Mechanism of neurodegenerative disease: role of the ubiquitin proteasome system

Many neurodegenerative disorders such as Alzheimer's disease (AD) Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD) are characterized by neuronal damage that may be caused by toxic, abnormal, aggregation-prone proteins. The purpose of this review is threefold: 1) to provide the reader with an overview of the genes involved in the abnormal processing and accumulation of misfolded proteins in neurodegenerative diseases using PD as a model disease; 2) to understand the cellular mechanisms for disposal of abnormal proteins, and the effects of toxic protein accumulation on ubiquitin proteasome system (UPS) and neuronal survival and 3) to discuss the development and challenges of cell culture and animal models for a rational and effective treatment for these disorders.     

Antioxidant gene therapy against neuronal cell death

Oxidative stress is a common hallmark of neuronal cell death associated with neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, as well as brain stroke/ischemia and traumatic brain injury. Increased accumulation of reactive species of both oxygen (ROS) and nitrogen (RNS) has been implicated in mitochondrial dysfunction, energy impairment, alterations in metal homeostasis and accumulation of aggregated proteins observed in neurodegenerative disorders, which lead to the activation/modulation of cell death mechanisms that include apoptotic, necrotic and autophagic pathways. Thus, the design of novel antioxidant strategies to selectively target oxidative stress and redox imbalance might represent important therapeutic approaches against neurological disorders. This work reviews the evidence demonstrating the ability of genetically encoded antioxidant systems to selectively counteract neuronal cell loss in neurodegenerative diseases and ischemic brain damage. Because gene therapy approaches to treat inherited and acquired disorders offer many unique advantages over conventional therapeutic approaches, we discussed basic research/clinical evidence and the potential of virus-mediated gene delivery techniques for antioxidant gene therapy.     

Developing intrabodies for the therapeutic suppression of neurodegenerative pathology

Many neurodegenerative diseases have misfolded proteins as a primary occurrence in pathogenesis. A combination of antibody and genetic engineering has emerged as a powerful tool for developing reagents that specifically target the misfolding process itself, and/or abnormal interactions of the misfolded protein species. This review focuses on the selection and testing of intracellular antibody fragments (intrabodies), with a particular focus on Huntington's disease (HD) and Parkinson's disease (PD), both of which show prominent intracellular protein aggregates in affected neurons. The most dramatic advances are in HD, where in vivo efficacy of intrabodies has been demonstrated. Targets in other neurodegenerative disorders, including Alzheimer's disease and prion diseases, are noted more briefly, with an emphasis on the potential for intracellular manipulations. Given the specificity and versatility of antibody-based reagents, the wide range of options for conformational and post-translationally-modified targets, and the recent improvement in gene delivery, this should be a fertile field for 21^st century pharmacology.     

Amyloid P component as a plasma marker for Parkinson's disease identified by a proteomic approach

ObjectivesParkinson's disease (PD) ranks the second among the neurodegenerative disorders. Proteins involved in Parkinson's disease (PD) have been investigated but none as the diagnostic markers in blood.Design and methodsIn this study, we applied a proteomic strategy, by utilizing two-dimensional electrophoresis and mass spectrometry, to analyze two sample pools of plasma from the healthy individuals and PD subjects.ResultsIgGκL and human serum amyloid P component (SAP) were found differentially expressed between these pools. SAP level increased by approximately 5-fold in PD samples, and the ELISA procedure revealed a significant (P < 0.001) increase in SAP concentration (65.9 ± 18.7 μg/mL) in the plasma of PD subjects (healthy individuals, 35.0 ± 12.5 μg/mL), with sensitivity of 94.1% and specificity of 87.5%.ConclusionOur results indicated a potential feasibility of plasma SAP as a marker to approach PD.     

Hepcidin and its therapeutic potential in neurodegenerative disorders

Abnormally high brain iron, resulting from the disrupted expression or function of proteins involved in iron metabolism in the brain, is an initial cause of neuronal death in neuroferritinopathy and aceruloplasminemia, and also plays a causative role in at least some of the other neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Friedreich's ataxia. As such, iron is believed to be a novel target for pharmacological intervention in these disorders. Reducing iron toward normal levels or hampering the increases in iron associated with age in the brain is a promising therapeutic strategy for all iron-related neurodegenerative disorders. Hepcidin is a crucial regulator of iron homeostasis in the brain. Recent studies have suggested that upregulating brain hepcidin levels can significantly reduce brain iron content through the regulation of iron transport protein expression in the blood-brain barrier and in neurons and astrocytes. In this review, we focus on the discussion of the therapeutic potential of hepcidin in iron-associated neurodegenerative diseases and also provide a systematic overview of recent research progress on how misregulated brain iron metabolism is involved in the development of multiple neurodegenerative disorders.     

经颅超声在帕金森病诊断和鉴别诊断中的应用进展

帕金森病（Parkinson''s disease,PD）是临床常见神经变性病,经颅超声(Transcranial sonography,TCS)发现黑质异常高回声(Substantia nigra,SN+)是PD诊断和鉴别诊断的重要辅助检查。但SN+出现的原因不甚清楚,其与症状严重程度的相关性仍有较大争议,与临床分型及分期方面的关系未有定论,TCS亦可通过对中脑中缝和基底节区的探查,提示几种运动及情感障碍的鉴别,越来越多的研究正在不断拓宽TCS在临床实践中的使用。     

Lentivirus Mediated Delivery of Neurosin Promotes Clearance of Wild-type α-Synuclein and Reduces the Pathology in an α-Synuclein Model of LBD

Neurosin is a predominant serine protease in the central nervous system (CNS) and has been shown to play a role in the clearance of α-synuclein (α-syn) which is centrally involved in the pathogenesis of Parkinson''s disease (PD) and dementia with Lewy bodies (DLB). Although it has been previously shown that neurosin and α-syn colocalize and that neurosin degrades α-syn aggregates in vitro, it is not clear if neurosin is dysregulated in the brains of patients with PD/DLB and to what extent delivery of neurosin into the CNS might ameliorate the deficits associated with α-syn accumulation in vivo. We analyzed the levels of neurosin in the brains of patients with PD/DLB and in α-syn transgenic (tg) models. With increased accumulation of α-syn, we observed decreased neurosin expression. Lentiviral vector (LV) driven expression of neurosin in neuronal cell cultures reduced the accumulation of wild type but not A53T α-syn and prevented α-syn associated toxicity. Neuropathological analysis following delivery of LV-Neurosin to α-syn tg mice resulted in reduced accumulation of α-syn and reversal of neurodegenerative alterations in wild type but not A53T α-syn tg mice. Therefore, viral vector driven expression of neurosin may warrant further investigation as a potential therapeutic tool for DLB.     

Polyamine patterns in the cerebrospinal fluid of patients with Parkinson's disease and multiple system atrophy

BackgroundPolyamines (PAs) are important modulators of physiological condition, and are associated with neurodegenerative disease. Thus, we investigated the change of PA concentration in the cerebrospinal fluid (CSF) of patients with Parkinson's disease (PD) and multiple system atrophy (MSA).MethodsCSF samples from patients with PD and MSA were examined by gas chromatography–mass spectrometry in selected ion monitoring mode using N-ethoxycarbonyl/N-pentafluoropropyonyl derivatives.ResultsPA concentrations were significantly different in patients with PD and MSA compared with those in the normal group. In the PD group, as compared with the MSA group, concentrations of putrescine, N¹-acetylspermidine, and putrescine spermidine^–1 were significantly increased, whereas the concentration of spermidine was significantly reduced.ConclusionsThese results could be helpful for understanding the complexity of biochemical events in patients with PD and MSA, and may serve as metabolic markers for diagnosis of PD and MSA.     

ESCRT-mediated Uptake and Degradation of Brain-targeted α-synuclein Single Chain Antibody Attenuates Neuronal Degeneration In Vivo

Parkinson''s disease and dementia with Lewy bodies are neurodegenerative disorders characterized by accumulation of α-synuclein (α-syn). Recently, single-chain fragment variables (scFVs) have been developed against individual conformational species of α-syn. Unlike more traditional monoclonal antibodies, these scFVs will not activate or be endocytosed by Fc receptors. For this study, we investigated an scFV directed against oligomeric α-syn fused to the LDL receptor-binding domain from apolipoprotein B (apoB). The modified scFV showed enhanced brain penetration and was imported into neuronal cells through the endosomal sorting complex required for transport (ESCRT) pathway, leading to lysosomal degradation of α-syn aggregates. Further analysis showed that the scFV was effective at ameliorating neurodegenerative pathology and behavioral deficits observed in the mouse model of dementia with Lewy bodies/Parkinson''s disease. Thus, the apoB modification had the effect of both increasing accumulation of the scFV in the brain and directing scFV/α-syn complexes for degradation through the ESCRT pathway, leading to improved therapeutic potential of immunotherapy.     

Imaging of Cholinergic and Monoaminergic Neurochemical Changes in Neurodegenerative Disorders

Positron emission tomography (PET) or single photon emission computer tomography (SPECT) imaging provides the means to study neurochemical processes in vivo. These methods have been applied to examine monoaminergic and cholinergic changes in neurodegenerative disorders. These investigations have provided important insights into disorders, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). The most intensely studied monoaminergic transmitter is dopamine. The extent of presynaptic nigrostriatal dopaminergic denervation can be quantified in PD and may serve as a diagnostic biomarker. Dopaminergic receptor imaging may help to distinguish idiopathic PD from atypical parkinsonian disorders. Cholinergic denervation has been identified not only in AD but also in PD and more severely in parkinsonian dementia. PET or SPECT can also provide biomarkers to follow progression of disease or evaluate the effects of therapeutic interventions. Cholinergic receptor imaging is expected to play a major role in new drug development for dementing disorders.     

The Role of Intrinsically Unstructured Proteins in Neurodegenerative Diseases

The number and importance of intrinsically disordered proteins (IUP), known to be involved in various human disorders, are growing rapidly. To test for the generalized implications of intrinsic disorders in proteins involved in Neurodegenerative diseases, disorder prediction tools have been applied to three datasets comprising of proteins involved in Huntington Disease (HD), Parkinson's disease (PD), Alzheimer's disease (AD). Results show, in general, proteins in disease datasets possess significantly enhanced intrinsic unstructuredness. Most of these disordered proteins in the disease datasets are found to be involved in neuronal activities, signal transduction, apoptosis, intracellular traffic, cell differentiation etc. Also these proteins are found to have more number of interactors and hence as the proportion of disorderedness (i.e., the length of the unfolded stretch) increased, the size of the interaction network simultaneously increased. All these observations reflect that, “Moonlighting” i.e. the contextual acquisition of different structural conformations (transient), eventually may allow these disordered proteins to act as network “hubs” and thus they may have crucial influences in the pathogenecity of neurodegenerative diseases.     

Alzheimer's disease and other neurodegenerative dementias in comorbidity: A clinical and neuropathological overview

Neuropathological diagnostic criteria of neurodegenerative disorders are based on the presence of specific inclusions in a specific area of brain tissue that correlate with clinical manifestations. Concomitant neurodegenerative disorders correspond to a combination of two (or more) different fully developed diseases in the same patient. Concomitant neurodegenerative pathology represents the presence of definite neurodegeneration and deposits of pathological proteins specific for another disease, which is not, however, fully developed. Very frequent overlaps include Alzheimer's disease and alpha-synuclein inclusions. Nevertheless, careful neuropathological investigations reveal an increasing frequency of different co-pathologies in examined brains. In Alzheimer's disease, protein TDP-43 may co-aggregate, but it is not clear whether this is atypical isolated Alzheimer's disease or overlap of Alzheimer's disease with early frontotemporal lobar degeneration. Comorbidities of Alzheimer's disease and tauopathies are relatively rare. A combination of vascular pathology with primary neurodegeneration (mostly Alzheimer's disease or dementia with Lewy bodies) is historically called mixed dementia. Overlap of different neuropathologically confirmed neurodegenerations could lead to atypical and unusual clinical presentations and may be responsible for faster disease progression. Several CSF biomarkers have been evaluated for their utility in diagnostic processes in different neurodegenerative dementias; however, evidence regarding their role in neurodegenerative overlaps is still limited.     

Zinc: indications in brain disorders

Zinc is the authoritative metal which is present in our body, and reactive zinc metal is crucial for neuronal signaling and is largely distributed within presynaptic vesicles. Zinc also plays an important role in synaptic function. At cellular level, zinc is a modulator of synaptic activity and neuronal plasticity in both development and adulthood. Different importers and transporters are involved in zinc homeostasis. ZnT‐3 is a main transporter involved in zinc homeostasis in the brain. It has been found that alterations in brain zinc status have been implicated in a wide range of neurological disorders including impaired brain development and many neurodegenerative disorders such as Alzheimer's disease, and mood disorders including depression, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and prion disease. Furthermore, zinc has also been implicated in neuronal damage associated with traumatic brain injury, stroke, and seizure. Understanding the mechanisms that control brain zinc homeostasis is thus critical to the development of preventive and treatment strategies for these and other neurological disorders.     

Role of nitric oxide in Parkinson's disease

As a signal molecule, nitric oxide (NO) plays an important role in a variety of signal transduction pathways that are crucial for maintaining the physiologic functions of vascular, respiratory, immune, muscular, and nervous systems. NO and its derivatives are also involved in the pathogenic processes in various types of diseases including, but not limited to, neurodegenerative disorders. Although the molecular mechanisms of how NO contributes to diseases are not completely understood, studies have shown that NO may cause neuronal injury and death by mediation of excitotoxicity, damage of DNA, and/or modification of proteins. Understanding the pathogenic mechanisms of NO and its role in Parkinson's disease (PD) and other neurodegenerative diseases may help to develop novel neuroprotective therapies for these diseases.     

Beta-asarone protects against MPTP-induced Parkinson’s disease via regulating long non-coding RNA MALAT1 and inhibiting α-synuclein protein expression

ObjectiveNumerous long non-coding RNAs (lncRNA) have been identified in neurodegenerative disorders including Parkinson’s disease (PD). Emerging evidence demonstrates that β-asarone functions as neuroprotective effects in both in vitro and in vivo models. However, the role of β-asarone and its potential mechanism in PD remain not completely clear.MethodsMPTP-induced PD mouse model and SH-SY5Y cells subjected to MPP+ as its in vitro model were used to evaluate the effects of β-asarone on PD. LncRNA MALAT1 and α-synuclein expression were determined by real-time PCR and western blot methods.Resultsβ-Asarone significantly increased the TH+ cells number and decreased the expression levels of MALAT1 and α-synuclein in midbrain tissue of PD mice. RNA pull-down and immunoprecipitation assays confirmed that MALAT1 associated with α-synuclein, leading to the increased stability of α-synuclein and its expression in SH-SY5Y cells. β-asarone elevated the viability of cells exposed to MPP+. Either overexpressed MALAT1 or α-synuclein could canceled the protective effect of β-asarone on cell viability. In PD mice, pcDNA-MALAT1 also decreased the TH+ cells number and increased the α-synuclein expression in PD mice with treatment of β-asarone.Conclusionβ-Asarone functions as a neuroprotective effect in both in vivo and in vitro models of PD via regulating MALAT1 and α-synuclein expression.     

Environmental neurotoxic chemicals-induced ubiquitin proteasome system dysfunction in the pathogenesis and progression of Parkinson's disease

Proteolytic degradation of unwanted proteins by the ubiquitin-proteasome system (UPS) is critical for normal maintenance of various cellular functions. Parkinson's disease (PD), one of the most prevalent neurodegenerative disorders, is characterized by prominent and irreversible nigral dopaminergic neuronal loss and intracellular protein aggregations. Epidemiological studies imply both environmental neurotoxins and genetic predisposition as potential risk factors for PD, though mechanisms underlying selective dopaminergic degeneration remain unclear. Studies with experimental PD models and postmortem PD brains have provided explicit evidence for mitochondria dysfunction and oxidative stress in PD pathogenesis. Recent identification of mutants in PINK1, DJ-1, Parkin, and LRRK-2 genes compliments the oxidative stress and mitochondrial dysfunction hypotheses in dopaminergic neuronal degeneration in PD. Mutants of alpha-synuclein, Uch-L1 and Parkin support the involvement of UPS dysfunction in PD. Furthermore, various Parkinsonian toxicants have been shown to impair mitochondrial function, redox balances, and to some extent protein degradation machinery. Because environmental exposure to various neurotoxic agents is considered a dominant risk for development of PD, the interrelationship between neurotoxicant exposures and UPS dysfunction must be clearly understood. Elucidation of this interrelationship will help clarify 2 areas: (i) whether UPS dysfunction in PD is a primary pathogenic factor leading to nigral neuronal death or if it simply occurs as a consequence of oxidative stress and mitochondrial dysfunction and (ii) the interaction of genes and environment in the acceleration of nigral dopaminergic degeneration by targeting UPS. We review the recent evidence for UPS deficits in dopaminergic degeneration triggered by neurotoxins.     

DNA vaccination against mutant huntingtin ameliorates the HDR6/2 diabetic phenotype

Immunization against extracellular neurotoxic proteins has shown promise in the treatment of several neurodegenerative disorders. We sought to determine whether immunization against mutant huntingtin, the intracellular protein that causes Huntington's disease (HD), could slow disease progression in the HD mouse model HDR6/2. DNA vaccination was used to present the mutant intracellular antigen to the immune system in a physiological context. Assay of a peripheral biomarker, pancreatic insufficiency, was used as an initial test of efficacy. DNA vaccination with a 5′ fragment of the HD cDNA prevented development of the HDR6/2 diabetic phenotype. Insulin staining demonstrated that HDR6/2 diabetes may be caused by a severe pancreatic insulin deficiency. Immunoresponsive HDR6/2 mice showed increased insulin staining more closely resembling wild-type levels. These observations suggest that DNA vaccination against toxic intracellular proteins may be therapeutic.