Ovarian Physiology and GWAS: Biobanks, Biology, and Beyond

Premature ovarian insufficiency - the need for a genomic map

Premature ovarian insufficiency (POI) is a life-long disorder of heterogeneous etiology, presenting as adolescent primary amenorrhea in its most severe form, with an overall incidence of 1%. Idiopathic POI accounts for up to 70% of women with POI; and genomic, genetic, epidemiological, familial and cohort studies demonstrate a genetic component to this condition. Currently, the only genetic tests routinely performed in non-syndromic POI are FMR1 premutation and cytogenetics, the latter specifically for X-chromosome abnormalities. However, a myriad of genetic aberrations has been identified and implicated, some of which act in a monogenic Mendelian fashion. The presence of multiple genetic aberrations and the complexity of POI genomics are hardly surprising since the embryological formation of the primordial oocyte pool, postnatal oogenesis and folliculogenesis are all highly complex pathways. With this review, the aim is to discuss the current genetic etiologies in the emerging field of POI genomics. Promising candidate genes include STAG3, SYCE1, FIGLA, NOBOX, FSHR, BMP15 and INHA. This area has the potential to progress rapidly in light of advances in genomic technologies. The development of a POI genomic map not only will assist in understanding the underlying molecular mechanisms affecting ovarian function but will also be essential in designing predictive and diagnostic gene panels as well as future novel therapeutic strategies.

Temporal transcriptomic landscape of postnatal mouse ovaries reveals dynamic gene signatures associated with ovarian aging

The ovary is the most important organ for maintaining female reproductive health, but it fails before most other organs. Aging-associated alterations in gene expression patterns in mammalian ovaries remain largely unknown. In this study, the transcriptomic landscape of postnatal mouse ovaries over the reproductive lifespan was investigated using bulk RNA sequencing in C57BL/6 mice. Gene expression dynamics revealed that the lifespan of postnatal mouse ovaries comprised four sequential stages, during which 2517 genes were identified as differentially enriched. Notably, the DNA repair pathway was found to make a considerable and specific contribution to the process of ovarian aging. Temporal gene expression patterns were dissected to identify differences in gene expression trajectories over the lifespan. In addition to DNA repair, distinct biological functions (including hypoxia response, epigenetic modification, fertilization, mitochondrial function, etc.) were overrepresented in particular clusters. Association studies were further performed to explore the relationships between known genes responsible for ovarian function and differentially expressed genes identified in this work. We found that the causative genes of human premature ovarian insufficiency were specifically enriched in distinct gene clusters. Taken together, our findings reveal a comprehensive transcriptomic landscape of the mouse ovary over the lifespan, providing insights into the molecular mechanisms underlying mammalian ovarian aging and supporting future etiological studies of aging-associated ovarian disorders.

TMEM150B is dispensable for oocyte maturation and female fertility in mouse

Premature ovarian insufficiency (POI) refers to severe decline of ovary function in females which usually leads to infertility. It has been reported that the TMEM150B gene is mostly associated with age at natural menopause, early menopause and POI, but its role in female reproduction remains unknown. In this study, we found Tmem150b was highly expressed in mouse oocytes, but its deletion had no obvious effect on meiotic maturation of oocytes indicated by first polar body emission and spindle morphology. There were also no obvious differences in follicle development and corpus luteum formation between knockout and wild type mice. Finally, knockout of Tmem150b did not affect female fertility and sexual hormone levels. In summary, our results suggest that TMEM150B is not essential for female fertility in mice.

Dynamic Changes of DNA Methylation and Transcriptome Expression in Porcine Ovaries during Aging

The biological function of human ovaries declines along with aging. To identify the underlying molecular changes during ovarian aging, pigs were used as model animals. Genome-wide DNA methylation and transcriptome-wide RNA expression analyses were performed via high-throughput sequencing of ovaries from young pigs (180 days, puberty stage of first ovulation) and old pigs (eight years, reproductive exhaustion stage). The results identified 422 different methylation regions between old and young pigs; furthermore, a total of 2,243 mRNAs, 95 microRNAs, 248 long noncoding RNAs (lncRNAs), and 116 circular RNAs (circRNAs) were differentially expressed during both developmental stages. Gene ontology analysis showed that these genes related to different methylation and expression are involved in the ovarian aging cycle. Specifically, these are involved in cell apoptosis, death effector domain binding, embryonic development, reproduction and fertilization process, ovarian cumulus expansion, and the ovulation cycle. Multigroup cooperative control relationships were also assessed, and competing endogenous RNA (ceRNA) networks were constructed in the ovarian aging cycle. These data will help to clarify ovary age-associated potential molecular changes in DNA methylation and transcriptional patterns over time.

Variation analysis of theTMEM150B gene in Chinese women with premature ovarian insufficiency

RESEARCH QUESTION

The TMEM150B gene, which promotes cell survival under stress conditions by modulating autophagy, is closely associated with age at natural menopause, early menopause and premature ovarian insufficiency (POI) in European women. However, whether gene variants of TMEM150B contribute to the pathogenesis of POI needs to be determined.

DESIGN

A case-control genetic study in 408 Han Chinese women with non-syndromic POI, in which all exons and exon-intron boundaries of the TMEM150B gene were screened by Sanger sequencing; the results were analysed by statistics and bioinformatics.

RESULTS

Two novel variants located in the 3' untranslated region of the TMEM150B gene were identified, but bioinformation analyses showed that neither was potentially disease-causing. Six known single-nucleotide polymorphisms (SNP) were found, and they were not potentially causative for POI. The intronic SNP rs11668344 was also detected in the POI patients; no significant differences were found in either genotype or allele frequencies compared with the control population.

CONCLUSION

The results suggest that the perturbations in the TMEM150B gene are not a common explanation for POI in Chinese women. The role of autophagy in the pathogenic mechanism of POI needs further exploration.

Molecular Genetics of Premature Ovarian Insufficiency

Premature ovarian insufficiency (POI) is highly heterogeneous in genetic etiology. Yet identifying causative genes has been challenging with candidate gene approaches. Recent approaches using next generation sequencing (NGS), especially whole exome sequencing (WES), in large POI pedigrees have identified new causatives and proposed relevant candidates, mainly enriched in DNA damage repair, homologous recombination, and meiosis. In the near future, NGS or whole genome sequencing will help better define genes involved in intricate regulatory networks. The research into miRNA and age at menopause represents an emerging field that will help unveil the molecular mechanisms underlying pathogenesis of POI. Shedding light on the genetic architecture is important in interpreting pathogenesis of POI, and will facilitate risk prediction for POI.

Complex genetics of female fertility

Variation in reproductive lifespan and female fertility have implications for health, population size and ageing. Fertility declines well before general signs of menopause and is also adversely affected by common reproductive diseases, including polycystic ovarian syndrome (PCOS) and endometriosis. Understanding the factors that regulate the timing of puberty and menopause, and the relationships with fertility are important for individuals and for policy. Substantial genetic variation exists for common traits associated with reproductive lifespan and for common diseases influencing female fertility. Genetic studies have identified mutations in genes contributing to disorders of reproduction, and in the last ten years, genome-wide association studies (GWAS) have transformed our understanding of common genetic contributions to these complex traits and diseases. These studies have made great progress towards understanding the genetic factors contributing to variation in traits and diseases influencing female fertility. The data emerging from GWAS demonstrate the utility of genetics to explain epidemiological observations, revealing shared biological pathways linking puberty timing, fertility, reproductive ageing and health outcomes. Many variants implicate DNA damage/repair genes in variation in the age at menopause with implications for follicle health and ageing. In addition to the discovery of individual genes and pathways, the increasingly powerful studies on common genetic risk factors help interpret the underlying relationships and direction of causation in the regulation of reproductive lifespan, fertility and related traits.

Effect of melatonin on the peripheral T lymphocyte cell cycle and levels of reactive oxygen species in patients with premature ovarian failure

The objective of the present study was to observe the curative effect and mechanism of melatonin for suppression of premature ovarian failure (POF). From December 2014 to June 2015, 128 patients were consecutively diagnosed with POF in the Department of Gynaecology and Obstetrics. The patients were randomly divided into the experimental and control groups. The experimental group received melatonin tablets (1–3 mg/day), while the control group received placebo tablets. The levels of six sex hormones, percentage of T lymphocytes in the G₁/M phase, and levels of reactive oxygen species (ROS) were determined at four different time-points (1 day before treatment, and at 1, 3 and 6 months after treatment) in both groups. After 6 months of treatment, the levels of luteinizing hormone and follicle-stimulating hormone were significantly decreased in the experimental group compared with the control group (P<0.05). Compared with the control group, the levels of ROS in plasma were significantly decreased in the experimental group (P<0.05). Correlation analysis showed that the levels of melatonin in peripheral blood were negatively related with the levels of ROS (rs=−0.481, P<0.05). One-year follow-up study showed that the normal excretion of ovarian hormones in the experimental group was significantly higher than that of the control group (P<0.05). In conclusion, treatment with melatonin is an effective approach to suppress POF. The potential mechanism of melatonin is inhibition of ROS production and protection of the process of normal follicle development.