The dopaminergic system in autoimmune diseases

Contributions of nonhematopoietic cells and mediators to immune responses: implications for immunotoxicology

Immunotoxicology assessments have historically focused on the effects that xenobiotics exhibit directly on immune cells. These studies are invaluable as they identify immune cell targets and help characterize mechanisms and/or adverse outcome pathways of xenobiotics within the immune system. However, leukocytes can receive environmental cues by cell-cell contact or via released mediators from cells of organs outside of the immune system. These organs include, but are not limited to, the mucosal areas such as the lung and the gut, the liver, and the central nervous system. Homeostatic perturbation in these organs induced directly by toxicants can initiate and alter the outcome of local and systemic immunity. This review will highlight some of the identified nonimmune influences on immune homeostasis and provide summaries of how immunotoxic mechanisms of selected xenobiotics involve nonimmune cells or mediators. Thus, this review will identify data gaps and provide possible alternative mechanisms by which xenobiotics alter immune function that could be considered during immunotoxicology safety assessment.

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.

Relationship between prevalence and severity of restless legs syndrome and anemia in patients with systemic lupus erythematosus

AIM

Our aim was to evaluate the relationship between the prevalence and severity of restless legs syndrome (RLS) and the anemia in patients with systemic lupus erythematosus (SLE).

METHODS

This was a case-control study which was conducted at the rheumatology clinic of a university affiliated hospital, including 62 patients with SLE and 62 age- and sex-matched healthy controls. The patients were divided into two groups in terms of their hemoglobin levels. The criterion for anemia was hemoglobin level lower than 12 g/dL in females and 13 g/dL in males.

RESULTS

Nineteen patients (30.6%) in the patient group were diagnosed with RLS, and International RLS Study Group Rating Scale (IRLSSG-RS) score was 10.7 ± 9.5 (median:10.0 [range:0.0-30.0]). Three subjects (4.8%) in the control group had RLS, and the IRLSSG-RS score was 0.7 ± 3.3 (median:0.0 [range:0.0-18.0]). The prevalence of RLS and the IRLSSG-RS score were higher in the patient group than those in the control group (P < 0.001). Ten SLE patients (50%) with anemia had RLS, and their IRLSSG-RS score was 14.5 ± 9.9 (median:21.0 [range:11.0-30.0]). Nine SLE patients (21.4%) without anemia had RLS and their IRLSSG-RS was 9.0 ± 8.9 (median:21.0 [range:11.0-24.0]). Significant differences were present in the prevalence of RLS and the IRLSSG-RS score between SLE patients with and without anemia (P = 0.024, P = 0.044, respectively).

CONCLUSION

The present study demonstrated that the prevalence of RLS was higher in patients with SLE than that of the normal population. Results of this study also suggested that anemia was associated with higher frequency of and more severe RLS in patients with lupus.

[Dopamine neurotransmission of peripheral blood lymphocytes is a potential biomarker of psychiatric and neurological disorders]

Current literature on a role of dopamine in the development of mental and neurological disorders suggests that the discovery of endogenous dopamine in peripheral blood lymphocytes gave rise to a new line of research. Dopamine receptors are not only found on cells of the innate immune response (nonspecific), but also on cells of adaptive immune response (specific): T and B lymphocytes. These facts bring a new evidence of interrelationships between the peripheral immune system, neuroinflammation and neurodegeneration and suggest new ways for investigation of the pathogenesis of different mental and neurological disorders, in particular Parkinson's disease, Alzheimer's disease and schizophrenia. There is strong evidence that ligands of dopamine receptors can change the expression of coding genes both in central neurons and in peripheral cells. Thus, peripheral blood lymphocytes may prove a cellular tool to identify dopamine transmission disturbances in neuropsychiatric diseases, as well as to monitor the effects of pharmacological treatment.

Role of autophagy in the pathogenesis of multiple sclerosis

Autophagy plays an important role in maintaining the cellular homeostasis. One of its functions is to degrade unnecessary organelles and proteins for energy recycling or amino-acids for cell survival. Ablation of autophagy leads to neurodegeneration. Multiple sclerosis (MS), a permanent neurological impairment typical of chronic inflammatory demyelinating disorder, is an auto-immune disease of the central nervous system (CNS). Autophagy is tightly linked to the innate and adaptive immune systems during the autoimmune process, and several studies have shown that autophagy directly participates in the progress of MS or experimental autoimmune encephalomyelitis (EAE, a mouse model of MS). Dysfunction of mitochondria that intensively influences the autophagy pathway is one of the important factors in the pathogenesis of MS. Autophagy-related gene (ATG) 5 and immune-related GTPase M (IRGM) 1 are increased, while ATG16L2 is decreased, in T-cells in EAE and active relapsing-remitting MS brains. Administration of rapamycin, an inhibitor of mammalian target of rapamycin ( mTOR), ameliorates relapsing-remitting EAE. Inflammation and oxidative stress are increased in MS lesions and EAE, but Lamp2 and the LC3-II/LC3-I ratio are decreased. Furthermore, autophagy in various glial cells plays important roles in regulating neuro-inflammation in the CNS, implying potential roles in MS. In this review, we discuss the role of autophagy in the peripheral immune system and the CNS in neuroinflammation associated with the pathogenesis of MS.

Adaptive Immunity in Schizophrenia: Functional Implications of T Cells in the Etiology, Course and Treatment

Schizophrenia is a severe and highly complex neurodevelopmental disorder with an unknown etiopathology. Recently, immunopathogenesis has emerged as one of the most compelling etiological models of schizophrenia. Over the past few years considerable research has been devoted to the role of innate immune responses in schizophrenia. The findings of such studies have helped to conceptualize schizophrenia as a chronic low-grade inflammatory disorder. Although the contribution of adaptive immune responses has also been emphasized, however, the precise role of T cells in the underlying neurobiological pathways of schizophrenia is yet to be ascertained comprehensively. T cells have the ability to infiltrate brain and mediate neuro-immune cross-talk. Conversely, the central nervous system and the neurotransmitters are capable of regulating the immune system. Neurotransmitter like dopamine, implicated widely in schizophrenia risk and progression can modulate the proliferation, trafficking and functions of T cells. Within brain, T cells activate microglia, induce production of pro-inflammatory cytokines as well as reactive oxygen species and subsequently lead to neuroinflammation. Importantly, such processes contribute to neuronal injury/death and are gradually being implicated as mediators of neuroprogressive changes in schizophrenia. Antipsychotic drugs, commonly used to treat schizophrenia are also known to affect adaptive immune system; interfere with the differentiation and functions of T cells. This understanding suggests a pivotal role of T cells in the etiology, course and treatment of schizophrenia and forms the basis of this review.

Dopamine receptors D3 and D5 regulate CD4(+)T-cell activation and differentiation by modulating ERK activation and cAMP production

Dopamine receptors have been described in T-cells, however their signalling pathways coupled remain unknown. Since cAMP and ERKs play key roles regulating T-cell physiology, we aim to determine whether cAMP and ERK1/2-phosphorylation are modulated by dopamine receptor 3 (D3R) and D5R, and how this modulation affects CD4(+) T-cell activation and differentiation. Our pharmacologic and genetic evidence shows that D3R-stimulation reduced cAMP levels and ERK2-phosphorylation, consequently increasing CD4(+) T-cell activation and Th1-differentiation, respectively. Moreover, D5R expression reinforced TCR-triggered ERK1/2-phosphorylation and T-cell activation. In conclusion, these findings demonstrate how D3R and D5R modulate key signalling pathways affecting CD4(+) T-cell activation and Th1-differentiation.

The dopamine imbalance hypothesis of fatigue in multiple sclerosis and other neurological disorders

Fatigue is one of the most pervasive symptoms of multiple sclerosis (MS), and has engendered hundreds of investigations on the topic. While there is a growing literature using various methods to study fatigue, a unified theory of fatigue in MS is yet to emerge. In the current review, we synthesize findings from neuroimaging, pharmacological, neuropsychological, and immunological studies of fatigue in MS, which point to a specific hypothesis of fatigue in MS: the dopamine imbalance hypothesis. The communication between the striatum and prefrontal cortex is reliant on dopamine, a modulatory neurotransmitter. Neuroimaging findings suggest that fatigue results from the disruption of communication between these regions. Supporting the dopamine imbalance hypothesis, structural and functional neuroimaging studies show abnormalities in the frontal and striatal regions that are heavily innervated by dopamine neurons. Further, dopaminergic psychostimulant medication has been shown to alleviate fatigue in individuals with traumatic brain injury, chronic fatigue syndrome, and in cancer patients, also indicating that dopamine might play an important role in fatigue perception. This paper reviews the structural and functional neuroimaging evidence as well as pharmacological studies that suggest that dopamine plays a critical role in the phenomenon of fatigue. We conclude with how specific aspects of the dopamine imbalance hypothesis can be tested in future research.

A genetic-demographic approach reveals a gender-specific association of SLC6A3/DAT1 40 bp-VNTR with life-expectancy

Several recent lines of evidence are proving an important role for dopamine in the aging process and in the determination of life span. Components of the dopaminergic system may represent good candidates for longevity studies. Herein, we tested the possible association of the functional SLC6A3/DAT1 40-bp VNTR with life-expectancy in a healthy population of Central Italy (N = 993) by applying a genetic-demographic approach that takes into account the demographic information and different survival rates between sexes for modeling the survival of specific allele carriers in the population. Male carriers of S*/S* genotype showed a lower survival chance across most of the lifespan respect to the survival of DAT1*L-carriers (P = 0.021). The same analyses gave non-significant results in females. Several studies already reported significant sex differences in dopamine metabolism and its related biological pathways. Thus, we can hypothesize that the SLC6A3/DAT1 40 bp-VNTR may affect life expectancy in a sex-specific way. Moreover, it is conceivable that DAT1 S*/S* carriers, who are prone to assume "risk" type behaviors, may be dropped out of the "healthy" population by a sort of "demographic selection".

Detection of auto-antibodies to DAT in the serum: interactions with DAT genotype and psycho-stimulant therapy for ADHD

Interest is rising for auto-immune contribution in neuro-psychiatry. We evaluated the auto-antibodies against dopamine transporter (DAT aAbs) in 61 children (46 ADHD who met DSM-IV-TR criteria, 15 healthy controls).

METHODS

ADHD patients were assigned, according to severity, either to a non-pharmacological therapy (NPT, N=32) or to a pharmacological treatment (PT, N=14) with methylphenidate (MPH). In ADHD children, blood samples were withdrawn twice, at recruitment (T0 basal) and after 6 weeks (T1); following 16 excluded subjects, DAT genotype was characterized (9-repeat or 10-repeat alleles; N=15 each). After 18 months of NPT or PT, some patients (carrying at least one 9-repeat allele) were blood sampled again (T2), for comparison with healthy controls (final n=8) RESULTS: Compared to NPT, basal DAT aAbs titers were higher within most severe patients (then assigned to PT), specifically if carrying a DAT 10/10 genotype. DAT aAbs levels of NPT group resulted highly correlated with distinct subscales of Conners' Parent/Teacher Scales (Rs>0.34), especially within DAT 10/10 genotype (Rs>0.53). While T1 titers were elevated over T0 baseline for NPT children, such an increase was not observed in PT patients carrying at least one 9-repeat allele, who also showed behavioral response to subchronic MPH. After 12-24 months of MPH exposure, DAT aAbs titers in PT subjects were comparable to those of healthy controls, while titers remained significantly elevated in NPT patients. Data warrant further research on serum DAT aAbs, which could be used to confirm ADHD diagnosis and/or to monitor therapeutic efficacy of MPH.

Dopamine receptor DR2 expression in B cells is negatively correlated with disease activity in rheumatoid arthritis patients

OBJECTIVE

Dopamine receptor (DR) signaling is involved in the pathogenesis of autoimmune diseases. We aimed to measure the expression levels of DR1-5 on B cells from patients with rheumatoid arthritis (RA) and to analyze the relationship between DRs and clinical manifestations, inflammatory biomarkers, functional status and disease activity.

METHODS

A total of 29 patients with RA, 12 healthy donors and 12 patients with osteoarthritis (OA) were recruited in this study. Flow cytometry was used to measure the levels of DR1-5 expressed on B cells. The relationships between B cell DR expressions and clinical features in RA patients were analyzed using the Spearman correlation test.

RESULTS

The expression levels of B cell DR1-5 in both the RA and OA groups were lower than those in healthy controls. After 3 months of medication, all five receptors were elevated in RA patients, with DR2 and DR3 being significantly increased from the baseline. DR2 expression on B cells was negatively correlated with inflammatory biomarkers and disease activity.

CONCLUSION

RA patients had lower expression level of DR2 on B cells compared to the healthy controls, and the level of DR2 negatively correlated with the disease activity. DR2 and DR3 might be novel predictors of patient responses to disease modifying antirheumatic drug therapy.