Dysregulation of granulosal bone morphogenetic protein receptor 1B density is associated with reduced ovarian reserve and the age-related decline in human fertility

Screening for causative mutations in ovine BMPR1B and BMP15 genes and their homologous fragments in human

PURPOSE

The BMPR1B and BMP15 genes are well known for their considerable associations with prolificacy in sheep. These genes may also affect fertility or prolificacy in other species, including human. This study was conducted to investigate possible causative mutations in BMPR1B and BMP15 genes in human and an indigenous breed of sheep.

METHODS

Blood samples were collected from 83 singleton- and prolific Mehraban ewes and 81 infertile, singleton- and twin-bearing women. A 190-bp fragment, containing the FecB mutation in ovine BMPR1B, a 380-bp fragment in ovine BMP15 gene and their homologous fragments in human were amplified and then investigated by single-stranded conformation polymorphism and DNA sequencing methods.

RESULTS

The FecB mutation of BMPR1B (g.159A>G) was detected in the sheep population, but no polymorphic loci were found in the homologous fragment in studied human samples. The studied fragments of BMP15 were monomorphic in both sheep and human samples. A total of nine and 69 point-differences in the studied fragments of BMPR1B and BMP15 genes were detected between the species, respectively. In sheep, the G allele of BMPR1B had a positive effect on litter size (p<0.05), whereby all AG or GG ewes were prolific.

CONCLUSION

The FecB mutation for the first time was detected in Mehraban sheep and therefore could be considered for marker-assisted selection in this breed. The studied fragments of BMPR1B and BMP15 genes are not responsible for reproduction variation in human. More studies on other genes, associated with fertility in human, are necessary in the future.

Anti-Mullerian Hormone-Based Phenotyping Identifies Subgroups of Women with Polycystic Ovary Syndrome with Differing Clinical and Biochemical Characteristics

Even though polycystic ovary syndrome (PCOS) was originally defined as "amenorrhea associated with bilateral polycystic ovaries", women without PCO morphology can be included in this diagnosis. This may contribute to the clinical heterogeneity seen in PCOS. Serum anti-Mullerian hormone (AMH) correlates with the number of ovarian cysts. We investigated whether phenotyping based on serum AMH can distinguish subgroups of PCOS with different clinical and biochemical characteristics. The electronic medical records of 108 women with PCOS (Rotterdam criteria) were reviewed. The serum AMH value correlated inversely (0.03 < p < 0.0001) with age, weight, and BMI values and directly with serum total testosterone (T), free T, and bioavailable T values. When divided into quartiles based on serum AMH values, the women in the highest quartile (AMH: 18.5 ± 9.9 ng/mL; n = 27) had lower BMI (29.4 ± 6.9 vs. 34.0 ± 10.6-36.7 ± 7.2 kg/m²) but higher total T (51.3 ± 27.2 vs. 26.5 ± 10.4-35.1 ± 16.3 ng/dL), free T (7.7 ± 6.0 vs. 4.4 ± 2.3-5.7 ± 3.2 ng/dL), and bioavailable T (22.1 ± 17.0 vs. 12.2 ± 6.6-16.5 ± 8.7 ng/dL) values. The combination of high AMH and high testosterone values may point to the ovaries and reproductive etiology for PCOS in this subgroup. Thus, AMH-based phenotyping may provide a practical and cost-effective tool to explore the heterogeneity in PCOS.

Paracrine regulation of granulosa cell development in the antral follicles in mammals

Background

Development of ovarian follicles is regulated by a complex interaction of intra- and extra-follicular signals. Oocyte-derived paracrine factors (ODPFs) play a central role in this process in cooperation with other signals.

Methods

This review provides an overview of the recent advances in our understanding of the paracrine regulation of antral follicle development in mammals. It specifically focuses on the regulation of granulosa cell development by ODPFs, along with other intrafollicular signals.

Main Findings

Bi-directional communication between oocytes and surrounding cumulus cells is a fundamental mechanism that determines cumulus cell differentiation. Along with estrogen, ODPFs promote the expression of forkhead box L2, a critical transcription factor required for mural granulosa cells. Follicle-stimulating hormone (FSH) facilitates these processes by stimulating estrogen production in mural granulosa cells.

Conclusion

Cooperative interactions among ODPFs, FSH, and estrogen are critical in determining the fate of cumulus and mural granulosa cells, as well as the development of oocytes.

Improvement in ovarian function following fecal microbiota transplantation from high-laying rate breeders

The underlying mechanism between the gut microbiota and reproductive function is not yet well-known. This study was conducted to investigate the effect of the administration of fecal microbiota transplantation (FMT) from highly laying rate donors on the cecal microbiota, intestinal health and ovarian function in broiler breeders. A total of 60 broiler breeders (53 wk of age) were selected by their laying rate [high (HP, 90.67 ± 0.69%; n = 10) and low (LP, 70.23 ± 0.87%; n = 20)]. The LP breeders were then be transplanted with fecal microbiota from HP hens (FMTHP; n = 10) or the same dosage of PBS (FMTCON; n = 10) for 28 d. The results revealed that FMT from HP donors increased egg-laying rate and serum hormone levels [17β-estradiol (E2), anti-Müller hormone], also decreased proinflammatory cytokine levels (interleukin-6, interleukin-8, tumor necrosis factor-α) of LP breeders (P < 0.05). The FMTHP group breeders had higher villus height, villus height/crypt depth ratio, and upregulated mRNA expression of jejunum barrier-related gene (ZO-2 and mucin-2) and estrogen, follicle-stimulating hormone (FSH) and anti-Müller hormone (AMH) receptor genes (ESR1, ESR2, FSHR, AMHR) (P < 0.05) than FMTCON group. FMT from HP donors led to higher mRNA expression of Bcl2 and sirtuin1 (SIRT1), while it downregulated the proapoptotic genes (Bax, caspase-3, caspase-8, and caspase-9) mRNA expressions in ovary compared with the FMTCON breeders (P < 0.05), and this pattern was also observed in HP donors. Also, HP breeder had higher observed_species and alpha-diversity indexes (Chao1 and ACE) than FMTCON group, while FMTHP can increase observed_species and alpha-diversity indexes (Chao1 and ACE) than FMTCON group (P < 0.05). The bacteria enrichment of Firmicutes (phylum), Bacteroidetes (phylum), Lactobacillus (genus), Enterococcus (genus), and Bacteroides (genus) were increased by FMTHP treatment. The genera Butyricicoccus, Enterococcus, and Lactobacillus were positively correlated with egg-laying rate. Therefore, cecal microbiomes of breeders with high egg-laying performance have more diverse activities, which may be related to the metabolism and health of the host; and FMT from high-yield donors can increase the hormone secretion, intestinal health, and ovarian function to improve egg-laying performance and the SIRT1-related apoptosis and cytokine signaling pathway were involved in this process.

Dietary apple pectic oligosaccharide improves reproductive performance, antioxidant capacity, and ovary function of broiler breeders

Reproduction performance is one of the most important economic traits for the poultry industry. Intriguingly, apple pectic oligosaccharide (APO) could promote gastrointestinal function and immune function to improve performance; however, literature about APO on reproduction performance in breeders is limited. This study aimed to determine whether APO administration can improve reproduction performance and ovary function of broiler breeders with different egg laying rates. Two hundred and fifty six Arbor Acres broiler breeders (48-week-old) were used in a 2 × 2 factorial design with 2 egg laying rates (average [AR] and low [LR]) and 2 dietary levels of APO (0 and 200 mg/kg APO). Results showed that the LR breeders presented higher egg weight but lower egg laying rate, qualified egg rate, and feed efficiency than the AR breeders (P(laying) < 0.05). Also, the LR breeders had decreased serum Anti-Müllerian hormone, leptin, and antioxidant enzyme (superoxide dismutase, total antioxidant capacity) levels than the AR breeders (P(laying) ≤ 0.05). Dietary supplementation with APO improved egg weight, feed efficiency, as well as egg albumen quality (higher albumen height and Haugh unit) (P(APO) < 0.05), and decreased the concentration of pro-inflammatory cytokine levels (interleukin [IL]-1β, IL-8) in serum (P(APO) ≤ 0.05). The apoptosis rate and pro-apoptosis-related gene expression (caspase 9 and Bax) in the ovary of LR breeders were higher, while the anti-apoptosis-related gene expression (Bcl-2, PCNA) was lower in LR compared with the AR breeders (P(laying) < 0.05). Dietary supplementation with APO decreased the caspase 9 and Bax expression in LR breeders (P(interaction) < 0.05), and increased the Bcl-2 and PCNA expression in the 2 breeders (P(APO) < 0.05). These findings indicate that breeders with a lower egg laying rate exhibit lower antioxidant capacity and high cell apoptosis in the ovary. Dietary supplementation with APO might improve albumen quality and antioxidant capacity, and decrease the inflammatory factors and ovary apoptosis-related genes expression to improve ovary function. Moreover, the effect of APO on decreasing ovarian pro-apoptosis-related gene expression was more pronounced in lower reproductive breeders.

Differential analysis of gut microbiota and the effect of dietary Enterococcus faecium supplementation in broiler breeders with high or low laying performance

The difference in microbiota was examined for breeders with different egg-laying rates, and the impact of dietary Enterococcus faecium (EF) was also determined in the present study. A total of 256 Arbor Acres broiler breeders (48-wk-old) were used in a 2 × 2 factorial design, which encompassed 2 egg-laying rate levels [average (average egg laying: AP, 80.45 ± 0.91%) and low (lower egg laying: LP, 70.61 ± 1.16%)] and 2 different dietary groups [control (no additive), 6 × 10⁸ cfu/kg EF]. The results showed that the AP breeders presented a lower egg weight, feed conversion ratio, abdominal fat rate, and serum leptin level (P_(laying) ≤ 0.05) as well as a higher egg-laying rate (P_(laying) < 0.01) than the LP breeders. Dietary supplementation with EF improved the egg weight (P_(EF) = 0.03) and had a higher concentration of follicle-stimulating hormone (FSH) in the serum (P_(EF) = 0.04). The relative expression of Caspase 9, Bax, AMHR, BMP15, and GATA4 in the ovary of AP breeders was lower, whereas the FSHR and BMPR1B expression was higher than that measured in LP breeders (P_(laying) ≤ 0.05). LP increased the abundance of Bacteroidetes (phylum), Firmicutes (phylum), Bacteroidia (class), Clostridia (class), Bacteroidales (order), Clostridiales (order), and Lachnospiraceae (family), whereas the AP promoted the enrichment of Proteobacteria (phylum) and Gammaproteobacteria (class) (P_(laying) < 0.05). The genera Bacillus, Rhodanobacter, and Streptomyces were positively correlated with the egg-laying rate and BMPR1B expression (P < 0.05) but negatively correlated with the abdominal fat rate (P < 0.05) and Caspase 9 (P < 0.05). These findings indicate that the low reproductive performance breeders had lower microbiota diversity and higher Firmicutes, which triggers the energy storage that led to higher fat deposition. Besides, increases in the abdominal fat rate, leptin level, and apoptosis (Caspase 9, Bax) and reproduction-related gene (BMP15, AMHR, BMPR1B, and GATA4) expression would possibly be the potential mechanisms under which breeders have different reproductive performance. Dietary EF increased the egg weight and serum FSH level and decreased the Bacteroidetes (phylum) in low reproductive breeders.

Impact of Dietary Selenium on Modulation of Expression of Several Non-Selenoprotein Genes Related to Key Ovarian Functions, Female Fertility, and Proteostasis: a Transcriptome-Based Analysis of the Aging Mice Ovaries

Female reproductive (ovarian) aging is characterized by a marked decline in quantity and quality of follicles and oocytes, as well as alterations in the surrounding ovarian stroma. In our previous report, we have shown that dietary selenium (Se) insufficiency and supplementation differentially impacted the reproductive efficiency in aging mice; however, the precise understanding of such modulation is still incomplete. In the present study, we sought to determine the impact of low (mildly low level) and moderately high (medium level) Se diets on expression profile of non-selenoprotein genes in the ovaries of aging mice. For this purpose, the aged mice were divided in two groups and fed either a low Se (Se-L; 0.08 mg Se/kg) diet or a moderately high Se (Se-M; 0.33 mg Se/kg) diet. RNA-seq analysis revealed that a total of 168 genes were differentially expressed between the two groups. From these, 72 and 96 differentially expressed genes (DEGs) were found to be upregulated and downregulated, respectively. Gene Ontology (GO) and pathways enrichment (KEGG) analyses revealed that these DEGs were enriched in several key GO terms and biological pathways including PI3K-Akt signaling pathway, steroid hormone biosynthesis, signaling pathways regulating pluripotency of stem cells, Hippo signaling pathway, ovarian steroidogenesis, and Wnt signaling pathway. Further filtering of RNA-seq data revealed that several DEGs such as Star, Hsd3b6, Scd1, Bmp7, Aqp8, Gas1, Fzd1, and Wwc1 were implicated in key ovarian- and fertility-related functions. In addition, some of the DEGs were related to ER homeostasis and/or proteostasis. These results highlight that dietary low and moderately high (medium level) Se diets, in addition to modulation of selenoproteins, can also have an impact on expression of several non-selenoprotein genes in the ovaries of aging mice. To sum up, these findings add more value to our understanding of Se modulation of ovarian functions and female fertility and will pave a way for the focused mechanistic and functional studies in this domain.

Study on the correlation between BMPR1B protein in sheep blood and reproductive performance

Sheep reproductive performance is one of the important economic traits in sheep farming. The bone morphogenetic protein receptor 1B (BMPR1B) gene and protein may play an important role in sheep fertility. This study was to investigate the association of blood BMPR1B protein expression with reproductive performance in sheep. Mongolian sheep with single and twin births and polytocous Small Tail Han sheep were selected due to differences in birth numbers. The BMPR1B mRNA in sheep blood was measured by a reverse transcription-polymerase chain reaction as well as the BMPR1B protein was measured by enzyme-linked immunosorbent assay in blood samples of Mongolian and Small Tail Han sheep. The results demonstrated that blood BMPR1B concentration in Mongolian sheep with twin birth was higher (P < 0.05) than Small Tail Han sheep and Mongolian sheep with single birth. The protein concentration in the anestrus season was higher (P < 0.045) than those in the estrus season for both Mongolian and Small Tail Han sheep. Moreover, BMPR1B concentration in Mongolian sheep increased (P < 0.05) at the age of 6 to 12 mo and that in Small Tail Han sheep increased (P < 0.05) at the age of 3 to 6 mo. The result indicates that the increase in BMPR1B protein concentrations in the blood of Mongolian ewes and Small Tail Han ewes may be beneficial to follicular development, but too high or too low of this blood protein concentration in Mongolian and Small Tail Han sheep is not conducive to ovulation.

BMPR1A and BMPR1B Missense Mutations Cause Primary Ovarian Insufficiency

CONTEXT

Primary ovarian insufficiency (POI) is a frequently occurring disorder affecting approximately 1% of women under 40 years of age. POI, which is characterized by the premature depletion of ovarian follicles and elevated plasma levels of follicle-stimulating hormone, leads to infertility. Although various etiological factors have been described, including chromosomal abnormalities and gene mutations, most cases remain idiopathic.

OBJECTIVE

To identify and to functionally validate new sequence variants in 2 genes that play a key role in mammalian ovarian function, BMPR1A and BMPR1B (encoding for bone morphogenic protein receptor), leading to POI.

METHODS

The impact on bone morphogenic protein (BMP) signaling of BMPR1A and BMPR1B variants, previously identified by whole-exome sequencing on 69 women affected by isolated POI, was established by different in vitro functional experiments.

RESULTS

We demonstrate that the BMPR1A-p.Arg442His and BMPR1B-p.Phe272Leu variants are correctly expressed and located but lead to an impairment of downstream BMP signaling.

CONCLUSION

In accordance with infertility observed in mice lacking Bmpr1a in the ovaries and in Bmpr1b-/- mice, our results unveil, for the first time, a link between BMPR1A and BMPR1B variants and the origin of POI. We show that BMP signaling impairment through specific BMPR1A and BMPR1B variants is a novel pathophysiological mechanism involved in human POI. We consider that BMPR1A and BMPR1B variants constitute genetic biomarkers of the origin of POI and have clinical utility.

Luteinizing Hormone Action in Human Oocyte Maturation and Quality: Signaling Pathways, Regulation, and Clinical Impact

The ovarian follicle luteinizing hormone (LH) signaling molecules that regulate oocyte meiotic maturation have recently been identified. The LH signal reduces preovulatory follicle cyclic nucleotide levels which releases oocytes from the first meiotic arrest. In the ovarian follicle, the LH signal reduces cyclic nucleotide levels via the CNP/NPR2 system, the EGF/EGF receptor network, and follicle/oocyte gap junctions. In the oocyte, reduced cyclic nucleotide levels activate the maturation promoting factor (MPF). The activated MPF induces chromosome segregation and completion of the first and second meiotic divisions. The purpose of this paper is to present an overview of the current understanding of human LH signaling regulation of oocyte meiotic maturation by identifying and integrating the human studies on this topic. We found 89 human studies in the literature that identified 24 LH follicle/oocyte signaling proteins. These studies show that human oocyte meiotic maturation is regulated by the same proteins that regulate animal oocyte meiotic maturation. We also found that these LH signaling pathway molecules regulate human oocyte quality and subsequent embryo quality. Remarkably, in vitro maturation (IVM) prematuration culture (PMC) protocols that manipulate the LH signaling pathway improve human oocyte quality of cultured human oocytes. This knowledge has improved clinical human IVM efficiency which may become a routine alternative ART for some infertile patients.

The Concept of Growth Hormone Deficiency Affecting Clinical Prognosis in IVF

The current understanding of human growth hormone (hGH; here GH) action is that the molecule is a 191-amino acid, single-chain polypeptide that is synthesized, stored and secreted by the somatotroph cells within the lateral wings of the anterior pituitary gland. It can be classified as a protein (comprising more than 50 amino acids) but true proteins have tertiary and quaternary chains creating a more complex structure, hence GH is usually classified as a polypeptide. GH is normally secreted at night during sleep and promotes skeletal, visceral and general body growth through the action of somatomedins or IGFs, notably IGF-1. In some tissues, GH action is directed via specific receptors GHRs; these are most abundant in liver, adipose and muscle tissues but have also been shown in granulosa cells, testicular tissues and on the oocyte, as well as in glandular cells of the luteal phase endometrium and decidua; such findings being recent and minimally researched to now. Following engagement with its receptor, the transduction process activates multiple signaling proteins. These all lead to extensive metabolic and mitogenic (growth promoting) responses. Clinically, GH is known to have an important role in pubertal development and is a key hormone for the vigor associated with adolescence and early adult life stages but has a faded presence and role for later adulthood, beyond age 30 years, and is minimally detected in advanced age, beyond 40 years. In association with the rapidly increasing trend for delaying reproduction beyond age 35 years, GH is being widely researched now as a potential adjuvant for infertility treatment in this group who, studies consistently show, have a poorer prognosis than younger females when relying on autologous oocytes. The idea that the age-related reduction in fertility prognosis is a feature of growth hormone deficiency is supported by our studies showing an elevated binding protein IGFBP-3/IGF-1 ratio and this can be reduced to a normal range (matching younger, good prognosis women) by the administration of GH as an adjuvant.

CDK4/6 inhibitor protects chemerin-induced human granulosa-lutein cells from apoptosis by inhibiting the p53/p21 waf pathway

Dysregulation of the cell cycle is common in human tumorigenesis. Therefore, CDK4/6 inhibitors targeting the cell cycle have been developed, and their antiapoptotic effects have been highly correlated with potential clinical therapies. The aim of this study was to identify the regulatory effect of the CDK4/6 inhibitor palbociclib on chemerin-induced apoptosis of immortalized human granulosa-lutein (hGL) cells and to elucidate its fundamental mechanism of action. Palbociclib enhanced antioxidative enzyme generation and diminished ROS generation in hGL cells. Furthermore, we found that palbociclib suppressed chemerin-induced apoptotic protein expression, reversing the Bcl-2/Bax ratio and inhibiting the p53/p21 ^waf pathway. Eventually, palbociclib decreased the level of cleaved caspase-3 and -9, hindering the apoptosis of hGL cells. In general, the antiapoptotic efficacy of palbociclib could be attributed in part to the modulation of the mitochondrial apoptotic pathway in hGL cells.

Growth hormone during in vitro fertilization in older women modulates the density of receptors in granulosa cells, with improved pregnancy outcomes

OBJECTIVE

To study the effect of aging and granulosa cell growth hormone receptor (GHR) expression, and the effect of growth hormone (GH) co-treatment during IVF on receptor expression.

DESIGN

Laboratory study.

SETTING

University.

PATIENT(S)

A total of 445 follicles were collected from 62 women undergoing standard infertility treatment.

INTERVENTION(S)

Preovulatory ovarian follicle biopsies of granulosa cells and follicular fluid.

MAIN OUTCOME MEASURE(S)

Older women with a poor ovarian reserve were co-treated with GH to determine the effect of the adjuvant during IVF on the granulosal expression density of FSH receptor (FSHR), LH receptor (LHR), bone morphogenetic hormone receptor (BMPR1B), and GHR. Ovarian reserve, granulosa cell receptor density, oocyte quality, and pregnancy and live birth rates were determined.

RESULT(S)

Growth hormone co-treatment increased the receptor density for granulosal FSHR, BMPR1B, LHR, and GHR compared with the non-GH-treated patients of the same age and ovarian reserve. Growth hormone co-treatment increased GHR density, which may increase GHR activity. The GH co-treatment was associated with a significant increase in pregnancy rate.

CONCLUSION(S)

Growth hormone co-treatment restored the preovulatory down-regulation of FSHR, BMPR1B, and LHR density of the largest follicles, which may improve the maturation process of luteinization in older patients with reduced ovarian reserve. The fertility of the GH-treated patients improved.

Gremlin, Noggin, Chordin and follistatin differentially modulate BMP induced suppression of androgen secretion by bovine ovarian theca cells

Bone morphogenetic proteins (BMP) are firmly implicated as intra-ovarian regulators of follicle function and steroidogenesis but information is lacking regarding the regulation of BMP signalling by extracellular binding proteins co-expressed in the ovary. In this study we compared the abilities of four BMP binding proteins (gremlin, noggin, chordin, follistatin) to antagonize the action of four different BMPs (BMP2 BMP4, BMP6, BMP7) on LH-induced androstenedione secretion by bovine theca cells in primary culture. Expression of the four BMP binding proteins and BMPs investigated here has previously been documented in bovine follicles. All four BMPs suppressed androstenedione secretion by >85%. Co-treatment with gremlin antagonized BMP2- and, less potently, BMP4-induced suppression of androgen secretion but did not affect responses to BMP6 and BMP7. Noggin antagonized the effects of three BMPs (rank order: BMP4 > BMP2 > BMP7) but did not affect the response to BMP6. Follistatin partially reversed the suppressive effects of BMP6 on androgen secretion but did not affect BMP2, BMP4 and BMP7 action. Chordin had no effect on the response to any of the four BMPs. BMP6 treatment upregulated thecal expression of GREM1, NOG, CHRD and SMAD6 mRNA whilst inhibiting expression of the four BMPs. Taken together with previous work documenting the intra-ovarian expression of different BMPs, BMP binding proteins and signalling receptors, these observations reinforce the conclusion that extracellular binding proteins selectively modulate BMP-dependent alterations in thecal steroidogenesis. As such they likely constitute an important regulatory component of this, and other intra-ovarian actions of BMPs.

GDF-9 and BMP-15 direct the follicle symphony

Understanding the physiology underlying the complex dialog between the oocyte and its surrounding somatic cells within the ovarian follicle has been crucial in defining optimal procedures for the development of clinical approaches in ART for women suffering from infertility and ovarian dysfunction. Recent studies have implicated oocyte-secreted factors like growth differentiation factor 9 (GDF-9) and bone morphogenetic protein 15 (BMP-15), members of the transforming growth factor-beta (TGFβ) superfamily, as potent regulators of folliculogenesis and ovulation. These two factors act as biologically active heterodimers or as homodimers in a synergistic cooperation. Through autocrine and paracrine mechanisms, the GDF-9 and BMP-15 system has been shown to regulate growth, differentiation, and function of granulosa and thecal cells during follicular development playing a vital role in oocyte development, ovulation, fertilization, and embryonic competence. The present mini-review provides an overview of recent findings relating GDF-9 and BMP-15 as fundamental factors implicated in the regulation of ovarian function and discusses their potential role as markers of oocyte quality in women.

The effect of ovarian reserve and receptor signalling on granulosa cell apoptosis during human follicle development

The poor oocyte quality in older women has previously been linked to the depletion of the ovarian reserve of primordial follicles and an increase in granulosal apoptosis. Granulosa cells were collected from 198 follicles and individually analysed by flow cytometry. In the young IVF patients, the level of apoptosis was inversely proportional to the expression of bone morphogenetic protein (BMPR1B) and follicle stimulating hormone (FSH) receptors. Conversely, in the older patients this relationship became dysregulated. In the older patients, at the time of preovulatory maturation, the reduced apoptosis reflects the poor mitogenic growth turnover rate of healthy follicles rather than the death rate in an atretic follicle. Restoring an optimum receptor density and down-regulation of receptors may improve oocyte quality and the pregnancy rate in older women.

Involvement of Bone Morphogenetic Proteins (BMP) in the Regulation of Ovarian Function

Primordial germ cells migrate to the fetal gonads and proliferate during gestation to generate a fixed complement of primordial follicles, the so-called ovarian reserve. Primordial follicles comprise an oocyte arrested at the diplotene stage of meiosis, surrounded by a layer of pregranulosa cells. Activation of primordial follicles to grow beyond this arrested stage is of particular interest because, once activated, they are subjected to regulatory mechanisms involved in growth, selection, maturation, and ultimately, ovulation or atresia. The vast majority of follicles succumb to atresia and are permanently lost from the quiescent or growing pool of follicles. The bone morphogenetic proteins (BMPs), together with other intraovarian growth factors, are intimately involved in regulation of follicle recruitment, dominant follicle selection, ovulation, and atresia. Activation of primordial follicles appears to be a continuous process, and the number of small antral follicles at the beginning of the menstrual cycle provides an indirect indication of ovarian reserve. Continued antral follicle development during the follicular phase of the menstrual cycle is driven by follicle stimulating hormone (FSH) and luteinizing hormone (LH) in conjunction with many intraovarian growth factors and inhibitors interrelated in a complex web of regulatory balance. The BMP signaling system has a major intraovarian role in many species, including the human, in the generation of transcription factors that influence proliferation, steroidogenesis, cell differentiation, and maturation prior to ovulation, as well as formation of corpora lutea after ovulation. At the anterior pituitary level, BMPs also contribute to the regulation of gonadotrophin production.

Granulosa Cell Apoptosis in the Ovarian Follicle-A Changing View

Recent studies challenge the previous view that apoptosis within the granulosa cells of the maturing ovarian follicle is a reflection of aging and consequently a marker for poor quality of the contained oocyte. On the contrary, apoptosis within the granulosa cells is an integral part of normal development and has limited predictive capability regarding oocyte quality or the ensuing pregnancy rate in in vitro fertilization programs. This review article covers our revised understanding of the process of apoptosis within the ovarian follicle, its three phenotypes, the major signaling pathways underlying apoptosis as well as the associated mitochondrial pathways.

Infertility and ovarian follicle reserve depletion are associated with dysregulation of the FSH and LH receptor density in human antral follicles

The low take-home baby rate in older women in Australia (5.8%) undergoing IVF (5.8%) is linked to the depletion of the ovarian reserve of primordial follicles. Oocyte depletion causes an irreversible change to ovarian function. We found that the young patient FSH receptor and LH receptor expression profile on the granulosa cells collected from different size follicles were similar to the expression profile reported in natural cycles in women and sheep. This was reversed in the older patients with poor ovarian reserve. The strong correlation of BMPR1B and FSH receptor density in the young was not present in the older women; whereas, the LH receptor and BMPR1B correlation was weak in the young but was strongly correlated in the older women. The reduced fertilisation and pregnancy rate was associated with a lower LH receptor density and a lack of essential down-regulation of the FSH and LH receptor. The mechanism regulating FSH and LH receptor expression appears to function independently, in vivo, from the dose of FSH gonadotrophin, rather than in response to it. Restoring an optimum receptor density may improve oocyte quality and the pregnancy rate in older women.

Oocyte-somatic cell interactions in the human ovary-novel role of bone morphogenetic proteins and growth differentiation factors

BACKGROUND

Initially identified for their capability to induce heterotopic bone formation, bone morphogenetic proteins (BMPs) are multifunctional growth factors that belong to the transforming growth factor β superfamily. Using cellular and molecular genetic approaches, recent studies have implicated intra-ovarian BMPs as potent regulators of ovarian follicular function. The bi-directional communication of oocytes and the surrounding somatic cells is mandatory for normal follicle development and oocyte maturation. This review summarizes the current knowledge on the physiological role and molecular determinants of these ovarian regulatory factors within the human germline-somatic regulatory loop.

OBJECTIVE AND RATIONALE

The regulation of ovarian function remains poorly characterized in humans because, while the fundamental process of follicular development and oocyte maturation is highly similar across species, most information on the regulation of ovarian function is obtained from studies using rodent models. Thus, this review focuses on the studies that used human biological materials to gain knowledge about human ovarian biology and disorders and to develop strategies for preventing, diagnosing and treating these abnormalities.

SEARCH METHODS

Relevant English-language publications describing the roles of BMPs or growth differentiation factors (GDFs) in human ovarian biology and phenotypes were comprehensively searched using PubMed and the Google Scholar database. The publications included those published since the initial identification of BMPs in the mammalian ovary in 1999 through July 2016.

OUTCOMES

Studies using human biological materials have revealed the expression of BMPs, GDFs and their putative receptors as well as their molecular signaling in the fundamental cells (oocyte, cumulus/granulosa cells (GCs) and theca/stroma cells) of the ovarian follicles throughout follicle development. With the availability of recombinant human BMPs/GDFs and the development of immortalized human cell lines, functional studies have demonstrated the physiological role of intra-ovarian BMPs/GDFs in all aspects of ovarian functions, from follicle development to steroidogenesis, cell–cell communication, oocyte maturation, ovulation and luteal function. Furthermore, there is crosstalk between these potent ovarian regulators and the endocrine signaling system. Dysregulation or naturally occurring mutations within the BMP system may lead to several female reproductive diseases. The latest development of recombinant BMPs, synthetic BMP inhibitors, gene therapy and tools for BMP-ligand sequestration has made the BMP pathway a potential therapeutic target in certain human fertility disorders; however, further clinical trials are needed. Recent studies have indicated that GDF8 is an intra-ovarian factor that may play a novel role in regulating ovarian functions in the human ovary.

WIDER IMPLICATIONS

Intra-ovarian BMPs/GDFs are critical regulators of folliculogenesis and human ovarian functions. Any dysregulation or variations in these ligands or their receptors may affect the related intracellular signaling and influence ovarian functions, which accounts for several reproductive pathologies and infertility. Understanding the normal and pathological roles of intra-ovarian BMPs/GDFs, especially as related to GC functions and follicular fluid levels, will inform innovative approaches to fertility regulation and improve the diagnosis and treatment of ovarian disorders.