Postnatal retinal ganglion cells in vitro: protection against reactive oxygen species (ROS)-induced axonal degeneration by cocultured astrocytes

Astrocytes and microglia in the coordination of CNS development and homeostasis

Glia have emerged as important architects of central nervous system (CNS) development and maintenance. While traditionally glial contributions to CNS development and maintenance have been studied independently, there is growing evidence that either suggests or documents that glia may act in coordinated manners to effect developmental patterning and homeostatic functions in the CNS. In this review, we focus on astrocytes, the most abundant glia in the CNS, and microglia, the earliest glia to colonize the CNS highlighting research that documents either suggestive or established coordinated actions by these glial cells in various CNS processes including cell and/or debris clearance, neuronal survival and morphogenesis, synaptic maturation, and circuit function, angio-/vasculogenesis, myelination, and neurotransmission. Some molecular mechanisms underlying these processes that have been identified are also described. Throughout, we categorize the available evidence as either suggestive or established interactions between microglia and astrocytes in the regulation of the respective process and raise possible avenues for further research. We conclude indicating that a better understanding of coordinated astrocyte-microglial interactions in the developing and mature brain holds promise for developing effective therapies for brain pathologies where these processes are perturbed.

Heat shock protein is a key therapeutic target for nerve repair in autoimmune peripheral neuropathy and severe peripheral nerve injury

Guillain-Barré syndrome (GBS) is an autoimmune peripheral neuropathy and a common cause of neuromuscular paralysis. Preceding infection induces the production of anti-ganglioside (GD) antibodies attacking its own peripheral nerves. In severe proximal peripheral nerve injuries that require long-distance axon regeneration, motor functional recovery is virtually nonexistent. Damaged axons fail to regrow and reinnervate target muscles. In mice, regenerating axons must reach the target muscle within 35 days (critical period) to reform functional neuromuscular junctions and regain motor function. Successful functional recovery depends on the rate of axon regeneration and debris removal (Wallerian degeneration) after nerve injury. The innate-immune response of the peripheral nervous system to nerve injury such as timing and magnitude of cytokine production is crucial for Wallerian degeneration. In the current study, forced expression of human heat shock protein (hHsp) 27 completely reversed anti-GD-induced inhibitory effects on nerve repair assessed by animal behavioral assays, electrophysiology and histology studies, and the beneficial effect was validated in a second mouse line of hHsp27. The protective effect of hHsp27 on prolonged muscle denervation was examined by performing repeated sciatic nerve crushes to delay regenerating axons from reaching distal muscle from 37 days up to 55 days. Strikingly, hHsp27 was able to extend the critical period of motor functional recovery for up to 55 days and preserve the integrity of axons and mitochondria in distal nerves. Cytokine array analysis demonstrated that a number of key cytokines which are heavily involved in the early phase of innate-immune response of Wallerian degeneration, were found to be upregulated in the sciatic nerve lysates of hHsp27 Tg mice at 1 day postinjury. However, persistent hyperinflammatory mediator changes were found after chronic denervation in sciatic nerves of littermate mice, but remained unchanged in hHsp27 Tg mice. Taken together, the current study provides insight into the development of therapeutic strategies to enhance muscle receptiveness (reinnervation) by accelerating axon regeneration and Wallerian degeneration.

Effect of dietary modification and antioxidant supplementation on intraocular pressure and open-angle glaucoma

Primary open-angle glaucoma (POAG) is an age-dependent, intraocular pressure (IOP)-related degeneration of the retinal ganglion cells (RGC). At present, IOP is the only modifiable factor that has been identified to prevent glaucomatous vision loss. Though the pathogenesis of glaucomatous optic neuropathy is still not well understood, increasing evidence suggests oxidative stress may contribute to the induction and progression of glaucoma. Furthermore, antioxidant use may be protective against glaucoma through various mechanisms, including reducing IOP, preserving vascular health, and preventing ganglion cell loss. This article provides a comprehensive review of the effect of oxidative stress, diet, and antioxidant therapy on IOP and open-angle glaucoma.

From Rust to Quantum Biology: The Role of Iron in Retina Physiopathology

Iron is essential for cell survival and function. It is a transition metal, that could change its oxidation state from Fe²⁺ to Fe³⁺ involving an electron transfer, the key of vital functions but also organ dysfunctions. The goal of this review is to illustrate the primordial role of iron and local iron homeostasis in retinal physiology and vision, as well as the pathological consequences of iron excess in animal models of retinal degeneration and in human retinal diseases. We summarize evidence of the potential therapeutic effect of iron chelation in retinal diseases and especially the interest of transferrin, a ubiquitous endogenous iron-binding protein, having the ability to treat or delay degenerative retinal diseases.

The role of glial-neuronal metabolic cooperation in modulating progression of multiple sclerosis and neuropathic pain

While the etiology of multiple sclerosis (MS) remains unclear, research from the clinic and preclinical models identified the essential role of inflammation and demyelination in the pathogenesis of MS. Current treatments focused on anti-inflammatory processes are effective against acute episodes and relapsing-remitting MS, but patients still move on to develop secondary progressive MS. MS progression is associated with activation of microglia and astrocytes, and importantly, metabolic dysfunction leading to neuronal death. Neuronal death also contributes to chronic neuropathic pain. Metabolic support of neurons by glia may play central roles in preventing progression of MS and chronic neuropathic pain. Here, we review mechanisms of metabolic cooperation between glia and neurons and outline future perspectives exploring metabolic support of neurons by glia.

Etidronate protects chronic ocular hypertension induced retinal oxidative stress and promotes retinal ganglion cells growth through IGF-1 signaling pathway

Glaucoma is a common heterogeneous eye disorder that may lead to irreversible blindness. In the present study, we examined whether etidronate, a member of bisphosphonates, may have neuroprotective effects in in vivo and in vitro rat model of glaucoma. In an in vivo setting, chronic ocular hypertension (COH) was induced in adult rat retina. We discovered that systemic injection of etidronate reduced COH-induced retinal oxidative stress, including caspase-3 activity and MDA level, as well as promoted retinal ganglion cell survival. In an in vitro setting, neonatal retinal ganglion cell was incubated with etidronate. We found etidronate incubation promoted neurite growth, upregulated IGF-1 and p-IGF-1R protein expressions in retinal ganglion cell. In addition, application of a selective IGF-1R antagonist effectively blocked the pro-neuronal effect of etidronate on retinal ganglion cell growth, and reduced p-IGF-1R protein expression. Thus, our results demonstrated that etidronate might reduce retinal oxidative stress and promote retinal neuronal growth through IGF-1 signaling pathway. Future work may define its clinical feasibility to treating human patients with glaucoma.

Neuroprotective potential of astroglia

Astroglia are the homoeostatic cells of the central nervous system, which participate in all essential functions of the brain. Astrocytes support neuronal networks by handling water and ion fluxes, transmitter clearance, provision of antioxidants, and metabolic precursors and growth factors. The critical dependence of neurons on constant support from the astrocytes confers astrocytes with intrinsic neuroprotective properties. On the other hand, loss of astrocytic support or their pathological transformation compromises neuronal functionality and viability. Manipulating neuroprotective functions of astrocytes is thus an important strategy to enhance neuronal survival and improve outcomes in disease states. © 2017 The Authors Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Facilitation of axon regeneration by enhancing mitochondrial transport and rescuing energy deficits

Zhou et al. show that reduced mitochondrial motility and energy deficits in injured axons are intrinsic mechanisms contributing to regeneration failure in mature neurons.

Although neuronal regeneration is a highly energy-demanding process, axonal mitochondrial transport progressively declines with maturation. Mature neurons typically fail to regenerate after injury, thus raising a fundamental question as to whether mitochondrial transport is necessary to meet enhanced metabolic requirements during regeneration. Here, we reveal that reduced mitochondrial motility and energy deficits in injured axons are intrinsic mechanisms controlling regrowth in mature neurons. Axotomy induces acute mitochondrial depolarization and ATP depletion in injured axons. Thus, mature neuron-associated increases in mitochondria-anchoring protein syntaphilin (SNPH) and decreases in mitochondrial transport cause local energy deficits. Strikingly, enhancing mitochondrial transport via genetic manipulation facilitates regenerative capacity by replenishing healthy mitochondria in injured axons, thereby rescuing energy deficits. An in vivo sciatic nerve crush study further shows that enhanced mitochondrial transport in snph knockout mice accelerates axon regeneration. Understanding deficits in mitochondrial trafficking and energy supply in injured axons of mature neurons benefits development of new strategies to stimulate axon regeneration.

Old Things New View: Ascorbic Acid Protects the Brain in Neurodegenerative Disorders

Ascorbic acid is a key antioxidant of the Central Nervous System (CNS). Under brain activity, ascorbic acid is released from glial reservoirs to the synaptic cleft, where it is taken up by neurons. In neurons, ascorbic acid scavenges reactive oxygen species (ROS) generated during synaptic activity and neuronal metabolism where it is then oxidized to dehydroascorbic acid and released into the extracellular space, where it can be recycled by astrocytes. Other intrinsic properties of ascorbic acid, beyond acting as an antioxidant, are important in its role as a key molecule of the CNS. Ascorbic acid can switch neuronal metabolism from glucose consumption to uptake and use of lactate as a metabolic substrate to sustain synaptic activity. Multiple evidence links oxidative stress with neurodegeneration, positioning redox imbalance and ROS as a cause of neurodegeneration. In this review, we focus on ascorbic acid homeostasis, its functions, how it is used by neurons and recycled to ensure antioxidant supply during synaptic activity and how this antioxidant is dysregulated in neurodegenerative disorders.

Dietary factors and the risk of glaucoma: a review

Glaucoma is an optic neuropathy characterized by a progressive typical pattern of optic neurodegeneration and visual field loss. A relatively high proportion of glauctomatous individuals admit to interest in dietary modification in an attempt to manage their disease. Heavy caffeine consumption appears to have a transient effect on increasing intraocular pressure (IOP). This effect may be clinically insignificant for nonglaucomatous individuals, but the association warrants clinical consideration in those with the disease. Studies investigating the relationship between self-reported antioxidant intake and risk of glaucomatous disease have reported conflicting results. Preliminary studies investigating the relationship between self-reported glaucoma diagnosis and consumption of the oxidants calcium and iron suggest a possible relationship indicating increased risk of the disease with increased consumption of these dietary factors. Initial reports in the literature suggest a potential role for dietary modification in the treatment of glaucomatous optic neuropathy. Further study, with randomized controlled trials, may be necessary to further characterize these relationships.

The behavior of ROS-scavenging nanoparticles in blood

Here, we report an interaction between blood and redox nanoparticles, prepared by self-assembly of amphiphilic block copolymers possessing 2,2,6,6-tetramethylpiperidine-N-oxyls as a side chain of hydrophobic segment. When 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl was added to rat whole blood, its electron spin resonance signal disappeared rapidly. In contrast, the signal from redox nanoparticles remained for a long period of time, indicating that nitroxide radicals were protected in the blood by their compartmentalization in the core of nanoparticle. Although most 2,2,6,6-tetramethylpiperidine-N-oxyls were located in the nanoparticle core, reactive oxygen species-scavenging activity was found outside of blood cells. For example, redox nanoparticles suppressed superoxide anion-induced hemolysis effectively, while 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl did not. It was revealed that redox nanoparticles were not internalized into the healthy blood cells, which was in sharp contrast to 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl. Due to its internalization into healthy platelets, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl induced mitochondrial dysfunction, while redox nanoparticles did not. Redox nanoparticles suppressed platelet adhesion and extended blood coagulation time, in contrast to 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl. These results indicate that redox nanoparticles scavenge reactive oxygen species outside of cells, but do not interfere with normal redox reactions inside of the cell. Based on these results, we determine that an anti-oxidative strategy based on nanotechnology is a rational and safe therapeutic approach.

Axons degenerate in the absence of mitochondria in C. elegans

Many neurodegenerative disorders are associated with mitochondrial defects [1-3]. Mitochondria can play an active role in degeneration by releasing reactive oxygen species and apoptotic factors [4-7]. Alternatively, mitochondria can protect axons from stress and insults, for example by buffering calcium [8]. Recent studies manipulating mitochondria lend support to both of these models [9-13]. Here, we identify a C. elegans mutant, ric-7, in which mitochondria are unable to exit the neuron cell bodies, similar to the kinesin-1/unc-116 mutant. When axons lacking mitochondria are cut with a laser, they rapidly degenerate. Some neurons even spontaneously degenerate in ric-7 mutants. Degeneration can be suppressed by forcing mitochondria into the axons of the mutants. The protective effect of mitochondria is also observed in the wild-type: a majority of axon fragments containing a mitochondrion survive axotomy, whereas those lacking mitochondria degenerate. Thus, mitochondria are not required for axon degeneration and serve a protective role in C. elegans axons.

Restoration of stressor-induced calcium dysregulation and autophagy inhibition by polyphenol-rich açaí (Euterpe spp.) fruit pulp extracts in rodent brain cells in vitro

OBJECTIVES

Oxidative damage to lipids, proteins, and nucleic acids in the brain often causes progressive neuronal degeneration and death that are the focal traits of chronic and acute pathologies, including those involving cognitive decline. The aim of this study was to investigate the specific effects of both Euterpe oleracea and Euterpe precatoria açaí fruit pulp on restoring stressor-induced calcium dysregulation, stunted growth of basal dendrites, and autophagy inhibition using embryonic hippocampal and HT22 hippocampal neurons.

METHODS

Water-soluble whole fruit pulp extracts from two açaí species were applied to rat primary neurons and HT22 hippocampal neurons with varied time and concentrations. Recovery of neurons from dopamine-induced Ca(2+) dysregulation was measured by live cell imaging using fluorescent microscopy. The effect of açaí fruit pulp extracts on neurons following chemically-induced autophagy inhibition was measured using both immunofluorescence and immunohistochemical techniques.

RESULTS

It has been postulated that at least part of the loss of cognitive function in aging may depend on a dysregulation in calcium ion (Ca(2+)) homeostasis and a loss of autophagy function in the brain, which affects numerous signaling pathways and alters protein homeostasis. In the present study, polyphenol-rich fruit pulp extracts from two species of açaí, Euterpe precatoria and Euterpe oleracea, when applied to rat hippocampal primary neuronal cells (E18), caused a significant (P < 0.05) recovery of depolarized brain cells from dopamine-induced Ca(2+) influx. Autophagy, a protein homeostasis mechanism in brain, when blocked by known inhibitors such as bafilomycin A1 or wortmannin, caused a significant reduction in the growth of primary basal dendrites in rodent primary hippocampal neurons and significant accumulation of polyubiquitinated proteins in mouse HT22 hippocampal neurons in culture. However, pretreatment with açaí extracts up to 1 mg/mL significantly increased the length of basal dendrites and attenuated the inhibitor-induced autophagy dysfunction. Açaí extracts activated the phosphorylation of mammalian target of rapamycin, increased the turnover of autophagosomes and MAP1 B LC3-II, and decreased accumulation of LC3-ubiquitin binding P62/SQSTM1.

CONCLUSION

Although the polyphenol profile of Euterpe precatoria showed substantially higher concentrations of major flavonoids han Euterpe oleracea, the relative effects were essentially similar for both species. The study adds to growing evidence that supports the putative health effects of açaí fruit species on brain cells.

Emerging role of glial cells in the control of body weight

Glia are the most abundant cell type in the brain and are indispensible for the normal execution of neuronal actions. They protect neurons from noxious insults and modulate synaptic transmission through affectation of synaptic inputs, release of glial transmitters and uptake of neurotransmitters from the synaptic cleft. They also transport nutrients and other circulating factors into the brain thus controlling the energy sources and signals reaching neurons. Moreover, glia express receptors for metabolic hormones, such as leptin and insulin, and can be activated in response to increased weight gain and dietary challenges. However, chronic glial activation can be detrimental to neurons, with hypothalamic astrocyte activation or gliosis suggested to be involved in the perpetuation of obesity and the onset of secondary complications. It is now accepted that glia may be a very important participant in metabolic control and a possible therapeutical target. Here we briefly review this rapidly advancing field.

Over-expression of map kinase phosphatase-1 (MKP-1) suppresses neuronal death through regulating JNK signaling in hypoxia/re-oxygenation

A pivotal role of c-jun N-terminal kinase (JNK) on neuronal apoptosis has been demonstrated in a rodent stroke model. MAP kinase phosphatase 1 (MKP-1) is an archetypal member of the dual-specificity protein phosphatase (DUSP) family, which inactivates mitogen-activated protein kinase (MAPK) including JNK through dephosphorylation. MKP-1, one of immediate early genes in stress conditions, was induced at transcriptional level in hypoxia/re-oxygenation (H/R) in neuroblastoma N1E115 cells, however the activation of JNK was not suppressed in the acute phase of re-oxygenation. Small interference RNA-mediated knock-down of MKP-1 enhanced phospho-JNK and neuronal death that is rescued by JNK inhibitor in H/R. Conversely, conditional over-expression of MKP-1 suppressed phospho-JNK, the expression of proapoptotic genes, and neuronal death in H/R. Further the immunoreactivity of MKP-1 was detected in the neurons and partially co-localized with that of phospho-JNK in the surrounding zone of ischemia in rat MCA-O (middle cerebral artery occlusion) reperfusion model. These findings indicate that over-expression of MKP-1 could suppress neuronal death possibly through regulating JNK signaling in vitro and be a prominent neuroprotective target for the treatment of acute cerebral infarction.

Astrocytic-neuronal crosstalk: implications for neuroprotection from brain injury

The older neurocentric view of the central nervous system (CNS) has changed radically with the growing understanding of the many essential functions of astrocytes. Advances in our understanding of astrocytes include new observations about their structure, organization, function and supportive actions to other cells. Although the contribution of astrocytes to the process of brain injury has not been clearly defined, it is thought that their ability to provide support to neurons after cerebral damage is critical. Astrocytes play a fundamental role in the pathogenesis of brain injury-associated neuronal death, and this secondary injury is primarily a consequence of the failure of astrocytes to support the essential metabolic needs of neurons. These needs include K+ buffering, glutamate clearance, brain antioxidant defense, close metabolic coupling with neurons, and the modulation of neuronal excitability. In this review, we will focus on astrocytic activities that can both protect and endanger neurons, and discuss how manipulating these functions provides a novel and important strategy to enhance neuronal survival and improve the outcome following brain injury.

Protective effects of decursin and decursinol angelate against amyloid β-protein-induced oxidative stress in the PC12 cell line: the role of Nrf2 and antioxidant enzymes

The protective effects of decursin (D) and decursinol angelate (DA) purified from Angelica gigas Nakai on amyloid β-protein (Aβ)-induced neurotoxicity and the underlying mechanisms were investigated. Aβ plays a major role in the pathogenesis of Alzheimer's disease (AD) by eliciting oxidative stress. It significantly increased cytotoxicity and lipid peroxidation, but decreased glutathione contents and antioxidant enzyme activities. All of these results were markedly reversed by pretreatment with D or DA. Nuclear transcription factor Nrf2, which regulates the expression of antioxidant enzymes, was significantly increased by D or DA pretreatment. Furthermore, D and DA suppressed Aβ aggregation. These results suggest that D and DA increase cellular resistance to Aβ-induced oxidative injury in the rat pheochromocytoma (PC12) cells, presumably through not only the induction of Nrf2 and related antioxidant enzymes, but also the anti-aggregation of Aβ. Thus D and DA have therapeutic potential in treating AD and other oxidative stress-related diseases.

The role of Nrf2 signaling in the regulation of antioxidants and detoxifying enzymes after traumatic brain injury in rats and mice

AIM

To determine whether Nrf2 signaling pathway activation could attenuate oxidative stress and neuronal damage following traumatic brain injury (TBI).

METHODS

Controlled cortical impact (CCI) injury was performed in Sprague-Dawley rats and Nrf2-knockout or control mice. Sulforaphane (SFN), a potent Nrf2 activator, was used to activate Nrf2. Oxidative stress, lesion volume, neuron degeneration, and neurologic dysfunction were determined using biochemical, histopathological and neuroethologic approaches. Protein and mRNA levels of Nrf2 and the antioxidant enzymes heme oxygenase 1 (HO-1) and NAD(P)H:quinine oxidoreductase 1 (NQO1) were assessed using Western blot analysis and RT-PCR.

RESULTS

Activation of Nrf2 by SFN( 5 mg/kg, ip) induced the nuclear translocation and activation of Nrf2, which resulted in an up-regulation of Nrf2-dependent antioxidant enzymes and a reduction of oxidative damage after TBI. In accordance with these biochemical changes, SFN also significantly reduced neuronal death, contusion volume, and neurological dysfunction after TBI. Furthermore, Nrf2-knockout mice showed more severe oxidative stress and neurologic deficits after TBI and did not benefit from the effects of SFN.

CONCLUSION

Nrf2 plays a pivotal role in cell defenses against the oxidative stress of TBI. In addition, pharmacological activation of the Nrf2 signaling pathway by small molecule inducers such as SFN attenuated oxidative stress and neuronal damage following TBI.

Dimethylfumarate inhibits microglial and astrocytic inflammation by suppressing the synthesis of nitric oxide, IL-1beta, TNF-alpha and IL-6 in an in-vitro model of brain inflammation

BACKGROUND

Brain inflammation plays a central role in multiple sclerosis (MS). Dimethylfumarate (DMF), the main ingredient of an oral formulation of fumaric acid esters with proven therapeutic efficacy in psoriasis, has recently been found to ameliorate the course of relapsing-remitting MS. Glial cells are the effector cells of neuroinflammation; however, little is known of the effect of DMF on microglia and astrocytes. The purpose of this study was to use an established in vitro model of brain inflammation to determine if DMF modulates the release of neurotoxic molecules from microglia and astrocytes, thus inhibiting glial inflammation.

METHODS

Primary microglial and astrocytic cell cultures were prepared from cerebral cortices of neonatal rats. The control cells were treated with LPS, an accepted inducer of pro-inflammatory properties in glial cells, and the experimental groups with LPS and DMF in different concentrations. After stimulation/incubation, the generation of nitric oxide (NO) in the cell culture supernatants was determined by measuring nitrite accumulation in the medium using Griess reagent. After 6 hours of treatment RT-PCR was used to determine transcription levels of iNOS, IL-1beta, IL-6 and TNF-alpha mRNA in microglial and astrocytic cell cultures initially treated with DMF, followed after 30 min by LPS treatment. Moreover, we investigated possible involvement of the ERK and Nrf-2 transduction pathway in microglia using western blot analysis.

RESULTS

Pretreatment with DMF decreased synthesis of the proinflammatory mediators iNOS, TNF-alpha, IL-1beta and IL-6 at the RNA level in activated microglia and astrocytes in vitro, associated with a decrease in ERK phosphorylation in microglia.

CONCLUSIONS

Collectively, these results suggest that the neuroprotective effects of DMF may be in part functionally attributable to the compound's ability to inhibit expression of multiple neuroinflammatory mediators in brain of MS patients.

The role of astroglia in neuroprotection

Astrocytes are the main neural cell type responsible for the maintenance of brain homeostasis. They form highly organized anatomical domains that are interconnected into extensive networks. These features, along with the expression of a wide array of receptors, transporters, and ion channels, ideally position them to sense and dynamically modulate neuronal activity. Astrocytes cooperate with neurons on several levels, including neurotransmitter trafficking and recycling, ion homeostasis, energy metabolism, and defense against oxidative stress. The critical dependence of neurons upon their constant support confers astrocytes with intrinsic neuroprotective properties which are discussed here. Conversely, pathogenic stimuli may disturb astrocytic function, thus compromising neuronal functionality and viability. Using neuroinflammation, Alzheimer's disease, and hepatic encephalopathy as examples, we discuss how astrocytic defense mechanisms may be overwhelmed in pathological conditions, contributing to disease progression.

Oxidative stress is linked to ERK1/2-p16 signaling-mediated growth defect in ATM-deficient astrocytes

The gene that encodes the ATM protein kinase is mutated in ataxia-telangiectasia (A-T). One of the prominent features of A-T is progressive neurodegeneration. We have previously reported that primary astrocytes isolated from Atm(-/-) mice grow slowly and die earlier than control cells in culture. However, the mechanisms for this remain unclear. We show here that intrinsic elevated intracellular levels of reactive oxygen species (ROS) are associated with the senescence-like growth defect of Atm(-/-) astrocytes. This condition is accompanied by constitutively higher levels of ERK1/2 phosphorylation and p16(Ink4a) in Atm(-/-) astrocytes. We also observe that ROS-induced up-regulation of p16(Ink4a) occurs correlatively with ERK1/2-dependent down-regulation and subsequent dissociation from chromatin of Bmi-1. Furthermore, both mitogen-activated protein kinase (MAPK)/ERK inhibitor PD98059 and antioxidant N-acetyl-l-cysteine restored normal proliferation of Atm(-/-) astrocytes. These results suggest that ATM is required for normal astrocyte growth through its ability to stabilize intracellular redox status and that the inability to control ROS is the molecular basis of limited cell growth of Atm(-/-) astrocytes. This defect may be mediated by a mechanism involving ERK1/2 activation and Bmi-1 derepression of p16(Ink4a). These data identify new potential targets for therapeutic intervention in A-T neurodegeneration.

Astrocytes from acyclic female rats exhibit lowered capacity for neuronal differentiation

Astrocytes comprise a large proportion of the central nervous system support cells and play a critical role in neural injury and repair. The present study examined the impact of ovarian aging using an ex vivo model system, where astrocytes were derived from the olfactory bulb of young, reproductively competent females and reproductive senescent females. Cellular morphology and the spatial pattern of laminin deposition was altered in astrocyte cultures derived from reproductive senescent females. Young adult astrocytes had a flattened polygonal shape with actin bundles at the cell edges, while reproductive senescent astrocytes had a contractile appearance with thick stress fibers visible throughout the cell. Moreover, in reproductive senescent astrocytes, BDNF was elevated with a concomitant reduction in expression of the BDNF receptor, TrkB. To examine the ability of astrocytes derived from young adult and reproductive senescent females to promote neuronal differentiation, neural progenitor cells (NPCs) were co-cultured with astrocytes derived from these groups. At day 4 in vitro, MAP-2(+) NPCs were located in smaller clusters when co-cultured with young adult astrocytes and in large clusters when co-cultured with older astrocytes. At days 6 and 10, neuronal differentiation was significantly reduced in reproductive senescent astrocyte-NPC co-cultures, as determined by NeuN(+) cell numbers and MAP-2(+) process lengths. Furthermore, estrogen only enhanced neuronal differentiation in young adult-NPC co-cultures. The ovarian age-related astrocyte phenotype thus limits the ability of this cell to promote neuronal differentiation in NPC populations and suggests that the astrocyte-mediated microenvironment in older acyclic females is less conducive to repair following neurovascular injury.

Nrf2-induced antioxidant protection: a promising target to counteract ROS-mediated damage in neurodegenerative disease?

Neurodegenerative diseases share various pathological features, such as accumulation of aberrant protein aggregates, microglial activation, and mitochondrial dysfunction. These pathological processes are associated with generation of reactive oxygen species (ROS), which cause oxidative stress and subsequent damage to essential molecules, such as lipids, proteins, and DNA. Hence, enhanced ROS production and oxidative injury play a cardinal role in the onset and progression of neurodegenerative disorders. To maintain a proper redox balance, the central nervous system is endowed with an antioxidant defense mechanism consisting of endogenous antioxidant enzymes. Expression of most antioxidant enzymes is tightly controlled by the antioxidant response element (ARE) and is activated by nuclear factor E2-related factor 2 (Nrf2). In past years reports have highlighted the protective effects of Nrf2 activation in reducing oxidative stress in both in vitro and in vivo models of neurodegenerative disorders. Here we provide an overview of the involvement of ROS-induced oxidative damage in Alzheimer's disease, Parkinson's disease, and Huntington's disease and we discuss the potential therapeutic effects of antioxidant enzymes and compounds that activate the Nrf2-ARE pathway.

Glaucoma risk and the consumption of fruits and vegetables among older women in the study of osteoporotic fractures

PURPOSE

To explore the association between the consumption of fruits and vegetables and the presence of glaucoma.

DESIGN

Cross-sectional cohort study.

METHODS

In a sample of 1,155 women located in multiple centers in the United States, glaucoma specialists diagnosed glaucoma in at least one eye by assessing optic nerve head photographs and 76-point suprathreshold screening visual fields. Consumption of fruits and vegetables was assessed using the Block Food Frequency Questionnaire. The relationship between selected fruit and vegetable consumption and glaucoma was investigated using adjusted logistic regression models.

RESULTS

Among 1,155 women, 95 (8.2%) were diagnosed with glaucoma. In adjusted analysis, the odds of glaucoma risk were decreased by 69% (odds ratio [OR], 0.31; 95% confidence interval [CI], 0.11 to 0.91) in women who consumed at least one serving per month of green collards and kale compared with those who consumed fewer than one serving per month, by 64% (OR, 0.36; 95% CI, 0.17 to 0.77) in women who consumed more than two servings per week of carrots compared with those who consumed fewer than one serving per week, and by 47% (OR, 0.53; 95% CI, 0.29 to 0.97) in women who consumed at least one serving per week of canned or dried peaches compared with those who consumed fewer than one serving per month.

CONCLUSIONS

A higher intake of certain fruits and vegetables may be associated with a decreased risk of glaucoma. More studies are needed to investigate this relationship.

Inflammation after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating clinical event without effective therapies. Increasing evidence suggests that inflammatory mechanisms are involved in the progression of ICH-induced brain injury. Inflammation is mediated by cellular components, such as leukocytes and microglia, and molecular components, including prostaglandins, chemokines, cytokines, extracellular proteases, and reactive oxygen species. Better understanding of the role of the ICH-induced inflammatory response and its potential for modulation might have profound implications for patient treatment. In this review, a summary of the available literature on the inflammatory responses after ICH is presented along with discussion of some of the emerging opportunities for potential therapeutic strategies. In the near future, additional strategies that target inflammation could offer exciting new promise in the therapeutic approach to ICH.

The rat retinal ganglion cell in culture: An accessible CNS neurone

Retinal ganglion cells are vital for vision, some have intrinsic light sensing properties and in retinal networks display complex computational abilities. Furthermore they are implicated in a very common form of blindness, glaucoma as well some the symptoms of AIDS. Retinal ganglion cells, unlike many neurones of the central nervous system, have a clearly defined physiological role and can be identified in primary cultures with ease. Here we detail the cell culture and electrophysiological methods required to obtain recordings on the voltage-gated and ligand-gated ion currents and channels expressed by these neurones. Information is given on the range of non-ionotropic receptors that are thought to be present on these cells and what role they may have as model systems in the pharmacological and pharmaceutical research environment.

The role of omega-3 long-chain polyunsaturated fatty acids in health and disease of the retina

In this work we advance the hypothesis that omega-3 (omega-3) long-chain polyunsaturated fatty acids (LCPUFAs) exhibit cytoprotective and cytotherapeutic actions contributing to a number of anti-angiogenic and neuroprotective mechanisms within the retina. omega-3 LCPUFAs may modulate metabolic processes and attenuate effects of environmental exposures that activate molecules implicated in pathogenesis of vasoproliferative and neurodegenerative retinal diseases. These processes and exposures include ischemia, chronic light exposure, oxidative stress, inflammation, cellular signaling mechanisms, and aging. A number of bioactive molecules within the retina affect, and are effected by such conditions. These molecules operate within complex systems and include compounds classified as eicosanoids, angiogenic factors, matrix metalloproteinases, reactive oxygen species, cyclic nucleotides, neurotransmitters and neuromodulators, pro-inflammatory and immunoregulatory cytokines, and inflammatory phospholipids. We discuss the relationship of LCPUFAs with these bioactivators and bioactive compounds in the context of three blinding retinal diseases of public health significance that exhibit both vascular and neural pathology. How is omega-3 LCPUFA status related to retinal structure and function? Docosahexaenoic acid (DHA), a major dietary omega-3 LCPUFA, is also a major structural lipid of retinal photoreceptor outer segment membranes. Biophysical and biochemical properties of DHA may affect photoreceptor membrane function by altering permeability, fluidity, thickness, and lipid phase properties. Tissue DHA status affects retinal cell signaling mechanisms involved in phototransduction. DHA may operate in signaling cascades to enhance activation of membrane-bound retinal proteins and may also be involved in rhodopsin regeneration. Tissue DHA insufficiency is associated with alterations in retinal function. Visual processing deficits have been ameliorated with DHA supplementation in some cases. What evidence exists to suggest that LCPUFAs modulate factors and processes implicated in diseases of the vascular and neural retina? Tissue status of LCPUFAs is modifiable by and dependent upon dietary intake. Certain LCPUFAs are selectively accreted and efficiently conserved within the neural retina. On the most basic level, omega-3 LCPUFAs influence retinal cell gene expression, cellular differentiation, and cellular survival. DHA activates a number of nuclear hormone receptors that operate as transcription factors for molecules that modulate reduction-oxidation-sensitive and proinflammatory genes; these include the peroxisome proliferator-activated receptor-alpha (PPAR-alpha) and the retinoid X receptor. In the case of PPAR-alpha, this action is thought to prevent endothelial cell dysfunction and vascular remodeling through inhibition of: vascular smooth muscle cell proliferation, inducible nitric oxide synthase production, interleukin-1 induced cyclooxygenase (COX)-2 production, and thrombin-induced endothelin 1 production. Research on model systems demonstrates that omega-3 LCPUFAs also have the capacity to affect production and activation of angiogenic growth factors, arachidonic acid (AA)-based vasoregulatory eicosanoids, and MMPs. Eicosapentaenoic acid (EPA), a substrate for DHA, is the parent fatty acid for a family of eicosanoids that have the potential to affect AA-derived eicosanoids implicated in abnormal retinal neovascularization, vascular permeability, and inflammation. EPA depresses vascular endothelial growth factor (VEGF)-specific tyrosine kinase receptor activation and expression. VEGF plays an essential role in induction of: endothelial cell migration and proliferation, microvascular permeability, endothelial cell release of metalloproteinases and interstitial collagenases, and endothelial cell tube formation. The mechanism of VEGF receptor down-regulation is believed to occur at the tyrosine kinase nuclear factor-kappa B (NFkappaB). NFkappaB is a nuclear transcription factor that up-regulates COX-2 expression, intracellular adhesion molecule, thrombin, and nitric oxide synthase. All four factors are associated with vascular instability. COX-2 drives conversion of AA to a number angiogenic and proinflammatory eicosanoids. Our general conclusion is that there is consistent evidence to suggest that omega-3 LCPUFAs may act in a protective role against ischemia-, light-, oxygen-, inflammatory-, and age-associated pathology of the vascular and neural retina.

alpha-keto-beta-methyl-n-valeric acid diminishes reactive oxygen species and alters endoplasmic reticulum Ca(2+) stores

Mitochondrial dysfunction and oxidative stress occur in neurodegenerative diseases. Other results show that bombesin-releasable calcium stores (BRCS) from the endoplasmic reticulum (ER) are exaggerated in fibroblasts from patients with Alzheimer's disease (AD) compared with controls and in fibroblasts from a young control treated with H(2)O(2). We hypothesize that alterations in oxidative stress underlie the exaggeration in BRCS in AD, and that appropriate antioxidants may be useful in treating this abnormality. Two indicators of different oxidant species were used to determine the effects of select oxidants on cellular oxidation status: carboxydichlorofluorescein (c-DCF) to detect reactive oxygen species (ROS), and 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF) to detect nitric oxide (NO(.-)). Various conditions that induce ROS, including H(2)O(2), oxygen/glucose deprivation, and 3-morpholinosyndnonimine (SIN-1), were used to test the ability of alpha-keto-ss-methyl-n-valeric acid (KMV) to scavenge ROS. KMV diminished c-DCF-detectable ROS that were induced by H(2)O(2), oxygen/glucose deprivation, or SIN-1 in PC12 cells, primary neuronal cultures, or fibroblasts. Furthermore, KMV reduced the H(2)O(2)-induced increase in BRCS and diminished the elevation in BRCS in cells from AD patients to control levels. On the other hand, DAF-detectable NO(.-) induced by SIN-1 was not scavenged by KMV and did not exaggerate BRCS. The results indicate that KMV is an effective antioxidant of c-DCF-detectable ROS. The effects of KMV are not cell type specific, but are ROS specific. The same H(2)O(2)-induced ROS that reacts with KMV may also underlie the changes in BRCS related to AD. Thus, KMV ameliorates the effects of ROS on calcium homeostasis related to oxidative stress and to AD.

Glial perspectives of metabolic states during cerebral hypoxia—calcium regulation and metabolic energy

Cooperation between astrocytes and neurons is a unique interaction between two highly specialized cell types of the brain. Therefore, lack of nutrient supply during ischemia requires tight coordination of metabolism between astrocytes and neurons to keep the brain functions intact. To understand the impact of energy limitation on astrocytes, the functions of astrocytes have to be considered: (i) supplementation of neuronal cells, (ii) modulation of the extracellular milieu, mainly of the glutamate level, and (iii) elimination of reactive oxygen species (ROS). In cultured astrocytes and neurons inhibition of oxidative phosphorylation, using rotenone, was tested. Interestingly, this had only a negligible effect on Ca2+ homeostasis in astrocytes, even in combination with a severe glutamate stress. In contrast, in neurons glutamate in the presence of rotenone induced Ca2+ deregulation. Ca2+ homeostasis is very critical for cell survival. A massive and prolonged Ca2+ rise will lead to deregulation of many processes in such a way that the cells affected can hardly survive. Ca2+ homeostasis depends on the energy-consuming processes, which maintain the steep gradient between intracellular and extracellular Ca2+ concentration. Deprivation of oxygen and glucose during ischemia leads to a depletion of ATP in the brain, due to inhibited glycolytic and mitochondrial activity, whereas energy-consuming processes like ion pumps drain the ATP pools. On the other hand, specific mechanisms can protect brain structures against the massive insult of ischemia. Glycogen, stored in astrocytes, can maintain both neurons and astrocytes alive during short limitation of oxygen and glucose. Moreover, astrocytes can fuel ATP generation by providing lactate for neurons.

Effects of adenoviral-mediated gene transfer of interleukin-10, interleukin-4, and transforming growth factor-beta on the survival of axotomized retinal ganglion cells

Nitric oxide, synthesized by reactive microglia and astrocytes has been implicated in promoting neuronal degeneration observed in many diseases and insults of the central nervous system. We have recently shown that inducible nitric oxide synthase is expressed by retinal glial cells following optic nerve transection and that inhibition of nitric oxide synthesis enhances the survival of injured retinal ganglion cells. Anti-inflammatory cytokines including interleukin-10 (IL-10), interleukin-4 (IL-4), and transforming growth factor-beta (TGF-beta) have been shown to prevent inducible nitric oxide synthase expression, and inhibit nitric oxide synthesis by microglia and astrocytes in culture. In the present study, we examined the effects of adenoviral mediated gene transfer of anti-inflammatory cytokines on the survival of axotomized retinal ganglion cells. Intraocular administration of adenoviral vectors encoding interleukin-10 (Ad.IL-10) and interleukin-4 (Ad.IL-4) enhanced the survival of axotomized retinal ganglion cells at 14 days after axotomy. Adenoviral vectors encoding TGF-beta (Ad.TGF-beta) had no effect on retinal ganglion cell survival. Separate animals were pretreated by injection of Ad.IL-10 or Ad.IL-4 into the superior colliculus (s.c.), the major target of ganglion cells, 7 days prior to axotomy. S.c. administration of Ad.IL-10 or Ad.IL-4 significantly increased ganglion cell survival compared with intraocular injection. IL-10 and IL-4 gene transfer also reduced the density of infiltrating ED1 positive monocytes in the nerve fiber layer at 14 days postaxotomy. Ad.TGF-beta increased the density of ED1 positive monocytes infiltrating the nerve fiber layer after axotomy. Vectors encoding IL-10 or IL-4 also decreased nitrotyrosine immunoreactivity in the inner retina at 7 days postaxotomy, suggesting that these cytokines protect retinal ganglion cells from peroxynitrite formation that results from nitric oxide synthesis by activated glial cells. The present study has implications for the treatment of CNS injury and diseases that involve reactive microglia and astrocytes. Our results suggest that interleukin-10 and interleukin-4 may help prevent neurodegeneration caused by the activation of glial cells after CNS injury.

Coordinate regulation of glutathione biosynthesis and release by Nrf2-expressing glia potently protects neurons from oxidative stress

Astrocytes have a higher antioxidant potential in comparison to neurons. Pathways associated with this selective advantage include the transcriptional regulation of antioxidant enzymes via the action of the Cap'n'Collar transcription factor Nrf2 at the antioxidant response element (ARE). Here we show that Nrf2 overexpression can reengineer neurons to express this glial pathway and enhance antioxidant gene expression. However, Nrf2-mediated protection from oxidative stress is conferred primarily by glia in mixed cultures. The antioxidant properties of Nrf2-overexpressing glia are more pronounced than those of neurons, and a relatively small number of these glia (< 1% of total cell number added) could protect fully cocultured naive neurons from oxidative glutamate toxicity associated with glutathione (GSH) depletion. Microarray and biochemical analyses indicate a coordinated upregulation of enzymes involved in GSH biosynthesis (xCT cystine antiporter, gamma-glutamylcysteine synthetase, and GSH synthase), use (glutathione S-transferase and glutathione reductase), and export (multidrug resistance protein 1) with Nrf2 overexpression, leading to an increase in both media and intracellular GSH. Selective inhibition of glial GSH synthesis and the supplementation of media GSH indicated that an Nrf2-dependent increase in glial GSH synthesis was both necessary and sufficient for the protection of neurons, respectively. Neuroprotection was not limited to overexpression of Nrf2, because activation of endogenous glial Nrf2 by the small molecule ARE inducer, tert-butylhydroquinone, also protected against oxidative glutamate toxicity.

Differential effects of immunophilin-ligands (FK506 and V-10,367) on survival and regeneration of rat retinal ganglion cells in vitro and after optic nerve crush in vivo

Immunophilins belong to the large family of peptidyl-prolyl-cis-trans-isomerases known to be involved in many cellular processes (e.g., protein trafficking and transcriptional regulation). Beside the widespread therapeutic use of ligands of immunophilins as immunosuppressants, it has been shown that some of these compounds such as FK506 and V-10,367 may mediate neuroprotection and improve axonal regeneration following damage to peripheral nerve fibers. Here, we have analyzed the effects of these two compounds on neurite outgrowth of retinal explants in vitro and on axonal regeneration of retinal ganglion cells, a population of central intrinsic neurons, ten days following optic nerve crush in vivo. FK506 enhanced neurite outgrowth/regrowth in vitro in a dose dependent manner up to 135% (control = 100%), while V-10,367 was more effective (up to 168%). In vivo, intravitreal V-10,367 and FK506 significantly reduced the number of dying retinal ganglion cells as demonstrated by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling. Local application of FK506 into the vitreous body, but not V-10,367, immediately provided after the optic nerve crush induced the elongation of regenerating fibers across the lesion site for around 1.2 mm. Our data provide evidence that the ligands of the FK506-binding proteins FK506 and V-10,367 protect (otherwise dying) retinal ganglion cells from optic nerve crush-induced cell death, promote neurite outgrowth in vitro and that locally applied FK506 enhances the sprouting of axotomized central intrinsic neurons such as retinal ganglion cells in vivo after optic nerve crush.

Astrocytes and brain injury

Astrocytes are the most numerous cell type in the central nervous system. They provide structural, trophic, and metabolic support to neurons and modulate synaptic activity. Accordingly, impairment in these astrocyte functions during brain ischemia and other insults can critically influence neuron survival. Astrocyte functions that are known to influence neuronal survival include glutamate uptake, glutamate release, free radical scavenging, water transport, and the production of cytokines and nitric oxide. Long-term recovery after brain injury, through neurite outgrowth, synaptic plasticity, or neuron regeneration, is influenced by astrocyte surface molecule expression and trophic factor release. In addition, the death or survival of astrocytes themselves may affect the ultimate clinical outcome and rehabilitation through effects on neurogenesis and synaptic reorganization.

Several antioxidant pathways are involved in astrocyte protection by melatonin

Neuroprotection provided by melatonin has been shown to be more relevant in vivo than in neuronal cultures. Given the role of astrocytes in neuronal support and protection, studies were initiated to elucidate the possible protective effect of the antioxidant melatonin against oxidative stress in these cells. Both low and high concentrations of melatonin were able to protect astrocytes with even higher efficiency than the known antioxidant glutathione (GSH). The mechanisms involved may be different for high (1 mm) and low (100 nm) concentrations of the indole. The GSH cycling appeared not to be involved in the protection at high doses. High doses of melatonin neither influenced GSH levels nor gene expression for the several antioxidant enzymes studied; thus, melatonin's protective effect was likely because of its free radical scavenging action in this case. However, melatonin concentrations in the nanomolar range require the presence of GSH to be effective. No increase in GSH synthesis was found, but low doses of melatonin increased gene expression and activity of glutathione peroxidase. As this enzyme requires GSH as substrate to be active, this may be the reason why the effect of this melatonin concentration is GSH dependent. In vivo, melatonin levels exhibit a wide range of concentrations with much lower levels in the blood and significantly higher concentrations in other body fluids and within cells. Thus, melatonin may normally function as an indirect and direct antioxidant in vivo.

Cerebrospinal fluid from patients with neurodegenerative and neuroinflammatory diseases: no evidence for rat glial activation in vitro

To determine the possible contribution of glial cells via oxidative stress/cytokine secretion in the pathogenesis of Parkinson's disease (PD), Alzheimer disease (AD), amyotrophic lateral sclerosis (ALS) or multiple sclerosis (MS) the concentration of nitric oxide (NO) (by the Griess method) and Interleukin-6 (IL-6) (by enzyme-linked immunosorbent assay) were measured in resting rat microglial and astrocytic cell culture supernatants stimulated by cerebrospinal fluid (CSF) (dilution 1:4, 1:10) from patients with the aforementioned diseases. Neither the concentration of NO (optical density at 450 nm: control, 0.036+/-0.006; MS, 0.034+/-0.008; AD, 0.031+/-0.006; PD, 0.02+/-0.01; lipopolysaccharide (LPS), 0.26+/-0.018) nor the amount of IL-6 (ng/ml: control, 0.112+/-0.026; PD, 0.12+/-0.027; MS, 0.123+/-0.008; ALS, 0.137+/-0.01; LPS, 1.81+/-0.11) differed in any disease group from those of unaffected controls. These findings suggest that the stimuli for inflammatory activation of glia are quite localized and not present in sufficient concentrations in the CSF of affected patients.

Astrocytes protect neurons from nitric oxide toxicity by a glutathione-dependent mechanism

Nitric oxide (NO) contributes to neuronal death in cerebral ischemia and other conditions. Astrocytes are anatomically well positioned to shield neurons from NO because astrocyte processes surround most neurons. In this study, the capacity of astrocytes to limit NO neurotoxicity was examined using a cortical co-culture system. Astrocyte-coated dialysis membranes were placed directly on top of neuronal cultures to provide a removable astrocyte layer between the neurons and the culture medium. The utility of this system was tested by comparing neuronal death produced by glutamate, which is rapidly cleared by astrocytes, and N-methyl-D-aspartate (NMDA), which is not. The presence of an astrocyte layer increased the LD(50) for glutamate by approximately four-fold, but had no effect on NMDA toxicity. Astrocyte effects on neuronal death produced by the NO donors S-nitroso-N-acetyl penicillamine and spermine NONOate were examined by placing these compounds into the medium of co-cultures containing either a control astrocyte layer or an astrocyte layer depleted of glutathione by prior exposure to buthionine sulfoximine. Neurons in culture with the glutathione-depleted astrocytes exhibited a two-fold increase in cell death over a range of NO donor concentrations. These findings suggest that astrocytes protect neurons from NO toxicity by a glutathione-dependent mechanism.

Metabolism and functions of glutathione in brain

The tripeptide glutathione is the thiol compound present in the highest concentration in cells of all organs. Glutathione has many physiological functions including its involvement in the defense against reactive oxygen species. The cells of the human brain consume about 20% of the oxygen utilized by the body but constitute only 2% of the body weight. Consequently, reactive oxygen species which are continuously generated during oxidative metabolism will be generated in high rates within the brain. Therefore, the detoxification of reactive oxygen species is an essential task within the brain and the involvement of the antioxidant glutathione in such processes is very important. The main focus of this review article will be recent results on glutathione metabolism of different brain cell types in culture. The glutathione content of brain cells depends strongly on the availability of precursors for glutathione. Different types of brain cells prefer different extracellular glutathione precursors. Glutathione is involved in the disposal of peroxides by brain cells and in the protection against reactive oxygen species. In coculture astroglial cells protect other neural cell types against the toxicity of various compounds. One mechanism for this interaction is the supply by astroglial cells of glutathione precursors to neighboring cells. Recent results confirm the prominent role of astrocytes in glutathione metabolism and the defense against reactive oxygen species in brain. These results also suggest an involvement of a compromised astroglial glutathione system in the oxidative stress reported for neurological disorders.

Astrocyte phenotype and prevention against oxidative damage in neurotoxicity

Astrocytes possess a potent array of protective systems. These are chiefly targeted against oxidised products and radicals, which are frequently present in increased amounts following exposure of nervous tissue to a range of toxic insults. Following exposure to the toxic chemicals astrocytes commonly respond by alteration in phenotype with upregulation of a large number of molecules, including those controlling the protective systems. This article summarizes evidence, largely obtained from in vitro studies, which supports the concept that some of the changes in astrocyte phenotype are associated with increased protection against the cytotoxicity caused by the oxidative damage that results from exposure to range of neurotoxicants.

Astrocyte cultures from transgenic mice to study the role of metallothionein in cytotoxicity of tert-butyl hydroperoxide

The cell viability, lipid peroxidation (LPO) and hydrogen peroxide (H(2)O(2)) generation were measured in cultured primary astrocytes, from metallothionein (MT)-I isoform overexpressing transgenic (MT-I*), MT-I/MT-II null and control mice after exposure to tert-butylhydroperoxide (tBH). Astrocytes from MT-I* mice have high basal levels of both MT-I mRNA and MT protein, whereas there is only MT-III isoform in astrocytes from MT-I/MT-II null mice. The results showed that (1) cultured astrocytes from MT-I* mice were most resistant to the cytotoxicity of tBH and those from MT-I/MT-II null mice were most sensitive to the cytotoxicity of tBH; (2) LPO after exposure to tBH were increased in all cells, but the levels were the highest in astrocytes from MT-I/MT-II null mice, while those in MT-I* mice were the lowest; (3) the levels of H(2)O(2) in cultured astrocytes from MT-I* mice were the lowest, while those in astrocytes from MT-I/MT-II null mice were the highest. These results support the hypothesis that MT can scavenge free radicals and protect astrocytes from oxidative stress.

The radioresponse of the central nervous system: a dynamic process

Radiation continues to be a major treatment modality for tumors located within and close to the central nervous system (CNS). Consequently, alleviating or protecting against radiation-induced CNS injury would be of benefit in cancer treatment. However, the rational development of such interventional strategies will depend on a more complete understand-ing of the mechanisms responsible for the development of this form of normal tissue injury. Whereas the vasculature and the oligodendrocyte lineage have traditionally been considered the primary radiation targets in the CNS, in this review we suggest that other phenotypes as well as critical cellular interactions may also be involved in determining the radio-response of the CNS. Furthermore, based on the assumption that the CNS has a limited repertoire of responses to injury, the reaction of the CNS to other types of insults is used as a framework for modeling the pathogenesis of radiation-induced damage. Evidence is then provided suggesting that, in addition to acute cell death, radiation induces an intrinsic recovery/repair response in the form of specific cytokines and may

Nitric oxide synthase inhibition delays axonal degeneration and promotes the survival of axotomized retinal ganglion cells

Nitric oxide (NO) synthesized by inducible nitric oxide synthase (iNOS) has been implicated in neuronal cytotoxicity following trauma to the central nervous system. The aim of the present study was to examine the role of NO in mediating axotomy-induced retinal ganglion cell (RGC) death. We observed increases in iNOS expression by microglia and Müller cells in the retina after optic nerve transection. This was paralleled by the induced expression of constitutive NOS (cNOS) in RGCs which do not normally express this enzyme. In order to determine if NO is cytotoxic to axotomized RGCs, the nonspecific NOS inhibitors Nomega-nitro-L-arginine (NOLA) or N-nitro-L-arginine methyl ester (L-NAME) were delivered to the vitreous chamber by intraocular injections. Both NOLA and L-NAME significantly enhanced RGC survival at 7, 10, and 14 days postaxotomy. The separate contributions of iNOS and cNOS to RGC degeneration were examined with intraocular injections of the specific iNOS inhibitor L-N(6)-(I-iminoethyl)lysine hydrochloride or the specific cNOS inhibitor L-thiocitrulline. Our results suggest that cNOS plays a greater role in RGC degeneration than iNOS. In addition to enhancing RGC survival, NOS inhibitors delayed the retrograde degeneration of RGC axons after axotomy. We conclude that NO synthesized by retinal iNOS and cNOS plays a major role in RGC death and retrograde axonal degeneration following axotomy.