α-Synuclein-specific T cell reactivity is associated with preclinical and early Parkinson's disease

Hidden face of Parkinson's disease: Is it a new autoimmune disease?

Parkinson's disease is a neurodegenerative disorder marked by the degeneration of dopaminergic neurons and clinical symptoms such as tremors, rigidity, and slowed movements. A key feature of Parkinson's disease is the accumulation of misfolded α-synuclein, forming insoluble Lewy bodies in the substantia nigra pars compacta, which contributes to neurodegeneration. These α-synuclein aggregates may act as autoantigens, leading to T-cell-mediated neuroinflammation and contributing to dopaminergic cell death. Our perspective explores the hypothesis that Parkinson's disease may have an autoimmune component, highlighting research that connects peripheral immune responses with neurodegeneration. T cells derived from Parkinson's disease patients appear to have the potential to initiate an autoimmune response against α-synuclein and its modified peptides, possibly leading to the formation of neo-epitopes. Recent evidence associates Parkinson's disease with abnormal immune responses, as indicated by increased levels of immune cells, such as CD4 + and CD8 + T cells, observed in both patients and mouse models. The convergence of T cells filtration increasing major histocompatibility complex molecules, and the susceptibility of dopaminergic neurons supports the hypothesis that Parkinson's disease may exhibit autoimmune characteristics. Understanding the immune mechanisms involved in Parkinson's disease will be crucial for developing therapeutic strategies that target the autoimmune aspects of the disease. Novel approaches, including precision medicine based on major histocompatibility complex/human leukocyte antigen typing and early biomarker identification, could pave the way for immune-based treatments aimed at slowing or halting disease progression. This perspective explores the relationship between autoimmunity and Parkinson's disease, suggesting that further research could deepen understanding and offer new therapeutic avenues. In this paper, it is organized to provide a comprehensive perspective on the autoimmune aspects of Parkinson's disease. It investigates critical areas such as the autoimmune response observed in Parkinson's disease patients and the role of autoimmune mechanisms targeting α-synuclein in Parkinson's disease. The paper also examines the impact of CD4 + T cells, specifically Th1 and Th17, on neurons through in vitro and ex vivo studies. Additionally, it explores how α-synuclein influences glia-induced neuroinflammation in Parkinson's disease. The discussion extends to the clinical implications and therapeutic landscape, offering insights into potential treatments. Consequently, we aim to provide a comprehensive perspective on the autoimmune aspects of Parkinson's disease, incorporating both supportive and opposing views on its classification as an autoimmune disorder and exploring implications for clinical applications.

The role of interleukin (IL)-2 cytokine family in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder, which primarily impacts the nervous system, marked by its immune and inflammatory characteristics. The interleukin-2 (IL-2) cytokine family has a crucial role in regulating both neuroinflammation and immune activity, positioning it as one of the critical immune pathways in PD. Balancing pro-inflammatory and anti-inflammatory signals in PD heavily depends on the IL-2 cytokine family, that includes IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21. This balance is vital for neuron survival and resistance to degeneration. Disruptions in IL-2 signaling can upset the equilibrium among regulatory T cells (Tregs) and pro-inflammatory T cells, such as Th1 and Th17, further aggravating the chronic neuroinflammation typical of PD. In PD, a decline in IL-2 or receptor dysfunction can hinder Treg activity, leading to increased inflammation and neurodegeneration. Similarly, IL-15 and IL-21 supports cytotoxic immune cell function, including natural killer (NK) cells and CD8+ T cells, which may exacerbate neuronal damage by sustaining pro-inflammatory processes. Moreover, IL-4 and IL-7 have anti-inflammatory roles in maintaining T cell homeostasis, and their dysregulation can contribute to interruption of the blood-brain barrier and increased infiltration of immune cells into the central nervous system. Targeting the IL-2 cytokine family in Parkinson's disease has shown therapeutic potential by expanding Tregs, which reduce neuroinflammation and promote dopaminergic neuron survival. Recombinant IL-2 and IL-2/anti-IL-2 complexes have demonstrated efficacy in animal models, enhancing Treg function and leading to improved neuroprotection. Additionally, IL-4-based therapies have been explored for their ability to shift microglia toward a neuroprotective phenotype, further enhancing neuronal survival by modulating inflammatory responses and cellular metabolism. Current research is exploring how to optimize cytokine delivery while minimizing immune side effects, with the goal of developing more targeted therapies for PD.

Sex-specific immune-biological profiles in Parkinson's disease

Depending on age, both the risk and characteristics of Parkinson's disease (PD) differ between the sexes. The immune system might have a role; however, human-based evidence remains scarce. Here, we investigated the relationship between peripheral immune cellular composition and the clinical-biological sexual dimorphism of PD. The leukocyte population count (neutrophils, lymphocytes, monocytes, eosinophils, and basophils), the neutrophil-to-lymphocyte ratio (NLR), and the monocytes-to-lymphocytes ratio (MLR) were collected and compared in 117 PD patients and 86 controls (CTLs), and then related to blood levels of sex hormones, CSF markers of neurodegeneration (α-synuclein, amyloid-β-42, amyloid-β-40, total tau, and phosphorylated-181-tau), and clinical features in male and female PD patients. Finally, a cluster analysis based on the three main leukocyte populations (neutrophils, lymphocytes, monocytes) was performed for the entire PD cohort. Male PD patients had lower lymphocyte counts and higher NLR than male CTLs. Females with PD had lower monocyte counts, NLR, and MLR than males with PD. Lymphocyte counts correlated with cognition in male, but not female, PD patients. Finally, two clusters of peripheral immune cellular composition were identified: the "high peripheral inflammation" one, mostly comprising male patients, with worse clinical features and greater central α-synuclein burden, and the "low peripheral inflammation cluster", which mainly comprised female patients, with milder clinical features and lower central synucleinopathy. In conclusion, the peripheral immune pattern entails sex-specific clinical-biological profiles in PD. Moreover, systemic inflammation clusters with sex, sexual hormones, clinical features, and central synucleinopathy in PD, supporting the relevance of immunity in sexual dimorphism of the disease.

Inhibiting Immune Crosstalk by Modulation of the Intracellular Function and Extracellular Environment of Diseased Microglia to Boost Parkinson's Disease Therapy

Microglia usually phagocytose excessive α-synuclein (α-syn) aggregates and turn into diseased analogues in Parkinson's disease (PD), which can present α-syn-associated antigens, secrete cytokines and chemokines to recruit peripheral immune cells, and form strong immune crosstalk to aggravate PD progression. Hence, targeting the diseased microglia and inhibiting their immune crosstalk emerge as promising strategies for PD therapy. Herein, we reprogram the diseased microglia to efficiently degrade α-syn aggregates and neutralize neuroinflammatory factors to reduce the detrimental immune crosstalk and enhance therapeutic efficacy using rationally designed core-shell IHM nanoparticles, which consist of a ligustilide-functionalized Cu2-xSe nanoparticle (CSL NP) core and a hybrid cell membrane shell. The CSL NPs can redress the diseased microglia to reduce over-presented antigens by dual roles of reducing microglial RAGE-mediated phagocytosis of α-syn aggregates and increasing the microglial mature cathepsin D (m-CTSD) to efficiently degrade α-syn aggregates. The hybrid cell membrane shell is formed by a MES23.5 cell membrane (MCM) and IFN-γ-treated RAW264.7 cell membrane (IRCM). It can not only target diseased microglia by the specific interactions between VCAM-1 on the MCM and α4β1 integrin on the microglial membrane but also absorb and reduce the secretion of neuroinflammatory factors by diseased microglia through upregulated neuroinflammatory cytokine receptors such as IL1R1, TNFR1, and CCR2 on the surface of IRCM. The biomimetic core-shell IHM nanoparticles can be effectively delivered into the brain via meningeal lymphatic vessels to modulate the diseased microglia for boosting PD therapy. Our study demonstrates the promise of targeting diseased microglia to reduce their immune crosstalk in the treatment of PD and other neurodegenerative diseases.

T cell responses towards PINK1 and α-synuclein are elevated in prodromal Parkinson's disease

A role of the immune system in Parkinson's disease (PD) progression has long been suspected due to the increased frequency of activated glial cells and infiltrating T cells in the substantia nigra. It was previously reported that PD donors have increased T cell responses towards PINK1 and α-synuclein (α-syn), two Lewy body-associated proteins. Further, T cell reactivity towards α-syn was highest closer to disease onset, highlighting that autoreactive T cells might play a role in PD pathogenesis. However, whether T cell autoreactivity is present during prodromal PD is unknown. Here, we investigated T cell responses towards PINK1 and α-syn in donors at high risk of developing PD (i.e. prodromal PD: genetic risk, hyposmia, and or REM sleep behavior disorder), in comparison to PD and healthy control donors. T cell reactivity to these two autoantigens was detected in prodromal PD at levels comparable to those detected in individuals with clinically diagnosed PD. Aligned with the increased incidence of PD in males, we found that males with PD, but not females, had elevated T cell reactivity compared to healthy controls. However, among prodromal PD donors, males and females had elevated T cell responses. These differing trends in reactivity highlights the need for further studies of the impact of biological sex on neuroinflammation and PD progression.

PINK1 deficiency rewires early immune responses in a mouse model of Parkinson's disease triggered by intestinal infection

Parkinson's disease is characterized by a period of non-motor symptoms, including gastrointestinal dysfunction, preceding motor deficits by several years to decades. This long prodrome is suggestive of peripheral immunity involvement in the initiation of disease. We previously developed a model system in PINK1 KO mice displaying PD-like motor symptoms at late stages following intestinal infections. Herein, we map the initiating immune events at the site of infection in this model. Using single-cell RNAseq, we demonstrate that peripheral myeloid cells are the earliest highly dysregulated immune cell type followed by an aberrant T cell response shortly after. We also demonstrate an increased propensity for antigen presentation and that activated myeloid cells acquire a proinflammatory profile capable of inducing cytotoxic T cell responses. Together, our study provides the first evidence that PINK1 is a key regulator of immune functions in the gut underlying early PD-related disease mechanisms.

Differential memory enrichment of cytotoxic CD4 T cells in Parkinson's disease patients reactive to α-synuclein

Parkinson's disease (PD) is a complex neurodegenerative disease with a largely unknown etiology. Although the loss of dopaminergic neurons in the substantia nigra pars compacta is the pathological hallmark of PD, neuroinflammation also plays a fundamental role in PD pathology. We have previously reported that PD patients have increased frequencies of T cells reactive to peptides from α-synuclein (α-syn). However, not all PD participants respond to α-syn. Furthermore, we have previously found that CD4 T cells from PD participants responding to α-syn (PD_R) are transcriptionally distinct from PD participants not responding to α-syn (PD_NR). To gain further insight into the pathology of PD_R participants, we investigated surface protein expression of 11 proteins whose genes had previously been found to be differentially expressed when comparing PD_R and healthy control participants not responding to α-syn (HC_NR). We found that Cadherin EGF LAG seven-pass G-type receptor 2 (CELSR2) was expressed on a significantly higher proportion of CD4 effector memory T cells (TEM) in PD_R compared to HC_NR. Single-cell RNA sequencing analysis of cells expressing or not expressing CELSR2 revealed that PD_R participants have elevated frequencies of activated TEM subsets and an almost complete loss of cytotoxic TEM cells. Flow cytometry analyses confirmed that Granulysin+ CD4 cytotoxic TEM cells are reduced in PD_R. Taken together, these results provide further insight into the perturbation of T cell subsets in PD_R, and highlights the need for further investigation into the role of Granulysin+ CD4 cytotoxic TEM in PD pathology.

Lipid nanoparticle (LNP) mediated mRNA delivery in neurodegenerative diseases

Neurodegenerative diseases (NDD) are characterized by the progressive loss of neurons and the impairment of cellular functions. Messenger RNA (mRNA) has emerged as a promising therapy for treating NDD, as it can encode missing or dysfunctional proteins and anti-inflammatory cytokines or neuroprotective proteins to halt the progression of these diseases. However, effective mRNA delivery to the central nervous system (CNS) remains a significant challenge due to the limited penetration of the blood-brain barrier (BBB). Lipid nanoparticles (LNPs) offer an efficient solution by encapsulating and protecting mRNA, facilitating transfection and intracellular delivery. This review discusses the pathophysiological mechanisms of neurological disorders, including Parkinson's disease (PD), Alzheimer's disease (AD), multiple sclerosis (MS), Huntington's disease (HD), ischemic stroke, spinal cord injury, and Friedreich's ataxia. Additionally, it explores the potential of LNP-mediated mRNA delivery as a therapeutic strategy for these diseases. Various approaches to overcoming BBB-related challenges and enhancing the delivery and efficacy of mRNA-LNPs are discussed, including non-invasive methods with strong potential for clinical translation. With advancements in artificial intelligence (AI)-guided mRNA and LNP design, targeted delivery, gene editing, and CAR-T cell therapy, mRNA-LNPs could significantly transform the treatment landscape for NDD, paving the way for future clinical applications.

Pathogenesis of Parkinson's Disease

Both genetic and environmental factors modulate the risk of Parkinson's disease. In this article, all these pathophysiologic processes that contribute to damages at the tissue, cellular, organelle, and molecular levels, and their effects are talked about.

Peripheral Immune pattern in a genetic cohort of p.A53T alpha-synuclein carriers

INTRODUCTION

Previous research has shown that inflammatory immune biomarkers including peripheral white blood cell subpopulations differ between Parkinson's disease (PD) patients and healthy controls (HC), with PD exhibiting higher neutrophil to lymphocyte ratio (NLR). The aim of the present report was to assess the peripheral immune profile in patients or asymptomatic carriers harboring the p.A53T alpha-synuclein (SNCA) mutation.

METHODS

Data regarding 31 p.A53T SNCA PD patients, 9 asymptomatic mutation carriers and 194 HCs were obtained from the database of the Parkinson's Progression Markers Initiative (PPMI). Focus was placed on peripheral immune blood cells subpopulations and clinical/imaging parameters at baseline.

RESULTS

NLR, Absolute Neutrophil cell count and Neutrophils to total Leukocytes ratio were increased in the p.A53T SNCA PD group as compared to HCs [2.77 vs 2.18 (p < 0.001), 4.32 × 10^3 cells/μL vs 3.67 × 10^3 cells/μL (p = 0.001), 65.67 % vs 59.55 % (p < 0.001)]. Differences in NLR were mainly driven by the male patient subgroup. Lymphocytes to total Leukocytes and Monocytes to total Leukocytes ratio were lower in the p.A53T SNCA cohort as compared to HC [(p = 0.001) and (p = 0.002)]. Finally, we observed a positive correlation between the absolute Lymphocyte count and the mean putamen DATSCAN signal. Asymptomatic carriers did not differ statistically from either group.

DISCUSSION

Our current study provides evidence of a specific pattern of peripheral immune response in the p.A53T SNCA PD group which aligns well with literature data in idiopathic and GBA-PD. Whether this peripheral immune activation represents a contributing cause or an effect of the neurodegenerative process will require further study.

Targeting CD38 immunometabolic checkpoint improves metabolic fitness and cognition in a mouse model of Alzheimer's disease

Protective immunity, essential for brain maintenance and repair, may be compromised in Alzheimer's disease (AD). Here, using high-dimensional single-cell mass cytometry, we find a unique immunometabolic signature in circulating CD4+ T cells preceding symptom onset in individuals with familial AD, featured by the elevation of CD38 expression. Using female 5xFAD mice, a mouse model of AD, we show that treatment with an antibody directed to CD38 leads to restored metabolic fitness, improved cognitive performance, and attenuated local neuroinflammation. Comprehensive profiling across distinct immunological niches in 5xFAD mice, reveals a high level of disease-associated CD4+ T cells that produce IL-17A in the dural meninges, previously linked to cognitive decline. Targeting CD38 leads to abrogation of meningeal TH17 immunity and cortical IL-1β, breaking the negative feedback loop between these two compartments. Taken together, the present findings suggest CD38 as an immunometabolic checkpoint that could be adopted as a pre-symptomatic biomarker for early diagnosis of AD, and might also be therapeutically targeted alone or in combination with other immunotherapies for disease modification.

Targeting chaperone-mediated autophagy in neurodegenerative diseases: mechanisms and therapeutic potential

The pathological hallmarks of various neurodegenerative diseases including Parkinson's disease and Alzheimer's disease prominently feature the accumulation of misfolded proteins and neuroinflammation. Chaperone-mediated autophagy (CMA) has emerged as a distinct autophagic process that coordinates the lysosomal degradation of specific proteins bearing the pentapeptide motif Lys-Phe-Glu-Arg-Gln (KFERQ), a recognition target for the cytosolic chaperone HSC70. Beyond its role in protein quality control, recent research underscores the intimate interplay between CMA and immune regulation in neurodegeneration. In this review, we illuminate the molecular mechanisms and regulatory pathways governing CMA. We further discuss the potential roles of CMA in maintaining neuronal proteostasis and modulating neuroinflammation mediated by glial cells. Finally, we summarize the recent advancements in CMA modulators, emphasizing the significance of activating CMA for the therapeutic intervention in neurodegenerative diseases.

Lack of neuroprotection after systemic administration of the soluble TNF inhibitor XPro1595 in an rAAV6-α-Syn + PFFs-induced rat model for Parkinson's disease

Parkinson's disease (PD) is characterized by dopaminergic neurodegeneration, α-Synuclein (α-Syn) pathology, and inflammation. Microglia in the substantia nigra pars compacta (SNpc) upregulate major histocompatibility complex class II (MHCII), and variants in genes encoding MHCII affect PD risk. Additionally, elevated TNF levels and α-Syn-reactive T cells in circulation suggest a strong link between innate and adaptive immune responses in PD. We have previously reported that reduced levels of the class II transactivator, the master regulator of MHCII expression, increases susceptibility to α-Syn-induced PD-like pathology in rats and are associated with higher serum levels of soluble TNF (sTNF). Here, we demonstrate that inhibiting sTNF with a dominant-negative TNF variant, XPro1595, known to be neuroprotective in endotoxin- and toxin-induced neurodegeneration models, fails to protect against robust α-Syn-induced PD-like pathology in rats. We used a model combining rAAV-mediated α-Syn overexpression in SNpc with striatal injection of α-Syn preformed fibrils two weeks later. Systemic XPro1595 treatment was initiated one-week post-rAAV-α-Syn. We observed up to 70 % loss of striatal dopaminergic fibers without treatment, and no protective effects on dopaminergic neurodegeneration after XPro1595 administration. Pathological α-Syn levels as well as microglial and astrocytic activation were not reduced in SNpc or striatum following XPro1595 treatment. An increase in IL-6 and IL-1β levels in CSF was observed in rats treated with XPro1595, possibly explaining a lack of protective effects following treatment. Our results highlight the need to determine the importance of timing of treatment initiation, which is crucial for future applications of sTNF therapies in PD patients.

Large-scale proteomic analyses of incident Parkinson's disease reveal new pathophysiological insights and potential biomarkers

The early pathophysiology of Parkinson's disease (PD) is poorly understood. We analyzed 2,920 Olink-measured plasma proteins in 51,804 UK Biobank participants, identifying 859 incident PD cases after 14.45 years. We found 38 PD-related proteins, with six of the top ten validated in the Parkinson's Progression Markers Initiative (PPMI) cohort. ITGAV, HNMT and ITGAM showed consistent significant association (hazard ratio: 0.11-0.57, P = 6.90 × 10-24 to 2.10 × 10-11). Lipid metabolism dysfunction was evident 15 years before PD onset, and levels of BAG3, HPGDS, ITGAV and PEPD continuously decreased before diagnosis. These proteins were linked to prodromal symptoms and brain measures. Mendelian randomization suggested ITGAM and EGFR as potential causes of PD. A predictive model using machine learning combined the top 16 proteins and demographics, achieving high accuracy for 5-year (area under the curve (AUC) = 0.887) and over-5-year PD prediction (AUC = 0.816), outperforming demographic-only models. It was externally validated in PPMI (AUC = 0.802). Our findings reveal early peripheral pathophysiological changes in PD crucial for developing early biomarkers and precision therapies.

Association of glymphatic system function with peripheral inflammation and motor symptoms in Parkinson's disease

Growing evidence highlights the roles of glymphatic system and peripheral inflammation in Parkinson's disease (PD). We evaluated their interrelationship and potential mechanisms contributing to motor symptoms using DTI-ALPS and inflammatory markers (leukocyte, lymphocyte, neutrophil counts, neutrophil-to-lymphocyte ratio [NLR], and platelet-to-lymphocyte ratio [PLR]) in 134 PD patients (52 tremor-dominant [TD], 62 postural instability and gait difficulty [PIGD]) and 81 healthy controls (HC, 33 with inflammatory markers). PD exhibited lower DTI-ALPS than HC (1.43 ± 0.19 vs. 1.52 ± 0.21, p = 0.001). DTI-ALPS was negatively correlated with NLR, PLR, and neutrophils in PD (all p < 0.05) and with neutrophils in PIGD (β = -0.043, p = 0.048), and positively correlated with lymphocytes in TD (β = 0.105, p = 0.034). DTI-ALPS mediated the relationship between peripheral inflammation (NLR and neutrophils) and MDS-UPDRS III score in PD. Overall, glymphatic dysfunction correlates with peripheral inflammation and may mediate effects of inflammation on motor symptoms in PD, with distinct inflammation profiles between TD and PIGD.

Evaluating the Molecular Interactions between Type 2 Diabetes Mellitus and Parkinson's Disease: Role of Antidiabetic Drugs as Promising Therapeutics

Evidence from previous research demonstrates a relationship between diabetes mellitus (DM) and Parkinson's disease (PD). T2DM is associated with chronic glucose dysregulation, as an etiological factor. It inhibits neuronal function through disrupted insulin signaling and oxidative stress, which ultimately lead to the loss of dopaminergic neurons in the substantia nigra (SN). Interactions between T2DM and PD were analyzed by gene expression, coexpression, and gene set enrichment via NCBI and STRING databases following pathways like KEGG and Reactome. The study identified nine key gene interactions through published literature on different databases and search engines that are involved in the progression of these chronic diseases. Furthermore, some genetic and nongenetic risk factors, gene mutations and environmental factors, are also involved in the progression of T2DM and PD. This review highlights the limitations of currently available drug treatments for these diseases and examines modern therapeutic approaches to address neurodegenerative and metabolic abnormalities. We critically assess the current experimental methodologies aimed at unraveling the pathophysiological mechanisms linking PD and T2DM while addressing the key challenges impeding a comprehensive understanding of the concurrent emergence of these debilitating age-related conditions.

Electrochemical Biosensors for the Detection of Exosomal microRNA Biomarkers for Early Diagnosis of Neurodegenerative Diseases

Early and precise diagnosis of neurodegenerative disorders like Alzheimer's (AD) and Parkinson's (PD) is crucial for slowing their progression and enhancing patient outcomes. Exosomal microRNAs (miRNAs) are emerging as promising biomarkers due to their ability to reflect the diseases' pathology, yet their low abundance poses significant detection hurdles. This review article delves into the burgeoning field of electrochemical biosensors, designed for the precise detection of exosomal miRNA biomarkers. Electrochemical biosensors offer a compelling solution, combining the sensitivity required to detect low-abundance biomarkers with the specificity needed to discern miRNA profiles distinctive to neural pathological states. We explore the operational principles of these biosensors, including the electrochemical transduction mechanisms that facilitate miRNA detection. The review also summarizes advancements in nanotechnology, signal enhancement, bioreceptor anchoring, and microfluidic integration that improve sensor accuracy. The evidence of their use in neurodegenerative disease diagnosis is analyzed, focusing on the clinical impact, diagnostic precision, and obstacles faced in practical applications. Their potential integration into point-of-care testing and regulatory considerations for their market entry are discussed. Looking toward the future, the article highlights forthcoming innovations that might revolutionize early diagnostic processes. Electrochemical biosensors, with their impressive sensitivity, specificity, and point-of-care compatibility, are on track to become instrumental in the early diagnosis of neurodegenerative diseases, possibly transforming patient care and prognosis.

MicroRNAs alteration and unique distribution in the soma and synapses of substantia nigra in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative condition after Alzheimer's. Abnormal accumulation of alpha-synuclein (α-syn) aggregates disrupts the balance of dopaminergic (DA-ergic) synapse components, interfering with dopamine transmission and leading to synaptic dysfunction and neuronal loss in PD. However exact molecular mechanism underlying DA-ergic neuronal cell loss in the SNpc in not known. MicroRNAs (miRNAs) are observed in various compartments of neural elements including cell bodies, nerve terminals, mitochondria, synaptic vesicles and synaptosomes. However, miRNAs expression and cellular distribution are unknown in the soma and synapse compartment in PD and healthy state. To address this void of information, we isolated synaptosomes and cytosolic fractions (soma) from post-mortem brains of PD-affected individuals and unaffected controls (UC) and processed for miRNA sequencing analysis. A group of miRNAs were significantly altered ( p < 0.05) with high fold changes (variance +/- > 2-fold) in their expressions in different comparisons: 1. UC synaptosome vs UC cytosol, 2. PD synaptosome vs PD cytosol, 3. PD synaptosome vs UC synaptosome, 4. PD cytosol vs UC cytosol. Our study unveiled some potential miRNAs in PD and their alteration and unique distribution in the soma and synapses of SNpc in PD and controls. Further, gene ontology enrichment analysis showed the involvement of deregulated miRNAs in several molecular function and cellular components: synapse assembly formation, cell junction organization, cell projections, mitochondria, Calcium ion binding and protein binding activities.

Transmission of peripheral blood α-synuclein fibrils exacerbates synucleinopathy and neurodegeneration in Parkinson's disease by endothelial Lag3 endocytosis

Parkinson's disease (PD) is an age-related neurodegenerative disorder. The pathological feature of PD is abnormal α-synuclein (α-syn) formation and transmission. Recent evidence demonstrates that α-syn preformed fibrils (α-syn PFFs) can be detected in the serum of patients with PD. The peripheral blood α-syn PFF can cross the blood-brain barrier (BBB) and aggravate neuronal damage, but the mechanism remains to be elucidated. We constructed the PD mouse models of different severity: the mild pathology (A53T ONLY) and the severe pathology (A53T + Brain FIB); this was followed by α-syn PFFs intravenous injection. Then, we used endothelium-specific Lag3 knockout mice (Lag3-ECs-CKO) to decrease the blood α-syn PFFs spreading. We observed that intravenous transmission of α-syn PFFs significantly aggravated motor deficits, dopaminergic neuron loss, neuroinflammation, and pathologic α-syn deposition in A53T ONLY, but not in A53T + Brain FIB. Blocking endothelial Lag3 endocytosis by Lag3-ECs-CKO decreased the blood α-syn PFFs spreading and improved the symptoms and pathogenesis of PD mice. Our findings reveal the role of peripheral blood α-syn PFFs transmission in the mild pathology or early-stage PD and the mechanism of endothelial Lag3 endocytosis in the pathology of α-syn transmission. Targeting endothelial Lag3 to prevent α-syn from spreading from the blood to the brain may be a disease-modifying therapy in early-stage PD.NEW & NOTEWORTHY This study highlights the transmission mechanism of peripheral blood α-synuclein preformed fibrils (α-syn PFFs) through endothelial Lag3 endocytosis in the mild pathology or early-stage Parkinson's disease (PD). Targeting endothelial Lag3 as a perspective of decreasing peripheral blood α-syn PFFs transmission may be a disease-modifying therapy in early-stage PD.

Microbial amyloids in neurodegenerative amyloid diseases

Human-disease associated amyloidogenic proteins are not unique in their ability to form amyloid fibrillar structures. Numerous microbes produce amyloidogenic proteins that have distinct functions for their physiology in their amyloid form, rather than solely detrimental. Emerging data indicate associations between various microbial organisms, including those which produce functional amyloids, with neurodegenerative diseases. Here, we review some of the evidence suggesting that microbial amyloids impact amyloid disease in host organisms. Experimental data are building a foundation for continued lines of enquiry and suggest that that direct or indirect interactions between microbial and host amyloids may be a contributor to amyloid pathologies. Inhibiting microbial amyloids or their interactions with the host may therefore represent a tangible target to limit various amyloid pathologies.

Ageing-related changes in the regulation of microglia and their interaction with neurons

Ageing is one of the most important risk factors for chronic health conditions, including neurodegenerative diseases. Inflammation is a feature of ageing, as well as a key pathophysiological mechanism for degenerative diseases. Microglia play multiple roles in the central nervous system; their states entail a complex assemblage of responses reflecting the multiplicity of functions they fulfil both under homeostatic basal conditions and in response to stimuli. Whereas glial cells can promote neuronal homeostasis and limit neurodegeneration, age-related inflammation (i.e. inflammaging) leads to the functional impairment of microglia and astrocytes, exacerbating their response to stimuli. Thus, microglia are key mediators for age-dependent changes of the nervous system, participating in the generation of a less supportive or even hostile environment for neurons. Whereas multiple changes of ageing microglia have been described, here we will focus on the neuron-microglia regulatory crosstalk through fractalkine (CX3CL1) and CD200, and the regulatory cytokine Transforming Growth Factor β1 (TGFβ1), which is involved in immunomodulation and neuroprotection. Ageing results in a dysregulated activation of microglia, affecting neuronal survival, and function. The apparent unresponsiveness of aged microglia to regulatory signals could reflect a restriction in the mechanisms underlying their homeostatic and reactive states. The spectrum of functions, required to respond to life-long needs for brain maintenance and in response to disease, would progressively narrow, preventing microglia from maintaining their protective functions. This article is part of the Special Issue on "Microglia".

Growth arrest and DNA damage-inducible 45: a new player on inflammatory diseases

Growth arrest and DNA damage-inducible 45 (GADD45) proteins are critical stress sensors rapidly induced in response to genotoxic/physiological stress and regulate many cellular functions. Even though the primary function of the proteins is to block the cell cycle, inhibit cell proliferation, promote cell apoptosis, and repair DNA damage to cope with the damage caused by internal and external stress on the body, evidence has shown that GADD45 also has the function to modulate innate and adaptive immunity and plays a broader role in inflammatory and autoimmune diseases. In this review, we focus on the immunomodulatory role of GADD45 in inflammatory and autoimmune diseases. First, we describe the regulatory factors that affect the expression of GADD45. Then, we introduce its immunoregulatory roles on immune cells and the critical signaling pathways mediated by GADD45. Finally, we discuss its immunomodulatory effects in various inflammatory and autoimmune diseases.

Treatment of Alzheimer's Disease subjects with expanded non-genetically modified autologous natural killer cells (SNK01): a phase I study

BACKGROUND

The importance of natural killer (NK) cells of the innate immune system in neurodegenerative disease has largely been overlooked despite studies demonstrating their ability to reduce neuroinflammation (thought to be mediated by the elimination of activated T cells, degradation of protein aggregates and secretion of anti-inflammatory cytokines). SNK01 is an autologous non-genetically modified NK cell product showing increased activity in vitro. We hypothesized that SNK01 can be safely infused to reduce neuroinflammation in Alzheimer's Disease (AD) patients.

METHODS

SNK01 was produced and characterized for its ability to eliminate activated T cells, degrade protein aggregates and secrete anti-inflammatory cytokines. In this phase 1 study, SNK01 was administered intravenously every three weeks for a total of 4 treatments using a 3 + 3 dose escalation design (1, 2 and 4 × 109 cells) in subjects with either mild, moderate, or severe AD (median CDR-SB 10.0). Cognitive assessments and cerebrospinal fluid biomarkers associated with protein aggregation, neurodegeneration and neuroinflammation including amyloid-β42 and 42/40, α-synuclein, total Tau, pTau217 and pTau181, neurofilament light, GFAP and YKL-40 analyses were performed at baseline, at 1 and 12 weeks after the last dose. The primary endpoint was safety; secondary endpoints included changes in cognitive assessments and biomarker levels.

RESULTS

In preclinical in vitro studies, SNK01 were able to uptake and degrade the protein aggregates of amyloid-β and α-synuclein, produce anti-inflammatory cytokines and eliminate activated T cells. In the phase 1 clinical study, eleven subjects were enrolled (10 evaluable). No drug-related adverse events were observed. Despite 70% of subjects being treated at relatively low doses of SNK01 (1 and 2 × 109 cells), 50-70% of all enrolled subjects had stable/improved CDR-SB, ADAS-Cog and/or MMSE scores and 90% had stable/improved ADCOMS at one-week after the last dose. SNK01 also appeared to have beneficial effects on protein aggregate levels and neuroinflammatory biomarkers in the cerebrospinal fluid, with decreases in pTau181 and GFAP appearing to be dose-dependent.

CONCLUSIONS

SNK01 was well tolerated and appeared to have clinical activity in AD while also having beneficial effects on cerebrospinal fluid protein and neuroinflammatory biomarker levels. A larger trial with a higher dosing/duration has been initiated in the USA in 2023.

TRIAL REGISTRATION

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CLINICALTRIALS

gov NCT04678453, date of registration: 2020-12-22.

Motor Functional Hierarchical Organization of Cerebrum and Its Underlying Genetic Architecture in Parkinson's Disease

Hierarchy has been identified as a principle underlying the organization of human brain networks. However, it remains unclear how the network hierarchy is disrupted in Parkinson's disease (PD) motor symptoms and how it is modulated by the underlying genetic architecture. The aim of this study was to explore alterations in the motor functional hierarchical organization of the cerebrum and their underlying genetic mechanism. In this study, the brain network hierarchy of each group was described through a connectome gradient analysis among 68 healthy controls (HC), 70 postural instability and gait difficulty (PIGD) subtype, and 69 tremor-dominant (TD) subtype, including both male and female participants, according to its motor symptoms. Furthermore, transcription-neuroimaging association analyses using gene expression data from Allen Human Brain Atlas and case-control gradient differences were performed to identify genes associated with gradient alterations. Different PD motor subtypes exhibited contracted principal and secondary functional gradients relative to HC. The identified genes in different PD motor subtypes enriched for shared biological processes like metal ion transport and inorganic ion transmembrane transport. In addition, these genes were overexpressed in Ntsr+ neurons cell, enriched in extensive cortical regions and wide developmental time windows. Aberrant cerebral functional gradients in PD-related motor symptoms have been detected, and the motor-disturbed genes have shared biological functions. The present findings may contribute to a more comprehensive understanding of the molecular mechanisms underlying hierarchical alterations in PD.

α-Synuclein orchestrates Th17 responses as antigen and adjuvant in Parkinson's disease

Recently, the role of T cells in the pathology of α-synuclein (αS)-mediated neurodegenerative disorders called synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy, has attracted increasing attention. Although the existence of αS-specific T cells and the immunogenicity of the post-translationally modified αS fragment have been reported in PD and DLB, the key cellular subset associated with disease progression and its induction mechanism remain largely unknown.Peripheral blood mononuclear cells (PBMCs) from synucleinopathy patients and healthy controls were cultured in the presence of the αS peptide pools. Cytokine analysis using culture supernatants revealed that C-terminal αS peptides with a phosphorylated serine 129 residue (pS129), a feature of pathological αS aggregates, promoted the production of IL-17A, IL-17F, IL-22, IFN-γ and IL-13 in PD patients compared with that in controls. In pS129 peptide-reactive PD cases, Ki67 expression was increased in CD4 T cells but not in CD8 T cells, and intracellular cytokine staining assay revealed the existence of pS129 peptide-specific Th1 and Th17 cells. The pS129 peptide-specific Th17 responses, but not Th1 responses, demonstrated a positive correlation with the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part III scores. A similar correlation was observed for IL-17A levels in the culture supernatant of PBMCs from PD patients with disease duration < 10 years. Interestingly, enhanced Th17 responses to pS129 peptides were uniquely found in PD patients among the synucleinopathies, suggesting that Th17 responses are amplified by certain mechanisms in PD patients. To investigate such mechanisms, we analyzed Th17-inducible capacity of αS-exposed dendritic cells (DCs). In vitro stimulation with αS aggregates generated Th17-inducible DCs with IL-6 and IL-23 production through the signaling of TLR4 and spliced X-box binding protein-1 (XBP1s). In fact, the levels of IL-6 and IL-23 in plasma, and the XBP1s ratio in type 2 conventional DCs were increased in PD patients compared with those in controls.Here, we propose the importance of αS-specific Th17 responses in the progression of PD and the underlying mechanisms inducing Th17 responses. These findings may provide novel therapeutic strategies to prevent disease development through the suppression of TLR4-XBP1s-IL-23 signaling in DCs.

Higher systemic immune-inflammation index is associated with increased risk of Parkinson's disease in adults: a nationwide population-based study

Background

This study aimed to explore the association between a new inflammatory marker, systemic immune-inflammation index (SII), and the risk of Parkinson's disease (PD) in adult population.

Methods

A cross-sectional design was used, participants were recruited from the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2020. Three logistic regression models were used to explore the association between SII and the risk of PD, and subgroup analysis and sensitivity analysis were used. In addition, the restricted cubic spline (RCS) was used to explore the dose-response relationship between SII and PD. Receiver operating characteristic (ROC) curves was used to explore the diagnostic value of SII for PD.

Results

A total of 54,027 adults (mean age 35 years) were included in this study. The results of logistic regression showed that after adjusted for all covariates, compared with the Q1 group (lowest quartile in SII), the risk of PD in the Q3 group (OR = 1.82, 95%CI = 1.20-2.82, p < 0.001) and the Q4 group increased (OR = 2.49, 95%CI = 1.69-3.77, p < 0.001), with p-trend < 0.001. After excluding individuals with any missing values, sensitivity analysis also found a positive association between SII and PD. Subgroup analysis showed that this association was more significant in women, younger than 60 years old, non-smokers, alcohol drinkers, non-obese, and without a history of stroke, diabetes, or coronary heart disease. In addition, there was a positive dose-response relationship between SII and PD, and SII had an acceptable diagnostic value for PD (AUC = 0.72).

Conclusion

SII is positively correlated with the prevalence of PD in the adult population, and SII can help differentiate between PD and non-PD cases.

Innate and adaptive immunity in neurodegenerative disease

Neurodegenerative diseases (NDs) are a group of neurological disorders characterized by the progressive loss of selected neurons. Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common NDs. Pathologically, NDs are characterized by progressive failure of neural interactions and aberrant protein fibril aggregation and deposition, which lead to neuron loss and cognitive and behavioral impairments. Great efforts have been made to delineate the underlying mechanism of NDs. However, the very first trigger of these disorders and the state of the illness are still vague. Existing therapeutic strategies can relieve symptoms but cannot cure these diseases. The human immune system is a complex and intricate network comprising various components that work together to protect the body against pathogens and maintain overall health. They can be broadly divided into two main types: innate immunity, the first line of defense against pathogens, which acts nonspecifically, and adaptive immunity, which follows a defense process that acts more specifically and is targeted. The significance of brain immunity in maintaining the homeostatic environment of the brain, and its direct implications in NDs, has increasingly come into focus. Some components of the immune system have beneficial regulatory effects, whereas others may have detrimental effects on neurons. The intricate interplay and underlying mechanisms remain an area of active research. This review focuses on the effects of both innate and adaptive immunity on AD and PD, offering a comprehensive understanding of the initiation and regulation of brain immunity, as well as the interplay between innate and adaptive immunity in influencing the progression of NDs.

Exploring the role of T cells in Alzheimer's and other neurodegenerative diseases: Emerging therapeutic insights from the T Cells in the Brain symposium

This proceedings article summarizes the inaugural "T Cells in the Brain" symposium held at Columbia University. Experts gathered to explore the role of T cells in neurodegenerative diseases. Key topics included characterization of antigen-specific immune responses, T cell receptor (TCR) repertoire, microbial etiology in Alzheimer's disease (AD), and microglia-T cell crosstalk, with a focus on how T cells affect neuroinflammation and AD biomarkers like amyloid beta and tau. The symposium also examined immunotherapies for AD, including the Valacyclovir Treatment of Alzheimer's Disease (VALAD) trial, and two clinical trials leveraging regulatory T cell approaches for multiple sclerosis and amyotrophic lateral sclerosis therapy. Additionally, single-cell RNA/TCR sequencing of T cells and other immune cells provided insights into immune dynamics in neurodegenerative diseases. This article highlights key findings from the symposium and outlines future research directions to further understand the role of T cells in neurodegeneration, offering innovative therapeutic approaches for AD and other neurodegenerative diseases. HIGHLIGHTS: Researchers gathered to discuss approaches to study T cells in brain disorders. New technologies allow high-throughput screening of antigen-specific T cells. Microbial infections can precede several serious and chronic neurological diseases. Central and peripheral T cell responses shape neurological disease pathology. Immunotherapy can induce regulatory T cell responses in neuroinflammatory disorders.

Low CD3 level is a risk factor for amyotrophic lateral sclerosis: a Mendelian randomization study

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal disease characterized by neuronal degeneration of the spinal cord and brain and believed to be related to the immune system. In this study, our aim is to use Mendelian randomization (MR) to search for immune markers related to ALS. A total of 731 immune cell traits were included in this study. MR analysis was used to identify the causality between 731 immune cell traits (with 3,757 Europeans) and ALS (with 138,086 Europeans). Colocalization analysis was used to verify the found causality, protein-protein interaction prediction was used to look for the interacting proteins that are known to be involved in ALS. We found low expression levels of CD3 on central memory CD8+ T cell is risk factor for ALS (OR = 0.90, 95% CI: 0.86-0.95, P = 0.0000303). CD3 can interact with three ALS-related proteins: VCP, HLA-DRA and HLA-DRB5, which are associated with adaptive immune response. Our study reported for the first time that low-level CD3 is a risk factor for ALS and the possible mechanism, which could provide a potential strategy for ALS diagnosis and therapy.

Immune mechanisms and shared immune targets in neurodegenerative diseases

The immune system plays a major part in neurodegenerative diseases. In some, such as multiple sclerosis, it is the primary driver of the disease. In others, such as Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, it has an amplifying role. Immunotherapeutic approaches that target the adaptive and innate immune systems are being explored for the treatment of almost all neurological diseases, and the targets and approaches are often common across diseases. Microglia are the primary immune cells in the brain that contribute to disease pathogenesis, and are consequently a common immune target for therapy. Other therapeutic approaches target components of the peripheral immune system, such as regulatory T cells and monocytes, which in turn act within the CNS. This Review considers in detail how microglia, monocytes and T cells contribute to the pathogenesis of multiple sclerosis, Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, and their potential as shared therapeutic targets across these diseases. The microbiome is also highlighted as an emerging therapeutic target that indirectly modulates the immune system. Therapeutic approaches being developed to target immune function in neurodegenerative diseases are discussed, highlighting how immune-based approaches developed to treat one disease could be applicable to multiple other neurological diseases.

Abatacept inhibits Th17 differentiation and mitigates α-synuclein-induced dopaminergic dysfunction in mice

Parkinson's disease (PD) is a multifaceted disease characterized by degeneration of nigrostriatal dopaminergic neurons, which results in motor and non-motor dysfunctions. Accumulation of α-synuclein (αSYN) in Lewy bodies is a key pathological feature of PD. Although the exact cause of PD remains unknown, accumulating evidence suggests that brain infiltration of T cells plays a critical role in the pathogenesis of disease, contributing to neuroinflammation and dopaminergic neurodegeneration. Here, we used a mouse model of brain-infused aggregated αSYN, which recapitulates motor and non-motor dysfunctions seen in PD patients. We found that αSYN-induced motor dysfunction in mice is accompanied by an increased number of brain-residing Th17 (IL17+ CD4+) cells, but not CD8+ T cells. To evaluate whether the modulation of T cell response could rescue αSYN-induced damage, we chronically treated animals with abatacept (8 mg/kg, sc, 3x per week), a selective T-cell co-stimulation modulator. We found that abatacept treatment decreased Th1 (IFNƔ+ CD4+) and Th17 (IL17+ CD4+) cells in the brain, rescued motor function and prevented dopaminergic neuronal loss in αSYN-infused mice. These results highlight the significance of effector CD4+ T cells, especially Th17, in the progression of PD and introduce novel possibilities for repurposing immunomodulatory drugs used for arthritis as PD-modifying therapies.

Inferring disease progression stages in single-cell transcriptomics using a weakly supervised deep learning approach

Application of single-cell/nucleus genomic sequencing to patient-derived tissues offers potential solutions to delineate disease mechanisms in humans. However, individual cells in patient-derived tissues are in different pathological stages, and hence, such cellular variability impedes subsequent differential gene expression analyses. To overcome such a heterogeneity issue, we present a novel deep learning approach, scIDST, that infers disease progression levels of individual cells with weak supervision framework. The disease progression-inferred cells display significant differential expression of disease-relevant genes, which cannot be detected by comparative analysis between patients and healthy donors. In addition, we demonstrate that pretrained models by scIDST are applicable to multiple independent data resources and are advantageous to infer cells related to certain disease risks and comorbidities. Taken together, scIDST offers a new strategy of single-cell sequencing analysis to identify bona fide disease-associated molecular features.

PINK1 is a target of T cell responses in Parkinson's disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder. While there is no curative treatment, the immune system's involvement with autoimmune T cells that recognize the protein α-synuclein (α-syn) in a subset of individuals suggests new areas for therapeutic strategies. As not all patients with PD have T cells specific for α-syn, we explored additional autoantigenic targets of T cells in PD. We generated 15-mer peptides spanning several PD-related proteins implicated in PD pathology, including glucosylceramidase β 1 (GBA), superoxide dismutase 1 (SOD1), PTEN induced kinase 1 (PINK1), Parkin RBR E3 ubiquitin protein ligase (parkin), oxoglutarate dehydrogenase (OGDH), and leucine rich repeat kinase 2 (LRRK2). Cytokine production (IFN-γ, IL-5, IL-10) against these proteins was measured using a fluorospot assay and PBMCs from patients with PD and age-matched healthy controls. We identified PINK1, a regulator of mitochondrial stability, as an autoantigen targeted by T cells, as well as its unique epitopes, and their HLA restriction. The PINK1-specific T cell reactivity revealed sex-based differences, as it was predominantly found in male patients with PD, which may contribute to the heterogeneity of PD. Identifying and characterizing PINK1 and other autoinflammatory targets may lead to antigen-specific diagnostics, progression markers, and/or novel therapeutic strategies for PD.

Single-cell sequencing insights into the transcriptional landscape of Parkinson's disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder, with an unknown etiology and no specific treatment. Emerging single-cell and single-nucleus RNA sequencing (sc/snRNA-seq) technologies have become instrumental in unravelling cellular heterogeneity and characterizing molecular signatures at single-cell resolution. Single-cell T cell receptor sequencing (scTCR-seq) and single-cell B cell receptor sequencing (scBCR-seq) technologies provide unprecedented opportunities to explore the immune repertoire diversity. These state-of-the-art technologies have been increasingly applied in PD research in the last five years, offering novel insights into the cellular susceptibilities and complex molecular mechanisms underlying PD pathogenesis. Herein we review recent advances in the applications of sc/snRNA-seq, scTCR-seq and scBCR-seq technologies in various PD models. Moreover, we focus on degenerative neurons, activated neuroglial cells, as well as pro-inflammatory immune cells, exploring their unique transcriptional landscapes in PD, as revealed by single-cell sequencing technologies. Finally, we highlight important challenges and the future directions of single-cell experiments in PD research.

Should We Consider Neurodegeneration by Itself or in a Triangulation with Neuroinflammation and Demyelination? The Example of Multiple Sclerosis and Beyond

Neurodegeneration is preeminent in many neurological diseases, and still a major burden we fail to manage in patient's care. Its pathogenesis is complicated, intricate, and far from being completely understood. Taking multiple sclerosis as an example, we propose that neurodegeneration is neither a cause nor a consequence by itself. Mitochondrial dysfunction, leading to energy deficiency and ion imbalance, plays a key role in neurodegeneration, and is partly caused by the oxidative stress generated by microglia and astrocytes. Nodal and paranodal disruption, with or without myelin alteration, is further involved. Myelin loss exposes the axons directly to the inflammatory and oxidative environment. Moreover, oligodendrocytes provide a singular metabolic and trophic support to axons, but do not emerge unscathed from the pathological events, by primary myelin defects and cell apoptosis or secondary to neuroinflammation or axonal damage. Hereby, trophic failure might be an overlooked contributor to neurodegeneration. Thus, a complex interplay between neuroinflammation, demyelination, and neurodegeneration, wherein each is primarily and secondarily involved, might offer a more comprehensive understanding of the pathogenesis and help establishing novel therapeutic strategies for many neurological diseases and beyond.

Neuroinflammation in Age-Related Neurodegenerative Diseases: Role of Mitochondrial Oxidative Stress

A shared hallmark of age-related neurodegenerative diseases is the chronic activation of innate immune cells, which actively contributes to the neurodegenerative process. In Alzheimer's disease, this inflammatory milieu exacerbates both amyloid and tau pathology. A similar abnormal inflammatory response has been reported in Parkinson's disease, with elevated levels of cytokines and other inflammatory intermediates derived from activated glial cells, which promote the progressive loss of nigral dopaminergic neurons. Understanding the causes that support this aberrant inflammatory response has become a topic of growing interest and research in neurodegeneration, with high translational potential. It has been postulated that the phenotypic shift of immune cells towards a proinflammatory state combined with the presence of immunogenic cell death fuels a vicious cycle in which mitochondrial dysfunction plays a central role. Mitochondria and mitochondria-generated reactive oxygen species are downstream effectors of different inflammatory signaling pathways, including inflammasomes. Dysfunctional mitochondria are also recognized as important producers of damage-associated molecular patterns, which can amplify the immune response. Here, we review the major findings highlighting the role of mitochondria as a checkpoint of neuroinflammation and immunogenic cell deaths in neurodegenerative diseases. The knowledge of these processes may help to find new druggable targets to modulate the inflammatory response.

Polygonatum sibiricum polysaccharides: A promising strategy in the treatment of neurodegenerative disease

Neurodegenerative diseases (NDDs), as a neurological disorder characterised by neuronal degeneration and death, are a serious threat to human health and have long attracted attention due to their complex pathogenesis and the ineffectiveness of therapeutic drugs. Existing studies have shown that Polygonatum Sibiricum polysaccharides (PSP) have immunoregulatory, antioxidant, anti-inflammatory and other pharmacological effects, and their neuroprotective effects have been demonstrated in several scientific studies. This paper reviews the main pharmacological effects and mechanisms of PSP in the protection and treatment of NDDs, to provide a reference for the clinical application and basic research of PSP in NDDs.

Alpha-synuclein fine-tunes neuronal response to pro-inflammatory cytokines

Pro-inflammatory cytokines are emerging as neuroinflammatory mediators in Parkinson's disease (PD) due to their ability to act through neuronal cytokine receptors. Critical questions persist regarding the role of cytokines in neuronal dysfunction and their contribution to PD pathology. Specifically, the potential synergy of the hallmark PD protein alpha-synuclein (α-syn) with cytokines is of interest. We therefore investigated the direct impact of pro-inflammatory cytokines on neurons and hypothesized that α-syn pathology exacerbates cytokine-induced neuronal deficits in PD. iPSC-derived cortical neurons (CNs) from healthy controls and patients with α-syn gene locus duplication (SNCA dupl) were stimulated with IL-17A, TNF-α, IFN-γ, or a combination thereof. For rescue experiments, CNs were pre-treated with α-syn anti-oligomerisation compound NPT100-18A prior to IL-17A stimulation. Cytokine receptor expression, microtubule cytoskeleton, axonal transport and neuronal activity were assessed. SNCA dupl CNs displayed an increased IL-17A receptor expression and impaired IL-17A-mediated cytokine receptor regulation. Cytokines exacerbated the altered distribution of tubulin post-translational modifications in SNCA dupl neurites, with SNCA dupl-specific IL-17A effects. Tau pathology in SNCA dupl CNs was also aggravated by IL-17A and cytokine mix. Cytokines slowed down mitochondrial axonal transport, with IL-17A-mediated retrograde slowing in SNCA dupl only. The pre-treatment of SNCA dupl CNs with NPT100-18A prevented the IL-17A-induced functional impairments in axonal transport and neural activity. Our work elucidates the detrimental effects of pro-inflammatory cytokines, particularly IL-17A, on human neuronal structure and function in the context of α-syn pathology, suggesting that cytokine-mediated inflammation represents a second hit to neurons in PD which is amenable to disease modifying therapies that are currently in clinical trials.

Single-cell transcriptomic and proteomic analysis of Parkinson's disease brains

Parkinson's disease (PD) is a prevalent neurodegenerative disorder, and recent evidence suggests that pathogenesis may be in part mediated by inflammatory processes, the molecular and cellular architectures of which are largely unknown. To identify and characterize selectively vulnerable brain cell populations in PD, we performed single-nucleus transcriptomics and unbiased proteomics to profile the prefrontal cortex from postmortem human brains of six individuals with late-stage PD and six age-matched controls. Analysis of nearly 80,000 nuclei led to the identification of eight major brain cell types, including elevated brain-resident T cells in PD, each with distinct transcriptional changes in agreement with the known genetics of PD. By analyzing Lewy body pathology in the same postmortem brain tissues, we found that α-synuclein pathology was inversely correlated with chaperone expression in excitatory neurons. Examining cell-cell interactions, we found a selective abatement of neuron-astrocyte interactions and enhanced neuroinflammation. Proteomic analyses of the same brains identified synaptic proteins in the prefrontal cortex that were preferentially down-regulated in PD. By comparing this single-cell PD dataset with a published analysis of similar brain regions in Alzheimer's disease (AD), we found no common differentially expressed genes in neurons but identified many shared differentially expressed genes in glial cells, suggesting that the disease etiologies, especially in the context of neuronal vulnerability, in PD and AD are likely distinct.

Peripheral biomarkers of Parkinson's disease and its correlation with clinical symptoms: a case-control study

BACKGROUND

Inflammation significantly impacts Parkinson's disease (PD), yet the intricate relationship between inflammatory markers and PD remains elusive.

OBJECTIVE

To identify the peripheral biomarkers of PD and its correlation with the motor and non-motor symptoms of PD.

METHODS

79 PD patients and 65 controls were included in this study. Clinical information and the serum levels of IL-8, IL-27, IL-33, β-NGF, AgRP, and TRAILR2 in the participants were collected. Appropriate scales were used to assess the symptoms of PD. For the factors with significant differences in the two groups, multivariable logistic regression was used to determine its relationship with PD. Moreover, spearman correlation was conducted to explore the correlation between the factors and PD related symptoms. The IL-27 level was compared between the cognitively healthy PD group and the mild cognitive impairment in PD (PD-MCI). The serum level of TRAILR2 was positively correlated with age and was not associated with other clinical characteristics related to PD.

RESULTS

Compared to controls, the serum levels of IL-27(P = 0.013) were increased whereas the levels of TRAILR2(P = 0.008) were decreased in PD patients. IL-8, IL-33, β-NGF, and AgRP showed no significant differences between the two groups. After controlling for the other variables, IL-27 was considered as an independent risk factor for PD in the multivariable logistic regression model. The receiver operating characteristic (ROC) curve for diagnosing PD with IL-27 yielded an area under the curve (AUC) of 0.621. Additionally, IL-27 level in PD patients was positively correlated with age, the disease duration, LEDD and negatively correlated with the MoCA scores. However, no significant difference was found in IL-27 levels between cognitively healthy PD and PD-MCI groups.

CONCLUSION

Elevated serum IL-27 was a risk factor for PD and positively correlated with the cognitive decline in PD.

The role of interferon signaling in neurodegeneration and neuropsychiatric disorders

Recent advances in transcriptomics research have uncovered heightened interferon (IFN) responses in neurodegenerative diseases including Alzheimer's disease, primary tauopathy, Parkinson's disease, TDP-43 proteinopathy, and related mouse models. Augmented IFN signaling is now relatively well established for microglia in these contexts, but emerging work has highlighted a novel role for IFN-responsive T cells in the brain and peripheral blood in some types of neurodegeneration. These findings complement a body of literature implicating dysregulated IFN signaling in neuropsychiatric disorders including major depression and post-traumatic stress disorder. In this review, we will characterize and integrate advances in our understanding of IFN responses in neurodegenerative and neuropsychiatric disease, discuss how sex and ancestry modulate the IFN response, and examine potential mechanistic explanations for the upregulation of antiviral-like IFN signaling pathways in these seemingly non-viral neurological and psychiatric disorders.

The immune system in Parkinson's disease: what we know so far

Parkinson's disease is characterized neuropathologically by the degeneration of dopaminergic neurons in the ventral midbrain, the accumulation of α-synuclein (α-syn) aggregates in neurons and chronic neuroinflammation. In the past two decades, in vitro, ex vivo and in vivo studies have consistently shown the involvement of inflammatory responses mediated by microglia and astrocytes, which may be elicited by pathological α-syn or signals from affected neurons and other cell types, and are directly linked to neurodegeneration and disease development. Apart from the prominent immune alterations seen in the CNS, including the infiltration of T cells into the brain, more recent studies have demonstrated important changes in the peripheral immune profile within both the innate and adaptive compartments, particularly involving monocytes, CD4+ and CD8+ T cells. This review aims to integrate the consolidated understanding of immune-related processes underlying the pathogenesis of Parkinson's disease, focusing on both central and peripheral immune cells, neuron-glia crosstalk as well as the central-peripheral immune interaction during the development of Parkinson's disease. Our analysis seeks to provide a comprehensive view of the emerging knowledge of the mechanisms of immunity in Parkinson's disease and the implications of this for better understanding the overall pathogenesis of this disease.

Novel human iPSC models of neuroinflammation in neurodegenerative disease and regenerative medicine

The importance of neuroinflammation in neurodegenerative diseases is becoming increasingly evident, and, in parallel, human induced pluripotent stem cell (hiPSC) models of physiology and pathology are emerging. Here, we review new advancements in the differentiation of hiPSCs into glial, neural, and blood-brain barrier (BBB) cell types, and the integration of these cells into complex organoids and chimeras. These advancements are relevant for modeling neuroinflammation in the context of prevalent neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). With awareness of current limitations, recent progress in the development and application of various hiPSC-derived models shows potential for aiding the identification of candidate therapeutic targets and immunotherapy approaches.

Intercellular Adhesion Molecule 1 (ICAM-1): An Inflammatory Regulator with Potential Implications in Ferroptosis and Parkinson's Disease

Intercellular adhesion molecule 1 (ICAM-1/CD54), a transmembrane glycoprotein, has been considered as one of the most important adhesion molecules during leukocyte recruitment. It is encoded by the ICAM1 gene and plays a central role in inflammation. Its crucial role in many inflammatory diseases such as ulcerative colitis and rheumatoid arthritis are well established. Given that neuroinflammation, underscored by microglial activation, is a key element in neurodegenerative diseases such as Parkinson's disease (PD), we investigated whether ICAM-1 has a role in this progressive neurological condition and, if so, to elucidate the underpinning mechanisms. Specifically, we were interested in the potential interaction between ICAM-1, glial cells, and ferroptosis, an iron-dependent form of cell death that has recently been implicated in PD. We conclude that there exist direct and indirect (via glial cells and T cells) influences of ICAM-1 on ferroptosis and that further elucidation of these interactions can suggest novel intervention for this devastating disease.

Protein tyrosine phosphatase receptor type O serves as a key regulator of insulin resistance-induced α-synuclein aggregation in Parkinson's disease

Insulin resistance (IR) was found to be a critical element in the pathogenesis of Parkinson's disease (PD), facilitating abnormal α-synuclein (α-Syn) aggregation in neurons and thus promoting PD development. However, how IR contributes to abnormal α-Syn aggregation remains ill-defined. Here, we analyzed six PD postmortem brain transcriptome datasets to reveal module genes implicated in IR-mediated α-Syn aggregation. In addition, we induced IR in cultured dopaminergic (DA) neurons overexpressing α-Syn to identify IR-modulated differentially expressed genes (DEGs). Integrated analysis of data from PD patients and cultured neurons revealed 226 genes involved in α-Syn aggregation under IR conditions, of which 53 exhibited differential expression between PD patients and controls. Subsequently, we conducted an integrated analysis of the 53 IR-modulated genes employing transcriptome data from PD patients with different Braak stages and DA neuron subclasses with varying α-Syn aggregation scores. Protein tyrosine phosphatase receptor type O (PTPRO) was identified to be closely associated with PD progression and α-Syn aggregation. Experimental validation in a cultured PD cell model confirmed that both mRNA and protein of PTPRO were reduced under IR conditions, and the downregulation of PTPRO significantly facilitated α-Syn aggregation and cell death. Collectively, our findings identified PTPRO as a key regulator in IR-mediated α-Syn aggregation and uncovered its prospective utility as a therapeutic target in PD patients with IR.

Immune responses to oligomeric α-synuclein in Parkinson's disease peripheral blood mononuclear cells

Parkinson's disease displays clinical heterogeneity, presenting with motor and non-motor symptoms. Heterogeneous phenotypes, named brain-first and body-first, may reflect distinct α-synuclein pathology starting either in the central nervous system or in the periphery. The immune system plays a prominent role in the central and peripheral pathology, with misfolded α-synuclein being placed at the intersection between neurodegeneration and inflammation. Here, we characterized the inflammatory profile and immune-phenotype of peripheral blood mononuclear cells (PBMCs) from Parkinson's disease patients upon stimulation with α-synuclein monomer or oligomer, and investigated relationships of immune parameters with clinical scores of motor and non-motor symptoms. Freshly isolated PBMCs from 21 Parkinson's disease patients and 18 healthy subjects were exposed in vitro to α-synuclein species. Cytokine/chemokine release was measured in the culture supernatant by Multiplex Elisa. The immune-phenotype was studied by FACS-flow cytometry. Correlation analysis was computed between immune parameters and parkinsonian motor and non-motor scales. We found that Parkinson's disease patients exhibited a dysregulated PBMC-cytokine profile, which remained unaltered after exposure to α-synuclein species and correlated with both motor and non-motor severity, with a strong correlation observed with olfactory impairment. Exposure of PBMCs from healthy controls to α-synuclein monomer/oligomer increased the cytokine/chemokine release up to patient's values. Moreover, the PBMCs immune phenotype differed between patients and controls and revealed a prominent association of the Mos profile with olfactory impairment, and of NK profile with constipation. Results suggest that a deranged PBMC-immune profile may reflect distinct clinical subtypes and would fit with the recent classification of Parkinson's disease into peripheral-first versus brain-first phenotype.

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.

Inflammation and heterogeneity in synucleinopathies

Neurodegenerative diseases represent a huge healthcare challenge which is predicted to increase with an aging population. Synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), present complex challenges in understanding their onset and progression. They are characterized by the abnormal aggregation of α-synuclein in the brain leading to neurodegeneration. Accumulating evidence supports the existence of distinct subtypes based on the site of α-synuclein aggregation initiation, genetics, and, more recently, neuroinflammation. Mediated by both central nervous system-resident cells, peripheral immune cells, and gut dysbiosis, neuroinflammation appears as a key process in the onset and progression of neuronal loss. Sex-based differences add another layer of complexity to synucleinopathies, influencing disease prevalence - with a known higher incidence of PD in males compared to females - as well as phenotype and immune responses. Biological sex affects neuroinflammatory pathways and the immune response, suggesting the need for sex-specific therapeutic strategies and biomarker identification. Here, we review the heterogeneity of synucleinopathies, describing the etiology, the mechanisms by which the inflammatory processes contribute to the pathology, and the consideration of sex-based differences to highlight the need for personalized therapeutics.

Microglia-specific IL-10 gene delivery inhibits neuroinflammation and neurodegeneration in a mouse model of Parkinson's disease

Neuroinflammation plays a key role in exacerbating dopaminergic neuron (DAN) loss in Parkinson's disease (PD). However, it remains unresolved how to effectively normalize this immune response given the complex interplay between the innate and adaptive immune responses occurring within a scarcely accessible organ like the brain. In this study, we uncovered a consistent correlation between neuroinflammation, brain parenchymal lymphocytes, and DAN loss among several commonly used mouse models of PD generated by a variety of pathological triggers. We validated a viral therapeutic approach for the microglia-specific expression of interleukin 10 (IL-10) to selectively mitigate the excessive inflammatory response. We found that this approach induced a local nigral IL-10 release that alleviated DAN loss in mice overexpressing the human SNCA gene in the substantia nigra. Single-cell transcriptomics revealed that IL-10 induced the emergence of a molecularly distinct microglial cell state, enriched in markers of cell activation with enhanced expression of prophagocytic pathways. IL-10 promoted microglial phagocytotic and clearance activities in vitro and reduced αSYN aggregate burden in the nigral area in mice overexpressing SNCA. Furthermore, IL-10 stimulated the differentiation of CD4+ T lymphocytes into active T regulatory cells and promoted inhibitory characteristics in CD8+ T cells. In summary, our results show that local and microglia-specific IL-10 transduction elicited strong immunomodulation in the nigral tissue with enhanced suppression of lymphocyte toxicity that was associated with DAN survival. These results offer insights into the therapeutic benefits of IL-10 and showcase a promising gene delivery approach that could minimize undesired side effects.

Prediction of Future Parkinson Disease Using Plasma Proteins Combined With Clinical-Demographic Measures

BACKGROUND AND OBJECTIVES

Identification of individuals at high risk of developing Parkinson disease (PD) several years before diagnosis is crucial for developing treatments to prevent or delay neurodegeneration. This study aimed to develop predictive models for PD risk that combine plasma proteins and easily accessible clinical-demographic variables.

METHODS

Using data from the UK Biobank (UKB), which recruited participants across the United Kingdom, we conducted a longitudinal study to identify predictors for incident PD. Participants with baseline plasma proteins and no PD were included. Through machine learning, we narrowed down predictors from a pool of 1,463 plasma proteins and 93 clinical-demographic. These predictors were then externally validated using the Parkinson's Progression Marker Initiative (PPMI) cohort. To further investigate the temporal trends of predictors, a nested case-control study was conducted within the UKB.

RESULTS

A total of 52,503 participants without PD (median age 58, 54% female) were included. Over a median follow-up duration of 14.0 years, 751 individuals were diagnosed with PD (median age 65, 37% female). Using a forward selection approach, we selected a panel of 22 plasma proteins for optimal prediction. Using an ensemble tree-based Light Gradient Boosting Machine (LightGBM) algorithm, the model achieved an area under the receiver operating characteristic curve (AUC) of 0.800 (95% CI 0.785-0.815). The LightGBM prediction model integrating both plasma proteins and clinical-demographic variables demonstrated enhanced predictive accuracy, with an AUC of 0.832 (95% CI 0.815-0.849). Key predictors identified included age, years of education, history of traumatic brain injury, and serum creatinine. The incorporation of 11 plasma proteins (neurofilament light, integrin subunit alpha V, hematopoietic PGD synthase, histamine N-methyltransferase, tubulin polymerization promoting protein family member 3, ectodysplasin A2 receptor, Latexin, interleukin-13 receptor subunit alpha-1, BAG family molecular chaperone regulator 3, tryptophanyl-TRNA synthetase, and secretogranin-2) augmented the model's predictive accuracy. External validation in the PPMI cohort confirmed the model's reliability, producing an AUC of 0.810 (95% CI 0.740-0.873). Notably, alterations in these predictors were detectable several years before the diagnosis of PD.

DISCUSSION

Our findings support the potential utility of a machine learning-based model integrating clinical-demographic variables with plasma proteins to identify individuals at high risk for PD within the general population. Although these predictors have been validated by PPMI, additional validation in a more diverse population reflective of the general community is essential.