Follicular Microvasculature and Angiogenic Factors in the Ovaries of Domestic Animals

Effects of P4 Antagonist RU486 on VEGF and Its Receptors' Signaling during the In Vivo Transition from the Preovulatory to Periovulatory Phase of Ovarian Follicles

The development of an adequate blood vessel network is crucial for the accomplishment of ovarian follicle growth and ovulation, which is necessary to support the proliferative and endocrine functions of the follicular cells. Although the Vascular Endothelial Growth Factor (VEGF) through gonadotropins guides ovarian angiogenesis, the role exerted by the switch on of Progesterone (P4) during the periovulatory phase remains to be clarified. The present research aimed to investigate in vivo VEGF-mediated mechanisms by inducing the development of periovulatory follicles using a pharmacologically validated synchronization treatment carried out in presence or absence of P4 receptor antagonist RU486. Spatio-temporal expression profiles of VEGF, FLT1, and FLK1 receptors and the two major MAPK/ERKs and PI3K/AKT downstream pathways were analyzed on granulosa and on theca compartment. For the first time, the results demonstrated that in vivo administration of P4 antagonist RU486 inhibits follicular VEGF receptors' signaling mainly acting on the theca layer by downregulating the activation of ERKs and AKTs. Under the effect of RU486, periovulatory follicles' microarchitecture did not move towards the periovulatory stage. The present evidence provides new insights on P4 in vivo biological effects in driving vascular and tissue remodeling during the periovulatory phase.

Description of the Follicular Fluid Cytokine and Hormone Profiles in Human Physiological Natural Cycles

PURPOSE

Exogenous gonadotrophins administration during in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles could significantly alter the endogenous follicular regulation system and could influence oocyte quality. The analysis of the follicular fluid (FF) cytokine and hormone profiles in physiological natural cycles is crucial to appreciate the role of FF milieu on follicle development. So far, the FF cytokine profile has been analyzed only in controlled ovarian stimulation cycles and in modified natural cycles. Our study defines, in physiological natural cycles, the cytokine and hormone profiles of individual FF aspirated from antral follicles.

METHODS

A total of 203 FFs obtained from 83 women with regular menstrual cycles undergoing ovarian tissue cryopreservation were analyzed: 115 FFs from Group 1 (10 to 29 years of age) and 88 FFs from Group 2 (30 to 40 years of age). In individual FF, 27 cytokines were measured with xMAP technology, and progesterone, estrone, estradiol, testosterone, androstenedione concentrations were determined by liquid chromatography-tandem mass spectrometry.

RESULTS

FF hormone profiles were not different in follicular and luteal phase, suggesting that FF hormones are regulated independently of the endogenous gonadotrophins-possibly because 74% of the punctured follicles, which were ≤6 mm, did not require cyclic pituitary function. The follicle size was influenced not only by the FF cytokine profile but also by the FF hormone profile, both of which are dependent on age.

MAIN CONCLUSIONS

In physiological natural cycles, FF hormones seems to be regulated independently of the endogenous gonadotropins. Age influences FF hormone and cytokine profiles and the compelling relationship between FF hormones and FF cytokines could influence the follicle development.

Vascular endothelial growth factor A isoforms modulate follicle development in peripubertal heifers independent of diet through diverse signal transduction pathways

Follicular progression during peripuberty is affected by diet. Vascular endothelial growth factor A (VEGFA) induces follicle progression in many species; however, there are limited studies to determine if diet may alter the effects of angiogenic VEGFA165-stimulated follicle progression or antiangiogenic VEGFA165b follicle arrest. We hypothesized that diet affects the magnitude of angiogenic and antiangiogenic VEGFA isoform actions on follicular development through diverse signal transduction pathways. To test this hypothesis, beef heifers in our first trial received Stair-Step (restricted and refeeding) or control diets from 8 to 13 months of age. Ovaries were collected to determine follicle stages, measure vascular gene expression and conduct ovarian cortical cultures. Ovarian cortical cultures were treated with phosphate-buffered saline (control), 50 ng/ml VEGFA165, VEGFA165b, or VEGFA165 + VEGFA165b. The Stair-Step heifers had more primordial follicles (P < 0.0001), greater messenger RNA abundance of vascular markers VE-cadherin (P < 0.0001) and NRP-1 (P < 0.0051) than controls at 13 months of age prior to culture. After culture, VEGFA isoforms had similar effects, independent of diet, where VEGFA165 stimulated and VEGFA165b inhibited VEGFA165-stimulated follicle progression from early primary to antral follicle stages. In vitro cultures were treated with VEGFA isoforms and signal transduction array plates were evaluated. VEGFA165 stimulated expression of genes related to cell cycle, cell proliferation, and growth while VEGFA165b inhibited expression of those genes. Thus, VEGFA isoforms can act independently of diet to alter follicle progression or arrest. Furthermore, follicle progression can be stimulated by VEGFA165 and inhibited by VEGFA165b through diverse signal transduction pathways.

Detection of the effects and potential interactions of FSH, VEGFA, and 2-methoxyestradiol in follicular angiogenesis, growth, and atresia in mouse ovaries

Ovarian follicular development is a complex process that requires codevelopment of the perifollicular vascular network, which is closely regulated by angiogenic factors, gonadotropins, sex steroids, and their metabolites. To detect the effects of vascular endothelial growth factor 120 (VEGF120), follicle-stimulating hormone (FSH), and 2-methoxyestradiol (2ME2) on follicular angiogenesis during development and atresia, we treated sexually immature and mature female mice with VEGF120, FSH, 2ME2, and FSH receptor (FSHR) antagonist singly or in combination via intraperitoneal injection. The number of follicles and their perifollicular angiogenesis and atresia rates at different developmental stages were examined in paraffin sections after hematoxylin and eosin staining. The results showed that the exogenous factors have specific and precise effects on developmental, angiogenesis, and atresia processes in follicles of different sizes in mature and immature mice. Perifollicular angiogenesis was regulated by VEGFA and closely related to follicular development and atresia. 2ME2 affected angiogenesis through VEGFA and might regulate atresia directly. FSH might control VEGFA function via both transcriptional and posttranscriptional mechanisms because FSHR was required for achieving VEGFA functions at all the follicular development stages. The present study presents insights into the mechanisms of FSH, 2ME2, and VEGFA in follicular development and disorders and provides a foundation for the development of new therapeutic strategies.

Identificação imuno-histoquímica de VEGF e IGF-1 em ovários de cadelas no anestro e estro

Com o objetivo de verificar a presença de VEGF e IGF-1 nos ovários de cadelas, foram realizadas análises imuno-histoquímicas do estroma cortical; teca e granulosa de folículos secundários, terciários e terciários pré-ovulatórios luteinizados; e ovócitos de folículos primários, secundários e terciários de ovários de cinco cadelas em anestro (Anest) e cinco em estro (Est). A identificação das fases do ciclo estral foi realizada por citologia vaginal associada a dosagem plasmática de progesterona. Os ovários foram submetidos a tratamento imuno-histoquímico para identificação de VEGF (anticorpo primário PU 360-UP, Biogenex, USA; diluição 1:30) e IGF-1 (anticorpo primário PabCa, Gro-Pep, Austrália; diluição 1:100). Determinou-se um índice de imunomarcação (IM), para cada tecido avaliado, pela razão entre a área positivamente marcada dividida pela área total analisada. Para os ovócitos, verificou-se imunomarcação positiva ou negativa. As comparações de IM entre tecidos foram realizadas pelo teste de Wilcoxon (diferentes tecidos em mesmo grupo) ou Mann-Whitney (mesmo tecido entre diferentes grupos), todas no nível de 5% de significância. VEGF e IGF-1 foram identificados, de forma semelhante (P>0,05), em todas as estruturas avaliadas em ambos os grupos experimentais. Conclui-se que esses fatores de crescimento estão presentes em cadelas no anestro e estro, no estroma cortical ovariano, folículos em diferentes estádios de desenvolvimento e ovócitos.

Effect of antiprogesterone RU486 on VEGF expression and blood vessel remodeling on ovarian follicles before ovulation

Background

The success of ovarian follicle growth and ovulation is strictly related to the development of an adequate blood vessel network required to sustain the proliferative and endocrine functions of the follicular cells. Even if the Vascular Endothelial Growth Factor (VEGF) drives angiogenesis before ovulation, the local role exerted by Progesterone (P₄) remains to be clarified, in particular when its concentration rapidly increases before ovulation.

Aim

This in vivo study was designed to clarify the effect promoted by a P₄ receptor antagonist, RU486, on VEGF expression and follicular angiogenesis before ovulation, in particular, during the transition from pre to periovulatory follicles induced by human Chorionic Gonadotropins (hCG) administration.

Material and Methods

Preovulatory follicle growth and ovulation were pharmacologically induced in prepubertal gilts by combining equine Chorionic Gonadotropins (eCG) and hCG used in the presence or absence of RU486. The effects on VEGF expression were analyzed using biochemical and immunohistochemical studies, either on granulosa or on theca layers of follicles isolated few hours before ovulation. This angiogenic factor was also correlated to follicular morphology and to blood vessels architecture.

Results and Conclusions

VEGF production, blood vessel network and follicle remodeling were impaired by RU486 treatment, even if the cause-effect correlation remains to be clarified. The P₄ antagonist strongly down-regulated theca VEGF expression, thus, preventing most of the angiogenic follicle response induced by hCG. RU486-treated follicles displayed a reduced vascular area, a lower rate of endothelial cell proliferation and a reduced recruitment of perivascular mural cells. These data provide important insights on the biological role of RU486 and, indirectly, on steroid hormones during periovulatory follicular phase. In addition, an in vivo model is proposed to evaluate how periovulatory follicular angiogenesis may affect the functionality of the corpus luteum (CL) and the success of pregnancy.

Vascular contributions to early ovarian development: potential roles of VEGFA isoforms

Vascularisation is an essential component of ovarian morphogenesis; however, little is known regarding factors regulating the establishment of vasculature in the ovary. Angiogenesis involving extensive endothelial cell migration is a critical component of vessel formation in the embryonic testis but vasculogenic mechanisms appear to play a prominent role in ovarian vascularisation. Vasculature has a strong influence on the formation of ovarian structures, and the early developmental processes of ovigerous cord formation, primordial follicle assembly and follicle activation are all initiated in regions of the ovary that are in close association with the highly vascular medulla. The principal angiogenic factor, vascular endothelial growth factor A (VEGFA), has an important role in both endothelial cell differentiation and vascular pattern development. Expression of VEGFA has been localised to ovigerous cords and follicles in developing ovaries and an increased expression of pro-angiogenic Vegfa isoform mRNA in relation to anti-angiogenic isoform mRNA occurs at the same time-point as the peak of primordial follicle assembly in perinatal rats. Elucidation of specific genes that affect vascular development within the ovary may be critical for determining not only the normal mechanisms of ovarian morphogenesis, but also for understanding certain ovarian reproductive disorders.

Chronic mastitis is associated with altered ovarian follicle development in dairy cattle

Connection between mastitis and fertility is multifaceted; therefore, several aspects need more elucidation. In particular, the aim was to investigate if naturally occurring chronic mastitis has an effect on ovarian function. At the time of slaughter, a milk sample and both ovaries were collected from 68 cows. The presence and intensity of chronic mastitis was diagnosed by the combined evaluation of bacteriological examination and somatic cell count of the milk of each individual quarter according to the measures of the National Mastitis Council. Animals were divided into 4 groups characterized by a low (n=15), mild (n=14), intense (n=19), or severe (n=16) degree of infection. A count of visible follicles on each ovary was followed by a quantitative analysis of microscopic traits on a selected group of animals (n=16). The latter included the classification and count of the entire preantral follicle population, and the morphometric analysis of the vascular bed extension and connective stroma in the cortical region. Finally, the expression of growth and differentiation factor-9 (GDF-9) was studied. The number of follicles with diameters ranging from 1 to 3 mm and 4 to 7 mm was not affected by the degree of infection. A significant effect of the degree of udder infection was observed on the number of follicles with a diameter larger than 8 mm. Furthermore, the intensity of mastitis had no effect on the number of primordial and primary follicles, but severely affected cows showed a lower number of secondary follicles (0.5±0.1 vs. 0.2±0.03). Quantitative analysis demonstrated a decrease in the density of blood vessels (6.30±1.08 vs. 4.68±0.28) expressed as ratio of vascular bed/total area) and a higher incidence of fibrous stroma (1.60±0.99 vs. 6.04±3.08 expressed as ratio of connective tissue/total area) in the cortical area of the most affected animals. Finally, the level of GDF-9 protein within the oocytes of different follicle size was lower in the animals with the severe form of chronic mastitis (1.34±0.05 vs. 0.78±0.21 expressed as arbitrary units). In conclusion, decreased fertility of cows with chronic mastitis takes place through an effect on the ovary altering the dynamics of folliculogenesis. Within the ovary, this implies a reduction of the vascular bed and an increase in the fibrotic tissue together with a direct effect on oocyte-specific factors as GDF-9, all of which are essential regulatory elements of folliculogenesis.

The balance of proangiogenic and antiangiogenic VEGFA isoforms regulate follicle development

Vascular endothelial growth factor A (VEGFA) has been extensively studied because of its role in follicular development and is a principal angiogenic factor essential for angiogenesis. Since vascularization of the theca layer increases as follicles progress in size through preantral and antral stages, VEGFA might influence follicle growth via the regulation of angiogenesis. However, VEGFA might also influence follicular development through nonangiogenic mechanisms, since its expression has been localized in nonvascular follicles and cells. Alternative mRNA splicing of eight exons from the VEGFA gene results in the formation of various VEGFA isoforms. Each isoform has unique properties and is identified by the number of amino acids within the mature protein. Proangiogenic isoforms (VEGFA_XXX) are encoded by exon 8a, whereas a sister set of isoforms (VEGFA_XXXB) with antiangiogenic properties is encoded by exon 8b. The antiangiogenic VEGFA_XXXB isoforms comprise the majority of VEGFA expressed in most tissues, whereas expression of the proangiogenic VEGFA isoforms is upregulated in tissues undergoing active angiogenesis. Although proangiogenic and antiangiogenic isoforms can now be distinguished from one another, many studies evaluating VEGFA in ovarian and follicular development up to now have not differentiated proangiogenic VEGFA from antiangiogenic VEGFA. Experiments from our laboratory indicate that proangiogenic VEGFA promotes follicle recruitment and early follicular development and antiangiogenic VEGFA inhibits these processes. The balance of proangiogenic versus antiangiognic VEGFA isoforms is thus of importance during follicle development. Further studies are warranted to elucidate the way that this balance regulates follicular formation and progression.

Importance of vascular endothelial growth factor (VEGF) in ovarian physiology of mammals

Ovarian folliculogenesis in mammals is a complex process. Several compounds have been tested during in vitro culture of follicular cells for a better understanding of the mechanisms and factors related to ovarian folliculogenesis in mammals. From these compounds, vascular endothelial growth factor (VEGF) can be highlighted, as it is strongly associated with angiogenesis and, in recent years, its presence in ovarian cells has been investigated extensively. Previous studies have shown that the presence of VEGF protein, as well as mRNA expression of its receptor 2 (VEGFR-2) increases during follicular development. Therefore, it is likely that the interaction between VEGF and VEGFR-2 is crucial to promote follicular development. However, few studies on the influence of this factor on follicular development have been reported. This review addresses aspects related to the structural characterization and mechanism of action of VEGF and its receptors, and their biological importance in the ovary of mammals.

Theca: the forgotten cell of the ovarian follicle

Theca cells function in a diverse range of necessary roles during folliculogenesis; to synthesize androgens, provide crosstalk with granulosa cells and oocytes during development, and provide structural support of the growing follicle as it progresses through the developmental stages to produce a mature and fertilizable oocyte. Thecal cells are thought to be recruited from surrounding stromal tissue by factors secreted from an activated primary follicle. The precise origin and identity of these recruiting factors are currently not clear, but it appears that thecal recruitment and/or differentiation involves not just one signal, but a complex and tightly controlled combination of multiple factors. It is clear that thecal cells are fundamental for follicular growth, providing all the androgens required by the developing follicle(s) for conversion into estrogens by the granulosa cells. Their function is enabled through the establishment of a vascular system providing communication with the pituitary axis throughout the reproductive cycle, and delivering essential nutrients to these highly active cells. During development, the majority of follicles undergo atresia, and the theca cells are often the final follicular cell type to die. For those follicles that do ovulate, the theca cells then undergo hormone-dependent differentiation into luteinized thecal cells of the corpus luteum. While the theca is an essential component of follicle development and ovulation, we do not yet fully understand the control of recruitment and function of theca cells, an important consideration since their function appears to be altered in certain causes of infertility.

Nerve growth factor induces vascular endothelial growth factor expression in granulosa cells via a trkA receptor/mitogen-activated protein kinase-extracellularly regulated kinase 2-dependent pathway

CONTEXT

Acquisition of ovulatory competence by antral follicles requires development of an adequate vascular supply. Although it is well established that ovarian angiogenesis is cyclically regulated by vascular endothelial growth factor (VEGF), the factors controlling VEGF production by ovarian follicles remain largely unknown. Nerve growth factor (NGF) may be one of these factors, because NGF promotes angiogenesis and synthesis of angiogenic factors in other tissues and is produced by human granulosa cells (hGCs).

OBJECTIVE

The aim of the study was to determine whether NGF influences the production of VEGF by hGCs and to identify a potential signaling pathway underlying this effect.

DESIGN

We conducted a prospective experimental study.

PATIENTS

hGCs were obtained from 41 women participating in the in vitro fertilization program of our institution.

METHODS

Changes in VEGF mRNA after exposure to NGF were evaluated in cultured hGCs by PCR and real-time PCR. The effect of NGF on VEGF secretion was determined by ELISA. The involvement of trkA, the high affinity NGF receptor, was examined by inhibiting the receptor's tyrosine kinase activity with K252a. The contribution of an ERK1/ERK2-mediated signaling pathway was identified by detecting NGF-dependent phosphorylation of these proteins and by blocking their activity with the inhibitor U0126.

RESULTS

NGF promotes VEGF production in cultured hGCs. Blockade of trkA receptor tyrosine kinase activity blocks this effect. NGF induces MAPK-ERK2 phosphorylation, and blockade of this signaling pathway prevents the NGF-induced increase in VEGF production.

CONCLUSIONS

NGF promotes ovarian angiogenesis by enhancing the synthesis and secretion of VEGF from hGCs via a trkA- and ERK2-dependent mechanism.

Metabolic programming of ovarian angiogenesis and folliculogenesis by maternal malnutrition during lactation

OBJECTIVE

To evaluate whether maternal malnutrition during lactation programs ovarian folliculogenesis and the expression of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) and its receptors KDR, Flt-1, and FGFR.

DESIGN

Experimental study.

SETTING

University-based research laboratory.

ANIMAL(S)

Adult female rats from a urogenital research laboratory.

INTERVENTION(S)

Six rat dams randomly assigned to the following groups: control group (C), with free access to a standard laboratory diet containing 23% protein; and a protein-energy-restricted group (PER), with free access to an isoenergy and protein-restricted diet containing 8% protein. After weaning, the female pups had free access to the standard laboratory diet until 90 days of age, when they were sacrificed at the proestrum stage.

MAIN OUTCOME MEASURE(S)

Quantification of ovarian follicles, vessels, and expression of growth factors and their receptors.

RESULT(S)

Maternal malnutrition during lactation caused a significant reduction in the number of primordial (C = 6.60 +/- 0.24, PER = 5.20 +/- 0.20), primary (C = 5.80 +/- 0.66, PER = 4.00 +/- 0.31), and Graafian follicles/section (C = 2.18 +/- 0.29, PER = 1.08 +/- 0.37), in KDR (C = 0.22 +/- 0.04, PER = 0.09 +/- 0.01), Flt-1 (C = 0.28 +/- 0.05, PER = 0.12 +/- 0.02), and FGFR mRNA expression (C = 0.34 +/- 0.05, PER = 0.13 +/- 0.05) and in the vessel density of follicles (C = 17.26 +/- 2.30, PER = 9.96 +/- 0.97).

CONCLUSION(S)

Maternal malnutrition during lactation programs the follicular development by a reduction of VEGF and FGF mRNA receptors expression, probably from a direct action on the follicular development or a reduction in vasculature resulting in a decreased delivery of folliculotrophic substances in PER animals.

Gene injections of vascular endothelial growth factor and growth differentiation factor-9 stimulate ovarian follicular development in immature female rats

OBJECTIVE

To examine the effect of vascular endothelial growth factor (VEGF) and growth differentiation factor-9 (GDF-9) on follicular development of the ovaries in immature female rats.

DESIGN

Superovulation and gene injection.

SETTING

Animal reproduction laboratory in Tohoku University, Sendai, Japan.

ANIMAL(S)

Wister-Imamichi female rats.

INTERVENTION(S)

The ovulated oocytes from rats with injected VEGF and GDF-9 gene fragments were counted, and the ovaries removed from those rats were used in the histologic observation.

MAIN OUTCOME MEASURE(S)

Follicular dynamics and angiogenesis after VEGF and GDF-9 gene fragments injection.

RESULT(S)

A single injection of the VEGF gene led to the production of a large number of oocytes (approximately 110 oocytes) from an individual animal that was injected with the gene at 21 days after birth, and after mating most of the oocytes were fertilized. Direct ovarian injection of GDF-9 stimulated the development of medium-sized antral follicles. The number of ovulated oocytes after injection of the VEGF plus GDF-9 gene fragments was the same as with a single injection of the VEGF gene.

CONCLUSION(S)

A single injection of the VEGF or GDF-9 gene stimulated follicular development, and injection of both genes did increase the number of ovulated oocytes from individual animals. An exogenous gene fragments injection promoted the maximum potential of ovarian function in immature female rats.

Progesterone induces the expression of vascular endothelial growth factor (VEGF) 120 and Flk-1, its receptor, in bovine granulosa cells

Vascular endothelial growth factor (VEGF) isoforms (VEGF 120 and VEGF 164) secreted by granulosa cells are involved in thecal angiogenesis during follicular development in the bovine ovary. The follicular fluid in the developing follicle includes a slight amount of the progesterone. However, the progesterone (P4) effects on VEGF120 and VEGF164 isoforms have not been well characterized in the bovine granulosa cells. We investigated the effects of progesterone on the gene expression of hypoxia-inducible factor 1alpha (HIF-1alpha, transcription factor), VEGF120, VEGF164 and Flk-1, its receptors, in cultured bovine granulosa cells. Messenger RNA expression for HIF-1alpha, VEGF120, VEGF164 and Flk-1 was quantified using real-time PCR methods. The levels of VEGF120, HIF-1alpha and Flk-1 mRNAs were increased significantly by P4 at a concentration of 10 ng/ml. In contrast, the expression of VEGF 164 gene is inhibited by P4. The level of VEGF120 and Flk-1 mRNAs in the granulosa cells treated with 10 ng/ml progesterone plus 1 ng/ml estradiol significantly decreased compared with progesterone alone. In contrast, the addition of 1 ng/ml estradiol to the culture medium increased the expression of VEGF164 gene. In conclusion, our data demonstrated that progesterone might stimulate the expression of the VEGF120 via HIF-1alpha, transcription factor, in bovine granulosa cells. These results suggest the hormone-dependent expression pattern of VEGF isoforms during follicular development. Thus, our study suggested the expression of VEGF isoforms in granulosa cells might be controlled by a different pathway during follicle development in cow.

Vascular endothelial growth factor (VEGF) suppresses ovarian granulosa cell apoptosis in vitro

Vascular endothelial growth factor (VEGF) inhibits the follicular atresia that resulted from granulosa cell apoptosis in the mammalian ovary. In the present study, we examined the effect of VEGF on granulosa cell apoptosis. Here, we report that VEGF suppresses granulosa cell apoptosis by inhibiting the release of caspase-activated DNase (CAD) without being associated with the mitochondrial pathway. VEGF did not stimulate or inhibit Bcl-xL and Bax, respectively, in granulosa cells. In addition, VEGF did not suppress the expression of active caspase-3, whereas follicle-stimulating hormone (FSH) inhibited caspase-3. However, VEGF and FSH suppressed the release of CAD resulting from the disintegration of the CAD-ICAD complex. These results demonstrate that VEGF is a strong survival factor for granulosa cell apoptosis (ovarian follicular atresia).

Differential Effect of Follicle-Stimulating Hormone and Estradiol on Expressions of Vascular Endothelial Growth Factor (VEGF) 120, VEGF164 and Their Receptors in Bovine Granulosa Cells

Vascular endothelial growth factor (VEGF) isoforms (VEGF 120 and VEGF 164) secreted by granulosa cells are involved in thecal angiogenesis during follicular development in the bovine ovary. However, whether the transcript of the VEGF120 and VEGF164 isoforms differs during follicular development in the ovary is still unknown. We first examined the gene expression of VEGF120, VEGF164, fms-like tyrosine kinase (Flt-1), and fetal liver kinase (Flk-1) in the granulosa cells (GCs) and theca cells (TCs) of pre-selection and post-selection follicles (PRF and POF respectively) from the bovine ovary. Then we examined the effects of FSH and estradiol (E2) on these factors in cultured bovine GCs. Messenger RNA (mRNA) expression was quantified using real-time PCR methods. The concentrations of E2 and P4 in the follicular fluid (FF) of the PRF and POF were estimated using an enzyme immunoassay (EIA). The concentrations of E2 and P4 in the FF were significantly higher in the POF than in the PRF. The ratio of E2/P4 in PRF and POF was 0.37 and 3.8, respectively. The expression levels of the VEGF120, VEGF164, and Flk-1 mRNAs in the GCs of POF with high E2 concentration were higher than those of PRF. The levels of the Flt-1 and Flk-1 mRNAs in the TCs were not different between PRF and POF. Since E2 in the FF of the POF used in the present study was high compared with the PRF, we examined the effects of E2 and FSH on the expression of the above genes using cultured GCs. Expression of VEGF120 mRNA was induced by a low concentration (1 ng/ml) of E2, whereas the levels of VEGF164 and Flk-1 mRNAs were not affected by E2. FSH stimulated the expression of the VEGF isoforms and Flk-1 genes. Moreover, the expression of those genes was enhanced when low E2 (1 ng/ml) was added to FSH. In conclusion, our data indicates that the VEGF isoforms have a follicle stage-dependent expression pattern. Thus, our results suggest that the expression of VEGF isoforms may be associated with characterization of the preovulatory phenotype during follicle development in the bovine ovary.

Nicotine does not affect vascularization but inhibits growth of freely transplanted ovarian follicles by inducing granulosa cell apoptosis

BACKGROUND

There is clear support for an association between smoking and decreased female fecundity and fertility. Cigarette smoke appears to have adverse effects along a continuum of reproductive processes. We therefore studied the effect of nicotine on follicular growth and vascularization of freely transplanted ovarian follicles.

METHODS

We used the skinfold chamber model in Syrian golden hamsters, which allows the in vivo microscopy of follicular grafts. Animals were treated daily with nicotine at doses mimicking low-rate and high-rate smokers (0.2 and 1.0 mg/kg body weight subcutaneously). Saline-treated animals served as controls. To further evaluate the effect of nicotine on angiogenesis, an in vitro aortic ring assay was used.

RESULTS

The re-vascularisation rate of follicles was similar in nicotine-treated animals and controls. During the 7 days after transplantation, nicotine further caused a dose-dependent inhibition of follicular growth. In contrast, the vascularized area and microvessel density were not affected by the nicotine exposure. In vitro aortic ring assays confirmed that nicotine does not influence sprouting and microvessel formation. However, immunohistochemistry for cleaved caspase-3 revealed a large extent of granulosa cell apoptosis within transplanted follicles of high-dose nicotine-treated animals.

CONCLUSIONS

Nicotine as one toxic component of cigarette smoke does not affect vascularization, but adversely influences follicular growth by an increase in apoptotic cell death. As follicular growth is a crucial step in normal ovulation and fertilization, nicotine-induced cell apoptosis may represent one of the mechanisms underlying the well-established link between smoking and fertility disorders.

Angiogenic activity of swine granulosa cells: effects of hypoxia and vascular endothelial growth factor Trap R1R2, a VEGF blocker

The possible role played by hypoxia and vascular endothelial growth factor (VEGF) in the regulation of follicular angiogenesis was studied in a three-dimensional fibrin gel model. Granulosa cells from follicles >5mm were subjected to normoxia (19% O2), partial (5% O2) or total (1% O2) hypoxia and their culture media were collected and used to stimulate porcine Aortic Endothelial Cells (AOC) included in the fibrin matrix. A suspension of AOC on microcarrier beads was pipetted in a fibrinogen solution (1 mg/ml PBS) before the addition of 1250 IU thrombine (250 microl) to catalize the gel formation. Granulosa cell conditioned media were tested in the presence or absence of VEGF Trap R1R2 (150 ng/ml), a potent VEGF inhibitor, that had its efficacy tested by adding VEGF (100 ng/ml) to AOC culture. Endothelial cell proliferation was measured at 48, 96, 144, 192 h by means of Scion Image Beta. A significant (p < 0.01) increase of AOC proliferation at each time of measurement was induced by culture media from granulosa cells subjected to partial (except at the end of the first 48 h) and total hypoxia compared to control and normoxia conditions, and by VEGF. VEGF Trap significantly (p < 0.01) inhibited the stimulatory effect of media conditioned by granulosa cells cultured in hypoxic conditions. These data suggest that hypoxia stimulates angiogenic activity of granulosa cells possibly by means of VEGF which could represent the main effector in promoting endothelial cell proliferation.

Acceleration of Follicular Development by Administration of Vascular Endothelial Growth Factor in Cycling Female Rats

To address the role of follicular angiogenesis in the determination of ovulatory follicles and the effects of different vascular endothelial growth factor (VEGF) isoforms on follicular angiogenesis and development, mature female rats were treated with an angiogenic inhibitor (TNP-470), and also with VEGF 120 or 164 at different dosages (0.4, 0.8, 4.0 or 8.0 microg/kg body weight) for 3 days during the estrous cycle. Ovarian follicular angiogenesis, the population of large follicles and ovulation were examined. VEGF 120 (0.8 microg/kg) and 164 (8.0 microg/kg) treatments stimulated follicular angiogenesis in the theca interna layer, while TNP-470 treatment showed severe depression of follicular angiogenesis, and completely inhibited ovulation. After administration of VEGF 120 or 164, the number of healthy preovulatory follicles and ovulated oocytes increased significantly, concomitantly with a decrease in the number of atretic preovulatory follicles. The oocytes ovulated had normal fertilizability and developed to term with the same litter size as in the control rats. Our findings suggest that follicular angiogenesis may be a determinant of follicular development during the periovulatory phase, and that VEGF isoforms may play different important roles in regulating follicular angiogenesis.