Slc6a3-dependent expression of a CAPS-associated Nlrp3 allele results in progressive behavioral abnormalities and neuroinflammation in aging mice

Abstract

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.

Neuronal NLRP3 is a parkin substrate that drives neurodegeneration in Parkinson’s disease

“…Molecular signatures of this process are evident in human postmortem DA neurons providing pathophysiologic relevance. Consistent with the idea of neuron-specific inflammasome activation is the observation of neuronal activation of the AIM2 inflammasome in synapse elimination during neurodevelopment (Lammert et al, 2020) and the observation of expression of NLRP3 in DA neurons (von Herrmann et al, 2020;von Herrmann et al, 2018) as well as the documentation of neuronal activation of Casp1 in pathologic a-Syn models (Ganjam et al, 2019;Wang et al, 2016). Assembly of the NLRP3 inflammasome complex in PARKIN-deficient hDA neurons did not result in detectable IL-1b or IL-18 secretion, although it did result in increased levels of gasdermin-D cleavage, suggesting that the neurons might be dying via pyroptotic cell death.…”

Role of NLRP3 in Parkinson's disease: Specific activation especially in dopaminergic neurons

“…In that study, Panicker et al further observed elevated expression levels of NLRP3 and the effector protein Caspase-1 in a PD animal model as well and confirmed by immunohistochemistry that the activation of NLRP3 inflammasome suggesting that NLRP3 inflammasome within DANs are activated in a cell-autonomous fashion [ 13 ]. Consistent with this, multiple in vitro models of PD confirm elevated NLRP3 expression in DANs [ 12 , 64 , 65 ]. For the construction of a PD model by treating DANs MES23.5 cells with 6-hydroxydopamine (6-OHDA), for example, elevated NLRP3, ASC, and Caspase-1 protein expression and decreased pro-Caspase-1 protein expression were detected in the model group, suggesting that there is activation of NLRP3 inflammasome in the MES23.5 cells further leading to apoptosis of DANs [ 65 ].…”

Intestinal Inflammation and Parkinson’s Disease

“…Moreover, α-synuclein can activate the NLRP3 inflammasome in human microglia [ 111 ]. It has been identified that the L351P NLRP3 mutation contributes to motor abnormalities in animals by activating astrocytes [ 112 ]. However, NLRP3 rs7525979 has been reported as an SNP associated with a significantly reduced risk of developing PD and this synonymous SNP alters the efficiency of NLRP3 translation, thereby affecting NLRP3 protein stability, ubiquitination state, and solubility [ 113 ].…”