Nicholas School of the Environment, Duke University, Box 90328, Durham, NC 27708, USA.
Aquat Toxicol. 2013 Oct 15;142-143:336-46. doi: 10.1016/j.aquatox.2013.09.007. Epub 2013 Sep 16.
Various environmental contaminants are known agonists for the aryl hydrocarbon receptor (AHR), which is highly conserved across vertebrate species. Due to gene duplication events before and after the divergence of ray- and lobe-finned fishes, many teleosts have multiple AHR isoforms. The zebrafish (Danio rerio) has three identified AHRs: AHR1A and AHR1B, the roles of which are not yet well elucidated, and AHR2, which has been shown to mediate the toxicity of various anthropogenic compounds including dioxins, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). In this study, we sought to explore the role of the two AHR1 isoforms in PAH- and PCB-induced toxicity in zebrafish embryos utilizing morpholino gene knockdown of the AHR isoforms. Knockdown of AHR1B did not affect the toxicity of PAH mixtures or PCB-126, whereas knockdown of AHR1A exacerbated the cardiac toxicity caused by PAH mixtures and PCB-126. Knockdown of AHR1A did not impact the mRNA expression of CYP1A, CYP1B1, and CYP1C1 in exposed embryos, but it did result in increased CYP1 activity in exposed embryos. As has been shown previously, knockdown of AHR2 resulted in protection from PAH- and PCB-induced cardiac deformities and prevented CYP1 enzyme activity in exposed embryos. Co-knockdown of AHR1A and AHR2 resulted in an intermediate response compared to knockdown of AHR1A and AHR2 individually; co-knockdown did not exacerbate nor protect from PAH-induced deformities and embryos exhibited an intermediate CYP1 enzyme activity response. In contrast, co-knockdown of AHR1A and AHR2 did protect from PCB-126-induced deformities. These results suggest that AHR1A is not a nonfunctional receptor as previously thought and may play a role in the normal physiology of zebrafish during development and/or the toxicity of environmental contaminants in early life stages.
各种环境污染物已知是芳香烃受体 (AHR) 的激动剂，AHR 在脊椎动物中高度保守。由于射线鳍鱼和肺鱼分化前后的基因复制事件，许多硬骨鱼有多个 AHR 同工型。斑马鱼 (Danio rerio) 有三种已鉴定的 AHR：AHR1A 和 AHR1B，其作用尚未得到很好的阐明，以及 AHR2，已显示出可介导各种人为化合物的毒性，包括二恶英、多氯联苯 (PCBs) 和多环芳烃 (PAHs)。在这项研究中，我们试图利用 AHR 同工型的 morpholino 基因敲低来探索两种 AHR1 同工型在 PAH 和 PCB 诱导的斑马鱼胚胎毒性中的作用。AHR1B 的敲低不影响 PAH 混合物或 PCB-126 的毒性，而 AHR1A 的敲低加剧了 PAH 混合物和 PCB-126 引起的心脏毒性。AHR1A 的敲低不影响暴露胚胎中 CYP1A、CYP1B1 和 CYP1C1 的 mRNA 表达，但确实导致暴露胚胎中 CYP1 活性增加。如前所述，AHR2 的敲低导致对 PAH 和 PCB 诱导的心脏畸形的保护，并防止暴露胚胎中 CYP1 酶活性。AHR1A 和 AHR2 的共敲低与单独敲低 AHR1A 和 AHR2 相比导致中间反应；共敲低既没有加剧也没有保护免受 PAH 诱导的畸形，胚胎表现出中间 CYP1 酶活性反应。相比之下，AHR1A 和 AHR2 的共敲低确实可以保护免受 PCB-126 引起的畸形。这些结果表明，AHR1A 不是以前认为的无功能受体，它可能在斑马鱼发育过程中的正常生理和/或早期生命阶段环境污染物的毒性中发挥作用。
