Innate and adaptive immune responses in Parkinson's disease

Suppression of the JAK/STAT pathway inhibits neuroinflammation in the line 61-PFF mouse model of Parkinson's disease

Parkinson's disease (PD) is characterized by neuroinflammation, progressive loss of dopaminergic neurons, and accumulation of α-synuclein (α-Syn) into insoluble aggregates called Lewy pathology. The Line 61 α-Syn mouse is an established preclinical model of PD; Thy-1 is used to promote human α-Syn expression, and features of sporadic PD develop at 9-18 months of age. To accelerate the PD phenotypes, we injected sonicated human α-Syn preformed fibrils (PFFs) into the striatum, which produced phospho-Syn (p-α-Syn) inclusions in the substantia nigra pars compacta and significantly increased MHC Class II-positive immune cells. Additionally, there was enhanced infiltration and activation of innate and adaptive immune cells in the midbrain. We then used this new model, Line 61-PFF, to investigate the effect of inhibiting the JAK/STAT signaling pathway, which is critical for regulation of innate and adaptive immune responses. After administration of the JAK1/2 inhibitor AZD1480, immunofluorescence staining showed a significant decrease in p-α-Syn inclusions and MHC Class II expression. Flow cytometry showed reduced infiltration of CD4+ T-cells, CD8+ T-cells, CD19+ B-cells, dendritic cells, macrophages, and endogenous microglia into the midbrain. Importantly, single-cell RNA-Sequencing analysis of CD45+ cells from the midbrain identified 9 microglia clusters, 5 monocyte/macrophage (MM) clusters, and 5 T-cell (T) clusters, in which potentially pathogenic MM4 and T3 clusters were associated with neuroinflammatory responses in Line 61-PFF mice. AZD1480 treatment reduced cell numbers and cluster-specific expression of the antigen-presentation genes H2-Eb1, H2-Aa, H2-Ab1, and Cd74 in the MM4 cluster and proinflammatory genes such as Tnf, Il1b, C1qa, and C1qc in the T3 cluster. Together, these results indicate that inhibiting the JAK/STAT pathway suppresses the activation and infiltration of innate and adaptive cells, reducing neuroinflammation in the Line 61-PFF mouse model.

Current insights and assumptions on α-synuclein in Lewy body disease

Lewy body disorders are heterogeneous neurological conditions defined by intracellular inclusions composed of misshapen α-synuclein protein aggregates. Although α-synuclein aggregates are only one component of inclusions and not strictly coupled to neurodegeneration, evidence suggests they seed the propagation of Lewy pathology within and across cells. Genetic mutations, genomic multiplications, and sequence polymorphisms of the gene encoding α-synuclein are also causally linked to Lewy body disease. In nonfamilial cases of Lewy body disease, the disease trigger remains unidentified but may range from industrial/agricultural toxicants and natural sources of poisons to microbial pathogens. Perhaps due to these peripheral exposures, Lewy inclusions appear at early disease stages in brain regions connected with cranial nerves I and X, which interface with inhaled and ingested environmental elements in the nasal or gastrointestinal cavities. Irrespective of its identity, a stealthy disease trigger most likely shifts soluble α-synuclein (directly or indirectly) into insoluble, cross-β-sheet aggregates. Indeed, β-sheet-rich self-replicating α-synuclein multimers reside in patient plasma, cerebrospinal fluid, and other tissues, and can be subjected to α-synuclein seed amplification assays. Thus, clinicians should be able to capitalize on α-synuclein seed amplification assays to stratify patients into potential responders versus non-responders in future clinical trials of α-synuclein targeted therapies. Here, we briefly review the current understanding of α-synuclein in Lewy body disease and speculate on pathophysiological processes underlying the potential transmission of α-synucleinopathy across the neuraxis.

The autoimmune response induced by α-synuclein peptides drives neuronal cell death and glial cell activation

Parkinson's disease (PD) is a progressive neurodegenerative disorder associated with the loss of dopaminergic neurons and neuroinflammation. Recent studies have identified a role of T cells in the pathogenesis of PD. Additionally, these studies suggested that α-synuclein (α-Syn) is related to abnormal T-cell responses and may act as an epitope and trigger autoimmune T-cell responses. However, it is unclear whether the α-Syn-mediated autoimmune response occurs and whether it is related to neuronal cell death and glial cell activation. In this study, we investigated the autoimmune T-cell response induced by α-Syn peptides and evaluated the neurotoxic effect of the α-Syn peptide-mediated autoimmune response. The immunization of mice with α-Syn peptides resulted in enhanced autoimmune responses, such as the peptide recall response, polarization toward Th1/Th17 cells, and regulatory T cell imbalance. Furthermore, the α-Syn autoimmune response led to the death of primary neurons cocultured with splenocytes. Treatment with conditioned media from α-Syn peptide-immunized splenocytes induced microglia and toxic A1-type astrocyte activation. Taken together, our results provide evidence of the potential role of the α-Syn-initiated autoimmune response and its contribution to neuronal cell death and glial cell activation.

Suppression of the JAK/STAT Pathway Inhibits Neuroinflammation in the Line 61-PFF Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is characterized by neuroinflammation, progressive loss of dopaminergic neurons, and accumulation of a-synuclein (a-Syn) into insoluble aggregates called Lewy pathology. The Line 61 a-Syn mouse is an established preclinical model of PD; Thy-1 is used to promote human a-Syn expression, and features of sporadic PD develop at 9-18 months of age. To accelerate the PD phenotypes, we injected sonicated human a-Syn preformed fibrils (PFFs) into the striatum, which produced phospho-Syn (p-a-Syn) inclusions in the substantia nigra pars compacta and significantly increased MHC Class II-positive immune cells. Additionally, there was enhanced infiltration and activation of innate and adaptive immune cells in the midbrain. We then used this new model, Line 61-PFF, to investigate the effect of inhibiting the JAK/STAT signaling pathway, which is critical for regulation of innate and adaptive immune responses. After administration of the JAK1/2 inhibitor AZD1480, immunofluorescence staining showed a significant decrease in p-a-Syn inclusions and MHC Class II expression. Flow cytometry showed reduced infiltration of CD4+ T-cells, CD8+ T-cells, CD19+ B-cells, dendritic cells, macrophages, and endogenous microglia into the midbrain. Importantly, single-cell RNA-Sequencing analysis of CD45+ cells from the midbrain identified 9 microglia clusters, 5 monocyte/macrophage (MM) clusters, and 5 T-cell (T) clusters, in which potentially pathogenic MM4 and T3 clusters were associated with neuroinflammatory responses in Line 61-PFF mice. AZD1480 treatment reduced cell numbers and cluster-specific expression of the antigen-presentation genes H2-Eb1, H2-Aa, H2-Ab1, and Cd74 in the MM4 cluster and proinflammatory genes such as Tnf, Il1b, C1qa, and C1qc in the T3 cluster. Together, these results indicate that inhibiting the JAK/STAT pathway suppresses the activation and infiltration of innate and adaptive cells, reducing neuroinflammation in the Line 61-PFF mouse model.

The major histocompatibility complex participates in Parkinson's disease

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

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

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

Lysosomal storage, impaired autophagy and innate immunity in Gaucher and Parkinson's diseases: insights for drug discovery

Impairment of autophagic-lysosomal pathways is increasingly being implicated in Parkinson's disease (PD). GBA1 mutations cause the lysosomal storage disorder Gaucher disease (GD) and are the commonest known genetic risk factor for PD. GBA1 mutations have been shown to cause autophagic-lysosomal impairment. Defective autophagic degradation of unwanted cellular constituents is associated with several pathologies, including loss of normal protein homeostasis, particularly of α-synuclein, and innate immune dysfunction. The latter is observed both peripherally and centrally in PD and GD. Here, we will discuss the mechanistic links between autophagy and immune dysregulation, and the possible role of these pathologies in communication between the gut and brain in these disorders. Recent work in a fly model of neuronopathic GD (nGD) revealed intestinal autophagic defects leading to gastrointestinal dysfunction and immune activation. Rapamycin treatment partially reversed the autophagic block and reduced immune activity, in association with increased survival and improved locomotor performance. Alterations in the gut microbiome are a critical driver of neuroinflammation, and studies have revealed that eradication of the microbiome in nGD fly and mouse models of PD ameliorate brain inflammation. Following these observations, lysosomal-autophagic pathways, innate immune signalling and microbiome dysbiosis are discussed as potential therapeutic targets in PD and GD. This article is part of a discussion meeting issue 'Understanding the endo-lysosomal network in neurodegeneration'.

The effects of cholesterol and statins on Parkinson's neuropathology: a narrative review

Parkinson disease (PD) is chronic and progressive neurodegenerative disease of the brain characterized by motor symptoms including tremors, rigidity, postural instability, and bradykinesia. PD neuropathology is due to the progressive degeneration of dopaminergic neurons in the substantia nigra and accumulation of Lewy bodies in the survival neurons. The brain contains a largest amount of cholesterol which is mainly synthesized from astrocytes and glial cells. Cholesterol is intricate in the pathogenesis of PD and may be beneficial or deleterious. Therefore, there are controversial points concerning the role of cholesterol in PD neuropathology. In addition, cholesterol-lowering agents' statins can affect brain cholesterol. Different studies highlighted that statins, via inhibition of brain HMG-CoA, can affect neuronal integrity through suppression of neuronal cholesterol, which regulates synaptic plasticity and neurotransmitter release. Furthermore, statins affect the development and progression of different neurodegenerative diseases in bidirectional ways that could be beneficial or detrimental. Therefore, the objective of the present review was to clarify the double-sward effects of cholesterol and statins on PD neuropathology.

Polypathologic Associations with Gray Matter Atrophy in Neurodegenerative Disease

Mixed pathologies are common in neurodegenerative disease; however, antemortem imaging rarely captures copathologic effects on brain atrophy due to a lack of validated biomarkers for non-Alzheimer's pathologies. We leveraged a dataset comprising antemortem MRI and postmortem histopathology to assess polypathologic associations with atrophy in a clinically heterogeneous sample of 125 human dementia patients (41 female, 84 male) with T1-weighted MRI ≤ 5 years before death and postmortem ordinal ratings of amyloid-[Formula: see text], tau, TDP-43, and [Formula: see text]-synuclein. Regional volumes were related to pathology using linear mixed-effects models; approximately 25% of data were held out for testing. We contrasted a polypathologic model comprising independent factors for each proteinopathy with two alternatives: a model that attributed atrophy entirely to the protein(s) associated with the patient's primary diagnosis and a protein-agnostic model based on the sum of ordinal scores for all pathology types. Model fits were evaluated using log-likelihood and correlations between observed and fitted volume scores. Additionally, we performed exploratory analyses relating atrophy to gliosis, neuronal loss, and angiopathy. The polypathologic model provided superior fits in the training and testing datasets. Tau, TDP-43, and [Formula: see text]-synuclein burden were inversely associated with regional volumes, but amyloid-[Formula: see text] was not. Gliosis and neuronal loss explained residual variance in and mediated the effects of tau, TDP-43, and [Formula: see text]-synuclein on atrophy. Regional brain atrophy reflects not only the primary molecular pathology but also co-occurring proteinopathies; inflammatory immune responses may independently contribute to degeneration. Our findings underscore the importance of antemortem biomarkers for detecting mixed pathology.

Intruders or protectors - the multifaceted role of B cells in CNS disorders

B lymphocytes are immune cells studied predominantly in the context of peripheral humoral immune responses against pathogens. Evidence has been accumulating in recent years on the diversity of immunomodulatory functions that B cells undertake, with particular relevance for pathologies of the central nervous system (CNS). This review summarizes current knowledge on B cell populations, localization, infiltration mechanisms, and function in the CNS and associated tissues. Acute and chronic neurodegenerative pathologies are examined in order to explore the complex, and sometimes conflicting, effects that B cells can have in each context, with implications for disease progression and treatment outcomes. Additional factors such as aging modulate the proportions and function of B cell subpopulations over time and are also discussed in the context of neuroinflammatory response and disease susceptibility. A better understanding of the multifactorial role of B cell populations in the CNS may ultimately lead to innovative therapeutic strategies for a variety of neurological conditions.

Clinical biomarkers for Lewy body diseases

Synucleinopathies are a group of neurodegenerative disorders characterized by pathologic aggregates of neural and glial α-synuclein (α-syn) in the form of Lewy bodies (LBs), Lewy neurites, and cytoplasmic inclusions in both neurons and glia. Two major classes of synucleinopathies are LB disease and multiple system atrophy. LB diseases include Parkinson's disease (PD), PD with dementia, and dementia with LBs. All are increasing in prevalence. Effective diagnostics, disease-modifying therapies, and therapeutic monitoring are urgently needed. Diagnostics capable of differentiating LB diseases are based on signs and symptoms which might overlap. To date, no specific diagnostic test exists despite disease-specific pathologies. Diagnostics are aided by brain imaging and cerebrospinal fluid evaluations, but more accessible biomarkers remain in need. Mechanisms of α-syn evolution to pathologic oligomers and insoluble fibrils can provide one of a spectrum of biomarkers to link complex neural pathways to effective therapies. With these in mind, we review promising biomarkers linked to effective disease-modifying interventions.

Ferroptosis-Related Immune Genes in Hematological Diagnosis of Parkinson's Diseases

Emerging evidence suggested that ferroptosis and immune activation, as well as their interactions, played a crucial role in the occurrence and progression of Parkinson's disease (PD). However, whether this interaction could serve as the basis for a hematological diagnosis of PD remained poorly understood. This study aimed to construct a novel hematological model for PD diagnosis based on the ferroptosis-related immune genes. The brain imaging of PD patients was obtained from the Affiliated Hospital of Nantong University. We used least absolute shrinkage and selection operator (LASSO) to identify the optimal signature ferroptosis-related immune genes based on six gene expression profile datasets of substantia nigra (SN) and peripheral blood of PD patients. Then we used the support vector machine (SVM) classifier to construct the hematological diagnostic model named Ferr.Sig for PD. Gene set enrichment analysis was utilized to execute gene functional annotation. The brain imaging and functional annotation analysis revealed prominent iron deposition and immune activation in the SN region of PD patients. We identified a total of 17 signature ferroptosis-related immune genes using LASSO method and imported them to SVM classifier. The Ferr.Sig model exhibited a high diagnostic accuracy, and its area under the curve (AUC) for distinguishing PD patients from healthy controls in the training and internal validation cohort reached 0.856 and 0.704, respectively. We also used the Ferr.Sig into other external validation cohorts, and a comparable AUC with the internal cohort was obtained, with the AUC of 0.727 in Scherzer's cohort, 0.745 in Roncagli's cohort, and 0.778 in Meiklejohn's cohort. Furthermore, the diagnostic performance of Ferr.Sig was not interfered by the other neurodegenerative diseases. This study revealed the value of ferroptosis-related immune genes in PD diagnosis, which may provide a novel direction and strategy for the development of novel biomarkers with less invasiveness, low cost, and high accuracy for PD screening and diagnosis.

Alpha-synuclein fibrils amplified from multiple system atrophy and Parkinson's disease patient brain spread after intracerebral injection into mouse brain

Parkinson's disease (PD), multiple system atrophy (MSA), and dementia with Lewy bodies (DLB) are neurodegenerative disorders with alpha-synuclein (α-syn) aggregation pathology. Different strains of α-syn with unique properties are suggested to cause distinct clinical and pathological manifestations resulting in PD, MSA, or DLB. To study individual α-syn spreading patterns, we injected α-syn fibrils amplified from brain homogenates of two MSA patients and two PD patients into the brains of C57BI6/J mice. Antibody staining against pS129-α-syn showed that α-syn fibrils amplified from the brain homogenates of the four different patients caused different levels of α-syn spreading. The strongest α-syn pathology was triggered by α-syn fibrils of one of the two MSA patients, followed by comparable pS129-α-syn induction by the second MSA and one PD patient material. Histological analysis using an antibody against Iba1 further showed that the formation of pS129-α-syn is associated with increased microglia activation. In contrast, no differences in dopaminergic neuron numbers or co-localization of α-syn in oligodendrocytes were observed between the different groups. Our data support the spreading of α-syn pathology in MSA, while at the same time pointing to spreading heterogeneity between different patients potentially driven by individual patient immanent factors.

The Molecular Mechanisms of the Relationship between Insulin Resistance and Parkinson's Disease Pathogenesis

Parkinson's disease (PD) is a degenerative condition resulting from the loss of dopaminergic neurons. This neuronal loss leads to motor and non-motor neurological symptoms. Most PD cases are idiopathic, and no cure is available. Recently, it has been proposed that insulin resistance (IR) could be a central factor in PD development. IR has been associated with PD neuropathological features like α-synuclein aggregation, dopaminergic neuronal loss, neuroinflammation, mitochondrial dysfunction, and autophagy. These features are related to impaired neurological metabolism, neuronal death, and the aggravation of PD symptoms. Moreover, pharmacological options that involve insulin signaling improvement and dopaminergic and non-dopaminergic strategies have been under development. These drugs could prevent the metabolic pathways involved in neuronal damage. All these approaches could improve PD outcomes. Also, new biomarker identification may allow for an earlier PD diagnosis in high-risk individuals. This review describes the main pathways implicated in PD development involving IR. Also, it presents several therapeutic options that are directed at insulin signaling improvement and could be used in PD treatment. The understanding of IR molecular mechanisms involved in neurodegenerative development could enhance PD therapeutic options and diagnosis.

Identification of novel immune-related biomarker and therapeutic drugs in Parkinson disease via integrated bioinformatics analysis

BACKGROUND

The present study was designed to identify immune-related biomarker and candidate drugs for Parkinson disease (PD) by weighted gene co-expression network analysis.

METHODS

Differentially expressed genes were identified in PD and healthy samples in the Gene Expression Omnibus (GEO) database. Besides, immune-related genes were obtained from the immunology database. Then, a co-expression network was constructed by the weighted gene co-expression network analysis package. Diagnostic model for PD was constructed by Lasso and multivariate Cox regression. Furthermore, differentially expressed genes (DEGs) were used to establish PPI and competing endogenous RNA (ceRNA) networks. Functional enrichment and pathway analysis were performed. Drug-hub gene interaction analysis was performed via DGIdb database.

RESULTS

PD samples and normal samples were found to have 220 upregulated genes and 216 downregulated genes in the GSE6613 dataset. The differentially expressed genes contained 50 immune-related genes, with 40 upregulated genes and 10 downregulated genes. We obtained 7 hub genes by intersecting the DEGs and candidate hub genes. As potential diagnostic markers, 2 immune-related DEGs were identified among the 7 hub genes. According to functional enrichment analysis, these DEGs were mainly enriched in immune response, inflammatory response, and cytokine-cytokine receptor interactions. Totally, we obtained 182 drug-gene interaction pairs in Drug-Gene Interaction database (DGIdb).

CONCLUSION

Our results revealed crucial genes and candidate drugs for PD patients and deepen our understanding of the molecular mechanisms involved in PD.

Border-associated macrophages mediate the neuroinflammatory response in an alpha-synuclein model of Parkinson disease

Dopaminergic cell loss due to the accumulation of α-syn is a core feature of the pathogenesis of Parkinson disease. Neuroinflammation specifically induced by α-synuclein has been shown to exacerbate neurodegeneration, yet the role of central nervous system (CNS) resident macrophages in this process remains unclear. We found that a specific subset of CNS resident macrophages, border-associated macrophages (BAMs), play an essential role in mediating α-synuclein related neuroinflammation due to their unique role as the antigen presenting cells necessary to initiate a CD4 T cell response whereas the loss of MHCII antigen presentation on microglia had no effect on neuroinflammation. Furthermore, α-synuclein expression led to an expansion in border-associated macrophage numbers and a unique damage-associated activation state. Through a combinatorial approach of single-cell RNA sequencing and depletion experiments, we found that border-associated macrophages played an essential role in immune cell recruitment, infiltration, and antigen presentation. Furthermore, border-associated macrophages were identified in post-mortem PD brain in close proximity to T cells. These results point to a role for border-associated macrophages in mediating the pathogenesis of Parkinson disease through their role in the orchestration of the α-synuclein-mediated neuroinflammatory response.

deCLUTTER2+ - a pipeline to analyze calcium traces in a stem cell model for ventral midbrain patterned astrocytes

Astrocytes are the most populous cell type of the human central nervous system and are essential for physiological brain function. Increasing evidence suggests multiple roles for astrocytes in Parkinson's disease, nudging a shift in the research focus, which historically pivoted around ventral midbrain dopaminergic neurons (vmDANs). Studying human astrocytes and other cell types in vivo remains challenging. However, in vitro-reprogrammed human stem cell-based models provide a promising alternative. Here, we describe a novel protocol for astrocyte differentiation from human stem cell-derived vmDAN-generating progenitors. This protocol simulates the regionalization, gliogenic switch, radial migration and final differentiation that occur in the developing human brain. We characterized the morphological, molecular and functional features of these ventral midbrain patterned astrocytes with a broad palette of techniques and identified novel candidate midbrain-astrocyte specific markers. In addition, we developed a new pipeline for calcium imaging data analysis called deCLUTTER2+ (deconvolution of Ca2+ fluorescent patterns) that can be used to discover spontaneous or cue-dependent patterns of Ca2+ transients. Altogether, our protocol enables the characterization of the functional properties of human ventral midbrain patterned astrocytes under physiological conditions and in disease.

Impact of Sex on Neuroimmune contributions to Parkinson's disease

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

The Impact of microRNAs on Mitochondrial Function and Immunity: Relevance to Parkinson's Disease

Parkinson's Disease (PD), the second most common neurodegenerative disorder, is characterised by the severe loss of dopaminergic neurons in the Substantia Nigra pars compacta (SNpc) and by the presence of Lewy bodies. PD is diagnosed upon the onset of motor symptoms, such as bradykinesia, resting tremor, rigidity, and postural instability. It is currently accepted that motor symptoms are preceded by non-motor features, such as gastrointestinal dysfunction. In fact, it has been proposed that PD might start in the gut and spread to the central nervous system. Growing evidence reports that the gut microbiota, which has been found to be altered in PD patients, influences the function of the central and enteric nervous systems. Altered expression of microRNAs (miRNAs) in PD patients has also been reported, many of which regulate key pathological mechanisms involved in PD pathogenesis, such as mitochondrial dysfunction and immunity. It remains unknown how gut microbiota regulates brain function; however, miRNAs have been highlighted as important players. Remarkably, numerous studies have depicted the ability of miRNAs to modulate and be regulated by the host's gut microbiota. In this review, we summarize the experimental and clinical studies implicating mitochondrial dysfunction and immunity in PD. Moreover, we gather recent data on miRNA involvement in these two processes. Ultimately, we discuss the reciprocal crosstalk between gut microbiota and miRNAs. Studying the bidirectional interaction of gut microbiome-miRNA might elucidate the aetiology and pathogenesis of gut-first PD, which could lead to the application of miRNAs as potential biomarkers or therapeutical targets for PD.

Application value of peripheral blood IgG and IgM combined with ultrasonic echo parameters of substantia nigra in the diagnosis of Parkinson's disease

We study the clinical value of peripheral blood immunoglobulin G (IgG) and immunoglobulin M (IgM) combined with ultrasonic echo parameters of substantia nigra (SN) in the diagnosis of Parkinson's disease (PD). The clinical data of 121 patients with PD (case group) in our hospital from November 2020 to November 2022 were selected for retrospective analysis, and 9 patients with poor sound transmission of temporal window were excluded. Finally, this study included 112 patients with PD and selected 108 health examination population in the same period (control group). The levels of IgG and IgM in both groups were detected, and ultrasound examination was carried out to observe the structure of SN and obtain strong echo area of SN, midbrain area and strong echo area of SN/midbrain area. The receiver operator characteristic curve of serum IgG and IgM combined with ultrasonic echo parameters of SN in the diagnosis of PD was drawn to evaluate the clinical efficacy of single diagnosis and combined diagnosis. Compared with the control group, the serum levels of IgG and IgM, strong echo area of SN, midbrain area and strong echo area of SN/midbrain area in the case group were obviously higher (P < 0.001), while the folic acid level was notably lower (P < 0.05). The AUC value, Youden index and sensitivity of combined diagnosis were higher than those of single detection. Peripheral blood IgG and IgM combined with ultrasonic echo parameters of SN have high clinical value in the diagnosis of PD, which can provide a new direction for the subsequent diagnosis of PD.

Opposing effects of β-2 and β-1 adrenergic receptor signaling on neuroinflammation and dopaminergic neuron survival in α-synuclein-mediated neurotoxicity

BACKGROUND

Noradrenergic neurons in the locus coeruleus (LC) are the primary source of norepinephrine (NE) in the brain and degeneration of these neurons is reported in the early stages of Parkinson's disease (PD), even prior to dopaminergic neuron degeneration in the substantia nigra (SN), which is a hallmark of PD pathology. NE depletion is generally associated with increased PD pathology in neurotoxin-based PD models. The effect of NE depletion in other models of PD-like α-synuclein-based models is largely unexplored. In PD models and in human patients, β-adrenergic receptors' (AR) signaling is associated with a reduction of neuroinflammation and PD pathology. However, the effect of NE depletion in the brain and the extent of NE and β-ARs signaling involvement in neuroinflammation, and dopaminergic neuron survival is poorly understood.

METHODS

Two mouse models of PD, a 6OHDA neurotoxin-based model and a human α-synuclein (hα-SYN) virus-based model of PD, were used. DSP-4 was used to deplete NE levels in the brain and its effect was confirmed by HPLC with electrochemical detection. A pharmacological approach was used to mechanistically understand the impact of DSP-4 in the hα-SYN model of PD using a norepinephrine transporter (NET) and a β-AR blocker. Epifluorescence and confocal imaging were used to study changes in microglia activation and T-cell infiltration after β1-AR and β2-AR agonist treatment in the hα-SYN virus-based model of PD.

RESULTS

Consistent with previous studies, we found that DSP-4 pretreatment increased dopaminergic neuron loss after 6OHDA injection. In contrast, DSP-4 pretreatment protected dopaminergic neurons after hα-SYN overexpression. DSP-4-mediated protection of dopaminergic neurons after hα-SYN overexpression was dependent on β-AR signaling since using a β-AR blocker prevented DSP-4-mediated dopaminergic neuron protection in this model of PD. Finally, we found that the β-2AR agonist, clenbuterol, reduced microglia activation, T-cell infiltration, and dopaminergic neuron degeneration, whereas xamoterol a β-1AR agonist showed increased neuroinflammation, blood brain barrier permeability (BBB), and dopaminergic neuron degeneration in the context of hα-SYN-mediated neurotoxicity.

CONCLUSIONS

Our data demonstrate that the effects of DSP-4 on dopaminergic neuron degeneration are model specific, and suggest that in the context of α-SYN-driven neuropathology, β2-AR specific agonists may have therapeutic benefit in PD.

Microglia and astrocyte activation is region-dependent in the α-synuclein mouse model of Parkinson's disease

Inflammation is a common feature in neurodegenerative diseases that contributes to neuronal loss. Previously, we demonstrated that the basal inflammatory tone differed between brain regions and, consequently, the reaction generated to a pro-inflammatory stimulus was different. In this study, we assessed the innate immune reaction in the midbrain and in the striatum using an experimental model of Parkinson's disease. An adeno-associated virus serotype 9 expressing the α-synuclein and mCherry genes or the mCherry gene was administered into the substantia nigra. Myeloid cells (CD11b⁺ ) and astrocytes (ACSA2⁺ ) were purified from the midbrain and striatum for bulk RNA sequencing. In the parkinsonian midbrain, CD11b⁺ cells presented a unique anti-inflammatory transcriptomic profile that differed from degenerative microglia signatures described in experimental models for other neurodegenerative conditions. By contrast, striatal CD11b⁺ cells showed a pro-inflammatory state and were similar to disease-associated microglia. In the midbrain, a prominent increase of infiltrated monocytes/macrophages was observed and, together with microglia, participated actively in the phagocytosis of dopaminergic neuronal bodies. Although striatal microglia presented a phagocytic transcriptomic profile, morphology and cell density was preserved and no active phagocytosis was detected. Interestingly, astrocytes presented a pro-inflammatory fingerprint in the midbrain and a low number of differentially displayed transcripts in the striatum. During α-synuclein-dependent degeneration, microglia and astrocytes experience context-dependent activation states with a different contribution to the inflammatory reaction. Our results point towards the relevance of selecting appropriate cell targets to design neuroprotective strategies aimed to modulate the innate immune system during the active phase of dopaminergic degeneration.

Disease mechanisms as subtypes: Inflammation in Parkinson disease and related disorders

Neuroinflammation is a core feature of Parkinson disease (PD) and related disorders. Inflammation is detectable early in PD and persists throughout the disease state. Both the innate and the adaptive arms of the immune system are engaged in both human PD as well as in animal models of the disease. The upstream causes of PD are likely multiple and complex, which makes targeting of disease-modifying therapies based on etiological factors difficult. Inflammation is a broadly shared common mechanism and likely makes an important contribution to progression in most patients with manifest symptoms. Development of treatments targeting neuroinflammation in PD will require an understanding of the specific immune mechanisms which are active, their relative effects on both injury and neurorestoration, as well as the role of key variables likely to modulate the immune response: age, sex, the nature of the proteinopathies present, and the presence of copathologies. Studies characterizing the specific state of immune response in individuals and groups of people affected by PD will be essential to the development of targeted disease-modifying immunotherapies.

α-Synuclein induces Th17 differentiation and impairs the function and stability of Tregs by promoting RORC transcription in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons (DA) and the accumulation of Lewy body deposits composed of alpha-Synuclein (α-Syn), which act as antigenic epitopes to drive cytotoxic T-cell responses in PD. Increased T helper 17 (Th17) cells and dysfunctional regulatory T cells (Tregs) have been reported to be associated with the loss of DA in PD. However, the mechanism underlying the Th17/Treg imbalance remains unknown.

METHODS

Here, we examined the percentage of Th17 cells, the percentage of Tregs and the α-Syn level and analysed their correlations in the peripheral blood of PD patients and in the substantia nigra pars compacta (SNpc) and spleen of MPTP-treated mice and A53 transgenic mice. We assessed the effect of α-Syn on the stability and function of Tregs and the differentiation of Th17 cells and evaluated the role of retinoid-related orphan nuclear receptor (RORγt) upregulation in α-Syn stimulation in vivo and in vitro.

RESULTS

We found that the α-Syn level and severity of motor symptoms were positively correlated with the increase in Th17 cells and decrease in Tregs in PD patients. Moreover, α-Syn stimulation led to the loss of Forkhead box protein P3 (FOXP3) expression in Tregs, accompanied by the acquisition of IL-17A expression. Increased Th17 differentiation was detected upon α-Syn stimulation when naïve CD4⁺ T cells were cultured under Th17-polarizing conditions. Mechanistically, α-Syn promotes the transcription of RORC, encoding RORγt, in Tregs and Th17 cells, leading to increased Th17 differentiation and loss of Treg function. Intriguingly, the increase in Th17 cells, decrease in Tregs and apoptosis of DA were suppressed by a RORγt inhibitor (GSK805) in MPTP-treated mice.

CONCLUSION

Together, our data suggest that α-Syn promotes the transcription of RORC in circulating CD4⁺ T cells, including Tregs and Th17 cells, to impair the stability of Tregs and promote the differentiation of Th17 cells in PD. Inhibition of RORγt attenuated the apoptosis of DA and alleviated the increase in Th17 cells and decrease in Tregs in PD.

Lumateperone Normalizes Pathological Levels of Acute Inflammation through Important Pathways Known to Be Involved in Mood Regulation

Lumateperone is indicated for the treatment of schizophrenia in adults and for depressive episodes associated with bipolar I or II disorder (bipolar depression) in adults, as monotherapy and as adjunctive therapy with lithium or valproate (Calabrese et al., 2021). It is currently under evaluation for the treatment of major depressive disorder (www.ClinicalTrials.gov). Lumateperone acts by selectively modulating serotonin, dopamine, and glutamate neurotransmission in the brain. However, other mechanisms could be involved in the actions of lumateperone, and because of the connection between the immune system and psychiatric health, we hypothesized that lumateperone might improve symptoms of depression, at least in part, by normalizing pathologic inflammation. Here, we show that in male and female C57BL/6 mice subjected to an acute immune challenge, lumateperone reduced aberrantly elevated levels of key proinflammatory cytokines (e.g., IL-1β, IL-6, and TNF-α) in both brain and serum; lumateperone also reduced proinflammatory cytokines in male mice under acute behavioral stress. Further, we demonstrate that lumateperone altered key genes/pathways involved in maintaining tissue integrity and supporting blood-brain barrier function, such as claudin-5 and intercellular adhesion molecule 1. In addition, in acutely stressed male Sprague Dawley rats, lumateperone conferred anxiolytic- and antianhedonic-like properties while enhancing activity in the mammalian target of rapamycin complex 1 pathway in the PFC. Together, our preclinical findings indicate that lumateperone, in addition to its ability to modulate multiple neurotransmitter systems, could also act by reducing the impact of acute inflammatory challenges.SIGNIFICANCE STATEMENT Lumateperone is indicated in adults to treat schizophrenia and depressive episodes associated with bipolar I or II disorder, as monotherapy and adjunctive therapy with lithium or valproate. Because aberrant immune system activity is associated with increased depressive symptoms, the relationship between lumateperone and immune function was studied. Here, lumateperone reduced the levels of proinflammatory cytokines that were increased following an immune challenge or stress in mice. Additionally, lumateperone altered genes and pathways that maintain blood-brain barrier integrity, restored an index of blood-brain barrier function, reduced anxiety-like behavior in rodents, and enhanced mammalian target of rapamycin complex 1 pathway signaling in the PFC. These results highlight the anti-inflammatory actions of lumateperone and describe how lumateperone may reduce immune pathophysiology, which is associated with depressive symptoms.

Unaltered T cell responses to common antigens in individuals with Parkinson's disease

BACKGROUND AND OBJECTIVES

Parkinson's disease (PD) is associated with a heightened inflammatory state, including activated T cells. However, it is unclear whether these PD T cell responses are antigen specific or more indicative of generalized hyperresponsiveness. Our objective was to measure and compare antigen-specific T cell responses directed towards antigens derived from commonly encountered human pathogens/vaccines in patients with PD and age-matched healthy controls (HC).

METHODS

Peripheral blood mononuclear cells (PBMCs) from 20 PD patients and 19 age-matched HCs were screened. Antigen specific T cell responses were measured by flow cytometry using a combination of the activation induced marker (AIM) assay and intracellular cytokine staining.

RESULTS

Here we show that both PD patients and HCs show similar T cell activation levels to several antigens derived from commonly encountered human pathogens/vaccines in the general population. Similarly, we also observed no difference between HC and PD in the levels of CD4 and CD8 T cell derived cytokines produced in response to any of the common antigens tested. These antigens encompassed both viral (coronavirus, rhinovirus, respiratory syncytial virus, influenza, cytomegalovirus) and bacterial (pertussis, tetanus) targets.

CONCLUSIONS

These results suggest the T cell dysfunction observed in PD may not extend itself to abnormal responses to commonly encountered or vaccine-target antigens. Our study supports the notion that the targets of inflammatory T cell responses in PD may be more directed towards autoantigens like α-synuclein (α-syn) rather than common foreign antigens.

Parkinson's Disease, It Takes Guts: The Correlation between Intestinal Microbiome and Cytokine Network with Neurodegeneration

Parkinson's disease is a progressive neurodegenerative disorder with motor, physical and behavioral symptoms that can have a profound impact on the patient's quality of life. Most cases are idiopathic, and the exact mechanism of the disease's cause is unknown. The current hypothesis focuses on the gut-brain axis and states that gut microbiota dysbiosis can trigger inflammation and advances the development of Parkinson's disease. This systematic review presents the current knowledge of gut microbiota analysis and inflammation based on selected studies on Parkinson's patients and experimental animal models. Changes in gut microbiota correlate with Parkinson's disease, but only a few studies have considered inflammatory modulators as important triggers of the disease. Nevertheless, it is evident that proinflammatory cytokines and chemokines are induced in the gut, the circulation, and the brain before the development of the disease's neurological symptoms and exacerbate the disease. Increased levels of tumor necrosis factor, interleukin-1β, interleukin-6, interleukin-17A and interferon-γ can correlate with altered gut microbiota. Instead, treatment of gut dysbiosis is accompanied by reduced levels of inflammatory mediators in specific tissues, such as the colon, brain and serum and/or cerebrospinal fluid. Deciphering the role of the immune responses and the mechanisms of the PD-associated gut microbiota will assist the interpretation of the pathogenesis of Parkinson's and will elucidate appropriate therapeutic strategies.

Transcriptome Analysis Reveals a Two-Gene Signature Links to Motor Progression and Alterations of Immune Cells in Parkinson's Disease

BACKGROUND

The motor impairment in Parkinson's disease (PD) can be managed but effective treatments for stopping or slowing the disease process are lacking. The advent of transcriptomics studies in PD shed light on the development of promising measures to predict disease progression and discover novel therapeutic strategies.

OBJECTIVE

To reveal the potential role of transcripts in the motor impairment progression of patients with PD via transcriptome analysis.

METHODS

We separately analyzed the differentially expressed genes (DEGs) between PD cases and healthy controls in two cohorts using whole blood bulk transcriptome data. Based on the intersection of DEGs, we established a prognostic signature by regularized regression and Cox proportional hazards analysis. We further performed immune cell analysis and single-cell RNA sequencing analysis to study the biological features of this signature.

RESULTS

We identified a two-gene-based prognostic signature that links to PD motor progression and the two-gene signature-derived risk score was associated with several types of immune cells in blood. Notably, the fraction of neutrophils increased 5% and CD4+ T cells decreased 7% in patients with high-risk scores compared to that in patients with low-risk scores, suggesting these two types of immune cells might play key roles in the prognosis of PD. We also observed the downregulated genes in PD patients with high-risk scores that enriched in PD-associated pathways from iPSC-derived dopaminergic neurons single-cell RNA sequencing analysis.

CONCLUSION

We identified a two-gene signature linked to the motor progression in PD, which provides new insights into the motor prognosis of PD.

Metagenomics of Parkinson's disease implicates the gut microbiome in multiple disease mechanisms

Parkinson's disease (PD) may start in the gut and spread to the brain. To investigate the role of gut microbiome, we conducted a large-scale study, at high taxonomic resolution, using uniform standardized methods from start to end. We enrolled 490 PD and 234 control individuals, conducted deep shotgun sequencing of fecal DNA, followed by metagenome-wide association studies requiring significance by two methods (ANCOM-BC and MaAsLin2) to declare disease association, network analysis to identify polymicrobial clusters, and functional profiling. Here we show that over 30% of species, genes and pathways tested have altered abundances in PD, depicting a widespread dysbiosis. PD-associated species form polymicrobial clusters that grow or shrink together, and some compete. PD microbiome is disease permissive, evidenced by overabundance of pathogens and immunogenic components, dysregulated neuroactive signaling, preponderance of molecules that induce alpha-synuclein pathology, and over-production of toxicants; with the reduction in anti-inflammatory and neuroprotective factors limiting the capacity to recover. We validate, in human PD, findings that were observed in experimental models; reconcile and resolve human PD microbiome literature; and provide a broad foundation with a wealth of concrete testable hypotheses to discern the role of the gut microbiome in PD.

Neuro faces of beneficial T cells: essential in brain, impaired in aging and neurological diseases, and activated functionally by neurotransmitters and neuropeptides

T cells are essential for a healthy life, performing continuously: immune surveillance, recognition, protection, activation, suppression, assistance, eradication, secretion, adhesion, migration, homing, communications, and additional tasks. This paper describes five aspects of normal beneficial T cells in the healthy or diseased brain. First, normal beneficial T cells are essential for normal healthy brain functions: cognition, spatial learning, memory, adult neurogenesis, and neuroprotection. T cells decrease secondary neuronal degeneration, increase neuronal survival after central nervous system (CNS) injury, and limit CNS inflammation and damage upon injury and infection. Second, while pathogenic T cells contribute to CNS disorders, recent studies, mostly in animal models, show that specific subpopulations of normal beneficial T cells have protective and regenerative effects in several neuroinflammatory and neurodegenerative diseases. These include Multiple Sclerosis (MS), Alzheimer's disease, Parkinson's disease, Amyotrophic Lateral Sclerosis (ALS), stroke, CNS trauma, chronic pain, and others. Both T cell-secreted molecules and direct cell-cell contacts deliver T cell neuroprotective, neuroregenerative and immunomodulatory effects. Third, normal beneficial T cells are abnormal, impaired, and dysfunctional in aging and multiple neurological diseases. Different T cell impairments are evident in aging, brain tumors (mainly Glioblastoma), severe viral infections (including COVID-19), chronic stress, major depression, schizophrenia, Parkinson's disease, Alzheimer's disease, ALS, MS, stroke, and other neuro-pathologies. The main detrimental mechanisms that impair T cell function are activation-induced cell death, exhaustion, senescence, and impaired T cell stemness. Fourth, several physiological neurotransmitters and neuropeptides induce by themselves multiple direct, potent, beneficial, and therapeutically-relevant effects on normal human T cells, via their receptors in T cells. This scientific field is called "Nerve-Driven Immunity". The main neurotransmitters and neuropeptides that induce directly activating and beneficial effects on naïve normal human T cells are: dopamine, glutamate, GnRH-II, neuropeptide Y, calcitonin gene-related peptide, and somatostatin. Fifth, "Personalized Adoptive Neuro-Immunotherapy". This is a novel unique cellular immunotherapy, based on the "Nerve-Driven Immunity" findings, which was recently designed and patented for safe and repeated rejuvenation, activation, and improvement of impaired and dysfunctional T cells of any person in need, by ex vivo exposure of the person's T cells to neurotransmitters and neuropeptides. Personalized adoptive neuro-immunotherapy includes an early ex vivo personalized diagnosis, and subsequent ex vivo → in vivo personalized adoptive therapy, tailored according to the diagnosis. The Personalized Adoptive Neuro-Immunotherapy has not yet been tested in humans, pending validation of safety and efficacy in clinical trials, especially in brain tumors, chronic infectious diseases, and aging, in which T cells are exhausted and/or senescent and dysfunctional.

Central and Peripheral Inflammation: Connecting the Immune Responses of Parkinson’s Disease

Inflammation has increasingly become a focus of study in regards to Parkinson’s disease (PD). Moreover, both central and peripheral sources of inflammation have been implicated in the pathogenesis of PD. Central inflammation consisting of activated microglia, astroglia, and T cell responses within the PD central nervous system; and peripheral inflammation referring to activated innate cells and T cell signaling in the enteric nervous system, gastrointestinal tract, and blood. This review will highlight important work that further implicates central and peripheral inflammation in playing a role in PD. We also discuss how these two distant inflammations appear related and how that may be mediated by autoantigenic responses to α-syn.

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

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

Identification and validation of key molecules associated with humoral immune modulation in Parkinson’s disease based on bioinformatics

Objective

Parkinson’s disease (PD) is the most common neurodegenerative movement disorder and immune-mediated mechanism is considered to be crucial to pathogenesis. Here, we investigated the role of humoral immune regulatory molecules in the pathogenesis of PD.

Methods

Firstly, we performed a series of bioinformatic analyses utilizing the expression profile of the peripheral blood mononuclear cell (PBMC) obtained from the GEO database (GSE100054, GSE49126, and GSE22491) to identify differentially expressed genes related to humoral immune regulatory mechanisms between PD and healthy controls. Subsequently, we verified the results using quantitative polymerase chain reaction (Q-PCR) and enzyme-linked immunosorbent assay (ELISA) in clinical blood specimen. Lastly, receiver operating characteristic (ROC) curve analysis was performed to determine the diagnostic effects of verified molecules.

Results

We obtained 13 genes that were mainly associated with immune-related biological processes in PD using bioinformatic analysis. Then, we selected PPBP, PROS1, and LCN2 for further exploration. Fascinatingly, our experimental results don’t always coincide with the expression profile. PROS1 and LCN2 plasma levels were significantly higher in PD patients compared to controls (p < 0.01 and p < 0.0001). However, the PPBP plasma level and expression in the PBMC of PD patients was significantly decreased compared to controls (p < 0.01 and p < 0.01). We found that PPBP, PROS1, and LCN2 had an area under the curve (AUC) of 0.663 (95%CI: 0.551–0.776), 0.674 (95%CI: 0.569–0.780), and 0.885 (95%CI: 0.814–0.955). Furthermore, in the biological process analysis of gene ontology (GO), the three molecules were all involved in humoral immune response (GO:0006959).

Conclusions

In general, PPBP, PROS1, and LCN2 were identified and validated to be related to PD and PPBP, LCN2 may potentially be biomarkers or therapeutic targets for PD. Our findings also provide some new insights on the humoral immune modulation mechanisms in PD.

What to Test in Parkinson Disease Prevention Trials? Repurposed, Low-Risk, and Gene-Targeted Drugs

Despite the sound epidemiologic and basic science rationales underpinning numerous "disease modification" trials in manifest Parkinson disease (PD), none has convincingly demonstrated that a treatment slows progression. Rapidly expanding knowledge of the genetic determinants and prodromal features of PD now allows realistic planning of prevention trials with initiation of putatively neuroprotective therapies earlier in the disease. In this article, we outline the principles of drug selection for PD prevention trials, focused on proof-of-concept opportunities that will help establish a methodological foundation for this fledgling field. We describe prototypical, relatively low-risk drug candidates for such trials (e.g., albuterol, ambroxol, caffeine, ibuprofen), tailored to specific at-risk populations ranging from pathogenic LRRK2 or GBA gene variant carriers to those defined by prodromal PD and α-synucleinopathy. Finally, we review gene-targeted approaches currently in development targeting clinically manifest PD for their potential in future prevention trials.

The many genomes of Parkinson's disease

Genetic component of Parkinson's disease, once firmly believed non-existent, involves the human genome, mitochondrial genome, and the microbiome. Understanding the genomics of PD requires identification of PD-relevant genes and learning how they interact within the hologenome and with their environment. This chapter is an evidence-based perspective of a geneticist on how far we have come in this endeavor. The contemporary scientific society started with a naive and simplistic view of PD, evolved to accept that Parkinson's disease is probably the most complex disease there is, the progress we have made in discovering the genes and elucidating their functions, and now assembling the parts to create the whole.

COVID-19 and Parkinson's Disease: Possible Links in Pathology and Therapeutics

The outbreak of SARs-CoV-2 with emerging new variants is leading to global health crisis and has brought a major concern for patients with comorbidities. Parkinson's disease (PD) is a motor neurodegenerative disease involving various metabolic and psychological ailments along with the common occurrence of hyposmia as observed in COVID-19 patients. In addition, the observed surplus inflammatory responses in both diseases are also alarming. Alongside, angiotensin-converting enzyme 2 (ACE2) receptor, essentially required by SARS-CoV-2 to enter the cell and dopamine decarboxylase (DDC), required for dopamine synthesis is known to co-regulate in the non-neuronal cells. Taken together, these conditions suggested the probable reciprocal pathological relation between COVID-19 and PD and also suggested that during comorbidities, the disease diagnosis and therapeutics are critical and may engender severe health complications. In this review, we discuss various events and mechanisms which may have implications for the exacerbation of PD conditions and must be taken into account during the treatment of patients.

Will Sirtuin 2 Be a Promising Target for Neuroinflammatory Disorders?

Neuroinflammatory disorder is a general term that is associated with the progressive loss of neuronal structure or function. At present, the widely studied diseases with neuroinflammatory components are mainly divided into neurodegenerative and neuropsychiatric diseases, namely, Alzheimer’s disease, Parkinson’s disease, depression, stroke, and so on. An appropriate neuroinflammatory response can promote brain homeostasis, while excessive neuroinflammation can inhibit neuronal regeneration and damage the central nervous system. Apart from the symptomatic treatment with cholinesterase inhibitors, antidepressants/anxiolytics, and neuroprotective drugs, the treatment of neuroinflammation is a promising therapeutic method. Sirtuins are a host of class III histone deacetylases, that require nicotinamide adenine dinucleotide for their lysine residue deacetylase activity. The role of sirtuin 2 (SIRT2), one of the sirtuins, in modulating senescence, myelin formation, autophagy, and inflammation has been widely studied. SIRT2 is associated with many neuroinflammatory disorders considering it has deacetylation properties, that regulate the entire immune homeostasis. The aim of this review was to summarize the latest progress in regulating the effects of SIRT2 on immune homeostasis in neuroinflammatory disorders. The overall structure and catalytic properties of SIRT2, the selective inhibitors of SIRT2, the relationship between immune homeostasis and SIRT2, and the multitasking role of SIRT2 in several diseases with neuroinflammatory components were discussed.

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

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

Calpain activation and progression of inflammatory cycles in Parkinson's disease

Parkinson's disease (PD) is a progressive, neurodegenerative condition of the central nervous system (CNS) affecting 6.3 million people worldwide with no curative treatments. Current therapies aim to mitigate PD's effects and offer symptomatic relief for patients. Multiple pathways are involved in the pathogenesis of PD, leading to neuroinflammation and the destruction of dopaminergic neurons in the CNS. This review focuses on PD pathology and the role of calpain, a neutral protease, as a regulator of various immune cells such as T-cells, microglia and astrocytes which lead to persistent neuroinflammatory responses and neuronal loss in both the brain and spinal cord (SC). Calpain plays a significant role in the cleavage and aggregation of toxic α-synuclein (α-syn), a presynaptic neural protein, and other organelles, contributing to mitochondrial dysfunction and oxidative stress. α-Syn aggregation results in the formation of Lewy bodies (LB) that further contribute to neuronal damage through lipid bilayer penetration, calcium ion (Ca2+) influx, oxidative stress and damage to the blood brain barrier (BBB). Dysfunctional mitochondria destabilize cytosolic Ca2+ concentrations, raising intracellular Ca2+; this leads to excessive calpain activation and persistent inflammatory responses. α-Syn aggregation also results in the disruption of dopamine synthesis through phosphorylation of tyrosine hydroxylase (TH), a key enzyme involved in the conversion of tyrosine to levodopa (L-DOPA), the amino acid precursor to dopamine. Decreased dopamine levels result in altered dopamine receptor (DR) signaling, ultimately activating pro-inflammatory T-cells to further contribute to the inflammatory response. All of these processes, together, result in neuroinflammation, degeneration and ultimately neuronal death seen in PD. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP-a prodrug to the neurotoxin 1-methyl-4-phenylpyridinium (MPP+)), rotenone (an environmental neurotoxin), and 6-hydroxydopamine (6-OHDA - a neurotoxic synthetic organic compound) induce PD-like conditions when injected into rodents. All three agents work through similar mechanisms and lead to degeneration of dopaminergic neurons in the substantia nigra (SN) and more recently discovered in motor neurons of the spinal cord (SC). These neurotoxins also increase calpain activity, furthering the neuroinflammatory response. Hence, calpain inhibitors have been posited as potential therapeutics for PD to prevent calpain-related inflammation and neurodegenerative responses in not only the SN but the SC as well.

Alpha-Synuclein Induced Immune Cells Activation and Associated Therapy in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder closely related to immunity. An important aspect of the pathogenesis of PD is the interaction between α-synuclein and a series of immune cells. Studies have shown that accumulation of α-synuclein can induce an autoimmune response that accelerates the progression of PD. This study discusses the mechanisms underlying the interaction between α-synuclein and the immune system. During the development of PD, abnormally accumulated α-synuclein becomes an autoimmune antigen that binds to Toll-like receptors (TLRs) that activate microglia, which differentiate into the microglia type 1 (M1) subtype. The microglia activate intracellular inflammatory pathways, induce the release of proinflammatory cytokines, and promote the differentiation of cluster of differentiation 4 + (CD4 +) T cells into proinflammatory T helper type 1 (Th1) and T helper type 17 (Th17) subtypes. Given the important role of α-synuclein in the immune system of the patients with PD, identifying potential targets of immunotherapy related to α-synuclein is critical for slowing disease progression. An enhanced understanding of immune-associated mechanisms in PD can guide the development of associated therapeutic strategies in the future.

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.

T-cell dysregulation is associated with disease severity in Parkinson's Disease

The dysregulation of peripheral immunity in Parkinson’s Disease (PD) includes changes in both the relative numbers and gene expression of T cells. The presence of peripheral T-cell abnormalities in PD is well-documented, but less is known about their association to clinical parameters, such as age, age of onset, progression rate or severity of the disease. We took a detailed look at T-cell numbers, gene expression and activation in cross-sectional cohorts of PD patients and age-matched healthy controls by means of flow cytometry and NanoString gene expression assay. We show that the well-pronounced decrease in relative T-cell numbers in PD blood is mostly driven by a decrease of CD8⁺ cytotoxic T cells and is primarily associated with the severity of the disease. In addition, we demonstrate that the expression of inflammatory genes in T cells from PD patients is also associated with disease severity. PD T cells presented with increased activation upon stimulation with phytohemagglutinin that also correlated with disease severity. In summary, our data suggest that the consequences of disease severity account for the changes in PD T cells, rather than age, age of onset, duration or the disease progression rate.

Association of ATG5 gene polymorphism with Parkinson's disease in a Han Chinese population

Purpose

There is growing evidence that autophagy-related gene 5 (ATG5) is involved in neural development, neuronal differentiation, and neurodegenerative diseases. The purpose of this study was to investigate the association between ATG5 gene single-nucleotide polymorphisms (SNPs) and Parkinson’s disease (PD) in the Han population.

Methods

A case–control study was conducted in 120 PD patients and 100 healthy volunteers. MassArray platform was used to analyze polymorphisms in three different regions of ATG5 gene (rs510432, rs573775 and rs17587319). In the included subjects, 50 PD patients and 50 healthy volunteers were selected, and the plasma ATG5 concentration was detected by enzyme-linked immunosorbent assay (ELISA). The allele and genotype frequencies of SNPs were assessed using the SHEsis program.

Results

We found a significant correlation between rs17587319 and PD, and the subcomponent showed a high correlation between rs17587319 with cognitive impairment and age at onset in PD patients. At the same time, the total plasma ATG5 level of PD patients and the plasma ATG5 expression level of early-onset Parkinson’s disease (EOPD) patients were significantly higher than the control group, while there was no significant difference of ATG5 expression between late-onset Parkinson’s disease (LOPD) patients and the control group.

Conclusion

These findings suggest that genetic variations in the ATG5 gene and low levels of the ATG5 protein are associated with susceptibility to PD and with cognitive impairment in PD patients. ATG5 could be a potential biomarker to assess the severity and prognosis of PD.

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.

Exploring human-genome gut-microbiome interaction in Parkinson's disease

The causes of complex diseases remain an enigma despite decades of epidemiologic research on environmental risks and genome-wide studies that have uncovered tens or hundreds of susceptibility loci for each disease. We hypothesize that the microbiome is the missing link. Genetic studies have shown that overexpression of alpha-synuclein, a key pathological protein in Parkinson’s disease (PD), can cause familial PD and variants at alpha-synuclein locus confer risk of idiopathic PD. Recently, dysbiosis of gut microbiome in PD was identified: altered abundances of three microbial clusters were found, one of which was composed of opportunistic pathogens. Using two large datasets, we found evidence that the overabundance of opportunistic pathogens in PD gut is influenced by the host genotype at the alpha-synuclein locus, and that the variants responsible modulate alpha-synuclein expression. Results put forth testable hypotheses on the role of gut microbiome in the pathogenesis of PD, the incomplete penetrance of PD susceptibility genes, and potential triggers of pathology in the gut.

Dysregulation of the Adaptive Immune System in Patients With Early-Stage Parkinson Disease

Objective

To determine the activation status and cytokine profiles of CD4⁺ T cells, CD8⁺ T cells, and CD19⁺ B cells from patients with early-stage Parkinson disease (PD) compared with healthy controls (HCs).

Methods

Peripheral blood samples from 41 patients with early-stage PD and 40 HCs were evaluated. Peripheral blood mononuclear cells were analyzed by flow cytometry for surface markers and intracellular cytokine production. Correlations of immunologic changes and clinical parameters were analyzed.

Results

Adaptive immunity plays a role in the pathogenesis of PD, yet the contribution of T cells and B cells, especially cytokine production by these cells, is poorly understood. We demonstrate that naive CD4⁺ and naive CD8⁺ T cells are significantly decreased in patients with PD, whereas central memory CD4⁺ T cells are significantly increased in patients with PD. Furthermore, IL-17–producing CD4⁺ Th17 cells, IL-4–producing CD4⁺ Th2 cells, and IFN-γ–producing CD8⁺ T cells are significantly increased in patients with PD. Regarding B cells, we observed a decrease in naive B cells and an increase in nonswitched memory and double-negative B cells. As well, TNF-α–producing CD19⁺ B cells were significantly increased in patients with PD. Notably, some of the changes observed in CD4⁺ T cells and B cells were associated with clinical motor disease severity.

Conclusions

These findings suggest that alterations in the adaptive immune system may promote clinical disease in PD by skewing to a more proinflammatory state in the early-stage PD patient cohort. Our study may shed light on potential immunotherapies targeting dysregulated CD4⁺ T cells, CD8⁺ T cells, and CD19⁺ B cells in patients with PD.