Vaccination for Parkinson's disease

Inhibition of Protein Aggregation and Endoplasmic Reticulum Stress as a Targeted Therapy for α-Synucleinopathy

α-synuclein (α-syn) is an intrinsically disordered protein abundant in the central nervous system. Physiologically, the protein regulates vesicle trafficking and neurotransmitter release in the presynaptic terminals. Pathologies related to misfolding and aggregation of α-syn are referred to as α-synucleinopathies, and they constitute a frequent cause of neurodegeneration. The most common α-synucleinopathy, Parkinson's disease (PD), is caused by abnormal accumulation of α-syn in the dopaminergic neurons of the midbrain. This results in protein overload, activation of endoplasmic reticulum (ER) stress, and, ultimately, neural cell apoptosis and neurodegeneration. To date, the available treatment options for PD are only symptomatic and rely on dopamine replacement therapy or palliative surgery. As the prevalence of PD has skyrocketed in recent years, there is a pending issue for development of new disease-modifying strategies. These include anti-aggregative agents that target α-syn directly (gene therapy, small molecules and immunization), indirectly (modulators of ER stress, oxidative stress and clearance pathways) or combine both actions (natural compounds). Herein, we provide an overview on the characteristic features of the structure and pathogenic mechanisms of α-syn that could be targeted with novel molecular-based therapies.

Pathological mechanisms of neuroimmune response and multitarget disease-modifying therapies of mesenchymal stem cells in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the degeneration of dopaminergic neurons in the substantia nigra (SN); the etiology and pathological mechanism of the disease are still unclear. Recent studies have shown that the activation of a neuroimmune response plays a key role in the development of PD. Alpha-synuclein (α-Syn), the primary pathological marker of PD, can gather in the SN and trigger a neuroinflammatory response by activating microglia which can further activate the dopaminergic neuron's neuroimmune response mediated by reactive T cells through antigen presentation. It has been shown that adaptive immunity and antigen presentation processes are involved in the process of PD and further research on the neuroimmune response mechanism may open new methods for its prevention and therapy. While current therapeutic regimens are still focused on controlling clinical symptoms, applications such as immunoregulatory strategies can delay the symptoms and the process of neurodegeneration. In this review, we summarized the progression of the neuroimmune response in PD based on recent studies and focused on the use of mesenchymal stem cell (MSC) therapy and challenges as a strategy of disease-modifying therapy with multiple targets.

Alpha-synuclein Immunization Strategies for Synucleinopathies in Clinical Studies: A Biological Perspective

The therapeutic strategies currently available for neurodegenerative diseases such as Parkinson's disease target only the symptoms of the disease. Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy can be summarized as synucleinopathies, as they are all characterized by the aggregation and accumulation of alpha-synuclein (α-syn) in the brain. Targeting α-syn by its formation and progression opens a new and promising disease-modifying therapeutic strategy. Thus, several distinct immunotherapeutic approaches are currently being evaluated in clinical trials. The objective of this article is to review, from a biological perspective, the most important properties of these passive and active immunotherapies to point out their relevance and suitability for the treatment of synucleinopathies.

Efficacy and immunogenicity of MultiTEP-based DNA vaccines targeting human α-synuclein: prelude for IND enabling studies

Accumulation of misfolded proteins such as amyloid-β (Aβ), tau, and α-synuclein (α-Syn) in the brain leads to synaptic dysfunction, neuronal damage, and the onset of relevant neurodegenerative disorder/s. Dementia with Lewy bodies (DLB) and Parkinson's disease (PD) are characterized by the aberrant accumulation of α-Syn intracytoplasmic Lewy body inclusions and dystrophic Lewy neurites resulting in neurodegeneration associated with inflammation. Cell to cell propagation of α-Syn aggregates is implicated in the progression of PD/DLB, and high concentrations of anti-α-Syn antibodies could inhibit/reduce the spreading of this pathological molecule in the brain. To ensure sufficient therapeutic concentrations of anti-α-Syn antibodies in the periphery and CNS, we developed four α-Syn DNA vaccines based on the universal MultiTEP platform technology designed especially for the elderly with immunosenescence. Here, we are reporting on the efficacy and immunogenicity of these vaccines targeting three B-cell epitopes of hα-Syn aa85-99 (PV-1947D), aa109-126 (PV-1948D), aa126-140 (PV-1949D) separately or simultaneously (PV-1950D) in a mouse model of synucleinopathies mimicking PD/DLB. All vaccines induced high titers of antibodies specific to hα-Syn that significantly reduced PD/DLB-like pathology in hα-Syn D line mice. The most significant reduction of the total and protein kinase resistant hα-Syn, as well as neurodegeneration, were observed in various brain regions of mice vaccinated with PV-1949D and PV-1950D in a sex-dependent manner. Based on these preclinical data, we selected the PV-1950D vaccine for future IND enabling preclinical studies and clinical development.

Parkinson Disease: Translating Insights from Molecular Mechanisms to Neuroprotection

Parkinson disease (PD) used to be considered a nongenetic condition. However, the identification of several autosomal dominant and recessive mutations linked to monogenic PD has changed this view. Clinically manifest PD is then thought to occur through a complex interplay between genetic mutations, many of which have incomplete penetrance, and environmental factors, both neuroprotective and increasing susceptibility, which variably interact to reach a threshold over which PD becomes clinically manifested. Functional studies of PD gene products have identified many cellular and molecular pathways, providing crucial insights into the nature and causes of PD. PD originates from multiple causes and a range of pathogenic processes at play, ultimately culminating in nigral dopaminergic loss and motor dysfunction. An in-depth understanding of these complex and possibly convergent pathways will pave the way for therapeutic approaches to alleviate the disease symptoms and neuroprotective strategies to prevent disease manifestations. This review is aimed at providing a comprehensive understanding of advances made in PD research based on leveraging genetic insights into the pathogenesis of PD. It further discusses novel perspectives to facilitate identification of critical molecular pathways that are central to neurodegeneration that hold the potential to develop neuroprotective and/or neurorestorative therapeutic strategies for PD. SIGNIFICANCE STATEMENT: A comprehensive review of PD pathophysiology is provided on the complex interplay of genetic and environmental factors and biologic processes that contribute to PD pathogenesis. This knowledge identifies new targets that could be leveraged into disease-modifying therapies to prevent or slow neurodegeneration in PD.

Parkinson's disease in women: Mechanisms underlying sex differences

Parkinson's disease is a neurodegenerative disease which is associated with different motor, cognitive and mood-related problems. Though it has been established that Parkinson's disease is less prevalent in women in comparison to men, the differences tend to diminish with the advancing age. Different genetic, hormonal, neuroendocrinal and molecular players contribute towards the differences in the Parkinson's disease pathogenesis. Furthermore, data available with respect to the therapeutic management of Parkinson's disease in females is limited; women often tend to suffer more from the side effects of the currently available drugs. The present review highlights the sex-specific differences which play a role in the manifestation of these symptoms and side effects of the currently available therapeutic strategies. We have also discussed the current and upcoming therapeutic strategies which are in the clinical trials such as adenosine 2A (A2A) receptor antagonists, estrogen replacement therapy, α-synuclein targeting vaccines and antibodies, Botulinum toxin A, Fas-associated factor-1 (FAF-1) inhibitors, thiazolidinediones, 5-HT1_A receptor agonists, dopamine D1/D5 receptor agonists, Glucagon-like peptide 1 (GLP-1) analogues and certain plant based principles for the treatment of Parkinson's disease in women.

Targeting α-synuclein by PD03 AFFITOPE® and Anle138b rescues neurodegenerative pathology in a model of multiple system atrophy: clinical relevance

Background

Misfolded oligomeric α-synuclein plays a pivotal role in the pathogenesis of α-synucleinopathies including Parkinson’s disease and multiple system atrophy, and its detection parallels activation of microglia and a loss of neurons in the substantia nigra pars compacta. Here we aimed to analyze the therapeutic efficacy of PD03, a new AFFITOPE® immunotherapy approach, either alone or in combination with Anle138b, in a PLP-α-syn mouse model.

Methods

The PLP-α-syn mice were treated with PD03 immunotherapy, Anle138b, or a combination of two. Five months after study initiation, the mice underwent behavioral testing and were sacrificed for neuropathological analysis. The treatment groups were compared to the vehicle group with regard to motor performance, nigral neuronal loss, microglial activation and α-synuclein pathology.

Results

The PLP-α-syn mice receiving the PD03 or Anle138b single therapy showed improvement of gait deficits and preservation of nigral dopaminergic neurons associated with the reduced α-synuclein oligomer levels and decreased microglial activation. The combined therapy with Anle138b and PD03 resulted in lower IgG binding in the brain as compared to the single immunotherapy with PD03.

Conclusions

PD03 and Anle138b can selectively target oligomeric α-synuclein, resulting in attenuation of neurodegeneration in the PLP-α-syn mice. Both approaches are potential therapies that should be developed further for disease modification in α-synucleinopathies.

Immunotherapies for Aging-Related Neurodegenerative Diseases-Emerging Perspectives and New Targets

Neurological disorders such as Alzheimer's disease (AD), Lewy body dementia (LBD), frontotemporal dementia (FTD), and vascular dementia (VCID) have no disease-modifying treatments to date and now constitute a dementia crisis that affects 5 million in the USA and over 50 million worldwide. The most common pathological hallmark of these age-related neurodegenerative diseases is the accumulation of specific proteins, including amyloid beta (Aβ), tau, α-synuclein (α-syn), TAR DNA-binding protein 43 (TDP43), and repeat-associated non-ATG (RAN) peptides, in the intra- and extracellular spaces of selected brain regions. Whereas it remains controversial whether these accumulations are pathogenic or merely a byproduct of disease, the majority of therapeutic research has focused on clearing protein aggregates. Immunotherapies have garnered particular attention for their ability to target specific protein strains and conformations as well as promote clearance. Immunotherapies can also be neuroprotective: by neutralizing extracellular protein aggregates, they reduce spread, synaptic damage, and neuroinflammation. This review will briefly examine the current state of research in immunotherapies against the 3 most commonly targeted proteins for age-related neurodegenerative disease: Aβ, tau, and α-syn. The discussion will then turn to combinatorial strategies that enhance the effects of immunotherapy against aggregating protein, followed by new potential targets of immunotherapy such as aging-related processes.

Parkinson disease and the immune system - associations, mechanisms and therapeutics

Multiple lines of evidence indicate that immune system dysfunction has a role in Parkinson disease (PD); this evidence includes clinical and genetic associations between autoimmune disease and PD, impaired cellular and humoral immune responses in PD, imaging evidence of inflammatory cell activation and evidence of immune dysregulation in experimental models of PD. However, the mechanisms that link the immune system with PD remain unclear, and the temporal relationships of innate and adaptive immune responses with neurodegeneration are unknown. Despite these challenges, our current knowledge provides opportunities to develop immune-targeted therapeutic strategies for testing in PD, and clinical studies of some approaches are under way. In this Review, we provide an overview of the clinical observations, preclinical experiments and clinical studies that provide evidence for involvement of the immune system in PD and that help to define the nature of this association. We consider autoimmune mechanisms, central and peripheral inflammatory mechanisms and immunogenetic factors. We also discuss the use of this knowledge to develop immune-based therapeutic approaches, including immunotherapy that targets α-synuclein and the targeting of immune mediators such as inflammasomes. We also consider future research and clinical trials necessary to maximize the potential of targeting the immune system.

Peripheral Immunity, Immunoaging and Neuroinflammation in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder among elderly population, characterized by the progressive degeneration of dopaminergic neurons in the midbrain. To date, exact cause remains unknown and the mechanism of neurons death uncertain. It is typically considered as a disease of central nervous system (CNS). Nevertheless, numerous evidence has been accumulated in several past years testifying undoubtedly about the principal role of neuroinflammation in progression of PD. Neuroinflammation is mainly associated with presence of activated microglia in brain and elevated levels of cytokine levels in CNS. Nevertheless, active participation of immune system as well has been noted, such as, elevated levels of cytokine levels in blood, the presence of auto antibodies, and the infiltration of T cell in CNS. Moreover, infiltration and reactivation of those T cells could exacerbate neuroinflammation to greater neurotoxic levels. Hence, peripheral inflammation is able to prime microglia into pro-inflammatory phenotype, which can trigger stronger response in CNS further perpetuating the on-going neurodegenerative process. In the present review, the interplay between neuroinflammation and the peripheral immune response in the pathobiology of PD will be discussed. First of all, an overview of regulation of microglial activation and neuroinflammation is summarized and discussed. Afterwards, we try to collectively analyze changes that occurs in peripheral immune system of PD patients, suggesting that these peripheral immune challenges can exacerbate the process of neuroinflammation and hence the symptoms of the disease. In the end, we summarize some of proposed immunotherapies for treatment of PD.

Antibodies against alpha-synuclein: tools and therapies

Synucleinopathies including Parkinson's disease, dementia with Lewy bodies and multiple system atrophy are characterized by the abnormal accumulation and propagation of α-synuclein (α-syn) pathology in the central and peripheral nervous system as Lewy bodies or glial cytoplasmic inclusions. Several antibodies against α-syn have been developed since it was first detected as the major component of Lewy bodies and glial cytoplasmic inclusions. Over the years, researchers have generated specific antibodies that alleviate the accumulation of intracellular aggregated α-syn and associated pathology in cellular and preclinical models of synucleinopathies. So far, antibodies have been the first choice as tools for research and diagnosis and currently, a wide variety of antibody fragments have been developed as an alternative to full-length antibodies for increasing its therapeutic usefulness. Recently, conformation specific antibody-based approaches have been found to be promising as therapeutic strategies, both to block α-syn aggregation and ameliorate the resultant cytotoxicity, and as diagnostic tools. In this review, we summarize different α-syn specific antibodies and provide their usefulness in tackling synucleinopathies. This article is part of the Special Issue "Synuclein".

Immune system and new avenues in Parkinson’s disease research and treatment

Parkinson’s disease (PD) is a progressive neurological disorder characterized by degeneration of dopaminergic neurons in the substantia nigra. However, although 200 years have now passed since the primary clinical description of PD by James Parkinson, the etiology and mechanisms of neuronal loss in this disease are still not fully understood. In addition to genetic and environmental factors, activation of immunologic responses seems to have a crucial role in PD pathology. Intraneuronal accumulation of α-synuclein (α-Syn), as the main pathological hallmark of PD, potentially mediates initiation of the autoimmune and inflammatory events through, possibly, auto-reactive T cells. While current therapeutic regimens are mainly used to symptomatically suppress PD signs, application of the disease-modifying therapies including immunomodulatory strategies may slow down the progressive neurodegeneration process of PD. The aim of this review is to summarize knowledge regarding previous studies on the relationships between autoimmune reactions and PD pathology as well as to discuss current opportunities for immunomodulatory therapy.

New Therapeutic Strategies for Lewy Body Dementias

This article reviews current treatment strategies and recent advances for the Lewy body dementias (LBDs). Current available symptom treatment strategies are based on monoaminergic, cholinergic and glutaminergic neurotransmitter systems. Relatively robust evidence exists for cholinesterase inhibitors for cognitive impairment in LBD and in Parkinson's disease for antidepressants, clozapine and recently pimavanserin for psychosis. interpidine (RVT 101) and nelotanserin are currently under investigation. Non-pharmacological interventions, such as cognitive stimulation, physical exercises and neuromodulation strategies, may be useful in Parkinson's disease but have not yet been tested in dementias. Disease-modifying approaches are aimed at preventing, slowing or ameliorating the production, aggregation and deposition of pathological proteins, including immunotherapy targeting α-synuclein and an ongoing trial using ambroxol which increases glucocerebrosidase activity to lower the levels of the protein alpha-synuclein. Other disease-modifying clinical trials are using agents to augment insulin signalling, stem cell therapy, reducing amyloid pathology and gene therapy.

Friend or foe: the dichotomous impact of T cells on neuro-de/re-generation during aging

The interaction between T cells and the central nervous system (CNS) in homeostasis and injury has been recognized being both pathogenic (CD4⁺ T-helper 1 - Th1, Th17 and γδT) and ameliorative (Th2 and regulatory T cells - Tregs). However, in-depth studies aimed to elucidate the precise in the aged microenvironment and the dichotomous role of Tregs have just begun and many aspects remain unclear. This is due, not only to a mutual dependency and reciprocal causation of alterations and diseases between the nervous and T cell immune systems, but also to an inconsistent aging of the two systems, which dynamically changes with CNS injury/recovery and/or aging process. Cellular immune system aging, particularly immunosenescence and T cell aging initiated by thymic involution - sources of chronic inflammation in the elderly (termed inflammaging), potentially induces an acceleration of brain aging and memory loss. In turn, aging of the brain via neuro-endocrine-immune network drives total body systemic aging, including that of the immune system. Therefore, immunotherapeutics including vaccination and “protective autoimmunity” provide promising means to rejuvenate neuro-inflammatory disorders and repair CNS acute injury and chronic neuro-degeneration. We review the current understanding and recent discoveries linking the aging immune system with CNS injury and neuro-degeneration. Additionally, we discuss potential recovery and rejuvenation strategies, focusing on targeting the aging T cell immune system in an effort to alleviate acute brain injury and chronic neuro-degeneration during aging, via the “thymus-inflammaging-neurodegeneration axis”.

The development of biological therapies for neurological diseases: moving on from previous failures

INTRODUCTION

Although years of research have expanded the use of biologics for several clinical conditions, such development has not yet occurred in the treatment of neurological diseases. With the advancement of biologic technologies, there is promise for these therapeutics as novel therapeutic approaches for neurological diseases. Areas covered: In this article, the authors review the therapeutic potential of different types of biologics for the treatment of neurological diseases. Preclinical and clinical studies that investigate the efficacy and safety of biologics in the treatment of neurological diseases, namely Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson disease, multiple sclerosis, and stroke, were reviewed. Moreover, the authors describe the key challenges in the development of therapeutically safe and effective biologics for the treatment of neurological diseases. Expert opinion: Several biologics have shown promise in the treatment of neurological diseases. However, the complexity of the CNS, as well as a limited understanding of disease progression, and restricted access of biologics to the CNS has limited successful development. Therefore, more research needs to be conducted to overcome these hurdles before developing effective and safe biologics for neurological diseases. The emergence of new technologies for the design, production and delivery of biologics will accelerate translating biologics to the clinic.

A novel panel of α-synuclein antibodies reveal distinctive staining profiles in synucleinopathies

Synucleinopathies are a spectrum of neurodegenerative diseases characterized by the intracellular deposition of the protein α-synuclein leading to multiple outcomes, including dementia and Parkinsonism. Recent findings support the notion that across the spectrum of synucleinopathies there exist diverse but specific biochemical modifications and/or structural conformations of α-synuclein, which would give rise to protein strain specific prion-like intercellular transmission, a proposed model that could explain synucleinopathies disease progression. Herein, we characterized a panel of antibodies with epitopes within both the C- and N- termini of α-synuclein. A comprehensive analysis of human pathological tissue and mouse models of synucleinopathy with these antibodies support the notion that α-synuclein exists in distinct modified forms and/or structural variants. Furthermore, these well-characterized and specific tools allow the investigation of biochemical changes associated with α-synuclein inclusion formation. We have identified several antibodies of interest with diverse staining and epitope properties that will prove useful in future investigations of strain specific disease progression and the development of targeted immunotherapeutic approaches to synucleinopathies.

Targets and Mechanisms in Prevention of Parkinson's Disease through Immunomodulatory Treatments

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world; however, there is no cure for it. Current treatments only relieve some of the symptoms, without ceasing the disease, and lose efficacy with prolonged treatment. Considerable evidence shows that persistent inflammatory responses, involving T cell infiltration and glial cell activation, are common characteristics of human patients and play a crucial role in the degeneration of dopaminergic neurons. Therefore, it is important to develop therapeutic strategies that can impede or halt the disease through the modulation of the peripheral immune system by aiming at controlling the existing neuroinflammation. Most of the immunomodulatory therapies designed for the treatment of Parkinson's disease are based on vaccines using AS or antibodies against it; yet, it is of significant interest to explore other formulations that could be used as therapeutic agents. Several vaccination procedures have shown that inducing regulatory T cells in the periphery is protective in PD animal models. In this regard, the formulation glatiramer acetate (Copaxone^® ), extensively used for the treatment of multiple sclerosis, could be a suitable candidate due to its capability to increase the number and suppressor capacity of regulatory T cells. In this review, we will present some of the recent immunomodulatory therapies for PD including vaccinations with AS or glatiramoids, or both, as treatments of PD pathology.

Immunochemical Detection of α-Synuclein Autoantibodies in Parkinson's Disease: Correlation between Plasma and Cerebrospinal Fluid Levels

Autoantibodies to Parkinson's disease (PD) amyloidogenic protein, α-synuclein, were recognized as a prospective biomarker for early disease diagnostics, yet there is inconsistency in previous reports, potentially related to PD status. Therefore, plasma and cerebrospinal fluid (CSF) of the cross-sectional cohort of 60 individuals, including recently diagnosed PD patients with mild and moderate PD and age-matched controls, were examined by enzyme-linked immunosorbent assay (ELISA). Nonparametric statistics was used for data analysis. We found significantly elevated levels of α-synuclein autoantibodies in both plasma and CSF in mild PD compared to controls, followed by some decrease in moderate PD. Receiver operating characteristic and effect size analyses confirmed the diagnostic power of α-synuclein antibodies in both plasma and CSF. For the first time, we showed the correlation between plasma and CSF α-synuclein antibody levels for mild, moderate, and combined PD groups. This indicates the potentiality of α-synuclein antibodies as PD biomarker and the increased diagnostic power of their simultaneous analysis in plasma and CSF.

α-Synuclein aggregation modulation: an emerging approach for the treatment of Parkinson's disease

Parkinson's disease (PD) is a multifactorial progressive neurological disorder. Pathological hallmarks of PD are characterized by the presence of α-synuclein (αSyn) aggregates known as Lewy bodies. αSyn aggregation is one of the leading causes for the neuronal dysfunction and death in PD. It is also associated with neurotransmitter and calcium release. Current therapies of PD are limited to only symptomatic relief without addressing the underlying pathogenic factors of the disease process such as aggregation of αSyn. Consequently, the progression of the disease continues with the current therapies. Therefore, the modulation of αSyn aggregation is an emerging approach as a novel therapeutic target to treat PD. There are two major aspects that might be targeted therapeutically: first, protein is prone to aggregation, therefore, anti-aggregative or compounds that can break the pre-existing aggregates should be helpful. Second, there are number of molecular events that may be targeted to combat the disease.

Sorting out release, uptake and processing of alpha-synuclein during prion-like spread of pathology

Parkinson's disease is a progressive neurological disorder that is characterized by the formation of intracellular protein inclusion bodies composed primarily of a misfolded and aggregated form of the protein α-synuclein. There is growing evidence that supports the prion-like hypothesis of α-synuclein progression. This hypothesis postulates that α-synuclein is a prion-like pathological agent and is responsible for the progression of Parkinson pathology in the brain. Potential misfolding or aggregation of α-synuclein that might occur in the peripheral nervous system as a result of some insult, environmental or genetic (or more likely a combination of both) that might spread into the midbrain, eventually causing degeneration of the neurons in the substantia nigra. As the disease progresses further, it is likely that α-synuclein pathology continues to spread throughout the brain, including the cortex, leading to deterioration of cognition and higher brain functions. While it is unknown why α-synuclein initially misfolds and aggregates, a great deal has been learned about how the cell handles aberrant α-synuclein assemblies. In this review, we focus on these mechanisms and discuss them in an attempt to define the role that they might play in the propagation of misfolded α-synuclein from cell-to-cell. The prion-like hypothesis of α-synuclein pathology suggests a method for the transmission of misfolded α-synuclein from one neuron to another. This hypothesis postulates that misfolded α-synuclein becomes aggregation prone and when released and taken up by neighboring cells, seeds further misfolding and aggregation. In this review we examine the cellular mechanisms that are involved in the processing of α-synuclein and how these may contribute to the prion-like propagation of α-synuclein pathology. This article is part of a special issue on Parkinson disease.

Gene therapy targeting mitochondrial pathway in Parkinson's disease

Parkinson's disease (PD) presents a relative selective localization of pathology to substantia nigra and well-defined motor symptoms caused by dopaminergic degeneration that makes it an ideal target for gene therapy. Parallel progress in viral vector systems enables the delivery of therapeutic genes directly into brain with reasonable safety along with sustained transgene expression. To date, gene therapy for PD that has reached clinical trial evaluation is mainly based on symptomatic approach that involves enzyme replacement strategy and restorative approach that depends on the addition of neurotrophic factors. Mitochondrial dysregulation, such as reduced complex I activity, increased mitochondria-derived reactive oxygen species (ROS) production, ROS-mediated mitochondrial DNA damage, bioenergetic failure, and perturbation of mitochondrial dynamics and mitophagy, has long been implicated in the pathogenesis of PD. Many of mutated genes linked to familial forms of PD affect these mitochondrial features. In this review, we discuss the recent progress that has been made in preclinical development of gene therapy targeting the mitochondrial pathway as disease modifying approach for PD. This review focuses on the potential therapeutic efficacy of candidate genes, including Parkin, PINK1, alpha synuclein, PGC-1 alpha, and anti-apoptotic molecules.

An update on potential therapeutic strategies for Parkinson's disease based on pathogenic mechanisms

INTRODUCTION

Parkinson's disease is a common neurodegenerative disorder mainly caused by the loss of nigral dopaminergic neurons, of which the pathogenesis remains essentially unknown. Current therapeutic strategies help manage signs and symptoms but have no effect in disease modification. Over the past several decades, scientists have devoted a lot of effort to clarifying the pathological mechanism and searching for new targets for Parkinson's disease treatment.

AREAS COVERED

Treatment of Parkinson's disease. Expert Commentary: Illustrated in this review are newly found discoveries and evidence that contribute to the understanding of Parkinson's disease pathogenic mechanism. Also discussed are potential therapeutic strategies that are being studied, including disease-modifying and genetically mediated small molecule compounds, cell- and gene-based therapeutic strategies, immunization strategies and anti-diabetic therapy, which may be very promising therapeutic methods in the future.

Motor and Nonmotor Features of Carriers of the p.A53T Alpha-Synuclein Mutation: A Longitudinal Study

BACKGROUND

G209A SNCA mutation carriers represent an important group of genetic PD. We describe motor and nonmotor features of G209A SNCA mutation carriers.

METHODS

Longitudinal clinical assessments over 2 years were collected in 22 symptomatic and 8 asymptomatic G209A SNCA mutation carriers. Motor and nonmotor rating scales were administered. Correlations were performed between clinical variables and disease duration or age. Penetrance was calculated using Kaplan-Meier survival curves.

RESULTS

Asymptomatic carriers did not manifest clear premotor symptoms, but symptomatic carriers often reported that olfactory dysfunction and rapid eye movement sleep behavior disorder preceded motor symptoms. Prominent motor decline and deterioration of autonomic and cognitive function occurred at follow-up; such nonmotor features correlated with disease duration, but not age. Disease penetrance was estimated at around 90%.

CONCLUSIONS

This study may help to inform clinical trials and provide the basis for studies of disease modifiers in genetic synucleinopathy cohorts. © 2016 International Parkinson and Movement Disorder Society.

Therapeutic approaches in Parkinson's disease and related disorders

The lack of effective therapies for neurodegenerative disorders is one of the most relevant challenges of this century, considering that, as the global population ages, the incidence of these type of diseases is quickly on the rise. Among these disorders, synucleinopathies, which are characterized by the abnormal accumulation and spreading of the synaptic protein alpha-synuclein in the brain, already constitute the second leading cause of parkinsonism and dementia in the elderly population. Disorders with alpha-synuclein accumulation include Parkinson's disease, dementia with Lewy bodies and multiple system atrophy. Numerous therapeutic alternatives for synucleinopathies are being tested in pre-clinical models and in the clinic; however, only palliative treatments addressing the dopaminergic deficits are approved to date, and no disease-modifying options are available yet. In this article, we provide a brief overview of therapeutic approaches currently being explored for synucleinopathies, and suggest possible explanations to the clinical trials outcomes. Finally, we propose that a deeper understanding of the pathophysiology of synucleinopathies, together with a combination of therapies tailored to each disease stage, may lead to better therapeutic outcomes in synucleinopathy patients. Synucleinopathies, neurodegenerative disorders characterized by the abnormal accumulation of the protein alpha-synuclein, constitute the second leading cause of parkinsonism and dementia in the elderly population, however, no disease-modifying options are available yet. In this review, we summarize the therapeutic approaches currently being explored for synucleinopathies, suggest possible explanations to the clinical outcomes, and propose areas of further therapeutic improvement. This article is part of a special issue on Parkinson disease.

Evaluation of an α synuclein sensitized dendritic cell based vaccine in a transgenic mouse model of Parkinson disease

In order to develop a cell-based vaccine against the Parkinson disease (PD) associated protein α-synuclein (α-Syn) 3 peptides were synthesized based upon predicted B cell epitopes within the full length α-Syn protein sequence. These peptide fragments as well as the full length recombinant human α-Syn (rh- α-Syn) protein were used to sensitize mouse bone marrow-derived dendritic cells (DC) ex vivo, followed by intravenous delivery of these sensitized DCs into transgenic (Tg) mice expressing the human A53T variant of α-Syn. ELISA analysis and testing of behavioral locomotor function by rotometry were performed on all mice after the 5th vaccination as well as just prior to euthanasia. The results indicated that vaccination with peptide sensitized DCs (PSDC) as well as DCs sensitized by rh-α-Syn induced specific anti-α-Syn antibodies in all immunized mice. In terms of rotometry performance, a measure of locomotor activity correlated to brain dopamine levels, mice vaccinated with PSDC or rh- α-Syn sensitized DCs performed significantly better than non-vaccinated Tg control mice during the final assessment (i.e. at 17 months of age) before euthanasia. As well, measurement of levels of brain IL-1α, a cytokine hypothesized to be associated with neuroinflammation, demonstrated that this proinflammatory molecule was significantly reduced in the PSDC and rh- α-Syn sensitized DC vaccinated mice compared to the non-vaccinated Tg control group. Overall, α-Syn antigen-sensitized DC vaccination was effective in generating specific anti- α-Syn antibodies and improved locomotor function without eliciting an apparent general inflammatory response, indicating that this strategy may be a safe and effective treatment for PD.

Immunotherapeutic Approaches Targeting Amyloid-β, α-Synuclein, and Tau for the Treatment of Neurodegenerative Disorders

Disease-modifying alternatives are sorely needed for the treatment of neurodegenerative disorders, a group of diseases that afflict approximately 50 million Americans annually. Immunotherapy is one of the most developed approaches in this direction. Vaccination against amyloid-β, α-synuclein, or tau has been extensively explored, specially as the discovery that these proteins may propagate cell-to-cell and be accessible to antibodies when embedded into the plasma membrane or in the extracellular space. Likewise, the use of passive immunization approaches with specific antibodies against abnormal conformations of these proteins has also yielded promising results. The clinical development of immunotherapies for Alzheimer’s disease, Parkinson’s disease, frontotemporal dementia, dementia with Lewy bodies, and other neurodegenerative disorders is a field in constant evolution. Results to date suggest that immunotherapy is a promising therapeutic approach for neurodegenerative diseases that progress with the accumulation and prion-like propagation of toxic protein aggregates. Here we provide an overview of the most novel and relevant immunotherapeutic advances targeting amyloid-β in Alzheimer’s disease, α-synuclein in Alzheimer’s disease and Parkinson’s disease, and tau in Alzheimer’s disease and frontotemporal dementia.

Immunomodulation as a neuroprotective and therapeutic strategy for Parkinson's disease

While immune control is associated with nigrostriatal neuroprotection for Parkinson's disease, direct cause and effect relationships have not yet been realized, and modulating the immune system for therapeutic gain has been openly debated. Here, we review how innate and adaptive immunity affect disease pathobiology, and how each could be harnessed for treatment. The overarching idea is to employ immunopharmacologics as neuroprotective strategies for disease. The aim of the current work is to review disease-modifying treatments that are currently being developed as neuroprotective strategies for PD in experimental animal models and for human disease translation. The long-term goal of this research is to effectively harness the immune system to slow or prevent PD pathobiology.

Active immunization therapies for Parkinson's disease and multiple system atrophy

Vaccination is increasingly being investigated as a potential treatment for synucleinopathies, a group of neurodegenerative diseases including Parkinson's disease, multiple system atrophy, and dementia with Lewy bodies associated with α-synuclein pathology. All lack a causal therapy. Development of novel, disease-altering treatment strategies is urgently needed. Vaccination has positioned itself as a prime strategy for addressing these diseases because it is broadly applicable, requires infrequent administration, and maintains low production costs for treating a large population or as a preventive measure. Current evidence points to a causal role of misfolded α-synuclein in the development and progression of synucleinopathies. In the past decade, significant progress in active immunization against α-synuclein has been shown both in preclinical animal models and in early clinical development. In this review, we describe the state-of-the-art in active immunization approaches to synucleinopathies, with a focus on advances in Parkinson's disease (PD) and multiple-system atrophy (MSA). We first review preclinical animal models, highlighting their progress in translation to the clinical setting. We then discuss current clinical applications, stressing different approaches taken to address α-synuclein pathology. Finally, we address challenges, trends, and future perspectives of current vaccination programs.

Insights into Neuroinflammation in Parkinson's Disease: From Biomarkers to Anti-Inflammatory Based Therapies

Parkinson's disease (PD) is the second most common neurodegenerative disorder worldwide, being characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Among several putative factors that may contribute to PD pathogenesis, inflammatory mechanisms may play a pivotal role. The involvement of microglial activation as well as of brain and peripheral immune mediators in PD pathophysiology has been reported by clinical and experimental studies. These inflammatory biomarkers evaluated by imaging techniques and/or by biological sample analysis have become valuable tools for PD diagnosis and prognosis. Regardless of the significant increase in the number of people suffering from PD, there are still no established disease-modifying or neuroprotective therapies for it. There is growing evidence of protective effect of anti-inflammatory drugs on PD development. Herein, we reviewed the current literature regarding the central nervous system and peripheral immune biomarkers in PD and advances in diagnostic and prognostic tools as well as the neuroprotective effects of anti-inflammatory therapies.

Active immunization against alpha-synuclein ameliorates the degenerative pathology and prevents demyelination in a model of multiple system atrophy

Background

Multiple system atrophy (MSA) is a neurodegenerative disease characterized by parkinsonism, ataxia and dysautonomia. Histopathologically, the hallmark of MSA is the abnormal accumulation of alpha-synuclein (α-syn) within oligodendroglial cells, leading to neuroinflammation, demyelination and neuronal death. Currently, there is no disease-modifying treatment for MSA. In this sense, we have previously shown that next-generation active vaccination technology with short peptides, AFFITOPEs®, was effective in two transgenic models of synucleinopathies at reducing behavioral deficits, α-syn accumulation and inflammation.

Results

In this manuscript, we used the most effective AFFITOPE® (AFF 1) for immunizing MBP-α-syn transgenic mice, a model of MSA that expresses α-syn in oligodendrocytes. Vaccination with AFF 1 resulted in the production of specific anti-α-syn antibodies that crossed into the central nervous system and recognized α-syn aggregates within glial cells. Active vaccination with AFF 1 resulted in decreased accumulation of α-syn, reduced demyelination in neocortex, striatum and corpus callosum, and reduced neurodegeneration. Clearance of α-syn involved activation of microglia and reduced spreading of α-syn to astroglial cells.

Conclusions

This study further validates the efficacy of vaccination with AFFITOPEs® for ameliorating the neurodegenerative pathology in synucleinopathies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-015-0008-9) contains supplementary material, which is available to authorized users.

Biomarkers of Parkinson's disease: present and future

Sporadic or idiopathic Parkinson's disease (PD) is an age-related neurodegenerative disorder of unknown origin that ranks only second behind Alzheimer's disease (AD) in prevalence and its consequent social and economic burden. PD neuropathology is characterized by a selective loss of dopaminergic neurons in the substantia nigra pars compacta; however, more widespread involvement of other CNS structures and peripheral tissues now is widely documented. The onset of molecular and cellular neuropathology of PD likely occurs decades before the onset of the motor symptoms characteristic of PD. The hallmark symptoms of PD, resting tremors, rigidity and postural disabilities, are related to dopamine (DA) deficiency. Current therapies treat these symptoms by replacing or boosting existing DA. All current interventions have limited therapeutic benefit for disease progression because damage likely has progressed over an estimated period of ~5 to 15years to a loss of 60%-80% of the nigral DA neurons, before symptoms emerge. There is no accepted definitive biomarker of PD. An urgent need exists to develop early diagnostic biomarkers for two reasons: (1) to intervene at the onset of disease and (2) to monitor the progress of therapeutic interventions that may slow or stop the course of the disease. In the context of disease development, one of the promises of personalized medicine is the ability to predict, on an individual basis, factors contributing to the susceptibility for the development of a given disease. Recent advances in our understanding of genetic factors underlying or contributing to PD offer the potential for monitoring susceptibility biomarkers that can be used to identify at-risk individuals and possibly prevent the onset of disease through treatment. Finally, the exposome concept is new in the biomarker discovery arena and it is suggested as a way to move forward in identifying biomarkers of neurological diseases. It is a two-stage scheme involving a first stage of exposome-wide association studies (EWAS) to profile omic features in serum to discover molecular biomarkers. The second stage involves application of this knowledge base in follow-up studies. This strategy is unique in that it promotes the use of data-driven (omic) strategies in interrogating diseased and healthy populations and encourages a movement away from using only reductionist strategies to discover biomarkers of exposure and disease. In this short review we will examine 1) advances in our understanding of the molecular mechanisms underlying PD that have led to candidate biomarkers for diagnosis and treatment efficacy and 2) new technologies on the horizon that will lead to novel approaches in biomarker development.

Anti-human α-synuclein N-terminal peptide antibody protects against dopaminergic cell death and ameliorates behavioral deficits in an AAV-α-synuclein rat model of Parkinson's disease

The protein α-synuclein (α-Syn) has a central role in the pathogenesis of Parkinson’s disease (PD) and immunotherapeutic approaches targeting this molecule have shown promising results. In this study, novel antibodies were generated against specific peptides from full length human α-Syn and evaluated for effectiveness in ameliorating α-Syn-induced cell death and behavioral deficits in an AAV-α-Syn expressing rat model of PD. Fisher 344 rats were injected with rAAV vector into the right substantia nigra (SN), while control rats received an AAV vector expressing green fluorescent protein (GFP). Beginning one week after injection of the AAV-α-Syn vectors, rats were treated intraperitoneally with either control IgG or antibodies against the N-terminal (AB1), or central region (AB2) of α-Syn. An unbiased stereological estimation of TH+, NeuN+, and OX6 (MHC-II) immunostaining revealed that the α-Syn peptide antibodies (AB1 and AB2) significantly inhibited α-Syn-induced dopaminergic cell (DA) and NeuN+ cell loss (one-way ANOVA (F (3, 30) = 5.8, p = 0.002 and (F (3, 29) = 7.92, p = 0.002 respectively), as well as decreasing the number of activated microglia in the ipsilateral SN (one-way ANOVA F = 14.09; p = 0.0003). Antibody treated animals also had lower levels of α-Syn in the ipsilateral SN (one-way ANOVA F (7, 37) = 9.786; p = 0.0001) and demonstrated a partial intermediate improvement of the behavioral deficits. Our data suggest that, in particular, an α-Syn peptide antibody against the N-terminal region of the protein can protect against DA neuron loss and, to some extent behavioral deficits. As such, these results may be a potential therapeutic strategy for halting the progression of PD.

Long-Term Consequences of Traumatic Brain Injury: Current Status of Potential Mechanisms of Injury and Neurological Outcomes

Traumatic brain injury (TBI) is a significant clinical problem with few therapeutic interventions successfully translated to the clinic. Increased importance on the progressive, long-term consequences of TBI have been emphasized, both in the experimental and clinical literature. Thus, there is a need for a better understanding of the chronic consequences of TBI, with the ultimate goal of developing novel therapeutic interventions to treat the devastating consequences of brain injury. In models of mild, moderate, and severe TBI, histopathological and behavioral studies have emphasized the progressive nature of the initial traumatic insult and the involvement of multiple pathophysiological mechanisms, including sustained injury cascades leading to prolonged motor and cognitive deficits. Recently, the increased incidence in age-dependent neurodegenerative diseases in this patient population has also been emphasized. Pathomechanisms felt to be active in the acute and long-term consequences of TBI include excitotoxicity, apoptosis, inflammatory events, seizures, demyelination, white matter pathology, as well as decreased neurogenesis. The current article will review many of these pathophysiological mechanisms that may be important targets for limiting the chronic consequences of TBI.

The ongoing pursuit of neuroprotective therapies in Parkinson disease

Many agents developed for neuroprotective treatment of Parkinson disease (PD) have shown great promise in the laboratory, but none have translated to positive results in patients with PD. Potential neuroprotective drugs, such as ubiquinone, creatine and PYM50028, have failed to show any clinical benefits in recent high-profile clinical trials. This 'failure to translate' is likely to be related primarily to our incomplete understanding of the pathogenic mechanisms underlying PD, and excessive reliance on data from toxin-based animal models to judge which agents should be selected for clinical trials. Restricted resources inevitably mean that difficult compromises must be made in terms of trial design, and reliable estimation of efficacy is further hampered by the absence of validated biomarkers of disease progression. Drug development in PD dementia has been mostly unsuccessful; however, emerging biochemical, genetic and pathological evidence suggests a link between tau and amyloid-β deposition and cognitive decline in PD, potentially opening up new possibilities for therapeutic intervention. This Review discusses the most important 'druggable' disease mechanisms in PD, as well as the most-promising drugs that are being evaluated for their potential efficiency in treatment of motor and cognitive impairments in PD.

Immunotherapy targeting α-synuclein, with relevance for future treatment of Parkinson's disease and other Lewy body disorders

Immunotherapy targeting α-synuclein has evolved as a potential therapeutic strategy for neurodegenerative diseases, such as Parkinson's disease, and initial studies on cellular and animal models have shown promising results. α-synuclein vaccination of transgenic mice reduced the number of brain inclusions, whereas passive immunization studies demonstrated that antibodies against the C-terminus of α-synuclein can pass the blood-brain barrier and affect the pathology. In addition, preliminary evidence suggests that transgenic mice treated with an antibody directed against α-synuclein oligomers/protofibrils resulted in reduced levels of such species in the CNS. The underlying mechanisms of immunotherapy are not yet fully understood, but may include antibody-mediated clearance of pre-existing aggregates, prevention of protein propagation between cells and microglia-dependent protein clearance. Thus, immunotherapy targeting α-synuclein holds promise, but needs to be further developed as a future disease-modifying treatment in Parkinson's disease and other α-synucleinopathies.

Agile delivery of protein therapeutics to CNS

A variety of therapeutic proteins have shown potential to treat central nervous system (CNS) disorders. Challenge to deliver these protein molecules to the brain is well known. Proteins administered through parenteral routes are often excluded from the brain because of their poor bioavailability and the existence of the blood-brain barrier (BBB). Barriers also exist to proteins administered through non-parenteral routes that bypass the BBB. Several strategies have shown promise in delivering proteins to the brain. This review, first, describes the physiology and pathology of the BBB that underscore the rationale and needs of each strategy to be applied. Second, major classes of protein therapeutics along with some key factors that affect their delivery outcomes are presented. Third, different routes of protein administration (parenteral, central intracerebroventricular and intraparenchymal, intranasal and intrathecal) are discussed along with key barriers to CNS delivery associated with each route. Finally, current delivery strategies involving chemical modification of proteins and use of particle-based carriers are overviewed using examples from literature and our own work. Whereas most of these studies are in the early stage, some provide proof of mechanism of increased protein delivery to the brain in relevant models of CNS diseases, while in few cases proof of concept had been attained in clinical studies. This review will be useful to broad audience of students, academicians and industry professionals who consider critical issues of protein delivery to the brain and aim developing and studying effective brain delivery systems for protein therapeutics.

Vaccination strategies for Parkinson disease: induction of a swift attack or raising tolerance?

Parkinson disease is the second most common neurodegenerative disease in the world, but there is currently no available cure for it. Current treatments only alleviate some of the symptoms for a few years, but they become ineffective in the long run and do not stop the disease. Therefore it is of outmost importance to develop therapeutic strategies that can prevent, stop, or cure Parkinson disease. A very promising target for these therapies is the peripheral immune system due to its probable involvement in the disease and its potential as a tool to modulate neuroinflammation. But for such strategies to be successful, we need to understand the particular state of the peripheral immune system during Parkinson disease in order to avoid its weaknesses. In this review we examine the available data regarding how dopamine regulates the peripheral immune system and how this regulation is affected in Parkinson disease; the specific cytokine profiles observed during disease progression and the alterations documented to date in patients' peripheral blood mononuclear cells. We also review the different strategies used in Parkinson disease animal models to modulate the adaptive immune response to salvage dopaminergic neurons from cell death. After analyzing the evidence, we hypothesize the need to prime the immune system to restore natural tolerance against α-synuclein in Parkinson disease, including at the same time B and T cells, so that T cells can reprogram microglia activation to a beneficial pattern and B cell/IgG can help neurons cope with the pathological forms of α-synuclein.

Alpha-synuclein repeat variants and survival in Parkinson's disease

OBJECTIVES

To determine whether α-synuclein dinucleotide repeat (REP1) genotypes are associated with survival in Parkinson's disease (PD).

METHODS

Investigators from the Genetic Epidemiology of Parkinson's Disease Consortium provided REP1 genotypes and baseline and follow-up clinical data for cases. The primary outcome was time to death. Cox proportional hazards regression models were used to assess the association of REP1 genotypes with survival.

RESULTS

Twenty-one sites contributed data for 6,154 cases. There was no significant association between α-synuclein REP1 genotypes and survival in PD. However, there was a significant association between REP1 genotypes and age at onset of PD (hazard ratio: 1.06; 95% confidence interval: 1.01-1.10; P value = 0.01).

CONCLUSIONS

In our large consortium study, α-synuclein REP1 genotypes were not associated with survival in PD. Further studies of α-synuclein's role in disease progression and long-term outcomes are needed.

Next-generation active immunization approach for synucleinopathies: implications for Parkinson's disease clinical trials

Immunotherapeutic approaches are currently in the spotlight for their potential as disease-modifying treatments for neurodegenerative disorders. The discovery that α-synuclein (α-syn) can transmit from cell to cell in a prion-like fashion suggests that immunization might be a viable option for the treatment of synucleinopathies. This possibility has been bolstered by the development of next-generation active vaccination technology with short peptides-AFFITOPEs(®) (AFF)- that do not elicit an α-syn-specific T cell response. This approach allows for the production of long term, sustained, more specific, non-cross reacting antibodies suitable for the treatment of synucleinopathies, such as Parkinson's disease (PD). In this context, we screened a large library of peptides that mimic the C-terminus region of α-syn and discovered a novel set of AFF that identified α-syn oligomers. Next, the peptide that elicited the most specific response against α-syn (AFF 1) was selected for immunizing two different transgenic (tg) mouse models of PD and Dementia with Lewy bodies, the PDGF- and the mThy1-α-syn tg mice. Vaccination with AFF 1 resulted in high antibody titers in CSF and plasma, which crossed into the CNS and recognized α-syn aggregates. Active vaccination with AFF 1 resulted in decreased accumulation of α-syn oligomers in axons and synapses, accompanied by reduced degeneration of TH fibers in the caudo-putamen nucleus and by improvements in motor and memory deficits in both in vivo models. Clearance of α-syn involved activation of microglia and increased anti-inflammatory cytokine expression, further supporting the efficacy of this novel active vaccination approach for synucleinopathies.

The specific PKR inhibitor C16 prevents apoptosis and IL-1β production in an acute excitotoxic rat model with a neuroinflammatory component

The double-stranded RNA-dependent protein kinase (PKR), an apoptotic inducer, regulates much pro-inflammatory cytokine production. The purpose of this study was to evaluate in vivo the effects of the specific PKR inhibitor C16 in the striatum in an acute excitotoxic rat model with an important neuroinflammatory component. Inflammation was induced by unilateral striatal injection of quinolinic acid (QA) in 10-week-old normotensive rats. Animals were separated into groups receiving either vehicle or C16 for both sham and QA rats. The effects were assessed in ipsi- and contralateral striata by immunoblotting for PKR activation, by Luminex assay for cytokine levels and by immunofluorescent staining for cleaved caspase-3 to detect neuronal apoptosis. The highest dose of C16 (600μg/kg; C16-2) in QA rats reduced expression of the active catalytic domain of the PKR vs. that in vehicle-injected QA rats. A robust increase of IL-1β levels on the contralateral side of QA rats was prevented by C16-2 (97% inhibition). Macroscopic and microscopic observation of cerebral tissue (Hematoxylin & Eosin staining) revealed that tissue integrity was more preserved with C16-2 treatment than its vehicle in QA rats. Furthermore, C16-2 treatment decreased by 47% the neuronal loss and by 37% the number of positive cleaved caspase-3 neurons induced by QA injection. In conclusion, C16 prevented not only the PKR-induced neuronal loss but also the inflammatory response in this acute excitotoxic in vivo model, highlighting its promising neuroprotective properties to rescue acute brain lesions.

Evidence for prion-like mechanisms in several neurodegenerative diseases: potential implications for immunotherapy

Transmissible spongiform encephalopathies (TSEs) are fatal, untreatable neurodegenerative diseases. While the impact of TSEs on human health is relatively minor, these diseases are having a major influence on how we view, and potentially treat, other more common neurodegenerative disorders. Until recently, TSEs encapsulated a distinct category of neurodegenerative disorder, exclusive in their defining characteristic of infectivity. It now appears that similar mechanisms of self-propagation may underlie other proteinopathies such as Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, and Huntington's disease. This link is of scientific interest and potential therapeutic importance as this route of self-propagation offers conceptual support and guidance for vaccine development efforts. Specifically, the existence of a pathological, self-promoting isoform offers a rational vaccine target. Here, we review the evidence of prion-like mechanisms within a number of common neurodegenerative disorders and speculate on potential implications and opportunities for vaccine development.

An update on the management of young-onset Parkinson's disease

In the text that follows, we review the main clinical features, genetic characteristics, and treatment options for Parkinson's disease (PD), considering the age at onset. The clinical variability between patients with PD points at the existence of subtypes of the disease. Identification of subtypes is important, since a focus on homogenous group may lead to tailored treatment strategies. One of the factors that determine variability of clinical features of PD is age of onset. Young-onset Parkinson's disease (YOPD) is defined as parkinsonism starting between the ages of 21 and 40. YOPD has a slower disease progression and a greater incidence and earlier appearance of levodopa-induced motor complications; namely, motor fluctuations and dyskinesias. Moreover, YOPD patients face a lifetime of a progressive disease with gradual worsening of quality of life and their expectations are different from those of their older counterparts. Knowing this, treatment plans and management of symptoms must be paid careful attention to in order to maintain an acceptable quality of life in YOPD patients.

Prion-like propagation of protein aggregation and related therapeutic strategies

Many neurodegenerative diseases are characterized by the progressive accumulation of aggregated protein. Recent evidence suggests the prion-like propagation of protein misfolding underlies the spread of pathology observed in these diseases. This review traces our understanding of the mechanisms that underlie this phenomenon and discusses related therapeutic strategies that derive from it.

Immunotherapy for neurodegenerative diseases: focus on α-synucleinopathies

Immunotherapy is currently being intensively explored as much-needed disease-modifying treatment for neurodegenerative diseases. While Alzheimer's disease (AD) has been the focus of numerous immunotherapeutic studies, less attention has been paid to Parkinson's disease (PD) and other neurodegenerative disorders. The reason for this difference is that the amyloid beta (Aβ) protein in AD is a secreted molecule that circulates in the blood and is readably recognized by antibodies. In contrast, α-synuclein (α-syn), tau, huntingtin and other proteins involved in neurodegenerative diseases have been considered to be exclusively of intracellular nature. However, the recent discovery that toxic oligomeric versions of α-syn and tau accumulate in the membrane and can be excreted to the extracellular environment has provided a rationale for the development of immunotherapeutic approaches for PD, dementia with Lewy bodies, frontotemporal dementia, and other neurodegenerative disorders characterized by the abnormal accumulation of these proteins. Active immunization, passive immunization, and T cell-mediated cellular immunotherapeutic approaches have been developed targeting Aβ, α-syn and tau. Most advanced studies, including results from phase III clinical trials for passive immunization in AD, have been recently reported. Results suggest that immunotherapy might be a promising therapeutic approach for neurodegenerative diseases that progress with the accumulation and propagation of toxic protein aggregates. In this manuscript we provide an overview on immunotherapeutic advances for neurodegenerative disorders, with special emphasis on α-synucleinopathies.

Models of multiple system atrophy

Multiple system atrophy (MSA) is a predominantly sporadic, adult-onset, fatal neurodegenerative disease of unknown etiology. MSA is characterized by autonomic failure, levodopa-unresponsive parkinsonism, cerebellar ataxia and pyramidal signs in any combination. MSA belongs to a group of neurodegenerative disorders termed α-synucleinopathies, which also include Parkinson's disease and dementia with Lewy bodies. Their common pathological feature is the occurrence of abnormal α-synuclein positive inclusions in neurons or glial cells. In MSA, the main cell type presenting aggregates composed of α-synuclein are oligodendroglial cells . This pathological hallmark, also called glial cytoplasmic inclusions (GCIs) , is associated with progressive and profound neuronal loss in various regions of the brain. The development of animal models of MSA is justified by the limited understanding of the mechanisms of neurodegeneration and GCIs formation, which is paralleled by a lack of therapeutic strategies. Two main types of rodent models have been generated to replicate different features of MSA neuropathology. On one hand, neurotoxin-based models have been produced to reproduce neuronal loss in substantia nigra pars compacta and striatum. On the other hand, transgenic mouse models with overexpression of α-synuclein in oligodendroglia have been used to reproduce GCIs-related pathology. This chapter gives an overview of the atypical Parkinson's syndrome MSA and summarizes the currently available MSA animal models and their relevance for pre-clinical testing of disease-modifying therapies.