Oocyte quality in health and disease

In vitro fertilisation (IVF) and associated technologies remain relatively inefficient and costly and the problems worsen with increasing maternal age. One of the main reasons for these low success rates is poor oocyte (egg) quality, as we know very little about the biology of mammalian egg development and the factor(s) which make eggs fertile. This issue is exacerbated by the limited available of human eggs for research. In order to improve the success of assisted conception treatments we need to maximise the number of good quality eggs we collect from a woman?s ovaries but we must be careful that egg quality does not suffer at the expense of egg quantity. The current momentum in assisted conception is therefore to produce a small number of good eggs from each patient and so maximise their change of a pregnancy. However, this goal can only be achieved if we can identify the best eggs for IVF and use this information to improve patient treatments and so maximise egg quality. The objective of this project is therefore to measure egg quality in healthy women and to use this information to establish a cellular and molecular signature of egg health from patients with defined causes of infertility. The project aims to: (1) define and link biochemical and metabolic markers of egg quality; (2) investigate a number of key genes which may contribute to egg health; and (3) measure the impact of different assisted reproduction treatment regimes on egg quality. Some aspects of the research will be conducted using cow eggs as these tissues are a good model for human egg development; other components of the project will be conducted using human eggs which have been donated for research by infertility patients. We have already developed and validated the molecular biology methods and assays of egg protein turnover and energy metabolism which will be utilised on this project to measure egg quality. The data generated by the proposed studies will significantly advance our understanding of human egg biology and will ultimately help reduce the cost and improve the success rates of assisted conception treatments.

In vitro fertilisation (IVF) and associated technologies remain relatively inefficient and costly and the problems worsen with increasing maternal age. One of the main reasons for these low success rates is poor oocyte quality, yet we know very little about the factors that confer developmental competence on these important cells. The objective of this project is to link molecular and metabolic markers of oocyte quality in individual oocytes and to characterise gene expression profiles during the terminal stages of gonadotrophin-stimulated folliculogenesis in vivo and oocyte maturation in vitro. Specifically the project aims to: (1) link non-invasive assays of amino acid turnover, energy metabolism and mitochondrial activity to oocyte quality; (2) characterise known and novel oocyte-specific and somatic genes in relation to developmental competence; and (3) measure the impact of controlled ovarian stimulation on oocyte quality. The key problems associated with human oocyte research include the shortage of gametes for research, the heterogeneity between oocytes and the lack of non-invasive methods to identify developmentally competent oocytes as molecular and genetic analysis commonly involve destruction of the egg. This application overcomes these problems by linking metabolic assays to molecular methods which are sensitive at the single cell level. Our extensive pilot studies have confirmed that we can track oocyte developmental competence in vitro and that HPLC measurements of amino acid turnover, ultra microfluorescent assays of glucose pyruvate and lactate metabolism and ratiometric assays of mitochondrial activity can be conducted on individual bovine and human oocytes and, importantly, that these measures can be linked to the molecular (microarray and real time PCR) or genetic normality (multiparameter FISH) of the same oocyte. In this programme, bovine oocytes matured in vitro and derived following controlled ovarian stimulation will be used to link metabolic indices of oocyte developmental competence to candidate genes associated with quality in the gamete or its companion cumulus cells. The results so generated will inform studies to directly quantify the molecular and metabolic signature of oocyte quality in donated human oocytes matured both in vivo and in vitro. This research will significantly advance our understanding of human oocyte biology and will drive the development of improved treatment regimes to maximise egg quality. The results of metabolic profiling of oocytes may lead to the development of novel diagnostic tests, whereas analysis of human oocyte gene products may provide future tissue-specific pharmacological targets which can be modulated to improve or alleviate infertile pathologies.