Mechanisms of Gene-Environment Interactions in Parkinson's Disease

Establishment of human cerebral organoid systems to model early neural development and assess the central neurotoxicity of environmental toxins

JOURNAL/nrgr/04.03/01300535-202501000-00032/figure1/v/2024-05-14T021156Z/r/image-tiff Human brain development is a complex process, and animal models often have significant limitations. To address this, researchers have developed pluripotent stem cell-derived three-dimensional structures, known as brain-like organoids, to more accurately model early human brain development and disease. To enable more consistent and intuitive reproduction of early brain development, in this study, we incorporated forebrain organoid culture technology into the traditional unguided method of brain organoid culture. This involved embedding organoids in matrigel for only 7 days during the rapid expansion phase of the neural epithelium and then removing them from the matrigel for further cultivation, resulting in a new type of human brain organoid system. This cerebral organoid system replicated the temporospatial characteristics of early human brain development, including neuroepithelium derivation, neural progenitor cell production and maintenance, neuron differentiation and migration, and cortical layer patterning and formation, providing more consistent and reproducible organoids for developmental modeling and toxicology testing. As a proof of concept, we applied the heavy metal cadmium to this newly improved organoid system to test whether it could be used to evaluate the neurotoxicity of environmental toxins. Brain organoids exposed to cadmium for 7 or 14 days manifested severe damage and abnormalities in their neurodevelopmental patterns, including bursts of cortical cell death and premature differentiation. Cadmium exposure caused progressive depletion of neural progenitor cells and loss of organoid integrity, accompanied by compensatory cell proliferation at ectopic locations. The convenience, flexibility, and controllability of this newly developed organoid platform make it a powerful and affordable alternative to animal models for use in neurodevelopmental, neurological, and neurotoxicological studies.

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 an 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 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 wk 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, 12, and 36 wk 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 differential modification of cytosines 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.

Understanding role of pesticides in development of Parkinson's disease: Insights from Drosophila and rodent models

Parkinson's disease is a neurodegenerative illness linked to ageing, marked by the gradual decline of dopaminergic neurons in the midbrain. The exact aetiology of Parkinson's disease (PD) remains uncertain, with genetic predisposition and environmental variables playing significant roles in the disease's frequency. Epidemiological data indicates a possible connection between pesticide exposure and brain degeneration. Specific pesticides have been associated with important characteristics of Parkinson's disease, such as mitochondrial dysfunction, oxidative stress, and α-synuclein aggregation, which are crucial for the advancement of the disease. Recently, many animal models have been developed for Parkinson's disease study. Although these models do not perfectly replicate the disease's pathology, they provide valuable insights that improve our understanding of the condition and the limitations of current treatment methods. Drosophila, in particular, has been useful in studying Parkinson's disease induced by toxins or genetic factors. The review thoroughly analyses many animal models utilised in Parkinson's research, with an emphasis on issues including pesticides, genetic and epigenetic changes, proteasome failure, oxidative damage, α-synuclein inoculation, and mitochondrial dysfunction. The text highlights the important impact of pesticides on the onset of Parkinson's disease (PD) and stresses the need for more research on genetic and mechanistic alterations linked to the condition.

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.

Understanding and applying gene-environment interactions: a guide for nutrition professionals with an emphasis on integration in African research settings

Noncommunicable diseases (NCDs) are influenced by the interplay between genetics and environmental exposures, particularly diet. However, many healthcare professionals, including nutritionists and dietitians, have limited genetic background and, therefore, they may lack understanding of gene-environment interactions (GxEs) studies. Even researchers deeply involved in nutrition studies, but with a focus elsewhere, can struggle to interpret, evaluate, and conduct GxE studies. There is an urgent need to study African populations that bear a heavy burden of NCDs, demonstrate unique genetic variability, and have cultural practices resulting in distinctive environmental exposures compared with Europeans or Americans, who are studied more. Although diverse and rapidly changing environments, as well as the high genetic variability of Africans and difference in linkage disequilibrium (ie, certain gene variants are inherited together more often than expected by chance), provide unparalleled potential to investigate the omics fields, only a small percentage of studies come from Africa. Furthermore, research evidence lags behind the practices of companies offering genetic testing for personalized medicine and nutrition. We need to generate more evidence on GxEs that also considers continental African populations to be able to prevent unethical practices and enable tailored treatments. This review aims to introduce nutrition professionals to genetics terms and valid methods to investigate GxEs and their challenges, and proposes ways to improve quality and reproducibility. The review also provides insight into the potential contributions of nutrigenetics and nutrigenomics to the healthcare sphere, addresses direct-to-consumer genetic testing, and concludes by offering insights into the field's future, including advanced technologies like artificial intelligence and machine learning.

Diabetes and Parkinson's Disease: Understanding Shared Molecular Mechanisms

Aging is a major risk factor for Parkinson's disease (PD). Genetic mutations account for a small percentage of cases and the majority appears to be sporadic, with yet unclear causes. However, various environmental factors have been linked to an increased risk of developing PD and, therefore, understanding the complex interplay between genetic and environmental factors is crucial for developing effective disease-modifying therapies. Several studies identified a connection between type 2 diabetes (T2DM) and PD. T2DM is characterized by insulin resistance and failure of β-cells to compensate, leading to hyperglycemia and serious comorbidities. Both PD and T2DM share misregulated processes, including mitochondrial dysfunction, oxidative stress, chronic inflammation, altered proteostasis, protein aggregation, and misregulation of glucose metabolism. Chronic or recurring hyperglycemia is a T2DM hallmark and can lead to increased methylglyoxal (MGO) production, which is responsible for protein glycation. Glycation of alpha-synuclein (aSyn), a central player in PD pathogenesis, accelerates the deleterious aSyn effects. Interestingly, MGO blood plasma levels and aSyn glycation are significantly elevated in T2DM patients, suggesting a molecular mechanism underlying the T2DM - PD link. Compared to high constant glucose levels, glycemic variability (fluctuations in blood glucose levels), can be more detrimental for diabetic patients, causing oxidative stress, inflammation, and endothelial damage. Accordingly, it is imperative for future research to prioritize the exploration of glucose variability's influence on PD development and progression. This involves moving beyond the binary classification of patients as diabetic or non-diabetic, aiming to pave the way for the development of enhanced therapeutic interventions.

Towards improved screening of toxins for Parkinson's risk

Parkinson's disease (PD) is a chronic, progressive and disabling neurodegenerative disorder. The prevalence of PD has risen considerably over the past decades. A growing body of evidence suggest that exposure to environmental toxins, including pesticides, solvents and heavy metals (collectively called toxins), is at least in part responsible for this rapid growth. It is worrying that the current screening procedures being applied internationally to test for possible neurotoxicity of specific compounds offer inadequate insights into the risk of developing PD in humans. Improved screening procedures are therefore urgently needed. Our review first substantiates current evidence on the relation between exposure to environmental toxins and the risk of developing PD. We subsequently propose to replace the current standard toxin screening by a well-controlled multi-tier toxin screening involving the following steps: in silico studies (tier 1) followed by in vitro tests (tier 2), aiming to prioritize agents with human relevant routes of exposure. More in depth studies can be undertaken in tier 3, with whole-organism (in)vertebrate models. Tier 4 has a dedicated focus on cell loss in the substantia nigra and on the presumed mechanisms of neurotoxicity in rodent models, which are required to confirm or refute the possible neurotoxicity of any individual compound. This improved screening procedure should not only evaluate new pesticides that seek access to the market, but also critically assess all pesticides that are being used today, acknowledging that none of these has ever been proven to be safe from a perspective of PD. Importantly, the improved screening procedures should not just assess the neurotoxic risk of isolated compounds, but should also specifically look at the cumulative risk conveyed by exposure to commonly used combinations of pesticides (cocktails). The worldwide implementation of such an improved screening procedure, would be an essential step for policy makers and governments to recognize PD-related environmental risk factors.

Developmental exposure to the Parkinson's disease-associated organochlorine pesticide dieldrin alters dopamine neurotransmission in α-synuclein pre-formed fibril (PFF)-injected mice

Parkinson's disease (PD) is the fastest-growing neurological disease worldwide, with increases outpacing aging and occurring most rapidly in recently industrialized areas, suggesting a role of environmental factors. Epidemiological, post-mortem, and mechanistic studies suggest that persistent organic pollutants, including the organochlorine pesticide dieldrin, increase PD risk. In mice, developmental dieldrin exposure causes male-specific exacerbation of neuronal susceptibility to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and synucleinopathy. Specifically, in the α-synuclein (α-syn) pre-formed fibril (PFF) model, exposure leads to increased deficits in striatal dopamine (DA) turnover and motor deficits on the challenging beam. Here, we hypothesized that alterations in DA handling contribute to the observed changes and assessed vesicular monoamine transporter 2 (VMAT2) function and DA release in this dieldrin/PFF 2-hit model. Female C57BL/6 mice were exposed to 0.3 mg/kg dieldrin or vehicle every 3 days by feeding, starting at 8 weeks of age and continuing throughout breeding, gestation, and lactation. Male offspring from independent litters underwent unilateral, intrastriatal injections of α-syn PFFs at 12 weeks of age, and vesicular 3H-DA uptake assays and fast-scan cyclic voltammetry were performed 4 months post-PFF injection. Dieldrin-induced an increase in DA release in striatal slices in PFF-injected animals, but no change in VMAT2 activity. These results suggest that developmental dieldrin exposure increases a compensatory response to synucleinopathy-triggered striatal DA loss. These findings are consistent with silent neurotoxicity, where developmental exposure to dieldrin primes the nigrostriatal striatal system to have an exacerbated response to synucleinopathy in the absence of observable changes in typical markers of nigrostriatal dysfunction and degeneration.

Ferritin Is Secreted from Primary Cultured Astrocyte in Response to Iron Treatment via TRPML1-Mediated Exocytosis

Impaired iron homeostasis has been proven to be one of the critical contributors to the pathology of Parkinson's disease (PD). Ferritin is considered an intracellular protein responsible for storing cytosolic iron. Recent studies have found that ferritin can be secreted from cells independent of the classical endoplasmic reticulum-Golgi system. However, the precise mechanisms underlying the secretion of ferritin in the brain were not elucidated. In the present study, we demonstrated that the primary cultured astrocytes do have the ability to secrete ferritin, which is enhanced by iron treatment. Increased ferritin secretion was accompanied by increased protein expression of ferritin response to iron stimulation. Further study showed that iron-induced expression and secretion of ferritin could be inhibited by CQ or 3-MA pretreatment. In addition, the knockdown of transient receptor potential mucolipin 1 (TRPML1) antagonized iron-induced ferritin secretion, accompanied by further increased intracellular protein levels of ferritin. Further study demonstrated that ferritin colocalized with LAMP1 in iron-treated astrocytes. On the contrary, ras-associated protein 27a (Rab27a) knockdown further enhanced iron-induced ferritin secretion and decreased intracellular protein levels of ferritin. Furthermore, we also showed that the secretory autophagy protein tripartite motif containing 16 (TRIM16) and sec22b decreased in iron-treated astrocytes. These results suggested that astrocytes might secrete ferritin via TRPML1-mediated exocytosis. This provides new evidence for the mechanisms underlying the secretion of ferritin in primary cultured astrocytes under a high iron environment.

Acetylcholinesterase biosensors for electrochemical detection of neurotoxic pesticides and acetylcholine neurotransmitter: A literature review

Neurotoxic pesticides are a group of chemicals that pose a severe threat to both human health and the environment. These molecules are also known to accumulate in the food chain and persist in the environment, which can lead to long-term exposure and adverse effects on non-target organisms. The detrimental effects of these pesticides on neurotransmitter levels and function can lead to a range of neurological and behavioral symptoms, which are closely associated with neurodegenerative diseases. Hence, the accurate and reliable detection of these neurotoxic pesticides and associated neurotransmitters is essential for clinical applications, such as diagnosis and treatment. Over the past few decades, acetylcholinesterase (AchE) biosensors have emerged as a sensitive and reliable tool for the electrochemical detection of neurotoxic pesticides and acetylcholine. These biosensors can be tailored to utilize the high specificity and sensitivity of AchE, enabling the detection of these chemicals. Additionally, enzyme immobilization and the incorporation of nanoparticles have further improved the detection capabilities of these biosensors. AchE biosensors have shown tremendous potential in various fields, including environmental monitoring, clinical diagnosis, and pesticide residue analysis. This review summarizes the advancements in AchE biosensors for electrochemical detection of neurotoxic pesticides and acetylcholine over the past two decades.

Neuroprotective Efficacy of a Nanomicellar Complex of Carnosine and Lipoic Acid in a Rat Model of Rotenone-Induced Parkinson's Disease

Oxidative stress, accompanied by mitochondrial dysfunction, is a key mechanism involved in the pathogenesis of Parkinson's disease (PD). Both carnosine and lipoic acid are potent antioxidants, the applicability of which in therapy is hindered by their limited bioavailability. This study aimed to evaluate the neuroprotective properties of a nanomicellar complex of carnosine and lipoic acid (CLA) in a rotenone-induced rat model of PD. Parkinsonism was induced via the administration of 2 mg/kg rotenone over the course of 18 days. Two doses of intraperitoneal CLA (25 mg/kg and 50 mg/kg) were administered alongside rotenone to assess its neuroprotective effect. At 25 mg/kg CLA decreased muscle rigidity and partially restored locomotor activity in animals that received rotenone. Furthermore, it caused an overall increase in brain tissue antioxidant activity, accompanied by a 19% increase in neuron density in the substantia nigra and increased dopamine levels in the striatum relative to animals that only received rotenone. Based on the acquired results, it may be concluded that CLA have neuroprotective properties and could potentially be beneficial in PD treatment when used in conjunction with the base therapy.

Contribution of Solar Radiation and Pollution to Parkinson's Disease

Background. Parkinson's disease (PD) is believed to develop from epigenetic modulation of gene expression through environmental factors that accounts for up to 85% of all PD cases. The main objective of this study was to examine the association between PD onset and a cumulative exposure to potentially modifiable ambient exposures. Methods. The study population comprised 3343 incident PD cases and 31,324 non-PD controls in Southern Israel. The exposures were determined based on the monitoring stations and averaged per year. Their association with PD was modeled using a distributed lag non-linear model and presented as an effect of exposure to the 75th percentile as compared to the 50th percentile of each pollutant, accumulated over the span of 5 years prior to the PD. Results. We recorded an adverse effect of particulate matter of size ≤10 μm in diameter (PM₁₀) and solar radiation (SR) with odds ratio (OR) = 1.06 (95%CI: 1.02; 1.10) and 1.23 (95%CI: 1.08; 1.39), respectively. Ozone (O₃) was also adversely linked to PD, although with a borderline significance, OR: 1.12 (95%CI: 0.99; 1.25). Immigrants arriving in Israel after 1989 appeared to be more vulnerable to exposure to O₃ and SR. The dose response effect of SR, non-existent for Israeli-born (OR = 0.67, 95%CI: 0.40; 1.13), moderate for immigrants before 1989 (OR = 1.17, 95%CI: 0.98; 1.40) and relatively high for new immigrants (OR = 1.25, 95%CI: 1.25; 2.38) indicates an adaptation ability to SR. Conclusions. Our findings supported previous reports on adverse association of PD with exposure to PM₁₀ and O₃. Additionally, we revealed a link of Parkinson's Disease with SR that warrants an extensive analysis by research groups worldwide.

The Etiology of Parkinson's Disease: New Perspectives from Gene-Environment Interactions

Parkinson's disease is now the most rapidly growing neurodegenerative disease worldwide. It is therefore critical to identify which factors, and to what extent, contribute to the multifactorial etiology of Parkinson's disease. Here, we address two interesting elements from the perspective of genetics, namely (a) the estimated age of several genetic risk factors related to Parkinson's disease; and (b) the relative contribution of genetics to the etiology of Parkinson's disease, as derived from twin studies. Based on these two perspectives, we argue that most genetic risk factors are by themselves insufficient to explain the majority of Parkinson's disease, and that environmental factors are required for these genetic factors to become pathophysiologically relevant.

Advancing the Genetics of Lewy Body Disorders with Disease-Modifying Treatments in Mind

In this article, a caveat for advancing the genetics of Lewy body disorders is raised, given the nosological controversy about whether to consider dementia with Lewy bodies (DLB) and Parkinson's disease (PD) as one entity or two separate entities. Using the framework of the sufficient and component causes model of causation, as further developed into an evolution-based model of causation, it is proposed that a disease of complex etiology is defined as having a relatively high degree of sharing of the component causes (a genetic or environmental factor), that is, a low degree of heterogeneity of the sufficient causes. Based on this definition, only if the sharing of component causes within each of two diseases is similar to their combined sharing can lumping be warranted. However, it is not known whether the separate and combined sharing are similar before conducting the etiologic studies. This means that lumping DLB and PD can be counterproductive as it can decrease the ability to detect component causes despite the potential benefit of conducting studies with larger sample sizes. In turn, this is relevant to the development of disease-modifying treatments, because non-overlapping causal genetic factors may result in distinct pathogenetic pathways providing promising targets for interventions.

How Well Do Rodent Models of Parkinson's Disease Recapitulate Early Non-Motor Phenotypes? A Systematic Review

The prodromal phase of Parkinson's disease (PD) is characterised by many non-motor symptoms, and these have recently been posited to be predictive of later diagnosis. Genetic rodent models can develop non-motor phenotypes, providing tools to identify mechanisms underlying the early development of PD. However, it is not yet clear how reproducible non-motor phenotypes are amongst genetic PD rodent models, whether phenotypes are age-dependent, and the translatability of these phenotypes has yet to be explored. A systematic literature search was conducted on studies using genetic PD rodent models to investigate non-motor phenotypes; cognition, anxiety/depressive-like behaviour, gastrointestinal (GI) function, olfaction, circadian rhythm, cardiovascular and urinary function. In total, 51 genetic models of PD across 150 studies were identified. We found outcomes of most phenotypes were inconclusive due to inadequate studies, assessment at different ages, or variation in experimental and environmental factors. GI dysfunction was the most reproducible phenotype across all genetic rodent models. The mouse model harbouring mutant A53T, and the wild-type hα-syn overexpression (OE) model recapitulated the majority of phenotypes, albeit did not reliably produce concurrent motor deficits and nigral cell loss. Furthermore, animal models displayed different phenotypic profiles, reflecting the distinct genetic risk factors and heterogeneity of disease mechanisms. Currently, the inconsistent phenotypes within rodent models pose a challenge in the translatability and usefulness for further biomechanistic investigations. This review highlights opportunities to improve phenotype reproducibility with an emphasis on phenotypic assay choice and robust experimental design.

Neurodegenerative Diseases: Implications of Environmental and Climatic Influences on Neurotransmitters and Neuronal Hormones Activities

Neurodegenerative and neuronal-related diseases are major public health concerns. Human vulnerability to neurodegenerative diseases (NDDs) increases with age. Neuronal hormones and neurotransmitters are major determinant factors regulating brain structure and functions. The implications of environmental and climatic changes emerged recently as influence factors on numerous diseases. However, the complex interaction of neurotransmitters and neuronal hormones and their depletion under environmental and climatic influences on NDDs are not well established in the literature. In this review, we aim to explore the connection between the environmental and climatic factors to NDDs and to highlight the available and potential therapeutic interventions that could use to improve the quality of life and reduce susceptibility to NDDs.

Neurotoxicity of pesticides - A link to neurodegeneration

Parkinson's disease (PD) is a neurodegenerative disorder which mainly targets motor symptoms such as tremor, rigidity, bradykinesia and postural instability. The physiological changes occur due to dopamine depletion in basal ganglia region of the brain. PD aetiology is not yet elucidated clearly but genetic and environmental factors play a prominent role in disease occurrence. Despite of various environmental factors, pesticides exposure has been convicted as major candidate in PD pathogenesis. Among various pesticides 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been widely investigated in PD following with paraquat (PQ), maneb (MB), organochlorines (OC) and rotenone. Effect of these pesticides has been suggested to be involved in oxidative stress, alterations in dopamine transporters, mitochondrial dysfunction, α-synuclein (αSyn) fibrillation, and neuroinflammation in PD. The present review discusses the influence of pesticides in neurodegeneration and its related epidemiological studies conducted in PD. Furthermore, we have deliberated the common pesticides involved in PD and its associated genetic alterations and the probable mechanism of them behind PD pathogenesis. Hence, we conclude that pesticides play a prominent role in PD pathogenesis and advance research is needed to investigate the alterations in genetic and mechanistic aspects of PD.

A systematic review on the risk of neurodegenerative diseases and neurocognitive disorders in professional and varsity athletes

Objective

The aim of this systematic review (SR) was to gather all available epidemiological evidence on former participation in any type of sport, at a professional and varsity level, as a potential risk factor for neurodegenerative diseases (NDs) and neurocognitive disorders (NCDs).

Design

Systematic searches were performed on PubMed, the Cochrane databases, and the ISI Web of Knowledge databases. Included studies were assessed using the NOS checklist.

Eligibility criteria for selecting studies

All epidemiological studies reporting data on the possible association between a clinical diagnosis of amyotrophic lateral sclerosis (ALS)/motor neuron disease (MND), dementia or mild cognitive impairment (MCI), Parkinson’s disease (PD), chronic traumatic encephalopathy (CTE) at any stage and with any clinical pattern and the former participation in any types of sport at a varsity and professional level were included.

Results

Data from the 17 included studies showed a higher frequency of NDs and NCDs in former soccer and American football players. Updating the previous SR confirmed a higher frequency of ALS/MND in former soccer players. Data reported a significantly higher risk of dementia/AD in former soccer players, and of MCI in former American football players. Results also showed a significantly higher risk of PD in former soccer and American football players, and a significantly higher risk of CTE in former boxers and American football players.

Summary/conclusions

This SR confirmed a higher risk of NDs and NCDs in former professional/varsity athletes. However, the pathological mechanisms underlying this association remain unclear, and further high-quality studies should be performed to clarify whether the association could be sport specific.

Altered neural cell junctions and ion-channels leading to disrupted neuron communication in Parkinson's disease

Parkinson's disease (PD) is a neurological disorder that affects the movement of the human body. It is primarily characterized by reduced dopamine levels in the brain. The causative agent of PD is still unclear but it is generally accepted that α-synuclein has a central role to play. It is also known that gap-junctions and associated connexins are complicated structures that play critical roles in nervous system signaling and associated misfunctioning. Thus, our current article emphasizes how, alongside α-synuclein, ion-channels, gap-junctions, and related connexins, all play vital roles in influencing multiple metabolic activities of the brain during PD. It also highlights that ion-channel and gap-junction disruptions, which are primarily mediated by their structural-functional changes and alterations, have a role in PD. Furthermore, we discussed available drugs and advanced therapeutic interventions that target Parkinson's pathogenesis. In conclusion, it warrants creating better treatments for PD patients. Although, dopaminergic replenishment therapy is useful in treating neurological problems, such therapies are, however, unable to control the degeneration that underpins the disease, thereby declining their overall efficacy. This creates an additional challenge and an untapped scope for neurologists to adopt treatments for PD by targeting the ion-channels and gap-junctions, which is well-reviewed in the present article.

Application of Neurotoxin-Induced Animal Models in the Study of Parkinson's Disease-Related Depression: Profile and Proposal

Depression can be a non-motor symptom, a risk factor, and even a co-morbidity of Parkinson's disease (PD). In either case, depression seriously affects the quality of life of PD patients. Unfortunately, at present, a large number of clinical and basic studies focused on the pathophysiological mechanism of PD and the prevention and treatment of motor symptoms. Although there has been increasing attention to PD-related depression, it is difficult to achieve early detection and early intervention, because the clinical guidelines mostly refer to depression developed after or accompanied by motor impairments. Why is there such a dilemma? This is because there has been no suitable preclinical animal model for studying the relationship between depression and PD, and the assessment of depressive behavior in PD preclinical models is as well a very challenging task since it is not free from the confounding from the motor impairment. As a common method to simulate PD symptoms, neurotoxin-induced PD models have been widely used. Studies have found that neurotoxin-induced PD model animals could exhibit depression-like behaviors, which sometimes manifested earlier than motor impairments. Therefore, there have been attempts to establish the PD-related depression model by neurotoxin induction. However, due to a lack of unified protocol, the reported results were diverse. For the purpose of further promoting the improvement and optimization of the animal models and the study of PD-related depression, we reviewed the establishment and evaluation strategies of the current animal models of PD-related depression based on both the existing literature and our own research experience, and discussed the possible mechanism and interventions, in order to provide a reference for future research in this area.

Multivariate genomic and transcriptomic determinants of imaging-derived personalized therapeutic needs in Parkinson's disease

Due to the marked interpersonal neuropathologic and clinical heterogeneity of Parkinson's disease (PD), current interventions are not personalized and fail to benefit all patients. Furthermore, we continue to lack well-established methods and clinical tests to tailor interventions at the individual level in PD. Here, we identify the genetic determinants of individual-tailored treatment needs derived from longitudinal multimodal neuroimaging data in 294 PD patients (PPMI data). Advanced multivariate statistical analysis revealed that both genomic and blood transcriptomic data significantly explain (P < 0.01, FWE-corrected) the interindividual variability in therapeutic needs associated with dopaminergic, functional, and structural brain reorganization. We confirmed a high overlap between the identified highly predictive molecular pathways and determinants of levodopa clinical responsiveness, including well-known (Wnt signaling, angiogenesis, dopaminergic activity) and recently discovered (immune markers, gonadotropin-releasing hormone receptor) pathways/components. In addition, the observed strong correspondence between the identified genomic and baseline-transcriptomic determinants of treatment needs/response supports the genome's active role at the time of patient evaluation (i.e., beyond individual genetic predispositions at birth). This study paves the way for effectively combining genomic, transcriptomic and neuroimaging data for implementing successful individually tailored interventions in PD and extending our pathogenetic understanding of this multifactorial and heterogeneous disorder.

Preventing Parkinson's Disease: An Environmental Agenda

Fueled by aging populations and continued environmental contamination, the global burden of Parkinson's disease (PD) is increasing. The disease, or more appropriately diseases, have multiple environmental and genetic influences but no approved disease modifying therapy. Additionally, efforts to prevent this debilitating disease have been limited. As numerous environmental contaminants (e.g., pesticides, metals, industrial chemicals) are implicated in PD, disease prevention is possible. To reduce the burden of PD, we have compiled preclinical and clinical research priorities that highlight both disease prediction and primary prevention. Though not exhaustive, the "PD prevention agenda" builds upon many years of research by our colleagues and proposes next steps through the lens of modifiable risk factors. The agenda identifies ten specific areas of further inquiry and considers the funding and policy changes that will be necessary to help prevent the world's fastest growing brain disease.

Polychlorinated biphenyls induce oxidative stress and metabolic responses in astrocytes

Exposure to environmental toxicants is prevalent, hazardous and linked to varied detrimental health outcomes and disease. Polychlorinated biphenyls (PCBs), a class of hazardous organic chlorines once widely used for industrial purposes, are associated with neurodegenerative disease and oxidative stress in both in vitro and in vivo models. Here, we investigated the impact of Aroclor 1254, a commercially available PCB mixture, on primary murine astrocytes to determine the response to this once ubiquitously used toxicant on the most numerous cells of the central nervous system (CNS). Astrocytes are a critical component of homeostasis throughout the CNS, including at the blood-brain barrier, where they serve as the primary defense against xenobiotics entering the CNS, and at the synapse, where they are closely coupled to neurons through several metabolic pathways. We hypothesized that PCBs cause astrocytic oxidative stress and related dysfunction including altered metabolism. We exposed primary murine cortical astrocytes to PCBs and report an increased expression of antioxidant genes (Prdx1, Gsta2, Gfap, Amigo2) in response to oxidative stress. Our data show increased ATP production and spare respiratory capacity in astrocytes exposed to 10 μM (∼ 3 ppm) PCBs. This dose also causes an increase in glucose uptake that is not seen at a higher dose (50 μM) suggesting that, at a lower dose, astrocytes are able to engage compensatory mechanisms to promote survival. Together, these data suggest that exposure to PCBs impact astrocytic metabolism, which is important to consider both in the context of human health and disease and in in vitro and in vivo disease models.

Genetic and environmental factors in Alzheimer's and Parkinson's diseases and promising therapeutic intervention via fecal microbiota transplantation

Neurodegenerative diseases are characterized by neuronal impairment and loss of function, and with the major shared histopathological hallmarks of misfolding and aggregation of specific proteins inside or outside cells. Some genetic and environmental factors contribute to the promotion of the development and progression of neurodegenerative diseases. Currently, there are no effective treatments for neurodegenerative diseases. It has been revealed that bidirectional communication exists between the brain and the gut. The gut microbiota is a changeable and experience-dependent ecosystem and can be modified by genetic and environmental factors. The gut microbiota provides potential therapeutic targets that can be regulated as new interventions for neurodegenerative diseases. In this review, we discuss genetic and environmental risk factors for neurodegenerative diseases, summarize the communication among the components of the microbiota-gut-brain axis, and discuss the treatment strategy of fecal microbiota transplantation (FMT). FMT is a promising treatment for neurodegenerative diseases, and restoration of the gut microbiota to a premorbid state is a novel goal for prevention and treatment strategies.

Probing the Pre-diagnostic Phase of Parkinson's Disease in Population-Based Studies

Parkinson's disease covers a wide spectrum of symptoms, ranging from early non-motor symptoms to the characteristic bradykinesia, tremor and rigidity. Although differences in the symptomatology of Parkinson's disease are increasingly recognized, there is still a lack of insight into the heterogeneity of the pre-diagnostic phase of Parkinson's disease. In this perspective, we highlight three aspects regarding the role of population-based studies in providing new insights into the heterogeneity of pre-diagnostic Parkinson's disease. First we describe several specific advantages of population-based cohort studies, including the design which overcomes some common biases, the broad data collection and the high external validity. Second, we draw a parallel with the field of Alzheimer's disease to provide future directions to uncover the heterogeneity of pre-diagnostic Parkinson's disease. Finally, we anticipate on the emergence of prevention and disease-modification trials and the potential role of population-based studies herein. In the coming years, bridging gaps between study designs will be essential to make vital advances in elucidating the heterogeneity of pre-diagnostic Parkinson's disease.

Family history of hand tremor in patients with early Parkinson's disease

Some patients with Parkinson's disease (PD) report hand tremors in their relatives. This study aimed to compare the clinical characteristics of early PD in patients with and without a family history of hand tremor. This study included 337 early and drug-naïve patients with PD. The family history of hand tremor was obtained from the patients and their caregivers. Motor and non-motor symptoms of PD were assessed using the appropriate scales. A family history of hand tremor was present in 27 of 337 patients with PD (8.0%). Patients with a family history of hand tremor had significantly higher scores for rest tremors than those without. No significant differences were found in action tremor, bradykinesia, rigidity, gait, or posture scores between the two groups. The proportion of tremor-dominant subtypes was higher in patients with a family history of hand tremor than in those without (51.8% vs. 28.7%). Patients with PD, with a family history of hand tremor, had significantly lower scores in the urinary and sexual subdomains of the Non-Motor Symptoms Scale for PD than in those without. A family history of hand tremor affects the motor and non-motor symptoms in patients with early PD. It is necessary to investigate the family history of hand tremor in patients with PD.

Environmental toxicants in the brain: A review of astrocytic metabolic dysfunction

Exposure to environmental toxicants is linked to long-term adverse outcomes in the brain and involves the dysfunction of glial and neuronal cells. Astrocytes, the most numerous cell type, are increasingly implicated in the pathogenesis of many diseases of the central nervous system, including neurodegenerative diseases. Astrocytes are critical for proper brain function in part due to their robust antioxidant and unique metabolic capabilities. Additionally, astrocytes are positioned both at the blood-brain barrier, where they are the primary responders to xenobiotic penetrance of the CNS, and at synapses where they are in close contact with neurons and synaptic machinery. While exposure to several classes of environmental toxicants, including chlorinated and fluorinated compounds, and trace metals, have been implicated in neurodegenerative diseases, their impact on astrocytes represents an important and growing field of research. Here, we review existing literature focused on the impact of a range of synthetic compounds on astrocytic function. We focus specifically on perturbed metabolic processes in response to these compounds and consider how perturbation of these pathways impacts disease pathogenesis.

Metal Exposure and SNCA rs356219 Polymorphism Associated With Parkinson Disease and Parkinsonism

Objective: In the province of Brescia, Italy, historical neurotoxic metal exposure has occurred for several decades. This study aimed to explore the role of metal exposure and genetics on Parkinson's Disease (PD) and Parkinsonism. Methods: Cases were enrolled from four local clinics for movement disorders. Randomly selected controls non-affected by neurological or psychiatric conditions were enrolled from the same health centers keeping a similar gender ratio and age distribution as for cases. Data on sociodemographic variables, clinical onset and life habits were collected besides accurate occupational and residential history. Blood samples were collected from all participants for genotyping of target polymorphisms in genes linked to PD and/or metal transport. Results: A total number of 432 cases and 444 controls were enrolled in the study, with average age of 71 years (72.2 for cases and 70 for controls). The average age at diagnosis was 65.9 years (SD 9.9). Among the potential risk factors, family history of PD or Parkinsonism showed the strongest association with the diseases (OR = 4.2, 95% CI 2.3, 7.6 on PD; OR = 4.3, 95% CI 1.9, 9.5 for Parkinsonism), followed by polymorphism rs356219 in the alpha-synuclein (SNCA) gene (OR = 2.03, 95% CI 1.3, 3.3 for CC vs. TT on PD; OR = 2.5, 95% CI 1.1, 5.3 for CC vs. TT on Parkinsonism), exposure to metals (OR = 2.4;, 95% CI 1.3, 4.2 on PD), being born in a farm (OR = 1.8; 95% CI 1.1, 2.8 on PD; OR = 2.6; 95% CI 1.4, 4.9 on Parkinsonism) and being born in the province of Brescia (OR = 1.7; 95% CI 1.0, 2.9 on PD). Conditional OR of having PD depending by SNCA polymorphism and metal exposure highlights higher risk of PD among CC SNCA carriers and being exposed to metals. However, the interaction term was not statistically significant. Conclusions: Lifetime exposure to metals and genetic variation in SNCA gene are relevant determinants of PD and Parkinsonism in the highly industrialized area of Brescia, Italy. The lack of evidence of statistical interaction between environmental and genetic factors may be due to the low frequencies of subjects representing the exposure categories and the polymorphism variants and does not rule out the biological interaction.

Purinergic Receptors in Basal Ganglia Diseases: Shared Molecular Mechanisms between Huntington's and Parkinson's Disease

Huntington's (HD) and Parkinson's diseases (PD) are neurodegenerative disorders caused by the death of GABAergic and dopaminergic neurons in the basal ganglia leading to hyperkinetic and hypokinetic symptoms, respectively. We review here the participation of purinergic receptors through intracellular Ca2+ signaling in these neurodegenerative diseases. The adenosine A2A receptor stimulates striatopallidal GABAergic neurons, resulting in inhibitory actions on GABAergic neurons of the globus pallidus. A2A and dopamine D2 receptors form functional heteromeric complexes inducing allosteric inhibition, and A2A receptor activation results in motor inhibition. Furthermore, the A2A receptor physically and functionally interacts with glutamate receptors, mainly with the mGlu5 receptor subtype. This interaction facilitates glutamate release, resulting in NMDA glutamate receptor activation and an increase of Ca2+ influx. P2X7 receptor activation also promotes glutamate release and neuronal damage. Thus, modulation of purinergic receptor activity, such as A2A and P2X7 receptors, and subsequent aberrant Ca2+ signaling, might present interesting therapeutic potential for HD and PD.

Incorporating multiple sets of eQTL weights into gene-by-environment interaction analysis identifies novel susceptibility loci for pancreatic cancer

It is of great scientific interest to identify interactions between genetic variants and environmental exposures that may modify the risk of complex diseases. However, larger sample sizes are usually required to detect gene-by-environment interaction (G × E) than required to detect genetic main association effects. To boost the statistical power and improve the understanding of the underlying molecular mechanisms, we incorporate functional genomics information, specifically, expression quantitative trait loci (eQTLs), into a data-adaptive G × E test, called aGEw. This test adaptively chooses the best eQTL weights from multiple tissues and provides an extra layer of weighting at the genetic variant level. Extensive simulations show that the aGEw test can control the Type 1 error rate, and the power is resilient to the inclusion of neutral variants and noninformative external weights. We applied the proposed aGEw test to the Pancreatic Cancer Case-Control Consortium (discovery cohort of 3,585 cases and 3,482 controls) and the PanScan II genome-wide association study data (replication cohort of 2,021 cases and 2,105 controls) with smoking as the exposure of interest. Two novel putative smoking-related pancreatic cancer susceptibility genes, TRIP10 and KDM3A, were identified. The aGEw test is implemented in an R package aGE.

The exploration of Parkinson's disease: a multi-modal data analysis of resting functional magnetic resonance imaging and gene data

Parkinson's disease (PD) is the most universal chronic degenerative neurological dyskinesia and an important threat to elderly health. At present, the researches of PD are mainly based on single-modal data analysis, while the fusion research of multi-modal data may provide more meaningful information in the aspect of comprehending the pathogenesis of PD. In this paper, 104 samples having resting functional magnetic resonance imaging (rfMRI) and gene data are from Parkinson's Progression Markers Initiative (PPMI) and Alzheimer's Disease Neuroimaging Initiative (ADNI) database to predict pathological brain areas and risk genes related to PD. In the experiment, Pearson correlation analysis is adopted to conduct fusion analysis from the data of genes and brain areas as multi-modal sample characteristics, and the clustering evolution random forest (CERF) method is applied to detect the discriminative genes and brain areas. The experimental results indicate that compared with several existing advanced methods, the CERF method can further improve the diagnosis of PD and healthy control, and can achieve a significant effect. More importantly, we find that there are some interesting associations between brain areas and genes in PD patients. Based on these associations, we notice that PD-related brain areas include angular gyrus, thalamus, posterior cingulate gyrus and paracentral lobule, and risk genes mainly include C6orf10, HLA-DPB1 and HLA-DOA. These discoveries have a significant contribution to the early prevention and clinical treatments of PD.

Mutated ATP10B increases Parkinson's disease risk by compromising lysosomal glucosylceramide export

Parkinson’s disease (PD) is a progressive neurodegenerative brain disease presenting with a variety of motor and non-motor symptoms, loss of midbrain dopaminergic neurons in the substantia nigra pars compacta and the occurrence of α-synuclein-positive Lewy bodies in surviving neurons. Here, we performed whole exome sequencing in 52 early-onset PD patients and identified 3 carriers of compound heterozygous mutations in the ATP10B P4-type ATPase gene. Genetic screening of a Belgian PD and dementia with Lewy bodies (DLB) cohort identified 4 additional compound heterozygous mutation carriers (6/617 PD patients, 0.97%; 1/226 DLB patients, 0.44%). We established that ATP10B encodes a late endo-lysosomal lipid flippase that translocates the lipids glucosylceramide (GluCer) and phosphatidylcholine (PC) towards the cytosolic membrane leaflet. The PD associated ATP10B mutants are catalytically inactive and fail to provide cellular protection against the environmental PD risk factors rotenone and manganese. In isolated cortical neurons, loss of ATP10B leads to general lysosomal dysfunction and cell death. Impaired lysosomal functionality and integrity is well known to be implicated in PD pathology and linked to multiple causal PD genes and genetic risk factors. Our results indicate that recessive loss of function mutations in ATP10B increase risk for PD by disturbed lysosomal export of GluCer and PC. Both ATP10B and glucocerebrosidase 1, encoded by the PD risk gene GBA1, reduce lysosomal GluCer levels, emerging lysosomal GluCer accumulation as a potential PD driver.

Mechanistic Interplay Between Autophagy and Apoptotic Signaling in Endosulfan-Induced Dopaminergic Neurotoxicity: Relevance to the Adverse Outcome Pathway in Pesticide Neurotoxicity

Chronic exposure to pesticides is implicated in the etiopathogenesis of Parkinson's disease (PD). Previously, we showed that dieldrin induces dopaminergic neurotoxicity by activating a cascade of apoptotic signaling pathways in experimental models of PD. Here, we systematically investigated endosulfan's effect on the interplay between apoptosis and autophagy in dopaminergic neuronal cell models of PD. Exposing N27 dopaminergic neuronal cells to endosulfan rapidly induced autophagy, indicated by an increased number of autophagosomes and LC3-II accumulation. Prolonged endosulfan exposure (>9 h) triggered apoptotic signaling, including caspase-2 and -3 activation and protein kinase C delta (PKCδ) proteolytic activation, ultimately leading to cell death, thus demonstrating that autophagy precedes apoptosis during endosulfan neurotoxicity. Furthermore, inhibiting autophagy with wortmannin, a phosphoinositide 3-kinase inhibitor, potentiated endosulfan-induced apoptosis, suggesting that autophagy is an early protective response against endosulfan. Additionally, Beclin-1, a major regulator of autophagy, was cleaved during the initiation of apoptotic cell death, and the cleavage was predominantly mediated by caspase-2. Also, caspase-2 and caspase-3 inhibitors effectively blocked endosulfan-induced apoptotic cell death. CRISPR/Cas9-based stable knockdown of PKCδ significantly attenuated endosulfan-induced caspase-3 activation, indicating that the kinase serves as a regulatory switch for apoptosis. Additional studies in primary mesencephalic neuronal cultures confirmed endosulfan's effect on autophagy and neuronal degeneration. Collectively, our results demonstrate that a functional interplay between autophagy and apoptosis dictate pesticide-induced neurodegenerative processes in dopaminergic neuronal cells. Our study provides insight into cell death mechanisms in environmentally linked neurodegenerative diseases.

Postnatal zinc or paraquat administration increases paraquat or zinc-induced loss of dopaminergic neurons: insight into augmented neurodegeneration

Epidemiological evidences have shown an association of exposure to pesticides or heavy metals with increased incidences of Parkinson's disease (PD) in humans. Exposure to pesticides or metals during the decisive period of the brain development increases the susceptibility of dopaminergic neurons upon re-exposure in adult rodents. However, the effect of early life exposure to pesticide on the heavy metal-induced neurodegeneration or heavy metal on pesticide-induced neurodegeneration is not yet explored. The current study explored the effect of developmental exposure to zinc (Zn), a metal or paraquat (PQ), a pesticide on the nigrostriatal dopaminergic neurons of rats challenged to Zn or PQ during adulthood. Exposure of Zn or PQ during adulthood alone exhibited marked reduction in motor activities, striatal dopamine and metabolites, glutathione content and number of dopaminergic neurons. However, the levels of lipid peroxidation, protein carbonyls, superoxide dismutase activity, pro-inflammatory cytokines and 4-hydroxynonenal-protein adducts were increased. While the expression of vesicular monoamine transporter-2 and tyrosine hydroxylase were attenuated, dopamine transporter and microglial marker Iba-1 expression, activated microglia, nuclear factor-kappa B activation, mitochondrial cytochrome c release and caspase-3/9 activation were augmented following Zn or PQ exposure. Albeit postnatal alone exposure did not alter any of the studied parameters, the developmental administration of Zn/PQ in re-challenged adult rats produced more pronounced changes in the aforementioned variables as compared with adulthood Zn or PQ alone intoxicated animals. The results demonstrate that postnatal Zn/PQ intoxication dents the oxidative stress, inflammation, cell death and dopamine metabolism and storage regulating machineries, which speed up the toxicant-induced degeneration during adulthood.

Nanoemulsions for targeting the neurodegenerative diseases: Alzheimer's, Parkinson's and Prion's

Neurodegenerative diseases need the drugs to be delivered right inside the brain to maximizing the therapeutic effects. This can be achieved by use of novel targeted delivery systems such as nanoemulsions. Nanoemulsions (NE) are nano-sized emulsions that are manufactured for enhancing the delivery of drugs to the targeted site and minimize adverse effects and toxic reactions. Looking into the advanced pharmaceutical applications of NE, the present review gives an insight to the understanding of the application of NE in NDs like AD, PD and Prion's disease. The review also touches upon the pathophysiology of these ND diseases to have a clear understanding of the molecular aspects of the disease. Finally, the review sets a standpoint of nanoemulsion's significance in the treatment therapy of ND besides the drawbacks associated with the current drug therapy in NDs.

SNHG1 promotes MPP+-induced cytotoxicity by regulating PTEN/AKT/mTOR signaling pathway in SH-SY5Y cells via sponging miR-153-3p

Background

Long non-coding RNA small molecule RNA host gene 1 (SNHG1) was previously identified to be relevant with Parkinson’s disease (PD) pathogenesis. This work aims to further elucidate the regulatory networks of SNHG1 involved in PD.

Methods

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-hydrochloride (MPTP)-induced mice and 1-methyl-4-phenylpyridinium (MPP⁺)-treated SH-SY5Y cells were respectively constructed as the in vivo and in vitro PD models. Expression levels of SNHG1 and miR-153-3p were detected by qRT-PCR. Protein expression levels of phosphate and tension homology deleted on chromosome ten (PTEN) were measured by western blotting assay. Cell viability and apoptosis were determined by MTT and flow cytometry assays. The interactions among SNHG1, miR-153-3p and PTEN were identified by luciferase reporter assay, RNA immunoprecipitation, and/or RNA pull-down analysis.

Results

Increased SNHG1 expression was found in midbrain of MPTP-induced PD mice and MPP⁺-treated SH-SY5Y cells. Overexpression of SNHG1 lowered viability and enhanced apoptosis in MPP⁺-treated SH-SY5Y cells. Moreover, SNHG1 acted as a molecular sponge to inhibit the expression of miR-153-3p. Furthermore, miR-153-3p-mediated suppression of MPP⁺-induced cytotoxicity was abated following SNHG1 up-regulation. Additionally, PTEN was identified as a direct target of miR-153-3p, and SNHG1 could serve as a competing endogenous RNA (ceRNA) of miR-153-3p to improve the expression of PTEN. Besides, enforced expression of PTEN displayed the similar functions as SNHG1 overexpression in regulating the viability and apoptosis of MPP⁺-treated SH-SY5Y cells. Finally, SNHG1 was found to activate PTEN/AKT/mTOR signaling pathway in SH-SY5Y cells by targeting miR-153-3p.

Conclusion

SNHG1 aggravates MPP⁺-induced cellular toxicity in SH-SY5Y cells by regulating PTEN/AKT/mTOR signaling via sponging miR-153-3p, indicating the potential of SNHG1 as a promising therapeutic target for PD.

The Effect of Human Umbilical Cord Mesenchymal Stromal Cells in Protection of Dopaminergic Neurons from Apoptosis by Reducing Oxidative Stress in the Early Stage of a 6-OHDA-Induced Parkinson's Disease Model

Oxidative stress is an important cause of dopaminergic (DA) neuron apoptosis in Parkinson’s disease (PD). Mesenchymal stromal cells (MSCs) possess antioxidative features. In this study, we investigated whether MSCs could reduce oxidative stress and protect DA neurons from apoptosis by intravenous (I.V.) injection in the early stage of a 6-hydroxydopamine (6-OHDA)-induced PD model. MSCs were injected into the tail vein of mice, and behavioral tests, immunofluorescence staining, western blot, and oxidative stress levels were assessed at different time points. After 6-OHDA exposure, DA neuron apoptosis was detected, together with severe oxidative stress in brain and periphery. Compared with the non-transplanted sham controls, motor function in the 6-OHDA-lesioned group after I.V. injection of MSCs was significantly improved, and the levels of DA neuron apoptosis and oxidative stress decreased. The results demonstrate that MSCs can rescue DA neurons from ongoing apoptosis by reducing oxidative stress, and provide insights on developing new therapeutic strategies to offset the degenerative process of PD.

Glia Maturation Factor and Mast Cell-Dependent Expression of Inflammatory Mediators and Proteinase Activated Receptor-2 in Neuroinflammation

Parkinson's disease (PD) is characterized by the presence of inflammation-mediated dopaminergic neurodegeneration in the substantia nigra. Inflammatory mediators from activated microglia, astrocytes, neurons, T-cells and mast cells mediate neuroinflammation and neurodegeneration. Administration of neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induces PD like motor deficits in rodents. 1-methyl-4-phenylpyridinium (MPP+), a toxic metabolite of MPTP activates glial cells, neurons and mast cells to release neuroinflammatory mediators. Glia maturation factor (GMF), mast cells and proteinase activated receptor-2 (PAR-2) are implicated in neuroinflammation. Alpha-synuclein which induces neurodegeneration increases PAR-2 expression in the brain. However, the exact mechanisms are not yet understood. In this study, we quantified inflammatory mediators in the brains of MPTP-administered wild type (Wt), GMF-knockout (GMF-KO), and mast cell knockout (MC-KO) mice. Additionally, we analyzed the effect of MPP+, GMF, and mast cell proteases on PAR-2 expression in astrocytes and neurons in vitro. Results show that the levels of interleukin-1beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and the chemokine (C-C motif) ligand 2 (CCL2) were lesser in the brains of GMF-KO mice and MC-KO mice when compared to Wt mice brain after MPTP administration. Incubation of astrocytes and neurons with MPP+, GMF, and mouse mast cell protease-6 (MMCP-6) and MMCP-7 increased the expression of PAR-2. Our studies show that the absence of mast cells and GMF reduce the expression of neuroinflammatory mediators in the brain. We conclude that GMF along with mast cell interactions with glial cells and neurons during neuroinflammation can be explored as a new therapeutic target for PD and other neuroinflammatory disorders.

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

Evidence indicates that complex gene-environment interactions underlie the incidence and progression of Parkinson's disease (PD). Neuroinflammation is a well-characterized feature of PD widely believed to exacerbate the neurodegenerative process. Environmental toxicants associated with PD, such as pesticides and heavy metals, can cause cellular damage and stress potentially triggering an inflammatory response. Toxicant exposure can cause stress and damage to cells by impairing mitochondrial function, deregulating lysosomal function, and enhancing the spread of misfolded proteins. These stress-associated mechanisms produce sterile triggers such as reactive oxygen species (ROS) along with a variety of proteinaceous insults that are well documented in PD. These associations provide a compelling rationale for analysis of sterile inflammatory mechanisms that may link environmental exposure to neuroinflammation and PD progression. Intracellular inflammasomes are cytosolic assemblies of proteins that contain pattern recognition receptors, and a growing body of evidence implicates the association between inflammasome activation and neurodegenerative disease. Characterization of how inflammasomes may function in PD is a high priority because the majority of PD cases are sporadic, supporting the widely held belief that environmental exposure is a major factor in disease initiation and progression. Inflammasomes may represent a common mechanism that helps to explain the strong association between exposure and PD by mechanistically linking environmental toxicant-driven cellular stress with neuroinflammation and ultimately cell death.

Paraquat and Parkinson's disease: a systematic review and meta-analysis of observational studies

This investigation aimed to conduct a systematic review of the literature and meta-analysis to determine whether exposure to the herbicide paraquat was associated with the development of Parkinson's disease (PD). Observational studies that enrolled adults exposed to paraquat with PD as the outcome of interest were searched in the PubMed, Embase, LILACS, TOXNET, and Web of Science databases up to May 2019. Two authors independently selected relevant studies, extracted data, and assessed methodological quality. The evidence certainty was assessed by the GRADE approach, which served as basis for a tentative causality assessment, supplemented by the Bradford Hill criteria when necessary. Results from nine case-control studies indicated that PD occurrence was 25% higher in participants exposed to paraquat. The only cohort investigation included demonstrated a non-significant OR of 1.08. Results from subgroup analyses also indicated higher PD frequency in participants that were exposed to paraquat for longer periods or individuals co-exposed with paraquat and any other dithiocarbamate. Data indicate apositive association between exposure to paraquat and PD occurrence, but the weight-of-evidence does not enable one to assume an indisputable cause-effect relationship between these two conditions. Better designed studies are needed to increase confidence in results. Systematic Review Registration: PROSPERO CRD42017069994.

Effect of the micro-immunotherapy medicine 2LPARK® on rat primary dopaminergic neurons after 6-OHDA injury: oxidative stress and survival evaluation in an in vitro model of Parkinson's disease

Background

Parkinson’s disease (PD) is a neurodegenerative disease characterized by motor impairments and resulting from progressive degenerative loss of midbrain dopaminergic (DAergic) neurons in the substantia nigra. Although the main cause of the loss of DAergic neurons is still unknown, various etiopathogenic mechanisms are distinguished, including release and accumulation of endogenous excitotoxic mediators along with the production of oxidative free radicals. Several neurotrophic and growth factors are known to increase DAergic neuronal survival and enhance antioxidant mechanisms. In this context, the micro-immunotherapy (MI) approach consists to regulate the immune system in order to protect DAergic neurons and control oxidative stress.

Purpose

The aim of the present study was to investigate the effect of the MI medicine (MIM), 2LPARK^® (Labo’Life), on oxidative stress and on the number of neurons positive for tyrosine hydroxylase (TH), in an in vitro model of PD.

Methods

Rat primary mesencephalic DAergic neurons cultures were pre-treated for 1 hr with the MIM (10 μM and 10 mM), placebo (10 μM and 10 mM) or brain-derived neurotrophic factor (BDNF; 3.3 μM) and then intoxicated with 6-hydroxydopamine (6-OHDA; 20 μM) for 48 hrs. After incubation, cells were incubated 30 mins at 37°C with CellROX green reagent and number of labeled cells were quantified. Then, cells were fixed and incubated with anti-TH antibody and the number of TH⁺ neurons was evaluated.

Results

We showed that, contrary to placebo, MIM was able to reduce oxidative stress and protect DAergic neurons from 6-OHDA-induced cell death.

Conclusion

Our results demonstrate the in vitro efficacy of MIM on two essential mechanisms of PD and propose the MI approach as a new ally in the regulation of neuroinflammation and in the treatment of this degenerative disease.

Genetic Defects in Mitochondrial Dynamics in Caenorhabditis elegans Impact Ultraviolet C Radiation- and 6-hydroxydopamine-Induced Neurodegeneration

Background: Parkinson’s disease (PD) is one of the most common neurodegenerative disorders involving devastating loss of dopaminergic neurons in the substantia nigra. Early steps in PD pathogenesis include mitochondrial dysfunction, and mutations in mitochondrial genes have been linked to familial forms of the disease. However, low penetrance of mutations indicates a likely important role for environmental factors in PD risk through gene by environment interactions. Herein, we study how genetic deficiencies in mitochondrial dynamics processes including fission, fusion, and mitophagy interact with environmental exposures to impact neurodegeneration. Methods: We utilized the powerful model organism Caenorhabditis elegans to study ultraviolet C radiation (UVC)- and 6-hydroxydopamine-induced degeneration of fluorescently-tagged dopaminergic neurons in the background of fusion deficiency (MFN1/2 homolog, fzo-1), fission deficiency (DMN1L homolog, drp-1), and mitochondria-specific autophagy (mitophagy) deficiency (PINK1 and PRKN homologs, pink-1 and pdr-1). Results: Overall, we found that deficiency in either mitochondrial fusion or fission sensitizes nematodes to UVC exposure (used to model common environmental pollutants) but protects from 6-hydroxydopamine-induced neurodegeneration. By contrast, mitophagy deficiency makes animals more sensitive to these stressors with an interesting exception—pink-1 deficiency conferred remarkable protection from 6-hydroxydopamine. We found that this protection could not be explained by compensatory antioxidant gene expression in pink-1 mutants or by differences in mitochondrial morphology. Conclusions: Together, our results support a strong role for gene by environment interactions in driving dopaminergic neurodegeneration and suggest that genetic deficiency in mitochondrial processes can have complex effects on neurodegeneration.

Developmental Dieldrin Exposure Alters DNA Methylation at Genes Related to Dopaminergic Neuron Development and Parkinson's Disease in Mouse Midbrain

Human and animal studies have shown that exposure to the organochlorine pesticide dieldrin is associated with increased risk of Parkinson's disease (PD). Despite previous work showing a link between developmental dieldrin exposure and increased neuronal susceptibility to MPTP toxicity in male C57BL/6 mice, the mechanism mediating this effect has not been identified. Here, we tested the hypothesis that developmental exposure to dieldrin increases neuronal susceptibility via genome-wide changes in DNA methylation. Starting at 8 weeks of age and prior to mating, female C57BL/6 mice were exposed to 0.3 mg/kg dieldrin by feeding (every 3 days) throughout breeding, gestation, and lactation. At 12 weeks of age, pups were sacrificed and ventral mesencephalon, containing primarily substantia nigra, was microdissected. DNA was isolated and dieldrin-related changes in DNA methylation were assessed via reduced representation bisulfite sequencing. We identified significant, sex-specific differentially methylated CpGs (DMCs) and regions (DMRs) by developmental dieldrin exposure (false discovery rate < 0.05), including DMCs at the Nr4a2 and Lmx1b genes, which are involved in dopaminergic neuron development and maintenance. Developmental dieldrin exposure had distinct effects on the male and female epigenome. Together, our data suggest that developmental dieldrin exposure establishes sex-specific poised epigenetic states early in life. These poised epigenomes may mediate sensitivity to subsequent toxic stimuli and contribute to the development of late-life neurodegenerative disease, including PD.