The Role of Anti-Müllerian Hormone in Ovarian Function

Anti-Müllerian hormone (AMH) is a member of the transforming growth factor β (TGFβ) superfamily, whose actions are restricted to the endocrine-reproductive system. Initially known for its role in male sex differentiation, AMH plays a role in the ovary, acting as a gatekeeper in folliculogenesis by regulating the rate of recruitment and growth of follicles. In the ovary, AMH is predominantly expressed by granulosa cells of preantral and antral follicles (i.e., post primordial follicle recruitment and prior to follicle-stimulating hormone (FSH) selection). AMH signals through a BMP-like signaling pathway in a manner distinct from other TGFβ family members. In this review, the latest insights in AMH processing, signaling, its regulation of spatial and temporal expression pattern, and functioning in folliculogenesis are summarized. In addition, effects of AMH variants on ovarian function are reviewed.

Effect of reduced water intake on ovarian reserve, leptin immunoexpression and impact of leptin on the in vitro culture of sheep secondary follicles

This study evaluated the effect of reduced water intake on survival, apoptosis and immunoexpression of leptin in sheep preantral follicles, activation of primordial follicles, serum levels of leptin, estradiol (E2) and progesterone (P4), and in vitro maturation (IVM) of oocytes antral follicles, as well evaluated the effects of leptin on in vitro culture of secondary follicles isolated these animals. Ewes (n = 32) were divided into four groups: water ad libitum (Control - 100%), 80%; 60% and 40% of ad libitum intake. Blood was collected to determine, leptin, E2 and P4, before and after experiment. After the slaughter, ovarian cortex was used to histological and immunohistochemistry analysis and oocytes IVM. Moreover, isolated secondary follicles were cultured in vitro for 12 days in control medium (α-MEM+) or α-MEM+ with 10 or 25 ng/mL leptin. The reduction of water intake caused a linear decreasing effect on the percentages of normal preantral follicles, especially of primordial (P < 0.05), increased the apoptosis (P < 0.05) and decreased leptin expression in preantral follicles. The treatment with 60% of water intake showed greater total growth rate of isolated secondary follicles cultured with 25 ng/L leptin (P < 0.05), compared to those cultured in α-MEM+ . In conclusion, reduced water intake impaired the number of normal sheep preantral follicles, especially of primordial follicles, increased apoptosis and decreased leptin expression in preantral follicles. Moreover, secondary follicles from of ewes that receive 60% water intake increased follicular growth after in vitro culture with 25 ng/mL leptin.

Anti-Müllerian hormone-mediated preantral follicle atresia is a key determinant of antral follicle count in mice

STUDY QUESTION

Does anti-Müllerian hormone (AMH) induce preantral follicle atresia in mice?

SUMMARY ANSWER

The present findings suggest that AMH-mediated follicle atresia only occurs in early follicles before they become sensitive to FSH.

WHAT IS KNOWN ALREADY

Most prior studies have investigated the ability of AMH to inhibit primordial follicle activation. Our previous study showed that AMH-overexpressing mice had fewer preantral follicles than expected after accounting for primordial follicle inhibition but the reason for this was not determined.

STUDY DESIGN, SIZE, DURATION

Cross-sectional-control versus transgenic/knockout mouse studies were carried out.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Studies were conducted on female wild-type (Amh+/+), AMH-knockout (Amh-/-) and AMH overexpressing (Thy1.2-AMHTg/0) mice on a C57Bl/6J background (age: 42-120 days). The follicle counts were conducted for primordial, transitioning, primary, secondary and antral follicles in Amh-/- and Amh+/+ mice. After confirming that follicle development speeds were identical (proliferating cell nuclear antigen immunohistochemistry), the ratio of follicles surviving beyond each stage of folliculogenesis was determined in both genotypes. Evidence for increased rates of preantral follicle atresia was assessed by active caspase-3 immunohistochemistry in wild-type and Thy1.2-AMHTg/0 mice.

MAIN RESULTS AND THE ROLE OF CHANCE

Amh -/- mice at 100-120 days of age had lower primordial follicle counts but higher primordial follicle activation rates compared to Amh+/+ mice. These counteracting effects led to equivalent numbers of primordial follicles transitioning to the primary stage in Amh+/+ and Amh-/- mice. Despite this, Amh+/+ mice had fewer primary, secondary, small antral and medium antral follicles than Amh-/- mice indicating differing rates of developing follicle atresia between genotypes. Cleaved caspase-3 immunohistochemistry in Thy1.2-AMHTg/0 ovaries revealed high rates of granulosa cell and oocyte apoptosis in late primary/early secondary follicles of Thy1.2-AMHTg/0 mice.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The findings were shown only in one species and additional research will be required to determine generalizability to other species.

WIDER IMPLICATIONS OF THE FINDINGS

This study is consistent with prior studies showing that Amh-/- mice have increased primordial follicle activation but these new findings demonstrate that AMH-mediated preantral follicle atresia is a predominant cause of the increased small antral follicle counts in Amh-/- mice. This suggests that the role of AMH is not to conserve the ovarian reserve to prolong fertility, but instead to prevent the antral follicle pool from becoming too large. While this study may demonstrate a new function for AMH, the biological purpose of this function requires further investigation, particularly in mono-ovulatory species.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the Health Research Council of New Zealand and the University of Otago. No competing interests to declare.

Effects and potential mechanism of Ca2+/calmodulin‑dependent protein kinase II pathway inhibitor KN93 on the development of ovarian follicle

Adequate regulation of the speed of follicular development has been reported to prolong the reproductive life of the ovary. The aim of the present study was to assess the potential effects and mechanism of the Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) pathway on the development of ovarian follicle. In the present study, the expression of CaMKII was measured in the ovary of mice at different developmental stages by immunofluorescence, confirming that CaMKII has a role in follicular development. Subsequently, the 17.5 days post-coitus (dpc) embryonic ovaries were collected and cultured with KN93 for 4 days in vitro. It was revealed that KN93 inhibited the development of follicles, where it reduced the expression levels of oocyte and granulosa cell markers DEAD-box helicase 4 (DDX4) and forkhead box L2 (FOXL2). These results suggested that KN93 could delay follicular development. Proteomics technology was then used to find that 262 proteins of KN93 treated 17.5 dpc embryonic ovaries were significantly altered after in vitro culture. Bioinformatics analysis was used to analyze these altered proteins. In total, four important Kyoto Encyclopedia of Genes and Genome pathways, namely steroid biosynthesis, p53 signaling pathway and retinol metabolism and metabolic pathways, were particularly enriched. Further analysis revealed that the upregulated proteins NADP-dependent steroid dehydrogenase-like (Nsdhl), lanosterol synthase (Lss), farnesyl-diphosphate farnesyltransferase 1 (Fdft1), cytochrome P450 family 51 family A member 1 (Cyp51a1), hydroxymethylglutaryl-CoA synthase 1 (Hmgcs1), fatty acid synthase (Fasn) and dimethylallyltranstransferase (Fdps) were directly interacting with each other in the four enriched pathways. In summary, the potential mechanism of KN93 in slowing down follicular development most likely lies in its inhibitory effects on CaMKII, which upregulated the expression of Nsdhl, Lss, Fdft1, Cyp51a1, Hmgcs1, Fasn and Fdps. This downregulated the expression of oocyte and granulosa cell markers DDX4 and FOXL2 in the follicles, thereby delaying follicular development. Overall, these results provide novel insight into the potential mechanism by which KN93 and CaMKII can delay follicular development.

Key signalling pathways underlying the aetiology of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine condition characterised by a range of reproductive, endocrine, metabolic and psychological abnormalities. Reports estimate that around 10% of women of reproductive age are affected by PCOS, representing a significant prevalence worldwide, which poses a high economic health burden. As the origin of PCOS remains largely unknown, there is neither a cure nor mechanism-based treatments leaving patient management suboptimal and focused solely on symptomatic treatment. However, if the underlying mechanisms underpinning the development of PCOS were uncovered then this would pave the way for the development of new interventions for PCOS. Recently, there have been significant advances in our understanding of the underlying pathways likely involved in PCOS pathogenesis. Key insights include the potential involvement of androgens, insulin, anti-Müllerian hormone and transforming growth factor beta in the development of PCOS. This review will summarise the significant scientific discoveries on these factors that have enhanced our knowledge of the mechanisms involved in the development of PCOS and discuss the impact these insights may have in shaping the future development of effective strategies for women with PCOS.

Overexpression of Lin28a induces a primary ovarian insufficiency phenotype via facilitation of primordial follicle activation in mice

Lin28a is an RNA binding protein and increasing evidence has indicated its role in regulating female fertility. Lin28a has been reported to be involved in ovarian follicle activation. However, its role and mechanisms in regulating primordial follicle activation have not yet been explored. To test whether overexpression of Lin28a activates ovarian primordial follicles, studies were conducted in wild type (WT) and Lin28a Tg mice. Female Lin28a Tg mice at 4-month old exhibited significantly smaller litter size and fewer ovulated oocytes when compared with the WT mice. By 6-month of age, these parameters in Lin28a Tg mice were less than 20% of the WT mice. At postnatal day (PD) 14, the number of primordial follicles was significantly decreased but the number of primary follicles was significantly increased in the transgenic mice. The number of primordial follicles, secondary and antral follicles in these mice were drastically reduced at PD21. In the ovary of Lin28a Tg mice, there were activation of Wnt/β-catenin signaling and its downstream mTOR pathway. Interestingly, overexpression of Lin28a, which can also act as transcriptional activator, activated Wnt signaling through enhancing the transcription of Wnt co-receptor LRP5. In conclusion, overexpression of Lin28a induced a primary ovarian insufficiency phenotype in long term via facilitating Wnt/β-catenin signaling leading to activation of primordial follicles.

Translational Physiology of Anti-Müllerian Hormone: Clinical Applications in Female Fertility Preservation and Cancer Treatment

Background

Whilst the ability of AMH to induce the regression of the Müllerian ducts in the male fetus is well appreciated, AMH has additional biological actions in relation to steroid biosynthesis and ovarian follicle dynamics. An understanding of the physiology of AMH illuminates the potential therapeutic utility of AMH to protect the ovarian reserve during chemotherapy and in the treatment of female malignancies. The translation of the biological actions of AMH into clinical applications is an emerging focus of research, with promising preliminary results.

Objective and Rationale

Studies indicate AMH restrains primordial follicle development, thus administration of AMH during chemotherapy may protect the ovarian reserve by preventing the mass activation of primordial follicles. As AMH induces regression of tissues expressing the AMH receptor (AMHRII), administration of AMH may inhibit growth of malignancies expressing AMHR II. This review evaluates the biological actions of AMH in females and appraises human clinical applications.

Search Methods

A comprehensive search of the Medline and EMBASE databases seeking articles related to the physiological functions and therapeutic applications of AMH was conducted in July 2021. The search was limited to studies published in English.

Outcomes

AMH regulates primordial follicle recruitment and moderates sex steroid production through the inhibition of transcription of enzymes in the steroid biosynthetic pathway, primarily aromatase and 17α-hydroxylase/17,20-lyase. Preliminary data indicates that administration of AMH to mice during chemotherapy conveys a degree of protection to the ovarian reserve. Administration of AMH at the time of ovarian tissue grafting has the potential to restrain uncontrolled primordial follicle growth during revascularization. Numerous studies demonstrate AMH induced regression of AMHR II expressing malignancies. As this action occurs via a different mechanism to traditional chemotherapeutic agents, AMH has the capacity to inhibit proliferation of chemo-resistant ovarian cancer cells and cancer stem cells.

Wider Implications

To date, AMH has not been administered to humans. Data identified in this review suggests administration of AMH would be safe and well tolerated. Administration of AMH during chemotherapy may provide a synchronistic benefit to women with an AMHR II expressing malignancy, protecting the ovarian reserve whilst the cancer is treated by dual mechanisms.

AMH and AMHR2 Involvement in Congenital Disorders of Sex Development

Anti-müllerian hormone (AMH) is 1 of the 2 testicular hormones involved in male development of the genitalia during fetal life. When the testes differentiate, AMH is secreted by Sertoli cells and binds to its specific receptor type II (AMHR2) on the müllerian ducts, inducing their regression. In the female fetus, the lack of AMH allows the müllerian ducts to form the fallopian tubes, the uterus, and the upper part of the vagina. The human AMH gene maps to 19p13.3 and consists of 5 exons and 4 introns spanning 2,764 bp. The AMHR2 gene maps to 12q13.13, consists of 11 exons, and is 7,817 bp long. Defects in the AMH pathway are the underlying etiology of a subgroup of disorders of sex development (DSD) in 46,XY patients. The condition is known as the persistent müllerian duct syndrome (PMDS), characterized by the existence of a uterus and fallopian tubes in a boy with normally virilized external genitalia. Approximately 200 cases of patients with PMDS have been reported to date with clinical, biochemical, and molecular genetic characterization. An updated review is provided in this paper. With highly sensitive techniques, AMH and AMHR2 expression has also been detected in other tissues, and massive sequencing technologies have unveiled variants in AMH and AMHR2 genes in hitherto unsuspected conditions.

Advanced maternal age perturbs mouse embryo development and alters the phenotype of derived embryonic stem cells

Advanced maternal age (AMA) is known to reduce fertility, increases aneuploidy in oocytes and early embryos and leads to adverse developmental consequences which may associate with offspring lifetime health risks. However, investigating underlying effects of AMA on embryo developmental potential is confounded by the inherent senescence present in maternal body systems further affecting reproductive success. Here, we describe a new model for the analysis of early developmental mechanisms underlying AMA by the derivation and characterisation of mouse embryonic stem cell (mESC-like) lines from naturally conceived embryos. Young (7-8 weeks) and Old (7-8 months) C57BL/6 female mice were mated with young males. Preimplantation embryos from Old dams displayed developmental retardation in blastocyst morphogenesis. mESC lines established from these blastocysts using conventional techniques revealed differences in genetic, cellular and molecular criteria conserved over several passages in the standardised medium. mESCs from embryos from AMA dams displayed increased incidence of aneuploidy following Giemsa karyotyping compared with those from Young dams. Moreover, AMA caused an altered pattern of expression of pluripotency markers (Sox2, OCT4) in mESCs. AMA further diminished mESC survival and proliferation and reduced the expression of cell proliferation marker, Ki-67. These changes coincided with altered expression of the epigenetic marker, Dnmt3a and other developmental regulators in a sex-dependent manner. Collectively, our data demonstrate the feasibility to utilise mESCs to reveal developmental mechanisms underlying AMA in the absence of maternal senescence and with reduced animal use.