Granulocyte-colony stimulating factor is neuroprotective in a model of Parkinson's disease

We have recently shown that the hematopoietic Granulocyte-Colony Stimulating Factor (G-CSF) is neuroprotective in rodent stroke models, and that this action appears to be mediated via a neuronal G-CSF receptor. Here, we report that the G-CSF receptor is expressed in rodent dopaminergic substantia nigra neurons, suggesting that G-CSF might be neuroprotective for dopaminergic neurons and a candidate molecule for the treatment of Parkinson's disease. Thus, we investigated protective effects of G-CSF in 1-methyl-4-phenylpyridinium (MPP+)-challenged PC12 cells and primary neuronal midbrain cultures, as well as in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease. Substantial protection was found against MPP+-induced dopaminergic cell death in vitro. Moreover, subcutaneous application of G-CSF at a dose of 40 microg/Kg body weight daily over 13 days rescued dopaminergic substantia nigra neurons from MPTP-induced death in aged mice, as shown by quantification of tyrosine hydroxylase-positive substantia nigra cells. Using HPLC, a corresponding reduction in striatal dopamine depletion after MPTP application was observed in G-CSF-treated mice. Thus our data suggest that G-CSF is a novel therapeutic opportunity for the treatment of Parkinson's disease, because it is well-tolerated and already approved for the treatment of neutropenic conditions in humans.     

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.     

Heat shock prevents alpha-synuclein-induced apoptosis in a yeast model of Parkinson's disease

We show that human wild-type alpha synuclein (WT alpha-syn), and the inherited mutants A53T or A30P, when expressed in the yeast Saccharomyces cerevisiae triggers events that are diagnostic of apoptosis: loss of membrane asymmetry due to the externalization of phosphatidylserine, accumulation of reactive oxygen species (ROS), and the release of cytochrome c from mitochondria. A brief heat shock was strikingly protective in that alpha-syn-expressing cells receiving a heat shock exhibited none of these apoptotic markers. Because the heat shock did not decrease the expression level of alpha-syn, a protective protein or proteins, induced by the heat shock, must be responsible for inhibition of alpha-syn-induced apoptosis. Using ROS accumulation as a marker of apoptosis, the role of various genes and various drugs in controlling alpha-syn-induced apoptosis was investigated. Treatment with geldanamycin or glutathione, overexpression of Ssa3 (Hsp70), or deletion of the yeast metacaspase gene YCA1 abolishes the ability of alpha-syn to induce ROS accumulation. Deletion of YCA1 also promotes vigorous growth of alpha-syn-expressing cells compared to cells that contain a functional copy of YCA1. These findings indicate that alpha-syn-induced ROS generation is mediated by the caspase, according to alpha-syn-->caspase-->ROS-->apoptosis. It is shown by co-immunoprecipitation that Ssa3 binds to alpha-syn in a nucleotide-dependent manner. Thus, we propose that Hsp70 chaperones inhibit this sequence of events by binding and sequestering alpha-syn.     

p53-dependent neuronal cell death in a DJ-1-deficient zebrafish model of Parkinson's disease

Mutations in DJ-1 lead to early onset Parkinson's disease (PD). The aim of this study was to elucidate further the underlying mechanisms leading to neuronal cell death in DJ-1 deficiency in vivo and determine whether the observed cell loss could be prevented pharmacologically. Inactivation of DJ-1 in zebrafish, Danio rerio, resulted in loss of dopaminergic neurons after exposure to hydrogen peroxide and the proteasome inhibitor MG132. DJ-1 knockdown by itself already resulted in increased p53 and Bax expression levels prior to toxin exposure without marked neuronal cell death, suggesting subthreshold activation of cell death pathways in DJ-1 deficiency. Proteasome inhibition led to a further increase of p53 and Bax expression with widespread neuronal cell death. Pharmacological p53 inhibition either before or during MG132 exposure in vivo prevented dopaminergic neuronal cell death in both cases. Simultaneous knockdown of DJ-1 and the negative p53 regulator mdm2 led to dopaminergic neuronal cell death even without toxin exposure, further implicating involvement of p53 in DJ-1 deficiency-mediated neuronal cell loss. Our study demonstrates the utility of zebrafish as a new animal model to study PD gene defects and suggests that modulation of downstream mechanisms, such as p53 inhibition, may be of therapeutic benefit.     

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.     

Oxidative post-translational modifications of alpha-synuclein in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease

Structural and functional alterations of alpha-synuclein is a presumed culprit in the demise of dopaminergic neurons in Parkinson's disease (PD). Alpha-synuclein mutations are found in familial but not in sporadic PD, raising the hypothesis that effects similar to those of familial PD-linked alpha-synuclein mutations may be achieved by oxidative post-translational modifications. Here, we show that wild-type alpha-synuclein is a selective target for nitration following peroxynitrite exposure of stably transfected HEK293 cells. Nitration of alpha-synuclein also occurs in the mouse striatum and ventral midbrain following administration of the parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Conversely, beta-synuclein and synaptophysin were not nitrated in MPTP-intoxicated mice. Our data demonstrate that alpha-synuclein is a target for tyrosine nitration, which, by disrupting its biophysical properties, may be relevant to the putative role of alpha-synuclein in the neurodegeneration associated with MPTP toxicity and with PD.     

Lipopolysaccharide-induced dopaminergic cell death in rat midbrain slice cultures: role of inducible nitric oxide synthase and protection by indomethacin

Glial cell activation associated with inflammatory reaction may contribute to pathogenic processes of neurodegenerative disorders, through production of several cytotoxic molecules. We investigated the consequences of glial activation by interferon-gamma (IFN-gamma)/lipopolysaccharide (LPS) in rat midbrain slice cultures. Application of IFN-gamma followed by LPS caused dopaminergic cell death and accompanying increases in nitrite production and lactate dehydrogenase release. Aminoguanidine, an inhibitor of inducible nitric oxide synthase (iNOS), or SB203580, an inhibitor of p38 mitogen-activated protein kinase, prevented dopaminergic cell loss as well as nitrite production. SB203580 also suppressed expression of iNOS and cyclooxygenase-2 (COX-2) induced by IFN-gamma/LPS. A COX inhibitor indomethacin protected dopaminergic neurons from IFN-gamma/LPS-induced injury, whereas selective COX-2 inhibitors such as NS-398 and nimesulide did not. Notably, indomethacin was able to attenuate neurotoxicity of a nitric oxide (NO) donor. Neutralizing antibodies against tumour necrosis factor-alpha and interleukin-1beta did not inhibit dopaminergic cell death caused by IFN-gamma/LPS, although combined application of these antibodies blocked lactate dehydrogenase release and decrease in the number of non-dopaminergic neurons. These results indicate that iNOS-derived NO plays a crucial role in IFN-gamma/LPS-induced dopaminergic cell death, and that indomethacin exerts protective effect by mechanisms probably related to NO neurotoxicity rather than through COX inhibition.     

Lanosterol induces mitochondrial uncoupling and protects dopaminergic neurons from cell death in a model for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder marked by the selective degeneration of dopaminergic neurons in the nigrostriatal pathway. Several lines of evidence indicate that mitochondrial dysfunction contributes to its etiology. Other studies have suggested that alterations in sterol homeostasis correlate with increased risk for PD. Whether these observations are functionally related is, however, unknown. In this study, we used a toxin-induced mouse model of PD and measured levels of nine sterol intermediates. We found that lanosterol is significantly (～50%) and specifically reduced in the nigrostriatal regions of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice, indicative of altered lanosterol metabolism during PD pathogenesis. Remarkably, exogenous addition of lanosterol rescued dopaminergic neurons from 1-methyl-4-phenylpyridinium (MPP+)-induced cell death in culture. Furthermore, we observed a marked redistribution of lanosterol synthase from the endoplasmic reticulum to mitochondria in dopaminergic neurons exposed to MPP+, suggesting that lanosterol might exert its survival effect by regulating mitochondrial function. Consistent with this model, we find that lanosterol induces mild depolarization of mitochondria and promotes autophagy. Collectively, our results highlight a novel sterol-based neuroprotective mechanism with direct relevance to PD.     

Microglial activation-mediated delayed and progressive degeneration of rat nigral dopaminergic neurons: relevance to Parkinson's disease

The etiology of sporadic Parkinson's disease (PD) remains unknown. Increasing evidence has suggested a role for inflammation in the brain in the pathogenesis of PD. However, it has not been clearly demonstrated whether microglial activation, the most integral part of the brain inflammatory process, will result in a delayed and progressive degeneration of dopaminergic neurons in substantia nigra, a hallmark of PD. We report here that chronic infusion of an inflammagen lipopolysaccharide at 5 ng/h for 2 weeks into rat brain triggered a rapid activation of microglia that reached a plateau in 2 weeks, followed by a delayed and gradual loss of nigral dopaminergic neurons that began at between 4 and 6 weeks and reached 70% by 10 weeks. Further investigation of the underlying mechanism of action of microglia-mediated neurotoxicity using rat mesencephalic neuron-glia cultures demonstrated that low concentrations of lipopolysaccharide (0.1-10 ng/mL)-induced microglial activation and production of neurotoxic factors preceded the progressive and selective degeneration of dopaminergic neurons. Among the factors produced by activated microglia, the NADPH oxidase-mediated release of superoxide appeared to be a predominant effector of neurodegeneration, consistent with the notion that dopaminergic neurons are particularly vulnerable to oxidative insults. This is the first report that microglial activation induced by chronic exposure to inflammagen was capable of inducing a delayed and selective degeneration of nigral dopaminergic neurons and that microglia-originated free radicals play a pivotal role in dopaminergic neurotoxicity in this inflammation-mediated model of PD.     

Involvement of cytochrome P450 2E1 in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced mouse model of Parkinson's disease

Elucidation of the biochemical steps leading to the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced degeneration of the nigrostriatal dopamine (DA) pathway has provided new clues to the pathophysiology of Parkinson's disease. In line with the enhancement of MPTP toxicity by diethyldithiocarbamate (DDC), here we demonstrate how other cytochrome P450 (CYP) 2E1 inhibitors, such as diallyl sulphide (DAS) and phenylethylisothiocyanate (PIC), also potentiate the selective DA neurone degeneration in C57/bl mice. In addition, we show that CYP 2E1 is present in the brain and in the basal ganglia of this mouse strain, as measured by RT-PCR, western blot analysis and immunohistochemistry. A kinetic analysis of MPTP and its metabolites, by means of the microdialysis technique in the striatum, indicates that no detoxification metabolic pathway is affected by any of these inhibitors. This does not rule out, however, that an undetected detoxification pathway involving CYP 2E1 is operating. In order to provide direct evidence for this isozyme involvement, CYP 2E1 knockout mice were challenged with MPTP or the combined treatment. Here we show that these transgenic mice have a low sensitivity to MPTP alone, similar to their wild-type counterparts, suggesting that it is likely that transgenic mice compensate for the missing enzyme. However, DDC pretreatment completely fails to enhance MPTP toxicity in CYP 2E1 knockout mice, whereas this enhancement is regularly present in wild-type animals. This study indicates that the occurrence of CYP 2E1 in C57/bl mouse brain is relevant to MPTP toxicity, and suggests that this isozyme may have a detoxificant role related to the efflux transporter of the toxin.     

VMAT2 and dopamine neuron loss in a primate model of Parkinson's disease

We used positron emission tomography (PET) to measure the earliest change in dopaminergic synapses and glial cell markers in a chronic, low-dose MPTP non-human primate model of Parkinson's disease (PD). In vivo levels of dopamine transporters (DAT), vesicular monoamine transporter-type 2 (VMAT2), amphetamine-induced dopamine release (AMPH-DAR), D2-dopamine receptors (D2R) and translocator protein 18 kDa (TSPO) were measured longitudinally in the striatum of MPTP-treated animals. We report an early (2 months) decrease (46%) of striatal VMAT2 in asymptomatic MPTP animals that preceded changes in DAT, D2R, and AMPH-DAR and was associated with increased TSPO levels indicative of a glial response. Subsequent PET studies showed progressive loss of all pre-synaptic dopamine markers in the striatum with expression of parkinsonism. However, glial cell activation did not track disease progression. These findings indicate that decreased VMAT2 is a key pathogenic event that precedes nigrostriatal dopamine neuron degeneration. The loss of VMAT2 may result from an association with α-synuclein aggregation induced by oxidative stress. Disruption of dopamine sequestration by reducing VMAT2 is an early pathogenic event in the dopamine neuron degeneration that occurs in the MPTP non-human primate model of PD. Genetic or environmental factors that decrease VMAT2 function may be important determinants of PD.     

Adenosine prevents the death of mesencephalic dopaminergic neurons by a mechanism that involves astrocytes

The purinergic nucleoside adenosine effectively prevented the death of dopaminergic neurons that occurs spontaneously and progressively in cultures of rat mesencephalon. Adenosine also significantly increased dopamine uptake, attesting to the state of differentiation and functional integrity of the neurons that were rescued. The effects of adenosine were (a) specific to the dopaminergic neurons in these cultures, (b) long-lived, (c) still observed when the treatment was delayed after plating, (d) potentiated by inhibition of adenosine deaminase, and (e) abolished when this enzyme was added in excess to the culture medium. The action of adenosine was mimicked by 5'-(N-ethylcarboxamido)adenosine and dibutyryl-cyclic AMP, but not by CGS-21680, suggesting the possible involvement of A2B subtype purinergic receptors. ATP was also neuroprotective, but its action resulted principally from conversion to adenosine by ectonucleotidases. Several anticancer drugs, including cytosine arabinoside, have been shown previously to prevent apoptosis in cultured dopaminergic neurons by a mechanism that requires the inhibition of proliferating astrocytes. In the presence of adenosine, astrocytes were more differentiated, and their proliferation rate was significantly reduced, suggesting that the neurotrophic effect of the adenine nucleoside resulted also from the repression of the astroglial cells. We did not find evidence of a trophic intermediary in adenosine-treated cultures, however, leading to the hypothesis that limitation of astrocyte replication in itself and/or ensuing changes in the glial phenotype were crucial. Our results suggest that molecules that modulate adenine nucleotide/nucleoside release may be useful for the treatment of chronic neurodegenerative conditions affecting dopaminergic neurons, such as Parkinson's disease.     

环加氧酶-2对帕金森病小鼠黑质多巴胺能神经元的影响

目的和方法 :选用C5 7BL种系环加氧酶 2 (cyclooxygenase 2 ,COX 2 )缺陷小鼠 ,腹腔注射 1 甲基 4 苯基 1,2 ,3,6 四氢吡啶 (MPTP)制备帕金森病小鼠模型 ,用免疫组织化学方法观察COX 2对帕金森病小鼠黑质多巴胺能神经元的影响。结果 :行为学及免疫组织化学观察显示 ,野生型帕金森病小鼠的死亡率明显高于COX 2缺陷杂合子帕金森病小鼠 (P <0 .0 1) ,野生型帕金森病小鼠黑质致密部酪氨酸羟化酶 (tyrosinehydroxylase,TH)免疫反应阳性神经元数目较杂合子帕金森病小鼠明显减少 (P <0 .0 1)。结论 :COX 2可能与帕金森病时黑质多巴胺能神经元的损伤有关     

UCH-L1 aggresome formation in response to proteasome impairment indicates a role in inclusion formation in Parkinson's disease

Aggresomes are associated with many neurodegenerative disorders, including Parkinson's disease, and polyglutamine disorders such as Huntington's disease. These inclusions commonly contain ubiquitylated proteins. The stage at which these proteins are ubiquitylated remains unclear. A malfunction of the ubiquitin/proteasome system (UPS) may be associated with their formation. Conversely, it may reflect an unsuccessful attempt by the cell to remove them. Previously, we demonstrated that overexpression of Parkin, a ubiquitin-protein ligase associated with autosomal recessive juvenile Parkinsonism, generates aggresome-like inclusions in UPS compromised cells. Mutations in the de-ubiquitylating enzyme, UCH-L1, cause a rare form of Parkinsonism. We now demonstrate that overexpression of UCH-L1 also forms ribbon-like aggresomes in response to proteasomal inhibition. Disease-associated mutations, which affect enzymatic activities, significantly increased the number of inclusions. UCH-L1 aggresomes co-localized with ubiquitylated proteins, HSP70, gamma-tubulin and, to a lesser extent, the 20S proteasome and the chaperone BiP. Similar to Parkin inclusions, we found UCH-L1 aggresomes to be surrounded by a tubulin rather than a vimentin cage-like structure. Furthermore, UCH-L1 aggregates with Parkin and alpha-synuclein in some, but not all inclusions, suggesting the heterogeneous nature of these inclusion bodies. This study provides additional evidence that aggregation-prone proteins are likely to recruit UPS components in an attempt to clear proteins from failing proteasomes. Furthermore, UCH-L1 accumulation is likely to play a pathological role in inclusion formation in Parkinson's disease.     

Expression and localization of Parkinson's disease-associated leucine-rich repeat kinase 2 in the mouse brain

Mutations in the gene encoding leucine-rich repeat kinase 2 (LRRK2) have been identified as the cause of familial Parkinson's disease (PD) at the PARK8 locus. To begin to understand the physiological role of LRRK2 and its involvement in PD, we have investigated the distribution of LRRK2 mRNA and protein in the adult mouse brain. In situ hybridization studies indicate sites of mRNA expression throughout the mouse brain, with highest levels of expression detected in forebrain regions, including the cerebral cortex and striatum, intermediate levels observed in the hippocampus and cerebellum, and low levels in the thalamus, hypothalamus and substantia nigra. Immunohistochemical studies demonstrate localization of LRRK2 protein to neurones in the cerebral cortex and striatum, and to a variety of interneuronal subtypes in these regions. Furthermore, expression of LRRK2 mRNA in the striatum of VMAT2-deficient mice is unaltered relative to wild-type littermate controls despite extensive dopamine depletion in this mouse model of parkinsonism. Collectively, our results demonstrate that LRRK2 is present in anatomical brain regions of direct relevance to the pathogenesis of PD, including the nigrostriatal dopaminergic pathway, in addition to other regions unrelated to PD pathology, and is likely to play an important role in the normal function of telencephalic forebrain neurones and other neuronal populations.     

Sustained extracellular signal-regulated kinase activation by 6-hydroxydopamine: implications for Parkinson's disease

Although the toxin 6-hydroxydopamine (6-OHDA) is utilized extensively in animal models of Parkinson's disease, the underlying mechanism of its toxic effects on dopaminergic neurons is not completely understood. We examined the effects of 6-OHDA on the CNS-derived tyrosine hydroxylase expressing B65 cell line, with particular attention to the regulation of the extracellular signal-regulated protein kinases (ERK). 6-OHDA elicited a dose-dependent cytotoxicity in B65 cells. Toxic doses of 6-OHDA also elicited a biphasic pattern of ERK phosphorylation with a prominent sustained phase, a pattern that differed from that observed with hydrogen peroxide (H(2)O(2)) treatment. 6-OHDA-elicited ERK phosphorylation was blocked by PD98059, an inhibitor of the upstream mitogen activated protein kinase kinase (MEK) that phosphorylates and activates ERK. PD98059 also conferred protection against 6-OHDA cytotoxicity, but did not affect H(2)O(2) toxicity in B65 cells. These results suggest that ERK activation plays a direct mechanistic role in 6-OHDA toxicity, rather than representing a protective compensatory response, and raise the possibility that abnormal patterns of ERK activation may contribute to dopaminergic neuronal cell death.     

Increased dopamine release in vivo by estradiol benzoate from the central amygdaloid nucleus of Parkinson's disease model rats

In addition to the dopaminergic neurons in the nigrostriatal system, the properties of dopaminergic neurons in the mesolimbic system, such as the amygdala, are also of interest and importance because of their specific neuromodulatory effects in the pathophysiology of Parkinson's disease (PD). Using the fast cyclic voltammetry (FCV) technique, we present evidence to indicate that electrically-evoked dopamine (DA) release from the amygdala, especially the central amygdaloid nucleus (CAN), of ovariectomized (OVX) female rats was significantly enhanced with increasing doses of estradiol benzoate (EB; 30, 50 and 100 microg/kg). Impaired DA release from the amygdala of an OVX rat PD model can also be increased by EB treatment (50 microg/kg) to a level similar to that of controls. The well established neuroprotective effects of estrogen may be beneficial for reducing the dysfunction of dopaminergic neurons in mesolimbic structures of rat PD models and PD patients.     

Neuroprotective effect of l-dopa on dopaminergic neurons is comparable to pramipexol in MPTP-treated animal model of Parkinson's disease: a direct comparison study

Parkinson's disease (PD) is a chronic neurodegenerative disease characterized by selective loss of dopaminergic neurons in the pars compacta of the substantia nigra. Levodopa ( l -dopa) and dopamine agonists have been most commonly used for symptomatic treatment. However, there are discrepancies between clinical and experimental data with respect to the neuroprotective effects of these drugs on dopaminergic neurons. In this study, to determine whether l -dopa is toxic or dopamine agonist is neuroprotective to dopaminergic neurons, we evaluated the neuroprotective properties of l -dopa and the pramipexol (PPX), one of dopamine agonists, with a focus on the regulatory effects of the anti-oxidant properties and cell survival or apoptotic signal pathways in the same experimental design, using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated PD animals. The glutathione level in MPTP-treated mice was significantly increased by PPX administration but not by L-dopa treatment. The expression of phosphorylated extracellular signal regulated kinase in MPTP-treated mice was significantly increased only with l -dopa treatment. Treatment with either l -dopa or PPX in MPTP-treated mice led to significantly decreased expressions of JNK phosphorylation, Bax, and cytochrome c and to an increased level of Bcl-2 expression with a similar degree, compared with the levels in MPTP-only treated mice. Immunohistochemical analysis showed that both l -dopa and PPX increased significantly survival of dopaminergic neurons in MPTP-treated mice. Our study demonstrated that both l -dopa and PPX had comparable neuroprotective properties for dopaminergic neurons in MPTP-treated PD animal models, through modulation of cell survival and apoptotic pathways.     

Biochemical aspects of the neuroprotective mechanism of PTEN-induced kinase-1 (PINK1)

Mutations in PTEN-induced kinase 1 (PINK1) gene cause PARK6 familial Parkinsonism. To decipher the role of PINK1 in pathogenesis of Parkinson's disease (PD), researchers need to identify protein substrates of PINK1 kinase activity that govern neuronal survival, and establish whether aberrant regulation and inactivation of PINK1 contribute to both familial Parkinsonism and idiopathic PD. These studies should take into account the several unique structural and functional features of PINK1. First PINK1 is a rare example of a protein kinase with a predicted mitochondrial-targeting sequence and a possible resident mitochondrial function. Second, bioinformatic analysis reveals unique insert regions within the kinase domain that are potentially involved in regulation of kinase activity, substrate selectivity and stability of PINK1. Third, the C-terminal region contains functional motifs governing kinase activity and substrate selectivity. Fourth, accumulating evidence suggests that PINK1 interacts with other signaling proteins implicated in PD pathogenesis and mitochondrial dysfunction. The most prominent examples are the E3 ubiquitin ligase Parkin, the mitochondrial protease high temperature requirement serine protease 2 and the mitochondrial chaperone tumor necrosis factor receptor-associated protein 1. How PINK1 may regulate these proteins to maintain neuronal survival is unclear. This review describes the unique structural features of PINK1 and their possible roles in governing mitochondrial import, processing, kinase activity, substrate selectivity and stability of PINK1. Based upon the findings of previous studies of PINK1 function in cell lines and animal models, we propose a model on the neuroprotective mechanism of PINK1. This model may serve as a conceptual framework for future investigation into the molecular basis of PD pathogenesis.