Increased expression of dopamine receptors on lymphocytes in Parkinson's disease

Analysis of LRRN3, MEF2C, SLC22A, and P2RY12 Gene Expression in the Peripheral Blood of Patients in the Early Stages of Parkinson's Disease

Parkinson's disease (PD) is one of the most common human neurodegenerative diseases. Belated diagnoses of PD and late treatment are caused by its elongated prodromal phase. Thus, searching for new candidate genes participating in the development of the pathological process in the early stages of the disease in patients who have not yet received therapy is relevant. Changes in mRNA and protein levels have been described both in the peripheral blood and in the brain of patients with PD. Thus, analysis of changes in the mRNA expression in peripheral blood is of great importance in studying the early stages of PD. This work aimed to analyze the changes in MEF2C, SLC22A4, P2RY12, and LRRN3 gene expression in the peripheral blood of patients in the early stages of PD. We found a statistically relevant and PD-specific change in the expression of the LRRN3 gene, indicating a disruption in the processes of neuronal regeneration and the functioning of synapses. The data obtained during the study indicate that this gene can be considered a potential biomarker of the early stages of PD.

Analysis of ADORA2A, MTA1, PTGDS, PTGS2, NSF, and HNMT Gene Expression Levels in Peripheral Blood of Patients with Early Stages of Parkinson's Disease

Parkinson's disease (PD) is a common chronic, age-related neurodegenerative disease. This disease is characterized by a long prodromal period. In this context, it is important to search for the genes and mechanisms that are involved in the development of the pathological process in the earliest stages of the disease. Published data suggest that blood cells, particularly lymphocytes, may be a model for studying the processes that occur in the brain in PD. Thus, in the present work, we performed an analysis of changes in the expression of the genes ADORA2A, MTA1, PTGDS, PTGS2, NSF, and HNMT in the peripheral blood of patients with early stages of PD (stages 1 and 2 of the Hoehn-Yahr scale). We found significant and PD-specific expression changes of four genes, i.e., MTA1, PTGS2, NSF, and HNMT, in the peripheral blood of patients with early stages of PD. These genes may be associated with PD pathogenesis in the early clinical stages and can be considered as potential candidate genes for this disease. Altered expression of the ADORA2A gene in treated PD patients may indicate that this gene is involved in processes affected by antiparkinsonian therapy.

Dopaminergic regulation of inflammation and immunity in Parkinson's disease: friend or foe?

Parkinson's disease (PD) is a neurodegenerative disease affecting 7-10 million people worldwide. Currently, there is no treatment available to prevent or delay PD progression, partially due to the limited understanding of the pathological events which lead to the death of dopaminergic neurons in the substantia nigra in the brain, which is known to be the cause of PD symptoms. The current available treatments aim at compensating dopamine (DA) deficiency in the brain using its precursor levodopa, dopaminergic agonists and some indirect dopaminergic agents. The immune system is emerging as a critical player in PD. Therefore, immune-based approaches have recently been proposed to be used as potential antiparkinsonian agents. It has been well-known that dopaminergic pathways play a significant role in regulating immune responses in the brain. Although dopaminergic agents are the primary antiparkinsonian treatments, their immune regulatory effect has yet to be fully understood. The present review summarises the current available evidence of the immune regulatory effects of DA and its mimics and discusses dopaminergic agents as antiparkinsonian drugs. Based on the current understanding of their involvement in the regulation of neuroinflammation in PD, we propose that targeting immune pathways involved in PD pathology could offer a better treatment outcome for PD patients.

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

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

Dopamine, Immunity, and Disease

The neurotransmitter dopamine is a key factor in central nervous system (CNS) function, regulating many processes including reward, movement, and cognition. Dopamine also regulates critical functions in peripheral organs, such as blood pressure, renal activity, and intestinal motility. Beyond these functions, a growing body of evidence indicates that dopamine is an important immunoregulatory factor. Most types of immune cells express dopamine receptors and other dopaminergic proteins, and many immune cells take up, produce, store, and/or release dopamine, suggesting that dopaminergic immunomodulation is important for immune function. Targeting these pathways could be a promising avenue for the treatment of inflammation and disease, but despite increasing research in this area, data on the specific effects of dopamine on many immune cells and disease processes remain inconsistent and poorly understood. Therefore, this review integrates the current knowledge of the role of dopamine in immune cell function and inflammatory signaling across systems. We also discuss the current understanding of dopaminergic regulation of immune signaling in the CNS and peripheral tissues, highlighting the role of dopaminergic immunomodulation in diseases such as Parkinson's disease, several neuropsychiatric conditions, neurologic human immunodeficiency virus, inflammatory bowel disease, rheumatoid arthritis, and others. Careful consideration is given to the influence of experimental design on results, and we note a number of areas in need of further research. Overall, this review integrates our knowledge of dopaminergic immunology at the cellular, tissue, and disease level and prompts the development of therapeutics and strategies targeted toward ameliorating disease through dopaminergic regulation of immunity. SIGNIFICANCE STATEMENT: Canonically, dopamine is recognized as a neurotransmitter involved in the regulation of movement, cognition, and reward. However, dopamine also acts as an immune modulator in the central nervous system and periphery. This review comprehensively assesses the current knowledge of dopaminergic immunomodulation and the role of dopamine in disease pathogenesis at the cellular and tissue level. This will provide broad access to this information across fields, identify areas in need of further investigation, and drive the development of dopaminergic therapeutic strategies.

Transcriptome Profiling Reveals Differential Expression of Circadian Behavior Genes in Peripheral Blood of Monozygotic Twins Discordant for Parkinson's Disease

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases. Investigating individuals with the most identical genetic background is optimal for minimizing the genetic contribution to gene expression. These individuals include monozygotic twins discordant for PD. Monozygotic twins have the same genetic background, age, sex, and often similar environmental conditions. The aim of this study was to carry out a transcriptome analysis of the peripheral blood of three pairs of monozygotic twins discordant for PD. We identified the metabolic process “circadian behavior” as a priority process for further study. Different expression of genes included in the term “circadian behavior” confirms that this process is involved in PD pathogenesis. We found increased expression of three genes associated with circadian behavior, i.e., PTGDS, ADORA2A, and MTA1, in twins with PD. These genes can be considered as potential candidate genes for this disease.

Expression Analysis of Genes Involved in Transport Processes in Mice with MPTP-Induced Model of Parkinson’s Disease

Processes of intracellular and extracellular transport play one of the most important roles in the functioning of cells. Changes to transport mechanisms in a neuron can lead to the disruption of many cellular processes and even to cell death. It was shown that disruption of the processes of vesicular, axonal, and synaptic transport can lead to a number of diseases of the central nervous system, including Parkinson’s disease (PD). Here, we studied changes in the expression of genes whose protein products are involved in the transport processes (Snca, Drd2, Rab5a, Anxa2, and Nsf) in the brain tissues and peripheral blood of mice with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced models of PD. We detected changes in the expressions of Drd2, Anxa2, and Nsf at the earliest modeling stages. Additionally, we have identified conspicuous changes in the expression level of Anxa2 in the striatum and substantia nigra of mice with MPTP-induced models of PD in its early stages. These data clearly suggest the involvement of protein products in these genes in the earliest stages of the pathogenesis of PD.

A Machine Learning Approach to Parkinson’s Disease Blood Transcriptomics

The increased incidence and the significant health burden associated with Parkinson’s disease (PD) have stimulated substantial research efforts towards the identification of effective treatments and diagnostic procedures. Despite technological advancements, a cure is still not available and PD is often diagnosed a long time after onset when irreversible damage has already occurred. Blood transcriptomics represents a potentially disruptive technology for the early diagnosis of PD. We used transcriptome data from the PPMI study, a large cohort study with early PD subjects and age matched controls (HC), to perform the classification of PD vs. HC in around 550 samples. Using a nested feature selection procedure based on Random Forests and XGBoost we reached an AUC of 72% and found 493 candidate genes. We further discussed the importance of the selected genes through a functional analysis based on GOs and KEGG pathways.

Development of early diagnosis of Parkinson's disease: Illusion or reality?

The fight against neurodegenerative diseases, Alzheimer disease and Parkinson's disease (PD), is a challenge of the 21st century. The low efficacy of treating patients is due to the late diagnosis and start of therapy, after the degeneration of most specific neurons and depletion of neuroplasticity. It is believed that the development of early diagnosis (ED) and preventive treatment will delay the onset of specific symptoms. This review evaluates methodologies for developing ED of PD. Since PD is a systemic disease, and the degeneration of certain neurons precedes that of nigrostriatal dopaminergic neurons that control motor function, the current methodology is based on searching biomarkers, such as premotor symptoms and changes in body fluids (BF) in patients. However, all attempts to develop ED were unsuccessful. Therefore, it is proposed to enhance the current methodology by (i) selecting among biomarkers found in BF in patients at the clinical stage those that are characteristics of animal models of the preclinical stage, (ii) searching biomarkers in BF in subjects at the prodromal stage, selected by detecting premotor symptoms and failure of the nigrostriatal dopaminergic system. Moreover, a new methodology was proposed for the development of ED of PD using a provocative test, which is successfully used in internal medicine.

Where Is Dopamine and how do Immune Cells See it?: Dopamine-Mediated Immune Cell Function in Health and Disease

Dopamine is well recognized as a neurotransmitter in the brain, and regulates critical functions in a variety of peripheral systems. Growing research has also shown that dopamine acts as an important regulator of immune function. Many immune cells express dopamine receptors and other dopamine related proteins, enabling them to actively respond to dopamine and suggesting that dopaminergic immunoregulation is an important part of proper immune function. A detailed understanding of the physiological concentrations of dopamine in specific regions of the human body, particularly in peripheral systems, is critical to the development of hypotheses and experiments examining the effects of physiologically relevant dopamine concentrations on immune cells. Unfortunately, the dopamine concentrations to which these immune cells would be exposed in different anatomical regions are not clear. To address this issue, this comprehensive review details the current information regarding concentrations of dopamine found in both the central nervous system and in many regions of the periphery. In addition, we discuss the immune cells present in each region, and how these could interact with dopamine in each compartment described. Finally, the review briefly addresses how changes in these dopamine concentrations could influence immune cell dysfunction in several disease states including Parkinson's disease, multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, as well as the collection of pathologies, cognitive and motor symptoms associated with HIV infection in the central nervous system, known as NeuroHIV. These data will improve our understanding of the interactions between the dopaminergic and immune systems during both homeostatic function and in disease, clarify the effects of existing dopaminergic drugs and promote the creation of new therapeutic strategies based on manipulating immune function through dopaminergic signaling. Graphical Abstract.

VCP expression decrease as a biomarker of preclinical and early clinical stages of Parkinson's disease

Valosin-containing human protein (VCP) or p97 performs enzyme functions associated with the maintenance of protein homeostasis and control of protein quality. Disruption of its normal functioning might be associated with the development of Parkinson’s disease (PD). Tissues of mice with toxin-induced presymptomatic and early symptomatic stages of PD, as well as 52 treated and untreated patients with newly diagnosed PD and nine patients with a “predicted” form of PD, were investigated. Significant changes in Vcp gene expression were observed in almost all studied mouse tissues. A significant decrease in VCP expression specific for PD was also detected at both the late preclinical and the early clinical stages of PD in untreated patients. Thus, a decrease in VCP expression is important for changes in the function of the nervous system at early stages of PD. Analysis of changes in VCP expression in all patients with PD and in Vcp in the peripheral blood of mice used as models of PD revealed significant decreases in expression specific for PD. These data suggest that a decrease in the relative levels of VCP mRNA might serve as a biomarker for the development of pathology at the early clinical and preclinical stages of human PD.

Critical Neurotransmitters in the Neuroimmune Network

Immune cells rely on cell-cell communication to specify and fine-tune their responses. They express an extensive network of cell communication modes, including a vast repertoire of cell surface and transmembrane receptors and ligands, membrane vesicles, junctions, ligand and voltage-gated ion channels, and transporters. During a crosstalk between the nervous system and the immune system these modes of cellular communication and the downstream signal transduction events are influenced by neurotransmitters present in the local tissue environments in an autocrine or paracrine fashion. Neurotransmitters thus influence innate and adaptive immune responses. In addition, immune cells send signals to the brain through cytokines, and are present in the brain to influence neural responses. Altered communication between the nervous and immune systems is emerging as a common feature in neurodegenerative and immunopathological diseases. Here, we present the mechanistic frameworks of immunostimulatory and immunosuppressive effects critical neurotransmitters - dopamine (3,4-dihydroxyphenethylamine), serotonin (5-hydroxytryptamine), substance P (trifluoroacetate salt powder), and L-glutamate - exert on lymphocytes and non-lymphoid immune cells. Furthermore, we discuss the possible roles neurotransmitter-driven neuroimmune networks play in the pathogenesis of neurodegenerative disorders, autoimmune diseases, cancer, and outline potential clinical implications of balancing neuroimmune crosstalk by therapeutic modulation.

Interaction of neurotransmitters and neurochemicals with lymphocytes

Neurotransmitters and neurochemicals can act on lymphocytes by binding to receptors expressed by lymphocytes. This review describes lymphocyte expression of receptors for a selection of neurotransmitters and neurochemicals, the anatomical locations where lymphocytes can interact with neurotransmitters, and the effects of the neurotransmitters on lymphocyte function. Implications for health and disease are also discussed.

Upgraded Methodology for the Development of Early Diagnosis of Parkinson's Disease Based on Searching Blood Markers in Patients and Experimental Models

Numerous attempts to develop an early diagnosis of Parkinson's disease (PD) by searching biomarkers in biological fluids were unsuccessful. The drawback of this methodology is searching markers in patients at the clinical stage without guarantee that they are also characteristic of either preclinical stage or prodromal stage (preclinical-prodromal stage). We attempted to upgrade this methodology by selecting only markers that are found both in patients and in PD animal models. HPLC and RT-PCR were used to estimate the concentration of amino acids, catecholamines/metabolites in plasma and gene expression in lymphocytes in 36 untreated early-stage PD patients and 52 controls, and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice at modeling the clinical ("symptomatic") stage and preclinical-prodromal ("presymptomatic") stage of PD. It was shown that among 13 blood markers found in patients, 7 markers are characteristic of parkinsonian symptomatic mice and 3 markers of both symptomatic and presymptomatic mice. According to our suggestion, the detection of the same marker in patients and symptomatic animals indicates adequate reproduction of pathogenesis along the corresponding metabolic pathway, whereas the detection of the same marker in presymptomatic animals indicates its specificity for preclinical-prodromal stage. This means that the minority of markers found in patients-decreased concentration of L-3,4-dihydroxyphenylalanine (L-DOPA) and dihydroxyphenylacetic acid (DOPAC) and increased dopamine D3 receptor gene expression-are specific for preclinical-prodromal stage and are suitable for early diagnosis of PD. Thus, we upgraded a current methodology for development of early diagnosis of PD by searching blood markers not only in patients but also in parkinsonian animals.

Peripheral Dopamine in Restless Legs Syndrome

Objective/Background

Restless Legs Syndrome (RLS) is a dopamine-dependent disorder characterized by a strong urge to move. The objective of this study was to evalulate blood levels of dopamine and other catecholamines and blood D2-subtype dopamine receptors (D2Rs) in RLS.

Patients/Methods

Dopamine levels in blood samples from age-matched unmedicated RLS subjects, medicated RLS subjects and Controls were evaluated with high performance liquid chromatography and dopamine D2R white blood cell (WBC) expression levels were determined with fluorescence-activated cell sorting and immunocytochemistry.

Results

Blood plasma dopamine levels, but not norepinepherine or epinephrine levels, were significantly increased in medicated RLS subjects vs unmedicated RLS subjects and Controls. The percentage of lymphocytes and monocytes expressing D2Rs differed between Control, RLS medicated and RLS unmedicated subjects. Total D2R expression in lymphocytes, but not monocytes, differed between Control, RLS medicated and RLS unmedicated subjects. D2Rs in lymphocytes, but not monocytes, were sensitive to dopamine in Controls only.

Conclusion

Downregulation of WBCs D2Rs occurs in RLS. This downregulation is not reversed by medication, although commonly used RLS medications increase plasma dopamine levels. The insensitivity of monocytes to dopamine levels, but their downregulation in RLS, may reflect their utility as a biomarker for RLS and perhaps brain dopamine homeostasis.

Transcriptome Profile Changes in Mice with MPTP-Induced Early Stages of Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Despite progress in the study of the molecular, genetic, and pathogenic mechanisms of PD, it is unclear which processes trigger the development of the pathology associated with PD. Models of the presymptomatic and early symptomatic stages of PD induced by MPTP have been used to analyze changes in transcriptome profile in brain tissues, to identify specific patterns and mechanisms underlying neurodegeneration in PD. The whole-transcriptome analysis in the brain tissues of the mice with MPTP-induced PD showed that striatum is involved in the pathogenesis in the earliest stages and the processes associated with vesicular transport may be altered. The expression profiles of the genes studied in the substantia nigra and peripheral blood confirm that lymphocytes from peripheral blood may reflect processes occurring in the brain. These data suggest that messenger RNA (mRNA) levels in peripheral blood may provide potential biomarkers of the neurodegeneration occurring in PD. The changes in expression at the mRNA and protein levels suggest that Snca may be involved in neurodegeneration and Drd2 may participate in the development of the compensatory mechanisms in the early stages of PD pathogenesis. Our data suggest that the brain cortex may be involved in the pathological processes in the early stages of PD, including the presymptomatic stage.

[Development of preclinical diagnosis and preventive treatment of neurodegenerative diseases]

Neurodegenerative diseases (NDD) are serious fatal neurological and mental diseases that resulted in disability and fethal outcome. Based on the advances of basic sciences over the last two decades, new knowledge on the risk factors for NDD and molecular mechanisms of the pathogenesis are obtained. It has been shown that the accelerated process of neuronal death which is the main cause of NDD development begins long before the appearance of clinical symptoms. The first symptoms appeared only after the death of most specific regulatory neurons and exhaustion of brain compensatory reserve. Only at that time, one can make the diagnosis and start traditional treatment of patients that accounts for the extremely low efficacy of the latter. Currently, complex preclinical diagnosis based on the identification of relatively specific clinical precursors and peripheral biomarkers has been developing. Development of preclinical diagnosis and preventive treatment is a strategic issue of modern neurology and psychiatry. The resolution of this issue allows to consider NDD as cured, but not fatal, diseases.

Pramipexole, a Dopamine D2/D3 Receptor-Preferring Agonist, Prevents Experimental Autoimmune Encephalomyelitis Development in Mice

Experimental autoimmune encephalomyelitis (EAE) is the most used animal model of multiple sclerosis (MS) for the development of new therapies. Dopamine receptors can modulate EAE and MS development, thus highlighting the potential use of dopaminergic agonists in the treatment of MS, which has been poorly explored. Herein, we hypothesized that pramipexole (PPX), a dopamine D2/D3 receptor-preferring agonist commonly used to treat Parkinson's disease (PD), would be a suitable therapeutic drug for EAE. Thus, we report the effects and the underlying mechanisms of action of PPX in the prevention of EAE. PPX (0.1 and 1 mg/kg) was administered intraperitoneally (i.p.) from day 0 to 40 post-immunization (p.i.). Our results showed that PPX 1 mg/kg prevented EAE development, abolishing EAE signs by blocking neuroinflammatory response, demyelination, and astroglial activation in spinal cord. Moreover, PPX inhibited the production of inflammatory cytokines, such as IL-17, IL-1β, and TNF-α in peripheral lymphoid tissue. PPX was also able to restore basal levels of a number of EAE-induced effects in spinal cord and striatum, such as reactive oxygen species, glutathione peroxidase, parkin, and α-synuclein (α-syn). Thus, our findings highlight the usefulness of PPX in preventing EAE-induced motor symptoms, possibly by modulating immune cell responses, such as those found in MS and other T helper cell-mediated inflammatory diseases.

Dopamine and T cells: dopamine receptors and potent effects on T cells, dopamine production in T cells, and abnormalities in the dopaminergic system in T cells in autoimmune, neurological and psychiatric diseases

Dopamine, a principal neurotransmitter, deserves upgrading to 'NeuroImmunotransmitter' thanks to its multiple, direct and powerful effects on most/all immune cells. Dopamine by itself is a potent activator of resting effector T cells (Teffs), via two independent ways: direct Teffs activation, and indirect Teffs activation by suppression of regulatory T cells (Tregs). The review covers the following findings: (i) T cells express functional dopamine receptors (DRs) D1R-D5R, but their level and function are dynamic and context-sensitive, (ii) DR membranal protein levels do not necessarily correlate with DR mRNA levels, (iii) different T cell types/subtypes have different DR levels and composition and different responses to dopamine, (iv) autoimmune and pro-inflammatory T cells and T cell leukaemia/lymphoma also express functional DRs, (v) dopamine (~10(-8) M) activates resting/naive Teffs (CD8(+) >>>CD4(+) ), (vi) dopamine affects Th1/Th2/Th17 differentiation, (vii) dopamine inhibits already activated Teffs (i.e. T cells that have been already activated by either antigen, mitogen, anti-CD3 antibodies cytokines or other molecules), (viii) dopamine inhibits activated Tregs in an autocrine/paracrine manner. Thus, dopamine 'suppresses the suppressors' and releases the inhibition they exert on Teffs, (ix) dopamine affects intracellular signalling molecules and cascades in T cells (e.g. ERK, Lck, Fyn, NF-κB, KLF2), (x) T cells produce dopamine (Tregs>>>Teffs), can release dopamine, mainly after activation (by antigen, mitogen, anti-CD3 antibodies, PKC activators or other), uptake extracellular dopamine, and most probably need dopamine, (xi) dopamine is important for antigen-specific interactions between T cells and dendritic cells, (xii) in few autoimmune diseases (e.g. multiple sclerosis/SLE/rheumatoid arthritis), and neurological/psychiatric diseases (e.g. Parkinson disease, Alzheimer's disease, Schizophrenia and Tourette), patient's T cells seem to have abnormal DRs expression and/or responses to dopamine or production of dopamine, (xiii) drugs that affect the dopaminergic system have potent effects on T cells (e.g. dopamine=Intropin, L-dopa, bromocriptine, haloperidol, quinpirole, reserpine, pergolide, ecopipam, pimozide, amantadine, tetrabenazine, nomifensine, butaclamol). Dopamine-induced activation of resting Teffs and suppression of Tregs seem beneficial for health and may also be used for immunotherapy of cancer and infectious diseases. Independently, suppression of DRs in autoimmune and pro-inflammatory T cells, and also in cancerous T cells, may be advantageous. The review is relevant to Immunologists, Neurologists, Neuroimmunologists, Hematologists, Psychiatrists, Psychologists and Pharmacologists.

Potential Biomarkers of the Earliest Clinical Stages of Parkinson's Disease

Parkinson's disease (PD) is a widespread neurodegenerative disorder. Despite the intensive studies of this pathology, in general, the picture of the etiopathogenesis has still not been clarified fully. To understand better the mechanisms underlying the pathogenesis of PD, we analyzed the expression of 10 genes in the peripheral blood of treated and untreated patients with PD. 35 untreated patients with PD and 12 treated patients with Parkinson's disease (Hoehn and Yahr scores 1-2) were studied. An analysis of the mRNA levels of ATP13A2, PARK2, PARK7, PINK1, LRRK2, SNCA, ALDH1A1, PDHB, PPARGC1A, and ZNF746 genes in the peripheral blood of patients was carried out using reverse transcription followed by real-time PCR. A statistically significant and specific increase by more than 1.5-fold in the expression of the ATP13A2, PARK7, and ZNF746 genes was observed in patients with PD. Based on these results, it can be suggested that the upregulation of the mRNA levels of ATP13A2, PARK7, and ZNF746 in untreated patients in the earliest clinical stages can also be observed in the preclinical stages of PD, and that these genes can be considered as potential biomarkers of the preclinical stage of PD.

Biosignatures for Parkinson's disease and atypical parkinsonian disorders patients

Diagnosis of Parkinson' disease (PD) carries a high misdiagnosis rate due to failure to recognize atypical parkinsonian disorders (APD). Usually by the time of diagnosis greater than 60% of the neurons in the substantia nigra are dead. Therefore, early detection would be beneficial so that therapeutic intervention may be initiated early in the disease process. We used splice variant-specific microarrays to identify mRNAs whose expression is altered in peripheral blood of early-stage PD patients compared to healthy and neurodegenerative disease controls. Quantitative polymerase chain reaction assays were used to validate splice variant transcripts in independent sample sets. Here we report a PD signature used to classify blinded samples with 90% sensitivity and 94% specificity and an APD signature that resulted in a diagnosis with 95% sensitivity and 94% specificity. This study provides the first discriminant functions with coherent diagnostic signatures for PD and APD. Analysis of the PD biomarkers identified a regulatory network with nodes centered on the transcription factors HNF4A and TNF, which have been implicated in insulin regulation.

The dopaminergic system in peripheral blood lymphocytes: from physiology to pharmacology and potential applications to neuropsychiatric disorders

Besides its action on the nervous system, dopamine (DA) plays a role on neural-immune interactions. Here we review the current evidence on the dopaminergic system in human peripheral blood lymphocytes (PBL). PBL synthesize DA through the tyrosine-hydroxylase/DOPA-decarboxylase pathway, and express DA receptors and DA transporter (DAT) on their plasma membrane. Stimulation of DA receptors on PBL membrane contributes to modulate the development and initiation of immune responses under physiological conditions and in immune system pathologies such as autoimmunity or immunodeficiency.

The characterization of DA system in PBL gave rise to a further line of research investigating the feasibility of PBL as a cellular model for studying DA derangement in neuropsychiatric disorders. Several reports showed changes of the expression of DAT and/or DA receptors in PBL from patients suffering from several neuropsychiatric disorders, in particular parkinsonian syndromes, schizophrenia and drug- or alcohol-abuse. Despite some methodological and theoretical limitations, these findings suggest that PBL may prove a cellular tool with which to identify the derangement of DA transmission in neuropsychiatric diseases, as well as to monitor the effects of pharmacological treatments.

Decreased expression of B cell related genes in leukocytes of women with Parkinson's disease

Background

Parkinson's disease (PD) is a complex disorder caused by genetic, environmental and age-related factors, and it is more prevalent in men. We aimed to identify differentially expressed genes in peripheral blood leukocytes (PBLs) that might be involved in PD pathogenesis. Transcriptomes of 30 female PD-patients and 29 age- and sex-matched controls were profiled using GeneChip Human Exon 1.0 ST Arrays. Samples were from unrelated Ashkenazi individuals, non-carriers of LRRK2 G2019S or GBA founder mutations.

Results

Differential expression was detected in 115 genes (206 exons), with over-representation of immune response annotations. Thirty genes were related to B cell functions, including the uniquely B cell-expressed IGHM and IGHD, the B cell surface molecules CD19, CD22 and CD79A, and the B cell gene regulator, PAX5. Quantitative-RT-PCR confirmation of these 6 genes in 79 individuals demonstrated decreased expression, mainly in women patients, independent of PD-pharmacotherapy status.

Conclusions

Our results suggest that the down regulation of genes related to B cell activity reflect the involvement of these cells in PD in Ashkenazi individuals and represents a molecular aspect of gender-specificity in PD.

Blood-based protein biomarkers for diagnosis and classification of neurodegenerative diseases: current progress and clinical potential

Biomarker research is a rapidly advancing field in medicine. Recent advances in genomic, genetic, epigenetic, neuroscientific, proteomic, and metabolomic knowledge and technologies have opened the way to thriving research. In the most general sense, a biomarker refers to any useful characteristic that can be measured and used as an indicator of a normal biologic process, a pathogenic process, or a pharmacologic response to a therapeutic agent. Despite the extensive resources concentrated on this area, there are very few biomarkers currently available that qualify and are satisfactorily validated for mental disorders, and there is still a major lack of biomarkers for typifying neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. This article provides an overview of this field of research and focuses on recent advances in biomarker research in Alzheimer's disease and Parkinson's disease.

Biomarkers of Parkinson's disease and Dementia with Lewy bodies

Parkinson's disease (PD) and Dementia with Lewy bodies (DLB) are progressive and disabling neurodegenerative disorders, in which signs and symptoms overlap with each other and with other neurodegenerative conditions. Currently, diagnosis, measurement of progression, and response to therapeutic intervention rely upon clinical observation. However, there remains a critical need for validated biomarkers in each of these areas. A definitive diagnostic test would improve clinical management and enrollment into clinical trials. An objective measure of progression is vitally important in identifying neuroprotective interventions. Biomarkers may also provide insight into pathogenesis, and might therefore suggest possible novel targets for therapeutic intervention. In addition, certain biomarkers might be of use in monitoring the biochemical and physiological effects of therapeutic interventions. Development of diagnostic biomarkers has focused until recently upon imaging techniques based upon measuring loss of dopamine neurons. Additionally, advances in understanding the genetic contribution to neurodegenerative disorders, in particular in PD, have identified multiple causative genes and risk factors that in some cases may help estimate PD risk. However, recent availability of increasingly sophisticated bioinformatics technology has rendered development of fluid biomarkers feasible, opening the possibility of generally accessible blood or cerebrospinal fluid (CSF) tests that could impact upon diagnosis, management, and research in PD, PDD, and DLB.

Dopamine D1-like receptor antagonist attenuates Th17-mediated immune response and ovalbumin antigen-induced neutrophilic airway inflammation

Allergic airway inflammation is generally considered a Th2-type immune response. Recent studies, however, demonstrated that Th17-type immune responses also play important roles in this process, especially in the pathogenesis of neutrophilic airway inflammation, a hallmark of severe asthma. We previously reported that dendritic cells release dopamine to naive CD4(+) T cells in Ag-specific cell-cell interaction, in turn inducing Th17 differentiation through dopamine D1-like receptor (D1-like-R). D1-like-R antagonist attenuates Th17-mediated diseases such as experimental autoimmune encephalomyelitis and autoimmune diabetes. However, the effect of antagonizing D1-like-R on Th17-mediated airway inflammation has yet to be studied. In this study, we examined whether D1-like-R antagonist suppresses OVA-induced neutrophilic airway inflammation in OVA TCR-transgenic DO11.10 mice and then elucidated the mechanism of action. DO11.10 mice were nebulized with OVA or PBS, and some mice received D1-like-R antagonist orally before OVA nebulization. D1-like-R antagonist significantly suppressed OVA-induced neutrophilic airway inflammation in DO11.10 mice. It also inhibited the production of IL-17 and infiltration of Th17 cells in the lung. Further, D1-like-R antagonist suppressed the production of IL-23 by lung CD11c(+) APCs. In contrast, D1-like-R antagonist did not increase Foxp3(+) regulatory T cells in the lung. D1-like-R antagonist neither suppressed nonspecific LPS-induced neutrophilic airway inflammation nor OVA-induced eosinophilic airway inflammation. These results indicate that D1-like-R antagonist could suppress Th17-mediated neutrophilic airway inflammation, raising the possibility that antagonizing D1-like-R serves as a promising new strategy for treating neutrophil-dominant severe asthma.

Identification of blood microRNAs associated to Parkinsonĭs disease

The present study demonstrates that blood samples can be used as a source of miRNA identification associated to Parkinson's disease (PD). A set of six differentially expressed microRNAs were identified. They form two groups according to their expression profile in control, non-treated, early-onset and treated Parkinson's disease subjects. While miR-1, miR-22* and miR-29 expression levels allowed to distinguish non-treated PD from healthy subjects, miR-16-2*, miR-26a2* and miR30a differentiated treated from untreated patients. This study is innovative in contributing to the development of effective PD biomarkers.

Peripheral biomarkers of cognitive response to dopamine receptor agonist treatment

RATIONALE

Using biological markers to objectively measure addiction severity or to identify individuals who might benefit most from pro-cognitive treatment could potentially revolutionize neuropsychopharmacology. We investigated the use of dopamine receptor mRNA levels in circulating blood cells as predictors of cognitive response following dopamine agonist treatment, and as biomarkers of the severity of stimulant drug dependence.

METHODOLOGY

We employed a double-blind, placebo-controlled cross-over design, administering a single dose of the selective dopamine D(2/3) receptor agonist pramipexole (0.5 mg) to increase dopamine transmission in one session and a placebo treatment in another session in 36 volunteers. Half the volunteers had a formal diagnosis of stimulant dependence, while half had no psychiatric history. Participants performed neurocognitive tests from the CANTAB battery on both occasions, and stimulant-dependent individuals rated drug craving using visual analog scales. Whole-blood mRNA levels were measured for three dopamine-related genes: DRD3 and DRD4 (dopamine receptors), and catechol-O-methyltransferase (COMT; a dopamine catabolic enzyme).

RESULTS

Stimulant users performed worse than healthy volunteers on the cognitive tests. The variation in peripheral dopamine D(3) receptor mRNA expression explained over one quarter of the variation in response to pramipexole on the spatial working memory test across all participants. The severity of stimulant dependence was also significantly associated with peripheral COMT mRNA expression in stimulant users.

CONCLUSIONS

Peripheral expression of dopamine-related genes may be useful as a biomarker of cognitive response to dopamine agonist drugs and of severity of addiction to dopamine-releasing stimulant drugs.

PGC-1α, a potential therapeutic target for early intervention in Parkinson's disease

Parkinson's disease affects 5 million people worldwide, but the molecular mechanisms underlying its pathogenesis are still unclear. Here, we report a genome-wide meta-analysis of gene sets (groups of genes that encode the same biological pathway or process) in 410 samples from patients with symptomatic Parkinson's and subclinical disease and healthy controls. We analyzed 6.8 million raw data points from nine genome-wide expression studies, and 185 laser-captured human dopaminergic neuron and substantia nigra transcriptomes, followed by two-stage replication on three platforms. We found 10 gene sets with previously unknown associations with Parkinson's disease. These gene sets pinpoint defects in mitochondrial electron transport, glucose utilization, and glucose sensing and reveal that they occur early in disease pathogenesis. Genes controlling cellular bioenergetics that are expressed in response to peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) are underexpressed in Parkinson's disease patients. Activation of PGC-1α results in increased expression of nuclear-encoded subunits of the mitochondrial respiratory chain and blocks the dopaminergic neuron loss induced by mutant α-synuclein or the pesticide rotenone in cellular disease models. Our systems biology analysis of Parkinson's disease identifies PGC-1α as a potential therapeutic target for early intervention.

Peripheral biomarkers of Parkinson's disease as early reporters of central neurodegeneration

Parkinson's disease (PD) is the most common age-related movement disorder, with a prevalence of approximately 2% among people over 65 years of age. The diagnosis of PD is currently based on the clinical manifestations of the disease; therefore, the availability of peripheral biomarkers would have a great impact. In this review, we discuss and compare several attempts made to find peripheral biomarkers of PD to achieve early diagnosis, differential diagnosis, therapy assessment and classification of disease subtypes. Several investigators focused on proteins that are involved in PD pathogenesis. However, the best choice for a sensible biomarker-discovery procedure makes use of global approaches such as metabolomics and proteomics. In addition, the tissue or compartment where biomarkers are located, plays a basic role. In this context, lymphocytes are of particular interest because they are circulating dopaminergic cells, and display several functional modifications in PD.

RNA biomarkers of Parkinson's disease: developing tools for novel therapies

By 2030 the number of individuals with Parkinson's disease (PD) will nearly double to approximately 9.3 million because of aging populations. No medications have been approved that address the progressive neurodegeneration that underlies the disease and existing symptomatic treatments are only partially effective. Reliance on insensitive and confounded clinical assessments has obstructed the development of novel therapeutics designed to prevent, delay or slow the disease. While PD symptoms reflect preferential neuronal death, DNA, RNA and biochemical traits of the disease are detectable in blood cells. To systematically search for lead RNA biomarkers of PD, genome-wide expression changes in the blood of patients with early-stage PD and controls have been probed by microarray. This scan identified a candidate gene signature, as well as lead single gene biomarkers associated with PD. Efforts are underway to refine and develop these hits into biomarkers that will enable risk-modifying therapies. This development process will progress through discovery, cross-sectional and prospective clinical biomarker studies, to Phase III clinical trials.

Alpha-synuclein nitration and autophagy response are induced in peripheral blood cells from patients with Parkinson disease

Several lines of evidence implicate a central role for alpha-synuclein (aSN) in the pathogenesis of Parkinson's disease (PD). Besides rare genetic mutations, post-translational mechanisms, such as oxidative stress-related nitration, may alter the protein properties in terms of propensity to aggregate or be degraded. Our group previously described increased reactive oxygen species (ROS) production within easily accessible peripheral blood mononuclear cells (PBMCs) in PD patients compared to healthy elderly subjects. In the present work, we demonstrated a significant induction of nitrotyrosine (NT)-modifications of aSN within PBMCs derived from individuals with idiopathic PD compared to controls, while aSN protein appeared similarly expressed in the two populations. The amount of NT-modified aSN within PBMCs was positively correlated with intracellular ROS concentration and inversely related to daily dosage of levodopa, making its measurement potentially relevant for disease-intervention studies. Neither aSN expression nor its NT-modifications showed any correlation to specific REP1 genotypes, polymorphic variants within aSN gene promoter whose association to PD susceptibility may occur through the modulation of aSN protein expression. Moreover, although NT-modified aSN has been linked to enhanced propensity to aggregate, we failed to detect an increased presence of insoluble aSN aggregates in PBMCs from PD subjects relative to controls, despite a lack of changes in the ubiquitin-proteasome expression or activity. Nonetheless, a significant activation of the autophagy response was identified within PBMCs from PD individuals, which could represent a protective mechanism against abnormal protein accumulation and may explain the lack of aSN aggregation. We discuss the relevance of these findings with respect to PD pathogenesis and biomarker development.

Expression analysis of suppression of tumorigenicity 13 gene in patients with Parkinson's disease

Parkinson's disease (PD) is the second most common progressive neurodegenerative disorder characterized by the degeneration of dopaminergic neurons. Detecting changes in gene expression in untreated de novo patients with PD is important for understanding disease pathogenesis and for identifying biomarkers for preclinical stage of PD. In this study we investigate ST13 gene expression in the peripheral blood of different groups of patients with neurological diseases using reverse transcription reaction and real-time polymerase chain reaction (PCR). Our results suggest that the expression levels of ST13 cannot serve as a biomarker for early stages of PD.

Chipping away at diagnostics for neurodegenerative diseases

Biomarkers are needed to overcome critical roadblocks in the development of disease-modifying therapeutics for neurodegenerative diseases. Evolving genome-wide expression technologies can comprehensively search for molecular biomarkers and allow fascinating insights into the expanding complexity of the human transcriptome. The technology has matured to the point where some applications are deemed reliable enough for use in patient care. In the neurosciences, it has led to the discoveries of osteopontin in multiple sclerosis and SORL1/LR11 in Alzheimer's, and recent studies indicate its potential for identifying neurogenomic biomarkers. Advances in pre-analytical and analytical methods are improving search efficiency and reproducibility and may lead to a pipeline of biomarker candidates suitable for development into future neurologic diagnostics.

Biomarkers for evaluation of clinical efficacy of multipotential neuroprotective drugs for Alzheimer's and Parkinson's diseases

During the last century, the world population has shown a staggering increase in its proportion of elderly members and thus neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD), respectively, are becoming an increasing burden on society. Among the diverse, significant challenges facing clinicians, is the improvement of diagnostic measures to detect early and subtle symptoms, a phase in which prevention efforts might be expected to have their greatest impact and provide a measure of disease progression that can be evaluated during the course of drug treatment. At present, clinical diagnosis of AD and PD is based on a constellation of symptoms and manifestations, although the disease originated several years earlier. Given the multiple etiological nature of AD and PD, it is reasonable to assume that the initial causative pathobiological processes may differ between the affected individuals. Therefore, the availability of biological markers or biomarkers will help not only early disease diagnosis, but also delineate the pathological mechanisms more definitively and reliably than the traditional cognitive and neurological phenotypes. In the current article, we review the literature on biochemical, genetic, and neuroimaging biomarkers and discuss their predictive value as indicative for disease vulnerability to detect individuals at risk for PD and AD, and to determine the clinical efficacy of novel, disease-modifying (neuroprotective) strategies.

Decreased NURR1 gene expression in patients with Parkinson's disease

NURR1 is a transcription factor essential for the development, survival, and functional maintenance of midbrain dopaminergic (DAergic) neurons and NURR1 is a potential susceptibility gene for Parkinson's disease (PD). To determine whether NURR1 gene expression is altered in patients with PD, we measured its expression in human peripheral blood lymphocytes (PBL) in 278 patients with PD, 166 healthy controls (HC), and 256 neurological disease controls (NDC) by quantitative real-time PCR. NURR1 gene expression was significantly decreased in patients with PD (particularly those with family history of PD) as compared with HC (p<0.01) and also as compared with NDC (p<0.05). There was no significant difference in NURR1 gene expression among PD patients with or without anti-PD medications. When adjusted for gender, age, and ethnicity, lower levels of NURR1 gene expression were associated with significantly increased risk for PD in women, in patients 60 years old or older, and in patients of Caucasian origin. The observed reduction in PBL NURR1 gene expression indicates possible systemic involvement in PD, and the finding may help identify individuals with PD and other disorders associated with impaired central DAergic system.

Dopamine receptors in human lymphocytes: radioligand binding and quantitative RT-PCR assays

Analysis of dopamine receptors (DR) in lymphocytes of the human peripheral blood mononuclear cell (PBMC) fraction is an attractive tool for evaluation of functional properties of dopaminergic function underlying variation in complex psychological/psychopathological traits. Receptor binding assays (RBAs) with selective radioligands, which are widely used in CNS studies, have not produced consistent results when applied to isolated PBMC. We tested the assay conditions that could be essential for detection of DR in human PBMC and their membrane preparations. Using [(3)H]SCH23390, a dopamine D1-like receptor antagonist, we demonstrated the presence of two binding sites in PBMC-derived membrane fraction. One of them is characterized by the K(d) value consistent with that reported for D5 dopamine receptors in human lymphocytes, whereas the other K(d) value possibly corresponds to serotonin receptor(s). Although D5 receptor binding sites in PBMC membranes could be characterized by binding assays, the low protein expression and the large volume of blood needed for membrane preparation render the binding method impracticable for individual phenotyping. In contrast, real-time RT-PCR may be used for this purpose, contingent on the relationship between DR expression in the brain and in lymphocytes. The expression of the DRD2-DRD5 genes, as detected by this method, varied widely among samples, whereas the DRD1 expression was not detected. The expression levels were comparable with those in the brain for DRD3 and DRD4, and were significantly lower for DRD2 and DRD5.

Proteasomal inhibition and apoptosis regulatory changes in human isolated lymphocytes: The synergistic role of dopamine

Abnormal deposition of protein aggregates and increased susceptibility to apoptotic cell death may result from defects in the activity of the ubiquitin-proteasome system (UPS); neurotoxicity related to UPS defects seems to require dopamine to be fully expressed. The aim of this study was to investigate the pro-apoptotic effects caused by proteasomal activity inhibition, as well as the synergistic effect of dopaminergic stimulation in human lymphocytes isolated from healthy volunteers. Cells were incubated 20 h at 37 degrees C, with: (1) lactacystin, (2) increasing concentrations of dopamine or (3) mixture of dopamine and lactacystin. Activities of proteasome 20S and pro-apoptotic caspases-3 and -9 and levels of anti-apoptotic Bcl-2 were measured with fluorimetric or immunochemical assays, while a "DNA diffusion" assay was used to determine the apoptosis. Incubation of lymphocytes with lactacystin, which caused reduction of proteasomal activity, was associated with activation of caspases. A clear, dose-dependent reduction of proteasomal activity was also seen in the presence of increasing doses of dopamine, which was accompanied by a slight dose-dependent increase of caspases activities and Bcl-2 levels. Both effects on proteasome and caspase activities were enhanced when cells were simultaneously exposed to lactacystin and elevated concentrations of dopamine. Apoptosis was detected in all treated samples, but not in controls, without significant differences among the treatment groups; however, the association of dopamine and lactacystin induced a clear reduction in the number of cells being analyzed, pointing to marked cytotoxicity. Our data confirm the potentiation of cytotoxicity related to proteasome inhibition, in the presence of dopaminergic stimulation.

Genetic variability in the SNCA gene influences alpha-synuclein levels in the blood and brain

Genetic variability in the promoter and 3' region of the SNCA gene coding alpha-synuclein modulates the risk to develop sporadic Parkinson's disease (PD). Whether this is mediated by regulating alpha-synuclein expression levels remains unknown. Therefore, we analyzed levels of alpha-synuclein in blood and human post mortem brain tissue including the substantia nigra using quantitative real-time reverse transcriptase-polymerase chain reaction and enzyme linked immunosorbent assay in vivo. Single nucleotide polymorphism (SNP) rs356219, a tagging SNP for a disease-associated haplotype in the 3' region of the SNCA gene, has a significant effect on SNCA mRNA levels in the substantia nigra and the cerebellum. Further, the "protective" genotype 259/259 of the PD-associated promoter repeat NACP-Rep1 is associated with lower protein levels in blood than genotypes 261/261, 259/261, and 259/263. In conclusion, we provide evidence that alpha-synuclein levels are influenced by genetic variability in the promoter and 3' region of the SNCA gene in vivo.

Gazing into the future: Parkinson's disease gene therapeutics to modify natural history

PD gene therapy clinical trials have primarily focused on increasing the production of dopamine (DA) through supplemental amino acid decarboxylase (AADC) expression, neurotrophic support for surviving dopaminergic neurons (DAN) or altering brain circuitry to compensate for DA neuron loss. The future of PD gene therapy will depend upon resolving a number of important issues that are discussed in this special issue. Of particular importance is the identification of novel targets that are amenable to early intervention prior to the substantial loss of DAN. However, for the most part the etiopathogenesis of PD is unknown making early intervention a challenge and the development of early biomarker diagnostics imperative.

Prodromal non-motor symptoms of Parkinson's disease

The motor symptoms of Parkinson's disease (PD), bradykinesia, muscular rigidity, and tremor depend upon degeneration of the dopaminergic neurons in the substantia nigra pars compacta. Recent neuropathological studies show that the Lewy bodies, the intraneuronal landmark of PD, accumulate in several neuronal cell types in the brain. An ascending gradient of pathological involvement, from the medulla oblongata to neocortical areas has been reported. Thus the original view of PD as a disease characterized by selective damage of the dopaminergic neurons in the mesencephalon should be updated into the concept of a severe multisystemic neurodegenerative disorder. Additionally, the neuropathological alterations outside the substantia nigra are soundly correlated with the non-motor symptoms of PD. As a result of these findings, interest is growing in the identification of prodromal non-motor symptoms of PD. Indeed, data from the literature suggest that autonomic disturbances, olfactory dysfunctions, depression and sleep disorders (in particular REM-sleep behavior disorder) may represent prodromal non-motor symptoms of PD. Several tests are available to detect most of these symptoms. Thus, the identification of prodromal non-motor symptoms may contribute to the precocious diagnosis of PD, and might be useful in the future to test the efficacy of neuroprotective agents.