Endometriosis is defined as the presence of endometrial glands and stroma outside the uterine cavity. This disease is associated with diminished protective effects of progesterone, which are usually explained by inadequate activation of progesterone receptors and also enhanced pre-receptor metabolism of progesterone. Endometriosis is often treated with progestins, which act as progesterone receptor agonists, although their exact mechanisms of action are not completely understood. The aim of the present study was to investigate how the progestins medroxyprogesterone acetate, dydrogesterone and dienogest, as well as progesterone, impact on the expression of genes of pre-receptor progesterone metabolism in Z-12 epithelial cell line, a model system of peritoneal endometriosis. Our data demonstrate that these progestins affect local pre-receptor metabolism to a different extent. The most favorable effects were seen for dydrogesterone and dienogest, where the first, dydrogesterone, significantly reduced SRD5A1, AKR1C2 and AKR1C3 expression, and additionally had a nonsignificant impact on progesterone receptor B (PR-B) protein levels. This might slow down the first step of pre-receptor metabolism, the conversion of progesterone to 5α-dihydroprogestrone by SRD5A1, and it might also affect further reduction of 3-keto and 20-keto groups catalyzed by AKR1C2 and AKR1C3. Similarly favorable effects were seen for dienogest, which promoted significant reduction of AKR1C1 and AKR1C2 expression and also showed no effect on PR-B protein levels. Different effects were seen for progesterone, which significantly decreased SRD5A1, PR-B and HSD17B2 protein levels. In contrast, treatment with medroxyprogesterone acetate resulted in increased AKR1C1 expression and decreased levels of PR-B, which might lead to enhanced progesterone metabolism and reduced signaling through progesterone receptors. Altogether, our data in this Z-12 cell model suggest that the beneficial effects of treatment with progestin observed in endometriosis patients might arise from decreased pre-receptor metabolism of the protective progesterone by the SRD5A1 and AKR1C enzymes.
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