Molecular mechanism of progesterone action in the female reproductive system / Molekularny mechanizm dzialania progesteronu w zenskim ukladzie rozrodczym.

Progesterone (P4) is a steroid hormone which participate in many processes in the female reproductive system. The hormone is produced mainly by the corpus luteum (CL), however, also the ovarian follicles, uterine tissues and placenta are able to produce P4. Progesterone is involved in the regulation of the sexual cycle, as well as in the initiation and maintenance of pregnancy. The hormone may affect cell function by genomic mechanism, through nuclear P4 receptors (PGR), and via nongenomic mechanism, through the membrane P4 receptors, such as progesterone receptor membrane component (PGRMC) 1 and 2, and membrane progestin receptors (mPR) α, ß and γ. The genomic mechanism of P4 action leads to the expression of target genes and the synthesis of new proteins, while the nongenomic mechanism modifies various intracellular signaling pathways. The integration of these two mechanisms of P4 activity leads to the suitable regulation of the cell, tissue and, consequently, the response of organism to the hormone.

Effect of Steroid Hormones, Prostaglandins (E2 and F2α), Oxytocin, and Tumor Necrosis Factor Alpha on Membrane Progesterone (P4) Receptors Gene Expression in Bovine Myometrial Cells.

Myometrium tissue shows the expression of non-genomic membrane progesterone (P4) receptors, such as progesterone receptor membrane components (PGRMC) 1 and 2 and membrane progestin receptors (mPR) alpha (mPRα), beta (mPRß), and gamma (mPRγ). Their variable expression in the bovine uterus during the estrous cycle and early pregnancy suggests that ovarian steroids and luteotropic and/or luteolytic factors may regulate the expression of these receptors in the myometrium. Therefore, this study aimed to examine the effect of P4, estradiol (E2), P4 with E2, prostaglandins (PG) E2 and F2α, oxytocin (OT), and tumor necrosis factor α (TNFα) on the gene expression of PGRMC1, PGRMC2, serpine-1 mRNA-binding protein (SERBP1), and mPRα, mPRß, and mPRγ in bovine myometrial cells from days 6 to 10 and 11 to 16 of the estrous cycle. The PGE2 concentration and mRNA expression were determined by EIA and real-time PCR, respectively. The data indicated that P4 and E2 can affect the mRNA expression of all studied receptors and SERPB1. However, PGE2, OT, and TNFα could only modulate the expression of PGRMC1, PGRMC2, and SERPB1, respectively. Steroids/factors changed the expression of PGRMC and mPR genes depending on the dose, the stage of the estrous cycle, and the types of receptors. This suggests that the local hormonal milieu may influence the activity of these receptors and P4 action in myometrial cells during the estrous cycle.

Steroid Receptor Coregulators Can Modulate the Action of Progesterone Receptor during the Estrous Cycle in Cow Endometrium.

Nuclear receptor coregulators include coactivators and corepressors which associate with the progesterone receptor (PGR) during its activation. Fluctuations in the transcription levels of their respective genes and subsequent protein production as well as in related activities for histone acetyltransferase (HAT) and histone deacetylase (HDAC) can affect PGR function and thus change the action of progesterone (P4) in bovine endometrium during the estrous cycle. Endometrial tissue on days 2-5, 6-10, 11-16, and 17-20 of the estrous cycle was used for determination of the mRNA expression levels of coactivators P300, CREB, and SRC-1 along with corepressor NCOR-2 using Real-Time PCR, with protein levels by Western blot. Coregulators cellular localizations were assessed by immunohistochemistry whereas the activities of HAT and HDAC by using EIA. The highest levels of mRNA and proteins for all of the investigated coregulators, as well as the highest levels of activity for HAT and HDAC, were detected over days 2-16 of the estrous cycle. All of the tested coregulatory proteins were localized in the nuclei of endometrial cells. This research indicates the important role of coregulators of the PGR receptor in regulating P4 activity in endometrial cells, especially during the pre-implantation period.

Progesterone Receptor Coregulators as Factors Supporting the Function of the Corpus Luteum in Cows.

Progesterone receptor (PGR) for its action required connection of the coregulatory proteins, including coactivators and corepressors. The former group exhibits a histone acetyltransferase (HAT) activity, while the latter cooperates with histone deacetylase (HDAC). Regulations of the coregulators mRNA and protein and HAT and HDAC activity can have an indirect effect on the PGR function and thus progesterone (P4) action on target cells. The highest mRNA expression levels for the coactivators-histone acetyltransferase p300 (P300), cAMP response element-binding protein (CREB), and steroid receptor coactivator-1 (SRC-1)-and nuclear receptor corepressor-2 (NCOR-2) were found in the corpus luteum (CL) on days 6 to 16 of the estrous cycle. The CREB protein level was higher on days 2-10, whereas SRC-1 and NCOR-2 were higher on days 2-5. The activity of HAT and HDAC was higher on days 6-10 of the estrous cycle. All of the coregulators were localized in the nuclei of small and large luteal cells. The mRNA and protein expression levels of the examined coactivators and corepressor changed with the P4 level. Thus, P4 may regulate CL function via the expression of coregulators, which probably affects the activity of the PGR.

Expression of membrane progestin receptors (mPRs) α, ß and γ in the bovine uterus during the oestrous cycle and pregnancy.

Progesterone (P4) affects cell function through the nuclear progesterone receptor and membrane-bound progesterone binding proteins, including the membrane progestin receptors (mPRs) alpha (mPRα), beta (mPRß) and gamma (mPRγ), which belong to the progestin and adipoQ receptor family (PAQR7, 8 and 5, respectively). The aim of this study was to determine the mRNA and protein expression levels of mPRα, mPRß and mPRγ through real-time PCR and Western blot analyses, respectively, and to determine the cellular localization of these proteins in the bovine endometrium and myometrium on days 2-5, 6-10, 11-16 and 17-20 of the oestrous cycle and weeks 3-5, 6-8 and 9-12 of pregnancy (n = 5/each time period). The resulting data showed the highest (P < 0.05) mPRα and mPRß mRNA expression in the endometrium on days 11-16 of the oestrous cycle compared to the other stages. In the myometrium, the level of mPRα mRNA was the lowest (P < 0.05) on days 6-16 of the oestrous cycle, while mPRß was the lowest on days 11-16. There were no changes (P > 0.05) in mPRγ mRNA expression in the endometrium and myometrium during the oestrous cycle. During pregnancy, in the endometrium and myometrium, the levels of mPRα and mPRß mRNA were comparable with those observed during the oestrous cycle. However, mPRγ mRNA expression was the highest (P < 0.001) during all stages of pregnancy compared with that observed during the oestrous cycle in both uterine tissues. The mPRα protein level only changed in the myometrium and was the highest (P < 0.05) during weeks 9-12 of pregnancy. However, in the endometrium, the expression of mPRß protein was higher (P < 0.05) on days 6-10 of the oestrous cycle than during weeks 6-8 of pregnancy. Strong positive immunoreactions for all mPR proteins were observed in the luminal and glandular epithelium but were less evident in the stromal cells and myocytes. In addition, all proteins were also localized in the endothelial cells of blood vessels in the uterus, suggesting that P4 may affect blood flow in this organ through mPRs. The presence of mPR receptors in the uterus indicates their participation in the regulation of uterine functions.