Nigrostriatal alpha-synucleinopathy induced by viral vector-mediated overexpression of human alpha-synuclein: a new primate model of Parkinson's disease

The impact of genetic research on our understanding of Parkinson's disease

Until recently, genetics was thought to play a minor role in the development of Parkinson's disease (PD). Over the last decade, a number of genes that definitively cause PD have been identified, which has led to the generation of disease models based on pathogenic gene variants that recapitulate many features of the disease. These genetic studies have provided novel insight into potential mechanisms underlying the aetiology of PD. This chapter will provide a profile of the genes conclusively linked to PD and will outline the mechanisms of PD pathogenesis implicated by genetic studies. Mitochondrial dysfunction, oxidative stress and impaired ubiquitin-proteasome system function are disease mechanisms that are particularly well supported by genetic studies and are therefore the focus of this chapter.

Adeno-associated viral vector serotypes 1 and 5 targeted to the neonatal rat and pig striatum induce widespread transgene expression in the forebrain

Viral vector-mediated gene transfer has emerged as a powerful means to target transgene expression in the central nervous system. Here we characterized the efficacy of serotypes 1 and 5 recombinant adeno-associated virus (rAAV) vectors encoding green fluorescent protein (GFP) after stereotaxic delivery to the neonatal rat and minipig striatum. The efficiency of GFP expression and the phenotype of GFP-positive cells were assessed within the forebrain at different time points up to 12 months after surgery. Both rAAV1-GFP and rAAV5-GFP delivery resulted in transduction of the striatum as well as striatal input and output areas, including large parts of the cortex. In both species, rAAV5 resulted in a more widespread transgene expression compared to rAAV1. In neonatal rats, rAAV5 also transduced several other areas such as the olfactory bulbs, hippocampus, and septum. Phenotypic analysis of the GFP-positive cells, performed using immunohistochemistry and confocal microscopy, showed that most of the GFP-positive cells by either serotype were NeuN-positive neuronal profiles. The rAAV5 vector further displayed the ability to transduce non-neuronal cell types in both rats and pigs, albeit at a low frequency. Our results show that striatal delivery of rAAV5 vectors in the neonatal brain represents a useful tool to express genes of interest both in the basal ganglia and the neocortex. Furthermore, we apply, for the first time, viral vector-mediated gene transfer to the pig brain providing the opportunity to study effects of genetic manipulation in this non-primate large animal species. Finally, we generated an atlas of the Göttingen minipig brain for guiding future studies in this large animal species.

Molecular pathology of the fibroblast growth factor family

The human fibroblast growth factor (FGF) family contains 22 proteins that regulate a plethora of physiological processes in both developing and adult organism. The mutations in the FGF genes were not known to play role in human disease until the year 2000, when mutations in FGF23 were found to cause hypophosphatemic rickets. Nine years later, seven FGFs have been associated with human disorders. These include FGF3 in Michel aplasia; FGF8 in cleft lip/palate and in hypogonadotropic hypogonadism; FGF9 in carcinoma; FGF10 in the lacrimal/salivary glands aplasia, and lacrimo-auriculo-dento-digital syndrome; FGF14 in spinocerebellar ataxia; FGF20 in Parkinson disease; and FGF23 in tumoral calcinosis and hypophosphatemic rickets. The heterogeneity in the functional consequences of FGF mutations, the modes of inheritance, pattern of involved tissues/organs, and effects in different developmental stages provide fascinating insights into the physiology of the FGF signaling system. We review the current knowledge about the molecular pathology of the FGF family.

Neuronal cell replacement in Parkinson's disease

Transplantation of foetal dopamine neurons into the striatum of Parkinson's disease patients can provide restoration of the dopamine system and alleviate motor deficits. However, cellular replacement is associated with several problems. As with pharmacological treatments, cell therapy can lead to disabling abnormal involuntary movements (dyskinesias). The exclusion of serotonin and GABA neurons, and enrichment of substantia nigra (A9) dopamine neurons, may circumvent this problem. Furthermore, although grafted foetal dopamine neurons can survive in Parkinson's patients for more than a decade, the occurrence of Lewy bodies within such transplanted cells and reduced dopamine transporter and tyrosine hydroxylase expression levels indicate that grafted cells are associated with pathology. It will be important to understand if such abnormalities are host- or graft induced and to develop methods to ensure survival of functional dopamine neurons. Careful preparation of cellular suspensions to minimize graft-induced inflammatory responses might influence the longevity of transplanted cells. Finally, a number of practical and ethical issues are associated with the use of foetal tissue sources. Thus, future cell therapy is aiming towards the use of embryonic stem cell or induced pluripotent stem cell derived dopamine neurons.

Differential transduction following basal ganglia administration of distinct pseudotyped AAV capsid serotypes in nonhuman primates

We examined the transduction efficiency of different adeno-associated virus (AAV) capsid serotypes encoding for green fluorescent protein (GFP) flanked by AAV2 inverted terminal repeats in the nonhuman primate basal ganglia as a prelude to translational studies, as well as clinical trials in patients with Parkinson's disease (PD). Six intact young adult cynomolgus monkeys received a single 10 microl injection of AAV2/1-GFP, AAV2/5-GFP, or AAV2/8-GFP pseudotyped vectors into the caudate nucleus and putamen bilaterally in a pattern that resulted in each capsid serotype being injected into at least four striatal sites. GFP immunohistochemistry revealed excellent transduction rates for each AAV pseudotype. Stereological estimates of GFP+ cells within the striatum revealed that AAV2/5-GFP transduces significantly higher number of cells than AAV2/8-GFP (P < 0.05) and there was no significant difference between AAV2/5-GFP and AAV2/1-GFP (P = 0.348). Consistent with this result, Cavalieri estimates revealed that AAV2/5-GFP resulted in a significantly larger transduction volume than AAV2/8-GFP (P < 0.05). Each pseudotype transduced striatal neurons effectively [>95% GFP+ cells colocalized neuron-specific nuclear protein (NeuN)]. The current data suggest that AAV2/5 and AAV2/1 are superior to AAV2/8 for gene delivery to the nonhuman primate striatum and therefore better candidates for therapeutic applications targeting this structure.

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.

Versatile somatic gene transfer for modeling neurodegenerative diseases

A growing variety of technical approaches allow control over the expression of selected genes in living organisms. The ability to deliver functional exogenous genes involved in neurodegenerative diseases has opened pathological processes to experimental analysis and targeted therapeutic development in rodent and primate preclinical models. Biological adaptability, economic animal use, and reduced model development costs complement improved control over spatial and temporal gene expression compared with conventional transgenic models. A review of viral vector studies, typically adeno-associated virus or lentivirus, for expression of three proteins that are central to major neurodegenerative diseases, will illustrate how this approach has powered new advances and opportunities in CNS disease research.

Large animal models of neurological disorders for gene therapy

he development of therapeutic interventions for genetic disorders and diseases that affect the central nervous system (CNS) has proven challenging. There has been significant progress in the development of gene therapy strategies in murine models of human disease, but gene therapy outcomes in these models do not always translate to the human setting. Therefore, large animal models are crucial to the development of diagnostics, treatments, and eventual cures for debilitating neurological disorders. This review focuses on the description of large animal models of neurological diseases such as lysosomal storage diseases, Parkinsons disease, Huntingtons disease, and neuroAIDS. The review also describes the contributions of these models to progress in gene therapy research.

Neuronal gene expression correlates of Parkinson's disease with dementia

Dementia is a common disabling complication in patients with Parkinson's disease (PD). The underlying molecular causes of Parkinson's disease with dementia (PDD) are poorly understood. To identify candidate genes and molecular pathways involved in PDD, we have performed whole genome expression profiling of susceptible cortical neuronal populations. Results show significant differences in expression of 162 genes (P < 0.01) between PD patients who are cognitively normal (PD-CogNL) and controls. In contrast, there were 556 genes (P < 0.01) significantly altered in PDD compared to either healthy controls or to PD-CogNL cases. These results are consistent with increased cortical pathology in PDD relative to PD-CogNL and identify underlying molecular changes associated with the increased pathology of PDD. Lastly, we have identified expression differences in 69 genes in PD cortical neurons that occur before the onset of dementia and that are exacerbated upon the development of dementia, suggesting that they may be relevant presymptomatic contributors to the onset of dementia in PD. These results provide new insights into the cortical molecular changes associated with PDD and provide a highly useful reference database for researchers interested in PDD.

Aggregate formation and toxicity by wild-type and R621C synphilin-1 in the nigrostriatal system of mice using adenoviral vectors

Synphilin-1 was described as a protein interacting with alpha-synuclein and is commonly found in Lewy bodies, the pathological hallmark of Parkinson's disease (PD). Our group has previously described and characterized in vitro a mutation in the synphilin-1 gene (R621C) in PD patients. Providing the first characterization of synphilin-1 expression in an animal model, we here used adenoviral gene transfer to study the effects of wild-type (WT) and R621C synphilin-1 in dopaminergic neurons in mouse brain. As synphilin-1 is commonly used to trigger aggregation of alpha-synuclein in cell culture, we investigated not only non-transgenic C57Bl/6 mice but also A30P-alpha-synuclein transgenic animals. Both WT synphilin-1 and R621C synphilin-1 led to the formation of Thioflavine-S positive inclusions in C57Bl/6 mice and degeneration of dopaminergic neurons in the substantia nigra. R621C synphilin-1 induced more aggregate formation than WT synphilin-1 in A30P-alpha-synuclein transgenic mice, consistent with the role of the R621C mutation as a susceptibility factor for PD. Synphilin-1 expression may be used to improve current mouse models of PD, as it induced both the formation of aggregates and degeneration of dopaminergic neurons, two core characteristics of PD that have not been well reproduced with expression of alpha-synuclein.

Functional models of Parkinson's disease: a valuable tool in the development of novel therapies

Functional models of Parkinson's disease (PD) have led to effective treatment for the motor symptoms. Toxin-based models, such as the 6-hydroxydopamine-lesioned rat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated primate, have resulted in novel dopaminergic therapies and new therapeutic strategies. They have also been used to study processes underlying motor complications, particularly dyskinesia, and for developing pharmacological approaches to dyskinesia avoidance and suppression. Symptomatic models of PD based on nigrostriatal degeneration have a high degree of predictability of clinical effect of dopaminergic drugs on motor symptoms in humans. However, the effects of nondopaminergic drugs in these models do not translate effectively into clinical efficacy. Newer experimental models of PD have attempted to reproduce the pathogenic process and to involve all areas of the brain pathologically affected in humans. In addition, models showing progressive neuronal death have been sought but so far unsuccessfully. Pathogenic modeling has been attempted using a range of toxins, as well as through the use of transgenic models of gene defects in familial PD and mutant rodent strains. However, there are still no accepted progressive models of PD that mimic the processes known to occur during cell death and that result in the motor deficits, pathology, biochemistry, and drug responsiveness as seen in humans. Nevertheless, functional models of PD have led to many advances in treating the motor symptoms of the disorder, and we have been fortunate to have them available. They are an important reason the treatment of PD is so much better compared with treatments for related illnesses.

alpha-Synuclein and neuronal cell death

α-Synuclein is a small protein that has special relevance for understanding Parkinson disease and related disorders. Not only is α-synuclein found in Lewy bodies characteristic of Parkinson disease, but also mutations in the gene for α-synuclein can cause an inherited form of Parkinson disease and expression of normal α-synuclein can increase the risk of developing Parkinson disease in sporadic, or non-familial, cases. Both sporadic and familial Parkinson disease are characterized by substantial loss of several groups of neurons, including the dopaminergic cells of the substantia nigra that are the target of most current symptomatic therapies. Therefore, it is predicted that α-synuclein, especially in its mutant forms or under conditions where its expression levels are increased, is a toxic protein in the sense that it is associated with an increased rate of neuronal cell death. This review will discuss the experimental contexts in which α-synuclein has been demonstrated to be toxic. I will also outline what is known about the mechanisms by which α-synuclein triggers neuronal damage, and identify some of the current gaps in our knowledge about this subject. Finally, the therapeutic implications of toxicity of α-synuclein will be discussed.

Gene and cell delivery to the degenerated striatum: status of preclinical efforts in primate models

Significant progress has been achieved in developing restorative neurosurgical strategies for movement disorders on the basis of preclinical gene and cell therapy experiments in primates. Because of the unique similarities between human and primate anatomy and physiology, experiments in primate models are the critical step in translating these innovative neurosurgical treatment concepts into successful human applications. To clarify progress toward this goal, we have examined recent preclinical data regarding the delivery of gene and cell therapy to the lesioned primate striatum. Improved behavioral outcomes after in vivo gene transduction, achieved by brain delivery of adeno-associated vectors, have resulted in the initiation of ongoing clinical trials. Cell transplantation experiments are transitioning from the grafting of fetal tissue, which has met with mixed clinical success, to the grafting of expanded neural stem cells, for which preliminary results in primates are encouraging. Careful attention to the surgical delivery parameters for these agents in primate studies, along with the ability to realistically model imaging and behavioral outcomes in these animals, is essential for optimizing the restoration of function for patients. The authors review data obtained from primate models that form the basis for ongoing clinical trials to consider how new preclinical models should be developed to answer questions that arise from experimental clinical data.

Molecular mechanisms of alpha-synuclein neurodegeneration

alpha-Synuclein is an abundant highly charged protein that is normally predominantly localized around synaptic vesicles in presynaptic terminals. Although the function of this protein is still ill-defined, genetic studies have demonstrated that point mutations or genetic alteration (duplications or triplications) that increase the number of copies of the alpha-synuclein (SCNA) gene can cause Parkinson's disease or the related disorder dementia with Lewy bodies. alpha-Synuclein can aberrantly polymerize into fibrils with typical amyloid properties, and these fibrils are the major component of many types of pathological inclusions, including Lewy bodies, which are associated with neurodegenerative diseases, such as Parkinson's disease. Although there is substantial evidence supporting the toxic nature of alpha-synuclein inclusions, other modes of toxicity such as oligomers have been proposed. In this review, some of the evidence for the different mechanisms of alpha-synuclein toxicity is presented and discussed.

Value of genetic models in understanding the cause and mechanisms of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized pathologically by the degeneration of nigrostriatal pathway dopaminergic neurons and other neuronal systems and the appearance of Lewy bodies that contain alpha-synuclein. PD is generally a sporadic disease, but a small proportion of cases have a clear genetic component. Mutations have been identified in six genes that clearly segregate with disease in rare families with PD. Transgenic, knockout, and virus-based models of disease have been developed in rodents to further understand how these genes contribute to the pathogenesis of PD. In general, these animal models recapitulate many key features of the disease, including derangements in dopaminergic synaptic transmission, selective neurodegeneration, neurochemical deficits, alpha-synuclein-positive neuropathology, and motor deficits. However, a genetic model with all or most of these pathogenic features has proved difficult to create. In this article, we discuss these mammalian genetic models of PD and what they have revealed about the cause and mechanisms of this disease.

Hsp104 antagonizes alpha-synuclein aggregation and reduces dopaminergic degeneration in a rat model of Parkinson disease

Parkinson disease (PD) is characterized by dopaminergic neurodegeneration and intracellular inclusions of alpha-synuclein amyloid fibers, which are stable and difficult to dissolve. Whether inclusions are neuroprotective or pathological remains controversial, because prefibrillar oligomers may be more toxic than amyloid inclusions. Thus, whether therapies should target inclusions, preamyloid oligomers, or both is a critically important issue. In yeast, the protein-remodeling factor Hsp104 cooperates with Hsp70 and Hsp40 to dissolve and reactivate aggregated proteins. Metazoans, however, have no Hsp104 ortholog. Here we introduced Hsp104 into a rat PD model. Remarkably, Hsp104 reduced formation of phosphorylated alpha-synuclein inclusions and prevented nigrostriatal dopaminergic neurodegeneration induced by PD-linked alpha-synuclein (A30P). An in vitro assay employing pure proteins revealed that Hsp104 prevented fibrillization of alpha-synuclein and PD-linked variants (A30P, A53T, E46K). Hsp104 coupled ATP hydrolysis to the disassembly of preamyloid oligomers and amyloid fibers composed of alpha-synuclein. Furthermore, the mammalian Hsp70 and Hsp40 chaperones, Hsc70 and Hdj2, enhanced alpha-synuclein fiber disassembly by Hsp104. Hsp104 likely protects dopaminergic neurons by antagonizing toxic alpha-synuclein assemblies and might have therapeutic potential for PD and other neurodegenerative amyloidoses.

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.

The 3R principle and the use of non-human primates in the study of neurodegenerative diseases: the case of Parkinson's disease

The aim of this paper is to offer an ethical perspective on the use of non-human primates in neurobiological studies, using the Parkinson's disease (PD) as an important case study. We refer, as theoretical framework, to the 3R principle, originally proposed by Russell and Burch [Russell, W.M.S., Burch, R.L., 1959. The Principles of Humane Experimental Technique. Universities Federation for Animal Welfare Wheathampstead, England (reprinted in 1992)]. Then, the use of non-human primates in the study of PD will be discussed in relation to the concepts of Replacement, Reduction, and Refinement. Replacement and Reduction result to be the more problematic concept to be applied, whereas Refinement offers relatively more opportunities of improvement. However, although in some cases the 3R principle shows its applicative limits, its value, as conceptual and inspirational tool remains extremely valuable. It suggests to the researchers a series of questions, both theoretical and methodological, which can have the results of improving the quality of life on the experimental models, the quality of the scientific data, and the public perception from the non-scientist community.

Proteome response to the panneural expression of human wild-type alpha-synuclein: a Drosophila model of Parkinson's disease

The alpha-synuclein protein is associated with several neurodegenarative diseases, including Parkinson's disease (PD). In humans, only mutated forms of alpha-synuclein are linked to PD; however, panneural expression of human wild-type (WT) alpha-synuclein induces Parkinson's like-symptoms in Drosophila. Here, we report a quantitative proteomic analysis of WT alpha-synuclein transgenic flies with age-matched controls at the presymptomatic stage utilizing a global isotopic labeling strategy combined with multidimensional liquid chromatographies and tandem mass spectrometry. The analysis includes two biological replicates, in which samples are isotopically labeled in forward and reverse directions. In total, 229 proteins were quantified from assignments of at least two peptide sequences. Of these, 188 (82%) proteins were detected in both forward and reverse labeling measurements. Twelve proteins were found to be differentially expressed in response to the expression of human WT alpha-synuclein; down-regulations of larval serum protein 2 and fat body protein 1 levels were confirmed by Western blot analysis. Gene Ontology analysis indicates that the dysregulated proteins are primarily associated with cellular metabolism and signaling, suggesting potential contributions of perturbed metabolic and signaling pathways to PD. An increased level of the iron (III)-binding protein, ferritin, typically found in the brains of PD patients, is also observed in presymptomatic WT alpha-synuclein expressing animals. The observed alterations in both pathology-associated and novel proteins may shed light on the pathological roles of alpha-synuclein that may lead to the development of diagnostic strategies at the presymptomatic stage.

Drug Targeting of α-Synuclein Oligomerization in Synucleinopathies

The heterogeneity of symptoms and disease progression observed in synucleinopathies, of which Parkinson's disease (PD) is the most common representative, poses large problems for the discovery of novel therapeutics. The molecular basis for pathology is currently unclear, both in familial and in sporadic cases. While the therapeutic effects of L-DOPA and dopamine receptor agonists constitute good options for symptomatic treatment in PD, the development of neuroprotective and/or neurorestorative treatments for PD and other synucleinopathies faces significant challenges due to the poor knowledge of the putative targets. Recent experimental evidence strongly suggests a central role for neurotoxic α-synuclein oligomeric species in neurodegeneration. The events leading to protein oligomerization, as well as the oligomeric species themselves, are likely amenable to modulation by small molecules, which are beginning to emerge in high throughput compound screens in a variety of model organisms. The therapeutic potential of small molecule modulators of oligomer formation demands further exploration and validation in cellular and animal disease models in order to accelerate human drug development.

Drug Targeting of alpha-Synuclein Oligomerization in Synucleinopathies

The heterogeneity of symptoms and disease progression observed in synucleinopathies, of which Parkinson's disease (PD) is the most common representative, poses large problems for the discovery of novel therapeutics. The molecular basis for pathology is currently unclear, both in familial and in sporadic cases. While the therapeutic effects of L-DOPA and dopamine receptor agonists constitute good options for symptomatic treatment in PD, the development of neuroprotective and/or neurorestorative treatments for PD and other synucleinopathies faces significant challenges due to the poor knowledge of the putative targets. Recent experimental evidence strongly suggests a central role for neurotoxic alpha-synuclein oligomeric species in neurodegeneration. The events leading to protein oligomerization, as well as the oligomeric species themselves, are likely amenable to modulation by small molecules, which are beginning to emerge in high throughput compound screens in a variety of model organisms. The therapeutic potential of small molecule modulators of oligomer formation demands further exploration and validation in cellular and animal disease models in order to accelerate human drug development.

Striatal and nigral pathology in a lentiviral rat model of Machado-Joseph disease

Machado-Joseph disease (MJD) is a fatal, dominant neurodegenerative disorder. MJD results from polyglutamine repeat expansion in the MJD-1 gene, conferring a toxic gain of function to the ataxin-3 protein. In this study, we aimed at overexpressing ataxin-3 in the rat brain using lentiviral vectors (LV), to generate an in vivo MJD genetic model and, to study the disorder in defined brain regions: substantia nigra, an area affected in MJD, cortex and striatum, regions not previously reported to be affected in MJD. LV encoding mutant or wild-type human ataxin-3 was injected in the brain of adult rats and the animals were tested for behavioral deficits and neuropathological abnormalities. Striatal pathology was confirmed in transgenic mice and human tissue. In substantia nigra, unilateral overexpression of mutant ataxin-3 led to: apomorphine-induced turning behavior; formation of ubiquitinated ataxin-3 aggregates; alpha-synuclein immunoreactivity; and loss of dopaminergic markers (TH and VMAT2). No neuropathological changes were observed upon wild-type ataxin-3 overexpression. Mutant ataxin-3 expression in striatum and cortex, resulted in accumulation of misfolded ataxin-3, and within striatum, loss of neuronal markers. Striatal pathology was confirmed by observation in MJD transgenic mice of ataxin-3 aggregates and substantial reduction of DARPP-32 immunoreactivity and, in human striata, by ataxin-3 inclusions, immunoreactive for ubiquitin and alpha-synuclein. This study demonstrates the use of LV encoding mutant ataxin-3 to produce a model of MJD and brings evidence of striatal pathology, suggesting that this region may contribute to dystonia and chorea observed in some MJD patients and may represent a target for therapies.

Contributions of non-human primates to neuroscience research

Non-human primates have a small but important role in basic and translational biomedical research, owing to similarities with human beings in physiology, cognitive capabilities, neuroanatomy, social complexity, reproduction, and development. Although non-human primates have contributed to many areas of biomedical research, we review here their unique contributions to work in neuroscience, and focus on four domains: Alzheimer's disease, neuroAIDS, Parkinson's disease, and stress. Our discussion includes, for example, the role of non-human primates in development of new treatments (eg, stem cells, gene transfer) before phase I clinical trials in patients; basic research on disease pathogenesis; and understanding neurobehavioural outcomes resulting from genotype-environment interactions.

Quantitative proteomics of a presymptomatic A53T alpha-synuclein Drosophila model of Parkinson disease

A global isotopic labeling strategy combined with multidimensional liquid chromatographies and tandem mass spectrometry was used for quantitative proteome analysis of a presymptomatic A53T alpha-synuclein Drosophila model of Parkinson disease (PD). Multiple internal standard proteins at different concentration ratios were spiked into samples from PD-like and control animals to assess quantification accuracy. Two biological replicates isotopically labeled in forward and reverse directions were analyzed. A total of 253 proteins were quantified with a minimum of two identified peptide sequences (for each protein); 180 ( approximately 71%) proteins were detected in both forward and reverse labeling measurements. Twenty-four proteins were differentially expressed in A53T alpha-synuclein Drosophila; up-regulation of troponin T and down-regulation of fat body protein 1 were confirmed by Western blot analysis. Elevated expressions of heat shock protein 70 cognate 3 and ATP synthase are known to be directly involved in A53T alpha-synuclein-mediated toxicity and PD; three up-regulated proteins (muscle LIM protein at 60A, manganese-superoxide dismutase, and troponin T) and two down-regulated proteins (chaoptin and retinal degeneration A) have literature-supported associations with cellular malfunctions. That these variations were observed in presymptomatic animals may shed light on the etiology of PD. Protein interaction network analysis indicated that seven proteins belong to a single network, which may provide insight into molecular pathways underlying PD. Gene Ontology analysis indicated that the dysregulated proteins are primarily associated with membrane, endoplasmic reticulum, actin cytoskeleton, mitochondria, and ribosome. These associations support prior findings in studies of the A30P alpha-synuclein Drosophila model (Xun, Z. Y., Sowell, R. A., Kaufman, T. C., and Clemmer, D. E. (2007) Protein expression in a Drosophila model of Parkinson's disease. J. Proteome Res. 6, 348-357; Xun, Z. Y., Sowell, R. A., Kaufman, T. C., and Clemmer, D. E. (2007) Lifetime proteomic profiling of an A30P alpha-synuclein Drosophila model of Parkinson's disease. J. Proteome Res. 6, 3729-3738) that defects in cellular components such as actin cytoskeleton and mitochondria may contribute to the development of later symptoms.

Variation in the miRNA-433 binding site of FGF20 confers risk for Parkinson disease by overexpression of alpha-synuclein

Parkinson disease (PD) is a common neurodegenerative disorder caused by environmental and genetic factors. We have previously shown linkage of PD to chromosome 8p. Subsequently, fibroblast growth factor 20 (FGF20) at 8p21.3-22 was identified as a risk factor in several association studies. To identify the risk-conferring polymorphism in FGF20, we performed genetic and functional analysis of single-nucleotide polymorphisms within the gene. In a sample of 729 nuclear families with 1089 affected and 1165 unaffected individuals, the strongest evidence of association came from rs12720208 in the 3' untranslated region of FGF20. We show in several functional assays that the risk allele for rs12720208 disrupts a binding site for microRNA-433, increasing translation of FGF20 in vitro and in vivo. In a cell-based system and in PD brains, this increase in translation of FGF20 is correlated with increased alpha-synuclein expression, which has previously been shown to cause PD through both overexpression and point mutations. We suggest a novel mechanism of action for PD risk in which the modulation of the susceptibility gene's translation by common variations interfere with the regulation mechanisms of microRNA. We propose this is likely to be a common mechanism of genetic modulation of individual susceptibility to complex disease.

Generation of a alpha-synuclein-based rat model of Parkinson's disease

Two missense mutations (A30P and A53T) in the gene for alpha-synuclein (alpha-syn) cause familial Parkinson's disease (PD) in a small cohort. There is increasing evidence to propose that abnormal metabolism and accumulation of alpha-syn in dopaminergic neurons play a role in the development of familial as well as sporadic PD. The complexity of the mechanisms underlying alpha-syn-induced neurotoxicity, however, has made difficult the development of animal models that faithfully reproduce human PD pathology. We now describe and characterize such a model, which is based on the stereotaxic injection into rat right substantia nigra pars compacta of the A30P mutated form of alpha-syn fused to a protein transduction domain (TAT). The TAT sequence allows diffusion of the fusion protein across the neuronal plasma membrane and results in a localized dopaminergic loss. Dopaminergic cell loss was evaluated both by tyrosine hydroxylase immunohistochemistry and by HPLC analysis of dopamine and its catabolite 3,4 dihydroxyphenylacetic acid. Infusion of TAT-alpha-synA30P induced a significant 26% loss in dopaminergic neurons. This dopaminergic loss was accompanied by a time-dependent impairment in motor function, evaluated utilizing the rotarod and footprint tests. In comparison to chemical neurotoxin-based (e.g. 6-hyroxydopamine, MPTP) animal models of PD, the alpha-syn-based PD animal model offers the advantage of mimicking the early stages and slow development of the human disease and should prove valuable in assessing specific aspects of PD pathogenesis in vivo and in developing new therapeutic strategies.

Microglial PHOX and Mac-1 are essential to the enhanced dopaminergic neurodegeneration elicited by A30P and A53T mutant alpha-synuclein

alpha-Synuclein, a gene whose mutations, duplication, and triplication has been linked to autosomal dominant familial Parkinson's disease (fPD), appears to play a central role in the pathogenesis of sporadic PD (sPD) as well. Enhancement of neurodegeneration induced by mutant alpha-synuclein has been attributed to date largely to faster formation of alpha-synuclein aggregates in neurons. Recently, we reported that microglial activation enhances wild type (WT) alpha-synuclein-elicited dopaminergic neurodegeneration. In the present study, using a primary mesencephalic culture system, we tested whether mutated alpha-synuclein could activate microglia more powerfully than WT alpha-synuclein, thereby contributing to the accelerated neurodegeneration observed in fPD. The results showed that alpha-synuclein with the A30P or A53T mutations caused greater microglial activation than WT alpha-synuclein. Furthermore, the extent of microglial activation paralleled the degree of dopaminergic neurotoxicity induced by WT and mutant alpha-synuclein. Mutant alpha-synuclein also induced greater production of reactive oxygen species than WT alpha-synuclein by NADPH oxidase (PHOX), and PHOX activation was linked to direct activation of macrophage antigen-1 (Mac-1) receptor, rather than alpha-synuclein internalization via scavenger receptors. These results have, for the first time, demonstrated that microglia are also critical in enhanced neurotoxicity induced by mutant alpha-synuclein.

Lifetime Proteomic Profiling of an A30P α-SynucleinDrosophilaModel of Parkinson's Disease

A survey of the proteome changes in an A30P alpha-synuclein Drosophila model of Parkinson's disease (PD) in comparison to age-matched controls is presented for seven different ages across the adult lifespan. The data were acquired by a shotgun proteomic approach that involves multidimensional liquid chromatographies coupled to mass spectrometry and database searching techniques. Semiquantitative analysis to assess relative changes in protein expression between the Drosophila PD model and age-matched controls provides evidence that 28, 19, 12, 5, 7, 23, and 17 proteins are significantly differentially expressed at days 1, 10, 20, 30, 40, 50, and 60, respectively. From the experimental approach employed, it appears that most dysregulated proteins are associated with narrow distributions of ages, such that disease-associated differences change substantially across the lifespan. Previous measurements [J. Proteome Res. 2007, 6, 348] at days 1, 10, and 30 showed dysregulation of actin cytoskeletal proteins at day 1 and mitochondrial proteins at day 10, suggesting that defects in the actin cytoskeleton and the mitochondria are associated with dopaminergic neuron degeneration in PD. Analysis of the day 20, 40, 50, and 60 animals supports the finding that these cytoskeletal and mitochondrial changes predominate in the youngest (pre-symtomatic and early disease stages) animals. Although studies across many time points appear to be important for characterizing disease state, an understanding of molecular changes at the youngest ages should be most important for addressing causation.

Investigation of alpha-synuclein fibril structure by site-directed spin labeling

The misfolding and fibril formation of alpha-synuclein plays an important role in neurodegenerative diseases such as Parkinson disease. Here we used electron paramagnetic resonance spectroscopy, together with site-directed spin labeling, to investigate the structural features of alpha-synuclein fibrils. We generated fibrils from a total of 83 different spin-labeled derivatives and observed single-line, exchange-narrowed EPR spectra for the majority of all sites located within the core region of alpha-synuclein fibrils. Such exchange narrowing requires the orbital overlap between multiple spin labels in close contact. The core region of alpha-synuclein fibrils must therefore be arranged in a parallel, in-register structure wherein same residues from different molecules are stacked on top of each other. This parallel, in-register core region extends from residue 36 to residue 98 and is tightly packed. Only a few sites within the core region, such as residues 62-67 located at the beginning of the NAC region, as well as the N- and C-terminal regions outside the core region, are significantly less ordered. Together with the accessibility measurements that suggest the location of potential beta-sheet regions within the fibril, the data provide significant structural constraints for generating three-dimensional models. Furthermore, the data support the emerging view that parallel, in-register structure is a common feature shared by a number of naturally occurring amyloid fibrils.

Novel rat Alzheimer's disease models based on AAV-mediated gene transfer to selectively increase hippocampal Abeta levels

Background

Alzheimer's disease (AD) is characterized by a decline in cognitive function and accumulation of amyloid-β peptide (Aβ) in extracellular plaques. Mutations in amyloid precursor protein (APP) and presenilins alter APP metabolism resulting in accumulation of Aβ42, a peptide essential for the formation of amyloid deposits and proposed to initiate the cascade leading to AD. However, the role of Aβ40, the more prevalent Aβ peptide secreted by cells and a major component of cerebral Aβ deposits, is less clear. In this study, virally-mediated gene transfer was used to selectively increase hippocampal levels of human Aβ42 and Aβ40 in adult Wistar rats, allowing examination of the contribution of each to the cognitive deficits and pathology seen in AD.

Results

Adeno-associated viral (AAV) vectors encoding BRI-Aβ cDNAs were generated resulting in high-level hippocampal expression and secretion of the specific encoded Aβ peptide. As a comparison the effect of AAV-mediated overexpression of APPsw was also examined. Animals were tested for development of learning and memory deficits (open field, Morris water maze, passive avoidance, novel object recognition) three months after infusion of AAV. A range of impairments was found, with the most pronounced deficits observed in animals co-injected with both AAV-BRI-Aβ40 and AAV-BRI-Aβ42. Brain tissue was analyzed by ELISA and immunohistochemistry to quantify levels of detergent soluble and insoluble Aβ peptides. BRI-Aβ42 and the combination of BRI-Aβ40+42 overexpression resulted in elevated levels of detergent-insoluble Aβ. No significant increase in detergent-insoluble Aβ was seen in the rats expressing APPsw or BRI-Aβ40. No pathological features were noted in any rats, except the AAV-BRI-Aβ42 rats which showed focal, amorphous, Thioflavin-negative Aβ42 deposits.

Conclusion

The results show that AAV-mediated gene transfer is a valuable tool to model aspects of AD pathology in vivo, and demonstrate that whilst expression of Aβ42 alone is sufficient to initiate Aβ deposition, both Aβ40 and Aβ42 may contribute to cognitive deficits.

Anti-fibrillogenic and fibril-destabilizing activity of nicotine in vitro: Implications for the prevention and therapeutics of Lewy body diseases

The aggregation of alpha-synuclein (alphaS) has been implicated as a critical step in the development of Lewy body diseases (LBD) and multiple system atrophy (MSA). Both retrospective and prospective epidemiological studies have consistently demonstrated an inverse association between cigarette smoking and Parkinson's disease (PD). We used fluorescence spectroscopy with thioflavin S, electron microscopy and atomic force microscopy to examine the effects of nicotine, pyridine, and N-methylpyrrolidine on the formation of alphaS fibrils (f alphaS) from wild-type alphaS (alphaS (WT)) and A53T mutant alphaS (A53T) and on preformed f alpha Ss. Nicotine dose-dependently inhibited the f alphaS formation from both alphaS (WT) and A53T. Moreover, nicotine dose-dependently destabilized preformed f alpha Ss. These effects of nicotine were similar to those of N-methylpyrrolidine. The anti-fibrillogenic activity of nicotine may be exerted not only by the inhibition of f alphaS formation but also by the destabilization of preformed f alphaS. Additionally, this effect may be attributed to N-methylpyrrolidine moieties of nicotine.

Assembly of lysine 63-linked ubiquitin conjugates by phosphorylated alpha-synuclein implies Lewy body biogenesis

alpha-Synuclein (alpha-syn) and ubiquitin (Ub) are major protein components deposited in Lewy bodies (LBs) and Lewy neurites, which are pathologic hallmarks of idiopathic Parkinson disease (PD). Almost 90% of alpha-syn in LBs is phosphorylated at serine 129 (Ser(129)). However, the role of Ser(129)-phosphorylated alpha-syn in the biogenesis of LBs remains unclear. Here, we show that compared with coexpression of wild type (WT)alpha-syn and Ub, coexpression of phospho-mimic mutant alpha-syn (S129D) and Ub in neuro2a cells results in an increase of Ub-conjugates and the formation of ubiquitinated inclusions. Furthermore, S129D alpha-syn fails to increase the Ub-conjugates and form ubiquitinated inclusions in the presence of a K63R mutant Ub. In addition, as compared with WT alpha-syn, S129D alpha-syn increased cytoplasmic and neuritic aggregates of itself in neuro2a cells treated with H(2)O(2) and serum deprivation. These results suggest that the contribution of Ser(129)-phosphorylated alpha-syn to the Lys(63)-linked Ub-conjugates and aggregation of itself may be involved in the biogenesis of LBs in Parkinson disease and other related synucleinopathies.

Effect of oculopharyngeal muscular dystrophy-associated extension of seven alanines on the fibrillation properties of the N-terminal domain of PABPN1

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant disease that usually manifests itself within the fifth decade. The most prominent symptoms are progressive ptosis, dysphagia, and proximal limb muscle weakness. The disorder is caused by trinucleotide (GCG) expansions in the N-terminal part of the poly(A)-binding protein 1 (PABPN1) that result in the extension of a 10-alanine segment by up to seven more alanines. In patients, biopsy material displays intranuclear inclusions consisting primarily of PABPN1. Poly l-alanine-dependent fibril formation was studied using the recombinant N-terminal domain of PABPN1. In the case of the protein fragment with the expanded poly l-alanine sequence [N-(+7)Ala], fibril formation could be induced by low amounts of fragmented fibrils serving as seeds. Besides homologous seeds, seeds derived from fibrils of the wild-type fragment (N-WT) also accelerated fibril formation of N-(+7)Ala in a concentration-dependent manner. Seed-induced fibrillation of N-WT was considerably slower than that of N-(+7)Ala. Using atomic force microscopy, differences in fibril morphologies between N-WT and N-(+7)Ala were detected. Furthermore, fibrils of N-WT showed a lower resistance against solubilization with the chaotropic agent guanidinium thiocyanate than those from N-(+7)Ala. Our data clearly reveal biophysical differences between fibrils of the two variants that are likely caused by divergent fibril structures.

Over-expression of alpha-synuclein in human neural progenitors leads to specific changes in fate and differentiation

Missense mutations and extra copies of the alpha-Synuclein gene result in Parkinson disease (PD). Human stem and progenitor cells can be expanded from embryonic tissues and provide a source of non-transformed neural cells to explore the effects of these pathogenic mutations specifically in human nervous tissue. We over-expressed the wild type, A53T and A30P forms of alpha-synuclein in expanded populations of progenitors derived from the human fetal cortex. The protein localized in the nucleus and around microvesicles. Only the A53T form was acutely toxic, suggesting a unique vulnerability of these progenitors to this mutation. Interestingly, constitutive over-expression of wild-type alpha-synuclein progressively impaired the innate ability of progenitors to switch toward gliogenesis at later passages. To explore the effect of alpha-synuclein on neuronal subtypes selectively affected in PD, such as dopaminergic neurons, alpha-synuclein and its mutations were also over-expressed in terminally differentiating neuroectodermal cultures derived from human embryonic stem cells (hESC). Alpha-synuclein induced acute cytotoxicity and reduced the number of neurons expressing either tyrosine hydroxylase or gamma-aminobutyric acid over time. Consistent with the selective vulnerability of ventral midbrain dopaminergic neurons, alpha-synuclein cytotoxicity appeared most pronounced following FGF8/SHH specification and was decreased by inhibition of dopamine synthesis. Together, these data show that alpha-synuclein over-expressed in human neural embryonic cells results in patterns of degeneration that in some cases match features of Parkinson Disease. Thus, neural cells derived from hESC provide a useful model system to understand the development of alpha-synuclein-related pathologies and allow therapeutic drug screening.

Long-term consequences of human alpha-synuclein overexpression in the primate ventral midbrain

Overexpression of human alpha-synuclein (alpha-syn) using recombinant adeno-associated viral (rAAV) vectors provides a novel tool to study neurodegenerative processes seen in Parkinson's disease and other synucleinopathies. We used a pseudotyped rAAV2/5 vector to express human wild-type (wt) alpha-syn, A53T mutated alpha-syn, or the green fluorescent protein (GFP) in the primate ventral midbrain. Twenty-four adult common marmosets (Callithrix jacchus) were followed with regular behavioural tests for 1 year after transduction. alpha-Syn overexpression affected motor behaviour such that all animals remained asymptomatic for at least 9 weeks, then motor bias comprising head position bias and full body rotations were seen in wt-alpha-syn expressing animals between 15 and 27 weeks; in the later phase, the animals overexpressing the A53T alpha -syn, in particular, showed a gradual worsening of motor performance, with increased motor coordination errors. Histological analysis from animals overexpressing either the wt or A53T alpha -syn showed prominent degeneration of dopaminergic fibres in the striatum. In the ventral midbrain, however, the dopaminergic neurodegeneration was more prominent in the A53T group than in the WT group suggesting differential toxicity of these two proteins in the primate brain. The surviving cell bodies and their processes in the substantia nigra were stained by antibodies to the pathological form of alpha-syn that is phosphorylated at Ser position 129. Moreover, we found, for the first time, ubiquitin containing aggregates after overexpression of alpha-syn in the primate midbrain. There was also a variable loss of oligodendroglial cells in the cerebral peduncle. These histological and behavioural data suggest that this model provides unique opportunities to study progressive neurodegeneration in the dopaminergic system and deposition of alpha-syn and ubiquitin similar to that seen in Parkinson's disease, and to test novel therapeutic targets for neuroprotective strategies.

Dopaminergic neuron loss and up-regulation of chaperone protein mRNA induced by targeted over-expression of alpha-synuclein in mouse substantia nigra

Several transgenic mouse lines with altered alpha-synuclein expression have been developed that show a variety of Parkinson's disease-like symptoms without specific loss of dopaminergic neurons. Targeted over-expression of human alpha-synuclein using viral-vector mediated gene delivery into the substantia nigra of rats and non-human primates leads to dopaminergic cell loss and the formation of alpha-synuclein aggregates reminiscent of Lewy bodies. In the context of these recent findings, we used adeno-associated virus (AAV) to over-express wild type human alpha-synuclein in the substantia nigra of mice. We hypothesized that this over-expression would recapitulate pathological hallmarks of Parkinson's disease, creating a mouse model to further characterize the disease pathogenesis. Recombinant AAV expressing alpha-synuclein was stereotaxically injected into the substantia nigra of mice, leading to a 25% reduction of dopaminergic neurons after 24 weeks of transduction. Furthermore, examination of mRNA levels of stress-related proteins using laser capture microdissection and quantitative PCR revealed a positive correlation of Hsp27 expression with the extent of viral transduction at 4 weeks and a positive correlation of Hsp40, Hsp70 and caspase 9 with the extent of viral transduction at 24 weeks. Taken together, our findings suggest that targeted over-expression of alpha-synuclein can induce pathology at the gross anatomical and molecular level in the substantia nigra, providing a mouse model in which upstream changes in Parkinson's disease pathogenesis can be further elucidated.

Nonhuman Primate Models of Parkinson's Disease

Nonhuman primate (NHP) models of Parkinson's disease (PD) play an essential role in the understanding of PD pathophysiology and the assessment of PD therapies. NHP research enabled the identification of environmental risk factors for the development of PD. Electrophysiological studies in NHP models of PD identified the neural circuit responsible for PD motor symptoms, and this knowledge led to the development of subthalamic surgical ablation and deep brain stimulation. Similar to human PD patients, parkinsonian monkeys are responsive to dopamine replacement therapies and present complications associated with their long-term use, a similarity that facilitated the assessment of new symptomatic treatments, such as dopaminergic agonists. New generations of compounds and novel therapies that use directed intracerebral delivery of drugs, cells, and viral vectors benefit from preclinical evaluation in NHP models of PD. There are several NHP models of PD, each with characteristics that make it suitable for the study of different aspects of the disease or potential new therapies. Investigators who use the models and peer scientists who evaluate their use need information about the strengths and limitations of the different PD models and their methods of evaluation. This article provides a critical review of available PD monkey models, their utilization, and how they compare to emerging views of PD as a multietiologic, multisystemic disease. The various models are particularly useful for representing different aspects of PD at selected time points. This conceptualization provides clues for the development of new NHP models and facilitates the clinical translation of findings. As ever, successful application of any model depends on matching the model to the scientific question to be answered. Adequate experimental designs, with multiple outcome measures of clinical relevance and an appropriate number of animals, are essential to minimize the limitations of models and increase their predictive clinical validity.

Impairment of microtubule-dependent trafficking by overexpression of α-synuclein

Abnormal accumulation of alpha-synuclein (alpha-syn) has been linked to several neurological disorders, including Parkinson's disease (PD). However, the underlying mechanism by which alpha-syn accumulation affects neuronal function and survival remains unknown. Here, we provide data suggesting a possible effect of aggregated alpha-syn on the microtubule (MT) network. Consistent with the MT dysfunction, we also observed other degenerative changes, such as neuritic degeneration, trafficking defects, and Golgi fragmentation, which are common pathological features shared by many human neurodegenerative diseases. Neuritic degeneration and Golgi fragmentation were confirmed in primary cultures of dorsal root ganglia (DRG) neurons overexpressing alpha-syn. This effect of alpha-syn seems to have some selectivity to the MT system, as actin microfilaments and MT-independent trafficking remain unaffected. Within the degenerating neurites, we found numerous spherical co-aggregates of alpha-syn and tubulins, from which actin was excluded. These studies suggest that the MT system is a potential target of alpha-syn, and impairment of this system might have impacts on neuronal structure and function.

Neuronal specificity of alpha-synuclein toxicity and effect of Parkin co-expression in primates

Recombinant adeno-associated viral (rAAV) vector-mediated overexpression of alpha-synuclein (alphaSyn) protein has been shown to cause neurodegeneration of the nigrostriatal dopaminergic pathway in rodents and primates. Using serotype-2 rAAV vectors, we recently reported the protective effect of Parkin on alphaSyn-induced nigral dopaminergic neurodegeneration in a rat model. Here we investigated the neuronal specificity of alphaSyn toxicity and the effect of Parkin co-expression in a primate model. We used another serotype (type-1) of AAV vector that was confirmed to deliver genes of interest anterogradely and retrogradely to neurons in rats. The serotype-1 rAAV (rAAV1) carrying alphaSyn cDNA (rAAV1-alphaSyn), and a cocktail of rAAV1-alphaSyn and rAAV1 carrying parkin cDNA (rAAV1-parkin) were unilaterally injected into the striatum of macaque monkeys, resulting in protein expression in striatonigral GABAergic and nigrostriatal dopaminergic neurons. Injection of rAAV1-alphaSyn alone decreased tyrosine hydroxylase immunoreactivity in the striatum compared with the contralateral side injected with a cocktail of rAAV1-alphaSyn and rAAV1-parkin. Immunostaining of striatonigral GABAergic neurons was similar on both sides. Overexpression of Parkin in GABAergic neurons was associated with less accumulation of alphaSyn protein and/or phosphorylation at Ser129 residue. Our results suggest that the toxicity of accumulated alphaSyn is not induced in non-dopaminergic neurons and that the alphaSyn-ablating effect of Parkin is exerted in virtually all neurons in primates.

Neuropeptide gene therapy for epilepsy: viral vectors, stem cells and neurogenesis

Gene therapy for epilepsy is a relatively novel concept compared with previous approaches, which have relied on primary embryonic cells to deliver gene products of interest into localized brain regions. In vivo and ex vivo gene transfer offer promising, but yet insufficiently explored, possibilities to inhibit seizures, either by genetically modifying postmitotic neurons of the brain using viral vectors, or by transplanting genetically modified and in vitro tested cell lines, particularly stem cell lines, to produce and release gene products of interest. In this regard, neuropeptides are discussed as emerging candidates for such gene therapy approaches. Selective modification of newly generated neurons in the dentate gyrus by retroviral vector-based gene delivery opens novel possibilities in gene therapy for epilepsy. However, the limited number of new neurons targeted remains a main obstacle. Despite its early stage, gene therapy for epilepsy might not be a remote prospect for clinical trials, particularly in patients with intractable temporal lobe epilepsy. Ex vivo gene transfer using encapsulated genetically modified cells could be of particular value for such initial trials.