Dong-Young Choi

Cyclooxygenase-2 mediates microglial activation and secondary dopaminergic cell death in the mouse MPTP model of Parkinson's disease

BackgroundAccumulating evidence suggests that inflammation plays an important role in the progression of Parkinsons disease (PD). Among many inflammatory factors found in the PD brain, cyclooxygenase (COX), specifically the inducible isoform, COX-2, is believed to be a critical enzyme in the inflammatory response. Induction of COX-2 is also found in an experimental model of PD produced by administration of 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).MethodCOX-2-deficient mice or C57BL/6 mice were treated with MPTP to investigate the effects of COX-2 deficiency or by using various doses of valdecoxib, a specific COX-2 inhibitor, which induces inhibition of COX-2 on dopaminergic neuronal toxicity and locomotor activity impairment. Immunohistochemistry, stereological cell counts, immunoblotting, an automated spontaneous locomotor activity recorder and rotarod behavioral testing apparatus were used to assess microglial activation, cell loss, and behavioral impariments.ResultsMPTP reduced tyrosine hydroxylase (TH)-positive cell counts in the substantia nigra pars compacta (SNpc); total distance traveled, vertical activity, and coordination on a rotarod; and increased microglia activation. Valdecoxib alleviated the microglial activation, the loss of TH-positive cells and the decrease in open field and vertical activity. COX-2 deficiency attenuated MPTP-induced microglial activation, degeneration of TH-positive cells, and loss of coordination.ConclusionThese results indicate that reducing COX-2 activity can mitigate the secondary and progressive loss of dopaminergic neurons as well as the motor deficits induced by MPTP, possibly by suppression of microglial activation in the SNpc.

Interleukin-10 protects against inflammation-mediated degeneration of dopaminergic neurons in substantia nigra

Inflammation has been increasingly recognized to play an important role in the pathogenesis of Parkinsons disease (PD). Using immunocytochemistry and electron microscopy, we found that intranigral injection of lipopolysaccharide (LPS) caused marked microglial activation and a dose-dependent selective loss of dopaminergic neurons, which was mediated by apoptosis as evidenced by prominent TUNEL labeling. RNase protection assays revealed that mRNA for Bax, Fas and the pro-inflammatory cytokines interleukin (IL)-1α, IL-1β, IL-6 and tumor necrosis factor (TNF)-α were significant increased ipsilaterally in LPS-injected side of SN, while expression of the anti-apoptotic gene Bcl-2 was decreased. Osmotic pump infusion of IL-10, a global inhibitor of cytokine synthesis, protected against LPS-induced cell death of dopaminergic neurons, with a corresponding decrease in the number of activated microglia, suggesting that the reduction in microglia-mediated release of inflammatory mediators may contribute to the anti-inflammatory effect of IL-10. Our results provide evidence that LPS induces apoptotic cell death in SNpc, which is likely through the expression of Fas, Bax, caspase-3, and the pro-inflammatory cytokines.

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.

Striatal Neuroinflammation Promotes Parkinsonism in Rats

Background Sporadic Parkinsons disease (PD) is a progressive neurodegenerative disorder with unknown cause, but it has been suggested that neuroinflammation may play a role in pathogenesis of the disease. Neuroinflammatory component in process of PD neurodegeneration was proposed by postmortem, epidemiological and animal model studies. However, it remains unclear how neuroinflammatory factors contribute to dopaminergic neuronal death in PD. Findings In this study, we analyzed the relationship among inducible nitric oxide synthase (iNOS)-derived NO, mitochondrial dysfunction and dopaminergic neurodegeneration to examine the possibility that microglial neuroinflammation may induce dopaminergic neuronal loss in the substantia nigra. Unilateral injection of lipopolysaccharide (LPS) into the striatum of rat was followed by immunocytochemical, histological, neurochemical and biochemical analyses. In addition, behavioral assessments including cylinder test and amphetamine-induced rotational behavior test were employed to validate ipsilateral damage to the dopamine nigrostriatal pathway. LPS injection caused progressive degeneration of the dopamine nigrostriatal system, which was accompanied by motor impairments including asymmetric usage of forelimbs and amphetamine-induced turning behavior in animals. Interestingly, some of the remaining nigral dopaminergic neurons had intracytoplasmic accumulation of α-synuclein and ubiquitin. Furthermore, defect in the mitochondrial respiratory chain, and extensive S-nitrosylation/nitration of mitochondrial complex I were detected prior to the dopaminergic neuronal loss. The mitochondrial injury was prevented by treatment with L-N6-(l-iminoethyl)-lysine, an iNOS inhibitor, suggesting that iNOS-derived NO is associated with the mitochondrial impairment. Conclusions These results implicate neuroinflammation-induced S-nitrosylation/nitration of mitochondrial complex I in mitochondrial malfunction and subsequent degeneration of the nigral dopamine neurons.

Protective properties afforded by pioglitazone against intrastriatal LPS in Sprague–Dawley rats

We created an inflammation-induced Parkinsons disease model, where microglia activation leads to oxidative stress, mitochondrial dysfunction, and dopaminergic neurodegeneration in the substantia nigra. Pioglitazone, an agonist of peroxisome proliferator activated receptor-gamma (PPAR-gamma), can prevent these deficits and protect dopaminergic neurons. To continue exploring the effects of pioglitazone in this model we focused on the expression of PPAR-gamma, uncoupling protein 2 (UCP2), and mitoNEET. We report that intrastriatal lipopolysaccharide (LPS) increases striatal PPAR-gamma, UCP2, and mitoNEET expression, and pioglitazone attenuates these LPS-induced changes.

Trichloroethylene induces dopaminergic neurodegeneration in Fisher 344 rats

J. Neurochem. (2010) 112, 773–783.

Intrastriatal lipopolysaccharide injection induces Parkinsonism in C57/B6 mice

A role for inflammation has been hypothesized in the etiology and progression of Parkinsons disease (PD). In this study, we generated, characterized, and validated the first progressive PD‐related mouse model (C57/B6) with intrastriatal injection of lipopolysaccharide (LPS). We showed progressive and specific dopaminergic neurodegeneration in the substantia nigra, which is accompanied by striatal dopamine depletion and progressive behavioral impairment, which was alleviated by the use of the PD drug L‐Dopa. We focused on the role of nitric oxide (NO) in inflammation‐promoted cell death and suggest that the expression of the inducible NO synthase plays a role in the progressive loss of dopaminergic neurons but not the initial loss induced by LPS. With this model, future research can be performed in gene knockout mice to study other potential mechanisms of inflammation‐induced neurodegeneration. In addition, this model can be used to screen therapeutics for PD at a more clinically relevant time (i.e., after LPS injection but before manifestation of PD‐related behavioral impairment), because most PD drugs are screened in animal models in which inhibitors are given predisease induction. Thus, this novel PD‐related model should be further characterized and strongly considered as a tool for future drug studies.

Prodynorphin knockout mice demonstrate diminished age-associated impairment in spatial water maze performance.

Dynorphins, endogenous kappa-opioid agonists widely expressed in the central nervous system, have been reported to increase following diverse pathophysiological processes, including excitotoxicity, chronic inflammation, and traumatic injury. These peptides have been implicated in cognitive impairment, especially that associated with aging. To determine whether absence of dynorphin confers any beneficial effect on spatial learning and memory, knockout mice lacking the coding exons of the gene encoding its precursor prodynorphin (Pdyn) were tested in a water maze task. Learning and memory assessment using a 3-day water maze protocol demonstrated that aged Pdyn knockout mice (13-17 months) perform comparatively better than similarly aged wild-type (WT) mice, based on acquisition and retention probe trial indices. There was no genotype effect on performance in the cued version of the swim task nor on average swim speed, suggesting the observed genotype effects are likely attributable to differences in cognitive rather than motor function. Young (3-6 months) mice performed significantly better than aged mice, but in young mice, no genotype difference was observed. To investigate the relationship between aging and brain dynorphin expression in mice, we examined dynorphin peptide levels at varying ages in hippocampus and frontal cortex of WT 129SvEv mice. Quantitative radioimmunoassay demonstrated that dynorphin A levels in frontal cortex, but not hippocampus, of 12- and 24-month mice were significantly elevated compared to 3-month mice. Although the underlying mechanisms have yet to be elucidated, the results suggest that chronic increases in endogenous dynorphin expression with age, especially in frontal cortex, may adversely affect learning and memory.

Aging enhances the neuroinflammatory response and α-synuclein nitration in rats

The Lewy body is a pathological hallmark of Parkinsons disease. It has been revealed that the Lewy body contains nitrated alpha-synuclein which is prone to oligomerization. We tested the hypothesis that aging may enhance nitration of alpha-synuclein due to an exaggerated neuroinflammatory reaction such as an excessive induction of the inducible nitric oxide synthase, which occurs post-intrapallidal lipopolysaccharide (LPS) injection. Here, we show microglia activation and proinflammatory cytokine expression are more evident in the substantia nigra of elderly rats following intrapallidal LPS. In addition, greater nitration of proteins like alpha-synuclein occurs in the substantia nigra of 16-month-old rats versus 3-month-old rats, which is accompanied by a higher expression level of inducible nitric oxide synthase. These results imply that an exaggerated neuroinflammatory response that occurs with aging might be involved in the increase in prevalence of neurodegenerative diseases like Parkinsons disease.

Involvement of inflammation in Alzheimer’s disease pathogenesis and therapeutic potential of anti-inflammatory agents

Abstract Alzheimer’s disease (AD) is the most common form of dementia. It is characterized by beta-amyloid (Aβ) peptide fibrils, which are extracellular depositions of a specific protein, and is accompanied by extensive neuroinflammation. Various studies have demonstrated risk factors that can affect AD pathogenesis, and they include accumulation of Aβ, hyperphosphorylation of tau protein, and neuroinflammation. Among these detrimental factors, neuroinflammation has been highlighted by epidemiologic studies suggesting that use of anti-inflammatory drugs could significantly reduce the incidence of AD. Evidence suggests that astrocytes, microglia, and infiltrating immune cells from periphery might contribute to or modify the process of neuroinflammation and neurodegeneration in AD brains. In addition, recent data indicate that microRNAs may affect neuroinflammatory responses in the brain. This article focuses on supportive evidence that neuroinflammation plays a critical role in AD development. In addition, we depict putative therapeutic capacity of anti-inflammatory drugs for AD prevention or treatment. We also discuss pathogenic mechanisms by which astrocytes, microglia, T cells and microRNA participate in AD and the neuroprotective mechanisms of anti-inflammatory drugs.