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Background: An association between neuroinflammation and age-related neurologic disorders has been established but the molecular mechanisms and cell types involved have not been thoroughly characterized. Activity of the proinflammatory NLRP3 inflammasome is implicated in Alzheimer's and Parkinson's disease and our recent studies in patients suggest that dopaminergic neurons within the degenerating mesencephalon express NLRP3 throughout the progression of PD. Here, we directly test the impact of enhanced inflammasome activity in mesencephalic neurons by characterizing motor function, tissue integrity, and neuroinflammation in aging mice harboring hyperactivating mutations within the endogenous murine Nlrp3 locus, enabled only in cells expressing the dopaminergic neuron-specific Slc6a3 promoter., Methods: We compared mice harboring inducible alleles encoding the cryopyrin-associated periodic syndrome activating mutations Nlrp3 A350V and Nlrp3 L351P inserted into the endogenous mouse Nlrp3 locus. Tissue specific expression was driven by breeding these animals with mice expressing Cre recombinase under the control of the dopaminergic neuron-specific Slc6a3 promoter. The experimental mice, designed to express hyperactive NLRP3 only when the endogenous mouse Nlrp3 promotor is active in dopaminergic neurons, were analyzed throughout 18 months of aging using longitudinal motor function assessments. Biochemical and histologic analyses of mesencephalic tissues were conducted in 1- and 18-month-old animals., Results: We observed progressive and significant deficits in motor function in animals expressing Nlrp3 L351P , compared with animals expressing Nlrp3 WT and Nlrp3 A350V . Age-dependent neuroinflammatory changes in the mesencephalon were noted in all animals. Analysis of GFAP-immunoreactive astrocytes in the substantia nigra revealed a significant increase in astrocyte number in animals expressing Nlrp3 L351P compared with Nlrp3 WT and Nlrp3 A350V . Further analysis of Nlrp3 L351P striatal tissues indicated genotype specific gliosis, elevated Il1b expression, and both morphologic and gene expression indicators of proinflammatory A1 astrocytes., Conclusions: Dopaminergic neurons have the potential to accumulate NLRP3 inflammasome activators with age, including reactive oxygen species, dopamine metabolites, and misfolded proteins. Results indicate the Nlrp3 locus is active in dopaminergic neurons in aging mice, and that the hyperactive Nlrp3 L351P allele can drive neuroinflammatory changes in association with progressive behavioral deficits. Findings suggest neuronal NLRP3 inflammasome activity may contribute to neuroinflammation observed during normal aging and the progression of neurologic disorders.

Complex interactions between genetic and environmental factors are widely believed to underlie the incidence and progression of Parkinson's disease (PD). Rotenone is a naturally occurring metabolic toxin employed as an insecticide and piscicide identified as a risk factor for the development of PD in agricultural workers. The Nlrp3 inflammasome is an intracellular mediator that can initiate an inflammatory cascade in response to cellular stress. Reports by others indicating that NLRP3 expression was detectable in tissues obtained from Alzheimer's disease patients and that the PD-associated protein α-synuclein could activate inflammasomes in cultured glial cells, prompted us to test the prediction that Nlrp3 was required for the development of Parkinson's-like changes resulting from rotenone exposure in mice. We exposed wild type and Nlrp3-/- mice to chronic low doses of intragastric rotenone and conducted longitudinal behavioral and serum cytokine analysis followed by evaluation of neuroinflammatory and neurodegenerative endpoints in brain tissues. We observed progressive rotenone-dependent changes in serum cytokine levels and circulating leukocytes in wild type mice not observed in Nlrp3-/- mice. Analysis of brain tissues revealed Nlrp3-dependent neuroinflammation and nigral cell loss in mice exposed to rotenone as compared with mice exposed to vehicle alone. Together, our findings provide compelling evidence of a role for Nlrp3 in nigral degeneration and neuroinflammation resulting from systemic rotenone exposure and suggest that the suppression of NLRP3 activity may be a rational neuroprotective strategy for toxin-associated PD., (© The Author 2017. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)