Effects of luteinizing hormone and human chorionic gonadotropin on corpus luteum cells in a spheroid cell culture system

Spheroid formation and luteinization of granulosa cells of felids in a long-term 3D culture

In the present study, granulosa cells (GCs) from domestic cats and Persian leopard were cultured and characterized from selected days. The culture period was divided into two phases: maintenance, which lasted for 7 days, and luteinization, which followed for up to 11 days. Luteinization was performed on ultra-low attachment plates, supporting the formation of spheroids in a medium supplemented with insulin, forskolin, and luteinizing hormone (LH). GCs of domestic cat produced estradiol (E2) and progesterone (P4) during the maintenance phase. The gene expressions of some proteins involved in steroidogenesis were stable (STAR, HSD3B1) or decreased over time (CYP11A1, HSD17B1, CYP17A1, and CYP19A1), which was similar to the expressions of gonatropin receptors (LHCGR and FSHR). During the luteinization phase, P4 concentration significantly increased (P < 0.05), and E2, in contrast to the proliferation phase, was below detection range. The expression of genes of proteins involved in steroidogenesis (STAR, CYP11A1, HSD3B1, HSD17B1, CYP17A1, and CYP19A1) and of gonadotropin receptors (LHCGR and FSHR) significantly increased during the luteinization period, but some expressions exhibited a decrease at the end of the phase (LHCGR, FSHR, HSD17B1, CYP19A1). The morphology of the luteinized GCs of domestic cat resembled large luteal cells and had numerous vacuole-like structures. Also, the GCs of Persian leopard underwent luteinization, shown by increasing P4 production and HSD3B1 expression. This study confirms that GCs from felids can be luteinized in a 3D spheroid system which can be a basis for further studies on luteal cell function of felids. Additionally, we could show that the domestic cat can serve as a model species for establishing cell culture methods which can be transferred to other felids.

Co-cultivation of human granulosa cells with ovarian cancer cells leads to a significant increase in progesterone production

PURPOSE

In humans, granulosa cells (GCs) are part of the follicle and nourish the growing oocyte. GCs produce estrogen and, after ovulation, progesterone. They are embedded in a multicellular tissue structure of the ovary, which consists of a variety of different cell types that are essential for the physiological function of the ovary. However, the extent to which individual ovarian cell types contribute to overall functionality has not yet been fully elucidated. In this study, we aim to investigate the effects of co-culturing human granulosa cells with ovarian cancer cells on their progesterone and estrogen production in an in vitro model.

METHODS

After seeding, the cells were stimulated with 200 µM forskolin in DMEM for 72 h and the medium of the different cell culture experiments was collected. Subsequently, progesterone and oestradiol concentrations were determined using an Elisa assay.

RESULTS

Morphologically, it was striking that the cells self-organize and form spatially separated areas. Compared to culturing granulosa cells alone, co-culturing human granulosa cells together with the ovarian cancer cell line OvCar-3 resulted in a significant increase in progesterone production (20.3 ng/ml versus 50.2 ng/ml; p < 0.01).

CONCLUSIONS

Using a simple in vitro model, we highlight the importance of cellular crosstalk between different ovarian cells in a complex cellular network and that it strongly influences granulosa cell hormone production. This could have potential implications for the procedure of transplanting endocrine tissues after cryopreservation, as it highlights the importance of survival of all cells for the functionality of the transplanted tissue.

A Histopathological Evaluation of Ovarian Hyperstimulation Syndrome on Reproductive and Vital Organs and the Role of the VEGF-PKA Pathway in a Mouse Model

Ovarian hyperstimulation syndrome (OHSS) is one of the most common and iatrogenic complications of in vitro fertilization therapy, which is an exaggerated response to excess hormones resulting in the development of a large number of maturing follicles. Although the complications of and reasons for the condition are well known, the overall histopathological effects on systemic organs and the extent of the damage have not been fully elucidated. Besides, the mechanism that underlies the situation is not very well known. The aim of the present work was to analyse the histopathological effects of OHSS on reproductive (uterus and ovary) and vital organs (liver and kidney) and the possible role of the VEGF-PKA pathway in triggering the condition. Balb/c mice were used to establish an OHSS model. The OHSS group were injected with overdose PMSG while the normal responder group were injected with an optimal dose. Histopathological evaluation was utilised in the liver, kidney, ovary, and uterus stained with hematoxylin and eosin, Masson's trichrome, and periodic acid-Schiff stain. The expression profiles of VEGF (vascular endothelial growth factor), PKA (protein kinase A), and p-PKA (an activated form of PKA) were detected with immunohistochemistry and Western blotting. OHSS was demonstrated to have a negative histopathological effect on all of the organs analysed. These effects were associated with an overall increase in the expression levels of VEGF, PKA, and p-PKA. OHSS has a serious histopathological negative effect on the systemic and reproductive organs and is proven to affect overall health, and thus should be considered a dangerous complication during ART techniques. The activation of the VEGF-PKA pathway, which is indicated by the expression levels of VEGF, PKA, and p-PKA, is demonstrated to accompany this complication, which should be further elucidated to understand the mechanisms underlying the condition.

CXADR-like membrane protein (CLMP) in the rat ovary: stimulation by human chorionic gonadotrophin during the periovulatory period

CXADR-like membrane protein (CLMP) is a novel cell-cell adhesion molecule. The present study investigated the spatiotemporal expression pattern of CLMP and its regulation in the rat ovary during the periovulatory period. Real-time polymerase chain reaction analysis revealed that Clmp mRNA was rapidly stimulated in intact ovaries by 4h after human chorionic gonadotrophin (hCG) treatment. In situ hybridisation analysis demonstrated that Clmp mRNA expression was stimulated in theca cells at 4h after hCG and remained elevated until 12h. Clmp mRNA was also upregulated in granulosa cells and was present in forming corpora lutea. Our data indicate that the protein kinase A but not the protein kinase C pathway regulates the expression of Clmp mRNA in granulosa cells. Phosphatidylinositol 3 kinase and p38 kinase are also involved in regulating Clmp mRNA expression. The stimulation of Clmp mRNA by hCG requires new protein synthesis. Furthermore, inhibition of epidermal growth factor receptor activation significantly inhibited Clmp mRNA expression, whereas inhibition of prostaglandin synthesis or progesterone action had no effect. The stimulation of CLMP in the rat ovary may be important in cell adhesion events during ovulation and luteal formation such as maintaining the structure and communication of ovarian follicular and luteal cells.

Regulation of endothelial permeability in the primate corpora lutea: implications for ovarian hyperstimulation syndrome

In a developing human corpus luteum, a closely regulated cellular communication system exists between the luteal steroidogenic cells and endothelial cells. This system guaranties the vascularization process during luteal formation. The process is combined with rapid release of large amounts of progesterone into the bloodstream. The regulation of endothelial proliferation and permeability by LH and human chorionic gonadotropin (hCG) is integral to this process. On the cellular level, endothelial permeability is regulated by intercellular junctions, such as adherens junctions (AJ) and tight junctions (TJ), which act as zipper-like structures between interacting endothelial cells. Several cell junctional proteins are localized to the corpus luteum, including Occludin, Nectin 2, Claudin 1, and Claudin 5, as well as, vascular endothelial (VE)-Cadherin. It has been assumed that regulation of AJ- and TJ-proteins is of particular importance for permeability, and accordingly, for the functionality of the corpus luteum in early pregnancy, because treatment with hCG induces downregulation of juntional proteins in the luteal vessels. The effect of hCG on the adhesive molecules is mediated by VE growth factor (VEGF). On a functional level, the hCG-dependent and VEGF-mediated decrease in junctional proteins causes a decrease in the density of cell-cell closure and, accordingly, an increase in endothelial permeability. In doing so, the different junctional proteins are not only directly influenced by VEGF but also interact among themselves and influence each other reciprocally. Disturbances in this strictly, regulated interactions may explain the development of pathologies with increased vascular permeability, such as the ovarian hyperstimulation syndrome.

Local VEGF inhibition prevents ovarian alterations associated with ovarian hyperstimulation syndrome

The relationship between human chorionic gonadotropin and ovarian hyperstimulation syndrome (OHSS) is partially mediated by vascular endothelial growth factor A (VEGF). The aim of this study was to investigate the effects of VEGF inhibition on the development of corpora lutea (CL) and cystic structures, steroidogenesis, apoptosis, cell proliferation, endothelial cell area, VEGF receptors (KDR and Flt-1), claudin-5 and occludin levels in ovaries from an OHSS rat model. The VEGF inhibitor used (VEGF receptor-1 (FLT-1)/Fc chimera, TRAP) decreased the concentrations of progesterone and estradiol as well as the percentage of CL and cystic structures in OHSS rats, and increased apoptosis in CL. Endothelial cell area in CL and KDR expression and its phosphorylation were increased, whereas claudin-5 and occludin levels were decreased in the OHSS compared to the control TRAP reversed these parameters. Our findings indicate that VEGF inhibition prevents the early onset of OHSS and decreases its severity in rats.

Polymorphisms of VEGF and VEGF receptors are associated with the occurrence of ovarian hyperstimulation syndrome (OHSS)-a retrospective case-control study

BACKGROUND

Ovarian hyperstimulation syndrome (OHSS) is the most serious complication of IVF/ICSI therapy. The pathophysiology and etiology of the disease is still not fully clarified.

METHODS

To assess whether polymorphisms of the VEGF/VEGF-receptor system contribute to the occurrence of ovarian hyperstimulation syndrome (OHSS), we performed a retrospective analysis of 116 OHSS patients, and 124 female controls. The following SNPs were genotyped: Rs2071559 (VEGFR2-604); rs2305948 (VEGFR2-1192); rs1870377 (VEGFR2-1719); rs2010963 (VEGF-405); and rs111458691 (VEGFR1-519). Odds ratios (ORs) were estimated with a 95% confidence interval (CI). Linkage disequilibrium (LD) analysis was performed in the three loci of the VEGFR2 gene.

RESULT

We found an overrepresentation of the T allele of the VEGFR1-519 polymorphism in OHSS patients (P = 0.02, OR: 3.62, CI: 1.16 - 11.27). By genotype modeling, we found that polymorphism of VEGFR1-519 and VEGF-405 showed significant differences in patients and controls (p = 0.02, OR: 3.79 CI: 1.98 - 11.97 and p = 0.000005, OR: 0.29, CI: 0.17 - 0.50). LD analysis revealed significant linkage disequilibrium in VEGFR2.

CONCLUSION

Polymorphisms in the VEGFR2 gene and in the VEGF gene are associated with the occurrence of OHSS. This strengthens the evidence for an important role of the VEGF/VEGF- receptor system in the occurrence of OHSS.

Regulation of Endothelial Permeability in the Corpus Luteum: A Review of the Literature

The development of the human corpus luteum (yellow body) is dictated by a strictly controlled system of mutually communicating cells, the luteal steroid hormone-producing cells and endothelial cells. This cell-to-cell communication facilitates control of neoangiogenesis which is a prerequisite for the development of the corpus luteum and its function, the rapid release of large amounts of progesterone into the blood-vascular system. Preconditions for this process are the hormonal regulation of endothelial cell proliferation as well as of vascular permeability through LH and hCG. The morphological correlates of endothelial permeability are cell-to-cell adhesion molecules such as adherens junctions (AJ) and tight junctions (TJ) that open and close the gaps between mutually interacting, neighbouring endothelial cells like a "zip fastener". Various types of cell adhesion molecules have been detected in the corpus luteum such as occludin, claudin 1 and claudin 5 as well as VE-cadherin. It may be assumed that the regulation of AJ and TJ proteins is of particular importance for the permeability and thus for the function of the corpus luteum in early pregnancy since hCG treatment leads to a down-regulation of cell adhesion molecules in the luteal vessels. This effect is apparently mediated by VEGF. From a functional point of view, the hCG-dependent and VEGF-mediated down-regulation of cell adhesion molecules leads to a reduced transmissibility of cell-to-cell contacts and thus to an increased endothelial permeability. In this process the various cell adhesion molecules are not only directly regulated by VEGF but they also mutually interact and thus influence one another.

Human chorionic gonadotropin controls luteal vascular permeability via vascular endothelial growth factor by down-regulation of a cascade of adhesion proteins

OBJECTIVE

To study the functional interactions of junctional proteins acting as regulators of vascular permeability in the human corpus luteum. We investigated the role of vascular endothelial (VE)-cadherin, nectin 2, and claudin 5 as controllers of vascular endothelial cell permeability.

DESIGN

Performing immunohistochemical dual staining, we colocalized the above-mentioned proteins in the human corpus luteum.

SETTING

Not applicable.

PATIENT(S)

Not applicable.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Using a granulosa-endothelial coculture system, we revealed that hCG-treatment down-regulates VE-cadherin, nectin 2, and claudin 5 in endothelial cells via vascular endothelial growth factor (VEGFA).

RESULT(S)

Furthermore, the interaction of VE-cadherin, nectin 2, and claudin 5 was investigated by silencing these proteins that perform siRNA knockdown. Interestingly, knockdown of VE-cadherin and claudin 5 induced a decrease of the respective other protein. This down-regulation was associated with changed rates of vascular permeability: hCG induced a VEGFA-dependent down-regulation of VE-cadherin, nectin 2, and claudin 5, which increased the endothelial permeability in the coculture system. Furthermore, knockdown of VE-cadherin, nectin-2, and claudin 5 also resulted in a consecutive increase of endothelial permeability for each different protein.

CONCLUSION(S)

These results demonstrate for the first time that VE-cadherin, nectin 2, and claudin 5 are involved in the regulation of vascular permeability in a mutually interacting manner, which indicates their prominent role for the functionality of the human corpus luteum.

GnRH analogues in the prevention of ovarian hyperstimulation syndrome

The GnRH analogue (agonist and antagonist GnRH) changed ovarian stimulation. On the one hand, it improved chances of pregnancy to obtain more oocytes and better embryos. This leads to an ovarian hyper-response, which can be complicated by the ovarian hyperstimulation syndrome (OHSS). On the other hand, the GnRH analogue can prevent the incidence of OHSS: GnRH antagonist protocols, GnRH agonist for triggering final oocyte maturation, either together or separately, coasting, and the GnRH analogue may prove useful for avoiding OHSS in high-risk patients. We review these topics in this article.

Involvement of Src family of kinases and cAMP phosphodiesterase in the luteinizing hormone/chorionic gonadotropin receptor-mediated signaling in the corpus luteum of monkey

BACKGROUND

In higher primates, during non-pregnant cycles, it is indisputable that circulating LH is essential for maintenance of corpus luteum (CL) function. On the other hand, during pregnancy, CL function gets rescued by the LH analogue, chorionic gonadotropin (CG). The molecular mechanisms involved in the control of luteal function during spontaneous luteolysis and rescue processes are not completely understood. Emerging evidence suggests that LH/CGR activation triggers proliferation and transformation of target cells by various signaling molecules as evident from studies demonstrating participation of Src family of tyrosine kinases (SFKs) and MAP kinases in hCG-mediated actions in Leydig cells. Since circulating LH concentration does not vary during luteal regression, it was hypothesized that decreased responsiveness of luteal cells to LH might occur due to changes in LH/CGR expression dynamics, modulation of SFKs or interference with steroid biosynthesis.

METHODS

Since, maintenance of structure and function of CL is dependent on the presence of functional LH/CGR its expression dynamics as well as mRNA and protein expressions of SFKs were determined throughout the luteal phase. Employing well characterized luteolysis and CL rescue animal models, activities of SFKs, cAMP phosphodiesterase (cAMP-PDE) and expression of SR-B1 (a membrane receptor associated with trafficking of cholesterol ester) were examined. Also, studies were carried out to investigate the mechanisms responsible for decline in progesterone biosynthesis in CL during the latter part of the non-pregnant cycle.

RESULTS AND DISCUSSION

The decreased responsiveness of CL to LH during late luteal phase could not be accounted for by changes in LH/CGR mRNA levels, its transcript variants or protein. Results obtained employing model systems depicting different functional states of CL revealed increased activity of SFKs [pSrc (Y-416)] and PDE as well as decreased expression of SR-B1 correlating with initiation of spontaneous luteolysis. However, CG, by virtue of its heroic efforts, perhaps by inhibition of SFKs and PDE activation, prevents CL from undergoing regression during pregnancy.

CONCLUSIONS

The results indicated participation of activated Src and increased activity of cAMP-PDE in the control of luteal function in vivo. That the exogenous hCG treatment caused decreased activation of Src and cAMP-PDE activity with increased circulating progesterone might explain the transient CL rescue that occurs during early pregnancy.

Co-culturing of follicles with interstitial cells in collagen gel reproduce follicular development accompanied with theca cell layer formation

BACKGROUND

The mechanism of theca cell layer formation in mammalian ovaries has not been elucidated; one reason is that there is no follicle culture system that can reproduce theca cell layer formation in vitro. Therefore, a three-dimensional follicle culture system that can reproduce theca cell layer formation is required.

METHODS

A collagen gel was used in the follicle culture system. To determine the optimum conditions for follicle culture that can reproduce theca cell layer formation, the effects of hormonal treatment and cell types co-cultured with follicles were examined. In addition, immunohistochemistry was used to examine the properties of the cell layers formed in the outermost part of follicles.

RESULTS

Follicles maintained a three-dimensional shape and grew in collagen gel. By adding follicle-stimulating hormone (FSH) and co-culturing with interstitial cells, the follicles grew well, and cell layers were formed in the outermost part of follicles. Immunohistochemistry confirmed that the cells forming the outermost layers of the follicles were theca cells.

CONCLUSION

In this study, follicle culture system that can reproduce theca cell layer formation in vitro was established. In our opinion, this system is suitable for the analysis of theca cell layer formation and contributes to our understanding of the mechanisms of folliculogenesis.

Ovarian hyperstimulation syndrome is correlated with a reduction of soluble VEGF receptor protein level and a higher amount of VEGF-A

BACKGROUND

Ovarian hyperstimulation syndrome (OHSS) is a potentially life-threatening condition associated with increased vascular permeability. The vascular endothelial growth factor (VEGF) system and its receptors have been identified as the main angiogenic factors responsible for increased capillary permeability and are therefore discussed as crucial for the occurrence of OHSS. Recently, a number of soluble receptors for the VEGFs have been detected (sVEGF-Rs) and it has been shown that these sVEGF-Rs compete with the membrane-standing VEGF-R to bind VEGFs.

METHODS

We analyzed the serum levels of soluble VEGF-R1, -R2 and -R3 in 34 patients suffering from OHSS and in 34 controls without this disease. In a subgroup analysis, we correlated the severity of the OHSS with the detected amounts of VEGF-R1, -R2 and -R3. In addition, we determined the amount of total VEGF-A in the samples.

RESULTS

All the three soluble VEGF receptors tended to be higher in the control group compared with that in the OHSS group but this difference only reached significance for sVEGF-R2 (mean ± SEM: 15.5 ± 0.6 versus 13.8 ± 0.5 ng/ml, respectively, P< 0.05). In the subgroup analysis, sVEGF-R2 levels decreased as the severity of OHSS increased (OHSS-I: 16.8 ± 1.9 ng/ml and OHSS-III: 12.7 ± 1.0 ng/ml, P< 0.05) Moreover, the serum levels of total VEGF-A were higher in the OHSS group than those in the controls (537.7 ± 38.9 versus 351 ± 53.4 pg/ml, respectively P< 0.05).

CONCLUSIONS

We propose that VEGF-A plays a role in the occurrence of OHSS, that the amount of biologically available VEGF-A is modulated by sVEGF-Rs and that different combinations of VEGF-A and sVEGF-R levels might contribute to the severity of OHSS.

Permselectivity of blood follicle barriers in mouse ovaries of the mifepristone-induced polycystic ovary model revealed by in vivo cryotechnique

Despite the potential association of polycystic ovary (PCO) syndrome with hemodynamic changes, follicular microenvironment and the involvement of blood follicle barriers (BFB), a histopathological examination has been hampered by artifacts caused by conventional preparation methods. In this study, mouse ovaries of a mifepristone-induced PCO model were morphologically and immunohistochemically examined byin vivocryotechnique (IVCT), which prevents those technical artifacts. Ovarian specimens of PCO model mice were prepared by IVCT or the conventional perfusion fixation after s.c. injection of mifepristone. Their histology and immunolocalization of plasma proteins, including albumin (molecular mass, 69 kDa), immunoglobulin G (IgG, 150 kDa), inter-α-trypsin inhibitor (ITI, 220 kDa), fibrinogen (340 kDa), and IgM (900 kDa), were examined. In the PCO model, enlarged blood vessels with abundant blood flow were observed in addition to cystic follicles with degenerative membrana granulosa. The immunolocalization of albumin and IgM in the PCO model were similar to those in normal mice. Albumin immunolocalized in the blood vessels, interstitium or follicles, and IgM was mostly restricted within the blood vessels. In contrast, immunolocalization of IgG, ITI, and fibrinogen changed in the PCO model. Both IgG and ITI were clearly blocked by follicular basement membranes, and hardly observed in the membrana granulosa, though fibrinogen was mostly observed within blood vessels. These findings suggest that increased blood flow and enhanced selectivity of molecular permeation through the BFB are prominent features in the PCO ovaries, and changes in hemodynamic conditions and permselectivity of BFB are involved in the pathogenesis and pathophysiology of PCO syndrome.

Regulation of tight junction proteins occludin and claudin 5 in the primate ovary during the ovulatory cycle and after inhibition of vascular endothelial growth factor

Ovarian follicular and corpus luteum development, including angiogenesis, are characterized by cell-cell rearrangements that may require dynamic changes in cell-cell adhesion. The present study investigates the expression of tight junction proteins occludin and claudin 5 during follicular and luteal development in the primate ovary and after inhibition of vascular endothelial growth factor (VEGF) by VEGF trap treatment. Occludin was localized to the plasma membrane of granulosa cells. During follicular development occludin staining decreased significantly (P < 0.05) and disappeared completely by the ovulatory stage. After inhibition of VEGF, occludin staining was significantly (P < 0.05) higher in the granulosa of secondary and tertiary follicles compared with controls. Claudin 5 was exclusively localized to the theca vasculature. A significant (P < 0.05) increase in staining was detected from the pre-antral to the antral and ovulatory stage. However, dual staining with CD31 revealed that within the theca endothelium the amount of claudin 5 remained constant during follicular development. Treatment with VEGF trap throughout the follicular phase revealed a lack of claudin 5 staining in the theca interna but no difference was observed in the remaining theca externa vasculature. In the corpus luteum, claudin 5 was also localized in the vasculature. Treatment with VEGF trap in the mid-luteal phase resulted in a significant increase in staining (P < 0.05). These results led us to hypothesize that tight junctions are involved in regulation of follicular growth, antrum transition and follicular angiogenesis which is compromised by VEGF inhibition. VEGF may influence luteal vascular permeability by regulation of the endothelial specific tight junction protein claudin 5.

A novel physiological culture system that mimics luteal angiogenesis

Luteal inadequacy is a major cause of poor embryo development and infertility. Angiogenesis, the formation of new blood vessels, is an essential process underpinning corpus luteum (CL) development and progesterone production. Thus, understanding the factors that regulate angiogenesis during this critical time is essential for the development of novel strategies to alleviate luteal inadequacy and infertility. This study demonstrates the development of a physiologically relevant primary culture system that mimics luteal angiogenesis. This system incorporates all luteal cell types (e.g. endothelial, steroidogenic cells, fibroblasts and pericytes). Using this approach, endothelial cells, identified by the specific marker von Willebrand factor (VWF), start to form clusters on day 2, which then proliferate and develop thread-like structures. After 9 days in culture, these tubule-like structures lengthen, thicken and form highly organized intricate networks resembling a capillary bed. Development of the vasculature was promoted by coating wells with fibronectin, as determined by image analysis (P<0.001). Progesterone production increased with time and was stimulated by LH re-enforcing the physiological relevance of the model in mimicking in vivo luteal function. LH also increased the area stained positively for VWF by twofold (P<0.05). Development of this endothelial cell network was stimulated by fibroblast growth factor 2 and vascular endothelial growth factor A, which increased total area of VWF positive staining on day 9, both independently (three- to fourfold; P<0.01) and in combination (tenfold; P<0.001). In conclusion, the successful development of endothelial cell networks in vitro provides a new opportunity to elucidate the physiological control of the angiogenic process in the developing CL.

Distinct responses of human granulosa lutein cells after hCG or LH stimulation in a spheroidal cell culture system

The growth and development of the corpus luteum (CL) is regulated by gonadotropic hormones. It is formed by granulosa cells (GCs), theca cells, and endothelial cells, and is the primary source of circulating progesterone. During early pregnancy only human chorionic gonadotropin (hCG) but not luteinizing hormone (LH) extends the life span of the CL, although hCG and LH interact with the same receptor and have similar actions on the CL. In this study a recently by our group established spheroidal GC culture assay served as a model of CL development on which we compared the actions of the gonadotropic hormones LH and hCG. To find out which signal pathways take part in the hormonal regulation of GC we stimulated GC-spheroids with modulators of protein kinases A and C dependent signaling cascades and determined their impact on sprout forming activity in GC. Our results indicate that PKA-dependent signaling pathways play a major role in mediating the hormonal-induced signaling cascades leading to sprouting in GC. Furthermore, this study strongly indicates that the different effects of hCG and LH in the maintenance of the CL may be reasoned in different signal transduction pathways triggered by hCG or LH.

Luteogenic hormones act through a vascular endothelial growth factor-dependent mechanism to up-regulate alpha 5 beta 1 and alpha v beta 3 integrins, promoting the migration and survival of human luteinized granulosa cells

The formation of the corpus luteum (CL) is critical for the establishment of a successful pregnancy. After ovulation, the CL develops from the remnants of the ovulated ovarian follicle. This process, which involves varying cell-matrix interactions, is poorly characterized. To understand the role and potential regulation of cell-matrix interactions in the formation of the CL, we investigated the expression and activity of the matrix protein fibronectin (FN) and several of its integrin receptors on luteinized granulosa cells (GCs). In situ, FN and several FN-binding integrins were detected around luteinizing GCs during the early luteal phase, although expression declined in the late luteal phase. In vitro, GCs released FN, and stimulation of these cells with human chorionic gonadotropin increased the surface expression of FN, alpha(5)beta(1), and alpha(v)beta(3). Up-regulation of these proteins on GCs was reproduced by stimulation with vascular endothelial growth factor (VEGF) and was inhibited by anti-VEGF antibody. Lastly, expression of alpha(5)beta(1) and alpha(v)beta(3) mediated adhesion to FN, facilitated migration, and prevented apoptosis. These data suggest that in vivo luteogenic hormones, in part through a VEGF-dependent mechanism, stimulate selected integrin-matrix adhesive interactions that promote the motility and survival of GCs and thus contribute to the formation and preservation of the CL.

Cell junctional proteins in the human corpus luteum: changes during the normal cycle and after HCG treatment

BACKGROUND

Regulation of tissue remodelling and ovarian permeability by intercellular adhesion complexes may be involved in normal and pathological ovarian function. Therefore, the occurrence, distribution and hormonal control of the adherens junction protein vascular endothelial cadherin (VE-cadherin) and the tight junction proteins occludin and claudin in the human corpus luteum (CL) were investigated.

METHODS

CLs from patients undergoing hysterectomy for benign reasons were enucleated during early, mid- and late stages of the functional luteal phase and after HCG rescue in vivo. Immunostaining for occludin, claudins 1 and 5 and VE-cadherin was carried out on fixed tissue. Endothelial cells, granulosa lutein cells and theca lutein cells were identified by reference to serial sections immunostained for CD34, 17alpha-hydroxylase and 3beta-hydroxy-steroid-dehydrogenase. Quantitative analyses were performed using image analyses.

RESULTS

Occludin was localized to the plasma membrane of granulosa lutein cells and endothelial cells but was absent in theca lutein cells. Claudin 1 was exclusively localized to the plasma membrane of steroidogenic cells. Claudin 5 and VE-cadherin were only present in endothelial cells. After HCG administration in vivo, adherens and tight junction proteins were significantly down-regulated (P < 0.05).

CONCLUSIONS

The decrease of junctional proteins after HCG treatment suggests a hormonal control of tight and adherens junctions in the CL associated with tissue remodelling and an increase in luteal permeability during early pregnancy.