T-Lymphocyte Deficiency Exacerbates Behavioral Deficits in the 6-OHDA Unilateral Lesion Rat Model for Parkinson's Disease

Impact of Sex on Neuroimmune contributions to Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. Inflammation has been observed in both the idiopathic and familial forms of PD. Importantly, PD is reported more often in men than in women, men having at least 1.5- fold higher risk to develop PD than women. This review summarizes the impact of biological sex and sex hormones on the neuroimmune contributions to PD and its investigation in animal models of PD. Innate and peripheral immune systems participate in the brain neuroinflammation of PD patients and is reproduced in neurotoxin, genetic and alpha-synuclein based models of PD. Microglia and astrocytes are the main cells of the innate immune system in the central nervous system and are the first to react to restore homeostasis in the brain. Analysis of serum immunoprofiles in female and male control and PD patients show that a great proportion of these markers differ between male and female. The relationship between CSF inflammatory markers and PD clinical characteristics or PD biomarkers shows sex differences. Conversely, in animal models of PD, sex differences in inflammation are well documented and the beneficial effects of endogenous and exogenous estrogenic modulation in inflammation have been reported. Targeting neuroinflammation in PD is an emerging therapeutic option but gonadal drugs have not yet been investigated in this respect, thus offering new opportunities for sex specific treatments.

B lymphocyte responses in Parkinson's disease and their possible significance in disease progression

Inflammation contributes to Parkinson's disease pathogenesis. We hypothesized that B lymphocytes are involved in Parkinson's disease progression. We measured antibodies to alpha-synuclein and tau in serum from patients with rapid eye movement sleep behaviour disorder (n = 79), early Parkinson's disease (n = 50) and matched controls (n = 50). Rapid eye movement sleep behaviour disorder cases were stratified by risk of progression to Parkinson's disease (low risk = 30, high risk = 49). We also measured B-cell activating factor of the tumour necrosis factor receptor family, C-reactive protein and total immunoglobulin G. We found elevated levels of antibodies to alpha-synuclein fibrils in rapid eye movement sleep behaviour disorder patients at high risk of Parkinson's disease conversion (ANOVA, P < 0.001) and lower S129D peptide-specific antibodies in those at low risk (ANOVA, P < 0.001). An early humoral response to alpha-synuclein is therefore detectable prior to the development of Parkinson's disease. Peripheral B lymphocyte phenotyping using flow cytometry in early Parkinson's disease patients and matched controls (n = 41 per group) revealed reduced B cells in Parkinson's disease, particularly in those at higher risk of developing an early dementia [t(3) = 2.87, P = 0.01]. Patients with a greater proportion of regulatory B cells had better motor scores [F(4,24) = 3.612, P = 0.019], suggesting they have a protective role in Parkinson's disease. In contrast, B cells isolated from Parkinson's disease patients at higher risk of dementia had greater cytokine (interleukin 6 and interleukin 10) responses following in vitro stimulation. We assessed peripheral blood lymphocytes in alpha-synuclein transgenic mouse models of Parkinson's disease: they also had reduced B cells, suggesting this is related to alpha-synuclein pathology. In a toxin-based mouse model of Parkinson's disease, B-cell deficiency or depletion resulted in worse pathological and behavioural outcomes, supporting the conclusion that B cells play an early protective role in dopaminergic cell loss. In conclusion, we found changes in the B-cell compartment associated with risk of disease progression in rapid eye movement sleep behaviour disorder (higher alpha-synuclein antibodies) and early Parkinson's disease (lower levels of B lymphocytes that were more reactive to stimulation). Regulatory B cells play a protective role in a mouse model, potentially by attenuating inflammation and dopaminergic cell loss. B cells are therefore likely to be involved in the pathogenesis of Parkinson's disease, albeit in a complex way, and thus warrant consideration as a therapeutic target.

Exploring the neuroprotective effects of montelukast on brain inflammation and metabolism in a rat model of quinolinic acid-induced striatal neurotoxicity

BACKGROUND

One intrastriatal administration of quinolinic acid (QA) in rats induces a lesion with features resembling those observed in Huntington's disease. Our aim is to evaluate the effects of the cysteinyl leukotriene receptor antagonist montelukast (MLK), which exhibited neuroprotection in different preclinical models of neurodegeneration, on QA-induced neuroinflammation and regional metabolic functions.

METHODS

The right and left striatum of Sprague Dawley and athymic nude rats were injected with QA and vehicle (VEH), respectively. Starting from the day before QA injection, animals were treated with 1 or 10 mg/kg of MLK or VEH for 14 days. At 14 and 30 days post-lesion, animals were monitored with magnetic resonance imaging (MRI) and positron emission tomography (PET) using [18F]-VC701, a translocator protein (TSPO)-specific radiotracer. Striatal neuroinflammatory response was measured post-mortem in rats treated with 1 mg/kg of MLK by immunofluorescence. Rats treated with 10 mg/kg of MLK also underwent a [18F]-FDG PET study at baseline and 4 months after lesion. [18F]-FDG PET data were then used to assess metabolic connectivity between brain regions by applying a covariance analysis method.

RESULTS

MLK treatment was not able to reduce the QA-induced increase in striatal TSPO PET signal and MRI lesion volume, where we only detected a trend towards reduction in animals treated with 10 mg/kg of MLK. Post-mortem immunofluorescence analysis revealed that MLK attenuated the increase in striatal markers of astrogliosis and activated microglia in the lesioned hemisphere. We also found a significant increase in a marker of anti-inflammatory activity (MannR) and a trend towards reduction in a marker of pro-inflammatory activity (iNOS) in the lesioned striatum of MLK-compared to VEH-treated rats. [18F]-FDG uptake was significantly reduced in the striatum and ipsilesional cortical regions of VEH-treated rats at 4 months after lesion. MLK administration preserved glucose metabolism in these cortical regions, but not in the striatum. Finally, MLK was able to counteract changes in metabolic connectivity and measures of network topology induced by QA, in both lesioned and non-lesioned hemispheres.

CONCLUSIONS

Overall, MLK treatment produced a significant neuroprotective effect by reducing neuroinflammation assessed by immunofluorescence and preserving regional brain metabolism and metabolic connectivity from QA-induced neurotoxicity in cortical and subcortical regions.

Neuroinflammation and Parkinson's Disease-From Neurodegeneration to Therapeutic Opportunities

Parkinson’s disease (PD) is the second most prevalent neurodegenerative disorder worldwide. Clinically, it is characterized by a progressive degeneration of dopaminergic neurons (DAn), resulting in severe motor complications. Preclinical and clinical studies have indicated that neuroinflammation can play a role in PD pathophysiology, being associated with its onset and progression. Nevertheless, several key points concerning the neuroinflammatory process in PD remain to be answered. Bearing this in mind, in the present review, we cover the impact of neuroinflammation on PD by exploring the role of inflammatory cells (i.e., microglia and astrocytes) and the interconnections between the brain and the peripheral system. Furthermore, we discuss both the innate and adaptive immune responses regarding PD pathology and explore the gut–brain axis communication and its influence on the progression of the disease.

Proteomics for comprehensive characterization of extracellular vesicles in neurodegenerative disease

Extracellular vesicles (EVs) are small lipid bilayer particles ubiquitously released by almost every cell type. A specific and selective constituents of EVs loaded with variety of proteins, lipids, small noncoding RNAs, and long non-coding RNAs are reflective of cellular events, type, and physiologic/pathophysiologic status of the cell of origin. Moreover, these molecular contents carry information from the cell of origin to recipient cells, modulating intercellular communication. Recent studies demonstrated that EVs not only play a neuroprotective role by mediating the removal of toxic proteins, but also emerge as an important player in various neurodegenerative disease onset and progression through facilitating of misfolded proteins propagation. For this reason, neurodegenerative disease-associated differences in EV proteome relative to normal EVs can be used to fulfil diagnostic, prognostic, and therapeutic purposes. Nonetheless, characterizing EV proteome obtained from biological samples (brain tissue and body fluids, including urea, blood, saliva, and CSF) is a challenging task. Herein, we review the status of EV proteome profiling and the updated discovery of potential biomarkers for the diagnosis of neurodegenerative disease with an emphasis on the integration of high-throughput advanced mass spectrometry (MS) technologies for both qualitative and quantitative analysis of EVs in different clinical tissue/body fluid samples in past five years.

Neuroinflammation in Parkinson's Disease - Putative Pathomechanisms and Targets for Disease-Modification

Parkinson’s disease (PD) is a progressive and debilitating chronic disease that affects more than six million people worldwide, with rising prevalence. The hallmarks of PD are motor deficits, the spreading of pathological α-synuclein clusters in the central nervous system, and neuroinflammatory processes. PD is treated symptomatically, as no causally-acting drug or procedure has been successfully established for clinical use. Various pathways contributing to dopaminergic neuron loss in PD have been investigated and described to interact with the innate and adaptive immune system. We discuss the possible contribution of interconnected pathways related to the immune response, focusing on the pathophysiology and neurodegeneration of PD. In addition, we provide an overview of clinical trials targeting neuroinflammation in PD.

Human organotypic brain model as a tool to study chemical-induced dopaminergic neuronal toxicity

Oxidative stress is caused by an imbalance between the generation and detoxification of reactive oxygen and nitrogen species (ROS/RNS). This imbalance plays an important role in brain aging and age-related neurodegenerative diseases. In the context of Parkinson’s disease (PD), the sensitivity of dopaminergic neurons in the substantia nigra pars compacta to oxidative stress is considered a key factor of PD pathogenesis. Here we study the effect of different oxidative stress-inducing compounds (6-OHDA, MPTP or MPP⁺) on the population of dopaminergic neurons in an iPSC-derived human brain 3D model (aka BrainSpheres). Treatment with 6-OHDA, MPTP or MPP⁺ at 4 weeks of differentiation disrupted the dopaminergic neuronal phenotype in BrainSpheres at (50, 5000, 1000 μM respectively). 6-OHDA increased ROS production and decreased mitochondrial function most efficiently. It further induced the greatest changes in gene expression and metabolites related to oxidative stress and mitochondrial dysfunction. Co-culturing BrainSpheres with an endothelial barrier using a transwell system allowed the assessment of differential penetration capacities of the tested compounds and the damage they caused in the dopaminergic neurons within the BrainSpheres In conclusion, treatment with compounds known to induce PD-like phenotypes in vivo caused molecular deficits and loss of dopaminergic neurons in the BrainSphere model. This approach therefore recapitulates common animal models of neurodegenerative processes in PD at similarly high doses. The relevance as tool for drug discovery is discussed.

Dopamine receptor D2 on CD4+ T cells is protective against neuroinflammation and neurodegeneration in a mouse model of Parkinson's disease

Parkinson's disease (PD) is a chronic neurodegenerative disease. Recently, neuroinflammation driven by CD4⁺ T cells has been involved in PD pathophysiology. Human and murine lymphocytes express all the five subtypes of dopamine receptors (DRs), DRD1 to DRD5. However, roles of DRs particularly DRD2 expressed on CD4⁺ T cells in PD remain elucidated. Global Drd1- or Drd2-knockout (Drd1^-/- or Drd2^-/-) mice or CD4⁺ T cell-specific Drd2-knockout (Drd2^fl/fl/CD4^Cre) mice were intraperitoneally injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to induce PD with the different mutants. On the 7th day following MPTP injection, mice were assessed for dopaminergic neurodegeneration, locomotor impairments, microglial activation, as well as CD4⁺ T-cell differentiation and function. Furthermore, in vitro CD4⁺ T cells were exposed to DRD2 agonist and antagonist and then differentiation and function of the cells were determined. MPTP induced dopaminergic neuronal loss in the nigrostriatal system, motor coordinative and behavioral impairments, microglial activation, and CD4⁺ T-cell polarization to pro-inflammatory T-helper (Th)1 and Th17 phenotypes. Importantly, either Drd2^-/- or Drd2^fl/fl/CD4^Cre mice manifested more severe dopaminergic neurodegeneration, motor deficits, microglial activation, and CD4⁺ T-cell bias towards Th1 and Th17 phenotypes in response to MPTP, but Drd1^-/- did not further alter MPTP intoxication. DRD2 agonist sumanirole inhibited shift of CD4⁺ T cells obtained from MPTP-intoxicated mice to Th1 and Th17 phenotypes and DRD2 antagonist L-741,626 reversed sumanirole effects. These findings suggest that DRD2 expressed on CD4⁺ T cells is protective against neuroinflammation and neurodegeneration in PD. Thus, developing a therapeutic strategy of stimulating DRD2 may be promising for mitigation of PD.

Protective Effect of the α7 Nicotinic Receptor Agonist PNU-282987 on Dopaminergic Neurons Against 6-Hydroxydopamine, Regulating Anti-neuroinflammatory and the Immune Balance Pathways in Rat

Neuroinflammation and inner immune dysfunction are increasingly accepted as important components of the etiopathogenesis of Parkinson’s disease (PD). According to emerging evidence, a7 nicotinic acetylcholine receptor (α7nAChR), a ligand-gated ion channel, plays an important role in inflammatory reactions and is also expressed on the surface of T cells. In particular, regulatory T cells (Tregs) are critical for the maintenance of immunological tolerance. In the present study, we investigated the roles of α7nAChR in inhibiting inflammation and maintaining the immune balance in rats with 6-hydroxydopamine (6-OHDA)-induced lesions and the possible mechanisms regulating the proportion of Tregs in vivo. Adult male Wistar rats (n = 90) were subjected to a unilateral injection of 6-OHDA into the left medial forebrain bundle, and PNU-282987, an α7nAChR agonist, was intraperitoneally injected 2 h prior to the induction of lesions by 6-OHDA and again at days 1, 7, and 13 postlesion. Behavioral tests and immunohistochemical staining to detect the expression of tyrosine hydroxylase (TH) in the bilateral substantial nigra (SN) were performed. Subsequently, CD4+ T lymphocytes and the expression of forkhead/winged helix transcription factor p3 (Foxp3, which is a marker of Treg cells) in the SN were also assessed using immunofluorescence staining. The expression of glial fibrillary acidic protein (GFAP) in the SN was determined by performing immunohistochemical staining. Additionally, the protein levels of α7nAChR, extracellular signal-regulated kinase (Erk) phosphorylated-Erk (p-Erk) and Foxp3 in the ventral midbrain were determined using Western blotting, and the relative expression of the TNF-α, IL-1β, and IL-10 mRNAs were detected using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). We found that PNU-282987 significantly improved the motor deficits induced by 6-OHDA, reduced the loss of TH in the SN, suppressed the overactivation of GFAP+ cells and expression of related inflammatory cytokines, and increased the number of Foxp3+ cells. In addition, we also showed that PNU-282987 significantly increased the protein expression of the a7nAchR, p-Erk, and Foxp3 in 6-OHDA-lesioned rats (p < 0.05). These results indicated that α7nAChR activation could exert an anti-inflammatory effect and participate in the process of modulating the immune balance during 6-OHDA-induced injury, potentially through the α7nAChR/p-Erk/Foxp3 signaling pathway.

Innate and adaptive immune responses in Parkinson's disease

Parkinson's disease (PD) has classically been defined as a movement disorder, in which motor symptoms are explained by the aggregation of alpha-synuclein (α-syn) and subsequent death of dopaminergic neurons of the substantia nigra pars compacta (SNpc). More recently, the multisystem effects of the disease have been investigated, with the immune system being implicated in a number of these processes in the brain, the blood, and the gut. In this review, we highlight the dysfunctional immune system found in both human PD and animal models of the disease, and discuss how genetic risk factors and risk modifiers are associated with pro-inflammatory immune responses. Finally, we emphasize evidence that the immune response drives the pathogenesis and progression of PD, and discuss key questions that remain to be investigated in order to identify immunomodulatory therapies in PD.

Differential proteomic analysis of serum exosomes reveals alterations in progression of Parkinson disease

Exosomes are nanometer-sized vesicles with intercellular communication functions, and their encapsulated proteins may participate in the pathological process of neurodegenerative disorders. The aim of this study was to identify the protein changes of serum exosomes in Parkinson disease (PD) patients with different disease progress types, and to identify potential biomarkers. The exosomes of PD patients with different severity and healthy control group were isolated from serum. The exosome proteins were analyzed by mass spectrometry with label-free quantitative proteomics. A total of 429 proteins were identified, of which 14 were significantly different in mild and severe PD patients. The expression levels of 7 proteins, including pigmented epithelium-derived factor, afamin, apolipoprotein D and J, were significantly increased in PD patients. The expression levels of 7 proteins, including complement C1q and protein Immunoglobulin Lambda Variable 1-33 (IGLV1-33)Cluster -33, were decreased in PD patients. These differentially expressed proteins were analyzed by gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis, which confirmed that the interaction between prion diseases and ECM receptors was the most significant pathways of enrichment. The changes of proteins and pathways may be related to the pathophysiological mechanism of PD. Therefore, some of these proteins could be considered as potential biomarkers for early PD diagnosis.

Peripheral-Central Neuroimmune Crosstalk in Parkinson's Disease: What Do Patients and Animal Models Tell Us?

The brain is no longer considered an immune privileged organ and neuroinflammation has long been associated with Parkinson's disease. Accumulating evidence demonstrates that innate and adaptive responses take place in the CNS. The extent to which peripheral immune alterations impacts on the CNS, or vice and versa, is, however, still a matter of debate. Gaining a better knowledge of the molecular and cellular immune dysfunctions present in these two compartments and clarifying their mutual interactions is a fundamental step in understanding and preventing Parkinson's disease (PD) pathogenesis. This review provides an overview of the current knowledge on inflammatory processes evidenced both in PD patients and in toxin-induced animal models of the disease. It discusses differences and similarities between human and animal studies in the context of neuroinflammation and immune responses and how they have guided therapeutic strategies to slow down disease progression. Future longitudinal studies are necessary and can help gain a better understanding on peripheral-central nervous system crosstalk to improve therapeutic strategies for PD.

Lymphoproliferation Impairment and Oxidative Stress in Blood Cells from Early Parkinson's Disease Patients

In Parkinson’s Disease (PD), the peripheral changes in the functional capacity and redox state of immune cells has been scarcely investigated, especially in the early PD stages. Aging is a risk factor for PD, and the age-related impairment of the immune system, based on a chronic-oxidative stress situation, is involved in the rate of aging. We analyzed several functions in isolated peripheral blood neutrophils and mononuclear cells from PD stage 2 patients, and compared the results to those in healthy elderly and adult controls. Several oxidative stress and damage parameters were studied in whole blood cells. The results showed an impairment of the lymphoproliferative response in stimulated conditions in the PD patients compared with age-matched controls, who also showed typical immunosenescence in comparison with adult individuals. Higher oxidative stress and damage were observed in whole blood cells from PD patients (lower glutathione peroxidase activity, and higher oxidized glutathione and malondialdehyde contents). Our results suggest an accelerated immunosenescence in PD stage 2, and that several of the parameters studied could be appropriate peripheral biomarkers in the early stages of PD.

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.

The Role of Immunosenescence in Neurodegenerative Diseases

Aging is characterized by the progressive decline of physiological function and tissue homeostasis leading to increased vulnerability, degeneration, and death. Aging-related changes of the innate and adaptive immune system include decline in the preservation and enhancement of many immune functions, such as changes in the number of circulating monocytic and dendritic cells, thymic involution, T cell polyfunctionality, or production of proinflammatory cytokines, and are defined as immunosenescence. Inflammatory functions are increased with age, causing the chronic low-grade inflammation, referred to as inflamm-aging, that contribute, together with immunosenescence, to neurodegenerative diseases. In this review, we discuss the link between the immune and nervous systems and how the immunosenescence and inflamm-aging can contribute to neurodegenerative diseases.

Botulinum Neurotoxin A Injected Ipsilaterally or Contralaterally into the Striatum in the Rat 6-OHDA Model of Unilateral Parkinson's Disease Differently Affects Behavior

Parkinson's disease (PD) is one of the most frequent neurodegenerative disorders. The loss of dopaminergic neurons in the substantia nigra leads to a disinhibition of cholinergic interneurons in the striatum. Pharmacotherapeutical strategies of PD-related hypercholinism have numerous adverse side effects. We previously showed that ipsilateral intrastriatal injections of 1 ng in unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats inhibit apomorphine-induced rotation behavior significantly up to 6 months. In this study, we extended the behavioral testing of ipsilateral botulinum neurotoxin A (BoNT-A)-injection and additionally investigated the impact of intrastriatal BoNT-A-injections contralateral to the 6-OHDA-lesioned hemisphere on the basal ganglia circuity and motor functions. We hypothesized that the interhemispheric differences of acetylcholine (ACh) concentration seen in unilateral hemi-PD should be differentially and temporally influenced by the ipsilateral or contralateral injection of BoNT-A. Hemi-PD rats were injected with 1 ng BoNT-A or vehicle substance into either the ipsilateral or contralateral striatum 6 weeks after 6-OHDA-lesion and various behaviors were tested. In hemi-PD rats intrastriatal ipsilateral BoNT-A-injections significantly reduced apomorphine-induced rotations and increased amphetamine-induced rotations, but showed no significant improvement of forelimb usage and akinesia, lateralized sensorimotor integration and also no effect on spontaneous locomotor activity. However, intrastriatal BoNT-A-injections contralateral to the lesion led to a significant increase of the apomorphine-induced turning rate only 2 weeks after the treatment. The apomorphine-induced rotation rate decreases thereafter to a value below the initial rotation rate. Amphetamine-induced rotations were not significantly changed after BoNT-A-application in comparison to sham-treated animals. Forelimb usage was temporally improved by contralateral BoNT-A-injection at 2 weeks after BoNT-A. Akinesia and lateralized sensorimotor integration were also improved, but contralateral BoNT-A-injection had no significant effect on spontaneous locomotor activity. These long-ranging and different effects suggest that intrastriatally applied BoNT-A acts not only as an inhibitor of ACh release but also has long-lasting impact on transmitter expression and thereby on the basal ganglia circuitry. Evaluation of changes of transmitter receptors is subject of ongoing studies of our group.

Complex Changes in the Innate and Adaptive Immunity Accompany Progressive Degeneration of the Nigrostriatal Pathway Induced by Intrastriatal Injection of 6-Hydroxydopamine in the Rat

We investigated changes in innate and adaptive immunity paralleling the progressive nigrostriatal damage occurring in a neurotoxic model of Parkinson's disease (PD) based on unilateral infusion of 6-hydroxydopamine (6-OHDA) into the rat striatum. A time-course analysis was conducted to assess changes in morphology (activation) and cell density of microglia and astrocytes, microglia polarization (M1 vs. M2 phenotype), lymphocyte infiltration in the lesioned substantia nigra pars compacta (SNc), and modifications of CD8+ and subsets of CD4+ T cell in peripheral blood accompanying nigrostriatal degeneration. Confirming previous results, we observed slightly different profiles of activation for astrocytes and microglia paralleling nigral neuronal loss. For astrocytes, morphological changes and cell density increases were mostly evident at the latest time points (14 and 28 days post-surgery), while moderate microglia activation was present since the earliest time point. For the first time, in this model, we described the time-dependent profile of microglia polarization. Activated microglia clearly expressed the M2 phenotype in the earlier phase of the experiment, before cell death became manifest, gradually shifting to the M1 phenotype as SNc cell death started. In parallel, a reduction in the percentage of circulating CD4+ T regulatory (Treg) cells, starting as early as day 3 post-6-OHDA injection, was detected in 6-OHDA-injected rats. Our data show that nigrostriatal degeneration is associated with complex changes in central and peripheral immunity. Microglia activation and polarization, Treg cells, and the factors involved in their cross-talk should be further investigated as targets for the development of therapeutic strategies for disease modification in PD.

Anti-Inflammatory Modulation of Microglia via CD163-Targeted Glucocorticoids Protects Dopaminergic Neurons in the 6-OHDA Parkinson's Disease Model

Increasing evidence supports a decisive role for inflammation in the neurodegenerative process of Parkinson's disease (PD). The immune response in PD seems to involve, not only microglia, but also other immune cells infiltrated into the brain. Indeed, we observed here the infiltration of macrophages, specifically CD163+ macrophages, into the area of neurodegeneration in the 6-hydroxydopamine (6-OHDA) PD model. Therefore, we investigated the therapeutic potential of the infiltrated CD163+ macrophages to modulate local microglia in the brain to achieve neuroprotection. To do so, we designed liposomes targeted for the CD163 receptor to deliver dexamethasone (Dexa) into the CD163+ macrophages in the 6-OHDA PD model. Our data show that a fraction of the CD163-targeted liposomes were carried into the brain after peripheral intravenous injection. The 6-OHDA-lesioned rats that received repeated intravenous CD163-targeted liposomes with Dexa for 3 weeks exhibited better motor performance than the control groups and had minimal glucocorticoid-driven side effects. Furthermore, these animals showed better survival of dopaminergic neurons in substantia nigra and an increased number of microglia expressing major histocompatibility complex II. Therefore, rats receiving CD163-targeted liposomes with Dexa were partially protected against 6-OHDA-induced dopaminergic neurodegeneration, which correlated with a distinctive microglia response. Altogether, our data support the use of macrophages for the modulation of brain neurodegeneration and specifically highlight the potential of CD163-targeted liposomes as a therapeutic tool in PD.

SIGNIFICANCE STATEMENT

The immune response now evident in the progression of Parkinson's disease comprises both local microglia and other immune cells. We provide evidence that CD163+ macrophages can be a target to modulate brain immune response to achieve neuroprotection in the 6-hydroxydopamine model. To do so, we targeted the CD163+ population, which to a low but significant extent infiltrated in the neurodegenerating area of the brain. Specially designed liposomes targeted for the CD163 receptor were loaded with glucocorticoids and injected peripherally to modify the infiltrated CD163 cells toward an anti-inflammatory profile. This modification of the CD163 population resulted in a distinctive microglial response that correlated with decreased dopaminergic cell death and better motor performance.

The biomarkers of immune dysregulation and inflammation response in Parkinson disease

Parkinson's disease (PD) is referring to the multi-systemic α-synucleinopathy with Lewy bodies deposited in midbrain. In ageing, the environmental and genetic factors work together and overactive major histocompatibility complex pathway to regulate immune reactions in central nerve system which resulting in neural degeneration, especially in dopaminergic neurons. As a series of biomarkers, the human leukocyte antigen genes with its related proteomics play cortical roles on the antigen presentation of major histocompatibility complex molecules to stimulate the differentiation of T lymphocytes and i-proteasome activities under their immune response to the PD-related environmental alteration and genetic variation. Furthermore, dopaminergic drugs change the biological characteristic of T lymphatic cells, affect the α-synuclein presentation pathway, and inhibit T lymphatic cells to release cytotoxicity in PD development. Taking together, the serum inflammatory factors and blood T cells are involved in the immune dysregulation of PD and inspected as the potential clinic biomarkers for PD prediction.

Lymphocytes reduce nigrostriatal deficits in the 6-hydroxydopamine mouse model of Parkinson's disease

Neuroinflammation is a well-known neuropathological feature of Parkinson's disease (PD), but it remains controversial whether it is causal or consequential to neurodegeneration. While the role of microglia in the pathogenesis has been thoroughly investigated in human and different rodent models, data concerning the impact of the adaptive immune system on the pathogenesis of PD are still rare, although lymphocyte populations were found in brain tissue of PD patients and have been implicated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-mediated neurodegeneration in mice. To test the hypothesis that the adaptive immune system contributes to the progression of PD in the murine 6-hydroxydopamine (6-OHDA) model, we performed unilateral 6-OHDA injection into the medial forebrain bundle and compared wild-type mice with recombination activating gene-1 deficient mice (RAG-1(-/-)), that lack mature lymphocytes. After 6-OHDA injection, immune-deficient mice moved significantly slower and less often than wild-type mice. Rotarod analysis displayed a shorter latency to fall in RAG-1(-/-) mice. Immunohistochemical analysis in wild-type mice demonstrated a higher CD8+ T cell density in the ipsilesional striatum compared to sham-operated animals. Cell counts of tyrosine hydroxylase positive dopaminergic neurons of the substantia nigra in immune compromised mice were significantly reduced compared to wild-type mice. Wild type bone marrow reconstitution into RAG-1(-/-) recipients rescued the clinical deterioration as well as the neurodegeneration in RAG-1(-/-) deficient recipients ameliorated clinical symptoms and neurodegeneration after 6-OHDA treatment. Our data indicate that lymphocytes reduce the clinical and neuropathological impact of 6-OHDA lesioning and thus may play a protective role in this toxic mouse model of PD.

Intensive Rehabilitation Enhances Lymphocyte BDNF-TrkB Signaling in Patients With Parkinson's Disease

Background In a combined animal and human study, we have previously found that a 5-day treatment that enhances cortical plasticity also facilitates brain-derived neurotrophic factor (BDNF)-tyrosine receptor kinase B (TrkB) signaling and increases activated TrkB and N-methyl-d-aspartate receptor (NMDAR) association in both the cortex and the peripheral lymphocytes. Patients with Parkinson's disease (PD), in general, show decreased cortical plasticity, as demonstrated by electrophysiological and behavioral studies. Here, we test the hypothesis that an exercise program that improves motor function and seems to slow down symptom progression can enhance BDNF-TrkB signaling in lymphocytes. Methods A total of 16 patients with PD underwent a 4-week multidisciplinary intensive rehabilitation treatment (MIRT), which included aerobic training and physical and occupational therapy. Blood was collected before and after 2 and 4 weeks of MIRT. Lymphocytes were isolated to examine BDNF-TrkB signaling induced by incubation with recombinant human BDNF. TrkB signaling complexes, extracellular-signal-regulated kinase-2 and protein-kinase-B were immunoprecipitated; the content of immunocomplexes was determined by Western blotting. Results After MIRT, all patients showed improvement in motor function. TrkB interaction with NMDAR and BDNF-TrkB signaling increased in peripheral lymphocytes at receptor, intracellular mediator, and downstream levels. The decrements in Unified Parkinson's Disease Rating Scale II (UPDRSII) and total scores were significantly correlated with the increases in TrkB signaling at receptor, intracellular mediator, and NMDAR interaction levels. Conclusions The significant correlation between reduced UPDRS scores and the changes in lymphocyte activity suggest that enhanced BDNF-TrkB signaling in lymphocyte and reduced severity of PD symptoms may be related.