Activated immune cells in Parkinson's disease

GM1 Oligosaccharide Efficacy in Parkinson's Disease: Protection against MPTP

Past evidence has shown that the exogenous administration of GM1 ganglioside slowed neuronal death in preclinical models of Parkinson's disease, a neurodegenerative disorder characterized by the progressive loss of dopamine-producing neurons: however, the physical and chemical properties of GM1 (i.e., amphiphilicity) limited its clinical application, as the crossing of the blood-brain barrier is denied. Recently, we demonstrated that the GM1 oligosaccharide head group (GM1-OS) is the GM1 bioactive portion that, interacting with the TrkA-NGF complex at the membrane surface, promotes the activation of a multivariate network of intracellular events regulating neuronal differentiation, protection, and reparation. Here, we evaluated the GM1-OS neuroprotective potential against the Parkinson's disease-linked neurotoxin MPTP, which destroys dopaminergic neurons by affecting mitochondrial bioenergetics and causing ROS overproduction. In dopaminergic and glutamatergic primary cultures, GM1-OS administration significantly increased neuronal survival, preserved neurite network, and reduced mitochondrial ROS production enhancing the mTOR/Akt/GSK3β pathway. These data highlight the neuroprotective efficacy of GM1-OS in parkinsonian models through the implementation of mitochondrial function and reduction in oxidative stress.

Lactobacillus plantarum CCFM405 against Rotenone-Induced Parkinson’s Disease Mice via Regulating Gut Microbiota and Branched-Chain Amino Acids Biosynthesis

Recent studies have demonstrated that disturbances in the gut microbiota and microbiota -derived metabolites contribute to the pathogenesis of Parkinson’s disease (PD), suggesting that probiotic treatments that restore them may delay disease progression. This study aimed to examine the attenuating efficacy of L. plantarum CCFM405 and the potential mechanisms in mice with rotenone-induced PD. Our results indicate that L. plantarum CCFM405 ameliorated rotenone-induced motor deficits and constipation, decreased dopaminergic neuronal death, reduced intestinal inflammation and neuroinflammation, and raised dopamine levels, 5-HT, and associated metabolites in the striatal region of the brain in mice with PD. Sequencing of 16S rRNA from fecal microbiota revealed that L. plantarum CCFM405 normalized the gut bacterial composition in mice with PD, as evidenced by the increased relative abundance of the following genus, Bifidobacterium, Turicibacter, and Faecalibaculum, and decreased relative abundance of Alistipes, Bilophila, Akkermansia, and Escherichia-Shigella. The PICRUSt-predicted gut microbiota function revealed that L. plantarum CCFM405 enhanced the biosynthesis of amino acid pathways, particularly valine, leucine, and isoleucine (branched-chain amino acids, BCAAs). A non-metabolomic analysis of the serum and feces showed that L. plantarum CCFM405 markedly increased the levels of BCAAs. Pathway enrichment analysis based on the KEGG database further suggested that L. plantarum CCFM405 supplementation can promote BCAAs biosynthesis. Collectively, L. plantarum CCFM405 can help to prevent rotenone-induced PD by modulating the gut microbiota–metabolite axis. BCAAs may play a dominant role in L. plantarum CCFM405-associated neuroprotection in PD mice. This probiotic could be utilized as a potential food supplement in the management of PD.

Microglial cGAS drives neuroinflammation in the MPTP mouse models of Parkinson's disease

BACKGROUND

Neuroinflammation has been widely accepted as a cause of the degenerative process. Increasing interest has been devoted to developing intervening therapeutics for preventing neuroinflammation in Parkinson's disease (PD). It is well known that virus infections, including DNA viruses, are associated with an increased risk of PD. In addition, damaged or dying dopaminergic neurons can release dsDNA during PD progression. However, the role of cGAS, a cytosolic dsDNA sensor, in PD progression remains unclear.

METHODS

Adult male wild-type mice and age-matched male cGAS knockout (cGas^-/- ) mice were treated with MPTP to induce neurotoxic PD model, and then behavioral tests, immunohistochemistry, and ELISA were conducted to compare disease phenotype. Chimeric mice were reconstituted to explore the effects of cGAS deficiency in peripheral immune cells or CNS resident cells on MPTP-induced toxicity. RNA sequencing was used to dissect the mechanistic role of microglial cGAS in MPTP-induced toxicity. cGAS inhibitor administration was conducted to study whether GAS may serve as a therapeutic target.

RESULTS

We observed that the cGAS-STING pathway was activated during neuroinflammation in MPTP mouse models of PD. cGAS deficiency in microglia, but not peripheral immune cells, controlled neuroinflammation and neurotoxicity induced by MPTP. Mechanistically, microglial cGAS ablation alleviated the neuronal dysfunction and inflammatory response in astrocytes and microglia by inhibiting antiviral inflammatory signaling. Additionally, the administration of cGAS inhibitors conferred the mice neuroprotection during MPTP exposure.

CONCLUSIONS

Collectively, these findings demonstrate microglial cGAS promote neuroinflammation and neurodegeneration during the progression of MPTP-induced PD mouse models and suggest cGAS may serve as a therapeutic target for PD patients.

LIMITATIONS OF THE STUDY

Although we demonstrated that cGAS promotes the progression of MPTP-induced PD, this study has limitations. We identified that cGAS in microglia accelerate disease progression of PD by using bone marrow chimeric experiments and analyzing cGAS expression in CNS cells, but evidence would be more straightforward if conditional knockout mice were used. This study contributed to the knowledge of the role of the cGAS pathway in PD pathogenesis; nevertheless, trying more PD animal models in the future will help us to understand the disease progression deeper and explore possible treatments.

Identification and validation of neurotrophic factor-related gene signatures in glioblastoma and Parkinson's disease

Background

Glioblastoma multiforme (GBM) is the most common cancer of the central nervous system, while Parkinson's disease (PD) is a degenerative neurological condition frequently affecting the elderly. Neurotrophic factors are key factors associated with the progression of degenerative neuropathies and gliomas.

Methods

The 2601 neurotrophic factor-related genes (NFRGs) available in the Genecards portal were analyzed and 12 NFRGs with potential roles in the pathogenesis of Parkinson's disease and the prognosis of GBM were identified. LASSO regression and random forest algorithms were then used to screen the key NFRGs. The correlation of the key NFRGs with immune pathways was verified using GSEA (Gene Set Enrichment Analysis). A prognostic risk scoring system was constructed using LASSO (Least absolute shrinkage and selection operator) and multivariate Cox risk regression based on the expression of the 12 NFRGs in the GBM cohort from The Cancer Genome Atlas (TCGA) database. We also investigated differences in clinical characteristics, mutational landscape, immune cell infiltration, and predicted efficacy of immunotherapy between risk groups. Finally, the accuracy of the model genes was validated using multi-omics mutation analysis, single-cell sequencing, QT-PCR, and HPA.

Results

We found that 4 NFRGs were more reliable for the diagnosis of Parkinson's disease through the use of machine learning techniques. These results were validated using two external cohorts. We also identified 7 NFRGs that were highly associated with the prognosis and diagnosis of GBM. Patients in the low-risk group had a greater overall survival (OS) than those in the high-risk group. The nomogram generated based on clinical characteristics and risk scores showed strong prognostic prediction ability. The NFRG signature was an independent prognostic predictor for GBM. The low-risk group was more likely to benefit from immunotherapy based on the degree of immune cell infiltration, expression of immune checkpoints (ICs), and predicted response to immunotherapy. In the end, 2 NFRGs (EN1 and LOXL1) were identified as crucial for the development of Parkinson's disease and the outcome of GBM.

Conclusions

Our study revealed that 4 NFRGs are involved in the progression of PD. The 7-NFRGs risk score model can predict the prognosis of GBM patients and help clinicians to classify the GBM patients into high and low risk groups. EN1, and LOXL1 can be used as therapeutic targets for personalized immunotherapy for patients with PD and GBM.

Ganoderma lucidum Modulates Inflammatory Responses following 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine (MPTP) Administration in Mice

Ganoderma lucidum, one of the most valued medicinal mushrooms, has been used for health supplements and medicine in China. Our previous studies have proved that Ganoderma lucidum extract (GLE) could inhibit activation of microglia and protect dopaminergic neurons in vitro. In the present study, we investigated the anti-neuroinflammatory potential of GLE in vivo on Parkinsonian-like pathological dysfunction. Male C57BL/6J mice were subjected to acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesion, and a treatment group was administered intragastrically with GLE at a dose of 400 mg/kg. Immunohistochemistry staining showed that GLE efficiently repressed MPTP-induced microglia activation in nigrostriatal region. Accordingly, Bio-plex multiple cytokine assay indicated that GLE treatment modulates abnormal cytokine expression levels. In microglia BV-2 cells incubated with LPS, increased expression of iNOS and NLRP3 were effectively inhibited by 800 μg/mL GLE. Furthermore, GLE treatment decreased the expression of LC3II/I, and further enhanced the expression of P62. These results indicated that the neuroprotection of GLE in an experimental model of PD was partially related to inhibition of microglia activation in vivo and vitro, possibly through downregulating the iNOS/NLRP3 pathway, inhibiting abnormal microglial autophagy and lysosomal degradation, which provides new evidence for Ganoderma lucidum in PD treatment.

Fat and Protein Combat Triggers Immunological Weapons of Innate and Adaptive Immune Systems to Launch Neuroinflammation in Parkinson's Disease

Parkinson's disease (PD) is the second-most common neurodegenerative disease in the world, affecting up to 10 million people. This disease mainly happens due to the loss of dopaminergic neurons accountable for memory and motor function. Partial glucocerebrosidase enzyme deficiency and the resultant excess accumulation of glycosphingolipids and alpha-synuclein (α-syn) aggregation have been linked to predominant risk factors that lead to neurodegeneration and memory and motor defects in PD, with known and unknown causes. An increasing body of evidence uncovers the role of several other lipids and their association with α-syn aggregation, which activates the innate and adaptive immune system and sparks brain inflammation in PD. Here, we review the emerging role of a number of lipids, i.e., triglyceride (TG), diglycerides (DG), glycerophosphoethanolamines (GPE), polyunsaturated fatty acids (PUFA), sphingolipids, gangliosides, glycerophospholipids (GPL), and cholesterols, and their connection with α-syn aggregation as well as the induction of innate and adaptive immune reactions that trigger neuroinflammation in PD.

MPTP-induced mouse model of Parkinson's disease: A promising direction of therapeutic strategies

Among the popular animal models of Parkinson's disease (PD) commonly used in research are those that employ neurotoxins, especially 1-methyl- 4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). This neurotoxin exerts it neurotoxicity by causing a barrage of insults, such as oxidative stress, mitochondrial apoptosis, inflammation, excitotoxicity, and formation of inclusion bodies acting singly and in concert, ultimately leading to dopaminergic neuronal damage in the substantia nigra pars compacta and striatum. The selective neurotoxicity induced by MPTP in the nigrostriatal dopaminergic neurons of the mouse brain has led to new perspectives on PD. For decades, the MPTP-induced mouse model of PD has been the gold standard in PD research even though it does not fully recapitulate PD symptomatology, but it does have the advantages of simplicity, practicability, affordability, and fewer ethical considerations and greater clinical correlation than those of other toxin models of PD. The model has rejuvenated PD research and opened new frontiers in the quest for more novel therapeutic and adjuvant agents for PD. Hence, this review summarizes the role of MPTP in producing Parkinson-like symptoms in mice and the experimental role of the MPTP-induced mouse model. We discussed recent developments of more promising PD therapeutics to enrich our existing knowledge about this neurotoxin using this model.

Immune Profiling of Parkinson's Disease Revealed Its Association With a Subset of Infiltrating Cells and Signature Genes

Parkinson’s disease (PD) is an age-related and second most common neurodegenerative disorder. In recent years, increasing evidence revealed that peripheral immune cells might be able to infiltrate into brain tissues, which could arouse neuroinflammation and aggravate neurodegeneration. This study aimed to illuminate the landscape of peripheral immune cells and signature genes associated with immune infiltration in PD. Several transcriptomic datasets of substantia nigra (SN) from the Gene Expression Omnibus (GEO) database were separately collected as training cohort, testing cohort, and external validation cohort. The immunoscore of each sample calculated by single-sample gene set enrichment analysis was used to reflect the peripheral immune cell infiltration and to identify the differential immune cell types between PD and healthy participants. According to receiver operating characteristic (ROC) curve analysis, the immunoscore achieved an overall accuracy of the area under the curve (AUC) = 0.883 in the testing cohort, respectively. The immunoscore displayed good performance in the external validation cohort with an AUC of 0.745. The correlation analysis and logistic regression analysis were used to analyze the correlation between immune cells and PD, and mast cell was identified most associated with the occurrence of PD. Additionally, increased mast cells were also observed in our in vivo PD model. Weighted gene co-expression network analysis (WGCNA) was used to selected module genes related to a mast cell. The least absolute shrinkage and selection operator (LASSO) analysis and random-forest analysis were used to analyze module genes, and two hub genes RBM3 and AGTR1 were identified as associated with mast cells in the training cohort. The expression levels of RBM3 and AGTR1 in these cohorts and PD models revealed that these hub genes were significantly downregulated in PD. Moreover, the expression trend of the aforementioned two genes differed in mast cells and dopaminergic (DA) neurons. In conclusion, this study not only exhibited a landscape of immune infiltrating patterns in PD but also identified mast cells and two hub genes associated with the occurrence of PD, which provided potential therapeutic targets for PD patients (PDs).

Principal component analysis of routine blood test results with Parkinson's disease: A case-control study

This study aimed to explore the association of routine blood test values and blood cell ratios with the risk or severity of Parkinson's disease (PD). The medical records of 453 PD patients and 436 controls were retrospectively reviewed. The severity of PD was quantified by the modified Hoehn-Yahr (HY) scale. We performed principal component analysis (PCA) of significant values/ratios and used logistic regression analysis to explore the relationship between principal components (PCs) and the risk of PD. Spearman correlation and ordinal logistic regression analyses were performed to explore the relationship between indicators and the severity of PD. The PCA generated 9 PCs, which contributed to 90.86% of the total variance. Logistic regression analysis revealed positive associations of PC2 (a measure monocyte ratios) and PC6 (a measure of platelet ratios and volume) and negative associations of PC1 (a comprehensive measure of lymphocyte, eosinophil, neutrophil, and red blood cell values), PC4 (a measure of red blood cell values), and PC7 (a measure of red blood cell values and platelet volume) with the risk of PD. However, we observed no associations of variables with the severity of PD. In conclusion, PCA reduced the dimensionality of the data. Peripheral blood disorders may be associated with PD.

Exercise Reverses Dysregulation of T-Cell-Related Function in Blood Leukocytes of Patients With Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease with movement and balance impairments. Although studies have reported improvement of motor symptoms with physical exercise, the mechanisms by which exercise is beneficial remains poorly understood. Our study addresses the exercise-induced changes to peripheral immune cells by interrogating the transcriptome of blood-derived leukocytes in PD patients before and after exercise. Patients attended 1 h exercise classes twice a week for 12 weeks. Leukocytes were collected at the beginning and end of the study for gene expression analysis by RNA-seq or quantitative real-time PCR. We correlated differentially expressed genes after exercise with clinical measures and analyzed the potential functions of gene changes with Kyoto Encyclopedia of Genes and Genomes pathway and Gene Ontology analysis. Exercise improved measures of movement and balance when compared with scores before the exercise program. Among the gene changes, Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analysis suggests that T-cell receptor signaling, T-cell activation, and T-cell migration pathways were downregulated, while the T-cell receptor signaling pathway was the most significantly correlated with clinical measures. To further investigate T-cell-related changes in PD leukocytes, we reanalyzed the differentially expressed genes from publicly available microarray data and found that genes in the T-cell activation, differentiation, and migration pathways were upregulated in PD samples compared to controls in a time-dependent manner. Together, our findings suggest that exercise rehabilitation may improve movement and balance in PD patients by reversing the upregulated T-cell activation pathways associated with PD. This study was registered with the Chinese Clinical Trial Registry under ChiCTR-TRC-14004707. Registered on May 27, 2014.

The key role of T cells in Parkinson's disease pathogenesis and therapy

This review focuses on the role of T lymphocytes in the pathogenesis of Parkinson's disease and highlights evidence for modulation of the T cell response as an effective neuroprotective strategy. In preclinical models of Parkinson's disease, modulation of the T cell response results in neuroprotection. Peripheral markers of T cell response show changes in Parkinson's patients relative to controls that have potential application as diagnostic and therapeutic biomarkers. The article also discusses the important immunomodulatory effects of dopamine which may confound study of T cells in patients on dopaminergic therapies, and highlights glatiramer acetate, an FDA-approved therapy for multiple sclerosis that works through modulating the T cell response, as a promising target for translation.

Immunology of West Nile Virus Infection and the Role of Alpha-Synuclein as a Viral Restriction Factor

West Nile virus (WNV) is a single-stranded RNA flavivirus and is a major cause of viral encephalitis worldwide. Experimental models of WNV infection in mice are commonly used to define acute neuroinflammatory responses in the brain. Alpha-synuclein (Asyn) is a protein of primarily neuronal origin and is a major cause of Parkinson's disease (PD), a disorder characterized by loss of dopaminergic neurons. Both WNV and PD pathologies are largely mediated by inflammation of the central nervous system (neuroinflammation) and have overlapping inflammatory pathways. In this review, we highlight the roles of the immune system in both diseases while comparing and contrasting both protective and pathogenic roles of immune cells and their effector proteins. Additionally, we review the current literature showing that Asyn is an important mediator of the immune response with diverging roles in PD (pathogenic) and WNV disease (neuroprotective).

Participation of perforin in mediating dopaminergic neuron loss in MPTP-induced Parkinson's disease in mice

Both resident innate and peripheral immune aberrations have been demonstrated to influence Parkinson's disease (PD) progression. However, it is still enigmatic how and which immune components are lethal to the dopaminergic neuron in PD. We now show that levels of perforin, a pore-forming protein expressed in cytotoxic immune cells, was significantly increased in the serum of wild-type mice 4 weeks after injection of MPTP, a toxin used to induce PD-like symptoms. We demonstrate that perforin-deficiency attenuated the acute striatal dopamine reduction by 33%, ablated microglia activation 3 days post MPTP-injection; and retarded dopaminergic neuron death 4 weeks post MPTP-injection. Our study suggests that perforin plays a role in dopaminergic neuron loss in PD.

Genome-wide pathway-based association analysis identifies risk pathways associated with Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease. It is generally believed that it is influenced by both genetic and environmental factors, but the precise pathogenesis of PD is unknown to date. In this study, we performed a pathway analysis based on genome-wide association study (GWAS) to detect risk pathways of PD in three GWAS datasets. We first mapped all SNP markers to autosomal genes in each GWAS dataset. Then, we evaluated gene risk values using the minimum P-value of the tagSNPs. We took a pathway as a unit to identify the risk pathways based on the cumulative risks of the genes in the pathway. Finally, we combine the analysis results of the three datasets to detect the high risk pathways associated with PD. We found there were five same pathways in the three datasets. Besides, we also found there were five pathways which were shared in two datasets. Most of these pathways are associated with nervoussystem. Five pathways had been reported to be PD-related pathways in the previous literature. Our findings also implied that there was a close association between immune response and PD. Continued investigation of these pathways will further help us explain the pathogenesis of PD.

Metformin Prevents Dopaminergic Neuron Death in MPTP/P-Induced Mouse Model of Parkinson's Disease via Autophagy and Mitochondrial ROS Clearance

BACKGROUND

Our previous study demonstrated that metabolic inflammation exacerbates dopaminergic neuronal degeneration in type 2 diabetes mice. Metformin, a typical oral hypoglycemic agent for diabetes, has been regarded as an activator of AMP-activated protein kinase and a regulator of systemic energy metabolism. Although metformin plays potential protective effects in many disorders, it is unclear whether metformin has a therapeutic role in dopaminergic neuron degeneration in Parkinson's disease.

METHODS

In the present study, a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid-induced mouse model of Parkinson's disease was established to explore the neuroprotective effect of metformin on dopaminergic neurons in substania nigra compacta. We next cultured SH-SY5Y cells to investigate the mechanisms for the neuroprotective effect of metformin.

RESULTS

We showed that treatment with metformin (5mg/mL in drinking water) for 5 weeks significantly ameliorated the degeneration of substania nigra compacta dopaminergic neurons, increased striatal dopaminergic levels, and improved motor impairment induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid. We further found that metformin inhibited microglia overactivation-induced neuroinflammation in substania nigra compacta of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid Parkinson's disease mice, which might contribute to the protective effect of metformin on neurodegeneration. Furthermore, metformin (2mM) activated AMP-activated protein kinase in SH-SY5Y cells, in turn inducing microtubule-associated protein 1 light chain 3-II-mediated autophagy and eliminating mitochondrial reactive oxygen species. Consequently, metformin alleviated MPP⁺-induced cytotoxicity and attenuated neuronal apoptosis.

CONCLUSIONS

Our findings demonstrate that metformin may be a pluripotent and promising drug for dopaminergic neuron degeneration, which will give us insight into the potential of metformin in terms of opening up novel therapeutic avenues for Parkinson's disease.

Converging mediators from immune and trophic pathways to identify Parkinson disease dementia

Objective:

To identify a panel of peripheral inflammatory/immune mediators that could discriminate Parkinson disease with dementia (PDD) from Parkinson disease (PD) without dementia.

Methods:

Plasma samples from 52 patients with PD and 22 patients with PDD were prepared from freshly collected blood following an institutional review board–approved protocol. A total of 160 proteins were measured using a multiplex antibody array. Plasma α-synuclein levels were analyzed by an electrochemiluminescence immunoassay. The main objective of the statistical analyses was to identify PDD discriminants using the plasma protein profile alone or in combination with age.

Results:

The PD and PDD groups differed significantly in cognitive measurements (Mini-Mental State Examination, Auditory Verbal Learning Test-A7, and Clinical Dementia Rating) and age. The age-adjusted levels of thymus and activation-regulated chemokine (TARC) and platelet-derived growth factor (PDGF)-AA were significantly different between disease groups. The levels of plasma α-synuclein significantly correlated with 26 proteins; among them, PDGF-BB, TARC, PDGF-AA, and epidermal growth factor were the highest. Linear discriminant analysis with leave-one-out cross-validation identified a 14-protein panel with age as discriminants of PDD (96% sensitivity, 89% specificity, area under the curve = 0.9615).

Conclusions:

We showed that multiple proteins that are mediators of growth/trophic and immune response-related pathways had discriminatory power for identifying PDD in patients with PD. Validation of this discovery-based study in longitudinal population-based studies is warranted.

Classification of evidence:

This study provides Class III evidence that a 14-protein panel plasma assay combined with age has a sensitivity of 96% and a specificity of 89% for PDD.

6-Hydroxydopamine as a tool to understand adaptive immune system-induced dopamine neurodegeneration in Parkinson's disease

CONTEXT

Neuroimmunological response is associated with neurodegeneration in the human substantia nigra (SN) in Parkinson's disease (PD).

OBJECTIVE

To explore the possibility that the neurotoxin, 6-hydroxydopamine (6-OHDA), could be used as a tool in mice to understand the immune response in PD.

MATERIALS AND METHODS

We employed unilateral administration of 6-OHDA into the mouse SN. At 1 week, 2 weeks and 4 weeks post-injection, we used immunohistochemistry for the markers Iba-1 and gp91PHOX to investigate activated microglia in the SN. To examine the adaptive immune response, we used immunohistochemistry for CD3-positive T-lymphocytes, CD45R-positive B-lymphocytes and anti-mouse immunoglobulin-G (IgG). Dopamine neuron loss was examined using immunohistochemistry for the dopamine neuron marker, tyrosine hydroxylase.

RESULTS

Compared to vehicle, 6-OHDA administration induced an intense IgG deposition in the SN as well as increased infiltration of both T- and B- lymphocytes into the injected side of the midbrain. The adaptive immune response was associated with extensive destruction of dopamine neurons and extensive microglial activation at every time point in the 6-OHDA groups.

CONCLUSION

Our results suggest that 6-OHDA administration in mice can a potential tool for understanding mechanisms underlying adaptive immune activation-induced neurodegeneration in PD.

Innate and adaptive immune responses in neurodegeneration and repair

Emerging evidence suggests important roles of the innate and adaptive immune responses in the central nervous system (CNS) in neurodegenerative diseases. In this special review issue, five leading researchers discuss the evidence for the beneficial as well as the detrimental impact of the immune system in the CNS in disorders including Alzheimer's disease, multiple sclerosis and CNS injury. Several common pathological mechanisms emerge indicating that these pathways could provide important targets for manipulating the immune reposes in neurodegenerative disorders. The articles highlight the role of the traditional resident immune cell of the CNS - the microglia - as well as the role of other glia astrocytes and oligodendrocytes in immune responses and their interplay with other immune cells including, mast cells, T cells and B cells. Future research should lead to new discoveries which highlight targets for therapeutic interventions which may be applicable to a range of neurodegenerative diseases.

ERK1/2 pathway is activated in degenerated Rpe65-deficient mice

The MAPK family is composed of three majors kinases, JNK, p38 and ERK1/2, and is implicated in many degenerative processes, including retinal cell death. The purpose of our study was to evaluate the activation of ERK1/2 kinase, and its potential role in Müller cell gliosis, during photoreceptor cell death in Rpe65(-/-) mice. We assayed ERK1/2 mRNA and protein levels, and evaluated ERK1/2 phosphorylation involved in kinase activation, in 2, 4 and 6 month-old Rpe65(-/-) mice and in age-matched wild-type controls. No differences in ERK1/2 expression were detected between Rpe65(-/-) and wild-type mice, however, ERK1/2 phosphorylation was dramatically increased in the knock out mice at 4 and 6 months-of-age. Phosphorylated ERK1/2 co-localized with GFAP in the ganglion cell layer, and correlated with an increase in GFAP protein expression and retinal cell death. Accumulation of cFOS protein in the ganglion cell layer occurred concomitant with pERK1/2 activation. Müller cell proliferation was not observed. ERK1/2 activation did not occur in 2 month-old Rpe65(-/-) or in the Rpe65(-/-)/Gnat1(-/-) mice, in which no degeneration was evident. The observed activation ERK1/2 and GFAP, both markers of Müller cell gliosis, in the absence of Müller cell proliferation, is consistent with the activation of atypical gliosis occurring during the slow process of degeneration in Rpe65(-/-) mice. As Müller cell gliosis is activated in many neuronal and retinal degenerative diseases, further studies will be needed to determine whether atypical gliosis in Rpe65(-/-) mice contributes to, or protects against, the pathogenesis occurring in this model of Leber congenital amaurosis.

Cellular and molecular mediators of neuroinflammation in the pathogenesis of Parkinson's disease

Neuroinflammation is a host-defense mechanism associated with restoration of normal structure and function of the brain and neutralization of an insult. Increasing neuropathological and biochemical evidence from the brains of individuals with Parkinson's disease (PD) provides strong evidence for activation of neuroinflammatory pathways. Microglia, the resident innate immune cells, may play a major role in the inflammatory process of the diseased brain of patients with PD. Although microglia forms the first line of defense for the neural parenchyma, uncontrolled activation of microglia may directly affect neurons by releasing various molecular mediators such as inflammatory cytokines (tumor necrosis factor-α, interleukin [IL]-6, and IL-1β), nitric oxide, prostaglandin E2, and reactive oxygen and nitrogen species. Moreover, recent studies have reported that activated microglia phagocytose not only damaged cell debris but also intact neighboring cells. This phenomenon further supports their active participation in self-enduring neuronal damage cycles. As the relationship between PD and neuroinflammation is being studied, there is a realization that both cellular and molecular mediators are most likely assisting pathological processes leading to disease progression. Here, we discuss mediators of neuroinflammation, which are known activators released from damaged parenchyma of the brain and result in neuronal degeneration in patients with PD.

Targeting metabolic inflammation in Parkinson's disease: implications for prospective therapeutic strategies

1. Parkinson's disease (PD) is one of the most common neurodegenerative disorders and is characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Although the aetiology of PD has not been clarified as yet, it is believed that ageing, diet, diabetes and adiposity are associated with PD. 2. Type 2 diabetes and lipid abnormalities share multiple common pathophysiological mechanisms with PD. In particular, inflammation plays a critical role in the destruction of both pancreatic islet β-cells and dopaminergic neurons in the substantia nigra. Emerging evidence indicates that dysfunctions of energy metabolism evoke metabolic inflammation, which differs to the narrow concept of inflammation, participating in systemic pathological processes such as neurodegenerative disease and diabetes. 3. The brain is considered an immunologically privileged organ, free from immune reactions, because it is protected by the blood-brain barrier (BBB). However, studies have shown that there is gradual impairment of neurovascular function with ageing and in neurodegenerative disorders, resulting in abnormal states, including increased BBB permeability. Consequently, harmful elements that would not normally be able to cross the BBB, such as pro-inflammatory factors, reactive oxygen species and neurotoxins, infiltrate into the brain, triggering neural injury. 4. Currently, the drugs available for the treatment of PD only ameliorate the symptoms of the disease. Therapeutic strategies aimed at stopping or modifying disease progression are still being sought. Most recent studies suggest that both central and peripheral inflammation may be dysregulated in PD. Therefore, therapeutic strategies aimed at modulating systemic inflammatory reactions or energy metabolism may represent a goal in neuroprotection in PD.

[The Parkinson puzzle]

Parkinson's disease is one of the most frequent progressive degenerative disorders with unknown origin of the nervous system. The commutation of the disease on Guam led to the discovery of a neurotoxin which was also found in other continents. This neurotoxin was identified in the common cyanobacteria (blue-green algae). Early clinical observations suggested some loose correlations with gastric and duodenal ulcer and Parkinson's disease, while recent studies revealed a toxin, almost identical to that found in cyanobacteria in one strain of Helicobacter pylori, which proved to cause Parkinson like symptoms in animals. Therefore, it cannot be ruled out that there is a slowly progressive poisoning in Parkinson's disease. The disease specific alpha-sinuclein inclusions can be found in nerve cells of the intestinal mucosa far before the appearance of clinical symptoms indicating that the disease may start in the intestines. These results are strengthened by the results of Borody's fecal transplants, after which in Parkinson patients showed a symptomatic improvement. Based on these observations the Parkinson puzzle is getting complete. Although these observations are not evidence based, they may indicate a new way for basic clinical research, as well as a new way of thinking for clinicians. These new observations in psycho-neuro-immunology strengthen the fact that immunological factors may also play a critical factor facilitating local cell necrosis which may be influenced easily.

Naloxone inhibition of lipopolysaccharide-induced activation of retinal microglia is partly mediated via the p38 mitogen activated protein kinase signalling pathway

OBJECTIVES

To investigate the effects and underlying mechanism of action of naloxone on lipopolysaccharide (LPS)-induced activation of retinal microglia in vitro.

METHODS

Rat retinal microglia primary cultures were divided into four treatment groups: untreated; 1 μg/ml LPS for 12 h; 0.5, 1.0 or 2.0 μM naloxone for 30 min before LPS; 2.5 or 5.0 μM SB203580 for 12 h before LPS and naloxone. Levels of tumour necrosis factor (TNF)-α and interleukin (IL)-1β were determined by enzyme-linked immuno sorbent assay. Western blot analysis and double immunofluorescence were used to examine activation of the mitogen activated protein kinase (MAPK) signalling pathway.

RESULTS

LPS induced an increase in TNF-α and IL-1β in culture supernatants, which was dose-dependently inhibited by naloxone. Naloxone also dose-dependently inhibited LPS-induced increases in phosphorylated p38 MAPK. Pretreatment of cells with SB203580 attenuated the inhibitory effect of naloxone on TNF-α and IL-1β production.

CONCLUSIONS

Naloxone suppressed LPS-induced activation of cultured retinal microglia and this suppression appeared to occur partly through the p38 MAPK signalling pathway. Naloxone may have therapeutic potential in neuro degenerative diseases characterized by the activation of microglia.

Toll-like receptor 4 signaling is involved in PACAP-induced neuroprotection in BV2 microglial cells under OGD/reoxygenation

OBJECT

The neuroprotective effects of pituitary adenylate cyclise-activating polypeptide (PACAP) have been well documented in vivo and in vitro. However, the mechanisms by which PACAP protected microglia from ischemic/hypoxic injury via inhibition of microglia activation remain unclear. Toll-like receptor 4 (TLR4) plays a considerable role in the induction of innate immune and inflammatory responses. The purpose of this study is to investigate the effect of PACAP on the oxygen and glucose deprivation (OGD)/reoxygenation BV2 microglia and to explore the role of TLR4/myeloid differentiation protein 88 (MyD88)/nuclear factor-kappa B (NF-kappaB) pathway in the neuroprotective effects of PACAP.

METHODS

We conducted OGD/reoxygenation by placing BV2 microglia into an airtight chamber and in glucose-free medium. BV2 microglia cell viability was determined by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide] assay. Western blot was utilized to detect TLR4, MyD88 expression, inhibitory protein of NF-kappaB (IkappaB) phosphorylation/degradation, NF-kappaB activation. Level of tumor necrosis factor-alpha (TNF-alpha) in culture medium was measured with enzyme-linked immunosorbent assay (ELISA). Apoptosis was determined by flow cytometry.

RESULTS

We found that pretreatment with PACAP to BV2 cells immediately before OGD/reoxygenation significantly alleviated microglia hypoxic injury. PACAP inhibited upregulation of TLR4, MyD88 and NF-kappaB in BV2 microglial cells exposed to OGD/reoxygenation. PACAP administration also significantly reduced the production of proinflammatory cytokines and apoptosis in BV2 microglia exposed to OGD/reoxygenation.

DISCUSSION

Pretreatment with PACAP inhibited activation of the TLR4/MyD88/NF-kappaB signaling pathway and decreased inflammatory cytokine levels, as well as apoptosis in microglia, thereby attenuating microglia hypoxic injury. Our results suggested that TLR4-mediated MyD88-dependent signaling pathway contributed to neuroprotection of PACAP to microglia against OGD/reoxygenation.

Inflammatory regulation of ATP binding cassette efflux transporter expression and function in microglia

ATP-binding cassette (ABC) efflux transporters, including multidrug resistance protein 1 (Mdr1), breast cancer resistance protein (Bcrp), and multidrug resistance-associated proteins (Mrps) extrude chemicals from the brain. Although ABC transporters are critical for blood-brain barrier integrity, less attention has been placed on the regulation of these proteins in brain parenchymal cells such as microglia. Prior studies demonstrate that inflammation after lipopolysaccharide (LPS) treatment alters transporter expression in the livers of mice. Here, we sought to determine the effects of inflammation on the expression and function of transporters in microglia. To test this, the expression and function of ABC efflux transport proteins were quantified in mouse BV-2 microglial cells in response to activation with LPS. Intracellular retention of fluorescent rhodamine 123, Hoechst 33342, and calcein acetoxymethyl ester was increased in LPS-treated microglia, suggesting that the functions of Mdr1, Bcrp, and Mrps were decreased, respectively. LPS reduced Mdr1, Bcrp, and Mrp4 mRNA and protein expression between 40 and 70%. Conversely, LPS increased expression of Mrp1 and Mrp5 mRNA and protein. Immunofluorescent staining confirmed reduced Bcrp and Mrp4 and elevated Mrp1 and Mrp5 protein in activated microglia. Pharmacological inhibition of nuclear factor κB (NF-κB) transcriptional signaling attenuated down-regulation of Mdr1a mRNA and potentiated up-regulation of Mrp5 mRNA in LPS-treated cells. Together, these data suggest that LPS stimulates microglia and impairs efflux of prototypical ABC transporter substrates by altering mRNA and protein expression, in part through NF-κB signaling. Decreased transporter efflux function in microglia may lead to the retention of toxic chemicals and aberrant cell-cell communication during neuroinflammation.

Contributions of central and systemic inflammation to the pathophysiology of Parkinson's disease

Idiopathic Parkinson's disease (PD) represents a complex interaction between the inherent vulnerability of the nigrostriatal dopaminergic system, a possible genetic predisposition, and exposure to environmental toxins including inflammatory triggers. Evidence now suggests that chronic neuroinflammation is consistently associated with the pathophysiology of PD. Activation of microglia and increased levels of pro-inflammatory mediators such as TNF-α, IL-1β and IL-6, reactive oxygen species and eicosanoids has been reported after post-mortem analysis of the substantia nigra from PD patients and in animal models of PD. It is hypothesised that chronically activated microglia secrete high levels of pro-inflammatory mediators which damage neurons and further activate microglia, resulting in a feed forward cycle promoting further inflammation and neurodegeneration. Moreover, nigrostriatal dopaminergic neurons are more vulnerable to pro-inflammatory and oxidative mediators than other cell types because of their low intracellular glutathione concentration. Systemic inflammation has also been suggested to contribute to neurodegeneration in PD, as lymphocyte infiltration has been observed in brains of PD patients and in animal models of PD, substantiating the current theory of a fundamental role of inflammation in neurodegeneration. We will examine the current evidence in the literature which offers insight into the premise that both central and systemic inflammation may contribute to neurodegeneration in PD. We will discuss the emerging possibility of the use of diagnostic tools such as imaging technologies for PD patients. Finally, we will present the immunomodulatory therapeutic strategies that are now under investigation and in clinical trials as potential neuroprotective drugs for PD.

Inflammation in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease that is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Inflammatory responses manifested by glial reactions, T cell infiltration, and increased expression of inflammatory cytokines, as well as other toxic mediators derived from activated glial cells, are currently recognized as prominent features of PD. The consistent findings obtained by various animal models of PD suggest that neuroinflammation is an important contributor to the pathogenesis of the disease and may further propel the progressive loss of nigral dopaminergic neurons. Furthermore, although it may not be the primary cause of PD, additional epidemiological, genetic, pharmacological, and imaging evidence support the proposal that inflammatory processes in this specific brain region are crucial for disease progression. Recent in vitro studies, however, have suggested that activation of microglia and subsequently astrocytes via mediators released by injured dopaminergic neurons is involved. However, additional in vivo experiments are needed for a deeper understanding of the mechanisms involved in PD pathogenesis. Further insight on the mechanisms of inflammation in PD will help to further develop alternative therapeutic strategies that will specifically and temporally target inflammatory processes without abrogating the potential benefits derived by neuroinflammation, such as tissue restoration.

Neuroprotective effects of riluzole in early phase Parkinson's disease on clinically relevant parameters in the marmoset MPTP model

The present study evaluates neuroprotection in a marmoset MPTP (1-methyl-1,2,3,6-tetrahydropyridine) model representing early Parkinson's disease (PD). The anti-glutamatergic compound riluzole is used as a model compound for neuroprotection. The compound is one of the few protective compounds used in the clinic for a neurodegenerative disorder. Marmoset monkeys were randomized into three groups of six: 1) an MPTP group receiving a total MPTP dose of 7 mg/kg (4 injections over two weeks, s.c.) 2) a riluzole group receiving besides MPTP, a twice daily dose of riluzole (10 mg/kg, p.o.), starting one week before MPTP and continuing for one week after the final MPTP injection and 3) a control group receiving saline instead of MPTP and riluzole. The marmosets' Parkinsonian symptoms were scored daily and their activity level, hand-eye coordination, jumping behavior, axial turning and night sleep parameters were tested and recorded weekly. At three weeks following the last MPTP challenge, brains were dissected and dopamine levels in the striatum and the tyrosine hydroxylase (TH) expressing dopamine (DA) neurons in the substantia nigra (SN) were compared. MPTP affected all behavioral parameters and sleep architecture and induced a relatively mild (50%) decline of DA neurons in the substantia nigra (SN). Riluzole relieved the Parkinsonian signs, and improved the hand-eye coordination as well as turning ability. Moreover, riluzole prevented the impact of MPTP on sleep architecture and rapid eye movement behavioral disorder (RBD). Riluzole also increased the number of surviving DA neurons in MPTP-treated marmosets to 75%. However, riluzole did not prevent the MPTP-induced impairments on locomotor activity and jumping activity. In conclusion, reduction of excitotoxicity by riluzole appeared to be effective in reducing progressive neurodegeneration and relieved several clinically relevant PD symptoms in an animal model representing the early phase of PD.

Role of microglia in CNS inflammation

There is increasing confusion about the meaning of the terms inflammation, neuroinflammation, and microglial inflammation. We aim in this review to achieve greater clarity regarding these terms, which are essential for our understanding of the role of microglia in CNS inflammatory conditions. The important concept of sterile inflammation is explained against the backdrop of classical inflammation, and its key differences from what researchers refer to when they use the terms neuroinflammation and microglial inflammation are illustrated. We propose to replace the term "neuroinflammation" with "microglial activation" or "CNS pseudo-inflammation", if microglial activation does not suffice. In addition, we recommend abandoning the terms "microglial inflammation" and "inflamed microglia" because of the lack of a clear concept behind them.