Parkin-associated Parkinson's disease

KF-1 Ubiquitin Ligase: An Anxiety Suppressor

Anxiety is an instinct that may have developed to promote adaptive survival by evading unnecessary danger. However, excessive anxiety is disruptive and can be a basic disorder of other psychiatric diseases such as depression. The KF-1, a ubiquitin ligase located on the endoplasmic reticulum (ER), may prevent excessive anxiety; kf-1^−/− mice exhibit selectively elevated anxiety-like behavior against light or heights. It is surmised that KF-1 degrades some target proteins, responsible for promoting anxiety, through the ER-associated degradation pathway, similar to Parkin in Parkinson's disease (PD). Parkin, another ER-ubiquitin ligase, prevents the degeneration of dopaminergic neurons by degrading the target proteins responsible for PD. Molecular phylogenetic studies have revealed that the prototype of kf-1 appeared in the very early phase of animal evolution but was lost, unlike parkin, in the lineage leading up to Drosophila. Therefore, kf-1^−/− mice may be a powerful tool for elucidating the molecular mechanisms involved in emotional regulation, and for screening novel anxiolytic/antidepressant compounds.

Cell death pathways in Parkinson's disease: proximal triggers, distal effectors, and final steps

Parkinson's disease (PD) is a common neurodegenerative disorder. Neuronal cell death in PD is still poorly understood, despite a wealth of potential pathogenic mechanisms and pathways. Defects in several cellular systems have been implicated as early triggers that start cells down the road toward neuronal death. These include abnormal protein accumulation, particularly of alpha-synuclein; altered protein degradation via multiple pathways; mitochondrial dysfunction; oxidative stress; neuroinflammation; and dysregulated kinase signaling. As dysfunction in these systems mounts, pathways that are more explicitly involved in cell death become recruited. These include JNK signaling, p53 activation, cell cycle re-activation, and signaling through bcl-2 family proteins. Eventually, neurons become overwhelmed and degenerate; however, even the mechanism of final cell death in PD is still unsettled. In this review, we will discuss cell death triggers and effectors that are relevant to PD, highlighting important unresolved issues and implications for the development of neuroprotective therapies.

Bacterial artificial chromosome transgenic mice expressing a truncated mutant parkin exhibit age-dependent hypokinetic motor deficits, dopaminergic neuron degeneration, and accumulation of proteinase K-resistant alpha-synuclein

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.

Identification of a novel Zn2+-binding domain in the autosomal recessive juvenile Parkinson-related E3 ligase parkin

Missense mutations in park2, encoding the parkin protein, account for approximately 50% of autosomal recessive juvenile Parkinson disease (ARJP) cases. Parkin belongs to the family of RBR (RING-between-RING) E3 ligases involved in the ubiquitin-mediated degradation and trafficking of proteins such as Pael-R and synphillin-1. The proposed architecture of parkin, based largely on sequence similarity studies, consists of N-terminal ubiquitin-like and C-terminal RBR domains. These domains are separated by a approximately 160-residue unique parkin sequence having no recognizable domain structure. We used limited proteolysis experiments on bacterially expressed and purified parkin to identify a new domain (RING0) within the unique parkin domain sequence. RING0 comprises two distinct, conserved cysteine-rich clusters between Cys(150)-Cys(169) and Cys(196)-His(215) consisting of CX(2)-(3)CX(11)CX(2)C and CX(4-6)CX(10-16)-CX(2)(H/C) motifs. The positions of the cysteine/histidine residues in this region bear similarity to parkin RING1 and RING2 domains, as well as other E3 ligase RING domains. However, in parkin a 26-residue linker region separates the motifs, which is not typical of other RING domain structures. Further, the RING0 domain includes all but one of the known ARJP mutation sites between the ubiquitin-like and RBR regions of parkin. Using electrospray ionization mass spectrometry and inductively coupled plasma-atomic emission spectrometry analysis, we determined that the RING0, RING1, IBR, and RING2 domains each bind two Zn(2+) ions, the first observation of an E3 ligase with the ability to bind eight metal ions. Removal of the zinc from parkin causes near complete unfolding of the protein, an observation that rationalizes cysteine-based ARJP mutations found throughout parkin, including RING0 (C212Y) that form cellular inclusions and/or are defective for ubiquitination likely because of poor zinc binding and misfolding. The identification of the RING0 domain in parkin provides a new overall domain structure for the protein that will be important in assessing the roles of ARJP mutations and designing experiments aimed at understanding the disease.

Regulation of DNA repair by parkin

Mutation of parkin is one of the most prevalent causes of autosomal recessive Parkinson's disease (PD). Parkin is an E3 ubiquitin ligase that acts on a variety of substrates, resulting in polyubiquitination and degradation by the proteasome or monoubiquitination and regulation of biological activity. However, the cellular functions of parkin that relate to its pathological involvement in PD are not well understood. Here we show that parkin is essential for optimal repair of DNA damage. Parkin-deficient cells exhibit reduced DNA excision repair that can be restored by transfection of wild-type parkin, but not by transfection of a pathological parkin mutant. Parkin also protects against DNA damage-induced cell death, an activity that is largely lost in the pathological mutant. Moreover, parkin interacts with the proliferating cell nuclear antigen (PCNA), a protein that coordinates DNA excision repair. These results suggest that parkin promotes DNA repair and protects against genotoxicity, and implicate DNA damage as a potential pathogenic mechanism in PD.

Hyperphosphorylated tau aggregates in the cortex and hippocampus of transgenic mice with mutant human FTDP-17 Tau and lacking the PARK2 gene

Mutations in the PARK2 gene encoding parkin cause autosomal recessive juvenile parkinsonism, but have also been found in patients diagnosed with certain tauopathies. Conversely, mutations in the MAPT gene encoding tau are present in some types of parkinsonism. In order to investigate the possible relationship between these two proteins, we generated a double mutant mouse that is deficient in PARK2 and that over-expresses the hTauVLW transgene, a mutant form of the tau protein present in FTDP-17. Independent deletion of PARK2 or over-expression of the hTauVLW transgene produces mild phenotypic alterations, while a substantial increase in parkin expression is observed in hTauVLW transgenic mice. However, double mutant mice present memory and exploratory deficits, and accumulation of PHF-1 and AT8 hyperphosphorylated tau epitopes in neurons. These phenomena are coupled with reactive astrocytosis, DNA fragmentation, and variable cerebral atrophy. Here, we show that cortical and hippocampal neurons of double mutant mice develop argyrophilic Gallyas-Braak aggregates of phosphorylated tau from 3 months of age. Their number decreases in old animals. Moreover, numerous phosphorylated tau aggregates were identified with the conformation-dependent Alz-50 antibody and the S-Thioflavin staining. Ventral motor nuclei of the spinal cord also present Alz-50, AT8, and PHF1 hyperphosphorylated tau aggregates when parkin is deleted in mice over-expressing the hTauVLW transgene, begining at early ages. Thus, the combination of PARK2 gene deletion with hTauVLW over-expression in mice produces abnormal hyperphosphorylated tau aggregates, similar to those observed in the brain of patients diagnosed with certain tauopathies. In the light of these changes, these mice may help to understand the molecular processes responsible for these diseases, and they may aid the development of new therapeutic strategies to treat neurodegenerative diseases related to tau and parkin proteins.

BAC to degeneration bacterial artificial chromosome (BAC)-mediated transgenesis for modeling basal ganglia neurodegenerative disorders

Basal ganglia neurodegenerative disorders, such as Parkinson's disease (PD) and Huntington's disease (HD), are characterized by not only spectrum of motor deficits, ranging form hypokinesia to hyperkinesia, but also emotional, cognitive, and psychiatric manifestations. The symptoms and pathogenic mechanism of these disorders should be viewed as dysfunctions of specific cortico-subcortical neurocircuits. Transgenic approaches using large genomic inserts, such as bacterial artificial chromosome (BAC)-mediated transgenesis, due to its capacity to propagate large-size genomic DNA and faithful production of endogenous-like gene expression pattern/lever, have provided an ideal basis for the generation of transgenic mice as model for basal ganglia neurodegenerative disorders, as well as the functional and structural analysis of neurocircuits. In this chapter, the basic concepts and practical approaches about application of BAC transgenic system are introduced. Existent major BAC transgenic mouse models for PD and HD are evaluated according to their construct, face, and predicative validity. Finally, considerations, possible solutions, and future perspectives of using BAC transgenic approach to study basal ganglia neurodegenerative disorders are discussed.

Proteomics in animal models of Alzheimer's and Parkinson's diseases

The risk of developing neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD) increases with age. AD and PD are the two most common neurodegenerative diseases that currently affect millions of persons within the United States population. While many clues about the mechanisms of these disorders have been uncovered, to date, the molecular mechanisms associated with the cause of these diseases are not completely understood. Furthermore, there are no available cures or preventive treatments for either disorder. Animal models of AD and PD, though not perfect, offer a means to gain knowledge of the basic biochemistry associated with these disorders and with drug efficacy. The field of proteomics which focuses on identifying the dynamic nature of the protein content expressed within a particular cell, tissue, or organism, has provided many insights into these disturbing disorders. Proteomic studies have revealed many pathways that are associated with disease pathogenesis and that may lead to the development of potential therapeutic targets. This review provides a discussion of key findings from AD and PD proteomics-based studies in various animal models of disease.

What causes cell death in Parkinson's disease?

Currently, there is no proven neuroprotective or neurorestorative therapy for Parkinson's disease (PD). Several advances in the genetics of PD have created an opportunity to develop mechanistic-based therapies that hold particular promise for identifying agents that slow and even halt the progression of PD, as well as restore function. Here we review many of the advances in the last decade regarding the identification of new targets for the treatment of PD based on understanding the molecular mechanisms of how mutations in genes linked to PD cause neurodegeneration.

Ubiquitin, the proteasome and protein degradation in neuronal function and dysfunction

Eukaryotic protein degradation by the proteasome and the lysosome is a dynamic and complex process in which ubiquitin has a key regulatory role. The distinctive morphology of the postmitotic neuron creates unique challenges for protein degradation systems with respect to cell-surface protein turnover and substrate delivery to proteolytic machineries that are required for both synaptic plasticity and self-renewal. Moreover, the discovery of ubiquitin-positive protein aggregates in a wide spectrum of neurodegenerative diseases underlines the importance and vulnerability of the degradative system in neurons. In this article, we discuss the molecular mechanism of protein degradation in the neuron with respect to both its function and its dysfunction.

Motor alterations are reduced in mice lacking the PARK2 gene in the presence of a human FTDP-17 mutant form of four-repeat tau

Independent deletion of the PARK2 gene and hTauVLW over-expression in mice produce mild alterations in the brain. However, the presence of both mutations in a parkin-deficient and hTauVLW double mutant mouse causes a tau neuropathology, reactive astrocytosis, and neuronal loss in the cortex and hippocampus, as well as lesions in nigrostriatal and motor neurons. Moreover, these mutants display some memory and exploratory defects that reflect a functional link between parkin and tau proteins. We have tested the motor activity and coordination of these double mutant mice to determine the effects of parkin deletion in mice over-expressing the hTauVLW transgene. While the loss of parkin alone produces increased exploration and alterations in gait and motor coordination, in hTauVLW transgenic mice the absence of parkin causes less prominent motor impairments. These effects suggest the existence of some compensatory mechanisms that are activated when the hTauVLW transgene is over-expressed in the absence of parkin. This mouse model will hopefully help to study the causes of the motor deficits associated with certain neuropathologies related to the tau and parkin proteins, and to find appropriate treatments.

Triggering aggresome formation. Dissecting aggresome-targeting and aggregation signals in synphilin 1

Abnormal polypeptides that escape proteasome-dependent degradation and aggregate in cytosol can be transported via microtubules to an aggresome, a recently discovered organelle where aggregated proteins are stored or degraded by autophagy. We used synphilin 1, a protein implicated in Parkinson disease, as a model to study mechanisms of aggresome formation. When expressed in naïve HEK293 cells, synphilin 1 forms multiple small highly mobile aggregates. However, proteasome or Hsp90 inhibition rapidly triggered their translocation into the aggresome, and surprisingly, this response was independent on the expression level of synphilin 1. Therefore, aggresome formation, but not aggregation of synphilin 1, represents a special cellular response to a failure of the proteasome/chaperone machinery. Importantly, translocation to aggresomes required a special aggresome-targeting signal within the sequence of synphilin 1, an ankyrin-like repeat domain. On the other hand, formation of multiple small aggregates required an entirely different segment within synphilin 1, indicating that aggregation and aggresome formation determinants can be separated genetically. Furthermore, substitution of the ankyrin-like repeat in synphilin 1 with an aggresome-targeting signal from huntingtin was sufficient for aggresome formation upon inhibition of the proteasome. Analogously, attachment of the ankyrin-like repeat to a huntingtin fragment lacking its aggresome-targeting signal promoted its transport to aggresomes. These findings indicate the existence of transferable signals that target aggregation-prone polypeptides to aggresomes.

Parkin is ubiquitinated by Nrdp1 and abrogates Nrdp1-induced oxidative stress

Parkin plays an important role in the pathogenesis of Parkinson's disease. We previously described that Nrdp1, a RING-finger ubiquitin E3 ligase, interacted with Parkin by the yeast two-hybrid assay and by co-immunoprecipitation. Here we further demonstrated that overexpression of Nrdp1 significantly reduced the endogenous Parkin level in an Nrdp1 dosage-dependent and proteasome-dependent manner. More importantly, Nrdp1 ubiquitinated Parkin and catalyzed the poly-ubiquitin chains on Parkin in vitro as well as in cells, indicating Parkin is an Nrdp1 substrate. In addition, we demonstrated that overexpression of Nrdp1 increased the production of reactive oxygen species (ROS), which was abrogated by co-expression of Parkin. Conversely, suppression of Nrdp1 by shRNA conferred SH-SY5Y cells a lower ROS level. Together, we provided evidence that interactions between Nrdp1 and Parkin negatively regulated Parkin level and affected ROS production, suggesting that Nrdp1 may play a role in Parkinson's disease.

Aggresome formation and neurodegenerative diseases: therapeutic implications

Accumulation of misfolded proteins in proteinaceous inclusions is a prominent pathological feature common to many age-related neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis. In cultured cells, when the production of misfolded proteins exceeds the capacity of the chaperone refolding system and the ubiquitin-proteasome degradation pathway, misfolded proteins are actively transported to a cytoplasmic juxtanuclear structure called an aggresome. Aggresome formation is recognized as a cytoprotective response serving to sequester potentially toxic misfolded proteins and facilitate their clearance by autophagy. Recent evidence indicates that aggresome formation is mediated by dynein/dynactin-mediated microtubule-based transport of misfolded proteins to the centrosome and involves several regulators, including histone deacetylase 6, E3 ubiquitin-protein ligase parkin, deubiquitinating enzyme ataxin-3, and ubiquilin-1. Characterization of the molecular mechanisms underlying aggresome formation and its regulation has begun to provide promising therapeutic targets that may be relevant to neurodegenerative diseases. In this review, we provide an overview of the molecular machinery controlling aggresome formation and discuss potential useful compounds and intervention strategies for preventing or reducing the cytotoxicity of misfolded and aggregated proteins.

Parkin analysis in early onset Parkinson's disease

We analysed the parkin gene in a large consecutive series (146) of unrelated early onset Parkinson's disease (onset ?40 years of age) patients. Twelve cases (8.2%) had homozygous or compound heterozygous point mutations and/or exon rearrangements, while a single mutation was found in four subjects (2.7%). We identified eight exon rearrangements and nine point mutations, two of which were novel: c.735delT (p.C212/X224) and c.815C>G (p.C238W). Genotype-phenotype correlation revealed that parkin carriers had features similar to those of non-carrier early onset Parkinson disease patients.

Differential effects of Parkin and its mutants on protein aggregation, the ubiquitin-proteasome system, and neuronal cell death in human neuroblastoma cells

Mutations in Parkin, an E3 ligase, which participates in the ubiquitin-proteasome system (UPS), cause juvenile onset Parkinson's disease (PD). Some mutants aggregate upon over-expression, but the effects of such aggregation on the UPS and neuronal survival have not been characterized. We show in this study that transient over-expression of wild type (WT) Parkin or various mutants in human neuroblastoma cells leads to localized accumulation of green fluorescent protein (GFP(u)), an artificial proteasomal substrate, indicative of UPS dysfunction. Parkin mutants, but not WT, aggregated, and GFP(u) and ubiquitin accumulated within such aggregates. Apoptotic death occurred only with mutant Parkin over-expression, and correlated with aggregation, but not GFP(u) accumulation. Enzymatic proteasomal activity was slightly increased with WT Parkin and decreased with mutant Parkin over-expression. This decrease was, at least in part, due to caspase activation. We conclude that mutant forms of Parkin can exert toxic effects on neuronal cells, possibly through their propensity to aggregate. Both WT and mutant forms can induce localized UPS dysfunction, likely through different mechanisms. This raises a note of caution regarding forced over-expression of Parkin as a neuroprotective strategy in PD or other neurodegenerative conditions and suggests a possible toxic gain of function for certain mutant forms of Parkin.

Structure of the Parkin in-between-ring domain provides insights for E3-ligase dysfunction in autosomal recessive Parkinson's disease

Mutations in Parkin are one of the predominant hereditary factors found in patients suffering from autosomal recessive juvenile Parkinsonism. Parkin is a member of the E3 ubiquitin ligase family that is defined by a tripartite RING1-in-between-ring (IBR)-RING2 motif. In Parkin, the IBR domain has been shown to augment binding of the E2 proteins UbcH7 and UbcH8, and the subsequent ubiquitination of the proteins synphilin-1, Sept5, and SIM2. To facilitate our understanding of Parkin function, the solution structure of the Parkin IBR domain was solved by using NMR spectroscopy. Folding of the IBR domain (residues M327-S378) was found to be zinc dependent, and the structure reveals the domain forms a unique pair scissor-like and GAG knuckle-like zinc-binding sites, different from other zinc-binding motifs such as the RING, LIM, PHD, or B-box motifs. The N terminus of the IBR domain, residues E307-E322, is unstructured. The disease causing mutation T351P causes global unfolding, whereas the mutation R334C causes some structural rearrangement of the domain. In contrast, the protein containing the mutation G328E appears to be properly folded. The structure of the Parkin IBR domain, in combination with mutational data, allows a model to be proposed where the IBR domain facilitates a close arrangement of the adjacent RING1 and RING2 domains to facilitate protein interactions and subsequent ubiquitination.

Dopaminergic and adrenergic toxicities on SK-N-MC human neuroblastoma cells are mediated through G protein signaling and oxidative stress

Dopamine and norepinephrine are neurotransmitters which participate in various regulatory functions of the human brain. These functions are lost in neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. In this study, we used SK-N-MC neuroblastoma cells to investigate the cytotoxicities of high concentrations of dopamine and norepinephrine on neuronal cells. Dopamine, norepinephrine, as well as their corresponding synthetic agonists (SKF38393 and isoproterenol, respectively) triggered SK-N-MC cell death when applied at 50-100 muM persistently for 2 days. This catecholamine-induced cell death appears to be neuronal specific, as demonstrated by their inabilities of triggering apoptosis of A549 lung carcinoma cells and Cos-7 kidney fibroblasts. By pretreating SK-N-MC cells with target-specific inhibitors before administration of catecholamine, components of G protein signaling (i.e. G( s )/cAMP/PKA), monoamine oxidases, nitric oxide synthase, c-Jun N-terminal kinase and oxidative stress were found to be involved in this dopamine/norepinephrine-induced cytotoxicity, which subsequently led to caspase-dependent and -independent apoptotic responses as well as DNA degradation. In contrast, agonists of G( i )-coupled dopamine receptors and adrenergic receptors (quinpirole and UK14,304, respectively) were incapable of triggering apoptosis of SK-N-MC cells. Our results suggest that both G protein (G( s ))-mediated signaling cascade and oxidative stress participate in the dopamine/norepinephrine-induced neuronal apoptosis.

Phosphorylation of Parkin by the Cyclin-dependent Kinase 5 at the Linker Region Modulates Its Ubiquitin-Ligase Activity and Aggregation

Mutations in Parkin are responsible for a large percentage of autosomal recessive juvenile parkinsonism cases. Parkin displays ubiquitin-ligase activity and protects against cell death promoted by several insults. Therefore, regulation of Parkin activities is important for understanding the dopaminergic cell death observed in Parkinson disease. We now report that cyclin-dependent kinase 5 (Cdk5) phosphorylates Parkin both in vitro and in vivo. We found that highly specific Cdk5 inhibitors and a dominant negative Cdk5 construct inhibited Parkin phosphorylation, suggesting that a significant portion of Parkin is phosphorylated by Cdk5. Parkin interacts with Cdk5 as observed by co-immunoprecipitation experiments of transfected cells and rat brains. Phosphorylation by Cdk5 decreased the auto-ubiquitylation of Parkin both in vitro and in vivo. We identified Ser-131 located at the linker region of Parkin as the major Cdk5 phosphorylation site. The Cdk5 phosphorylation-deficient S131A Parkin mutant displayed a higher auto-ubiquitylation level and increased ubiquitylation activity toward its substrates synphilin-1 and p38. Additionally, the S131A Parkin mutant more significantly accumulated into inclusions in human dopaminergic cells when compared with the wild-type Parkin. Furthermore, S131A Parkin mutant increased the formation of synphilin-1/alpha-synuclein inclusions, suggesting that the levels of Parkin phosphorylation and ubiquitylation may modulate the formation of inclusion bodies relevant to the disease. The data indicate that Cdk5 is a new regulator of the Parkin ubiquitin-ligase activity and modulates its ability to accumulate into and modify inclusions. Phosphorylation by Cdk5 may contribute to the accumulation of toxic Parkin substrates and decrease the ability of dopaminergic cells to cope with toxic insults in Parkinson disease.

MPTP and DSP-4 susceptibility of substantia nigra and locus coeruleus catecholaminergic neurons in mice is independent of parkin activity

Mutations in the parkin gene cause autosomal recessive familial Parkinson's disease (PD). Parkin-deficient mouse models fail to recapitulate nigrostriatal dopaminergic neurodegeneration as seen in PD, but produce deficits in dopaminergic neurotransmission and noradrenergic-dependent behavior. Since sporadic PD is thought to be caused by a combination of genetic susceptibilities and environmental factors, we hypothesized that neurotoxic insults from catecholaminergic toxins would render parkin knockout mice more vulnerable to neurodegeneration. Accordingly, we investigated the susceptibility of catecholaminergic neurons in parkin knockout mice to the potent dopaminergic and noradrenergic neurotoxins 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) respectively. We report that nigrostriatal dopaminergic neurons in parkin knockout mice do not show increased susceptibility to the parkinsonian neurotoxin, MPTP, in acute, subacute and chronic dose regimens of the neurotoxin. Additionally, parkin knockout mice do not show increased vulnerability to the noradrenergic neurotoxin, DSP-4, regarding levels of norepinephrine in cortex, brain stem and spinal cord. These findings suggest that absence of parkin in mice does not increase susceptibility to the loss of catecholaminergic neurons upon exposure to both dopaminergic and noradrenergic neurotoxins.

THE DOPAMINERGIC NIGROSTRIATAL SYSTEMAND PARKINSON'S DISEASE

For several decades, the clinical study of Parkinson's disease has driven an increasingly sophisticated understanding of the dopaminergic system and its complex role in modulating motor behavior. This article reviews salient areas of research in this field, commencing with the molecular biology of the development of the mesencephalic dopaminergic system. We then discuss events thought to be crucial in the cellular and molecular pathology of Parkinson's disease, proposed mechanisms of cell death, and relevant toxin models. These advancements are used as a template to review emerging therapeutic techniques, including neuroprotection strategies, surgical treatment of trophic factors, gene therapy, and neural transplantation.

Pathogenic mutations in Parkinson disease

Parkinson disease (PD; Parkinson's) is the second most common neurodegenerative disease, characterized by the progressive loss of dopamine neurons and the accumulation of Lewy bodies. Increasing evidence suggests that deficits in mitochondrial function, oxidative and nitrosative stress, the accumulation of aberrant or misfolded proteins, and ubiquitin-proteasome system (UPS) dysfunction may represent the principal molecular pathways that commonly underlie the pathogenesis. The relative role of genetic and environmental factors has been the focus of research and debate. The recent discovery of a number of disease-causing genes (SNCA, Parkin/PARK2, UCHL1, PINK1, DJ1/PARK7, and LRRK2) in familial and sporadic forms of PD has provided considerable insights into the pathophysiology of this complex disorder. The frequency of these gene mutations may vary according to ethnicity and to the specific gene. A gene dosage effect is observed in some cases, and the phenotype of some of the mutation carriers closely resembles typical PD. Penetrance of some of the recurrent mutations is incomplete and may vary with age. Further research to unravel the etiopathology could identify biochemical or genetic markers for potential neuroprotective trials.

Genetics of Parkinson's disease and parkinsonism

Until 10 years ago, conventional wisdom held that Parkinson's disease was not a genetic disorder. Since that time, there have been a plethora of genetic findings, culminating in the cloning of several genes that derive from the loci given the nomenclature PARK1-PARK12 (OMIM 168600). Recently, these research findings have begun to impact clinical practice, and this impact is likely to increase. The primary purpose of this article is to outline these genetic advances, discuss their importance for current practice in clinical and related settings, and outline briefly how they are influencing research into the causes of and possible future treatments for this prevalent disorder.

Parkin: a multifaceted ubiquitin ligase

Mutations in the parkin gene are a common cause of autosomal recessive early-onset parkinsonism. Parkin functions as an E3 ubiquitin ligase where it can polyubiquitinate a number of its protein substrates, thus targeting them for degradation by the 26 S proteasomal complex. Recent studies have demonstrated that alternative modes of parkin-mediated ubiquitination may serve other non-degradative regulatory roles. In addition, parkin appears to function as a multipurpose neuroprotectant in a number of toxic paradigms. Coupled with these observations, parkin may integrate other gene products associated with parkinsonism, including α-synuclein, LRRK2 (leucine-rich repeat kinase 2), DJ-1 and PINK1 [PTEN (phosphatase and tensin homologue deleted on chromosome 10)-induced putative kinase 1], into a common biochemical pathway of potential relevance to disease pathogenesis. Parkin therefore represents a unique multifaceted ubiquitin ligase consistent with an important housekeeping role in maintaining the integrity or survival of dopaminergic neurons.

Understanding the molecular causes of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease that is both common and incurable. The majority of cases are sporadic and of unknown origin but several genes have been identified that, when mutated, give rise to rare, familial forms of the disease. The principal genes that have been shown to cause PD are alpha-synuclein (SNCA), parkin, leucine-rich repeat kinase 2 (LRRK2), PTEN-induced putative kinase 1 (PINK1) and DJ-1. Here, we discuss what has been learnt from the study of these genes and what has been elucidated of the molecular pathways that lead to cell degeneration. Of importance is what these molecular events and pathways tell scientists of the common sporadic form of PD. Although complete knowledge of these genes' functions remains elusive, recent work implicates abnormal protein accumulation, protein phosphorylation, mitochondrial dysfunction and oxidative stress as common pathways to PD pathogenesis.

Redox proteomics in some age-related neurodegenerative disorders or models thereof

Neurodegenerative diseases cause memory loss and cognitive impairment. Results from basic and clinical scientific research suggest a complex network of mechanisms involved in the process of neurodegeneration. Progress in treatment of such disorders requires researchers to better understand the functions of proteins involved in neurodegenerative diseases, to characterize their role in pathogenic disease mechanisms, and to explore their roles in the diagnosis, treatment, and prevention of neurodegenerative diseases. A variety of conditions of neurodegenerative diseases often lead to post-translational modifications of proteins, including oxidation and nitration, which might be involved in the pathogenesis of neurodegenerative diseases. Redox proteomics, a subset of proteomics, has made possible the identification of specifically oxidized proteins in neurodegenerative disorders, providing insight into a multitude of pathways that govern behavior and cognition and the response of the nervous system to injury and disease. Proteomic analyses are particularly suitable to elucidate post-translational modifications, expression levels, and protein-protein interactions of thousands of proteins at a time. Complementing the valuable information generated through the integrative knowledge of protein expression and function should enable the development of more efficient diagnostic tools and therapeutic modalities. Here we review redox proteomic studies of some neurodegenerative diseases.

CSA-dependent degradation of CSB by the ubiquitin-proteasome pathway establishes a link between complementation factors of the Cockayne syndrome

Mutations in the CSA or CSB complementation genes cause the Cockayne syndrome, a severe genetic disorder that results in patients' death in early adulthood. CSA and CSB act in a transcription-coupled repair (TCR) pathway, but their functional relationship is not understood. We have previously shown that CSA is a subunit of an E3 ubiquitin ligase complex. Here we demonstrate that CSB is a substrate of this ligase: Following UV irradiation, CSB is degraded at a late stage of the repair process in a proteasome- and CSA-dependent manner. Moreover, we demonstrate the importance of CSB degradation for post-TCR recovery of transcription and for the Cockayne syndrome. Our results unravel for the first time the functional relationship between CSA and CSB.

Identification of far upstream element-binding protein-1 as an authentic Parkin substrate

Aminoacyl-tRNA synthetase-interacting multifunctional protein type 2 was recently identified as an authentic substrate of the ubiquitin E3 ligase, parkin, a gene associated with autosomal recessive juvenile parkinsonism. Far upstream element-binding protein 1 is known to be degraded in an aminoacyl-tRNA synthetase interacting multifunctional protein type 2 dependent manner, which is crucial for lung cell maturation in early development. Therefore, we wondered whether far upstream element-binding protein 1 levels are altered in the absence of Parkin and in Parkinson disease. We herein report that far upstream element-binding protein 1 accumulates in Parkin knock-out mice, patients with autosomal recessive juvenile parkinsonism, sporadic Parkinson disease, and diffuse Lewy Body disease as well as the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson disease. Moreover, Parkin interacts with and ubiquitinates far upstream element-binding protein 1 facilitating its degradation through the ubiquitin proteasome system. Taken together, these results suggest that far upstream element-binding protein 1 is an authentic substrate of Parkin and that far upstream element-binding protein 1 might play an important role in development of Parkinson disease pathology along with aminoacyl-tRNA synthetase interacting multifunctional protein type 2.

Genética de las enfermedades neurodegenerativas más prevalentes

A large number of mutations and polymorphisms associated with neurodegenerative disorders have been described during the last years. These findings have been helpful to improve our knowledge about the pathogenesis of these disorders. In this review we describe the genetic alterations and variants that cause or predispose to develop several neurodegenerative disorders, such as Huntington's disease, Alzheimer's disease, frontotemporal dementia, Parkinson's disease and other parkinsonisms. We also comment on the possible pathogenic mechanism of these mutations, clinical features and the usefulness of this information for the diagnosis and management of these disorders.

Parkin Protects against Mitochondrial Toxins and β-Amyloid Accumulation in Skeletal Muscle Cells

Mutations in the ubiquitin ligase-encoding Parkin gene have been implicated in the pathogenesis of autosomal recessive Parkinson disease. Outside of the central nervous system, Parkin is prominently expressed in skeletal muscle. We have found accumulations of Parkin protein in skeletal muscle biopsies taken from patients with inclusion body myositis, a degenerative disorder in which intramyofiber accumulations of the beta-amyloid peptide are pathognomonic. In comparing primary cultures of skeletal muscle derived from parkin knock-out and wild-type mice, we have found the absence of parkin to result in greater sensitivity to mitochondrial stressors rotenone and carbonyl cyanide 3-chlorophenylhydrazone, without any alteration in sensitivity to calcium ionophore or hydrogen peroxide. Utilizing viral expression constructs coding for the Alzheimer disease and inclusion body myositis-linked beta-amyloid precursor protein and for its metabolic byproducts A beta42 and C100, we found that parkin knock-out muscle cells are also more sensitive to the toxic effects of intracellular A beta. We also constructed a lentiviral system to overexpress wild-type Parkin and have shown that boosting the levels of parkin expression in normal skeletal muscle cultures provides substantial protection against both mitochondrial toxins and overexpressed beta-amyloid. Correspondingly, exogenous Parkin significantly lowered A beta levels. These data support the hypothesis that in myocytes parkin has dual properties in the maintenance of skeletal muscle mitochondrial homeostasis and in the regulation of A beta levels.

Inclusion body formation and neurodegeneration are parkin independent in a mouse model of alpha-synucleinopathy

Mutations in the genes coding for alpha-synuclein and parkin cause autosomal-dominant and autosomal-recessive forms of Parkinson's disease (PD), respectively. Alpha-synuclein is a major component of Lewy bodies, the proteinaceous cytoplasmic inclusions that are the pathological hallmark of idiopathic PD. Lewy bodies appear to be absent in cases of familial PD associated with mutated forms of parkin. Parkin is an ubiquitin E3 ligase, and it may be involved in the processing and/or degradation of alpha-synuclein, as well as in the formation of Lewy bodies. Here we report the behavioral, biochemical, and histochemical characterization of double-mutant mice overexpressing mutant human A53T alpha-synuclein on a parkin null background. We find that the absence of parkin does not have an impact on the onset and progression of the lethal phenotype induced by overexpression of human A53T alpha-synuclein. Furthermore, all major behavioral, biochemical, and morphological characteristics of A53T alpha-synuclein-overexpressing mice are not altered in parkin null alpha-synuclein-overexpressing double-mutant mice. Our results demonstrate that mutant alpha-synuclein induces neurodegeneration independent of parkin-mediated ubiquitin E3 ligase activity in nondopaminergic systems and suggest that PD caused by alpha-synuclein and parkin mutations may occur via independent mechanisms.

Accumulation of the authentic parkin substrate aminoacyl-tRNA synthetase cofactor, p38/JTV-1, leads to catecholaminergic cell death

Autosomal-recessive juvenile parkinsonism (AR-JP) is caused by loss-of-function mutations of the parkin gene. Parkin, a RING-type E3 ubiquitin ligase, is responsible for the ubiquitination and degradation of substrate proteins that are important in the survival of dopamine neurons in Parkinson's disease (PD). Accordingly, the abnormal accumulation of neurotoxic parkin substrates attributable to loss of parkin function may be the cause of neurodegeneration in parkin-related parkinsonism. We evaluated the known parkin substrates identified to date in parkin null mice to determine whether the absence of parkin results in accumulation of these substrates. Here we show that only the aminoacyl-tRNA synthetase cofactor p38 is upregulated in the ventral midbrain/hindbrain of both young and old parkin null mice. Consistent with upregulation in parkin knock-out mice, brains of AR-JP and idiopathic PD and diffuse Lewy body disease also exhibit increased level of p38. In addition, p38 interacts with parkin and parkin ubiquitinates and targets p38 for degradation. Furthermore, overexpression of p38 induces cell death that increases with tumor necrosis factor-alpha treatment and parkin blocks the pro-cell death effect of p38, whereas the R42P, familial-linked mutant of parkin, fails to rescue cell death. We further show that adenovirus-mediated overexpression of p38 in the substantia nigra in mice leads to loss of dopaminergic neurons. Together, our study represents a major advance in our understanding of parkin function, because it clearly identifies p38 as an important authentic pathophysiologic substrate of parkin. Moreover, these results have important implications for understanding the molecular mechanisms of neurodegeneration in PD.

Expanding insights of mitochondrial dysfunction in Parkinson's disease

The quest to disentangle the aetiopathogenesis of Parkinson's disease has been heavily influenced by the genes associated with the disease. The alpha-synuclein-centric theory of protein aggregation with the adjunct of parkin-driven proteasome deregulation has, in recent years, been complemented by the discovery and increasing knowledge of the functions of DJ1, PINK1 and OMI/HTRA2, which are all associated with the mitochondria and have been implicated in cellular protection against oxidative damage. We critically review how these genes fit into and enhance our understanding of the role of mitochondrial dysfunction in Parkinson's disease, and consider how oxidative stress might be a potential unifying factor in the aetiopathogenesis of the disease.

Parkin gene variations in late-onset Parkinson's disease: comparison between Norwegian and German cohorts

OBJECTIVES

Mutations in the Parkin gene can cause autosomal recessive early-onset Parkinson's disease (PD). Recently, Parkin mutations were also suggested to play a role in the commoner late-onset forms of PD.

METHODS

We compared a German cohort of PD patients (95) with a Norwegian cohort of PD patients (96). Both cohorts have predominant late-onset form of PD. Mutation and polymorphism frequencies were compared via single-strand conformation polymorphism and sequence analyses.

RESULTS

Three heterozygous missense mutations (Arg256Cys, Arg402Cys and Thr240Met) were found in late-onset PD patients in the German patient cohort (1.6%). A missense mutation (Arg402Cys) was also found in one of 149 healthy control subjects (0.3%). Only one heterozygous missense mutation (Arg256Cys) was identified in a Norwegian patient suffering from late-onset PD (0.5%). The frequencies of four known single nucleotide polymorphisms significantly differ between the two distant European populations.

CONCLUSION

The results support the hypothesis that heterozygous mutations in the Parkin gene may act as susceptibility alleles for late-onset forms of PD in rare cases.

The role of chaperones in Parkinson's disease and prion diseases

The etiologies of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, polyglutamine diseases, or prion diseases may be diverse; however, aberrations in protein folding, processing, and/or degradation are common features of these entities, implying a role of quality control systems, such as molecular chaperones and the ubiquitin-proteasome pathway. There is substantial evidence for a causal role of protein misfolding in the pathogenic process coming from neuropathology, genetics, animal modeling, and biophysics. The presence of protein aggregates in all neurodegenerative diseases gave rise to the hypothesis that protein aggregates, be it intracellular or extracellular deposits, may perturb the cellular homeostasis and disintegrate neuronal function (Table 1). More recently, however, an increasing number of studies have indicated that protein aggregates are not toxic per se and might even serve a protective role by sequestering misfolded proteins. Specifically, experimental models of polyglutamine diseases, Alzheimer's disease, and Parkinson's disease revealed that the appearance of aggregates can be dissociated from neuronal toxicity, while misfolded monomers or oligomeric intermediates seem to be the toxic species. The unique features of molecular chaperones to assist in the folding of nascent proteins and to prevent stress-induced misfolding was the rationale to exploit their effects in different models of neurodegenerative diseases. This chapter concentrates on two neurodegenerative diseases, Parkinson's disease and prion diseases, with a special focus on protein misfolding and a possible role of molecular chaperones.

Assessing neuroprotection in Parkinson's disease: from the animal models to molecular neuroimaging in vivo

An important goal in Parkinson's Disease research is to identify neuroprotective therapy, and the interaction between basic science and clinical research is needed to discover drugs that can slow or halt the disorder progression. At present there is not a perfect animal model of PD to test neuroprotective strategies, however the models that portray the basic characteristics needed are toxin-induced and gene-based models. The first group comprehends 6-OHDA e MPTP and recently rotenone, paraquat and epoxomicin treated animals that shows some of human disease characteristics. Gene-based models are various and, even if with limits, they seem suitable models to test neuroprotection in PD since they present replicable lesions, a predictable pattern of neurodegeneration and a well-characterized behavior, biochemistry and morphology to assist in the understanding of induced changes. In clinical trials researchers have first used as marker of disease progression clinical scores and motor tasks which are limited by the potential symptomatic effect of tested drugs and are not useful in the pre-clinical phases of PD. Recently has emerged the important role of neuroimaging (Dopamine Transporter SPECT, 18FDopa-PET) as surrogate biomarker of PD progression. Even if there are still concerns about the influence of regulatory effects of tested drugs, neuroimaging features could represent a good outcome measure to evaluate PD progression and putative neuroprotective effect of pharmacological and non-pharmacological manipulations.

Parkin and defective ubiquitination in Parkinson's disease

Parkinson's Disease (PD) is a common neurodegenerative disorder that is characterized by the progressive loss of dopamine (DA) neurons. Accompanying the loss the of DA neurons is the accumulation of Lewy bodies and neurites, intracytoplasmic proteinaceous inclusions that contain alpha-synuclein, synphilin-1, components of the ubiquitin proteasomal pathway and parkin. Recent advances indicate that PD is due in some individuals to genetic mutations in alpha-synuclein, DJ-1, PINK-1, LRRK2, and parkin. Understanding the molecular mechanisms by which mutations in familial-linked genes cause PD holds great promise for unraveling the mechanisms by which DA neurons degenerate in PD. Parkin is E3-ubiquitin-protein ligase that ubiquitinates itself and promotes its own degradation. Familial associated mutations of parkin have impaired ubiquitin ligase function suggesting that this may be the cause of familial autosomal recessive PD. Parkin might be required for formation of Lewy bodies as Lewy bodies are absent in patients with parkin mutations. Parkin interacts with and ubiquitinates the alpha-synuclein interacting protein, synphilin-1. Formation of Lewy-body-like ubiquitin-positive cytosolic inclusions occurs upon coexpression of alpha-synuclein, synphilin-1 and parkin. Nitric oxide inhibits Parkin's E-3 ligase activity and its protective function by nitric oxide through S-nitrosylation both in vitro and in vivo. Nitrosative and oxidative stress link parkin function with the more common sporadic form of Parkinson's disease and the related alpha-synucleinopathy, DLBD. Development of new therapies for PD and other disorders associated with nitrosative and oxidative stress may follow the elucidation of the pathways by which NO S-nitrosylates and inhibits parkin. Moreover, parkin and alpha-synuclein are linked in common pathogenic mechanism through their interaction with synphilin-1 and parkin may be important for the formation of Lewy bodies.

Functional expansion of aminoacyl-tRNA synthetases and their interacting factors: new perspectives on housekeepers

Aminoacyl-tRNA synthetases (ARSs) are essential enzymes that join amino acids to tRNAs, thereby linking the genetic code to specific amino acids. Once considered a class of 'housekeeping' enzymes, ARSs are now known to participate in a wide variety of functions, including transcription, translation, splicing, inflammation, angiogenesis and apoptosis. Three nonenzymatic proteins--ARS-interacting multi-functional proteins (AIMPs)--associate with ARSs in a multi-synthetase complex of higher eukaryotes. Similarly to ARSs, AIMPs have novel functions unrelated to their support role in protein synthesis, acting as a cytokine to control angiogenesis, immune response and wound repair, and as a crucial regulator for cell proliferation and DNA repair. Evaluation of the functional roles of individual ARSs and AIMPs might help to elucidate why these proteins as a whole contribute such varied functions and interactions in complex systems.

The N-end rule pathway as a nitric oxide sensor controlling the levels of multiple regulators

The conjugation of arginine to proteins is a part of the N-end rule pathway of protein degradation. Three amino (N)-terminal residues--aspartate, glutamate and cysteine--are arginylated by ATE1-encoded arginyl-transferases. Here we report that oxidation of N-terminal cysteine is essential for its arginylation. The in vivo oxidation of N-terminal cysteine, before its arginylation, is shown to require nitric oxide. We reconstituted this process in vitro as well. The levels of regulatory proteins bearing N-terminal cysteine, such as RGS4, RGS5 and RGS16, are greatly increased in mouse ATE1-/- embryos, which lack arginylation. Stabilization of these proteins, the first physiological substrates of mammalian N-end rule pathway, may underlie cardiovascular defects in ATE1-/- embryos. Our findings identify the N-end rule pathway as a new nitric oxide sensor that functions through its ability to destroy specific regulatory proteins bearing N-terminal cysteine, at rates controlled by nitric oxide and apparently by oxygen as well.

Parkin-mediated lysine 63-linked polyubiquitination: a link to protein inclusions formation in Parkinson's and other conformational diseases?

Most, if not all, neurodegenerative diseases are marked by the presence of ubiquitin-positive protein inclusions. How proteins within these inclusion bodies escape proteasomal degradation despite being enriched with ubiquitin remains a conundrum. Current evidence suggests a relationship between proteasomal impairment and inclusion formation, a persuasive explanation for the inability of the cell to remove ubiquitinated protein aggregates. Alternatively, the formation of ubiquitin-enriched inclusion may be uncoupled from the proteasome. Supporting this, we recently uncovered a novel, proteasomal-independent, catalytic activity for the Parkinson disease (PD)-linked ubiquitin ligase, parkin, that significantly enhances the formation of Lewy body (LB)-like inclusions generated in cultured cells by the co-expression of alpha-synuclein and synphilin-1. This unique activity of parkin mediates a non-classical, lysine (K) 63-linked ubiquitin multichain assembly on synphilin-1 that is distinct from the classical, degradation-associated, K48-linked ubiquitination. Interestingly, two other PD-linked gene products, alpha-synuclein and UCHL1, have recently also been associated with K63-linked ubiquitination. Inclusive of parkin, there are therefore now three PD-related gene products that are known to potentiate K63-linked ubiquitination, thus signalling an important functional relationship between this unique mode of ubiquitin tagging and PD pathogenesis. Mechanistically, the involvement of a "non-degradative" mode of ubiquitination in protein inclusion formation is an attractive explanation for how proteins are seemingly stabilized within inclusions.

Molecular pathophysiology of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder that results primarily from the death of dopaminergic neurons in the substantia nigra. Although the etiology of PD is incompletely understood, the recent discovery of genes associated with rare monogenic forms of the disease, together with earlier studies and new experimental animal models, has provided important and novel insight into the molecular pathways involved in disease pathogenesis. Increasing evidence indicates that deficits in mitochondrial function, oxidative and nitrosative stress, the accumulation of aberrant or misfolded proteins, and ubiquitin-proteasome system dysfunction may represent the principal molecular pathways or events that commonly underlie the pathogenesis of sporadic and familial forms of PD .

The biochemistry of Parkinson's disease

Several genes have been identified for monogenic disorders that variably resemble Parkinson's disease. Dominant mutations in the gene encoding alpha-synuclein enhance the propensity of this protein to aggregate. As a consequence, these patients have a widespread disease with protein inclusion bodies in several brain areas. In contrast, mutations in several recessive genes (parkin, DJ-1, and PINK1) produce neuronal cell loss but generally without protein aggregation pathology. Progress has been made in understanding some of the mechanisms of toxicity: Parkin is an E3 ubiquitin ligase and DJ-1 and PINK1 appear to protect against mitochondrial damage. However, we have not yet fully resolved how the recessive genes relate to alpha-synuclein, or whether they represent different ways to induce a similar phenotype.

Familial-associated mutations differentially disrupt the solubility, localization, binding and ubiquitination properties of parkin

Mutations in parkin are largely associated with autosomal recessive juvenile parkinsonism. The underlying mechanism of pathogenesis in parkin-associated Parkinson's disease (PD) is thought to be due to the loss of parkin's E3 ubiquitin ligase activity. A subset of missense and nonsense point mutations in parkin that span the entire gene and represent the numerous inheritance patterns that are associated with parkin-linked PD were investigated for their E3 ligase activity, localization and their ability to bind, ubiquitinate and effect the degradation of two substrates, synphilin-1 and aminoacyl-tRNA synthetase complex cofactor, p38. Parkin mutants vary in their intracellular localization, binding to substrates and enzymatic activity, yet they are ultimately deficient in their ability to degrade substrate. These results suggest that not all parkin mutations result in loss of parkin's E3 ligase activity, but they all appear to manifest as loss-of-function mutants due to defects in solubility, aggregation, enzymatic activity or targeting proteins to the proteasome for degradation.

A proteomic approach in the study of an animal model of Parkinson's disease

BACKGROUND

The aetiology of Parkinson's disease (PD), an age-related disorder characterized by a progressive degeneration of dopaminergic neurons of the substantia nigra (SN) pars compacta, remains unclear. Current treatments, such as administration of L-DOPA, are only symptomatic and do not stop or delay the progressive loss of neurons. In fact, it has been suggested that the dopamine precursor L-DOPA, increases generation of reactive oxygen species (ROS) leading to further neuronal damage. A similar loss in nigrostriatal dopaminergic neurons is produced on intracerebral administration of the catecholaminergic neurotoxin 6-hydroxydopamine (6-OHDA). In an animal model of PD, termed 'the hemiparkinsonian rat', unilateral injection of 6-OHDA into the nigrostriatal pathway results in extensive loss of dopaminergic cells in the ipsolateral SN. In an attempt to identify some of the proteins that are involved in dopaminergic neuronal death, we used the proteomic methods to analyze this animal model of PD.

METHODS

Five hemiparkinsonian rats were obtained by intranigral stereotaxic injection of 6-OHDA. The right 6-OHDA-lesioned substantia nigra and striatum tissues along with the left, unlesioned controlateral tissues, were excised and homogenized, using urea-based buffer, to extract the tissues protein. The separation of the protein mixtures and the visualization of the protein patterns obtained were performed using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Protein profiles of control and treated tissues were compare by the PDQuest 2D-gel analysis software (BIO-Rad laboratory). The protein spots showing differential expression were analysed by matrix assisted laser desorption/ionizing time of flight (MALDI-TOF) mass spectrometry.

RESULTS

The brain protein extraction and solubilization protocol was validated obtaining a satisfactory protein profile. In comparison to the normal rats, hemiparkinsonian animals exhibited a different expression in alpha-enolase and beta-actin in substantia nigra and striatum, respectively.

CONCLUSION

The proteomic study of 6-OHDA-induced lesions in the nigrostriatial pathway allowed us to identify two proteins, alpha-enolase and beta-actin, showing increased levels in the 6-OHDA-lesioned brain tissues compared to control. Previous studies described the same proteins as oxidized and proteins in Alzheimer's disease (AD) brain. Our preliminary data could mirror those results pointing out a common mechanism of neurodegenerative diseases.

Cancer in xeroderma pigmentosum and related disorders of DNA repair

Nucleotide-excision repair diseases exhibit cancer, complex developmental disorders and neurodegeneration. Cancer is the hallmark of xeroderma pigmentosum (XP), and neurodegeneration and developmental disorders are the hallmarks of Cockayne syndrome and trichothiodystrophy. A distinguishing feature is that the DNA-repair or DNA-replication deficiencies of XP involve most of the genome, whereas the defects in CS are confined to actively transcribed genes. Many of the proteins involved in repair are also components of dynamic multiprotein complexes, transcription factors, ubiquitylation cofactors and signal-transduction networks. Complex clinical phenotypes might therefore result from unanticipated effects on other genes and proteins.