Recently, we established an in vitro model with immortalized dog uterine stromal (DUS) cells for investigations into canine-specific decidualization. Their capability to decidualize was assessed with cAMP and prostaglandin (PG) E2. Here, we show that the effects of PGE2 are mediated through both of the cAMP-mediating PGE2 receptors (PTGER2/4). Their functional inhibition suppressed gene expression of PRLR and PGR in DUS cells. We also assessed the effects of cAMP and PGE2 on selected extracellular matrix components and CX43, and showed that cAMP, but not PGE2, increases COL4, extracellular matrix protein 1 (ECM1) and CX43 protein levels during in vitro decidualization, indicating a mesenchymal-epithelial decidual transformation in these cells. Thus, although PGE2 is involved in decidualization, it does not appear to regulate extracellular matrix. Further, the role of progesterone (P4) during in vitro decidualization was addressed. P4 upregulated PRLR and PGR in DUS cells, but these effects were not influenced by PGE2; both P4 and PGE2 hormones appeared to act independently. P4 did not affect IGF1 expression, which was upregulated by PGE2, however, it suppressed expression of IGF2 , also in the presence of PGE2. Similarly, P4 did not affect PGE2 synthase ( PTGES ), but in the presence of PGE2 it increased PTGER2 levels and, regardless of the presence of PGE2, suppressed expression of PTGER4 . Our results indicate a reciprocal regulatory loop between PGE2 and P4 during canine in vitro decidualization: whereas P4 may be involved in regulating PGE2-mediated decidualization by regulating the availability of its receptors, PGE2 regulates PGR levels in a manner dependent on PTGER2 and -4.

Feto-maternal communication in the dog involves the differentiation of stromal cells into decidual cells. As the only placental cells expressing the nuclear progesterone (P4) receptor (PGR), decidual cells play crucial roles in the maintenance and termination of pregnancy. Accordingly, to investigate possible PGR-mediated mechanisms in canine decidual cells, in vitro decidualized dog uterine stromal (DUS) cells were treated with functional PGR-blockers, mifepristone and aglepristone. Effects on decidualization markers, epithelial and mesenchymal factors, and markers of cellular viability were assessed. Decidualization increased the expression of PTGES, PGR, IGF1, and PRLR, along with ECM1, COL4 and CX43, but downregulated IGF2. DUS cells retained their mesenchymal character, and the expression of COL4 indicated the mesenchymal-epithelial transformation. Antigestagen treatment decreased the availability of PTGES, PRLR, IGF1 and PGR. Furthermore, antigestagens decreased the mRNA and protein expression of CX43, and transcriptional levels of ECM1 and COL4. Additionally, antigestagens increased levels of activated-CASP3 (a proapoptotic factor), associated with lowered levels of PCNA (a proliferation marker). These data reveal important aspects of the functional involvement of PGR in canine decidual cells, regarding the expression of decidualization markers and acquisition of epithelial-like characteristics. Some of these mechanisms may be crucial for the maintenance and/or termination of canine pregnancy.

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ZusammenfassungAntigestagene (Antiprogestine) sind funktionelle Antagonisten von Progesteron (P4), welche die Vermittlung der biologischen Wirkungen von P4 verhindern, indem sie entweder seine Produktion oder seine Funktionen unterdrücken. Unter Letzteren befinden sich Progesteronrezeptorantagonisten, die die Bindung von P4 an seinen nukleären Rezeptor PGR kompetitiv hemmen. Diese finden sowohl in der Human- als auch in der Veterinärmedizin Anwendung, in der Kleintiermedizin insbesondere zur Nidationsverhütung und zum Trächtigkeitsabbruch. Progesteronrezeptorantagonisten können entsprechend ihrer Wirkungsweise in 2 Klassen eingeteilt werden. Klasse-I-Antagonisten binden an den PGR ohne eine Bindung an Promotoren von Zielgenen zu induzieren (kompetitive Inhibitoren). Antigestagene der Klasse II, einschließlich des in der Veterinärmedizin verwendeten Aglepristons, binden an den PGR, aktivieren dessen Assoziation mit einem Promoter, interferieren jedoch mit den nachgeschalteten Signalkaskaden, z. B. durch Rekrutierung von Transkriptionsrepressoren. Sie wirken dabei als transdominante Repressoren, die negative Auswirkungen auf die Zielgenexpression haben. Wichtig für die experimentellen Wissenschaften ist, dass Antagonisten der Klasse II, als aktive Antagonisten, für ihre Wirkung nicht die Anwesenheit des natürlichen Liganden benötigen. Neben ihrer klinischen Anwendung werden Antigestagene in der Forschung zur Untersuchung P4-abhängiger physiologischer und pathologischer Prozesse eingesetzt. Dieser Artikel gibt einen Überblick über die Geschichte und den aktuellen Einsatz von Progesteronrezeptorblockern in der Veterinärmedizin und Forschung.