Osteoprotective Effects of Melatonin on Bone Loss Associated with Dopaminergic Neuron Degeneration in a Rat Model of Parkinson Disease.

Delayed Dominant-Negative TNF Gene Therapy Halts Progressive Loss of Nigral Dopaminergic Neurons in a Rat Model of Parkinson's Disease

Proteasome dysfunction has been demonstrated in Parkinson disease (PD), and proteasome inhibitors have been shown to induce degeneration of dopaminergic neurons in vitro and in vivo. The mechanism whereby proteasome dysfunction leads to dopaminergic cell death, however, is unknown. In this study, we show that proteasome inhibition in both PC12 cells and dopaminergic neurons derived from embryonic stem cells is associated with mitochondrial membrane permeabilization, activation of caspase-3, and nuclear changes consistent with apoptosis. Prior to the emergence of apoptotic features, we found that proteasome inhibition induced increased levels of phosphorylated p53. Inhibition of p53 by pifithrin-alpha or by RNA interference prevented mitochondrial membrane permeabilization and cytotoxicity. There was no increase in p53 mRNA in proteasome-inhibited cells, suggesting that p53 was increased in a transcription-independent manner. Further, there was no increase in Puma or Bax mRNA and p53 co-immunoprecipitated with Bcl-xL and Mdm2. These findings suggest that p53 mediates cell death by way of a direct mitochondrial effect in this model. We also observed increased levels of phosphorylated p53 in dopamine neurons of the substantia nigra pars compacta of mice following systemic administration of a proteasome inhibitor. These changes preceded degeneration of dopaminergic neurons. Increased phosphorylated p53 was also demonstrated in the substantia nigra pars compacta of post-mortem PD brains. These results suggest that abnormalities in p53 signaling play a role in dopaminergic cell death induced by proteasome inhibition and may be relevant to neurodegeneration in PD.

Dopamine quinone toxicity has been implicated in the degeneration of nigral dopaminergic (DA) neurons in Parkinson’s disease (PD). NAD(P)H:quinone oxidoreductase (NQO1) may protect against this quinone toxicity. In Parkinsonian brains, levels of NQO1 are increased in reactive glia cells that are located around the remaining DA neurons in the substantia nigra pars compacta (SNc), suggesting a neuroprotective role of NQO1.It is not known at which stage of the disease process the upregulation of glial NQO1 starts. Furthermore, it is at present not clear whether NQO1 indeed plays a neuroprotective role in the disease process. As a first step to experimentally study a potential neuroprotective role of NQO1, it was examined whether activation of glia cells and changes in the distribution of NQO1-positive glia cells and the expression levels of glial NQO1, as seen in PD brains, also occurred in a 6-hydroxydopamine (6-OHDA) rat model of PD.Our results show that astroglia cells and microglia cells were activated. Furthermore, NQO1 was upregulated in astroglia cells in the SNc in those areas in which DA neurons degenerated. The time course and pattern of upregulation of NQO1 paralleled those of the degeneration of DA neurons. Activated microglia were seen at a later stage during the course of degeneration of DA neurons.In conclusion, in the present model, astroglia cells and microglia cells are activated in response to 6-OHDA-induced oxidative stress. Furthermore, levels of NQO1 are increased in astroglia cells. The findings in the present model are in line with the findings as seen in parkinsonian brains. The 6-OHDA rat model of PD is, therefore, suitable for further research to examine a potential neuroprotective role of NQO1.KeywordsTyrosine HydroxylaseAstroglia CellGlia CellGFAP ImmunoreactivityParkinsonian BrainThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Ventral midbrain dopaminergic neurons: From neurogenesis to neurodegeneration

Autotransplantation for Parkinson's disease goes a step further.

Parkinson's disease (PD) is a common neurodegenerative disorder, which is characterized by the selective and progressive death of dopaminergic (DA) neurons in the substantia nigra. Increasing evidence suggests that inflammation is important in the degeneration of DA neurons. The purinergic receptor subtype P2X7 receptor (P2X7R) is key in the activation and proliferation of microglia. The present study aimed to examine whether inhibiting purinergic P2X7 receptors is neuroprotective in a rat model of PD, specifically via inhibiting p38 mitogen-activated protein kinase (MAPK). In an intranigral lipopolysaccharide (LPS) rat model of PD, immunohistochemical analysis revealed enhanced expression of P2X7R was observed in microglia. The administration of the P2X7R antagonist, brilliant blue G (BBG), reduced activation of the microglia and the loss of nigral DA neurons. In addition, immunohistochemistry and western blot analysis revealed the phosphorylation level of p38 MAPK increased in the microglia of the LPS-injected rats, which was inhibited by BBG treatment. The p38 MAPK inhibitor, SB203580, reduced microglial activation and the loss of DA neurons. Thus, these findings suggested that inhibition of P2X7R by BBG attenuated microglial activation and the loss of substantia nigra DA neurons via p38 MAPK in the rat LPS model of PD.

Parkinson’s disease is a neurodegenerative disorder characterized by severe motor deficits mainly due to degeneration of dopaminergic neurons in the substantia nigra. Decreased levels of the cell’s most important anti-oxidant, glutathione, have been detected in nigral neurons of Parkinson patients, but it is unknown if they are the cause or merely the consequence of the disease. To elucidate if glutathione depletion causes selective degeneration of nigral dopaminergic neurons, we down-regulated glutathione synthesis in different brain areas of adult rats by a viral vector-based RNAi approach. Decreased glutathione synthesis resulted in progressive degeneration of nigral dopaminergic neurons, while extra-nigral and striatal neurons were significantly less vulnerable. Degeneration of dopaminergic neurons was accompanied by progressive protein aggregate formation and functional motor deficits and was partially rescued by α-synuclein. That the survival of nigral dopaminergic neurons depends on the precise control of glutathione levels was further demonstrated by significant degeneration induced through moderate overproduction of glutathione. Over-expression of either of the two subunits of glutamate–cysteine ligase induced aberrant glutathiolation of cellular proteins and significant degeneration of dopaminergic neurons. Thus, while glutathione depletion was demonstrated to be a selective trigger for dopaminergic neuron degeneration, a glutathione replacement approach as a potential treatment option for Parkinson’s patients must be considered with great care. In conclusion, our data demonstrate that survival of nigral dopaminergic neurons crucially depends on a tight regulation of their glutathione levels and that the depleted glutathione content detected in the brains of Parkinson’s disease patients can be a causative insult for neuronal degeneration.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-010-0791-x) contains supplementary material, which is available to authorized users.

Recessive mutations in parkin are the most common cause of familial early-onset Parkinson's disease (PD). Recent studies suggest that certain parkin mutants may exert dominant toxic effects to cultured cells and such dominant toxicity can lead to progressive dopaminergic (DA) neuron degeneration in Drosophila. To explore whether mutant parkin could exert similar pathogenic effects to mammalian DA neurons in vivo, we developed a BAC (bacterial artificial chromosome) transgenic mouse model expressing a C-terminal truncated human mutant parkin (Parkin-Q311X) in DA neurons driven by a dopamine transporter promoter. Parkin-Q311X mice exhibit multiple late-onset and progressive hypokinetic motor deficits. Stereological analyses reveal that the mutant mice develop age-dependent DA neuron degeneration in substantia nigra accompanied by a significant loss of DA neuron terminals in the striatum. Neurochemical analyses reveal a significant reduction of the striatal dopamine level in mutant mice, which is significantly correlated with their hypokinetic motor deficits. Finally, mutant Parkin-Q311X mice, but not wild-type controls, exhibit age-dependent accumulation of proteinase K-resistant endogenous alpha-synuclein in substantia nigra and colocalized with 3-nitrotyrosine, a marker for oxidative protein damage. Hence, our study provides the first mammalian genetic evidence that dominant toxicity of a parkin mutant is sufficient to elicit age-dependent hypokinetic motor deficits and DA neuron loss in vivo, and uncovers a causal relationship between dominant parkin toxicity and progressive alpha-synuclein accumulation in DA neurons. Our study underscores the need to further explore the putative link between parkin dominant toxicity and PD.

Parkinson's disease (PD) is characterized by progressive dopaminergic neurodegeneration. Melatonin (MLT) is implicated in neuroprotection, yet the effects of modulating its receptors remain unclear. This study investigated the impact of the MLT receptor agonist agomelatine (AG) and antagonist luzindole (LU) on motor behavior, serum MLT levels, and dopaminergic neuron survival in a 6-hydroxydopamine (6-OHDA) rat model of PD. A PD model was induced by stereotaxic injection of 6-OHDA into the medial forebrain bundle. Rats received intraperitoneal AG or LU for 2 or 4 weeks. Motor function was assessed using the apomorphine-induced rotation test. Tyrosine hydroxylase (TH) and MLT receptor (MEL-1A/B) expression in the substantia nigra and striatum were evaluated by immunohistochemistry and Western blot. Serum MLT concentrations were measured using ELISA. Pearson's correlation analysis was performed to examine associations among serum MLT levels, TH expression, and motor performance. AG significantly improved motor function, increased serum MLT levels, and enhanced TH expression in PD rats. LU also mitigated motor deficits and preserved dopaminergic neurons, despite reducing serum MLT levels. Correlation analysis revealed a dynamic temporal relationship between MLT levels, behavioral outcomes, and dopaminergic neuron survival, indicating that MLT signaling may differentially influence PD pathology at various stages. Both AG and LU demonstrated neuroprotective potential in 6-OHDA-induced PD rats. AG may exert its effects by enhancing endogenous MLT signaling, while LU may protect neurons by modulating excessive MLT activity. These findings highlight the complex regulatory role of the MLT pathway in PD progression and suggest stage-dependent therapeutic benefits of MLT receptor modulators.

To investigate the role of astrocytic JWA expression in dopaminergic (DA) neuron degeneration and in the pathogenesis of Parkinson's disease (PD). Conditional astrocytic JWA null (JWA∆2/∆2/GFAP-Cre) mice and U251 glioma cells were used to evaluate the effects of JWA gene on DA neuron degeneration. The oxidative stress-driven molecular events were determined in both in vivo and in vitro models. Conditional astrocytic JWA knockout resulted in significant activation of astrocytes measured by increase in glial fibrillary acidic protein-positive cells (1.34×10(3)±74.5 vs. 8.44×10(3)±1.35×10(3), P<0.01) in mouse substantia nigra, accompanied by loss of DA neurons (1.03×10(4)±238 vs. 6.17×10(3)±392, P<0.001). Deficiency of JWA significantly aggravated reactive oxygen species (ROS) accumulation in substantia nigra compared with the wild-type mice. Increasing JWA expression in U251 glioma cells inhibited ROS with a concomitant increase in intracellular glutathione. Furthermore, suppression of IKKβ-nuclear factor (NF)-κB signaling pathway was shown to regulate JWA in a PD model. The JWA gene exerts neuroprotective roles against DA neuronal degeneration via modulating intracellular redox status and NF-κB signaling pathway and is a potential treatment target for PD.

BackgroundNoradrenergic neurons in the locus coeruleus (LC) are the primary source of norepinephrine (NE) in the brain and degeneration of these neurons is reported in the early stages of Parkinson’s disease (PD), even prior to dopaminergic neuron degeneration in the substantia nigra (SN), which is a hallmark of PD pathology. NE depletion is generally associated with increased PD pathology in neurotoxin-based PD models. The effect of NE depletion in other models of PD-like α-synuclein-based models is largely unexplored. In PD models and in human patients, β-adrenergic receptors’ (AR) signaling is associated with a reduction of neuroinflammation and PD pathology. However, the effect of NE depletion in the brain and the extent of NE and β-ARs signaling involvement in neuroinflammation, and dopaminergic neuron survival is poorly understood.MethodsTwo mouse models of PD, a 6OHDA neurotoxin-based model and a human α-synuclein (hα-SYN) virus-based model of PD, were used. DSP-4 was used to deplete NE levels in the brain and its effect was confirmed by HPLC with electrochemical detection. A pharmacological approach was used to mechanistically understand the impact of DSP-4 in the hα-SYN model of PD using a norepinephrine transporter (NET) and a β-AR blocker. Epifluorescence and confocal imaging were used to study changes in microglia activation and T-cell infiltration after β1-AR and β2-AR agonist treatment in the hα-SYN virus-based model of PD.ResultsConsistent with previous studies, we found that DSP-4 pretreatment increased dopaminergic neuron loss after 6OHDA injection. In contrast, DSP-4 pretreatment protected dopaminergic neurons after hα-SYN overexpression. DSP-4-mediated protection of dopaminergic neurons after hα-SYN overexpression was dependent on β-AR signaling since using a β-AR blocker prevented DSP-4-mediated dopaminergic neuron protection in this model of PD. Finally, we found that the β-2AR agonist, clenbuterol, reduced microglia activation, T-cell infiltration, and dopaminergic neuron degeneration, whereas xamoterol a β-1AR agonist showed increased neuroinflammation, blood brain barrier permeability (BBB), and dopaminergic neuron degeneration in the context of hα-SYN-mediated neurotoxicity.ConclusionsOur data demonstrate that the effects of DSP-4 on dopaminergic neuron degeneration are model specific, and suggest that in the context of α-SYN-driven neuropathology, β2-AR specific agonists may have therapeutic benefit in PD.

Objective:Selective degeneration of dopaminergic neurons is the pathological hallmark of Parkinson disease (PD). Enhanced oxidative stress, lipid peroxidation and susceptibility of dopaminergic neurons to apoptotic cellular death are the leading pathogenetic mechanisms. Chrysin is an active flavonoid. Its neuroprotective effects have been reported. This study examined the neuroprotective effects of chrysin in ameliorating the dopaminergic neuronal degeneration and motor behavioral changes in rotenone model of PD.Methods:Thirty Sprague-Dawley rats were assigned into three groups: Control, rotenone-treated, and rotenone+chrysin treated groups. Rotenone was given at a dose of 3 mg/kg daily intraperitoneally, and chrysin was given at a dose of 50 mg/kg daily intraperitoneally for 4 weeks. Using five neurobehavioral assessment tests, evaluation was done weekly to record the motor behavioral changes. After 4 weeks, animals were sacrificed, brains were removed, and section from striatum and substantia nigra were stained using hematoxylin and eosin and cresyl violet stains. Immunohistochemical sections were also prepared using anti-tyrosine hydroxylase (TH) antibody.Results:Rotenone-induced Parkinson like changes were evident from deteriorating motor behavior. These animals showed extensive loss of dopaminergic neurons, decreased immunoreactivity against anti-TH antibodies and number of TH positive dopaminergic neurons in the nigrostriatal region. Chrysin treated animals showed a significant reduction in motor behavioral changes, degeneration and loss of nigrostriatal dopaminergic neurons and increased immunoreactivity to anti-TH antibody.Conclusion:This study concludes that chrysin confers neuroprotection in rat model of PD. It attenuates the degeneration of the nigrostriatal dopaminergic neurons and motor behavioral abnormalities.

Melatonin protects dopaminergic neurons in paraquat-induced Parkinson in rats through PI3K/AKT/Nrf2 pathway.

Implantation of human olfactory ecto-mesenchymal stem cells restores locomotion in a rat model of Parkinson's disease

Dephosphorylation of Six2Y129 protects tyrosine hydroxylase-positive cells in SNpc by regulating TEA domain 1 expression