Leucine-rich repeat kinase-2 (LRRK2) modulates paraquat-induced inflammatory sickness and stress phenotype

Selective dopaminergic neurotoxicity modulated by inherent cell-type specific neurobiology

Parkinson's disease (PD) is a debilitating neurodegenerative disease affecting millions of individuals worldwide. Hallmark features of PD pathology are the formation of Lewy bodies in neuromelanin-containing dopaminergic (DAergic) neurons of the substantia nigra pars compacta (SNpc), and the subsequent irreversible death of these neurons. Although genetic risk factors have been identified, around 90 % of PD cases are sporadic and likely caused by environmental exposures and gene-environment interaction. Mechanistic studies have identified a variety of chemical PD risk factors. PD neuropathology occurs throughout the brain and peripheral nervous system, but it is the loss of DAergic neurons in the SNpc that produce many of the cardinal motor symptoms. Toxicology studies have found specifically the DAergic neuron population of the SNpc exhibit heightened sensitivity to highly variable chemical insults (both in terms of chemical structure and mechanism of neurotoxic action). Thus, it has become clear that the inherent neurobiology of nigral DAergic neurons likely underlies much of this neurotoxic response to broad insults. This review focuses on inherent neurobiology of nigral DAergic neurons and how such neurobiology impacts the primary mechanism of neurotoxicity. While interactions with a variety of other cell types are important in disease pathogenesis, understanding how inherent DAergic biology contributes to selective sensitivity and primary mechanisms of neurotoxicity is critical to advancing the field. Specifically, key biological features of DAergic neurons that increase neurotoxicant susceptibility.

LRRK2 kinase inhibition protects against Parkinson's disease-associated environmental toxicants

Idiopathic Parkinson's disease (PD) is epidemiologically linked with exposure to toxicants such as pesticides and solvents, which comprise a wide array of chemicals that pollute our environment. While most are structurally distinct, a common cellular target for their toxicity is mitochondrial dysfunction, a key pathological trigger involved in the selective vulnerability of dopaminergic neurons. We and others have shown that environmental mitochondrial toxicants such as the pesticides rotenone and paraquat, and the organic solvent trichloroethylene (TCE) appear to be influenced by the protein LRRK2, a genetic risk factor for PD. As LRRK2 mediates vesicular trafficking and influences endolysosomal function, we postulated that LRRK2 kinase activity may inhibit the autophagic removal of toxicant damaged mitochondria, resulting in elevated oxidative stress. Conversely, we suspected that inhibition of LRRK2, which has been shown to be protective against dopaminergic neurodegeneration caused by mitochondrial toxicants, would reduce the intracellular production of reactive oxygen species (ROS) and prevent mitochondrial toxicity from inducing cell death. To do this, we tested in vitro if genetic or pharmacologic inhibition of LRRK2 (MLi2) protected against ROS caused by four toxicants associated with PD risk - rotenone, paraquat, TCE, and tetrachloroethylene (PERC). In parallel, we assessed if LRRK2 inhibition with MLi2 could protect against TCE-induced toxicity in vivo, in a follow up study from our observation that TCE elevated LRRK2 kinase activity in the nigrostriatal tract of rats prior to dopaminergic neurodegeneration. We found that LRRK2 inhibition blocked toxicant-induced ROS and promoted mitophagy in vitro, and protected against dopaminergic neurodegeneration, neuroinflammation, and mitochondrial damage caused by TCE in vivo. We also found that cells with the LRRK2 G2019S mutation displayed exacerbated levels of toxicant induced ROS, but this was ameliorated by LRRK2 inhibition with MLi2. Collectively, these data support a role for LRRK2 in toxicant-induced mitochondrial dysfunction linked to PD risk through oxidative stress and the autophagic removal of damaged mitochondria.

Genetic variation and pesticide exposure influence blood DNA methylation signatures in females with early-stage Parkinson's disease

Although sex, genetics, and exposures can individually influence risk for sporadic Parkinson's disease (PD), the joint contributions of these factors to the epigenetic etiology of PD have not been comprehensively assessed. Here, we profiled sex-stratified genome-wide blood DNAm patterns, SNP genotype, and pesticide exposure in agricultural workers (71 early-stage PD cases, 147 controls) and explored replication in three independent samples of varying demographics (n = 218, 222, and 872). Using a region-based approach, we found more associations of blood DNAm with PD in females (69 regions) than in males (2 regions, Δβadj| ≥0.03, padj ≤ 0.05). For 48 regions in females, models including genotype or genotype and pesticide exposure substantially improved in explaining interindividual variation in DNAm (padj ≤ 0.05), and accounting for these variables decreased the estimated effect of PD on DNAm. The results suggested that genotype, and to a lesser degree, genotype-exposure interactions contributed to variation in PD-associated DNAm. Our findings should be further explored in larger study populations and in experimental systems, preferably with precise measures of exposure.

Occupational Pesticide Exposure in Parkinson's Disease Related to GBA and LRRK2 Variants

Background

The penetrance of common genetic risk variants for Parkinson's disease (PD) is low. Pesticide exposure increases PD risk, but how exposure affects penetrance is not well understood.

Objective

To determine the relationship between occupational pesticide exposure and PD in people with LRRK2 and GBA risk variants.

Methods

Participants of the Parkinson's Progression Markers Initiative (PPMI) with a LRRK2-G2019 S or GBA risk variant provided information about occupational pesticide exposure. We compared exposure in carriers with and without PD. Among carriers with PD, we used Cox proportional hazard models to compare time-to impairment in balance, cognition, and activities of daily living (ADLs) between participants with and without prior occupational pesticide exposure.

Results

378 participants with a risk variant provided exposure information; 176 with LRRK2-G2019 S (54 with and 122 without PD) and 202 with GBA variants (47 with and 155 without PD). Twenty-six participants reported pesticide exposure. People with a GBA variant and occupational pesticide exposure had much higher odds of PD (aOR: 5.4, 95% CI 1.7-18.5, p < 0.01). People with a LRRK2 variant and a history of occupational pesticide exposure had non-significantly elevated odds of PD (aOR 1.3, 95% CI 0.4-4.6, p = 0.7). Among those with PD, pesticide exposure was associated with a higher risk of balance problems and cognitive impairment in LRRK2-PD and functional impairment in GBA-PD, although associations were not statistically significant.

Conclusions

Occupational pesticide exposure may increase penetrance of GBA-PD and may be associated with faster symptom progression. Further studies in larger cohorts are necessary.

The Body, the Brain, the Environment, and Parkinson's Disease

The brain- and body-first models of Lewy body disorders predict that aggregated alpha-synuclein pathology usually begins in either the olfactory system or the enteric nervous system. In both scenarios the pathology seems to arise in structures that are closely connected to the outside world. Environmental toxicants, including certain pesticides, industrial chemicals, and air pollution are therefore plausible trigger mechanisms for Parkinson's disease and dementia with Lewy bodies. Here, we propose that toxicants inhaled through the nose can lead to pathological changes in alpha-synuclein in the olfactory system that subsequently spread and give rise to a brain-first subtype of Lewy body disease. Similarly, ingested toxicants can pass through the gut and cause alpha-synuclein pathology that then extends via parasympathetic and sympathetic pathways to ultimately produce a body-first subtype. The resulting spread can be tracked by the development of symptoms, clinical assessments, in vivo imaging, and ultimately pathological examination. The integration of environmental exposures into the brain-first and body-first models generates testable hypotheses, including on the prevalence of the clinical conditions, their future incidence, imaging patterns, and pathological signatures. The proposed link, though, has limitations and leaves many questions unanswered, such as the role of the skin, the influence of the microbiome, and the effects of ongoing exposures. Despite these limitations, the interaction of exogenous factors with the nose and the gut may explain many of the mysteries of Parkinson's disease and open the door toward the ultimate goal -prevention.

LRRK2 G2019S promotes astrocytic inflammation induced by oligomeric α-synuclein through NF-κB pathway

Parkinson's disease (PD) is characterized by the irreversible loss of dopaminergic neurons and the accumulation of α-synuclein in Lewy bodies. The oligomeric α-synuclein (O-αS) is the most toxic form of α-synuclein species, and it has been reported to be a robust inflammatory mediator. Mutations in Leucine-Rich Repeat Kinase 2 (LRRK2) are also genetically linked to PD and neuroinflammation. However, how O-αS and LRRK2 interact in glial cells remains unclear. Here, we reported that LRRK2 G2019S mutation, which is one of the most frequent causes of familial PD, enhanced the effects of O-αS on astrocytes both in vivo and in vitro. Meanwhile, inhibition of LRRK2 kinase activity could relieve the inflammatory effects of both LRRK2 G2019S and O-αS. We also demonstrated that nuclear factor κB (NF-κB) pathway might be involved in the neuroinflammatory responses. These findings revealed that inhibition of LRRK2 kinase activity may be a viable strategy for suppressing neuroinflammation in PD.

Pesticides and the Microbiome-Gut-Brain Axis: Convergent Pathways in the Pathogenesis of Parkinson's Disease

The increasing global burden of Parkinson's disease (PD), termed the PD pandemic, is exceeding expectations related purely to population aging and is likely driven in part by lifestyle changes and environmental factors. Pesticides are well recognized risk factors for PD, supported by both epidemiological and experimental evidence, with multiple detrimental effects beyond dopaminergic neuron damage alone. The microbiome-gut-brain axis has gained much attention in recent years and is considered to be a significant contributor and driver of PD pathogenesis. In this narrative review, we first focus on how both pesticides and the microbiome may influence PD initiation and progression independently, describing pesticide-related central and peripheral neurotoxicity and microbiome-related local and systemic effects due to dysbiosis and microbial metabolites. We then depict the bidirectional interplay between pesticides and the microbiome in the context of PD, synthesizing current knowledge about pesticide-induced dysbiosis, microbiome-mediated alterations in pesticide availability, metabolism and toxicity, and complex systemic pesticide-microbiome-host interactions related to inflammatory and metabolic pathways, insulin resistance and other mechanisms. An overview of the unknowns follows, and the role of pesticide-microbiome interactions in the proposed body-/brain-first phenotypes of PD, the complexity of environmental exposures and gene-environment interactions is discussed. The final part deals with possible further steps for translation, consisting of recommendations on future pesticide use and research as well as an outline of promising preventive/therapeutic approaches targeted on strengthening or restoring a healthy gut microbiome, closing with a summary of current gaps and future perspectives in the field.

LRRK2 deficiency protects the heart against myocardial infarction injury in mice via the P53/HMGB1 pathway

LRRK2 is a Ser/Thr kinase with multiple functional domains. Studies have shown that LRRK2 mutations are closely related to hereditary Parkinson's disease. However, its role in cardiovascular disease, especially in myocardial infarction, is unclear. The aim of this study was to explore the functional role of LRRK2 in myocardial infarction. Wild-type and LRRK2-knockout mice were subjected to coronary artery ligation (left anterior descending) to establish a myocardial infarction model. Neonatal rat cardiomyocytes were subjected to hypoxia to induce hypoxic injury in vitro. We found increased LRRK2 expression levels in the infarct periphery in mouse hearts and hypoxic cardiomyocytes. LRRK2-deficient mice exhibited decreased death rates and reduced infarction areas compared to wild-type controls 14 days after infarction. LRRK2-deficient mice showed reduced left ventricular fibrosis and inflammatory responses, as well as improved cardiac function. In the in vitro study, LRRK2 silencing decreased cleaved caspase-3 activity, reduced cardiomyocyte apoptosis, and diminished hypoxia-induced inflammation. However, LRRK2 overexpression enhanced cleaved caspase-3 activity, increased the number of apoptotic cardiomyocytes, and caused remarkable hypoxia-induced inflammation. When examining the underlying mechanisms, we found that hypoxia increased HIFα expression, which enhanced LRRK2 expression. LRRK2 induced high expression of HMGB1 via P53. When HMGB1 was blocked using an anti-HMGB1 antibody, the deleterious effects caused by LRRK2 overexpression following hypoxia were inhibited in cardiomyocytes. In summary, LRRK2 deficiency protects the heart against myocardial infarction injury. The mechanism underlying this effect involves the P53-HMGB1 pathway.

DNA methylation as a mediator of genetic and environmental influences on Parkinson's disease susceptibility: Impacts of alpha-Synuclein, physical activity, and pesticide exposure on the epigenome

Parkinson's disease (PD) is a neurodegenerative disorder with a complex etiology and increasing prevalence worldwide. As PD is influenced by a combination of genetic and environment/lifestyle factors in approximately 90% of cases, there is increasing interest in identification of the interindividual mechanisms underlying the development of PD as well as actionable lifestyle factors that can influence risk. This narrative review presents an outline of the genetic and environmental factors contributing to PD risk and explores the possible roles of cytosine methylation and hydroxymethylation in the etiology and/or as early-stage biomarkers of PD, with an emphasis on epigenome-wide association studies (EWAS) of PD conducted over the past decade. Specifically, we focused on variants in the SNCA gene, exposure to pesticides, and physical activity as key contributors to PD risk. Current research indicates that these factors individually impact the epigenome, particularly at the level of CpG methylation. There is also emerging evidence for interaction effects between genetic and environmental contributions to PD risk, possibly acting across multiple omics layers. We speculated that this may be one reason for the poor replicability of the results of EWAS for PD reported to date. Our goal is to provide direction for future epigenetics studies of PD to build upon existing foundations and leverage large datasets, new technologies, and relevant statistical approaches to further elucidate the etiology of this disease.

Environmental Impact on the Epigenetic Mechanisms Underlying Parkinson’s Disease Pathogenesis: A Narrative Review

Parkinson’s disease (PD) is the second most common neurodegenerative disorder with an unclear etiology and no disease-modifying treatment to date. PD is considered a multifactorial disease, since both genetic and environmental factors contribute to its pathogenesis, although the molecular mechanisms linking these two key disease modifiers remain obscure. In this context, epigenetic mechanisms that alter gene expression without affecting the DNA sequence through DNA methylation, histone post-transcriptional modifications, and non-coding RNAs may represent the key mediators of the genetic–environmental interactions underlying PD pathogenesis. Environmental exposures may cause chemical alterations in several cellular functions, including gene expression. Emerging evidence has highlighted that smoking, coffee consumption, pesticide exposure, and heavy metals (manganese, arsenic, lead, etc.) may potentially affect the risk of PD development at least partially via epigenetic modifications. Herein, we discuss recent accumulating pre-clinical and clinical evidence of the impact of lifestyle and environmental factors on the epigenetic mechanisms underlying PD development, aiming to shed more light on the pathogenesis and stimulate future research.

Inhibitory effect of pirfenidone on pulmonary fibrosis in patients with acute paraquat poisoning

OBJECTIVE

To study the efficacy of pirfenidone (PFD) on patients with pulmonary fibrosis caused by acute paraquat (PQ) poisoning.

METHODS

A total of 86 patients with pulmonary fibrosis caused by acute PQ poisoning admitted to our hospital were analyzed retrospectively. All of them successfully received the standard 21-day treatment based on "Taishan Consensus", and they were assigned to the PFD group or the NO-PFD group according to whether they received PFD treatment (at 200 mg/time, 3 times/day) for 6 months after discharge. The two groups were compared in effective treatment rate, mortality and incidence of adverse reactions such as liver and kidney function damage, pulmonary fibrosis-associated indexes, pulmonary function-associated indexes, and arterial blood gas indexes before and after therapy.

RESULTS

The PFD group showed a notably higher effective treatment rate than the NO-PFD group (P<0.05). Additionally, the PFD group showed notably lower levels of serum hyaluronic acid (HA), laminin (LN), type IV collagen (CIV), and type III procollagen (PCIII), and notably higher levels of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC than the NO-PFD group (all P<0.001), and the PFD group also showed significantly higher levels of arterial blood gas indexes including arterial partial pressure of oxygen (PaO2) and PaO2/inspired oxygen (FIO2) than the NO-PFD group (both P<0.001). Moreover, the Kaplan-Meier survival curves showed that the survival rate of the patients in PFD group was significantly higher than that in the NO-PFD group (P<0.05).

CONCLUSION

With a high safety, PFD can effectively improve the treatment efficacy in patients with pulmonary fibrosis caused by acute PQ poisoning. PFD can improve the pulmonary function and arterial blood gas status of patients, without causing obvious liver and kidney damage.

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.

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.

Effect of paraquat on cytotoxicity involved in oxidative stress and inflammatory reaction: A review of mechanisms and ecological implications

Paraquat (PQ) is a cheap and an effective herbicide, which is widely being used worldwide to remove weeds in cultivated crop fields. However, it can cause soil and water pollution, and pose serious harm to the environment and organisms. Several countries have started to limit or prohibit the use of PQ because of the increasing number of human deaths. Its toxicity can damage the organisms with a multi-target mechanism, which has not been fully understood yet. That is why it is hard to treat as well. The current research on PQ focuses on its targeted organ, the lungs, in which PQ mostly trigger pulmonary fibrosis. While there is a lack of systematic research, there are few studies published discussing its toxic effects at systematic level. This review summarizes the major damages caused by PQ in different organisms and partial mechanisms by which it causes these damages. For this purpose, we consulted several research articles that studied the toxicity of PQ in various tissues. We also listed some drugs that can be used to alleviate the toxicity of PQ. However, at present, the effectiveness of these drugs is still being explored in animal experiments and the study of their mechanism will also help in understanding the poisoning mechanism of PQ, which will ultimately lead to effective treatment in future.

In silico comparative analysis of LRRK2 interactomes from brain, kidney and lung

Mutations in LRRK2 are the most frequent cause of familial Parkinson's disease (PD), with common LRRK2 non-coding variants also acting as risk factors for idiopathic PD. Currently, therapeutic agents targeting LRRK2 are undergoing advanced clinical trials in humans, however, it is important to understand the wider implications of LRRK2 targeted treatments given that LRRK2 is expressed in diverse tissues including the brain, kidney and lungs. This presents challenges to treatment in terms of effects on peripheral organ functioning, thus, protein interactors of LRRK2 could be targeted in lieu to optimize therapeutic effects. Herein an in-silico analysis of LRRK2 direct interactors in brain tissue from various brain regionswas conducted along with a comparative analysis of the LRRK2 interactome in the brain, kidney, and lung tissues. This was carried out based on curated protein-protein interaction (PPI) data from protein interaction databases such as HIPPIE, human gene/protein expression databases and Gene ontology (GO) enrichment analysis using Bingo. Seven targets (MAP2K6, MATK, MAPT, PAK6, SH3GL2, CDC42EP3 and CHGB) were found to be viable objectives for LRRK2 based investigations for PD that would have minimal impact on optimal functioning within peripheral organs. Specifically, MAPT, CHGB, PAK6, and SH3GL2 interacted with LRRK2 in the brain and kidney but not in lung tissue whilst LRRK2-MAP2K6 interacted only in the cerebellum and MATK-LRRK2 interaction was absent in kidney tissues. CDC42EP3 expression levels were low in brain tissues compared to kidney/lung. The results of this computational analysis suggest new avenues for experimental investigations towards LRRK2-targeted therapeutics.

Characterizing the protracted neurobiological and neuroanatomical effects of paraquat in a murine model of Parkinson's disease

The primary motor symptoms of Parkinson's disease (PD) result from the degeneration of dopamine-producing neurons of the substantia nigra pars compacta (SNc), and often, the loss is asymmetrical, resulting in unilateral tremor presentation. Notably, age is the primary risk factor for PD, and it is likely that the disease ultimately stems from the impact of environmental factors, which interact with the aging process. Recent research has focused on the role of microglia and pro-oxidative responses in dopaminergic neuronal death. In this study, we sought to examine the neurodegenerative, inflammatory, and stress effects of exposure to the etiologically relevant pesticide, paraquat, over time (up to 6 months after injections). We also were interested in whether a high-resolution, 7-Tesla animal magnetic resonance imaging would be sensitive enough to detect the degenerative impact of paraquat. We found that paraquat induced a loss of dopaminergic SNc neurons and activation of microglia that surprisingly did not change over 6 months after the last injection. A long-lasting reduction was evident for body weight, and alterations in organ (lung and heart) weight were evident, which reflect the peripheral impact of the toxicant. The microglial proinflammatory actin-remodeling factor, WAVE2, along with the inflammatory transcription factor, nuclear factor kappa B were also elevated within the brain. Remarkably, the stress hormone, corticosterone, was still significantly elevated 1 month after paraquat, whereas the inflammasome factor, caspase-1, and antigen presentation factor, MFG-E8, both displayed delayed rises after the 6-month time. Using high-resolution magnetic resonance imaging, we detected no striatal changes but modest hemispheric differences in the SNc and time-dependent volumetric enlargement of the ventricles in paraquat-treated mice. These data suggest that paraquat induces long-term nigrostriatal pathology (possibly asymmetric) and inflammatory changes and stress and trophic/apoptotic effects that appear to either increase with the passage of time or are evident for at least 1 month. In brief, paraquat may be a useful nonspecific means to model widespread stress and inflammatory changes related to PD or age-related disease in general, but not the progressive nature of such diseases.

The industrial solvent trichloroethylene induces LRRK2 kinase activity and dopaminergic neurodegeneration in a rat model of Parkinson's disease

Gene-environment interaction is implicated in the majority of idiopathic Parkinson's disease (PD) risk, and some of the most widespread environmental contaminants are selectively toxic to dopaminergic neurons. Pesticides have long been connected to PD incidence, however, it has become increasingly apparent that other industrial byproducts likely influence neurodegeneration. For example, organic solvents, which are used in chemical, machining, and dry-cleaning industries, are of growing concern, as decades of solvent use and their effluence into the environment has contaminated much of the world's groundwater and soil. Like some pesticides, certain organic solvents, such as the chlorinated halocarbon trichloroethylene (TCE), are mitochondrial toxicants, which are collectively implicated in the pathogenesis of dopaminergic neurodegeneration. Recently, we hypothesized a possible gene-environment interaction may occur between environmental mitochondrial toxicants and the protein kinase LRRK2, mutations of which are the most common genetic cause of familial and sporadic PD. In addition, emerging data suggests that elevated wildtype LRRK2 kinase activity also contributes to the pathogenesis of idiopathic PD. To this end, we investigated whether chronic, systemic TCE exposure (200 mg/kg) in aged rats produced wildtype LRRK2 activation and caused nigrostriatal dopaminergic dysfunction. Interestingly, we found that TCE not only induced LRRK2 kinase activity in the brain, but produced a significant dopaminergic lesion in the nigrostriatal tract, elevated oxidative stress, and caused endolysosomal dysfunction and α-synuclein accumulation. Together, these data suggest that TCE-induced LRRK2 kinase activity contributed to the selective toxicity of dopaminergic neurons. We conclude that gene-environment interactions between certain industrial contaminants and LRRK2 likely influence PD risk.

Genetic and Environmental Factors Influence the Pleomorphy of LRRK2 Parkinsonism

Missense mutations in the LRRK2 gene were first identified as a pathogenic cause of Parkinson's disease (PD) in 2004. Soon thereafter, a founder mutation in LRRK2, p.G2019S (rs34637584), was described, and it is now estimated that there are approximately 100,000 people worldwide carrying this risk variant. While the clinical presentation of LRRK2 parkinsonism has been largely indistinguishable from sporadic PD, disease penetrance and age at onset can be quite variable. In addition, its neuropathological features span a wide range from nigrostriatal loss with Lewy body pathology, lack thereof, or atypical neuropathology, including a large proportion of cases with concomitant Alzheimer's pathology, hailing LRRK2 parkinsonism as the "Rosetta stone" of parkinsonian disorders, which provides clues to an understanding of the different neuropathological trajectories. These differences may result from interactions between the LRRK2 mutant protein and other proteins or environmental factors that modify LRRK2 function and, thereby, influence pathobiology. This review explores how potential genetic and biochemical modifiers of LRRK2 function may contribute to the onset and clinical presentation of LRRK2 parkinsonism. We review which genetic modifiers of LRRK2 influence clinical symptoms, age at onset, and penetrance, what LRRK2 mutations are associated with pleomorphic LRRK2 neuropathology, and which environmental modifiers can augment LRRK2 mutant pathophysiology. Understanding how LRRK2 function is influenced and modulated by other interactors and environmental factors-either increasing toxicity or providing resilience-will inform targeted therapeutic development in the years to come. This will allow the development of disease-modifying therapies for PD- and LRRK2-related neurodegeneration.

The impact of dextran sodium sulphate and probiotic pre-treatment in a murine model of Parkinson's disease

BACKGROUND

Recent work has established that Parkinson's disease (PD) patients have an altered gut microbiome, along with signs of intestinal inflammation. This could help explain the high degree of gastric disturbances in PD patients, as well as potentially be linked to the migration of peripheral inflammatory factors into the brain. To our knowledge, this is the first study to examine microbiome alteration prior to the induction of a PD murine model.

METHODS

We presently assessed whether pre-treatment with the probiotic, VSL #3, or the inflammatory inducer, dextran sodium sulphate (DSS), would influence the PD-like pathology provoked by a dual hit toxin model using lipopolysaccharide (LPS) and paraquat exposure.

RESULTS

While VSL #3 has been reported to have anti-inflammatory effects, DSS is often used as a model of colitis because of the gut inflammation and the breach of the intestinal barrier that it induces. We found that VSL#3 did not have any significant effects (beyond a blunting of LPS paraquat-induced weight loss). However, the DSS treatment caused marked changes in the gut microbiome and was also associated with augmented behavioral and inflammatory outcomes. In fact, DSS markedly increased taxa belonging to the Bacteroidaceae and Porphyromonadaceae families but reduced those from Rikencellaceae and S24-7, as well as provoking colonic pro-inflammatory cytokine expression, consistent with an inflamed gut. The DSS also increased the impact of LPS plus paraquat upon microglial morphology, along with circulating lipocalin-2 (neutrophil marker) and IL-6. Yet, neither DSS nor VSL#3 influenced the loss of substantia nigra dopamine neurons or the astrocytic and cytoskeleton remodeling protein changes that were provoked by the LPS followed by paraquat treatment.

CONCLUSIONS

These data suggest that disruption of the intestinal integrity and the associated microbiome can interact with systemic inflammatory events to promote widespread brain-gut changes that could be relevant for PD and at the very least, suggestive of novel neuro-immune communication.

Microglia depletion prior to lipopolysaccharide and paraquat treatment differentially modulates behavioral and neuronal outcomes in wild type and G2019S LRRK2 knock-in mice

BACKGROUND

Substantial data have implicated microglial-driven neuroinflammation in Parkinson's disease (PD) and environmental toxicants have been long expected as triggers of such inflammatory processes. Of course, these environmental insults act in the context of genetic vulnerability factors and in this regard, leucine rich repeat kinase 2 (LRRK2), may play a prominent role.

METHODS

We used a double hit, lipopolysaccharide (LPS; endotoxin) followed by paraquat (pesticide toxicant) model of PD in mice with the most common LRRK2 mutation G2019S, knockin mice and wild type littermates. In order to assess the contribution of microglia, we depleted these cells (through 14 days of the CSF-1 antagonist, PLX-3397) prior to LPS and paraquat exposure.

RESULTS

We found that the G2019S mice displayed the greatest signs of behavioral pathology, but that the PLX-3397 induced microglial depletion at the time of LPS exposure diminished toxicity and weight loss and blunted the reduction in home-cage activity with subsequent paraquat exposure. However, neither the PLX-3397 pre-treatment nor the G2019S mutation affected the LPS ​+ ​paraquat induced loss of substantia nigra pars compacta (SNc) dopamine neurons or elevation of circulating immune (IL-6) or stress (corticosterone) factors. Intriguingly, microglial morphological ratings were basally enhanced in G2019S mice and the PLX-3397 pre-treatment reversed this effect. Moreover, PLX-3397 pre-treatment selectively elevated soluble a-synuclein and SIRT3 levels, while reducing SNc caspase-1 and 3, along with CX3CR1. Hence, the re-populated "new" microglia following cessation of PLX-3397 clearly had an altered phenotype or were immature at the time of sacrifice (i.e. after 11 days).

CONCLUSIONS

Collectively, these findings suggest that G2019S knock-in and PLX-3397 microglial depletion at the time of LPS exposure affects behavioral, but not neurodegenerative responses to subsequent environmental toxin exposure.