An Aryl Hydrocarbon Receptor Agonist Amplifies the Mitogenic Actions of Estradiol in Granulosa Cells: Evidence of Involvement of the Cognate Receptors1

Abstract

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that, besides mediating toxic responses, may have a central role in ovarian physiology. Studying the actions of AHR ligands on granulosa cells function, we have found that beta-naphthoflavone amplifies the comitogenic actions of FSH and 17beta-estradiol in a dose-dependent manner. This amplification was even greater in cells that overexpress the AHR and was reversed by cotreatment with the AHR antagonist alpha-naphthoflavone, suggesting that this effect is mediated by the AHR. The estrogen receptor is likewise implicated in this phenomenon, because a pure antiestrogen abolished the described synergism. However, the more traditional inhibitory AHR-estrogen receptor interaction was observed on the estrogen response element-driven transcriptional activity. On the other hand, alpha-naphthoflavone inhibited dose-dependently the mitogenic actions of FSH and 17beta-estradiol. Beta-naphthoflavone induced the expression of Cyp1a1 and Cyp1b1 transcripts, two well-characterized AHR-inducible genes that code for hydroxylases that metabolize estradiol to catecholestrogens. Nevertheless, the positive effect of beta-naphthoflavone on proliferation was not caused by increased metabolism of estradiol to catecholestrogens, because these compounds inhibited the hormonally stimulated DNA synthesis. This latter inhibition exerted by catecholestrogens suggests that these hydroxylases would play a regulatory point in granulosa cell proliferation. Our study indicates that AHR ligands modulate the proliferation of rat granulosa cells, and demonstrates for the first time that an agonist of this receptor is able to amplify the comitogenic action of classical hormones through a mechanism that might implicate a positive cross-talk between the AHR and the estrogen receptor pathways.

The Aryl Hydrocarbon Receptor Affects Mouse Ovarian Follicle Growth via Mechanisms Involving Estradiol Regulation and Responsiveness1

“…Thus, the data also indicate that the slow growth of AhRKO follicles is due to reduced granulosa cell proliferation in AhRKO follicles compared to WT follicles in vitro. These findings are consistent with the recent work of Bussman et al [34], which indicates that AHR ligands modulate the proliferation of rat granulosa cells.…”

Testosterone-Dependent Interaction between Androgen Receptor and Aryl Hydrocarbon Receptor Induces Liver Receptor Homolog 1 Expression in Rat Granulosa Cells

“…ARNT is an AHR-interacting protein found in the nucleus that facilitates AHR regulation of gene expression (43). Both AHR and ARNT are expressed in granulosa cells of several species (44,45). AHR knockout mice are subfertile due to folliculogenesis defects, impaired aromatase expression (46), and slow growth of early antral follicles (47).…”

Improvement of Chicken Primordial Germ Cell Maintenance In Vitro by Blockade of the Aryl Hydrocarbon Receptor Endogenous Activity

“…The primer sequences and PCR protocol and parameters used to amplify the hydroxylase target cDNA were those described by Bussmann et al (2013). We have previously demonstrated that minor changes in CYP1A mRNA levels are certainly detected with this technique (Bussmann and Barañao, 2008;Bussmann et al, 2006Bussmann et al, , 2013, and we have shown and established that AHR activation and blockade through antagonist treatment can be definitely verified with this methodological approach and with these techniques in chicken cells (Bussmann et al, 2013).…”