New insights into the regulation of cyp3a65 expression in transgenic tg(cyp3a65:GFP) zebrafish embryos

Facing the need for alternative models allowing assessment of metabolic-endocrine disrupting chemicals (MDCs), especially in poorly investigated tissues such as the intestine, we recently developed a transgenic zebrafish embryo in vivo model, tg(cyp3a65:GFP), expressing the Green Fluorescent Protein (GFP) under the control of the zebrafish cyp3a65 promoter, ortholog of human cyp3a4, a gene coding for a key enzyme of intestinal xenobiotic and endobiotic metabolism. In this study, we aimed to better understand the regulation of cyp3a65 expression by zfPXR, zfAhR2, and zfGR zebrafish orthologs of well-known human xenosensors PXR and AhR, and steroid nuclear receptor GR. For this purpose, we performed zebrafish embryo tg(cyp3a65:GFP) (co)exposures to a variety of agonists (clotrimazole, TCDD, fluticasone propionate) and antagonists (econazole nitrate, CH223181, RU486), which were characterized using in vitro zebrafish reporter gene assays. We show that zfPXR and zfAhR2 cooperate to positively regulate cyp3a65 expression, involving different transcription factors and their interaction. Moreover, for the first time, we show that zfGR agonist strongly inhibits the constitutive expression of cyp3a65, and we hypothesized the possible involvement of the transcriptional factor zfHNF4α. These results provide a better understanding of the regulation of zebrafish cyp3a65 expression, highlighting the complex interaction between different transcription factors, which is consistent with the multiple regulatory pathways of cyp3a4 in humans. Our data support the idea that this gene is a target of multiple contaminants capable of interacting with zfPXR, zfAhR2 and zfGR and highlights the relevance of the tg(cyp3a65:GFP) model to screen chemicals potentially acting as MDCs based on their modes of action at the intestinal level, which could be relevant for hazard assessment of chemicals for human and environmental health.