Inflammasomes: An Emerging Mechanism Translating Environmental Toxicant Exposure Into Neuroinflammation in Parkinson's Disease

Parkinson's disease-associated shifts between DNA methylation and DNA hydroxymethylation in human brain in PD-related genes, including PARK19 (DNAJC6) and PTPRN2 (IA-2β)

Background The majority of Parkinson's disease (PD) cases are due to a complex interaction between aging, genetics, and environmental factors; epigenetic mechanisms are thought to act as important mediators of these risk factors. While multiple studies to date have explored the role of DNA modifications in PD, few focus on 5-hydroxymethylcytosine (5hmC). Because 5hmC occurs at its highest levels in the brain and is thought to be particularly important in the central nervous system, particularly in the response to neurotoxicants, it is important to explore the potential role of 5hmC in PD. This study expands on our previously published epigenome-wide association study (EWAS) performed on DNA isolated from neuron-enriched nuclei from human postmortem parietal cortex from the Banner Sun Health Research Institute Brain Bank. The study aimed to identify paired changes in 5hmC and 5mC in PD in enriched neuronal nuclei isolated from PD post-mortem parietal cortex and age- and sex-matched controls. We performed oxidative bisulfite (oxBS) conversion and paired it with our previously published bisulfite (BS)-based EWAS on the same samples to identify cytosines with significant shifts between these two related epigenetic marks. Interaction differentially modified cytosines (iDMCs) were identified using our recently published mixed-effects model for co-analyzing β mC and β hmC data. Results We identified 1,030 iDMCs with paired changes in 5mC and 5hmC (FDR < 0.05) that map to 695 genes, including PARK19 (DNAJC6), a familial PD gene, and PTPRN2 (IA-2), which has been previously implicated in PD in both epigenetic and mechanistic studies. The majority of iDMC-containing genes have not previously been implicated in PD and were not identified in our previous BS-based EWAS. Conclusions These data potentially link epigenetic regulation of the PARK19 and PTPRN2 loci in the pathogenesis of idiopathic PD. In addition, iDMC-containing genes have known functions in synaptic formation and function, cell cycle and senescence, neuroinflammation, and epigenetic regulation. These data suggest that there are significant shifts between 5mC and 5hmC associated with PD in genes relevant to PD pathogenesis that are not captured by analyzing BS-based data alone or by analyzing each mark as a distinct dataset.

Developmental origins of parkinson's disease risk: perinatal exposure to the organochlorine pesticide dieldrin leads to sex-specific DNA modifications in critical neurodevelopmental pathways in the mouse midbrain

Epidemiological studies show that exposure to the organochlorine pesticide dieldrin is associated with increased risk of Parkinson's disease (PD). Animal studies support a link between developmental dieldrin exposure and increased neuronal susceptibility in the α-synuclein preformed fibril (α-syn PFF) and MPTP models in adult male C57BL/6 mice. In a previous study, we showed that developmental dieldrin exposure was associated with sex-specific changes in DNA modifications within genes related to dopaminergic neuron development and maintenance at 12 weeks of age. Here, we used capture hybridization-sequencing with custom baits to interrogate DNA modifications across the entire genetic loci of the previously identified genes at multiple time points-birth, 6 weeks, 12 weeks, and 36 weeks old. We identified largely sex-specific dieldrin-induced changes in DNA modifications at each time point that annotated to pathways important for neurodevelopment, potentially related to critical steps in early neurodevelopment, dopaminergic neuron differentiation, synaptogenesis, synaptic plasticity, and glial-neuron interactions. Despite large numbers of age-specific DNA modifications, longitudinal analysis identified a small number of DMCs with dieldrin-induced deflection of epigenetic aging. The sex-specificity of these results adds to evidence that sex-specific responses to PD-related exposures may underly sex-specific differences in disease. Overall, these data support the idea that developmental dieldrin exposure leads to changes in epigenetic patterns that persist after the exposure period and disrupt critical neurodevelopmental pathways, thereby impacting risk of late life diseases, including PD.

Developmental origins of Parkinson's disease risk: perinatal exposure to the organochlorine pesticide dieldrin leads to sex-specific DNA modifications in critical neurodevelopmental pathways in the mouse midbrain

Epidemiological studies show that exposure to the organochlorine pesticide dieldrin is associated with increased risk of Parkinson's disease (PD). Animal studies support a link between developmental dieldrin exposure and increased neuronal susceptibility in the α-synuclein preformed fibril (α-syn PFF) and MPTP models in adult male C57BL/6 mice. In a previous study, we showed that developmental dieldrin exposure was associated with sex-specific changes in DNA modifications within genes related to dopaminergic neuron development and maintenance at 12 weeks of age. Here, we used capture hybridization-sequencing with custom baits to interrogate DNA modifications across the entire genetic loci of the previously identified genes at multiple time points - birth, 6 weeks, 12 weeks, and 36 weeks old. We identified largely sex-specific dieldrin-induced changes in DNA modifications at each time point that annotated to pathways important for neurodevelopment, potentially related to critical steps in early neurodevelopment, dopaminergic neuron differentiation, synaptogenesis, synaptic plasticity, and glial-neuron interactions. Despite large numbers of age-specific DNA modifications, longitudinal analysis identified a small number of DMCs with dieldrin-induced deflection of epigenetic aging. The sex-specificity of these results adds to evidence that sex-specific responses to PD-related exposures may underly sex-specific differences in disease. Overall, these data support the idea that developmental dieldrin exposure leads to changes in epigenetic patterns that persist after the exposure period and disrupt critical neurodevelopmental pathways, thereby impacting risk of late life diseases, including PD.

Role of NLRP3 in Parkinson's disease: Specific activation especially in dopaminergic neurons

Parkinson's disease (PD) is a neurodegenerative disorder with motor symptoms like bradykinesia, tremors, and balance issues. The pathology is recognized by progressively degenerative nigrostriatal dopaminergic neurons (DANs) loss. Its exact pathogenesis is unclear. Numerous studies have shown that nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) contributes to the pathogenesis of PD. Previous studies have demonstrated that the over-activation of NLRP3 inflammasome in microglia indirectly leads to the loss of DANs, which can worsen PD. In recent years, autopsy analyses of PD patients and studies in PD models have revealed upregulation of NLRP3 expression within DANs and demonstrated that activation of NLRP3 inflammasome in neurons is sufficient to drive neuronal loss, whereas microglial activation occurs after neuronal death, and that inhibition of intraneuronal NLRP3 inflammasome prevents degeneration of DANs. In this review, we provide research evidence related to NLRP3 inflammasome in DANs in PD as well as focus on possible mechanisms of NLRP3 inflammasome activation in neurons, aiming to provide a new way of thinking about the pathogenesis and prevention of PD.

Oral administration of Limonin (LM) exerts neuroprotective effects by inhibiting neuron autophagy and microglial activation in 6-OHDA-injected rats

Parkinson's disease (PD) is a neurodegenerative disorder that occurs most frequently in middle-aged and elderly people. It is characterized by an insidious onset and a complex etiology, and no effective treatment has been developed. The primary characteristic of PD is the degenerative death of midbrain dopaminergic neurons. The excessive autophagy of neurons and hyperactivation of microglia were shown to be involved in the apoptosis of dopaminergic neurons. Limonin (LM), a type of pure natural compound present in grapefruit or citrus fruits (e. g., lemon, orange) has been reported to inhibit apoptosis and inflammation. However, its role and mechanism of action in PD are unclear. In this study, we explored the effect and mechanism of action of LM in PD. In vivo experiments revealed that LM ameliorated 6-OHDA-induced reduced motor activity and PD-related pathological damage in rats. In vitro experiments revealed that LM inhibited the 6-OHDA-induced apoptosis of PC12 cells by inhibiting the excessive autophagy of neurons. In addition, LM inhibited microglial inflammation by activating the AKT/Nrf-2/HO-1 pathway and protected neurons against microglial inflammation-mediated neurotoxicity. In conclusion, the findings of this experiment demonstrated that LM exerted neuroprotective effects by inhibiting neuronal autophagy-mediated apoptosis and microglial activation in 6-OHDA-injected rats, thus indicating that LM can serve as a candidate for PD by targeting neuroinflammation and neuronal autophagy to inhibit neuronal apoptosis.

The Endotoxin Hypothesis of Parkinson's Disease

The endotoxin hypothesis of Parkinson's disease (PD) is the idea that lipopolysaccharide (LPS) endotoxins contribute to the pathogenesis of this disorder. LPS endotoxins are found in, and released from, the outer membrane of Gram-negative bacteria, for example in the gut. It is proposed that gut dysfunction in early PD leads to elevated LPS levels in the gut wall and blood, which promotes both α-synuclein aggregation in the enteric neurons and a peripheral inflammatory response. Communication to the brain via circulating LPS and cytokines in the blood and/or the gut-brain axis leads to neuroinflammation and spreading of α-synuclein pathology, exacerbating neurodegeneration in brainstem nuclei and loss of dopaminergic neurons in the substantia nigra, and manifesting in the clinical symptoms of PD. The evidence supporting this hypothesis includes: (1) gut dysfunction, permeability, and bacterial changes occur early in PD, (2) serum levels of LPS are increased in a proportion of PD patients, (3) LPS induces α-synuclein expression, aggregation, and neurotoxicity, (4) LPS causes activation of peripheral monocytes leading to inflammatory cytokine production, and (5) blood LPS causes brain inflammation and specific loss of midbrain dopaminergic neurons, mediated by microglia. If the hypothesis is correct, then treatment options might include: (1) changing the gut microbiome, (2) reducing gut permeability, (3) reducing circulating LPS levels, or (4) blocking the response of immune cells and microglia to LPS. However, the hypothesis has a number of limitations and requires further testing, in particular whether reducing LPS levels can reduce PD incidence, progression, or severity. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Aflatoxin B1 Increases Soluble Epoxide Hydrolase in the Brain and Induces Neuroinflammation and Dopaminergic Neurotoxicity

Parkinson's disease (PD) is an increasingly common neurodegenerative movement disorder with contributing factors that are still largely unexplored and currently no effective intervention strategy. Epidemiological and pre-clinical studies support the close association between environmental toxicant exposure and PD incidence. Aflatoxin B1 (AFB1), a hazardous mycotoxin commonly present in food and environment, is alarmingly high in many areas of the world. Previous evidence suggests that chronic exposure to AFB1 leads to neurological disorders as well as cancer. However, whether and how aflatoxin B1 contributes to the pathogenesis of PD is poorly understood. Here, oral exposure to AFB1 is shown to induce neuroinflammation, trigger the α-synuclein pathology, and cause dopaminergic neurotoxicity. This was accompanied by the increased expression and enzymatic activity of soluble epoxide hydrolase (sEH) in the mouse brain. Importantly, genetic deletion or pharmacological inhibition of sEH alleviated the AFB1-induced neuroinflammation by reducing microglia activation and suppressing pro-inflammatory factors in the brain. Furthermore, blocking the action of sEH attenuated dopaminergic neuron dysfunction caused by AFB1 in vivo and in vitro. Together, our findings suggest a contributing role of AFB1 to PD etiology and highlight sEH as a potential pharmacological target for alleviating PD-related neuronal disorders caused by AFB1 exposure.

The inflammasome pathway: A key player in ocular surface and anterior segment diseases

Inflammasomes are multicomplex molecular regulators with an emerging importance in regulating ocular surface and anterior segment health and disease. Key components found in the eye include NF-κB, NLRP3, NLRC4, NLRP6, ASC, IL-1β, IL-18, and caspase-1. The role of NLRP1, NLRC4, AIM2, and NLRP3 inflammasomes in the pathogenesis of infectious ulcers, DED, uveitis, glaucoma, corneal edema, and other diseases is being studied with many developments. Attenuation of these diseases has been explored by blocking various molecules along the inflammasome pathway with agents like NAC, polydatin, calcitriol, glyburide, YVAD, and disulfiram. We provide a background on the inflammasome pathway as it relates to the ocular surface and anterior segment of the eye, discuss the role of inflammasomes in the above diseases in animals and humans, investigate new therapeutic targets, and explore the efficacy of new anti-inflammasome therapies.

NLRP3 inflammasome in neurodegenerative disease

Neurodegenerative diseases are characterized by a dysregulated neuro-glial microenvironment, culminating in functional deficits resulting from neuronal cell death. Inflammation is a hallmark of the neurodegenerative microenvironment and despite a critical role in tissue homeostasis, increasing evidence suggests that chronic inflammatory insult can contribute to progressive neuronal loss. Inflammation has been studied in the context of neurodegenerative disorders for decades but few anti-inflammatory treatments have advanced to clinical use. This is likely due to the related challenges of predicting and mitigating off-target effects impacting the normal immune response while detecting inflammatory signatures that are specific to the progression of neurological disorders. Inflammasomes are pro-inflammatory cytosolic pattern recognition receptors functioning in the innate immune system. Compelling pre-clinical data has prompted an intense interest in the role of the NLR family pyrin domain containing 3 (NLRP3) inflammasome in neurodegenerative disease. NLRP3 is typically inactive but can respond to sterile triggers commonly associated with neurodegenerative disorders including protein misfolding and aggregation, mitochondrial and oxidative stress, and exposure to disease-associated environmental toxicants. Clear evidence of enhanced NLRP3 inflammasome activity in common neurodegenerative diseases has coincided with rapid advancement of novel small molecule therapeutics making the NLRP3 inflammasome an attractive target for near-term interventional studies. In this review, we highlight evidence from model systems and patients indicating inflammasome activity in neurodegenerative disease associated with the NLRP3 inflammasome's ability to recognize pathologic forms of amyloid-β, tau, and α-synuclein. We discuss inflammasome-driven pyroptotic processes highlighting the potential utility of evaluating extracellular inflammasome-related proteins in the context of biomarker discovery. We complete the report by pointing out gaps in our understanding of intracellular modifiers of inflammasome activity and mechanisms regulating the resolution of inflammasome activation. The literature review and perspectives provide a conceptual platform for continued analysis of inflammation in neurodegenerative diseases through the study of inflammasomes and pyroptosis, mechanisms of inflammation and cell death now recognized to function in multiple highly prevalent neurological disorders.

Inflammasome Activation in Parkinson’s Disease

Chronic sterile inflammation and persistent immune activation is a prominent pathological feature of Parkinson’s disease (PD). Inflammasomes are multi-protein intracellular signaling complexes which orchestrate inflammatory responses in immune cells to a diverse range of pathogens and host-derived signals. Widespread inflammasome activation is evident in PD patients at the sites of dopaminergic degeneration as well as in blood samples and mucosal biopsies. Inflammasome activation in the nigrostriatal system is also a common pathological feature in both neurotoxicant and α-synuclein models of PD where dopaminergic degeneration occurs through distinct mechanisms. The NLRP3 (NLR Family Pyrin Domain Containing 3) inflammasome has been shown to be the primary driver of inflammatory neurotoxicity in PD and other neurodegenerative diseases. Chronic NLRP3 inflammasome activation is triggered by pathogenic misfolded α-synuclein aggregates which accumulate and spread over the disease course in PD. Converging lines of evidence suggest that blocking inflammasome activation could be a promising therapeutic strategy for disease modification, with both NLRP3 knockout mice and CNS-permeable pharmacological inhibitors providing robust neuroprotection in multiple PD models. This review summarizes the current evidence and knowledge gaps around inflammasome activation in PD, the pathological mechanisms by which persistent inflammasome activation can drive dopaminergic degeneration and the therapeutic opportunities for disease modification using NLRP3 inhibitors.

Inflammasome Signaling in the Aging Brain and Age-Related Neurodegenerative Diseases

Inflammasomes are intracellular protein complexes, members of the innate immune system, and their activation and regulation play an essential role in maintaining homeostatic conditions against exogenous and endogenous stimuli. Inflammasomes occur as cytosolic proteins and assemble into a complex during the recognition of pathogen-associated or danger-associated molecular patterns by pattern-recognition receptors in host cells. The formation of the inflammasome complex elicits signaling molecules of proinflammatory cytokines such as interleukin-1β and interleukin 18 via activation of caspase-1 in the canonical inflammasome pathway whereas caspase-11 in the case of a mouse and caspase-4 and caspase-5 in the case of humans in the non-canonical inflammasome pathway, resulting in pyroptotic or inflammatory cell death which ultimately leads to neuroinflammation and neurodegenerative diseases. Inflammasome activation, particularly in microglial cells and macrophages, has been linked to aging as well as age-related neurodegenerative diseases. The accumulation of abnormal/ misfolded proteins acts as a ligand for inflammasome activation in neurodegenerative diseases. Although recent studies have revealed the inflammasomes' functionality in both in vitro and in vivo models, many inflammasome signaling cascade activations during biological aging, neuroinflammation, and neurodegeneration are still ambiguous. In this review, we comprehensively unveil the cellular and molecular mechanisms of inflammasome activation during neuronal aging and age-related neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, prion disease, and amyotrophic lateral sclerosis.

Environmental neurotoxicants and inflammasome activation in Parkinson's disease - A focus on the gut-brain axis

Inflammasomes are multi-protein complexes expressed in immune cells that function as intracellular sensors of environmental, metabolic and cellular stress. Inflammasome activation in the brain, has been shown to drive neuropathology and disease progression by multiple mechanisms, making it one of the most attractive therapeutic targets for disease modification in Parkinson's Disease (PD). Extensive inflammasome activation is evident in the brains of people with PD at the sites of dopaminergic degeneration and synuclein aggregation. While substantial progress has been made on validating inflammasome activation as a therapeutic target for PD, the mechanisms by which inflammasome activation is triggered and sustained over the disease course remain poorly understood. A growing body of evidence point to environmental and occupational chemical exposures as possible triggers of inflammasome activation in PD. The involvement of the gastrointestinal system and gut microbiota in PD pathophysiology is beginning to be elucidated, especially the profound link between gut dysbiosis and immune activation. While large cohort studies confirmed specific changes in the gut microbiota in PD patients compared to age-matched healthy controls, recent research suggest that synuclein pathology could be initiated in the gastrointestinal tract. In this review, we present a summarized perspective on current understanding on inflammasome activation and the gut-brain-axis link during PD pathophysiology. We discuss multiple environmental toxicants that are implicated as the etiological agents in causing idiopathic PD and their mechanistic underpinnings during neuroinflammatory events. We additionally present future directions that needs to address the research questions related to the gut-microbiome-brain mechanisms in PD.

Disease modifying therapies III: Novel targets

Despite significant research advances, treatment of Parkinson's disease (PD) remains confined to symptomatic therapies. Approaches aiming to halt or reverse disease progression remain an important but unmet goal. A growing understanding of disease pathogenesis and the identification of novel pathways contributing to initiation of neurodegeneration and subsequent progression has highlighted a range of potential novel targets for intervention that may influence the rate of progression of the disease process. Exploiting techniques to stratify patients according to these targets alongside using them as biomarkers to measure target engagement will likely improve patient selection and preliminary outcome measurements in clinical trials. In this review, we summarize a number of PD-related mechanisms that have recently gained interest such as neuroinflammation, lysosomal dysfunction and insulin resistance, while also exploring the potential for targeting peripheral interfaces such as the gastrointestinal tract and its ecosystem to achieve disease modification. We explore the rationale for these approaches based on preclinical studies, while also highlighting the status of relevant clinical trials as well as the promising role biomarkers may play in current and future studies.

Triggering Receptor Expressed on Myeloid Cells 2 Protects Dopaminergic Neurons by Promoting Autophagy in the Inflammatory Pathogenesis of Parkinson's Disease

Parkinson's disease is a neurodegenerative disorder with an inflammatory response as the core pathogenic mechanism. Previous human genetics findings support the view that the loss of TREM2 function will aggravate neurodegeneration, and TREM2 is one of the most highly expressed receptors in microglia. However, the role of TREM2 in the inflammatory mechanism of PD is not clear. In our study, it was found both in vivo and in vitro that the activation of microglia not only promoted the secretion of inflammatory factors but also decreased the level of TREM2 and inhibited the occurrence of autophagy. In contrast, an increase in the level of TREM2 decreased the expression of inflammatory factors and enhanced the level of autophagy through the p38 MAPK/mTOR pathway. Moreover, increased TREM2 expression significantly decreased the apoptosis of dopaminergic (DA) neurons and improved the motor ability of PD mice. In summary, TREM2 is an important link between the pathogenesis of PD and inflammation. Our study provides a new view for the mechanism of TREM2 in PD and reveals TREM2 as a potential therapeutic target for PD.

LRRK2 and WAVE2 regulate microglial-transition through distinct morphological phenotypes to induce neurotoxicity in a novel two-hit in vitro model of neurodegeneration

We report a novel in vitro classification system that tracks microglial activation state and their potential neurotoxicity. Mixed live-cell imaging was used to characterize transition through distinct morphological phenotypes, production of reactive oxygen species (ROS), formation of reactive microglial aggregates, and subsequent cytokine production. Transwell cultures were used to determine microglial migration (control and lipopolysaccharide (LPS) treated) to glutamate pre-stressed or healthy neurons. This two-hit paradigm was developed to model the vast evidence that neurodegenerative conditions, like Parkinson's disease (PD), may stem from the collective impact of multiple environmental stressors. We found that healthy neurons were resistant to microglial-mediated inflammation, whereas glutamate pre-stressed neurons were highly susceptible and in fact, appeared to recruit microglia. The LPS treated microglia progressed through distinct morphological states and expressed high levels of ROS and formed large cellular aggregates. Recent evidence implicates leucine-rich repeat kinase 2 (LRRK2) as an important player in the microglial inflammatory state, as well as in the genesis of PD. We found that inhibition of the LRRK2 signaling pathway using the kinase inhibitor cis-2,6-dimethyl-4-(6-(5-(1-methylcyclopropoxy)-1H-indazol-3-yl)pyrimidin-4-yl)morpholine (MLi2) or inhibition of the actin regulatory protein, Wiskott-Aldrich syndrome family Verprolin-homologous Protein-2 (WAVE2), stunted microglial activation and prevented neurotoxicity. Furthermore, inhibition of LRRK2 kinase activity reduced pro-inflammatory chemokines including MIP-2, CRG-2, and RANTES. These data together support the notion that LRRK2 and WAVE2 are important mediators of cytokine production and cytoskeletal rearrangement necessary for microglial-induced neurotoxicity. Furthermore, our model demonstrated unique microglial phenotypic changes that might be mechanistically important for better understanding neuron-microglial crosstalk.

Ambient particulate matter, ozone, and neurologic symptoms in U.S. Gulf states adults

Research on neurologic effects of air pollution has focused on neurodevelopment or later-life neurodegeneration; other effects throughout adulthood have received less attention. We examined air pollution levels and neurologic symptoms among 21,467 adults in US Gulf Coast states. We assigned exposure using Environmental Protection Agency estimates of daily ambient particulate matter 2.5 (PM_2.5) and ozone. Gulf Long-term Follow-up Study participants reported neurologic symptoms at enrollment (2011-2013). We estimated cross-sectional associations between each air pollutant and prevalence of "any" neurologic, central nervous system (CNS), or peripheral nervous system (PNS) symptoms. Ambient PM_2.5 was consistently associated with prevalence of neurologic symptoms. The highest quartile of 30-day PM_2.5 was associated with any neurologic symptom (prevalence ratio [PR] = 1.16; 95% confidence interval [CI] = 1.09, 1.23) and there were increasing monotonic relationships between 30-day PM_2.5 and each symptom category (P-trend ≤ 0.01). Associations with PM_2.5 were slightly stronger among nonsmokers and during colder seasons. The highest quartile of 7-day ozone was associated with increased prevalence of PNS symptoms (PR = 1.09; 95% CI = 1.00, 1.19; P-trend = 0.03), but not with other outcomes. Ozone concentrations above regulatory levels were suggestively associated with neurologic symptoms (PR = 1.06; 95% CI = 0.99, 1.14). Mutual adjustment in co-pollutant models suggests that PM_2.5 is more relevant than ozone in relation to prevalence of neurologic symptoms.

Lifestyle Factors and Parkinson's Disease Risk in a Rural New England Case-Control Study

Introduction

Parkinson's disease (PD) is an age-related neurodegenerative disease likely caused by complex interactions between genetic and environmental risk factors. Exposure to pesticides, toxic metals, solvents, and history of traumatic brain injury have been implicated as environmental risk factors for PD, underscoring the importance of identifying risk factors associated with PD across different communities.

Methods

We conducted a questionnaire-based case-control study in a rural area on the New Hampshire/Vermont border, enrolling PD patients and age- and sex-matched controls from the general population between 2017 and 2020. We assessed frequent participation in a variety of recreational and occupational activities and surveyed potential chemical exposures.

Results

Suffering from “head trauma or a concussion” prior to diagnosis was associated with a fourfold increased risk of PD. Adjustment for head trauma negated any risk of participation in “strenuous athletic activities.” We observed a 2.7-fold increased risk of PD associated with activities involving lead (adjusted p=0.038).

Conclusion

Implicating these factors in PD risk favors public health efforts in exposure mitigation while also motivating future work mechanisms and intervention opportunities.

LINC00943 knockdown exerts neuroprotective effects in Parkinson's disease through regulates CXCL12 expression by sponging miR-7-5p

BACKGROUND

Parkinson's disease (PD) is a common neurodegenerative movement disorder, but the pathogenesis is still unclear. Long non-coding RNAs (lncRNAs) have been reported to play a prominent role in PD.

OBJECTIVE

This study is designed to explore the role and mechanism of long intergenic non-coding RNA 00943 (LINC00943) in the N-methyl-4-phenylpyridine (MPP⁺)-inducted PD model.

METHODS

LINC00943, microRNA-7-5p (miR-7-5p), and the chemokine (C-X-C motif) ligand 12 (CXCL12, also referred to as SDF-1) level were examined by real-time quantitative polymerase chain reaction (RT-qPCR). Cell viability and apoptosis were analyzed by 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT), and flow cytometry assays, severally. Protein levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and CXCL12 were assessed by western blot assay. The ROS generation and SOD activity were detected by the corresponding kits. The binding relationship between miR-7-5p and LINC00943 or CXCL12 was predicted by Starbase and then verified by a dual-luciferase reporter and RNA Immunoprecipitation (RIP) assays.

RESULTS

LINC00943 and CXCL12 were increased, and miR-7-5p was decreased in MPP⁺-inducted SK-N-SH cells. LINC00943 silencing promoted cell viability, and repressed apoptosis and the inflammatory response in MPP⁺-treated SK-N-SH cells. The mechanical analysis discovered that LINC00943 acted as a sponge of miR-7-5p to regulate CXCL12 expression.

CONCLUSIONS

LINC00943 knockdown could attenuate MPP⁺-triggered neuron injury by regulating the miR-7-5p/CXCL12 axis, hinting at a promising therapeutic target for PD treatment.

Inflammatory Mechanisms in Parkinson's Disease: From Pathogenesis to Targeted Therapies

Inflammation is a critical factor contributing to the progressive neurodegenerative process observed in Parkinson's disease (PD). Microglia, the immune cells of the central nervous system, are activated early in PD pathogenesis and can both trigger and propagate early disease processes via innate and adaptive immune mechanisms such as upregulated immune cells and antibody-mediated inflammation. Downstream cytokines and gene regulators such as microRNA (miRNA) coordinate later disease course and mediate disease progression. Biomarkers signifying the inflammatory and neurodegenerative processes at play within the central nervous system are of increasing interest to clinical teams. To be effective, such biomarkers must achieve the highest sensitivity and specificity for predicting PD risk, confirming diagnosis, or monitoring disease severity. The aim of this review was to summarize the current preclinical and clinical evidence that suggests that inflammatory processes contribute to the initiation and progression of neurodegenerative processes in PD. In this article, we further summarize the data about main inflammatory biomarkers described in PD to date and their potential for regulation as a novel target for disease-modifying pharmacological strategies.

A mechanistic view on the neurotoxic effects of air pollution on central nervous system: risk for autism and neurodegenerative diseases

Many reports have shown a strong association between exposure to neurotoxic air pollutants like heavy metal and particulate matter (PM) as an active participant and neurological disorders. While the effects of these toxic pollutants on cardiopulmonary morbidity have principally been studied, growing evidence has shown that exposure to polluted air is associated with memory impairment, communication deficits, and anxiety/depression among all ages. So, these toxic pollutants in the environment increase the risk of neurodegenerative disease, ischemia, and autism spectrum disorders (ASD). The precise mechanisms in which air pollutants lead to communicative inability, social inability, and declined cognition have remained unknown. Various animal model studies show that amyloid precursor protein (APP), processing, oxidant/antioxidant balance, and inflammation pathways change following the exposure to constituents of polluted air. In the present review study, we collect the probable molecular mechanisms of deleterious CNS effects in response to various air pollutants.

Plasma-borne indicators of inflammasome activity in Parkinson's disease patients

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by motor and non-motor symptoms and loss of dopaminergic neurons of the substantia nigra. Inflammation and cell death are recognized aspects of PD suggesting that strategies to monitor and modify these processes may improve the management of the disease. Inflammasomes are pro-inflammatory intracellular pattern recognition complexes that couple these processes. The NLRP3 inflammasome responds to sterile triggers to initiate pro-inflammatory processes characterized by maturation of inflammatory cytokines, cytoplasmic membrane pore formation, vesicular shedding, and if unresolved, pyroptotic cell death. Histologic analysis of tissues from PD patients and individuals with nigral cell loss but no diagnosis of PD identified elevated expression of inflammasome-related proteins and activation-related “speck” formation in degenerating mesencephalic tissues compared with controls. Based on previous reports of circulating inflammasome proteins in patients suffering from heritable syndromes caused by hyper-activation of the NLRP3 inflammasome, we evaluated PD patient plasma for evidence of inflammasome activity. Multiple circulating inflammasome proteins were detected almost exclusively in extracellular vesicles indicative of ongoing inflammasome activation and pyroptosis. Analysis of plasma obtained from a multi-center cohort identified elevated plasma-borne NLRP3 associated with PD status. Our findings are consistent with others indicating inflammasome activity in neurodegenerative disorders. Findings suggest mesencephalic inflammasome protein expression as a histopathologic marker of early-stage nigral degeneration and suggest plasma-borne inflammasome-related proteins as a potentially useful class of biomarkers for patient stratification and the detection and monitoring of inflammation in PD.

Andrographolide suppresses NLRP3 inflammasome activation in microglia through induction of parkin-mediated mitophagy in in-vitro and in-vivo models of Parkinson disease

Cellular communication linking microglia activation and dopaminergic neuronal loss play an imperative role in the progression of Parkinson's disease (PD); however, underlying molecular mechanisms are not precise and require further elucidation. NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome activation is extensively studied in context to microglial activation and progressive dopaminergic neuronal loss in PD. Several pathophysiological factors such as oxidative stress, mitochondrial dysfunction impaired mitophagy plays a crucial role in activating NLRP3 inflammasome complex. Hence, regulation of microglial activation through mitophagy could be a valuable strategy in controlling microglia mediated neurodegeneration. In this study we have developed a model of inflammasome activation by combining LPS with a mitochondrial complex-I inhibitor MPP⁺. The idea of using MPP⁺ after priming mouse microglia with LPS was to disrupt mitochondria and release reactive oxygen species, which act as Signal 2 in augmenting NLRP3 assembly, thereby releasing potent inflammatory mediators such as active interleukin-1 beta (IL-1β) and IL-18. LPS-MPP⁺ combination was seen to impaired the mitophagy by inhibiting the initial step of autophagosome formation as evidenced by protein expression and confocal imaging data. Treatment with Andrographolide promoted the parkin-dependent autophagic flux formation in microglia; resulting in the removal of defective mitochondria which in turn inhibit NLRP3 inflammasome activation. Additionally, the neuroprotective role of Andrographolide in inhibiting NLRP3 activation together with salvage ATP level via promoting parkin-dependent mitophagy was seen in the substantial nigra par compacta (SNpc) region of mice brain. Furthermore, Andrographolide rescued the dopaminergic neuron loss and improved the behavioural parameters in animal model. Collectively, our results reveal the role of mitophagy in the regulation of NLRP3 inflammasome by removing defective mitochondria. In addition, andrographolide was seen to abate NLRP3 inflammasome activation in microglia and rescue dopaminergic neuron loss.

Deficiency of NEAT1 prevented MPP+-induced inflammatory response, oxidative stress and apoptosis in dopaminergic SK-N-SH neuroblastoma cells via miR-1277-5p/ARHGAP26 axis

Noncoding RNAs including long noncoding RNAs (lncRNAs) and microRNAs (miRNAs) have been documented to play prominent role in neurodegenerative diseases including Parkinson's disease (PD). This study intended to investigate the role of lncRNA nuclear enriched assembly transcript 1 (NEAT1) in MPP⁺-induced PD model in dopaminergic neuronblastoma SK-N-SH cells, as well as its mechanism through sponging miRNA (miR)-1277-5p. Real-time PCR and western blotting revealed that NEAT1 and ARHGAP26 were upregulated, and miR-1277-5p was downregulated in MPP⁺-treated SK-N-SH cells in a certain of concentration- and time- dependent manner. MPP⁺ induced apoptosis in SK-N-SH cells, as evidenced by decreased cell viability and Bcl-2 expression, and elevated apoptosis rate and levels of Bax and cleaved caspase-3, which were examined by MTT assay, flow cytometry and western blotting. Moreover, commercial assay kits indicated that inflammatory response and oxidative stress were provoked in response to MPP⁺, due to promoted contents of interleukin (IL)-6, IL-1β, tumor necrosis factor-α, malondialdehyde, and lactate dehydrogenase, accompanied with suppressed superoxide dismutase and glutathione peroxidase levels. Notably, MPP⁺-induced apoptosis, inflammatory response and oxidative stress in SK-N-SH cells were mitigated by NEAT1 knockdown and/or miR-1277-5p overexpression. Moreover, silencing of miR-1277-5p could abrogate the suppression of NEAT1 deficiency on MPP⁺-induced cell injury. Similarly, upregulating miR-1277-5p-elicited neuroprotection in MPP⁺-induced SK-N-SH cells was reversed by ARHGAP26 restoration. Dual-luciferase reporter assay demonstrated a direct interaction between miR-1277-5p and NEAT1 or ARHGAP26. Collectively, NEAT1 upregulation might contribute to MPP⁺-induced neuron injury via NEAT1-miR-1277-5p-ARHGAP26 competing endogenous RNAs (ceRNAs) pathway.

"Repair Me if You Can": Membrane Damage, Response, and Control from the Viral Perspective

Cells are constantly challenged by pathogens (bacteria, virus, and fungi), and protein aggregates or chemicals, which can provoke membrane damage at the plasma membrane or within the endo-lysosomal compartments. Detection of endo-lysosomal rupture depends on a family of sugar-binding lectins, known as galectins, which sense the abnormal exposure of glycans to the cytoplasm upon membrane damage. Galectins in conjunction with other factors orchestrate specific membrane damage responses such as the recruitment of the endosomal sorting complex required for transport (ESCRT) machinery to either repair damaged membranes or the activation of autophagy to remove membrane remnants. If not controlled, membrane damage causes the release of harmful components including protons, reactive oxygen species, or cathepsins that will elicit inflammation. In this review, we provide an overview of current knowledge on membrane damage and cellular responses. In particular, we focus on the endo-lysosomal damage triggered by non-enveloped viruses (such as adenovirus) and discuss viral strategies to control the cellular membrane damage response. Finally, we debate the link between autophagy and inflammation in this context and discuss the possibility that virus induced autophagy upon entry limits inflammation.

Slc6a3-dependent expression of a CAPS-associated Nlrp3 allele results in progressive behavioral abnormalities and neuroinflammation in aging mice

BACKGROUND

An association between neuroinflammation and age-related neurologic disorders has been established but the molecular mechanisms and cell types involved have not been thoroughly characterized. Activity of the proinflammatory NLRP3 inflammasome is implicated in Alzheimer's and Parkinson's disease and our recent studies in patients suggest that dopaminergic neurons within the degenerating mesencephalon express NLRP3 throughout the progression of PD. Here, we directly test the impact of enhanced inflammasome activity in mesencephalic neurons by characterizing motor function, tissue integrity, and neuroinflammation in aging mice harboring hyperactivating mutations within the endogenous murine Nlrp3 locus, enabled only in cells expressing the dopaminergic neuron-specific Slc6a3 promoter.

METHODS

We compared mice harboring inducible alleles encoding the cryopyrin-associated periodic syndrome activating mutations Nlrp3A350V and Nlrp3L351P inserted into the endogenous mouse Nlrp3 locus. Tissue specific expression was driven by breeding these animals with mice expressing Cre recombinase under the control of the dopaminergic neuron-specific Slc6a3 promoter. The experimental mice, designed to express hyperactive NLRP3 only when the endogenous mouse Nlrp3 promotor is active in dopaminergic neurons, were analyzed throughout 18 months of aging using longitudinal motor function assessments. Biochemical and histologic analyses of mesencephalic tissues were conducted in 1- and 18-month-old animals.

RESULTS

We observed progressive and significant deficits in motor function in animals expressing Nlrp3L351P, compared with animals expressing Nlrp3WT and Nlrp3A350V. Age-dependent neuroinflammatory changes in the mesencephalon were noted in all animals. Analysis of GFAP-immunoreactive astrocytes in the substantia nigra revealed a significant increase in astrocyte number in animals expressing Nlrp3L351P compared with Nlrp3WT and Nlrp3A350V. Further analysis of Nlrp3L351P striatal tissues indicated genotype specific gliosis, elevated Il1b expression, and both morphologic and gene expression indicators of proinflammatory A1 astrocytes.

CONCLUSIONS

Dopaminergic neurons have the potential to accumulate NLRP3 inflammasome activators with age, including reactive oxygen species, dopamine metabolites, and misfolded proteins. Results indicate the Nlrp3 locus is active in dopaminergic neurons in aging mice, and that the hyperactive Nlrp3L351P allele can drive neuroinflammatory changes in association with progressive behavioral deficits. Findings suggest neuronal NLRP3 inflammasome activity may contribute to neuroinflammation observed during normal aging and the progression of neurologic disorders.

Status and future directions of clinical trials in Parkinson's disease

Novel therapies are needed to treat Parkinson's disease (PD) in which the clinical unmet need is pressing. Currently, no clinically available therapeutic strategy can either retard or reverse PD or repair its pathological consequences. l-DOPA (levodopa) is still the gold standard therapy for motor symptoms yet symptomatic therapies for both motor and non-motor symptoms are improving. Many on-going, intervention trials cover a broad range of targets, including cell replacement and gene therapy approaches, quality of life improving technologies, and disease-modifying strategies (e.g., controlling aberrant α-synuclein accumulation and regulating cellular/neuronal bioenergetics). Notably, the repurposing of glucagon-like peptide-1 analogues with potential disease-modifying effects based on metabolic pathology associated with PD has been promising. Nevertheless, there is a clear need for improved therapeutic and diagnostic options, disease progression tracking and patient stratification capabilities to deliver personalized treatment and optimize trial design. This review discusses some of the risk factors and consequent pathology associated with PD and particularly the metabolic aspects of PD, novel therapies targeting these pathologies (e.g., mitochondrial and lysosomal dysfunction, oxidative stress, and inflammation/neuroinflammation), including the repurposing of metabolic therapies, and unmet needs as potential drivers for future clinical trials and research in PD.

The gut microbiota attenuate neuroinflammation in manganese exposure by inhibiting cerebral NLRP3 inflammasome

Manganese (Mn) exposure has been reported to cause neurodegenerative disorders. β-Amyloid (Aβ) induced Tau pathology in an NLRP3-dependent manner is at the heart of Alzheimer's and Parkinson's diseases. The gut microbiota plays a crucial role in the bidirectional gut-brain axis that integrates the gut and central nervous system (CNS) activities. In this study, we found that Mn exposure increases Aβ_1-40 and Tau production in brain, and causes hippocampal degeneration and necrosis. Meanwhile, Mn exposure can stimulate neurotoxicity by increasing inflammation either in peripheral blood and CNS. Importantly, we found that transplantation of gut microbiota from normal rats into Mn exposure rats reduced Aβ and Tau expression, and the cerebral expression of NLRP3 was downregulated, and the expression of neuroinflammatory factors was also downregulated. Therefore, improving the composition of gut microbiota in Mn exposure rats can attenuate neuroinflammation, which is considered as a novel therapeutic strategy for Mn exposure by remodelling the gut microbiota.

Effects of air pollution on the nervous system and its possible role in neurodevelopmental and neurodegenerative disorders

Recent extensive evidence indicates that air pollution, in addition to causing respiratory and cardiovascular diseases, may also negatively affect the brain and contribute to central nervous system diseases. Air pollution is comprised of ambient particulate matter (PM) of different sizes, gases, organic compounds, and metals. An important contributor to PM is represented by traffic-related air pollution, mostly ascribed to diesel exhaust (DE). Epidemiological and animal studies have shown that exposure to air pollution may be associated with multiple adverse effects on the central nervous system. In addition to a variety of behavioral abnormalities, the most prominent effects caused by air pollution are oxidative stress and neuro-inflammation, which are seen in both humans and animals, and are supported by in vitro studies. Among factors which can affect neurotoxic outcomes, age is considered most relevant. Human and animal studies suggest that air pollution may cause developmental neurotoxicity, and may contribute to the etiology of neurodevelopmental disorders, including autism spectrum disorder. In addition, air pollution exposure has been associated with increased expression of markers of neurodegenerative disease pathologies, such as alpha-synuclein or beta-amyloid, and may thus contribute to the etiopathogenesis of neurodegenerative diseases, particularly Alzheimer's disease and Parkinson's disease.

The gut microbiota confers protection in the CNS against neurodegeneration induced by manganism

Among all types of pollution, heavy metals are considered the greatest threat to human health, and heavy metals are associated with an increased risk of cardiovascular disease, coronary heart disease and neurodegenerative disorders. Manganese (Mn) exposure is well reported to exert neurotoxicity and various neurodegenerative disorders, but the mechanisms are not clear. The gut microbiota plays a crucial role in the bidirectional gut-brain axis that integrates the gut and central nervous system (CNS) activities. The changes in chemical signaling, metabolism and gut microbiota associated with Mn exposure have provided deeper insight into the neurotoxic mechanism of Mn. We observed that Mn exposure increases host manganic bioaccumulation, and β-amyloid (Aβ), receptor-interacting protein kinase 3 (RIP3) and caspase-3 production in the brain, and causes hippocampal degeneration and necrosis. Mn exposure led to decreased gut bacterial richness, especially for Prevotellaceae, Fusobacteriaceae and Lactobacillaceae. In addition, Mn exposure altered the metabolism of tryptamine, taurodeoxycholic acid, β-hydroxypyruvic acid and urocanic acid. Meanwhile, we found correlations between the abundance of certain bacterial species and the level of tryptamine, taurodeoxycholic acid, β-hydroxypyruvic acid and urocanic acid. Fecal microbiome transplantation from normal rats could alleviate the neurotoxicity of Mn exposure by shaping the gut microbiota. Our findings highlight the role of gut dysbiosis-promoted neurotoxicity in Mn exposure and suggest a novel therapeutic strategy of remodeling the gut microbiota.

The gut microbiome in Parkinson's disease: A culprit or a bystander?

In recent years, large-scale metagenomics projects such as the Human Microbiome Project placed the gut microbiota under the spotlight of research on its role in health and in the pathogenesis several diseases, as it can be a target for novel therapeutical approaches. The emerging concept of a microbiota modulation of the gut-brain axis in the pathogenesis of neurodegenerative disorders has been explored in several studies in animal models, as well as in human subjects. Particularly, research on changes in the composition of gut microbiota as a potential trigger for alpha-synuclein (α-syn) pathology in Parkinson's disease (PD) has gained increasing interest. In the present review, we first provide the basis to the understanding of the role of gut microbiota in healthy subjects and the molecular basis of the gut-brain interaction, focusing on metabolic and neuroinflammatory factors that could trigger the alpha-synuclein conformational changes and aggregation. Then, we critically explored preclinical and clinical studies reporting on the changes in gut microbiota in PD, as compared to healthy subjects. Furthermore, we examined the relationship between the gut microbiota and PD clinical features, discussing data consistently reported across studies, as well as the potential sources of inconsistencies. As a further step toward understanding the effects of gut microbiota on PD, we discussed the relationship between dysbiosis and response to dopamine replacement therapy, focusing on Levodopa metabolism. We conclude that further studies are needed to determine whether the gut microbiota changes observed so far in PD patients is the cause or, instead, it is merely a consequence of lifestyle changes associated with the disease. Regardless, studies so far strongly suggest that changes in microbiota appears to be impactful in pathogenesis of neuroinflammation. Thus, dysbiotic microbiota in PD could influence the disease course and response to medication, especially Levodopa. Future research will assess the impact of microbiota-directed therapeutic intervention in PD patients.

Diet in Parkinson's Disease: Critical Role for the Microbiome

Background: Parkinson's disease (PD) is the most common movement disorder affecting up to 1% of the population above the age of 60 and 4–5% of those above the age of 85. Little progress has been made on efforts to prevent disease development or halt disease progression. Diet has emerged as a potential factor that may prevent the development or slow the progression of PD. In this review, we discuss evidence for a role for the intestinal microbiome in PD and how diet-associated changes in the microbiome may be a viable approach to prevent or modify disease progression.

Methods: We reviewed studies demonstrating that dietary components/foods were related to risk for PD. We reviewed evidence for the dysregulated intestinal microbiome in PD patients including abnormal shifts in the intestinal microbiota composition (i.e., dysbiosis) characterized by a loss of short chain fatty acid (SCFA) bacteria and increased lipopolysaccharide (LPS) bacteria. We also examined several candidate mechanisms by which the microbiota can influence PD including the NLRP3 inflammasome, insulin resistance, mitochondrial function, vagal nerve signaling.

Results: The PD-associated microbiome is associated with decreased production of SCFA and increased LPS and it is believed that these changes may contribute to the development or exacerbation of PD. Diet robustly impacts the intestinal microbiome and the Western diet is associated with increased risk for PD whereas the Mediterranean diet (including high intake of dietary fiber) decreases PD risk. Mechanistically this may be the consequence of changes in the relative abundance of SCFA-producing or LPS-containing bacteria in the intestinal microbiome with effects on intestinal barrier function, endotoxemia (i.e., systemic LPS), NLRP3 inflammasome activation, insulin resistance, and mitochondrial dysfunction, and the production of factors such as glucagon like peptide 1 (GLP-1) and brain derived neurotrophic factor (BDNF) as well as intestinal gluconeogenesis.

Conclusions: This review summarizes a model of microbiota-gut-brain-axis regulation of neuroinflammation in PD including several new mechanisms. We conclude with the need for clinical trials in PD patients to test this model for beneficial effects of Mediterranean based high fiber diets.

Health effects associated with occupational exposure to hand-arm or whole body vibration

Workers in a number of different occupational sectors are exposed to workplace vibration on a daily basis. This exposure may arise through the use of powered-hand tools or hand-transmitted vibration (HTV). Workers might also be exposed to whole body vibration (WBV) by driving delivery vehicles, earth moving equipment, or through use of tools that generate vibration at low dominant frequencies and high amplitudes, such as jackhammers. Occupational exposure to vibration has been associated with an increased risk of musculoskeletal pain in the back, neck, hands, shoulders, and hips. Occupational exposure may also contribute to the development of peripheral and cardiovascular disorders and gastrointestinal problems. In addition, there are more recent data suggesting that occupational exposure to vibration may enhance the risk of developing certain cancers. The aim of this review is to provide an assessment of the occupations where exposure to vibration is most prevalent, and a description of the adverse health effects associated with occupational exposure to vibration. This review will examine (1) various experimental methods used to measure and describe the characteristics of vibration generated by various tools and vehicles, (2) the etiology of vibration-induced disorders, and (3) how these data were employed to assess and improve intervention strategies and equipment that reduces the transmission of vibration to the body. Finally, there is a discussion of the research gaps that need to be investigated to further reduction in the incidence of vibration-induced illnesses and injuries.