Combined Active Humoral and Cellular Immunization Approaches for the Treatment of Synucleinopathies

The immune system in Parkinson's disease: what we know so far

Parkinson's disease is characterized neuropathologically by the degeneration of dopaminergic neurons in the ventral midbrain, the accumulation of α-synuclein (α-syn) aggregates in neurons and chronic neuroinflammation. In the past two decades, in vitro, ex vivo and in vivo studies have consistently shown the involvement of inflammatory responses mediated by microglia and astrocytes, which may be elicited by pathological α-syn or signals from affected neurons and other cell types, and are directly linked to neurodegeneration and disease development. Apart from the prominent immune alterations seen in the CNS, including the infiltration of T cells into the brain, more recent studies have demonstrated important changes in the peripheral immune profile within both the innate and adaptive compartments, particularly involving monocytes, CD4+ and CD8+ T cells. This review aims to integrate the consolidated understanding of immune-related processes underlying the pathogenesis of Parkinson's disease, focusing on both central and peripheral immune cells, neuron-glia crosstalk as well as the central-peripheral immune interaction during the development of Parkinson's disease. Our analysis seeks to provide a comprehensive view of the emerging knowledge of the mechanisms of immunity in Parkinson's disease and the implications of this for better understanding the overall pathogenesis of this disease.

Evolving insights into erythrocytes in synucleinopathies

Synucleinopathies, including Parkinson's disease (PD), multiple system atrophy (MSA), and dementia with Lewy bodies (DLB), are characterized by neuronal loss accompanied by α-synuclein (α-syn) accumulation in the brain. While research conventionally focused on brain pathology, there is growing interest in peripheral alterations. Erythrocytes, which are rich in α-syn, have emerged as a compelling site for synucleinopathies-related alterations. Erythrocyte-derived extracellular vesicles (EVs), containing pathological α-syn species, can traverse the blood-brain barrier (BBB) under certain conditions and the gastrointestinal tract, where α-syn and gut microbiota interact extensively. This review explores the accumulating evidence of erythrocyte involvement in synucleinopathies, as well as their potential in disease pathogenesis and diagnosis. Given their unique properties, erythrocytes and erythrocyte-derived EVs may also serve as an ideal therapeutic platform for treating synucleinopathies and beyond.

Neurovascular and immune factors of vulnerability of substantia nigra dopaminergic neurons in non-human primates

Dopaminergic neurons in the ventral tier of the substantia nigra pars compacta (SNc) degenerate prominently in Parkinson's disease (PD), while those in the dorsal tier and ventral tegmental area are relatively spared. The factors determining why these neurons are more vulnerable than others are still unrevealed. Neuroinflammation and immune cell infiltration have been demonstrated to be a key feature of neurodegeneration in PD. However, the link between selective dopaminergic neuron vulnerability, glial and immune cell response, and vascularization and their interactions has not been deciphered. We aimed to investigate the contribution of glial cell activation and immune cell infiltration in the selective vulnerability of ventral dopaminergic neurons within the midbrain in a non-human primate model of PD. Structural characteristics of the vasculature within specific regions of the midbrain were also evaluated. Parkinsonian monkeys exhibited significant microglial and astroglial activation in the whole midbrain, but no major sub-regional differences were observed. Remarkably, the ventral substantia nigra was found to be typically more vascularized compared to other regions. This feature might play some role in making this region more susceptible to immune cell infiltration under pathological conditions, as greater infiltration of both T- and B- lymphocytes was observed in parkinsonian monkeys. Higher vascular density within the ventral region of the SNc may be a relevant factor for differential vulnerability of dopaminergic neurons in the midbrain. The increased infiltration of T- and B- cells in this region, alongside other molecules or toxins, may also contribute to the susceptibility of dopaminergic neurons in PD.

Immunotherapy: An emerging treatment option for neurodegenerative diseases

Accumulation of misfolded proteins and protein aggregates leading to degeneration of neurons is a hallmark of several neurodegenerative diseases. Therapy mostly relies on symptomatic relief. Immunotherapy offers a promising approach for the development of disease-modifying routes. Such strategies have shown remarkable results in oncology, and this promise is increasingly being realized for neurodegenerative diseases in advanced preclinical and clinical studies. This review highlights cases of passive and active immunotherapies in Parkinson's and Alzheimer's diseases. The reasons for success and failure, wherever available, and strategies to cross the blood-brain barrier, are discussed. The need for conditional modulation of the immune response is also reflected on.

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.

Neuroinflammation, immune response and α-synuclein pathology: how animal models are helping us to connect dots

INTRODUCTION

A key pathological event occurring in Parkinson's disease (PD) is the transneuronal spreading of alpha-synuclein (α-syn). Other hallmarks of PD include neurodegeneration, glial activation, and immune cell infiltration in susceptible brain regions. Although preclinical models can mimic most of the key characteristics of PD, it is crucial to know the biological bases of individual differences between them when choosing one over another, to ensure proper interpretation of the results and to positively influence the outcome of the experiments.

AREAS COVERED

This review provides an overview of current preclinical models actively used to study the interplay between α-syn pathology, neuroinflammation and immune response in PD but also to explore new potential preclinical models or emerging therapeutic strategies intended to fulfill the unmet medical needs in this disease. Lastly, this review also considers the current state of the ongoing clinical trials of new drugs designed to target these processes and delay the initiation or progression of the disease.

EXPERT OPINION

Anti-inflammatory and immunomodulatory agents have been demonstrated to be very promising candidates for reducing disease progression; however, more efforts are needed to reduce the enormous gap between these and dopaminergic drugs, which have dominated the therapeutic market for the last sixty years.

Antiparkinsonian Agents in Investigational Polymeric Micro- and Nano-Systems

Parkinson's disease (PD) is a devastating neurodegenerative disease characterized by progressive destruction of dopaminergic tissue in the central nervous system (CNS). To date, there is no cure for the disease, with current pharmacological treatments aimed at controlling the symptoms. Therefore, there is an unmet need for new treatments for PD. In addition to new therapeutic options, there exists the need for improved efficiency of the existing ones, as many agents have difficulties in crossing the blood-brain barrier (BBB) to achieve therapeutic levels in the CNS or exhibit inappropriate pharmacokinetic profiles, thereby limiting their clinical benefits. To overcome these limitations, an interesting approach is the use of drug delivery systems, such as polymeric microparticles (MPs) and nanoparticles (NPs) that allow for the controlled release of the active ingredients targeting to the desired site of action, increasing the bioavailability and efficacy of treatments, as well as reducing the number of administrations and adverse effects. Here we review the polymeric micro- and nano-systems under investigation as potential new therapies for PD.

FDA-Approved Kinase Inhibitors in Preclinical and Clinical Trials for Neurological Disorders

Cancers and neurological disorders are two major types of diseases. We previously developed a new concept termed "Aberrant Cell Cycle Diseases" (ACCD), revealing that these two diseases share a common mechanism of aberrant cell cycle re-entry. The aberrant cell cycle re-entry is manifested as kinase/oncogene activation and tumor suppressor inactivation, which are hallmarks of both tumor growth in cancers and neuronal death in neurological disorders. Therefore, some cancer therapies (e.g., kinase inhibition, tumor suppressor elevation) can be leveraged for neurological treatments. The United States Food and Drug Administration (US FDA) has so far approved 74 kinase inhibitors, with numerous other kinase inhibitors in clinical trials, mostly for the treatment of cancers. In contrast, there are dire unmet needs of FDA-approved drugs for neurological treatments, such as Alzheimer's disease (AD), intracerebral hemorrhage (ICH), ischemic stroke (IS), traumatic brain injury (TBI), and others. In this review, we list these 74 FDA-approved kinase-targeted drugs and identify those that have been reported in preclinical and/or clinical trials for neurological disorders, with a purpose of discussing the feasibility and applicability of leveraging these cancer drugs (FDA-approved kinase inhibitors) for neurological treatments.

The Role of CD4+ T Cells in the Immunotherapy of Brain Disease by Secreting Different Cytokines

Upon different stimulation, naïve CD4⁺ T cells differentiate into various subsets of T helper (Th) cells, including Th1, Th2, Th17, and Tregs. They play both protective and pathogenic roles in the central nervous system (CNS) by secreting different cytokines. Failure of the homeostasis of the subgroups in the CNS can result in different brain diseases. Recently, immunotherapy has drawn more and more attention in the therapy of various brain diseases. Here, we describe the role of different CD4⁺ T cell subsets and their secreted cytokines in various brain diseases, as well as the ways in which by affecting CD4⁺ T cells in therapy of the CNS diseases. Understanding the role of CD4⁺ T cells and their secreted cytokines in the immunotherapy of brain disease will provide new targets and therapeutics for the treatment of brain disease. The role of CD4 + T cell subtypes in different diseases and their associated regulatory genes, proteins, and enzymes. CD4 + T cell subtypes play both protective (green) and pathogenic (red) roles in different brain diseases. The immune regulatory effects of CD4 + T cells and their subtypes are promoted or inhibited by different genes, proteins, and enzymes.

A Novel C-Type Lectin Receptor-Targeted α-Synuclein-Based Parkinson Vaccine Induces Potent Immune Responses and Therapeutic Efficacy in Mice

The progressive accumulation of misfolded α-synuclein (α-syn) in the brain is widely considered to be causal for the debilitating clinical manifestations of synucleinopathies including, most notably, Parkinson's disease (PD). Immunotherapies, both active and passive, against α-syn have been developed and are promising novel treatment strategies for such disorders. To increase the potency and specificity of PD vaccination, we created the 'Win the Skin Immune System Trick' (WISIT) vaccine platform designed to target skin-resident dendritic cells, inducing superior B and T cell responses. Of the six tested WISIT candidates, all elicited higher immune responses compared to conventional, aluminum adjuvanted peptide-carrier conjugate PD vaccines, in BALB/c mice. WISIT-induced antibodies displayed higher selectivity for α-syn aggregates than those induced by conventional vaccines. Additionally, antibodies induced by two selected candidates were shown to inhibit α-syn aggregation in a dose-dependent manner in vitro. To determine if α-syn fibril formation could also be inhibited in vivo, WISIT candidate type 1 (CW-type 1) was tested in an established synucleinopathy seeding model and demonstrated reduced propagation of synucleinopathy in vivo. Our studies provide proof-of-concept for the efficacy of the WISIT vaccine technology platform and support further preclinical and clinical development of this vaccine candidate.

Alpha-Synuclein Aggregation Pathway in Parkinson's Disease: Current Status and Novel Therapeutic Approaches

Following Alzheimer’s, Parkinson’s disease (PD) is the second-most common neurodegenerative disorder, sharing an unclear pathophysiology, a multifactorial profile, and massive social costs worldwide. Despite this, no disease-modifying therapy is available. PD is tightly associated with α-synuclein (α-Syn) deposits, which become organised into insoluble, amyloid fibrils. As a typical intrinsically disordered protein, α-Syn adopts a monomeric, random coil conformation in an aqueous solution, while its interaction with lipid membranes drives the transition of the molecule part into an α-helical structure. The central unstructured region of α-Syn is involved in fibril formation by converting to well-defined, β-sheet rich secondary structures. Presently, most therapeutic strategies against PD are focused on designing small molecules, peptides, and peptidomimetics that can directly target α-Syn and its aggregation pathway. Other approaches include gene silencing, cell transplantation, stimulation of intracellular clearance with autophagy promoters, and degradation pathways based on immunotherapy of amyloid fibrils. In the present review, we sum marise the current advances related to α-Syn aggregation/neurotoxicity. These findings present a valuable arsenal for the further development of efficient, nontoxic, and non-invasive therapeutic protocols for disease-modifying therapy that tackles disease onset and progression in the future.

Yeast as carrier for drug delivery and vaccine construction

Yeast has been employed as an effective derived drug carrier as a unicellular microorganism. Many research works have been devoted to the encapsulation of nucleic acid compounds, insoluble small molecule drugs, small molecules, liposomes, polymers, and various nanoparticles in yeast for the treatment of disease. Recombinant yeast-based vaccine carriers (WYV) have played a major role in the development of vaccines. Herein, the latest reports on the application of yeast carriers and the development of related research are summarized, a conceptual description of gastrointestinal absorption of yeast carriers, as well as the various package forms of different drug molecules and nanoparticles in yeast carriers are introduced. In addition, the advantages and development of recombinant yeast vaccine carriers for the disease, veterinary and aquaculture applications are discussed. Moreover, the current challenges and future directions of yeast carriers are proposed.

Slowing Parkinson's Disease Progression with Vaccination and Other Immunotherapies

Parkinson's disease (PD) is the second most common neurodegenerative disorder. There are several recognized pathways leading up to dopaminergic neuron loss in the substantia nigra pars compacta and other cells in the brain as a result of age-related, genetic, environmental, and other processes. Of these, the most prominent is the role played by the protein α-synuclein, which aggregates and is the primary component of Lewy bodies, the histopathological hallmark of PD. The latest disease-modifying treatment options being investigated in PD are active and passive immunization against α-synuclein. There are currently five different monoclonal antibodies investigated as passive immunization and three drugs being studied as active immunization modalities in PD. These work through different mechanisms but with a common goal-to minimize or prevent α-synuclein-driven neurotoxicity by reducing α-synuclein synthesis, increasing α-synuclein degradation, and preventing aggregation and propagation from cell to cell. These promising strategies, along with other potential therapies, may favorably alter disease progression in PD.

Alpha-Synuclein Induced Immune Cells Activation and Associated Therapy in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder closely related to immunity. An important aspect of the pathogenesis of PD is the interaction between α-synuclein and a series of immune cells. Studies have shown that accumulation of α-synuclein can induce an autoimmune response that accelerates the progression of PD. This study discusses the mechanisms underlying the interaction between α-synuclein and the immune system. During the development of PD, abnormally accumulated α-synuclein becomes an autoimmune antigen that binds to Toll-like receptors (TLRs) that activate microglia, which differentiate into the microglia type 1 (M1) subtype. The microglia activate intracellular inflammatory pathways, induce the release of proinflammatory cytokines, and promote the differentiation of cluster of differentiation 4 + (CD4 +) T cells into proinflammatory T helper type 1 (Th1) and T helper type 17 (Th17) subtypes. Given the important role of α-synuclein in the immune system of the patients with PD, identifying potential targets of immunotherapy related to α-synuclein is critical for slowing disease progression. An enhanced understanding of immune-associated mechanisms in PD can guide the development of associated therapeutic strategies in the future.

NANOTECHNOLOGY-MEDIATED THERAPEUTIC STRATEGIES AGAINST SYNUCLEINOPATHIES IN NEURODEGENERATIVE DISEASE

Synucleinopathies are a subset of debilitating neurodegenerative disorders for which clinically approved therapeutic options to either halt or retard disease progression are currently unavailable. Multiple synergistic pathological mechanisms in combination with the characteristic misfolding of proteins are attributable to disease pathogenesis and progression. This complex interplay, as well as the difficult and multiscale nature of therapeutic delivery into the central nervous system, make finding effective treatments difficult. Nanocarriers (NCs) are a class of materials that can significantly improve therapeutic brain delivery and enable multifunctional therapies. In this review, an update on the known pathology of synucleinopathies is presented. Then, NC-enabled therapeutics designed to target the multiple mechanisms by combination therapies and multiscale targeting methods is reviewed. The implications of these strategies are synthesized and evaluated to suggest opportunities for the rational design of anti-neurodegenerative NC therapeutics.

Treating Parkinson's Disease with Antibodies: Previous Studies and Future Directions

Parkinson's disease is a neurodegenerative disorder mainly characterized by the degeneration of dopaminergic neurons in the substantia nigra. Degenerating neurons contain abnormal aggregates called Lewy bodies, that are predominantly composed of the misfolded and/or mutated alpha-synuclein protein. Post-translational modifications, cellular stress, inflammation and gene mutations are thought to trigger its pathological misfolding and aggregation. With alpha-synuclein pathology being strongly associated with dopaminergic neuronal toxicity, strategies aimed to reduce its burden are expected to be beneficial in slowing disease progression. Moreover, multiple sources of evidence suggest a cell-to-cell transmission of pathological alpha-synuclein in a prion-like manner. Therefore, antibodies targeting extra- or intracellular alpha-synuclein could be efficient in limiting the aggregation and transmission. Several active and passive immunization strategies have been explored to target alpha-synuclein. Here, we summarize immunotherapeutic approaches that were tested in pre-clinical or clinical studies in the last two decades in an attempt to treat Parkinson's disease.

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.

In Search of Effective Treatments Targeting α-Synuclein Toxicity in Synucleinopathies: Pros and Cons

Parkinson's disease (PD), multiple system atrophy (MSA) and Dementia with Lewy bodies (DLB) represent pathologically similar, progressive neurodegenerative disorders characterized by the pathological aggregation of the neuronal protein α-synuclein. PD and DLB are characterized by the abnormal accumulation and aggregation of α-synuclein in proteinaceous inclusions within neurons named Lewy bodies (LBs) and Lewy neurites (LNs), whereas in MSA α-synuclein inclusions are mainly detected within oligodendrocytes named glial cytoplasmic inclusions (GCIs). The presence of pathologically aggregated α-synuclein along with components of the protein degradation machinery, such as ubiquitin and p62, in LBs and GCIs is considered to underlie the pathogenic cascade that eventually leads to the severe neurodegeneration and neuroinflammation that characterizes these diseases. Importantly, α-synuclein is proposed to undergo pathogenic misfolding and oligomerization into higher-order structures, revealing self-templating conformations, and to exert the ability of "prion-like" spreading between cells. Therefore, the manner in which the protein is produced, is modified within neural cells and is degraded, represents a major focus of current research efforts in the field. Given that α-synuclein protein load is critical to disease pathogenesis, the identification of means to limit intracellular protein burden and halt α-synuclein propagation represents an obvious therapeutic approach in synucleinopathies. However, up to date the development of effective therapeutic strategies to prevent degeneration in synucleinopathies is limited, due to the lack of knowledge regarding the precise mechanisms underlying the observed pathology. This review critically summarizes the recent developed strategies to counteract α-synuclein toxicity, including those aimed to increase protein degradation, to prevent protein aggregation and cell-to-cell propagation, or to engage antibodies against α-synuclein and discuss open questions and unknowns for future therapeutic approaches.

Neuroinflammation is associated with infiltration of T cells in Lewy body disease and α-synuclein transgenic models

BACKGROUND

α-Synuclein (α-syn) is a pre-synaptic protein which progressively accumulates in neuronal and non-neuronal cells in neurodegenerative diseases such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy. Recent evidence suggests that aberrant immune activation may be involved in neurodegeneration in PD/DLB. While previous studies have often focused on the microglial responses, less is known about the role of the peripheral immune system in these disorders.

METHODS

To understand the involvement of the peripheral immune system in PD/DLB, we evaluated T cell populations in the brains of α-syn transgenic (tg) mice (e.g., Thy1 promoter line 61) and DLB patients.

RESULTS

Immunohistochemical analysis showed perivascular and parenchymal infiltration by CD3+/CD4+ helper T cells, but not cytotoxic T cells (CD3+/CD8+) or B cells (CD20+), in the neocortex, hippocampus, and striatum of α-syn tg mice. CD3+ cells were found in close proximity to the processes of activated astroglia, particularly in areas of the brain with significant astrogliosis, microgliosis, and expression of pro-inflammatory cytokines. In addition, a subset of CD3+ cells co-expressed interferon γ. Flow cytometric analysis of immune cells in the brains of α-syn tg mice revealed that CD1d-tet+ T cells were also increased in the brains of α-syn tg mice suggestive of natural killer T cells. In post-mortem DLB brains, we similarly detected increased numbers of infiltrating CD3+/CD4+ T cells in close proximity with blood vessels.

CONCLUSION

These results suggest that infiltrating adaptive immune cells play an important role in neuroinflammation and neurodegeneration in synucleinopathies and that modulating peripheral T cells may be a viable therapeutic strategy for PD/DLB.

Elevated Percentage of CD3+ T-Cells and CD4+/CD8+ Ratios in Multiple System Atrophy Patients

α-synuclein is involved in the pathogenesis of multiple system atrophy (MSA) and can be regulated by peripheral immune activation (PIA). We aimed to clarify the correlations between PIA and the prevalence of MSA and to analyze the role of PIA in the progression of the disease. A total of 321 patients with probable MSA and 321 age- and gender-matched healthy controls were included in this study. Lymphocyte subsets, including CD3⁺, CD4⁺, and CD8⁺ cells, and the levels of immunoglobulins IgG, IgM, and IgA were evaluated. The proportions of CD3⁺ and CD4⁺ T-lymphocytes were significantly increased in MSA patients compared with those of normal controls. In addition, the ratio of CD4⁺ to CD8⁺ cells was significantly increased in male MSA patients and IgG concentrations were decreased in female MSA patients. Furthermore, the concentrations of IgM in female MSA patients were dynamically different at various disease stages and gradually decreased from the early stage until the end stage of the disease (p = 0.029). Other detected immunological indexes were not significantly different during the entire disease course. In this study, high proportions of CD3⁺ and CD4⁺ T-lymphocytes and decreased IgG levels were associated with an increased risk for MSA in a Chinese patient population. In addition, PIA may be involved in the progression of MSA.

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.

Targeting α-synuclein for PD Therapeutics: A Pursuit on All Fronts

Parkinson's Disease (PD) is characterized both by the loss of dopaminergic neurons in the substantia nigra and the presence of cytoplasmic inclusions called Lewy Bodies. These Lewy Bodies contain the aggregated α-synuclein (α-syn) protein, which has been shown to be able to propagate from cell to cell and throughout different regions in the brain. Due to its central role in the pathology and the lack of a curative treatment for PD, an increasing number of studies have aimed at targeting this protein for therapeutics. Here, we reviewed and discussed the many different approaches that have been studied to inhibit α-syn accumulation via direct and indirect targeting. These analyses have led to the generation of multiple clinical trials that are either completed or currently active. These clinical trials and the current preclinical studies must still face obstacles ahead, but give hope of finding a therapy for PD with time.

Neuroprotection in Parkinson's disease: facts and hopes

Parkinson’s disease (PD) is the second most common neurodegenerative disease worldwide. Behind the symptoms there is a complex pathological mechanism which leads to a dopaminergic cell loss in the substantia nigra pars compacta. Despite the strong efforts, curative treatment has not been found yet. To prevent a further cell death, numerous molecules were tested in terms of neuroprotection in preclinical (in vitro, in vivo) and in clinical studies as well. The aim of this review article is to summarize our knowledge about the extensively tested neuroprotective agents (Search period: 1991–2019). We detail the underlying pathological mechanism and summarize the most important results of the completed animal and clinical trials. Although many positive results have been reported in the literature, there is still no evidence that any of them should be used in clinical practice (Cochrane analysis was performed). Therefore, further studies are needed to better understand the pathomechanism of PD and to find the optimal neuroprotective agent(s).

The good and bad of therapeutic strategies that directly target α-synuclein

Synucleinopathies are neurodegenerative diseases characterized by the accumulation of either neuronal/axonal or glial insoluble proteinaceous aggregates mainly composed of α-synuclein (α-syn). Among them, the most common disorders are Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, and some forms of familial parkinsonism. Both α-syn fibrils and oligomers have been found to exert toxic effects on neurons or oligodendroglial cells, can activate neuroinflammatory responses, and mediate the spreading of α-syn pathology. This poses the question of which is the most toxic α-syn species. What is worst, α-syn appears as a very peculiar protein, exerting multiple physiological functions in neurons, especially at synapses, but without acquiring a stable tertiary structure. Its conformation is particularly plastic, and the protein can exist in a natively unfolded state (mainly in solution), partially α-helical folded state (when it interacts with biological membranes), or oligomeric state (tetramers or dimers with debated functional profile). The extent of α-syn expression impinges on the resilience of neuronal cells, as multiplications of its gene locus, or overexpression, can cause neurodegeneration and onset of motor phenotype. For these reasons, one of the main challenges in the field of synucleinopathies, which still nowadays can only be managed by symptomatic therapies, has been the development of strategies aimed at reducing α-syn levels, oligomer formation, fibrillation, or cell-to-cell transmission. This review resumes the therapeutic approaches that have been proposed or are under development to counteract α-syn pathology by direct targeting of this protein and discuss their pros and cons in relation to the current state-of-the-art α-syn biology.

Effects of single and combined immunotherapy approach targeting amyloid β protein and α-synuclein in a dementia with Lewy bodies-like model

INTRODUCTION

Immunotherapeutic approaches targeting amyloid β (Aβ) protein and tau in Alzheimer's disease and α-synuclein (α-syn) in Parkinson's disease are being developed for treating dementia with Lewy bodies. However, it is unknown if single or combined immunotherapies targeting Aβ and/or α-syn may be effective.

METHODS

Amyloid precursor protein/α-syn tg mice were immunized with AFFITOPEs® (AFF) peptides specific to Aβ (AD02) or α-syn (PD-AFF1) and the combination.

RESULTS

AD02 more effectively reduced Aβ and pTau burden; however, the combination exhibited some additive effects. Both AD02 and PD-AFF1 effectively reduced α-syn, ameliorated degeneration of pyramidal neurons, and reduced neuroinflammation. PD-AFF1 more effectively ameliorated cholinergic and dopaminergic fiber loss; the combined immunization displayed additive effects. AD02 more effectively improved buried pellet test behavior, whereas PD-AFF1 more effectively improved horizontal beam test; the combined immunization displayed additive effects.

DISCUSSION

Specific active immunotherapy targeting Aβ and/or α-syn may be of potential interest for the treatment of dementia with Lewy bodies.

TNFα inhibitors as targets for protective therapies in MSA: a viewpoint

Multiple system atrophy (MSA) is a unique and fatal α-synucleinopathy associated with oligodendroglial inclusions and secondary neurodegeneration affecting striatum, substantia nigra, pons, and cerebellum. The pathogenesis remains elusive; however, there is emerging evidence suggesting a prominent role of neuroinflammation. Here, we critically review the relationship between αS and microglial activation depending on its aggregation state and its role in neuroinflammation to explore the potential of TNFα inhibitors as a treatment strategy for MSA and other neurodegenerative diseases.

Effect of naturally occurring α-synuclein-antibodies on toxic α-synuclein-fragments

Alpha-synuclein (α-Syn) is a soluble protein primarily expressed in presynaptic terminals in the central nervous system (CNS). Aggregates of fibrillated α-Syn are the major component of Lewy bodies (LB), a pathologic hallmark of idiopathic Parkinson's disease (PD). Recently, naturally occurring autoantibodies against human α-Syn (nAbs α-Syn) were detected in the peripheral blood of PD patients and controls. Here, we investigated the inhibitory effects of nAbs α-Syn on distinct α-Syn fragments, as well as inflammatory responses and cytotoxicity evoked by nAbs α-Syn in primary microglia. All α-Syn fragments induced the release of the pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) from microglia in primary culture. Cotreatment with nAbs α-Syn alleviated the release of pro-inflammatory cytokines induced by α-Syn fragments α-Syn 1-95, α-Syn 61-140, α-Syn 96-140 and α-Syn 112. Treatment with the α-Syn fragments α-Syn 1-95, α-Syn 61-140 and α-Syn 112 impaired the viability of primary microglia. This effect could not be counteracted by cotreatment with nAbs α-Syn. Data suggest an important role of nAbs α-Syn in the α-Syn-induced inflammation cascade, and indicate the potential importance of nAbs in the pathogenesis of PD. This could provide an experimental therapeutic target for patients with PD.

Immune system responses in Parkinson's disease: Early and dynamic

The neuropathological hallmarks of Parkinson's disease (PD) are the degeneration and death of dopamine-producing neurons in the ventral midbrain, the widespread intraneuronal aggregation of alpha-synuclein (α) in Lewy bodies and neurites, neuroinflammation, and gliosis. Signs of microglia activation in the PD brain postmortem as well as during disease development revealed by neuroimaging, implicate immune responses in the pathophysiology of the disease. Intensive research during the last two decades has advanced our understanding of the role of these responses in the disease process, yet many questions remain unanswered. A transformative finding in the field has been the confirmation that in vivo microglia are able to respond directly to pathological a-syn aggregates but also to neuronal dysfunction due to intraneuronal a-syn toxicity well in advance of neuronal death. In addition, clinical research and disease models have revealed the involvement of both the innate and adaptive immune systems. Indeed, the data suggest that PD leads not only to a microglia response, but also to a cellular and humoral peripheral immune response. Together, these findings compel us to consider a more holistic view of the immunological processes associated with the disease. Central and peripheral immune responses aimed at maintaining neuronal health will ultimately have consequences on neuronal survival. We will review here the most significant findings that have contributed to the current understanding of the immune response in PD, which is proposed to occur early, involve peripheral and brain immune cells, evolve as neuronal dysfunction progresses, and is likely to influence disease progression.

Extracellular Interactions of Alpha-Synuclein in Multiple System Atrophy

Multiple system atrophy, characterized by atypical Parkinsonism, results from central nervous system (CNS) cell loss and dysfunction linked to aggregates of the normally pre-synaptic α-synuclein protein. Mostly cytoplasmic pathological α-synuclein inclusion bodies occur predominantly in oligodendrocytes in affected brain regions and there is evidence that α-synuclein released by neurons is taken up preferentially by oligodendrocytes. However, extracellular α-synuclein has also been shown to interact with other neural cell types, including astrocytes and microglia, as well as extracellular factors, mediating neuroinflammation, cell-to-cell spread and other aspects of pathogenesis. Here, we review the current evidence for how α-synuclein present in the extracellular milieu may act at the cell surface to drive components of disease progression. A more detailed understanding of the important extracellular interactions of α-synuclein with neuronal and non-neuronal cell types both in the brain and periphery may provide new therapeutic targets to modulate the disease process.

The role of T cells in the pathogenesis of Parkinson's disease

Recent evidence has shown that neuroinflammation plays a key role in the pathogenesis of Parkinson's disease (PD). However, different components of the brain's immune system may exert diverse effects on neuroinflammatory events in PD. The adaptive immune response, especially the T cell response, can trigger type 1 pro-inflammatory activities and suppress type 2 anti-inflammatory activities, eventually resulting in deregulated neuroinflammation and subsequent dopaminergic neurodegeneration. Additionally, studies have increasingly shown that therapies targeting T cells can alleviate neurodegeneration and motor behavior impairment in animal models of PD. Therefore, we conclude that abnormal T cell-mediated immunity is a fundamental pathological process that may be a promising translational therapeutic target for Parkinson's disease.

Immunotherapy targeting toll-like receptor 2 alleviates neurodegeneration in models of synucleinopathy by modulating α-synuclein transmission and neuroinflammation

BACKGROUND

Synucleinopathies of the aging population are an heterogeneous group of neurological disorders that includes Parkinson's disease (PD) and dementia with Lewy bodies (DLB) and are characterized by the progressive accumulation of α-synuclein in neuronal and glial cells. Toll-like receptor 2 (TLR2), a pattern recognition immune receptor, has been implicated in the pathogenesis of synucleinopathies because TLR2 is elevated in the brains of patients with PD and TLR2 is a mediator of the neurotoxic and pro-inflammatory effects of extracellular α-synuclein aggregates. Therefore, blocking TLR2 might alleviate α-synuclein pathological and functional effects. For this purpose, herein, we targeted TLR2 using a functional inhibitory antibody (anti-TLR2).

METHODS

Two different human α-synuclein overexpressing transgenic mice were used in this study. α-synuclein low expresser mouse (α-syn-tg, under the PDGFβ promoter, D line) was stereotaxically injected with TLR2 overexpressing lentivirus to demonstrate that increment of TLR2 expression triggers neurotoxicity and neuroinflammation. α-synuclein high expresser mouse (α-Syn-tg; under mThy1 promoter, Line 61) was administrated with anti-TLR2 to examine that functional inhibition of TLR2 ameliorates neuropathology and behavioral defect in the synucleinopathy animal model. In vitro α-synuclein transmission live cell monitoring system was used to evaluate the role of TLR2 in α-synuclein cell-to-cell transmission.

RESULTS

We demonstrated that administration of anti-TLR2 alleviated α-synuclein accumulation in neuronal and astroglial cells, neuroinflammation, neurodegeneration, and behavioral deficits in an α-synuclein tg mouse model of PD/DLB. Moreover, in vitro studies with neuronal and astroglial cells showed that the neuroprotective effects of anti-TLR2 antibody were mediated by blocking the neuron-to-neuron and neuron-to-astrocyte α-synuclein transmission which otherwise promotes NFκB dependent pro-inflammatory responses.

CONCLUSION

This study proposes TLR2 immunotherapy as a novel therapeutic strategy for synucleinopathies of the aging population.

Microglia Response During Parkinson's Disease: Alpha-Synuclein Intervention

The discovery of the central role played by the protein alpha-synuclein in Parkinson's disease and other Lewy body brain disorders has had a great relevance in the understanding of the degenerative process occurring in these diseases. In addition, during the last two decades, the evidence suggesting an immune response in Parkinson's disease patients have multiplied. The role of the immune system in the disease is supported by data from genetic studies and patients, as well as from laboratory animal models and cell cultures. In the immune response, the microglia, the immune cell of the brain, will have a determinant role. Interestingly, alpha-synuclein is suggested to have a central function not only in the neuronal events occurring in Parkinson's disease, but also in the immune response during the disease. Numerous studies have shown that alpha-synuclein can act directly on immune cells, such as microglia in brain, initiating a sterile response that will have consequences for the neuronal health and that could also translate in a peripheral immune response. In parallel, microglia should also act clearing alpha-synuclein thus avoiding an overabundance of the protein, which is crucial to the disease progression. Therefore, the microglia response in each moment will have significant consequences for the neuronal fate. Here we will review the literature addressing the microglia response in Parkinson's disease with an especial focus on the protein alpha-synuclein. We will also reflect upon the limitations of the studies carried so far and in the therapeutic possibilities opened based on these recent findings.

Region-Specific Effects of Immunotherapy With Antibodies Targeting α-synuclein in a Transgenic Model of Synucleinopathy

Synucleinopathies represent a group of neurodegenerative disorders which are characterized by intracellular accumulation of aggregated α-synuclein. α-synuclein misfolding and oligomer formation is considered a major pathogenic trigger in these disorders. Therefore, targeting α-synuclein species represents an important candidate therapeutic approach. Our aim was to analyze the biological effects of passive immunization targeting α-synuclein and to identify the possible underlying mechanisms in a transgenic mouse model of oligodendroglial α-synucleinopathy. We used PLP-α-synuclein mice overexpressing human α-synuclein in oligodendrocytes. The animals received either antibodies that recognize α-synuclein or vehicle. Passive immunization mitigated α-synuclein pathology and resulted in reduction of total α-synuclein in the hippocampus, reduction of intracellular accumulation of aggregated α-synuclein, particularly significant in the spinal cord. Lowering of the extracellular oligomeric α-synuclein was associated with reduction of the density of activated iba1-positive microglia profiles. However, a shift toward phagocytic microglia was seen after passive immunization of PLP-α-synuclein mice. Lowering of intracellular α-synuclein was mediated by autophagy degradation triggered after passive immunization in PLP-α-synuclein mice. In summary, the study provides evidence for the biological efficacy of immunotherapy in a transgenic mouse model of oligodendroglial synucleinopathy. The different availability of the therapeutic antibodies and the variable load of α-synuclein pathology in selected brain regions resulted in differential effects of the immunotherapy that allowed us to propose a model of the underlying mechanisms of antibody-aided α-synuclein clearance.