Expression of vascular endothelial growth factor in human luteinizing granulosa cells and its correlation with the response to controlled ovarian hyperstimulation

The direct and indirect effects of kisspeptin-54 on granulosa lutein cell function

STUDY QUESTION

What are the in vivo and in vitro actions of kisspeptin-54 on the expression of genes involved in ovarian reproductive function, steroidogenesis and ovarian hyperstimulation syndrome (OHSS) in granulosa lutein (GL) cells when compared with traditional triggers of oocyte maturation?

SUMMARY ANSWER

The use of kisspeptin-54 as an oocyte maturation trigger augmented expression of genes involved in ovarian steroidogenesis in human GL cells including, FSH receptor (FSHR), LH/hCG receptor (LHCGR), steroid acute regulatory protein (STAR), aromatase, estrogen receptors alpha and beta (ESR1, ESR2), 3-beta-hydroxysteroid dehydrogenase type 2 (3BHSD2) and inhibin A (INHBA), when compared to traditional maturation triggers, but did not alter markers of OHSS.

WHAT IS KNOWN ALREADY

hCG is the most widely used trigger of oocyte maturation, but is associated with an increased risk of OHSS. The use of GnRH agonists to trigger oocyte maturation is a safer alternative to hCG. More recently, kisspeptin-54 has emerged as a novel therapeutic option that safely triggers oocyte maturation even in women at high risk of OHSS. Kisspeptin indirectly stimulates gonadotropin secretion by acting on hypothalamic GnRH neurons. Kisspeptin and its receptor are also expressed in the human ovary, but there is limited data on the direct action of kisspeptin on the ovary.

STUDY DESIGN SIZE, DURATION

Forty-eight women undergoing IVF treatment for infertility consented to kisspeptin-54 triggering and/or granulosa cell collection and were included in the study. Twelve women received hCG, 12 received GnRH agonist and 24 received kisspeptin-54 to trigger oocyte maturation. In the kisspeptin-54 group, 12 received one injection of kisseptin-54 (9.6 nmol/kg) and 12 received two injections of kisspeptin-54 at a 10 h interval (9.6 nmol/kg × 2).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Follicular fluid was aspirated and pooled from follicles during the retrieval of oocytes for IVF/ICSI. GL cells were isolated and either RNA extracted immediately or cultured in vitro ± kisspeptin or hCG.

MAIN RESULTS AND THE ROLE OF CHANCE

GL cells from women who had received kisspeptin-54 had a 14-fold and 8-fold higher gene expression of FSHR and a 2-fold (ns) and 2.5-fold (P < 0.05) higher expression of LHCGR than GL cells from women who had received hCG or GnRH agonist, respectively. CYP19A1 expression was 3.6-fold (P < 0.05) and 4.5-fold (P < 0.05) higher, STAR expression was 3.4-fold (P < 0.01) and 1.8-fold (P < 0.05) higher, HSD3B2 expression was 7.5- (P < 0.01) and 2.5-fold higher (P < 0.05), INHBA was 2.5-fold (P < 0.01) and 2.5-fold (P < 0.01) higher in GL cells from women who had received kisspeptin-54 than hCG or GnRHa, respectively. ESR1 (P < 0.05) and ESR2 (P < 0.05) both showed 3-fold higher expression in cells from kisspeptin treated than GnRHa treated women. Markers of vascular permeability and oocyte growth factors were unchanged (VEGFA, SERPINF1, CDH5, amphiregulin, epiregulin). Gene expression of kisspeptin receptor was unchanged. Whereas treating GL cells in vitro with hCG induced steroidogenic gene expression, kisspeptin-54 had no significant direct effects on either OHSS genes or steroidogenic genes.

LIMITATIONS REASONS FOR CAUTION

Most women in the study had PCOS, which may limit applicability to other patient groups. For the analysis of the in vitro effects of kisspeptin-54, it is important to note that GL cells had already been exposed in vivo to an alternate maturation trigger.

WIDER IMPLICATIONS OF THE FINDINGS

The profile of serum gonadotropins seen with kisspeptin administration compared to other triggers more closely resemble that of the natural cycle as compared with hCG. Thus, kisspeptin could potentially permit an ovarian environment augmented for steroidogenesis, in particular progesterone synthesis, which is required for embryo implantation.

STUDY FUNDING/COMPETING INTEREST(S)

Dr Owens is supported by an Imperial College London PhD Scholarship. Dr Abbara is supported by an National Institute of Health Research Academic Clinical Lectureship. The authors do not have any conflict of interest to declare.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov NCT01667406.

A unique human chorionic gonadotropin antagonist suppresses ovarian hyperstimulation syndrome in rats

Ovarian hyperstimulation syndrome (OHSS) is a complication of in vitro fertilization associated with physiological changes after hCG administration to induce final oocyte maturation. It presents as widespread increases in vascular permeability and, in rare cases, results in cycle cancellation, multi-organ dysfunction, and pregnancy termination. These physiological changes are due primarily to activation of the vascular endothelial growth factor (VEGF) system in response to exogenous human chorionic gonadotropin (hCG). An hCG antagonist (hCG-Ant) could attenuate these effects by competitively binding to the LH/CG receptor, thereby blocking LH activity in vivo. We expressed a form of hCG that lacks three of its four N-linked glycosylation sites and tested its efficacy as an antagonist. The hCG-Ant binds the LH receptor with an affinity similar to native hCG and inhibits cAMP response in vitro. In a rat model for ovarian stimulation, hCG-Ant dramatically reduces ovulation and steroid hormone production. In a well-established rat OHSS model, vascular permeability and vascular endothelial growth factor (VEGF) expression are dramatically reduced after hCG-Ant treatment. Finally, hCG-Ant does not appear to alter blastocyst development when given after hCG in mice. These studies demonstrate that removing specific glycosylation sites on native hCG can produce an hCG-Ant that is capable of binding without activating the LH receptor and blocking the actions of hCG. Thus hCG-Ant will be investigated as a potential therapy for OHSS.

VEGF system expression in different stages of estrous cycle in the corpus luteum of non-treated and superovulated water buffalo

Water buffaloes are easily adaptable animals, whose raising and economical exploitation have been growing in the last three decades all over the world. Hyperstimulation of ovarian function in this species is a common technique aiming to improve reproductive performance. Superovulatory treatment affects corpus luteum (CL) function, which is highly correlated to angiogenic process. The aim of this study was therefore to assess the temporal protein and mRNA expression of VEGF and its receptors in the CL of non-treated and superovulated buffaloes. For that purpose blood samples and CL from 36 healthy (30 untreated, groups 1-5, and 6 superovulated, group 6) non-pregnant buffaloes were collected and the samples were divided into 6 groups according to the age of CL. Plasma samples were submitted to RIA to measure progesterone concentration and CL were subjected to immunohistochemistry and real time PCR for VEGF (vascular endothelial growth factor), Flt-1 (fms-like tyrosine kinase receptor 1) and KDR (kinase insert domain containing region). The VEGF system protein and mRNA expression during CL life span of untreated animals showed a specific time-dependent profile, although protein did not always reflect mRNA concentrations. VEGF expression in luteal cells was high correlated to plasma progesterone levels. Superovulated CL showed a significant increase of the VEGF-system protein and a significant decrease of mRNA expression compared to untreated animals in the same stage of the oestrous cycle. We conclude that VEGF, Flt-1 and KDR protein and mRNA expression in buffalo CL is dependent of estrous cycle stage and superovulatory treatment is able to increase the translation rate of this system.

Ovarian hyperstimulation syndrome and assisted reproductive technologies: why some and not others?

BACKGROUND

alpha(2)-Macroglobulin (alpha(2)M) is a multifactorial binding protein, found in follicular fluid, that is a naturally occurring inhibitor of vascular endothelial growth factor (VEGF). The aim of this study was to determine if there is a relationship between serum VEGF levels, alpha(2)M levels and the development of OHSS in hyperstimulated subjects undergoing IVF (those with 15 or more oocytes).

METHODS

Venous blood was collected at the time of oocyte retrieval from subjects who yielded 15 or more oocytes. Serum samples were analysed for VEGF and alpha(2)M concentrations.

RESULTS

There was no statistically significant difference in serum VEGF levels at the time of oocyte retrieval between hyperstimulated subjects who did and did not subsequently develop OHSS [3.95 (3.3-4.4) versus 3.85 (3.3-4.5); P = 0.79]. By contrast, the serum level of alpha(2)M was statistically significantly higher in the group of subjects who did not develop OHSS [2.27 (1.91-2.58) versus 1.67 (1.45-1.73)].

CONCLUSIONS

These results suggest that elevated alpha(2)M levels are associated with a decreased risk of developing OHSS. alpha(2)M may act by 'removing and inactivating' VEGF, with higher levels providing increased protection against the syndrome. alpha(2)M measurements may help to differentiate those for whom it is safe to proceed with embryo transfer from those for whom it is not, because of the risk of OHSS.

What's new in the pathogenesis and prevention of ovarian hyperstimulation syndrome?

Several pathophysiological mechanisms have been proposed for the development of ovarian hyperstimulation syndrome (OHSS), such as activation of the ovarian renin--prorenin--angiotensin system, release of ovarian cytokines and nitric oxide, but numerous reports now attest to the role of vascular endothelial growth factor (VEGF), an endothelial cell mitogen, as an important mediator of the syndrome. Luteinizing hormone (LH) or human chorionic gonadotrophin (hCG) regulates VEGF production by the ovary. Formation of multiple follicles, as seen in regimens of ovarian stimulation used for in vitro fertilization (IVF), and intensified sensitivity towards human menopausal gonadotrophin (hMG) and hCG, as seen in women with polycystic ovaries (PCO) or polycystic ovary syndrome (PCOS), result in increased serum VEGF concentrations, probably due to enhanced VEGF production by the ovaries. It is possible that the hypersecretion of VEGF in women with PCO is due to an increase in the number of VEGF secreting cells or that the cells individually hypersecrete VEGF. This hypothesis was tested by in vitro studies on granulosa lutein cells. After the cells were stimulated with gonadotrophins and hCG, VEGF production was higher in granulosa cells obtained from women with PCO compared with those obtained from women with normal ovaries under similar culture conditions. The studies performed in vivo and in vitro were consistent with increased VEGF expression as a constitutive feature of PCO. Increased VEGF may be responsible for the fluid shift from the vascular bed to the extravascular space, which characterizes OHSS. Prevention of OHSS focuses on predicting the possibility of developing OHSS. Markers such as serum oestradiol concentrations and number of follicles on the day of hCG administration, the presence of PCO and the number of oocytes retrieved may be subject to inter-observer and inter-operator variations. As individual markers of OHSS, each of these factors predicts less than a quarter of cases of the syndrome. It has been shown that a combination of pretreatment diagnosis of PCO along with number of follicles on the day of hCG administration and 'VEGF rise' gives the highest prediction rates for the risk of developing OHSS. Neither pathogenesis nor prevention and treatment of OHSS are specific. Therefore, at present, OHSS remains a condition that cannot be avoided altogether.

Evidence for a role of capillary pericytes in vascular growth of the developing ovine corpus luteum

Because of rapid growth followed by spontaneous regression, the ovarian corpus luteum (CL) is an excellent model to study angiogenesis in vivo. To evaluate the expression of vascular endothelial growth factor (VEGF) protein during luteal development, ovaries were collected from FSH-stimulated ewes throughout the estrous cycle. VEGF was immunolocalized in tissue sections by using an affinity-purified antibody. VEGF protein localized exclusively to the thecal layer of preovulatory follicles, while the granulosa was devoid of staining. Associated with the periovulatory period was intense expression of VEGF by thecal cells at the basement membrane and subsequent invasion of the granulosa layers by these VEGF-positive cells immediately after ovulation. The early CL showed staining for VEGF in thecal-derived compartments, and strong staining for VEGF was also seen in cells within the granulosa-derived parenchymal lobules. Dual immunohistochemical localization of VEGF and smooth muscle cell alpha-actin indicated that the VEGF-positive cells were capillary pericytes or vascular smooth muscle cells. In another experiment, we quantified proliferation of endothelial cells and pericytes throughout luteal development. Pericytes represented a large proportion of the proliferating cells during the early luteal phase and then decreased dramatically. Perivascular cells, therefore, may play a critical role in angiogenesis that occurs during transformation of the follicle into the highly vascular CL of the sheep. As angiogenesis occurs only at the level of capillaries, and pericytes are integral members of these microvessels, regulation of pericytes may provide a novel mechanism for regulating luteal growth and tissue growth in general.

Angiogenesis of the ovary

We present current data pertaining to angiogenesis of the ovary throughout the follicular and luteal phases of the ovarian cycle, in various ovarian pathologic conditions and in benign and neoplastic diseases. MEDLINE, Current Contents, and Index Medicus were searched for studies published between January 1966 and October 1998. All studies that incorporated human and animal models of angiogenesis of the normal ovarian physiologic state and pathologic conditions including both benign and neoplastic ovarian diseases were reviewed. Current literature supports that angiogenesis is an important component of both follicular and luteal phases of the ovarian cycle that correlates well with maturation of secretory endometrium. Angiogenesis also participates in various pathologic processes of the ovary, including follicular cyst formation, polycystic ovary, ovarian hyperstimulation syndrome, and both benign and malignant ovarian neoplasms. In the future a knowledge of specific angiogenic patterns of various pathologic processes may assist in the application of antiangiogenic medications in targeted therapy of benign and neoplastic diseases of the ovary.

Correlation between the amount of follicle-stimulating hormone administered and plasma and follicular fluid vascular endothelial growth factor concentrations in women undergoing in vitro fertilization

Vascular endothelial growth factor (VEGF) is a powerful mediator for vessel permeability and it is strongly implicated in angiogenesis, stimulating endothelial cell proliferation as well as capillary permeability. We studied 30 women undergoing in vitro fertilization (IVF) programs and evaluated, on the day of oocyte retrieval, VEGF levels in plasma and follicular fluid and related such concentrations to the amount of follicle-stimulating hormone (FSH) administered. Furthermore, the correlation between the number of oocytes retrieved and the VEGF concentrations both in plasma and in follicular fluid were also investigated. Results indicate that follicular fluid VEGF concentrations and the amount of pure FSH administered were directly proportional (p < 0.05). On the day of oocyte retrieval, the VEGF plasma concentrations and the number of oocytes collected were directly proportional (p < 0.05). VEGF plasma levels increased after human chorionic gonadotropin (hCG) administration (30.37 +/- 18.60 pg/ml up to 52.62 +/- 43.63 pg/ml). In conclusion, this study demonstrates that the doses of pure FSH administered to women undergoing IVF cycles have a crucial role in hCG-dependent VEGF production.