Selective vulnerability of pigmented dopaminergic neurons in Parkinson's disease

Abstract– From a neuropathological point, the diagnosis of Parkinson's disease is confirmed by a neuronal cell loss and the presence of Lewy bodies in the substantia nigra. In Parkinson's disease, the precise type of nigral neuron which degenerate still remains unknown. Are all types of neuron similarly injured, are only subpopulations of neurons vulnerable? In an attempt to answer the question, a qualitative and quantitative analysis of the distribution of dopaminergic cells, as identified by immunohistochemistry with a specific antibody against tyrosine hydroxylase, was performed in the ventral mesencephalon of control subjects and patients died with a clinical diagnostic of Parkinson's disease. In control brains, two types of catecholaminergic neurons were evidenced, some contain visible-neuromelanin other do not. In patients with Parkinson's disease, the tyrosine hydroxylase positive cells which contained the pigment were the most vulnerable.     

Particular vulnerability of rat mesencephalic dopaminergic neurons to tetrahydrobiopterin: Relevance to Parkinson's disease

We determined whether tetrahydrobiopterin(BH4), an endogenous cofactor for dopamine(DA) synthesis, causes preferential damage to DArgic neurons among primary cultured rat mesencephalic neurons and whether the death mechanism has relevance to Parkinson's disease (PD). DArgic neurons were more vulnerable to BH4 than non-DArgic neurons, exhibiting sensitivity at lower concentrations, evident by morphological and neurotransmitter uptake studies. BH4-exposed DArgic neurons showed (1) increased TUNEL staining and activated caspase-3 immunoreactivity, indicative of apoptotic death; (2) mitochondrial membrane potential loss and increased cytosolic cytochrome c, suggesting mitochondrial dysfunction; (3) increased level of oxidized proteins and protection by antioxidants, indicative of oxidative stress; and (4) increased ubiquitin immunoreactivity, suggesting alteration of protein degradation pattern. Percent of cells positive for these parameters were much higher for DArgic neurons, demonstrating preferential vulnerability. Therefore, the DArgic neuronal damage induced by BH4, the molecule synthesized and readily upregulated in DArgic neurons and activated microglia, suggests physiological relevance to the pathogenesis of PD.     

Preservation of hypothalamic dopaminergic neurons in Parkinson's disease

The integrity of the hypothalamic neuroendocrine dopaminergic neurons in Parkinson's disease was assessed by comparing the numbers and distribution of melanin-pigmented neurons in the arcuate and periventricular nuclei in 7 parkinsonian and 5 normal brains. No significant differences were observed. In contrast to theories suggesting that Parkinson's disease involves a universal degeneration of central catecholaminergic neurons, the hypothalamic neuroendocrine dopaminergic neurons do not appear to be involved by the disease.     

Striatal dysfunctions associated with mitochondrial DNA damage in dopaminergic neurons in a mouse model of Parkinson's disease

Parkinson's disease (PD) is one of the most common progressive neurodegenerative disorders, characterized by resting tremor, rigidity, bradykinesia, and postural instability. These symptoms are associated with massive loss of tyrosine hydroxylase-positive neurons in the substantia nigra (SN) causing an estimated 70-80% depletion of dopamine (DA) in the striatum, where their projections are located. Although the etiology of PD is unknown, mitochondrial dysfunctions have been associated with the disease pathophysiology. We used a mouse model expressing a mitochondria-targeted restriction enzyme, PstI or mito-PstI, to damage mitochondrial DNA (mtDNA) in dopaminergic neurons. The expression of mito-PstI induces double-strand breaks in the mtDNA, leading to an oxidative phosphorylation deficiency, mostly due to mtDNA depletion. Taking advantage of a dopamine transporter (DAT) promoter-driven tetracycline transactivator protein (tTA), we expressed mito-PstI exclusively in dopaminergic neurons, creating a novel PD transgenic mouse model (PD-mito-PstI mouse). These mice recapitulate most of the major features of PD: they have a motor phenotype that is reversible with l-DOPA treatment, a progressive neurodegeneration of the SN dopaminergic population, and striatal DA depletion. Our results also showed that behavioral phenotypes in PD-mito-PstI mice were associated with striatal dysfunctions preceding SN loss of tyrosine hydroxylase-positive neurons and that other neurotransmitter systems [noradrenaline (NE) and serotonin (5-HT)] were increased after the disruption of DA neurons, potentially as a compensatory mechanism. This transgenic mouse model provides a novel model to study the role of mitochondrial defects in the axonal projections of the striatum in the pathophysiology of PD.     

The differences between high and low-dose administration of VEGF to dopaminergic neurons of in vitro and in vivo Parkinson's disease model

Vascular endothelial growth factor (VEGF) has previously been shown to display neuroprotective effects on dopaminergic (DA) neurons. In this study, we investigated whether the effects of VEGF were dose-dependent or not. First, VEGF was shown to be neuroprotective on 6-hydroxydopamine (6-OHDA)-treated murine DA neurons in vitro, although the 1 ng/ml of VEGF displayed more neuroprotective effects than 100 ng/ml. Furthermore, using 2 sizes of capsules (small/large) with different secreting quantities, 6-OHDA-treated rats receiving the small capsule filled with VEGF-secreting cells (BHK-VEGF) into the striatum showed a significant decrease in amphetamine-induced rotational behavior in number and a significant preservation of TH-positive fibers compared to those receiving the large BHK-VEGF capsule as well as those receiving BHK-Control capsule. Rats receiving the large BHK-VEGF capsule showed much more glial proliferation, angiogenesis, and brain edema around the capsule than those with the small one. High-dose administration of VEGF might cause poor circulation related to brain edema, although low-dose administration of VEGF displays neuroprotective effects on DA neurons. Our results demonstrate the importance of administration dose of VEGF, suggesting that low-dose administration of VEGF might be desirable for Parkinson's disease.     

Dopamine transporter glycosylation correlates with the vulnerability of midbrain dopaminergic cells in Parkinson's disease

The dopamine transporter (DAT) is a membrane glycoprotein responsible for dopamine (DA) uptake, which has been involved in the degeneration of DA cells in Parkinson's disease (PD). Given that DAT activity depends on its glycosylation status and membrane expression, and that not all midbrain DA cells show the same susceptibility to degeneration in PD, we have investigated a possible relationship between DAT glycosylation and function and the differential vulnerability of DA cells. Glycosylated DAT expression, DA uptake, and DAT V_max were significantly higher in terminals of nigrostriatal neurons than in those of mesolimbic neurons. No differences were found in non-glycosylated DAT expression and DAT K_m, and DA uptake differences disappeared after deglycosylation of nigrostriatal synaptosomes. The expression pattern of glycosylated DAT in the human midbrain and striatum showed a close anatomical relationship with DA degeneration in parkinsonian patients. This relationship was confirmed in rodent and monkey models of PD, and in HEK cells expressing the wild-type and a partially deglycosylated DAT form. These results strongly suggest that DAT glycosylation is involved in the differential vulnerability of midbrain DA cells in PD.     

Epidemiological approaches to the etiology of Parkinson's disease

Abstract– In the search for the cause of Parkinson's disease epidemiology serves several purposes. Valuable clues to the etiology may be derived from the epidemiological features of the disease, and the subsequent search for risk factors in analytical studies can be narrowed correspondingly. On the other hand, knowledge of the epidemiology of Parkinson's disease is necessary in creating etiological hypotheses, since only hypotheses consistent with the epidemiological profile deserve careful testing.     

Possible mechanisms underlying the special vulnerability of dopaminergic neurons

Endogenous or exogenous agents may account for the special vulnerability of dopaminergic neutrons. The present paper deals primarily with the possible role of toxic quinoid metabolites of catechols formed by autoxidation. The study of 5-S-cysteinyl adducts of these, metabolites may provide clues to underlying mechanisms. In addition these adducts may serve as markers of Parkinson's disease.     

Production of dopaminergic neurons for cell therapy in the treatment of Parkinson's disease

Dopaminergic cell therapy is a potential viable treatment for Parkinson's disease. However, lack of a well-characterized cell preparation of known phenotypic composition containing a high percentage of dopaminergic neurons, has prevented a definitive, controlled, pilot clinical trial from being conducted. We report the successful in vitro expansion of rat E12 mesencephalic progenitors to produce 5-fold the normal number of dopaminergic neurons. The expanded neurons (MAP2+) were detached, resuspended, and formed into small aggregates of 10-200 neurons containing 25-50% of dopaminergic neurons (TH+) that will likely be optimal for use in successful cell therapy. After storage in DPBS, in 0 mM Ca(2+) for up to 24 h at room temperature, aggregated cells were still 90% viable. These results demonstrate that it might be feasible to use a similar protocol to expand human dopaminergic progenitors in vitro. If successful, the requisite large numbers of dopaminergic neurons required to conduct a pilot clinical trial for Parkinson's disease will be produced in vitro. Indications are that the cells can be maintained at optimal viability for the duration of the neural transplantation procedure, under real operating conditions.     

Does adrenal graft enhance recovery of dopaminergic neurons in Parkinson's disease?

A 54-year-old man with a 5-year history of Parkinson's disease was treated with and autograft of adrenal medulla into the right caudate nucleus and died 4 months after surgery. Postmortem examination revealed that the graft was necrotic. It consisted mainly of reticulin and collagen fibrosis without catecholaminergic cell bodies identified either by immunohistochemistry or by in situ hybridization with labeled human tyrosine hydroxylase (TH) cDNA probe. Sparse TH-immunoreactive fibers, which did not stain for dopamine-beta-hydroxylase (DBH), ran through the graft. In contrast, intense staining for these catecholaminergic markers was found in the untransplanted adrenal medulla. Densely packed TH-positive, DHB-negative fibers were found in a restricted zone of the host striatum at the periphery of the graft. This effect was selective since the density of other neurons was not modified. The present study describes an additional patient in whom adrenal medulla autotransplantation failed to improve the parkinsonian disability. It suggests, however, that adrenal medulla grafts may stimulate the sprouting of striatal dopaminergic fibers in a limited zone of the grafted striatum.     

镁对帕金森病大鼠黑质多巴胺神经元的影响

目的观察镁对帕金森病(PD)大鼠黑质多巴胺神经元影响及其作用机制。方法应用6-羟基多巴胺(6-OHDA)制备偏侧PD大鼠模型后分为硫酸镁组、美多巴组、混合组(硫酸镁+美多巴)和对照组(生理盐水),并给予相应药物灌胃治疗28d。观察治疗后各组大鼠旋转行为的变化;免疫组化法检测黑质酪氨酸羟化酶(TH)阳性神经元数量;生化法测定损毁侧纹状体超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)活性及丙二醛(MDA)含量;逆转录聚合酶链反应检测损毁侧黑质caspase-3 mRNA表达;Western Blot法检测核因子(NF)-кBP65水平。结果治疗后仅混合组出现较稳定的向对侧的旋转行为;TH阳性神经元数混合组较其他各组明显增加(均P<0.05);与对照组和美多巴组比较,硫酸镁组和混合组SOD、GSH-Px活性显著增高,MDA、caspase-3 mRNA、NF-кBP65水平显著降低(均P<0.05);硫酸镁组与混合组间差异无统计学意义。结论镁及美多巴联合治疗可提高PD模型脑内多巴胺神经元存活、降低氧化应激损伤、减少神经元凋亡,改善PD大鼠症状。     

Translocation of zinc may contribute to seizure-induced death of neurons

Rats were subjected to seizures induced by kainic acid, and the resulting changes in CNS zinc staining were studied with the toluene sulfonamide quinoline fluorescence method. Seizures caused a loss of zinc staining from presynaptic boutons in many limbic and cerebrocortical regions. Simultaneously, the postsynaptic neurons that were degenerating (acidophilic) in those regions as a result of the seizure developed intense fluorescence for zinc. A possible role for zinc in the death of the postsynaptic neurons is suggested.     

共聚物-1对帕金森病模型小鼠多巴胺能神经元的保护作用

目的探讨共聚物-1(Cop-1)免疫或致敏淋巴细胞移植对帕金森病模型小鼠黑质多巴胺(DA)神经元的保护作用。方法选用雄性C57BL/6J小鼠随机分为Cop-1/BSA免疫组、Cop-1/BSA致敏淋巴细胞移植组、MPTP模型组和正常对照组。Cop-1/BSA免疫组在注射MPTP之前10天接受Cop-1/BSA抗原免疫;Cop-1/BSA致敏淋巴细胞移植组动物在MPTP末次注射后,立即接受Cop-1/BSA致敏淋巴细胞移植;MPTP模型组动物仅接受MPTP注射;正常对照组动物仅接受生理盐水注射。MPTP末次注射7天后处死动物,取脑。酪氨酸羟化酶免疫组化及体视学方法定量分析黑质DA神经元数。结果 MPTP注射显著地减少了模型动物黑质DA神经元数量。Cop-1免疫和Cop-1致敏淋巴细胞移植明显增加了MPTP模型动物黑质DA神经元数,对黑质DA神经元有保护作用。BSA免疫或BSA致敏淋巴细胞移植则没有表现出这种保护作用。结论在C57BL/6J小鼠,Cop-1免疫和Cop-1致敏淋巴细胞移植可有效对抗MPTP毒性,保护黑质DA神经元。     

Superoxide dismutase overexpression protects dopaminergic neurons in a Drosophila model of Parkinson's disease

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Some of the inherited forms of the disease are caused by mutations in the alpha-synuclein gene and the triplication of its locus. Oxidative stress has been proposed as a central mechanism for the progression of the disease although its relation with alpha-synuclein toxicity remains obscure. Targeted expression of human alpha-synuclein has been effectively used to recreate the pathology of PD in Drosophila melanogaster and it has been proved an excellent tool for the study of testable hypothesis in relation to the disease. We show that dopaminergic neurons are specifically sensitive to hyperoxia induced oxidative stress and that mutant forms of alpha-synuclein show an enhanced toxicity under these conditions suggesting synergic interactions. In addition, the co-expression of Cu/Zn superoxid dismutase protects against the dopaminergic neuronal loss induced by mutant alpha-synuclein overexpression thus identifying oxidative stress as an important causative factor in the pathology of autosomal-dominant Parkinsonism.