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Neurotoxicity of the Parkinson’s Disease-Associated Pesticide Ziram is Synuclein Dependent

  • Author(s): Lulla, Aaron
  • Advisor(s): Bronstein, Jeff M
  • et al.

Parkinson’s disease (PD) is the second most common neurodegenerative disease, affecting seven to ten million people worldwide. Familial forms of PD account for 5-10% of all PD cases suggesting that other factors such as the environment have a role in the development of sporadic cases of PD. Epidemiological studies have indicated that exposure to pesticides increases the risk for PD. Ziram, a dithiocarbamate fungicide commonly used in California, increases the risk of PD for individuals living and working in areas where the pesticide is sprayed. Ziram has previously been found in vitro to cause selective dopaminergic cell toxicity, inhibition of the ubiquitin proteasome system (UPS), and increased α-synuclein (α-syn) levels in primary neuronal cultures. In this dissertation we utilize zebrafish embryos (ZF, Danio rerio) to study ziram in an in vivo system and to determine if ziram’s toxicity is mediated via synuclein.

We found that ziram is toxic to ZF at nanomolar concentrations and caused selective loss of dopaminergic (DA) neurons and impaired swimming behavior in ZF. Since ziram increases α-syn concentrations in rat primary neuronal cultures, we investigated the effect of ziram on ZF γ-synuclein 1 (γ1). ZF express 3 synuclein isoforms and ZF γ1 appears to be a functional homologue of α-syn. We found that recombinant ZF γ1 formed fibrils in vitro and overexpression of ZF γ1 in ZF embryos led to the formation of neuronal aggregates and neurotoxicity similarly to α-syn. Importantly, knockdown of ZF γ1 with morpholinos or disruption of oligomers with the molecular tweezer CLR01 protected against ziram’s DA toxicity.

Over the course of this dissertation we have demonstrated that ziram is selectively toxic to DA neurons in vivo and that its toxicity is synuclein-dependent. These findings provide potentially important mechanistic implications on how ziram and possibly other environmental toxins can contribute to the pathogenesis of neurodegenerative disorders such as PD.

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