Induction of nitric oxide synthase in glial cells

The Role of Glial Cells in Neurobiology and Prion Neuropathology

Prion diseases are rare and neurodegenerative diseases that are characterized by the misfolding and infectious spread of the prion protein in the brain, causing progressive and irreversible neuronal loss and associated clinical and behavioral manifestations in humans and animals, ultimately leading to death. The brain has a complex network of neurons and glial cells whose crosstalk is critical for function and homeostasis. Although it is established that prion infection of neurons is necessary for clinical disease to occur, debate remains in the field as to the role played by glial cells, namely astrocytes and microglia, and whether these cells are beneficial to the host or further accelerate disease. Here, we review the current literature assessing the complex morphologies of astrocytes and microglia, and the crosstalk between these two cell types, in the prion-infected brain.

Hypoxia-induced expression of neuronal nitric oxide synthase in astrocytes of human corpus callosum

Nitric oxide (NO) is a gaseous neurotransmitter largely diffused in the brain; among other functions, it regulates the cerebral blood flow in response to hypoxia. NO can be synthetized by three different isoforms of the enzyme NO synthase: neuronal (nNOS), typical of neurons, endothelial and inducible. The aim of this study was to assess nNOS expression in human corpus callosum (CC) astrocytes, and its relationship with the hypoxia duration. Autoptic samples of CC from adult human subjects have been processed with immunohistochemistry and immunofluorescence using antibodies anti-nNOS and anti-glial fibrillary acidic protein (GFAP), the astrocyte marker. Results demonstrated for the first time the presence of nNOS-immunopositive astrocytes in the human CC. In particular, nNOS-positive astrocytes were absent in subjects deceased after a short hypoxia; their number and labeling intensity, however, increased with hypoxia prolongation. Neuronal NOS immunopositivity of CC astrocytes seems thus related to the hypoxia duration and the consequent brain damage.

Large magnitude of force leads to NO-mediated cell shrinkage in single osteocytes implying an initial apoptotic response

Damage accumulation in the bone under continuous daily loading causes local mechanical overloading known to induce osteocyte apoptosis, which promotes bone resorption to repair bone damage. However, only a few studies have investigated the mechanism of apoptosis in mechanically overloaded osteocytes. As mechanically stimulated osteocytes produce nitric oxide (NO), which triggers apoptosis in various cell types, we aimed to elucidate the mechanism underlying apoptosis in mechanically overloaded osteocytes, focusing on intracellular NO. To investigate the effects of force magnitude on apoptosis and intracellular NO production, we isolated osteocytes from DMP1-EGFP mice and subjected them to quantitative local forces via fibronectin-coated micro beads targeting integrin on the cell surface using a magnetic tweezer. Cell shrinkage was microscopically examined, and intracellular NO production was visualized using DAR-4 M. Mechanical stimulation revealed relationships between force magnitude, apoptosis, and intracellular NO production. The application of a smaller force resulted in no significant cell shrinkage or intracellular NO production; however, a larger force caused a rapid increase in intracellular NO production followed by cell shrinkage. Besides, intracellular NOS (NO synthase) inhibition and NO donation revealed the pro-apoptotic roles of NO in osteocytes. L-NAME (NOS inhibitor)-treated cells displayed no significant shrinkage under a larger force, whereas SNP (NO donor)-treated cells showed cell shrinkage and Annexin V fluorescence, indicating apoptosis. Collectively, our study demonstrates that larger force leads to NO production-mediated osteocyte shrinkage, implying an initial apoptotic response and highlighting the importance of NO production in bone damage.

Dual PPARα/γ agonist aleglitazar confers stroke protection in a model of mild focal brain ischemia in mice

Abstract

Peroxisome proliferator-activated receptors (PPARs) control the expression of genes involved in glucose homeostasis, lipid metabolism, inflammation, and cell differentiation. Here, we analyzed the effects of aleglitazar, a dual PPARα and PPARγ agonist with balanced affinity for either subtype, on subacute stroke outcome. Healthy young adult mice were subjected to transient 30 min middle cerebral artery occlusion (MCAo)/reperfusion. Daily treatment with aleglitazar was begun on the day of MCAo and continued until sacrifice. Blood glucose measurements and lipid profile did not differ between mice receiving aleglitazar and mice receiving vehicle after MCAo. Aleglitazar reduced the size of the ischemic lesion as assessed using NeuN immunohistochemistry on day 7. Sensorimotor performance on the rotarod was impaired during the first week after MCAo, an effect that was significantly attenuated by treatment with aleglitazar. Smaller lesion volume in mice treated with aleglitazar was accompanied by a decrease in mRNA transcription of IL-1β, Vcam-1, and Icam-1, suggesting that reduced proinflammatory signaling and reduced vascular inflammation in the ischemic hemisphere contribute to the beneficial effects of aleglitazar during the first week after stroke. Further experiments in primary murine microglia confirmed that aleglitazar reduces key aspects of microglia activation including NO production, release of proinflammatory cytokines, migration, and phagocytosis. In aggregate, a brief course of PPARα/γ agonist aleglitazar initiated post-event affords stroke protection and functional recovery in a model of mild brain ischemia. Our data underscores the theme of delayed injury processes such as neuroinflammation as promising therapeutic targets in stroke.

Key messages

PPARα/γ agonist aleglitazar improves stroke outcome after transient brain ischemia.

Aleglitazar attenuates inflammatory responses in post-ischemic brain.

Aleglitazar reduces microglia migration, phagocytosis, and release of cytokines.

Beneficial effects of aleglitazar independent of glucose regulation.

Aleglitazar provides extended window of opportunity for stroke treatment.

Targeting strategies for chemotherapy-induced peripheral neuropathy: does gut microbiota play a role?

Chemotherapy-induced peripheral neuropathy (CIPN) is a progressive, often irreversible condition that produces severe neurological deficits. Emerging data suggest that chemotherapy also exerts detrimental effects on gut microbiota composition and intestinal permeability, contributing to dysbiosis and inflammation. Compared with other complications associated with chemotherapy, such as diarrhoea and mucositis, CIPN is of particular concern because it is the most common reason for terminating or suspending treatment. However, specific and effective curative treatment strategies are lacking. In this review, we provide an update on current preclinical and clinical understandings about the role of gut microbiota in CIPN. The gut microbiota serves as an intersection between the microbiome-gut-brain and the neuroimmune-endocrine axis, forming a complex network that can directly or indirectly affect key components involved in the manifestations of CIPN. Herein, we discuss several potential mechanisms within the context of the networks and summarize alterations in gut microbiome induced by chemotherapeutic drugs, providing great potential for researchers to target pathways associated with the gut microbiome and overcome CIPN.

Expression and Purification of Quinine Dihydro Pteridine Reductase from astrocytes and its significance in the astrocyte pathology

Quinine dihydropteridinereductase (QDPR) is involved in the synthesis of tetradihydrobiopteridine (BH4) that serve as cofactor for many aromatic hydroxylases including induced nitric oxide synthase (NOS) leading to NO production. Increased activity of QDPR has been associated with decrease levels of TGF-β, a cytokine that regulates the immune response and that elevated levels of NO has been associated with neurodegenerative diseases. Thus, expression of QDPR in astrocytes is essential to study the pathological changes observed in many neurodegenerative disorders. We have expressed QDPR in astrocytes and generated stably expressing clones that overexpresses QDPR. We further verified the specificity of QDPR expression using immunofluorescence and immunoblotting. To further confirm, we purified QDPR using Ni-NTA column and subjected the purified fraction to immunoblotting using anti-QDPR antibody and identified two major protein products of QDPR resolving at 25 and 17 kDa as reported in the literature. In order to further assess the significance of QDPR expression, we verified the expression of iNOS in QDPR over expressing cells. We show for the first time statistically significant up regulation of iNOS in QDPR overexpressing astrocytes. Increased expression of iNOS associated with astrocyte pathology seen in many neurodegenerative disorders may have implications in autoimmune neurodegenerative disorders.

The importance of controlling in vitro oxygen tension to accurately model in vivo neurophysiology

The majority of in vitro studies modeling in vivo conditions are performed on the lab bench in atmospheric air. However, the oxygen tension (pO₂) present in atmospheric air (160mm Hg, ∼21% O₂) is in great excess to the pO₂ that permeates tissues within the brain (5-45mm Hg, ∼1-6% O₂). This review will discuss the differentiation between pO₂ in the in vivo environment and the pO₂ commonly used during in vitro experiments, and how this could affect assay outcomes. Also highlighted are studies linking changes in pO₂ to changes in cellular function, particularly the role of pO₂ in mitochondrial function, reactive oxygen species production, and cellular growth and differentiation. The role of hypoxia inducible factor 1 and oxygen sensing is also presented. Finally, emerging literature exploring sex differences in tissue oxygenation is discussed.

NOS Expression and NO Function in Glioma and Implications for Patient Therapies

SIGNIFICANCE

Gliomas are central nervous system tumors that primarily occur in the brain and arise from glial cells. Gliomas include the most common malignant brain tumor in adults known as grade IV astrocytoma, or glioblastoma (GBM). GBM is a deadly disease for which the most significant advances in treatment offer an improvement in survival of only ∼2 months.

CRITICAL ISSUES

To develop novel treatments and improve patient outcomes, we and others have sought to determine the role of molecular signals in gliomas. Recent Advances: One signaling molecule that mediates important biologies in glioma is the free radical nitric oxide (NO). In glioma cells and the tumor microenvironment, NO is produced by three isoforms of nitric oxide synthase (NOS), NOS1, NOS2, and NOS3. NO and NOS affect glioma growth, invasion, angiogenesis, immunosuppression, differentiation state, and therapeutic resistance.

FUTURE DIRECTIONS

These multifaceted effects of NO and NOS on gliomas both in vitro and in vivo suggest the potential of modulating the pathway for antiglioma patient therapies. Antioxid. Redox Signal. 26, 986-999.

Reflections on 60 years of publication of the Journal of Neurochemistry

This review reflects on the origins, development, publishing trends, and scientific directions of the Journal of Neurochemistry over its 60 year lifespan as seen by key contributors to the Journal's production. The Journal first appeared in May 1956 with just two issues published in that inaugural year. By 1963, it appeared monthly and, by 2002, 24 hard copy issues were published yearly. In 2014, the Journal became online only. For much of its time, the Journal was managed through two separate editorial offices each with their respective Chief Editor (the 'Western' and 'Eastern' hemispheres). The Journal was restructured to operate through a single editorial office and Editor-in-Chief from 2013. Scientifically, the Journal progressed through distinct scientific eras with the first two decades generally centered around developments in methodology followed by a period when publications delved deeper into underlying mechanisms. By the late 1980s, the Journal had entered the age of genetics and beyond, with an increasing focus on neurodegenerative diseases. Reviews have played a regular part in the success of J Neurochem with focused special and virtual issues being a highlight of recent years. Today, 60 years and onwards, J Neurochem continues to be a leading source of top-quality, original and review articles in neuroscience. We look forward to its continued success at the forefront of neurochemistry in the decades to come. This article celebrates 60 years of publication of Journal of Neurochemistry including personal reminiscences from some of the Chief Editors, past and present, as well as input from some of the key contributors to the Journal over this period. We highlight the scientific, technological, and publishing developments along the way, with reference to key papers published in the Journal. The support of the Journal toward the aims and objectives of the International Society for Neurochemistry (ISN) is also emphasized. This article is part of the 60th Anniversary special issue.

Induction of inducible nitric oxide synthase expression in ammonia-exposed cultured astrocytes is coupled to increased arginine transport by upregulated y(+)LAT2 transporter

One of the aspects of ammonia toxicity to brain cells is increased production of nitric oxide (NO) by NO synthases (NOSs). Previously we showed that ammonia increases arginine (Arg) uptake in cultured rat cortical astrocytes specifically via y(+)L amino acid transport system, by activation of its member, a heteromeric y(+)LAT2 transporter. Here, we tested the hypothesis that up-regulation of y(+)LAT2 underlies ammonia-dependent increase of NO production via inducible NOS (iNOS) induction, and protein nitration. Treatment of rat cortical astrocytes for 48 with 5 mM ammonium chloride ('ammonia') (i) increased the y(+)L-mediated Arg uptake, (ii) raised the expression of iNOS and endothelial NOS (eNOS), (iii) stimulated NO production, as manifested by increased nitrite+nitrate (Griess) and/or nitrite alone (chemiluminescence), and consequently, (iv) evoked nitration of tyrosine residues of proteins in astrocytes. Except for the increase of eNOS, all the above described effects of ammonia were abrogated by pre-treatment of astrocytes with either siRNA silencing of the Slc7a6 gene coding for y(+)LAT2 protein, or antibody to y(+)LAT2, indicating their strict coupling to y(+)LAT2 activity. Moreover, induction of y(+)LAT2 expression by ammonia was sensitive to Nf-κB inhibitor, BAY 11-7085, linking y(+)LAT2 upregulation to the Nf-κB activation in this experimental setting as reported earlier and here confirmed. Importantly, ammonia did not affect y(+)LAT2 expression nor y(+)L-mediated Arg uptake activity in the cultured cerebellar neurons, suggesting astroglia-specificity of the above described mechanism. The described coupling of up-regulation of y(+)LAT2 transporter with iNOS in ammonia-exposed astrocytes may be considered as a mechanism to ensure NO supply for protein nitration. Ammonia (NH4(+)) increases the expression and activity of the L-arginine (Arg) transporter (Arg/neutral amino acids [NAA] exchanger) y(+)LAT2 in cultured rat cortical astrocytes by a mechanism involving activation (nuclear translocation) of the transcription factor nuclear factor-Nuclear factor-κB (Nf-κB-p65). Up-regulation of y(+)LAT2 transporter is coupled with increased inducible nitric oxide synthase (iNOS) expression, which leads to increase nitric oxide (NO) synthesis and protein nitration.

Hyperglycemia reduces functional expression of astrocytic Kir4.1 channels and glial glutamate uptake

Diabetics are at risk for a number of serious health complications including an increased incidence of epilepsy and poorer recovery after ischemic stroke. Astrocytes play a critical role in protecting neurons by maintaining extracellular homeostasis and preventing neurotoxicity through glutamate uptake and potassium buffering. These functions are aided by the presence of potassium channels, such as Kir4.1 inwardly rectifying potassium channels, in the membranes of astrocytic glial cells. The purpose of the present study was to determine if hyperglycemia alters Kir4.1 potassium channel expression and homeostatic functions of astrocytes. We used q-PCR, Western blot, patch-clamp electrophysiology studying voltage and potassium step responses and a colorimetric glutamate clearance assay to assess Kir4.1 channel levels and homeostatic functions of rat astrocytes grown in normal and high glucose conditions. We found that astrocytes grown in high glucose (25 mM) had an approximately 50% reduction in Kir4.1 mRNA and protein expression as compared with those grown in normal glucose (5mM). These reductions occurred within 4-7 days of exposure to hyperglycemia, whereas reversal occurred between 7 and 14 days after return to normal glucose. The decrease in functional Kir channels in the astrocytic membrane was confirmed using barium to block Kir channels. In the presence of 100-μM barium, the currents recorded from astrocytes in response to voltage steps were reduced by 45%. Furthermore, inward currents induced by stepping extracellular [K(+)]o from 3 to 10mM (reflecting potassium uptake) were 50% reduced in astrocytes grown in high glucose. In addition, glutamate clearance by astrocytes grown in high glucose was significantly impaired. Taken together, our results suggest that down-regulation of astrocytic Kir4.1 channels by elevated glucose may contribute to the underlying pathophysiology of diabetes-induced CNS disorders and contribute to the poor prognosis after stroke.

Inducible nitric oxide synthase in neutrophils and endothelium contributes to ischemic brain injury in mice

NO produced by inducible NO synthase (iNOS) contributes to ischemic brain injury, but the cell types expressing iNOS and mediating tissue damage have not been elucidated. To examine the relative contribution of iNOS in resident brain cells and peripheral leukocytes infiltrating the ischemic brain, we used bone marrow (BM) chimeric mice in which the middle cerebral artery was occluded and infarct volume was determined 3 d later. iNOS(-/-) mice engrafted with iNOS(+/+) BM exhibited larger infarcts (44 ± 2 mm(3); n = 13; mean ± SE) compared with autologous transplanted iNOS(-/-) mice (24 ± 3 mm(3); n = 10; p < 0.01), implicating blood-borne leukocytes in the damage. Furthermore, iNOS(+/+) mice transplanted with iNOS(-/-) BM had large infarcts (39 ± 6 mm(3); n = 13), similar to those of autologous transplanted iNOS(+/+) mice (39 ± 4 mm(3); n = 14), indicating the resident brain cells also play a role. Flow cytometry and cell sorting revealed that iNOS is highly expressed in neutrophils and endothelium but not microglia. Surprisingly, postischemic iNOS expression was enhanced in the endothelium of iNOS(+/+) mice transplanted with iNOS(-/-) BM and in leukocytes of iNOS(-/-) mice with iNOS(+/+) BM, suggesting that endothelial iNOS suppresses iNOS expression in leukocytes and vice versa. To provide independent evidence that neutrophils mediate brain injury, neutrophils were isolated and transferred to mice 24 h after stroke. Consistent with the result in chimeric mice, transfer of iNOS(+/+), but not iNOS(-/-), neutrophils into iNOS(-/-) mice increased infarct volume. The findings establish that iNOS in both neutrophils and endothelium mediates tissue damage and identify these cell types as putative therapeutic targets for stroke injury.

AMP-activated protein kinase is involved in induction of protective autophagy in astrocytes exposed to oxygen-glucose deprivation

AMP-activated kinase (AMPK) acts as the intracellular ATP depletion sensor, which detects and limits increases in the AMP/ATP ratio. AMPK may be significantly activated under stress conditions that deplete cellular ATP levels such as ischemia/hypoxia or glucose deprivation. Recent studies strongly suggest that AMPK participates in autophagy regulation, but it is not known whether AMPK activated by ischemia regulates autophagy in astrocytes and the consequence of autophagy activation in ischemic astrocytes are unclear. We have investigated the contribution of AMPK to autophagy activation in rat primary astrocyte cultures subjected to ischemia-simulating conditions (combined oxygen glucose deprivation, OGD) and its potential effects on astrocyte damage induced by OGD (1-12 h). The evidence supports the conclusion that AMPK activation at early stages of OGD is involved in induction of protective autophagy in astrocytes. Inhibition of AMPK, either by siAMPKα1 or by compound C, significantly attenuated the expression of autophagy-related proteins and decrease of astrocyte viability following OGD. The findings provide additional data about the role of AMPK in ischemic astrocytes and downstream responses that may be involved in OGD-induced protective autophagy.

Protective effect of pitavastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, on ischemia-induced neuronal damage

We investigated the neuroprotective effects of a novel 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor (pitavastatin) on ischemic neuronal damage in gerbils using immunohistochemistry. The animals were allowed to survive for 14 days after 5 min of ischemia induced by bilateral occlusion of the common carotid arteries. Five days after ischemia, severe neuronal cell loss was observed in the hippocampal CA1 sector. Prophylactic treatment with pitavastatin dose-dependently prevented the hippocampal CA1 neuronal cell loss 5 days after ischemia. Immunohistochemical study did not show the change of nNOS and iNOS expression in the hippocampus except for, in a few regions, up to 1 day after ischemia. Thereafter, the expression of iNOS was observed in the hippocampal CA1 sector 5 and 14 days after ischemia. In contrast, the expression of nNOS and eNOS gradually decreased in the hippocampal CA1 sector up to 14 days after ischemia. Prophylactic treatment with pitavastatin also prevented the expression of iNOS and the decrease of eNOS expression and the number of nNOS-positive cells in the hippocampal CA1 sector 5 days after ischemia. However, prophylactic treatment with pitavastatin at a dose of 10 mg kg(-1) did not change the immunoreactivity of iNOS and nNOS in the hippocampus at an early phase after ischemia. In contrast, this drug prevented the reduction of eNOS immunoreactivity in the hippocampal CA1 neurons at an early phase after ischemia. These findings demonstrate that the HMG-CoA reductase inhibitor pitavastatin can protect hippocampal CA1 neurons after transient forebrain ischemia through up-regulation of eNOS expression in this region. Thus pharmacological modulation of eNOS expression may offer a novel therapeutic strategy for cerebral ischemic stroke.

Nitric oxide as a regulatory molecule in the processing of the visual stimulus

Nitric oxide (NO) is a highly reactive gas with considerable diffusion power that is produced pre- and post synaptically in the central nervous system (CNS). In the visual system, it is involved in the processing of the visual information from the retina to superior visual centers. In this review we discuss the main mechanisms through which nitric oxide acts, in physiological levels, on the retina, lateral geniculate nucleus (LGN) and primary visual cortex. In the retina, the cGMP-dependent nitric oxide activity initially amplifies the signal, subsequently increasing the inhibitory activity, suggesting that the signal is "filtered". In the thalamus, on dLGN, neuronal activity is amplified by NO derived from brainstem cholinergic cells, in a cGMP-independent mechanism; the result is the amplification of the signal arriving from retina. Finally, on the visual cortex (V1), NO acts through changes on the cGMP levels, increasing signal detection. These observations suggest that NO works like a filter, modulating the signal along the visual pathways.

The role of astrocytes in CNS tumors: pre-clinical models and novel imaging approaches

Brain metastasis is a significant clinical problem, yet the mechanisms governing tumor cell extravasation across the blood-brain barrier (BBB) and CNS colonization are unclear. Astrocytes are increasingly implicated in the pathogenesis of brain metastasis but in vitro work suggests both tumoricidal and tumor-promoting roles for astrocyte-derived molecules. Also, the involvement of astrogliosis in primary brain tumor progression is under much investigation. However, translation of in vitro findings into in vivo and clinical settings has not been realized. Increasingly sophisticated resources, such as transgenic models and imaging technologies aimed at astrocyte-specific markers, will enable better characterization of astrocyte function in CNS tumors. Techniques such as bioluminescence and in vivo fluorescent cell labeling have potential for understanding the real-time responses of astrocytes to tumor burden. Transgenic models targeting signaling pathways involved in the astrocytic response also hold great promise, allowing translation of in vitro mechanistic findings into pre-clinical models. The challenging nature of in vivo CNS work has slowed progress in this area. Nonetheless, there has been a surge of interest in generating pre-clinical models, yielding insights into cell extravasation across the BBB, as well as immune cell recruitment to the parenchyma. While the function of astrocytes in the tumor microenvironment is still unknown, the relationship between astrogliosis and tumor growth is evident. Here, we review the role of astrogliosis in both primary and secondary brain tumors and outline the potential for the use of novel imaging modalities in research and clinical settings. These imaging approaches have the potential to enhance our understanding of the local host response to tumor progression in the brain, as well as providing new, more sensitive diagnostic imaging methods.

Depression after myocardial infarction: TNF-α-induced alterations of the blood-brain barrier and its putative therapeutic implications

Patients experiencing an acute myocardial infarction (AMI) have a three times higher chance to develop depression. Vice versa, depressive symptoms increase the risk of cardiovascular events. The co-existence of both conditions is associated with substantially worse prognosis. Although the underlying mechanism of the interaction is largely unknown, inflammation is thought to be of pivotal importance. AMI-induced peripheral cytokines release may cause cerebral endothelial leakage and hence induces a neuroinflammatory reaction. The neuroinflammation may persist even long after the initial peripheral inflammation has subsided. Among those selected brain regions that are prone to blood-brain barrier dysfunction, the paraventricular nucleus of the hypothalamus (PVN), a major center for cardiovascular autonomic regulation, is indicated to play a mediating role. Optimal cardiovascular therapy improves cardiovascular prognosis without major effects on depression. By the same token, antidepressant therapy in cardiovascular disease is associated with modest improvement in depressive symptoms, however without improvement in cardiac outcome. The failure of current antidepressants and the growing number of patients suffering from both conditions legitimize the search for better antidepressive therapies, from patients as well as society perspectives. Though we appreciate the mutual character of the interaction between depression and AMI, the present review focuses on the side of AMI induced depression and discusses the role of inflammation, represented by the proinflammatory cytokine TNF-α, as potential underlying mechanism. It is conceivable that inhibition of the inflammatory response post-AMI, through targeted anti-inflammatory pharmacotherapeutical agents may prevent the development of depressive symptoms and ultimately may improve cardiovascular outcomes.

Neuronal-glial Interactions Define the Role of Nitric Oxide in Neural Functional Processes

Nitric oxide (NO) is a versatile cellular messenger performing a variety of physiologic and pathologic actions in most tissues. It is particularly important in the nervous system, where it is involved in multiple functions, as well as in neuropathology, when produced in excess. Several of these functions are based on interactions between NO produced by neurons and NO produced by glial cells, mainly astrocytes and microglia. The present paper briefly reviews some of these interactions, in particular those involved in metabolic regulation, control of cerebral blood flow, axonogenesis, synaptic function and neurogenesis. Aim of the paper is mainly to underline the physiologic aspects of these interactions rather than the pathologic ones.

SOD1 aggregation in astrocytes following ischemia/reperfusion injury: a role of NO-mediated S-nitrosylation of protein disulfide isomerase (PDI)

Background

Ubiquitinated-protein aggregates are implicated in cerebral ischemia/reperfusion injury. The very presence of these ubiquitinated-protein aggregates is abnormal and seems to be disease-related. However, it is not clear what leads to aggregate formation and whether the aggregations represent a reaction to aggregate-mediated neurodegeneration.

Methods

To study the nitrosative stress-induced protein aggregation in cerebral ischemia/reperfusion injury, we used primary astrocyte cultures as a cell model, and systematically examined their iNOS expression and consequent NO generation following oxygen glucose deprivation and reperfusion. The expression of protein disulfide isomerase (PDI) and copper-zinc superoxide dismutase (SOD1) were also examined, and the biochemical interaction between PDI and SOD1 was determined by immunoprecipitation. In addition, the levels of S-nitrosylated PDI in cultured astrocytes after oxygen glucose deprivation and reperfusion treatment were measured using the biotin-switch assay. The formation of ubiquitinated-protein aggregates was detected by immunoblot and immunofluorescence staining.

Results

Our data showed that the up-regulation of iNOS expression after oxygen glucose deprivation and reperfusion treatment led to excessive NO generation. Up-regulation of PDI and SOD1 was also identified in cultured astrocytes following oxygen glucose deprivation and reperfusion, and these two proteins were found to bind to each other. Furthermore, the increased nitrosative stress due to ischemia/reperfusion injury was highly associated with NO-induced S-nitrosylation of PDI, and this S-nitrosylation of PDI was correlated with the formation of ubiquitinated-protein aggregates; the levels of S-nitrosylated PDI increased in parallel with the formation of aggregates. When NO generation was pharmacologically inhibited by iNOS specific inhibitor 1400W, S-nitrosylation of PDI was significantly blocked. In addition, the formation of ubiquitinated-protein aggregates in cultured astrocytes following oxygen glucose deprivation and reperfusion was also suppressed by 1400W. Interestingly, these aggregates were colocalized with SOD1, which was found to co-immunoprecipitate with PDI.

Conclusions

NO-mediated S-nitrosylation of PDI may be involved in the formation of the SOD1-linked ubiquitinated-protein aggregates in cerebral ischemia/reperfusion injury.

Regulation of injury-induced neurogenesis by nitric oxide

The finding that neural stem cells (NSCs) are able to divide, migrate, and differentiate into several cellular types in the adult brain raised a new hope for restorative neurology. Nitric oxide (NO), a pleiotropic signaling molecule in the central nervous system (CNS), has been described to be able to modulate neurogenesis, acting as a pro- or antineurogenic agent. Some authors suggest that NO is a physiological inhibitor of neurogenesis, while others described NO to favor neurogenesis, particularly under inflammatory conditions. Thus, targeting the NO system may be a powerful strategy to control the formation of new neurons. However, the exact mechanisms by which NO regulates neural proliferation and differentiation are not yet completely clarified. In this paper we will discuss the potential interest of the modulation of the NO system for the treatment of neurodegenerative diseases or other pathological conditions that may affect the CNS.

Generation of primary astrocyte cultures devoid of contaminating microglia

Microglia, resident phagocytic cells of the central nervous system, are frequent contaminants of astrocyte cultures. Unfortunately and not always fully appreciated, contamination by microglia can confound results of studies designed to elucidate the molecular mechanisms underlying astrocyte-specific responses. The paradigm described herein employs the mitotic inhibitor, cytosine β-D: -arabinofuranoside, followed by the lysosomotropic agent, leucine methylester, to maximally deplete microglia, thereby generating highly enriched astrocyte monolayers that remain viable and functional. Successful removal of microglia from confluent monolayers of primary astrocyte cultures is achieved without the need for cell passage and successful reduction is confirmed by depletion of microglial-specific markers.

Microglia are required for astroglial Toll-like receptor 4 response and for optimal TLR2 and TLR3 response

Within the central nervous system, astrocytes and microglia are the primary responders to endogenous ligands released upon injury and stress, as well as to infectious pathogens. Toll-like receptors (TLRs) are implicated in recognition of both types of stimulus. Whether astrocytes respond as strongly as microglia to TLR agonists remains contentious. In this study, we have rigorously purified astrocytes to determine their capacity for autonomous TLR response, in absence of microglia. We used flow cytometry and differential adhesion as well as a myeloid lineage-specific suicide gene to purify astrocytes from mixed glial cultures and measured their response to TLR agonists. Our results show that the response of astrocytes to TLR2 and TLR3 agonists is greatly enhanced by, and response to TLR4 agonists is completely dependent on, the presence of functional microglia. In the case of the TLR4 response to lipopolysaccharide, microglia exert their effect on astrocytes at least partially through release of soluble mediators that directly activate or facilitate astrocyte responses. Our findings underline the contribution of glial crosstalk in CNS responses to injury or inflammation.

Induction of nitric oxide synthase-2 expression and measurement of nitric oxide production in enriched primary cortical astrocyte cultures

Astrocytes produce numerous mediators under conditions of inflammation in the central nervous system. One such mediator is nitric oxide (NO) derived from nitric oxide synthase-2 (NOS-2), the high output, inducible NOS isoform. Expression of NOS-2 and production of NO can be stimulated in astrocyte cultures by combinations of cytokines and lipopolysaccharide, a gram-negative bacterial endotoxin. This chapter details methods to induce and analyze NOS-2 expression and NO production in astrocyte cultures.

Curcuminoid analogs inhibit nitric oxide production from LPS-activated microglial cells

The chemically modified analogs, the demethylated analogs 4-6, the tetrahydro analogs 7-9 and the hexahydro analogs 10-12, of curcumin (1), demethoxycurcumin (2) and bisdemethoxycurcumin (3) were evaluated for their inhibitory activity on lipopolysaccharide activated nitric oxide (NO) production in HAPI microglial cells. Di-O-demethylcurcumin (5) and O-demethyldemethoxycurcumin (6) are the two most potent compounds that inhibited NO production. The analogs 5 and 6 were twofold and almost twofold more active than the parent curcuminoids 1 and 2, respectively. Moreover, the mRNA expression level of inducible NO synthase was inhibited by these two compounds. The strong neuroprotective activity of analogs 5 and 6 provide potential alternative compounds to be developed as therapeutics for neurological disorders associated with activated microglia.

Nitric oxide regulation of colonic epithelial ion transport: a novel role for enteric glia in the myenteric plexus

Enteric glia are increasingly recognized as important in the regulation of a variety of gastrointestinal functions.Here we tested the hypothesis that nicotinic signalling in the myenteric plexus results in the release of nitric oxide (NO) from neurons and enteric glia to modulate epithelial ion transport. Ion transport was assessed using full-thickness or muscle-stripped segments of mouse colon mounted in Ussing chambers. The cell-permeant NO-sensitive dye DAR-4M AM and amperometry were utilized to identify the cellular sites of NO production within the myenteric plexus and the contributions from specific NOS isoforms. Nicotinic receptors were localized using immunohistochemistry. Nicotinic cholinergic stimulation of colonic segments resulted in NO-dependent changes in epithelial active electrogenic ion transport that were TTX sensitive and significantly altered in the absence of the myenteric plexus. Nicotinic stimulation of the myenteric plexus resulted in NO production and release from neurons and enteric glia, which was completely blocked in the presence of nitric oxide synthase (NOS) I and NOS II inhibitors. Using the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), neuronal and enteric glial components of NO production were demonstrated. Nicotinic receptors were identified on enteric neurons, which express NOS I, and enteric glia, which express NOS II. These data identify a unique pathway in the mouse colon whereby nicotinic cholinergic signalling in myenteric ganglia mobilizes NO from NOS II in enteric glia, which in coordinated activity with neurons in the myenteric plexus modulates epithelial ion transport, a key component of homeostasis and innate immunity.

Anti-neuroinflammatory activity of Kamebakaurin from Isodon japonicus via inhibition of c-Jun NH₂-terminal kinase and p38 mitogen-activated protein kinase pathway in activated microglial cells

Compelling evidence supports the notion that the majority of neurodegenerative diseases are associated with microglia-mediated neuroinflammation. Therefore, quelling of microglial activation may lead to neuronal cell survival. The present study investigated the effects of Kamebakaurin (KMBK), a kaurane diterpene isolated from Isodon japonicus HARA (Labiatae), on the production of pro-inflammatory mediators in lipopolysaccharide (LPS)-stimulated cytotoxicity in rat primary microglial cultures and the BV-2 cell line. KMBK significantly inhibited the LPS-induced production of nitric oxide (NO) in a concentration-dependent fashion in activated microglial cells. The mRNA and protein levels of inducible nitric oxide synthase (iNOS) and cyclooxycenase-2 (COX-2) were also decreased dose-dependently. Furthermore KMBK inhibited the JNK and p38 mitogen-activated protein kinases (MAPKs) in LPS-stimulated BV-2 microglial cells. Considering the results obtained, the present study authenticated the potential benefits of KMBK as a therapeutic target in ameliorating microglia-mediated neuroinflammatory diseases.

Reduced gap junctional communication among astrocytes in experimental diabetes: contributions of altered connexin protein levels and oxidative-nitrosative modifications

Experimental diabetes increases production of reactive oxygen-nitrogen species and inhibits astrocytic gap junctional communication in tissue culture and brain slices from streptozotocin (STZ)-diabetic rats by unidentified mechanisms. Relative connexin (Cx) protein levels were assessed by Western blotting using extracts from cultured astrocytes grown in high (25 mmol/liter) or low (5.5 mmol/liter) glucose for 2-3 weeks and STZ-diabetic rat brain. Chemiluminescent signals for diabetic samples were normalized to those of controls on the same blot and same protein load. Growth in high glucose did not alter relative Cx26 level, whereas Cx30 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were reduced by ∼30%, and Cx43 increased ∼1.9-fold. In the inferior colliculus of STZ-diabetic rats, Cx30 and Cx43 levels in three of four rats were half those of controls, whereas GAPDH and actin were unaffected. Diabetes did not affect levels of Cx30, Cx43, or GAPDH in cerebral cortex, but actin level rose 24%. Cx43 was predominantly phosphorylated in control and diabetic samples, so the reduced dye transfer is not due to overall dephosphorylation of Cx43. Astrocytic growth in high glucose reduced the dye-labeled area by 75%, but 10 min of treatment with dithiothreitol restored normal dye transfer. In contrast, nitric oxide donors inhibited dye transfer among astrocytes grown in low glucose by 50-65% within 1 hr. Thus, modifications arising from oxidative-nitrosative stress, not altered connexin levels, may underlie the reduced dye transfer among severely hyperglycemic cultured astrocytes, whereas both oxidative-nitrosative stress and regionally selective down-regulation of connexin protein content may affect gap junctional communication in the brains of STZ-diabetic rats.

Methyleugenol reduces cerebral ischemic injury by suppression of oxidative injury and inflammation

The present study tested the cytoprotective effect of methyleugenol in an in vivo ischemia model (i.e. middle cerebral artery occlusion (MCAO) for 1.5 h and subsequent reperfusion for 24 h) and further investigated its mechanism of action in in vitro cerebral ischemic models. When applied shortly after reperfusion, methyleugenol largely reduced cerebral ischemic injury. Methyleugenol decreased the caspase-3 activation and death of cultured cerebral cortical neurons caused by oxygen-glucose deprivation (OGD) for 1 h and subsequent re-oxygenation for 24 h. Methyleugenol markedly reduced superoxide generation in the ischemic brain and decreased the intracellular oxidative stress caused by OGD/re-oxygenation. It was found that methyleugenol elevated the activities of superoxide dismutase and catalase. Further, methyleugenol inhibited the production of nitric oxide and decreased the protein expression of inducible nitric oxide synthase. Methyleugenol down-regulated the production of pro-inflammatory cytokines in the ischemic brain as well as in immunostimulated mixed glial cells. The results indicate that methyleugenol could be useful for the treatment of ischemia/inflammation-related diseases.

The mTOR kinase inhibitor rapamycin decreases iNOS mRNA stability in astrocytes

Background

Reactive astrocytes are capable of producing a variety of pro-inflammatory mediators and potentially neurotoxic compounds, including nitric oxide (NO). High amounts of NO are synthesized following up-regulation of inducible NO synthase (iNOS). The expression of iNOS is tightly regulated by complex molecular mechanisms, involving both transcriptional and post-transcriptional processes. The mammalian target of rapamycin (mTOR) kinase modulates the activity of some proteins directly involved in post-transcriptional processes of mRNA degradation. mTOR is a serine-threonine kinase that plays an evolutionarily conserved role in the regulation of cell growth, proliferation, survival, and metabolism. It is also a key regulator of intracellular processes in glial cells. However, with respect to iNOS expression, both stimulatory and inhibitory actions involving the mTOR pathway have been described. In this study the effects of mTOR inhibition on iNOS regulation were evaluated in astrocytes.

Methods

Primary cultures of rat cortical astrocytes were activated with different proinflammatory stimuli, namely a mixture of cytokines (TNFα, IFNγ, and IL-1β) or by LPS plus IFNγ. Rapamycin was used at nM concentrations to block mTOR activity and under these conditions we measured its effects on the iNOS promoter, mRNA and protein levels. Functional experiments to evaluate iNOS activity were also included.

Results

In this experimental paradigm mTOR activation did not significantly affect astrocyte iNOS activity, but mTOR pathway was involved in the regulation of iNOS expression. Rapamycin did not display any significant effects under basal conditions, on either iNOS activity or its expression. However, the drug significantly increased iNOS mRNA levels after 4 h incubation in presence of pro-inflammatory stimuli. This stimulatory effect was transient, since no differences in either iNOS mRNA or protein levels were detected after 24 h. Interestingly, reduced levels of iNOS mRNA were detected after 48 hours, suggesting that rapamycin can modify iNOS mRNA stability. In this regard, we found that rapamycin significantly reduced the half-life of iNOS mRNA, from 4 h to 50 min when cells were co-incubated with cytokine mixture and 10 nM rapamycin. Similarly, rapamycin induced a significant up-regulation of tristetraprolin (TTP), a protein involved in the regulation of iNOS mRNA stability.

Conclusion

The present findings show that mTOR controls the rate of iNOS mRNA degradation in astrocytes. Together with the marked anti-inflammatory effects that we previously observed in microglial cells, these data suggest possible beneficial effects of mTOR inhibitors in the treatment of inflammatory-based CNS pathologies.

The role of tumour-derived iNOS in tumour progression and angiogenesis

Background:

Progressive tumour growth is dependent on the development of a functional tumour vasculature and highly regulated by growth factors and cytokines. Nitric oxide (NO) is a free radical, produced both by tumour and host cells, and functions as a signalling molecule downstream of several angiogenic factors. Both pro- and antitumourigenic properties have been attributed to NO.

Methods:

The expression of the inducible isoform of NO synthase (iNOS) was knocked down in the C6 glioma cell line using constitutive expression of antisense RNA, and the effect of tumour-derived NO on tumour progression and angiogenesis was investigated.

Results:

Tumours in which iNOS expression was decreased displayed significantly reduced growth rates compared with tumours derived from parental C6 cells. Quantitative non-invasive magnetic resonance imaging and fluorescence microscopy of tumour uptake of Hoechst 33342, and haematoxylin and eosin staining, revealed significantly impaired vascular development and function in antisense iNOS tumours compared with control in vivo, primarily associated with the more necrotic tumour core. Decreased iNOS expression had no effect on tumour VEGF expression.

Conclusion:

Nitric oxide derived from tumour iNOS is an important modulator of tumour progression and angiogenesis in C6 gliomas and further supports the therapeutic strategy of inhibiting iNOS for the treatment of cancer.

Etoposide Reduces Peroxynitrite-Induced Cytotoxicity via Direct Scavenging Effect

Previously, we reported that glucose-deprived astrocytes are more vulnerable to the cytotoxicity of peroxynitrite, the reaction product of nitric oxide and superoxide anion. The augmented vulnerability of glucose-deprived astrocytes to peroxynitrite cytotoxicity was dependent on their proliferation rate. Inhibition of cell cycle progression has been shown to inhibit the apoptotic cell death occurring in cerebral ischemia-reperfusion. In the present study, we demonstrate that the increased death of glucose-deprived astrocytes by peroxynitrte was largely blocked by the cell cycle phase G2/M transition blocker etoposide. However, the cytoprotective effect of etoposide was not associated with its inhibition of cell cycle progression. Instead, etoposide effectively scavenged peroxynitrite. However, etoposide did not scavenge individual nitric oxide and superoxide anion and it did not prevent the hydrogen peroxide-induced cytotoxicity. The present results indicate that etoposide prevents the toxicity of peroxynitrite in astrocytes by directly scavenging peroxynitrite, not by inhibiting cell cycle progression.

CB(1) cannabinoid receptors and their associated proteins

CB1 receptors are G-protein coupled receptors (GPCRs) abundant in neurons, in which they modulate neurotransmission. The CB(1) receptor influence on memory and learning is well recognized, and disease states associated with CB(1) receptors are observed in addiction disorders, motor dysfunction, schizophrenia, and in bipolar, depression, and anxiety disorders. Beyond the brain, CB(1) receptors also function in liver and adipose tissues, vascular as well as cardiac tissue, reproductive tissues and bone. Signal transduction by CB(1) receptors occurs through interaction with Gi/o proteins to inhibit adenylyl cyclase, activate mitogen-activated protein kinases (MAPK), inhibit voltage-gated Ca(2+) channels, activate K(+) currents (K(ir)), and influence Nitric Oxide (NO) signaling. CB(1) receptors are observed in internal organelles as well as plasma membrane. beta-Arrestins, adaptor protein AP-3, and G-protein receptor-associated sorting protein 1 (GASP1) modulate cellular trafficking. Cannabinoid Receptor Interacting Protein1a (CRIP1a) is an accessory protein whose function has not been delineated. Factor Associated with Neutral sphingomyelinase (FAN) regulates ceramide signaling. Such diversity in cellular signaling and modulation by interacting proteins suggests that agonists and allosteric modulators could be developed to specifically regulate unique, cell type-specific responses.

Neuroinflammatory processes in Alzheimer's disease

Generation of neurotoxic amyloid beta peptides and their deposition along with neurofibrillary tangle formation represent key pathological hallmarks in Alzheimer's disease (AD). Recent evidence suggests that inflammation may be a third important component which, once initiated in response to neurodegeneration or dysfunction, may actively contribute to disease progression and chronicity. Various neuroinflammatory mediators including complement activators and inhibitors, chemokines, cytokines, radical oxygen species and inflammatory enzyme systems are expressed and released by microglia, astrocytes and neurons in the AD brain. Degeneration of aminergic brain stem nuclei including the locus ceruleus and the nucleus basalis of Meynert may facilitate the occurrence of inflammation in their projection areas given the antiinflammatory and neuroprotective action of their key transmitters norepinephrine and acetylcholine. While inflammation has been thought to arise secondary to degeneration, recent experiments demonstrated that inflammatory mediators may stimulate amyloid precursor protein processing by various means and therefore can establish a vicious cycle. Despite the fact that some aspects of inflammation may even be protective for bystander neurons, antiinflammatory treatment strategies should therefore be considered. Non-steroidal anti-inflammatory drugs have been shown to reduce the risk and delay the onset to develop AD. While, the precise molecular mechanism underlying this effect is still unknown, a number of possible mechanisms including cyclooxygenase 2 or gamma-secretase inhibition and activation of the peroxisome proliferator activated receptor gamma may alone or, more likely, in concert account for the epidemiologically observed protection.

Reactive nitroxidative species and nociceptive processing: determining the roles for nitric oxide, superoxide, and peroxynitrite in pain

Pain is a multidimensional perception and is modified at distinct regions of the neuroaxis. During enhanced pain, neuroplastic changes occur in the spinal and supraspinal nociceptive modulating centers and may result in a hypersensitive state termed central sensitization, which is thought to contribute to chronic pain states. Central sensitization culminates in hyperexcitability of dorsal horn nociceptive neurons resulting in increased nociceptive transmission and pain perception. This state is associated with enhanced nociceptive signaling, spinal glutamate-mediated N-methyl-D: -aspartate receptor activation, neuroimmune activation, nitroxidative stress, and supraspinal descending facilitation. The nitroxidative species considered for their role in nociception and central sensitization include nitric oxide (NO), superoxide ([Formula: see text]), and peroxynitrite (ONOO(-)). Nitroxidative species are implicated during persistent but not normal nociceptive processing. This review examines the role of nitroxidative species in pain through a discussion of their contributions to central sensitization and the underlying mechanisms. Future directions for nitroxidative pain research are also addressed. As more selective pharmacologic agents are developed to target nitroxidative species, the exact role of nitroxidative species in pain states will be better characterized and should offer promising alternatives to available pain management options.

Nitric oxide: promoter or suppressor of programmed cell death?

Nitric oxide (NO) is a short-lived gaseous free radical that predominantly functions as a messenger and effector molecule. It affects a variety of physiological processes, including programmed cell death (PCD) through cyclic guanosine monophosphate (cGMP)-dependent and - independent pathways. In this field, dominant discoveries are the diverse apoptosis networks in mammalian cells, which involve signals primarily via death receptors (extrinsic pathway) or the mitochondria (intrinsic pathway) that recruit caspases as effector molecules. In plants, PCD shares some similarities with animal cells, but NO is involved in PCD induction via interacting with pathways of phytohormones. NO has both promoting and suppressing effects on cell death, depending on a variety of factors, such as cell type, cellular redox status, and the flux and dose of local NO. In this article, we focus on how NO regulates the apoptotic signal cascade through protein S-nitrosylation and review the recent progress on mechanisms of PCD in both mammalian and plant cells.

Graptopetalum paraguayense E. Walther Leaf Extracts Protect Against Brain Injury in Ischemic Rats

As practice in folk medicine, Graptopetalum paraguayense E. Walther possesses several biological/pharmacological activities including hepatoprotective, anti-oxidant, and anti-inflammatory. We investigated the neuroprotective potential of Graptopetalum paraguayense E. Walther leaf extracts on inflammation-mediated ischemic brain injury. Water (GWE), 50% alcohol (GE50) extracts of Graptopetalum paraguayense E. Walther, and extracts obtained from further extraction of GE50 with ethyl acetate (GEE) were used. Oral administration of GEE, but not GWE or GE50, for 2 weeks protected animals against cerebral ischemia/reperfusion brain injury. The neuroprotective effect of GEE was accompanied by reductions in brain infarction, neurological deficits, caspase-3 activity, malondialdehyde content, microglia activation, and inducible nitric oxide synthase (iNOS) expression. Since microglia-mediated inflammation plays critical roles in ischemic brain injury, anti-inflammatory potential of Graptopetalum paraguayense E. Walther leaf extracts was further investigated on lipopolysaccharide (LPS)/interferon-γ (IFN-γ-activated BV-2 microglial cells. GEE decreased H2O2 - and LPS/IFN-γ-induced free radical generation and LPS/IFN-γ-induced iNOS expression. Mechanistic study revealed that the neuroactive effects of GEE were markedly associated with anti-oxidative potential, activation of serine/threonine and tyrosine phosphatases, and down-regulation of extracellular signal-regulated kinase, c-Jun N-terminal kinase, p38, Akt, Src, Janus kinase-1, Tyk2, signal transducer and activator of transcription-1, and NF-κB and might be attributed to the presence of polyphenolic compounds such as gallic acid, genistin, daidzin, and quercetin. Together, our findings point out its potential therapeutic strategies that target microglia activation, oxidative stress, and iNOS expression to reduce ischemic brain injury and suggest that Graptopetalum paraguayense E. Walther leaf extracts represent a valuable source for the development of neuroprotective agents.

Ischemia Increases TREK-2 Channel Expression in Astrocytes: Relevance to Glutamate Clearance

The extent of an ischemic insult is less in brain regions enriched in astrocytes suggesting that astrocytes maintain function and buffer glutamate during ischemia. Astrocytes express a wide variety of potassium channels to support their functions including TREK-2 channels which are regulated by polyunsaturated fatty acids, intracellular acidosis and swelling; conditions that pertain to ischemia. The present study investigated the possible involvement of TREK-2 channels in cultured cortical astrocytes during experimental ischemia (anoxia/hypoglycemia) by examining TREK-2 protein levels, channel activity and ability to clear glutamate. We found that TREK-2 protein levels were increased rapidly within 2 hrs of the onset of simulated ischemia. This increase corresponded to an increase in temperature-sensitive TREK-2-like channel conductance and the ability of astrocytes to buffer extracellular glutamate even during ischemia. Together, these data suggest that up-regulation of TREK-2 channels may help rescue astrocyte function and lower extracellular glutamate during ischemia.

Glutathione--a review on its role and significance in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, affecting over a million people in the United States alone, and is characterized by rigidity, bradykinesia, resting tremor, and postural instability. Its main neuropathological feature is the loss of dopaminergic neurons of the substantia nigra pars compacta. However, the pathogenesis of this loss is not understood fully. One of the earliest biochemical changes seen in PD is a reduction in the levels of total glutathione, a key cellular antioxidant. Traditionally, it has been thought that this decrease in GSH levels is the consequence of increased oxidative stress, a process heavily implicated in PD pathogenesis. However, emerging evidence suggests that GSH depletion may itself play an active role in PD pathogenesis. This review aims to explore the contribution of GSH depletion to PD pathogenesis.