Dept. of Environmental Toxicology, Evolutionary Biology, Centre, Uppsala University, Norbyvägen 18A, 752 36 Uppsala, Sweden.
Toxicol Appl Pharmacol. 2012 Dec 1;265(2):166-74. doi: 10.1016/j.taap.2012.09.023. Epub 2012 Oct 2.
The teleost swim bladder is assumed a homolog of the tetrapod lung. Both swim bladder and lung are developmental targets of persistent aryl hydrocarbon receptor (AHR(2)) agonists; in zebrafish (Danio rerio) the swim bladder fails to inflate with exposure to 3,3',4,4',5-pentachlorobiphenyl (PCB126). The mechanism for this effect is unknown, but studies have suggested roles of cytochrome P450 1 (CYP1) and cyclooxygenase 2 (Cox-2) in some Ahr-mediated developmental effects in zebrafish. We determined relationships between swim bladder inflation and CYP1 and Cox-2 mRNA expression in PCB126-exposed zebrafish embryos. We also examined effects on β-catenin dependent transcription, histological effects, and Ahr2 dependence of the effect of PCB126 on swim bladder using morpholinos targeting ahr2. One-day-old embryos were exposed to waterborne PCB126 or carrier (DMSO) for 24h and then held in clean water until day 4, a normal time for swim bladder inflation. The effects of PCB126 were concentration-dependent with EC(50) values of 1.4 to 2.0 nM for induction of the CYP1s, 3.7 and 5.1 nM (or higher) for cox-2a and cox-2b induction, and 2.5 nM for inhibition of swim bladder inflation. Histological defects included a compaction of the developing bladder. Ahr2-morpholino treatment rescued the effect of PCB126 (5 nM) on swim bladder inflation and blocked induction of CYP1A, cox-2a, and cox-2b. With 2nM PCB126 approximately 30% of eleutheroembryos(3) failed to inflate the swim bladder, but there was no difference in CYP1 or cox-2 mRNA expression between those embryos and embryos showing inflated swim bladder. Our results indicate that PCB126 blocks swim bladder inflation via an Ahr2-mediated mechanism. This mechanism seems independent of CYP1 or cox-2 mRNA induction but may involve abnormal development of swim bladder cells.
硬骨鱼的鳔被认为是四足动物肺的同源物。鳔和肺都是持久性芳香烃受体（AHR（2））激动剂的发育靶标；在斑马鱼（Danio rerio）中，暴露于 3,3',4,4',5-五氯联苯（PCB126）会导致鳔无法充气。这种效应的机制尚不清楚，但研究表明细胞色素 P450 1（CYP1）和环氧化酶 2（Cox-2）在一些 Ahr 介导的斑马鱼发育效应中起作用。我们确定了在 PCB126 暴露的斑马鱼胚胎中鳔充气与 CYP1 和 Cox-2 mRNA 表达之间的关系。我们还使用靶向 ahr2 的 morpholino 检查了对β-连环蛋白依赖性转录、组织学效应和 Ahr2 对 PCB126 对鳔影响的依赖性，以研究对β-连环蛋白依赖性转录、组织学效应和 Ahr2 对 PCB126 对鳔影响的依赖性。将 1 天大的胚胎暴露于水相 PCB126 或载体（DMSO）中 24 小时，然后在干净的水中饲养至第 4 天，这是鳔充气的正常时间。PCB126 的作用呈浓度依赖性，CYP1s 的 EC（50）值为 1.4 至 2.0 nM，cox-2a 和 cox-2b 的诱导分别为 3.7 和 5.1 nM（或更高），而对鳔充气的抑制则为 2.5 nM。组织学缺陷包括发育中膀胱的紧密性。Ahr2-morpholino 处理挽救了 PCB126（5 nM）对鳔充气的作用，并阻断了 CYP1A、cox-2a 和 cox-2b 的诱导。用 2nM PCB126 约 30%的 eleutheroembryos（3）未能使鳔充气，但在这些胚胎和显示充气鳔的胚胎之间，CYP1 或 cox-2 mRNA 的表达没有差异。我们的结果表明，PCB126 通过 Ahr2 介导的机制阻断鳔充气。该机制似乎独立于 CYP1 或 cox-2 mRNA 的诱导，但可能涉及鳔细胞的异常发育。
