Clinical heterogeneity of alpha-synuclein gene duplication in Parkinson's disease

α-Synuclein gene may interact with environmental factors in increasing risk of Parkinson's disease

BACKGROUND

Although of great interest and suggested in prior reports, possible α-synuclein (SNCA) gene-environment interactions have not been well investigated in humans.

METHODS

We used a population-based approach to examine whether the risk of Parkinson's disease (PD) depended on the combined presence of SNCA variations and two important environmental factors, pesticide exposures and smoking.

RESULTS/CONCLUSIONS

Similar to recent meta- and pooled analyses, our data suggest a lower PD risk in subjects who were either homozygous or heterozygous for the SNCA REP1 259 genotype, and a higher risk in subjects who were either homozygous or heterozygous for the REP1 263 genotype, especially among subjects with an age of onset ≤68 years. More importantly, while analyses of interactions were limited by small cell sizes, risk due to SNCA variations seemed to vary with pesticide exposure and smoking, especially in younger onset cases, suggesting an age-of-onset effect.

Genetic etiology of Parkinson disease associated with mutations in the SNCA, PARK2, PINK1, PARK7, and LRRK2 genes: a mutation update

To date, molecular genetic analyses have identified over 500 distinct DNA variants in five disease genes associated with familial Parkinson disease; alpha-synuclein (SNCA), parkin (PARK2), PTEN-induced putative kinase 1 (PINK1), DJ-1 (PARK7), and Leucine-rich repeat kinase 2 (LRRK2). These genetic variants include approximately 82% simple mutations and approximately 18% copy number variations. Some mutation subtypes are likely underestimated because only few studies reported extensive mutation analyses of all five genes, by both exonic sequencing and dosage analyses. Here we present an update of all mutations published to date in the literature, systematically organized in a novel mutation database (http://www.molgen.ua.ac.be/PDmutDB). In addition, we address the biological relevance of putative pathogenic mutations. This review emphasizes the need for comprehensive genetic screening of Parkinson patients followed by an insightful study of the functional relevance of observed genetic variants. Moreover, while capturing existing data from the literature it became apparent that several of the five Parkinson genes were also contributing to the genetic etiology of other Lewy Body Diseases and Parkinson-plus syndromes, indicating that mutation screening is recommendable in these patient groups.

Alpha-synuclein, lipids and Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disease, after Alzheimer's disease, among the aging human population. The main symptoms of Parkinson's disease such as tremor and movement disabilities are the result of degeneration of dopaminergic neurons in substantia nigra pars compacta. The widely-accepted subcellular factor which underlies Parkinson's disease neuropathology is the presence of Lewy bodies with characteristic inclusions of aggregated alpha-synuclein. This small soluble protein has been implicated in a range of interactions with phospholipid membranes and free fatty acids. The precise biological function of this protein is, however, still under investigation. Here we review the evidence linking alpha-synuclein, lipid metabolism, fatty acid oxidation, mitochondrial damage and Parkinson's disease. We propose that association of alpha-synuclein with oxidized lipid metabolites can lead to mitochondrial dysfunction in turn leading to dopaminergic neuron death and thus to Parkinson's disease.

Alpha-synuclein polymorphisms are associated with Parkinson's disease in a Saskatchewan population

Alpha-synuclein gene (SNCA) mutations cause familial Parkinsonism but the role of SNCA variability in idiopathic Parkinson's disease (PD) remains incompletely defined. We report a study of SNCA genetic variation in 452 idiopathic PD cases and 245 controls. SNCA copy number mutations were not associated with early-onset disease in this population. The minor allele "G" at rs356165 was associated with increased odds of PD (P = 0.013) and genetic variation in D4S3481 (Rep1) was associated with age of disease onset (P = 0.007). There was a trend toward association between variation at rs2583988 and rapid PD progression.

Gene therapy in Parkinson's disease: rationale and current status

Parkinson's disease is the second most common age-related neurodegenerative disorder, typified by the progressive loss of substantia nigra pars compacta dopamine neurons and the consequent decrease in the neurotransmitter dopamine. Patients exhibit a range of clinical symptoms, with the most common affecting motor function and including resting tremor, rigidity, akinesia, bradykinesia and postural instability. Current pharmacological interventions are palliative and largely aimed at increasing dopamine levels through increased production and/or inhibition of metabolism of this key neurotransmitter. The gold standard for treatment of both familial and sporadic Parkinson's disease is the peripheral administration of the dopamine precursor, levodopa. However, many patients gradually develop levodopa-induced dyskinesias and motor fluctuations. In addition, dopamine enhancement therapies are most useful when a portion of the nigrostriatal pathway is intact. Consequently, as the number of substantia nigra dopamine neurons and striatal projections decrease, these treatments become less efficacious. Current translational research is focused on the development of novel disease-modifying therapies, including those utilizing gene therapeutic approaches. Herein we present an overview of current gene therapy clinical trials for Parkinson's disease. Employing either recombinant adeno-associated virus type 2 (rAAV2) or lentivirus vectors, these clinical trials are focused on three overarching approaches: augmentation of dopamine levels via increased neurotransmitter production; modulation of the neuronal phenotype; and neuroprotection. The first two therapies discussed in this article focus on increasing dopamine production via direct delivery of genes involved in neurotransmitter synthesis (amino acid decarboxylase, tyrosine hydroxylase and GTP [guanosine triphosphate] cyclohydrolase 1). In an attempt to bypass the degenerating nigrostriatal pathway, a third clinical trial utilizes rAAV2 to deliver glutamic acid decarboxylase to the subthalamic nucleus, converting a subset of excitatory neurons to GABA-producing cells. In contrast, the final clinical trial is aimed at protecting the degenerating nigrostriatum by striatal delivery of rAAV2 harbouring the neuroprotective gene, neurturin. Based on preclinical studies, this gene therapeutic approach is posited to slow disease progression by enhancing neuronal survival. In addition, we discuss the outcome of each clinical trial and discuss the potential rationale for the marginal yet incremental clinical advancements that have thus far been realized for Parkinson's disease gene therapy.

Molecular mechanisms of pathogenesis of Parkinson's disease

Parkinson's disease is a complex disease characterized by a progressive degeneration of nigrostriatal dopaminergic neurons. The development of this condition is defined by the interaction between the genetic constitution of an organism and environmental factors. Analysis of the genes associated with development of monogenic forms of disease has allowed pointing out several mechanisms involved in Parkinson's disease pathogenesis such as the ubiquitin-proteasome degradation, differentiation of dopaminergic neurons, mitochondrial dysfunction, oxidative damage, and others. In this review, a variety of data which throw light on molecular mechanisms underlying pathogenesis of Parkinson's disease will be considered.

Expanding the clinical phenotype of SNCA duplication carriers

SNCA duplication is a recognized cause of familial Parkinson's disease (PD). We aimed to explore the genetic and clinical variability in the disease manifestation. Molecular characterization was performed using real-time PCR, SNP arrays, and haplotype analysis. We further studied those patients who were found to harbor SNCA duplication with olfactory function tests, polysomnography, and PET. We identified four new families and one sporadic patient with SNCA duplication. Eleven symptomatic patients from these four families presented with parkinsonism, of which three subsequently developed dementia. The lifetime estimate of overall penetrance was 43.8%. FDG-PET study of symptomatic patients showed hypometabolism in the occipital lobe, whereas asymptomatic carriers of SNCA duplication demonstrated normal glucose metabolism. Symptomatic patients showed abnormal olfactory function and polysomnography and asymptomatic carriers showed normal results. The clinical features of SNCA duplication include parkinsonism with or without dementia. Asymptomatic carriers displayed normal test results with the eldest individual aged 79 years; thus, even a carrier of SNCA duplication may escape the development of PD. This difference in age-associated penetrance may be due to the genetic background or environmental exposures. Further studies of SNCA duplication carriers will help identify disease-modifiers and may open novel avenues for future treatment.

Parkinson's disease: Exit toxins, enter genetics

Parkinson's disease was long considered a non-hereditary disorder. Despite extensive research trying to find environmental risk factors for the disease, genetic variants now stand out as the major causative factor. Since a number of genes have been implicated in the pathogenesis it seems likely that several molecular pathways and downstream effectors can affect the trophic support and/or the survival of dopamine neurons, subsequently leading to Parkinson's disease. The present review describes how toxin-based animal models have been valuable tools in trying to find the underlying mechanisms of disease, and how identification of disease-linked genes in humans has led to the development of new transgenic rodent models. The review also describes the current status of the most common genetic susceptibility factors for Parkinson's disease identified up to today.

alpha-Synuclein multiplication analysis in Italian familial Parkinson disease

The alpha-synuclein gene (SNCA) multiplication causes autosomal dominant Parkinson Disease (PD): triplication is associated with early-onset rapidly progressing parkinsonism with a strong likelihood of developing dementia, while duplication is associated with a less severe phenotype similar to idiopathic PD. We tested for SNCA multiplication 144 unrelated PD patients with a dominant family history. We identified one patient with SNCA duplication (0.7%). The SNCA-duplicated patient was a woman of 45 years of age with PD onset at 41 years of age. She experienced a rapidly progressive disease with early motor complications (on/off fluctuations and dyskinesias). Medical records confirmed that the proband's mother developed PD at 47 years of age and died at 63 with dementia. She experienced rapid progression in both motor and cognitive symptoms: development of dementia at 54 years of age, 7 years after onset. Although SNCA duplication is an unusual cause of familial PD testing for it is worthwhile. The clinical presentation of duplicated cases may be more aggressive than usual.

Parkin and PINK1 parkinsonism may represent nigral mitochondrial cytopathies distinct from Lewy body Parkinson's disease

Recent authors have concluded that Parkinson's disease (PD) is too heterogeneous to still be considered a single discrete disorder. They advise broadening the concept of PD to include genetic parkinsonisms, and discard Lewy pathology as the confirmatory biomarker. However, PD seen in the clinic is more homogeneous than often recognized if viewed from a long-term perspective. With appropriate diagnostic criteria, it is consistently associated with Lewy neuropathology, which should remain the gold standard for PD diagnostic confirmation. PD seen in the clinic has an inexorable course with eventual development of not only levodopa-refractory motor symptoms, but often cognitive dysfunction and prominent dysautonomia. This contrasts with homozygous parkin, PINK1 or DJ1 parkinsonism, characterized by young-onset (usually <40 years), and a comparatively benign course of predominantly levodopa-responsive symptoms without dementia or prominent dysautonomia. Parkin neuropathology is non-Lewy, with neurodegeneration predominantly confined to substantia nigra (and locus ceruleus), consistent with the limited clinical phenotype. Given the restricted and persistently levodopa-responsive phenotype, these familial cases might be considered "nigropathies". Based on emerging laboratory evidence linking parkin and PINK1 (and perhaps DJ1) to mitochondrial dysfunction, these nigropathies may represent nigral mitochondrial cytopathies. The dopaminergic substantia nigra is uniquely vulnerable to mitochondrial challenges, which might at least be partially attributable to large energy demands consequent to thin, unmyelinated axons with enormous terminal fields. Although sporadic PD is also associated with mitochondrial dysfunction, Lewy neurodegeneration represents a more pervasive disorder with perhaps a second, or different primary mechanism.

A cellular model to monitor proteasome dysfunction by alpha-synuclein

Impairment of the ubiquitin-proteasome degradation system has recently been suggested to be related to the onset of neurodegenerative disorders such as Alzheimer′s disease and Parkinson's disease. In this study, we investigated whether intracellular α-synuclein affects proteasome activity in SH-SY5Y cells. To monitor intracellular proteasome activity, we used a reporter consisting of a short peptide degron fused to the carboxyl-terminus of green fluorescent protein (GFP-CL1), which is known to be degraded by proteasome. The level of intact GFP-CL1 was dramatically increased by coexpression of GFP-CL1 and α-synuclein, as judged by confocal microscopic and immunoblot analyses. Expression of two pathogenic mutants of α-synuclein, A30P and A53T, and phosphomimetic S129D mutant increased the intensities of GFP more effectively than did wild-type α-synuclein. GFP fluorescence in cells transfected with Δ73-83 mutant or β-synuclein, which does not assemble into filaments in vitro, was not changed as compared with that in cells expressing GFP-CL1 alone. Thus, the ability of α-synuclein to inhibit proteasome activity is related to its propensity to assemble into filaments. Furthermore, we observed that some compounds inhibiting α-synuclein filament formation in vitro prevented the α-synuclein-mediated proteasome dysfunction in cells transfected with both GFP-CL1 and α-synuclein. The cellular model expressing both GFP-CL1 and α-synuclein may be a useful tool to screen compounds protecting neurons from α-synuclein-mediated proteasome dysfunction.

Pathogenesis of familial Parkinson's disease: new insights based on monogenic forms of Parkinson's disease

Parkinson's disease (PD) is one of the most common movement disorders caused by the loss of dopaminergic neuronal cells. The molecular mechanisms underlying neuronal degeneration in PD remain unknown; however, it is now clear that genetic factors contribute to the pathogenesis of this disease. Approximately, 5% of patients with clinical features of PD have clear familial etiology, which show a classical recessive or dominant Mendelian mode of inheritance. Over the decade, more than 15 loci and 11 causative genes have been identified so far and many studies shed light on their implication in not only monogenic but also sporadic form of PD. Recent studies revealed that PD-associated genes play important roles in cellular functions, such as mitochondrial functions, ubiquitin-proteasomal system, autophagy-lysosomal pathway and membrane trafficking. Furthermore, the proteins encoded by PD-associated genes can interact with each other and such gene products may share a common pathway that leads to nigral degeneration. However, their precise roles in the disease and their normal functions remain poorly understood. In this study, we review recent progress in knowledge about the genes associated with familial PD.

Cell death pathways in Parkinson's disease: role of mitochondria

Parkinson's disease (PD) is a progressive neurodegenerative disease and is characterized pathologically by selective loss of nigrostriatal dopaminergic neurons and the formation of Lewy bodies. Although in the majority of cases the cause of PD is unknown, mitochondrial dysfunction, environmental toxins, oxidative stress, and abnormal protein accumulation may all be involved in disease pathogenesis. The discovery of genes causing rare familial forms of PD (including alpha-synuclein, parkin, DJ-1, PINK1, and LRRK2) has shed light on our understanding of the molecular mechanisms of the development of the disease. Further studies from transgenic or toxin-induced experimental models have also provided insights into the etiology of human disease. Recently, accumulating evidence has suggested that mitochondrial dysfunction is one of the key players in molecular cell death pathways of PD. In this review, we provide an overview of the role of mitochondria in the pathogenesis of both sporadic and familial forms of PD. We also discuss the links between different pathways and highlight novel therapeutic opportunities which target mitochondria.

Alterations in lysosomal and proteasomal markers in Parkinson's disease: relationship to alpha-synuclein inclusions

We explored the relationship between ubiquitin proteasome system (UPS) and lysosomal markers and the formation of alpha-synuclein (alpha-syn) inclusions in nigral neurons in Parkinson disease (PD). Lysosome Associated Membrane Protein 1(LAMP1), Cathepsin D (CatD), and Heat Shock Protein73 (HSP73) immunoreactivity were significantly decreased within PD nigral neurons when compared to age-matched controls. This decrease was significantly greater in nigral neurons that contained alpha-syn inclusions. Immunoreactivity for 20S proteasome was similarly reduced in PD nigral neurons, but only in cells that contained inclusions. In aged control brains, there is staining for alpha-syn protein, but it is non-aggregated and there is no difference in LAMP1, CatD, HSP73 or 20S proteasome immunoreactivity between alpha-syn positive or negative neuromelanin-laden nigral neurons. Targeting over-expression of mutant human alpha-syn in the rat substantia nigra using viral vectors revealed that lysosomal and proteasomal markers were significantly decreased in the neurons that displayed alpha-syn-ir inclusions. These findings suggest that alpha-syn aggregation is a key feature associated with decline of proteasome and lysosome and support the hypothesis that cell degeneration in PD involves proteosomal and lysosomal dysfunction, impaired protein clearance, and protein accumulation and aggregation leading to cell death.

A single nucleotide polymorphism in the 3'UTR of the SNCA gene encoding alpha-synuclein is a new potential susceptibility locus for Parkinson disease

In Parkinson disease, the second most common neurodegenerative disorder in humans, increased alpha-synuclein (SNCA) levels are pathogenic, as evidenced by gene copy number mutations and increased alpha-synuclein levels detected in some familial and sporadic PD cases, respectively. Gene expression can be regulated at the post-transcriptional level by elements in the 3' untranslated region (3'UTR) of mRNAs. The goal of this study was to determine whether the 3'UTR of human SNCA can affect gene expression. Comparative sequence analysis revealed very high conservation across the entire 3'UTR of human SNCA over millions of years, suggesting the presence of multiple functionally important domains. EST and RT-PCR analyses showed that four different polyadenylation events occur in the 3'UTR of human SNCA. Finally, using luciferase assays, we examined the effect of the minor allele of five naturally occurring single nucleotide polymorphisms (SNPs) in the 3'UTR of SNCA on gene expression. The minor allele of SNP rs17016074 increased luciferase expression by 32% in a transient transfection assay in SHSY5Y neuroblastoma cells. Understanding the role of the 3'UTR of human SNCA and identifying functionally important naturally occurring SNPs using reporter assays can complement disease association studies in humans, uncovering potential susceptibility or protective polymorphisms in Parkinson disease. Our findings demonstrate that the 3'UTR of human SNCA, as a whole, and rs17016074, in particular, are loci of potential clinical importance for Parkinson disease.

Mutant alpha-synuclein overexpression mediates early proinflammatory activity

Microglia provide immune surveillance for the brain through both the removal of cellular debris and protection against infection by microorganisms and "foreign" molecules. Upon activation, microglia display an altered morphology and increased expression of proinflammatory molecules. Increased numbers of activated microglia have been identified in a number of neurodegenerative diseases including Parkinson's disease (PD). What remains to be determined is whether activated microglia result from ongoing cell death or are involved in disease initiation and progression. To address this question we utilized a transgenic mouse model that expresses a mutated form of a key protein involved in Parkinson's disease, alpha-synuclein. Herein, we report an increase in activated microglia and proinflammatory molecules in 1-month-old transgenic mice well before cell death occurs in this model. Frank microglial activation is resolved by 6 months of age while a subset of proinflammatory molecules remain elevated for 12 months. Both tyrosine hydroxylase mRNA expression and alpha-synuclein protein are decreased in the striatum of older animals evidence of dystrophic neuritic projections. To determine whether mutated alpha-synuclein could directly activate microglia primary microglia-enriched cell cultures were treated with exogenous mutated alpha-synuclein. The data reveal an increase in activated microglia and proinflammatory molecules due to direct interaction with mutated alpha-synuclein. Together, these data demonstrate that mutated alpha-synuclein mediates a proinflammatory response in microglia and this activity may participate in PD pathogenesis.

Parkinson's disease: from monogenic forms to genetic susceptibility factors

Research in Parkinson's disease (PD) genetics has been extremely prolific over the past decade. More than 13 loci and 9 genes have been identified, but their implication in PD is not always certain. Point mutations, duplications and triplications in the alpha-synuclein (SNCA) gene cause a rare dominant form of PD in familial and sporadic cases. Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are a more frequent cause of autosomal dominant PD, particularly in certain ethnic groups. Loss-of-function mutations in Parkin, PINK1, DJ-1 and ATP13A2 cause autosomal recessive parkinsonism with early-onset. Identification of other Mendelian forms of PD will be a main challenge for the next decade. In addition, susceptibility variants that contribute to PD have been identified in several populations, such as polymorphisms in the SNCA, LRRK2 genes and heterozygous mutations in the beta-glucocerebrosidase (GBA) gene. Genome-wide associations and re-sequencing projects, together with gene-environment interaction studies, are expected to further define the causal role of genetic determinants in the pathogenesis of PD, and improve prevention and treatment.

Molecular pathology of Lewy body diseases

Lewy body diseases are characterized by the presence of Lewy bodies, alpha-synuclein(AS)-positive inclusions in the brain. Since their main component is conformationally modified AS, aggregation of the latter is thought to be a key pathogenic event in these diseases. The analysis of inclusion body constituents gives additional information about pathways also involved in the pathology of synucleinopathies. Widespread mitochondrial dysfunction is very closely related to disease development. The impairment of protein degradation pathways, including both the ubiquitin-proteasome system and the autophagy-lysosome pathway also play an important role during the development of Lewy body diseases. Finally, differential expression changes of isoforms corresponding to genes primarily involved in Lewy body formation point to alternative splicing as another important mechanism in the development of Parkinson’s disease, as well as dementia with Lewy bodies. The present paper attempts to give an overview of recent molecular findings related to the pathogenesis of Lewy body diseases.

Imaging the impact of genes on Parkinson's disease

Although Parkinson's disease (PD) has traditionally been considered to be a non-genetic disorder, recent progress in the neurogenetics of PD provided converging evidence that genetic factors play a relevant role in the etiology of PD. The strongest case for a genetic contribution to PD was made by the discovery of mutations in single genes that can cause autosomal dominant (alpha-synuclein (SNCA)) and leucine rich repeat kinase 2 (LRRK2) gene) or recessive (Parkin, PTEN-induced putative kinase 1 (PINK1), DJ-1, and ATP13A2 gene) forms of PD. Here, we review how structural and functional neuroimaging of individuals carrying a mutation in one of the PD genes has offered a unique avenue of research into the pathogenesis of PD. In symptomatic mutation carriers (i.e. those with overt disease), brain mapping can help to link the molecular pathogenesis of PD more directly with functional and structural changes in the intact human brain. In addition, neuroimaging of presymptomatic (i.e. non-manifesting) mutation carriers has emerged as a valuable tool to identify mechanisms of adaptive motor reorganization at the preclinical stage that may prevent or delay clinical manifestation. In addition to mutations causing monogenic forms of PD, common polymorphisms in genes that influence mono-aminergic signaling or synaptic plasticity may have modifying effects on distinct aspects of PD. We also discuss how functional and structural neuroimaging can be used to better characterize these genotype-phenotype correlations.

Conversion of wild-type alpha-synuclein into mutant-type fibrils and its propagation in the presence of A30P mutant

Fibrillization or conformational change of alpha-synuclein is central in the pathogenesis of alpha-synucleinopathies, such as Parkinson disease. We found that the A30P mutant accelerates nucleation-dependent fibrillization of wild type (WT) alpha-synuclein. Electron microscopy observation and ultracentrifugation experiments revealed that shedding of fragments occurs from A30P fibrils and that these fragments accelerate fibrillization by serving as seeds. Immunochemical analysis using epitope-specific antibodies and biochemical analyses of protease-resistant cores demonstrated that A30P fibrils have a distinct conformation. Interestingly, WT fibrils formed with A30P seeds exhibited the same character as A30P fibrils, as did A30P fibrils formed with WT seeds, indicating that the A30P mutation affects the conformation and fibrillization of both WT and A30P. These effects of A30P mutation may explain the apparent conflict between the association of A30P with Parkinson disease and the slow fibrillization of A30P itself and therefore provide new insight into the molecular mechanisms of alpha-synucleinopathies.

Aggregates assembled from overexpression of wild-type alpha-synuclein are not toxic to human neuronal cells

Filamentous alpha-synuclein (alpha-syn) aggregates form Lewy bodies (LBs), the neuropathologic hallmarks of Parkinson disease and related alpha-synucleinopathies. To model Lewy body-associated neurodegeneration, we generated transfectant 3D5 of human neuronal-type in which expression of human wild-type alpha-syn is regulated by the tetracycline off (TetOff)-inducible mechanism. Retinoic acid-elicited differentiation promoted assembly of alpha-syn aggregates after TetOff induction in 3D5 cells. The aggregates accumulated 14 days after TetOff induction were primarily soluble and showed augmented thioflavin affinity with concomitant phosphorylation and nitration of alpha-syn. Extension of the induction led to the formation of sarkosyl-insoluble aggregates that appeared concurrently with thioflavin-positive inclusions. Immunoelectron microscopy revealed that the inclusions consist of dense bundles of 8- to 12-nm alpha-syn fibrils that congregate in the perikarya and resemble Lewy bodies. Most importantly, accumulation of soluble and insoluble aggregates after TetOff induction for 14 and 28 days was reversible and did not compromise the viability of the cells or their subsequent survival. Thus, this chemically defined culture paradigm provides a useful means to elucidate how oxidative injuries and other insults that are associated with aging promote alpha-syn to self-assemble or interact with other molecules leading to neuronal degeneration in alpha-synucleinopathies.

Clinical utility of contemporary molecular cytogenetics

The development of microarray-based comparative genomic hybridization (array CGH) methods represents a critical new advance in molecular cytogenetics. This new technology has driven a technical convergence between molecular diagnostics and clinical cytogenetics, questioned our naïve understanding of the complexity of the human genome, revolutionized the practice of medical genetics, challenged conventional wisdom related to the genetic bases of multifactorial and sporadic conditions, and is poised to impact all areas of medicine. The use of contemporary molecular cytogenetic techniques in research and diagnostics has resulted in the identification of many new syndromes, expanded our knowledge about the phenotypic spectrum of recognizable syndromes, elucidated the genomic bases of well-established clinical conditions, and refined our view about the molecular mechanisms of some chromosomal aberrations. Newer methodologies are being developed, which will likely lead to a new understanding of the genome and its relationship to health and disease.

In vivo silencing of alpha-synuclein using naked siRNA

BACKGROUND

Overexpression of alpha-synuclein (SNCA) in families with multiplication mutations causes parkinsonism and subsequent dementia, characterized by diffuse Lewy Body disease post-mortem. Genetic variability in SNCA contributes to risk of idiopathic Parkinson's disease (PD), possibly as a result of overexpression. SNCA downregulation is therefore a valid therapeutic target for PD.

RESULTS

We have identified human and murine-specific siRNA molecules which reduce SNCA in vitro. As a proof of concept, we demonstrate that direct infusion of chemically modified (naked), murine-specific siRNA into the hippocampus significantly reduces SNCA levels. Reduction of SNCA in the hippocampus and cortex persists for a minimum of 1 week post-infusion with recovery nearing control levels by 3 weeks post-infusion.

CONCLUSION

We have developed naked gene-specific siRNAs that silence expression of SNCA in vivo. This approach may prove beneficial toward our understanding of the endogenous functional equilibrium of SNCA, its role in disease, and eventually as a therapeutic strategy for alpha-synucleinopathies resulting from SNCA overexpression.

Alpha-synuclein multiplications with parkinsonism, dementia or progressive myoclonus?

Duplications and triplications of the alpha-synuclein (SNCA) gene have been reported in Parkinson's disease patients belonging to the Southern Swedish "Lister family". Further genealogical research has now shown that these individuals are descended from a large kindred characterized by Herman Lundborg in 1901-1913. In the expanded pedigree, a total of 25 individuals had Parkinson's disease with an autosomal dominant pattern of inheritance. Hereditary dementia, and, historically, dementia praecox have been described in other family members. Furthermore, an autosomal recessively inherited pediatric disease with nocturnal tonic-clonic fits, subsequent progressive myoclonus, startle reactions, tremor and muscle rigidity was described by Lundborg in the same pedigree. The entity was later designated Unverricht-Lundborg disease (ULD) or progressive myoclonus epilepsy type 1 (EPM1). However, Lundborg's clinical description of this disease, based on 17 patients within this kindred, differs from the modern definition of EPM1, which relies on patients with a mutation in the cystatin B (CSTB) gene. We hypothesize that the former pediatric disease, as well as the parkinsonism and dementia phenotypes, are associated with duplications, triplications and possibly higher-order multiplications of the alpha-synuclein (SNCA) gene. This hypothesis is supported by the distribution of afflicted family members within the pedigree and by recently obtained genealogical information.

Progress in the pathogenesis and genetics of Parkinson's disease

Recent progresses in the pathogenesis of sporadic Parkinson's disease (PD) and genetics of familial PD are reviewed. There are common molecular events between sporadic and familial PD, particularly between sporadic PD and PARK1-linked PD due to alpha-synuclein (SNCA) mutations. In sporadic form, interaction of genetic predisposition and environmental factors is probably a primary event inducing mitochondrial dysfunction and oxidative damage resulting in oligomer and aggregate formations of alpha-synuclein. In PARK1-linked PD, mutant alpha-synuclein proteins initiate the disease process as they have increased tendency for self-aggregation. As highly phosphorylated aggregated proteins are deposited in nigral neurons in PD, dysfunctions of proteolytic systems, i.e. the ubiquitin-proteasome system and autophagy-lysosomal pathway, seem to be contributing to the final neurodegenerative process. Studies on the molecular mechanisms of nigral neuronal death in familial forms of PD will contribute further on the understanding of the pathogenesis of sporadic PD.

Neuroinflammation and oxidation/nitration of alpha-synuclein linked to dopaminergic neurodegeneration

alpha-Synuclein (SYN) is the major component of Lewy bodies, the neuropathological hallmarks of Parkinson's disease (PD). Missense mutations and multiplications of the SYN gene cause autosomal dominant inherited PD. Thus, SYN is implicated in the pathogenesis of PD. However, the mechanism whereby SYN promotes neurodegeneration remains unclear. Familial PD with SYN gene mutations are rare because the majority of PD is sporadic and emerging evidence indicates that sporadic PD may result from genetic and environmental risk factors including neuroinflammation. Hence, we examined the relationship between SYN dysfunction and neuroinflammation in mediating dopaminergic neurodegeneration in mice and dopaminergic neuronal cultures derived from wild-type SYN and mutant A53T SYN transgenic mice in a murine SYN-null (SYNKO) background (M7KO and M83KO, respectively). Stereotaxic injection of an inflammagen, lipopolysaccharide, into substantia nigra of these SYN genetically engineered mice induced similar inflammatory reactions. In M7KO and M83KO, but not in SYNKO mice, the neuroinflammation was associated with dopaminergic neuronal death and the accumulation of insoluble aggregated SYN as cytoplasmic inclusions in nigral neurons. Nitrated/oxidized SYN was detected in these inclusions and abatement of microglia-derived nitric oxide and superoxide provided significant neuroprotection in neuron-glia cultures from M7KO mice. These data suggest that nitric oxide and superoxide released by activated microglia may be mediators that link inflammation and abnormal SYN in mechanisms of PD neurodegeneration. This study advances understanding of the role of neuroinflammation and abnormal SYN in the pathogenesis of PD and opens new avenues for the discovery of more effective therapies for PD.

Genomic investigation of alpha-synuclein multiplication and parkinsonism

OBJECTIVE

Copy number variation is a common polymorphic phenomenon within the human genome. Although the majority of these events are non-deleterious they can also be highly pathogenic. Herein we characterize five families with parkinsonism that have been identified to harbor multiplication of the chromosomal 4q21 locus containing the alpha-synuclein gene (SNCA).

METHODS

A methodological approach using fluorescent in situ hybridization and Affymetrix (Santa Clara, CA) 250K SNP microarrays was used to characterize the multiplication in each family and to identify the genes encoded within the region. The telomeric and centromeric breakpoints of each family were further narrowed using semiquantitative polymerase chain reaction with microsatellite markers and then screened for transposable repeat elements.

RESULTS

The severity of clinical presentation is correlated with SNCA dosage and does not appear to be overtly affected by the presence of other genes in the multiplicated region. With the exception of the Lister kindred, in each family the multiplication event appears de novo. The type and position of Alu/LINE repeats are also different at each breakpoint. Microsatellite analysis demonstrates two genomic mechanisms are responsible for chromosome 4q21 multiplications, including both SNCA duplication and recombination.

INTERPRETATION

SNCA dosage is responsible for parkinsonism, autonomic dysfunction, and dementia observed within each family. We hypothesize dysregulated expression of wild-type alpha-synuclein results in parkinsonism and may explain the recent association of common SNCA variants in sporadic Parkinson's disease. SNCA genomic duplication results from intraallelic (segmental duplication) or interallelic recombination with unequal crossing over, whereas both mechanisms appear to be required for genomic SNCA triplication.

Clinical, neuropathological and genotypic variability in SNCA A53T familial Parkinson's disease. Variability in familial Parkinson's disease

Individuals with familial Parkinson's disease (PD) due to a monogenic defect can show considerable clinical and neuropathological variability. To identify factors underlying this variability, histopathological analysis was performed in two clinically different A53T alpha-synuclein heterozygotes from Family H, a multigenerational alpha-synuclein A53T kindred. To determine whether additional genetic factors could contribute to phenotypic variability, Family H and another multigenerational A53T kindred were analyzed for parkin polymorphisms. We identified a previously described variant in parkin exon 4 associated with increased PD risk (S167N). The two A53T heterozygotes had markedly different neuropathology and different parkin genotypes: A N167 homozygote had early onset rapidly progressive disease, early dementia, myoclonus and sleep disorder, while a S167 homozygote had late onset, slowly progressive disease and late dementia. Both had brainstem, cortical, and intraneuritic Lewy bodies (LB). The N167 individual had widespread cortical neurofibrillary degeneration, while the S167 individual had only medial temporal lobe neurofibrillary degeneration. The N167 individual had severe neuronal loss in CA2 associated with Lewy neurites (LN), while the S167 individual had severe neuronal loss in CA1 associated with TDP-43 immunoreactive neuronal inclusions. These findings implicate TDP-43 in the pathology of familial PD and suggest that parkin may act as a modifier of the A53T alpha-synuclein phenotype of familial PD. Furthermore, they suggest a mechanism by which a rare genetic variant that is associated with a minor increase of PD risk in the heterozygous state may, in the homozygous state, exacerbate a disease phenotype associated with a highly penetrant dominant allele.

Direct quantification of CSF alpha-synuclein by ELISA and first cross-sectional study in patients with neurodegeneration

Because accumulation of alpha-synuclein (alphaS) in the brain is a hallmark of Parkinson disease (PD) and related disorders, we examined its occurrence in human cerebrospinal fluid (CSF). Following affinity enrichment and trypsin digestion of CSF collected from a neurologically healthy donor, we identified several alphaS-derived peptides by mass spectrometry. The concentration of alphaS amounted to <0.001% of the CSF proteome. We then built, validated and optimized a sandwich-type, enzyme-linked immunoadsorbent assay (ELISA) to measure total alphaS levels in unconcentrated CSF. In a cross-sectional study of 100 living donors, we examined cell-free CSF samples from subjects clinically diagnosed with advanced PD, dementia with Lewy bodies (DLB), Alzheimer disease (AD), and a group of non-neurodegenerative disease controls (NCO). In these four groups the CSF alphaS concentrations ranged from 0.8 to 16.2 pg/microl. Mean CSF alphaS values were lower in donors with a primary synucleinopathy (PD, DLB: n=57) than in the other two groups (AD, NCO: n=35; p=0.025). By contrast, living Creutzfeldt-Jakob disease patients showed markedly elevated CSF alphaS levels (n=8; mean, 300 pg/microl; p<0.001). Our results unequivocally confirm the presence of alphaS in adult human CSF. In a first feasibility study employing a novel ELISA, we found relatively low CSF alphaS concentrations in subjects with parkinsonism linked to synucleinopathy, PD and DLB. In definite prion disease cases, we recorded a marked rise in total CSF alphaS resulting from rapid cell death. Our results will likely aid future biomarker explorations in neurodegenerative conditions and facilitate target validation studies.

A genome-wide scan in an Amish pedigree with parkinsonism

The identification of familial Parkinson Disease (PD) genes is yielding important molecular pathogenetic insights. In an effort to identify additional PD genes, we studied an eight generation Amish pedigree with apparent autosomal dominant parkinsonism with incomplete penetrance. Phenotypic variability ranged from idiopathic PD to progressive supranuclear palsy (PSP), with the average age at onset 53 years (range of 39 to 74 years). We identified markers on chromosome 3 and 7 that were significant at a genome-wide level by parametric and nonparametric criteria, lod > 3 and non-parametric P-value < 0.10, respectively. We also identified markers on chromosomes 10 and 22 with lod > 3. These data suggest that parkinsonism in this pedigree is genetically complex, with contributions from several loci.

DJ-1 modulates alpha-synuclein aggregation state in a cellular model of oxidative stress: relevance for Parkinson's disease and involvement of HSP70

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative pathology whose molecular etiopathogenesis is not known. Novel contributions have come from familial forms of PD caused by alterations in genes with apparently unrelated physiological functions. The gene coding for alpha-synuclein (alpha-syn) (PARK1) has been investigated as alpha-syn is located in Lewy bodies (LB), intraneuronal inclusions in the substantia nigra (SN) of PD patients. A-syn has neuroprotective chaperone-like and antioxidant functions and is involved in dopamine storage and release. DJ-1 (PARK7), another family-PD-linked gene causing an autosomal recessive form of the pathology, shows antioxidant and chaperone-like activities too.

METHODOLOGY/PRINCIPAL FINDINGS

The present study addressed the question whether alpha-syn and DJ-1 interact functionally, with a view to finding some mechanism linking DJ-1 inactivation and alpha-syn aggregation and toxicity. We developed an in vitro model of alpha-syn toxicity in the human neuroblastoma cell line SK-N-BE, influencing DJ-1 and alpha-syn intracellular concentrations by exogenous addition of the fusion proteins TAT-alpha-syn and TAT-DJ-1; DJ-1 was inactivated by the siRNA method. On a micromolar scale TAT-alpha-syn aggregated and triggered neurotoxicity, while on the nanomolar scale it was neuroprotective against oxidative stress (induced by H(2)O(2) or 6-hydroxydopamine). TAT-DJ-1 increased the expression of HSP70, while DJ-1 silencing made SK-N-BE cells more susceptible to oxidative challenge, rendering TAT-alpha-syn neurotoxic at nanomolar scale, with the appearance of TAT-alpha-syn aggregates.

CONCLUSION/SIGNIFICANCE

DJ-1 inactivation may thus promote alpha-syn aggregation and the related toxicity, and in this model HSP70 is involved in the antioxidant response and in the regulation of alpha-syn fibril formation.

Elevated alpha-synuclein mRNA levels in individual UV-laser-microdissected dopaminergic substantia nigra neurons in idiopathic Parkinson's disease

The presynaptic protein α-synuclein is involved in several neurodegenerative diseases, including Parkinson's disease (PD). In rare familial forms of PD, causal mutations (PARK1) as well as multiplications (PARK4) of the α-synuclein gene have been identified. In sporadic, idiopathic PD, abnormal accumulation and deposition of α-synuclein might also cause degeneration of dopaminergic midbrain neurons, the clinically most relevant neuronal population in PD. Thus, cell-specific quantification of α-synuclein expression-levels in dopaminergic neurons from idiopathic PD patients in comparison to controls would provide essential information about contributions of α-synuclein to the etiology of PD. However, a number of previous studies addressing this question at the tissue-level yielded varying results regarding α-synuclein expression. To increase specificity, we developed a cell-specific approach for mRNA quantification that also took into account the important issue of variable RNA integrities of the individual human postmortem brain samples. We demonstrate that PCR –amplicon size can confound quantitative gene-expression analysis, in particular of partly degraded RNA. By combining optimized UV-laser microdissection- and quantitative RT–PCR-techniques with suitable PCR assays, we detected significantly elevated α-synuclein mRNA levels in individual, surviving neuromelanin- and tyrosine hydroxylase-positive substantia nigra dopaminergic neurons from idiopathic PD brains compared to controls. These results strengthen the pathophysiologic role of transcriptional dysregulation of the α-synuclein gene in sporadic PD.

Early α-synuclein lipoxidation in neocortex in Lewy body diseases

Previous studies in Lewy body diseases (LBDs), including Parkinson's disease (PD) and Dementia with Lewy bodies (DLB), have shown oxidative stress damage more extended than the expected for the distribution of Lewy pathology. Since malondialdehyde (MDA) can form adducts with lysine residues of proteins, MDA-Lys immunoprecipitation and alpha-synuclein immunoblotting has been carried out in frontal cortex and substantia nigra homogenates from five patients with PD, five DLB, three iPD and seven aged-matched controls to decipher the extent of lipoxidized alpha-synuclein in LBDs. MDA-Lys-lipoxidation of alpha-synuclein in the substantia nigra and frontal cortex has been found in all DLB and PD cases examined, but also in the frontal cortex in 3/3 and in the substantia nigra in 2/3 cases with iPD. In addition, one control case had MDA-Lys-modified alpha-synuclein in the frontal cortex, and another in the substantia nigra. This work provides evidence of extended lipoxidative modification of alpha-synuclein in LBDs. Moreover, it demonstrates that alpha-synuclein lipoxidation is an early event in LBDs which precedes alpha-synuclein solubility modification and aggregation, and formation of Lewy bodies and neurites.

Alpha-synuclein aggregation alters tyrosine hydroxylase phosphorylation and immunoreactivity: lessons from viral transduction of knockout mice

Tyrosine hydroxylase (TH), the rate limiting enzyme in catecholamine synthesis, is frequently used as a marker of dopaminergic neuronal loss in animal models of Parkinson's disease (PD). We have been exploring the normal function of the PD-related protein alpha-synuclein (alpha-Syn) with regard to dopamine synthesis. TH is activated by the phosphorylation of key seryl residues in the TH regulatory domain. Using in vitro models, our laboratory discovered that alpha-Syn inhibits TH by acting to reduce TH phosphorylation, which then reduces dopamine synthesis [X.-M. Peng, R. Tehranian, P. Dietrich, L. Stefanis, R.G. Perez, Alpha-synuclein activation of protein phosphatase 2A reduces tyrosine hydroxylase phosphorylation in dopaminergic cells, J. Cell. Sci. 118 (2005) 3523-3530; R.G. Perez, J.C. Waymire, E. Lin, J.J. Liu, F. Guo, M.J. Zigmond, A role for alpha-synuclein in the regulation of dopamine biosynthesis, J. Neurosci. 22 (2002) 3090-3099]. We recently began exploring the impact of alpha-Syn on TH in vivo, by transducing dopaminergic neurons in alpha-Syn knockout mouse (ASKO) olfactory bulb using wild type human alpha-Syn lentivirus. At 3.5-21 days after viral delivery, alpha-Syn expression was transduced primarily in periglomerular dopaminergic neurons. Cells with modest levels of alpha-Syn consistently co-labeled for Total-TH. However, cells bearing aggregated alpha-Syn, as revealed by proteinase K or Thioflavin-S treatment had significantly reduced Total-TH immunoreactivity, but high phosphoserine-TH labeling. On immunoblots, we noted that Total-TH immunoreactivity was equivalent in all conditions, although tissues with alpha-Syn aggregates again had higher phosphoserine-TH levels. This suggests that aggregated alpha-Syn is no longer able to inhibit TH. Although the reason(s) underlying reduced Total-TH immunoreactivity on tissue sections await(s) confirmation, the dopaminergic phenotype was easily verified using phosphorylation-state-specific TH antibodies. These findings have implications not only for normal alpha-Syn function in TH regulation, but also for measuring cell loss that is associated with synucleinopathy.