Pesticide-Mediated Generation of a Toxic Neurotransmitter Metabolite

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PROJECT SUMMARY. Exposure to the organochlorine dieldrin predisposes individuals to Parkinson's Disease (PD); however, the mechanisms linking exposure to disease unknown. Dieldrin can disrupt DA homeostasis but alone may be insufficient for loss of dopamine (DA) neurons, and neurodegeneration may require an additional “hit”. Several animal models have demonstrated that altering DA homeostasis, metabolism and/or trafficking, yields progressive loss of DA neurons; therefore, a genetic variation modifying DA metabolism may be an additional “hit” that has toxic synergy with pesticide exposure. Disruption of DA homeostasis generates toxic intermediates such as ROS and aldehydes (3,4-dihydroxyphenylacetaldehyde, DOPAL), via monoamine oxidase. Similar to PD, there is evidence that dieldrin is a risk factor for Alzheimer's Disease (AD). It has been proposed that altered NE homeostasis is linked to the production of toxic species and cell injury relevant to AD. As with DA, NE is biotransformed via monoamine oxidase to an aldehyde (3,4- dihydroxyphenylglycolaldehyde, DOPEGAL), which is highly protein reactive and toxic. Early AD neuropathology occurs in the locus coeruleus (LC), a major site of NE innervation in the brain, and involves neurofibrillary tangles of the protein Tau, following its cleavage by an asparagine proteinase (AEP). Recent reports demonstrated that the NE metabolite, DOPEGAL, activates AEP to cleave Tau and induce Tau aggregation. Modulation of the extracellular matrix (ECM) is thought to be important for AD pathology and may influence LC dynamics and NE metabolism. We hypothesize NE metabolism/trafficking as a target for dieldrin, producing elevated levels of DOPEGAL which affects Tau processing and yields Tau aggregation. In addition, we posit that modulation of ECM as the second “hit” that influences cellular responses to dieldrin. The proposed work is highly relevant to AD neuropathogenesis and builds upon the previously funded application. The goal of this supplement is to elucidate mechanisms underlying environmental risk factors for AD, specifically focusing on the interaction of the pesticide dieldrin with NE metabolism in neurons and the role of the ECM. The central hypothesis is that dieldrin targets NE metabolism and/or trafficking in neurons, yielding build-up of reactive metabolites that initiate toxic pathways, such as tau fibrillization, injuring neurons in an ECM-dependent manner. Two specific aims will be completed: 1) Elucidate the outcomes of pesticide/dieldrin exposure on noradrenergic cells for production of the toxic species DOPEGAL. 2) Determine the contribution of the ECM to pesticide- and DOPEGAL-mediated cellular injury. These Specific Aims will build upon previous work to address key mechanistic questions for AD regarding critical cellular interactions yielding vulnerability of neurons to pesticides. These innovative studies are significant to identifying key mechanistic targets of neurotoxic pesticides and to identifying potential biomarkers for individuals at risk for developing AD.