Female reproductive health: Species and ligand-specific endometrial differences to hormones and aryl hydrocarbon receptor activation

Abstract

Endometrial diseases affect up to approximately 10% of women in their reproductive age. Yet, current testing strategies in chemical risk assessment do not adequately address endometrial health, partly because good (animal-free and human relevant) models are lacking. The overall aim of this thesis was to address the species-specific differences between human and rat endometrium, as well as to assess tissue-specific and ligand-specific differences in response to aryl hydrocarbon receptor (AHR) activation. A 3D endometrial model was developed in Chapter 2 using healthy human primary endometrial cells. This endometrial model consists of a bottom layer where an extracellular matrix scaffold encloses endometrial primary stromal cells, and an upper layer of endometrial primary epithelial cells. The endometrial model was subjected to hormones to mimic the proliferative phase and secretory phase of the menstrual cycle. A comparable model was established using primary rat endometrial cells. This chapter showed that hormones modulated the gene expression comparable to the human in vivo situation. Also, differences were observed between responses in the human and rat endometrial models with respect to hormones, as well as AHR ligands TCDD, laquinimod and its primary metabolite DELAQ. In Chapter 3 the interplay between the AHR and estrogen signaling in endometrial tissue was further explored in primary endometrial epithelial cells. Again, we observed the opposing effects of AHR ligands between human and rat endometrial cells. Differential regulation of this receptor between human and rat tissue was also observed with respect to hormonal action. In addition, the inhibitory effect on estrogen signaling upon AHR activation was only observed in the human endometrial cells, and not in the rat endometrial cells. The research in Chapter 2 and Chapter 3 showed that the rat endometrium does not reflect the human situation. We assessed another aspect of human-rat differences within the hormonal regulatory feedback system in Chapter 4. The effect of AHR activation on prolactin secretion from the pituitary in rats was assessed. In Chapter 4, the prolactin regulation was compared between rat primary pituitary cells and two rat pituitary cell lines, GH-3 and RC-4BC. It was observed that these pituitary cell lines do not reflect prolactin regulation in vivo, as they showed different responses to prolactin inhibitor quinpirole and prolactin stimulant thyrotropin-releasing hormone compared to the primary pituitary cells. In addition, it was demonstrated that AHR ligands TCDD and DELAQ, although both activating the AHR, exerted different effects on prolactin gene expression in primary pituitary cells. The activation of AHR ligands were also assessed in endometrial adenocarcinoma (Chapter 5) and breast cancer (Chapter 6) cell lines, to address tissue specific differences of AHR activation. In Chapter 5, it appeared that the resveratrol analogue tetramethoxystilbene (TMS) exerted stronger anti-tumorigenic properties in ECC-1 cells, whereas it did not affect Ishikawa cells. In Chapter 6, we observed anti-tumorigenic properties of the resveratrol analogues in the MCF-7 breast cancer cell line. Moreover, the most potent TMS inhibited the cell cycle of MCF-7 cells, but did not affect the cell cycle of the non-tumorigenic breast epithelial cell line MCF-10A.