Parkinson?s disease (PD) is a progressive, neurodegenerative disorder characterized by debilitating motor symptoms. PD progression is characterized by loss of dopaminergic (DA) neurons in the substantia nigra pars compacta and accumulation of alpha-synuclein immunoreactive protein aggregates. PD has long been associated with neuroinflammation but it is not clear how PD-associated neuroinflammation is related to neuronal cell death. While a small percentage of PD cases can be attributed to genetic mutations, the molecular mechanisms underlying the initiation and progression of the more common sporadic form of PD are currently not well understood. The NLRP3 inflammasome is a multi-protein complex capable of initiating inflammation in response to cellular stress, including PD-associated factors such as reactive oxygen species and pathologically misfolded proteins. NLRP3 activity is best characterized in innate immune cells and microglia but our recent studies have identified elevated levels of NLRP3 expression in surviving DA neurons in mesencephalic tissues obtained from PD patients suggesting the possibility that DA neurons themselves may also be a cellular origin for inflammasome activity. In parallel studies, we identified an NLRP3 variant, single nucleotide polymorphism (SNP) rs7525979, to be associated with a decreased risk of classical PD using exome sequencing data obtained from the Parkinson?s Progression Markers Initiative. Our mechanistic studies in HEK293 cells suggest that rs7525979 inactivates NLRP3 but we do not know whether the SNP suppresses inflammasome activity in neurons. Additionally, we do not know if neuronal inflammasome activity is associated with neurodegeneration. We present two aims to directly address these outstanding questions. In our first aim, we will determine the impact of rs7525979 on NLRP3 inflammasome function in CNS cells including DA neurons. After genetically engineering a panel of CNS cell models, we will conduct studies to characterize classical indications of NLRP3 inflammasome activation, PD-associated neuronal pathologies including mitochondrial stress and misfolded protein aggregates, and measure levels of inflammasome-induced cell death, a process known as pyroptosis. In our second aim, we will determine if enhanced NLRP3 activity in DA neurons results in neuroinflammation and nigral cell loss in mice. To do so, we developed a DA neuron specific gain-of-function NLRP3 mouse model, and have already aged our first cohort of animals to 18 months observing longitudinal impairment of motor function. We plan to conduct a complete biochemical and histologic longitudinal analysis of the model to more fully understand the impact of enhanced NLRP3 inflammasome activity in DA neurons on both age-related neuroinflammation and neurodegeneration. Characterizing the functional impact of a neuroprotective genetic alteration in NLRP3 and determining whether neurogenic inflammasome activity can cause parkinsonism in mice will shed light on the underlying mechanisms of PD- associated neuroinflammation and help identify novel therapeutic targets for treatment and prevention of PD.
Neuroinflammation is associated with the development and progression of Parkinson?s disease. We propose to evaluate the cellular origins of neuroinflammation and characterize changes in the pro-inflammatory NLRP3 gene associated with a reduced risk of PD. Studies will shed light on the molecular basis of Parkinson?s disease and may help identify novel therapeutic targets for the treatment of patients with PD.
