Methamphetamine causes depletion of glutathione and an increase in oxidized glutathione in the rat striatum and prefrontal cortex

The administration of methamphetamine to experimental animals results in damage to dopaminergic neurons. The hypothesis that methampheta-mine-induced neurotoxicity is mediated by reactive oxygen species was evaluated. It was found that acute administration of methamphetamine (5 and 15 mg kg^-1) resulted in production of oxidative stress as demonstrated by decreased glutathione and increased oxidized glutathione levels in the rat striatum and prefrontal cortex. These changes in glutathione and oxidized glutathione levels were dose-dependent in striatum, but not in prefrontal cortex. In conclusion, the results of present study provide further evidence in support of the notion that oxidative stress may play an important role in the metham-phetamine-induced neurotoxicity.     

Compromised reactive microgliosis in MPTP-lesioned IL-6 KO mice

Reactive gliosis, the cellular manifestation of neuroinflammation, is a pathological hallmark of neurodegenerative diseases including Parkinson's disease. The persistent gliosis observed in the Parkinson's disease substantia nigra (SN) and in humans and animals exposed to the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) may represent a chronic inflammatory response that contributes to pathology. We have previously shown that in the absence of interleukin-6 (IL-6) dopaminergic neurons are more vulnerable to MPTP. Since IL-6 is both an autocrine and paracrine proliferation factor for CNS glia, we investigated reactive gliosis in MPTP-lesioned IL-6 (-/-) mice. While astrogliosis was similar in injured IL-6 (+/+) and IL-6 (-/-) SN pars compacta (pc), microgliosis was severely compromised in IL-6 (-/-) mice. In the absence of IL-6, an acute reactive microgliosis was transient with a complete absence of reactive microglia at day 7 post-lesion. Extensive reactive microgliosis was observed in the SNpc of MPTP-lesioned IL-6 (+/+) mice. Because glial derived inducible nitric oxide synthase (iNOS) has been implicated in dopaminergic cell death, we examined glial iNOS expression in the IL-6 genotypes to determine if it correlated with the greater vulnerability and reduced microgliosis observed in the MPTP-lesioned IL-6 (-/-) nigrostriatal system. Both reactive microglia and astrocytes expressed iNOS in the lesioned SNpc. In the IL-6 (-/-) mice, microglial iNOS expression diminished as reactive microgliosis declined. The data suggest IL-6 regulation of microglia activation, while iNOS expression appears to be secondary to cell activation.     

Methamphetamine causes lipid peroxidation and an increase in superoxide dismutase activity in the rat striatum

The administration of methamphetamine to experimental animals results in damage to nigrostriatal dopaminergic neurons. In the present study, we demonstrated that both the acute repeated and the chronic administration of methamphetamine causes an increase in thiobarbituric acid reactive substances, which are indicators of lipid peroxidation, and superoxide dismutase activity in the rat striatum. The results of present study strengthen the notion that reactive oxygen species may play an important role in the methamphetamine-induced neurotoxicity.     

Protection of methamphetamine nigrostriatal toxicity by dietary selenium

Multiple dose administration of methamphetamine (MA) results in long-lasting toxic effects in the nigrostriatal dopaminergic system. These effects are considered to be primarily due to oxidative damage mediated by increased production of hydrogen peroxide or other reactive oxygen species in the dopaminergic system. The present study was designed to determine the protective effects of dietary antioxidant selenium on MA-induced neurotoxicity in the nigrostriatal dopaminergic system. Male C57BL/6J mice were fed either selenium-deficient (< 0.01 ppm Se) or selenium-replete (0.2 ppm Se) diets for 90 days. MA treatment decreased the dopamine (DA) levels in the striatum and substantia nigra (SN) of both Se-replete and Se-deficient animals. However, in Se-replete animals, this DA depletion was significantly attenuated in both the striatum and SN. A novel observation is that MA administration resulted in increased activity of Cu,Zn-SOD in the brains of both Se-deficient and Se-replete animals. However, MA administration to Se-deficient animals exhibited a higher Cu,Zn-SOD activity in the nigrostriatal system than the control animals. Elevated malondialdehyde (MDA) levels in the striatum and SN were also observed in Se-deficient MA-treated animals. Se repletion significantly increased the glutathione peroxidase (GPx) activity and the ratio of reduced glutathione (GSH)/oxidized glutathione (GSSG) in the MA-treated animals. In conclusion, we have shown that dietary Se attenuated methamphetamine neurotoxicity and that this protection involves GPx-mediated antioxidant mechanisms. Even though Cu,Zn-SOD activity was significantly elevated by MA treatment, the role of this enzyme in MA-mediated neurotoxicity is not yet clear.     

Elevated locomotor activity without altered striatal dopamine contents in Nurr1 heterozygous mice after acute exposure to methamphetamine

Gene targeting experiments, in which both alleles of the Nurr1 gene were deleted, have shown that this molecule plays an essential role in the development of midbrain dopaminergic neurons, as shown by the loss of dopaminergic markers and the neurotransmitter dopamine (DA) in the ventral mesencephalon of Nurr1 null mutant mice. Nurr1-deficient mice die within a few hours of birth. Herein, we investigated whether adult mice (12-15-month-old), heterozygous for the Nurr1 mutation (Nurr1(+/-)), show alterations in locomotor function and in the nigrostriatal dopaminergic system after acute exposure to methamphetamine. We first evaluated spontaneous and amphetamine-induced (5mg/kg) locomotor response of >12-month-old wildtype (Nurr1(+/+)) and Nurr1(+/-) mice. Both, spontaneous and methamphetamine-induced locomotor behavior was significantly increased in the Nurr1(+/-) animals as compared to Nurr1(+/+) mice. Striatal DA and DA metabolite levels were measured in untreated animals and methamphetamine-treated animals. No significant differences in striatal dopamine levels or its metabolites DOPAC and HVA were found in the Nurr1(+/-) as compared to Nurr1(+/+) mice in untreated or methamphetamine-treated animals. These data show that deletion of a single allele of the Nurr1 gene alters the locomotor activity of 12-15-month-old Nurr1(+/-) animals. While total dopamine levels were not altered in the striatum of Nurr1(+/-) mice, future studies will be necessary to determine if processes involved with the dynamics of DA release/clearance within the nigrostriatal system may be altered in Nurr1(+/-) mutant mice.     

Neuroinflammation of the nigrostriatal pathway during progressive 6-OHDA dopamine degeneration in rats monitored by immunohistochemistry and PET imaging

We investigated the microglial response to progressive dopamine neuron degeneration using in vivo positron emission tomography (PET) imaging and postmortem analyses in a Parkinson's disease (PD) rat model induced by unilateral (right side) intrastriatal administration of 6-hydroxydopamine (6-OHDA). Degeneration of the dopamine system was monitored by PET imaging of presynaptic dopamine transporters using a specific ligand (11)C-CFT (2beta-carbomethoxy-3beta-(4-fluorophenyl) tropane). Binding of (11)C-CFT was markedly reduced in the striatum indicating dopaminergic degeneration. Parallel PET studies of (11)C-PK11195 (1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3 isoquinoline carboxamide) (specific ligand for activated microglia) showed increased binding in the striatum and substantia nigra indicative of a microglial response. Postmortem immunohistochemical analyses were performed with antibodies against CR3 for microglia/macrophage activation. Using a qualitative postmortem index for microglial activation we found an initially focal, then widespread microglial response at striatal and nigral levels at 4 weeks postlesion. These data support the hypothesis that inflammation is a significant component of progressive dopaminergic degeneration that can be monitored by PET imaging.     

MPP(+) injection into rat substantia nigra causes secondary glial activation but not cell death in the ipsilateral striatum

Injection of MPP(+) into the substantia nigra causes extensive necrosis and anterograde degeneration of pars compacta dopaminergic neurons. We studied secondary effects in the ipsilateral striatum by examining dopaminergic terminals, signs of neuronal damage, and glial reactivity at 1, 2, 3, and 7 days after injection of MPP(+) into the substantia nigra. Dopaminergic terminals and uptake sites were evaluated with [(3)H]GBR-12935 binding and tyrosine hydroxylase immunoreactivity. Glial reaction was examined with markers of astrocytes and microglia. Stereology was used to evaluate any changes in neuronal density. Tyrosine hydroxylase immunoreactivity and [(3)H]GBR-12935 binding markedly decreased (74%) from days 2 to 7. Loss of dopaminergic terminals in the ipsilateral striatum was accompanied by an intense astroglial and, to a lesser extent, microglial reaction. However, no signs of cell damage, neuronal loss, or disruption of the blood-brain barrier were found in the striatum. Resident astroglial and microglial cells showed a morphological shift and notable changes in protein expression typical of glial reactivity, yet the presence of macrophage-like cells was not detected. This study shows that injection of MPP(+) in the substantia nigra causes a secondary reaction within the ipsilateral striatum involving the transformation of quiescent glia to reactive glia. It is suggested that stimuli derived from damaged dopaminergic terminals within the striatum are able to activate resident glia and that this glial transformation may promote repair and regeneration.     

Differences in origin of reactive microglia in bone marrow chimeric mouse and rat after transient global ischemia

Current understanding of microglial involvement in disease is influenced by the observation that recruited bone marrow (BM)-derived cells contribute to reactive microgliosis in BM-chimeric mice. In contrast, a similar phenomenon has not been reported for BM-chimeric rats. We investigated the recruitment and microglial transformation of BM-derived cells in radiation BM-chimeric mice and rats after transient global cerebral ischemia, which elicits a characteristic microglial reaction. Both species displayed microglial hyperplasia and rod cell transformation in the hippocampal CA1 region. In mice, a subpopulation of lesion-reactive microglia originated from transformed BM-derived cells. By contrast, no recruitment or microglial transformation of BM-derived cells was observed in BM-chimeric rats. These results suggest that reactive microglia in rats originate from resident microglia, whereas they have a mixed BM-derived and resident origin in mice, depending on the severity of ischemic tissue damage.     

MK-801 and dextromethorphan block microglial activation and protect against methamphetamine-induced neurotoxicity

Methamphetamine causes long-term toxicity to dopamine nerve endings of the striatum. Evidence is emerging that microglia can contribute to the neuronal damage associated with disease, injury, or inflammation, but their role in methamphetamine-induced neurotoxicity has received relatively little attention. Lipopolysaccharide (LPS) and the neurotoxic HIV Tat protein, which cause dopamine neuronal toxicity after direct infusion into brain, cause activation of cultured mouse microglial cells as evidenced by increased expression of intracellular cyclooxygenase-2 and elevated secretion of tumor necrosis factor-alpha. MK-801, a non-competitive NMDA receptor antagonist that is known to protect against methamphetamine neurotoxicity, prevents microglial activation by LPS and HIV Tat. Dextromethorphan, an antitussive agent with NMDA receptor blocking properties, also prevents microglial activation. In vivo, MK-801 and dextromethorphan reduce methamphetamine-induced activation of microglia in striatum and they protect dopamine nerve endings against drug-induced nerve terminal damage. The present results indicate that the ability of MK-801 and dextromethorphan to protect against methamphetamine neurotoxicity is related to their common property as blockers of microglial activation.     

Microglia in the aging brain

The aging brain is characterized by a demonstrable decrease in weight and volume, particularly after the age of 50. This atrophy, which affects both grey and white matter, is presumed to result from a loss of neurons and myelinated axons. Glial cells, on the other hand, appear to increase in the aging brain, which exhibits greater immunoreactivity with both astrocytic and microglial markers. This review is focused on the morphologic and phenotypic changes that occur in microglial cells with normal aging. Although there is a consistent aging-related upregulation of microglial activation markers in experimental animals and humans that could be interpreted as aging-related neuroinflammation, it is generally difficult to show a direct correlation between ostensible microglial activation and neurodegeneration. This raises questions about whether aging-related microglial activation indeed represents reactive gliosis in the conventional sense. As an alternative, we discuss the possibility that structural and phenotypic changes that occur in microglia are a direct reflection of the aging process on microglia. Thus, microglia cells themselves may be subject to cellular senescence in the sense that they no longer function efficiently. The concept of microglial senescence offers a novel perspective on aging-related neurodegeneration, namely that neurodegeneration could also occur secondary to microglial degeneration.     

Immunocytochemical evidence for methamphetamine-induced serotonergic axon loss in the rat brain.

Central serotonin (5-HT) axons were visualized by immunocytochemistry to assess both acute and long-lasting changes in innervation density following methamphetamine administration to rats. Two morphologically distinct subtypes of 5-HT axons (fine and beaded) were differentially affected by d-methamphetamine (d-MA); the density of fine serotonergic axons was selectively decreased both 4 hours and 2 weeks after administration of d-MA. Acute depletion of 5-HT from fine axons, but not from beaded axons, was observed in the brains of all rats treated 4 hours previously with either a 100 mg/kg or 15 mg/kg dose of d-MA. Persistent loss of 5-HT axons was observed in 30% of rats treated 1 or 2 weeks previously with doses of d-MA which produce long-term deficits in biochemical markers for 5-HT. In the fraction of animals that exhibited denervation, fine serotonergic fibers were selectively ablated by d-MA, but beaded serotonergic fibers were spared. Thus, d-MA is similar to other amphetamine derivatives (e.g., p-chloroamphetamine, 3,4-methylenedioxyamphetamine) in that it acts selectively upon a morphologically distinct class of 5-HT axons but differs in that it produces long-lasting axon loss in only a fraction of animals. These data provide morphologic evidence of 5-HT axon loss following methamphetamine administration and further confirm the differential vulnerability of a particular morphological subtype of serotonergic axons to the neurotoxic effects of substituted amphetamines.     

Reactive microgliosis engages distinct responses by microglial subpopulations after minor central nervous system injury

Microglia are bone marrow-derived cells that constitute a facultative macrophage population when activated by trauma or pathology in the CNS. Endogenous CNS-resident microglia as well as exogenous (immigrant) bone marrow-derived cells contribute to reactive microgliosis, raising fundamental questions about the cellular composition, kinetics, and functional characteristics of the reactive microglial cell population. Bone marrow chimeric mice reconstituted with green fluorescent protein-expressing (GFP(+)) donor bone marrow cells were subjected to entorhinal cortex lesion, resulting in selective axonal degeneration and a localized microglial reaction in the hippocampus. Flow cytometric evaluation of individually dissected hippocampi differentiated immigrant GFP(+) microglia from resident GFP(-) microglia (CD11b(+)CD45(dim)) and identified a subset of mainly resident CD11b(+) microglia that was induced to express CD34. The proportion of immigrant GFP(+) microglia (CD11b(+)CD45(dim)) increased signficantly by 3 and 5 days postlesion and reached a maximum of 13% by 7 days. These cells expressed lower CD11b levels than resident microglia, forming a distinct subpopulation on CD11b/CD45 profiles. The proportion of CD34(+)CD11b(+) microglia was significantly increased at 3 days postlesion but had normalized by 5 and 7 days, when the microglial reaction is known to be at its maximum. Our results show that distinct subpopulations of microglia respond to minor CNS injury. The heterogeneity in microglial response may have functional consequences for repair and possibly therapy.     

Following nerve injury neuregulin-1 drives microglial proliferation and neuropathic pain via the MEK/ERK pathway

Following peripheral nerve injury microglia accumulate within the spinal cord and adopt a proinflammatory phenotype a process which contributes to the development of neuropathic pain. We have recently shown that neuregulin-1, a growth factor released following nerve injury, activates erbB 2, 3, and 4 receptors on microglia and stimulates proliferation, survival and chemotaxis of these cells. Here we studied the intracellular signaling pathways downstream of neuregulin-1-erbB activation in microglial cells. We found that neuregulin-1 in vitro induced phosphorylation of ERK1/2 and Akt without activating p38MAPK. Using specific kinase inhibitors we found that the mitogenic effect of neuregulin-1 on microglia was dependant on MEK/ERK1/2 pathway, the chemotactic effect was dependant on PI3K/Akt signaling and survival was dependant on both pathways. Intrathecal treatment with neuregulin-1 was associated with microgliosis and development of mechanical and cold pain related hypersensitivity which was dependant on ERK1/2 phosphorylation in microglia. Spinal nerve ligation results in a robust microgliosis and sustained ERK1/2 phosphorylation within these cells. This pathway is downstream of neuregulin-1/erbB signaling since its blockade resulted in a significant reduction in microglial ERK1/2 phosphorylation. Inhibition of the MEK/ERK1/2 pathway resulted in decreased spinal microgliosis and in reduced mechanical and cold hypersensitivity after peripheral nerve damage. We conclude that neuregulin-1 released after nerve injury activates microglial erbB receptors which consequently stimulates the MEK/ERK1/2 pathway that drives microglial proliferation and contributes to the development of neuropathic pain.     

Neuromelanin Activates Microglia and Induces Degeneration of Dopaminergic Neurons: Implications for Progression of Parkinson’s Disease

In Parkinson’s disease (PD), there is a progressive loss of neuromelanin (NM)-containing dopamine neurons in substantia nigra (SN) which is associated with microgliosis and presence of extracellular NM. Herein, we have investigated the interplay between microglia and human NM on the degeneration of SN dopaminergic neurons. Although NM particles are phagocytized and degraded by microglia within minutes in vitro, extracellular NM particles induce microglial activation and ensuing production of superoxide, nitric oxide, hydrogen peroxide (H₂O₂), and pro-inflammatory factors. Furthermore, NM produces, in a microglia-depended manner, neurodegeneration in primary ventral midbrain cultures. Neurodegeneration was effectively attenuated with microglia derived from mice deficient in macrophage antigen complex-1, a microglial integrin receptor involved in the initiation of phagocytosis. Neuronal loss was also attenuated with microglia derived from mice deficient in phagocytic oxidase, a subunit of NADPH oxidase, that is responsible for superoxide and H₂O₂ production, or apocynin, an NADPH oxidase inhibitor. In vivo, NM injected into rat SN produces microgliosis and a loss of tyrosine hydroxylase neurons. Thus, these results show that extracellular NM can activate microglia, which in turn may induce dopaminergic neurodegeneration in PD. Our study may have far-reaching implications, both pathogenic and therapeutic.     

Protective effects of MK-801 on methamphetamine-induced depletion of dopaminergic and serotonergic terminals and striatal astrocytic response: An immunohistochemical study

It has been shown previously that methamphetamine induces dopaminergic nerve terminal degeneration, serotonin depletion and striatal reactive astrogliosis, and that the noncompetitive N-methyl-D-aspartate (NMDA) antagonist MK-801 can block methamphetamine (MA)-induced depletion of dopamine and serotonin and reduction in activity of their synthetic enzymes. In this study, immunohistochemistry was used to evaluate the effect of MK-801 on methamphetamine-induced neuropathological alterations of dopaminergic and serotonergic terminals and striatal astrocytic responses. Adult male rats were treated with methamphetamine (4 injections of 10 mg/kg at 2 hour intervals) in conjunction with MK-801 which was administered 15 min before each methamphetamine administration at doses of 1 mg/kg or 2 mg/kg. Brains were examined three days following treatment. MK-801 administration prevented methamphetamine-induced depletion of 5-hydroxytryptophan (5-HT) terminals in the forebrain and depletion of tyrosine hydroxylase-positive dopaminergic terminals and astrocytic response in the neostriatum in most animals. These results support the concept that excitatory amino acids acting through an NMDA receptor are involved in methamphetamine-induced neuronal damage on dopaminergic and serotonergic terminal fields. A minor depletion of TH-positive terminals and astrogliosis in the neostriatum was seen in three of nine MA-MK-801-treated animals. This indicates that the protective effects of MK-801 on MA-induced dopaminergic terminal degeneration varies among animals with complete protection in most animals and partial protection in the others using the present doses and dosing regimen. © 1995 Wiley-Liss, Inc.     

Early Effects of FGF-2 on Glial Cells in the MPTP-Lesioned Striatum

Fibroblast growth factor-2 (FGF-2), locally administered in gelfoam to the striatum of mice treated with the neurotoxic drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), has restorative and neuroprotective effects on dopaminergic neurons and associated striatal transmitter systems. Most of the beneficial alterations are apparently indirect. FGF-2 must therefore act through a series of cellular and molecular intermediate steps, which have not been explored. We have previously shown that FGF-2 does not significantly affect the astroglial reaction at the time, when the neuroprotective effect of FGF-2 reaches a peak (Day 11). In this study we have investigated the effect of FGF-2 at earlier time points after MPTP treatment. We report now that as early as 6 h after administration of the gelfoam containing either FGF-2 or control protein, FGF-2 immunoreactivity disappears from astroglial nuclei, while appearing in small ramified GFAP- and S-100-negative cells, most likely microglia. At 18 h, numbers and staining intensities of GFAP-ir astroglial cells are greater in FGF-2- than in cytochrome C-treated animals. At this time FGF-2-ir reappears in astroglia nuclei of cytochrome C-treated animals, but remains undetectable in the striatum carrying the FGF-2-containing gelfoam. Ramified GFAP/S-100-negative presumed microglial cells are now intensely ir for FGF-2. Signs of an FGF-2-mediated astrogliotic reaction are very pronounced at 18 h and 2 days, but no longer at 11 days, when the astrogliosis reaction has become equally strong in FGF-2- and cytochrome C-treated striata. Our results suggest that administration of FGF-2 to the MPTP-lesioned striatum has early effects on astro- and presumed microglia cells, notably on the nuclear FGF-2-ir of astrocytes. These changes may be involved in mediating the neuro-protective effects of FGF-2 in the MPTP-model of Parkinsonism.     

Neuroprotective Effect of Ghrelin in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Mouse Model of Parkinson’s Disease by Blocking Microglial Activation

Ghrelin is an endogenous ligand for growth hormone (GH) secretagogue receptor 1a (GHS-R1a) and is produced and released mainly from the stomach. It was recently demonstrated that ghrelin can function as a neuroprotective factor by inhibiting apoptotic pathways. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic neurotoxicity in rodents; previous studies suggest that activated microglia actively participate in the pathogenesis of Parkinson’s disease (PD) neurodegeneration. However, the role of microglia in the neuroprotective properties of ghrelin is still unknown. Here we show that, in the mouse MPTP PD model generated by an acute regimen of MPTP administration, systemic administration of ghrelin significantly attenuates the loss of substantia nigra pars compacta (SNpc) neurons and the striatal dopaminergic fibers through the activation of GHS-R1a. We also found that ghrelin reduced nitrotyrosine levels and improved the impairment of rota-rod performance. Ghrelin prevents MPTP-induced microglial activation in the SNpc and striatum, the expression of pro-inflammatory molecules tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β), and the activation of inducible nitric oxide synthase. The inhibitory effect of ghrelin on the activation of microglia appears to be indirect by suppressing matrix metalloproteinase-3 (MMP-3) expression in stressed dopaminergic neurons because GHS-R1a is not expressed in SNpc microglial cells. Finally, in vitro administration of ghrelin prevented 1-methyl-4-phenylpyridinium-induced dopaminergic cell loss, MMP-3 expression, microglial activation, and the subsequent release of TNF-α, IL-1β, and nitrite in mesencephalic cultures. Our data indicate that ghrelin may act as a survival factor for dopaminergic neurons by functioning as a microglia-deactivating factor and suggest that ghrelin may be a valuable therapeutic agent for neurodegenerative diseases such as PD.     

Nerve injury‐activated microglia engulf myelinated axons in a P2Y12 signaling‐dependent manner in the dorsal horn

The mechanisms underlying neuropathic pain are poorly understood. However, several studies have implied a role for reactive microglia located in the dorsal horn in neuropathic pain. To clarify the roles of activated microglia in neuropathic pain, we investigated the interactions among microglia and other neural components in the dorsal horn using electron microscopy. Microglia were more abundantly localized in layers II–III of the dorsal horn than in other areas, and some of them adhered to and engulfed both injured and uninjured myelinated axons. This microglial engulfment was rarely observed in the normal dorsal horn, and the number of microglia attached to myelinated axons was markedly increased on postoperative day 7 on the operated side. However, after blocking the P2Y12 ATP receptor in microglia by intrathecal administration of its antagonist, AR‐C69931MX, the increase in the number of microglia attached to myelinated axons, as well as the development of tactile allodynia, were markedly suppressed, although the number of activated microglia did not change remarkably. These results indicate that engulfment of myelinated axons by activated microglia via P2Y12 signaling in the dorsal horn may be a critical event in the pathogenesis of neuropathic pain. © 2010 Wiley‐Liss, Inc.     

Nrf2 regulates microglial dynamics and neuroinflammation in experimental Parkinson's disease

Neural injury leads to inflammation and activation of microglia that in turn may participate in progression of neurodegeneration. The mechanisms involved in changing microglial activity from beneficial to chronic detrimental neuroinflammation are not known but reactive oxygen species (ROS) may be involved. We have addressed this question in Nrf2‐knockout mice, with hypersensitivity to oxidative stress, submitted to daily inoculation of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) for 4 weeks. Basal ganglia of these mice exhibited a more severe dopaminergic dysfunction than wild type littermates in response to MPTP. The amount of CD11b‐positive/CD45‐highly‐stained cells, indicative of peripheral macrophage infiltration, did not increase significantly in response to MPTP. However, Nrf2‐deficient mice exhibited more astrogliosis and microgliosis as determined by an increase in messenger RNA and protein levels for GFAP and F4/80, respectively. Inflammation markers characteristic of classical microglial activation, COX‐2, iNOS, IL‐6, and TNF‐α were also increased and, at the same time, anti‐inflammatory markers attributable to alternative microglial activation, such as FIZZ‐1, YM‐1, Arginase‐1, and IL‐4 were decreased. These results were confirmed in microglial cultures stimulated with apoptotic conditioned medium from MPP⁺‐treated dopaminergic cells, further demonstrating a role of Nrf2 in tuning balance between classical and alternative microglial activation. This study demonstrates a crucial role of Nrf2 in modulation of microglial dynamics and identifies Nrf2 as molecular target to control microglial function in Parkinson's disease (PD) progression. © 2009 Wiley‐Liss, Inc.