Regulation of uterine AHR battery gene expression by 17β-Estradiol is predominantly mediated by estrogen receptor α

The aryl hydrocarbon receptor (AHR) is known to mediate the cellular response to numerous xenobiotics including dioxin. Surprisingly AHR knockout mice provide evidence for the involvement of the AHR signalling cascade in estrogen regulated physiological functions of the female reproductive system. Several studies already aimed to investigate the impact of the AHR mediated xenobiotic response pathway on estrogen receptor (ER) signalling, whereas on contrary availability of data describing the effect of 17 beta-Estradiol (E2) on the AHR signalling cascade is rather limited. In this study we observed an inhibitory effect of E2 treatment on uterine Ahr, Arnt, Arnt2, Ahrr, Cyp1a1, Ugt1 and Nfe2l2 gene expression in ovariectomized Wistar rats, whereas Cyp1b1, Nqo1 and Gsta2 displayed an increased transcription. The usage of the ER selective agonists, 16 alpha-LE2 (ER alpha selective) and 8 beta-VE2 (ER beta selective), enabled us to distinguish between ER subtype specific responses. On mRNA level the observed changes in gene expression were mainly mediated by ER alpha except for the expression of Nqo1. In most cases the activation of ER beta caused effects opposite to the ones observed following activation of ER alpha. Despite the significant changes in AHR mRNA levels immunohistochemical staining uterine tissue section did not reveal changes of the AHR protein level. Taken together our results validate, support and extend the hypothesis of uterine crosstalk between AHR and ER signalling pathways. Furthermore they give an insight into how the AHR and its related genes may participate in E2 dependent uterine physiological processes and provide another potential mechanism of action for xenoestrogens.