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Review
. 2019 May:197:61-82.
doi: 10.1016/j.pharmthera.2019.01.001. Epub 2019 Jan 22.

Environmental neurotoxicant-induced dopaminergic neurodegeneration: a potential link to impaired neuroinflammatory mechanisms

Affiliations
Review

Environmental neurotoxicant-induced dopaminergic neurodegeneration: a potential link to impaired neuroinflammatory mechanisms

Arthi Kanthasamy et al. Pharmacol Ther. 2019 May.

Abstract

With the increased incidence of neurodegenerative diseases worldwide, Parkinson's disease (PD) represents the second-most common neurodegenerative disease. PD is a progressive multisystem neurodegenerative disorder characterized by a marked loss of nigrostriatal dopaminergic neurons and the formation of Lewy pathology in diverse brain regions. Although the mechanisms underlying dopaminergic neurodegeneration remain poorly characterized, data from animal models and postmortem studies have revealed that heightened inflammatory responses mediated via microglial and astroglial activation and the resultant release of proinflammatory factors may act as silent drivers of neurodegeneration. In recent years, numerous studies have demonstrated a positive association between the exposure to environmental neurotoxicants and the etiology of PD. Although it is unclear whether neuroinflammation drives pesticide-induced neurodegeneration, emerging evidence suggests that the failure to dampen neuroinflammatory mechanisms may account for the increased vulnerability to pesticide neurotoxicity. Furthermore, recent studies provide additional evidence that shifts the focus from a neuron-centric view to glial-associated neurodegeneration following pesticide exposure. In this review, we propose to summarize briefly the possible factors that regulate neuroinflammatory processes during environmental neurotoxicant exposure with a focus on the potential roles of mitochondria-driven redox mechanisms. In this context, a critical discussion of the data obtained from experimental research and possible epidemiological studies is included. Finally, we hope to provide insights on the pivotal role of exosome-mediated intercellular transmission of aggregated proteins in microglial activation response and the resultant dopaminergic neurodegeneration after exposure to pesticides. Collectively, an improved understanding of glia-mediated neuroinflammatory signaling might provide novel insights into the mechanisms that contribute to neurodegeneration induced by environmental neurotoxicant exposure.

Keywords: Parkinson’s disease; exosomes; mitochondrial dysfunction; neuroinflammation; oxidative stress; pesticide.

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Conflict of interest statement

Conflict of Interest Statement

The authors declare no conflict of interest.

Figures

Figure 1:
Figure 1:. Rotenone induced architectural structure damage to the mitochondria of N27 dopaminergic neuronal cells.
N27 cells were exposed to rotenone (1 μM) for 3 h. Structural changes to mitochondria were then stained by the MitoTracker red dye. The z-stack images were captured on using a 63× oil immersion lens of the Leica Confocal Microscopy system and the processing of images were performed using IMARIS 10.0 software. Health mitochondrial looked hair or string like structures, whereas the damaged mitochondria exhibited a fragment or circular appearance.
Figure 2:
Figure 2:. Inhibition of mitochondrial respiration dynamics in the mouse microglial cells post exposure to the complex I inhibitor rotenone.
(A) Bioenergetics study to measure and analyze the effects of rotenone on mitochondrial dynamics in microglia. The microglial cells were incubated with rotenone (20 nM) for 24 h and then the plate was de-gassed and made ready for the OCR measurement using the Seahorse XFe24 analyzer. Mitochondrial dynamics were measured using three-stage injections of mito-stressors with stage 1: 0.75 μM oligomycin, stage 2: 1 μM FCCP, and stage 3: 1 μM antimycin A/Rotenone. Throughout these stages, the analyzer continuously measures OCR. (B) Phenogram (OCR vs. ECAR) depicting the comparison of oxidative phosphorylation and glycolytic states of the microglial mitochondria post treatment with rotenone.
Figure 3:
Figure 3:
Exposure of Dopaminergic neurons to neurotoxicants triggers exosome release-mediated activation of microglia, highlighting the interplay between neurodegeneration and neuroinflammation mechanisms involved in PD.

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