Integrin CD11b mediates locus coeruleus noradrenergic neurodegeneration in a mouse Parkinson's disease model

Microglial gp91phox-mediated neuroinflammation and ferroptosis contributes to learning and memory deficits in rotenone-treated mice

Apart from dopaminergic neurotoxicity, exposure to rotenone, a commonly used insecticide in agriculture, also adversely affects hippocampal and cortical neurons, resulting in cognitive impairments in mice. We recently established a role of microglia-mediated neuroinflammation in rotenone-elicited deficits of cognition, yet the mechanisms remain elusive. Here, we investigated the involvement of NADPH oxidase 2 (NOX2) catalytic subunit gp91phox in rotenone-induced cognitive deficits and the associated mechanisms. Our study demonstrated that rotenone exposure elevated expression of gp91phox and phosphorylation of the NOX2 cytosolic subunit p47phox, along with NADPH depletion in the hippocampus and cortex of mice, indicating NOX2 activation. Specific knockdown of gp91phox in microglia via adeno-associated virus delivery resulted in reduced microglial activation, proinflammatory gene expression and improved learning and memory capacity in rotenone-intoxicated mice. Genetic deletion of gp91phox also reversed rotenone-elicited cognitive dysfunction in mice. Furthermore, microglial gp91phox knockdown attenuated neuronal damage and synaptic loss in mice. This intervention also suppressed iron accumulation, disruption of iron-metabolism proteins and iron-dependent lipid peroxidation and restored the balance of ferroptosis-related parameters, including GPX4, SLC711, PTGS2, and ACSL4 in rotenone-lesioned mice. Intriguingly, pharmacological inhibition of ferroptosis with liproxstatin-1 conferred protection against rotenone-induced neurodegeneration and cognitive dysfunction in mice. In summary, our findings underscored the contribution of microglial gp91phox-dependent neuroinflammation and ferroptosis to learning and memory dysfunction in rotenone-lesioned mice. These results provided valuable insights into the pathogenesis of cognitive deficits associated with pesticide-induced Parkinsonism, suggesting potential therapeutic avenues for intervention.

Inflammasomes in neurological disorders - mechanisms and therapeutic potential

Inflammasomes are molecular scaffolds that are activated by damage-associated and pathogen-associated molecular patterns and form a key element of innate immune responses. Consequently, the involvement of inflammasomes in several diseases that are characterized by inflammatory processes, such as multiple sclerosis, is widely appreciated. However, many other neurological conditions, including Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, stroke, epilepsy, traumatic brain injury, sepsis-associated encephalopathy and neurological sequelae of COVID-19, all involve persistent inflammation in the brain, and increasing evidence suggests that inflammasome activation contributes to disease progression in these conditions. Understanding the biology and mechanisms of inflammasome activation is, therefore, crucial for the development of inflammasome-targeted therapies for neurological conditions. In this Review, we present the current evidence for and understanding of inflammasome activation in neurological diseases and discuss current and potential interventional strategies that target inflammasome activation to mitigate its pathological consequences.

Rutin prevents pyroptosis and M1 microglia via Nrf2/Mac-1/caspase-1-mediated inflammasome axis to improve POCD

BACKGROUND

Neuroinflammation following peripheral surgery plays a key role in postoperative cognitive dysfunction (POCD) development and there is no effective therapy to inflammation-mediated cognitive impairment. Recent studies showed that rutin, a natural flavonoid compound, conferred neuroprotection. However, the effects and mechanisms of rutin on cognition of surgical and aged mice and LPS-induced BV2 need deeper exploration.

METHODS

The effect of rutin in vivo and vitro were evaluated by Morris water maze test, HE stainin, Golgi-Cox staining, IF, IHC, RT-PCR, Flow Cytometer and Western blotting. In vivo, aged mice were treated with rutin and surgery. In vitro, rutin, Nrf2 knockdown, MAC-1 overexpression and VX765, a caspase-1 inhibitor, were administration on BV2 microglial cells.

RESULTS

Surgery led to compensatory increase in nuclear Nrf2 and rutin could further increase it. Neural damage was accompanied with high level in MAC-1, caspase-1-mediated pyroptosis and M1 microglia, while rutin recovered the process. Nrf2 inhibition abolished the effect of rutin with the increase of MAC-1, caspase-1-mediated pyroptosis and M1 microglia. Activation of MAC-1 abrogated protection of rutin by increase in pyroptosis and M1 microglia. Finally, we found that treatment with VX765 improved injury and increased M2 microglia against overexpression of MAC-1.

CONCLUSIONS

Our study indicated that rutin may be a potential therapy in POCD and exerted neural protection via Nrf2/ Mac-1/ caspase-1-mediated inflammasome axis to regulate pyroptosis and microglial polarization.

Complement receptor 3-mediated neurotoxic glial activation contributes to rotenone-induced cognitive decline in mice

Microglia-mediated chronic neuroinflammation has been associated with cognitive decline induced by rotenone, a well-known neurotoxic pesticide used in agriculture. However, the mechanisms remain unclear. This work aimed to elucidate the role of complement receptor 3 (CR3), a highly expressed receptor in microglia, in cognitive deficits induced by rotenone. Rotenone up-regulated the expression of CR3 in the hippocampus and cortex area of mice. CR3 deficiency markedly ameliorated rotenone-induced cognitive impairments, neurodegeneration and phosphorylation (Ser129) of α-synuclein in mice. CR3 deficiency also attenuated rotenone-stimulated microglial M1 activation. In microglial cells, siRNA-mediated knockdown of CR3 impeded, while CR3 activation induced by LL-37 exacerbated, rotenone-induced microglial M1 activation. Mechanistically, CR3 deficiency blocked rotenone-induced activation of nuclear factor κB (NF-κB), signal transducer and activator of transcription 1 (STAT1) and STAT3 signaling pathways. Pharmacological inhibition of NF-κB or STAT3 but not STAT1 was confirmed to suppress microglial M1 activation elicited by rotenone. Further study revealed that CR3 deficiency or knockdown also reduced rotenone-induced expression of C3, an A1 astrocyte marker, and production of microglial C1q, TNFα and IL-1α, a cocktail for activated microglia to induce neurotoxic A1 astrocytes, via NF-κB and STAT3 pathways. Finally, a small molecule modulator of CR3 efficiently mitigated rotenone-elicited cognitive deficits in mice even administered after the establishment of cognitive dysfunction. Taken together, our findings demonstrated that CR3 is a key factor in mediating neurotoxic glial activation and subsequent cognitive impairments in rotenone-treated mice, giving novel insights into the immunopathogenesis of cognitive impairments in pesticide-related Parkinsonism.

The Integrin Pathway Partially Mediates Stretch-Induced Deficits in Primary Rat Microglia

Stretch-injured microglia display significantly altered morphology, function and inflammatory-associated gene expression when cultured on a synthetic fibronectin substrate. However, the mechanism by which stretch induces these changes is unknown. Integrins, such as α5β1, mediate microglial attachment to fibronectin via the RGD binding peptide; following integrin ligation the integrin-associated signaling enzyme, focal adhesion kinase (FAK), autophosphorylates tyrosine residue 397 and mediates multiple downstream cellular processes. We therefore hypothesize that blocking the RGD binding/integrin pathway with a commercially available RGD peptide will mimic the stretch-induced morphological alterations and functional deficits in microglia. Further, we hypothesize that upregulation of stretch-inhibited downstream integrin signaling will reverse these effects. Using primary rat microglia, we tested the effects of RGD binding peptide and a FAK activator on cellular function and structure and response to stretch-injury. Similar to injured cells, RGD peptide administration significantly decreases media nitric oxide (NO) levels and iNOS expression and induced morphological alterations and migratory deficits. While stretch-injury and RGD peptide administration decreased phosphorylation of the tyrosine 397 residue on FAK, 20 nM of ZINC 40099027, an activator specific to the tyrosine 397 residue, rescued the stretch-induced decrease in FAK phosphorylation and ameliorated the injury-induced decrease in media NO levels, iNOS expression and inflammatory associated gene expression. Additionally, treatment alleviated morphological changes observed after stretch-injury and restored normal migratory behavior to control levels. Taken together, these data suggest that the integrin/FAK pathway partially mediates the stretch-injured phenotype in microglia, and may serve as a pathway to modulate microglial responses.

Integrin Mac1 mediates paraquat and maneb-induced learning and memory impairments in mice through NADPH oxidase-NLRP3 inflammasome axis-dependent microglial activation

INTRODUCTION

The mechanisms of cognitive impairments in Parkinson's disease (PD) remain unknown. Accumulating evidence revealed that brain neuroinflammatory response mediated by microglial cells contributes to cognitive deficits in neuropathological conditions and macrophage antigen complex-1 (Mac1) is a key factor in controlling microglial activation.

OBJECTIVES

To explore whether Mac1-mediated microglial activation participates in cognitive dysfunction in PD using paraquat and maneb-generated mouse PD model.

METHODS

Cognitive performance was measured in wild type and Mac1^-/- mice using Morris water maze test. The role and mechanisms of NADPH oxidase (NOX)-NLRP3 inflammasome axis in Mac1-mediated microglial dysfunction, neuronal damage, synaptic degeneration and phosphorylation (Ser129) of α-synuclein were explored by immunohistochemistry, Western blot and RT-PCR.

RESULTS

Genetic deletion of Mac1 significantly ameliorated learning and memory impairments, neuronal damage, synaptic loss and α-synuclein phosphorylation (Ser129) caused by paraquat and maneb in mice. Subsequently, blocking Mac1 activation was found to mitigate paraquat and maneb-elicited microglial NLRP3 inflammasome activation in both in vivo and in vitro. Interestingly, stimulating activation of NOX by phorbol myristate acetate abolished the inhibitory effects of Mac1 blocking peptide RGD on paraquat and maneb-provoked NLRP3 inflammasome activation, indicating a key role of NOX in Mac1-mediated NLRP3 inflammasome activation. Furthermore, NOX1 and NOX2, two members of NOX family, and downstream PAK1 and MAPK pathways were recognized to be essential for NOX to regulate NLRP3 inflammasome activation. Finally, a NLRP3 inflammasome inhibitor glybenclamide abrogated microglial M1 activation, neurodegeneration and phosphorylation (Ser129) of α-synuclein elicited by paraquat and maneb, which were accompanied by improved cognitive capacity in mice.

CONCLUSIONS

Mac1 was involved in cognitive dysfunction in a mouse PD model through NOX-NLRP3 inflammasome axis-dependent microglial activation, providing a novel mechanistic basis of cognitive decline in PD.

Exposure to dithiocarbamate fungicide maneb in vitro and in vivo: Neuronal apoptosis and underlying mechanisms

Maneb, a widely-used dithiocarbamate fungicide, remains in the environment and exerts adverse health effects. Epidemiological evidence shows that maneb exposure is associated with a higher risk of Parkinson's disease (PD), one of the most common neurodegenerative diseases. However, the molecular mechanisms underlying maneb-induced neurotoxicity remain unclear. Here we investigated the toxic effects and the underlying mechanisms of maneb on the degeneration of dopaminergic cells and α-synuclein in A53T transgenic mice. In SH-SY5Y cells, exposure to maneb reduces cell viability, triggers neuronal apoptosis, induces mitochondrial dysfunction, and generates reactive oxidative species (ROS) in a dose-dependent manner. Furthermore, Western blot analysis found that the mitochondrial apoptosis pathway (Bcl-2, Bax, cytochrome c, activated caspase-3) and the PKA/CREB signaling pathway (PKA, PDE10A, CREB, p-CREB) were changed by maneb both in vitro and in vivo. In addition, the activation of the mitochondrial apoptosis pathway induced by maneb was attenuated by activating PKA. Therefore, these results suggest that the PKA/CREB signaling pathway is involved in maneb-induced apoptosis. This study provides novel insights into maneb-induced neurotoxicity and the underlying mechanisms, which may serve as a guide for further toxicological assessment and standard application of maneb.

Exposure to the environmentally toxic pesticide maneb induces Parkinson's disease-like neurotoxicity in mice: A combined proteomic and metabolomic analysis

Maneb is a typical dithiocarbamate fungicide that has been extensively used worldwide. Epidemiological evidence shows that exposure to maneb is an environmental risk factor for Parkinson's disease (PD). However, the mechanisms underlying maneb-induced neurotoxicity have yet to be elucidated. In this study, we exposed SH-SY5Y cells to maneb at environmentally relevant concentrations (0, 0.1, 5, 10 mg/L) and found that maneb dose-dependently decreased the cell viability. Furthermore, maneb (60 mg/kg) induced PD-like motor impairment in α-synuclein A53T transgenic mice. The results of tandem mass tag (TMT) proteomics and metabolomics studies of mouse brain and serum revealed significant changes in proteins and metabolites in the pathways involved in the neurotransmitter system. The omics results were verified by targeted metabolomics and Western blot analysis, which demonstrated that maneb induced disturbance of the PD-related pathways, including the phenylalanine and tryptophan metabolism pathways, dopaminergic synapse, synaptic vesicle cycle, mitochondrial dysfunction, and oxidative stress. In addition, the PD-like phenotype induced by maneb was attenuated by the asparagine endopeptidase (AEP) inhibitor compound #11 (CP11) (10 mg/kg), indicating that AEP may play a role in maneb-induced neurotoxicity. To the best of our knowledge, this is the first study to investigate the molecular mechanisms underlying maneb-induced PD-like phenotypes using multiomics analysis, which identified novel therapeutic targets for PD associated with pesticides and other environmental pollutants.

Pathogenesis of α-Synuclein in Parkinson's Disease: From a Neuron-Glia Crosstalk Perspective

Parkinson's disease (PD) is a progressive neurodegenerative disorder. The classical behavioral defects of PD patients involve motor symptoms such as bradykinesia, tremor, and rigidity, as well as non-motor symptoms such as anosmia, depression, and cognitive impairment. Pathologically, the progressive loss of dopaminergic (DA) neurons in the substantia nigra (SN) and the accumulation of α-synuclein (α-syn)-composed Lewy bodies (LBs) and Lewy neurites (LNs) are key hallmarks. Glia are more than mere bystanders that simply support neurons, they actively contribute to almost every aspect of neuronal development and function; glial dysregulation has been implicated in a series of neurodegenerative diseases including PD. Importantly, amounting evidence has added glial activation and neuroinflammation as new features of PD onset and progression. Thus, gaining a better understanding of glia, especially neuron-glia crosstalk, will not only provide insight into brain physiology events but also advance our knowledge of PD pathologies. This review addresses the current understanding of α-syn pathogenesis in PD, with a focus on neuron-glia crosstalk. Particularly, the transmission of α-syn between neurons and glia, α-syn-induced glial activation, and feedbacks of glial activation on DA neuron degeneration are thoroughly discussed. In addition, α-syn aggregation, iron deposition, and glial activation in regulating DA neuron ferroptosis in PD are covered. Lastly, we summarize the preclinical and clinical therapies, especially targeting glia, in PD treatments.

Experimental and Clinical Biomarkers for Progressive Evaluation of Neuropathology and Therapeutic Interventions for Acute and Chronic Neurological Disorders

This article describes commonly used experimental and clinical biomarkers of neuronal injury and neurodegeneration for the evaluation of neuropathology and monitoring of therapeutic interventions. Biomarkers are vital for diagnostics of brain disease and therapeutic monitoring. A biomarker can be objectively measured and evaluated as a proxy indicator for the pathophysiological process or response to therapeutic interventions. There are complex hurdles in understanding the molecular pathophysiology of neurological disorders and the ability to diagnose them at initial stages. Novel biomarkers for neurological diseases may surpass these issues, especially for early identification of disease risk. Validated biomarkers can measure the severity and progression of both acute neuronal injury and chronic neurological diseases such as epilepsy, migraine, Alzheimer's disease, Parkinson's disease, Huntington's disease, traumatic brain injury, amyotrophic lateral sclerosis, multiple sclerosis, and other brain diseases. Biomarkers are deployed to study progression and response to treatment, including noninvasive imaging tools for both acute and chronic brain conditions. Neuronal biomarkers are classified into four core subtypes: blood-based, immunohistochemical-based, neuroimaging-based, and electrophysiological biomarkers. Neuronal conditions have progressive stages, such as acute injury, inflammation, neurodegeneration, and neurogenesis, which can serve as indices of pathological status. Biomarkers are critical for the targeted identification of specific molecules, cells, tissues, or proteins that dramatically alter throughout the progression of brain conditions. There has been tremendous progress with biomarkers in acute conditions and chronic diseases affecting the central nervous system.

The role of the locus coeruleus/norepinephrine system in the pathogenesis of neurodegenerative disorders: An update

PURPOSE OF REVIEW

The aim of this review was to provide an update on current and emerging knowledge of the neuropathological processes affecting the locus coeruleus/norepinephrine (LC/NE) system, their effect on Alzheimer's disease and Parkinson's disease symptomatology, including efforts to translate these notions into therapeutic actions targeting the noradrenergic system.

RECENT FINDINGS

Over the past 2 years, work from multiple groups has contributed to support an early role of locus coeruleus degeneration and/or hyperactivation in the neurodegenerative process, including a trigger of neuroinflammation. Imaging advances are allowing the quantification of locus coeruleus structural features in vivo, which is critical in the early stages of disease. Nonmotor and noncognitive symptoms, often secondary to the involvement of the LC/NE system, are becoming more important in the definition of these diseases and their treatment.

SUMMARY

The diverse symptomatology of Parkinson's disease and Alzheimer's disease, which is not limited to cardinal motor and cognitive abnormalities, strongly suggests a multisystem neurodegenerative process. In this context, it is increasingly clear how the LC/NE system plays a key role in the initiation and maintenance of the neurodegenerative process.

Microglial Activation Damages Dopaminergic Neurons through MMP-2/-9-Mediated Increase of Blood-Brain Barrier Permeability in a Parkinson's Disease Mouse Model

Chronic neuroinflammation has been considered to be involved in the progressive dopaminergic neurodegeneration in Parkinson’s disease (PD). However, the mechanisms remain unknown. Accumulating evidence indicated a key role of the blood–brain barrier (BBB) dysfunction in neurological disorders. This study is designed to elucidate whether chronic neuroinflammation damages dopaminergic neurons through BBB dysfunction by using a rotenone-induced mouse PD model. Results showed that rotenone dose-dependently induced nigral dopaminergic neurodegeneration, which was associated with increased Evans blue content and fibrinogen accumulation as well as reduced expressions of zonula occludens-1 (ZO-1), claudin-5 and occludin, three tight junction proteins for maintaining BBB permeability, in mice, indicating BBB disruption. Rotenone also induced nigral microglial activation. Depletion of microglia or inhibition of microglial activation by PLX3397 or minocycline, respectively, greatly attenuated BBB dysfunction in rotenone-lesioned mice. Mechanistic inquiry revealed that microglia-mediated activation of matrix metalloproteinases-2 and 9 (MMP-2/-9) contributed to rotenone-induced BBB disruption and dopaminergic neurodegeneration. Rotenone-induced activation of MMP-2/-9 was significantly attenuated by microglial depletion and inactivation. Furthermore, inhibition of MMP-2/-9 by a wide-range inhibitor, SB-3CT, abrogated elevation of BBB permeability and simultaneously increased tight junctions expression. Finally, we found that microglial depletion and inactivation as well as inhibition of MMP-2/-9 significantly ameliorated rotenone-elicited nigrostriatal dopaminergic neurodegeneration and motor dysfunction in mice. Altogether, our findings suggested that microglial MMP-2/-9 activation-mediated BBB dysfunction contributed to dopaminergic neurodegeneration in rotenone-induced mouse PD model, providing a novel view for the mechanisms of Parkinsonism.

SK-Channel Activation Alters Peripheral Metabolic Pathways in Mice, but Not Lipopolysaccharide-Induced Fever or Inflammation

Purpose

Previously, we have shown that CyPPA (cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine), a pharmacological small-conductance calcium-activated potassium (SK)–channel positive modulator, antagonizes lipopolysaccharide (LPS)-induced cytokine expression in microglial cells. Here, we aimed to test its therapeutic potential for brain-controlled sickness symptoms, brain inflammatory response during LPS-induced systemic inflammation, and peripheral metabolic pathways in mice.

Methods

Mice were pretreated with CyPPA (15 mg/kg IP) 24 hours before and simultaneously with LPS stimulation (2.5 mg/kg IP), and the sickness response was recorded by a telemetric system for 24 hours. A second cohort of mice were euthanized 2 hours after CyPPA or solvent treatment to assess underlying CyPPA-induced mechanisms. Brain, blood, and liver samples were analyzed for inflammatory mediators or nucleotide concentrations using immunohistochemistry, real-time PCR and Western blot, or HPLC. Moreover, we investigated CyPPA-induced changes of UCP1 expression in brown adipose tissue (BAT)–explant cultures.

Results

CyPPA treatment did not affect LPS-induced fever, anorexia, adipsia, or expression profiles of inflammatory mediators in the hypothalamus or plasma or microglial reactivity to LPS (CD11b staining and CD68 mRNA expression). However, CyPPA alone induced a rise in core body temperature linked to heat production via altered metabolic pathways like reduced levels of adenosine, increased protein content, and increased UCP1 expression in BAT-explant cultures, but no alteration in ATP/ADP concentrations in the liver. CyPPA treatment was accompanied by altered pathways, including NFκB signaling, in the hypothalamus and cortex, while circulating cytokines remained unaltered.

Conclusion

Overall, while CyPPA has promise as a treatment strategy, in particular according to results from in vitro experiments, we did not reveal anti-inflammatory effects during severe LPS-induced systemic inflammation. Interestingly, we found that CyPPA alters metabolic pathways inducing short hyperthermia, most likely due to increased energy turnover in the liver and heat production in BAT.

Inflammasome activation in neurodegenerative diseases

Approximately ten million people are diagnosed with dementia annually since they experience difficulties with memory and thinking skills. Since neurodegenerative diseases are diagnosed late, most of them are difficult to treat. This is due to the increased severity of the disease during the progression when neuroinflammation plays a critical role. The activation of immune cells, especially microglia, plays a crucial role in the development of neurodegenerative diseases. Molecular sensors within these microglia, such as the NLRP3 inflammasome, are activated by signals that represent the hallmarks of neurodegenerative diseases. Here, we first summarize the two activation steps of NLRP3 inflammasome activation. Furthermore, we discuss the key factors that contribute to NLRP3 inflammasome activation in the different neuroinflammatory diseases, like Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). The prominent NLRP3 inflammasome triggers include amyloid β and tau oligomers in AD, α-synuclein in PD, and superoxide dismutase (SOD1) and TAR DNA-binding protein 43 (TDP43) in ALS. NLRP3 inhibitor treatment has shown promising results in several preclinical mouse models of AD, PD, and ALS. Finally, we postulate that current understandings underpin the potential for NLRP3 inhibitors as a therapeutic target in neurodegenerative diseases.

Animal models of Parkinson's disease: a guide to selecting the optimal model for your research

Parkinson's disease (PD) is a complex, multisystem disorder characterised by α-synuclein (SNCA) pathology, degeneration of nigrostriatal dopaminergic neurons, multifactorial pathogenetic mechanisms and expression of a plethora of motor and non-motor symptoms. Animal models of PD have already been instructive in helping us unravel some of these aspects. However, much remains to be discovered, requiring continued interrogation by the research community. In contrast with the situation for many neurological disorders, PD benefits from of a wide range of available animal models (pharmacological, toxin, genetic and α-synuclein) but this makes selection of the optimal one for a given study difficult. This is especially so when a study demands a model that displays a specific combination of features. While many excellent reviews of animal models already exist, this review takes a different approach with the intention of more readily informing this decision-making process. We have considered each feature of PD in turn - aetiology, pathology, pathogenesis, motor dysfunctions and non-motor symptoms (NMS) - highlighting those animal models that replicate each. By compiling easily accessible tables and a summary figure, we aim to provide the reader with a simple, go-to resource for selecting the optimal animal model of PD to suit their research needs.

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

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

Neuromechanobiology: An Expanding Field Driven by the Force of Greater Focus

The brain processes information by transmitting signals through highly connected and dynamic networks of neurons. Neurons use specific cellular structures, including axons, dendrites and synapses, and specific molecules, including cell adhesion molecules, ion channels and chemical receptors to form, maintain and communicate among cells in the networks. These cellular and molecular processes take place in environments rich of mechanical cues, thus offering ample opportunities for mechanical regulation of neural development and function. Recent studies have suggested the importance of mechanical cues and their potential regulatory roles in the development and maintenance of these neuronal structures. Also suggested are the importance of mechanical cues and their potential regulatory roles in the interaction and function of molecules mediating the interneuronal communications. In this review, the current understanding is integrated and promising future directions of neuromechanobiology are suggested at the cellular and molecular levels. Several neuronal processes where mechanics likely plays a role are examined and how forces affect ligand binding, conformational change, and signal induction of molecules key to these neuronal processes are indicated, especially at the synapse. The disease relevance of neuromechanobiology as well as therapies and engineering solutions to neurological disorders stemmed from this emergent field of study are also discussed.

Inhibition of NLRP3 inflammasome by glibenclamide attenuated dopaminergic neurodegeneration and motor deficits in paraquat and maneb-induced mouse Parkinson's disease model

Pesticides exposure can lead to damage of dopaminergic neurons, which are associated with increased risk of Parkinson's disease (PD). However, the etiology of PD remains poorly understood and no therapeutic strategy is available. Previous studies suggested the involvement of NLRP3 inflammasome in the onset of PD. This study was designed to investigate whether glibenclamide, an inhibitor of NLRP3 inflammasome, could offer a reliable protective strategy for PD in a mouse PD model induced by paraquat and maneb. We found that glibenclamide exerted potent neuroprotection against paraquat and maneb-induced upregulation of α-synuclein, dopaminergic neurodegeneration and motor impairment in brain of mice. Mechanistically, glibenclamide treatment blocked NLRP3 inflammasome activation evidenced by reduced expressions of NLRP3, activated caspase-1 and mature interleukin-1β in glibenclamide co-treated mice compared with those in paraquat and maneb group mice. Furthermore, glibenclamide treatment mitigated paraquat and maneb-induced microglial M1 proinflammatory response and nuclear factor-κB activation in mice. Finally, the increased superoxide production, lipid peroxidation, protein levels of NADPH oxidase 2 (NOX2) and inducible nitric oxide synthase (iNOS) induced by paraquat and maneb were all attenuated by glibenclamide. Overall, our findings demonstrated that glibenclamide protected dopaminergic neurons in a mouse PD model induced by combined exposures of paraquat and maneb through suppression of NLRP3 inflammasome activation, microglial M1 polarization and oxidative stress.

Ddx20, DEAD box helicase 20, is essential for the differentiation of oligodendrocyte and maintenance of myelin gene expression

Oligodendrocytes form myelin sheaths that surround axons, contributing to saltatory conduction and proper central nervous system (CNS) function. Oligodendrocyte progenitor cells (OPCs) are generated during the embryonic stage and differentiate into myelinating oligodendrocytes postnatally. Ddx20 is a multifunctional, DEAD-box helicase involved in multiple cellular processes, including transcription, splicing, microRNA biogenesis, and translation. Although defects in each of these processes result in abnormal oligodendrocyte differentiation and myelination, the involvement of Ddx20 in oligodendrocyte terminal differentiation remains unknown. To address this question, we used Mbp-Cre mice to generate Ddx20 conditional knockout (cKO) mice to allow for the deletion of Ddx20 from mature oligodendrocytes. Mbp-Cre;Ddx20 cKO mice demonstrated small body sizes, behavioral abnormalities, muscle weakness, and short lifespans, with mortality by the age of 2 months old. Histological analyses demonstrated significant reductions in the number of mature oligodendrocytes and drastic reductions in the expression levels of myelin-associated mRNAs, such as Mbp and Plp at postnatal day 42. The number of OPCs did not change. A thin myelin layer was observed for large-diameter axons in Ddx20 cKO mice, based on electron microscopic analysis. A bromodeoxyuridine (BrdU) labeling experiment demonstrated that terminal differentiation was perturbed from ages 2 weeks to 7 weeks in the CNS of Mbp-Cre;Ddx20 cKO mice. The activation of mitogen-activated protein (MAP) kinase, which promotes myelination, was downregulated in the Ddx20 cKO mice based on immunohistochemical detection. These results indicate that Ddx20 is an essential factor for terminal differentiation of oligodendrocytes and maintenance of myelin gene expression.

Association of Locus Coeruleus and Substantia Nigra Pathology With Cognitive and Motor Functions in Patients With Parkinson Disease

OBJECTIVE

To investigate the contribution of substantia nigra (SN) and locus coeruleus (LC) pathology to clinical signs and symptoms in Parkinson's disease (PD) by applying neuromelanin-weighted imaging.

METHODS

Forty-seven patients with PD and 53 matched controls underwent motor assessment, a neuropsychological test battery and neuromelanin-weighted MRI. Patients with PD have been enrolled after fulfilling the criteria for 'clinically established PD' as defined by the Movement Disorders Society Clinical Diagnostic Criteria. Two independent raters identified SN and LC and calculated the contrast-to-noise ratio (CNR).

RESULTS

The intra-rater reliability demonstrated a good reliability between raters with an intraclass correlation coefficient of .88 (p<.001) and an inter-rater reliability of .80 (p<.001). Both, SN and LC CNRs were lower in patients with PD (p≤.001) compared to controls. The CNR of SN but not of LC was strongly correlated with disease duration (p≤.001). Neuromelanin pathology of the pars compacta-containing dorso-lateral SN correlated with MDS-UPDRS I, II and III but not cognitive functions. In contrast, neuromelanin pathology of LC was associated with cognitive functions in all tested domains but not with motor impairment or activities of daily living. No such associations were present in controls.

CONCLUSIONS

Neuromelanin imaging of the SN and LC is well-suited to map neurodegeneration in PD. Neuromelanin pathology of the SN correlates with motor dysfunction whereas LC pathology is related to cognitive impairment. Neuromelanin-weighted imaging of the LC could thus serve as an imaging marker of executive and other cognitive dysfunctions in PD.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that neuromelanin-weighted imaging was associated with the severity of various signs and symptoms in patients with PD.

Neurons and Glia Interplay in α-Synucleinopathies

Accumulation of the neuronal presynaptic protein alpha-synuclein within proteinaceous inclusions represents the key histophathological hallmark of a spectrum of neurodegenerative disorders, referred to by the umbrella term a-synucleinopathies. Even though alpha-synuclein is expressed predominantly in neurons, pathological aggregates of the protein are also found in the glial cells of the brain. In Parkinson's disease and dementia with Lewy bodies, alpha-synuclein accumulates mainly in neurons forming the Lewy bodies and Lewy neurites, whereas in multiple system atrophy, the protein aggregates mostly in the glial cytoplasmic inclusions within oligodendrocytes. In addition, astrogliosis and microgliosis are found in the synucleinopathy brains, whereas both astrocytes and microglia internalize alpha-synuclein and contribute to the spread of pathology. The mechanisms underlying the pathological accumulation of alpha-synuclein in glial cells that under physiological conditions express low to non-detectable levels of the protein are an area of intense research. Undoubtedly, the presence of aggregated alpha-synuclein can disrupt glial function in general and can contribute to neurodegeneration through numerous pathways. Herein, we summarize the current knowledge on the role of alpha-synuclein in both neurons and glia, highlighting the contribution of the neuron-glia connectome in the disease initiation and progression, which may represent potential therapeutic target for a-synucleinopathies.

Microglial Activation Mediates Noradrenergic Locus Coeruleus Neurodegeneration via Complement Receptor 3 in a Rotenone-Induced Parkinson's Disease Mouse Model

Background

Chronic exposure to the insecticide rotenone can damage dopaminergic neurons and lead to an increased risk of Parkinson’s disease (PD). Whereas it is not clear whether rotenone induces neurodegeneration of noradrenergic locus coeruleus (LC/NE) neurons. Chronic neuroinflammation mediated by microglia has been involved in the pathogenesis of PD. Evidence shows that complement receptor 3 (CR3) is a crucial regulator of microglial activation and related neurodegeneration. However, it is not clear whether CR3 mediates rotenone-elicited degeneration of LC/NE neurons through microglia-mediated neuroinflammation.

Materials and Methods

Wild type (WT) and CR3 knockout (KO) mice were treated with rotenone. PLX3397 and minocycline were used to deplete or inactivate the microglia. Leukadherin-1 (LA-1) was used to modulate CR3. LC/NE neurodegeneration, microglial phenotype, and expression of CR3 were determined by using immunohistochemistry, Western blot and real-time polymerase chain reaction (PCR) techniques. The glutathione (GSH) and malondialdehyde (MDA) contents were measured by using commercial kits.

Results

Rotenone exposure led to dose- and time-dependent LC/NE neuronal loss and microglial activation in mice. Depletion of microglia by PLX3397 or inhibition of microglial activation by minocycline significantly reduced rotenone-induced LC/NE neurodegeneration. Mechanistic studies revealed that CR3 played an essential role in the rotenone-induced activation of microglia and neurodegeneration of LC/NE neurons. Rotenone elevated the expression of CR3, and genetic ablation of CR3 markedly reduced rotenone-induced microglial activation and M1 polarization. LA-1 also suppressed rotenone-induced toxic microglial M1 activation. Furthermore, lack of CR3 or treatment with LA-1 reduced oxidative stress in the brainstem of rotenone-intoxicated mice. Finally, we found that mice deficient in CR3 or treated with LA-1 were more resistant to rotenone-induced LC/NE neurodegeneration than WT or vehicle-treated mice, respectively.

Conclusion

Our results indicate that CR3-mediated microglial activation participates in rotenone-induced LC/NE neurodegeneration, providing novel insight into environmental toxin-induced neurotoxicity and related Parkinsonism.