Pre-differentiation exposure to low-dose of atrazine results in persistent phenotypic changes in human neuronal cell lines

Exposures to organic pesticides, particularly during a developmental window, have been associated with various neurodegenerative diseases later in life. Atrazine (ATZ), one of the most used pesticides in the U.S., is suspected to be associated with increased neurodegeneration later in life but few studies assessed the neurotoxicity of developmental ATZ exposure using human neuronal cells. Here, we exposed human SH-SY5Y cells to 0.3, 3, and 30 ppb of ATZ prior to differentiating them into dopaminergic-like neurons in ATZ-free medium to mimic developmental exposure. The differentiated neurons exhibit altered neurite outgrowth and SNCA pathology depending on the ATZ treatment doses. Epigenome changes, such as decreases in 5mC (for 0.3 ppb only), H3K9me3, and H3K27me3 were observed immediately after exposure. These alterations persist in a compensatory manner in differentiated neurons. Specifically, we observed significant reductions in 5mC and H3K9me3, as well as, an increase in H3K27me3 in ATZ-exposed cells after differentiation, suggesting substantial chromatin rearrangements after developmental ATZ exposure. Transcriptional changes of relevant epigenetic enzymes were also quantified but found to only partially explain the observed epigenome alteration. Our results thus collectively suggest that exposure to low-dose of ATZ prior to differentiation can result in long-lasting changes in epigenome and increase risks of SNCA-related Parkinson’s Disease.