The etiology of Parkinson's disease (PD) involves gene/environment interaction. While most of the identified genetic mutations affect the ubiquitin-proteasome system (UPS), epidemiological studies and clinical case reports have strongly suggested the association between pesticide exposure and increased incidence of PD. In animal models, selective toxicities to the nigrostriatal dopaminergic neurons occur after systemic exposure to rotenone and paraquat. Oxidative stress is a common mediator of pesticide-induced neurotoxicity. It contributes to PD-related pathological changes such as formation of a-synuclein aggregates and inhibition of proteasomal function. However, the molecular targets of oxidative damage have not been clearly defined and the mechanistic link between mitochondria! and proteasomal dysfunction remains to be determined. In our preliminary studies, we have shown that mitochondrial thioredoxin (mtTrx; Trx2) is particularly susceptible to oxidation induced by a variety of environmental toxicants, including peroxides, rotenone, MPP+ and paraquat. Submicromolar concentrations of rotenone induced persistent oxidation of mtTrx and redistribution of mtTrx to the cytoplasm. Chronic exposure to nanomolar concentrations of rotenone resulted in decreased mtTrx protein. Overexpression of mtTrx protected cells from oxidant-induced apoptosis and inhibited a-synuclein aggregation caused by chronic rotenone toxicity. Downregulation of the mitochondrial thioredoxin reductase (TrxR 2) led to decreased mature mtTrx while increased its precursor form. Furthermore, we identified that mtTrx interacted with mitochondrial heat shock protein 60 which is a key component of the mitochondrial protein processing machinery. Based on these findings, we hypothesize that selective targeting of mtTrx by pesticides and the ensuring oxidation of mtTrx lead to impaired mitochondrial protein import. The hypothesis will be tested with two specific aims.
Specific aim 1 is to determine whether the redox status and expression level of mtTrx control the sensitivity to pesticide-induced toxicity in cultured neuronal cells.
Specific aim 2 is to determine whether the pesticide-induced oxidation inhibits the import of mtTrx and other nuclear DMA-encoded mitochondrial proteins. Results from these studies will define novel protein targets of oxidative injury and will facilitate our understanding towards the molecular mechanisms of environmental toxicities associated with PD.
