Detrimental deletions: mitochondria, aging and Parkinson's disease

As individuals enter their 80s, they are inevitably confronted with the problem of neuronal loss in the brain. The incidence of the common movement disorder 'mild parkinsonian signs' (MPS) is approximately 50% over the age of 85 years. It has long been known that the loss of dopaminergic neurons in the substantia nigra pars compacta is a neuropathological hallmark of Parkinson's disease (PD). Recently, two papers present clear evidence for a high burden of mitochondrial DNA deletions within substantia nigra neurons in aged individuals and individuals with PD, pointing towards a common pathway inevitably leading to neuronal dysfunction and death.     

Are ubiquitination pathways central to Parkinson's disease?

Parkinson's disease (PD) is the most common neurodegenerative movement disorder. The major motor disabilities of PD are associated with the extensive loss of dopaminergic neurons in the substantia nigra pars compacta. The physiological changes and biochemical pathways involved in the selective demise of these neurons are still unclear. Recent studies have demonstrated that alterations or reductions in ubiquitin-mediated proteasome function can be causal of at least some forms of parkinsonism, and multiple lines of evidence suggest that this mechanism of protein degradation may play an important role in the etiology of PD.     

Increased Protein Oxidation in Human Substantia Nigra Pars Compacta in Comparison with Basal Ganglia and Prefrontal Cortex Measured with an Improved Dinitrophenylhydrazine Assay

Abstract: The dopaminergic phenotype of neurons in human substantia nigra deteriorates during normal aging, and loss of these neurons is prominent in Parkinson's disease. These degenerative processes are hypothesized to involve oxidative stress. To compare oxidative stress in the nigra and related regions, we measured carbonyl modifications of soluble proteins in postmortem samples of substantia nigra, basal ganglia, and prefrontal cortex from neurologically normal subjects, using an improved 2,4-dinitrophenylhydrazine assay. The protein carbonyl content was found to be about twofold higher in substantia nigra pars compacta than in the other regions. To further analyze this oxidative damage, the distribution of carbonyl groups on soluble proteins was determined by western immunoblot analysis. This method revealed that carbonyl content of the major proteins in each region was linearly dependent on molecular weight. This distribution raises the possibility that protein carbonyl content is controlled by a size-dependent mechanism in vivo. Our results suggest that oxidative stress is elevated in human substantia nigra pars compacta in comparison with other regions and that oxidative damage is higher within the dopaminergic neurons. Elevated oxidative damage may contribute to the degeneration of nigral dopaminergic neurons in aging and in Parkinson's disease.     

Deficiency of inducible nitric oxide synthase protects against MPTP toxicity in vivo

MPTP produces clinical, biochemical, and neuropathologic changes reminiscent of those that occur in idiopathic Parkinson's disease (PD). In the present study we show that MPTP treatment led to activation of microglia in the substantia nigra pars compacta (SNpc), which was associated and colocalized with an increase in inducible nitric oxide synthase (iNOS) expression. In iNOS-deficient mice the increase of iNOS expression but not the activation of microglia was blocked. Dopaminergic SNpc neurons of iNOS-deficient mice were almost completely protected from MPTP toxicity in a chronic paradigm of MPTP toxicity. Because the MPTP-induced decrease in striatal concentrations of dopamine and its metabolites did not differ between iNOS-deficient mice and their wild-type littermates, this protection was not associated with a preservation of nigrostriatal terminals. Our results suggest that iNOS-derived nitric oxide produced in microglia plays an important role in the death of dopaminergic neurons but that other mechanisms contribute to the loss of dopaminergic terminals in MPTP neurotoxicity. We conclude that inhibition of iNOS may be a promising target for the treatment of PD.     

The role of iron in Parkinson disease and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity

Parkinson disease (PD) involves the specific degeneration of dopaminergic neurons of the pars compacta of the substantia nigra. Although the cause of the degeneration of nigrostriatal dopaminergic neurons in PD is unknown, there is significant evidence to suggest that oxidative stress may be involved in this process. This review specifically examines the current status of evidence suggesting iron may contribute to oxidative damage associated with PD.     

Activation of CNTF/CNTFRα Signaling Pathway by hRheb(S16H) Transduction of Dopaminergic Neurons In Vivo

Ciliary neurotrophic factor (CNTF) is one of representative neurotrophic factors for the survival of dopaminergic neurons. Its effects are primarily mediated via CNTF receptor α (CNTFRα). It is still unclear whether the levels of CNTFRα change in the substantia nigra of Parkinson’s disease (PD) patients, but CNTF expression shows the remarkable decrease in dopaminergic neurons in the substantia nigra pars compacta (SNpc), suggesting that the support of CNTF/CNTFRα signaling pathway may be a useful neuroprotective strategy for the nigrostriatal dopaminergic projection in the adult brain. Here, we report that transduction of rat SNpc dopaminergic neurons by adeno-associated virus with a gene encoding human ras homolog enriched in brain (hRheb), with an S16H mutation [hRheb(S16H)], significantly upregulated the levels of both CNTF and CNTFRα in dopaminergic neurons. Moreover, the hRheb(S16H)-activated CNTF/CNTFRα signaling pathway was protective against 1-methyl-4-phenylpyridinium-induced neurotoxicity in the nigrostriatal dopaminergic projections. These results suggest that activation of CNTF/CNTFRα signaling pathway by specific gene delivery such as hRheb(S16H) may have therapeutic potential in the treatment of PD.     

Molecular mechanisms of selective dopaminergic neuronal death in Parkinson's disease

Parkinson's disease (PD) is a progressive neurological disease caused by selective degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc). Although PD has been heavily researched, the precise etiology of nigral cell loss is still unknown and, consequently, treatment is largely symptomatic rather than preventive. There are conflicting data regarding the mode of dopaminergic cell death in PD and, hence, this remains controversial. Several mutations in specific genes have recently been linked with hereditary forms of PD. Although none of these mutations are seen in idiopathic disease cases, the elucidation of these genetic defects sheds light on the nature of idiopathic PD. It is possible that dopaminergic neurogenesis also contributes to the etiology of idiopathic PD. In addition, intracellular as well as extracellular substances found in the SNc are believed to function as damaging pathogenetic factors. These factors, and the interactions among them, might hold the secret to the underlying causes of the selective death of dopaminergic neurons in PD.     

Cell Transplantation for Parkinson's Disease: Present Status

1. Parkinson's disease (PD) is a neurodegenerative disorder caused by the loss of neurons in the substantia nigra pars compacta and a striatal deficiency of dopamine. PD typically affects people in late middle age and progresses slowly. In the early stages of the disease, treatment targeting the dopaminergic network is effective. However, with disease progression, transplantation is an option for repairing and replacing missing dopaminergic neurons. 2. In this review, we evaluate the tissue grafts and cellular therapies that have and are being considered. Clinical trials were originally derived from transplants of adrenal medullary chromaffin cells and embryonic nigral dopaminergic neurons in patients with PD. 3. Recently, novel molecular and cellular treatments are being utilized in animals and these include embryonic stem cells, fetal cells from pigs, or transfected cells. In spite of new molecular techniques and some 20 years of experience, the transplantation therapy for PD has today the same problems and results as the first reports which used neural fetal tissue or adrenal grafts.     

帕金森病动物模型:揭开人类帕金森病奥秘的钥匙

帕金森病（Parkinson‘s disease,PD)是一种以黑质致密部多巴胺能神经元的特异性,进行性坏死为特征的神经系统退行性疾病,尽管PD的发病原因还不十分清楚,目前的证据表明环境因素和遗传因素是PD可能的主要致病因素,针对这两大因素,神经科学家们发展了很多制造PD动物模型的方法,MPTP（1-甲基-4-氨基-1,2,3,6-四氢吡啶）模型是目前比较经典的模型。而新近兴起的基因工程模型亦具有广阔的应用前景咯种PD动物模型推动着人们对PD认识的深入和治疗手段的发展,恰当的动物模型必将成为最终揭开人类帕金森病奥秘的钥匙。     

Alpha-Synuclein and Mitochondrial Dysfunction in Parkinson’s Disease

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases. The development of pathology is associated with the loss of dopaminergic neurons, mainly in substantia nigra pars compacta. Dopamine deficiency causes a whole range of severe motor symptoms, including bradykinesia, postural instability, muscle rigidity, and tremor. Studies have shown the primary role of the alpha-synuclein protein in this neurodegenerative disease. A large amount of data indicates different mechanisms of the toxic effect of alpha-synuclein. The process of neurodegeneration in PD is the result of significant disturbances in mitochondrial functions and/or genetic mutations. The number of mutated genes in hereditary and sporadic forms of Parkinson’s disease includes genes encoding PINK1 and Parkin, which are the main participants in the mitochondrial “quality control” system. The earliest biochemical hallmarks of the disease are disturbances of the mitochondrial interaction with endoplasmic reticulum, mitochondrial dynamics, Ca²⁺ homeostasis, and an increase in the level of mitochondrial reactive oxygen species. All these factors exert damaging effects on dopaminergic neurons.     

Ultrastructural characterization of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-induced cell death in embryonic dopaminergic neurons

Developing neuronal populations undergo significant attrition by natural cell death. Dopaminergic neurons in the substantia nigra pars compacta undergo apoptosis during synaptogenesis. Following this time window, destruction of the anatomic target of dopaminergic neurons results in dopaminergic cell death but the morphology is no longer apoptotic. We describe ultrastructural changes that appear unique to dying embryonic dopaminergic neurons. In primary cultures of mesencephalon, death of dopaminergic neurons is triggered by activation of glutamate receptors sensitive to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and differs ultrastructurally from both neuronal apoptosis or typical excitotoxicity. AMPA causes morphological changes selectively in dopaminergic neurons, without affecting other neurons in the same culture dishes. Two hours after the onset of treatment swelling of Golgi complexes is apparent. At 3 h, dopaminergic neurons display loss of membrane asymmetry (coinciding with commitment to die), as well as nuclear membrane invagination, irregular aggregation of chromatin, and mitochondrial swelling. Nuclear changes continue to worsen until loss of cytoplasmic structures and cell death begins to occur after 12 h. These changes are different from those described in neurons undergoing either apoptosis or excitotoxic death, but are similar to ultrastructural changes observed in spontaneous death of dopaminergic neurons in the natural mutant weaver mouse.     

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.     

Celastrol protects against MPTP- and 3-nitropropionic acid-induced neurotoxicity

Oxidative stress and inflammation are implicated in neurodegenerative diseases including Parkinson's disease (PD) and Huntington's disease (HD). Celastrol is a potent anti-inflammatory and antioxidant compound extracted from a perennial creeping plant belonging to the Celastraceae family. Celastrol is known to prevent the production of proinflammatory cytokines, inducible nitric oxide synthase and lipid peroxidation. Mice were treated with celastrol before and after injections of MPTP, a dopaminergic neurotoxin, which produces a model of PD. A 48% loss of dopaminergic neurons induced by MPTP in the substantia nigra pars compacta was significantly attenuated by celastrol treatment. Moreover, celastrol treatment significantly reduced the depletion in dopamine concentration induced by MPTP. Similarly, celastrol significantly decreased the striatal lesion volume induced by 3-nitropropionic acid, a neurotoxin used to model HD in rats. Celastrol induced heat shock protein 70 within dopaminergic neurons and decreased tumor necrosis factor-alpha and nuclear factor kappa B immunostainings as well as astrogliosis. Celastrol is therefore a promising neuroprotective agent for the treatment of PD and HD.     

Pathological changes in dendrites of substantia nigra neurons in Parkinson's disease: a Golgi study.

Neurons of the substantia nigra show severe morphological changes in Parkinson's disease. Pathological alterations of cell bodies have been described, whereas those of neuronal processes have hardly been investigated. Golgi impregnation has been the chosen method for demonstrating neuronal processes and dendritic and somatic spines. We therefore used the Golgi-Braitenberg method to qualitatively and semi-quantitatively study the substantia nigra of eight patients with Parkinson's disease compared with eight control cases. Golgi impregnation of substantia nigra neurons was good in all control cases. In full agreement with the analysis of Braak and Braak (1986) three neuronal types within the substantia nigra were found. In cases of Parkinson's disease, severe pathological changes such as decrease of dendritic length, loss of dendritic spines and several types of dendritic varicosities were found only in the melanin-containing pars compacta neurons. Pars reticulata nerve cells were intact. These findings support the predominant role played by the dopaminergic efferent pathway in the degenerative process. The afferent pathway was not affected. This suggests that the substantia nigra lesion is primary in Parkinson's disease. Loss of neurons found in H & E sections corresponded to a lesser amount of impregnated pars compacta neurons in cases with Parkinson's disease when compared to controls. Evidences exist that the duration of the disease may be related to the extent of pathologically altered Golgi-impregnated pars compacta cells. The amount of Lewy bodies in H & E sections corresponded to the quantity of round varicosities in impregnated pars compacta neurons. These round dendritic varicosities were considered to be Lewy body inclusions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alpha-synuclein up-regulation in substantia nigra dopaminergic neurons following administration of the parkinsonian toxin MPTP

Mutations in alpha-synuclein cause a form of familial Parkinson's disease (PD), and wild-type alpha-synuclein is a major component of the intraneuronal inclusions called Lewy bodies, a pathological hallmark of PD. These observations suggest a pathogenic role for alpha-synuclein in PD. Thus far, however, little is known about the importance of alpha-synuclein in the nigral dopaminergic pathway in either normal or pathological situations. Herein, we studied this question by assessing the expression of synuclein-1, the rodent homologue of human alpha-synuclein, in both normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. In normal mice, detectable levels of synuclein mRNA and protein were seen in all brain regions studied and especially in ventral midbrain. In the latter, there was a dense synuclein-positive nerve fiber network, which predominated over the substantia nigra, and only few scattered synuclein-positive neurons. After a regimen of MPTP that kills dopaminergic neurons by apoptosis, synuclein mRNA and protein levels were increased significantly in midbrain extracts; the time course of these changes paralleled that of MPTP-induced dopaminergic neurodegeneration. In these MPTP-injected mice, there was also a dramatic increase in the number of synuclein-immunoreactive neurons exclusively in the substantia nigra pars compacta; all synuclein-positive neurons were tyrosine hydroxylase-positive, but none coexpressed apoptotic features. These data indicate that synuclein is highly expressed in the nigrostriatal pathway of normal mice and that it is up-regulated following MPTP-induced injury. In light of the synuclein alterations, it can be suggested that, by targeting this protein, one may modulate MPTP neurotoxicity and, consequently, open new therapeutic avenues for PD.     

Harpagoside attenuates MPTP/MPP⁺ induced dopaminergic neurodegeneration and movement disorder via elevating glial cell line-derived neurotrophic factor

Parkinson's disease is a chronic neurodegenerative movement disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. New therapeutic approaches aiming at delaying or reversing the neurodegenerative process are under active investigations. In this work, we found that harpagoside, an iridoid purified from the Chinese medicinal herb Scrophularia ningpoensis, could not only prevent but also rescue the dopaminergic neurodegeneration in MPTP/MPP(+) intoxication with promising efficacy. Firstly, in cultured mesencephalic neurons, harpagoside significantly attenuated the loss of TH-positive neuron numbers and the shortening of axonal length. Secondly, in a chronic MPTP mouse model, harpagoside dose-dependently improved the loco-motor ability (rotarod test), increased the TH-positive neuron numbers in the substantia nigra pars compacta (unbiased stereological counting) and increased the striatal DAT density ((125) I-FP-CIT autoradiography). Thirdly, harpagoside markedly elevated the GDNF mRNA and GDNF protein levels in MPTP/MPP(+) lesioned models. However, the protecting effect of harpagoside on the dopaminergic degeneration disappeared when the intrinsic GDNF action was blocked by either the Ret inhibitor PP1 or the neutralizing anti-GDNF antibody. Taken together, we conclude that harpagoside attenuates the dopaminergic neurodegeneration and movement disorder mainly through elevating glial cell line-derived neurotrophic factor.     

Superoxide dismutase/catalase mimetics are neuroprotective against selective paraquat-mediated dopaminergic neuron death in the substantial nigra: implications for Parkinson disease

Exposure of mice to the herbicide paraquat has been demonstrated to result in the selective loss of dopaminergic neurons of the substantia nigra, pars compacta (SNpc) akin to what is observed in Parkinson disease (PD). In this study, we investigate the efficacy of two synthetic superoxide dismutase/catalase mimetics (EUK-134 and EUK-189) in protecting against paraquat-induced dopaminergic cell death in both the rat dopaminergic cell line 1RB3AN27 (N27) and primary mesencephalic cultures in vitro and in adult mice in vivo. Our data demonstrate that pretreatment with either EUK-134 or EUK-189 significantly attenuates paraquat-induced neurotoxicity in vitro in a concentration-dependent manner. Furthermore, systemic administration of EUK-189 decreases paraquat-mediated SNpc dopaminergic neuronal cell death in vivo. These findings support a role for oxidative stress in paraquat-induced neurotoxicity and suggest novel therapeutic approaches for neurodegenerative disorders associated with oxidative stress such as PD.     

The neurotoxicity of DOPAL: behavioral and stereological evidence for its role in Parkinson disease pathogenesis

Background

The etiology of Parkinson disease (PD) has yet to be fully elucidated. We examined the consequences of injections of 3,4-dihydroxyphenylacetaldehyde (DOPAL), a toxic metabolite of dopamine, into the substantia nigra of rats on motor behavior and neuronal survival.

Methods/Principal Findings

A total of 800 nl/rat of DOPAL (1 µg/200 nl) was injected stereotaxically into the substantia nigra over three sites while control animals received similar injections of phosphate buffered saline. Rotational behavior of these rats was analyzed, optical density of striatal tyrosine hydroxylase was calculated, and unbiased stereological counts of the substantia nigra were made. The rats showed significant rotational asymmetry ipsilateral to the lesion, supporting disruption of dopaminergic nigrostriatal projections. Such disruption was verified since the density of striatal tyrosine hydroxylase decreased significantly (p<0.001) on the side ipsilateral to the DOPAL injections when compared to the non-injected side. Stereological counts of neurons stained for Nissl in pars compacta of the substantia nigra significantly decreased (p<0.001) from control values, while counts of those in pars reticulata were unchanged after DOPAL injections. Counts of neurons immunostained for tyrosine hydroxylase also showed a significant (p = 0.032) loss of dopaminergic neurons. In spite of significant loss of dopaminergic neurons, DOPAL injections did not induce significant glial reaction in the substantia nigra.

Conclusions

The present study provides the first in vivo quantification of substantia nigra pars compacta neuronal loss after injection of the endogenous toxin DOPAL. The results demonstrate that injections of DOPAL selectively kills SN DA neurons, suggests loss of striatal DA terminals, spares non-dopaminergic neurons of the pars reticulata, and triggers a behavioral phenotype (rotational asymmetry) consistent with other PD animal models. This study supports the “catecholaldehyde hypothesis” as an important link for the etiology of sporadic PD.