel safe preventive and/or therapeutic medicine for preventing fetal lung injury from IUI and for improving lung maturation in prematurity.

Melatonin-A Potent Therapeutic for Stroke and Stroke-Related Dementia

Secreted by the pineal gland to regulate the circadian rhythm, melatonin is a powerful antioxidant that has been used to combat oxidative stress in the central nervous system. Melatonin-based therapies have been shown to provide neuroprotective effects in the setting of ischemic stroke by mitigating neuroinflammation and accelerating brain tissue restoration. Melatonin treatment includes injection of exogenous melatonin, pineal gland grafting and melatonin-mediated stem cell therapy. This review will discuss the current preclinical and clinical studies investigating melatonin-based therapeutics to treat stroke.

Restoration of L-OPA1 alleviates acute ischemic stroke injury in rats via inhibiting neuronal apoptosis and preserving mitochondrial function

BACKGROUND

Ischemic stroke can induce changes in mitochondrial morphology and function. As a regulatory gene in mitochondria, optic atrophy 1 (OPA1) plays a pivotal role in the regulation of mitochondrial dynamics and other related functions. However, its roles in cerebral ischemia-related conditions are barely understood.

METHODS

Cultured rat primary cortical neurons were respectively transfected with OPA1-v1ΔS1-encoding and OPA1-v1-encoding lentivirus before exposure to 2-h oxygen-glucose deprivation (OGD) and subsequent reoxygenation (OGD/R). Adult male SD rats received an intracranial injection of AAV-OPA1-v1ΔS1 and were subjected to 90 min of transient middle cerebral artery occlusion (tMCAO) followed by reperfusion. OPA1 expression and function were detected by in vitro and in vivo assays.

RESULTS

OPA1 was excessively cleaved after cerebral ischemia/reperfusion injury, both in vitro and in vivo. Under OGD/R condition, compared with that of the LV-OPA1-v1-treated group, the expression of OPA1-v1ΔS1 efficiently restored L-OPA1 level and alleviated neuronal death and mitochondrial morphological damage. Meanwhile, the expression of OPA1-v1ΔS1 markedly improved cerebral ischemia/reperfusion-induced motor function damage, attenuated brain infarct volume, neuronal apoptosis, mitochondrial bioenergetics deficits, oxidative stress, and restored the morphology of mitochondrial cristae and mitochondrial length. It also preserved the mitochondrial integrity and reinforced the mtDNA content and expression of mitochondrial biogenesis factors in ischemic rats.

INTERPRETATION

Our results demonstrate that the stabilization of L-OPA1 protects ischemic brains by reducing neuronal apoptosis and preserving mitochondrial function, suggesting its significance as a promising therapeutic target for stroke prevention and treatment.

Melatonin Attenuates Calcium Deposition from Vascular Smooth Muscle Cells by Activating Mitochondrial Fusion and Mitophagy via an AMPK/OPA1 Signaling Pathway

Mitochondrial fusion/mitophagy plays a role in cardiovascular calcification. Melatonin has been shown to protect against cardiovascular disease. This study sought to explore whether melatonin attenuates vascular calcification by regulating mitochondrial fusion/mitophagy via the AMP-activated protein kinase/optic atrophy 1 (AMPK/OPA1) signaling pathway. The effects of melatonin on vascular calcification were investigated in vascular smooth muscle cells (VSMCs). Calcium deposits were visualized by Alizarin Red S staining, while calcium content and alkaline phosphatase (ALP) activity were used to evaluate osteogenic differentiation. Western blots were used to measure expression of runt-related transcription factor 2 (Runx2), mitofusin 2 (Mfn2), mito-light chain 3 (mito-LC3) II, and cleaved caspase 3. Melatonin markedly reduced calcium deposition and ALP activity. Runx2 and cleaved caspase 3 were downregulated in response to melatonin, whereas Mfn2 and mito-LC3II were enhanced and accompanied by decreased mitochondrial superoxide levels. Melatonin also maintained mitochondrial function and promoted mitochondrial fusion/mitophagy via the OPA1 pathway. However, OPA1 deletion abolished the protective effects of melatonin on VSMC calcification. Melatonin treatment significantly increased p-AMPK and OPA1 protein expression, whereas treatment with compound C ablated the observed benefits of melatonin treatment. Collectively, our results demonstrate that melatonin protects VSMCs against calcification by promoting mitochondrial fusion/mitophagy via the AMPK/OPA1 pathway.

The Role and Regulatory Mechanism of Hippo Signaling Components in the Neuronal System

The Hippo signaling pathway, an evolutionarily conserved protein kinase cascade, plays a critical role in controlling organ size, cancer development, and tissue regeneration. Recently, mounting evidence has suggested that Hippo signaling also has an important role in regulating immunity, including innate and adaptive immune activation. In the neuronal system, Our laboratory results, together with those from other studies, demonstrate that the Hippo signaling pathway is involved in neuroinflammation, neuronal cell differentiation, and neuronal death. In the present review, we summarize the recent findings pertaining to the function and regulatory mechanism of Hippo signaling components in the neuronal system, implicating the potential of Hippo signaling as a therapeutic target for the treatment of neuronal system diseases.

The emerging role of Hippo signaling in neurodegeneration

Neurodegeneration refers to the complex process of progressive degeneration or neuronal apoptosis leading to a set of incurable and debilitating conditions. Physiologically, apoptosis is important in proper growth and development. However, aberrant and unrestricted apoptosis can lead to a variety of degenerative conditions including neurodegenerative diseases. Although dysregulated apoptosis has been implicated in various neurodegenerative disorders, the triggers and molecular mechanisms underlying such untimely and faulty apoptosis are still unknown. Hippo signaling pathway is one such apoptosis-regulating mechanism that has remained evolutionarily conserved from Drosophila to mammals. This pathway has gained a lot of attention for its tumor-suppressing task, but recent studies have emphasized the soaring role of this pathway in inflaming neurodegeneration. In addition, strategies promoting inactivation of this pathway have aided in the rescue of neurons from anomalous apoptosis. So, a thorough understanding of the relationship between the Hippo pathway and neurodegeneration may serve as a guide for the development of therapy for various degenerative diseases. The current review focuses on the mechanism of the Hippo signaling pathway, its upstream and downstream regulatory molecules, and its role in the genesis of numerous neurodegenerative diseases. The recent efforts employing the Hippo pathway components as targets for checking neurodegeneration have also been highlighted.

Melatonin ameliorates cerebral ischemia/reperfusion injury through SIRT3 activation

AIMS

Previous literature has shown that melatonin plays a critical role in protecting against cerebral ischemia/reperfusion (I/R) injury. Sirtuin3(SIRT3), as one member of the sirtuin family, protects against oxidative stress-related diseases. However, the association between melatonin and SIRT3 in cerebral I/R injury is not well understood. Our experiment was planned to investigate whether melatonin protects against cerebral I/R injury through SIRT3 activation.

MAIN METHODS

We selected transient middle cerebral artery occlusion (tMCAO) mice as the model of cerebral I/R injury. Male C57/BL6 mice were pre-treated with or without a selective SIRT3 inhibitor and then subjected to tMCAO surgery. Melatonin (20 mg/kg) was given to mice by intraperitoneal injection after ischemia and before reperfusion. Then, we observed the changes in the SIRT3 and downstream relative proteins, infarction volume, neurological score, Nissl, H&E and TUNEL staining, and the expression of apoptosis proteins after tMCAO.

KEY FINDINGS

Melatonin upregulated the expression of SIRT3 after tMCAO, and alleviated the neurological dysfunction and cell apoptosis through SIRT3 activation.

SIGNIFICANCE

Our research proved that melatonin promoted SIRT3 expression after tMCAO and alleviated cerebral I/R injury by activating the SIRT3 signaling pathway. This study provides novel therapeutic targets and mechanisms for the treatment of ischemic stroke in the clinic, especially during cerebrovascular reperfusion.

Pharmacological Effects of Melatonin as Neuroprotectant in Rodent Model: A Review on the Current Biological Evidence

The progressive loss of structure and functions of neurons, including neuronal death, is one of the main factors leading to poor quality of life. Promotion of functional recovery of neuron after injury is a great challenge in neuroregenerative studies. Melatonin, a hormone is secreted by pineal gland and has antioxidative, anti-inflammatory, and anti-apoptotic properties. Besides that, melatonin has high cell permeability and is able to cross the blood-brain barrier. Apart from that, there are no reported side effects associated with long-term usage of melatonin at both physiological and pharmacological doses. Thus, in this review article, we summarize the pharmacological effects of melatonin as neuroprotectant in central nervous system injury, ischemic-reperfusion injury, optic nerve injury, peripheral nerve injury, neurotmesis, axonotmesis, scar formation, cell degeneration, and apoptosis in rodent models.

Melatonin ameliorates endoplasmic reticulum stress in N2a neuroblastoma cell hypoxia-reoxygenation injury by activating the AMPK-Pak2 pathway

Endoplasmic reticulum (ER) stress has been identified as a primary factor involved in brain ischemia-reperfusion injury progression. p21-activated kinase 2 (Pak2) is a novel ER function regulator. The aim of our study is to explore the influence of Pak2 on ER stress and determine whether melatonin attenuates ER stress-mediated cell death by modulating Pak2 expression in vitro using N2a cells. The results of our study demonstrated that hypoxia-reoxygenation (HR) injury repressed the levels of Pak2, an effect that was accompanied by activation of ER stress. In addition, decreased Pak2 was associated with oxidative stress, calcium overload, and caspase-12-mediated apoptosis activation in HR-treated N2a cells. Interestingly, melatonin treatment reversed the decreased Pak2 expression under HR stress. Knockdown of Pak2 abolished the protective effects of melatonin on ER stress, oxidative stress, and caspase-12-related N2a cells death. Additionally, we found that Pak2 was regulated by melatonin via the AMPK pathway; inhibition of AMPK prevented melatonin-mediated Pak2 upregulation, a result that was accompanied by an increase in N2a cell death. Altogether, these results identify the AMPK-Pak2 axis as a new signaling pathway responsible for ER stress and N2a cell viability under HR injury. Modulation of the AMPK-Pak2 cascade via supplementation of melatonin might be considered an effective approach to attenuate reperfusion-mediated N2a cell damage via repression of ER stress.