Localization of Oestrogen Receptors Within Various Bovine Ovarian Cell Types at Different Stages of the Oestrous Cycle

Non-classical mechanisms of steroid sensing in the ovary: lessons from the bovine oxytocin model

Steroidogenic tissues such as the ovary, testes or adrenal glands are paradoxical in that they often indicate actions of steroid hormones within a dynamic range of ligand concentration in a high nanomolar or even micromolar level, i.e. at the natural concentrations existing within those organs. Yet ligand-activated nuclear steroid receptors act classically by direct interaction with DNA in the picomolar or low nanomolar range. Moreover, global genomic studies suggest that less than 40% of steroid-regulated genes involve classical responsive elements in gene promoter regions. The bovine oxytocin gene is a key element in the maternal recognition of pregnancy in ruminants and is regulated via an SF1 site in its proximal promoter. This gene is also regulated by steroids acting in a non-classical manner, involving nuclear receptors which do not interact directly with DNA. Dose-response relationships for these actions are in the high nanomolar range. Similar 'steroid sensing' mechanisms may prevail for other SF1-regulated genes and predict alternative pathways by which environmental endocrine disruptors might influence the functioning of steroid-producing organs and hence indirectly the steroid-dependent control of physiology and development.

In vivo and in vitro studies on apoptosis in OSE cells and inclusion cysts of pregnant heifers

Elevated progesterone concentration during pregnancy and use of progesterone-like contraceptives are known to reduce ovarian cancers. This study was undertaken to decipher whether or not there is any relationship between progesterone (also oestrogen)-mediated ovarian surface epithelium (OSE) apoptosis and expression of p53, a cell-cycle arresting protein and potential tumour suppressor. Immunohistochemical staining with cytokeratin confirmed epithelial nature of the cells in the OSE layer and inclusion cysts that invaginate inside stroma after ovulation takes place. The in situ apoptosis index was determined during oestrus, and at mid and late-pregnancy stages in heifers. Epithelia of both tissues exhibited significantly high nuclear staining, suggesting that these cells are aiming to apoptotic destruction. To further establish a role of progesterone, the OSE cells were exposed in vitro to two concentrations of oestrogen and progesterone. It was revealed that progesterone at both concentrations and oestrogen only at high concentration converted a large proportion of these cells apoptotic. The stimulatory effect of progesterone (and to some extent oestrogen) was also seen on p53 expression in the same cultivated OSE cells. The steroid dosage dependence for apoptosis and p53 expression was also somewhat similar. Assuming that progesterone action is mediated through p53-caused apoptosis as a mechanism to evade malignant transformation of OSE cells, p53 expression at mRNA and protein level was investigated in the OSE layer in proximity to stroma, antrum and corpus luteum (CL). In cycling animals CL produces a large amount of progesterone and also oestrogen to maintain the post-ovulatory cycle and to suppress the gonadotropin production. Hence, cells undergoing re-epithelialization and which are in contact with CL were expected to undergo maximum apoptotic modification. Indeed we got the maximum p53/p53 gene expression in these cells. We conclude that progesterone during cycling and pregnancy may reduce the risk of developing ovarian cancer by ceasing cell cycle and diverting damaged and mutagenized OSE cells for apoptosis, and the process may be mediated through elevated p53 synthesis. However, it is also possible that progesterone and p53-induced apoptosis may be entirely different cancer suppressive actions but coincidently happening together.

The G-protein-coupled estrogen receptor (GPER) is expressed in normal human ovaries and is upregulated in ovarian endometriosis and pelvic inflammatory disease involving the ovary

Estrogens play a crucial role in maintaining ovarian function. Deregulation of estrogen signals is associated with fertility-impairing disorders. The aim of this study was to investigate whether the G-protein-coupled estrogen receptor (GPER) is present in the human ovary. Additionally, we  analyzed the folliculogenesis and ovarian endometriosis in GPER expression. Seventy-nine patients (ovarian endometriosis, n = 26; ovarian pelvic inflammatory disease [PID], n = 10; normal ovaries/endometrium, n = 30/13) were analyzed by immunohistochemistry. Normal ovaries were also assessed by real-time polymerase chain reaction and double immunofluorescence. The most intense expression of GPER was noted in the ovarian surface epithelium. Theca cells and oocytes were also significantly positive. Expression of GPER was more frequent in mature follicles/oocytes than in primordial ones, implying that GPER could be a selector during folliculogenesis. Moreover, GPER was upregulated in ovarian endometriosis and PID. Overexpression of GPER in both inflammation and endometriosis affecting the ovary may prove useful in explaining/predicting the main endometriosis-related symptoms.

The effect of elevated progesterone and pregnancy status on mRNA expression and localisation of progesterone and oestrogen receptors in the bovine uterus

To investigate the effects of pregnancy or post-ovulatory progesterone (P4) supplementation on the expression of oestrogen and P4 receptors (ESRs and PGRs) in the bovine uterus, heifers (n=263) were randomly assigned to the following treatments: i) cyclic, normal P4; ii) cyclic, high P4; iii) pregnant, normal P4; and iv) pregnant, high P4 on days 5, 7, 13 and 16 of pregnancy/oestrous cycle. Elevated P4 was achieved through P4-releasing intravaginal device insertion on day 3 after oestrus, resulting in increased concentrations from day 3.5 to 8 (P<0.05) in the high groups than in the normal groups. Irrespective of treatment, PGR and ESR1 mRNA expressions were highest on days 5 and 7 and decreased on day 13 (P<0.05), while ESR2 mRNA expression increased on day 7 (P<0.05) and similar levels were maintained within the normal P4 groups subsequently. Expression in the high P4 groups decreased on day 13 (P<0.05). PGR-AB and PGR-B protein expressions were high in the luminal and superficial glands on days 5 and 7, but by day 13, expression had declined to very low or undetectable levels and high P4 concentration tended to decrease or decreased significantly (P<0.05) the expression in these regions on days 5 and 7. ESR1 protein expression was high, with no treatment effect. ESR2 protein was also highly expressed, with no clear effect of treatment. In conclusion, early post-ovulatory P4 supplementation advances the disappearance of PGR protein from the luminal epithelium on days 5 and 7, and decreases ESR2 mRNA expression during the mid-luteal phase, but has no effect on PGR or ESR1 mRNA expression.

The normal genital tract of the female California sea lion (Zalophus californianus): cyclic changes in histomorphology and hormone receptor distribution

Changes in reproductive tract histomorphology, and estrogen (ERalpha) and progesterone receptor (PR) expression throughout the breeding cycle were evaluated in free-ranging stranded female California sea lions (Zalophus californianus). Hormone receptor expression in the ovaries, uterus, cervix, and vagina was evaluated using an immunohistochemical technique with monoclonal antibodies. During a large portion of the cycle, ovaries contained both a corpora lutea (CL) and follicles in varying stages of development. In the periods of pupping and estrus during June and July, and in the spring morphologic features of the endometrium suggested estrogen influence. There were areas of squamous differentiation in the pseudostratified columnar epithelium of the cervix and vagina in some animals during estrus and in the spring. Estrogen receptor immunohistochemical scores were highest during pupping and estrus and in the spring and lowest during embryonic diapause. Cyclic changes in uterine PR expression throughout the cycle were minimal. Both ERalpha and PR were expressed in epithelial and stromal cells throughout the cervix and vagina, however, receptor expression was typically higher in the stroma. Stromal cell hormone receptors may play an important role in epithelial responses to circulating sex hormones. The results of this investigation add to the general knowledge of California sea lion reproduction and establish baseline information on reproductive tract hormone receptors that will aid in determining the factors involved in urogenital cancer development in sea lions.

Normal morphology and hormone receptor expression in the male California sea lion (Zalophus californianus) genital tract

Histomorphology and estrogen alpha (ER alpha), and progesterone receptor (PR) expression were evaluated in free-ranging stranded male California sea lions (Zalophus californianus). Hormone receptor expression was evaluated using an immunohistochemical technique with monoclonal antibodies. Estrogen and PRs were identified in the efferent ductules, prostate gland, corpus cavernosa, corpus spongiosium, penile urethra, and in the epithelium and stroma of both the penis and prepuce. In some tissues, ER alpha expression was more intense in the stroma, emphasizing the importance of the stroma in hormone-mediated growth and differentiation of reproductive organs. To our knowledge, this is the first study to localize ER alpha and PR to the epithelium of the glans penis. The results of this investigation add to the general knowledge of male California sea lion reproduction and suggest that estrogens could have a role in the function of the male reproductive tract.