Induction of oxidative stress and the transcription of genes related to apoptosis in rare minnow (Gobiocypris rarus) larvae with Aroclor 1254 exposure

• Aroclor 1254 induced genes involved in oxidative stress responses and apoptotic pathway.
• Aroclor 1254 induced H2O2 and reduced protein thiol content.
• Nrf2 and NF-κB may be involved in induction of antioxidant genes.
• DNA damage, disrupting mitochondrial membrane integrity and JNK-mediated apoptotic pathway may be involved in waterborne Aroclor1254-induced apoptosis.

Polychlorinated biphenyls (PCBs) are a group of environmental contaminants widely dispersed in aquatic system. Recent data have shown that Aroclor 1254 (a highly chlorinated PCB mixture) has the potential to induce oxidative stress. The antioxidant genes are usually up-regulated in response to the oxidative stress. However, the mechanisms underlying the modulation are little known. We hypothesized that nuclear factors erythroid 2-related factor 2 (Nrf2) and nuclear factor-kappa B (NF-κB) might be involved in the regulation. In this study, rare minnow (Gobiocypris rarus) larvae were exposed to the Aroclor 1254 at four concentrations (5, 50, 500 and 5000 μg/L) for 7 days. We found that the mRNA expressions of antioxidant genes (Cu/Zn-sod, Mn-sod, Cat, Gpx1 and Gclc) were strongly enhanced by Aroclor 1254 at high concentrations. H2O2 was significantly induced by 500 and 5000 μg/L Aroclor 1254 exposure and protein thiol significantly decreased with 5000 μg/L Aroclor 1254 exposure. The expression of Nrf2 and NF-κB were significantly up-regulated. Taken together, we proposed that the activation of Nrf2 and NF-κB by ROS might be a potential mechanism underlying the antioxidant gene expression induction in G. rarus larvae by Aroclor 1254. Furthermore, we investigated that the expression of genes related with apoptosis. The gene expression patterns reveal that waterborne Aroclor 1254-induced apoptosis is probably through DNA damage (p53 and p53 upregulated modulator of apoptosis (Puma)), disrupting mitochondrial membrane integrity (B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X (Bax)) and c-jin N-terminal kinase (JNK)-mediated apoptotic pathway (thioredoxin 1 (Trx1) and c-jun N-terminal kinase (JNK)). Aroclor 1254 at 5 μg/L did not cause any changes in G. rarus. The findings will help us to understand the toxicological mechanism of Aroclor 1254 in fish and properly assess the risk of the environmental contaminant.