Oocyte peptides as paracrine tools for ovarian stimulation and oocyte maturation

Application of platelet-rich plasma in the in vitro production of bovine embryos

The aim of this study was to replace fetal bovine serum (FBS) with platelet-rich plasma (PRP) for in vitro production of bovine embryos. The maturation media (TCM-199 medium) for the cumulus-oocyte complexes (COCs) was supplemented with 5% (G5) and 10% (G10) PRP or 10% FBS (GC). After fertilization, the presumed zygotes were randomly distributed in culture medium supplemented with 5% (G5) and 10% (G10) PRP or 10% FBS (GC) for 7 days. Cumulus cell (CC) expansion was greater (P < 0.05) in the GC (88.9%) group than in G5 (34.1%) or G10 (50.0%). Nevertheless, the expansion of CCs in group G10 was greater than in G5 (P < 0.05). Cleavage was higher in group G5 (86.0%) than in G10 (79.0%) (P < 0.05) and did not differ from group GC (82.0%). The percentage of blastocysts in group G5 (50.0%) was higher than in CG (40.2%) and G10 (34.2%) (P < 0.05). In addition, the number of blastomeres was higher in G5 (159.0 ± 4.18) than in GC (132.4 ± 4.11) and in G10 (127.1 ± 5.88) (P < 0.05). The addition of PRP into the oocytes maturation medium is not beneficial. On the other hand, the PRP addition into the embryo culture medium at 5% concentration is recommended where it increased the quantity and quality of in vitro-produced bovine embryos.

Signalling pathways involved in the synergistic effects of human growth differentiation factor 9 and bone morphogenetic protein 15

Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) act synergistically to regulate granulosa cell proliferation and steroid production in several species. Several non-Sma and mothers against decapentaplegic (SMAD) signalling pathways are involved in the action of murine and ovine GDF9 and BMP15 in combination, with the pathways utilised differing between the two species. The aims of this research were to determine if human GDF9 and BMP15 also act in a synergistic manner to stimulate granulosa cell proliferation and to identify which non-SMAD signalling pathways are activated. Human GDF9 with BMP15 (GDF9+BMP15) stimulated an increase in (3)H-thymidine incorporation (P<0.001), which was greater than the increase with BMP15 alone, while GDF9 alone had no effect. The stimulation of (3)H-thymidine incorporation by GDF9+BMP15 was reduced by the addition of inhibitors to the SMAD2/3, nuclear factor-KB (NF-KB) and c-Jun N-terminal kinase (JNK) signalling pathways. Inhibitors to the SMAD1/5/8, extracellular signal-regulated kinase mitogen-activated protein kinase (ERK-MAPK) or p38-MAPK pathways had no effect. The addition of the BMP receptor 2 (BMPR2) extracellular domain also inhibited stimulation of (3)H-thymidine incorporation by GDF9+BMP15. In conclusion, human GDF9 and BMP15 act synergistically to stimulate granulosa cell proliferation, a response that also involves species-specific non-SMAD signalling pathways.

Temporal expression of GDF-9 and BMP-15 mRNAs in canine ovarian follicles

This study aimed to investigate the expression profiles of growth differentiation factor 9 (GDF-9) and bone morphogenetic protein 15 (BMP-15) mRNA in canine oocytes and follicular cells throughout development at the different phases of the estrus cycle. Ovarian structures (follicles and CL) and plasma progesterone concentration were used to confirm the physiological status of each donor. Denuded oocytes and their follicular cells were recovered from follicles (n = 675) distributed into 4 types (preantral, small antral ∼0.2-0.39 mm, medium antral ∼0.4-5.9 mm, and large antral ∼6-8 mm). Total RNA was extracted and reverse transcribed, and the levels of expression for these 2 genes were determined using a quantitative real-time polymerase chain reaction technique; the data were evaluated by ANOVA. Relative expressions levels of GDF-9 and BMP-15 transcripts were detected in the oocyte and follicular cells in all follicular stages evaluated, showing differential changes (P < 0.05) during development over the estrus cycle. The expression patterns of both transcripts were highly correlated between follicles cells and oocytes (r > 0.8; P < 0.05 for GDF-9 and BMP-15), although GDF-9 was expressed at higher levels (P < 0.05) in the oocyte compared with the follicle cells. All cell types showed more GDF-9 mRNA abundance at early developing stages, mainly in the anestrus phase, and declining levels in the later stages (P < 0.05), whereas BMP-15 mRNA levels increased (P < 0.05) in follicular cells and oocytes from the preantral to the later stages, and remained constant during the final preovulatory stage. In conclusion, these two genes were detected in follicular cells and oocytes and were differentially expressed during the follicular development across the estrus cycle.

Modifications of human growth differentiation factor 9 to improve the generation of embryos from low competence oocytes

Growth differentiation factor 9 (GDF9) is an oocyte-derived growth factor that plays a critical role in ovarian folliculogenesis and oocyte developmental competence and belongs to the TGF-β family of proteins. Recombinant human GDF9 (hGDF9) is secreted in a latent form, which in the case of the fully processed protein, has the proregion noncovalently associated with the mature region. In this study, we investigated a number of amino acid residues in the mature region of hGDF9 that are different from the corresponding residues in the mouse protein, which is not latent. We designed, expressed, and purified 4 forms of chimeric hGDF9 (M1-M4) that we found to be active in a granulosa cell bioassay. Using a porcine in vitro maturation model with inherent low developmental competence (yielding 10%-20% blastocysts), we tested the ability of the chimeric hGDF9 proteins to improve oocyte maturation and developmental competence. Interestingly, one of the chimeric proteins, M3, was able to significantly increase the level of embryo production using such low competence oocytes. Our molecular modeling studies suggest that in the case of hGDF9 the Gly(391)Arg mutation probably increases receptor binding affinity, thereby creating an active protein for granulosa cells in vitro. However, for an improvement in oocyte developmental competence, a second mutation (Ser(412)Pro), which potentially decreases the affinity of the mature region for the proregion, is also required.

The fundamental role of bone morphogenetic protein 15 in ovarian function and its involvement in female fertility disorders

BACKGROUND

A large number of studies have contributed to understanding the general mechanisms driving ovarian folliculogenesis in humans and show a complex endocrine dialog between the central nervous system, the pituitary and the ovary, integrated by various intraovarian paracrine messages. The role of intraovarian paracrine regulation has acquired more relevance in the recent years owing to the discovery of previously unknown factors, such as the oocyte-derived bone morphogenetic protein (BMP)15.

METHODS

A thorough literature search was carried out in order to summarize what has been reported so far on the role of BMP15, and the BMP15 paralog, growth and differentiation factor 9 (GDF9), in ovarian function and female fertility. Research articles published in English until March 2014 were included.

RESULTS

The biological actions of BMP15 include: (i) the promotion of follicle growth and maturation starting from the primary gonadotrophin-independent phases of folliculogenesis; (ii) the regulation of follicular granulosa cell (GC) sensitivity to FSH action and the determination of ovulation quota; (iii) the prevention of GC apoptosis and (iv) the promotion of oocyte developmental competence. The existence of biologically active heterodimers with GDF9, and/or the synergistic co-operation of BMP15 and GDF9 homodimers are indeed relevant in this context. Experimental disruption of the bmp15 gene in mice resulted in a mild fertility defect limited to females, whereas natural missense mutations in ewes cause variable phenotypes (ranging from hyperprolificacy to complete sterility) depending on a fine gene dosage mechanism also involving GDF9. Strong evidence supports the concept that such a mechanism plays an important role in the regulation of ovulation rate across mammalian and non-mammalian species. Following the discovery of sheep fecundity genes, several research groups have focused on alterations in human BMP15 associated with primary ovarian insufficiency (POI) or polycystic ovary syndrome. Several variants of BMP15 are significantly associated with POI supporting their pathogenic role, but the underlying biological mechanism is still under investigation and of great interest in medicine. BMP15 maps to the Xp locus involved in the determination of the ovarian defect in Turner syndrome and significantly contributes to the determination of ovarian reserve. Pioneering studies in women undergoing controlled ovarian stimulation indicate that BMP15 may represent a marker of ovarian response or oocyte quality.

CONCLUSIONS

BMP15, an oocyte-derived growth and differentiation factor, is a critical regulator of folliculogenesis and GC activities. Variations in BMP15 gene dosage have a relevant influence on ovarian function and can account for several defects of female fertility. The modulation of BMP15 action may have interesting pharmacological perspectives and the analysis of BMP15 may become a useful marker in IVF procedures. Recent outcomes indicate that the close interactions of BMP15/GDF9 have a critical biological impact that should be taken into account in future studies.

Investigations of TGF-β signaling in preantral follicles of female mice reveal differential roles for bone morphogenetic protein 15

Bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are 2 closely related TGF-β ligands implicated as key regulators of follicle development and fertility. Animals harboring mutations of these factors often exhibit a blockage in follicle development beyond the primary stage and therefore little is known about the role of these ligands during subsequent (preantral) stages. Preantral follicles isolated from immature mice were cultured with combinations of BMP15, GDF9, and activin receptor-like kinase (ALK) inhibitors. Individually, GDF9 and BMP15 promoted follicle growth during the first 24 hours, whereas BMP15 subsequently (48-72 h) caused follicle shrinkage and atresia with increased granulosa cell apoptosis. Inhibition of ALK6 prevented the BMP15-induced reduction in follicle size and under basal conditions promoted a rapid increase in granulosa cell proliferation, suggesting BMP15 signals through ALK6, which in turn acts to restrain follicle growth. In the presence of GDF9, BMP15 no longer promoted atresia and in fact follicle growth was increased significantly more than with either ligand alone. This cooperative effect was accompanied by differential expression of Id1-3, Smad6-7, and Has2 and was blocked by the same ALK5 inhibitor used to block GDF9 signaling. Immunostaining for SMAD2/3 and SMAD1/5/8, representing the 2 main branches of TGF-β signaling, supported the fact that both canonical pathways have the potential to be active in growing follicles, whereas primordial follicles only express SMAD2/3. Overall results highlight differential effects of the 2 main TGF-β signaling pathways during preantral follicle growth.

Characterization of bmp15 and its regulation by human chorionic gonadotropin in the follicle of gibel carp (Carassius auratus gibelio)

Bone morphogenetic protein (BMP15) is a member of the transforming growth factor β (TGF-β) superfamily with a key role in regulating follicle development in mammals and birds. However, potential ovarian roles of BMPs remain unexplored in teleosts. In this study, the full-length sequences of bmp15 were obtained using rapid-amplification of cDNA ends (RACE). The full-length cDNA sequence of bmp15 is 2217 bp which contained 214 bp 5'-UTR and 845 bp 3'-UTR. The open reading frame (ORF) sequence of bmp15 is 1158 bp, encoding a predicted protein of 385 amino acid residues. BMP15 has a specific RXXR protease cleavage site of TGF-β superfamily (is RIRR) and six conserved cysteine residues. Using real-time quantitative PCR revealed that bmp15 mRNA was largely expressed in the ovary and testis and mostly in oocytes within the follicle, slightly expressed in muscle, liver and pituitary. BMP15 is mainly present at stage I follicles by real-time quantitative PCR and immunohistochemistry. Phylogenetic analysis showed that gibel carp bmp15 was similar to bmp15 of zebrafish and other fish species. Treatment with human chorionic gonadotropin (hCG) in isolated follicles of gibel carp in vitro showed altered bmp15 mRNA expression: when treated with 10 ng/mL hCG for 10h, the expression level of bmp15 was significantly increased. However, with proceeding cultivation, the expression level of BMP15 mRNA decreased. The results of this study indicate that bmp15 may play a key role during development of follicles in gibel carp, especially in early stage follicles.

A covalently dimerized recombinant human bone morphogenetic protein-15 variant identifies bone morphogenetic protein receptor type 1B as a key cell surface receptor on ovarian granulosa cells

Genetic studies have identified bone morphogenetic protein-15 (BMP15) as an essential regulator of female fertility in humans and in sheep. Oocyte-derived BMP15 is a noncovalently linked dimeric growth factor mediating its effects to ovarian somatic cells in a paracrine manner. Although receptor ectodomains capable of binding BMP15 have previously been reported, no cell surface receptor complex involved in BMP15 signaling has previously been characterized. Here we have expressed and purified recombinant human BMP15 noncovalent and covalent dimer variants. The biological effects of these BMP15 variants were assessed in cultured human granulosa-luteal cells or COV434 granulosa cell tumor cells using BMP-responsive transcriptional reporter assays and an inhibin B ELISA. Biochemical characterization of ligand-receptor interactions was performed with affinity-labeling experiments using [(125)I]iodinated BMP15 variants. Both ligand variants were shown to form homodimers and to stimulate Smad1/5/8 signaling and inhibin B production in human granulosa cells in a similar manner. [(125)I]Iodination of both ligands was achieved, but only the covalent dimer variant retained receptor binding capacity. The [(125)I]BMP15(S356C) variant bound preferentially to endogenous BMP receptor 1B (BMPR1B) and BMPR2 receptors on COV434 cells. Binding experiments in COS cells with overexpression of these receptors confirmed that the [(125)I]BMP15(S356C) variant binds to BMPR1B and BMPR2 forming the BMP15 signaling complex. The results provide the first direct evidence in any species on the identification of specific cell surface receptors for a member of the GDF9/BMP15 subfamily of oocyte growth factors. The fact that BMP15 uses preferentially BMPR1B as its type I receptor suggests an important role for the BMPR1B receptor in human female fertility. The result is well in line with the demonstration of ovarian failure in a recently reported human subject with a homozygous BMPR1B loss-of-function mutant.

Signalling pathways mediating specific synergistic interactions between GDF9 and BMP15

Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are two proteins selectively expressed in the oocyte which are essential for normal fertility. Both of these proteins are members of the transforming growth factor beta (TGF-β) superfamily and as such are produced as pre-proproteins, existing after proteolytic processing as a complex of the respective pro and mature regions. Previous work has shown that these two proteins interact both at the genetic and cellular signalling levels. In this study, our aim was to determine if the purified mature regions of GDF9 and BMP15 exhibit synergistic interactions on granulosa cells and to determine if such interactions are specific to these two proteins. We have used primary cultures of murine granulosa cells and [(3)H]-thymidine incorporation or transcriptional reporter assays as our readouts. We observed clear synergistic interactions between the mature regions of GDF9 and BMP15 when either DNA synthesis or SMAD3 signalling were examined. GDF9/BMP15 synergistic interactions were specific such that neither factor could be replaced by an analogous TGF-β superfamily member. The GDF9/BMP15 synergistic signalling response was inhibited by the SMAD2/3 phosphorylation inhibitor SB431542, as well as inhibition of the mitogen-activated protein kinase or rous sarcoma oncogene (SRC) signalling pathways, but not the nuclear factor kappa B pathway. In this study, we show that purified mature regions of GDF9 and BMP15 synergistically interact in a specific manner which is not dependent on the presence of a pro-region. This synergistic interaction is targeted at the SMAD3 pathway, and is dependent on ERK1/2 and SRC kinase signalling.

Influence of follicular fluid GDF9 and BMP15 on embryo quality

OBJECTIVE

To evaluate the association between follicular fluid levels of propeptide and mature forms of growth differentiation factor (GDF) 9 and bone morphogenetic protein (BMP) 15 with subsequent oocyte and embryo quality.

DESIGN

Prospective clinical study.

SETTING

University hospital.

PATIENT(S)

Eighty-one infertile patients who underwent in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI).

INTERVENTION(S)

The expression levels of the propeptide and mature forms of follicular fluid GDF9 and BMP15 were determined by western blot analysis. The levels of follicular fluid hormones (FSH, E2, and P) were measured with automated chemiluminescent enzyme immunoassays.

MAIN OUTCOME MEASURE(S)

The relationships between the levels of GDF9 and BMP15, hormones, oocyte maturation, and embryo quality.

RESULT(S)

Mature GDF9 levels were significantly correlated with the nuclear maturation of oocytes. The mean mature GDF9 level was 4.87±0.60 in the high-embryo-quality group and 1.45±0.81 in the low-embryo-quality group. There were no statistically significant differences in embryo quality among the patients regarding propeptide GDF9 and BMP15 expression status. There was a negative correlation between follicular fluid levels of P and the mature form of GDF9.

CONCLUSION(S)

Higher mature GDF9 levels in the follicular fluid were significantly correlated with oocyte nuclear maturation and embryo quality.

The bioactivity of human bone morphogenetic protein-15 is sensitive to C-terminal modification: characterization of the purified untagged processed mature region

Oocyte-derived bone morphogenetic protein-15 (BMP15) is critical for the regulation of mammalian fertility. Previously we have found that a C-terminal His(6)-tag destroys the bioactivity of growth differentiation-9 (GDF9, a homolog of BMP15). In this study we found that recombinant human BMP15 is produced by HEK-293T cells in an active form, but the bioactivity is lost by C-terminal modification, specifically, fusion to a Flag tag. After purification the mature BMP15 wt is active in transcriptional reporter assays specific for Smad1/5/8 in human granulosa-luteal (hGL) and COV434 granulosa tumor cells, whereas BMP15 with a carboxy-terminal Flag tag remains inactive. Using these same cell models we found that treatment with purified mature BMP15 wt causes a rapid phosphorylation of Smad1. The purified BMP15 wt is a potent stimulator of rat granulosa cell DNA synthesis, which could be antagonized by the BMPRII ectodomain-Fc fusion molecule, whereas the BMP15C-Flag was completely inactive. Further, the BMP15 wt form is a potent stimulator of inhibin B production in hGL cells. We found that the purified BMP15 wt consists of P16 and -17, both of which are post-translationally modified forms. This is the first characterization of a purified untagged human BMP15 mature region, which is stable and highly bioactive in human and rodent granulosa cells and as such is of importance for studies on human fertility.

Fibroblast growth factor 10 enhances bovine oocyte maturation and developmental competence in vitro

The ability of oocytes to resume meiosis, become fertilized, and generate viable pregnancies is controlled during folliculogenesis by several endocrine and paracrine factors. The aim of this work is to determine whether fibroblast growth factor 10 (FGF10) is an oocyte competent factor. Transcripts for each of the four FGF receptor types (FGFR) were present in cumulus and oocytes after their extraction from the follicles. FGFR1 transcripts predominated in cumulus cells whereas FGFR2 was most abundant in oocytes. Exposing the cumulus-oocyte complexes to FGF10 during in vitro maturation did not affect cleavage rates, but increases (P<0.05) in the percentage of embryos at the 8-16-cell stage on day 3 and at the blastocyst stage on day 7, which were evident in FGF10-supplemented oocytes. The progression of oocytes through meiosis and cumulus expansion was increased (P<0.05) by FGF10. The importance of the endogenous sources of FGFs was examined by adding anti-FGF10 IgG during oocyte maturation. Blocking endogenous FGF10 activity decreased (P<0.05) the percentage of oocytes developing into blastocysts and limited (P<0.05) cumulus expansion. Expression profiles of putative cumulus and oocyte competency markers were examined for their involvement in FGF10-mediated responses. FGF10 influenced the expression of CTSB and SPRY2 in cumulus cells and BMP15 in oocytes. In summary, this work provides new insight into the importance of FGFRs and locally derived FGF10 during oocyte maturation in cattle. Its subsequent impact on in vitro embryo development implicates it as a noteworthy oocyte competent factor.