A transcriptomics-based analysis of mechanisms involved in the neurobehavioral effects of 6PPD-quinone on early life stages of zebrafish

As an emerging pollutant frequently detected in aquatic ecosystems, the toxicity of N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine-quinone (6PPD-quinone) on fish has been confirmed, but insight into the mechanisms underlying those adverse effects is still limited. Thus, we exposed zebrafish embryos to 6PPD-quinone at 0, 0.25, 2.5, and 25 μg/L until 120 h post-fertilization (hpf), and investigated the variations in their development, behavior, monoamine neurotransmitter levels, and transcriptional profile. Exposure to 6PPD-quinone notably elevated the heart rate of zebrafish at 48 hpf (at 2.5 and 25 μg/L) and 72 hpf (at 0.25, 2.5, and 25 μg/L). In the dark-light transition test, the locomotor activity of zebrafish larvae exposed to 6PPD-quinone significantly increased, especially in the dark periods. Exposure to 6PPD-quinone also altered the dopamine level and its turnover in zebrafish, which exhibited significant correlations to their locomotor activity. RNA sequencing identified 394 differentially expressed genes (DEGs), most of which have the molecular function of binding and catalytic activity. Five DEGs were predicted as the key driver genes in the protein-protein interaction networks associated with circadian rhythm (i.e., npas2), protein processing in endoplasmic reticulum (i.e., hsp90b1 and pdia4), and estrogen signaling pathway (i.e., hsp90aa1.1 and hsp90aa1.2). Our findings provide more insights into mechanisms underlying the toxicity of 6PPD-quinone to teleosts and highlight the necessity to assess its potential risks to aquatic ecosystems.