Evidence for a role of adaptive immune response in the disease pathogenesis of the MPTP mouse model of Parkinson's disease

The major histocompatibility complex participates in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease characterized by progressive loss of dopaminergic neurons in the substantia nigra and the aggregation of alpha-synuclein (α-syn). The central nervous system (CNS) has previously been considered as an immune-privileged area. However, studies have shown that the immune responses are involved in PD. The major histocompatibility complex (MHC) presents antigens from antigen-presenting cells (APCs) to T lymphocytes, immune responses will be induced. MHCs are expressed in microglia, astrocytes, and dopaminergic neurons. Single nucleotide polymorphisms in MHC are related to the risk of PD. The aggregated α-syn triggers the expression of MHCs by activating glia cells. CD4+ and CD8+ T lymphocytes responses and microglia activation are detected in brains of PD patients. In addiction immune responses further increase blood-brain barrier (BBB) permeability and T cell infiltration in PD. Thus, MHCs are involved in PD through participating in immune and inflammatory responses.

Experimental Models to Study Immune Dysfunction in the Pathogenesis of Parkinson's Disease

Parkinson's disease (PD) is a chronic, age-related, progressive multisystem disease associated with neuroinflammation and immune dysfunction. This review discusses the methodological approaches used to study the changes in central and peripheral immunity in PD, the advantages and limitations of the techniques, and their applicability to humans. Although a single animal model cannot replicate all pathological features of the human disease, neuroinflammation is present in most animal models of PD and plays a critical role in understanding the involvement of the immune system (IS) in the pathogenesis of PD. The IS and its interactions with different cell types in the central nervous system (CNS) play an important role in the pathogenesis of PD. Even though culture models do not fully reflect the complexity of disease progression, they are limited in their ability to mimic long-term effects and need validation through in vivo studies. They are an indispensable tool for understanding the interplay between the IS and the pathogenesis of this disease. Understanding the immune-mediated mechanisms may lead to potential therapeutic targets for the treatment of PD. We believe that the development of methodological guidelines for experiments with animal models and PD patients is crucial to ensure the validity and consistency of the results.

Myeloid-specific blockade of notch signaling alleviates dopaminergic neurodegeneration in Parkinson's disease by dominantly regulating resident microglia activation through NF-κB signaling

Yolk sac-derived microglia and peripheral monocyte-derived macrophages play a key role during Parkinson's disease (PD) progression. However, the regulatory mechanism of microglia/macrophage activation and function in PD pathogenesis remains unclear. Recombination signal-binding protein Jκ (RBP-J)-mediated Notch signaling regulates macrophage development and activation. In this study, with an 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) hydrochloride-induced acute murine PD model, we found that Notch signaling was activated in amoeboid microglia accompanied by a decrease in tyrosine hydroxylase (TH)-positive neurons. Furthermore, using myeloid-specific RBP-J knockout (RBP-JcKO) mice combined with a PD model, our results showed that myeloid-specific disruption of RBP-J alleviated dopaminergic neurodegeneration and improved locomotor activity. Fluorescence-activated cell sorting (FACS) analysis showed that the number of infiltrated inflammatory macrophages and activated major histocompatibility complex (MHC) II+ microglia decreased in RBP-JcKO mice compared with control mice. Moreover, to block monocyte recruitment by using chemokine (C-C motif) receptor 2 (CCR2) knockout mice, the effect of RBP-J deficiency on dopaminergic neurodegeneration was not affected, indicating that Notch signaling might regulate neuroinflammation independent of CCR2+ monocyte infiltration. Notably, when microglia were depleted with the PLX5622 formulated diet, we found that myeloid-specific RBP-J knockout resulted in more TH+ neurons and fewer activated microglia. Ex vitro experiments demonstrated that RBP-J deficiency in microglia might reduce inflammatory factor secretion, TH+ neuron apoptosis, and p65 nuclear translocation. Collectively, our study first revealed that RBP-J-mediated Notch signaling might participate in PD progression by mainly regulating microglia activation through nuclear factor kappa-B (NF-κB) signaling.

Parkinson's Disease: Exploring Different Animal Model Systems

Disease modeling in non-human subjects is an essential part of any clinical research. To gain proper understanding of the etiology and pathophysiology of any disease, experimental models are required to replicate the disease process. Due to the huge diversity in pathophysiology and prognosis in different diseases, animal modeling is customized and specific accordingly. As in other neurodegenerative diseases, Parkinson's disease is a progressive disorder coupled with varying forms of physical and mental disabilities. The pathological hallmarks of Parkinson's disease are associated with the accumulation of misfolded protein called α-synuclein as Lewy body, and degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc) area affecting the patient's motor activity. Extensive research has already been conducted regarding animal modeling of Parkinson's diseases. These include animal systems with induction of Parkinson's, either pharmacologically or via genetic manipulation. In this review, we will be summarizing and discussing some of the commonly employed Parkinson's disease animal model systems and their applications and limitations.

Food restriction and hyperactivity induce changes in corticolimbic brain dopamine and serotonin levels in female rats

Compelling data support altered dopamine (DA) and serotonin (5-HT) signaling in anorexia nervosa (AN). However, their exact role in the etiopathogenesis of AN has yet to be elucidated. Here, we evaluated the corticolimbic brain levels of DA and 5-HT in the induction and recovery phases of the activity-based anorexia (ABA) model of AN. We exposed female rats to the ABA paradigm and measured the levels of DA, 5-HT, the metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and the dopaminergic type 2 (D2) receptors density in feeding- and reward-implicated brain regions (i.e., cerebral cortex, Cx; prefrontal cortex, PFC; caudate putamen, CPu; nucleus accumbens, NAcc; amygdala, Amy; hypothalamus, Hyp; hippocampus, Hipp). DA levels were significantly increased in the Cx, PFC and NAcc, while 5-HT was significantly enhanced in the NAcc and Hipp of ABA rats. Following recovery, DA was still elevated in the NAcc, while 5-HT was increased in the Hyp of recovered ABA rats. DA and 5-HT turnover were impaired at both ABA induction and recovery. D2 receptors density was increased in the NAcc shell. These results provide further proof of the impairment of the dopaminergic and serotoninergic systems in the brain of ABA rats and support the knowledge of the involvement of these two important neurotransmitter systems in the development and progression of AN. Thus, providing new insights on the corticolimbic regions involved in the monoamine dysregulations in the ABA model of AN.

Anti-oxidative and anti-neuroinflammatory role of Necrostatin-1s and docosahexaenoic acid in RIP-1-mediated neurotoxicity in MPTP-induced Parkinson's disease model

Parkinson's disease (PD) is a neuromuscular ailment that affects people in their later years and causes both motor and non-motor deficits. Receptor-interacting protein-1 (RIP-1) is a critical participant in necroptotic cell death, possibly through an oxidant-antioxidant imbalance and cytokine cascade activation in PD pathogenesis. The present study examined the role of RIP-1-mediated necroptosis and neuroinflammation in the MPTP-induced PD mouse model, as well as their protection by Necrostatin-1s (an RIP signalling inhibitor), antioxidant DHA and their functional interaction. BALB/c mice were given acute MPTP therapy (4 injections of 15 mg/kg i.p. at 2-h intervals) on day 1. After MPTP intoxication, Necrostatin-1s (Nec-1s; 8 mg/kg/day, i.p.) and DHA (300 mg/kg/day, p.o.) treatments were given once daily for 7 days. The Nec-1s treatment prevented MPTP-induced behavioural, biochemical and neurochemical alterations, and the addition of DHA increases Nec-1s' neuroprotective impact. In addition, Nec-1s and DHA significantly improve the survival of TH-positive dopaminergic neurons and lower expression levels of the inflammatory cytokines, IL-1β and TNF-α. Furthermore, Nec-1s dramatically reduced RIP-1 expression, whereas DHA had little effect. Our research raises the possibility that neuroinflammatory signalling and acute MPTP-induced necroptosis are both mediated by TNFR1-driven RIP-1 activity. In this study, RIP-1 ablation through Nec-1s and the addition of DHA showed a reduction in the levels of pro-inflammatory and oxidative markers, as well as protection from MPTP-driven dopaminergic degeneration and neurobehavioural changes, suggesting potential therapeutic applications. For a better understanding, additional research about the mechanism(s) behind Nec-1s and DHA is required.

Role of Astrocytes in Parkinson's Disease Associated with Genetic Mutations and Neurotoxicants

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons and the aggregation of Lewy bodies in the basal ganglia, resulting in movement impairment referred to as parkinsonism. However, the etiology of PD is not well known, with genetic factors accounting only for 10-15% of all PD cases. The pathogenetic mechanism of PD is not completely understood, although several mechanisms, such as oxidative stress and inflammation, have been suggested. Understanding the mechanisms of PD pathogenesis is critical for developing highly efficacious therapeutics. In the PD brain, dopaminergic neurons degenerate mainly in the basal ganglia, but recently emerging evidence has shown that astrocytes also significantly contribute to dopaminergic neuronal death. In this review, we discuss the role of astrocytes in PD pathogenesis due to mutations in α-synuclein (PARK1), DJ-1 (PARK7), parkin (PARK2), leucine-rich repeat kinase 2 (LRRK2, PARK8), and PTEN-induced kinase 1 (PINK1, PARK6). We also discuss PD experimental models using neurotoxins, such as paraquat, rotenone, 6-hydroxydopamine, and MPTP/MPP+. A more precise and comprehensive understanding of astrocytes' modulatory roles in dopaminergic neurodegeneration in PD will help develop novel strategies for effective PD therapeutics.

Is Disrupted Mitophagy a Central Player to Parkinson's Disease Pathology?

Whilst the pathophysiology at a cellular level has been defined, the cause of Parkinson's disease (PD) remains poorly understood. This neurodegenerative disorder is associated with impaired dopamine transmission in the substantia nigra, and protein accumulations known as Lewy bodies are visible in affected neurons. Cell culture models of PD have indicated impaired mitochondrial function, so the focus of this paper is on the quality control processes involved in and around mitochondria. Mitochondrial autophagy (mitophagy) is the process through which defective mitochondria are removed from the cell by internalisation into autophagosomes which fuse with a lysosome. This process involves many proteins, notably including PINK1 and parkin, both of which are known to be coded on genes associated with PD. Normally in healthy individuals, PINK1 associates with the outer mitochondrial membrane, which then recruits parkin, activating it to attach ubiquitin proteins to the mitochondrial membrane. PINK1, parkin, and ubiquitin cooperate to form a positive feedback system which accelerates the deposition of ubiquitin on dysfunctional mitochondria, resulting in mitophagy. However, in hereditary PD, the genes encoding PINK1 and parkin are mutated, resulting in proteins that are less efficient at removing poorly performing mitochondria, leaving cells more vulnerable to oxidative stress and ubiquitinated inclusion bodies, such as Lewy bodies. Current research that looks into the connection between mitophagy and PD is promising, already yielding potentially therapeutic compounds; until now, pharmacological support for the mitophagy process has not been part of the therapeutic arsenal. Continued research in this area is warranted.

Cell Biology of Parkin: Clues to the Development of New Therapeutics for Parkinson's Disease

Parkinson's disease is the second most prevalent neurodegenerative disease and contributes significantly to morbidity globally. Currently, no disease-modifying therapies exist to combat this disorder. Insights from the molecular and cellular pathobiology of the disease seems to indicate promising therapeutic targets. The parkin protein has been extensively studied for its role in autosomal recessive Parkinson's disease and, more recently, its role in sporadic Parkinson's disease. Parkin is an E3 ubiquitin ligase that plays a prominent role in mitochondrial quality control, mitochondrial-dependent cell death pathways, and other diverse functions. Understanding the numerous roles of parkin has introduced many new possibilities for therapeutic modalities in treating both autosomal recessive Parkinson's disease and sporadic Parkinson's disease. In this article, we review parkin biology with an emphasis on mitochondrial-related functions and propose novel, potentially disease-modifying therapeutic approaches for treating this debilitating condition.

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.

CIITA expression is regulated by histone deacetylase enzymes and has a role in α-synuclein pre-formed fibril-induced antigen presentation in murine microglial cell line

AIM

Parkinson's disease(PD) is a chronic neurodegenerative disorder related with several genetic and epigenetic factors. In the context of epigenetic factors, histone acetylation is one of the most associated mechanisms with Parkinson's disease progression. This study investigates the effects of the increased histone acetylation on antigen presentation in microglial cells which were induced by pre-formed fibrils of α-synuclein(pFF α-synuclein).

METHODS

Parkinson's disease model was created with pFF α-synuclein administration to the BV-2 microglial cells. BV-2 cells were co-treated with CUDC-907 and TMP-195 to increase histone acetylation in the presence of α-synuclein. Antigen representation was evaluated by determining expression levels of major histocompatibility complex-II(MHC-II) and class-II major histocompatibility complex(CIITA).

RESULTS

Our results showed that pFF α-synuclein significantly increased MHC-II expression, and that effect was most severe at 6 hours of administration of α-synuclein. Increasing histone acetylation via CUDC-907 and TMP-195 enhanced MHC-II levels expression, which was more severe in CUDC-907. Additionally, CIITA expression levels were significantly increased with pFF α-synuclein administration and intensified with the co-treatment of CUDC-907 and TMP-195. Furthermore, pFF α-synuclein caused a time-dependent increase in the IFN-gamma(IFN-ɣ) and interleukin-16(IL-16) levels, and that increase was potentiated with CUDC-907 and TMP-195.

CONCLUSION

Changes in MHC-II and CIITA expression indicate that histone acetylation increases the antigen presentation properties of microglial cells after pFF α-synuclein or histone deacetylase inhibitor(HDACi) administration. Our results show that microglial antigen presentation might have an essential role in the pathology of Parkinson's disease, and α-synuclein likely to play a primary role in this mechanism.

Celastrol Downmodulates Alpha-Synuclein-Specific T Cell Responses by Mediating Antigen Trafficking in Dendritic Cells

Parkinson’s Disease (PD) is a neurodegenerative disease that affects the elderly. It is associated with motor dysfunction due to the accumulation of misfolded or aggregated fibrillar alpha-synuclein (α-syn) in the mid-brain. Current treatments are mainly focused on relieving the symptoms but are accompanied by side effects and are limited in halting disease progression. Increasing evidence points to peripheral immune cells underlying disease development, especially T cells contributing to α-syn-related neuroinflammation in PD. The onset of these cells is likely mediated by dendritic cells (DCs), whose role in α-syn-specific responses remain less studied. Moreover, Traditional Chinese medicine (TCM)-derived compounds that are candidates to treat PD may alleviate DC-T cell-mediated immune responses. Therefore, our study focused on the role of DC in response to fibrillar α-syn and subsequent induction of antigen-specific T cell responses, and the effect of TCM Curcumin-analog C1 and Tripterygium wilfordii Hook F-derived Celastrol. We found that although fibrillar α-syn did not induce significant inflammatory or T cell-mediating cytokines, robust pro-inflammatory T cell responses were found by co-culturing fibrillar α-syn-pulsed DCs with α-syn-specific CD4⁺ T cells. Celastrol, but not C1, reduced the onset of pro-inflammatory T cell differentiation, through promoting interaction of endosomal, amphisomal, and autophagic vesicles with fibrillar α-syn, which likely lead to its degradation and less antigen peptides available for presentation and T cell recognition. In conclusion, regulating the intracellular trafficking/processing of α-syn by DCs can be a potential approach to control the progression of PD, in which Celastrol is a potential candidate to accomplish this.

Role of JAK/STAT in the Neuroinflammation and its Association with Neurological Disorders

Background:

Innate immunity is mediated by a variety of cell types, including microglia, macrophages, and neutrophils, and serves as the immune system's first line of defense. There are numerous pathways involved in innate immunity, including the interferon (IFN) pathway, TRK pathway, mitogen-activated protein kinase (MAPK) pathway, Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, interleukin (IL) pathways, chemokine pathways (CCR5), GSK signaling, and Fas signaling.

Summary:

JAK/STAT is one of these important signaling pathways and this review focused on JAK/STAT signaling pathway only. The overactivation of microglia and astrocytes influences JAK/STAT's role in neuroinflammatory disease by initiating innate immunity, orchestrating adaptive immune mechanisms, and ultimately constraining inflammatory and immunological responses. The JAK/STAT signaling pathway is one of the critical factors that promotes neuroinflammation in neurodegenerative diseases.

Key message:

Given the importance of the JAK/STAT pathway in neurodegenerative disease, this review discussed the feasibility of targeting the JAK/STAT pathway as a neuroprotective therapy for neurodegenerative diseases in near future.

Specificity of Adaptive Immune Responses in Central Nervous System Health, Aging and Diseases

The field of neuroimmunology endorses the involvement of the adaptive immune system in central nervous system (CNS) health, disease, and aging. While immune cell trafficking into the CNS is highly regulated, small numbers of antigen-experienced lymphocytes can still enter the cerebrospinal fluid (CSF)-filled compartments for regular immune surveillance under homeostatic conditions. Meningeal lymphatics facilitate drainage of brain-derived antigens from the CSF to deep cervical lymph nodes to prime potential adaptive immune responses. During aging and CNS disorders, brain barriers and meningeal lymphatic functions are impaired, and immune cell trafficking and antigen efflux are altered. In this context, alterations in the immune cell repertoire of blood and CSF and T and B cells primed against CNS-derived autoantigens have been observed in various CNS disorders. However, for many diseases, a causal relationship between observed immune responses and neuropathological findings is lacking. Here, we review recent discoveries about the association between the adaptive immune system and CNS disorders such as autoimmune neuroinflammatory and neurodegenerative diseases. We focus on the current challenges in identifying specific T cell epitopes in CNS diseases and discuss the potential implications for future diagnostic and treatment options.

T cells, α-synuclein and Parkinson disease

The notion that autoimmune responses to α-synuclein may be involved in the pathogenesis of this disorder stems from reports that mutations in α-synuclein or certain alleles of the major histocompatibility complex (MHC) are associated with the disease and that dopaminergic and norepinephrinergic neurons in the midbrain can present antigenic epitopes. Here, we discuss recent evidence that a defined set of peptides derived from α-synuclein act as antigenic epitopes displayed by specific MHC alleles and drive helper and cytotoxic T cell responses in patients with PD. Moreover, phosphorylated α-synuclein may activate T cell responses in a less restricted manner in PD. While the roles for the acquired immune system in disease pathogenesis remain unknown, preclinical animal models and in vitro studies indicate that T cells may interact with neurons and exert effects related to neuronal death and neuroprotection. These findings suggest that therapeutics that target T cells and ameliorate the incidence or disease severity of inflammatory bowel disorders or CNS autoimmune diseases such as multiple sclerosis may be useful in PD.

Partial depletion and repopulation of microglia have different effects in the acute MPTP mouse model of Parkinson's disease

OBJECTIVES

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the progressive and selective degeneration of dopaminergic neurons. Microglial activation and neuroinflammation are associated with the pathogenesis of PD. However, the relationship between microglial activation and PD pathology remains to be explored.

MATERIALS AND METHODS

An acute regimen of MPTP was administered to adult C57BL/6J mice with normal, much reduced or repopulated microglial population. Damages of the dopaminergic system were comprehensively assessed. Inflammation-related factors were assessed by quantitative PCR and Multiplex immunoassay. Behavioural tests were carried out to evaluate the motor deficits in MPTP-challenged mice.

RESULTS

The receptor for colony-stimulating factor 1 inhibitor PLX3397 could effectively deplete microglia in the nigrostriatal pathway of mice via feeding a PLX3397-formulated diet for 21 days. Microglial depletion downregulated both pro-inflammatory and anti-inflammatory molecule expression at baseline and after MPTP administration. At 1d post-MPTP injection, dopaminergic neurons showed a significant reduction in PLX3397-fed mice, but not in control diet (CD)-fed mice. However, partial microglial depletion in mice exerted little effect on MPTP-induced dopaminergic injuries compared with CD mice at later time points. Interestingly, microglial repopulation brought about apparent resistance to MPTP intoxication.

CONCLUSIONS

Microglia can inhibit PD development at a very early stage; partial microglial depletion has little effect in terms of the whole process of the disease; and microglial replenishment elicits neuroprotection in PD mice.

Activation of Nrf2 in Astrocytes Suppressed PD-Like Phenotypes via Antioxidant and Autophagy Pathways in Rat and Drosophila Models

The oxidative-stress-induced impairment of autophagy plays a critical role in the pathogenesis of Parkinson's disease (PD). In this study, we investigated whether the alteration of Nrf2 in astrocytes protected against 6-OHDA (6-hydroxydopamine)- and rotenone-induced PD-like phenotypes, using 6-OHDA-induced rat PD and rotenone-induced Drosophila PD models. In the PD rat model, we found that Nrf2 expression was significantly higher in astrocytes than in neurons. CDDO-Me (CDDO methyl ester, an Nrf2 inducer) administration attenuated PD-like neurodegeneration mainly through Nrf2 activation in astrocytes by activating the antioxidant signaling pathway and enhancing autophagy in the substantia nigra and striatum. In the PD Drosophila model, the overexpression of Nrf2 in glial cells displayed more protective effects than such overexpression in neurons. Increased Nrf2 expression in glial cells significantly reduced oxidative stress and enhanced autophagy in the brain tissue. The administration of the Nrf2 inhibitor ML385 reduced the neuroprotective effect of Nrf2 through the inhibition of the antioxidant signaling pathway and autophagy pathway. The autophagy inhibitor 3-MA partially reduced the neuroprotective effect of Nrf2 through the inhibition of the autophagy pathway, but not the antioxidant signaling pathway. Moreover, Nrf2 knockdown caused neurodegeneration in flies. Treatment with CDDO-Me attenuated the Nrf2-knockdown-induced degeneration in the flies through the activation of the antioxidant signaling pathway and increased autophagy. An autophagy inducer, rapamycin, partially rescued the neurodegeneration in Nrf2-knockdown Drosophila by enhancing autophagy. Our results indicate that the activation of the Nrf2-linked signaling pathways in glial cells plays an important neuroprotective role in PD models. Our findings not only provide a novel insight into the mechanisms of Nrf2-antioxidant-autophagy signaling, but also provide potential targets for PD interventions.

T Cells: A Growing Universe of Roles in Neurodegenerative Diseases

T cells play a central role in homeostasis and host defense against infectious diseases. T cell dysregulation can lead to recognizing self-antigens as foreign antigens, causing a detrimental autoimmune response. T cell involvement in multiple sclerosis (MS), long understood to be an autoimmune-mediated neurodegenerative disease, is well characterized. More recently, a role for T cells has also been identified for the neurodegenerative diseases Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Interestingly, several alleles and variants of human leukocyte antigen (HLA) genes have been classified as AD and PD risk genes. HLA codes for components of major histocompatibility complex (MHC) class I or class II, both of which are expressed by microglia, the innate immune cells of the central nervous system (CNS). Thus, both microglia and T cells may potentially interact in an antigen-dependent or independent fashion to shape the inflammatory cascade occurring in neurodegenerative diseases. Dissecting the antigen specificity of T cells may lead to new options for disease-modifying treatments in neurodegenerative diseases. Here, we review the current understanding of T cells in neurodegenerative diseases. We summarize the subsets of T cells, their phenotype and potential functions in animal models and in human studies of neurodegenerative diseases.

The Pathogenesis of Parkinson's Disease: A Complex Interplay Between Astrocytes, Microglia, and T Lymphocytes?

Parkinson's disease (PD), the second most common neurodegenerative disease, is characterised by the motor symptoms of bradykinesia, rigidity and resting tremor and non-motor symptoms of sleep disturbances, constipation, and depression. Pathological hallmarks include neuroinflammation, degeneration of dopaminergic neurons in the substantia nigra pars compacta, and accumulation of misfolded α-synuclein proteins as intra-cytoplasmic Lewy bodies and neurites. Microglia and astrocytes are essential to maintaining homeostasis within the central nervous system (CNS), including providing protection through the process of gliosis. However, dysregulation of glial cells results in disruption of homeostasis leading to a chronic pro-inflammatory, deleterious environment, implicated in numerous CNS diseases. Recent evidence has demonstrated a role for peripheral immune cells, in particular T lymphocytes in the pathogenesis of PD. These cells infiltrate the CNS, and accumulate in the substantia nigra, where they secrete pro-inflammatory cytokines, stimulate surrounding immune cells, and induce dopaminergic neuronal cell death. Indeed, a greater understanding of the integrated network of communication that exists between glial cells and peripheral immune cells may increase our understanding of disease pathogenesis and hence provide novel therapeutic approaches.

Neuroprotective and Preventative Effects of Molecular Hydrogen

One of the beneficial effects of molecular hydrogen (H₂, hydrogen gas) is neuroprotection and prevention of neurological disorders. It is important and useful if taking H₂ every day can prevent or ameliorate the progression of neurodegenerative disorders, such as Parkinson's disease or Alzheimer's disease, both lacking specific therapeutic drugs. There are several mechanisms of how H₂ protects neuronal damage. Anti-oxidative, anti-inflammatory, and the regulation of the endocrine system via stomach-brain connection seem to play an important role. At the cellular and tissue level, H₂ appears to prevent the production of reactive oxygen species (ROS), and not only hydroxy radical (•OH) but also superoxide. In Parkinson's disease model mice, chronic intake of H₂ causes the release of ghrelin from the stomach. In Alzheimer's disease model mice, sex-different neuroprotection is observed by chronic intake of H₂. In female mice, declines of estrogen and estrogen receptor-β (ERβ) are prevented by H₂, upregulating brain-derived neurotrophic factor (BDNF) and its receptor, tyrosine kinase receptor B (TrkB). The question of how drinking H₂ upregulates the release of ghrelin or attenuates the decline of estrogen remains to be investigated and the mechanism of how H₂ modulates endocrine systems and the fundamental question of what or where is the target of H₂ needs to be elucidated for a better understanding of the effects of H₂.

Single-Cell Transcriptomics and In Situ Morphological Analyses Reveal Microglia Heterogeneity Across the Nigrostriatal Pathway

Microglia are the resident immune effector cells of the central nervous system (CNS) rapidly reacting to various pathological stimuli to maintain CNS homeostasis. However, microglial reactions in the CNS may also worsen neurological disorders. Hence, the phenotypic analysis of microglia in healthy tissue may identify specific poised subsets ultimately supporting or harming the neuronal network. This is all the more important for the understanding of CNS disorders exhibiting regional-specific and cellular pathological hallmarks, such as many neurodegenerative disorders, including Parkinson's disease (PD). In this context, we aimed to address the heterogeneity of microglial cells in susceptible brain regions for PD, such as the nigrostriatal pathway. Here, we combined single-cell RNA-sequencing with immunofluorescence analyses of the murine nigrostriatal pathway, the most affected brain region in PD. We uncovered a microglia subset, mainly present in the midbrain, displaying an intrinsic transcriptional immune alerted signature sharing features of inflammation-induced microglia. Further, an in situ morphological screening of inferred cellular diversity showed a decreased microglia complexity in the midbrain when compared to striatum. Our study provides a resource for the identification of specific microglia phenotypes within the nigrostriatal pathway, which may be relevant in PD.

A bibenzyl compound 20C protects rats against 6-OHDA-induced damage by regulating adaptive immunity associated molecules

Parkinson's disease (PD) is a neurodegenerative disease with complicated pathogenesis. A novel bibenzyl compound 2-[4-hydroxy-3-(4-hydroxyphenyl)benzyl]-4-(4-hydroxyphenyl)phenol (20C) has been shown to have some neuroprotective effects, and its mechanism still needs further research. In this study, we used a 6-hydroxydopamine (6-OHDA)-induced PD rat model to evaluate the protective effect of 20C. Our study found that 20C could improve behavioral defects in 6-OHDA-lesion rats, decrease neuroinflammation and protect their DA neurons. It could inhibit the activity of inducible nitric oxide synthase (iNOS) induced by 6-OHDA, and lead to a decrease in the expression of nitrated-α-synuclein. When exposed to AMT-an inhibitor of iNOS, the nitrated-α-synuclein in PC12 decreased, and 20C demonstrated the same function on nitrated-α-synuclein as AMT. Besides, we also found that nitrated-α-synuclein was displayed in microglia. And 20C could decrease the expression of antigen-presenting molecule major histocompatibility complex I (MHC I) in dopamine (DA) neurons and MHC II in microglia induced by 6-OHDA. So, these imply that nitrated-α-synuclein might act as an endogenous antigen activating adaptive immunity, and the neuroprotection of 20C might be associated with inhibiting the activity of iNOS, decreasing the expression of the antigen molecule nitrated-α-synuclein and the antigen presenting molecule MHC. Our results indicated that inhibiting iNOS might be an effective strategy to protect neurons from oxidative stress.

TLR7/8 in the Pathogenesis of Parkinson's Disease

Neuroinflammation and autoimmune mechanisms have a key part in the pathogenesis of Parkinson’s disease (PD). Therefore, we evaluated the role of Toll-like receptors (TLRs) as a link between inflammation and autoimmunity in PD. An in vivo model of PD was performed by administration of 1-metil 4-fenil 1,2,3,6-tetraidro-piridina (MPTP) at the dose of 20 mg/kg every 2 h for a total administration of 80/kg, both in single Knock Out (KO) mice for TLR7, TLR 8, and TLR9 and in double KO mice for TLR 7/8^-/-. All animals were compared with WT animals used as a control group. All animals were sacrificed after 7 days form the first administration of MPTP. The genetic absence of TLR 7 and 8 modified the PD pathway, increasing the immunoreactivity for TH and DAT compared to PD groups and decreasing microglia and astrocytes activation. Moreover, the deletion of TLR7 and TLR8 significantly reduced T-cell infiltration in the substantia nigra and lymph nodes, suggesting a reduction of T-cell activation. Therefore, our result highlights a possibility that an immunotherapy approach, by using a dual antagonist of TLR 7 and 8, could be considered as a possible target to develop new therapies for Parkinson diseases.

Calpain mediated expansion of CD4+ cytotoxic T cells in rodent models of Parkinson's disease

Parkinson's disease (PD), a debilitating progressive degenerative movement disorder associated with loss of dopaminergic (DA) neurons in the substantia nigra (SN), afflicts approximately one million people in the U.S., including a significant number of Veterans. Disease characteristics include tremor, rigidity, postural instability, bradykinesia, and at a cellular level, glial cell activation and Lewy body inclusions in DA neurons. The most potent medical/surgical treatments do not ultimately prevent disease progression. Therefore, new therapies must be developed to halt progression of the disease. While the mechanisms of the degenerative process in PD remain elusive, chronic inflammation, a common factor in many neurodegenerative diseases, has been implicated with associated accumulation of toxic aggregated α-synuclein in neurons. Calpain, a calcium-activated cysteine neutral protease, plays a pivotal role in SN and spinal cord degeneration in PD via its role in α-synuclein aggregation, activation/migration of microglia and T cells, and upregulation of inflammatory processes. Here we report an increased expression of a subset of CD4+ T cells in rodent models of PD, including MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mice and DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride]/6-hydroxydopamine rats, which produced higher levels of perforin and granzyme B - typically found in cytotoxic T cells. Importantly, the CD4+ cytotoxic subtype was attenuated following calpain inhibition in MPTP mice, suggesting that calpain and this distinct CD4+ T cell subset may have critical roles in the inflammatory process, disease progression, and neurodegeneration in PD.

Regulation of immune-driven pathogenesis in Parkinson's disease by gut microbiota

Parkinson's disease (PD) is one of the most significant medical and social burdens of our time. The prevalence of PD increases with age and the number of individuals diagnosed with PD is expected to double from 6.9 million in 2015 to 14.2 million in 2040. To date, no drugs can stop the ongoing neurodegeneration caused by PD due to its unclear and complex pathogenic mechanisms. It has been wildly recognized that both gut microbiota and neuro-immunity are involved in the pathology of PD. In this review, we intend to provide a comprehensive overview of current knowledge on how gut microbiota involved in immune-driven pathogenesis of PD, and its potential as a new target of dietary and/or therapeutic interventions for PD.

Remodeling microglia to a protective phenotype in Parkinson's disease?

Parkinson's disease (PD) is the most widespread movement disorder with a prevalence of 1 in 1000 individuals above 60 years of age. Until now, understanding the pathological mechanisms of PD to translate them into therapy has remained a high research priority. In this review, we highlight evidence describing the involvement of microglial dysfunction in PD. Thereafter, we provide current knowledge suggesting that the substantia nigra pars compacta and putamen, compared to other brain regions, show a reduced microglial density, as well as altered morphological and functional properties in homeostatic conditions, while presenting dystrophic features associated with aging. Further, we describe that this defective microglial programing emerges as early as the second postnatal week, persists until adulthood and impacts negatively on their transcriptional pattern and provision of local trophic support. We emphasize the role of α-synuclein oligomers as a major dysfunctional signal underlining microglial-mediated phenotypic switch and adaptive response contributing to neurodegeneration. Moreover, we explore available avenues should microglia be considered as target for neuroprotective or restorative strategies including preventing the aggregation of α-synuclein protofibrils formation. However, we provide a note of caution regarding the success of microglial-targeted PD strategies, using minocycline as an example. In conclusion, we discuss putative neuroprotective agents that were unsuccessful in previous trials but could be reconsidered by focusing on the stage of microglial-dependent pathogenic events during PD in suitable cohorts of patients.

Chronic Infiltration of T Lymphocytes into the Brain in a Non-human Primate Model of Parkinson's Disease

Study of interactions between the nervous system and immunity offers insights into the pathogenesis of Parkinson's disease (PD) and potential therapeutic strategies for neurodegenerative diseases. Studies on rodents have revealed regulatory mechanisms of microglial activation and T lymphocyte recruitment in PD. However, the mechanisms underlying chronic T lymphocyte infiltration into the brain after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injection into a non-human primate (NHP) model of PD remain unknown. This study aimed to investigate changes in serum RANTES (regulated on activation, normal T cell expression and secretion) and analyze the chronic infiltration of T lymphocytes into the brain and microglia activation in NHPs at 48 weeks post-MPTP administration. We found selective and local chronic infiltration of CD4+ and CD8+ T lymphocytes, loss of dopaminergic neurons, dopamine transporter expression, chronic normalization of RANTES in the peripheral blood, and altered microglial morphology at 48 weeks after MPTP injection. This study confirms the involvement of CD4+ and CD8+ T lymphocyte infiltration in MPTP-induced NHP models of PD. Additionally, we corroborated previous findings regarding the mechanisms of T lymphocyte-induced neurodegeneration. The findings of chronic infiltration of T lymphocytes in our NHP model of PD provide novel insights into PD pathogenesis and the development of preventive and therapeutic agents.

Molecular Signatures of Neuroinflammation Induced by αSynuclein Aggregates in Microglial Cells

Alpha-synuclein (αSyn_Agg) are pathological hallmarks of Parkinson's disease (PD) and other synucleinopathies that induce microglial activation and immune-mediated neurotoxicity, but the molecular mechanisms of αSyn_Agg-induced immune activation are poorly defined. We performed quantitative proteomics by mass spectrometry coupled with PCR, immunohistochemical and functional validations studies to define the molecular characteristics of alpha synuclein mediated microglial activation. In mouse microglia, αSyn_Agg induced robust pro-inflammatory activation (increased expression of 864 genes including Irg1, Ifit1, and Pyhin) and increased nuclear proteins involved in RNA synthesis, splicing, and anti-viral defense mechanisms. Conversely, αSyn_Agg decreased expression several proteins (including Cdc123, Sod1, and Grn), which were predominantly cytosolic and involved in metabolic, proteasomal and lysosomal mechanisms. Pathway analyses and confirmatory in vitro studies suggested that αSyn_Agg partly mediates its effects via Stat3 activation. As predicted by our proteomic findings, we verified that αSyn_Agg induces mitochondrial dysfunction in microglia. Twenty-six proteins differentially expressed by αSyn_Agg were also identified as PD risk genes in genome-wide association studies (upregulated: Brd2, Clk1, Siglec1; down-regulated: Memo1, Arhgap18, Fyn, and Pgrn/Grn). We validated progranulin (PGRN) as a lysosomal PD-associated protein that is downregulated by αSyn_Agg in microglia in-vivo and is expressed by microglia in post-mortem PD brain, congruent with our in vitro findings. Conclusion: Together, proteomics approach both reveals novel molecular insights into αSyn-mediated neuroinflammation in PD and other synucleinopathies.

Pro-survival and anti-inflammatory roles of NF-κB c-Rel in the Parkinson's disease models

The pathological hallmarks of Parkinson's disease (PD) are the progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) and the presence of overactivated glial cells and neuroinflammation. Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) c-Rel subunit is closely related in the pathological progress of PD, however the roles and mechanisms of c-Rel in PD development remain unclear. Here, in neurotoxins-induced PD models, the dynamic changes of NF-κB c-Rel and its functions were evaluated. We found that c-Rel was rapidly activated in the nigrostriatal pathway, which mainly occurred in dopaminergic neurons and microglia. c-Rel could maintain neuronal survival by initiating the anti-apoptotic gene expression in MPP⁺-treated SH-SY5Y cells and it could inhibit microglial overactivation by suppressing the inflammatory gene expression in LPS-challenged BV2 cells. c-Rel inhibitor IT901 aggravated the damage of MPTP on dopaminergic neurons and promoted the activation of microglia in the nigrostriatal pathway of mice. Moreover, the expression of c-Rel in blood samples of PD patients decreased dramatically. Our results indicate that the NF-κB/c-Rel subunit plays an important role in neuroprotection and neuroinflammation inhibition during PD progression.

•

NF-κB c-Rel subunit is rapidly activated in the nigrostriatal pathway of PD mice.

•

c-Rel promotes neuronal survival in MPP⁺-treated SH-SY5Y cells.

•

c-Rel inhibits microglial overactivation in LPS-challenged BV2 cells.

•

c-Rel inhibitor IT901 aggravates MPTP-induced damages in the nigrostriatal pathway.

•

c-Rel is pro-survival, anti-oxidative stress and anti-inflammation in PD progression.

Ablation of RIP3 protects from dopaminergic neurodegeneration in experimental Parkinson's disease

Parkinson’s disease (PD) is driven by dopaminergic neurodegeneration in the substantia nigra pars compacta (SN) and striatum. Although apoptosis is considered the main neurodegenerative mechanism, other cell death pathways may be involved. In this regard, necroptosis is a regulated form of cell death dependent on receptor interacting protein 3 (RIP3), a protein also implicated in apoptosis and inflammation independently of its pro-necroptotic activity. Here, we explored the role of RIP3 genetic deletion in in vivo and in vitro PD models. Firstly, wild-type (Wt) and RIP3 knockout (RIP3ko) mice were injected intraperitoneally with MPTP (40 mg/kg, i.p.), and sacrificed after either 6 or 30 days. RIP3ko protected from dopaminergic neurodegeneration in the SN of MPTP-injected mice, but this effect was independent of necroptosis. In keeping with this, necrostatin-1s (10 mg/kg/day, i.p.) did not afford full neuroprotection. Moreover, MPTP led to DNA fragmentation, caspase-3 activation, lipid peroxidation and BAX expression in Wt mice, in the absence of caspase-8 cleavage, suggesting intrinsic apoptosis. This was mimicked in primary cortical neuronal cultures exposed to the active MPTP metabolite. RIP3 deficiency in cultured cells and in mouse brain abrogated all phenotypes. Curiously, astrogliosis was increased in the striatum of MPTP-injected Wt mice and further exacerbated in RIP3ko mice. This was accompanied by absence of microgliosis and reposition of glial cell line-derived neurotrophic factor (GDNF) levels in the striata of MPTP-injected RIP3ko mice when compared to MPTP-injected Wt mice, which in turn showed a massive GDNF decrease. RIP3ko primary mixed glial cultures also presented decreased expression of inflammation-related genes upon inflammatory stimulation. These findings hint at possible undescribed non-necroptotic roles for RIP3 in inflammation and MPTP-driven cell death, which can contribute to PD progression.

Neuroinflammation as a Common Feature of Neurodegenerative Disorders

Neurodegenerative diseases share the fact that they derive from altered proteins that undergo an unfolding process followed by formation of β-structures and a pathological tendency to self-aggregate in neuronal cells. This is a characteristic of tau protein in Alzheimer’s disease and several tauopathies associated with tau unfolding, α-synuclein in Parkinson’s disease, and huntingtin in Huntington disease. Usually, the self-aggregation products are toxic to these cells, and toxicity spreads all over different brain areas. We have postulated that these protein unfolding events are the molecular alterations that trigger several neurodegenerative disorders. Most interestingly, these events occur as a result of neuroinflammatory cascades involving alterations in the cross-talks between glial cells and neurons as a consequence of the activation of microglia and astrocytes. The model we have hypothesized for Alzheimer’s disease involves damage signals that promote glial activation, followed by nuclear factor NF-kβ activation, synthesis, and release of proinflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-1, IL-6, and IL-12 that affect neuronal receptors with an overactivation of protein kinases. These patterns of pathological events can be applied to several neurodegenerative disorders. In this context, the involvement of innate immunity seems to be a major paradigm in the pathogenesis of these diseases. This is an important element for the search for potential therapeutic approaches for all these brain disorders.

Pharmacological Inhibition of Necroptosis Protects from Dopaminergic Neuronal Cell Death in Parkinson's Disease Models

Dysfunctions in mitochondrial dynamics and metabolism are common pathological processes associated with Parkinson’s disease (PD). It was recently shown that an inherited form of PD and dementia is caused by mutations in the OPA1 gene, which encodes for a key player in mitochondrial fusion and structure. iPSC-derived neural cells from these patients exhibited severe mitochondrial fragmentation, respiration impairment, ATP deficits, and heightened oxidative stress. Reconstitution of normal levels of OPA1 in PD-derived neural cells normalized mitochondria morphology and function. OPA1-mutated neuronal cultures showed reduced survival in vitro. Intriguingly, selective inhibition of necroptosis effectively rescued this survival deficit. Additionally, dampening necroptosis in MPTP-treated mice protected from DA neuronal cell loss. This human iPSC-based model captures both early pathological events in OPA1 mutant neural cells and the beneficial effects of blocking necroptosis, highlighting this cell death process as a potential therapeutic target for PD.

•

OPA1 mutant iPSC-derived NPCs contain dysfunctional mitochondria

•

OPA1 mutant iPSC-derived NPCs present high levels of oxidative stress

•

Nec-1s can improve survival of OPA1 mutant human neurons in vitro

•

Nec-1s counteracts the dopaminergic cell loss in MPTP-treated neurons

Autoimmunity in Parkinson's Disease: The Role of α-Synuclein-Specific T Cells

Evidence from a variety of studies implicates a role for the adaptive immune system in Parkinson's disease (PD). Similar to multiple sclerosis (MS) patients who display a high number of T cells in the brain attacking oligodendrocytes, PD patients show higher numbers of T cells in the ventral midbrain than healthy, age-matched controls. Mouse models of the disease also show the presence of T cells in the brain. The role of these infiltrating T cells in the propagation of disease is controversial; however, recent studies indicate that they may be autoreactive in nature, recognizing disease-altered self-proteins as foreign antigens. T cells of PD patients can generate an autoimmune response to α-synuclein, a protein that is aggregated in PD. α-Synuclein and other proteins are post-translationally modified in an environment in which protein processing is altered, possibly leading to the generation of neo-epitopes, or self-peptides that have not been identified by the host immune system as non-foreign. Infiltrating T cells may also be responding to such modified proteins. Genome-wide association studies (GWAS) have shown associations of PD with haplotypes of major histocompatibility complex (MHC) class II genes, and a polymorphism in a non-coding region that may increase MHC class II in PD patients. We speculate that the inflammation observed in PD may play both pathogenic and protective roles. Future studies on the adaptive immune system in neurodegenerative disorders may elucidate steps in disease pathogenesis and assist with the development of both biomarkers and treatments.

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.

Simvastatin as a Potential Disease-Modifying Therapy for Patients with Parkinson's Disease: Rationale for Clinical Trial, and Current Progress

Many now believe the holy grail for the next stage of therapeutic advance surrounds the development of disease-modifying approaches aimed at intercepting the year-on-year neurodegenerative decline experienced by most patients with Parkinson’s disease (PD). Based on recommendations of an international committee of experts who are currently bringing multiple, potentially disease-modifying, PD therapeutics into long-term neuroprotective PD trials, a clinical trial involving 198 patients is underway to determine whether Simvastatin provides protection against chronic neurodegeneration. Statins are widely used to reduce cardiovascular risk, and act as competitive inhibitors of HMG-CoA reductase. It is also known that statins serve as ligands for PPARα, a known arbiter for mitochondrial size and number. Statins possess multiple cholesterol-independent biochemical mechanisms of action, many of which offer neuroprotective potential (suppression of proinflammatory molecules & microglial activation, stimulation of endothelial nitric oxide synthase, inhibition of oxidative stress, attenuation of α-synuclein aggregation, modulation of adaptive immunity, and increased expression of neurotrophic factors). We describe the biochemical, physiological and pharmaceutical credentials that continue to underpin the rationale for taking Simvastatin into a disease-modifying trial in PD patients. While unrelated to the Simvastatin trial (because this conducted in patients who already have PD), we discuss conflicting epidemiological studies which variously suggest that statin use for cardiovascular prophylaxis may increase or decrease risk of developing PD. Finally, since so few disease-modifying PD trials have ever been launched (compared to those of symptomatic therapies), we discuss the rationale of the trial structure we have adopted, decisions made, and lessons learnt so far.

Linking Glycation and Glycosylation With Inflammation and Mitochondrial Dysfunction in Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, affecting about 6.3 million people worldwide. PD is characterized by the progressive degeneration of dopaminergic neurons in the Substantia nigra pars compacta, resulting into severe motor symptoms. The cellular mechanisms underlying dopaminergic cell death in PD are still not fully understood, but mitochondrial dysfunction, oxidative stress and inflammation are strongly implicated in the pathogenesis of both familial and sporadic PD cases. Aberrant post-translational modifications, namely glycation and glycosylation, together with age-dependent insufficient endogenous scavengers and quality control systems, lead to cellular overload of dysfunctional proteins. Such injuries accumulate with time and may lead to mitochondrial dysfunction and exacerbated inflammatory responses, culminating in neuronal cell death. Here, we will discuss how PD-linked protein mutations, aging, impaired quality control mechanisms and sugar metabolism lead to up-regulated abnormal post-translational modifications in proteins. Abnormal glycation and glycosylation seem to be more common than previously thought in PD and may underlie mitochondria-induced oxidative stress and inflammation in a feed-forward mechanism. Moreover, the stress-induced post-translational modifications that directly affect parkin and/or its substrates, deeply impairing its ability to regulate mitochondrial dynamics or to suppress inflammation will also be discussed. Together, these represent still unexplored deleterious mechanisms implicated in neurodegeneration in PD, which may be used for a more in-depth knowledge of the pathogenic mechanisms, or as biomarkers of the disease.

Long-term Changes in the Nigrostriatal Pathway in the MPTP Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is a common and progressive neurodegenerative disorder. The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD is widely used to study the progression of this disease. Behavior impairment is closely related to the damage of the dopaminergic system in the basal ganglia. Here, MPTP-induced changes in mouse behavior and glial activation were evaluated at different time points after the treatment and the long-term changes in the nigrostriatal pathway were analyzed. We found that mice exposed to MPTP displayed a full recovery in the rotarod test and the pole test but not in the wire hanging test at 65 days post-injection. A biphasic activation of microglial cells was revealed in the nigrostriatal pathway of MPTP-treated mice. However, activation of astrocytes displayed an approximately bell-shaped kinetics and an approximately S-shaped kinetics in the striatum and the substantia nigra, respectively. In addition, the numbers of complement component 3 (C3)-positive neurotoxic astrocytes in the substantia nigra of MPTP-treated mice increased with time and reached a maximum at 42 days, and declined at 74 days, after the treatment. Three months later, the dopaminergic system was partially recovered from the lesion of MPTP. The time course of pathophysiological events has important implications for the interventions or treatment of PD.

Immunization with α-synuclein/Grp94 reshapes peripheral immunity and suppresses microgliosis in a chronic Parkinsonism model

Neuroinflammation mediated by chronically activated microglia, largely caused by abnormal accumulation of misfolded α-synuclein (αSyn) protein, is known to contribute to the pathophysiology of Parkinson's disease (PD). In this work, based on the immunomodulatory activities displayed by particular heat-shock proteins (HSPs), we tested a novel vaccination strategy that used a combination of αSyn and Grp94 (HSPC4 or Gp96) chaperone and a murine PD model. We used two different procedures, first, the adoptive transfer of splenocytes from αSyn/Grp94-immunized mice to recipient animals, and second, direct immunization with αSyn/Grp94, to study the effects in a chronic mouse MPTP-model of parkinsonism. We found that both approaches promoted a distinct profile in the peripheral system-supported by humoral and cellular immunity-consisting of a Th1-shifted αSyn-specific response accompanied by an immune-regulatory/Th2-skewed general phenotype. Remarkably, this mixed profile sustained by αSyn/Grp94 immunization led to strong suppression of microglial activation in the substantia nigra and striatum, pointing to a newly described positive effect of anti-αSyn Th1-responses in the context of PD. This strategy is the first to target αSyn and report the suppression of PD-associated microgliosis. Overall, we show that the αSyn/Grp94 combination supports a distinct and long-lasting immune profile in the peripheral system, which has an impact at the CNS level by suppressing chronic microglial activation in an MPTP model of PD. Furthermore, our study demonstrates that reshaping peripheral immunity by vaccination with appropriate misfolding protein/HSP combinations could be highly beneficial as a treatment for neurodegenerative misfolding diseases.

Dynamic Changes in the Nigrostriatal Pathway in the MPTP Mouse Model of Parkinson's Disease

The characteristic brain pathology and motor and nonmotor symptoms of Parkinson's disease (PD) are well established. However, the details regarding the causes of the disease and its course are much less clear. Animal models have significantly enriched our current understanding of the progression of this disease. Among various neurotoxin-based models of PD, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model is the most commonly studied model. Here, we provide an overview of the dynamic changes in the nigrostriatal pathway in the MPTP mouse model of PD. Pathophysiological events, such as reductions in the striatal dopamine (DA) concentrations and levels of the tyrosine hydroxylase (TH) protein, depletion of TH-positive nerve fibers, a decrease in the number of TH-positive neurons in the substantia nigra pars compacta (SNpc), and glial activation, are addressed. This article will assist with the development of interventions or therapeutic strategies for PD.

Effect of dental pulp stem cells in MPTP-induced old-aged mice model

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disease caused by the loss of dopaminergic (DA-ergic) neurons in the substantia nigra (SN) and represented as a huge threat to the geriatric population. Cell replacement therapies (CRTs) have been proposed as a promising strategy to slow down or replace neuronal loss. Among the widely available cell sources, dental pulp stem cells (DPSCs) portray as an attractive source primarily due to their neural crest origin, ease of tissue procurement and less ethical hurdles.

MATERIALS AND METHODS

We first demonstrated the in vitro differentiation ability of DPSCs towards DA-ergic-like cells before evaluating their neuro-protection/neuro-restoration capacities in MPTP-induced mice. Transplantation via intrathecal was performed with behavioural assessments being evaluated every fortnight. Subsequent analysis investigating their immuno-modulatory behaviour was conducted using neuronal and microglial cell lines.

RESULTS

It was apparent that the behavioural parameters began to improve corresponding to tyrosine hydroxylase (TH), dopamine transporter (DAT) and dopamine decarboxylase (AADC) immunostaining in SN and striatum as early as 8-week post-transplantation (P < 0·05). About 60% restoration of DA-ergic neurons was observed at SN in MPTP-treated mice after 12-week post-transplantation. Similarly, their ability to reduce toxic effects of MPTP (DNA damages, reactive oxygen species and nitric oxide release) and regulate cytokine levels was distinctly noted (P < 0·05) upon exposure in in vitro model.

CONCLUSIONS

Our results suggest that DPSCs may provide a therapeutic benefit in the old-aged PD mice model and may be explored in stem cell-based CRTs especially in geriatric population as an attempt towards 'personalized medicine'.

TracMouse: A computer aided movement analysis script for the mouse inverted horizontal grid test

In rodents, detection and quantification of motor impairments is difficult. The traction test (inverted grid with mice clinging to the underside) currently has no objective rating system. We here developed and validated the semi-automatic MATLAB script TracMouse for unbiased detection of video-recorded movement patterns. High precision videos were analyzed by: (i) principal identification of anatomical paw details frame-by-frame by an experimentally blinded rater; (ii) automatic retrieval of proxies by TracMouse for individual paws. The basic states of Hold and Step were discriminated as duration and frequency, and these principle parameters were converted into static and dynamic endpoints and their discriminating power assessed in a dopaminergic lesion model. Relative to hind paws, forepaws performed ~4 times more steps, they were ~20% longer, and Hold duration was ~5 times shorter in normal C57Bl/6 mice. Thus, forepaw steps were classified as exploratory, hind paw movement as locomotive. Multiple novel features pertaining to paw sequence, step lengths and exploratory touches were accessible through TracMouse and revealed subtle Parkinsonian phenotypes. Novel proxies using TracMouse revealed previously unidentified features of movement and may aid the understanding of (i) brain circuits related to motor planning and execution, and (ii) phenotype detection in experimental models of movement disorders.

Tetramethylpyrazine Ameliorates Rotenone-Induced Parkinson's Disease in Rats: Involvement of Its Anti-Inflammatory and Anti-Apoptotic Actions

Parkinson's disease (PD) is a slowly progressive neurodegenerative movement disorder. Apoptosis, neuroinflammation, and oxidative stress are the current hypothesized mechanisms for PD pathogenesis. Tetramethylpyrazine (TMP), the major bioactive component of Ligusticum wallichii Franchat (ChuanXiong), Family Apiaceae, reportedly has anti-apoptotic, anti-inflammatory and antioxidant effects. This study investigated the role of 'TMP' in preventing rotenone-induced neurobiological and behavioral sequelae. A preliminary dose-response study was conducted where rats received TMP (10, 20, and 40 mg/kg, i.p.) concomitantly with rotenone (2 mg/kg, s.c.) for 4 weeks. Catalepsy, locomotor activity, striatal dopamine content, and tyrosine hydroxylase "TH" and α-synuclein immunoreactivity were evaluated. The selected TMP dose (20 mg/kg) was used for western blot analysis of Bax, Bcl2, and DJ-1, immunohistochemical detection of nuclear factor kappa B (NF-кB), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX2), and glial fibrillary acidic protein (GFAP) expression, in addition to biochemical analysis of caspase-3 activity, nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) levels. Results showed that TMP (20 mg/kg) significantly improved midbrain and striatal TH expression and striatal dopamine content as well as the motor deficits, compared to rotenone-treated group. These results were correlated with reduction in caspase-3 activity and α-synuclein expression, along with improvement of midbrain and striatal Bax/Bcl2 ratio compared to rotenone-treated group. TMP also attenuated rotenone-induced upregulation of Nrf2/HO-1 pathway. Furthermore, TMP downregulated rotenone-induced neuroinflammation markers: NF-кB, iNOS, COX2, and GFAP expression in both the midbrain and striatum. Taken together, the current study suggests that TMP is entitled to, at least partially, preventing PD neurobiological and behavioral deficits by virtue of its anti-apoptotic, anti-inflammatory, and antioxidant actions.

Type-1 interferons contribute to the neuroinflammatory response and disease progression of the MPTP mouse model of Parkinson's disease

Type-1 interferons (IFNs) are pleiotropic cytokines with a critical role in the initiation and regulation of the pro-inflammatory response. However, the contribution of the type-1 IFNs to CNS disorders, specifically chronic neuropathologies such as Parkinson's disease is still unknown. Here, we report increased type-1 IFN signaling in both post mortem human Parkinson's disease samples and in the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) mouse model. In response to MPTP, mice lacking the type-1 IFN receptor (IFNAR1(-/-) ) displayed decreased type-1 IFN signaling, an attenuated pro-inflammatory response and reduced loss of dopaminergic neurons. The neuroprotective potential of targeting the type-1 IFN pathway was confirmed by reduced neuroinflammation and DA cell death in mice treated with a blocking monoclonal IFNAR1 (MAR-1) antibody. The MPTP/MAR-1 treated mice also displayed increased striatal dopamine levels and improved behavioural outcomes compared to their MPTP/IgG controls. These data, implicate for the first time, a deleterious role for the type-1 IFNs as key modulators of the early neuroinflammatory response and therefore the neuronal cell death in Parkinson's disease. GLIA 2016;64:1590-1604.

Parkinson's Disease-Related Proteins PINK1 and Parkin Repress Mitochondrial Antigen Presentation

Antigen presentation is essential for establishing immune tolerance and for immune responses against infectious disease and cancer. Although antigen presentation can be mediated by autophagy, here we demonstrate a pathway for mitochondrial antigen presentation (MitAP) that relies on the generation and trafficking of mitochondrial-derived vesicles (MDVs) rather than on autophagy/mitophagy. We find that PINK1 and Parkin, two mitochondrial proteins linked to Parkinson's disease (PD), actively inhibit MDV formation and MitAP. In absence of PINK1 or Parkin, inflammatory conditions trigger MitAP in immune cells, both in vitro and in vivo. MitAP and the formation of MDVs require Rab9 and Sorting nexin 9, whose recruitment to mitochondria is inhibited by Parkin. The identification of PINK1 and Parkin as suppressors of an immune-response-eliciting pathway provoked by inflammation suggests new insights into PD pathology.

Neutralization of RANTES and Eotaxin Prevents the Loss of Dopaminergic Neurons in a Mouse Model of Parkinson Disease

Parkinson disease (PD) is second only to Alzheimer disease as the most common human neurodegenerative disorder. Despite intense investigation, no interdictive therapy is available for PD. Recent studies indicate that both innate and adaptive immune processes are active in PD. Accordingly, we found a rapid increase in RANTES (regulated on activation normal T cell expressed and secreted) and eotaxin, chemokines that are involved in T cell trafficking, in vivo in the substantia nigra pars compacta and the serum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. RANTES and eotaxin were also up-regulated in the substantia nigra pars compacta of post-mortem PD brains as compared with age-matched controls. Therefore, we investigated whether neutralization of RANTES and eotaxin could protect against nigrostriatal degeneration in MPTP-intoxicated mice. Interestingly, after peripheral administration, functional blocking antibodies against RANTES and eotaxin reduced the infiltration of CD4(+) and CD8(+) T cells into the nigra, attenuated nigral expression of proinflammatory molecules, and suppressed nigral activation of glial cells. These findings paralleled dopaminergic neuronal protection, normalized striatal neurotransmitters, and improved motor functions in MPTP-intoxicated mice. Therefore, we conclude that attenuation of the chemokine-dependent adaptive immune response may be of therapeutic benefit for PD patients.

e-Cadherin in 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-Induced Parkinson Disease

Today a large number of studies are focused on clarifying the complexity and diversity of the pathogenetic mechanisms inducing Parkinson disease. We used 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin that induces Parkinson disease, to evaluate the change of midbrain structure and the behavior of the anti-inflammatory factor e-cadherin, interleukin-6, tyrosine hydroxylase, phosphatase and tensin homolog, and caveolin-1. The results showed a strong expression of e-cadherin, variation of length and thickness of the heavy neurofilaments, increase of interleukin-6, and reduction of tyrosine hydroxylase known to be expression of dopamine cell loss, reduction of phosphatase and tensin homolog described to impair responses to dopamine, and reduction of caveolin-1 known to be expression of epithelial-mesenchymal transition and fibrosis. The possibility that the overexpression of the e-cadherin might be implicated in the anti-inflammatory reaction to MPTP treatment by influencing the behavior of the other analyzed molecules is discussed.