Dopamine receptor D2 on CD4+ T cells is protective against neuroinflammation and neurodegeneration in a mouse model of Parkinson's disease

A review of current therapeutics targeting the mitochondrial protease ClpP in diffuse midline glioma, H3 K27-altered

Diffuse midline gliomas (DMGs) are devastating pediatric brain tumors recognized as the leading cause of cancer-related death in children. DMGs are high-grade gliomas (HGGs) diagnosed along the brain's midline. Euchromatin is the hallmark feature of DMG, caused by global hypomethylation of H3K27 either through point mutations in histone H3 genes (H3K27M), or by overexpression of the enhancer of zeste homolog inhibitory protein. In a clinical trial for adults with progressive HGGs, a 22-year-old patient with a thalamic DMG, H3 K27-altered, showed a remarkable clinical and radiological response to dordaviprone (ONC201). This response in an H3 K27-altered HGG patient, coupled with the lack of response of patients harboring wildtype-H3 tumors, has increased the clinical interest in dordaviprone for the treatment of DMG. Additional reports of clinical benefit have emerged, but research defining mechanisms of action (MOA) fall behind dordaviprone's clinical use, with biomarkers of response unresolved. Here, we summarize dordaviprone's safety, interrogate its preclinical MOA identifying the mitochondrial protease "ClpP" as a biomarker of response, and discuss other ClpP agonists, expanding the arsenal of potential weapons in the fight against DMG. Finally, we discuss combination strategies including ClpP agonists, and their immunomodulatory effects suggestive of a role for the tumor microenvironment in DMG patient response.

Chronic Stress Exacerbates the Immunosuppressive Microenvironment and Progression of Gliomas by Reducing Secretion of CCL3

As understanding of cancer has deepened, increasing attention has been turned to the roles of psychological factors, especially chronic stress-induced depression, in the occurrence and development of tumors. However, whether and how depression affects the progression of gliomas are still unclear. In this study, we have revealed that chronic stress inhibited the recruitment of tumor-associated macrophages (TAM) and other immune cells, especially M1-type TAMs and CD8+ T cells, and decreased the level of proinflammatory cytokines in gliomas, leading to an immunosuppressive microenvironment and glioma progression. Mechanistically, by promoting the secretion of stress hormones, chronic stress inhibited the secretion of the chemokine CCL3 and the recruitment of M1-type TAMs in gliomas. Intratumoral administration of CCL3 reprogrammed the immune microenvironment of gliomas and abolished the progression of gliomas induced by chronic stress. Moreover, levels of CCL3 and M1-type TAMs were decreased in the tumor tissues of glioma patients with depression, and CCL3 administration enhanced the antitumor effect of anti-PD-1 therapy in orthotopic models of gliomas undergoing chronic stress. In conclusion, our study has revealed that chronic stress exacerbates the immunosuppressive microenvironment and progression of gliomas by reducing the secretion of CCL3. CCL3 alone or in combination with an anti-PD-1 may be an effective immunotherapy for the treatment of gliomas with depression. See related Spotlight by Cui and Kang, p. 514.

The major histocompatibility complex participates in Parkinson's disease

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

Regulation of Pain Perception by Microbiota in Parkinson Disease

Pain perception involves current stimulation in peripheral nociceptive nerves and the subsequent stimulation of postsynaptic excitatory neurons in the spinal cord. Importantly, in chronic pain, the neural activity of both peripheral nociceptors and postsynaptic neurons in the central nervous system is influenced by several inflammatory mediators produced by the immune system. Growing evidence has indicated that the commensal microbiota plays an active role in regulating pain perception by either acting directly on nociceptors or indirectly through the modulation of the inflammatory activity on immune cells. This symbiotic relationship is mediated by soluble bacterial mediators or intrinsic structural components of bacteria that act on eukaryotic cells, including neurons, microglia, astrocytes, macrophages, T cells, enterochromaffin cells, and enteric glial cells. The molecular mechanisms involve bacterial molecules that act directly on neurons, affecting their excitability, or indirectly on non-neuronal cells, inducing changes in the production of proinflammatory or anti-inflammatory mediators. Importantly, Parkinson disease, a neurodegenerative and inflammatory disorder that affects mainly the dopaminergic neurons implicated in the control of voluntary movements, involves not only a motor decline but also nonmotor symptomatology, including chronic pain. Of note, several recent studies have shown that Parkinson disease involves a dysbiosis in the composition of the gut microbiota. In this review, we first summarize, integrate, and classify the molecular mechanisms implicated in the microbiota-mediated regulation of chronic pain. Second, we analyze the changes on the commensal microbiota associated to Parkinson disease and propose how these changes affect the development of chronic pain in this pathology. SIGNIFICANCE STATEMENT: The microbiota regulates chronic pain through the action of bacterial signals into two main locations: the peripheral nociceptors and the postsynaptic excitatory neurons in the spinal cord. The dysbiosis associated to Parkinson disease reveals increased representation of commensals that potentially exacerbate chronic pain and reduced levels of bacteria with beneficial effects on pain. This review encourages further research to better understand the signals involved in bacteria-bacteria and bacteria-host communication to get the clues for the development of probiotics with therapeutic potential.

The iron-dopamine D1 coupling modulates neural signatures of working memory across adult lifespan

Brain iron overload and decreased integrity of the dopaminergic system have been independently reported as brain substrates of cognitive decline in aging. Dopamine (DA), and iron are co-localized in high concentrations in the striatum and prefrontal cortex (PFC), but follow opposing age-related trajectories across the lifespan. DA contributes to cellular iron homeostasis and the activation of D1-like DA receptors (D1DR) alleviates oxidative stress-induced inflammatory responses, suggesting a mutual interaction between these two fundamental components. Still, a direct in-vivo study testing the iron-D1DR relationship and their interactions on brain function and cognition across the lifespan is rare. Using PET and MRI data from the DyNAMiC study (n=180, age=20-79, %50 female), we showed that elevated iron content was related to lower D1DRs in DLPFC, but not in striatum, suggesting that dopamine-rich regions are less susceptible to elevated iron. Critically, older individuals with elevated iron and lower D1DR exhibited less frontoparietal activations during the most demanding task, which in turn was related to poorer working-memory performance. Together, our findings suggest that the combination of elevated iron load and reduced D1DR contribute to disturbed PFC-related circuits in older age, and thus may be targeted as two modifiable factors for future intervention.

Facilitating Pro-survival Mitophagy for Alleviating Parkinson's Disease via Sequence-Targeted Lycopene Nanodots

The pathogenesis of Parkinson's disease is closely linked to impaired mitochondrial function and abnormal mitophagy. Biocompatible natural antioxidants effectively protect dopaminergic neurons. However, the main challenge in using natural antioxidants for Parkinson's disease therapy is creating a delivery platform to achieve neuron-targeted enrichment. Herein, we synthesized rationally sequence-targeted lycopene nanodots using recombinant human H-ferritin nanocages with lycopene loading into the cavity and lipophilic triphenylphosphonium (TPP) coupling on the outer surface. The nanodots allow for the neural enrichment and mitochondrial regulation of lycopene through blood-brain barrier transcytosis and neuronal mitochondria-targeting capability. These anti-ROS nanodots protect neuronal mitochondrial function and promote PINK1/Parkin-mediated mitophagy in MPTP toxicity-induced neurons in vivo and in vitro, which favors the secretory efflux of pathogenic α-synuclein and the survival of dopaminergic neurons. Moreover, these nanodots restore the Parkinson-like motor symptoms in Parkinson's model mice. This noninvasive sequence-targeted delivery strategy with excellent biocompatibility for pro-survival mitophagy-mediated pathology alleviation makes it a promising approach for treating and preventing Parkinson's disease.

Xanthine-Dopamine Hybrid Molecules as Multitarget Drugs with Potential for the Treatment of Neurodegenerative Diseases

Multitarget drugs based on a hybrid dopamine-xanthine core were designed as potential drug candidates for the treatment of neurodegenerative diseases. Monoamine oxidase B (MAO-B) inhibitors with significant ancillary A_2A adenosine receptor (A_2AAR) antagonistic properties were further developed to exhibit additional phosphodiesterase-4 and -10 (PDE4/10) inhibition and/or dopamine D₂ receptor (D₂R) agonistic activity. While all of the designed compounds showed MAO-B inhibition in the nanomolar range mostly combined with submicromolar A_2AAR affinity, significant enhancement of PDE-inhibitory and D₂R-agonistic activity was additionally reached for some compounds through various structural modifications. The final multitarget drugs also showed promising antioxidant properties in vitro. In order to evaluate their potential neuroprotective effect, representative ligands were tested in a cellular model of toxin-induced neurotoxicity. As a result, protective effects against oxidative stress in neuroblastoma cells were observed, confirming the utility of the applied strategy. Further evaluation of the newly developed multitarget ligands in preclinical models of Alzheimer's and Parkinson's diseases is warranted.

Dopamine D2 receptor on CD4+ T cells is protective against inflammatory responses and signs in a mouse model of rheumatoid arthritis

BACKGROUND

Dopamine is a neurotransmitter and has been found to regulate lymphocytes by acting on dopamine receptors (DRs). CD4⁺ T cells express all the five subtypes of DRs, D1R to D5R. Although CD4⁺ T cells have been involved in pathogenesis of rheumatoid arthritis (RA), roles of DRs expressed on these cells in RA are poorly understood. This study determined whether D2R expressed on CD4⁺ T cells regulates inflammatory responses and signs in collagen type II (CII)-induced arthritis (CIA), a mouse model of RA.

METHODS

DBA/1 mice and C57BL/6 mice with global D1r or D2r deficiency (D1r^-/- or D2r^-/-) or CD4⁺ T cell-specific D2r deletion (D2r^fl/fl/CD4^Cre) were used to prepare CIA model by intradermal injection of CII. D2R agonist sumanirole was intraperitoneally administered in CIA mice. CD4⁺ T cells obtained from CIA mice were exposed to sumanirole or/and D2R antagonist L-741,626 in vitro. Arthritic symptoms were assessed by clinical arthritis scores. Flow cytometric assay measured frequencies of CD4⁺ T cell subsets (Th1, Th2, Th17 and Treg cells). Expression of specific transcription factors for the CD4⁺ T cell subsets was tested by Western blot. Cytokine production was estimated by quantitative PCR and ELISA.

RESULTS

CIA mice manifested a bias of CD4⁺ T cells towards Th1 and Th17 cells. D2r^-/- CIA mice showed a stronger bias towards Th1 and Th17 phenotypes than CIA mice, while D1r^-/- CIA mice did not show the changes. CD4⁺ T cell-specific D2r deletion exacerbated both the polarization towards Th1 and Th17 cells and the symptoms of arthritis. Sumanirole administration in CIA mice ameliorated the bias of CD4⁺ T cells towards Th1 and Th17 phenotypes as well as arthritic symptoms. Sumanirole treatment of in vitro CD4⁺ T cells obtained from CIA mice promoted the shift to Treg cells, and the effect of sumanirole was blocked by L-741,626.

CONCLUSIONS

D2R expressed on CD4⁺ T cells is protective against imbalance between pro-inflammatory and anti-inflammatory T cells and arthritic symptoms in CIA.

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.

Mechanisms of Autoimmune Cell in DA Neuron Apoptosis of Parkinson's Disease: Recent Advancement

Parkinson's disease (PD) is a prevalent neurodegenerative disorder that manifests as motor and nonmotor symptoms due to the selective loss of midbrain DArgic (DA) neurons. More and more studies have shown that pathological reactions initiated by autoimmune cells play an essential role in the progression of PD. Autoimmune cells exist in the brain parenchyma, cerebrospinal fluid, and meninges; they are considered inducers of neuroinflammation and regulate the immune in the human brain in PD. For example, T cells can recognize α-synuclein presented by antigen-presenting cells to promote neuroinflammation. In addition, B cells will accelerate the apoptosis of DA neurons in the case of PD-related gene mutations. Activation of microglia and damage of DA neurons even form the self-degeneration cycle to deteriorate PD. Numerous autoimmune cells have been considered regulators of apoptosis, α-synuclein misfolding and aggregation, mitochondrial dysfunction, autophagy, and neuroinflammation of DA neurons in PD. The evidence is mounting that autoimmune cells promote DA neuron apoptosis. In this review, we discuss the current knowledge regarding the regulation and function of B cell, T cell, and microglia as well as NK cell in PD pathogenesis, focusing on DA neuron apoptosis to understand the disease better and propose potential target identification for the treatment in the early stages of PD. However, there are still some limitations in our work, for example, the specific mechanism of PD progression caused by autoimmune cells in mitochondrial dysfunction, ferroptosis, and autophagy has not been clarified in detail, which needs to be summarized in further work.

Trimetazidine, an Anti-Ischemic Drug, Reduces the Antielectroshock Effects of Certain First-Generation Antiepileptic Drugs

Trimetazidine (TMZ), an anti-ischemic drug for improving cellular metabolism, is mostly administered to patients with poorly controlled ischemic heart disease (IHD). Since IHD is considered the most frequent causative factor of cardiac arrhythmias, and these often coexist with seizure disorders, we decided to investigate the effect of TMZ in the electroconvulsive threshold test (ECT) and its influence on the action of four first-generation antiepileptic drugs in the maximal electroshock test (MES) in mice. The TMZ (up to 120 mg/kg) did not affect the ECT, but applied at doses of 20–120 mg/kg it decreased the antielectroshock action of phenobarbital. The TMZ (50–120 mg/kg) reduced the effect of phenytoin, and, when administered at a dose of 120 mg/kg, it diminished the action of carbamazepine. All of these revealed interactions seem to be pharmacodynamic, since the TMZ did not affect the brain levels of antiepileptic drugs. Furthermore, the combination of TMZ with valproate (but not with other antiepileptic drugs) significantly impaired motor coordination, evaluated using the chimney test. Long-term memory, assessed with a passive-avoidance task, was not affected by either the TMZ or its combinations with antiepileptic drugs. The obtained results suggest that TMZ may not be beneficial as an add-on therapy in patients with IHD and epilepsy.

Lymphocyte Count and Neutrophil-to-Lymphocyte Ratio Are Associated with Mild Cognitive Impairment in Parkinson’s Disease: A Single-Center Longitudinal Study

Lymphocyte count and neutrophil-to-lymphocyte ratio (NLR) may represent useful biomarkers of Parkinson’s disease (PD), but their role in PD-related mild cognitive impairment (MCI) has not been fully elucidated. The present study aimed to confirm whether these immunological measures can discriminate PD patients from healthy controls (HC) and establish their feasibility as prognostic biomarkers of MCI in PD. Immunological data at baseline were analyzed in 58 drug-naïve PD patients and 58 HC matched 1:1 for age, sex, and cardiovascular comorbidities. We selected a subgroup of 51 patients from this initial cohort who underwent longitudinal neuropsychological assessments through the Addenbrooke’s Cognitive Examination Revised (ACE-R) test. We considered the last examination available to analyze the relationship between ACE-R test scores and immunological measures. We found that lymphocyte count was lower and NLR higher in PD than HC (p = 0.006, p = 0.044), with AUC = 0.649 and 0.608, respectively. Secondly, in PD-MCI there were significantly higher levels of circulating lymphocytes (p = 0.002) and lower NLR (p = 0.020) than PD with normal cognitive status (PD-NC). Correlations between lymphocyte count and ACE-R total score and memory subitem (r = −0.382, p = 0.006; r = −0.362, p = 0.01), as well as between NLR and ACE-R total score and memory subitem (r = 0.325, p = 0.02; r = 0.374, p = 0.007), were also found. ROC curve analysis showed that lymphocyte count and NLR displayed acceptable discrimination power of PD-MCI with AUC = 0.759 and 0.691, respectively. In conclusion, we suggest that an altered peripheral immune phenotype could foster cognitive decline development in PD, thus opening the possibility of immune-targeting strategies to tackle this disabling non-motor feature.

Emerging Roles of T Helper Cells in Non-Infectious Neuroinflammation: Savior or Sinner

CD4⁺ T cells, also known as T helper (Th) cells, contribute to the adaptive immunity both in the periphery and in the central nervous system (CNS). At least seven subsets of Th cells along with their signature cytokines have been identified nowadays. Neuroinflammation denotes the brain’s immune response to inflammatory conditions. In recent years, various CNS disorders have been related to the dysregulation of adaptive immunity, especially the process concerning Th cells and their cytokines. However, as the functions of Th cells are being discovered, it’s also found that their roles in different neuroinflammatory conditions, or even the participation of a specific Th subset in one CNS disorder may differ, and sometimes contrast. Based on those recent and contradictory evidence, the conflicting roles of Th cells in multiple sclerosis, Alzheimer’s disease, Parkinson’s disease, epilepsy, traumatic brain injury as well as some typical mental disorders will be reviewed herein. Research progress, limitations and novel approaches concerning different neuroinflammatory conditions will also be mentioned and compared.

Age-Related Midbrain Inflammation and Senescence in Parkinson’s Disease

Immune responses are arising as a common feature of several neurodegenerative diseases, such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and Amyotrophic Lateral Sclerosis (ALS), but their role as either causative or consequential remains debated. It is evident that there is local inflammation in the midbrain in PD patients even before symptom onset, but the underlying mechanisms remain elusive. In this mini-review, we discuss this midbrain inflammation in the context of PD and argue that cellular senescence may be the cause for this immune response. We postulate that to unravel the relationship between inflammation and senescence in PD, it is crucial to first understand the potential causative roles of various cell types of the midbrain and determine how the possible paracrine spreading of senescence between them may lead to observed local immune responses. We hypothesize that secretion of pro-inflammatory factors by senescent cells in the midbrain triggers neuroinflammation resulting in immune cell-mediated killing of midbrain dopaminergic (DA) neurons in PD.

Contributions of the Catechol-O-Methyltransferase Val158Met Polymorphism to Changes in Brain Iron Across Adulthood and Their Relationships to Working Memory

Ageing is associated with excessive free brain iron, which may induce oxidative stress and neuroinflammation, likely causing cognitive deficits. Lack of dopamine may be a factor behind the increase of iron with advancing age, as it has an important role in cellular iron homoeostasis. We investigated the effect of COMT Val 158 Met (rs4680), a polymorphism crucial for dopamine degradation and proxy for endogenous dopamine, on iron accumulation and working memory in a longitudinal lifespan sample (n = 208, age 20–79 at baseline, mean follow-up time = 2.75 years) using structural equation modelling. Approximation of iron content was assessed using quantitative susceptibility mapping in striatum and dorsolateral prefrontal cortex (DLPFC). Iron accumulated in both striatum and DLPFC during the follow-up period. Greater iron accumulation in DLPFC was associated with more deleterious change in working memory. Older (age 50–79) Val homozygotes (with presumably lower endogenous dopamine) accumulated more iron than older Met carriers in both striatum and DLPFC, no such differences were observed among younger adults (age 20–49). In conclusion, individual differences in genetic predisposition related to low dopamine levels increase iron accumulation, which in turn may trigger deleterious change in working memory. Future studies are needed to better understand how dopamine may modulate iron accumulation across the human lifespan.

The role of Th17 cells/IL-17A in AD, PD, ALS and the strategic therapy targeting on IL-17A

Neurodegenerative diseases are a group of disorders characterized by progressive loss of certain populations of neurons, which eventually lead to dysfunction. These diseases include Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). Immune pathway dysregulation is one of the common features of neurodegeneration. Recently, there is growing interest in the specific role of T helper Th 17 cells and Interleukin-17A (IL-17A), the most important cytokine of Th 17 cells, in the pathogenesis of the central nervous system (CNS) of neurodegenerative diseases. In the present study, we summarized current knowledge about the function of Th17/IL-17A, the physiology of Th17/IL-17A in diseases, and the contribution of Th17/IL-17A in AD, PD, and ALS. We also update the findings on IL-17A-targeting drugs as potentially immunomodulatory therapeutic agents for neurodegenerative diseases. Although the specific mechanism of Th17/IL-17A in this group of diseases is still controversial, uncovering the molecular pathways of Th17/IL-17A in neurodegeneration allows the identification of suitable targets to modulate these cellular processes. Therapeutics targeting IL-17A might represent potentially novel anti-neurodegeneration drugs.

T Lymphocytes in Parkinson's Disease

T cells are key mediators of both humoral and cellular adaptive immune responses, and their role in Parkinson’s disease (PD) is being increasingly recognized. Several lines of evidence have highlighted how T cells are involved in both the central nervous system and the periphery, leading to a profound imbalance in the immune network in PD patients. This review discusses the involvement of T cells in both preclinical and clinical studies, their importance as feasible biomarkers of motor and non-motor progression of the disease, and recent therapeutic strategies addressing the modulation of T cell response.