Correction: Nanorod-associated plasmonic circular dichroism monitors the handedness and composition of α-synuclein fibrils from Parkinson's disease models and post-mortem brain.

Correction for 'Nanorod-associated plasmonic circular dichroism monitors the handedness and composition of α-synuclein fibrils from Parkinson's disease models and post-mortem brain' by Francesca Longhena et al., Nanoscale, 2024, 16, 18882-18898, https://doi.org/10.1039/D4NR03002H.

Nanorod-associated plasmonic circular dichroism monitors the handedness and composition of α-synuclein fibrils from Parkinson's disease models and post-mortem brain.

Human full-length (fl) αSyn fibrils, key neuropathological hallmarks of Parkinson's disease (PD), generate intense optical activity corresponding to the surface plasmon resonance of interacting gold nanorods. Herein, we analysed fibril-enriched protein extracts from mouse and human brain samples as well as from SK-N-SH cell lines with or without human fl and C-terminally truncated (Ctt) αSyn overexpression and exposed them to αSyn monomers, recombinant fl αSyn fibrils or Ctt αSyn fibrils. In vitro-generated human recombinant fl and Ctt αSyn fibrils and fibrils purified from SK-N-SH cells with fl or Ctt αSyn overexpression were also analysed using transmission electron microscopy (TEM) to gain insights into the nanorod-fibril complexes. We found that under the same experimental conditions, bisignate circular dichroism (CD) spectra of Ctt αSyn fibrils exhibited a blue-wavelength shift compared to that of fl αSyn fibrils. TEM results supported that this could be attributed to the different properties of nanorods. In our experimental conditions, fibril-enriched PD brain extract broadened the longitudinal surface plasmonic band with a bisignate CD couplet centred corresponding to the absorption band maximum. Plasmonic CD (PCD) couplets of in vivo- and in vitro-generated fibrils displayed sign reversal, suggesting their opposite handedness. Moreover, the incubation of in vitro-generated human recombinant fl αSyn fibrils in mouse brain extracts from αSyn null mice resulted in PCD couplet inversion, indicating that the biological environment may shape the handedness of αSyn fibrils. These findings support that nanorod-based PCD can provide useful information on the composition and features of αSyn fibrils from biological materials.

Immune landscape of the enteric nervous system differentiates Parkinson's disease patients from controls: The PADUA-CESNE cohort.

BACKGROUND: Gastrointestinal dysfunction has emerged as a prominent early feature of Parkinson's Disease, shedding new light on the pivotal role of the enteric nervous system in its pathophysiology. However, the role of immune-cell clusters and inflammatory and glial markers in the gut pathogenetic process needs further elucidation. OBJECTIVES: We aimed to study duodenum tissue samples to characterize PD's enteric nervous system pathology further. Twenty patients with advanced PD, six with early PD, and 18 matched controls were included in the PADUA-CESNE cohort. METHODS: Duodenal biopsies from 26 patients with early to advanced stage PD and 18 age-matched HCs were evaluated for the presence of surface markers (CD3+, CD4+, CD8+, CD20+, CD68+, HLA-DR), presence of misfolded alpha-synuclein and enteric glial alteration (GFAP). Correlation of immulogic pattern and clinical characteristic were analyzed. RESULTS: The findings validate that in patients with Parkinson's Disease, the activation and reactive gliosis are linked to the neurodegeneration triggered by the presence of misfolded alpha-synuclein in the enteric nervous system. This process intensifies from the initial to the advanced stages of the disease. The clusters of T- and B-lymphocytes in the enteric system, along with the overall expression of HLA-DR in antigen-presenting cells, exceeded those in the control group. Conversely, no differences in terms of macrophage populations were found. CONCLUSIONS: These findings broaden our understanding of the mechanisms underlying the enteric nervous system's involvement in PD and point to the gastrointestinal system as a potential therapeutic target, especially in the early stages of the disease. Moreover, our results propose a role of T- and B-lymphocytes in maintaining inflammation and ultimately influencing alpha-synuclein misfolding and aggregation.

Inhibition of Protease-Activated Receptor-2 Activation in Parkinson's Disease Using 1-Piperidin Propionic Acid.

In Parkinson's disease, neuroinflammation is a double-edged sword; when inflammation occurs it can have harmful effects, despite its important role in battling infections and healing tissue. Once triggered by microglia, astrocytes acquire a reactive state and shift from supporting the survival of neurons to causing their destruction. Activated microglia and Proteinase-activated receptor-2 (PAR2) are key points in the regulation of neuroinflammation. 1-Piperidin Propionic Acid (1-PPA) has been recently described as a novel inhibitor of PAR2. The aim of our study was to evaluate the effect of 1-PPA in neuroinflammation and microglial activation in Parkinson's disease. Protein aggregates and PAR2 expression were analyzed using Thioflavin S assay and immunofluorescence in cultured human fibroblasts from Parkinson's patients, treated or untreated with 1-PPA. A significant decrease in amyloid aggregates was observed after 1-PPA treatment in all patients. A parallel decrease in PAR2 expression, which was higher in sporadic Parkinson's patients, was also observed both at the transcriptional and protein level. In addition, in mouse LPS-activated microglia, the inflammatory profile was significantly downregulated after 1-PPA treatment, with a remarkable decrease in IL-1ß, IL-6, and TNF-α, together with a decreased expression of PAR2. In conclusion, 1-PPA determines the reduction in neuroglia inflammation and amyloid aggregates formation, suggesting that the pharmacological inhibition of PAR2 could be proposed as a novel strategy to control neuroinflammation.

Rapidly progressive multiple system atrophy in a patient carrying LRRK2 G2019S mutation.

BACKGROUND: Multiple system atrophy (MSA) is considered a primarily sporadic neurodegenerative disease, but the role of genetic is poorly understood. CASE: We present a female patient of Moroccan origin who developed a rapidly progressive non-levodopa responsive parkinsonism, gait and balance problems, and dysautonomia including severe bulbar symptoms. She was diagnosed with MSA Parkinsonian-type (MSA-P) and suddenly died at night at 58 years of age. Reduced striatal DAT-SPECT, putaminal hyperintensity on T2-MRI, and hypometabolism with FDG-PET were present. Genetic testing documented a G2019S mutation in the LRRK2 gene. A skin biopsy was obtained and used to perform alpha-synuclein RT-QuIC, which was negative, and immunohistochemical analysis, which demonstrated abnormal alpha-synuclein deposits in cutaneous nerves. Elevated blood neurofilament light chain levels were also documented. CONCLUSIONS: LRRK2 mutations are the most common cause of monogenic Parkinson's disease (PD) and G2019S is the most frequent variant. Our patient presented with biological, clinical, and radiological features of MSA, but genetic testing revealed a G2019S LRRK2 mutation, which has been previously reported only in one other case of pathologically proven MSA but with mild progression. In our patient, post-mortem confirmation could not be performed, but RT-QuIC and immunohistochemical findings on skin biopsy support the diagnosis of MSA. G2019S LRRK2 may be linked to an increased risk of MSA. Cases of atypical parkinsonism with rapid disease course should be screened for PD-related genes especially in populations with a high prevalence of mutations in known genes.

SARS-CoV-2-Mimicking Pseudoviral Particles Accelerate α-Synuclein Aggregation In Vitro.

Since the SARS-CoV-2 virus started spreading worldwide, evidence pointed toward an impact of the infection on the nervous system. COVID-19 patients present neurological manifestations and have an increased risk of developing brain-related symptoms in the long term. In fact, evidence in support of the neuroinvasive potential of SARS-CoV-2 has emerged. Considering that viral parkisonism was observed as a consequence of encephalopathies caused by viral infections, it has been already suggested that COVID-19 could affect the dopaminergic neurons and contribute to neurodegeneration in Parkinson's disease (PD), by promoting the formation of amyloid fibrils constituted by the PD-related protein α-synuclein. Here, we observe not only that SARS-CoV-2 viral spike protein and nucleocapsid protein can alone promote α-synuclein aggregation but also that the spike protein organization in a corona shape on the viral envelope may be crucial in triggering fast amyloid fibrils formation, thus possibly contributing to PD pathogenesis.

Epitope-Specific Anti-SerpinB3 Antibodies for SerpinB3 Recognition and Biological Activity Inhibition.

SerpinB3 is a serine protease inhibitor that plays a relevant role in disease progression and cancer by increasing fibrosis, cell proliferation, and invasion, besides conferring resistance to apoptosis. The mechanisms underlying these biological activities are not yet fully understood. The aim of this study was to generate antibodies directed against different SerpinB3 epitopes to better investigate their biological role. Five exposed epitopes were identified using the software DNASTAR Lasergene and the corresponding synthetic peptides were used for NZW rabbit immunization. Anti-P#2 and anti-P#4 antibodies were able to recognize both SerpinB3 and SerpinB4 by ELISA. Anti-P#5 antibody, produced against the reactive site loop of SerpinB3, showed the greatest specific reactivity for human SerpinB3. This antibody was able to recognize SerpinB3 at nuclear level, while anti-P#3 antibody recognized SerpinB3 only at cytoplasmic level, both by immunofluorescence and by immunohistochemistry. The biological activity of each antibody preparation was assessed in HepG2 cells overexpressing SerpinB3 and anti-P#5 antibody reduced proliferation by 12% cell and cell invasion by 75%, while trivial results were obtained with the other antibody preparations. These findings indicate that the reactive site loop of SerpinB3 is essential for the invasiveness features induced by this serpin and it could become a novel druggable target.

ACE2 Receptor and TMPRSS2 Protein Expression Patterns in the Human Brainstem Reveal Anatomical Regions Potentially Vulnerable to SARS-CoV-2 Infection.

Angiotensin-converting enzyme 2 receptor (ACE2R) is a transmembrane protein expressed in various tissues throughout the body that plays a key role in the regulation of blood pressure. Recently, ACE2R has gained significant attention due to its involvement in the pathogenesis of COVID-19, the disease caused by the Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2). While ACE2 receptors serve as entry points for the novel coronavirus, Transmembrane Serine Protease 2 (TMPRSS2), an enzyme located on the cell membrane, is required for SARS-CoV-2 S protein priming. Even though numerous studies have assessed the effects of COVID-19 on the brain, very little information is available concerning the distribution of ACE2R and TMPRSS2 in the human brain, with particular regard to their topographical expression in the brainstem. In this study, we investigated the expression of ACE2R and TMPRSS2 in the brainstem of 18 adult subjects who died due to pneumonia/respiratory insufficiency. Our findings indicate that ACE2R and TMPRSS2 are expressed in neuronal and glial cells of the brainstem, particularly at the level of the vagal nuclei of the medulla and the midbrain tegmentum, thus confirming the expression and anatomical localization of these proteins within specific human brainstem nuclei. Furthermore, our findings help to define anatomically susceptible regions to SARS-CoV-2 infection in the brainstem, advancing knowledge on the neuropathological underpinnings of neurological manifestations in COVID-19.

DOPAL initiates αSynuclein-dependent impaired proteostasis and degeneration of neuronal projections in Parkinson's disease.

Dopamine dyshomeostasis has been acknowledged among the determinants of nigrostriatal neuron degeneration in Parkinson's disease (PD). Several studies in experimental models and postmortem PD patients underlined increasing levels of the dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL), which is highly reactive towards proteins. DOPAL has been shown to covalently modify the presynaptic protein αSynuclein (αSyn), whose misfolding and aggregation represent a major trait of PD pathology, triggering αSyn oligomerization in dopaminergic neurons. Here, we demonstrated that DOPAL elicits αSyn accumulation and hampers αSyn clearance in primary neurons. DOPAL-induced αSyn buildup lessens neuronal resilience, compromises synaptic integrity, and overwhelms protein quality control pathways in neurites. The progressive decline of neuronal homeostasis further leads to dopaminergic neuron loss and motor impairment, as showed in in vivo models. Finally, we developed a specific antibody which detected increased DOPAL-modified αSyn in human striatal tissues from idiopathic PD patients, corroborating the translational relevance of αSyn-DOPAL interplay in PD neurodegeneration.

Scavenging neurotoxic aldehydes using lysine carbon dots.

Reactive aldehydes generated in cells and tissues are associated with adverse physiological effects. Dihydroxyphenylacetaldehyde (DOPAL), the biogenic aldehyde enzymatically produced from dopamine, is cytotoxic, generates reactive oxygen species, and triggers aggregation of proteins such as α-synuclein implicated in Parkinson's disease. Here, we demonstrate that carbon dots (C-dots) prepared from lysine as the carbonaceous precursor bind DOPAL molecules through interactions between the aldehyde units and amine residues on the C-dot surface. A set of biophysical and in vitro experiments attests to attenuation of the adverse biological activity of DOPAL. In particular, we show that the lysine-C-dots inhibit DOPAL-induced α-synuclein oligomerization and cytotoxicity. This work underlines the potential of lysine-C-dots as an effective therapeutic vehicle for aldehyde scavenging.

Duodenal alpha-Synuclein Pathology and Enteric Gliosis in Advanced Parkinson's Disease.

BACKGROUND: The role of the gut-brain axis has been recently highlighted as a major contributor to Parkinson's disease (PD) physiopathology, with numerous studies investigating bidirectional transmission of pathological protein aggregates, such as α-synuclein (αSyn). However, the extent and the characteristics of pathology in the enteric nervous system have not been fully investigated. OBJECTIVE: We characterized αSyn alterations and glial responses in duodenum biopsies of patients with PD by employing topography-specific sampling and conformation-specific αSyn antibodies. METHODS: We examined 18 patients with advanced PD who underwent Duodopa percutaneous endoscopic gastrostomy and jejunal tube procedure, 4 untreated patients with early PD (disease duration <5 years), and 18 age- and -sex-matched healthy control subjects undergoing routine diagnostic endoscopy. A mean of four duodenal wall biopsies were sampled from each patient. Immunohistochemistry was performed for anti-aggregated αSyn (5G4) and glial fibrillary acidic protein antibodies. Morphometrical semiquantitative analysis was performed to characterize αSyn-5G4+ and glial fibrillary acidic protein-positive density and size. RESULTS: Immunoreactivity for aggregated α-Syn was identified in all patients with PD (early and advanced) compared with controls. αSyn-5G4+ colocalized with neuronal marker ß-III-tubulin. Evaluation of enteric glial cells demonstrated an increased size and density when compared with controls, suggesting reactive gliosis. CONCLUSIONS: We found evidence of synuclein pathology and gliosis in the duodenum of patients with PD, including early de novo cases. Future studies are required to evaluate how early in the disease process duodenal pathology occurs and its possible contribution to levodopa effect in chronic patients. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Detection of SARS-CoV-2 viral proteins and genomic sequences in human brainstem nuclei.

Neurological manifestations are common in COVID-19, the disease caused by SARS-CoV-2. Despite reports of SARS-CoV-2 detection in the brain and cerebrospinal fluid of COVID-19 patients, it is still unclear whether the virus can infect the central nervous system, and which neuropathological alterations can be ascribed to viral tropism, rather than immune-mediated mechanisms. Here, we assess neuropathological alterations in 24 COVID-19 patients and 18 matched controls who died due to pneumonia/respiratory failure. Aside from a wide spectrum of neuropathological alterations, SARS-CoV-2-immunoreactive neurons were detected in the dorsal medulla and in the substantia nigra of five COVID-19 subjects. Viral RNA was also detected by real-time RT-PCR. Quantification of reactive microglia revealed an anatomically segregated pattern of inflammation within affected brainstem regions, and was higher when compared to controls. While the results of this study support the neuroinvasive potential of SARS-CoV-2 and characterize the role of brainstem inflammation in COVID-19, its potential implications for neurodegeneration, especially in Parkinson's disease, require further investigations.

DJ-1 promotes energy balance by regulating both mitochondrial and autophagic homeostasis.

The protein DJ-1 is mutated in rare familial forms of recessive Parkinson's disease and in parkinsonism accompanied by amyotrophic lateral sclerosis symptoms and dementia. DJ-1 is considered a multitasking protein able to confer protection under various conditions of stress. However, the precise cellular function still remains elusive. In the present work, we evaluated fruit flies lacking the expression of the DJ-1 homolog dj-1ß as compared to control aged-matched individuals. Behavioral evaluations included lifespan, locomotion in an open field arena, sensitivity to oxidative insults, and resistance to starvation. Molecular analyses were carried out by analyzing the mitochondrial morphology and functionality, and the autophagic response. We demonstrated that dj-1ß null mutant flies are hypoactive and display higher sensitivity to oxidative insults and food deprivation. Analysis of mitochondrial homeostasis revealed that loss of dj-1ß leads to larger and more circular mitochondria, characterized by impaired complex-I-linked respiration while preserving ATP production capacity. Additionally, dj-1ß null mutant flies present an impaired autophagic response, which is suppressed by treatment with the antioxidant molecule N-Acetyl-L-Cysteine. Overall, our data point to a mechanism whereby DJ-1 plays a critical role in the maintenance of energy homeostasis, by sustaining mitochondrial homeostasis and affecting the autophagic flux through the maintenance of the cellular redox state. In light of the involvement of DJ-1 in neurodegenerative diseases and considering that neurons are highly energy-demanding cells, particularly sensitive to redox stress, our study sheds light on a key role of DJ-1 in the maintenance of cellular homeostasis.

Neuroprotective Effect of Antiapoptotic URG7 Protein on Human Neuroblastoma Cell Line SH-SY5Y.

Up-regulated Gene clone 7 (URG7) is a protein localized in the endoplasmic reticulum (ER) and overexpressed in liver cells upon hepatitis B virus (HBV) infection. Its activity has been related to the attenuation of ER stress resulting from HBV infection, promoting protein folding and ubiquitination and reducing cell apoptosis overall. While the antiapoptotic activity of URG7 in HBV-infected cells may have negative implications, this effect could be exploited positively in the field of proteinopathies, such as neurodegenerative diseases. In this work, we aimed to verify the possible contribution of URG7 as a reliever of cellular proteostasis alterations in a neuronal in vitro system. Following tunicamycin-induced ER stress, URG7 was shown to modulate different markers of the unfolded protein response (UPR) in favor of cell survival, mitigating ER stress and activating autophagy. Furthermore, URG7 promoted ubiquitination, and determined a reduction in protein aggregation, calcium release from the ER and intracellular ROS content, confirming its pro-survival activity. Therefore, in light of the results reported in this work, we hypothesize that URG7 offers activity as an ER stress reliever in a neuronal in vitro model, and we paved the way for a new approach in the treatment of neurodegenerative diseases.

Smell deficits in COVID-19 and possible links with Parkinson's disease.

Olfactory impairment is a common symptom in Coronavirus Disease 2019 (COVID-19), the disease caused by Severe Acute Respiratory Syndrome-Coronavirus 2 (SARS-CoV-2) infection. While other viruses, such as influenza viruses, may affect the ability to smell, loss of olfactory function is often smoother and associated to various degrees of nasal symptoms. In COVID-19, smell loss may appear also in absence of other symptoms, frequently with a sudden onset. However, despite great clinical interest in COVID-19 olfactory alterations, very little is known concerning the mechanisms underlying these phenomena. Moreover, olfactory dysfunction is observed in neurological conditions like Parkinson's disease (PD) and can precede motor onset by many years, suggesting that viral infections, like COVID-19, and regional inflammatory responses may trigger defective protein aggregation and subsequent neurodegeneration, potentially linking COVID-19 olfactory impairment to neurodegeneration. In the following chapter, we report the neurobiological and neuropathological underpinnings of olfactory impairments encountered in COVID-19 and discuss the implications of these findings in the context of neurodegenerative disorders, with particular regard to PD and alpha-synuclein pathology.

Topography and distribution of adenosine A2A and dopamine D2 receptors in the human Subthalamic Nucleus.

The human Subthalamic Nucleus (STh) is a diencephalic lens-shaped structure located ventrally to the thalamus and functionally implicated in the basal ganglia circuits. Despite recent efforts to characterize the neurochemical and functional anatomy of the STh, little to no information is available concerning the expression and distribution of receptors belonging to the dopaminergic and purinergic system in the human STh. Both systems are consistently implicated in basal ganglia physiology and pathology, especially in Parkinson's Disease, and represent important targets for the pharmacological treatment of movement disorders. Here, we investigate the topography and distribution of A2A adenosine and D2 dopamine receptors in the human basal ganglia and subthalamic nucleus. Our findings indicate a peculiar topographical distribution of the two receptors throughout the subthalamic nucleus, while colocalization between the receptors opens the possibility for the presence of A2AR- D2R heterodimers within the dorsal and medial aspects of the structure. However, further investigation is required to confirm these findings.

Long-term safety, discontinuation and mortality in an Italian cohort with advanced Parkinson's disease on levodopa/carbidopa intestinal gel infusion.

INTRODUCTION: Levodopa/carbidopa intestinal gel (LCIG) is an effective treatment in patients with advanced Parkinson's disease (PD) with consolidated evidence of clinical efficacy. However, only few studies have assessed long-term safety, causes of discontinuation, mortality, and relative predictors. METHODS: We conducted a retrospective analysis of 79 PD patients treated with LCIG between 2005 and 2020 in two Italian Neurological Centers, recording all adverse events (AEs), including weight loss (WL). Kaplan-Meier curve was used to estimate the time to discontinuation and survival. Cox proportional hazard model was employed to identify predictors of discontinuation and mortality, while Pearson's correlation was used to analyze predictors of WL. RESULTS: The average follow-up was 47.7 ± 40.5 months and the median survival from disease onset was 25 years. There were three cases of polyradiculoneuropathy Guillain-Barre syndrome-like, all occurred in the early years of LCIG treatment. Twenty-five patients died (32%), 18 on LCIG (including one suicide) and seven after discontinuation. The mean WL was 3.62 ± 7.5 kg, which correlated with levodopa dose at baseline (p = 0.002), levodopa equivalent daily dose (LEDD) baseline (p = 0.017) and off-duration (p = 0.0014), but not dyskinesia. Peristomal complications emerged as a negative predictor of discontinuation (p = 0.008). CONCLUSIONS: LCIG has a relatively satisfactory long-term safety profile and efficacy and a relatively low rate of discontinuation. Peristomal complications may represent a predictor of longer duration of therapy. According to the mortality analysis, LCIG patients show a long lifespan. Delaying the initiation of LCIG does not affect the sustainability of LCIG therapy.

Nerve growth factor transfer from cardiomyocytes to innervating sympathetic neurons activates TrkA receptors at the neuro-cardiac junction.

Sympathetic neurons densely innervate the myocardium with non-random topology and establish structured contacts (i.e. neuro-cardiac junctions, NCJ) with cardiomyocytes, allowing synaptic intercellular communication. Establishment of heart innervation is regulated by molecular mediators released by myocardial cells. The mechanisms underlying maintenance of cardiac innervation in the fully developed heart, are, however, less clear. Notably, several cardiac diseases, primarily affecting cardiomyocytes, are associated with sympathetic denervation, supporting the hypothesis that retrograde 'cardiomyocyte-to-sympathetic neuron' communication is essential for heart cellular homeostasis. We aimed to determine whether cardiomyocytes provide nerve growth factor (NGF) to sympathetic neurons, and the role of the NCJ in supporting such retrograde neurotrophic signalling. Immunofluorescence on murine and human heart slices shows that NGF and its receptor, tropomyosin-receptor-kinase-A, accumulate, respectively, in the pre- and post-junctional sides of the NCJ. Confocal immunofluorescence, scanning ion conductance microscopy and molecular analyses, in co-cultures, demonstrate that cardiomyocytes feed NGF to sympathetic neurons, and that this mechanism requires a stable intercellular contact at the NCJ. Consistently, cardiac fibroblasts, devoid of NCJ, are unable to sustain SN viability. ELISA assay and competition binding experiments suggest that this depends on the NCJ being an insulated microenvironment, characterized by high [NGF]. In further support, real-time imaging of tropomyosin-receptor-kinase-A vesicle movements demonstrate that efficiency of neurotrophic signalling parallels the maturation of such structured intercellular contacts. Altogether, our results demonstrate the mechanisms which link sympathetic neuron survival to neurotrophin release by directly innervated cardiomyocytes, conceptualizing sympathetic neurons as cardiomyocyte-driven heart drivers. KEY POINTS: CMs are the cell source of nerve growth factor (NGF), required to sustain innervating cardiac SNs; NCJ is the place of the intimate liaison, between SNs and CMs, allowing on the one hand neurons to peremptorily control CM activity, and on the other, CMs to adequately sustain the contacting, ever-changing, neuronal actuators; alterations in NCJ integrity may compromise the efficiency of 'CM-to-SN' signalling, thus representing a potentially novel mechanism of sympathetic denervation in cardiac diseases.

Dopamine signaling modulates microglial NLRP3 inflammasome activation: implications for Parkinson's disease.

BACKGROUND: Parkinson's disease (PD) is characterized by the loss of nigral dopaminergic neurons leading to impaired striatal dopamine signaling, α-synuclein- (α-syn-) rich inclusions, and neuroinflammation. Degenerating neurons are surrounded by activated microglia with increased secretion of interleukin-1ß (IL-1ß), driven largely by the NLRP3 inflammasome. A critical role for microglial NLRP3 inflammasome activation in the progression of both dopaminergic neurodegeneration and α-syn pathology has been demonstrated in parkinsonism mouse models. Fibrillar α-syn activates this inflammasome in mouse and human macrophages, and we have shown previously that the same holds true for primary human microglia. Dopamine blocks microglial NLRP3 inflammasome activation in the MPTP model, but its effects in this framework, highly relevant to PD, remain unexplored in primary human microglia and in other in vivo parkinsonism models. METHODS: Biochemical techniques including quantification of IL-1ß secretion and confocal microscopy were employed to gain insight into dopamine signaling-mediated inhibition of the NLRP3 inflammasome mechanism in primary human microglia and the SYN120 transgenic mouse model. Dopamine and related metabolites were applied to human microglia together with various inflammasome activating stimuli. The involvement of the receptors through which these catecholamines were predicted to act were assessed with agonists in both species. RESULTS: We show in primary human microglia that dopamine, L-DOPA, and high extracellular K+, but not norepinephrine and epinephrine, block canonical, non-canonical, and α-syn-mediated NLRP3 inflammasome-driven IL-1ß secretion. This suggests that dopamine acts as an inflammasome inhibitor in human microglia. Accordingly, we provide evidence that dopamine exerts its inhibitory effect through dopamine receptor D1 and D2 (DRD1 and DRD2) signaling. We also show that aged mice transgenic for human C-terminally truncated (1-120) α-syn (SYN120 tg mice) display increased NLRP3 inflammasome activation in comparison to WT mice that is diminished upon DRD1 agonism. CONCLUSIONS: Dopamine inhibits canonical, non-canonical, and α-syn-mediated activation of the NLRP3 inflammasome in primary human microglia, as does high extracellular K+. We suggest that dopamine serves as an endogenous repressor of the K+ efflux-dependent microglial NLRP3 inflammasome activation that contributes to dopaminergic neurodegeneration in PD, and that this reciprocation may account for the specific vulnerability of these neurons to disease pathology.