Changes of messenger RNA expression of angiogenic factors and related receptors during follicular development in gilts

The vascular endothelial growth factor (VEGF) system as a key regulator of ovarian follicle angiogenesis and growth

The vascular endothelial growth factor-A (VEGFA) system is a complex set of proteins, with multiple isoforms and receptors, including both angiogenic (VEGFxxx, VEGFR2) and antiangiogenic members (VEGFxxxb, VEGFR1 and soluble forms of VEGFR). The members of the VEGF system affect the proliferation, survival, and migration of endothelial and nonendothelial cells and are involved in the regulation of follicular angiogenesis and development. The production of VEGF by secondary follicles stimulates preantral follicular development by directly affecting follicular cells and promoting the acquisition of the follicular vasculature and downstream antrum formation. Additionally, the pattern of expression of the components of the VEGF system may provide a proangiogenic milieu capable of triggering angiogenesis and stimulating follicular cells to promote antral follicle growth, whereas, during atresia, this milieu becomes antiangiogenic and blocks follicular development.

Expression and distribution patterns of VEGF, TGF‐β 1 and HIF‐1α in the ovarian follicles of Tibetan sheep

Background

Hypoxia‐inducible factor‐1α (HIF‐1α), vascular endothelial growth factor (VEGF) and transforming growth factor β₁ (TGF‐β₁) are multifunctional growth factors that play an important role in follicular growth and development. However, its biological function in the follicular development of Tibetan sheep at different stages has not been described.

Objectives

The purpose of this study was to investigate the effect of VEGF, TGF‐β₁ and HIF‐1α expression and distribution on the development of follicles of different sizes.

Methods

Immunohistochemistry (IHC), western blot (WB) and quantification real‐time polymerase chain reaction (qRT‐PCR) were used to detect the localisation and quantitative expression of VEGF, TGF‐β₁ and HIF‐1α proteins and mRNA in small‐ (< 3 mm), medium‐ (3 mm < diameter < 5 mm)‐, and large‐ (> 5 mm) sized follicles.

Results

The results showed that the proteins VEGF, TGF‐β₁ and HIF‐1α, as well as their mRNA, were expressed in follicles. However, the expression in medium‐sized follicles was significantly higher than that in large‐ and small‐sized follicles (p <0.05). IHC also showed that the proteins VEGF, TGF‐β₁, and HIF‐1α were distributed in granulosa cells (GCs) in small‐, medium‐, and large‐sized follicles.

Conclusions

This study indicates that VEGF, TGF‐β₁ and HIF‐1α, which operate in an autocrine or paracrine manner with the GCs, influence the follicular progressive growth, suggesting that these growth factors are closely associated with the follicular growth and development in ovarian.

The distribution and expression of vascular endothelial growth factor A (VEGFA) during follicular development and atresia in the pig

The involvement of vascular endothelial growth factor A (VEGFA) in ovarian physiological processes has been widely reported, but the location and role of VEGFA during follicular atresia remain unknown. This study investigated the distribution and expression of VEGFA during porcine follicular development and atresia. Pig ovaries were obtained, individual medium-sized (3-5mm in diameter) antral follicles were separated and classified into healthy, early atretic or progressively atretic groups. Immunobiology and quantitative techniques were used to investigate the varied follicular distribution of VEGFA at both the morphological and molecular level. The results indicated that VEGFA protein expression peaked in tertiary follicles, mostly distributed in the thecal and inner granulosa layers, during follicular development while VEGFA mRNA was mainly expressed in the inner granulosa layers. Additionally, healthy antral follicles showed a significantly higher expression of VEGFA than atretic follicles in both theca and granulosa cells. Knockdown of VEGFA using siRNA revealed an antiapoptosis effect of VEGFA in cultured pig granulosa cells. Our results increase the knowledge of VEGFA functions in follicles.

miR-361-5p Mediates SMAD4 to Promote Porcine Granulosa Cell Apoptosis through VEGFA

Follicular atresia is an inevitable degenerative process that occurs in mammalian ovarian follicles. The molecular events involved in atresia, particularly granulosa cell apoptosis, have long attracted researchers’ attention. Vascular endothelial growth factor A (VEGFA) is downregulated during follicular atresia in porcine ovaries and serves as an inhibitor of apoptosis in granulosa cells. In addition, transforming growth factor (TGF)-βsignaling has been considered a central trigger in granulosa cell apoptosis. However, the link between TGF-β signaling and VEGFA is unknown. We proved that miR-361-5p is significantly upregulated during the atresia process and that it promotes GC apoptosis by directly targeting the VEGFA 3′UTR. In addition, we revealed that the miR-361-5p coding gene MIR361 was significantly downregulated by SMAD4, the central intracellular mediator of TGF-β signaling, that bound to the MIR361 promoter. In conclusion, our findings expanded what is known about VEGFA posttranscriptional regulation and revealed a complete SMAD4/miR-361-5p/VEGFA regulatory network in ovarian granulosa cell apoptosis. These data provide useful references for follicular atresia and ovarian physiological function studies.

Deficiency in proliferative, angiogenic, and LH receptors in the follicle wall: implications of season toward the anovulatory condition

This study aimed to gain insight on the effect of different seasons of the year on the expression pattern of growth factor and hormone receptors involved in follicle development. A novel follicle wall biopsy technique was used to collect in vivo follicle wall layers (ie, granulosa, theca interna, and theca externa) and follicular fluid samples from growing dominant follicles, simultaneously and repeatedly, using the same mares during the spring anovulatory (SAN), spring ovulatory (SOV), summer (SU), and fall ovulatory (FOV) seasons. The immunofluorescent expression patterns of epidermal growth factor receptor (EGFR), Ki-67, vascular endothelial growth factor receptor (VEGFR), and LH receptor (LHR) were evaluated in each follicle wall layer, in addition to intrafollicular estradiol and nitric oxide (NO). Proliferative proteins (EGFR and Ki-67) were highly (P < 0.05-P < 0.001) expressed during the SOV season compared with the SAN and FOV seasons. Lower (P < 0.05-P < 0.001) expression of both proteins was observed during SU compared with the SOV season. The expression of VEGFR was greater (P < 0.05-P < 0.01) in the theca interna of dominant follicles during the SOV season compared with the SAN and SU seasons. Similarly, in the overall quantification, the VEGFR expression was greater (P < 0.001) during the SOV season compared with the SU and FOV seasons. A higher (P < 0.05) LHR expression was detected in the theca interna during the SOV season than the SAN season. Furthermore, a higher (P < 0.05-P < 0.001) expression of LHR was observed in the granulosa, theca interna, and in the overall quantification during the SOV season compared with the SU and FOV seasons. Intrafollicular NO concentration did not differ (P > 0.05) among different seasons of the year. The intrafollicular estradiol concentration was higher (P < 0.05) during the SU compared with the SAN season and higher (P < 0.05) during the FOV season compared with the SAN and SOV seasons. In conclusion, the synergistic effect of lower expression of proliferative protein, angiogenic, and LH receptors in at least some of the layers of the follicle wall seems to trigger dominant follicles toward the anovulation process during the spring and fall transitional seasons.

Transition to the ovulatory season in mares: An investigation of antral follicle receptor gene expression in vivo

The inability to obtain in vivo samples of antral follicle wall layers without removing the ovaries or sacrificing the animals has limited more in-depth studies on folliculogenesis. In this study, a novel ultrasound-guided follicle wall biopsy (FWB) technique was used to obtain in vivo follicle wall layers and follicular fluid samples of growing antral follicles. The expression of proliferative, hormonal, angiogenic, and pro-/antiapoptotic receptors and proteins in the follicular wall among three follicle classes were compared during the spring transitional anovulatory (SAN) and spring ovulatory (SOV) seasons in mares. The main findings observed in the granulosa, theca interna, and/or all follicle layers during the SOV season compared with the SAN season were (a) small-sized follicles (10-14 mm) had greater epidermal growth factor receptor (EGFR) and Bcl-2 expression; (b) medium-sized follicles during the expected deviation/selection diameter (20-24 mm) had greater expression of EGFR, Ki-67, luteinizing hormone receptor (LHR), and Bcl-2; and (c) dominant follicles (30-34 mm) had greater EGFR, Ki-67, vascular endothelial growth factor, LHR, and Bcl-2 expression. Estradiol related receptor alpha expression and intrafollicular estradiol concentration increased, along with an increase in follicle diameter in both seasons. In this study, the application of the FWB technique allowed a direct comparison of different receptors' expression among follicles in different stages of development and between two seasons using the same individuals, without jeopardizing their ovarian function. The successful utilization of the FWB technique and the mare as an experimental animal offer a great combination for future folliculogenesis studies on mechanisms of follicle selection, development, and ovulation in different species, including women.

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.

Human amnion-derived mesenchymal stem cell (hAD-MSC) transplantation improves ovarian function in rats with premature ovarian insufficiency (POI) at least partly through a paracrine mechanism

Background

Chemotherapy can induce premature ovarian insufficiency (POI) and reduce fertility in young female patients. Currently, there is no effective therapy for POI. Human amnion-derived mesenchymal stem cells (hAD-MSCs) may be a promising seed cell for regenerative medicine. This study investigated the effects and mechanisms of hAD-MSC transplantation on chemotherapy-induced POI in rats.

Methods

Chemotherapy-induced POI rat models were established by intraperitoneal injection of cyclophosphamide. Seventy-two female SD rats were randomly divided into control, POI, and hAD-MSC-treated groups. hAD-MSCs were labeled with PKH26 and injected into the tail veins of POI rats. To examine the underlying mechanisms, the differentiation of transplanted hAD-MSCs in the POI ovaries was analyzed by immunofluorescent staining. The in vitro expression of growth factors secreted by hAD-MSCs in hAD-MSC-conditioned media (hAD-MSC-CM) was analyzed by ELISA. Sixty female SD rats were divided into control, POI, and hAD-MSC-CM-treated groups, and hAD-MSC-CM was injected into the bilateral ovaries of POI rats. After hAD-MSC transplantation or hAD-MSC-CM injection, serum sex hormone levels, estrous cycles, ovarian pathological changes, follicle counts, granulosa cell (GC) apoptosis, and Bcl-2, Bax, and VEGF expression in ovaries were examined.

Results

PKH26-labeled hAD-MSCs mainly homed to ovaries after transplantation.

hAD-MSC transplantation reduced ovarian injury and improved ovarian function in rats with POI. Transplanted hAD-MSCs were only located in the interstitium of ovaries, rather than in follicles, and did not express the typical markers of oocytes and GCs, which are ZP3 and FSHR, respectively. hAD-MSCs secreted FGF2, IGF-1, HGF, and VEGF, and those growth factors were detected in the hAD-MSC-CM. hAD-MSC-CM injection improved the local microenvironment of POI ovaries, leading to a decrease in Bax expression and an increase in Bcl-2 and endogenous VEGF expression in ovarian cells, which inhibited chemotherapy-induced GC apoptosis, promoted angiogenesis and regulated follicular development, thus partly reducing ovarian injury and improving ovarian function in rats with POI.

Conclusions

hAD-MSC transplantation can improve ovarian function in rats with chemotherapy-induced POI at least partly through a paracrine mechanism. The presence of a paracrine mechanism accounting for hAD-MSC-mediated recovery of ovarian function might be attributed to the growth factors secreted by hAD-MSCs.

Epigenetic changes of hepatic glucocorticoid receptor in sheep male offspring undernourished in utero

The aim of this study was to characterise the effects of maternal undernutrition during gestation on hepatic gluconeogenic enzyme gene expression and to determine whether such effects are mediated through epigenetic changes in the glucocorticoid receptor (GR). Pregnant ewes were fed a 50% nutrient-restricted diet from Day 0 to 30 (R1) or from Day 31 to 100 of gestation (R2) or a 100% diet throughout gestation (Control). After parturition lambs were fed to appetite. At 10 months of age offspring were euthanised and livers were removed. Maternal undernutrition did not affect offspring bodyweight at birth or at 10 months of age. However, liver weight of males of the R2 group was lower (P<0.05) in relation to other groups. A significant (P<0.05) hypomethylation of the hepatic GR promoter was revealed in males of the R2 group and a tendency towards the same in the R1 group, along with increased (P<0.001) GR gene expression in both restricted groups. A significant increase (P<0.05) in hepatic phosphoenolpyruvate carboxykinase (PEPCK) gene expression was found in male lambs of both undernourished groups, accompanied by increased (P<0.01) protein levels, while no differences were detected for glucose-6-phosphatase (G6Pase) mRNA abundance and protein levels. In female lambs, no differences between groups were observed for any parameter studied. These data represent potential mechanisms by which insults in early life may lead to persistent physiological changes in the offspring.

Initiation of follicular atresia: gene networks during early atresia in pig ovaries

In mammals, more than 99% of ovarian follicles undergo a degenerative process known as atresia. The molecular events involved in atresia initiation remain incompletely understood. The objective of this study was to analyze differential gene expression profiles of medium antral ovarian follicles during early atresia in pig. The transcriptome evaluation was performed on cDNA microarrays using healthy and early atretic follicle samples and was validated by quantitative PCR. Annotation analysis applying current database (Sus scrofa 11.1) revealed 450 significantly differential expressed genes between healthy and early atretic follicles. Among them, 142 were significantly upregulated in early atretic with respect to healthy group and 308 were downregulated. Similar expression trends were observed between microarray data and quantitative RT-PCR confirmation, which indicated the reliability of the microarray analysis. Further analysis of the differential expressed genes revealed the most significantly affected biological functions during early atresia including blood vessel development, regulation of DNA-templated transcription in response to stress and negative regulation of cell adhesion. The pathway and interaction analysis suggested that atresia initiation associates with (1) a crosstalk of cell apoptosis, autophagy and ferroptosis rather than change of typical apoptosis markers, (2) dramatic shift of steroidogenic enzymes, (3) deficient glutathione metabolism and (4) vascular degeneration. The novel gene candidates and pathways identified in the current study will lead to a comprehensive view of the molecular regulation of ovarian follicular atresia and a new understanding of atresia initiation.

Stem cell therapy in Asherman syndrome and thin endometrium: Stem cell- based therapy

The endometrium is one of the essential components of the uterus. The endometrium of human is a complex and dynamic tissue, which undergoes periods of growth and turn over during any menstrual cycle. Stem cells are initially undifferentiated cells that display a wide range of differentiation potential with no distinct morphological features. Stem cell therapy method recently has become a novel procedure for treatment of tissue injury and fibrosis in response to damage. Currently, there is massive interest in stem cells as a novel treatment method for regenerative medicine and more specifically for the regeneration of human endometrium disorder like Asherman syndrome (AS) and thin endometrium. AS also known as intrauterine adhesion (IUA) is a uterine disorder with the aberrant creation of adhesions within the uterus and/or cervix. Patients with IUA are significantly associated with menstrual abnormalities and suffer from pelvic pain. In addition, IUA might prevent implantation of the blastocyst, impair the blood supply to the uterus and early fetus, and finally result in the recurrent miscarriage or infertility in the AS patients. It has been evidenced that the transplantation of different stem cells with a diverse source in the endometrial zone had effects on endometrium such as declined the fibrotic area, an elevated number of glands, stimulated angiogenesis, the enhanced thickness of the endometrium, better formed tissue construction, protected gestation, and improved pregnancy rate. This study presents a summary of the investigations that indicate the key role of stem cell therapy in regeneration and renovation of defective parts.

Regeneration of the Fallopian Tube Mucosa Using Bone Marrow Mesenchymal Stem Cell Transplantation After Induced Chemical Injury in a Rat Model

In this study, we describe a novel insight about the use of bone marrow-derived mesenchymal stem cells (BM-MSCs) for fallopian tube (FT) regeneration. Seventy rats' tubes were involved in this study and divided into 4 groups: control (15), ethanol injured (20), mesenchymal stem cell (MSC)-recipient without injury (15), and MSC recipient after injury (20). The BM-MSCs were isolated from male rats, and their incorporation into the tissues was confirmed by the detection of Sry gene in MSC-recipient rats using RT-PCR. Histological and immunohistological sections of the 4 groups were comparably evaluated. We found that direct injection of ethanol into FT caused structural impairment, which was restored largely after receiving MSCs. We have revealed for the first time that prominin 1 (Prom1, stem cell marker) was expressed in the fimbriated distal tubal end. The MSC transplantation caused (1) significant increase in the tissue level and immunoexpresstion of Prom1 ( P < .001 and P = .017, respectively) and vascular endothelial growth factor (VEGF; vasculogenic marker; P < .001 and P = .004, respectively), (2) significant increase in the immunoexpresstion of proliferating cell nuclear antigen (PCNA; proliferation marker; P < .001), and (3) significant decrease in the immunoexpresstion of caspase 3 (CASP-3; apoptotic marker; P < .001) compared to the injured tissues. In conclusion, MSCs could exhibit its restorative effect on FT through their ability to (1) activate the resident stem cells in the distal tubal end, (2) mediate the expression of VEGF and PCNA, and (3) influence tissue apoptosis. This study laid the foundation for assessing the contribution of stem cells in the distal tubal end in direct repair of the tube when required to assist reproduction.

Effects of leptin administration on development, vascularization and function of Corpus luteum in alpacas submitted to pre-ovulatory fasting

The objective of this study was to determine the effect of leptin administration on the development, vascularization and function of Corpus luteum (CL) in alpacas submitted to pre-ovulatory fasting. Fourteen alpacas were kept in fasting conditions for 72h and received five doses of o-leptin (2μg/kg e.v.; Leptin group) or saline (Control group) every 12h. Ovulation was induced with a GnRH dose (Day 0). The ovaries were examined every other day by trans-rectal ultrasonography (7.5MHz; mode B and power Doppler) from Day 0 to 13 to determine the pre-ovulatory follicle diameter and ovulation, and then to monitor CL diameter and vascularization until the regression phase. Serial blood samples were taken after GnRH treatment to determine plasma LH concentration; and every other day from Days 1 to 13 to determine plasma progesterone and leptin concentrations. The pre-ovulatory follicle and CL diameter, LH, progesterone and leptin plasma concentrations were not affected by treatment (P>0.05). The vascularization area of the CL was, nevertheless, affected by the treatment (P<0.01) with significant differences between groups at Days 3, 7 and 9 (P<0.05). The Leptin group had a larger maximum vascularization area (0.67±0.1 compared with 0.35±0.1cm²; P<0.05). In addition, there was a positive correlation between CL vascularization, CL diameter and plasma progesterone. The exogenous administration of leptin during pre-ovulatory fasting increased the vascularization of the CL in alpacas in vivo.

Human umbilical cord mesenchymal stem cells improve the reserve function of perimenopausal ovary via a paracrine mechanism

Background

Human umbilical cord mesenchymal stem cells (hUCMSCs) are a type of pluripotent stem cell which are isolated from the umbilical cord of newborns. hUCMSCs have great therapeutic potential. We designed this experimental study in order to investigate whether the transplantation of hUCMSCs can improve the ovarian reserve function of perimenopausal rats and delay ovarian senescence.

Method

We selected naturally aging rats confirmed by vaginal smears as models of perimenopausal rats, divided into the control group and the treatment group, and selected young fertile female rats as normal controls. hUCMSCs were transplanted into rats of the treatment group through tail veins. Enzyme-linked immunosorbent assay (ELISA) detected serum levels of sex hormones, H&E staining showed ovarian tissue structure and allowed follicle counting, immunohistochemistry and western blot analysis revealed ovarian expression of hepatocyte growth factor (HGF), vascular endothelial cell growth factor (VEGF), and insulin-like growth factor-1 (IGF-1), polymerase chain reaction (PCR) and western blot analysis revealed hUCMSCs expression of HGF, VEGF, and IGF-1.

Results

At time points of 14, 21, and 28 days after hUCMSCs transplantation, estradiol (E₂) and anti-Müllerian hormone (AMH) increased while follicle-stimulating hormone (FSH) decreased; ovarian structure improved and follicle number increased; ovarian expression of HGF, VEGF, and IGF-1 protein elevated significantly. Meanwhile, PCR and western blot analysis indicated hUCMSCs have the capacity of secreting HGF, VEGF, and IGF-1 cytokines.

Conclusions

Our results suggest that hUCMSCs can promote ovarian expression of HGF, VEGF, and IGF-1 through secreting those cytokines, resulting in improving ovarian reserve function and withstanding ovarian senescence.

Ovarian Folliculogenesis

The ovary, the female gonad, serves as the source for the germ cells as well as the major supplier of steroid sex hormones. During embryonic development, the primordial germ cells (PGCs) are specified, migrate to the site of the future gonad, and proliferate, forming structures of germ cells nests, which will eventually break down to generate the primordial follicles (PMFs). Each PMF contains an oocyte arrested at the first prophase of meiosis, surrounded by a flattened layer of somatic pre-granulosa cells. Most of the PMFs are kept dormant and only a selected population is activated to join the growing pool of follicles in a process regulated by both intra- and extra-oocyte factors. The PMFs will further develop into secondary pre-antral follicles, a stage which depends on bidirectional communication between the oocyte and the surrounding somatic cells. Many of the signaling molecules involved in this dialog belong to the transforming growth factor β (TGF-β) superfamily. As the follicle continues to develop, a cavity called antrum is formed. The resulting antral follicles relay on the pituitary gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) for their development. Most of the follicles undergo atretic degeneration and only a subset of the antral follicles, known as the dominant follicles, will reach the preovulatory stage at each reproductive cycle, respond to LH, and subsequently ovulate, releasing a fertilizable oocyte. The remaining somatic cells in the raptured follicle will undergo terminal differentiation and form the corpus luteum, which secretes progesterone necessary to maintain pregnancy.

Expression and localization of members of the thrombospondin family during final follicle maturation and corpus luteum formation and function in the bovine ovary

The aim of this study was to characterize the expression patterns and localization of the thrombospondin family members (THBS1, THBS2) and their receptors (CD36 and CD47) in bovine ovaries. First, the antral follicles were classified into 5 groups based on the follicle size and estradiol-17beta (E2) concentration in the follicular fluid (< 0.5, 0.5-5, 5-40, 40-180 and >180 E2 ng/ml). Second, the corpus luteum (CL) was assigned to the following stages: days 1-2, 3-4, 5-7, 8-12, 13-16 and >18 of the estrous cycle and of pregnancy (month 1-2, 3-4, 6-7 and > 8). Third, the corpora lutea were collected by transvaginal ovariectomy before and 0.5, 2, 4, 12, 24, 48 and 64 h after inducing luteolysis by injecting a prostaglandin F2alpha analog. The mRNA expression of examined factors was measured by RT-qPCR, steroid hormone concentration by EIA, and localization by immunohistochemistry. The mRNA expression of THBS1, THBS2, CD36, and CD47 in the granulosa cells and theca interna was high in the small follicles and reduced in the preovulatory follicles. The mRNA expression of THBS1, THBS2, and CD47 in the CL during the estrous cycle was high, but decreased significantly during pregnancy. After induced luteolysis, thrombospondins increased significantly to reach the maximum level at 12 h for THBS1, 24 h for THBS2, and 48 h for CD36. The temporal expression and localization pattern of the thrombospondins and their specific receptors in the antral follicles and corpora lutea during the different physiological phases of the estrous cycle and induced luteolysis appear to be compatible with their inhibitory role in the control of ovarian angiogenesis.

Vascular endothelial growth factor and angiopoietins during hen ovarian follicle development

Growth and maturation of ovarian follicles in the hen (Gallus gallus) requires a network of blood vessels that increases in complexity during development. The present studies investigate expression of vascular endothelial growth factor A (VEGF), angiopoietin1 (ANGPT1) and ANGPT2 mRNAs together with their associated receptors (VEGFR and TIE2, respectively) during maturation. Elevated expression of VEGF and its receptors is associated with healthy, compared to atretic, follicles. Levels of VEGF significantly increase, while antagonistic ANGPT2 decrease, in granulosa cells (GC) at follicle selection. By comparison, levels of VEGF, VEGFR1, VEGFR2, ANGPT1, ANGPT2 and TIE2 within the theca layer do not change (P>0.05) relative to developmental stages surrounding follicle selection (6-8mm versus 9-12mm follicles). Prior to selection, treatment with transforming growth factor β1 (TGFβ1) significantly increases levels of VEGF in undifferentiated GC from prehierarchal (6-8mm) follicles and actively differentiating GC from selected (9-12 and F4) follicles. Moreover, subsequent to selection follicle stimulating hormone (FSH) increases VEGF expression in GC from 9 to 12mm follicles, and eventually luteinizing hormone (LH) promotes VEGF expression in GC from more mature preovulatory follicles. It is concluded that prior to follicle selection VEGF expression is regulated by autocrine and paracrine actions of TGFβ1 (but not FSH), and that a comparatively limited extent of vasculature is sufficient to maintain prehierarchal follicles in a viable and undifferentiated state. At follicle selection, FSH- and subsequently LH-induced VEGF production within the GC layer enhance angiogenesis within the theca layer, which facilitates the rapid growth of preovulatory follicles via enhanced incorporation of yellow yolk.

Molecular and cellular mechanisms for the regulation of ovarian follicular function in cows

Ovary is an important organ that houses the oocytes (reproductive cell). Oocyte growth depends on the function of follicular cells such as the granulosa and theca cells. Two-cell two gonadotropin systems are associated with oocyte growth and follicular cell functions. In addition to these systems, it is also known that several growth factors regulate oocyte growth and follicular cell functions. Vascular endothelial growth factor (VEGF) is involved in thecal vasculature during follicular development and the suppression of granulosa cell apoptosis. Metabolic factors such as insulin, growth hormone (GH) and insulin-like growth factor 1 (IGF-1) also play critical roles in the process of follicular development and growth. These factors are associated not only with follicular development, but also with follicular cell function. Steroid hormones (estrogens, androgens, and progestins) that are secreted from follicular cells influence the function of the female genital tract and its affect the susceptibility to bacterial infection. This review covers our current understanding of the mechanisms by which gonadotrophins and/or steroid hormones regulate the growth factors in the follicular cells of the bovine ovary. In addition, this review describes the effect of endotoxin on the function of follicular cells.

Intraovarian control of selective follicular growth and induction of oocyte maturation in mammals

In newborn mammals, most of the germ cell population rests in a pool of quiescent small follicles in the ovaries. Regularly throughout adulthood, a small percentage of these oocytes and follicles grows to a certain stage of development and then either degenerates or matures and ovulates. This entire process is under both exogenous and endogenous control. Recent work, including my laboratory's, has clarified that cytokines and glycosaminoglycans are involved as exogenous and endogenous factors in ovarian follicular development, atresia, and maturation in mammals. The present article describes our contribution regarding the cytokines and ovarian glycosaminoglycans that act as intraovarian regulators of follicular development and oogenesis, including oocyte maturation, in mammals.

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.

Luteinizing hormone, insulin like growth factor-1, and epidermal growth factor stimulate vascular endothelial growth factor production in cultured bubaline granulosa cells

The objective of this study was to characterize in vitro expression and secretion of vascular endothelial growth factor (VEGF) in bubaline granulosa cells (GC), grown in serum containing media supplemented with luteinizing hormone (LH), insulin like growth factor-1 (IGF-1), and epidermal growth factor (EGF) at three different doses and time durations. GCs were collected from ovarian follicles of varying diameters [Gp-I (small), 4-6 mm; Gp-II (medium), 7-9 mm; Gp-III (large), 10-13 mm; Gp-IV (pre-ovulatory), >13 mm]. In general, each of the three treatments resulted in a dose as well as time dependent increase in the mRNA expression and secretion of VEGF in the cultured GCs of Gp-IV follicles. These results were well supported by our observations on immunocytochemistry in Gp IV granulosa cell culture (GCC). We also looked into the expression dynamics of an anti-apoptotic factor--proliferating cellular antigen (PCNA) and a pro-apoptotic factor--Bcl-2-associated X protein (BAX) in GCs of Gp IV follicles on treatments with LH, IGF-1, and EGF to evaluate their cytoprotective/anti-apoptotic property. Relative expressions of PCNA and BAX showed a mutually opposite trend with the PCNA expression increasing and BAX expression decreasing with increase in dose and time to reach the zenith (P<0.05) and nadir (P<0.05) at the highest dose(s) at the maximum time duration (72 h) for PCNA and BAX respectively on treatment with all the three factors. Thus, it can be concluded that LH, IGF-1, and EGF treatments have a cytoprotective/anti-apoptotic effect and stimulate VEGF production in granulosa cells of bubaline pre-ovulatory follicles.

Mechanistic action of mesenchymal stem cell injection in the treatment of chemically induced ovarian failure in rabbits

BACKGROUND

No curative treatment is known for primary ovarian failure; however, mesenchymal stem cells (MSCs), through self-renewal and regeneration, push the trial to evaluate their role in the treatment of ovarian failure. The aim of this study was to explore the impact of MSCs on cyclophosphamide (CTX)-induced ovarian failure in rabbits and to clarify the mechanism(s) by which MSCs exert their action.

METHODS

Thirty-five adult female rabbits were injected with CTX to induce ovarian failure. Five rabbits were euthanized after the last injection of CTX for histological examination. The others (30 rabbits) were further subdivided into two groups: group 1 (ovarian failure group, 15 rabbits) received no treatment; group 2 (ovarian failure and MSC recipient group, 15 rabbits) received MSCs isolated from extracted bone marrow of male rabbits.

RESULTS

A decrease of follicle-stimulating hormone and an increase of estrogen and vascular endothelial growth factor (VEGF) levels in the MSC recipient group versus the ovarian failure group were found. Weak caspase-3 expression and +ve proliferating cell nuclear antigen staining after MSC injection were detected. Cytological and histological examinations showed increased follicle numbers with apparent normal structure of ovarian follicles in the MSC recipient group. Moreover, Y chromosome-containing cells from male donors were present within the ovarian tissues in group 2.

CONCLUSIONS

The current study suggests that intravenous injection of MSCs into rabbits with chemotherapy-induced ovarian damage improved ovarian function. MSCs accomplish this function by direct differentiation into specific cellular phenotypes and by secretion of VEGF, which influence the regeneration of the ovary.

The fibroblast growth factor family: involvement in the regulation of folliculogenesis

Several growth factors have been identified as local regulators of follicle development and ovulation. Fibroblast growth factor (FGF) family members are potent mitogens and are involved in cell differentiation, cell migration and angiogenesis in many tissues and organs. In addition to FGF-2, which is the most-studied FGF, other important members are FGF-1, -5, -7, -8, -9 and -10. A number of studies have indicated that FGFs play important roles in regulating the initiation of primordial follicle growth, oocyte and follicle survival, granulosa and theca cell proliferation and differentiation, corpus luteum formation, steroidogenesis and angiogenesis. The purpose of this review is to highlight the importance of the FGFs on mammalian female reproduction, providing a better understanding of the roles of this family in ovarian physiology and female fertility.

The levels of hepatocyte growth factor in serum and follicular fluid and the expression of c-Met in granulosa cells in patients with polycystic ovary syndrome

OBJECTIVE

To evaluate the levels of hepatocyte growth factor (HGF) in follicular fluid (FF) and the expression of c-Met in granulosa cells (GCs) with respect to the quality of the oocyte and embryo both in patients with polycystic ovary syndrome (PCOS) and in the normal ovary during controlled ovarian hyperstimulation cycles.

DESIGN

Prospective controlled study.

SETTING

University hospital.

PATIENT(S)

Fifty-nine women undergoing IVF treatment (of whom 21 had PCOS and 38 were in the control group).

INTERVENTION(S)

A total of 168 FF samples were collected at the time of oocyte retrieval. The HGF levels were measured by ELISA, and the mRNA expression of c-Met in GCs was detected by real-time polymerase chain reaction.

MAIN OUTCOME MEASURE(S)

The predictive values of HGF levels in serum and FF and the mRNA expression of c-Met in GCs for successful fertilization and oocyte-embryo quality.

RESULT(S)

The levels of HGF in serum and FF and the c-Met expression in GCs were similar between the PCOS and control groups. Granulosa cells of fertilized oocytes (2PN) had a significantly higher level of c-Met expression than that in oocytes that failed to fertilize. The mean HGF level in FF was significantly higher in the grade 1 embryos than in the grades 2-4 embryos.

CONCLUSION(S)

This study suggests that HGF/c-Met signaling may be a crucial determinant of fertilization success.

Seasonal Changes in Testes Vascularisation in the Domestic Cat (Felis domesticus): Evaluation of Microvasculature, Angiogenic Activity, and Endothelial Cell Expression

Some male seasonal breeders undergo testicular growth and regression throughout the year. The objective of this study was to understand the effect of seasonality on: (i) microvasculature of cat testes; (ii) angiogenic activity in testicular tissue in vitro; and (iii) testicular endothelial cells expression throughout the year. Testicular vascular areas increased in March and April, June and July, being the highest in November and December. Testes tissue differently stimulated in vitro angiogenic activity, according to seasonality, being more evident in February, and November and December. Even though CD143 expression was higher in December, smaller peaks were present in April and July. As changes in angiogenesis may play a role on testes vascular growth and regression during the breeding and non-breeding seasons, data suggest that testicular vascularisation in cats is increased in three photoperiod windows of time, November/December, March/April and June/July. This increase in testicular vascularisation might be related to higher seasonal sexual activity in cats, which is in agreement with the fact that most queens give birth at the beginning of the year, between May and July, and in September.

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.

Effect of VEGF (vascular endothelial growth factor) on expression of IL-8 (interleukin-8), IL-1beta and their receptors in bovine theca cells

Cytokines such as VEGF (vascular endothelial growth factor) and ILs (interleukins) are involved in follicular development in the mammalian ovary. The aim of the present study is to examine the transcripts of IL-8 and -1 that differ during follicular development; the relationships between IL-8, IL-1 and VEGF in theca cells is still unknown. We first examined the gene expression of IL-8, IL-1beta and their respective receptors, CXCR1 and IL-1R1 in the theca cells of PRF (preselection) and POF (postselection follicles) from the bovine ovary. Expression of IL-8 and CXCR1 genes were observed in POF, whereas expression of IL-1beta and IL-1R1 genes was observed in both follicles. Secondly, we examined the effects of VEGF on the expression of IL-8, IL-1beta and their receptors genes in cultured bovine theca cells. mRNA expression was quantified by using real-time PCR methods. VEGF stimulates the expression of IL-8 and CXCR1 mRNA. However, VEGF down-regulates the expression of CXCR2 mRNA during the culture period. Expression of IL-1beta and -1R1 mRNA was induced in the cultured theca cells at 48 h. Our data demonstrate that VEGF stimulated the expression of the IL-8 and CXCR1 genes and that CXCR2 expression was suppressed by VEGF, suggesting a follicle stage-dependent expression pattern for the IL-8 system. Furthermore, our results suggest that the transcription system for CXCR genes may have different pathways of VEGF stimulation in bovine theca cells. Taken together, our data suggested that VEGF is associated with the IL system in theca cells in bovine ovary.

The expression of angiogenic growth factors and their receptors in ovarian follicles throughout the estrous cycle in the ewe

Healthy follicles are highly vascularized whereas those undergoing atresia have poor vascularity, suggesting a relationship between follicular vascularization and follicular function. Vascularization is regulated by angiogenic factors, and among them vascular endothelial growth factor (VEGF) and angiopoietin-Tie (Ang-Tie) systems are of central importance. The objectives of this study were to determine if VEGF, VEGF receptor-2 (VEGFR-2), and components of the Ang-Tie system are expressed in ovarian follicles at both the protein and mRNA levels and to explore if their expression is related to the stage of the estrous cycle in the ewe. Ovaries from cyclic ewes were collected during the luteal phase (n=5) or before (n=5), during (n=4), and after (n=4) the preovulatory luteinizing hormone (LH) surge. After fixation, ovaries were wax-embedded, serially sectioned, and analyzed for both protein and mRNA expression of VEGF, VEGFR-2, angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), Tie-1 (mRNA only), and Tie-2. mRNA was studied by in situ hybridization using digoxigenin-11-UTP-labeled ovine riboprobes. A similar pattern of expression was observed for mRNA and protein for all of the factors. Both mRNA and protein expression of VEGF, VEGFR-2, Ang-1, Ang-2, Tie-1 (mRNA only), and Tie-2 in the granulosa and theca cells of follicles >or=2mm in diameter was significantly different among the stages of the estrous cycle, with the highest expression detected at the post-LH surge stage. Theca cells expressed significantly greater levels of the six angiogenic factors compared with granulosa cells at all stages of the estrous cycle. Expression levels in granulosa and theca cells were comparable between small (2.0 to 2.5mm) and medium (2.5 to 4.0mm) follicles, but large follicles (>4.0mm) expressed higher mRNA and protein levels (all P<0.05) for all factors at all stages of the estrous cycle. These data show (i) that VEGF, VEGFR-2, and the Ang-Tie system are present in both granulosa and theca cells of the ovarian follicle, (ii) that thecal cells consistently express greater levels of all of these factors compared with granulosa cells, and (iii) that their levels of expression are related to the stage of the estrous cycle and to follicle size.

Angiogenesis and vascular function in the ovary

Ovarian function is dependent on the establishment and continual remodelling of a complex vascular system. This enables the follicle and/or corpus luteum (CL) to receive the required supply of nutrients, oxygen and hormonal support as well as facilitating the release of steroids. Moreover, the inhibition of angiogenesis results in the attenuation of follicular growth, disruption of ovulation and drastic effects on the development and function of the CL. It appears that the production and action of vascular endothelial growth factor A (VEGFA) is necessary at all these stages of development. However, the expression of fibroblast growth factor 2 (FGF2) in the cow is more dynamic than that of VEGFA with a dramatic upregulation during the follicular–luteal transition. This upregulation is then likely to initiate intense angiogenesis in the presence of high VEGFA levels. Recently, we have developed a novel ovarian physiological angiogenesis culture system in which highly organised and intricate endothelial cell networks are formed. This system will enable us to elucidate the complex inter-play between FGF2 and VEGFA as well as other angiogenic factors in the regulation of luteal angiogenesis. Furthermore, recent evidence indicates that pericytes might play an active role in driving angiogenesis and highlights the importance of pericyte–endothelial interactions in this process. Finally, the targeted promotion of angiogenesis may lead to the development of novel strategies to alleviate luteal inadequacy and infertility.

Blood vessel remodeling in pig ovarian follicles during the periovulatory period: an immunohistochemistry and SEM-corrosion casting study

BACKGROUND

The present research aims to describe the process of vascular readjustment occurring in pig ovary during the periovulatory phase (from LH surge to ovulation) that drives the transformation of the follicle, a limited blood supplied structure, into the corpus luteum, a highly vascularised endocrine gland required to maintain high levels of progesterone in pregnancy. The swine model was chosen because it is characterized by a long periovulatory window (about 40-44 hrs-similar to human) that permits to recover follicles at a precise endocrinological timing.

METHODS

By validated hormonal protocol (eCG+hCG), able to mimic the physiologic gonadotropin stimulation, preovulatory follicles (PreOFs, 60 h-eCG), follicles in the middle (early periovulatory follicles, EPerOFs, 18 h-hCG) or late (LPerOFs, 36 h-hCG) periovulatory phase were isolated from prepubertal gilts. To understand the angiogenic process, morphological/morphometrical analyses were performed by combining immunohistochemistry (IHC) and SEM of vascular corrosion casts (VCC) techniques.

RESULTS

PreOFs showed a vascular plexus with proliferating endothelial cells (EPI). This plexus was characterized by a dense inner capillary network, with angiogenic figures, connected to the outer network by anastomotic vessels (arterioles and venules of the middle network). EPerOFs decreased their EPI, blood vessel extension in the outer network, and evidenced a reduced compactness of blood vessels. In LPerOFs, a rapid neovascularization was associated to an intensive tissue remodeling: the follicle acquired an undulated aspect presenting arterioles/venules near the basal membrane, increased vascular extension by EPI, sprouting and non-sprouting angiogenesis.The analysis of vascular geometric relations and branching angles evidenced similar values at all stages.

CONCLUSION

These data allow us to hypothesize that EPerOFs are in a quiescent status. LPerOFs represent the "metamorphic" follicles that rapidly turn-on angiogenesis to sustain a successful corpus luteum formation. Particularly, it is interesting to underlie that the non-sprouting angiogenesis, typical of structures in rapid neovascularization, occurred only in the LPerOFs. Moreover, vascular geometric relations showed as blood vessel remodeling occurs with the "maximum output and the minimum energetic expense".This knowledge will allow to better understand the mechanisms regulating the reproductive success and to clarify the complex physiological angiogenic process in adult tissues.

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.

Microarray analysis of insulin-like growth factor-I-induced changes in messenger ribonucleic acid expression in cultured porcine granulosa cells: possible role of insulin-like growth factor-I in angiogenesis

Insulin-like growth factor-I in conjunction with gonadotropins are important stimulators of mitosis and ovarian steroid production by granulosa and thecal cells, which are required for normal oocyte development and hormonal feedback signaling to the hypothalamus and pituitary. However, a comprehensive evaluation of the changes in gene expression induced by IGF-I has not been conducted. Our objective was to characterize granulosa cell gene expression in response to IGF-I treatment. Porcine granulosa cells were pooled in 4 biological replicates and treated with FSH (baseline) or FSH+IGF-I for 24 h in vitro. The RNA was collected and hybridized to 8 Affymetrix Porcine GeneChips (Affymetrix, Santa Clara, CA) in a paired design. Differentially regulated gene sequence element sets (P < 0.01) were used as queries in the UniGene database searching for annotated genes. Abundance of messenger RNA (mRNA) for genes differentially expressed in the microarray analysis was determined through multiplex assays of one-step real-time reverse transcription-PCR and further analyzed under a statistical model including the fixed effect of treatment. A total of 388 gene sequence element sets were differentially expressed, and 42 matched annotated genes in the UniGene database. Of the 3 upregulated target genes selected for further quantitative reverse transcription-PCR analysis, only FGF receptor 2 III c (FGFR2IIIc) mRNA abundance was significantly increased by IGF-I. Of the 3 downregulated target genes selected for further analysis, only thrombospondin-1 (THBS1) mRNA abundance was significantly decreased by IGF-I. Further study revealed that neither FSH nor estradiol affected the IGF-I-induced suppression of THBS1 mRNA abundance. These results provide the first comprehensive assessment of IGF-I-induced gene expression in granulosa cells and will contribute to a better understanding of the molecular mechanisms of IGF-I regulation of follicular development. Involvement of FGFR2IIIc and THBS1 in mediating IGF-I-induced granulosa cell steroidogenesis and proliferation during follicular development is novel, but their specific roles will require further elucidation.

Expression of vascular endothelial growth factor (VEGF) receptor in goat ovaries and improvement of in vitro caprine preantral follicle survival and growth with VEGF

The aim of the present study was to evaluate the effect of vascular endothelial growth factor (VEGF) on the survival and growth of goat preantral follicles after in vitro culture and to verify the expression of VEGF receptor (VEGFR)-2 in goat ovaries. Ovarian fragments were cultured for 1 or 7 days in minimal essential medium (MEM) with different concentrations of VEGF (1, 10, 50, 100 or 200 ng mL–1). Non-cultured (fresh control) and cultured tissues were processed for histological and ultrastructural studies. The results showed that 200 ng mL–1 VEGF resulted in a similar percentage of normal preantral follicles after 1 and 7 days of culture compared with control. Compared with basic culture medium alone, an increase in follicular and oocyte diameters was observed in the presence of 10 ng mL–1 VEGF after 7 days culture. Ultrastructural analysis confirmed follicular integrity after 7 days culture in the presence of 200 ng mL–1 VEGF. Immunohistochemical studies demonstrated the expression of VEGFR-2 in oocytes and granulosa cells of all follicular stages, except in granulosa cells of primordial follicles. In conclusion, the present study has shown that VEGF maintains follicular ultrastructural integrity and promotes follicular growth. In addition, VEGFR-2 is expressed in oocytes of caprine ovarian follicles at all developmental stages and in granulosa cells of developing follicles.

Vascular supply as a discriminating factor for pig preantral follicle selection

This research analyses how somatic and vascular compartments change during preantral follicle growth. To address this aim, theca-granulosa (somatic) proliferation indexes (PIs), proportion of proliferating endothelial cells (PE), vascular area (VA) and vascular endothelial growth factor A (VEGFA) expression were simultaneously recorded on single healthy preantral follicles, classified into six different stages on the basis of the diameter and the granulosa layers. An autonomous blood vessel network starts to appear only in class 3. Vascular remodelling requires VEGFA expression, and VEGFA mRNA and VA significantly increase between class 3 and classes 4 and 5 and, further, in class 6. In addition, a positive correlation exists between these parameters in classes 3-5. Despite variation in angiogenesis results from classes 3 to 5, the statistical analysis reveals that the vascular parameters are positively and strictly correlated with somatic PIs. Conversely, class 6, also characterized by higher values of somatic PIs, displays a stable proportion of PEs ( congruent with 40%) without showing any correlation among the different parameters analysed. To identify follicular subpopulations within different classes, a multivariate hierarchical cluster analysis was performed. This analysis reveals that the majority of classes 3 and 4 are quiescent follicles or structures that grow very slowly. Class 5 represents a transitory category, where half of the follicles maintain a low activity and the remaining express significantly higher levels of granulosa PI and VA. The follicles with this high activity are probably able to reach class 6 becoming dominant structures where somatic and vascular parameters are constantly on high levels and the VA remains the unique differentiating element.

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.

Effect of direct ovarian injection of vascular endothelial growth factor gene fragments on follicular development in immature female rats

Vascular endothelial growth factor (VEGF) expression in granulosa cells is associated with the thecal vasculature growth during ovarian follicular development. We hypothesized that injection of VEGF gene fragments directly into the rat ovary would induce production of a large number of ovulatory follicles and that these follicles would ovulate. To test this hypothesis, we treated immature female rats with combinations of hormones and VEGF gene fragments. The animals were divided into two groups: one group received solution containing transfection reagents as a control (n= 5), while the other group received direct ovarian injection of VEGF gene fragments at 19 (n= 5), 21 (n= 5), 23 (n= 5), or 25 (n= 5) days after birth followed by i.p. administration of 20 IU equine chorionic gonadotropin (eCG) at the age of 26 days. Forty-eight hours after eCG injection, animals were given 20 IU human chorionic gonadotropin (hCG) i.p. and then the oocytes in both groups were counted. The maximum number of ovulated oocytes was obtained when the VEGF gene fragments were injected into the rat ovary at 21 days after birth. Histological examination revealed that the injection of VEGF gene fragments markedly increased the vascular density around the preovulatory follicles and also the number of these follicles. Our data provide the first reported evidence that most ovulatory follicles generated by injection of VEGF gene fragments are able to ovulate upon hCG treatment. These results demonstrate that injection of VEGF gene fragments directly into the ovary stimulates the development of antral follicles by inducing the formation of thecal vasculature in immature female rats.

Characterization and differential expression of vascular endothelial growth factor isoforms and receptors in swine corpus luteum throughout estrous cycle

Corpus luteum (CL) undergoes growth and regression during each estrous cycle; these processes are accompanied by growth and regression of the luteal vascular bed. Vascular endothelial growth factor (VEGF) is the main regulator of angiogenesis, inducing endothelial cell proliferation, migration, vascular permeability, and vessel lumen formation. VEGF presents several isoforms that are produced by alternative splicing of the same mRNA transcript. We determined by real time RT-PCR the expression patterns of VEGF isoform and receptor mRNAs, as well as the VEGF protein levels in pig CL throughout a whole estrous cycle. Four novel VEGF isoforms (VEGF144, VEGF147, VEGF182, and VEGF164b) were found for the first time in swine and the seven identified isoforms can be grouped in four different patterns of expression. The most expressed splice variants were VEGF120 and VEGF164. All isoforms showed their highest mRNA levels in newly formed CLs (day 1), followed by a decrease during mid-late luteal phase (days 10-17), except for VEGF182, VEGF188 and VEGF144 that showed a differential regulation during late luteal phase (day 14) or at luteolysis (day 17). VEGF protein levels paralleled the most expressed and secreted VEGF120 and VEGF164 isoforms. The VEGF receptors mRNAs showed a different pattern of expression in relation to their ligands, increasing between day 1 and 3 and gradually decreasing during the mid-late luteal phase. The differential regulation of VEGF isoforms may suggest specific physiological roles for some of them, particularly in angioregression occurring during the apoptotic structural luteolysis.

The Plant Alkaloid Sanguinarine is a Potential Inhibitor of Follicular Angiogenesis

Sanguinarine (SA), a phytobiotic from Sanguinaria Canadensis, has been demonstrated to inhibit vessel growth. Current restrictions on the use of antibiotic growth promoters have motivated addition of this alkaloid as a naturally appetizing feed additive for farm animals. However, concern may araise since angiogenesis is a fundamental event in ovarian follicle growth. Therefore, the aim of this study was to evaluate the potential negative role of SA in follicular angiogenesis. For this purpose, we studied the effect of 300 nM SA on the production of vascular endothelial growth factor (VEGF) by swine granulosa cells from follicles >5 mm and on the activation of Akt, the main effector of the VEGF signalling pathway. In addition, the potential interference of SA in vessel development was tested in an in vitro angiogenesis bioassay. SA inhibited both VEGF production and VEGF-induced Akt activation in swine granulosa cells. Moreover, it was able to block vessel growth induced by VEGF. Taken together, our results suggest that SA could be detrimental to follicular angiogenesis, and therefore supplementation of feed with this alkaloid should be carefully considered.

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.

Messenger ribonucleic acid expressions of hepatocyte growth factor, angiopoietins and their receptors during follicular development in gilts

Angiogenic factors are associated with angiogenesis during follicular development in the mammalian ovary. The aim of the present study was to determine the relationships between the vascular network and mRNA expressions of angiopoietins (Ang)-1, Ang-2 and hepatocyte growth factor (HGF), and their receptors in follicles at different developmental stages during follicular development. Ovaries in gilts were collected 72 h after equine chorionic gonadotropin (eCG, 1250 IU) treatment for histological observation of the capillary network. Granulosa cells and thecal tissues in small (<4 mm), medium (4-5 mm) or large (>5 mm) individual follicles were collected for detection of mRNA expression of HGF, Ang-1 and Ang-2 in granulosa cells, and HGF receptor (HGF-R) and Tie-2 in the theca cells by semi-quantitative RT-PCR. The number of capillaries in the thecal cell layer increased significantly in healthy follicles at all developmental stages in the eCG group compared with those in controls. The expression of Ang-1 mRNA declined in granulosa cells of medium and large follicles and the level of Ang-2 mRNA increased in granulosa cells of small follicles after eCG treatment. The ratio of Ang-2/Ang-1 increased in small, medium and large follicles from ovaries after eCG treatment, but Tie-2 mRNA expression in the theca cells did not change. The level of HGF mRNA increased in granulosa cells of small follicles after eCG treatment but HGF-R in theca cells was not increased by eCG. These data suggested that the angiopoietins might be associated with thecal angiogenesis during follicular development in eCG-treated gilts.