Interleukin (IL)-1 beta, IL-2, IL-4, IL-6 and transforming growth factor-alpha levels are elevated in ventricular cerebrospinal fluid in juvenile parkinsonism and Parkinson's disease

The role of Toll-like receptors and neuroinflammation in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder, characterized by motor and non-motor symptoms, significantly affecting patients' life. Pathologically, PD is associated with the extensive degeneration of dopaminergic neurons in various regions of the central nervous system (CNS), specifically the substantia nigra. This neuronal loss is accompanied by the aggregation of misfolded protein, named α-synuclein.

MAIN TEXT

Recent studies detected several clues of neuroinflammation in PD samples using postmortem human PD brains and various PD animal models. Some evidence of neuroinflammation in PD patients included higher levels of proinflammatory cytokines in serum and cerebrospinal fluid (CSF), presence of activated microglia in various brain regions such as substantia nigra, infiltration of peripheral inflammatory cells in affected brain regions, and altered function of cellular immunity like monocytes phagocytosis defects. On the other side, Toll-like receptors (TLRs) are innate immune receptors primarily located on microglia, as well as other immune and non-immune cells, expressing pivotal roles in recognizing exogenous and endogenous stimuli and triggering inflammatory responses. Most studies indicated an increased expression of TLRs in the brain and peripheral blood cells of PD samples. Besides, this upregulation was associated with excessive neuroinflammation followed by neurodegeneration in affected regions. Therefore, evidence proposed that TLR-mediated neuroinflammation might lead to a dopaminergic neural loss in PD patients. In this regard, TLR2, TLR4, and TLR9 have the most prominent roles.

CONCLUSION

Although the presence of inflammation in acute phases of PD might have protective effects concerning the clearance of α-synuclein and delaying the disease advancement, the chronic activation of TLRs and neuroinflammation might lead to neurodegeneration, resulting in the disease progression. Therefore, this study aimed to review additional evidence of the contribution of TLRs and neuroinflammation to PD pathogenesis, with the hope that TLRs could serve as novel disease-modifying therapeutic targets in PD patients in the future.

Dysregulated Gene Expression in Lymphoblasts from Parkinson’s Disease

Parkinson’s disease is the second largest neurodegenerative disease worldwide and is caused by a combination of genetics and environment. It is characterized by the death of neurons in the substantia nigra of the brain but is not solely a disease of the brain, as it affects multiple tissues and organs. Studying Parkinson’s disease in accessible tissues such as skin and blood has increased our understanding of the disease’s pathogenesis. Here, we used lymphoblast cell lines generated from Parkinson’s disease patient and healthy age- and sex-matched control groups and obtained their whole-cell transcriptomes and proteomes. Our analysis revealed, in both the transcriptomes and the proteomes of PD cells, a global downregulation of genes involved in protein synthesis, as well as the upregulation of immune processes and sphingolipid metabolism. In contrast, we discovered an uncoupling of mRNA and protein expression in processes associated with mitochondrial respiration in the form of a general downregulation in associated transcripts and an upregulation in proteins. Complex V was different to the other oxidative phosphorylation complexes in that the levels of its associated transcripts were also lower, but the levels of their encoded polypeptides were not elevated. This may suggest that further layers of regulation specific to Complex V are in play.

Peripheral inflammatory cytokines and motor symptoms in persons with Parkinson's disease

Background

Many of the motor symptoms of Parkinson's disease (PD) impact quality of life and are not fully ameliorated by current pharmacological and surgical treatments. A better understanding of the pathophysiology underlying these symptoms is needed. Previous research has suggested that inflammation may play a significant role in PD pathophysiology and progression, but there is limited research exploring how inflammation directly relates to motor symptoms in PD. Thus, the purpose of this study was to evaluate associations between peripheral immune inflammatory markers and motor symptoms of PD, specifically, tremor, bradykinesia, and postural and gait instability. We hypothesized that peripheral inflammatory cytokines would predict the severity of motor symptoms in persons with PD, and that there will be higher levels of peripheral inflammatory cytokine markers in persons with PD when compared to age-matched healthy older adults.

Methods

Twenty-six participants with PD and fourteen healthy older adults completed the study. For participants with PD, the motor section of the Unified Parkinson's Disease Rating Scale (UPDRS) was recorded and scored by two Movement Disorders Neurologists masked to the study. A blood sample was collected from both participants with PD and the healthy older adults. Through the MILLIPLEX® map High Sensitivity Human Cytokine Kit, key inflammation-related markers were analyzed (TNF-α, IFN-γ, IL-1β, IL-8, IL-2, IL-7, IL-5, IL-13, IL, 4, IL-10 IL-12p70, GM-CSF, and IL-6).

Results

Results revealed significantly higher levels of IL-6 in persons with PD when compared to healthy older adults (p ​= ​0.005). Moreover, results revealed that higher levels of IL-4 (p ​= ​0.011) and lower levels of IFNγ (p ​= ​0.003) significantly predicted more severe tremor in persons with PD. No other associations between the peripheral inflammation markers and other motor symptoms were observed.

Conclusions

Overall, these results are consistent with a growing body of literature that implicates inflammatory cytokines in the PD, and further suggests that inflammatory cytokines, or lack thereof, may be associated with tremor in persons with PD.

Biomarker of Neuroinflammation in Parkinson's Disease

Parkinson's disease (PD) is caused by abnormal accumulation of α-synuclein in dopaminergic neurons of the substantia nigra, which subsequently causes motor symptoms. Neuroinflammation plays a vital role in the pathogenesis of neurodegeneration in PD. This neuroinflammatory neurodegeneration involves the activation of microglia, upregulation of proinflammatory factors, and gut microbiota. In this review, we summarized the recent findings on detection of PD by using inflammatory biomarkers, such as interleukin (IL)-1β, IL-2, IL-6, IL-10, tumor necrosis factor (TNF)-α; regulated upon activation, normal T cell expressed and presumably secreted (RANTES) and high-sensitivity c-reactive protein (hsCRP); and radiotracers such as [11C]PK11195 and [18F]-FEPPA, as well as by monitoring disease progression and the treatment response. Many PD-causing mutations in SNCA, LRRK2, PRKN, PINK1, and DJ-1 are also associated with neuroinflammation. Several anti-inflammatory medications, including nonsteroidal anti-inflammatory drugs (NSAID), inhibitors of TNF-α and NLR family pyrin domain containing 3 (NLRP3), agonists of nuclear factor erythroid 2-related factor 2 (NRF2), peroxisome proliferator-activated receptor gamma (PPAR-γ), and steroids, have demonstrated neuroprotective effects in in vivo or in vitro PD models. Clinical trials applying objective biomarkers are required to investigate the therapeutic potential of anti-inflammatory medications for PD.

Induction of Heme Oxygenase-1 by 15d-Prostaglandin J2 Mediated via a ROS-Dependent Sp1 and AP-1 Cascade Suppresses Lipopolysaccharide-Triggered Interleukin-6 Expression in Mouse Brain Microvascular Endothelial Cells

Heme oxygenase-1 (HO-1) has been shown to exert antioxidant, anti-inflammatory, and anti-apoptotic effects in various types of cells. Therefore, the induction of HO-1 is an excellent rationale for the development of protective drugs. 15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) can modulate the expression of antioxidant defense proteins and be beneficial for neuroinflammation. Brain endothelial cells play an important role in the pathophysiology of brain disorders. Whether 15d-PGJ₂ can induce HO-1 expression and protect against the inflammatory responses in mouse brain microvascular endothelial (bEnd.3) cells remains unclear. Here, we reveal that 15d-PGJ₂ stimulated HO-1 protein and mRNA expression in a time- and concentration-dependent manner in bEnd.3 cells, which was attenuated by diphenyleneiodonium chloride (DPI) and MitoTempo. Thus, activation of NADPH oxidase (NOX)- and mitochondria-derived reactive oxygen species (ROS) mediated 15d-PGJ₂-induced HO-1 expression. ROS generation could cause phosphorylation of protein kinase C (PKC)δ, leading to HO-1 expression, which was suppressed by Rottlerin (selective inhibitor PKCδ), DPI, and MitoTempo. We further demonstrated that phosphorylation of c-Jun N-terminal kinase (JNK)1/2 participated in 15d-PGJ₂-upregulated HO-1 expression, which was blocked by SP600125 or Rottlerin. Moreover, 15d-PGJ₂-induced HO-1 expression was mediated through the activation of c-Jun (a subunit of activator protein 1 (AP-1)) and specificity protein 1 (Sp1), leading to their interaction with the HO-1 promoter, revealed by chromatin immunoprecipitation assay, which was attenuated by SP600125, Mithramycin A, or Tanshinone II A. We further verified the anti-inflammatory effect of HO-1 expression. Our results showed that 15d-PGJ₂-induced HO-1 could mitigate the lipopolysaccharide-triggered interleukin-6 expression and secretion, as measured by an ELISA assay kit. These results suggest that 15d-PGJ₂-induced HO-1 expression is mediated through the activation of NOX- and mitochondria-derived ROS-dependent PKCδ/JNK1/2/Sp1 and the AP-1 signaling pathway and protects against inflammatory responses in bEnd.3 cells.

Deciphering the contributions of neuroinflammation to neurodegeneration: lessons from antibody-mediated encephalitis and coronavirus disease 2019

PURPOSE OF REVIEW

Does neuroinflammation promote neurodegeneration? Does neurodegeneration promote neuroinflammation? Or, is the answer to both questions, yes? These questions have proven challenging to answer in patients with typical age-related neurodegenerative diseases in whom the onset of neuroinflammation and neurodegeneration are largely unknown. Patients recovering from diseases associated with abrupt-onset neuroinflammation, including rare forms of antibody-mediated encephalitis (AME) and common complications of novel coronavirus disease 2019 (COVID-19), provide a unique opportunity to untangle the relationship between neuroinflammation and neurodegeneration. This review explores the lessons learned from patients with AME and COVID-19.

RECENT FINDINGS

Persistent cognitive impairment is increasingly recognized in patients recovering from AME or COVID-19, yet the drivers of impairment remain largely unknown. Clinical observations, neuroimaging and biofluid biomarkers, and pathological studies imply a link between the severity of acute neuroinflammation, subsequent neurodegeneration, and disease-associated morbidity.

SUMMARY

Data from patients with AME and COVID-19 inform key hypotheses that may be evaluated through future studies incorporating longitudinal biomarkers of neuroinflammation and neurodegeneration in larger numbers of recovering patients. The results of these studies may inform the contributors to cognitive impairment in patients with AME and COVID-19, with potential diagnostic and therapeutic applications in patients with age-related neurodegenerative diseases.

Better Outcomes with Intranigral versus Intrastriatal Cell Transplantation: Relevance for Parkinson’s Disease

Intrastriatal embryonic ventral mesencephalon grafts have been shown to integrate, survive, and reinnervate the host striatum in clinical settings and in animal models of Parkinson’s disease. However, this ectopic location does not restore the physiological loops of the nigrostriatal pathway and promotes only moderate behavioral benefits. Here, we performed a direct comparison of the potential benefits of intranigral versus intrastriatal grafts in animal models of Parkinson’s disease. We report that intranigral grafts promoted better survival of dopaminergic neurons and that only intranigral grafts induced recovery of fine motor skills and normalized cortico-striatal responses. The increase in the number of toxic activated glial cells in host tissue surrounding the intrastriatal graft, as well as within the graft, may be one of the causes of the increased cell death observed in the intrastriatal graft. Homotopic localization of the graft and the subsequent physiological cell rewiring of the basal ganglia may be a key factor in successful and beneficial cell transplantation procedures.

The potential convergence of NLRP3 inflammasome, potassium, and dopamine mechanisms in Parkinson's disease

The pathology of Parkinson's disease (PD) is characterized by α-synuclein aggregation, microglia-mediated neuroinflammation, and dopaminergic neurodegeneration in the substantia nigra with collateral striatal dopamine signaling deficiency. Microglial NLRP3 inflammasome activation has been linked independently to each of these facets of PD pathology. The voltage-gated potassium channel Kv1.3, upregulated in microglia by α-synuclein and facilitating potassium efflux, has also been identified as a modulator of neuroinflammation and neurodegeneration in models of PD. Evidence increasingly suggests that microglial Kv1.3 is mechanistically coupled with NLRP3 inflammasome activation, which is contingent on potassium efflux. Potassium conductance also influences dopamine release from midbrain dopaminergic neurons. Dopamine, in turn, has been shown to inhibit NLRP3 inflammasome activation in microglia. In this review, we provide a literature framework for a hypothesis in which Kv1.3 activity-induced NLRP3 inflammasome activation, evoked by stimuli such as α-synuclein, could lead to microglia utilizing dopamine from adjacent dopaminergic neurons to counteract this process and fend off an activated state. If this is the case, a sufficient dopamine supply would ensure that microglia remain under control, but as dopamine is gradually siphoned from the neurons by microglial demand, NLRP3 inflammasome activation and Kv1.3 activity would progressively intensify to promote each of the three major facets of PD pathology: α-synuclein aggregation, microglia-mediated neuroinflammation, and dopaminergic neurodegeneration. Risk factors overlapping to varying degrees to render brain regions susceptible to such a mechanism would include a high density of microglia, an initially sufficient supply of dopamine, and poor insulation of the dopaminergic neurons by myelin.

Immune Dysregulation in Autism Spectrum Disorder: What Do We Know about It?

Autism spectrum disorder (ASD) is a group of complex multifactorial neurodevelopmental disorders characterized by a wide and variable set of neuropsychiatric symptoms, including deficits in social communication, narrow and restricted interests, and repetitive behavior. The immune hypothesis is considered to be a major factor contributing to autism pathogenesis, as well as a way to explain the differences of the clinical phenotypes and comorbidities influencing disease course and severity. Evidence highlights a link between immune dysfunction and behavioral traits in autism from several types of evidence found in both cerebrospinal fluid and peripheral blood and their utility to identify autistic subgroups with specific immunophenotypes; underlying behavioral symptoms are also shown. This review summarizes current insights into immune dysfunction in ASD, with particular reference to the impact of immunological factors related to the maternal influence of autism development; comorbidities influencing autism disease course and severity; and others factors with particular relevance, including obesity. Finally, we described main elements of similarities between immunopathology overlapping neurodevelopmental and neurodegenerative disorders, taking as examples autism and Parkinson Disease, respectively.

Cytokines, miRNAs, and Antioxidants as Combined Non-invasive Biomarkers for Parkinson's Disease

Parkinson's disease (PD) is one of the most common long-term degenerative disorders of the CNS that primarily affects the human locomotor system. Owing to the heterogeneity of PD etiology and the lack of appropriate diagnostic tests, blood-based biomarkers became the most promising method for diagnosing PD. Even though various biomarkers for PD have been found, their specificity and sensitivity are not optimum when used alone. Therefore, the aim of this study was directed to evaluate changes in a group of sensitive blood-based biomarkers in the same PD patients compared to healthy individuals. Serum samples were collected from 20 PD patients and 15 age-matched healthy controls. We analyzed serum levels of cytokines (IL10, IL12, and TNF-α), α-synuclein proteins, miRNAs (miR-214, miR-221, and miR-141), and antioxidants (UA, PON1, ARE). Our results showed an increase in sera levels of cytokines in PD patients as well as a positive correlation among them. Also, we found a significant increase in sera levels of α-synuclein protein associated with a decrease in miR-214 which regulates its gene expression. Lastly, we observed a decrease in sera levels of miR-221, miR-141, UA, PON1, and ARE, which have a prominent role against oxidative stress. Because of the many etiologies of PD, a single measure is unlikely to become a useful biomarker. Therefore, to correctly predict disease state and progression, a mix of noninvasive biomarkers is required. Although considerable work has to be done, this study sheds light on the role of certain biomarkers in the diagnosis of PD.

An Integrative Network Approach to Identify Common Genes for the Therapeutics in Tuberculosis and Its Overlapping Non-Communicable Diseases

Tuberculosis (TB) is the leading cause of death from a single infectious agent. The estimated total global TB deaths in 2019 were 1.4 million. The decline in TB incidence rate is very slow, while the burden of noncommunicable diseases (NCDs) is exponentially increasing in low- and middle-income countries, where the prevention and treatment of TB disease remains a great burden, and there is enough empirical evidence (scientific evidence) to justify a greater research emphasis on the syndemic interaction between TB and NCDs. The current study was proposed to build a disease-gene network based on overlapping TB with NCDs (overlapping means genes involved in TB and other/s NCDs), such as Parkinson’s disease, cardiovascular disease, diabetes mellitus, rheumatoid arthritis, and lung cancer. We compared the TB-associated genes with genes of its overlapping NCDs to determine the gene-disease relationship. Next, we constructed the gene interaction network of disease-genes by integrating curated and experimentally validated interactions in humans and find the 13 highly clustered modules in the network, which contains a total of 86 hub genes that are commonly associated with TB and its overlapping NCDs, which are largely involved in the Inflammatory response, cellular response to cytokine stimulus, response to cytokine, cytokine-mediated signaling pathway, defense response, response to stress and immune system process. Moreover, the identified hub genes and their respective drugs were exploited to build a bipartite network that assists in deciphering the drug-target interaction, highlighting the influential roles of these drugs on apparently unrelated targets and pathways. Targeting these hub proteins by using drugs combination or drug repurposing approaches will improve the clinical conditions in comorbidity, enhance the potency of a few drugs, and give a synergistic effect with better outcomes. Thus, understanding the Mycobacterium tuberculosis (Mtb) infection and associated NCDs is a high priority to contain its short and long-term effects on human health. Our network-based analysis opens a new horizon for more personalized treatment, drug-repurposing opportunities, investigates new targets, multidrug treatment, and can uncover several side effects of unrelated drugs for TB and its overlapping NCDs.

Role of exosomes in the pathogenesis of inflammation in Parkinson's disease

Inflammatory responses, including glial cell activation and peripheral immune cell infiltration, are involved in the pathogenesis of Parkinson’s disease (PD). These inflammatory responses appear to be closely related to the release of extracellular vesicles, such as exosomes. However, the relationships among different forms of glial cell activation, synuclein dysregulation, mitochondrial dysfunction, and exosomes are complicated. This review discusses the multiple roles played by exosomes in PD-associated inflammation and concludes that exosomes can transport toxic α-synuclein oligomers to immature neurons and into the extracellular environment, inducing the oligomerization of α-synuclein in normal neurons. Misfolded α-synuclein causes microglia and astrocytes to activate and secrete exosomes. Glial cell-derived exosomes participate in communications between glial cells and neurons, triggering anti-stress and anti-inflammatory responses, in addition to axon growth. The production and release of mitochondrial vesicles and exosomes establish a new mechanism for linking mitochondrial dysfunction to systemic inflammation associated with PD. Given the relevance of exosomes as mediators of neuron-glia communication in neuroinflammation and neuropathogenesis, new targeted treatment strategies are currently being developed that use these types of extracellular vesicles as drug carriers. Exosome-mediated inflammation may be a promising target for intervention in PD patients.

The Neuroinflammatory Acute Phase Response in Parkinsonian-Related Disorders

BACKGROUND

Neuroinflammation is implicated in the pathophysiology of Parkinson's disease (PD) and related conditions, yet prior clinical biomarker data report mixed findings.

OBJECTIVES

The aim was to measure a panel of neuroinflammatory acute phase response (APR) proteins in the cerebrospinal fluid (CSF) of participants with PD and related disorders.

METHODS

Eleven APR proteins were measured in the CSF of 867 participants from the BioFINDER cohort who were healthy (612) or had a diagnosis of PD (155), multiple system atrophy (MSA) (26), progressive supranuclear palsy (PSP) (22), dementia with Lewy bodies (DLB) (23), or Parkinson's disease with dementia (PDD) (29).

RESULTS

CSF APR proteins were mostly unchanged in PD, with only haptoglobin and α1-antitrypsin significantly elevated compared to controls. These proteins were variably increased in the other disorders. Certain protein components yielded unique signatures according to diagnosis: ferritin and transthyretin were selectively elevated in MSA and discriminated these patients from all others. Haptoglobin was selectively increased in PSP, discriminating this disease from MSA when used in combination with ferritin and transthyretin. This panel of proteins did not correlate well with severity of motor impairment in any disease category, but several (particularly ceruloplasmin and ferritin) were associated with memory performance (Mini-Mental State Examination) in patients with DLB and PDD.

CONCLUSIONS

These findings provide new insights into inflammatory changes in PD and related disorders while also introducing biomarkers of potential clinical diagnostic utility. © 2022 International Parkinson and Movement Disorder Society.

The Therapeutic Prospects of Targeting IL-1R1 for the Modulation of Neuroinflammation in Central Nervous System Disorders

The interleukin-1 receptor type 1 (IL-1R1) holds pivotal roles in the immune system, as it is positioned at the “epicenter” of the inflammatory signaling networks. Increased levels of the cytokine IL-1 are a recognized feature of the immune response in the central nervous system (CNS) during injury and disease, i.e., neuroinflammation. Despite IL-1/IL-1R1 signaling within the CNS having been the subject of several studies, the roles of IL-1R1 in the CNS cellular milieu still cause controversy. Without much doubt, however, the persistent activation of the IL-1/IL-1R1 signaling pathway is intimately linked with the pathogenesis of a plethora of CNS disease states, ranging from Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS), all the way to schizophrenia and prion diseases. Importantly, a growing body of evidence is showing that blocking IL-1R1 signaling via pharmacological or genetic means in different experimental models of said CNS diseases leads to reduced neuroinflammation and delayed disease progression. The aim of this paper is to review the recent progress in the study of the biological roles of IL-1R1, as well as to highlight key aspects that render IL-1R1 a promising target for the development of novel disease-modifying treatments for multiple CNS indications.

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.

Neurodegenerative Disorders and the Current State, Pathophysiology, and Management of Parkinson's Disease

In the last few decades, major knowledge has been gained about pathophysiological aspects and molecular pathways behind Parkinson's Disease (PD). Based on neurotoxicological studies and postmortem investigations, there is a general concept of how environmental toxicants (neurotoxins, pesticides, insecticides) and genetic factors (genetic mutations in PD-associated proteins) cause depletion of dopamine from substantia nigra pars compacta region of the midbrain and modulate cellular processes leading to the pathogenesis of PD. α-Synuclein, a neuronal protein accumulation in oligomeric form, called protofibrils, is associated with cellular dysfunction and neuronal death, thus possibly contributing to PD propagation. With advances made in identifying loci that contribute to PD, molecular pathways involved in disease pathogenesis are now clear, and introducing therapeutic strategy at the right time may delay the progression. Biomarkers for PD have helped monitor PD progression; therefore, personalized therapeutic strategies can be facilitated. In order to further improve PD diagnostic and prognostic accuracy, independent validation of biomarkers is required.

Respiratory disorders of Parkinson's disease

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra, mainly affecting people over 60 yr of age. Patients develop both classic symptoms (tremors, muscle rigidity, bradykinesia, and postural instability) and nonclassical symptoms (orthostatic hypotension, neuropsychiatric deficiency, sleep disturbances, and respiratory disorders). Thus, patients with PD can have a significantly impaired quality of life, especially when they do not have multimodality therapeutic follow-up. The respiratory alterations associated with this syndrome are the main cause of mortality in PD. They can be classified as peripheral when caused by disorders of the upper airways or muscles involved in breathing and as central when triggered by functional deficits of important neurons located in the brainstem involved in respiratory control. Currently, there is little research describing these disorders, and therefore, there is no well-established knowledge about the subject, making the treatment of patients with respiratory symptoms difficult. In this review, the history of the pathology and data about the respiratory changes in PD obtained thus far will be addressed.

Neuro-Immunity and Gut Dysbiosis Drive Parkinson's Disease-Induced Pain

Parkinson's disease (PD) is the second most common neurodegenerative disorder, affecting 1-2% of the population aged 65 and over. Additionally, non-motor symptoms such as pain and gastrointestinal dysregulation are also common in PD. These impairments might stem from a dysregulation within the gut-brain axis that alters immunity and the inflammatory state and subsequently drives neurodegeneration. There is increasing evidence linking gut dysbiosis to the severity of PD's motor symptoms as well as to somatosensory hypersensitivities. Altogether, these interdependent features highlight the urgency of reviewing the links between the onset of PD's non-motor symptoms and gut immunity and whether such interplays drive the progression of PD. This review will shed light on maladaptive neuro-immune crosstalk in the context of gut dysbiosis and will posit that such deleterious interplays lead to PD-induced pain hypersensitivity.

Astrocyte inflammatory signaling mediates α-synuclein aggregation and dopaminergic neuronal loss following viral encephalitis

Viral infection of the central nervous system (CNS) can cause lasting neurological decline in surviving patients and can present with symptoms resembling Parkinson's disease (PD). The mechanisms underlying postencephalitic parkinsonism remain unclear but are thought to involve increased innate inflammatory signaling in glial cells, resulting in persistent neuroinflammation. We therefore studied the role of glial cells in regulating neuropathology in postencephalitic parkinsonism by studying the involvement of astrocytes in loss of dopaminergic neurons and aggregation of α-synuclein protein following infection with western equine encephalitis virus (WEEV). Infections were conducted in both wildtype mice and in transgenic mice lacking NFκB inflammatory signaling in astrocytes. For 2 months following WEEV infection, we analyzed glial activation, neuronal loss and protein aggregation across multiple brain regions, including the substantia nigra pars compacta (SNpc). These data revealed that WEEV induces loss of SNpc dopaminergic neurons, persistent activation of microglia and astrocytes that precipitates widespread aggregation of α-synuclein in the brain of C57BL/6 mice. Microgliosis and macrophage infiltration occurred prior to activation of astrocytes and was followed by opsonization of ⍺-synuclein protein aggregates in the cortex, hippocampus and midbrain by the complement protein, C3. Astrocyte-specific NFκB knockout mice had reduced gliosis, α-synuclein aggregate formation and neuronal loss. These data suggest that astrocytes play a critical role in initiating PD-like pathology following encephalitic infection with WEEV through innate immune inflammatory pathways that damage dopaminergic neurons, possibly by hindering clearance of ⍺-synuclein aggregates. Inhibiting glial inflammatory responses could therefore represent a potential therapy strategy for viral parkinsonism.

Parkinson Disease: Translating Insights from Molecular Mechanisms to Neuroprotection

Parkinson disease (PD) used to be considered a nongenetic condition. However, the identification of several autosomal dominant and recessive mutations linked to monogenic PD has changed this view. Clinically manifest PD is then thought to occur through a complex interplay between genetic mutations, many of which have incomplete penetrance, and environmental factors, both neuroprotective and increasing susceptibility, which variably interact to reach a threshold over which PD becomes clinically manifested. Functional studies of PD gene products have identified many cellular and molecular pathways, providing crucial insights into the nature and causes of PD. PD originates from multiple causes and a range of pathogenic processes at play, ultimately culminating in nigral dopaminergic loss and motor dysfunction. An in-depth understanding of these complex and possibly convergent pathways will pave the way for therapeutic approaches to alleviate the disease symptoms and neuroprotective strategies to prevent disease manifestations. This review is aimed at providing a comprehensive understanding of advances made in PD research based on leveraging genetic insights into the pathogenesis of PD. It further discusses novel perspectives to facilitate identification of critical molecular pathways that are central to neurodegeneration that hold the potential to develop neuroprotective and/or neurorestorative therapeutic strategies for PD. SIGNIFICANCE STATEMENT: A comprehensive review of PD pathophysiology is provided on the complex interplay of genetic and environmental factors and biologic processes that contribute to PD pathogenesis. This knowledge identifies new targets that could be leveraged into disease-modifying therapies to prevent or slow neurodegeneration in PD.

Inhibition of NLRP3 inflammasome by glibenclamide attenuated dopaminergic neurodegeneration and motor deficits in paraquat and maneb-induced mouse Parkinson's disease model

Pesticides exposure can lead to damage of dopaminergic neurons, which are associated with increased risk of Parkinson's disease (PD). However, the etiology of PD remains poorly understood and no therapeutic strategy is available. Previous studies suggested the involvement of NLRP3 inflammasome in the onset of PD. This study was designed to investigate whether glibenclamide, an inhibitor of NLRP3 inflammasome, could offer a reliable protective strategy for PD in a mouse PD model induced by paraquat and maneb. We found that glibenclamide exerted potent neuroprotection against paraquat and maneb-induced upregulation of α-synuclein, dopaminergic neurodegeneration and motor impairment in brain of mice. Mechanistically, glibenclamide treatment blocked NLRP3 inflammasome activation evidenced by reduced expressions of NLRP3, activated caspase-1 and mature interleukin-1β in glibenclamide co-treated mice compared with those in paraquat and maneb group mice. Furthermore, glibenclamide treatment mitigated paraquat and maneb-induced microglial M1 proinflammatory response and nuclear factor-κB activation in mice. Finally, the increased superoxide production, lipid peroxidation, protein levels of NADPH oxidase 2 (NOX2) and inducible nitric oxide synthase (iNOS) induced by paraquat and maneb were all attenuated by glibenclamide. Overall, our findings demonstrated that glibenclamide protected dopaminergic neurons in a mouse PD model induced by combined exposures of paraquat and maneb through suppression of NLRP3 inflammasome activation, microglial M1 polarization and oxidative stress.

The Positive Role and Mechanism of Herbal Medicine in Parkinson's Disease

Parkinson's disease (PD) is a complex neurodegenerative disease, manifested by the progressive functional impairment of the midbrain nigral dopaminergic neurons. Due to the unclear underlying pathogenesis, disease-modifying drugs for PD remain elusive. In Asia, such as in China and India, herbal medicines have been used in the treatment of neurodegenerative disease for thousands of years, which recently attracted considerable attention because of the development of curative drugs for PD. In this review, we first summarized the pathogenic factors of PD including protein aggregation, mitochondrial dysfunction, ion accumulation, neuroinflammation, and oxidative stress, and the related recent advances. Secondly, we summarized 32 Chinese herbal medicines (belonging to 24 genera, such as Acanthopanax, Alpinia, and Astragalus), 22 Chinese traditional herbal formulations, and 3 Indian herbal medicines, of which the ethanol/water extraction or main bioactive compounds have been extensively investigated on PD models both in vitro and in vivo. We elaborately provided pictures of the representative herbs and the structural formula of the bioactive components (such as leutheroside B and astragaloside IV) of the herbal medicines. Also, we specified the potential targets of the bioactive compounds or extractions of herbs in view of the signaling pathways such as PI3K, NF-κB, and AMPK which are implicated in oxidative and inflammatory stress in neurons. We consider that this knowledge of herbal medicines or their bioactive components can be favorable for the development of disease-modifying drugs for PD.

Microglia in Neuroinflammation and Neurodegeneration: From Understanding to Therapy

Microglia are the resident macrophages of the central nervous system (CNS) acting as the first line of defense in the brain by phagocytosing harmful pathogens and cellular debris. Microglia emerge from early erythromyeloid progenitors of the yolk sac and enter the developing brain before the establishment of a fully mature blood-brain barrier. In physiological conditions, during brain development, microglia contribute to CNS homeostasis by supporting cell proliferation of neural precursors. In post-natal life, such cells contribute to preserving the integrity of neuronal circuits by sculpting synapses. After a CNS injury, microglia change their morphology and down-regulate those genes supporting homeostatic functions. However, it is still unclear whether such changes are accompanied by molecular and functional modifications that might contribute to the pathological process. While comprehensive transcriptome analyses at the single-cell level have identified specific gene perturbations occurring in the "pathological" microglia, still the precise protective/detrimental role of microglia in neurological disorders is far from being fully elucidated. In this review, the results so far obtained regarding the role of microglia in neurodegenerative disorders will be discussed. There is solid and sound evidence suggesting that regulating microglia functions during disease pathology might represent a strategy to develop future therapies aimed at counteracting brain degeneration in multiple sclerosis, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis.

Mice Treated Subcutaneously with Mouse LPS-Converted PrPres or LPS Alone Showed Brain Gene Expression Profiles Characteristic of Prion Disease

Previously, we showed that bacterial lipopolysaccharide (LPS) converts mouse PrP^C protein to a beta-rich isoform (moPrP^res) resistant to proteinase K. In this study, we aimed to test if the LPS-converted PrP^res is infectious and alters the expression of genes related to prion pathology in brains of terminally sick mice. Ninety female FVB/N mice at 5 weeks of age were randomly assigned to 6 groups treated subcutaneously (sc) for 6 weeks either with: (1) Saline (CTR); (2) LPS from Escherichia coli 0111:B4 (LPS), (3) one-time sc administration of de novo generated mouse recombinant prion protein (moPrP; 29-232) rich in beta-sheet by incubation with LPS (moPrP^res), (4) LPS plus one-time sc injection of moPrP^res, (5) one-time sc injection of brain homogenate from Rocky Mountain Lab (RLM) scrapie strain, and (6) LPS plus one-time sc injection of RML. Results showed that all treatments altered the expression of various genes related to prion disease and neuroinflammation starting at 11 weeks post-infection and more profoundly at the terminal stage. In conclusion, sc administration of de novo generated moPrPres, LPS, and a combination of moPrP^res with LPS were able to alter the expression of multiple genes typical of prion pathology and inflammation.

Alpha-Synuclein as a Biomarker of Parkinson's Disease: Good, but Not Good Enough

Parkinson's disease (PD) is the second most common neurodegenerative disorder of the elderly, presenting primarily with symptoms of motor impairment. The disease is diagnosed most commonly by clinical examination with a great degree of accuracy in specialized centers. However, in some cases, non-classical presentations occur when it may be difficult to distinguish the disease from other types of degenerative or non-degenerative movement disorders with overlapping symptoms. The diagnostic difficulty may also arise in patients at the early stage of PD. Thus, a biomarker could help clinicians circumvent such problems and help them monitor the improvement in disease pathology during anti-parkinsonian drug trials. This review first provides a brief overview of PD, emphasizing, in the process, the important role of α-synuclein in the pathogenesis of the disease. Various attempts made by the researchers to develop imaging, genetic, and various biochemical biomarkers for PD are then briefly reviewed to point out the absence of a definitive biomarker for this disorder. In view of the overwhelming importance of α-synuclein in the pathogenesis, a detailed analysis is then made of various studies to establish the biomarker potential of this protein in PD; these studies measured total α-synuclein, oligomeric, and post-translationally modified forms of α-synuclein in cerebrospinal fluid, blood (plasma, serum, erythrocytes, and circulating neuron-specific extracellular vesicles) and saliva in combination with certain other proteins. Multiple studies also examined the accumulation of α-synuclein in various forms in PD in the neural elements in the gut, submandibular glands, skin, and the retina. The measurements of the levels of certain forms of α-synuclein in some of these body fluids or their components or peripheral tissues hold a significant promise in establishing α-synuclein as a definitive biomarker for PD. However, many methodological issues related to detection and quantification of α-synuclein have to be resolved, and larger cross-sectional and follow-up studies with controls and patients of PD, parkinsonian disorders, and non-parkinsonian movement disorders are to be undertaken.

Intranasal HSP70 administration protects against dopaminergic denervation and modulates neuroinflammatory response in the 6-OHDA rat model

HSP70 is one of the main molecular chaperones involved in the cellular stress response. Besides its chaperone action, HSP70 also modulates the immune response. Increased susceptibility to toxic insults in intra- and extracellular environments has been associated with insufficient amounts of inducible HSP70 in adult neurons. On the other hand, exogenous HSP70 administration has demonstrated neuroprotective effects in experimental models of age-related disorders. In this regard, this study investigated the effects of exogenous HSP70 in an animal model of dopaminergic denervation of the nigrostriatal axis. After unilateral intrastriatal injection with 6-hydroxydopamine (6-OHDA), the animals received purified recombinant HSP70 through intranasal administration (2 μg/rat/day) for 15 days. Our results indicate a neuroprotective effect of intranasal HSP70 against dopaminergic denervation induced by 6-OHDA. Exogenous HSP70 improved motor impairment and reduced the loss of dopaminergic neurons caused by 6-OHDA. Moreover, HSP70 modulated neuroinflammatory response in the substantia nigra, an important event in Parkinson's disease pathogenesis. Specifically, HSP70 treatment reduced microglial activation and astrogliosis induced by 6-OHDA, as well as IL-1β mRNA expression in this region. Also, recombinant HSP70 increased the protein content of HSP70 in the substantia nigra of rats that received 6-OHDA. These data suggest the neuroprotection of HSP70 against dopaminergic neurons damage after cellular stress. Finally, our results indicate that HSP70 neuroprotective action against 6-OHDA toxicity is related to inflammatory response modulation.

The Add-On Effect of Lactobacillus plantarum PS128 in Patients With Parkinson's Disease: A Pilot Study

Background: Lactobacillus plantarum PS128 (PS128) is a specific probiotic, known as a psychobiotic, which has been demonstrated to alleviate motor deficits and inhibit neurodegenerative processes in Parkinson's disease (PD)-model mice. We hypothesize that it may also be beneficial to patients with PD based on the possible mechanism via the microbiome-gut-brain axis. Methods: This is an open-label, single-arm, baseline-controlled trial. The eligible participants were scheduled to take 60 billion colony-forming units of PS128 once per night for 12 weeks. Clinical assessments were conducted using the Unified Parkinson's Disease Rating Scale (UPDRS), modified Hoehn and Yahr scale, and change in patient "ON-OFF" diary recording as primary outcome measures. The non-motor symptoms questionnaire, Beck depression inventory-II, patient assessment of constipation symptom, 39-item Parkinson's Disease Questionnaire (PDQ-39), and Patient Global Impression of Change (PGI-C) were assessed as secondary outcome measures. Results: Twenty-five eligible patients (32% women) completed the study. The mean age was 61.84 ± 5.74 years (range, 52-72), mean disease duration was 10.12 ± 2.3 years (range, 5-14), and levodopa equivalent daily dosage was 1063.4 ± 209.5 mg/daily (range, 675-1,560). All patients remained on the same dosage of anti-parkinsonian and other drugs throughout the study. After 12 weeks of PS128 supplementation, the UPDRS motor scores improved significantly in both the OFF and ON states (p = 0.004 and p = 0.007, respectively). In addition, PS128 intervention significantly improved the duration of the ON period and OFF period as well as PDQ-39 values. However, no obvious effect of PS128 on non-motor symptoms of patients with PD was observed. Notably, the PGI-C scores improved in 17 patients (68%). PS128 intervention was also found to significantly reduce plasma myeloperoxidase and urine creatinine levels. Conclusion: The present study demonstrated that PS128 supplementation for 12 weeks with constant anti-parkinsonian medication improved the UPDRS motor score and quality of life of PD patients. We suggest that PS128 could serve as a therapeutic adjuvant for the treatment of PD. In the future, placebo-controlled studies are needed to further support the efficacy of PS128 supplementation. Clinical Trial Registration: https://clinicaltrials.gov/, identifier: NCT04389762.

Polymorphisms of Interleukin-6 and Interleukin-8 Are Not Associated with Parkinson's Disease in Taiwan

Background: Studies have suggested that cytokines are crucial mediators in the pathogenesis of Parkinson’s disease (PD). The multifunctional cytokine interleukin (IL)-6 and its single nucleotide polymorphisms (SNPs) were found to have an impact on the development of PD. However, different studies in associations of IL-6 genetic variants with PD showed inconsistent results and it has never been explored in a Taiwanese population. Both IL-1α and IL-8 contribute to the same inflammation pathway. IL-1α genetic polymorphism has an effect on late-onset PD in Taiwan, whereas the associations of IL-8 genetic variants with PD in Taiwan remain to be investigated. Methods: This study examined the frequencies of polymorphisms within the critical promoter areas of the proinflammatory cytokine genes: IL-6 G-174C (rs1800795) and IL-8 A-251T (rs4073) in Taiwanese PD patients compared with age-and gender-matched healthy subjects. Comparisons were also made in genotype and allele frequencies of IL-6 G-174C (rs1800795) and IL-8 A-251T (rs4073) among different populations in previous studies. Results: In total, 1120 subjects, including 509 PD patients (female/male: 259/250) and 511 control subjects (female/male: 252/259), were recruited. We found no statistically significant differences in IL-6 G-174C (rs1800795) or IL-8 A-251T (rs4073) genotypic and allelic distribution between PD and controls, even after being stratified by age at onset and gender. Conclusions: The results did not demonstrate any association of IL-6 G-174C (rs1800795) or IL-8 A-251T (rs4073) with PD in a Taiwanese population. Despite the negative results, this is the first study in associations of IL-6 G-174C (rs1800795) and IL-8 A-251T (rs4073) with PD in Taiwan. The relevance of genetic variants of IL-6 G-174C (rs1800795) or IL-8 A-251T (rs4073) on PD susceptibility warrants further investigation.

Role of IL-6 in the regulation of neuronal development, survival and function

The pleiotropic cytokine interleukin-6 (IL-6) is emerging as a molecule with both beneficial and destructive potentials. It can exert opposing actions triggering either neuron survival after injury or causing neurodegeneration and cell death in neurodegenerative or neuropathic disorders. Importantly, neurons respond differently to IL-6 and this critically depends on their environment and whether they are located in the peripheral or the central nervous system. In addition to its hub regulator role in inflammation, IL-6 is recently emerging as an important regulator of neuron function in health and disease, offering exciting possibilities for more mechanistic insight into the pathogenesis of mental, neurodegenerative and pain disorders and for developing novel therapies for diseases with neuroimmune and neurogenic pathogenic components.

Papaverine Exerts Neuroprotective Effect by Inhibiting NLRP3 Inflammasome Activation in an MPTP-Induced Microglial Priming Mouse Model Challenged with LPS

Microglial priming is the process of microglial proliferation and activation in response to neurodegeneration and abnormal protein accumulation. Priming makes microglia susceptible to secondary inflammatory stimuli and causes exaggerated inflammatory responses. In the present study, we established a microglial priming model in mice by administering a single injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 20 mg/kg). MPTP induced microglial activation without dopaminergic degeneration; however, subsequent treatment with a sub-toxic dose of lipopolysaccharides (LPS) induced an amplified inflammatory response and caused nigrostriatal dopaminergic degeneration. These pathological and inflammatory changes, including microglial activation and dopaminergic cell loss in the substantia nigra (SN) area were reversed by papaverine (PAP) administration. In addition, MPTP/LPS enhanced interleukin-1β (IL-1β) expression and processing via nod-like receptor protein 3 (NLRP3) inflammasome activation in the SN region of mice. However, PAP treatment suppressed inflammasome activation and subsequent IL-1β maturation. Moreover, PAP inhibited nuclear factor-κB (NF-κB) and enhanced cAMP-response element binding protein (CREB) activity in the SN of MPTP/LPS mice. These results suggest that PAP inhibits the activation of NLRP3 inflammasome by modulating NF-κB and CREB signaling pathways, which results in reduced microglial activation and neuronal cell death. Thus, PAP may be a potential candidate for the treatment of Parkinsons’s disease, which is aggravated by systemic inflammation.

Neuro-Immune Cross-Talk in the Striatum: From Basal Ganglia Physiology to Circuit Dysfunction

The basal ganglia network is represented by an interconnected group of subcortical nuclei traditionally thought to play a crucial role in motor learning and movement execution. During the last decades, knowledge about basal ganglia physiology significantly evolved and this network is now considered as a key regulator of important cognitive and emotional processes. Accordingly, the disruption of basal ganglia network dynamics represents a crucial pathogenic factor in many neurological and psychiatric disorders. The striatum is the input station of the circuit. Thanks to the synaptic properties of striatal medium spiny neurons (MSNs) and their ability to express synaptic plasticity, the striatum exerts a fundamental integrative and filtering role in the basal ganglia network, influencing the functional output of the whole circuit. Although it is currently established that the immune system is able to regulate neuronal transmission and plasticity in specific cortical areas, the role played by immune molecules and immune/glial cells in the modulation of intra-striatal connections and basal ganglia activity still needs to be clarified. In this manuscript, we review the available evidence of immune-based regulation of synaptic activity in the striatum, also discussing how an abnormal immune activation in this region could be involved in the pathogenesis of inflammatory and degenerative central nervous system (CNS) diseases.

T Cells Limit Accumulation of Aggregate Pathology Following Intrastriatal Injection of α-Synuclein Fibrils

BACKGROUND

α-Synuclein (α-syn) is the predominant protein in Lewy-body inclusions, which are pathological hallmarks of α-synucleinopathies, such as Parkinson's disease (PD) and multiple system atrophy (MSA). Other hallmarks include activation of microglia, elevation of pro-inflammatory cytokines, as well as the activation of T and B cells. These immune changes point towards a dysregulation of both the innate and the adaptive immune system. T cells have been shown to recognize epitopes derived from α-syn and altered populations of T cells have been found in PD and MSA patients, providing evidence that these cells can be key to the pathogenesis of the disease.ObjectiveTo study the role of the adaptive immune system with respect to α-syn pathology.

METHODS

We injected human α-syn preformed fibrils (PFFs) into the striatum of immunocompromised mice (NSG) and assessed accumulation of phosphorylated α-syn pathology, proteinase K-resistant α-syn pathology and microgliosis in the striatum, substantia nigra and frontal cortex. We also assessed the impact of adoptive transfer of naïve T and B cells into PFF-injected immunocompromised mice.

RESULTS

Compared to wildtype mice, NSG mice had an 8-fold increase in phosphorylated α-syn pathology in the substantia nigra. Reconstituting the T cell population decreased the accumulation of phosphorylated α-syn pathology and resulted in persistent microgliosis in the striatum when compared to non-transplanted mice.

CONCLUSION

Our work provides evidence that T cells play a role in the pathogenesis of experimental α-synucleinopathy.

Sex-based differences in the activation of peripheral blood monocytes in early Parkinson disease

Increasing evidence supports the role of brain and systemic inflammation in the etiology of Parkinson disease (PD). We used gene expression profiling to examine the activation state of peripheral blood monocytes in 18 patients with early, untreated PD and 16 healthy control (HC) subjects. Monocytes were isolated by negative selection, and gene expression studied by RNA-seq and gene set enrichment analysis. A computational model that incorporated case/control status, sex, and the interaction between case/control status and sex was utilized. We found that there was a striking effect of sex on monocyte gene expression. There was inflammatory activation of monocytes in females with PD, with enrichment of gene sets associated with interferon gamma stimulation. In males, the activation patterns were more heterogeneous. These data point to the importance of systemic monocyte activation in PD, and the importance of studies which examine the differential effects of sex on pathophysiology of the disease.

Targeting Adenosine Receptors in Neurological Diseases

Adenosine plays a significant role in neurotransmission process by controlling the blood pressure, while adenosine triphosphate (ATP) acts as a neuromodulator and neurotransmitter and by activation of P2 receptors, regulates the contractility of the heart. Adenosine signaling is essential in the process of regeneration by regulating proliferation, differentiation, and apoptosis of stem cells. In this review, we have selected neurological disorders (Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and epilepsy) with clinical trials using antagonists and epigenetic tools targeting adenosine receptor as a therapeutic approach in the treatment of these disorders. Promising results have been reported from many clinical trials. It has been found that higher expression levels of A2A and P2X7 receptors in neurological disorders further complicate the disease condition. Therefore, modulations of these receptors by using antagonists of these receptors or SAM (S-adenosylmethionine) therapy as an epigenetic tool could be useful in reversing the complications of these disorders. Finally, we suggest that modulation of adenosine receptors in neurological disorders can increase the regenerative phase by increasing the rate of proliferation and differentiation in the damaged tissues.

Interferon-γ Involvement in the Neuroinflammation Associated with Parkinson's Disease and L-DOPA-Induced Dyskinesia

Interferon-γ (IFN-γ) is a proinflammatory cytokine that activates glial cells. IFN-γ is increased in the plasma and brain of Parkinson's disease patients, suggesting its potential role in the disease. We investigated whether the IFN-γ deficiency could interfere with nigrostriatal degeneration induced by the neurotoxin 6-hydroxydopamine, L-DOPA-induced dyskinesia, and the neuroinflammatory features as astrogliosis, microgliosis, and induced nitric oxide synthase (iNOS) immunoreactivity induced by L-DOPA treatment. Wild type (WT) and IFN-γ knockout (IFN-γ/KO) mice received unilateral striatal microinjections of 6-hydroxydopamine. Animals were sacrificed 1, 3, 7, and 21 days after lesions. Additional group of WT and IFN-γ/KO parkinsonian mice, after 3 weeks of neurotoxin injection, received L-DOPA (intraperitoneally, for 21 days) resulting in dyskinetic-like behavior. Tyrosine hydroxylase immunostaining indicated the starting of dopaminergic lesion since the first day past toxin administration, progressively increased until the third day when it stabilized. There was no difference in the lesion and L-DOPA-induced dyskinesia intensity between WT and IFN-γ/KO mice. Remarkably, IFN-γ/KO mice treated with L-DOPA presented in the lesioned striatum an increase of iNOS and glial fibrilary acid protein (GFAP) density, compared with the WT group. Morphological analysis revealed the rise of astrocytes and microglia reactivity in IFN-γ/KO mice exibiting dyskinesia. In conclusion, IFN-γ/KO mice presented an intensification of the inflammatory reaction accompanying L-DOPA treatment and suggest that iNOS and GFAP increase, and the activation of astrocytes and microglia induced afterward L-DOPA treatment was IFN-γ independent events. Intriguingly, IFN-γ absence did not affect the degeneration of dopaminergic neurons or LID development.

Cytokine Profile in Plasma Extracellular Vesicles of Parkinson's Disease and the Association with Cognitive Function

Plasma extracellular vesicles (EVs) containing various molecules, including cytokines, can reflect the intracellular condition and participate in cell-to-cell signaling, thus emerging as biomarkers for Parkinson’s disease (PD). Inflammation may be a crucial risk factor for PD development and progression. The present study investigated the role of plasma EV cytokines as the biomarkers of PD. This cross-sectional study recruited 113 patients with PD, with mild to moderate stage disease, and 48 controls. Plasma EVs were isolated, and the levels of cytokines, including pro-interleukin (IL)-1β, IL-6, IL-10, tumor necrosis factor (TNF)-α, and transforming growth factor (TGF)-β1, were evaluated. Patients with PD had significantly increased plasma EV pro-IL-1β and TNF-α levels compared with controls after adjustment for age and sex. Despite the lack of a significant association between plasma EV cytokines and motor symptom severity in patients with PD, cognitive dysfunction severity, assessed using the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment, was significantly associated with plasma EV pro-IL-1β, IL-6, IL-10, and TNF-α levels. This association was PD specific and not found in controls. Furthermore, patients with PD cognitive deficit (MMSE < 26) exhibited a distinguished EV cytokine profile compared to those without cognitive deficit. The findings support the concept of inflammatory pathogenesis in the development and progression of PD and indicate that plasma EV cytokines may serve as PD biomarkers in future.

Parkinson's Disease: Can Targeting Inflammation Be an Effective Neuroprotective Strategy?

The reason why dopamine neurons die in Parkinson’s disease remains largely unknown. Emerging evidence points to a role for brain inflammation in neurodegeneration. Essential questions are whether brain inflammation happens sufficiently early so that interfering with this process can be expected to slow down neuronal death and whether the contribution from inflammation is large enough so that anti-inflammatory agents can be expected to work. Here I discuss data from human PD studies indicating that brain inflammation is an early event in PD. I also discuss the role of T-lymphocytes and peripheral inflammation for neurodegeneration. I critically discuss the failure of clinical trials targeting inflammation in PD.

Harnessing the immune system for the treatment of Parkinson's disease

Current treatment options for Parkinson's disease (PD) typically aim to replace dopamine, and hence only provide symptomatic relief. However, in the long run, this approach alone loses its efficacy as it is associated with debilitating side effects. Hence there is an unmet clinical need for addressing levodopa resistant symptoms, and an urgency to develop therapies that can halt or prevent the course of PD. The premise that α-syn can transmit from cell-to-cell in a prion like manner has opened up the possibility for the use of immunotherapy in PD. There is evidence for inflammation in PD as is evidenced by microglial activation, as well as the involvement of the peripheral immune system in PD, and peripheral inflammation can exacerbate dopaminergic degeneration as seen in animal models of the disease. However, mechanisms that link the immune system with PD are not clear, and the sequence of immune responses with respect to PD are still unknown. Nevertheless, our present knowledge offers avenues for the development of immune-based therapies for PD. In order to successfully employ such strategies, we must comprehend the state of the peripheral immune system during the course of PD. This review describes the developments in the field of both active and passive immunotherapies in the treatment of PD, and highlights the crucial need for future research for clarifying the role of inflammation and immunity in this debilitating disease.

Mini Review: Correlations of Cognitive Domains With Cerebrospinal Fluid α-Synuclein Levels in Patients With Parkinson's Disease

The level of α-synuclein, a component of Lewy bodies, in cerebrospinal fluid (CSF) in Parkinson's disease (PD) has attracted recent attention. Most meta-analyses conclude that CSF levels of α-synuclein are decreased in PD. Patients with PD present with cognitive impairment, including frontal/executive dysfunction in the early phase and later emergence of visuospatial and mnemonic deficits. To examine whether CSF α-synuclein levels reflect the activities of various cognitive domains, we reviewed reports examining the association of these levels with cognitive performance in each domain in PD. Among 13 cross-sectional studies, five showed that a lower CSF α-synuclein level was associated with worse cognitive function. In four of these five reports, frontal/executive function showed this association, suggesting a link of the pathophysiology with Lewy bodies. In three other reports, a higher CSF α-synuclein level was associated with temporal-parieto-occipital cognitive deterioration such as memory. In the other five reports, the CSF α-synuclein level did not correlate with cognitive performance for any domain. In four longitudinal studies, a higher baseline CSF α-synuclein level was associated with a worse cognitive outcome, including cognitive processing speed, visuospatial function and memory in two, but not with any cognitive outcome in the other two. The different associations may reflect the heterogeneous pathophysiology in PD, including different pathogenic proteins, neurotransmitters. Thus, more studies of the association between cognitive domains and CSF levels of pathogenic proteins are warranted.

Current and emerging therapeutic targets for Parkinson's disease

Parkinson's disease (PD) is characterized by gradual neurodegeneration and forfeiture of dopamine neurons in substantia nigra pars compacta which ultimately leads to depletion of dopamine levels. PD patients not only display motor features such as rigidity, tremor, and bradykinesia but also non-motor features such as depression, anxiety, etc. Various treatments are available for PD patients such as dopamine replacement are well established but it is only partially or transiently effective. As these therapies not able to restore dopaminergic neurons and delay the development of Parkinson's disease, therefore, the need for an effective therapeutic approach is crucial. The present review discusses a comprehensive overview of current novel targets for PD which includes molecular chaperone, neuroinflammation, mitochondrial dysfunction, neuromelanin, Ubiquitin-proteasome system, protein Abelson, Synaptic vesicle glycoprotein 2C, and Cocaine-amphetamine-regulated transcript, etc. These approaches will help to identify new targets for the treatment of disease and may provide a ray of hope for PD patient treatment. Graphical abstract.

P2X4R Overexpression Upregulates Interleukin-6 and Exacerbates 6-OHDA-Induced Dopaminergic Degeneration in a Rat Model of PD

The pathogenesis of Parkinson’s disease (PD) remains elusive. Current thinking suggests that the activation of microglia and the subsequent release of inflammatory factors, including interleukin-6 (IL-6), are involved in the pathogenesis of PD. P2X4 receptor (P2X4R) is a member of the P2X superfamily of ion channels activated by ATP. To study the possible effect of the ATP-P2X4R signal axis on IL-6 in PD, lentivirus carrying the P2X4R-overexpression gene or empty vector was injected into the substantia nigra (SN) of rats, followed by treatment of 6-hydroxydopamine (6-OHDA) or saline 1 week later. The research found the relative expression of P2X4R in the 6-OHDA-induced PD rat models was notably higher than that in the normal. And P2X4R overexpression could upregulate the expression of IL-6, reduce the amount of dopaminergic (DA) neurons in the SN of PD rats, suggesting that P2X4R may mediate the production of IL-6 to damage DA neurons in the SN. Our data revealed the important role of P2X4R in modulating IL-6, which leads to neuroinflammation involved in PD pathogenesis.

The erythrocyte sedimentation rate in male adolescents and subsequent risk of Parkinson's disease: an observational study

Systemic inflammation may be implicated in the pathophysiology of Parkinson’s disease (PD). Since PD occurs usually in later life, most studies of causal factors are conducted in older populations, so potentially important influences from early life cannot be adequately captured. We investigated whether the erythrocyte sedimentation rate (ESR) in early adulthood is associated with the subsequent development of PD in men. As part of Swedish national conscription testing conducted from 1968 through 1983 (N = 716,550), the erythrocyte sedimentation rate, as a measure of inflammation, was measured in 659,278 young men. The cohort was observed for subsequent PD events (N = 1513) through December 2016. Cox proportional hazards models were used to estimate the hazard ratios (HR) with 95% CI with adjustment for potential confounders. Individuals with higher ESRs were significantly less likely to be diagnosed with PD, as ESR was linearly and inversely associated with PD risk. The magnitude of the association between ESR and PD risk was similar for increases up to 15 mm/h, leveled off thereafter, and was non-significant for ESR values > 20 mm/h. The HR for PD with basic adjustments (age at conscription, year of conscription, test center and erythrocyte volume fraction) was 0.94 (95% CI 0.89–0.99, P = 0.02) per log₂ increase in ESR, corresponding to a two-fold increase in ESR. Further adjustments for potential confounders (parental education, systolic and diastolic blood pressures, and IQ) scarcely altered the HR. The results suggest a prospective association between high ESR and reduced risk for PD.

Cypermethrin Induces the Activation of Rat Primary Microglia and Expression of Inflammatory Proteins

Cypermethrin activates microglia, which is found to be decisive in neurodegeneration in the experimental rats. While the involvement of microglial activation in toxicant-induced neurodegeneration is reported, the effect of low concentration of cypermethrin on the expression of inflammatory proteins from the rat primary microglia is not yet properly understood. The study intended to delineate the effect of low concentration of cypermethrin on the expression and release of proteins from the microglia. Rat primary microglial cells were treated with cypermethrin to check the expression of inflammatory proteins. Cypermethrin-treated microglia conditioned media and cells were collected to measure the expression and release of inflammatory proteins. Cypermethrin augmented the protein kinase C-δ (PKC-δ), inducible nitric oxide synthase (iNOS), phosphorylated mitogen-activated protein kinase (MAPK) p38 and p42/44, matrix metalloproteinase (MMP)-3, and MMP-9 levels in the cell lysate and tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) levels in the microglia conditioned media. Pre-treatment with minocycline, a microglial activation inhibitor or rottlerin, a PKC-δ inhibitor, notably reduced the release of TNF-α in the conditioned media and expression of iNOS protein in the microglia. Minocycline reduced the expression of PKC-δ, phosphorylated p38 and p42/44 MAPKs, MMP-3, and MMP-9 proteins in the microglia. While cypermethrin-treated conditioned media induced the toxicity in the rat primary neurons, minocycline or rottlerin reduced the cypermethrin treated microglia conditioned media-induced toxicity. The outcomes of the present study suggest that cypermethrin activates microglia and releases TNF-α and IL-1β as well as up-regulates the expression of PKC-δ, iNOS, phosphorylated p38 and p42/44 MAPKs, MMP-3, and MMP-9 proteins, which could contribute to neurodegeneration.

Protective effect of Indole-3-carbinol, an NF-κB inhibitor in experimental paradigm of Parkinson's disease: In silico and in vivo studies

Parkinson's disease (PD) is a progressive neurodegenerative disorder, majorly with symptoms of motor dysfunction. Study was performed to explore the effect of nuclear factor κB (NF-κB) inhibitors against neurobehavioral abnormalities and neuroinflammation in PD. Cost effective in silico approaches of docking-based ligand -target complex predictions and optimal physicochemical properties were utilised to identify lead NF-κB inhibitor using database. Our studies revealed the potential hit Indole-3-carbinol (I3C) which was considered for the next phase, pharmacological validations. Intranigral administration of lipopolysaccharide (LPS) in rats is utilized as a neuroinflmmation model of PD. In the present study it caused an impairment in motor functions, its coordination, learning and memory as demonstrated in rotarod apparatus, beam balance test, open field test and Morris water maze test. Chronic administration of I3C for 21 days in intranigral LPS treated rats led to a significant improvement in motor functions, coordination, learning and memory which were associated with a decrease in the activity of inflammatory cytokines such as TNF-α and IL-6. Further, it was found to inhibit NF-κB whose levels increased after LPS administration. Moreover, decreased levels of malondialdehyde and increased levels of reduced glutathione, superoxide dismutase and catalase were observed in cortex and striatum after I3C administration in LPS rats. These results suggest a possible neuroprotective effect of I3C via amelioration of LPS-induced behavioural alterations, oxidative damage and neuroinflammation which in turn is attributed to its potent antioxidant and anti-inflammatory (NF-κB inhibition) property. The effect produced by I3C (50 mg/kg) was found to be comparable with levodopa-carbidopa combination (LD:CD) while, I3C (50 mg/kg) in combination with LD:CD exhibited a potentiating effect in improving motor impairments and cognitive deficit. The results thus depict I3C as a promising agent to delay neurodegeneration of the neurons in PD with improvement in motor functions and cognitive function.

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.

Transcriptomic approach predicts a major role for transforming growth factor beta type 1 pathway in L-Dopa-induced dyskinesia in parkinsonian rats

Dyskinesia induced by long-term L-Dopa (LID) therapy in Parkinson disease is associated with altered striatal function whose molecular bases remain unclear. Here, a transcriptomic approach was applied for comprehensive analysis of distinctively regulated genes in striatal tissue, their specific pathways, and functional- and disease-associated networks in a rodent model of LID. This approach has identified transforming growth factor beta type 1 (TGFβ1) as a highly upregulated gene in dyskinetic animals. TGFβ1 pathway is a top aberrantly regulated pathway in the striatum following LID development based on differentially expressed genes (> 1.5 fold change and P < 0.05). The induction of TGFβ1 pathway specific genes, TGFβ1, INHBA, AMHR2 and PMEPA1 was also associated with regulation of NPTX2, PDP1, SCG2, SYNPR, TAC1, TH, TNNT1 genes. Transcriptional network and upstream regulator analyses have identified AKT-centered functional and ERK-centered disease networks revealing the association of TGFβ1, IL-1β and TNFα with LID development. Therefore, results support that TGFβ1 pathway is a major contributor to the pathogenic mechanisms of LID.

Protein Interaction Studies for Understanding the Tremor Pathway in Parkinson's Disease

BACKGROUND

Tremor is one of the most noticeable features, which occurs during the early stages of Parkinson's Disease (PD). It is one of the major pathological hallmarks and does not have any interpreted mechanism. In this study, we have framed a hypothesis and deciphered protein- protein interactions between the proteins involved in impairment in sodium and calcium ion channels and thus cause synaptic plasticity leading to a tremor.

METHODS

Literature mining for retrieval of proteins was done using Science Direct, PubMed Central, SciELO and JSTOR databases. A well-thought approach was used, and a list of differentially expressed proteins in PD was collected from different sources. A total of 71 proteins were retrieved, and a protein interaction network was constructed between them by using Cytoscape.v.3.7. The network was further analysed using the BiNGO plugin for retrieval of overrepresented biological processes in Tremor-PD datasets. Hub nodes were also generated in the network.

RESULTS

The Tremor-PD pathway was deciphered, which demonstrates the cascade of protein interactions that might lead to tremors in PD. Major proteins involved were LRRK2, TUBA1A, TRAF6, HSPA5, ADORA2A, DRD1, DRD2, SNCA, ADCY5, TH, etc. Conclusion: In the current study, it is predicted that ADORA2A and DRD1/DRD2 are equally contributing to the progression of the disease by inhibiting the activity of adenylyl cyclase and thereby increases the permeability of the blood-brain barrier, causing an influx of neurotransmitters and together they alter the level of dopamine in the brain which eventually leads to tremor.

Explorative Combined Lipid and Transcriptomic Profiling of Substantia Nigra and Putamen in Parkinson's Disease

Parkinson’s disease (PD) is characterized by the loss of dopaminergic neurons from the substantia nigra (SN) that project to the dorsal striatum (caudate-putamen). To better understand the molecular mechanisms underlying PD, we performed combined lipid profiling and RNA sequencing of SN and putamen samples from PD patients and age-matched controls. SN lipid analysis pointed to a neuroinflammatory component and included elevated levels of the endosomal lipid Bis (Monoacylglycero)Phosphate 42:8, while two of the three depleted putamen lipids were saturated sphingomyelin species. Remarkably, we observed gender-related differences in the SN and putamen lipid profiles. Transcriptome analysis revealed that the top-enriched pathways among the 354 differentially expressed genes (DEGs) in the SN were “protein folding” and “neurotransmitter transport”, and among the 261 DEGs from putamen “synapse organization”. Furthermore, we identified pathways, e.g., “glutamate signaling”, and genes, encoding, e.g., an angiotensin receptor subtype or a proprotein convertase, that have not been previously linked to PD. The identification of 33 genes that were common among the SN and putamen DEGs, which included the α-synuclein paralog β-synuclein, may contribute to the understanding of general PD mechanisms. Thus, our proof-of-concept data highlights new genes, pathways and lipids that have not been explored before in the context of PD.