Neurotoxicity of the Parkinson Disease-Associated Pesticide Ziram Is Synuclein-Dependent in Zebrafish Embryos

BACKGROUND: Exposure to the commonly used dithiocarbamate (DTC) pesticides is associated with an increased risk of developing Parkinson disease (PD), although the mechanisms by which they exert their toxicity are not completely understood. OBJECTIVE: We studied the mechanisms of zirams (a DTC fungicide) neurotoxicity in vivo. METHODS: Zebrafish (ZF) embryos were utilized to determine zirams effects on behavior, neuronal toxicity, and the role of synuclein in its toxicity. RESULTS: Nanomolar-range concentrations of ziram caused selective loss of dopaminergic (DA) neurons and impaired swimming behavior. Because ziram increases alpha-synuclein (alpha-syn) concentrations in rat primary neuronal cultures, we investigated the effect of ziram on ZF gamma-synuclein 1 (gamma 1). ZF express 3 synuclein isoforms, and ZF gamma 1 appears to be the closest functional homologue to alpha-syn. We found that recombinant ZF gamma 1 formed fibrils in vitro, and overexpression of ZF gamma 1 in ZF embryos led to the formation of neuronal aggregates and neurotoxicity in a manner similar to that of alpha-syn. Importantly, knockdown of ZF gamma 1 with morpholinos and disruption of oligomers with the molecular tweezer CLR01 prevented zirams DA toxicity. CONCLUSIONS: These data show that ziram is selectively toxic to DA neurons in vivo, and this toxicity is synuclein-dependent. These findings have important implications for understanding the mechanisms by which pesticides may cause PD.