Cyclic changes of the ovarian surface epithelium in the rat

Identification and characterization of multipotential stem cells in immortalized normal ovarian surface epithelial cells

The ovarian surface epithelium (OSE) is a single layer of squamous-to-cuboidal epithelial cells that experience repetitive ovulatory rupture and subsequent repair. However, the characteristics of human immortalized ovarian surface epithelial cells (IOSE80) remain elusive. This study aims to determine whether IOSE80 cells have the characteristics of stem cell proliferation and multilineage differentiation and their application in regenerative medicine. IOSE80 cells are sequenced by high-throughput transcriptome analysis, and 5 sets of public data are used to compare the differences between IOSE80 cells and bone marrow mesenchymal stem cells, pluripotent stem cells, and oocytes in transcriptome profiling. The IOSE80 cells present a cobblestone-like monolayer and express the epithelial cell marker KRT18; the stem cell markers IFITM3, ALDH1A1, and VIM; lowly express stem cell marker LGR5 and germ cell markers DDX4 and DAZL. In addition, the GO terms "regulation of stem cell proliferation", "epithelial cell proliferation", etc., are significantly enriched ( P<0.05). IOSE80 cells have the potential to act as mesenchymal stem cells to differentiate into adipocytes with lipid droplets, osteoblasts, and chondroblasts in vitro. IOSE80 cells express pluripotent stem cell markers, including OCT4, SSEA4, TRA-1-60, and TRA-1-81, and they can be induced into three germ layers in vitro. IOSE80 cells also form oocyte-like cells in vitro and in vivo. In addition, IOSE80 cells exhibit robust proliferation, migration, and ovarian repair functions after in vivo transplantation. This study demonstrates that IOSE80 cells have the characteristics of pluripotent/multipotent stem cells, indicating their important role in tissue engineering and regenerative medicine.

Does the ovarian surface epithelium differentiate into primordial follicle and primary follicle precursor structures?

Purpose: The aim of this study is to investigate the differentiation capacity of ovarian surface epithelial cells both in cell culture conditions and in ovarian tissue sections. Materials and Methods: The ovaries of two prepubertal (4 weeks old) female rats were divided into small pieces and explant cell culture was created. Ovarian surface epithelium proliferating together with ovarian stromal cells in mixed cell culture was isolated and reproduced. In addition, ovarian surface epithelium was examined in histological sections of ovarian tissue and images were taken under the microscope. Results: The morphological appearance of the ovarian surface epithelium was found to be cobblestone. In the count performed under phase contrast microscopy, it was observed that 2x106 and 3x106 cells were grown in the culture dishes, respectively. Primordial follicle-like structures were observed in some areas of the petri dishes. On the histological sections, primordial and primary follicle precursor structures were observed on the basement membrane. Conclusion: Showing oocyte markers (Gdf-9, C-Mos, Zpc, Stella) and germ cell markers (Dazl, Vasa, Blimp1, Fragilis) both in cell cultures and in histological sections can give us valuable information in terms of monitoring the differentiation capacity of these cells.

Selective YAP activation in Procr cells is essential for ovarian stem/progenitor expansion and epithelium repair

Ovarian surface epithelium (OSE) undergoes recurring ovulatory rupture and OSE stem cells rapidly generate new cells for the repair. How the stem cell activation is triggered by the rupture and promptly turns on proliferation is unclear. Our previous study has identified that Protein C Receptor (Procr) marks OSE progenitors. In this study, we observed decreased adherent junction and selective activation of YAP signaling in Procr progenitors at OSE rupture site. OSE repair is impeded upon deletion of Yap1 in these progenitors. Interestingly, Procr+ progenitors show lower expression of Vgll4, an antagonist of YAP signaling. Overexpression of Vgll4 in Procr+ cells hampers OSE repair and progenitor proliferation, indicating that selective low Vgll4 expression in Procr+ progenitors is critical for OSE repair. In addition, YAP activation promotes transcription of the OSE stemness gene Procr. The combination of increased cell division and Procr expression leads to expansion of Procr+ progenitors surrounding the rupture site. These results illustrate a YAP-dependent mechanism by which the stem/progenitor cells recognize the murine ovulatory rupture, and rapidly multiply their numbers, highlighting a YAP-induced stem cell expansion strategy.

COX2 is induced in the ovarian epithelium during ovulatory wound repair and promotes cell survival†

The ovarian surface epithelium (OSE) is a monolayer of cells surrounding the ovary that is ruptured during ovulation. After ovulation, the wound is repaired, however, this process is poorly understood. In epithelial tissues, wound repair is mediated by an epithelial-to-mesenchymal transition (EMT). Transforming Growth Factor Beta-1 (TGFβ1) is a cytokine commonly known to induce an EMT and is present throughout the ovarian microenvironment. We, therefore, hypothesized that TGFβ1 induces an EMT in OSE cells and activates signaling pathways important for wound repair. Treating primary cultures of mouse OSE cells with TGFβ1 induced an EMT mediated by TGFβRI signaling. The transcription factor Snail was the only EMT-associated transcription factor increased by TGFβ1 and, when overexpressed, was shown to increase OSE cell migration. A polymerase chain reaction array of TGFβ signaling targets determined Cyclooxygenase-2 (Cox2) to be most highly induced by TGFβ1. Constitutive Cox2 expression modestly increased migration and robustly enhanced cell survival, under stress conditions similar to those observed during wound repair. The increase in Snail and Cox2 expression with TGFβ1 was reproduced in human OSE cultures, suggesting these responses are conserved between mouse and human. Finally, the induction of Cox2 expression in OSE cells during ovulatory wound repair was shown in vivo, suggesting TGFβ1 increases Cox2 to promote wound repair by enhancing cell survival. These data support that TGFβ1 promotes ovulatory wound repair by induction of an EMT and activation of a COX2-mediated pro-survival pathway. Understanding ovulatory wound repair may give insight into why ovulation is the primary non-hereditary risk factor for ovarian cancer.

Kisspeptin treatment induces gonadotropic responses and rescues ovulation in a subset of preclinical models and women with polycystic ovary syndrome

STUDY QUESTION

Can kisspeptin treatment induce gonadotrophin responses and ovulation in preclinical models and anovulatory women with polycystic ovary syndrome (PCOS)?

SUMMARY ANSWER

Kisspeptin administration in some anovulatory preclinical models and women with PCOS can stimulate reproductive hormone secretion and ovulation, albeit with incomplete efficacy.

WHAT IS KNOWN ALREADY

PCOS is a prevalent, heterogeneous endocrine disorder, characterized by ovulatory dysfunction, hyperandrogenism and deregulated gonadotrophin secretion, in need of improved therapeutic options. Kisspeptins (encoded by Kiss1) are master regulators of the reproductive axis, acting mainly at GnRH neurons, with kisspeptins being an essential drive for gonadotrophin-driven ovarian follicular maturation and ovulation. Altered Kiss1 expression has been found in rodent models of PCOS, although the eventual pathophysiological role of kisspeptins in PCOS remains unknown.

STUDY DESIGN, SIZE, DURATION

Gonadotrophin and ovarian/ovulatory responses to kisspeptin-54 (KP-54) were evaluated in three preclinical models of PCOS, generated by androgen exposures at different developmental windows, and a pilot exploratory cohort of anovulatory women with PCOS.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Three models of PCOS were generated by exposure of female rats to androgens at different periods of development: PNA (prenatal androgenization; N = 20), NeNA (neonatal androgenization; N = 20) and PWA (post-weaning androgenization; N = 20). At adulthood (postnatal day 100), rats were subjected to daily treatments with a bolus of KP-54 (100 μg/kg, s.c.) or vehicle for 11 days (N = 10 per model and treatment). On Days 1, 4, 7 and 11, LH and FSH responses were assessed at different time-points within 4 h after KP-54 injection, while ovarian responses, in terms of follicular maturation and ovulation, were measured at the end of the treatment. In addition, hormonal (gonadotrophin, estrogen and inhibin B) and ovulatory responses to repeated KP-54 administration, at doses of 6.4-12.8 nmol/kg, s.c. bd for 21 days, were evaluated in a pilot cohort of anovulatory women (N = 12) diagnosed with PCOS, according to the Rotterdam criteria.

MAIN RESULTS AND THE ROLE OF CHANCE

Deregulated reproductive indices were detected in all PCOS models: PNA, NeNA and PWA. Yet, anovulation was observed only in NeNA and PWA rats. However, while anovulatory NeNA rats displayed significant LH and FSH responses to KP-54 (P < 0.05), which rescued ovulation, PWA rats showed blunted LH secretion after repeated KP-54 injection and failed to ovulate. In women with PCOS, KP-54 resulted in a small rise in LH (P < 0.05), with an equivalent elevation in serum estradiol levels (P < 0.05). Two women showed growth of a dominant follicle with subsequent ovulation, one woman displayed follicle growth but not ovulation and desensitization was observed in another patient. No follicular response was detected in the other women.

LIMITATIONS, REASONS FOR CAUTION

While three different preclinical PCOS models were used in order to capture the heterogeneity of clinical presentations of the syndrome, it must be noted that rat models recapitulate many but not all the features of this condition. Additionally, our pilot study was intended as proof of principle, and the number of participants is low, but the convergent findings in preclinical and clinical studies reinforce the validity of our conclusions.

WIDER IMPLICATIONS OF THE FINDINGS

Our first-in-rodent and -human studies demonstrate that KP-54 administration in anovulatory preclinical models and women with PCOS can stimulate reproductive hormone secretion and ovulation, albeit with incomplete efficacy. As our rat models likely reflect the diversity of PCOS phenotypes, our results argue for the need of personalized management of anovulatory dysfunction in women with PCOS, some of whom may benefit from kisspeptin-based treatments.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by research agreements between Ferring Research Institute and the Universities of Cordoba and Edinburgh. K.S. was supported by the Wellcome Trust Scottish Translational Medicine and Therapeutics Initiative (STMTI). Some of this work was undertaken in the MRC Centre for Reproductive Health which is funded by the MRC Centre grant MR/N022556/1. M.T.-S. is a member of CIBER Fisiopatología de la Obesidad y Nutrición, which is an initiative of Instituto de Salud Carlos III. Dr Mannaerts is an employee of Ferring International PharmaScience Center (Copenhagen, Denmark), and Drs Qi, van Duin and Kohout are employees of the Ferring Research Institute (San Diego, USA). Dr Anderson and Dr Tena-Sempere were recipients of a grant support from the Ferring Research Institute, and Dr Anderson has undertaken consultancy work and received speaker fees outside this study from Merck, IBSA, Roche Diagnostics, NeRRe Therapeutics and Sojournix Inc. Dr Skorupskaite was supported by the Wellcome Trust through the Scottish Translational Medicine and Therapeutics Initiative 102419/Z/13/A. The other authors have no competing interest.

Non-canonical WNT5a regulates Epithelial-to-Mesenchymal Transition in the mouse ovarian surface epithelium

The ovarian surface epithelium (OSE) is a monolayer that covers the ovarian surface and is involved in ovulation by rupturing and enabling release of a mature oocyte and by repairing the wound after ovulation. Epithelial-to-mesenchymal transition (EMT) is a mechanism that may promote wound healing after ovulation. While this process is poorly understood in the OSE, in other tissues wound repair is known to be under the control of the local microenvironment and different growth factors such as the WNT signaling pathway. Among WNT family members, WNT4 and WNT5a are expressed in the OSE and are critical for the ovulatory process. The objective of this study was to determine the potential roles of WNT4 and WNT5a in regulating the OSE layer. Using primary cultures of mouse OSE cells, we found WNT5a, but not WNT4, promotes EMT through a non-canonical Ca2+-dependent pathway, up-regulating the expression of Vimentin and CD44, enhancing cell migration, and inhibiting the CTNNB1 pathway and proliferation. We conclude that WNT5a is a stimulator of the EMT in OSE cells, and acts by suppressing canonical WNT signaling activity and inducing the non-canonical Ca2+ pathway.

Procr-expressing progenitor cells are responsible for murine ovulatory rupture repair of ovarian surface epithelium

Ovarian surface epithelium (OSE) undergoes recurring ovulatory rupture and repair. The OSE replenishing mechanism post ovulation remains unclear. Here we report that the expression of Protein C Receptor (Procr) marks a progenitor population in adult mice that is responsible for OSE repair post ovulation. Procr+  cells are the major cell source for OSE repair. The mechanism facilitating the rapid re-epithelialization is through the immediate expansion of Procr+  cells upon OSE rupture. Targeted ablation of Procr+  cells impedes the repairing process. Moreover, Procr+  cells displayed robust colony-formation capacity in culture, which we harnessed and established a long-term culture and expansion system of OSE cells. Finally, we show that Procr+  cells and previously reported Lgr5+ cells have distinct lineage tracing behavior in OSE homeostasis. Our study suggests that Procr marks progenitor cells that are critical for OSE ovulatory rupture and homeostasis, providing insight into how adult stem cells respond upon injury.

The ovary is covered by a surface epithelium (OSE) and cells mediating its repair post ovulation are unclear. Here, the authors identify the Protein C Receptor (Procr) as marking progenitor cells, distinct from Lgr5+ stem cells, on the murine surface epithelium that repair the OSE post ovulation.

Expression of genes involved in BMP and estrogen signaling and AMPK production can be important factors affecting total number of antral follicles in ewes

Follicular growth and ovulation of healthy oocytes is a complicated process which is regulated by several endocrine and paracrine factors as well as cross-talk between the oocyte and its surrounding somatic cells. This study compared the expression profile of some candidate genes involved in BMP signaling as well as estrogen and AMPK production in cumulus-oocyte complex (COC) of small and large antral follicles and their associated somatic cell layers in ovaries from ewes with high- and low-antral follicle count (AFC). Expression of GDF9 was increased by increasing the size of antral follicles, while BMP15 expression was decreased by follicular size. It should be noteworthy that transcription of both GDF9 and BMP15 was also detected in the adjacent cellular layers under the follicles. There was a very strong positive correlation between BMP15 and BMPR2 in ovary tissues. Expression of GDF9 was highly correlated with BMP15, BMPR1B, and BMPR2 in large antral follicles. Expression of BMP7 in small antral follicles and BMPR2 in ovary tissues was significantly increased in the high-AFC group. Expression of ESR1 and ESR2 involved in estrogen production as well as PRKAA1 which involved in AMPK production were significantly greater in large antral follicles of high-AFC. There was a very high correlation between Cyp19 and ESR1 in large antral follicles and ovary tissues. Expression of Cyp19 and PRKAA1 were positively correlated with GDF9, BMP15, and BMP7 in large follicles. In conclusion, this study suggests that apart from the BMP signaling, genes involved in AMPK and estrogen production can be pivotal players in ewe's follicular development process. In addition, a strong cross-talk can exist among AMPK, BMP signaling, and estrogen synthesis systems in ewe ovary.

Ovary and fimbrial stem cells: biology, niche and cancer origins

The mammalian ovary is covered by a single-layered epithelium that undergoes rupture and remodelling following each ovulation. Although resident stem cells are presumed to be crucial for this cyclic regeneration, their identity and mode of action have been elusive. Surrogate stemness assays and in vivo fate-mapping studies using recently discovered stem cell markers have identified stem cell pools in the ovary and fimbria that ensure epithelial homeostasis. Recent findings provide insights into intrinsic mechanisms and local extrinsic cues that govern the function of ovarian and fimbrial stem cells. These discoveries have advanced our understanding of stem cell biology in the ovary and fimbria, and lay the foundations for evaluating the contribution of resident stem cells to the initiation and progression of human epithelial ovarian cancer.

Scaffold-based delivery of adipose tissue-derived stem cells in rat frozen-thawed ovarian autografts: preliminary studies in a rat model

PURPOSE

This study aimed to evaluate whether a gelatin-based Gelfoam sponge is feasible as a scaffold for adipose tissue-derived stem cell (ASC) therapy in rat frozen-thawed ovarian autografts.

METHODS

Two sets of studies were performed. The in vitro set evaluated ASCs' viability in the Gelfoam scaffold at different times of co-culturing (after 24, 48, 72, 96, and 120 h). The in vivo set used 20 12-week-old adult female Wistar rats. Frozen-thawed ovarian grafts were treated with ASCs delivered in Gelfoam scaffolds immediately after an autologous retroperitoneal transplant (ASCs-GS, n = 10). The controls received Gelfoam with a culture medium (GS, n = 10). Assessment of graft quality was conducted by vaginal smears (until euthanasia on the 30th postoperative day), histological analyses, follicular density, and viability and fibrosis. Immunohistochemical staining for VEGF-A expression, vascular network (vWF), apoptosis (caspase-3 and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)), cell proliferation (Ki-67), and hormone receptors (estrogen and progesterone) were performed.

RESULTS

The cells remained viable in Gelfoam for up to 120 h of co-culturing. The graft morphology was similar among the groups. ASC therapy promoted the earlier resumption of the estrous phase (GS 16.6 ± 3 vs. ASCs-GS 12.8 ± 1.3 days) and enhanced estrogen receptors compared with the controls (p < 0.05) without interfering with the quantity and viability of the ovarian follicles, fibrosis, endothelial cells, VEGF immunoexpression, apoptosis, or cell proliferation (p > 0.05).

CONCLUSION

The Gelfoam scaffold could be a feasible and safe non-invasive technique for ASC delivery in the treatment of frozen-thawed ovarian autografts. Future studies should evaluate the real benefit of this treatment on the survival and endocrine activity of the graft.

FSH-FSHR3-stem cells in ovary surface epithelium: basis for adult ovarian biology, failure, aging, and cancer

Despite extensive research, genetic basis of premature ovarian failure (POF) and ovarian cancer still remains elusive. It is indeed paradoxical that scientists searched for mutations in FSH receptor (FSHR) expressed on granulosa cells, whereas more than 90% of cancers arise in ovary surface epithelium (OSE). Two distinct populations of stem cells including very small embryonic-like stem cells (VSELs) and ovarian stem cells (OSCs) exist in OSE, are responsible for neo-oogenesis and primordial follicle assembly in adult life, and are modulated by FSH via its alternatively spliced receptor variant FSHR3 (growth factor type 1 receptor acting via calcium signaling and the ERK/MAPK pathway). Any defect in FSH-FSHR3-stem cell interaction in OSE may affect folliculogenesis and thus result in POF. Ovarian aging is associated with a compromised microenvironment that does not support stem cell differentiation into oocytes and further folliculogenesis. FSH exerts a mitogenic effect on OSE and elevated FSH levels associated with advanced age may provide a continuous trigger for stem cells to proliferate resulting in cancer, thus supporting gonadotropin theory for ovarian cancer. Present review is an attempt to put adult ovarian biology, POF, aging, and cancer in the perspective of FSH-FSHR3-stem cell network that functions in OSE. This hypothesis is further supported by the recent understanding that: i) cancer is a stem cell disease and OSE is the niche for ovarian cancer stem cells; ii) ovarian OCT4-positive stem cells are regulated by FSH; and iii) OCT4 along with LIN28 and BMP4 are highly expressed in ovarian cancers.

Differential expression of the P2X7 receptor in ovarian surface epithelium during the oestrous cycle in the mouse

Purinergic signalling has been proposed as an intraovarian regulatory mechanism. Of the receptors responsible for purinergic transmission, the P2X7 receptor is an ATP-gated cationic channel that displays a broad spectrum of cellular functions ranging from apoptosis to cell proliferation and tumourigenesis. In the present study, we investigated the functional expression of P2X7 receptors in ovarian surface epithelium (OSE). P2X7 protein was detected in the OSE layer of the mouse, both in situ and in primary cultures. In cultures, 2'(3')-O-(4-Benzoylbenzoyl)adenosine-5'-triphosphate (BzATP) activation of P2X7 receptors increased [Ca(2+)]i and induced apoptosis. The functionality of the P2X7 receptor was investigated in situ by intrabursal injection of BzATP on each day of the oestrous cycle and evaluation of apoptosis 24h using the terminal deoxyribonucleotidyl transferase-mediated dUTP-fluorescein nick end-labelling (TUNEL) assay. Maximum effects of BzATP were observed during pro-oestrus, with the effects being blocked by A438079, a specific P2X7 receptor antagonist. Immunofluorescence staining for P2X7 protein revealed more robust expression during pro-oestrus and in OSE regions behind the antral follicles, strongly supporting the notion that the differences in apoptosis can be explained by increased receptor expression, which is regulated during the oestrous cycle. Finally, P2X7 receptor expression was detected in the OSE layer of human ovaries, with receptor expression maintained in human ovaries diagnosed with cancer, as well as in the human ovarian carcinoma SKOV3 cell line.

The mouse ovarian surface epithelium contains a population of LY6A (SCA-1) expressing progenitor cells that are regulated by ovulation-associated factors

The ovarian surface epithelium, a single layer of poorly differentiated epithelial cells, covers the surface of the ovary and is ruptured during ovulation. Little is known about the changes that occur in this layer before or during ovulation, and even less is known about the regenerative processes that occur after the surface is ruptured to release a mature oocyte. Recently, a population of mouse ovarian surface epithelial (MOSE) cells that exhibit progenitor/stem cell characteristics has been identified, though neither a genetic marker nor how these cells are regulated has been determined. We have identified a defined population of MOSE cells with progenitor cell characteristics that express the stem cell marker lymphocyte antigen 6 complex, locus A (LY6A; also known as stem cell antigen-1 [SCA-1]). By testing the effect of factors found in the follicular fluid at ovulation on proliferation, sphere formation, and LY6A expression, we have determined that the size of the LY6A-expressing (LY6A+) progenitor cell population is regulated by at least two ovulation-associated factors present in the follicular fluid: transforming growth factor beta 1 and leukemia-inhibitory factor. Our work has identified a population of LY6A+ MOSE progenitor cells on the surface of the ovary that may play a role in ovulatory wound healing.

In vitro regulation of sheep ovarian surface epithelium (OSE) proliferation by local ovarian factors

The ovarian surface epithelium (OSE) forms a lining around the entire ovary and actively participates in the ovulatory cycle. To investigate how specific growth factors and hormones affect OSE proliferation, the present study used sheep as a model to examine the effects of follicular and luteal products on the proliferation of sheep OSE cells in culture, and to analyse the influences of large antral follicles and corpora lutea (CL) on the expression of gonadotrophin receptors (FSHR and LHR) in the OSE. In the present study, follicular fluids from medium and large follicles, and extracts of corpora lutea stimulated the growth of OSE cells. The results of the present study showed that factors in the follicular fluid can induce OSE proliferative activity, and this stimulation effect could not be attributed to steroids in the follicular fluid since oestrogen and progesterone treatments failed to stimulate OSE cells. The expression of LH and FSH receptors over large follicles (5 mm or larger) was two and four times higher than those over stroma and CL, respectively. In conclusion, OSE proliferation in cycling sheep is associated with underlying developing follicles and CL, mediated by, at least in part, the up-regulation of gonadotrophin receptors, and facilitated by the action of mitogenic glycopeptides and growth factors, but not steroids.

Dynamics of the primate ovarian surface epithelium during the ovulatory menstrual cycle

BACKGROUND

Epithelial ovarian cancer (EOC) risk correlates strongly with the number of ovulations that a woman experiences. The primary source of EOC in women is the ovarian surface epithelium (OSE). Mechanistic studies on the etiology of OSE transformation to EOC cannot be realistically performed in women. Selecting a suitable animal model to investigate the normal OSE in the context of ovulation should be guided by the model's reproductive similarities to women in natural features that are thought to contribute to EOC risk.

METHODS

We selected the non-human primate, rhesus macaque, as a surrogate to study the normal OSE during the natural menstrual cycle. We investigated OSE morphology and marker expression, plus cell proliferation and death in relation to menstrual cycle stage and ovulation.

RESULTS

OSE cells displayed a morphological range from squamous to columnar. Cycle-independent parameters and cycle-dependent changes were observed for OSE histology, steroid receptor expression, cell death, DNA repair and cell adhesion. Contrary to findings in non-primates, primate OSE cells were not manifestly cleared from the site of ovulation, nor were proliferation rates affected by ovulation or stage of the menstrual cycle. DNA repair proteins were more highly expressed in OSE than in other ovarian cells.

CONCLUSIONS

This study identifies significant differences between primate and non-primate OSE. In contrast to established views, ovulation-induced death and proliferation are not indicated as prominent contributors to EOC risk, but disruption of OSE cadherin-mediated adhesion may be, as could the loss of ovary-mediated chronic suppression of proliferation and elevation of DNA repair potential.

Whole ovary immunohistochemistry for monitoring cell proliferation and ovulatory wound repair in the mouse

BACKGROUND

Ovarian surface epithelial cells are thought to be a precursor cell type for ovarian carcinoma. It has been proposed that an increased rate of ovarian surface epithelial cell proliferation during ovulatory wound repair contributes to the accumulation of genetic changes and cell transformation. The proliferation of ovarian surface epithelial cells during ovulatory wound repair has been studied primarily using immunohistochemical staining of paraffin-embedded ovary sections. However, such analyses require complex reconstruction from serially-cut ovary sections for the visualization and quantification of the cells on the ovarian surface. In order to directly visualize the proliferation and organization of the ovarian surface epithelial cells, we developed a technique for immunohistochemical staining of whole mouse ovaries. Using this method, we analyzed cell proliferation and morphologic changes in mouse ovarian surface epithelial cells during follicle growth and ovulatory wound repair.

METHODS

Three-week old FVB/N female mice were superovulated by sequential administration of pregnant mare's serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG). Ten hours after hCG administration, mice were given 5-bromo-2-deoxyuridine (BrdU) and euthanized two hours after BrdU administration for ovary isolation. The levels of incorporated BrdU in the ovarian surface epithelial cells were measured by staining paraffin-embedded ovary sections and whole ovaries with the BrdU antibody. Re-epithelialization of the ovarian surface after ovulatory rupture was visualized by immunohistochemical staining with E-cadherin and Keratin 8 in paraffin-embedded ovary sections and whole ovaries.

RESULTS

We determined that active proliferation of ovarian epithelial surface cells primarily occurs during antral follicle formation and, to a lesser extent, in response to an ovulatory wound. We also demonstrated that ovarian surface epithelial cells exhibit a circular organization around the wound site

CONCLUSION

Whole ovary immunohistochemistry enables efficient and comprehensive three-dimensional visualization of ovarian surface epithelial cells without the need for laborious reconstruction from immunohistochemically-stained serial ovary sections.

Nuclear entry of activated MAPK is restricted in primary ovarian and mammary epithelial cells

Background

The MAPK/ERK1/2 serine kinases are primary mediators of the Ras mitogenic signaling pathway. Phosphorylation by MEK activates MAPK/ERK in the cytoplasm, and phospho-ERK is thought to enter the nucleus readily to modulate transcription.

Principal Findings

Here, however, we observe that in primary cultures of breast and ovarian epithelial cells, phosphorylation and activation of ERK1/2 are disassociated from nuclear translocalization and transcription of downstream targets, such as c-Fos, suggesting that nuclear translocation is limited in primary cells. Accordingly, in import assays in vitro, primary cells showed a lower import activity for ERK1/2 than cancer cells, in which activated MAPK readily translocated into the nucleus and activated c-Fos expression. Primary cells express lower levels of nuclear pore complex proteins and the nuclear transport factors, importin B1 and importin 7, which may explain the limiting ERK1/2 import found in primary cells. Additionally, reduction in expression of nucleoporin 153 by siRNA targeting reduced ERK1/2 nuclear activity in cancer cells.

Conclusion

ERK1/2 activation is dissociated from nuclear entry, which is a rate limiting step in primary cells and in vivo, and the restriction of nuclear entry is disrupted in transformed cells by the increased expression of nuclear pores and/or nuclear transport factors.

Effects of hexarelin (a ghrelin analogue) on fertilisation and the pre- and postnatal development of mice

Ghrelin (Ghr) has been associated with reproductive physiology and pre- and postnatal development. The objectives of the present study were to evaluate the effects of hexarelin (HEX; 100 or 200 µg kg−1 day−1), a therapeutic Ghr analogue, on: (1) embryo development 60 h post ovulation, induced pharmacologically, in pregnant mice; (2) the physical, neurobiological and sexual development of offspring of female mice injected with HEX during the first, second or third week of pregnancy or throughout the entire pregnancy; and (3) adult memory acquisition in these offspring. We also evaluated the effects of chronic HEX administration on memory acquisition in adult mice. Treatment of non-pregnant female mice with HEX decreased ovulation rate. However, treatment of pregnant mice with HEX at any time during pregnancy tended to accelerate offspring maturation, regardless of bodyweight. This effect was only significant on neurobiological parameters following treatment during the first week. HEX treatment during the first week and/or throughout the entire pregnancy resulted in impaired memory acquisition in the offspring, with female mice being more susceptible to these effects. Similar results were observed for the effects of chronic HEX treatment on memory acquisition in adult mice. In conclusion, HEX seems to exert differential effects depending on when it is administered. Because HEX has started to be used therapeutically, its deleterious effects on ovulation and memory acquisition must be further evaluated.

Regulation of the proliferative activity of ovarian surface epithelial cells by follicular fluid

Despite critical roles of the ovarian surface epithelium (OSE) in ovulation and post-ovulatory wound repair, little is known about the physiological mechanism regulating OSE proliferation. A role of follicles and corpora lutea in locally regulating the proliferative activity of OSE has been suggested. In this study, the effects of follicular and luteal products on proliferation of cultured OSE cells were tested using cells obtained from seasonally anoestrous ewes. Follicular fluid but not luteal extracts induced OSE cell proliferation (2.5-fold relative to untreated controls; P<0.0001). The response of OSE cells was not affected by follicle size or previous charcoal-extraction of follicular fluid (P>0.1). Treatment with IGF-1 (2.2-fold; P<0.01), EGF (1.9-fold; P<0.01) and, to a lesser extent, FSH (P<0.05) also induced OSE cell proliferation. In contrast, oestradiol or progesterone did not induce cell proliferation or enhance the effects of FSH on proliferation (P>0.1). It was concluded that follicular fluid can directly stimulate ovine OSE cell proliferation and that this effect is attributable to non-steroidal mitogens.

Expression of gonadotrophin releasing hormone receptor I is a favorable prognostic factor in epithelial ovarian cancer

The majority of epithelial ovarian cancers originate in the ovarian surface epithelium. The ovarian surface epithelium is a hormonally responsive tissue, and hormones are thought to play a key role in the development of this type of cancer. Gonadotrophin releasing hormone II is one of 2 isoforms which are thought to act through gonadotrophin releasing hormone receptor I, and gonadotrophin releasing hormone II has been shown to cause growth inhibition of cultured ovarian surface epithelium. The aim of this study was to investigate the expression levels and prognostic significance of gonadotrophin releasing hormone II and the gonadotrophin releasing hormone receptor I in epithelial ovarian cancer. Gonadotrophin releasing hormone II and gonadotrophin releasing hormone receptor I messenger RNA expression was examined in 23 cancers and 7 normal ovarian surface epithelium samples by quantitative real time polymerase chain reaction. An ovarian cancer tissue microarray containing 139 cases was constructed and immunohistochemical analysis of gonadotrophin releasing hormone II and gonadotrophin releasing hormone receptor I protein expression was performed and correlated with clinical outcome data. Gonadotrophin releasing hormone II messenger RNA expression was lower in cancer samples compared to normal ovarian surface epithelium samples (P < .05). Gonadotrophin releasing hormone II protein expression correlated with histologic subtype (25% serous versus 45% nonserous, P < .05) but not with overall survival. Gonadotrophin releasing hormone receptor I messenger RNA expression was highest in serous tumors when compared to non serous (P < .05) and normal tissue (P < .001). Expression of the gonadotrophin releasing hormone receptor I protein was also found to correlate with patient survival (P < .05). We have demonstrated gonadotrophin releasing hormone II and its receptor, gonadotrophin releasing hormone receptor I, are present in clinical ovarian samples, and that gonadotrophin releasing hormone receptor I protein expression is a favorable prognostic factor, suggesting these proteins play an important role in the development of epithelial ovarian cancer.

Role of endocrine and growth factors on the ovarian surface epithelium

Epithelial ovarian cancer is a highly fatal disease for which prevention strategies have been limited; in part because of our poor understanding of the underlying biology of its precursor, the ovarian surface epithelium (OSE). The OSE is a single layer of flat-to-cuboidal mesothelial cells that covers the surface of the ovary. Despite its inconspicuous appearance in vivo, it is believed that OSE cells actively participate in the cyclical ovulatory rupture and repair process. The continuous rupture of the OSE at ovulation and the subsequent proliferation to repair the wound renders the cells susceptible to genetic damage and malignant transformation. As the ovary is a rich source of multiple hormones, and normal OSE and ovarian carcinomas secrete and have receptors for hormones, growth factors and cytokines, these factors are strong candidates to regulate normal OSE physiology and the transformation and progression of ovarian cancers. In particular, alterations of hormone/growth factor production and receptor expression are common in ovarian tumors. This review summarizes the current knowledge in the field of endocrinology and its relationship to the biology and pathology of the OSE.

Gonadotropin-induced superovulation drives ovarian surface epithelia proliferation in CD1 mice

The ovarian surface epithelium (OSE) is a monolayer of cells that surround the ovary and accommodate repeated tear and repair in response to ovulation. OSE cells are thought to be the progenitors of 90% of ovarian cancers. Currently, the total amount of proliferation of the OSE has not been reported in response to one ovulatory event. In this study, proliferation of the OSE was quantified in response to superovulation induced by ip injection of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) in immature 27-d-old CD1 mice using bromodeoxyuridine (BrdU). BrdU incorporation into the OSE cells was measured from the time of hCG injection for a total cumulative label of 12 h. BrdU incorporation was also measured from the time of PMSG injection for a total label of 60 h to correlate proliferation with specific gonadotropin stimulation. The OSE proliferation was significantly higher in superovulated animals compared with control mice at all time points. Proliferation was also analyzed in discrete anatomical sections and indicated that OSE covering antral follicles and corpora lutea proliferated more rapidly than OSE distal to follicular growth. Finally, apoptosis was assessed in response to ovulation, and virtually no cell death within the OSE was detected. These data demonstrate that the OSE, especially near antral follicles and corpora lutea, proliferates significantly in response to the gonadotropins PMSG and hCG. Therefore, ovarian surface cell division in response to ovulation could contribute to ovarian cancer by proliferation-induced DNA mutations and transformed cell progression.