Menaquinone-4 Alleviates Neurological Deficits Associated with Intracerebral Hemorrhage by Preserving Corticospinal Tract in Mice.

Menaquinone-4 (MK-4) is an isoform of vitamin K2 that has been shown to exert various biological actions besides its functions in blood coagulation and bone metabolism. Here we examined the effect of MK-4 on a mouse model of intracerebral hemorrhage (ICH). Daily oral administration of 200 mg/kg MK-4 starting from 3 h after induction of ICH by intrastriatal collagenase injection significantly ameliorated neurological deficits. Unexpectedly, MK-4 produced no significant effects on various histopathological parameters, including the decrease of remaining neurons and the increase of infiltrating neutrophils within the hematoma, the increased accumulation of activated microglia/macrophages and astrocytes around the hematoma, as well as the injury volume and brain swelling by hematoma formation. In addition, ICH-induced increases in nitrosative/oxidative stress reflected by changes in the immunoreactivities against nitrotyrosine and heme oxygenase-1 as well as the contents of malondialdehyde and glutathione were not significantly affected by MK-4. In contrast, MK-4 alleviated axon tract injury in the internal capsule as revealed by neurofilament-H immunofluorescence. Enhanced preservation of the corticospinal tract by MK-4 was also confirmed by retrograde labeling of neurons in the primary motor cortex innervating the spinal cord. These results suggest that MK-4 produces therapeutic effect on ICH by protecting structural integrity of the corticospinal tract.

Goreisan regulates cerebral blood flow according to barometric pressure fluctuations in female C57BL/6J mice.

Goreisan is a Kampo medicine used to treat headaches associated with climate change. Here, by using an implantable complementary metal-oxide-semiconductor (CMOS) device, we evaluated the effects of Goreisan and loxoprofen on cerebral blood flow (CBF) dynamics associated with barometric pressure fluctuations in freely moving mice. In the vehicle group, decreasing barometric pressure increased CBF that was prevented by Goreisan and loxoprofen. Notably, Goreisan, but not loxoprofen, reduced CBF after returning to atmospheric pressure. These results indicate that, unlike the mechanism of action of antipyretic analgesics, Goreisan normalizes CBF abnormalities associated with barometric pressure fluctuations by actively reducing CBF increase.

Therapeutic effect of allicin in a mouse model of intracerebral hemorrhage.

Natural compounds with sulfur moiety produce various biological actions that may be beneficial for the therapies of several devastative disorders of the central nervous system. Here we investigated potential therapeutic effect of allicin, an organosulfur compound derived from garlic, in a mouse model of intracerebral hemorrhage (ICH) based on intrastriatal collagenase injection. Daily intraperitoneal administration of allicin (50 mg/kg) from 3 h after induction of ICH afforded neuroprotective effects, as evidenced by the increase of surviving neurons in the hematoma, reduction of axonal transport impairment, and prevention of axon tract injury. In addition, allicin inhibited accumulation of activated microglia/macrophages around the hematoma and infiltration of neutrophils within the hematoma. Allicin also suppressed ICH-induced mRNA upregulation of pro-inflammatory factors such as interleukin 6 and C-X-C motif ligand 2 in the brain, suggesting its anti-inflammatory effect. Moreover, ICH-induced increase of malondialdehyde as well as decrease of total glutathione in the brain was attenuated by allicin. Finally, allicin-treated mice showed better recovery of sensorimotor functions after ICH than vehicle-treated mice. These results indicate that allicin produces a therapeutic effect on ICH pathology via alleviation of neuronal damage, inflammatory responses and oxidative stress in the brain.

Wild-type and pathogenic forms of ubiquilin 2 differentially modulate components of the autophagy-lysosome pathways.

Missense mutations of ubiquilin 2 (UBQLN2) have been identified to cause X-linked amyotrophic lateral sclerosis (ALS). Proteasome-mediated protein degradation is reported to be impaired by ALS-associated mutations of UBQLN2. However, it remains unknown how these mutations affect autophagy-lysosome protein degradation, which consists of macroautophagy (MA), microautophagy (mA), and chaperone-mediated autophagy (CMA). Using a CMA/mA fluorescence reporter we found that overexpression of wild-type UBQLN2 impairs CMA. Conversely, knockdown of endogenous UBQLN2 increases CMA activity, suggesting that normally UBQLN2 negatively regulates CMA. ALS-associated mutant forms of UBQLN2 exacerbate this impairment of CMA. Using cells stably transfected with wild-type or ALS-associated mutant UBQLN2, we further determined that wild-type UBQLN2 increased the ratio of LAMP2A (a CMA-related protein) to LAMP1 (a lysosomal protein). This could represent a compensatory reaction to the impairment of CMA by wild-type UBQLN2. However, ALS-associated mutant UBQLN2 failed to show this compensation, exacerbating the impairment of CMA by mutant UBQLN2. We further demonstrated that ALS-associated mutant forms of UBQLN2 also impair MA, but wild-type UBQLN2 does not. These results support the view that ALS-associated mutant forms of UBQLN2 impair both CMA and MA which may contribute to the neurodegeneration observed in patients with UBQLN2-mediated ALS.

Pharmacological inhibition of Na+/K+-ATPase induces neurovascular degeneration and glial cell alteration in the rat retina.

Na+/K+-ATPase (NKA) plays an important role in ion homeostasis and neurotransmitter uptake. In the retina, multidirectional communications among neurons, glia, and blood vessels (that is, neuro-glio-vascular interaction) are crucial for maintaining tissue homeostasis. We investigated the role of NKA in the elements of neuro-glio-vascular unit in neonatal and adult rat retinas. Male Sprague-Dawley rats (1- and 8-week-old) were injected intravitreally with ouabain (20 nmol/eye), an inhibitor of NKA. Morphological changes in retinal neurons, glia, and blood vessels were examined. The intravitreal injection of ouabain decreased the number of cells in the ganglion cell layer, as well as the thicknesses of the inner plexiform and inner nuclear layers in neonatal and adult rats compared to age-matched controls. The ouabain-induced neuronal cell damage was partially prevented by D-(-)-2-amino-5-phosphonopentanoic acid, an antagonist of N-methyl-D-aspartic acid receptors. In the deep retinal vascular plexus of the ouabain-injected eyes, angiogenesis was delayed in neonatal rats, whereas capillary degeneration occurred in adult rats. The immunoreactivity of glutamine synthetase and vascular endothelial growth factor (VEGF) decreased in the retinas of neonatal and adult rats injected intravitreally with ouabain. The immunoreactivity of glial fibrillary acidic protein was enhanced in the retinas of ouabain-injected adult eyes. After the ouabain injection, CD45-positive leukocytes and Iba1-positive microglia increased in the inner retinal layer of neonatal rats, whereas they increased in the middle retinal layer of adult rats. These results suggest that the inhibition of NKA induces the degeneration of neuronal and vascular cells and alteration of glial cells in both neonatal and adult retinas. In addition to the direct effects of NKA inhibition, the disturbance of retinal glutamate metabolism and decreased VEGF expression may contribute to neurovascular degeneration. The activity of NKA is crucial for maintaining elements of neuro-glio-vascular unit in the retina.

Distinct Pharmacological Profiles of Monosulfide and Trisulfide in an Experimental Model of Intracerebral Hemorrhage in Mice.

Hydrogen sulfide and polysulfides are increasingly recognized as bioactive signaling molecules to produce various actions and regulate (patho)physiological processes. Here we examined the effects of sodium sulfide (Na2S) and sodium trisulfide (Na2S3) on an experimental model of intracerebral hemorrhage (ICH) in mice. Na2S or Na2S3 (25 µmol/kg, intraperitoneally (i.p.)) was administered 30 min before ICH induction by intrastriatal injection of collagenase. We found that Na2S significantly ameliorated sensorimotor functions of mice after ICH. Histopathological examinations revealed that Na2S inhibited neuron loss in the striatum, prevented axon degeneration in the internal capsule, and ameliorated axonal transport dysfunction in the striatum and the cerebral cortex where the edge of hematoma was located. Although Na2S did not suppress accumulation of activated microglia/macrophages in the peri-hematoma region, it suppressed ICH-induced upregulation of inflammatory mediators such as C-X-C motif ligand 2. On the other hand, Na2S3 did not ameliorate ICH-induced sensorimotor dysfunction. Although the effect of Na2S3 on several parameters such as axon degeneration and axonal transport dysfunction was comparable to that of Na2S, Na2S3 did not significantly inhibit neuron loss and upregulation of inflammatory mediators. These results suggest that the regulation of multiple pathological events is involved in the effect of Na2S leading to amelioration of neurological symptoms associated with ICH.

Ataxic phenotype and neurodegeneration are triggered by the impairment of chaperone-mediated autophagy in cerebellar neurons.

AIMS: Chaperone-mediated autophagy (CMA) is a pathway involved in the autophagy lysosome protein degradation system. CMA has attracted attention as a contributing factor to neurodegenerative diseases since it participates in the degradation of disease-causing proteins. We previously showed that CMA is generally impaired in cells expressing the proteins causing spinocerebellar ataxias (SCAs). Therefore, we investigated the effect of CMA impairment on motor function and the neural survival of cerebellar neurons using the micro RNA (miRNA)-mediated knockdown of lysosome-associated protein 2A (LAMP2A), a CMA-related protein. METHODS: We injected adeno-associated virus serotype 9 vectors, which express green fluorescent protein (GFP) and miRNA (negative control miRNA or LAMP2A miRNA) under neuron-specific synapsin I promoter, into cerebellar parenchyma of 4-week-old ICR mice. Motor function of mice was evaluated by beam walking and footprint tests. Immunofluorescence experiments of cerebellar slices were conducted to evaluate histological changes in cerebella. RESULTS: GFP and miRNA were expressed in interneurons (satellite cells and basket cells) in molecular layers and granule cells in the cerebellar cortices, but not in cerebellar Purkinje cells. LAMP2A knockdown in cerebellar neurons triggered progressive motor impairment, prominent loss of cerebellar Purkinje cells, interneurons, granule cells at the late stage, and astrogliosis and microgliosis from the early stage. CONCLUSIONS: CMA impairment in cerebellar interneurons and granule cells triggers the progressive ataxic phenotype, gliosis and the subsequent degeneration of cerebellar neurons, including Purkinje cells. Our present findings strongly suggest that CMA impairment is related to the pathogenesis of various SCAs.

Intracerebroventricular Treatment with 2-Hydroxypropyl-ß-Cyclodextrin Decreased Cerebellar and Hepatic Glycoprotein Nonmetastatic Melanoma Protein B (GPNMB) Expression in Niemann-Pick Disease Type C Model Mice.

Niemann-Pick disease type C (NPC) is a recessive hereditary disease caused by mutation of the NPC1 or NPC2 gene. It is characterized by abnormality of cellular cholesterol trafficking with severe neuronal and hepatic injury. In this study, we investigated the potential of glycoprotein nonmetastatic melanoma protein B (GPNMB) to act as a biomarker reflecting the therapeutic effect of 2-hydroxypropyl-ß-cyclodextrin (HP-ß-CD) in an NPC mouse model. We measured serum, brain, and liver expression levels of GPNMB, and evaluated their therapeutic effects on NPC manifestations in the brain and liver after the intracerebroventricular administration of HP-ß-CD in Npc1 gene-deficient (Npc1-/-) mice. Intracerebroventricular HP-ß-CD inhibited cerebellar Purkinje cell damage in Npc1-/- mice and significantly reduced serum and cerebellar GPNMB levels. Interestingly, we also observed that the intracerebral administration significantly reduced hepatic GPNMB expression and elevated serum ALT in Npc1-/- mice. Repeated doses of intracerebroventricular HP-ß-CD (30 mg/kg, started at 4 weeks of age and repeated every 2 weeks) drastically extended the lifespan of Npc1-/- mice compared with saline treatment. In summary, our results suggest that GPNMB level in serum is a potential biomarker for evaluating the attenuation of NPC pathophysiology by intracerebroventricular HP-ß-CD treatment.

Glucocorticoids negatively regulates chaperone mediated autophagy and microautophagy.

Glucocorticoids are released from the adrenal cortex and are important for regulating various physiological functions. However, a persistent increase in glucocorticoids due to chronic stress causes various dysfunctions in the central nervous system which can lead to mental disorders such as depression. Macroautophagy, one of the pathways of the autophagy-lysosome protein degradation system, is dysregulated in psychiatric disorders, implicating a disturbance of protein degradation in the pathogenesis of psychiatric disorders. In the present study, we investigated whether glucocorticoids affect the activity of chaperone-mediated autophagy (CMA) and microautophagy (mA), the other two pathways of the autophagy-lysosome system. Treatment of human-derived AD293 cells and primary cultured rat cortical neurons with dexamethasone, a potent glucocorticoid receptor agonist, and endogenous glucocorticoids decreased both CMA and mA activities. However, this decrease was significantly suppressed by treatment with RU-486, a glucocorticoid receptor antagonist. In addition, dexamethasone significantly decreased lysosomal Hsc70. These findings suggest that glucocorticoids negatively regulate CMA and mA in a glucocorticoid receptor-dependent manner, and provide evidence for CMA and mA as novel therapeutic targets for depression.

Interactions between rat cortico-striatal slice cultures and neutrophil-like HL60 cells under thrombin challenge: Toward elucidation of pathological events in intracerebral hemorrhage.

Neutrophils constitute the major population of infiltrating leukocytes after stroke including intracerebral hemorrhage (ICH), and these cells may exhibit pro-inflammatory and anti-inflammatory phenotypes depending on the external stimuli. Here we constructed an experimental system to evaluate how the properties of neutrophils were influenced by the injured brain tissues. HL60 cells differentiated into neutrophils were added to the culture medium of neonatal rat cortico-striatal slices maintained at liquid-air interface. Thrombin was applied to the cultures to mimic the pathogenic events associated with ICH. HL60 cells responded to thrombin by increasing mRNA expression of pro-inflammatory IL-1ß and anti-inflammatory IL-10 with a different time course. Co-presence of cortico-striatal slice cultures significantly enhanced IL-1ß mRNA expression, whereas attenuated IL-10 mRNA expression, in HL60 cells. Toll-like receptor 4 (TLR4) agonist lipopolysaccharide synergistically enhanced IL-1ß mRNA expression with thrombin, and TLR4 inhibitor TAK-242 abolished thrombin-induced IL-1ß mRNA expression in the presence of slice cultures. On the other hand, thrombin-induced cell death in cortico-striatal cultures was attenuated by the presence of HL60 cells. This experimental system may provide a unique platform to elucidate complex cell-to-tissue interactions during ICH pathogenesis.

Involvement of exosomes in dopaminergic neurodegeneration by microglial activation in midbrain slice cultures.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive degeneration of dopamine neurons in the substantia nigra. Microglial activation is frequently observed in the brains of patients with PD and animal models. Interferon-γ (IFN-γ)/lipopolysaccharide (LPS) treatment triggers microglial activation and the reduction of dopamine neurons in midbrain slice cultures. We have previously reported that nitric oxide (NO) is mainly involved in this dopaminergic degeneration. However, this degeneration was not completely suppressed by the inhibition of NO synthesis, suggesting that factors other than NO also contribute to dopaminergic neurodegeneration. Exosomes are extracellular vesicles with diameters of 40-200 nm that contain various proteins and micro RNAs and are regarded as a novel factor that mediates cell-to-cell interactions. Previous studies have demonstrated that exosome release is enhanced by microglial stimulation and that microglia-derived exosomes increases neuronal apoptosis. In the present study, we investigated whether exosomes are involved in dopaminergic neurodegeneration triggered by microglial activation in midbrain slice cultures. IFN-γ/LPS treatment to the midbrain slice cultures activated microglia, increased exosomal release, and decreased dopamine neurons. GW4869, an inhibitor of a neutral sphingomyelinase 2, decreased exosomal release and significantly prevented dopaminergic neurodegeneration by IFN-γ/LPS without affecting NO production. In contrast, D609, an inhibitor of sphingomyelin synthase and NO synthase, did not affect dopaminergic neurodegeneration, although it strongly inhibited NO production. The protective effect mediated by inhibition of NO synthase would be counteracted by enhanced exosomal release caused by D609 treatment. In addition, dopaminergic neurodegeneration is triggered by the treatment of exosomes isolated from culture media of IFN-γ/LPS-treated slices. These results suggest that exosomes are involved in dopaminergic neurodegeneration by microglial activation.

Propranolol prevents cerebral blood flow changes and pain-related behaviors in migraine model mice.

Propranolol, a ß-adrenergic receptor blocker, is one of the most commonly used prophylactic drugs for migraines. Cortical spreading depression (CSD) is the propagation wave of neuronal excitation along with cerebral blood flow (CBF) changes over the cerebral cortex and has been implicated in the pathological process of migraine auras and its pain response. However, the effect of propranolol on CSD-related CBF changes and behavioral responses remains poorly understood. In this study, we measured CSD-related CBF responses using a micro-device with a green light emitting diode (LED) and micro-complementary-metal-oxide-semiconductor (CMOS) image sensor and evaluated pain-related reduced locomotor activity in mice. An injection of KCl into the visual cortex led to CSD-related CBF changes; however, propranolol prevented the increase in CBF as well as delayed the propagation velocity in KCl-induced CSD. Furthermore, an injection of KCl reduced locomotor activity and induced freezing behavior in awake and freely moving mice, which were prevented by propranolol treatment. These results suggest that the modulation of CSD-related CBF responses by the blockade of ß-adrenergic receptor contributes to its prophylactic effects on migraines.

Chronic memantine administration prevents ouabain-induced hyperactivity in mice via maintenance of Na+, K+-ATPase activity in the hippocampus.

We have previously reported that mice received intracerebroventricular injection of ouabain, an inhibitor of Na+, K+-ATPase, exhibited hyperactivity via overactivation of glutamatergic neurons. Here we investigated the effects of memantine, a blocker of N-methyl-d-aspartate receptors, on ouabain-induced hyperactivity. In mice that received ouabain injection, chronic memantine administration prevented the hyperactivity and the decrease in the Na+, K+-ATPase activity in the hippocampus. Memantine also protected neurons without affecting glial activation in the hippocampus of these mice. Our results suggest that memantine improves hyperactivity via the maintenance of Na+, K+-ATPase activity and neurons in the hippocampus in this mouse model.

Rapamycin activates mammalian microautophagy.

Autophagy-lysosome proteolysis is classified into macroautophagy (MA), microautophagy (mA) and chaperone-mediated autophagy (CMA). In contrast to MA and CMA, mA have been mainly studied in yeast. In 2011, mammalian mA was identified as a pathway to deliver cytosolic proteins into multivesicular bodies. However, its molecular mechanism is quite different from yeast mA. Using a cell-based method to evaluate mA and CMA, we revealed that rapamycin, an activator of yeast mA, significantly activated mammalian mA. Although rapamycin activates MA, mA was also activated by rapamycin in MA-deficient cells. These findings suggest that rapamycin is a first-identified activator of mammalian mA.

Reciprocal Regulation of Chaperone-Mediated Autophagy/Microautophagy and Exosome Release.

Autophagy-lysosome proteolysis is involved in protein quality control and classified into macroautophagy (MA), microautophagy (mA) and chaperone-mediated autophagy (CMA), by the routes of substrate delivery to lysosomes. Both autophagy-lysosome proteolysis and exosome release are strongly associated with membrane trafficking. In the present study, we investigated how chemical and small interfering RNA (siRNA)-mediated activation and inhibition of these autophagic pathways affect exosome release in AD293 cells. Activation of MA and mA by rapamycin and activation of CMA by mycophenolic acid significantly decreased exosome release. Although lysosomal inhibitors, NH4Cl and bafilomycin A1, significantly increased exosome release, a MA inhibitor, 3-methyladenine, did not affect. Exosome release was significantly increased by the siRNA-mediated knockdown of LAMP2A, which is crucial for CMA. Inversely, activity of CMA/mA was significantly increased by the prevention of exosome release, which was induced by siRNA-mediated knockdown of Rab27a. These findings indicate that CMA/mA and exosome release are reciprocally regulated. This regulation would be the molecular basis of extracellular release and propagation of misfolded proteins in various neurodegenerative diseases.

d-Cysteine promotes dendritic development in primary cultured cerebellar Purkinje cells via hydrogen sulfide production.

Hydrogen sulfide and reactive sulfur species are regulators of physiological functions, have antioxidant effects against oxidative stresses, and are endogenously generated from l-cysteine. Recently, a novel pathway that generates hydrogen sulfide and reactive sulfur species from d-cysteine has been identified. d-Amino acid oxidase (DAO) is involved in this pathway and, among the various brain regions, is especially abundant in the cerebellum. d-Cysteine has been found to be a better substrate in the generation of hydrogen sulfide in the cerebellum than l-cysteine. Therefore, d-cysteine might be a novel neuroprotectant against cerebellar diseases such as spinocerebellar ataxia (SCA). However, it remains unknown if d-cysteine affects cerebellar Purkinje cells (PCs), which are important for cerebellar functions and are frequently degenerated in SCA patients. In the present study, we investigated whether the production of hydrogen sulfide from d-cysteine affects the dendritic development of cultured PCs. d-Cysteine was found to enhance the dendritic development of PCs significantly, while l-cysteine impaired it. The effect of d-cysteine was inhibited by simultaneous treatment with DAO inhibitors and was reproduced by treatment with 3-mercaptopyruvate, a metabolite of d-cysteine produced by the action of DAO, and disodium sulfide, a donor of hydrogen sulfide. In addition, hydrogen sulfide was immediately produced in cerebellar primary cultures after treatment with d-cysteine and 3-mercaptopyruvate. These findings suggest that d-cysteine enhances the dendritic development of primary cultured PCs via the generation of hydrogen sulfide.

Antileukemic Activity of Twig Components of Caucasian Beech in Turkey.

Despite the development of a range of anti-cancer agents, cancer diagnoses are still increasing in number, remaining a leading cause of death. Anticancer drug treatment is particularly important for leukemia. We screened Turkish plants and found the unique antileukemic activity of twig components in Turkish Caucasian beech, selectively inducing apoptosis in leukemia cells. This effect is unique among some kinds of beeches, presumably related to oxidative stress. This study would lead to effective use of discarded material, i.e., twig of beech, and a new anti-leukemic drug based on large tree.

Lysosomal dysfunction and early glial activation are involved in the pathogenesis of spinocerebellar ataxia type 21 caused by mutant transmembrane protein 240.

Spinocerebellar ataxia type 21 (SCA21) is caused by missense or nonsense mutations of the transmembrane protein 240 (TMEM240). Molecular mechanisms of SCA21 pathogenesis remain unknown because the functions of TMEM240 have not been elucidated. We aimed to reveal the molecular pathogenesis of SCA21 using cell and mouse models that overexpressed the wild-type and SCA21 mutant TMEM240. In HeLa cells, overexpressed TMEM240 localized around large cytoplasmic vesicles. The SCA21 mutation did not affect this localization. Because these vesicles contained endosomal markers, we evaluated the effect of TMEM240 fused with a FLAG tag (TMEM-FL) on endocytosis and autophagic protein degradation. Wild-type TMEM-FL significantly impaired clathrin-mediated endocytosis, whereas the SCA21 mutants did not. The SCA21 mutant TMEM-FL significantly impaired autophagic lysosomal protein degradation, in contrast to wild-type. Next, we investigated how TMEM240 affects the neural morphology of primary cultured cerebellar Purkinje cells (PCs). The SCA21 mutant TMEM-FL significantly prevented the dendritic development of PCs, in contrast to the wild-type. Finally, we assessed mice that expressed wild-type or SCA21 mutant TMEM-FL in cerebellar neurons using adeno-associated viral vectors. Mice expressing the SCA21 mutant TMEM-FL showed impaired motor coordination. Although the SCA21 mutant TMEM-FL did not trigger neurodegeneration, activation of microglia and astrocytes was induced before motor miscoordination. In addition, immunoblot experiments revealed that autophagic lysosomal protein degradation, especially chaperone-mediated autophagy, was also impaired in the cerebella that expressed the SCA21 mutant TMEM-FL. These dysregulated functions in vitro, and induction of early gliosis and lysosomal impairment in vivo by the SCA21 mutant TMEM240 may contribute to the pathogenesis of SCA21.

Na+, K+-ATPase inhibition induces neuronal cell death in rat hippocampal slice cultures: Association with GLAST and glial cell abnormalities.

Na+, K+-ATPase is a highly expressed membrane protein. Dysfunction of Na+, K+-ATPase has been implicated in the pathophysiology of several neurodegenerative and psychiatric disorders, however, the underlying mechanism of neuronal cell death resulting from Na+, K+-ATPase dysfunction is poorly understood. Here, we investigated the mechanism of neurotoxicity due to Na+, K+-ATPase inhibition using rat organotypic hippocampal slice cultures. Treatment with ouabain, a Na+, K+-ATPase inhibitor, increased the ratio of propidium iodide-positive cells among NeuN-positive cells in the hippocampal CA1 region, which was prevented by MK-801 and d-AP5, specific blockers of the N-methyl-d-aspartate (NMDA) receptor. EGTA, a Ca2+-chelating agent, also protected neurons from ouabain-induced injury. We observed that astrocytes expressed the glutamate aspartate transporter (GLAST), and ouabain changed the immunoreactive area of GFAP-positive astrocytes as well as GLAST. We also observed that ouabain increased the number of Iba1-positive microglial cells in a time-dependent manner. Furthermore, lithium carbonate, a mood-stabilizing drug, protected hippocampal neurons and reduced disturbances of astrocytes and microglia after ouabain treatment. Notably, lithium carbonate improved ouabain-induced decreases in GLAST intensity in astrocytes. These results suggest that glial cell abnormalities resulting in excessive extracellular concentrations of glutamate contribute to neurotoxicity due to Na+, K+-ATPase dysfunction in the hippocampal CA1 region.

Polysulfide protects midbrain dopaminergic neurons from MPP+-induced degeneration via enhancement of glutathione biosynthesis.

Polysulfides are endogenous sulfur-containing molecular species that may regulate various cellular functions. Here we examined the effect of polysulfides exogenously applied to rat midbrain slice cultures, to address their potential neuroprotective actions. Na2S3 at concentrations of 10 µM or higher prevented 1-methyl-4-phenylpyridinium (MPP+)-induced loss of dopaminergic neurons. Na2S4 at 10 µM also protected dopaminergic neurons from MPP+ cytotoxicity, whereas Na2S and Na2S2 at the same concentration had no significant effect. We also found that Na2S3 (10 µM) prevented MPP+-induced increase in intracellular reactive oxygen species as detected by 2',7'-dichlorofluorescein fluorescence. In addition, the protective effect of Na2S3 was abolished by l-buthionine sulfoximine, an inhibitor of glutathione synthesis. In cellular models of neurons (SH-SY5Y cells) and glial cells (C6 cells), Na2S3 (30 and 100 µM) increased expression of mRNAs encoding the subunits of glutamate cysteine ligase, the rate-limiting enzyme for glutathione biosynthesis. Consistently, the cellular content of total glutathione was increased by Na2S3, and the effect was more prominent in SH-SY5Y cells than in C6 cells. These results suggest that polysulfides are efficient neuroprotectants superior to monosulfur species such as H2S and HS-, and that the neuroprotective effect of polysulfides is mediated by upregulation of glutathione biosynthesis.