The Life Cycle And Legacy of Human Oocytes In Health, Age and Infertility

Infertility is a major problem in humans which affects 1 in 6 couples. While assisted reproductive technologies (ARTs) have enabled infertility to be treated, in vitro fertilisation (IVF) and associated technologies remain relatively inefficient and costly. One of the main reasons for these low success rates is poor oocyte (egg) quality, as we know very little about the biology of egg development and we do not know the identity of factor(s) which make eggs healthy and fertile. Furthermore, egg fertility declines as women get older. This issue is important as a major trend in western societies in the late 20th century has been the postponement of childbearing. This change in behavior means that an increasing number of women in their mid to late 30s now have to seek medical treatment such as IVF to overcome the involuntary childlessness which occurs as a result of reproductive ageing. Despite the increasing need for assisted conception, it has historically been very difficult to study human egg biology as human eggs are rarely available for research. Unfortunately, the methods used to advance the science usually destroys the cells being studied. Much of our understanding of human egg biology has therefore been pieced together from studies of mouse eggs. However, the recent development by the applicants and others, of a series of highly sensitive assays means that is it now possible to measure multiple parameters of egg biology directly in the same cell. Further, we have developed animal models using species such as sheep which can be used to advance our understanding of human egg development as sheep eggs grow and mature in a way that closely mimics the same processes in humans. The stage is now set to use these innovative tools to test the hypothesis that a detailed insight into human egg biology will help us to define human egg health and fertility and to better understand how these process can be altered with age and lead to infertility. If we can identify and produce better quality eggs during infertility treatments, we may be able to increase the success of assisted conception treatments. The proposed programme of research will address these important issues by studying human and animals eggs and ovarian cells. The research will measure the nutrients requirements of eggs and show how these important cells utilise energy and protein as they develop and how egg metabolism changes with age. We will study key components of the molecular and metabolic machinery of human and animal eggs so that we can identify which genes, switches and mechanisms regulate egg development and fertility. The relationship between the eggs and their supporting ovarian follicle cells, which provide eggs with the required nutrients throughout their development, will be investigated. The distribution and functional significance of the most promising, novel genes we identify as regulators of egg development and fertility will be tested in the laboratory using eggs grown in vitro. Having established the parameters of normal egg development in healthy women we will use this yardstick to measure how the switches and mechanisms regulating egg quality change as women age and/or become infertile. Finally, we will use the data generated from our series of experiments to build a mathematical model of human egg health. The results generated from these studies will significantly advance our understanding of human egg biology in young women and as women age. The outcome of this research will help improve the efficiency of assisted conception treatments and the long-term management of womens' reproductive health.

Infertility is a major problem which affects 1 in 6 couples. While assisted reproductive technologies (ARTs) have revolutionised the treatment of infertility, treatments remain costly and inefficient and the problems worsen with age. One of the main reasons for the low success rates of ART is poor oocyte quality, as we know little about the mechanisms that confer oocyte developmental competence. We hypothesise that a detailed understanding of the fundamental biology of human oogenesis is vital if we are to define oocyte quality and characterise the impact of age and infertile pathologies on female reproduction. The proposed program of work aims to address these important issues by integrating targeted studies of human oocytes with mechanistic in vivo and in vitro models of oocyte development in sheep. Our multidisciplinary approach will quantify energy and amino acid metabolism, mitochondrial activity, chromosome health and gene expression in the same oocyte. Next generation sequencing will be conducted on staged human oocytes and cumulus cells. This strategy will generate the first high-resolution map of the metabolome, transcriptome and epigenome characterising the milestones of human oogenesis and defining the legacy of human oocytes in the peri-conceptual window. The function of 2 known candidate genes relevant to oocyte development will be tested using siRNAi and we will identify novel biomarkers of oocyte quality. We will quantify the impact of both the sustained endocrine disturbance associated with reproductive ageing and common infertile pathologies and ARTs on key functional and molecular indices of oocyte quality. Data on the transcriptome and metabolome of human oocytes will be used to create a mathematical model of human oocyte quality in health and age. This program of research will significantly advance our understanding of human oocyte biology and will help improve the success of assisted conception and the management of female reproductive health.

This programme addresses fundamental scientific issues which impact directly on the health, wealth & well being of mankind. People do not die of infertility but the urge to reproduce is fundamental & the morbidity of infertility is considerable & wide ranging. Further, the impact of reproductive aging transcends infertility & impacts all aspects of society & this is reflected in the high priority given to ageing research in the UK & internationally. The benefits of a detailed understanding of the biology of human oocytes are considerable & will be easily appreciated by the general public, scientific & infertile community & healthcare professionals working in reproductive medicine & women reproductive health as well the pharmaceutical industry.

(i) Technology Development: The integration of sophisticated metabolic assays & molecular techniques for quantification of cellular metabolism, gene expression & methylation status in individual oocytes means that we can directly analyse the health status of human oocytes & interpret the results so generated in relation to the risk of human disease, the success of infertility treatments & the management of womens' reproductive health. Metabolic profiling of individual oocytes has the potential to be developed as a rapid diagnostic test for selecting the best oocytes for treatment or cryopreservation & it can be used to refocus ovarian stimulation regimens towards oocyte quality rather than quantity. Metabolism measurement across oocyte development & in patients with different aetiologies will help improve the formulation of next generation oocyte culture media & may support the development of a personalised medicine approach in ART. We will maximize the impact of our research by exploring the potential for commercial exploitation of these findings through a long established relationship with the Intellectual Property Management Unit (IPMU) of Leeds University and Medipex- the northern innovation hub for the NHS. HMP currently hold two patents with Medipex and IPMU and she co-ordinates a multicentre, industry funded clinical trial testing the utility of amino acid profiling for embryo selection. We therefore have the relevant experience and industry links to exploit the potential of the translational aspects of our research. The RNA-Seq studies will facilitate the design of a bespoke real time array which combines oocyte and cumulus biomarkers of quality.

(ii) Infertility & ageing: Infertility affects 1 in 6 couples & the success rates of fertility treatment remain low and variable, particularly in older patients for whom the impact of the age-related decline in oocyte quality has no current effective treatment. The outcome of the proposed research is therefore highly relevant to the infertile patient community & to ART healthcare professions and the pharmaceutical industry. We will maximize the impact of this research by dissemination of our results to patient support groups and infertility specialists.

(iii) Reproductive ageing & health: Womens' reproductive health is increasingly being recognised as a sentinel for chronic diseases of later life. Loss of ovarian function can have far-reaching clinical & psychological consequences on female health through effects on metabolism, cardiovascular function, cognition, response to stress, osteoporosis, increased risk of breast cancer and mortality. As the longevity of the human population increases, so the long-term health consequences of ovarian ageing achieve an increasing significance & research on reproductive ageing a potentially greater impact. The current work is focused on the age-related decline in oocyte quality which occurs in relatively young women but an in-depth understanding of the biology of the age-related decline in female fertility will help us to identify those women at risk of early reproductive failure & to develop improved clinical treatments for individuals who face age-related subfertility.