Endometrial expression of progesterone receptor and uteroglobin genes during early pregnancy in the rabbit

Expression of nuclear progesterone receptor, progesterone receptor membrane components 1 and 2 and prostaglandin-endoperoxide synthase 2 in the endometrium and oviduct of spontaneously ovulating cats

Although ovulations not followed by pregnancy occur regularly in cats, differences in endometrial function between cats in the luteal and non-luteal phase have not been studied so far. Progesterone exerts its effects through a nuclear progesterone receptor (PGR) and via cell-membrane bound receptors referred to as progesterone receptor membrane component (PGRMC) 1 and 2. Progesterone receptor expression is regulated by gonadal steroid hormones and therefore may change throughout the oestrous cycle. Protein expression of PGR, PGRMC-1 and 2 and prostaglandin-endoperoxide synthase 2 (PTGS2) was analysed in the endometrium and oviduct of non-pregnant female cats in the follicular (n = 8) and luteal phase (n = 9). We hypothesized that the presence of corpora lutea (CL) is associated with downregulation of progesterone receptors and PTGS2. Cells of the luminal endometrial epithelium, endometrial stroma and oviductal epithelium were assessed by immunohistochemistry. The PGR protein expression was more pronounced in the endometrial epithelium than stroma (p < 0.001) and less pronounced in cats with a CL than without CL (p < 0.001) but did not differ between groups in the oviduct. The PTGS2 was localized only in the endometrial and oviductal epithelium and its expression was reduced in cats with CL (p = 0.001). In the endometrial epithelium, PGRMC-1 expression was reduced in cats with CL (p < 0.05). Expression of PGRMC-2 was highest in the endometrial epithelium and lowest in the endometrial stroma (p = 0.01) but did not differ between cats with and without CL. In conclusion, progesterone receptor and PTGS2 downregulation in the female cat closely resembles findings in other spontaneously ovulating domestic animal species.

Regional differences in expression of progesterone receptor in oviduct and uterus of rabbit during early pregnancy

We characterized the expression pattern of progesterone receptor (PR) in two regions of the oviduct (ampullae and isthmus), and the uterus (epithelium and stroma) of the rabbit (Oryctolagus cuniculus) during early pregnancy (1-4 days) by RT-PCR and immunohistochemistry. We observed a significant increase in the expression of PR at mRNA level in the uterus on days 1 and 2 of pregnancy, followed by a decrease on days 3 and 4. These changes were also observed at protein level in the uterine epithelium. Interestingly, PR immunoreactivity decreased in stromal cells in all days of pregnancy as compared with non-pregnant rabbits (NG). In the isthmus PR mRNA expression significantly increased on day 2 of pregnancy and diminished on days 3 and 4, whereas no significant changes were observed in the ampullae. In epithelial and stromal cells of the isthmus, PR immunostaining was reduced through pregnancy as compared with NG group. In contrast, a reduction in PR immunostaining was observed on days 1-3 with an increase on day 4 in epithelial and stromal cells of the ampullae. The overall results suggest that PR exhibit a differential expression pattern in the oviduct and the uterus during early pregnancy of the rabbit, and that these differences are related to different functions of PR in the reproductive tract during early pregnancy.

Regulated expression of osteopontin in the peri-implantation rabbit uterus

Blastocyst attachment to the lining of the mammalian uterus during early implantation involves the initial apposition of the trophoblast to the uterine epithelial surface. Osteopontin (OPN) is a glycoprotein component of the extracellular matrix that is secreted by the glandular epithelium of mammalian uteri at the time of implantation. This protein is recognized by several members of the integrin family and promotes cell-cell attachment and adhesion. In the present study, rabbit uteri were examined using Northern and in situ hybridization to evaluate the temporal and spatial distribution of OPN mRNA during early pregnancy. Northern blot analysis demonstrated a dramatic increase in OPN expression on Days 4-7 of pregnancy, corresponding to the rise in circulating progesterone and the time of initial embryo attachment in this species. In situ hybridization analysis revealed OPN mRNA expression on Day 6.75 of pregnancy, which was most prominent on endometrial epithelium. Using immunofluorescence, OPN protein was present on the glandular epithelium on Day 6.75 of pregnancy, but was absent on blastocysts. Further, no expression of OPN mRNA or protein was found in the nonpregnant endometrium. Induction of endometrial OPN expression was observed in unmated rabbits treated with progesterone alone and was prevented by cotreatment with the antiprogestin ZK137.316. Estradiol-17beta had no effect on OPN expression by itself, and estrogen priming was not necessary to demonstrate the stimulatory effect of progesterone. In The rabbit uterus, as in other mammalian species studied, OPN is expressed in a stage-specific manner by the endometrial glands during the peri-implantation period and is regulated by progesterone.

Expression of TCF, TPF/YY1, and the Sp family transcription factors in rabbit endometrium throughout pregnancy

BACKGROUND

TCF, TPF/YY1, and the Sp family are specific transcription factors that bind sequences found within the uteroglobin (UG) gene promoter region that are necessary for transcription. To date, UG gene expression and regulation in vivo are not fully understood. The purpose of this study was to assess the expression patterns of these factors in the rabbit endometrium throughout pregnancy.

METHODS

Endometrial nuclear extracts were obtained from female rabbits on days 0, 3, 5, 7, 15, and 28 after mating. Transcription factor expression was assessed by DNA-protein binding assays using endometrial nuclear proteins and specific oligonucleotides. Band shifts were observed on 4% acrylamide gels and analyzed by densitometry.

RESULTS

The expression patterns of the transcription factors analyzed here differed, as TPF/YY1 and Sp3/SpR-2 were expressed constitutively while TCF and Sp1 showed variable expression patterns throughout pregnancy.

CONCLUSIONS

Our results suggest that UG gene expression in the intact pregnant rabbit is controlled by two constitutive and two regulated factors, and that the DNA-binding sites are located at the TATA box and the GT1 sites within the gene promoter.

Progesterone exposure prevents matrix metalloproteinase-3 (MMP-3) stimulation by interleukin-1alpha in human endometrial stromal cells

Suppression of endometrial matrix metalloproteinases (MMPs) is necessary to maintain tissue stability during the invasive events of implantation and placental development. Several laboratories have shown that inflammatory cytokines, including interleukin-lalpha (IL-1alpha), can oppose progesterone suppression of MMPs in the human endometrium. Furthermore, we have recently demonstrated colocalization of epithelial cell IL-1alpha and MMP-7 expression at sites of ectopic pregnancy. The current study extends these findings, revealing a previously unrecognized interrelationship between progesterone and IL-1alpha in regulation of MMP-3. Although IL-1alpha is a potent stimulator of MMP-3 in proliferative phase endometrium in organ culture, we demonstrate that progesterone exposure in vivo reduces IL-1alpha stimulation of MMP-3 in secretory phase tissue. This loss of sensitivity to IL-1alpha was duplicated in isolated stromal cells treated with progesterone in vitro, and IL-1alpha stimulation of MMP-3 returned in a dose-dependent manner with progesterone withdrawal. The antiprogestin, onapristone, partially blocked the ability of progesterone to prevent stimulation of MMP-3 by IL-1alpha. These data suggest a novel mechanism by which progesterone may preserve tissue integrity during the establishment and maintenance of pregnancy by limiting stimulation of MMPs by inflammatory cytokines such as IL-1a.

5alpha-reduction of norethisterone enhances its binding affinity for androgen receptors but diminishes its androgenic potency

Norethisterone (NET), a 19-nor synthetic progestin, undergoes enzyme-mediated 5alpha-reduction and exerts potent androgenic effects in target organs. To investigate its mode of androgenic action we examined, in a comparative manner, the in vitro metabolism of NET and testosterone (T), as well as the binding affinities to androgen receptors (AR) and the androgenic potency of NET, T, and their 5alpha-reduced derivatives. Bioconversion of [3H]-NET and [3H]-T was studied in rat prostate homogenates, AR binding affinity was assessed in rat ventral prostates using [3H]-mibolerone as the radioligand, and the androgenic potency was evaluated by the increase of beta-glucuronidase activity in the mouse kidney, and by the growth of accessory sex organs in castrated male rats. The results demonstrated that 5alpha-NET displayed a higher AR binding affinity but a significantly lower androgenic potency than unchanged NET. The bioconversion studies indicated that the metabolism of NET was similar to that of T, although to a lesser extent, thus ruling out the possibility that the synthetic progestin metabolizes rapidly into less active derivatives. To investigate the nature of the paradoxical effect of 5alpha-reduction upon the NET molecule, the interaction with AR and the androgenic potency of T, 19-nortestosterone (19norT), 17alpha-ethynyl testosterone (ET) and their 5alpha-reduced derivatives were examined. The results of AR binding studies revealed that 5alpha-reduction of T and ET significantly enhanced their affinities, and that the 5alpha-derivative of 19norT displayed a similar binding affinity to that exhibited by 19norT. In terms of biological activity, the results showed that 5alpha-reduction of T and 19norT significantly increased their androgenic potency, whereas 5alpha-reduction of ET resulted in a significant diminution of its androgenicity in a manner similar to that observed with the 5alpha-reduction of NET. When NET and 19norT were simultaneously administered with 5alpha-dihydrotestosterone they exhibited a potent synandrogenic activity, an effect that was cancelled by their 5alpha-reduction. Interestingly, ET displayed an antiandrogenic activity, an effect that was also suppressed by its 5alpha-reduction. The overall results demonstrated a distinctive, paradoxical effect of 5alpha-reduction upon the NET molecule, which was different from that seen in naturally occurring androgens, and which suggests that the presence of the 17alpha-ethynyl group plays a key role in this phenomenon. The data provided further evidence that the metabolism of synthetic contraceptive progestins modulates the expression of their hormone-like actions.

Uteroglobin gene expression in the rabbit uterus throughout gestation and in the fetal lung. Relationship between uteroglobin and eicosanoid levels in the developing fetal lung

Uteroglobin (UG) gene encodes a cytokine-like, multifunctional, antiinflammatory protein, with potent phospholipase A2-inhibitory activity. It has been suggested that during implantation this protein protects the embryos from maternal immunological assault, facilitates the maintenance of quiescence in the uterus throughout pregnancy, prevents the onset of premature labor, and helps maintain an inflammation-free respiratory organ. This latter function of UG is suggested to be accomplished by preventing hydrolysis of surfactant phospholipids by a lung-specific phospholipase A2. Using reverse transcription polymerase chain reaction, in situ hybridization, immunofluorescence, and radioimmunoassay, we studied UG gene expression in the rabbit uterus throughout gestation and in the fetal lung. Here, we report that: (a) contrary to previous reports, UG gene expression in the rabbit uterus occurs throughout gestation with a precipitous decline just before parturition; (b) this gene expression is dramatically increased in the fetal lung with increasing gestational age; and (c) while there is an inverse relationship between the levels of UG, PGE2, and PGF2 alpha, a positive correlation was found in that of UG and leukotriene C4 in the fetal lung. Our results raise the possibility that dysregulation of UG gene expression, at least in part, may contribute to the onset of premature labor and the development of inflammatory lung disease in premature neonates.

Molecular mechanisms of the antihormonal and antiimplantation effects of norethisterone and its A-ring reduced metabolites

Norethisterone (NET) has been used as a contragestational postcoital agent. It is biotransformed to 5 alpha dihydro-NET (5 alpha-NET) and 3 beta,5 alpha tetrahydro-NET (3 beta,5 alpha-NET) in target tissues. The participation of these metabolites in NET effects is unknown. We have examined the antiimplantation and antiprogestational effects of NET and its metabolites, in adult mated female rabbits, by assessing the number of implantation sites and the expression products of the uteroglobin (UTG) gene in the uterus, and by comparing them with those of RU-486 and estradiol. Steroids were daily administered s.c. at several doses for 7 consecutive days, starting 24 hr after coitus. To assure that fertilization occurred in all animals, the presence of early pregnancy factor was determined. The results demonstrated that high doses (5 mg/kg) of NET reduced both implantation and the expression of the UTG gene. On the other hand, lower doses (1.5 mg/kg) of 5 alpha-NET produced an antiimplantation effect and suppressed UTG synthesis and its mRNA. These effects were similar to those of RU-486. At lower doses (1 mg/kg), both estradiol and the estrogenic metabolite 3 beta,5 alpha-NET were also effective in inhibiting implantation and UTG gene expression. The overall results suggest that NET metabolites exert antiimplantation and antiprogestational effects through their interaction with progesterone and estrogen receptors, and provide an explanation for the molecular mechanisms involved in the postcoital contraceptive action of NET.