Neuroimmunological processes in Parkinson's disease and their relation to α-synuclein: microglia as the referee between neuronal processes and peripheral immunity

Assessing serum anti-nuclear antibodies HEp-2 patterns in synucleinopathies

This study investigates the presence of antinuclear antibodies (ANA) in three primary synucleinopathies - Parkinson's disease (PD), multiple system atrophy (MSA), and dementia with Lewy bodies (DLB), compared to healthy controls. Autoinflammatory disorders typically involve the immune system mistakenly attacking the body's own cells and start producing ANA. There is an increasing body of evidence that immune-mediated inflammation is a pathological feature linked to synucleinopathies. To investigate whether this could be autoimmune mediated we analyzed for ANA in the plasma of 25 MSA, 25 PD, and 17 DLB patients, along with 25 healthy controls, using the ANA HEp-2 indirect immunofluorescence antibody assay (ANA HEp-2 IFA). Contrary to initial expectations, results showed ANA HEp-2 positivity in 12% of PD, 8% of MSA patients, 18% of DLB patients, and 17% of healthy controls, indicating no increased prevalence of ANA in synucleinopathies compared to age-matched healthy individuals. Various ANA HEp-2 patterns were identified, but no specific pattern was associated with individual synucleinopathies. We conclude hereby that synucleinopathies are not associated with detectable presence of ANA in plasma.

Immunomodulator-Derived Nanoparticles Induce Neuroprotection and Regulatory T Cell Action to Alleviate Parkinsonism

Post-translational modification, mitochondrial abruptions, neuroinflammation, and α-synuclein (α-Syn) aggregation are considered as major causes of Parkinson's disease (PD) pathogenesis. The recent literature highlights neuroimmune cross talk and the negative role of immune effector T (Teff) and positive regulation by regulatory T (Treg) cells in PD treatment. Herein, a strategy to endow Treg action paves the path for development of PD treatment. Thus, we explored the neuroprotective efficiency of the immunomodulator and PP2A (protein phosphatase 2) activator, FTY720 nanoparticles in in vivo experimental PD models. Repurposing of FTY720 for PD is known due to its protective effect by reducing PD and its camouflaged role in endowing EZH2-mediated epigenetic regulation of PD. EZH2-FOXP3 interaction is necessary for the neuroprotective Treg cell activity. Therefore, we synthesized FTY720 nanoparticles to improve FTY720 protective efficacy in an in vivo PD model to explore the PP2A mediated signaling. We confirmed the formation of FTY720NPs, and the results of the behavioral and protein expression study showed the significant neuroprotective efficiency of our nanoformulations. In the exploration of neuroprotective mechanism, several lines of evidence confirmed FTY720NPs mediated induction of PP2A/EZH2/FOXP3 signaling in the induction of Treg cells effect in in vivo PD treatment. In summary, our nanoformulations have novel potential to alleviate PD by inducing PP2A-induced epigenetic regulation-mediated neuroimmunomodulation at the clinical setup.

Unraveling the Intricacies of OPG/RANKL/RANK Biology and Its Implications in Neurological Disorders-A Comprehensive Literature Review

The OPG/RANKL/RANK framework, along with its specific receptors, plays a crucial role in bone remodeling and the functioning of the central nervous system (CNS) and associated disorders. Recent research and investigations provide evidence that the components of osteoprotegerin (OPG), receptor activator of NF-kB ligand (RANKL), and receptor activator of NF-kB (RANK) are expressed in the CNS. The CNS structure encompasses cells involved in neuroinflammation, including local macrophages, inflammatory cells, and microglia that cross the blood-brain barrier. The OPG/RANKL/RANK trio modulates the neuroinflammatory response based on the molecular context. The levels of OPG/RANKL/RANK components can serve as biomarkers in the blood and cerebrospinal fluid. They act as neuroprotectants following brain injuries and also participate in the regulation of body weight, internal body temperature, brain ischemia, autoimmune encephalopathy, and energy metabolism. Although the OPG/RANKL/RANK system is primarily known for its role in bone remodeling, further exploring deeper into its multifunctional nature can uncover new functions and novel drug targets for diseases not previously associated with OPG/RANKL/RANK signaling.

The raphe nuclei are the early lesion site of gastric α-synuclein propagation to the substantia nigra

Parkinson's disease (PD) is a neurodegeneration disease with α-synuclein accumulated in the substantia nigra pars compacta (SNpc) and most of the dopaminergic neurons are lost in SNpc while patients are diagnosed with PD. Exploring the pathology at an early stage contributes to the development of the disease-modifying strategy. Although the "gut-brain" hypothesis is proposed to explain the underlying mechanism, where the earlier lesioned site in the brain of gastric α-synuclein and how α-synuclein further spreads are not fully understood. Here we report that caudal raphe nuclei (CRN) are the early lesion site of gastric α-synuclein propagating through the spinal cord, while locus coeruleus (LC) and substantia nigra pars compacta (SNpc) were further affected over a time frame of 7 months. Pathological α-synuclein propagation via CRN leads to neuron loss and disordered neuron activity, accompanied by abnormal motor and non-motor behavior. Potential neuron circuits are observed among CRN, LC, and SNpc, which contribute to the venerability of dopaminergic neurons in SNpc. These results show that CRN is the key region for the gastric α-synuclein spread to the midbrain. Our study provides valuable details for the "gut-brain" hypothesis and proposes a valuable PD model for future research on early PD intervention.

Exploring [11C]CPPC as a CSF1R-targeted PET Imaging Marker for Early Parkinson's Disease Severity

Neuroinflammation through enhanced innate immunity is thought play a role in the pathogenesis of Parkinson's disease (PD). Methods for monitoring neuroinflammation in living patients with PD are currently limited to positron emission tomography (PET) ligands that lack specificity in labeling immune cells in the nervous system. The colony stimulating factor 1 receptor (CSF1R) plays a crucial role in microglial function, an important cellular contributor to the nervous system's innate immune response. Using immunologic methods, we show that CSF1R in human brain is colocalized with the microglial marker, ionized calcium binding adaptor molecule 1 (Iba1). In PD, CSF1R immunoreactivity is significantly increased in PD across multiple brain regions, with the largest differences in the midbrain versus controls. Autoradiography revealed significantly increased [3H]JHU11761 binding in the inferior parietal cortex of PD patients. PET imaging demonstrated that higher [11C]CPPC binding in the striatum was associated with greater motor disability in PD. Furthermore, increased [11C]CPPC binding in various regions correlated with more severe motor disability and poorer verbal fluency. This study finds that CSF1R expression is elevated in PD and that [11C]CPPC-PET imaging of CSF1R is indicative of motor and cognitive impairments in the early stages of the disease. Moreover, the study underscores the significance of CSF1R as a promising biomarker for neuroinflammation in Parkinson's disease, suggesting its potential use for non-invasive assessment of disease progression and severity, leading to earlier diagnosis and targeted interventions.

Anti-inflammatory and antioxidative actions of tacrolimus (FK506) on human microglial HMC3 cell line

Microglial cells are indispensable for the normal development and functioning of neurons in the central nervous system, where they play a crucial role in maintaining brain homeostasis by surveilling the microenvironment for signs of injury or stress and responding accordingly. However, in neurodegenerative diseases, the density and phenotypes of microglial cells undergo changes, leading to chronic activation and inflammation. Shifting the focus from neurons to microglia in drug discovery for neurodegenerative diseases has become an important therapeutic target. This study was aimed to investigate the potential of Tacrolimus (FK506) an FDA-approved calcineurin inhibitor, to modulate the pathology of neurodegenerative diseases through anti-inflammatory and antioxidative effects on microglial activation. The human microglia clone 3 (HMC3) cells were exposed to 1 μg/mL LPS in the presence and absence of doses of FK506. Survival rates of cells were determined using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) method. Morphological evaluation of cells showed that FK506 restored the normal morphology of activated microglia. Furthermore, FK506 treatment increases the total antioxidant capacity and reduces the total oxidative capacity, indicating its potential antioxidant effects. Data from ELISA and RT-PCR analyses showed that LPS abolished its promoting effects on the release of proinflammatory IL-1β and IL-6 cytokines in HMC3 cells, reflecting the anti-inflammatory effect of FK506. These findings support the idea that FK506 could be a promising therapeutic agent for neurodegenerative diseases by modulating microglial activation and reducing inflammation and oxidative stress.

Neuroinflammatory gene expression profiles of reactive glia in the substantia nigra suggest a multidimensional immune response to alpha synuclein inclusions

Parkinson's disease (PD) pathology is characterized by alpha-synuclein (α-syn) aggregates, degeneration of dopamine neurons in the substantia nigra pars compacta (SNpc), and neuroinflammation. The presence of reactive glia correlates with deposition of pathological α-syn in early-stage PD. Thus, understanding the neuroinflammatory response of microglia and astrocytes to synucleinopathy may identify therapeutic targets. Here we characterized the neuroinflammatory gene expression profile of reactive microglia and astrocytes in the SNpc during early synucleinopathy in the rat α-syn pre-formed fibril (PFF) model. Rats received intrastriatal injection of α-syn PFFs and expression of immune genes was quantified with droplet digital PCR (ddPCR), after which fluorescent in situ hybridization (FISH) was used to localize gene expression to microglia or astrocytes in the SNpc. Genes previously associated with reactive microglia (Cd74, C1qa, Stat1, Axl, Casp1, Il18, Lyz2) and reactive astrocytes (C3, Gbp2, Serping1) were significantly upregulated in the SN of PFF injected rats. Localization of gene expression to SNpc microglia near α-syn aggregates identified a unique α-syn aggregate microglial gene expression profile characterized by upregulation of Cd74, Cxcl10, Rt-1a2, Grn, Csf1r, Tyrobp, C3, C1qa, Serping1 and Fcer1g. Importantly, significant microglial upregulation of Cd74 and C3 were only observed following injection of α-syn PFFs, not α-syn monomer, confirming specificity to α-syn aggregation. Serping1 expression also localized to astrocytes in the SNpc. Interestingly, C3 expression in the SNpc localized to microglia at 2- and 4-months post-PFF, but to astrocytes at 6-months post-PFF. We also observed expression of Rt1-a2 and Cxcl10 in SNpc dopamine neurons. Cumulatively our results identify a dynamic, yet reproducible gene expression profile of reactive microglia and astrocytes associated with early synucleinopathy in the rat SNpc.

Lindenane sesquiterpenoid dimers from Chloranthus holostegius with anti-neuroinflammatory activities in BV-2 microglia

Fifteen undescribed lindenane-type sesquiterpenoid dimers, designated chloranholides F-T (1-15), together with twenty-five known analogs (16-40), were isolated from the whole plants of Chloranthus holostegius. The isolate structures were elucidated by analysis of spectroscopic data and chemical methods, and their absolute configurations were determined by X-ray crystallography and electronic circular dichroism spectra. In anti-neuroinflammatory assays, all isolates were evaluated by examination of their inhibitory effect on nitric oxide (NO) in LPS-stimulated BV-2 cells, and the results showed that 21-24, 26, 30, 32 and 36 significantly inhibited the production of the inflammatory mediator NO, with IC50 values ranging from 3.18 to 11.46 μM, which was better than that of quercetin. Structure-activity relationship analysis revealed that two essential functional groups played an indispensable role in the anti-inflammatory effects. Moreover, 22 and 24 inhibited the LPS-induced upregulation of iNOS and COX-2 enzymes in BV-2 microglia at the protein level.

Microglia mediated neuroinflammation in neurodegenerative diseases: A review on the cell signaling pathways involved in microglial activation

Microglia, the immune sentinels of the central nervous system (CNS), have emerged to be the central players in many neurological and neurodegenerative diseases. Recent studies on large genome databases and omics studies in fact provide support to the idea that microglial cells could be the drivers of these diseases. Microglial cells have the capacity to undergo morphological and phenotypic transformations depending on its microenvironment. From the homeostatic ramified state, they can shift their phenotypes between the two extremes, known as the proinflammatory M1 and anti-inflammatory M2 phenotype, with intermediate transitional states, characterized by different transcriptional signature and release of inflammatory mediators. The temporal regulation of the release of the inflammatory factors are critical for damage control and steering the microglia back towards homeostatic conditions. A dysregulation in these can lead to excessive tissue damage and neuronal death. Therefore, targeting the cell signaling pathways that are the underpinnings of microglial modulations are considered to be an important avenue for treatment of various neurodegenerative diseases. In this review we have discussed various signaling pathways that trigger microglial activation from its ramified state and highlight the mechanisms of microglia-mediated neuroinflammation that are associated with various neurodegenerative diseases. Most of the cellular factors that drive microglia towards a proinflammatory phenotype are components of the immune system signaling pathways and cell proliferation, along with certain ion channels. The anti-inflammatory phenotype is mainly elicited by purinoceptors, metabolic receptors and other receptors that primarily suppress the production proinflammatory mediators.

Impaired aldehyde detoxification exacerbates motor deficits in an alpha-synuclein mouse model of Parkinson's disease

INTRODUCTION

The discovery of biogenic aldehydes in the postmortem parkinsonian brain and the ability of these aldehydes to modify and cross-link proteins has called attention to their possible role in Parkinson's disease. For example, many in vitro studies have found that the aldehyde metabolite of dopamine, 3,4-dihydroxyphenylacetaldehyde (DOPAL), induces the formation of stable, neurotoxic alpha-synuclein oligomers.

METHODS

To study this in vivo, mice deficient in the two aldehyde dehydrogenase enzymes (Aldh1a1 and Aldh2, DKO) primarily responsible for detoxification of DOPAL in the nigrostriatal pathway were crossed with mice that overexpress human wild-type alpha-synuclein. DKO overexpressing human wild-type alpha-synuclein (DKO/ASO) offspring were evaluated for impairment on motor tasks associated with Parkinsonism.

RESULTS

DKO/ASO mice developed severe motor deficits greater than that of mice overexpressing human wild-type alpha-synuclein alone.

CONCLUSION

These results provide evidence to support the idea that biogenic aldehydes such as DOPAL interact with human wild-type alpha-synuclein, directly or indirectly, in vivo to exacerbate locomotor deficits in Parkinson's disease.

Coumarin-chalcone hybrid LM-021 and indole derivative NC009-1 targeting inflammation and oxidative stress to protect BE(2)-M17 cells against α-synuclein toxicity

Parkinson's disease (PD) is featured mainly by the loss of dopaminergic neurons and the presence of α-synuclein-containing aggregates in the substantia nigra of brain. The α-synuclein fibrils and aggregates lead to increased oxidative stress and neural toxicity in PD. Chronic inflammation mediated by microglia is one of the hallmarks of PD pathophysiology. In this report, we showed that coumarin-chalcone hybrid LM-021 and indole derivative NC009-1 reduced the expression of major histocompatibility complex-II, NLR family pyrin domain containing (NLRP) 3, caspase-1, inducible nitric oxide synthase, interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in α-synuclein-activated mouse BV-2 microglia. Release of pro-inflammatory mediators including nitric oxide, IL-1β, IL-6 and TNF-α was also mitigated. In BE(2)-M17 cells expressing A53T α-synuclein aggregates, LM-021 and NC009-1 reduced α-synuclein aggregation, neuroinflammation, oxidative stress and apoptosis, and promoted neurite outgrowth. These protective effects were mediated by downregulating NLRP1, IL-1β and IL-6, and their downstream pathways including nuclear factor (NF)-κB inhibitor alpha (IκBα)/NF-κB P65 subunit (P65), c-Jun N-terminal kinase (JNK)/proto-oncogene c-Jun (JUN), mitogen-activated protein kinase 14 (P38)/signal transducer and activator of transcription (STAT) 1, and Janus kinase 2 (JAK2)/STAT3. The study results indicate LM-021 and NC009-1 as potential new drug candidates for PD.

Prussian blue nanozymes: progress, challenges, and opportunities

Prussian Blue Nanozymes (PBNZs) have emerged as highly efficient agents for reactive oxygen species (ROS) elimination, owing to their multiple enzyme-like properties encompassing catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities. As a functional nanomaterial mimicking enzyme, PBNZs not only surmount the limitations of natural enzymes, such as instability and high manufacturing costs, but also exhibit superior stability, tunable activity, low storage expenses, and remarkable reusability. Consequently, PBNZs have gained significant attention in diverse biomedical applications, including disease diagnosis and therapy. Over the past decade, propelled by advancements in catalysis science, biotechnology, computational science, and nanotechnology, PBNZs have witnessed remarkable progress in the exploration of their enzymatic activities, elucidation of catalytic mechanisms, and wide-ranging applications. This comprehensive review aims to provide a systematic overview of the discovery and catalytic mechanisms of PBNZ, along with the strategies employed to modulate their multiple enzyme-like activities. Furthermore, we extensively survey the recent advancements in utilizing PBNZs for scavenging ROS in various biomedical applications. Lastly, we analyze the existing challenges of translating PBNZs into therapeutic agents for clinical use and outline future research directions in this field. By presenting a comprehensive synopsis of the current state of knowledge, this review seeks to contribute to a deeper understanding of the immense potential of PBNZs as an innovative therapeutic agent in biomedicine.

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

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

Disease mechanisms as subtypes: Immune dysfunction in Parkinson's disease

In recent years, the contraposition between inflammatory and neurodegenerative processes has been increasingly challenged. Inflammation has been emphasized as a key player in the onset and progression of Parkinson disease (PD) and other neurodegenerative disorders. The strongest indicators of the involvement of the immune system derived from evidence of microglial activation, profound imbalance in phenotype and composition of peripheral immune cells, and impaired humoral immune responses. Moreover, peripheral inflammatory mechanisms (e.g., involving the gut-brain axis) and immunogenetic factors are likely to be implicated. Even though several lines of preclinical and clinical studies are supporting and defining the complex relationship between the immune system and PD, the exact mechanisms are currently unknown. Similarly, the temporal and causal connections between innate and adaptive immune responses and neurodegeneration are unsettled, challenging our ambition to define an integrated and holistic model of the disease. Despite these difficulties, current evidence is providing the unique opportunity to develop immune-targeted approaches for PD, thus enriching our therapeutic armamentarium. This chapter aims to provide an extensive overview of past and present studies that explored the implication of the immune system in neurodegeneration, thus paving the road for the concept of disease modification in PD.

Protective effects of evening primrose oil on behavioral activities, nigral microglia and histopathological changes in a rat model of rotenone-induced parkinsonism

Parkinson's disease (PD) is a neurodegenerative illness described as damage to dopaminergic neurons. There is increasing evidence that neuroinflammatory activity mediated by microglia is extensively involved in the initiation and development of PD. This study assessed the protective effect of evening primrose oil [EPO] as an anti-inflammatory mediator in rotenone-induced Parkinsonism in rats. Forty-eight adult male albino rats were distributed into four groups. Group I: control. Group II: rotenone [1.5 mg/kg/48 h] was administered subcutaneously to the rats. Groups III and IV: the rats had rotenone plus daily oral [EPO] 5 and 10 mg/kg respectively. After 24 days, motor behaviour was assessed by the open field and rotarod tests. The brain striata were isolated and tested for tumor necrosis factor (TNF)-α, interleukin 6, NF-B [nuclear factor-kappa B], and dopamine levels. The mid-brain tissues were processed for light and electron microscopy examinations, and immunohistochemical staining for tyrosine hydroxylase [TH], and microglia cells' markers: [CD68 and IBA1]. Results revealed that rotenone-treated rats had poor motor function, a significantly increased striatal level of inflammatory markers, markedly shrunken neurons, degeneration, pyknotic neuroglia, neuropil vacuolation, markedly destructed swollen mitochondria with loss of their cristae, and dilated rough endoplasmic reticulum, as well as decreased TH and increased CD68 and IBA1-positive cells. Treatment with EPO ameliorates all the neuropathological changes of rotenone in the rat brain. In conclusion, EPO enhanced the motor performance, reduced the inflammatory marker levels, restored dopamine levels, and ameliorated the neurohistopathological lesions of rats with experimental parkinsonism, suggesting its neuroprotective and anti-inflammatory effects.

Inflammation and immune dysfunction in Parkinson disease

Parkinson disease (PD) is a progressive neurodegenerative disease that affects peripheral organs as well as the central nervous system and involves a fundamental role of neuroinflammation in its pathophysiology. Neurohistological and neuroimaging studies support the presence of ongoing and end-stage neuroinflammatory processes in PD. Moreover, numerous studies of peripheral blood and cerebrospinal fluid from patients with PD suggest alterations in markers of inflammation and immune cell populations that could initiate or exacerbate neuroinflammation and perpetuate the neurodegenerative process. A number of disease genes and risk factors have been identified as modulators of immune function in PD and evidence is mounting for a role of viral or bacterial exposure, pesticides and alterations in gut microbiota in disease pathogenesis. This has led to the hypothesis that complex gene-by-environment interactions combine with an ageing immune system to create the 'perfect storm' that enables the development and progression of PD. We discuss the evidence for this hypothesis and opportunities to harness the emerging immunological knowledge from patients with PD to create better preclinical models with the long-term goal of enabling earlier identification of at-risk individuals to prevent, delay and more effectively treat the disease.

Hydrogels for Brain Repair: Application to Parkinson's Disease

INTRODUCTION

Parkinson's disease is the second most common neurodegenerative disease. Currently, there are no curative therapies, with only symptomatic treatment available. One of the principal reasons for the lack of treatments is the problem of delivering drugs to the brain, mainly due to the blood-brain barrier. Hydrogels are presented as ideal platforms for delivering treatments to the brain ranging from small molecules to cell replacement therapies.

AREAS COVERED

The potential application of hydrogel-based therapies for Parkinson's disease is addressed. The desirable composition and mechanical properties of these therapies for brain application are discussed, alongside the preclinical research available with hydrogels in Parkinson's disease. Lastly, translational and manufacturing challenges are presented.

EXPERT OPINION

Parkinson's disease urgently needs novel therapies to delay its progression and for advanced stages, at which conventional therapies fail to control motor symptoms. Neurotrophic factor-loaded hydrogels with stem cells offer one of the most promising therapies. This approach may increase the striatal dopamine content while protecting and promoting the differentiation of stem cells although the generation of synapses between engrafted and host cells remains an issue to overcome. Other challenges to consider are related to the route of administration of hydrogels and their large-scale production, required to accelerate their translation toward the clinic.

Establishment of the Carrot-Made LTB-Syn Antigen Cell Line in Shake Flask and Airlift Bioreactor Cultures

Carrot (Daucus carota) cells have been used to effectively manufacture recombinant biopharmaceuticals such as cytokines, vaccines, and antibodies. We generated the carrot cell line Z4, genetically modified to produce the LTB-Syn antigen, which is a fusion protein proposed for immunotherapy against synucleinopathies. In this work, the Z4 cell suspension line was cultivated to produce the LTB-Syn protein in a 250 mL shake flask and 2 L airlift bioreactor cultures grown for 45 and 30 days, respectively. Maximum biomass was obtained on day 15 in both the airlift bioreactor (35.00 ± 0.04 g/L DW) and shake flasks (17.00 ± 0.04 g/L DW). In the bioreactor, the highest LTB-Syn protein yield (1.52 ± 0.03 µg/g FW) was obtained on day 15; while the same occurred on day 18 for shake flasks (0.92 ± 0.02 µg/g FW). LTB-Syn protein levels were analyzed by GM1-ELISA and western blot. PCR analysis confirmed the presence of the transgene in the Z4 line. The obtained data demonstrate that the carrot Z4 cell suspension line grown in airlift bioreactors shows promise for a scale-up cultivation producing an oral LTB-Syn antigen.

MhcII Regulates Transmission of α-Synuclein-Seeded Pathology in Mice

MHCII molecules, expressed by professional antigen-presenting cells (APCs) such as T cells and B cells, are hypothesized to play a key role in the response of cellular immunity to α-synuclein (α-syn). However, the role of cellular immunity in the neuroanatomic transmission of α-syn pre-formed fibrillar (PFF) seeds is undetermined. To illuminate whether cellular immunity influences the transmission of α-syn seeds from the periphery into the CNS, we injected preformed α-syn PFFs in the hindlimb of the Line M83 transgenic mouse model of synucleinopathy lacking MhcII. We showed that a complete deficiency in MhcII accelerated the appearance of seeded α-syn pathology and shortened the lifespan of the PFF-seeded M83 mice. To characterize whether B-cell and T-cell inherent MhcII function underlies this accelerated response to PFF seeding, we next injected α-syn PFFs in Rag1-/- mice which completely lacked these mature lymphocytes. There was no alteration in the lifespan or burden of endstage α-syn pathology in the PFF-seeded, Rag1-deficient M83+/- mice. Together, these results suggested that MhcII function on immune cells other than these classical APCs is potentially involved in the propagation of α-syn in this model of experimental synucleinopathy. We focused on microglia next, finding that while microglial burden was significantly upregulated in PFF-seeded, MhcII-deficient mice relative to controls, the microglial activation marker Cd68 was reduced in these mice, suggesting that these microglia were not responsive. Additional analysis of the CNS showed the early appearance of the neurotoxic astrocyte A1 signature and the induction of the Ifnγ-inducible anti-viral response mediated by MhcI in the MhcII-deficient, PFF-seeded mice. Overall, our data suggest that the loss of MhcII function leads to a dysfunctional response in non-classical APCs and that this response could potentially play a role in determining PFF-induced pathology. Collectively, our results identify the critical role of MhcII function in synucleinopathies induced by α-syn prion seeds.

Neuroprotective effect of quercetin against rotenone-induced neuroinflammation and alterations in mice behavior

Various studies suggested that neuroinflammation leads to the development of several neurodegenerative disorders like Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington's disease (HD). Rotenone is an organic pesticide and potent inhibitor of complex I of electron transport chain widely used to develop the PD model. Numerous studies reported rotenone toxicity in the dopaminergic system but very few studies are available on rotenone-induced glial cell activation and subsequent neurodegeneration and alterations in various types of behavior. Therefore, the present study was designed to explore the effect of rotenone on neuroinflammation and its deleterious effect on the behavior of mice, and also how these effects can be protected through quercetin. Quercetin, a natural flavonoid having strong antioxidant and anti-inflammatory properties, is found in vegetables and fruits. The finding of the study indicated that rotenone 5 mg/kg body weight for 60 days through oral gavage leads to the release of inflammatory markers in blood serum, astrocytes activation in substantia nigra and hippocampus, and subsequently decreased density of dopaminergic fibers in the striatum. Rotenone also altered the memory of the mice as indicated by decreased spontaneous alteration in Y-maze and T-maze tests and reduction in exploration time in novel object recognition, increased immobility time in the forced swim test and reduced muscular strength. Co-treatment of quercetin 30 mg/kg/day through oral gavage for 60 days along with rotenone significantly reversed all these adverse effects, suggesting that quercetin could reduce neuroinflammation, and improve memory, and cognitive function.

Age-Related Midbrain Inflammation and Senescence in Parkinson’s Disease

Immune responses are arising as a common feature of several neurodegenerative diseases, such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and Amyotrophic Lateral Sclerosis (ALS), but their role as either causative or consequential remains debated. It is evident that there is local inflammation in the midbrain in PD patients even before symptom onset, but the underlying mechanisms remain elusive. In this mini-review, we discuss this midbrain inflammation in the context of PD and argue that cellular senescence may be the cause for this immune response. We postulate that to unravel the relationship between inflammation and senescence in PD, it is crucial to first understand the potential causative roles of various cell types of the midbrain and determine how the possible paracrine spreading of senescence between them may lead to observed local immune responses. We hypothesize that secretion of pro-inflammatory factors by senescent cells in the midbrain triggers neuroinflammation resulting in immune cell-mediated killing of midbrain dopaminergic (DA) neurons in PD.

The Double-Faceted Role of Leucine-Rich Repeat Kinase 2 in the Immunopathogenesis of Parkinson’s Disease

Leucine-rich repeat kinase 2 (LRRK2) is one of the most common causative genes in Parkinson’s disease (PD). The complex structure of this multiple domains’ protein determines its versatile functions in multiple physiological processes, including migration, autophagy, phagocytosis, and mitochondrial function, among others. Mounting studies have also demonstrated the role of LRRK2 in mediating neuroinflammation, the prominent hallmark of PD, and intricate functions in immune cells, such as microglia, macrophages, and astrocytes. Of those, microglia were extensively studied in PD, which serves as the resident immune cell of the central nervous system that is rapidly activated upon neuronal injury and pathogenic insult. Moreover, the activation and function of immune cells can be achieved by modulating their intracellular metabolic profiles, in which LRRK2 plays an emerging role. Here, we provide an updated review focusing on the double-faceted role of LRRK2 in regulating various cellular physiology and immune functions especially in microglia. Moreover, we will summarize the latest discovery of the three-dimensional structure of LRRK2, as well as the function and dysfunction of LRRK2 in immune cell-related pathways.

Prussian Blue Nanozyme as a Pyroptosis Inhibitor Alleviates Neurodegeneration

Current pharmacological interventions for Parkinson's disease (PD) remain unsatisfactory in clinical settings. Inflammasome-mediated pyroptosis represents a potential therapeutic target for the alleviation of neurodegenerative diseases. The development of inflammasome-mediated pyroptosis agonists or antagonists may transform the treatment of neurodegenerative diseases. However, the identification of specific compounds that inhibit pyroptosis remains challenging. Herein, Prussian blue nanozyme (PBzyme) is revealed as a pyroptosis inhibitor to alleviate the neurodegeneration in mouse and cell models of PD. PBzyme protects the microglia and neurons against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). PBzyme alleviates motor deficits, attenuates the damage of mitochondrial membrane potential, and rescues dopaminergic neurons. Furthermore, intra-cerebroventricular injection of PBzyme reduces dopaminergic degeneration and inhibits neuroinflammation in an MPTP-induced PD mouse model. Both in vitro and in vivo results demonstrate that PBzyme reduces the activation of microglial nucleotide-binding domain and leucine-rich repeat family pyrin domain containing 3 (NLRP3) inflammasomes and caspase-1 by scavenging reactive oxygen species, thereby downregulating gasdermin D (GSDMD) cleavage as well as inflammatory factor production, and eventually leading to the inhibition of microglia pyroptosis. Overall, this work highlights the neuroprotective effects of PBzyme as a pyroptosis inhibitor and provides valuable mechanistic insights and a potential therapeutic strategy for the treatment of PD.

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.

Fibroblast Growth Factor 21 Modulates Microglial Polarization That Attenuates Neurodegeneration in Mice and Cellular Models of Parkinson's Disease

Microglial polarization and the subsequent neuroinflammatory response were identified as key contributors to the progress of Parkinson's disease (PD). Researchers have shown that fibroblast growth factor 21 (FGF21) plays multiple biological functions, including anti-inflammation and neuroprotection. However, the knowledge of FGF21 on microglial polarization in PD in vivo is far from completion. In this study, both in vivo and in vitro models were used to investigate whether FGF21 enhances the brain function by modulating microglial polarization in PD. The protective effects of FGF21 in vivo were conducted using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced PD mice model alongside intraperitoneally received FGF21. A behavioral test battery and tyrosine hydroxylase (TH) immunohistochemistry were conducted to evaluate the neuronal function and nigrostriatal tract integrity. Immunofluorescence assay and Western blot were used to examine M1/M2 microglial polarization. Then, a microglia-neuron co-culture system was adopted in vitro to identify the underlying molecular mechanisms of FGF21. The results showed that FGF21 significantly alleviated motor and cognitive impairment in mice with PD. FGF21 also protected TH-positive neuron cells in the striatum and midbrain. Mechanistically, FGF21 suppressed M1 microglial polarization and the subsequent mRNA expression of pro-inflammatory factors while promoting M2 microglial polarization with increasing anti-inflammatory factors in mice with PD. Furthermore, sirtuin 1 (SIRT1) and the nuclear factor-kappa B (NF-κB) pathway were involved in the FGF21-induced M2 microglial polarization. Conversely, SIRT1 inhibitor EX527 significantly prevented both the FGF21-induced SIRT1 expression and M2 microglial polarization. Moreover, FGF21 pretreatment of microglia significantly prevented neuronal cell apoptosis in a microglia-neuron co-culture system. In conclusion, our data demonstrate that FGF21 exerted its protective effects in the pathology of PD through SIRT1/NF-κB pathway-mediated microglial polarization. Given the safety record of human clinical trials, FGF21 could be a promising therapy for clinical trials to ameliorate motor and nonmotor deficits in patients with PD.

Increased expression of pathological markers in Parkinson's disease dementia post-mortem brains compared to dementia with Lewy bodies

BACKGROUND

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are common age-related neurodegenerative diseases comprising Lewy body spectrum disorders associated with cortical and subcortical Lewy body pathology. Over 30% of PD patients develop PD dementia (PDD), which describes dementia arising in the context of established idiopathic PD. Furthermore, Lewy bodies frequently accompany the amyloid plaque and neurofibrillary tangle pathology of Alzheimer's disease (AD), where they are observed in the amygdala of approximately 60% of sporadic and familial AD. While PDD and DLB share similar pathological substrates, they differ in the temporal onset of motor and cognitive symptoms; however, protein markers to distinguish them are still lacking.

METHODS

Here, we systematically studied a series of AD and PD pathogenesis markers, as well as mitochondria, mitophagy, and neuroinflammation-related indicators, in the substantia nigra (SN), temporal cortex (TC), and caudate and putamen (CP) regions of human post-mortem brain samples from individuals with PDD and DLB and condition-matched controls.

RESULTS

We found that p-APPT668 (TC), α-synuclein (CP), and LC3II (CP) are all increased while the tyrosine hydroxylase (TH) (CP) is decreased in both PDD and DLB compared to control. Also, the levels of Aβ42 and DD2R, IBA1, and p-LRRK2S935 are all elevated in PDD compared to control. Interestingly, protein levels of p-TauS199/202 in CP and DD2R, DRP1, and VPS35 in TC are all increased in PDD compared to DLB.

CONCLUSIONS

Together, our comprehensive and systematic study identified a set of signature proteins that will help to understand the pathology and etiology of PDD and DLB at the molecular level.

Environmental factors in Parkinson's disease: New insights into the molecular mechanisms

Parkinson's disease is a chronic, progressive neurodegenerative disorder affecting 2-3% of the population ≥65 years. It has long been characterized by motor impairment, autonomic dysfunction, and psychological and cognitive changes. The pathological hallmarks are intracellular inclusions containing α-synuclein aggregates and the loss of dopaminergic neurons in the substantia nigra. Parkinson's disease is thought to be caused by a combination of various pathogenic factors, including genetic factors, environmental factors, and lifestyles. Although much research has focused on the genetic causes of PD, environmental risk factors also play a crucial role in the development of the disease. Here, we summarize the environmental risk factors that may increase the occurrence of PD, as well as the underlying molecular mechanisms.

Trophoblast glycoprotein is a new candidate gene for Parkinson’s disease

Parkinson’s disease (PD) is a movement disorder caused by progressive degeneration of the midbrain dopaminergic (mDA) neurons in the substantia nigra pars compacta (SNc). Despite intense research efforts over the past decades, the etiology of PD remains largely unknown. Here, we discovered the involvement of trophoblast glycoprotein (Tpbg) in the development of PD-like phenotypes in mice. Tpbg expression was detected in the ventral midbrain during embryonic development and in mDA neurons in adulthood. Genetic ablation of Tpbg resulted in mild degeneration of mDA neurons in aged mice (12–14 months) with behavioral deficits reminiscent of PD symptoms. Through in silico analysis, we predicted potential TPBG-interacting partners whose functions were relevant to PD pathogenesis; this result was substantiated by transcriptomic analysis of the SNc of aged Tpbg knockout mice. These findings suggest that Tpbg is a new candidate gene associated with PD and provide a new insight into PD pathogenesis.

Neuroinflammation in Parkinson's disease: a meta-analysis of PET imaging studies

Increasingly, evidence implicates an important role of neuroinflammation in neurodegeneration progression. Yet, brain imaging has not reached a consistent conclusion that neuroinflammation is involved in the pathogenesis of Parkinson's disease (PD). We aimed to review the evidence to quantitatively assess the existence and spatial distribution of neuroinflammation in the brain of PD patients. We systematically searched literature databases for case-control studies which used positron emission tomography to detect neuroinflammation represented by translocator protein (TSPO) levels in PD patients compared with healthy controls (HC). Standardized mean differences (SMD) were selected as effect sizes and random-effects models were used to combine effect sizes. Subgroup analyses for separate brain regions were conducted. Fifteen studies comprising 455 (HC = 198, PD = 238) participants and 19 brain regions were included. Compared to HC, PD patients had elevated TSPO levels in midbrain, putamen, anterior cingulate, posterior cingulate, thalamus, striatum, frontal, temporal, parietal, occipital, cortex, hippocampus, substantia nigra, pons, cerebellum, and caudate when using 1st-generation ligands. TSPO levels were elevated in the midbrain of PD patients when 2nd-generation ligands were used. We discussed the possible explanations of contrasting difference between these outcomes.

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

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

Functions of Intracellular Alpha-Synuclein in Microglia: Implications for Parkinson's Disease Risk

Alpha-synuclein accumulation in dopaminergic neurons is one of the primary features of Parkinson’s disease (PD). Despite its toxic properties during PD, alpha-synuclein has some important physiological functions. Although the activity of the protein has been extensively studied in neurons, the protein is also expressed in other cell types including immune cells and glia. Genetic studies show that mutations in synuclein alpha (SNCA), the gene that encodes alpha-synuclein, and alterations in its expression levels are a significant risk factor for PD, which likely impact the functions of a broad range of cell types. The consequences of altered SNCA expression in other cell types is beginning to be explored. Microglia, the primary macrophage population in the Central Nervous System (CNS), for example, are affected by variations in alpha-synuclein levels and functions. Studies suggest that deviations of alpha-synuclein’s normal activity influence hematopoiesis, the process that gives rise to microglia, and microglia’s immune functions. Alpha-synuclein levels also dictate the efficiency of SNARE-mediated vesicle formation, which could influence autophagy and cytokine release in microglia. Starting from the time of conception, these effects could impact one’s risk for developing PD. Further studies are needed to determine the physiological role of alpha-synuclein and how the protein is affected during PD in non-neuronal cells such as microglia. In this review we will discuss the known roles of alpha-synuclein in differentiation, immune responses, and vesicle formation, with insights into how abnormal alpha-synuclein expression and activity are linked to altered functions of microglia during PD.

Fine mapping of the HLA locus in Parkinson's disease in Europeans

We fine mapped the leukocyte antigen (HLA) region in 13,770 Parkinson’s disease (PD) patients, 20,214 proxy-cases, and 490,861 controls of European origin. Four HLA types were associated with PD after correction for multiple comparisons, HLA-DQA1*03:01, HLA-DQB1*03:02, HLA-DRB1*04:01, and HLA-DRB1*04:04. Haplotype analyses followed by amino acid analysis and conditional analyses suggested that the association is protective and primarily driven by three specific amino acid polymorphisms present in most HLA-DRB1*04 subtypes—11V, 13H, and 33H (OR = 0.87, 95% CI: 0.83–0.90, p < 8.23 × 10⁻⁹ for all three variants). No other effects were present after adjustment for these amino acids. Our results suggest that specific HLA-DRB1 variants are associated with reduced risk of PD, providing additional evidence for the role of the immune system in PD. Although effect size is small and has no diagnostic significance, understanding the mechanism underlying this association may lead to the identification of new targets for therapeutics development.

LncRNA HOXA-AS2 regulates microglial polarization via recruitment of PRC2 and epigenetic modification of PGC-1α expression

Background

Microglia-mediated neuroinflammation plays an important role in Parkinson’s disease (PD), and it exerts proinflammatory or anti-inflammatory effects depending on the M1/M2 polarization phenotype. Hence, promoting microglia toward the anti-inflammatory M2 phenotype is a potential therapeutic approach for PD. Long noncoding RNAs (lncRNAs) are crucial in the progression of neurodegenerative diseases, but little is known about their role in microglial polarization in PD.

Methods

In our study, we profiled the expression of lncRNAs in the peripheral blood mononuclear cells (PBMCs) of PD patients using a microarray. RT-qPCR was used to evaluate the lncRNA levels and mRNA levels of cytokines and microglial cell markers both in vitro and in vivo. RIP and ChIP assays were analyzed for the underlying mechanism of lncRNA regulating microglial polarization.

Results

We found that HOXA-AS2 was upregulated in the PBMCs of PD patients and negatively associated with peroxisome proliferator-activated receptor gamma coactivator-1a (PGC-1α) expression. Moreover, HOXA-AS2 knockdown significantly repressed microglial M1 polarization and promoted M2 polarization by regulating PGC-1α expression. Mechanistic investigations demonstrated that HOXA-AS2 could directly interact with polycomb repressive complex 2 (PRC2) and modulate the histone methylation of the promoter of PGC-1α.

Conclusions

Our findings identify the upregulated lncRNA HOXA-AS2 promotes neuroinflammation by regulating microglial polarization through interacts with the PRC2 complex and epigenetically silencing PGC-1α. HOXA-AS2 may be a potential therapeutic target for microglia-mediated neuroinflammation in patients with PD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02267-z.

Alpha-Synuclein as a Prominent Actor in the Inflammatory Synaptopathy of Parkinson's Disease

Parkinson’s disease (PD) is considered the most common disorder of synucleinopathy, which is characterised by intracellular inclusions of aggregated and misfolded α-synuclein (α-syn) protein in various brain regions, and the loss of dopaminergic neurons. During the early prodromal phase of PD, synaptic alterations happen before cell death, which is linked to the synaptic accumulation of toxic α-syn specifically in the presynaptic terminals, affecting neurotransmitter release. The oligomers and protofibrils of α-syn are the most toxic species, and their overexpression impairs the distribution and activation of synaptic proteins, such as the SNARE complex, preventing neurotransmitter exocytosis and neuronal synaptic communication. In the last few years, the role of the immune system in PD has been increasingly considered. Microglial and astrocyte activation, the gene expression of proinflammatory factors, and the infiltration of immune cells from the periphery to the central nervous system (CNS) represent the main features of the inflammatory response. One of the actors of these processes is α-syn accumulation. In light of this, here, we provide a systematic review of PD-related α-syn and inflammation inter-players.

NPT520-34 improves neuropathology and motor deficits in a transgenic mouse model of Parkinson's disease

NPT520-34 is a clinical-stage, small molecule being developed for the treatment of Parkinson's disease and other neurodegenerative disorders. The therapeutic potential of NPT520-34 was first suggested by findings from cell-based assays of alpha-synuclein (ASYN) clearance. As reported here, NPT520-34 was subsequently evaluated for therapeutically relevant actions in a transgenic animal model of Parkinson's disease that overexpresses human ASYN and in an acute lipopolysaccharide (LPS)-challenge model using wild-type mice. Daily administration of NPT520-34 to mThy1-ASYN (Line 61) transgenic mice for one or three months resulted in reduced ASYN pathology, reduced expression of markers of neuroinflammation, and improvements in multiple indices of motor function. In an LPS-challenge model using wild-type mice, a single-dose of NPT520-34 reduced LPS-evoked increases in the expression of several pro-inflammatory cytokines in plasma. These findings demonstrate the beneficial effects of NPT520-34 on both inflammation and protein-pathology endpoints, with consequent improvements in motor function in an animal model of Parkinson's disease. These findings further suggest that NPT520-34 may have two complementary actions: (1) to increase the clearance of neurotoxic protein aggregates and (2) to directly attenuate inflammation. NPT520-34 treatment may thereby address two of the predominate underlying pathophysiological aspects of neurodegenerative disorders such as Parkinson's disease.

Implications of VIP and PACAP in Parkinson's Disease: What do we Know So Far?

BACKGROUND

Parkinson's disease is one of the most common neurodegenerative disorders and although its aetiology is not yet fully understood, neuroinflammation has been identified as a key factor in the progression of the disease. Vasoactive intestinal peptide and pituitary adenylate-cyclase activating polypeptide are two neuropeptides that exhibit anti-inflammatory and neuroprotective properties, modulating the production of cytokines and chemokines and the behaviour of immune cells. However, the role of chemokines and cytokines modulated by the endogenous receptors of the peptides varies according to the stage of the disease.

METHODS

We present an overview of the relationship between some cytokines and chemokines with vasoactive intestinal peptide, pituitary adenylate cyclase activating polypeptide and their endogenous receptors in the context of Parkinson's disease neuroinflammation and oxidative stress, as well as the modulation of microglial cells by the peptides in this context.

RESULTS

The two peptides exhibit neuroprotective and anti-inflammatory properties in models of Parkinson's disease, as they ameliorate cognitive functions, decrease the level of neuroinflammation and promote dopaminergic neuronal survival. The peptides have been tested in a variety of in vivo and in vitro models of Parkinson's disease, demonstrating the potential for therapeutic application.

CONCLUSION

More studies are needed to establish the clinical use of vasoactive intestinal peptide and pituitary adenylate cyclase activating polypeptide as safe candidates for treating Parkinson's disease, as the use of the peptides in different stages of the disease could produce different results concerning effectiveness.

Evidence for Peripheral Immune Activation in Parkinson's Disease

BACKGROUND

Accumulating evidence has revealed that peripheral immunity is involved in Parkinson's disease (PD). However, the results regarding the percentage of T-cell subsets are inconsistent, and the changes of immunoglobins levels have been seldom studied in PD patients.

METHODS

Serum levels of the percentage of T-cell subsets and immunoglobulins were measured in 761 PD patients and 761 age- and gender-matched healthy controls. The correlations between the variables of peripheral immune activation (PIA) and the clinical characteristics of PD were analyzed using correlation analysis.

RESULTS

The pooled results showed that PD patients had higher proportional levels of CD3+ T and CD4+ T lymphocytes than healthy controls. CD8+ T cell percentages were similar in PD patients and controls, and the CD4/CD8 ratio was significantly higher in the PD population. No significant differences in IgG, IgA, or IgM levels between these two groups were found. CD4+ T cell percentage was inversely correlated with the H&Y stage, and IgG level was positively correlated with disease duration and UPDRS part III. Subgroup analyses showed that these associations existed in female patients, but not in male patients.

CONCLUSION

The enhanced immune activation in the peripheral system is indicated in PD, and dynamic alterations in CD4+ T cell percentage and IgG level suggest an active role for peripheral immunity in the disease progression, especially in female PD patients.

Neuroprotective effects of pomegranate (Punica granatum L.) juice and seed extract in paraquat-induced mouse model of Parkinson's disease

BACKGROUND

Paraquat, (PQ), an herbicide that can induce Parkinsonian-like symptoms in rodents and humans. The consumption of phytochemical-rich plants can reduce the risk of chronic illnesses such as inflammation and neurodegenerative diseases. The present study aimed to investigate the protective effects of pomegranate seed extract (PSE) and juice (PJ) against PQ-induced neurotoxicity in mice.

METHODS

Mice were assigned into 4 groups; three groups received PQ (10 mg/kg, i.p.) twice a week for 3 weeks. Two of the PQ-induced groups pretreated with either PSE or PJ. Detection of phytochemicals, total phenolics, and total flavonoids in PSE and PJ was performed. Tyrosine hydroxylase (TH) level was measured in the substantia nigra (SN) by Western blotting technique. Striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were detected using high-performance liquid chromatography (HPLC). The levels of adenosine triphosphate (ATP), malondialdehyde (MDA), and the activity of the antioxidant enzymes were estimated in the striatum by colorimetric analysis. Striatal pro-inflammatory and anti-inflammatory markers using enzyme-linked immunosorbent assay (ELISA) as well as DNA fragmentation degree by qualitative DNA fragmentation assay, were evaluated. Real-time polymerase chain reaction (qPCR) assay was performed for the detection of nuclear factor kappa B (NF-кB) gene expression. Moreover, Western blotting analysis was used for the estimation of the cluster of differentiation 11b (CD11b), transforming growth factor β (TGF-β), and glial cell-derived neurotrophic factor (GDNF) levels in the striatum.

RESULTS

Pretreatment with PSE or PJ increased the levels of TH in the SN as well as DA and its metabolite in the striatum that were reduced by PQ injection. PSE and PJ preadministration improved the PQ-induced oxidative stress via a significant reduction of the MDA level and the augmentation of antioxidant enzyme activities. PSE and PJ also significantly downregulated the striatal NF-кB gene expression, reduced the PQ-enhanced apoptosis, decreased the levels of; pro-inflammatory cytokines, CD11b, and TGF-β coupled with a significant increase of; interleukin-10 (IL-10), GDNF, and ATP levels as compared with PQ-treated mice.

CONCLUSIONS

The current study indicated that PSE and PJ consumption may exhibit protective effects against PQ-induced neurotoxicity in mice.

Periphery and brain, innate and adaptive immunity in Parkinson's disease

Parkinson’s disease (PD) is a neurodegenerative disorder where alpha-synuclein plays a central role in the death and dysfunction of neurons, both, in central, as well as in the peripheral nervous system. Besides the neuronal events observed in patients, PD also includes a significant immune component. It is suggested that the PD-associated immune response will have consequences on neuronal health, thus opening immunomodulation as a potential therapeutic strategy in PD. The immune changes during the disease occur in the brain, involving microglia, but also in the periphery with changes in cells of the innate immune system, particularly monocytes, as well as those of adaptive immunity, such as T-cells. This realization arises from multiple patient studies, but also from data in animal models of the disease, providing strong evidence for innate and adaptive immune system crosstalk in the central nervous system and periphery in PD. Here we review the data showing that alpha-synuclein plays a crucial role in the activation of the innate and adaptive immune system. We will also describe the studies suggesting that inflammation in PD includes early changes in innate and adaptive immune cells that develop dynamically through time during disease, contributing to neuronal degeneration and symptomatology in patients. This novel finding has contributed to the definition of PD as a multisystem disease that should be approached in a more integratory manner rather than a brain-focused classical approach.

Modification of Glial Cell Activation through Dendritic Cell Vaccination: Promises for Treatment of Neurodegenerative Diseases

Accumulation of misfolded tau, amyloid β (Aβ), and alpha-synuclein (α-syn) proteins is the fundamental contributor to many neurodegenerative diseases, namely Parkinson's (PD) and AD. Such protein aggregations trigger activation of immune mechanisms in neuronal and glial, mainly M1-type microglia cells, leading to release of pro-inflammatory mediators, and subsequent neuronal dysfunction and apoptosis. Despite the described neurotoxic features for glial cells, recruitment of peripheral leukocytes to the brain and their conversion to neuroprotective M2-type microglia can mitigate neurodegeneration by clearing extracellular protein accumulations or residues. Based on these observations, it was speculated that Dendritic cell (DC)-based vaccination, by making use of DCs as natural adjuvants, could be used for treatment of neurodegenerative disorders. DCs potentiated by disease-specific antigens can also enhance T helper 2 (Th2)-specific immune response and by production of specific antibodies contribute to clearance of intracellular aggregations, as well as enhancing regulatory T cell response. Thus, enhancement of immune response by DC vaccine therapy can potentially augment glial polarization into the neuroprotective phenotype, enhance antibody production, and at the same time balance neuronal cells' repair, renewal, and protection. The characteristic feature of this method of treatment is to maintain the equilibrium in the immune response rather than targeting a single mediator in the disease and their application in other neurodegenerative diseases should be addressed. However, the safety of these methods should be investigated by clinical trials.

Inflammatory Mechanisms in Parkinson's Disease: From Pathogenesis to Targeted Therapies

Inflammation is a critical factor contributing to the progressive neurodegenerative process observed in Parkinson's disease (PD). Microglia, the immune cells of the central nervous system, are activated early in PD pathogenesis and can both trigger and propagate early disease processes via innate and adaptive immune mechanisms such as upregulated immune cells and antibody-mediated inflammation. Downstream cytokines and gene regulators such as microRNA (miRNA) coordinate later disease course and mediate disease progression. Biomarkers signifying the inflammatory and neurodegenerative processes at play within the central nervous system are of increasing interest to clinical teams. To be effective, such biomarkers must achieve the highest sensitivity and specificity for predicting PD risk, confirming diagnosis, or monitoring disease severity. The aim of this review was to summarize the current preclinical and clinical evidence that suggests that inflammatory processes contribute to the initiation and progression of neurodegenerative processes in PD. In this article, we further summarize the data about main inflammatory biomarkers described in PD to date and their potential for regulation as a novel target for disease-modifying pharmacological strategies.

Pathomechanism Characterization and Potential Therapeutics Identification for Parkinson's Disease Targeting Neuroinflammation

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the loss of dopaminergic (DAergic) neurons and the presence of α-synuclein-containing Lewy bodies. The unstructured α-synuclein forms insoluble fibrils and aggregates that result in increased reactive oxygen species (ROS) and cellular toxicity in PD. Neuroinflammation engaged by microglia actively contributes to the pathogenesis of PD. In this study, we showed that VB-037 (a quinoline compound), glycyrrhetic acid (a pentacyclic triterpenoid), Glycyrrhiza inflata (G. inflata, a Chinese herbal medicine), and Shaoyao Gancao Tang (SG-Tang, a formulated Chinese medicine) suppressed the nitric oxide (NO) production and interleukin (IL)-1β maturation in α-synuclein-stimulated BV-2 cells. Mouse inflammation antibody array further revealed increased IL-1α, IL-1β, tumor necrosis factor (TNF)-α, interferon (IFN)-γ, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) expression in α-synuclein-inflamed BV-2 cells and compound pretreatment effectively reduced the expression and release of these pro-inflammatory mediators. The test compounds and herbal medicines further reduced α-synuclein aggregation and associated oxidative stress, and protected cells against α-synuclein-induced neurotoxicity by downregulating NLR family pyrin domain containing 1 (NLRP1) and 3 (NLRP3), caspase 1, IL-1β, IL-6, and associated nuclear factor (NF)-κB inhibitor alpha (IκBα)/NF-κB P65 subunit (P65), c-Jun N-terminal kinase (JNK)/proto-oncogene c-Jun (JUN), mitogen-activated protein kinase 14 (P38)/signal transducer and activator of transcription 1 (STAT1) and Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) pathways in dopaminergic neurons derived from α-synuclein-expressing SH-SY5Y cells. Our findings indicate the potential of VB-037, glycyrrhetic acid, G. inflata, and SG-Tang through mitigating α-synuclein-stimulated neuroinflammation in PD, as new drug candidates for PD treatment.

Microglia in neurodegenerative diseases

A major feature of neurodegeneration is disruption of central nervous system homeostasis, during which microglia play diverse roles. In the central nervous system, microglia serve as the first line of immune defense and function in synapse pruning, injury repair, homeostasis maintenance, and regulation of brain development through scavenging and phagocytosis. Under pathological conditions or various stimulations, microglia proliferate, aggregate, and undergo a variety of changes in cell morphology, immunophenotype, and function. This review presents the features of microglia, especially their diversity and ability to change dynamically, and reinterprets their role as sensors for multiple stimulations and as effectors for brain aging and neurodegeneration. This review also summarizes some therapeutic approaches for neurodegenerative diseases that target microglia.

Iron Dysregulation and Inflammagens Related to Oral and Gut Health Are Central to the Development of Parkinson's Disease

Neuronal lesions in Parkinson's disease (PD) are commonly associated with α-synuclein (α-Syn)-induced cell damage that are present both in the central and peripheral nervous systems of patients, with the enteric nervous system also being especially vulnerable. Here, we bring together evidence that the development and presence of PD depends on specific sets of interlinking factors that include neuroinflammation, systemic inflammation, α-Syn-induced cell damage, vascular dysfunction, iron dysregulation, and gut and periodontal dysbiosis. We argue that there is significant evidence that bacterial inflammagens fuel this systemic inflammation, and might be central to the development of PD. We also discuss the processes whereby bacterial inflammagens may be involved in causing nucleation of proteins, including of α-Syn. Lastly, we review evidence that iron chelation, pre-and probiotics, as well as antibiotics and faecal transplant treatment might be valuable treatments in PD. A most important consideration, however, is that these therapeutic options need to be validated and tested in randomized controlled clinical trials. However, targeting underlying mechanisms of PD, including gut dysbiosis and iron toxicity, have potentially opened up possibilities of a wide variety of novel treatments, which may relieve the characteristic motor and nonmotor deficits of PD, and may even slow the progression and/or accompanying gut-related conditions of the disease.

Regulatory Roles of Bone in Neurodegenerative Diseases

Osteoporosis and neurodegenerative diseases are two kinds of common disorders of the elderly, which often co-occur. Previous studies have shown the skeletal and central nervous systems are closely related to pathophysiology. As the main structural scaffold of the body, the bone is also a reservoir for stem cells, a primary lymphoid organ, and an important endocrine organ. It can interact with the brain through various bone-derived cells, mostly the mesenchymal and hematopoietic stem cells (HSCs). The bone marrow is also a place for generating immune cells, which could greatly influence brain functions. Finally, the proteins secreted by bones (osteokines) also play important roles in the growth and function of the brain. This article reviews the latest research studying the impact of bone-derived cells, bone-controlled immune system, and bone-secreted proteins on the brain, and evaluates how these factors are implicated in the progress of neurodegenerative diseases and their potential use in the diagnosis and treatment of these diseases.

Immune-associated biomarkers for early diagnosis of Parkinson's disease based on hematological lncRNA-mRNA co-expression

Early stage diagnosis of Parkinson's disease (PD) is challenging without significant motor symptoms. The identification of effective molecular biomarkers as a hematological indication of PD may help improve the diagnostic timeliness and accuracy. In this paper, we analyzed and compared the blood samples of PD and control (CTR) patients to identify the disease-related changes and determine the putative biomarkers for PD diagnosis. Based on the RNA sequencing analysis, differentially expressed genes (DEGs) were identified, and the co-expression network of DEGs was constructed using the weighted correlation network analysis (WGCNA). The analysis leads to the identification of 87 genes that were exclusively regulated in the PD group, whereas 66 genes were significantly increased and 21 genes were significantly decreased in contrast to the control group. The results indicate that the core lncRNA-mRNA co-expression network greatly changes the immune response in PD patients. Specifically, the results showed that PWAR6, LINC00861, AC83843.1, IRF family, IFIT family and CaMK4 may play important roles in the immune system of PD. Based on the findings from this the present study, future research aims at identify novel therapeutic strategies for PD.

Inflammation in Experimental Models of α-Synucleinopathies

Neuroinflammation has long been associated with central nervous system pathology in α-synucleinopathy disorders including Parkinson's disease and multiple system atrophy. In the past decade, research-focused efforts in preclinical and experimental models have rallied around this idea, and considerable effort has been made to delineate critical neuroinflammatory processes. In this article, we discuss challenges in preclinical research, notably the use of animal models to recapitulate and dissect disease phenotypes as well as the need for more sensitive, reliable radiotracers to detect on-target efficacy of immunomodulatory treatments in both human Parkinson's disease as well as preclinical models. © 2020 International Parkinson and Movement Disorder Society.