Long-Term Exposure to 6-PPD Quinone Inhibits Glutamate Synthesis and Glutamate Receptor Function Associated with Its Toxicity Induction in <i>Caenorhabditis elegans</i>

Abstract

6-PPD quinone (6-PPDQ) is widely distributed in environments. In Caenorhabditis elegans, we first examined the effects of 6-PPDQ on glutamate synthesis and receptor function by analyzing glutamate content, related gene expression, and phenotypes after RNAi of these genes. Moreover, we performed glutamate treatment after 6-PPDQ exposure to determine the potential pharmacological effects of glutamate against 6-PPDQ toxicity. After exposure, the glutamate content was reduced by 0.1–10 μg/L 6-PPDQ, which was due to decreased expression of W07E1.1, glna-1/2/3, and alh-6 governing glutamate synthesis from α-ketoglutarate, glutamine, and proline. RNAi of W07E1.1, glna-1/2/3, and alh-6 decreased glutamate content in 6-PPDQ-exposed nematodes, and caused susceptibility to 6-PPDQ toxicity. Among glutamate transporter genes, glt-1 expression was decreased by 0.1–10 μg/L 6-PPDQ. Moreover, 0.1–10 μg/L 6-PPDQ decreased glutamate receptor genes (glr-1, glr-2, and glr-4), and their expression was decreased by RNAi of W07E1.1, glna-1/2/3, alh-6, and glt-1. RNAi of these receptor genes resulted in susceptibility to 6-PPDQ toxicity, and daf-7, jnk-1, and dbl-1 were identified as targets of neuronal glr-1, glr-2, and glr-4. Furthermore, 5 mM glutamate suppressed 6-PPDQ toxicity and increased expression of glr-1, glr-2, and glr-4. Our results demonstrated the risk of 6-PPDQ exposure in disrupting glutamate synthesis and affecting function of glutamate receptors, which was related to 6-PPDQ toxicity induction.

Keywords

• 6-PPDQ toxicity
• glutamate metabolism
• glutamate receptor
• nematode