Ahr2-dependence of PCB126 effects on the swim bladder in relation to expression of CYP1 and cox-2 genes in developing zebrafish

Abstract

The teleost swimbladder is assumed a homolog of the tetrapod lung. Both swimbladder and lung are developmental targets of persistent aryl hydrocarbon receptor (AHR1) agonists; in zebrafish (Danio rerio) the swimbladder 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 P4501 (CYP1) and cyclooxygenase 2 (Cox-2) in some Ahr-mediated developmental effects in zebrafish. We determined relationships between swimbladder 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 dependance of the effect of PCB126 on swimbladder using morpholinos targeting ahr2. One-day-old embryos were exposed to waterborne PCB126 or carrier (DMSO) for 24 h and then held in clean water until day 4, a normal time for swimbladder inflation. The effects of PCB126 were concentration-dependent with EC50 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 swimbladder inflation. Histological defects included a compaction of the developing bladder. Ahr2-morpholino treatment rescued the effect of PCB126 (5 nM) on swimbladder inflation and blocked induction of CYP1A, cox-2a, and cox-2b. With 2 nM PCB126 approximately 30% of eleutheroembryos2 failed to inflate the swimbladder, but there was no difference in CYP1 or cox-2 mRNA expression between those embryos and embryos showing inflated swimbladder. Our results indicate that PCB126 blocks swimbladder inflation via an Ahr2-mediated mechanism. This mechanism seems independent of CYP1 or cox-2 mRNA induction but may involve abnormal development of swimbladder cells.

Diluted bitumen causes deformities and molecular responses indicative of oxidative stress in Japanese medaka embryos

“…Malformation of the swim bladder has been a characteristic indicator of developmental toxicity demonstrated in many species of fishes in response to numerous types of waterborne chemicals, e.g., disinfectants (Sanabria et al, 2009), biphenyls (Jönsson et al, 2012), herbicides (González-Doncel et al, 2008), and even urban storm water run-off (Skinner et al, 1999). This condition may be attributed to compounds that alter the air-water interface, like oil itself.…”

Involvement of COX2–thromboxane pathway in TCDD-induced precardiac edema in developing zebrafish

“…Tissue localization of COX2b, as well as COX2a, should be examined in future studies, A single study reported that COX2a was detected within sprouting gill arteries and vasculature of the intestine of 4 dpf eleutheroembryos (Grosser et al, 2002). Recently, it was reported that PCB126 induced both COX2a and COX2b in 4 dpf eleutheroembryos (Jönsson et al, 2012), which is reminiscent of the results of Dong et al (2010), who reported COX2 induction by TCDD and the correlation between COX2 induction and pericardial edema in developing medaka. The present results provide important evidence for the involvement of COX2b in precardiac edema formation around heart by TCDD.…”

“…qRT-PCR analysis was performed in Real-Time PCR Detector (Chromo4: Bio-Rad, Hercules, CA) using Thunderbird qPCR mix containing SYBR Green (Toyobo, Osaka, Japan). The same primers as reported in Jönsson et al (2012) were used; COX2b (GenBank ID: NM_001025504.2): F-GGCTCATCCTTATTGGTGAGACTAT and R-TCGGGATCAAACTTGAGCTTAAAATA (5' to 3' sequences), and COX2a (GenBank ID: NM_153657.1): F-ACTACCCCTGAGCTTCTCACA and R-GATGCTGTTGATGATATCCCAGATTG.…”

Mixture-specific gene expression in zebrafish ( Danio rerio ) embryos exposed to perfluorooctane sulfonic acid (PFOS), perfluorohexanoic acid (PFHxA) and 3,3′,4,4′,5-pentachlorobiphenyl (PCB126)

“…The latter was selected as a reference chemical as it represents one of the most abundant planar polychlorobiphenyl which can be found in the ng/L range in the environment (Ge et al, 2014). Moreover, its toxicity during zebrafish development is well described (Brown et al, 2002;Grimes et al, 2008;Jonsson et al, 2007a;Jonsson et al, 2012;Liu et al, 2015;. PCB126 is recognized as a strong inducer of biotransformation enzymes (i.e.…”