Protective action of the peroxisome proliferator-activated receptor-gamma agonist pioglitazone in a mouse model of Parkinson's disease

We examined the effect of pioglitazone, a peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist of the thiazolidinedione class, on dopaminergic nerve cell death and glial activation in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. The acute intoxication of C57BL/6 mice with MPTP led to nigrostriatal injury, as determined by tyrosine hydroxylase (TH) immunocytochemistry, and HPLC detection of striatal dopamine and metabolites. Damage to the nigrostriatal dopamine system was accompanied by a transient activation of microglia, as determined by macrophage antigen-1 (Mac-1) and inducible nitric oxide synthase (iNOS) immunoreactivity, and a prolonged astrocytic response. Orally administered pioglitazone (approximately 20 mg/kg/day) attenuated the MPTP-induced glial activation and prevented the dopaminergic cell loss in the substantia nigra pars compacta (SNpc). In contrast, there was little reduction of MPTP-induced dopamine depletion, with no detectable effect on loss of TH immunoreactivity and glial response in the striatum of pioglitazone-treated animals. Low levels of PPARgamma expression were detected in the ventral mesencephalon and striatum, and were unaffected by MPTP or pioglitazone treatment. Since pioglitazone affects primarily the SNpc in our model, different PPARgamma-independent mechanisms may regulate glial activation in the dopaminergic terminals compared with the dopaminergic cell bodies after acute MPTP intoxication.     

Protection by pioglitazone in the MPTP model of Parkinson's disease correlates with I kappa B alpha induction and block of NF kappa B and iNOS activation

Inflammation has been implicated in the pathogenesis of Parkinson's disease (PD). In the chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD, inducible NO synthase (iNOS) derived nitric oxide (NO) is an important mediator of dopaminergic cell death. Ligands of the peroxisome proliferator-activated receptor (PPAR) exert anti-inflammatory effects. We here investigated whether pioglitazone, a PPARgamma agonist, protected mice from MPTP-induced dopaminergic cell loss, glial activation, and loss of catecholamines in the striatum. As shown by western blot, PPARgamma was expressed in the striatum and the substantia nigra of vehicle- and MPTP-treated mice. Oral administration of 20 mg/(kg day) of pioglitazone protected tyrosine hydroxylase (TH)-positive substantia nigra neurons from death induced by 5 x 30 mg/kg MPTP. However, the decrease of dopamine in the striatum was only partially prevented. In mice treated with pioglitazone, there were a reduced activation of microglia, reduced induction of iNOS-positive cells and less glial fibrillary acidic protein positive cells in both striatum and substantia nigra pars compacta. In addition, treatment with pioglitazone almost completely blocked staining of TH-positive neurons for nitrotyrosine, a marker of NO-mediated cell damage. Because an increase in inhibitory protein-kappa-Balpha (IkappaBalpha) expression and inhibition of translocation of the nuclear factor kappaB (NFkappaB) subunit p65 to the nucleus in dopaminergic neurons, glial cells and astrocytes correlated with the protective effects of pioglitazone, our results suggest that pioglitazone sequentially acts through PPARgamma activation, IkappaBalpha induction, block of NFkappaB activation, iNOS induction and NO-mediated toxicity. In conclusion, treatment with pioglitazone may offer a treatment opportunity in PD to slow the progression of disease that is mediated by inflammation.     

Nitric oxide and reactive oxygen species in Parkinson's disease

Parkinson's disease is a neurodegenerative disorder of unknown pathogenesis. Oxidative stress has been proposed as one of several pathogenic hypotheses. Evidence for the participation of oxidative processes in the pathogenesis of Parkinson's disease have been obtained in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model by the use of genetically altered mice. MPTP administration has been shown to increase levels of superoxide both intracellularly, via the inhibition of mitochondrial respiration and other mechanisms and extracellularly, via the activation of NADPH-oxidase in microglia. In addition to superoxide, nitric oxide production by nNOS or by microglial iNOS also contributes to the MPTP neurotoxocity. Mice with endowed defences against superoxide or with deficiency in the nNOS and iNOS are protected from MPTP toxicity suggesting that formation of reactive oxygen and nitrogen intermediates both intracellularly and extracellularly contributes to the demise of dopaminergic neurons. Similar contribution of reactive nitrogen and oxygen species may well underlie the neurodegenerative processes in Parkinson's disease.     

Inducible nitric oxide synthase stimulates dopaminergic neurodegeneration in the MPTP model of Parkinson disease

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) damages dopaminergic neurons as seen in Parkinson disease. Here we show that after administration of MPTP to mice, there was a robust gliosis in the substantia nigra pars compacta associated with significant upregulation of inducible nitric oxide synthase (iNOS). These changes preceded or paralleled MPTP-induced dopaminergic neurodegeneration. We also show that mutant mice lacking the iNOS gene were significantly more resistant to MPTP than their wild-type littermates. This study demonstrates that iNOS is important in the MPTP neurotoxic process and indicates that inhibitors of iNOS may provide protective benefit in the treatment of Parkinson disease.     

Preventive role of PD‐1 on MPTP‐induced dopamine depletion in mice

Many current studies of Parkinson's disease (PD) suggest that inflammation is involved in the neurodegenerative process. PD‐1, a traditional Korean medicine, used to treat various brain diseases in Korea. This study was designed to investigate the effect of PD‐1 extract in the Parkinson's model of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) lesioned mice. The MPTP administration caused the dopamine neuron loss in the striatum and substantia nigra pars compacta (SNpc), which was demonstrated by a depletion of tyrosine hydroxylase (TH). In addition, a reduction of bcl‐2 expression with elevation of bax expression, caspase‐3 activation, and release of cytochrome c into cytosol in dopaminergic neurons of SNpc were noted. Oral administration of PD‐1 extract (50 and 100 mg kg^?1) attenuated the MPTP‐induced depletion of TH proteins in the striatum and SNpc and prevented the apoptotic effects. These results indicate that PD‐1 extract is able to protect dopaminergic neurons from MPTP‐induced neuronal death, with important implications for the treatment of PD. Copyright © 2010 John Wiley & Sons, Ltd.     

MicroRNA-30e regulates neuroinflammation in MPTP model of Parkinson’s disease by targeting Nlrp3

Accumulating evidences suggest that neuroinflammation is a pathological hallmark of Parkinson’s disease (PD), a neurodegenerative disorder characterized by loss of dopaminergic neurons in substantia nigra pars compacta (SNpc). MicroRNAs have been recently recognized as crucial regulators of inflammatory responses. Here, we found significant downregulation of microRNA-30e (miR-30e) in SNpc of MPTP-induced PD mice. Next, we employed miR-30e agomir to upregulate miR-30e expression in MPTP-treated mice. Our results showed that delivery of miR-30e agomir remarkably improved motor behavioral deficits and neuronal activity, and inhibited the loss of dopamine neurons. Moreover, the increased α-synuclein protein expression in SNpc of MPTP-PD mice was alleviated by the upregulation of miR-30e. Further, miR-30e agomir administration also attenuated the marked increase of inflammatory cytokines, such as TNF-α, COX-2, iNOS, and restored the decreased secretion of BDNF in SNpc. In addition, we demonstrated for the first time that miR-30e directly targeted to Nlrp3, thus suppressing Nlrp3 mRNA and protein expression. Finally, miR-30e upregulation significantly inhibited the activation of Nlrp3 inflammasome as evident from the decreased Nlrp3, Caspase-1 and ASC expressions and IL-18 and IL-1β secretions. Taken together, our study demonstrates that miR-30e ameliorates neuroinflammation in the MPTP model of PD by decreasing Nlrp3 inflammasome activity. These findings suggesting that miR30e may be a key inflammation-mediated molecule that could be a potential target for PD therapeutics.     

Catalpol protects dopaminergic neurons from LPS-induced neurotoxicity in mesencephalic neuron-glia cultures

Inflammation plays an important role in the pathogenesis of Parkinson's disease (PD). Microglia, the resident immune cells in the central nervous system, are pivotal in the inflammatory reaction. Activated microglia can induce expression of inducible nitric-oxide synthase (iNOS) and release significant amounts of nitric oxide (NO) and TNF-alpha, which can damage the dopaminergic neurons. Catalpol, an iridoid glycoside, contained richly in the roots of Rehmannia glutinosa, was found to be neuroprotective in gerbils subjected to transient global cerebral ischemia. But the effect of catalpol on inflammation-mediated neurodegeneration has not been examined. In this study, microglia in mesencephalic neuron-glia cultures were activated with lipopolysaccharide (LPS) and the aim of the study was to examine whether catalpol could protect dopaminergic neurons from LPS-induced neurotoxicity. The results showed that catalpol significantly reduced the release of reactive oxygen species (ROS), TNF-alpha and NO after LPS-induced microglial activation. Further, catalpol attenuated LPS-induced the expression of iNOS. As determined by immunocytochemical analysis, pretreatment by catalpol dose-dependently protected dopaminergic neurons against LPS-induced neurotoxicity. These results suggest that catalpol exerts its protective effect on dopaminergic neurons by inhibiting microglial activation and reducing the production of proinflammatory factors. Thus, catalpol may possess therapeutic potential against inflammation-related neurodegenerative diseases.     

MicroRNA-326 suppresses iNOS expression and promotes autophagy of dopaminergic neurons through the JNK signaling by targeting XBP1 in a mouse model of Parkinson's disease

Parkinson's disease (PD) is characterized by a progressive loss of dopaminergic neurons, and substantia nigra is primarily one of the damaged brain regions. Evidence indicates that microRNAs (miRNAs) is involved in the pathophysiology of this disease. The present study aimed to investigate the biological function of miR-326 in PD through the JNK signaling pathway by targeting X-box binding protein 1 (XBP1). After liposome complexes were prepared, healthy male C57BL/6 mice were selected to construct a mouse model of PD. The targeting relationship between miR-326 and XBP1 was confirmed. The expression of miR-326 and XBP1 was measured in PD mice, and gain- and loss-function assay was conducted to examine the regulatory effect of miR-326 and XBP1 on inducible nitric oxide synthase (iNOS) expression and autophagy of dopaminergic neurons of PD mice. Mice treated with miR-326 mimic and siRNA-XBP1 showed increased traction test scores, activation of autophagy, expression of LC3-II, c-Jun, and p-α-Syn, but diminished climbing time and expressions of iNOS, α-Syn, and p-c-Jun. The siRNA-XBP1 treatment could reverse the effect of miR-326 inhibitor on PD mice. Overexpression of miR-326 inhibits iNOS expression and promotes autophagy of dopaminergic neurons through JNK signaling by targeting XBP1.     

Differential protection against MPTP or methamphetamine toxicity in dopamine neurons by deletion of ppN/OFQ expression

Nociceptin (N/OFQ) is an endogenous neuropeptide that plays a role in the behavioral deficits associated with Parkinson's disease (PD). The purpose of the present study was to characterize the protective effects of prepro (pp)N/OFQ gene deletion against two dopamine toxins, MPTP and methamphetamine (METH). Results demonstrate that ppN/OFQ gene deletion attenuates the loss of both the number of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNpc) and loss of TH and vesicular monoamine transporter-2 (VMAT) immunoreactivity in the caudate putamen (CPu) of MPTP-treated mice. This protection was unaffected by age or gender, although, when loss of TH exceeded 90% in 5-6 month-old mice, the protective effect was greatly diminished. In contrast, METH administration preferentially damaged dopaminergic terminals in the CPu with little effect on dopamine neurons in the SNpc, an effect not reversed by ppN/OFQ gene deletion. To determine if N/OFQ and MPP+ act directly and synergistically on dopamine neurons, differentiated SH-SY5Y cells were incubated with N/OFQ and/or MPP+. N/OFQ did not increase MPP+-mediated cell loss, suggesting an indirect action of N/OFQ. These studies demonstrate that inhibition of the endogenous N/OFQ system may represent a new therapeutic target for prevention of neuronal loss associated with PD.     

Reduced sensitivity of inducible nitric oxide synthase-deficient mice to chronic colitis.

BACKGROUND: Overproduction of nitric oxide by the inducible form of nitric oxide synthase (iNOS) has been implicated in colitis. Different authors have postulated both toxic and protective effects of nitric oxide (NO) in the pathophysiology of active inflammation. The objective of this study was to examine the role of iNOS in experimental chronic colitis using iNOS-deficient mice. METHODS: For induction of colitis, mice received three cycles of 2% of dextran sodium sulfate (DSS) (M.W. 40,000) treatment in drinking water. The degree of colonic inflammation, leukocyte infiltration, and the expression of cell adhesion molecules were determined. INOS expression and nitrotyrosine were also determined by immunohistochemistry. RESULTS: After DSS treatment, a moderate colitis with marked cell infiltration was observed. Intense expression of iNOS was observed on infiltrating cells as well as on the colonic mucosal epithelium in these animals. In the iNOS-deficient mice, tissue damage was significantly diminished. No iNOS or nitrotyrosine staining was found in iNOS-deficient mice. The number of infiltrating cells and the expression of mucosal adressin cell adhesion molecule-1 were significantly attenuated in the DSS-treated colon of iNOS-deficient mice. CONCLUSION: Induction of iNOS seems to act as a critical toxic effector molecule in the pathogenesis of chronic colonic inflammation.     

Effective inhibition of miR-330/SHIP1/NF-κB signaling pathway via miR-330 sponge repolarizes microglia differentiation

Neuroinflammation mediated by microglia has been identified as vital pathogenesis in Parkinson's disease (PD). This study aimed to investigate the role and potential regulatory mechanism of microRNA-330 in the lipopolysaccharide (LPS)-induced chronic neuroinflammatory model. Primary microglia chronic inflammation model and PD animal model were established by LPS treatment. Bulged microRNA-330 sponges containing six microRNA binding sites were constructed and delivered by plasmid or recombinant adeno-associated virus (rAAV2)/5-green fluorescent protein (GFP) vector. The expression levels of microRNA-330 were assessed by a quantitative real-time polymerase chain reaction. Primary microglia polarization was determined by flow cytometry; meanwhile, dopamine and pro-(anti-)inflammatory cytokines were measured by enzyme-linked immunosorbent assay. Expression levels of GFAP, lba1, inducible nitric oxide synthase (iNOS), Arg1, SHIP1, cytoplasmic, and nuclear factor-κB (NF-κB) were analyzed by Western blot. The behavioral deficit was determined by the rotarod test. The expression of microRNA-330 increased in the first 4 days and reached a plateau subsequently after LPS treatment. The sponges-mediated repression effect on M1 polarization was gradually enhanced with time. Treatment of miR-330 sponges increased the SHIP1 and Arg1 expression, and decreased the translocation of NF-κB and iNOS expression, suggesting the repression of inflammation. In the LPS-induced PD mice, administration of rAAV-sponge-GFP suppressed activation of microglia, downregulated proinflammatory cytokines, resumed the secretion of dopamine, rescued the dopaminergic neurons, and alleviated motor dysfunction. Our results demonstrated that microRNA-330 sponges could sustainably suppress LPS-induced polarization of microglia both in vivo and in vitro probably by negatively regulating NF-κB activity via target SHIP1 in microglia, which might be a promising neuroprotective strategy in neurological diseases, such as PD.     

Post-MPTP Treatment with Granulocyte Colony-Stimulating Factor Improves Nigrostriatal Function in the Mouse Model of Parkinson’s Disease

The neuroprotective effects of granulocyte colony-stimulating factor (G-CSF) were reported in several neurological disease models, including Parkinson’s disease (PD). In the present study, we investigated the therapeutic effect of G-CSF after the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD was established. G-CSF was subcutaneously administered into C57BL/6 mice that had undergone systemic MPTP injections. We found that G-CSF treatment markedly increased the number of dopaminergic neurons in the substantia nigra pars compacta (SNpc) of the G-CSF-treated group. Consistent with this finding, we found a significant increase in dopamine release under high K⁺ stimulation in the striatum of the G-CSF-treated animals compared to the MPTP-exposed mice. Finally, we observed a persistent recovery of locomotor function in the G-CSF-treated animals. These results suggest the potential therapeutic value of G-CSF in treating PD. However, our bromodeoxyuridine labeling experiment failed to identify any newly generated dopaminergic neurons in SNpc. This might indicate an indirect effect of G-CSF on cell proliferation. The underlying mechanism of G-CSF is under further investigation.     

Partial depletion and repopulation of microglia have different effects in the acute MPTP mouse model of Parkinson’s disease

ObjectivesParkinson''s disease (PD) is a common neurodegenerative disorder characterized by the progressive and selective degeneration of dopaminergic neurons. Microglial activation and neuroinflammation are associated with the pathogenesis of PD. However, the relationship between microglial activation and PD pathology remains to be explored.Materials and MethodsAn acute regimen of MPTP was administered to adult C57BL/6J mice with normal, much reduced or repopulated microglial population. Damages of the dopaminergic system were comprehensively assessed. Inflammation‐related factors were assessed by quantitative PCR and Multiplex immunoassay. Behavioural tests were carried out to evaluate the motor deficits in MPTP‐challenged mice.ResultsThe receptor for colony‐stimulating factor 1 inhibitor PLX3397 could effectively deplete microglia in the nigrostriatal pathway of mice via feeding a PLX3397‐formulated diet for 21 days. Microglial depletion downregulated both pro‐inflammatory and anti‐inflammatory molecule expression at baseline and after MPTP administration. At 1d post‐MPTP injection, dopaminergic neurons showed a significant reduction in PLX3397‐fed mice, but not in control diet (CD)‐fed mice. However, partial microglial depletion in mice exerted little effect on MPTP‐induced dopaminergic injuries compared with CD mice at later time points. Interestingly, microglial repopulation brought about apparent resistance to MPTP intoxication.ConclusionsMicroglia can inhibit PD development at a very early stage; partial microglial depletion has little effect in terms of the whole process of the disease; and microglial replenishment elicits neuroprotection in PD mice.     

Nitric oxide-producing microglia mediate thrombin-induced degeneration of dopaminergic neurons in rat midbrain slice culture

Activated microglia are considered to play important roles in degenerative processes of midbrain dopaminergic neurons. Here we examined mechanisms of neurotoxicity of thrombin, a protease known to trigger microglial activation, in organotypic midbrain slice cultures. Thrombin induced a progressive decline in the number of dopaminergic neurons, an increase in nitric oxide (NO) production, and whole tissue injury indicated by lactate dehydrogenase release and propidium iodide uptake. Microglia expressed inducible NO synthase (iNOS) in response to thrombin, and inhibition of iNOS rescued dopaminergic neurons without affecting whole tissue injury. Inhibitors of mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK), p38 MAPK and c-Jun N-terminal kinase (JNK) attenuated thrombin-induced iNOS induction and dopaminergic cell death. Whole tissue injury was also attenuated by inhibition of ERK and p38 MAPK. Moreover, depletion of resident microglia from midbrain slices abrogated thrombin-induced NO production and dopaminergic cell death, but did not inhibit tissue injury. Finally, antioxidative drugs prevented thrombin-induced dopaminergic cell death without affecting whole tissue injury. Hence, NO production resulting from MAPK-dependent microglial iNOS induction is a crucial event in thrombin-induced dopaminergic neurodegeneration, whereas damage of other midbrain cells is MAPK-dependent but is NO-independent.     

Reduced MPTP toxicity in noradrenaline transporter knockout mice

The noradrenergic neurons of the locus coeruleus (LC) are damaged in Parkinson's disease (PD). Neurotoxin ablation of the LC noradrenergic neurons has been shown to exacerbate the dopaminergic toxicity of MPTP, suggesting that the noradrenergic system protects dopamine neurons. We utilized mice that exhibit elevated synaptic noradrenaline (NA) by genetically deleting the noradrenaline transporter (NET), a key regulator of the noradrenergic system (NET KO mice). NET KO and wild-type littermates were administered MPTP and striatal dopamine terminal integrity was assessed by HPLC of monoamines, immmunoblotting for dopaminergic markers and tyrosine hydroxylase (TH) immunohistochemistry. MPTP significantly reduced striatal dopamine in wild-type mice, but not in the NET KO mice. To confirm that the protection observed in the NET KO mice was due to the lack of NET, we treated wild-type mice with the specific NET inhibitor, nisoxetine, and then challenged them with MPTP. Nisoxetine conferred protection to the dopaminergic system. These data indicate that NA can modulate MPTP toxicity and suggest that manipulation of the noradrenergic system may have therapeutic value in PD.     

Gene disruption of caspase-3 prevents MPTP-induced Parkinson's disease in mice

The development of Parkinson’s disease is accompanied by concurrent activation of caspase-3 and apoptosis of dopaminergic neurons of human patients and rodent models. The role of caspase-3, a final executioner of apoptosis, in the pathogenesis of Parkinson’s disease, however, remains to be determined. Here, we show that gene disruption of caspase-3 protects mice from 1-methyle-4-phenyl-1,2,3,6-tetrahmydropyridine (MPTP)-induced Parkinsonian syndrome, as reflected by reversal of MPTP-induced bradykinesia and decreased tyrosine hydroxylase expression in the nigra-striatum. MPTP treatment resulted in increased caspase-3 activation and apoptosis in the substantia nigra of wild-type mice at 24 h after the inception of MPTP treatment, as compared with vehicle-treated control animals. Gene disruption of caspase-3 prevented MPTP-induced apoptosis in the substantia nigra. At 7 days after MPTP treatment, tyrosine hydroxylase expression was suppressed and infiltration of activated microglia and astrocytes was markedly increased in the nigra-striatum of wild-type mice. All of these alterations following MPTP treatment were blocked by disruption of caspase-3 in mice. These results clearly indicate that caspase-3 activation is required for the development of MPTP-induced Parkinson’s disease in mice. These findings suggest that activation of caspase-3-mediated apoptosis of dopaminergic neurons in the early stage may play an important role in the pathogenesis of Parkinson’s disease.     

Progranulin Gene Delivery Protects Dopaminergic Neurons in a Mouse Model of Parkinson’s Disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by tremor, rigidity and akinesia/bradykinesia resulting from the progressive loss of nigrostriatal dopaminergic neurons. To date, only symptomatic treatment is available for PD patients, with no effective means of slowing or stopping the progression of the disease. Progranulin (PGRN) is a 593 amino acid multifunction protein that is widely distributed throughout the CNS, localized primarily in neurons and microglia. PGRN has been demonstrated to be a potent regulator of neuroinflammation and also acts as an autocrine neurotrophic factor, important for long-term neuronal survival. Thus, enhancing PGRN expression may strengthen the cells resistance to disease. In the present study, we have used the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD to investigate the possible use of PGRN gene delivery as a therapy for the prevention or treatment of PD. Viral vector delivery of the PGRN gene was an effective means of elevating PGRN expression in nigrostriatal neurons. When PGRN expression was elevated in the SN_C, nigrostriatal neurons were protected from MPTP toxicity in mice, along with a preservation of striatal dopamine content and turnover. Further, protection of nigrostriatal neurons by PGRN gene therapy was accompanied by reductions in markers of MPTP-induced inflammation and apoptosis as well as a complete preservation of locomotor function. We conclude that PGRN gene therapy may have beneficial effects in the treatment of PD.     

Increased Dopaminergic Neuron Sensitivity to 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine (MPTP) in Transgenic Mice Expressing Mutant A53T α-Synuclein

Familial Parkinson’s disease (PD) has been linked to point mutations and duplication of the α-synuclein gene and mutant α-synuclein expression increases the vulnerability of neurons to exogenous insults. In this study, we analyzed the levels of dopamine and its metabolites in the olfactory bulb (OB), and nigrostriatal regions of transgenic mice expressing human, mutant A53T α-synuclein (α-syn tg) and their non-transgenic (ntg) littermates using a sub-toxic, moderate dose of MPTP to determine if mutant human α-synuclein sensitizes the central dopaminergic systems to oxidative stress. We observed that after a single, sub-lethal MPTP injection, dopamine levels were reduced in striatum and SN in both the α-syn tg and ntg mice. In the olfactory bulb, a region usually resistant to MPTP toxicity, levels were reduced only in the α-syn tg mice. In addition, we identified a significant increase in dopamine metabolism in the α-syn transgenic, but not ntg mice. Finally, MPTP treatment of α-syn tg mice was associated with a marked elevation in the oxidative product, 3-nitrotyrosine that co-migrated with α-synuclein. Cumulatively, the data support the hypothesis that mutant α-synuclein sensitizes dopaminergic neurons to neurotoxic insults and is associated with greater oxidative stress. The α-syn tg line is therefore useful to study the genetic and environmental inter-relationship in PD.     

Inhibition of p38 pathway-dependent MPTP-induced dopaminergic neurodegeneration in estrogen receptor alpha knockout mice

Approximately, 7–10 million people in the world suffer from Parkinson's disease (PD). Recently, increasing evidence has suggested the protective effect of estrogens against nigrostriatal dopaminergic damage in PD. In this study, we investigated whether estrogen affects 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced behavioral impairment in estrogen receptor alpha (ERα)-deficient mice. MPTP (15 mg/kg, four times with 1.5-h interval)-induced dopaminergic neurodegeneration was evaluated in ERα wild-type (WT) and knockout (KO) mice. Larger dopamine depletion, behavioral impairments (Rotarod test, Pole test, and Gait test), activation of microglia and astrocytes, and neuroinflammation after MPTP injection were observed in ERα KO mice compared to those in WT mice. Immunostaining for tyrosine hydroxylase (TH) after MPTP injection showed fewer TH-positive neurons in ERα KO mice than WT mice. Levels of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC, metabolite of dopamine) were also lowered in ERα KO mice after MPTP injection. Interestingly, a higher immunoreactivity for monoamine oxidase (MAO) B was found in the substantia nigra and striatum of ERα KO mice after MPTP injection. We also found an increased activation of p38 kinase (which positively regulates MAO B expression) in ERα KO mice. In vitro estrogen treatment inhibited neuroinflammation in 1-methyl-4-phenyl pyridium (MPP +)-treated cultured astrocyte cells; however, these inhibitory effects were removed by p38 inhibitor. These results indicate that ERα might be important for dopaminergic neuronal survival through inhibition of p38 pathway.