Dynamics of the membrana granulosa during expansion of the ovarian follicular antrum

Exploring the Impact of Controlled Ovarian Stimulation and Non-Invasive Oocyte Assessment in ART Treatments

Invasive and noninvasive features are normally applied to select developmentally competent oocytes and embryos that can increase the take-home baby rates in assisted reproductive technology. The noninvasive approach mainly applied to determine oocyte and embryo competence has been, since the early days of IVF, the morphological evaluation of the mature cumulus-oocyte complex at the time of pickup, first polar body, zona pellucida thickness, perivitelline space and cytoplasm appearance. Morphological evaluation of oocyte quality is one of the options used to predict successful fertilization, early embryo development, uterine implantation and the capacity of an embryo to generate a healthy pregnancy to term. Thus, this paper aims to provide an analytical revision of the current literature relating to the correlation between ovarian stimulation procedures and oocyte/embryo quality. In detail, several aspects of oocyte quality such as morphological features, oocyte competence and its surrounding environment will be discussed. In addition, the main noninvasive features as well as novel approaches to biomechanical parameters of oocytes that might be correlated with the competence of embryos to produce a healthy pregnancy and live birth will be illustrated.

Telomerase Activity in Somatic Tissues and Ovaries of Diploid and Triploid Rainbow Trout (Oncorhynchus mykiss) Females

Telomerase activity has been found in the somatic tissues of rainbow trout. The enzyme is essential for maintaining telomere length but also assures homeostasis of the fish organs, playing an important role during tissue regeneration. The unique morphological and physiological characteristics of triploid rainbow trout, when compared to diploid specimens, make them a promising model for studies concerning telomerase activity. Thus, in this study, we examined the expression of the Tert gene in various organs of subadult and adult diploid and triploid rainbow trout females. Upregulated Tert mRNA transcription was observed in all the examined somatic tissues sampled from the triploid fish when compared to diploid individuals. Contrastingly, Tert expression in the ovaries was significantly decreased in the triploid specimens. Within the diploids, the highest expression of Tert was observed in the liver and in the ovaries of the subadult individuals. In the triploids, Tert expression was increased in the somatic tissues, while the ovaries exhibited lower activity of telomerase compared to other organs and decreased compared to the ovaries in the diploids. The ovaries of triploid individuals were underdeveloped, consisting of only a few oocytes. The lack of germ cells, which are usually characterized by high Tert expression, might be responsible for the decrease in telomerase activity in the triploid ovaries. The increase in Tert expression in triploid somatic tissues suggests that they require higher telomerase activity to cope with environmental stress and maintain internal homeostasis.

Advances of xenogeneic ovarian extracellular matrix hydrogels for in vitro follicle development and oocyte maturation

Research aimed at preserving female fertility is increasingly using bioengineering techniques to develop new platforms capable of supporting ovarian cell function in vitro and in vivo. Natural hydrogels (alginate, collagen, and fibrin) have been the most exploited approaches; however they are biologically inert and/or biochemically simple. Thus, establishing a suitable biomimetic hydrogel from decellularized ovarian cortex (OC) extracellular matrix (OvaECM) could provide a complex native biomaterial for follicle development and oocyte maturation. The objectives of this work were (i) to establish an optimal protocol to decellularize and solubilize bovine OC, (ii) to characterize the histological, molecular, ultrastructural, and proteomic properties of the resulting tissue and hydrogel, and (iii) to assess its biocompatibility and adequacy for murine in vitro follicle growth (IVFG). Sodium dodecyl sulfate was identified as the best detergent to develop bovine OvaECM hydrogels. Hydrogels added into standard media or used as plate coatings were employed for IVFG and oocyte maturation. Follicle growth, survival, hormone production, and oocyte maturation and developmental competence were evaluated. OvaECM hydrogel-supplemented media best supported follicle survival, expansion, and hormone production, while the coatings provided more mature and competent oocytes. Overall, the findings support the xenogeneic use of OvaECM hydrogels for future human female reproductive bioengineering.

Squeezing the eggs to grow: The mechanobiology of mammalian folliculogenesis

The formation of functional eggs (oocyte) in ovarian follicles is arguably one of the most important events in early mammalian development since the oocytes provide the bulk genetic and cytoplasmic materials for successful reproduction. While past studies have identified many genes that are critical to normal ovarian development and function, recent studies have highlighted the role of mechanical force in shaping folliculogenesis. In this review, we discuss the underlying mechanobiological principles and the force-generating cellular structures and extracellular matrix that control the various stages of follicle development. We also highlight emerging techniques that allow for the quantification of mechanical interactions and follicular dynamics during development, and propose new directions for future studies in the field. We hope this review will provide a timely and useful framework for future understanding of mechano-signalling pathways in reproductive biology and diseases.

At the crossroads of fertility and metabolism: the importance of AMPK-dependent signaling in female infertility associated with hyperandrogenism

STUDY QUESTION

What biological processes are linked to the signaling of the energy sensor 5'-AMP-activated protein kinase (AMPK) in mouse and human granulosa cells (GCs)?

SUMMARY ANSWER

The lack of α1AMPK in GCs impacted cell cycle, adhesion, lipid metabolism and induced a hyperandrogenic response.

WHAT IS KNOWN ALREADY

AMPK is expressed in the ovarian follicle, and its activation by pharmacological medications, such as metformin, inhibits the production of steroids. Polycystic ovary syndrome (PCOS) is responsible for infertility in approximately 5-20% of women of childbearing age and possible treatments include reducing body weight, improving lifestyle and the administration of a combination of drugs to improve insulin resistance, such as metformin.

STUDY DESIGN, SIZE, DURATION

AMPK signaling was evaluated by analyzing differential gene expression in immortalized human granulosa cells (KGNs) with and without silencing α1AMPK using CRISPR/Cas9. In vivo studies included the use of a α1AMPK knock-out mouse model to evaluate the role of α1AMPK in folliculogenesis and fertility. Expression of α1AMPK was evaluated in primary human granulosa-luteal cells retrieved from women undergoing IVF with and without a lean PCOS phenotype (i.e. BMI: 18-25 kg/m2).

PARTICIPANTS/MATERIALS, SETTING, METHODS

α1AMPK was disrupted in KGN cells and a transgenic mouse model. Cell viability, proliferation and metabolism were evaluated. Androgen production was evaluated by analyzing protein levels of relevant enzymes in the steroid pathway by western blots, and steroid levels obtained from in vitro and in vivo models by mass spectrometry. Differential gene expression in human GC was obtained by RNA sequencing. Analysis of in vivo murine folliculogenesis was performed by histology and immunochemistry, including evaluation of the anti-Müllerian hormone (AMH) marker. The α1AMPK gene expression was evaluated by quantitative RT-PCR in primary GCs obtained from women with the lean PCOS phenotype (n = 8) and without PCOS (n = 9).

MAIN RESULTS AND THE ROLE OF CHANCE

Silencing of α1AMPK in KGN increased cell proliferation (P < 0.05 versus control, n = 4), promoted the use of fatty acids over glucose, and induced a hyperandrogenic response resulting from upregulation of two of the enzymes involved in steroid production, namely 3β-hydroxysteroid dehydrogenase (3βHSD) and P450 side-chain cleavage enzyme (P450scc) (P < 0.05, n = 3). Female mice deficient in α1AMPK had a 30% decrease in their ovulation rate (P < 0.05, n = 7) and litter size, a hyperandrogenic response (P < 0.05, n = 7) with higher levels of 3βHSD and p450scc levels in the ovaries, and an increase in the population of antral follicles (P < 0.01, n = 10) compared to controls. Primary GCs from lean women with PCOS had lower α1AMPK mRNA expression levels than the control group (P < 0.05, n = 8-9).

LARGE SCALE DATA

The FastQ files and metadata were submitted to the European Nucleotide Archive (ENA) at EMBL-EBI under accession number PRJEB46048.

LIMITATIONS, REASONS FOR CAUTION

The human KGN is a not fully differentiated, transformed cell line. As such, to confirm the role of AMPK in GC and the PCOS phenotype, this model was compared to two others: an α1AMPK transgenic mouse model and primary differentiated granulosa-lutein cells from non-obese women undergoing IVF (with and without PCOS). A clear limitation is the small number of patients with PCOS utilized in this study and that the collection of human GCs was performed after hormonal stimulation.

WIDER IMPLICATIONS OF THE FINDINGS

Our results reveal that AMPK is directly involved in steroid production in human GCs. In addition, AMPK signaling was associated with other processes frequently reported as dysfunctional in PCOS models, such as cell adhesion, lipid metabolism and inflammation. Silencing of α1AMPK in KGN promoted folliculogenesis, with increases in AMH. Evaluating the expression of the α1AMPK subunit could be considered as a marker of interest in infertility cases related to hormonal imbalances and metabolic disorders, including PCOS.

STUDY FUNDING/COMPETING INTEREST(S)

This study was financially supported by the Institut National de la Recherche Agronomique (INRA) and the national programme « FERTiNERGY » funded by the French National Research Agency (ANR). The authors report no intellectual or financial conflicts of interest related to this work. R.K. is identified as personnel of the International Agency for Research on Cancer/World Health Organization. R.K. alone is responsible for the views expressed in this article and she does not necessarily represent the decisions, policy or views of the International Agency for Research on Cancer/World Health Organization.

TRIAL REGISTRATION NUMBER

N/A.

Signaling mechanisms and their regulation during in vivo or in vitro maturation of mammalian oocytes

In vitro fertilization (IVF) is currently one of the most effective methods of infertility treatment. An alternative to commonly used ovarian hyperstimulation can become extracorporeal maturation of oocytes (in vitro maturation; IVM). Fertilization and normal development of the embryo depends on the cytoplasmic, nuclear and genomic maturity of the oocyte. The microenvironment of the ovarian follicle and maternal signals, which mediate bidirectional communication between granulosa, cumulus and oocyte cells, influence the growth, maturation and acquisition of oocyte development capability. During oogenesis in mammals, the meiosis is inhibited in the oocyte at the prophase I of the meiotic division due to the high cAMP level. This level is maintained by the activity of C-type natriuretic peptide (CNP, NPPC) produced by granulosa cells. The CNP binds to the NPR2 receptor in cumulus cells and is responsible for the production of cyclic guanosine monophosphate (cGMP). The cGMP penetrating into the oocyte through gap junctions inhibits phosphodiesterase 3A (PDE3A), preventing cAMP hydrolysis responsible for low MPF activity. The LH surge during the reproductive cycle reduces the activity of the CNP/NPR2 complex, which results in a decrease in cGMP levels in cumulus cells and consequently in the oocyte. Reduced cGMP concentration unblocks the hydrolytic activity of PDE3A, which decreases cAMP level inside the oocyte. This leads to the activation of MPF and resumption of meiosis. The latest IVM methods called SPOM, NFSOM or CAPA IVM consist of two steps: prematuration and maturation itself. Taking into account the role of cAMP in inhibiting and then unblocking the maturation of oocytes, they have led to a significant progress in terms of the percentage of mature oocytes in vitro and the proportion of properly developed embryos in both animals and humans.

Ovarian Telomerase and Female Fertility

Women's fertility is characterized both quantitatively and qualitatively mainly by the pool of ovarian follicles. Monthly, gonadotropins cause an intense multiplication of granulosa cells surrounding the oocyte. This step of follicular development requires a high proliferation ability for these cells. Telomere length plays a crucial role in the mitotic index of human cells. Hence, disrupting telomere homeostasis could directly affect women's fertility. Strongly expressed in ovaries, telomerase is the most effective factor to limit telomeric attrition and preserve ovarian reserve. Considering these facts, two situations of infertility could be correlated with the length of telomeres and ovarian telomerase activity: PolyCystic Ovary Syndrome (PCOS), which is associated with a high density of small antral follicles, and Premature Ovarian Failure (POF), which is associated with a premature decrease in ovarian reserve. Several authors have studied this topic, expecting to find long telomeres and strong telomerase activity in PCOS and short telomeres and low telomerase activity in POF patients. Although the results of these studies are contradictory, telomere length and the ovarian telomerase impact in women's fertility disorders appear obvious. In this context, our research perspectives aimed to explore the stimulation of ovarian telomerase to limit the decrease in the follicular pool while avoiding an increase in cancer risk.

Upsurge in autophagy, associated with mifepristone-treated polycystic ovarian condition, is reversed upon thymoquinone treatment

Polycystic ovarian syndrome (PCOS) is a multi-factorial gynecological endocrine disorder. It affects fertility in women and also predisposes to insulin resistance, type 2 diabetes mellitus, obesity etc. Earlier, significance of autophagy has been explored in PCOS-related metabolic disorders and during normal folliculogenesis. Increasing evidences reveal connection of autophagy with chronic inflammatory behaviour, an associated phenomena in polycystic ovaries. However, understanding of the association of autophagy with PCOS is still obscure. This study reveals that increased autophagy in mifepristone (RU486) treated KK-1 cells and in vivo PCO rat model is characterized by upregulated Androgen Receptor (AR) expression and downregulated PCO biomarker aromatase. The prevalence of autophagy has been observed to be concomitant with increased expression of two autophagic markers Beclin1 and MAP-LC3-II while the autophagy substrate p62/SQSTM1 was downregulated. Immunohistochemical staining revealed increased localization of MAP-LC3 in the compacted granulosa layers of the follicular cysts in the PCO model. The PCO rat models also demonstrated augmented levels of p65, the active subunit of NF-κB, which acts as a transcriptional regulator of several pro-inflammatory factors. NF-κB repressor and anti-inflammatory herbal drug thymoquinone, known to alleviate PCO condition, downregulated autophagy modules substantially. Pre-treatment with thymoquinone upregulated aromatase, reduced AR levels and decreased autophagic markers as well as p65 levels, simulating super-ovulated condition. In conclusion, the anti-inflammatory phytochemical thymoquinone alleviated PCO condition.

Evaluation of stemness marker expression in bovine ovarian granulosa cells

The objective of this study was to assess the stemness marker expressions (Oct4, Nanog, and Sox2) of granulosa cells (GCs) collected from bovine ovarian follicles and in vitro expansion. The single bovine ovarian follicles were isolated and categorized into 4 groups according to their diameter including group A (<2 mm), group B (2-3 mm), group C (3-4 mm), and group D (>4 mm). Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and immunostaining were applied to evaluate the stemness marker expression of bovine GCs from ovarian follicles. We also estimated the stemness marker transcript expressions of GCs during in vitro expression by qRT-PCR. qRT-PCR analysis demonstrated that fresh GCs from bovine ovarian follicles expressed the stemness markers (Oct4, Nanog, Sox2). These markers were down-regulated during antral stage follicular development. We also estimated stemness marker transcript expressions of GCs which were isolated and in vitro expanded from ovarian follicles of group A. The qRT-PCR results showed that Oct4 and Sox2 transcript expressions were reduced during in vitro expansion while Nanog transcript was not expressed.

Effect of Prenatal and Neonatal Anti-Androgen Flutamide Treatment on Aquaporin 5 Expression in the Adult Porcine Ovary

The growth of ovarian follicles is accompanied by fluid-filled antrum formation. Water movement within the follicular wall is predominantly transcellular via membranous water channels named aquaporins (AQPs). Androgens are important regulators of mammalian folliculogenesis, and their prenatal and/or neonatal deficiency affects female fertility in adulthood. Therefore, this study was performed to determine whether gestational or neonatal exposure to the anti-androgen flutamide influences androgen-dependent AQP5 expression in pre-antral and large antral follicles of adult pigs. Flutamide was injected into pregnant gilts between days 80 and 88 of gestation and into female piglets between days 2 and 10 post-natally. The ovaries were collected from flutamide-treated and non-treated (control) sexually mature pigs. In pre-antral follicles, AQP5 mRNA and protein levels were both downregulated following maternal (p < 0.01 and p < 0.01, respectively) and neonatal (p < 0.01 and p < 0.01, respectively) flutamide exposure. Likewise, the expression of mRNA (p < 0.01 and p < 0.001, respectively) and protein (p < 0.05 and p < 0.01, respectively) for AQP5 were diminished in large antral follicles in both groups. Immunohistochemistry showed decreased intensity of AQP5 immunoreaction in pre-antral (p < 0.01) and large antral (p < 0.001) follicles following flutamide treatment. Moreover, radioimmunological analysis revealed that changes observed in AQP5 expression corresponded with diminished follicular androgens production after both maternal (p < 0.05 and p < 0.05, respectively) and neonatal (p < 0.05 and p < 0.01, respectively) flutamide administration. Therefore, AQP5 appears to be a potential regulator of follicular fluid accumulation, under androgen control, and may be a key factor in antral follicle growth.

Selective Regulation of Oocyte Meiotic Events Enhances Progress in Fertility Preservation Methods

Following early embryonic germ cell migration, oocytes are surrounded by somatic cells and remain arrested at diplotene stage until luteinizing hormone (LH) surge. Strict regulation of both meiotic arrest and meiotic resumption during dormant stage are critical for future fertility. Inter-cellular signaling system between the somatic compartment and oocyte regulates these meiotic events and determines the follicle quality. As well as the collected number of eggs, their qualities are also important for in vitro fertilization (IVF) outcome. In spontaneous and IVF cycles, germinal vesicle (GV)–stage oocytes, premature GV breakdown, and persistence of first meiotic arrest limit the reproductive performance. Likewise, both women with premature ovarian aging and young cancer women are undergoing chemoradiotherapy under the risk of follicle loss because of unregulated meiotic events. Understanding of oocyte meiotic events is therefore critical for the prevention of functional ovarian reserve. High levels of cyclic guanosine monophophate (cGMP), cyclic adenosine monophophate (cAMP) and low phosphodiesterase (PDE) 3A enzyme activity inside the oocyte are responsible for maintaining of meiotic arrest before the LH surge. cGMP is produced in the somatic compartment, and natriuretic peptide precursor C (Nppc) and natriuretic peptide receptor 2 (Npr2) regulate its production. cGMP diffuses into the oocyte and reduces the PDE3A activity, which inhibits the conversion of cAMP to the 5′AMP, and cAMP levels are enhanced. In addition, oocyte itself has the ability to produce cAMP. Taken together, accumulation of cAMP inside the oocyte induces protein kinase activity, which leads to the inhibition of maturation-promoting factor and meiotic arrest also continues. By stimulating the expression of epidermal growth factor, LH inhibits the Nppc/Npr2 system, blocks cGMP synthesis, and initiates meiotic resumption. Oocytes lacking the functional of this pathway may lead to persistence of the GV oocyte, which reduces the number of good quality eggs. Selective regulation of somatic cell signals and oocyte meiotic events enhance progress in fertility preservation methods, which may give us the opportunity to prevent follicle loss in prematurely aging women and young women with cancer are undergoing chemoradiotherapy.

Identification and characterization of epithelial cells derived from human ovarian follicular fluid

Introduction

Follicular fluid is important for follicular development and oocyte maturation. Evidence suggests that follicular fluid is not only rich in proteins but cells. Besides oocytes, the follicular fluid contains granulosa, thecal, and ovarian surface epithelial cells, and both granulosa and thecal cells are well-characterized. However, epithelial cells in follicular fluid are poorly studied. This study aims to isolate and characterize in vitro epithelial cells that originate from human ovarian follicular fluid retrieved in the assisted fertilization program.

Methods

Follicular fluid samples were collected from 20 women in the assisted reproduction program. Epithelial cells were characterized by flow cytometry assay, immunofluorescence staining, real-time PCR, and time lapse photography.

Results

Epithelial cell cultures were established from 18 samples. A small population of epithelial cells expresses germ-line stem cell markers, such as octamer-binding transcription factor 4 (OCT4), NANOG, and DEAD box polypeptide 4 (DDX4). In the epithelial cell culture system, oocyte-like cells formed spontaneously in vitro and expressed the following transcription markers: deleted in azoospermia-like (DAZL), developmental pluripotency associated protein 3 stella-related protein (STELLA), zona pellucida gene family C (ZPC), Syntaptonemal complex protein (SCP), and growth and differentiation factor 9 (GDF9). Some of the oocyte-like cells developed a zona pellucida-like structure. Both the symmetric and asymmetric division split of epithelial cells and early developing oocytes were observed using time lapse photography. Cell colonies were formed during epithelial culturing, which maintained and proliferated in an undifferentiated way on the feeder layer and expressed some pluripotency markers. These colonies differentiated in vitro into various somatic cell types in all three germ layers, but did not form teratoma when injected into immunodeficient mice. Furthermore, these epithelial cells could be differentiated directly to functional hepatocyte-like cells, which do not exist in ovarian tissues.

Conclusions

The epithelial cells derived from follicular fluid are a potential stem cell source with a pluripotent/multipotent character for safe application in oogenesis and regenerative medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0004-6) contains supplementary material, which is available to authorized users.

Stem cells, progenitor cells, and lineage decisions in the ovary

Exploring stem cells in the mammalian ovary has unleashed a Pandora's box of new insights and questions. Recent evidence supports the existence of stem cells of a number of the different cell types within the ovary. The evidence for a stem cell model producing mural granulosa cells and cumulus cells is strong, despite a limited number of reports. The recent identification of a precursor granulosa cell, the gonadal ridge epithelial-like cell, is exciting and novel. The identification of female germline (oogonial) stem cells is still very new and is currently limited to just a few species. Their origins and physiological roles, if any, are unknown, and their potential to produce oocytes and contribute to follicle formation in vivo lacks robust evidence. The precursor of thecal cells remains elusive, and more compelling data are needed. Similarly, claims of very small embryonic-like cells are also preliminary. Surface epithelial cells originating from gonadal ridge epithelial-like cells and from the mesonephric epithelium at the hilum of the ovary have also been proposed. Another important issue is the role of the stroma in guiding the formation of the ovary, ovigerous cords, follicles, and surface epithelium. Immune cells may also play key roles in developmental patterning, given their critical roles in corpora lutea formation and regression. Thus, while the cellular biology of the ovary is extremely important for its major endocrine and fertility roles, there is much still to be discovered. This review draws together the current evidence and perspectives on this topic.

The global effect of follicle-stimulating hormone and tumour necrosis factor α on gene expression in cultured bovine ovarian granulosa cells

BACKGROUND

Oocytes mature in ovarian follicles surrounded by granulosa cells. During follicle growth, granulosa cells replicate and secrete hormones, particularly steroids close to ovulation. However, most follicles cease growing and undergo atresia or regression instead of ovulating. To investigate the effects of stimulatory (follicle-stimulating hormone; FSH) and inhibitory (tumour necrosis factor alpha; TNFα) factors on the granulosa cell transcriptome, bovine ovaries were obtained from a local abattoir and pools of granulosa cells were cultured in vitro for six days under defined serum-free conditions with treatments present on days 3-6. Initially dose-response experiments (n = 4) were performed to determine the optimal concentrations of FSH (0.33 ng/ml) and TNFα (10 ng/ml) to be used for the microarray experiments. For array experiments cells were cultured under control conditions, with FSH, with TNFα, or with FSH plus TNFα (n = 4 per group) and RNA was harvested for microarray analyses.

RESULTS

Statistical analysis showed primary clustering of the arrays into two groups, control/FSH and TNFα/TNFα plus FSH. The effect of TNFα on gene expression dominated that of FSH, with substantially more genes differentially regulated, and the pathways and genes regulated by TNFα being similar to those of FSH plus TNFα treatment. TNFα treatment reduced the endocrine activity of granulosa cells with reductions in expression of FST, INHA, INBA and AMH. The top-ranked canonical pathways and GO biological terms for the TNFα treatments included antigen presentation, inflammatory response and other pathways indicative of innate immune function and fibrosis. The two most significant networks also reflect this, containing molecules which are present in the canonical pathways of hepatic fibrosis/hepatic stellate cell activation and transforming growth factor β signalling, and these were up regulated. Upstream regulator analyses also predicted TNF, interferons γ and β1 and interleukin 1β.

CONCLUSIONS

In vitro, the transcriptome of granulosa cells responded minimally to FSH compared with the response to TNFα. The response to TNFα indicated an active process akin to tissue remodelling as would occur upon atresia. Additionally there was reduction in endocrine function and induction of an inflammatory response to TNFα that displays features similar to immune cells.

Increased expression of kindlin 2 in luteinized granulosa cells correlates with androgen receptor level in patients with polycystic ovary syndrome having hyperandrogenemia

Hyperandrogenemia is the leading defect in patients with polycystic ovary syndrome (PCOS) and considered to be involved in the ovulation dysfunction of PCOS. During the process of ovulation, granulosa cells (GCs) undergo epithelial-mesenchymal transition (EMT), and integrin-interacting protein kindlin 2 is a well-known regulator in EMT. Therefore, our objective here was to compare the expression levels of kindlin 2 in luteinized GCs between patients with PCOS and control women and the relationship between kindlin 2 and PCOS pathogenesis. In this study, kindlin 2 expression was significantly increased in luteinized GCs from patients with PCOS, and kindlin 2 could be induced by testosterone both in vitro and in vivo. Meanwhile, kindlin 2 was positively correlated with androgen receptor (AR) in PCOS GCs. Taken together, kindlin 2 may play a role in luteinized GCs, especially in the case of excess androgen. Further studies are required to assess the specific role of kindlin 2 in follicular development and PCOS pathogenesis.

In vivo collection of follicular fluid and granulosa cells from individual follicles of different diameters in cattle by an adapted ovum pick-up system

BACKGROUND

Most studies on granulosa cell (GC) function in cattle have been performed using GC and follicular fluid (FF) samples collected from slaughterhouse ovaries. Using this approach, the follicular developmental stage and functional status are unknown and indirectly inferred, limiting data interpretation. Ultrasound-guided follicle aspiration has previously been used to recover GC or FF samples, but this was mostly carried out in large follicles or pools of small follicles, without recording the efficiency of recovery. The present study was aimed at adapting and evaluating an ovum pick-up (OPU) system for the in vivo recovery of FF and GC from individual follicles of different diameters.

METHODS

In the first trial, the losses of fluid inside the tubing system were calculated using a conventional or an adapted-OPU system. Blood plasma volumes equivalent to the amount of FF in follicles of different diameters were aspirated using a conventional OPU Teflon circuit. The OPU system was then adapted by connecting 0.25 mL straws to the circuit. A second trial evaluated the efficiency of FF recovery in vivo. Follicles ranging from 4.0 to 16.8 mm in diameter were aspirated individually using the conventional or adapted-OPU systems. A third trial assessed the in vivo recovery of GC and the subsequent amount of RNA obtained from the follicles of different diameters from Holstein and Gir cattle.

RESULTS

In Trial I, the plasma recovery efficiency was similar (P > 0.05) for the volumes expected for 12 and 10 mm follicles, but decreased (P < 0.05) for smaller follicles (45.7+/-4.0%, 12.4+/-4.3% and 0.0+/-0.0% for 8, 6, and 4 mm follicles, respectively). Using the adaptation, the losses intrinsic to the aspiration system were similar for all follicle diameters. In Trial II, the expected and recovered volumes of FF were correlated (r = 0.89) and the efficiency of recovery was similar among follicles <12 mm, while larger follicles had a progressive increase in FF losses that was not related to the tubing system. In Trial III, the number of GC and amount of RNA obtained were not affected (P > 0.05) by follicle size, but differed according to breed (615,054+/-58,122 vs 458,095+/-36,407 for Holstein and Gir, respectively; P < 0.05).

CONCLUSIONS

The adapted-OPU system can be successfully used for the in vivo collection of FF and GC from follicles of different diameters. This will enable further endocrine, cellular, and gene expression analyses.

Plasticity of granulosa cells: on the crossroad of stemness and transdifferentiation potential

The ovarian follicle represents the basic functional unit of the ovary and consists of an oocyte, which is surrounded by granulosa cells (GCs). GCs play an important role in the growth and development of the follicle. They are subject to increased attention since it has recently been shown that the subpopulation of GCs within the growing follicle possesses exceptionally plasticity showing stem cell characteristics. In assisted reproduction programs, oocytes are retrieved from patients together with GCs, which are currently discarded daily, but could be an interesting subject to be researched and potentially used in regenerative medicine in the future. Isolated GCs expressed stem cell markers such as OCT-4, NANOG and SOX-2, showed high telomerase activity, and were in vitro differentiated into other cell types, otherwise not present within ovarian follicles. Recently another phenomenon demonstrated in GCs is transdifferentiation, which could explain many ovarian pathological conditions. Possible applications in regenerative medicine are also given.

Testosterone influences water transport in porcine granulosa cells

The development of antral ovarian follicles entails fluid accumulation, but the mechanisms regulating water flux are unknown. Aquaporins are small, integral membrane proteins facilitating passive movement of water, some of which are known to be regulated by steroid hormones. The aim of this study was to determine whether testosterone (T) influences water transport in porcine granulosa cells. To assess water movement, the swelling of granulosa cells when moved from isotonic (319 mOsm) to hypotonic (95 mOsm) medium was measured after 12-hour pre-incubation in the presence of either testosterone (T), the antiandrogen 2-hydroxyflutamide (HF) or HF and T together. Pre-incubation with T increased the swelling of granulosa cells (p < 0.01) and this was abolished by HF (p < 0.001). Neither T nor HF affected cells in isotonic medium (319 mOsm). The results indicate that T acting via intracellular androgen receptors increases water permeability of porcine granulosa cells, probably through the regulation of aquaporin activity.

Insulin-like growth factor II (IGF-II) and follicle stimulating hormone (FSH) combinations can improve the in vitro development of grown oocytes enclosed in caprine preantral follicles

OBJECTIVE

Evaluate the possible role of IGF-II alone or in association with FSH on in vitro development of isolated caprine preantral follicles.

METHODS

Preantral follicles (≥150 μm) were isolated from goat ovaries and cultured for 18 days in basic αMEM medium (control) or supplemented with IGF-II alone at 20 or 50 ng/ml, named IGF20 and IGF50, respectively, or in combination with recombinant FSH (FSH, IGF20F or IGF50F). During in vitro culture, the follicles were analyzed by using morphology criteria, antrum formation and growth rate as parameters. After 18 days of follicular culture, oocytes equal to or larger than 110 μm were used for in vitro maturation (IVM). Oocyte viability and meiosis resumption were assessed by fluorescence microscopy after labeling with calcein-AM, ethidium homodimer and Hoechst 33342.

RESULTS

The IGF20 treatment was the only treatment capable of maintaining the percentage of morphologically normal follicles from D0 until D6 and from D12 to D18 (p>0.05), while in all other treatments the percentage of morphologically normal follicles decreased progressively during 18 days of in vitro culture (p<0.05). At D18, all treatments with IGF-II or FSH resulted in a significantly higher percentage of normal follicles when compared to αMEM alone. The IGF50F treatment provided a significantly higher early antrum formation rate when compared to αMEM and FSH alone. The addition of IGF-II alone (20 or 50 ng/ml) or in combination with FSH prevented oocyte degeneration after IVM. Moreover, the FSH treatment demonstrated a lower percentage of oocyte degeneration when compared to control (4.35% vs. 26.3%, respectively; p<0.05). Regarding meiosis resumption, the IGF20F treatment was the only treatment that significantly differed from αMEM alone. All treatments except the control (αMEM alone) presented oocytes at metaphase II.

CONCLUSION

IGF-II associated with FSH stimulated in vitro follicular development, oocyte viability and meiotic resumption of caprine oocytes after IVM.

Cells with stem cell characteristics in somatic compartments of the ovary

Antral follicular growth in the ovary is characterized by rapid expansion of granulosa cells accompanied by a rising complexity of their functionality. Within two weeks the number of human granulosa cells increases from less than 500,000 to more than 50 millions cells per follicle and differentiates into groups of cells with a variety of specialized functions involved in steroidogenesis, nursing the oocyte, and forming a functional syncitium. Both the rapid proliferation and different specialized functions of the granulosa cells can only be explained through the involvement of stem cells. However, luteinizing granulosa cells were believed to be terminally differentiated cells. Only recently, stem and progenitor cells with FSH-receptor activity were identified in populations of luteinizing granulosa cells obtained during oocyte collected for assisted reproduction. In the presence of the leukaemia-inhibiting factor (LIF), it was possible to culture a subpopulation of the luteinizing granulosa cells over prolonged time periods. Furthermore, when embedded in a matrix consisting of collagen type I, these cells continued to express the FSH receptor over prolonged time periods, developed globular formations that surrogated as follicle-like structures, providing a promising tool for reproductive biology.

Spatial differences within the membrana granulosa in the expression of focimatrix and steroidogenic capacity

In the ovarian follicular membrana granulosa there are morphological and functional differences between cells adjacent to the follicular fluid lumen, or aligning the basal lamina. Amongst the observed functional differences are steroidogenic capacity and expression levels of a novel basal lamina, focimatrix; both of which increase in the later stages of antral follicle growth. A number of different studies have produced apparently inconsistent results as to which cell layers are more steroidogenic. To examine this systematically, individual bovine follicles, confirmed as healthy by post hoc histological examination, were used to isolate populations of apical and basal granulosa cells. Cell counts revealed that the respective groups did not differ in the numbers of cells, thus confirming the separation of these populations. We measured gene expression (quantitative RT-PCR, n=8-10, follicle diameter 14.0±0.5 mm) and protein levels (Western immunoblotting, n=14, follicle diameter 11.9±0.5 mm) and hormone production from granulosa cells (2.5×10(5) viable cells/well in serum-free conditions for 24 h, n=15, diameter 12±0.5 mm). Levels of mRNA of HSD3B1 and CYP19A1 and three focimatrix genes COL4A1, HSPG2 and LAMB2 and LHCGR were significantly lower in apical granulosa cells (P<0.05), whereas, expression of CYP11A1 and HSD17B1 were not different (P>0.05). The protein levels of steroidogenic enzymes P450scc and P450arom were significantly higher in apical cells (P<0.05), whereas those of 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase type 1 were not different (P>0.05). Progesterone production was significantly lower and oestradiol production was significantly higher in apical granulosa cells (P<0.05). These results confirm that apical and basal cells are functionally different, and the differences might be explained by the location of cells of different ages and maturity within the membrana granulosa. Discrepancies in the literature on their steroidogenic capacity may reflect differences in the steroidogenic parameters measured.

Acute doxorubicin insult in the mouse ovary is cell- and follicle-type dependent

Primary ovarian insufficiency (POI) is one of the many unintended consequences of chemotherapy faced by the growing number of female cancer survivors. While ovarian repercussions of chemotherapy have long been recognized, the acute insult phase and primary sites of damage are not well-studied, hampering efforts to design effective intervention therapies to protect the ovary. Utilizing doxorubicin (DXR) as a model chemotherapy agent, we defined the acute timeline for drug accumulation, induced DNA damage, and subsequent cellular and follicular demise in the mouse ovary. DXR accumulated first in the core ovarian stroma cells, then redistributed outwards into the cortex and follicles in a time-dependent manner, without further increase in total ovarian drug levels after four hours post-injection. Consistent with early drug accumulation and intimate interactions with the blood supply, stroma cell-enriched populations exhibited an earlier DNA damage response (measurable at 2 hours) than granulosa cells (measurable at 4 hours), as quantified by the comet assay. Granulosa cell-enriched populations were more sensitive however, responding with greater levels of DNA damage. The oocyte DNA damage response was delayed, and not measurable above background until 10-12 hours post-DXR injection. By 8 hours post-DXR injection and prior to the oocyte DNA damage response, the number of primary, secondary, and antral follicles exhibiting TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling)-positive granulosa cells plateaued, indicating late-stage apoptosis and suggesting damage to the oocytes is subsequent to somatic cell failure. Primordial follicles accumulate significant DXR by 4 hours post-injection, but do not exhibit TUNEL-positive granulosa cells until 48 hours post-injection, indicating delayed demise. Taken together, the data suggest effective intervention therapies designed to protect the ovary from chemotherapy accumulation and induced insult in the ovary must act almost immediately to prevent acute insult as significant damage was seen in stroma cells within the first two hours.

Women with high telomerase activity in luteinised granulosa cells have a higher pregnancy rate during in vitro fertilisation treatment

OBJECTIVE

To study the effect of telomerase activity (TA) in human luteinised granulosa cells (GCs) on the outcome of in vitro fertilisation treatment.

METHODS

Fifty-six women, aged 23 to 39 years, were enrolled and divided into four groups according to their levels of TA.

RESULTS

Seventeen cases in group A exhibited nondetectable TA, 16 cases in group B expressed low levels of TA (between 0.1 and 0.65 OD × mm), 14 cases in group C expressed moderate TA levels (between 0.66 and 1.00 OD × mm) and 9 cases in group D expressed high levels of TA (more than 1.00 OD × mm). The level of total serum testosterone (T) was significantly higher in groups C and D than in group A (1.43±0.10 vs. 1.08±0.11 nmol/L, P<0.030 and 1.56±0.08 vs. 1.08±0.11 nmol/L, P<0.005, respectively). The TA level was positively correlated with T (r=0.291, P<0.011). No obvious differences were observed in rates of fertilisation, cleavage, mature oocyte formation or good-quality embryos among the groups. The patients in group D exhibited the highest rates of embryo implantation and clinical pregnancy (with rates of 52.63% and 77.78%, respectively, compared with 18.92% and 29.41% in group A, 25.71% and 37.50% in group B and 48% and 50% in group C, with P<0.018 and P=0.112, respectively). The patients in group D also had a greater likelihood of becoming pregnant than those in group A (OR: 9.703, P < 0.023), group B (OR: 14.765, P<0.009) or group C (OR: 5.560, P=0.103).

CONCLUSIONS

Luteinised GCs have a certain potential for proliferation and TA of luteinised GCs may predict the clinical outcomes of IVF treatment. Some unknown regulatory mechanisms between TA and T should be studied in further trials.

Estrogen deficiency reversibly induces telomere shortening in mouse granulosa cells and ovarian aging in vivo

Estrogen is implicated as playing an important role in aging and tumorigenesis of estrogen responsive tissues; however the mechanisms underlying the mitogenic actions of estrogen are not fully understood. Here we report that estrogen deficiency in mice caused by targeted disruption of the aromatase gene results in a significant inhibition of telomerase maintenance of telomeres in mouse ovaries in a tissue-specific manner. The inhibition entails a significant shortening of telomeres and compromised proliferation in the follicular granulosa cell compartment of ovary. Gene expression analysis showed decreased levels of proto-oncogene c-Myc and the telomerase catalytic subunit, telomerase reverse transcriptase (TERT), in response to estrogen deficiency. Estrogen replacement therapy led to increases in TERT gene expression, telomerase activity, telomere length and ovarian tissue growth, thereby reinstating ovary development to normal in four weeks. Our data demonstrate for the first time that telomere maintenance is the primary mechanism mediating the mitogenic effect of estrogen on ovarian granulosa cell proliferation by upregulating the genes of c-Myc and TERT in vivo. Estrogen deficiency or over-activity may cause ovarian tissue aging or tumorigenesis, respectively, through estrogen regulation of telomere remodeling.

Formation of the ovarian follicular antrum and follicular fluid

The formation of the follicular antrum and follicular fluid has received scant attention from researchers, yet both are important processes in follicular development. The central hypothesis on follicular fluid formation suggests that production by granulosa cells of hyaluronan and the chondroitin sulfate proteoglycan versican generates an osmotic gradient. This gradient draws in fluid derived from the thecal vasculature. Inter-alpha-trypsin inhibitor is also present in follicular fluid at least in species with large follicles, and inter-alpha-trypsin inhibitor and versican could additionally bind or cross-link with hyaluronan, resulting in the retention of these molecules within the follicular antrum. Barriers to the movement of fluid across the membrana granulosa are apparently minimal, as even relatively large serum proteins are present in follicular fluid. Despite the relative permeability of the follicular wall, aquaporins are present in granulosa cells and could be actively involved in the transport of water into the follicle. The formation of an antrum also requires movement of granulosa cells relative to each other to allow the fluid to accumulate. This presumably involves remodeling of cell-cell junctions and in species with small follicles may involve death of centrally located granulosa cells. Remodeling of the stroma and thecal layers also accompanies growth and expansion of the antrum and presumably involves similar processes that accompany growth of other glands.

Morphological classification of bovine ovarian follicles

Follicle classification is an important aid to the understanding of follicular development and atresia. Some bovine primordial follicles have the classical primordial shape, but ellipsoidal shaped follicles with some cuboidal granulosa cells at the poles are far more common. Preantral follicles have one of two basal lamina phenotypes, either a single aligned layer or one with additional layers. In antral follicles <5 mm diameter, half of the healthy follicles have columnar shaped basal granulosa cells and additional layers of basal lamina, which appear as loops in cross section ('loopy'). The remainder have aligned single-layered follicular basal laminas with rounded basal cells, and contain better quality oocytes than the loopy/columnar follicles. In sizes >5 mm, only aligned/rounded phenotypes are present. Dominant and subordinate follicles can be identified by ultrasound and/or histological examination of pairs of ovaries. Atretic follicles <5 mm are either basal atretic or antral atretic, named on the basis of the location in the membrana granulosa where cells die first. Basal atretic follicles have considerable biological differences to antral atretic follicles. In follicles >5 mm, only antral atresia is observed. The concentrations of follicular fluid steroid hormones can be used to classify atresia and distinguish some of the different types of atresia; however, this method is unlikely to identify follicles early in atresia, and hence misclassify them as healthy. Other biochemical and histological methods can be used, but since cell death is a part of normal homoeostatis, deciding when a follicle has entered atresia remains somewhat subjective.

Phenotypes of the ovarian follicular basal lamina predict developmental competence of oocytes

BACKGROUND

The ovarian follicular basal lamina underlies the epithelial membrana granulosa and maintains the avascular intra-follicular compartment. Additional layers of basal lamina occur in a number of pathologies, including pili annulati and diabetes. We previously found additional layers of follicular basal lamina in a significant percentage of healthy bovine follicles. We wished to determine if this phenomenon existed in humans, and if it was related to oocyte function in the bovine.

METHODS AND RESULTS

We examined follicles from human ovaries (n = 18) by electron microscopy and found that many follicles had additional layers of basal lamina. Oocytes (n = 222) from bovine follicles with normal or unusual basal laminas were isolated and their ability to undergo in vitro maturation, fertilization and culture to blastocyst was compared. Healthy bovine follicles with a single layer of basal lamina had oocytes with significantly (P < 0.01) greater developmental competence than healthy follicles with additional layers of follicular basal lamina (65% versus 28%).

CONCLUSIONS

These findings provide direct evidence that the phenotype of the follicular basal lamina is related to oocyte competence.

The distribution of type IV collagen alpha chains in the mouse ovary and its correlation with follicular development

The present study aims to identify alpha chains of type IV collagen in the basement membrane of the mouse ovarian follicle and examine their changes during follicular development using immunofluorescence microscopy with specific monoclonal antibodies. The basement membrane of the serous mesothelium enveloping the ovary contained all alpha chains of type IV collagen, alpha1(IV) through alpha6(IV) chains. Primordial follicles showed a distinct immunoreactivity against all six alpha chains in their basement membranes. Immunolabeling for alpha3(IV) and alpha4(IV) chains was almost eliminated in the primary follicles. In basement membranes of secondary and Graafian follicles, the immunofluorescent reaction of alpha3(IV) and alpha4(IV) chains disappeared in Graafian follicles, a partial reduction in fluorescent immunostaining intensity to alpha5(IV) and alpha6(IV) chains was observed; only alpha1(IV) and alpha2(IV) chains were not degraded throughout follicular development. On atretic follicles, in addition to alpha1(IV) and alpha2(IV) chains, alpha3(IV), alpha4(IV), alpha5(IV) and alpha6(IV) chains frequently persisted. A basement membrane-like matrix within the follicular granulosa cell layer, such as the focimatrix (focal intraepithelial matrix) and/or Call-Exner body, was also recognized in mouse secondary and Graafian follicles and contained alpha1(IV), alpha2(IV), alpha5(IV) and alpha6(IV) chains but not alpha3(IV) and alpha4(IV) chains. We expect that the decrease in alpha(IV) chains prompts follicular development and is a prerequisite condition for follicular maturation.

Telomerase activity in pig granulosa cells proliferating and differentiating in vitro

The aim of the work was to analyze the telomerase activity (TA) in two different populations of pig granulosa cells (GC) proliferating and differentiating in vitro: (a) in relatively undifferentiated granulosa cells isolated from small (1-2 mm) antral follicles and (b) in functionally advanced, differentiated cells obtained from large (5-7 mm) antral follicles. The proliferative potential in vitro of small follicle granulosa cells (SF-GC) was higher than that of large follicle granulosa cells (LF-GC). EGF stimulated significantly (p<0.01) proliferation in SF-GC as well as LF-GC. FSH did not have a stimulating effect on proliferation in both of the GC populations. Steroidogenesis was induced in both SF- and LF-GC in vitro. Significantly higher (p<0.01) levels of estradiol were measured in LF-GC cultures. In SF-GC, no significantly different effects of EGF and FSH on estradiol production were found. The production of progesterone in vitro was higher in LF-GC than in SF-GC and its production was specifically promoted by FSH in contrast to estradiol the synthesis of which in vitro was less dependent on culture conditions. Using the TRAP assay telomerase activity was detected in freshly isolated and in vitro cultured pig SF- and LF-GC. In EGF, but not FSH stimulated SF-GC, significantly enhanced (p<0.05) TA in comparison with the control was observed at an interval of 24 h of culture. After the 48 h in vitro, levels of TA in both EGF and FSH treated cells were comparable with control. In LF-GC, both EGF and FSH stimulated significantly (p<0.05) TA after the 24h of in vitro culture. At an interval of 48 h, no significant differences in the level of TA were observed between control, EGF and FSH stimulated LF-GC. Comparing the levels of TA in SF- and LF-GC, significantly higher levels of TA were found in control (p<0.05) and EGF (p<0.01) treated SF-GC after 24 h in vitro. On the other hand, absolutely, but not significantly, higher levels of TA were found in LF-GC versus SF-GC in all culture conditions after 48 h in vitro.

The role of the extracellular matrix in ovarian follicle development

Regulation of ovarian follicle development depends on endocrine- and paracrine-acting hormones, the 3-dimensional architecture of the follicle, and the physical rigidity of the surrounding tissue. These 3 forces are integrated throughout the life cycle of the follicle to ensure appropriate hormone secretion, differentiation of the somatic cells, and maturation of the oocyte. The process of in-follicle maturation provides a new tool for understanding ovarian follicle development under the influence of these factors.

Insulin-like growth factor binding proteins in follicular fluid from morphologically distinct healthy and atretic bovine antral follicles

In bovine follicles 2-5 mm in diameter, two morphologically distinct types of healthy follicles and two types of atretic follicles have been described recently. Healthy follicles either have columnar basal granulosa cells with follicular basal lamina composed of many layers or 'loops' or they have rounded basal cells with a conventional single-layered, aligned follicular basal lamina. In atretic follicles, cell death either commences at the basal layer and progresses to the antrum (basal atresia) with macrophage penetration of the membrana granulosa or death progresses from the antrum in a basal direction (antral atresia). Little is known about how these different phenotypes develop. To determine whether insulin-like growth factor binding protein (IGFBP) levels in follicular fluid differ between these different types of follicles, we measured IGFBP levels in fluids from these follicles. A total of 61 follicles were assessed by light microscopy and characterized by morphological analysis as either healthy, with columnar or rounded basal granulosa cells, or as undergoing antral or basal atresia. The IGFBP concentration in the follicular fluid of individual follicles from the four groups (n = 12-20 per group) was identified by Western ligand blots using (125)I-insulin-like growth factor (IGF)-II as a probe. Insulin-like growth factor binding proteins 2, 3 (44 and 40 kDa), 4 (glycosylated and non-glycosylated) and 5 were observed. The levels (per volume of fluid) of IGFBPs 2, 4 and 5 were greater in atretic follicles than in healthy follicles. However, there were no statistical differences in levels of each IGFBP between either the two types of healthy follicle or between the two types of atretic follicles. Thus, IGFBP levels are not related to the different types of healthy or atretic follicles.

Management of ovarian stromal cell tumors

PURPOSE

To describe the clinical management of ovarian stromal cell tumors, which are a heterogeneous group of neoplasms that develop from the sex cords and the ovarian stroma.

DESIGN

We reviewed the current evidence on the clinical management of these relatively rare ovarian malignancies, which are typically detected at an early stage and may recur as late as 30 years following the initial treatment. The overall prognosis is favorable with a long-term survival ranging from 75% to 90% for all stages. Adult granulosa cell tumor (GCT) is the most common malignancy among these tumors.

RESULTS

Surgery is the cornerstone of initial treatment. In women of childbearing age and with disease limited to one ovary, a fertility-sparing surgery can be a reasonable approach. Tumor stage represents the most important clinical parameter of prognostic relevance. The value of postoperative adjuvant therapy for high-risk patients has not been proven by prospective randomized studies. Platinum-based chemotherapy is used currently for patients with advanced stages or recurrent disease, with an overall response rate of 63% to 80%. Taxane and platinum combination chemotherapy seems to be a reasonable candidate for future trials. Little evidence exists for the use of radiation or hormonal therapy, and these modalities should be restricted to selected cases. Given the propensity of GCT for late relapse, prolonged follow-up is required.

CONCLUSION

Surgery remains the most effective treatment for ovarian stromal tumors and, whenever feasible, for relapsing disease. Platinum-based chemotherapy is currently used in metastatic or recurrent tumors.

Extracellular matrix of the human cyclic corpus luteum

Extracellular matrix regulates many cellular processes likely to be important for development and regression of corpora lutea. Therefore, we identified the types and components of the extracellular matrix of the human corpus luteum at different stages of the menstrual cycle. Two different types of extracellular matrix were identified by electron microscopy; subendothelial basal laminas and an interstitial matrix located as aggregates at irregular intervals between the non-vascular cells. No basal laminas were associated with luteal cells. At all stages, collagen type IV alpha1 and laminins alpha5, beta2 and gamma1 were localized by immunohistochemistry to subendothelial basal laminas, and collagen type IV alpha1 and laminins alpha2, alpha5, beta1 and beta2 localized in the interstitial matrix. Laminin alpha4 and beta1 chains occurred in the subendothelial basal lamina from mid-luteal stage to regression; at earlier stages, a punctate pattern of staining was observed. Therefore, human luteal subendothelial basal laminas potentially contain laminin 11 during early luteal development and, additionally, laminins 8, 9 and 10 at the mid-luteal phase. Laminin alpha1 and alpha3 chains were not detected in corpora lutea. Versican localized to the connective tissue extremities of the corpus luteum. Thus, during the formation of the human corpus luteum, remodelling of extracellular matrix does not result in basal laminas as present in the adrenal cortex or ovarian follicle. Instead, novel aggregates of interstitial matrix of collagen and laminin are deposited within the luteal parenchyma, and it remains to be seen whether this matrix is important for maintaining the luteal cell phenotype.

Formation of ovarian follicular fluid may be due to the osmotic potential of large glycosaminoglycans and proteoglycans

During mammalian follicle development, a fluid-filled antrum develops in the avascular centre of the follicle. We investigated the hypothesis that follicular fluid contains osmotically-active molecules, sufficiently large so as to not freely escape the follicular fluid. Such molecules could generate an osmotic differential and thus recruit fluid from the surrounding vascularised stroma into the antrum. Follicular fluid was collected from bovine follicles classified histologically as healthy (n= 4 pools) or atretic (n= 4 pools). Dialysis of the follicular fluid at 300 kDa or 500 kDa resulted in a reduction in colloid osmotic pressure of 35% and 60%, respectively, in fluid from healthy follicles and 29% and 80% from atretic follicles. Digestion of follicular fluid withStreptomyceshyaluronidase, chondroitinase ABC or DNase 1 followed by dialysis resulted in reductions in osmotic pressure of 43%, 53% and 43% respectively for fluids from healthy follicles and 34%, 20% and 31% for atretic follicles. Digestion with collagenase I, proteinase K, heparanase 1 or keratanase had no significant effect on the osmotic pressure of follicular fluid of healthy follicles. Ion exchange and size exclusion, Western blotting and ELISA identified the proteoglycans versican and inter-alpha trypsin inhibitor and the glycosaminoglycan hyaluronan in follicular fluid. We conclude that these molecules or aggregates of them are of sufficient size to contribute to the osmotic potential of follicular fluid and thus recruit fluid into the follicular antrum. DNA may also contribute but it is probably not a component that is regulated for this role.

Distribution of extracellular matrix proteins type I collagen, type IV collagen, fibronectin, and laminin in mouse folliculogenesis

The extracellular matrix (ECM) plays a prominent role in ovarian function by participating in processes such as cell migration, proliferation, growth, and development. Although some of these signaling processes have been characterized in the mouse, the relative quantity and distribution of ECM proteins within developing follicles of the ovary have not been characterized. This study uses immunohistochemistry and real-time PCR to characterize the ECM components type I collagen, type IV collagen, fibronectin, and laminin in the mouse ovary according to follicle stage and cellular compartment. Collagen I was present throughout the ovary, with higher concentrations in the ovarian surface epithelium and follicular compartments. Collagen IV was abundant in the theca cell compartment with low-level expression in the stroma and granulosa cells. The distribution of collagen was consistent throughout follicle maturation. Fibronectin staining in the stroma and theca cell compartment increased throughout follicle development, while staining in the granulosa cell compartment decreased. Heavy staining was also observed in the follicular fluid of antral follicles. Laminin was localized primarily to the theca cell compartment, with a defined ring at the exterior of the follicular granulosa cells marking the basement membrane. Low levels of laminin were also apparent in the stroma and granulosa cell compartment. Taken together, the ECM content of the mouse ovary changes during follicular development and reveals a distinct spatial and temporal pattern. This understanding of ECM composition and distribution can be used in the basic studies of ECM function during follicle development, and could aid in the development of in vitro systems for follicle growth.

Remodeling of extracellular matrix at ovulation of the bovine ovarian follicle

Using immunohistochemistry and RNA analyses we examined the fate of components of a newly identified matrix that develops between granulosa cells (focimatrix, abbreviated from focal intraepithelial matrix) and of the follicular basal lamina in ovulating bovine ovarian follicles. Pre- and postovulatory follicles were generated by treatment with estradiol (Day 1), progesterone (Days 1-10), and prostaglandin analogue (Day 9) with either no further treatment (Group 1, n = 6) and or with 25 mg porcine LH (Day 11, Group 2, n = 8 or Day 10, Group 3, n = 8) and ovariectomy on Day 12 (12-14 hr post LH in Group 2, 38-40.5 hr in Group 3). In the time frame examined no loss of follicular basal lamina laminin chains beta2 and gamma1 or nidogen 1 was observed. In the follicular basal lamina collagen type IV alpha1 and perlecan were present prior to ovulation; after ovulation collagen type IV alpha1 was discontinuously distributed and perlecan was absent. Versican in the theca interna adjacent to the follicular basal lamina in preovulatory follicles was not observed post ovulation, however, the granulosa cells then showed strong cytoplasmic staining for versican. Expression of versican isoforms V0, V1, and V3 was detected at all stages. Focimatrix was observed in preovulatory follicles. It contained collagen type IV alpha1, laminins beta2 and gamma1, nidogen 1 and perlecan and underwent changes in composition similar to that of the follicular basal lamina. In conclusion focimatrix and the follicular basal lamina are degraded at ovulation. Individual components are lost at different times.

Extracellular matrix in ovarian follicular development and disease

The ovarian follicle contains several different cell types and separate compartments and undergoes substantial development during its growth and maturation. Extracellular matrix (ECM) could be expected to play a major role in these processes. Most research on ECM in follicles has focused on the follicular basal lamina and its changing composition during folliculogenesis and on the specialised matrix formed at ovulation by the cumulus cells surrounding the oocyte and the zona pellucida. We review these aspects. Few naturally occurring gene mutations have identified unique roles for ECM molecules in follicular function. Presumably, any mutations leading to reduced fertility are eliminated quickly by natural selection and, when mutations are not eliminated, considerable redundancy occurs to ensure successful reproduction. In mice, in which the genome can be easily manipulated, the modification of matrix components associated with cumulus and oocytes has often resulted in partial infertility, suggesting redundancy. We provide an update of basal lamina components focusing on newer discoveries. In addition, we review matrix associated with the occyte and cumulus cells (excluding the zona pellucida) and other components of ECM. Where possible, we examine evidence for the role of the ECM in follicular development and diseases.

Regulation of mouse follicle development by follicle-stimulating hormone in a three-dimensional in vitro culture system is dependent on follicle stage and dose

The developmental requirements of ovarian follicles are dependent on the maturation stage of the follicle; in particular, elegant studies with genetic models have indicated that FSH is required for antral, but not preantral, follicle growth and maturation. To elucidate further the role of FSH and other regulatory molecules in preantral follicle development, in vitro culture systems are needed. We employed a biomaterials-based approach to follicle culture, in which follicles were encapsulated within matrices that were tailored to the specific developmental needs of the follicle. This three-dimensional system was used to examine the impact of increasing doses of FSH on follicle development for two-layered secondary (100-130 microm; two layers of granulosa cells surrounding the oocyte) and multilayered secondary (150-180 microm, several layers of granulosa cells surrounding the oocyte) follicles isolated from mice. Two-layered secondary follicles were FSH responsive when cultured in alginate-collagen I matrices, exhibiting FSH dose-dependent increases in follicle growth, lactate production, and steroid secretion. Multilayered secondary follicles were FSH dependent, with follicle survival, growth, steroid secretion, metabolism, and oocyte maturation all regulated by FSH. However, doses greater than 25 mIU/ml of FSH negatively impacted multilayered secondary follicle development (reduced follicle survival). The present results indicate that the hormonal and environmental needs of the follicular complex change during the maturation process. The culture system can be adapted to each stage of development, which will be especially critical for translation to human follicles that have a longer developmental period.

Mouse ovary developmental RNA and protein markers from gene expression profiling

To identify genes involved in morphogenetic events during mouse ovary development, we started with microarray analyses of whole organ RNA. Transcripts for 60% of the 15,000 gene NIA panel were detected, and about 2000 were differentially expressed in nascent newborn compared to adult ovary. Highly differentially expressed transcripts included noncoding RNAs and newly detected genes involved in transcription regulation and signal transduction. The phased pattern of newborn mouse ovary differentiation allowed us to (1) extend information on activity and stage specificity of cell type-specific genes; and (2) generate a list of candidate genes involved in primordial follicle formation, including podocalyxin (Podxl), PDGFR-beta, and a follistatin-domain-encoding gene Flst1. Oocyte-specific transcripts included many (e.g., Deltex2, Bicd2, and Zfp37) enriched in growing oocytes, as well as a novel family of untranslated RNA's (RLTR10) that is selectively expressed in early stage follicles. The results indicate that global expression profiling of whole organ RNA provides sensitive first-line information about ovarian histogenesis for which no in vitro cell models are currently available.

Cytoskeleton reorganization mediates alpha6beta1 integrin-associated actions of laminin on proliferation and survival, but not on steroidogenesis of ovine granulosa cells

BACKGROUND

Laminin (LN) is one of the most abundant extracellular matrix components of the basal lamina and granulosa cell layers of ovarian follicles. Culture of ovine granulosa cells (GC) on LN substratum induces cell spreading, enhances cell survival and proliferation, and promotes luteinization. Previous investigations have shown that these effects are mostly mediated by the alpha6beta1 integrin, but its signalization pathways have not been investigated. This study aimed to assess the importance of the cytoskeleton in the alpha6beta1 integrin-mediated actions of laminin on survival, proliferation and steroidogenesis of ovine GC.

METHODS

The relationships between morphology and functions of ovine GC cultured on substrata containing LN or/and RGD peptides were investigated. The effects of (1) cytochalasin D, an actin cytoskeleton-disrupting drug, (2) a specific function-blocking antibody raised against alpha6 integrin subunit (anti-alpha6 IgG), and (3) an inhibitor of the ERK1/2 signalization pathway (PD98059) were assessed for GC shape, pyknosis and proliferation rates, oestradiol and progesterone secretions.

RESULTS

Cytoskeleton disruption by cytochalasin D induced cell rounding, inhibited proliferation, promoted pyknosis, inhibited progesterone secretion and enhanced oestradiol secretion by GC cultured on LN. When GC were cultured on various substrata containing LN and/or RGD peptides in the presence or absence of anti-alpha6 IgG, both the existence of close correlations between the percentage of round cells, and the GC proliferation rate (r = -0.87) and pyknotic rate (r = 0.76) were established, but no relationship was found between cell shape and steroidogenesis. Inhibition of the ERK1/2 signalization pathway by PD98059 had no effect on GC shape, proliferation or pyknotic rates. However, it dramatically reduced progesterone secretion, expression of cytochrome P450 cholesterol side-chain cleavage and 3beta-hydroxysteroid deshydrogenase enzymes, and enhanced oestradiol secretion, thereby reproducing all the effects of the anti-alpha6 IgG on steroidogenesis of GC cultured on LN.

CONCLUSION

LN may participate in the paracrine control of follicular development through different mechanisms. It could enhance proliferation and survival of GC through its alpha6beta1 integrin-mediated actions on cytoskeleton. In contrast, its stimulating action on GC luteinization could be partly mediated by the ERK1/2 pathway, irrespective of cell shape.

Gene expression for LH receptor, 17α-hydroxylase and StAR in the theca interna of preantral and early antral follicles in the bovine ovary

The onset of gene expression for three proteins that play pivotal roles in theca interna function, namely the LH receptor (LH-R), cytochrome P450 17α-hydroxylase (17αOH) and the steroidogenic acute regulatory protein (StAR), was determined. Ovaries were obtained on day 9 of the oestrus cycle from mature synchronized dairy cows (n= 5) and gene expression in preantral and antral follicles up to 4 mm in diameter was evaluated byin situhybridization. LH-R and 17αOH mRNAs were observed first, in the theca interna of large preantral follicles (type 4), concurrent with its morphological differentiation. StAR mRNA appeared later during follicular growth, in follicles >1 mm in diameter (type 6). LH-R and 17αOH mRNAs were found exclusively in the thecal cells, whereas StAR mRNA appeared in thecal cells, granulosa cells of late atretic follicles and oocytes. In early atresia, thecal cells expressed all three mRNAs, and their expression decreased gradually as atresia progressed. Atresia in granulosa cells was characterized by massive apoptosis of periantral, but not peribasal cells, that differentiated into luteal-like cells expressing StAR.

In summary, our study suggests that in spite of the presence of 17αOH, a key enzyme in steroidogenesis, the ability to produce steroids by bovine follicles smaller than 1 mm in diameter must be very limited due to the absence of StAR protein. During the early stages of atresia, thecal cells remain morphologically and functionally healthy, and continue to express all three studied mRNAs.

Theca Interna: The Other Side of Bovine Follicular Atresia1

Currently, histological classifications of ovarian follicular atresia are almost exclusively based on the morphology of the membrana granulosa without reference to the theca interna. Atresia in the bovine small antral ovarian follicle has been redefined into antral or basal atresia where cell death commences initially within antral or basal regions of the membrana granulosa, respectively. To examine cell death in the theca interna in the two types of atretic follicles, bovine ovaries were collected and processed for immunohistochemistry and light microscopy. Follicles were classified as healthy, antral atretic, or basal atretic. Follicle diameter was recorded and sections stained with lectin from Bandeiraea simplicifolia to identify endothelial cells or with an antibody to cytochrome P450 cholesterol side-chain cleavage to identify steroidogenic cells and combined with TUNEL labeling to identify dead cells. The numerical density of steroidogenic cells within the theca interna was significantly reduced (P < 0.001) in basal atretic follicles in comparison with other follicles. Cell death was greater in both endothelial cells (P < 0.05) and steroidogenic cells (P < 0.01) of the theca interna of basal atretic follicles compared with healthy and antral atretic follicles. Thus, we conclude that the theca interna is susceptible to cell death early in atresia, particularly in basal atretic follicles.

A novel basal lamina matrix of the stratified epithelium of the ovarian follicle

Basal laminas are important sheets of specialized extracellular matrix that underlie and surround groups of cells, such as epithelia or endothelia, enabling the cells to orientate their basal/apical polarity and creating a microenvironment for them. Basal laminas can also individually encapsulate whole cells, such as muscle cells, thereby forming a microenvironment but not polarizing the enclosed cells. Other mesenchymal or stromal cells exist with no basal lamina. In the course of studying the bovine follicular basal lamina which underlies the multilayered epithelium of the ovarian follicle, we identified a developmentally regulated novel extracellular matrix (which we call focimatrix for focal intra-epithelial matrix). Focimatrix is composed of basal lamina-like material deposited as plaques or aggregates between the multilayers of the epithelial granulosa cells. The focimatrix does not encapsulate individual or groups of cells and therefore does not form a microenvironment for them. Focimatrix contains collagen type IV subunits alpha1 and alpha2 (but not alpha3-alpha6), and laminin chains alpha1, beta2 and gamma1 (but not alpha2 or beta1), and nidogen-1 and perlecan (but not versican). The amount of focimatrix increases with increasing follicular size, and its appearance precedes the expression by granulosa cells of the enzymes for steroid hormone synthesis, cholesterol side-chain cleavage cytochrome P450 (SCC) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD), in the days preceding ovulation. The expression in granulosa cells of two components examined, nidogen-1 and perlecan, also increases substantially when follicles enlarge to a sufficient size capable of ovulating. Following ovulation the follicular basal lamina is degraded, and presumably focimatrix is too since it is not detected in corpora lutea that develop from the ovulating follicles. During this development the granulosa cells undergo an epithelial-mesenchymal transition (EMT) into luteal cells following ovulation, and substantially increase their expression of steroidogenic enzymes in the process. During EMT epithelial cells lose polarity. Since focimatrix exists on more than one side of the granulosa cells, we propose that it disrupts the polarity induced by the follicular basal lamina in the lead up to ovulation. Hence focimatrix maybe a key part of the follicular/luteal EMT.